ISSN:
0947-6539
Schlagwort(e):
benzene
;
benzyne
;
osmium clusters
;
photochemistry
;
polymer films
;
Chemistry
;
General Chemistry
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
The highly efficient photoinduced isomerisation of [Os3(CO)9(μ3-η2:η2:η2-C6H6)] (1) to the previously characterised μ3-benzyne complex [H2Os3(CO)9(μ3-η2:η1:η1-C6H4)] (2) is described. We find that for the more electron-rich clusters [Os3(CO)9-n(PPh3)n(μ3-η2:η2:η2-C6H6)] (n = 1 or 2) the efficiency of the photolytic process is improved. We suggest that photolysis generates a vacant site at osmium (mimicking the inherent coordinative unsaturation of a metal complex) and that this transformation offers a compelling model for the interconversion of associatively and dissociatively chemisorbed benzene. Moreover, we can fine-tune our molecular “work function” (really the separation of HOMO/LUMO energies) by protonation or by phosphine substitution for CO at the metal. Thus, the cation [HOs3(CO)9(μ3-η2:η2:η2-C6H6)]+ does not undergo internal metalation, while photoisomerisation of the electron-rich phosphine derivatives proceeds more readily than for 1. We find that these photolytic reactions are easily monitored by IR spectroscopy for samples suspended in polymethylmethacrylate films under ambient conditions. This method permits “matrix isolation” experiments under ideal conditions. Finally, we speculate that the mechanism of interconversion almost certainly involves the symmetric cleavage of a Os—Os bond (σ-σ* transition) to produce an extremely reactive diradical intermediate.
Zusätzliches Material:
6 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/chem.19950010409
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