Nickel complexes supported by quinoline-based ligands: synthesis, characterization and catalysis in the cross-coupling of arylzinc reagents and aryl chlorides or aryltrimethylammonium salts.

Lithium and nickel complexes bearing quinoline-based ligands have been synthesized and characterized. Reaction of 8-azidoquinoline with Ph(2)PNHR (R = p-MeC(6)H(4), Bu(t)) affords N-(8-quinolyl)iminophosphoranes RNHP(Ph(2))=N(8-C(9)H(6)N) (1a, R = p-MeC(6)H(4); 1b, R = Bu(t). C(9)H(6)N = quinolyl)). Reaction of 1a with (DME)NiCl(2) generates a nickel complex [NiCl(2){N(8-C(9)H(6)N)=P(Ph(2))NH(p-MeC(6)H(4))}] (2a). Treatment of 1b with (DME)NiCl(2) and following with NaH produces [NiCl{(1,2-C(6)H(4))P(Ph)(NHBu(t))=N(8-C(9)H(6)N)}] (4). Complex 4 was also obtained by reaction of (DME)NiCl(2) with [Li{(1,2-C(6)H(4))P(Ph)(NHBu(t))=N(8-C(9)H(6)N)}] (5) prepared through lithiation of 1b. Reaction of 2-PyCH(2)P(Ph(2))=N(8-C(9)H(6)N) (6, Py = pyridyl) and PhN=C(Ph)CH(2)P(Ph(2))=N(8-C(9)H(6)N) (8), respectively, with (DME)NiCl(2) yields two five-coordinate N,N,N-chelate nickel complexes, [NiCl(2){2-PyCH(2)P(Ph(2))=N(8-C(9)H(6)N)}] (7) and [NiCl(2){PhN=C(Ph)CH(2)P(Ph(2))=N(8-C(9)H(6)N)}] (9). Similar reaction between Ph(2)PCH(2)P(Ph(2))=N(8-C(9)H(6)N) (10) and (DME)NiCl(2) results in five-coordinate N,N,P-chelate nickel complex [NiCl(2){Ph(2)PCH(2)P(Ph(2))=N(8-C(9)H(6)N)}] (11). Treatment of [(8-C(9)H(6)N)N=P(Ph(2))](2)CH(2) (12) [prepared from (Ph(2)P)(2)CH(2) and 2 equiv. of 8-azidoquinoline] with LiBu(n) and (DME)NiCl(2) successively affords [NiCl{(8-C(9)H(6)N)NP(Ph(2))}(2)CH] (13). The new compounds were characterized by (1)H, (13)C and (31)P NMR spectroscopy (for the diamagnetic compounds), IR spectroscopy (for the nickel complexes) and elemental analysis. Complexes 2a, 4, 7, 9, 11 and 13 were also characterized by single-crystal X-ray diffraction techniques. The nickel complexes were evaluated for the catalysis in the cross-coupling reactions of arylzinc reagents with aryl chlorides and aryltrimethylammonium salts. Complex 7 exhibits the highest activity among the complexes in catalyzing the reactions of arylzinc reagents with either aryl chlorides or aryltrimethylammonium bromides.