Syntheses and Structures of the First Heavy‐Alkali‐Metal Tris(trimethylsilyl)germanides

Abstract

The first heavy-alkali-metal tris(trimethylsilyl)germanides were obtained in high yield and purity by a simple one-pot reaction involving the treatment of tetrakis(trimethylsilyl)germane, Ge(SiMe3)4, with various alkali metal tert-butoxides. The addition of different sizes of crown ethers or the bidentate TMEDA (TMEDA=N,N,N',N'-tetramethylethylenediamine) provided either contact or separated species in the solid state, whereas in aromatic solvents the germanides dissociate into separated ions, as shown by 29Si NMR spectroscopic studies. Here we report on two series of germanides, one displaying M-Ge bonds in the solid state with the general formula [M(donor)n Ge(SiMe3)3] (M=K, donor=[18]crown-6, n=1, 1; Rb, donor=[18]crown-6, n=1, 4; and M=K, donor=TMEDA, n=2, 6). The silicon analogue of 6, [K(tmeda)2Si(SiMe3)3] (7) is also included to provide a point of reference. The second group of compounds consists of separated ions with the general formula [M(donor)2][Ge(SiMe3)3] (M=K, donor=[15]crown-5, 2; M=K, donor=[12]crown-4, 3; and M=Cs, donor=[18]crown-6, 5). While all target compounds are highly sensitive towards hydrolysis, use of the tridentate nitrogen donor PMDTA (PMDTA=N,N,N',N'',N''-pentamethyldiethylenetriamine) afforded even more reactive species of the composition [K(pmdta)2Ge(SiMe3)3] (8). We also include the silanide analogue [K(pmdta)2Si(SiMe3)3] (9) for sake of comparison. The compounds were typically characterized by X-ray crystallography, and 1H, 13C, and 29Si NMR and IR spectroscopy, unless extremely high reactivity, as observed for the PMDTA adducts 8 and 9, prevented a more detailed characterization.

The Multidentate Ligand (MeOMe2Si)3Si−: Unusual Coordination Modes in Alkali Metal Silanides

“…Consequently, the siliconpotassium bonds (average ca. 356 pm) are significantly longer than in the closely related dimeric and monomeric hypersilanides [{(Me 3 Si) 3 Si(m-K)} 2 ] (337-342 pm), [12] [(Me 3 Si) 3 SiK-(C 6 H 6 ) 3 ] (332-335 pm), [12] [(Me 3 Si) 3 SiK(tmeda) 2 ] (339 pm), [18] and [(Me 3 Si) 3 SiK( [18]crown-6)] (345 pm). [19] Similar structural behavior has been observed in the tridentate 3-sila-b-diketiminates, [Me 3 SiSi{C(R)= NSiMe 3 } 2 M], in which the metal ion is coordinated to the internal N-donors to give either monomeric (Li) or dimeric (Na) zwitterionic cyclohexane structures; the latter, has significant intramolecular Si···Na (318 pm) contacts.…”

“…[5] In the solid state, the majority of these silanides form either solvated monomers, such as [R 3 SiM(donor) n ] (M = Li, Na, K, Rb, Cs; donor = THF, TMEDA (N,N,N',N'-tetramethylethylenediamine), DME (1,2-dimethoxyethane), C 6 H 6 , [18] [1f] Herein we report that lithium, sodium, and potassium derivatives of the new ligand Si(SiMe 2 OMe) 3 (trimethoxyhypersilanide) have very different structures, crystallizing as a result of strong coordinative interactions of the methoxy groups to the metal centers as clusters (K) or polymeric chains (Li, Na).[6] NMR spectroscopic investigations show that even in THF solutions, in which these aggregates dissociate into monomers, intramolecular oxygen-to-metal coordination is maintained.The synthetic route to the metal trimethoxyhypersilanides 4-6 is given in Scheme 2. Reaction of (Me 3 Si) 4 Si (1) with AlCl 3 and acetyl chloride furnishes (ClMe 2 Si) 4 Si (2) in 90-95 % yield.…”

Synthetic, Structural, and Theoretical Investigations of Alkali Metal Germanium Hydrides—Contact Molecules and Separated Ions

“…These observations agree with ion-association trends in crown ether containing silanides and germanides. [21,30] In accordance with the small size of the GeH 3 À ion relative to GeA C H T U N G T R E N N U N G (SiMe 3…”

Der mehrzähnige Ligand (MeOMe2Si)3Si−: ungewöhnliche Koordinationsweisen in Alkalimetallsilaniden

“…[5] Die meisten dieser Silanide bilden im festen Zustand entweder solvatisierte Monomere des Typs [R 3 SiM(Donor) n ] (M = Li, Na, K, Rb, Cs; Donor = THF, TMEDA (N,N,N',N'-Tetramethylethylendiamin), DME (1,2-Dimethoxyethan), C 6 H 6 , [18]Krone-6, [15]Krone-5, [12]Krone-4) oder nichtsolvatisierte Dimere [{R 3 Si(m-M)} 2 ] (Schema 1).…”

“…Folglich sind die Si-KAbstände (ca. 356 pm) deutlich größer als in den verwandten dimeren und monomeren Hypersilaniden [{(Me 3 Si) 3 Si(m-K)} 2 ] (337-342 pm), [12] [(Me 3 Si) 3 SiK(C 6 H 6 ) 3 ] (332-335 pm), [12] [(Me 3 Si) 3 SiK(tmeda) 2 ] (339 pm) [18] und [(Me 3 Si) 3 SiK-([18]Krone-6)] (345 pm). [19] Eine ähnliche Struktur wurde für 3-Sila-b-diketiminate Me 3 SiSi[C(R) = NSiMe 3 ] 2 M beschrieben, bei denen die internen N-Donoren an das Metallion koordinieren, sodass entweder monomere (Li) oder dimere (Na) zwitterionische Cyclohexanstrukturen resultieren (letztere mit beträchtlichen intramolekularen Si···Na-Wechselwirkungen (318 pm)).…”