HRh PPh

Oxidative addition of an unreacti e C—C bond occurs in the reaction of the diter-tiary phosphine shown in eq (44) with HRh(PPh )j. the reaction being preceded by the kinetically favored C—H activation [54]. The intermediates have been isolated and characterized. A similar reaction takes place using RhCl(PEt3)3. 

Allylic and homoallylic alcohols undergo amidocarbonylation in the presence of two catalysts [HRh(PPh ) (CO)] to isomerize to the corresponding aldehydes and [Co (C0)ol to achieve the amido-carbonylation of the aldehydes (Scheme 56). Epoxides undergo a similar reaction in the presence of [Co2(C0)g] and a Lewis acid such as Ti(OPr ), the latter presumably causing rearrangement of the epoxide to the aldehyde required for amidocarbonylation (Scheme... 

The monosulfonated PPh derivative, Ph2P(m-C6H4S03K) (DPM) and its rhodium complex, HRh(CO)(DPM)3 have been synthesized and characterized by IR and NMR spectroscopic techniques. The data showed that the structure was similar to [HRh(CO)(PPh3)3]. The catalytic activity and selectivity of [HRh(CO)(DPM)3] in styrene hydroformylation were studied in biphasic catalytic systems.420 421 Rh1 complexes [Rh(acac)(CO)(PR3)] with tpa (131), cyep (132), (126), ompp (133), pmpp (134), tmpp (135), PPh2(pyl), PPh(pyl)2, and P(pyl)3 were characterized with NMR and IR spectra. Complexes with (131), (132), and (126) were catalysts for hydrogenation of C—C and C—O bonds, isomerization of alkenes, and hydroformylation of alkenes.422 Asymmetric hydroformylation of styrene was performed using as catalyst precursor [Rh(//-0 Me)(COD)]2 associated with sodium salts of m-sulfonated diarylphosphines.423... 

Rhodium is a nmcii more active hydroJoimylation metal than cobalt, and is capable of operating effectively under much milder temperature and pres> sure conditions. As with Co2(CO)g. the rhodium can be introduced into the reaction medium in a number of different forms (e. rhodium on a support. RlijOj. Rli salts. RhCOfPPhahCl, RluiCO),. (Rh CO)jClI, and. finally. HRh(CO)(PPh.,h). 

The regioselectivity of HRh(CO)(PPh3)2 is strongly related to the concentration of PPhs in solution (up to a certain point) and the H2/CO ratio used. Coimnercial hydroformylation reactions are run using solutions that have PPhs concentrations of 0.3 M or higher. This corresponds to PPhs weight percentages of 8 50% of the total solution in coimnercial reactors. The effect of PPhs concentration on the rate and selectivity for the hydroformylation of 1-hexene can be seen in Table 2. 

Matsumoto and Tamura (at Kuraray Co.) have demonstrated that the combination of simple bis(diphenylphosp-hino)alkane ligands and PPhs has a very positive effect on catalyst stabihty and the reduction of unwanted side reactions. This is most evident in the hydroformylation of a reactive alkene substrate such as allyl alcohol. The use of HRh(CO)(PPh3)2 in the presence of excess PPhs leads to relatively rapid catalyst deactivation to unidentified species. The addition of just over 1 equivalent of dppb, for example, leads to a stable, active hydroformylation catalyst. Use of dppb either by itself, or in quantities higher than 2 equivalents, leads to catalyst deactivation and/or poor activities and selectivities. ARCO Chemical Co. licensed the Kuraray technology to build the first conunercial plant (1990) for the hydroformylation of allyl alcohol to produce 1,4-butanediol (Scheme 11). 

HRh(CO)(PPh3)3 was supported In molten PPhs for use as a heterogeneous catalyst for the hydroformylatlon of propene. ... 

The hydroformylation and amidocarbonylation of esters of methylvinylphosphinic acid have been studied in relation to the synthesis of probably the best known molecule t)f the types under consideration, viz. 2-amino-4-(hydroxymethylphosphinyl)butanoic acid, (398), also known as phosphinothricin or glufosinate. The outcome of the hydroformylation of the ester (401) depends on the nature of the catalyst employed. Thus the u.se of Rh (CO)j2. Rh2Cl2(CO)4, or HRh(CO)(PPh )2, leads to relatively high total yields of (402) and (403) but with low selectivity in contrast, when Co2(CO)j is employed, high selectivity with relatively low total yields are observed. Reactions in methanol afford a 90% relative yield of (402), Subsequent amidocarbonylation using the... 

The reaction times in Table 15 suggest that hydroformylation of 1-octene is relatively fast using PPhs. Ogata and co-workers report that hydroformylation of styrene (at 50°) is 2.5 times as fast using HRh(DBP-Ph)4 as the catalyst as with HRh(PPh3)4. DBP-Ph is 5-phenyl-5-H-diben-zophosphole (83). 

The Rh/PPhs hydroformylation catalyst system was developed approximately simultaneously by Geoffrey Wilkinson (and students),Union Carbide, BASF, and Celanese. This catalyst system has been extensively studied, and the key species is HRh(CO)(PPh3)2. Once again the core mechanism is the same as that discussed previously for the cobalt systems and shown in Figure 12. Rhodium catalysts are approximately 1,000 times faster than ones based on cobalt (Rh is also about 1,000 times more expensive). Thus, rhodium catalysts can be run at considerably milder pressures and temperatures (8-10 bar, 125 °C), which dramatically reduces the capital expenditures for industrial plant construction. The increased activity of Rh over Co mainly derives from the stronger electronic preference of... 

Figure 13 HRh(CO)x(PPh3)3 x (x=0-3) species formed by CO/PPhs ligand-substitution equilibria.

Hydroformylation of 1,4-diacetoxybutene HRh(CO)(PPh3)3 or Rh complex without PPh,3 4-Acetoxy-2-methyl crotonaldehyde—an intermediate in vitamin A synthesis Stinson (1986)... 

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