Mechanistic Studies of CX Bond Activation at Transition-Metal Centers

Algarra, Andrés G.; Macgregor, Stuart A.; Panetier, Julien A.

doi:10.1016/b978-0-08-097774-4.00929-3

Cited by 7 publications

(13 citation statements)

References 257 publications

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“…As one may expect, binding energies change in the following order: R = ethynyl > vinyl > Me, Ph (Figure ). Various mechanisms of the RX oxidative addition to Pd 0 complexes with different ligands L have been studied in the literature. ,,, In the current work, the accepted mechanism of the concerted oxidative addition of the R–X bond through the transition state 3-TS and leading to the formation of product 4 was considered. All studied oxidative addition reactions are either exothermic (Δ E 1→4 = −38.7 to –42.3 kcal mol –1 for R = Me, Ph, vinyl) or highly exothermic processes (Δ E 1‑Eth→4‑Eth = −62.0 kcal mol –1 ).…”

Section: Resultssupporting

confidence: 79%

“…Let us further consider the thermodynamics of the reaction (Table and Figure S1 in the Supporting Information). According to the calculations, formation of the complexes 4 from the intermediate 2 should be thermodynamically favorable and give rise to an essentially irreversible reaction for all groups R (Table ), which agrees with numerous literature reports for oxidative addition of different R–X reagents (X = halogen) to various Pd 0 complexes. ,,, However, the further reductive elimination of NHC and R ligands via R–NHC coupling is significantly influenced by the group R. Thus, the formation of the complexes 6 from 4 is a thermodynamically unfavorable process for R = Me, Ph. However, if R = ethynyl, an equilibrium between the complexes 4-Eth and 6-Eth is anticipated.…”

Section: Resultssupporting

confidence: 76%

“…The calculated activation barriers correlate well with the theoretical predictions for oxidative addition of R–Br reagents (R = Me, Ph, vinyl) to Pd 0 phosphine complexes. , Geometry changes are in agreement with those expected for the R–X oxidative addition (Figure ). …”

Section: Resultsmentioning

confidence: 99%

“…Formation of complex 4 required overcoming a small (Δ E ⧧ 2‑Ph→3‑TS‑Ph = 10.2 kcal mol –1 for R = Ph) or moderate (Δ E ⧧ 2→3‑TS = 23.3–25.5 kcal mol –1 for R = Me, vinyl, ethynyl) activation barrier (Figure ). The calculated activation barriers correlate well with the theoretical predictions for oxidative addition of R–Br reagents (R = Me, Ph, vinyl) to Pd 0 phosphine complexes. , Geometry changes are in agreement with those expected for the R–X oxidative addition (Figure ). …”

Section: Resultsmentioning

confidence: 99%

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Influence of R–NHC Coupling on the Outcome of R–X Oxidative Addition to Pd/NHC Complexes (R = Me, Ph, Vinyl, Ethynyl)

et al. 2017

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Oxidative addition of organic halides (R−X) to (NHC)Pd 0 L complexes is involved in numerous metalcatalyzed reactions, and this step is expected to afford (NHC)Pd II (R)(X)L intermediate complexes. However, these complexes may undergo further transformation via R−NHC coupling, which removes the NHC ligands from the metal and results in the generation of "bare" NHC-free metal species. The comparative theoretical study carried out in the present work revealed that the kinetic and thermodynamic stability of the (NHC)Pd II (R)(X)L oxidative addition intermediates depends strongly on the nature of the organic group R. The predicted reactivity in the R−NHC coupling process decreases in the following order: R = Vinyl > Ethynyl > Ph > Me. Accordingly, for R = Me, a classical (NHC)Pd II (R)(X)L intermediate can be expected as a product of the oxidative addition step, whereas for R = Ph, the outcome of the oxidative addition may already contain the NHC-free palladium complex. For R = Ethynyl, comparable amounts of both complexes should be formed, while for R = Vinyl, the NHC-free palladium complex can be the major product of the oxidative addition process. Unusual thermodynamic and kinetic instability of the (NHC)Pd(vinyl)(X)L complex and the tendency to vinyl−NHC coupling predicted by the computational modeling has been confirmed by experimental measurements with online mass spectrometric reaction monitoring. Thus, the outcome of the oxidative addition strongly depends on the type of organic group R and the R−NHC coupling process greatly influences the activity and stability of metal catalysts.

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Section: Resultssupporting

confidence: 79%

Section: Resultssupporting

confidence: 76%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Influence of R–NHC Coupling on the Outcome of R–X Oxidative Addition to Pd/NHC Complexes (R = Me, Ph, Vinyl, Ethynyl)

et al. 2017

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“…DFT calculations are used to probe the possible mechanisms of the HDF reactions and explore the competition between C−F and C−H bond activation. 13 ■ RESULTS Experimental Studies on the Hydrodefluorination of C 5 F 5−x H x (x = 0−2) with Ru(NHC)(PPh 3 ) 2 (CO)H 2 (NHC = IPr 1, IMes 2). The most active of the Ru-NHC catalysts, the N-diisopropylphenyl substituted species Ru(IPr)(PPh 3 ) 2 (CO)-H 2 (1), was initially employed for the HDF of a range of fluoropyridines with Et 3 SiH as the reductant.…”

Section: ■ Introductionmentioning

confidence: 99%