Aluminium Functionalized Germanes: Intramolecular Activation of Ge–H Bonds, Formation of a Dihydrogen Bond and Facile Hydrogermylation of Unsaturated Substrates

Abstract

A series of alkenylhydrogermanes, RR′(H)Ge‐C(AlR′′ 2 )=C(H)‐ t Bu [ 4a , R = R′ = Mes, R′′ = t Bu; 4b , R = R′ = Mes, R′′ = CH(SiMe 3 ) 2 ; 5a , R = R′′ = t Bu, R′ = CH 2 CH 2 t Bu; 5b , R = t Bu, R′ = CH 2 CH 2 t Bu, R′′ = CH(SiMe 3 ) 2 ], was synthesized by hydroalumination of the respective alkynylgermanes, RR′(H)Ge‐C≡C‐ t Bu 3 , with R′′ 2 Al–H [R′′ = t Bu, CH(SiMe 3 ) 2 ]. In the solid state compound 5b showed a contact between Al and the Ge bound H atom (293 pm) which according to quantum chemical calculations results in Ge–H bond activation. In case of less bulky substituents on Al ( 5a , R′′ = t Bu) a mixture of isomers was observed that reacted with Et 2 NH to yield the simple Lewis acid‐base adduct [( t Bu)( t BuCH 2 CH 2 )(H)Ge‐C(Al t Bu 2 )=C(H)‐ t Bu](HNEt 2 ) ( 6 ). 6 features a dihydrogen bond (Ge–H ··· H–N) as evident from typical downfield (N–H) and high‐field (Ge–H) shifts in the NMR spectrum, red shifts of ν Ge‐H and ν N‐H in the IR spectrum, a short H ··· H contact (210 pm) in the solid state and a bond critical point between both H atoms. The presence of a hard Lewis‐acidic Al atom in geminal position to the Ge–H bond in 5a facilitates reactions with Ph 2 CO, OC 4 H 8 N‐C≡N and Ph–NCO under surprisingly mild conditions by hydrogermylation of the heteronuclear π‐bonds and formation of four‐membered Ge–O/N–Al–C ( 7 , 9 ) or six‐membered Ge–N–C–O–Al–C ( 8 ) heterocycles. Reaction with Ph–C≡C–H afforded the cis ‐addition product 10 , in which the α‐C atom of the new alkenyl group showed a close contact [258.3(2) pm] to the Al atom.