Palladium-catalysed C(sp 2 )-N cross-coupling (that is, Buchwald-Hartwig amination) is employed widely in synthetic chemistry, including in the pharmaceutical industry, for the synthesis of (hetero)aniline derivatives. However, the cost and relative scarcity of palladium provides motivation for the development of alternative, more Earth-abundant catalysts for such transformations. Here we disclose an operationally simple and air-stable ligand/nickel(II) pre-catalyst that accommodates the broadest combination of C(sp 2 )-N coupling partners reported to date for any single nickel catalyst, without the need for a precious-metal co-catalyst. Key to the unprecedented performance of this pre-catalyst is the application of the new, sterically demanding yet electron-poor bisphosphine PAd-DalPhos. Featured are the first reports of nickel-catalysed room temperature reactions involving challenging primary alkylamine and ammonia reaction partners employing an unprecedented scope of electrophiles, including transformations involving sought-after (hetero)aryl mesylates for which no capable catalyst system is known.

The use of (L)Ni( o-tolyl)Cl precatalysts (L = PAd-DalPhos or CyPAd-DalPhos) enables the C( sp)-O cross-coupling of primary, secondary, or tertiary aliphatic alcohols with (hetero)aryl electrophiles, including unprecedented examples of such nickel-catalyzed transformations employing (hetero)aryl chlorides, sulfonates, and pivalates. In addition to offering a competitive alternative to palladium catalysis, this work establishes the feasibility of utilizing ancillary ligation as a complementary means of promoting challenging nickel-catalyzed C( sp)-O cross-couplings, without recourse to precious-metal photoredox catalytic methods.

Structurally diverse (hetero)aryl chloride, bromide, and tosylate electrophiles were employed in the Ni-catalyzed monoarylation of ammonia, including chemoselective transformations. The employed JosiPhos/[Ni(cod)2] catalyst system enables the use of commercially available stock solutions of ammonia, or the use of ammonia gas in these reactions, thereby demonstrating the versatility and potential scalability of the reported protocol. Proof-of-principle experiments established that air-stable [(JosiPhos)NiCl2] precatalysts can be employed successfully in such transformations.

The synthesis and characterization of the new airstable precatalyst (L1)Ni(o-tol)Cl (C1; where L1 = JosiPhos CyPF-Cy) is reported, along with the results of a comparative reactivity survey involving C1 and analogous PAd-DalPhos-and DPPFcontaining precatalysts (C2 and C3, respectively) in representative nickel-catalyzed C(sp 2 )−N cross-coupling reactions. Precatalyst C1 was found to be competitive with, and in some cases complementary to, C2 in the monoarylation of ammonia and primary alkylamines with (hetero)aryl chlorides, including in otherwise challenging room temperature transformations. (Pseudo)halide comparison studies involving the cross-coupling of furfurylamine at room temperature revealed that in contrast to C2 precatalyst C1 performs less effectively with aryl bromides. Whereas C3 was found to be ineffective for such transformations, this DPPF-derived precatalyst proved superior to C1 and C2 in reactions involving the secondary dialkylamine test substrate morpholine.

Whereas the metal-catalyzed C­(sp2)–N cross-coupling of cyclopropylamine with aryl electrophiles represents an attractive route to pharmaceutically relevant N-arylcyclopropylamines, few catalysts that are capable of effecting such transformations have been identified. Herein, the nickel-catalyzed C­(sp2)–N cross-coupling of cyclopropylamine and related nucleophiles, including ammonium salts, with (hetero)­aryl (pseudo)­halides is reported for the first time, with the demonstrated scope of reactivity exceeding that displayed by all previously reported catalysts (Pd, Cu, or other). Our preliminary efforts to effect the N-arylation of cyclopropylamine with (hetero)­aryl chlorides at room temperature by use of (L)­NiCl­(o-tolyl) precatalysts (L = PAd-DalPhos, C1; L = JosiPhos CyPF-Cy, C2) were unsuccessful, despite the established efficacy of C1 and C2 in transformations of other primary alkylamines. However, systematic modification of the ancillary ligand (L) structure enabled success in such transformations, with crystallographically characterized (L)­NiCl­(o-tolyl) precatalysts incorporating o-phenylene-bridged bisphosphines featuring phosphatrioxaadamantane and PCy2 (L = L3, CyPAd-DalPhos; C3), P­(o-tolyl)2 and P­(t-Bu)2 (L = L4; C4), or PCy2 and P­(t-Bu)2 (L = L5; C5) donor pairings proving to be particularly effective. In employing the air-stable precatalyst C3 in cross-couplings of cyclopropylamine, substituted electrophiles encompassing an unprecedentedly broad range of heteroaryl (pyridine, isoquinoline, quinoline, quinoxaline, pyrimidine, purine, benzothiophene, and benzothiazole) and (pseudo)­halide (chloride, bromide, mesylate, tosylate, triflate, sulfamate, and carbamate) structures were employed successfully, in the majority of cases under mild conditions (3 mol % of Ni, 25 °C). Preliminary studies also confirmed the ability of C3 to effect the N-arylation of cyclopropanemethylamine hydrochloride and cyclobutylamine hydrochloride under similar conditions. A notable exception in this chemistry was observed specifically in the case of electron-rich aryl chlorides, where the use of C4 in place of C3 proved more effective. In keeping with this observation, catalyst inhibition by 4-chloroanisole was observed in the otherwise efficient cross-coupling of cyclopropylamine and 3-chloropyridine when using C3. Competition studies involving C3 revealed a (pseudo)­halide reactivity preference (Cl > Br, OTs).

The base metal-catalyzed C À Nc ross-coupling of bulky a,a,a-trisubstituted primary alkylamines with (hetero)aryl electrophiles represents ac hallenging and under-developed class of transformations that is of significant potential utility,i ncluding in the synthesis of lipophilic active pharmaceutical ingredients.H erein, we report that an ew,a ir-stable Ni(II) pre-catalyst incorporating the optimizedancillary ligand PhPAd-DalPhos enables such transformations of (hetero)aryl chloride,b romide,a nd tosylate electrophiles to be carried out for the first time with substrate scope rivalling that achieved using state-of-the-art Pd catalysts,including room temperature cross-couplings of (hetero)aryl chlorides that are unprecedented for any catalyst (Pd, Ni, or other).

The first nickel-catalyzed N-arylation of amides with (hetero)aryl (pseudo)halides is reported, enabled by use of the air-stable pre-catalyst (PAd-DalPhos)Ni(o-tolyl)Cl (C1). A range of structurally diverse primary amides and lactams were cross-coupled successfully with activated (hetero)aryl chloride, bromide, triflate, tosylate, mesylate, and sulfamate electrophiles.

This review highlights recent advances in continuous flow strategies toward enabling the use of fluorinated greenhouse gases in fluoroalkylations.