Rh-Ir complex

The photochemistry152 of Rh(NH3)5N + also seems to have a component of a nitrene generation pathway as in reaction (61), but at higher excitation energies CT states are populated which decay to give azido radicals and presumably Rh(NH3)f+ species. A comparison of quantum yields for the M(NH3)SN3+ (M = Co, Rh, Ir) complexes are given in Table 25.151 153 The Co(NH3)5N3+ gives no... 

The novel aspect of this mechanism to be demonstrated is the mode of substrate activation. Synthetic complexes have been useful in corroborating aspects of the proposed mechanism. Bianchini et al. demonstrated reversible dioxygen adduct formation for [(tri-phos)M "(catecholate)] [triphos = l,l,l-tris(diphenylphosphinomethyl)ethane M = Rh, Ir] complexes ". A crystal structure of the Ir adduct reveals the formation of an alkylperoxy moiety, similar to that proposed in the mechanism, coordinated in a tridentate manner to the metal center. However, oxidative ring cleavage of the complexes does not occur. 

Reactivity of [M (por)] Species. The mononuclear square-planar d [M (por)] (M = Rh, Ir) complexes (either as stable entities for the TMP, TTEPP, or TTiPP complexes, or as transient intermediates for the other complexes) behave very much like organic radicals. For example, they tend to dimerize, either directly via metal-metal bonds (only for TXP, TTP, TPP, or OEP) or via reducible ligands like CO or olefins (with net 2e ligand reduction). The [(por)M ] complexes also show a remarkable reactivity toward a variety of otherwise rather inert substrates. Activation under mild conditions of H2, benzylic, and aUylic C—H bonds, and even methane has been reported. 

Cramer et al. observed ethylene rotation in M( n -CjH5XC2H4)2 (M Rh, Ir) complexes with the following structure ... 

In 2004, Carmona et al. reported the enantioselective reaction of the 1,3-dipolar cycloaddition reaction of nitrones with methacrolein employing [(Cp )M((R)-Prophos) (H20)] (M = Rh, Ir) complexes as catalyst precursors (Scheme 16.2, Table 16.6). Reactions occur with perfect endo selectivity and excellent enantioselectivity up to 96% [31] Recently, they reported highly regio-, diastereoselectivity and good to excellent enantioselectivity for the dipolar cycloaddition reaction between nitrones and methacrolein catalyzed by [Cp M((R)-Prophos)] complexes (98) [31b]. 

For metal precursors that do not have a suitably basic ligand, it was often possible to carry out a salt metathesis with a reagent such as sodium ethoxide to form a reactive metal complex in situ, which then deprotonated the azolium salt. For example, Herrmann showed that [M(p,-OEt)(COD)]2 (M = Rh, Ir) complexes could be formed in situ by the reaction of [M(p-Cl)(COD)]2 with sodium ethoxide the former complex deprotonated (two equivalents of) an azolium salt NHC-HX to form two molecules of [(NHC)MX(COD)] (12 or 13) (Scheme 2.3). ... 

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