Syntheses, X-ray Crystal Structures, and Solution Behavior of Cationic, Two-Coordinate Gold(I) η²-Diene Complexes

Abstract

A family of cationic gold π-diene complexes of the form {[P(t-Bu) 2 o-biphenyl]Au(η 2 -diene)} þ SbF 6 À were isolated in >80% yield from reaction of various dienes with a mixture of [P(t-Bu) 2 o-biphenyl]AuCl and AgSbF 6 and were characterized by spectroscopy and, in four cases, by X-ray crystallography. Solution and solid-state analysis of these complexes established selective binding of gold to the less substituted CdC bond of the diene in the case of dienes that possessed differentially substituted CdC bonds. 13 C NMR analysis and evaluation of the relative binding affinities of substituted dienes point to a bonding model in which the goldÀalkene interaction is stabilized via donation of electron density from the uncomplexed CdC bond to the complexed CdC bond of the diene. Variable-temperature NMR analysis of gold π-diene complexes revealed fluxional behavior consistent with facile (ΔG ‡ = 9.6À11.9 kcal mol À1 ) intramolecular exchange of the complexed and uncomplexed CdC bonds of the diene ligand.

Synthesis and Study of Cationic, Two‐Coordinate Triphenylphosphine– Gold–π Complexes

“…Indeed, we have previously established an intramolecular mechanism for the interconversion of the complexed and uncomplexed C=C bonds of {[PA C H T U N G T R E N N U N G (tBu) 2 . [14] Conversely, an intermolecular pathway for exchange would necessarily occur with A C H T U N G T R E N N U N G concomitant exchange of the two faces of the 1,3-cyclo-A C H T U N G T R E N N U N G hexadiene ligand, producing a single, time-averaged allylic resonance in the fast-exchange spectrum, as was observed for 7·SbF 6 . Supporting this contention, the 1 H NMR spectrum of a solution of 7·SbF 6 (42 mm) that contained a trace of free 1,3-cyclohexadiene (ca.…”

“…[6] Due to the central role of gold-p complexes in these mechanisms, there has been recent interest in the synthesis and study of cationic, two-coordinate gold-p complexes. [7] From these efforts, a number of mononuclear, cationic gold(I) complexes containing a p alkene, [8,9] alkyne, [10,11] allene, [12] conjugated diene, [13,14] or arene [15,16] p ligand and a sterically hindered, electron-rich supporting ligand, such as 1,3-bis- 3 , or PA C H T U N G T R E N N U N G (tBu) 2 -o-biphenyl, have been isolated and characterized both in the solid state and in solution. Conversely, mononuclear, cationic, two-coordinate goldp complexes containing a triphenylphosphine ligand have not been isolated.…”

Supra-molecular synthons based on gold…π(arene) interactions

“…There has been little detailed theoretical analysis of the energy associated with intermolecular Au…π interactions but the aforementioned Au…π(alkene) interactions provide a benchmark. Thus, based on variable temperature Nuclear Magnetic Resonance (NMR) spectroscopy, the energy of interaction between gold and an alkene is approximately 10 kcal mol −1 [22], a value that must be considered an upper estimate for Au…π(alkene) interactions described herein.…”

“…There are approximately 60, 360 and 100 examples of de-localised, semi-localised and localised Au…π interactions, respectively. As yet, no detailed analysis of semi-localised and localised Au…π interactions is available but in this context, it is salutary to consider emerging discoveries on rare Au…π(alkene) interactions [22,23], an example of which is described below. There has been little detailed theoretical analysis of the energy associated with intermolecular Au…π interactions but the aforementioned Au…π(alkene) interactions provide a benchmark.…”

Mechanistic insights and functionalization of alkynes in homogeneous gold catalysis.

“…As expected, hydrogen bond acceptors with lower gold affinity (e.g., DMPU, DMF) [141][142][143][144][145][146][147][148] enhanced the rate of reaction (Scheme 14b), and ionic hydrogen bond acceptors (e.g., Bu4N Other research groups reported that certain compounds improved the chemical yields in selected gold catalyzed reactions. 153,154 One notable example is the …”