Gold Carbenoids: Lessons Learnt from a Transmetalation Approach

Abstract

Carbophilic catalysts that are based on Au I allow a host of different nucleophiles to be added across various p systems. [1][2][3] Although many of these reactions are thought to proceed via gold carbenoids, the challenge to observe and characterize these putative intermediates has basically been unmet. [4] The current mechanistic interpretation therefore largely relies on indirect evidence and computational data, some of which are subject to debate. [5] In an attempt to fill this gap, we pursued a potential route to gold carbenoids by formal transmetalation of chromium or tungsten Fischer carbene complexes with [LAu] + . Whereas this transformation proceeds with exceptional ease as long as a stabilizing heteroelement is present on the carbene center, it stops half-way in its absence. Rather unusual bimetallic arrays are formed, which allow the charge density to delocalize over several positions. The obvious difficulty of releasing an "unstabilized" gold carbenoid has potential mechanistic implications for the understanding of p-acid catalysis in general.

Synthesis, Structure, and Reactivity of a Gold Carbenoid Complex That Lacks Heteroatom Stabilization

“…[1] Nevertheless, there remains considerable debate regarding the nature of these complexes, [2][3][4] which is in large part due to the lack of direct experimental information regarding the structure and behavior of cationic gold carbenoid complexes. [1][2][3][4][5] In 2008, Hammond reported the spectroscopic detection of a gold carbenoid/oxonium complex, [6] and since then, a number of cationic gold carbenoid complexes have been isolated, [7][8][9][10] including Fürstners recent disclosure of a reactive dianisylcarbenoid complex ( Figure 1). [1][2][3][4][5] In 2008, Hammond reported the spectroscopic detection of a gold carbenoid/oxonium complex, [6] and since then, a number of cationic gold carbenoid complexes have been isolated, [7][8][9][10] including Fürstners recent disclosure of a reactive dianisylcarbenoid complex ( Figure 1).…”

“…[8] In an effort to impart greater stability in a heteroatomfree gold carbenoid complex, we sought to exploit the potential aromatic stabilization of the cycloheptatrienylidene ligand. [6][7][8][9] [*] R. 4 ), which are presumably formed through the attack of unreacted 3 on 4·B(C 6 F 5 ) 4 . Attempted synthesis of gold diphenylcarbenoid complex 1.…”

Katalyseforschung auf dem Computer

“…B. mit Au und Cr), die auf DFT-Niveau hinsichtlich ihrer elektronischen Struktur und der Bindungsverhältnisse charakterisiert wurden. [67] 3.3. Gemeinsame Projekte mit der Alcarazo-Gruppe Die Forschung in der Alcarazo-Gruppe zielt auf das Design und die Synthese ungewçhnlicher Liganden und Koordinationsverbindungen und deren Anwendung in neuartigen katalytischen Umsetzungen.…”

Katalyse und Totalsynthese: eine persönliche Zwischenbilanz

“…[ 35] Wird die Reaktionslçsung auf Raumtemperatur erwärmt, zersetzt sich der Dimetallkomplex 7 (X = H).…”

“…Dazu wurden geeignete Chromcarbene als Ausgangsmaterialien herangezogen (Schema 4). [35] Obwohl die Chrom!Gold-Transmetallierung von Fischer-Carbenen bekanntlich außerordentlich leicht erfolgt, [36] ließ sich Verbindung 5 (Ar = Ph) auf diese Weise nicht zum entsprechenden Goldkomplex umsetzen. Vielmehr wurde lediglich die Koordination des Goldkomplexfragments an die Cr = C-Einheit beobachtet, was letztere so elektronenarm macht, dass das Primäraddukt 6 selbst bei niedriger Temperatur einen der ebenfalls stark elektronenziehenden CO-Liganden abgeben muss.…”