Iodide ligands exchange

What British Petroleum discovered was that Ru(CO)4l2 (as well as some other metals) catalyzed the exchange of iodide for CO in the transformation of MeIr(CO)2l3 to MeIr(CO)3l2 (equation [29]) allowing the Ir catalyst to operate without being slowed by the pesky, and previously rate limiting, carbon monoxide for iodide ligand exchange. Complete mechanistic details are available for the process. In the presence of Ru, Ir operated under the same conditions as the Rh based methanol carbonylation, was equally active as a catalyst, and had acceptable ease of operation. Advantages associated with the Ir process are that the Ir process used only half as much methyl iodide co-catalyst and the Ir and Ru catalyst components were (and continue to be) much less expensive than Rh. 

Tetrachlorooxotechnetate(V) results from action of cone. HC1 on perteeh-netate at ambient temperatures and is preferably isolated as the tetrabutyl-ammonium salt [19]. Tetrabromooxotechnetate(V) was similarly obtained with hydrobromic add at 0 °C [8]. The molecular structures of both compounds are reported in [20,21]. The analogous iodo complex, tetraiodooxotechnetate(V), was synthesized by ligand exchange of the chloro compound with sodium iodide in acetone [22]. However, it suffers from considerable decomposition during isolation. 

In a donor solvent the iodide ions is much more strongly solvated than the neutral donor and hence the donor properties of the iodide ion are lowered in solution. This event has been described as the thermodynamic solvatation effect. It becomes increasingly important with an increase of the ratio of the free enthalpy of solvation to the free enthalpy of the ligand exchange reaction. 

A couple of subsequent reactions which were carried out with the Cp complex 27 all proceeded diastereoselectively, presumably with retention at Ru. These included exchange of the chloride for an iodide ligand under retention as determined by X-ray diffraction, reaction with NaOMe in MeOH to give the neutral monohydride as a single diastereomer, and removal of the chloride with AgBp4... 

As described above, two fundamental modes of the reaction of organo-A3-iodanes involve ligand exchange, occurring at iodine(III) with no change in the oxidation state, and reduction of hypervalent A3-iodane to iodide, called reductive elimination. These processes are discussed in detail. 

Reaction of diarylhalo-A3-iodanes with sodium AT,AT-dialkyldithiocarbamates results in the formation of yellow or orange dialkylcarbamoyl(diaryl)-A3-iodanes, which are stable in the dark but decompose to aryl iodides and aryl dialkyldithiocarbamates in daylight via light-promoted homolytic pathway [29]. For ligand exchange of A3-iodanes with sulfides, see Section 3.2.5.4. 

Iodotris(2,4-pentanedionato) zirconium (IV) has been prepared by reaction of zirconium (IV) iodide with 2,4-pentanedione in isopropyl ether and by the ligand-exchange reaction between zirconium (IV) iodide and tetrakis(2,4-pentane-dionato)zirconium(IV) in tetrahydrofuran.7 The latter approach, which yields a higher-purity product, is described here. 

Ligand exchange reactions of monodentate amides, iodides, or alkoxide complexes with other amides, alkoxides as well as sulfides, and carbon ligands has been documented [23,25]. A rather unique reaction of a trimethylsilylmethyl ligand bound to a chromium nitride has been reported thus, reaction of tert-butyl isocyanide with 52 is reported to furnish 53 (Eq. (17)). 

Fig. 13.21. Representative mechanism of the Pd(0)-catalyzed arylation and alkenylation of organozinc iodides. Steps 1,2, and 4-6 correspond to steps that can also be found—in some cases with different numbers—in Figures 13.7 and 13.14. Step 3, which is new, represents a ligand exchange reaction of the aryl-Pd(II) complex.

Bipyridine reacts with [ RufCOjaChh] in ethanol to yield the binuclear product 41 (02JOM(655)31). 2,4 -Bipyridine under the same conditions forms the mononuclear complex 42 (X = Cl) with the monodentate coordination of the ligand, which on ligand exchange with potassium iodide gives 42 (X = I). 

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