Methylidyne

The simple methylidyne compound [HC=Co]+ has been formulated as a CoIV species.1102 The norbornyl anion (nor), as the lithium salt, reacts with CoCl2 to produce the brown, paramagnetic tetrahedral Co(nor)4. This can undergo both reduction (to [Co(nor)4] ) and oxidation (with AgBF4) to what appears to be [Co(nor)4]+, a diamagnetic tetrahedral compound. This remains one of the very few established examples of Cov. 

Protonation of 12 yields a compound best described as a face-protonated methylidyne complex, the tungsten-carbon bond length lying in the range observed for a triple bond (28). Protonation of the osmium compound 13 yields a true carbene complex, which for R = Ph has been characterized by X-ray crystallography (see Sections IV and VI). 

Photolysis of the methylidyne cluster HRu3(CO)] (/1, 71"COCH3) (A) (14) in cyclohexane solution leads to an unprecedented oxygen-to-carbon alkyl migration to form the bridging acyl complex HRu3(CO)10( i-> 2-C(O)CH3) (B) ... 

Any proposed mechanism for the unprecedented transformation described by Equation 18 must account for the promotion of this photoisomerization by CO, although CO is not required by the stoichiometry. A possible initial step would be similar to that for the Ru3(CO)i2 fragmentation (Scheme 1). In this a Ru-Ru bond is broken concomitant with the movement of a CO from a terminal to a bridging site to form an unsaturated intermediate analogous to I. A speculative proposal along these lines is presented in Figure 5. The key feature of this proposal would be the formation of III with one unsaturated ruthenium, which could be captured by CO to promote the subsequent steps leading from the /1-methylidyne to the acyl... 

Examples of O-alkylation have also been demonstrated for triruthenium and triosmium anionic clusters, as well as the tetrairon cluster Fe CO)] - (31-33). This reaction has considerable promise as an entry into many different methylidyne complexes through the replacement of the OR" group, eq. 20 (38). 

Methylidine chloride, 6 249 Methylidyne complex, 26 949 Methyliminodiacetic acid (MIDA), 19 265 Methyl iodide, 14 376 Methyl ionone, 3 232 a-iso-Methylionone, 24 562, 566 a-n-Methylionone, 24 565 p-iso-Methylionone, 24 566 P-n-Methylionone, 24 565 Methyl isoamyl ketone (MIAK),... 

Chemical shift for the methylidyne carbon in ppm relative to TMS. b Chemical shift for the phosphorus atom of the metallacycle in ppm relative to H3P04. 

H2salen bis(salicylidene)ethylenediamine 2,2 -[ethane-1,2-diylbis(nitrilo-methylidyne)]diphenol... 

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... 

METHYLIDYNE (CARBYNE) COMPLEXES. fnmHBROMO-TETRACARBONYL(PHENYLMETHYLIDYNE)TUNGSTEN]... 

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