Palladium tricyclohexylphosphine

Recently, the groups of Fu and Buchwald have coupled aryl chlorides with arylboronic acids [34, 35]. The methodology may be amenable to large-scale synthesis because organic chlorides are less expensive and more readily available than other organic halides. Under conventional Suzuki conditions, chlorobenzene is virtually inert because of its reluctance to oxidatively add to Pd(0). However, in the presence of sterically hindered, electron-rich phosphine ligands [e.g., P(f-Bu)3 or tricyclohexylphosphine], enhanced reactivity is acquired presumably because the oxidative addition of an aryl chloride is more facile with a more electron-rich palladium complex. For... 

As a polar solvent for the catalyst ethylene carbonate (EC), propylene carbonate (PC) and acetonitrile were used. Tricyclohexylphosphine, triphenyl-phosphine and the monosulfonated triphenylphosphine (TPPMS) were investigated as ligands with Pd(acac)2 as the precursor. Cyclohexane, dodecane, p-xylene and alcohols (1-octanol, 2-octanol and 1-dodecanol) were tested as non-polar solvents for the product. To determine the distribution of the product and of the catalyst, the palladium precursor and the hgand were dissolved in the polar solvent and twice as much of the non-polar solvent was added. After the addition of 5-lactone, the amounts of the product in both phases was determined by gas chromatography. The product is not soluble in cyclohexane and dodecane, more than 99% of it can be found in the polar catalyst phase. With the alcohols 1-octanol, 2-octanol and dodecanol about 50 to 60% of the 5-lactone are located in the non-polar phase. With p-xylene biphasic systems can only be achieved when EC is used as the polar solvent and even in this solvent system one homogeneous phase is formed at a temperature higher than 70 °C. In a 1 1 mixture of EC and p-xylene about 50 to 60% of the product is contained in the polar phase. 

The distribution of the catalyst depends on the choice of the non-polar solvent and on the ligand used. With cyclohexane and the alcohols the palladium complexes of tricyclohexylphosphine and triphenylphosphine are located in the polar phase, with p-xylene the complex of triphenylphosphine is dispersed in both phases, and the complex of tricyclohexylphosphine can be predominantly found in the non-polar phase. Because of the low solubility of... 

To investigate the use of a non-polar catalyst phase and a polar product phase EC, PC and acetonitrile were chosen as polar solvents and cyclohexane and p-xylene as non-polar solvents. Tricyclohexylphosphine, triphenylphos-phine and bisadamantyl-n-butyl-phosphine were used as the ligand for Pd(acac)2. If cyclohexane is used as the non-polar solvent, the palladium complexes of tricyclohexylphosphine and triphenylphosphine are situated in the polar solvent and with p-xylene the complex of tricyclohexylphosphine is located in the non-polar phase, hi the solvent system EC/cyclohexane the palladium complex of bisadamantyl-n-butyl-phosphine can be found in the cyclohexane phase. 

The properties of bis(tricyclohexylphosphine)palladium(0) are described with those of the other bicoordinate complexes (see below). 

Significant advances in organonickel chemistry followed the discovery of frtzws,fraws,fraws-(l,5,9-cyclododecatriene)nickel, Ni(cdt), and bis(l,5-cycloocta-diene)nickel Ni(cod)2 by Wilke et. al.1 In these and related compounds, in which only olefinic ligands are bonded to the nickel, the metal is especially reactive both in the synthesis of other compounds and in catalytic behavior. Extension of this chemistry to palladium and to platinum has hitherto been inhibited by the lack of convenient synthetic routes to zero-valent complexes of these metals in which mono- or diolefins are the only ligands. Here we described the synthesis of bis(l,5-cyclooctadiene)platinum, tris(ethylene)-platinum, and bis(ethylene)(tricyclohexylphosphine)platinum. The compound Pt(cod)2 (cod = 1,5-cyclooctadiene) was first reported by Muller and Goser,2 who prepared it by the following reaction sequence ... 

The carbonylation of the 2-aminostyrene 187 in dichloromethane under a carbon monoxide and hydrogen atmosphere produces the lactam in the presence of a palladium acetate/tricyclohexylphosphine catalyst in excellent yield and selectivity (Equation 123) <1996JA4264>. 

