Carbene Complexes Of Iridium Research Articles

1Pyridine and phosphine functionalised N-heterocyclic carbene complexes of rhodium and iridium

The pyridine functionalised N-heterocyclic carbene complexes [M(κ 2-NC DIPP)(COD)] +A −, NC DIPP = 3 - ( 2 , 6 - Pr 2 i C 6 H 3 ) - 1 - [ 2 - ( 3 - picolyl ) ] - imidazol - 2 - ylidene , A - = [ Ar 4 F B ] - , [{3,5-(CF 3) 2C 6H 2} 4B] −, M = Rh, 1b, Ir, 4, have been prepared in two steps by reaction of the [M(COD)Cl] 2 with the isolated NC DIPP to [Rh(κ 1-NC DIPP)(COD)Cl], 2, and [Ir(κ 2-NC DIPP)(COD)Cl], 3, followed by anion exchange with Na +A −. The phosphine functionalised N-heterocyclic carbene complex [Rh(PCH 2C mes) 2]Br, 6, PCH 2C mes = 1-(diphenylphosphino-methyl)-3-(2,4,6-Me 3C 6H 2)-imidazol-2-ylidene, was prepared by the reaction of the [Rh(COD)Cl] 2 with the corresponding N-heterocyclic carbene generated in situ. Monomeric [Rh(PCH 2CH 2C DIPP)(acac)], 7 was prepared by an analogous reactions from [Rh(COE) 2(acac)]. In contrast, phosphine functionalised N-heterocyclic carbene complexes of iridium (I) were not easily accessible. However, the reaction of [Ir(COD)(μ-Cl)2(μ-H)]2 with PCH 2CH 2C mes gave complex [Ir(COD)(PCH 2CH 2C mes )Br], 8, in which the carbene is coordinated to the metal in an ‘abnormal’ mode.

Synthesis of New Cationic Cp*Ir N-Heterocyclic Carbene Complexes and Their High Catalytic Activities in the Oppenauer-Type Oxidation of Primary and Secondary Alcohols

Several new cationic Cp*Ir N-heterocyclic complexes have been synthesized and their catalytic activities in the Oppenauer-type oxidation have been investigated in order to improve the catalytic activity of [Cp*IrCl(μ-Cl)]2. The reactions of [Cp*IrCl(μ-Cl)]2 (1) with N-heterocyclic carbene ligands afforded Cp*Ir(L)Cl2 (3a−d; L = N-heterocyclic carbene ligands). The cationic complexes [Cp*Ir(L)(MeCN)2]2+ (5a−d) were obtained by the treatment of 3a−d with 2 equiv of AgOTf followed by addition of CH3CN. Structures of complexes 3a−d and 5a−d were determined by X-ray crystallographic studies. Complex 5a (L = 1,3,4,5-tetramethylimidazol-2-ylidene) catalyzed the Oppenauer-type oxidation of primary and secondary alcohols very selectively under mild conditions. In the oxidation of 1-phenylethanol and cyclopentanol using 5a as a catalyst, turnover numbers reached 3200 and 6640, respectively. These results demonstrate that, to the best of our knowledge, the cationic carbene complex 5a is the most effective catalyst in homogeneous oxidation of alcohols in terms of its high catalytic activity and wide applicability to the oxidation of primary and secondary alcohols. In this catalytic system, the stronger electron-donating ability of the N-heterocyclic carbene ligand than the phosphine ligand is more favorable for acceleration of the hydride transfer to acetone as a hydrogen acceptor. Additionally, dihydrido carbene complex Cp*Ir(L)(H)2 (6) and dinuclear iridium carbene complex [Cp*Ir(L)(μ-H)]22+ (7) were prepared to investigate the catalytically active species and fate of the catalyst. Thus, it is highly probable that an iridium-monohydride complex is the catalytically active species and that 7, which could be generated by dimerization of the iridium-monohydride complex in the catalytic system, is inactive.

