Rh(I) carbonyl carboxylato complexes: Spectral and structural characteristics. Some reactions of coordinated formate group

Abstract

Complexes [Rh(µ-RCOO)(CO) 2 ] 2 , where R = H, CH 3 , CF 3 (I, II, III, respectively) are synthesized by reacting anhydrous carboxylic acids with Rh(Acac)(CO) 2 crystals. In compounds I, II, III, and trans-Rh(RCOO)(PPh 3 ) 2 (CO), where R = H, CH 3 , CF 3 (IV, V, VI, respectively), ν(CO) and 1 J(CRh) increase and δ 13 C decreases with the increasing electronegativity of R (CH 3 < H < CF 3 ). In the case complexes IV, V, and VI, the values of δ 31 P and 1 J(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(PPh 3 ) 2 (CO). When heated with an excess of PPh 3 in propanol-2, compound IV transforms to HRh(PPh 3 ) 3 (CO). The latter reaction was suggested as a basis of a new method that can be used to obtain HRh(PPh 3 ) 3 (CO).

Binuclear Rhodium(I) Carbonyl Carboxylate Complexes: DFT Study of Structural and Spectral Properties

“…2055 (0) 2163 (0) 2047 (1577) 2156 (1658) 2033 (0) 2140 (0) 2032 (642) 2139 (777) Certainly, it should be born in mind that the calculated Rh-Rh distances refer to isolated molecules; the experimental r(Rh-Rh) values for R = CF 3 and R = H [1,20] differ insignificantly, which may be due to the pronounced influence of the molecule environment in the crystal lattice.…”

“…-whether the calculation results reported previously [1] reflect the correlations between these parameters and what characteristics of the electronic structure of the complex (atomic charges, orbital populations, bond orders) may by considered responsible for these correlations; SIZOVA et al .…”

“…In a previous publication [1], the spectral (IR and NMR) characteristics of the carbonyl groups in rhodium(I) carbonyl carboxylate complexes have been determined and some correlations between these characteristics and the electronegativity of the substituent R in the carboxylate ligand were found. It was also found that transition from dicarbonyl (per one rhodium atom) complexes, [ Rh ( µ -RCOO )( CO ) 2 ] 2 , to monocarbonyl diphosphine complexes, trans -[Rh ( RCOO )( CO )( PPh 3 ) 2 ], is accompanied by substantial changes in the spectroscopic parameters of the carbonyl groups.…”

“…It was also found that transition from dicarbonyl (per one rhodium atom) complexes, [ Rh ( µ -RCOO )( CO ) 2 ] 2 , to monocarbonyl diphosphine complexes, trans -[Rh ( RCOO )( CO )( PPh 3 ) 2 ], is accompanied by substantial changes in the spectroscopic parameters of the carbonyl groups. These observations were interpreted [1] using the intuitive views on ligand effect transfer through the central atom. The authors of [1] also paid attention to the fact that the IR spectra of the binuclear carbonyl carboxylate complexes differ appreciably in the carbonyl stretching region (the intensity ratio of the observed absorption bands) from the spectrum of the chloride analog [ Rh ( µ -Cl )( CO ) 2 ] 2 .…”

“…These observations were interpreted [1] using the intuitive views on ligand effect transfer through the central atom. The authors of [1] also paid attention to the fact that the IR spectra of the binuclear carbonyl carboxylate complexes differ appreciably in the carbonyl stretching region (the intensity ratio of the observed absorption bands) from the spectrum of the chloride analog [ Rh ( µ -Cl )( CO ) 2 ] 2 . This difference was tentatively attributed to the change in the dihedral angle ( q ) formed by the coordination planes of the rhodium atoms on passing from the carboxylate complexes to the complex with monoatomic chloride bridges.…”