Syntheses and structures of molybdenum and tungsten pentabenzylcyclopentadienyl complexes: new chlorination reactions

(Pentabenzylcyclopentadienyl)molybdenum Complexes: Synthesis, Structures and Redox Properties

“…Li[MCpBz(CO) 3 ] [M = Mo (1), W (2)] are readily prepared in thf or dmf solution, respectively, by treating M(CO) 6 with LiCpBz. [5] [6,7] The 1 H NMR spectra of [MCpBz(CO) 3 ] 2 in CD 2 Cl 2 display only one resonance for the benzyl protons at δ = 3.88 ppm for 3 and δ = 3.92 ppm for 4.…”

“…[5] [6,7] The 1 H NMR spectra of [MCpBz(CO) 3 ] 2 in CD 2 Cl 2 display only one resonance for the benzyl protons at δ = 3.88 ppm for 3 and δ = 3.92 ppm for 4. This means that there are no constraints on the free rotation of the pentabenzylcyclopentadienyl ligands around the metal-C 5ring and the C 5ring -CH 2 Ph bonds and, considering the arrangement of the CpBz ligands in relation to the metal-metal bonds, is indicative of the presence of only one isomer in solution. The 13 C NMR spectra of 3 and 4 corroborate this result and also show that there is a fluxional process in solution that renders the six carbonyl groups equivalent, which gives rise to only one resonance at δ = 234.7 ppm (Mo) and δ = 224.3 ppm (W).…”

“…Thus, in contrast to their Cp analogues, cis/trans isomerisation processes in 3 and 4 are hampered. [6,9] Treatment of Li[MoCpBz(CO) 3 3 ], which, upon dimerisation and a thermally induced Mo-CO bond cleavage, [10] finally gives [MoCpBz(CO) 2 )] may, however, be excluded, as it goes against the usual reactivity trend that affords π-allyl coordination by thermal or photochemical activation of σ-allyl precursors. [11,12] [10,13] should reflect extensive Mo-CO backbonding.…”

“…In this context, we recently became interested in pentabenzylcyclopentadienyl (CpBz) derivatives with the aim of assessing the influence of the five bulky benzyl groups on the structures and properties of half-sandwich Mo and W complexes. Preliminary studies with [MoCpBz(O) 2 Cl] have shown an enhanced performance in the catalytic epoxidation of cyclooctene. A comparison of [MoCpЈ(O) 2 Cl] (CpЈ = Cp, Cp*, CpiPr 4 , CpBz) complexes showed that the CpBz derivative leads to the most active and stable catalyst system when activated with tBuOOH.…”

“…Preliminary studies with [MoCpBz(O) 2 Cl] have shown an enhanced performance in the catalytic epoxidation of cyclooctene. A comparison of [MoCpЈ(O) 2 Cl] (CpЈ = Cp, Cp*, CpiPr 4 , CpBz) complexes showed that the CpBz derivative leads to the most active and stable catalyst system when activated with tBuOOH. [1] Moreover, chlorination reactions of low oxidation-state (CpBz)carbonylmolybdenum and -tungsten complexes also differ from those of their Cp and Cp* analogues.…”