New Aryloxy and Benzyloxy Derivatives of Titanium as Catalysts for Bulk Ring‐Opening Polymerization of ϵ‐Caprolactone and δ‐Valerolactone

Abstract

A variety of aryloxy compounds and benzyloxy derivatives of Ti IV were synthesized from Ti(iPrO) 4 using the alcoholysis route. These compounds were characterized using various analytical methods and single-crystal X-ray diffraction. Multinuclear NMR studies prove high degree of fluxional behavior of these compounds in solution. They adopt a dimeric structure in the solid state as seen from X-ray diffraction studies on a few of them. These compounds are powerful catalysts for the ring-opening polymerization of ε-caprolactone (CL) and δ-valerolactone (VL) resulting in high polymers with good number average molecular weights (M n ). Signifi-

Aryloxy and benzyloxy compounds of zirconium: Synthesis, structural characterization and studies on solvent-free ring-opening polymerization of ɛ-caprolactone and δ-valerolactone

“…These results proved our contentions that metal complexes containing elaborate ligands may not be necessary for developing a viable technology for lactone polymerization. We were able to confirm our assessment by developing suitable titanium aryloxy and benzyloxy compounds that effectively catalyze the polymerization of CL and VL [59]. Having obtained encouraging results from this work, we were inspired to evaluate the role of zirconium analogues to understand the effect of other group 4 metals in such polymerizations.…”

“…In compounds 10, 12 and 13, there is a molecule of residual toluene which could not be removed completely by drying these compounds under high vacuum. Similar observation was noted with a few titanium analogues [59]. For the zirconium aryloxy compounds 1e13, the eOH signal of the coordinated HO-iPr remains silent with the exception of 3 where it appears at d ¼ 5.52 ppm as a broad peak.…”

“…The spectra were found to simplify considerably at 55 C. The signals appear broad, suggesting a fluxional behavior exhibited by these compounds in solution. The degree of broadening was found to be much higher than the corresponding titanium analogues [59]. The expected multiplicity for each signal was found to disappear completely.…”

“…The benzyloxy derivatives namely Zr(O-CH 2 -4-MeC 6 H 4 ) 4 (14) and Zr(O-CH 2 -4-OMeC 6 H 4 ) 4 (15) were synthesized by using a similar procedure and isolated as colorless viscous oils. The synthetic route is viable under ambient conditions in sharp contrast to the titanium analogues where several reaction mixtures were heated [59]. These compounds were thoroughly characterized employing 1 H and 13 C NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and X-ray diffraction studies.…”

“…For VL polymerization, 26.9 mmol was used for 0.50 mL (0.54 g, 5.38 mmol) of monomer and a similar procedure was followed. The progress of the polymerization was followed by monitoring the disappearance of the monomer using TLC technique [58,59]. The polymerizations were quenched by pouring the contents into cold heptane.…”