Iridium Porphyrin Complexes Research Articles

Iridium porphyrin complexes with μ-nitrido, hydroxo, hydrosulfido and alkynyl ligands.

Iridium porphyrin complexes containing μ-nitrido, hydroxo, hydrosulfido, and alkynyl ligands have been synthesized and structurally characterized, and their oxidation has been studied. The alkyl-IrIII porphyrin complex [Ir(tpp)R] (tpp2- = 5,10,15,20-tetraphenylporphyrin dianion; R = C8H13; 1) was synthesized by reaction of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) with H2tpp in refluxing monoethylene glycol. Treatment of 1 with PPh3 and [(LOEt)Ru(N)Cl2] (LOEt- = [(η5-C5H5)Co{P(O)(OEt)2}3]-) gave [Ir(tpp)(R)(PPh3)] (2) and the μ-nitrido complex [R(tpp)Ir(μ-N)RuCl2(LOEt)] (3), respectively. The cyclic voltammogram of 3 exhibited a reversible oxidation couple at 0.44 V versus Fc+/0 (Fc = ferrocene). The oxidation of 3 with [(4-BrC6H4)3N](SbCl6) resulted in Ir-C bond homolysis and formation of the chloride complex [Cl(tpp)Ir(μ-N)RuCl2(LOEt)] (4). The short Ir-N(nitrido) bond distances in 3 [1.944(3) Å] and 4 [1.831(4) Å] are indicative of multiple bond character and thus these two μ-nitrido complexes can be described by the two resonance forms: IrIII-N[triple bond, length as m-dash]RuVI and IrV[double bond, length as m-dash]N[double bond, length as m-dash]RuIV. Similarly, the oxidation of 2 with [(4-BrC6H4)3N](SbCl6) yielded [Ir(tpp)Cl(PPh3)] (5). Chloride abstraction of 5 with TlPF6 in tetrahydrofuran (thf) afforded [Ir(tpp)(PPh3)(thf)](PF6) (6) that reacted with CsOH·H2O and Li2S to give the hydroxo [Ir(tpp)(OH)(PPh3)] (7) and hydrosulfido [Ir(tpp)(PPh3)(SH)] (8) complexes, respectively. Treatment of 6 with phenylacetylene in the presence of CuI and Et3N yielded the bimetallic complex [Ir(tpp)(PPh3)(μ-η1:η2-C[triple bond, length as m-dash]CPh)(CuI)] (9), whereas the transmetallation of 6 with LiC[triple bond, length as m-dash]CPh afforded the mononuclear alkynyl complex [Ir(tpp)(PPh3)(C[triple bond, length as m-dash]CPh)] (10). The electrochemistry of the Ir porphyrin complexes has been studied using cyclic voltammetry. On the basis of the measured redox potentials of [Ir(tpp)(PPh3)X], the ability of X- to stabilize the IrIV state is ranked in the order: R- > PhC[triple bond, length as m-dash]C- > Cl- ∼ OH-. Oxidation of 8 and 9 with [(4-BrC6H4)3N](SbCl6) led to isolation of 5 and [Ir(tpp)(PPh3)(H2O)]+, respectively. The crystal structures of complexes 3, 4, and 7-10 have been determined.

Competitive Aryl–Fluorine and Aryl–Halogen (Halogen = Cl, Br) Bond Cleavage with Iridium Porphyrin Complexes

Base-promoted competitive Ar–F and Ar–X (X = Cl, Br) bond cleavage with iridium porphyrin complexes was investigated. Mechanistic studies suggested that Ir(ttp)− (ttp = 5,10,15,20-tetra-p-tolylporphyrinato dianion) cleaves the Ar–F bond via nucleophilic aromatic substitution and Ir2(ttp)2 cleaves the Ar–X (X = Cl, Br) bond via metalloradical ipso substitution. Therefore, a stronger base, polar solvent, lower temperature, and iridium anion precursor favor Ar–F bond cleavage, while a weaker base, nonpolar solvent, higher temperature, and Ir2(ttp)2 precursor favor Ar–X (X = Cl, Br) bond cleavage.

Efficient Intramolecular C–H Insertion Catalyzed by Iridium Porphyrin Complexes

Octaethylporphyrin and tetraphenylporphyrin Ir(I) and Ir(III) complexes are useful catalysts for intramolecular C–H insertion processes of stabilized diazo compounds. While the Ir(I) complex TPP[Ir(CO)₃]₂ is the most efficient and selective catalyst, the others afford mixtures of cyclization and dimerization products. The effect of the solvent polarity on the selectivity of the reaction is also presented.

Synthesis, structure, and reactions of iridium(I) complexes with 5,10,15,20-tetraphenyl-21H,23H-porphine and 5,10,15,20-tetraphenyl-21H,23H-porphine dianion

One-step joint synthesis of two iridium porphyrin complexes, a donor-acceptor SAT (sitting a top) complex μ-(5,10,15,20-tetraphenylporphine)-bis-chloroiridium(I) and the covalent complex (5,10,15,20-tetraphenylporphinato)chloroiridium(III) by the reaction of free porphyrin and chloroiridic acid (H3O)2IrCl6 in boiling phenol was studied. The structure of complexes was confirmed by spectroscopy (UV/Vis, IR, 1H NMR) and TLC. The iridium(III) SAT complex with the hydride ligand in the first coordination sphere, (acetato)hydrido(5,10,15,20-tetraphenylporphine)iridium(III), was obtained by oxidative addition reaction, which is quite rare for porphyrin complexes. The thermodynamic stability of the complexes to oxidants (aerated acids) was studied by spectrophotometric titration.

Syntheses and reactions of iridium complexes of octaethylporphyrin

New iridium porphyrin complexes (I-V) have been prepared by the reactions of octaethylporphyrin (OEPH 2) or N-methyloctaethylporphyrin (N-Me·OEPH) with μ-dichloro-hexacarbonyl-diiridium(I) ([Ir(CO) 3Cl] 2) or μ-dichlorobis[π-cyclooctadiene-(1,5)]-diiridium(I) ([Ir(COD)Cl] 2). Hydrido- and organo-iridium(III)OEP complexes (VI-XII) have been synthesized by various methods and characterized on the basis of spectroscopic measurements.