Nucleophilicity of metal carbonyl anions in vinylic substitution reactions

Second order rate constants are reported for the reactions of metal carbonyl anions ([M(CO)(n)L](-)) with several vinyl halides: PhCCI=C(CN)(2), Z- and E-Ph(CN)C=CHHal (Hal=Cl, Br) which follow the addition-elimination (Ad(N)E) 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 S(N)2 reactions, but much more steeply, by 14 orders of magnitude in the row log{k([M(CO)nL]M') /k([CpMo(CO)3]K)}: [CpFe(CO)(2)](-) (similar to 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)(n)L](-) anions towards vinyl (sp(2)-carbon) and alkyl halides (sp(3)-carbon) with slope 2.7. The reactivity of [M(CO)(n)L](-) in a halogen-metal exchange process (with Z-PhC(CN)=CHI) follows a similar 'large'scale as in the Ad(N)E process. The nucleophilicity of [M(CO)(n)L](-) anions correlates better with their one-electron oxidation potentials (E..) than with their basicity (pK(a) of [M(CO)(n)L]H). Copyright (c) 2008 John Wiley & Sons, Ltd.