Mono- and Dinuclear Pincer Nickel Catalyzed Activation and Transformation of C–Cl, C–N, and C–O Bonds

Condensation of 2-NH2C6H4P­(Et)­Ph (2) with pyrrole-2-carboxaldehyde generated 2-(C4H4N-2′-CHN)­C6H4P­(Et)­Ph (3). Treatment of 3 with NaH and followed by (DME)­NiX2 (X = Cl, Br) afforded mononuclear pincer nickel complexes [Ni­{2-(C4H3N-2′-CHN)­C6H4P­(Et)­Ph}­X] (4a, X = Cl; 4b, X = Br). Reaction of [2-NH2C6H4P­(Ph)]2(CH2)n (5a, n = 3; 5b, n = 4) with pyrrole-2-carboxaldehyde or 5-tert-butyl-1H-pyrrole-2-carbaldehyde formed [2-(C4H4N-2′-CHN)­C6H4P­(Ph)]2(CH2)n (6a, n = 3; 6b, n = 4) and [2-(5′-tBuC4H3N-2′-CHN)­C6H4P­(Ph)]2(CH2)4 (6c). Respective treatment of 6a–c with NaH followed by (DME)­NiX2 (X = Cl, Br) gave the dinuclear nickel complexes [Ni­{2-(5′-RC4H2N-2′-CHN)­C6H4P­(Ph)}­X]2(CH2)n (7a, R = H, X = Cl, n = 3; 7b, R = H, X = Cl, n = 4; 7c, R = H, X = Br, n = 4; 7d, R = tBu, X = Cl, n = 4). Catalysis of the complexes for the activation and transformation of C–Cl, C–N, and C–O bonds was evaluated. Complex 7c exhibited excellent catalytic activity in the cross-coupling of aryl chlorides or aryltrimethylammonium iodides with arylzinc reagents as well as of aryl sulfamates with aryl Grignard reagents. The dinuclear nickel complexes 7b–d showed higher catalytic activity than the mononuclear complexes in each type of reaction.