Unusual reactivity of the bis(pyrazolyl)borate Chelate: B-H for B-X (X = F, Cl, OH) Substitution in Complexes of Ruthenium

Abstract

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.