Cations fluorenyl

The 9-fluorenyl cation, being a 4 -electron system, should be antiaromatic, as has been generally believed. However, Richard and coworkers provided experimental and theoretical data suggesting that this cation is not antiaromatic.Recent preparation of several fluorenyl dications, on the other hand, does prove that the fluorenyl system is antiaromatic in the dicationic systems. Mills and coworkers have generated the fluorenyl dications (115-120) by SbFs-oxidation of the tetraben-zofulvalene derivatives containing fluorenylidene and —five- and seven-membered... 

The 9-fluorenyl cation also reacts at the diffusion limit with substituted styrenes, as indicated by the observation that the rate constants are 3 x 10 M s independent of the styrene substituent. The reaction of styrene with the phenethyl cation (71), the first step in the polymerization of styrene (Sty) catalyzed by Brpnsted acids, has also been directly observed (Scheme 1.8). Photoprotonation of styrene... 

The transient zwitterion (15), obtained from the /(-hydroxy acid precursor by laser flash photolysis, has been characterized 46 it reacts with nucleophiles more slowly than does the 9-fluorenyl cation itself. The parent acid was also characterized.46 Evidence has been presented that (16) undergoes substantial El elimination via a primary carbocation.47 An analysis of solvolysis results for (17) is indicative of extensive charge delocalization throughout the fluorenyl ring at the transition state apparently... 

The low reactivity of 9-fluorenyl derivatives was long considered to be due to the antiaromatic character of the An 7t-electron 9-fluorenyl cation 204. 380,424 Later>... 

Attempts to observe intramolecular rearrangements of 9-methyl-9-fluorenyl cation via capped pyramidal ions [58] have been unsuccessful (Olah et aL 1980a). 

The photoisomerisation kinetics and other properties of the 1 1 inclusion complexes formed between aromatic derivatives of norbomadiene and P-cyclo-dextrin have been measured." (S)- or (R)-2-Chloropropiophenone affords partially racemised (S)- or (R)-2-phenylpropionic acid respectively by a photo-induced rearrangement via what is probably an ion or radieal intermediate," and (Z)-N-substituted benzoyl-a-dehydrophenylalanines such as (7) are photo-isomerised to 1-azetidine derivatives (8) by a 1,3-acyl migration. Irradiation of 9,9 -bifluorene-9,9 -diol (9) gives a mixture of fluoren-9-one and spiro[9H-fluorene-9,9 (10 -H)-phenanthren]-10 -one (10) whose composition is solvent dependent with the more polar solvents favouring (10). Laser flash photolysis shows the presence of two transients, one of which can be identified with the 9-fluorenyl cation (11), and which originates from photoheterolysis of the diol (9). There is also evidence to support the view that unimolecular rearrange-... 

Carbon-oxygen bond heterolysis is responsible for the observed photolyses of 9-aryl-9-xanthenols ° and llH-benzo[b]fluoren-11-ol. - - Evidence for the formation of the 9-fluorenol radical cation as well as the 9-fluorenyl cation has been obtained from a laser flash photolysis study of 9-fluorenol. 1, l-Di-2-thienylethanol undergoes light-induced dehydration to give i,i-di-2-thienylethylene.Single electron transfer pathways, however, are implicated in the ring cleavage reactions of a,j8-epoxy ketones in the presence of allyltributyltin - or alkylamines. 

Gurzadyan, G. G., Steenken, S., Solvent dependent C OH Homolysis and Heterolysis in Electronically Excited 9 Fluorenol the Life and Solvation Time of the 9 Fluorenyl Cation in Water, Chem. Eur. J. 2001, 7, 1808 1815. 

In accordance with the above mentioned data are those reported in Ref. 234.235) indicating that the 9-isopropyl-9-fluorenyl cation (32b) does not reveal any tendency to rearrangement even at —20 °C while the rearrangement of a 9-/ert-butylfluorenyl analogue (32c) into a 9,9,10-trimethylphenanthrenonium ion (33c) proceeds very quickly even at lower temperatures 218.220) oq 2 min... 

Both the 9-methyl and 9-trifluoromethyl-9-fluorenyl cations (7 and 8) have been generated by laser flash photolysis of corresponding alcohol precursors. The product ions were then studied by time-resolved spectroscopy. Consistent with previous studies related to carbocation-bearing electron-withdrawing groups, ion (8) exhibits a significant bathochromic shift in the UV absorption compared to (7). The ions were quenched with methanol and reaction rates showed cation (8) to be a more reactive species. 

A numerical scale of calculated values for antiaromaticity was derived from values of the HOMO— LUMO gap for different cations for which a value of 0 indicates no antiaromatic destabilization and with a maximum value of 1.0 for the cyclopentadienyl cation. On this scale of antiaromaticity, the value for the indenyl cation is 0.47 and that for the 9-fluorenyl cation is 0.33. ... 

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