Extremely short H center dot center dot center dot H distances and intermolecular hydrogen-bonding patterns of dialkyl alpha-aryl-alpha-(diphenylmethylamino)methanephosphonates

摘要

Single crystal X-ray diffraction studies of four N-benzhydryl protected diethyl alpha-amino-alpha-arylmethanephosphonates (aryl = phenyl, 1-naphthyl, 1-anthryl, and 1-pyrenyl) reveal several distinct types of hydrogen bonding, leading to the formation of (a) dimers containing two molecules of the same stereochemistry (SS or RR) in one case, (b) centrosymmetric dimers containing two enantiomeric molecules (RS) (both involving P=O center dot center dot center dot H-N interactions) in two crystals, and (c) in the anthryl derivative, a short intramolecular C-H center dot center dot center dot O=P contact distance but no involvement of the amino N-H. The anthryl derivative forms chains of molecules, with a possible interaction between phosphoryl oxygen and a phenyl hydrogen atom of one of the benzhydryl groups in an adjacent molecule. These molecules adopt a staggered conformation about the C-P bond, with the H atom of the chiral alpha-carbon atom approximately anti to the N-H. A further peculiarity is in the extremely short approaches of the "shoulder" H-atoms of the 1-naphthyl, 1-anthryl, and 1-pyrenyl moieties to the chiral alpha-carbon H atom at about 0.4-0.6 angstrom shorter than the sum of the van der Waals radii. In the 1-anthryl substituted crystal, a similar short approach to the N-H might be a reason for the vanishing N-H center dot center dot center dot O=P hydrogen bond.