Isolation and reactivity of heteroleptic magnesium 1,3-benzazaphospholide complexes

Abstract

Reactions of 2,5-disubstituted-1H-1,3-benzazaphosphole (HBp) 1 [HBp¹ (1a): R¹ = Ph, R² = Me; HBp² (1b): R¹ = Ph, R² = H] with one equivalent of the β-diketiminate complex [CH{C(Me)NAr}₂MgⁿBu] (Ar = 2,6-ⁱPr₂C₆H₃) [(^DippBDI)MgⁿBu], respectively, produce in good yields low-coordinate magnesium compounds (^DippBDI)Mg [κ¹(N)-η³-Bp] 2 (Bp¹(2a), Bp²(2b)), in which the ambident Bp⁻ ligand coordinates to the magnesium centers through the Mg–N bond in both solution and solid phases. Compounds 2a and 2b can coordinate with THF to form four-coordinate magnesium 1,3-benzazaphospholides (^DippBDI)Mg(THF)[κ¹(N)-Bp] 3 (Bp¹(3a), Bp²(3b)). 2a and 2b readily reacted with elemental sulfur to give new compounds (^DippBDI)Mg(κ²(S,S)-BpS₂) 4 (Bp¹(4a), Bp²(4b)). Compounds 2a and 2b when treated with 2,2′-dipyridyl disulfide (PyS)₂ afforded unexpected racemic axially restricted Bp(p)–(p)Bp rac-5 (Bp¹(5a), Bp²(5b)). These new magnesium 1,3-benzazaphospholide complexes have been characterised by X-ray crystallography, except for 4b and rac-5b.