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

Abstract

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.

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“…Slightly lower barriers for inversion were previously reported for the titanium and zirconium complexes of the {OSSO} ligand featuring the less bulky tert-butyl substituents (ΔG ‡ = 11.6 Ϯ 0.5 kcal/mol for Ti; ΔG ‡ = 17.0 Ϯ 0.5 kcal/mol for Zr). [10] The dependence of inversion barriers on the bulk of phenolate substituents has been previously recorded for other systems, such as aminetris(phenolate) complexes. [19] Crystals of [{OSSO}Ti(O-iPr) 2 ] and [{OSSO}Zr(O-tBu) 2 ] suitable for X-ray analysis were grown at -30°C from toluene/pentane and ether solutions, respectively, and the structures were solved to reveal the expected geometry (Figure 2).…”

“…[10] Alkoxide complexes of the group 4 triad of the type [{OSSO}M(OR) 2 ] (M = Ti, R = isopropyl; M = Zr, Hf, R = tert-butyl) were obtained in practically quantitative yields by alcohol elimination reactions between the {OSSO}H 2 ligand precursor and the corresponding M(OR) 4 complexes.…”

“…These octahedral complexes are fluxional, exhibiting low barriers to inversion between the two C 2 -symmetric fac-fac enantiomers. [10] The dibenzylzirconium complex led to aspecific 1-hexene polymerization following activation with tris(pentafluorophenyl)-borane. [11,12] Ishii and co-workers later reported that, by constructing an analogous {OSSO} ligand around the trans-1,2-dithiocyclooctane core, a rigid dibenzylzirconium complex was obtained that led to isospecific 1-hexene polymerization catalysis under similar polymerization conditions ([mmmm] Ͼ 95 %).…”

Preparation, Structure, and Ethylene (Co)Polymerization Behavior of Group IV Metal Complexes with an [OSSO]‐Carborane Ligand

“…[2] Kol et al reported Group IV metal complexes of a new [OSSO]-type dianionic ligand, which features an ethyl-enedithiol core bridged by methylene groups to substituted phenols, thus representing the S analogue of the [ONNO]-type diamine diphenolate Salan ligands. [3] They described the coordination chemistry of this ligand around Ti and Zr. Dibenzyl complex [OSSO]-Zr(bn) 2 (bn = benzyl) was found to be an active 1-hexene polymerization catalyst upon activation with BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 .…”

“…[3] They described the coordination chemistry of this ligand around Ti and Zr. Dibenzyl complex [OSSO]-Zr(bn) 2 (bn = benzyl) was found to be an active 1-hexene polymerization catalyst upon activation with BA C H T U N G T R E N N U N G (C 6 F 5 ) 3 . Recently, Ishii and co-workers have reported a zirconium complex of a tetradentate [OSSO]-type diphenolate ligand that bears a trans-1,2-cyclooctane diylbisA C H T U N G T R E N N U N G (thio)core and was effective in isospecific 1-hexene polymerization.…”