Carbide complex, terminal

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. 

R. G. Carlson, M. A. Gile, J. A. Heppert, M. H. Mason, D. R. Powell, D. Yander Velde, and J. M. Vilain, The Metathesis-Facilitated Synthesis of Terminal Ruthenium Carbide Complexes A Unique Carbon Atom Transfer Reaction, J. Am. Chem. Soc. 124, 1580-1581 (2002). 

The first terminally bonded carbide complex was characterized by Peters, Odom, and Cummins in 1997 (see... 

Similarly, Fischer carbene complexes are formed when Grubbs systems react with vinyl esters, vinyl carbonates, and vinyl halides. However, these Fischer car-benes are known to decompose to give terminal ruthenium carbide species by elimination of HX (X = OjCR, OjCOR, halide) [83-86]. Notably, the formation of the carbide complexes is less favorable in phosphine-free systems, which enables the Hoveyda [56] and Piers [87] catalysts to promote the cross metathesis of vinyl hahdes and terminal or internal olefins [88]. 

Acetylenes RCsCH are readily deprotonated. Some carbynes, L MsCH, also having an acidic CH proton, can be deprotonated to give terminal carbide complexes, [L MsCl. For example, Peters and co-workers have deprotonated l(ArN /-Bu )3MosCH] with KCH2Ph. After the counterion was sequestered by complexation to a crown ether, [(ArN r-Bu )3MosC)(K(crown)] was isolated and structurally characterized. Bridging acetylides, L M—CsC—ML , and poly-acetylides, L M- CsC v-ML , are also well known. ... 

The bond between tetrahedral carbon and transition metals mainly exists in the form of terminal metal-alkyl complexes such as [WCCHs) ]. - Metal-alkyl complexes are now numerous. It has been understood that they are stable if the p-elimination path is blocked either because the complexes have 18 valence electrons, - or have less valence electrons, but no p hydrogen. - Complexes of other tetrahedral carbon are also known in which two, three or four metal substituents are metal fragments. They are respectively bridging alkylidene, alkylidyne and carbide complexes, below ... 

In the realm of all-carbon ligands in the formation of transition-metal complexes, the naked carbon atom holds a special position. Based on the geometry of metal-carbon interaction, these compounds can be divided into four classes terminal carbide (I), 1,3-dimetallaallene (II), C-metalated carbyne (III), and carbido cluster (IV) ... 

C. C. Cummins, Terminal, Anionic Carbide, Nitride, and Phosphide Transition-Metal Complexes as Synthetic Entries to Low-Coordinate Phosphorus Derivatives, Angew. Chem. Int. Ed. 45, 862-870 (2006). 

Mo(N[f-Bu]Ar)3 has also been demonstrated to activate white phosphorous forming the terminal phosphide P = Mo(N[f-Bu]Ar)3.122 Additional interesting molecules containing multiple bonds such as the terminal carbide (C =Mo(N[/-Bu] Ar)3 ), selenide (Se Mo(N f-Bu Ar)3), and telluride (Te=Mo(N[i-Bu]Ar)3) have also been isolated.123 Reaction with PhE-EPh complexes have also been investigated and shown to proceed by a radical mechanism.124... 

The chemistry of metal-to-carbon multiply bonded complexes continues to flourish. The critical role olefin metathesis chemistry now plays in so many areas of synthesis and materials science has provided important impetus for the continued discovery and study of such species. " While the scope of this contribution is far too narrow to even begin to touch upon this broad area of organometallic chemistry, the authors wish to highlight one new class of organometallic complexes that falls within this category, that of the terminally bonded carbides. 

The reaction mechanism of FTS is fairly complex, composing a network of the elementary bond-breaking and bond-formation steps, which include the activation of CO and H2 as well as hydrogenation and chain growth/termination over metal catalysts. FTS is assumed to follow a chain growth mechanism via the addition of CH2 groups while alternative mechanisms, such as CO insertion via carbide, have also been proposed. A better understanding of the reaction mechanism, the key reaction... 

It is evident from the earlier discussion that scaling among adsorption energies should not be limited to transition metal surfaces. In fact, even for metal-terminated surfaces of more complex systems like transition metal compounds (oxides, nitrides, sulfides, and carbides), where there is mixed covalent, ionic bonding between the... 

Cummins CC (2006) Terminal, anionic carbide, nitride, and phosphide transition-metal complexes as synthetic entries to low-coordinate phosphcnus derivatives. Angew Chem Int Ed 45 862-870... 

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