Iridium sulfoxide complexes

Limited reports on substitution reactions of iridium(III) sulfoxide complexes are available, and some amine sulfoxide complexes have been synthesized (368). 

A Cr(VI) sulfoxide complex has been postulated after interaction of [CrOjtClj] with MejSO (385), but the complex was uncharacterized as it was excessively unstable. It was observed that hydrolysis of the product led to the formation of dimethyl sulfone. The action of hydrogen peroxide on mesityl ferrocencyl sulfide in basic media yields both mesityl ferrocenyl sulfoxide (21%) and the corresponding sulfone (62%) via a reaction similar to the Smiles rearrangement (165). Catalytic air oxidation of sulfoxides by rhodium and iridium complexes has been observed. Rhodium(III) and iridium(III) chlorides are catalyst percursors for this reaction, but ruthenium(III), osmium(III), and palladium(II) chlorides are not (273). The metal complex and sulfoxide are dissolved in hot propan-2-ol/water (9 1) and the solution purged with air to achieve oxidation. The metal is recovered as a noncrystalline, but still catalytically active, material after reaction (272). The most active precursor was [IrHClj(S-Me2SO)3], and it was observed that alkyl sulfoxides oxidize more readily than aryl sulfoxides, while thioethers are not oxidized as complex formation occurs. 

Iridium(IV) sulfoxide complexes, including [IrCS-MejSOljCU] and [HCMejSOljiPrClg] have been prepared the former complex is assigned as S-bonded by spectroscopic data (30). Some work on the solvent extraction of rhodium and iridium during refining processes, which utilizes sulfoxides, has been reported (416). 

Hydrogen transfer reactions are catalyzed by several iridium complexes, including the dimethyl sulfoxide (DMSO) complexes cis- and trans-[Ir(Cl)4(DMSO)2]", [Ir(Cl)3(DMSO)3] and [lr(H)-(Cl)2(DMSO)3], as well as the cyclooctadiene (cod) complexes [Ir(Cl)(cod)]2 and [Ir(3,4,7,8-Me4phen)(cod)], and tra 5-[Ir(Cl)(CO)(PPh3)2]. Vaska s complex catalyzes the conversion of p-methoxybenzoyl chloride to the corresponding aldehyde. The dimethyl sulfoxide iridium(III) complexes catalyze hydrogen transfer from propan-2-ol to unhindered cyclohexanones to yield cyclohexanols, while the cod complexes serve as catalysts in the transfer of hydrogen from propan-2-ol to alkenes, ketones and a,/3-unsaturated ketones. ... 

Henbest and Trocha-Grimshaw have shown that sulfoxides may be oxidized to sulfones in the presence of iridium and rhodium complexes [139, 140]. Oxidations were studied by passing air through a solution of the sulfoxide in hot wopropanol containing 10% water in the presence of the catalyst. Sulfones were formed when chlorides of iridium or rhodium were used while chlorides of ruthenium, osmium and palladium were not effective. Under reaction conditions the chlorides should be converted wholly or partly to metal sulfoxide complexes. 

Iridium dimethyl sulfoxide complex isopropanol Ketones from a,) -ethyleneketones s. 23,69 s. a. Soc. Perkin I 1974, 601... 

Henbest and Mitchell [78] have shown that water can be used as hydrogen source with chloroiridic acid (6) as the catalyst through oxidation of phosphorous acid (59) to phosphoric acid (60) in aqueous 2-propanol. Under these conditions, no hydrogen transfer occurs from 2-propanol. However, iridium complexes with sulfoxide or phosphine ligands show the usual transfer from 2-pro-panol [79-81]. 

Other functional groups which have a heteroatom rather than a hydroxyl group capable of directing the hydrogenation include alkoxyl, alkoxycarbonyl, carboxylate, amide, carbamate, and sulfoxide. The alkoxy unit efficiently coordinates to cationic iridium or rhodium complexes, and high diastereoselectivity is induced in the reactions of cyclic substrates (Table 21.3, entries 11-13) [25, 28]. An acetal affords much lower selectivity than the corresponding unsaturated ketone (Table 21.3, entries 14 and 15) [25]. 

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 iridium complex 240 reacts with 2equiv of tetra- -butylammonium hydroxide to give the sulfoxide 252 and the methyl ketone 253 in 23% and 37% yields, respectively <2000CCR63>. The mechanism shown in Scheme 77 has been proposed. 

Oxidation of sulfoxides to sulfones with oxygen in the presence of soluble iridium and rhodium complexes has also been reported. Metachloroperbenzoic acid has also been reported to be a good laboratory oxidizing agent for converting sulfides to sulfones. 

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