Pentamethylcyclopentadienyl-supported

The conversion of CO + H2 (syn-gas) to hydrocarbons and oxygenates (Fischer-Tropsch chemistry)119 is of considerable industrial importance and recently the activation and fixation of carbon monoxide in homogeneous systems has been an active area for research.120,121 The early transition elements and the early actinide elements, in particular zirconium124 and thorium,125 126 supported by two pentamethylcyclopentadienyl ligands have provided a rich chemistry in the non-catalytic activation of CO. Reactions of alkyl and hydride ligands attached to the Cp2M centers with CO lead to formation of reactive tf2-acyl or -formyl compounds.125,126 These may be viewed in terms of the resonance forms (1) and (2) shown below. 

Cyclovoltammetric data show that 82 cannot be reduced in the region available (up to —1.7 V versus SCE)182, consistent with the chemical behaviour of 82 in reduction processes, as shown in equations 64 and 65. An irreversible oxidation process takes place at +0.4 V versus SCE. Presumably, the radical cation of 82 is unstable due to the easy loss of the pentamethylcyclopentadienyl radical186,187. The mass-spectrometric observations support this assumption The molecular ion cannot be observed in El as well as in Cl studies, and the fragment with the highest mass corresponds to the M05(. 5Si1 ion. It is evident from these studies that the (MesC5)2Si+ radical ion, which has its positive charge... 

Another route to lanthanide dialkyls is a metathesis reaction. Lanthanide dihalides supported by a bulky monoanionic ancillary ligand, such as pentamethylcyclopentadienyl and related derivatives [4], P-diketiminato and guanidinato groups [49, 50], and so on, are generally used as the starting materials. A variety of lanthanide dialkyl compounds, including methyl compounds have been prepared and structurally characterized via successive metathesis reactions (Figure 8.11). 

Although the monomeric complexes of actinides with N, P or O donor Hg-ands are stable and could be synthesized without much problem, mono- and dithiol complexes are very difficult to synthesized because they tend to support a monomer-dimer equilibrium [244]. Only lately have a few complexes of bis(pentamethylcyclopentadienyl) metallocene dithiolates, (Ti -C5Me5)2 Th(SPr)2 [202] and (ii5-C5Me5)2U(SR)2 (where R = Me, f-Pr, t-Bu, Ph) [284] appeared. 

Astruc and coworkers [69] took this type of catalysis a step further when they developed a recyclable Ru(II) complex that was supported on magnetic nanoparticles. The cattilyst was prepared by immobilizing a pentamethylcyclopentadienyl ruthenium complex on iron oxide nanoparticles. 

CuiP, Chen Y, Borzov MV. Neodymium(III) phosphinidene complexes supported by pentamethylcyclopentadienyl and hydrotris(pyrazolyl)borate ligands. Dalton Trans. 2010 39 6886-6890. 

Scheme 3 Reactivity of dialkyl compounds of thorium and uranium supported by a pentamethylcyclopentadienyl ligand.

Several aqua complexes having a supporting pentamethylcyclopentadienyl ligand have been prepared and characterized in terms of acidity. For example, the Group 4 complex [Cp 2Ti(H20)2] " has a first plQ value predicted to be around 0 [14]. The Co(III) derivative [Cp Co( 1120)3] " has a first pK value of 5.9 [75], with [Co(H20)i5] having a reported first pKa value that is around 3.5-5.0 units lower. This difference can be rationalized in part on the basis of the difference... 

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