Halide abstraction

One way to reactive cations - stabilized by the weakly coordinating anions [Al(OR^F)₄]^- - is the abstraction of a halide anion with the silver salt Ag[Al(OR^F)₄] from a halogene containing compound like CX₄ or PX₃. The driving force in these reactions is the big lattice energy of the precipitating AgX. In case of the tetrahalomethanes CX₄ (X = Cl, Br, I) this leads directly to the trihalocarbenium cations [CX₃]⁺. With the phosphorus trihalides PX₃ (X = Br, I) an electrophilic carbene-analogous [PX₂]⁺ intermediate (not isolable) is built, which can insert in different bonds like X-X, X₂P-X (X = Br, I) or in a P-P bond of white phosphorus (P₄) for example.

On this way the halocarbenium cations [CX₃]⁺ (X = Cl, Br, I) and several reactive phosphorus cations were isolated as salts of the [Al(OR^F)₄]^- anion and could be characterized in solution and in the solid state by X-Ray diffraction, vibrational (Raman and IR) and NMR spectroscopy (especially ¹³C and ³¹P).

Literature:

[CCl₃]⁺ und [CBr₃]⁺:

A. J. Lehner, N. Trapp, H. Scherer, I. Krossing, Dalton Transactions 2010, 40, 1448.

[CI₃]⁺

I. Krossing, A. Bihlmeier, I. Raabe, N. Trapp, Angewandte Chemie 2003, 115, 1569.
I. Raabe, D. Himmel, S. Muller, N. Trapp, M. Kaupp, I. Krossing, Dalton Transactions 2008, 946.

[P₅X₂]⁺ (X = Br, I)

I. Krossing, I. Raabe, Angewandte Chemie 2001, 113, 4544.

[PX₄]⁺, [P₂X₅]⁺ und [P₅X₂]⁺ (X = Br, I)

[P₂I₅]⁺  from P₂I₅[Al(OC(CF₃)₃)₄]

M. Gonsior, I. Krossing, L. Müller, I. Raabe, M. Jansen, L. van Wüllen, Chemistry – A European Journal 2002, 8, 4475.

[P₃I₆]⁺ and [P₅I₂]⁺

[P₅I₂]⁺  calculated (RI-MP2/TZVPP)

I. Krossing, Journal of the Chemical Society, Dalton Transactions 2002, 500.