Zwitterion enhanced performance in palladium–phosphine catalyzed ethylene methoxycarbonylation

Khokarale, Santosh Govind; García-Suárez, Eduardo J.; Xiong, Jianmin; Mentzel, Uffe Vie; Fehrmann, Rasmus; Riisager, Anders

doi:10.1016/j.catcom.2013.09.005

Cited by 11 publications

(10 citation statements)

References 14 publications

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“…The employed BAILs were synthesized in two reaction steps following a slightly different procedure to that previously reported in the literature. 12 The first reaction step involved the synthesis of zwitterions 13 which were subsequently converted to BAILs by reaction with an equimolar amount of the corresponding acid (Scheme 2, see ESI † for details).…”

Section: Synthesis and Characterization Of Brønsted Acid Ionic Liquid...mentioning

confidence: 99%

Pd-catalyzed ethylene methoxycarbonylation with Brønsted acid ionic liquids as promoter and phase-separable reaction media

et al. 2014

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Brønsted acid ionic liquids (BAILs) were prepared and applied as combined acid promoters and reaction media in Pd-phosphine catalyzed methoxycarbonylation of ethylene to produce methyl propionate. The BAILs served as alternatives to common mineral acids required for the reaction, e.g. methanesulfonic acid or sulfuric acid, resulting in high catalytic activity and selectivity towards methyl propionate. In addition, the BAILs yielded a biphasic system with the product and provided stability to palladium intermediates avoiding the undesirable formation of palladium black after reaction. These special features enabled facile methyl propionate separation and recovery of the ionic liquid catalyst system, thus allowing its re-use up to 15 times without apparent loss of catalytic activity or selectivity.Scheme 1 Pd-catalyzed alkoxycarbonylation of olefins. † Electronic supplementary information (ESI) available. See

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Section: Synthesis and Characterization Of Brønsted Acid Ionic Liquid...mentioning

confidence: 99%

Pd-catalyzed ethylene methoxycarbonylation with Brønsted acid ionic liquids as promoter and phase-separable reaction media

et al. 2014

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“…If ligand 2 reacted with metal centers solely as a bis-pyridine-type N Py ,N Py ligand, the zwitterionic core would not be affected and would retain its strong dipolar nature. This could have a beneficial effect in subsequent reactivity studies since it has been shown recently that the addition of an ionic liquid-type zwitterion to a palladium complex improved its catalytic performance in ethylene methoxycarbonylation …”

Section: Resultsmentioning

confidence: 99%

Reversible Switching of the Coordination Modes of a Pyridine-Functionalized Quinonoid Zwitterion; Its Di- and Tetranuclear Palladium Complexes

