Amine-Functionalized Indazolin-3-ylidene Complexes of Palladium(II) by Postmodification of a Single Precursor

Abstract

A series of five trans-[PdBr2(amine)(indy)] complexes (amine = diethylamine, dipropylamine, dibutylamine, diisobutylamine, morpholine; indy = indazolin-3-ylidene) with pendant teriary amine functionalities in the side chain of the NHC ligand has been prepared by postcoordinative modification of a single bromoalkyl-functionalized precursor complex. This approach allows for a synthesis of functionalized N-heterocyclic carbene complexes more efficient than the metalation of prefunctionalized azolium salts. All complexes have been fully characterized, and the molecular structures of three complexes are reported. A correlation exists between the 13C NMR shift of Ccarbene and the pKb values of the coordinated amines. Furthermore, all complexes were found to be active catalysts for the direct arylation of 1-methylpyrrole with good to excellent yields.