Reduction–oxidation properties of organotransition-metal complexes. Part 20. Oxidative and thermolytic cyclopropane ring-opening reactions; X-ray crystal structure of [Fe2(CO)6(η4:η′4-C16H18)]

Publisher Website
Google Scholar
Abstract
Oxidation of [Fe2(CO)6(η4:η′4-C16H18)](1) with ferrocenium hexafluorophosphate results in regioselective cyclopropane ring-opening and the formation of [Fe2(CO)6(η5:η′5-C16H18)]2+(2), a derivative of trans-1,2-bis(cycloheptadienyl)ethylene. The same hydrocarbon ligand is formed when (1) is thermolysed to give the insoluble polymer [{Fe2(CO)2(µ-CO)2(η5:η′5-C16H18)}n](3). An X-ray diffraction study has shown that the regio- and stereo-specificity observed in the formation of (2) and (3) derives from the stereochemistry of (1). The molecule (1) as a whole has near two-fold symmetry, but this is not crystallographically required. Two ring systems comprising fused cyclopropane and cyclohepta-1,3-diene fragments are joined by a single bond between the two apical cyclopropane atoms. Four atoms of each C7 ring are essentially co-planar, giving an ‘envelope’ conformation to the ring, and are bonded to an Fe(CO)3 fragment; the remainder of the C7 ring is also planar, and incorporates the two C atoms shared with the C3 ring and the CH2 group. The C7 ring folds away from the metal atom, and there are further folds at the junction with the C3 ring and again at the apex of the C3 ring, all in the same sense. The C2 symmetry thus confers an overall S shape on the dimeric species when viewed along the two-fold axis. Along the Fe Fe vector, by contrast, the C3 rings are seen nearly edgewise and the two C7 rings are almost eclipsed. Crystals of [Fe2(CO)6(η4:η′4-C16H18)](1) are triclinic, space group P, and the structure has been refined to R 0.043 for 3468 reflections measured at 293 K. Complex (3) undergoes metal–metal bond cleavage with iodine to yield [Fe2I2(CO)4(η5:η′5-C16H18)](4) which may also be prepared from the reaction of (2) and iodide ion. Triphenylphosphine adds to the terminal carbon atoms, adjacent to the CH2 groups, of the dienyl units of (2), giving the bis(phosphonium) salt [Fe2(CO)6{η4:η′4-C16H18(PPh3)2}][PF6]2(5).

This publication has 0 references indexed in Scilit: