Arrested B–H Activation en Route to Installation of a PBP Pincer Ligand on Ruthenium and Osmium

The reaction of HB­(NCH2PPh2)2C6H4-1,2 with [MCl2(PPh3)3] (M = Ru, Os) affords the six-coordinate σ-borane complexes [MCl2(PPh3)­{σ-BH-κ2-P,P′-HB­(NCH2PPh2)2-C6H4}], in which the B–H bond remains intact while coordinated to the metal center. Replacement of the unique phosphine by π-acceptor ligands, e.g., CO and CNC6H2Me3, induces B–H activation followed by spontaneous dehydrochlorination with the formation of the boryl pincer complexes [RuCl­(CA)2{B­(NCH2PPh2)2C6H4}] (A = O, NC6H2Me3-2,4,6).