Design and synthesis of functionalized alkynyl gold(I) and gold(III) complexes as building blocks for supramolecular assembly and metallogels

Abstract

A class of luminescent cyclometalated gold(III) complexes with L-valine-modified alkynyl ligands, [Au(RC^N^CR)(C≡CR’)] (R = H, R’ = C6H4Val- OMe, C6H4ValValOMe; R = tBu, R’ = C6H4ValValOMe, C6H4ValValValOMe; R = Me, R’ = C6H4ValValValOMe) and [Au{C^N(R)^C}(C≡CR’)] (R = (4-OC6H13)C6H4, R’ = C6H4ValValOMe; R = (4-OC12H25)C6H4, R’ = C6H4ValValOMe; R = (4-OC18H37)C6H4, R’ = C6H4ValValOMe; R = 3,4,5-(OC12H25)3C6H2, R’ = C6H4ValValValOMe), has been synthesized and characterized. The X-ray crystal structure of [Au(C^N^C)(C≡CC6H4ValOMe)] has been determined. The complex was found to exhibit an unusual head-to-head conformation which was ascribed to the presence of directional hydrogen bonding interaction. The presence of π−π stacking interactions was also observed between adjacent complex molecules. The photophysical properties of the complexes were explored. The supramolecular assembly properties of the complexes have been studied and it was found that [Au(MeC^N^CMe)(C≡CC6H4ValValValOMe)] and [Au{C^N(R)^C}(C≡CR’)] (R = (4-OC12H25)C6H4, R’ = C6H4ValValOMe; R = (4-OC18H37)C6H4, R’ = C6H4ValValOMe; R = 3,4,5-(OC12H25)3C6H2, R’ = C6H4ValValValOMe) could form metallogels in DMSO. The gelation process was mainly driven by hydrogen bonding interactions, π−π stacking interactions and hydrophobichydrophobic interactions. The morphologies of the metallogels have been examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and the gelation mechanism has been revealed by variable-temperature 1H NMR, UV-vis absorption and emission spectroscopic studies.

A series of luminescent L-valine-modified alkynylgold(I) complexes with different substituted isocyanide ligands, [RNCAuCCR’] (R = 2,6-Me2C6H3, R’ = C6H4ValOMe, C6H4ValValOMe; R = H25C12C6H4, R’ = C6H4ValValOMe, C6H4ValValValOMe), and phosphine ligands, [MeOValValC6H4CCAu(PPh3)] and [RCCAu(PPh2PhSO3)]Na+ (R = C6H4ValOMe, C6H4ValValOMe, C6H4ValValValOMe), was synthesized and characterized. The X-ray crystal structure of [2,6-Me2C6H3NCAuCCC6H4ValOMe] has been determined. The complex molecules were found to pack in an octameric structure with significant intermolecular aurophilic interactions between adjacent Au(I) centers and appreciable hydrogen bonding interactions between each octamer. The UV-vis absorption and emission properties of these two series of complexes have been studied. The self-assembly processes of [RCCAu(PPh2PhSO3)]Na+ (R = C6H4ValOMe, C6H4ValValOMe, C6H4ValValValOMe) in water were studied by variable-concentration UV-vis absorption spectroscopy, variable-solvent composition UV-vis absorption, emission and 1H NMR spectroscopy and the corresponding aggregation morphologies were revealed by TEM. The self-assembly processes of these complexes were suggested to be mediated by aurophilic interactions and governed by isodesmic growth mechanism.

A class of luminescent cyclometalated gold(III) complexes with oligo- and poly(ethylene glycol)-based alkynyl ligands, [Au{C^N(R)^C}(C≡CR’)] (R = C6H4-OC12H25-4, R’ = C6H4(OCH2CH2)3OMe; R = C6H4-OC12H25-4, R’ = C6H2{(OCH2CH2)3OMe}3-3,4,5; R = H, R’ = C6H4COOEt) and [(RC^N^CR)Au- (C≡C-{R’}-C≡C)Au(RC^N^CR)] (R = H, R’ = C6H4CO(OCH2CH2)3OOCC6H4; R = H, R’ = C6H4COO-(PEO-PPO-PEO)-OOCC6H4; R = tBu, R’ = C6H4COO-(PEO-PPO-PEO)-OOCC6H4; R = H, R’ = C6H4(OCH2CH2)2OC6H4; R = H, R’ = C6H4(OCH2CH2)3OC6H4; R = H, R’ = C6H4(OCH2CH2)4OC6H4), has been designed, synthesized and characterized. The photophysical properties of the complexes have been investigated. The supramolecular assembly morphologies of the complexes, [Au{C^N(C6H4-OC12H25-4)^C}(C≡CR)] (R = C6H4(OCH2CH2)3OMe, C6H2{(OCH2CH2)3OMe}3-3,4,5), were studied by SEM and TEM. The aggregation processes were examined by variable-temperature UV-vis absorption and 1H NMR spectroscopy. The LCST properties of [(RC^N^CR)Au- (C≡CC6H4COO-(PEO-PPO-PEO)-OOCC6H4C≡C)Au(RC^N^CR)] (R = H, tBu) were studied by monitoring the transmittance of the complex solutions at different temperature.