Cyclopalladation to form Planar Tridentate [ N-C-N] - Intramolecular Coordination Systems involving Pyridine Donor Groups, including Ligand Synthesis and X-Ray Structural Studies

Abstract

Reaction of palladium(II) acetate with l,3-bis[l - (pyridin-2-yl)ethyl] benzene and 1,3- bis(2-pyridinecarbonyl) benzene results in cyclopalladation and formation of 2,6-bis[l-(pyridin-2-yl)ethyl] phenyl and 2,6-bis(2-pyridinecarbonyl)phenyl complexes [Pd{(NC5H4CHMe)2C6H3}(O2CMe)].1.5H2O (1) and [Pd{(NC5H4CO)2C6H3}(O2CMe)] (4), respectively. X- Ray crystallographic studies reveal square-planar co-ordination and unidentate acetate groups, with tridentate [N-C-N]- intramolecular co-ordination involving two six-membered palladocycle rings. Proton n.m.r. spectra of complex (1) and its chloro-derivative [Pd{(NC5H4CHMe)2C6H3}Cl] (2) indicate the presence of meso and rac diastereoisomers, but the crystal of (1) used for X-ray study contained the meso form only [monoclinic, space group C2/c with a = 26.08(1 ), b = 11.093(6), c = 15.846(7) A, beta = 116.19(3), and Z = 8; R = 0.042 for 2909 'observed' reflections]. Crystals of (4) contain two molecules in the asymmetric unit, with the molecules having different conformations of the tridentate ligand [monoclinic, space group Pc with a = 11.373(6), b = 10.925(6), c = 15.640(10) A, beta = 11 6.98(4), Z = 4; R = 0.043 (both chiralities) for 2677 'observed' reflections]. Syntheses of the new ligands are described.