Photochemistry of some group 6A and 8 metal–metal bonded cyclopentadienylcarbonyl dimers in poly(vinyl chloride) films at 12–298 K

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Abstract
Infrared and electronic spectral evidence is presented which shows that photolysis of the dinuclear complexes [Ni2(η5-C5H4Me)2(µ-CO)2], [M2(η5-C5R6)2(CO)6](M = Mo Or W, R = H Or Me), and [Cr2(η5-C5R5)2(CO)4] in poly(vinyl chloride)(pvc) films at ca. 12–77 K produces dissociative CO loss as the primary process. The products are assigned as [Ni2(η5-C5H4Me2)2(µ-CO)], [M2(η5-C5R5)2(CO)5](M = Mo or W; two terminal CO, two semibridging CO, one four-electron bridging CO ligand), and [Cr2(η5-C5R5)2(µ-CO)3]. Annealing the films to 100–200 K resulted in facile reversal of the primary process. Similar reversal was achieved by irradiating into the long wavelength absorptions of the products at 12–77 K. Photolysis of the cis and trans bridged isomers of [Ru2(η5-C5H5)2(CO)4] in pvc films did not lead to CO ejection at 12 K but only to bridge opening. Photolysis of trans-[Ru2(η5-C5Me5)2(CO)4] afforded neither CO loss nor even bridge opening, probably due to steric factors. Photolysis of the complexes [M2(η5-C5R5)2(CO)6](M = Mo or W, R = H or Me) and [M2(η5-C5R5)2(CO)4](M = Fe or Ru, R = H or Me) in pvc films at 298 K afforded the mononuclear complexes [M(η5-C5R5)(CO)3Cl] and [Ru(η5-C5R5)(CO)2Cl] arising from abstraction of Cl from the films, cf. the photoreactions observed in chlorocarbon solvents. The mechanisms of the photochemical reactions in pvc films are discussed in relation to solution photochemical reactions.

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