STRUCTURE OF ETA-3-CYCLOOCTENYLTRIS(TRIMETHYL PHOSPHITE)IRON(I) - BONDING OF THE ETA-3-ALKENYL GROUP TO 16-ELECTRON, 17-ELECTRON, AND 18-ELECTRON ML3 SYSTEMS

The crystal and molecular structure of Fe(η-C8H13)(P(OMe)3)3 has been determined at -80 °C by X-ray diffraction. The monoclinic crystals (C2/c) have unit cell dimensions a = 14.940 (3) Å, b = 1 1.626 (3) Å, c = 29.952 (5) Å, β = 103.88 (2)°. and V = 5050.5 Å3. Full-matrix least-squares refinement led to R(Fo) = 0.035 and RW(Fo) = 0.036. The coordination sphere about the iron atom is a distorted square pyramid if the η3-cyclooctenyl group is considered to be a bidentate ligand. The η3-allylic group is symmetrical but skewed with respect to the basal plane. This twisting allows a hydrogen atom on a carbon atom attached to the η3-allylic group to have a very weak (2.77 (2) Å) interaction with the metal center. Extended Hiickel theory, with the inclusion of two-body repulsion, has been used to reproduce molecular geometries, including bond lengths, of 16-, 17-, and 18-electron complexes of the type [M(η3-alkenyl)(P(OMe)3] + x. Barriers to several intramolecular rearrangements have been calculated for these species and agree well with N MR and ESR measurements. The bonding in the 16-, 17-, and 18-electron species is discussed. © 1979, American Chemical Society. All rights reserved.