Photochemistry of some transition metal carbonyl complexes in polymer film media at 12-298K

The new application of polymer film media in infrared spectroscopic studies of unstable intermediates in photochemical reactions of organometallic complexes is described. Ultraviolet (uv) irradiation of the complexes M(CO)6 (M = Cr, Mo or W) in poly(vinylchloride) (PVC) films at 12K is shown to lead to the formation of square pyramidal M(CO)5 species. These species react with donor ligands L in films warmed to above ca 90K to form complexes of the type M(CO)5L. Irradiation of the metal-metal bonded dimers (η5-C5R5)2M2(CO)6 (M = Mo or W; R = H or CH3), (η5-C5R5)2M'2(CO)4 (M' = Cr or Fe) and (η5-C5H4CH3)2Ni2(μ-CO)_2 in PVC films at 12 - 77K leads to the formation of the novel CO-bridged dimers (η5-C_5R_5)_2M_2(CO)_5, (η5-C_5R_5)_2M'_2(μ-CO)3 and (η5-C5H4CH3)2Ni2(μ-CO), respectively. The complexes (η5-C_5H_5)Cr(CO)_3CH_3, (η5-C_5H_5)M(CO)_3R (M = Mo or W; R = CH_3 or C_2H_5), (η5-C_5H_5)M'(CO)_2R (M = Fe or Ru) and (η5-C_5H_5)W(CO)_3R' (R' = C_6H_5 or CH_2C_6H_5) undergo dissociative loss of a CO ligand as the primary photoprocess on uv irradiation in PVC films at 12K. Thermal β- hydrogen elimination in the photogenerated species (η5-C5H5)M(CO)2C2H5 occurs on warming films to above ca 140K, leading to the formation of the complexes trans-(η5-C5H5)M(CO)2(C2H4)H. Thermal conversion of the species (η5-C5H5)W(CO)2(σ-CH_2C_6H_5) to the stable complex (η5-C_5H_5)W(CO)_2(η3-CH_2C_6H_5) occurs in films at temperatures above ca 40K. The species (η5-C_5H_5)M'(CO)C_2H_5 undergoes photoinduced β-hydrogen elimination to form the complexes (η5-C5H5)M'(CO)(C2H4)H, whilst (η5-C5H5Cr(CO)2CH3 undergoes photoinduced α-hydrogen elimination to form trans-(η5-C_5H_5)Cr(CO)_2(=CH_2)H. Both processes are thermally reversible. On uv irradiation of the complex Fe(CO)_5 in poly(tetrafluoroethylene) [PTFE], low density poly(ethylene) [LDPE] and PVC films at 12K, the species Fe(CO)_4 and Fe(CO)_3 are observed to form. (D75974/87)