Trans–cis octahedral interconversion pathway in diorganotin compounds

Using structural data from bis(bidentate)diorganotin compounds in the Cambridge Structural Database a potential pathway for trans–cis interconversion is envisaged with nondissociative Sn-donor bonds and retaining metal coordination number 6. C–Sn–C bond angles in the range 180–145° correspond to skewed trapezoid bipyramidal geometry for 6- and 5-membered O,O′ chelates; geometries that resemble the transition state of the trans–cis pathway starts forming at about C–Sn–C 134°. cis-Diorganotins explored in this work have C–Sn–C bond angles in the range 102–110°; it is the statistically favored configuration for diphenyltins. The proposed trans–cis conversion pathway is deduced from a series of geometries associated with decreasing the C–Sn–C bond angle and shows 2 weakly (secondary) bound chelating atoms lengthening their bonds until near the transition state and later strengthening; they end up cis to each other and opposite to the organic groups. Conversely, the other 2 (primary) donors shorten their bonds until the transition state is reached and later lengthen; they end up trans to each other. The entire transformation from trans to cis configuration occurs with relative rotation of 3 bonds.