Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula RC(S)NHP(S)(OiPr)(2) [R = morpholin-N-yl (HL(a)), piperidin-N-yl (HL(b)), NH(2) (HL(c)), PhCH(2)NH (HL(d))] with Cu(PPh(3))(3)I in aqueous EtOH/CH(2)Cl(2) leads to mononuclear [Cu(PPh(3))(2)L-S,S'] complexes. Using copper(i) iodide instead of Cu(PPh(3))(3)I, polynuclear complexes [Cu(n)(L-S,S')(n)] were obtained. The structures of these compounds were investigated by ES-MS, elemental analyses, 1H and 31P NMR in solution, IR and 31P solid-state MAS NMR spectroscopy. The crystal structures of [Cu(3)L(3)(a)] and [Cu(PPh(3))(2)L(b)] were determined by single-crystal X-ray diffraction.

Anagostic C−H•••M (M = a metal center) intramolecular interactions, one of the most fundamental and elusive forces in organometallic chemistry, are intuitively considered as repulsive and purely electrostatic in nature because of significant metal−hydrogen distances (∼2.3−3.0 Å). Contrary to the current state of knowledge, it is shown herein by quantum chemical computations based on the case study of new square-planar Ni II isomers based on Nthiophosphorylated thiourea that despite significant metal− hydrogen anagostic distances, the covalent-type charge delocalization contribution [Ni(d z 2 ) → σ*(C−H) and σ(C− H) → Ni(d z 2)] exists and it covers, together with the London dispersion energy, up to ∼40% of the overall anagostic stabilization. This charge delocalization component is found to amplify the metalloaromaticity phenomenon although a lack of any stabilizing charge transfer is expected at such long metalhydrogen distances (>3 Å). Remarkably, for the relatively short regime (<3 Å) of anagostic distances, the electrostatic Coulomb forces are destabilizing, which leads to the repulsive anagostic interactions, whereas, surprisingly, an increase of anagostic distance above 3 Å makes anagostic interactions stabilizing mostly because of attractive Coulomb forces. It shows unprecedented agostic (attractive) ↔ anagostic (repulsive) transitions in ubiquitous d 8 square-planar Ni II complexes containing elongated metal−hydrogen distances.

Reaction of the deprotonated N-thiophosphorylated thioureas RNHC(S)NHP(S)(OiPr)(2) (R = Ph, HL(I); 2-MeC(6)H(4)-, HL(II); 2,6-Me(2)C(6)H(3)-, HL(III); 2,4,6-Me(3)C(6)H(2)-, HL(IV); Me-, HL(V)) with Ni(II) leads to complexes of the formula [NiL(I-V)(2)]. The molecular structures of the thioureas HL(II-V) and the complexes [NiL(II-V)(2)] 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-N(2)S(2) ([NiL(II-IV)(2)]) environment formed by the C=S sulfur atoms and the P-N nitrogen atoms, or in a square planar trans-S(2)S'(2) ([NiL(V)(2)]) environment formed by the C=S and P=S sulfur atoms of two deprotonated ligands. DFT calculations confirmed that the [Ni(L(II-IV)-N,S)(2)] isomers are more stable (by 16-21 kcal mol(-1)) than the corresponding [Ni(L(II-IV)-S,S')(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-H···S=P hydrogen bonds. In solution the complexes [Ni(L(II-V)-N,S)(2)] have an exclusive 1,3-N,S coordination, while the compound [Ni(L(I)-N,S)(2)] exhibits two isomers in the (1)H and (31)P NMR spectra. The major species is assigned to the 1,3-N,S coordinated isomer, while the minor (∼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.

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