SYNTHESIS AND FLUXIONAL BEHAVIOR OF INTRAMOLECULAR ETA(2)-ARENE COMPLEXES VIA INSERTION OF SUBSTITUTED 7-OXANORBORNENE INTO PALLADIUM CARBON BONDS

The complexes [C6H6O(CO2CH3)(2)R]PdI(PPh(3)) (R = p-anisyl (4), m-anis yl (5), p-tolyl (6), phenyl (7), 1-naphthyl (8) and 2-thienyl (9)) wer e prepared by treating Pd(PPh(3))(2)(R)I with exo-5,6-dicarbomethoxy-7 -oxanorbornene (3) or from the reaction of Pd(PPh(3))(4) with the corr esponding organic iodide (RI) followed by addition of 3 and methyliodi de. In complexes 4-8, the carbon-carbon double bond between ipso and o rtho positions of the aryl ring attached to the 7-oxanorbornyl group i s weakly bound to the palladium (II) center in a eta 2 fashion, in add ition to the three ligands-the 7-oxanorbornyl group, PPh, and I-. This eta(2)-interaction leads to a dramatic upfield shift of C-13 NMR sign als of the ipso carbons by 30-40 ppm. Variable-temperature NMR studies indicate that complexes 4-7 are nonrigid on the NMR time scale. Rotat ion of the weakly eta(2)-bound aryl group is proposed to account for t he observed fluxional behavior. In contrast to 4-7, 8 is static at roo m temperature, presumably, due to the unsymmetrical nature and the lar ge size of the naphthyl group. In complex 9, the sulfur atom in the th ienyl group is coordinated to the palladium center and no intramolecul ar eta(2)-bonding is involved.