Norbornene Copolymerization with Polar Monomers Catalyzed by Palladium Catalysts Containing Imidazolidin-2-imine/Guanidine Ligands

The development of a palladium catalyst that has enhanced catalytic performance, such as low aluminum cocatalyst loading, good copolymerization ability, high molecular weight, and excellent solubility of the (co)polymers, is still a challenge in norbornene copolymerizations. Here, a series of PdCl2 and PdMeCl complexes containing differently substituted anilines and imidazolidin-2-imine/guanidine ligands was successfully synthesized and characterized. X-ray diffraction analysis results revealed that these Pd complexes adopted an almost square-planar geometry, and the six-membered chelate ring showed structural distinctions as compared to traditional N^N-based α-diimine and β-diimine Pd complexes. These Pd complexes were activated by EtAlCl2 and then exhibited moderate activity (104-105 g mol-1 h-1) and good thermal stability (up to 90 °C) for norbornene polymerization to produce high-molecular-weight PNBs (Mn up to 96.4 kg mol-1) with narrow polydispersities (PDI as low as 1.39). These Pd complexes also exhibited good polar group tolerance in the copolymerization of norbornene with methyl 5-norbornene-2-carboxylate and methyl 10-undecenoate, in which the activity was achieved up to 7.04 × 104 g mol-1 h-1. It furnished polar functionalized norbornene-based copolymers with high molecular weight (Mn up to 63.1 kg mol-1), narrow PDI, reasonable polar monomer incorporation, and good solubility. These Pd catalysts exhibited an enhanced copolymerization ability to produce PNB or NB-based copolymers, representing significant progress in this field.

Homo- and copolymerization of norbornene using tridentate IzQO palladium catalysts with dimethylaminoethyl as a side arm

Rigid IzQO–Pd catalysts were synthesized by Rh(iii)-catalyzed C–H/alkyne annulation and applied for the homo- and copolymerizations of norbornene with polar vinyl monomers.

Synthesis and crystal structures of tetra-meric [2-(4,4-dimethyl-2-oxazolin-2-yl)anilido]sodium and tris-[2-(4,4-dimethyl-2-oxazolin-2-yl)anilido]ytterbium(III)

Reaction of 2-(4,4-dimethyl-2-oxazolin-2-yl)aniline (H2-L1) with one equivalent of Na[N(SiMe3)2] in toluene afforded pale-yellow crystals of tetra-meric poly[bis-[μ3-2-(4,4-dimethyl-2-oxazolin-2-yl)anilinido][μ2-2-(4,4-dimethyl-2-oxa-zolin-2-yl)aniline]tetra-sodium(I)], [Na4(C11H13N2O)4] n or [Na4(H-L1)4] n (2), in excellent yield. Subsequent reaction of [Na4(H-L1)4] n (2) with 1.33 equivalents of anhydrous YbCl3 in a 50:50 mixture of toluene-THF afforded yellow crystals of tris-[2-(4,4-dimethyl-2-oxazolin-2-yl)anilinido]ytterbium(III), [Yb(C11H13N2O)3] or Yb(H-L1)3 (3) in moderate yield. Direct reaction of three equivalents of 2-(4',4'-dimethyl-2'-oxazolin-yl)aniline (H2-L1) with Yb[N(SiMe3)2]3 in toluene resulted in elimination of hexa-methyl-disilazane, HN(SiMe3)2, and produced Yb(H-L1)3 (3) in excellent yield. The structure of 2 consists of tetra-meric Na4(H-L1)4 subunits in which each Na+ cation is bound to two H-L1 bridging bidentate ligands and these subunits are connected into a polymeric chain by two of the four oxazoline O atoms bridging to Na+ cations in the adjacent tetra-mer. This results in two 4-coordinate and two 5-coordinate Na+ cations within each tetra-meric unit. The structure of 3 consists of a distorted octa-hedron where the bite angle of ligand L1 ranges between 74.72 (11) and 77.79 (11) degrees. The oxazoline (and anilide) N atoms occupy meridional sites such that for one ligand an anilide nitro-gen is trans to an oxazoline nitro-gen while for the other two oxazoline N atoms are trans to each other. This results in a significantly longer Yb-N(oxazoline) distance [2.468 (3) Å] for the bond trans to the anilide compared to those for the oxazoline N atoms trans to one another [2.376 (3), 2.390 (3) Å].

Nickel(II) and Palladium(II) Complexes Bearing an Unsymmetrical Pyrrole-Based PNN Pincer and Their Norbornene Polymerization Behaviors versus the Symmetrical NNN and PNP Pincers

