Steric Considerations in Copper(I)-olefin Complexes Incorporating Substituted Bis(2-pyridyl)amines
Allen, John Jeffrey
Barron, Andrew R.
Doctor of Philosophy
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)(1l2-0Iefin)]BF4 have been prepared for numerous aliphatic/aromatic a-olefins, internal cis-/transaliphatic/ aromatic olefins, as well as for cyclic olefins (2-norbornylene and 1,5- cyclooctadiene). Preparation of complexes and characterization via IH and l3C NMR, FTIR, and TGIDT A reveals clear trends amongst compounds in the different spectroscopic methods. Of particular note is the direct relation between olefin dissociation temperature (TGIDT A) and upfield NMR shifts, ~8, 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-ipr2C6H3, and I-naph] and di(quinolyl)amine [ArN(2-quin)2: Ar = Mes and 2,6-ipr2C6H3] 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- 4 py)(2-quin): Ar = H, Ph, Mes, 2,6-ipr2C6H3] were prepared in a similar manner, with two steps in the coupling reactions: (l) initial 1: 1 molar ratio of 2-bromopyridine:aniline allowed the isolation of aryl(pyridyl)amine compounds [ArN(H)py: Ar = Ph, Mes, 2,6- EhC6H3, 2)PrC6H4, 2,6)Pr2C6H3, and I-naph]. A second cross-coupling with 2- chloroquinoline resulted in the desired ArN(2-py)(2-quin) ligand. Characterization of new ligands was performed via IH and 13C NMR, EI-MS, FT-IR, TGIDTA, 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 dimeric copper(II) complexes [Cu(Ar-dpa)(CI)(/-l-CI)b Structural data confirmed theoretical predictions concerning distortions in complexed-ligand geometry. Thus, complexes [Cu(R-dpa)(T\2-0Iefin)]BF4 (where R = Ph, Mes, 2-iPrC6~, and I-naph) were then prepared for styrene, as well as several internal cis/trans-octenes. TGIDT A 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)PrC6H4 (largest difference in strength). Thus, the identity of the remote ligand substituent (Ar) controls the differentiation of binding between cisand trans-isomers, as a consequence of increased ligand geometric distortion.