On Pentakis(pentafluoroethyl)stannate, [Sn(C₂F₅)₅]⁻, and the Gas‐Free Generation of Pentafluoroethyllithium, LiC₂F₅

Abstract

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. In this contribution we communicate an alternative gas-free and highly efficient protocol for the synthesis of LiC F from the already commercialized stannate salt [PPh ][Sn(C F ) ]. The [Sn(C F ) ] anion represents not only the first example of a structurally characterized hypervalent pentaalkylstannate but also serves as a precursor for the synthesis of the homoleptic tetrakis(pentafluoroethyl)stannane, Sn(C F ) . The reaction of the latter with n-butyllithium provides an insight into the mechanism of LiC F generation.

Pentafluoroethylated Compounds of Silicon, Germanium and Tin

“…Above a temperature of −40 °C the decomposition of excess LiC 2 F 5 to insoluble LiF and volatile tetrafluoroethylene facilitates its removal. The treatment of the Lewis acidic inorganic element chlorides SiCl 4 , GeCl 4 and SnCl 4 with LiC 2 F 5 reveals element‐specific reactivity patterns (Scheme ) . While in the reaction with GeCl 4 the anticipated formation of Ge(C 2 F 5 ) 4 becomes apparent, the increased Lewis acidity of SnCl 4 results in the precipitation of its diethyl ether complex followed by an unselective formation of various pentafluoroethyltin compounds .…”

“…The thermally induced elimination of the pentafluoroethyl substituent, however, can be exploited for the synthesis of Sn(C 2 F 5 ) 4 . The treatment of an ethereal solution of LiC 2 F 5 with an excess of SnCl 4 does not result in the anticipated mixture of pentafluoroethyltin chlorides, Sn(C 2 F 5 ) n Cl 4−n ( n= 0–4), but invariably affords the pentakis(pentafluoroethyl)stannate anion, [Sn(C 2 F 5 ) 5 ] − .…”

“…According to the calculated FIA values (Table ) the tetrakis(pentafluoroethyl)element species are less Lewis acidic than the fluorotris(pentafluoroethyl)element derivatives but also represent valuable starting materials for the synthesis of chloride and fluoride complexes like [Si(C 2 F 5 ) 4 Cl] − and [Sn(C 2 F 5 ) 4 F 2 ] 2− …”

“…In addition to this, the homoleptic hypervalent pentakis(pentafluoroethyl)germanate and ‐stannate anions are accessible by pentafluoroethylation of [Ge(C 2 F 5 ) 3 F 2 ] − or SnCl 4 , respectively. Whereas [PPh 4 ][Ge(C 2 F 5 ) 5 ] is an elusive species with a half‐life time of 8.5 min at ambient temperature the pentafluoroethyl substituents lend sufficient stability to the corresponding stannate anion [Sn(C 2 F 5 ) 5 ] − . This species could also be structurally investigated in form of its [HBDMAN] + salt by X‐ray diffraction.…”

The Dynamic Equilibrium of Hexakis(pentafluoroethyl)distannane Adducts [XSn(C2F5)3{Sn(C2F5)3}]− (X=Cl, Br, I, Sn(C2F5)3)

“…Therefore, no apicophilicity of the chloro and C 2 F 5 substituents is predictable. In addition to this, the 19 F NMR spectrum of the homoleptical [Sn(C 2 F 5 ) 5 ] − shows a broadened set of signals for all C 2 F 5 groups in accordance with a fluctuating structure . However, it should be considered that in the solid‐state structures of the hypervalent stannates with the general composition [SnX 2 (C 2 F 5 ) 3 ] − (X=Cl, Br, I) the three C 2 F 5 groups occupy the equatorial positions and show only one sharp set of signals in the 19 F NMR spectrum, which indicates a preserved symmetry in the liquid phase .…”