An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate

Rocchigiani, Luca; Bellachioma, Gianfranco; Zuccaccia, Cristiano; Macchioni, Alceo

doi:10.1016/j.jorganchem.2012.02.011

Cited by 9 publications

(5 citation statements)

References 36 publications

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“…Under the assumption that bulk solvation effects of the medium might be neglected, it can be speculated that cation–anion interactions within the OSIP slightly increase the energy barrier of the IPS process, possibly making the (partial) toluene dissociation somewhat more difficult than in the free cation. This agrees with previous studies on the interionic structure in solution of metallocenium OSIPs, ,− which showed that the anion sits preferentially in front of the coordination site adjacent to the Zr–Me moiety (i.e., the coordinated toluene molecule in the case of [1Me · C 7 D 8 ] + ), which is the site from which IPS originates.…”

Section: Resultssupporting

confidence: 92%

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

et al. 2022

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The solution structure and dynamics of three prototypical bis-indenyl ansa-zirconocenium methyl cations (Me 2 Si-(2-methyl-4-phenyl-6-tert-butylindenyl) 2 ZrMe + , [1Me] + ; Me 2 Si(2,4dimethylindenyl) 2 ZrMe + , [2Me] + ; Me 2 Si(indenyl) 2 ZrMe + , [3Me] + ) paired with the weakly coordinating B(C 6 F 5 ) 4− anion have been investigated by NMR spectroscopy in aromatic hydrocarbons with different polarities (toluene, ε r = 2.38; chlorobenzene, ε r = 5.69; 1,2difluorobenzene (ODFB), ε r = 13.38). These highly electrophilic cations are stabilized by solvent coordination, as evidenced by the unequivocal identification of [1Me•C 7 H 8 ] + B(C 6 F 5 ) 4 − , a rare example of a toluene-stabilized ion pair that has been fully characterized in solution. Combining spectroscopic and DFT methods allowed us to evaluate how solvent coordination modulates the dynamic processes typical of this class of catalysts. An exchange between the two faces of coordinated toluene (face inversion, FI) occurs without solvent decomplexation (ΔH ⧧ FI = 14.6 kcal mol −1 ; ΔS ⧧ FI = 3 cal mol −1 K −1 ; ΔG ⧧ FI (298) = 13.7 kcal mol −1 ) and is about 20 times faster than the exchange between coordinated and free solvent (solvent decomplexation, SD, ΔH ⧧ SD = 17.9 kcal mol −1 ; ΔS ⧧ SD = 10 cal mol −1 K −1 ; ΔG ⧧ SD (298) = 14.9 kcal mol −1 ) and ion pair symmetrization (IPS, ΔH ⧧ IPS = 18.6 kcal mol −1 ; ΔS ⧧ IPS = 12 cal mol −1 K −1 ; ΔG ⧧ IPS (298) = 14.9 kcal mol −1 ). For the ion pairs [1− 3Me•solvent] + B(C 6 F 5 ) 4 − , IPS rate constants (k IPS ) do not correlate with the solvent polarity (k IPS (ODFB) > k IPS (toluene) > k IPS (chlorobenzene)). For the more coordinating toluene and chlorobenzene solvents, ΔG ⧧ IPS nicely tracks with the amount of positive charge at the metal, increasing as the positive charge increases (q ZrMe 2 ,CM5 ; 1Me 2 > 3Me 2 > 2Me 2 ). In contrast, in the less coordinating ODFB, differences in the IPS barriers for [1−3Me•ODFB] + B(C 6 F 5 ) 4− appear to correlate better with steric parameters, as measured by the percent buried volume on the open quadrants (%V Bur,open ) for the corresponding neutral precursors (%V Bur,open = 34.8, 35.5,34.6% for 1Me 2 , 2Me 2 , and 3Me 2 , respectively).

