INFLUENCE OF LIGANDS AND ANIONS ON THE INSERTION OF ALKENES INTO PALLADIUM ACYL AND PALLADIUM CARBOMETHOXY BONDS IN THE NEUTRAL COMPLEX (DPPP)PD(C(O)CH3)CL AND THE IONIC COMPLEXES [(P-P)PDR(L)]+SO3CF3- (P-P = DPPE, DPPP, DPPB, R = C(O)CH3, L = CH3CN, PPH3, R = C(O)OCH3, L = PPH3)

Insertions of alkenes in Pd-acetyl bonds of (dppp)Pd(C(O)CH3)Cl and [(P-P)Pd(C(O)CH3)-L)]+ SO3CF3- (P-P = dppe, dppp, dppb; L = CH3CN, PPh3) have been studied as a function of the ligand, the anion and the alkene. The neutral acetyl complex (dppp)Pd(C(O)CH3)Cl underwent insertion only with norbornadiene and norbornene, while the ionic acetyl complexes [(P-P)Pd(C(O)CH3)(L)]+ SO3CF3- (P-P = dppe, dppp, dppb) reacted with norbornadiene, norbornene, styrene, cis-stilbene, 1-pentene, 3,3-dimethyl-1-butene, vinyltrimethylsilane, methyl vinyl ketone, methyl acrylate, diethyl fumarate, and diethyl maleate. The insertion was observed to give an intermediate in which there was intramolecular coordination of the ketone oxygen atom to the palladium centre. In monosubstituted alkenes the acetyl group migrates to the unsubstituted carbon atom. The insertion products underwent beta-elimination to give (trans) unsaturated ketones and a palladium hydride. The rate of this elimination was higher for complexes containing ligands L-L with smaller bite angles (dppe > dppp), and the rate of insertion showed the reverse order. The carbomethoxy complexes [(P-P)Pd(C(O)OCH3)(PPh3)]+ SO3CF3- (P-P = dppe, dppp, dppb) were prepared from (P-P)Pd(SO3CF3)2 with CO, CH3OH and PPh3. The carbomethoxy complex reacted with norbornadiene to give a carbomethoxy oxgyen-coordinated intermediate. The carbomethoxy complexes were less reactive than the analogous acetyl complexes towards alkenes.