Diverse catalytic reactivity of a dearomatized PN3P*–nickel hydride pincer complex towards CO2 reduction (original) (raw)
Related papers
Polyhedron, 2012
A new nickel bis(phosphinite) pincer complex [2,6-(R 2 PO) 2 C 6 H 3 ]NiCl (L R NiCl, R = cyclopentyl) has been prepared in one pot from resorcinol, ClP(C 5 H 9 ) 2 , NiCl 2 , and 4-dimethylaminopyridine. The reaction of this pincer compound with LiAlH 4 produces a nickel hydride complex, which is capable of reducing CO 2 rapidly at room temperature to give a nickel formate complex. X-ray structures of two related nickel formate complexes L R NiOCHO (R = cyclopentyl and isopropyl) have shown an ''in plane'' conformation of the formato group with respect to the coordination plane. The stoichiometric reaction of nickel formate complexes L R NiOCHO (R = cyclopentyl, isopropyl, and tert-butyl) with catecholborane has suggested that the reaction is favored by a bulky R group. L R NiOCHO (R = tert-butyl) does not react with PhSiH 3 at room temperature; however, it reacts with 9-borabicyclo[3.3.1]nonane and pinacolborane to generate a methanol derivative and a boryl formate species, respectively. The catalytic reduction of CO 2 with catecholborane is more effectively catalyzed by a more sterically hindered nickel pincer hydride complex with bulky R groups on the phosphorus donor atoms. The nickel pincer hydride complexes are inactive catalysts for the hydrosilylation of CO 2 with PhSiH 3 .
Inorganic Chemistry, 2013
Nickel pincer complexes of the type [2,6-(R 2 PO) 2 C 6 H 3 ]NiH (R = t Bu, 1a; R = i Pr, 1b; R = c Pe, 1c) react with BH 3 ·THF to produce borohydride complexes [2,6-(R 2 PO) 2 C 6 H 3 ]Ni(η 2 -BH 4 ) (2a−c), as confirmed by NMR and IR spectroscopy, X-ray crystallography, and elemental analysis. The reactions are irreversible at room temperature but reversible at 60°C. Compound 1a exchanges its hydrogen on the nickel with the borane hydrogen of 9-BBN or HBcat, but does not form any observable adduct. The less bulky hydride complexes 1b and 1c, however, yield nickel dihydridoborate complexes reversibly at room temperature when mixed with 9-BBN and HBcat. The dihydridoborate ligand in these complexes adopts an η 2 -coordination mode, as suggested by IR spectroscopy and X-ray crystallography. Under the catalytic influence of 1a−c, reduction of CO 2 leads to the methoxide level when 9-BBN or HBcat is employed as the reducing agent. The best catalyst, 1a, involves bulky substituents on the phosphorus donor atoms. Catalytic reactions involving 1b and 1c are less efficient because of the formation of dihydridoborate complexes as the dormant species as well as partial decomposition of the catalysts by the boranes.
Catalysts
Transition metal-catalysed homogeneous hydrogenation of CO2 to formate or formic acid has emerged as an appealing strategy for the reduction of CO2 into value-added chemicals. Since the state-of-the-art catalysts in this realm are primarily based on expensive precious metals and require demanding reaction conditions, the design and development of economically viable non-noble metal catalysts are in great demand. Herein, we exploit the thermodynamic correlation between the crucial reaction steps of CO2 hydrogenation, that is, base-promoted H2-splitting and hydride transfer to CO2 as a guide to estimate the catalytic efficiency of non-noble metal complexes possessing a ligand backbone containing a secondary amine as an “internal base”. A set of three non-noble metal complexes, one bearing tri-coordinated PNP-pincer (1Mn) and the other two based on tetra-coordinated PNPN-pincer (2Mn and 3Fe), have been investigated in this study. The computational mechanistic investigation establishes ...
