Analysis of Stereochemical Nonrigidity in Five-Coordinate Cyclopentadienylmetal Complexes by the Structure Correlation Method

Smith, Jeremy M.; Coville, Neil J.

doi:10.1021/om960092u

Cited by 17 publications

(12 citation statements)

References 28 publications

(35 reference statements)

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“…Earlier work suggested that the direction of the reaction related to a trans-cis geometry preference and that this could be associated with intramolecular effects [18]. The current data suggest that not even this influence determines the isomerisation direction.…”

Section: Mechanismsupporting

confidence: 44%

Solid-state isomerisation reactions of (η5-C5H4R)M(CO)2(PR3′)I (M=W, Mo; R=tBu, Me; R′=Ph, OiPr3)

Adeyemi

Eke

Cheng

et al. 2004

Journal of Organometallic Chemistry

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Section: Mechanismsupporting

confidence: 44%

Solid-state isomerisation reactions of (η5-C5H4R)M(CO)2(PR3′)I (M=W, Mo; R=tBu, Me; R′=Ph, OiPr3)

Adeyemi

Eke

Cheng

et al. 2004

Journal of Organometallic Chemistry

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“…Examples of pseudo-trigonal bipyramidal structures for CpML4 complexes are known, 27,28 and the interconversion mechanism between these two geometries has been addressed. 29 In conclusion, the combined IR and NMR investigation of compound complexes. 12 Calculations were also run for the ion pair, [Cp*Mo(PMe3)3H] + PF6 -, in the gas phase, in order to probe the nature of the cation-anion interaction.…”

Section: This Possibility Was Addressed In More Detail By Dft Calculations (See Section D Below)mentioning

confidence: 98%

Investigation of the [Cp*Mo(PMe₃)₃H]ⁿ⁺ (n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales

et al. 2008

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The compound [Cp*Mo(PMe3)3H] (1) is reversibly oxidized at E1/2 = -1.40 V vs ferrocene in MeCN. Its oxidation with Cp2FePF6 yields thermally stable [Cp*Mo(PMe3)3H]PF6 (2), which has been isolated and characterized by IR and EPR spectroscopy and by single-crystal X-ray diffraction. The 1H and 31P NMR spectra of 1 show two types of PMe3 ligands in a 1:2 ratio at low temperature, but only one average signal at room temperature, with activation parameters of DeltaH++ = 11.7(3) kcal mol-1 and DeltaS++ = -3(1) eu for the exchange process. Although only one species is evidenced by NMR for 1 and by EPR for 2, the solution IR spectra of each complex show two bands in the v(Mo-H) region (1, major at 1794 cm-1 and minor at ca. 1730 cm-1; 2, ca. 1800 and 1770 cm-1 with approximately equal intensity), the position and relative intensity being little dependent on the solvent. A thorough DFT investigation suggests that these are different rotamers involving different relative orientations of the Cp* ring and the PMe3 ligands in these complexes. This ring rotation process is very rapid on the NMR and EPR time scale but slow on the IR time scale. The X-ray data and the theoretical calculations suggest the presence of weak Mo-H...F interactions in compound 2. The possibility of PMe3 dissociation, as well as other intramolecular rearrangements, for 1 and 2 is excluded by experimental and computational studies. Protonation of 1 yields [Cp*Mo(PMe3)3H2]+ (3), which also reveals a dynamic process interconverting the two inequivalent H ligands and the three PMe3 ligands (two sets in a 1:2 ratio in the frozen structure) on the NMR time scale (activation parameters of DeltaH++ = 9.3(1) kcal/mol and DeltaS++ = -4.1(4) eu). A DFT study suggests that this exchange process occurs via a low-energy symmetric dihydride intermediate and not through a dihydrogen complex.

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“…For complex 5, all three Mo-bound carbonyl groups show chemical shift anisotropy in the solid state and appear at 226.59, 230.16 and 242.25 ppm, in contrast to [CpMo(CO) 3 Me] where the two cis-CO are equivalent at 230.3 ppm and the third appears at 242.3 ppm. This suggests that the possible fluxional processes, namely, rotation of Cp about the Mo-(η 5 -Cp) C 5 axis, rapid interchangeability equivalence of the square pyramidal basal cis-CO ligands, rotation about the Mo-αC σ bond, and Berry-type pseudorotation [52][53][54][55][56] might be slower or restricted probably due to the presence of bulky substituents in compounds 2-5. However, for the [CpMo(CO) 3 Me] complex, no such inequivalence is apparent and only two carbonyl peaks can be observed in solution and solid-state 13 C NMR spectra.…”

Section: Nmr Spectroscopymentioning

confidence: 99%

Cyclopentadienyl molybdenum alkyl ester complexes as catalyst precursors for olefin epoxidation

Grover

Pöthig

Kühn

2014

Catal. Sci. Technol.

