Facile C−H Bond Activation: Synthesis of the N<sub>4</sub>C Donor Set Pentadentate Ligand 1,4-Bis(2-pyridylmethyl)-1,4-diazacyclononane (dmpdacn) and a Structural Study of Its Alkyl−Cobalt(III) Complex [Co(dmpdacn-<i>C</i>)(OH<sub>2</sub>)](ClO<sub>4</sub>)<sub>2</sub>·H<sub>2</sub>O and Its Hydro
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The 1,4-bis(2-pyridylmethyl)-1,4-diazacyclononane (dmpdacn) ligand with a N4C donor set deprotonates at a CH2 γ to an amine under extraordinarily mild conditions (pH 7) and binds as a pentadentate ligand to Co(III) as the [Co(dmpdacn-C)(OH2)]2+ complex. This complex was characterized by 1D and 2D NMR techniques, and a single-crystal X-ray structure is reported. In an alternative synthesis from Co(II), dmpdacn, and air, the same C-bonded complex is obtained along with a novel hydroxylated Co(III) complex [Co(dmpdacnOH-O)Cl]2+ which has been similarly characterized. Here the carbanion has been oxidized, a C- to O-bonded rearrangement has taken place, and the bound aqua group is replaced by Cl-. The base hydrolysis kinetics of the hydroxylated Co(III) complex are reported, and mechanisms for this and the unusually facile C−H cleavage and CH2 oxidation reactions are discussed.
