ControllingFirst-Row Catalysts: Amination of Aryland Heteroaryl Chlorides and Bromides with Primary Aliphatic AminesCatalyzed by a BINAP-Ligated Single-Component Ni(0) Complex

摘要

First-row metal complexes often undergo undesirable one-electron redox processes during two-electron steps of catalytic cycles. We report the amination of aryl chlorides and bromides with primary aliphatic amines catalyzed by a well-defined, single-component nickel precursor (BINAP)Ni(η²-NC-Ph) (BINAP = 2,2′-bis(biphenylphosphino)-1,1′-binaphthalene) that minimizes the formation of Ni(I) species and (BINAP)2Ni. The scope of the reaction encompasses electronically varied aryl chlorides and nitrogen-containing heteroaryl chlorides, including pyridine, quinoline, and isoquinoline derivatives. Mechanistic studies support the catalytic cycle involving a Ni(0)/Ni(II) couple for this nickel-catalyzed amination and are inconsistent with a Ni(I) halide intermediate. Monitoring the reaction mixture by ³¹P NMR spectroscopy identified (BINAP)Ni(η²-NC-Ph) as the resting state of the catalyst in the amination of both aryl chlorides and bromides. Kinetic studies showed that the amination of aryl chlorides and bromides is first order in both catalyst and aryl halide and zero order in base and amine. The reaction of a representative aryl chlorideis inverse first order in PhCN, but the reaction of a representativearyl bromide is zero order in PhCN. This difference in the order ofthe reaction in PhCN indicates that the aryl chloride reacts with(BINAP)Ni(0), formed by dissociation PhCN from (BINAP)Ni(η²-NC-Ph), but the aryl bromide directly reacts with (BINAP)Ni(η²-NC-Ph). The overall kinetic behavior is consistent with turnover-limitingoxidative addition of the aryl halide to Ni(0). Several pathways forcatalyst decomposition were identified, such as the formation of thecatalytically inactive bis(amine)-ligated arylnickel(II) chloride,(BINAP)2Ni(0), and the Ni(I) species [(BINAP)Ni(μ-Cl)]2. By using a well-defined nickel complex as catalyst, theformation of (BINAP)2Ni(0) is avoided and the formationof the Ni(I) species [(BINAP)Ni(μ-Cl)]2 is minimized.