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From the catalytic conversion of CO and ethene to polyketone with [Pd(Me)(NCSH4C02Me-2)-(PPh3)]BF4 1, the reaction of ethene with [Pd(COMe)(NC5H4CO2Me-2)-(PPh3)]BF4 2 yields a rare example of an isolable product from the insertion of an unstrained alkene into a Pd-acyl bond, and the crystal structure of [Pd(CH2CH2COMe)-(NCSH4C02Me-2)(PPh3)]BF4 3 showing a novel square-pyramidal intermediate with a weakly interacting oxygen in the apical position.

A series of cationic methylpalladium() complexes containing bidentate N᎐O ligands, of the general formula [PdMe(N᎐O)L]BF 4 (N᎐O = methyl picolinate, methyl 6-methylpicolinate, N,N-diisopropylpicolinamide, 6-methyl-N,N-diisopropylpicolinamide; L = PPh 3 or PCy 3 ) have been prepared and characterised. The solid-state structure of [PdMe(N᎐O)(PPh 3 )]BF 4 (N᎐O = N,N-diisopropylpicolinamide), in comparison with that for the complex with N᎐O = methyl picolinate, indicates a significant lengthening of the Pd᎐P bond [∆(Pd᎐P) = 0.018(3) Å] possibly due to the presence of the more strongly co-ordinating N᎐O ligand. Complexes with L = PPh 3 were found to be active for the copolymerisation of CO and ethylene to give polyketone. The complexes [PdMe(N᎐O)(PPh 3 )]BF 4 (N᎐O = methyl 6-methylpicolinate or diisopropylpicolinamide) have the highest catalytic activities (80 g polymer per g Pd per hour and 58 g polymer per g Pd per hour respectively, at 20 ЊC). Examples of the complexes form simple acyl complexes when treated with CO at room temperature and pressure and the spectroscopic data of the resulting acetyl complexes are reported. The stepwise migratory insertion of CO and ethylene into the complex [PdMe(N᎐O)(PPh 3 )]BF 4 (N᎐O = methyl picolinate) has been carefully monitored and the individual insertion products have been characterised. Insertion of ethylene into the Pd᎐acyl bond of [Pd(COMe)(N᎐O)(PPh 3 )]BF 4 (N᎐O = methyl picolinate) affords one of the first examples of an isolable product from insertion of an unstrained alkene into a Pd᎐acyl bond. A detailed mechanism for the co-reaction of CO and ethylene catalysed by complexes containing chelate ligands with distinct donor groups is discussed and an explanation of the observed reaction behaviour provided. The proposed mechanism represents one of the most comprehensive interpretations of this important reaction.

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Palladium complexes of a series of functionalised phosphines bearing the OPN donor set [2-pyCH(2)P(Ph)CH(2)(CHOCH(2)CH(2)CH(2)), 1; 2-py CH(2)P(Ph)-CH(2)CH(2)(CHOCH(2)CH(2)O), 2; 2-pyCH(2)P(Ph)CH(2)CH(2)CO(2)Me, 3; 2-pyP(Ph)CH(2)(CHOCH(2)CH(2)CH(2)), 4; 2-py = 2-pyridyl] have been prepared and characterised. Ligands 1-3 form five membered P-N chelates which is confirmed for PdCl(2) complexes of and by X-ray crystallography. O-coordination appears to be generally disfavoured although there is evidence of transient O-coordination for selected Pd complexes of 4. Palladium methyl and acetate complexes of all four ligands have been tested for catalytic activity in ethene/CO copolymerisation as well as alkoxy-carbonylation of propyne. Complexes of 1 and 4 show some activity in the copolymerisation reaction and complexes of 4 are active in the methoxy carbonylation of propyne. Unlike related pyridyl(diaryl)phosphines, 4 produces a much more stable catalyst system that does not require large excesses of ligand to maintain activity.