Effect of ring size on the properties of μ3-Cycloalkyne complexes: Synthesis of triruthenium complexes containing a perpendicularly coordinated μ3-Allenyl ligand

Publication date: Available online 8 February 2019Source: Journal of Organometallic ChemistryAuthor(s): Moeko Saito, Shuhei Kojima, Akiko Inagaki, Koichi Seki, Toshiro TakaoAbstractA series of triruthenium complexes, [{Cp*Ru(μ-H)}3(μ3-η2:η2-CnH2n-4)] (2a, n = 6; 2b, n = 7; 2c, n = 8), containing a triply bridgin cycloalkyne ligand was synthesized. Although no noticeable differences were detected in the ground state, the rate of dynamic motion of the cycloalkyne ligand increased remarkably as the ring size increased. Owing to the flexibility of the larger rings, an allylic CH bond can interact with one of the metal centers, stabilizing the transition state of the dynamic process. This interaction also caused allylic CH bond scission upon chemical oxidation. In the case of 2b and 2c, a cationic μ3-η2:η2:η2-allenyl complex, [{Cp*Ru(μ-H)}3(μ3-η2:η2:η2-CnH2n-5)]+ (3b, n = 7; 3c, n = 8), was obtained. X-ray diffraction studies of 3 clearly show that the allenyl group is coordinated to one of the Ru-Ru bonds in a perpendicular fashion, unlike the known "parallel" μ3-allenyl complexes. In contrast to the reactions of 2b and 2c, chemical oxidation of 2a occurred via the incorporation of adventitious H2O rather than intramolecular C-H bond cleavage. Consequently, cationic μ3-cyclohexyne-μ-hydroxo complex, [{Cp*Ru(μ-H)}3(μ-OH)(μ3-η2-C6H8)]+ (5a) was obtained in 38% yield by the reaction with 2 equiv [Cp2Fe]+ in the presence of excess water. These results clearly show...

Source: Journal of Organometallic Chemistry - February 9, 2019 Category: Chemistry Source Type: research