ION SITE STRUCTURE AND CHEMICAL REACTIVITY IN NON-AQUEOUS SOLUTIONS OF PENTACARBONYLMANGANATE(-I)
Abstract
High resolution infrared spectra of NaMn(CO)(,5) in THF, THP, pyridine and HMPA have determined that the anion exists primarily in two ion pair sites in these solvents. Besides the previously characterized contact ion pair site of C(,2)v symmetry (site II), we are able to detect the subtle band changes caused by a small but significant perturbation on the anion in the other ion site (site V). This ion pair site could be produced exclusively in all solutions by the addition of one equivalence of the alkali metal ion complexing reagent cryptand C221. Band frequencies and identities were established through temperature variation studies, second derivative plots, and computer band fitting. Analysis of the composite force constants show that this ion site has Cs symmetry caused by the interaction of both an axial and an equatorial CO with the cation. Thermodynamic data and force constant changes indicate that the anion is situated (TURN)8.2 A from the cation, protruding somewhat into the first solvation sphere of the cation. The reaction rates and mechanisms of the oxidative addition of alkyl halides to Mn(CO)(,5)('-) were found to depend on the amount and types of ions sites present. The contact ion pair site can react through a cation assisted mechanism in its reaction with benzyl halides. This mechanism is characterized by a high (DELTA)H and (DELTA)S of activation. Products for the reaction of the Na('+) and Na*C221('+) salts of Mn(CO)('5-) were varying amounts of RMn(CO)(,5) and (RCO)Mn(CO)(,4)X('-) depending on the solvent, the alkyl group and the halide. The reaction of Na*C221Cl with BzMn(CO)(,5) in THF results in the rapid formation of the insertion product Na*C221(BzCO)Mn(CO)(,4)Cl (II') in which the Na('+)-Cl('-) interaction are strong and the acyl carbonyl is positioned such that it cannot interact with the cation. These two facts suggest that this reaction is assisted by a Cl-Bz interaction in the transition state. Thus the reaction of Na*C221Mn(CO)(,5) with BzCl to form II' may occur in a concerted manner rather than proceeding through the BzMn(CO)(,5) intermediate.
Degree
Ph.D.
Subject Area
Chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.