Osmium pentaammine

In addition to the high regiochemistry observed, the bulky osmium pentaammine metal center also effectively blocks one face of the pyrrole ring from attack. This directs each transformation carried out on the complex to occur on the same face of the pyrrole ring. For example, in the synthesis of 3-pyrroline complex 74, both protonation and hydride addition occur from the same face of the pyrrole ring, producing 74 exclusively as the c/s-isomer. This feature is also illustrated in the synthesis of pyrrolizinone 109 vide infra), where a stereoselective hydride reduction allows the preparation of 109 as only one diastereomer. 

Until recently ammine complexes of osmium have been little studied compared with their ruthenium analogs. This appears to have been caused by the lack of suitable synthetic routes to them. The discovery of pentaammine(dini-trogen)osmium (II) opened convenient routes to pentaammines of osmium (III), and a convenient synthesis of hexaammineosmium(IIl)2 gave new routes to the previously unknown nitrosyls of osmium(II). Here are given the synthesis of [Os(NH3)s(N2)]l2 and its conversion to [Os(NH3)5l]l2 the synthesis of [Os(NH3)6]l3 and its conversion to [Os(NH3)5(NO)]X3 H20(X = Cl, Br, I) and the preparation of [OsX(NH3)4(NO)]2+(X = OH, Cl, Br, I) from [Os(NH3)5(NO)]3+. 

Cl2H,sN30s, Osmium(n), pentaammine(di-nitrogen)-, didiloride, 24 270 Cl2HfC2oH3o, Hafnium, dichlorobis(T -pen-tamethylcyclopentadienyl)-, 24 154 CI2M02N4C8H24, Molybdenum, dichlorotet-raki (dimethylamido)di-, M—Mo), 21 56... 

FgNtOgOsSaCsHu, Osmium(III), (acetoni-trile)pentaammine-, tris(trifluoro-methanesulfonate), 24 275 F9N609RhS3C3H,8, Rhodium(III), hexaam-mine-, tris(trifluoromethanesulfonate), 24 255... 

OsF9NjO,S3CsHi8, Osmium(III), (acetoni-tTile)pentaammine-, tris(trifluorome-thanesulfonate), 24 275 OSIO2C7HS, Osmium, dicarbonyI(Ti -cyclo-pentadienyl)iodo-, 25 191 OSIO2C12H13, Osmium, dicarbonyliodo(Ti -pentamethylcyclopentadienyl)-, 25 191 0s2l20tC6, Osmium(I), hexacarbonyl-di-p.-iododi-, 25 188... 

The mechanism of this activation of the C-H bond is unknown although the reaction may proceed by an oxidative addition. Generally, the pentaammine-osmium(II) system is known to activate phenols, anilines, and anisoles toward electrophilic addition and substitution reactions by binding the aromatic ligand in an T -fashion. Protonation, for example, results in the formation of a heterotriene system [30b] ... 

The total time required for this procedure is 3-4 hr. Pentaammine(trifluoromethanesulfonato-0)osmium(lII) trifluoromethanesul-fonate, [0s(NH3)5(0S02CF,)](CF3S03)2 (0.30 g, 0.42 mmol), is added to a 0.1 M aqueous solution of CF3SO3H (1 mL) contained in a 15-mL beaker. The solution is boiled for 5 min. After being cooled to room temperature, the solution is cooled further to <5° in an ice bath. Neat CF3SO3H (1 mL) is added slowly in dropwise fashion, while the solution is stirred rapidly. 

The total time required for the synthesis and recrystallization is 1 day. Pentaammine(trifluoromethanesulfonato-0)osmium(III) trifluoromethanesul-fonate, [0s(NH3)s(0S02CF3)KCF3S03)2 (0.10 g, 0.14 mmol), is placed in a 100-mL two-necked round-bottomed flask, and the flask and solid are heated in a vacuum oven at 110°. A second 100-mL two-necked round-bottomed flask is connected to a KOH drying tower and placed in a dish containing Dry Ice. Liquid ammonia (—40 mL) is transferred to this flask, and the flask is stoppered. 

This procedure requires 1 day. Pentaammine(trifluoromethanesulfonato-O)osmium(III) trifluoromethanesulfonate, [0s(NH3)5(0S02CF3)](CF3S03)2 (0.5 g, 0.69 mmol), is added to spectrophotometric grade acetonitrile [Aldrich Chemical] (2 mL) containing several drops of trifluoromethanesulfonic anhydride (triflic anhydride) all contained in a 10-mL test tube. 

H2O2—hydrogen peroxide HRP—horseradish peroxidase PVP—poly(4-vinylpiridine) CpFeC2B9Hii—3i-cyclopentadiennyl-3i-dicarbollyliron Ru(NH3)5py(PFg)—pentaammine-pyridineruthenium(II) ttb-CuPc— tetra-tert-butyl-copper phtalocyanine GA—glutaraldehyde BSA—bovine serum albumin mPEG—methoxypolyethylene [Os(bpy)2pyCl] -—Osmium dibypyridine pyridine chloride cation. 

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