Electronic communication in heterobinuclear organometallic complexes through unsaturated hydrocarbon bridges

Much of the interest about the construction of model compounds suitable for investigating the phenomena associated with the interaction of two or more metal centers, the so-called cooperative effect, has been concentrated on homobimetallic complexes and less attention has been paid to the class of heterobimetallic derivatives. This review will feature experimental detection and the effects of the electronic communication in heterobinuclear organometallic complexes through unsaturated hydrocarbon bridges. The described systems are classified according to the nature of the bridging ligand, in three main groups: (i) carbon sigma-bonded molecular wires; (ii) fulvalene and fulvalene-like bridges; (iii) fused delocalized polycyclic bridges. In this contribution, we discuss the flexibility of heterobimetallic complexes, and more in general of asymmetric bimetallic species, in terms of tailoring the cooperative effects, i.e. of controlling and tuning the reactivity of one metal center by acting on the adjacent one. Satisfactory quantitative estimate of the degree of metal to metal communication through the bridging ligand is obtained in illustrative examples combining efficient electrochemical and spectroscopic techniques with consolidated theories. A review with almost 350 references. (C) 2004 Elsevier B.V. All rights reserved.