Boron Functionalization of Bis(pyrazolyl)borate Ligands: Molecular Structures of [RuX(PPh<sub>3</sub>)<sub>2</sub>{(MeO)<sub>2</sub>B(pz)<sub>2</sub>}] (X = H, Cl; pz = pyrazol-1-yl)
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The reaction of [RuCl2(PPh3)3] with K[H2B(pz)2] (pz = pyrazol-1-yl) in tetrahydrofuran at room temperature provides the known hydrotris(pyrazolyl)borate complex [RuH(PPh3)2{HB(pz)3}] (1b) via pyrazole scrambling. In contrast, the reaction of [RuCl2(PPh3)3] with K[H2B(pz)2] in methanol does not, as previously reported, provide [Ru(PPh3)2{H2B(pz)2}2] but, rather, a mixture of the complexes [RuX(PPh3)2{κ3O,N,N′-(MeO)2B(pz)2}] (X = H (2a), Cl (2b)) and ttt-[RuCl2(Hpz)2(PPh3)2] (3), each of which have been structurally characterized. Although the resulting bulk admixtures of 2a,b have so far proved inseparable, treatment with mercuric chloride cleanly converts the 2a component to 2b. Heating 2b with 1,2-bis(dicyclohexylphosphino)ethane (dcpe) results in substitution of both phosphine ligands and the formation of [RuCl(dcpe){κ3O,N,N′-(MeO)2B(pz)2}] (4) in which the ruthenium−ether linkage is ultimately retained.
