A series of new pentacoordinated nickel complexes NiCl 2 (NZN) based on nitrogen-, oxygen-, or sulfurbridged bis(pyrazolyl) ligands (NZN) were synthesized and characterized by elemental analysis and an X-ray diffraction study for NiCl 2 {bis[2-(3,5-dimethylpyrazolyl)ethyl)]amine} (1). Upon activation with methylaluminoxane (MAO), these complexes show high activity in ethylene oligomerization (TOF ) 7-80 × 10 3 h -1 ), which varies according to the ligand environment. Up to 92% selectivity for 1-butene, combined with a TOF of 60 × 10 3 h -1 , has been obtained under moderate conditions (30 °C, 40 bar, MAO-to-Ni ) 250) using NiCl 2 {bis[2-(5-phenylpyrazolyl)ethyl)]ether} (3) as the catalyst precursor.

A set of chromium(III) complexes CrCl 3 (L) based on tridentate ligands (1, L ) bis [2-(3,5dimethylpyrazolyl)have been prepared and characterized by elemental analysis, ESI-HRMS, and an X-ray diffraction study for 3. Upon activation with methylaluminoxane (MAO), these precatalysts show high activity in ethylene oligomerization (TOF ) (3.4-131.0) × 10 3 (mol ethylene) (mol Cr) -1 h -1 at 80 °C), producing R-olefins in the range C 4 -C 14+ with high selectively. The catalytic performances are substantially affected by the ligand environment, especially the bridge donor atom, and reaction conditions. Under optimized conditions ([Cr] ) 10 µmol, 80 °C, 40 bar ethylene, MAOto-Cr ) 300), precatalyst 5 leads to TOF ) 131.0 × 10 3 h -1 and selectivity for R-olefins in the range 89-97%.

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Summary: Linear low‐density polyethylene (LLDPE) samples with different properties were prepared from ethylene, without the addition of an α‐olefin co‐monomer, using a combination of the catalyst precursors TpMsNiCl (TpMs = hydridotris(3‐mesitylpyrazol‐1‐yl) and Cp2ZrCl2/SMAO‐4, by varying the nickel loading mole fraction (xNi). Upon activation with methylaluminoxane (MAO), this binary catalytic system showed activities varying from 12.3 to 309.1 kg of PE · (mol[M] · atm · h)−1. The properties of the polymeric materials are influenced by xNi as well as by the temperature of polymerization, affording the copolymers with a melting point (Tm) between 118 and 135 °C. The GPC results show that the molecular weight ($\overline M _{\rm w}$) of the polymers is sensitive to the xNi. In all of the cases studied, the GPC curves displayed monomodal molecular weight distributions (MWDs) with the average molecular weight varying from 30 000 to 507 000 g · mol−1. Studies using dynamic mechanical thermal analysis (DMTA) show that the formation of different polymeric materials is associated with the branching content, with the stiffness varying according to the xNi and the temperature used in the polymerization reaction.Overview of the copolymerization process, from ethylene in the presence of MAO, mediated by catalysts 1 and 2/SMAO.imageOverview of the copolymerization process, from ethylene in the presence of MAO, mediated by catalysts 1 and 2/SMAO.

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A polimerização do estireno com uma série de complexos de níquel e titânio contendo ligantes tris(pirazolil)borato estericamente impedidos, Tp Ms = HB(3-mesitila-pirazolil) 3 e Tp Ms* = HB(3-mesitila-pirazolil) 2 (5-mesitila-pirazolil) foi estudada na presença do cocatalisador MAO sob várias condições de polimerização. Todos complexos mostraram-se ativos na polimerização do estireno produzindo quase exclusivamente poliestireno atático. As atividades catalíticas bem como as conversões com os complexos de níquel foram maiores em relação àquelas obtidas com os complexos de titânio. Maiores atividades foram encontradas a 80 °C. As propriedades dos poliestirenos são substancialmente afetadas pelas condições de reação tais como temperatura de polimerização, tempo e razão molar [Al]/ [M]. Os resultados de GPC mostram que o peso molecular (M w ) dos poliestirenos é sensível à temperatura de polimerização variando de 16.300 a 138.300 g mol -1 .Styrene polymerization with a series of nickel and titanium complexes based on sterically hindered tris(pyrazolyl)borate ligands, Tp Ms = HB(3-mesityl-pyrazolyl) 3 and Tp Ms* = HB(3-mesitylpyrazolyl) 2 (5-mesityl-pyrazolyl) have been studied in the presence of MAO cocatalyst under various polymerization conditions. All complexes showed to be active for styrene polymerization producing almost exclusively atactic polystyrene. The catalytic activities as well as the styrene conversions with nickel complexes were higher than those with the titanium analogues. Higher activities were found at 80 °C. Polystyrene properties are substantially affected by the reaction conditions such as temperature of polymerization, time, and [Al]/[M] molar ratio. The GPC results showed that the molecular weight (M w ) of the polystyrene is sensitive to the temperature of polymerization varying from 16,300 to 138,300 g mol -1 .Keywords: nickel, titanium, tris(pyrazolyl)borate ligand, polystyrene IntroductionThe chemistry of the non-metallocene catalysts has grown considerably over the past two decade, largely due to the remarkable variety of non-cyclopentadienyl ligands available and their high-performance in olefin polymerization. 1 Many contributions have thus been made concerning this topic, especially using Group 4 and Group 10 metals for polymerization of ethylene, 2 propylene, 3 and in copolymerization reactions. 4 Among linear α-olefins, special attention has been devoted to the use of styrene as monomer for production of polystyrene considering their interesting chemical and physical properties for industrial applications. The polymerization process of styrene can lead to three tactic structures which are depend on the nature of the catalyst precursor, including isotactic (iPS), syndiotactic (sPS) and atactic (aPS) polystyrenes. 5 In contrast to the well-known isotactic polystyrene, which has a very low crystallization rate and is therefore useless for most industrial purposes, 6 the syndiotactic polystyrene (sPS) shows a fast crystallization rate (more than an order of magnitude higher than that of...