Attempted isolation of heavier group 14 element ketone analogues: Effect of O-H center dot center dot center dot pi-Ar hydrogen bonding on geometry

The terphenyl group 14 element gem-dihydroxy (gem-diol) derivatives Ar2M(OH )(2) Ar = C6H3-2,6-Mes(2); Mes = C6H2-2,4,6-Me-3), M = Ge (1); Sn (2), were synthesized and characterized by X-ray crystallography, NMR, IR spectrosco py, and combustion analysis. The synthetic route involved treatment of the divalent MAr2 compounds with N2O or Me3NO in hydrocarbon solution. The obje ctive was the isolation of the heavier group 14 element ketone analogues Ar 2MO. Despite stringent precautions to exclude moisture and oxygen during th e synthesis, the products 1 and 2 were isolated in ca. 30-50% yield. These results are in contrast to the recently reported stabilization of the terph enyl-protected, essentially strain-free, species (bisap)(2)GeO (bisap = 2,6 -di(1 ' -naphthyl)phenyl). Seemingly, 1 and 2 represent the addition of H2O to Ar2MO. The identity of the other products is currently unknown. Compoun d 1 represents the second example of a germanium gem-diol to be structurall y characterized, and it features the expected distorted tetrahedral germani um environment. Compound 2 is the first instance of a monomeric gem-dihydro xy derivative of tin. Surprisingly, the C-Sn-C angle is ca. 20 degrees wide r than the corresponding angle in 1 even though the larger size of tin is e xpected to reduce steric congestion and so afford a narrower C-Sn-C angle. This unanticipated result was attributed to the nonclassical hydrogen-bondi ng interaction of the O-H groups with the mesityl ring substituents, which for geometric reasons is more favorable in the tin compound.