186594-22-9Relevant academic research and scientific papers
A Triad of Variable-Valent Rhenium Aldimine and Amide Systems Interrelated by Successive Oxygen Atom Transfer
Dirghangi, Bimal Kumar,Menon, Mahua,Pramanik, Amitava,Chakravorty, Animesh
, p. 1095 - 1101 (2008/10/09)
The title systems are ReVOCl3(RA), 1, ReIII(OPPh3)Cl3RA), 2, and Re(OPPh3)Cl3(RB), 3, where RA is a 2-pyridinecarboxaldimine, p-RC6H4N-CHC5H4N, and RB- is the corresponding 2-picolinamide, p-RC6H4NC(=O)C5H4N- (R = H, Me, OMe, Cl). Controlled reaction of ReOCl3(PPh3)2 with RA affords 1, which is converted to 2 upon reaction with PPh3. The oxidation of 2 in aqueous media by Ce4+ or H2O2 furnishes 3. The X-ray structure of 1 (R = Me) has revealed meridional ReCh geometry, the oxo atom lying trans to the pyridine nitrogen of chelated MeA. The metal atom is displaced by 0.35 A toward the oxo atom from the ReCl2N(aldimine) plane. The couples 2+/2 (E1/2 ～ 0.3 V vs SCE), 3+/3 (E1/2 ～ 1.3 V), and 3/3- (E1/2 ～ -0.5 V) are observable electrochemically. The conversion 1→- 2 follows a second-order rate law with a large and negative entropy of activation (～-40 eu). The reaction is proposed to proceed via nucleophilic attack by the phosphine on Re=O; the observed effects of R and phosphine variation on the rate are consistent with this. In the conversion of 2 to 3, the active species is 2+, the stoichiometry of the reaction being 32+ 4 H2O → 22 + 3 + 3H+. The amide oxygen in 3 originates from the water molecule. The reaction follows a second-order law, and the entropy of activation is large and negative, ～-30 eu. The rate-determining addition of water to the aldimine function is believed to afford an α-hydroxy amine intermediate which undergoes induced electron transfer and associated changes, affording 3. Crystal data for ReOCl3(MeA) are as follows: empirical formula C13H12Cl3N2ORe; crystal system triclinic; space group P1; a = 7.136(4) A, b = 8.329(5) A, c = 14.104(9) A, α = 73.88(5)°, β= 76.35(5)°, γ = 85.64(5)°; V = 782.5(8) A3; Z = 2.
