Intramolecular hydrogen bonding controls 1,3-N,S- vs. 1,5-S,S′-coordination in NiII complexes of N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)2

Reaction of the deprotonated N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)2 (R = Ph, HLI; 2-MeC6H4-, HLII; 2,6-Me2C6H3-, HLIII; 2,4,6-Me3C6H2-, HLIV; Me-, HLV) with NiII leads to complexes of the formula [NiLI-V2]. The molecular structures of the thioureas HLII-V and the complexes [NiLII-V2] in the solid were elucidated by single-crystal X-ray diffraction analysis. In the complexes, the metal is found to be in a square planar trans-N2S2 ([NiLII-IV2]) environment formed by the C[double bond, length as m-dash]S sulfur atoms and the P-N nitrogen atoms, or in a square planar trans-S2S"2 ([NiLV2]) environment formed by the C[double bond, length as m-dash]S and P[double bond, length as m-dash]S sulfur atoms of two deprotonated ligands. DFT calculations confirmed that the [Ni(LII-IV-N,S)2] isomers are more stable (by 16-21 kcal mol-1) than the corresponding [Ni(LII-IV-S,S[prime or minute])2] conformers. The main reason for higher stability of the 1,3-N,S vs. 1,5-S,S" isomers is the formation of intramolecular N-HS[double bond, length as m-dash]P hydrogen bonds. In solution the complexes [Ni(LII-V-N,S)2] have an exclusive 1,3-N,S coordination, while the compound [Ni(LI-N,S)2] exhibits two isomers in the 1H and 31P NMR spectra. The major species is assigned to the 1,3-N,S coordinated isomer, while the minor ([similar]25%) signals are due to the 1,5-S,S" isomer. UV-Vis spectroscopic results are in line with this. The electrochemical measurements reveal reversible one-electron reduction and irreversible oxidations, both assigned to ligand-centred processes.