Steric Considerations in Copper(I)-olefin Complexes Incorporating Substituted Bis(2-pyridyl)amines.

摘要

The separation of olefin isomers by traditional methods (e.g., distillation) is generally a costly process, as the range of phase-transition temperatures for a given set of isomers is usually quite small. Complexes of the type [Cu(H-dpa)eta 2-olefin)]BF4 have been prepared for numerous aliphatic/aromatic alpha-olefins, internal cis-/trans-aliphatic/aromatic olefins, as well as for cyclic olefins (2-norbornylene and 1,5--cyclooctadiene). Preparation of complexes and characterization via 1H and 13C NMR, FT-IR, and TG/DTA reveals clear trends amongst compounds in the different spectroscopic methods. Of particular note is the direct relation between olefin dissociation temperature (TG/DTA) and upfield NMR shifts, Deltadelta, for olefin signals, giving a convenient means of assessing complex strength. Molecular structures of several such olefin complexes have been determined via single crystal X-ray diffraction. Features in the determined structural geometries are discussed. Theoretical models served to predict advantageous structural changes (i.e., steric preference for a given isomer) in complexes having functionalized ancillary ligands. Aryl substitution at the amine nitrogen yielded subtle distortions to calculated geometries, loosely indicating preferential binding of terminal and cis-olefin isomers. The synthesis of several novel di(pyridyl)amine [ArN(2-py)2 : Ar = Ph, Mes, 2,6-Et2C6H3, 2- iPrC6H4, 2,6-iPr 2C6H3, and 1-naph] and di(quinolyl)amine [ArN(2-quin) 2: Ar = Mes and 2,6-iPr2C 6H3] ligands was accomplished via Buchwald-Hartwig type palladium-catalyzed cross-coupling of the appropriate halogenated heterocycle with substituted anilines (2:1 molar ratio). Asymmetric (pyridyl)(quinolyl)amines [ArN(2-py)(2-quin): Ar = H, Ph, Mes, 2,6-iPr2C 6H3] were prepared in a similar manner, with two steps in the coupling reactions: (I) initial I:1 molar ratio of 2-bromopyridine:aniline allowed the isolation of aryl(pyridyl)amine compounds [ArN(H)py: Ar = Ph, Mes, 2,6-Et2C6H3, 2-iPrC 6H4, 2,6-iPr2C 6H3, and 1-naph]. A second cross-coupling with 2-chioroquinoline resulted in the desired ArN(2-py)(2-quin) ligand. Characterization of new ligands was performed via 1H and 13C NMR, EI-MS, FT-IR, TG/DTA, and X-ray crystallography; the resulting trends from spectroscopic and structural data are discussed. Synthesis and spectroscopic/structural investigations of complexes incorporating novel ligands were initially performed on protonated salts, e.g., [H(Ar-dpa)]BF4, in addition to dimcric copper(II) complexes [Cu(Ar-dpa)(C])(mu-C1)]2. Structural data confirmed theoretical predictions concerning distortions in complexed-ligand geometry. Thus, complexes [Cu(R-dpa)(eta2-olefin)]BF 4 (where R = Ph, Mes, 2-iPrC6H 4, and 1-naph) were then prepared for styrene, as well as several internal cis/trans-octenes. TG/DTA and 13C NMR data indicate an increasing difference in complex strength between cis/trans-3-octene complexes as the substituent is varied from R = H (smallest difference in strength), to R Mes, to R = 2-iPrC6H 4 (largest difference in strength). Thus, the identity of the remote. ligand substituent (Ar) controls the differentiation of binding between cis- and trans-isomers, as a consequence of increased ligand geometric distortion.