Unusual reactivity of the bis(pyrazolyl)borate chelate: B-H for B-X (X = F, Cl, OH) substitution in complexes of ruthenium

Reaction of the complex [RuTp(Bp)PPh ₃] (6, where Tp = tris(pyrazolyl)borate and Bp = bis(pyrazolyl)borate) with AgBF ₄, AgOTf,and SOCl ₂ was observed to yield the highly unusual B-F- and B-OH-containing compounds [RuTp(Bp ^F2)PPh ₃] (7), [RuTp(Bp ^OH)PPh ₃]OTf (9), and [RuTp-(Bp ^OH) PPh ₃]Cl (10), respectively, via substitution of the Bp boron-hydride groups. The complexes 7 and 9 were structurally characterized by X-ray crystallography. Formation of the B-F product 7 represents a rare example of BF ₄ anion reactivity under relatively mild conditions, whereas the B-OH product 9 contains the first example of a stable trivalent pyrazolyl-borane moiety. These substitution processes are thought to be assisted by the interaction of the boron-hydride moieties of 6 with the Lewis acidic Ag(I) and S(IV) centers of the reactive agents, which polarize the B-H bond and activate the boron center toward electrophilic attack of available halogen- and hydroxy-containing species.