Iridium complexes, reaction with

Schemes 6-13 Reaction of the cationic iridium complex 67 with carboxylic acids...

Following this observation, a general approach for the synthesis of pincer-type methylene arenium compounds was developed (Scheme 3.4). Upon reaction of the methyl rhodium (or iridium) complexes 5 with a slight excess of triflic acid, dihydrogen (not methane ) was evolved to form the methylene arenium complexes 4a.11 Thus, the methylene arenium form is clearly preferred over the benzylic M(III) form, in which the positive charge is localized at the metal center. 

Scheme 3.29 Reaction of the butatrienylidene iridium complex 11 with HCI.

Ferrocenoylamino acids have been converted into 2-ferrocenyl-5(477)-oxazo-lones 348 and 350 that act as N donors in palladium, platinum, and iridium complexes. Reaction of 348 with chloro-bridged palladium(II) and platinum(II) complexes affords a series of N-coordinated oxazolone complexes 349. Reaction of the unsubstituted 2-ferrocenyl-5(477)-oxazolone 350 with the chloro-bridged iridium(III) complex [(ri -C5Me5)IrCl2]2 produces a dinuclear complex 351, analogous to that obtained from 2-phenyl-5(477)-oxazolone (Scheme 7.113)." ° ... 

The dihydrido complex [RhH2(ri5-C5Me5)(PMe3)] forms C—H insertion products when irradiated in the presence of alkanes (ethane, propane).227,228 Reaction with CHBr3 leads to bromoalkylrhodium complexes, which on treatment with bromine give ethyl bromide or 1-bromopropane in 70-85% yield. The less stable iridium complex formed with neopentane could not be converted directly to neopentyl bromide.229 It gave, however, a mercury derivative that yielded the bromide after treatment with bromine. 

Vaska, L. and DiLuzio, J.W. (1961) Carbonyl and hydrido-carbonyl complexes of iridium by reaction with alcohols-hydrido complexes by reaction with acid. J. Am. Chem. Soc., 83, 2784. 

In the reaction of iridium complexes 54 with two equivalents of carbodiimides, mixtures of cyclic carbamate complexes 55 and organometaUic guanidinates 56 are obtained. ... 

Evidence for a radical pathway includes the observation that the reaction is accelerated by radical initiators (such as oxygen or peroxides) and the presence of UV light. Moreover, the order of reactivity for the R group is IIP > II0 > 1°, which is inconsistent with a direct displacement mechanism, but is in accord with the stability of alkyl radicals. Radical inhibitors (such as steri-cally hindered phenols) retard the rate of reaction with sterically-hindered alkyl halides, but not when R = methyl, allyl, and benzyl. When stereoisomerically pure alkyl halides are used, OA results in the formation of a 1 1 mixture of stereoisomeric alkyl iridium complexes, consistent with the formation of an intermediate radical R-. 

A combination of proton NMR and far-infrared spectroscopy has been used to determine the configurations of adducts formed from the reaction in solution of the planar iridium complex (IV) with a variety of reagents (41). 

Oxidative addition reactions to form metal alkyls or aryls have been observed for low-valent rhodium (37, 38), iridium 37, 39, 40), ruthenium 41), nickel 42), and platinum 11, 43, 44) complexes. Reactions with perfluoroalkyl halides extend this list to cobalt 45) and iron 46). Some examples are... 

Scheme 12.9 Proposed mechanism for the reaction of iridium complex 18 with O2.

Several cationic cyclopentadienylrhodium and iridium complexes 175 with attached chiral ligands behave like Lewis acids and have found their way as catalysts for Diels-Alder reaction. The complexes with chiral iminopyridine 175a,b [113], chiral oxazoline 175d,e [114], and chiral phosphine ligands 175c [115] were studied in the cycloaddition of cyclopentadiene with methacrolein into 176 (Scheme 78). Some typical examples are given in Table 34. 

Palladium remains the most widely recognized transition metal to effect stereoselective allylic alkylation reactions. Consequently, diastereoselective and enantioselective Pd-catalyzed processes are extensively discussed in Sections 14.2 and 14.3. More recent advances in the field of metal-catalyzed al-lylation reactions include the use of chiral iridium complexes, dealt with in Section 14.4 [33, 34]. Section 14.5 describes selected stereoselective copper-catalyzed SN2 -allylation reactions [33, 35-37], while a brief presentation of allylation reactions with other transition metals including Mo and Rh is given in Section 14.6 [8, 13, 33, 38, 39]. The closing Section 14.7 deals with selected methods for asymmetric ring-opening reactions of unsaturated heterocycles [38, 40, 41]. 

Reaction of the cyclopentadienyl rhodium and iridium tris(acetone) complexes with indole leads to the species 118 (M = Rh, Ir) [77JCS(D)1654 79JCS(D)1531]. None of these compounds deprotonates easily in acetone, but the iridium complex loses a proton in reaction with bases (Na2C03 in water, r-BuOK in acetone) to form the ri -indolyl complex 119. This reaction is easily reversed in the presence of small amounts of trifluoroacetic acid. 

Complex [(CXI )Ir(/j,-pz)(/i,-SBu )(/j,-Ph2PCH2PPh2)Ir(CO)] reacts with iodine to form 202 (X = I) as the typical iridium(II)-iridium(II) symmetrical species [90ICA(178)179]. The terminal iodide ligands can be readily displaced in reactions with silversalts. Thus, 202 (X = I), upon reaction with silver nitrate, produces 202 (X = ONO2). Complex [(OC)Ir(/i,-pz )(/z-SBu )(/i-Ph2PCH2PPh2)Ir(CO)] reacts with mercury dichloride to form 203, traditionally interpreted as the product of oxidative addition to one iridium atom and simultaneous Lewis acid-base interaction with the other. The rhodium /i-pyrazolato derivative is prepared in a similar way. Unexpectedly, the iridium /z-pyrazolato analog in similar conditions produces mercury(I) chloride and forms the dinuclear complex 204. 

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