C—E Bond Activation

Ruthenium has also been found to be very efficient promoting C-E bond activation under mild conditions [8]. In 1997, Perutz and co-workers reported C-E bond activation of C F with [RuHj(dmpe)2] [10]. More recendy, Whittlesey and co-workers described a similar dihydrido-ruthenium complex bearing an NHC, which achieved... 

Amii H, Uneyama K (2009) C-E bond activation in organic chemistry. Chem Rev 109 2119-2183... 

Metallocycles as intermediates in synthesis of heterocycles by transition metal-catalyzed coupling reactions under C—H bond activation 99AG(E)1698. 

From these data, some key information can be drawn in both cases, the couple methane/pentane as well as the couple ethane/butane have similar selectivities. This implies that each couple of products (ethane/butane and methane/pentane) is probably formed via a common intermediate, which is probably related to the hexyl surface intermediate D, which is formed as follows cyclohexane reacts first with the surface via C - H activation to produce a cyclohexyl intermediate A, which then undergoes a second C - H bond activation at the /-position to give the key 1,3-dimetallacyclopentane intermediate B. Concerted electron transfer (a 2+2 retrocychzation) leads to a non-cychc -alkenylidene metal surface complex, C, which under H2 can evolve towards a surface hexyl intermediate D. Then, the surface hexyl species D can lead to all the observed products via the following elementary steps (1) hydrogenolysis into hexane (2) /1-hydride elimination to form 1-hexene, followed by re-insertion to form various hexyl complexes (E and F) or (3) a second carbon-carbon bond cleavage, through a y-C - H bond activation to the metallacyclic intermediate G or H (Scheme 40). Under H2, intermediate G can lead either to pentane/methane or ethane/butane mixtures, while intermediate H would form ethane/butane or propane. 

A free carbene B base-containing complex C transmetallation D oxidative addition E C=C activation F C-H bond activation... 

Synthetic Reactions via C-H Bond Activation C-C and C-E Bond Formation... 

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