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Crystalline Diphenylchloroborante.Tetrahydrofuran is unexpectedly stable complex containing an intact THF ligand in the presence of a boron halide bond. Using Gillespie's ligand close-packing arguments, the short B - O and long B - Cl bonds of this ether cleavage precursor complex are rationalized.

An experiment was conducted to derive a structural characterization of ((2,6-Pr(super i)(sub 2)C6H3)-NC(Me)C(H)C(Me)N(2,6-Pr(super i)(sub 2)C6H3)K*PhCH3)sub infiniti which is considered a heavy alkali metal complex. The characterization was carried by using nuclear magnetic resonance spectroscopy. Results revealed that the molecular structure of the complex exhibited a monomeric and polymerized features.

New cationic enamine-β-diimine cobalt complex [LCoBr·THF][BArF] (I) and its neutral analogue [LCoBr2] (II) where L = [(2,4,6-Me3-C6H2)NHCMe=C{CMe=(N-2,4,6-Me3(C6H2))}2] and BArF− = [{3,5-(CF3)2C6H3}4B]−, were synthesised and then characterized by single-crystal X-ray diffraction, MALDI-MS, IR and elemental analysis. These complexes, the first examples reported where putatively tridentate β-triketimines prefer a bidentate coordination mode, were examined as catalysts for the polymerization of isoprene, activated by diethylaluminium chloride (DEAC) or ethylaluminium sesquichloride (EASC). The weakly coordinating BArF anion in I strongly improved activity in comparison to II. Both I and II produced polyisoprene of ca. 80% cis-1,4 and 20% 3,4 enchainment, with trace levels of trans-1,4 and no 1, 2 polymer. A kinetic study for both I and II demonstrated that the polymerization was first-order in monomer and that approximately 46% and 50% of cobalt formed active centres for I and II respectively. EASC was the most active of a range of organoaluminium compounds screened for both I and II. The resulting activities of up to 6 × 105 mol isoprene per mol Co per h are the highest yet recorded for catalysts selective for cis-1,4 enchained polyisoprene. [ABSTRACT FROM AUTHOR]

A computational study is presented of a complex of thallium with a neutral β-triketimine ligand which was found to form dimers with close Tl–Tl interactions. Single point energies, using the crystallographic structures, suggest that the system is bound only when BArF counter ions are included in the calculations. Energy decomposition analysis of the system was carried out in order to investigate the nature of the bonding. Across the methods, calculations show the electrostatic interaction to be repulsive for the dimer with no counter ions, but attractive when BArF counter ions are included. This suggests the metallophilic interaction is counter ion-mediated, requiring the anions to provide favourable electrostatics, even in the case of spatially diffuse and distant counter ions such as the 3,5-bistrifluoromethylphenyl borate ions used here. [ABSTRACT FROM AUTHOR]

Enantioselective base (R, R')-bis(1-phenylethyl)amidolithium was crystallized from THF/hexane. X-ray crystallography characterized it as a bis-THF-solvated cyclic dimer which takes an a conformation that maximizes methylithium contacts. This contradicts earlier justifications of its enantioselectivity in enolizations of cyclic ketones.

A low-symmetry nickel(II) ?-diimine complex [(2,4,6-trimethylphenyl)imino)-((2,6-diisopropylphenyl)imino)-acenaphthene nickel(II) dibromide] (C1) was synthesized and characterized crystallographically. Response surface method (RSM) was employed to study the interactive effects of critical factors on ethylene polymerization.The maximum activity ofC1, when activated by methylaluminoxane (MAO) cocatalyst {4960 kgPE [(mol Ni)?1 h?1]} was achieved at 10 °C, 7 bar and CC (cocatalyst-to-catalyst ratio) equal to 1550, which is higher than most similar counterparts. Considering surface plots of MW, it is concluded that at high levels (>1000) of CC, there is competition between chain transfer to aluminum and reinsertion of macromonomer to newly formed metal-methyl bonds. In this contribution, the synthesis and characterization of a non-symmetric nickel(II) ?-diimine complex [(2,4,6-trimethylphenyl)imino)-((2,6-diisopropylphenyl)imino)-acenaphthene nickel(II) dibromide] have been reported as a catalyst precursor for ethylene polymerization. Response surface method (RSM) has been applied successfully for investigation of operational conditions; it provides predictive models for activity, weight-average molecular weight (Mw), and crystallinity with adequate goodness of fit. The resultant activities challenge the best achieved with other unsymmetrical nickel (II) ?-diimine systems. Considering the most critical factors and also their interactions on catalyst performance has been provided possibility to design final polymer characteristics. Further studies on nickel-catalyzed polymerizations may benefit from similar treatment of all relevant variables using RSM. [ABSTRACT FROM AUTHOR]

