[4-(N,N-Dimethylamino)phenyl]diphenylphosphine Oxide and its Partial Oxides: An Isomorphous Crystal Series

Abstract

The title compound [4-(N,N-dimethylamino)phenyl]diphenylphosphine oxide (1) has been synthesized and its single-crystal X-ray structure determined. The structures of two ‘partial’ oxides of the parent compound, (2) and (3) (50% and 25% oxidized), isolated from the intermediate phosphine reaction product have also been determined, yielding an unusual isomorphous crystal series. An apparent P–O bond shortening with increasing oxidation is also observed across the series (1)–(3) (1.480(4), 1.351(4), 1.280(4) Å respectively) and is considered an artifact of the structure refinement. The packing in the crystals shows primary one-dimensional chains with weak head-to-tail associations between the oxide oxygen (three-centre) and two hydrogen atoms from separate methyl groups of the N-substituted amine (range C–H … O 3.115(4)–3.356(8) Å), extended into a sheet structure by peripheral inter-chain C–H (aromatic) … O (oxide) associations.