A TUNGSTENDIIRON CLUSTER [NET4][WFE2(MU-3-ETA-3, ETA-5-CH=C=C(TERTBU)C(O)C2B9H8ME2)(CO)8] DERIVED FROM [FE2(CO)9] AND [NET4][W(=CC=CTERTBU)(CO)2-(ETA-5-C2B9H9ME2)]

Treatment of a tetrahydrofuran solution of [NEt4][W(= CC = C(t)Bu)(CO)2(eta-5-C2B9H9Me2)] with [Fe2(CO)9] affords the trimetal complex [NEt4][WFe2{mu-3-eta-3,eta-5-CH = C = C((t)Bu)C(O)C2B9H8Me2}(CO)8], the structure of which has been established by X-ray diffraction. The anion has a core based on an essentially isosceles triangle of metal atoms [Fe-Fe 2.663(3), W-Fe 2.811(2) and 2.829(2) angstrom]. Each iron atom carries three CO groups, whereas the tungsten atom is co-ordinated by two such groups, and by the open face of a nido-icosahedral C2B9 cage. In the five-membered activated BBBCC ring forming the face of the cage, the boron atom occupying the beta site with respect to the two carbon atoms is sigma bonded to the carbon atom of a ketonic group [B-C 1.57(3) angstrom]. The latter in turn is linked to an allenyl fragment C((t)Bu) = C = CH [C-C average 1.35(2) angstrom, C-C-C 150(1)-degrees] which spans the face of the WFe2 triangle. The terminal CH group is attached to the tungsten and to an iron atom [C-W 2.25(1), C-Fe 1.96(1) angstrom], and the central carbon is linked to the tungsten atom [C-W 2.07 (1) angstrom] and also to the second iron atom [C-Fe 2.05(1) angstrom]. The latter is also bonded to the C((t)Bu) fragment [C-Fe 2.20(2) angstrom] which in turn is connected to the ketonic group [C((t)Bu)-C(O) 1.47(2) angstrom] linking the mu-3-C3 moiety to the cage. The NMR data (H-1, C-13-{H-1}, and B-11-{H-1}) for the new cluster compound are reported and discussed.