Solution behavior of half sandwich ruthenium(II) complexes ligated by sym N,N'-diarylthiourea: Structural aspects and temperature dependent NMR

Abstract

The bridge-splitting reaction of [(η6-C10H14)RuCl(μ-Cl)]2 (η6-C10H14 = η6-p-cymene) with sym N,N′-diarylthiourea (2 equiv.), (ArNH)2C=S in toluene at room temperature afforded [(η6-C10H14)RuCl2{(S)C(NHAr)2}]⋅xH2O (sym = symmetrical; Ar = C6H5 (1), 2-MeC6H4 (2), 2,4-Me2C6H3 (3), 2,5-Me2C6H3 (4), 2,6-Me2C6H3 (5), and 2,6-iPr2C6H3 (6); x = none (1–2, and 4–6) and 1 (3)) in 86%−95% yields. However, the aforementioned reaction afforded [(η6-C10H14)RuCl{(S)C(NHAr)2}2]+[(ArNH)2C(S)⋅Cl]–⋅toluene (Ar = 2,6-Me2C6H3; 7) in 90% yield when carried out with four equiv of (ArNH)2C=S. The mode of coordination in all the Ru(II) complexes was confirmed by spectroscopic methods and X-ray crystallography. In solution, complexes 2 and 7 exhibited two isomers in about 2:1 and 1:0.15 ratios respectively and confirmed by a temperature dependent 1H NMR spectral titration. The spectral pattern was attributed to the rotation through C−N(H)Ar single bond of thiourea in 2 and sulfur inversion of one of the coordinated thiourea in 7. Various reasons that are responsible for the presence of two isomers for 2 and 7 in solution have been discussed.