Reactions of diazo-compounds with the electron-rich germylene Ge[N(SiMe3)2]2. Characterisation and some addition reactions of [(Me3Si)2N]2GeNNC(COOMe)2: crystal and molecular structure of [(Me3Si)2N]2Ge[NHNC(COOMe)2][C(N2)COPh]

Abstract

Two forms of the stable germyleneazine [(Me₃Si)₂N]₂GeNNC(COOMe)₂, formed by addition of the diazo-compound N₂C(COOMe)₂ to the electron-rich germylene Ge[N(SiMe₃)₂]₂ have been characterised in solution by ¹H and ¹³C n.m.r. spectroscopy. MNDO calculations on the simpler analogue [(H₃Si)₂N]₂GeNNC(COOMe)₂ indicate that the two forms have planar transoid and cisoid GeNNC groups respectively, with the cisoid isomer as the more stable: the calculations also indicate that charge-controlled additions of electrophiles will occur at N¹, adjacent to germanium, while all nucleophilic addition will occur at Ge. Some adducts of [(Me₃Si)₂N]₂GeNNC(COOMe)₂ with weak acids HX are described; in all cases 1,2-addition of HX occurs across the Ge–N¹ bond to yield [(Me₃Si)₂N]₂Ge(X)[NHNC(COOMe)₂]. Crystals of one such adduct [(Me₃Si)₂N]₂Ge[NHNC(COOMe)₂][C(N₂)COPh] are triclinic, space group P, with a= 9.627(2), b= 12.672(19), c= 15.702(3)Å, α= 101.66(4), β= 85.02(2), γ= 77.65(5)°, and Z= 2. The structure was refined from diffractometer data (5 173 observed reflections) to an R value of 0.046. The structure determination confirms the 1,2-addition of HC(N₂)COPh across the Ge–N¹ bond of [(Me₃Si)₂N]₂-GeNNC(COOMe)₂ and reveals a free diazo-group, sterically unconstrained. Reaction of tosyl azide with Ge[N(SiMe₃)₂] follows a different course from the reactions involving diazo-compounds; nitrogen is lost and the product is a polygermazane {[(Me₃Si)₂N]₂GeNSO₂C₆H₄Me-p}_n, which is insoluble in aqueous media and all common organic solvents, wholly resistant to hot 50% aqueous alkali, but readily hydrolysed by concentrated hydrochloric acid.