Supplementary Material Available: Tables I-IX of atomic coordinates, temperature factors, hydrogen coordinates, and structure factors for disordered anisotropic and ordered model refinement and crystallographic data (30 pages). Ordering information is given on any current masthead page.Abstract: 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 'BA 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 'BA and 'BA compared with that of fluorenylidene. The effect of carbene structure on the magnitude of this energy gap is discussed.The chemical and physical properties of carbenes have intrigued Intensive experimental and computational research has focused on the difference in structure, in energy, and in reactivity between the two lowest electronic states a generation of chemists.'
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