The bonding network and structural arrangement of simply borane polyhedra are initially discussed in this chapter. Borane clusters may be categorized as having closo, nido or arachno cages. A correlation between the total number of skeletal electrons, with the total number of skeletal atoms, was established by Wade in the form of a set of empirical rules. These were further extended to include the bonding in the heteroboranes, namely, [TeB10H11]- (5), [As2B9H10]- (6), [SB9H12]- (7) and [S2B6H9]- (8) which are of interest to the present work. Structure determination according to Wade's rules was further supported by results obtained from a symmetry Molecular Orbital (M.O.) theory approach. Numerous transition element derivatives of the heteroborane nido-[TeB10H11]- (5), nido-[As2B9H10]- (6), arachno-[SB9H12]- (7) and hypho-[S2B6H9]- (8) are reported in literature and have been characterized with each of the closo, nido, arachno and hypho structural classes. A general overview, with particular emphasizes on the structures of these metallaheteroboranes, has been given in this chapter. Phosphine ligands have played a major role in the chemistry of transition element complexes. The bidentate ligands dpm, dppe and dppf have been employed in the synthesis of monodentate, chelating and bridging metal complexes. Bis(diphenylphosphino)methane (dpm) can chelate to metals to form strained four-membered rings with small P-M-P angles. It also has a tendancy to act as a monodentate or bridging ligand. In contrast, bis(diphenylphosphino)ethane (dppe) is an excellent chelating ligand. Metal complexes containing the dppf ligand exhibit unusually large P-M-P angles. This thesis combines the chemistry of the heteroboranes nido-[TeB10H11]- (5), nido-[As2B9H10]- (6), arachno-[SB9H12]- (7) and hypho-[S2B6H9]- (8) with that of transition element complexes containing various bidentate ligands, to form neutral and cationic metallaheteroborane compounds. The influence of the ligands on the bonding and basic cage geometry of the metallaheteroboranes is discussed in detail. In addition the preferred mode of coordination of the dpm, and dppf lifands to the various heteroborane cages is also discussed.

The field of transition metal catalysis has experienced incredible growth during the past decade. The reasons for this are obvious when one considers the world's energy problems and the need for new and less energy demanding syntheses of important chemicals. Heterogeneous catalysis has played a major industrial role; however, such reactions are generally not selective and are exceedingly difficult to study. Homogeneous catalysis suffers from on-site engineering difficulties; however, such reactions usually provide the desired selectivity. For example, Monsanto's synthesis of optically-active amino acids employs a chiral homogeneous rhodium diphosphine catalyst. Industrial uses of homogeneous catalyst systems are increasing. It is not by accident that many homogeneous catalysts contain tertiary phosphine ligands. These ligands possess the correct steric and electronic properties that are necessary for catalytic reactivity and selectivity. This point will be emphasized throughout the book. Thus the stage is set for a comprehensive be treatment of the many ways in which phosphine catalyst systems can designed, synthesized, and studied.