Methanide ion

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 formation of the (SiN)2 ring can be explained by a nucleophilic 1,3-rearrangement of a methanide ion at silicon. The cyclic ylide is formed because the two nitrogen atoms are identically substituted and a silyl group migration would be without energy profit in such a molecule. 

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

If the central silicon carries two silylamino groups, only half an equivalent of the iminosilene undergoes migration of a methanide ion. The result is a cross dimer of the two ylides,25 as shown in Scheme 9.15... 

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

The reaction of SiF-coupled six-membered rings with lithium organyls first produces ring contraction and subsequently eliminates LiF. As discussed in Section II, we have now obtained an intermediate ylide that contains silicon atoms with the coordination numbers three and five. This gives rise to a nucleophilic migration of a methanide ion. A fused bicyclic compound is formed (Scheme 24). This compound has also been characterized by an X-ray analysis and the structure is shown in Fig. 13. Both the four-membered rings are planar.42,46,50... 

Several conventions are observed for inferring oxidation numbers, the use of which is particularly common in the names of compounds of transition elements. Hydrogen is considered positive (oxidation number I) in combination with non-metallic elements and negative (oxidation number —I) in combination with metallic elements. Organic groups combined with metal atoms are treated sometimes as anions (for example, a methyl ligand is usually considered to be a methanide ion, CH3 ), sometimes as neutral (e.g. carbon monooxide). Bonds between atoms of the same species make no contribution to oxidation number. 

The reaction of a methanide ion [(Ph2PO)3C] with the chlorides or nitrates of scandium or yttrium produce stable six-coordinate metal species (13) where the metal is coordinated to six oxygens in the form of three bidentate ligands.56... 

Similarly, the Iricyclopropylcyclopropenylium ion (23) reacted in chloroform with the tris(7/7-dibenzo[c ]fluorenylidenemethyl)methanide ion (24), which is known as the most stable allhydrocarbon carbanion, to give a covalent cyclopropene 25, which was directly observed by NMR spectroscopy but could exist only in solution evaporation or cooling of the chloroform solution of 25 afforded the heterolytically dissociated salt 23 24 quantitatively. In a polar solvent such as dimethyl sulfoxide the salt dissolved to give the free ions. As far as the reaction in tetrahydrofuran/acetonitrile was concerned, cyclopropenylium ions 26 (X = 4-Cl, H) reacted with carbanion 24 to give the covalent cyclopropene 27, whereas the slightly more stable cations 26 (X = 3-Me, 4-Me, 4-OMe) gave the completely ionized salts, the so-called hydrocarbon salts . The most stable cyclopropenylium ions 28 (pATr in 50 /o aqueous acetonitrile > 10) and 27 (pA t 8.9) also afforded the ionic salts under similar conditions. ... 

The silyl-bridged four-membered rings are not A, B observed in these reactions with aminofluorosilyl-substituted rings. These Li salts react by one route to triply substituted products they also form bicyclo[4.2.0]octanes by an intramolecular reaction with LiF elimination and silyl group and methanide ion migration . Figure 4 shows the structure of compound... 

The (ethyloxycarbonyl)methanide ion is produced in the reaction mixture from the potassium salt of the monoethyl ester of the malonic acid. Ring opening by cleavage of the N-S bond is followed by cyclization and / -elimination. This results in a ring transformation to give substituted thiophenes. 

In contrast to reactions with Lewis bases little is known about reactions of iminosilanes with Lewis acids. So addition of AlMea and Me2AlCl to iminosilanes at low temperature gave monomeric aminoalanes for the first time by a nucleophilic methanide-ion migration from the aluminum to the silicon atom (Scheme 6) [6]. 

Dichlorocarbene (Cl C) can be made from chloroform (CHCy, and a strong base such as tert-butoxide, (CH l CO" or potassium hydroxide. Chloroform has three electron ative chlorine atoms, which inductively withdraw electron density from the carbon atom. Thus, the hydrogen atom of CHCI3 is much more acidic than the hydrogen atom of an alkane. The hase removes a proton from CHCI3, leaving the electron pair with the carbon atom. The product is a carhanion, the trichloro-methanide ion. 

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