Formation of a nickel carbon dioxide adduct and its transformation mediated by a Lewis acid

An uncommon nickel dinitrogen adduct and its tendency toward CO2 binding are investigated using a (PP(Me)P)Ni scaffold. (PP(Me)P)Ni(N2) (1) and {(PP(Me)P)Ni}2(μ-N2) (2) were prepared and their treatment with CO2 revealed the formation of (PP(Me)P)Ni(η(2)-CO2) (3). This is a new type of CO2 binding for a zero-valent nickel center supported by three donor ligands, reminiscent of the CODH active site environment. Clear unique structural differences in 3 are evident when compared with previous 4-coordinate Ni-CO2 adducts. Compound 3 when treated with B(C6F5)3 gives the Lewis acid-base adduct (PP(Me)P)Ni{COOB(C6F5)3} (4) possessing a Ni-μ-CO2-κ(2)C,O-B moiety.

Structurally simple complexes of CO2

A wide range of structurally characterized adducts of CO₂are discussed in this review, from the strongly bound, charge assisted carbamate complexes through the weaker halide and pseudo-halide complexes to the weakest possible inclusion complexes.

Binuclear complexes of Ni(i) from 4-terphenyldithiophenol

The preparation and characterisation of binuclear Ni(i) complexes from a 4-terphenyldithiophenol ligand is described.

Carbon Dioxide Cleavage by a Ni2 Complex Supported by a Binucleating Bis(N-Heterocyclic Carbene) Framework

A binucleating bis(N-heterocyclic carbene) ligand was designed as a means to coordinate and proximally constrain two transition metal centers. Using an imidazopyridine-based NHC afforded a framework structurally related to previously reported para-terphenyl diphosphines. Bimetallic copper, cobalt, and nickel complexes supported by this framework were synthesized and structurally characterized. Strong interactions between the metal centers and the central arene were observed in all nickel complexes. Dinickel(0) complexes of this ligand framework were found to react with CO₂ to form a dicarbonyl-bridged dinickel(0) product, demonstrating facile CO₂ reduction.

The mechanism of homogeneous CO2 reduction by Ni(cyclam): product selectivity, concerted proton-electron transfer and C-O bond cleavage

Homogeneous CO2 reduction catalyzed by [Ni(I)(cyclam)](+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) exhibits high efficiency and selectivity yielding CO only at a relatively low overpotential. In this work, a density functional theory study of the reaction mechanism is presented. Earlier experiments have revealed that the same reaction occurring on mercury surfaces generates a mixture of CO and formate. According to the proposed mechanism, an η(1)-CO2 adduct is the precursor for CO evolution, whereas formate is obtained from an η(1)-OCO adduct. Our calculations show that generation of the η(1)-CO2 adduct is energetically favored by ∼14.0 kcal/mol relative to that of the η(1)-OCO complex, thus rationalizing the product selectivity observed experimentally. Binding of η(1)-CO2 to Ni(I) only leads to partial electron transfer from the metal center to CO2. Hence, further CO2 functionalization likely proceeds via an outer-sphere electron-transfer mechanism, for which concerted proton coupled electron transfer (PCET) is calculated to be the most feasible route. Final C-O bond cleavage involves rather low barriers in the presence of H3O(+) and H2CO3 and is therefore essentially concerted with the preceding PCET. As a result, the entire reaction mechanism can be described as concerted proton-electron transfer and C-O bond cleavage. On the basis of the theoretical results, the limitations of the catalytic activity of Ni(cyclam) are discussed, which sheds light on future design of more efficient catalysts.

Arene C-H amination at nickel in terphenyl-diphosphine complexes with labile metal-arene interactions

The meta-terphenyl diphosphine, m-P2, 1, was utilized to support Ni centers in the oxidation states 0, I, and II. A series of complexes bearing different substituents or ligands at Ni was prepared to investigate the dependence of metal-arene interactions on oxidation state and substitution at the metal center. Complex (m-P2)Ni (2) shows strong Ni(0)-arene interactions involving the central arene ring of the terphenyl ligand both in solution and the solid state. These interactions are significantly less pronounced in Ni(0) complexes bearing L-type ligands (2-L: L=CH3CN, CO, Ph2CN2), Ni(I)X complexes (3-X: X=Cl, BF4, N3, N3B(C6F5)3), and [(m-P2)Ni(II)Cl2] (4). Complex 2 reacts with substrates, such as diphenyldiazoalkane, sulfur ylides (Ph2 S=CH2 ), organoazides (RN3: R=para-C6H4OMe, para-C6H4CF3, 1-adamantyl), and N2O with the locus of observed reactivity dependent on the nature of the substrate. These reactions led to isolation of an η(1)-diphenyldiazoalkane adduct (2-Ph2CN2), methylidene insertion into a Ni-P bond followed by rearrangement of a nickel-bound phosphorus ylide (5) to a benzylphosphine (6), Staudinger oxidation of the phosphine arms, and metal-mediated nitrene insertion into an arene C-H bond of 1, all derived from the same compound (2). Hydrogen-atom abstraction from a Ni(I)-amide (9) and the resulting nitrene transfer supports the viability of Ni-imide intermediates in the reaction of 1 with 1-azido-arenes.