Vaska s complex

Examples of the isolation of hydrido(carboxylato) complexes by oxidative addition of carboxylic acid are very rare. Wilkinson [55] examined oxidative addition of fluoro carboxylic acids to Vaska s complex, trans-[lrCl(CO)(PPh3)2]. They isolated colorless hydrido(carboxylato) complexes of stoichiometry, [lrCl(H)(OCORF)(CO)(PPh3)2] (RE = CE3, C2F5), but did not completely succeed in characterizing the products of the oxidative addition. The complex is claimed to be a mixture of four closely similar... 

Iridium made its first major mark in 1965, in the arena of organometallic chemistry with the discovery of Vaska s complex, [IrCl(CO)(PPh3)2] (1) [1]. Only weakly catalytic itself, Vaska s complex is nevertheless highly relevant to cataly-... 

The 16-electron square planar complex is converted into an octahedral 18-electron complex. In Figure 2.14 we have depicted the oxidative addition of methyl iodide to Vaska s complex (L=phosphine). Iodide ions accelerate the reaction and addition of an anion to the metal is the first step in that instance [10]. 

As in the case of the H-H and C-I addition to Vaska s complex, reaction 1 proceeds via addition to Ir(I) to give a stable formally six-coordinate Ir(III) complex. 

Vaska s complex ([IrCl(CO)(PPh3)2]) also catalyzed the carbonylative coupling of diynes, which provided bicyclic cyclopentadienones (Scheme 11.23) [35]. Due to the instability of the products, the substrates are limited to symmetrical diynes with aromatic groups on their termini nonetheless, this reaction still serves as the catalytic and practical procedure for the synthesis of cyclopentadienones, which are anti-aromatic with a 47t system and serve as active synthetic intermediates. 

Vaska s complex catalyzed the transformahon of aUenylcyclopropane into 2-alkenylidenecyclohex-3-enone under conditions of pressurized CO (Scheme 11.25) [38]. In this reaction, the jr-coordination to internal oleflnic moiety of the aUene brings the metal closer to the cyclopropane ring. Release of the cyclopropane ring strain then facilitates the oxidative addition of vinylcyclopropane moiety along with C-C bond cleavage, such that metallacyclohexene is obtained a subsequent carbonyl insertion and reductive elimination then provides the product Hence, the reaction can be recognized as a [5+1] cycloaddition of vinylcyclopropane and CO. 

In contrast to the Pt(0) and Pt(II) complexes and the corresponding Rh(I) and Rh(III) complexes, the iridium complexes have rarely been employed as hydrosilylation catalysts [1-4]. Iridium-phosphine complexes with d metal configura-tion-forexample, [Ir(CO)Cl(PPh3)2] (Vaska s complex) and [Ir(CO)H(PPh3)3]-were first tested some 40 years ago in the hydrosilylation of olefins. Although they underwent oxidative addition with hydrosilanes (simultaneously to Rh(I) com-... 

The direct silylation of arenes through C—H bond activation provides an attractive route for the synthesis of useful aromatic compounds [64]. Vaska s complex was the first of the iridium catalysts to be reported for activation of the C—H bond in benzene by Si—H of pentamethyldisiloxane to yield phenylsubstituted siloxane [65]. However, a very attractive method for the aromatic C—H silylation with disilanes has been recently reported by the groups of Ishiyama and Miyaura [66-68]. 

The Co2(CO)g- and [Ir(COD)Cl]2-catalyzed processes may be carried out in the presence of the appropriate ligand under a CO atmosphere. These conditions, as well as the direct use of Vaska s complex [IrCl(CO)(PPh3)2], are applicable to alkynes bearing bulky substituents, such as 59, for synthesis of the parent products 60. However, it should be noted that, in many cases, the thermodynamically more stable products 60 ... 

Figure 1.35 H NMR spectrum obtained upon addition of parahydrogen to Vaska s complex trans-lrCI(CO)(PPh3)2 in QDg at 295 K, showing the extra species resulting from addition of Hj over the P-lr-P axis.

SnMe Brj addition, 34 278 sulfur donors as ligands, 44 305-307 thionitrosyls, 26 344, 348 Vaska s complex, 44 295-296 xenon fluoride reactions, 46 89... 

The addition reaction of normal, triplet dioxygen to Vaska s complex, fra/is-Ir(CO)Cl(PPh3)2, has been well studied (126,127). The kinetics... 

An unusual sulfur-nitrogen donor, benzothiazole-2-thiolate (58), has been reacted with Vaska s complex to produce 59 in high yield no bidentate adducts of 58 are produced even in refluxing solvent (156). Upon reaction with dioxygen, the extremely sensitive and reactive complex 60 is produced. Addition of water to 60 caused rearrangement to the carboxylate complex 61, while the addition of sulfur dioxide to 60 produces 62 (see Scheme 11). A proposed mechanism for the reaction of water with 60, based on labeling experiments, was outlined and can be found in Scheme 12. 

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