A laser flash photolysis study of a carbene-ether ylide

Laser flash photolysis (308 nm) of carbomethoxy-2-naphththyldiazomethane in deoxygenated Freon-113 (CF2-ClCFCl2) solution containing tetrahydrofuran ( THF) produces a transient spectrum with a sharp absorption maximum at 330 n m and a shoulder at 375 nm. The observed rate constant of formation of tran sient absorption is the same at 330 and 400 nm. The transient spectrum is t he same 100 ns, 1 mus, and 10 mus after the laser pulse at ambient temperat ure and is attributable to a single carrier. The transient shows little dec ay over 10 mus in the presence and absence of oxygen. Similar results were obtained at -60 degrees C. This pattern of observations is not consistent w ith assigning the transient to triplet carbomethoxy-2-naphthylcarbene or it s related radical. The rate constant of formation of the transient, k(THF), is first order in the concentration of THF: thus, the transient is attribu ted to a carbene-ether ylide. To our knowledge, this is the first direct ob servation of a carbene-ether ylide. An Arrhenius plot of k(THF) is nonlinea r due to a change in mechanism of the the carbene with THF or to reversion of the ylide to carbene and THF at elevated temperatures.