replacing chloride by alkoxide: cp 2 zr(h)or, searching for alternatives...

pubs.acs.org/Organometallics Published on Web 08/19/2009 r 2009 American Chemical Society

4912 Organometallics 2009, 28, 4912–4922

DOI: 10.1021/om8008734

Replacing Chloride by Alkoxide: Cp2Zr(H)OR, Searching for

Alternatives to Schwartz’s Reagent

Philippe Perrotin, Ibrahim El-Zoghbi, Paul O. Oguadinma, and Frank Schaper*

D�epartement de Chimie, Universit�e de Montr�eal, Montr�eal, Qu�ebec, H3C 3J7, Canada

Received September 8, 2008

Attempts to synthesize zirconocene hydrido alkoxide species, Cp2Zr(H)OR, via several syntheticpathways consistently failed to yield the targeted complexes, which seem prone to undergodisproportionation into Cp2ZrH2 and a bisalkoxide complex. Reaction of Cp2ZrH2 with HOR,Me3SiOR, or Ph2CO yielded the corresponding bisalkoxide complexes Cp2Zr(OR)2, of whichCp2Zr{OC(H)Ph2}2 was characterized by an X-ray diffraction study. Insertion of vinyl ethers intoCp2ZrH2 yielded Cp2Zr(OR)2 and Cp2Zr(Et)OR. Attempted hydrogenation of Cp2Zr(Me)OR orreaction of Cp2Zr(BH4)OR with NEt3 did not yield the targeted complexes. Cp2Zr(H)OC6H5 andCp2Zr(H)OC6F5 could be obtained, however, as transient species by β-H elimination from Cp2Zr-(tBu)OR, ligand exchange between Cp2ZrH2 and Cp2Zr(OC6F5)2, or protonation in the presence ofolefin to yield the corresponding hydrozirconation products. In hydrozirconation reactions ofstyrene both species are highly regioselective. The alkoxide substituent failed to inhibit β-Helimination in hydrozirconations of trans-3-hexene or β-OR elimination in reactions with vinylethers. On the other hand, it imparted a vastly increased thermal stability to the tert-butyl complexesCp2Zr(tBu)OR, which were stable for up to several months in solution, before they isomerize to therespective isobutyl complexes. Cp2Zr(iBu)OC6H5 was characterized by X-ray crystallography.

Introduction

Hydrozirconation with Schwartz’s reagent, Cp2Zr(H)Cl,1

has found application in the direct functionalization of non-activatedolefins andalkynes, inparticularwhencombinedwithtransmetalation.2 While the hydrozirconation of alkynes iswidely used, particularly in transmetalation reactions, hydro-zirconation of olefins to generate valuable synthons is some-what limited by the peculiarities of the hydrozirconationreagent, Cp2Zr(H)Cl. One of its most noteworthy features isthat only primary zirconocene alkyl complexes are obtained.Secondary alkyls, formed by hydrozirconation of internalolefinsorbyputative2,1-insertionof terminal olefins, isomerizerapidly along the aliphatic chain to a terminal position, pre-sumably via a β-H elimination/olefin reinsertion pathway.3,4

Secondary alkyl species were obtained in mixtures with theterminal species when aromatic or polar substituents werepresent.5-7 Attempts to control the regioisomeric ratio ofthermodynamic product mixtures or to trap kinetic productsmet only limited success.7-9 The lack of access to secondaryalkyl complexes precluded enantioselective hydrozirconationreactions, with the notable exception of Sita’s cyclopentadienylacetamidinate zirconiumcomplexes.10The reduced tendencyofthis mixed ligand system to undergo β-H eliminations allowedthe isolation of a secondary alkyl zirconium complex as adiastereomeric mixture due to the chirality of the zirconiumcenter.Several attempts have been undertaken to improve on the

original Schwartz’s reagent, Cp2Zr(H)Cl. Substituted cyclo-pentadienyl ligands, such as C5H4Me and C5Me5, have beenemployed, mainly with the goal to increase solubility.8,9,11

Exchange of the chloride ligand with bromide proved*Corresponding author. E-mail; [email protected].(1) Wailes, P. C.; Weigold, H. J. Organomet. Chem. 1970, 24, 405.

Wailes, P. C.; Weigold, H.; Bell, A. P. J. Organomet. Chem. 1972, 43, C32.Hart, D. W.; Schwartz, J. J. Am. Chem. Soc. 1974, 96, 8115.(2) Wipf, P.; Kendall, C. Top. Organomet. Chem. 2004, 8, 1. Negishi,

E.-i.; Huo, S. In Titanium and Zirconium in Organic Synthesis; Marek, I.,Ed.; Wiley-VCH: Weinheim, 2002; p 1. Negishi, E.-i.; Montchamp, J.-L. InMetallocenes; Togni, A.; Halterman, R. L., Eds.; Wiley-VCH: Weinheim,1998; p 241. Lipshutz, B. H.; Pfeiffer, S. S.; Noson, K.; Tomioka, T. InTitanium and Zirconium in Organic Synthesis; Marek, I., Ed.; Wiley-VCH:Weinheim, 2002; p 110. Wipf, P.; Jahn, H. Tetrahedron 1996, 52, 12853.(3) Schwartz, J.; Labinger, J. A. Angew. Chem., Int. Ed. Engl. 1976,

15, 333. Annby, U.; Alvhaell, J.; Gronowitz, S.; Hallberg, A. J. Organomet.Chem. 1989, 377, 75.(4) Chirik, P. J.; Day, M. W.; Labinger, J. A.; Bercaw, J. E. J. Am.

Chem. Soc. 1999, 121, 10308.(5) Buchwald, S. L.; Nielsen, R. B.; Dewan, J. C. Organometallics

1988, 7, 2324.

(6) Karlsson, S.; Hallberg, A.; Gronowitz, S. J. Am. Oil Chem. Soc.1989, 66, 1815. Annby, U.; Gronowitz, S.; Hallberg, A. J. Organomet.Chem. 1989, 365, 233. Gibson, T.Organometallics 1987, 6, 918. Annby, U.;Gronowitz, S.; Hallberg, A. Chem. Scr. 1987, 27, 445. Alvhaell, J.;Gronowitz, S.; Hallberg, A. Chem. Scr. 1985, 25, 393. Karlsson, S.;Hallberg, A.; Gronowitz, S. J. Organomet. Chem. 1991, 403, 133. Karlsson,S.; Hallberg, A.; Gronowitz, S. J. Organomet. Chem. 1992, 430, 53.

(7) Wipf, P.; Takahashi, H.; Zhuang, N. Pure Appl. Chem. 1998, 70,1077.

(8) Annby, U.; Gronowitz, S.; Hallberg, A. Acta Chem. Scand. 1990,44, 862.

(9) Alvh€all, J.; Gronowitz, S.; Hallberg, A. Chem. Scr. 1988, 28, 285.(10) Zhang,Y.;Keaton,R. J.; Sita, L.R. J.Am.Chem.Soc. 2003, 125,

8746.(11) Erker, G.; Schlund, R.; Krueger, C. Organometallics 1989, 8,

2349.

Article Organometallics, Vol. 28, No. 17, 2009 4913

to reduce reactivity,9 while exchange with a sulfonateanion yielded highly active and soluble hydrozirconationreagents.12 H€usgen and Luinstra found that hydrozircona-tion of styrene with the latter complexes favored 1,2-inser-tion products under kinetic control, while isomerization tothe thermodynamically controlled product mixture in-creased the amount of secondary alkyl species present.12

Wipf et al. were able to trap secondary alkyl complexes,formed initially in the hydrozirconation of 2- and 4-octene,in mixtures with the thermodynamically favored terminalalkyl species using in situ generated Cp2Zr(H)OTf.7

We decided to investigate the effects of replacing thechloride ligand with alkoxide on reactivities and selectivitiesin hydrozirconation. The more Lewis-basic alkoxide ligandis supposed to render the zirconocene less prone to undergoβ-H eliminations, and the wide variety of available alcohols,including chiral derivatives, would drastically increase thepossibilities to control the hydrozirconation reaction. Pre-cedence for zirconocene hydrido alkoxide species has beenreported in the literature. Hydrido enolate complexes wereobtained after CO insertion into zirconacycles,13-15 whilehydrogenation after CO insertion in several cases yieldedhydrido alkoxide species.15-17 Bradley et al. obtained bis-(indenyl)zirconiumhydrido alkoxide complexes by oxidativeaddition of ethers to Zr(II) complexes or reactions of dihy-dride complexes with vinyl ether.18,19 Finally, in two casesthe direct synthesis of a Cp*2Zr(H)OR complex (Cp* =C5Me5) by protonation of [Cp*2ZrH3]Li

20 or Cp*2ZrH221

with alcohol was reported. It is noteworthy that isolatedzirconocene hydrido alkoxide complexes carried at least onehighly substituted cyclopentadienyl or indenyl ligand. Forapplications as stoichiometric or catalytic reagents, however,unsubstituted zirconocene complexes would be of muchhigher interest, partly due to the reduced reactivity of sub-stituted zirconocene complexes for insertion into the metalhydride bond,22 partly due to economic reasons. To the bestof our knowledge, synthesis of Cp2Zr(H)OR complexes hasnot been reported before, although their intermediate for-mation has been postulated from NMR data,14,17 and

coordination of an oxygen atom to a zirconocene alkylor hydride complex has been evoked to explain the obser-ved regiochemistry in hydrozirconations of unsaturatedalcohols.7,23

In the following we present our attempts to synthesizeunsubstituted Cp2Zr(H)OR complexes and our investiga-tions into the reactivity of these complexes in hydrozircona-tion reactions.

Results and Discussion

Zirconocene Dihydride as Precursor. Protonation of com-mercially available zirconocene dihydride by an alcohol,following the procedure established by Schock and Marksfor the synthesis of Cp*2Zr(H)OtBu,21 would provide astraightforward access to the targeted zirconocene hydridoalkoxide complexes. In our case, room-temperature additionof 1 equiv of ROH (R: Ph, C6F5, tBu) to a stirred suspensionof Cp2ZrH2 only resulted in the formation of the toluene-soluble zirconocene dialkoxide complexes Cp2Zr(OR)2,1a-c, and a white residue (Scheme 1). Compounds 1a-c

were identified by their NMR spectra in comparison toliterature data.21,24-26 The remaining insoluble materialisolated in these reactions was identified as Cp2ZrH2 bytreatment with excess acetone, which revealed only 1HNMR signals associated with the formation of the 1,2-insertion product of acetone: Cp2Zr(OiPr)2 (1H NMR:δ 6.03 (s, 10H), 4.10 (q, 2H, J = 6 Hz), 1.07 (d, 12H, J =6 Hz)).27 Treatment with acetone proved to be a convenientand reliable technique to test for zirconium hydride bonds ininsoluble zirconocene complexes. Modifying the reactionsolvent (THF or toluene) or the rate of addition of thealcohol to the Cp2ZrH2 suspension in THF did not affectthe outcome of the reaction.

