Metal Activation of a Germylenoid, a New Approach to Metal−Germanium Triple Bonds: Synthesis and Reactions of theGermylidyne Complexes [Cp(CO)2MGe−C(SiMe3)3] (M = Mo, W)Alexander C. Filippou,* Kai W. Stumpf, Oleg Chernov, and Gregor Schnakenburg

Institut fur Anorganische Chemie, Universitat Bonn, Gerhard-Domagk-Straße 1, 53121 Bonn, Germany

*S Supporting Information

ABSTRACT: The reactions of the germylenoid Li-(THF)3GeCl2C(SiMe3)3 with the carbonyl metalates Li-[CpMo(CO)3] and K[CpW(CO)3] (Cp = η5-C5H5) intoluene afford selectively the germylidyne complexes [Cp-(CO)2MGe−C(SiMe3)3] (1-Mo, M = Mo; 1-W, M = W).The compounds 1-Mo and 1-W rapidly add 1,3,4,5-tetramethylimidazol-2-ylidene (Im-Me4) at the electrophilicgermanium center to give the zwitterionic germylidenecomplexes [Cp(CO)2MGe(Im-Me4){C(SiMe3)3}] (2-Mo,M = Mo; 2-W, M = W). The molecular structures of 1-Mo/1-W and 2-Mo/2-W were determined by single-crystal X-raydiffraction studies, and the structural and spectroscopic features of all complexes are discussed.

■ INTRODUCTIONCompounds featuring triple bonds to the heavier homologuesof carbon are of fundamental importance for the understandingof chemical bonding. In recent years, a series of ylidynecomplexes of the general formula [Cp(CO)2ME−R] (M =Cr, Mo, W; E = Si, Ge; R = m-terphenyl)1,2 and trans-[X(L)4ME−R] (M = Mo, W; E = Ge−Pb; R = C5Me5, m-terphenyl; L = phosphane; X = Cl−I)3 have been isolatedfeaturing linearly coordinated triply bonded Si−Pb atoms.Two methods have been employed for the synthesis of these

compounds, which both require the use of thermally stableorganoelement(II) halides of Ge−Pb4 or N-heterocycliccarbene stabilized arylchlorosilylenes.5 This requirement limitsto some extent the approach to ylidyne complexes of theheavier group 14 elements, since thermally stableorganoelement(II) halides of Si−Pb remain rather rare.4 Inthe present work a new approach to ylidyne complexes isreported, which takes advantage of the potential of ylenoids6−8

to act as electrophiles. This is exemplified by the preparation ofthe first germylidyne complexes bearing a C(SiMe3)3 (trisyl)substituent. Furthermore, the electrophilic character of thetriply bonded germanium center is demonstrated by addition ofan N-heterocyclic carbene (NHC) to give the first zwitterionicgermylidene complexes.

■ RESULTS AND DISCUSSIONThe entry into the chemistry presented below was provided bythe germylenoid Li(THF)3GeCl2C(SiMe3)3, which was gen-erated by reacting [Li(THF)4][Li{C(SiMe3)3}2]

9 with 2 equivof GeCl2(1,4-dioxane) in THF as described by Ando et al.8a

After removal of the solvent, the germylenoid was obtained as a

pale yellow solid in quantitative yield and was characterized by1H and 29Si{1H} NMR spectroscopy.When a mixture of the germylenoid and Li[CpMo(CO)3] or

K[CpW(CO)3] was suspended in toluene at 0 °C, a rapid colorchange of the solution from yellow to brown to red (in the caseof molybdenum) and to red-brown (in the case of tungsten)was observed.10 IR monitoring of the reactions revealed theselective formation of the germylidyne complexes [Cp-(CO)2MGe−C(SiMe3)3] (1-Mo, M = Mo; 1-W, M = W)within a few hours (eq 1).

Compounds 1-Mo and 1-W were isolated after workup andcrystallization from hexane as red-orange (1-Mo) and red-brown (1-W) microcrystalline solids in 73 and 60% yields,respectively. The germylidyne complexes are quite air-sensitive,thermally stable solids, which melt at 85 °C (1-Mo) and 86 °C(1-W) without decomposition.The solid-state structures of 1-Mo and 1-W were determined

by single-crystal X-ray diffraction studies. Suitable orange singlecrystals of 1-Mo and 1-W were obtained upon coolingsaturated hexane solutions to −60 °C. The compounds 1-Mo

Received: November 24, 2011Published: January 9, 2012

Article

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and 1-W are isotypic and crystallize in the monoclinic spacegroup P21/n. The isostructural three-legged piano-stoolcomplexes feature almost linearly coordinated germaniumatoms (1-Mo, Mo−Ge−C1 = 169.60(3)°; 1-W, W−Ge−C1 =170.5(1)°) (Figure 1). The slight deviation of the

M−Ge−C1 atom array from linearity has been also observedin other germylidyne complexes3b,g,h,i and results probablyfrom intramolecular steric repulsions and/or crystal-packingforces.11

The M−Ge bond lengths of 1-Mo (228.05(2) pm) and 1-W(228.42(6) pm) compare well with those of the m-terphenyl-substituted analogues [Cp(CO)2MGe−C6H3-2,6-Mes2](Mo−Ge = 227.1(1) pm; W−Ge = 227.7(1) pm).2 Notably,the Mo/W−Ge distance of 1-Mo/1-W matches well withthat calculated for a Mo/W−Ge triple bond (d(MoGe) =227 pm; d(WGe) = 229 pm) using the theoretically pre-dicted triple-bond covalent radii of Mo/W (rMo = 113 pm; rW =115 pm) and Ge (114 pm).12

The solution IR and NMR spectra of 1-Mo and 1-Wcorroborate the solid-state structures. The IR spectra of 1-Moand 1-W display two very strong absorption bands of almostequal intensity, which are assigned to the A′ symmetric and A″antisymmetric CO stretching modes (Table 1, Figure 2). Theposition of these bands is solvent dependent; the bands appearat lower wavenumbers in toluene (1-Mo, ν(CO) 1930, 1869cm−1; 1-W, ν(CO) 1924, 1860 cm−1) than in hexane (1-Mo,ν(CO) 1941, 1881 cm−1; 1-W, ν(CO) 1935, 1875 cm−1).Solvent-induced frequency shifts of the ν(CO) modes ofcarbonyl complexes are common13 and have been accountedfor by the dipolar and dispersive interactions of the solute withthe solvent.14 A comparison of the ν(CO) bands of 1-Mo and1-W with those of related germylidyne, silylidyne, andalkylidyne complexes reveals the following trends (Table 1).Replacement of the trisyl by the m-terphenyl substituents

C6H3-2,6-Mes2 (ArMes) and C6H3-2,6-Trip2 (Ar

Trip) causes only

a slight shift of the ν(CO) bands to higher wavenumbers (cf.ν(CO) of 1-Mo in hexane (1941, 1881 cm−1) and of[Cp(CO)2MoGeArMes] in pentane (1945, 1885 cm−1)15),indicating a similar σ-donor/π-acceptor ratio of the germyli-dyne ligands GeC(SiMe3)3 and GeArMes/GeArTrip. In compar-ison, replacement of germanium by carbon induces a large shiftof the ν(CO) bands to higher wavenumbers (cf. ν(CO) inhexane of 1-W (1935, 1875 cm−1) and [Cp(CO)2WCPh](1992, 1922 cm−1)16b). This shows that the germylidyneligands Ge−R (R = C(SiMe3)3, Ar

