Cyclopropenylidenes: From Interstellar Space to an Isolated Derivative in the Laboratory

Like many of the molecular species that have been detected in the interstellar medium, the singlet carbene cyclopropenylidene (C₃H₂) has been presumed to be too unstable to isolate in the laboratory. However, by appending π-electron-donating amino groups to the triangular skeleton, we prepared a cyclopropenylidene derivative that is stable at room temperature. In contrast to previously isolated carbenes, this compound does not require a heteroatom adjacent to the electron-deficient carbon to confer stability. Despite the presence of amino groups, the geometric parameters of the cyclic skeleton, revealed by x-ray crystallography, are only slightly perturbed relative to those of the calculated structure of unsubstituted cyclopropenylidene. Stable cyclopropenylidene derivatives might thus serve as models for a better understanding of the formation of carbon-bearing molecules in the interstellar medium.