Iron Pivalate Complexes Containing PNN Pincer Ligand: Synthesis and Application to Dehydrogenative Hydrosilane Coupling

With the exception of iron, metals suitable for hydrosilylation
catalysis are typically cross-applicable to dehydrogenative hydrosilane
homocoupling reactions that afford useful σ-conjugated oligosilanes
and polysilanes. Herein, we report the synthesis of iron pivalate
complexes supported by a PNN pincer ligand and their application in
the dehydrogenative coupling of hydrosilanes, showing that tertiary
silanes are not consumed even under thermal conditions, whereas primary
and secondary silanes are converted into poly- and disilanes, respectively.
Disproportionation reactions are found to compete with coupling reactions,
similar to previous studies using noble-metal catalysts. The addition
of B2pin2 as a hydrogen acceptor is shown to
increase the overall fraction and yield of coupling products, whereas
the addition of alkenes is revealed to afford hydrosilylation products.
Finally, a mechanism for the initial activation of iron pivalate complexes
by hydrosilanes and a catalytic mechanism involving the silyl migration
of a silyl–silylene iron complex are proposed based on the
results of reaction mixture monitoring by nuclear magnetic resonance
spectroscopy and the observed (by)products.

除铁元素外，适用于硅氢加成（hydrosilylation）催化的金属，通常可交叉应用于脱氢硅烷均偶联反应，该反应可生成具有实用价值的σ共轭低聚硅烷与聚硅烷。本文报道了一类由PNN钳型配体（PNN pincer ligand）负载的新戊酸铁配合物的合成，及其在硅烷脱氢偶联反应中的催化应用。研究表明，即便在热条件下，叔硅烷也不会被消耗，而伯硅烷与仲硅烷则分别转化为聚硅烷与二硅烷。研究还发现，歧化反应会与偶联反应形成竞争，这与此前采用贵金属催化剂的相关研究结果一致。向反应体系中加入联硼酸频那醇酯(B2pin2)作为氢受体，可提升偶联产物的总占比与分离收率；而加入烯烃则可得到硅氢加成产物。最后，基于核磁共振波谱法（nuclear magnetic resonance spectroscopy）对反应混合物的监测数据，以及观测到的产物与副产物，本文提出了硅烷对新戊酸铁配合物的初始活化机制，以及涉及硅基-硅宾铁配合物硅基迁移步骤的催化循环机制。