Infrared spectrum and vibrational assignments for pentacarbonylmanganese hydride

Edgell, Walter F.; Fisher, Jack W.; Asato, G.; Risen, William M.

doi:10.1021/ic50075a016

Cited by 15 publications

(13 citation statements)

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“…Not only the band positions but also the spectral intensities are well reproduced. Our results confirm the assignment 11 of the MnC stretching modes ν 19 (e symmetry) and ν 5 (a 1 symmetry) to one single band in the experimental spectrum (462 cm -1 ); its intensity comes apparently mainly from the e mode.…”

Section: Resultssupporting

confidence: 88%

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Isomers of Manganese Tetracarbonyl Hydride: A Density Functional Study of Structure and Vibrational Spectra

Frigyes

Fogarasi

1999

Organometallics

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Density functional theory (DFT) calculations have been used to find and characterize various isomers of HMn(CO) 4 , a coordinatively unsaturated complex. For comparison, its saturated parent compound HMn(CO) 5 has been included in the study. Optimized geometries and vibrational spectra were calculated for each species. For the pentacarbonyl, the theoretical geometry allows a critical discussion of various experimental results. Its calculated vibrational spectrum agrees with experiment within an average error of less than 10 cm -1 and maximum deviation of ∼30 cm -1 . In a search for isomeric forms of the tetracarbonyl complex, two minima have been found on the potential surface. The most stable form is a C s structure, with a second isomer of C 4v symmetry lying about 3 kcal/mol higher in energy. The existence of these two structures is in agreement with the conclusions of a sophisticated matrix isolation photolysis study by Church et al. 18 The calculated vibrational spectrum supports the interpretation of the CO region of the infrared spectrum, a crucial part of the experimental evidence, in every detail. This refers not only to the dominant C s form but also to the very difficult experimental proof of the presence of a small amount of the C 4v isomer. We suggest, in addition, that the Mn-H stretching frequency, although difficult to observe, could be used for identification: we predict an unexpectedly large frequency shift of ∼140 cm -1 between the C s and the C 4v isomers. A third isomer, the C 2v structuressuggested in some studies as an alternative to C s swas found to be a saddle point, rather than a minimum, in our study. For the heterolytic Mn-CO bond cleavage the calculations predict a dissociation energy of 41.8 kcal/mol.

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Section: Resultssupporting

confidence: 88%

“… a Relative to the total absorption intensity (=1000; in parentheses). b Ref ; new assignments (concerning the bands at 77, 106, 120, and 462 cm -1 ) have been accepted from ref . c Ref .…”

Section: Resultsmentioning

confidence: 99%

Isomers of Manganese Tetracarbonyl Hydride: A Density Functional Study of Structure and Vibrational Spectra

Frigyes

Fogarasi

1999

Organometallics

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“…Bending modes of metal hydrides normally appear in the 700−950 cm -1 region, , but numerous absorptions appear in that region of the IR spectrum, so δ(M−H) bending modes are often difficult to assign. An IR and Raman spectroscopic study of Cp(CO) 3 WH did not locate the δ(W−H) bending modes, but δ(M−H) bending modes were located and assigned in related metal carbonyl hydrides, 731 cm -1 for (CO) 5 MnH and 708 cm -1 for (CO) 4 CoH . A recent computational study supported these assignments and also calculated δ(M−H) bending modes for several related metal carbonyl hydrides .…”

Section: Resultsmentioning

confidence: 98%

Isotope Effects on Hydride Transfer Reactions from Transition Metal Hydrides to Trityl Cation. An Inverse Isotope Effect for a Hydride Transfer

Cheng

Bullock

1999

J. Am. Chem. Soc.

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Hydride transfer from transition metal hydrides (MH) to Ph3C+BF4 - gives M−FBF3 and Ph3CH. Deuterium kinetic isotope effects were determined for several MH/MD pairs (CH2Cl2 solution, 25 °C). For hydride transfer from Cp*(CO)3MoH (Cp* = η5-C5Me5) to substituted trityl cations containing zero, one, two, or three p-MeO groups [Ph n (p-MeOC6H4)3 - n C+BF4 -; n = 3, 2, 1, 0], the isotope effect remains essentially constant at k MoH/k MoD = 1.7−1.9 as the rate constant decreases from k H − = 6.5 × 103 to 1.4 M-1 s-1. For hydride transfer to Ph3C+BF4 - from five metal hydrides [Cp(CO)3MoH, Cp*(CO)3WH, (indenyl)(CO)3WH, Cp*(CO)3MoH, and trans-Cp(CO)2(PCy3)MoH; Cp = η5-C5H5] with second-order rate constants k H − ≥ 3.8 × 102 M-1 s-1, the kinetic isotope effects are also k MH/k MD = 1.7−1.8. For a series of five tungsten hydrides with substituted Cp ligands, the kinetic isotope effects decrease from k WH/k WD = 1.8 to 0.47 as the rate constant decreases (from k H − = 2.0 × 103 to 0.72 M-1 s-1). The steadily decreasing values of k MH/k MD with decreasing rate constants of hydride transfer are interpreted as indicating progressively stronger force constants of isotopically sensitive modes of the transition state, as the reaction slows down in progressing from more electron-donating Cp ligands to less electron-rich Cp ligands. The inverse isotope effect (k WH/k WD = 0.47) found for the slowest tungsten hydride, (C5H4CO2Me)(CO)3WH, is proposed to be due to a product-like transition state for irreversible hydride transfer.

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“…For this purpose we chose one representative compound out of each group of the Ti, V, Mn and Fe complexes; namely [TiCl 3 Me], [36] [VO(OCH 2 CH 2 O) 3 N], [37] [Mn(CO) 5 H] [38,39] and [FeCp 2 ]. [40,41] Note that these compounds contain hydrogen atoms, which in the 6-31G* basis carry no polarization functions; therefore basis set deficiencies should be most pronounced in these compounds.…”

Section: Methodsmentioning

confidence: 99%

Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical Shifts

Grigoleit

Bühl

2004

Chemistry A European J

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Both zero-point and classical thermal effects on the chemical shift of transition metals have been calculated at appropriate levels of density functional theory for a number of complexes of titanium, vanadium, manganese and iron. The zero-point effects were computed by applying a perturbational approach, whereas classical thermal effects were probed by Car-Parrinello molecular dynamics simulations. The systematic investigation shows that both procedures lead to a deshielding of the magnetic shielding constants evaluated at the GIAO-B3 LYP level, which in general also leads to a downfield shift in the relative chemical shifts, delta. The effect is small for the titanium and vanadium complexes, where it is typically on the order of a few dozen ppm, and is larger for the manganese and iron complexes, where it can amount to several hundred ppm. Zero-point corrections are usually smaller than the classical thermal effect. The pronounced downfield shift is due to the sensitivity of the shielding of the metal centre with regard to the metal-ligand bond length, which increase upon vibrational averaging. Both applied methods improve the accuracy of the chemical shifts in some cases, but not in general.

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Infrared spectrum and vibrational assignments for pentacarbonylmanganese hydride

Cited by 15 publications

References 0 publications

Isomers of Manganese Tetracarbonyl Hydride: A Density Functional Study of Structure and Vibrational Spectra

Isomers of Manganese Tetracarbonyl Hydride: A Density Functional Study of Structure and Vibrational Spectra

Isotope Effects on Hydride Transfer Reactions from Transition Metal Hydrides to Trityl Cation. An Inverse Isotope Effect for a Hydride Transfer

Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical Shifts

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