Biomimetic organometallic chemistry: Regio- and stereoselectivity in the hydroxylation reaction of cyclohexyltriphenyltin with metalloporphyrins as the biomimetic catalysts and iodosylbenzene as the oxygen transfer agent

Article abstract of DOI:10.1021/om00103a029

The regio- and stereoselectivity in the hydroxylation reaction of cyclohexyltriphenyltin (1), with biomimetic catalysts that mimic the active site of cytochrome P-450 monooxygenase enzyme, iron(III), and manganese(III) tetrakis(pentafluorophenyl)porphyrin derivatives [Fe^III or Mn^IIITF₅PP(Br,OAc)], was studied with the oxygen transfer agent, iodosylbenzene, and the results were compared to those results previously obtained with the P-450 enzyme from rat liver microsomes. The Mn^IIITF₅PP(OAc) biomimetic catalyst provided a 22% conversion of 1 to a mixture of cis- and trans-hydroxycyclohexyltriphenyltin compounds that included the trans-4 (5.9%), 2; cis-3 (22%), 3; trans-3 (3.3%), 4; and trans-2 (68.8%), 5, isomers. The regiochemistry on a per hydrogen basis shows a C4:C3:C2:C1 ratio of 1:2:6:0 and a high stereoselectivity for equatorial over axial hydroxyl products with a EQ/AX ratio of 29. The corresponding Fe^IIITF₅PP(Br) catalyst gave the same pattern of hydroxylation as with the above-mentioned Mn catalyst. In comparison to the P-450 enzyme, which had a different regioselectivity ratio on a per hydrogen basis for C4:C3:C2:C1 of 109:7:1:0, the biomimics appear to have less steric requirements at the active site. Mechanistically the tin atom also appears to control the regiochemistry of the hydroxylation reaction by the fact that 3 and 5 are the major hydroxylation products due to a stabilization of radical intermediates on carbons 2 and 3 by the tin-carbon σ bond. As well, the hydroxyl rebound reaction to give products 2-5 also appears to be stereoselective for the sterically more favorable equatorial product.