Stable versions of transient push-pull carbenes: Extending lifetimes from nanoseconds to weeks

A (phosphanyl) (trifluoromethyl)carbene is shown to be stable for weeks in solution at temperatures up to -30 degrees C. Its chemical behavior exactly matches that of its transient congeners, even to the extent that subtle ef fects, such as the recently discovered weak a interaction with aromatics, a re observed. The influence of substituents on the structure of push-pull ca rbenes is demonstrated by a single-crystal x-ray diffraction study of a (ph osphanyl)[2,6-bis(trifluoromethyl)phenyl]carbene. The lifetime of these mol ecules makes them accessible to a wider range of standard techniques, allow ing their chemical and physical behaviors to be studied in more detail than was previously possible.