The Influence of Phosphane Coligands on the Nuclearity of Rhodium(I) 4-Thiolatobenzoic Acid Complexes

Abstract

[RhCl(PR3)3] (R = Ph, Et) reacts with the potassium salt of 4-mercaptobenzoic acid to give a mixture of the monomeric and dimeric complexes, [Rh(SC6H4COOH)(PR3)3] and [{Rh(-SC6H4COOH)(PR3)2}2], respectively. With the labile PPh3 coligand, the dimer is the major product, while for the electron-richer coligand PEt3, the equilibrium is easily shifted to the monomer by the addition of excess PEt3. Phosphane dissociation and dimerization could be prevented by using the chelating coligand PPh(C2H4PPh2)2. [{Rh(-SC6H4COOH)(PPh3)2}2] (2b), [Rh(SC6H4COOH)(PEt3)3] (3a), and [Rh(SC6H4COOH){PPh(C2H4PPh2)2}] (4) were fully characterized by nuclear magnetic resonance and infrared spectroscopy, mass spectrometry, and elemental analysis. The molecular structures of 2b and 4 were determined by X-ray structure analysis. In solution, the lability of the phosphane ligands leads to the decomposition of 2b. One of the decomposition products, namely, the mixed-valent complex [{RhIRhIII(-SC6H4COO)(-SC6H4COOH)(SC6H4COOH)(PPh3)3}2] (5), was characterized by X-ray structural analysis. The dinuclear rhodium(III) complex [{Rh(-SC6H4COO)(SC6H4COOH)(PEt3)2}2] (6) was shown to be a byproduct in the synthesis of 3a, and this demonstrates the reactivity of the rhodium(I) complexes toward oxidative addition. The structurally characterized complexes 2b, 4, 5, and 6 show hydrogen bonding of the free carboxyl groups.

4‐Thiolatobenzoato‐Bridged Rhodium/Zirconium Complexes: 32‐Membered Metallamacrocycles and Their Linear Dinuclear Counterparts

“…The reaction of the metalloligands [{Rh(SC 6 H 4 COOH)-(PPh 3 ) 2 } 2 ] (1) [13] and [Rh(SC 6 H 4 COOH)(PEt 3 ) 3 ] (2) [13] with [Cp* 2 ZrMe 2 ] (Cp* = C 5 Me 5 ) yielded the mono-and bis-(carboxylato) complexes of the zirconocenes, depending on the stoichiometry and the reactivity of the starting materials. At room temperature, 2 gives only the monosubstitution product (Scheme 1), while disubstitution is achieved at ele- vated temperatures.…”

“…Solvents were dried with the appropriate drying agents and distilled under nitrogen. K(Hmba) (H 2 mba = 4-mercaptobenzoic acid), [13] [RhCl(PPh 3 ) 3 ], [23] [RhCl(PEt 3 ) 3 ] [24] and [Cp* 2 ZrMe 2 ] [25] were prepared according to literature procedures. Complexes 1 and 2 were prepared in situ; their synthesis and spectroscopic data are given in ref.…”

“…At room temperature, a very broad signal is observed at δ = 38 ppm, which splits into two broad doublets (δ =37.7 ppm, 1 J P-Rh = 153 Hz, PPh 3 of isomer 1, and 38.4 ppm, 1 J P-Rh = 149 Hz, PPh 3 of isomer 2) on cooling the sample to -100°C. Considering that fluxional behaviour of zirconocene bis(carboxylato) complexes in solution is known from the literature [12b] (one of the ligands coordinates alternatingly in a mono-or bidentate fashion) and that dynamic behaviour, that is exchange between different conformers of the Rh 2 S 2 ring, could be observed for 1, [13] one could consider different isomers in solution. However, because of solvent restrictions, the sample could not be cooled down sufficiently to achieve fine splitting and to gain deeper insights into the species present in solution.…”

“…Information about the change in electron density at the rhodium atom after introduction of the second metal centre can be obtained by comparing the spectroscopic and electrochemical properties of the monometallic complex [Rh(SC 6 H 4 COOH)(PEt 3 ) 3 ] (2) [13] and the corresponding heterometallic complex [Cp* 2 Zr(Me){(µ-O 2 CC 6 H 4 S)-Rh(PEt 3 ) 3 }] (3). For this purpose, the 31 P NMR chemical shifts of the phosphorus nuclei of the phosphane ligands, the oxidation potentials (Table 1) and the wavelengths of the S-Rh charge-transfer bands of 2 and 3 ( Figure 6) were compared.…”

“…[12] By changing the bridging ligand from saturated mercaptocarboxylic acids to unsaturated ones, we have now extended our studies to the 4-thiolatobenzoate dianion and have already prepared several rhodium(I) complexes of 4-thiolatobenzoic acid. [13] The special feature of these complexes is the free carboxyl group, which allows further coordination to a second metal ion. For this, we chose zirconocene derivatives, which are known to form stable carboxylato complexes.…”