9-Mesityl-9,10-dihydro-9-boraanthrylidene: A Probe of Structure and Reactivity for Aromatic Carbenes

Article abstract of DOI:10.1021/ja00319a032

Photolysis of 10-diazo-9-mesityl-9,10-dihydro-9-boraanthracene (1) causes loss of nitrogen and formation of 9-mesityl-9,10-dihydro-9-boraanthrylidene (BA).Direct irradiation leads first to the singlet carbene, which intersystem crosses to the triplet.Photosensitization with triplet 2-acetonaphthone gives the triplet carbene directly.The singlet carbene reacts with isopropyl alcohol to give the appropriate ether.The triplet carbene forms cyclopropanes nonstereospecifically from terminal olefins and abstracts hydrogen atoms from hydrocarbons and alcohols.Kinetic and product analysis shows that, in contrast to fluorenylidene, the rate of equilibrium between ¹BA and ³BA is slow compared with most of the bimolecular reactions of the triplet.This is believed to be a consequence of the larger energy gap between ground-state ³BA and ¹BA compared with that of fluorenylidene.The effect of carbene structure on the magnitude of this energy gap is discussed.