Activation of Nitroarenes in the Homogenous Catalytic Carbonylation of Nitroaromatics via an Oxygen-Atom-Transfer Mechanism Induced by Inner-Sphere Electron Transfer

Abstract

Kinetic and mechanistic studies on the deoxygenation of nitroarenes by Ru(dppe)(CO)3, where dppe = 1,2-bis(diphenylphosphino)ethane, are described. The products of the reaction included 1 equiv of carbon dioxide and an η2-nitrosoarene ruthenium complex (Ru(dppe)(CO)2[ON(Ar)] for Ar = 4-chloro-2-trifluoromethylphenyl), which was isolated and fully characterized by solution spectroscopic methods and by single crystal X-ray diffraction [monoclinic crystal system, space group P21/c (#14), a = 14.556 (8) Å, b = 12.903 (6) Å, c = 20.10 (1) Å, β = 105.60 (6)°, V = 3636 (8) Å3, Z = 4]. The deoxygenation reaction was determined to be first-order with respect to both Ru(dppe)(CO)3 and nitroarene. Electron withdrawing substituents on the nitroarene and polar solvents accelerated the rate, and a substituent study provided a ρ of +3.45 indicating negative charge buildup on the nitroarene in the rate determining step of the reaction. Activation enthalpies for 2-CF3, 4-Cl, 4-H, and 4-CH3 substituted nitroarenes were 9.3, 9.9, 10.5, and 10.7 kcal mol-1, and the entropies of activation were −35, −33, −36, and −37 eu, respectively. Correlation between the reduction potentials of the nitroarenes (E°ArNO2) and log k 2 was also observed for substituted nitroarenes yielding a slope of 10 V-1. Monosubstituted nitroarenes bearing a single methyl, phenyl, or chloro group in the ortho position and disubstituted 2,6-dimethyl- and 2,3-dichloronitrobenzene showed no attenuation in the rate, from what would be expected based on the E°ArNO2 − log k 2 correlation. Large rate attenuation was observed for nitroarenes bearing both ortho and meta groups. Analysis of the kinetic and thermodynamic data using Marcus theory indicated that the rates were too high for an outer-sphere electron-transfer mechanism. The data were interpreted in terms of an inner-sphere electron-transfer mechanism where the unfavorable energetics are mitigated by bonding interactions between the donor and acceptor.

Interaction between Dioxoruthenium(VI) Porphyrins and Hydroxylamines: Coordination ofN-Substituted Hydroxylamine to Ruthenium and X-ray Crystal Structures of Ruthenium Complexes with a Unidentate Nitrosoarene Ligand

“…For all the three complexes, the axial Ru-N(O)-C moiety [38] but smaller than the corresponding bond lengths of 2.093(4) ± 2.115(7) in ruthenium complexes with h 2 -nitrosoarene ligands. [40,42,43] The two axial PhNO ligands in either 3 a or 3 e adopt a staggered conformation, as can be seen from Figure 5. Such a conformation is considered beneficial to the axial M 3 N(O)Ar (9) 178.9(1) Ru1-N5-C51 [b] 127.7(2) 125.2(2) 122.3(2) Ru1-N5-O1 117.6(2) 122.0(2) Ru1-N6-C45 [c] 124.0(2) 127.1(2) 118.9(2) Ru1-N6-O2 [a] 123.7(2) 121.6(2) 118.6(2) O1-N5-C51 [b] 113. groups.…”

Nitrobenzene transformations in the carbonylation reaction in the presence of the PdCl2/Fe/I2/Py catalyst system

“…Catalytic activity in the reaction was found for rhodium [1][2][3], ruthenium [4][5][6], palladium [7][8][9][10] and selenium [11][12][13] compounds. The palladium catalysts, on account of their relatively lower price and a high activity and selectivity, arouse greater interest.…”

Harnessing the Power of the Water‐Gas Shift Reaction for Organic Synthesis

“…The generally accepted catalytic cycle, supported by the isolation of some reactive intermediates, [100] involves two sequential deoxygenation steps (Scheme 7). Following the formation of cycloadduct xviii between the nitro group and ligated CO decarboxylation produces the η 2 -nitrosoarene complex xix .…”