Hexanuclear and higher nuclearity clusters of the Groups 4-7 metals with stabilizing π-donor ligands

The chemistry of early transition element clusters with pi-donor ligands is growing rapidly. We review the syntheses of these compounds, with an emphasis on progress in the last 6 years. The predominant synthetic routes to such clusters are spontaneous self-assembly, apparent fragment condensation, excision from solids, and global ligand substitution. Mechanistic conclusions about cluster-forming reactions are discussed where possible. We conclude with prospects for future research. (C) 2003 Elsevier B.V. All rights reserved.