Rhodium protonation/deprotonation

H,Rhi3(CO)24]( -")- (x = 1-4) was the first close-packed metal cluster to be isolated and structurally characterized the metal skeleton is based on a hexagonal close-packed metal framework with each of the outer rhodium atoms associated with a terminal CO and there are twelve bridging COs (see Fig. 24). All the above clusters are interconvertable by protonation/deprotonation reactions and are iso-structural,(see Fig. 24). 

Reaction of the cyclopentadienyl rhodium and iridium tris(acetone) complexes with indole leads to the species 118 (M = Rh, Ir) [77JCS(D)1654 79JCS(D)1531]. None of these compounds deprotonates easily in acetone, but the iridium complex loses a proton in reaction with bases (Na2C03 in water, r-BuOK in acetone) to form the ri -indolyl complex 119. This reaction is easily reversed in the presence of small amounts of trifluoroacetic acid. 

Once 26 or 27 has been formed, the rhodium-aUcoxide complex is protonated by a nucdeophile molecule, generating the cationic rhodium complex 29 and an alkoxide or phenoxide nucdeophile. This proton transfer step is supported by kinetics experiments and has two effects [14]. Firstly, the organorhodium species is made more electrophilic as a result of the positive charge, and secondly, the nucleophile is rendered more nu-cdeophihc by becoming deprotonated. 

Iron(u), Rhodium(i), and Iridium(i).— Arguably iron(n) is square-planar in ferrous phthalocyanine in DMSO solution (c/. [PtClJ - in water ). The reaction of this compound with imidazole has been much studied, but kinetic ambiguities have prevented the unequivocal assignment of mechanism. Now the kinetic pattern for the analogous reactions with A-methylimidazole and with iV-n-butylimidazole, where there is no possibility of proton removal from nitrogen, has been shown to be very similar to that with imidazole. It is therefore now reasonable to rule out reaction of ferrous phthalocyanine with the deprotonated imidazole anion as a plausible pathway. ... 

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