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An investigation of the coordination chemistry of N,N`-disubstituted sulfonylthiourea ligands with d⁶ and d⁸ transition metal centres.

The coordination chemistry of both square-planar and piano-stool metal complexes derived from an array of disubstituted sulfonylthiourea ligands with the d⁸ and d⁶ transition metal centres of nickel(II), palladium(II), platinum(II), gold(III) and ruthenium(II) was investigated. It was found that these ligands coordinate to the metal centre through both the S and N atoms of the thiourea moiety in a bidentate fashion, which is reminiscent of the coordination chemistry of traditional thiourea complexes. Square-planar d⁸ metal complexes derived from sulfonylthioureas were characterised by both single crystal XRD and ³¹P{¹H} NMR aided by ¹⁹⁵Pt coupling, to be in the distal isomer with no isomerisation detected. This is to say that the non-coordinated nitrogen atom of the core thiourea bears the sulfonyl group and is positioned away from the metal centre. This is in contrast to the coordination observed for the analogous acylthiourea complexes which tend to favour a bidentate S and O coordination mode through the acyl oxygen. This indicates the coordination mode observed for square-planar sulfonylthiourea complexes more closely resembles that of unsubstituted thioureas. Interestingly, single crystal XRD analysis of the piano-stool ruthenium complexes reveals the sulfonylthiourea ligand coordinated to the ruthenium metal centre in the unexpected proximal isomer. Comparison of this structure to some analogous piano-stool acylthiourea complexes show extremely similar structure and coordination and may indicate piano-stool structures derived from sulfonylthioureas resemble those of acylthioureas which in-turn is similar to the coordination mode adopted by simple thioureas. Moreover, through monitoring of the observed decomposition of Ni(II) and Pd(II) sulfonylthiourea complexes by ESI-MS and ³¹P NMR and the attempted synthesis of monodentate Au(I) phosphine sulfonylthiourea complexes, it was discovered that these complexes have a tendency to form stable trinuclear aggregates of the formula [M₃S₂L₃]⁺ (L = bidentate chelating ligand). The formation of these sulfide complexes is theorised to be a result of a hydroxide induced S-C bond cleavage promoted by the electron withdrawing sulfonyl subsistent. This observation matches closely to the well-known ability of thioureas to act as a source of sulfide upon reactions with metal ions.
Type of thesis
Risi, M. (2020). An investigation of the coordination chemistry of N,N`-disubstituted sulfonylthiourea ligands with d⁶ and d⁸ transition metal centres. (Thesis, Master of Science (Research) (MSc(Research))). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/14002
The University of Waikato
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