Nickel(I) monomers and dimers with cyclopentadienyl and indenyl ligands.
Nickel(I) monomers and dimers with cyclopentadienyl and indenyl ligands.
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具有环戊二烯基和茚基配体的镍(I)单体和二聚体。
作者：
Jianguo Wu;A. Nova;David Balcells;G. Brudvig;W. Dai;Louise M. Guard;N. Hazari;Po‐Heng Lin;R. Pokhrel;M. Takase
（μ-Cl）_2Ni_2（NHC）_2反应（NHC = 1，3-双（2，6-二异丙基苯基）-1，3-二氢-2H-咪唑-2-亚基（IPr）或1，3-双（二、6-二异丙基苯基）咪唑烷-2-亚基（SIPr））与1当量的NaCp或LiInd反应，生成了（μ-Cp）（μ-Cl）Ni 2（NHC）2（NHC = IPr（1 a）或SIPr（1 B）; Cp = C5 H5）或（μ-Ind）（μ-Cl）Ni 2（NHC）2（NHC = IPr（2 a）或SIPr（2 B）; Ind = C7 H9），其含有桥接Cp和茚基配体。两当量的NaCp或LiInd与（μ-Cl）_2Ni_2（NHC）_2（NHC = IPr或SIPr）反应，生成了（η（5）-Cp）Ni（NHC）（NHC = IPr（3 a）或SIPr（3 B））或（η（5）-Ind）Ni（NHC）（NHC = IPr（4 a）或SIPr（4 B））形式的17价电子Ni（I）单体，它们具有非线性几何构型. DFT计算和NBO分析的结合表明，Ni（I）单体被Cp配体比被茚基配体更强地稳定，这与实验结果一致。这些计算还表明，单体的价层中有一个孤的未配对的单电子，这是非线性结构的原因。在室温下，Cp桥联二聚体（μ-Cp）（μ-Cl）Ni 2（NHC）2经历Ni-Ni键的均裂，并与（η（5）-Cp）Ni（NHC）和（μ-Cl）2Ni 2（NHC）2处于平衡。没有证据表明（μ-Ind）（μ-Cl）Ni 2（NHC）2存在这种平衡。DFT计算表明，热可及的三重态有利于均裂解离的Cp桥接二聚体，而对于桥接茚基物种，这种激发三重态是显着更高的能量。在化学计量反应中，Ni（I）单体（η（5）-Cp）Ni（NHC）或（η（5）-Ind）Ni（NHC）用温和试剂经历氧化和还原过程。此外，它们是Suzuki-Miyaura反应的活性Ni（I）预催化剂的罕见实例。配合物1a、2 B、3 a、4 a和4 B的晶体结构经X-射线衍射表征。
The reaction of (μ-Cl)2Ni2(NHC)2 (NHC = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)) with either one equivalent of sodium cyclopentadienyl (NaCp) or lithium indenyl (LiInd) results in the formation of diamagnetic NHC supported Ni(I) dimers of the form (μ-Cp)(μ-Cl)Ni2(NHC)2 (NHC = IPr (1 a) or SIPr (1 b); Cp = C5H5) or (μ-Ind)(μ-Cl)Ni2(NHC)2 (NHC = IPr (2 a) or SIPr (2 b); Ind = C7H9), which contain bridging Cp and indenyl ligands. The corresponding reaction between two equivalents of NaCp or LiInd and (μ-Cl)2Ni2(NHC)2 (NHC = IPr or SIPr) generates unusual 17 valence electron Ni(I) monomers of the form (η(5)-Cp)Ni(NHC) (NHC = IPr (3 a) or SIPr (3 b)) or (η(5)-Ind)Ni(NHC) (NHC = IPr (4 a) or SIPr (4 b)), which have nonlinear geometries. A combination of DFT calculations and NBO analysis suggests that the Ni(I) monomers are more strongly stabilized by the Cp ligand than by the indenyl ligand, which is consistent with experimental results. These calculations also show that the monomers have a lone unpaired-single-electron in their valence shell, which is the reason for the nonlinear structures. At room temperature the Cp bridged dimer (μ-Cp)(μ-Cl)Ni2(NHC)2 undergoes homolytic cleavage of the Ni-Ni bond and is in equilibrium with (η(5)-Cp)Ni(NHC) and (μ-Cl)2Ni2(NHC)2. There is no evidence that this equilibrium occurs for (μ-Ind)(μ-Cl)Ni2(NHC)2. DFT calculations suggest that a thermally accessible triplet state facilitates the homolytic dissociation of the Cp bridged dimers, whereas for bridging indenyl species this excited triplet state is significantly higher in energy. In stoichiometric reactions, the Ni(I) monomers (η(5)-Cp)Ni(NHC) or (η(5)-Ind)Ni(NHC) undergo both oxidative and reductive processes with mild reagents. Furthermore, they are rare examples of active Ni(I) precatalysts for the Suzuki-Miyaura reaction. Complexes 1 a, 2 b, 3 a, 4 a and 4 b have been characterized by X-ray crystallography.
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