Disproportionation Reactions of an Organometallic Ni(I) Amidate Complex: Scope and Mechanistic Investigations

Abstract

The N-heterocyclic carbene supported three-coordinate Ni­(I) complex (IPr)­Ni­(κ1-N-N­( i Pr)­C­(O) t Bu)­(CNXyl) ([2-CNXyl]; CNXyl = 2,6-dimethylphenyl isocyanide) undergoes disproportionation with 1 equiv of CNXyl to afford an equimolar mixture of Ni(0) and Ni­(II) complexes (IPr)­Ni­(CNXyl)3 ([3-CNXyl]) and (IPr)­Ni­(κ2-N,O-N­( i Pr)­CO­( t Bu))2 ([4]), respectively. Complexes [3-CNXyl] and [4] are also produced when 2 equiv of the isonitrile CNXyl is added to (IPr)­Ni­(κ3-N,bis­(H 2 CMe)-N­( i Pr)­C­(O) t Bu) ([1]). Furthermore, we show that reactions with π-acceptors CO and select alkenes also result in disproportionation. In the case of CO we show that reactions in the solid state afford selectivity for and isolation of the reaction intermediate (IPr)­Ni­(κ1-N-N­( i Pr)­C­(O) t Bu)­(CO) ([2-CO]), which is not isolable by solution methods. Kinetic analysis of the disproportionation reaction with alkenes suggests that the reaction is first order in both nickel and alkene. Preliminary trapping experiments rule out amidyl radicals as intermediates in these reactions. We propose instead that a bimolecular ligand transfer is operative, in part due to the hemilabile nature of amidate ligands.

LiCl-Accelerated Multimetallic Cross-Coupling of Aryl Chlorides with Aryl Triflates

“…Lithium chloride 21 can overcome zinc inhibition and was generally the most useful additive studied ( Table 1 , entries 1–6, and Table S2 ). 22 , 23 While we found that reduction of octyl bromide to octylzinc bromide was also inhibited by zinc salts, 21d , 24 reduction of palladium(II) phosphine complexes to palladium(0) was fast with or without added LiCl or Zn ( Figures S11–S16 ). 25 , 26 …”

Direct metal-carbon bonding in symmetric bis(C-H) agostic Nickel(I) complexes

“…30,33 We previously reported the linear nickel(I) complexes with pairs of nearly symmetric δ-bis(C-H) contacts from pendant methyl groups that were tentatively assigned as pseudo-bis-agostic complexes based on existing norms for the assignment of such species. 34,35 Herein, we report additional spectroscopic data that correct our original assignment and identify a previously unrecognized mode of bis-agostic interaction that results from direct C-…”

“…2a). 34,35 Fig. 2b shows the Ni K-edge pre-edge region for analogous complexes both with (1,3) and without (2,4) bis-agostic interactions: the spectra are strikingly different in this region.…”

Four Oxidation States in a Single Photoredox Nickel‐Based Catalytic Cycle: A Computational Study

“…This SET has a barrier of 12.3 kcal mol −1 and the overall process is slightly endergonic, although the low barrier found for the halide abstraction from Ni 0 catalyst will push the reaction again to force the turnover of the catalytic cycle. Although this step is the most likely to close the catalytic cycle and provide the catalytic turnover, other pathways such as Ni I disproportionation may coexist in the reaction media …”

“…Finally,t he initial species 1 and the Ru II photoredox catalyst are regenerated by as econd SET.T his SET has ab arrier of 12.3 kcal mol À1 and the overall process is slightly endergonic,a lthough the low barrier found for the halide abstraction from Ni 0 catalyst will push the reaction again to force the turnover of the catalytic cycle.A lthough this step is the most likely to close the catalytic cycle and provide the catalytic turnover, other pathways such as Ni I disproportionation may coexist in the reaction media. [27] We summarize the calculated mechanism of the Ni/Ru catalyzed indoline formation in Scheme 2. Thee lementary steps that can be run without irradiation (upper part of the catalytic cycle) move between Ni 0 ,N i I ,a nd Ni II oxidation states.T hose steps consist of the activation ofiodoacetanilide and alkene substrates,and the formation of aC ÀCbond.…”