Tantalum organometallics containing bulky oxy donors: Utilization of tri-tert-butylsiloxide and 9-oxytriptycene

Article abstract of DOI:10.1021/om00129a022

Procedures entailing the preparation of alkyl- and chlorotantalum complexes containing 9-oxytriptycene (TpO) and (t-Bu)₃SiO^- (silox) are described. Addition of 2 equiv of TpOSiMe₃ to TaCl₅ yielded (TpO)₂TaCl₃ (2); alcoholysis of Np₃Ta=C(H)CMe₃ (Np = neopentyl) with TpOH produced (TpO)₂TaNp₃ (3). An X-ray structure determination of 3 indicated that the axially disposed TpO units are nearly eclipsed in this pseudo-tbp complex. Crystal data: orthorhombic, Pn2₁a, a = 16.024 (2) A?, b = 13.607 (4) A?, c = 21.377 (1) A?, Z = 4, and T = 25 °C. From 2651 data were |F₀| ≥ 3σ (\F_o|), an R factor of 0.054 was obtained via standard refinement methods. Short Ta-O bonds (1.869 (16) A? average) concomitant with near linear Ta-O-C angles (170.3 (19) and 163.9 (16)°) suggest that strong π-bonding is evident. Treatment of TaCl₅ and R₃TaCl₂ (R = Me, CH₂Ph, Np) with stoichiometric amounts of Na(silox) gave (silox)₂TaCl₃ (4), (silox)₂TaR₃ (R = Me (5), CH2 Ph (6)), (silox)₂NpTa=C(H)CMe₃ (11), and (silox)TaNp₃Cl (9), respectively. From Np₂TaCl₃ and 2Na(silox), (silox)₂TaNp₂Cl (10) was obtained. Either 9 and Na(silox) or 10 and NpLi also afforded 11. Thermolysis of 6 provided (silox)₂Ta=C(H)Ph(CH₂Ph) (7), and the addition of PhCH₂MgCl to 4 in Et₂O resulted in (silox)₂TaCl₂(CH₂Ph) (8). Np₃Ta=C(H)CMe₃ reacted with (silox)H to form (silox)Np₂Ta=C(H)CMe₃ (12), but further silanolysis was not observed. Discussions pertaining to the effective size of the oxygen donor ligands, the stability of the complexes, and their relationship to analogous Cp species are presented.