Indian Journal of ChemistryVol. 34A, June 1995, pp. 449-453

Synthesis and characterization of some heterotbi- and tri- )-metallicisopropoxides of magnesium(II)

S Sogani, A Singh" & R C MehrotraDepartment of Chemistry, University of Rajasthan, Jaipur 302 004

Received 28 July 1994; revised and accepted 29 December 1994

Isopropoxometallate derivatives of magnesium of the types, CIMg{Zr2(OPri)91,CIMg{M(OPri)nl(M=Al, n=4~ M=Nb, n=6) Mg{Zr2(OPri)9lz.and Mg{M(OPri)nb (M=Al, n"'4; M=Nb, n=6)have been synthesized by the reactions of MgCl2 with an appropriate alkoxometallate in the requiredmolar ratio. Reactions of CIMg{Zr2(OPri)91with potassium isopropoxide, potassium isopropoxoalu-minate, or -niobate in benzene yield (PriO)Mg{Zr2(OPri)91, {Al(OPri)4IMg{Zr2(OPri)91,and{Nb(OPri)6IMg{Zr2(OPri)91respectively. All these derivatives have been characterized by elementalanalyses, spectroscopic (IR and NMR) studies and ebullioscopic molecular weight determinations.

Although a number of heterobimetallic chloridealkoxides of 3d transition-, main group-, and lan-thanide-metals are now known 1 - 10, to our best ofknowledge, no report appears to be available onthe synthesis of heteroleptic derivatives of thetype CIML, where M is a strongly electropositiveGroup 2 metals like, Mg, Ca, Sr, Ba with L as anisopropoxometallate ligand.

In view of the applicability of heterobimetallicchloride alkoxides as precursors for the synthesisof heterotrimetallic alkoxides'?" " and the use ofheterometal alkoxides, e.g. Mg{Al(OPri)4}z' as mo-lecular precursors'v= " for oxide ceramics likeMgAl204 (ref. 24), we describe herein the synthe-sis of a number of interesting heterobimetallicchloride isopropoxides of Mg(II). The use of suchchloro derivatives for synthesis of stable trimetal-lie derivatives of Mg(II) has also been demonstrat-ed for the first time. The previously reported der-ivatives Mg{M(OPri)nlz (M = Al, n = 4; M = Nb,n=6) and Mg{Zr2(OPri)9lz have also been syn-thesized by an alternative route using anhydrousMgCI2•

Materials and MethodsAll manipulations were carried out under anhy-

drous conditions. The solvents and reagents werepurified and dried prior' to use by appropriateprocedures described in the literature".

Isopropoxides of aluminium"; zirconium'" andniobiurrr" were prepared by the literature meth-ods.

Anhydrous magnesium chloride was preparedby heating a mixture of MgCl2.6HzO (BDH) and

NH4CI, in a current of dry HCI gas. Analysis:Found (Calcd.) MgClz:Mg, 25.52 (25.52); Cl,74.47 (74.47%).

Aluminium, zirconium and niobium in the he-terometal isopropoxides of magnesium were esti-mated'? as aluminium oxinate, zirconium oxide,and niobium oxide respectively. The magnesiumin the filtrate after removal of the above metalions was estimated as MgNH4P04.6H20.

Isopropoxy contents were estimated byan oxid-imetric method " using N - K2Cr207 solution in12.5% H2S04, Chloride was estimated volumetri-cally by Volhard's methods".

The IR spectra (4000-200 cm - I) were re-corded on a Perkin-Elmer 577 spectrometer usingCsI optics. The IH (89.55 MHz), I,C (22.49MHz) and 27 AI (23.29 MHz) NMR were re-corded on a JEOL FX 90Q FT NMR spectrome-ter in CDCl1 or CCl4 respectively using TMS asinternal and 1M AlCl3(H20)6 as external refer-ence respectively. The molecular weights weremeasured with Gallenkamp ebulliometcr usingthermister sensing device.

Preparation o!ClMmZr2( OPf)9}A benzene ( - 20 ml) solution of K{Zr2(OPri)~}

freshly prepared by the reaction of potassium(0.18 g, 4.60 mmol) in isopropyl.alcohol ( - 2 ml)and benzene (- 20 ml), followed by addition ofZr(OPri)4.PriOH (3.57 g, 9.20 mmol) and reflux-ing for - 2h and finally stripping of the volatileswas added dropwise to a benzene suspension ofMgCl2 (0.44 g, 4.68 mmol), The resulting reactionmixture was stirred for - 10 h at 70°C. The pre-

450 INDIAN J CHEM. SEe. A. JUNE 1995

cipitated KCl (0.34 g. 4.55 mmol) was filtered off.The volatiles were removed from the filtrate un-der reduced pressure ( - 1 mm) at room tempera-ture ( - 2rC) to obtain a white crystalline solid ofcomposition CIMg{Zrz(OPri)9} (4.61 g, 99%). Theproduct was purified either by recrystallizationfrom n-hexane/toluene or by volatilization at21O°C/O.01 mm Hg in 70% or 30% yield respect-ively.

