Hydrogen bonding and self-assembly in the crystal structures of ferrocenylmethanol derivatives having different phosphorus substituents on the ferrocene unit

Abstract

Ferrocenylmethanol derivatives bearing a phosphorus substituent in position two of the ferrocene unit, rac-2-(diphenylphosphino)ferrocenylmethanol (3), rac-2-(diphenylphosphinoyl)ferrocenylmethanol (4), and rac-2-(diphenylthiophosphoryl)ferrocenylmethanol (5), have been synthesized and structurally characterized by single-crystal X-ray diffraction. While the overall molecular geometry does not differ significantly in the whole series, showing only differences in the arrangement at the phosphorus atom owing to a replacement of the lone electron pair (2, 3) with oxygen (4) and sulfur (5), and in the conformation of the hydroxylmethyl group, the compounds form different crystal packing patterns that result from a counterplay of hydrogen bonding of various types and non-polar interactions. Alcohol 3 associates into dimers by double O–H⋯O hydrogen bridges between disordered hydroxy groups of neighbouring molecules. The distribution of molecules in the crystal of 4 appears identical to that of 3. However, the structure of 4 comprises intermolecular O–H⋯OP hydrogen bridges instead. The packing of phosphine sulfide 5 is different, featuring intramolecular O–H⋯S bridges. Although the molecular entities are involved in further interactions such as O–H⋯P and C–H⋯O hydrogen bonding, and π-π stacking interaction of the phenyl rings, which further propagate the molecular network, the principal force towards self-assembly always results in the formation of entropically favoured, closed cyclic systems. The solid state structure of the common precursor, rac-2-(diphenylphosphino)ferrocenylmethyl acetate (2) shows only C–H⋯O intermolecular interactions due to the lack of a better hydrogen bond donor.