Synthese, struktur und reaktivität zweikerniger hydridoverbrückter osmium-komplexe mit OsOs-Doppel- und Dreifach-Bindung

Abstract

The dinuclear mesitylene osmium complexes [(Mes) 2Os 2(μ-H) 3]X ( 2a, b) and [(Mes)OsH(μ-H)] 2 ( 3) are prepared from [(Mes)OsCl 2] n ( 1) and NaBH 4. The complex 2a (X = Cl) and its corresponding BF 4 salt 2c can also be obtained from the reaction of 3 with HCl or HBF 4, respectively. The structures of 2a and 3 have been determined by single-crystal X-ray diffraction studies. The cation of 2a contains two equivalent (Mes)Os fragments linked by a rather short OsOs bond (247.41(2) pm) and three bridging hydride ligands. The midpoints of the six-membered rings together with the two osmium atoms form a linear unit. The metal—metal distance in compound 3 (267.34(6) pm) is significantly longer than that in the cation of 2a and corresponds to an OsOs double bond. The trans arrangement of the mesitylene rings with regard to the metal—metal bond axis indicates that two of the hydride ligands in 3 are terminal and two are bridging. An equilibrium between the cis and trans isomers of 3 probably exists in CD 2Cl 2 solution. Treatment of [(Mes)OsCl 2(PMe 3)] ( 4) with NaBH 4 or LiAlH 4 affords the dihydrido complex [(Mes)OsH 2(PMe 3)] ( 5) which is also one of the products of the reaction of 3 with PMe 3. Compound 5 is photoreactive and on UV irradiation in benzene gives the hydrido phenyl complex [(Mes)OsH(C 6H 5)PMe 3].