Synthesis and reactivity of some multiply bonded diosmium complexes

Thomas Wayne Johnson, Purdue University

Abstract

The monomeric hexabromoosmate(IV) anion, (OsBr$\sb6\rbrack\sp{2-}$, reacts with molten 2-hydroxypyridine (Hhp) to form the dinuclear complex $\rm Os\sb2(hp)\sb4Br\sb2$. This compound can also be formed by substitution of bromide for the axial chloride ligands in the complex $\rm Os\sb2(hp)\sb4 Cl\sb2$ with the use of liquid HBr at $-77\sp\circ$C. The compound $\rm Os\sb2(hp)\sb4Br\sb2$ can then be treated with hydrogen halide gas in ethanol solvent to form the complexes (n-$\rm Bu\sb4 N)\sb2 Os\sb2 X\sb8$(X = Cl, Br). Also, $\rm Os\sb2(hp)\sb4Br\sb2$ reacts with refluxing acetic acid to generate $\rm Os\sb2(O\sb2 CCH\sb3)\sb4Br\sb2$. The triply bonded diosmium(III) complexes (n-$\rm Bu\sb4 N)\sb2 Os\sb2 X\sb8$ (X = Cl, Br) react with isocyanide ligands RNC (R = CHMe$\sb2$, CMe$\sb3$, xylyl, mesityl) in ethanol at room temperature to afford the 17-electron, paramagnetic mononuclear osmium(III) species (n-$\rm Bu\sb4 N)\sb2\lbrack OsX\sb4(CNR)\sb2$) in very high yield. A similar reaction with carbon monoxide in hot ethanol gives (n-Bu$\sb4$N) (OsX$\sb4$(CO)L), where L = DMSO, THF, CH$\sb3$CN, py, PPh$\sb3$, PEt$\sb3$ or xylylNC. The spectroscopic and electrochemical properties, as well as single crystal X-ray structural studies on (n-Bu$\sb4$N) (OsCl$\sb4$(CNxylyl)$\sb2$) and a crystal of composition (n-Bu$\sb4$N) (OsCl$\sb{2.68}$Br$\sb{1.32}$(CO)(DMSO)) show that the anions possess trans- (OsX$\sb4$(CNR)$\sb2\rbrack\sp-$ and ($\rm OsX\sb4(CO)L\rbrack\sp-$ geometries. The reactions of (n-$\rm Bu\sb4 N)\sb2 Os\sb2 Cl\sb8$ with sodium borohydride in the presence of a phosphine, arsine or stibine ligand in ethanol solvent at room temperature produces either $\rm OsH\sb4(ER\sb3)\sb3$ or cis-$\rm OsH\sb2(ER\sb3)\sb4$ (E = P, As, Sb). The compounds synthesized by these methods are $\rm OsH\sb4(SbPh\sb3)\sb3$, cis-$\rm OsH\sb2(AsPh\sb3)\sb4$ and cis-$\rm OsH\sb2(SbPh\sb3)\sb4$. The reactions of the diosmium(III) acetate $\rm Os \sb2 (O \sb2 CCH \sb3)\sb4 Cl \sb2 $ with phosphines give a variety of products. With monodentate phosphines in refluxing n-propanol, the products $\rm OsCl\sb3(PR\sb3)\sb3$($ \rm PR\sb3$ = PEt$\sb2$Ph, PMe$\sb2$Ph, PMePh$\sb2$) or $\rm OsCl \sb2 (PPh \sb3)\sb3$ are produced. When $\rm Os \sb2(O \sb2 CCH \sb3) \sb2(C \sb6 H \sb4 PPh \sb2) \sb2 Cl \sb2$ is treated with the mild oxidizing agent ferrocinium hexafluorophosphate it forms the corresponding monocation. This is the first example of a diosmium(IV,III) complex which may have a formal Os-Os bond order of 3.5. Reaction of the compound $\rm Os \sb2 (O \sb2 CCH \sb3)\sb4 Cl \sb2$ with $\rm Re \sb2 Cl \sb4 (PMe \sb3)\sb4$ produces the novel paramagnetic mixed-metal salt ($\rm Re \sb2 Cl \sb4 (PMe \sb3)\sb4$) ($\rm Os \sb2 (O \sb2 CCH \sb3)\sb4 Cl \sb2$).

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

COinS