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

Abstract

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.

Hydrosilylative Reduction of Tertiary Amides to Amines Catalyzed by N‐(Phosphinoaryl)anilido Complexes of Iron and Cobalt

“…1 H NMR (300 MHz, benzene-d 6 ): δ 30. 30,25.71,14.59,13.60,11.43,7.40,5.30,2.91. 1.94,0.61,0.28,À 3.45,À 6.53,À 30.68.…”

Architecture and synthesis of P,N-heterocyclic phosphine ligands

“…Application References pyridyl phosphines OLEDs [13] Heck coupling [14] metal organic frameworks [15] polymerization of lactides [16] alkene hydroxylation [17] addition reaction [18] ethylene oligomerization [19] synthesis of pyrazolines [20] triazolyl phosphines Suzuki cross coupling [21] asymmetric hydrogenation [22] luminescence [23] hydroformylation [24] pyrazolyl phosphines coordination polymers [25] Heck coupling [26] imidazolyl phosphines Suzuki coupling [27] hydroamination [28] OLEDs [29] ethylene oligomerization [30] amination [31] olefin metathesis [32] hydroformylation [33] pyrrolyl phosphines hydroformylation [34,35] ethylene polymerization [36] oxazolyl phosphines asymmetric cycloaddition [37] asymmetric hydrogenation [38] carbonylation of alkynes [39] allylic substitution [40] asymmetric addition [41] allylic amination [42,43] The presence of soft donor atoms such as phosphorus results in the formation of hemilabile ligands. These are multidentate ligands having hard P-donor and soft N-and/or O-donor atoms [44].…”

Highly efficient palladium catalysts supported on nitrogen contained polymers for Suzuki-Miyaura reaction

“…The C\ \P coupling was synthesized according to reference [32]. Pd (OAc) 2 (10.3 mg, 0.046 mmol), 1.1′-bis(diisopropylphosphino) -ferrocene (DIPPF, 3.2 mg, 0.0075 mmol), tris(4-bromophenyl)amine (602.5 mg, 1.25 mmol), di-1-adamantylphosphine (75.6 mg, 0.25 mmol) and NaOtBu (36.0 mg, 0.375 mmol) were added in a Schlenk tube with 2.0 mL of toluene.…”