Browsing by Author "Bi, David W."
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- ItemOpen AccessActivation of Si-H bonds across the nickel carbene bond in electron rich nickel PCcarbeneP pincer complexes(Royal Society of Chemistry, 2015-11-27) Piers, Warren E.; LaPierre, Etienne A.; Spasyuk, Denis M.; Bi, David W.Silicon–hydrogen bonds are shown to add to a nickel carbon double bond to yield nickel α-silylalkyl hydrido complexes. Kinetic and isotope labeling studies suggest that a concerted 4-centred addition across the Ni[double bond, length as m-dash]C bond is operative rather than a mechanism involving Si–H oxidative addition. This constitutes an example of Si–H bond activation via ligand cooperativity.
- ItemOpen AccessCationic PCP iridaepoxide and carbene complexes for facile water elimination and activation processes(2017-03) Piers, Warren E.; Doyle, Lauren E.; Bi, David W.Iridaepoxide dihydride complexes of a PCP ligand bearing benzo[b]thiophene linkers are synthesized through ligand coopertive N2O and H2 activations. These neutral complexes also eliminate water at elevated temperatures to form the corresponding PCcarbeneP complexes which results in the formal hydrogenation of N2O to water. The synthesis of cationic iridaepoxide dihydride complexes are reported herein where the room temperature elimination of water is observed when a donating solvent is used. This supports a previously proposed mechanism for this water elimination where hydrides cis to the epoxide are required. Ir(I) and Ir(III) cationic PCcarbeneP complexes are also synthesized through protonation and through O–H oxidation additions of water and phenol.
- ItemOpen AccessReactions of Neutral Co(II) Complexes of a Dianionic Tetrapodal Pentadentate Ligand: Co(III) Amides from Imido Radicals(2017-03-15) Piers, Warren E.; Nurdin, Lucie; Spasyuk, Denis M.; Maron, Laurent; Bi, David W.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.