Reactions of carbonylmetallate anions with 1-haloalkynes

Article abstract of DOI:10.1007/BF02496023

The main regularities of the reactions of 1-haloalkynes RC≡CX with carbonylmetallate anions [(η⁵-C₅R′₅)(CO)₃M]^- (R′ = H (1-3), M = Cr (1), M = Mo (2), or M = W (3); R′ = Me (4-6), M = Cr (4), M = Mo (5), or M = W (6)) were revealed. It was established that the first stage of the reactions of anions 1-6 with bromo- or iodoalkynes RC≡CX (X=Br or 1) involved the transfer of the halogen atom from the sp-hybridized carbon atom to the transition metal atom to form carbonyl halides (η⁵-C₅R′₅)(CO)₃MX. To the contrary, the reactions of anions 1-6 with chloroalkynes RC≡CCl proceeded selectively as a nucleophilic substitution at the unsaturated carbon atom, the reaction rate being governed by the nucleophilicity of the carbonylmetallate anions and the electron-withdrawing ability of the R group. These reaction paths are consistent with the structures of the lowest unoccupied molecular orbitals (LUMO) in the PhC≡CX molecules (X = Cl, Br, or I) calculated by the MNDO/PM3 method. In the case of the reactions of 1-chloroheptyne-1 ClC≡CC₅H₁₁ⁿ, anions 1-3 appeared to be insufficiently nucleophilic, but these reactions can be performed as cross-coupling of the carbonylmetallate anions with chloroalkynes catalyzed by palladium complexes.