Tetrahydrofuran solutions of the 30-electron anions Mo_2Cp_2(μ-PA_2)(μ-CO)_2~- (A = Cy, Et, Ph, OEt)are conveniently prepared through a two-step approach. In the first step, Mo_2Cp_2(CO)_6 is treated withthe chlorophosphines ClPR_2(R = Cy, Et, Ph) or the chlorophosphite CIP(OEt),, in refluxing toluene ordiglyme respectively, to give the corresponding 32-electron chloro-complexes Mo_2Cp_2(μ-Cl)(μ-PA_2)-(CO)_2 as major products. In the second step, these air-sensitive intermediates are treated intetrahydrofuran solution at room temperature with one of several reducing agents such as LiBHEtd,Li(Hg), Na(Hg) or KBH~sBu_3 to give red solutions of the corresponding alkali-metal salts of theanions, which display significant ion pairing involving one or both oxygen atoms of the bridgingcarbonyl ligands, depending on the cation. All these triply bonded species are quite air-sensitive andcould not be isolated as pure solids, but they can be easily protonated using a weak acid such asNH_4PF_6to give with good yield the corresponding unsaturated hydrides Mo_2Cp_2(μ-H)(μ-PA_2)(CO)_2,which are species of low to moderate sensitiveness to air, and also formally containing an intermetallictriple bond. The reactivity of the dicyclohexylphosphide-bridged anion (mainly as its Li~+ salt) towardsdifferent hydrocarbon halides RX was studied in detail. These reactions were found to be rathercomplex, critically depending on the reagent used, and generally resulting in the formation of severalproducts, of which four types were identified: (a) the known agostic products Mo_2CP_2(μ-PCy_2)(μ-R)-(C0)_2 (R = Me, CH_2Ph), (b) the new alkoxycarbyne products Mo_2Cp_2(μ-COR)(μ-PCy_2)(μ-CO) R =Me, Et, C(O)Ph, 'Pr, Cy, which could be conveniently isolated as pure solids, (c) the iodoxycarbynecomplex Mo_2Cp_2(μ-COI)(μ-PCy_2)(μ-CO), a very unstable species formed in the reaction with EtI, and(d) the halide complexes Mo_2Cp_2(μ-PCy_2)(μ-X)(CO)_2X = Cl, Br,I,which were more convenientlyprepared by the direct reaction of the anion with the pertinent halogen (X = Br, I). The analysis of theabove results suggests that at least three primary reaction pathways are in operation: (a) nucleophilicattack of the anion through its dimetal centre, (b) nucleophilic attack of the anion through the oxygenatoms of its bridging carbonyls and (c) electron-transfer with the reagent, this being the main path tothe halo-complexes Mo_2Cp_2(μ-PCy_2)(μ-X)(CO)_2.
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