Synthesis and ethylene trimerisation capability of new chromium(II) and chromium(III) heteroscorpionate complexes.

Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, UK.
Dalton Transactions (Impact Factor: 4.1). 04/2010; 39(15):3653-64. DOI: 10.1039/b926333k
Source: PubMed

ABSTRACT Reaction of (Me(2)pz)(2)CHSiMe(2)N(H)R (R = (i)Pr or Ph) or (Me(2)pz)(2)CHSiMe(2)NMe(2) with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(3) (R(1) = H, R(2) = (i)Pr (10) or Ph (11); R(1) = R(2) = Me (15)) or Cr{(Me(2)pz)(2)CHSiMe(2)NR(1)R(2)}Cl(2)(THF) (R(1) = H, R(2) = (i)Pr (12) or Ph (13); R(1) = R(2) = Me (16)), respectively. Compounds 10 and 11 were crystallographically characterized and the magnetic behaviour of all the new compounds was evaluated using SQUID magnetometry. Reaction of CrCl(3)(THF)(3) with Li{C(Me(2)pz)(3)}(THF) gave the zwitterionic complex Cr{C(Me(2)pz)(3)}Cl(2)(THF) (17) containing an apical carbanion. Reaction of the analogous phenol-based ligand (Me(2)pz)(2)CHArOH (ArO = 2-O-3,5-C(6)H(2)(t)Bu(2)) with CrCl(3)(THF)(3) gave Cr{(Me(2)pz)(2)CHArOH}Cl(3) (19) whereas the corresponding reaction with CrCl(2)(THF)(2) unexpectedly gave the Cr(III) phenolate derivative Cr{(Me(2)pz)(2)CHArO}Cl(2)(THF) (20) which could also be prepared from CrCl(3)(THF)(3) and the sodiated ligand [Na{(Me(2)pz)(2)CHArO}(THF)](2). Reaction of the corresponding ether (Me(2)pz)(2)CHArOMe with CrCl(3)(THF)(3) or CrCl(2)(THF)(2) gave Cr{(Me(2)pz)(2)CHArOMe}Cl(3) (23) and Cr{(Me(2)pz)(2)CHArOMe}Cl(2)(THF) (24), respectively. The catalytic performance in ethylene oligomerisation/polymerisation of all of the new Cr(II) and Cr(III) complexes was evaluated. Most of the complexes showed high activity, but produced a Schultz-Flory distribution of alpha-olefins. Compound 23 had an exceptionally low alpha-value of 0.37 and showed a preference for 1-hexene and 1-octene formation. While replacing a secondary amine (10-13) for a tertiary amine (15-16) resulted in loss of catalytic activity, replacing a phenol (19) for an anisole (23) group afforded a more selective and more active catalyst. Changing from MAO to DIBAL-O as cocatalyst induced a switch in selectivity to ethylene polymerisation.

