The coordination chemistry of tin porphyrin complexes

The complexes of porphyrins with tin(IV) are readily prepared and are stable even in the presence of strong acids. The Sn(IV) centre is usually six-coordinate with two trans axial ligands, and many derivatives have been prepared with a variety of anions, ranging from very weakly coordinated oxyanions through to carbanions. Due to the oxophilic nature of the Sn(IV) centre, the complexes with carboxylate and aryloxide axial anions are readily prepared and tractable, making them ideal building blocks for the construction of elaborate arrays containing more than one porphyrin. The spectroscopic properties of the Sn(IV) porphyrins, particularly their diamagnetism and luminescence, make them convenient for chemical study. This review concentrates on the coordination chemistry and structures of mainly Sn(IV) porphyrins, although the rarer Sn(II) complexes are also described. Studies of mechanisms of axial substitution reactions are included, as are descriptions of multiporphyrin arrays based on Sn(IV) porphyrin cores. References to various uses of Sn(IV) porphyrin complexes are also included.