Organic syntheses via transition metal complexes .84. Stereoselective route to (aminoalkynylcarbene)chromium complexes via addition of (1-alkynyl)lithium compounds to isocyanide ligands

N-Lithio iminoacylates (CO)(5)Cr=C(NRLi)Cr=CR(1) [(E)-3a-e] are obtained by addition of 1-lithioalkynes LiC=CR(1) (2a,b) (R(1) = Ph, SiMe(3)) to isocyano complexes (CO)(5)Cr(CNR) (1a-d) (R = c-C6H11, Ph, p-MeC(6)H(4), o-MeC(6)H(4)). Protonation and alkylation, respectively, of the N-cyclohexyl compound 3a with EX {H2O, MeI, [Et(3)O]BF4, BrCR(2)CH(O)CH2} (5a-d) produces aminocarbene complexes (CO)(5)Cr=C(NRE)C=CR(1) (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 degrees 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)(5)Cr-C(NArLi)C=CR(1) (3c-e) (Ar = Ph, p-MeC(6)H(4), o-MeC(6)H(4)) yields aminocarbene complexes 6 predominately of (Z) configuration by kinetic reaction control. Parent (CH)-alkynylcarbene complexes (CO)(5)Cr=C(N-c-C(6)H(11)R)C=CH (6h,i) (R = H, Me) were obtained by fluorine-induced desilylation of the Me(3)Si derivatives 6e,f. (Z)-6i was characterized by X-ray diffraction.