Reactivity Differences in the Syntheses of Chelating N-Heterocyclic Carbene Complexes of Rhodium Are Ascribed to Ligand Anisotropy

Mata, José A.; Chianese, Anthony R.; Miecznikowski, John R.; Poyatos, Macarena; Peris, Eduardo; Faller, J. W.; Crabtree, Robert H.

doi:10.1021/om034240+

Cited by 205 publications

(186 citation statements)

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“…[8] Furthermore, palladium complexes of the type Pd(pyridine)Cl 2 (NHC) and PdCl 2 (NHC) 2 have been found to exhibit potent anticancer activity. [9] Various bis-NHC ligands have been reported, which are usually linked by alkenic chains [7,[10][11][12][13] or an N-donor such as a pyridyl derivative or amine, [14][15][16] and tend to form chelating complexes with metals. NHC ligands containing a xylylene-bridge are surprisingly rare.…”

Section: Introductionmentioning

confidence: 99%

Bis(N‐heterocyclic carbene) Dipalladium Complexes: Synthesis, Solid‐State Conformational Studies and Solution Behaviour

et al. 2009

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New palladium(II) bis(N-heterocyclic carbene) (NHC) complexes have been prepared via metallomacrocyclic Ag I ligand transfer agents. Reaction of 1,4-bis(3-isopropylimidazolium)xylene (1a) hexafluorophosphate with Ag 2 O gives a Ag I macrocyclic NHC complex in which two silver ions are sandwiched between two dipodal ligands (2a). The NHC moieties adopt a cisoid conformation relative to one another. Upon transfer to palladium to give [{PdCl 2 (MeCN)} 2 (bis-NHC)] (3a) the NHC ligands in the complexes adopt a mixture of cisoid and transoid conformers in the solid state,

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Section: Introductionmentioning

confidence: 99%

Bis(N‐heterocyclic carbene) Dipalladium Complexes: Synthesis, Solid‐State Conformational Studies and Solution Behaviour

et al. 2009

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“…While HPLC-MS analysis suggests a pure compound, NMR spectroscopic analysis shows two distinct sets of signals that were attributed to the rac and meso diastereoisomers of 5 as a consequence of the chirality of the complex at each ruthenium center. [15,24] Solubility tests revealed that one of the two isomers is less soluble in MeCN and was thus successfully separated by repetitive precipitation and filtration. This isomer is stable in solution over several days, which demonstrates that racemization at ruthenium is very slow.…”

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confidence: 99%

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

Nussbaum

Schuster

Albrecht

2013

Chemistry A European J

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A ditopic benzobis(carbene) ligand precursor was prepared that contained a chelating pyridyl moiety to ensure co‐planarity of the carbene ligand and the coordination plane of a bound octahedral metal center. Bimetallic ruthenium complexes comprising this ditopic ligand [L4Ru‐C,N‐bbi‐C,N‐RuL4] were obtained by a transmetalation methodology (C,N‐bbi‐C,N=benzobis(N‐pyridyl‐N′‐methyl‐imidazolylidene). The two metal centers are electronically decoupled when the ruthenium is in a pseudotetrahedral geometry imparted by a cymene spectator ligand (L4=[(cym)Cl]). Ligand exchange of the Cl−/cymene ligands for two bipyridine or four MeCN ligands induced a change of the coordination geometry to octahedral. As a consequence, the ruthenium centers, separated through space by more than 10 Å, become electronically coupled, which is evidenced by two distinctly different metal‐centered oxidation processes that are separated by 134 mV (L4=[(bpy)2]; bpy=2,2′‐bipyridine) and 244 mV (L4=[(MeCN)4]), respectively. Hush analysis of the intervalence charge‐transfer bands in the mixed‐valent species indicates substantial valence delocalization in both complexes (delocalization parameter Γ=0.41 and 0.37 in the bpy and MeCN complexes, respectively). Spectroelectrochemical measurements further indicated that the mixed‐valent RuII/RuIII species and the fully oxidized RuIII/RuIII complexes gradually decompose when bound to MeCN ligands, whereas the bpy spectators significantly enhance the stability. These results demonstrate the efficiency of carbenes and, in particular, of the bbi ligand scaffold for mediating electron transfer and for the fabrication of molecular redox switches. Moreover, the relevance of spectator ligands is emphasized for tailoring the degree of electronic communication through the benzobis(carbene) linker.

