Abdessamad Arbaoui

Metal catalysts for ε-caprolactone polymerisation

Economic pressure, environmental issues and ever increasing demand are driving the shift from oil-based polymers to those available from renewable resources. Ring opening polymerisation of cyclic esters is currently a topical field with metal complex-induced coordination/insertion type polymerisation leading the way. Such a polymerisation method offers a wide range of advantages from control over the polymer structure to kinetic enhancement; however industrially available catalysts based on tin suffer from inherent toxicity and as a result a policy change from the Food and Drug Administration (FDA) is not unrealistic. This review underlines the efforts made in the past five years or so, and shows how low toxicity metals are attracting increasing attention in the field of e-caprolactone polymerisation.

Iron(III) and Zinc(II) Calixarene Complexes: Synthesis, Structural Studies, and Use as Procatalysts for ε-Caprolactone Polymerization

Treatment of the heterobimetallic iron(II) alkoxides [(THF)MFe(OtBu)(3)](2) with p-tert-butylcalix[4]areneH(4) (L(1)H(4)) affords the oxo-bridged diiron(III) complexes {Fe[M(NCMe)(x)](2)L(1)}(2)(mu-O), M = Na, x = 2 1 x 8(CH(3)CN), M = K, x = 3 2 x 3.5(CH(3)CN); similar use of p-tert-butylcalix[6]areneH(6) (L(2)H(6)) afforded [{Fe(2)(mu-O)Na(2)(OH(2))(NCMe)(2)L(2)}(2)][{Fe(2)(mu-O)Na(OH(2))(NCMe)(6)L(2)}(2)](2-)[Na(NCMe)(5)](2)(2+) 3 x 9.46(CH(3)CN) and [{Fe(2)(mu-O)L(2)(K(NCMe)(2))(2)}(2)] 4 x 10.8(MeCN), respectively. In the case of 4, a minor product {(L(2)(2)Fe(8)O(8))[K(NCMe)(1.5)K(H(2)O)(NCMe)(2.5)](2)} 5 x 6(CH(3)CN), which is comprised of chains of (L(2)(2)Fe(8)O(8)) clusters bridged by K/MeCN fragments, is also isolated. Use of p-tert-butylcalix[8]areneH(8) (L(3)H(8)) and two equivalents of [(THF)KFe(OtBu)(3)](2) affords [(K(2)(mu-NCCH(3))(4)(mu-OH(2)))(2)(Fe(2)(mu-O)L(3)H(2))(2)(CH(3)CN)(2)] 6 x 9(CH(3)CN). In the case of p-tert-butyltetrahomodioxacalix[6]areneH(6) (L(4)H(6)), reaction with [(THF)MFe(OtBu)(3)](2) (two equivalents) leads to isolation of the pseudoisomorphic complexes [M(2)(CH(3)CN)(4)L(4)Fe(2)(mu-O)] x 4 CH(3)CN M = Na 7 x 4(CH(3)CN), M = K 8 x 2(CH(3)CN); similar use of p-tert-butylhexahomotrioxacalix[3]areneH(3) (L(5)H(3)) led to [Na(2)Fe(2)(mu-OH)(2)(L(5))(2)(CH(3)CN)(4)] 9 x 2(CH(2)Cl(2)). The complex [L(4)(ZnEt)(4)Zn(2)(CH(3)CN)(4)(mu-OEt)(2)], 10 x 2(CH(3)CN), isolated from the reaction of L(4)H(6) and ZnEt(2) is also reported. Complexes 1-10 are structurally characterized (partially in the case of 4) and screened (not 5) as catalysts for the ring opening polymerization of epsilon-caprolactone.

One-pot conversion of tetraiminodiphenols to diiminodiaminodiphenols via methyl transfer at aluminium

The [2+2] macrocyclic Schiff base {[2-(OH)-5-(tBu)C6H2-1,3-CH][(CH2CH2)(2-C6H4N)2]}2 (1) is readily converted to the diiminodiamine {[2-(OH)-5-(tBu)C6H2-1-(CH)-3-C(Me)H][(CH2CH2)(2-(N)-2′-C6H4NH)2]}2 (2) via methyl group transfer from Me3Al (four equivalents) and subsequent hydrolysis. When compound 1 is reacted with two equivalents of Me3Al, the dinuclear complex {(Me2Al)[2-(O)-5-(tBu)C6H2-1,3-(CH)2][(CH2CH2)(2-C6H4)2N)2]}2 (3) is formed. The structures of the macrocycles 1 and 2 are described (in the case of 1, the toluene solvate has also been structurally characterised).

Amine influence in vanadium-based ethylene polymerisation pro- catalysts bearing bis(phenolate) ligands with ‘pendant’ arms

Two families of vanadium complexes bearing diphenolate ligands with different ‘pendant’ arms have been screened under various conditions for the polymerisation behaviour of ethylene. The presence of a bound amine arm was found to favour enhanced thermal stability.

Early transition metal calixarene and tripod ligand complexes for ethylene polymerisation

The field of calixarene chemistry has grown substantially in the past decade. There are now many reported applications including sensors, medical diagnostics and phase transfer agents. [1] Use in polymerisation catalysis for a variety of chemical systems has, however, only recently gained attention with mixed success. [2-6] This paper focuses on our discoveries with early transition metal (primarily vanadium) oxo or organoimido fragments supported on the hexahomotrioxacalix[3]arene ligand (see figure for an example) or by one of a range of new tripodal ligands. Oxacalix[3] ligands have gained very little attention in the literature thus far, in contrast to the rich literature for the well-known calix[4]arenes. Here we report the structures and high ethylene polymerisation catalytic activity of the new compounds. The structural work has been undertaken using both laboratorybased conventional X-ray sources and synchrotron radiation at Daresbury Laboratory, all at low temperature.