Copper and Silver Trispyrazolylborate-Phosphinoazide Complexes: Synthesis, Characterization, and Nitrene Generation.

Phosphinoazide complexes of the composition TpM-L (M = Cu, Ag, and L = 2-azido-1,3-bis(2,6-diisopropylphenyl)-2,3-dihydro-1-1,3,2-diazaphosphole) have been synthesized and structurally characterized. Their thermal decomposition led to cyclodiphosphazenes as a result of the metal-mediated coupling of two nitrene units in a process that takes place in both a stoichiometric and catalytic manner. Experimental data have allowed proposing a mechanistic pathway for this new transformation.

Rare Gold-Catalyzed 4-- Cyclization for Ring Expansion of Propargylic Aziridines toward Stereoselective ()-Alkylidene Azetidines, via Diborylalkyl Homopropargyl Amines.

We report an uncommon 4-- cyclization of -tosyl homopropargyl amines, catalyzed by [AuCl(PEt)]/AgOTf, to prepare stereoselective ()-2-alkylidene-1-tosylazetidine compounds. The reaction outcome contrasts with the gold-catalyzed cyclization of -tosyl homopropargyl amines containing a methyl group at the propargylic position that provides substituted 2,3-dihydropyrroles via a 5-- mechanism. The access to -tosyl homopropargyl amines is possible by the regioselective nucleophilic attack of α-diboryl alkylidene lithium salts to propargylic aziridines.

Non-innocent Role of the Halide Ligand in the Copper-Catalyzed Olefin Aziridination Reaction.

In the context of copper-catalyzed nitrene transfer to olefins, many systems operate upon mixing a CuX salt (X = halide, OTf) and a polydentate N-based ligand, assuming that the X ligand is displaced from the coordination sphere toward a counterion position. Herein, we demonstrated that such general assumption should be in doubt since studies carried out with the well-defined copper(I) complexes (TTM)CuCl and [(TTM)Cu(NCMe)]PF (TTM = tris(triazolyl)methane ligand) demonstrate a dual behavior from a catalytic and mechanistic point of view that exclusively depends on the presence or absence of the chloride ligand bonded to the metal center. When coordinated, the turnover-limiting step corresponds to the formation of the carbon-nitrene bond, whereas in its absence, the highest barrier corresponds to the formation of the copper-nitrene intermediate.

Introducing the Catalytic Amination of Silanes via Nitrene Insertion.

The direct functionalization of Si-H bonds by the nitrene insertion methodology is described. A copper(I) complex bearing a trispyrazolylborate ligand catalyzes the transfer of a nitrene group from PhI═NTs to the Si-H bond of silanes, disilanes, and siloxanes, leading to the exclusive formation of Si-NH moieties in the first example of this transformation. The process tolerates other functionalities in the substrate such as several C-H bonds and alkyne and alkene moieties directly bonded to the silicon center.

Intermolecular Allene Functionalization by Silver-Nitrene Catalysis.

Under silver catalysis conditions, using [Tp*Ag] as the catalyst precursor, allenes react with PhI═NTs in the first example of efficient metal-mediated intermolecular nitrene transfer to such substrates. The nature of the substituent at the allene seems crucial for the reaction outcome since arylallenes are converted into azetidine derivatives, whereas methylene aziridines are the products resulting from alkylallenes. Mechanistic studies allow proposing that azetidines are formed through unstable cyclopropylimine intermediates, which further incorporate a second nitrene group, both processes being silver-mediated.