109 research outputs found
From Atactic to Isotactic CO/p-Methylstyrene Copolymer by Proper Modifications of Pd(II) Catalysts Bearing Achiral alpha-Diimines
No full textCationic Pd(II) complexes modified with achiral C2v-symmetric α-diimine ligands allow preparation of atactic or isotactic stereoblock CO/p-methylstyrene copolymers; both catalyst activity and polyketone microstructure depend on the choice of α-diimine substituents and counterion
Mechanistic Aspects of Isotactic CO/Styrene Copolymerization Catalyzed by Oxazoline Pd(II) Complexes
No full textCatalytic systems of the type [Pd(CH3)(NCCH3)(N−N)]+[B{3,5-(CF3)2C6H3}4]-, where N−N = (4S,4‘S)-(−)-4,4‘,5,5‘-tetrahydro-4,4‘-bis(1-methylethyl)-2,2‘-bioxazole (BIOX) or N−N = (4S,4‘S)-(−)-2,2‘-(1-methylethylidene)bis[4,5-dihydro-4-(phenylmethyl)oxazole]) (BISOX), afford highly isotactic CO/styrene or p-methylstyrene copolymers. The reactivity of the catalyst with the BIOX ligand toward carbon monoxide was studied and the corresponding methyl carbonyl Pd complex was isolated and identified as the real catalytic species. Starting from this compound the first steps of the copolymerization process were investigated and particular attention was paid to the stereochemistry of the intermediates. Specifically, NOE experiments carried out on the five-membered palladacycle, obtained from the first insertion of p-methylstyrene, indicated that regiochemistry is of the 2,1 type and that one diastereoisomeric species is exclusively generated, with an R configuration of the new −CHAr− stereogenic center. Moreover, the investigation of the intermediate resulting after the second sequence of p-methylstyrene and CO insertion showed the presence of only one diastereoisomer. This evidence indicates that the stereocontrol of the isospecific catalyst is already very efficient at the first stages of copolymerization
Application of NOE and PGSE NMR methodologies to investigate non-covalent intimate inorganic adducts in solution
No full textNOE and PGSE NMR experiments provide crucial information for the structural characterization of non-covalent intimate adducts in solution. The possible presence and the favorite relative orientation of the interacting units can be deduced from NOE results, while the size of the non-covalent adducts can be estimated through PGSE measurements. The complementarity of the two methodologies has been successfully used to investigate transition metal complex ion pairs and, to a lesser extent, intermolecular adducts. The main results concerning the solution structures of non-covalent inorganic adducts are reported and compared with those in the solid state and those from theoretical calculations
Stereochemical Control in CO/p-Methylstyrene Copolymerization Catalyzed by a-Diimine Pd(II) Complexes
No full text
From atactic to isotactic CO/p-methylstyrene copolymerizations by proper modifications of Pd(II) catalysts bearing achiral a-diimines
No full textIntegration of SEWGS for carbon capture in natural gas combined cycle. Part B: Reference case comparison
No full textCationic palladium complexes with mono- and bidentate nitrogen-donor ligands: synthesis, characterization and reactivity in CO/styrene copolymerization reaction
No full text- …
