Reductive functionalization of 3d metal–methyl complexes: The greater importance of ligand than metal

Fallah, Hengameh; Cundari, Thomas R.

doi:10.1016/j.comptc.2015.06.011

Cited by 8 publications

(48 citation statements)

References 24 publications

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“…The difference in calculated Gibbs free energies of activation for deprotonation of the Cr II −methyl complex (d 4 Cr II −methyl complex is very low, and it is almost identical with the calculated kinetic barrier of the corresponding RF reaction: i.e., +2.6 kcal/mol. 20 The RF reaction is also highly exergonic (ΔG = −35.5 kcal/mol), but it is less exergonic than deprotonation of the preceding 3d metal (V II −methyl complex) by ∼6 kcal/mol. Deprotonation is also much less exergonic than the corresponding RF reaction, in which the free energy of those products relative to the reactants is −70.2 kcal/mol.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Interestingly, deprotonation is less exergonic than the corresponding RF reaction (ΔG = −63.8 kcal/mol). 20 Figure 2a depicts the structure of the lowest energy quartet transition state for the deprotonation reaction pathway for the vanadium(II)−methyl complex. It has a quartet spin state, and the imaginary frequency, which corresponds to the motion of hydrogen between the methyl group carbon and the hydroxide oxygen atom, is 965i cm −1 .…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Finally, it may be possible to "protect" the methyl from deprotonation by the use of bulky supporting ligands, given that deprotonation requires the nucleophile/base to attack from the side (i.e., roughly perpendicular to the metal−methyl carbon bond axis) as opposed to the linear arrangement seen in reductive functionalization transition states. On the basis of the present research and a previous study of reductive functionalization, 20 and also knowing the importance of utilizing Earth-abundant transition metals in catalysis, 28 this research further suggests that catalysts based on earlier (groups 4−6), heavier transition metals with hard ligands may be interesting subjects for research, since the second and third row metals of groups 7−11 of transition metals are either expensive or radioactive (Tc). Highly exergonic pathways with low free energy barriers were found for C−O bond formation via RF pathways, and therefore to make the reaction closer to thermoneutral, reactants should be stabilized and products should be destabilized.…”

Section: ■ Conclusionmentioning

confidence: 89%

“…20 It was observed that RF reactions of such complexes by hydroxide ion are both kinetically and thermodynamically favorable. However, in practice, while studying a reaction, many possible side reactions may occur and reduce the selectivity of the desired reaction.…”

Section: ■ Introductionmentioning

confidence: 98%

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Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal–Methyl Complexes by Hydroxide Ion: Deprotonation and Metal–Methyl Bond Dissociation

2016

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A DFT study of two possible competitive reactions for reductive functionalization (RF) of metal−methyl complexes ([M II (diimine) 2 (CH 3 )(Cl)], M II = V II through Cu II ) was performed to understand the factors that lower the selectivity of C−O bond forming reactions. One of the possible side reactions is deprotonation of the methyl group, which leads to formation of a methylene complex and water. The other possible side reaction is metal−methyl bond dissociation, which was assessed by calculating the bond dissociation free energies of M− CH 3 bonds. Deprotonation was found to be competitive kinetically for most of the first-row transition-metal−methyl complexes (except for Cr II , Mn II , and Cu II ) but less favorable thermodynamically in comparison to reductive functionalization for all of the studied first-row transition metals. Metal−carbon bond dissociation was found to be less favorable than the RF reactions for most 3d transition-metal complexes studied. Therefore, this study suggests that Earth-abundant catalysts for alkane oxidation should focus on chromium-triad metals. ■ INTRODUCTIONOxidation of light alkanes to their corresponding alcohols, especially methane to methanol, has attracted much attention recently. 1−14 Various computational studies have been done of the catalytic conversion of light alkanes to alcohols. 11−14 For example, in research by Periana and co-workers, the conversion of methane to methanol with a Hg II catalyst model (HgF + ) was studied by ab initio computational methods. 11 The efficiency of the reaction was high, and it was found to be improved by the high solvation energy of the proton. 11 In another computational study by Periana and co-workers, a catalytic mechanism was modeled for the functionalization of a metal−carbon bond. 12 The mechanism deduced from theory was similar to that previously reported by the same research group in which C−H activation occurs via an alkoxo complex (M−OR, M = Ir III ), producing M−R and the desired functionalized product, R− OH. In this mechanism, regeneration of M−OR from M−R took place with O atom donor ligands. Experimental and computational evidence was reported for facile oxygen atom transfer in the conversion of Re VII −R to Re VII −OR with nonperoxo oxygen atom donors. 12 A DFT study of rhodium− amidinate catalysts for methane to methanol conversion was reported by Gunnoe and co-workers. 14 In this study, quantum mechanical virtual screening was applied to select the optimum combination of ligand and solvent. The Rh(NN F ) complex, w h e r e N N F i s b i s ( N -p e n t a fl u o r o p h e n y l ) -pentafluorobenzylamidinate, was identified as a highly promising catalyst for methane to methanol conversion. The transition state barriers at 298 K for methane activation were found to be 27.6 kcal/mol in trifluoroacetic acid (TFAH) and 35.0 kcal/ mol in water; the barriers for functionalization were found to be 36.9 kcal/mol in TFAH and 31.7 kcal/mol in water. 13 In a study by Hush and co-workers, homogeneous conversion of methane to me...

