Alkyne oligomerization and CO activation on ruthenium clusters. Synthesis and crystal structure of Ru 3(CO) 5(C 12H 20)(C 19H 30O). The stepwise formation of a heterocyclic ring without cluster degradation

Abstract

The title complex was obtained in a reversible reaction by treating Ru 3(CO) 6(C 12H 20)(C 13H 20O) with excess t-butylacetylene in hydrocarbon solvents. From the two isomers of the starting product, the corresponding isomers of the new complex were obtained. The structure of one of the isomers has been determined by X-ray methods; crystals are triclinic, space group P 1 , with two molecules in a unit cell of dimensions a = 11.830(8), b = 17.096(7), c = 10.368(9) Å, α = 102.31(4), β = 113.61(5), γ = 96.23(5)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares to R = 5.0% for 2299 observed reflections. The complex consists of a nearly equilateral triangle of ruthenium atoms bonded to five terminal carbonyls; two independent organic moieties interact with all the metals of the cluster. The former is formed by two oligomerized alkynes and is responsible for the isomerism of the complex, the latter is an heterocyclic organic ring obtained by the insertion of one carbonyl into three molecules of alkyne. The formation mechanism of the complex, starting from Ru 3(CO) 12 and alkynes, is discussed on the basis of deuteration experiments and of the structures of intermediate derivatives.