Pentafluoroethylated Compounds of Silicon, Germanium and Tin.

In this contribution we present an account on pentafluoroethylated compounds of silicon, germanium and tin. The pronounced electron-withdrawing effect of the pentafluoroethyl group leads to a markedly increased Lewis acidity at the central atom which results in the stabilization of hypervalent complexes, anionic element(II) species as well as remarkable reactivities of element-element and element-hydrogen bonds. By addition to unsaturated C-C bonds or by reaction with organic halides as well as transition-metal complexes the molecules bearing a pentafluoroethyl-element group are readily accessible.

Synthesis and Reactivity of Donor-Stabilized Bis(pentafluoroethyl)stannylene [Sn(C F ) (D) ] (D=THF, DMAP, PMe , [Sn(C F ) ] ).

In this contribution we report on the synthesis of bis(pentafluoroethyl)stannane, H Sn(C F ) . In the reaction with donor molecules a ready elimination of hydrogen and the formation of the corresponding donor-stabilized monomeric bis(pentafluoroethyl)stannylene, Sn(C F ) , becomes apparent. With dependence on the Lewis basicity and steric demand of the donor, varying coordination numbers are realized.

The Dynamic Equilibrium of Hexakis(pentafluoroethyl)distannane Adducts [XSn(C F ) {Sn(C F ) }] (X=Cl, Br, I, Sn(C F ) ).

The tin-tin bond cleavage of hexaorganodistannanes by nucleophiles is a long-known reaction and widely used for stannate formation or stannyl group transfer. Herein, we detail our experiments to provide analytical evidence for the existence of the reasonably stable anionic complexes [XSn(C F ) {Sn(C F ) }] (X=Cl, Br, I, Sn(C F ) ) derived from hexakis(pentafluoroethyl)distannane. NMR investigations at low temperature lend further mechanistic insights.

Tris(pentafluoroethyl)stannane: Tin Hydride Chemistry with an Electron-Deficient Stannane.

A versatile two-step synthesis of tris(pentafluoroethyl)stannane, HSn(C F ) , is presented. Electron-withdrawing C F groups significantly influence the polarity of the tin-hydrogen bond, which allows facile deprotonation of the compound, even in water. The utility of this electron-deficient stannane was illustrated in hydrostannylations of alkenes and alkynes, as well as in dehalogenation reactions.

On Pentakis(pentafluoroethyl)stannate, [Sn(C F ) ] , and the Gas-Free Generation of Pentafluoroethyllithium, LiC F.

Pentafluoroethyllithium, LiC F , has been established as an efficient and versatile reagent for the transfer of the pentafluoroethyl unit to a number of electrophiles. Here, the stability of this species up to -40 °C is of advantage, particularly in comparison to its smaller congener LiCF . The usual production of LiC F , however, from gaseous HC F or IC F and strong bases requires specially designed apparatuses, which severely impeded its value as a laboratory reagent.

The Tris(pentafluoroethyl)stannate(II) Anion, [Sn(C F ) ] -Synthesis and Reactivity.

Syntheses of salts containing the tris(pentafluoroethyl)stannate(II) ion, [Sn(C F ) ] , were achieved through deprotonation of the corresponding stannane, HSn(C F ) , as well as by direct pentafluoroethylation of SnCl with LiC F . The electron-withdrawing substituents have substantial influence on the stability and reactivity of the anion as documented by its treatment with main group halides. Alkyl halides (R-X) underwent nucleophilic substitutions to afford RSn(C F ) , whereas Si, Ge, Sn, P halides gave rise to oxidation processes yielding hypervalent [SnX (C F ) ] salts (X=Cl, Br, I).

Synthesis of Mono-, Bis- and Tris(pentafluoroethyl)tin Derivatives, (C F ) SnX (X=Ph, Me, Cl, Br, Cp; n=1-3).

For (pentafluoroethyl)phenylstannanes, (C F )  SnPh (n=1-3), and dimethylbis(pentafluoroethyl)stannane, (C F ) SnMe , a high yield synthesis was developed by the use of LiC F as a C F transfer reagent. The treatment of these products with gaseous hydrogen chloride or hydrogen bromide afforded (C F ) SnX (X=Cl, Br; n=1-3) in good yields. The (pentafluoroethyl)stannanes were fully characterized by H, C, F and Sn NMR, IR spectroscopy and mass spectrometry.