Mechanistic Implications for the Ni(I)-Catalyzed Kumada Cross-Coupling Reaction

Abstract

Herein we report on the cross-coupling reaction of phenylmagnesium bromide with aryl halides using the well-defined tetrahedral Ni(I) complex, [(Triphos)Ni I Cl] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane). In the presence of 0.5 mol % [(Triphos)Ni I Cl], good to excellent yields (75-97%) of the respective coupling products within a reaction time of only 2.5 h at room temperature were achieved. Likewise, the tripodal Ni(II)complexes [(κ 2 -Triphos)Ni II Cl 2 ] and [(κ 3 -Triphos)Ni II Cl](X) (X = ClO 4 , BF 4 ) were tested as potential pre-catalysts for the Kumada cross-coupling reaction. While the Ni(II) complexes also afford the coupling products in comparable yields, mechanistic investigations by UV/Vis and electron paramagnetic resonance (EPR) spectroscopy indicate a Ni(I) intermediate as the catalytically active species in the Kumada cross-coupling reaction. Based on experimental findings and density functional theory (DFT) calculations, a plausible Ni(I)-catalyzed reaction mechanism for the Kumada cross-coupling reaction is presented.

Low-coordinate first-row transition metal complexes in catalysis and small molecule activation

“…44 EPR spectroscopy of a stoichiometric mixture of 5b and 4-bromoanisole provided evidence of both Ni(I) and Ni(III) species in solution, providing direct support for the involvement of a Ni(III) intermediate in the catalytic cycle. Such Ni(I)/Ni(III) redox cycles have previously been proposed for a number of nickel catalysts, [45][46][47] but this study provides some of the best direct evidence for the existence of a Ni(III) intermediate. 44 The catalytic cycle proposed by Matsubara et al is presented in Scheme 4.…”

Isolation and Catalytic Reactivity of Mononuclear Palladium(I) Complexes

“…40 In one case, Apfel and coworkers were able to demonstrate that their Ni I complexes stabilized by the Triphos ligand catalyzed the aryl-aryl Kumada cross-coupling at RT with low catalyst loadings (0.5 mol%). 41 However, the complex did not afford any product with an alkyl Grignard, even at elevated temperatures. Another example of a Ni I -catalyzed Kumada cross-coupling has been reported by the Fu group, 42 in which the Ni I Br(Ph-BOX) complex catalyzed a Csp 2 -Csp 3 cross-coupling reaction, the organohalide used was an activated α-halocarbonyl substrate, and the reaction required longer reaction times (20 hr) and slightly higher catalyst loadings (7 mol%).…”

Direct Arylation in the Presence of Palladium Pincer Complexes

“…In addition to some agrochemical compounds, relevant materials such as liquid crystal displays and molecular switches comprise the (hetero)biaryl motif [7][8][9][10]. Among the methods developed for the preparation of (hetero)biaryl compounds, Ullmann, Scholl, and Gomberg-Bachmann reactions are considered to be classical strategies [11][12][13], whereas palladium or nickel-catalyzed cross-coupling reactions (Suzuki-Miyaura [14], Kumada [15], Stille [16] and Negishi couplings [17]) were discovered at the end of the 20th century and have been extensively utilized due to the large substrate scope and milder conditions involved. Nevertheless, pre-activated or functionalized coupling partners are required for the latter cross-coupling reactions, as (hetero)aryl halides or pseudohalides are coupled with organometallic reagents (organoboron, organomagnesium, organotin, organozinc compounds, respectively).…”