New Method for Intramolecular Cyclization of Osmium-Coordinated Diynes Avoiding Os-3(mu-H)(2)(CO)(10) as Starting Material

A new method of synthesis was carried out for the preparation of the hydride clusters [Os-3(mu-H)(CO)(9)-{mu(3),eta(1):eta(3):eta(1)-RC2COHC CR}] (R = C4H3S (1a), BrC4H2S (1b), Ph (1c)) by reaction between RC CC CR (R = C4H3S (a), BrC4H2S (b), Ph (c)) and the "non-hydride" [Os-3(CO)(11)(CH3CN)] in dichloromethane at room temperature and in the presence of water, avoiding the starting material [Os-3(mu-H)(2)(CO)(10)]. The complexes [Os-3(mu-CO)(CO)(9){mu(3),eta(1):eta(2):eta(1)-RC4R}] (R = C4H3S (2a), BrC4H2S (2b), Ph (2c)) were also obtained as byproducts. 1a-c and 2a-c contain a "closed" Os-3 triangular core in mu(3),eta(1):eta(3):eta(1)-allylic and mu(3),eta(1):eta(2):eta(1)-alkyne coordination modes, respectively. When the reaction is carried out in wet polar and donor solvents [Os-3(mu-H)(CO)(9){mu(3),eta(1):eta(3):eta(1)- RC2CH=COCR}] (R = C4H3S (3a), BrC4H2S (3h), Ph (3c)) are obtained, where the organic ligand turns into a furan ring by an intramolecular cyclization process. These reactions proceed through 1a-c as intermediates, identified by H-1 NMR. Therefore, 3a-c have also been obtained as the only products in high yield (ca. 98%), when 1a-c were stirred in dry donor solvents at room temperature. In order to get further information about the possible mechanisms that take place, the reactions have been studied using D2O and different solvents. 1a,c, 2b, and 3c have been characterized by single-crystal X-ray diffraction analyses. A possible pathway for this reaction is suggested.