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)PPh3] (6, where Tp = tris(pyrazolyl)borate and Bp = bis(pyrazolyl)borate) with AgBF4, AgOTf,and SOCl2 was observed to yield the highly unusual B−F- and B−OH-containing compounds [RuTp(BpF2)PPh3] (7), [RuTp(BpOH)PPh3]OTf (9), and [RuTp(BpOH)PPh3]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 BF4 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.