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“…6, 17 The reaction 20 was carried out with 3b in order to avoid a potential mixture of Cl and I on the Rh and Ru centres. It was conducted in the presence of excess Ag 2 O in dichloromethane at reflux.…”

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confidence: 99%

Rhodium(iii) and ruthenium(ii) complexes of redox-active, chelating N-heterocyclic carbene/thioether ligands

et al. 2011

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Dedicated to Professor Didier Astruc on the occasion of his 65th birthday.Half-sandwich rhodium(III) and ruthenium(II) complexes bearing a new redox-active ferrocenyl NHCthioether ligand have been prepared. The synthesis of ferrocenyl thioether-imidazolium salts 3a and 3b was carried out via intermediate 2 using an improved procedure. Rhodium(III) complex 4 and ruthenium(II) complex 5 were obtained in good yields and were fully characterised by NMR 10 spectroscopy, X-ray diffraction analysis and electrochemistry. Complex 4 shows a complex ABCD system by 1 H NMR, which denotes conformational rigidity due to the presence of several bulky groups.Electrochemical analysis by cyclic voltammetry reveals reversible redox behaviour about the iron centre in 4 and 5, and indicates electronic communication between iron and rhodium or ruthenium. Introduction 15N-Heterocyclic carbenes (NHCs) have become widely used ligands in many areas from transition metal catalysis, 1 organocatalysis, 2 to biochemistry and medicine. 3 They are generally described as organophosphine analogues, although their -donor character is more pronounced. Unlike phosphines, they 20 generally lead to air-stable, robust complexes which do not easily undergo ligand dissociation. However, the M-C bond stability could be detrimental to the catalytic activity. Functionalized Nheterocyclic carbene ligands combine the robust nature of the resulting metal-NHC bond with the flexibility of the secondary 25 donor function (hemilability, stereoelectronic control on the active site) and have been successfully used in many catalytic reactions. [4][5][6] However, any alteration of steric or electronic properties of a ligand implies structural modifications and thus more synthetic work. 30Fine tuning of the electronic properties can also be achieved by introduction of redox-active moieties in the ligands. 7 This has been demonstrated in the field of small molecule sensing 8,9 and in catalysis. 10 In the latter domain, transition metal complexes containing either substitutionally inert 11 or hemilabile 12 redox-35 active ligands have shown charge-dependent behaviour. Our group has a strong interest in the chemistry and catalytic activity of functionalised N-heterocyclic carbene complexes. We have shown that NHCs bearing thioether or phosphine donors give very efficient and robust catalysts. 13,14 The work reported 40 here describes the preparation of redox-active NHC-thioether ligands incorporating the ubiquitous ferrocene group and the study of their coordination chemistry and electrochemical behaviour. Results and discussion 45 SynthesisScheme 1 Synthesis of imidazolium salts 3a and 3b.The synthesis of the imidazolium salt 3b, i.e. the NHC-thioether precursor, was achieved in three steps from bromoferrocene 1. 50Although the preparation of intermediate 2 and its 1,1'-disubstituted analogue have been described by Mirkin et al., 15,16 we decided to follow a different synthetic route. Mirkin's reported procedures involved the monolithiation of ferrocene and afforded th...

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Reactivity Differences in the Syntheses of Chelating N-Heterocyclic Carbene Complexes of Rhodium Are Ascribed to Ligand Anisotropy

Cited by 205 publications

References 28 publications

Bis(N‐heterocyclic carbene) Dipalladium Complexes: Synthesis, Solid‐State Conformational Studies and Solution Behaviour

Bis(N‐heterocyclic carbene) Dipalladium Complexes: Synthesis, Solid‐State Conformational Studies and Solution Behaviour

Efficient Electronic Communication of Two Ruthenium Centers through a Rigid Ditopic N‐Heterocyclic Carbene Linker

Rhodium(iii) and ruthenium(ii) complexes of redox-active, chelating N-heterocyclic carbene/thioether ligands

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