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: PhCClC(CN) 2 , Z ‐ and E ‐Ph(CN)CCHHal (Hal = Cl, Br) which follow the addition–elimination (Ad N E) substitution mechanism. The obtained data show that the nucleophilic reactivity of [M(CO) n L] − 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{ $k_{[{\bf M}({\bf CO})_n {\bf L}]{\bf M'}} {\rm /}k_{[{\bf CpMo}({\bf CO})_3 ]{\bf K}}$ }: [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) 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 ox ) than with their basicity (p K a of [M(CO) n L]H). Copyright © 2008 John Wiley & Sons, Ltd.