Synthesis and Characterization of Amido Pincer Complexes of Lithium and Nickel and Catalysis of the Nickel Complexes in the Kumada Cross-Coupling

Reaction of N-benzylidene-2-(diphenylphosphino)benzenamine (2) with Ph2PLi yielded [Li{N{CH(Ph)-PPh2}C6H4(PPh2)-2}] (3), and that with Ph2PCH2Li center dot TMEDA generated [Li{N{CH(Ph)-CH2PPh2}C6H4(PPh2)(2)}] (4). Treatment of 3 with (DME)NiCl2 gave [Ni(Cl){N{CH(Ph)PPh2}C6H4-(PPh2)-2}] (5). Reaction of 4 with (Et3P)(2)NiCl2 afforded [Ni(Cl){N{CH(Ph)CH2PPh2}C6H4(PPh2)-2}] (6). N-(2-(Diphenylphosphino)benzylidene)-2-(diphenylphosphino)benzenamine reacted with LiMe to give [Li{N{CH(Me)C6H4-(PPh2)-2} {C6H4(PPh2)-2})] (8), which reacted with (Et3P)(2)NiCl2 to produce [Ni(Cl){N{CH(Me)C6H4-(PPh2)-2} {C6H4(PPh2)-2})] (9). 2 was converted to iminophosphoranes 2-{ArN=P(Ph-2)}C6H4N=CHPh (Ar = p-MeC6H4, 10a; Ar = 2,6-(Pr2C6H3)-C-i, 10b) by reaction with p-MeC6H4N3 and 2,6-(Pr2C6H3N3)-C-i, respectively. 10a reacted with Ph2PLi and then (DME)NiCl2 to form [Ni(Cl){N{CH(Ph)PPh2}C6H4(P(Ph-2)= NC6H4Me-4}-2}] (11). The respective reaction of 10a and 10b with Ph2PCH2Li center dot TMEDA afforded [Li{N{CH(Ph)CH2PPh2)C6H4(P(Ph-2)=NAr}-2}] (Ar = p-MeC6H4, 12a; Ar = 2,6-(Pr2C6H3)-C-i, 12b). Treatment of 12a and 12b, respectively, with (DME)NiCl2 yielded corresponding nickel complexes [Ni(Cl){N{CH(Ph)CH2PPh2}C6H4{P(Ph2)=NAr}-2}] (Ar = p-MeC6H4, 13a; Ar = 2,6-(Pr2C6H3)-C-i, 13b). Compounds 10a and lob and the lithium complexes 3, 4, 8, 12a, and 12b were characterized by elemental analyses and NMR spectroscopy. The diamagnetic nickel complexes 6, 9, 13a, and 13b were characterized by elemental analyses, NMR spectroscopy, and mass spectra. The paramagnetic nickel complexes 5 and 11 were characterized by elemental analyses and mass spectra. The structures of compounds 2, 6, and 13a were further characterized by single-crystal X-ray diffraction techniques. Catalysis of the nickel complexes in the Kumada cross-coupling was investigated. Complexes 5, 6, 11, and 13a exhibited high catalytic activity, while complexes 9 and 13b showed relatively low catalytic activity.