Synthesis and structure of N-heterocyclic carbene complexes of rhodium and iridium derived from an imidazolium-linked cyclophane

This paper describes the synthesis, spectroscopic and structural characterisation, and electrochemical behaviour of some rhodium and iridium complexes of the form LM(X 1)(X 2) +, where L is a chelating bis(carbene) derived from an imidazolium-linked ortho-cyclophane. The complexes where X 1/X 2 = 1,5-cycooctadiene or norbornadiene were prepared from the imidazolium-linked cyclophane and the appropriate metal source. In these complexes, the M–L bonding was quite robust, but the diene could be displaced by CO to give the dicarbonyl complexes LM ( CO ) 2 + , from which one or both carbonyl ligands could be displaced by monodentate or bidentate phosphines, respectively. Structural studies revealed only minor variations in the cyclophane unit upon exchange of the ancillary ligands, in each case the rhodium complex being isomorphous with its iridium analogue. In cyclovoltammetric studies of LRh(dppe) +, reversible Rh(I/II) and Rh(II/III) redox couples were observed. The other rhodium complexes displayed more complex electrochemical behaviours and did not undergo simple reversible redox reactions.

Purine-based carbenes at rhodium and iridium

Purine-based carbenes can be attached to catalysis-related metals like rhodium and iridium through the standard method of in situ deprotonation of the respective azolium salts. Thus, 1,3,7,9-tetramethylxanthinium tetrafluoroborate is obtained by the reaction of trimethyloxonium tetrafluoroborate and caffeine. The salt and 7,9-dimethylhypoxanthinium iodide were used as a consecutive precursor to form rhodium (I) and iridium (I) carbene complexes of the type [M(L)(L Carbene) 2]I and M(L)(L Carbene)(I) (M = Rh, Ir, L Carbene = 1,3,7,9-tetramethylxanthine-8-ylidene, 7,9-dimethylhypoxanthine-8-ylidene, L = η 4-1,5-COD, CO) (COD = 1,5-cyclooctadiene). All compounds were characterized by 1H NMR, 13C NMR, mass spectrometry and/or elemental analysis.

Carbene complexes of rhodium and iridium from tripodal N-heterocyclic carbene ligands: synthesis and catalytic properties.

Two tripodal trisimidazolium ligand precursors have been tested in the synthesis of new N-heterocyclic carbene rhodium and iridium complexes. [Tris(3-methylbenzimidazolium-1-yl)]methane sulfate gave products with coordination of the decomposed precursor. [1,1,1-Tris(3-butylimidazolium-1-yl)methyl]ethane trichloride (TIMEH(3)(Bu)) coordinated to the metal in a chelate and bridged-chelate form, depending on the reaction conditions. The crystal structures of two of the products are described. The compounds resulting from the coordination with TIME(Bu) were tested in the catalytic hydrosilylation of terminal alkynes.

Carbene Iridium(I) and Iridium(III) Complexes Containing the Metal Center in Different Stereochemical Environments