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New molybdenum complexes of the type [CpMo(CO) 3 X] containing ligands of the formula X = CHR 2 CO(OR 1 )where R 1 = ethyl (1), menthyl (4), and bornyl (5) and R 2 = H; R 1 = ethyl and R 2 = methyl (2) and phenyl (3) have been synthesized and characterized by NMR and IR spectroscopy and X-ray crystallography.These compounds have been applied as catalyst precursors for achiral and chiral epoxidation of unfunctionalized olefins with tert-butyl hydroperoxide (TBHP) as the oxidant at 22°C (in CH 2 Cl 2 ) and 55°C (in CHCl 3 ). The substrates cis-cyclooctene, 1-octene, cis-and trans-stilbene, and trans-β-methylstyrene were selectively and quantitatively converted into their epoxides using a catalyst :substrate : oxidant ratio of 1 : 100 : 200 within 4 h at room temperature in CH 2 Cl 2 and within 15 min at 55°C in CHCl 3 . Complexes 1-5 are precursors of active epoxidation catalysts and turnover frequencies (TOFs) of ca. 1200 h −1 are obtained with cis-cyclooctene as the substrate. No enantioselectivity is observed with trans-β-methylstyrene as the substrate despite the application of enantiomerically pure precatalysts. In situ monitoring of catalytic epoxidation of cis-cyclooctene with complex 5 by 1 H and 13 C NMR spectroscopy suggests that the chiral alkyl ester side chain is retained during oxidation with TBHP. During epoxidation, the primary catalytic species is the dioxo complex [CpMoO 2 X]. After near complete conversion of cis-cyclooctene to its epoxide, further oxidation of the dioxo complex to oxo-peroxo complex [CpMo(η 2 -O 2 )(O)X] takes place. The oxo-peroxo complex is also an active epoxidation catalyst.

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Analysis of Stereochemical Nonrigidity in Five-Coordinate Cyclopentadienylmetal Complexes by the Structure Correlation Method

Abstract: The intramolecular cis/trans isomerization mechanism of solid-state pseudo-five-coordinate complexes of the type CpML4 was examined by the structure correlation technique, and the data revealed that the mechanism most likely proceeds via a combined Berry−turnstile mechanism.

Cited by 17 publications

References 28 publications

Solid-state isomerisation reactions of (η5-C5H4R)M(CO)2(PR3′)I (M=W, Mo; R=tBu, Me; R′=Ph, OiPr3)

Solid-state isomerisation reactions of (η5-C5H4R)M(CO)2(PR3′)I (M=W, Mo; R=tBu, Me; R′=Ph, OiPr3)

Investigation of the [Cp*Mo(PMe₃)₃H]ⁿ⁺ (n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales

Cyclopentadienyl molybdenum alkyl ester complexes as catalyst precursors for olefin epoxidation

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Analysis of Stereochemical Nonrigidity in Five-Coordinate Cyclopentadienylmetal Complexes by the Structure Correlation Method

Abstract: The intramolecular cis/trans isomerization mechanism of solid-state pseudo-five-coordinate complexes of the type CpML4 was examined by the structure correlation technique, and the data revealed that the mechanism most likely proceeds via a combined Berry−turnstile mechanism.

Cited by 17 publications

References 28 publications

Solid-state isomerisation reactions of (η5-C5H4R)M(CO)2(PR3′)I (M=W, Mo; R=tBu, Me; R′=Ph, OiPr3)

Solid-state isomerisation reactions of (η5-C5H4R)M(CO)2(PR3′)I (M=W, Mo; R=tBu, Me; R′=Ph, OiPr3)

Investigation of the [Cp*Mo(PMe3)3H]n+ (n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales

Cyclopentadienyl molybdenum alkyl ester complexes as catalyst precursors for olefin epoxidation

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Investigation of the [Cp*Mo(PMe₃)₃H]ⁿ⁺ (n = 0, 1) Redox Pair: Dynamic Processes on Very Different Time Scales