STRUCTURAL CHEMISTRY OF MULTIPLY BUTYLATED CYCLOPENTADIENE TRANSITION-METAL COMPLEXES. Ling-Kang Liu, Lung-Shiang Luh, Institute of Chemistry, Academia Sinica, Nankang, Taipei, Taiwan 11529, Republic of China

Representative structures of polybutylcyclopentadiene dicarbonyl triphenyl phosphineiron have been determined with single crystal X-ray diffraction to see to what extent the structure deformations are as caused by the presence of bulky butyl groups on the ring. Revealed in these structures is the common feature of complexes -- a square-pyramidal Fe(0) center with one of the CO groups in the apical position and one olefin of diene moiety trans to the second CO, and the other olefin of diene trans to PPh₃ in the basal plane. The IR data indicates that the increase of butyl substitution on the ring red-shifts the v_CO stretching frequencies by 4-5 cm^-1 per butyl group. With increasing number of butyl substitutions on the ring, the Fe-P bond length increases from 2.211(1)Å in 1Bu, 2.216(1)Å in 1,2,5-3Bu, 2.229(1)Å in 1,2,3,5-4Bu, to 2.236(1)Å in 5Bu where 1Bu = ([[eta]]⁴-exo-BuC₅H₅)-Fe(CO)₂Ph₃, 1,2,5-3Bu = ([[eta]]⁴-exo-1,2,5-Bu₃C₅H₃)F(CO)₂PPh3, 1,2,3,5-4Bu = ([[eta]]⁴-exo-1,2,3,5-Bu₄C₅H₂Fe(CO)₂PPh₃ and 5Bu = ([[eta]]⁴exo-Bu₅C₅H)Fe(CO)₂PPh₃.