title: Reactions of Neutral Cobalt(II) Complexes of a Dianionic Tetrapodal Pentadentate Ligand: Cobalt(III) Amides from Imido Radicals.
abstract: Neutral cobalt(II) complexes of the dianionic tetrapodal pentadentate ligand B2Pz4Py, in which borate linkers supply the anionic charges, are reported. Both the six-coordinate THF adduct 1-THF and the five-coordinate THF-free complex 1 are in a high-spin S = 3/2 configuration in the ground state and have been structurally characterized by X-ray crystallography. These two Co(II) starting materials react rapidly with aryl azides of moderate steric bulk. The thermodynamic products of these reactions are low-spin, diamagnetic, Co(III) amido complexes that are either monomeric, when an external hydrogen atom source such as 1,4-cyclohexadiene is present, or dimeric products formed via C-C coupling of the azide aryl group and internal transfer of H•to the nitrogen. These products are fully characterized and are rare examples of octahedral Co amido compounds; structural determinations reveal significant pyramidalization of the amido nitrogens due to π-π repulsion wherein the amido ligand is primarily a σ donor. The amido products arise from highly reactive Co(III) imido radical intermediates that are the kinetic products of the reactions of 1 or 1-THF with the azide reagents. The imido radicals can be detected by X-band EPR spectroscopy and have been probed by density functional theory computations, which indicate that this doublet species is characterized by a high degree of spin localization on the imido ligand, accounting for the reactivity with hydrogen atom sources and dimerization chemistry observed. The high coordination number and the electron-rich nature of the dianionic B2Pz4Py ligand framework render the imido ligand formed highly reactive.
authors.affiliation: Department of Chemistry, University of Calgary , 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
authors.forename: Lucie
authors.initials: L
authors.lastname: Nurdin
authors.affiliation: Department of Chemistry, University of Calgary , 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.|Canadian Light Source Inc. , 44 Innovation Boulevard, Saskatoon, Saskatchewan, Canada S7N 2V3.
authors.forename: Denis M
authors.initials: DM
authors.lastname: Spasyuk
authors.affiliation: Department of Chemistry, University of Calgary , 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4.
authors.forename: Warren E
authors.identifier: http://orcid.org/0000-0003-2278-1269
authors.initials: WE
authors.lastname: Piers
authors.affiliation: LPCNO, Université de Toulouse, INSA, UPS, LPCNO , 135 Avenue de Rangueil, and CNRS, LPCNO, F-31077 Toulouse, France.
authors.forename: Laurent
authors.identifier: http://orcid.org/0000-0003-2653-8557
authors.initials: L
authors.lastname: Maron