Synthesis of Group 4 Metal rac-(EBI)M(NR₂)₂ Complexes by Amine Elimination. Scope and Limitations

The synthesis of (EBI)M(NR2)2 (M = Ti, Zr, Hf; EBI = ethylene-1,2-bis(1-indenyl)) complexes by amine elimination reactions of (EBI)H2 (1,2-bis(3-indenyl)ethane) and M(NR2)4 complexes has been investigated. The reaction of (EBI)H2 and Zr(NEt2)4 in toluene at 100 °C (15 h) yields the mono(indenyl) complex (η5-C9H6CH2CH2C9H7)Zr(NEt2)3 via a single amine elimination. Under more forcing conditions (1,2-dichlorobenzene, 180 °C, 21 h) this reaction yields the metallocene dichloride derivative (EBI)ZrCl2 (80% NMR, rac/meso ratio = 1.7/1). The reaction of (EBI)H2 with Zr(NMe2)2(NiPr2)2 in m-xylene at 140 °C (16 h) affords the sterically least hindered ansa-metallocene product, (EBI)Zr(NMe2)2 (70% NMR, rac/meso ratio = 2/1), via NiPr2H elimination. The reaction of (EBI)H2 with the pyrrolidide complex Zr(NC4H8)4 in m-xylene at 140 °C (7 h) yields (EBI)Zr(NC4H8)2 (95%, rac/meso ratio = 6/1) and pure rac-(EBI)Zr(NC4H8)2 in 42% isolated yield. (EBI)H2 reacts with the sterically open titanium azetidide complex Ti(NC3H6)4 to yield the mono(indenyl) species (η5-C9H6CH2CH2C9H7)Ti(NC3H6)3 but does not react with Ti(NMe2)4 (toluene, 100 °C, 17 h). The reaction of (EBI)H2 and Hf(NMe2)4 in m-xylene at 140 °C (21 h) provides (EBI)Hf(NMe2)2 in 85% NMR yield (rac/meso ratio = 6/1) and rac-(EBI)Hf(NMe2)2 in 47% isolated yield.