High-Temperature Catalysts for the Production of α-Olefins Based on Iron(II) and Iron(III) Tridentate Bis(imino)pyridine Complexes with Double Pattern of Substitution: <i>o</i><i>rtho</i>-Methyl plus <i>m</i><i>eta</i>-Aryl^†

Four types of bis(imino)pyridine ligands and their corresponding Fe complexes with the same meta-aryl pattern were synthesized for high-temperature α-olefin production (A: 9 and 13; B: 18, 19, 20 and 21, 22, 23, 24; C: 27 and 30; and D: 33 and 34). Pattern A (9 and 13) consists of four meta-aryl groups without ortho-methyls. The coordination of FeCl2 with the ligand [3,5-bis(4-F-Ph)2-Ph-NC(Me)-Py-C(Me)N-Ph-3,5-bis(4-F-Ph)2] (9) of type A resulted in the isolation of ion-paired complexes [L2Fe]2+FeCl42- 13. Coordination of ligands 18, 19, and 20 of pattern B with two meta-aryl groups on the same side with two ortho-methyls of the imino aryl group afforded the following 1:1 complexes: [{3-(4-F-Ph)-2-Me-Ph-NC(Me)-Py-C(Me)N-Ph-2-Me-3-(4-F-Ph)}FeCl2] (21), [{3-(3,5-bis-(CF3)2-Ph)-2-Me-Ph-NC(Me)-Py-C(Me)N-Ph-2-Me-3-(3,5-bis-(CF3)2-Ph)}FeCl2] (22), [{3-(3-Me-thiophene-2-yl)-2-Me-Ph-NC(Me)-Py-C(Me)N-Ph-2-Me-3-(3-Me-thiophene-2-yl)}FeCl2] (23), and [{3-(3,5-bis-(CF3)2-Ph)-2-Me-Ph-NC(Me)-Py-C(Me)N-Ph-2-Me-3-(3,5-bis-(CF3)2-Ph)}FeCl3] (24). Reduction of trivalent complex 24 in THF solution yields divalent complex 22. Ligand 27 of pattern C contains two meta-aryl groups on the side opposite two ortho-methyls of the imino aryl group and coordinates with FeCl2 to form complex [{5-(3,5-bis-(CF3)2-Ph)-2-Me-Ph-NC(Me)-Py-C(Me)N-Ph-2-Me-5-(3,5-bis-(CF3)2-Ph)}FeCl2] (30). Complex 34 of unsymmetrical pattern D has two meta-aryls in one imino aryl group and two ortho-methyls in the second imino aryl group: [{2,6-dimethyl-4-(3,5-bis-(CF3)2-Ph)-2-Me-Ph-NC(Me)-Py-C(Me)N-Ph-2-Me-3,5-bis(3,5-bis-(CF3)2-Ph)}FeCl2]. The introduction of aryl groups into the meta positions of all four types of bis(imino)pyridine ligands was accomplished by palladium-catalyzed Suzuki cross-coupling reaction between aryl boronic acid 5, 16, and 17 and the appropriate meta-bromo-substituted bis(imino)pyridine ligands 4, 15, 25, and 32. Di-tert-butyl(2,2-dimethylpropyl)phosphane (7) and benzyl-di-tert-butylphosphane (28) were used as ligands for the Suzuki coupling. According to X-ray analysis, there are shortenings and therefore strengthening of the axial Fe−N bond lengths (up to 0.02 Å) in complex 22 of type B versus the Fe(II) complex without meta-aryl groups [{o-Me-Ph-NC(Me)-Py-C(Me)N-Ph-o-Me}FeCl2] (1). Complexes of patterns B and D (21, 22, 23, 24, and 34) afforded very active catalysts for the production of α-olefins with more ideal Schultz−Flory distributions of α-olefins and with higher K values than the parent methyl-substituted Fe(II) complex 1 without meta-aryl groups.