Unexpectedly efficient activation of push-pull nitriles by a Pt-II center toward dipolar cycloaddition of Z-nitrones

作者：Kritchenkov Andreii S; Bokach Nadezhda A^*; Haukka Matti; Kukushkin Vadim Yu

来源：Dalton Transactions, 2011, 40(16): 4175-4182.

DOI：10.1039/c0dt01689f

Pt-II-coordinated NCNR'(2) species are so highly activated towards 1,3-dipolar cycloaddition (DCA) that they react smoothly with the acyclic nitrones ArCH = N+(O-)R '' (Ar/R '' = C6H4Me-p/Me; C6H4OMe-p/CH2Ph) in the Z-form. Competitive reactivity study of DCA between trans-[PtCl2(NCR)(2)] (R= Ph and NR'(2)) species and the acyclic nitrone 4-MeC6H4CH = N+(O-)Me demonstrates comparable reactivity of the coordinated NCPh and NCNR'(2), while alkylnitrile ligands do not react with the dipole. The reaction between trans-[PtCl2(NCNR'(2))(2)] (R'(2) = Me-2, Et-2, C5H10) and the nitrones proceed as consecutive two-step intermolecular cycloaddition to give mono-(1a-d) and bis-2,3-dihydro-1,2,4-oxadiazole (2a-d) complexes (Ar/R '' = p-tol/Me: R'(2) = Me-2 a, R'(2) = Et-2 b, R'(2) = C5H10 c; Ar/R '' = p-MeOC6H4/CH2Ph: R'(2) = Me-2 d). All complexes were characterized by elemental analyses (C, H, N), high resolution ESI-MS, IR, H-1 and C-13{H-1} NMR spectroscopy. The structures of trans-1b, trans-2a, trans-2c, and trans-2d were determined by single-crystal X-ray diffraction. Metal-free 5-NR'(2)-2,3-dihydro-1,2,4-oxadiazoles 3a-3d were liberated from the corresponding (dihydrooxadiazole)(2)Pt-II complexes by treatment with excess NaCN and the heterocycles were characterized by high resolution ESI+-MS, H-1 and C-13{H-1} spectroscopy.

• 出版日期2011