Methane dication

Scherbaum, F., Grohmann, A., Huber, B., Kruger, C. and Schmidbaur, H. (1988) Aurophilicity as a Consequence of Relativistic Effects The Hexakis (triphenylphosphaneaurio)methane Dication [(Ph3PAu)6C]2. Angewandte Chemie International Edition, 27, 1544-1546. 

By ionizing the respective alkenediol, Olah and co-workers403 were able to prepare the (hexaphenyltrimethylene)methane dication 188 [Eq. (3.47)] 403 The dication possesses C3 symmetry and adopts a propeller-like structure, but no evidence for Y-aromatic stabilization was found. Furthermore, the phenyl groups themselves are twisted, which prevents the optimum overlap between the 7t-system and the vacant p-orbitals at the three C(2) carbon atoms. Calculated charge density distributions and the 13C NMR data show that C(l) is not significantly deshielded for an sp2 atom, indicating that the three C(2) carbon atoms and their phenyl substituents bear the charge of dication 188 similar to the trityl cation 135. 

Varied Methane Cations. The methane molecular ion (methane radical cation, CH4+ ), the parent ion in mass spectrometry, and the methane dication (CH42+) are of great significance and have been studied both experimentally and theoretically.800 802 Recent advanced studies have shown that the methane radical cation, CH4+ has a fivecoordinate planar structure as suggested in early calculations by Olah and Klopman.800... 

The methane dication (CH42+) with a lifetime of only 3 jxs803 has been detected experimentally in the gas phase.804-807 A square-planar D4h symmetrical structure was predicted by early calculations.808,809 However, the planar but not square C2v symmetrical form (443) was shown to be the preferred structure by Wong and Radom.810 The cation contains an, vp2-hybridized carbon, an empty p-orbital perpendicular to the plane of the molecule, and a 2e-3c interaction. It can be visualized as a complex of a hydrogen molecule weakly bounded by a 2e-3c bond to the CH22+ core as shown by ab initio calculations [MP2 and B3LYP levels with 6-311++G(2df,2pd) basis set].811 The pentacoordinate CH52+ radical dication was studied by Stahl... 

Scherbaum, F. Crohmann. A. Huber. B. Kruger, C. Schmidbaur. H. Aurophilicity" as a consequence of relativistic effects The hexalus-(triphenylphosphinaneaur-io)methane dication [(Ph3PAu 6C]. Angew. Chem.. Int. Ed. Engl. 1988.27. 1544. 

Mathur, D. and F. A. Rajgara. 2006. Nonadiabatic response of molecules to strong fields of picosecond, femtosecond, and subfemtosecond duration an experimental study of the methane dication. 7. Chem. Phys. 124 194308-194316. 

Aurophilicity as a consequence of relativistic effects - the hexakis(triphenylphosphane-aurio)methane dication [(Ph3PAu)gC] +, F. Scherbaum, A. Grohmann, B. Huber, C. Kruger, and H. Schmidbam, Angew. Chem. Int. Ed., 1988, 27, 1544. 

Although the poly(pyrazolyl)borate complexes of iron(II) have been well known for many years, [1] it is only recently that the complexes with the tris(l-pyrazolylmethane ligand, HC(pz)3, [45-48] have been studied in detail. It should be noted that poly(pyrazolyl)methane ligands, such as the tris(l-pyrazolylmethane ligand, are neutral, whereas the poly(pyrazolyl)bo-rate ligands, such as the tris(l-pyrazolyl)borate ligand, HB(pz)3", are monoanions. As a consequence, the metal(II) poly(pyrazolyl)methane complexes are dications and often have quite different properties from those of the analogous metal(II) poly(pyrazolyl)borate molecular complexes. But, in spite of these differences there are often very close structural similarities between the dicationic complexes and the neutral complexes. Therefore the study of the pyrazolylmethane complexes will parallel that of the borate complexes discussed above. 

