Chelate-Enforced Phosphine Coordination Enables -Abstraction to Give Zirconium Alkylidenes
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- 作者：Wei Weng ; Lin Yang ; Bruce M. Foxman ; and Oleg V. Ozerov
- 刊名：Organometallics
- 出版年：2004
- 出版时间：September 27, 2004
- 年：2004
- 卷：23
- 期：20
- 页码：4700 - 4705
- 全文大小：100K
- 年卷期：v.23,no.20(September 27, 2004)
- ISSN：1520-6041
文摘
The rigid PNP pincer ligand (PNP = deprotonated anion of bis(ortho-diisopropylphoshinoaryl)amine) is shown to stabilize the (Zr=CHR)2+ fragment. (PNP)Li(THF) (2-THF) containsP-Li bonds, as evinced by the observation of the Li-P coupling in the solution 31P NMRspectrum and by the X-ray structural determination in the solid state. 2-THF reacts withZrCl4(Et2O)2 to give (PNP)ZrCl3 (3). (PNP)ZrCl3 (3) can be alkylated with RCH2MgCl to give(PNP)Zr(CH2R)3 (4a-c). (PNP)ZrMe3 (4a) is thermally stable, and its solid-state structureis characterized by severe distortions from the octahedral geometry. The (PNP)Zr(CH2R)3(R = phenyl (4b) or p-tolyl (4c)) compounds undergo 
-abstraction at ambient temperatureto give isolable Zr alkyl/alkylidenes (PNP)Zr(=CHR)(CH2R) (5b,c). The reaction follows afirst-order rate law (t1/2 at 298 K 
2.3 h). The activation parameters were determined fromthe VT NMR studies (4b 
5b): 
H
= 19(1) kcal/mol; S = -14(3) cal/(mol K); G298 =23(2) kcal/mol. The importance of the enforcement of the phosphine coordination by the rigidPNP ligand is discussed.
-abstraction at ambient temperatureto give isolable Zr alkyl/alkylidenes (PNP)Zr(=CHR)(CH2R) (5b,c). The reaction follows afirst-order rate law (t1/2 at 298 K 2.3 h). The activation parameters were determined fromthe VT NMR studies (4b 5b): H = 19(1) kcal/mol; S = -14(3) cal/(mol K); G298 =23(2) kcal/mol. The importance of the enforcement of the phosphine coordination by the rigidPNP ligand is discussed.