Earlier success in the synthesis of Cp*2Zr(H)OR (R= 2,6-iPr2C6H3,

20 tBu21)might be related to the inaccessibility of thesterically crowded dialkoxide complexes in the presence of theCp* ligands, while the less hindered unsubstituted zircono-cenes favor the formation of a mixture of the dialkoxide

Scheme 1

(12) Luinstra, G. A.; Rief, U.; Prosenc, M. H.Organometallics 1995,14, 1551. H€usgen, N. S.; Luinstra, G. A. Inorg. Chim. Acta 1997, 259, 185.(13) Moore, E. J.; Straus, D. A.; Armantrout, J.; Santarsiero, B. D.;

Grubbs, R. H.; Bercaw, J. E. J. Am. Chem. Soc. 1983, 105, 2068. Barger,P. T.; Bercaw, J. E.Organometallics 1984, 3, 278. McDade, C.; Bercaw, J. E.J. Organomet. Chem. 1985, 279, 281. Elsner, F. H.; Tilley, T. D.; Rheingold,A. L.; Geib, S. J. J. Organomet. Chem. 1988, 358, 169. Roddick, D. M.;Bercaw, J. E. Chem. Ber. 1989, 122, 1579. Roddick, D. M.; Heyn, R. H.;Tilley, T. D. Organometallics 1989, 8, 324. Choukroun, R.; Douziech, B.;Soleil, F. J. Chem. Soc., Chem. Commun. 1995, 2017. Karsch, H. H.;Schreiber, K. A.; Reisky, M. Organometallics 1998, 17, 5052.(14) Akita, M.; Yasuda, H.; Yamamoto, H.; Nakamura, A. Polyhe-

dron 1991, 10, 1. Swanson, D. R.; Rousset, C. J.; Negishi, E.; Takahashi, T.;Seki, T.; Saburi, M.; Uchida, Y. J. Org. Chem. 1989, 54, 3521.(15) Manriquez, J.M.;McAlister, D. R.; Sanner, R.D.; Bercaw, J. E.

J. Am. Chem. Soc. 1978, 100, 2716.(16) Manriquez, J.M.;McAlister, D. R.; Sanner, R.D.; Bercaw, J. E.

J. Am. Chem. Soc. 1976, 98, 6733. Wolczanski, P. T.; Threlkel, R. S.;Bercaw, J. E. J. Am. Chem. Soc. 1979, 101, 218. Threlkel, R. S.; Bercaw, J.E. J. Am. Chem. Soc. 1981, 103, 2650. Vaughan, G. A.; Hillhouse, G. L.;Rheingold, A. L. J. Am. Chem. Soc. 1990, 112, 7994.(17) Gell, K. I.; Posin, B.; Schwartz, J.;Williams,G.M. J. Am. Chem.

Soc. 1982, 104, 1846.(18) Bradley, C. A.; Veiros, L. F.; Pun, D.; Lobkovsky, E.; Keresztes,

I.; Chirik, P. J. J. Am. Chem. Soc. 2006, 128, 16600.(19) Bradley, C. A.; Veiros, L. F.; Chirik, P. J.Organometallics 2007,

26, 3191.(20) Hoskin, A. J.; Stephan, D. W. Organometallics 2000, 19, 2621.(21) Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.(22) Chirik, P. J.; Bercaw, J. E. Organometallics 2005, 24, 5407.

(23) Liu, X.; Ready, J. M. Tetrahedron 2008, 64, 6955. Zhang, D. H.;Ready, J. M. J. Am. Chem. Soc. 2007, 129, 10288.

(24) Andr€a, K.; Hille, E. Z. Chem. 1968, 8, 65. Andr€a, K.; Hille, E. Z.Naturforsch., B: Chem. Sci. 1969, 24, 169.

(25) Howard,W. A.; Trnka, T.M.; Parkin, G. Inorg. Chem. 1995, 34,5900.

(26) Amor, J. I.; Burton, N. C.; Cuenca, T.; G�omez-Sal, P.; Royo, P.J. Organomet. Chem. 1995, 485, 153.

(27) Buchwald, S. L.; LaMaire, S. J.; Nielsen, R. B.; Watson, B. T.;King, S. M. Org. Synth. 1993, 71, 77.

(28) Averaged structural data from unsubstituted zirconocene dia-lkoxide complexes in the CSDdatabase: JAFYUK, JAQSOJ, JAQSUP,KARKUJ, WEKYOB, XENXIX, YIVWUV, YUWDUP, ZIMXUO,ZIMXUO01

(29) Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, B58,380.

4914 Organometallics, Vol. 28, No. 17, 2009 Perrotin et al.

complex and zirconocene dihydride. This might be due tokinetic reasons (higher solubility and thus reactivity ofCp2Zr-(H)OR compared with Cp2ZrH2), thermodynamic reasons(disproportionation of Cp2Zr(H)OR into Cp2ZrH2 andCp2Zr(OR)2), or both.

Wipf et al. demonstrated the in situ formation of Cp2Zr-(H)OTf fromCp2ZrH2 andTMSOTf.7NMR-scale reactionsof Cp2ZrH2 with 1 equiv of PhOSiMe3 or C6F5OSiMe3 at60 �C, however, again provided evidence only for the for-mation of the respective dialkoxide complexes 1a and 1b,respectively, alongwith the formation ofMe3SiH (1HNMR:δ 4.16 (m, 4Hz), 0.01 (d, 4Hz)) and an unidentified, benzene-d6-insoluble precipitate (Scheme 2). The latter did not con-tain any Zr-H bonds, as evidenced by the absence of areaction product with acetone. No reaction was observedbetween Cp2ZrH2 and tBuOSiMe3 even at 80 �C.

Alternatively to protonation by an alcohol, insertion of acarbonyl bond into the Zr-H bond may provide a suitableroute to a Cp2Zr(H)OR complex. NMR spectra of thereaction of Cp2ZrH2 with 1 equiv of benzophenone inC6D6, however, displayed only signals for the dialkoxidecomplex Cp2Zr(OCHPh2)2, 1d (Scheme 3). Reactions on apreparative scale with 1 equiv of benzophenone yieldedanalytically pure 1d 3 1/2 toluene in moderate yields of24%. The 1H NMR of the complex exhibits a singlet at5.99 ppm (2H) for the CHPh2 protons, which shows correla-tion by HSQC with a 13C NMR signal at 86.9 ppm.

Further confirmation of the assignment of 1d as a dialk-oxide complex was obtained by X-ray crystallography(Figure 1). As often observed in sterically more crowdedalkoxide complexes, the substituents at the oxygen atomsare directed to theoutside of the complex.BothCHPh2 groupsrotate in a way to orientate the hydrogen atom toward acyclopentadienyl ligand. Bond distances and angles aroundthe zirconium central atomare in the range observed for otherzirconocene dialkoxides (Figure 1). Despite the four phenylsubstituents present, neither intramolecular nor intermolecu-lar π-π interactions were observed in the structure.

The preparation of (η5-1,3-iPr2C9H5)2Zr(H)OMe by reac-tion of the corresponding bis(indenyl)zirconium dihydridecomplex with methyl vinyl ether18 drew our attention be-cause of the commercial availability of various alkyl vinylethers. Reaction of Cp2ZrH2 with 1 equiv of ethyl vinyl etherin toluene at 60 �C in a sealed vessel afforded after 12 ha homogeneous greenish solution. Formation of ethylene(5.25 ppm) was established bymonitoring the reaction by 1HNMR.Removal of the volatiles yielded a thick brown oil, theNMR spectra of which exhibit two sets of signals in an

approximate 1:1 ratio that were assigned to Cp2Zr(OEt)2,1e,5,30 and Cp2Zr(Et)OEt, 2e,31 by comparison to publishedNMRdata (Scheme 4). Reaction of Cp2ZrH2 with 1 equiv ofn-butyl vinyl ether under identical conditions afforded amixture of Cp2Zr(OnBu)2, 1f, and Cp2Zr(Et)OnBu, 2f, theidentity of which was established by NMR spectroscopy.The 1H NMR resonances of the ethyl group in Cp2Zr-(Et)OnBu exhibit a characteristic pattern with a triplet at1.56 ppm and an upfield quadruplet at 1.02 ppm, whichintegrate for 3H and 2H, respectively, relative to the 10cyclopentadienyl protons. Confirmation of our assignmentfor 1f was obtained by independent preparation from thereaction of Cp2ZrH2 with excess n-butanol (Scheme 4).

Scheme 2

Scheme 3

Figure 1. Molecular structure of 1d. Disordered solvent andhydrogen atoms (with the exception of H23 and H36) wereomitted for clarity. Thermal ellipsoids are drawn at the 50%probability level. Selected structural data (average literaturevalues in square brackets, Z1: centroid C1-C5, Z2: centroidC6-C10):28,29 Zr-O1: 1.961(2) A, Zr-O2: 1.984(2) A [1.993(5)],O1-Zr-O2: 98.3(1)� [98.6(4)], Zr1-Z1: 2.25 A, Zr-Z2: 2.24 A[2.24(1)], Z1-Zr-Z2: 127� [129(1)].

Scheme 4

(30) Gray, D. R.; Brubaker, C. H. Inorg. Chem. 1971, 10, 2143.(31) Alt, H. G.; Denner, C. E. J. Organomet. Chem. 1990, 391, 53.


