Concerning the silicon-germanium bond. The structures of isomeric Ph3EE′Me3, E = Ge, E′ = Si and E = Si, E′ = Ge

The synthesis and structure of the unknown trimethylgermyltriphenylsilane (I, Ph 3 SiGeMe 3 ) is reported. The molecular geometry is compared to that of the isomeric Me 3 SiGePh 3 (II) and the related Ph 3 SiSiMe 3 (III) and (η 5 -C 5 H 5 )Fe(CO) 2 SiMe 2 GePh 3 (IV). The SiGe bond of I is significantly longer than that for II. We suggest that this is due to expansion of Ge bonding orbitals by the relatively electron-donating methyl groups in conjunction with the contraction of the corresponding orbitals of Si due to the electron-withdrawing phenyl groups. The overall result is a better orbital overlap between the Si and Ge atoms for II.