121072-51-3Relevant academic research and scientific papers
Bi- and polynuclear complexes with short-bite ligands bridging metal atoms. [(η5-C5H5)Rh(μ-CH3O 2CC2CO2CH3)(μ-Ph 2Ppy)Rh(CO)(μ-Cl)]2: Synthesis, X-ray crystal structure, structural dynamics, and reactions with CO and SO2
Rotondo, Enrico,Lo Schiavo, Sandra,Bruno, Giuseppe,Arena, Carmela Grazia,Gobetto, Roberto,Faraone, Felice
, p. 2944 - 2949 (2008/10/08)
Treatment of [(η5-C5H5)Rh(μ-CO)(μ-Ph 2Ppy)Rh(CO)Cl] (1) (Ph2Ppy = 2-(diphenylphosphino)pyridine) with the activated acetylenes dimethyl acetylenedicarboxylate (DMA) and diethyl acetylenedicarboxylate (DEA), in CH2Cl2 solution, yields the tetranuclear complexes {[(η5-C5H5)Rh(μ-DMA)(μ-Ph 2Ppy)Rh(CO)(μ-Cl)]2·CH2Cl 2} (2) and {[(η5-C5H5)Rh(μ-DEA)(μ-Ph 2Ppy)Rh(CO)(μ-Cl)]2·CH2Cl 2} (3), respectively. The alkyne in both the complexes adopts the μ-η2-∥ (cis-dimetalated olefinic) bonding mode. The structure of 2 was established by X-ray crystallography: the crystals are triclinic, space group P1, with a = 11.805 (1) A?, b = 11.791 (1) A?, c = 12.042 (2) A?, α = 98.7 (2)°, β = 108.9 (2)°, γ = 90.2 (2)°, and Z = 2. Least-squares refinement of 381 parameters using 3971 reflections yields R = 0.035 and Rw = 0.036. The molecule shows a crystallographic inversion center originating from the presence of two asymmetrical bridging chloro ligands that link two bimetallic units. Each rhodium dimer unit is completely asymmetrical and consists of two rhodium atoms bridged by the Ph2Ppy and the DMA ligands. The Rh(1)-Rh(2) bond distance is 2.661 (1) A? and the Rh(1)?Rh(1′) separation is 3.900 (1) A?. The structural parameters concerning the inner coordination sphere provide useful information about the formation of the tetranuclear species 2. Both Rh-Cl distances are somewhat long [Rh(1)-Cl(1) = 2.516 (1) A?, and Rh(1)-Cl(1′) = 2.670 (1) A?]. DMA is attached essentially parallel to the Rh(1)-Rh(2) axis in a cis-dimetalated olefinic geometry; the Rh(1)-C(24) and Rh(2)-C(25) bond distances are significantly different (2.022 (5) and 2.040 (4) A?, respectively). 31P{1H} and 1H NMR spectra of 2 in CD2Cl2 solution, at different temperatures, indicate the presence of an equilibrium between the tetranuclear, 2, and the binuclear, [(η5-C5H5)Rh(μ-DMA)(μ-Ph 2Ppy)Rh-(CO)(Cl)] (4), species. The unsaturation of the rhodium(II), 16-electron center in 4 seems to be the key to the reactivity of this species, and it accounts for both the formation of the tetranuclear chloro-bridged species 2 and the reactions of 2 with small molecules such as CO and SO2. The reaction of 2 with CO and SO2 leads to adducts that could not be isolated owing to the reversibility of the process. 31P, 1H, and 13C NMR spectra indicate that in these adducts CO and SO2 are both terminally bonded to rhodium. Hints of a dynamic process involving the formation of acyl derivatives, presumably by insertion of 13CO into the Rh-C(acetylene) bond, are also reported.
