New titanium imido complexes containing piperazine-based diamido-diamine ligands

Syntheses of the new piperazine derivatives 1,4-bis(2-amino-4-tert-butylbenzyl)piperazine (2) and 1,4-bis(2-trimethylsilylamino-4-R-benzyl)piperazine (R=H 3 or But 4; H2L1 and H2L2, respectively) are described along with the X-ray crystal structure of 2. Treatment of H2L1 and H2L2 with n-butyl lithium gives the amido derivatives Li2L1 (5) and Li2L2 (6), which react with [Ti(NBut)Cl2(py)3] to form [Ti(NBut)(L1)] (7) and [Ti(NBut)(L2)] (8). Reaction of Li2L1 with [Ti(N-4-C6H4Me)Cl2(py)3] gives the corresponding arylimido homologue [Ti(N-4-C6H4Me)(L1)] (9). The X-ray structure of 8 shows a strongly transoid disposition of the aryl rings of the L1 ligand and this geometry is maintained in solution. Somewhat surprisingly 7 does not undergo tert-butylimide/arylamine exchange with 4-methylphenylamine to form 9. The related compound N,N′-bis(2-trimethylsilylaminobenzyl)-N,N′-dimethyl-1,3- diaminopropane (12, H2L3) and its lithium salt Li2L3 (13) are also described. However, reaction of 13 with [Ti(NBut)Cl2(py)3] affords no tractable product. © 1999 Elsevier Science S.A