80865-88-9Relevant academic research and scientific papers
Rhodium A-frame complexes with small-molecule bridgeheads. Synthesis and structure of [Rh2(μ-H)(μ-CO)(CO)2(PPh2CH 2PPh2)2](p-CH3C6H 4SO3)·2THF and catalytic properties
Kubiak, Clifford P.,Woodcock, Carrie,Eisenberg, Richard
, p. 2119 - 2129 (2008/10/08)
The reaction of [Rh2Cl2(CO)2(dpm)2] with NaBH4 in EtOH leads to [Rh2(CO)2(dpm)2]. Subsequent reactions with H+, CO, acetylenes, and CO2 lead to new complexes having the A-frame structure with the addendum molecule in the bridging position. Solutions of [Rh2(CO)2(dpm)2] under H2 are active in the hydrogenation of acetylene. Sequential treatment of [Rh2(CO)2(dpm)2] with H+ and CO gives [Rh2(μ-H)(μ-CO)(CO)2(dpm)2]+, and a single-crystal X-ray structure determination of its p-toluenesulfonate salt has been performed. The complex [Rh2(μ-H)(μ-CO)(CO)2(dpm)2](p-MeC 6H4SO3)·2THF crystallizes in the monoclinic space group C2/m in a unit cell of dimensions a = 24.391 (11) A?, b = 18.863 (9) A?, c = 14.440 (6) A?, and β = 107.81 (2) A? with Z = 4. The structural study reveals the presence of both bridging hydride and bridging CO, a Rh-Rh separation of 2.732 (2) A?, and an average angle between the bridging hydride and the terminal CO ligands of 152 (3)°. The complex is also found to result from the decomposition of a related formate species [Rh2(μ-O2CH)(CO)2(dpm)2] + in the presence of CO. In 1-propanol or bis(2-ethoxyethyl) ether solution, [Rh2(μ-H)(μ-CO)(CO)2(dpm)2]+ is a catalyst for the water-gas shift reaction CO + H2O ? H2 + CO2. At 90°C under 1 atm of CO, a rate corresponding to 0.58 turnover per complex/h is observed. This rate is maintained for approximately 35 h after which it gradually decreases, completely ceasing in 70 h. The complex is also a catalyst for the hydrogenation and hydroformylation of olefins with CO + H2O as the source of hydrogen. The rate and duration of catalysis for these reactions are similar to those found for the water-gas shift reaction. Reactions relating to the product forming steps in these systems are discussed.
