Product distribution rhodium catalysis

The metal-catalyzed decomposition of diazo compounds has broad applications in organic synthesis [1-8]. Transient metal carbenoids provide important reactive intermediates that are capable of a wide variety of useful transformations, in which the catalyst dramatically influences the product distribution [5]. Indeed, the whole field of diazo compound decomposition was revolutionized in the early 1970s with the discovery that dirhodium tetracarboxylates 1 are effective catalysts for this process [9]. Many of the reactions that were previously low-yielding using conventional copper catalysts were found to proceed with unparalleled efficiency using this particular rhodium catalysis. The field has progressed extensively and there are some excellent reviews describing the breadth of this chemistry [5, 7, 10-17]. 

Padwa et al. (48) examined the behavior of diazoketone 127 under rhodium catalysis and found that the ligands associated with rhodium had a dramatic effect on the distribution of products 128 (from the carbonyl ylide) and 129 (from intramolecular C—H insertion). When rhodium acetate was employed there was a... 

Iridium and rhodium nanoparticles have also been studied in the hydrogenation of various aromatic compoimds. In all cases, total conversions were not observed in BMI PF6. TOFs based on mol of cyclohexane formed were 44 h for toluene hydrogenation with Ir (0) and 24 h and 5 h for p-xylene reduction with lr(0) or Rh(0) nanoparticles, respectively. The cis-1,4-dimethylcyclohexane is the major product and the cisitrans ratio depends on the nature of the metal 5 1 for lr(0) and 2 1 for Rh(0). TEM experiments show a mean diameter of 2.3 nm and 2.1 nm for rhodium and iridium particles, respectively. The same nanoparticle size distribution is observed after catalysis (Fig. 4). 

However, the carbonyl of the methoxycarbonyl group may be involved in the formation of an oxallyiic intermediate (23), which affords a path to both syn and anti isomers. A similar structure was proposed by Teratani et al. to explain the distribution of deuterium in the products of deuteration of 2-methylcyclo-hexanone catalyzed by palladium such a structure was not required to explain the results of catalysis by rhodium. ... 

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