No abstract

A series of novel titanium(IV) complexes bearing tetradentate [ONNO] salan type ligands: [Ti{2,2 0 -(OC 6 H 3 -5-t-Bu) 2 -NHRNH}Cl 2 ] (Lig 1 TiCl 2 : R 5 C 2 H 4 ; Lig 2 TiCl 2 : R 5 C 4 H 8 ; Lig 3-TiCl 2 : R5 C 6 H 12 ) and [Ti{2,2 0 -(OC 6 H 2 -3,5-di-t-Bu) 2 -NHC 6 H 12 NH} Cl 2 ] (Lig 4 TiCl 2 ) were synthesized and used in the (co)polymerization of olefins. Vanadium and zirconium complexes: [M{2,2 0 -(OC 6 H 3 -3,5-di-t-Bu) 2 -NHC 6 H 12 NH}Cl 2 ] (Lig 4 VCl 2 : M5 V; Lig 4 ZrCl 2 : M 5 Zr) were also synthesized for comparative investigations. All the complexes turned out active in 1-octene polymerization after activation by MAO and/or Al(i-Bu) The catalytic performance of titanium complexes was strictly dependent on their structures and it improves for the increasing length of the aliphatic linkage between nitrogen atoms (Lig 1 TiCl 2 << Lig 2 TiCl 2 < Lig 3 TiCl 2 ) and declines after adding additional tert-Bu group on the aromatic rings (Lig 3 TiCl 2 < Lig 4 TiCl 2 ). The activity of all titanium complexes in ethylene polymerization was moderate and the properties of polyethylene was dependent on the ligand structure, cocatalyst type, and reaction conditions. The Et 2 AlCl-activated complexes gave polymers with lover molecular weights and bimodal distribution, whereas ultra-high molecular weight PE (up to 3588 kg mol 21 ) and narrow MWD was formed for MAO as a cocatalyst. Vanadium complex yielded PE with the highest productivity (1925.3 kg mol v 21 ), with high molecular weight (1986 kg mol 21 ) and with very narrow molecular weight distribution (1.5). Copolymerization tests showed that titanium complexes yielded ethylene/1-octene copolymers, whereas vanadium catalysts produced product mixtures.

A phenoxy-imine proligand with the additional OH donor group, 4,6-tBu2-2-(2-CH2(OH)-C6H4N = CH)C6H3OH (LH2), was synthesized and used to prepare group 4 and 5 complexes by reacting with Ti(OiPr)4 (LTi) and VO(OiPr)3 (LV). All new compounds were characterized by the FTIR, 1H and 13C NMR spectroscopy and LTi by the single-crystal X-ray diffraction analysis. The complexes were used as catalysts in the ring opening polymerization of ε-caprolactone. The influence of monomer/transition metal molar ratio, reaction time, polymerization temperature as well as complex type was investigated in detail. The complexes showed high (LTi) and moderate (LV) activity in ε-caprolactone polymerization and the resultant polycaprolactones exhibited Mn and Mw/Mn values ranging from 4.0 · 103 to 18.7 · 103 g/mol and from 1.4 to 2.5, respectively.

The reduction of the phenoxyimine moiety in three individual speciesnamely free ligand, aluminum complex, and titanium complexwith aluminum alkyls and aluminum hydride has been studied by means of DFT. It was demonstrated that the free phenoxyimine ligand in an equimolar mixture with trimethylaluminum does not undergo reduction. Instead, experimentally observed formation of the six-membered cyclic aluminum−phenoxyimine complex, useful in the ring-opening polymerization of lactones, takes place as the kinetically and thermodynamically favored process. However, it is anticipated that a 2-fold excess of the aluminum compound, especially aluminum hydride, acting on the resulting cyclic complex can convert the imine to the aluminum-subsituted amine functionality easily with an energetic barrier of approximately 10 kcal/mol. Finally, the propensity of the imine moiety in the titanium-based precursor of the coordinative olefin polymerization toward reduction with organoaluminum compounds is revealed and the mechanism of this reaction is also suggested.

Contrary to other N-(pyridyl)nitramines, the title compound cannot be rearranged to 3-amino-2-nitropyridine or other isomers. Hypothetical products of its transformation under influence of concentrated sulphuric acid, viz. 3-hydroxypyridine, 3,3′-azoxypyridine and 3,3′-azopyridine, were obtained from 3-nitro- and 3-aminopyridine in oxidation and reduction reactions. N-(3-Pyridyl)nitramine was prepared and rearranged in concentrated sulphuric acid. 3-Hydroxypyridine and 3,3′-azoxypyridine were isolated from the reaction mixture, other products were identified by the HPLC and GCMS methods. The results indicate that N-(3-pyridyl)hydroxylamine is an intermediate formed from N-(3-pyridyl)nitramine under the influence of concentrated sulphuric acid. The reaction path, leading to the final products, is discussed in context of the mechanism of nitramine rearrangement.