Eight rhodium catalysts

Wender et al. reported a [5+2] cycloaddition in water by using a water-soluble rhodium catalyst having a bidentate phosphine ligand to give a 7-membered ring product (Eq. 4.69). This water-soluble catalyst was reused eight times without any significant loss in catalytic activity.133... 

The oxidative C-arylation of five- to eight-membered (NH)-heterocycles such as pyrrolidine, piperidine, morpholine, etc., is observed in the reaction with iodoarenes in the presence of a rhodium catalyst, RhCl(CO)[P(Fur)3]2.95... 

III) on faces. With the ultradispersed catalysts, the particles were thought to be two-dimensional rafts composed of about eight rhodium atoms. Such particles would have only comer atoms. With somewhat larger three-dimensional particles the number of edge atoms would increase. With larger particles there would be an increase in the number of face atoms. A more complete discussion of the nature of the active sites on a catalyst surface is presented in Chapter 3. 

A novel enone transposition has been described by Grieco et al. an olefinic double bond can be caused to migrate about a six- or eight-membered carbocyclic ring to attain the most stable arrangement using a rhodium catalyst [i.e. (40)->... 

In 2010, Stuart and Fagnou reported an oxidative Larock-type heterocycle synthesis using rhodium catalysis and applied it to the synthesis of paullone (Scheme 16.8) [17]. In the synthesis of paullone, acetanilide (41) was coupled with alkyne 42 in the presence of a rhodium catalyst and Cu(0Ac)2-H20 as an oxidant under air to form disubstituted indole 44 via intermediate 43 in 71% yield. Removal of acetyl and Boc groups, followed by treatment with DBU (l,8-diazabicyclo[5.4.0]undec-7-ene), resulted in paullone in a total of eight steps. 

Besides the formation of carbenes from diazo compounds and the hydroformyla-tion, rhodium (as described previously for palladium) has also been used as catalyst in domino processes involving cycloadditions. Thus, Evans and coworkers developed a new Rh(I)-catalyzed [4+2+2] cycloaddition for the synthesis of eight-membered rings as 6/2-105 using a lithium salt of N-tosylpropargylamines as 6/2-104, allyl carbonates and 1,3-butadiene (Scheme 6/2.22) [221]. The first step is an al-... 

A [2 + 2 + 2]-cycloaddition reaction is also known, facilitated by Ni(cod)2 or a cobalt catalyst. " " [2 + 2 + 1]-Cycloaddition is known.A cobalt catalyst is used for a [4- -2- -2]-cycloaddition of 1,3-butadiene and bicyclo[2.2.2]octa-2,5-diene. " " " Eight-membered rings are products by a rhodium catalyzed [4- -2- -2]-cycloaddition. " " Chromium catalysts are available for [6-1-4]-cycloadditions... 

Rhodium pivalate dirhodium tetrakis[ X-(2,2-dimethylpropanato 0 0 )] was synthesized by refluxing commercially available rhodium trifluoroacetate in eight equivalents of pivalic acid for 24 hours followed by removal of excess acid under vacuum. The crude catalyst was purified by flash chromatography using an MTBE petroleum... 

Gilbertson and DeBoef demonstrated that the [4 + 2 + 2]-cycloaddition of the yne—dienes 149 with the alkyne 150 took place in the presence of rhodium and silver catalysts to give the eight-membered trienes 151 in good yields (Scheme 51).127... 

Acceleration of the reaction has been achieved by the use of the polar solvent tri-fluoroethanol and also by the addition of silver triflat thus, it can be assumed that cationic rhodium complexes act as the active catalyst. Eight-membered metallacycles such as 9 are probably key intermediates. [6] Cyclopropyl-substituted five-membered metallacycles 8 and homoallyl complexes 10 can be considered as precursors of 9 [7] (Scheme 4). 

On the mesoporous material MCM-41, immobilized catalysts (compare Scheme 2.165) were tested in the multiple hydroformylation of 1-octene and reused for eight cycles [35]. With MCM-41 (R = Mes), in the first two cycles 80% of aldehyde formation was registered. Up to 20 ppm rhodium leaching was observed in the first catalytic cycle, but there was no loss in the fourth and eighth cycles. In the beginning, also 20% of the corresponding alcohol was found, but as more runs were performed the formation of the latter decreased (up to 2%). Simultaneously, the yields of aldehydes increased (up to >99% in run 3). The catalyst showed an initial linear selectivity of 1.9, which decreased in run 8 to 1.1. This decrease was attributed to the change in the microstructure of MCM-41 due to the harsh reaction conditions. With MCM-41 (R = fBu), formation of aldehyde remained stable over all runs (95->99%) and reduction to the alcohol was only... 

With a catalyst formed from [HRh(CO)(PPh3)3]/12 P(OPh)3, aldehyde yields in 1-octene hydroformylation remained constant above 90% over eight cycles representing averaged TOFs of 660h. However, three equivalents of P(OPh)3 per rhodium were added after each run to maintain the performance of the catalyst [25]. 

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