α- and β-Agostic Alkyl–Titanocene Complexes

Dunlop-Brière, Alexandre F.; Budzelaar, Peter H. M.; Baird, Michael C.

doi:10.1021/om3001197

Cited by 31 publications

(24 citation statements)

References 55 publications

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“…These features strongly suggest a selective α‐agostic interaction between the hafnium center and C1−H1b bond. In agreement with the literature, the diastereotopic proton resonating at lower frequency has a lower 1 J (C,H) value …”

Section: Resultssupporting

confidence: 82%

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Tensi

Froese

Kuhlman

et al. 2020

Chemistry A European J

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Heterobimetallic complexes with inequivalent bridging alkyl chains are very often invoked as key intermediates in many catalytic processes, yet their interception and structural characterization are lacking. Such complexes have been prepared from reactions of the cationic cyclometalated hafnocene [CpPrCpCH2CH2CH2 Hf][B(C6F5)4] (1) with main group metal alkyls to afford the corresponding hetero‐bridged cationic products, [CpPrCpCH2CH2(μ-CH2) Hf(μ‐R)E(R)n][B(C6F5)4] (E=Al or Zn; R=Me, Et, or iBu). NMR and DFT studies demonstrate that both bridging alkyls establish agostic interactions with Hf, which are appreciably stronger for ethyl rather than methyl groups. Hf–Al and Hf–Zn distances are surprisingly short and only slightly longer than computed Hf–Al or Hf–Zn single bond lengths (2.80 Å). Finally, a reaction of [CpPrCpCH2CH2(μ-CH2) Hf(μ‐Me)Zn(Me)][B(C6F5)4] with excess ZnMe2 yields an unprecedented heterotrimetallic species, [(CpPr)2Hf(μ‐Me)(ZnMe)(μ3‐CH2)ZnMe][B(C6F5)4], the detailed structure of which is elucidated by a combination of NMR spectroscopic methods and molecular calculations.

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Section: Resultssupporting

confidence: 82%

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Tensi

Froese

Kuhlman

et al. 2020

Chemistry A European J

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“…Although many computational studies have been carried out on these complexes and their role in oligo-and polymerization reactions (67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83), the electronic structures and relative energies of relevant reactants, intermediates, and transition states are computed with the same method used for optimizing the geometries for NMR calculations for consistency. ZrEt + is more deshielded in both the β-H and α-H agostic structures, but this effect is much more pronounced in the latter (Fig.…”

Section: Resultsmentioning

confidence: 99%

NMR chemical shift analysis decodes olefin oligo- and polymerization activity of d ⁰ group 4 metal complexes

Gordon

Shirase

Yamamoto

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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d metal-alkyl complexes (M = Ti, Zr, and Hf) show specific activity and selectivity in olefin polymerization and oligomerization depending on their ligand set and charge. Here, we show by a combined experimental and computational study that the C NMR chemical shift tensors of the α-carbon of metal alkyls that undergo olefin insertion signal the presence of partial alkylidene character in the metal-carbon bond, which facilitates this reaction. The alkylidene character is traced back to the π-donating interaction of a filled orbital on the alkyl group with an empty low-lying metal d-orbital of appropriate symmetry. This molecular orbital picture establishes a connection between olefin insertion into a metal-alkyl bond and olefin metathesis and a close link between the Cossee-Arlmann and Green-Rooney polymerization mechanisms. TheC NMR chemical shifts, the α-H agostic interaction, and the low activation barrier of ethylene insertion are, therefore, the results of the same orbital interactions, thus establishing chemical shift tensors as a descriptor for olefin insertion.

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“…Some compounds were observed under different agostomers. We will choose a few examples of agostomers based on experimental investigations carried out by Baird et al 63,64 In the case of [Cp 2 TiCH 2 CHMe t-Bu] + , they observed that the a-agostic isomer is preferentially formed although a b-agostic isomer could have been formed. Such a situation is relatively rare: when both a-and b-agostic isomers may be formed, generally the b-agostic form is more stable.…”

Section: Elfmentioning

confidence: 99%

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

Zins

Silvi

Alikhani

2015

Phys. Chem. Chem. Phys.

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Agostic bonding is of paramount importance in C-H bond activation processes. The reactivity of the σ C-H bond thus activated will depend on the nature of the metallic center, the nature of the ligand involved in the interaction and co-ligands, as well as on geometric parameters. Because of their importance in organometallic chemistry, a qualitative classification of agostic bonding could be very much helpful. Herein we propose descriptors of the agostic character of bonding based on the electron localization function (ELF) and Quantum Theory of Atoms in Molecules (QTAIM) topological analysis. A set of 31 metallic complexes taken, or derived, from the literature was chosen to illustrate our methodology. First, some criteria should prove that an interaction between a metallic center and a σ X-H bond can indeed be described as "agostic" bonding. Then, the contribution of the metallic center in the protonated agostic basin, in the ELF topological description, may be used to evaluate the agostic character of bonding. A σ X-H bond is in agostic interaction with a metal center when the protonated X-H basin is a trisynaptic basin with a metal contribution strictly larger than the numerical uncertainty, i.e. 0.01 e. In addition, it was shown that the weakening of the electron density at the X-Hagostic bond critical point with respect to that of X-Hfree well correlates with the lengthening of the agostic X-H bond distance as well as with the shift of the vibrational frequency associated with the νX-H stretching mode. Furthermore, the use of a normalized parameter that takes into account the total population of the protonated basin, allows the comparison of the agostic character of bonding involved in different complexes.

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α- and β-Agostic Alkyl–Titanocene Complexes

Cited by 31 publications

References 55 publications

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

NMR chemical shift analysis decodes olefin oligo- and polymerization activity of d ⁰ group 4 metal complexes

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

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α- and β-Agostic Alkyl–Titanocene Complexes

Cited by 31 publications

References 55 publications

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

Interception of Elusive Cationic Hf–Al and Hf–Zn Heterobimetallic Adducts with Mixed Alkyl Bridges Featuring Multiple Agostic Interactions

NMR chemical shift analysis decodes olefin oligo- and polymerization activity of d 0 group 4 metal complexes

Activation of C–H and B–H bonds through agostic bonding: an ELF/QTAIM insight

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NMR chemical shift analysis decodes olefin oligo- and polymerization activity of d ⁰ group 4 metal complexes