Reactivity of the B-H Bond in tris(pyrazolyl)hydroborato zinc complexes: unexpected example of zinc hydride formation in a protic solvent and its relevance towards hydrogen transfer to NAD(+) mimics by tris(pyrazolyl)hydroborato zinc complexes in alcoholic media.

Solutions of the zinc hydroxide complex [Tp(Bu(t),Me)]ZnOH in alcohols (ROH; R = Me, Et, Pr(i)) achieve hydride transfer to the NAD(+) model, 10-methylacridinium perchlorate. Deuterium labeling studies, however, demonstrate that the source of the hydride is not the alcohol but, rather, the B [bond] H group of the [Tp(Bu(t),Me)] ligand. A further example in which a [Tp(Bu(t),Me)] ligand acts as a hydride donor is provided by the reaction of the aqua complex [[Tp(Bu(t),Me)]Zn(OH(2))][HOB(C(6)F(5))(3)] with MeOH to generate the zinc hydride complex [Tp(Bu(t),Me)]ZnH. The present study therefore provides a caveat for the often assumed inertness of the B [bond] H group in tris(pyrazolyl)hydroborato ligands, especially in the presence of reactive cationic species.