Observation of an Unusual Molecular Switching Device. The Position of One 1,2-Dimethylimidazole Switched “On” or “Off” the Rotation of the Other 1,2-Dimethylimidazole in cis,cis,cis-Ru^IICl₂(Me₂SO)₂(1,2-dimethylimidazole)₂

Abstract

Some cis,cis,cis-RuX(2)(Me(2)SO)(2)(1,2-Me(2)Im)L complexes [L = 1,2-Me(2)Im (1,2-dimethylimidazole) or Me(3)Bzm (1,5,6-trimethylbenzimidazole), X = Cl or Br, and Me(2)SO = S-bonded DMSO] have been synthesized and their rotamers studied in CDCl(3). From 2D NMR data, cis,cis,cis-RuCl(2)(Me(2)SO)(2)(1,2-Me(2)Im)(Me(3)Bzm) has 1,2-Me(2)Im in position "a" (cis to both Me(2)SO's and cis to "b") and Me(3)Bzm in position "b" (trans to one Me(2)SO and cis to the other). There are two stable atropisomers [head-to-tail (HT, 84%) and head-to-head (HH, 16%), defining the aromatic H of Ru-N-C-H as head for both ligands]. Me(3)Bzm has the same orientation in both atropisomers. In this orientation, the unfavorable interligand steric interactions of Me(3)Bzm with the Me(2)SO and 1,2-Me(2)Im ligands appear to be countered by favorable electrostatic attraction between the delta+ N(2)CH moiety of Me(3)Bzm and the delta- cis Cl ligands. The 1,2-Me(2)Im lacks a delta+ N(2)CH group, and its orientation is dominated by steric effects of the 2-Me group. The NMR spectrum of cis,cis,cis-RuCl(2)(Me(2)SO)(2)(1,2-Me(2)Im)(2) is consistent with four rotamers in restricted rotation about both Ru-N bonds: two HH and two HT. 2D NMR techniques (NOESY and ROESY) afforded complete proton signal assignments. The ligand disposition could be assessed from the large chemical shift dispersion of some 1,2-Me(2)Im ligand signals (Delta 0.86-1.52 ppm) arising from cis-1,2-Me(2)Im shielding modulated by deshielding influences of the cis halides. The relative stability of the four rotamers correlates best with steric interactions between the 2-Me groups and the Me(2)SO ligands. The most favorable conformer (46%) is the HH rotamer with both 2-Me groups pointing away from the Me(2)SO ligands. The least favorable conformer (14%) was also HH, but the methyl groups in this case point toward the Me(2)SO ligands. In the HT conformers of intermediate stability ( approximately 20%), one 2-Me group is toward and the other is away from the Me(2)SO ligands. The exchange cross-peaks in the 2D spectra are unusually informative about the dynamic processes in solution; the spectra provide evidence that the rotamers interchange in a definite pattern of succession. Thus, all conceivable exchange pathways are not available. 1,2-Me(2)Im "b" can rotate regardless of the orientation of 1,2-Me(2)Im "a". 1,2-Me(2)Im "a" can rotate only when "b" has the orientation with its 2-Me group directed away from "a". Thus, 1,2-Me(2)Im "b" can switch 1,2-Me(2)Im "a" rotation on or off.

Structure-dependent in vitro cytotoxicity of the isomeric complexes [Ru(L)2Cl2] (L=o-tolylazopyridine and 4-methyl-2-phenylazopyridine) in comparison to [Ru(azpy)2Cl2]

“…S1 in Electronic Supplementary Material). The assignment of the H11 and H14 atoms has been done using deshielding arguments caused by the deshielding effect [38] of the Cl ligands. In general, in ruthenium azpy complexes, [Ru(azpy) 2 Cl 2 ], particularly the H6 and H(o) protons, are characteristically shifted due to the shielding and deshielding effect of neighbouring ligands in the distinct isomers [11].…”

The Complexes [OsCl2(azole)2(dmso)2] and [OsCl2(azole)(dmso)3]: Synthesis, Structure, Spectroscopic Properties and Catalytic Hydration of Chloronitriles

“…[18] In cis-[OsCl 2 (dmso)(dmso) 3 ], for example, this signal is observed at δ = 2.76 ppm. In the 13 C NMR spectrum the dmso resonance is present at δ = 45.4 (1) and 45.6 ppm (3). Two resonances in the 1 H NMR spectrum at δ = 3.64 and 3.35 ppm, with a 2:1 relative intensity in 5, and three signals of equal intensity at δ = 3.59, 3.45 and 3.28 ppm in 7, are indicative of the presence of three dmso ligands coordinated through sulfur.…”

“…Two resonances in the 1 H NMR spectrum at δ = 3.64 and 3.35 ppm, with a 2:1 relative intensity in 5, and three signals of equal intensity at δ = 3.59, 3.45 and 3.28 ppm in 7, are indicative of the presence of three dmso ligands coordinated through sulfur. Three resonances for S-bonded dmso ligands at δ = 48.8, 48.1 and 45.8 (5) and 48.9, 47.1 and 45.7 ppm (7) are seen in the 13 C NMR spectra of 5 and 7. This is in agreement with the C 2 symmetry of 1 and 3 and the The presence of singlet resonances at δ = 3.34 (2), 3.13 (4), 3.60, 3.59 and 3.29 (6), and 3.51, 3.45 and 3.25 ppm (8) in the 1 H NMR spectra of 2, 4, 6 and 8 indicates coordination of the dmso ligands to osmium(II) through sulfur.…”

“…This is in agreement with the C 2 symmetry of 1 and 3 and the The presence of singlet resonances at δ = 3.34 (2), 3.13 (4), 3.60, 3.59 and 3.29 (6), and 3.51, 3.45 and 3.25 ppm (8) in the 1 H NMR spectra of 2, 4, 6 and 8 indicates coordination of the dmso ligands to osmium(II) through sulfur. In the 13 C NMR spectra the resonances of the dmso carbon N4-H4A···Cl2 (N4-H4A 0.880, H4A···Cl2 2.530, N4···Cl2 3.086 Å; N4-H4A-Cl2 121.78°). The water molecules are involved in a number of hydrogen-bonding interactions with coordinated dmso and indazole molecules that stabilise the crystal lattice.…”

Ligands Rock & Roll: Stepwise Twisting of Two cis‐Coordinated Lopsided N‐Heterocycles in an Octahedral Bis(2‐phenylazopyridine)–Ruthenium(II) Complex with Seven Atropisomers

“…[65,66] Octahedral six-coordinated ruthenium complexes with sterically hindered rotation of coordinated monodentate ligands might well contribute to this rising field of research. [34,35,67] In particular, complex 2 appears to be a complicated but interesting molecule showing different aspects of molecular rotation, including the synchronous rotation of two ligands, as well as temperature-dependent stepwise atropisomerization. Ruthenium(ii) complexes prove to be most suitable compounds in which various aspects of ligand rotation can be investigated, tuning the physicochemical aspects of the backbone as well as the rotating ligands.…”