Exploring Au(i) involving halogen bonding with N-heterocyclic carbene Au(i) aryl complexes in crystalline media

Abstract

Among the known types of non-covalent interactions with Au(I) metal center, Au(I) involving halogen bonding (XB) remains a rare phenomenon that has not been studied systematically. Herein, using five N-heterocyclic...

Halogen bonding–driven chiral amplification of a bimetallic gold-copper cluster through hierarchical assembly

“…For Au 2 Cu 2 , although the potential of iodine atom is negative, the electron-rich region of iodine is too disperse compared with that of pyridine N, which is more concentrated to have superior binding affinity toward the σ-hole in IFB. Moreover, as reported in a recent literature, the Au(I) center of the NHC-Au complex can serve as a nucleophilic acceptor toward halogen bonding, forming Au(I)···I─C interactions ( 60 ). However, in our cases, the Au atoms in Au 2 Cu 2 are incapable to display obvious negative areas to interact with the σ-hole of IFBs because they are surrounded by the ligands and form Au─Cu bond, which lead to the decrease in electron density.…”

Redox Activation of Acyclic (Aryl)(amino)carbene Gold(I) Complexes

“…Consequently, the proposed active species 4a-X and [4b′]­[X] form in the presence of coordinating anions X – . This contrasts the conventional gold­(I) catalysis requiring the scavenging of coordinating chloride anions to form the catalytically active species [Au I (L)] + . − The ferrocenium hole reservoir prevents irreversible nanoparticle formation as found for organic 4-DMA and 2-furyl substituents in 2a , 2b , 3a , and 3b and allows regeneration of the precatalyst by reduction as also observed for the L / [L] •+ redox couple (Chart b) showing redox-switchable catalysis …”

“…Chlorido gold­(I) complexes with phosphane or carbene ligands are highly useful precatalysts for a variety of organic transformations, in particular with substrates containing carbon–carbon multiple bonds with a considerable number of reviews documenting the huge progress of the research field. − Activation of the precatalyst to a cationic species with a vacant coordination site for substrate binding is required. This is most often realized by halide abstraction using silver­(I), copper­(I), or alkali metal salts with weakly coordinating counterions or halogen-bond donors, either isolated in a separate step before the catalysis or prepared in situ. − Silver- or additive-free methods, using so-called self-activating precatalysts, operate by intramolecular hydrogen bonding to activate the halido–gold bond. − Potentially self-activating (and counterion-binding) precatalysts A–E (Chart a) with N–H groups in ligand side arms reported by Gabbaï, Helaja, Marinetti & Guinchard, and Echavarren have been suggested to abstract the chlorido ligand from the gold­(I) center providing the cationic gold­(I) species with a vacant coordination site. − …”

Competition between Binding to Various Sites of Substituted Imidazoliums

“…It has been understood for some time that the formation of an HB induces changes in the chemical shielding of not only the bridging proton but also neighboring atoms such as the atom bonded to H and the electron-donating base atom. More recent work has documented evidence that the formation of other noncovalent bonds that are closely related to HBs, such as halogen and chalcogen bonds, also induces clear shifts in the NMR signal of the atoms involved. − Of this set of atoms, the one that appears to bear the closest correlation with the strength of the bond is the electron donor atom, ,, which in this case would be the N of NH 3 .…”