Stability of the cyclobutenyl group in Fe(C=CFCF2CF2)(CO)2(η-C5H5) towards isomerisation by ring-opening. X-ray crystal structures of Fe(C=CFCF2CF2)(CO)(L)(η-C5H5) (L=CO and PPh3)

Article abstract of DOI:10.1016/0022-328X(88)80644-2

The perfluorocyclobutenyl-iron complex Fe(c-C4F5)(CO)2(η-C5H5) does not undergo ring-opening isomerisation to a buta-1,3-dien-2-yl derivative either on pyrolysis or on UV irradiation.This difference from related cyano-cyclobutenyl complexes, and from cyclobutenes in general, has been traced, by a structural study of the complexes Fe(C=CFCF2CF2)(CO)(L)(η-C5H5) (L=CO (1a), PPh3 (1c)), to a shorter (and therefore stronger) C-C bond opposite the C=C double bond, i.e. the bond that would be broken in the isomerisation reaction.Crystals of 1a are monoclinic, space group P2₁/n, with unit cell dimensions a 6.437(1), b 15.864(4), c 11.585(3) Angstroem and β 96.54(2) deg, with Z=4.Crystals of 1c are triclinic, space group P<*>, with cell parameters a 9.358(8), b 14.890(5), c 17.865(4) Angstroem, α 103.37(3), β 95.06(4), γ 91.13(5) deg, Z=4.Both structures was refined by full-matrix least-squares methods to final R of 0.041 and 0.072, for 766 and 2472 reflections with I>2.5?(I), for 1a and 1c, respectively.