Multiply Protonated Methane Ions and Their Analogs. In addition to the involvement in a single 2e-3c bond formation, carbon is also capable of simultaneously participating in two 2e-3c bonds in some carbodications. Diproto-nated methane (protiomethonium dication, CH62+) is the parent of such carbodications. 

Computational methods have also been used frequently to estimate the thermodynamic stabilities of superelectrophiles. These calculations have often involved the estimation of barriers to gas phase dissociation or deprotonation, and the proton affinities of conventional electrophilic intermediates. Other useful studies have calculated the heats of reactions for isodesmic processes. An interesting example of these calculations comes from a study of the protoacetyl dication (Cf COH2"1- ).42 In calculations at the 6-31G //4-31G level of theoiy, the protoacetyl dication (83) is estimated to react with methane by hydride abstraction with a very favorable... 

Varied one carbon geminal dications have been generated in the gas-phase and studied by theoretical methods. For example, mass spectroscopic studies of methane have detected dicationic species, CH42+, CH3 2+, CH22+, and CH 2+, while other studies have examined the structures of halogenated one carbon geminal dications.13 The halogenated systems... 

For the reactions of cations 119-121 with methane, all the conversions are endothermic (eq 36). Hydride abstractions involving the dications (125-127) are, however, strongly exothermic (eq 37). Thus, the isodesmic reactions go from being moderately endothermic to strongly exothermic upon changing involvement of monocationic species (119-121) to the superelectrophilic, dicationic species (125-127). 

The reaction is suggested to proceed via a two-electron three-center bound carbocationic transition state (218) formed by insertion of dication 214 into the C-H cr-bond of methane. 

The studies of the linkage isomers of the bis(thioimidazolyl)methane family reported the cyclization of the chloromethylthioimidazole 148 into the unstable ionic dithiadiazocine chloride 149 (mp 224 °C, dec.) which was converted into the stable hexafluorophosphate 150 (mp 234 °C, dec.) (Scheme 14) <2005JOC8755>. The dication 150 was characterized by single-crystal X-ray diffraction and was shown to have a chair conformation. Electrochemical studies of the salt 150 in acetonitrile showed an irreversible reduction wave centered at —1.09 V <2005JOC8755>. 

Similar results are obtained for 6, in which the redox sites are separated by an additional saturated carbon. For 6" the largest CO shift is +113 cm , the smallest +6 cm . We conclude that even in Mn sites separated by bis(cyclopentadienyl)methane, there is a small amount of site interaction. Oxidation of 6 to a dication again produces a pair of CO bands with the value of co(syro) shifting by an additional +9 cm" from the cation. 

It will be noted that formation of the dipolar species 89 requires two hydroxide ions, so it is not too surprising that the reaction takes a totally different course in dilute base. Here the products are tetramethyl-oxamide (73), bis(dimethylamino)methane (75), cation 76, dimethyl-amine, formaldehyde, and 1 With the exception of the last two, these products were also obtained in the reaction of dication 50 with aqueous sodium peroxide (see section III.B.5), and their formation may be rationahzed in the same manner. The identification of formaldehyde and 1 in this experiment supports Urry and Sheeto s interpretation of the peroxide reaction. Both products were proposed in this scheme, but both were shown to be oxidized rapidly by aqueous sodium peroxide. 

The reactivity of doubly charged rare earth cations with small hydrocarbons was also investigated by FTICR-MS. In early studies, Freiser and coworkers examined reactions of Sc and Y " " (Hill et al., 1997), as well as La (Ranasinghe et al., 1992), with linear Cj-Cg alkanes combinations of electron transfer, hydride transfer, carbanion transfer, dehydrogenation, and alkane-loss products were observed. None of the metal ions reacted with methane, and La + was also unreactive with ethane. Since the metal dications have only one valence electron, oxidative addition to form two covalent bonds to the metal center is not possible, and alternative multicentered mechanisms were proposed. Another interesting aspect of these studies was the observation... 

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