| Summary: | The complexes Ru(OEP)(DPS)₂ (1) and Ru(OEP)(DecHS)₂ (2) were prepared in vacuo on a 100-mg scale by treatment of the dimeric species [Ru(OEP)]₂ (3) with a CH₂CI₂ solution containing a slight excess of the appropriate thioether [OEP= dianion of octaethylporphyrin; DPS= diphenylsulphide; DecMS= decylmethylsulphide]. In vacuo recrystallization, from n-heptane in the case of 1, and from n-pentane/methanol for 2, gave analytically pure material in 40 and 80 % yields, respectively. Both products were characterized by X-ray diffraction analysis, uv/vis absorption and nmr spectrometry, as well as elemental analysis.
Variable temperature nmr studies were carried out with both complexes. JL was found to be in thermodynamic equilibrium with 3, the dimer being favoured at about 80° C, and 1 at lower temperatures. Sharp nmr signals for the OEP protons of both equilibrating species, even at 80° C, indicated that exchange between them was slow on the nmr time scale; but, broadening and eventual coalescence at 80° C of the nmr signals for free and coordinated DPS suggested that the axial ligands of JL were quite labile. Cooling solutions of 2 caused the thioether methylene signals to broaden, and at -60° C the signals due to the methylenes closest to the sulphur split into broad doublets, this resulting from the prochiral nature of DecMS. The fact that only one nmr signal was observed for these methylene protons at room temperature implies rapid alternate coordination of the sulphur lone pairs.
The crystal structures of 1 and 2 revealed Ru-S bond lengths typical of Ru complexes containing trans-thioethers. The bond distances and angles of the porphyrin core were typical of those of monomeric Ru(Porp) complexes.
Dv/vis absorption, and nmr spectrometric studies, showed that 1 was extremely air-sensitive in solution, readily giving [Ru(OEP)OH]₂O and free DPS. Dv/vis absorption, nmr, and gc/mass spectrometric studies revealed that 2 reacted with dioxygen over a period of months to give Ru(OEP)(DecMS)(DecMSO) and Ru(OEP)(DecMSO)₂ as major products, as well as Ru(OEP)(CO)L (L= DecMS and DecMSO), and two other unidentified Ru(Porp) complexes as minor by-products [DecMSO= decylmethylsulphoxide].
In the presence of excess DecMS 2 catalyzed slow autoxidation of the free ligand to give DecMSO, DecMSO₂, and didecyldisulphide; the rate of this reaction was increased by addition of small quantities of HOAc [DecMSO₂ = decylmethyl-sulphone]. A major Ru(Porp) end-product both in the presence and absence of HOAc was Ru(OEP)(CO)L, the CO coming from Ru[sup II] (Porp)-mediated decarbonylation reactions. === Science, Faculty of === Chemistry, Department of === Graduate
|
|---|
