116076-71-2Relevant academic research and scientific papers
Cross-coupling reactions of d2 tantalum alkyne complexes: Selective 1,3-diene syntheses and their relevance to alkyne cyclization chemistry
Strickler, Jamie R.,Wexler, Pamela A.,Wigley, David E.
, p. 118 - 127 (2008/10/08)
Ta(DIPP)3Cl2(OEt2) (DIPP = 2,6-diisopropylphenoxide) can be reduced by two electrons in the presence of the bulky alkynes PhC≡CPh and Me3SiC≡CMe to provide the pale yellow adducts (DIPP)3Ta-(PhC≡CPh) (1) and (DIPP)3Ta(Me3SiC≡CMe) (2). The reduction of Ta(DIPP)3Cl2(OEt2) in the presence of smaller internal alkynes (viz. EtC≡CEt) or the terminal alkynes Me3SiC≡CH or Me3CC≡CH affords the metallacyclopentadienes (DIPP)3Ta(CEt=CEtCEt=CEt) (3) or (DIPP)3Ta(CR=CHCR=CH) (4, R = SiMe3; 5, R = CMe3) directly. The molecular structure of the PhC≡CPh adduct 1 is approximately tetrahedral (L-Ta-L angles average 109.4°) and features very short Ta-Calkyne distances (2.070 (3) and 2.076 (3) A?, respectively) and an elongated "C≡C" bond (1.346 (5) A?, which indicate a strongly bound and substantially reduced alkyne ligand. The molecular structure of metallacycle 3 reveals a trigonal bipyramidal geometry (Lax-Ta-Lax = 164.9 (3)°) with the metallacyclic α carbons occupying one axial and one equatorial site. The alkyne complex (DIPP)3Ta(PhC≡CPh) (1) reacts with MeC≡CMe, EtC≡CEt, Me3CC≡CH, Me3SiC≡CH, or PhC≡CH to afford high yields of the metallacyclization products (DIPP)3Ta(CPh=CPhCMe=CMe) (6), (DIPP)3Ta(CPh=CPhCEt=CEt) (7), (DIPP)3Ta-(CPh=CPhCH=CCMe3) (8), (DIPP)3Ta(CPh=CPhCH=CSiMe3) (9), and (DIPP)3Ta-(CPh=CPhCH=CPh) (10), respectively, while 1,7-octadiyne HC≡C(CH2)4C≡CH reacts with 2 equiv of (DIPP)3Ta(PhC≡CPh) to provide the unusual bimetallic complex (DIPP)3Ta(CPh=CPhCH=C(CH2) 4-C=CHCPh=PhC)Ta(DIPP)3 (11). The alkyne adduct (DIPP)3Ta(Me3SiC≡CMe) (2) also engages in metallacyclization chemistry as it reacts with MeC≡CMe to afford (DIPP)3Ta(CMe=CSiMe3CMe=CMe) (12), with PhC≡CH to provide (DIPP)3Ta(CSiMe3=CMeCPh=CH) (13), and with Me3CC≡CH to afford (DIPP)3Ta(CCMe3=CHCSiMe3=CMe) (14). All of the metallacyclopentadiene complexes can be hydrolyzed with H2O/acetone solutions to afford the corresponding 1,3-dienes in essentially quantitative yields. However, iodination of metallacycles 6, 7, and 13 does not yield the expected 1,4-diiodo-1,3-dienes, but rather the ring-opened monoiodinated butadienyl compounds (DIPP)3(I)TaCPh=CPhCMe=CMe(I) (15), (DIPP)3(I)TaCPh=CPhCEt=CEt(I) (16), and (DIPP)3(I)TaCSiMe3=CMeCPh=CH(I) (17), respectively. The subsequent hydrolysis of compounds 15-17 provides the corresponding 1-iodo-1,3-dienes.
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.
