Insertion of Pyridine into an Iron−Silicon Bond and Photochemical Conversion of the Insertion Product Cp*(OC)Fe{η³(<i>C,C,C</i>)-C₅H₅NSiMe₂NPh₂} to a Sandwich Compound

Irradiation of Cp*(OC)2FeSiMe2ERn (ERn = NPh2, NMe2, OMe) in the presence of pyridine affords Cp*(OC)(C5H5N)FeSiMe2ERn, which are converted to Cp*(OC)Fe{η3(C,C,C)-C5H5NSiMe2ERn} upon mild heating via insertion of pyridine into the iron−silicon bond. This type of pyridine insertion does not proceed in the thermal reactions of Cp*(OC)(C5H5N)FeSiMe2R (R = Cl, Me) and the germanium analogues, Cp*(OC)(C5H5N)FeGeMe2ERn (ERn = NPh2, NMe2, Me), even under more severe conditions. Treatment of Cp*(OC)(C5H5N)RuMe with HSiMe2NPh2 at room temperature gives a 5:4 equilibrium mixture of Cp*(OC)(C5H5N)RuSiMe2NPh2 and Cp*(OC)HRu{κ2(Si,C)-SiMe2N(o-C6H4)(Ph)}. Heating the mixture at 100 °C does not afford an analogous insertion product, although the equilibrium is shifted to the side of the orthometalated compound. These results indicate that the insertion of pyridine is specific for the heteroatom-substituted silyliron(II) system. The insertion reaction is considered to proceed via the mechanism that involves the initial formation of an η2(N,C)-pyridine complex. Migratory insertion of pyridine into the iron−silicon bond accompanied by coordination of the terminal heteroatom then results in a congested transition state, leading to the formation of an η1-allyl intermediate, Cp*(OC)Fe{κ2(C,E)-C5H5NSiMe2ER2}. The formation of such a transition state is supported by kinetic analysis of the thermal conversion of Cp*(OC)(C5H5N)FeSiMe2NPh2 to Cp*(OC)Fe{η3(C,C,C)-C5H5NSiMe2NPh2}, giving activation parameters of ΔH⧧ = 93(2) kJ mol-1, ΔS⧧ = −53(6) J mol-1 K-1, and ΔG⧧298 K = 109(3) kJ mol-1. The η3-allyl complex is finally formed through dissociation of the amino part. Irradiation of Cp*(OC)Fe{η3(C,C,C)-C5H5NSiMe2NPh2} causes dissociation of a carbonyl ligand to produce a new type of sandwich compound, Cp*Fe(η5-C5H5NSiMe2NPh2).在吡啶存在下对Cp*(OC)₂FeSiMe₂ERn（ERn = NPh₂、NMe₂、OMe）进行光解，可得到Cp*(OC)(C₅H₅N)FeSiMe₂ERn；该产物经温和加热后，可通过吡啶在铁-硅键中的插入反应，转化为Cp*(OC)Fe{η³(C,C,C)-C₅H₅NSiMe₂ERn}。这类吡啶插入反应在Cp*(OC)(C₅H₅N)FeSiMe₂R（R = Cl、Me）以及锗类似物Cp*(OC)(C₅H₅N)FeGeMe₂ERn（ERn = NPh₂、NMe₂、Me）的热反应中均无法发生，即便在更严苛的反应条件下也无产物生成。将Cp*(OC)(C₅H₅N)RuMe与HSiMe₂NPh₂在室温下反应，可得到Cp*(OC)(C₅H₅N)RuSiMe₂NPh₂与Cp*(OC)HRu{κ²(Si,C)-SiMe₂N(o-C₆H₄)(Ph)}的5:4平衡混合物。将该混合物加热至100℃，虽可使平衡向邻位金属化化合物一侧偏移，但并未得到类似的吡啶插入产物。上述结果表明，吡啶插入反应对杂原子取代的甲硅烷基铁(II)体系具有特异性。该插入反应的可能机理为：首先形成η²(N,C)-配位的吡啶配合物；随后吡啶发生迁移插入至铁-硅键中，同时末端杂原子参与配位，由此形成拥挤的过渡态，进而生成η¹-烯丙基中间体Cp*(OC)Fe{κ²(C,E)-C₅H₅NSiMe₂ER₂}。通过对Cp*(OC)(C₅H₅N)FeSiMe₂NPh₂热转化为Cp*(OC)Fe{η³(C,C,C)-C₅H₅NSiMe₂NPh₂}的动力学分析，证实了此类过渡态的存在，其得到的活化参数为：ΔH‡ = 93(2) kJ·mol⁻¹，ΔS‡ = −53(6) J·mol⁻¹·K⁻¹，ΔG‡298K = 109(3) kJ·mol⁻¹。该η³-烯丙基配合物最终通过氨基部分的解离得到。对Cp*(OC)Fe{η³(C,C,C)-C₅H₅NSiMe₂NPh₂}进行光解，会引发羰基配体解离，从而生成一类新型夹心配合物Cp*Fe(η⁵-C₅H₅NSiMe₂NPh₂)。