Bis- pentafluorophenyl borane X H

In the solid state, [HB(C6F5)2]2 is dimeric, but is distinguished from other diorganoboranes in that observable amounts of the monomeric species HB(C6F5)2 appear in solution. This is clearly demonstrated by the nB NMR spectra in benzene, which show a minor peak centered around 60 ppm (three coordinate boron) and a major peak at 18 ppm (four coordinate, neutral boron).35 Recent quantitative analysis of this monomer/dimer equilibrium using variable temperature 19F NMR spectroscopy36 at various temperatures confirmed our earlier, more qualitative assessment that the dissociation enthalpy in benzene is much less (4.6 kcal mol-1) than that observed for [(Mes)2BH]2 (16.7 kcal mol-1),37 the only other borane for which this monomer/dimer equilibrium is assessable in solution. As expected, the AS° for this equilibrium is positive (15.3 cal K-1 mol-1), but less so than that observed for dissociation of [(Mes)2BH]2 

Further surveys of the reactivity of HB(C6F5)2 with simple organometallic compounds have led to the discovery of more novel boron-based ligand systems. For example, reactions with Schrock s tungsten methylidyne family L4W(X)=CH63 (L = phosphine, X = Cl, OTf) result in electrophilic attack on the methylidyne ligand hydride abstraction 

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