One-step preparation, structural assignment, and X-ray study of 2,2-di-n-butyl- and 2,2-diphenyl-6-aza-1,3-dioxa-2-stannabenzocyclononen-4-ones derived from amino acids

Twenty-four 2,2-di-n-butyl-and 2,2-diphenyl-6-aza-1,3-dioxa-2-stannabenzocyclononen-4-ones, each having a transannular N-->Sn bond, have been prepared by one-step reactions of alpha-amino acids (1a-l), salicylaldehyde (2), and either di-n-butyltin(iv) oxide (3) or diphenyltin(iv) oxide (4). The new methodology constitutes an easy, highly efficient one-step synthesis of diorganotin(v) derivatives, such as 5a-l and 6a-l, from iminic tridentate ligands without isolation of the Schiff bases. The structures of all the compounds have been established by a combination of H-1, C-13, N-15, and Sn-119 NMR spectroscopy, IR spectroscopy, mass spectrometry, and elemental analysis. In all cases, the Sn-119 chemical shifts, as well as the (1)J(Sn-119,C-13) coupling constants, are indicative of pentacoordinated tin atoms in solution. The structures of compounds 5 a, d, f, 6 a, b, b-racemic, c, d, f, g, and 1 have been established by single-crystal X-ray diffraction analyses. The tin atoms in 5d, f, 6a, b, b-racemic, c, d, g, and 1 each have a distorted trigonal-bipyramidal (TBP) geometry, with the oxygen atoms from the phenol and carboxylate moieties occupying the axial positions, and the imine nitrogen and phenyl or n-butyl substituents occupying the equatorial positions. Compounds 5 a and 6 f show distorted octahedral (DOC) geometries due to intermolecular coordination of the carbonyl oxygen to the tin atom, in a trans disposition to the N --> Sn bond, leading to trimeric 5a and a polymeric structure for compound 6f. Additionally, measurement of the one-bond coupling constants (1)J(Sn-119,C-13) in diphenyltin(iv) complexes (6a-l) and their correlation with the C-Sn-C bond angles has allowed the derivation of an equation that can be applied to assess the geometry around the tin atom for other diphenyltin(iv) compounds in solution.