Additional heating (5 days, 70 �C) of the 1e/2emixture didnot affect their ratio, nor did the addition of furtherEtOCHdCH2 (5 days, 70 �C). These results indicate thatCp2Zr(H)OEt was indeed obtained as a transient species andirreversibly trapped either by ethylene (formed during thereaction) or by another molecule of vinyl ether.32 Reactionsof Cp2ZrH2 with n-butyl vinyl ether conducted under anopen N2 atmosphere in THF to decrease the partial pressureof ethylene or in the presence of styrene to trap the zircono-cene hydride intermediate afforded only mixtures of severalzirconocene complexes, with 2f as themain reaction product.None of these reaction products indicated the presence ofan inserted styrene (NMR) or contained a Zr-H bond(no reaction with acetone).Hydrogenation of Zirconium Alkyls. Preparation of zirco-

nocene hydride and dihydride complexes has been reportedin the literature via hydrogenation of the correspondingzirconocene methyl complexes with various degrees of suc-cess. To this effect, following the reported procedure for thepreparation of Cp2Zr(Me)OtBu, 3c,33 the methyl alkoxidezirconocenes Cp2Zr(Me)OPh, 3a, and Cp2Zr(Me)OC6F5,3b, were prepared by reaction of Cp2ZrMe2 with 0.9 equivof the corresponding alcohol (Scheme 5). The reaction isquantitative with respect to the alcohol (1H NMR), andspectroscopic data were in agreement with literature valuesfor these complexes obtained by other pathways.26,34 NMRspectra of benzene-d6 solutions containing these complexesunder an atmosphere of hydrogen remained, however,unchanged even after prolonged heating (days) at 110 �C.At the same time, NMR signals of residual Cp2ZrMe2,present due to the slight excess employed in the preparation,disappeared readily even at room temperature.

Synthesis via a Borohydride Complex. H€usgen and Luin-stra reported the preparation of several zirconocene hydridosulfonate complexes by a two-step procedure:12 the borohy-dride complex Cp2Zr(BH4)OSO2R, prepared by ligand re-distribution between an equimolar mixture of Cp2Zr-(OSO2R)2 and Cp2Zr(BH4)2, was reacted with triethylamineto generate in high yield the corresponding hydrido sulfonateCp2Zr(H)OSO2R. NMR-scale reactions of Cp2Zr(BH4)2with 1 equiv of 1a in benzene-d6 showed the formation of anovel zirconocene of the formula Cp2Zr(BH4)OPh, 4, asrevealed by the appearance of new resonances in the 1HNMR spectrum for the Cp protons (5.80 ppm) and themetaprotons of the phenoxide substituent (6.63 ppm) (Scheme 6).After 2 days at room temperature, 4 was found to be inequilibrium with the starting material: Cp2Zr(BH4)2 and 1a.The same product mixture could be obtained directly by

protonation of Cp2Zr(H)(BH4) with 1 equiv of phenol. Theequilibrium is readily displaced by providing 1a in excess,and only traces of Cp2Zr(BH4)2 could be detected by NMRafter equilibration (48 h) of a 2:1 ratio solution of 1a andCp2Zr(BH4)2. Unfortunately, addition of triethylamine tothis reaction mixture resulted only in the formation ofCp2Zr(H)(BH4) and re-formation of 1a. Presumably thereaction of triethylamine with even trace amounts of Cp2Zr-(BH4)2 is faster than with Cp2Zr(BH4)OPh, thus completelydisplacing the ligand exchange reaction to the left.Hydride Eliminations from tert-Butyl Complexes. Chirik

and co-workers reported the preparation of several ring-sub-stituted zirconocene chloro hydride complexes by reaction ofthe corresponding zirconocenedichloridewith tBuLi, followedby spontaneous β-H elimination of the unstable Zr-tBu inter-mediate.35 Under comparable conditions, unsubstituted zirco-nocene reinserts isobutene to form Cp2Zr(iBu)Cl,

36 which canreact nevertheless as a hydrozirconation reagent.37 Motivatedby these reports, we investigated the possibility to generate aCp2Zr(H)OR species by isobutene elimination from the corre-sponding tert-butyl complex. Initial reactions of the zircono-cene chloro alkoxide complex Cp2Zr(OtBu)Cl38 with tert-butyllithium afforded a mixture of products, presumably dueto unselective substitution of the chloride or the alkoxideligand. We thus turned our attention to the correspondingdialkoxide complexes. Addition of 1 equiv of tBuLi (1.5 M inpentane) to a cooled (-78 �C) solution of diphenolate complex1a, followed by filtration of PhOLi, afforded a hexane-soluble,bright yellow powder. The presence of a singlet at 1.43 ppmintegrating to 9H in the aliphatic region of its 1H NMRspectrum and resonances at 50.0 and 37.3 ppm in its 13CNMR spectrum indicate the presence of a tert-butyl group,allowing the structural assignment of Cp2Zr(tBu)OPh, 5a

(Scheme 7). No indication for the formation of an isobutylor a hydride species could be gained from the NMR spectra.Elemental analyses consistentwith this formulawere obtained,but despite repeated efforts, we were unable to obtain a singlecrystal to confirm the rather unusual presence of a Zr-bondedtBu group by X-ray diffraction. Derivatization of 5a byinsertionof 2,6-xylyl isonitrile into theZr-tBubond, however,afforded crystals of Cp2Zr(OPh)C(tBu)dN(C6Me2H3), 6, sui-table for an X-ray diffraction study (Scheme 7, Figure 2).Unlike most literature examples,39 insertion of isonitrile into5a required heating to proceed.

An X-ray diffraction study confirmed the structure ofthe insertion product 6 and thus the initial assignment of5a (Figure 2). The main feature of this structure is the

Scheme 5

Scheme 6

(32) The proposed course of the reaction would require that approxi-mately one-third of Cp2ZrH2 remains unreacted. However, neither didwe observe any remaining precipitate nor did the spectra exhibitresonances of the sparingly soluble dihydride complex. While we didnot investigate the fate of the dihydride in detail, coloration of thesolution seems to indicate a certain amount of reduction to zirconium(II)species.(33) Stoebenau, E. J.; Jordan, R. F. J. Am. Chem. Soc. 2006, 128, 8162.(34) Firth, A. V.; Stewart, J. C.; Hoskin, A. J.; Stephan, D. W. J.

Organomet. Chem. 1999, 591, 185.

(35) Pool, J. A.; Bradley,C.A.; Chirik, P. J.Organometallics 2002, 21,1271.

(36) Barr, K. J.; Watson, B. T.; Buchwald, S. L. Tetrahedron Lett.1991, 32, 5465. Swanson, D. R.; Negishi, E.Organometallics 1991, 10, 825.

(37) Swanson, D. R.; Nguyen, T.; Noda, Y.; Negishi, E. J. Org.Chem. 1991, 56, 2590.

(38) Casey, C. P.; Jordan, R. F.; Rheingold, A. L. J. Am. Chem. Soc.1983, 105, 665.

(39) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059.


three-membered ring formed by a dative donation of the Nlone pair to the metal center. Structural data of 6, inparticular of the three-membered ring, are comparable tothose for similar insertion products of isonitriles into a Zr-Cbond (see Figure 2, caption).

In benzene-d6 solution at room temperature, all signalsassociated with 5a disappeared over a period of 2 months.At 65 �C, complete decomposition of 5a was observed in3 days. The colorless, benzene-insoluble precipitate formedduring the reaction showed no further reaction with acet-one. Of the benzene-soluble fraction, which accounts forapproximately half of the initial zirconocene concentration,the major decomposition species (60%) was identifiedby 1H and 13C NMR as Cp2Zr(iBu)OPh, 7a (Scheme 7),accompanied by 1a (40%). The zirconium-bound isobutylgroup in 7a gives rise to a multiplet at 2.21 ppm and twodoublets at 1.15 and 1.05 ppm in the 1H NMR spectra,integrating for one, six, and two protons, respectively. Toconfirm this assignment, 7awas prepared independently byreaction of 1a with iBuMgCl in Et2O and obtained as athick oil in 90% purity. Although small amounts ofcolorless crystals suitable for X-ray diffraction analysis(vide infra) formed after 2 weeks at room temperature(accompanied by extensive decomposition), several at-tempts to obtain analytically pure, solid samples of 7a

failed. Heating of solid 5a under a dynamic vacuum for20 h at 90 �C to force elimination of isobutene yielded onlyunchanged 5a, traces of 7a, and a precipitate, which showedno reaction with acetone. When 1 atm of H2 was added to asample of 5a in benzene-d6, no hydrogenation of the tert-butyl group was observed either at room temperature or at110 �C.After 5 days at this temperature only decompositionproducts were obtained, namely, 1a, isobutene, CpH,PhOH, and some insoluble materiel (no reaction withacetone).

Compound 7a is the first isobutyl zirconocene complexcharacterized by X-ray diffraction (Figure 3). The alkylligand displays neither β- nor γ-agostic interactions withthe metal center, as expected for a bulky alkyl substituentand in the presence of aπ-donating alkoxide ligand. It adopts

instead a conformation minimizing steric interactions of theisobutyl group with the phenoxide and cyclopentadienylligands. The zirconium carbon bond of the isobutyl ligandof 2.307(3) A is at the longer end of the range observed inzirconocene neo-pentyl complexes (2.256-2.296 A),41 butstill close to the average for zirconocene alkyl com-plexes (2.243-2.397 A) in general, or (C5R5)2Zr(CH2R)ORcomplexes in particular (2.265-2.337 A).29,42

The observed stability of the obtained zirconocene tert-butyl complex 5a is quite remarkable. As amatter of fact, weare aware of only two other zirconium complexes carryingtert-butyl substituents that do not readily decompose orrearrange at room temperature: a tetrahedral complex bear-ing a tripodal triamide ligand prepared by Gade and co-workers43 and Sita’s cyclopentadienyl zirconium acetamidi-nates.44 Both complexes include N donors in their ligandframework, which suggests a crucial influence of π-donationfrom the N to the metal center. Our results advocate that thealkoxide ligand reduces the propensity of the complexes toundergo β-H elimination in the same way, presumably byfilling the a1 orbital of the transition metal,45 thus reducing

Scheme 7

Figure 2. Molecular structure of 6. Hydrogen atoms and thedisorder of a cyclopentadienyl ring were omitted for clarity.Thermal ellipsoids are drawn at the 50% level. Selected geome-trical data (averaged literature values in square brackets):29,40

Zr1-C25: 2.247(3) [2.240(5)]; Zr1-N1: 2.254(2) [2.238(7)];C25-N1: 1.279(3) [1.274(2)], Zr1-O1: 2.075(2) A, O1-C11:1.323(3) A, Zr1-O1-C11: 143.3(2)�.

(40) Values determined from 16 comparable complexes in the CSDdatabase with the following ref codes: BEHWAM, CUYHIN, FAZ-MUO, GERSEC, ICAJUS, IGOCAI, KIHLES, LIFVAX, NETYOA,NETYUG, NIKXEK, NIYXEY, PUXSUW, RAQXEM, UKIBEV,YUVMAD

(41) Jeffery, J.; Lappert, M. F.; Luong-Thi, N. T.; Webb, M.; At-wood, J. L.; Hunter, W. E. J. Chem. Soc., Dalton Trans. 1981, 1593.Dreier, T.; Bergander, K.; Wegelius, E.; Frohlich, R.; Erker, G. Organome-tallics 2001, 20, 5067.Chirik, P. J.; Dalleska,N. F.; Henling, L.M.; Bercaw, J.E. Organometallics 2005, 24, 2789.

