Ruthenacydes

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]. 

A related intramolecular coupling between a monodentate acetate ligand and a transient diphenylallenylidene moiety occurs when the hydroxyalkynyl derivative 34 is treated with HPFg, affording the ruthenacyde 36 (Scheme 2.13) [68]. This cyclization process is strongly dependent on the electronic properties of the organometallic... 

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. 

In contrast to the above ruthenium(O) complexes, the reaction of the Ru(II) complex 13, bearing a cyclopentadienyl (Gp) ligand, with electronically neutral phenyl-acetylene gave rise to the coordinatively unsaturated ruthenacyde 14 (Scheme 4.4) [20]. On the basis of X-ray structural analysis, the original authors claimed that 14 is the first formally 18-electron rathenmm(ll)-metallacYclopentatrwne. In accordance with this claim, the NMR resonance corresponding to the metal-carbene a car-... 

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... 

In the case that the alkyne partner contains a propargylic hydroxyl group, the flexibility of Ru to form higher oxidation states may allow ionization of this hydroxyl group followed by recombination as shown in Equation 1.57, ruthenacyde 46 to 47 to 48. Indeed, the simple addition of propargyl alcohol 49 and methyl vinyl ketone produces the nicely functionalized 1,5-diketone 50 (Equation 1.58) [53], Such functionality sets the stage well for further elaborations. 

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