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Title:Competing reaction pathways in the photochemical reactions of metal carbonyl compounds
Author(s):Sullivan, Richard Joseph
Doctoral Committee Chair(s):Brown, Theodore L.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Abstract:The photochemical reaction of Mn$\sb2$(CO)$\sb{10}$ with HSnBu$\sb3$ has been studied by continuous photolysis. Sunlamp irradiation of a CO-saturated hexane solution of Mn$\sb2$(CO)$\sb{10}$ and HSnBu$\sb3$ results in formation of HMn(CO)$\sb5$ and Bu$\sb3$SnMn(CO)$\sb5$ in equimolar quantities. The rate of disappearance of Mn$\sb2$(CO)$\sb{10}$ and formation of products exhibit an inverse (CO) dependence.
When the reaction of Mn$\sb2$(CO)$\sb{10}$ with HSnBu$\sb3$ is performed under 1 atm AR, the rate of disappearance of Mn$\sb2$(CO)$\sb{10}$ is much faster than when CO is present, HMn(CO)$\sb5$ forms in much greater quantities than Bu$\sb3$SnMn(CO)$\sb5$, and a third product, identified as HMn(CO)$\sb4$(SnBu$\sb3$)$\sb2$, forms as the other major product. The above observations are consistent with a mechanism involving oxidative addition of HSnBu$\sb3$ to Mn$\sb2$(CO)$\sb9$.
The reactions of HSnBu$\sb3$ with Mn(CO)$\sb4$L$\cdot$ (L = CO or PR$\sb3$) and Mn$\sb2$(CO)$\sb7$L$\sb2$ were studied by flash photolysis. In every case examined, HSnBu$\sb3$ undergoes oxidative addition with Mn$\sb2$(CO)$\sb7$L$\sb2$. However, H-atom transfer to Mn(CO)$\sb4$L$\cdot$ does not occur. For L = CO, PMe$\sb3$, P(i-Bu)$\sb3$, and P(O-i-Pr)$\sb3$, the initial product of oxidative addition, Mn$\sb2$(CO)$\sb7$L$\sb2$(H)(SnBu$\sb3$), is observed. At longer time intervals, this intermediate disappears by reductive elimination of HMn(CO)$\sb4$L. Mn$\sb2$(CO)$\sb7$L$\sb2$(H)(SnBu$\sb3$) is not observed when the metal center is crowded as in the cases of L = P(i-Pr)$\sb3$ and P(C$\sb6$H$\sb{11}$)$\sb3$ because oxidative addition is slow relative to reductive elimination.
The transient absorbance decay of Mn$\sb2$(CO)$\sb7$L$\sb2$ in the presence of HSnBu$\sb3$ obeys pseudo-first-order kinetics. Plots of K$\sb{\rm obs}$ vs. (HSnBu$\sb3$) are linear for L = P(i-Bu)$\sb3$, P(i-Pr)$\sb3$, and P(C$\sb6$H$\sb{11}$)$\sb3$. However, for L = PMe$\sb3$ and P(n-Bu)$\sb3$, the k$\sb{\rm obs}$ vs (HSnBu$\sb3$) plot is non-linear throughout the entire (HSnBu$\sb3$) range. A mechanism involving a rate determining equilibrium between unbridged Mn$\sb2$(CO)$\sb7$L$\sb2$ and semi-bridged Mn$\sb2$(CO)$\sb7$L$\sb2$ prior to oxidative addition of HSnBu$\sb3$ accounts for the experimental observations.
Issue Date:1990
Rights Information:Copyright 1990 Sullivan, Richard Joseph
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9114428
OCLC Identifier:(UMI)AAI9114428

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