Preparation of bis(diazo) compounds incorporated into butadiyne and thiophene units, and generation and characterization of bis(carbene) from these compounds.

Abstract

[9-[10-(4-t-Butyl-2,6-dimethyl)phenyl]anthryl](4-bromo-2,6-dimethylphenyl)diazomethane (1-N(2)) was found to be stable enough to survive under Sonogashira and Suzuki coupling reaction conditions, and bis(diazo) compounds incorporated into the 1,4-positions of butadiyne (3-2N(2)) and the 2,5-position of thiophene (4-2N(2)) were prepared. Irradiation of those bis(diazo) compounds generated bis(carbenes), which were characterized by ESR and UV-vis spectroscopic techniques in a matrix at low temperature, as well as time-resolved UV-vis spectroscopy in solution at room temperature. These studies revealed that both of the bis(carbenes), 3 and 4, have a singlet quinoidal diradical ground state with a very small singlet-triplet energy gap of less than 1 kcal/mol. A remarkable increase in the lifetime of bis(carbenes) as opposed to that of monocarbene (1) was noted and was interpreted to indicate that bis(carbenes) are thermodynamically stabilized as a result of delocalization of unpaired electrons throughout a pi-net framework. Despite the stability, both bis(carbenes) are readily trapped by molecular oxygen to afford bis(ketones) as main products.