Aluminium Functionalized Germanes: Intramolecular Activation of Ge–H Bonds, Formation of a Dihydrogen Bond and Facile Hydrogermylation of Unsaturated Substrates

Abstract

A series of alkenylhydrogermanes, RR′(H)Ge‐C(AlR′′2)=C(H)‐tBu [4a, R = R′ = Mes, R′′ = tBu; 4b, R = R′ = Mes, R′′ = CH(SiMe3)2; 5a, R = R′′ = tBu, R′ = CH2CH2tBu; 5b, R = tBu, R′ = CH2CH2tBu, R′′ = CH(SiMe3)2], was synthesized by hydroalumination of the respective alkynylgermanes, RR′(H)Ge‐C≡C‐tBu 3, with R′′2Al–H [R′′ = tBu, CH(SiMe3)2]. In the solid state compound 5b showed a contact between Al and the Ge bound H atom (293 pm) which according to quantum chemical calculations results in Ge–H bond activation. In case of less bulky substituents on Al (5a, R′′ = tBu) a mixture of isomers was observed that reacted with Et2NH to yield the simple Lewis acid‐base adduct [(tBu)(tBuCH2CH2)(H)Ge‐C(AltBu2)=C(H)‐tBu](HNEt2) (6). 6 features a dihydrogen bond (Ge–H···H–N) as evident from typical downfield (N–H) and high‐field (Ge–H) shifts in the NMR spectrum, red shifts of νGe‐H and νN‐H in the IR spectrum, a short H···H contact (210 pm) in the solid state and a bond critical point between both H atoms. The presence of a hard Lewis‐acidic Al atom in geminal position to the Ge–H bond in 5a facilitates reactions with Ph2CO, OC4H8N‐C≡N and Ph–NCO under surprisingly mild conditions by hydrogermylation of the heteronuclear π‐bonds and formation of four‐membered Ge–O/N–Al–C (7, 9) or six‐membered Ge–N–C–O–Al–C (8) heterocycles. Reaction with Ph–C≡C–H afforded the cis‐addition product 10, in which the α‐C atom of the new alkenyl group showed a close contact [258.3(2) pm] to the Al atom.

Changes in Electron Structure of the Triple Bond in Substituted Acetylene and Diacetylene Derivatives

“…This example shows the problem often encountered in chemistry of finding the reliable reference system. [70][71][72][73][74][75][76] If computed in this way, then the calculated values of the transferred charge are 0.079 au (H 2 NAcNO 2 ), 0.048 au (H 2 NAcAcNO 2 ), 0.039 au (p-H 2 NPhNO 2 ) and 0.045 au (H 2 NBdNO 2 ), respectively, which gives the following quantitative order: p-H 2 NphNO 2 < H 2 NbdNO 2 �H 2 NacAcNO 2 �H 2 NAcNO 2 . Although this result suggests a similar electron charge transmission in double-substituted diacetylene and butadiene, it still shows almost doubled transmission in the acetylene derivative, which is in full agreement with the previous result based on CT defined by eq.…”

Cooperative activation of azides by an Al/N-based active Lewis pair – unexpected insertion of nitrogen atoms into C–Si bonds and formation of AlCN3 heterocycles

“…201 pm very similar and comparable to those of the starting materials. By contrast, the Al-N bond lengths of molecules 2 are with around 196 pm much shorter than in compounds 1 [1a: 214.5(1); 1b: 210.3(3) pm] and in the typical range of fourcoordinate Al atoms [42][43][44][45]. Both N-N bond lengths of the azide groups are with 130-132 pm in a narrow range and between standard values for N-N single (142 pm) and N-N double bonds (128 pm).…”

Hydrosilylation and Hydrogermylation of CO2 and CS2 by Al and Ga Functionalized Silanes and Germanes – Cooperative Reactivity with Formation of Silyl Formates and Disilylacetals

“…The addition of a donor (CO 2 ) to the starting mixture may initiate commutation similar to the reaction of 2a with HNEt 2 . [16] Hydrosilylation reactions are very fast and may proceed before commutation is significant, while hydrogermylation is slower and may occur after equilibration is achieved. The sterically most shielded silane 2b is a single, well defined species and afforded the CO 2 adduct 3b in a highly selective reaction.…”

“…As previously reported, aluminum functionalized germanes showed similar structural motifs with the Ge-H groups either pointing towards the Lewis acidic Al atom or in opposite direction. [16] Quantum chemical calculations based on the openclosed method [14,16,20] suggested low Ge •••H interaction energies of less than 8 kcal/mol and only a small stabilization of the isomer with E-H•••M interaction. The divinylaluminum or -gallium compounds 2′ are highly interesting starting materials for secondary reactions, but we were not able to increase the concentration of 2′ by heating samples of 2 in vacuo up to 100°C in order to remove volatile AltBu 3 and to shift the equilibrium towards the divinyl compounds (see below). Above 75°C decomposition was observed.…”

“…These compounds showed a surprising reactivity that allowed hydrogermylation reactions of an alkyne and various polar double bonds under mild conditions. [ 16 ] The increased reactivity may be the result of the activation of the substrates by the Lewis acid. CO 2 is relatively inert, but the specific functionality of such silanes and germanes with Lewis acids and reductive E–H bonds in single molecules may contribute to its activation and may help to support its chemical transformation.…”