Magnesium amido N-heterocyclic carbene complexes

Abstract

Magnesium dications bind strongly to a tridentate anionic dicarbene ligand L = [N{CH₂CH₂(CNCHCHNMes)}₂] forming dinuclear and trinuclear Mg complexes with some particularly short Mg–C bonds. Treatment of the proligand H₄LCl₃ with three equivalents of methyl magnesium chloride or benzyl magnesium chloride affords Mg₃(HL)Cl₆ in high yield. A suspension of 1 in thf was heated to 80 °C for 2 h to afford Mg₂(L)Cl₃, consistent with the loss of one equivalent of MgCl₂, and the deprotonation of the remaining acidic NH, lost as HCl gas. Treatment of Mg₃(HL)Cl₆ with one equivalent of KC₈ results in deprotonation of the ligand amine NH to afford Mg₃(L)Cl₅; treatment with a second equivalent forms the radical anion of the complex, K[Mg₃(L)Cl₅], which decomposes upon storage, precluding its structural characterisation. The acidic NH proton of the ligand in Mg₃(HL)Cl₆ can also be removed by deprotonation with Li{N(SiMe₃)₂}; additional equivalents of which also exchange the magnesium-bound chlorides for silylamido ligands, affording Mg₂(L)Cl₂N″ and Mg₂(L)Cl(N″)₂, which have both been characterised by single-crystal X-ray diffraction studies.