Tuning the Gold(I)‐Carbon σ Bond in Gold‐Alkynyl Complexes through Structural Modifications of the NHC Ancillary Ligand: Effect on Spectroscopic Observables and Reactivity

Abstract

Understanding the features of the gold(I)-carbon σ bond and its modulation induced by an ancillary ligand has become fundamental for the purposes of ligand design, due to the increasing interest towards gold(I)-alkynyl complexes and their wide range of applications. We carry out a systematic computational analysis of 16 gold(I)-acetylide complexes bearing different N-Heterocyclic Carbenes (NHCs) as ancillary ligands [NHCÀ Au(I)À CCH]. The results show that the strength and features of the AuÀ C bond can be efficiently tuned by performing specific structural modifications on the NHC, enabling a more efficient π communication between the alkynyl and the ancillary ligand. We also demonstrate that the effect of the bond modulation can be revealed via NMR spectroscopy, as highlighted by the tight correlation between the computed nuclear shielding constants and the bonding parameters. Finally, we show that, for the dual-gold-catalyzed Bergman cyclization as case study, suitable structural modifications on the NHC ligand, which modulate the π-acidity of the metal fragment σ-coordinated to an enediyne substrate, could affect the reaction barrier and the thermodynamic stability of the product. All the reported results can be well rationalized in the framework of distortion/interaction analysis, which has been recently extended to the dual (σ,π-type) Au catalytic systems by Alabugin et al (J. Am. Chem. Soc. 2017, 137, 3406-3416).

Unraveling differences in aluminyl and carbene coordination chemistry: bonding in gold complexes and reactivity with carbon dioxide

“…30 Similar tuning has also been reported for the trans effect in gold(I)-alkynyl complexes. 31 Analogous experimental and/or theoretical systematic studies assessing this relationship for metal-aluminyl complexes have been never reported to the best of our knowledge, despite the interesting and novel chemistry of metalaluminyl compounds. In this regard, it was recently revealed that the gold complex of aluminyl anion I, the [ t Bu 3 PAuAl(NON)] complex, is surprisingly able to insert CO 2 into the Au-Al bond, leading to the [ t Bu 3 PAuCO 2 Al(NON)] product with the CO 2 carbon atom coordinated to Au.…”

NMR Spectroscopic Signatures of Cationic Surface Sites from Supported Coinage Metals Interacting with N-Heterocyclic Carbenes

“…While no change was seen for 1*-Au , it enables the estimation of the two-bond 13 C scalar coupling constant in 2*-Au , 2 J (c‑c) = 26 ± 3 Hz (see SI, Figures S6–S7). The relatively high value for 2 J (c‑c) is in accordance with the directly bonded electronegative Au­(I) cation. − …”