Owing to the highly electron-withdrawing C 2 F 5 groups, the tris(pentafluoroethyl)germane (C 2 F 5 ) 3 GeH represents an interesting Brønsted acidic compound. The germane is accessible by the treatment of the corresponding halogenogermanes( C 2 F 5 ) 3 GeX (X = Cl, Br) with Bu 3 SnH. After clarifying its molecular structure in the solid state by X-ray diffraction,t he acidity of (C 2 F 5 ) 3 GeH was examined by treatment with different bases, for example, 1,8-bis(dimethylamino)naphthalene. The resulting germanate(II)i on [Ge(C 2 F 5 ) 3 ] À serves as ag ermyl group transfer reagent. The reactionw ith main-group and transition-metal complexes or organohalides opens accesst oav ariety of different compounds, the structures of which were mostly determined by X-ray diffraction. The correspondingt ricarbonylnickelate(0) complex [(CO) 3 NiGe(C 2 F 5 ) 3 ] À also gives information about the p-acceptor properties of the [Ge(C 2 F 5 ) 3 ] À ligand.F urthermore, hydrogermylation reactions of (C 2 F 5 ) 3 GeH with alkynes afforded different stereoisomers (a,b-cis, b-trans)d epending on the respective reactionconditions and substrates.

This paper gives an account on hypervalent fluoro- and chloro(pentafluoroethyl)germanium compounds. The selective synthesis of the tris(pentafluoroethyl)dichlorogermanate salt [PNP][(C F ) GeCl ] as well as its X-ray structural analysis is described. As a representative example for pentafluoroethylfluorogermanates, the synthesis and structure of 2,4,6-triphenylpyryliumtris(pentafluoroethyl)difluorogermanate [C H O][(C F ) GeF ] is reported. Fluoride-ion affinities for pentafluoroethylgermanes were calculated using quantum chemical methods, disclosing (C F ) GeF as a weaker Lewis acid than (C F ) SiF or (C F ) PF . The theoretical results were confirmed by experiments and give the basis of a synthetic protocol for (C F ) GeF. Pentakis(pentafluoroethyl)germanate [PPh ][Ge(C F ) ] was detected as an intermediate during the synthesis of [PPh ][(C F ) GeF] starting from tris(pentafluoroethyl)difluorogermanate and LiC F .

The synthesis of tris(pentafluoroethyl)germanium derivatives is described. The reaction of germanium tetrachloride with three equivalents of the pentafluoroethylation reagent LiC F does not lead selectively to the formation of tris(pentafluoroethyl)chlorogermane, (C F ) GeCl. Here the introduction of a diethylamino function as a protecting group was beneficial. Thus, treatment of Cl GeNEt with LiC F smoothly afforded (C F ) GeNEt . The replacement of the amino substituent by halides was accomplished by reaction with HBr or HCl on a multigram scale. The combination of (C F ) GeCl with Ag CO gave rise to the formation of the digermoxane [(C F ) Ge] O. An obtuse Ge-O-Ge angle of 150.2(1)° was determined by X-ray diffraction. Attempted hydrolysis of the digermoxane leads to an equilibrium mixture of the precursor, (C F ) GeOH, and water.

The chemistry of bis(pentafluoroethyl)germanes (C2F5)2 GeX2 is presented. The synthesis of such species requires Br2 GePh2 , wherein the phenyl substituents function as suitable protecting groups. After treatment with two equivalents of LiC2 F5, (C2F5)2 GePh2 is produced. The replacement of the phenyl rings is smoothly effected by gaseous HBr or HCl in the presence of a Lewis acidic catalyst. The trigermoxane [(C2F5)2 GeO]3 results from the reaction of (C2F5)2 GeBr2 with Ag2 CO3. Its crystalline 1,10-phenanthroline adduct was fully characterised by X-ray diffraction. The combination of (C2F5)2 GeBr2 with Bu3 SnH gave rise to the formation of (C2F5)2 GeH2 .

The synthesis of the germylene phosphane adduct (C2 F5 )2 Ge⋅PMe3 is described. Starting from (C2 F5 )3 GeH in an excess of PMe3 , heating was applied, whereupon reductive elimination of C2 F5 H occurred. The molecular structure was ascertained by X-ray diffraction and compared with information obtained by quantum chemical methods. The ligand properties were derived by studying the IR spectrum of the nickel(0) complex [Ni(CO)3 {Ge(C2 F5 )2 (PMe3 )}] in the CO region. (C2 F5 )2 Ge⋅PMe3 turned out to be a π-accepting ligand comparable to PMe3 , in terms of Tolman's electronic parameter. Furthermore a [2+4] cycloaddition reaction with 2,3-dimethyl-1,3-butadiene, and σ-bond insertion reactions were recorded. Activation of the C-Cl bond in dichloromethane gives rise to the formation of the phosphonium ylide complex [(C2 F5 )2 Cl2 Ge-CH2 PMe3 ], which was fully characterized by X-ray diffraction.