Catalytic Activity of trans-Bis(pyridine)gold Complexes

Abstract

Gold catalysis has become one of the fastest growing fields in chemistry, providing new organic transformations and offering excellent chemoselectivities under mild reaction conditions. Methodological developments have been driven by wide applicability in the synthesis of complex structures, whereas the mechanistic understanding of Au(III)-mediated processes remains scanty and have become the Achilles' heel of methodology development. Herein, the systematic investigation of the reactivity of bis(pyridine)-ligated Au(III) complexes is presented, based on NMR spectroscopic, X-ray crystallographic, and DFT data. The electron density of pyridines modulates the catalytic activity of Au(III) complexes in propargyl ester cyclopropanation of styrene. To avoid strain induced by a ligand with a nonoptimal nitrogen−nitrogen distance, bidentate bis(pyridine)−Au(III) complexes convert into dimers. For the first time, bis(pyridine)Au(I) complexes are shown to be catalytically active, with their reactivity being modulated by strain.

P,N-Chelated Gold(III) Complexes: Structure and Reactivity

“…This geometry is energetically feasible, as predicted by DFT. Analogous stability differences of the cis and trans orientations of chlorides, favoring the trans orientation, have previously been reported for the gold(III) 56 and palladium(II) 66 complexes. The dynamic nature of the complex ([ 1 -Au(III)]SbF 6 ) 2 was indicated by the inability to observe the δ 15 N of this complex, even at high concentration and with prolonged experiments.…”

Symmetry of three-center, four-electron bonds

“…44 Furthermore, they will aid synthetic chemistry by improving the development of novel transition metal, hydrogen and halogen bond catalysts. 43,45,46 Conflicts of interest There are no conicts to declare.…”

“…The transition metal complexes possessing tight PESs are vastly stable, which is well reected by the applicability of 1-Au as catalyst for organic transformations. 43 We obtained statistical trends from solid state observations by collecting the available X-ray structures that possess an N-X-N motif involving heterocyclic Lewis bases from the Cambridge Structural Database (CSD, search June 2020). (Table 1).…”

Au(III) complexes with tetradentate-cyclam-based ligands

“…This was evidenced by changes in NMR shift values, Δδ 15 N coord = δ 15 N complex – δ 15 N ligand , by coordination. The observed Δδ 15 N coord values were in the range of 16.3–32.0 ppm for both the primary and secondary amine nitrogens, indicating a characteristic deshielding effect upon the Au(III) coordination [ 43 , 45 – 46 ], Likewise, Δδ 1 H coord 0.3–0.5 ppm for all the neighboring N–C H and N–C H 2 protons indicated ligand tetra-coordination to Au(III), as well. Upon coordination of ligand 5a , four different 15 N NMR values for the nitrogens were observed.…”