Phosphines catalysts for

Conventional triorganophosphite ligands, such as triphenylphosphite, form highly active hydroformylation catalysts (95—99) however, they suffer from poor durabiUty because of decomposition. Diorganophosphite-modified rhodium catalysts (94,100,101), have overcome this stabiUty deficiency and provide a low pressure, rhodium catalyzed process for the hydroformylation of low reactivity olefins, thus making lower cost amyl alcohols from butenes readily accessible. The new diorganophosphite-modified rhodium catalysts increase hydroformylation rates by more than 100 times and provide selectivities not available with standard phosphine catalysts. For example, hydroformylation of 2-butene with l,l -biphenyl-2,2 -diyl... 

Hereafter, the factors ruling the activity and selectivity of Pd(II)-phosphine catalysts for the carbonylation of ethene in MeOH are presented. In order to make the exposition clearer some of the concepts already discussed in other reviews will be shortly resumed. It will deal first with copolymerisation because it includes more general aspects, several of which are involved also in the catalysis to monocarbonylated non-polymeric products. The literature search covers all up to 2004. 

Concerning monodentate amphiphilic phosphines one of the latest developments is the use of Rh/phosphonate-phosphine catalysts for the hydroformylation of 1-octene and 1-dodecene [54]. The catalysts were prepared in situ from [Rh(acac)(CO)2] and from the appropriate Ph2P(CH2)ioP03M2 (M = Na, K", NKi, l aPr) phosphine. Pretreatment under 30 bar syngas significantly improved the catalytic performance. At 120 °C, 30 bar syngas, [P]/[Rh] = 5, in 4 h, 1-octene reacted with 52 % conversion and 47 % aldehyde yield. This means a 91 % selectivity to... 

Amine, Alcohol and Phosphine Catalysts for Acyl Transfer Reactions... 

Scheme 3. Chiral phosphine catalyst for kinetic resolution of secondary alcohols...

The solution to this problem has been to attach these catalysts to polymer supports. The ideal polymer-bound catalyst must satisfy a formidable list of requirements. It should be easily prepared from low cost materials. The support must be compatible with the solvent system employed, and be chemically and thermally stable under the reaction conditions. The catalyst should show minimal losses in reaction rate or selectivity when bound to the support, and should be able to be recycled many times without loss of activity. Finally, the interactions between the catalytic site and the support must be either negligible or beneficial. The development of polymer supported rhodium-phosphine catalysts for the asymmetric hydrogenation of amino acid precursors illustrates the incremental process which has led to supports which approach the ideal support. 

The Shell process uses a cobalt/phosphine catalyst for the homologation of methanol CH3 - OH 4- CO + 2Hj - CH3CH2OH 4- H20... 

The NHC-coordinated catalysts 2 and 5 also exhibit dramatically improved substrate scope relative to bis(phosphine) catalysts. For example, whereas catalyst 1 is unreactive toward sterically congested substrates and cannot form tetra-substituted RCM products, catalysts 2 and 5 readily form tetra-substituted olefins in five- and six-membered rings systems (Eq. 4.17 E = C02Et) [98,100]. They also mediate CM between terminal olefins and 2,2-disubstituted olefins to form new trisubstituted double bonds [102]. Previously, these transformations could only be accomplished using molybdenum-based catalysts. 

In addition to cobalt and Union Carbide s rhodium-phosphine catalysts for the hydroformylation process. Shell s cobalt/phosphine system has potential advantages, providing higher n-/iso-ratios than cobalt alone while producing mainly the alcohol in one step. 

The regioselectivity of the catalysts based on PPh has been extensively studied (see reviews [5]). The regioselectivity of 1 -alkene hydroformylation varies from 70 to 92 % for the linear aldehyde. The highest selectivity is obtained at high concentrations ofPPhs [5, 25], or even hquid PPhs [2, 30], and low pressures of CO. Isomerization should be considered as well, as this forms an escape route for the branched alkyl intermediate leading to internal alkene isomers instead of branched aldehyde. Since the activity of most phosphine catalysts for internal aUcenes is low, the apparent linearity of... 

Uozumi, Y. and Nakazono, M., Amphiphilic resin-supported rhodium-phosphine catalysts for C—C bond forming reactions in water, Adv. Synth. CataL, 2002, 344, 27i-m. 

