Photolysis of 3-methyl- and 3-isopropyl-3-ferrocenylcyclopropenes

The photochemistry of 3-methyl- and 3-isopropyl-3-ferrocenylcyclopropenes (10 and 11) has been studied. Upon triplet excitation (sensitized irradiation) both cyclopropenes are dimerized to a tricyclohexane dimers whereas in the singlet state (direct irradiation) cyclopropene 10 is converted to 3-ferrocenyl-3-methylidenepropyne and trans-2-ferrocenyl-2-butene indicating that there is an intermediate vinyl carbene. Cyclopropene 11 is converted to 1-ferrocenyl-4,4-dimethylcyclobutene. Direct irradiation of the mixture of 11 with 2-ferrocenyl-3-methyl-1-butene leads to the formation of 1,3-diferrocenyl-6,6-dimethyl-3-isopropenylcyclohexene (24). A possible reaction pathway via intermediate radicals is discussed. X-ray structural data are presented for 3,6-diferrocenyl-3,6-diisopropyltricyclo[3.1.0.0.2,4]hexane and compound 24.