Diphosphametacyclophanes: structural and electronic influences of substituent variation within a family of bis(diketophosphanyl) macrocycles

The condensation of MeP(SiMe3)2 with a series of 5-substituted isophthaloyl chlorides (5-R'C6H3-2,6-{C(O)Cl}2) affords the diphosphametacyclophanes m-{-C(O)-C6H3-5-R'-(C-(O)PMe)}2 (R' = I, Me, tBu, Ph, and p-NCC6H4); the analogues m-{-C(O)-C5H3N-(C(O)PMe)}2 and m-{-C(O)-C6H4-(C(O)-PPh)}2 are similarly obtained in preference to higher oligomers, in contrast to precedent reports. The cyclophanes all adopt butterfly-like conformations in the solid state with the P-organyl substituents adopting mutually exo arrangements. Structural and computatiosnal data suggest the nature of the 5-R substituent is key in directing the inter-ring angle and the extent of LUMO stabilization about the diketophophanyl scaffold. The latter is substantiated by UV/vis pectroscopy and cyclic voltammetry, which demonstrate these cyclophanes to be appreciably comparable to the diketophosphanyl systems commonly explored in the context of organic electronic materials; intriguingly, the distinct dikeophosphanyl moieties within the macrocycles appear effectively “insulated” by the macrocycle geometry, rather than acting as a through-conjugate.