Reactions of isocyanide-substituted dimanganese carbonyl complexes with alkynes. Alkyne-isocyanide coupling and the synthesis of metalated n-substituted pyridines

Article abstract of DOI:10.1021/om00001a069

When activated by Me3NO in the presence of MeCN, the compounds Mn₂(CO)₉(CNR) (la,b; R = Me, Ph) react with MeO₂CC≡CCO₂Me to yield the new compounds Mn₂(CO)₈[μ-(MeO₂C)C=C(CO₂Me)C=N ] (2a,b; R = Me, Ph) in yields of 40% and 32%, respectively. Minor products, Mn₂(CO)₇(CNR)[μ-(MeO₂C)C=C(CO₂Me) C=O] 3a,b; R = Me, Ph) were also formed. Compound 2a was characterized crystallographically. The structure shows that isocyanide ligand was coupled to the alkyne, and the nitrogen atom is coordinated to one of the manganese atoms to form a five-membered cyclo-mangana enimine ring. One of the carboxylate groups is coordinated to the other manganese atom. The compounds (4a), (4b), and (4c) were prepared in yields of 27%, 32%, and 31%, respectively, by treatment of 2a,b with C₂H₂, and of 2a with HC₂(CO₂Me) in the presence of UV irradiation. Compound 4a was characterized crystallographically. This compound contains a metalated N-methylpyridine ring formed by a 1,4-cycloaddition of the alkyne to the enimine grouping in compound 2a. One of the metal atoms was shifted to a n-bonding coordination involving four of the carbon atoms of the pyridine ring.