Structure and bonding: The synthesis and characterization of heteronuclear clusters

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Title: Structure and bonding: The synthesis and characterization of heteronuclear clusters
Author: Bachman, Robert Edward
Advisor: Whitmire, Kenton H.
Degree: Doctor of Philosophy thesis
Abstract: The reaction of $\rm NaAsO\sb2, TeO\sb2$, and $\rm SeO\sb2$ with methanolic solutions of KOH and $\rm Fe(CO)\sb5$ produces the isoelectronic clusters ($\rm HAs\{Fe(CO)\sb4\}\sb3\rbrack\sp{2-}, \lbrack Te\{Fe(CO)\sb4\}\sb3\rbrack\sp{2-}$, and $\rm \lbrack Se\{Fe(CO)\sb4\}\sb3\rbrack\sp{2-}$. The selenium cluster, however, is unstable and rapidly loses CO to form the closo cluster $\lbrack\rm SeFe\sb3(CO)\sb9\rbrack\sp{2-}. \lbrack Te\{Fe(CO)\sb4\}\sb3\rbrack\sp{2-}$ can also be transformed into the related closo cluster ($\rm TeFe\sb3(CO)\sb9\rbrack\sp{2-}$ by either pyrolysis or photolysis. In contrast, pyrolysis or photolysis of $\rm\lbrack HAs\{Fe(CO)\sb4\}\sb3\rbrack\sp{2-}$ yields the higher nuclearity species $\rm \lbrack As\sb2Fe\sb5(CO)\sb{17}\rbrack\sp{2-}$. The stepwise protonation of $\rm\lbrack EFe\sb3(CO)\sb9\rbrack\sp{2-}$ (E = Se, Te) allows for the preparation of either $\rm \lbrack HEFe\sb3(CO)\sb9\rbrack\sp-$ or $\rm H\sb2EFe\sb3(CO)\sb9$ in good yield. Low temperature $\rm\sp1H$ NMR studies of the protonation process suggest that the basic sites on the cluster are the iron-iron bonds rather than the main-group element. Spectral and structural characterization of these related clusters allows for the effect of cluster charge on structure to be probed. Reaction of $\rm\lbrack TeFe\sb3(CO)\sb9\rbrack\sp{2-}$ with solid CuCl produces the unusual Lewis acid-base adduct $\rm\lbrack TeFe\sb3(CO)\sb9(CuCl)\rbrack\sp{2-}$. This cluster can also be viewed as the initial step in the copper oxidation of the metal cluster, which produces the well known cluster $\rm Fe\sb3(CO)\sb9Te\sb2$. The reaction of elemental tellurium with $\rm Na\sb2Fe(CO)\sb4$ yields the unstable cluster $\rm\lbrack Fe\sb2(CO)\sb6(Te\sb2)\sb2\rbrack\sp{2-}$. Reaction of this unstable cluster with alkylating agents such as iodomethane and diiodomethane produces $\rm Fe\sb2(CO)\sb6(TeMe)\sb2$ and $\rm Fe\sb2(CO)\sb6(Te\sb2CH\sb2)$ respectively, along with elemental tellurium. Oxidation of $\rm\lbrack Fe\sb2(CO)\sb6(Te\sb2)\sb2\rbrack\sp{2-}$ with $\rm\lbrack Cu(MeCN)\sb4\rbrack BF\sb4$ gives the known cluster $\rm Fe\sb2(CO)\sb6Te\sb2$ and tellurium metal. The reaction of $\rm TeCl\sb4$ with iron carbonylate anions produces a variety of products: $\rm Fe\sb2(CO)\sb6Te\sb2, Fe\sb3(CO)\sb9Te\sb2$, or $\rm\lbrack TeFe\sb3(CO)\sb9\rbrack\sp{2-}$, depending on the conditions employed. The reactive cluster $\rm Fe\sb2(CO)\sb6Te\sb2$ was structurally characterized as a 2:1 adduct with $\rm\lbrack Et\sb4N\rbrack Cl$. The reaction of the dinuclear group VI anions $\rm\lbrack M\sb2(CO)\sb{10}\rbrack\sp{2-}$ (M = Cr, Mo, W) with $\rm Ph\sb2BiCl$ produces the metallated organobismuth clusters $\rm\lbrack Ph\sb2Bi\{M(CO)\sb5\}\sb2\rbrack\sp-$. The analogous reaction with $\rm\lbrack Fe\sb2(CO)\sb8\rbrack\sp{2-}$ generates $\rm\lbrack Ph\sb2Bi\{Fe(CO)\sb4\}\sb2\rbrack\sp-$. The reaction of the previously synthesized cluster $\rm\lbrack Ph\sb2BiFe(CO)\sb4\rbrack\sp-$ with $\rm Fe\sb2(CO)\sb9$ or $\rm Cr(CO)\sb5THF$ produces $\rm\lbrack Ph\sb2Bi\{Fe(CO)\sb4\}\sb2\rbrack\sp-$ or the heterometallic $\rm\lbrack Ph\sb2Bi\{Fe(CO)\sb4\}\{Cr(CO)\sb5\}\rbrack\sp-$ respectively. Comparison of the structural parameters seen in these clusters and other related organobismuth species provides insight into the nature of the bonding at bismuth in compounds of this type. Additionally, in contrast to previous reports, the reactivity of $\rm\lbrack Ph\sb2BiFe(CO)\sb4\rbrack\sp-$ observed in these studies suggests that the bismuth atom is the site of nucleophillic attack.
Citation: Bachman, Robert Edward. (1994) "Structure and bonding: The synthesis and characterization of heteronuclear clusters." Doctoral Thesis, Rice University.
Date: 1994

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