Organic Syntheses via Transition Metal Complexes. 84.1 Stereoselective Route to (Aminoalkynylcarbene)chromium Complexes via Addition of (1-Alkynyl)lithium Compounds to Isocyanide Ligands

N-Lithio iminoacylates (CO)5CrC(NRLi)C⋮CR1 [(E)-3a−e] are obtained by addition of 1-lithioalkynes LiC⋮CR1 (2a,b) (R1 = Ph, SiMe3) to isocyano complexes (CO)5Cr(CNR) (1a−d) (R = c-C6H11, Ph, p-MeC6H4, o-MeC6H4). Protonation and alkylation, respectively, of the N-cyclohexyl compound 3a with EX {H2O, MeI, [Et3O]BF4, BrCH2CH(O)CH2} (5a−d) produces aminocarbene complexes (CO)5CrC(NRE)C⋮CR1 (6a−d) in 75−90% overall yield. The latter compounds are generated stereoselectively in (E) configuration (E/Z = 14:1 to 29:1) by kinetic reaction control and are isomerized at 80 °C to give the corresponding (Z) stereoisomers as main products. The stereochemical course of alkylation of 3 is strongly influenced by substituents at the nitrogen atom of 3 as well as by the type of electrophile EX involved. Alkylation of N-aryl compounds (CO)5CrC(NArLi)C⋮CR1 (3c−e) (Ar = Ph, p-MeC6H4, o-MeC6H4) yields aminocarbene complexes 6 predominately of (Z) configuration by kinetic reaction control. Parent (CH)-alkynylcarbene complexes (CO...