Synthesis, Photochemical, and Redox Properties of Gold(I) and Gold(III) Pincer Complexes Incorporating a 2,2′:6′,2″-Terpyridine Ligand Framework

Abstract

Reaction of [Au(C6F5)(tht)] (tht = tetrahydrothiophene) with 2,2′:6′,2″-terpyridine (terpy) leads to complex [Au(C6F5)(η1-terpy)] (1). The chemical oxidation of complex (1) with 2 equiv of [N(C6H4Br-4)3](PF6) or using electrosynthetic techniques affords the Au(III) complex [Au(C6F5)(η3-terpy)](PF6)2 (2). The X-ray diffraction study of complex 2 reveals that the terpyridine acts as tridentate chelate ligand, which leads to a slightly distorted square-planar geometry. Complex 1 displays fluorescence in the solid state at 77 K due to a metal (gold) to ligand (terpy) charge transfer transition, whereas complex 2 displays fluorescence in acetonitrile due to excimer or exciplex formation. Time-dependent density functional theory calculations match the experimental absorption spectra of the synthesized complexes. In order to further probe the frontier orbitals of both complexes and study their redox behavior, each compound was separately characterized using cyclic voltammetry. The bulk electrolysis of a solution of complex 1 was analyzed by spectroscopic methods confirming the electrochemical synthesis of complex 2.

Gold Catalyzed Decarboxylative Cross-Coupling of Iodoarenes

“…The redox stability of gold­(I) complexes has limited development of complementary methods utilizing redox gold catalysts. − This work describes a gold catalyzed decarboxylative cross-coupling reaction, where the redox events are proposed to occur from a gold­(I) complex. Pioneering studies demonstrated that gold­(I) complexes can participate in oxidative addition with methyl iodide, , trifluoromethyl iodide, , aryl diazonium salts, − iodine­(III) reagents, − and other strong oxidants. ,, Initially Lloyd-Jones and co-workers demonstrated a catalytic oxidative coupling of aryl-silanes in the presence of a strong acid and a stoichiometric iodine­(III) oxidant (Scheme a). , A limiting feature of this and subsequent work − ,, is that the site selectivity of C–H bond activation is governed by an apparent electrophilic aromatic substitution (EAS) mechanism. Patil and co-workers demonstrated a dual gold/photoredox catalyzed cross-coupling with aryl silanes or aryl stannanes, which is thought to occur via a radical mechanism (Scheme b) …”

“…Pioneering studies demonstrated that gold(I) complexes can participate in oxidative addition with methyl iodide, 19,20 trifluoromethyl iodide, 21,22 aryl diazonium salts, 23−29 iodine(III) reagents, 30−41 and other strong oxidants. 16,42,43 Initially Lloyd-Jones and co-workers demonstrated a catalytic oxidative coupling of aryl-silanes in the presence of a strong acid and a stoichiometric iodine(III) oxidant (Scheme 1a). 31,34 A limiting feature of this and subsequent work [35][36][37][38][39][40]44,45 is that the site selectivity of C−H bond activation is governed by an apparent electrophilic aromatic substitution (EAS) mechanism.…”

Gold(I)–Alkynyl Complexes with an N‐Donor Heterocyclic Ligand: Synthesis and Photophysical Properties

“…Complexes with dual emission are particularly interesting from the viewpoint of practical applications, since this type of photophysical behaviour makes, in principle, 100 % harvesting of excitation energy possible (e.g., in OLEDs) and also opens up an avenue to the fabrication of white‐light devices, so‐called white‐light organic light‐emitting devices (WOLEDs) , . In this respect, it must be mentioned that various phosphine and alkynyl ligands with fluorescent aromatic backbones were widely used as auxiliary chromophoric centres in gold(I) complexes,, , , whereas analogous chemistry with N‐donor aromatic ligands is relatively less successful,, and the obtained complexes are either nonluminescent under ambient conditions, , or display a very weak triplet emission with nearly negligible contribution from the N‐donor‐ligand chromophores. It is also worth noting that the known pyridyl–gold–alkynyl complexes (L–Au–C 2 Ph) proved to be only stable provided that the pyridyl ligands possessed strong electron‐donating substituents, like NH 2 and NMe 2 (4‐NH 2 Py and 4‐dmap).…”

Influence of structural changes on photophysical properties of terpyridine derivates: Experimental studies and theoretical calculations

“…As shown in the anodic profile, the cathodic scan shows irreversible waves in all cases, but when the electrode potential is increased to more negative potentials, an exponential current appears. 45 In all cases, the first anodic and cathodic peak are very sensitive to the scan rate since both move to more anodic or more cathodic potentials, respectively, when the scan rate increases. The electrochemical data (anodic and cathodic peaks potentials (E ap , E cp ), and anodic and cathodic peaks currents (i ap , i cp )) are summarized in table 4.…”