Ruthenium porphyrins synthesis

Oxidative amination of carbamates, sulfamates, and sulfonamides has broad utility for the preparation of value-added heterocyclic structures. Both dimeric rhodium complexes and ruthenium porphyrins are effective catalysts for saturated C-H bond functionalization, affording products in high yields and with excellent chemo-, regio-, and diastereocontrol. Initial efforts to develop these methods into practical asymmetric processes give promise that such achievements will someday be realized. Alkene aziridina-tion using sulfamates and sulfonamides has witnessed dramatic improvement with the advent of protocols that obviate use of capricious iminoiodinanes. Complexes of rhodium, ruthenium, and copper all enjoy application in this context and will continue to evolve as both achiral and chiral catalysts for aziridine synthesis. The invention of new methods for the selective and efficient intermolecular amination of saturated C-H bonds still stands, however, as one of the great challenges. 

A review has appeared on the synthesis of enantiomerically enriched aziridines by the addition of nitrenes to alkenes and of carbenes to imines.45 A study of the metal-catalysed aziridination of imines by ethyl diazoacetate found that mam group complexes, early and late transition metal complexes, and rare-earth metal complexes can catalyse the reaction.46 The proposed mechanism did not involve carbene intermediates, the role of the metal being as a Lewis acid to complex the imine lone pah. Ruthenium porphyrins were found to be efficient catalysts for the cyclopropana-tion of styrenes 47 High diastereoselectivities in favour of the //-product were seen but the use of chiral porphyrins gave only low ees. 

If Ru3(CO)12 is used, the product is again the porphyrin, in a mixture with its Ru2 + complex. The catalytic action of ruthenium in expanding the macrocycle core has not been further investigated. The yield of ruthenium porphyrinate increases with time this is not surprising since the reaction of triruthenium dodecacarbonyl with porphyrins is a standard procedure for the synthesis of such complexes [26]. 

The first HNO complex, Os(PPh3)2(CO)(HNO)Cl2, was reported in 1970 upon exposure of HC1 to Os(PPh3)2(CO)(NO)Cl (173), and the X-ray crystal structure was published in 1979 (174). Recent interest has resulted in isolation of additional examples of HNO complexes, and the structures of three similar complexes have been reported [(Ru(HNO)(2,6-bis(2-mercapto-3,5-di-fert-butyl-phenylthio)dimethylpyridine) (175), ReCl(CO)2(PR3)2(HNO) (176), and IrHCl2 (PPh3)2(FINO) (177)]. Preparative routes generally involve protonation, hydride addition, or reduction of a coordinated nitrosyl (175, 176, 178-186). Farmer and co-workers also described the first synthesis of an HNO complex directly as a result of exposure to a donor compound (187) while Lee and Richter-Addo recently observed the HNO adduct of a heme model complex [ruthenium porphyrin (188)]. 

Miranda KM, Bu X, Lorkovic IM, Ford PC. Synthesis and structural characterization of several ruthenium porphyrin nitrosyl complexes. Inorg Chem 1997 36 4838. 

Collman JP, Barnes CE, Swepston PN, Ibers JA (1984) Synthesis, proton NMR spectroscopy, and structural characterization of binuclear ruthenium porphyrins. J Am Chem Soc 106 3500-3510... 

The first ruthenium porphyrin-catalyzed intramolecular carbenoid C - H insertion to afford selectively cis-2,3-disubstituted-2,3-dihydroergocornine using tosylhydrazone salts as the carbene source was reported by Zheng et al. [192]. This general strategy was applied in natural product synthesis to provide a route to the total synthesis of racemic epi-conocarpan. Enantio-selective synthesis of 2,3-dihydrobenzofurans was also achieved by a similar route using chiral ruthenium porphyrins as catalysts for this interesting carbon-carbon bond formation [193]. Recently, it was found that dinuclear fx-oxo osmium porphyrins are able to catalyze intermolecular carbene insertion into C - H bonds in cyclohexene [153]. 

In terms of miscellaneous reactions associated with aziridine synthesis, a ruthenium porphyrin catalyst was reported to facilitate a unique three-component coupling of nitroarenes with alkynes and a-diazo compounds to produce multifunctional aziridines (14OL1048). Pictured below is an intriguing palladium-catalyzed C-H bond activation/amination leading to the selective transformation of an aminolactone methyl group adjacent to an unprotected secondary amine into an aziridine (14NAT129). 

Rani-Beeram S, Meyer K, McCrate A, Hong Y, Nielsen M, Swavey S (2008) A fluorinated ruthenium porphyrin as a potential photodynamic therapy agent synthesis, characterization, DNA binding, and melanoma ceU studies. Inorg Chem 47(23) 11278-11283... 

Lachaud F, Jeandon C, Monari A, Assfeld X, Beley M, Ruppert R, Gros PC (2012) New dyads using (metallo)porphyrins as ancillary ligands in polypyridine ruthenium complexes. Synthesis and electronic properties. Dalton Trans 41(41) 12865-12871... 

Ferrand Y, Le Maux P, Simonneaux G (2004) Highly enantioselective synthesis of cyclopropylphosphonates catalyzed by Chiral Ruthenium Porphyrins. Org Lett 6 3211-3214... 

Le Maux P, Bahri H, Simonneaux G (1993) Synthesis and stereochemieal studies of ehiral ruthenium porphyrins. Tetrahedron 49 1401-1408... 

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