Convenient syntheses for Cp, Cp*, and related cyclopentadienyl derivatives ( 4 Cp = C 5 HiPr 4 ; CpЈЈЈ = C 5 H 2 tBu 3 -1,2,4) of formula [(Ring) 2 Mo 2 O 5 ] are described. Compound [Cp 2 Mo 2 O 5 ] was produced in good yields by the rapid oxidation of red [CpMoO 2 ] 4 with PhIO in CH 2 Cl 2 . [Cp* 2 Mo 2 O 5 ] was obtained by CH 3 COOH acidification of aqueous solutions of [Cp*MoO 3 ] − Na + , the latter being generated in a single step from [Cp*MoCl 4 ] and more than 5 equiv. of aqueous NaOH in air. Minor quantities of [Cp*MoO 2 ] 2 were also isolated from this reaction, although the formation of this by-

Use of aqueous conditions and the ROOH (R = tBu or H) compounds as oxidizing agents affords a simple two-step, one-pot synthetic procedure leading to [Cp à 2 M 2 O 5 ] (M = Mo, W) from [M(CO) 6 ] selectively and in high yields. The hexacarbonyl compounds are converted to Na[Cp * M(CO) 3 ] in refluxing THF, then the mixture is diluted with water (W) or aqueous NaOH (Mo) and directly treated with 6 equiv. of ROOH. Acidification of an aqueous solution of the Na[Cp * MO 3 ] product affords spectroscopically pure [Cp à 2 M 2 O 5 ] in high isolated yields (global yields from [M(CO) 6 ], for R = tBu: Mo, 91%; W, 87%). The X-ray structures of Na[Cp * MoO 3 ] AE 5H 2 O and [Cp à 2 W 2 O 5 ] are also reported.

The catalytic activity of [Cp*2M2O5] (M = Mo, W) for the homogeneous epoxidation of cyclooctene in a MeCN/toluene solvent mixture follows the order Mo >> W when using TBHP/decane as oxidant, in contrast to the inverse order (W >> Mo) when using aqueous H2O2 as oxidant. The catalytic activity for the Mo system strongly depends on the solvent used to deliver the oxidant (TBHP/decane >> TBHP/H2O). The low activity of the W system is also decreased when using TBHP/water in place of TBHP/decane. For both metals, H2O2/H2O is a better oxidant than TBHP/H2O. However, while the Mo-based catalyst is much more active for the TBHP/decane epoxidation in spite of the lower TBHP oxidizing power (TBHP/decane > H2O2/H2O > TBHP/H2O), the W-based system is much more active for the H2O2/H2O epoxidation in spite of the negative effect of water (H2O2/H2O > TBHP/decane > TBHP/H2O). The kinetic profile of the TBHP/decane epoxidation process is affected by product inhibition. Initial rate measurements show that the rate law is first order in substrate and has saturation behaviour in oxidant.

Compound ½Cp à 2 Mo 2 O 5 reacts with thioglycolic acid, HSCH 2 COOH, in an acidic (CF 3 COOH) mixed water-methanol solvent, to yield compound [{Cp*Mo(l-SCH 2 CO 2 )} 2 (l-S)]. During this reaction, the thioglycolic acid acts as a reducing agent, as a ligand, and provides a sulfide ion for the Mo-S-Mo bridge. The molecular structure of the product can be described as containing two four-legged piano stools that share three legs. The Mo-Mo distance of 2.792(7) Å indicates metal-metal bonding, in agreement with the compound diamagnetism.

2+ ion as its trifluoroacetate or trifluoromethanesulfonate salt. The structure of the compound was confirmed by X-ray analyses. The anions establish hydrogen-bonding interactions with all four bridging OH groups. Density functional calculations afford bonding parameters in close agreement with the observed structure and indicate that the cluster is best described as a valence-delocalized Mo 3 13+ species. The five metal electrons are distributed among an a-type (z 2 ) orbital, which accounts for