Synthesis and Characterization of (C5Me5)2Os2Br4 and the Osmium Polyhydride (C5Me5)OsH5: A New Synthetic Entry into Mono(pentamethylcyclopentadienyl)osmium Chemistry

Synthesis and structural characterization of unsymmetrical osmocenes containing the pentamethylcyclopentadienyl ligand

“…[(C 5 (CH 3 ) 5 )OsBr(l-Br)] 2 [14], 3,5-di-tert-butylpyrazole [20a], and 3,5-di-tert-butylpyrazolato-potassium [20b] were prepared according to published procedures. Potassium hydride (35% dispersion in mineral oil) was purchased from Aldrich Chemical Company and was washed with hexane prior to use to remove the mineral oil.…”

“…While (C 5 (CH 3 ) 5 )RuCl(PiPr 3 ) was reported in 1988 [12], an analogous osmium complex, (C 5 (CH 3 ) 5 )OsBr-(PiPr 3 ), was prepared only recently [13]. In 1994, Girolami and coworkers [14] reported the synthesis and characterization of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer, [(C 5 (CH 3 ) 5 )OsBr(l-Br)] 2 . This complex has served as a starting material for many half-sandwich pentamethylcyclopentadienylosmium complexes [13][14][15].…”

“…In 1994, Girolami and coworkers [14] reported the synthesis and characterization of dibromo(pentamethylcyclopentadienyl)osmium(III) dimer, [(C 5 (CH 3 ) 5 )OsBr(l-Br)] 2 . This complex has served as a starting material for many half-sandwich pentamethylcyclopentadienylosmium complexes [13][14][15]. In addition, [(C 5 (CH 3 ) 5 )OsBr(l-Br)] 2 can be easily reduced to various complexes in the +2 oxidation state [13,15a,15d].…”

Synthesis, characterization, and X-ray crystal structure of the octabromodiosmate(III) salt [(C5Me4H)2OsBr]2[Os2Br8] and its conversion to [(C5Me4H)2OsBr][Os2HBr4(cod)2]

“…We previously reported that the reaction of H 2 OsBr 6 with pentamethylcyclopentadiene affords either the dinuclear species (C 5 Me 5 ) 2 Os 2 Br 4 [14] or the salt [(C 5 Me 5 ) 2 OsH] 2 [Os 2 Br 8 ] [4] depending on the choice of solvent, the reaction time, and other reaction conditions. The dinuclear complex contains one C 5 Me 5 ring per osmium center, but in the salt the osmium centers are bound either to two rings or to none.…”

“…Each osmium center is, however, d 6 and quasi-octahedral; on this basis, there is no obvious need for an Os-Os bond. The Os-Os bond distance in 2 lies at the upper end of those for other known dinuclear complexes containing bridging hydrides (Table 4) [14][15][16][17]. Dinuclear osmium complexes containing bridging hydrides are rare; of the known polynuclear osmium compounds that contain bridging hydrides, the majority are triosmium carbonyls.…”