Platinum(II), palladium(II), and nickel(II) complexes of bisthiourea ligands

Abstract A series of alkyl-bridged bisthiourea ligands and their group 10 complexes, of the types [Pt2{(SC(NPh)NHC6H4)2CH2}(PPh3)4]·2BPh4, [M2{(SC(NPh)NHC6H4)2CH2}(dppe)2]·2BPh4 (M = Pd, Ni), [Pt2{SC(NPh)NH}2(CH2)n(PPh3)4]·2BPh4 (n = 4, 6, 8, 12), and [M2{SC(NPh)NH}2(CH2)4(dppe)2]·2BPh4 (M = Pd, Ni) have been synthesised, where dppe = Ph2PCH2CH2PPh2. The ESI mass spectral analysis of the complexes showed the presence of monochelated and dichelated species, with respectively one or two metal centres coordinated to the bisthiourea. Increasing the molar ratio of the metal precursor and reaction time (from 2 to 8 hours) resulted in the disappearance of the monochelated species from the ESI mass spectra of the platinum complexes. 31P{1H} NMR characterisation of the diarylmethane-bridged bisthiourea complexes [M2{(SC(NPh)NHC6H5)2CH2}L4]·2BPh4 (M = Pt, Pd, Ni; L = PPh3 or L2 = dppe) showed complex multiplets indicative of the formation of several isomers of the products. In contrast, the complexes with bridging alkylene chains showed only a single isomer in solution, and X-ray crystallographic studies on several derivatives confirmed the formation of a four-membered M-S-C-N ring involving the chelating thiourea monoanions, with a coordinated NPh group in each case. The cytotoxicities of the ligands and metal complexes towards HepG2 and DLD-1 cell lines are also reported.