Carbide anion

The carbide anion C, is the base formed when HC CH loses two H s. 

Calcium carbide, CaC2, reacts with water to produce acetylene, C2H2, and is sometimes used as a convenient source of that substance. Use the MO diagram in Figure 7.18a to describe the bonding in the carbide anion, C22-. What is its bond order ... 

There are two well-characterized examples of a naked carbon atom bound by a triple bond to a metal center (Fig 14.3.8). The molybdenum carbide anion [CMo N(R)Ar 3]- (R = C(CD3)2(CH3), Ar = C6H3Me2-3,5), an isoelectronic analog of NMo N(R)Ar 3, can be prepared in a multistep procedure via deprotonation of the d° methylidyne complex HCMo N(R)Ar 3. The Mo=C distance of 171.3(9) pm is at the low end of the known range for molybdenum-carbon multiple bonds. In the diamagnetic, air-stable terminal ruthenium carbide complex Ru(=C )C12(LL/)(L = L = PCy3, or L = PCy3 and L = l,3-dimesityl-4,5-dihydroimidazol-2-ylidene), the measured Ru-C distance of 165.0(2) pm is consistent with the existence of a very short Ru=C triple bond. 

The saltlike carbides formed from beryllium (Be2C) and from aluminum (AI4C3) are best described as methides they yield methane upon hydrolysis, and the carbon atoms have been found to be far enough apart from each other to preclude any type of carbon-carbon binding. One of the two carbides of magnesium has the composition Mg2C3 and yields methylacetylene, CH3C=CH, upon hydrolysis the carbide anion here is presumably [-3C—C=C <-> 20=C=C-2]. 

Deprotonation (LiBu, Li Bu, LDA) of the methylidyne complex Tp (OC)2W=CH (7 Scheme 3) affords orange Tp (OC)2W=CLi (8) which was not isolated but could be characterized by its broad 13C signal at 8 5 56.96 The v(CO) spectrum indicates the negative charge is mainly in the carbon s orbital. The pAa of the methylidyne is estimated at 28.7 (vs. 2-benzylpyridine), it being less acidic than HC=CPh or HC=CBu (pAa 23.2, 25.5, both vs. NH2Cy). Nucleophilic properties of the carbide anion are shown in reactions with electrophiles such as Mel, SiMe3(OTf), I2, and acyl compounds. 

The carbide anion C2 is the base formed when HC=CH loses two H+ s. 

The carbido anion [MoC(NRAr)3] (R = C(CD3)2CH3 Ar = C6H3Me2-2,5) was obtained from three-coordinate [Mo(NRAr)3] (45) via [Mo(CO)(NRAr)3] and the latter s decarbonylation and reduction using sodium amalgam, followed by deprotonation of [Mo(CH)(NRAr)3] using KBz. The carbide anion is a strong reductant and nucleophile, forming alkylidyne derivatives readily. 

The second stage of the synthesis is the transport of carbon by the carbide anions through the salt melt to the metal surface. The motive force of the carbon transport is the gradient of the carbon chemical potential at the boundaries between the solid phases and the salt melt ... 

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