RuII,OsII, and IrIII Complexes with Chelating Pyridyl–Mesoionic Carbene Ligands: Structural Characterization and Applications in Transfer Hydrogenation Catalysis |
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| Authors: | Aljoša Bolje Dr. Stephan Hohloch Margarethe van der Meer Janez Košmrlj Prof. Dr. Biprajit Sarkar |
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| Affiliation: | 1. Institut für Chemie und Biochemie, Anorganische Chemie, Freie Universtit?t Berlin, Fabeckstrasse?34–36, 14195, Berlin (Germany);2. Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ve?na?pot?113, 1000, Ljubljana (Slovenia) |
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| Abstract: | Chelating ligands with one pyridine donor and one mesoionic carbene donor are fast establishing themselves as privileged ligands in homogeneous catalysis. The synthesis of several new IrIII–Cp*‐ and OsII–Cym complexes (Cp*=pentamethylcyclopentadienyl, Cym=p‐cymene=4‐isopropyl‐toluene) derived from chelating pyridyltriazolylidenes where the additional pyridine donor was incorporated via the azide part of the triazole is presented. Furthermore, different 4‐substituted phenylacetylene building blocks have been used to introduce electronic fine‐tuning in the ligands. The ligands thus can be generally described as 4‐(4‐R‐phenyl)‐3‐methyl‐1‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐5‐ylidene (with R being H (L1), Me (L2), OMe (L3), CN (L4), CF3 (L5), Br (L6) or NO2 (L7)). The corresponding complexes (Ir‐ 1 to Ir‐ 7 and Os‐ 1 to Os‐ 7 ) were characterized by standard spectroscopic methods, and the expected three‐legged, piano‐stool type coordination was unambiguously confirmed by X‐ray diffraction analysis of selected compounds. Together with RuII analogues previously reported by us, a total of 21 complexes were tested as (pre)catalysts for the transfer hydrogenation of carbonyl groups, showing a remarkable reactivity even at very low catalyst loadings. The electronic effects of the ligands as well as different substrates were investigated. Some mechanistic elucidations are also presented. |
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| Keywords: | carbenes iridium osmium ruthenium transfer hydrogenation |
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