Three β-triketimine ligands, (L¹: [CH{CMeN(2,4,6-Me3-C6H2)}2C(CMe3N(2-MeO-C6H4)], L²: [CH{CMeN-(2,4-Me2-C6H3)}2C(CMe3N(2-MeO-C6H4)] and L³: [CH{CMeN(2-Me-C6H4)}2C(CMe3N(2-MeO-C6H4)]), were synthesized and then characterized by ¹H and 13C{¹H} NMR spectroscopy, elemental analysis and electrospray (ES) MS. β-triketimine cobalt(II) complexes were then prepared by the interaction of cobalt(II) bromide with L1-3 in the presence of NaBArF (BArF = [{3,5-(CF3)2-C6H3}4B]-). Five-coordinate dimeric bromide-bridged species [(LCoµ-Br)2][BArF]2 were obtained. The geometry of the complexes was found by single-crystal X-ray diffraction to be slightly distorted square-pyramidal. The polymerization of 1,3-butadiene catalysed by these complexes upon activation with methylaluminoxane (MAO) in chlorobenzene yielded high cis-1,4-polybutadiene (>97% cis). The effect of steric and electronic properties of the ligands on the performance of the catalytic system was investigated: it was found that ligands with fewer methyl substituents gave more active catalytic systems. It was also found that increasing MAO: Co ratio resulted in higher activity. Stereoselectivity of all catalysts slightly decreased at higher temperature, whereas activities were maximised at 20 °C, where very high values of activity were recorded. [ABSTRACT FROM AUTHOR]

The synthesis and characterization by single-crystal X-ray diffraction of two thallium salts of the non-co-ordinating anion [B{3,5-(CF3)2C6H3}4] are reported. They possess Tl–Tl contacts supported by Tl–aryl interaction. This cation association overcomes both electrostatic repulsion and cation–anion size and charge matching considerations in the [LTl2L]2+ dications so formed. [ABSTRACT FROM AUTHOR]

The reaction of N-(4-(mesitylamino)pent-3-en-2-ylidene)-2,4,6-trimethylbenzenamine ( 1) with n-butyl lithium and then with N-(2,4,6-trimethyl-phenyl)-acetimidoyl chloride yields a new β-triketimine ligand, N-(4-(mesitylamino)-3-(1-(mesitylimino)ethyl)pent-3-en-2-ylidene)-2,4,6-trimethylbenzenamine, 2. The addition of 2 to nickel (II) dibromide 1,2-dimethoxyethane (NiBr2(DME)) in the presence of [Na]+[3,5-(CF3)4C6H3]4B]− (NaBAr'4) gives a five-coordinate dimeric complex [( 2.NiBr)2].2 [(BAr'4)], 3. The structure of 3 has been determined by single crystal X-ray diffraction. This complex generates catalytically active species for the homopolymerization of ethylene in combination with methylaluminoxane to produce elastomeric, branched polyethylene. The effect of factors (temperature, pressure, and cocatalyst to catalyst molar ratio (CC)) on the polymerization process has been investigated using regression models of responses (catalyst activity, crystallinity, and weight-average molecular weight of polymer ( Mw)) and visualized via the response surface method (RSM). Activity and Mw responses show a second-order variation with temperature and vary linearly with pressure. Conversely, crystallinity follows a second-order model while varying temperature, pressure, and CC. Furthermore, a set of polymerization conditions for reaching desirable responses was predicted and then experimentally verified. The activities achieved challenge the best reported activities for Ni(II) catalysts with β-connected imine ligand supports, but fall short of those for α-diimines. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 [ABSTRACT FROM AUTHOR]

Abstract: The complexes l-[CMe2{CHMeN(2-Pr i -C6H4)}2TiCl2] (2) and (3), C 2- and C s -symmetric analogues, respectively, of McConville’s C 2v hexene polymerization precatalyst (1), were prepared by high-dilution salt-elimination from the lithium amides and characterized spectroscopically and crystallographically. Complex 2, though less active than 1, was a highly active catalyst of polymerization of 1-hexene when activated by MAO. Complex 3 was inactive under similar conditions. NMR analysis confirmed that there were more mmmm pentads in polymer produced by 2 than in the statistically atactic material produced by 1, though the isotacticity index was not high. The results are interpreted in terms of an isotactic/atactic block structure, caused by syn/anti fluxion of the two 2-isopropylphenyl rings in 2. Kinetic profiles and polydispersities were consistent with a slow initiation step involving monomer, followed by rapid propagation, with some chain transfer to aluminium and only a small extent of β-hydride elimination. The rubber-like polymers were indistinguishable by thermal analysis from those prepared by Ziegler–Natta catalyst systems. [Copyright &y& Elsevier]

Examines a magnesium-bis (diaryldiketiminate) complex. Chemical composition; Coordination geometry about the magnesium atom; Molecular structure.