The nickel pincer complexes [Ni(Cl){N(2-R₂PC₆H₄)(2′-Me₂NC₆H₄)}] (R=Ph, 1 a; R=iPr, 1 b; R=Cy, 1 c) were demonstrated to catalyze cross-coupling of aryl or heteroaryl chlorides with aryllithium compounds under mild reaction conditions. The catalytic activity of 1 a was highest and resulted in biaryl products in 23–96 % yields. A series of aryl chlorides including deactivated ones, such as 1-chloro-4-methoxybenzene, 4-chloro-N,N-dimethylaniline, and 1-chloro-4-methylbenzene, and heteroaryl chlorides, including 2- and 3-chloropyridine, 2-chloro-4-methylquinoline, 2-chlorothiophene, 2-chlorobenzofuran, 2-chlorobenzo[d]oxazole, and 2-chlorobenzo[d]thiazole, were used in this coupling reaction.

The nickel N,N,N-pincer complex 2 was demonstrated to effectively catalyze the cross-coupling of aryl sulfamates with arylzinc chlorides under mild conditions. The reaction is suitable for a wide range of substrates, and tolerates various functional groups.

The nickel-catalyzed cross-coupling reaction of arene- or heteroarenecarbonitriles with aryl- or heteroarylmanganese reagents via CCN bond activation has been developed. Both electron-rich and electron-deficient nitriles can be employed as the electrophilic substrates. The reaction tolerates a range of functional groups and aromatic heterocycles.

Transition-metal-catalyzed cross-coupling reactions are powerful tools for constructing carbon–carbon and carbon–heteroatom bonds. In this microreview we summarize the nickel-catalyzed cross-coupling reactions with pincer ligands. The reactions presented here include Kumada, Negishi, Suzuki, and Sonogashira reactions for the formation of different types of C–C bonds, as well as the thiolation of aryl iodides.

Reaction between 2-(1H-pyrrol-1-yl)benzenamine and 2-hydroxybenzaldehyde or 3,5-di-tert-butyl-2-hydroxybenzaldehyde afforded 2-(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)phenol (HOL¹NH, 1a) or 2,4-di-tert-butyl-6-(4,5-dihydropyrrolo[1,2-a]quinoxalin-4-yl)phenol (HOL²NH, 1b). Both 1a and 1b can be converted to 2-(H-pyrrolo[1,2-a]quinoxalin-4-yl)phenol (HOL³N, 2a) and 2,4-di-tert-butyl-6-(H-pyrrolo[1,2-a]quinoxalin-4-yl)phenol (HOL⁴N, 2b), respectively, by heating 1a and 1b in toluene. Treatment of 1b with an equivalent of AlEt₃ afforded [Al(Et₂)(OL²NH)] (3). Reaction of 1b with two equivalents of AlR₃ (R = Me, Et) gave dinuclear aluminum complexes [(AlR₂)₂(OL²N)] (R = Me, 4a; R = Et, 4b). Refluxing the toluene solution of 4a and 4b, respectively, generated [Al(R₂)(OL⁴N)] (R = Me, 5a; R = Et, 5b). Complexes 5a and 5b were also obtained either by refluxing a mixture of 1b and two equivalents of AlR₃ (R = Me, Et) in toluene or by treatment of 2b with an equivalent of AlR₃ (R = Me, Et). Reaction of 2a with an equivalent of AlMe₃ afforded [Al(Me₂)(OL³N)] (5c). Treatment of 1b with an equivalent of ZnEt₂ at room temperature gave [Zn(Et)(OL²NH)] (6), while reaction of 1b with 0.5 equivalent of ZnEt₂ at 40 °C afforded [Zn(OL²NH)₂] (7). Reaction of 1b with two equivalents of ZnEt₂ from room temperature to 60 °C yielded [Zn(Et)(OL⁴N)] (8). Compound 8 was also obtained either by reaction between 6 and an equivalent of ZnEt₂ from room temperature to 60 °C or by treatment of 2b with an equivalent of ZnEt₂ at room temperature. Reaction of 2b with 0.5 equivalent of ZnEt₂ at room temperature gave [Zn(OL⁴N)₂] (9), which was also formed by heating the toluene solution of 6. All novel compounds were characterized by NMR spectroscopy and elemental analyses. The structures of complexes 3, 5c and 6 were additionally characterized by single-crystal X-ray diffraction techniques. The catalysis of complexes 3, 4a, 5a–c, 6 and 8 toward the ring-opening polymerization of ε-caprolactone was evaluated. Copyright © 2008 John Wiley & Sons, Ltd.