Electroreductive formation of tetraalkylammonium-metal composites, and application to the reduction of organic compounds

The cathodic behavior of o-(3-butenyl)fluorobenzene (1f) at Hg and Ph cathodes was investigated by cyclic voltammetry (CV) and preparative electrolysis. At either cathode 1-methylindane (3) and 3-butenylbenzene (2) were formed. The effects of reaction conditions on the product composition were studied and the highest yield of 3 was obtained at a lead cathode at 22{dollar}spcirc{dollar}C (3/2 = 3.8). Dimethylpyrrolidinium (Me{dollar}sb2{dollar}Py{dollar}sp+{dollar}) was found to catalyze the reduction of 1f and increase 3/2. It was proposed that Me{dollar}sb2{dollar}Py{dollar}sp+{dollar} participates in an electrocatalytic cycle at Hg via formation of an intermediate identified as the composite Me{dollar}sb2{dollar}PyHg{dollar}sb5{dollar}.; It was found that preformed Me{dollar}sb2{dollar}PyHg{dollar}sb5{dollar} was unable to efficiently reduce 1f. Preformed Me{dollar}sb2{dollar}PyHg{dollar}sb5{dollar} was able to reduce chloro and bromoaromatics efficiently, but was unable to effect reductive cyclization of o-(3-butenyl)chlorobenzene (1c). These results were contradictory to the results obtained for catalytic reduction by Me{dollar}sb2{dollar}Py{dollar}sp+{dollar}. Evidence was presented indicating that the actual reactive intermediate formed during catalytic reduction by Me{dollar}sb2{dollar}Py{dollar}sp+{dollar} is a mixed Me{dollar}sb2{dollar}Py{dollar}sp+{dollar}/Bu{dollar}sb4{dollar}N{dollar}sp+{dollar}/Hg composite (Bu{dollar}sb4{dollar}N{dollar}sp+{dollar} is the supporting electrolyte cation).; In addition to the composite formation exhibited by Me{dollar}sb2{dollar}Py{dollar}sp+{dollar}, it initiated surface effects at potentials positive of Me{dollar}sb2{dollar}PyHg{dollar}sb5{dollar} formation. The most pronounced effect is exhibited by o-bromoanisole reduction. With no Me{dollar}sb2{dollar}Py{dollar}sp+{dollar} present its reduction peak occurs at {dollar}-{dollar}2.67 V. Upon addition of 2 mM Me{dollar}sb2{dollar}Py{dollar}sp+{dollar}, E{dollar}rm sbsp{lcub}p{rcub}{lcub}c{rcub}{dollar} p of o-bromoanisole appears at {dollar}-{dollar}2.18 V. {dollar}Delta{dollar}E{dollar}rm sbsp{lcub}p{rcub}{lcub}c{rcub}{dollar} for o-bromoanisole is linear with ln(Me{dollar}sb2{dollar}Py{dollar}sp+{dollar}), which is in accord with reports in which the smaller Me{dollar}sb4{dollar}N{dollar}sp+{dollar} cation displaced the supporting electrolyte cation in the double layer and increased the rate of electron transfer.; Using a series of 1,1{dollar}spprime{dollar}-n methylenebis(1-methylpyrrolidinium iodide) dications with varying chain length (n = tri, tetra, penta, hexa, octa, deca), it was demonstrated that the pyrrolidinium moieties have a strong influence on the rate of electron transfer and that alkyl chains are involved in blocking of the electrode surface, resulting in an inhibition of electron transfer.