Mes, ArTrip) have a larger σ-donor/π-acceptor ratio than the alkylidyne ligands C−Ar (Ar =aryl group), which strengthens the M−CCO and weakens theC−O bonds in 1-Mo/1-W. Additional evidence for thestronger metal−carbonyl back-bonding in 1-Mo/1-W isprovided by the M−CO bonds of 1-Mo (196.5(6) pm) and1-W (196.5(2) pm),17 which are slightly shorter than those ofthe alkylidyne complexes [Cp(CO)2MoC−C6H4-4-Me](Mo−CCO = 198.1(3) pm),17,18 ([Cp(CO)2MoC−CRu3(CO)5(Cp)3] (Mo−CCO = 198.6(3) pm).17,19

The 1H NMR spectra of 1-Mo/1-W in C6D6 display asharp singlet for the Cp ring protons and a sharp singlet forthe methyl groups of the trisyl substituent (Table 2). Themethyl groups remain equivalent in toluene-d8 at −80 °C(1H NMR, 300 MHz), indicating a rapid exchange of themethyl sites by rotation.20 The most distinctive signal of thegermylidyne complexes in the 13C{1H} NMR spectra is thatof the Ge-bonded carbon atom, which appears at con-siderably lower field (1-Mo, δ 72.6 ppm; 1-W, δ 68.4 ppm)than that of the NHC adducts 2-Mo (δ 39.5 ppm) and 2-W(δ 36.8 ppm) (Table 2). The 29Si{1H} NMR spectra of thegermylidyne complexes show a singlet resonance at aposition (1-Mo, δ −5.5 ppm; 1-W, δ −6.1 ppm) close tothat of the germylenoid Li(THF)3GeCl2C(SiMe3)3 (δ −4.4 ppm)and the NHC adducts 2-Mo (δ −5.9 ppm) and 2-W(δ −7.0 ppm).The germylidyne complexes 1-Mo and 1-W bear an

electrophilic germanium center, which is susceptible to additionof nucleophiles. For example, addition of the N-heterocycliccarbene Im-Me4 (1,3,4,5-tetramethylimidazol-2-ylidene)

21 to atoluene solution of 1-Mo at ambient temperature wasaccompanied by a rapid color change from red-orange to red-brown and led selectively to the zwitterionic germylidene

complex [Cp(CO)2MGe(Im-Me4){C(SiMe3)3}] (2-Mo; eq 2).Similarly, the analogous tungsten compound 2-W wasselectively obtained from 1-W and Im-Me4 (eq 2). Thegermylidene complexes were isolated as red-brown (2-Mo) anddark red-violet (2-W) solids, which are sparingly soluble in hexanebut readily soluble in toluene. Both compounds are thermallystable solids, which decompose upon heating at 174 °C (2-Mo)and 140 °C (2-W).The solid-state structures of 2-Mo and 2-W were determined

by single-crystal X-ray diffraction studies. Suitable red singlecrystals of 1-Mo and red-purple single crystals of 1-W were

Figure 1. DIAMOND plot of the molecular structure of 1-Mo in thesolid state. Thermal ellipsoids are set at the 50% probability level.Hydrogen atoms are omitted for clarity. Selected bond lengths (pm)and bond angles (deg) of 1-Mo (bond lengths and angles of 1-W aregiven in brackets): Mo−Ge = 228.05(2) [228.42(6)], Mo−C11 =195.9(1) [196.3(6)], Mo−C12 = 197.1(1) [196.6(6)], Ge−C1 =194.3(1) [193.9(5)], C1−Si1 = 191.2(1) [191.6(5)], C1−Si2 =191.5(1) [191.6(6)], C1−Si3 = 191.9(1) [190.9(5)], C11−O1 =115.8(2) [115.6(7)], C12−O2 = 115.6(2) [115.1(7)]; Mo−Ge−C1 =169.60(3) [170.5(1)], Ge−Mo−C11 = 84.93(4) [85.6(2)], Ge−Mo−C12 = 88.45(4) [88.7(2)], C11−Mo−C12 = 89.09(5) [89.5(2)], Ge−C1−Si1 = 107.03(5) [107.0(3)], Ge−C1−Si2 = 104.46(5)[104.4(2)], Ge−C1−Si3 = 105.85(5) [105.5(2)], Si1−C1−Si2 =113.20(5) [113.1(2)], Si1−C1−Si3 = 111.17(5) [111.3(3)], Si2−C1−Si3 = 114.33(6) [114.6(3)].

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obtained from warm saturated toluene−hexane (2:1) solutionsupon slow cooling to room temperature. The compounds2-Mo and 2-W are isotypic and crystallize in the monoclinicspace group P21/n.The isostructural three-legged piano-stool complexes are

the first examples of zwitterionic germylidene complexes tobe reported and display trigonal-planar-coordinated germanium

centers (sum of angles at Ge: 2-Mo, 359.8°; 2-W, 359.9°)(Figure 3). The angles at Ge differ markedly; the M−Ge−Ctrisylangles of 2-Mo (142.8(1)°) and 2-W (142.78(9)°) areconsiderably widened, due to the steric bulk of the trisylsubstituent. The zwitterionic germylidene ligand adopts inboth complexes an upright conformation, with the trisylgroup pointing toward the cyclopentadienyl ring. Theupright conformation is best described by the dihedralangles of 9.6° (2-Mo) and 9.2° (2-W) between thegermylidene ligand least-squares plane, which passes throughthe atoms Mo/W, Ge, Ctrisyl, and Ccarbene, and the planedefined by the atoms Mo/W, Ge, and Cg, for which Cgdenotes the center of gravity of the cyclopentadienyl ring.The N-heterocyclic carbene is arranged almost perpendi-cular to the germanium coordination plane, as evidenced bythe interplanar angle between the imidazol-2-ylidene least-squares plane (C11, N1, C12, C13, N2) and the germylideneligand plane (M, Ge, C1, C11) in 2-Mo (87.4(2)°) and 2-W(87.4(2)°).The M−Ge distances of 2-Mo and 2-W are the shortest

reported so far for M−Ge double bonds.22,23 For example, theMo−Ge bond of 2-Mo (240.04(5) pm) is considerably shorterthan those of Mo(0) complexes bearing N-heterocyclicgermylene (NHGe) ligands, e.g. fac-[Mo(CO)3(NHGe)3](d(Mo−Ge)av = 253.7 pm; NHGe = 1,3-dineopentyl-1,3,2-diazagermoline-2-ylidene)22a and cis-[Mo(CO)4(NHGe)2](d(Mo−Ge)av = 252.0 pm; (NHGe)2 = 1,3-bis(N-neo-pentylbenzimidazoline-2-germylene)-2,2-dimethylpropane),22b

which suggests the presence of a strong Mo−Ge π bond in 2-Mo. The Mo−Ge bond length of 2-Mo compares well with theMoGe bond lengths in a series of germylidene complexeswhich have been isolated and fully characterized in our grouprecently (Table 3).24 Similarly, the W−Ge bond of 2-W(240.15(4) pm) is considerably shorter than those of thetungsten(0) germylidene complexes [(CO)5WGe(R1)R2](d(W−Ge) = 250.5(2)−263.2(4) pm; R1, R2 = singly bondedsubstituent),23a−e and shorter than those of the few tungsten(II)