(42) Determined from a structural search on Cp and Ind zirconiumcomplexes with unchelated terminal alkyl ligands in the CambridgeStructural Database.

(43) Gade, L.H.; Renner, P.;Memmler, H.; Fecher, F.; Galka, C. H.;Laubender, M.; Radojevic, S.; McPartlin, M.; Lauher, J. W. Chem.;Eur. J. 2001, 7, 2563. Renner, P.; Galka, C.;Memmler, H.; Kauper, U.; Gade,L. H. J. Organomet. Chem. 1999, 591, 71.

(44) Harney, M. B.; Keaton, R. J.; Fettinger, J. C.; Sita, L. R. J. Am.Chem. Soc. 2006, 128, 3420. Keaton, R. J.; Koterwas, L. A.; Fettinger, J. C.;Sita, L. R. J. Am. Chem. Soc. 2002, 124, 5932.

(45) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729.


its availability for the β-H elimination step.46 The resistanceof Cp2Zr(Me)OR complexes 3a-c and of 5a to undergohydrogenation (vide supra), whichwas also observed in Sita’sacetamidinate complexes,10 is in agreement with these re-sults. Jordan et al. observed a 4 times faster hydrogenation of[Cp2ZrMe(THF)]BPh4 in CH2Cl2 than in THF and attrib-uted the difference to the π-donation of the THF-oxygen,which raises the energy of the Zr LUMO required foreffective hydrogenation.47 Since phenoxide coordination isstrongly influenced by steric considerations,48 there is nodirect evidence for an increased π-donation in the structuraldata of 7a. Complex 6 shows a longer Zr-O and a shorterO-C bond than 7a (Zr1-O1: 2.075(2) and 1.993(2) A,O1-C11: 1.323(3) and 1.334(3) A), which would be inagreement with reduced π-donation to the less Lewis-acidicmetal center in 6, but the differences are barely significant.

Nevertheless, but extremely slowly at room temperature(2 months), 5a does reorganize itself to the sterically lessdemanding isobutyl complex 7a. Most likely, formation of7a occurs by β-H elimination and reinsertion of isobutene.3,4

It is unknown at themoment if in this or comparable systemsthe isomerization rather involves rotation of a zirconium-bonded isobutene or dissociation and reassociation of theolefin. For the sake of simplicity, we propose dissociation ofisobutene and transient formation of Cp2Zr(H)OPh, 9a, butformation of the corresponding olefin complex Cp2Zr(H)-(H2CdCMe2)OPh cannot be excluded.

Further indirect evidence agrees with the existence of anintermediary hydride species. Heating of a C6D6 solution of5a in the presence of 1.6 equiv of phenol quantitatively (1HNMR) yielded the diphenolate 1a along with free isobutene(δ 4.75, 1.60 ppm) and isobutane in approximate 4:1 ratio

(Scheme 7). Reactions of 5awith 1 equiv of benzophenone at65 �C for 3 days afforded a mixture of 1a (22-24%), 1d(21-23%), and a new species (53-57%) identified as Cp2Zr-(OPh)(OCHPh2), 8, based on resonances at 5.93 ppm (10H)for the cyclopentadienyl protons, at 6.02 ppm (1H) forCHPh2, and the associated resonances for the aromaticprotons. In agreement with this assignment, the same mix-ture of products was obtained by ligand exchange reactionsbetween 1a and 1d (Scheme 7). Reaction between 5a andstyrene or 1-hexene did not afford the corresponding inser-tion products.

The fact that reaction of 5a with phenol generates iso-butene rather than isobutane indicates that direct proton-ation of the alkyl group is only a minor process and 1a isinstead predominately formed by protonation of the zirco-nocene hydride 9a after isobutene elimination. Hydride 9a

can also be trapped by benzophenone to yield the corre-sponding alkoxide complexes. Only a statistical mixtureof the dialkoxide complexes 1a, 1d, and 8 was obtained,indicating facile exchange of the alkoxide ligands under theseconditions. The lack of reactivity of 5a toward hexene andparticularly (vide infra) styrene is somewhat surprising, butmight be related to the rather harsh reaction conditionsrequired for the elimination of isobutene (70 �C, days).

To decrease the electron-donating properties of the OPhligand in 5a, we prepared the pentafluorophenolate deriva-tive Cp2Zr(tBu)OC6F5, 5b, by addition of 1 equiv of tBuLi toa cooled (-78 �C) solution of 1b in Et2O (Scheme 8). Thehexane-soluble product was isolated in moderate yield afterfiltration to remove theC6F5OLi formed during the reaction.Complex 5b is remarkably moisture sensitive, as evidencedby the formation of [Cp2Zr(OC6F5)]2(μ-O)26 in sealed J.Young tubes despite rigorously anhydrous handling andthe use of carefully dried benzene-d6.

Monitoring the decomposition of 5b in benzene-d6 byNMR spectrometry reveals the formation of Cp2Zr(iBu)-OC6F5, 7b, in 13 days at room temperature or 3 h at 70 �C(Scheme 8). Again, 7b could be prepared independently byreacting 1b with iBuMgCl in diethyl ether as a viscous oil,which could not be further purified by crystallization. Inter-estingly, thermolysis (70 �C, 3 h) of 5b inC6D6 in the presenceof excess styrene (4 equiv) afforded Cp2Zr(CH2CH2Ph)-OC6F5, 10, and in the presence of ethyl vinyl ether (4 equiv)Cp2Zr(OEt)(OC6F5), 11, and free ethylene. The identity of

Figure 3. Molecular structure of 7a. Hydrogen atoms and thedisorder of a cyclopentadienyl ring were omitted for clarity.Thermal ellipsoids are drawn at the 50% level. Selected geome-trical data (Z1: centroid C1-C5, Z2: centroid C6-C10):Zr-C20: 2.307(3) A, Zr1-Z1: 2.19 A, Zr1-Z2: 2.23 A,Z1-Zr1-Z2: 129�, Zr1-O1: 1.993(2) A, O1-C11: 1.334(3) A,Zr1-O1-C11: 145. 9(2)�.

Scheme 8

(46) In the rare cases where stable zirconocene complexes with β-H-containing alkyl substiuents were obtained in the absence of π-donorligands, their relative stability is attributed to steric crowding of themetal center. Wendt, O. F.; Bercaw, J. E. Organometallics 2001, 20,3891.(47) Jordan, R. F.; Bajgur, C. S.; Dasher, W. E.; Rheingold, A. L.

Organometallics 1987, 6, 1041.(48) Cf. the Zr-O-CAr angle in Cp2Zr(OPh)2 and Cp*2Zr(OPh)2 of

147� and 173�, respectively. Howard, W. A.; Trnka, T. M.; Parkin, G.Inorg. Chem. 1995, 34, 5900.


10was established byNMR spectroscopy and its subsequentreaction with 2,6-xylyl isonitrile (vide infra). Assignment of11was confirmed by reaction of 5bwith 1 equiv of ethanol inC6D6 at 70 �C. In the presence of trans-3-hexene, thermolysisof 5b afforded a mixture of the n-hexyl complex Cp2Zr-(OC6F5)(CH2)5Me, 12 (vide infra), and 7b in a ratio of 60:40.In the presence of 1-hexene, the same product mixture wasobtained, albeit in a ratio of 93:7. The rate of disappearanceof 5b during the formation of 7b, 10, and 11 in benzene-d6was monitored by 1H NMR at 70 �C. All reactions observedsimilar kinetics consistent with a first-order reaction andwith comparable rate constants of k343K = 1.4-1.6 h-1. Onthe other hand, reaction of the iso-butyl complex 7b withEtOCHdCH2 at 70 �C yielded 11 with a lower first-orderrate constant of k343K= 0.13 h-1, and only traces of 11weredetected (1H NMR) after 10 was reacted for 5 days withEtOCHdCH2 at 70 �C.

Substitution of the hydrogen atoms of the phenolateligand by fluorine in 5b reduces O-π-donation to the metalcenter and thus increases the lability of the tert-butyl groupversus β-H elimination. Consequently, at 25 or 70 �C for-mation of the corresponding isobutyl derivative is about1 order of magnitude faster from 5b than from 5a. Theputative hydride intermediate Cp2Zr(H)OC6F5, 9b, couldbe trapped in the presence of either styrene or ethyl vinylether to yield the corresponding insertion products(Scheme 8). No traces of the isobutyl complex 7b wereobserved in these reactions, which is in agreement withrelative insertion rates into M-H bonds of styrene andisobutene, reported by Bercaw and Chirik.22 An internalolefin, such as trans-3-hexene, is barely able to compete withisobutene for 9b, while reactions with 1-hexene contain onlysmall amounts of the isobutyl complex. Identical rate con-stants for the formation of 7b, 10, and 11 indicate thatformation of the zirconocene hydride 9b is rate-determining,followed by trapping of 9b with the appropriate olefin. Amechanism involving prior isomerization to the isobutylcomplex 7b can be ruled out due to its significant lowerreaction rate with ethyl vinyl ether under the same condi-tions. Assuming that β-H elimination is also rate-determin-ing in reactions of 7b and 10with vinyl ethyl ether to yield 11,β-H eliminations inCp2Zr(OR)R complexes follow the trendtBu>iPr>CH2CH2Ph.

The evidence for the intermediate existence of the hydrides9a and 9b prompted us to investigate other methods togenerate the hydride as a transient species. Erker and

co-workers reported the activity of a mixture of Cp02ZrH2

and Cp02ZrCl2 (Cp0 =C5H4Me), obtained in the attemptedsynthesis of Cp02Zr(H)Cl, in hydrozirconation reactions,most probably via Cp02Zr(H)Cl formed in equilibrium.11

Reactions between Cp2ZrH2 and 1 or 2 equiv of 1a inC6D6, however, did not show any indication for the forma-tion of 9a, and reactions effectuated in the presence of 1 equivof styrene afforded after 3 days at room temperature onlytraces of an olefin insertion product (CH2Ph: 2.97 ppm) thatcould not be identified with certainty as Cp2Zr(CH2CH2Ph)-OPh. Reaction of an equimolar mixture of Cp2ZrH2 and 1.2equiv of 1b with styrene in C6D6, however, cleanly affordedafter 3 days at room temperature the styrene 1,2-insertionproduct 10 as the major species (58%, Scheme 9), accom-panied by 31% of 1b and minor amounts of decompositionor side products ({Cp2Zr(OC6F5)}2(μ-O): 1%, others: 10%,based on Cp resonances). 1H NMR spectra of 10 containedtwo multiplets of identical intensity at 2.90 and 1.43 ppm,which showed cross-peaks in the COSY spectra.49 Thecorresponding signals in the 13C spectra at 50.5 and40.1 ppm were identified as CH2 groups (DEPT). All ofthese observations agree with the assignment of 10 as Cp2Zr-(CH2CH2Ph)OC6F5.

