N-Heterocyclic and Mesoionic Carbene Complexes of the Group 4 Metals

Normand, Adrien T.

doi:10.1016/b978-0-12-820206-7.00003-2

Cited by 3 publications

(2 citation statements)

References 145 publications

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“…To date, a C2-deprotonation of imidazolium salts has been the most reliable approach for the synthesis of NHC pincer complexes . For instance, the report of monoanionic CCC-NHC pincer complexes 1 and 2 and neutral CNC-NHC pincer complexes 3 and 4 (Chart ) relied on C2-deprotonation of the azolium salts because of the higher acidity of the C2 protons . Due to the weaker acidity of C4 and C5 protons versus the C2 proton of the imidazolium salts, the most frequently synthesized aNHC pincer complexes are the 1,2,3-triazole based complexes 5 .…”

Section: Introductionmentioning

confidence: 99%

A Cationic Pt(II) Dinitrogen Adduct: Synthesis and Characterization of a CCC-aNHC Pincer Pt Complex with Abnormal N-Heterocyclic Carbene Donor Arms

Fosu,

Le,

Abdulraheem

et al. 2024

Organometallics

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In contrast to the reported CCC-NHC pincer ligands that contain normal N-heterocyclic carbenes (NHC), herein we report an imidazole-based abnormal NHC (aNHC) pincer ligand, CCC-aNHC. The CCC-aNHC pincer Pt complex with two aNHC donors was synthesized via the in situ metalation and transmetalation methodology. The 1,3-phenylene(bis-2phenyl-3-butyl imidazolium) diiodide salt was reacted with Zr(NMe 2 ) 4 to generate a CCC-aNHC pincer zirconium complex in situ. It was transmetalated to Pt using [Pt(COD)Cl 2 ]. Electrospray ionization of the Pt pincer complex [( Bu C a-i C a-i C Bu )-PtI] in acetonitrile generated an intense peak at m/z = 696.2375, which was assigned to the dinitrogen adduct [M−I+N 2 ] + of the cationic CCC-aNHC pincer Pt(II) complex [( Bu C a-i C a-i C Bu )Pt− N 2 ] + , representing a rare example of the platinum dinitrogen organometallic complex. The super electron-donating ability of the pincer ligands with abnormal NHC enabled the cationic CCC-aNHC pincer Pt(II) complex to selectively bind N 2 over MeCN in a first-order analysis. A collision-induced dissociation (CID) study was conducted on the N 2 and MeCN adducts, suggesting that more energy was required to dissociate N 2 than MeCN. A computational study suggested that the N 2 adduct was kinetically stable in the gas phase whereas the MeCN adduct was thermodynamically preferred. The computational results reconciled the mass spectral data experiment with an attempt to isolate the N 2 adduct. DFT computation suggested that N 2 dissociation is more challenging due to higher energy transition states, and there is a competitive pathway of N 2 tumbling within the coordination sphere of the Pt. This tumbling path is not available from the MeCN ligand due to ligand structural differences.

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Section: Introductionmentioning

confidence: 99%

A Cationic Pt(II) Dinitrogen Adduct: Synthesis and Characterization of a CCC-aNHC Pincer Pt Complex with Abnormal N-Heterocyclic Carbene Donor Arms

Fosu,

Le,

Abdulraheem

et al. 2024

Organometallics

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“…Coordination of N-heterocyclic carbenes (NHCs) to high-oxidation-state early transition metals such as Ti IV is inherently labile, yet a handful of unsupported NHC–Ti IV complexes have been isolated . However, when it comes to catalytic applications in which higher thermal and kinetic stabilities are desired, chelating NHCs with one or two monoanionic side arms are better . The side arms not only anchor the NHC–Ti motif but also invoke extra stereoelectronic variation.…”

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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The Chemistry of Vanadium bis‐Phenolate NHC Complexes in Three Oxidation States

et al. 2023

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Twenty‐one vanadium bis‐phenolate benzimidazolylidene complexes, spanning three oxidation states, have been investigated. Special emphasis is placed on their salt metathesis reactivity and the accessibility of the +IV oxidation state by reductive or oxidative routes, starting from vanadium(V) or vanadium(III) respectively. While the reductive route is highly dependent on the reducing agent and starting material used, the oxidative route gives clean access to vanadium(IV) dihalide complexes. The low‐valent vanadium(III) complexes are excellent precursors for salt metathesis reactions which lead to the isolation of a rare vanadium(III) NHC alkyl complex. All new complexes have been characterized by (paramagnetic) 1H NMR and 51V NMR, UV–VIS, IR and EPR spectroscopy as well as elemental analysis. Cyclic voltammetry has been performed in selected cases to study the influence of imido or phenolate supporting ligands towards the redox‐potential of the vanadium(V/IV) redox couple compared to the parent oxo‐chlorido complex A.

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N-Heterocyclic and Mesoionic Carbene Complexes of the Group 4 Metals

Cited by 3 publications

References 145 publications

A Cationic Pt(II) Dinitrogen Adduct: Synthesis and Characterization of a CCC-aNHC Pincer Pt Complex with Abnormal N-Heterocyclic Carbene Donor Arms

A Cationic Pt(II) Dinitrogen Adduct: Synthesis and Characterization of a CCC-aNHC Pincer Pt Complex with Abnormal N-Heterocyclic Carbene Donor Arms

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

The Chemistry of Vanadium bis‐Phenolate NHC Complexes in Three Oxidation States

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