Isolation of a Reactive Tricoordinate α‐Oxo Gold Carbene Complex

Abstract

The [(P,P)Au=C(Ph)CO2Et]+ complex 3 [where (P,P) is an o‐carboranyl diphosphine ligand] was prepared by diazo decomposition at −40 °C. It is the first α‐oxo gold carbene complex to be characterized. Its crystallographic structure was determined and DFT calculations have been performed, unraveling the key influence of the chelating (P,P) ligand. The gold center is tricoordinate and the electrophilicity of the carbene center is decreased. Complex 3 mimics transient α‐oxo gold carbenes in a series of catalytic transformations, and provides support for the critical role of electrophilicity in the chemoselectivity of phenol functionalization (O−H vs. C−H insertion).

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C−H Bond Functionalization

“…This regioselectivity is quite unusual, since pyrrole typically reacts with electrophiles at the C2-position. [105] Reactions involving the transfer of the carbene moiety of diazotized compounds via gold catalysis have also emerged as promising tools for CÀ H activation. Au-carbenoids, highly electrophilic species generated in situ from diazo molecules and Au(I)-complexes, have been shown to undergo insertion into Csp 3 À H bonds in a selective manner.…”

Evidence for genuine hydrogen bonding in gold(I) complexes

“…1). The hemilabile character of the DalPhos ligands has been shown by Zhang and coworkers (27)(28)(29)(30)(31)(32) to efficiently temper the reactivity of α-oxocarbenes. In addition, our group recently demonstrated the feasibility and easiness of oxidative addition to gold thanks to such (P,N) ligands [the hard N center stabilizes the Au(III) product and lowers the activation barrier] providing a new pathway for Au(I)/Au(III) catalysis (33).…”

Gold-Catalyzed Synthesis of Small Rings

“… 562 The design of hemilabile P,N-ligand 563 , 564 394 endowed with a C 2 -symmetric piperidine ring was key to achieve good enantiocontrol. It was proposed that coordination of the N atom to the metal center and steric shielding temper the high reactivity of the very electrophilic α-oxo gold carbene intermediate 395 , 565 , 566 while the piperidine provides a suitable chiral environment. Previous attempts to perform this reaction using axially chiral diphosphine ligands resulted in very low levels of enantioselectivity.…”

“…Through careful ligand design, Borissou and co-workers reported the isolation and solid-state characterization of a tricoordinated α-oxo gold(I) carbene complex generated from ethyl diazo(phenyl)acetate at −40 °C, which was competent in the cyclopropanation of styrene when generated in situ from the diazo-compound. 566 Other groups have also contributed to the characterization of gold(I) carbenes, using different strategies to stabilize the otherwise reactive species. 629 − 633 …”