Synthesis, Structure, and Unusual Reactivity of β-Halovinyl Cobalt Porphyrin Complexes

The preparation, structures, and reactivity of tetraphenylporphyrin (TPP) cobalt halovinyl complexes are reported. β-Halovinyl complexes of (TPP)Co(<i>E</i>-CHCHX) (X = Br and I) were prepared from the insertion of acetylene into the cobalt halide bonds of the corresponding halide complexes. The reactivity of these compounds and of the previously reported (TPP)Co(<i>E</i>-CHCHCl), was studied in depth, and it was found that complex reactivity increased with the leaving group ability of the halide. A <i>trans</i>-dichlorovinyl cobalt porphyrin complex, (TPP)Co(<i>Z</i>-CClCHCl), was also prepared through the reaction of (TPP)CoNa and TCE. The structures of (TPP)Co(<i>E</i>-CHCHBr), (TPP)Co(<i>Z</i>-CClCHCl), and (TPP)Co(C<sub>2</sub>H) are reported. The C−C bond length of the vinyl group was found to vary for the β-halovinyl complexes (TPP)Co(<i>E</i>-CHCHX) from 1.211 Å for X = Br to 1.234 Å for X = Cl and 1.320 Å for (TPP)Co(<i>Z</i>-CClCHCl). A comparison of these structures to many chlorovinyl cobalt complexes shows that <i>trans</i>-2-halo substitution results in a dramatically decreased vinyl C−C bond length. The mechanism of halide substitution for the β-halovinyl complexes was investigated with kinetic experiments that indicated a dissociative mechanism and supported the intermediacy of a cobalt acetylene complex.