With rhodium organic substrate reactions

As water is immiscible with most organic substrates, most reactions involving water are done with liquid-liquid biphasic systems. The use of biphasic organometallic catalysts to catalyze aqueous-phase reactions is a novel method to address this issue. The catalyst in such reactions is a water-soluble transition metal complex with substrates that are partially water-soluble. The Ruhrchemie-Rhone-Poulenc process, which involves hydrofor-mylation of propylene to n-butanol, is an example of biphasic organometallic catalysts being used on an industrial scale (Comils and Kuntz, 1995). The catalyst employed is a water-soluble Rhodium (I) complex of trisulfonated triphenylphosphine (tppts) (see Fig. 5.3). 

Organometallic reactions of dimeric rhodium (II) or iridium(II) porphyrins - The review of Guilard, Radish, and coworkers [306] has already been cited. This gives a clear evaluation of the reactions of [Rh(OEP)]2 and [Ir(OEP)]2 with a variety of organic substrates as far as described up to 1987. The important reactions with aliphatic and benzylic CH bonds have already been mentioned in Sect. 3.3, see Eq. (20). Here, some more recent developments, especially concerning the reactions with CO or olefins, will be elaborated. 

Polymerised preformed [(N,N -dimethyl-l,2-diphenylethane diamine)2Rh] complex allows us to obtain enantioselective material. We have then shown that it is possible to imprint an optically pure template into the rhodium-organic matrix and to use the heterogeneous catalyst in asymmetric catalysis with an obvious template effect. The study of yield versus conversion graphs has shown that the mechanism occurs via two parallel reactions on the same site without any inter-conversion of the final products. Adjusting the cross-linker ratio at 50/50 allows us to find a compromise between activity and selectivity. Phenyl ethyl ketone (propiophenone) was reduced quantitatively in 2 days to (R)-l-phenyl propanol with 7tf% enantiomeric excess We have then shown that the imprinting effect is obvious for molecules related in structure to the template (propiophenone, 4 -trifluoromethyl acetophenone). It is not efficient if the structure of the substrate is too different to that of the template. 

Ylide generation from diazo compounds by reaction of carbenoids is a better method than photochemical or thermal dediazoniation in the presence of organic substrates containing heteroatoms, because these dediazoniations without metal catalysis yield, in most cases, not very selective carbenes. Here again, the copper-catalyzed route is in most cases inferior to that with rhodium catalysts. The diazoketo ester with a terminal thioalkyl group (8.145) can be obtained from the... 

Barium bis-(3-triiluoroacetylcamphorate) is easily obtainable through addition of barium chloride solution to the product of a Grignard reaction between ( + )-3-bromocamphor and ethyl trifluoroacetate. Treatment of Ba(tfacam)3 with (COlaRhjClj in chloroform yields the rhodium chelate (39),i68,i6 which shows promise as a gas-chromatographic stationary phase for olefin separations. - Data are also available regarding the use of solutions in squalane of other Ln(tfacam)g chelates as stationary phases for g.l.c. analysis of nucleophilic organic substrates. ... 

From a synthetic chemistry standpoint, reaction of the metaUated intermediates with electrophiles other than a proton is more attractive. Indeed, one of the most important recent developments in boronic acid chemistry strove from the discoveries that transition metals such as palladium(O), rhodium(I), and copper(I) can oxidatively insert into the B-C bond and undergo further chemistry with organic substrates. These processes are discussed in Sections 1.5.3 and 1.5.4. 

Horvath performed experiments using substrates with different solubilities in water and showed that, under optimal conditions, this solubility did not influence the activity [67]. These experiments clearly support the fact that the reaction takes place at the organic-water interphase. Furthermore, he performed a hydroformylation reaction in a continuous system and even under reaction conditions no leaching of rhodium complex was detected. Water obviously leaches if the SAPC is used in a continuous flow system, which in a practical application should be compensated for by using water-saturated organic solvents. 

The prototype reaction was the hydroformylation of oleyl alcohol (water insoluble) with a water-soluble rhodium complex, HRh(C0)[P(m-C6H4S03Na)3]3 (Figure 6.5). Oleyl alcohol was converted to the aldehyde (yield = 97%) using 2 mol % Rh with respect to the substrate and cyclohexane as the solvent, at 50 atmospheres CO/H2, and 100°C. The SAPCs were shown to be stable upon recycling, and extensive work proved that Rh is not leached into the organic phase. Since neither oleyl alcohol nor its products are water soluble, the reaction must take place at the aqueous-organic interface where Rh must be immobilized. Also, if the metal catalyst was supported on various controlled pore glasses with... 

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