| Abstract
| - The new bulky aryl-bridged ligands bis(aryliminopyridyl)benzene (L1) and bis(aryliminopyridyl)phenolate [(L2)-] have been found to act as compatible supports for the assembly of bimetallic halide complexes. While L1 promotes the formation of remote bis(MX2) species, (L2)- favors the formation of M2(μ-X)X2-type complexes in which the metal centers (M = Fe, Co, Ni, Zn) are more closely located; the dinickel and dicobalt systems of both ligand types are active ethylene oligomerization catalysts upon treatment with MAO.
- Two new bulky aryl-bridged pyridyl-imine compartmental (pro)ligands, 2,6-{(2,6-i-Pr2C6H3)NC(Me)C5H3N}2C6H3Y(Y = H L1, OH L2-H), have been prepared in moderate to good overall yields via a Stille-type cross-couplingapproach. The molecular structure of L2-H reveals a transoid configuration within the pyridyl-imine units with ahydrogen-bonding interaction maintaining the phenol coplanar with one of the adjacent pyridine rings. The interactionof 2 equiv of MX2 with L1 in n-BuOH at 110 °C gives the binuclear complexes, [(L1)M2X4] (M = Fe, X = Cl (1a);M = Co, X = Cl (1b); M = Ni, X = Br (1c); M = Zn, X = Cl (1d)), in which the metal centers adopt distortedtetrahedral geometries and occupy the two pyridyl-imine cavities in L1. In contrast, deprotonation of L2-H occursupon reaction with 2 equiv of MX2 to afford the phenolate-bridged species [(L2)M2(μ-X)X2] (M = Fe, X = Cl (2a);M = Co, X = Cl (2b); M = Ni, X = Br (2c); M = Zn, X = Cl (2d)). 1H NMR studies of diamagnetic 1d and 2dreveal that the limited rotation of the N-aryl groups in 1d is further impeded in 2d by steric interactions impartedby the two closely located N-aryl groups. Partial displacement of the bridging bromide in 2c results upon its treatmentwith acetonitrile to afford [(L2)Ni2Br3(NCMe)] [2c(MeCN)]; no such reaction occurs for 2a, 2b, or 2d. Upon activationwith excess methylalumoxane (MAO), 1b, 1c, 2b, and 2c show some activity for alkene oligomerization forminglow molecular-weight materials with methyl-branched products predominating for the nickel systems. Single-crystalX-ray diffraction studies have been performed on L2-H, 1c, 2b, 2c, 2c(NCMe), and 2d.
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