Calcium Complexes with a Bulky -(2-N-Piperidinomethyl)-Phenyl)Methoxide Ligand. Synthesis and Catalytic Activity in the Dearomatization of N-Heterocycles

The reaction of equimolar amounts of tris-((2--piperidinomethyl)-phenyl)methanol ((2-CHNCH--CH)COH) with [(MeSi)N]Ca(THF) (toluene, 23°C) allows to obtain a mixed-ligand calcium alkoxide-amide complex [(2-CHNCHCH)CO]CaN(SiMe) (I) in 70% yield. X-ray diffraction analysis showed that in I the monoanionic alkoxide ligand is coordinated to the metal in the κ-O,N,N-fashion. Complex I catalyzes the addition of PhSiH to annelated N-containing heterocycles: quinoline, 4-methylquinoline, 6-methylquinoline and isoquinoline. The reactions are chemo- and regioselective and are complied within 24-120 hours. The reaction of I with PhSiH (molar ratio 1 : 2) leads to the formation of the (alkoxide) complex [κ-O,N-(2-CHNCHCH)CO]Ca (II) and CaH, which are the result of symmetrization of the intermediately formed calcium alkoxyhydride complex. In the crystal, complex has a nonlinear structure with an OCa(1)O angle of 112.65(4)°, and only one of the piperidine fragments of both ligands is coordinated to the metal ion. The molecular structure of complexes I and II was established using X-ray diffraction (CCDC № 2443979 (I), 2443980 (II)).