Synthesis and characterization of heterotrimetallic Mg–Ni–Mg complexes with amidinato ligands†

Treatment of amidinato-based magnesium ethyl compounds LMgEt [L = ⁱPr₂PNC(^tBu)NAr; Ar = 2,6-ⁱPr₂C₆H₃ (L^a) or 2,6-(Ph₂CH)₂-4-ⁱPr-(C₆H₂) (L^b)] with Ni(COD)₂ (COD: 1,5-cyclooctadiene) afforded heterotrimetallic Mg–Ni–Mg complexes [(LMg)₂Ni(C₂H₄)₂] through β-H elimination. These complexes exhibit approximately linear Mg–Ni–Mg linkage with the central nickel arranged in a planar configuration; the Ni(C₂H₄)₂ unit can be considered as nickela-bis-cyclopropane. Reaction of [(LMg)₂Ni(C₂H₄)₂] with tetrahydrofuran (THF) gave a coordination product [(LMg·THF)₂Ni(C₂H₄)₂], in which the central structure remained intact and THF coordinated to two magnesium atoms respectively. In contrast, exposure of the nickela-bis-cyclopropane complex to 1 bar of CO led to the formation of a nickela-mono-cyclopropane complex [(LMg)₂Ni(C₂H₄)(CO)₂], in which two CO ligands were coordinated to the nickel center.