Matrix Isolation of Aryl(trifluoromethyl)carbenes, Heteroaryl(trifluoromethyl)carbenes and Phenylbis(trifluoromethyl)carbenes

Abstract

We have isolated and studied 2-naphthyl(trifluoromethyl)carbene, 1-naphthyl(trifluoromethyl)carbene, 4-pyridyl (trifluoromethyl)carbene, 2-pyridyl(trifluoromethyl)carbene, 3-pyridyl (trifluoromethyl)carbene, 3-bromo-5-pyridyl(trifluoromethyl)carbene, meta-phenylbis(trifluoromethyl)carbene and paraphenylbis(trifluoromethyl)carbene in low temperature matrices for the first time. Thenaphthyl(trifluoromethyl)carbenes are photostable and have triplet ground states in matrices asmost of the other studied ary(trifluoromethyl)carbenes. The 1- and 2-naphthyl(trifluoromethyl)diazirines, the precursors of 1- and 2-naphthyl(trifluoromethyl)carbenes, have dissimilar geometric structures leading to differentUV/Vis absorptions. In the studied pyridyl(trifluoromethyl)carbenes, 4-pyridyl(trifluoromethyl)carbene was the most stable one in matrice: no photoproduct from 4-pyridyl(trifluoromethyl)carbene was observed. However, we obtained a small amount ofphotoproducts of 2 - pyridyl(trifluoromethyl)carbene, even though the result was not repeatable.The most reactive isomer was 3 - pyridyl(trifluoromethyl)carbene, which could decompose underprolonged irradiation. The derivative of 3 - pyridyl(trifluoromethyl)carbene, 3 - bromo - 5 -pyridyl(trifluoromethyl)carbene, was more photolabile and could be converted to otherintermediates with comparatively short term irradiation. All the studied pyridylcarbenes havetriplet ground states. Although they were photostable, phenyl(trifluoromethyl)biscarbenesattracted our attention due to their interesting electronic structures. meta-Phenyl(trifluoromethyl)carbene has a quintet ground state, while the overall multiplicity of para- phenyl(trifluoromethyl)carbene is a singlet with a diradical structure.