Simon P. D. Baugh

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.

The role of bulky substituents in the polymerization of ethylene using late transition metal catalysts: a comparative study of nickel and iron catalyst systems

Abstract A series of nickel(II) and iron(II) complexes of the general formula [LMX2] containing bidentate (for M=Ni) and tridentate (for M=Fe) heterocycle-imine ligands L have been synthesized and characterized. Compared to the well-known α-diimine nickel and bis(imino)pyridine iron catalysts, these systems contain a bulky imine substituent on one side and a non-bulky N-heterocycle on the other. Depending on the ligand and the conditions used, either four- or five-coordinate complexes are obtained in the case of nickel. Iron complexes are generally five-coordinate, even with potentially tetradentate ligands. Activation of these precatalysts with MAO affords active catalyst systems for the oligomerization/polymerization of ethylene. Compared to α-diimine nickel and bis(imino)pyridine iron catalysts, both metal systems provide only half of the steric protection and consequently the catalytic activities and the degree of polymerization are significantly lower. Lower activities are attributed to a reduced stability of the active species under polymerization conditions, whereas the lower molecular weights are a result of increased β-H transfer rates. Variations within the heterocyclic component of the ligand reveal that both steric and electronic factors influence the polymerization behavior of these catalysts.

Alkene metathesis in the synthesis of novel β-lactams

Both monocyclic and bicyclic β-lactams systems are prepared via alkene metathesis reactions using Mo(CHC-Me2Ph)(NC6H3Pr2i-2,6)[OCMe(CF3)2]2 or Ru(HPh)-Cl2(PCy3)2.

An extremely fast and efficient acylation reaction of alcohols with acid anhydrides in the presence of trimethylsilyl trifluoromethanesulfonate as catalyst

Alcohols are converted to esters in a fast, clean and efficient reaction with acid anhydrides in the presence of trimethylsilyl trifluoromethanesulfonate.

Enyne metathesis for the facile synthesis of highly functionalisednovel bicyclic β-lactams

A wide range of bicyclic β-lactam systems have been prepared via the enyne metathesis reaction using catalytic quantities of trans-(Cy 3 P) 2 Cl 2 RuCHPh (Cy = cyclohexyl).

Highly functionalised monocyclic and bicyclic β-lactamsvia alkene metathesis

Both monocyclic and bicyclic β-lactam systems are prepared via alkene metathesis reactions using Mo(CHCPhMe 2 )- (NC 6 H 3 Pr i 2 )[(OCMe(CF 3 ) 2 ] 2 or Ru(CHPh)Cl 2 (PCy 3 ) 2 .