Michael Adducts of (Alkynylcarbene)pentacarbonylchromium Complexes: Formation, Stereochemistry, and Thermal Rearrangement

β‐Donor‐substituted α,β‐unsaturated chromium carbene complexes (CO) 5 CrC(OEt)C = CR(XR′ n ) ( X = N, O, S; 3, 9, 11–16, 22–25 ) have been synthesized by Michael addition of amines, alcohols, and thiols to alkynylcarbene complexes (CO) 5 CrC‐(OEt)CCR ( 1 ). The configurations of the newly formed C–C double bonds have been determined by NOE/NOESY measurements and X‐ray crystal structure analysis. These vinylcarbene complexes lose one carbonyl ligand in refluxing tetrahydrofuran to give tetracarbonyl complexes (CO)4CrC(OEt)C = CR(XR′ n ) (X = N, O, S; 26–28 ).