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Chiral Rodlike Platinum Complexes, Double Helical Chains, and Potential Asymmetric Hydrogenation Ligand Based on “Linear” Building Blocks:  1,8,9,16-Tetrahydroxytetraphenylene and 1,8,9,16-Tetrakis(diphenylphosphino)tetraphenylene

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posted on 06.07.2005, 00:00 by Hai-Yan Peng, Chi-Keung Lam, Thomas C. W. Mak, Zongwei Cai, Wai-Tang Ma, Yu-Xue Li, Henry N. C. Wong
This paper is concerned with the synthesis of 1,8,9,16-tetrahydroxytetraphenylene (3a) via copper(II)-mediated oxidative coupling, its resolution to optical antipodes, and its conversion to 1,8,9,16-tetrakis(diphenylphosphino)tetraphenylene (3b). On the basis of these chiral “linear” building blocks, three rodlike chiral complexes, triblock (R,R,R,R)-17 and (S,S,S,S)-20 and pentablock (R,R,R,R,R,R,R,R)-22, were constructed. As a hydrogen bond donor, racemic and optically active 3a was allowed to assemble with linear acceptors to afford highly ordered structures. A 1:1 adduct of 4,4‘-bipyridyl and (±)-3a exists in a dimeric form of 3a linked by 4,4‘-bipyridyl through hydrogen bonds. Pyrazine serves as a short linker between achiral parallel chains each formed by (±)-3a, while self-assembly of homochiral 3a into alternate parallel chains occurs in the adduct of 5,5‘-dipyrimidine with (±)-3a. Self-assembly of (S,S)-3a or (R,R)-3a with 4,4‘-dipyridyl yielded a packing of chiral double helical chains formed by chiral tetrol 3a molecules. A novel chiral ligand, (S,S)-23, derived from 3a was used in the asymmetric catalytic hydrogenation of α-acetamidocinnamate, yielding up to 99.0% ee and 100% conversion.