Carl Redshaw

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 >99u2009% 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.

Synthesis and structural characterisation of aluminium imino-amide and pyridyl-amide complexes: bulky monoanionic N,N chelate ligands via methyl group transfer

Abstract Treatment of the imines [ArNue605CH-CHue605NAr] and [ArNue605CH-2-py] (Ar=2,6-Pr2iC6H3) with AlMe3 in toluene affords the highly crystalline complexes [AlMe2{ArN-CH2-C(Me)ue605NAr}] (1) and [AlMe2{ArN-CH(Me)-2-py}] (2); the molecular structures of 1 and 2 show that the aluminiums are bonded to imino-amide and pyridyl-amide ligands respectively arising from methyl group transfer from the aluminium centre to the backbone carbon of the imine ligand.

Organoimido complexes of tungsten. X-ray crystal structures of W(NC6H11)Cl2(PMe3)3, [W(NC6H11)Cl2(PMe3)3]O3SCF3, [W(NC6H11)Cl(PMe3)4]BPh4, W[NSi(o-MeC6H4)3]Cl2(PMe3)3, W[NB(mes2)]2Cl2(PMe3)2, {W(NPh)Cl[O2C2(CF3)4]2}Li and WCl4(PMe2Ph)3

Abstract The cyclohexylimido complex of tungsten(VI), [W(NCy)Cl4]2 (1), is reduced by Na/Hg in the presence of PMe3 to give cis,mer-WIV(NCy)Cl2(PMe3)3 (2). Interaction of 2 with AgO3SCF3 in THF gives the tungsten(V) complex [W(NCy)Cl2(PMe3)3]O3SCF3(3); with NaBPh4 in the presence of PMe3 [W(NCy)Cl(PMe3)4]BPh4 (4) is obtained. Interaction of WCl2(PMe3)4 with the new organoazide (o-tolyl)3Si(N3) produced W[NSi(o-tolyl)3] Cl2(PMe3)3 (5), while with (mesityl)2B(N3), cis,cis,trans-W[NB(mes)2]2Cl2(PMe3)2 (6) is obtained. Interaction of [W(NPh)Cl4]2 with dilithium perfluoropinacolate gives Li{W (NPh)Cl[O2C2(CF3)4]2} (7). The structures listed in the title have been determined by X-ray crystallographic study. In complexes 2–7 the metal has octahedral geometry. The Wue5f8N(imido) distances vary from 1.69(1) A in complex 4, a tungsten(IV) species, to 1.78(1) A in the tungsten(VI) bis-imido complex 6, with no simple correlation with the oxidation state of the metal. The trans-lengthening effect of the imido function also varies, with the greatest effect generally in the tungsten(V) complex 3. No lengthening seems to occur in the tungsten(IV) complexes 2 and 4, but there is a slight effect in complex 5. The complex WCl4(PMe2Ph)3 has a capped octahedral geometry.

Group 6 transition metal complexes containing the σ-bonded 2,4,6-tris(trifluoromethyl) phenyl (“fluoromes”) ligand

Abstract Group 6 transition metal complexes containing the σ-bonded 2,4,6-tris(trifluoromethyl)phenyl (“fluoromes” or “fmes”) ligand are described. Treatment of CrCl 2 (thf) with two equivalents of Li(fmes) in the presence of PMe 3 affords divalent [Cr(PMe 3 ) 2 (fmes) 2 ] ( 1 ), whereas reaction of Cr(N t Bu) 2 Cl 2 with two equivalents of Li(fmes) in diethylether gives the hexavalent bis(imido)chromium complex [Cr(N t Bu) 2 (fmes) 2 ] ( 2a ). The molybdenum analogue, [Mo(N t Bu) 2 (fmes) 2 ] ( 2b ), is obtained upon treatment of Mo(N t Bu) 2 Cl 2 (dme)(dme = 1,2-dimethoxyethane) with Li(fmes) under similar conditions.

Synthesis and structural characterization of some novel metalloboroxides bearing boron-bound mesityl and fluoromesityl substituents: the molecular structure of the first metallaboroxane complex

Abstract Treatment of the new boronous acid HOB(fmes)2 (1) (fmes = 2,4,6-(CF3)3C6H2) with n-butyllithium in diethyl ether/pentane affords after work-up the dimer [Li(thf)OB(fmes)2]2 (2). Reaction of [Mo2(NMe2)6] with two equivalents of 1 in toluene gives the amido-boroxide complex Mo2(NMe2)4[OB(fmes)2]2 (3). Treatment of CuBr2 with LiOB(Mes)2 (mes = 2,4,6-Me3C6H2) in tetrahydrofuran affords after work-up and addition of excess pyridine the monomeric copper(II) boroxide Cu[O3B2(mes)2]2[Li(CH3CN)(C5H5N)]2 (4), containing the new ligand mesB(O)OB(O)mes, as a result of loss of mesitylene and formation of a Bue5f8Oue5f8B bond. 2 and 4 have been structurally characterized.

Neuartige Aluminium-haltige Ringsysteme: ein achtkerniges Strukturanalogon eines Calix[4]pyrrols

In Abhangigkeit vom Hydrazin-Reagens reagiert Me3Al zu neuartigen Aluminium-haltigen Makrocyclen. So liefert die Reaktion von Me3Al mit Me2NNH2 das achtkernige Calix[4]pyrrol-Analogon 1, wahrend die Reaktion mit MePhNNH2 unter gleichen Bedingungen zu einem vierkernigen Komplex fuhrt. Beide Komplexe entstehen durch Einlagerung von Acetonitril.

Synthesis and structure of bis(methylaluminium · HCCH3) p-tert-butylcalix[4]arene

Treatment of p - tert -butylcalix[4]areneH 4 iwth AlMe 3 in toluene at elevated temperature affords after work-up the complex {[MeAl(NCMe)] 2 ( p - tert -butylcalix[4]arene)}, which adopts a flattened partial cone conformation as characterized by X-ray crystallographu.

Synthesis and characterisation of neutral and cationic alkyl aluminium complexes bearing N,O-Schiff base chelates with pendant donor arms

The Schiff base ligands [3,5-But2-2-(OH)C6H2CHNL] [L = CH2CH2NMe2 (1a), 2-(PhO)C6H4 (1b), 2-CH2C5H3N (1c), 8-C9H6N (quinoline) (1d) and 2-(PPh2)C6H4 (1e)] are accessed in good yields (>85%) via standard imine condensation reactions. Reaction of 1a–e with Me3Al at room temperature affords the corresponding complexes [(3,5-But2-2-(O)C6H2CHNL)AlMe2] (2a–e); nin the case of L = 8-quinoline, the same reaction conducted in refluxing toluene affords binuclear {[3,5-But2-2-(O)C6H2CHMeN-8-C9H6N]AlMe}2 (3) by methyl migration from metal to ligand. Further reaction of the dimethyl compounds with B(C6F5)3 in CD2Cl2 or C6D6 affords the cationic systems [(3,5-But2-2-(O)C6H2CHNL)AlMe]+ (4a–e). The crystal structures of 2a, 2c, 2e and 3 have been determined. In 2a and 2c nthe respective ligands bind to the metal centre via all three heteroatoms, the aluminium having a trigonal bipyramidal geometry, whereas in 2e coordination is via nitrogen and oxygen only, and the aluminium is tetrahedral. Complex 3 has a dimeric structure with the ligand adopting both tridentate and binucleating roles; the aluminium centres are trigonal bipyramidal.