Table 1. Infrared ν(CO) Absorption Bands of 1-Mo, 1-W, and Related Silylidyne and Alkylidyne Complexes and ν(CO)Absorption Bands of 2-Mo, 2-W, and Related NHC Adducts of Germylidyne and Silylidyne Complexes

ν(CO)/cm‑1 solvent ref

Ylidyne Complexes[Cp(CO)2MoGeC(SiMe3)3] (1-Mo) 1941, 1881 hexane this work

1930, 1868 toluene this work[Cp(CO)2MoGeArMes]a 1945, 1885 pentane this work[Cp(CO)2MoGeArTrip]a 1945, 1887 pentane this work

1939, 1876 toluene this work[Cp(CO)2MoSiArTrip] 1945, 1886 pentane 1a

1937, 1875 toluene 1a[Cp(CO)2MoC(C6H3-2,6-Me2)] 1992, 1919 CH2Cl2 16a[Cp(CO)2WGeC(SiMe3)3] (1-W) 1935, 1875 hexane this work

1924, 1860 toluene this work[Cp(CO)2WCPh] 1992, 1922 hexane 16b

NHC Adducts of Ylidyne Complexes[Cp(CO)2MoGe(Im-Me4)C(SiMe3)3] (2-Mo) 1861, 1785 toluene this work[Cp(CO)2MoGe(Im-Me4)Ar

Mes] 1854, 1783 toluene this work[Cp(CO)2MoGe(Im-Me4)Ar

Trip] 1862, 1786 toluene this work[Cp(CO)2MoSi(Im-Me4)Ar

Mes] 1854, 1779 toluene this work[Cp(CO)2MoSi(Im-Me4)Ar

Trip] 1862, 1786 toluene this work[Cp(CO)2WGe(Im-Me4)C(SiMe3)3] (2-W) 1854, 1779 toluene this work[Cp(CO)2WSi(Im-Me4)Ar

Mes] 1849, 1775 toluene this workaArMes, C6H3-2,6-Mes2 (Mes = 2,4,6-trimethylphenyl); ArTrip, C6H3-2,6-Trip2 (Trip = 2,4,6-triisopropylphenyl).

Figure 2. Solution FTIR spectra of complexes 1-Mo, 2-Mo, 1-W, and2-W in toluene at 20 °C; spectral range 1970−1740 cm−1.

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germylidene complexes reported so far (d(W−Ge =242.89(8)−245.9(2) pm) (Table 3),3i,23f,g which implies thepresence of a strong W−Ge π bond in 2-W. The Ge−Ccarbene

bond lengths (2-Mo, 206.0(4) pm; 2-W, 205.3(3) pm)compare well with the Ge−Ctrisyl bond lengths (2-Mo,205.6(4) pm; 2-W, 204.6(3) pm), indicating the presence ofa rather strong Ccarbene−Ge donor−acceptor interaction. TheGe−Ccarbene bond lengths of 2-Mo/2-W are slightly shorterthan those of the carbene adducts GeCl2(Im-Me4) (208.2(3) pm)

5

and GeCl(C6H3-2,6-Trip2)(Im-Me4) (207.1(3) pm).5

The spectroscopic data of 2-Mo and 2-W are consistent withthe zwitterionic structure of these compounds. The IR spectraof 2-M in toluene display two very strong ν(CO) absorptionbands of almost equal intensity at wavenumbers (2-Mo, 1861,1785 cm−1; 2-W, 1854, 1779 cm−1) lower than those of thegermylidyne complexes 1-M (1-Mo, 1930, 1868 cm−1; 1-W,1924, 1860 cm−1) (Figure 2, Table 1). This evinces theconsiderably higher σ-donor/π-acceptor ratio of the germyli-dene ligand Ge(Im-Me4)C(SiMe3)3 as compared to that ofthe germylidyne ligand GeC(SiMe3)3, leading to a stronger

metal−carbonyl back-bonding in 2-Mo/2-W. Further evidence forthis is provided by the shorter M−CCO bonds of the zwitterionicgermylidene complexes 2-Mo/2-W (193.0(4)/192.9(5) pm),17

as compared to those of the germylidyne complexes 1-Mo/1-W(196.5(6)/196.5(2) pm).17 Furthermore, a comparison of theν(CO) absorption bands of 2-Mo/2-W with those of otherzwitterionic ylidene complexes, [Cp(CO)2ME(Im-Me4)R](M = Mo, W; E = Si, Ge; R = ArMes, ArTrip)24 reveals thatreplacement of the trisyl by the m-terphenyl substituents ArMes

and ArTrip, or that of germanium by silicon has a minorinfluence on the position of the ν(CO) absorption bands(Table 1). This indicates that the zwitterionic ylidene ligandsE(Im-Me4)R (E = Si, Ge; R = C(SiMe3)3, Ar

Mes, ArTrip) havesimilar electronic properties.The 1H and 13C{1H} NMR spectra of 2-Mo/2-W confirm

the overall Cs symmetry of the complexes in solution. The13C{1H} NMR spectra of 2-Mo/2-W display a distinctive signalfor the Ge-bonded Ccarbene atom (2-Mo, 172.9 ppm, 2-W, 178.3ppm), which appears between that of the imidazol-2-ylideneIm-Me4 (δ 212.7 ppm (C6D6))

21 and the imidazolium salt (Im-Me4H)Cl (δ 136.9 ppm (CDCl3)), reflecting the donor−acceptor character of the Ge−Ccarbene bond.

Figure 3. DIAMOND plot of the molecular structure of 2-Mo in thesolid state. Thermal ellipsoids are set at the 50% probability level.Hydrogen atoms are omitted for clarity. Selected bond lengths (pm)and bond angles (deg) of 2-Mo (bond lengths and angles of 2-W aregiven in brackets): Mo−Ge = 240.04(5) [240.15(4)], Mo−C23 =193.3(4) [193.3(4)], Mo−C24 = 192.6(4) [192.4(4)], Ge−C1 =205.6(4) [204.6(3)], Ge−C11 = 206.0(4) [205.3(3)], C11−N1 =134.7(5) [135.9(4)], C11−N2 = 135.8(5) [135.5(4)], C1−Si1 =191.3(4) [191.5(3)], C1−Si2 = 191.3(4) [191.3(3)], C1−Si3 =190.2(3) [190.4(3)], C23−O1 = 117.0(5) [116.9(4)], C24−O2 =117.6(5) [117.9(4)]; Mo−Ge−C1 = 142.8(1) [142.78(9)], Mo−Ge−C11 = 111.5(1) [111.3(1)], C1−Ge−C11 = 105.6(1) [105.8(1)],Ge−Mo−C23 = 87.9(1) [88.3(1)], Ge−Mo−C24 = 86.3(1)[86.5(1)], C23−Mo−C24 = 82.5(2) [82.8(2)], Ge−C1−Si1 =103.1(2) [103.4(2)], Ge−C1−Si2 = 109.1(2) [109.3(2)], Ge−C1−Si3 = 114.7(2) [114.9(2)], N1−C11−N2 = 104.6(3) [104.2(3)].

