Organometallic Reactions of Rhodium and Iridium Porphyrins

Acetylrhodium(III) tetraphenylporphyrin was formed on warming N,N-dimethylacetamide solutions of RhH(TPP) [319]. Obviously, an acetyl group had been abstracted from a solvent molecule. 

Reactions of rhodium porphyrins with diazo esters - According to Callot et al., iodorhodium(III) porphyrins are efficient catalysts for the cyclopropanation of alkenes by diazo esters [320,321], The transfer of ethoxycarbonylcarbene to a variety of olefins was found to proceed with a large syn-selectivity as compared with other catalysts. In their study to further develop this reaction to a shape-selective and asymmetric process [322], Kodadek et al. [323] have delineated the reaction sequences (29, 30) and identified as the active catalyst the iodoalkyl-rhodium(III) complex resulting from attack of a metal carbene moiety Rh(CHCOOEt) by iodide. 

The product of reaction (30) is thought to coordinate a further molecule of ethyldiazoacetate trans to the iodoalkyl group which looses dinitrogen, yielding a hexacoordinate rhodium carbene complex according to Eq. (31) which transfers its carbene moiety to an attacking alkene molecule. 

Nucleophilic additions to alkylrhodium(lll) porphyrins - An interesting reaction sequence (31) was observed when RhMe(OEP) was treated with an excess of 

RhMe(OEP) - [RhAr2(OEP)] - [RhAr(OEPAr)] brown green 

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Some electrochemically initiated organometallic reactions of rhodium and iridium porphyrins have been explored and reviewed by Kadish et al. [178,306], For more recent papers concerning this matter, the reader is referred to Sect. 5. 

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