Ammonia (NH3) is one of the essential chemicals as a fertilizer and as a starting reagent for various chemicals with a production expectation of 200 million tonnes for 2018. With the development of renewable energy technologies such as hydrogen fuel cells, hydrogen also has emerged as an innovative clean energy source. Ammonia is a suitable hydrogen fuel carrier since a molecule of ammonia can carry up to three atoms of hydrogen. Recently, photochemical synthesis via nitrogen reduction has gained considerable attention as a sustainable method for the production of ammonia. The performance of the photoreduction of nitrogen lies in the developments of the photocatalysts and photoelectrocatalysts. Therefore, it is essential to understand the fundamentals of nitrogen reduction processes along with apprehending the challenges that limit the progress of catalysts. In this review, the basic understanding of photoreduction of nitrogen is highlighted, emphasizing on the challenges and effective methods to control defects, structures, and morphologies of materials for the catalyst development. The methods for ammonia detection and uncertainties in calculating the efficiency of the photochemical process are also addressed.
Monoamidation of 1,4-diaminobenzene with alpha-chiral carboxylic acids leads to a carrier strategy for absolute stereochemical determination with bis-zinc porphyrin tweezers by exciton-coupled circular dichroism (ECCD). The helicity induced in the porphyrin tweezers upon complexation with the derivatized carrier originates from the preferred conformation of the C(carbonyl)-C(chiral) bond. Correct ECCD signs can be predicted by the rotamer that places the large group perpendicular to the carbonyl group with the small group facing the porphyrin. [reaction: see text]
The tandem N-arylation/carboamination of γ-amino alkenes with two different aryl bromides provides rapid entry to differentially arylated N-aryl-2-benzyl pyrrolidine derivatives in good yields with good to excellent levels of diastereoselectivity. The selective diarylation is achieved in a onepot process by an in situ modification of the palladium catalyst via phosphine ligand exchange.In recent years much effort has been devoted to the development of tandem or sequential reactions that effect the formation of several different bonds, stereocenters, and/or rings in onepot transformations. 1 These types of reactions lead to the conversion of simple starting materials to relatively complex molecules in a rapid and efficient manner, and have considerable potential utility for the construction of diverse libraries of compounds. Transition metal catalysis has played a central role in the development of many of these processes. 1, 2 Transformations effected through tandem metal-catalyzed reactions can be broadly grouped into two categories: 1) sequences that involve multiple iterations of the same reaction, 2 and 2) sequences that involve two or more fundamentally different reactions. 3 The latter tend to be more challenging as the efficiency and selectivity of many metal-catalyzed reactions is highly dependent on catalyst structure.We have recently described a new method for the stereoselective synthesis of N-aryl-2-benzylpyrrolidines via Pd-catalyzed reactions of γ-(N-arylamino)alkenes with aryl bromides (Scheme 1, eq 1). 4,5,6 In our initial studies, several of the substrates for these transformations were prepared by Pd-catalyzed N-arylation of primary amines. 7 Since both the carboamination and the N-arylation reactions were effected using palladium/phosphine catalysts, we reasoned that a modular synthesis of N-aryl-2-benzylpyrrolidines might be achieved in a one-pot, Pdcatalyzed process via sequential treatment of a 4-pentenylamine derivative with two different aryl bromides (Scheme 1, eq 2). A transformation of this type would lead to the formation of two C-N bonds, one C-C bond, one ring, and one stereocenter in a single operation. Additionally, this protocol could potentially be employed in the conversion of readily available jpwolfe@umich.edu . starting materials into pyrrolidine libraries in which two groups on the heterocycle could be easily varied. 8 Our preliminary studies on the development of this one-pot reaction sequence are described herein. NIH Public AccessAuthor Manuscript Org Lett. Author manuscript; available in PMC 2009 September 24.Both palladium-catalyzed N-arylations of amines and Pd-catalyzed carboamination reactions are known to be very sensitive to catalyst structure. 4,7 A search of the literature revealed that relatively few ligands are highly effective and selective for the Pd-catalyzed monoarylation of primary aliphatic amines; (rac)-BINAP (2) 9 and 2-di-tert-butylphosphinobiphenyl (3) appeared to be the most general with respect to substrate scope. 7 Our previous studies ...
CD and NMR spectroscopic evidence of cooperative binding between an α-halogen atom and a carboxamide group with a zinc porphyrin leads to an unprecedented conformation for the determination of the absolute stereochemistry of α-haloamides (α-halocarboxylic acids derivatized with 1,4-phenylenediamine) through the use of exciton-coupled circular dichroism (ECCD). With the use of chiral lactams, whose rotomeric contributions are minimized, both ECCD and NMR spectroscopy demonstrate that the porphyrin favors binding
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