This chapter discusses the carbonyl derivatives of titanium, zirconium, and hafnium. The synthesis and reactivity of the group 4B (Ti, Zr, Hf) metal carbonyls have developed relatively slowly. In contrast to the vast number of mono- and multinuclear binary carbonyl complexes of the transition metals, no isolable binary carbonyls of titanium, zirconium, or hafnium have been reported. While the majority of group 4B metal–carbonyl complexes contain π-bonded hydrocarbon ligands, most notably η-cyclopentadienyl, recent studies by Wreford and coworkers have led to the identification and isolation of three novel phosphine-stabilized titanium carbonyl complexes. The first phosphine-substituted derivatives of CP2Hi (CO)2 were reported by Rausch and coworkers in 1979 and were prepared photochemically, similarly to the zirconium congeners. Only two carbonyl complexes of group 4B have been reported that contain π-bonded acyclic hydrocarbon ligands that are not metallocenes. Mono (η-cyclopentadienyl) carbonyl complexes of Ti, Zr, and Hf have been noted only in the patent literature.
Bibliographical noteFunding Information:
The authors are very grateful to the National Science Foundation and to the donors to the Petroleum Research Fund, administered by the American Chemical Society, for grants that have made possible their contributions to the research described herein. They are also grateful to Professor Jerry Atwood of the University of Alabama for fruitful collaborative efforts in this area.
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