Formation of germanium–nitrogen double bonds in reactions of the electron-rich germylene bis[bis(trimethylsilyl)amido]germanium(<scp>II</scp>) with a range of diazo-compounds

Abstract

The electron-rich germylene Ge[N(SiMe3)2]2 reacts with the diazo-compounds R1CH2COC(N2)R2[R1= H, R2= CO(OEt), SO2C6H4Me-p, or COPh; R1, R2=–CMe2CH2C(O)–], which contain an enolisable function, to yield the heterocycles [graphic omitted]; the weakly acidic diazo-compounds ethyl diazoacetate and diazoacetophenone yield bis-adducts Ge[N(SiMe3)2]2[C(N2)COR][NHNC(H)COR](R = OEt or Ph). Diazo-compounds containing two non-enolisable substituents yield mono-adducts with Ge[N(SiMe3)2]2 which can be hydrolysed to yield the diol Ge(OH)2[N(SiMe3)2]2 and, in one example, the corresponding hydrazone H2NNC(COPh)CO(OEt). These adducts appear to be thermodynamically stable in an aprotic solvent, but can be trapped by addition of ethanol, to yield Ge[N(SiMe3)2]2(OEt){NHNC[CCO(OMe)]2}, or of diazoacetophenone to yield Ge[(SiMe3)2]2[C(N2)COPh]{NHNC[CO(OMe)]2}. All the reactions of the germylene with diazo-compounds can be rationalised in terms of the initial formation of a germyleneazine [(Me3Si)2N]2GeN–NC(X)Y, which readily adds any available protic species to give a germane derivative. MNDO calculations on model systems are in accord with the experimental findings and also explain their differences from results previously obtained using the simpler germylene GePh2.