Crystal and molecular structure of di-µ-carbonyl-cis-µ-(1–5-η: 1′–5′-η-dicyclopentadienyldimethylsilane)bis(carbonyliron)(Fe–Fe)

Abstract

Crystals of the title compound are monoclinic, space group P2₁/n, with Z= 4 in a unit cell of dimensions: a= 11·66, b= 13·27, c= 10·82 Å, β= 105° 50′. The structure was determined from diffractometer data by the symbolic addition method and refined to R 0·072 for 1309 independent reflections. The silicon atom is tetra-hedrally σ bonded to two methyl groups and to two cyclopentadienyl rings; the latter are in turn each π-bonded to one iron atom. The two iron atoms are bonded to one another (2·51 Å) and are also linked by two symmetrical carbonyl bridges; the four-membered ring so defined is non-planar, being folded along the Fe–Fe axis away from the C₅ rings at an angle of ca. 160°. Each iron atom also carries one terminal carbonyl group, which makes the overall co-ordination approximately octahedral.

The Si atom does not lie in the Fe₂(CO)₂(terminal) plane, nor are the cyclopentadienyl rings symmetrically related to it (though their centroids lie in it), and the overall symmetry of the molecule is only C_s(m). Reasons for this configuration are discussed. The Fe–C and C–O distances are as expected; the four Si–C distances relatively equal, mean 1·88 Å.