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-RuII
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- 作者：Marian Iwamoto ; Enzo Alessio ; and Luigi G. Marzilli
- 刊名：Inorganic Chemistry
- 出版年：1996
- 出版时间：April 10, 1996
- 年：1996
- 卷：35
- 期：8
- 页码：2384 - 2389
- 全文大小：199K
- 年卷期：v.35,no.8(April 10, 1996)
- ISSN：1520-510X
文摘
Somecis,cis,cis-RuX2(Me2SO)2(1,2-Me2Im)Lcomplexes [L = 1,2-Me2Im (1,2-dimethylimidazole) orMe3Bzm(1,5,6-trimethylbenzimidazole), X = Cl or Br, andMe2SO = S-bonded DMSO] have been synthesizedand theirrotamers studied in CDCl3. From 2D NMR data,cis,cis,cis-RuCl2(Me2SO)2(1,2-Me2Im)(Me3Bzm)has 1,2-Me2Im in position "a" (cis to bothMe2SO's and cis to "b") andMe3Bzm in position "b" (trans to oneMe2SO and cisto the other). There are two stable atropisomers [head-to-tail(HT, 84%) and head-to-head (HH, 16%), definingthe aromatic H of Ru-N-C-H as head for both ligands].Me3Bzm has the same orientation in bothatropisomers.In this orientation, the unfavorable interligand stericinteractions of Me3Bzm with theMe2SO and1,2-Me2Imligands appear to be countered by favorable electrostatic attractionbetween the 
+ N2CH moiety ofMe3Bzmand the - cis Cl ligands. The1,2-Me2Im lacks a + N2CH group,and its orientation is dominated by stericeffects of the 2-Me group. The NMR spectrum ofcis,cis,cis-RuCl2(Me2SO)2(1,2-Me2Im)2is consistent with fourrotamers in restricted rotation about both Ru-N bonds: two HH andtwo HT. 2D NMR techniques (NOESYand ROESY) afforded complete proton signal assignments. The liganddisposition could be assessed from thelarge chemical shift dispersion of some 1,2-Me2Imligand signals (
0.86-1.52 ppm) arising fromcis-1,2-Me2Im shielding modulated by deshielding influences of the cishalides. The relative stability of the four rotamerscorrelates best with steric interactions between the 2-Me groups andthe Me2SO ligands. The mostfavorableconformer (46%) is the HH rotamer with both 2-Me groups pointing awayfrom the Me2SO ligands. Theleastfavorable conformer (14%) was also HH, but the methyl groups in thiscase point toward the Me2SO ligands.Inthe HT conformers of intermediate stability (~20%), one 2-Me groupis toward and the other is away from theMe2SO ligands. The exchange cross-peaks inthe 2D spectra are unusually informative about the dynamicprocessesin solution; the spectra provide evidence that the rotamers interchangein a definite pattern of succession. Thus,all conceivable exchange pathways are not available.1,2-Me2Im "b" can rotate regardless of theorientation of1,2-Me2Im "a". 1,2-Me2Im"a" can rotate only when "b" has the orientationwith its 2-Me group directed awayfrom "a". Thus, 1,2-Me2Im "b" can switch1,2-Me2Im "a" rotation on or off.
+ N2CH moiety ofMe3Bzmand the - cis Cl ligands. The1,2-Me2Im lacks a + N2CH group,and its orientation is dominated by stericeffects of the 2-Me group. The NMR spectrum ofcis,cis,cis-RuCl2(Me2SO)2(1,2-Me2Im)2is consistent with fourrotamers in restricted rotation about both Ru-N bonds: two HH andtwo HT. 2D NMR techniques (NOESYand ROESY) afforded complete proton signal assignments. The liganddisposition could be assessed from thelarge chemical shift dispersion of some 1,2-Me2Imligand signals ( 0.86-1.52 ppm) arising fromcis-1,2-Me2Im shielding modulated by deshielding influences of the cishalides. The relative stability of the four rotamerscorrelates best with steric interactions between the 2-Me groups andthe Me2SO ligands. The mostfavorableconformer (46%) is the HH rotamer with both 2-Me groups pointing awayfrom the Me2SO ligands. Theleastfavorable conformer (14%) was also HH, but the methyl groups in thiscase point toward the Me2SO ligands.Inthe HT conformers of intermediate stability (~20%), one 2-Me groupis toward and the other is away from theMe2SO ligands. The exchange cross-peaks inthe 2D spectra are unusually informative about the dynamicprocessesin solution; the spectra provide evidence that the rotamers interchangein a definite pattern of succession. Thus,all conceivable exchange pathways are not available.1,2-Me2Im "b" can rotate regardless of theorientation of1,2-Me2Im "a". 1,2-Me2Im"a" can rotate only when "b" has the orientationwith its 2-Me group directed awayfrom "a". Thus, 1,2-Me2Im "b" can switch1,2-Me2Im "a" rotation on or off.