Pentamethylcyclopentadienyl halo- and alkyl-alkoxo tantalum(V) complexes. Crystal structure of

Abstract

Reaction of TaCp" C! 4 with MOR (M -Li, Na) in different molar ratios gives halo alkoxides TaCp" CI,(OR)4_,, (n -3: R -tBu 1; $iPh 3 2; 2,6-Me2C6H 3 3; n --2: R -~Bu 4; SiPh 3 5; 2,6-Me2C6H3 6; a -!: R -SiMe 3 7) in good yields. The alkylidene complex TaCp'(CH2SiMe,02(CHSiMe ~) is hydrolyzed in the presence of traces of water to give the oxo dialkyl derivative [TaCp'(CH2SiM¢3)~O],, 8, and reacts with I equivalent of 2,6-MezC6H~NC affording a new 'q2-iminoacyi compound TaCp" (CH 2$iMe3XCHSiMe3){~ 2"C(CH 2SiMe3 ) = N(2,6"MeaC6 H 3)} 9. Reactions of TaCp "(CH 2SiMe3)a(CHSiMe3 ) with I equivalent of C6HsOH and 4-MeC6H3(OH) 2 result in the formation of the alkyl phenoxo TaCp'(CH2SiMe3)3(OC6Hs) 10 and 4-methyl pyrocatecholate TaCp'(CH2SiMe~)2(O2C6H3Me) 11, whereas the related re,",,:don with 2,6-Me2C6H 3OH leads to the cyclic alkyi-aikoxo compound TaCp (CH2SiMej)2(~2-O(2-CH2-6-MeC6H3)) 12. All the complexes were characterized by IR and NMR (tH and 13C) spectroscopy. The crystal and molecular structure of 12 has been determine~i. C~ystals of 12 are triclinic, space group P'[ with Z -2 in a unit cell of dimensions a-9.

Insertion of Isocyanide into Metal−Carbon Bonds of Alkylchloro(pentamethylcyclopentadienyl)niobium- and -tantalum Complexes − X-ray Structure of [TaCp*Cl2(CH2CMe2Ph){η2-C(CH2CMe2Ph)=N(2,6-Me2C6H3)}] and Unexpected Decomposition of Alkyldichloro(η2-iminoacyl) Complexes of Tantalum

“…The 1 H-and 13 C{ 1 H}-NMR spectra of 1 in [D 6 ]benzene solution at room temperature show only one signal for the three methyl groups, whereas the 1 H-NMR spectrum in [D 8 ]toluene solution at 223 K shows two narrow resonances in a 1:2 ratio. This NMR behaviour corresponds to a Berry pseudorotation process, [3g,14] akin to that reported for other tantalum complexes, [15] and is consistent with a four-legged pianostool geometry in the ground state. The kinetic parameters (log A ϭ 12.2 Ϯ 0.3, E a ϭ 12.2 Ϯ 0.4 kcal·mol Ϫ1 , ∆H ϶ ϭ 11.6 Ϯ 0.4 kcal·mol Ϫ1 , ∆S ϶ ϭ Ϫ4.4 Ϯ 1.3 e.u., ∆G ϶298K ϭ 12.9 kcal·mol Ϫ1 ), calculated on the basis of the 1 H-DNMR data, [16] are consistent with such an intramolecular process with only a small variation in the entropy and thus support our proposed interpretation.…”

High‐resolution thermogravimetry/coupled mass spectrometry analysis of flame‐retardant rubber

“…The Ta1O1 bond length in 3 (1.962(6) Å) is in the normal range for tantalumalkoxide complexes 13. The Ta1O2 bond length (2.017(6) Å) is longer, probably to allow coordination of C9.…”

Monocyclopentadienyl(niobium) Compounds with Imido and Silsesquioxane Ligands: Synthetic, Structural and Reactivity Studies

“…IR spectra show characteristic absorptions for the trimethylsilylcyclopentadienyl ring (ν C-H ≈ 839 cm -1 ) [33,34] and for the -1 , and the lowest frequencies occur for high-valent transition metals, which in our case can be attributed to the carbene character of the acyl carbon atom.…”

“…The IR spectra of all complexes show the characteristic absorptions for bis(trimethylsilyl)cyclopentadienyl (ν C-H ≈ 839 cm -1 ), [33,34] the trimethylsilyl substituent [ν δs (CH 3 ) ≈ 1250 cm -1 ] [3,17d,35] and the Nb=N stretching vibration (ν ≈ 1360 cm -1 ). [3a,17d] At room temperature, chiral complex 2 shows the expected 1 H NMR spectroscopic behaviour with three and two resonances for the protons of the disubstituted cyclopentadienyl ring and the SiMe 3 substituents, respectively, due to the absence of local symmetry in the C 5 H 3 (SiMe 3 ) 2 moiety.…”