ChemistrySelect, 2019
The conversion mechanisms of CO into methanol through hydrogenation and CO 2 through hydrolysis catalyzed by (PNP) RuH 2 CO (1) pincer complex have been explored employing density functional theory (DFT). For both the reactions, we have identified two pathways. In pathway-I, at first the CO takes part in the reaction by interacting with the Ru-center of pincer complex and after that the H 2 /H 2 O molecule participates in the reaction, whereas in pathway-II, the generation of hydrogenated/hydrolyzed pincer from initial pincer via the assistance of H 2 or H 2 O molecule occurs first, followed by the reaction with CO. In case of hydrogenation, for both the pathways, CO is first converted to HCHO through hydrogenation which further undergoes hydrogenation to form methanol. In pathway-I, the reaction of HCHO with H 2 in presence of dehydrogenated pincer leads to produce methanol, whereas for pathway-II the hydrogenated pincer formed at the beginning of this pathway carries out the aforementioned conversion. Further in presence of methanol, CO is catalytically converted to methyl formate. On the other hand, in case of hydrolysis, the conversion of CO to CO 2 can be achieved in two ways, where 2 nd step, i. e. formic acid to CO 2 via formate ion formation follows similar mechanism for both the pathways. Overall, from our study it is revealed that the Rupincer complex acts as a promising homogeneous catalyst for converting CO to various organic chemical commodities.
Nickel-Catalyzed Cross-Couplings Involving Carbon−Oxygen Bonds
Chemical Reviews, 2011
as a precursor to organozinc intermediates. Kumada observed a rate-acceleration of the homocoupling when iodide anions were added. The iodide anions seemed to act as electrontransfer accelerants presumably vis-à-vis a bridging interaction between Ni and Zn. Through the use of stoichiometric KI, the homocoupling yield of bromobenzene after 24 h at room temperature was increased from 24% to 81%.
Frontiers in Chemistry, 2019
We report the synthesis of a rigid phosphine-substituted, redox-active pincer ligand and its application to electrocatalytic CO 2 reduction with first-row transition metal complexes. The tridentate ligand was prepared by Stille coupling of 2,8-dibromoquinoline and 2-(tributylstannyl)pyridine, followed by a palladium-catalyzed cross-coupling with HPPh 2. Complexes were synthesized from a variety of metal precursors and characterized by NMR, high-resolution mass spectrometry, elemental analysis, and cyclic voltammetry. Formation of bis-chelated metal complexes, rather than mono-chelated complexes, was favored in all synthetic conditions explored. The complexes were assessed for their ability to mediate electrocatalytic CO 2 reduction, where the cobalt complex was found to have the best activity for CO 2-to-CO conversion in the presence of water as an added proton source.
ACS Catalysis, 2018
Inspired by the metal active sites of formate dehydrogenase and CO-dehydrogenase, a nickel complex containing a NiS 4 motif with two dithiolene ligands mimicking molybdopterin has been prepared and structurally characterized. During electroreduction, it converts into a good catalyst for the reduction of CO 2 into formate as the major product, together with minor amounts of carbon monoxide and hydrogen, with reasonable overpotential requirement, good faradaic yield and notable stability. Catalysis operates on a mercury electrode and dramatically less on a carbon electrode, as observed in the case of [Ni(cyclam)] 2+ complexes. DFT computations indicate the key role of a Ni(III)-hydride intermediate and provide insights into the different reaction pathways leading to HCOOH, CO and H 2. This study opens the route towards a new class of mononuclear sulfur-coordinated Ni catalysts for CO 2 reduction, unexplored yet.
Nickel(II) Pincer Carbene Complexes: Oxidative Addition of an Aryl C–H Bond to Form a Ni(II) Hydride
Organometallics, 2014
The synthesis and characterization of a series of nickel(II) pincer complexes of the meta-phenylene-bridged bis-N-heterocyclic DIPP CCC ligand framework are reported. Characterization of the Ni(II)Cl complex revealed a square planar species with Cl − and the anionic carbon trans to one another. Formation of Ni(II) alkyl complexes derived from complex 1 was accomplished by addition of LiR [R = CH 3 (2); CH 2 SiMe 3 (3)]. Furthermore, we report a synthetic pathway to access the catalytically relevant Ni(II)H species (DIPP CCC)-NiH (4), by direct oxidative addition of an aryl C−H bond across a Ni(0) center. Complexes 1−4 have been characterized by 1 H and 13 C NMR and electronic absorption spectroscopies as well as X-ray crystallography.