THE SYNTHESIS AND CHARACTERIZATION OF ARYL ISOCYANIDE COMPLEXES OF RHENIUM
Abstract
The reactions of aryl isocyanides ArNC with the quadruply-bonded dirhenium(III) complexes Re(,2)(O(,2)CCH(,3))(,4)Cl(,2) and (n-Bu(,4)N)(,2)Re(,2)Cl(,8) in refluxing methanol provide an excellent high yield synthetic route to the homoleptic rhenium(I) species {Re(CNAr)(,6)}PF(,6). When the reactions between ArNC and (n-Bu(,4)N)(,2)Re(,2)Cl(,8) are conducted at room temperature, then mononuclear rhenium(III) containing intermediates of the types {Re(CNAr(,6)}(,2)Re(,2)Cl(,8), {Re(CNAr)(,6)}{ReCl(,4)(CNAr)(,2)} and mer-ReCl(,3)(CNAr)(,3) can be isolated. These aryl isocyanide complexes all display well defined electrochemistry (cyclic voltammetry) in 0.2M TBAH-CH(,2)Cl(,2). Characterization of the salts {Re(CNAr)(,6)}{ReCl(,4)(CNAr)(,2)} has shown that freshly prepared samples contain the trans-anion, but that dichloromethane solutions slowly isomerize to the corresponding cis-isomer. The ('1)H NMR spectra of these same salts reveal substantial Knight shifts associated with the paramagnetic d('4) {ReCl(,4)(CNAr)(,2)}('-) anions. The reactions of ArNC with the rhenium halide salts K(,2)ReX(,6) (X = Br or I) have been investigated. When they are treated with neat isocyanide at room temperature, the homoleptic isocyanide complexes {Re(CNAr)(,6)}I(,3) are isolated. Under less forcing conditions, the rhenium(I) species, e.g. Re(CNAr)(,5)I and Re(CNAr)(,5)(I(,3)) can be obtained. The rhenium(I) complexes Re(CNAr)(,5)(I(,3)), which are believed to contain the coordinated triiodido ligand, can be synthesized through the reaction of Re(CNAr)(,5)I with I(,2). A preliminary investigation of the reaction chemistry of the sterically encumbered isocyanide ligand 2,4,6-tri-tert-butylphenyl isocyanide (TBPhNC) has been undertaken. A reaction of TBPhNC with the quadruply bonded complex Re(,2)(O(,2)CCH(,3))(,4)Cl(,2) in refluxing methanol affords, among other products, the rhenium(I) species {Re(CNTBPh)(,6)}PF(,6). A computer generated molecular model of an octahedral molecule of the {M(CN-TBPh)(,6)} stoichiometry indicates that this must be a sterically demanding molecule with severe rotational barriers about the M-CNC axis and the C(aryl)-C(tert-butyl) bonds.
Degree
Ph.D.
Subject Area
Chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.