Reactions of co-ordinated ligands. Part 18. Ring-expansion reactions of tricarbonyl(η4-tetramethylcyclobutadiene)iron; molecular and crystal structures of [Fe{η4-C6Me4(CF3)2}(CO)3] and [Fe{C8Me4(CF3)2O2}(CO)3]

Abstract

lrradiation (u.v.) of a solution of [Fe(η⁴-C₄Me₄)(CO)₃] and hexafluorobut-2-yne affords the arene tricarbonyl iron complex [Fe{η⁴-C₆Me₄(CF₃)₂}(CO)₃] identified by X-ray crystallography. The crystals are monoclinic, space group P2₁/n, Z= 4, in a unit cell of dimensions a= 13.377(5), b= 8.959(5), c= 13.544(6)Å, and β 100.54(3)°. A second product in the reaction is a bicyclic diketone [Fe{C₈Me₄(CF₃)₂O₂}(CO)₃], which has also been structurally characterized by X-ray crystallography. The crystals are monoclinic, space group P2₁/n, Z= 4, in a unit cell of dimensions a= 9.031 (7), b= 17.865(16), c= 11.519(10)Å, and β 105.49(6)°. A similar irradiatron reaction between trifluoroethylene and [Fe(η⁴-C₄Me₄)(CO)₃] afforded two isomeric η-cyclobutenyl complexes, one of which arises by a formal fluorine migration reaction and contains the arrangement FeCH(CF₃)C. Thermolysis of this latter species results in a ring-enlargement reaction and the formatron of [Fe₂(CO)₄{η⁴-C₅Me₄(CF₃)}]. A minor product in this reactrin is obtained in higher yield by carbonylation, and is formulated as a ring-expanded η³-C₅Me₄CO complex. The mechanism of formation of these products is discussed.