DOUBLE-DECKER ACTINIDE PORPHYRINS AND PHTHALOCYANINES - SYNTHESIS AND SPECTROSCOPIC CHARACTERIZATION OF NEUTRAL, OXIDIZED, AND REDUCED HOMOLEPTIC AND HETEROLEPTIC COMPLEXES

The synthesis, spectroscopic characterization, and electrochemistry of 26 different neutral and singly-oxidized homoleptic and heteroleptic actinide double-decker complexes are reported. The investigated compounds are represented as [M(P)2]n, [M(P)(P')]n, [M(Pc)2]n, and [M(P)(Pc)]n where n = 0 or 1+, M = U or Th, Pc = the dianion of phthalocyanine, and P or P' = the dianions of octaethylporphyrin (OEP), tetraphenylporphyrin (TPP), or tetra-p-tolylporphyrin (TpTP). Each neutral compound was characterized by H-1 NMR, UV-visible, and IR spectroscopy and comparisons made to the cationic singly-oxidized double-decker derivatives which were chemically generated and isolated as a SbCl6-salt. The initial neutral species can undergo up to six reversible one-electron transfers in nonaqueous media, and U(IV) or Th(IV) compounds with a given set of porphyrin or phthalocyanine macrocycles could be electrogenerated in up to seven different oxidation states. Some of these species were characterized by UV-visible or FTIR thin-layer spectroelectrochemistry and the resulting spectral data then used along with the redox potentials to assign the site of each electron transfer. The first two reductions of M(P)(Pc) occur mainly at the Pc ring while the first two oxidations of the same heteroleptic compound involve primarily orbitals of the porphyrin macrocycle. This result contrasts with the homoleptic M(P)2 and M(Pc)2 derivatives which undergo initial one-electron oxidations and reductions which are localized not at a single porphyrin or phthalocyanine ring but rather at orbitals involving both macrocycles. The ESR spectra of [Th(OEP)(Pc)]+ and [Th(TPP)(Pc)]+ show triplet character in toluene or methylene chloride and give data consistent with the presence of dimers held together by pi-pi interactions between two Pc macrocycles. The calculated distance between the two electrons in the dimer varies between 8.8 and 9.0 angstrom, which is consistent with the hole of [Th(P)(Pc)]+ being localized on the porphyrin ring and the two cation radicals being separated in the pi-pi complex by an average of about 3.3 angstrom. No pi-pi interactions are observed for the singly-oxidized homoleptic species, and the ESR spectra of [Th(P)2]+ and [Th(Pc)2]+ suggest simple monomeric cation radicals, both-as SbCl6- salts in the solid state and in frozen solutions of CH2Cl2 or pyridine at 110 K.