N-Phenylbenzenesulfonamides exist preferentially in (+)-or (−)-synclinal conformations, which place the aromatic rings at both ends in the same direction with a twist. We have systematically analyzed the crystal structure of secondary aromatic sulfonamides bearing methyl, ethyl, and/ or methoxy groups on the benzene rings. Intermolecular hydrogen bonding between the sulfonamide protons and sulfonyl oxygens was observed in 81 out of 85 crystals. The intermolecular hydrogen-bonding patterns could be classified into four types, i.e. Dimeric, Zigzag, Helical, and Straight patterns, with retention of the synclinal conformation of the sulfonamide moiety. We investigated the relationship between the hydrogen-bonding pattern and the proportion of the compounds that show chiral crystallization. On the basis of our classification of the intermolecular hydrogen bonds of aromatic sulfonamides, the crystals with Dimeric and Zigzag patterns, which both have enantiomeric synclinal conformers, intrinsically become achiral, except for kryptoracemates. In contrast, a high proportion of compounds with Helical or Straight patterns in the crystals showed chiral crystallization. Our classification is useful for discussion regarding the chirality of molecular assemblies, on the basis of the conformational chirality of the molecules in the crystal.
[Structure: see text] Bis(phosphine)boronium salts 3a-c were designed and prepared as key building blocks for the synthesis of highly congested diphosphinobenzenes. The preparation of sterically hindered ortho-phenylene-bridged diphosphines 1a-c was achieved by the reaction of the bis(phosphine)boronium salts 3a-c with difluorobenzenechromium complex 2 and subsequent removal of the BH2 group. The steric nature of diphosphine 1a was revealed in single-crystal X-ray analysis of its Rh complex.
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