Chiral palladium(II) complexes bearing tetradentate nitrogen ligands: synthesis, crystal structure and reactivity towards the polymerization of norbornene

A synthesis for a series of tetrapodal nitrogen ligands (N,N'-dibenzyl-N,N'-di(quinoline-2-methyl)-1,2-ethylene diamine (DBQED, 1), N,N'-dimethyl-N,N'-di(quiqoline-2-methyl)-1,2-ethylene diamine (DMQED, 2) (1R,2R)-(-)-N,N'-di(quinoline-2-methylene) diiminocyclohexane (DQEDC, 3), N,N'-di(quinoline-2-methylene)-1,2-phenylene diimine (DQPD, 4) and for their corresponding neutral and cationic palladium(II) complexes of the types [(1,2,4)PdCl2] (5a, 6a, 7) and [(1,2,3,4)Pd(NCCH3)(x)](Y)(2) (5b, 5c, 6b, 6c, 8, 9), x = 0, 2; Y = BF4-, NO3- is reported. The dicationic palladium(II) complex [Pd(DBQED)(NO3)(2). H2O] (5c) crystallizes in the monoclinic space groups P2(1)/c (no. 14) with a = 11.458(1), b = 15.302(1) Angstrom, c = 20.644(2) Angstrom, beta = 99.23(1)degrees and V = 3572.7 Angstrom(3), Z = 4. All four nitrogen donors are attached, to the Pd(II) center in the chiral and C-2-symmetric complex 5c. The two quinoline nitrogen atoms of the more rigid, Schiff bases (DQEDC, 3; DQPD, 4) do not coordinate coincidentally to Pd(II). A fluxional coordination behavior is suggested for these quinoline donors, which enables this new complex family to act as catalysts for norbornene polymerization, even When chloride is present as a counter ion. Introduction of an enantiomerically pure tans-1,2-cyclohexyl bridge into the Schiff base ligand systems afforded the formation of partially stereoregular polynorbornene. (C) 1999 Elsevier Science S.A. All rights reserved.