Gregory A. Solan

Oligomerisation of Ethylene by Bis(imino)pyridyliron and -cobalt Complexes

A series of bis(imino)pyridyliron and -cobalt complexes [{2, 6-(CR=NAr)2C5H3N}MX2] (R=H, Me; MFe, Co; X=Cl, Br) 8-16 containing imino-aryl rings (Ar) with at least one small ortho substituent, as well as Ar=biphenyl and Ar=naphthyl, has been synthesised. Crystallographic analyses of complexes 9 (Ar=2,3-dimethylphenyl), 13 and 14 (Ar=biphenyl; X=Cl or Br, respectively) reveal a distorted trigonal-bipyramidal geometry in the solid state. These complexes, in combination with methyl aluminoxane (MAO), are active catalysts for the oligomerisation of ethylene, yielding >99 % linear α-olefin mixtures that follow a Schulz-Flory distribution. Iron ketimine (R=Me) precatalysts give the highest activities and a greater α-value than their aldimine (R=H) analogues. Cobalt precatalysts follow a similar trend, though their activities are almost two orders of magnitude lower than those of the corresponding iron catalysts. Ethylene pressure studies on cobalt precatalyst 15 reveal a first-order dependence on ethylene for both the rate of propagation and the rate of chain transfer, and a pressure independence of the α value.

Imine Versus Amine Donors in Iron-Based Ethylene Polymerisation Catalysts

The synthesis and characterisation of iron(II) dichloro complexes containing neutral tridentate nitrogen ligands of the type 2-arylaminoalkyl-6-aryliminoalkylpyridine [2-ArNHCR(Me)-6-ArN=CR]C5H3N (R = H, Ar = 2,6-iPr2C6H3 or 2,4,6-Me3C6H2; R = Me, Ar = 2,6-iPr2C6H3)] and 2,6-bis(arylaminomethyl)pyridine [2,6-(ArNHCH2)2]C5H3N (Ar = 2,6-iPr2C6H3) are described and their activity in ethylene polymerisation is compared with their 2,6-bis(aryliminoalkyl)pyridine analogues.

Synthesis, Structures and Ethylene Polymerisation Behaviour of Low Valent β‐Diketiminato Chromium Complexes

The preparation, reaction chemistry and ethylene polymerisation behaviour of low valent β-diketiminato chromium complexes are described. [(DDP)CrCl(µ-Cl)]2 (1) [DDPH = 2-{(2,6diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}pent-2-ene] is formed by treatment of CrCl3(THF)3 with LiDDP. Alkylation of 1 with AlMe3 results in the formation of the binuclear dimethyl complex [(DDP)CrMe(µ-Cl)]2 (2). In contrast, the attempted alkylation of 1 with benzylmagnesium chloride results in reduction to form the dichromium(II) complex [(DDP)Cr(µ-Cl)]2 (3). Depending on the conditions of crystallisation, 3 can be obtained as the THF adduct [3(THF)2·THF] or co-crystallised with a molecule of dibenzyl [3·Bz-Bz]. Cleavage of the dimeric unit in 1 can be achieved by the addition of carboxylates or β-diketonates to give [(DDP)CrCl(O2CR)(THF)] (R = Me 4a, Ph 4b) and [(DDP)CrCl({O(R)C}2CH)] (R = Me 5a, Ph 5b), respectively. Single crystal X-ray diffraction studies have been performed on 1, 2, 3(THF)2·THF, 3·Bz-Bz, 4a, and 5b. Complexes 1, 2 and 3(THF)2·THF are dimeric and have molecular C2h symmetry. Complex 3·Bz Bz is also dimeric but has its potential C2h symmetry removed by a significant tetrahedral distortion of the chromium coordination geometry. Compound 4a has an octahedral chromium centre coordinated to a single bidentate diketiminate ligand, a bidentate acetate, a chloride and a THF molecule. Complex 5b has a square pyramidal chromium with apical chloride and basal η2 diketiminate and diketonate ligands. The complex contains strong intramolecular C−H···π stabilising interactions. All the complexes are active in ethylene polymerisation on treatment with suitable aluminium activators, affording high molecular weight polyethylene.

Titanium and zirconium complexes bearing (S,S′)-ferrocenyldithiolate ligands

Abstract The ferrocenyldithiolate complexes of formula {(C 5 H 4 S) 2 Fe}M(NMe 2 ) 2 (M=Ti or Zr) can be prepared in good yield by treatment of M(NMe 2 ) 4 with {(C 5 H 4 SH) 2 Fe} at elevated temperature; in the presence of trimethylaluminium (TMA)–methylaluminoxane (MAO) both complexes polymerize ethylene under mild conditions.

A five-coordinate chromium alkyl complex stabilised by salicylaldiminato ligands

The five-coordinate bis(salicylaldiminato)chromium(III) complex [3,5-(t-Bu)2(O)C6H2CHN(2,6-i-Pr2C6H3)]2CrCl (2) reacts with triethylaluminium in THF at room temperature to give the air sensitive ethyl species [3,5-(t-Bu)2(O)C6H2CHN(2,6-i-Pr2C6H3)]2CrEt (3); in the presence of aluminium activators, 2 and 3 are moderately active ethylene polymerisation catalysts.

Chromium complexes bearing pyrrolide-imine N,N-chelate ligands: synthesis, structures and ethylene polymerisation behaviour

Chromium(II) and chromium(III) complexes bearing two bulky monoanionic N,N-chelating pyrrolide-imine ligands, {ArNCH(C4H3N-2)}2Cr (1) and {ArNCH(C4H3N-2)}2Cr(µ-Cl)2Li(THF)2 (2), have been prepared in high yield by treatment of the sodium and lithium salts of ArNCH(C4H3NH-2) (Ar = 2,6-i-Pr2C6H3) with CrCl2(THF) and CrCl3(THF)3, respectively. The molecular structure of 1 reveals a square planar geometry about chromium with the pyrrolide-N units disposed mutually trans. Conversely, an octahedral geometry is exhibited by the chromium centre in 2 with mutually cis-oriented pyrrolide-N units and cis-chloride ligands which, in turn, link to a Li(THF)2 unit. Complex 2 can be alkylated with AlR3 to give the five-coordinate mono-alkyl species {ArNCH(C4H3N-2)}2CrR (3a R = Me; 3b R = Et), in which two pyrrolide-imine ligands occupy the square base of the square pyramidal chromium centre. Complexes 1–3 behave as ethylene polymerisation catalysts upon treatment with an excess of a range of aluminium activators including MAO, Et2AlCl and Me2AlCl, converting ethylene to high molecular weight polyethylene. In all cases the dialkylaluminium chlorides are superior co-catalysts to MAO, affording acitivities up to 120 g mmol−1 h−1 bar−1. The coordinatively unsaturated bis(pyrrolide-imine) chromium alkyl complexes 3a and 3b are inactive for the polymerisation of ethylene in the absence of activator.