Amphoteric Zinc(II) Hydride Cations [ZnH]+: Effect of a Bipyridyl Ligand

Terminal zinc hydride cations [(Me₂bpy)ZnH(L)][BAr^F₄] (Me₂bpy = 6,6′-dimethyl-2,2′-dipyridyl; Ar^F = 3,5-(CF₃)₂C₆H₃; L = THF, 1a; 4-(dimethylamino)pyridine, DMAP, 1b; pyridine, 1c; 4-(trifluoromethyl)pyridine, 1d) show Zn–H distances in the expected range, as exemplified by single-crystal X-ray diffraction for the THF adduct 1a and the pyridine adduct 1c. With the exception of labile 1a, the ν(ZnH) stretching frequencies correlate with the electron donating character of the L ligand. The Zn–H bond shows amphoteric behavior. Reaction of 1a with ZnEt₂ gives the cationic ethyl complex [(Me₂bpy)ZnEt(thf)][BAr^F₄] (2a), while it undergoes CO₂ insertion to form the cationic formato complex [(Me₂bpy)Zn(OCHO)(thf)][BAr^F₄] (3a). Thermolysis of 3a at 80 °C gives the dinuclear metalation product 4a, which is also formed by photolysis of 1a. The Zn–H bond of 1a acts as a proton donor when treated with the N-heterocyclic carbene I^tBu (I^tBu = 1,3-di-tert-butylimidazol-2-ylidene), giving the imidazolium salt [I^tBuH][BAr^F₄], zinc metal, and Me₂bpy. The deprotonation of the Zn–H bond in 1a occurs with ZnCp*₂ (Cp* = pentamethylcyclopentadienyl) to give the dizinc(I) cation [(Me₂bpy)Zn–ZnCp*(thf)][BAr^F₄] (6a) and Cp*H. Reaction of 1a with Cp₂MoH₂ (Cp = η⁵-cyclopentadienyl) leads to the heterobimetallic complex [(Me₂bpy)Zn(μ-H)MoCp₂]⁺[BAr^F₄]⁻ (7) under H₂ elimination.