The photochemistry of the complex FpSi2Me5 (Fp = (η5-C5H5)Fe(CO)2) is compared to that of FpSiMe3 using a variety of IR spectroscopic techniques. UV photolysis of FpSi2Me5 in Ar, N2, or CO matrices leads to CO loss and formation of CpFe(CO)Si2Me5 (Cp = (η5-C5H5)). The equivalent product is not observed on identical treatment of FpSiMe3, but, in N2 matrices, small quantities of CpFe(CO)(N2)SiMe3 are generated. Fast time-resolved IR spectroscopy is used to identify primary CO loss photoproducts on flash photolysis of both FpSi2Me5 and FpSiMe3 in room temperature n-heptane solution. Under these conditions, CpFe(CO)SiMe3 reacts rapidly with CO to regenerate FpSiMe3 or with PPh3 to give CpFe(CO)-(PPh3)SiMe3. By contrast, CpFe(CO)Si2Me5 is unreactive toward CO or PPh3 and undergoes an intramolecular decay to give a thermally stable secondary product, X. X is shown to undergo a secondary photochemical reaction with a variety of ligands to give monosilyl products, CpFe(CO)(L)SiMe3 (L = CO, PPh3, C2H4, or N2). A species with a ν(Si-H) IR band is also produced in each of these reactions. For the reactions of FpSi2Me5 and FpSiMe3 with N2, liquid xenon was employed as a cryogenic solvent to stabilize CpFe(CO)(N2)SiMe3. A mechanism is proposed in which decay of CpFe(CO)Si2Me5 occurs by intramolecular oxidative addition of the Si-Si bond to the Fe center, giving a thermally stable silyl(silylene) complex, CpFe(CO)(=SiMe2)SiMe3 (X). Ejection of the SiMe2 fragment from X occurs as a second photochemical step in the deoligomerization. It is suggested that isomerization of the SiMe2 moiety occurs under photochemical conditions, giving a species with Si-H bond(s) and explaining why free silylene fragments have not been trapped in previous studies.
ASJC Scopus subject areas
- Chemistry (all)
- Colloid and Surface Chemistry