210693-70-2Relevant academic research and scientific papers
Synthesis of Palladium Complexes with ortho-Functionalized Aryl Ligands
Vicente, José,Abad, José-Antonio,Martínez-Viviente, Eloísa,Ramírez De Arellano, M. Carmen,Jones, Peter G.
, p. 752 - 760 (2008/10/08)
The complexes [Pd(C6H4X-2)BrL2] (L2 = trans-(PR3)2, R = Ph, X = CH=CH2 (1a), CHO (1b), C(O)Me (1c), CN (1d); R = p-To = 4-tolyl, X = CH=CH2 (1a′); L2 = bpy = 2,2′-bipyridine, X = CHO (2b), C(O)Me (2c), CN (2d); L2 = tmeda = N,N,N′,N′-tetramethylethylenediamine, X = CHO (2b′), CN (2d′)) have been prepared by oxidative addition of the corresponding bromoarene BrC6H4X-2 to "Pd(dba)2" (=[Pd2(dba)3]·dba, dba = dibenzylideneacetone) in the presence of the appropriate ligand. The compound [Pd{C6H4(CH=CH2)-2}(bpy)(PPh3)]TfO (3a; TfO = CF3SO3) has been obtained by reacting 1a with bpy in the presence of TlOTf. The cyclopalladated [Pd{κ2-C,O-C6H4{C(O)Me}-2}(bpy)]TfO (4c) has been prepared from 2c and TlOTf. The dimeric complexes [Pd(μ-Br)(C6H4X-2)(PR3)]2 (R = Ph, X = CHO (5b), C(O)-Me (5c), CN (5d); R = o-To = 2-tolyl, X = CHO (5b″), CN (5d″)) have been synthesized by reacting complexes 1b-d with [PdCl2(NCPh)2] in a 2:1 molar ratio or C6H4Br-1-X-2 with "Pd(dba)2" and P(o-To)3 in 1:1:1 molar ratio. The latter method leads to the monomeric [Pd{κ2-C,O-C6H 4{C(O)Me}-2})Br{P(o-To)3}] (6c″) when X = C(O)Me. The complex 2c reacts with the alkyne PhC≡CPh or EtC≡CEt and TlOTf to give 1-methyl-2,3-diphenyl-1H-indenol (7) or 1-methyl-2,3-diethyl-1H-indenol (8), respectively. The crystal structures of complexes 1a·2CH2Cl2, 1b·CH2Cl2, 2b,d, and 6c″ have been determined by X-ray diffraction studies. An interesting supramolecular layered structure is formed through CN. . .H-Cbpy and Br. . .H-Cbpy hydrogen bonds in complex 2d.
Electronic dependence of C-O reductive elimination from palladium (aryl)neopentoxide complexes
Widenhoefer, Ross A.,Buchwald, Stephen L.
, p. 6504 - 6511 (2007/10/03)
Thermal decomposition of the palladium (aryl)neopentoxide complexes [P-P]Pd(Ar)OCH2CMe3 [P-P =Tol-BINAP or BINAP; Ar p-C6H4CHO (1b), p-C6H4COPh (1c), p-C6H4NO2 (1d), o-C6H4NO2 (1e), o-C6H4CN (1F)] possessing substituents on the palladium-bound aryl group suitable for delocalization of negative charge led to quantitative (≤95%) formation of aryl ether without detectable β-hydride elimination. Thermal decomposition of 1b-f obeyed first-order kinetics, and the rate of reductive elimination decreased in the order o-NO2 > p-NO2 > p-CHO > p-COPh > o-CN. Conversely, thermal decomposition of the related derivatives [P-P]Pd(Ar)OCH2CMe3 [P-P = Tol-BINAP or BINAP; Ar p-C6H4Cl (1g), m-C6H4NO2 (1h), m-C6H4CN (1i)] which did not possess a resonance stabilizing group on the palladium-bound aryl group led to no detectable formation of aryl ether. These and related data point to the buildup of negative charge in the palladium-bound aryl group in the transition state for C-O reductive elimination and are consistent with a mechanism initiated by inner-sphere nucleophilic attack of the alkoxide ligand at the ipso-carbon atom of the palladium-bound aryl group through a zwitterionic Meisenheimer-type intermediate or transition state.
