Photochemical Formation of Mononuclear Bis- and Tris(ethylene) Complexes from Irradiation of Iron Pentacarbonyl or Triruthenium Dodecacarbonyl: Species Involved in Catalytic Alkene Isomerization.

Abstract : In alkane or CF3C6F11 solutions which contain excess C2H4, near-UV irradiation of Ru(CO)4(C2H4), formed quantitatively in situ from visible flight (wavelength 420nm) irradiation of Ru3(CO)12, yields Ru(CO)3(C2H4)2 at 298K. At temperatures below 253K further substitution can be effected photochemically to give trans-Ru(CO)2(C2H4)3. Near-UV irradiation of Ru(CO)4(C2H4) in rigid, C2H4-saturated, 3-methylpentane glasses at 90K yields Ru(CO)3(C2H4)2, but further CO loss to give cis-Ru(CO)2(C2H4) is observed after only approx. 5% consumption of Ru(CO)4(C2H4). Isomerization of photogenerated cis-Ru(CO)2(C2H4)3 to trans-Ru(CO)2(C2H4)3 is only observed on warming the glass above 210K. Prolonged irradiation of photogenerated cis-Ru(CO)2(C2H4)3 at 90K yields loss of additional CO to give a monocarbonyl complex, formulated as Ru(CO)(C2H4)4, which reacts on warming with photoreleased CO to initially regenerate cis-Ru(CO)2(C2H4)3. The photochemistry of Fe(CO)2(C2H4)3 could only be detected by IR spectroscopy at temperatures below 210K. The new results show that species previously formulated as Fe2(CO)6(alkene)2 are in fact Fe(CO)3(alkene)2. In solution, the M(CO)3(C2H4)2 (M = Fe, Ru) and Ru(CO)2(C2H4)3 are substitutionally labile and may serve as versatile reagents in preparative chemistry.