RhH2 L

Rhodium(III) hydrides L(H20)RhH2+ (L = L1, L2, or (NH3)4) do not react with 02 in acidic solutions, but are rapidly converted to the corresponding hydroperoxides at pH > 10 (72). The mechanism has not been fully elucidated, but the observed pH effect suggests deprotonation (83) of the hydride followed by 02 capture and reprotonation, Eq. (7). In view of the low acidity of these hydrides (84),... 

The dihydride complexes [RhH2S L ]+ are in equilibrium with monohydride species according to equation 18. 

RhHI 3 (L=P(i-Pr)3) is capable of forming the water adduct (21). The water addition to RhHL3 takes place in pyridine readily at room temperature to give an ionic product [RhH2(py)2L2]0H (eq. 17), which can be isolated as its BPh salt (v(Rh-H) 2076, 2112... 

Path C (Scheme 17.5), which involves reductive elimination of formic acid before reaction with H2, is only possible for dihydride and polyhydride catalysts. This pathway was proposed for the catalyst precursor [Rh(nbd)(PMe2Ph)3]+ by Tsai and Nicholas [19], who observed the intermediates [RhH2(PMe2Ph)3L]+ and [RhH( /2-02CH)(PMe2Ph)2L]+ (L=HzO or solvent). 

Rh CO) (L = P(iso-Pr)3) reacts with water producing H2 and Complex 6a which with CO regenerates Complex 7 producing C02. These observations imply that RhHL3, [RhH2(py)2L2]+OH", RhH(CO)L2, [Rh(CO)(py)L2] +OH", and Rh2(CO)3L3 should be able to catalyze the water gas shift reaction. Indeed, these chloride-free systems proved to be the active catalysts, as we describe elsewhere (12). 

J. Eckert, C.E. Webster, M.B. Hall, A. Albinati L.M. Venanzi (2002). Inorg. Chim. Acta, 330, 240-249. The vibrational spectrum of Tp(3,5-Me)RhH2(H2)] a computational and inelastic neutron scattering study. 

Systems that reduce unsaturated groupings in addition to C=C or C=C, e.g., >C=0, —N=N—, —CH=N—, —N02, are [RhH2(PMe3)2L2]+, where L=solvent, and the complex RhCl3py3 in dimethylformamide solution in the presence of sodium borohydride.57 A phosphorus-containing polystyrene polymer forms a complex with rhodium on treatment with RhCl(PPh3)3 and can act as an efficient heterogeneous catalyst.58... 

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