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

• Published in: Organometallics Vol. 35; no. 17; pp. 2806 - 2821
• Main Authors: Hering, Florian, Berthel, Johannes H. J, Lubitz, Katharina, Paul, Ursula S. D, Schneider, Heidi, Härterich, Marcel, Radius, Udo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12-09-2016
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.6b00374

The synthesis of a series of cobalt NHC complexes of the types [Co­(NHC)2(CO)­(NO)] (NHC = iPr2Im (2), nPr2Im (3), Cy2Im (4), Me2Im (5), iPr2ImMe (6), Me2ImMe (7), MeiPrIm (8), MetBuIm (9); R2Im = 1,3-dialkylimidazolin-2-ylidene) and [Co­(NHC)­(CO)2(NO)] (NHC = iPr2Im (13), nPr2Im (14), Me2Im (15), iPr2ImMe (16), Me2ImMe (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 cases 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(Dipp2Im)­(CO)2(NO)] (11), [Co­(Mes2Im)­(CO)2(NO)] (12), and [Co­(MecAAC)­(CO)2(NO)] (20). For tBu2Im a preferred coordination via the NHC backbone (“abnormal” coordination at the 4-position) was observed and the complex [Co­(tBu2 aIm)­(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(NHC)­(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.