Adopting a similar procedure, the reaction ofMgCl2 with K{Zrz(OPri)9} (1:2) affordedMg{Zr~(OPri)l}lz, in 99% yield, which could be vo-latilized at 175°C/O.l mm Hg in 70% yield.

Synthesis ofCIMfltAI( OPt) .•}A solution of K{AI(OPri) .•} (freshly prepared by

reaction of K(0.21 g, 5.37 mmol) and AI(OPri)3(1.09 g, 5.34 mmol) in isopropyl alcohol ( - 1 ml)and benzene (- 20 ml) was added slowly to thesuspension of MgCl2 (0.51 g, 5.35 mmol) in ben-zene ( - 20 mI). The reaction mixture was stirredat room temperature (- 2rC) for - 12 h. Theprecipitated KCl (0.40 g, 5.36 mmol) was re-moved by filtration. The volatiles from the filtratewere removed under reduced pressure (1 mm Hgat 2rC) to afford CIMg{(AI(OPri)4} (1.72 g, 99%as a white sticky solid. The product was recrystal-lized from n-hexane/toluene mixture at - 10°C in40% yield.

In a similar manner, reaction of MgClz withK{Nb(OPri)o in 1:1 or 1:2 molar ratios afford pro-ducts of compositions CIMg{Nb(OPri)6} orMg{Nb(OPri)olz respectively. These two productswere also purified by recrystallization at - 10°Cfrom CH,Cl,-n-hexane in 65 and 50% yield re-spectively. Further, an already known compoundMg{AI(OPri)4h could also be prepared by theabove procedure by carrying out the reaction ofMgCl2 and KAl(OPri)4 in 1:2 molar ratio inCoHo-PriOH.

Reaction of CIMfltZr2( OPt')l}} with KOPrA benzene suspension ( - 15 rnl) of KOPri pre-

pared by dissolving potassium (0.15 g, 3.83 mmol)in isopropyl alcohol (2 rnl) and benzene ( -10 ml)followed by removal of volatiles was added drop-wise to a benzene (- 30 ml) solution ofCIMg{Zr2(OPri)9} (2.77 g, 3.58 mmol). The reac-tion mixture was first stirred at room temperaturefor - 12h followed by heating at -70°C for 2h.After removal of the precipitated KCl (0.28 g,3.75 mmol) by filtration, the volatiles from thefiltrate were removed under reduced pressure (1mm Hg at 27°C) to yield (priO)Mg{Zrz(OPri)9}

(2.90 g, 97%) as a colourless viscous mass, whichwas purified by distillation at 240°C/O.05 mm Hgin 50% yield.

•Preparation of {A I (OPt)4} Mg{ Zr2( OPt)9}

A benzene ( - 25 ml) suspension ofK{AI(OPri)4} freshly prepared by the refluxing ofK (0.12 g, 3.07 mmol) and AI(OPri)3 (0.63 g, 3.08mmol) in benzene (- 15 ml) and isopropyl alco-hol (- 5 ml) followed by removal of volatiles wasadded slowly to the benzene ( - 25 ml) solution-ofCIMg{Zr2(OPri)9} (2.37 g, 2.07 mmol). The reac-tion mixture was stirred first at room temperaturefor - 7h followed by stirring at 80°C for 2 h. The·precipitated KCI (0.23 g, 3.08 mmol) was re-moved by filtration. The volatiles from the filtratewere removed under reduced pressure (1 mm at27°C) to afford {AI(OPri)4}Mg{Zr2(OPri)9} whichwas purified by distillation at 240°C/O.02 mm Hgin 54% yield.

Similar reactions of KNb(OPri)6 withCIMg{Zr2(OPri)9} in 1:1 molar ratio in benzeneafforded {Nb(OPri)6}Mg{Zrz(OPri)9} in quantitativeyield which could be purified by recrystallizationfrom CH2Cl21 n-hexane mixture at - 15°C in 60%yield.

