Methanide anions

M. N., Jones, P.G. and Erdhruegger, C.F. (1989) (Diphenylphosphinomethyl) diphenylphosphine sulfide (Ph2PCH2PPh2S) and its methanide anion Ph2PCHPPh2S- as ligands in organogold chemistry. X-ray crystal structure of [(diphenylphosphino) (diphenylthiophosphinoyl)methanido-P, S]his(pentafluorophenyl)gold(l 11). 

As depicted in Figure 34, the NNCM anion is planar within experimental error (E < (Cl) = 359.9°) like most of the known NO, NO2 and CN substituted methanide anions (except from trinitromethanide, in which the balance between resonance stabilization... 

Carbanions of the type [HjCR ], [HCR R ] and [CR R R ] (R = NO and R R = CN, NO, NO2) can be considered to be resonance-stabilized, nonlinear pseudohalides. All experimentally known resonance-stabilized methanides are reported to be planar or nearly planar (Table 1). While the parent ion, the methanide anion HsC, adopts a pyramidal structure [Afipianar-pyramidai = 9.8 kJmol rf(CH) = 1.099 A, <(HCH) = 109.7° cf. rf(CH) = 1.093 A, <(HCH) = 109.6°] due to the lack of delocalization (no resonance for the p-AO-type lone pair possible) , substitution of one H atom by NO results in a planar anion since the empty jr -orbitals of the NO group are perfectly suitable to delocalize the carbon lone pair. Further substitution of the second H atom again results in planar anions, and the same holds for the third substitution in case of R = CN. In case of R = NO and NO2, the third substitution leads either to a propeller-type structure with only a small distortion from planarity or one NO2 group is twisted by 90°, nevertheless leaving the central carbon in an almost trigonal planar environment . ... 

In contrast to most of the high energy-density alkali and silver (NO- and NO2-substituted) methanides, the ionic liquids of these methanides with a bulky organic cation are neither heat nor shock sensitive, and hence can be prepared and stored in large scale. Nevertheless, this type of methanide-based ionic liquids can also be considered energetic ionic liquids since the thermodynamically unstable methanide anion is only kinetically... 

Monocarbides. Brewer and Krikorian (1956) and Dancy et al. (1962) had reported the monocarbide of cerium, but its existence has been discredited. Spedding et al. (1958) found that the lattice parameter reported by Brewer and Krikorian (1956) for CeC was identical with that of Ce metal saturated with C, and the reported CeC was most likely a solid solution of C in Ce. Anderson et al. (1969) re-examined the binary cerium-carbon system, and gave no evidence for the existence of any phase structurally based on monoatomic (methanide) anions. 

Figure 3.1 (a) sp -Hybridized methanide anion (b) inversion of configuration. 

FIGURE 9.23 Tris(diphenylthiophosphinyl)methanide anion [PhjP(S)]3C]. Filled circles = P, shaded circles = S. 

Further reaction produces the tris(dialkylthiophosphinyl)methanide anion. This anion is resonance stabilised with the three P and the central C atom forming a coplanar arrangement (9.588) (Fignre 9.23) [13,14]. 

Janikowski, J., Razali, M.R., Forsyth, C.M., Nairn, K.M., Batten, S.R., MacFarlane, D.R. and Pringle, J.M., Physical properties and structural characterization of ionic liquids and solid electrolytes utilizing the carbamoylcyano(nitroso)methanide anion, ChemPlusChem 78 (6), 486-497 (2013). 

Salt-like carbides containing individual C anions are sometimes called methanides since they yield predominantly CH4 on hydrolysis. Be2C and AI4C3 are the best-characterized examples, indicating the importance of small... 

Kuhn s carbanion, the all-hydrocarbon anion tris(7//-dibenzo[c,g]-fluorenylidenemethyl)methanide ion [2 ] (Kuhn and Rewicki, 1967a,b), is a stabilized system with tt electrons widely spread over the sp hybridized carbon framework, and was isolated as the potassium salt. It also appears in DMSO solution by dissolving the parent hydrocarbon, resulting in a deep green colour. The pKg value of the precursor hydrocarbon [2]-H is 5.9 in aqueous HCl-DMSO (Kuhn and Rewicki, 1967a,b), and its enormous stability, as compared with cyclopentadiene [9]-H, pKa 18 in DMSO... 

In view of the ease of dissociation of the a bond into resonance-stabilized hydrocarbon ions, it is expected that an authentic hydrocarbon salt could be isolated from an extraordinarily stable cation and anion. The first synthesis of a salt composed solely of carbon and hydrogen was achieved on the combination of tris(3-guaiazulenyl)cyclopropenylium ion [1" ] and tris(7//-dibenzo[c,g]fluorenylidenemethyl)methanide ion [2 ] (Okamoto et al., 1985). 

The methyl group migrates with its pair of electrons, as a methyl anion, CH3 (a methanide ion). 

Structural parameters, such as the fairly short C—NO, C—NO2 and C—CN bond lengths, together with the planarity, indicate the presence of delocalized jr-bonds over the whole anion. MO and NBO calculations displayed the existence of an w 7r-electron, m-center bond unit in all methanides (Scheme 20, with n = 2 + 4x + 2y+2z and m = 1 + 3x + 2y - -2z X = number of NO2 groups, y = number of NO groups and z = number of CN groups in the anion plane). 

Lithium tris(phenylthio)methanide, LiC(SC6H5)3 (1). This anion of Iris(phenythio)methane1 is prepared with n-butyllithium in THF at —78°. 

The existence of two differently coordinated silicon atoms in the same molecule or anion leads to nucleophilic migration of a methanide ion. 

The former is one of the few anionic methanides reported to date, probably due to their low stability. In fact, this complex is obtained as a yellow air and moisture-sensitive oil, which makes its complete characterization difficult. 

Similarly, the trinuclear anionic AuVAu111 complexes PPN[(C6F5)Au p,-PPh2 CH(AuX)PPh2 Au(C6F5)3] (X = Cl, Cgl s) are obtained when the same dinuclear methanide is treated with one equivalent of [AuX(tht)] instead of [Au(PPh3)(tht)]C104 [Eq. (32)].90... 

Although none of them have been structurally characterized by X-ray diffraction, no intramolecular Au- -Au interaction is expected in these species because of the presence of a large number of pentafluorophenyl rings in each anion. Thus, in the crystal structure of the trinuclear starting methanide, which is less hindered, the shortest intramolecular Au- -Au separation is 6.10 A.90... 

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