Catalytic hydrogenation of carbon dioxide with the cationic bis(chelate)rhodium complex [Rh(P⌢O)2][BPh4]

The interconversion of formic acid and hydrogen/carbon dioxide using a binuclear ruthenium complex catalyst

“…4-8 When the pressure was increased to 1020 psi, the yield of formic acid was significantly higher, as found with other systems (runs 5 and 6, Table 3). 8, 20 The yield of formic acid was much lower in the absence of triethylamine, as expected (run 7, Table 3). 4, 5 Evaporation of the solution obtained after a catalytic reaction gave back the starting complex 1 in high yield.…”

“…Similarly, the catalytic reaction was inhibited by addition of phenylacetylene, which can bind to the diruthenium centre. 20 If the catalysis was carried out in a vessel from which gaseous products could escape, the coordinatively unsaturated complex 6 could be detected in solution when the formic acid was completely decomposed. Addition of more formic acid led to very rapid catalytic decomposition, indicating that 6 is a much more active catalyst precursor than the coordinatively saturated complex 1.…”

Theoretical Study on the Thermodynamics of the Elimination of Formic Acid in the Last Step of the Hydrogenation of CO2 Catalyzed by Rhodium Complexes in the Gas Phase and Supercritical CO2

“…Such a relatively high energy requirement for the release of HCOOH does not meet the expected standards for a process that occurs rapidly at moderate temperatures and that is fully reversible ,,, although no conclusive data on this point have been reported to date. On the other hand, it has been also pointed out 18 that substitution of HCOOH by CO 2 may follow an associative mechanism that should be less energy demanding than the dissociative one depicted in Scheme .…”

“…The homogeneous catalytic hydrogenation of CO 2 to formic acid catalyzed by transition-metal complexes, usually rhodium diphosphine complexes, is a promising approach to the use of CO 2 as a raw material in chemical synthesis. − The most widely accepted catalytic cycle for this hydrogenation catalyzed by rhodium complexes involves four steps, as shown in Scheme : 1,5-11 (1) insertion of the incoming CO 2 molecule into the Rh−H bond of the unsaturated T-shaped neutral 14-valence-electron (VE) active species 1,4,9-12,15,17 [P 2 RhH] complex 2 to yield complex 3 , (2) oxidative addition of H 2 to the vacant site of complex 3 , (3) reductive elimination to yield complex 1 , and (4) release of HCOOH from complex 1 to recover the catalytic species complex 2 . In a series of recent works, Dedieu et al − have explored theoretically the possibility that a single step consisting of a σ-bond metathesis instead of the two-step oxidative-addition/reductive-elimination process (steps 2 and 3) can occur during the transformation from complex 3 to complex 1 , by taking the [(PH 3 ) 2 RhH] species as a model for the catalytically active site.…”

Heterogeneous transfer hydrogenation involves pairwise hydrogen transfer from the same position of two molecules of formic acid

“…A major effort has already been directed to the understanding of the mechanism of this reaction in homogeneous systems with the formato-(hydrido) metal complex proposed as a key intermediate 1 [Scheme 1(a)], based on deuterium labelling studies and ab initio calculations. [9][10][11] Recent studies using NMR spectroscopy have provided evidence for the existence of this intermediate, 12,13 however, as discussed by Halpern, 14 such thermodynamically stable compounds may not be the active species on hydrogenation pathways.…”