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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{$k_{[{\bf M}({\bf CO})_n {\bf L}]{\bf M'}} {\rm /}k_{[{\bf CpMo}({\bf CO})_3 ]{\bf K}}$}: [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.

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In the reaction of the [CpFe(CO) 2 ]

The mechanism of the reaction of carbonylate anions ([M(CO) n L] -) with highly activated vinyl halides (Hal = Cl, Br, I) was investigated by the method of "anion traps" -the effect of proton donors on the composition of the reaction products. It was demonstrated that the reactions with PhCHal=C(Z) 2 (Hal = Br, I; Z = CN, CO 2 Et) and PhCN=CClI take place through initial attack by the carbonylate at the halogen atom, the reactions with PhCCl=C(CO 2 Et) 2 and PhCOCH=CHHal (Hal = Cl, I) take place through attack by the carbonylate at the ð bond (Ad N E mechanism), and in the case of E-and Z-PhCN=CHI the two mechanisms operate concurrently. The main laws determining the reaction mechanisms are analyzed.Nucleophilicity and nucleophilic substitution are among the most important concepts and processes in organic chemistry. Among the enormous variety of nucleophilic reagents a quite special class is presented by nucleophiles in which the reaction center is localized at a metal atom. The reactivity of such metal-centered anions [1-9] differs fundamentally from that observed in "classical" N-, O-, or S-nucleophiles and is largely not understood. Even in aliphatic substitution reactions metal-centered anions behave unusually, which has in due course stimulated discussion of the mechanism of single-electron transfer (SET) and its relationship with the S N 2 mechanism [10-13].For a number of years the laws governing nucleophilic vinylic and aromatic substitution involving the anions of transition metal carbonyls (carbonylates) -an extensive class of metal-centered anions widely used in synthesis and acting as intermediates in a series of practically important catalytic processes such as the carbonylation of alkyl halides and 350 0040-5760/11/4606-0350 Scheme 1. The addition-elimination mechanism (Ad N E).

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