CYCLOPALLADATION TO FORM PLANAR TRIDENTATE [N-C-N]- INTRAMOLECULAR COORDINATION SYSTEMS INVOLVING PYRIDINE DONOR GROUPS, INCLUDING LIGAND SYNTHESIS AND X-RAY STRUCTURAL STUDIES

Reaction of palladium(II) acetate with 1,3-bis[1-(pyridin-2-yl)ethyl] benzene and 1,3-bis(2-pyridinecarbonyl) benzene results in cyclopalladation and formation of 2,6-bis[1-(pyridin-2-yl)ethyl] phenyl and 2,6-bis( 2-pyridinecarbonyl)phenyl complexes [Pd{(NC5H4CHMe) 2C6H3}(O2CMe)]·1.5H 2O (1) and [Pd{(NC5H4CO)2C 6H3}(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 PdNC3C palladocycle rings. Proton n.m.r. spectra of complex (1) and its chloro-derivative [Pd{(NC5H 4CHMe)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) Å, β = 116.19(3)°, and Z = 8; R = 0.042 for 2 909 '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) Å, β = 116.98(4)°, Z = 4; R = 0.043 (both chiralities) for 2 677 'observed' reflections]. Syntheses of the new ligands are described.