Photochemistry of iron and ruthenium carbonyl complexes: Evidence for light-induced loss of carbon monoxide and reductive elimination of triethylsilane from cis-mer-HM(SiEt3)(CO)3(PPh3)

Article abstract of DOI:10.1021/om00088a001

The near-UV photochemistry of M(CO)₄PPh₃ and HM(SiEt₃)(CO)₃(PPh₃) (M = Fe, Ru) has been investigated. The HM(SiEt₃)(CO)₃(PPh₃) complexes have a meridional structure with the H cis to both PPh₃ and the SiEt₃ and are referred to as the cis-mer isomer. In low-temperature (～100 K) rigid organic glasses the M(CO)₄PPh₃ undergoes dissociative loss of CO to form the 16-electron M(CO)₃PPh₃, M-(CO)₃(PPh₃)(2-MeTHF), M(CO)₃(PPh₃)(1-C₅H₁₀), or cis-mer- and fac-HM(SiEt₃)(CO)₃(PPh₃) complex when the organic glass is an alkane, 2-MeTHF, 1-C₅H₁₀, or Et₃SiH, respectively. The fac-HM(SiEt₃)(CO)₃(PPh₃) complexes undergo thermal isomerization to the cis-mer isomer upon warmup to 298 K. Near-UV excitation of cis-mer-HM(SiEt₃)(CO)₃(PPh₃) at ～100 K in an organic glass gives evidence for both the loss of CO and reductive elimination of Et₃SiH. Photochemistry of the complexes at 298 K in fluid solution accords well with photoreactions observed at ～100 K in rigid media. Irradiation of cis-mer-HM(SiEt₃) (CO)₃(PPh₃) in a hydrocarbon solution of Ph₃SiH at 298 K results in the formation of cis-mer-HM(SiPh₃) (CO)₃(PPh₃) and Et₃SiH with a 313-nm quantum yield of ～0.6. The process is photochemically reversed if the cis-mer-HM(SiPh₃) (CO)₃(PPh₃) is irradiated in the presence of excess Et₃SiH. Irradiation of cis-mer-HM-(SiEt₃)(CO)₃(PPh₃) in a hydrocarbon solution at 298 K in the presence of ¹³CO yields both ¹³CO-enriched M(CO)₄PPh₃ and ¹³CO-enriched cis-mer-HM(SiEt₃)(CO)₃(PPh₃). Irradiation of cis-mer-HM(SiR₃)-(CO)₃(PPh₃) (R = OMe, OEt) or cis-mer-HRu(SiMeCl₂)(CO)₃(PPh₃) at 298 K in the presence of Et₃SiH yields cis-mer-HM(SiEt₃)(CO)₃(PPh₃), establishing the light-induced reductive elimination of R₃SiH to occur for a wide range of R groups for these complexes.