STRATEGIES DIRECTED TOWARDS THE SYNTHESIS OF DIOSMIUM COMPLEXES
Abstract
At room temperature the reactions between osmium tetroxide, concentrated hydrohalic acids (HCl or HBr) and tertiary phosphines in ethanol have been shown to produce the diamagnetic, light-sensitive Os(VI) compounds OsO(,2)X(,2)(PR(,3))(,2)(PR(,3) = PPh(,3), PMePh(,2), PEtPh(,2) and PEt(,2)Ph) as intermediates on the way to the more familiar trans-OsX(,4)(PR(,3))(,2) and mer-OsX(,3)(PR(,3))(,3). The compound previously formulated as OsOBr(,3)(PPh(,3))(,2) has been shown to be a mixture of OsO(,2)Br(,2)(PPh(,3))(,2) and trans-OsBr(,4)(PPh(,3))(,2). The reactions of OsO(,2)X(,2)(PR(,3))(,2)(X = Cl or Br; PR(,3) = PPh(,3) or PEt(,2)Ph) with refluxing carboxylic acids have produced a new class of diosmium(IV) complexes of the type Os(,2)((mu)-O(,2)CR')(,2)X(,4)(PR(,3))(,2)(R' = CH(,3) or C(,2)H(,5)). The X-ray crystal structure of the diethyl ether solvate of Os(,2)((mu)-O)((mu)-O(,2)CCH(,3))(,2)Cl(,4)(PPh(,3))(,2) has been determined. This molecule is the only known example of a diosmium complex containing a single bent bridging oxide ligand. Besides the bridging oxide ligand, two distorted acetate ligands bridge the long Os-Os distance of 3.440(2) (ANGSTROM). Either Os(,2)((mu)-O)((mu)-O(,2)CCH(,3))(,2)Cl(,4)(PPh(,3))(,2) or OsO(,2)Cl(,2)(PPh(,3))(,2) reacts with tert-butyl isocyanide in hot toluene to produce trans-OsCl(,2){CNC(CH(,3))(,3)}(,4). The reactions of OsO(,2)X(,2)(PPh(,3))(,2) (X = Cl and Br) with HL (HL = 2-hydroxypyridine, 2-hydroxy-6-methylpyridine and picolinic acid) in refluxing ethanol gave the mononuclear Os(III) complexes OsX(,2)(L)(PPh(,3))(,2). When OsO(,2)X(,2)(PPh(,3))(,2) (X = Cl and Br) is reacted with a mixture of 1,3-diphenyltriazine and n-butyl lithium in tetrahydrofuran under reflux conditions the related Os(III) species OsX(,2)(PhN(,3)Ph)(PPh(,3))(,2) are produced. In contrast to this, OsO(,2)Cl(,2)(PEt(,2)Ph)(,2) reacts with 2-hydroxy-6-methylpyridine in hot ethanol to yield the mono-carbonyl of Os(III) OsCl(,3)(CO)(PEt(,2)Ph)(,2), thereby demonstrating the sensitivity of these reactions to the nature of the phosphine ligand. The mono-carbonyl derivatives of Os(II) OsX(mhp)(CO)(PPh(,3))(,2) are prepared by reacting trans-OsX(,4)(PPh(,3))(,2) with 2-hydroxy-6-methylpyridine(Hmhp) in hot ethanol. Characterization of these complexes includes ('1)H nuclear magnetic resonance, infrared, electron spin resonance and electronic absorption spectroscopy, magnetic moment measurements and cyclic voltammetry.
Degree
Ph.D.
Subject Area
Chemistry
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