Anna Maria Romano

Polymerization of styrene with nickel complex/methylaluminoxane catalytic systems

Polymerization of styrene using catalytic systems based on nickel derivatives and methylaluminoxane (MAO) was studied. Among tested catalysts, nickel bis(acetylacetonate) and nickel dichloride show the maximum activity. Bis(phosphine)nickel dichlorides exhibit lower activity, depending on the nature of the phosphine ligand. Polymer yields decrease by lowering the catalyst concentration, by increasing the reaction temperature, or by carrying out the polymerization in a polar donor solvent. Weight average molecular weight of most of the prepared polystyrenes ranges from 9000 to 25,000, with polydispersity indexes of 1.6–3.8. However, polystyrene prepared in dioxane solvent exhibits a small fraction of very high molecular weight (about 140,000). From NMR analysis, the products seem generally to be constituted of two polymers with different steric microstructure: atactic polystyrene and partially isotactic polystyrene (ca. 75–85% meso diads). Catalytic site specificity is correlated with the type of nickel ligand, while the effect of reaction temperature is less defined.

Palladium and silver reductive catalyzed carbonylation of nitrobenzene to methyl N-phenylcarbamate

Abstract Methyl N-phenylcarbamate has been synthesized by reductive carbonylation of nitrobenzene. Homogeneous catalytic systems based on palladium and silver salts, 1,10-phenanthroline (phen) and p-toluensulfonic acid (PTS) were found highly active and selective yielding nitrobenzene conversion up to 96%. The effect of Ag Pd molar ratio has been studied. Copper (II) and mercury (II) acetates as cocatalysts in palladium based bimetallic systems also behaved satisfactorily.

New palladium (substituted 1,10-phenanthroline) bis(methoxycarbonyl) complexes [Pd(L–L)(CO2CH3)2]: preparation and structural features

Abstract New complexes of general formula Pd(L–L)(CO 2 CH 3 ) 2 (L–L=1,10-phenanthroline 1 ; 2,9-dimethyl-1,10-phenanthroline 2 ; 4,7-dimethyl-1,10-phenanthroline 3 ; 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline 4 , 3,4,7,8-tetramethyl-1,10-phenanthroline 5 ; and 4,7-diphenyl-1,10-phenanthroline 6 ) were prepared either by exchange reaction between Pd(bipyridine)(CO 2 CH 3 ) 2 7 and the appropriate free ligand or by reacting Pd(L–L)Cl 2 suspended in MeOH under carbon monoxide, at room temperature, in the presence of a base. The structure of 1 was determined ab initio from X-ray powder diffraction data by using a simulated annealing technique and refined by the Rietveld method. 1 crystallizes in the orthorhombic Pbca space group with cell parameters a =8.0787(4), b =16.2797(8), c =22.843(1) A and Z =8.

New efficient catalysts for the aerobic oxidation of ethers

Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported.

Synthesis and crystal structure of an ansa-disilylene-bridged zirconocene complex

Reaction of lithiated 1,1′,2,2′-tetramethyl-disilyl-1,2-bis[2-(4,5,6,7,8-pentahydro)-azulene] (I) with ZrCl4 in THF at −78°C gave the new {1,1′,2,2′-tetramethyl-disilyl-1,2-bis[2-(4,5,6,7,8-pentahydro)-azulenyl]}rcub;zirconium dichloride complex (II) in reasonable yield. It crystallizes in the orthorhombic Pnma space group with a = 19.792(4), b = 18.493(3), c = 7.105(1) Å and Z = 4. The complex (II) is symmetric with respect to a mirror plane passing through the Zr and the two Cl atoms. The coordination geometry of Zr atom is that of a distorted tetrahedron formed by the two Cl atoms and the centroids of the two cyclopentadienyl rings of the pentahydroazulenyl moieties. The Zr—Cl bond lengths are 2.451(2) and 2.419(2) Å and the Zr—C distances vary in the range 2.437(4)–2.588(4) Å.