REACTIONS OF MONOCYCLOPENTADIENYL COMPLEXES OF MOLYBDENUM AND TUNGSTEN WITH DERIVATIVES OF PHENOLS AND PENTAFLUOROBENZENESELENOL

Reactions of [WI3(CO)(2)(cp)] (cp = eta(5)-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(OC(6)H(4)Me-p)(6)] or the thallium tritungsten derivative [Tl{W(CO)(3)(cp)}(3)] (when R = C6H3Pr2i: 2,6). 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 Se-2(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)] 11 b. Variable-temperature F-19 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(l) is co-ordinated by the selenolate ligands of the organometallic anion and coupling between Tl-103/105 and F-19 ortho fluorine nuclei is observed in the F-19 NMR spectra. Complex 12 comprises two conformers in equilibrium which are detected by NMR studies at tow temperature. Comparisons are drawn between properties of the new selenium complexes and related sulfur derivatives.