Rowan D. Young

Observation of a Tungsten Alkane σ-Complex Showing Selective Binding of Methyl Groups Using FTIR and NMR Spectroscopies

The alkane σ-complex (HEB)W(CO)(2)(pentane) (HEB = η(6)-hexaethylbenzene) is produced from the UV photolysis of (HEB)W(CO)(3) in alkane solvents at low temperature. IR and (1)H and (13)C NMR spectroscopic data are reported, representing the first NMR data for a group 6 alkane complex. Only binding of the methyl functionality of the pentane ligand was observed in (HEB)W(CO)(2)(pentane). This contrasts with the previously reported binding of pentane to rhenium fragments, wherein both methylene and methyl groups were observed to bind, with a slight preference for binding of the former. The reason for the preference for binding through the methyl group is investigated, and the steric requirement for the pentane to adopt an unfavorable gauche conformation when bound via a methylene is identified as a contributing factor.

Characterisation of Alkane σ-Complexes

Alkane σ-complexes have evolved from a curious phenomenon to an intermediate of intense interest, fuelling research into the area. Over the last fifteen years, metal alkane complex characterisation has evolved to incorporate reports employing UV/Vis, IR and NMR spectroscopy, and X-ray and neutron diffractometry. Previously, due to the sparse geometric characterisation of alkane σ-complexes, assumptions regarding bonding geometries and selectivities were made by comparison to related σ-complexes, or by analysis of C-H activation products. This minireview assembles relevant literature that illuminates the metrics of alkane-metal bonding, and critically analyses the binding mode, selectivity and stability of alkane complexes.

Aluminum-Catalyzed Cross-Coupling of Silylalkynes with Aliphatic C–F Bonds

We report the generation of aliphatic and benzylic acetylenes via reaction of primary, secondary, and tertiary aliphatic fluorides with various trimethylsilyl acetylides. These reactions are catalyzed by Al and B Lewis acids, most effectively by the extremely fluorophilic tris(pentafluorophenyl)alane, representing the first example of catalytic incorporation of alkynes into aliphatic C-F positions. The fluorophilicity of the catalysts gives rise to fluorine selectivity over other halogens, allowing orthogonal reactivity pathways.

Catalytic halodefluorination of aliphatic carbon–fluorine bonds

A variety of halosilanes, in conjunction with aluminum catalysts, convert fluorocarbons into higher halocarbons. Bromination and iodination of fluorocarbons are more effective than chlorination in terms of yield and activity. The mechanism for the reaction is investigated utilizing experimental and computational evidence and preliminary results suggest an alternate mechanism to that reported for the related hydrodefluorination reaction.

Stable Carbocation Generated via 2,5-Cyclohexadien-1-one Protonation

Protonation of a substituted cyclohexadien-1-one (1) leads to the generation of carbocation [3]+, capable of effecting hydride abstraction and oxidation reactions. The molecular structure of [3]+ shows it to be structurally similar to [(p-MeO-C6H4)Ph2C]+. The ability to easily access [3]+ from stable and available precursors, such as 1 and commercially available acids, may allow a wider application of the growing number of trityl-based reactions in organic syntheses.