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)A, 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.