Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 55. Coupling of methylene and alkylidyne groups at a trimetal centre; crystal structures of [Ru2W{µ-σ:η-trans-CHC(H)R}(µ-CO)(CO)3(η-C5H5)2(η-C5Me5)]·CH2Cl2and [Ru2W(µ3-CCH2R)(µ-CO)3(CO)(η-C5H5)3](R = C6H4Me-4)

Davies, David; Parrott, M. J.; Sherwood, Paul; Stone, F. Gordon A.

doi:10.1039/dt9870001201

Cited by 11 publications

(1 citation statement)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Surface vinylidene {CH 2 C (ad) } and ethylidyne {CH 3 C⋮ (ad) } have also been detected at 500−550 K and below 400 K, respectively, over Ru . In a catalytic system, in the absence of an added vinylic probe, the initiator could arise by combination of a methylidyne and a methylene, CH (ad) + CH 2(ad) → CHCH 2(ad) ; a related organometallic reaction has been reported for a trinuclear cluster complex …”

Section: Discussionmentioning

confidence: 94%

Investigations by¹³C NMR Spectroscopy of Ethene-Initiated Catalytic CO Hydrogenation

et al. 2002

View full text Add to dashboard Cite

13C NMR spectroscopy shows that the n-alkene and n-alkane products from the catalytic hydrogenation of CO in the presence of (13)C(2)H(4) probes over Ru/150 degrees C, Co/180 degrees C, Fe/220 degrees C, or Rh/190 degrees C (1 atm, CO:H(2) 1:1, "mild conditions") contain terminal (13)CH(3)(13)CH(2)- units. This is consistent with their formation by a regiospecific polymerization of C(1) species derived from CO and initiated by (13)C(2)H(4). Although the activities toward individual products differed somewhat, similar distributions and similar product labeling patterns were obtained over all the four catalysts. 1-Butene and the higher 1-n-alkenes from all the catalysts were largely (13)CH(3)(13)CH(2)(CH(2))(n)()CH=CH(2) (n = 0-3), propene formed over Ru or Co was (13)CH(3)(13)CH=CH(2), while both (13)CH(3)(13)CH=CH(2) and (13)CH(2)=(13)CHCH(3) were formed over Fe or Rh. Comparison of the conclusions from these probe experiments with those from isotope transient experiments by other workers indicates that the ethene initiator does not significantly modify the course of the CO hydrogenation. The reaction products are largely kinetically determined, and the primary products are mainly linear 1-n-alkenes, while the n-alkanes and 2-n-alkenes largely arise via secondary processes. Since the distribution of products and the labeling in them is so similar, it is concluded that one basic primary mechanism applies over all the four metals. Several different reaction paths involving a polymerization of surface methylene, [CH(2(ad))], have been proposed. Although the predictions based on several of these mechanisms agree with many of the results, the alkenyl + [CH(2(ad))] mechanism, initiated by a surface vinyl [CH(2)=CH((ad))], most easily accommodates the experimental evidence. An alternative path involving sequential addition of surface methylidyne and hydride either to a growing alkylidene chain (alkylidene + [CH(ad) + H(ad)]) or to an alkyl chain (alkyl + [CH((ad)) + H(ad)]) has recently been proposed by van Santen and Ciobica. The [CH(2(ad))] mechanism offers an easier explanation for the formation of the various alkenes, the distribution of products, and of the initiation, while the [CH(ad) + H(ad)] mechanism can explain any n-alkanes formed as primary products and not derived from alkenes. At higher reaction temperatures over Ru and Co, considerable (13)C(1) incorporation (from natural abundance in the CO and from cleavage of the (13)C(2)H(4) probe) was found in all the hydrocarbons. Thus, at higher temperatures (13)C(1(ad)) in addition to (13)C(2(ad)) species participate in both chain growth and initiation. In summary, adsorbed CO is transformed very easily into surface C(1(ad)), probably [CH(2(ad))] in equilibrium with [CH((ad))+H(ad)], which act as the propagating species.

show abstract

Section: Discussionmentioning

confidence: 94%