Salt metathesis versus protonolysis routes for the synthesis of silylamide Hauser base (R2NMgX; X = halogen) and amido-Grignard (R2NMgR) complexes. Issue 14 (14th August 2015) - Goodwin, Conrad A. P.
Abstract : The effectiveness of simple synthetic routes to access silylamide Hauser base (R2 NMgX; X = halogen) and amido-Grignard (R2 NMgR) complexes from commercially available Grignard reagents is explored herein. Abstract : The preparation of silylamide Hauser base (R2 NMgX; X = halide) and amido-Grignard (R2 NMgR) complexes from simple Grignard reagents using [K{N(SiMe2 t Bu)2 }] n, [K{N(SiMe2 t Bu)(Si i Pr3 )}] n and [K{N(Si i Pr3 )2 }] n, and their parent silylamines, was explored. Both salt metathesis and protonolysis routes proved ineffective with allylmagnesium chloride as a starting material due to complex Schlenk equilibria, with [Mg(N RR′ )(μ-Cl)(THF)]2 (N RR′ = {N(Si t BuMe2 )2 } −, 1 ; {N(Si t BuMe2 )(Si i Pr3 )} −, 2 ; {N(Si i Pr3 )2 } −, 3 ) and [Mg{N(Si i Pr3 )2 }(μ-C3 H5 )]∞ (4 ) identified as minor products. In contrast, salt metathesis protocols using potassium silylamides and methylmagnesium iodide gave [Mg(N RR′ )(μ-CH3 )]2 (N RR′ = {N(Si t BuMe2 )2 } −, 7a ; {N(Si t BuMe2 )(Si i Pr3 )} −, 8 ; {N(Si i Pr3 )2 } −, 9 ) and [Mg{N(Si t BuMe2 )2 }(CH3 )(DME)] (7b ), with [Mg{N(Si t BuMe2 )2 }(μ-I)(THF)]2 (10 ) isolated as a side-product during the preparation of7a . Unusually, methylmagnesium iodide, di- n -butylmagnesium and7–9 did not react with HN RR′ under the conditions we employed. The synthesis of [Na{N(Si t BuMe2 )2 }(THF)]2 (5a ) and [Na{N(Si t BuMe2 )2 }(DME)2 ] (5b ) from benzyl sodium and HN(Si t BuMe2 )2, and a solvent-free structure of [K{N(Si t BuMe2 )2 }] (6 ), are also reported. Complexes1, 5b, 7a, 7b, 8, 9 and10 are fully characterised by single crystal XRD, multinuclear NMR and IR spectroscopy and elemental analysis, whereas complexes2–4, 5a and6 were identified by XRD only.