Arylation rhodium catalysis

Close inspection of 2 reveals that it can be thought of as a metal-aryl complex in a low oxidation state. Thus it meets the conditions for another type of C-H transformation - cross-coupling. Various N-heterocycles bearing the N-CH-X motif will react with aryl iodides, under the action of rhodium catalysis, to give arylated products in moderate yield [11]. 

Yanagisawa S, Sudo T, Noyori R, Itami K (2006) Direct C-H arylation of (Hetero)arenes with aryl iodides via rhodium catalysis. J Am Chem Soc 128 11748-11749... 

Enantioselective arylation of ketimines has been carried out using rhodium catalysis with chiral sulfur-olefin ligands arylboronic acids are added in up to 99/99% yield/cc. 0... 

Other functionalizations described include the direct alkylation of the title compound. For example, it was demonstrated that applying similar alkenes describe vide supra under rhodium catalysis leads to a direct hydroalkenylation, furnishing the corresponding 2-alkyl pyridine -oxides. Conversely, benzyl chlorides were effectively coupled to the title compound under similar conditions described for direct sp arylation (eq 30). ... 

Arylation. Arylation of the 2-position of quinoline is also possible using rhodium catalysis. A C-H activation protocol employing both electron-rich and electron-poor aryl halides results in arylation of the 2-position of quinoline (eq 20). ... 

Too et al. demonstrated that isoquinoUne synthesis can be conducted by coupling of aryl ketone O-acyloxime 110 with 2c under rhodium catalysis without addition of any external oxidant (Scheme 25.54) [51]. Similar annulation of aryl ketone O-benzyloximes under nickel catalysis was also disclosed by Yoshida et al. [52]. 

Recently, hydrosilanes are also employed for the silylation of aryl halides in the presence of a palladium,platinum, or rhodium catalyst. In view of atom efficiency, this procedure has an advantage. Palladium-catalyzed reactions are suitable for the silylation of electron-rich aryl halides, whereas rhodium-catalysis works well with a wide range of aryl halides (Scheme 3-17). Silylation of allyl halides with trichlorosilane proceeds in the presence of a copper catalyst. ... 

Rh2(OAc)4-catalyzed decomposition of 2-diazocyclohexane-l,3-dione 380a or its 5,5-dimethyl derivate 380b in the presence of an aryl iodide leads to an iodonium ylide 381 355). The mild reaction conditions unique to the rhodium catalyst are essential to the successful isolation of the ylide which rearranges to 382 under the more forcing conditions required upon copper catalysis (copper bronze, Cu(acac)2, CuCl2) 355). 

It has not been shown unambiguously, however, whether the rhodium remains coordinated to the ligands 2 and 3 during the catalysis. Kantam and associates [23] have used a Pd(II) catalyst anchored onto MCM-41/silylamine (MCM-41 a molecular-sieve) for hydrodehalogenation of aryl halides by atmospheric hydrogen. The catalyst was reused for several cycles with constant activity. 

Isocyanates can be prepared from azides by reaction with carbon monoxide. The reaction has been at first reported to proceed only with catalysis of rhodium or iridium carbonyl complexes . Later work has however shown that aryl azides and carbon monoxide interact without catalysis at temperatures of 160-180° and pressures of 200-300 atm, yielding aryl isocyanates (86) in good yields. Ethyl azidoformate yielded under these conditions ethoxyisocyanate . 

Catalysis of aryl group interchange in triarylphosphines is not unique to rhodium. Other group 8 transition metals show varying degrees of activity (Table 2). 

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