Low-temperature neutron structure determinations of a series of scorpionate complexes of molybdenum containing BHMo agostic bonds

The structures of four dihydrobis(pyrazol-1-yl)borate (Bp) complexes of molybdenum have been determined at low temperature by single crystal neutron diffraction in order to accurately characterize the three-center BHMo agostic bonding. The BH1A (agostic) distance is found to be elongated by about 0.05–0.08Å compared to the BH1B distance (not agostically bound to the metal center). This systematic study of a series of molecules with different substituents on the Bp ligand permits us to examine the effects of electronic and steric factors on the overall structure and bonding, and particularly on the agostic bond. It is observed that a closer approach of H1A to Mo leads to a longer trans-MoCO bond distance, analogous to the trans hydride structural effect in hydride complexes. In addition Fenske–Hall calculations were performed on these complexes, and the results are reported herein.