Roberto Santi

Polymerization of 1,3-dienes with iron complexes based catalysts: Influence of the ligand on catalyst activity and stereospecificity

Abstract Various iron dichloride complexes with aliphatic and aromatic bidentate amine ligands have been synthesized and used, in combination with aluminium-compounds (AlR3 or methylaluminoxane (MAO)), for the polymerization of 1,3-dienes. Catalyst activity, chemo- and stereoselectivity are strongly influenced by the type of ligand; systems based on iron complexes with aromatic bidentate amines (e.g. bypiridine or phenantroline), in particular, exhibit an extremely high activity, giving from butadiene a 1,2-syndiotactic polymer. These systems are also able to polymerize substituted butadienes (e.g. isoprene, (E)-1,3-pentadiene, 2,3-dimethyl-1,3-butadiene) giving polymers with different structure from the different monomers; these results have permitted to confirm some aspects of the polymerization mechanism previously proposed.

Synthesis and Structural Characterization of Iron(II) Derivatives of Heterocyclic Tridentate Amines

Abstract Compounds of general formula FeX2(L) {L=2,6-bis(3,5-dimethyl-N-pyrazolyl)pyridine, C15H17N5; bis[3,5-dimethyl-N-pyrazolyl)methyl]-isopropylamine, C15H25N5; bis(benzimidazol-2-yl-methyl)amine, C16H15N5, 1,3-bis(benzimidazolyl)propane, C17H16N4; bis(benzimidazolyl-2-methyl)ether, C16H14N4O; bis(benzimidazolyl-2-methyl)thioether, C16H14N4S} have been synthesized by reacting the amine with Fe4Cl8(THF)6 or FeI2(CO)4 in toluene. The complexes FeCl2(C15H17N5)·MeCN and FeCl2(C16H15N5)(MeOH) have been characterized by single crystal X-ray diffraction together with the parent triamines, C15H17N5 and C16H15N5, for comparison. The reaction of FeI2(CO)4 with bis(benzimidazolyl-2-methyl)thioether, C16H14N4S, led to the product of partial carbonyl substitution FeI2(CO)2(C16H14N4S).

Synthesis and characterization of some trans-hydridomethylbis(phosphine)-platinum(II) and -palladium(II) complexes

Abstract Several trans -hydridomethylbis(phosphine)-platinum(II) and -palladium(II) complexes have been made by the reaction: trans -M(H)Cl(PR 3 ) 2 + CH 3 MgBr → trans -M(CH 3 )(PR 3 ) 2 + MgClBr and their structures determined by 1 H NMR and IR spectroscopy. The complexes in which M  Pt and R  Cy (cyclohexyl) or i-Pr (isopropyl) are very stable in the solid state and in solution, while the compounds in which M  Pt, R  Et (ethyl) and M  Pd, R  i-Pr slowly decompose either in the solid state or in solution. The compound in which M  Pd and R  Cy was not isolated but was identified in solution.

Bis(arylimino)pyridine Derivatives of Group 4 Metals: Preparation, Characterization and Activity in Ethylene Polymerization

Titanium tetrachloride reacts with 2,6-bis[(1-phenylimino)ethyl]pyridine, 1, and 2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine, 2, giving the adducts of general formulae [Ti1Cl3]Cl, 3, and [Ti2Cl3]Cl, 6, the latter through the intermediacy of the covalently bonded [Ti2Cl4], 4. Heating 6 leads to reduction to the titanium(III) derivative [Ti2Cl3], 12, the latter characterized by X-ray diffraction methods. The reaction of [Ti1Cl3]Cl with a toluene solution of MAO proceeds with methylation at the ortho-position of the pyridine ring to give the titanium(iv) derivative [Ti(C22H21N3)Cl3], 8. The reaction of [Ti2Cl3]Cl with MAO gives a mixture of products containing [Ti2Cl2(OAlCl3)], 9. Compound 9, which has been prepared independently by reacting 6 with AlOCl, is a rare case of a compound containing the -OAlCl3 moiety, as shown by a single-crystal X-ray diffraction study. From the tetrachlorides of zirconium and hafnium with 1 or 2, the corresponding adducts [M(L)Cl4] have been obtained in high yields. These derivatives of Group 4 metals act as ethylene polymerization catalytic precursors: the substitution of the phenyl ring of the imino fragment strongly influences the catalytic activity which is 5,544 kg(PE) mol(Ti)(-1) h(-1) in the case of 3 and 267 kg(PE) mol(Ti)(-1) h(-1) with 6. Catalytic activity has been observed for zirconium and hafnium too, the activity decreasing from zirconium to hafnium, under comparable conditions.

A Comparison of the Behavior of Nickel/MAO Catalytic Systems in the Polymerization of Styrene and 1,3-Cyclohexadiene

Several nickel complexes activated with MAO have been tested in the polymerization of styrene and cyclic conjugated diolefins. The effect of the ligands, temperature, solvents, metal concentration has been investigated. The most active complex is nickel bis(acetylacetonate), but polystyrene was obtained in fairly good yields also with other catalysts (NiCl2, Cp2Ni, etc.). The prepared polystyrene samples have been examined from the point of view of steric microstrueture. On the contrary, the only satisfactory catalyst for 1,3-cyclohexadiene polymerization is Ni(acac)2. Larger cyclic diolefins do not polymerize. Attempts to prepare copolymers of styrene and 1,3-cycloexadiene failed and only pure 1,3-cyclohexadiene homopolymer was recovered, suggesting that the active species for the two monomers have a very different structure.