Unsymmetrical pincers have been shown to be better than the corresponding symmetrical pincers in several catalysis reactions. A new unsymmetrical PNN propincer, 2-(3,5-dimethylpyrazolylmethyl)-5-(diphenylphosphinomethyl)pyrrole (1), was synthesized from pyrrole through Mannich bases in a good yield. In addition, the new byproduct 2-(3,5-dimethylpyrazolylmethyl)-5-(dimethylaminomethyl)- N-(hydroxymethyl)pyrrole was also isolated. The reaction of 1 with [PdCl₂(PhCN)₂] and Et₃N in toluene yielded [PdCl{C₄H₂N-2-(CH₂Me₂pz)-5-(CH₂PPh₂)-κ³ P,N,N}] (2). The analogous reaction between 1 and [NiCl₂(DME)] or NiX₂ (X = Br, I) in the presence of NEt₃ in acetonitrile afforded [NiX{C₄H₂N-2-(CH₂Me₂pz)-5-(CH₂PPh₂)-κ³ P,N,N}] (3; X = Cl, Br, I). All complexes were structurally characterized. The norbornene polymerization behaviors of the unsymmetrical pincer complexes 2 and 3 in the presence of MMAO or EtAlCl₂ were compared with those of the symmetrical pincer complexes chloro[2,5-bis(3,5-dimethylpyrazolylmethyl)pyrrolido]palladium(II) (NNN), chloro[2,5-bis(diphenylphosphinomethyl)pyrrolido]palladium(II), and chloro[2,5-bis(diphenylphosphinomethyl)pyrrolido]nickel(II) (PNP) at different temperatures. The PNN and NNN complexes exhibited far greater activity on the order of 10⁷ g of PNB/mol/h, with quantitative yields in some cases, in comparison to the PNP pincer palladium and nickel complexes. This trend was also supported by the ⁱPr group substituted PNP nickel and palladium pincer complexes. These polymerization behaviors are explained using steric crowding around the metal atom with the support of NMR studies and suggested that the activity increases as the N_pyrazole donor increases. Polymers were characterized by ¹H NMR, IR, TGA, and powder XRD methods.

Synthesis of nickel and palladium complexes with diarylamido-based unsymmetrical pincer ligands and application for norbornene polymerization

A set of diarylamido-based unsymmetrical [PNNox] pincer ligands containing a chiral oxazoline ring have been synthesized and their nickel and palladium complexes [(2-PPh2(R1)ArN(R1)Ar-2-(R)oxazoline)MCl] (R1 = 4-H, R = (S)-4-iPr, M = Pd (Pd1); R1 = 4-H, R = (S)-4-Bn, M = Pd (Pd2); R1 = 4-H, R = (S)-4-Ph, M = Pd (Pd3); R1 = 4-Me, R = (S)-4-Bn, M = Pd (Pd4); R1 = 4-Me, R = (S)-4-Ph, M = Pd (Pd5); R1 = 4-H, R = 4-Me2, M = Pd (Pd6); R1 = 4-H, R = Benzo[d]-, M = Pd (Pd7); R1 = 4-H, R = (S)-4-Bn, M = Ni (Ni1); R1 = 4-H, R = (S)-4-Ph, M = Ni (Ni2); R1 = 4-Me, R = (S)-4-Bn, M = Ni (Ni3); R1 = 4-Me, R = (S)-4-Ph, M = Pd (Ni4)) were tested to show high catalytic activities for polymerization of norbornene. After activation of methylaluminoxane (MAO), all the nickel and palladium complexes could catalyze the polymerization of norbornene to yield vinyl-type polymers with activities up to 40.3 × 105 g of PNB (mol of Pd)-1 h-1. The copolymerization of norbornene with functional norbornene comonomers was also investigated by catalyst Pd2, accompanied by decreased catalytic activity and low incorporation of functional comonomers.

Tridentate diarylamido-based pincer complexes of nickel and palladium: sidearm effects in the polymerization of norbornene

The sidearm effects were found in the polymerization of norbornene catalyzed by the Ni and Pd complexes bearing new diarylamido based unsymmetrical quinolino [NNN^ox] and phenylthio [SNN^ox] pincer ligands.

Polymerization of 1-chloro-2-phenylacetylene by cationic monoanionic tridentate (S,S)-bis(oxazolinylphenyl)amido-ligated palladium catalysts: is it a coordination–insertion mechanism?

Cationic (S,S)-bis(oxazolinylphenyl)amido-ligated palladium species were first used for the coordination–insertion polymerization of 1-chloro-2-phenylacetylenes.

Kinetics, Mechanism and Theoretical Studies of Norbornene-Ethylene Alternating Copolymerization Catalyzed by Organopalladium(II) Complexes Bearing Hemilabile α-Amino-pyridine

Cationic methylpalladium complexes bearing hemilabile bidentate α-amino-pyridines can serve as effective precursors for catalytic alternating copolymerization of norbornene (N) and ethylene (E), under mild conditions. The norbornyl palladium complexes in the formula of {[RHNCH₂(o-C₆H₄N)]Pd(C₇H10Me)(NCMe)}(BF₄) (R = iPr (2a), tBu (2b), Ph (2c), 2,6-Me₂C₆H₃ (2d), 2,6-iPr₂C₆H₃ (2e)) were synthesized via single insertion of norbornene into the corresponding methylpalladium complexes 1a-1e, respectively. Both square planar methyl and norbornyl palladium complexes exhibit facile equilibria of geometrical isomerization, via sterically-controlled amino decoordination-recoordination of amino-pyridine. Kinetic studies of E-insertion, N-insertion of complexes 1 and 2, and the geometric isomerization reactions have been examined by means of VT-NMR, and found in excellent agreement with the results estimated by DFT calculations. The more facile N-insertion in the cis-isomers, and ready geometric isomerization, cooperatively lead to a new mechanism that accounts for the novel catalytic formation of alternating COC.