INSERTION REACTIONS INTO PALLADIUM-CARBON BONDS OF COMPLEXES CONTAINING NEW RIGID BIDENTATE NITROGEN LIGANDS

The neutral complexes Pd(Me)Cl(DPIA) (3) and Pd(Me)CI(DQIA) (4), conta ining the novel rigid bidentate nitrogen ligands (5,6-dihydro-[1]pyrin din-7-ylidene)-isopropylamine (DPIA) and (6,7-dihydro-5H-quinolin-8-yl idene)-isopropylamine (DQIA), respectively, have been synthesized. Com plexes 3 and 4 react quantitatively with CO to give the neutral acylpa lladium complexes Pd(C(O)Me)Cl(DPIA) (6) and Pd(C(O)Me)Cl(DQIA) (7), r espectively. Complexes 3, 4, 6, and 7, which were present as mixtures of the cis and trans isomers, were fully characterized, and in the cas e of complexes 6 and 7 single crystal X-ray structures have been deter mined. The molecular structure of 6 and 7 show a square planar geometr y with the alpha-diimine ligands coordinated in a bidentate fashion wi th comparable bite angles of about 78 degrees. The acylpalladium compl exes 6, 7, and Pd(C(O)Me)Cl(iPr-PyCa) (5), containing the nitrogen lig and 2-(N-2-propanecarbaldimino)pyridine (iPr-PyCa), which is the flexi ble analogue of DPIA and DQIA, react with norbornadiene to yield the i onic alkyl complexes [Pd(C7H8C(O)Me)(DPIA)]Cl (9a), [Pd(C7H8C(O)Me)(DQ IA)]Cl (10a), and [Pd(C7H8C(O)Me)(iPr-PyCa)]Cl (8a), respectively. Int erestingly, the nature of the cr-diimine ligand influences the reactio n rate of the norbornadiene insertion in the order N-N = DQIA much les s than iPr-PyCa < DPIA. Competition experiments and comparison of the crystal data from 6 and 7 indicate that the complexation strength of t he alpha-diimine ligand is exactly opposite to the reactivity of the c orresponding acylpalladium complexes toward norbornadiene, which sugge st a mechanism via intermediates containing a unidentate coordinated a lpha-diimine ligand. (C) 1998 Elsevier Science.