THE REACTIVITY OF THE BISCARBOXYLATE COMPLEXES OF DIRHENIUM(III)

ANN ROBERTA CUTLER, Purdue University

Abstract

The preparation and electrochemistry of the biscarboxylate complexes of dirhenium(III), Re$\sb2$(O$\sb2$CR)$\sb2$X$\sb4$L$\sb2$ (R = CH$\sb3$ or C$\sb2$H$\sb5$; X = Cl, Br or I; L = H$\sb2$O, py, 4-Mepy, DMF or Me$\sb2$SO) are discussed. The reactivity of these complexes toward a number of ligands is examined. Reactions of the complexes Re$\sb2$(O$\sb2$CR)$\sb2$X$\sb4$L$\sb2$ with a series of monodentate tertiary phosphines containing alkyl substituents led to isolation of the previously characterized Re$\sb2$X$\sb4$P$\sb4$ complexes. Reactions of the biscarboxylate complexes with PPh$\sb3$ or mixed valent complexes of the form Re$\sb2$(O$\sb2$CR)X$\sb4$(PPh$\sb3$)$\sb2$ led to mixed valent complexes of the type (RO)$\sb2$X$\sb2$ReReX$\sb2$(PPh$\sb3$)$\sb2$. The product formed was dependent upon the solvent and upon the nature of the axial ligand, L, in the dirhenium starting complex. Bidentate phosphines such as Ph$\sb2$PCH$\sb2$PPh$\sb2$ and Ph$\sb2$PCH$\sb2$CH$\sb2$PPh$\sb2$ react with Re$\sb2$(O$\sb2$CR)$\sb2$X$\sb4$L$\sb2$ to form the complexes Re$\sb2$X$\sb4$(LL)$\sb2$ (where LL = bridging bidentate phosphine). The reaction with the former ligand, Ph$\sb2$PCH$\sb2$PPh$\sb2$, proceeds through an isolable intermediate of the stoichiometry Re$\sb2$(O$\sb2$CR)X$\sb4$(Ph$\sb2$PCH$\sb2$PPh$\sb2)\sb2.$ Addition of acetate anion to these reactions leads to formation of the complexes Re$\sb2$(O$\sb2$CR)$\sb2$X$\sb2$(Ph$\sb2$PCH$\sb2$PPh$\sb2$)$\sb2$ in which the bridging bidentate phosphine ligands are cis to one another about the metal-metal bond. Hydroxypyridine (Hhp) and 2-methyl-6-hydroxypyridine (Hmhp) react with the biscarboxylate complexes of dirhenium(III) to form Re$\sb2$(hp)$\sb2$X$\sb4\cdot$Hhp or Re$\sb2$(mhp)$\sb2$X$\sb4\cdot$Hmhp. A mixed-ligand complex Re$\sb2$(hp)(mhp)$\sb2$X$\sb3$ can also be isolated. Reactions of the complex Re$\sb2$(O$\sb2$CR)$\sb2$X$\sb4$L$\sb2$ with Hmhp in nitrile solvents (R$\sp\prime$CN) yield monocarboxylate compounds, Re$\sb2$(O$\sb2$CR$\sp\prime$)(mhp)$\sb2$X$\sb3$, which form from hydrolysis of the solvent to a coordinated carboxylate group. This chemistry proceeds through the intermediacy of the compound Re$\sb2$(mhp)$\sb2$X$\sb4\cdot$Hmhp.

Degree

Ph.D.

Subject Area

Chemistry

COinS