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Title:Substitution and redox reactions of heptarhenium cluster derivatives
Author(s):Simerly, Scott W.
Doctoral Committee Chair(s):Shapley, John R.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
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.
Issue Date:1991
Rights Information:Copyright 1991 Simerly, Scott W.
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9210992
OCLC Identifier:(UMI)AAI9210992

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