David J. Duncalf

N-alkyl-2-pyridylmethanimines as tuneable alternatives to bipyridine ligands in copper mediated atom transfer radical cyclisation

Abstract Copper halide complexes of N-alkyl-2-pyridylmethanimines ( 3, 11–14 ) catalyse atom transfer radical cyclisation reactions of activated ( 6a-b ) and unactivated α-haloallylacetamides ( 9 ) at room temperature.

[N-Alkyl-(2-pyridyl)methanimine]copper(I) Complexes: Characterisation and Application as Catalysts for Atom-Transfer Polymerisation

The synthesis and characterisation of a series of novel bis(imine)copper(I) complexes and their use in atom-transfer polymerisation of methyl methacrylate is described. Several N-alkyl-(2-pyridyl)methanimines (alkyl = n-butyl, isobutyl, sec-butyl, n-propyl) and N-(n-propyl)-1-(2-pyridyl)ethanimine as ligands have been fully characterised. Three bis[N-alkyl-(2-pyridyl)methanimine]copper(I) complexes, [Cu{(C5H4N)CH=N(iBu)}2][BF4], [Cu{(C5H4N)C(CH3)=N(nPr)}2][PF6], and [Cu{(C5H4N)CH=N(sBu)}2][BF4] have been structurally characterised; all having a distorted tetrahedral arrangement of co-ordinating nitrogen atoms surrounding the metal centre. All of the catalysts were found to be effective atom-transfer polymerisation catalysts for the polymerisation of MMA in hydrocarbon solution. However, it was discovered that the performance of the catalysts containing n-alkyl substituents was superior to those containing branched alkyl substituents. The presence of branching in the alkyl substituent results in a reduction of reaction rate and a corresponding broadening of the polydispersity index.

Atom transfer radical polymerisation (ATRP) of methyl methacrylate in the presence of radical inhibitors

Atom transfer radical polymerisation of methyl methacrylate mediated by copper(I) bromide, alkyl bromides and N-pentyl-2-pyridylmethanimine has been shown to be enhanced by the addition of substituted phenols, traditionally used as radical inhibitors.

Atom transfer polymerisation of methyl methacrylate : use of chiral aryl/alkyl pyridylmethanimine ligands; with copper(I) bromide and as structurally characterised chiral copper(I) complexes

The use ofchiral catalysts in the living radical polymerisation of methyl methacrylate via atom transfer polymerisation (ATP) has been investigated in an effort to control the stereochemistry of the polymer backbone. Two enantiomerically pure chiral catalysts have been prepared and used in the ATP of methyl methacrylate: the structurally characterised complex, bis[N-(1-phenylethyl)-2-pyridylmethanimine]copper() tetrafluoroborate, [Cu(C14H14N2)2 ][BF4 ], and the reaction product of copper() bromide with N-(1-cyclohexylethyl)-2-pyridylmethanimine, [Cu(C14H20N2)2 ][Br]. Both catalysts were found to be suitable for the ATP of methyl methacrylate in conjunction with either ethyl 2-bromo-2-methylpropanoate in xylene at 90 °C or 4-methoxybenzenesulfonyl chloride in diphenyl ether at 90 °C. The system yields polymer of relatively narrow polydispersity; however, the use of these chiral catalysts did not significantly affect the stereochemistry of the polymer backbone. This may be due to the chiral centre being too distant from the propagating site to exert any influence over the monomer addition step, or that the reaction proceeds via a completely free-radical mechanism. This is, however, the first time a discrete, structurally characterised copper complex has been used as an effective ATP catalyst. The bond lengths of the complexed ligand indicate the oxidation state of the copper to be +1 in the complex.

Synthesis and characterisation of (η5-cyclopentadienyl)(η5-ring)titanium alkyl (ring = indenyl or C5H4But) complexes. Crystal and molecular structure of racemic [Ti(η5-C5H5)(η5-C9H7)(CH2SiMe3)Cl]

New, selective and high-yielding preparations of the mixed-ring complexes [Ti(η5-C5H5)(η5-C9H7)C2] and [Ti(η5-C5H5)(η5-C5H4But)Cl2] are reported. These have been used to prepare a range of mono- and di-substituted titanium(IV) alkyl and benzenethiolate complexes of the form [Ti(η5-C5H5)(η5-ring)(CH2SiMe3)Cl] and [Ti(η5-C5H5)(η5-ring)R2](ring = indenyl or C5H4But; R = Me, CH2Ph, CH2SiMe3 or SPh). While the indenyl ligand in the racemic, chiral-at-metal complex [Ti(η5-C5H5)(η5-C9H7)(CH2SiMe3)Cl] is bound in an η5 fashion, X-ray structural data clearly indicate that there is some ‘η3 ring-slip’ character to the bonding. The NMR and nuclear Overhauser effect experiments conducted on [Ti(η5-C5H5)(η5-C5H4But)(CH2SiMe3)Cl] demonstrate hindered rotation around the Ti–C5H4But bond and show the geometry to be fixed such that the But and SiMe3 groups are remote.

C–H activation and nitrile insertion reactions of a cationic niobium alkylidene complex

Oxidation of [Nb(η5-C5H4But)2(CH2Ph)2] yields the stable cationic benzylidene complex [Nb(η5-C5H4But)2(CHPh)(thf)]BPh4, which readily loses thf to form the C–H activation product [Nb(η5-C4H4But)(η5:η1-C5H4CMe2CH2)(η2–CH2Ph)]BPh4 and reacts with acetonitrile to give the double-insertion product [Nb(η5-C5H4But)2{η2-NC(Me)C(Ph)C(Me)NH}]BPh4.

Substituent effects on the cyclo-manganation reaction X-ray crystal structure of Mn{2-(nBu-N=CH) 5-(NO2) C6H3}(CO)4

Abstract The cyclometallation reaction between methylmanganese pentacarbonyl and a number of Schiffs bases has been studied. The dependence of the rate of reaction upon ligand substituents has been investigated, demonstrating a rate enhancement with more electron-rich ligands. The X-ray structure of Mn2-(nBu-N=CH)5-(NO2)C6H3(CO)4 has been determined.

Polymerisation of ethene by the novel titanium complex [Ti(Me3SiNCH2CH2NSiMe3)Cl2]; a metallocene analogue

Reaction of the trimethylsilylated diamine ligand (Me3Si)NHCH2CH2NH(SiMe3) with titanium(IV) precursors affords the novel distorted-tetrahedral complex [Ti(Me3SiNCH2CH2NSiMe3)Cl2] which, when activated by methylaluminoxane, is an active ethene polymerisation catalyst.

First structurally authenticated inorganic polymers of CuBr and CuI containing chiral bidentate N-donor ligands. Use of the Schiff base 2,2′-bis[(4S)-4-benzyl-2-oxazoline] as ligand

The products from the reaction of CuBr and CuI with equimolar quantities of 2,2′-bis[(4S)-4-benzyl-2-oxazoline] have been characterised by X-ray crystallography and shown to comprise two different polymeric arrangements of (CuBr)n or (CuI)n ‘sheathed’ by bridging bidentate oxazoline ligands.

Synthesis of racemic chiral-at-metal complexes of the Group 4 metals

Abstract A protocol for asymmetric synthesis of chiral-at-metal complexes is described, but enantiomerically-enriched products can not be isolated due to formation of complexes between the Group 4 metallocene products and the borane by-products. An efficient method for synthesis of racemic chiral-at-metal metallocenes, through lithium chloride catalysed ligand redistribution reactions, is described. Sterically-hindered racemic chiral-at-metal complexes are prepared by nucleophilic substitution of prochiral dichlorides.