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Trifluoromethylcarbene, generated photolytically from 2,2,2-trifluorodiazoethane, reacts with the C-H bonds of saturated hydrocarbons in the liquid phase to give high yields of the corresponding insertion products. The primary and secondary C-H bonds in n-butane undergo insertion a t essentially the same rate, but the tertiary C-H bond in isobutanc is some 30% more reactive than the primary C-H.In the vapour phase very low yields of insertion product result, and 1.1.1 -trifluoroethane and trifluoroethylene are also produced. Liquid-phase photolysis i n trimethylsilane gives more rapid insertion into Si-H than into C-H bonds. The mechanistic implications of the results are discussed.

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Trifluoromethylcarbene, generated photolytically from 2,2,2-trifluorodiazoethane, reacts essentially stereospecifically with trans-and cis-but-2-enes in the liquid phase, to give dimethyltrifluoromethylcyclopropanes, and olefinic insertion products. In the vapour phase, or in solution in an inert solvent, the degree of stereospecificity of the cyclopropane formation and the yield of insertion products are both lower, consistent with the formation of singlet trifluoromethylcarbene and its decay to a triplet state of lower energy. The vapour-phase reaction appears to involve a unimolecular singlet-triplet crossover.THE higher yield of trifluoromethylcyclopropanes formed by reaction in the vapour phase of trifluoromethylcarbene with hydrocarbon olefins rather than fluorinated olefins suggested that the carbene reacted in an electrophilic, and therefore presumably singlet, state. The addition of trifluoromethylcarbene to trans-and cis-but-2-enes has now been found to be stereospecific when the carbene is formed in an excess of the pure liquid olefin, confirming that under these conditions at least the carbene reacts in the singlet state, but the results of reactions in the vapour phase are less clear cut.When the liquid phase of a mixture of 2,2,2-trifluorodiazoethane and a four-fold excess of trans-but-2-ene was irradiated with ultraviolet light (A >3000 A), nitrogen (73%) was evolved, and the major products were l , l , 1,4,4,4-hexafluorobut-tra.ns-2-ene (22y0), a mixture (41 yo) with molecular formula C,H,F,, corresponding to reaction of one carbene species with one molecule of butene, and a complex high-boiling mixture, very similar to that obtained1 by photolysis of the diazoalkane alone. The recovered butene was entirely the trans-isomer. No trifluoroethylene was obtained, implying that migration of fluorine is slower than the other reactions open to the carbene. This is in contrast to the situation in alkylcarbenes, where hydrogen migration is often faster than addition of the carbene to olefins.2 The diazoalkane itself, however, still competes effectively with the added olefin for the carbene.The fraction comprising the 1 : 1 adducts was separated by gas-liquid chromatography (g.1.c.) into an olefinic (43%) and a cyclopropane (57%) fraction. The olefinic fraction was identified by infrared and 19F nuclear magnetic resonance (n.m.r.) spectroscopy, and by hydrogenation to l , l , l-trifluorohexane and 1,1, l-trifluoro-3-meth~lpentane,~ as a mixture of 6,6,6-trifluorohextrans-2-ene (I) (36% of the 1 : 1 adduct) and 5,5,5-trifluoro-3-methylpent-cis-2-ene (11) (7y0), formed by insertion of the carbene into the allylic and vinylic C-H bonds, respectively, without change in configuration at the double bond. The cyclopropane fraction was shown to be mainly (98%) one compound, but a second isomer was detected by 19F n.m.r. This result is in accord with a mainly stereospecific formation of the trans-dimethyl-R.