148051-65-4Relevant academic research and scientific papers
Rigid five- and six-membered C,N,N′-bound aryl, benzyl, and alkyl organopalladium complexes: sp2 vs sp3 C-H activation during cyclopalladation and palladium (IV) intermediates in oxidative addition reactions with dihalogens and alkyl halides
Alsters, Paul L.,Engel, Pim F.,Hogerheide, Marinus P.,Copijn, Marc,Spek, Anthony L.,Van Koten, Gerard
, p. 1831 - 1844 (2008/10/08)
The synthesis of new terdentate C,N,N′-bound aryl, benzyl, and alkyl organopalladium compounds (N,N′ is -CH2N(Me)CH2CH2NMe2 or -CH2N(CH2CH2)2NMe) via cyclopalladation is reported. X-ray crystal structure determinations of [PdI{C6H4(CH2N(Me)CH2CH 2NMe2)-2}] (2c) and [PdI{CH2C6H2(CH2N(Me)CH 2CH2NMe2)-2-Me2-3,5}] (3c) have been carried out By suitable ligand design, the palladation can be directed toward sp2 or sp3 C-H activation and toward five-membered or six-membered ring formation. A study of coordination adducts of the bidentate N2 part of the terdentate C,N,N′ ligands with PdX2 has revealed that the C-H bond activation likely proceeds via loss of an acido anion (X) to an electron-deficient, cationic 14-electron species [C,N,N′PdX] that subsequently attacks an intramolecular C-H bond via an in-plane interaction. The crystal structure of the PdI2 coordination adduct of N-(2-iodobenzyl)-N,N′ ,N′ -trimethylethane-1,2-diamine (7e) shows an oblique, above-plane approach of the aryl ring toward the metal center with the C-H bond in the ortho position wih respect to the ethylenediamme unit pointing toward an iodine atom, the hydrogen atom being involved in short nonbonding contacts with both this iodine atom (3.02(2) ?) and the palladium center (2.97(2) ?). Crystals of 2c are orthorhombic, space group Pnaa, a = 8.5216(3) ?, b = 17.6034(5) ?, c = 18.8696(8) ?, Z = 8, R = 0.038 for 2677 observed reflections with I > 2.5σ(I) and 157 parameters. Crystals of 3c are monoclinic, space group P21/c, a = 9.506(1) ?, b = 13.582(1) ?, c = 13.148(1) ?, β = 91.36(4),°, Z = 4, R = 0.021 for 3326 observed reflections with I > 2.5σ(I) and 249 parameters. Crystals of 7e are triclinic, space group P1, a = 8.545(1) ?, b = 8.797(1) ?, c = 13.829(1) ?, α = 81.77(1)°, β = 75.47(1)°, γ = 63.33(1)°, Z = 2, R = 0.064 for 2810 observed reflections with I > 2.5σ(I) and 175 parameters. A conformational analysis of 7e by means of 1H NMR spectroscopy showed that the solid-state structure is likely retained to a large extent in solution. Based on sp2/sp3 C-H activation competition in two ligands, it is concluded that this approach may be responsible for the generally easier palladation of aryl rings compared to alkyl groups. The use of these rigid C,N,N′-bound palladium complexes in controlling their behavior in oxidative addition/reductive elimination reactions is exemplified by the detection of an unusually stable organometallic Pd(IV) dichloride adduct and by the use of a C,N,N′ group as spectator ligand in oxidative addition/reductive elimination reactions with alkyl halides.
