Chromium Complexes with N,N,N‑Tridentate Quinolinyl Anilido-Imine Ligand: Synthesis, Characterization, and Catalysis in Ethylene Polymerization

The treatment of 2-(ArNCH)­C6H4-HNC9H6N ([NQNANIMe]­H, Ar = 2,6-Me2C6H3; [NQNANIEt]­H, Ar = 2,6-Et2C6H3; [NQNANIiPr]­H, Ar = 2,6-iPr2C6H3) with nBuLi and CrCl3(THF)3 achieves the hetero-dinuclear complexes [NQNANIR]CrCl­(μ-Cl)2Li­(THF)2 (1a, R = Me; 1b, R = Et; 1c, R = iPr) or bisligated complex κ5-[NQNANIiPr]2CrCl (2c) depending on the reactant ratios used. Reactions of these ligands with nBuLi and CrCl2(THF)2 could achieve the square-pyramidal complexes [NQNANIR]CrCl­(THF) (3b, R = Et; 3c, R = iPr). Complex 3c can be oxidized by alkyl chloride to dimeric complex {[NQNANIiPr]CrCl}2(μ-Cl)2 (4) through a single-electron-transfer mechanism. Similar reaction of 2-(C9H6N)­NCHC6H4-HNAr ([NQNINAMe]­H, Ar = 2,6-Me2C6H3; [NQNINAEt]­H, Ar = 2,6-Et2C6H3; [NQNINAiPr]­H, Ar = 2,6-iPr2C6H3) with nBuLi and CrCl3(THF)3 furnishes [NQNINAR]CrCl­(μ-Cl)2Li­(THF)2 (5a, R = Me; 5b, R = Et; 5c, R = iPr) in high yields. However, a chromium complex with a butyl-substituted ligand, [NQBuNINAiPr]CrCl2 (6), is obtained when 2 equiv of nBuLi is used. The molecular structures of 1c, 2c, 3c, 4, 5c, and 6 are confirmed by X-ray crystallography. Upon activation with MAO, the Cr­(III) complexes (1a–1c, 4, and 5a–5c) show moderate catalytic activities (50 to 218 kg of PE·mol­(Cr)−1·h–1) in ethylene polymerization, whereas the Cr­(II) complexes 2c, 3b, and 3c are inert under the same conditions.