Stability of the cyclobutenyl group in Fe( [formula omitted]F 2)(CO) 2)(η-C 5H 5) towards isomerisation by ring-opening. X-ray crystals structures of Fe( [formula omitted]F 2)(CO)(L)(η-C 5H 5) (L  CO and PPh) 3

Abstract

The perfluorocyclobutenyl-iron complex Fe(c-C 4F 5)(CO) 2(η-C 5H 5) 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CFCF 2C F 2)(CO)(L)(η-C 5H 5) (L  CO ( 1a), PPh 3, ( 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 P2 1/ n, with unit cell dimensions a 6.437(1), b 15.864(4), c 11.585(3) Å and β 96.54(2)°, with Z = 4. Crystals of 1c are triclinic, space group P 1 − , with cell parameters a 9.358(8), b 14.890(5), c 17.865(4) Å, α 103.37(3), β 95.06(4), γ 91.13(5)°, Z = 4. Both structures were refined by full-matrix least-squares methods to final R of 0.041 and 0.072, for 766 and 2472 reflections with I > 2.5σ( I), for 1a and 1c, respectively.