Alkyl complexes iridium porphyrins

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. ... 

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. 

Many iridium porphyrins, specifically lr(OEP)R, R = H, alkyl or aryl derivatives, and Ir(OEP)l and Ir(OEP)OOH, catalyze the direct four-electron reduction of oxygen at substantially low overpotentials [55]. With the exception of Ir(OEP)H, the rest of the complexes require preconditioning at specific potentials to be activated, the required conditioning potential varying depending on the nature of substiment groups. 

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... 

Complexes (77) and (78) (see reactions 44 and 45) have been synthesized via reaction of oc-taethylporphyrin (OEPH2) or iV-methyloctaethylporphyrin (AT-MeOEPH) with [Ir(Cl)(CO)3]2. The IR and visible spectra of (77) are quite similar to those of /i-OEP[Rh (CO)2], indicative of similar structures for the two complexes. No evidence for centrosymmetry in (77) was obtained, probably due to the reduction in molecular symmetry by coordination of three CO ligands to each Ir atom, 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, and thus similar structures for the Ir and Rh 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. ... 

An alternative route used in organometallic chemistry is the reaction of low valent organometallic derivatives with alkyl (aryl) halides. The two electron oxidative addition of alkyl (aryl) halides or cyclopropane derivatives to metalloporphyrins such as [M (Por)] leads to metal alkyl (aryl) o-bonded porphyrins of cobalt " rhodium and iridium ° (Scheme 2). Substitution of aryl and vinyl halides by electrochemically generated iron(I) porphyrins also leads to o-bonded Fe complexes ... 

---