Towards NHC stabilized alkylgallium alkoxide/aryloxide cations – The advances, the limitations and the challenges

Dąbrowska, Anna; Hurko, Aleksander; Dranka, Maciej; Varga, Vojtěch; Urbańczyk, Mateusz; Horeglad, Paweł

doi:10.1016/j.jorganchem.2017.03.046

Cited by 8 publications

(4 citation statements)

References 41 publications

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“…The O , C bidentate and monoanionic NHC-aryloxide [ Ar O–CH 2 – NHC ] − ligand class with a flexible –CH 2 – linker has so far been explored with metals like Y, 12 Yb, 13 Fe, 14 Ni, 15 Mg, 15 b Ag, 16 Ir, 17 Ru, 16 and Ga. 18 Introducing a new [ Ar O–CH 2 – NHC ] − derivative of [ O -4,6-Bu t 2 -C 6 H 2 -2-CH 2 {C(NCHCHNDipp)}] − (L; Dipp = 2,6-Pr i 2 -C 6 H 3 ), we recently reported its Ti complex [Ti(L)(NMe 2 ) 2 Br] as the first NHC-bound Ti( iv ) catalyst for the ROP of ε-caprolactone (CL). 19 The polymerization works without a cocatalyst and at room temperature through a bifunctional MLC-type (metal–ligand cooperation) mechanism, where the NHC itself acts as an internal nucleophile in the initiation step, conforming to the weakness of the C NHC –Ti bond (Fig.…”

Section: Introductionmentioning

confidence: 99%

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

Goswami,

Mandal,

Sarkar

et al. 2024

Dalton Trans.

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Section: Introductionmentioning

confidence: 99%

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

Goswami,

Mandal,

Sarkar

et al. 2024

Dalton Trans.

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“…NHCs with a -CH 2 -connected aryloxide sidearm constitute a bidentate and monoanionic ligand class (Figure ). But, reaching them from their doubly acidic imidazolium-phenol precursor shows an interesting twist. To illustrate, the N -methyl imidazolium salt (Figure ) is deprotonated by two equiv of NaHMDS at −78 °C to result the expected [( Me NHC–CH 2 –Ar t Bu2 O)]Na complex, which can transfer the ligand as shown by the in situ transmetalation with MesMgBr .…”

Section: Introductionmentioning

confidence: 99%

An Imidazolium Salt That Uncharacteristically Avoids the Imminent Deprotonation of Its Acidic 2-H Proton by KN(SiMe₃)₂

Goswami,

Sarkar,

Mallick

et al. 2024

Organometallics

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KN(SiMe 3 ) 2 , a non-nucleophilic strong base, rarely misses deprotonating an imidazolium-2-H to give its N-heterocyclic carbene (NHC). We report a rare case of a -CH 2 -linked bifunctional imidazolium-phenol t Bu 2 -C 6 H 2 -2-CH 2 {CH(NCH�CHNAr)}]Br [LH 2 Br; Ar = 2,6-i Pr 2 −C 6 H 3 (Dipp)], whose attempted double deprotonation by KN(SiMe 3 ) 2 majorly gives an unusual substitution product [Apparently, the second KN(SiMe 3 ) 2 , instead of deprotonating the imidazolium-2-H, substitutes the whole imidazolium moiety from the benzylic carbon. Control experiments indicate a S N 1-type mechanism. But the intermediate LH, seemingly a zwitterionic imidazolium aryloxide, also shows a steady self-fragmentation by releasing free Dipp Imd to suggest a complex formative route for 1. Interestingly, LiN(SiMe 3 ) 2 in contrast favors the expected double deprotonation but further undergoes a 1,2-benzyl migration to give trimeric [Li(O-4,6-t Bu 2 -C 6 H 2 -2-CH 2 {C(NCH�CHNAr)}] 3 [4] 3 . Two plausible routes for the substitution and deprotonation are proposed using DFT calculations. However, considering the complexities involved, a better clarity of the Li/K divergence would require a more accurate modeling of the reaction species and explicit solvent molecules.

