Rhodium complexes bromo

The most characteristic catalytic activity of the rhodium complex was observed with the reaction of aroyl halides. The decarbonylation of aroyl halides was not satisfactory with palladium catalyst whereas they decarbonylated smoothly on heating to 200°C. with the rhodium complex. For example, when benzoyl chloride was heated with the complex at 200°C., chlorobenzene distilled oflF rapidly ith the evolution of carbon monoxide. Benzoyl bromide reacts similarly to give bromo-benzene. Phenylacetyl chloride was coi verted into benzyl chloride. Additional results are in Table II. 

In view of these previous developments, we directly coupled various N-substituted imidazoles, which display nucleophilic reactivity, with 2-bromo-oxazolines to give the imidazolium precursors (Scheme 15.15) [55]. This direct condensation of an oxazoline and an imidazole salt provided a straightforward and modular route to the development of a new family of stereodirecting ligands. NHC - rhodium complexes could be obtained by reaction of the imidazolium salt with [ Rh(p-OtBu)(nbd))2] (nbd, norbornadiene) generated iw sifn [56]. 

Asymmetric hydrogenation of itaconic acids.1 Japanese chemists have prepared a new bisphosphine ligand (2), which is more efficient than DIOP for asymmetric hydrogenation of itaconic acids when complexed with rhodium. It is available in four steps from 4-bromo-2,6-dimethylphenol. 

Bis(3-diphenylphosphinopropyl)phenylphosphine (99) forms chloro, bromo and iodo rhodium(I) complexes (equations 253 and 254). The bromo complex can be obtained by addition of a large excess of LiBr to [RhCl(cod)]2 prior to addition of the neutral ligand.1051 The iodo complex has also been prepared from [RhI(CgH12)]2.1051,1052 The halo complexes (100) have been shown to be square planar by X-ray crystallography.1051... 

In an intramolecular Mizoroki-Heck-type alkenylation of alkenes, Wilkinson s catalyst [RhCl(PPh3)3] (84) proved superior than other rhodium compounds (Scheme 10.29) [56]. Notably, the selectivities of the cyclization of various 2-bromo-1,6-dienes were found to be improved with Wilkinson s catalyst when compared with those observed with palladium complexes. Thereby, the corresponding l,2-bis(methylene)cyclopentanes, which themselves are valuable substrates for further cycloaddition reactions, such as 1,3-diene 86, could be isolated in high yields. 

There are only a few reports on the use of N-heterocyclic carbene complexes in biphasic hydroformylation (160). In one of the successful attempts, a rhodium(I)-NHC complex prepared from bromo( l,5-cyclooctadiene)[l-(2 -hydroxyethyl)-3-methylimidazoline-2-ylidene]rhodium(I) and an amphiphilic block copolymer was used for the hydroformylation of 1-octene in an aqueous-organic biphasic system at 100°C and 5 MPa of H2 CO = 1 1. The reaction rate was high (TOF up to 2360 h ) however, regioselectivity (n iso) was only around 60 40 (161). 

P. Royo and F. Terreras, Reactions of bromo- and hydroxy-bis(pentafluorophenyl)thallium-(ill) with some carbonyl complexes of rhodium(i) and iridium(i). Chem. Abs., 1978, 89, 109916. 

Murakami et al. reported the total synthesis of (-)-(/ )-herbertenol via construction of the sterically-congested quaternary stereocenter by enantioselective C-C bond cleavage (Scheme 8.7) [26]. The symmetrical cyclobutanone 39 was prepared from 2-bromo-5-methylbenzaldehyde (38). Treatment of 39 with a catalytic amount of a rhodium(I)/SEGPHOS (5,5 -bis(diphenylphosphino)-4,4 -bi-l,3-benzodioxole) complex induced enantioselective cleavage of the prochiral C-C bond to produce indanone 40. Mechanistically, transmetalation of the boryl... 

Heterobimetallic complexes in which a half-sandwich complex of rhodium ill) is cormected by three bromo-bridges to Re(CO)3 were prepared from metathesis reactions of [Cp RhBr2]2 and [Re( -Br)(C0)3(C4H80)]2- The crystal structure of Cp Rh(/t-Br)3Re(CO)3 was determined by X-ray analysis. The treatment of a mixture of [(rf-CjH8)RuCl2]2 and [Cp RhCl2]2 with silver carboxylates and subsequent hydrogenation afforded mixed metal... 

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