138753-51-2Relevant 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.
Cyclopalladation of N-mesitylbenzylideneamines. Aromatic versus aliphatic C-H activation
Albert, Joan,Ceder, Rosa Maria,Gómez, Montserrat,Granell, Jaume,Sales, Joaquim
, p. 1536 - 1541 (2008/10/08)
The action of Pd(AcO)2 on the imines 2,4,6-(CH3)3C6H2CH=N(CH 2)n-2′-RC6H4 (R = H, n = 0-2 (1a-c); R = CH3, n = 1 (1d)), in refluxing acetic acid, affords six-membered endo metallacycles possessing an aliphatic carbon-metal bond, in preference to four-, five-, or six-membered exo metallacycles with an aromatic carbon-metal bond. The five-membered exo metallacycles can be obtained by working under milder conditions and isomerize to the more stable six-membered endo metallacycles in refluxing acetic acid. The action of Pd(AcO)2 on the imines 2-CH3-3-R1-4-R2C6H 2CH=NC6H5 (R1 = H, R2 = CH3 (1f); R1 = CH3, R2 = CH3O (1g)) affords the five-membered endo metallacycles with an aromatic carbon-metal bond, but with the imine 2,5-(CH3)2C6H3CH=NC 6H5 (1e) the methyl group at carbon 5 prevents the metalation of the ortho carbon atom and the endo six-membered metallacycle with an aliphatic carbon-metal bond is formed. The reasons for the preference to form endo compounds and the high stability of six-membered derivatives containing Pd-C benzylic bonds are discussed.
