REDOX AND SUBSTITUTION CHEMISTRY OF THE RHENIUM POLYHYDRIDES

JOE DOUGLAS ALLISON, Purdue University

Abstract

The electrochemistry of phosphine complexes of the rhenium polyhydrides was investigated using the cyclic voltammetry technique. Complexes of the type ReH(,5)(PPh(,3))(,2)L (where L = monodentate ligand) were found to possess an irreversible oxidation in the potential range +0.24V to +0.12V vs SCE, whereas the dirhenium polyhydrides Re(,2)H(,8)(PR(,3))(,4) (PR(,3) = tertiary phosphine) exhibit a reversible one-electron oxidation between ca. -0.20V to -0.40V vs SCE together with a second, irreversible oxidation at more positive potentials. The first oxidation can be carried out chemically using Ph(,3)C('+)PF(,6)('-) in dichloromethane to afford {Re(,2)H(,8)(PR(,3))(,4)}PF(,6). The mononuclear and dinuclear polyhydrides react with C(,3)H(,5)X (X = Cl, Br or I) to yield {C(,3)H(,5)PPh(,3)}(,2)ReX(,6) and {C(,3)H(,5)PPh(,3)}(,2)Re(,2)X(,8), respectively. Reaction of the mononuclear polyhydrides with HBF(,4) in CH(,3)CN gives {ReH(NCCH(,3))(,3)L(PPh(,3))(,2)}(BF(,4))(,2) (L = C(,5)H(,5)N, CH(,3)CN, H(,2)NC(,6)H(,11)). Re(,2)H(,8)(PR(,3))(,4) reacts with Ph(,3)C('+)PF(,6)('-) in RCN (R = CH(,3), C(,2)H(,5), Ph) to give {Re(,2)H(,7)(PR(,3))(,4)(NCR)}PF(,6) which can be oxidized chemically and electrochemically to {Re(,2)H(,7)(PR(,3))(,4)(NCR)}('2+). Alkyl isocyanides (RNC) react with the polyhydrides to give {Re(CNR)(,4)(PR(,3))(,2)}PF(,6) as the final reaction product. Reaction of {ReH(NCCH(,3))(,3)L(PPh(,3))(,2)}(BF(,4))(,2) and {Re(,2)H(,7)(PR(,3))(,4)(NCR)}PF(,6) with RNC affords {Re(CNR)(,2)(NCMe)L(PPh(,3))(,2)}(BF(,4))(,2) and {Re(,2)H(,7)(PR(,3))(,4)(CNR)}PF(,6), respectively. Addition of tert-butyl isocyanide to solutions of {Re(,2)H(,8)(PPh(,3))(,4)}PF(,6) produces {Re(,2)H(,5)(PPh(,3))(,4)(CNBu('t))(,2)}PF(,6) which can in turn be oxidized to paramagnetic {Re(,2)H(,5)(PPh(,3))(,4)(CNBu('t))(,2)}(PF(,6))(,2).

Degree

Ph.D.

Subject Area

Chemistry

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