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

Abstract

A set of diarylamido-based unsymmetrical [PNN^ox] 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.