F Benvenuti

Selective synthesis of octadienyl and butenyl ethers via reaction of 1,3-butadiene with alcohols catalyzed by homogeneous palladium complexes

The selective synthesis, by telomerization of 1,3-butadiene with alcohols in the presence of palladium catalysts, both of octadienyl ethers (especially from higher linear primary alcohols) and of butenyl ethers is reported. The variation of the alcohol/diene molar ratio plays a decisive role in both the cases, excess of alcohol favouring in the former case the synthesis of octadienyl ethers with respect to octatrienes, being useful in the latter case, together with other factors such as high P/Pd and low Pd/diene molar ratios, to favour the formation of butenyl ethers. It has in fact been discovered that, for palladium catalysts, the formation of butenyl ethers is ruled by a complex mechanism involving both the reversible formation of butenyl ethers and their direct transformation into octadienyl ethers.

Homogeneous telomerization of 1,3-butadiene with alcohols in the presence of palladium catalysts modified by hybrid chelate ligands

Abstract 1,3-Butadiene telomerization with methanol and higher alcohols was investigated in the presence of different palladium(0) and palladium(II) complexes based on hybrid chelate ligands. When P ∩ O ligands were used, the resulting palladium complexes displayed poor activity and low selectivity to telomers, also in the presence of alkoxide promoters. Even worse performances were found when ionic palladium(II) or neutral palladium(0) and palladium(II) complexes based on N ∩ N chelate ligands were employed in combination with alkoxide promoters. Better results were obtained by using ionic palladium(II) complexes with P ∩ N ∩ N ligands in combination with an alkoxide promoter. Very promising results were achieved when the telomerization reaction was catalyzed by palladium(0) complexes obtained in situ from Pd(dba) 2 and P ∩ N ligands. The data are discussed and interpreted in terms of different capability of the chelate ligands, depending on their size and donor power, to give palladium complexes with metal sites at low oxidation state characterized at the same time by a sufficient stability and coordinative unsaturation to promote high catalytic activity and selectivity.

Telomerization of 1,3-butadiene with alcohols catalyzed by homogeneous palladium(0) complexes in the presence of mono- and diphosphine ligands

The homogeneous telomerization of 1,3-butadiene with alcohols for the selective synthesis of linear octadienyl ethers in the presence of catalysts prepared in situ from palladium(0) bis-dibenzylidene-acetone and different mono- and diphosphine ancillary ligands is described. With monophosphines, a correlation between basicity as well as steric hindrance of the ligand and activity and selectivity of the resulting catalyst was found. When diphosphines were used, the effect of the bite of the chelating ligand, as well as its basicity and steric hindrance on the activity and selectivity of the process was studied and discussed in terms of the relative stability of the metallacyclo moieties involved in the catalytic cycle. The above results have allowed to gain more light on the reaction mechanism.

Hydrogenation of organic substrates by an heterogenized catalyst based on a bis(diphenylphosphino)methane polymer-bound palladium(II) complex

Abstract Pd(OAc) 2 undergoes easy and quantitative coordination to a cross-linked styrene/divinylbenzene resin functionalized with bis(diphenylphosphino)methane ligands to yield a supported palladium complex which behaves as a versatile and recyclable heterogenized catalyst for the hydrogenation of nitrocompounds and α,β-unsaturated aldehydes under mild conditions. Whereas nitrobenzene is converted only into aniline, cinnamaldehyde is selectively converted into hydrocinnamaldehyde.

Telomerization of butadiene with methanol catalysed by cationic palladium complexes containing a bidentate phosphinoamino ligand

Abstract The cationic complexes [Pd(η 3 -allyl){Ph 2 P( o -C 6 H 4 NMe 2 )}]PF 6 ( 1 ) and [PdMe(PPh 3 ){Ph 2 P( o -C 6 H 4 NMe 2 )}]CF 3 SO 3 ·C 6 H 6 ( 2 ) catalyse, without any added phosphine, the telomerization reaction of 1,3-butadiene with methanol, showing high chemio- (>95%) and regioselectivity towards the linear 1-methoxy-2,7-octadiene (>93%).

1,3-butadiene telomerization with methanol catalyzed by heterogenized palladium complexes

Abstract The heterogenization of palladium complexes on silica as well as on functionalized styrene/divinylbenzene crosslinked resins and linear poly(styrene) is described. In particular, palladium (0) and palladium (II) derivatives were anchored to the above polymeric systems through their functionalization with bidentate ligands such as acetylacetonate and 1,3-bis(diphenylphosphino)propane moieties. The resulting heterogenized complexes were checked in the catalytic telomerization of 1,3-butadiene with methanol. Their performances were studied in terms of activity and selectivity to telomers. Whereas the heterogenization of palladium complexes either on silica or on polymer resins via the acetylacetonate ligand resulted labile during the catalytic cycle, the polymer-bound palladium complexes via the diphosphine ligand, when activated by an alkoxide, displayed activity and selectivity comparable with those of the corresponding homogeneous counterparts, without appreciable metal leaching in solution.

