Bipyridinium and Phenanthrolinium Dications for Metal-Free Hydrodefluorination: Distinctive Carbon-Based Reactivity.

The development of novel Lewis acids derived from bipyridinium and phenanthrolinium dications is reported. Calculations of Hydride Ion Affinity (HIA) values indicate high carbon-based Lewis acidity at the ortho and para positions. This arises in part from extensive LUMO delocalization across the aromatic backbones.

P(v) dications: carbon-based Lewis acid initiators for hydrodefluorination.

The P(iii) dication [(terpy)PPh] is oxidized by reaction with o-chloranil or 9,10-phenanthrenequinone to give the P(v) dications [(terpy)(CClO)PPh] and [(terpy)(CHO)PPh], respectively. These species are coordinatively saturated at phosphorus and yet display the ability to effect Lewis acid initiation of hydrodefluorination of fluoroalkanes. Experimental and computational data support the notion that the P(v) dications are Lewis acidic at the para-carbon of the central ring of the terpy ligand.

Nitrogen-Based Lewis Acids Derived from Phosphonium Diazo Cations.

Reaction of PPh and [(p-ClC H )N ][BF ] affords [(p-ClC H )N(PPh )N(PPh )][BF ] 1, while reaction with (Ph PCH ) gave [(p-ClC H )(NPh PCH ) )][BF ] 2. These species confirm the Lewis acidity of [(p-ClC H )N (PR )][BF ] cations at N. In contrast, use of bulky phosphines afford the species [ArN (PR )][BF ] (R=tBu 3, Mes 4).

Halogenated triphenylgallium and -indium in frustrated Lewis pair activations and hydrogenation catalysis.

The Lewis acids Ga(CF), In(CF) and Ga(CCl) are prepared and their Lewis acidity has been probed experimentally and computationally. The species Ga(CF) and In(CF) in conjunction with phosphine donors are shown to heterolytically split H and catalyse the hydrogenation of an imine. In addition, frustrated Lewis pairs (FLPs) derived from Ga(CF) and In(CF) and phosphines react with diphenyldisulfide to phosphoniumgallates or indates of the form [BuPSPh][PhSE(CF)] and [BuPSPh][(μ-SPh)(E(CF))] (E = Ga, In).

S(vi) Lewis acids: fluorosulfoxonium cations.

Avenues to S-based Lewis acids were developed via the oxidation of aryl-sulfoxides with XeF, giving difluorodiarylsulfoxides which react via fluoride abstraction to afford Lewis acidic fluorosulfoxonium cations; this acidity is derived from the S-F σ* orbital and has been probed both experimentally and computationally.