Giovanni Carturan

Atomically dispersed palladium as a borderline case between heterogeneous and homogeneous hydrogenation of olefins

Highly dispersed palladium was prepared by reacting diallylpalladium with vitreous supports and reducing with molecular hydrogen. The conversion of 1-hexene, 1-heptene, cyclohexene, 1-octene, 2-methyl-2-butene, and cyclooctene on the most active of these catalysts, which had a palladium particle size distribution of 2-20 A., was independent of olefin concentration, which is characteristic of heterogeneous catalysis, was apparently controlled by the rate of hydrogen activation, and had rate constants which decreased in the above order of olefins. The dependence of the catalytic activity on the olefin species suggested that bond formation between olefin and palladium precedes the hydrogen activation, as in homogeneous catalysis. The hydrogenation of 1,5-cyclooctadiene, 1,3-cyclooctadiene, dicyclopentadiene, 1,4-octadiene, and 1,7-octadiene proceeded in two pseudo-zero-order steps without isomerization during the first step. The ratios of the first and second step rate constants were always Vertical Bar3:Vertical Bar3: 1, were independent of palladium particle size and concentration, and were higher for cyclic than linear dienes.

Selective hydrogenation of dienes to monoenes catalyzed by allyl-Pd(II) complexes

Abstract Hydrogenation of 1,5-COD, 1,3-COD, 1,4-octadiene and 1,7-octadiene to the corresponding monoenes has been carried out under mild conditions, using different (allyl)Pd(II) derivatives in N,N-dimethylacetamide solution. Experiments on the 1,3-COD system suggest a mechanism involving the formation of hydrido-Pd(II) species followed by insertion of diene to restore the allylic moiety. Non conjugated dienes are isomerized prior to hydrogenation. The complete selectivity appears to result from an intrinsic property due to formation of η 3 -allylic intermediates.

Synthesis of Novel σ-allyl platinum(II) complexes

The reaction of [Pt(allyl)Cl]4 with isocyanides gives dimeric allyl complexes of type [Pt(σ-allyl)(CNR)Cl]2 (R = CH3, C6H11, and 2,6-dimethylphenyl) which dissolved in CH2Cl2 lead to [(η3-allyl)Pt(CNR)Cl] derivatives. These latter react further with isocyanides to give the novel complexes [(σ-allyl)Pt(CNR)2Cl]. The mode of coordination of the allyl group has been studied by PMR and IR spectroscopy. The results obtained are compared with those related to the analogous palladium derivatives and methoxydienyl-PtII complexes.

Isomerization, ligand exchange and solvent effect in the η1 ⇄ η3 allyl conversion of [(η1-allyl)Pt(PPh3)(2,6-Me2C6H3NC)Cl]

Abstract The behaviour of the title compound was studied in toluene and in CH 2 Cl 2 solution by 1 H and 31 P NMR spectroscopy at various temperatures. In toluene at low temperature only one η 1 -allyl species is present, whereas in CH 2 Cl 2 five species are present, among which are the possible isomers of [(η 1 -allyl)Pt(PPh 3 )(2,6-Me 2 C 6 H 3 NC)Cl], [(η 3 -C 3 H 5 )Pt(PPh 3 ) 2 ] Cl and [(η 1 -C 3 H 5 )Pt(2,6-Me 2 C 6 H 3 NC) 2 Cl]. This behaviour has been discussed in terms of ligands exchange and isormerization reactions which take place along with the η 1 ⇄ η 3 allyl conversion.

η1 ⇌ η3 Conversion of [(η1-allyl)Pt(PPh3)(CH3NC)Cl] in CH2Cl2 solution

Abstract PMR and 31P NMR spectroscopy on dichloromethane solution of the title compound indicates at room temperature extensive η1 ⇌ η3 ally conversion through PPh3, Cl− and CH3NC and ligand displacements. At lower temperatures this conversion occurs to a far lower extent this conversion occurs to a cement; possible structure isomers of the title compound are also assumed isomers at lower temperatured.

Tetracyanoethylene addition to Fe (allyl)2(CO)2: occurrence of a 16-electron Fe(II) complex

Addition conduisant a un complexe Fe(η 3 -allyl) (−CHCH 2 -C(CN) 2 C(CN) 2 -CH 2 ) (CO) 2 ) qui reagit avec PPH 3 pour donner Fe(η 3 -C 3 H 5 ) (−CHCH 2 C(CN) 2 C(CN) 2 −CH 2 ) (CO) 2 (PPh 3 )