et al. 2014

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The coordination chemistry of a new functional quinonoid zwitterion (E)-3-oxo-4-((2-(pyridin-2-yl)ethyl)amino)-6-((2-(pyridin-2-yl)ethyl)iminio)cyclohexa-1,4-dienolate (2, H2L), in which a CH2CH2 spacer connects the N substituents of the quinonoid core with a pyridine group, was explored in Pd(II) chemistry. Different coordination modes have been observed, depending on the experimental conditions and the reagents. The reaction of H2L with [Pd(μ-Cl)(dmba)]2 (dmba = o-C6H4CH2NMe2-C,N) afforded the dinuclear complex [{PdCl(dmba)}2(H2L)] (3) in which H2L acts as a NPy,NPy bidentate ligand. Deprotonation of this complex with NaH resulted in the formation of the dinuclear complex [{Pd(dmba)}2(μ-L)] (4) in which a shift of the Pd(II) centers from the NPy sites to the N,O donor sites of the zwitterion core has occurred, resulting in a N2O2 tetradentate behavior of ligand L. Reaction of 4 with HCl regenerates 3 quantitatively. Chloride abstraction from 3 with AgOTf (OTf = trifluoromethanesulfonate) resulted in loss of one of the two dmba ligands and formation of an unusual tetranuclear Pd(II) complex, [{Pd(dmba)}(μ-L)Pd]2(OTf)2 (5), in which two dinuclear entities have dimerized, one pyridine donor group from each dimer forming a bridge with the other dinuclear entity. This results in a N2, O2, NPy, NPy hexadentate behavior for the ligand L. Complexes 3 and 4 constitute an unprecedented reversible, switchable system where deprotonation or protonation promotes the reversible migration of the [Pd(dmba)](+) moieties, from the NPy sites in 3, to the N,O donor sites of the quinonoid core in 4, respectively. This switch modifies the extent of π-delocalization involving the potentially antiaromatic quinonoid moiety and is accompanied by a significant color change, from red in 3 to green in 4. The presence of uncoordinated pyridine donor groups in 4 allowed the use of this complex for the preparation of the neutral tetranuclear complex [{Pd(dmba)}2(μ-L){PdCl(dmba)}2] (6) in which 4 acts as a NPy,NPy-bidentate metalloligand toward two PdCl(dmba) moieties. Halide abstraction from 6 afforded the monocationic, tetranuclear complex [{Pd(dmba)}2(μ-L){Pd(dmba)}2(μ-Cl)]PF6 (7) in which the two Pd(dmba) moieties are connected by ligand L and a bridging chloride. By Cl/PF6 anion metathesis, it was possible to switch quantitatively from complex 6 to 7 and vice versa. All new compounds were unambiguously characterized by IR, NMR, and mass spectroscopy. Single-crystal X-ray diffraction is also available for molecules 2-5 and 7.

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“…Riisager et al presented highly active, stable and selective catalyst systems for making methyl propanoate (17) by ethylene methoxycarbonylation comprising a Pd-PPh 3 complex and four different zwitterions in the presence of small amounts of acids (Scheme 15). 45…”

Section: Short Review Syn Thesismentioning

confidence: 99%

Zwitterionic Imidazolium Salt: Recent Advances in Organocatalysis

et al. 2016

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Imidazole-based zwitterionic-type molten salts have been explored as a new class of organocatalyst in various chemical transformations. It is known that imidazolium motifs provide an unconventional C-H bond for bonding. It is experimentally proven that C2-H of the imidazole moiety plays a crucial role in catalyzing the reaction via electrophilic activation. This review is based on the role of imidazole-based zwitterionic-type molten salts as an organocatalyst for some useful chemical transformations in organic synthesis. One of the most important features of this catalyst is that it can easily be recovered from the reaction media. The recovered catalyst can be reused for subsequent reactions without losing its catalytic activity significantly. 1 Introduction 2 Zwitterionic-type Molten Salt Catalyzed syn-Selective Aza-Henry Reaction 3 Synthesis of 1-(Amidoalkyl)-and 1-(Carbamatoalkyl)-2-naphthols 4 Synthesis of 3-Aminoalkylated Indoles 5 Synthesis of Highly Substituted Imidazoles 6 Synthesis of 5-Substituted 1H-Tetrazoles by the Cycloaddition of Arenecarbonitriles with Sodium Azide 7 Synthesis of 4-Arylidene-2-phenyloxazol-5(4H)-ones 8 Zwitterion-Promoted Ethylene Methoxycarbonylation 9 Synthesis of 5,6-Unsubstituted 1,4-Dihydropyridines 10 Regioselective Ring Opening of Aziridines 11 Conclusions

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Zwitterion enhanced performance in palladium–phosphine catalyzed ethylene methoxycarbonylation

Cited by 11 publications

References 14 publications

Pd-catalyzed ethylene methoxycarbonylation with Brønsted acid ionic liquids as promoter and phase-separable reaction media

Pd-catalyzed ethylene methoxycarbonylation with Brønsted acid ionic liquids as promoter and phase-separable reaction media

Reversible Switching of the Coordination Modes of a Pyridine-Functionalized Quinonoid Zwitterion; Its Di- and Tetranuclear Palladium Complexes

Zwitterionic Imidazolium Salt: Recent Advances in Organocatalysis

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