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

Abstract

The synthesis of a series of cobalt NHC complexes of the types [Co(NHC) 2 (CO)(NO)] (NHC = i Pr 2 Im ( 2 ), n Pr 2 Im ( 3 ), Cy 2 Im ( 4 ), Me 2 Im ( 5 ), i Pr 2 ImMe ( 6 ), Me 2 ImMe ( 7 ), Me i PrIm ( 8 ), Me t BuIm ( 9 ); R 2 Im = 1,3-dialkylimidazolin-2-ylidene) and [Co(NHC)(CO) 2 (NO)] (NHC = i Pr 2 Im ( 13 ), n Pr 2 Im ( 14 ), Me 2 Im ( 15 ), i Pr 2 ImMe ( 16 ), Me 2 ImMe ( 17 ), Me i PrIm ( 18 ), Me t BuIm ( 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(Dipp 2 Im)(CO) 2 (NO)] ( 11 ), [Co(Mes 2 Im)(CO) 2 (NO)] ( 12 ), and [Co( Me cAAC)(CO) 2 (NO)] ( 20 ). For t Bu 2 Im a preferred coordination via the NHC backbone (“abnormal” coordination at the 4-position) was observed and the complex [Co( t Bu 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(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.