Salt metathesis: Versus protonolysis routes for the synthesis of silylamide Hauser base (R2NMgX; X = halogen) and amido-Grignard (R2NMgR) complexes

Abstract

The preparation of silylamide Hauser base (R2NMgX; X = halide) and amido-Grignard (R2NMgR) complexes from simple Grignard reagents using [K{N(SiMe2tBu)2}]n, [K{N(SiMe2tBu)(SiiPr3)}]n and [K{N(SiiPr3)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(NRR′)(μ-Cl)(THF)]2 (NRR′ = {N(SitBuMe2)2}-, 1; {N(SitBuMe2)(SiiPr3)}-, 2; {N(SiiPr3)2}-, 3) and [Mg{N(SiiPr3)2}(μ-C3H5)]∞ (4) identified as minor products. In contrast, salt metathesis protocols using potassium silylamides and methylmagnesium iodide gave [Mg(NRR′)(μ-CH3)]2 (NRR′ = {N(SitBuMe2)2}-, 7a; {N(SitBuMe2)(SiiPr3)}-, 8; {N(SiiPr3)2}-, 9) and [Mg{N(SitBuMe2)2}(CH3)(DME)] (7b), with [Mg{N(SitBuMe2)2}(μ-I)(THF)]2 (10) isolated as a side-product during the preparation of 7a. Unusually, methylmagnesium iodide, di-n-butylmagnesium and 7-9 did not react with HNRR′ under the conditions we employed. The synthesis of [Na{N(SitBuMe2)2}(THF)]2 (5a) and [Na{N(SitBuMe2)2}(DME)2] (5b) from benzyl sodium and HN(SitBuMe2)2, and a solvent-free structure of [K{N(SitBuMe2)2}] (6), are also reported. Complexes 1, 5b, 7a, 7b, 8, 9 and 10 are fully characterised by single crystal XRD, multinuclear NMR and IR spectroscopy and elemental analysis, whereas complexes 2-4, 5a and 6 were identified by XRD only.