Mechanism of Cyclopropanation Reactions Mediated by (5,10,15,20-Tetra-p-tolylporphyrinato)osmium(II) Complexes

Catalytic systems derived from [Os(TTP)] 2 or Fe(TTP) (TTP = 5,10,15,20-tetra- p -tolylporphyrinato) are extremely efficient at converting styrenes and diazo reagents to cyclopropanes in high yields and high stereoselectivity. A number of mechanistic studies have been undertaken to elucidate the catalytic pathway. A mono(carbene) complex, (TTP)Os CHCO 2 Et, has been isolated but is not the catalytically active species. An electron-withdrawing ligand trans to the carbene in (TTP)Os CHCO 2 Et activates the carbon fragment toward transfer to an olefin. Labeling studies with (TTP)Os CHX and N 2 CHY and substrate reactivity profiles are consistent with a trans -osmium(II) bis(carbene) species as the active catalyst.