Ligand Stereoelectronic Effects in Complexes of Phospholanes, Phosphinanes, and Phosphepanes and Their Implications for Hydroformylation Catalysis
详细信息 查看全文
- 作者：R. Angharad Baber ; Mairi F. Haddow ; Ann J. Middleton ; A. Guy Orpen ; Paul G. Pringle ; Anthony Haynes ; Gary L. Williams ; Rainer Papp
- 刊名：Organometallics
- 出版年：2007
- 出版时间：January 29, 2007
- 年：2007
- 卷：26
- 期：3
- 页码：713 - 725
- 全文大小：258K
- 年卷期：v.26,no.3(January 29, 2007)
- ISSN：1520-6041
文摘
Convenient syntheses are described for the five-, six-, and seven-membered phosphacycles PhP(CH2)x-1,where x = 5 (La5), 6 (La6), 7 (La7), and ButP(CH2)x-1 where x = 5 (Lb5), 6 (Lb6), 7 (Lb7). Treatment of[PtCl2(cod)] with La5-7 gives cis-[PtCl2(La5-7)2] (1a5-7), whereas with Lb5-7 a mixture of cis-[PtCl2(Lb5-7)2] (1b5-7) and trans-[PtCl2(Lb5-7)2] (2b5-7) is obtained. Metathesis of 1a7 with NaI gives a mixtureof cis-[PtI2(La7)2] (3a7) and trans-[PtI2(La7)2] (4a7). The crystal structures of 1a5, 1a6, 1a7, and 4a7 havebeen determined. Comparison of the structures of 1a7 and 4a7 reveals that La7 has variable steric bulk,with the crystallographically determined cone angle ranging from 137
(smaller than La5) to 172 (largerthan La6), depending on the particular twist-chair seven-membered-ring conformations adopted. Thecomplex cis-[PtCl2(Lb6)] (1b6) is fluxional on the NMR time scale at ambient temperatures, as a resultof restricted PtP rotation. Treatment of [Rh2Cl2(CO)4] with La5-7 or Lb5-7 gives the expected trans-[RhCl(CO)(La5-7)2] (5a5-7) or trans-[RhCl(CO)(Lb5-7)2] (5b5-7), and from the 
CO values, it is deducedthat the donor strengths to rhodium(I) are in the order Lb5-7 > La5-7 and, within the La and Lb series,L7, L6 > L5. An investigation into the kinetics of the oxidative addition of MeI to 5a5-7 showed that therate of reaction is in the order 5a5 > 5a7 > 5a6; i.e., the smallest ligand gives the highest rate. It ispostulated that the flexible La7 ligand adopts a lower bulk conformation and the order of decreasing rateis then in the order of increasing bulk. The rate of reaction of MeI with 5b5 is 4 times faster than with5a5, but oxidative addition was not observed with 5b6 or 5b7, perhaps because steric congestion destabilizesthe rhodium(III) product. A study of the rhodium-catalyzed hydroformylation of 1-octene is reportedusing ligands La5-7 and Lb5-7, but no systematic trends were observed, and the results for La5-7 weresimilar to those for the acyclic analogue PhPEt2. An anomalous but reproducible result is that the catalystderived from Lb7 shows negligible hydroformylation activity but rapid octene isomerization activity.The overall conclusion is that, with the rhodium complexes of the simple phosphacycles described here,no special effect of the rings was observed in the hydroformylation catalysis. An 
-substituent effect isidentified as a common feature in several high-activity hydroformylation catalysts derived fromphosphinanes.
(smaller than La5) to 172 (largerthan La6), depending on the particular twist-chair seven-membered-ring conformations adopted. Thecomplex cis-[PtCl2(Lb6)] (1b6) is fluxional on the NMR time scale at ambient temperatures, as a resultof restricted PtP rotation. Treatment of [Rh2Cl2(CO)4] with La5-7 or Lb5-7 gives the expected trans-[RhCl(CO)(La5-7)2] (5a5-7) or trans-[RhCl(CO)(Lb5-7)2] (5b5-7), and from the CO values, it is deducedthat the donor strengths to rhodium(I) are in the order Lb5-7 > La5-7 and, within the La and Lb series,L7, L6 > L5. An investigation into the kinetics of the oxidative addition of MeI to 5a5-7 showed that therate of reaction is in the order 5a5 > 5a7 > 5a6; i.e., the smallest ligand gives the highest rate. It ispostulated that the flexible La7 ligand adopts a lower bulk conformation and the order of decreasing rateis then in the order of increasing bulk. The rate of reaction of MeI with 5b5 is 4 times faster than with5a5, but oxidative addition was not observed with 5b6 or 5b7, perhaps because steric congestion destabilizesthe rhodium(III) product. A study of the rhodium-catalyzed hydroformylation of 1-octene is reportedusing ligands La5-7 and Lb5-7, but no systematic trends were observed, and the results for La5-7 weresimilar to those for the acyclic analogue PhPEt2. An anomalous but reproducible result is that the catalystderived from Lb7 shows negligible hydroformylation activity but rapid octene isomerization activity.The overall conclusion is that, with the rhodium complexes of the simple phosphacycles described here,no special effect of the rings was observed in the hydroformylation catalysis. An -substituent effect isidentified as a common feature in several high-activity hydroformylation catalysts derived fromphosphinanes.