THE ELECTROCHEMICAL PROPERTIES OF ALKYL ISOCYANIDE COMPLEXES OF MOLYBDENUM(II) AND TUNGSTEN(II) AND THE REACTIONS OF ALKYL ISOCYANIDES WITH MULTIPLY BONDED DI- AND TRI-RHENIUM SYSTEMS
Abstract
After the discovery that the metal-metal quadruple bond in di-molybdenum systems such as Mo(,2)(O(,2)CR)(,4) and K(,4)Mo(,2)Cl(,8) is readily cleaved by alkyl isocyanide ligands yielding Mo(CNR)(,7)('2+), a detailed electrochemical study of both the homoleptic and mixed tertiary phosphine isocyanide complexes of molybdenum(II) and tungsten(II) was undertaken. In all cases a single, reversible one electron oxidation is observed between +0.9V and 1.2V vs. SCE. This work has also led to the reformulation of the supposed molybdenum(I) complex {Mo(CNCMe(,3))(,4)Cl}(,2) as {Mo(CNCMe(,3))(,6)Cl}Cl. Reactions of alkyl isocyanides with the dirhenium(III) systems has also been investigated. Reactions with halide rich compounds such as (n-Bu(,4)N)(,2)Re(,2)Cl(,8) were found to yield monomeric rhenium(III) species of the type {Re(CNR)(,6)Cl}('+), whereas Re(,2)(O(,2)CR)(,4)Cl(,2) yields the homoleptic rhenium(I) species {Re(CNR)(,6)}('+). Also, phosphine substituted products of both rhenium(I) and rhenium(III) (not attainable by direct substitution of {Re(CNR)(,6)Cl}('+) or {Re(CNR)(,6)}('+)) can be obtained by reacting Re(,2)Cl(,6)(PR(,3))(,2) and Re(,2)Cl(,4)(PR(,3))(,4) with alkyl isocyanides. The electrochemical properties of the rhenium(I) and rhenium(III) isocyanide complexes were studied. For the rhenium(I) systems a one electron oxidation is observed between +0.7V and +0.9V vs. SCE. For the rhenium(III) species only an irreversible reduction is observed near -1.0V vs. SCE and is accompanied by rapid decomposition to {Re(CNR)(,6)}('+). Extending the reactions of isocyanide ligands to other multiply bonded rhenium systems the tri-rhenium(III) chloride clusters were studied. The initial adduct formation (Re(,3)Cl(,9)(CNR)(,3)) is followed, under reflux conditions, by reductive cleavage of the cluster to yield {Re(CNR)(,6)}('+). Likewise, when Re(,3)Cl(,9)(PR(,3))(,3) adducts are reacted with alkyl isocyanides reduction to {Re(CNR)(,4)(PR(,3))(,2)}('+) occurs. The electrochemical properties of these trinuclear clusters revealed an accessible reduction between -0.1V and -0.25V vs. SCE. For the Re(,3)Cl(,9) cluster and the phosphine adducts this reduction approaches reversibility, whereas the isocyanide complexes have an irreversible reduction followed by the rapid formation of a purple colored reduction product.
Degree
Ph.D.
Subject Area
Chemistry
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