Table 3. M−Ge Bond Lengths (pm) of SelectedMolybdenum and Tungsten Germylidene Complexes

Molybdenum Germylidene Complexes

d(Mo−Ge) ref

[Cp(CO)2MoGe(Im-Me4)C(SiMe3)3] (2-Mo) 240.04(5) this work[Cp(CO)2(H)MoGe(Cl)ArMes] 239.21(5) 24[Cp(CO)2(H)MoGe(OH)ArMes] 240.31(7) 24[Cp(CO)2(H)MoGe(OMe)ArMes] 241.19(5) 24[Cp(CO)2MoGe(Im-Me4)Ar

Mes] 239.24(2) 24[Cp(CO)2MoGe(Im-Me4)Ar

Trip] 240.15(5) 24[Cp*(Et2PCH2CH2PEt2)(H)MoGePh2]

a 241.42(7) 22c[Cp*(Et2PCH2CH2PEt2)(H)MoGeEt2]

a 241.11(4) 22cfac-[Mo(CO)3(NHGe)3]

b 253.7c 22aTungsten Germylidene Complexes

d(W−Ge) ref

[Cp(CO)2WGe(Im-Me4)C(SiMe3)3] (2-W) 240.15(4) this work[(CO)5WGe(W2(CO)10)] 250.5(2) 23a[(CO)5WGe(Cp*)Cl] 257.1(1) 23b[(CO)5WGe(Cp*)(CH(SiMe3)2)] 263.2(4) 23c[(CO)5WGe(SeR)2]

d 252.8(1) 23d[(CO)5WGe(Tb)(Trip)]e 259.34(8) 23e[(η5-C5Me4Et)(CO)2(GeMe3)WGeMe2] 245.9(2) 23f[Cl(PMe3)3(H)WGe(R)CH2PMe2]

f 245.43(4) 3i[Cp*(CO)2(H)WGeH(C(SiMe3)3)] 242.89(8) 23g

aCp* = η5-C5Me5.bNHGe = N-heterocyclic germylene. cMean Mo−

Ge bond length. dR = 2,4,6-tri-tert-butylphenyl. eTb = 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, Trip = 2,4,6-triisopropylphenyl.fR = C6H3-2,6-Trip2.

Table 2. Selected NMR Spectroscopic Data of Complexes 1-Mo, 1-W, 2-Mo, and 2-W in C6D6 at 25 °Ca

1H NMR 13C{1H} NMR

29Si{1H} NMRC(SiMe3)3

C(SiMe3)3 C5H5 C(SiMe3)3 C(SiMe3)3 C5H5 CO

1-Mo 0.34 4.88 4.7 72.6 86.6 231.7 −5.51-W 0.34 4.83 4.5 68.4 84.7 220.2 −6.12-Mo 0.36 5.34 6.2 39.5 89.6 243.7 −5.92-W 0.35 5.31 6.0 36.8 88.1 234.1 −7.0

aChemical shifts δ in ppm.

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■ CONCLUSION

The present work demonstrates that germylenoids can bevaluable synthetic equivalents of germylenes and can be usedfor the assembly of new compounds featuring metal−germanium triple bonds. Further studies on the reactivity ofthe germylidyne complexes [Cp(CO)2MGe−C(SiMe3)3](M = Mo, W) toward nucleophiles and substrates containingpolar σ bonds are in progress.

■ EXPERIMENTAL SECTION1. General Considerations. All experiments were carried out

under an atmosphere of argon using Schlenk or glovebox techniques.The glassware was dried in the oven at approximately 110 °C andbaked in vacuo prior to use. The solvents were refluxed over thecorresponding drying agent (pentane, CaH2; hexane, sodium/benzophenone ketyl/tetraglyme; toluene, sodium; THF, sodium/benzophenone ketyl; 1,2-dimethoxyethane (DME), sodium/benzo-phenone ketyl), purged several times during reflux with argon, anddistilled under argon. All solvents were stored in the glovebox.The C, H, N analyses were carried out in triplicate for each sample

on an Elementar Vario Micro elemental analyzer. The individual C, H,N values did not differ by more than ±0.3. The mean C, H, N valuesare given below for each compound. The melting points of 1-Mo, 1-W, 2-Mo, and 2-W were determined in duplicate for each sample usinga Buchi melting point apparatus. The samples were sealed in capillarytubes under vacuum and heated rapidly to approximately 20 K lowerthan the temperature at which melting started. Heating was thencontinued slowly until the sample melted or decomposed. The IRspectra of solutions (2200−1500 cm−1) were recorded at 20 °C on aNicolet 380 FT-IR spectrometer using a cell of KBr windows and werebackground-corrected for the solvent absorptions. The KBr windowswere separated by a Teflon spacer with a thickness of 0.2 mm. The IRspectra of the solids (4000−400 cm−1) were recorded on a BrukerAlpha FT-IR spectrometer in the glovebox using the platinum single-reflection diamond ATR module. The following abbreviations wereused for the intensities and shape of the IR absorption bands: vs, verystrong; s, strong; m, medium; w, weak; vw, very weak; sh, shoulder.The NMR spectra were recorded on a Bruker Avance DMX-300 orDPX-400 NMR spectrometer in benzene-d6, toluene-d8, THF-d8, oracetonitrile-d3. Benzene-d6, toluene-d8, and THF-d8 were trap-to-trapcondensed from Na and acetonitrile-d3 from CaH2. The

1H and13C{1H} NMR spectra were calibrated against the residual proton andnatural-abundance 13C resonances of the deuterated solvent relative totetramethylsilane (benzene-d6, δH 7.15 ppm and δC 128.0 ppm;toluene-d8, δH 2.09 ppm and δC 20.4 ppm; THF-d8, δH 1.73 ppm andδC 25.3 ppm; acetonitrile-d3, δH 1.93 ppm and δC 1.3 ppm). The29Si{1H} NMR spectra were calibrated against external pure SiMe4.The standard was filled in a capillary, which was sealed off andintroduced in a 5 mm NMR tube containing benzene-d6. The NMRtube was finally vacuum-sealed and used for the calibration.CH(SiMe3)3 was prepared as described in the literature25 and

metalated with LiMe following the prodecure of Eaborn et al.9 Theorganolithium compound was obtained as a white crystalline solid,which was characterized by 1H, 13C{1H}, and 29Si{1H} NMRspectroscopy.26 GeCl2(1,4-dioxane) was prepared by following theprocedure of Kouvetakis et al.27 and shown by elemental analysis to bepure. Li[CpMo(CO)3] was obtained by reacting [CpMo(CO)3H]with 1 equiv of LinBu in pentane and isolated as a cream-colored solidin 95% yield.28 It was characterized by IR, 1H NMR, and 13C{1H}NMR spectroscopy.29 K[CpW(CO)3] was prepared upon refluxing anequimolar mixture of W(CO)6 and KCp for 40 h in DME and isolatedin the following way: the reaction solution was filtered aftercompletion of the reaction (IR monitoring), and the filtrate wasevaporated to dryness. The residue was treated with hexane, theresulting suspension immersed for a short time in an ultrasonic bath,and then the solvent removed in vacuo. The obtained solid was driedin vacuo (50 °C, 4 h, 0.05 mbar) to give K[CpW(CO)3] as a brownish

yellow powder in nearly quantitative yield. The solid was characterizedby IR and NMR spectroscopy.30

