om060873n_si_003.cif (17.33 kB)

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

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posted on 18.12.2006, 00:00 by Masatoshi Iwata, Masaaki Okazaki, Hiromi Tobita
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 ΔG298 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).