Cooperative Ge–N Bond Activation in Hydrogallation Products of Alkynyl(diethylamino)germanes (Et₂N)_nGe(C≡C^tBu)_4–n

Abstract

Treatment of the alkynyl(diethylamino)germanes Et 2 NGe(CC t Bu) 3 ( 1) and (Et 2 N) 2 Ge(CC t Bu) 2 (2) with dialkylelement hydrides t Bu 2 MH (M = Al, Ga) afforded in high yields the hydrometalation products). The Lewis acidic aluminum and gallium atoms showed a close contact to the nitrogen atoms of the amino groups attached to germanium, which resulted in relatively long Ge−N bonds and short Al−N or Ga−N distances. The structures of these molecules and the strengths of the interactions were investigated by dispersion-corrected density functional theory. This activation of the Ge−N bonds caused an unprecedented reactivity of compounds 4b and 6. 4b reacted with PhCCH under mild conditions and elimination of HNEt 2 to give the mixed dialkynyl compound ( t BuCC)(PhCC)Ge[C(Ga t Bu 2 )C(H) t Bu] 2 (5), while facile insertion of RNCX into a Ge−N bond of 6 led to the formation of the six-membered Ge−C−Ga−X−C−N heterocycles 7 (R = Ph, Et; X = O, S).

Spontaneous vs. Base‐Induced Dehydrochlorination of Group 14 ortho‐Carboranylamidinates

“…[18] In 1-6, the E-C-(carborane) separations are comparable with those in other group 14 organyl compounds, [24][25][26][27][28][29][30] while the E-N separations are considerably larger than those observed for classical covalent E-N bonds. [26,30,31] Within the amidine fragment, the C3-N1 separation is 126-131 pm, while the C3-N2 bond is slightly longer, at 132-137 pm. Thus in the HL -ligand, the π-electron density is probably located between the amidine C atom and the coordinated N atom, and the E-N contact should be described as a secondary coordinative interaction, rather than a covalent bond.…”

“…In particular, the Ge-N contact is strongly reduced from 204.8(2) pm to 180.0(3) pm, which corresponds to a strong covalent bond. [26,30] Figure 3. Molecular structure of 8 in the crystal.…”

Alkenyl‐Alkynylgermanes Functionalised by Lewis Acids: Intramolecular Aluminium– and Gallium–Alkyne Interactions and Potential Ge–C Bond Activation

“…It may help to activate the Ge–alkynyl bond and to facilitate secondary reactions such as the 1,1‐carbometallation, which was discussed above (see the Introduction). Similar compounds with an amine group bonded to Ge and coordinatively unsaturated Ga atoms showed a strong intramolecular Ga–N interaction by means of the lone pair of electrons at N. The significant weakening of the Ge–N bond was derived from quantum chemical calculations and resulted in a facile amine‐alkynyl exchange by C–H and Ge–N bond activation 11. Systematic investigations of the spectroscopic properties of the alkenyl‐alkynylgermanes 13 to 24 revealed remarkable tendencies in the 13 C NMR spectra.…”

“…Instead we isolated mixtures with the spiro compound 9,9′‐bis(germafluorene) that could not be separated by repeated recrystallisation. Therefore, we started with the dialkynyl‐bis(diethylamine)germane 10 (Scheme ), which is accessible by treatment of dichloride 9 with LiC≡C–CMe 3 11. Compound 10 was transformed to dichloride 11 by reaction with HCl (yield 94 %).…”

“…General: All procedures were carried out under an atmosphere of purified argon in dried solvents ( n ‐hexane, n ‐pentane and cyclopentane with LiAlH 4 ; 1,2‐difluorobenzene with molecular sieves; toluene, diethyl ether and THF with Na/benzophenone). (Me 3 C) 2 Al–H,19 (Me 3 C) 2 Ga–H,20 Cl 2 Ge(NEt 2 ) 2 ( 9 )11 and (Et 2 N) 2 Ge(C≡C–CMe 3 ) 2 ( 10 )11 were obtained according to literature procedures. Commercially available GeCl 4 (99.9 %, ABCR), Cl 2 Ge(C 6 H 5 ) 2 (95 %, ABCR), Cl 2 GeMe 2 (99 %, ABCR), tert ‐butylethyne, 2,2′‐dibrombiphenyl, 1‐hexyne, Br–Mg–C≡C–CH 3 and diethylamine were employed as purchased.…”