2. Preparation of [Cp(CO)2MoGeC(SiMe3)3] (1-Mo). Asolution of [Li(THF)4][Li{C(SiMe3)3}2] (1.15 g, 1.50 mmol) in 10 mLof THF was added to a solution of GeCl2(1,4-dioxane) (0.69 g,2.98 mmol) in 15 mL of THF at 0 °C. The reaction mixture wasstirred for 15 min at 0 °C, the cooling bath was removed, and stirringwas continued for 1 h at room temperature. The solvent was removedin vacuo to give Li(THF)3GeCl2{C(SiMe3)3} as a yellow solid.31

Li[CpMo(CO)3] (0.76 g, 3.02 mmol) was added, and the mixture wastreated with 20 mL of precooled toluene at 0 °C and stirred for 2.5 h.During this time the mixture was warmed to room temperature, andthe reaction solution changed from yellow to brown to red. Thesolvent was removed in vacuo, and the product was extracted withhexane (3 × 5 mL). The extract was concentrated to about 4 mL andstored at −30 °C for 16 h. The mother liquor was removed byfiltration at −30 °C, and the precipitate was dried in vacuo at roomtemperature for 1 h to afford complex 1-Mo as a red-orange,crystalline solid. Yield: 1.13 g (2.17 mmol, 73% based on GeCl2(1,4-dioxane)), mp 85 °C. Anal. Calcd for C17H32GeMoO2Si3 (521.23): C,39.17; H, 6.19. Found: C, 39.28; H, 6.38. IR (toluene, ν(cm−1)): 1930(vs), 1868 (vs) (ν(CO)). IR (diethyl ether, ν (cm−1)): 1935 (vs), 1873(vs) (ν(CO)). IR (hexane, ν (cm−1)): 1941 (vs), 1881 (vs) (ν(CO)).IR (solid, ν (cm−1)): 3122 (vw), 3100 (vw), 2949 (m), 2898 (m),1916 (vs) (ν(CO)), 1865 (vs) (ν(CO)), 1410 (m), 1301 (vw), 1264(s), 1253 (s), 1248 (s), 1105 (w), 1056 (m), 1009 (w), 1001 (w), 819(vs), 789 (vs), 714 (s), 658 (vs), 618 (s), 596 (s), 539 (s), 510 (s), 484(s), 470 (vs). 1H NMR (300.1 MHz, C6D6, 298 K, δ (ppm)): 0.34 (s,27H, C(SiMe3)3), 4.88 (s, 5H, C5H5).

13C{1H} NMR (75.47 MHz,C6D6, 298 K, δ (ppm)): 4.7 (s, 1J(C,Si) = 52.5 Hz, 9C, C(SiMe3)3),72.6 (s, 1C, C(SiMe3)3), 86.6 (s, 5C, C5H5), 231.7 (s, 2C, 2 × CO).29Si{1H} NMR (59.63 MHz, C6D6, 298 K, δ (ppm)): −5.5 (s, 1J(Si,C) =52.5 Hz, C(SiMe3)3).

3. Preparation of [Cp(CO)2WGeC(SiMe3)3] (1-W). A solutionof [Li(THF)4][Li{C(SiMe3)3}2] (0.57 g, 0.74 mmol) in 10 mL ofTHF was added to a solution of GeCl2(1,4-dioxane) (0.35 g, 1.51 mmol)in 10 mL of THF at 0 °C. The reaction mixture was stirred for15 min at 0 °C, the cooling bath was removed, and stirring wascontinued for 1 h at room temperature. The solvent was removed invacuo to give the germylenoid Li(THF)3GeCl2C(SiMe3)3 as a yellowsolid, to which K[CpW(CO)3] (0.56 g, 1.51 mmol) was added. Themixture was treated with 20 mL of precooled toluene at 0 °C. After themixture was stirred for 10 min at 0 °C, the cooling bath was removed,and stirring was continued for 5 h at room temperature. During thistime the reaction mixture turned from brown to red-brown. Thesolvent was removed in vacuo, and the product was extracted withhexane (3 × 5 mL). The extract was concentrated to about 3 mL andstored at −30 °C for 16 h. The mother liquor was removed byfiltration at −30 °C, and the precipitate was dried in vacuo at roomtemperature for 1 h to afford the complex 1-W as a red-brown,crystalline solid. Yield: 0.55 g (0.90 mmol, 60% based on GeCl2(1,4-dioxane)), mp 86 °C. Anal. Calcd for C17H32GeO2Si3W (609.14): C,33.52; H, 5.30. Found: C, 33.82; H, 5.53. IR (toluene, ν (cm−1)): 1924(vs), 1860 (vs) (ν(CO)). IR (solid, ν (cm−1)): 3124 (vw), 3103 (vw),2950 (m), 2898 (m), 1909 (vs) (ν(CO)), 1857 (vs) (ν(CO)), 1413(m), 1302 (vw), 1253 (s), 1248 (s), 1104 (w), 1055 (m), 1007 (w),1000 (w), 821 (vs), 804 (vs), 790 (vs), 715 (s), 661 (vs), 618 (s), 589(s), 538 (s), 517 (m), 475 (vs). 1H NMR (300.1 MHz, C6D6, 298 K, δ(ppm)): 0.34 (s, 27H, C(SiMe3)3), 4.83 (s, 5H, C5H5).

13C{1H} NMR(75.47 MHz, C6D6, 298 K, δ (ppm)): 4.5 (s, 1J(C,Si) = 52.5 Hz, 9C,C(SiMe3)3), 68.4 (s, 1C, C(SiMe3)3), 84.7 (s, 5C, C5H5), 220.2 (s, 2C,2 × CO). 29Si{1H} NMR (59.63 MHz, C6D6, 298 K, δ (ppm)): −6.1(s, 1J(Si,C) = 52.5 Hz, C(SiMe3)3).

4. Preparation of [Cp(CO)2MoGe(Im-Me4)C(SiMe3)3] (2-Mo).A solution of Im-Me4 (48 mg, 0.39 mmol) in 5 mL of toluene wasadded slowly to a solution of 1-Mo (200 mg, 0.38 mmol) in 5 mL oftoluene at room temperature. During addition the solution changedfrom red-orange to red-brown. Stirring was continued for 30 min, andthen all volatiles were removed in vacuo. The residue was extractedwith a toluene−hexane mixture (1:1, 2 × 3 mL). The extract was

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concentrated to about 2 mL, 5 drops of hexane were added to theconcentrated solution, and the solution was stored at −60 °C for 16 h.The resulting precipitate was separated from the mother liquor byfiltration at −60 °C and dried for 1 h at room temperature in vacuo toafford the compound 2-Mo as a red-brown, crystalline solid. Yield: 170mg (0.26 mmol, 69%). 2-Mo starts to decompose at 174 °C, turningdark brown. Anal. Calcd for C24H44GeMoN2O2Si3 (645.41): C, 44.66;H, 6.87; N, 4.34. Found: C, 44.49; H, 6.75; N, 4.24. IR (toluene, ν(cm−1)): 1861 (vs), 1785 (vs) (ν(CO)). IR (solid, ν (cm−1)): 3688(vw), 3603 (vw), 3537 (vw), 3112 (vw), 3070 (vw), 2989 (w), 2953(m), 2903 (w), 1847 (vs) (ν(CO)), 1770 (vs) (ν(CO)), 1651 (m),1468 (m), 1449 (m), 1432 (m), 1399 (m), 1382 (m), 1367 (w), 1290(vw), 1255 (s), 1241 (sh), 1164 (vw), 1109 (w), 1092 (w), 1060 (vw),1004 (m), 822 (vs), 775 (vs), 738 (m), 713 (m), 675 (s), 650 (s), 619(m), 599 (s), 564 (s), 530 (m), 501 (s), 468 (m), 407 (w). 1H NMR(300.1 MHz, C6D6, 298 K, δ (ppm)): 0.36 (s, 27H, C(SiMe3)3), 1.29(s, 6H, C4,5-Me, Im-Me4), 3.59 (s, 6H, N1,3-Me, Im-Me4), 5.34 (s, 5H,C5H5).