50

The reduced amount of decomposition products obtainedhere, when compared to the preparation of 10 by thermolysisof 5b in the presence of styrene, allowed the observation of adoublet of minor intensity at 1.56 ppm, coupled to anunresolved resonance at 2.9 ppm beneath the CH2Ph signalof 10 (COSY). Both resonances shifted (1.13, 3.59 ppm) afterreaction with xylyl isonitrile. These signals were putativelyassigned to the 2,1-insertion product of styrene Cp2Zr-(OC6F5)CH(Me)(Ph), 13 (Scheme 9). The ratio of 10:13was approximately 95:5 and remained unchanged afterheating for 20 h at 70 �C. Coordination of the zirconium tothe R-position of styrene was attributed to a stabilizingcoordination of the aryl ring to the metal center, and hydro-zirconations of aryl alkenes usually yield a mixture ofregioisomers.5-7 While the formation of a 2,1-insertionproduct can be suppressed by extensive substitution of thecyclopentadienyl ring,22 1b/Cp2ZrH2 is to our knowledge themost regioselective hydrozirconation reagent for styrenewith unsubstituted cyclopentadienyl ligands. Increasedπ-donation of the alkoxy ligand as well as steric effects mightdisfavor the formation of the secondary alkyl species 13.

The absence of isobutene in hydrozirconations with 1b/Cp2ZrH2 allowed the preparation of single products with lessreactive olefins as substrates. Reactions of trans-3-hexenewith 1b/Cp2ZrH2 in C6D6 afforded after 3 days at roomtemperature only the 1-hexyl species Cp2Zr(OC6F5)-(CH2)5Me, 12 (Scheme 9). 1H spectra of 12 contained foursignals for the hexyl protons with an integral ratio of 2:8:2:3,and COSY spectra allowed the identification of the CH2

Scheme 9

(49) Addition of 2,6-xylylisonitrile to the C6D6 solution gave rise to anew zirconocene species, which contained the two now resolved triplets,shifted to 2.77 and 2.45 ppm, in addition to peaks assigned to insertedisonitrile.

(50) Assignment of 10 and 12 was further confirmed by reaction ofthe benzene-d6 solutions with I2.

1HNMRandGC-MS analyses showedthe formationof 1-iodo-2-phenylethane and iodohexane, respectively, in51% and 90% yield (relative to initial olefin). 1-Iodo-1-phenylethane(expected upon reaction of 13 with iodine) was not identified in theobtained reaction mixtures, although a minor, iodine-containing com-pound was observed in GC-MS analyses, which showed identicalfragmentation patterns and similar retention times to 1-iodo-2-pheny-lethane.


groups in R- and β-position relative to the zirconium centerat 1.23 and 1.66 ppm, respectively. The aliphatic region of the13C spectra of 12 displayed six signals, five of which wereidentified by DEPT as CH2 groups, the Zr-boundmethyleneappearing at 50.0 ppm. Consequently, complex 12 could beprepared as well by reaction of 1b/Cp2ZrH2 with 1-hexenefor 3 days at room temperature or 3 h at 60 �C. The presenceof a Zr-bound alkyl group was further confirmed by thereaction of 12 with 2,6-xylylisonitrile. When the reaction ofsubstoichiometric amounts of trans-3-hexene with 1b/Cp2ZrH2 in C6D6 was followed by NMR, the aliphaticregion of the NMR spectra contained no signals that couldbe assigned to other Zr alkyl species than 12, even at <5%conversion. Instead, resonances assigned to 2-hexene bycomparison with literature data and by GC-MS analysiswere observed in increasing amounts,51 which however neverexceeded 25% of that of trans-3-hexene. After 21 h, all olefinhad reacted and only resonances of 12, 1b, and (Cp2ZrH2)2remained. To test the involvement of Cp2ZrH2, its reactionwith trans-3-hexene was investigated under the same condi-tions. No indication for the formation of any zirconocenealkyl species could be obtained, but the NMR spectraindicated isomerization of trans-3-hexene to an approxi-mately 1:1 mixture of 3-hexene and 2-hexene after 21 h,51

accompanied by approximately 5% of hexane. Continuedreaction for 4 days afforded exclusively hexane. In repeatedexperiments, isomerization of trans-3-hexene by Cp2ZrH2

was subject to an induction period ranging from 2 to 24 h,indicating that, rather than by Cp2ZrH2 itself, the isomeriza-tion is catalyzed by one of its decomposition products. Inagreement with the assignment of the reaction products withCp2ZrH2 as mixture of isomerized olefins, addition of 1b tosuch a mixture yielded again exclusively the 1-hexyl species12 (accompanied by small amounts of hexane).

Formation of 12 (and other zirconocene alkyl complexes)by reaction of olefins with 1b/Cp2ZrH2 can be envisioned bytwo mechanisms: Comproportionation between 1b andCp2ZrH2 yields 9b, which inserts 3-hexene, followed by iso-merization to the 1-hexyl product (Scheme 10, A). Alterna-tively, insertion of olefin might occur into Cp2ZrH2, whichwould lead to the corresponding Cp2Zr(H)R complexes(Scheme 10, B). Isomerization by β-H elimination/reinsertioninto Cp2ZrH2 leads to the formation of Cp2Zr(H)(CH2)5Me,which is now irreversibly trapped by 1b to form 12. Observedrelative reactivities seem to disfavor pathway B: only minorisomerization to 2-hexene (∼5%) was observed in reactionsbetween Cp2ZrH2 and trans-3-hexene after 3 h, while ∼40%of trans-3-hexene was converted into 12 by 1b/Cp2ZrH2 afterthe same time, in addition to the formation of∼5% 2-hexene.The available data did not allow to distinguish if 2-hexenewasderived via pathway A or B. Formation of 12, however,proceeds faster than possible via pathway B (maximum twiceas fast as the rate of isomerization to 2-hexene), which arguesstrongly in favor of the formationof themore reactivehydridospecies 9b. The absence of significant amounts of 2-hexeneformed during hydrozirconation of trans-3-hexene indicatesthat the olefin remains to a certain extent attached to thezirconium center during the isomerization, which is in agree-ment with hydrozirconations with Schwartz’s reagent, whereisomerized olefins are rarely observed, mainly in the case ofless reactive olefins.3

In light of these results, we revisited the direct protonationin the presence of olefin, which proved unsuccessful whenphenol was employed. Addition of C6F5OH to a mixture ofCp2ZrH2 and excess 1-hexene in C6D6 yielded after heatingfor 1.5 h at 70 �C a dark solution. The only species present inits 1HNMRspectrumwere12and 1 (6%).Hydrozirconationswith 9b can thus be achieved on a reasonable time scale bypreparing 9b in situ from commercially available precursors.

Conclusions

Hydrido alkoxide complexes of unsubstituted zircono-cene, Cp2ZrH(OR), remained elusive synthetically, mostlikely due to fast disproportionation to Cp2ZrH2 andCp2Zr-(OR)2. They can be accessed, however, as a transient speciesby thermolysis of Cp2Zr(tBu)OR or comproportionationbetween Cp2ZrH2 and Cp2Zr(OC6F5)2. Their formation inthe presence of olefins or ketone yields the correspondinghydrozirconation products. While exchange of chloride withalkoxide was expected to impede β-H elimination reactions,experimental evidence in this regard is so far inconclusive.tert-Butyl complexes 5a,b with OPh and OC6F5 ligandsdisplayed drastically increased stabilities when comparedto their chloride counterparts. On the other hand, no alkylspecies other than n-hexyl could be identified in reactions oftrans-3-hexene with 1b/Cp2ZrH2, which is in apparent dis-agreement with the slow isomerization of Cp2Zr(Cl)C(H)-(Me)R complexes reported by Chirik and Bercaw.4 Overall,thermolysis of 5b, comproportionation of 1b/Cp2ZrH2, and,in particular, reaction of Cp2ZrH2 with C6F5OH in thepresence of olefins gave access to Cp2Zr(H)OC6F5 as a newhydrozirconation reagent, whose properties differ notablyfrom Schwarz’s reagent, e.g., a strongly increased regiospe-cificity in styrene hydrozirconation. We are currently inves-tigating the reactivities and selectivities of these hydro-zirconations in general and in particular the conflictingevidence with regard to β-H elimination and the suitabilityof other alcohols than the “pseudo-halogen” C6F5OH.

Experimental Section

All reactions were carried out under an inert atmosphereusing Schlenk and glovebox techniques. Cp2Zr(OPh)2,24 Cp2Zr-(BH4)2,

52 Cp2Zr(H)(BH4),53 Cp2ZrMe2,

54 Cp2Zr(OPh)2,24

Scheme 10

(51) Neither NMR nor GC-MS data allowed a complete assignmentof the cis- and trans-isomers for 2- or 3-hexene, respectively.

(52) Nanda, R. K.; Wallbridge, M. G. H. Inorg. Chem. 1964, 3, 1798.(53) James, B. D.; Nanda, R. K.; Walbridge, M. G. H. Inorg. Chem.

1967, 6, 1979.(54) Frauenrath, H. Polymerization of Olefins and Functionalized

Monomers with Zirconocene Catalysts; Techn. Hochsch. Aachen, 2001.Samuel, E.; Rausch, M. D. J. Am. Chem. Soc. 1973, 95, 6263.


Cp2Zr(OC6F5)226 PhOSiMe3,

55 C6F5OSiMe3,26 and tBuO-

SiMe356 were prepared according to literature procedures.

