University of Illinois Urbana-Champaign

Substitution and redox reactions of heptarhenium cluster derivatives

Simerly, Scott W.

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Description

Title
Substitution and redox reactions of heptarhenium cluster derivatives
Author(s)
Simerly, Scott W.
Issue Date
1991
Doctoral Committee Chair(s)
Shapley, John R.
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 second-order rate constants for the reactivity of (Re$\sb7$C(CO)$\sb{21}$Rh(CO)$\sb2$) $\sp{2-}$ towards phosphorus donors were determined. In order to correlate the results to electronic and/or steric effects, steric profiles relating log k$\sb2$ to an intrinsic reactivity $(\alpha),$ an electronic parameter $(\beta),$ and a steric parameter $(\theta)$ were constructed. From differences in intrinsic reactivity for phosphines and phosphites, an intermediate configuration involving a bridging carbonyl has been proposed for the reaction of (Re$\sb7$C(CO)$\sb{21}$Rh(CO)$\sb2$) $\sp{2-}$ with various phosphorus donors (PY$\sb3).$
  • Nitrosylation of a series of mixed-metal heptarhenium clusters, (Re$\sb7$C(CO)$\sb{21}$ML$\sb{\rm n}$) $\sp{2-},$ gave the mono-substituted products, (Re$\sb7$C(CO)$\sb{20}$ML$\sb{\rm n}\rbrack\sp-.$ A variety of spectroscopic techniques were used to characterize the reaction products. Variable temperature $\sp{13}$C NMR studies determined the solution structure of (Re$\sb7$C(CO)$\sb{20}$(NO)Rh(CO)$\sb2$) $\sp-.$ From kinetic studies, the nitrosyl substituted cluster (Re$\sb7$C(CO)$\sb{20}$(NO)Rh(CO)$\sb2$) $\sp-$ exhibits enhanced reactivity toward phosphorus ligands in comparison with (Re$\sb7$C(CO)$\sb{21}$Rh(CO)$\sb2$) $\sp{2-}.$
  • The carbonyl ligands bound to (Re$\sb7$C(CO)$\sb{21}$Rh(CO)$\sb2$) $\sp{2-}$ display unusual intermolecular and intramolecular exchange. Upon treatment with $\sp{13}$CO, (Re$\sb7$C(CO)$\sb{21}$Rh(CO)$\sb2$) $\sp{2-}$ is selectively $\sp{13}$CO enriched to ($\rm Re(CO)\sb3Re\sb6C(\sp{13}CO)\sb{18}Rh(\sp{13}CO)\sb2\rbrack \sp{2-}$. A capping Re(CO)$\sb3$ moiety trans to the rhodium cap remains unenriched. Formation of the radical species (Re$\sb7$C(CO)$\sb{21}$Rh(CO)$\sb2\rbrack\sp-$ by chemical oxidation results in complete carbonyl scrambling, which is revealed upon reduction to the parent cluster ($\rm Re(\sp{13}CO)\sb3Re\sb6C(\sp{13}CO)\sb{18}Rh(\sp{13}CO)\sb 2\rbrack \sp{2-}.$ The selectively $\sp{13}$Co enriched cluster (Re(CO)$\sb3$Re$\sb6$C($\sp{13}$CO)$\sb{18}$) $\sp{2-}$ has been formed in a decapping reaction of ($\rm Re(CO)\sb3Re\sb6C(\sp{13}CO)\sb{18}Rh(\sp{13}CO\sb2\rbrack \sp{2-}$ with excess PPh$\sb3$ in acetonitrile.
  • Two-electron oxidation of (Re$\sb7$C(CO)$\sb{21}$) $\sp{3-}$ in the presence of P(OPh)$\sb3$ affords (Re$\sb7$C(CO)$\sb{21}$(P(OPh)$\sb3)$) $\sp-.$ $\sp{13}$C NMR indicates that this cluster exhibits partial charge separation. (Re$\sb7$C(CO)$\sb{21}$(P(OPh)$\sb3)$) $\sp-$ decomposes in acetonitrile to form (Re$\sb6$C(CO)$\sb{19}$) $\sp{2-}$ and (Re(CO)$\sb3$(P(OPh)$\sb3)\sb2$(NCCH$\sb3)$) $\sp+,$ and therefore it represents a directly observed intermediate in a cluster decapping reaction.
Type of Resource
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Copyright and License Information
Copyright 1991 Simerly, Scott W.

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