Wilkinson s complex

The hydrogenation activity of the isolated hydrides 3 and 6 towards cyclooctene or 1-octene was much lower than the Wilkinson s complex, [RhCKPPhj) ], under the same conditions [2] furthermore, isomerisation of the terminal to internal alkenes competed with the hydrogenation reaction. The reduced activity may be related to the high stability of the Rh(III) hydrides, while displacement of a coordinated NHC by alkene may lead to decomposition and Rh metal formation. 

PEGs with average molecular weights above 1000 are waxy solids under ambient conditions, but they melt under C02 pressure to become liquids under typical conditions of scC02 catalysis [63], The approach was demonstrated for the rhodium catalysed hydrogenation of styrene as a test reaction using Wilkinson s complex [(PPhs RhCl] as the catalyst (Scheme 8.6) [61],... 

The first homogeneously catalyzed synthetic C02 reduction was reported in 1976 by Inoue96 to show that [RhCl(PPh3)3] (Wilkinson s complex) in benzene solution in the presence of Et3N produced formic acid. Small amounts of water increased the activity. The accelerating effect of added water in organic solvents has also been observed in other systems.97 98 According to one study, the reaction... 

The coupling of independent catalytic cycles for both radical generation and reduction has been realized by the combination of the titanocene catalyzed reductive epoxide opening [36—4-0] via electron transfer and the catalytic reduction of radicals after H2 activation by Wilkinson s complex [Rh(PPh3)3Cl] as shown in Scheme 16 [41—43],... 

The basic mechanism of hydrogenation is shown by the catalytic cycle in Fig. 7.3. This cycle is simplified, and some reactions are not shown. Intermediate 7.9 is a 14-electron complex (see Section 2.1). Phosphine dissociation of Wilkinson s complex leads to its formation. Conversion of 7.9 to 7.10 is a simple oxidative addition of H2 to the former. Coordination by the alkene, for example, 1-butene, generates 7.11. Subsequent insertion of the alkene into the metal-hydrogen bond gives the metal alkyl species 7.12. The latter undergoes reductive elimination of butane and regenerates 7.9. 

A method for covalently incorporating Wilkinson s complex onto a multi-walled carbon nanotube is described. Semiconductor carbon nanotubes derived from these materials had mobilities and transconductance properties that were superior to those of existing semiconductors. 

A Schlenk apparatus was charged with the briefly sonicated Step 1 product dispersed in DMSO and treated with the drop wise addition of 10 ml of a lOmM solution of Wilkinson s complex in DMSO. The reaction mixture was stirred at 55°C to 60°C for 80 hours and filtered through a 0.2 pm nylon membrane. Dissolved tubes were precipitated out by treating the solution with saturated brine. The precipitated material was purified by filtering over a 0.2 pm nylon membrane and washing in DMSO, ethanol, and water. 

P-, C-, and — NMR spectroscopy confirmed the coordination of Wilkinson s complex with the nanotubes. 

The discovery of facile hydrosilation of carbonyl compounds employing Wilkinson s complex RhCl3(PPh3)3 initiated a broad interest in this synthetically useful reaction (equation 7). 

Wilkinson s complex also underwent substitution of phosphines by IMes. The reaction afforded [(IMes)RhCl(PPh3)2] (86), in which the two phosphines are in cis, in contrast to the general behavior of [(L)RhCl(PPh3)2]-type derivatives that usually adopt a trans geometry. ... 

Since 1957 and the discovery of the Speir s catalyst H2PtCl6/ PrOH, considerable efforts have been made to find new catalysts with high activity and selectivity. Along with the platinum-based catalysts, the Wilkinson s complex [103] Rh(Ph3P)3Cl is one of the most popular hydrosilylation catalysts. Ruthenium catalysts are also able to promote the addition of silanes to unsaturated carbon-carbon bonds, and several reports have shown during the past decade that the well-defined ruthenium complexes of type Ru(H)(Cl)(CO)L can provide excellent activity and selectivity [104—... 

Pt " ") and 1 + (Rh, Ir ). Square-planar geometry is also more common for second- and third-row transition metal complexes than for first-row complexes. Some square-planar complexes have important catalytic behavior. Two examples of square-planar complexes that are used as catalysts are Wilkinson s complex and Vaska s complex, shown in Figure 13-10. 

Rhodium complexes such as 16 with A-heterocyclic carbenes can be prepared in one step proceeding from commercially available precursors (e. g. [( /" -1,5-COD)RhCl]2 (eq. (20)) or Wilkinson s complex [RhCl(PPh3)3] and the free carbene, which is generated from the storable imidazolium salt by deprotonation [47 9]. For more details, see Section 3.1.10. 

The addition of a catalytic amount of Cp2TiCl2 dramatically increases the yield of the hydroacylated ketone formed in the hydroacylation of 1-alkenes with heteroaromatic aldehydes by using Wilkinson s complex and 2-amino-3-picoline as co-catalysts.1264 Cp2TiCl2 catalyzes the reduction of aryl halides by sodium borohydride. The reaction scope and mechanism are solvent dependent.1265... 

Since the discovery of Wilkinson s complex RhCKPPh ) in 1966 [39], many useful catalytic reactions have been reported which are catalyzed by this and related complexes. In particular, RhCl(PPh is a very useful catalyst precursor for hydrogenation of variety of alkenes. The chemical reaciivitv of RhCl(PPh3)3 is summarized in Scheme 11.4 [40]. 

Transition metal phosphine complexes provide another important class of hydrogenation catalysts. Wilkinson s complexes, RhClfPPhjlj and RuHClfPPhjlj, well known for their olefin hydrogenation activity, were shown by Fish [77, 97] to be also good precursors for the reduction of polyaromatic substrates under mild reaction conditions (85° C, ca. 20 atm H, ). following a general activity trend consistent with a combination of electronic and steric factors ... 

The metal complexes most often studied as polymer-bound catalysts have been Rh(I) complexes, such as analogues of Wilkinson s complex. The catalytic activity of a bound metal complex is nearly the same as that of the soluble analogue. Rhodium complexes are active for alkene hydrogenation, alkene hydroformylation, and, in the presence of CH3I cocatalyst, methanol carbonylation, etc. Polymer supports thus allow the chemistry of homogeneous catalysis to take place with the benefits of an insoluble, easily separated catalyst . ... 

Wilkinson s complex, RhCl(PPh3)3, was found to catalyze the addition of hydrosilanes to 1-alkynes to give the corresponding 1-silylalkenes under mild conditions in high yield61,62. The reaction tends to proceed through trans-addition, resulting in cis-products (equation 15). 

A Rh catalyst mediated anti-Markovnikov hydrophosphonylation of alkenes in a polymer to give a linear product (Scheme 16). A catalyst formed from Wilkinson s complex and four equiv of dpph was the most active this ligand was suggested to be bidentate, but the active Rh species was not identified [26, 27]. 

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