500783-19-7Relevant academic research and scientific papers
Alkyne exchange reactions of silylalkyne complexes of tantalum: Mechanistic investigation and its application in the preparation of new tantalum complexes having functional alkynes (PhC≡CR (R = COOMe, CONMe2))
Oshiki, Toshiyuki,Yamada, Atsushi,Kawai, Kimio,Arimitsu, Hirotaka,Takai, Kazuhiko
, p. 173 - 182 (2008/10/09)
Silylalkyne complexes of tantalum with the general formula TaCl 3(R1C≡CR2)L2 (1, R1 = R2 = SiMe3, L2 = DME; 2, R1 = SiMe3, R2 = Me, L2 = DME; 6, R1 = R2 = SiMe3, L = py; 7, R1 = SiMe3, R2 = Me, L = py) reacted with an internal alkyne to give corresponding alkyne complexes via an alkyne exchange reaction. These silylalkyne complexes were newly prepared and structurally characterized. Kinetic measurements revealed that the rates of the exchange reactions of the DME complexes 1 and 2 were first-order dependent on the concentration of the complex and the reaction proceeded via dissociative pathway. The exchange reaction rates of the bis(pyridine) complexes 6 and 7 were slower. In contrast to the DME complexes, the exchange reaction of 6 proceeded via an associative interchange pathway, and the exchange mechanism for 7 was an associative pathway. During the exchange, two pyridine ligands coordinated strongly to the tantalum center and the intermediate is proposed to be a bis(alkyne) complex. New tantalum complexes having functional alkynes (PhC≡CR (R = COOMe, CONMe2)) were prepared from the silylalkyne complexes via the alkyne exchange reaction.
Preparation, structural characterization, and reactions of tantalum-alkyne complexes TaCl3(R1C≡CR2)L2 (L2 = DME, Bipy, and TMEDA; L = Py)
Oshiki, Toshiyuki,Tanaka, Kouji,Yamada, Jun,Ishiyama, Takaya,Kataoka, Yasutaka,Mashima, Kazushi,Tani, Kazuhide,Takai, Kazuhiko
, p. 464 - 472 (2008/10/08)
Tantalum-alkyne complexes with the general formula TaCl3(R1C≡CR2)(dme) (1a, R1 = R2 = Et; 1b, R1 = R2 = n-C5H11; 1c, R1 = Ph, R2 = Me; 1d, R1 = R2 = Ph; DME = 1,2-dimethoxyethane) were synthesized by treatment of the corresponding alkynes with a low-valent tantalum derived by reduction of tantalum pentachloride with zinc powder in a mixed solvent of toluene and DME. The DME ligand can be replaced by 2 equiv of pyridine to afford the corresponding dipyridine complexes TaCl3(R1C≡CR2)(py)2 (2a, R1 = R2 = Et; 2b, R1 = R2 = n-C5H11; 2c, R1 = Ph, R2 = Me; 2d, R1 = R2 = Ph). Additionally, the reaction of 1a with the bidentate nitrogen ligands bipyridine and N,N,N′,N′-tetramethyethylenediamine (= TMEDA) gave TaCl3(EtC≡CEt)(bipy) (3) and TaCl3(EtC≡CEt)(tmedia) (4), respectively. The η2- and 4e-coordination mode of an alkyne with a large contribution of a metalacyclopropene canonical structure was revealed by spectroscopic methods (NMR and IR) and crystallographic analyses of 1a, 1c, 2a, and 4. The reactivies of the tantalum-3-hexyne complexes 1a, 2a, 3, and 4 toward 3-phenylpropanal were investigated. Only the pyridine complex 2a reacted with a stoichiometric amount of the aldehyde to afford the corresponding allylic alcohol in 77% yield upon hydrolysis. The reaction proceeded via an oxatantalacyclopentene species.
