Synthesis and characterization of aryl substituted bis(2-pyridyl)amines and their copper olefin complexes: Investigation of remote steric control over olefin binding

Abstract

The aryl-functionalized pyridylamine 2-ⁱPrC₆H₄N(H)py (1) and bis(2-pyridyl)amines of the type ArN(py)₂ for Ar = Mes (2), 2,6-Et₂C₆H₃ (3), 2-ⁱPrC₆H₄ (4), 2,6-ⁱPr₂C₆H₃ (5), and 1-naph (6), have been prepared by the palladium-catalyzed cross-coupling of substituted anilines with 2-bromopyridine, and have been characterized by ¹H and ¹³C NMR NMR, FTIR, MS, and TGA. Complexes of these new N-aryl bis(2-pyridyl)amines have been prepared for the acid salts [H{ArN(py)₂}]BF₄ where Ar = Mes (7) and 2-ⁱPrC₆H₄ (8), and the dimeric bridged complexes [Cu{ArN(py)₂}(μ-X)(Y)]₂ where X/Y = Cl⁻ and Ar = Ph (9), 2-ⁱPrC₆H₄ (10), and 1-naph (11), in addition to X = OH⁻, Y = H₂O and Ar = Mes (12). The olefin complexes [Cu(Ar-dpa)(styrene)]BF₄ for Ar = Ph (13), Mes (14), 2-ⁱPrC₆H₄ (15), and 1-naph (16), in addition to the norborylene complexes of Ar = Mes (17) and 2-ⁱPrC₆H₄ (18) have been prepared and characterized by ¹H and ¹³C NMR, FTIR, and TGA. The crystal structures have been determined for compounds 1–17. Secondary amine 1 crystallizes in hydrogen-bonded head-to-tail dimers, while the N-aryl bis(2-pyridyl)amines 2–6 crystallize in a three-bladed propellar conformation, having nearly planar geometries about the amine nitrogen. The geometry about copper centers in the dimeric complexes 9–12 is distorted trigonal bypyramidal, with the axial positions occupied by one of the two pyridyl nitrogens and one of the bridging ligands (i.e., Cl or OH). The copper atoms in each of the olefin complexes 13–17 are coordinated to the two pyridine nitrogen atoms and the appropriate olefin; consistent with a pseudo three-coordinate Cu(I) cation. Distortion of pyridyl ring geometries about the copper centers, and concomitant bending of the aryl groups away from the Cu⋯N(amine) vectors were found to correlate with the steric bulk of the aryl group present in both dimeric and olefin complexes. Such distortion is also observed to a lesser extent in the acid salts as well. The ¹H and ¹³C NMR spectra of [Cu(Ar-dpa)(olefin)]BF₄ exhibit an upfield shift in the olefin signal as compared to free olefin. A good correlation exists between the ¹H and ¹³C NMR Δδ values and olefin dissociation temperatures, confirming that the shift of the olefin NMR resonances upon coordination is associated with the binding strength of the complex.