Oxidative addition of the imidazolium cation to zerovalent Ni, Pd, and Pt: A combined density functional and experimental study
Oxidative addition of the imidazolium cation to zerovalent Ni, Pd, and Pt: A combined density functional and experimental study
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DOI：
10.1021/ja010628p
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发表时间：
2001-08-29
影响因子：
15
通讯作者：
White, AH
中科院分区：
文献类型：
--
作者：
McGuinness, DS;Cavell, KJ;White, AH
用密度泛函理论(DFT)和实验研究了不同的咪唑阳离子与零价族金属的氧化加成反应，得到了杂环卡宾配合物。理论分析表明，咪唑类化合物在Pt0和Ni0中的加成反应比在PdL中的放热更大，而Nil的反应势垒要比Pd0和Pd0低得多。金属表面的强碱性支持配体和顺式络合配体增加了反应的放热，也降低了活化势垒。与2-烷基咪唑的加成相比，2-H咪唑的加成更容易，放热更大，卤代咪唑有望进一步降低氧化加成的势垒，增加放热。密度泛函分析结果表明，在合适的条件下，这三种金属都能氧化加成咪唑阳离子。实验研究证实了氧化加成的可能性，并通过咪唑盐类化合物与MO前驱体的氧化加成反应制备了一系列铂、钯-卡宾配合物。1，3-二甲基咪唑四氟硼酸盐与铂(PPh3)(2)和铂(PCy3)2反应生成[PtH(Dmiy)(PPh3)(2)]BF4(10)和[Pth(Dmiy)(PCy3)(2)]BF4(11)，而3，4-二甲基四氟唑盐与铂(PCy3)(2)反应生成[PtH(Dmty)(PCy3)(2)]BF4(12)(dmiy=1，3-二甲基-2-亚甲基-2-亚甲基-2-亚甲基)。将2-碘-1，3，4，5-四甲基咪唑四氟硼酸盐与铂(PPh3)(4)或钯(Dcype)(Dba)加成，分别得到[Pti(Tmiy)(PPh3)(2)]BF4(9)和[PdI(Tmiy)(Dcype)]BF4(14)，(tmiy=1，3，4，5-四甲基咪唑啉-2-亚甲基，dcype=1，3-双(二环己基膦)乙烷)。报道了配合物9和11(顺式和反式)的X射线晶体结构。这些研究首次清楚地表明，咪唑和噻唑阳离子的氧化加成是可能的，并根据结果在含有卡宾和非卡宾络合物的咪唑基离子液体中的催化作用方面进行了讨论。
Oxidative addition of different imidazolium cations to zerovalent group 10 metals, to afford heterocyclic carbene complexes, has been investigated by both density functional theory (DFT) and experimental studies. The theoretical analysis shows that addition of imidazoliums to Pt-0 and Ni-0 is more exothermic than to Pdl, and Nil is predicted to react with a much lower barrier than either Pt-0 or Pd-0. Strongly basic supporting ligands on the metal, as well as cis-chelating ligands, increase the exothermicity of the reaction and also lower the activation barrier. The addition of 2-H imidazoliums is easier and more exothermic than addition of 2-alkylimidazoliums, and a halo-imidazolium is expected to further lower the barrier to oxidative addition and increase the exothermicity. The DFT results show that all three of the metals should be able to oxidatively add imidazolium cations under appropriate conditions. Experimental studies confirmed that oxidative addition is possible, and a number of Pt- and Pd-carbene complexes were prepared via oxidative addition of imidazolium salts to MO precursors. Most significantly, oxidative addition of 2-H azolium salts was found to readily occur, and the reaction of 1,3-dimethylimidazolium tetrafluoroborate with Pt(PPh3)(2) and Pt(PCy3)2 affords [PtH(dmiy)(PPh3)(2)]BF4 (10) and [PtH(dmiy)(PCy3)(2)]BF4 (11), while reaction between 3,4-dimethylthiazolium tetrafluoroborate and Pt(PCy3)(2) yields [PtH(dmty)(PCy3)(2)]BF4 (12) (dmiy = 1,3-dimethylimidazolin-2-ylidene, dmty = 3,4-dimethylthiazolin-2-ylidene). Addition of 2-iodo-1,3,4,5-tetramethylimidazolium tetrafluoroborate to Pt(PPh3)(4) or Pd(dcype)(dba) yields [PtI(tmiy)(PPh3)(2)]BF4 (9) and [PdI(tmiy)(dcype)]BF4 (14), respectively (tmiy = 1,3,4,5-tetramethylimidazolin-2-ylidene, dcype = 1,3-bis(dicyclohexylphosphino)ethane)). X-ray crystal structures are reported for complexes 9 and 11 (cis and trans). These studies clearly show for the first time that oxidative addition of imidazolium and thiazolium cations is possible, and the results are discussed in terms of the ramifications for catalysis in imidazolium-based ionic liquids with both carbene-based and non-carbene-based complexes.