Palladium(II) complexes derived from the potentially chelating ligands 2,2,NN-tetramethylpent-4-enylamine and 2,2-dimethylpent-4-enyl methyl sulphide. Crystal structures of dichloro[2,2-dimethylpent-(E)-3-enyl methyl sulphide]palladium(II) and chloro[1–3-η-syn-1-(1,1′-dimethyl-2′-methylthioethyl)allyl]palladium(II)

Abstract

Reaction of PdX₂·2PhCN(X = Cl or Br) with 2,2,NN-tetramethylpent-4-enylamine (1a) gives complexes (2) of stoicheiometry PdX₂·(1a) in which Pd–X has added to the olefinic bond to generate a seven-membered chelate ring. In contrast, 2,2-dimethylpent-4-enyl methyl sulphide (1b) initally gives labile olefinic complexes, which readily rearrange to the derivatives (5a) and (5b) of 2,2-dimethylpent-(E)-3-enyl methyl sulphide (13). Variable-temperature ¹H n.m.r. studies show that at low temperatures (5a) and (5b) exist in solution as pairs of epimers at sulphur, while heating leads first to equilibration of the epimers and then to labilisation of the metal–olefin bond. The π-allyl species (6a) and (6b) have been prepared from (5a) and (5b). X-Ray structures of (5a) and (6a) are reported. Crystals of (5a) are monoclinic, space group P2₁/n with Z= 4 in a unit cell of dimensions a= 8.365(2), b= 15.068(2), c= 9.595(1)Å, and β= 94.00(1)°. Crystals of 6(a) are monoclinic, space group P2₁/c, with Z= 4 in a unit cell of dimensions a= 6.583, b= 12.462, c= 12.859(6)Å, and β= 96.20(5)°. Both structures have been solved by the heavy-atom method and refined by full-matrix least-squares calculations to R= 0.023 for 2 414 reflections for (5a) and to R= 0.046 for 2 515 reflections for (6a). The five-membered chelate rings in (5a) and(6a) have C(2)-envelope conformations. In (5a) principal dimensions are Pd–Cl 2.313 and 2.320(1), Pd–S 2.269(1), and Pd–C 2.195 and 2.231(3)Å, and the interplanar angle between the PdCl₂S plane ad the Pd–ethylenic carbon plane is 96.0°. In (6a) dimensions are Pd–Cl 2.381(1), Pd–S 2.364(1), Pd–C 2.089, 2.120, and 2.173(5)Å; the plane of the allyl moiety forms a dihedral angle of 116.4° with the PdSCIC(5) plane.