Sterically demanding cyclopentadienyl chemistry. synthesis of iron and zirconium complexes of 1-phenyl-3-methyl-4,5,6,7-tetrahydroindenyl

Reaction of phenyl magnesium bromide with the alpha,beta-unsaturated ketone 3-methyl-2,3,4,5,6,7-hexahydroind-8(9)-en-one, followed by an aqueous work-up, generates the pro-chiral tetra-substituted cyclopentadiene, 1-phenyl-3-methyl-4,5,6,7-tetrahydroindene, (CpH)-H-double dagger, a precursor to the eta(5)-cyclopentadienyl ligand in (Cp-double dagger)(2)Fe and [(Cp-double dagger)Fe(CO)](2)(mu-CO)(2). Both complexes were generated as mixtures of rac-(RR and SS)- and meso-(RS)-isomers, and in either case pure meso-isomer was isolated by crystallisation and characterised by single crystal X-ray structure, both molecules having crystallographic Ci symmetry. Reduction with Na/Hg cleaves meso-(RS)-[(Cp-double dagger)Fe(CO)](2)(mu-CO)(2) and the resulting mixture of (R)- and (S)-[(Cp-double dagger)Fe(CO)(2)](-) anions reacts with MeI to give racemic (Cp-double dagger)Fe(CO)(2)Me, which was characterised by the X-ray crystal structure. The Cp-double dagger ligand is more electron donating than (eta-C5H5) as revealed by the reduction potential of the (Cp-double dagger)(2)Fe+/(Cp-double dagger)(2)Fe couple, E degrees = - 0.127 V (vs. Ag \ AgCl). Reaction of LiCpdouble dagger with ZrCl4 yields the zirconocene dichloride [Zr(Cp-double dagger)(2)Cl-2] as mixture of rac- and meso-isomers, from which pure rac-isomer is obtained as a mixture of RR and SS crystals by recrystallisation. The reaction of rac-[Zr(Cp-double dagger)(2)Cl-2] with LiMe gives rac-[Zr(Cp-double dagger)(2)Me-2]. The structures of RR-[Zr(Cp-double dagger)(2)Cl-2] and rac-[Zr(Cp-double dagger)(2)Me-2] have been determined by X-ray diffraction. The structural studies reveal the influence of the bulky substituted cyclopentadienyl ligand on the metal-Cp-double dagger distances and other metric parameters. (C) 1999 Elsevier Science S.A. All rights reserved.