Iridium complexes porphyrins

An exception is found with alkyl iridium porphyrins and re-acceptor ligands. In the n-propyl iridium complex, Ir(C3H7)(OEP)L with L = PPh3 (entry 41) and DMSO, type C is found. The sulfoxide is S-bound in the DMSO complex. 

The first experiments in this direction were carried out on the triads 244+ and 254+ (Fig. 8), by exciting preferentially the metal centre around 340-355 nm. Excitation at this wavelength region produces to a predominant extent the excited state localized on the iridium complex unit, the ligand centered triplets PH2 - 3Ir - PAu or PZn - 3Ir - PAu [48]. Energy transfer to the porphyrin triplets dominates the deactivation of PH2 - 3Ir - PAu in 244+, with rate constants of 2.9 x 1010 s 1 for the transfer to the gold porphyrin localized excited state and ca. 1011 s 1 to the free base porphyrin localized excited state, respectively (Scheme 9). 

This is in contrast to the results obtained following selective excitation of the PH2 unit discussed above, and yielding a multi-step electron transfer leading to charge separation. The different outcome can be discussed on the basis of the overlap of the HOMO and LUMO orbitals involved in the electron transfer reaction for the Ir acceptor unit and the PH2 donor unit, with the aid of semi-empirical calculations [48]. Remarkably, the zinc porphyrin based array PZn-Ir-PAu, 254+, displays an efficient electron transfer with the formation of a CS state with unitary yield also upon excitation of the iridium complex. This happens because the selective excitation of the zinc porphyrin chromophore discussed above, and the deactivation of the excited state PZn-3Ir- PAu, follow the same paths as those reported in Scheme 8. 

Few iridium(I) porphyrin complexes are known, owing to the difficulty in incorporating the iridium and the high resistance to reduction of the iridium(III) complex to an iridium(I) complex. 

The reaction of mam-porphyrin IX diethyl ester with [Ir(Cl)(CO)3]2 or [Ir(Cl)(CO)(cot)2] yields the iridium(III) porphyrin derivative [Ir(CO)(HePDEE)] (HePDEE = hematoporphyrin diethyl ester).457 This complex, along with the dimethyl ester derivative, has been characterized by electronic, IR, electron spin resonance and mass spectroscopic techniques as well as magnetic susceptibility measurements. The iridium complexes differ from their rhodium analogues in that they retain a CO ligand in the coordination shell. 

The iridium complex contained a tightly bound carbonyl group, unlike the rhodium complex, in accord with the stronger bonding of CO groups to 5d than to transition metals (216). Related iron and ruthenium carbonyl porphyrins have also been described 14, 217, 461). 

These approaches have been adopted more recently to incorporate phosphorescent chromophores into PF in order to make use of the fact that a large proportion (up to 75%) of all excitons formed in LEDs are triplet states, whose energy can only be harvested by using phosphorescent units. The first fluorene copolymers with phosphorescent units 34-35 were made by Holmes and coworkers who added monobrominated red- or green-emitting iridium complexes to an AA-BB Suzuki polycondensation [57]. With short fluorene chains, only emission from the iridium complexes are observed, but with longer fluorene chains some blue emission is also seen. Other groups have since incorporated different phosphorescent units such as platinum [58] or zinc salen [59] units or porphyrins [60,61 ]. 

Flamigni, L., G. Marconi, I.M. Dixon, J.P Collin, and J.P Sauvage (2002). Switching of electron- to energy-transfer by selective excitation of different chromophores in arrays based on porphyrins and a polypyridyl iridium complex. J. Phys. Chem. B 106, 6663-6671. 

The chemistry of organorhodium and -iridium porphyrin derivatives will be addressed in a separate section. Much of the exciting chemistry of rhodium (and iridium) porphyrins centers around the reactivity of the M(ll) dimers. M(Por) 2-and the M(III) hydrides, M(Por)H. Neither of these species has a counterpart in cobalt porphyrin chemistry, where the Co(ll) porphyrin complex Co(Por) exists as a monomer, and the hydride Co(Por)H has been implicated but never directly observed. This is still the case, although recent developments are providing firmer evidence for the existence of Co(Por)H as a likely intermediate in a variety of reactions. 

Structural types for organometallic rhodium and iridium porphyrins mostly comprise five- or six-coordinate complexes (Por)M(R) or (Por)M(R)(L), where R is a (T-bonded alkyl, aryl, or other organic fragment, and Lisa neutral donor. Most examples contain rhodium, and the chemistry of the corresponding iridium porphyrins is much more scarce. The classical methods of preparation of these complexes involves either reaction of Rh(III) halides Rh(Por)X with organolithium or Grignard reagents, or reaction of Rh(I) anions [Rh(Por)] with alkyl or aryl halides. In this sense the chemistry parallels that of iron and cobalt porphyrins. 

The syntheses and spectroscopic and electrochemical characterization of the rhodium and iridium porphyrin complexes (Por)IVI(R) and (Por)M(R)(L) have been summarized in three review articles.The classical syntheses involve Rh(Por)X with RLi or RMgBr, and [Rh(Por) with RX. In addition, reactions of the rhodium and iridium dimers have led to a wide variety of rhodium a-bonded complexes. For example, Rh(OEP)]2 reacts with benzyl bromide to give benzyl rhodium complexes, and with monosubstituted alkenes and alkynes to give a-alkyl and fT-vinyl products, respectively. More recent synthetic methods are summarized below. Although the development of iridium porphyrin chemistry has lagged behind that of rhodium, there have been few surprises and reactions of [IrfPorih and lr(Por)H parallel those of the rhodium congeners quite closely.Selected structural data for rr-bonded rhodium and iridium porphyrin complexes are collected in Table VI, and several examples are shown in Fig. 7. ... 

A number of iridium-porphyrin systems, including mononuclear and cofacial diporphyrins, have been adsorbed on pyrolytic edge-plane graphite electrodes and tested for their ability to reduce dioxygen to water (82). The original system investigated, [Ir(oep)H], where oep = 2,3,7,8,12,13,17,18-octaethylprophyrinato, was unique in that, while monomeric, the complex was still active in acidic solutions at potentials of +0.72 V vs NHE at pH 1 (82a). The [Ir(oep)H] did become inactive at potentials less than +0.2 V vs NHE, unlike the cofacial dicobalt diporphyrin systems. In the more recent report of these systems (82b),... 

Abstract Pressure-sensitive paint (PSP) is applied to the areodynamics measurement. PSP is optical sensor based on the luminescence of dye probe molecules quenching by oxygen gas. Many PSPs are composed of probe dye molecules, such as polycyclic aromatic hydrocarbons (pyrene, pyrene derivative etc.), transition metal complexes (ruthenium(II), osumium(II), iridium(III) etc.), and metalloporphyrins (platinum (II), palladium(II), etc.) immobilized in oxygen permeable polymer (silicone, polystyrene, fluorinated polymer, cellulose derivative, etc.) film. Dye probe molecules adsorbed layer based PSPs such as pyrene derivative and porphyrins directly adsorbed onto anodic oxidised aluminium plat substrate also developed. In this section the properties of various oxygen permeable polymer for matrix and various dye probes for PSP are described. 

Complex (78) is more readily formed than (77), probably the result of the distortion of the porphyrin ring due to N-alkylation of the pyrrolic N—H bond. The spectroscopic properties of (78) appear similar to those of iV-MeOEP[Rh(Cl)(CO)2]2,184 and thus similar structures for the Ir1 and Rh1 porphyrin complexes have been proposed, in which the two Ir atoms of the iridium dimer are bonded to the two adjacent nitrogen atoms of the porphyrinato core.183... 

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