Synthesis and Characterization of Zirconium and Hafnium Aryloxide Compounds and Their Reactivity Towards Lactide and ϵ‐Caprolactone Polymerization

Abstract

Reactions of 2 equiv. pyrrole with [C4H3N(CH2NMe2)‐2]2M(NEt2)2 in toluene generated tetra‐pyrrolyl metal compounds [C4H3N(CH2NMe2)‐2]2M(C4H4N)2 (3, M = Zr; 4, M = Hf) in moderate yields. Similarly, treatment of metal amides [C4H3N(CH2NMe2)‐2]2M(NEt2)2 with 2,6‐dimethylphenol or 2,6‐diisopropylphenol in heptane resulted in the elimination of diethylamine along with the formation of the corresponding metal alkoxides [C4H3N(CH2NMe2)‐2]2M(OR)2 (5, M = Zr, R = C6H3‐2,6‐Me2; 6, M = Hf, R = C6H3‐2,6‐Me2; 7, M = Zr, R = C6H3‐2,6‐iPr2; 8, M = Hf, R = C6H3‐2,6‐iPr2) in moderate yields. All the new compounds were characterized by 1H and 13C NMR spectroscopy and the structures of 3, 4, 6, 7, and 8 have also been determined by X‐ray crystallographic studies. The aryloxides and the substituted pyrrolyl ligands in both compounds 5 and 6 show fluxionality as observed by 1H NMR signals. A kinetic study on the ring‐opening polymerization of lactide exhibits a first‐order reaction of lactide monomer with compound 8. The catalytic properties of all the metal complexes have been studied for the ring‐opening polymerization of ϵ‐caprolactone. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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

“…We have obtained the highest molecular weight poly(caprolactone) in comparison to the results known for organometallic initiators of titanium. [30,[35][36][37]41,[43][44][45][46]48] The It may be intriguing to understand what happens to the identity of 1-20 in the presence of BnOH added during polymerization. To answer this, we have independently performed reactions by heating 9, 13 and 20 in the presence of 5 equiv.…”

“…To the best of our belief, such polymerizations in the presence of an alcoholic initiator like BnOH has not been reported so far using titanium derivatives. [30,[35][36][37]41,[43][44][45][46]48] We also considered it appropriate to compare the results using different aryloxy compounds 1-18 to those using the benzyloxy derivatives 19 and 20, respectively. These polymerizations were performed under bulk conditions at 80°C using 1-20.…”

“…[49] Only a few compounds derived from these ligands have been employed towards the polymerization of CL. [30,[35][36][37]41,[43][44][45][46]48] The polymerizations described from such initiators have exclusively relied upon the coordination-insertion mechanism. [1] Systematic correlation between the structural compositions of such ligands with polymer properties along with any practical advantage on polymer microstructure is not available.…”

“…(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) with one or more alkoxide-based initiating groups. The establishment of such a principle has been documented recently by demonstrating the applications of alkoxides with a ligating backbone containing chiral phenoxyimine, [28] tris-(phenoxy)amine, [29] bis(β-ketoamidate), [30] bis(iminophenoxy), [31][32] N-heterocyclic carbene, [33] bis(phenoxy)-amine, [34][35][36] pyrrolylamine, [37] tris(alkoxy), [38][39] tris(alkoxy)-amine, [40][41][42] bis(amido), [43] chalcogen-bridged bis(aryloxy) [44] and methylene-bridged bis(phenoxy) [45] derivatives. In addition, there are reports employing titanium n-butoxide, zirconium n-propoxide [46] and titanium phenoxide [47] as initiators.…”

Magnesium Pyrazolyl-Indolyl Complexes as Catalysts for Ring-Opening Polymerization of L-Lactide

“…Due to the promising catalytic activities, metal-based initiators/catalysts have been attractive interest over the past decades [6][7][8][9][10][11][12][13][14]. Among these studies, some metal complexes bearing anionic N-heterocyclic ligands, such as pyrrole [15][16][17][18][19][20][21][22][23][24][25][26], indole [27,28] or carbazole [29], have displayed good catalytic activities towards ROP (ring-opening polymerization) of cyclic esters. The indole ring system, one of the most important heterocycles in nature, keeps continuous attraction due to the potential biological activities demonstrated by various indole derivatives.…”