Ruthenium complexes, reactions mixtures, analysis

The reactions of dihydrobilin (1,19-dideoxybiladiene-a, c) with transition metals are strongly influenced by the nature of the metal ion. Thus with Mn(OAc)3 or FeClj the corresponding metallocorrolates have been obtained in high yield, in the presence of chromium or ruthenium salts the reaction product isolated has been the metal free macrocycle, while coordination of rhodium requires the presence of an axial ligand such as a phosphine, arsine or amine [21]. Neutral pentacoordinated rhodium complexes have thus been obtained. Although analysis of the electronic spectra of the reaction mixtures demonstrated that cyclization of the open-chain precursor and formation of metallocorrolates occur even in the absence of extra ligands, no axially unsubstituted rhodium derivative has been reported. 

Laine (43-47) used potassium hydroxide to promote the catalytic activity of [Ru3(CO),2] and [H4Ru4(CO),2] for the hydroformylation of pent-1-ene. Under 64 bar of CO pressure, at 135 or 150°C, high selectivities for straight-chain aldehydes were obtained, for example, 97%. As the subsequent reduction of aldehydes to alcohols is lower, important aldol condensations occurred owing to the presence of a base in solution. Analysis of the reaction mixtures has shown that the anionic [H3Ru4(CO),2] cluster is likely to be the active species. Since this complex was recognized as the major component of the low pressure ruthenium-catalyzed water gas shift... 

Treatment of an alkyne/alkene mixture with ruthenium carbene complexes results in the formation of diene derivatives without the evolution of byproducts this process is known as enyne cross-metathesis (Scheme 22). An intramolecular version of this reaction has also been demonstrated, sometimes referred to as enyne RCM. The yield of this reaction is frequently higher when ethylene is added to the reaction mixture. The preferred regiochemistry is opposite for enyne cross-metathesis and enyne RCM. The complex mechanistic pathways of Scheme 22 have been employed to account for the observed products of the enyne RCM reaction. Several experiments have shown that initial reaction is at the alkene and not the alkyne. The regiochemistry of enyne RCM can be attributed to the inability to form highly strained intermediate B from intermediate carbene complex A in the alkene-first mechanism. Enyne metathesis is a thermodynamically favorable process, and thus is not a subject to the equilibrium constraints facing alkene cross-metathesis and RCM. In a simple bond energy analysis, the 7r-bond of an alkyne is... 

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