CO₂ Activation. 7. Formation of the Catalytically Active Intermediate in the Hydrogenation of Carbon Dioxide to Formic Acid Using the [{(COD)Rh(μ-H)}₄]/Ph₂P(CH₂)₄PPh₂ Catalyst:  First Direct Observation of Hydride Migration from Rhodium to Coordinated 1,5-Cyclooctadiene

Abstract

The nature of the catalytically active intermediate formed in situ from the tetrameric cluster [{(COD)Rh(μ-H)}4] (COD = 1,5-cyclooctadiene; 1) and the bidentate phosphane Ph2P(CH2)4PPh2 (dppb) during hydrogenation of CO2 to formic acid was investigated. Kinetic measurements suggest the initial formation of a catalyst precursor that reacts with dihydrogen to give the actual active species. NMR spectroscopic investigations of the reaction of 1 with dppb in THF-d 8 reveal three phosphorus-containing products that were fully characterized by one- and two-dimensional techniques, including 2D-(31P,1H)-COLOC spectra. The tetrameric hydride cluster [{(dppb)Rh(μ-H)}4] (2) and the double-phosphane-substituted monomeric rhodium hydride [(dppb)2RhH] (3) are formed as byproducts in low yield. The (phosphane)rhodium η3-cyclooctenyl complex [(dppb)Rh(η3-C8H13)] (4), arising via hydride transfer from rhodium to coordinated COD, is the major product, containing about 80% of the dppb. Complex 4 was isolated from the mixture of products, and its molecular structure was determined by X-ray crystal diffraction. Hydrogenolysis of the allyl moiety in the presence of excess dppb was shown to yield 3 presumably via the 14e species [(dppb)RhH]. The results are most consistent with the formation of 4 as the actual precursor for the active species [(dppb)RhH] in the rhodium-catalyzed hydrogenation of CO2 to formic acid using in situ catalysts consisting of 1 and dppb.

Emission Spectroscopy and Ab Initio Calculations for TaN

“…This gives an order of magnitude for the dynamical correlation energy contributions introduced by the large scale CMRCI approach. One can thus conclude that except for the 2 3 state, which could be close to the 25 000 cm −1 limit, all other states are predicted to be significantly higher.…”

“…Transition-metal-containing molecules are of importance as catalysts in organic and organometallic chemistry (1)(2)(3)(4)(5) and their spectroscopic studies provide insight into chemical bonding in simple metal-containing systems (6). Transition-metalcontaining species are also of astrophysical importance (7)(8)(9)(10).…”

Fourier Transform Emission Spectroscopy of the F2Σ+–X2Σ+ System of RuN

“…These species are also of chemical importance, particularly in catalysis (2)(3)(4). Because of the high cosmic abundance of transition metal elements in stars, some diatomic species are also of astrophysical importance and several diatomic oxide and hydride molecules have been identified in the atmospheres of cool M-and S-type stars (5)(6)(7)(8)(9).…”

Chemical Technologies for Exploiting and Recycling Carbon Dioxideinto the Value Chain

“…Typically, high-energy reaction partners such as hydrogen, unsaturated compounds, or strained cyclic molecules can be used to drive the chemical reactions towards low energy products (e.g., Refs. [20,[22][23][24]). Therefore, the overall energy balance and the primary source of energy used to generate the starting materials have to be carefully considered and critically evaluated to assess whether or not a given transformation has the potential to lead to a net reduction of the CO 2 footprint.…”