Chemistry of the metal carbonyls. Part LXXIII. Tricarbonyl-iron and ruthenium complexes of bicyclo[4.2.0]octa-2,4,7-trienes

Abstract

Cyclo-octatetraene complexes [M(CO)₃(C₈H₇R)](M = Fe, R = SiMe₃, Ph, or CPh₃; M = Ru, R = CPh₃) isomerise on heating in octane to give the corresponding tricarbonylmetal complexes of the bicyclo[4.2.0]octa-2,4,7-triene ligands. These rearrangements, especially in the case of the ruthenium compounds, are accompained by formation of polynuclear complexes [M¹₂(CO)₅(C₈H₇M²Me₃)](M¹= Fe or Ru, M²= Si; M¹= Ru, M²= Ge), [Ru₂(CO)₆(C₈H₇CPh₃)], or [Ru₃(CO)₄(C₈H₇CPh₃)₂]. The disubstituted cyclo-octatetraene complex (IIg)[Fe(CO)₃{C₈H₆(SiMe₃)(CPh₃)}] also isomerises to a bicyclo [4.2.0] octa-2.4.7-triene structure, a fact established by a single-crystal X-ray diffraction study. Crystals of (IIg) are triclinic, space group P, with two molecules in a unit cell of dimensions a= 10.968(4), b= 11.496(4), c= 12.213(5)Å, α= 95.63(3), β= 108.56(3), γ= 91.60(3)°. The structure was solved by the heavy-atom method and refined by block-matrix least-squares to R 0.055 for 3 842 observed reflections measured by diffractometer. The crystal structure reveals existence of a fused six- and four-membered ring system, the bridgehead bond being significantly the longest. The cyclobutene ring carries an SiMe₃ group on one of the bridgehead atoms and a triphenylmethyl group trans to this.

The hexadiene ring is folded into two planar segments; the first embraces the bridgehead bond, while the second comprises a diene system which is in turn η⁴-bonded to the Fe(CO)₃ group. The ring system presents a convex face to the metal atom, and the pivotal atom of the CPh₃ group is coplanar with the cycloobutene ring. The SiMe₃ group lies endo to the metal.