ABSTRACT
Dinuclear polymerization catalysts can show high activity and control. Understanding how to design for synergy between the metals is important to improving catalytic performances. Three heterodinuclear Co(III)K(I) catalysts, featuring very similar coordination chemistries, are prepared with different intermetallic separations. The catalysts are compared for the ring-opening copolymerization (ROCOP) of propene oxide (PO) with CO2 or with phthalic anhydride (PA). The catalyst with a fixed, wide intermetallic separation, LwideCoK(OAc)2 (Co-K = 8.06 Å), shows very high activity for PO/PA ROCOP, but is inactive for PO/CO2 ROCOP. On the other hand, the catalyst with a fixed, narrow intermetallic separation, LshortCoK(OAc)2 (Co-K, 3.59 Å), shows high activity for PO/CO2 ROCOP, but is much less active for PO/PA ROCOP. A bicomponent catalyst system, comprising a monometallic complex LmonoCoOAc used with an equivalent of KOAc[18-crown-6], shows high activity for both PO/CO2 and PO/PA ROCOP, provided the catalyst concentration is sufficiently high, but underperforms at low catalyst loadings. It is proposed that the two lead catalysts, LwideCoK(OAc)2 and LshortCoK(OAc)2, operate by different mechanisms for PO/PA and PO/CO2 ROCOP. The new wide separation catalyst, LwideCoK(OAc)2, shows some of the best performances yet reported for PO/PA ROCOP, and suggests other catalysts featuring larger intermetallic separations should be targeted for epoxide/anhydride copolymerizations.
ABSTRACT
While outstanding catalysts are known for the ring-opening copolymerization (ROCOP) of CO2 and propene oxide (PO), few are reported at low CO2 pressure. Here, a new series of Co(III)M(I) heterodinuclear catalysts are compared. The Co(III)K(I) complex shows the best activity (TOF = 1728 h-1) and selectivity (>90% polymer, >99% CO2) and is highly effective at low pressures (<10 bar). CO2 insertion is a prerate determining chemical equilibrium step. At low pressures, the concentration of the active catalyst depends on CO2 pressure; above 12 bar, its concentration is saturated, and rates are independent of pressure, allowing the equilibrium constant to be quantified for the first time (Keq = 1.27 M-1). A unified rate law, applicable under all operating conditions, is presented. As proof of potential, published data for leading literature catalysts are reinterpreted and the CO2 equilibrium constants estimated, showing that this unified rate law applies to other systems.
ABSTRACT
BACKGROUND: The natural history, management, and outcome of takotsubo (stress) cardiomyopathy are incompletely understood. METHODS: The International Takotsubo Registry, a consortium of 26 centers in Europe and the United States, was established to investigate clinical features, prognostic predictors, and outcome of takotsubo cardiomyopathy. Patients were compared with age- and sex-matched patients who had an acute coronary syndrome. RESULTS: Of 1750 patients with takotsubo cardiomyopathy, 89.8% were women (mean age, 66.8 years). Emotional triggers were not as common as physical triggers (27.7% vs. 36.0%), and 28.5% of patients had no evident trigger. Among patients with takotsubo cardiomyopathy, as compared with an acute coronary syndrome, rates of neurologic or psychiatric disorders were higher (55.8% vs. 25.7%) and the mean left ventricular ejection fraction was markedly lower (40.7±11.2% vs. 51.5±12.3%) (P<0.001 for both comparisons). Rates of severe in-hospital complications including shock and death were similar in the two groups (P=0.93). Physical triggers, acute neurologic or psychiatric diseases, high troponin levels, and a low ejection fraction on admission were independent predictors for in-hospital complications. During long-term follow-up, the rate of major adverse cardiac and cerebrovascular events was 9.9% per patient-year, and the rate of death was 5.6% per patient-year. CONCLUSIONS: Patients with takotsubo cardiomyopathy had a higher prevalence of neurologic or psychiatric disorders than did those with an acute coronary syndrome. This condition represents an acute heart failure syndrome with substantial morbidity and mortality. (Funded by the Mach-Gaensslen Foundation and others; ClinicalTrials.gov number, NCT01947621.).