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RESEARCH PRODUCT

Coordination properties of imino(2-pyridyl)methylpalladium(II) compounds. Reactions with the chloride-bridged allyl dimers [MCl(η3-2-MeC3H4)]2 (MPd, Pt)

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Abstract The imino(2-pyridyl)methylpalladium(II) compounds py-2-CR 1 NR [R 1 = trans -PdCl(PPh 3 ) 2 , R = C 6 H 4 OMe- p ( Ia ), Me ( Ib ), CMe 3 ( Ic ); R 1 = Pd(dmtc)(PPh 3 ), R = C 6 H 4 OMe- p ( Id )] react with [MCl(η 3 - 2-MeC 3 H 4 )] 2 (M = Pd, Pt) in a molar ratio 1/0.5 and in the presence of NaClO 4 to yield the binuclear cationic complexes II , [M(η 3 -2-MeC 3 H 4 )(py-2-CR 1 NR)]ClO 4 , where the α-diimino group acts as σ,σ N , N ′ chelating ligand. In the absence of NaClO 4 and with a molar ratio 1/1, the reaction leads initially to formation of a ionic intermediate A , [M(η 3 - 2-MeC 3 H 4 )(py-2-CR 1 NR)] [MCl 2 (η 3 -2-MeC 3 H 4 )], which subsequently undergoes exchange of ancillary ligands between the cationic and anionic species to give the zwitterionic binuclear complexes III , [M(η 3 - 2-MeC 3 H 4 )(py-2-CR 2 NR)] (R 2 = cis -PdCl 2 (PPh 3 )) and [MCl(η 3 -2-MeC 3 H 4 )(PPh 3 )] or [M(η 3 -2- MeC 3 H 4 )(dmtc)]. The rates of ligand migration are strongly dependent on the substituents R 1 and R. The great increase in reactivity when the substituent R is changed from C 6 H 4 OMe- p ( Ia ) to Me ( Ib ) or CMe 3 ( Ic ) is due to a predominant mechanism involving PPh 3 dissociation from the trans -PdCl- (PPh 3 ) 2 unit of the cationic species in the intermediates A . This is supported by the fast formation of Ph 3 PS in the reaction of IIb (R = Me) with an excess of sulphur. No trace of Ph 3 PS is formed in the corresponding reaction with IIa (R = C 6 H 4 - OMe- p ), even after prolonged time. An increased reactivity is also observed when the R 1 group is changed from trans -PdCl(PPh 3 ) 2 to Pd(dmtc)(PPh 3 ). For the reaction Id /[PtCl(η 3 -2-MeC 3 H 4 )] 2 , a mechanism is proposed in which ligand migration occurs by direct interaction of [PtCl 2 (η 3 -2-MeC 3 H 4 )] − with the Pd(dmtc)(PPh 3 ) unit of the cationic species of A . The 1 H and 31 P NMR spectra of III indicate only a diastereoisomer to be initially present in solution. With time, a second diastereoisomer is formed at different rates, depending on the metal M (Pd>Pt), until an equilibrium mixture of c . 1/1 molar ratio is obtained.