Polymer-Supported Carbene Complexes of Palladium: Well-Defined, Air-Stable, Recyclable Catalysts for the Heck Reaction

Abstract

N-Heterocyclic dicarbene chelate complexes of formula [cis-CH2N(H)C=C(H)N(R)C2PdX2] (X = Br, I; R = (CH2)nOH; n = 2, 3) have been prepared and structurally characterized (for X= I, n = 2). The complexes were immobilized on a functionalized polystyrene support (Wang resin) through one of the oxygen centres. The complexes efficiently catalyze the Heck reaction of activated and non-activated arylbromides, are recyclable under aerobic conditions and exhibit hardly any leaching, which is in line with our theoretical investigations on ligand dissociation energies related to Pd0 and PdII centres.

N-heterocyclic carbenes of the late transition metals: a computational and structural database study

“…For example, NHC complexes of Pd have been investigated for their utility in the Heck coupling reaction in organic synthesis [3]. The Heck coupling reaction utilizes NHC complexes as catalysts (scheme 3).…”

Structures, Energies, and Bonding Analysis of Monoaurated Complexes with N-Heterocyclic Carbene and Analogues

“…The chemical bonding between NHCs and group 11 metals have been investigated theoretically (Nemcsok et al 2004;Hu et al 2004). Moreover, theoretical studies of the electronic structure of transition metal complexes with NHCs ligand have been recently carried out by other group (Schwarz et al 2000;Weskamp et al 1999;Lee et al 2004). The fact was that, the type of NHC ligands that have been developed by Arduengo et al [1991] have found recent use in the synthesis of molecular gold(I) fluoride and chloride complexes.…”

Shape-Controllable Formation of Poly-imidazolium Salts for Stable Palladium N-Heterocyclic Carbene Polymers

“…To improve recyclability of such NHC complexes, great efforts have been devoted to develop heterogeneous NHC organometallic catalytic systems34567. Imidazolium-based ionic salts are well known to be excellent precursors of metal NHCs, and various solid supports containing imidazolium groups have been used as precursors of heterogeneous palladium NHCs3456.…”

“…To improve recyclability of such NHC complexes, great efforts have been devoted to develop heterogeneous NHC organometallic catalytic systems34567. Imidazolium-based ionic salts are well known to be excellent precursors of metal NHCs, and various solid supports containing imidazolium groups have been used as precursors of heterogeneous palladium NHCs3456. In the context, di- or poly-cationic imidazolium salts were well known to possess superior performances over monocationic analogues, but heterogeneous catalytic systems consisting of stable chelating palladium NHC units were seldom explored34, despite the discrete chelating palladium NHC complexes were frequently investigated in catalysis2.…”

“…Imidazolium-based ionic salts are well known to be excellent precursors of metal NHCs, and various solid supports containing imidazolium groups have been used as precursors of heterogeneous palladium NHCs3456. In the context, di- or poly-cationic imidazolium salts were well known to possess superior performances over monocationic analogues, but heterogeneous catalytic systems consisting of stable chelating palladium NHC units were seldom explored34, despite the discrete chelating palladium NHC complexes were frequently investigated in catalysis2. Very recently, a series of metal-organic frameworks (MOFs) containing methylene-bridged bis-imidazolium groups were reported8, but the relative instability of these MOFs against moisture, acid or base have restricted the scope of catalytic applications.…”