241489-06-5Relevant academic research and scientific papers
Steric isomerization of alkyne-dialkyltungsten complexes with a chelating diaryloxo ligand: Crystal structures of Cs- and (CH2SiMe3)2
Takashima, Yoshinori,Nakayama, Yuushou,Yasuda, Hajime,Nakamura, Akira,Harada, Akira
, p. 234 - 244 (2002)
Dichlorotungsten complexes, W(η2-EtC≡CEt) (Me2tbp)Cl2 (Me2tbp = 2,2′-thiobis(4,6-dimethylphenoxo)) and W(η2-EtC≡CEt) (tBu2 tbp)Cl2 (tBu2tbp = 2,2′-thiobis(4-methyl-6-tert-butylphenoxo)) were reacted with Mg(CH2SiMe3)2 to give the corresponding Cs -dialkyl complexes, Cs-W (η2-EtC≡CEt)(Me2tbp)(CH 2SiMe3)2(1-Cs) and Cs-W(η2-EtC≡CEt)(t Bu2tbp)(CH2SiMe3)2 (2-Cs ). These Cs symmetric dialkyltungsten complexes 1-Cs and 2-Cs were found to undergo steric isomerization to C1 symmetric isomers, 1-C1 and 2-C1, at 30 °C. The thermodynamic parameters for isomerization from 1-Cs to 1-C1 were estimated. The structures of both the Cs - and C1-isomers of 1 were determined by X-ray crystallography, indicating that the alkyne ligands in the Cs symmetric complexes could be regarded as four-electron donor ligands and that those in the C1 symmetric complexes are donating two electrons. The C1 symmetric dialkyltungsten complexes were heated to 30-60 °C to generate alkylidene species. The substituent effects of the ligands on the catalytic behavior for the ring-opening metathesis polymerization of norbornene derivatives were studied. cis-Contents of the poly(norbornene)s were controlled by the steric effect of alkyne and aryloxo ligands in these dialkyl complexes. The polymerization of 7-methylnorbornene catalyzed by 2, W(η 2-PhC≡CPh)(tBu2tbp) (CH2Ph)2(3-C1) and Mo(η 2-PhC≡CPh)(tBu2tbp)Cl 2 (5)-Mg(CH2SiMe3)2 gave the polymers with a cis -atactic structure.
