Complete and Partial 1,2-Additions across Transition Metal–Boron Double Bonds

The
first 1,2-additions across a metal–boron double bond
are reported, one a definitive chlorogallation of a FeB bond,
the other a partial chlorogallation of a MoB bond that leads
to a highly unusual, planar Mo–B–Ga–Cl rhombus.
The two reactions occur with opposite regiochemistry, with the Ga
atom bound to the Fe atom in the former and to both the Mo and B atoms
in the latter. The bonding in the Mo adduct and the reasons for the
differing regiochemistry of the reaction are explored computationally.