Disproportionation reactions of (methoxy/hydroxy)diorganotin(IV) methanesulfonates with carboxylic acids: Synthesis and structure of new diorganotin(IV) carboxylates

Disproportionation reactions between equimolar quantities of R2Sn(X)OSO2Me [X=OMe or OH] and ethylmalonic/maleic acid in acetonitrile under mild conditions afford new diorganotin dicarboxylates, R2Sn(O2CR′COOH)2 [R′=CHEt, R=n-Pr (3a), n-Bu (3b); R′=CHCH, R=n-Pr (3c), n-Bu (3d)] along with R2Sn(OSO2Me)2 [R=n-Pr (4a), n-Bu (4b)]. Similar reactions of the tin precursors with pyridine-2-carboxylic acid provide an access to novel trinuclear tin complexes, R6Sn3(O2CC5H4N-2)3(OSO2Me)3 [R=n-Pr (5a), n-Bu (5b)]. These have been characterized by IR and multinuclear (1H, 13C, 119Sn) NMR spectroscopies. The molecular structures of 3b, 4b and 5b have been determined by X-ray crystallography. Compound 3b is monomeric with bicapped tetrahedron geometry by virtue of anisobidentate coordination of one carboxylate group of each ligand, while the other carboxylic acid group remains free. The polymeric structure of 4b features centrosymmetric eight-membered rings comprising bridging methanesulfonate groups and nearly perfect octahedral geometry around each tin atom. Compound 5b crystallizes as 5b·2H2O·Et2O. Its molecular structure comprises of mixed ligand tin ester, n-Bu2Sn(O2CC5H4N-2)OSO2Me and its disproportionated products, n-Bu2Sn(O2CC5H4N-2)2 and n-Bu2Sn(OSO2Me)2 which are coordinatively associated by varying bonding modes of pyridine-2-carboxylate groups. A possible rationalization of these results are discussed in terms of the intermediacy of mixed ligand tin complexes, R2Sn(L)OSO2Me (L=carboxylate) formed by the selective substitution of SnOMe group or by the dehydration of SnOH group in the tin precursors with the carboxylic acid.