Crucial Influence of the Intramolecular Hydrogen Bond on the Coordination Mode of RC(S)NHP(S)(OiPr)₂ in Homoleptic Complexes with Ni^II

Abstract

Reaction of the deprotonated N-thiophosphorylated thioureas RC(S)NHP(S)(OiPr) 2 [R = EtNH (HL I ), iPrNH (HL II ), Et 2 N (HL III ), 2,5-Me 2 C 6 H 3 NH (HL IV ), 4-Me 2 NC 6 H 4 NH (HL V )] with Ni II leads to complexes of the formula [NiL I-V 2 ]. The molecular structures of the complexes in the solid were elucidated by single-crystal X-ray diffraction analysis. In the complexes, the metal atom 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 SЈ 2 ([NiL I,III 2 ]) environment formed by the C=S and P=S sulfur atoms of two deprotonated ligands. Reaction of deprotonated N-thiophosphorylated thiourea HL V with NiCl 2 leads to violet [Ni(L-1,3-N,S) 2 ] or dark violet [Ni(L-1,5-S,SЈ) 2 ]· (CH 3 ) 2 C=O crystals that were isolated by recrystallization from a mixture of CH 2 Cl 2 or acetone, respectively, and nhexane. DFT calculations confirmed that the [Ni(L I,II,IV,V -[a] Institute of Condensed Matter and Nanosciences, 545 N,S) 2 ] conformers are more stable (by 5-7 kcal/mol) than [Ni-(L I,II,IV,V -S,SЈ) 2 ], whereas [Ni(L III -N,S) 2 ] is less stable (by 7-9 kcal/mol) than [Ni(L III -S,SЈ) 2 ]. The main reason for higher stability of the 1,3-N,S versus 1,5-S,SЈ isomers is the formation of intramolecular N-H···S=P hydrogen bonds. The same hydrogen bonds are impossible in complex [NiL III 2 ]. In solution, complex [NiL III 2 ] has revealed an exclusively 1,5-S,SЈ coordination, whereas compounds [NiL I,II,IV,V 2 ] reveal at least two isomers in the 1 H and 31 P{ 1 H} NMR spectra. The major species is assigned to the 1,3-N,S-coordinated isomer, and the minor signals are assigned to the 1,5-S,SЈ isomer, which was confirmed by UV/Vis spectroscopic results. The electrochemical measurements reveal reversible one-electron reduction and irreversible oxidations both assigned to ligand-centred processes. Ligand-based oxidation processes agree well with TD-DFT results.Eur. J. Inorg. Chem. 2013, 545-555 [NiL I,II,IV,V 2 ] contain the characteristic band for the alk-ylNH or arylNH group at 3138-3369 cm -1 . Furthermore, the spectrum of the acetone solvate [Ni(L V -1,5-S,SЈ) 2 ]· (CH 3 ) 2 C=O contains an intense band at 1702 cm -1 corresponding to the C=O group.The 31 P{ 1 H} NMR spectra of [NiL I,II,IV,V 2 ] in CDCl 3 are rather complicated and contain two signals at δ = 50.7-50.9 and 53.6-54.3 ppm for [NiL I,IV 2 ] and four signals at δ = 50.7-51.0, 53.5-54.4, 55.0-55.3 and 58.0-58.4 ppm for [NiL II,V 2 ]. The same was previously observed in the spectra of the complexes [Ni{RNHC(S)NP(S)(OiPr) 2 } 2 ] (R = tBu, Ad, Ph, 2-MeC 6 H 4 , 2,6-Me 2 C 6 H 3 , 2,4,6-Me 3 C 6 H 2 ) in CD 2 Cl 2 or CDCl 3 . [4d,8,10] The high-field signal corresponds to the trans-1,5-S,SЈ coordination, whereas the second signal is typical for the trans-1,3-N,S coordination of the deprotonated ligands. [4d,8,10] In view of the similar intensity and line width of the two low-field signals in the spectra of [NiL II,V 2 ], they are diastereot...

Influence of the Homopolar Dihydrogen Bonding CH⋅⋅⋅HC on Coordination Geometry: Experimental and Theoretical Studies

“…The 31 P{ 1 H} NMR spectrum of the raw material [NiL 2 ] in CDCl 3 contains a singlet at δ =52.3 ppm, which is in the characteristic region for the exclusive presence of diamagnetic 1,5‐ S , S′ ‐coordinated complex forms of the deprotonated N‐thiophosphorylated thioureas (NTTUs) [RR′NC(S)NP(S)(O i Pr) 2 ] − 22. Furthermore, a singlet in the 31 P{ 1 H} NMR spectrum testifies to the exclusive formation of one isomer, whereas the simultaneous presence of two or more isomers is reflected in several signals, as recently reported for complexes of the NTTU ligands with nickel(II)22b,c,e, 23 and palladium(II) 24. The 1 H NMR spectrum of the raw material in the same solvent contains one set of signals.…”

Chirality Control in Crystalline Ni(II) Complexes of Thiophosphorylated Thioureas

“…In addition, they have several donor atoms able to coordinate metal ions, thereby they can display a variety of coordination modes in the complexes with transition metals, depending on the intramolecular interactions and the corresponding preferable conformations. As it was shown in a series of publications [17][18][19][20][21][22][23][24][25], the most abundant coordination mode of thiophosphorylated thioureas is 1,5-S,S metal coordination with the formation of the six-membered metal containing cyclic fragments, while the 1,3-N,S mode is rare [12,20,24,26,27].…”

Chiral Thiophosphorylated Thioureas: Synthesis, Structure, and Cyclization Reaction

“…It is well known that thiophosphorylated thioureas are excellent complexing agents, which react with the transition metal salts to form a variety of chelate complexes . Generally, the complexation reaction is carried out in two stages.…”

“…Recently, thiophosphorylated thioureas attracted much attention because the introduction of the thiophosphoryl group into the molecule may add new properties, e.g., the ability to form hydrogen bonds or coordinate metals . These compounds are easily available by the addition of various amines to thiophosphoryl isothiocyanates.…”