Brandon R. Barnett

Direct observation of β-chloride elimination from an isolable β-chloroalkyl complex of square-planar nickel.

Reported here are the isolation, structural characterization, and decomposition kinetics of the four-coordinate pentachloroethyl nickel complex, NiCl(CCl2CCl3)(CNAr(Mes2))2 (Ar(Mes2) = 2,6-(2,4,6-Me3C6H2)2C6H3). This complex is a unique example of a kinetically persistent β-chloroalkyl in a system relevant to coordination-insertion polymerization of polar olefins. Kinetic analysis of NiCl(CCl2CCl3)(CNAr(Mes2))2 decomposition indicates that β-chloride (β-Cl) elimination proceeds by a unimolecular mechanism that does not require initial dissociation of a CNAr(Mes2) ligand. The results suggest that a direct β-Cl elimination pathway is available to four-coordinate, Group 10 metal vinyl chloride polymerization systems.

Solution Dynamics of Redox Noninnocent Nitrosoarene Ligands: Mapping the Electronic Criteria for the Formation of Persistent Metal-Coordinated Nitroxide Radicals

The redox-noninnocence of metal-coordinated C-organo nitrosoarenes has been established on the basis of solid-state characterization techniques, but the solution-phase properties of this class of metal-coordinated radicals have been relatively underexplored. In this report, the solution-phase properties and dynamics of the bis-nitrosobenzene diradical complex trans-Pd(κ(1)-N-PhNO)2(CNAr(Dipp2))2 are presented. This complex, which is best described as containing singly reduced phenylnitroxide radical ligands, is shown to undergo facile nitrosobenzene dissociation in solution to form the metalloxaziridine Pd(η(2)-N,O-PhNO)(CNAr(Dipp2))2 and thus is not a persistent species in solution. An equilibrium between trans-Pd(κ(1)-N-PhNO)2(CNAr(Dipp2))2, Pd(η(2)-N,O-PhNO)(CNAr(Dipp2))2, and free nitrosobenzene is established in solution, with the metalloxaziridine being predominantly favored. Efforts to perturb this equilibrium by the addition of excess nitrosobenzene reveal that the formation of trans-Pd(κ(1)-N-PhNO)2(CNAr(Dipp2))2 is in competition with insertion-type chemistry of Pd(η(2)-N,O-PhNO)(CNAr(Dipp2))2 and is therefore not a viable strategy for the production of a kinetically persistent bis-nitroxide radical complex. Electronic modification of the nitrosoarene framework was explored as a means to generate a persistent trans-Pd(κ(1)-N-ArNO)2(CNAr(Dipp2))2 complex. While most substitution schemes failed to significantly perturb the kinetic lability of the nitrosoarene ligands in the corresponding trans-Pd(κ(1)-N-ArNO)2(CNAr(Dipp2))2 complexes, utilization of para-formyl or para-cyano nitrosobenzene produced bis-nitroxide diradical complexes that display kinetic persistence in solution. The origin of this persistence is rationalized by the ability of para-formyl- and para-cyano-aryl groups to both attenuate the trans effect of the corresponding nitrosoarene and, more importantly, delocalize spin density away from the aryl-nitroxide NO unit. The results presented here highlight the inherent instability of metal-coordinated nitroxide radicals and suggest a general synthetic strategy for kinetically stabilizing these species in solution.

Oxidative‐Insertion Reactivity Across a Geometrically Constrained Metal→Borane Interaction

While interest in cooperative reactivity of transition metals and Lewis acids is receiving significant attention, the scope of known reactions that directly exploit the polarized reverse-dative σ-bond of metal-borane complexes (i.e., M→BR3 ) remains limited. Described herein is that the platinum (boryl)iminomethane (BIM) complex [Pt(κ2 -N,B-Cy2 BIM)(CNArDipp2 )] can effect the oxidative insertion of a range of unsaturated organic substrates, including azides, isocyantes, and nitriles, as well as CO2 and elemental sulfur (S8 ). In addition, alkyl migration processes available to the BIM framework allow for post-insertion reaction sequences resulting in product release from the metal center.

CCDC 1529296: Experimental Crystal Structure Determination

Related Article: Brandon R. Barnett, Michael L. Neville, Curtis E. Moore, Arnold L. Rheingold, Joshua S. Figueroa|2017|Angew.Chem.,Int.Ed.|56|7195|doi:10.1002/anie.201702151

CCDC 1414433: Experimental Crystal Structure Determination

Related Article: Brandon R. Barnett, Liezel A. Labios, Curtis E. Moore, Jason England, Arnold L. Rheingold, Karl Wieghardt, and Joshua S. Figueroa|2015|Inorg.Chem.|54|7110|doi:10.1021/acs.inorgchem.5b01252