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“…Compared to [ Ar O C ] − , the more flexible [ Ar O CH 2 C ] − ligand class with a -CH 2 - linker has been less explored. A few examples include Y, Yb, Fe, Ni, Mg, Ag, Ir, Ru, and Ga (Chart ), while a Ti chemistry has not yet been documented. One reason could be the knack of their alkali metal salts [( Ar O CH 2 C )M] (M = Li or Na), the primary ligand transfer agents, for 1,2-benzyl migration from nitrogen to the adjacent C carbene , ,, a known carbene deactivation route .…”

Section: Introductionmentioning

confidence: 99%

“…A few examples include Y, Yb, Fe, Ni, Mg, Ag, Ir, Ru, and Ga (Chart ), while a Ti chemistry has not yet been documented. One reason could be the knack of their alkali metal salts [( Ar O CH 2 C )M] (M = Li or Na), the primary ligand transfer agents, for 1,2-benzyl migration from nitrogen to the adjacent C carbene , ,, a known carbene deactivation route . The tridentate ( Ar O CH 2 C CH 2 O Ar ) 2– also suffers from the same…”

Section: Introductionmentioning

confidence: 99%

A Bifunctional NHC-Aryloxido Titanium Catalyst for the Ring-Opening Polymerization of ε-Caprolactone and an Unusual Fragmentation of Its Ligand Backbone

et al. 2023

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N-Heterocyclic carbenes (NHCs) with a methylene-linked aryloxide side arm constitute a flexible bidentate ligand platform whose usability is partly hindered as their alkali metal salts, the primary ligand transfer agents, are prone to carbene deactivation by 1,2-benzyl migration. Reacting an imidazolium precursor of this ligand class [HO-4,6-Bu t 2-C6H2-2-CH2{CH(NCHCHNAr)}]Br [LH 2Br; Ar = 2,6-Pr i 2-C6H3 (Dipp)] with Ti(NMe2)4 in 1:1 ratio readily gives the monoligated titanium complex [(L)Ti(NMe2)2Br] (1). Reacting 1 with an additional 1 equiv of LH 2Br shows an interesting fragmentation behavior of L–, distinct from that 1,2-migration, and gives the cationic Ti complex [(LH)Ti{κ2-(O-4,6-Bu t 2-C6H2-2-CH2NMe2)}(NMe2)Br]Br ([2]Br). This shows the vulnerability of the NHC–Ti motif in 1 and presents a rare case in which an imidazolium moiety acts as a leaving group, departing as an aryl imidazole. The nature of the NHC–Ti bond in 1 and its conversion into [2]Br are probed by computational analyses. In addition, 1 is established as a catalyst for the ring-opening polymerization of ε-caprolactone (CL), where it exhibits high activity and good control over polymer growth under ambient conditions. A kinetic analysis suggests the classic coordination–insertion mechanism with a typical first-order dependence on CL concentration, while the end group characterization indicates a bifunctional nature of the NHC–Ti combo in which the labile NHC makes the nucleophilic attack in the ring-opening initiation step.

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Towards NHC stabilized alkylgallium alkoxide/aryloxide cations – The advances, the limitations and the challenges

Cited by 8 publications

References 41 publications

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

An Imidazolium Salt That Uncharacteristically Avoids the Imminent Deprotonation of Its Acidic 2-H Proton by KN(SiMe₃)₂

A Bifunctional NHC-Aryloxido Titanium Catalyst for the Ring-Opening Polymerization of ε-Caprolactone and an Unusual Fragmentation of Its Ligand Backbone

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Towards NHC stabilized alkylgallium alkoxide/aryloxide cations – The advances, the limitations and the challenges

Cited by 8 publications

References 41 publications

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

Flexible NHC-aryloxido aluminum complex and its zwitterionic imidazolium aluminate precursor in ring-opening polymerization of ε-caprolactone

An Imidazolium Salt That Uncharacteristically Avoids the Imminent Deprotonation of Its Acidic 2-H Proton by KN(SiMe3)2

A Bifunctional NHC-Aryloxido Titanium Catalyst for the Ring-Opening Polymerization of ε-Caprolactone and an Unusual Fragmentation of Its Ligand Backbone

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An Imidazolium Salt That Uncharacteristically Avoids the Imminent Deprotonation of Its Acidic 2-H Proton by KN(SiMe₃)₂