Helen A. Joly

Electron paramagnetic resonance study of the reaction of ground-state aluminium atoms with a series of ethers in a rotating cryostat

Ground-state Al atoms react with symmetric cyclic and acyclic ethers at 77 K in a rotating cryostat to give a host of mononuclear organoaluminium compounds. Magnetic parameters determined from EPR spectra given by Al atoms and acyclic ethers are consistent with the formation of novel C—C and C—H aluminium atom insertion products. A third species has been tentatively assigned to the product given by Al atom insertion into the C—O bond. In addition a carbon-centred radical is formed by loss of a hydrogen atom from carbon adjacent to the alkoxyl group. In contrast the cyclic ethers are resistant to alumino hydride formation and in most cases a carbon radical resulting from ring opening at the C—O bond is formed. Mono- and di-ligand complexes, Al[ether] and Al[ether]2, are tentatively identified and may be the primary intermediates for all the reactions that occur.

Reaction of ground-state aluminium atoms with diethyl ether. Electron spin resonance evidence for insertion into the CH and CC bonds

Ground-state Al atoms react with diethyl ether on solid hydrocarbon surfaces at 77 K in a rotating cryostat to give several mononuclear aluminium(o) compounds. The magnetic parameters of two of these compounds are consistent with the formation of CH3CHAlH(OCH2CH3) and/or CH3CH2OCH2CH2AlH and CH3AlCH2OCH2CH3 produced by insertion of the Al atom into the CH and CC bonds of the ether. A third species could be CH3CH2OAlCH2CH3, given by insertion into the CO bond, but this assignment is somewhat tentative.

The observation of pseudorotating lithium and potassium clusters Li5 and K7 in an adamantane matrix

Abstract The pseudorotating clusters, Li5 and K7, have been identified in an adamantane matrix by EPR spectroscopy. These new clusters were synthesised by depositing the parent alkali metal atoms at 77 K in the hydrocarbon matrix followed by careful annealing to temperatures above 200 K.

The reactions of silicon monoxide and aluminium monofluoride with 2,2′-bipyridyl

Abstract The high temperature species, SiO and AlF, have each been treated with 2,2′-bipyridyl in tetrahydrofuran solution at − 105 °C and in an adamatane matrix at − 196 °C to give products which have spectroscopic properties closely resembling the known compound [SiCl 2 (bipy) 2 ]. When initially formed the products are highly coloured and paramagnetic in solution or in the adamantane matrix and their EPR spectra show the presence of singlet and triplet species. In the triplet species, two electrons are transferred from the silicon or aluminium centre to two bipyridyl ligands which must lie orthogonal to each other across the metal centres but it is uncertain whether the species are monomeric or oligomeric. Evaporation of the solutions causes irreversible precipitation of pyrophoric solids of composition SiO(bipy) or AlF(bipy).

Electron spin resonance studies of the reactions of aluminium atoms with some alkenes in a rotating cryostat

Al atoms react with propenes and butenes in a rotating cryostat at 77 K to give a range of organoaluminium products including aluminium monoalkene complexes, π-allyl aluminium hydrides and aluminacyclopentanes, but no β-aluminoalkyls. In addition allyls are major paramagnetic products. The magnetic parameters of these species are reported, and possible reaction mechanisms are discussed. cis-But-2-ene is unique in that a cluster-alkene complex Al3[cis-C4H8]x appears to be the major paramagnetic product.

Electron paramagnetic resonance study of the reaction of group 11 metal atoms with higher alkenes in a rotating cryostat

Cu, Ag and Au atoms have been reacted with a range of higher acyclic and cyclic alkenes and unconjugated dienes in inert hydrocarbon matrices at 77 K in a rotating cryostat and the paramagnetic products examined by electron paramagnetic resonance spectroscopy. In general the products are similar to those that are formed from ethene and propene, but there are some subtle and important differences. Thus Cu atoms give mainly mono- and di-ligand complexes, Ag atoms give monoligand complexes, cluster–alkene complexes and microcrystallites, but mononuclear diligand complexes are not formed, and Au atoms give mono- and di-ligand complexes. There is tentative evidence for the formation of a triligand complex from Cu and cis-cyclooctene. In most cases allyls are formed by hydrogen-atom abstraction from the alkenes, perhaps by adventitious metal oxide.

Electron paramagnetic resonance spectra of coinage metal atoms trapped in evaporated alkali-metal chloride matrices at low temperatures

Copper, silver and gold atoms have been isolated in vapour-deposited alkali-metal chlorides in a rotating cryostat at 77 K. Their EPR spectra show much lower hyperfine interactions than gas-phase metal atoms or atoms prepared in alkali-metal chloride single crystals from metal ions in cationic substitutional sites by electron capture. The difference is thought to arise because the metal atoms in the rotating-cryostat experiments are located in asymmetric trapping sites at the interface between layers of the alkali-metal chloride, and resemble species trapped at surfaces and grain boundaries rather than those in the bulk solid.

EPR spectra of Al[P(CH3)3]2 and Al[P(OCH3)3]2 in hydrocarbon matrices

Abstract EPR examination of the products of the reaction between Al atoms and P(CH 3 ) 3 and P(OCH 3 ) 3 on a rotating cryostat in hydrocarbon matrices at 77 K reveals the presence of the seven-electron binary complexes Al[P(CH 3 ) 3 ] 2 and Al[P(OCH 3 ) 3 ] 2 . The magnetic parameters of these complexes are consistent with bent π radicals of C 2v symmetry. The unpaired electron is located in a molecular orbital perpendicular to the P—Al—P plane which is constituted largely from the Al atomic 3p x orbital with a contribution from P 3p x and/or 3d xz , 3d xy atomic orbitals.

Studies of the reactions of SiO and silver atoms in hydrocarbon matrices at 77 K

Electron paramagnetic resonance (EPR) spectroscopic studies indicate that reaction of Ag atoms with SiO in an adamantane matrix at 77 K yields Ag(SiO), Ag(SiO), Ag(Si2O2), Ag(Si3O3), and Ag(SinOn); the bonding in these species is discussed.

EPR spectra of the complexes of P(OMe)3 and PMe3 with Cu atoms in hydrocarbon matrices at 77 K

Abstract The paramagnetic products from reacting Cu atoms with P(OMe) 3 and PMe 3 on a rotating cryostat have been examined by EPR spectroscopy and shown to be mainly the seventeen-electron tris(trivalent phosphorus) complexes, Cu[PX 3 ] 3 . Their magnetic parameters are consistent with a planar π radical structure in D 3h symmetry. The Cu undergoes sp 2 hybridization with the phosphorus ligands donating their lone-pair electrons into these three empty orbitals and the unpaired electron occupying mainly the remaining Cu 4p z orbital perpendicular to the molecular plane. There is less back donation of unpaired spin population into P σ* or 3d orbitals than there is into the π* orbitals of CO in the isostructural carbonyl complex, Cu(CO) 3 .