In the last ten years, the more relevant catalysts for stereoselective olefin polymerization have been discovered by high throughput screening techniques (HTS) [1,2]. The catalyst discovery workflow using the HTS infrastructure reached such a level [3] that the “familiar” concept of “catalyst ligand design” by basic principles [4] seems to play a marginal role at the present stage. By using this approach a greater number of pyridyl-amine ligands with enhanced structural diversity were synthesized (see Figure 1). In designing the expanded ligand array, three convenient positions for structural amplification were identified, labeled in the Figure as R1, R2 and the presence of unusual reactivity of metal-aryl bond (see Hf-CAryl and Hf-CAlkyl bonds in system 3 of Figure 1). However, the stereoselectivity mechanism of propene polymerization promoted by such systems is still unknown [1,2]. In this communication, by means of computational methods, we investigated the enantioselectivity of propene insertion for systems 1-3 reported in Figure 1. Surprisingly, the generally accepted model of "chiral growing chain orientation" [5] was ineffective for this class of catalysts and a new model for the propene enantioselectivity has been sorted out. Despite the computational results tuned by DFT methods combined with dispersion and solvent corrections [6], there are two aspects that we would like to stress: a) our model is able to explain the subtle interplay between the steric and electronic effects as well as the reactivity of metal-aryl bond; b) it appears a general model, able after 35 years to reconnect the Ziegler-Natta catalysis to the more general asymmetric catalysis [7]. Let us make a final comment: we are well aware that discoveries of such systems were possible thanks to experimental HTS technologies because of the huge number of variables involved; nevertheless, we are still convinced that a rational catalysts design is not over the game as soon as new models are developed.
New polymerization catalysts discovered by high throughput screening techniques: a further challenge for computational methods / Talarico, Giovanni; DE ROSA, Claudio; DI GIROLAMO, Rocco. - (2015), pp. 20-21. (Intervento presentato al convegno Winter Modeling 2015 Complex Molecular System: Accuracy and Interpretation tenutosi a Pisa, Italy, nel December 18, 2015).
New polymerization catalysts discovered by high throughput screening techniques: a further challenge for computational methods
TALARICO, GIOVANNI;DE ROSA, CLAUDIO;DI GIROLAMO, ROCCO
2015
Abstract
In the last ten years, the more relevant catalysts for stereoselective olefin polymerization have been discovered by high throughput screening techniques (HTS) [1,2]. The catalyst discovery workflow using the HTS infrastructure reached such a level [3] that the “familiar” concept of “catalyst ligand design” by basic principles [4] seems to play a marginal role at the present stage. By using this approach a greater number of pyridyl-amine ligands with enhanced structural diversity were synthesized (see Figure 1). In designing the expanded ligand array, three convenient positions for structural amplification were identified, labeled in the Figure as R1, R2 and the presence of unusual reactivity of metal-aryl bond (see Hf-CAryl and Hf-CAlkyl bonds in system 3 of Figure 1). However, the stereoselectivity mechanism of propene polymerization promoted by such systems is still unknown [1,2]. In this communication, by means of computational methods, we investigated the enantioselectivity of propene insertion for systems 1-3 reported in Figure 1. Surprisingly, the generally accepted model of "chiral growing chain orientation" [5] was ineffective for this class of catalysts and a new model for the propene enantioselectivity has been sorted out. Despite the computational results tuned by DFT methods combined with dispersion and solvent corrections [6], there are two aspects that we would like to stress: a) our model is able to explain the subtle interplay between the steric and electronic effects as well as the reactivity of metal-aryl bond; b) it appears a general model, able after 35 years to reconnect the Ziegler-Natta catalysis to the more general asymmetric catalysis [7]. Let us make a final comment: we are well aware that discoveries of such systems were possible thanks to experimental HTS technologies because of the huge number of variables involved; nevertheless, we are still convinced that a rational catalysts design is not over the game as soon as new models are developed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
