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Nucleophilicity of metal carbonyl anions in vinylic substitution reactions
Authors:Petr K. Sazonov  Galina A. Artamkina  Irina P. Beletskaya
Affiliation:Chemistry Department, M.V. Lomonosov Moscow State University, Leninskie Gory 1, Moscow 119992, Russian Federation
Abstract:
Second order rate constants are reported for the reactions of metal carbonyl anions ([M(CO)nL]?) with several vinyl halides: PhCCl?C(CN)2, Z‐ and E‐Ph(CN)C?CHHal (Hal = Cl, Br) which follow the addition–elimination (AdNE) substitution mechanism. The obtained data show that the nucleophilic reactivity of [M(CO)nL]? anions towards vinyl halides increases in the same order as in aliphatic SN2 reactions, but much more steeply, by 14 orders of magnitude in the row log{equation image }: [CpFe(CO)2]? (~14), [Re(CO)5]? (7.8), [Mn(CO)5]? 2.1, [CpW(CO)3]? (0.7) > [CpMo(CO)3]? (0). A good correlation exists between nucleophilicities of [M(CO)nL]? anions towards vinyl (sp2‐carbon) and alkyl halides (sp3‐carbon) with slope 2.7. The reactivity of [M(CO)nL]? in a halogen–metal exchange process (with Z‐PhC(CN)?CHI) follows a similar ‘large’ scale as in the AdNE process. The nucleophilicity of [M(CO)nL]? anions correlates better with their one‐electron oxidation potentials (Eox) than with their basicity (pKa of [M(CO)nL]H). Copyright © 2008 John Wiley & Sons, Ltd.
Keywords:nucleophilicity  metal carbonyl anions  SNV  nucleophilic vinylic substitution  reaction mechanisms
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