Methanides

Another triflate ester that recently has found growing application in organic synthesis is commercially available trimethylsilylmethyl trifluoromethanesul fonate. This powerful alkylating reagent can be used for the synthesis of various methylides by an alkylation-desilylation sequence A representative example is the generation and subsequent trapping by 1,3-dipolar cycloaddition of indolium methanides from the corresponding indole derivatives and trimethylsilylmethyl trifluoromethanesulfonate [108] (equation 54)... 

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... 

The effect of the counterion on the diastereomer ratio was investigated in detail for the Peterson condensation3 of phenyl(trimethylsilyl)methanide with benzaldehyde2 or substituted cyclohexanones4 and was found to be remarkably low. The variation of the solvent and the temperature has an influence of similar magnitude. 

Fig. 7. The solid state structures of the di(pyridyl)methanide [53], -amide [52], -phos-phide[27] 13 and -arsenide [43] all containing the Me2Al cationic fragment. Although the Al-N distance is almost invariant in all structures the more acute C-E-C angle (As < P < N < CH) forces the complex in a more pronounced butterfly arrangement...

Very few examples of bridging non-cyclic methanides of gold are known. Among them the complex 79 has been reported as the result of the reaction of phosphine-phosphonium derivatives with acetylacetonate derivatives of gold(I) [103,104]. The complexes 80 [89,98], already seen in previous paragraphs, cor-... 

It must be noted that the saturated ring system, the 1 -chloro-A -phosphirane was synthesized [84] a cyclic phospheniiun cation was postulated which is stable towards ring opening [85]. A corresponding cation could not be isolated, due to a methanid shift from a trimethylsilyl substituent. 

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 excess of electron density on the methanide carbon of complex ]Au(CgF5) (Ph2PCHPPh2Me)] [84] causes it to act as a C-donor nucleophile, producing a... 

Elimination of the chlorine atom from [Au(C6E5)2Cl(dpma)] [29] with AgC104 gives the corresponding chelate bis(diphenylarsine)methanegold derivative, which evolves to the methanide [Au(C6F5)2(Ph2AsCHAsPh2)] under deprotonation reaction with NaH. 

The presence of an excess of electron density on the carbon atom in methanide gold (III) complexes permits them to act as C-donor nucleophiles forming dinuclear or even polynuclear derivatives. 

Thus, the abstraction of the chlorine atom in [Au(QF5)2Cl(dppm)j [175] provides a mononuclear gold(I II) derivative with the diphosphine acting as a chelate ligand, which is an excellent starting material in the synthesis of dinuclear or polynuclear methanide and methanidiide complexes after deprotonation of the dppm ligand (first deprotonation with HNa and the second with acetylacetonate gold(I) derivatives) [198-201] (Scheme 3.3)... 

Another way to describe this non-cyclic phosphino methanide derivatives consists of theuse of monodentate complexes with themono-oxide [203] or monosulfide [204] dppm giving the methanide or methanediide derivatives (14) after addition of the appropriate amounts of [Au(acac)PPh3[. A mixed-valence Au(I)-Au(III) can be isolated by coordination of the fragment AuPPh3 to the free sulfur atom in the mono-oxide starting material [204]. 

A five-membered methanide auracycle [Au(C6F5)2(SPPli2CFl2PPh2)]C104 (25) is described with the monosulfonated dppm, obtained after chlorine elimination of [Au (C6F5)2Cl(SPPh2CH2PPh2)j with a silver salt. After deprotonation of the methylene group (26) and later coordination of additional metal centers affords dinuclear and trinuclear methanide derivatives (27, 28) [210]. 

Laguna, A. and Laguna, M. (1990) Bis (Diphenylphosphino)Methanide Or Bis (Diphenylphosphino)Methamide And Its Derivatives As Ligands In Gold Chemistry - A Review. Journal of Organometallic Chemistry, 394(1-3), 743-756. 

Fernandez, E.J., Gimeno, M.C., Laguna, A., Lopez-De-Luzuriaga, J.M. and Olmos, E. (1998) Two alternatives for the synthesis of non-cyclic phosphino-methanide derivatives of gold. Polyhedron, 17(22), 3919-3925. 

Bardaji, M., Gimeno, M.C., Jones, P.G., Laguna, A., Laguna, M., Merchan, F. and Romeo, I. (1997) Carbon-Carbon Coupling via Nucleophilic Addition of a Gold(l) Methanide Complex to Heterocumulenes. Organometallics, 16(5), 1083-1085. 

Jones, P.G. (1992) [(Methyldiphenylphosphonio)methanide] tris(pentafluorophenyl)gold(III) acetone solvate. Acta Cr/staUographica, Section C Crystal Structure Communications, C48(7), 1209-1211. 

L, Jones, P.G. and Fittschen, C. (1988) Mono- and bi-nuclear four-memhered methanide auracycles synthesis and reactivity. X-ray structure of ds-diphenylthiophosphinato [(mefhyldiphenylphosphonio)mefhanide] his(pentafluorophenyl)gold(III). Journal of the Chemical Society, Dalton Transactions, (9), 2323-2327. 

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). 

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