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Title:Flash Photolysis and Chemical Reactivity Studies Related to Transition Metal Carbonyl Radicals
Author(s):Olsen, Robert James
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:Flash photolysis experiments were performed on hexanesolutions of Re(,2)(CO)(,10), Mn(,2)(CO)(,10), Mn(,2)(CO)(,8){P(n-Bu)(,3)}(,2),Mn(,2)(CO)(,8){P(i-Bu)(,3)}(,2), Mn(,2)(CO)(,8){P(i-Pr)(,3)}(,2), Mn(,2)(CO)(,8){PPh(,3)}(,2),Mn(,2)(CO)(,8){P(OPh)(,3)}(,2), Mn(,2)(CO)(,8){P(OEt)(,2)Ph}(,2), and Mn(,2)(CO)(,8){PMe(,3)}(,2).The concentrations of the dinuclear compounds varied from 1 x 10('-5)
M to 2 x 10('-5) M. With an initial CO concentration of 1 x 10('-2) M, the^change in the solution absorbance following the flash obeys second-^order kinetics. This second-order reaction has been attributed to^simple bimolecular recombination of M(CO)(,4)L(.) species (M = Mn,^Re; L = CO, phosphine). For the unsubstituted radical species,^Mn(CO)(,5)(.) and Re(CO)(,5)(.), the rate of recombination is diffusion-^controlled. The recombination rate constants, kr, for Mn(CO)(,5)(.),^Mn(CO)(,4){P(n-Bu)(,3)}(.), Mn(CO)(,4){P(i-Bu)(,3)}(.), and Mn(CO)(,4){P(i-Pr)(,3)}(.)^are 9 x 10('8) M('-1) s('-1), 1 x 10('8) M('-1) s('-1), 2 x 10('7) M('-1) s('-1), and 4 x 10('6)
M('-1) s('-1) respectively at 22(DEGREES)C, illustrating that the rate of recombination decreases well below the diffusion-controlled limit as L becomes larger than CO. Electronic factors do not influence the recombination rate as Mn(CO)(,4){P(OPh)(,3)}(.) has the same kr value as Mn(CO)(,4){P(n-Bu)(,3)}(.) and the rate of recombination of Mn(CO)(,4){P(i-Bu)(,3)}(.) is the same as that of Mn(CO)(,4){PPh(,3)}(.) at 22(DEGREES)C. Computer modeling determined that the dissociation rate constant of phosphine from Mn(CO)(,4)L(.) is less than 1.0 s('-1).
Hexane solutions of Mn(,2)(CO)(,10), Re(,2)(CO)(,10), and Mn(,2)(CO)(,8){P(i-Bu)(,3)}(,2) were flash photolysed without an initial CO concentration present solution absorbances immediately following the flash did not behave second-order kinetics; rather, intermediate species were generated which were more strongly absorbing than Mn(,2)(CO)(,10), Re(,2)(CO)(,10), or Mn(,2)(CO)(,8){P(i-Bu)(,3)}(,2). The strongly absorbing intermediates have been ascribed to the unsaturated dinuclear compounds, M(,2)(CO)(,8) and/or M(,2)(CO)(,9) (M = Mn, Re) as well as Mn(,2)(CO)(,6){P(i-Bu)(,3)}(,2) and/or Mn(,2)(CO)(,7){P(i-Bu)(,3)}(,2). The radical species initially present upon flashing, thermally lose CO to form unsaturated radicals. Upon reaction of the unsaturated radicals with one another, the unsaturated dinuclear compounds are generated. Computer modeling has determined that the rate constant for the loss of CO from the radical centers is 100 s('-1).
The photochemical reaction of Re(,2)(CO)(,10) with HCo{P(OEt)(,3)}(,4) generates HRe(CO)(,3){P(OEt)(,3)}(,2) and HCo{P(OEt)(,3)}(,3)(CO).
Issue Date:1982
Description:215 p.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.
Other Identifier(s):(UMI)AAI8302948
Date Available in IDEALS:2014-12-15
Date Deposited:1982

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