Iridium carbonyl cations

By contrast, reaction of XeFi with the iridium carbonyl complex cation [Ir(CO)3(PEt3)2] in CH2CI2 results in addition across one of the Ir-CO bonds to give the first example of a metal fluoroacyl complex ... 

There are marked differences between the carbonyl cations of cobalt and its congeners, rhodium and iridium. For instance, the heavier elements form square-planar carbonyl cations as well as higher coordinate complexes. This is paralleled by the isocyanide cations thus cobalt forms [Co(CNR)5]+ cations (191), whereas rhodium and iridium form [M(CNR)4]+ cations (191, 192, 194). 

The cationic complexes [Ir(CO)2(SbPh3)3]+ and [Ir(CO)2(PR3)2]+ (R = Ph, C6Hn) have been synthesized from iridium carbonyl halide derivatives with halogen acceptors in the presence of CO.109... 

For M(V) and M(VI), no binary compounds with the heavier halogens and no oxides are known. Iridium(VI) fluoride is the precursor to [Ir(CO)g] +, the only example to date of a tripositive, binary metal carbonyl cation. Compare reaction... 

The amide group shows a prominent directivity in the hydrogenation of cyclic unsaturated amides by a cationic iridium catalyst, and much higher diastereo-selectivity is realized than in the corresponding ester substrates (Table 21.7). In the case of / ,y-unsaturated bicyclic amide (entry 3), the stereoselectivity surpasses 1000 1 [41]. An increase of the distance between the amide carbonyl and olefmic bond causes little decrease in the selectivity (d, -unsaturated amide, entry 6) compared with the case of the less-basic ester functionality (Table 21.6, entry 5). 

In the case of cyclopentenyl carbamate in which a directive group is present at the homoallyl position, the cationic rhodium [Rh(diphos-4)]+ or iridium [Ir(PCy3)(py)(nbd)]+ catalyst cannot interact with the carbamate carbonyl, and thus approaches the double bond from the less-hindered side. This affords a cis-product preferentially, whereas with the chiral rhodium-duphos catalyst, directivity of the carbamate unit is observed (Table 21.7, entry 7). The presence of a hydroxyl group at the allyl position induced hydroxy-directive hydrogenation, and higher diastereoselectivity was obtained (entry 8) [44]. 

Recently, Shibita et al. reported catalysis of alkyne insertion into an arylamide sp C-H bond to give allylamides (42) by a cationic iridium complex [118]. An interesting aspect of this work is the unusually selective cleavage of an sp C-H bond over sp aromatic C-H bonds so that the alkenyl arylamide (43) is only a very minor product (30). The carbonyl group is required for the reaction as no coupling... 

The products of oxidative addition of acyl chlorides and alkyl halides to various tertiary phosphine complexes of rhodium(I) and iridium(I) are discussed. Features of interest include (1) an equilibrium between a five-coordinate acetylrhodium(III) cation and its six-coordinate methyl(carbonyl) isomer which is established at an intermediate rate on the NMR time scale at room temperature, and (2) a solvent-dependent secondary- to normal-alkyl-group isomerization in octahedral al-kyliridium(III) complexes. The chemistry of monomeric, tertiary phosphine-stabilized hydroxoplatinum(II) complexes is reviewed, with emphasis on their conversion into hydrido -alkyl or -aryl complexes. Evidence for an electronic cis-PtP bond-weakening influence is presented. 

The dicarbonyl iridium and rhodium phosphine [M(CO)2L2] h cations are known [L = PPh3, P(C6Hn)3] (127), obtained by mild carbonylation. 

A number of pentacoordinated dicarbonyl cations of rhodium and iridium have been prepared. The triphenylstibine derivatives are obtained by mild carbonylation. 

Fig. 4.6 Molecular structure of the solvated cation in the iridium(III) carbonyl complex [Ir(CO)g](SbFg)3-4HF (from ref. 97 reproduced with permission of the American Chemical Society)...

In both cases 3C NMR showed the carbonyls attached to the rhodium or iridium precursor exhibited an important high field shift (31) upon CH.I addition, indicative of CO coordinated to high oxidation state cation. Furthermore it was shown that such carbonyl carbons were highly electron deficient thus particularly suited for a nucleophilic attack by species such as alkyls etc. 

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