13C{1H} NMR (75.47 MHz, C6D6, 298 K, δ (ppm)): 6.2 (s,1J(C,Si) = 51.1 Hz, 9C, C(SiMe3)3), 7.9 (s, 2C, C

4,5-Me, Im-Me4), 34.8(s, 2C, N1,3-Me, Im-Me4), 39.5 (s, 1C, C(SiMe3)3), 89.6 (s, 5C, C5H5),125.0 (s, 2C, C4,5-Me, Im-Me4), 172.9 (s, 1C, Ge-C2, Im-Me4), 243.7(s, 2C, 2 × CO). 29Si{1H} NMR (59.63 MHz, C6D6, 298 K, δ (ppm)):−5.9 (s, 1J(Si,C) = 51.1 Hz, C(SiMe3)3).5. Preparation of [Cp(CO)2WGe(Im-Me4)C(SiMe3)3] (2-W).

A solution of Im-Me4 (41 mg, 0.33 mmol) in 5 mL of toluene wasadded slowly to a solution of 1-W (200 mg, 0.33 mmol) in 5 mL oftoluene at room temperature. During addition the solution changedfrom red-orange to red-brown-purple. Stirring was continued for 0.5 h,all volatiles were then removed in vacuo, and the residue was washedwith hexane (2 × ca. 5 mL) at −30 °C and dried in vacuo at ambienttemperature to afford complex 2-W as a dark red-violet solid. Yield:

190 mg (0.26 mmol, 79%). 2-W starts to decompose at 140 °C,turning dark brown. Anal. Calcd for C24H44GeN2O2Si3W (733.32): C,39.31; H, 6.05; N, 3.82. Found: C, 40.27; H, 6.05; N, 3.75. IR(toluene, ν (cm−1)): 1854 (vs), 1779 (vs) (ν(CO)). IR (solid, ν(cm−1)): 3679 (vw), 3593 (vw), 3528 (vw), 3070 (vw), 2983 (w),2953 (m), 2902 (w), 1842 (vs) (ν(CO)), 1765 (vs) (ν(CO)), 1652(m), 1576 (vw), 1467 (m), 1449 (m), 1432 (m), 1399 (m), 1382 (m),1367 (w), 1255 (s), 1241 (sh), 1164 (vw), 1108 (w), 1093 (w), 1061(vw), 1010 (w), 1003 (w), 971 (vw), 824 (vs), 803 (sh), 784 (vs), 738(m), 713 (w), 676 (s), 651 (s), 603 (s), 562 (s), 500 (m), 487 (m),466 (w). 1H NMR (300.1 MHz, C6D6, 298 K, δ (ppm)): 0.35 (s, 27H,C(SiMe3)3), 1.30 (s, 6H, C4,5-Me, Im-Me4), 3.68 (s, 6H, N1,3-Me, Im-Me4), 5.31 (s, 5H, C5H5).

13C{1H} NMR (75.5 MHz, C6D6, 298 K, δ(ppm)): 6.0 (s, 1J(C,Si) = 51.4 Hz, 9C, C(SiMe3)3), 7.8 (s, 2C, C4,5-Me, Im-Me4), 33.7 (s, 2C, N1,3-Me, Im-Me4), 36.8 (s, 1C, C(SiMe3)3),88.1 (s, 5C, C5H5), 124.9 (s, 2C, C4,5-Me, Im-Me4), 178.3 (s, 1C, Ge-C2, Im-Me4), 234.1 (s, 2C, 2 × CO). 29Si{1H} NMR (59.6 MHz, C6D6,298 K, δ (ppm)): −7.0 (s, 1J(Si,C) = 51.4 Hz, C(SiMe3)3).

6. Crystal Structure Determination of 1-Mo, 1-W, 2-Mo and2-W. The data collection was performed on a Bruker X8-Kappa ApexIIdiffractometer (1-Mo), a STOE IPDS 2T diffractometer (1-W, 2-Mo),or a Nonius Kappa CCD diffractometer (2-W). All threediffractometers used graphite-monochromated Mo Kα radiation (λ =0.710 73 Å) and were equipped with a low-temperature device(Kryoflex, Bruker AXS GmbH, or Cryostream, Oxford Cryosystems).Intensities were measured by fine slicing ω and Φ scans and correctedfor background, polarization, and Lorentzian effects. A semiempiricalabsorption correction from equivalent reflections was applied for alldata sets by using Blessing’s method.32 The structures were solved bydirect methods and refined anisotropically by the least-squaresprocedure implemented in the SHELX program system.33

Table 4. Crystallographic Data of the Complexes 1-Mo, 1-W, 2-Mo, and 2-W

1-Mo 1-W 2-Mo 2-W

empirical formula C17H32GeMoO2Si3 C17H32GeO2Si3W C24H44GeMoN2O2Si3 C24H44GeN2O2Si3Wmoiety formula C17H32GeMoO2Si3 C17H32GeO2Si3W C24H44GeMoN2O2Si3 C24H44GeN2O2Si3Wformula wt 521.23 609.14 645.41 733.32temp, K 100(2) 123(2) 123(2) 123(2)wavelength, Å 0.710 73 0.710 73 0.710 73 0.710 73cryst syst, space group monoclinic, P21/n monoclinic, P21/n monoclinic, P21/n monoclinic, P21/nunit cell dimens

a, Å 9.0868(4) 9.0559(3) 9.4339(3) 9.4099(2)b, Å 22.4891(10) 22.4170(9) 20.2764(11) 20.2971(6)c, Å 11.4638(5) 11.5366(3) 15.1795(6) 15.1689(4)α, deg 90 90 90 90β, deg 93.0170(10) 92.938(2) 90.680(3) 90.5347(16)γ, deg 90 90 90 90

V, Å3 2339.43(18) 2338.92(14) 2903.4(2) 2897.04(13)Z; calcd density, g cm−3 4; 1.480 4; 1.730 4; 1.477 4; 1.681abs coeff, mm−1 1.982 6.360 1.614 5.153F(000) 1064 1192 1336 1464cryst size, mm3 0.60 × 0.32 × 0.08 0.30 × 0.10 × 0.05 0.13 × 0.08 × 0.04 0.30 × 0.19 × 0.11θ range for data collecn, deg 2.88−28.00 2.79−26.00 2.95−26.00 2.75−28.00limiting indices −12 ≤ h ≤ 12 −11 ≤ h ≤ 11 −11 ≤ h ≤ 11 −12 ≤ h ≤ 10

