HX Addition and Photochemical H2 Elimination by Ni NHC Complexes

Ni(H)(X)(IMes)2 was prepared by the addition of HX to Ni(IMes)2 (X = Cl, Br; IMes = 1,3-dimesitylimidazol-2-ylidene). Ni(H)(Cl)(IMes)2 (1) was isolated from the reaction mixture of Ni(IMes)2 and 2 equiv of 2,6-lutidine·HCl. Ni(H)(Br)(IMes)2 was prepared in a similar way. Although treatment of Ni(IMes)2 with a HCl·dioxane solution gives rise to a mixture of 1, NiCl2(IMes)2, and NiCl(IMes)2, 1 was not isolable from the mixture. All three complexes cocrystallized. Photolysis of these nickel hydrides activates their Ni−H bonds by populating Ni−H σ* orbitals, which results in the formation of H2. Treatment of 1 with HCl·dioxane gives rise to H2 and NiCl2(IMes)2.