The discovery of new catalysts that can generate complex organic compounds via enantioselective transformations is central to advances in the life sciences;i for this reason, many chemists try to discover catalysts that can be used to produce chiral molecules with a strong preference for one mirror image isomer.ii The ideal catalyst should be devoid of precious elementsiii and should bring reactions to completion in a few hours using operationally simple procedures. In this manuscript, we introduce a set of small organic molecules that can catalyze reactions of unsaturated organoboron reagents with imines and carbonyls; the products of the reactions are enantiomerically pure amines and alcohols, which can be used to synthesize more complex, biologically active molecules. A distinguishing feature of this new catalyst class is the presence of a 'key' proton embedded within their structure. The catalyst is derived from the abundant amino acid valine and was prepared in large quantities in four steps using inexpensive reagents. Reactions are scalable, do not demand stringent conditions, and can be performed with as little as 0.25 mol % catalyst in less than six hours at room temperature to generate products in >85% yield and ≥97:3 enantiomeric ratio. The efficiency, selectivity and operational simplicity of the transformations and the range of boron-based reagents render this advance vital to future progress in chemistry, biology and medicine.
Ethoxy substitution crosslinked and enhanced transport properties in novel ROMP and addition-type polynorbornenes for reverse-selectivity, heavy-hydrocarbon separations.
Hierarchical structures of zeolite beta with Si/Al ratios in the range of 14−250 are optimized by post-synthetic base leaching, including direct alkaline treatments in NaOH solutions, fluorination− desilication sequences, and alkaline treatments in the presence of tetrapropylammonium cations (TPA + ) as the pore-directing agent (PDA). Mesoporosity can be conveniently obtained by a single step of base leaching in NaOH (e.g., 0.2 M NaOH at 65 °C) for high Al beta zeolites (Si/Al < 20) with good preservation of microporosity, which is attributed to the dual play of framework stability and Al inhibition. For high Si beta zeolites (Si/Al > 20), the alkaline treatments in the presence of PDA (e.g., TPA + ) are crucial for creating mesopores without sacrificing the original zeolite framework. In the absence of TPA + , the high Si zeolite framework is very sensitive to NaOH leaching, resulting in severe structural amorphization. High Al zeolite beta can also be leached by alkaline treatments with TPA + , which features smaller mesopores as compared to the ones desilicated by NaOH alone. According to the NH 3 -TPD characterization, the acidity is well preserved for the alkaline-treated samples with reference to the parent zeolite beta (Si/Al:14), with preservation of total amounts of acid sites up to 85% and similar NH 3 desorption activation energy. The sequential fluorination−desilication protocol, while effective for creating hierarchical high Al MFI-type zeolites, is not effective for zeolite beta under similar conditions due to the excessive framework activation upon fluorination that results in severe loss of microporosity and crystallinity.
In this paper we report the synthesis of several new Mo(NR)Cl 4 (THF) species (R ) C 6 F 5 , 3,5-(CF 3 ) 2 C 6 H 3 , 1-adamantyl, CPh 3 , and 2,6-i-Pr 2 C 6 H 3 ) via the treatment of MoCl 4 (THF) 2 with azides and their reactions with neopentyl reagents. Addition of Mo(NR)Cl 4 (THF) complexes in toluene to a cold solution of NpMgCl in ether gave Mo(NR)Np 3 Cl species (R ) C 6 F 5 , 3,5-(CF 3 ) 2 C 6 H 3 , Ad, Ph 3 C, and 2,6-i-Pr 2 C 6 H 3 (Ar); Np ) CH 2 -t-Bu) in poor (35%) to modest (51%) yields. Heating Mo(NAr)Np 3 Cl in C 6 D 6 to 50 °C results in R-hydrogen abstraction to give neopentane and a molecule whose NMR spectra are consistent with it being Mo(NAr)(CH-t-Bu)(CH 2 -t-Bu)Cl; it decomposed bimolecularly upon attempted isolation. The other Mo(NR)Np 3 Cl species were found to be more stable than Mo(NAr)Np 3 Cl, but when they did decompose at elevated temperatures, no neopentylidene complex could be observed. Addition of neopentyllithium to Mo(NR)Np 3 Cl species (R ) Ar, CPh 3 , or Ad) yielded Mo(NR)(CH-t-Bu)Np 2 species, the adamantylimido version of which is unstable toward bimolecular decomposition. Addition of neopentyllithium to Mo(NR)Np 3 Cl complexes in which R ) pentafluorophenyl or 3,5-trifluoromethylphenyl led to intractable mixtures. Addition of 1 equiv of 2,6-diisopropylphenol, 2,6-dimethylphenol, or 3,5-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 OH (HIPTOH) to Mo(NCPh 3 )(CH-t-Bu)Np 2 led to formation of Mo(NCPh 3 )(CH-t-Bu)Np(OR) species, while treatment of Mo(NCPh 3 )(CH-t-Bu) 2 (CH 2 -t-Bu) with C 6 F 5 OH gave Mo(NCPh 3 )-Np 3 (OC 6 F 5 ). The three monophenoxide neopentylidene complexes showed poor to moderate metathesis activity for ring-closing a small selection of substrates. X-ray studies were completed for Mo
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