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Conclusionmentioning

confidence: 89%

Section: ■ Introductionmentioning

confidence: 98%

See 2 more Smart Citations

Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal–Methyl Complexes by Hydroxide Ion: Deprotonation and Metal–Methyl Bond Dissociation

2016

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“…This study showed that substitution of the bipyridine ligand with electron withdrawing groups can lower functionalization barriers by greater than 10 kcal/mol, which was attributed to inducing a more electron poor metal center. Cundari and Gunnoe also examined terpyridine-coordinated Rh III -methyl bond functionalization. , Cundari has also used DFT calculations to examine reductive functionalization of first-row transition-metal-methyl reactions . It was found that d-electron occupation could not explain functionalization barrier heights; rather, ligand size and electronics are more important.…”

Section: Resultsmentioning

confidence: 99%

Electrophilic Impact of High-Oxidation State Main-Group Metal and Ligands on Alkane C–H Activation and Functionalization Reactions

et al. 2018

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High-oxidation state main-group metal complexes are potential alternatives to transition metals for electrophilic alkane C−H functionalization reactions. However, there is little known about how selection of the p-block, main-group metal and ligand impact alkane C−H activation and functionalization thermodynamics and reactivity. This work reports density functional theory calculations used to determine qualitative and quantitative features of C−H activation and metal-methyl functionalization energy landscapes for reaction between high-oxidation state d 10 s 0 In III , Tl III , Sn IV , and Pb IV carboxylate complexes with methane. While the main-group metal influences the C−H activation barrier height in a periodic manner, the carboxylate ligand has a much larger quantitative impact on C−H activation with stabilized carboxylate anions inducing the lowest barriers. For metal-methyl reductive functionalization reactions, the main-group metal dramatically influences the barrier heights, which are correlated to reaction thermodynamics and bond heterolysis energies as a model for two-electron reduction energies. Overall, this work begins to outline which main-group metals and carboxylate ligands could be useful for alkane functionalization systems that utilize electrophilic C−H activation and metal-alkyl functionalization reactions.

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DFT investigation of C F bond activation by a low-coordinate cobalt(I) complex

Jiang

Cundari

2017

Computational and Theoretical Chemistry

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Reductive functionalization of 3d metal–methyl complexes: The greater importance of ligand than metal

Abstract: Reductive functionalization of metal-methyl bonds in [M(diimine) 2 (CH 3)(Cl)] complexes (M = V II through Cu II) by nucleophilic attack of hydroxide to yield methanol.

Cited by 8 publications

References 24 publications

Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal–Methyl Complexes by Hydroxide Ion: Deprotonation and Metal–Methyl Bond Dissociation

Theoretical Study of Two Possible Side Reactions for Reductive Functionalization of 3d Metal–Methyl Complexes by Hydroxide Ion: Deprotonation and Metal–Methyl Bond Dissociation

Electrophilic Impact of High-Oxidation State Main-Group Metal and Ligands on Alkane C–H Activation and Functionalization Reactions

DFT investigation of C F bond activation by a low-coordinate cobalt(I) complex

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