The molybdenum-molybdenum triple bond. 11. 1,1- and 1,2-Disubstituted dimolybdenum compounds of formula Mo2X2(CH2SiMe3)4. Observation of rotation about the triple bond Mo.tplbond.Mo

Chisholm, M. H.; Folting, Kirsten; Huffman, John C.; Rothwell, Ian P.

doi:10.1021/om00062a005

Cited by 35 publications

(50 citation statements)

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“…An example of hindered rotation about metal−phosphorus bonds has been reported for a square planar Rh(I) complex with bulky phosphines . Another particularly well-studied example concerns hindered rotation of dialkylamido ligands in some four-coordinate molybdenum dimers where, however, the Mo−NR 2 bond has a partial double-bond character. , …”

Section: Introductionmentioning

confidence: 99%

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl₂(Me₂SO)₄

et al. 1996

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The solution and solid state structures of two octahedral Ru(II) complexes, cis,cis,cis-RuCl(2)(Me(2)SO)(2)(py)(Me(3)Bzm) (Me(3)Bzm = 1,5,6-trimethylbenzimidazole, py = pyridine) (1) and cis,cis,cis-RuCl(2)(Me(2)SO)(2)(Me(3)Bzm)(2) (2), were compared. 2, the subject of a preliminary report, is described in more detail here. 1 has two possible geometric isomers with py trans to Cl in one (position "a") and trans to Me(2)SO in the other (position "b"), Me(3)Bzm occupying the other position in each isomer. The X-ray structure of 1 revealed that py is at "a". Since Me(3)Bzm is lopsided, each Me(3)Bzm has two possible orientations related by a rotation of approximately 180 degrees about the Ru-N3 bond; there are two possible atropisomers for each geometric isomer of 1 and four for 2. For 1, the solid state structure shows that Me(3)Bzm adopts the orientation with H2 (H on C between the two N's) pointing between the two cis Cl ligands, the same disposition as Me(3)Bzm "b" in 2 in the solid. For 1, the py signals (two broad py alpha and beta signals, a sharp gamma signal) in CDCl(3) show that py "a" is rotating on the NMR time scale and that only one atropisomer is present. This interpretation was supported by ROESY and EXSY (1)H NMR spectra. The (1)H NMR shift pattern and the NOE data can be understood best if Me(3)Bzm "b" remains primarily in the orientation found in the solid. The solution data for 1, with the nonlopsided and sterically less demanding py ligand, provide insight into the more complicated properties of 2. For 2, there is a marked dispersion of (1)H NMR signals of Me(3)Bzm "a" between the two atropisomers, which have nearly equal stability. One atropisomer is a head-to-head (HH) and the other a head-to-tail (HT) species. Me(3)Bzm "a" flips between the two species. Thus, ligand "a" is fluxional in both complexes. The dispersion of Me(3)Bzm "a" signals is due to the effect of Me(3)Bzm "b" anisotropy. For 1 and both atropisomers of 2, Me(3)Bzm "b" prefers one orientation, which appears to be the most hindered orientation. We postulate that the H2 of Me(3)Bzm "b" is electrostatically attracted to the two cis halides, accounting for this surprising result. Crystallographic details for 1 are as follows: C(19)H(29)Cl(2)N(3)O(2)RuS(2), P2(1)/c, a = 10.947(1) Å, b = 9.046(1) Å, c = 24.221(2) Å, D(calcd) = 1.580 g cm(-)(3), Z = 4, R = 0.026 for 4627 independent reflections.

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Section: Introductionmentioning

confidence: 99%

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl₂(Me₂SO)₄

et al. 1996

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“…The phenomenon of restricted rotation about metal−ligand σ bonds in simple coordination compounds has been studied in detail in a few square-planar complexes − but has seldom been investigated in complexes with 6 or higher coordination number. , Higher-coordinate inorganic stereodynamic systems typically studied involve fluxional isomerism in π-bound ligands or scrambling in carbonyl clusters. , …”

Section: Introductionmentioning

confidence: 99%

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

1996

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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.

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“…Cooling of the sample to −60 °C produces a limiting spectrum with the two signals further separated and methine proton coupling only slightly visible. Using this variable-temperature NMR data, it is possible to calculate Δ G ⧧ 305 K , the barrier to this fluxional process, to be 14.1(1) kcal mol -1 , which falls in the expected range for this type of process. 25b, …”

Section: Resultsmentioning

confidence: 95%

Amide-Stabilized, Diamagnetic Chromium(II) Nitrosyl Complexes¹

et al. 1999

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Treatment of Cr(NO)(N i Pr 2 ) 3 with 2 equiv of PhCO 2 H affords Cr(NO)(N i Pr 2 )(O 2 CPh) 2 (1) in good yields. Reaction of CpNa‚DME with 1 produces CpCr(NO)(N i Pr 2 )(OC(O)Ph) (2), which subsequently yields a series of 18-valence-electron (18e) complexes, CpCr(NO)(N i Pr 2 )(R) (R ) η 1 -Cp (3), CH 2 SiMe 3 (4), η 1 -CH 2 Ph (5), Ph (6), CPhdCH 2 (7), CtCCMe 3 (8), CtCPh ( 9)) when treated with additional CpNa‚DME or 1 equiv of the appropriate R 2 Mg‚x(dioxane) reagent. 2-9 are low-spin (S ) 0) compounds, and their electronic stability is attributed to the strong, synergic π-bonding interactions present in the [Cr(NO)(N i Pr 2 )] 2+ core, as indicated both by the NMR and IR spectra of these complexes and by the solid-state molecular structures of 2-4. The "strong-field" nitrosyl and amide ligands also enforce a diamagnetic configuration on the 14e bis(hydrocarbyl) complexes Cr(NO)(N i Pr 2 )R 2 (R ) CH 2 SiMe 3 (10), CH 2 Ph (11), o-tolyl (12)), which are obtained in good yields by reaction of 1 with 2 equiv of the corresponding R 2 Mg‚x(dioxane) reactants. The solid-state molecular structures of 10 and 11 have also been established by single-crystal X-ray crystallographic analyses. Variabletemperature NMR spectroscopy was employed to study the fluxional processes occurring in 1, 10, and 11.

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The molybdenum-molybdenum triple bond. 11. 1,1- and 1,2-Disubstituted dimolybdenum compounds of formula Mo2X2(CH2SiMe3)4. Observation of rotation about the triple bond Mo.tplbond.Mo

Cited by 35 publications

References 3 publications

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl₂(Me₂SO)₄

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl₂(Me₂SO)₄

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

Amide-Stabilized, Diamagnetic Chromium(II) Nitrosyl Complexes¹

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The molybdenum-molybdenum triple bond. 11. 1,1- and 1,2-Disubstituted dimolybdenum compounds of formula Mo2X2(CH2SiMe3)4. Observation of rotation about the triple bond Mo.tplbond.Mo

Cited by 35 publications

References 3 publications

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl2(Me2SO)4

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl2(Me2SO)4

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-RuIICl2(Me2SO)2(1,2-dimethylimidazole)2

Amide-Stabilized, Diamagnetic Chromium(II) Nitrosyl Complexes1

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Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl₂(Me₂SO)₄

Orientation and Restricted Rotation of Lopsided Aromatic Ligands. Octahedral Complexes Derived from cis-RuCl₂(Me₂SO)₄

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

Amide-Stabilized, Diamagnetic Chromium(II) Nitrosyl Complexes¹