Quantifying the Electron Donor and Acceptor Abilities of the Ketimide Ligands in M(N鈺怌tBu2)4 (M = V, Nb, Ta)
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- 作者：Peter L. Damon ; Cameron J. Liss ; Richard A. Lewis ; Simona Morochnik ; David E. Szpunar ; Joshua Telser ; Trevor W. Hayton
- 刊名：Inorganic Chemistry
- 出版年：2015
- 出版时间：October 19, 2015
- 年：2015
- 卷：54
- 期：20
- 页码：10081-10095
- 全文大小：755K
- ISSN：1520-510X
文摘
Addition of 4 equiv of Li(N鈺怌up>t up>Buub>2 ub>) to VClub>3 ub> in THF, followed by addition of 0.5 equiv of Iub>2 ub>, generates the homoleptic V(IV) ketimide complex, V(N鈺怌up>t up>Buub>2 ub>)ub>4 ub> (1), in 42% yield. Similarly, reaction of 4 equiv of Li(N鈺怌up>t up>Buub>2 ub>) with NbClub>4 ub>(THF)ub>2 ub> in THF affords the homoleptic Nb(IV) ketimide complex, Nb(N鈺怌up>t up>Buub>2 ub>)ub>4 ub> (2), in 55% yield. Seeking to extend the series to the tantalum congener, a new Ta(IV) starting material, TaClub>4 ub>(TMEDA) (3), was prepared via reduction of TaClub>5 ub> with Etub>3 ub>SiH, followed by addition of TMEDA. Reaction of 3 with 4 equiv of Li(N鈺怌up>t up>Buub>2 ub>) in THF results in the isolation of a Ta(V) ketimide complex, Ta(Cl)(N鈺怌up>t up>Buub>2 ub>)ub>4 ub> (5), which can be isolated in 32% yield. Reaction of 5 with Tl(OTf) yields Ta(OTf)(N鈺怌up>t up>Buub>2 ub>)ub>4 ub> (6) in 44% yield. Subsequent reduction of 6 with Cp*ub>2 ub>Co in toluene generates the homoleptic Ta(IV) congener Ta(N鈺怌up>t up>Buub>2 ub>)ub>4 ub> (7), although the yields are poor. All three homoleptic group 5 ketimide complexes exhibit squashed tetrahedral geometries in the solid state, as determined by X-ray crystallography. This geometry leads to a dub>xup>2 up>鈥?i>yup>2 up> ub>up>1 up> (up>2 up>Bub>1 ub> in Dub>2d ub>) ground state, as supported by DFT calculations. EPR spectroscopic analysis of 1 and 2, performed at X- and Q-band frequencies (鈭? and 35 GHz, respectively), further supports the up>2 up>Bub>1 ub> ground-state assignment, whereas comparison of 1, 2, and 7 with related group 5 tetra(aryl), tetra(amido), and tetra(alkoxo) complexes shows a higher M鈥揕 covalency in the ketimide鈥搈etal interaction. In addition, a ligand field analysis of 1 and 2 demonstrates that the ketimide ligand is both a strong 蟺-donor and strong 蟺-acceptor, an unusual combination found in very few organometallic ligands.