Unstrained difluorotetramethyldisilane (84) gives the 1 1 adduct 85 as the main product and the 1 2 adduct 86 as a minor product[78,79]. On the other hand, the dimerization and double silylation of conjugated dienes with (Me3Si)2 catalyzed by PdCl2(PhCN)2 take place at 90" C[80]. Pd(dba)2 without phosphine is an active catalyst for the reaction, which proceeds in DMF to give 87 at room temperature[81], A five-membered ring is formed by the application of the reaction to the di-(2,4-pentadienyl)malonate (69)[82]. 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

Rhodium Ca.ta.lysts. Rhodium carbonyl catalysts for olefin hydroformylation are more active than cobalt carbonyls and can be appHed at lower temperatures and pressures (14). Rhodium hydrocarbonyl [75506-18-2] HRh(CO)4, results in lower -butyraldehyde [123-72-8] to isobutyraldehyde [78-84-2] ratios from propylene [115-07-17, C H, than does cobalt hydrocarbonyl, ie, 50/50 vs 80/20. Ligand-modified rhodium catalysts, HRh(CO)2L2 or HRh(CO)L2, afford /iso-ratios as high as 92/8 the ligand is generally a tertiary phosphine. The rhodium catalyst process was developed joindy by Union Carbide Chemicals, Johnson-Matthey, and Davy Powergas and has been Hcensed to several companies. It is particulady suited to propylene conversion to -butyraldehyde for 2-ethylhexanol production in that by-product isobutyraldehyde is minimized. 

The search for catalyst systems which could effect the 0x0 reaction under milder conditions and produce higher yields of the desired aldehyde resulted in processes utilizing rhodium. Oxo capacity built since the mid-1970s, both in the United States and elsewhere, has largely employed tertiary phosphine-modified rhodium catalysts. For example, over 50% of the world s butyraldehyde (qv) is produced by the LP Oxo process, technology Hcensed by Union Carbide Corporation and Davy Process Technology. 

High enantioselectivities and regioselectivities have been obtained using both mono- and 1,2-disubstituted prochinal olefins employing chiral phosphine phosphite (33,34) modified rhodium catalysts. For example, i7j -2-butene ia the presence of rhodium and (12) (33) gave (3)-2-meth5ibutanal ia an optical yield of 82% at a turnover number of 9.84. ... 

This is an ion-exchanger like the sulfonated polymer. The siUca surface can also be functionalized with phosphine complexes when combined with rhodium, these give anchored complexes that behave like their soluble and polymer-supported analogues as catalysts for olefin hydrogenation and other reactions ... 

AC2O or AcCl, Pyr, DMAP, 24-80°, 1-40 h, 72-95% yield. The use of DMAP increases the rate of acylation by a factor of lO. These conditions acylate most alcohols, including tertiary alcohols. The use of DMAP (4-A,A-dimethylaminopyridine) as a catalyst to improve the rate of esterification is quite general and works for other esters as well, but it is not effective with hindered anhydrides such as pivaloic anhydride. The phosphine i (48-99% yield) and Bu3P have been developed as active acylation catalysts for acetates and benzoates. 

Sodium pyrazolate and 3,5-dimethylpyrazolate, [( " -cod)Rh(/A-Cl)]2, carbon monoxide, 3-(diphenylphosphino)benzoic acid, or (2-formylphenyl)diphenyl-phosphine give rise to complexes 120 (R = H, Me) and 121 (R = H, Me) [94JOM(469)213]. However, 2-(diphenylphosphino)benzoic acid (the carboxyl group in the ortho position) leads to formation of the mononuclear complexes 122. The products appear to be catalysts for hydroformylation reactions [93MI2]. 

A quinoline-phosphine ligand has been developed by Buono et ah, and its complex 29 with Cu(OTf)2 found to be an effective catalyst for the Diels-Alder reaction between acryloyl-oxazolidinone and cyclopentadiene, affording the cycloadduct... 

In addition to the neutral nickel/phosphine complexes used in the Shell Higher Olefins Process (SHOP), cationic Ni-complexes such as [(mall)Ni(dppmo)][SbF6] (see Figure 5.2-7) have attracted some attention as highly selective and highly active catalysts for ethylene oligomerization to HAOs [106]. 

The ease of formation of the carbene depends on the nucleophilicity of the anion associated with the imidazolium. For example, when Pd(OAc)2 is heated in the presence of [BMIM][Br], the formation of a mixture of Pd imidazolylidene complexes occurs. Palladium complexes have been shown to be active and stable catalysts for Heck and other C-C coupling reactions [34]. The highest activity and stability of palladium is observed in the ionic liquid [BMIM][Brj. Carbene complexes can be formed not only by deprotonation of the imidazolium cation but also by direct oxidative addition to metal(O) (Scheme 5.3-3). These heterocyclic carbene ligands can be functionalized with polar groups in order to increase their affinity for ionic liquids. While their donor properties can be compared to those of donor phosphines, they have the advantage over phosphines of being stable toward oxidation. 

---