Mono- and Dinuclear Nickel Complexes with Phosphino-, Phosphinito-, and Phosphonitopyridine Ligands: Synthesis, Structures, and Catalytic Oligomerization of Ethylene

The P,N-type ligands 2-[(diphenylphosphino)methyl]pyridine (12), 2-[2-(diphenylphosphino)ethyl]pyridine (13), 2-methyloxy(diphenylphosphino)pyridine (14), 2-methyloxy(dibenzyl-1,2-oxaphosphorino)pyridine (15), and 2-methyloxy(di-tert-butylphosphino)pyridine (16) have been prepared in good yields, and 12 and 13 have been used to synthesize Ni(II) complexes of formula [Ni(P,N)Cl2], 17 (P,N = 12) and 18 (P,N = 13), by reaction with NiCl2 in methanol. The crystal structure of 18 has been determined by X-ray diffraction to be dinuclear with a distorted square-base pyramidal geometry around the Ni(II) centers. To examine the possible influence of the nature of the spacer link between the P and N donor atoms, we compared ligand 13, with a CH2CH2 spacer, with 14 and 16, which have a isosteric CH2-O spacer. Reactions of the phosphinitopyridine ligands 14 and 16 and of the phosphonitopyridine 15 with [NiX2(DME)] (X = Cl or Br) afforded the complexes [Ni(P,N)Cl2] 20 (X = Cl; P,N = 14), 21 (X = Br; P,N = 14), 22 (X =...