Rhodium monovalent, complexes

The transition-metal catalyzed decomposition of thiirene dioxides has been also investigated primarily via kinetic studies103. Zerovalent platinum and palladium complexes and monovalent iridium and rhodium complexes were found to affect this process, whereas divalent platinum and palladium had no effect. The kinetic data suggested the mechanism in equation 7. 

Metallation of dioxacorrole with Rh(CO)2Cl 2 gives a mono-Rh complex in which the monovalent rhodium atom is coordinated by two corrole nitrogens (Scheme S4).244... 

Equilibration with carbon monoxide at room temperature and low pressure (a few torr ) yielded the rhodium(I)-dicarbonyl compound (13) in addition to the Rh(I)(C0) paramagnetic complexe (11). The structure of this complex was elucidated by ESCA and UV measurements (13) which showed that the trivalent rhodium was indeed reduced to the monovalent state and by infrared spectroscopy which provided evidence for a gem dicarbonyl (14). Use of 1 1 C0 ... 

To date, only one example of a monovalent metallocorrole has been reported. It was reported in 1976 by Grigg, et al. and involves a rhodium corrole, which was obtained in 36% yield as the result of reacting free-base diethyl-hexamethyl corrole 2.6 with Rh2(CO)4Cl2. Unlike the trivalent corrole complex 2.134, obtained earlier by the treatment of a dideoxybiladiene-ac with this same metal salt, the complex isolated in this instance analyzed as being the monovalent Rh(CO)2Corrole, 2.157 (Scheme 2.1.42). This complex was later prepared in 72% yield,although it was... 

Pracejus was fascinated by the idea of functionalizing cellulose as the cheapest chiral material and to use it in this form as a carrier for monovalent rhodium for asymmetric hydrogenation. Rh was shown by Wilkinson to be useful as a catalyti-cally active central metal in phosphane complexes. However, the catalytic activities of the new cellulose immobilized complexes in the hydrogenation of unsaturated amino acid precursors were low and the enantioselectivities did not exceed 35%... 

However, whereas in solution, rhodium catalysts were shown to be the most active, in zeolites, iridium appeared to be an order of magnetitude more active than rhodium. Moreover, CH3CI could be used as the promoter while it could not be in solution. This is due, probably, to the fact that this molecule is strongly polarized by the electrostatic field and, possibly, to the modification of the redox properties of the monovalent precursor complex. This hypothesis was confirmed by the observation that the Si/Al ratio has a large influence on the activity of the rhodium complex (66). 

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