Gorsi, B. L.

Kapoor, P. N.

Mehrotra, R. C.

English

NOPR

Indian Journal of ChemistryVol. lo1A. JUDe I"' •.pp. _.487Reactions of Pyruvoaitrile with Nb(V) & Ta(V) AlkoxidesB. L. GORSI,P. N. KAPOOR* & R. C. MEHROTRAtDepartment of Chemistry, University of Rajasthan, Jaipur 302004Received 20 June 1975; accepted 1 September 1975Reaction of pyruvonitrile with the alkoxldes (Isopropoxides and ethoxides) of Nb(V) and Ta(V)give products of the type M(OR)._n (CN)nPX (where M=Nb. Ta; R=Pr/• Et; n;~l to 5; P=005 to2·5; X=GH3COOR). The reverse reaction of pentacyanlde derivatives of these metals with excessof isopropanol has been studied.'IN recentyears a number of cyanide complexes>"of different metals have been synthesized andcharacterized. There is no reference availablein the literature on the cyanide complexes of metalalkoxides. We have now synthesized the cyanidederivatives of Nb(V) and Ta(V) alkoxides by thereaction of pentaalkoxides of these metals withpyruvonitrile, similar to the reaction of acyl halides!in the synthesis of halide derivatives (mainly chlorideand bromide) of metal alkoxides,The reaction of pyruvonitrile with these alkoxideshave been carried out in different molar ratios incyclohexane and are found to be exothermic innature. These can be represented by the generalEq. (1):M(OR)s+nCH3COCN~M(OR)s_,,(CN),,'mCH3COOR(1\1 = Nb or Ta)... (1)When R=Pri; n=1, m=O; »=2, m=0·5;n = 3, m = 1; n = 4, m = 1·5; n = 5, m = 2·0(for 1\1= Nb) and 2·5 (for 1\1= Ta) and whenR=Et; n=1, m=O; n=5, m=2·0 (for M=Nb) and 2·5 (for M = Ta).All the products are reddish brown, crystallinesolids or pasty solids (in some cases) (Table 1).It appears that as the isopropoxy groups of theNb(V) and Ta(V) isopropoxides are replaced bythe cyanide groups, the new complexes formedexhibit an increasing tendency to add on additionalmolecules of the ester. The penta-derivative ofniobium adds two molecules of the ester, whilein the case of tantalum, the corresponding pentaderivative adds 2·5 molecules of the ester. Theester molecules .cannot be removed even whenthe compound is heated up to 80° (bath temperature)under reduced pressure (0·1 mm) for a long time.To study the reversibility of these reactions,isopropanol was added to Nb(CNk2'OCHaCOOPriand Ta(CNk2'5CH3COOPr' and the reaction mix-tures were refluxed for 1 hr. The compoundsobtained were the same as obtained by the reactionsof Nb(OPri)s and Ta(OPri>S with CHaCOCN in-Present address: Laboratoriurn Fiir Anorg Chelll1eEddgen Technische Hochschule CH-8006,UniversitatTrasse-6,Ziirich, Switzerland.[Present address: Vice-Chancellor, University ofDelhi,Delhi.406the molar ratio 1: 3. The reactions can be repre-sentcd by Eqs. (2) and (3):Nb(CNh2'OCHaCOOPr' + PriOH-+(excess)Nb(OPril2(CN)31'OCHaCOOPri+CHaCOOPri+2HCN ... (2)Ta(CN)52'SCH3COOPri+PriOH-+(excess)Ta(OPri)2(CNla1'OCHaCOOPri+ HCH3COOPri+2HCN ... (3)It seems that the above reactions proceed onlyup to 1: 2 molar ratio. It may be of interest torecord that similar reactions of NbCls and TaClswith PriOH proceed with the formation of dichloricetri-isopropoxide derivatives".IR spectra (nujol, "max in crrr+) of the mixedcyanide derivatives of the Nb(V) and Ta(V) alkoxidesshow peaks ,...,2070, 2170, 2220 in the CN stretchingregion. The first two bands may be attributedto the isocyanide" and cyanide ferms respectively.The position of the CN absorption band of isocyanideis approximately 100 lower than the correspondingposition for a nitrile. In some cases the absenceof the band near about 2070 does not exclude thepossibility of the isocyanide isomer being presentin very low concentration. Thus we can assumethat these alkoxy cyanide derivatives consist ofequilibrium mixtures of the iso (M-NC) and normal(M-CN) structures similar to the trimethyl deri-vativesi-" of silicon and germanium. The band,...,2220 may be assigned to the bridging cyanide(M-CN-M) group similar to those observed inthe compounds K2Ni(CN)4·4BF3 (ref. 9) and(NH3>SCONCCO(CN>S(ref. 10).Molecular weigbts of few of these freshly preparedcomplexes have been determined ebnllioscopically(Table 1). These data depict that molecular asso-ciation increases with the replacement of isopropoxygroups. All the penta der ivatives are polymericand are sparingly soluble in refluxing benzene. Theassociation of the molecules can be explained onthe basis of cyanide bridge formation. This