Attempted Isolation of Heavier Group 14 Element Ketone Analogues: Effect of O−H···π-Ar Hydrogen Bonding on Geometry

Abstract

The terphenyl group 14 element gem-dihydroxy (gem-diol) derivatives Ar2M(OH)2 (Ar = C6H3-2,6-Mes2; Mes = C6H2-2,4,6-Me3), M = Ge (1); Sn (2), were synthesized and characterized by X-ray crystallography, NMR, IR spectroscopy, and combustion analysis. The synthetic route involved treatment of the divalent MAr2 compounds with N2O or Me3NO in hydrocarbon solution. The objective was the isolation of the heavier group 14 element ketone analogues Ar2MO. Despite stringent precautions to exclude moisture and oxygen during the 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 terphenyl-protected, essentially strain-free, species (bisap)2GeO (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. Compound 1 represents the second example of a germanium gem-diol to be structurally characterized, and it features the expected distorted tetrahedral germanium environment. Compound 2 is the first instance of a monomeric gem-dihydroxy derivative of tin. Surprisingly, the C−Sn−C angle is ca. 20° wider than the corresponding angle in 1 even though the larger size of tin is expected to reduce steric congestion and so afford a narrower C−Sn−C angle. This unanticipated result was attributed to the nonclassical hydrogen-bonding interaction of the O−H groups with the mesityl ring substituents, which for geometric reasons is more favorable in the tin compound.