Cationic tris N-heterocyclic carbene rhodium carbonyl complexes: Molecular structures and solution NMR studies
Cationic tris N-heterocyclic carbene rhodium carbonyl complexes: Molecular structures and solution NMR studies
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DOI：
10.1021/om060202p
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发表时间：
2006-05-08
期刊：
影响因子：
2.8
通讯作者：
Whittlesey, Michael K.
中科院分区：
文献类型：
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作者：
Burling, Suzanne;Douglas, Susie;Whittlesey, Michael K.
阳离子型N -杂环卡宾（NHC）铑配合物[Rh(NHC)(3)(CO)]⁺（NHC = ICy（1），(IPr2Me2)-Pr - i（2））已从RhH(PPh3)(3)(CO)与游离NHC的反应中分离出来。这两种化合物的六氟磷酸盐，1[PF6]和2[PF6]，已通过X射线衍射进行了表征。1[PF6]和2[PF6]的¹H NMR谱所观察到的温度依赖性是与三个Ph - C - NHC键相关的受限旋转的结果。对1[PF6]、1[BAr4F]和2[PF6]（BAr4F = B(3,5 - C6H3(CF3)₂)₄）进行的NMR研究的线形分析得出两个处于反位的Rh - C - NHC键的活化能垒分别为35、38和40 kJ mol⁻¹。脉冲梯度自旋回波（PGSE）NMR测量表明，在二氯甲烷溶液中这些盐只有相对少量的离子对。¹H - ¹⁹F HOESY数据有助于确定阴离子相对于阳离子的位置。对1和2形成的初步机理研究表明中性双核前体起到了一定作用，正如(PPh3)₂Rh(μ - CO)₂Rh((IPr2Me2)-Pr - i)₂与ICy的反应所揭示的那样，该反应得到了结构经表征的混合NHC配合物[Rh((IPr2Me2)-Pr - i)(1)(ICy)(CO)][PF6]（3[PF6]）。
The cationic N-heterocyclic carbene (NHC) rhodium complexes [Rh(NHC)(3)(CO)](+) (NHC = ICy (1), (IPr2Me2)-Pr-i (2)) have been isolated from the reactions of RhH(PPh3)(3)(CO) with the free NHCs. The hexafluorophosphate salts of both compounds, 1[PF6] and 2[PF6], have been characterized by X-ray diffraction. The observed temperature dependences of the H-1 NMR spectra for 1[PF6] and 2[PF6] are a consequence of restricted rotation associated with the three Ph-C-NHC bonds. Line shape analyses from the NMR studies on 1[PF6], 1[BAr4F], and 2[PF6] (BAr4F = B(3,5-C6H3(CF3)(2))(4)) afford activation barriers for the two trans-positioned Rh-C-NHC bonds of 35, 38, and 40 kJ mol(-1), respectively. Pulsed-gradient spin-echo (PGSE) NMR measurements show that there is only a relatively small amount of ion pairing for these salts in dichloromethane solution. H-1-F-19 HOESY data help to place the anions relative to the cations. Preliminary mechanistic studies on the formation of 1 and 2 suggest a role for neutral dinuclear precursors, as revealed by the reaction of (PPh3)(2)Rh(mu-CO)(2)Rh((IPr2Me2)-Pr-i)(2) with ICy, which affords the structurally characterized mixed NHC complex [Rh((IPr2Me2)-Pr-i)(1)(ICy)(CO)][PF6] (3[PF6]).