Osmium(IV) complexes TpOs(X)Cl2 and their Os(III) counterparts: oxidizing compounds with an unusual resistance to ligand substitution

TpOsIV(X)Cl2 complexes (Tp = hydrotris(1-pyrazolyl)borate) are formed upon treatment of TpOs(NPPh3)Cl2 with the protic acids HX: triflic acid (HOTf), HCl, HBr, CF3COOH, and CH3COOH. The reaction with acetic acid is slow but is catalyzed by HOTf. The triflate ligand in TpOs(OTf)Cl2 (1) is remarkably inert and does not undergo simple substitution reactions. For instance, no reaction is observed between 1 and anhydrous Cl− salts, but conversion to TpOsCl3 occurs upon addition of small amounts of H2O or HCl. Substitution appears to be catalyzed by protic reagents. Treatment of 1 with PPh3 or pyridine (py) yields the substituted osmium(III) complexes TpOs(L)Cl2 (L = PPh3, py). A more general route to Os(III) complexes involves reduction of 1 by decamethylferrocene (Cp*2Fe) to give [Cp*2Fe][TpOs(OTf)Cl2], which undergoes substitution at 65 °C forming the Os(III) complexes TpOs(L)Cl2 (L = MeCN, C6H5CN, PPh3, py, imidazole, and NH3) in 70–90% yields. Oxidation of the neutral Os(III) complexes with [NO]BF4 in CH2Cl2 affords Os(IV) salts of the formula [TpOs(L)Cl2]BF4 in near quantitative yields. This indirect synthetic approach yields osmium(IV) complexes that are not accessible by direct substitution. The Os(IV) complexes are strong oxidants, with E1/2 values from +0.00 to +0.70 V in MeCN vs. Cp2Fe+/0. The inertness of the triflate ligand in 1, and the acetonitrile ligand in [TpOs(NCMe)Cl2]BF4, appear to be in part a consequence of the electrophilic character of the Os(IV) center.

[1]  W. Kaminsky,et al.  Activation of an anilido ligand for nucleophilic aromatic substitution by an oxidizing Os(IV) center. , 2001, Journal of the American Chemical Society.

[2]  J. Mayer,et al.  Nitrogen abstraction from nitriles by osmium(IV) complexes. , 2001, Journal of the American Chemical Society.

[3]  J. Mayer,et al.  Protonation and deprotonation of TpOs(NHPh)Cl(2): an unusually inert amido ligand. , 2001, Inorganic chemistry.

[4]  W. Kaminsky,et al.  C--N bond formation on addition of aryl carbanions to the electrophilic nitrido ligand in TpOs(N)Cl(2). , 2001, Journal of the American Chemical Society.

[5]  J. Mayer,et al.  Nitric Oxide Abstracts a Nitrogen Atom from an Osmium Nitrido Complex To Give Nitrous Oxide , 2000 .

[6]  J. Guan,et al.  Dinitrogen Labile Coordination versus Four-Electron Reduction, THF Cleavage, and Fragmentation Promoted by a (calix-tetrapyrrole)Sm(II) Complex , 2000 .

[7]  Samuel A. Johnson,et al.  The continuing story of dinitrogen activation , 2000 .

[8]  D. Tellers,et al.  C-H bond activation by a rare cationic iridium dinitrogen complex. An important electronic effect in the chemistry of the hydridotris(pyrazolyl)borate ligand , 2000 .

[9]  Y. Matano,et al.  Synthesis and Reactivity of Aryl- and Alkyl-Rhenium(V) Imido−Triflate Compounds: An Unusual Mechanism for Triflate Substitution , 1999 .

[10]  T. Meyer,et al.  Structural and redox chemistry of osmium(III) chloro complexes containing 2,2′:6′,2″-terpyridyl and tris-pyrazolyl borate ligands , 1999 .

[11]  T. Meyer,et al.  OsIII(N2)OsII Complexes at the Localized-to-Delocalized, Mixed-Valence Transition , 1999 .

[12]  W. Jones,et al.  11B NMR: A New Tool for the Determination of Hapticity of Tris(pyrazolyl)borate Ligands , 1998 .

[13]  I. Guzei,et al.  CHALCOGEN ATOM TRANSFER TO A METAL NITRIDO. THE FIRST TRANSITION METAL SELENONITROSYL COMPLEX , 1998 .

[14]  T. Meyer,et al.  Nitrogen atom transfer and redox chemistry of terpyridyl phosphoraniminato complexes of osmium (IV) , 1998 .

[15]  David J. Williams,et al.  Polyazolyl Chelate Chemistry. 6.1 Bidentate Coordination of HB(pz)3 (pz = Pyrazol-1-yl) to Ruthenium and Osmium: Crystal Structure of [RuH(CO)(PPh3)2{κ2-HB(pz)3}] , 1998 .

[16]  W. M. Davis,et al.  Triamidoamine Complexes of Molybdenum and Tungsten That Contain Metal−E (E = N, P, and As) Single, Double, or Triple Bonds , 1997 .

[17]  P. T. Wolczanski.  Chemistry of electrophilic metal centres coordinated by silox (tBu3SiO), tritox (tBu3CO) and related binfunctional ligands , 1995 .

[18]  Maria Cristina Burla,et al.  SIR92 – a program for automatic solution of crystal structures by direct methods , 1994 .

[19]  J. Kochi.  Electron Transfer and Charge Transfer: Twin Themes in Unifying the Mechanisms of Organic and Organometallic Reactions , 1988 .

[20]  M. Sekine,et al.  Nitrile complexes of pentaammineosmium(II) and -(III) , 1988 .

[21]  P. A. Lay,et al.  (Trifluoromethanesulfonato-O)pentaammine complexes: versatile synthetic intermediates , 1983 .

[22]  E. Frauendorfer,et al.  Optically active polypyrazolylborate molybdenum complexes with aminophosphines as chiral ligands , 1982 .

[23]  R. D. Shannon.  Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides , 1976 .

[24]  Z. Otwinowski,et al.  [20] Processing of X-ray diffraction data collected in oscillation mode. , 1997, Methods in enzymology.