Synthesis of triosmium clusters containing amidine ligands: X-ray structural characterization of [Os3(µ-H)(CO)9{NPhC(Ph)NH}]

Abstract

Reactions of [Os₃(CO)₁₀(NCMe)₂] with amidines have been used to synthesize the complexes [Os₃(µ-H)(CO)₁₀{NHC(Me)NH}](1) and [Os₃(µ-H)(CO)₁₀{NPhC(Ph)NH}](2); these amidine clusters have been thermally decarbonylated to the corresponding nonacarbonyl compounds of which [Os₃(µ-H)(CO)₉(MeCN₂H₂)](3), alone, exists as two tautomeric forms in CDCl₃ solution at 20 °C. The structure of [Os₃(µ-H)(CO)₉{NPhC(Ph)NH}](4) was established by X-ray crystallography. The complex crystallises in the monoclinic space group P2₁/c with a= 20.002(10), b= 14.492(7), c= 17.999(6)Å, β= 102.80(3)°, and Z= 8. The structure was solved by a combination of direct methods and Fourier-difference techniques, and refined to R= 0.047 for 3 565 unique, observed diffractometer data. There are two independent but structurally similar molecules of (4) per asymmetric unit. In each molecule the Os atoms define an isosceles triangle one edge of which is bridged by the protonated nitrogen atom of the NPhC(Ph)NH ligand; the other N atom is terminally bound to the third Os atom in an axial site. In this way the amidine-ligand caps one triangular face of the metal framework and formally donates five electrons to the cluster.