C-H Activation by Isolable Cationic Bis(phosphine) Cobalt(III) Metallacycles

Five-and six-coordinate cationic bis(phosphine) cobalt (III) metallacycle complexes were synthesized with the general structures, [(depe)Co(cycloneophyl)(L)(L ')][BArF4] (depe = 1,2-bis(diethylphosphino)ethane; cycloneophyl = [Kappa-C:C-(CH2C(Me)2)C6H4]; L/L ' = pyridine, pivalonitrile, or the vacant site, BAr4F = B[(3,5(CF3)2)C6H3]4). Each of these compounds promoted facile directed C(sp2)-H activation with exclusive selectivity for ortho-alkylated products, consistent with the selectivity of reported cobalt-catalyzed arene-alkene-alkyne coupling reactions. The direct observation of C-H activation by cobalt(III) metallacycles provided experimental support for the intermediacy of these compounds in this class of catalytic C-H functionalization reaction. Deuterium labeling and kinetic studies provided insight into the nature of C-H bond cleavage and C-C bond reductive elimination from isolable cobalt(III) precursors.

Automated summary

Cationic bis(phosphine) cobalt (III) metallacycle complexes with five and six coordination were successfully synthesized, which exhibited high selectivity towards ortho-alkylated products in C(sp2)-H activation reactions. The direct observation of C-H activation by cobalt(III) metallacycles provided experimental support for their role as intermediates in catalytic C-H functionalization reactions, and deuterium labeling and kinetic studies further revealed the nature of C-H bond cleavage and C-C bond reductive elimination from isolable cobalt(III) precursors.