Competing reaction pathways in the photochemical reactions of metal carbonyl compounds

Sullivan, Richard Joseph

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https://hdl.handle.net/2142/22666 Copy

Description

Title

Competing reaction pathways in the photochemical reactions of metal carbonyl compounds

Author(s)

Sullivan, Richard Joseph

Issue Date

1990

Doctoral Committee Chair(s)

Brown, Theodore L.

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Chemistry, Inorganic

Language

eng

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.

Type of Resource

text

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Copyright and License Information

Copyright 1990 Sullivan, Richard Joseph

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