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