Multifunctional phosphorus compounds: Molecular structures of 1,2,4,5-tetra(phosphinyl)-, tetra(dimethoxyphosphoryl)-, and tetra(dihydroxyphosphoryl)benzene

1,2,4,5-Tetra(phosphinyl)benzene (1) and -tetrakis(dimethoxyphosphoryl) benzene (4) have molecular structures of point group C_i symmetry with conformations largely determined by steric factors. In the crystal of compound 1 there are no discernible effects of intra- or inter molecular P-H⋯P hydrogen bonding. By contrast, the crystal structure of the corresponding phosphonic acid, 1,2,4,5-tetrakis(dihydroxyphosphoryl)benzene (3), is governed by a network of hydrogen bonds between PO(OH)₂ groups with monofunctional P-OH donors and difunctional P=O acceptors as required for a maximum set of hydrogen bonds under the given stoichiometry. The aggregation of the molecules (C_i symmetry) leads to narrow channels formed by 14- and 16-membered rings which comprise POH⋯OP bridges between P-CC-P and P-CCC-P units, respectively. Accordingly, the crystals of compound 3 are mechanically extremely robust. A tri(phosphinyl)benzene (2) with an interesting 1,2,4- substitution pattern has been obtained as a by-product of the synthesis of the tetra(phosphinyl)-benzene (1) where it is formed by reductive P-C cleavage.