Reactions of m-Terphenyl-Stabilized Germylene and Stannylene with Water and Methanol: Oxidative Addition versus Arene Elimination and Different Reaction Pathways for Alkyl- and Aryl-Substituted Species

Reactions of the divalent germylene Ge(Ar-Me6)(2) (Ar-Me6 = C6H3-2,6-{C6H2-2,4,6-(CH3)(3)}(2)) with water or methanol gave the Ge(IV) insertion product (Ar-Me6)(2)Ge(H)-OH (1) or (Ar-Me6)(2)Ge(H)OMe (2), respectively. In contrast, its stannylene congener Sn(Ar-Me6)(2) reacted with water or methanol to produce the Sn(II) species {(ArSn)-Sn-Me6(mu-OH)}(2) (3) or {(ArSn)-Sn-Me6(mu-OMe)}(2) (4), respectively, with elimination of (ArH)-H-Me6. Compounds 1-4 were characterized by IR and NMR spectroscopy as well as by X-ray crystallography. Density functional theory calculations yielded mechanistic insight into the formation of (Ar-Me6)(2)Ge(H)OH and {(ArSn)-Sn-Me6(mu-OH)}(2). The insertion of an m-terphenyl-stabilized germylene into the O-H bond was found to be catalytic, aided by a second molecule of water. The lowest energy pathway for the elimination of arene from the corresponding stannylene involved sigma-bond metathesis rather than separate oxidative addition and reductive elimination steps. The reactivity of Sn(Ar-Me6)(2) with water or methanol contrasts with that of Sn{(CH(SiMe3)(2)}(2), which affords the Sn(IV) insertion products {(Me3Si)(2)CH}(2)Sn(H)OH and {(Me3SO2CH}(2)Sn(H)OMe. The differences were tentatively ascribed to the Lewis basicity of the employed solvent (Et2O vs THF) and the use of molar vs millimolar concentrations of the substrate.