Reactions of <i>m</i>‑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(ArMe6)2 (ArMe6 = C6H3-2,6-{C6H2-2,4,6-(CH3)3}2) with water or methanol
gave the Ge­(IV) insertion product
(ArMe6)2Ge­(H)­OH (1)
or (ArMe6)2Ge­(H)­OMe (2), respectively. In contrast, its stannylene congener Sn­(ArMe6)2 reacted with water or methanol to produce
the Sn­(II) species {ArMe6Sn­(μ-OH)}2 (3) or {ArMe6Sn­(μ-OMe)}2 (4), respectively, with elimination of ArMe6H. 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 (ArMe6)2Ge­(H)­OH and {ArMe6Sn­(μ-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(ArMe6)2 with water or methanol contrasts with that of Sn­{(CH­(SiMe3)2}2, which affords the Sn­(IV) insertion products
{(Me3Si)2CH}2Sn­(H)­OH and {(Me3Si)2CH}2Sn­(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.