Ruthenacyde intermediates

Linear Intermolecular Couplings Involving Ruthenacyde Intermediates... 

One of the most reported pathways for C=C and C=C bonds coupling involves the oxidative coupling and the ruthenacyde intermediate formation. The first ruthenium-catalyzed Unear codimerization of disubstituted alkynes and alkenes involved acrylates or acrylamides and selectively produced 1,3-dienes [33] (Eq. 23). The proposed mechanism involves a ruthenacyclopentene via oxidative coupUng on the Ru(0) catalyst Ru(COD)(COT). The formation of 1,3-di-ene results from intracyclic /1-hydride eUmination, this process taking place only when a favored exocyclic /1-elimination is not possible. 

The above mthenium(II)-catalyzed intramolecular alkyne cyclotrimerizations probably proceeded via a ruthenacycle intermediate similar to the aforementioned ruthenacyclopentatriene complex 18 reported by Dinjus (see Scheme 4.5) [24]. This was confirmed by the isolation of a bicyclic ruthenacyde intermediate and its reaction with acetylene (Scheme 4.11) [25]. The stoichiometric reaction of 17 with the internal diyne 31 possessing phenyl terminal groups in CDCI3 at ambient temperature afforded the expected mthenacycle complex 32 in 51% yield as single crystals. X-ray analysis of 32 disdosed that its Ru-Ca bond distances of 1.995(3) and... 

The proposed mechanism involves coordination of allene and ce,/j-unsaturated ketone to the cationic cydopentadienylruthenium species 137. Subsequent formation of the ruthenacyde 139, followed by /3-hydride elimination, generates the ruthenium hydride species 140. Finally, reductive elimination closes the cycle and regenerates the ruthenium intermediate 137 (Scheme 14.33) [68, 71]. 

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See also in sourсe #XX -- [ ]

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