Cp2ZrH2, Cp2ZrCl2, and other chemicals were purchased fromcommon commercial suppliers. 1H and 13C NMR spectra wereacquired on a Bruker AMX 300 spectrometer (300 MHz 1H) oron a Bruker Avance 500 spectrometer (500MHz 1H). 19FNMRspectra were acquired on a Bruker Avance 300 (300 MHz 1H).Chemical shifts were referenced to the residual signals of thedeuterated solvent (C6D6:

1H: δ 7.16 ppm, 13C: δ 128.38 ppm).Relaxation delays of 15 s were used in 1H NMR to obtainreliable integration data. Complete assignments of the 1H and13C NMR resonances of the zirconocene products wereobtained using information from COSY, DEPT 135, HSQC(heteronuclear single quantum coherence), and/or HMBC(heteronuclear multiple bond coherence) spectra. 13C reso-nances of the OC6F5 group could not be detected using acquisi-tion times sufficient to observe all other resonances. THF wasdistilled from sodium/benzophenone; all other solvents weredried by passage through activated aluminum oxide (MBrownSPS) and deoxygenated by repeated extraction with nitrogen.Benzene-d6 was dried over sodium and distilled under reducedpressure, then degassed by three freeze-pump-thaw cycles.Reagents were dried using the suitable drying agent and distilledunder reduced pressure prior to use (tert-butanol: K2CO3; ethylvinyl ether, n-butyl vinyl ether, 1-hexene, 3-hexene: CaH2;C6F5OH, 1-butanol; ethanol: activated 4 A molecular sieves).Phenol and 2,4-di-tert-butylphenol were sublimed under re-duced pressure prior to use. Styrene was evacuated undervacuum and dried over 4 Amolecular sieves. Elemental analyseswere performed by the Laboratoire d’Analyse �El�ementaire atthe University of Montreal. Some zirconocene complexes wereobtained as noncrystallizable oils, precluding appropriate pur-ifications for elemental analyses. Analyses of the oils returnedinconsistent results, indicating a high tendency to decompose.Cp2Zr(OCHPh2)2, 1d. THF (10 mL) was added at room

temperature to a Schlenk flask containing Cp2ZrH2 (200 mg,0.90 mmol) and benzophenone (163 mg, 0.90 mmol). The graysuspension was stirred overnight at room temperature, yieldinga pale yellow solution. The solution was filtered, the filtrateevaporated, and the residue recrystallized from a concentratedtoluene/hexane (ca. 1:1) solution chilled to -30 �C. The color-less crystals (137 mg, 24%) were washed with cold hexane andbriefly dried under vacuum. Cp2Zr(OCHPh2)2 cocrystallizedwith 0.5 molecule of toluene (1H NMR).

1H NMR (300 MHz, C6D6): δ 7.40 (d, 8H, J = 7 Hz, orthoAr), 7.20 (t, 8H, J= 7.5 Hz,metaAr), 7.10 (d, 4H, J= 7.5 Hz,para Ar), 5.99 (s, 1H, OCHPh2), 5.89 (s, 10H, C5H5) ppm. 13CNMR: δ 147.6 (ipsoAr), 128.9 (Ar), 127.4 (Ar), 127.2 (Ar), 112.5(C5H5), 86.9 (CHPh2) ppm. Anal. Calcd for C39.5H36O2Zr: C,74.84; H, 5.72. Found: C, 74.50; H, 5.05.Cp2Zr(OnBu)2, 1f. At room temperature, a 4 mL toluene

solution of 1-butanol (90 mg, 1.21 mmol) was added at one timeto a suspension of Cp2ZrH2 in 10 mL of toluene. A vigorousbubbling ensued, and the reaction mixture was allowed to stir15 h at room temperature, yielding a pale yellow solution. Thevolatiles were removed in vacuo (3 h, 25 �C). Then 15 mLof hexanes was added, the mixture filtered, and the solventremoved in vacuo, affording 1f as a yellow oil.

1H NMR (benzene-d6): 6.02 (s, 10H, C5H5), 3.91 (t, 4 H,OCH2), 1.43 (m, 8H, CH2CH2), 0.96 (t, 6H, CH3) ppm. 13CNMR (benzene-d6): 112.0 (C5H5), 73.5 (OCH2), 37.2(OCH2CH2CH2), 20.0 (OCH2CH2CH2) 14.7 (CH3) ppm.Reaction of Cp2ZrH2 with EtOCHdCH2. In aN2-filled glove-

box a 25 mL glass bomb was charged with Cp2ZrH2 (50 mg,0.22 mmol), EtOCHdCH2 (16 mg, 0.22 mmol), a magnetic stirbar, and toluene (5 mL). The vessel was hermetically sealed and

sent out of the glovebox, and the suspension was stirred 12 h at60 �C. Over the reaction time the reaction mixture turned darkorange-green. Removal of the volatiles yielded a light brown,thick oil. Analysis of the cyclopentadienyl proton integration(1H NMR) of the crude mixture showed a ∼1:1 ratio of Cp2Zr-(OEt)2, 1e, and Cp2Zr(Et)OEt, 2e.

Cp2Zr(OEt)2, 1e.1H NMR (300MHz, C6D6): δ 6.01 (s, 10H,

C5H5), 3.95 (t, 4H, OCH2, J=7 Hz), 1.12 (m, 8H, CH3, J =7 Hz) ppm. 13C NMR: δ 111.9 (C5H5), 68.9 (OCH2), 20.5(CH2CH2CH3) ppm.

Cp2Zr(Et)OEt, 2e. 1H NMR (300 MHz, C6D6): δ 5.76 (s,10H, C5H5), 3.81 (q, OCH2, J=7 Hz), 1.59 (t, 3H, CH2CH3,J=7.5 Hz), 1.06 (q, 2H, CH2CH3, J=7.5 Hz), 0.99 (t, 3H,OCH2CH3, J=7 Hz) ppm. 13C NMR: δ 110.6 (C5H5), 69.0(OCH2), 32.0 (H2CH3)), 20.4 (OCH2CH3), 18.2 (CH2CH3) ppm.

Reaction of Cp2ZrH2 with nBuOCHdCH2. In a N2-filledglovebox a 25 mL glass bomb was charged with Cp2ZrH2

(200 mg, 0.90 mmol), nBuOCHdCH2 (90 mg, 0.90 mmol), amagnetic stir bar, and toluene (8 mL). The vessel was hermeti-cally sealed and sent out of the glovebox, and the suspensionwasstirred 12 h at 65 �C. Over the reaction time the reactionmixtureturned brown-gray. The volatiles were removed under vacuum,and the residue was taken into 10 mL of hexanes. Filtration andevaporation of the filtrate afforded a brown, thick oil. Analysisof the cyclopentadienyl proton integration (1H NMR) of thecrude mixture showed a ∼1:1 ratio of Cp2Zr(OnBu)2, 1f (NMRdata vide supra), and Cp2Zr(Et)OnBu, 2f.

Cp2Zr(Et)OnBu, 2f.1H NMR (300 MHz, C6D6): δ 5.77

(s, 10H, C5H5), 3.78 (t, 4H, OCH2), 1.56 (t, ZrCH2CH3),1.46-1.25 (m, 4H, CH2CH2CH3), 1.02 (q, ZrCH2CH3), 0.90(t, 3H, CH2CH2CH3) ppm. 13C NMR: δ 110.7 (C5H5), 73.4(OCH2), 36.8 (CH2CH2CH3), 32.1 (ZrCH2CH3), 19.8 (CH2-CH2CH3), 18.1 (ZrCH2CH3), 14.6 (CH2CH2CH3) ppm.

NMR-Scale Preparation of Cp2Zr(Me)OR, 3a. In a nitrogen-filled glovebox, a C6D6 solution of Cp2ZrMe2 (ca. 10 mg in0.6 mL) was added at one time to 0.9 equiv of the alcohol ina small test tube. Vigorous bubbling ensued (C6F5 > Ph ∼C6tBu2H3 > tBu). After 30 s, the bubbling ceased and thecolorless solution was transferred to a J. Young tube andallowed to stand 30 min at room temperature. NMR spectramatched those obtained in preparations by other pathways(3a and 3b)26,34 or the same protocol (3c).33

Cp2Zr(Me)OPh, 3a. 34 1H NMR (300 MHz, C6D6): δ 7.19 (t,2H, J=7Hz,metaOPh), 6.85 (t, 1H, J=7Hz, paraOPh), 6.59(d, 2H, J=7.5 Hz, orthoOPh), 5.74 (s, 10H, C5H5), 0.49 (s, 3H,Zr-CH3) ppm. 13C NMR (C6D6): δ 165.8 (ipso OPh), 123.0(orthoOPh), 119.9 (paraOPh), 118.6 (metaOPh), 111.5 (C5H5),22.8 (Zr-CH3) ppm.

Cp2Zr(Me)OC6F5, 3b.26 1HNMR(300MHz,C6D6): δ 5.69 (s,

10H, C5H5), 0.54 (s, 3H, Zr-CH3) ppm. 13C NMR (C6D6): δ112.5 (C5H5), 27.2 (Zr-CH3) ppm. 19F (C6D6):δ-165.55 (m,orthoC6F5), -167.52 (m, meta C6F5), -174.25 (m, para C6F5) ppm.

Cp2Zr(BH4)OPh, 4a. (a) A J. Young NMR tube was char-ged with 1a (24.3 mg, 0.060 mmol), Cp2Zr(BH4)4 (7.5 mg,0.030 mmol), and 0.6 mL of benzene-d6. The colorless solutionwas allowed to stand 2 days at room temperature to yield amixture of 1a, 4a, and traces (ca. 1%) of Cp2Zr(BH4)4.

(b) In a N2-filled glovebox, a PhOH (6.7 mg, 0.072 mmol)solution in benzene-d6 (0.6 mL) was added to Cp2Zr(H)(BH4)(17.0 mg, 0.072 mmol). Vigorous bubbling ensued. After 5 minthe colorless solution was transferred to a J. Young NMR tube.NMR analysis revealed a mixture of 4a (42%), Cp2Zr(BH4)2(20%), and 1a (31%).

Cp2Zr(BH4)OPh, 4a.1H NMR (300 MHz, C6D6): δ 7.19 (t,

2H, J=8Hz,metaOPh), 6.87 (t, 1H, J=7, paraOPh), 6.63 (d,2H, J= 8, ortho OPh), 5.80 (s, 10H, C5H5), 1.04 (q, J= 80 Hz,Zr-BH4) ppm. 13CNMR(C6D6): δ 166.4 (ipsoOPh), 130.1 (orthoOPh), 120.9 (para OPh), 119.0 (meta OPh), 113.1 (C5H5) ppm.

Reaction of Cp2Zr(BH4)OPh, 4a, with Triethylamine. In aN2-filled glovebox, a J. Young tube was charged with 1a (27.7 mg,

(55) Poisson, T.; Dalla, V.; Papamicael, C.; Dupas, G.; Marsais, F.;Levacher, V. Synlett 2007, 0381.(56) Langer, S. H.; Connell, S.;Wender, I. J. Org. Chem. 1958, 23, 50.