is sup-ported by IR data (peak ,...,2220 cm+).All the alkoxy metal cyanide complexesundergo disproportionation when heated undervacuum to give corresponding alkoxides. WhenGORS! et al.: CYANIDES OF Nb(V) & Ta(V) ALKOXIDESExperimental ProcedureStringent precautions were taken to excludemoisture throughout these investigations.Pyruvonitrile (Fluka) was used after distillation(b.p. 93°). Molecular weights were determinedin a sernimicro ebulliometer (GaUenkamp) in reflux-ing benzene. IR spectra were recorded in the range4000-400 cm-1 on a Perkin-Elmer 337 spectrophoto-meter using KBr plates.Niobium and tantalum were estimated as theiroxides and nitrogen was estimated by Kjeldahlmethod.Reaction of Nb(OPrih with CHaCOCN (1: 1)-An exothermic [faction took place when Nb(OPri)(2·17 g, 0·055 mole) is treated withCHaCOCN (0·38 g,0·055 mole) in cyclohexane (SO ml). The reactionmixture was refluxed for 20 min. Removal of thesolvent under reduced pressure gave a brownishviscous liquid which tended to solidify on longstanding.Reaction of Nb(OPri)5 with CHaCOCN (1:5)-To a solution of Nb(OPri)5 (2·77 g, 0·07 mole) incyclohexane (SO ml), CHaCOCN (2·46 g, 0·35 mole)was added and the reaction mixture refluxed for20 min. The solvent was removed under reducedpressure and the product dried for 8 hr (0·1 mm!70°C bath temp.). A reddish solid compound wasobtained.To Nb(CNh2'OCHaCOOPri (0·49 g), excess ofisopropanol was added and the reaction mixtureis refluxed for 1 hr. The brown solid was driedunder reduced pressure [Found: Nb, 25·50; N,10·71. Nb(OPri)2(CN)3·CHaCOOPri requires Nb,23·75; N, 10·74%J.The products obtained by the reactions of Nb(V)and Ta(V) isopropoxides and ethoxides withCHaCOCN are given in Table 1.AcknowledgementOne of the authors (B.L.G.) thanks the UGC,New Delhi, for the award of a junior researchfellowship.TABLE 1 -CYANIDES OF Nb(V) AND Ta(V) ALKOXIDESMolar Product" Found (%) (calc.) Mol. com-ratio plexityMetal NREACTION OF Nb (OPri). WITH CH3COCN1:1 Nb(OPri).(CN), 25·64brown viscous (26'17)1:2 Nb(OPri)3(CN). 25'200·5 X. brown (24'99)viscous1:3 Nb(OPri).(CN). X, 24·31brown solid (23'75)1: 4 Nb(OPri) (CN). 22·751·5X. reddish .(22-72)solid1:5 Nb(CN).2X. 21·75reddish solid (21'76)4'07(3-94)7'45(7'50)2·011-12(10'74)13'79(13-69)2'342'6216'00(16-40)PolymerREACTION OF Nb(OEt). WITH CH3COCN1: 1 Nb(OEt).(CN). 30·78 4'50 doreddish semi -solirl (31-08) (4-68)1:5 Nb(CN) s-2Y, reddish 23·24 17'00 dosolid '(23'29) (17.54)REACTION OF Nb(CNls.2X WITH Pr'OH1: ex- Nb(OPri)2(CN)3X, 25'30 10·71cess brown solid (23'75) (10·74)REACTIONOF Ta(OPri). WITH CH3COCN1 : 1 Ta(OPri)4(CN), 41'68 3'25yellow solid (40'85) (3-16)1:2 Ta(OPri)3(CN)2 40·55 5'850'5X, brown semi- (39'25) (6'07)solid1:3 Ta(OPr~b(CN) 3X, 38'24 8·54brown solid (37-77) (8'77)1: 4 Ta(OPri)(CN).1·5X. 37-15 11-12reddish solid (36-40) (11'27)1; 5 Ta(CNis2'5X, 31'97 12'10reddish brown (31'96) (12'37)solidREACTIONOF Ta(OEtj. WITH CH3COCN1 : 1 Ta(OEt)~(CN) 46'20 3'50reddish semi-solid (46'78) (3-61)1:5 Ta(CN).2·5Y. 35·84 12'88reddish solid (34-10) (13·18)3'04'04'0PolymerdodoREACTION OF Ta(CN) s-2·5XWITH PrjOH1: ex- Ta(OPri).(CN).X, 37'67 8.37cess brown solid (37'70) (8'77)X=CH3COOPri; Y =CH3COOC2H s-*Near quantitative yield.·Nb(CN)52·OCHaCOOPri and Ta(CNls2·5CH3COOPriare heated (0-5 mm) up to 300° (bath temperature).these, decompose slowly.References1. MALATESTA.L. & BONATI. F .• Isocyanide complexes ofmetals (Wiley Iriterscience, London). 1969.2. SHRIVER. D. F., SHRIVER. SHIRLEY A. & ANDERSONSTANLEY. E., I-norg, Chem .• 5 (1965), 725.3. VVANG. BI-CHENG. SCHAEFER. WILLIAM P. & MARSH,RICHARD. E., Inorg. Chem. (1971). 1492.4. MEHROTRA. R. C. & KAPOOR, P. N .• J. less-common.Metals. 10 (1966). 348.5. FUNK, H. & N1EDERLANDER,K.. Ber. dt. chem. Ges.,62B (1929). 1688.6. LAPPERT. M. F. & PYSZORA.H., Advances inorg, cu«.Radio Chem., 9 (1966), 133.7. BITHER, T. A.• KNOTH. W. H .• LINDSEY. (Jr) R. U. &SHARKLY.W. H .• J. Am. chem, Soc., 80 (1958). 4151.8. SEYFERTH,D. & KAHLEN,N .•J. org, Cbem., 25 (1960), 809.9. SHRIVER, D. F., J. Am. chem. Soc .• 84 (1962), 4610.10.CASTELLS. R. A. DE. MACCOLL.C. P .• EGEN, N. B. &HAIM. A.• Inorg, Chem .• 8 (1969). 699.407

Reactions of Pyruvonitrile with Nb(V) & Ta(V) Alkoxides

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Reactions of Pyruvonitrile with Nb(V) & Ta(V) Alkoxides

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