Synthesis and reactivity of novel iron complexes supported by neutral tris(phosphino)borane ligands

Of central importance to elucidating iron's role in biol. nitrogen fixation are the accessible geometries and oxidn. states of proposed iron intermediates. Our group has an ongoing interest in exploring the chem. of Fe- N_xH_y species and have successfully described terminal imide and nitride species supported by anionic tris(phosphino)borate ligands as well as terminal N_2 complexes stabilized by anionic tris(phosphino)silyl ligands in pseudo-tetrahedral and trigonal-bipyramidal geometries, resp. A single ligand scaffold capable of stabilizing low-valent complexes with a π-acidic N_2 mol., as well as high-valent complexes with a π-basic nitride ligand would certainly be of interest; accordingly, the synthesis of a series of iron complexes supported by the neutral tris(phosphino)borane ligand, [TPB^R] ([TPB^R] = (o-(R_2P)C_6H_4)_3B), R = iPr, Ph) will be presented and their structures and chem. reactivity discussed within the context of the hemi-lability of the apical Lewis-acidic borane