A Remote Lewis Acid Trigger Dramatically Accelerates Biaryl Reductive Elimination from a Platinum Complex

Liberman‐Martin, Allegra L.; Bergman, Robert G.; Tilley, T. Don

doi:10.1021/ja404339u

Cited by 49 publications

(44 citation statements)

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“…Of possible interest in this regard is the termination shock (TS), produced by super-magnetosonic reconnection outflows impinging upon dense, closed magnetic loops in a cusp-shaped reconnection geometry (6). Although often invoked in the standard picture of solar flares (7,8) and predicted in numerical simulations (6,(9)(10)(11), its presence has yet to be firmly established observationally and, because of the paucity of direct observation-al evidence, its role as a possible particle accelerator has received limited attention (2,3). Previous reports of coronal hard x-ray (HXR) sources in some flares have shown convincing evidence of the presence of accelerated electrons at or above the top of flare loops (referred to as the "loop-top" hereafter, or LT) (7,12), where a TS is presumably located.…”

Section: -mentioning

confidence: 99%

“…Successful realization of catalytic cycles requires the careful orchestration of elementary steps: Should any step prove particularly slow, the overall rate will become retarded, and in extreme cases, reactivity can be precluded altogether. Although certain stoichiometric additives have been shown to accelerate elementary organometallic reactions (11)(12)(13)(14)(15), the catalysis of such reactions is less common (16)(17)(18). Rather than altering catalyst structure in a way that influences each elementary step, a synthetic microenvironment catalyst could be leveraged to specifically target one step without sacrificing reactivity elsewhere along the catalytic cycle, enabling an otherwise inaccessible catalytic process.…”

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confidence: 99%

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A supramolecular microenvironment strategy for transition metal catalysis

Kaphan

Levin

Bergman

et al. 2015

Science

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422

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A self-assembled supramolecular complex is reported to catalyze alkyl-alkyl reductive elimination from high-valent transition metal complexes [such as gold(III) and platinum(IV)], the central bond-forming elementary step in many catalytic processes. The catalytic microenvironment of the supramolecular assembly acts as a functional enzyme mimic, applying the concepts of enzymatic catalysis to a reactivity manifold not represented in biology. Kinetic experiments delineate a Michaelis-Menten-type mechanism, with measured rate accelerations (k(cat)/k(uncat)) up to 1.9 × 10(7) (here k(cat) and k(uncat) are the Michaelis-Menten enzymatic rate constant and observed uncatalyzed rate constant, respectively). This modality has further been incorporated into a dual catalytic cross-coupling reaction, which requires both the supramolecular microenvironment catalyst and the transition metal catalyst operating in concert to achieve efficient turnover.

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Section: -mentioning

confidence: 99%

mentioning

confidence: 99%

A supramolecular microenvironment strategy for transition metal catalysis

Kaphan

Levin

Bergman

et al. 2015

Science

Self Cite

422

352

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“…The control over the metal electronic character via remote binding of a Lewis acid resembles effects reported by Nolan and Moloy, 86 and Bergman and Tilley. 87 Further examples demonstrate that Lewis acid cocatalysts can enable challenging C-N coupling reactions. chloride 80 with 78 catalysed by Pd 2 (dba) 3 /xantphos yields 78 in only 3% yield.…”

Section: Enabling Transmetalation and Reductive Elimination With Lewimentioning

confidence: 99%

The roles of Lewis acidic additives in organotransition metal catalysis

Becica

Dobereiner

2019

Org. Biomol. Chem.

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“…The latter phenomenon resembles the accelerating effect of ligand−Lewis acid interactions on reductive elimination, for which there are both stoichiometric 8 and catalytic examples, such as hydrocyanation. 9 We stress that this qualitative picture is based on an understanding of Lewis acid interactions with aldehydes and ketones.…”

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confidence: 96%

Palladium and Platinum Acyl Complexes and Their Lewis Acid Adducts. Experimental and Computational Study of Thermodynamics and Bonding

2015

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The interactions of Pt and Pd acyl complexes with Lewis acids are investigated through experiment and computation. Variabletemperature NMR studies indicate BF 3 association with trans-[(PPh 3 ) 2 (CO)Pt(COCH 2 Ph)] [BAr F 4 ] (3; BAr F 4 = tetrakis(3,5-bis-(trifluoromethyl)phenyl)borate) at 298 K is endergonic (ΔG°= 2.0 kcal mol −1 ) yet exothermic (ΔH°= −3.4 kcal mol −1 ), suggesting a Lewis basicity comparable to or greater than aldehydes and ketones. Despite the accelerating effect of Lewis acids in the formation of the Pd congener trans-[(PPh 3 ) 2 (CO)Pd(COCH 2 Ph)][BAr F 4 ] (4), no evidence for adduct formation was obtained. DFT (M06-L/def2-TZVP/QZVP) suggests that BF 3 /trans-[(PPh 3 ) 2 (CO)M(COCH 2 Ph)] + adduct formation is more favored for M = Pt than M = Pd. Natural bond orbital analysis shows that upon Lewis acid coordination, the acyl C−O bond is weakened, the natural charge of the acyl C is more positive, and the π* acyl C−O orbital is lowered in energy relative to other unoccupied orbitals. ■ INTRODUCTIONLewis acids promote metal-centered reactivity through ligandbased interactions with transition metal complexes, 1 such as facilitating migratory insertion of CO. 2 Shriver and co-workers established that Lewis acids can accelerate CO insertion into metal−carbon bonds and stabilize the resulting acyl complexes through association to the acyl oxygen. 3 Since Shriver's seminal work, only a handful of reports 4 address the thermodynamic stability of Lewis acid−acyl adducts. Moreover, Lewis acids are seldom added to transition-metal-catalyzed carbonylations, 5 despite the likelihood of acyl intermediates in these reactions.A Lewis acid should increase acyl electrophilicity for the same reasons that Lewis acids influence organic carbonyl reactivity. Chart 1 shows illustrations comparing the LUMO of organic carbonyls and acyls. 6 Early metal η 2 -acyls are highly electrophilic at the acyl carbon, 7 and Lewis acid O-coordination to η 1 -acyl complexes should similarly polarize the acyl carbon and decrease the LUMO (π* CO ) energy. Rare, late transition metal η 2 -acyl complexes have reduced electrophilicity due to dπ/π* CO interactions. 7 However, such overlap is minimized in η 1 coordination shown in Chart 1, bottom.A lower LUMO energy could (a) make π* CO more available for reactions with exogenous nucleophiles and (b) promote internal attack by nucleophilic coligands, such as amines or alkyl ligands. The latter phenomenon resembles the accelerating effect of ligand−Lewis acid interactions on reductive elimination, for which there are both stoichiometric 8 and catalytic examples, such as hydrocyanation. 9 We stress that this qualitative picture is based on an understanding of Lewis acid interactions with aldehydes and ketones. Shriver and co-workers 3 rationalized the C−O acyl bond lengthening of CpFeL 2 (COR) upon BF 3 binding as a resonance effect, shortening the M−C bond and increasing Fischer carbene character. Later theoretical work by Green and co-workers 10 provided a more nuanced picture: the...

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A Remote Lewis Acid Trigger Dramatically Accelerates Biaryl Reductive Elimination from a Platinum Complex

Cited by 49 publications

References 17 publications

A supramolecular microenvironment strategy for transition metal catalysis

A supramolecular microenvironment strategy for transition metal catalysis

The roles of Lewis acidic additives in organotransition metal catalysis

Palladium and Platinum Acyl Complexes and Their Lewis Acid Adducts. Experimental and Computational Study of Thermodynamics and Bonding

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