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

The coordination chemistry of diisopropylaminoborane H2B−NiPr2 with valence
isoelectronic metal fragments to form, essentially isostructural,
[MH2(η2:η2-H2B−NiPr2)(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(σ-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···B distances in the
first two. These tighter interactions are mirrored in the spectroscopic
data, with the Ru and Ir complexes showing more deshielded 11B chemical shifts and 1H M−H−B
resonances that are more shielded than observed for the rhodium complex.
Analysis of the bonding between metal and borane 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.