Highly fluorinated tris(indazolyl)borate silylamido complexes of the heavier alkaline earth metals: Synthesis, characterization, and efficient catalytic intramolecular hydroamination

Article abstract of DOI:10.1002/chem.201405454

Heteroleptic silylamido complexes of the heavier alkaline earth elements calcium and strontium containing the highly fluorinated 3-phenyl hydrotris(indazolyl)borate {F₁₂-Tp^4Bo,3Ph}^- ligand have been synthesized by using salt metathesis reactions. The homoleptic precursors [Ae{N-(SiMe₃)₂}₂] (Ae=Ca, Sr) were treated with [Tl(F₁₂-Tp^4Bo,3Ph)] in pentane to form the corresponding heteroleptic complexes [(F₁₂-Tp^4Bo,3Ph)Ae{N(SiMe₃)₂}] (Ae=Ca (1); Sr (3)). Compounds 1 and 3 are inert towards intermolecular redistribution. The molecular structures of 1 and 3 have been determined by using X-ray diffraction. Compound 3 exhibits a Sr...MeSi agostic distortion. The synthesis of the homoleptic THF-free compound [Ca{N(SiMe₂H)₂}₂] (4) by transamination reaction between [Ca{N(SiMe₃)₂}₂] and HN(SiMe₂H)₂ is also reported. This precursor constitutes a convenient starting material for the subsequent preparation of the THF-free complex [(F₁₂-Tp^4Bo,3Ph)Ca{N(SiMe₂H)₂}] (5). Compound 5 is stabilized in the solid state by a Ca...β-Si-H agostic interaction. Complexes 1 and 3 have been used as precatalysts for the intramolecular hydroamination of 2,2-dimethylpent-4-en-1-amine. Compound 1 is highly active, converting completely 200 equivalents of aminoalkene in 16 min with 0.50 mol% catalyst loading at 25°C.