A series of porphyrins substituted in one or two meso positions by diphenylphosphine oxide groups has been prepared by the palladium-catalyzed reaction of diphenylphosphine or its oxide with the corresponding bromoporphyrins. Compounds {MDPP-[P(O) Ph-2](n)} (M) H-2, Ni, Zn; H2DPP) 5,15-diphenylporphyrin; n = 1, 2) were isolated in yields of 60-95%. The reaction is believed to proceed via the conventional oxidative addition, phosphination, and reductive elimination steps, as the stoichiometric reaction of eta(1)-palladio(II)porphyrin [PdBr(H2DPP)(dppe)] (H2DPP) 5,15-diphenylporphyrin; dppe = 1,2-bis(diphenylphosphino) ethane) with diphenylphosphine oxide also results in the desired mono-porphyrinylphosphine oxide [H2DPP-P(O) Ph-2]. Attempts to isolate the tertiary phosphines failed due to their extreme air-sensitivity. Variable-temperature H-1 NMR studies of [H2DPP-P(O) Ph-2] revealed an intrinsic lack of symmetry, while fluorescence spectroscopy showed that the phosphine oxide group does not behave as a "heavy atom" quencher. The electron-withdrawing effect of the phosphine oxide group was confirmed by voltammetry. The ligands were characterized by multinuclear NMR and UV-visible spectroscopy, as well as mass spectrometry. Single-crystal X-ray crystallography showed that the bis(phosphine oxide) nickel(II) complex {[NiDPP-[P(O) Ph-2](2)} is monomeric in the solid state, with a ruffled porphyrin core and the two P = O fragments on the same side of the average plane of the molecule. On the other hand, the corresponding zinc(II) complex formed infinite chains through coordination of one Ph2PO substituent to the neighboring zinc porphyrin through an almost linear P = O center dot center dot center dot Zn unit, leaving the other Ph2PO group facing into a parallel channel filled with disordered water molecules. These new phosphine oxides are attractive ligands for supramolecular porphyrin chemistry.