Exploring the reactions of CO<sub>2</sub>with PCP supported nickel complexes

Schmeier, Timothy J.; Hazari, Nilay; Incarvito, Christopher D.; Raskatov, Jevgenij A.

doi:10.1039/c0cc03898a

Cited by 122 publications

(119 citation statements)

References 24 publications

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“…In addition to the resorcinol-derived complexes 1−3, hydride 7 ( Figure 3) bearing an aliphatic backbone was shown by Jonasson and Wendt to react rapidly with CO 2 to give a nickel formate complex. 21 Similarly fast CO 2 insertion was observed by Hazari and co-workers with the phosphine-based nickel pincer hydride complexes (8, 22 9, 23 and 10 23 ), all of which involve a strongly trans-influencing central donor. In contrast, the insertion of CO 2 into PNP-pincer nickel hydrides was reported to be very slow; 11 24 needed 24 h to complete the insertion, whereas 12 25 required 10 days.…”

Section: ■ Nickel Pocop-pincer Complexesmentioning

confidence: 72%

Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

et al. 2015

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CONSPECTUS: The reductions of aldehydes, ketones, and esters to alcohols are important processes for the synthesis of chemicals that are vital to our daily life, and the reduction of CO 2 to methanol is expected to provide key technology for carbon management and energy storage in our future. Catalysts that affect the reduction of carbonyl compounds often contain ruthenium, osmium, or other precious metals. The high and fluctuating price, and the limited availability of these metals, calls for efforts to develop catalysts based on more abundant and less expensive first-row transition metals, such as nickel and iron. The challenge, however, is to identify ligand systems that can increase the thermal stability of the catalysts, enhance their reactivity, and bypass the one-electron pathways that are commonly observed for first-row transition metal complexes. Although many other strategies exist, this Account describes how we have utilized pincer ligands along with other ancillary ligands to accomplish these goals. The bis(phosphinite)-based pincer ligands (also known as POCOP-pincer ligands) create well-defined nickel hydride complexes as efficient catalysts for the hydrosilylation of aldehydes and ketones and the hydroboration of CO 2 to methanol derivatives. The hydride ligands in these complexes are substantially nucleophilic, largely due to the enhancement by the strongly trans-influencing aryl groups. Under the same principle, the pincer-ligated nickel cyanomethyl complexes exhibit remarkably high activity (turnover numbers up to 82,000) for catalytically activating acetonitrile and the addition of H−CH 2 CN across the CO bonds of aldehydes without requiring a base additive. Cyclometalation of bis(phosphinite)-based pincer ligands with low-valent iron species "Fe(PR 3 ) 4 " results in diamagnetic Fe(II) hydride complexes, which are active catalysts for the hydrosilylation of aldehydes and ketones. Mechanistic investigation suggests that the hydride ligand is not delivered to the carbonyl substrates but is important to facilitate ligand dissociation prior to substrate activation. In the presence of CO, the amine-bis(phosphine)-based pincer ligands are also able to stabilize lowspin Fe(II) species. Iron dihydride complexes supported by these ligands are bifunctional as both the FeH and NH moieties participate in the reduction of CO bonds. These iron pincer complexes are among the first iron-based catalysts for the hydrogenation of esters, including fatty acid methyl esters, which find broad applications in industry. Our studies demonstrate that pincer ligands are promising candidates for promoting the first-row transition metal-catalyzed reduction of carbonyl compounds with high efficiency. Further efforts in this research area are likely to lead to more efficient and practical catalysts. ■ INTRODUCTIONOne of the rapidly growing areas of research involves the development of first-row transition metal-based catalysts for chemical transformations. The need for such efforts has been motivated by the fact that prec...

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Section: ■ Nickel Pocop-pincer Complexesmentioning

confidence: 72%

Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

et al. 2015

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“…27) [39]. It can be noted that at least one exception has been reported, proposing no interaction of CO 2 with nickel [52]. For rhodium, CO 2 interaction with the metal may occur prior to the C-C bond formation TS, however, the strength of such an interaction does not correlate with subsequent barriers [37].…”

Section: Trendsmentioning

confidence: 87%

Carbon-carbon bonds with CO2: Insights from computational studies

Obst

Pavlovic

Hopmann

2018

Journal of Organometallic Chemistry

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a b s t r a c tIn this mini-review, we provide an overview of recent computational studies on homogeneous transition metal-catalyzed carbon-carbon bond formation with CO 2 . We cover substitution and addition reactions involving different metals (mainly Ni, Rh, Cu) and substrates (alkanes, alkenes, alkynes, arenes) with focus on the mechanistic details. The CO 2 insertion step is generally found to be rate-limiting. The reported transition state geometries for C-C bond formation mostly display three-membered cyclic arrangements involving the metal and the two reacting carbon atoms, except for reaction with C sp atoms, where acyclic conformations are observed. Other reported exceptions point to that an interaction of CO 2 with the metal catalyst may not be essential. Several studies suggest that Lewis acid additives could help activating CO 2 during C-C bond formation.

