Probing the utility of palladium complexes supported by morpholine-functionalized <i>N</i>-heterocyclic carbene ligands in Buchwald–Hartwig amination

WheatonCraig, A; Stradiotto, Mark

doi:10.1139/cjc-2013-0132

Cited by 6 publications

(4 citation statements)

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“…As an extension of our previous work on morpholine-functionalized NHC ligands, we have chosen to pursue a directly analogous ligand design in which an o -phenylene group rigidly links the phosphine and NHC donors. A series of NHC–phosphine ligands of this type have been prepared previously by Zhou and co-workers .…”

Section: Resultsmentioning

confidence: 99%

“…However, the reported synthetic route is low-yielding and inconvenient and is limited to diphenylphosphino derivatives. We therefore sought to develop a more convenient and flexible synthetic route similar to what we developed previously for the synthesis of morpholino-functionalized NHC ligands . Such morpholine-functionalized NHC ligands are prepared from o -bromoiodobenzene, whereby the ligand is generated through two palladium-catalyzed C–N cross-coupling steps.…”

Section: Resultsmentioning

confidence: 99%

“…In this context, we were motivated to examine analogous heterobidentate NHC ligands for application in BHA chemistry. Encouraged by the remarkable reactivity properties exhibited by catalysts featuring Mor-DalPhos, we recently developed a heterobidentate ligand variant featuring an NHC in place of the phosphorus donor group . However, these morpholino-tethered NHC ligands performed rather poorly in BHA in comparison with both their monodentate NHC counterparts and Mor-DalPhos.…”

Section: Introductionmentioning

confidence: 99%

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New Phosphine-Functionalized NHC Ligands: Discovery of an Effective Catalyst for the Room-Temperature Amination of Aryl Chlorides with Primary and Secondary Amines

2013

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We report convenient and high-yielding syntheses of new phosphine-functionalized dihydroimidazolium salts and demonstrate their utility as ligand precursors for Buchwald−Hartwig amination. Several examples of the general formula [1-Mes-3-{2-(PR 2 )phenyl}imidazolidin-2-ylium][BF 4 ] have been prepared, where phosphines of varying steric and electronic properties (R = Ph (9), Cy (10), 1-Ad (11)) are tethered by an o-phenylene group. The synthesis was not adaptable to N-aryl groups other than mesityl, giving unexpected phosphonium salt species instead. The synthesis was adapted to flexible benzyl-linked variants of the formula [1-Ar-3-{2-(PCy 2 )benzyl}imidazolidin-2-ylium][BF 4 ], which allowed more steric variation of the dihydroimidazolium Naryl group (Ar = Mes (21), Dipp ( 22)). A preliminary study of these hybrid NHC/P ligands in Buchwald−Hartwig amination catalysis (in situ precatalyst formation) revealed 11 to be the most active of the series. Premixing the isolated free NHC ligand 1-Mes-3-{2-(PAd 2 )phenyl}imidazolidin-2-ylidene ( 23) with [Pd(cinnamyl)Cl] 2 provided a highly active precatalyst that performed well at room temperature and 1 mol % catalyst loading. The system was shown to have an unprecedented ability to arylate both primary alkylamines (monoarylation) and secondary dialkylamines with aryl chlorides at room temperature. Electron-rich and -poor aryl and heteroaryl halides, as well as those featuring ortho substitution, were well tolerated, while substrates featuring both primary and secondary amine groups were selectively arylated at the NH 2 position. Furthermore, a preliminary examination of performance in ammonia arylation and acetone α-arylation showed promising results, giving good conversion and high selectivity for monoarylation in both cases.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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New Phosphine-Functionalized NHC Ligands: Discovery of an Effective Catalyst for the Room-Temperature Amination of Aryl Chlorides with Primary and Secondary Amines

2013

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“…Based upon the earlier research employing morpholinyl aminophenolate metal complexes, − we pondered whether species containing such a structural motif could be considered a privileged class of ligand for polymerization of polar monomers including ε-CL and epoxides. Furthermore, Stradiotto and co-workers have found that morpholinyl-containing phosphines provide exceptionally stable and active catalyst systems for cross-coupling and other important reactions in organic synthesis, − giving further credence to the privileged role that morpholine can play in stabilizing catalytic intermediates. In this paper, we report the synthesis and characterization of a family of cationic aluminum complexes with various counterions and their application as initiators for well-controlled ROP of ε-CL.…”

Section: Introductionmentioning

confidence: 99%

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

2019

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The first structures exhibiting bidentate (N, O) chelation of a morpholine group to a p-block element (aluminum) have been prepared and characterized by X-ray diffraction methods: Al[L] + [WCA] − , where [L] = 4-(2aminoethyl)morpholinylamino-N,N-bis(2-methylene-4,6-tert-butylphenolate) and [WCA] − is a weakly coordinating anion. These compounds are easily synthesized by reacting Al[L]Cl with an equimolar amount of anhydrous Lewis acid and were characterized by elemental analyses, ESI−MS, MALDI−TOF MS, 1 H, 13 C{ 1 H}, and multinuclear NMR spectroscopy. DFT calculations showed that Al[L] + cations containing bidentate NO coordination of the morpholine group are at least 21.1 kJ/mol more stable when compared to hypothetical monodentate (N bound) structures. When combined with protic co-initiators (EtOH, glycerol carbonate), the cationic complexes, where [WCA] − = [GaCl 4 ] − or [InCl 4 ] − , are living catalyst systems for the polymerization of ε-caprolactone, producing polycaprolactone with narrow dispersity (D̵ = 1.00−1.05). Employing glycidol as a co-initiator furnished polymers with narrow dispersity (D̵ = 1.01−1.07) but experimental molecular weights diverged considerably from the calculated values. Similar reactivity toward ROP was observed for all complexes containing a stable [WCA] − but where [WCA] − = [AlCl 4 ] − , upon combination with alcohols, alcoholysis was observed. Kinetic studies (Eyring analyses) allowed the determination of activation parameters, which were consistent with a coordination−insertion mechanism for the catalysts containing [WCA] − = [GaCl 4 ] − or [InCl 4 ] − . End group analyses using MALDI−TOF mass spectrometry and 1 H NMR spectroscopy showed hydroxyl and ester end groups within the polymer, corroborating the proposed mechanism. Stoichiometric reactions of EtOH, glycidol or tert-butyl alcohol with the complex, where [WCA] − = [GaCl 4 ] − , showed protonation of the ligand at the N-morpholine site, which leads to dissociation of this pendent group.

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ChemInform Abstract: Probing the Utility of Palladium Complexes Supported by Morpholine‐Functionalized N‐Heterocyclic Carbene Ligands in Buchwald—Hartwig Amination.

Wheaton

Stradiotto

2014

ChemInform

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Probing the utility of palladium complexes supported by morpholine-functionalized N-heterocyclic carbene ligands in Buchwald–Hartwig amination

Cited by 6 publications

References 32 publications

New Phosphine-Functionalized NHC Ligands: Discovery of an Effective Catalyst for the Room-Temperature Amination of Aryl Chlorides with Primary and Secondary Amines

New Phosphine-Functionalized NHC Ligands: Discovery of an Effective Catalyst for the Room-Temperature Amination of Aryl Chlorides with Primary and Secondary Amines

Morpholine-Stabilized Cationic Aluminum Complexes and Their Reactivity in Ring-Opening Polymerization of ε-Caprolactone

ChemInform Abstract: Probing the Utility of Palladium Complexes Supported by Morpholine‐Functionalized N‐Heterocyclic Carbene Ligands in Buchwald—Hartwig Amination.

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