Generation and direct observation of the 9-fluorenyl cation in non-acidic zeolites

9-Alkyl-9-fluorenyl cations and the parent 9-fluorenyl cation are generated via photoheterolysis of the corresponding 9-fluor-enols within alkali meta l zeolites such as LiY, NaY and Na beta, and observed directly using nanose cond laser flash photolysis. The observation of the highly reactive and hig hly unstable 9-fluorenyl cation under these conditions provides a remarkabl e example of the extraordinary ability of non-proton exchanged zeolites to provide kinetic stabilisation for electrophilic guests. The reactivity of t he carbocations is found to be highly influenced by the nature of the alkal i metal counterion as well as the inclusion of cosolvents within the zeolit e matrix. The availability of several reaction pathways, other than heterol ysis, to photoexcited 9-fluorenols within the zeolite cavities is also demo nstrated and shown to be modified by co-adsorbed protic reagents in a manne r consistent with solvent-assisted dehydroxylation. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.