INSERTION REACTIONS INVOLVING PALLADIUM COMPLEXES WITH NITROGEN LIGANDS .2. CARBON-MONOXIDE AND ALKENE INSERTION REACTIONS WITH NOVEL PALLADIUM COMPOUNDS CONTAINING TERDENTATE LIGANDS

Neutral and ionic methylpalladium compounds containing trinitrogen lig ands (N-N-N)-Pd(Me)(Y) (N-N-N = trinitrogen ligand; Y = Cl-, CF3SO3-, 4-Me-C6H4SO3-) have been synthesized and characterized by spectroscopi c methods. The coordination mode of the trinitrogen ligand depends not only on the rigidity of the ligand but also on the solvent and on the anion Y. With the weakly coordinating ligands CF3SO3- and BF4- the tr initrogen ligands readily adopt a terdentate coordination mode, result ing in complexes of the type [(sigma(3)-N-N-N)Pd(Me)]Y. In methylchlor opalladium compounds, the flexible trinitrogen ligands adopt a bidenta te coordination mode, resulting in the complexes (sigma(2)-N-N-N)Pd(Me )(Cl), whereas the terdentate coordination mode has been found for rig id ligands, resulting in the ionic complexes [(sigma(3)-N-N-N)Pd(Me]CI . Polar solvents, such as acetonitrile, stabilize the formation of ion ic complexes. The methylpalladium compounds readily insert carbon mono ;dde, resulting in the facile formation of the acetylpalladium compoun ds (sigma(2)-N-N-N)Pd(C(O)Me)(Cl) and [(sigma(3)-N-N-N)Pd(C(O)Me)]Y CY = Cl-, OTf(-)), in which the coordination mode of the ligands remains unchanged. CO insertion half-lives of the methylpalladium compounds s how that substituents adjacent to one nitrogen donor atom accelerate t he insertion for both the neutral and the ionic complexes. Interesting ly, the CO insertion half-life is not correlated to the rigidity of th e trinitrogen ligand, since the compound [(terpy)Pd(Me)]Cl, which cont ains the rigid ligand terpy, undergoes a faster carbon monoxide insert ion than analogous complexes with the flexible ligands C5H4N-2-C(H)=N( CH2)(2)C5H4N. Alkene insertion has been tested by reacting the acetylp alladium compounds with norbornadiene (NBD). The NBD-inserted compound s contain the C7H8C(O)CH3 moiety coordinating in an unprecedented mono dentate sigma-C fashion. Peculiarly, [(terpy)Pd(C(O)Me)]Cl not only un dergoes NBD insertion but does so at a very high rate. On the basis of these findings a tentative mechanism is suggested.