143238-07-7Relevant academic research and scientific papers
Exchange reaction of bridging acetate ligands and reversible electrophilic rhodium-carbon activation in ortho-metalated rhodium (II) compounds with acetic acid. Kinetic study of the exchange reaction of acetates with CD3CO2D in the compound Rh2(O2CCH3)3[(C6H 4)P(C ...
Lahuerta,Peris
, p. 4547 - 4551 (2008/10/08)
Full title: Exchange reaction of bridging acetate ligands and reversible electrophilic rhodium-carbon activation in ortho-metalated rhodium (II) compounds with acetic acid. Kinetic study of the exchange reaction of acetates with CD3CO2D in the compound Rh2(O2CCH3)3[(C6H 4)P(C6H5)2]·2HO 2CCH3. Stepwise exchange reactions of CH3CO2- groups by CD3CO2- groups are observed for Rh2(O2CCH3)3[(C6H 4)P(C6H5)2]·2HO 2CCH3 in CHCl3/CD3CO2D mixtures. The first reaction step involves a fast exchange of the acetate group trans to the metalated phosphine as well as exchange of the two axial molecules of acetic acid. In a second and slower step the exchange of the acetate groups cis to the metalated phosphine occurs. The kinetics of the second process has been studied by 1H NMR spectroscopy using different CHCl3/CD3CO2D mixtures as reaction solvents. The kinetic data follow a two-term rate law, v = [k1 + k2[CD3CO2D]1/2][Rh2]. The first-order constant k1 at 298 K is (2.08 ± 0.02) × 10-6 s-1 (ΔH? = 98 ± 5 kJ mol-1; ΔS? = 45 ± 20 J K-1 mol-1), and the second-order rate constant at the same temperature is k2 = (3.83 ± 0.01) × 10-6 s-1 M-1/2 (ΔH? = 103 ± 5 kJ mol-1; ΔS? = -15 ± 15 J K-1 mol-1). Electrophilic attack at one oxygen atom of the bridging acetate group by a proton of acetic acid is concluded to be the first and rate-determining step of the exchange process. The axially coordinated acetic acid is likely responsible for the intramolecular attack. Very fast exchange of all the CH3CO2- groups by CD3CO2- is observed for the compound Rh2(O2CCH3)2[(C6H 4)P(C6H5)2] 2·2HO2CCH3 in the presence of CD3CO2D. The partially deuterated compound Rh2(O2CCH3)3[(C6D 4)P(C6D5)2]·2HO 2CCH3 undergoes 90% D-H exchange at the ortho position of the phenyl rings of the phosphine after 3 h of reflux in acetic acid. Much slower exchange is observed for Rh2(O2CCH3)2[(C6D 4)P(C6D5)2] 2·2HO2CCH3 in the same conditions. The observed D-H exchange is explained by an electrophilic attack at the rhodium-carbon bond by acetic acid, which produces the protonation of the ortho aromatic carbon atom, followed by a cyclometalation at one of the ortho C-H bonds.
