Sergio Mastroianni

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.

Transition Metal Imido Catalysts for Ethylene Polymerisation

Abstract The imido complexes CpV(N-2-MeC 6 H 4 )Cl 2 ( 1 ), Cr(N- t Bu) 2 Cl 2 ( 2 ), CpNb(N-2- t BuC 6 H 4 )Cl 2 ( 3 ) and Mo(N- t Bu) 2 Cl 2 ( 4 ) have been tested as procatalysts for the polymerisation of ethylene in combination with diethylaluminium chloride or methylaluminoxane (MAO) co-catalysts. The vanadium precursors give the highest activities but are short-lived, while the chromium system gives a long-lived catalyst of moderate activity. The niobium and molybdenum derivatives gave relatively low activities under all test conditions. The polyethylene generated by the vanadium and chromium catalysts is of high molecular weight with little branching. The dialkyl complexes Cr(N- t Bu) 2 (CH 2 Ph) 2 ( 5 ), Cr(N-2,6-Pr i 2 C 6 H 3 ) 2 (CH 2 Ph) 2 ( 6 ), Cr(N-2,6-Pr i 2 C 6 H 3 ) 2 Me 2 ( 7 ), Mo(N- t Bu) 2 (CH 2 Ph) 2 ( 8 ), Mo(N-2,6-Pr i 2 C 6 H 3 ) 2 (CH 2 Ph) 2 ( 9 ), (C 5 Me 5 )Nb(N-2,6-Pr i 2 C 6 H 3 )Me 2 ( 10 ) and (C 5 Me 5 )Ta(N- t Bu)(CH 2 Ph) 2 ( 11 ) have been prepared by treatment of the dihalide precursors with appropriate alkylating reagents and investigated as precursors to well-defined cationic alkyl catalysts. Treatment of ( 5 ) with [Ph 3 C][B(C 6 F 5 ) 4 ] affords the cationic η 2 -benzyl species [Cr(N- t Bu) 2 (η 2 -CH 2 Ph)][B(C 6 F 5 ) 4 ] ( 12 ) while its reaction with [PhNMe 2 H][B(C 6 F 5 ) 4 ] liberates toluene to give a mixture of the mono and bis(dimethylaniline) adducts [Cr(N- t Bu) 2 (η 2 -CH 2 Ph)(NMe 2 Ph)][B(C 6 F 5 ) 4 ] ( 14 ) and [Cr(N- t Bu) 2 (η 2 -CH 2 Ph)(NMe 2 Ph) 2 ][B(C 6 F 5 ) 4 ] ( 15 ). Complex 12 reacts with trimethylphosphine to give the mono-phosphine adduct [Cr(N- t Bu) 2 (η 2 -CH 2 Ph)(PMe 3 )][B(C 6 F 5 ) 4 ] ( 13 ). Solutions containing cationic species ( 12 , 14 , 15 ) are active for ethylene polymerisation in the absence of co-catalyst, affording high-molecular-weight polyethylene with relatively broad molecular-weight distributions.

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.