Linkage isomerism in thiophene cyclometallated palladium(II) complexes.: Crystal and molecular structure of the isomers [Pd{n-SC4H2C(H)=NCy}-(O2CMe-O)(PPh3)] (n=3, 4)

Treatment of 2-SC4H3C(H)=NCy, a, or 3-SC4H3C(H)=NCy, b, with palladium(II) acetate in toluene gave the dinuclear cyclometallated complexes [Pd{n-SC4H2C(H)=NCy} (O2CMe)](2) (n = 5, 1a; n = 3, 1b; n = 4, 1b'), the latter two as a 1:1 mixture of linkage isomers, whose subsequent reactions produced isomeric mixtures in all cases. Reaction of la and 1b, 1b' with aqueous sodium chloride or bromide yielded the corresponding halide-bridged complexes [Pd{n-SC4H2C(H)=NCy}(X)](2) (n = 5: X = Cl, 2a; X = Br, 3a; n = 3,4: X = Cl, 2b, 2b'; X = Br, 3b, 3b') after metathesis. Reactions of the dinuclear compounds with tertiary phosphines in the appropriate molar ratio gave the mononuclear [Pd{n-SC4H2C(H)=NCy} (Cl)(PPh3)] (n = 5, 6a; n = 3, 4 4b, 4b') and [Pd{5-SC4H2C(H)=NCy}{(Ph2PCH2CH2)(2)PPh-P,P,P}](Cl), (5a), and the dinuclear [{Pd[5-SC4H2C(H)=NCy](O2CMe)}(2)-{mu-Ph2P)(CH2)(n)PPh2}] n = 2, 7a; n = 3, 8a; n = 4, 9a) complexes. The X-ray crystal structure of complex 4b, 4b' is described, establishing the presence of two isomers in the crystal lattice.