Selective oxygenation of amphiphilic thiacalix[3]pyridine Rh(i) diene complexes in both water and organic solvents

Abstract

Thiacalix[3]pyridine (Py₃S₃) reacted with [Rh(diene)(μ-Cl)]₂ (diene = 1,5-cyclooctadiene (cod), 2,5-norbornadiene (nbd)) to give amphiphilic trigonal bipyramidal complexes, [Rh(Py₃S₃)(diene)]Cl. Sulfur bridges of the Py₃S₃ ligand in these complexes were selectively oxygenated by m-chloroperoxybenzoic acid in dichloromethane to give sulfinylcalix[3]pyridine complexes, [Rh{Py₃(SO)₃}(diene)]⁺, in which all three oxygen atoms of the SO groups occupy the equatorial positions. Structures of the complexes were analysed by X-ray crystallography and the oxidation reaction was investigated using ¹H NMR spectroscopy and electrospray ionisation mass spectrometry showing that the oxygenation of the sulfur atoms in the ligand proceeded stepwise and further oxygenation of the SO moiety occurred only for the nbd complex having the smaller diene ligand resulting in [Rh{Py₃(SO)₂(SO₂)}(nbd)]⁺. On the other hand, the oxidation of [Rh(Py₃S₃)(cod)]⁺ by H₂O₂ in water did not result in oxygenation of the sulfur bridges but the cod ligand is hydroxygenated to give 1,4,5,6-η⁴-2-hydroxycycloocta-4-ene-1,6-di-yl.