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The variable temperature 13 C-nmr of M 3 (CO) 12 (M = Fe, Ru, Os) have been studied. Fe3(CO)12 and Ru 3 (CO) 12 give one sharp resonance down to −100° C. Os 3 (CO) 12 shows two resonances at room temperature which coalesce to a single resonance at +150 C. Possible mechanisms for carbonyl averaging are considered. The 13C-nmr of the acetylenic complexes HM3(CO)9C2C(CH3)3 (M = Ru, Os) were examined and shown to be stereochemically nonrigid. Both the osmium and ruthenium compounds show axial equatorial exchange on the metal atom which is sigmabonded to one of the acetylenic carbons. Only the ruthenium compound shows exchange between metal atoms in the temperature range examined. The importance of bridging intermediates in this exchange process is discussed.

Isomerization and rearrangement of ligands L, such as 1,4-trans,trans-diphenyl-1,3-butadiene, hexadiene isomers, isoprene and 1,3-butadiene, occur in the reactions with Ru3(CO)12 to give trimetallic complexes of molecular formula HRu3(O)9(L-H), in addition to bi- and monometallic complexes of known structure. On the contrary the diene skeleton is always maintained when L is 2,3-dimethyl-1,3-butadiene. Structures of HRu3(CO)9(L-H) complexes are suggested and some novel features in their proton n.m.r. spectra are described.