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, NiCl(2)(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 H(2). Treatment of 1 with HCl·dioxane gives rise to H(2) and NiCl(2)(IMes)(2).