Synthesis, structural characterization and electrical properties of highly conjugated soluble poly(furan)s

Abstract The polymerization of furan by different oxidants has been studied. Particular attention has been devoted to the nature of the reaction medium in combination with FeCl 3 as oxidizing agent. The use of a polar aprotic solvent with high donicity, such as propionitrile, allows one to obtain soluble oligo(furan)s with an ordered aromatic structure and hence high conjugation degree. These products, when blended with polar polymers such as poly(ethylene- co -vinyl acetate), give rise to films with good mechanical properties which, after I 2 -doping, display electrical conductivity of several orders of magnitude higher than that reported up to date for I 2 -doped powdery and intractable poly(furan)s.

Novel nickel catalysts based on perfluoroalkyl-β-diketone ligands for the selective dimerization of propylene to 2,3-dimethylbutenes

The propylene dimerization to 2,3-dimethylbutenes (DMB) by novel homogeneous catalysts prepared in situ by two alternative routes was described. The former synthetic procedure was based on the oxidative addition of hexafluoro-2,4-pentandione (hfacac) to bis(1,5-cyclooctadiene)nickel(0) [Ni(cod) 2 ] in the presence of an ancillary phosphine ligand and an organoaluminium compound. The latter route consisted in the reaction of bis(perfluoroalkyl-β-diketonato)nickel(II) complexes with the organoaluminium compound in the presence of the phosphine ligand. In this context the novel bis(tetradecafluoro-4,6-nonandionato)nickel(II)·2 dimethylformamide complex [Ni(tdfnd) 2 (dmf) 2 ] was synthesized and its crystal and molecular structures were determined. The catalytic systems obtained with both procedures resulted highly active in the oligomerization of propylene (TOF>20000 h −1 ). In particular, when Ni(hfacac) 2 was combined with the bulky and basic tricyclohexylphosphine (PCy 3 ) and MAO was adopted as co-catalyst a very high regioselectivity to DMB within the C 6 cut was achieved (ca. 90%). The use of Ni(tdfnd) 2 (dmf) 2 in the place of Ni(hfacac) 2 gave similar results under the same reaction conditions. Changing the type of phosphine ligand and the nature of the organoaluminium co-catalyst it was possible to deeply modify both regio- and chemo-selectivity of the process, thus allowing to orientate the reaction towards specific target oligomeric products.

1,3-Butadiene telomerization with methanol catalyzed by heterogenized palladium(II) complexes anchored to polymer-bound bis(diphenylphosphino)methane moieties

The telomerization of 1,3-butadiene with methanol in the presence of heterogenized palladium(II) catalysts, obtained by anchoring the metal on both a styrene/divinylbenzene macroporous resin and a linear poly(styrene) functionalized with bis(diphenylphosphino)methane moieties, is reported. In particular, the activity and selectivity to telomers of the above catalytic systems is compared with the corresponding homogeneous counterpart and with those previously obtained with analogous heterogenized systems via polymer-bound 1,3-bis(diphenylphosphino)propane moieties. The effect of a methoxide promoter is also studied. Finally, the performances and metal leaching in solution of the above heterogenized catalysts are checked after several reaction cycles in order to verify their real heterogeneous character.

Selective propylene dimerization to 2,3-dimethylbutenes by heterogenized polymer-supported β-dithioacetylacetonate nickel(II) precursors activated by organoaluminium co-catalysts

Heterogenized nickel catalysts, prepared in situ by anchoring nickel(II) phosphino complexes to polymer-bound β-dithioacetylacetonate (sacsac) chelate ligands and activated by organoaluminium co-catalysts, have been employed for the selective propylene oligomerization to 2,3-dimethylbutenes (DMB). In particular, the effect of reaction conditions as well as of nature of phosphine ligand and organoaluminium activator was studied. The obtained data have shown that the above catalysts, at temperatures below 0°C and in the presence of chlorobenzene as reaction medium, display a very high activity and selectivity to DMB, when basic and bulky alkyl phosphine ligands and organoaluminium co-catalysts of medium Lewis acidity are used. The performances given above are very similar to those obtained with the corresponding homogeneous catalysts. Flow experiments have allowed to check that the heterogenized catalysts given above are substantially stable, maintaining their performances during the time. No significant metal leaching was detected in the course of the reaction, at least under the adopted conditions, thus suggesting that these polymer-supported nickel catalysts behave as really heterogeneous catalysts, due to the presence of the bidentate sacsac ligand able to permanently fix the metal to the resin.