Synthesis and spectral and electrochemical studies of a series of oxo-tungsten(V) porphyrins

Abstract

A series of oxo–tungsten(V) porphyrin complexes of the general formula [W^VO(TPP)X] were synthesized [where TPP = dianion of 5,10,15,20-meso-tetraphenylporphyrin and X = –4-ClBz (p-chlorobenzoate) (1), –OH (2), –OMe (3), –Cl (4), –Br (5), or –NCS (6)]. Complexes 1, 2, and 5 were structurally characterized. In 2 the two W–O axial bond lengths in the (O=W–OH) moiety were identical [1.834(7) Å] owing to disorder in the oxo and hydroxo groups. Spectroscopic evidence confirms the presence of both the groups coordinated to tungsten in the complex. The electrochemistry of these complexes was investigated in dichloromethane. All the complexes undergo three one-electron reductions, the first of which involves WV/W^IV; the other two are porphyrin-based. Complexes 4 and 5 were irreversibly reduced to generate pentacoordinate [W^IVO(TPP)], which subsequently responded to reversible redox reaction at almost zero potential.