Insertion of pyridine into an iron-silicon bond and photochemical conversion of the insertion product Cp*(OC)Fe{η³(C,C,C)- C₅H₅NSiMe₂NPh₂} to a sandwich compound

Irradiation of Cp*(OC)₂FeSiMe₂ER_n (ER_n = NPh₂, NMe₂, OMe) in the presence of pyridine affords Cp*(OC)(C₅H₅N)FeSiMe ₂ER_n, which are converted to Cp*(OC) Fe{η³(C,C,C)-C₅H₅NSiMe₂ER _n} 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) FeGeMe₂ER_n (ER_n = NPh₂, NMe ₂, Me), even under more severe conditions. Treatment of Cp*(OC)(C₅H₅N)RuMe with HSiMe₂NPh ₂ at room temperature gives a 5:4 equilibrium mixture of Cp*(OC)(C₅H₅N)RuSiMe₂NPh₂ and Cp*(OC)HRu{κ²(Si,C)-SiMe₂N(o-C ₆H₄)(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)-C₅H₅NSiMe ₂ER₂}. The formation of such a transition state is supported by kinetic analysis of the thermal conversion of Cp*(OC)(C ₅H₅N)FeSiMe₂NPh₂ to Cp*(OC)Fe{η³(C,C,C)-C₅H₅NSiMe ₂NPh₂}, 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)-C₅H₅NSiMe₂NPh ₂} causes dissociation of a carbonyl ligand to produce a new type of sandwich compound, Cp*Fe(η⁵-C₅H ₅NSiMe₂NPh₂).