Triphos catalyst

Wagner, B, Heneghan, M, Schnabel, G, Ernst, B, Catal)4ic glycosylation with rhodium(III)-triphos catalysts, Synlett, 1303-1306, 2003. 

The proposed mechanisms for the base-assisted hydrogenolysis of prototypical thiophenes to the corresponding thiols catalyzed by [MH(TRIPHOS)]" catalysts (M = Ru, n = -1 Rh, Ir, n = 0) are illustrated in Scheme 4. 

Scheme 8.5 Synthesis of a rhodium triphos catalyst and the mechanism of the catalytic...

With the Rh(triphos) catalyst, n-dodecanal and citronellal were converted in refluxing diglyme to the corresponding alkanes with almost quantitative yields (Scheme 8.11) [13]. TOFs of 0.4-20h were calculated. Noteworthy, 2-formyl ethylbenzene gave a mixture of ethylbenzene and styrene. 

As to most chiral atropisomeric ligand, resolution or asymmetric synthesis is requisite. Mikami developed a novel ligand-accelerated catalyst. The chirality of atropos, but achiral triphos ligand-Ru complex, can be controlled by chiral diamines. Using ( -dm-dabn as controller, the single diastereomeric triphos-Ru complex was achieved through isomerization of (i )-triphos-Ru complex in dichloroethane at 80 °G (Scheme l).44... 

The Elsevier system has since been shown to carry out several ester hydrogenations that were previously deemed impossible [114]. The hydrogenation of dimethyl phfhalate to phfhalide with ruthenium cluster catalysts has already been discussed (Table 15.15, Entry 4). The application of [Ru(acac)3] and triphos -this time with a 20-fold excess of Et3N as additive - delivers good yields of phthalide. However, the use of isopropanol (I PA) as solvent and 24% HBF4 allows further hydrogenation to 1,2,-bis-hydroxylmethyl benzene for the first time. Both of these reactions were carried out under milder conditions (100°C, 85 bar H2, 16 h) than those reported previously. 

Muller compared the activity of several metal catalysts for this reaction. He later reported that AuCl3 was not at all effective for the conversion [113]. However, later studies showed that the complex [AuCl(triphos)](N03)2 (1 mol%) could provide much better results TOF = 212 h-1 and quantitative conversions [114]. Lok et al. showed that gold can catalyze the rearrangements of alkynylamino heterocycles, albeit with concomitant gold mirror formation (Equation 8.50) [115]. 

QCjimirBF [RuCl(p-cymene)(TRIPHOS)]+ Arenes 60 bar, 90 °C catalyst now believed to be heterogeneous. [36]... 

Removal of sulfur from these complexes remains challenging. Catalysts such as [M(COD)(PPh3)2]+ (M = Rh, Ir) only hydrogenate the C=C bond of benzothio-phene, whereas the hydrogenation with rhodium triphos complexes gives 2-ethyl-thiophenol.148 The addition of Co4(CO)i2 to (21-XXVIII, ML, = Cp Ir), however, leads to partial desulfurization, presumably with formation of cobalt sulfide.149... 

One of the best catalysts developed so far is the Ru(ll) complex [(triphos) RuH], obtained by hydrogenation of the precursor [Ru(MeCN)3(triphos)](S03CF3)2, This shows a reasonable turnover frequency of about 2000, but a serious drawback of this system is the deactivation of the catalyst in solvents containing even traces of water. 

An example of a noncovalent attachment of a metal-phosphine complex to a solid support is presented in Figure 31, as reported by Bianchini et al. (120). The complex is attached via a sulfonated variant of the "triphos" ligand, which is known for its successful application in several catalytic reactions. The ligand is attached to the silica by an ionic bond, which is stable in the absence of water. The catalyst was used for the hydroformylation of styrene and of hex-1-ene in batch mode and showed moderate activity. The triply coordinated rhodium atom is strongly boimd although the conditions were rather harsh (120 °C, 30 bar) the concentration of leached metal measured by atomic emission spectroscopy was at most at the parts per million level. However, for commercial applications, for example, in a process such as hydroformylation of bulk products, these concentrations should be less than 10 ppb 111,121). 

Figure 5 Mechanism for the hydrogenolysis of BT to ETP using (triphos)Rh(H) as the catalyst. ...

While metal complexes capable of desulfurizing or hydrodesulfurizing thiophenes are relatively numerous, homogeneous catalysts are very rare, being limited to rhodium and iridium TRIPHOS precursors that are unique in tolerating the harsh experimental conditions required for the second C-S bond cleavage of thiophenes [2 b]. 

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