Journal article
Multiple metal-carbon bonds. 15. Octahedral alkylidene complexes of niobium and tantalum by ligand-promoted .alpha. abstraction
Journal of the American Chemical Society, Vol.102(20), pp.6236-6244
09/01/1980
DOI: 10.1021/ja00540a010
Abstract
Complexes of the type M(CH2R)2X3 (M = Nb or Ta; R = CMe3, Ph, or SiMe3; X = Cl or Br) react with donor ligands to give a mixture of cis,mer- and trans,mer-M(CHR)L2X3 (L = PMe3, PPhMe2, PPh2Me, py, THF) in the presence of two or more L, [M(CHCMe3)LX3]2 in the presence of one L (a phosphine), or mer-M(CHCMe3)(L-L)X3 in the presence of L-L (L-L = dmpe, diars, diphos, tmeda, bpy). The rate of this ligand promoted α-hydrogen abstraction reaction varies qualitatively in the order R = CMe3 > Ph ≈ SiMe3, X = Br > Cl, L = PMe3 > PPhMe2 > PPh2Me > L-L (except dmpe), and solvent = dichloromethane ≈ chloroform > pentane. The most likely immediate precursor to M(CHR)L2X3 is seven-coordinate M(CH2R)2L2X3. Transient, five-coordinate M(CHR)LX3 forms at a rate which is rapid on the NMR time scale from [M(CHCMe3)LX3]2 or M(CHR)L2X3. This is believed to be the reason why cis,mer- and trans,mer-M(CHR)L2X3 interconvert so readily. NMR and IR data for all complexes (δ(Cα) ca. 250-275, JCHα = 70-100 Hz, vCHα = 2400-2700 cm-1) suggest that the metal attracts electron density from the CHα bond. Therefore the coordination sphere probably is distorted significantly from an octahedron in all cases. © 1980 American Chemical Society.
Details
- Title: Subtitle
- Multiple metal-carbon bonds. 15. Octahedral alkylidene complexes of niobium and tantalum by ligand-promoted .alpha. abstraction
- Creators
- Gregory A RupprechtLouis W MesserleJere D FellmannRichard R Schrock
- Resource Type
- Journal article
- Publication Details
- Journal of the American Chemical Society, Vol.102(20), pp.6236-6244
- Publisher
- American Chemical Society
- DOI
- 10.1021/ja00540a010
- ISSN
- 0002-7863
- eISSN
- 1520-5126
- Language
- English
- Date published
- 09/01/1980
- Academic Unit
- Chemistry; Radiology
- Record Identifier
- 9984216569002771
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