Evidence for Specific Solvation of Two Halocarbene Amides

Laser flash photolysis (LFP, 308 nm) of endo-10-halo-10‘-N,N-dimethylcarboxamidetricyclo[4.3.1.0]-deca-2,4-diene (1Cl and 1F) releases indan and halocarbene amide (2Cl and 2F). Although the
carbenes are not UV−vis active, they react rapidly with pyridine to form ylides (4Cl, 4F), which are readily
detected in LFP experiments (λmax = 450 nm). Dioxane decreases the observed rate of carbene reaction
with pyridine in CF2ClCFCl2. Small amounts of THF decrease the observed rate of reaction of carbene 2F
with pyridine but increase the rate of reaction of carbene 2Cl with pyridine. LFP (266 nm) of dienes 1Cl
and 1F in CF2ClCFCl2 with IR detection produces carbenes 2Cl and 2F with carbonyl vibrations at 1635
and 1650 cm-1, respectively. In dioxane or THF solvent, LFP produces the corresponding ether ylides
(5Cl, 5F) by capture of carbenes 2Cl and 2F. The ylides have broad carbonyl vibrations between 1560
and 1610 cm-1. The addition of a small amount of dioxane in CFCl2CF2Cl extends the lifetime of the carbene.
This observation, together with the ether-induced retardation of the rates of carbene capture by
tetramethylethylene and pyridine, is evidence for solvation of the carbene by dioxane.