Fluorenyl Cations: Synthesis and Reactivity.

This review covers the history of fluorenyl cations from Deno's first report in 1954 on the parent fluorenyl cation to the present. The parent cation and most derivatives have only been observed as a fleeting species by mass spectrometry, UV/Vis spectroscopy, IR spectroscopy, or NMR spectroscopy. The most common synthetic routes to fluorenyl cations are by dehydroxylation and halide abstraction of substituted fluorenyl precursors. Over the 71 year history, many advancements have been made with recent developments leading to isolable species including two characterized by X-ray diffraction. The scope of this review covers the field of fluorenyl cations in addition to related species with different aromatic groups in place of benzene fused to the cycopentadienyl core.