Metallomimetic Chemistry of a Cationic, Geometrically Constrained Phosphine in the Catalytic Hydrodefluorination and Amination of Ar-F Bonds.

The synthesis, isolation, and reactivity of a cationic, geometrically constrained σ3-P compound in the hexaphenyl-carbodiphosphoranyl-based pincer-type ligand (1+) are reported. 1+ reacts with electron-poor fluoroarenes via an oxidative addition-type reaction of the C-F bond to the PIII-center, yielding new fluorophosphorane-type species (PV). This reactivity of 1+ was used in the catalytic hydrodefluorination of Ar-F bonds with PhSiH3, and in a catalytic C-N bond-forming cross-coupling reactions between fluoroarenes and aminosilanes. Importantly, 1+ in these catalytic reactions closely mimics the mode of action of the transition metal-based catalysts.

Metal-Free Catalytic Reductive Cleavage of Enol Ethers.

In contrast to the well-known reductive cleavage of the alkyl-O bond, the cleavage of the alkenyl-O bond is much more challenging especially using metal-free approaches. Unexpectedly, alkenyl-O bonds were reductively cleaved when enol ethers were reacted with Et3SiH and a catalytic amount of B(C6F5)3. Supposedly, this reaction is the result of a B(C6F5)3-catalyzed tandem hydrosilylation reaction and a silicon-assisted ß-elimination. A mechanism for this cleavage reaction is proposed based on experiments and density functional theory (DFT) calculations.

B(C6 F5 )3 -Catalyzed Selective Chlorination of Hydrosilanes.

The chlorination of Si-H bonds often requires stoichiometric amounts of metal salts in conjunction with hazardous reagents, such as tin chlorides, Cl2 , and CCl4 . The catalytic chlorination of silanes often involves the use of expensive transition-metal catalysts. By a new simple, selective, and highly efficient catalytic metal-free method for the chlorination of Si-H bonds, mono-, di-, and trihydrosilanes were selectively chlorinated in the presence of a catalytic amount of B(C6 F5 )3 or Et2 O⋅B(C6 F5 )3 and HCl with the release of H2 as a by-product. The hydrides in di- and trihydrosilanes could be selectively chlorinated by HCl in a stepwise manner when Et2 O⋅B(C6 F5 )3 was used as the catalyst. A mechanism is proposed for these catalytic chlorination reactions on the basis of competition experiments and density functional theory (DFT) calculations.