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

A series of Sn(IV)PhCl3, Sn(IV)Ph2Cl2, Sn(IV)Ph3Cl or Sn(II)Cl-2 complexes of nitrogen based 1,3,5-heterocyclohexanes: 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 Sn-119, P-31, C-13 and H-1 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)Cl-2 is a suitable Lewis acid with low steric hindrance that gives strong bonds with these amine phosphines. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

A series of nitrogen-based 1,3,5-heterocyclohexanes Sn(IV) and Sn(II) complexes were synthesized and characterized. Their structures and properties were analyzed by NMR experiments and DFT calculations, revealing different conformations and coordination bond types.