Synthesis, Structure, and Properties of Dicarbonyl Bis(phosphine) 1, 4-Diphenyltetraazabutadiene Complexes of Molybdenum and Tungsten

摘要

Transition-metal complexes that have unsaturated metallacycles containing the 1,4-disubstituted tetraazabutadiene ligand (also called tetraazadiene, tetrazene, or tetrazenido) have attracted interest because of their novel bonding features. Attention has focused on the delocalization of pielectron density in the metallacycles and the role of the metal d orbitals in bonding. Since 1967 several transition-metal tetrazene complexes have been reported, including derivatives of Co, Rh, Ir, Fe, Ni, and Pt. They haven been prepared by coupling reactions between either an organic azide (RN) or a diazonium salt (RN) and a late-transition-metal complex in a low oxidation state. Because only late-transition-metal complexes have been prepared (to the right of the manganes triad) and because tetrazene ligands are known as good piacceptor groups, it has been believed that metal to ligand pi back-bonding plays an important role in stabilizing the complexes. Recently we reported the preparation of tetrazene complexes of group V111 metals (Ni, Pd, and Pt) from the readily available tetrazendio dianion (I), which is prepared by nonoxidative N-N bond formation (eq1).