Ruthenium, Rhodium, and Iridium Bis(σ-B-H) Diisopropylaminoborane Complexes

The coordination chemistry of diisopropylaminoborane H2B-(NPr2)-Pr-i with valence isoelectronic metal fragments to form, essentially isostructural, [MH2(eta(2):eta(2)-H2B-(NPr2)-Pr-i)(PCy3)(2)](n+) (M = Ru, n = 0; Rh and Ir, n = 1) has been explored by a combination of X-ray crystallography, NMR spectroscopy, and computational techniques. In the solid state and solution the aminoborane interacts with the metal centers through one four-center four-electron interaction, forming bis(sigma-B-H) complexes. The structural data point to tighter interactions between both the Ru and Ir congeners compared to the Rh with significantly shorter M center dot center dot center dot B distances in the first two. These tighter interactions are mirrored in the spectroscopic data, with the Ru and Ir complexes showing more deshielded B-11 chemical shifts and H-1 M-H-B resonances that are more shielded than observed for the rhodium complex. Analysis of the bonding between metal and bonnie using the NBO approach is in very good agreement with the variations in the geometrical and spectroscopic parameters. There is overall a stronger interaction between the borane and the metal fragment for neutral Ru compared to cationic Rh, with cationic Ir in an intermediate situation.