Synthesis, Structures, and Norbornene Polymerization Behavior of Aryloxide-N-Heterocyclic Carbene Ligated Palladacycles

Abstract

Treatment of the o-hydroxyaryl imidazolinium pro-ligands (2-OH-3,5- 5), Ph (6), Mes (7), t Bu (8)]. Notably, without isolating 2, complexes 4-8 could also be obtained by one-pot, threecomponent, sequential reaction of N,N-dimethylbenzylamine, PdCl 2 , and the pro-ligands in refluxing acetonitrile in the presence of K 2 CO 3 . When the N-functional group on the NHCs is tert-butyl, the NHC in 8 adopts an abnormal binding (C4-bonding). All these complexes were fully characterized by 1 H and 13 C NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. Singlecrystal X-ray diffraction analysis results further confirmed the molecular structures of 4-8 and the abnormal binding of NHC in 8. With methylaluminoxane (MAO) as cocatalyst these palladacycles showed excellent catalytic activities up to 10 7 g of PNB (mol of Pd) -1 h -1 in the addition polymerization of norbornene.

Synthesis and Catalytic Properties of Cyclopalladated Complexes Bearing a Phosphane‐Sulfonate Ligand

“…Recently, our group has reported some C(sp 3 ),N‐chelated and C(sp 2 ),N‐chelated palladacycles that showed high activities in the vinyl polymerization of norbornene in the presence of MAO . By introduction of a phosphane‐sulfonate ligand instead of the NHC ligand into the palladacycle framework, we envisioned that the palladacycles bearing a phosphane‐sulfonate ligand should have potential uses in catalysis as well.…”

“…Since the first report of cyclopalladated azobenzene by Cope et al in 1965, a large number of palladacycles were synthesized and widely used in catalytic organic reactions . Recently, we have successfully synthesized a series of o ‐aryloxide‐NHC‐ligated palladacycles (Scheme , A )[7a], [7b] and NHC‐sulfonate‐ligated palladacycles (Scheme , B ). [7c] These complexes showed excellent catalytic properties in the vinyl polymerization of norbornene with methylaluminoxane (MAO) as cocatalyst.…”

“…Recently, we have successfully synthesized a series of o ‐aryloxide‐NHC‐ligated palladacycles (Scheme , A )[7a], [7b] and NHC‐sulfonate‐ligated palladacycles (Scheme , B ). [7c] These complexes showed excellent catalytic properties in the vinyl polymerization of norbornene with methylaluminoxane (MAO) as cocatalyst. Though meanwhile, one major deficiency of these Pd(II) catalyst systems was the requirement of thousands of equivalents of the MAO cocatalyst in order to show any activity in norbornene polymerization.…”

Sulfonated palladium(II) N‐heterocyclic carbene complex immobilized on nano–micro size poly(4‐vinylpyridinium chloride) for Suzuki‐Miyauracross‐coupling reaction

“…NHC complexes as homogeneous catalysts have been used in a number of organic transformations such as olefin metathesis and C–C and C–N bond formation reactions . Therefore, the discovery of catalytic properties of Pd–NHC complexes in the Mizoroki–Heck and Suzuki–Miyaura cross‐coupling reactions is of great importance since these reactions have very many applications in the synthesis of natural products, numerous drugs and high‐performance modern organic materials . Despite the wide application of these homogeneous catalysts in organic transformations, their recycling is complicated and their separation is very difficult.…”

Immobilization of palladium(II)‐containing bis(imidazolium) ligand on ion‐exchange resins: efficient and reusable catalysts for CC coupling reactions

“…Construction of biaryl compounds via palladium‐catalysed Suzuki reactions is an interesting area in organic synthesis. The products of Suzuki reactions (biaryl units) are important molecular components in pharmaceuticals, herbicides and natural products, as well as in engineering materials such as conducting polymers, molecular wires and liquid crystals . Homogenous palladium catalysts used in Suzuki reactions cannot be recovered from reaction media.…”