Pentamethylcyclopentadienyl cation

DFT-calculated 13C NMR chemical shifts for the pentamethylcyclopentadienyl cation and the (CH3)5-cyclopentenyl cation 97 provide conclusive evidence that the... 

In a recent report, Lambert and coworkers have claimed the synthesis of the stable pentamethylcyclopentadienyl cation 221 by hydride transfer from pentamethylcyclopentadiene (220) with the trityl cation [Eq. (5.33)]. It, however, quickly became obvious that the isolated product is not cation 221 but the known zrans-l,2,3,4,5-pentamethyl-l-cyclopentenyl allylic cation... 

The (pentamethylcyclopentadienyl)zirconium amidinate unit also served as a platform for the synthesis and characterization of remarkable cationic and zwitterionic allyl zirconium complexes derived from trimethylenemethane (TMM). A direct synthetic route to the neutral precursors was found in the... 

Jutzi et al. have studied reactions of bis(pentamethylcyclopentadienyl)tin with very strong acids such as HBF4, HA1C14 or the methyl esters of CF3COOH and CCljCOOH 173,174). In these reactions only one pentamethylcyclopentadienyl group is surprinsingly replaced and a very stable cationic species (Me5C5)Sn+ is formed ... 

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... 

The first cyclopentadienyl n complexes of phosphorus, arsenic, and antimony have been characterized only recently. The salt-like species LXXXV-LXXXVII containing a cationic n complex are prepared via halide ion abstraction from pentamethylcyclopentadienyl element halides according to Eq. (47) (248-250). 

FIGURE 11. (a) Possible silicocene conformers and their symmetry notation, (b) (Hel) PE spectrum (6-10 eV) of bis(j)5-pentamethylcyclopentadienyl)silicon with Koopmans assignment, IE = gMNDO for tjje most j)5d conformer and (c) comparison of radical cation states with analogous Ge and Sn pentamethylcyclopentadienyl sandwiches... 

Scheme 6.7 Main group triple-decker cations 15 and 16 with a bent structure and a bridging pentamethylcyclopentadienyl ring...

In some remarakable work by W.J. Evans and his research group (W.J. Evans and B.L. Davis, Chem. Rev., 2002, 102, 2119), various syntheses have been developed which do not involve the use of THF, such as the reaction between tetramethylfulvene and a dimeric hydride, and the reaction of KCp with a cationic bis(pentamethylcyclopentadienyl) species (Figure 6.9). 

A cationic bis(pentamethylcyclopentadienyl)uranium(lll) complex has been reported. [Cp 2U(THF)2][BPli4] is generated by protonation of the complex Cp 2U[N(SiMe3)2] with [NH4][BPh4]. ... 

A fascinating analogy between cp and Ps became apparent by the isolation of the mixed ferrocene cp Fe(P5), where cp represents pentamethylcyclopentadienyl and (P5) the planar, strictly pentagonal phosphoras unit (52). The compound is prepared in the thermolysis of [cp Fe(CO)2]2 in the presence of white phosphorus. The Ps unit, which clearly acts as a six-electron donor in this mononuclear complex, can also function as a central unit in a cationic triple-decker cation [(cp)Fe(P5)Fe(cp )]+ (53).i ... 

A bis(pentamethylcyclopentadienyl)element cation Cp2 E (Cp = CsMcs E = As, Sb) was prepared from Cp2 EF and BF3 as its BF4" salt. The X-ray structure analysis revealed a non-centrosymmetric E—Cp bond situation. Therefore the E—Cp bond may best be described by a. rj or rj rather than a. coordination. As expected, the Cp ligands are not in a coplanar position, they form an angle of 36.5°. The BF4" anion seems to be important in stabilizing the cation attempts with AlC ", BC , BBr4 and SbClg were not successful This may very well be explained by the exceptionally weak basicity of the BF4" anion and one could predict that AsFg and SbFg" salts should also be stable. 

Similar compounds containing the bis(pentamethylcyclopentadienyl)aluminum cation have been reported by other workers. 

The even more reactive SiH cation ( silyliximylidene ) has been observed in the laboratory by discharge of SiHi [7] and also in the solar spectrum. If there is at aU a chance to prepare a persistent derivative, then this would probably be with pentamethylcyclopentadienyl as it-bonded substituent... 

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