Ethylidyne complex

Species D is most likely an ethylidyne complex which forms from self-hydrogenation on the palladium surface. Such species along with species E have been suggested to be part of the compounds formed from platinum and acetylene. 

Scheme 10. Thermochemical cycle for determination of reductively induced C-H bond activation in dinuclear ethylidyne complexes.

Katz and co-workers reported the reactions of the chromium and tungsten ethylidyne complexes 249 and 250 with l-alkynyl-l -vinylbiphenyl (193.194). For both metals the reactions lead to the incorporation of the carbyne ligand into the organic substrate, but in slightly different ways as shown by formation of the products 251-253 [Eq. (187)]. The product of... 

INS spectra are shown in Fig. 7.17. The peak positions, Table 7.9, are close to those in the HREELS of ethene on Pt(lll) (the predominant exposed crystal faces) [64]. The spectrum was modelled with a non-planar ethene (H-C-C-H dihedral 82.8°). Spectral changes as the temperature was raised were attributed to ethylidyne, CH3C, by comparison with the spectra of a cobalt ethylidyne complex ( 7.2.2.6). 

The molecular chemisorption of ethylene is observed below room temperature, but at higher temperatures the alkene can be cleaved with formation of ethylidyne complexes of the type ... 

The equivalent alkyne-insertion reaction with PhC = CR (R = H or Ph) gives only -vinyl products, whereas RCH2C = CH (R = H or "Pr) gives f/ -vinyl and metallafuran products, though the same substrate with HC = CH yields exclusively the ethylidyne complex Tp W( = CMe)(CO)2. For the latter, an identical reaction course resulted from stoichiometric addition of Li[HBEt3] to a tetrahydrofuran solution of [Tp W(HC = CH)(CO)2][OTf] and this complex may also be prepared by an alternative route involving elaboration of an alkylidyne ligand (vide infra). ... 

Aldehydes and ketones can also be used as electrophiles in reactions with the vinylidene anion [Tp M( = C = CH2)(CO)2] . Low-temperature reaction of [Tp M( = C = CH2)(CO)2] with RR C = 0 (R = Ph, Pr, R = H R = Ph, R = Me) followed by protonation yields Tp W = CCH2C(OH)RR (CO)2. When R = Ph and R = H, one equivalent of base leads to deprotonation and hydroxide elimination to form the conjugated vinyl carbyne complex Tp W (= CCH = CHPh)(CO)2 (as the E isomer) in 53% yield two equivalents of base produces a 1 1 mixture of the vinyl carbyne and the ethylidyne complex. With base, Tp W = CCH2C(OH)PhMe (CO)2 simply regenerates the starting ethylidyne complex and ketone,reminiscent of the tendency of propargylic alcohols to eliminate aldehyde or ketone under basic conditions. 

As an extension of the studies described above [3] and our previous work [2] with carbyne complexes having a tolyl substituent on the carbyne carbon, we turned to the corresponding ethylidyne complexes 22a,b. It was quickly found that these complexes readily deprotonate to form the neutral vinylidene complexes 23a,b. eq. 8 [5]. For the... 

The equilibrating mixture of ethylidyne complex 22 and vinylidene complex 23 have been found to give a variety of new reactions with imines, azines, and carbodiimides (see Scheme VUI) [5]. Although the products of the reactions described below are... 

As shown in Equation (11), the tris(/i-alkylidene) complex 36 is formed by the two-electron oxidation of the 3-diruthena-allyl complex 35. Although two-electron oxidation is required to complete the reaction, the product 36 is monocationic. It was proposed that liberation of from a dicationic intermediate took place during the reaction. Two-electron oxidation accompanied by liberation was also reported for the oxidation of the /t3-ethylidyne complex to yield a /t3- -vinylidene complex. ... 

---