Titanium complexes with chiral amino alcohol ligands: synthesis and structure of complexes related to hydroamination catalysts

Titanium complexes with chiral amino alcohol ligands are useful precatalysts for the intramolecular hydroamination of aminoallenes. They can be synthesized via protonolysis of titanium dimethylamide starting materials with the free ligand. In most cases, the resulting materials are not isolable due to their oily nature. However, several complexes were prepared in pure form and isolated as solid materials. [Ti(Cl)(NMe2)(–OCH2CH(Ph)N(CHMe2)–]2 was prepared at room temperature from TiCl(NMe2)3 and the corresponding N-substituted d-amino alcohol; the dimeric nature of the complex was established by X-ray crystallography. [Ti(NMe2)2(–OCH2CH(Ph)N(2-Ad)–)]2 (2-Ad = 2-Adamantyl) was prepared from Ti(NMe2)4 and the corresponding N-substituted l-amino alcohol after prolonged heating. An intermediate complex that could not be purified or isolated is believed to be Ti(NMe2)3(–OCH2CH(Ph)NH(2-Ad)). Two complexes with the composition TiCl2(–OCH2CH(R*)N(CHMe2)–)(HNMe2) (where R* = CH2Ph or CHMe2) were prepared at room temperature by protonolysis of TiCl2(NMe2)2 with the corresponding N-substituted l-amino alcohols. These two complexes exhibit dynamic behavior on the NMR timescale that is believed to be a dimer–monomer equilibrium, but they decompose at elevated temperatures.