The methyl group geometry in trichloromethyltitanium: a reinvestigation by gas electron diffraction

Briant, Peter; Green, Jennifer; Haaland, Arne; Moellendal, H.; Rypdal, Kristin; Tremmel, J.

doi:10.1021/ja00191a054

Cited by 33 publications

(24 citation statements)

References 2 publications

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“…For a long time this molecule was considered to be the archetypal a-agostic compound on account of its VE count of only 8 and its low CN of 4. [76] However, contrary to earlier reports based on a variety of experimental and theoretical techniques, [34,41,50, 51b, 77a-h] 12 has been unambiguously shown to possess no agostic interactions of any significance. Several attempts have sought to explain why the complex [MeTiCl 3 (dmpe)] (10) is agostic whilst the basefree molecule 12 shows no such behavior.…”

Section: Angewandte Chemiementioning

confidence: 90%

“…Although 12 was originally reported to possess a significantly distorted methyl group implying a triple a-agostic Ti···HC interaction, [33] a reinvestigation found the TiÀCH 3 geometry to be normal. [34] A subsequent study of [EtTiCl 3 ] (14) showed a Ti-C-C angle of 116.6(11)8 and Ti···H b separations of 3.24-3.97 . [35] [Cp* In principle, the redistribution of bonding electron density on development of a M···HC interaction should be revealed unambiguously by the NMR spectroscopic properties of the system, with changes in chemical shifts and coupling constants for the 1 H, 13 C, and possibly also the metal nuclei.…”

Section: Characterization Of Agostic Interactionsmentioning

confidence: 99%

“…+ (34), and the h 2 -CH ligand in complexes appears to be reversibly displaced by other weakly bound ligands, such as N 2 , C 2 H 4 , and SO 2 . [61] That h 2 -CH acts as a ligand at all in these systems is remarkable.…”

Section: The Agostic Bond As a Labile Ligand Interactionmentioning

confidence: 99%

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Agostic Interactions in d⁰Metal Alkyl Complexes

2004

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The phenomenon of agostic interactions is reviewed and the nature of the interaction is revisited. A historical perspective is followed by an overview of experimental techniques used to diagnose agostic behavior, and previous interpretations of agostic bonding are presented. A series of simple metal alkyl complexes is considered and a new model for the phenomenon in d(0) systems is developed which sets them apart from agostic late-transition-metal complexes. Factors such as the valence electron count and coordination number of the metal center are revealed to be unimportant in facilitating the interaction in most d(0) systems. The charge density distribution in several transition-metal alkyl complexes is explored by experimental and theoretical techniques, including the powerful "Atoms in Molecules" approach. Local charge concentrations are shown to play an important role in the agostic interaction. Finally, we demonstrate for the first time a way to manipulate and control the magnitude and disposition of such local charge concentrations, and hence the strength of agostic interactions in d(0) metal alkyl complexes.

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Section: Angewandte Chemiementioning

confidence: 90%

Section: Characterization Of Agostic Interactionsmentioning

confidence: 99%

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Agostic Interactions in d⁰Metal Alkyl Complexes

2004

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“…The important geometrical parameters of these complexes, optimized or simulated by using the BP86 functional, are collected in Tables 2-5, together with corresponding www.chemeurj.org data observed in the gas phase [37,[52][53][54][55][56][57][58][59][60][61][62] or in the solid state. [63][64][65][66][67][68][69] The tables include the equilibrium bond lengths computed with both Gaussian98 and the CPMD program, as well as zero-point corrected and thermal averaged bond lengths.…”

Section: Geometriesmentioning

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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“…Refinements of additional data sets confirm these conclusions. For the C-H bond of methyl in (trichloromethyl)titanium, the vibrational amplitude for the blackness correction C1 was 0.039/~ (Briant, Green, Haaland, Mollendal, Rypdal & Tremmel, 1989). A reinvestigation using C2 increased this amplitude to the more reasonable value of 0.056 A.…”

Section: Discussionmentioning

confidence: 97%

On the apparent response of photographic emulsions according to least-squares determinations of the `blackness correction' from gas electron diffraction data

Gundersen¹,

Strand²,

Volden³

1992

J Appl Cryst

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The single-hit assumption for the response of a photographic emulsion to electrons leads to a simple relationship between the exposure and the measured optical densities with the saturation density of the emulsion as the only parameter. With the inverse of this saturation density as a least-squares variable of the corresponding multiplicative 'blackness correction', this correction has been determined from data sets of gas electron diffraction plates of different exposures. For optical densities from our standard photometer procedure, the computed values of the saturation density are smaller than the real values for the plates used. The computed values increase with increasing optical density of the darkest plate applied and increase by reducing the amount of light scattered by the silver grains of the emulsion. Computer simulations indicate that relatively small changes in the direction of the specular optical densities would be necessary to obtain the agreement predicted by the single-hit assumption between the computed and the real saturation density. A good blackness correction for our standard procedures is easily obtained by least-squares calculations when plates of relatively high optical densities are included in the applied data set.

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The methyl group geometry in trichloromethyltitanium: a reinvestigation by gas electron diffraction

Cited by 33 publications

References 2 publications

Agostic Interactions in d⁰Metal Alkyl Complexes

Agostic Interactions in d⁰Metal Alkyl Complexes

Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical Shifts

On the apparent response of photographic emulsions according to least-squares determinations of the `blackness correction' from gas electron diffraction data

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The methyl group geometry in trichloromethyltitanium: a reinvestigation by gas electron diffraction

Cited by 33 publications

References 2 publications

Agostic Interactions in d0Metal Alkyl Complexes

Agostic Interactions in d0Metal Alkyl Complexes

Thermal Effects and Vibrational Corrections to Transition Metal NMR Chemical Shifts

On the apparent response of photographic emulsions according to least-squares determinations of the `blackness correction' from gas electron diffraction data

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Product

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Agostic Interactions in d⁰Metal Alkyl Complexes

Agostic Interactions in d⁰Metal Alkyl Complexes