Nuclearity of Triosmium Clusters

Ultraviolet photolysis of Os3(CO)12 in the presence of dienes such as butadiene (291), cyclooctatetraene (291), or cyclooctadienes (412) leads to mononuclear species of type Os(CO)3 (diene). Irradiation of methylacrylate 

Other methods have been applied to obtaining higher clusters. Vacuum 

Heating Os3(CO)12 in hexane with H2 under pressure gives Os4H4(CO)12 quantitatively (301), while a similar treatment with C2H4 (20 atm, 160°C) gives Os3H2(C=CH2)(CO)9 as the major product (422), which is also formed under milder conditions (33). Other products isolated from the pressure treatment were Os4(CO)12(CH=CH) and Os4(CO)12(CH=CEt), the X-ray structures of which involve Os4C2 octahedra (422). 

The clusters Os3(CO)12 (CNR)n (n = 1 to 4) readily form the higher clusters Os6(CO)i8 (CNR) (n = 1 to 5) in refluxing octane (321,323). This process occurs much more readily than for Os3(CO)12, which is indefinitely stable in refluxing octane and only gives Os6(CO)18 at a significant rate at 150°C or above. The structure of Os6(CO)16(CN Bu)2 relates directly to that of Os6(CO)18 (423). 

The reaction of Os3H2(CO)10 with azobenzene PhN=NPh does not occur under mild conditions, but at 125°C cluster reformation leads to Os5H-(CO)13(PhNC6H4N) (434). This compound forms simple adducts with PEt3, CN Bu, or CO which surprisingly have essentially the same cluster skeleton as their parent (435). 

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