Synthesis and Reactivity of Re(III) and Re(V) Fischer Carbenes

Brown, Caleb A.; Lilly, Cassandra P.; Lambic, Nikola S.; Sommer, Roger D.; Ison, Elon A.

doi:10.1021/acs.organomet.9b00600

Cited by 6 publications

(2 citation statements)

References 61 publications

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“…The ReÀ C5 bond (2.164(2) Å) is appreciably shorter than the ReÀ C1 bond (2.287(3) Å) consistent with their formally different bond orders. The ReÀ C5 bond length is within the range of those reported for amino-carbene complexes L n Re=CR(NR' 2 ) (2.020-2.205 Å), [21,22] while the ReÀ C1 bond length is within the range of those reported for typical ReÀ C(sp 3 ) bond. [23] The C2À C3 bond length (1.349(4) Å) is typical of a C=C double bond.…”

supporting

confidence: 79%

Dewar Metallabenzenes from Reactions of Metallacyclobutadienes with Alkynes

Wei

Sung

et al. 2022

Angewandte Chemie

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Dewar benzenes, the metastable valence isomers of benzenes, have been extensively studied both experimentally and theoretically. In contrast, little is known about Dewar metallabenzenes having a transition metal in the skeletal framework, despite the recent intensive interest in the development of chemistry of metallabenzenes. Herein, we report the isolation and characterization of the first examples of structurally characterized Dewar metallabenzenes. These compounds were generated via unprecedented reactions of metallacyclobutadienes with aminoalkynes.

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supporting

confidence: 79%

Dewar Metallabenzenes from Reactions of Metallacyclobutadienes with Alkynes

Wei

Sung

et al. 2022

Angewandte Chemie

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“…In addition to lowering Δ G ° H2 , the mechanism and kinetics for formation of the metal formyl intermediate are also important to consider in the design of molecular catalysts for CO reduction. Insertion of CO into a M–H bond is generally a thermodynamically unfavorable process, , though exceptions have been reported. − More commonly, metal formyls are generated by intermolecular hydride transfer from a donor species to a metal carbonyl, which could have a large kinetic barrier depending on the identity of the species involved. Achieving the proper balance of thermodynamics, kinetics, and mechanism will be critical to enable efficient CO reduction under mild conditions.…”

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confidence: 99%

Thermodynamic Trends for Reduction of CO by Molecular Complexes

et al. 2021

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Selective reduction of CO 2 into fuels and chemical feedstocks is highly desirable to reduce our dependence on fossil fuels. Most molecular catalysts afford 2e − reduction products, such as CO or HCO 2 − , as opposed to more reduced products. Here we present an analysis of the thermodynamic limitations for reduction of the CO ligand in the form of a series of isostructural group 6 carbonyl complexes, Cp*M(CO) 3 (P(OMe) 3 ) + (M = Cr, Mo, and W). The free energy for stepwise transfer of a hydride (H − ) and a proton (H + ) to the CO ligand, resulting in a hydroxycarbene (CHOH) complex, was measured by equilibration with H − /H + donors and acceptors with known hydricity or acidity. Together, these two reaction steps are equivalent to a net addition of H 2 across the CO ligand. A large and unfavorable free energy for H 2 addition (ΔG°H 2 ) was measured for all three complexes and decreases in the order Cr > Mo > W. The trend for these complexes is opposite to the trend previously reported for group 7 carbonyl complexes, for which ΔG°H 2 decreases moving up the group, Re > Mn. Computational analysis indicates the trends can be described in terms of electrostatic effects, where a low ΔG°H 2 is obtained in complexes that balance the atomic charges of the M−CO fragment of the complex. These findings can be used to design metal carbonyl complexes with a more energetically accessible H 2 addition, which will facilitate the development of molecular catalysts for reduction of CO.

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