SYNTHESIS AND REACTIONS OF TUNGSTEN(II) NORBORNADIENE (NBD) COMPLEXES - THE CRYSTAL AND MOLECULAR-STRUCTURE OF [WBR(SC6F5)(CO)2(NBD)]

The reaction of [WBr2(CO)2(nbd)] 1 (nbd = norbornadiene) with Tl(C5H5) gave a monocarbonyl derivative [WBr(CO)(nbd)(eta5-C5H5)] 2. With Tl(O2CMe) and Tl[O(S)CMe], complex 1 gave monosubstituted derivatives [WBr(O2CMe)(CO)2(nbd)] 3a and [WBr{O(S)CMe}(CO)2(nbd)] 3b which appear to be seven-co-ordinate according to IR data. In contrast 1 and TI(SC6F5) (1:1 molar ratio) gave the six-co-ordinate complex [WBr(S6C6F5) (CO)2(nbd)] 4. An X-ray diffraction study of 4 established that it has a distorted-octahedral structure with trans W-CO bonds approximately perpendicular to a plane containing the W, Br and S atoms and the midpoints of the nbd C=C bonds. Simple electronic arguments provide a rationalisation of many of the structural features of 4. Reaction of 1 with 2 molar equivalents of Tl(SC6F5) gave the bis(thiolate) derivative [W(SC6F5)2(CO)2(nbd)] 5 again with a trans arrangement of CO ligands. The reactions of 5 with L = PEt3, PMe2Ph or P(OMe)3 gave the six-coordinate complexes [W(SC6F5)2(CO)2L2] 6 which exist in two isomeric forms, red or green. Dynamic NMR studies have been used to characterise the isomeric behaviour and fluxional processes in the complexes.