0.0674 mmol), Cp2Zr(BH4)2 (8.6 mg, 0.034 mmol), and 0.6 mLof benzene-d6. The mixture was allowed to stand 2 days, andNMR was taken to ensure completion of the reaction. Thespectrum showed a mixture of 1a (57%), 4a (40%) and 3% ofCp2Zr(BH4)2/Cp2Zr(H)(BH4). Et3N (9.4 μL, 0.0674 mmol) wasadded to the NMR tube with a microsyringe and the reactionallowed to stand at room temperature. After 20 h, 1H NMRshowed a mixture of 1a (70%), 4a (13%), and Cp2Zr(H)(BH4)(18%). After 40 h no residual 4awas detected and the remainingmixture consisted of 1a (77%) and Cp2Zr(H)(BH4) (23%).Cp2Zr(tBu)OPh, 5a. 1a (550 mg, 1.35 mmol) was dissolved in

40 mL of Et2O. Upon cooling to -78 �C, a fair amount of thezirconocene precipitated out of the solution as a white powder.A tBuLi solution (900 μL, 1.5M solution in pentane) was addeddropwise over 5 min to the reaction flask. The white precipitaterapidly disappeared, and the resulting bright yellow solutionwas stirred for 1 h at-78 �C. The dry ice bath was removed andthe reaction mixture stirred an additional hour. After evapora-tion of the volatiles, 10 mL of hexanes was added, stirred, andremoved under vacuum. Addition of 30 mL of hexanes to theyellow residue, followed by filtration and removal of the solventunder vacuum, afforded 5a (343 mg, 68%) as a yellow powder.

1H NMR (300 MHz, C6D6): δ 7.18 (m, 2H, meta OPh), 6.86(t, 1H, J=7, paraOPh), 6.58 (d, 2H, J=9, orthoOPh), 5.78 (s,10H, C5H5), 1.43 (s, 9H, Zr-C(CH3)) ppm. 13C NMR (C6D6): δ165.5 (ipso OPh), 129.9 (ortho OPh), 120.1 (para OPh), 118.6(meta OPh), 112.1 (C5H5), 50.0 (Zr-C(CH3)3), 37.3 (Zr-C-(CH3)3) ppm. Anal. Calcd for C20H24OZr: C, 64.64; H, 6.51.Found: C, 64.68; H, 6.24.Cp2Zr(tBu)OC6F5, 5b. A tBuLi solution (340 μL, 1.5 M

solution in pentane) was added dropwise to a cooled (-78 �C)solution of 1b (300 mg, 0.51 mmol) in 25 mL of Et2O (someprecipitation of 1b occurred). The mixture was stirred 2 h at-78 �C, then allowed to gradually warm to room temperatureand stirred an additional hour. The bright yellow solution wasevaporated to dryness. The following procedure was repeatedtwice: hexane (ca. 10 mL) was added, the reaction mixture wasvigorously stirred, and the volatiles were stripped off. The brightyellow residuewas then extractedwith 20mLof hexane, filtered,and dried under vacuum, yielding Cp2Zr(OC6F5)(tBu), 5b

(131 mg, 56%), as a bright yellow powder.1H NMR (300 MHz, C6D6): δ 5.74 (s, 10H, C5H5), 1.36 (s,

9H, C(CH3)3) ppm. 13C NMR (C6D6): δ 113.2 (C5H5), 53.8(C(CH3)3), 36.6 (C(CH3)3) ppm. 19F (C6D6): δ -164.12 (m,ortho C6F5), -167.37 (m, meta C6F5), -173.97 (m, para C6F5)ppm. Anal. Calcd for C20H19F5OZr: C, 52.04; H, 4.15. Found:C, 52.08; H, 4.00.Cp2Zr(OPh)C(tBu)dN(2,6-Me2C6H3), 6. In a nitrogen-filled

glovebox, a Schlenk flask was charged with 5a (150 mg, 0.40mmol), 2,6-dimethylphenylisocyanide (52 mg, 0.40 mmol), amagnetic stir bar, and toluene (15 mL). The reaction flask wasclosed and stirred 15 h at 65 �C under N2. The resulting darkorange solution was decanted and evaporated to dryness, yieldinganorange residue.Colorless crystals of thedesiredproduct suitablefor X-ray analyses were obtained from a cooled (-30 �C) toluene/hexane solution. The crystals were washed twice with cold hexanes(0.5 mL) and briefly dried under vacuum (62 mg, 31%).

1H NMR (300 MHz, C6D6): δ 7.16 (m, 2H, meta OPh),6.81-6.90 (m, 3 H, C6H3), 6.72 (tt, 1H, J=7, 1 Hz, paraOPh),6.52 (dm, ortho OPh), 5.90 (s, 10H, C5H5), 1.93 (s, 6H, C6H3-(CH3)3), 0.95 (s, 9H, C(CH3)3) ppm. 13CNMR (C6D6): δ 168.20(ipso OPh), 146.8, 129.0, 128.4, 128.3, 124.6, 119.1, 116.2, 109.4(C5H5), 42.4 (C(CH3)3), 27.7 (C6H3(CH3)2), 19.5 (C(CH3)3)ppm. The 13C NMR signal for Zr-C(tBu)dN) could not beobserved after a reasonable acquisition time; however theHMBC exhibits a cross-peak for C-C(CH3)3. Anal. Calcd forC29H33NOZr: C, 69.23; H, 6.62; N, 2.79. Found: C, 68.93; H,5.93; N, 2.94.Cp2Zr(iBu)OPh, 7a. 1a (400 mg, 0.98 mmol) was dissolved in

40 mL of Et2O, yielding a colorless solution. Upon cooling to

-78 �C, some white crystals formed. To this cooled suspensionwas added dropwise iBuMgCl (0.490 mL, 0.98 mmol, 2 Msolution in Et2O) with a syringe. After 1 h at -78 �C, thecolorless solution was allowed to warm to room temperatureand stirred an additional 2 h. The solution turned yellow withformation of some precipitate. The solvent was removed underreduced pressure, yielding a yellow foam, to which 10 mL ofhexanes was added, stirred, and removed under vacuum tofacilitate removal of the volatiles. The resulting yellow-brownresidue was then dried for 2 h under dynamic vacuum. Additionof hexane, subsequent filtration, and evaporation of the filtrateto dryness yielded an orange oil that turned brown uponstanding (at room temperature or -30 �C).

1H NMR (300 MHz, C6D6): δ 7.18 (t, 2H, J = 7 Hz, metaOPh), 6.85 (t, 1H, J= 7 Hz, para OPh), 6.58 (d, 2H, J= 8 Hz,orthoOPh), 5.75 (s, 10H, C5H5), 2.21 (m, 1H, CH2CH), 1.15 (d,6H, J=7Hz, CH(CH3)2), 1.05 (d, 2H, J=7Hz, ZrCH2) ppm.13C NMR (C6D6): δ 165.8 (ispo OPh), 130.0 (o-OPh), 120.0(para OPh), 118.7 (meta OPh), 111.5 (C5H5), 56.0 (CH(CH3)2),33.2 (ZrCH2), 28.8 (CH(CH3)2) ppm.

On one occasion, small amounts of colorless crystals formedfrom the oil that showed identical 1H and 13CNMR spectra, butcould not be separated from the oil for elemental analysis.

Cp2Zr(iBu)OC6F5, 7b. An Et2O (20 mL) solution of 1b(300 mg, 0.51mmol) was cooled to-78 �C, which induced someprecipitation of the starting material. Isobutyl magnesiumchloride (260 μL, 2.0 M solution in Et2O) was added dropwiseto the cooled reaction mixture and the solution stirred 1 h at-78 �C, then 1.5 h at room temperature, yielding a bright yellowsolution with a white precipitate. The volatiles were removedunder vacuum, and the yellow residue was dried an additional15 min. Hexane (10 mL) was added, stirred, and evaporated.The product was extracted with hexane (20 mL), filtrated, andevaporated to dryness, affording 7b (80 mg, 35%) as a thickyellow oil.

1H NMR (300 MHz, C6D6): δ 5.72 (s, 10H, C5H5), 2.17 (m,1H, CH2CH(CH3)2), 1.11 (d, 2H, CH2CH(CH3)2, J = 7 Hz),1.06 (d, 6H, CH2CH(CH3)2) ppm. 13C NMR: δ 112.5 (C5H5),61.2 (s, CH2), 33.7 (s, CHMe2), 28.4 (CH2CH(CH3)2) ppm.δ112.5 (C5H5), 61.2 (CH2CH(CH3)2), 33.7 (CH2CH(CH3)2),28.4 ppm. 19F NMR (C6D6): δ -166.18 (m, ortho C6F5),-167.50 (m, meta C6F5), -174.22 (m, para C6F5) ppm.

Cp2Zr(OCHPh2)OPh, 8. (a)A J.Young tubewas chargedwith1a (26.1mg, 0.064mmol), 1e (40.5mg, 0.064mmol), and0.6mLofbenzene-d6. The tube was heated 3 days to 65 �C, yielding a paleorange solution. The relative abundance of the zirconocene com-plexeswas obtained fromanalysis of the intensity of theCp signalsin 1H NMR: 1a (28%) 1d (17%), and 8 (58%).

(b) A J. Young tube was charged with 5a (25.4 mg, 0.068mmol), benzophenone (12.5 mg, 0.068 mmol), and 0.6 mL ofbenzene-d6.The tubewasheated 3days to 65 �C inanoil bath.Theinitiallybright yellow solutiondiscolored to apale yellow solution.The relative abundance of the zirconocene complexes was ob-tained fromanalysis of the intensity of theCpsignals: 1a (22%),1d(21%), and Cp2Zr(OCHPh2)OPh, 8 (54%). Another experimentusing about half the initial concentrations (0.033 mmol of 5a andbenzophenone in 0.6mLofC6D6) yielded after 3 days at 65 �C thesame product mixture in a comparable ratio of 24:23:57.

Cp2Zr(OCHPh2)OPh, 8.1H NMR (300 MHz, C6D6): δ 7.42

(m, 4H, ortho Ar), 7.28-7.17(m, meta Ar), 7.09 (m, 2H, paraAr), 6.89 (m, 1H, paraOPh), 6.72 (d, 2H, J=7Hz, orthoOPh),6.02 (s, 1H, OCHPh2), 5.93 (s, 10H, C5H5) ppm. 13C NMR: δ166.7 (ipsoOPh), 147.1 (ipsoAr), 130.1 (orthoOPh), 128.9 (Ar),127.6 (Ar), 127.3 (Ar), 119.5 (para OPh), 118.9 (meta OPh),113.0 (C5H5), 87.5 (CHPh2) ppm.

