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Chemistry of Constrained Dioxocyclam Ligands with Co(III):  Unusual Examples of C−H and C−N Bond Cleavage

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posted on 2003-10-15, 00:00 authored by Chuanjiang Hu, Robert M. Chin, Thoi D. Nguyen, Khoi T. Nguyen, Paul S. Wagenknecht, Lawrence C. Nathan
The reactions between H2dc3 and Co(acac)3 have been studied in the presence and absence of base. In the presence of base, a complex with an intramolecular Co−C bond, Co(dc3-C-(8))(H2O), 1, is formed, presumably through heterolytic C−H bond activation. An X-ray crystallographic study demonstrates the presence of a Co−C bond and shows that the diazacyclooctane (daco) subunit adopts the chair−boat conformation with respect to the metal. The cobalt−carbon bond induces strain in the macrocycle as demonstrated by bond angles significantly deviating from tetrahedral. The 13C NMR resonance of the carbon atom bound to cobalt (−10.5 ppm) suggests significant ionic character in the cobalt−carbon bond. However, we were unable to cleave this bond in the presence of strong acid. In the absence of base, the reaction of Co(acac)3 with H2dc3 resulted in C−N cleavage of the ligand and the formation of a complex of dioxocyclam, Co(dc)(acac), 2. This complex has subsequently been prepared in high yield by the reaction of Co(acac)3 with dioxocyclam. An X-ray crystallographic study demonstrates that dioxocyclam adopts the heretofore unreported cis configuration, having folded along a N−Co−N axis that is perpendicular to the Co-acac plane.

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