Asymmetric Synthesis of Rigid C2-Symmetric Bis(ferrocenyl) Diol and Diamine Ligands
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Abstract
We report herein the asymmetric synthesis of C2-symmetric fused diferrocenyl diamine and diol ligands. The synthesis begins with the Cu(II)-mediated coupling of the diastereomerically and enantiomerically pure lithiated derivative of Kagan's ferrocenyl acetal to yield, after deprotection, the C2-symmetric biferrocenyl dialdehyde 4. Conversion of dial 4 to a bis(methylimine) followed by a SmI2 mediated aza−pinacol coupling, yielded the enantio− and diastereomerically pure C2-symmetric trans−diamine 1. The direct pinacol coupling of dialdehyde 4 by SmI2 yields the enantio- and diastereomerically pure C2-symmetric trans-diol 2. The former diamine was coordinated to the Lewis acid (ArO)2TiCl2 (Ar = 4-vinyl-2,6-dimethylphenyl) and characterized by solution and X-ray methods. The diol ligand was reacted with (dppe)Pt(CO3) to form a (dppe)PtII diolate, which was also characterized by solution and solid-state means.
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