Site-selective metallation of dicarbene precursors

Bente, Stefanie; Kampert, Florian; Tan, Tristan Tsai Yuan; Hahn, F. Ekkehardt

doi:10.1039/c8cc08440h

Cited by 23 publications

(23 citation statements)

References 43 publications

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“…We have noted previously that Pd II C-azolato complexes obtained by oxidative addition of 2-halogenoimidazole or 2-halogenobenzimidazole derivatives tend to form dinuclear species by nucleophilic attack of the unsubstituted azolato ring nitrogen atom at the metal center of a second complex molecule with elimination of one ligand. ,, The formation of such dinuclear species is less common for the more substitution inert Pt II complexes, where the mononuclear azolato complex has been isolated . No dinuclear complexes have been detected in the oxidative addition of 8-halogenotheophyllines to [Pd(PPh 3 ) 4 ].…”

Section: Resultsmentioning

confidence: 99%

“…However, the activation barriers to reach these products differ for the reactions with Ni 0 and Pd 0 . In contrast to benzimidazolato and imidazolato palladium(II) complexes, ,, the theophyllinato complexes [ 1 ]–[ 3 ] show no tendency to form dinuclear derivatives by attack of the unsubstituted ring nitrogen atom N9 at another complex molecule. This is apparently a consequence of the electron-poor theophylline backbone, which reduces the nucleophilicity of atom N9.…”

Section: Discussionmentioning

confidence: 99%

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Synthesis of Pd^II Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd⁰

2020

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Various 8-halogenotheophyllines (halogen = Cl, Br, I) were selectively C8 metalated by an oxidative addition of the C8–halogen bond to [Pd(PPh3)4] to give the PdII azolato complexes [1]–[3]. The complexes were protonated at the N9 nitrogen atom to yield the NH,NH-NHC (pNHC) complexes [4]BF4–[6]BF4. Due to the unsymmetrical nature of the backbone of the theophylline-derived pNHC ligands, two NH resonances were observed by 1H NMR spectroscopy. In addition, 8-bromoadenine was also regioselectively C8 metalated via an oxidative addition of the C8–Br bond to [Pd(PPh3)4] in the presence of the proton source pyridinium tetrafluoroborate to give [7]BF4.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Synthesis of Pd^II Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd⁰

2020

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“…The proton source py ⋅ HBF 4 was added to convert the azolato complex initially formed in the oxidative addition into the p NHC complex. Without the N‐protonation, the azolato complexes often exhibit a tendency to form dinuclear complexes through an attack of the strongly basic unsubstituted ring‐nitrogen atom N24 at a metal center of a second complex molecule [8a,9a,d,11a] …”

Section: Methodsmentioning

confidence: 99%

Regioselective Double Oxidative Addition of Bis‐NHC Precursors

et al. 2021

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The 4,4'-dimethylenebiphenyl linked symmetric bis-(2-chlorobenzimidazole) 1 and the unsymmetric 2-chlorobenzimidazolium/2-chlorobenzimidazole 2(BF 4 ) have been reacted with one equivalent [Pd(PPh 3 ) 4 ] in oxidative addition reactions. For the symmetric bis-NHC precursor 1, double metallation of both 2chlorobenzimidazole sites to give the dinuclear bis-pNHC complex [3](BF 4 ) 2 was observed. The unsymmetric compound 2(BF 4 ) was only metallated at the 2-chlorobenz-imidazolium site with formation of the mononuclear NHC complex [4](BF 4 ). The remaining 2-chlorobenzimidazole moiety was subsequently metallated in a second oxidative addition reaction with [M-(PPh 3 ) 4 ] (M = Pd, Pt) to give the homobimetallic NHC/pNHC complex [5](BF 4 ) 2 (M = Pd) and the heterobimetallic complex [6](BF 4 ) 2 demonstrating the unique site-selective metallation of the bis-NHC precursor 2(BF 4 ) by two consecutive oxidative additions.

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“…However, certain examples have shown that the heterometallic NHC-M C complexes formed during the treatment of the corresponding metalcontaining imidazolium salts with Ag 2 O [152][153][154][155][156][157] or Cu 2 O [115] are stable and can be isolated. The similar heterometallic NHC-M C complexes (pre-synthesized or generated in situ) can be involved in the transmetalation reaction at the M C atom with preservation of the other metal coordinated at the neighbor covalently bound ligand (Scheme 30) [114,115,[158][159][160][161][162][163][164][165][166][167][168][169][170][171][172]. A common feature of these examples is that the potential carbene-accepting metal in the structure of such complexes is strongly chelated [114, 115, 158-163, 167, 168] or involved in a metallocene [164-166, 171, 172] and, hence, cannot be involved in the transmetalation.…”

Section: Transmetalation Retaining the Other Atom In The Productmentioning

confidence: 99%

Alternative Transformations of N-Heterocyclic Carbene Complexes of the Group 11 Metals in Transmetalation Reactions (A Review)

Mikhaylov

Балова

2021

Russ J Gen Chem

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The carbene transfer from N-heterocyclic carbene complexes of Group 11 metals (NHC-M C ) (especially silver and copper) to other metals is considered a convenient and universal, sometimes having no alternative, method for the synthesis of a wide range of important N-heterocyclic carbene complexes of transition metals. As the number of successful examples of transmetalation with the formation of the target product has increased, the data were accumulated on alternative or unexpected results of the interaction of NHC-M C complexes with compounds of other metals. This review considers the examples of NHC-M C reactions with compounds of other metals which proceed with a change in the metals oxidation state, conversion of (NHC)M C X into cationic homoleptic [(NHC) 2 M C ] + forms, transmetalation retaining the other metal in the coordination sphere of the product, or formation of heterometallic adducts preserving the M C -C carbene bond, rather than these occurring according to the standard reaction pathway. Unusual "reverse" carbene transfer reactions have been considered separately. The review material reveals a promising new synthetic potential of NHC-M C in the reactions with other metals and discusses the possible mechanisms and driving forces of such transformations. The most important aspects of the application of the obtained products, primarily in various catalytic processes, have been considered as well.

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Site-selective metallation of dicarbene precursors

Abstract: Heterobimetallic bis-NHC complexes have been obtained by the site-selective metallation of imidazolium/2-chlorobenzimidazole bis-NHC precursors using two different reactions.

Cited by 23 publications

References 43 publications

Synthesis of Pd^II Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd⁰

Synthesis of Pd^II Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd⁰

Regioselective Double Oxidative Addition of Bis‐NHC Precursors

Alternative Transformations of N-Heterocyclic Carbene Complexes of the Group 11 Metals in Transmetalation Reactions (A Review)

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Site-selective metallation of dicarbene precursors

Abstract: Heterobimetallic bis-NHC complexes have been obtained by the site-selective metallation of imidazolium/2-chlorobenzimidazole bis-NHC precursors using two different reactions.

Cited by 23 publications

References 43 publications

Synthesis of PdII Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd0

Synthesis of PdII Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd0

Regioselective Double Oxidative Addition of Bis‐NHC Precursors

Alternative Transformations of N-Heterocyclic Carbene Complexes of the Group 11 Metals in Transmetalation Reactions (A Review)

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Synthesis of Pd^II Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd⁰

Synthesis of Pd^II Complexes Bearing pNHC Ligands by Oxidative Addition of 8-Halogenotheophyllines and 8-Bromoadenine to Pd⁰