L. Reginald Mills, Junho Kim, Eric M. Simmons, Steven R. Wisniewski and Paul J. Chirik*,
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引用次数: 0
Abstract
A series of six-coordinate, idealized octahedral phenoxyimine (FI)–cobalt(III) dimethyl bis(trimethylphosphine) complexes was synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The thermal stability of the parent Ph-FI complex was evaluated at 60 °C in benzene-d6, and a 13(1):1 ratio of ethane to methane was observed. The major detectable cobalt product of this reaction was the bis(chelate) cobalt derivative (Ph-FI)2Co formed by disproportionation of the (FI)cobalt(I) product following ethane reductive elimination. Addition of excess PMe3 inhibited C(sp3)–C(sp3) reductive elimination, consistent with phosphine dissociation preceding C–C bond formation from a five-coordinate (FI)cobalt(III) dimethyl intermediate. The reductive elimination of substituted (R-FI)cobalt(III) dimethyl bis(trimethylphosphine) compounds was evaluated in acetonitrile-d3, where ligands bearing electron-donating aniline substituents underwent reductive elimination the fastest and electron-withdrawing substituents the slowest. These data support a buildup of positive charge in the rate-limiting step, consistent with the formation of a more electropositive five-coordinate cobalt center prior to rate-limiting C–C reductive elimination. Attempted synthesis of a cobalt(III) dimethyl complex bearing a sterically hindered FI ligand with a tert-butyl substituent ortho to the phenol led exclusively to the corresponding bis(chelate) cobalt derivative, whose formation was rationalized by steric destabilization of pre–reductive elimination intermediates.
期刊介绍:
Organometallics is the flagship journal of organometallic chemistry and records progress in one of the most active fields of science, bridging organic and inorganic chemistry. The journal publishes Articles, Communications, Reviews, and Tutorials (instructional overviews) that depict research on the synthesis, structure, bonding, chemical reactivity, and reaction mechanisms for a variety of applications, including catalyst design and catalytic processes; main-group, transition-metal, and lanthanide and actinide metal chemistry; synthetic aspects of polymer science and materials science; and bioorganometallic chemistry.