Syntheses of η5-Heterocyclic Manganese Tricarbonyls. Effect of the Heteroatom and Heterocycle Ring Substituents on CO Substitution Reactions

Article abstract of DOI:10.1021/ja00258a024

The syntheses and characterizations of some new η⁵-heterocyclic manganese tricarbonyl complexes are described.Kinetic studies are reported for CO substitution reactions of these nitrogen family η⁵-dimethylheterocyclic manganese tricarbonyl complexes.The results show that only the N-heterocycle compounds undergo CO substitution by phosphorus nucleophiles.These results are attributed to the greater electonegativity of N than that of C, P, or As.Both tricarbonyl(η⁵-3,4-dimethylpyrrolyl)manganese(I) and tricarbonyl(η⁵-2,5-dimethylpyrrolyl)manganese(I) substitute CO by an associative pathway in which the reaction rates are first order in concenration of metal complex and first order in concentration of entering nucleophile.The former compound also substitutes CO by a pathway that is independent of the concentration of incoming nucleophile.The second-order pathway is believed to involve a ring-slippage (η⁵ -> η³ -> η⁵) mechanism, whereas the first-order pathway appears to involve a ligand-dissociation mechanism.