Group 4 Complexes of a New [OSSO]-Type Dianionic Ligand. Coordination Chemistry and Preliminary Polymerization Catalysis Studies

A straightforward synthesis of a new type of tetradentate dianionic [OSSO]-type ligand is described. This ligand features an ethylenedithiol core bridged via methylene groups to substituted phenols, thus representing an S analogue of the [ONNO]-type Salan ligands. The [OSSO]H₂ ligand precursor reacted with titanium(IV) isopropoxide and with zirconium(IV) tert-butoxide to give the corresponding [OSSO]−M(OR)₂ complexes, which formed as single C₂-symmetric isomers but were fluxional according to variable-temperature NMR. An X-ray structure of [OSSO]−Zr(O-t-Bu)₂ supported the fac−fac wrapping mode of the ligand. The dibenzyl complex [OSSO]−Zr(bn)₂ that was obtained by a reaction between the ligand precursor and tetrabenzylzirconium was found to be an active 1-hexene polymerization catalyst upon activation with B(C₆F₅)₃, leading to a stereoirregular polymer despite its C₂ symmetry.