Synthesis and coordination chemistry of noble metal porphyrins

Abstract

The noble metals ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, and gold form a variety of complexes M(P) LL′ with tetrapyrrole ligands which are studied in many laboratories because their coordination chemistry and catalytic power is similar to that of the corresponding iron and cobalt tetrapyrroles forming the prosthetic groups in heme proteins and vitamin B12. Apart from the corrins and corroles which are treated in the second article of this volume, the main interest is devoted to noble metal complexes of porphyrins, but complexes of hydroporphyrins, porphyrin analogs, homologs, porphyrinoids, and phthalocyanines are also mentioned where appropriate.The treatise is organized into four main topics: metal insertion (“equatorial coordination chemistry”, Sect. 2, formation of the M(P) entity), substitution and redox reactions (“axial coordination chemistry”, Sect. 3, exchange of axial ligands L and L′), organometallic chemistry (a special case of axial coordination chemistry, Sect. 4), and notes on current special chemical topics like electrochemistry, catalysis, supramolecular chemistry, and biological applications.Where possible, the material is compressed in schemes and tables giving a synopsis of consecutive reactions of Ru/Os and Rh/Ir dyads. The two other dyads, Pd/Pt and Ag/Au, are so strongly governed by the square planar d8 configuration that they are practically devoid of axial coordination chemistry. The redox reactions of the Ru/Os dyad live on the switches between d6-d5 and d6-d4-d2 configurations mostly with octahedral geometry about the metal, those of the Rh/Ir dyad on the switches between the d6-d7-d8 configurations, giving rise to octahedral, square-pyramidal, and square planar geometries. The occurrence of the dinuclear or mononuclear Rh d7 systems give a special touch of radical chemistry to the organometallic chemistry of rhodium porphyrins which is expected to be fruitful to organometallic chemistry as a whole.Although a broad overview was intended, many entries are just given in keywords or tables in order to give the reader a chance to get more information. Nevertheless, out of nearly 500 papers scrutinized, only nearly 400 references appear in order to keep the volume and the writing time within certain limits, and any research group missing a paper in this review is asked for patience with the authors.