Cleavage of Carbon Dioxide C=O Bond Promoted by Nickel-Boron Cooperativity in a PBP-Ni Complex

Mechanistic Studies of Alkyl Chloride Acetoxylation by Pt-Sb Complexes

The bis-acetate complexes (SbQ3)Pt(OAc)2 (1) and (SbQ2Ph)Pt(OAc)2 (2) (Q = 8-quinolinyl) were used to study C-Cl acetoxylation of 1,2-dichloroethane (DCE) to generate 2-chloroethyl acetate and the complexes (SbQ3)PtCl2 (1b) and (SbQ2Ph)PtCl2 (2b), respectively. The first acetoxylation step produced the intermediates (SbQ3)Pt(Cl)(OAc) (1a) and (SbQ2Ph)Pt(Cl)(OAc) (2a). The reaction was studied using pseudo first order kinetics (excess DCE) in order to compare the rates of reaction of 1 and 2, which revealed that k obs = 2.44(6) × 10-4 s-1 for 1 and 0.51(2) × 10-4 s-1 for 2. The intermediate 1a was synthesized independently, and the solid-state structure was determined using single crystal X-ray diffraction. A non-Sb containing control complex, (tbpy)Pt(OAc)2 (3) (tbpy = 4,4'-di-tert-butyl-2,2'bipyridine), was studied for the acetoxylation of DCE to form (tbpy)Pt(Cl)(OAc) with k obs = 0.46(1) × 10-4 s-1. Density Functional Theory (DFT) calculations were used to examine possible Pt-mediated mechanisms for the reactions of 1, 2, or 3 with DCE. The lowest energy calculated substitution mechanism occurs with nucleophilic attack by the Pt center on the C-Cl bond followed acetate reaction with the Pt-C bond. However, close in energy and potentially also a viable mechanism is a direct substitution mechanism where the coordinated acetate anion directly reacts with the C-Cl bond of DCE. In addition, the rate of acetoxylation for complex 1 in heated dichloromethane-d 2 and chloroform-d was determined (0.43(1) × 10-4 s-1 for dichloromethane-d 2 and 0.37(1) × 10-4 s-1 for chloroform-d) and compared to the rate of acetoxylation of DCE.

Carbon Dioxide Electroreduction and Formic Acid Oxidation by Formal Nickel(I) Complexes of Di-isopropylphenyl Bis-iminoacenaphthene

Processing CO2 into value-added chemicals and fuels stands as one of the most crucial tasks in addressing the global challenge of the greenhouse effect. In this study, we focused on the complex (dpp-bian)NiBr2 (where dpp-bian is di-isopropylphenyl bis-iminoacenaphthene) as a precatalyst for the electrochemical reduction of CO2 into CH4 as the sole product. Cyclic voltammetry results indicate that the realization of a catalytically effective pattern requires the three-electron reduction of (dpp-bian)NiBr2. The chemically reduced complexes [K(THF)6]+[(dpp-bian)Ni(COD)]- and [K(THF)6]+[(dpp-bian)2Ni]- were synthesized and structurally characterized. Analyzing the data from the electron paramagnetic resonance study of the complexes in solutions, along with quantum-chemical calculations, reveals that the spin density is predominantly localized at their metal centers. The superposition of trajectory maps of the electron density gradient vector field∇ ρ r ${\nabla \rho \left({\bf r}\right)}$ and the electrostatic force density fieldF e s r ${{{\bf F}}_{{\rm e}{\rm s}}\left({\bf r}\right)}$ per electron, as well as the atomic charges, discloses that, within the first coordination sphere, the interatomic charge transfer occurs from the metal atom to the ligand atoms and that the complex anions can thus be formally described by the general formulae (dpp-bian)2-Ni+(COD) and (dpp-bian)2 -Ni+. It was also shown that the reduced nickel complexes can be oxidized by formic acid; resulting from this reaction, the two-electron and two-proton addition product dpp-bian-2H is formed.

Contrasting reactivity of B-Cl and B-H bonds at [Ni(IMes)2] to form unsupported Ni-boryls

[Ni(IMes)2] reacts with chloroboranes via oxidative addition to form rare unsupported Ni-boryls. In contrast, the oxidative addition of hydridoboranes is not observed and products from competing reaction pathways are identified. Computational studies relate these differences to the mechanism of oxidative addition: B-Cl activation proceeds via nucleophilic displacement of Cl-, while B-H activation would entail high energy concerted bond cleavage.