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.