Rh(I) Carbonyl Carboxylato Complexes: Spectral and Structural Characteristics. Some Reactions of Coordinated Formate Group

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Complexes [Rh(μ-RCOO)(CO2)]2, where R = H, CH 3,CF 3 (I, II, III, respectively) are synthesized by reacting anhydrous carboxylic acids with Rh(Acac)(CO2) crystals. In compounds I, II, III, and trans-Rh(RCOO)(PPh3)2(CO), where R = H, CH3,CF3 (IV, V, VI, respectively), ν(CO) and 1J(CRh) increase and δ13C decreases with the increasing electronegativity of R (CH3 < H < CF3). In the case complexes IV, V, and VI, the values of δ31P and 1J(PRh) decrease in the same order. Complexes I and V are studied by X-ray diffraction analysis. Intramolecular (2.946 Å) and intermolecular (3.127 Å) Rh-Rh distances in a columnar structure I are close, i.e., the structure contains infinite chains of metal atoms. Interaction of IV with chlorinated solvents results in trans-RhCl(PPh3)2(CO). When heated with an excess of PPh3 in propanol-2, compound IV transforms to HRh(PPh3)3(CO). The latter reaction was suggested as a basis of a new method that can be used to obtain HRh(PPh3)3(CO).

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