Exploring Alternative Synthetic Routes for the Preparation of Five-Coordinate Diamidoamine Group 4 Metal Complexes

Efficient synthetic routes for the preparation of electrophilic titanium and zirconium complexes featuring a tridentate diamidoamine ligand have been developed. The five-coordinate titanium dichloride complexes [(MesNCH 2 CH 2 ) 2 NR]TiCl 2 (R = H ( 3 ), SiMe 3 ( 4 )) are conveniently prepared from the amine elimination reactions of the triamines (MesNHCH 2 CH 2 ) 2 NR (R = H ( 1 ), SiMe 3 ( 2 )) with Ti(NEt 2 ) 2 Cl 2 . Treatment of Ti(NEt 2 ) 4 with 2 equiv of SiMe 3 Cl offers an effective method for the preparation of Ti(NEt 2 ) 2 Cl 2 . The corresponding five-coordinate zirconium homologues [(MesNCH 2 CH 2 ) 2 NR]ZrCl 2 (R = H ( 5 ), SiMe 3 ( 6 )) are synthesized via the toluene elimination reactions of Zr(benzyl) 2 Cl 2 (Et 2 O) 2 with 1 and 2, respectively. The thermally unstable and photosensitive Zr(benzyl) 2 Cl 2 (Et 2 O) 2 species may be prepared in situ from the reaction of Zr(benzyl) 4 with 2 equiv of [NEt 3 H]Cl in diethyl ether at 0 °C in the dark. The toluene elimination reaction of Hf(benzyl) 4 with 1 affords the dibenzyl Hf complex [(MesNCH 2 CH 2 ) 2 NH]Hf(benzyl) 2, 7 . The X-ray structural and solution NMR data for 4, 5, 6, and 7 reveal that these electrophilic group 4 metal complexes adopt the facial structure with either a chloride or a η 2 -benzyl ligand trans to the central amino N atom of the tridentate diamidoamine ligand.