A 500-ml flask was charged with the step 2 product (0.105 mol), the step 3 product (0.245 mol), and 70 ml of toluene, and then stirred at ambient temperature. Thereafter the solution was treated with bis(2,4-pentanedionato)palladium (0.070 mmol) and tricyclohexylphosphine (0.070 mmol) dissolved in 10 ml of toluene and dimethylanilinium tetrakispentafluorophenyl borate (0.28 mmol) dissolved in 5 ml of CH2C12. The mixture was stirred at 80°C for 1 hour, during which time toluene was suitably added as the viscosity of the reaction solution increased. After the reaction was completed, the solution was diluted with toluene and the mixture precipitated in excess methanol. The precipitate was filtered off and washed with a large amount of methanol, the polymer dried in vacuo at 110°C for 6 hours, and 61.4 g of product isolated. 

The intramolecular palladium catalyzed ring closure of the tetrahydro-isoquinoline derivative depicted in 8.41. led to the formation of the aporphine derivative in good yield, which was then converted into racemic aporphine in three steps. In the ring closing step 20 mol% palladium acetate and 40 mol% tricyclohexylphosphine were used as catalyst. The removal of the hydroxyl group was also achieved by palladium catalysis through its conversion to triflate and the subsequent reduction with ammonium formate in the presence of palladium acetate and dppf.53... 

The corresponding palladium complexes are also known.3 Since the original preparative method is rather complicated, a simpler one4 for the preparation of chlorohydridobis(tricyclohexylphosphine)palladium is described in this synthesis. ... 

Chlorohydridobis(tricyclohexylphosphine)palladium is a white solid. It is thermally stable at ambient temperatures. It is not very sensitive to air in the solid state, but it is advisable to store it in an inert atmosphere. It is soluble in benzene and tetrahydrofuran. The infrared spectrum shows a sharp v(Pd—H) band at 2002 cm -1 (Nujol mull). The high-field H nmr spectrum in benzene solution shows a triplet at t24.4 (TMS) with 7PH 4.1 Hz. The splitting is caused by the coupling of the hydride proton with two equivalent 31P nuclei. This is consistent with a trans square-planar configuration. 

TABLE 1. Effect of varying the Lewis acid and hexafluoroisopropanol catalyst compositions on the polymerization of norbomene while keeping both palladium acetate and tricyclohexylphosphine concentrations constant at 8.5 x 10 mol. ... 

Chloroaryls, which are electronically deactivated and thus resistant to enter to the oxidative addition, were coupled with phenyltributyltin (PhSnBus) by using tricyclohexylphosphine (Pcys) adducts of palladium in K3PO4 and 1,4-dioxane to yield the corresponding biaryls in good yield. ... 

B. ETHYLENEBIS(TRICYCLOHEXYLPHOSPHINE)PALLADIUM(0) AND ETHYLENEBIS(TRI-o-TOLYL PHOSPHITE)PALLADIUM(O)... 

The ethylenebis(tricyclohexylphosphine)palladium(0) and ethylenebis(tri-u-tolyl phosphite)palladium(0) complexes dissolve in diethyl ether when argon is passed through the suspension. Upon evaporation of these solutions in vacuo, the corresponding bis(tert-phosphine)palladium(0) complexes are obtained. ... 

Reactions with palladium compounds share many common features with reactions involving other transition metals. During a reaction, palladium is coordinated to a variety of groups called ligands, which donate electron density to (or sometimes withdraw electron density from) the metal. A common electron-donating ligand is a phosphine, such as triphenylphosphine, tri(o-tolyl)phosphine, or tricyclohexylphosphine. 

It should also be noted that less-reactive chloroarenes can be carbonylated under biphasic conditions using bis(tricyclohexylphosphine)palladium dichloride as the metal catalyst. Again, the presence of a PT agent does not alfect the reaction... 

Ishiyama, T., Ishida, K., Miyaura, N. Synthesis of pinacol arylboronates via cross-coupling reaction of bis(pinacolato)diboron with chloroarenes catalyzed by palladium(0)-tricyclohexylphosphine complexes. Tetrahedron 2001, 57, 9813-9816. 

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