116076-68-7Relevant academic research and scientific papers
Synthesis and structural characterization of a Meerwein-Ponndorf-Verley/Oppenauer redox intermediate at a tantalum(V) center
Strickler,Bruck,Wexler,Wigley
, p. 266 - 273 (2008/10/08)
The alkyne adducts (DIPP)3Ta(PhC≡CPh) (1) and (DIPP)3Ta(Me3SiC≡CMe) (2, DIPP = 2,6-diisopropylphenoxide) are precursors to the metallacyclic products (DIPP)3Ta(CPh=CPhCPh(Me)O) (3) and (DIPP)3Ta(C(SiMe3)=CMeCPh2O) (4) from their reactions with 1 equiv of acetophenone and benzophenone, respectively. (DIPP)3Ta(PhC≡CPh) (1) also reacts with 1 equiv of benzaldehyde to form the related metallacyclic compound (DIPP)3Ta(CPh=CPhCH(Ph)O) (5) in high yield. Excess benzaldehyde reacts with 1 and 2 to form the benzyl alkoxide complexes (DIPP)3(PhCH2O)Ta(η2-CR=CR′CPh=O) (6, R = R′ = Ph; 7, R = Me3Si, R′ = Me) with a dative bonding interaction between the ring oxygen and the tantalum (V) center. Deuterium-labeling experiments and reactivity studies of this reaction have implicated the oxophilic complex 5 as an intermediate that is capable of transferring a hydride to a weakly coordinated (probably η1, O-bound), second molecule of an aldehyde or ketone. Thus, (DIPP)3(PhCH2O)Ta(η2-CPh=CPhCPh=O) (6), (DIPP)3(CH3CH2O)Ta(η2-CPh=CPhCPh=O) (8), and (DIPP)3(CH3CH2(CH3)-CHO)Ta(η2-CPh=CPhCPh= O) (9) are formed from the reaction of 5 with benzaldehyde, acetaldehyde, and 2-butanone, respectively.
Reactive alkyne complexes of tantalum and their metallacyclization chemistry: Models for alkyne cyclotrimerization by the early transition metals
Strickler, Jamie R.,Wexler, Pamela A.,Wigley, David E.
, p. 2067 - 2069 (2008/10/08)
The reduction of Ta(DIPP)3Cl2 (DIPP = 2,6-diisopropylphenoxide) in the presence of bulky alkynes RC≡CR′ (R = R′ = Ph; R = Me3Si, R′ = Me) provides the alkyne adducts (DIPP)3Ta(RC≡CR′) in high yield. Unlike all previously known tantalum alkyne complexes, (DIPP)3Ta(PhC≡CPh) readily undergoes metallacyclization reactions with smaller alkynes RC≡CR′ (R = R′ = Me or Et) and terminal alkynes RC≡CR′ (R = CMe3, SiMe3, or Ph; R′ = H) to form the tantalacyclopentadienes (DIPP)3Ta(CPh=CPhCR′=CR). The molecular structure of the related metallacyclic complex (DIPP)3Ta(CEt=CEtCEt=CEt) has been determined. This compound crystallizes in the monoclinic space group P21/n [No. 14] with a = 14.340 (15) ?, b = 16.322 (22) ?, c = 19.929 (11) ?, β = 94.05 (7)°, V = 4655.9 ?3, and ρ(calcd) = 1.25 g cm-3 for mol wt 877.05 and Z = 4. Structure solution and refinement included 3191 reflections with Fo2 > 3.0σ(Fo2) of 9088 total (8245 unique) reflections measured for final discrepancy indices of RF = 4.6% and RwF = 4.5%. The molecular structure reveals a severely crowded coordination sphere, which is consistent with the fact that alkyne cyclotrimerization does not proceed beyond this point. By using the less crowded precursor Ta(DIPP)2Cl3 and decreasing the alkyne size from Me3SiC≡CSiMe3 to PhC≡CPh to MeC≡ CMe, successively higher coordinated alkyne cyclooligomers (C2, C4, and C6 compounds, respectively) can be isolated.
