Synthesis and characterization of heterotrimetallic Mg-Ni-Mg complexes with amidinato ligands.

Treatment of amidinato-based magnesium ethyl compounds LMgEt [L = PrPNC(Bu)NAr; Ar = 2,6-PrCH (La) or 2,6-(PhCH)-4-Pr-(CH) (Lb)] with Ni(COD) (COD: 1,5-cyclooctadiene) afforded heterotrimetallic Mg-Ni-Mg complexes [(LMg)Ni(CH)] through β-H elimination. These complexes exhibit approximately linear Mg-Ni-Mg linkage with the central nickel arranged in a planar configuration; the Ni(CH) unit can be considered as nickela-bis-cyclopropane. Reaction of [(LMg)Ni(CH)] with tetrahydrofuran (THF) gave a coordination product [(LMg·THF)Ni(CH)], 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--cyclopropane complex [(LMg)Ni(CH)(CO)], in which two CO ligands were coordinated to the nickel center.