−29 ≤ k ≤ 28 −27 ≤ k ≤ 27 −24 ≤ k ≤ 23 −26 ≤ k ≤ 26−15 ≤ l ≤ 15 −14 ≤ l ≤ 14 −14 ≤ l ≤ 18 −20 ≤ l ≤ 15

no. of collected/unique rflns 54 504/5627 14 159/4571 15 079/5682 30 145/6908Rint 0.0305 0.0582 0.0753 0.0675completeness to θmax, % 99.8 99.4 99.5 98.7max/min transmissn 0.8576/0.3827 0.8380/0.3364 0.9263/0.7827 0.6061/0.3098no. of data/restraints/params 5627/2/226 4571/3/227 5682/6/311 6908/0/312goodness of fit on F2 1.053 0.939 0.964 0.950final R indices (I > 2σ(I)) R1 = 0.015, wR2 = 0.038 R1 = 0.034, wR2 = 0.074 R1 = 0.044, wR2 = 0.074 R1 = 0.029, wR2 = 0.056R indices (all data) R1 = 0.015, wR2 = 0.039 R1 = 0.049, wR2 = 0.078 R1 = 0.071, wR2 = 0.079 R1 = 0.044, wR2 = 0.059largest diff peak/hole, e Å−3 0.388/−0.275 1.295/−2.323 0.468/−0.895 1.215/−1.853

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The hydrogen atoms were included isotropically by using the ridingmodel on the bound carbon atoms. The illustrations of the molecularstructures were prepared with Diamond 2.1.c.34 Crystallographic datafor the four complexes are given in Table 4.

■ ASSOCIATED CONTENT*S Supporting InformationCIF files giving the crystallographic details for 1-Mo, 1-W, 2-Mo, and 2-W. This material is available free of charge via theInternet at http://pubs.acs.org.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: filippou@uni-bonn.de.

■ ACKNOWLEDGMENTSWe thank the Deutsche Forschungsgemeinschaft (SFB 813,DFG INST 217/468-1 FUGG) for generous financial supportof this work. We also thank S. Schwieger and M. Straßmann fortheir contributions to the crystal structure determinations,C. Schmidt, K. Prochnicki, and H. Spitz for recording thesolution NMR spectra, and A. Martens for the elementalanalyses. We thank Chemetall for the supply of chemicals.

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(7) Selected literature referring to silylenoids: (a) Oehme, H.; Weiss, H.J. Organomet. Chem. 1987, 319, C16. (b) Tamao, K.; Kawachi, A.Angew. Chem. 1995, 107, 886; Angew. Chem., Int. Ed. 1995, 34, 818.(c) Kawachi, A.; Tamao, K. Bull. Chem. Soc. Jpn. 1997, 70, 945.(d) Tamao, K.; Kawachi, A.; Asahara, M.; Toshimitsu, A. Pure Appl.Chem. 1999, 71, 393. (e) Sekiguchi, A.; Lee, V. Y.; Nanjo, M. Coord.Chem. Rev. 2000, 210, 11. (f) Hatano, K.; Tokitoh, N.; Takagi, N.;Nagase, S. J. Am. Chem. Soc. 2000, 122, 4829. (g) Wiberg, N.;Niedermayer, W. J. Organomet. Chem. 2001, 628, 57. (h) Lee, M. E.;Cho, H. M.; Lim, Y. M.; Choi, J. K.; Park, C. H.; Jeong, S. E.; Lee, U.Chem. Eur. J. 2004, 10, 377. (i) Likhar, R.; Zirngast, M.; Baumgartner,J.; Marshner, C. Chem. Commun. 2004, 1764. (j) Antolini, F.; Gehrhus,B.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 2005, 5112.(k) Flock, M.; Marschner, C. Chem. Eur. J. 2005, 11, 4635. (l) Molev,G.; Bravo-Zhivotoskii, D.; Karni, M.; Tumanskii, B.; Botoshansky, M.;Apeloig, Y. J. Am. Chem. Soc. 2006, 128, 2784.(8) Selected references on germylenoids: (a) Ohtaki, T.; Ando, W.Organometallics 1996, 15, 3103. (b) Sekiguchi, A.; Lee, V. Y. Chem.Rev. 2003, 103, 1429. (c) Tajima, T.; Sasamori, T.; Takeda, N.;Tokitoh, N.; Yoshida, K.; Nakahara, M. Organometallics 2006, 25, 230.(d) Sasamori, T.; Tokitoh, N. Organometallics 2006, 25, 3522.(9) (a) Cook, M. A.; Eaborn, C.; Jukes, A. E.; Walton, D. R. M. J.Organomet. Chem. 1970, 24, 529. (b) Eaborn, C.; Hitchcock, P. B.;Smith, J. D.; Sullivan, A. C. J. Chem. Soc. Chem. Commun. 1983, 827.(c) Aiube, Z. H.; Eaborn, C. J. Organomet. Chem. 1984, 269, 217.(10) Notably, the germylenoid does not react with the metalates inTHF. This suggests a strong solvent effect on the electrophilicity ofthe germylenoid.(11) Quantum chemical calculations of various ylidyne complexes ofthe general formula [LnME−R] (M = Mo, W; E = Si−Pb; R is asingly bonded substituent such as H, Me, Ph, m-terphenyl) haveshown that the potential energy hypersurface for bending thesubstituent R is rather flat at M−E−R bond angles close to 180°:(a) Reference 3e. (b) Schnakenburg, G. Dissertation, UniversitatBonn, 2008.(12) Pyykko, P.; Riedel, S.; Patschke, M. Chem. Eur. J. 2005, 11,3511.(13) Several cyclopentadienyl dicarbonyl complexes of Cr−W havebeen reported to display a solvent-induced shift of their CO stretchingmodes: (a) Filippou, A. C.; Grunleitner, W. J. Organomet. Chem. 1991,407, 61. (b) Filippou, A. C.; Grunleitner, W.; Kiprof, P. J. Organomet.Chem. 1991, 410, 175. (c) Filippou, A. C.; Grunleitner, W.; Volkl, C.;Kiprof, P. J. Organomet. Chem. 1991, 413, 181. (d) Filippou, A. C.;Volkl, C.; Kiprof, P. J. Organomet. Chem. 1991, 415, 375. (e) Filippou,A. C.; Wanninger, K.; Mehnert, C. J. Organomet. Chem. 1993, 461, 99.(f) Filippou, A. C.; Wossner, D.; Kociok-Kohn, G.; Hinz, I.J. Organomet. Chem. 1997, 541, 333.(14) (a) Barraclough, C. C.; Lewis, J.; Nyholm, R. S. J. Chem. Soc.1961, 2582. (b) de Witt-Horrocks, W. Jr.; Mann, R. H. Spectrochim.Acta 1965, 21, 349. (c) Foffani, A.; Poletti, A.; Cataliotti, R.Spectrochim. Acta A 1968, 24, 1437. (d) Gould, N. J.; Parker, D. J.Spectrochim. Acta A 1975, 31, 1785. (e) Gutmann, V. Mon. Chem.1977, 108, 429. (f) Creaser, C. S.; Fey, M. A.; Stephenson, G. R.Spectrochim. Acta A 1994, 50, 1295.(15) The germylidyne complexes [Cp(CO)2MoGeR] (R = ArMes,ArTrip) display in hexane or toluene only two ν(CO) absorption bands.In comparison, several ν(CO) absorption bands have been reportedfor the germylidyne complex [Cp(CO)2MoGeArTrip] in Nujolmull.2b

(16) (a) Dossett, S. J.; Hill, A. F.; Jeffrey, J. C.; Marken, F.;Sherwood, P.; Stone, F. G. A. J. Chem. Soc., Dalton Trans. 1988, 2453.(b) Fischer, E. O.; Lindner, T. L.; Huttner, G.; Friedrich, P.; Kreißl, F.R.; Besenhard, J. O. Chem. Ber. 1977, 110, 3397.(17) The mean value xu of the M−CO bond lengths is given. Thestandard deviation σ of xu (value in parentheses) was calculated usingthe equation σ2 = ∑(xι − xu)

2/(n2 − n), where xi is the respectiveindividual value and n = 2.(18) Uedelhoven, W. Dissertation, Technische Universitat Munchen,1979.

