Rhodium and iridium complexes of lutidine-based NHC/Amino Pincer ligands: From monodentate to tetradentate coordination enabled by C–H activation

González-Lainez, Miguel ; Jiménez, M. Victoria ; Passarelli, Vincenzo ; Modrego, F. Javier (Universidad de Zaragoza) ; Pérez-Torrente, Jesús J. (Universidad de Zaragoza)

Resumen: A series of rhodium and iridium complexes derived from lutidine-based ligands (lutidine, 2,6-dimethylpyridine) with NHC and amino side-donor functions have been prepared and characterized. Deprotonation of the functionalized imidazolium salts, [tBuHImCH2PyCH2NR2]Br, by the bridging methoxo ligands of the dinuclear complexes [M(μ-OMe)(cod)]2 affords [MBr(cod)(κC-tBuImCH2PyCH2NR2)] (M = Rh and Ir) complexes from which a series of Rh(I) and Ir(I) complexes including [M(cod)(κ3C,N,N′-tBuImCH2PyCH2NR2)]+, [Rh(CO)(κ3C,N,N′-tBuImCH2PyCH2NR2)]+, and [IrBr(CO)2(κC-tBuImCH2PyCH2NR2)] are readily accessible by halide abstraction and/or carbonylation reactions. In contrast, direct metalation of imidazolium salts with the dinuclear compounds [M(μ-Cl)(cod)]2 (M = Rh and Ir) in the presence of potassium acetate and potassium iodide, a well-established synthetic route to M(III) species, provides access to unusual di-iodido M(III) cyclometalated compounds [MI2{κ4C,C′,N,N′-(CH2CMe2ImCH2PyCH2NR2)}] in low yield. Experimental studies combined with DFT calculations suggest that cyclometalated M(III) hydrido [MH(CH3CN){κ4C,C′,N,N′-(CH2CMe2ImCH2PyCH2NR2)}]+ compounds and square-planar cyclometalated M(I) [M{κ4C,C′,N,N′-(CH2CMe2ImCH2PyCH2NR2)}] species resulting from their deprotonation by acetate could be intermediates involved in the formation of these compounds. Based on the observed formation of elemental rhodium, disproportionation of square-planar cyclometalated M(I) complexes to afford M(0) and the cationic M(II) species [M{κ4C,C′,N,N′-(CH2CMe2ImCH2PyCH2NR2)}]+ is proposed. Reaction of the latter with iodide (I–) would regenerate the M(I) intermediate to give an iodo radical (I•) that in turn could dimerize to form diiodine I2. In this regard, DFT calculations have shown that the oxidative addition of diiodine to the cyclometalated M(I) intermediates leading to the di-iodido M(III) cyclometalated compounds is a highly exergonic process.

Idioma: Inglés

DOI: 10.1021/acs.organomet.3c00403

Año: 2023

Publicado en: Organometallics 42, 22 (2023), 3292-3306
ISSN: 0276-7333

Financiación: info:eu-repo/grantAgreement/ES/DGA/E42-23R
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PID2019-103965GB-I00/AEI/10.13039/501100011033
Financiación: info:eu-repo/grantAgreement/ES/MINECO/BES-2014-069624

Tipo y forma: Artículo (Versión definitiva)

Área (Departamento): Área Química Inorgánica (Dpto. Química Inorgánica)