Results and DiscussionReactions in 1:1 or 1:2 of MgCl2 with

K{Zrz(OPri)9} or K{M(OPri)n} (M=Nb, n=6;M = AI, n = 4) afforded derivatives of the typesCI2_xMg{Zr2(OPri)9}x (x= 1 or 2) andClz_xMg{M(OPri)n}x (M=Nb. n=6., x= 1 or 2;M = AI, n = 4, x = 1 or 2) in quantitative yields ac-cording to the following general equations:

NgCla +.I<{zr2(OPrlJ,}~ CIa-«Mg{zrz(OPr11tl.r+.KCI ~

(I)

10; •• '; Ib: •• 2.

MgCl2+.K{NIOPrll.} ~ Ciz-. Mg{MIOPrll.1. +xKCI 4

(II)

Do: M• AI. n .4 ••• 1 ; Db: M. AI. n .4.x' 2;

lie: M.NII. n.6 ••• 1; lid: M.Nb •.,.6, •• 2.

Replacement of chloride in CIMg{Zr2(OPri)9}with Pr'O", AI(OPri),;- and Nb(OPri)i producedderivatives of the types (PriO)Mg{Zr2(OPri)\I},[Al(OPri)4}Mg{Zr2(OPriM and {Nb(OPri)6}-Mg{Zr2(OPri)9} respectively, according to the fol-lowing equations:

SOGANI et al: STUDIES ON SOME ISOPROPOXOMET ALlATE DERIVATIVES OF Mg(II) 451

CI"'{Zrl"'''It}+KOPrI~(prIOIN'{Zrl (OPrllt)+J(CI.

lUll

C\Mt {Zrz 10Pri It}+K{NporIl.} - {N10Pr11.} Ng{ZrzlOPrlltl+KCI •

nVI

lYo: N • AI. n • 411Yb: N. Nb. n • t.

All these new hetero (bi- and tri-) metallic isop-ropoxides are highly moisture sensitive, colourlesssolids or viscous compounds, soluble in commonorganic solvents (such as CIIHII, CIIH5CH.;,CH2CI2, CHCI3, CCI4, THF, n-hexane, etc.). Anal-ytical data is shown in Table 1. Most of these ex-

hibit monomeric behaviour (ebullioscopically) inbenzene except the derivatives lIa and lie whichare dimeric and can be represented by the for-mulations:[(PriObAI(.u - OPrihMg(.u - ClhMg(.u - OPri)2x Al(OPrih] and [(PriO)4Nb(.u - OPrihMg(.u - CI}z

x Mg(.u - OPri}zNb(OPriL] respectively.Most of these (such as Ia, Ib, lib, lVa and III)

compounds could be volatilized in analyticallypure state under reduced pressure, whereas thederivatives (lIa) and (llefor lid) disproportionateon being heated under reduced pressure with the

Table I-Preparative and analytical data of the hetero-metallic isopropoxide of magnesium(II)SI. Reactants(g; mmol) Product yield (g; %) Found (Calcd.), %No.

Mg AI Zr Nb PriO CI1. MgCI2 + K{AI(OPri)41 CIMg{AI(OPri)41 7.51 8.30 73.14 10.92

(0.51; 5.35) (K(0.21; 5.37) (1.72, 99) (7.52) (8.35) (73.14) (10.98)+AI(OPrih( 1.09; 5.34)]

2. MgCI2 + 2K{AI(OPri)4 Mg{AI(OPri)4b 4.39 9.82 85.7510.35; 3.67) [K(0.28; 7.16) (2.01,99) (4.41) (9.90) (85.77)

+AI(OPrih (1.46; 7.15)]

3. MgCI2 + K{Zr2(OPr')ql CIMg{Zr2(OPri).I* 1.32 23.61 68.60 4.50(0.44; 4.62) [K(0.18;4.60) (3.45,99) (3.41) (23.59) (68.68) (3.58)

+Zr(OPri)4.PriOH (3.57;9.20)]

4. MgCl2 + 2K{Zr2(OPriM Mg{Zr2(OPri).I! 1.62 25.20 73.10(0.25; 2.62) [K(0.20; 5.11) (3.32,99) (1.67) (25.14) (73.18)

+Zr(OPri)4.PriOH(3.96; 10.21)]

5. MgCI2 + K{Nb(OPri)61 CIMg{Nb(OPri)61 4.71 18.25 69.89 6.91(0.51; 5.35) [K(0.21; 5.37) (2.97,99) (4.79) (18.31) (68.89) (6.99)

+Nb(OPri)5 (2.08; 5.35)]

6. MgCI2 + 2K{Nb(OPriM Mg!Nb(OPri)6b 2.79 20.10 77.02(0.31; 3.25) [K(0.25; 6.40) (2.96,99) (2.64) (20.23) (77.12)

+Nb(OPri)S (2.48; 6.38)]

