Metal iridium III

Ir(H)(PBu2(C6H40) 2]. Complex (37) in benzene, when allowed to stand for 24 h, affords the C-metallated iridium(III) complex [Ir PBu2(C6H40) PBu (C6H40)(CMe2CH2) ] (40).103... 

Ichimura, K. Kobayashi, T. King, K A. Watts, R J. (1987). Excited-state absorption spectroscopy of ortho-metalated iridium(III) complexes. Journal of Physical Chemistry, Vol. 91, pp. 6104-6106. 

Functionalized 6 -phenyl-2,2 -bipyridine ligands react with dimer [(2-Phpy)2lrCl]2 and further with excess ammonium hexafluorophosphate to yield the cationic ortho-metalated iridium(III) 15 (R = OC12H25,... 

Muegge BD, Richter MM (2003) Multicolored electrogenerated chemiluminescence from ortho-metalated iridium(iii) systems. Anal Chem 76(l) 73-77... 

There is also clear evidence of a change from predominantly class-a to class-b metal charactristics (p. 909) in passing down this group. Whereas cobalt(III) forms few complexes with the heavier donor atoms of Groups 15 and 16, rhodium(III), and more especially iridium (III), coordinate readily with P-, As- and S-donor ligands. Compounds with Se- and even Te- are also known. Thus infrared. X-ray and nmr studies show that, in complexes such as [Co(NH3)4(NCS)2]" ", the NCS acts as an A -donor ligand, whereas in [M(SCN)6] (M = Rh, Ir) it is an 5-donor. Likewise in the hexahalogeno complex anions, [MX ] ", cobalt forms only that with fluoride, whereas rhodium forms them with all the halides except iodide, and iridium forms them with all except fluoride. 

As already mentioned, complexes of chromium(iii), cobalt(iii), rhodium(iii) and iridium(iii) are particularly inert, with substitution reactions often taking many hours or days under relatively forcing conditions. The majority of kinetic studies on the reactions of transition-metal complexes have been performed on complexes of these metal ions. This is for two reasons. Firstly, the rates of reactions are comparable to those in organic chemistry, and the techniques which have been developed for the investigation of such reactions are readily available and appropriate. The time scales of minutes to days are compatible with relatively slow spectroscopic techniques. The second reason is associated with the kinetic inertness of the products. If the products are non-labile, valuable stereochemical information about the course of the substitution reaction may be obtained. Much is known about the stereochemistry of ligand substitution reactions of cobalt(iii) complexes, from which certain inferences about the nature of the intermediates or transition states involved may be drawn. This is also the case for substitution reactions of square-planar complexes of platinum(ii), where study has led to the development of rules to predict the stereochemical course of reactions at this centre. 

The first transition metal-catalyzed hydroamination of an olefin was reported in 1971 by Coulson who used rhodium(I), rhodium(III) or iridium(III) catalysts (Eq. 4.8) [105,106]. 

Boehm et al.100 have synthesised and studied a series of half-sandwich rhodium (III) and iridium (III) complexes, derivatives of salicylaldehyde and L-amino acid esters. The diastereoselectivity has shown strong dependence on the type of metal as well as amino acid residue. The labile configuration of the metal atoms was suggested because of changes in the diastereomers ratio with increasing temperature. Fast epimerisation at the metal atom was suggested for some S-phenylalanine complexes. 

K. Dedeian, P.I. Djurovich, F.O. Garces, G. Carlson, and R.J. Watts, A new synthetic route to the preparation of a series of strong photoreducing agents fac tris-ortho-metalated complexes of Iridium (III) with substituted 2-phenylpyridines, Inorg. Chem., 30 1685-1687 (1991). 

R. J. Watts, J. S. Harrington, and J. Van Houten, A stable monodentate 2,2-bipyridine complex of iridium (III) A model for reactive intermediates in ligand displacement reactions of tris 2,2-bipyridine metal complexes, J. Am. Chem. Soc. 99, 2179-2187 (1977). 

Transition metal complexes added might also play a role in aiding the reduction of iridium(III) species, but no evidence for this has been reported. 

The first example of dehydrogenation of alkanes by a transition metal complex was also achieved with iridium. The cationic iridium(III) complex, [IrH2-(acetone)2(PPh3)2]" BF4, with TBE (3,3-dimethyl-l-butene or t-butylethene) as... 

Cerium(IV) oxidations of organic substrates are often catalysed by transition metal ions. The oxidation of formaldehyde to formic acid by cerium(IV) has been shown to be catalysed by iridium(III). The observed kinetics can be explained in terms of an outer-sphere association of the oxidant, substrate, and catalyst in a pre-equilibrium, followed by electron transfer, to generate Ce "(S)Ir", where S is the hydrated form of formaldehyde H2C(OH)2- This is followed by electron transfer from S to Ir(IV) and loss of H+ to generate the H2C(0H)0 radical, which is then oxidized by Ce(IV) in a fast step to the products. Ir(III) catalyses the A -bromobenzamide oxidation of mandelic acid and A -bromosuccinimide oxidation of cycloheptanol in acidic solutions. ... 

The de- and re-aromatization of the pyridine moiety of the pincer ligand appears to be crucial for this process. This is also the key underlying feature in the oxidative addition of H2 by complex 19 in an apparent iridium(111) oxidation state, which results in the formation of the dihydride complex 20 (Scheme 12.9). Similarly, the addition of CO to the iridium(I) complex 18 formally results in oxidation of the metal center and provides the iridium(III) complex 21 (Equation 12.9). 

A few examples are known using homogeneous transition-metal-catalyzed additions. Rhodium(III) and iridium(III) salts catalyze the addition of dialkylamines to ethylene.302 These complexes are believed to activate the alkene, thus promoting hydroamination. A cationic iridium(I) complex, in turn, catalyzes the addition of aniline to norbornene through the activation of the H—N bond.303 For the sake of comparison it is of interest to note that dimethylamino derivatives of Nb, Ta, and Zr can be used to promote the reaction of dialkylamines with terminal alkenes.304 In this case, however, C-alkylation instead of /V-alkylation occurs. 

The cleavage of polynuclear hydroxo-bridged rhodium(III) and iridium(III) complexes into the corresponding mononuclear fragments has been reported in only a few instances, but the well-established tendency of mononuclear complexes of these metal ions to undergo substitution reactions with retention of configuration indicates the possibility of analytical and synthetic applications such as described above for chromium (III). 

Structural, thermodynamic, and kinetic studies have shown that hydroxo-bridged polynuclear complexes of (diromium(III), cobalt(III), rhodium(III), and iridium(III) have many general features in common. Structurally, the four metal ions exhibit an almost identical pattern, and in particular the occurrence of many well-characterized oligomers... 

Only a few compounds containing Ru, Os, Rh or Ir do not possess type C. Notable are the metalloporphyrin dimers with Ru = Ru (entry 3) or Rh-In bonds (entry 34), the alkyl or acyl rhodium(III) (entries 31, 36, 38), alkyl-iridium(III) (entry 39) or arylruthenium(III) compounds (entry 12). All these species contain pentacoordinate noble metal ions, Type B. A reason for this unusual behavior of the metal ions is seen in the strong trans effect of the axial ligand L in these systems which is a strong o-donor (metalloporphyrinyl, alkyl, aryl, acyl) which precludes further coordination in the trans position of L. The reluctance of RhMe(OEP) to accept an axial ligand is shown by its crystallization as a re-dimer from n-hexane in presence of the base 1-Meim. 

---