Metal carbonyl anions ([M(CO)_nL]^-) are characterized by a very broad nucleophilicity span, which in aliphatic S_N2 reactions increases by eight orders of magnitude from [Co(CO)₄]^- to supernucleophilic [CpFe(CO)₂]^-. Studying the nucleophilic vinylic substitution (SNV) reactions with [M(CO)_nL]^- anions [1] allowed us to compile a nucleophilicity scale of these anions in vinylic substitution (Ad_NE mechanism). The scale was obtained by combining the kinetic data from several overlapping series of [M(CO)_nL]^- anions reacting with vinyl halides of different activity (PhCF=CFHal, Ph(CN)C=CHHal, Ph(Cl)C=(CN)₂, ets.). The nucleophilicity span of [M(CO)_nL]^- anions found in SNV reactions is twice as large as in aliphatic S_N2 reactions, though good correlation exists between the N_VinHal and log(k _CH3I) parameters (see the Figure). The problem of interpreting the nucleophilicity data in terms of reaction mechanism, and the question whether it is indicative of latent single electron transfer (SET) step are to be discussed in the presentation.

[1] P. K. Sazonov, V. A. Ivushkin, G. A. Artamkina, I. P. Beletskaya, Arkivoc 2003, Part (X), http://www.arkat-usa.org/ark/journal/2003/I10_Rossi-Ruveda/RR-839C/839C.pdf.

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1. Mechanistic Aspects and Synthetic Application of Carbon-Carbon and Carbon Heteroatom Bonds Formation in Substitution and Addition Reactions Catalyzed by Transition Metal Complexes