Synthesis of cobalt complexes supported by tris(phosphino)borate

The tris(phosphino)borate ligand, [PhBP_3]-, is unusual in that it is a very strong field donor ligand that can support unsaturated and electron deficient transition metal complexes. For example, it can be used to support distorted tetrahedral cobalt(ll) complexes that are low spin, distinct from the many high spin systems previously reported. Our attempts to study the reactivity of "[PhBP_3]Co" systems to explore group transfer and small molecule activation chemistry will be highlighted. Two illustrative examples of reactivity readily afforded by the novel low spin [PhBP_3]Col complex are shown below. Stoichiometric oxygen addition affords a novel high spin cobalt iodide in which the donor ligand has undergone a formal 4-electron oxidation. The low spin iodide complex also binds CO readily, chemically distinct from the many 4-coordinate high spin cobalt(ll) systems known.