Tin complexes derived from nitrogen-based 1,3,5-heterocyclohexanes bearing 2-hydroxypropan-1-yl, 2-diphenylphosphitepropan-1-yl and 2-diphenylphosphinepropan-1-yl as pendant N-substituents

Abstract

A series of Sn(IV)PhCl3, Sn(IV)Ph2Cl2, Sn(IV)Ph3Cl or Sn(II)Cl2 complexes of nitrogen based 1,3,5-hetero-cyclohexanes: 5-methyl-[1,3,5]-dithiazinane (1), (R)-2-hydroxy-prop-1-yl-[1,3,5]-dithiazinane (2), (R)-2-diphenylphosphinite-prop-1-yl-[1,3,5]-dithiazinane (3), 3,5-bis((R)-2-diphenylphosphinopropyl)-1,3,5-thiadiazinane (4) 1,3,5-tris((R)-2-diphenylphosphinoprop-1-yl)-1,3,5-triazinane (5) were synthesised and their structure analysed in solution by 119Sn, 31P, 13C and 1H and variable temperature NMR experiments. Gas phase DFT calculations were performed to obtain the preferred conformation of complexes and the configuration of tin atoms. Ligands 1-5 have in common that the heterocycle is in conformational equilibrium with the N-substituents in axial position, with exception of compound 5 that has one N-R in equatorial position. Ligands 1 and 3 afforded monodentate adducts, whereas 2, 4 and 5 produced bidentate complexes. Compound 4 gave binuclear bidentate complexes and 5 trinuclear derivatives. In the studied compounds, the phosphorus atoms are strongly coordinated to tin atoms, whereas the intracyclic nitrogen atoms gave weak coordination bonds. The pnicogen bonds N→P found in ligands 3-5 were preserved in the coordination products. By coordination, hypervalent tetra- [Sn(II)]; penta- and hexacoordinate [Sn(IV)] tin atoms were obtained. It was found that Sn(II)Cl2 is a suitable Lewis acid with low steric hindrance that gives strong bonds with these amine phosphines.