Synthesis and Thermal Properties of Novel NHC-Stabilized Cobalt Carbonyl Nitrosyl Complexes

The synthesis of series of cobalt NHC complexes of the types [Co(NHC)(2)(CO)(NO)] (NHC = iPr(2)Im (2), nPr(2)Im (3), Cy(2)Im (4), Me(2)Im (5), iPr(2)ImMe (6), Me(2)ImMe (7), MeiPrIm (8), MetBuIrn (9); R(2)Im = 1,3-dialkylimidazolin-2-ylidene) and [Co(NHC)(CO)(2)(NO)] (NHC = iPr(2)Im (13), nPr(2)Im (14), Me(2)Im (15), iPr(2)ImMe (16), Me(2)ImMe (17), MeiPrIm (18), MetBuIm (19)) from the reaction of the NHC with [Co(CO)(3)(NO)] (1) is reported. These complexes have been characterized using elemental analysis, IR spectroscopy, multinuclear NMR spectroscopy, and in many eases by X-ray crystallography. Bulky NHCs tend to form the mono-NHC-substituted complexes [Co(NHC)(CO)(2)(NO)], even from the reaction with an stoichiometric excess of the NHC, as demonstrated by the synthesis of [Co(Dipp(2)Im)(CO)(2)(NO)] (11), [Co(Mes(2)Im)(CO)(2)(NO)] (12), and [Co((Me)cAAC)-(CO)(2)(NO)] (20). For tBu(2)(a)Im a preferred coordination via the NHC backbone ("abnormal" coordination at the 4-position), was observed and the complex [Co(tBu(2)(a)Im)(CO)(2)(NO)] (10) was isolated. All of these complexes are volatile, are stable upon sublimation and prolonged storage in the gas phase, and readily decompose at higher temperatures. Furthermore, DTA/TG analyses revealed that the complexes [Co(NHC)(2)(CO)(NO)] are seemingly more stable toward thermal decomposition in comparison to the complexes [Co(NHO(CO)(2)(NO)]. We thus conclude that the cobalt complexes of the type [Co(NHC)(CO)(2)(NO)] and [Co(NHC)(2)(CO)(NO)] have potential for application as precursors in the vapor deposition of thin cobalt films.