Photochemical studies of (η5-C5H5)Ru(PPh3)2Cl and (η5-C5H5)Ru(PPh3)2Me: formation of Si–H and C–H bond activation products

Abstract

Studies examining the photochemical reactivity of CpRu(PPh₃)₂Cl and CpRu(PPh₃)₂Me towards the two electron donor ligands PEt₃, C₂H₄, DMSO, the CH bond activatable reagents tetrahydrofuran, toluene, and pyridine, and the SiH bond activatable reagents HSiEt₃ and HSi(Me)₂CHCH₂) are presented. Broadband UV irradiation of CpRu(PPh₃)₂Cl leads to the formation of mono-substitution products such as CpRu(PPh₃)(PEt₃)Cl which are inert to further photochemical reaction, although thermally bis-substituted products such as CpRu(PEt₃)₂Cl can be formed. Room temperature irradiation of the related complex CpRu(PPh₃)₂Me with L = PEt₃, C₂H₄, and DMSO also produces CpRu(PPh₃)(L)Me. However, when these reactions are followed by in situ laser irradiation (325 nm source) at low temperature, three solvent activated isomers (ortho, meta and para) of CpRu(PPh₃)₂(C₆H₄Me) are detected in toluene in addition to η¹- and η³-coordinated benzyl species. Furthermore, photolysis in THF leads to both the C–D bond activation product CpRu(PPh₃)₂(OC₄D₇) and the labile coordination complex CpRu(PPh₃)(THF)Me. Now CH₄ rather than CH₃D is liberated which suggests the involvement of an orthometallated species. The photochemically driven reaction of CpRu(PPh₃)₂Me with HSiEt₃ at 198 K generates CpRu(κ²-2-C₆H₄PPh₂)(SiEt₃)H and thereby confirms a role for an orthometallated complex is this process. Irradiation in cyclohexane produces the known orthometallated complex, CpRu(κ²-2-C₆H₄PPh₂)(PPh₃), and CH₄ in accordance with this reactivity.