Michele Soleilhavoup

Carbene-stabilized main group radicals and radical ions

Shortly after their discovery at the end of the 80s, stable singlet carbenes have been recognized as excellent ligands for transition metal based catalysts, and as organo-catalysts in their own right. At the end of the 2000s, it has been shown that they can coordinate main group elements in their zero oxidation state, and even activate small molecules. This review covers examples in the literature dealing with the most recent application of stable singlet carbenes, namely their use to stabilize radicals and radical ions that are otherwise unstable.

Cyclic (Alkyl)(amino)carbenes (CAACs): Recent Developments

Discovered in 2005, cyclic (alkyl)(amino)carbenes (CAACs) are among the most nucleophilic (σ donating) and also electrophilic (π-accepting) stable carbenes known to date. These properties allow them to activate a variety of small molecules and enthalpically strong bonds, to stabilize highly reactive main-group and transition-metal diamagnetic and paramagnetic species, and to bind strongly to metal centers, which gives rise to very robust catalysts. The most important results published up to the end of 2013 are briefly summarized, while the majority of this Review focuses on findings reported within the last three years.

Two-Coordinate Fe^0 and Co^0 Complexes Supported by Cyclic (alkyl)(amino)carbenes

The CAAC [CAAC=cyclic (alkyl)(amino)carbene] family of carbene ligands have shown promise in stabilizing unusually low-coordination number transition-metal complexes in low formal oxidation states. Here we extend this narrative by demonstrating their utility in affording access to the first examples of two-coordinate formal Fe(0) and Co(0) [(CAAC)2M] complexes, prepared by reduction of their corresponding two-coordinate cationic Fe(I) and Co(I) precursors. The stability of these species arises from the strong σ-donating and π-accepting properties of the supporting CAAC ligands, in addition to steric protection.

Air‐Stable (CAAC)CuCl and (CAAC)CuBH4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH3NH3

The first stable copper borohydride complex [(CAAC)CuBH4] [CAAC = cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH4 or BH3NH3 to the corresponding [(CAAC)CuCl] complex. Both complexes are air-stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H2/BH3 NH3 with a turnover frequency of 8400 mol H2 molcat(-1) h(-1) at 25 °C. In a fifteen-cycle experiment, the catalyst was reused without any loss of efficiency.

Gold(III)- versus gold(I)-induced cyclization: synthesis of six-membered mesoionic carbene and acyclic (aryl)(heteroaryl) carbene complexes.

The golden state: selective 5-exo- and 6-endo-cyclizations of an alkynyl benzothioamide have been achieved. The selectivity is controlled by the oxidation state of the gold precursor (+I or +III), yielding two new types of carbene ligand: an (aryl)(heteroaryl)carbene and a six-membered mesoionic carbene. Mes=2,4,6-trimethylphenyl.