Synthesis of tetraphenylporphyrinate manganese(III) siloxides by silyl group transfer from silanethiols

Abstract

Reaction of [Mn(OAc)(TPP)] (TPP = dianion of meso-tetraphenylporphine) with both HSSiiPr3 and HSSiPh3 in the presence of air leads to formation of the corresponding siloxide complexes, [Mn(OSiR3)(TPP)] (R = iPr, Ph), via silyl group transfer from S to O. The new compounds have been fully characterized in solution and the solid state and represent rare examples of Mn(III) porphyrinates containing Lewis basic axial ligands. X-ray crystallographic analyses of both complexes reveal very short Mn–O bond distances consistent with the presence of a siloxide ligand. Investigations of the reaction pathway are consistent with initial reduction of [Mn(OAc)(TPP)] to [MnII(TPP)] by the silanethiol. Subsequent aerobic oxidation of the reaction mixture is proposed to generate a Mn(III) porphyrinate and the corresponding silanol, which combine to yield the observed siloxide complex. These findings stand in sharp contrast to those of iron(III) porphyrinates, where silanethiolate complexes are stable.