Maximilian Joost

Reactivity of Gold Complexes towards Elementary Organometallic Reactions

For a while, the reactivity of gold complexes was largely dominated by their Lewis acid behavior. In contrast to the other transition metals, the elementary steps of organometallic chemistry-oxidative addition, reductive elimination, transmetallation, migratory insertion-have scarcely been studied in the case of gold or even remained unprecedented until recently. However, within the last few years, the ability of gold complexes to undergo these fundamental reactions has been unambiguously demonstrated, and the reactivity of gold complexes was shown to extend well beyond π-activation. In this Review, the main achievements described in this area are presented in a historical context. Particular emphasis is set on mechanistic studies and structure determination of key intermediates. The electronic and structural parameters delineating the reactivity of gold complexes are discussed, as well as the remaining challenges.

Facile oxidative addition of aryl iodides to gold(I) by ligand design: bending turns on reactivity.

Thanks to rational ligand design, the first gold(I) complexes to undergo oxidative addition of aryl iodides were discovered. The reaction proceeds under mild conditions and is general. The ensuing aryl gold(III) complexes have been characterized by spectroscopic and crystallographic means. DFT calculations indicate that the bending induced by the diphosphine ligand plays a key role in this process.

Oxidative Addition of Carbon–Carbon Bonds to Gold

The oxidative addition of strained CC bonds (biphenylene, benzocyclobutenone) to DPCb (diphosphino-carborane) gold(I) complexes is reported. The resulting cationic organogold(III) complexes have been isolated and fully characterized. Experimental conditions can be adjusted to obtain selectively acyl gold(III) complexes resulting from oxidative addition of either the C(aryl)C(O) or C(alkyl)C(O) bond of benzocyclobutenone. DFT calculations provide mechanistic insight into this unprecedented transformation.

Enhanced π‐Backdonation from Gold(I): Isolation of Original Carbonyl and Carbene Complexes

The specific electronic properties of bent o-carborane diphosphine gold(I) fragments were exploited to obtain the first classical carbonyl complex of gold [(DPCb)AuCO](+) (ν(CO)=2143 cm(-1) ) and the diphenylcarbene complex [(DPCb)Au(CPh2 )](+) , which is stabilized by the gold fragment rather than the carbene substituents. These two complexes were characterized by spectroscopic and crystallographic means. The [(DPCb)Au](+) fragment plays a major role in their stability, as substantiated by DFT calculations. The bending induced by the diphosphine ligand substantially enhances π-backdonation and thereby allows the isolation of carbonyl and carbene complexes featuring significant π-bond character.

Direct Evidence for Intermolecular Oxidative Addition of σ(SiSi) Bonds to Gold

Oxidative addition plays a major role in transition-metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl3, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative (31)P and (29)Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si-Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si-Si) bonds to gold and open promising perspectives for the development of new gold-catalyzed redox transformations.

Copper: σ-SiH Coordination to Cu(I)

This chapter gives firstly an introduction concerning σ-complexes and in particular σ-SiH complexes. Afterwards, the obtained results concerning the coordination of diphosphino-hydrosilanes to Cu(I) will be described.

General Conclusion and Perspective

The major objectives of the initially envisioned research project that evolved in the course of this work were focused on the elucidation of the coordination chemistry of copper and gold. Unexpected reactivities of these two coinage metals with regard to fundamental elementary steps were disclosed and studied in detail by experimental means and accompanying theoretical analyses by the groups of Dr. Karinne Miqueu (Pau) and Prof. Dr. Laurent Maron (Toulouse). These findings contribute to the precise understanding of the chemistry of copper and gold complexes and hopefully may influence further fundamental and application-oriented research in these fields.

Fundamental Elementary Steps in Gold Chemistry

The interest in the coordination chemistry of gold was considerably revived following the discovery of the catalytic potential of this metal at the end of the 1990s (Hashmi in Chem Rev 107:3180–3211, 2007). The advent and rise of gold catalysis clearly led to a more profound understanding of organogold chemistry. However, the reactivity of gold complexes is essentially dominated by their pronounced π-acidic properties. Other reactivities, as typically known from the chemistry of transition metal compounds, are hardly explored in the case of gold.

Gold: Migratory Insertion at Au(I)

It has been established that organogold compounds are mostly inert towards migratory insertion reactions with olefins and alkynes (see Sect. 3.5). By contrast, the analogous reactivity of silyl gold complexes has not been explored. In this chapter, the experimental results concerning our studies on the reactivity of AuSi bonds towards alkynes and allenes, as well as a theoretical analysis will be discussed.

Gold: Oxidative Addition to Au(I)

In this chapter, the results obtained during the course of this Ph.D. work concerning intermolecular σ-bond activation processes with gold(I) are exposed: (i) the oxidative addition of σ-SiSi bonds at monoligated cationic gold(I) complexes, (ii) the design of diphosphine gold(I) complexes suitable for oxidative addition reactions and (iii) application of the latter in σ-bond activation processes (strained carbocycles and simple aryl halides) will be discussed.