95029-14-4Relevant academic research and scientific papers
Solution Behaviour, Kinetics and Mechanism of the Acid-Catalysed Cyclopalladation of Imines
Gomez, Montserrat,Granell, Jaume,Martinez, Manuel
, p. 37 - 44 (2007/10/03)
The cyclometallation reactions of N-benzylidene-benzylamines, -anilines and -propylamine with palladium acetate have been studied in acetic acid solution.Carbon-hydrogen electrophilic bond activation occurs to produce different types of metallacycles, given the polyfunctional nature of the ligands selected.The cyclometallated compounds formed indicate that the stability of the final species is, with respect to the activated C-H bond, in the order: five-membered aromatic endo > six-membered aliphatic endo > five-membered aromatic exo, >>> five-membered exo, four-membered.The nature of the final cyclometallated compounds in acetic acid solution has been ascertained via 1H NMR spectroscopy; as a whole the spectra are complex, indicating that the nature of the cyclometallated species in solution is not simple, and that a wide variety of compounds is present depending on the imine used.The metallation reactions have been monitored kinetically via UV/VIS spectroscopy at different temperatures and pressures in order to establish the mechanism through which these acid-assisted reactions occur.Although the thermal activation parameters cover a wide range of values (ΔH(excit.) = 49 to 73 kJ mol-, ΔS(excit.) = -52 to -138 J K-1 mol-1), the activation volume is in a very narrow range, -15 +/- 3 cm3 mol-1.The results are interpreted as the formation of a highly ordered four-centred transition state, involving the C-H and Pd-O (acetato) bonds, which is found to be very sensitive to the presence of any protons that could enhance the leaving-group characteristics of the MeCO2H ligand, converting it into its protonated MeCO2H2+ form.
Five- and six-membered exo-cyclopalladated compounds of N-benzylideneamines. Synthesis and X-ray crystal structure of [PdBr{p-MeOC6H3(CH2) 2N=CH(2,6-Cl2C6H3)}(PPh 3)] and [PdBr{C6H4CH2N=CH(2,6-Cl2C 6H3)}(PEt3)2]
Albert, Joan,Gómez, Montserrat,Granell, Jaume,Sales, Joaquim,Solans, Xavier
, p. 1405 - 1413 (2008/10/08)
The reaction of N-(2,6-dichlorobenzylidene)amines, 2,6-Cl2C6H3CH=N(CH2) nC6H4-p-R (n = 1, 2; R = H, MeO), with Pd(AcO)2 in refluxing acetic acid has been studied. With N-benzylidenebenzylamines (n = 1) exo five-membered derivatives were obtained. From N-benzylidene(2-phenylethyl)amines (n = 2) endo five-membered cyclopalladated compounds were formed by oxidative addition of C-Cl bonds of the ligand to Pd(0) formed in situ. Under milder conditions (acetic acid at 80°C) the exo six-membered compound [Pd(AcO){p-MeOC6H3(CH2) 2N=CH(2,6-Cl2C6H3)}]2 was obtained. All exo derivatives contain the imine ligand in the syn form. By reaction with PR3 (R = Et, Ph), monophosphine complexes [PdX(CN)(PR3)] and bisphosphine derivatives [PdX(CN)(PR3)2], where the Pd-N bond has been broken, can be obtained. [PdBr{p-MeOC6H3(CH2) 2N=CH(2,6-Cl2C6H3)}(PPh 3)] (6f) crystallizes in the monoclinic space group P21/n with a = 20.321 (4) A?, b = 12.561 (3) A?, c = 12.608 (3) A?, β = 97.50 (2)°, and Z = 4. The exo six-membered ring displays a boat conformation with Pd and C(7) atoms out of the plane defined by the remaining atoms. [PdBr{C6H4CH2N=CH(2,6-Cl2C 6H3)}(PEt3)2] (9c) has been characterized by X-ray crystallography; it crystallizes in the monoclinic space group P21/a with a = 45.352 (6) A?, b = 8.884 (2) A?, c = 7.556 (2) A?, β = 99.02 (3)°, and Z = 4. The Pd atom has a roughly planar coordination, and the imine ligand is in the anti form.
