Cationic Ir complexes

A cationic Ir complex possessing phosphanodihydrooxazole 26 is usable for asymmetric hydrogenation of allylic alcohols. (E)-2-Methyl-3-phenyl-2-propen-l-ol can be converted in CH2C12 containing 1 mol % of the Ir complex to the saturated product in 95% yield and 96% ee (Scheme 1.26) [141]. The process is used in the enantioselective synthesis of the artificial fragrance filial. 

Another recent development is hydrogenolyses of C-F bonds triggered by heterolytic activation of H2 on cationic Ir complexes with either piano stool (93) or octahedral (94) geometries. 

Nolan and coworkers have described the use of their cationic Ir complex 27 as an effective catalyst for transfer hydrogenations [73]. While complex 27 was found to be effective, the analog bearing the NHC ICy was found to be su-... 

Table 1 Differences in total energies ( tot) of five-membered heterocycles with one heteroatom and cationic ir-complexes formed on their protonation for ot- (d ) and /i-positions AEp), as well as values of AE p = AE —AEp (all in kcal/mol) ...

Isomerisation ofallyl silyl ethers. Double bond migration promoted by cationic Ir complexes provides silyl enol ethers (10 examples, 71-97%). 

Propose a catalytic cycle for hydrogenation step in the production of (S)-metolachlor using the cationic Ir complex described in Section 9-7-2. 

SbF6)2 [61], and an oxovanadium(IV) complex [62] are effective catalysts. Matsuda et al. recenfly reported that a cationic Ir complex generated in situ from [Ir(COD) (PPh3)2]OTf and H2 catalyzes aldol and aldol-type reactions of aldehydes and acetals with silyl enolates in CH2CI2 [63]. 

Treatment of a bismuth trihalide with electron-rich arenes affords arene-BiX3 TT-complexes. When the reaction is carried out in the presence of AICI3, the corresponding cationic ir-complexes are formed [87AG(E)74]. The arenes employed so far are benzene, toluene, mesitylene, hexamethyl-benzene, perylene, pyrene, acenaphthene, phenanthrene, fluorene, and fluor-anthene-p-xylene (1/0.5). The isolated compounds are summarized in Table 2.29. 

Carmona et al.466 reported a series of cationic Ir complexes containing the neutral ligand HC(pz )3 and compared their reactivity and structure with those found for analogous Tp derivatives. X-ray single-crystal studies carried out on (HC(pz )3) derivatives show a striking similarity between the structural parameters of Ir(HC(pz )3) and Ir(Tp ) species.466... 

Figure 6.4 Cationic Ir-complex encapsulated within C, i.e. [C z> lr -complex] (this notation denotes that C encapsulates an lr -complex). [61 Reproduced by permission of The Royal Society of Chemistry (RSC)...

Heterolytic activation of H2 can also trigger hydrogenolyses of C-F bonds on cationic Ir complexes with piano stool geometry (Equation (12)). ... 

In a subsequent study. Sola and coworkers [62] reported the synthesis of cationic Ir " complexes supported by bis(phosphinoalkyl)silyl PSiP hgation. Thus, treatment... 

The cyclometalated Ir complexes investigated earlier with a formula of [Ir(C N)2(N N)] are complexes [Ir(ppy)2(bpy)]Cl (6) and [Ir(ppy)2(bpy)]PF6 (7) (bpy and PFg represent 2,2 -bipyridine and hexafluorophosphate, respectively) [39]. The two cationic Ir complexes were prepared by a modified method employed by Nonoyama [83]. The detailed synthetic route is shown in Fig. 9. The stereo structure of these [Ir(C N)2(N N)] complexes is similar to those of Ir(C N)2(LX) complexes, with a trans-N,N configuration of the C N ligands, whereas the diimine ligand is located opposite c/s-oilented carbon atoms, completing an octahedral arrangement [84]. 

The photophysical properties of [Ir(C N)2(N N)] -type cationic Ir complexes are complicated. In some excited complexes, the neutral, diimine and cyclometalated ligands provide orbitals that participate in excited-state transitions. The cyclometalated ligand tends to be associated with the LC transition, and the diimine ligand with the MLCT transition [93]. In such cases, the excited state of the complex can be tuned directly through ligand modification because each ligand is linked to a... 

It was proved that photophysical properties of [Ir(C N)2(N N)] -type complexes can also be adjusted by modifying the conjugated lengths of the diimine ligand [84]. Theoretical calculations, photophysical studies and electrochemical studies of a series of cationic Ir complexes 34—39 (Fig. 17) showed that their excited... 

The size of the K-system chosen has important implication on the structural and functional aspects of metal binding. To explore the size effect calculations were performed on the cation-ir complexes of Li+ and Mg + with the Jt-face of linear and cyclic unsaturated hydrocarbons [45]. In the case of the acyclic Jt-systems, we started with the simplest system, e.g. ethylene followed by buta-1,3-diene, hexa-l,3,5-triene, and octa-1,3,5, 7-tetraene with 2, 3 and 4, conjugated jt units, respectively. These linear systems with two and more number of jt units can have various conformations wherein the jt units can have cis, trans or a combination of both cis and trans orientations. Similarly for cyclic systems cyclobutadiene, benzene, cyclooctateraene, naphthalene, anthracene, phenanthrene and naphthacene have been included. Thus a wide range of sizes for aromatic systems have been covered. 

In order to achieve selective deuterium incorporation in ortho positions to a directing gronp, chelate-assisted C-H deuterations can be performed with cationic Ir complexes such as Crabtree s catalyst 27 (Scheme 23.49) [155, 158, 159]. Moreover, Pd complexes catalyze the same type of reactivity, even with weakly directing groups (Scheme 23.50) [22]. The proposed mechanisms for... 

DeWall, S. L., Barbour, L.., and Gokel, G. W. "Cation-ir Complexation of Potassium Cation with the Phenolic Sidechain of Tyrosine."/. Am. Chan. SoC 121,8405-8406 (1999). (The iodide counterion is shown as a dark sphere.)... 

As shown in Scheme 54, Frontier et al. successfully developed a synthetic route to ( )-merrilactone A using Nazarov-type cydization of a,p-unsaturated ketone 126 bearing silyloxyfuran moiety [92], They used a cationic Ir-complex as an effective catalyst for this cydization of 126. Under similar conditions, several functionalized cyclic lactones have been prepared. 

Martin-Matute and co-workers reported the cationic Ir" complexes 131, with chelating NHC-alcohol ligands (Figure 13.14). These complexes were highly active in the Af-alkylation of amines with alcohols, at low temperatures and under base-free reaction conditions. ... 

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