Catalytic cyclopropanation with iron(II) complexes

Iron(II) complexes of meso-tetra-p-tolylporphyrin (TTP), tetramethyldibenzo tetraaza[14]-annulene (tmtaa), and trans-1,2-bis(salicylidene)cyclohexanedi amine (saldach) catalyzed the cyclopropanation of styrene with aryldiazomet hanes. When p-tolydiazomethane was used as the carbene source, trans-cyclop ropanes were the major products. Trans/cis ratios of up to 17:1 were obtain ed. However, using mesityldiazomethane resulted in a reversal of stereosele ctivity, giving cis-cyclopropanes as the major product (cis/trans ratios of up to 2.9: 1). The stereoselectivity of iron(II) porphyrin-catalyzed cyclo propanation reactions was enhanced by performing the reactions at low tempe rature or by using bulky porphyrin ligands. Using trimethylsilyldiazomethan e as the carbene source, trimethylsilycyclopropanes were produced in excell ent yields with (TTP)Fe. On treatment of (TTP)Fe with diazoreagents, carben e complexes were observed spectroscopically. These complexes transferred th eir carbene ligand to styrene to produce cyclopropanes stoichiometrically.