Journal of Organometallic Chemistry 577 (1999) 211 – 218 Synthesis of ring-substituted bis- 5 -cyclopentadienyl derivatives of the Group IV elements containing the bicyclic ligands  5 -C 5 H 3 (1,2-CH 2 –) n , n = 4, 5, or 6 Eleonora Polo a, *, Ronan M. Bellabarba b , Giansiro Prini a , Orazio Traverso a , Malcolm L.H. Green b a CNR – Centro di Studio su Fotoreattiita ` e Catalisi, Dipartimento di Chimica dell’Uniersita ` di Ferrara, ia L. Borsari 46, I -44100 Ferrara, Italy b Inorganic Chemistry Laboratory, South Parks Road, Oxford OX13QR, UK Received 2 September 1998; received in revised form 6 October 1998 Abstract The synthesis of unsubstituted and substituted bicyclic  5 -cyclopentadienyl ligands and their Group IV metal complexes [M{ 5 -C 5 H 3 (1,2-CH 2 –) n } 2 Cl 2 ], where n =4, 5, 6 and M=Ti, Zr, Hf, is reported. An example of an ansa -bridged zirconium analogue is also described. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Titanium; Zirconium; Hafnium; Metallocenes; Tetrahydroindenes; ansa -Metallocenes 1. Introduction Metallocene complexes of Group IV metals having ansa -bridged ligands of the bis-indenyl, bis-fluorenyl type, or mixed ligands systems, such as fluorenyl-cy- clopentadienyl ligands [1] are well established as highly active co-catalysts for the homo- and co-polymerisation of  -olefins. Tetrahydroindenyl derivatives can be more effective co-catalysts than the parent unsaturated deriva- tives, particularly for the incorporation of co- and ter-monomers [2]. The unsubstituted indenyl and fluorenyl ligands are directly available, whilst the normal route to tetrahy- droindenyl ligands is via the catalytic hydrogenation of the corresponding unsaturated  5 -indenyl metallocenes [3]. Moreover, it appears that the hydrogenation modifies the steric and electronic properties of these metallocenes leading to a greater resistance to hydrolysis [4]. We were interested in developing more versatile and flexible routes to tetrahydroindenyl systems and also to related ligands containing seven- and eight-membered saturated ring systems attached to the cyclopentadienyl ring, as illustrated by the structure shown in Fig. 1. The synthesis of tetrahydroindenyl-type ligands prior to their attachment to the transition metal has been explored by others [5] and elegant synthetic routes have been found. However the overall yields were often low or the method used was of limited applicability. We report here a new and general synthetic pathway to construct fused cyclopentadienyl bicyclic ligands start- ing from readily available cycloalkanones. Fig. 1. General formula of bicyclic ligands. * Corresponding author. Tel.: +39-0532-291-159; fax: +39-0532- 240-709. E-mail address: tr3@dns.unife.it (E. Polo) 0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0022-328X(98)01042-0