1. Carbene-anchored/pendent-imidazolium species as precursors to di-N-heterocyclic carbene-bridged mixed-metal complexesElectronic supplementary information (ESI) available: 1H and 13C{1H} NMR spectra of 2c, 8b, 10band 23b; decoupled spectra for 9b; variable temperature spectral data for 18b. CCDC reference numbers 726822–726827. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b906884h
- Author
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Matthew T. Zamora, Michael J. FergusonX-Ray Crystallography Laboratory., Robert McDonald, and Martin Cowie
- Subjects
CARBENES ,METAL complexes ,IMIDAZOLES ,HETEROCYCLIC compounds ,NUCLEAR magnetic resonance spectroscopy ,CHEMICAL reactions ,BROMIDES ,PROTON transfer reactions - Abstract
Reaction of a series of linked diimidazolium dibromide salts with one-half equivalent of [Rh(μ-OAc)(COD)]2under reflux conditions generates a series of carbene-anchored/pendent-imidazolium complexes, [RhBr(COD)(RC(H)-η1-Ceth)][Br] (MeC(H)-η1-Ceth= ethylene[(N-methyl)imidazolium][(N-methyl)imidazole-2-ylidene] and tBuC(H)-η1-Ceth= ethylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imidazole-2-ylidene]) viadeprotonation of one end of the diimidazolium salt and coordination of the resulting carbene to Rh. Reaction of these complexes with carbon monoxide or the appropriate diphosphine yields either [RhBr(CO)2(RC(H)-η1-Ceth)][Br] (R = Me, tBu) or [RhBr(P∩P)(MeC(H)-η1-Ceth)][Br] (P∩P = Ph2PCH2PPh2, Ph2PCH2CH2PPh2, Et2PCH2PEt2), respectively. The resulting diphosphine complexes readily decompose in solution. A series of palladium complexes [PdI3-n(PR3)n(L)][I]n(n = 1,2) and [PdI(P∩P)(L)][I]2(L = tBuC(H)-η1-Cmeth, tBuC(H)-η1-Ceth; tBuC(H)-η1-Cmeth= methylene[(N-tert-butyl)imidazolium][(N-tert-butyl)imidazole-2-ylidene]), containing the linked NHC-imidazolium moiety, have also been prepared by reacting the triiodo complexes, [PdI3(tBuC(H)-η1-Cmeth)] and [PdI3(tBuC(H)-η1-Ceth)] with several mono- and diphosphines. Attempts to generate mixed Rh/Pd complexes using Pd(OAc)2to deprotonate the pendent arm of several of the above carbene-anchored/pendent-imidazolium complexes of Rh have proven unsuccessful. However, a targeted di-NHC-bridged heterobimetallic complex [PdI2(PEt3)(μ-tBuCCmeth)RhI(COD)] (tBuCCmeth= 1,1′-methylene-3,3′-di-tert-butyldiimidazol-2,2′-diylidene) can be generated by deprotonation of the imidazolium group in [PdI2(PEt3)(tBuC(H)-η1-Cmeth)][I] using half an equivalent of [Rh(μ-OAc)(COD)]2. The X-ray structure determination of this Pd/Rh complex confirms the dicarbene-bridged formulation and shows a metal-metal separation of approximately 6.2 Å. Reaction of this Rh/Pd complex with CO yields the corresponding dicarbonyl product [PdI2(PEt3)(μ-tBuCCmeth)RhI(CO)2] viareplacement of the COD ligand. The related dicarbene-bridged Ir/Rh complex [IrBr(COD)(μ-tBuCCmeth)RhBr(COD)] can be generated by reaction of [IrBr(COD)(tBuC(H)-η1-Cmeth)][Br] with [Rh(μ-OAc)(COD)]2, while the Pd/Ir complexes [PdI2(PR3)(μ-tBuCCmeth)IrI(COD)] (PR3= PPh3, PMe2Ph) can be generated by reaction of the monometallic [PdI2(PR3)(tBuC(H)-η1-Cmeth)][I] species with K[N(SiMe3)2] in the presence of [Ir(μ-Cl)(COD)]2. The carbonyl analogues, [PdI2(PR3)(μ-tBuCCmeth)IrI(CO)2], can be generated viaa gentle purge of CO gas. These di-NHC-bridged heterobimetallic species represent some of the first examples of this class and are the first involving palladium. [ABSTRACT FROM AUTHOR]
- Published
- 2009
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