Methylidyne ligand

Applications of the model to Ru clusters have been reported namely by Toma etal. [78] and Keister etal. [79, 80], and, for example, for the single-electron oxidation of the 48-electron complexes of the type ]Ru3(/r-H)3(/r3-CX) (CO)9 L [, expression (20) is followed [79, 80], being derived from the general Lever s equation with inclusion of a Hammett term concerning the methylidyne X substituent. The observed value of 5 m3 (0.37) (vs. the unity expected for a monometallic Ru center) is indicative of an effective delocalization of the ligand effects over the three Ru atoms [79]. 

Alkoxy carbene complexes are useful starting compounds for other organometallic complexes,1 5 particularly methylidyne (carbyne) complexes.16 By modification of the coordinated (noncarbene) ligands or of the carbene ligand, other carbene complexes can be synthesized. The use of carbene complexes in organic syntheses has been reviewed recently.17 18... 

The methylene isomer 15 eliminates carbon monoxide when heated at 110°C (toluene, xylene 24 h), and yet another carbon-metal hydrogen shift takes place (75). The methylidyne species 16formed in this irreversible reaction has been characterized by its NMR spectra [S(CH) 9.36, quartet (76) 8(CH) 118.4 (CD3)2CO (77)] which implies a structure analogous to the previously known ethylidyne derivative (/i.-H)3(/i.-CCH3)-Os3(CO)io (138). NMR data obtained for partially deuterated samples of the methyl complex 14 have yielded evidence that the methyl ligand occupies an unsymmetrical bridging position between two metal centers, a coordination mode which implies significant C H Os interaction... 

The rapid development of the chemistry of transition metal complexes containing terminal carbene (A) or carbyne (B) ligands (7) has been followed more recently by much research centered on bridged methylene compounds (C) (2). The importance of /t-methylidyne complexes, whether in recently established binuclear examples (D), the well-known trinuclear derivatives (E), or the unusual complexes (F), has also become apparent. All are based on one-carbon (C,) fragments, and considerable interest is centered on their possible significance as models for intermediates in surface-catalyzed reactions between carbon monoxide and hydrogen (Fischer -Tropsch reactions) and related processes. These topics have been extensively ... 

Further surveys of the reactivity of HB(C6F5)2 with simple organometallic compounds have led to the discovery of more novel boron-based ligand systems. For example, reactions with Schrock s tungsten methylidyne family L4W(X)=CH63 (L = phosphine, X = Cl, OTf) result in electrophilic attack on the methylidyne ligand hydride abstraction... 

The reactivity of the methylidyne cluster 45, formed along with 46 from Ru3( T-H)( r-COMe)(CO)io and the diphosphine ligand 4,5-bis(diphenyl-phosphino)-4-cyclopenten-l,3-dione, has been reported. Mild thermolysis... 

S. J. Holmes, D. N. Clark, H. W. Turner, and R. R. Schrock, o-Hydride Elimination from Methylene and Neopentylidene Ligands. Preparation and Protonation of Tungsten(IV) Methylidyne and Neopentylidyne Complexes, J. Am. Chem. Soc. 104, 6322-6329 (1982). 

The bis(methyIidyne)hydridotricobalt cluster [Co3( U,-H)(ju,3-CH)2Cp3]+ reacts with carbon monoxide to form 37 by coupling of a HOC+ fragment with a cluster-bound methylidyne ligand.134 Carbon monoxide deinsertion and methylidyne-methylidyne coupling occur when 37 is treated with carbon monoxide under pressure to afford 38. (See Formulae 37 and 38.)... 

The most notable features of this structure center on the methylidyne, CH, ligand which forms a strong, closed three-center, two-electron bond with the apical iron atom Fe(l). There are two molecules in the asymmetric unit. The distances shown are for molecule (I) no experimentally significant differences exist between the two molecules. Each iron atom in this cluster has three terminally bound carbonyl ligands. 

In addition to complexes containing carbenes bonded to a single metal atom (M=CRR ), complexes are also known where the carbene ligand bridges two metal atoms (M-CRR -M, p-methylenes) similarly there is an extensive chemistry of metal-carbynes (M=CR, with a formal triple bond between the metal and the ligand) and p-methylidynes where the ligand is again... 

A trinuclear ruthenium cluster blocked by three pentamethylcydopentadienyl ligands showed a unique reaction environment for C-C bond cleavage. C-C bonds in cydopentadiene and branched alkane are easily cleaved on the triruthenium cluster, giving organo(methylidyne)triruthenium complexes. For example, cydopentadiene coordinates to the trinuclear Ru cluster and cleaves a C-C bond to form ruthenacy-... 

Nucleophilic displacement at a terminal methylidyne ligand, with regeneration of a metal - carbon triple bond in 199 (E = S or Se, R = Me, Ph, or P-NO2QH4) to form a new methylidyne ligand, occurs in the reaction of 198 [L = HB(3,5-Mc2—C3HN2)3] with thiolate or selenolate anions under phase-transfer conditions 149). 

Likewise, the ligand HC will have at least three different bonding modes bridging three metals ( r3-methanetriyl), bridging two metals ((r-methanylylidene) and coordinating to one metal (methylidyne, see Section IR-10.2.4). 

The methylidyne cubane [Cp Ti(/x-CH)]4 (Scheme 202) is obtained as a dark brown crystalline solid by thermolysis of Cp TiMe in toluene with methane elimination. This transformation was monitored by NMR and no intermediates are observed. The signals assignable to the methylidyne groups appear as singlets at 6 17.75 in the NMR and at 6 490.8 in the 13C NMR spectra. In order to analyze the interaction between the /i3-ligand and the titanium centers, extended Huckel molecular orbital calculations have been carried out. In contrast, the thermolysis of the trinuclear oxo alkyls [Cp Ti(/i-0)(CH2R)]3 (R = H, Me) affords the //3-alkylidyne derivatives [Cp Ti(//-0)]3-(/x3-CR).505-507... 

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