M Marchionna

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.

A review of low temperature methanol synthesis

It has been more than ten years since the discovery of highly active catalysts which allow low temperature (< 150°C), single pass conversion of syngas to methanol. Detailed studies including catalyst refinements, reactor engineering, and process development have been conducted at the Snamprogetti and Amoco laboratories. The presence of electron-rich metal hydrides is the key to the unusual activity of these catalytic systems. Catalyst deactivation phenomena have till now hampered the development of a commercially viable process.

Striking different behavior in the activation of α-olefins by homogeneous and heterogenized catalysts based on η5-cyclopentadienyl nickel derivatives

Abstract Homogeneous η5-cyclopentadienyl nickel catalysts have been applied to ethylene oligomerization. Their activity, enhanced by the presence of Al(OEt)Et 2 as co-catalyst, resulted the highest up to now reported for this type of complexes. The same catalytic systems were also able to oligomerize propylene as well as ethylene/propylene mixtures. In particular propylene was converted into branched dimers, mostly 2,3-dimethylbutenes. Heterogenization of the above system, carried out by anchoring the nickel derivative to a styrene/divinylbenzene resin properly functionalized with the cyclopentadienyl group, caused a drastic change of the selectivity of the process, ethylene polymerization to HDPE taking place instead of oligomerization.

Hydrogenolysis of formic esters with homogeneous and heterogeneous rhenium catalysts

Abstract The hydrogenolysis of formic esters to methanol, as the second step of the low temperature methanol synthesis from syngas, has been studied using rhenium catalysts. ‘Rhenium blacks’ containing reduced Re(0) species produced ‘in situ’ starting from soluble rhenium precursors like Re 2 O 7 or Re 2 (CO) 10 are active and generally very selective (99%) in the hydrogenation of the formyl group to methanol. Unfortunately this catalyst suffers from CO poisoning: however, the poisoning is reversible and the catalytic activity can be restored by treatment with pure hydrogen. Rhenium catalysts supported on oxides generally are less active and selective: the acid or basic centres of the support, which strongly interact with the oxophilic rhenium cations, make difficult the generation of the active Re(0) species and on other hand promote the decarboxylation of the formic ester.

Alcohols carbonylation to alkyl formates catalyzed by strongly basic resins

Heterogeneous basic polymeric resins were checked as catalysts for the carbonylation of methanol and higher alcohols to alkyl formates and their activity compared with that of the conventional homogeneous systems. The data were interpreted in terms of different morphology, basicity and swelling degree of the strongly basic resins.