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“…7 For a related nickel PCP-pincer system [PCP = 2,6-C 6 H 3 (CH 2 P t Bu 2 ) 2 ], Hazari et al have studied the insertion of CO 2 into NiÀR (R = H, Me, and allyl) bonds. 19 In the present case, CO 2 insertion crosses a barrier of 19.0 kcal/mol (TSa1) and is exergonic by 4.3 kcal/mol. The low barrier and small exergonicity are consistent with the experimental observation that the insertion reaction is rapid and reversible at ambient temperature.…”

Section: Computational Detailsmentioning

confidence: 98%

How Does the Nickel Pincer Complex Catalyze the Conversion of CO₂ to a Methanol Derivative? A Computational Mechanistic Study

et al. 2011

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The mechanistic details of nickel-catalyzed reduction of CO(2) with catecholborane (HBcat) have been studied by DFT calculations. The nickel pincer hydride complex ({2,6-C(6)H(3)(OP(t)Bu(2))(2)}NiH = [Ni]H) has been shown to catalyze the sequential reduction from CO(2) to HCOOBcat, then to CH(2)O, and finally to CH(3)OBcat. Each process is accomplished by a two-step sequence at the nickel center: the insertion of a C═O bond into [Ni]H, followed by the reaction of the insertion product with HBcat. Calculations have predicted the difficulties of observing the possible intermediates such as [Ni]OCH(2)OBcat, [Ni]OBcat, and [Ni]OCH(3), based on the low kinetic barriers and favorable thermodynamics for the decomposition of [Ni]OCH(2)OBcat, as well as the reactions of [Ni]OBcat and [Ni]OCH(3) with HBcat. Compared to the uncatalyzed reactions of HBcat with CO(2), HCOOBcat, and CH(2)O, the nickel hydride catalyst accelerates the H(δ-) transfer by lowering the barriers by 30.1, 12.4, and 19.6 kcal/mol, respectively. In general, the catalytic role of the nickel hydride is similar to that of N-heterocyclic carbene (NHC) catalyst in the hydrosilylation of CO(2). However, the H(δ-) transfer mechanisms used by the two catalysts are completely different. The H(δ-) transfer catalyzed by [Ni]H can be described as hydrogen being shuttled from HBcat to nickel center and then to the C═O bond, and the catalyst changes its integrity during catalysis. In contrast, the NHC catalyst simply exerts an electronic influence to activate either the silane or CO(2), and the integrity of the catalyst remains intact throughout the catalytic cycle. The comparison between [Ni]H and Cp(2)Zr(H)Cl in the stoichiometric reduction of CO(2) has suggested that ligand sterics and metal electronic properties play critical roles in controlling the outcome of the reaction. A bridging methylene diolate complex has been previously observed in the zirconium system, whereas the analogous [Ni]OCH(2)O[Ni] is not a viable intermediate, both kinetically and thermodynamically. Replacing HBcat with PhSiH(3) in the nickel-catalyzed reduction of CO(2) results in a high kinetic barrier for the reaction of [Ni]OOCH with PhSiH(3). Switching silanes to HBcat in NHC-catalyzed reduction of CO(2) generates a very stable NHC adduct of HCOOBcat, which makes the release of NHC less favorable.

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Exploring the reactions of CO₂with PCP supported nickel complexes

Abstract: The reactions of PCP supported Ni hydride, methyl and allyl species with CO(2) to generate Ni carboxylates are described. Computational studies suggest that all three reactions follow different pathways.

Cited by 122 publications

References 24 publications

Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

Carbon-carbon bonds with CO2: Insights from computational studies

How Does the Nickel Pincer Complex Catalyze the Conversion of CO₂ to a Methanol Derivative? A Computational Mechanistic Study

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Exploring the reactions of CO2with PCP supported nickel complexes

Abstract: The reactions of PCP supported Ni hydride, methyl and allyl species with CO(2) to generate Ni carboxylates are described. Computational studies suggest that all three reactions follow different pathways.

Cited by 122 publications

References 24 publications

Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

Nickel and Iron Pincer Complexes as Catalysts for the Reduction of Carbonyl Compounds

Carbon-carbon bonds with CO2: Insights from computational studies

How Does the Nickel Pincer Complex Catalyze the Conversion of CO2 to a Methanol Derivative? A Computational Mechanistic Study

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Exploring the reactions of CO₂with PCP supported nickel complexes

How Does the Nickel Pincer Complex Catalyze the Conversion of CO₂ to a Methanol Derivative? A Computational Mechanistic Study