Thiosemicarbazonates of palladium(II): The presence of methyl/phenyl substituents (R2) at C2 carbon atom induces C–H activation of R1 rings of thiosemicarbazones {R1R2C2double bond; length as m-dashN3–N2H–C1(double bond; length as m-dashS)–N1HR3}

A series of palladium(II) complexes involving C–H and N–H bond activations of the R1 rings of thiosemicarbazones {R1(R2)C2–N3–N2(H)–C1(double bond; length as m-dashS)–N1HR3; R1, R2: thiopheneyl, Me, H2L1 (R3 = Me), H2L2 (R3 = Ph); R1, R2: Ph, Me, H2L3 (R3 = Me), H2L4 (R3 = Ph); R1, R2: Ph, Ph, H2L5 (R3 = Me), H2L6 (R3 = Ph) and R1, R2: pyrrole, Me, H2L7 (R3 = Me), H2L8 (R3 = Ph)} are described. Methyl group (R2) at C2 carbon in H2L1 and H2L2 induced C–H bond activation of the thiopheneyl ring and formed cyclometallated complexes, [Pd(κ3–C4,N3,S–L)(PPh3)] (L = L1, 1; L2, 2). Similarly, phenyl rings (R1) in H2L3, H2L4, H2L5, H2L6 at C2 carbon have shown C–H activations forming cyclometallated complexes, [Pd(κ3–C4,N3,S–L)(PPh3)] (L = L3, 3; L4, 4; L5, 5; L6, 6). However, pyrrole ring did not exhibit similar C–H activation behavior, rather involved N–H activation and formed complexes, [Pd(κ3–N4,N3,S–L)(PPh3)] {L = L7, 7; L8, 8}. All these complexes have been characterized with the help of analytical data, spectroscopic techniques (IR, 1H and 31P NMR), and single crystal X-ray crystallography (1, 2, 4, 5, 7 and 8). The thiosemicarbazone ligands behave as dinegative C4, N3, S-chelating in 1–6 and N4, N3, S-chelating in complexes 7 and 8. Interestingly, complexes 2, 4 and 8, with phenyl substituent at N1 atom, have two independent molecules in their respective crystal lattices.