Stable Ionic Rh(I,II,III) Complexes Ligated by an Imidazolium-Substituted Phosphine with 蟺-Acceptor Character: Synthesis, Characterization, and Application to Hydroformylation

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• 作者：Hongxing You ; Yongyong Wang ; Xiaoli Zhao ; Shengjie Chen ; Ye Liu
• 刊名：Organometallics
• 出版年：2013
• 出版时间：May 13, 2013
• 年：2013
• 卷：32
• 期：9
• 页码：2698-2704
• 全文大小：332K
• 年卷期：v.32,no.9(May 13, 2013)
• ISSN：1520-6041

文摘

The stable ionic Rh(I,II,III) complexes [Rh^I(acac)(CO)(L)]PF₆ (2), [Rh^II₂(OAc)₄(L)₂]2PF₆ (3), and [Rh^IIICl₄(L)₂]PF₆ (4) were synthesized through the complexation of Rh^I(acac)(CO)₂, Rh^II₂(OAc)₄(H₂O)₂, and Rh^IIICl₃路3H₂O with the phosphine-functionalized ionic liquid (FIL) 1 ([L]PF₆, L = 1-butyl-2-diphenylphosphino-3-methylimidazolium), respectively. The cation of L in 1 is an imidazolium-substituted phosphine with a positive charge vicinal to the P(III) atom, which acts as an electron-deficient donor with 蟺-acceptor character to afford the stable complexes 2鈥?b>4 due to the presence of retrodonating 蟺-binding between Rh鈥揚 linkage. Due to the weakened reducing ability of L, the redox reaction between L and RhCl₃路3H₂O during the complexation is avoided, leading to the formation of 4, in which the Rh center is in the +3 valence state. Single-crystal X-ray analyses show that 2鈥?b>4 are all composed of a Rh-centered cation and a PF₆^{鈥?/sup> counteranion. The cation of 2 possesses structural similarity to RhI(acac)(CO)(PPh₃), the cation of 3 with a D_4h geometry possesses a structural similarity to RhII₂(OAc)₄(PPh₃)₂, and the cation of 4 exhibits an ideal RhIII-centered octahedral geometry, in which the Rh(III) (d6) ion is six-coordinated by four chlorine atoms in the equatorial plane and two L ligands in the axial positions. TG/DTG analyses indicated that the thermal stabilities of 2鈥?b>4 in air flow were improved dramatically in comparison to the corresponding analogues RhI(acac)(CO)(PPh₃), RhII₂(OAc)₄(PPh₃)₂, and RhICl(PPh₃)₃. 2鈥?b>4 were found to be good to excellent catalysts for homogeneous hydroformylation of 1-octene free of any auxiliary ligand; 3 was the best candidate. The 鈥渙n water鈥?effect in rate acceleration was evidently observed over 2 and 4 due to their insensitivity to moisture and oxygen.}