NMR-STUDY ON THE COORDINATION BEHAVIOR OF DISSYMMETRIC TERDENTATE TRINITROGEN LIGANDS ON METHYLPALLADIUM(II) COMPOUNDS

Neutral compounds of the type [(6-RC(5)H(3)N-2-C=NCH2CH2-2-C5H4N)Pd(CH 3)(Cl)] (R = H (MAP), CH3 (6'-CH3-MAP)) have been synthesized starting from [(cyclooctadiene)Pd(CH3)(Cl)], while ionic compounds of the type (3)N-2-C=NCH2CH2-2-C5H4N)Pd(CH3)](+)[(Y)](-)(Y=Cl, CF3SO3,NO3;R=H,CH3 ) were formed by reacting the chlorides in a polar solvent with silver triflate and silver nitrate, respectively. An X-ray structure of the ionic compound [(C5H4N-2-C=NCH2CH2-2-C5H4N)Pd(CH3)(CF3SO3)] is present ed. The crystals are of the triclinic spacegroup P-1(-), with a=7.690( 1)Angstrom, b=8.653(2)Angstrom, c=13.888(1) Angstrom, alpha=98.01(1)de grees, beta=99.83(1)degrees, and gamma=95.55(1)degrees. The X-ray stru cture shows a square planar palladium complex in which the MAP ligand is terdentate coordinated to the palladium atom. The fourth coordinati on site is occupied by the methyl ligand. The triflate anion is not co ordinating. The methyl-palladium distance is 2.024(8) Angstrom; the le ngths of the palladium-nitrogen bonds are 2.039(7), 2.058(7),and 2.024 (8) Angstrom for N(1), N(2), and N(3), respectively. The neutral compo unds exist in various isomeric forms. In a noncoordinating solvent, a bidentate coordination of the alpha-diimine moiety is preferred at ele vated temperatures. At lower temperatures, a terdentate coordination f ashion of the ligands is preferred, resulting in five-coordinate compo unds. For N-N-N = MAP, a square pyramidal five-coordinate configuratio n is observed, whereas for 6'-CH3-MAP an initially formed ionic square planar configuration at 223 K isomerizes to a trigonal bipyramidal fi ve-coordinate configuration. These isomerization reactions proved to b e reversible. In a polar solvent both neutral and ionic compounds were observed in a varying ratio for both ligands. The neutral and the ion ic compounds could reversibly be converted into each other by intercha nging the solvent. Synthesis in benzene or diethyl ether of [(6-CH3C5H 3N-2-C=NCH2CH2-2-C5H4N)Pd(CH3)(Cl)] resulted in the formation of two k inetic products. These consist of a bidentate coordination of the liga nd with the nitrogen atoms of the NCH2CH2C5H4N moiety, resulting in a six-membered ring, in a cis isomer, and in a trans isomer. The kinetic products could be converted into the mixture of thermodynamic isomers in which the ligand is bidentate coordinated with the alpha-diimine m oiety, vide supra, upon heating. The mechanisms of the ligand rearrang ements in the palladium complexes are discussed.