A study of the reduction of substituted fulvenes using spectro-electrochemistry and ab initio theory

Synthesis and Structural Characterisation of a Novel Chiral ansa-Cobaltocenium Hexafluorophosphate

“…To be the former of the two, the cyclopentadienyl rings should consist of alternating single and double bonds, with the two phenyl substituents located at the exocyclic double bond. These bond lengths should mirror the values determined both theoretically [19] and experimentally [26] for the 6,6-diphenylfulvene. Alternatively, to be the ferrocene derivative, the cyclopentadienyl rings should be more aromatic in character due to their reduction by the iron centre.…”

“…[16] 6-Phenylfulvene [18] is the ligand of choice for this synthesis, undergoing reductive coupling to give solely the bridged metallocene. As reported earlier [19] this fulvene produces a radical anion that is readily formed and selective enough to give exclusive formation of the bridging moiety, thus eliminating the possibility of any unbridged metallocenes forming as an inseparable impurity.…”

“…In order to synthesise an ansa-metallocene, the groups present on the exocyclic carbon must not be so sterically demanding that they prevent dimerisation occurring, as in the case of 6,6-diphenylfulvene. Despite its suitability for radical anion stabilisation, [19] the steric hindrance between the four phenyl rings results in the sole production of the unbridged metallocene. Changing the phenyl groups for methyl groups reduces these clashes and bridge formation occurs.…”

“…The structure of the 6,6-diphenylfulvene radical anion has previously been calculated, using the 6-31G** basis set. [19] It can clearly be seen that the CϪC bonds in the cyclopentadienyl ring are no longer comprised of distinct single and double bonds and lie in the range of 1.387 Å to 1.446 Å . The exocyclic bond has elongated to 1.434 Å , showing increased single bond character.…”

Substituted titanocenes induce caspase-dependent apoptosis in human epidermoid carcinoma cells in vitro and exhibit antitumour activity in vivo

“…Ansa-Titanocenes are a novel series of drugs synthesised from titanium dichloride and fulvenes (Teuber et al, 1997;Hartl et al, 2001;Tacke et al, 2001b;Siddik, 2003) that contain highly substituted ethylene bridge (Tacke et al, 2001a(Tacke et al, , 2004Rehmann et al, 2005). The subsequent synthesis of unbridged titanocene analogues led to increased cytotoxicity, suggesting a promising structure -function activity of these compounds .…”