Intramolecular interactions in 2,6-pyridylacetylenes and their Co2(CO)4dppm complexes

A series of 2,6-ethynylpyridyl compounds BrC5H3N(C2)R, C5H3N[(C2)R]2, BrC5H3N[RC2Co2(CO)4dppm], C5H3N{[R′C2Co2(CO)4dppm]C2R} and C5H3N[(R2C2Co2(CO)4dppm)]2 (R′=H, SiMe3, Fc), C5H3N(C2SiMe3)(C2R) R=H, Fc, {C5H3N(C2SiMe3)2} and {C5H3N[C2C5H3N(C2SiMe3)]2} have been prepared in order to study through-space and through-bond interactions between the ethynyl arms. The structure of BrC5H3N[FcC2Co2(CO)4dppm] shows that the Co2-alkyne unit is preferentially distorted, rather than the ethynyl arms bent, in order to minimise steric interactions. Although, there is no evidence for through-bond or through-space electronic communication between the redox centres, intramolecular interactions force a η2(dppm)–η1(dppm) equilibrium upon the oxidised Co2(CO)4dppm unit, which is seen in the electrochemistry and OTTLE data.