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Cooperative Hydrogen-Bond Pairing in Organocatalytic Ring-Opening Polymerization.

Kazakov OI, Datta PP, Isajani M, Kiesewetter ET, Kiesewetter MK - Macromolecules (2014)

Bottom Line: In this work, several of the most active cocatalyst pairs are shown by (1)H NMR binding studies to be highly associated in solution, dominating all other known noncovalent catalyst/reagent interactions during ROP.One strongly binding catalyst pair behaves kinetically as a unimolecular catalyst species.The high selectivity and activity exhibited by these ROP organocatalysts are attributed to the strong binding between the two cocatalysts, and the predictive utility of these binding parameters is applied for the discovery of a new, highly active cocatalyst pair.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Rhode Island , Kingston, Rhode Island 02881, United States.

ABSTRACT
Thiourea (TU)/amine base cocatalysts are commonly employed for well-controlled, highly active "living" organocatalytic ring-opening polymerizations (ROPs) of cyclic esters and carbonates. In this work, several of the most active cocatalyst pairs are shown by (1)H NMR binding studies to be highly associated in solution, dominating all other known noncovalent catalyst/reagent interactions during ROP. One strongly binding catalyst pair behaves kinetically as a unimolecular catalyst species. The high selectivity and activity exhibited by these ROP organocatalysts are attributed to the strong binding between the two cocatalysts, and the predictive utility of these binding parameters is applied for the discovery of a new, highly active cocatalyst pair.

No MeSH data available.


Related in: MedlinePlus

For the ROP of VL, observedrate constant (kobs) vs [1] + [DBU]. Conditions: VL (2 M, 100mg):benzyl alcohol 50:1 in C6D6. Rate = kobs[VL], where kobs = kP([1] + [DBU])[benzylalcohol].
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fig1: For the ROP of VL, observedrate constant (kobs) vs [1] + [DBU]. Conditions: VL (2 M, 100mg):benzyl alcohol 50:1 in C6D6. Rate = kobs[VL], where kobs = kP([1] + [DBU])[benzylalcohol].

Mentions: Kinetic studieswere undertaken tohelp elucidate the roles of 1 and DBU in the ROP of δ-valerolactone(VL). While holding the concentration of VL (2 M, 1.00 mmol) and benzylalcohol (0.04 M, 0.020 mmol) constant in C6D6, the concentrations of 1 and DBU were varied from [1] = [DBU] = 0.05 to 0.20 M (see SupportingInformation). The resulting plot (Figure 1) of observed rate constant, kobs, versus([1] + [DBU]), where [1] = [DBU], is linear,which describes an ROP reaction that is first order in cocatalysts:Rate = kobs[VL], where kobs = kP([1]+ [DBU])[benzyl alcohol], and kP is thepolymerization rate constant. This observation is in contrast to aprevious report which assumed for purposes of kinetic fitting thatrate is proportional to both [1] and [base] (i.e., kobs = kP[1][base][benzyl alcohol]).4 The ROP ratebeing proportional to ([1] + [DBU]) suggests a cocatalystsystem that behaves as a discrete catalyst species, yet the role ofthe individual cocatalyst moieties is unclear.


Cooperative Hydrogen-Bond Pairing in Organocatalytic Ring-Opening Polymerization.

Kazakov OI, Datta PP, Isajani M, Kiesewetter ET, Kiesewetter MK - Macromolecules (2014)

For the ROP of VL, observedrate constant (kobs) vs [1] + [DBU]. Conditions: VL (2 M, 100mg):benzyl alcohol 50:1 in C6D6. Rate = kobs[VL], where kobs = kP([1] + [DBU])[benzylalcohol].
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230384&req=5

fig1: For the ROP of VL, observedrate constant (kobs) vs [1] + [DBU]. Conditions: VL (2 M, 100mg):benzyl alcohol 50:1 in C6D6. Rate = kobs[VL], where kobs = kP([1] + [DBU])[benzylalcohol].
Mentions: Kinetic studieswere undertaken tohelp elucidate the roles of 1 and DBU in the ROP of δ-valerolactone(VL). While holding the concentration of VL (2 M, 1.00 mmol) and benzylalcohol (0.04 M, 0.020 mmol) constant in C6D6, the concentrations of 1 and DBU were varied from [1] = [DBU] = 0.05 to 0.20 M (see SupportingInformation). The resulting plot (Figure 1) of observed rate constant, kobs, versus([1] + [DBU]), where [1] = [DBU], is linear,which describes an ROP reaction that is first order in cocatalysts:Rate = kobs[VL], where kobs = kP([1]+ [DBU])[benzyl alcohol], and kP is thepolymerization rate constant. This observation is in contrast to aprevious report which assumed for purposes of kinetic fitting thatrate is proportional to both [1] and [base] (i.e., kobs = kP[1][base][benzyl alcohol]).4 The ROP ratebeing proportional to ([1] + [DBU]) suggests a cocatalystsystem that behaves as a discrete catalyst species, yet the role ofthe individual cocatalyst moieties is unclear.

Bottom Line: In this work, several of the most active cocatalyst pairs are shown by (1)H NMR binding studies to be highly associated in solution, dominating all other known noncovalent catalyst/reagent interactions during ROP.One strongly binding catalyst pair behaves kinetically as a unimolecular catalyst species.The high selectivity and activity exhibited by these ROP organocatalysts are attributed to the strong binding between the two cocatalysts, and the predictive utility of these binding parameters is applied for the discovery of a new, highly active cocatalyst pair.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Rhode Island , Kingston, Rhode Island 02881, United States.

ABSTRACT
Thiourea (TU)/amine base cocatalysts are commonly employed for well-controlled, highly active "living" organocatalytic ring-opening polymerizations (ROPs) of cyclic esters and carbonates. In this work, several of the most active cocatalyst pairs are shown by (1)H NMR binding studies to be highly associated in solution, dominating all other known noncovalent catalyst/reagent interactions during ROP. One strongly binding catalyst pair behaves kinetically as a unimolecular catalyst species. The high selectivity and activity exhibited by these ROP organocatalysts are attributed to the strong binding between the two cocatalysts, and the predictive utility of these binding parameters is applied for the discovery of a new, highly active cocatalyst pair.

No MeSH data available.


Related in: MedlinePlus