Giovanni Talarico

Polymer properties are profoundly impacted by tacticity, necessitating an understanding of the origins of stereocontrol to make high-performance materials. Recently, we reported that controlled incorporation of stereoerrors into trans-poly(3-hydroxy-2-methylbutyrate) (trans-PHMB) through the isoselective polymerization of rac-trans-3,4-dimethylpropiolactone (trans-DMPL) using racemic “sandwich” (BDI)Zn alkoxide complexes (where BDI = β-diketiminate) enables tuning of mechanical properties to match those of low-density polyethylene. However, the mechanism of stereocontrol of these catalysts was not explored. Herein, we report a thorough experimental and computational investigation uncovering a distinct manifestation of cooperative enantiomorphic-site and chain-end control, which we describe as site-mediated asymmetric chain-end control, where catalyst (Δ and Λ) and chain-end chiralities (R,R or S,S) work synergistically to influence the reaction’s stereoselectivity and rate. Experimental and computational data converge remarkably well, revealing that a Δ-catalyst with an (R,R)-chain end (Δ-RR) is isoselective 90% of the time. In contrast, a Δ-catalyst with an (S,S)-chain end (Δ-SS) is unselective. Detailed Density Functional Theory (DFT) investigations suggest molecular-level rationale for this mechanism of stereocontrol, demonstrating that chain positioning, monomer distortion, and ligand interactions work in conjunction to foster isoselectivity. Finally, DFT and kinetic modeling reveal that when polymerizing rac-trans-DMPL, the populations of Δ-RR and Δ-SS are equal and the high overall isoselectivity (mm% = 71–73%; where mm% is the percent of triads with a meso configuration across both ester linkages) of the catalyst is attributed to Δ-RR being faster than Δ-SS.

Polyolefins with melting temperatures above 200°C are rare, as their synthesis typically relies on the polymerization of highly sterically congested α‐olefins, which is challenging for both industrial Ziegler–Natta and homogeneous catalysts. Pyridylamido‐Hf complexes are molecular catalysts known for their high activity and ability to incorporate sterically demanding monomers, for example, allyltrimethylsilane (ATMS) giving isotactic poly(allyltrimethylsilane) with a melting temperature of 310°C and high turnover frequency. However, they are unable to polymerize efficiently monomers such as vinylcyclohexane (VCH) or 4,4‐dimethyl‐1‐pentene (44DMP). In this study, we report a novel synthetic strategy that enables the polymerization of such sterically challenging monomers, based on a pre‐activation of the Hf catalyst by using ATMS as ligand modifier in situ. We show that ATMS acts as an effective pre‐activator of the Hf complex, enabling controlled formation of highly active species and unlocking the polymerization of sterically demanding α‐olefins. This afforded the first synthesis of isotactic poly(4,4‐dimethyl‐1‐pentene) with an unprecedented melting temperature of 420°C, and efficient polymerization of VCH and 3‐methyl‐1‐butene. These findings demonstrate how the tuning of the pyridylamido‐Hf active species through rational choice of the activating monomer can be leveraged to expand the access to ultrahigh melting temperature polyolefins.

Polyolefins with melting temperatures above 200°C are rare, as their synthesis typically relies on the polymerization of highly sterically congested α‐olefins, which is challenging for both industrial Ziegler–Natta and homogeneous catalysts. Pyridylamido‐Hf complexes are molecular catalysts known for their high activity and ability to incorporate sterically demanding monomers, for example, allyltrimethylsilane (ATMS) giving isotactic poly(allyltrimethylsilane) with a melting temperature of 310°C and high turnover frequency. However, they are unable to polymerize efficiently monomers such as vinylcyclohexane (VCH) or 4,4‐dimethyl‐1‐pentene (44DMP). In this study, we report a novel synthetic strategy that enables the polymerization of such sterically challenging monomers, based on a pre‐activation of the Hf catalyst by using ATMS as ligand modifier in situ. We show that ATMS acts as an effective pre‐activator of the Hf complex, enabling controlled formation of highly active species and unlocking the polymerization of sterically demanding α‐olefins. This afforded the first synthesis of isotactic poly(4,4‐dimethyl‐1‐pentene) with an unprecedented melting temperature of 420°C, and efficient polymerization of VCH and 3‐methyl‐1‐butene. These findings demonstrate how the tuning of the pyridylamido‐Hf active species through rational choice of the activating monomer can be leveraged to expand the access to ultrahigh melting temperature polyolefins.

Bisurea anions have shown high activity and selectivity in the ring-opening polymerization (ROP) of cyclic esters. By integrating density functional theory modeling with experimental investigations, we elucidate the key mechanistic features underlying their catalytic behavior in the ROP of ε-caprolactone (ε-CL). Our study reveals that hydrogen-bond cooperativity between the urea groups, enforced by an ortho-phenylene linker, generates a semi-rigid catalytic pocket that is central to both activity and selectivity. The K+ counterion further stabilizes this architecture by reinforcing catalyst preorganization and substrate binding. This cooperative structural arrangement efficiently promotes ε-CL polymerization while suppressing transesterification pathways. Collectively, these insights establish design principles for next-generation hydrogen-bonding organocatalysts for ROP.