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    ABSTRACT: To gain a deeper knowledge of the nature of the species formed in situ by reaction of a catalyst precursor complex and typical cocatalysts used for ethylene oligomerization or polymerization, the Cr(III) complex fac-[Cr(NPN)Cl3] (1; NPN = bis(2-picolyl)phenylphosphine) was reacted with MAO and partial methylation to give the mononuclear complex fac-[Cr(NPN)Cl2.23Me0.77] (2) was observed, whereas reaction with AlMe3 in toluene led to partial halide abstraction and produced the dinuclear, chloride-bridged dicationic complex [{fac-Cr(NPN)Me(μ-Cl)}2][AlMexCl4–x]2 (3·[AlMexCl4–x]2), in which the metal centers are bridged by two chloride ligands. The complex fac-[Cr(NPN)Cl2Et] (4) was isolated in high yield from the reaction of 1 with AlEt3 and contains a rare example of CrIII–Et function. Upon treatment of 1 with EtAlCl2, the dinuclear Cr(III) complex [{fac-Cr(NPN)}2(μ-Cl)3][AlCl4]3 (5·[AlCl4]3) was obtained, which contains three bridging chlorides. Thus, under the conditions investigated, MAO and AlEt3 behaved as alkylation agents, whereas AlMe3 and EtAlCl2 reacted as cationization agents. On activation with MAO and under comparable conditions, 1–5 exhibited similar catalytic properties, with activities between 2700 and 2800 g of C2H4/((g of Cr) h), but the major oligomer produced using the 4/MAO system was 1-decene. The neutral alkyl complexes 2 and 4 and the cationic complexes 3 and 5 did not exhibit catalytic activity for ethylene oligomerization in the absence of MAO. The structures of the complexes 2, 3·[AlMexCl4–x]2, 4, and 5·[AlCl4]3 have been determined by single-crystal X-ray diffraction.
    Organometallics 06/2011; 30(13):3549–3558. · 4.25 Impact Factor
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    ABSTRACT: A series of chromium(III) complexes, LCrCl3 (C1–C6: L = 2-(1H-benzo[d]imidazol-2-yl)-N-(2,6-R1-4-R2-phenyl)quinoline-8-carboxamide; C1: R1 = iPr, R2 = H; C2: R1 = Et, R2 = H; C3: R1 = Me, R2 = H; C4: R1 = Me, R2 = Me; C5: R1 = H, R2 = H; C6: R1 = F, R2 = H), was synthesized and characterized by IR spectroscopy, elemental analysis, mass spectra, and magnetic moments. The X-ray crystallographic analysis of complexes C2 and C3 reveals distorted octahedral geometries around the chromium atoms. Upon activation with MAO, these complexes exhibit high activities for ethylene oligomerization (up to 1.28 × 107 g·mol–1(Cr)·h–1) and ethylene polymerization (up to 6.30 × 106 g·mol–1(Cr)·h–1). The oligomers were produced with high selectivity for α-olefins (>99%), and the distribution closely resembled the Schultz–Flory rule. Various reaction parameters were investigated in detail, and the results revealed that both the steric and electronic effects of the ligands effect the catalytic activities of these chromium complexes as well as the distribution of the products formed.
    Organometallics 05/2011; 30(11):3001–3009. · 4.25 Impact Factor
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    ABSTRACT: Treatment of heteroscorpionate ligand precursors pbptamH, pbpamH, sbpamH and (S)-mbpamH with 2 equivalents of AlR3 (R = Et, Me) yielded the corresponding binuclear organoaluminium complexes [Al2R4(μ-pbptam)] (R = Me , Et ), [Al2R4(μ-pbpam)] (R = Me , Et ), [Al2R4(μ-sbpam)] (R = Me , Et ) and [Al2R4{μ-(S)-mbpam}] (R = Me , Et ). These complexes have helical chirality due to the demands of the fixed pyrazole rings. The stereoisomerism and the self-assembly processes of these helicates have been studied in some detail in solution by NMR and in the solid state by X-ray diffraction. Mixtures of M- and P-handed enantiomers and mixtures of M- and P-handed diastereoisomers were obtained when achiral () and chiral () heteroscorpionate ligands were used as scaffolds, respectively. Re-crystallization from hexane allowed us to obtain M-homochiral architectures in the solid state for the helical complexes [Al2Et4(μ-sbpam)] () and [Al2Et4{μ-(S)-mbpam}] (). The reaction of heteroscorpionate ligands with 3 equivalents of AlR3 (R = Me, Et) led to the corresponding trinuclear organoaluminium complexes [Al3R7(μ3-pbptam)] (R = Me , Et ), [Al3R7(μ3-pbpam)] (R = Me , Et ), [Al3R7(μ3-sbpam)] (R = Me , Et ) and [Al3R7{μ3-(S)-mbpam}] (R = Me , Et ). The extra AlR3 molecule contributes to the formation of a diastereomeric excess of the PS helicate for complexes and . X-ray determination of some of the helical complexes allowed us to witness a versatile and efficient self-assembly process of the building blocks (heteroscorpionate aluminium complexes) directed by noncovalent intermolecular CH-π interactions. The structures of these complexes have been determined by spectroscopic methods and the X-ray crystal structures of , , , and have also been established. Concentration-dependent (1)H pulsed field-gradient spin echo (PFGSE) NMR experiments provided evidence for the self-assembly of the single molecular species of complex in solution. The degree of aggregation was calculated for complex , with the average number of units constituting the aggregate (N) estimated to be a maximum of 4 molecules in solution before reaching the solid state.
    Dalton Transactions 08/2013; · 4.10 Impact Factor


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