Electrochemical, spectroelectrochemical, and infrared investigations of late transition metal diphosphine-bridged complexes

Gregory Mark Ferrence, Purdue University

Abstract

The class of nickel dimers, $\rm \lbrack Ni\sb2(CNR)\sb3(dppm)\sb2\rbrack$ (I) were prepared from Ni(cod)$\sb2,$ dppm, and the corresponding isocyanide. These compounds each exhibit two single electron oxidations. Specular reflectance infrared spectroelectrochemical (SEC) measurements demonstrate the reversible conversion between I, $\bf I\sp+,$ and $\bf I\sp{2{+}}.$ $\bf I\sp+$ was prepared in bulk via the conproportionation of I and $\bf I\sp{2{+}}.$ Displacement of a triply-bridging iodide ligand in $\rm Ni\sb3(\mu\sb3$-$\rm I)\sb2(\mu\sb2$-$\rm dppm)\sb3$ by $\pi$-acceptor ligands produces a class of 48-electron trinuclear nickel clusters of the general formula $\rm \lbrack Ni\sb3(\mu\sb3$-$\rm L)(\mu\sb3$-$\rm I)(\mu\sb2$-$\rm dppm)\sb3\rbrack\sp+$ (L = CO; CNR). These clusters possess strikingly similar spectroscopic and electrochemical properties. The unexpected appearance of two $\nu$(C$\equiv$N) bands in the FT-IR spectra was demonstrated to be the result of a Fermi resonance involving the $\nu$(C$\equiv$N) fundamental and the first overtone of the $\nu$(N-C(alkyl)) fundamental of the capping isocyanide. The bromide capped clusters $\lbrack \rm Ni\sb3(\mu\sb3$-$\rm L)(\mu\sb3$-$\rm Br)(\mu\sb2$-$\rm dppm)\sb3\rbrack\sp+$ were prepared to further verify the Fermi resonance. Infrared SEC measurements show that the capping isocyanide or carbonyl ligand remains triply bridging $(\mu\sb3,\eta\sp1)$ upon single electron reduction, but predictably cease Fermi resonance. Sulfide incorporated nickel trimers, $\rm \lbrack Ni\sb3(\mu\sb3$-$\rm I)(\mu\sb2$-$\rm dppm)\sb3$-$\rm (\mu\sb3,\eta\sb1$-$\rm C{\equiv}NC\sb6H\sb4S$-)) are attached to gold electrodes. After deposition, the redox behavior of the Chemically Modified Electrodes (CME) were investigated. The electron acceptors methylviologen and (CoCpCpCOOMe) (PF$\sb6\rbrack$ were used to demonstrate rectification in the interfacial electron transfer from nickel cluster CME to the electron acceptors. $\rm Ni\sb3(\mu\sb2$-$\rm dppm)\sb3(\mu\sb3$-$\rm Te)\sb2$ is prepared from Ni(cod)$\sb2,$ dppm, and TePR$\sb3.$ Cyclic voltammetry shows the reversible conversion of this complex between four oxidation states: $\rm Ni\sb3(\mu\sb2$-$\rm dppm)\sb3(\mu\sb3$-$\rm Te)\sb{2\sp{n}}$ (n = $1\sp-,0,1\sp+,2\sp+).$ This completes an electronic series of nickel trimer cores ranging from Ni$\sb3\sp{6{+}}$ to Ni$\sb3\sp0.$ The diphosphine bridged ruthenium dimers $\rm Ru\sb2(\mu$-$\rm CO)(CO)\sb4(\mu$-dppm)$\sb2,$ and $\rm Ru\sb2(\mu$-$\rm CO)(CO)\sb4(\mu$-$\rm dppm)(\mu$-dmpm), and the mononuclear ruthenium chealate Ru(CO)$\sb3$(dcypm) have been prepared from Ru$\sb3$(CO)$\sb{12}$ and the corresponding phosphine under CO pressure. The reactivity of these compounds have been investigated.

Degree

Ph.D.

Advisors

Kubiak, Purdue University.

Subject Area

Chemistry

COinS