The recycling of low-density polyethylene (LDPE) is challenging due to difficulties with sorting and contamination, leading to environmental harm. Polyhydroxyalkanoates (PHAs) are at the forefront of high-performance biodegradable alternatives to olefinic plastics, but few offer LDPE-like properties such as low strength and crystallinity while maintaining high ductility and thermal stability. Herein, we report a series of isoenriched trans-poly(3-hydroxy-2-methylbutyrates) (trans-PHMBs) with tunable mechanical and thermal properties. These polymers were synthesized through ring-opening polymerization of racemic trans-3,4-dimethylpropiolactone (rac-trans-DMPL), sourced from C1 and C4 feedstocks, using a new class of "sandwich" C₂ symmetric rac-(^ArBDI*)ZnOⁱPr catalysts (where BDI = β-diketiminate). Variation of aromatic groups (Ar) and polymerization temperature yielded mm%s between 45-79% and melting temperatures (T_m) between 141-174 °C. trans-PHMB with intermediate isotacticities of 73 and 75 mm% exhibit similar stress-strain profiles to LDPE, indicating that these polymers have the potential to serve as higher melting, degradable substitutes for LDPE.

We present a comprehensive mechanistic investigation of the well‐defined precatalyst [Pd(IMes ^Me )(cin)Cl], which has exhibited high catalytic efficiency in the Miyaura borylation of various aryl chlorides. Despite its proven catalytic performance, key aspects of the mechanism, particularly the transmetalation step, remained elusive. In this study, we addressed these mechanistic aspects through detailed density functional theory (DFT) calculations. Our results elucidate the role of the second equivalent of base, pinpointing its specific involvement within the catalytic cycle. Furthermore, we unraveled the activation pathway of bis(pinacolato)diboron (B ₂ Pin ₂ ), determining whether base‐mediated cleavage occurs independently or requires direct coordination to the palladium center. The mechanism reveals a surprising concerted fusion of the oxidative addition and transmetalation steps, paving the way not only for a new avenue in the Miyaura reaction, but potentially for other cross‐coupling processes. This synergy may prompt a re‐evaluation of previous studies, suggesting that similar pathways could enable milder reaction conditions.

Selective ring-opening polymerization (ROP) of chiral lactones enables access to biodegradable polyesters with precisely controlled microstructures. Here, combined DFT modeling and experimental validation elucidate how fine-tuning of enantiopure SalBinam aluminum catalysts (through introduction of bromine atoms and tert-butyl groups, respectively, in ortho- and para-positions) modulates regio- and stereocontrol in the ROP of methyl glycolide (MeG) and lactide (LA). Computations reveal that regioselectivity in MeG polymerization arises mainly from steric repulsion, with a small contribution from weak stabilizing C-H···Br interactions that favor ring-opening at the glycolic site, consistent with the experimentally enhanced regioselectivity for (R)-MeG. In contrast, the same steric congestion at the ligand’s ortho positions destabilizes the key transition states in rac-LA polymerization, reducing the calculated stereoselectivity. Experiments confirm the predicted loss of stereocontrol, yielding nearly atactic PLA under standard conditions. Extension of the computational framework to rac-MeG polymerization promoted by racemic catalyst identified a low-barrier, stepwise polymer chain exchange pathway that rationalizes the experimentally observed syndiotacticity of poly(lactic-co-glycolic acid).

An earth-abundant Fe­(II)-based catalyst was employed for efficient and sustainable ring-opening polymerization of naturally occurring ε- and δ-lactones. High turnover frequencies (TOFs) and excellent control over the polymerization of δ-substituted δ-lactones demonstrate the catalyst’s ability to process monomers traditionally considered challenging or poorly polymerizable. Density Functional Theory (DFT) calculations suggest the formation of dinuclear iron species and underscore the mechanistic complexity of the system, including a monomer-dependent variation in the rate-determining step.

Enantiopure isotactic poly(cyclohexene carbonate) (PCHC) has been synthesized with chiral Zn‐β‐diiminate catalyst. PCHC crystallizes both as enantiopure polymer ( R )‐PCHC and ( S )‐PCHC and upon stereocomplexation of the two enantiomers. We report the crystal structures of the enantiopure polymer and of the stereocomplex ( R / S )‐PCHC and explain their crystallization based on the establishment of multiple attractive H‐‐‐O═C interactions between oxygen atoms of carbonyl groups and the hydrogen atoms of the cyclohexyl rings and C═O‐‐‐C═O intimate dipole interactions between carbonyl groups of chains of opposite chirality in the stereocomplex. The crystal structure of the enantiopure polymer is characterized by chains in 2/1 helical conformation packed in the orthorhombic unit cell with axes a  = 11.55 Å , b  = 9.42 Å, and c  = 7.36 Å, according to the space group P 2 ₁ 2 ₁ 2 ₁ , with steric interdigitation between chains of similar chirality favored by multiple attractive H‐‐‐O═C interactions. The stereocomplex crystallizes in an orthorhombic unit cell with axes a = 10.40 Å, b  = 8.41 Å, and c = 7.36 Å, according to the space group Pbc 2 ₁ , driven by establishment of additional C═O‐‐‐C═O dipole interactions between carbonyl groups of chains of opposite chirality, besides of the multiple attractive H‐‐‐O═C interactions.