7. CiMg/Zr2(OPril.1 + KOPri (PrO)Mg{Zr2(OPri).I* 3.01 23.21 74.0(2.90; 3.75) [K(O.IS; 3.83) (2.89; 96) (3.05) (22.89) (74.05)

+Pri()H(2 mI)]

8. ClMg{Zr 2(OPri)91 + K{AI(OPri)41 {AI(OPri)4]Mg{Zr2 18.25 76.30(3.59; 4.64) [K(0.18; 4.60) (OPri)"I* (4.59, 99) (18.20) (76.67)

+AI(OPrih (0.95; 4.65)]

9. CIMglZr2(OPril.1 + K{Nb(OPri)61 {Nb(OPri)6IMg{Zr 2 15.50 74.52(2.19; 2.83) [K(O.l1; 2.81)] (OPri).} (3.32, 99) (15.38) (74.71)

+Nb(OPri)s (1.10; 2.83))

*Volatile un,der reduce pressure (160·C-240·C/0.05 mm)

452 INDIAN J CHEM, SEe. A, JUNE 1995

liberation of Mg!Al(OPri}412and Nb(OPri), as vol-atile fragments respectively. The attempted volati-lization of {Nb(OPri)6}Mg{Zr2(OPri)9} under re-duced pressure affords Nb(OPri)5 (113°C/O.02mm) and (PriO)Mg{Zr2(OPri)9} (240°C/0.05 mm).

The IR spectra of these new heterornetallicisopropoxide derivatives show absorptions char-actcristic30-32 of metal-isopropoxide groups andmetal-chlorine bond in the regions: 1140-1170v(OCH(CH3}z); 1010-930 v(C-O); 550-570v(Zr-O); 660-550 v(Nb-O and AI-O); 460-410 v(Mg - 0); and 360-300 em - , due- tov(Mg-CI).

The 'H and DC{'H} spectra of Ib, IIa-IId & IIIhcterobimetallic isopropoxides are poorly re-solved in which it has not been possible to distin-guish clearly between signals' for bridging andterminal isopropoxy groups. However, the deriva-tive ClMg{Zr2(OPri)lj} (Ia) shows three doubletscentred at <5 1.29, 1.37 and l.46 due to gem-dimethyl protons, approximately in 4:3:2 intensityratio corresponding to eight terminal, six doubly('u2-0Pri) bridged and four triply ('uJ-OPri)bridged isopropoxy groups respectively, and amultiplet at <54.44 arising from overlapping sep-tets due to methine protons of isopropoxy groups.The DC NMR spectrum of (I) shows three peaksat <572.53, 70.80 and 69.90 due to a-carbon at-oms of triply bridged, doubly bridged and termi-nal isopropoxy groups respectively and two peaksat ~ 26.16 and 27.46 due to p-carbon atoms.

The 'H NMR spectrum of (IVa) exhibits (i) adoublet (J = 6 Hz) at ~ 1.25 due to gem-dimethylprotons of both doubly bridged and terminalisopropoxy groups; (ii) a doublet (J = 6 Hz) cen-tred at <5 1.48 due to methyl protons of triplybridged isopropoxy groups, and (iii) overlappingseptets appearing as a broad multiplet at ~ 4.41due to methine protons of isopropoxy groups.The J1C NMR spectrum of (IVa) shows peaks dueto a-carbons at <569.0L 70.19 and those of P-carbons at <527.0, 27.5. The 27 AI NMR spectrumshows broad absorption centred at <564.0 charac-teristic of a tetra-coordinate environment aroundaluminium ".

The 'H NMR spectrum of IVb shows two dou-blets (J = 6 Hz) at <51.30 and 1.35 due to methylprotons of terminal and bridging isopropoxygroups. This also exhibit two septets at ~ 4.42and 4.75 due to methine protons of terminal andbridging isopropoxy groups. The i3C NMR spect-ra of IVb shows peak at <566.21, 69.52 due toa-carbon atoms and at ~ 25.62, 26.91 due to P-carbon atoms of bridging and terminal isopropoxygroups.

Although attempts made for structural elucida-tion by single crystal X-ray diffraction studieshave been futile so far, the structures depicted inStructure I appear to be more plausible on the basis ofthe above physico-chemical data and recently re-ported crystal structures of [{CICd[Zr2(OPri)9lbl(ref. 1) and [(Zrz{OPri)9}CuClj34.

(I)

Proposed structures for (A) [ClMg{Zr2(OPri)9}l,(B) [Mg{Zr2(OPri)9bl, and(C) {A1(OPri)4}Mg{Zr2(OPri)9}

AcknowledgementWe gratefully acknowledge the DST, New Delhi

for the financial support.

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