Synthesis, Structure, and Reactivity of High-Nuclearity Carbido Clusters of Rhenium

Henly, Timothy James

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Description

Title

Synthesis, Structure, and Reactivity of High-Nuclearity Carbido Clusters of Rhenium

Author(s)

Henly, Timothy James

Issue Date

1988

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

Abstract

• The cluster anion (Re$\sb7$C(CO)$\sb{21}\rbrack\sp{3-}$ reacts with late transition metal-based electrophiles to yield the mixed-metal clusters (Re$\sb7$C(CO)$\sb{21}$ML$\sb{\rm n}\rbrack\sp{2-}$ and with H$\sp+$ to yield the hydrido species (HRe$\sb7$C(CO)$\sb{21}\rbrack\sp{2-}$. These complexes have been fully characterized by IR, $\sp1$H NMR, and fast-atom bombardment mass spectroscopies. $\sp1$H and $\sp $C NMR, IR, and cyclic voltammetry studies on selected complexes indicate that the (Re$\sb7$C(CO)$\sb{21}\rbrack\sp{3-}$ cap is a poorer electron donor to the ML$\sb{\rm n}\sp+$ moiety than the cyclopentadienide ligand in the analogous compounds $(\eta\sp5$-C$\sb5$H$\sb5$)ML$\sb{\rm n}$. Variable-temperature $\sp $C NMR studies and X-ray diffraction experiments on several of the mixed-metal clusters demonstrate that each of these compounds adopts a trans-bicapped octahedral configuration of metal atoms, i.e., the ML$\sb{\rm n}$ fragment symmetrically caps the triangular face opposite the unique Re(CO)$\sb3$ group. The compound (HRe$\sb7$C(CO)$\sb{21}\rbrack\sp{2-}$ is a mixture of two isomers, which differ in the position of the hydride ligand on the metal framework.
• A set of clusters (Re$\sb7$C(CO)$\sb{21}$HgY) $\sp{2-}$ (Y = halide, pseudohalide, or hydrocarbyl) has also been prepared and characterized. Some of these compounds undergo ligand-exchange reactions of the type: (Re$\sb7$C(CO)$\sb{21}$HgY) $\sp{2-}$ + YHgZ ${}\sbsp{\gets}{\to}$ (Re$\sb7$C(CO)$\sb{21}$HgZ) $\sp{2-}$ + HgY$\sb2$. The position of the equilibrium depends on the electronic properties of Y and Z, with electron-withdrawing groups facilitating ligand redistribution.
• The reaction of Re$\sb2$(CO)$\sb $ with sodium in a 1:1.2 molar ratio in triglyme at 200$\sp\circ$C yields the new rhenium carbido clusters (HRe$\sb6$C(CO)$\sb \rbrack\sp{3-}$ and (HRe$\sb5$C(CO)$\sb \rbrack\sp{2-}$. The former complex contains an octahedral arrangement of Re(CO)$\sb3$ units; it reacts with transition metal electrophiles to give the mixed-metal clusters (HRe$\sb6$C(CO)$\sb $ML$\sb{\rm n}\rbrack\sp{2-}$. The latter cluster consists of a square-based pyramid of rhenium atoms with a $\mu\sb5$-carbido atom 0.10 A below the basal plane and a semibridging carbonyl on one basal-apical edge. This compound is the first example of such a M$\sb5$C complex outside of the iron triad elements.

Graduation Semester

1988

Type of Resource

text

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