Bonding in silatranes and boratranes and where it gets confusing

Our group has reported an array of mid-to-late first row transition metal complexes supported by tris(phosphino)silyl and tris(phosphino)borane ligands. Some of these complexes have interesting electronic structures and warrant consideration of appropriate valence and oxidn. state assignments. Because of the highly covalent nature of these complexes no limiting formalism is ever to be fully satisfying. In this talk I will present some of the more interesting and hence more confusing scenarios that have arisen, including cases were 1-electron sigma bonding may be prevalent.