The mixed-ligand complex [IrCl(C2H4)(SbiPr3)(PiPr3)] (2), prepared from [IrCl(C2H4)(PiPr3)]2 (1) and SbiPr3, reacts not only with CO, diphenylacetylene, and H2 by ligand substitution or oxidative addition but also with diaryldiazomethanes R2CN2 to give the four-coordinate iridium(I) carbenes [IrCl(CR2)(SbiPr3)(PiPr3)] (8−10) in 60−70% isolated yield. In contrast, treatment of 2 and of the related cyclooctene derivative trans-[IrCl(C8H14)(SbiPr3)2] (12) with C5Cl4N2 affords the diazoalkane complexes trans-[IrCl(N2C5Cl4)(SbiPr3)(EiPr3)] (11, E = P; 13, E = Sb) without elimination of N2. Displacement of the stibine ligand in 8−10 by PiPr3 leads to the corresponding bis(phosphine) compounds trans-[IrCl(CR2)(PiPr3)2] (14−16), while the reaction of 8 (R = C6H5) with NaC5H5 yields the half-sandwich-type complex [(η5-C5H5)Ir(CPh2)(PiPr3)] (17). Protonation of 17 with HCl occurs stepwise to give via the iridium(III) alkyl [(η5-C5H5)IrCl(CHPh2)(PiPr3)] (20) the ring-substituted isomer [(η5-C5H4CHPh2)IrHCl(PiPr3)] (21); however, if 17 is treated with HBF4, a cationic complex is formed which probably contains a η3-coordinated benzylic ligand. The square-planar iridium(I) carbenes 8 and 14 react with HBX4 (X = F, ArF) to afford the ionic products [IrHCl(CPh2)(PiPr3)(EiPr3)]BX4 (23, 24, E = P; 25, E = Sb) and with HCl to give the relatively labile octahedral species [IrHCl2(CPh2)(PiPr3)(EiPr3)] (26, E = P; 27, E = Sb). Treatment of 8 and 14 with ethene yields, besides [IrCl(C2H4)2(SbiPr3)2] (18) and/or trans-[IrCl(C2H4)(PiPr3)2] (28), a mixture of two isomeric olefinic products CH2CHCHPh2 (29) and CH3CHCPh2 (30), the ratio of which is independent of the ligand sphere of the iridium precursor. The molecular structures of 13, 14, 17, and 24 have been determined by X-ray crystallography.

C–H activation with N-heterocyclic carbene complexes of iridium and rhodium

The first example of intramolecular, room temperature activation of a C–H bond in N-pyridine functionalised heterocyclic carbene complexes of iridium is reported.

A Cationic Iridium Complex Bearing an Imidazol-2-ylidene Ligand as Alkene Hydrogenation Catalyst

The new cationic iridium carbene complex [Ir(cod)(py)(SIMes)]PF6 (2) has been synthesized by reaction of [Ir(cod)(py)2]PF6 with SIMes. Complex 2 is an active hydrogenation catalyst capable of hydrogenating simple olefins at room temperature and atmospheric pressure of hydrogen.

Generation of Heteroatom-Substituted Carbene Complexes of Iridium by Double C−H Activation of Ether and Amine Substrates

Regioselektive, doppelte C-H-Aktivierung unterschiedlicher Ether- [siehe Beispiel in Gl. (1)] und Aminsubstrate wird durch die IrI-Verbindung [Ir(κ3-TpPh)(η4-isopren)] bewirkt (TpPh=Hydridotris(3-phenylpyrazol-1-yl)borat). Die Bildung eines entsprechenden Fischer-Carbenkomplexes ist das Resultat dieser Reaktionssequenz.

Generation of Heteroatom-Substituted Carbene Complexes of Iridium by Double C-H Activation of Ether and Amine Substrates This work was supported by the "Fonds zur Förderung der wissenschaftlichen Forschung" with a Schrödinger Stipendium for C.S. (J1756-CHE), the Spanish Ministry of Education (DGES, Project PB97-0733), and the Junta de Andalucía.

Regioselective, double C−H activation of a variety of ether and amine substrates, as exemplified with an ether in [Eq. (1)], is effected by the IrI compound [Ir(κ3-TpPh)(η4-isoprene)]). The formation of the corresponding Fischer-type carbenes follows the activation reaction. TpPh=hydridotris(3-phenylpyrazol-1-yl)borate. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2000/z14616_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Synthesis of Fischer Carbene Complexes of Iridium by C−H Bond Activation of Methyl and Cyclic Ethers: Evidence for Reversible α-Hydrogen Migration

We report here a mild and versatile route to Fischer carbene complexes of iridium via the activation of C-H bonds of methyl and cyclic ethers, along with our preliminary studies of this rare family of carbene complexes. Theoretical studies suggest that {alpha}-hydrogen migrations can be kinetically favorable if a coordinatively unsaturated species can be accessed. Thus, the lability of the triflate ligand presumably facilitates this process. Further evidence for the rapidity, as well as reversibility, of this rearrangement was obtained by NMR analysis. 20 refs.

