Mechanistic Study of Isotactic Poly(propylene oxide) Synthesis using a Tethered Bimetallic Chromium Salen Catalyst

Abstract

Initial catalyst dormancy has been mitigated for the enantioselective polymerization of propylene oxide using a tethered bimetallic chromium­(III) salen complex. A detailed mechanistic study provided insight into the species responsible for this induction period and guided efforts to remove them. High-resolution electrospray ionization–mass spectrometry and density functional theory computations revealed that a μ-hydroxide and a bridged 1,2-hydroxypropanolate complex are present during the induction period. Kinetic studies and additional computation indicated that the μ-hydroxide complex is a short-lived catalyst arrest state, where hydroxide dissociation from one metal allows for epoxide enchainment to form the 1,2-hydroxypropanolate arrest state. While investigating anion dependence on the induction period, it became apparent that catalyst activation was the main contributor for dormancy. Using a 1,2-diol or water as chain transfer agents (CTAs) led to longer induction periods as a result of increased 1,2-hydroxyalkanolate complex formation. With a minor catalyst modification, rigorous drying conditions, and avoiding 1,2-diols as CTAs, the induction period was essentially removed.

A Binary Silicon‐Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

“…In both cases, the living alkoxide‐end capped growth chain interacts with boron atoms, and formed a stable bridged linkage structure. The dinuclear metal catalysts that have been extensively demonstrated in numerous studies indicate that the overly stable bridging structures may inhibit the reaction [23a,b] . In our case, as shown in Figure 6, IN5 formed by the Si‐centered catalyst apparently had a freer and looser bridging structure than IN5′ formed by the N + ‐centered catalyst.…”

Autonomous Reaction Network Exploration in Homogeneous and Heterogeneous Catalysis

“…Moreover, the adsorption site location of ASE is implemented only for certain surfaces, while more advanced surfaces would require manual definitions [179]. Owing to the general, atomistic nature of their core algorithm, the AFIR and GSM method, both Maeda et al [186][187][188] and Zimmerman et al [189][190][191][192][193][194][195][196][197][198][199] have studied homogeneous catalysis more extensively, also incorporating experimental information. Their algorithms can also be applied in a semiautomatic fashion by steering the exploration into certain branches of the reaction network, either by specifying specific internal coordination transformations or fragments of the molecules that shall be combined or dissociated.…”

Cooperative Initiation in a Dinuclear Indium Complex for CO2 Epoxide Copolymerization

“…Dinuclear catalysts can be classified into three structure types: dimeric, tethered, and dinucleating catalysts (Chart ). Based on these structure types, a wide range of dinuclear complexes have been developed to date, involving metals such as Mg, , Y, , Ti, Zr, Hf, V, Cr, , Re, Fe, , Co, − Rh, Ni, Pd, , Cu, − Zn, − Al, − and Ga. − …”

“…19−21 Dinuclear catalysts can be classified into three structure types: dimeric, tethered, and dinucleating catalysts (Chart 1). 16 Based on these structure types, a wide range of dinuclear complexes have been developed to date, involving metals such as Mg, 22,23 Y, 24,25 Ti, 26 Zr, 27 Hf, 27 V, 28 Cr, 29,30 Re, 31 Fe, 32,33 Co, 34−37 Rh, 38 Ni, 39 Pd, 40,41 Cu, 42−44 Zn, 45−49 Al, 50−55 and Ga. 56−58 Recently, dinuclear indium catalysts have received increased attention due to their exceptional combination of reactivity and stability toward air and water impurities. 59−62 We reported the first dimeric indium complex (A) that exhibited efficient and highly controlled ROP of lactide.…”