Rhodium catalytic compounds heterocycles

Abstract The purpose of this chapter is to present a survey of the organometallic chemistry and catalysis of rhodium and iridium related to the oxidation of organic substrates that has been developed over the last 5 years, placing special emphasis on reactions or processes involving environmentally friendly oxidants. Iridium-based catalysts appear to be promising candidates for the oxidation of alcohols to aldehydes/ketones as products or as intermediates for heterocyclic compounds or domino reactions. Rhodium complexes seem to be more appropriate for the oxygenation of alkenes. In addition to catalytic allylic and benzylic oxidation of alkenes, recent advances in vinylic oxygenations have been focused on stoichiometric reactions. This review offers an overview of these reactions... 

The first account on the carbonylation of heterocyclic compounds with metallo-dendrimers was recently reported by Lu and Alper using Rh-complexed dendrimers on a resin [207]. The building-block techniques of solid-phase chemistry were used to synthesize dendrimers, followed by phosphonation of the dendrimers with diphenylphosphinomethanol. The resulting phosphonated dendrimers were then reacted with chloro(dicarbonyl)rhodium(I) dimer to give dendritic catalysts A and B (31P NMR, 8 - 25 ppm loading of rhodium A, 0.74 mmol g-1 B, 0.83 mmol g ). As a model study, the reaction of l-ferf-butyl-2-phenylaziridine with carbon monoxide in catalytic presence of A afforded the desired [3-lactam... 

Catalytic hydrogenation of benzo[f]quinoline over platinum in trifluoroacetic acid and subsequent treatment with acetic anhydride affords a mixture of 4-acetyl-l,2,3,4,7,8,9,10-octahydrobenzo[f]quinoline (57) m.p. 68-69°C, 7,8,9,10-tetrahydrobenzo[f]quinoline (58) m.p. 55-56°C, and 5,6,6a,7.8,9,10,10a-octahydrobenzo[f]quinoline (59) m.p. 146-147°C. These three compounds can be separated (M. Cardellini et al., J. org. Chem., 1982, 47, 688). Selective reduction of the heterocyclic ring occurs under mild conditions using l drogen in the presence of chlorotris(triphenylphosphine) rhodium (I) (Ph2P)2RhCl (R.H. Fish, J.L. Tan and A.D. Thormodsen, J. org. Chem., 1984, 4500). 

The catalytic [2 + 2 + 1]-cycloaddition reaction of two carbon—carbon multiple bonds with carbon monoxide has become a general synthetic method for five-membered cyclic carbonyl compounds. In particular, the Pauson-Khand reaction has been widely investigated and established as a powerful tool to synthesize cyclopentenone derivatives.110 Various kinds of transition metals, such as cobalt, titanium, ruthenium, rhodium, and iridium, are used as a catalyst for the Pauson-Khand reaction. The intramolecular Pauson-Khand reaction of the allyl propargyl ether and amine 91 produces the bicyclic ketones 93, which bear a heterocyclic ring as shown in Scheme 31. The reaction proceeds through formation of the bicyclic metallacyclopentene intermediate 92, which subsequently undergoes insertion of CO to give 93. 

Research in the chemistry of rhodium and iridium Af-heterocyclic carbene (NHC) complexes has extraordinarily evolved since 2000. A quick search for rhodiimi-NHC and iridiimi-NHC complexes in the SCl-expanded database, with a 2005-2013 timespan, results in more than 360 hits for rhodium, and more than 340 for iridiiun, which gives a good idea on the interest that rhodium and iridium NHC-based chemistry have achieved in the last few years. It is important to note that a nimiber of reviews and book chapters specifically concerning the chemistry of NHC-based compounds of rhodium and iridiiun have recently appeared [1]. This chapter will deal with all new aspects of the NHC-M (M = Rh, Ir) chemistry not reviewed before, and therefore is mainly restricted to the last 4-5 years. The chapter is classified into two main sections, the first of which deals with relevant structural and electronic features of Rh-NHC and Ir-NHC complexes, and the second with the catalytic applications of these compounds. While not pretending to be completely comprehensive, we have tried to describe the most relevant examples assigned to each section. Some other relevant applications of these complexes have not been considered, such as the emerging biochemical applications, mostly referred to Rh-NHC complexes [2], and the luminescent properties of some Ir-NHC complexes, mostly used for the fabrication of electro-optical devices [3]. 

Catalytic systems based on rhodium clusters or [Rh(CO)4] for the carbonylation of nitro compounds to carbamates have been described in Chapter 3. The application of the same or similar systems to the reduction of nitro compounds to anilines have been described in Chapter 4. Initial work has shown that rhodium clusters Rh4(CO)i2 and Rh<5(CO)i6, but even several mononuclear compounds such as Rh(CO)2(acac) (acac = acetylacetonate), are active catalyst precursor for the carbonylation of nitrobenzene to carbamates, when promoted by an heterocyclic nitrogen base [56, 140, 187, 188]. Later, Liu and Cheng and us independently reported that even higher catalytic activities could be obtained by the use of preformed [PPN][Rh(CO)4] (PPN = (PPh3)2N ) [189, 190]. We have also conducted a mechanistic study of the catalytic cycle using this last complex [1, 192] and the initial stage of the reaction has also been reinvestigated by Liu et al. [193]. Since no mechanistic study has been yet reported on the cluster-based systems, we will first discuss the [PPN][Rh(CO)4] system and then draw a comparison with the other systems. 

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