ChemInform Abstract: Carbene and Carbyne Complexes of Ruthenium, Osmium, and Iridium

ChemInform Abstract: Carbene and Carbyne Complexes of Ruthenium, Osmium, and Iridium

ChemInform Abstract: FORMYL, HYDROXYMETHYL, AND CARBENE COMPLEXES OF IRIDIUM

Chemischer InformationsdienstVolume 15, Issue 16 Reviews ChemInform Abstract: FORMYL, HYDROXYMETHYL, AND CARBENE COMPLEXES OF IRIDIUM D. L. THORN, D. L. THORNSearch for more papers by this author D. L. THORN, D. L. THORNSearch for more papers by this author First published: April 17, 1984 https://doi.org/10.1002/chin.198416350AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume15, Issue16April 17, 1984 RelatedInformation

Carbene complexes of iridium, rhodium, manganese, chromium, and iron containing thiazolidinylidene and pyridinylidene ligands

New carbene complexes of IrI, RhI, MnI, Cr0, and Fe0 have been prepared by reactions of the appropriate carbonylmetal anions with N-methyl- and N-ethyl-2-chloro-4-methylthiazolium tetrafluoroborate and N-methyl-2-chloropyridinium tetrafluoroborate. The anions [Ir(CO)3PPh3]–, [Rh(CO)2(PPh3)2]–, and [Mn(CO)5]– afford cationic carbene complexes, whereas [Cr(CO)5]2– and [Fe(CO)4]2– yield neutral carbene complexes. Treatment of [Mn(CO)5{[graphic omitted]}][BF4] with iodide ion gives a neutral complex [cis-Mnl(CO)4{[graphic omitted]}].The cation [Ir(CO){[graphic omitted]}(PPh3)2]+ reacts with hydrogen to give [IrH2(CO){[graphic omitted]}(PPh3)2]+. The cation also reacts oxidatively to give IrIII complexes with HCl, Cl2, and I2. Lithium chloride or bromide reacts to give [IrH(X)(CO){[graphic omitted]}(PPh3)2][BF4](X = Cl or Br), whereas [Ir(CO){[graphic omitted]H}(PPh3)2][BF4] affords the neutral IrIII species [IrCl3{[graphic omitted]H}(PPh3)2]. Methyl iodide reacts with [Ir(CO){[graphic omitted]}(PPh3)2][BF4] to give [Irl2Me(CO){[graphic omitted]}(PPh3)].Some spectroscopic properties of the new complexes are reported.

Cationic cyclic carbene complexes of iridium(III), nickel(II), palladium(II), and platinum(II)

Reaction of the 2-chloro-derivatives of 5-methyl-1,3-thiazole, benzthiazole, and benzoxazole with IrCl(CO)(PMe2Ph)2 affords IrIII complexes which on protonation yield cationic carbene complexes [IrCl2(CO)(PMe2Ph)2(L)]+(L = [graphic omitted], [graphic omitted], [graphic omitted]). Treatment of IrCl(CO)(PMe2Ph)2 with the N-methyl salt of 2-chloro-5-methyl-1,3-thiazole, [Cl[graphic omitted]][BF4], affords the carbene complex [IrCl2(CO)(PMe2Ph)2{[graphic omitted]}][BF4]. Similar oxidative-addition of [Cl[graphic omitted]][BF4] to Pt(PEt3)2(stilbene), Pt(PMePh2)4, PdL4(L = PPh3, PMePh2) or Ni(PPh3)4 gives cationic carbene complexes of PtII, PdII, and NiII. The complex [PtCl{[graphic omitted]}(PEt3)2][BF4] was obtained by treating PtCl([graphic omitted])(PEt3)2 with fluoroboric acid. Some chemical and spectroscopic properties of the new complexes are discussed.

Cationic cyclic carbene or carbon-bonded ylide complexes of iridium(III) and platinum(II)

2-Chloro-4-methylthiazole, 2-chlorobenzoxazole and 2-chlorobenzthiazole oxidatively add to both [IrCl(CO)(PMe 2Ph) 2] and [Pt(PhCHCHPh)(PEt 3) 2]; protonation of the products at nitrogen produces cationic carbene complexes.