Redox reactions between small molecules and dirhenium complexes containing multiple metal-metal bonds

Paul Ward Schrier, Purdue University

Abstract

The triply bonded dirhenium(II) complexes $\rm Re\sb2X\sb4(dppm)\sb2$ (X = Cl, Br; dppm = $\rm Ph\sb2PCH\sb2PPh\sb2)$ and $\rm Re\sb2Br\sb4(dpam)\sb2\ (dpam = Ph\sb2AsCH\sb2AsPh\sb2)$ react with CS$\sb2$ via a 2-electron redox process to afford the dirhenium(III) compounds $\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb3(CS)(\mu$-$\rm LL)\sb2$ (LL = dppm, dpam). These complexes can be derivatized by reaction with TlPF$\sb6$ in the presence of various monodentate ligands L$\sp\prime$ to give salts of the type ($\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb2(CS)(\mu$-$\rm LL)\sb2(L\sp\prime)\rbrack PF\sb6$ where $\rm L\sp\prime = CH\sb3CN, C\sb2H\sb5CN,4$-$\rm CH\sb3C\sb6H\sb4CN,$ t-BuNC, or xylylNC. The $\mu\sb2$-sulfido-bridged dirhenium(III) complexes $\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb3(CS)(\mu$-$\rm LL)\sb2$ and ($\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm Cl)Cl\sb2(CS)(\mu$-$\rm dppm)\sb2(NCR)\rbrack PF\sb6$ (R = Me or ET) react with the one-electron oxidant NOPF$\sb6$ in the presence of O$\sb2$ to afford in high yield the analogous diamagnetic $\mu\sb2$-$\rm SO\sb2$ complexes $\rm Re\sb2(\mu$-$\rm SO\sb2)(\mu$-$\rm X)X\sb3(CS)(\mu$-$\rm LL)\sb2$ and ($\rm Re\sb2(\mu$-$\rm SO\sb2)(\mu$-$\rm Cl)Cl\sb2(CS)(\mu$-$\rm dppm)\sb2(NCR)\rbrack PF\sb6,$ respectively. The oxygenation can also be effected through the use of gaseous NO$\sb2$ or 3-chloroperbenzoic acid in place of NOPF$\sb6.$ The mechanism for the oxygenation of the $\mu\sb2$-S complexes in the presence of NOPF$\sb6$ involves the direct attack of NO$\sb2$ upon the $\mu\sb2$-sulfido bridge. NO$\sb2$ is produced by the reaction of NO (the byproduct of the oxidation of $\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)\sb3(CS)(\mu$-$\rm LL)\sb2$ or ($\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm Cl)Cl\sb2(CS)(\mu$-$\rm dppm)\sb2(NCR)\rbrack PF\sb6)$ with small amounts of O$\sb2$ in the system. These oxygenation reactions are catalytic in NOPF$\sb6.$ The reactions of $\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb3(CS)(dppm)\sb2$ with TlPF$\sb6$ and CO mixtures in $\rm CH\sb2Cl\sb2$ afford green complexes of the type ($\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb2(CS)(dppm)\sb2(CO)\rbrack PF\sb6.$ The treatment of these carbonyl-containing products with $\rm NOPF\sb6/O\sb2$ mixtures leads to the formation of the corresponding sulfur dioxide complexes ($\rm Re\sb2(\mu$-$\rm SO\sb2)(\mu$-$\rm X)X\sb2(CS)(dppm)\sb2(CO)\rbrack PF\sb6.$ The $\rm \mu$-$\rm S$ and $\rm \mu$-$\rm SO\sb2$ complexes exhibit a rich redox chemistry, which in the case of ($\rm Re\sb2(\mu$-$\rm SO\sb2)(\mu$-$\rm X)X\sb2(CS)(dppm)\sb2(CO)\rbrack PF\sb6$ has led to the isolation of the stable one and two-electron reduction products $\rm Re\sb2(\mu$-$\rm SO\sb2)(\mu$-$\rm X)X\sb2(CS)(dppm)\sb2(CO)$ and ($\rm (\eta\sp5$-$\rm C\sb5H\sb5)\sb2Co\rbrack \lbrack Re\sb2(\mu$-$\rm SO\sb2)(\mu$-$\rm X)X\sb2(CS)(dppm)\sb2(CO)\rbrack .$ A comparison of the cyclic voltammetric and IR spectral properties of these carbonyl complexes with those of the species $\rm Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb3(CS)(dppm)\sb2, \lbrack Re\sb2(\mu$-$\rm S)(\mu$-$\rm X)X\sb2(CS)(dppm)\sb2(L)\rbrack PF\sb6$ (L = RCN or RNC) and their $\rm \mu$-$\rm SO\sb2$ analogues, reveals a clear dependence of the potentials of the metal-base d redox couples and the frequencies of the $\nu$(CS) mode upon the electron-withdrawing ability of the ancillary ligand (CO, RCN or RNC). The complexes cis-$\rm Re\sb2(O\sb2CR)\sb2X\sb2(Ph\sb2Ppy)\sb2$ (R = $\rm CH\sb3, C\sb2H\sb5$; X = Cl, Br) have been prepared by the reaction of $\rm Re\sb2(O\sb2CR)\sb2 X\sb4(4$-$\rm Mepy)\sb2$ with $\rm Ph\sb2Ppy$ in hot acetone and/or the reaction of $\rm Re\sb2X\sb4(Ph\sb2Ppy)\sb2(PEt\sb3)$ with $\rm LiO\sb2CCH\sb3$ or $\rm NaO\sb2CC\sb2H\sb5$ in hot methanol. The chloride complexes have been oxidized by ($\rm (\eta\sp5$-$\rm C\sb5H\sb5)\sb2Fe\rbrack PF\sb6$ in $\rm CH\sb2Cl\sb2$ to give cis- ($\rm Re\sb2(O\sb2CCR)\sb2Cl\sb2(Ph\sb2Ppy)\sb2\rbrack PF\sb6.$

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

COinS