C-H CLEAVAGES IN THE PHOTOREACTIONS OF [M(2)(ETA(5)-C5H5)(2)(CO)(6)] (M=MO, W) - ISOLATION AND CHARACTERIZATION OF THE V-SHAPED TRINUCLEAR CLUSTERS )M'(MU-ETA(1),ETA(5)-C5H4)(ETA(5)-C5H5)(2)(CO)(6)] (M, M'=MO OR W)

Irradiation of toluene solutions of the complexes [M(2)Cp(2)(CO)(6)] ( M = Mo, W; Cp = eta(5)-C5H5) with UV-visible light at -35 degrees C gi ves the new trinuclear compounds [M(3)(mu-eta(1),eta(5)-C5H4)Cp(2)(CO) (6)] in moderate (M = Mo) or medium (M = W) yields, along with the kno wn complexes [MH(CO)(3)Cp], [W-2(mu-H)(2)(CO)(4)Cp(2)], and [M(2)Cp(2) (CO)(4)]. Similar treatment of equimolar mixtures of [W(2)Cp(2)(CO)(6) ] and [Mo(2)Cp(2)(CO)(4)] gives a complex mixture containing (in order of decreasing yield) the mixed-metal compounds [Mo2W(mu-eta(1),eta(5) -C5H4)Cp(2)(CO)(6)], [MoW2(mu-eta(1),eta(5)-C5H4)Cp(2)(CO)(6)] (two is omers), and [W-3(mu-eta(1),eta(5)-C5H4)Cp(2)(CO)(6)], along with [WH(C O)(3)Cp] as dominant hydride species. The structure of the new trinucl ear compounds has been determined by single crystal X-ray diffraction studies on those species with W-3, Mo2W, and W2Mo metal cores. Crystal s of the W2Mo compound were found to be an equimolar mixture of both i somers detected in solution, so that two of the three metal positions are best described as 0.5 Mo + 0.5 W. Otherwise, the three crystal str uctures are virtually identical. These 46 electron molecules exhibit a V-shaped metal core (angle ca. 105 degrees) with a short (ca. 2.52 An gstrom) and a long (ca. 3.12 Angstrom) intermetallic separation, the c entral position being always occupied by a tungsten atom. Each of the metal atoms involved in the short bond carries out a cyclopentadienyl group and a carbonyl ligand which bridges that bond in a linear semibr idging fashion. The outer metal atom has also a terminal carbonyl grou p. Finally, the third metal atom bears a mu-eta(1),eta(5)-cyclopentadi enylidene ligand, sigma-bonded to the central tungsten atom, and three terminal carbonyl groups. Variable-temperature H-1 NMR spectroscopy r eveals that all trinuclear compounds exhibit fluxional behavior in sol ution, which is thought to result from two independent rearrangements. In addition, the trimolybdenum complex undergoes a slower dynamic pro cess which implies a proton exchange between cyclopentadienylidene and cyclopentadienyl ligands in the molecule, as suggested by 2D EXSY exp eriments.