Synthesis and characterization of rhenium and dirhenium polyhydride complexes containing mono-, bi-, tri-, and tetradentate phosphines

Michael Thomas Costello, Purdue University

Abstract

The complex $\rm ReH\sb7(PPh\sb3)\sb2$ was thermalized with a variety of ligands (L) to form complexes of the type $\rm ReH\sb5(PPh\sb3)\sb2$L. The complex $\rm ReH\sb7(PPh\sb3)\sb2$ reacts with $\rm Ph\sb2PCH\sb2CH\sb2AsPh\sb2$ (arphos) in refluxing ethanol to give a mixture of the P- and As-bound linkage isomers $\rm ReH\sb5(PPh\sb9)\sb2$(P-arphos) (1) and $\rm ReH\sb5(PPh\sb3)\sb2$(As-arphos) (2). This mixture has been characterized by $\sp1$H and $\sp{31}$P$\{\sp1$H$\}$ NMR spectroscopy. The related reaction of $\rm ReH\sb7(PPh\sb3)\sb2$ with $\rm Ph\sb2AsCH\sb2CH\sb2AsPh\sb2$ (dpae) in hot toluene affords $\rm ReH\sb5(PPh\sb3)\sb2$(As-dpae) (3). The As-bound complexes 2 and 3 have been structurally characterized by X-ray crystallography and have been shown to possess isostructural dodecahedral geometries. The investigation of the electrochemistry of $\rm ReH\sb7(PR\sb3)\sb2$ complexes revealed that the formulation of a dihydrogen complex of the type, $\rm ReH\sb5(H\sb2)(PR\sb3)\sb2,$ is favored under the conditions of the cyclic voltammetric experiment. While several different methods have been used in the past to generate the dirhenium octahydrides, none were adapted to cover a wide range phosphine ligands until we developed a synthetic strategy that we found was suitable for use with monodentate and bidentate phosphine ligands. The dirhenium complexes $\rm Re\sb2Cl\sb6(PR\sb2Ph)\sb2$ and $\rm Re\sb2Cl\sb5(PRPh\sb2)\sb3$ (R = Me or Et) were refluxed in ethanol with NaBH$\sb4$ and EPh$\sb3$ to prepare dirhenium octahydrides of the type $\rm Re\sb2H\sb8(PR\sb2Ph)\sb2(EPh\sb3)\sb2$ and $\rm Re\sb2H\sb8(PRPh\sb2)\sb3(EPh\sb3)$ (R = Me or Et, E = P, As, or Sb). These products have been characterized by $\sp1$H NMR spectroscopy as well as cyclic voltammetry. An anomalous reaction of (n-$\rm Bu\sb4N)\sb2Re\sb2Cl\sb8$ with SbPh$\sb3$ and NaBH$\sb4$ in ethanol formed the dirhenium hexahydride $\rm Re\sb2H\sb6(SbPh\sb3)\sb5.$ The single-crystal X-ray structure was determined and all six hydride ligands (three terminal, three bridging) were located. The Re-Re bond distance was 2.5340(6) A. The synthesis of compounds of the types $\rm ReH\sb5L\sb3$ and $\rm ReH\sb3L\sb4$ from their respective halides $\rm ReCl\sb3L\sb3$ and $\rm ReCl\sb2L\sb4$ (where L$\sb3$ = $\rm CH\sb3C(CH\sb2PPh\sb2)\sb3$ (triphos) or $\rm PhP(CH\sb2CH\sb2PPh\sb2)\sb2$ (PP$\sb2),$ and L$\sb4$ = $\rm P(CH\sb2CH\sb2PPh\sb2)\sb3$ (tetraphos)) in refluxing ethanol and NaBH$\sb4$ was described. A dinucleation reaction involving the conversion of ReH$\sb5$(triphos) to $\rm Re\sb2H\sb4(triphos)\sb2$ led to a full investigation of the reactivity of ReH$\sb5$(triphos) toward Lewis acids and bases. In contrast the other tri- and tetradentate phosphine complexes are readily protonated with Lewis acids but are unreactive toward Lewis bases.

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

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