Reaction of 5b with Olefins. A J. Young NMR tube wascharged with ca. 10 mg of 5b, 4 equiv of the corresponding olefin,and 0.6mLofC6D6. The tubewas hermetically closed and heated3 h at 70 �C. The solution gradually discolored, and the disap-pearance of signals for 5b indicated complete conversion


(1H NMR). The volatiles were removed under vacuum, and theresidue was taken up in 0.6 mL of benzene-d6. NMR spectrashowed the reaction product and small amounts of decomposi-tion products (1a: <15%, {Cp2Zr(OC6F5)2](μ-O): <5%).Cp2Zr(CH2CH2Ph)OC6F5, 10.

1HNMR (300MHz, C6D6): δ7.32 (m, 5H,Ar), 5.69 (s, 10H, C5H5), 2.90 (m, 2H, CH2Ph), 1.43(m, 2H, ZrCH2) ppm. 13C NMR: δ 148.9 (Ar), 129.6 (Ar), 125.9(Ar), 115.5 (Ar), 112.6 (C5H5), 50.5 (ZrCH2), 40.1 (CH2Ph)ppm. 19F (C6D6): δ-165.32 (m, ortho C6F5),-167.34 (m, metaC6F5), -174.08 (m, para C6F5) ppm.Cp2Zr(OC6F5)(OEt), 11. 1H NMR (300 MHz, C6D6): δ 5.90

(s, 10H, C5H5), 3.90 (q, 2H, J = 7 Hz OCH2CH3), 1.05 (t, 3H,J = 7 Hz, OCH2CH3) ppm. 13C NMR: δ 113.6 (C5H5), 70.6(OCH2CH3), 19.8 (CH2CH3) ppm. 19FNMR(C6D6): δ-165.71(m, ortho C6F5), -168.02 (m, meta C6F5), -175.63 (m, paraC6F5) ppm.Cp2Zr(OC6F5)(OEt), 11, by Reaction of 5b with EtOH. A J.

Young NMR tube was charged with 5b (15.0 mg, 0.032 mmol),2 μL of EtOH (0.054mmol), and 0.6 mL of benzene-d6. The tubewas closed and heated 17 h at 70 �C, during which time thesolution turned colorless. After cooling to room temperature, the1H NMR spectra revealed the formation of 11, isobutene, andisobutane (in 4:1 ratio) and decomposition products (C5H6, 1b).Cp2Zr(OC6F5)(CH2)5CH3, 12. (a) By Ligand Exchange.A J.

Young tube was charged with Cp2ZrH2 (5.0 mg, 0.022 mmol),Cp2Zr(OC6F5)2 (17.0 mg, 0.030 mmol), trans-3-hexene (4.0 mg,0.048 mmol), and 0.6 mL of benzene-d6. The NMR tube wasclosed and allowed to stand at room temperature for 6 days,during which the tube was shaken a few times (7 or 8) to ensuremixing of the reactants (Cp2ZrH2 is mostly insoluble). Afterremoval of the volatiles in vacuo, the residue was redissolved inC6D6. The solution contained excess 1b (25%), [Cp2Zr-(OC6F5)]2O (4%), and 12 (71%).Cp2Zr(OC6F5)(CH2)5CH3.

1H NMR (C6D6): δ 5.73 (s, 10H,C5H5), 1.66 (m, 2H, ZrCH2CH2), 1.47 (m, 6H, (CH2)3Me), 1.23(m, 2H, ZrCH2), 1.02 (m, 2H, CH3) ppm. 13C NMR (C6D6): δ112.5 (C5H5), 50.0 (ZrCH2), 36.9 (CH2), 34.1 (ZrCH2CH2), 32.5(CH2), 23.7 (CH2), 14.9 (CH3) ppm.

Addition of an excess of 2,6-dimethylisocyanide (8.1 mg,0.060mmol) to the C6D6 solution yielded in 30min the insertionproduct Cp2Zr(OC6F5)(C(hexyl)dN(xylyl)): 1H NMR (C6D6):δ 6.90-6.69 (m, 3H, C6H3), 5.90 (s, 10H, C5H5), 2.13 (m, 2H,Zr-CCH2), 1.77 (s, 6H, C6H3(CH3)2), 1.52 (m, 2H, CH2), 1.24(m, 2H, CH2), 1.14 (m, 4H, CH2), 0.89 (t, 3H, J = 7 Hz,CH2CH3) ppm. 13C NMR (C6D6): δ 110.6 (C5H5), 38.1 (CH2),32.2 (CH2), 30.3 (CH2), 27.5 (CH2), 23.3 (CH2), 18.9 (C6H3-(CH3)2), 14.6 (CH3) ppm.(b) By Reaction of 5b with 1-Hexene. A J. Young NMR tube

was charged with 5b (20.4 mg, 0.044 mmol), 1-hexene (15.1 mg,0.179mmol), and 0.6mLof benzene-d6. The tubewas closed andthe solution heated in an oil bath 3 h at 70 �C, during which timethe bright yellow solution turned pale yellow. The volatiles wereremoved in vacuo, and the residue was taken up in benzene-d6.The 1H NMR spectra of the mixture confirmed the presence of7b (7%) and 12 (93%).(c) By Reaction of 5b with 3-Hexene. A J. Young NMR tube

was charged with 5b (24.3 mg, 0.052 mmol), trans-3-hexene(12.4 mg, 0.147 mmol), and 0.6 mL of benzene-d6. The sealed tubewas heated in an oil bath for 3 h at 70 �C, during which time thesolution turned frombright yellow topale yellow.The volatileswereremoved in vacuo, and the residue was taken up in benzene-d6. TheNMR spectra revealed a mixture of 7b (40%) and 12 (60%).Cp2Zr(CH2CH2Ph)OC6F5, 10, from Cp2ZrH2 and 1b. In a

nitrogen-filled glovebox, a J. Young NMR tube was chargedwith Cp2ZrH2 (7.0 mg, 0.031 mmol), 1b (21.2 mg, 0.036 mmol),styrene (10.0 mg, 0.096 mmol), and 0.6 mL of benzene-d6. TheNMR tube was closed and allowed to stand at room tempera-ture several days, during which the tube was shaken a few times

(7 or 8) to ensure mixing of the reactants (Cp2ZrH2 is mostlyinsoluble). After 3 days the reaction is nearly completed (littleprecipitate left). After 6 days the volatiles were removed undervacuum, and the residue was redissolved in C6D6. The

1HNMRdisplayed signals for 10 (vide supra) and 1b (used in excess).A doublet of minor intensity (5%) was observed at 1.56 ppm(d, J=7Hz),whichdisplayedaCOSYcross-peak to a resonanceat 2.90 ppm, buried under the CH2Ph resonance of 10. Bothresonances were putatively assigned to the 2,1-insertion product13. No 13C resonances could be observed for 13, nor didNOESYexperiments identify which of resonances of minor intensity inthe Cp region of the spectra could be associated with 13.

To the obtained C6D6 was added a solution of 2,6-dimethy-lisocyanide (4.0 mg, 0.030 mmol) in C6D6, and the tube closedand shaken. After 30 min at room temperature the reaction isnearly complete (1H NMR), and all signals of 10 (and 13)disappeared after 16 h.

Cp2Zr(OC6F5)(C(CH2CH2Ph)dN(Xylyl)). 1HNMR (C6D6):δ 7.13-7.04 (m, 3H, C6H5), 6.93 (m, 2H, C6H5), 6.81 (m, 1H,C6H3), 6.74 (d, 2H, J=7Hz,C6H3), 5.82 (s, 10H,C5H5), 2.77 (t,2H, J=8Hz, CH2CH2Ph), 2.45 (t, 2H, J=8Hz, CH2CH2Ph),1.74 (s, 6H,CH3) ppm. 13CNMR(C6D6): 144.0 (Ar), 141.2 (Ar),129.5 (Ar), 128.9 (Ar), 128.7 (Ar), 127.2 (Ar), 126.8 (Ar), 110.7(C5H5), 39.8 (CH2CH2Ph), 33.2 (CH2CH2Ph), 18.9 (CH3) ppm.

The doublet assigned to the insertion product of 13 appearedat [1H NMR (C6D6)] 1.14 (d, J=7Hz) ppm. No 13C resonancewas observed after a reasonable time of acquisition. A NOESYexperiment did not show any correlation between this doubletand the methyl groups of the N(C6H3(CH3)2).

Kinetic Experiments. A 0.6 mL amount of a stock solution(0.036M) of 5b (0.0216mmol) and hexamethylbenzene (0.050M)in benzene-d6 was added to 4 equiv of the corresponding olefin,and the resulting solutionwas transferred to a J.Young tube. Thetubes were heated to 70 �C in an oil bath, and 1H NMR spectrawere acquired every 35 min.

X-rayDiffraction Studies.Diffraction datawere collected on aBruker Smart 6000 (4K) (1e, 7a) and a Bruker Microstar/Platinum 135 diffractometer (6), both equipped with a rotatinganode source and Mirror Montel 200-monochromated Cu KRradiation. Cell refinement and data reduction were done usingAPEX2.57 Structures were solved by direct methods usingSHELXS9758 and refined on F2 by full-matrix least-squaresusing SHELXL97.58 All non-hydrogen atoms were refinedanisotropically. Hydrogen atoms were refined isotropically oncalculated positions using a riding model. The structure of 1econtained one molecule of toluene disordered around an inver-sion center. In 6 and 7a one cyclopentadienyl ring was found tobe slightly disordered, as indicated by elevated thermal para-meters for the CCp atoms. All disorders have been resolved andrefined anisotropically with appropriate restraints. Furtherexperimental details are given in the Supporting Information.

Acknowledgment. We thank Dr. P. V. M. Tan and S.Bilodeau for assistance with NMR experiments, Dr. D.Zargarian and D. Spasyuk for GC-MS analyses, and M.Teillard for the synthesis of several compounds. Fundingfor this research was provided by the Natural Sciencesand Engineering Research Council of Canada and theUniversit�e de Montr�eal.

Supporting Information Available: NMR spectra of noniso-lated products orNMR reactions. Details of the X-ray structuredeterminations. This material is available free of charge via theInternet at http://pubs.acs.org.

(57) APEX2, Release 2.1-0; Bruker AXS Inc.: Madison, WI, 2006.(58) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.

replacing chloride by alkoxide: cp 2 zr(h)or, searching for alternatives...

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