Nickel(II), Palladium(II) and Rhodium(I) Complexes of New NHC‐Thioether Ligands: Efficient Ketone Hydrosilylation Catalysis by a Cationic Rh Complex

Wolf, J. G.; Labande, Agnès; Daran, Jean‐Claude; Poli, Rinaldo

doi:10.1002/ejic.200700670

Cited by 62 publications

(41 citation statements)

References 66 publications

(53 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Indeed, the measured coupling constants are in good agreement with those predicted from the measured dihedral angles from the X-ray structure of complex 4, allowing us to assign these resonances more precisely as shown in figure 1. As in the 13 C NMR spectrum, differentiation of the two aromatic 60 protons (slight) and ortho, ortho' methyl substituents (large) is observed in the 1 H NMR spectrum. The 1 H NMR spectrum of the ruthenium complex 5 showed a very different pattern, as all signals were broad even at low temperatures.…”

Section: Characterisation Of Complexes 4 Andmentioning

confidence: 83%

“…The 1 H NMR spectrum of the ruthenium complex 5 showed a very different pattern, as all signals were broad even at low temperatures. The formation of the Ru-NHC bond, however, was 65 confirmed by 13 C NMR with a signal at δ 164.5, similar to other NHC ruthenium(II) complexes bearing a p-cymene substituent. 6 Most signals were assigned by 13 C NMR: the o,o'-CH 3 substituents of the mesityl group were barely distinct, whereas both CH(CH 3 ) 2 signals from the p-cymene moiety were well 70 separated at δ 20.4 and 24.8.…”

Section: Characterisation Of Complexes 4 Andmentioning

confidence: 97%

“…The formation of the Ru-NHC bond, however, was 65 confirmed by 13 C NMR with a signal at δ 164.5, similar to other NHC ruthenium(II) complexes bearing a p-cymene substituent. 6 Most signals were assigned by 13 C NMR: the o,o'-CH 3 substituents of the mesityl group were barely distinct, whereas both CH(CH 3 ) 2 signals from the p-cymene moiety were well 70 separated at δ 20.4 and 24.8. The signals for the CH 2 Im carbon appeared in the expected region at δ 49.2, as well as the CH 2 S signal at δ 33.7.…”

Section: Characterisation Of Complexes 4 Andmentioning

confidence: 97%

“…The 40 coordination of the carbene on rhodium was evidenced by 13 C NMR by a doublet at δ 166.3, with a coupling constant J Rh-C of 54 Hz, typical of rhodium(III)-NHC complexes. [13][14]20 All three methyl groups from the mesityl moiety are now distinct, whereas the two ortho methyl groups had the same chemical shift in 3b. 45 This means that the rotation of the mesityl group along the C-N bond is blocked, presumably because of close contact with the Cp* ligand.…”

Section: Characterisation Of Complexes 4 Andmentioning

confidence: 99%

“…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. …”

mentioning

confidence: 99%

See 4 more Smart Citations

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

et al. 2011

Self Cite

View full text Add to dashboard Cite

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...

show abstract

Section: Characterisation Of Complexes 4 Andmentioning

confidence: 83%

Section: Characterisation Of Complexes 4 Andmentioning

confidence: 97%