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(Bul,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-H group of the [Tp(Bul,Me)] ligand. A further example in which a [Tp(Bul,Me)] ligand acts as a hydride donor is provided by the reaction of the aqua complex {[Tp(Bul,Me)]Zn(OH2)}[HOB(C6F5)(3)] with MeOH to generate the zinc hydride complex [Tp(Bul,me)]ZnH. The present study therefore provides a caveat for the often assumed inertness of the B-H group in tris(pyrazolyl)hydroborato ligands, especially in the presence of reactive cationic species.