SYNTHESIS, CRYSTAL-STRUCTURE AND CHARACTERIZATION OF NICKEL(0) ACRYLONITRILE COMPLEXES WITH A BIDENTATE N-DONOR LIGAND

Three nickel(0) acrylonitrile complexes with a bidentate N-donor ligand, [Ni(biL)(AN)(2)] (bit = 4,4'-dimethyl-2,2'-bipyridine (Me(2)bpy); 1, 2,2'-dipyridylamine (dpa); 2, 2,2'-pyridylbenzimidazole (pbi); 3, AN=acrylonitrile), have been prepared and characterized. The crystal structures have been determined by X-ray single-crystal diffraction. Complex 1 is triclinic, space group P1, with a=10.279(2), b=11.071(1), c=7.5409(9) Angstrom, alpha=95.68(1), beta=99.26(1), gamma=85.03(1)degrees, U=840.6(2) Angstrom(3), Z=2, R=0.032 and R(W)=0.038. The nickel atom of 1 is coordinated by two N atoms of Me(2)bpy and the C=C moiety of two AN molecules, providing a distorted tetrahedral geometry. Complexes 2 and 3 have the following crystal data: 2, monoclinic space group P2(1)/n, a=8.755(4), b=13.713(2), c=12.740(2) Angstrom, beta=92.94(2)degrees, U=1527.5(8) Angstrom(3), Z=4, R=0.038 and R(W)=0.039; 3, monoclinic space group P2(1)/n, a=12.829(3), b= 8.068(1), c=17.024(2) Angstrom, beta=107.62(1)degrees, U=1679.5(5) Angstrom(3), Z=4, R=0.033 and R(W)=0.036. The geometries of 2 and 3 are similar to that of 1 except for the dihedral angles. The average Ni-N distance is 2.004, 2.034 and 2.045 Angstrom for 1, 2 and 3, respectively. The average C=C distance of AN is 1.402(2), 1.403(6) and 1.409(4) Angstrom for 1, 2 and 3, respectively. These C=C distances are rather longer than that of free AN (1.343 Angstrom), indicating contribution from a large pi back-donation. The IR and H-1 NMR results also support the presence of pi back-donation.