Iridium bonding

Oxidative addition of XY substrates to [IrL2(/x-pz)]2 [La = (CO)2, cod] and [Ir(CD)(PPh3)(/i,-pz)]2 occurs via a two-center, two-electron route toward the iridium-iridium bond-containing species 131 (960M3785 980M2743). Complex 132, which is prepared by the ligand-substitution reaction from [Ir(CO)2 (/x-pz)]2, adds methyl iodide to give 133. 

The irreversible electrochemical oxidation of [Ir(X)(CO)(PR3)2] (X = Cl, Br, I PR3 = PPh3, PPh2Et, PPhEt2, PEt3) on rotating Pt electrodes in Bu4NC104/CH2Cl2 reportedly proceeds at diffusion-controlled rates. In the redox addition process, atom transferability predominates over complex redox properties. Evidence indicates that the insoluble product of the one-electron oxidation of [Ir(X)(CO)(PR3)2] is a dimeric iridium(II) complex with an iridium-iridium bond.96... 

Because of the great strength of iridium-iridium bonds, there is a wealth of information on polynuclear metal-carbonyl cluster compounds of iridium (see Dinuclear Organometallic Cluster Complexes mA Polynuclear Organometallic Cluster Complexes). It4(CO)i2 (45) may be synthesized from... 

The first step of the reaction is the formation of the intermediate species E (Scheme 7) containing a single iridium-iridium bond. The migration of the methylene group leads to the formation of the final Ir111 111 symmetric complex. The intermediate unsymmetrical species E was isolated in the reaction of CH2I2 with 115. 

The reaction is believed to proceed via the formation of an aza iridacyclopentene that undergoes protolytic cleavage of the nitrogen iridium bond (Scheme 1.27). Subsequent reductive elimination leads to the product. 

OBu In] with metal hexacarbonyls gives the unusual cmnplexes [(CO)jMSn(p.-OBu ),InM(CO)3] (M=Mo,Cr) via initial coordination of the metal at the indium and tin sites . Two papers include both indium and thallium compounds. Thus, the preparation of [ CpM(CX>)3 3E] (MssMo,Cr,Es In,Tl) is described, extended Hiickel calculations indicating that the In-Mo bond is polar, and tire ic-bonding interaction is only weak . The synthesis and electrochemistry of the porphyrin (P) complexes [(P)ERe((X))s] is also described . Hnally one report describes the synthesis of phosphine substituted crown complexes containing a thallium-iridium bond. The nature of this interaction has been studied in some detail . 

The spectacular iridium compound HH,HT,HH-[Ir6(/t-OPy)6(I)2(CO)i2] 231 containing an unprecedented almost linear metal chain made up of six iridium atoms has been prepared by Tejel et al. by oxidation of [Ir2(/t-OPy)2(CO)4] with iodine at 0°C in toluene. The formal oxidation state of the iridium atoms is 1.33. The new hexairidium compound has been characterized by X-ray diffraction analysis showing a linear array of iridium-bonded atoms with an HT-[Ir2(/t-OPy)2(CO)4] complex sandwiched in between two HH-[Ir2(/t-OPy)2(I)(CO)4] units (Figure 18). Complex 231 represents the longest polyiridium chain complex so far know. Other polyiridium species with as many as four iridium atom chain have been reported, see Ref 112,112a,l 12b... 

In an attempt to evaluate the impact of chelation, the Albrecht group observed that cyclometalated complex 29 underwent acidolysis of the Cph-Ir bond in the presence of HCl [eqn (3.6)]. The formed complex 30 was stable over several days and no traces of triazolium salt were observed. According to these results, the Cafyi-Ir bond would be substantially less stable than the Ctrz-Ir bond. Despite the lack of support through chelation, the Ct -Ir bond resisted cleavage, suggesting that the bond might be intrinsically more stable than imidazolylidene iridium bonds [see eqn (3.4)] and does not need to be supported in a metalacyclic structure for acid resistance. 

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