Generating new catalysts
Functionalized heterocyclic carbene
Oeiras, 17.06.9
Carbene molecules are an extremely reactive class of compounds with increasing applications as catalysts in the chemical industry. In fact, since the successful isolation of a stable N-heterocyclic carbene (NHC) there has been a spectacular interest in this class of ligands. ITQB researchers from the Laboratory of Homogeneous Catalysis in collaboration with Universitat Jaume I in Castellón (Spain) have prepared the first NHC-functionalized with a cyclopentadienyl ring. This new molecule can be combined with late transition metals by metallation to catalyse a wide set of reactions. The results can be found online in the journal of Dalton Transactions.
New catalyst systems that allow for rapid and selective chemical transformations have a significant impact in the chemical industry minimizing energy consumption and waste. Because stable N- heterocyclic carbenes are powerful electron donors and can bind strongly to the metal in a complex, they are exceptionally useful spectator ligands in catalysis, surpassing the traditionally used phospines both in activity and scope. And just as phosphines, NHCs can be designed to carry functional groups thus altering their catalytical properties. The novel metal-based species prepared in this work display high catalytic activity in the β-alkylation of secondary alcohols and amines with primary alcohols: a catalytic system for environmentally benign synthesis of amines and alcohols with the formation of only water as a byproduct.
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Researchers were able to develop a convenient and high-yielding method for the preparation of a Cp*-NHC ligand, starting from easily accessible precursors. The novel pro-ligand can be easily coordinated to iridium and rhodium metals by intramolecular C-H activation processes providing versatile catalysts in a wide set of reactions implying C-H activations. The X-ray studies showed that intramolecular C-H activation processes afford unprecedented rigid tridentate coordination for the iridium complex. |
The methodology described in this work constitutes a valuable protocol for the preparation of NHC – late transition metal complex that can be extended to the preparation of complexes with other transition metals for different applications.
Original paper:
Dalton Trans, 2009, DOI: 10.1039/b901195a
Easy preparation of Cp*-functionalized N-heterocyclic carbenes and their coordination to rhodium and iridium
André Pontes da Costa, Mercedes Sanaú, Eduardo Peris and Beatriz Royo
