Reactions of monocyclopentadienyl complexes of molybdenum and tungsten with derivatives of phenols and pentafluorobenzeneselenol

Abstract

Reactions of [WI₃(CO)₂(Cp)](cp =η⁵-C₅H₅) with thallium salts Tl(OR)(R = aryl) in tetrahydrofuran did not produce simple substitution products but afforded reduced species [W(OC₆F₅)(CO)₃(Cp)]2, oxidised species [W(OC₆H₄Me-p)₆] or the thallium tritungsten derivative [Tl{W(CO)₃(cp)}₃](when R = C₆H₃Prⁱ₂2,6). Complex 2 is a rare example of a derivative of type [WX(CO)₃(Cp)] in which X is an oxygen-bonded ligand. Photolysis of [{Mo(CO)₃(cp)}₂] with Se₂(C₆F₅)₂ in toluene yields [Mo(SeC₆F₅)(CO)₃(Cp)]8a, and the thermal reaction of [MoCl(CO)₃(Cp)] with two equivalents of Tl(SeC₆F₅) in diethyl ether gives the thallium complex Tl[Mo(SeC₆F₅)₂(CO)₂(Cp)]9, via complex 8a isolated as a by-product. Reaction of [WBr₃(CO)₂(Cp)] with three equivalents of Tl(SeC₆F₅) produces [W(SeC₆F₅)₃(CO)(Cp)]12, with [W(SeC₆F₅)(CO)₃(Cp)]8b as a by-product, and further reaction of 12 with Tl(SeC₆F₅) forms [TlW(SeC₆F₅)₄(Cp)]11b. Variable-temperature ¹⁹F NMR studies show that complexes 9, 11b and 12 are fluxional and show hindered motion of the C₆F₅ rings. In complexes 9 and 11b, thallium(I) is co-ordinated by the selenolate ligands of the organometallic anion and coupling between ^103/105Tl and ¹⁹F ortho-fluorine nuclei is observed in the ¹⁹FNMR spectra. Complex 12 comprises two conformers in equilibrium which are detected by NMR studies at low temperature. Comparisons are drawn between properties of the new selenium complexes and related sulfur derivatives.