Extremely short H···H distances and intermolecular hydrogen-bonding patterns of dialkyl α-aryl-α-(diphenylmethylamino)methanephosphonates

GRAPHICAL ABSTRACT

ABSTRACT

Single crystal X-ray diffraction studies of four N-benzhydryl protected diethyl α-amino-α-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···H–N interactions) in two crystals, and (c) in the anthryl derivative, a short intramolecular C–H···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 α-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 α-carbon H atom at about 0.4–0.6 Å 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···O=P hydrogen bond.

KEYWORDS:

• Aminophosphonate
• X-ray diffraction
• crystal structure

Acknowledgments

We thank Mr. Alan Bashall for practical assistance with the X-ray diffraction measurements.