Borane-Bridged Ruthenium Complex Bearing a PNP Ligand: Synthesis and Structural Characterization

Reaction
of the precursor complex [RuHCl­(CO)­(PPh3)3]
with the PNP protioligand CbzdiphosH in toluene resulted
in the formation of two stereoisomeric hydrido complexes, [(CbzdiphosH)­RuHCl­(CO)]
(A). The addition of a strong base (KOtBu
or LiEt3BH), on the other hand, led to the formation of
the 1,2-dehydrochlorination product [(Cbzdiphos)­RuH­(CO)]. The reaction
of the latter with BH3·THF at room temperature led
to the 1,2-addition of the BH3 moiety to the Ru–N
function, forming a RuNBH cycle in [(CbzdiphosHBH2)­RuH­(CO)]
(B). The same borane-bridged compound was obtained when
complex A was treated with NaBH4 in THF. The
BH2 group forms a bridging unit between the carbazole-N
atom and one of the ruthenium-bound hydrides.