Insertion Elimination Mechanism Research Articles

Theoretical Investigation of the Reaction of Co+ with OCS

The reaction of Co+ with OCS on both triplet and quintet surfaces has been investigated at the B3LYP level of theory of density functional theory with the standard 6-311+G(d) basis set. The object of this investigation was the elucidation of the reaction mechanism. The calculated results indicate that both the C−S and C−O bond activations proceed via an insertion-elimination mechanism. Although the direct sulfur and oxygen atom abstractions by Co+ might contribute to the formations of CoS+ and CoO+, the tight transition state structures were not found in the present calculations. Intersystem crossing between the triplet and quintet surfaces may occur along both the C−S and C−O bond activation branches. The ground states of CoS+ and CoO+ were found to be quintets, whereas CoCO+ and CoCS+ have triplet ground states. The C−S bond activation is energetically much more favorable than the C−O bond activation. All theoretical results are in line with early experiments.

Theoretical study of the reaction of Fe + with CS 2 in gas phase

The reaction of Fe + with CS 2, which was selected as a representative system of the reactions of transition metals with CS 2, has been investigated using density functional theory at B3LYP/6-311+G(d) level of theory. The geometries, energies and frequencies of reactant, intermediates, transition states and products were explored in detail on both the quartet and sextet potential energy surfaces of [Fe, C, S 2] +. Our calculations indicate the reaction proceeds via an insertion–elimination mechanism but not a direct abstract mechanism. All of the observed products in the early experiment has been explained according to the cleavage of different bonds in the insertion intermediate S–Fe +–C–S. The connectivity in [Fe,C,S] +, which cannot be specified by experiment, was revealed as [S–C–Fe] + in our study. By comparing the Fe ++CS 2 and V ++CS 2, we suppose all the reactions of first-row transition metal ions with CS 2 could proceed according to the similar insertion–elimination mechanism.

Identification of an elusive catalyst: IrH( η2-C 6H 4P tBu 2) (Cl)(P tBu 2Ph) as a precursor for C=C bond migration

The catalytic isomerization of allylbenzene to cis/trans-β-Me styrene in solutions containing Ir(III) hydride halide, hydrido hydroxide and hydrido alkoxide Ir(H) 2X(P tBu 2Ph) 2 (X = F, Cl, Br, I, OH, OCH 2 CF 3) is described. Large variations in isomerization rate ( k obs) are found to correlate with the electron donating ability ( π + σ) of the X ligand: the rate is enhanced by more effective donation by the X ligands. A number of kinetic studies and phosphine exchange experiments utilizing a deuterium labeled phosphine, P 1Bu 2( d 2)Ph, indicate that the active isomerization catalyst is a 14-valence-electron Ir(III) species derived from the ortho-metallated complex, IrH( η 2-C 6H 4P tBu 2)-(X) (P tBu 2Ph), by phosphine dissociation. Using IrH( η 2-C 6H 4P tBu 2) (Cl) (P tBu 2Ph) as a catalyst precursor, the catalytic isomerization of α, α- d 2-allylbenzene in the presence of an excess of 4-allyl anisole has yielded primarily d 1- cis/ trans- β-Me styrene, which confirms that the isomerization proceeds via an insertion-elimination mechanism of a metal hydride bond.

Kinetics of methylidyne (CH X 2Π) radical reactions with ammonia and methylamines

Laser photolysis/laser-induced fluorescence (LIF) was employed to measure the rate constants for CH (X 2Π) radical reactions with NH 3, CH 3NH 2, (CH 3) 2NH, and (CH 3) 3N. The ground state CH radicals were generated by the multiphoton dissociation of CHBr 3 at 266 nm. The relative CH concentration was probed by LIF at 429.8 nm. The experiments were performed on flowing gas mixtures thus allowing pressure and temperature studies to be performed. No variation of the measured rate constants with pressure was observed over the range 30 to 100 Torr total pressure (mostly argon). The following Arrhenius equations, covering the temperature range 297 to 677 K, are derived: CH + NH 3, k 2 = (8.6±0.6 )×10 −11 exp [(230±30) / T] cm 3 s −1; CH + CH 3NH 2, k 2 = (3.1±0.2)×10 −10 exp [(170±30)/ T] cm 3s −1; CH + (CH 3) 2NH, k 2 = (2.4±0.2)×10 −10 exp [(290±30)/ T] cm 3 s −1; CH + (CH 3) 3N, k 2 = (2.6±0.2)×10 −10 exp [ (230±30)/ T] cm 3 s −1. The observed temperature and pressure dependences are in accord with an insertion-elimination mechanism. On a per bond basis, CH reactivity toward NH bonds is only slightly larger than its reactivity toward CH bonds. The observed large rate constants for the methylamine reactions could be attributed to the change in ionization potential (lowering) and polarizability (increasing) as compared with alkanes.