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

The treatment of 2-(ArN═CH)C 6 H 4 -HNC 9 H 6 N ( [N Q N A N I Me ]H, Ar = 2,6-Me 2 C 6 H 3; [N Q N A N I Et ]H, Ar = 2,6-Et 2 C 6 H 3; [N Q N A N I iPr ]H, Ar = 2,6- i Pr 2 C 6 H 3 ) with n BuLi and CrCl 3 (THF) 3 achieves the hetero-dinuclear complexes [N Q N A N I R ] CrCl(μ-Cl) 2 Li(THF) 2 ( 1a, R = Me; 1b, R = Et; 1c, R = i Pr) or bisligated complex κ 5 - [N Q N A N I iPr ] 2 CrCl ( 2c ) depending on the reactant ratios used. Reactions of these ligands with n BuLi and CrCl 2 (THF) 2 could achieve the square-pyramidal complexes [N Q N A N I R ] CrCl(THF) ( 3b, R = Et; 3c, R = i Pr). Complex 3c can be oxidized by alkyl chloride to dimeric complex { [N Q N A N I iPr ] CrCl} 2 (μ-Cl) 2 ( 4 ) through a single-electron-transfer mechanism. Similar reaction of 2-(C 9 H 6 N)N═CHC 6 H 4 -HNAr ( [N Q N I N A Me ]H, Ar = 2,6-Me 2 C 6 H 3; [N Q N I N A Et ]H, Ar = 2,6-Et 2 C 6 H 3; [N Q N I N A iPr ]H, Ar = 2,6- i Pr 2 C 6 H 3 ) with n BuLi and CrCl 3 (THF) 3 furnishes [N Q N I N A R ] CrCl(μ-Cl) 2 Li(THF) 2 ( 5a, R = Me; 5b, R = Et; 5c, R = i Pr) in high yields. However, a chromium complex with a butyl-substituted ligand, [N Q Bu N I N A iPr ] CrCl 2 ( 6 ), is obtained when 2 equiv of n BuLi 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.