Syntheses and reactivities of rhenium polyhydride complexes that contain bidentate organic ligands

Malee Leeaphon, Purdue University

Abstract

Reaction of $\rm Re\sb2H\sb8(PPh\sb3)\sb4$ with acetic acid yields the homoleptic acetate complex $\rm Re\sb2(\mu-O\sb2CCH\sb3)\sb4(O\sb2CCH\sb3)\sb2$ and small amounts of the carbonyl complex $\rm Re(O\sb2CCH\sb3)(CO)\sb2(PPh\sb3)\sb2$. Treatment of $\rm ReH\sb7(PPh\sb3)\sb2$ with acetic acid, in the presence of PPh$\sb3$, affords $\rm Re(O\sb2CCH\sb3)(CO)(PPh\sb3)\sb3$ in high yield. Reactions of $\rm ReH\sb7(PPh\sb3)\sb2$ with other organic acids yield the monohydrido rhenium(III) complexes $\rm ReH(L)\sb2(PPh\sb3)\sb2$, where L represents the monoanion of pyridine-2-carboxylic acid (Hpic), 1-isoquinolinecarboxylic acid (Hisoquin), pyridine-2,3-dicarboxylic acid (Hquin), 2-hydroxypyridine (Hhp), 2-hydroxy-6-methylpyridine (Hmhp), 2-mercaptopyridine (Hmp), and acetylacetone (Hacac). Oxidation of these complexes yields their paramagnetic, 17-electron Re(IV) congeners $\lbrack \rm ReH(L)\sb2(PPh\sb3)\sb2\rbrack PF\sb6$, which are rare examples of mononuclear Re(IV) hydride complexes. Further oxidation of the acac derivative, to $\lbrack \rm ReH(acac)\sb2(PPh\sb3)\sb2\rbrack \sp{2+}$, is followed by a rapid and irreversible deprotonation to give cis-$\lbrack \rm Re(acac)\sb2(PPh\sb3)\sb2\rbrack PF\sb6$. Protonation of $\rm ReH(L)\sb2(PPh\sb3)\sb2$, where L = hp, mhp and mp, yields $\lbrack \rm ReH\sb2(L)\sb2(PPh\sb3)\sb2\rbrack PF\sb6$. In the mhp case, the stereochemically rigid trans-$\lbrack \rm ReH\sb2(mhp)\sb2(PPh\sb3)\sb2\rbrack PF\sb6$, which, in solution, converts slowly to the cis isomeric form. This is the first instance where eight-coordinate geometrical isomers have been structurally characterized and where the stereoisomers retain their structural identity in solution. The presence of methyl groups on the mhp ligands provides a barrier to rotation of the ReH$\sb2$ unit which may be necessary for the isomerization to occur. Reaction of $\rm ReH\sb7(PPh\sb3)\sb2$ with the ligands quinoline (qn), 2-hydroxyquinoline (Hhq) and 2-quinolinethiol (Hqt) yield $\rm ReH\sb xL(PPh\sb3)\sb2$ where x = 5 for L = qn and x = 4 for L = hq and qt. Reactions of the tetrahydride complex $\rm ReH\sb4(qt)(PPh\sb3)\sb2$ with various alkynes in the presence of HPF$\sb6$ or $\rm (Ph\sb3C)PF\sb6$ yield the alkylidyne complexes $\lbrack\rm ReH\sb2(\equiv CR)(qt)(PPh\sb3)\sb2\rbrack PF\sb6$ (where R = $-$CH$\sb2$Ph, $-$CH$\sb2$tol, $-$CH$\sb2$CH$\sb2$Ph, $-\rm CH\sb2CH\sb2CH\sb2CH\sb3$, $-\rm CH\sb2CH\sb2CH\sb2CH\sb2CH\sb3)$. Formation of these complexes probably involves metal to alkyne hydrogen transfer in such a way that allows both terminal and internal acetylenes to form triple bonds with the metal.

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

COinS