Browsing by Author "Spasyuk, Denis M."

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    Activation 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.
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    Reactions 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.
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    Systematic Dismantling of a Carefully Designed PCcarbeneP Pincer Ligand via C-C Bond Activations at an Iridium Centre
    (NRC Press, 2015-07-28) Piers, Warren E.; Smith, Joel D.; Borau-Garcia, Javier; Spasyuk, Denis M.
    An electron-rich PCsp2P ligand, incorporating N,N-dimethylamino groups para to the anchoring carbene donor of the ligand, was prepared and coordinated to iridium, producing the iridium carbene chloride 2. This species undergoes facile reaction with N2O to afford an iridaepoxide complex, 3, in which an oxygen atom has been transferred to the Ir=C bond. The rate of this reaction is significantly faster than that observed for the less electron rich, unsubstituted ligand. However, further reaction of 3 involving cleavage of one of the ligand C–C bonds was observed, producing the bis-phosphine chorido complex 4. This process was accelerated by the presence of H2. Heating 4 under H2 resulted in hydrogenolysis of the ortho-metalated phosphine ligand to give a hydrido complex (5) and decarbonylation of the acyl phosphine ligand to give, finally, Vaska’s complex analog 6. All compounds were fully characterized, and the sequence represents the dismantling of the PCsp2P ligand framework.
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    Zirconocene-based methods for the preparation of BN indenes: application to the synthesis of 1,5-dibora-4a,8a-diaza-1,2,3,5,6,7-hexaaryl-4,8-dimethyl-s-indacenes.
    (American Chemical Society, 2017-03-08) Piers, Warren E.; Morgan, Matthew M.; Patrick, Evan A.; Rautiainen, J. Mikko; Tuononen, Heikki M.; Spasyuk, Denis M.
    A method for the preparation of 3-bora-9-azaindene heterocycles based on zirconocene-mediated functionalization of the o-CH bonds of pyridines has been developed and used to make two such compounds. Unlike other methods, the boron center in these heterocycles remains functionalized with a chloride ligand, and so the compounds can be further elaborated through halide abstraction and reduction. The utility of the method was further demonstrated by applying it toward the preparation of 1,5-dibora-4a,8a-diaza BN analogues of the intriguing hydrocarbon s-indacene starting from 2,5-dimethylpyrazine. Gram quantities of one such compound were prepared and fully characterized, and both experimental and computational data are presented to compare its properties to those of the parent hydrocarbon s-indacene. These data indicate that the BN-substituted derivative exhibits lowered aromaticity in relation to the hydrocarbon.