Preparation of aminomethyl functionalised silanes via an α-lithiated amine: From their synthesis, stability and crystal structures to stereochemical issues

Abstract

The preparation of aminomethyl functionalised silanes based on the α-lithiated amine, (1R,2R)-N,N,N',N'-tetramethylcyclohexane-1,2-diamine [(R,R)-TMCDA] is reported. This methodology can be applied for the synthesis of mono-aminomethyl substituted systems, but most remarkably also for di- and trifunctionalised compounds. The trapping of the lithiated amine is accompanied by transmetallation reactions resulting in the formation of (silylmethyl)silanes depending on the reaction temperature. The zinc(II) halide complexes of the mono-functionalised systems show the formation of exclusively one configuration of the stereogenic nitrogen atom, in which the spatially more demanding substituent exhibits the pseudo-equatorial position. The di- and trifunctionalised systems feature high sensitivity towards Si-C bond cleavage under re-formation of the (R,R)-TMCDA fragment.

A Route to Stereochemically Pure Benzyllithium Reagents by Stereocontrolled Epimerisation

“…(R,R)-TMCDA offers the possibility of metalation at the methyl groups, therefore it can easily be introduced in benzylsilanes by reaction with a chlorosilane. [15] The precursor benzylchlorodimethylsilane can be obtained by the reaction of dichlordimethylsilane with a benzyl Grignard reagent (1 equiv) according to a literature procedure. [16] By this method the silane (R,R)-6 can be synthesised in two steps with 60 % overall yield.…”

Crystal structure of boratedN,N,N′,N′-tetramethyldiaminomethane

“…This Lewis acidity is used to enable the -deprotonation of tertiary amines (Kessar et al, 1991;Ebden et al, 1995). Our group frequently uses methods to deprotonate compounds in -position (Strohmann & Gessner, 2007;Gessner & Strohmann, 2012). For crystal structures containing the borated N,N,N 0 ,N 0 -tetramethyldiaminomethane motif, see: Fang et al (1994); Hanic & Š ubrtová (1969); Flores-Parra et al (1999); Rojas-Lima et al (2000).…”

Formation of Specific Configurations at Stereogenic Nitrogen Centers upon Their Coordination to Zinc and Mercury

“…The H atoms were refined on a riding model in their ideal geometric positions. Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication CCDC 873207 (7), 873208 (8), 873209 (9), 873210 (10), 873203 (11), 873204 (12), 873205 (13), 873206 (14a), and 880491 (14b). Data collection and structure refinement details are shown in Tables 1 and 2.…”

“…For tertiary bidentate cyclohexane-1,2-diamine derivatives, however, little is known about the configuration of the stereogenic nitrogen centers, although the configuration plays an important role in some proposed reaction mechanisms . We recently noted the specific formation of ( S )-configuration at the stereogenic nitrogen center in coordination compounds with silyl substituted TMCDA derivatives . Extensive literature research revealed only one additional crystal structure of a copper complex with ( S )-configuration at all stereogenic nitrogen centers. , NMR studies by Rafii et al, however, indicate that upon coordination of such a tertiary cyclohexane-1,2-diamine derivative to PdCl 2 , a mixture of all three possible stereoisomers is formed .…”

“…9 We recently noted the specific formation of (S)-configuration at the stereogenic nitrogen center in coordination compounds with silyl substituted TMCDA derivatives. 10 Extensive literature research revealed only one additional crystal structure of a copper complex with (S)-configuration at all stereogenic nitrogen centers. 11,12 NMR studies by Rafii indicate that upon coordination of such a tertiary cyclohexane-1,2-diamine derivative to PdCl 2 , a mixture of all three possible stereoisomers is formed.…”