Mechanism of Alkyne Alkoxycarbonylation at a Pd Catalyst with P,N Hemilabile Ligands: A Density Functional Study

Crawford, Luke; Cole‐Hamilton, David J.; Drent, Eite; Bühl, Michæl

doi:10.1002/chem.201403983

Cited by 84 publications

(53 citation statements)

References 37 publications

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“…We have already proposed a simple ligand modification that should lower the turnover-determining barrier, 51 and further studies along these lines are in progress.…”

Section: ■ Conclusionmentioning

confidence: 99%

Uncovering the Mechanism of Homogeneous Methyl Methacrylate Formation with P,N Chelating Ligands and Palladium: Favored Reaction Channels and Selectivities

2015

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The catalytic alkoxycarbonylation of alkynes via palladium and P,N ligands, studied through a prototypical reaction involving propyne methoxycarbonylation yielding methyl methacrylate, has been explored at the B3PW91-D3/PCM level of density functional theory. Four different reaction routes have been probed in detail, spanning those involving one or two hemilabile P,N ligands and either hydride or carbomethoxy mechanisms. The cycle that is both energetically most plausible and congruent with experimental data involves Pd(0) and two P,N ligands acting cocatalytically in turn to shuffle protons via both protonation and deprotonation reactions. Other mechanisms proposed in the literature can be discounted because they would lead to insurmountable barriers or incorrect selectivities. For the preferred mechanism, the P,N ligand is found to be crucial in determining the strong regioselectivity and intrinsically controls the overall turnover of the catalytic cycle with moderate barriers (ΔG ⧧ of 20.1 to 22.9 kcal/mol) predicted. Furthermore, the necessary acidic conditions are rationalized via a potential dicationic channel. ■ INTRODUCTIONAlkyne alkoxycarbonylation is a transformation with 100% atom efficiency that forms acrylate esters. 1−8 Methoxycarbonylation of propyne yields methyl methacrylate (MMA), a small-molecule feedstock crucial in industry due to its polymer poly(methyl methacrylate), more commonly known as Perspex. This material has a wide range of uses, which include important surgical roles, 9 cosmetics and coatings, and as a rigid transparent plastic for windows, especially in transport. 10 There is also a growing demand from use in LCD screens. 11 Functionalization of propyne yielding the branched product of methoxycarbonylation has received considerable attention, 2,3,5−7 and such chemistry has been extended to higher alkynes such as ethynyl benzene 12 and alkynols. 13 Transition metals are key to many industrial processes, 14−16 and in the example of MMA formation from propyne, palladium complexes with P,N chelating ligands play a key role in this transformation (Scheme 1).Drent has reported that the presence of a P,N ligand, 2-pyridyldiphenylphosphine (2-PyPPh 2 ), is necessary for both high selectivity for the branched product and a high turnover frequency (TOF) for carbonylation. 2,3 Ligands based upon 3-PyPPh 2 , 4-PyPPh 2 , and PPh 3 exhibit a reduced efficiency, suggesting that both the presence and location of the nitrogen atom are important. 2-PyPPh 2 allows the methoxycarbonylation of propyne to proceed under mild conditions of 45°C, attaining a turnover frequency of 40 000 mol (mol Pd h) −1 with a selectivity of ∼99% toward MMA. P,N ligands are known to coordinate in a number of binding modes. While monocoordination and multiple unidentate coordination are typically through the softer phosphorus atom, 17 many structures have been isolated that show chelation. 18−24 2-PyPPh 2 may also coordinate metal (hetero)dimers, 4,25−27 and structures involving iridium suggest that two 2-PyPPh 2 ligands ...

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“…We have already proposed a simple ligand modification that should lower the turnover-determining barrier, 51 and further studies along these lines are in progress.…”

Section: ■ Conclusionmentioning

confidence: 99%

Uncovering the Mechanism of Homogeneous Methyl Methacrylate Formation with P,N Chelating Ligands and Palladium: Favored Reaction Channels and Selectivities

2015

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“…A DFT study of the mechanism of the propyne methoxycarbonylation to produce methyl methacrylate, catalyzed by a Pd complex of 2-pyridyldiphenylphosphine ligand and methanesulphonic acid (MesOH) co-catalyst, has been recently reported [13]. This study proposes two steps where the hemilabile ability of the P,N-donor ligand plays a crucial and distinctive role.…”

Section: Resultsmentioning

confidence: 94%

“…For instance, Pd complexes with P,N-donor ligands are active in the reductive carbonylation of nitroaromatics [10] and CO-alkene polymerization [11,12], but the most important process of this type is undoubtedly the industrial carbonylation of alkynes to produce methyl methacrylate and related products catalyzed by a palladium complex of 2-diphenylphosphino-pyridine (Ph 2 Ppy), Fig. 1 [13]. Furthermore, a Pd(II) complex of 2-(diphenylphosphinoamino)-pyridine (Ph 2 PNHpy) is active in the carbonylation of ethanol to ethyl propionate [14].…”

Section: Introductionmentioning

confidence: 99%

Methoxycarbonylation of Styrene Using a New Type of Palladium Complexes Bearing P,N-donor Ligands as Catalysts

et al. 2015

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Artículo de publicación ISIPalladium complexes of the type [Pd(L)Cl(PPh3)]Cl (L = 2-diphenylphosphinoamino)pyrimidine, or 2-diphenylphosphinoaniline), generated in situ by addition of one equivalent of PPh3 to the corresponding neutral complexes [Pd(L)Cl-2], were tested as catalysts for the methoxycarbonylation of styrene. The catalyst containing the pyrimidinyl ligand shows almost complete chemo- and regioselectivity together with a high conversion rate. However, in identical conditions, the [Pd(Ph2PNHC6H4PPh2)Cl-2] complex, where the P,N-ligand has been replaced by a related bidentate P-donor one, shows a significantly lesser performance.Fondecyt-Chile 112014

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“…[15][16][17][18][19][20][21] However, Gusev 22 recently stated that the continuing use of the B3LYP method may be related to a lack of confidence in the newer methods rather than its performance. Furthermore, Gusev demonstrated that the M06-L functional is a good quality and Fig.…”

Section: Theoretical Methodsmentioning

confidence: 96%

Binuclear cyclooctatetraene–iron carbonyl complexes: examples of fluxionality and valence tautomerism

et al. 2016

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Mechanism of Alkyne Alkoxycarbonylation at a Pd Catalyst with P,N Hemilabile Ligands: A Density Functional Study

Cited by 84 publications

References 37 publications

Uncovering the Mechanism of Homogeneous Methyl Methacrylate Formation with P,N Chelating Ligands and Palladium: Favored Reaction Channels and Selectivities

Uncovering the Mechanism of Homogeneous Methyl Methacrylate Formation with P,N Chelating Ligands and Palladium: Favored Reaction Channels and Selectivities

Methoxycarbonylation of Styrene Using a New Type of Palladium Complexes Bearing P,N-donor Ligands as Catalysts

Binuclear cyclooctatetraene–iron carbonyl complexes: examples of fluxionality and valence tautomerism

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