Osmium 5 2+ photolysis

To substitute the strongly bound axial CO ligand of the ruthenium or osmium center, it is necessary to employ more drastic conditions than simple stirring at room temperature. Imamura (11,20) used photolysis to synthesize porphyrin trimers on the basis of simultaneous coordination of two 4-pyridyl porphyrins to the same ruthenium porphyrin (12, Fig. 3). Some interesting photophysical behavior was observed for these systems. The trimers have an extra UV-Vis absorption band at about 450 nm which is ascribed to metal-ligand charge transfer (MLCT), a d7r(Ru(II))-7r (OEP) transition. This band shows a batho-chromic shift in more polar solvents, and decreased in intensity when... 

Photoinduced and chemical oxidation of coordinated imines to amides in isomeric osmium(II) complexes of AT-arylpyridine-2-carboxaldimines has been studied by Ghosh and coworkers [34]. The complexes [Os(Br)2(Rimpy)2] (Scheme 1) were prepared and characterized structurally, indicating the pyridines of the two Rimpy ligands are trans to one another and the bromides are cis. Broadband photolysis of the complex in aerated acetonitrile resulted in oxidation of one Rimpy ligand to yield the RimOpy ligand and oxidation of the osmium to Os(III). The overall yield of the photochemical process is reported to be greater than 95%. The authors propose a mech-... 

A binuclear bis(/z-germylene) osmium carbonyl complex [(OC)4Os(GeMe2)]2 on photolysis or thermolysis yields a mixture of an interesting series of (/z-germylene) osmium clusters36. Bis(metalcarbonyl)germacyclopentene complexes on photolysis or thermolysis... 

Norton and co-workers 102) briefly noted that photolysis of Os(CH3)2(CO)4 in hexane solution led to the formation methane but produced no ethane. Presumably, methane derives from photoinduced homolysis of an osmium-methyl bond and scavenging of hydrogen by the resultant methyl radical. 

Recently, we have studied such a photoredox reaction (6) that proceeds in analogy to the photolysis of the binuclear osmium complex Eq. (23) ... 

A positional isomer of xylopinine of structure (345), prepared by synthesis, has been subjected to Hofmann degradation to the olefin (346), which on oxidation with osmium tetroxide gives the diol (347). Cleavage of the diol gave the dialdehyde (348), photolysis of which yields a mixture of cis-alpen-igenine (30%) and alpenigenine (339) (1%) (S.B. Prabhakar, et al., J.Chem.Soc., Perkin I 1981, 1273). The 7,8,13,14-tetra-... 

In addition to metal-yne n complexation, Pu and co-workers (522) synthesized and crystaUographically characterized a water soluble, metal-ene n-complex by reacting [Os(en)2H2H20] with a TMS-substituted enediyne (TMS=Tetramethylethylene). The X-ray structure shows q -enediyne complexation to osmium (Scheme 79), however, no metal-promoted Bergman cyclization reactivity is observed, and only enediyne dissociation occurs upon oxidation or photolysis of the metal complex. 

Photochemical reactions of Ru3(CO)i2 and Os3(CO)i2 with nitrogen hetero-cycles have been studied, with substitution products being formed in most cases. For example, with pyridine the ruthenium compound forms the ortho-metallated complex Ru3H(CO)i i(CsH4N), while the osmium compound gives the simple substitution product Os3(CO)n(py). The novel dihydrido triruthenium cluster H2Ru3(CO)io can be synthesized by photolysis of Ru3(CO)i2 under an atmosphere of dihydrogen. 

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