Salt metathesis routes to homoleptic near-linear Mg(ii) and Ca(ii) bulky bis(silyl)amide complexes

Abstract

Herein we investigate salt metathesis reactions of bulky bis(silyl)amide potassium salts [K{N(SiMe₂^tBu)₂}]_n, [K{N(SiMe₂^tBu)(SiⁱPr₃)}]_n, [K{N(SiⁱPr₃)₂}]_n and [K{N(SiPh₃)₂}]_n (1) with AeI₂ (Ae = Mg, Ca, Sr) in an effort to synthesise rare homoleptic two-coordinate complexes. Recrystallization of 1 from THF provided structural authentication of the solvated adduct [K{N(SiPh₃)₂}(THF)₃] (1-THF). For Ae = Mg we were able to identify products for three of the four bis(silyl)amides investigated: [Mg{N(SiMe₂^tBu)₂}₂(THF)] (2), [Mg{N(SiMe₂^tBu)(SiⁱPr₃)}₂] (3) and [Mg{N(SiPh₃)₂}₂] (4). Complexes 2–4 were isolated in good yields, and on one occasion during recrystallization of 2 a crystal of the heteroleptic complex [Mg{N(SiMe₂^tBu)₂}(I)(THF)₂] (5) was identified by XRD. We found that these methodologies were not widely applicable for larger Ae = Ca and Sr, as large quantities of the parent bis(silyl)amines formed in reaction mixtures; however, we were able to isolate the first near-linear Ca(II) amide [Ca{N(SiⁱPr₃)₂}₂] (6) from these studies. No Ae-containing products could be isolated from KC₈/crown ether reductions of 3, 4 and 6. Complexes 1–4 and 6 were characterised by single crystal XRD, multinuclear NMR and FTIR spectroscopy and elemental analysis, whereas complex 5 was identified by single crystal XRD only.