Molecular structures and bonding of η-cyclopentadienyl(substituted diene)cobalt complexes

Abstract

The structures of four [Co(η-C₅H₅)(diene)] complexes have been determined from X-ray data. The dienes of complexes (1)–(3) are 1,2,3,4-tetraphenyl-1-triethylsilylbuta-1,3-diene, 4-cyano-1-(1′,2′-methoxycarbonylethyl)-1-methoxycarbonyl-2-phenylbuta-1,3-diene, and 1,3,5,6-tetramethoxycarbonyl-2,4-diphenylcyclohexa-1,3-diene respectively. The substituents at positions 2 and 3 lie in the plane of these dienes, but those at 1 and 4 are markedly out of the plane. This deviation from planarity is explained in terms of extended-Hückel molecular-orbital theory. Finally, X-ray crystallographic analysis of the related but highly strained diene complex, [Co(η⁵C₅H₄CH₂[graphic omitted]Ph)C(CO₂Me)–C(Ph)C(CO₂Me)H}](4), is reported and compared with the above three diene complexes. Crystals of (1) are monoclinic, space group P2₁/a, a= 20.364(3), b= 17.603(2), c= 9.141(3)Å, β= 104.46(3)°, Z= 4. Crystals of (2) are triclinic, P, a= 9.584(1), b= 17.942(4), c= 7.099(2)Å, α= 101.52(2), β= 90.90(2), γ= 95.22(2)°, Z= 2. Crystals of (3) are triclinic, P, a= 14.253(2), b= 19.508(3), c= 10.815(2)Å, α= 87.70(2), β= 95.14(3), γ= 110.87(3)°, Z= 4. Crystals of (4) are monoclinic, C2/c, a= l8.639(4), b= 7.372(2), c= 36.708(6)Å, β= 90.90(3)°, and Z= 8.