138459-71-9Relevant academic research and scientific papers
Mechanism of the Acid-catalysed Cyclometallation Reaction of Dirhodium(II) Compounds with General Formula (OH2)>
Gonzalez, Gabriel,Lahuerta, Pascual,Martinez, Manuel,Peris, Eduardo,Sanau, Mercedes
, p. 545 - 550 (2007/10/02)
Compounds of general formula (OH2)> 2 (X = H, p-Me, p-Cl, m-Me or m-Cl) have been prepared by photochemical reaction of the corresponding adduct (HO2CMe)> 1.These compounds contain one equatorial phosphine which undergoes a facile cyclometallation reaction, catalysed in the presence of protic acids, to give doubly metallated compounds (HO2CMe)2> 3.The kinetics and mechanism of this cyclometallation have been studied in chloroform and toluene solutions.A mechanism in which protons facilitate loss of one of the acetate groups in the starting compounds is proposed.Preliminary experiments showed that the addition of phosphines enhances the cyclometallation rate.The mechanism is fully concerted with a highly ordered transition state as seen by the very negative activation entropies.The values obtained for the deuterium kinetic isotopic effect indicate that, for the acid-catalysed path, the transition state lies in a more advanced position on the reaction coordinate than for the thermal process.The gap between the isokinetic plots for the acid-catalysed and thermal reactions is ca. 20 kJ mol-1.
Fast ortho-metalation reactions in binuclear dirhodium compounds. Syntheses and molecular structures of a monometalated compound and two doubly metalated compounds with head-to-head configurations
Lahuerta, Pascual,Payá, Jorge,Pellinghelli, Maria Angela,Tiripicchio, Antonio
, p. 1224 - 1232 (2008/10/08)
The reactions of Rh2(O2CCH3)4(MeOH)2 and triphenylphosphine, in 1:4, 1:2, and 1:1 molar ratios, have been spectroscopically studied using different reaction conditions. Very reactive intermediate products, Rh2(O2CCH3)3[(C6H 4)PPh2](HO2CCH3)2 (1(HO2CCH3)2) and Rh2(O2CCH3)3[(C6H 4)PPh2][PPh3](HO2CCH3) (2(HO2CCH3)) have been isolated. The structure of 1(HO2CCH3)2 has been determined by X-ray diffraction. Crystal data: space group P1, a = 9.807 (6) ?, b = 19.822 (10) ?, c = 8.476 (5) ?, α = 80.10 (2)°, β = 111.02 (2)°, γ = 93.67 (2)°, Z = 2, 3374 reflections, R = 0.0289. 1(HO2CCH3)2 readily reacts with an excess of triphenylphosphine at room temperature to form the already reported doubly metalated compound Rh2(O2CCH3)2[(C6H 4)PPh2]2(PPh3)2 (3(PPh3)2) with a head-to-tail structure. However under thermal conditions 1(HO2CCH3)2 reacts with excess of triphenylphosphine giving in addition to 3(PPh3)2, Rh2(O2CCH3)2[(C6H 4)PPh2]2(PPh3)(HO 2CCH3) (4-(PPh3,HO2CCH3)), a doubly metalated compound with the orthometalated ligands in a head-to-head configuration. The structure of the closely related bis(acetic acid) adduct Rh2(O2CCH3)2[(C6H 4)PPh2]2(HO2CCH3) 2 (4(HO2CCH3)2) has been determined by X-ray diffraction. Crystal data: space group C2/c, a = 23.443 (9) ?, b = 19.868 (8) ?, c = 20.158 (9) ?, β = 106.60 (2)°, Z = 8, 4873 reflections, R = 0.0451. The same mixture of compounds is formed from the reaction of Rh2(O2CCH3)4(MeOH)2 and a 4-mol excess of PPh3 in refluxing acetic acid. Para-substituted triarylphosphines P(p-XC6H4)3 (X = CH3, Cl) behave in a similar way, yielding a mixture of compounds with head-to-tail and head-to-head configurations. The structure of the compound Rh2(O2CCH3)2[(ClC6H 3)P(p-ClC6H4)2]2(HO 2CCH3)2 (8(HO2CCH3)2), having a head-to-head configuration, has been determined by X-ray diffraction. Crystal data: space group C2/c, a = 36.063 (9) ?, b = 16.558 (6) ?, c = 23.531 (8) ?, β = 125.34 (2)°, Z = 8, 4316 reflections, R = 0.0525. Two different reaction pathways are proposed to justify this chemical behavior.
