Crystal and molecular structure of µ-pentalene-bis[dicarbonyl(trimethylgermyl)ruthenium]

Abstract

Reaction of cis-[Ru(GeMe₃)₂(CO)₄] with cyclo-octatetraene yields a complex [Ru₂(GeMe₃)₂(CO)₄(C₈H₆)] which was believed, from spectroscopic evidence, to contain a pentalene species. An X-ray diffraction study has shown this to be true, the pentalene being bonded to a nearly linear Ge–Ru–Ru–Ge spine. The two carbon atoms common to both rings are bonded to both ruthenium atoms in the form of a transverse bridge; the remaining two groups of three carbon atoms of the pentalene are each bonded as individual η- allyl interannular units to one ruthenium atom. The trimethylgermyl groups adopt an eclipsed configuration with respect to the bond axis, and the two carbonyl groups attached to each ruthenium atom are likewise eclipsed and are mutually orthogonal. The molecule as a whole has mirror symmetry (not required crystallographically) perpendicular to the Ru–Ru bond. Crystals of [Ru₂(GeMe₃)₂(CO)₄(C₈H₆)] are monoclinic, space group P 2₁, with a= 9.395(3), b= 22.555(9), c= 10.984(5)Å and β= 96.93(3)°. The structure was solved by heavy-atom methods from 2 089 intensity data [I >2.5 σ(I)] measured on a four-circle diffractometer and refined to R 0.067.