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:T l(OR) (R = aryl) in tetrahydrofuran did not produce simple substitutio n products but afforded reduced species [W(OC6F5)(CO)(3)(cp)] 2, oxidi sed species [W(OC(6)H(4)Me-p)(6)] or the thallium tritungsten derivati ve [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 oxyg en- 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 reac tion of [MoCl(CO)(3)(cp)] - with two equivalents of Tl(SeC6F5) in diet hyl ether gives the thallium complex Tl[Mo(SeC6F5)(2)(CO)(2)(cp)] 9, v ia 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)] 1 2, with [W(SeC6F5)(CO)(3)(cp)] 8b as a by-product, and further reactio n of 12 with Tl(SeC6F5) forms [TlW(SeC6F5)(4)(cp)] 11 b. Variable-temp erature F-19 NMR studies show that complexes 9. 11b and 12 are fluxion al-and show hindered motion of the C6F5 rings. In complexes 9 and 11b, thallium(l) is co-ordinated by the selenolate ligands of the organome tallic anion and coupling between Tl-103/105 and F-19 ortho fluorine n uclei is observed in the F-19 NMR spectra. Complex 12 comprises two co nformers in equilibrium which are detected by NMR studies at tow tempe rature. Comparisons are drawn between properties of the new selenium c omplexes and related sulfur derivatives.