54294-45-0Relevant academic research and scientific papers
Direct observation of (Me3ECH2)5Ta (E = C, Si) as the precursors to (Me3ECH2)3Ta=CHEMe3 and (Me3SiCH2)2Ta(μ-CSiMe3) 2Ta(CH2SiMe3)2. Kinetic and mechanistic studies of the formation of alkylidene and alkylidyne ligands
Li, Liting,Hung, Meiling,Xue, Ziling
, p. 12746 - 12750 (2007/10/03)
Pentaalkyl complexes (Me3ECH2)5Ta (E = C (1), Si (2)) were found to convert to alkyl alkylidene compounds (Me3ECH2)3Ta=CHEMe3 (E = C (3), Si (4)) with the elimination of EMe4. Np5Ta (1, Np = Me3-CCH2) was observed as an intermediate to 3 in both the reaction of Np3TaCl2 with 2 equiv of NpLi and the reaction of Np4TaCl (5) with 1 equiv of NpLi. In addition to 1, 5 was also observed as an intermediate in the reaction between Np3TaCl2 and 2 equiv of NpLi. Ns5Ta (2, Ns = Me3SiCH2) was synthesized and isolated. Its quantitative conversion to 4 follows first-order kinetics. The further conversion of 4 to a bridged-alkylidyne complex Ns2Ta-(μ-CSiMe3)2TaNs2 (7) follows second-order kinetics. The activation parameters are ΔH1? = 21.6 (1.4) kcal/mol and ΔS1? = -5(5) eu for the conversion 2 → 4 and ΔH2? = 6.2(0.3) kcal/mol and ΔS2? = -61.6(0.8) eu for 4 → 7. Based on these results we propose mechanistic pathways for the formation of the alkylidene and bridged-alkylidyne complexes.
Tantalum organometallics containing bulky oxy donors: Utilization of tri-tert-butylsiloxide and 9-oxytriptycene
LaPointe, Robert E.,Wolczanski, Peter T.,Van Duyne, Gregory D.
, p. 1810 - 1818 (2008/10/08)
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 (\Fo|), 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.
