Chemistry and kinetics of (i) cyclopentadienylidene, (ii) fluorenylidene, and (iii) tetrachlorocyclopentadienylidene

Cyclopentadienylidene (CP), fluorenylidene (Fl), and tetrachlorocyclo-pentadienylidene (ClCP) were studied by laser flash photolysis (LFP) techniques. LFP of diazocyclopentadiene in the presence of a wide variety of carbonyl compounds including aldehydes, ketones, anhydrides, esters, carbonates and possibly amides results in observable transients assigned to carbene-carbonyl ylides. This is not the case for Fl and ClCP generated by LFP of diazofluorene and diazotetrachlorocyclopentadiene. For ClCP no carbonyl ylides were observed, while for Fl a carbene-ketone ylide is the only carbonyl ylide observed. Transients of biphotonic origin were observed in the reaction of CP and ClCP with solvents containing phenyl groups, while these transients were absent for Fl.;The rates of reaction of CP, Fl and ClCP with alcohols and other quenchers were determined by laser flash photolysis methods. The rates of reaction of CP and Fl with various alcohols increased with increasing alcohol acidity and alcohols as a group reacted faster than likely ylide formers such as pyridine, ethyl acetate, and tetrahydrofuran. Bronsted plots of the reaction of CP and Fl with alcohols are linear with slopes of 0.061 and 0.082 respectively. In the case of ClCP, an ylide formation mechanism of reaction with alcohols is indicated by a reversal of reactivity from CP and Fl, with 2-propanol as the most reactive alcohol and likely ylide formers such as tetramethylurea, pyridine, and tetrahydrofuran are found to be more reactive than methanol.