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(19) Griffith, C. S.; Koutsantonis, G. A.; Skelton, B. W.; White, A. H.J. Organomet. Chem. 2003, 672, 17.(20) 1H NMR and 13C{1H} NMR spectra of trisyl compoundsbearing a bulky substituent at the central carbon atom often show adecoalescence of the methyl resonance to several signals at lowtemperature, which has been attributed to a correlated motion of theSiMe3 groups: Avent, A. G.; Bott, S. G.; Ladd, J. A.; Lickiss, P. D.;Pidcock, A. J. Organomet. Chem. 1992, 427, 9.(21) Kuhn, N.; Kratz, T. Synthesis 1993, 561.(22) A CSD survey (Nov 21, 2011) revealed that only very fewmolybdenum germylidene complexes have been structurally charac-terized: (a) Kuhl, O.; Lonnecke, P.; Heinicke, J. Inorg. Chem. 2003,42, 2836. (b) Zabula, V.; Hahn, F. E.; Pape, T.; Hepp, A.Organometallics 2007, 26, 1972. (c) Shinohara, A.; McBee, J.; Tilley,T. D. Inorg. Chem. 2009, 48, 8081.(23) For structurally characterized tungsten germylidene complexes,see: (a) Huttner, G.; Weber, U.; Sigwarth, B.; Scheidsteger, O.; Lang,H.; Zsolnai, L. J. Organomet. Chem. 1985, 282, 331. (b) Jutzi, P.;Hampel, B.; Stroppel, K.; Kruger, C.; Angermund, K.; Hofman, P.Chem. Ber. 1985, 118, 2789. (c) Jutzi, P.; Hampel, B.; Hursthouse, M.B.; Howes, A. J. J. Organomet. Chem. 1986, 299, 19. (d) Du Mont,W.-W.; Lange, L.; Pohl, S.; Saak, W. Organometallics 1990, 9, 1395.(e) Tokitoh, N.; Manmaru, K.; Okazaki, R. Organometallics 1994, 13,167. (f) Ueno, K.; Yamaguchi, K.; Ogino, H. Organometallics 1999, 18,4468. (g) Hashimoto, H.; Tsubota, T.; Fukuda, T.; Tobita, H. Chem.Lett. 2009, 38, 1196.(24) The germylidene complexes [Cp(CO)2(H)Mo=Ge(X)R] (X =Cl, OH, OMe; R = ArMes, ArTrip) were obtained upon addition of HXat the Mo−Ge triple bond of the germylidyne complexes[Cp(CO)2MoGe−R]. The zwitterionic germylidene complexes[Cp(CO)2MoGe(Im-Me4)R] (R = ArMes, ArTrip) were prepared inthe same way as 2-Mo: Filippou, A. C.; Stumpf, K. W.; Schnakenburg,G., Personal communication. Filippou, A. C.; Stumpf, K. W.; Chernov,O.; Schnakenburg, G. Private communication to the CambridgeStructural Database, deposition numbers CCDC 855235−855239,2011.(25) Cowley, A. H.; Norman, N. C.; Pakulski, M.; Becker, G.; Layh,M.; Kirchner, E.; Schmidt, M. Inorg. Synth. 1990, 27, 235.(26) Spectroscopic data of Li(THF)4][Li{C(SiMe3)3}2]:

1H NMR(300.1 MHz, C6D6, 298 K, δ (ppm)): 0.46 (s, 54H, 2 × C(SiMe3)3),1.23 (m, 16H, 8 × CH2, THF), 3.28 (m, 16H, 8 × CH2, THF);13C{1H} NMR (75.47 MHz, C6D6, 298 K, δ (ppm)): 7.9 (s, 18C, 2 ×C(SiMe3)3), 25.1 (s, 8C, 8 × CH2, THF), 68.3 (s, 8C, 8 × CH2, THF),the signal of the carbon atom bonded to lithium was not detected;29Si{1H} NMR (59.63 MHz, C6D6, 298 K, δ (ppm)): −10.8 (s,1J(Si,C) = 48.0 Hz, 2 × C(SiMe3)3).(27) Kouvetakis, J.; Haaland, A.; Shorokhov, D. J.; Volden, H. V.;Girichev, G. V.; Sokolov, V. I.; Matsunaga, P. J. Am. Chem. Soc. 1998,120, 6738.(28) Filippou, A. C.; Winter, J. G.; Kociok-Kohn, G.; Hinz, I. J. Chem.Soc., Dalton Trans. 1998, 2029.(29) Spectroscopic data of Li[CpMo(CO)3]: IR (THF, ν (cm−1)):1906 (s), 1898 (m), 1806 (vs), 1782 (m), 1717 (s) (ν(CO)); 1HNMR (400.1 MHz, CD3CN, 298 K, δ (ppm)): 5.06 (s, 5H, C5H5);13C{1H} NMR (100.6 MHz, CD3CN, 298 K, δ (ppm)): 87.1 (s, 5C,C5H5), 236.6 (s, 3C, 3 × CO).(30) Spectroscopic data of K[CpW(CO)3]: IR (DME, ν (cm−1)):1891 (vs), 1782 (vs), 1750 (s) (ν(CO)); 1H NMR (300.1 MHz, THF-d8, 298 K, δ (ppm)): 5.03 (s, 5H, C5H5).(31) The yellow solid was shown by NMR spectroscopy to be pureenough for further conversion. NMR spectroscopic data ofLi(THF)3GeCl2C(SiMe3)3 are as follows: 1H NMR (300.1 MHz,C6D6, 298 K, δ (ppm)): 0.56 (s, 27H, C(SiMe3)3), 1.31 (m, 12H, CH2,3 × THF), 3.53 (m, 12H, CH2, 3 × THF); 29Si{1H} NMR (59.63MHz, C6D6, 298 K, δ (ppm)): −4.4 (s, C(SiMe3)3).(32) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33.(33) Sheldrick, G. M. SHELXS97 and SHELXL97; University ofGottingen, Gottingen, Germany, 1997.

(34) Brandenburg, K. DIAMOND 2.1.c; Crystal Impact GbR, Bonn,Germany, 1999.

■ NOTE ADDED AFTER ASAP PUBLICATIONIn the version of this paper published on January 9, 2012, therewas an incorrect reference given in Table 3. The version of thistable that appears as of January 12, 2012 is correct.

Organometallics Article

dx.doi.org/10.1021/om201176n | Organometallics 2012, 31, 748−755755