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Section: Resultssupporting

confidence: 92%

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

et al. 2022

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“…Solvent was removed in vacuo, yielding a white solid (272 mg, 87%) of the title compound. All recorded data are consistent with literature values …”

Section: Methodssupporting

confidence: 91%

“…The resulting solution was filtered through Celite, the volume was reduced to ∼5 mL, and the temperature was lowered to −20 °C, which resulted in the precipitation of white crystals of the title compound (172 mg, 80%). All recorded data are consistent with literature values …”

Section: Methodsmentioning

confidence: 99%

Catalytic Dehydrocoupling of Amine–Boranes using Cationic Zirconium(IV)–Phosphine Frustrated Lewis Pairs

Metters¹,

Flynn²,

Dowds

et al. 2016

ACS Catal.

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. Full terms of use are available: http://www.bristol.ac.uk/pure/about/ebr-terms ] is shown to give unprecedented turnover frequencies (TOF) for a catalyst based on a group 4 metal (TOF = > 600 h -1 ), whilst also proving to be the most efficient FLP catalyst reported to date. The mechanism of this reaction has been probed using analogous intermolecular Zr(IV)/P FLPs, permitting deconvolution of the reactions taking place at both the Lewis acidic and basic sites. Elucidation of this mechanism revealed an interesting cooperative two-cycle process where one cycle is FLP mediated, the other, a redistribution of a linear diborazane intermediate, relies solely on the presence of a Zr(IV) Lewis acid.

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“…The inner-sphere ion pair 3 is stable for weeks in solution at room temperature. In contrast, both 4 and 7 undergo C–H activation of a propyl moiety, forming methane and metallacyclic ion pairs 5 and 8 , respectively. At room temperature in benzene- d 6 , the formation of 5 is complete within ∼24 h. Complex 8 forms faster (∼3 h) but its purity is rather low due to side reactions.…”

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C–H Activation and Olefin Insertion as Sources of Multiple Sites in Olefin Polymerization Catalyzed by Cp^AlkylHf(IV) Complexes

et al. 2016

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Intramolecular activation of hydrocarbyls to form metallacyclic complexes is a relatively fast process in cationic hafnocene catalysts bearing propyl-substituted Cp ligands. The resulting metallacycles are effective 1-hexene polymerization catalysts with activities comparable to that of the nonmetalated precursor. Ad hoc polymerizations of 1-hexene, using (Cp Pr )2HfMe2 as catalyst precursor, allow the isolation and characterization, via nuclear magnetic resonance (NMR) and matrix-assisted laser desorption ionization (MALDI) techniques, of polymers containing (Cp CH 2–CH 2–CR 3 )2HfCl2 (R = H or polymeryl) units. The polymeryl substitutions arise from irreversible incorporation of polymer chains onto the cyclopentadienyl ligand substituent(s) via metallacycle intermediates. As a consequence of such “self-modification”, multiple active sites are generated by a nominally single-site catalyst; this may explain the broadening of the molecular weight distribution (MWD) and chemical composition distribution (CCD) observed in olefin polymerization.

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An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate

Cited by 9 publications

References 36 publications

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

Catalytic Dehydrocoupling of Amine–Boranes using Cationic Zirconium(IV)–Phosphine Frustrated Lewis Pairs

C–H Activation and Olefin Insertion as Sources of Multiple Sites in Olefin Polymerization Catalyzed by Cp^AlkylHf(IV) Complexes

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An NMR study on the reaction of substituted dimethyl zirconocenes with dimethylanilinium borate

Cited by 9 publications

References 36 publications

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

Role of Solvent Coordination on the Structure and Dynamics of ansa-Zirconocenium Ion Pairs in Aromatic Hydrocarbons

Catalytic Dehydrocoupling of Amine–Boranes using Cationic Zirconium(IV)–Phosphine Frustrated Lewis Pairs

C–H Activation and Olefin Insertion as Sources of Multiple Sites in Olefin Polymerization Catalyzed by CpAlkylHf(IV) Complexes

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C–H Activation and Olefin Insertion as Sources of Multiple Sites in Olefin Polymerization Catalyzed by Cp^AlkylHf(IV) Complexes