Diphenylcarbenes laser flash photolysis

The reaction of triplet diphenylcarbene with pyridine has been well studied, and a mechanism proposed from kinetic data (90TL953). The carbenes generated from laser flash photolysis of alkylbromo- and alkylfluoro-diazirines were trapped by pyridine to form the pyridinium ylides... 

The kinetics of the reaction of triplet diphenylcarbene with pyridine has been studied.108 Laser flash photolysis of diphenyldiazomethane in the presence of pyridine results in the formation of pyridinium ylide 200. This reactive species shows an absorption band at 500 nm. Based on the low activation energy of the reaction, it was concluded that the data were inconsistent with a simple preequilibrium model. Instead, it was suggested that the intersystem crossing step occurs at a point other than at the minimum of singlet diphenylcarbene.108... 

Triplet diphenylcarbene, detected spectroscopically on excimer laser flash photolysis of diphenyldiazomethane, readily abstracts hydrogen from cyclohexane to give the CHPh2 radical.Analogous hydrogen abstraction also occurs from alcohols but at low temperatures and in a polycrystalline matrix in contrast to reaction in solution in which O-H bond insertion is preferred. In a similar fashion, irradiation of diphenyldiazomethane in polycrystalline (S)-butan-2-ol at — gave amongst other products an enantiomerically pure... 

The formation of diphenylcarbene by laser flash photolysis of diphenyldiazomethane was studied in SC-CO2 and other supercritical media. [18] A laser-flash induced ring-closure reaction of a bipyridyl complex (Scheme 2) revealed solvation properties. [19] Laser-flash impact to metal carbonyl complexes activated hydrogen and simple alkanes like CH4, C2H4, C2H6, and further inorganic reactions in supercritical fluids have been reviewed. [20]... 

In 1976, Closs and Rabinow made the first measurement of rate constants for the reaction of a carbene. They used a flash photolysis technique. A brief flash of radiation generated carbene intermediates, and their decay was then monitored spectrophotometri-cally. In this way the rate constant for reaction of diphenylcarbene with 1,1 -diphenylethylene was found to be 4.8 x 10 s h Using this technique, measurements were possible on a microsecond time scale. With the advent of laser flash photolysis techniques, the resolution time was reduced to nanoseconds, causing a resurgence of interest in the kinetics of carbene reactions. The early results of use of this technique have been discussed by Griller and coworkers. ... 

A two-electron oxidation of allenes (1) (A = S, NMe) has been found to yield carbenes (2) (Scheme 1) dimerization and reaction with (2,2,6,6-tetraamethyl-piperidin-l-yl)oxyl (TEMPO) support a triplet ground state as predicted by computations. Triplet diphenylcarbenes bearing bulky substituents at the para positions have been generated and studied in rigid matrixes at low temperatures by electron spin resonance (ESR) and UV-Vis spectroscopy as well as by laser flash photolysis (LFP) in solution at room temperature. Their reactivity upon LFP was shown to be dominated by dimerization unless triplet carbene quenchers (such as oxygen and cyclohexadiene) were present. 

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