Gas-phase ion chemistry of Cr(.eta.6-arene)(CO)3 complexes by FTMS techniques

Abstract

The gas-phase reactivities of eight Cr({eta}{sup 6}-arene)(CO){sub 3} complexes (arene = toluene, mesitylene, PhCOOOMe, PhCOMe, PhCOEt, PhCO-n-Pr, PhCO-t-Bu, PhCH{sub 2}COMe) have been studied by FTMS techniques. Self-condensation processes occur that follow different reaction pathways when the coordinated arene is a hydrocarbon or a phenyl ketone. PhCOOOMe and PhCH{sub 2}COMe show an intermediate behavior. Reactions with free arenes or propene give substitution of the carbonyl groups, yielding Cr(arene)(arene{prime}){sup +} and Cr(arene)(propene){sup +}, respectively. The extent to which displacement takes place depends on the nature of the original coordinated arene and is higher when it contains a CO group. With suitable free arenes as reagent gases, arene displacement is also observed, producing Cr(arene{prime}){sub 2}{sup +}. The formation of the disubstituted ions depends, once again, on the nature of the coordinated arene as well as on the relative bond energy of Cr{sup +}-arene{prime} with respect to Cr{sup +}-arene. CID experiments have been performed in order to obtain a sequence of relative binding energies of the arenes to Cr{sup +}. The results are consistent with the electronic and steric properties of the arene ligands, which affect the Cr{sup +}-arene bond strength.