Actinide porphyrin complexes

Milam, Stanley Nemec

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https://hdl.handle.net/2142/19431 Copy

Description

Title

Actinide porphyrin complexes

Author(s)

Milam, Stanley Nemec

Issue Date

1989

Doctoral Committee Chair(s)

Kenneth S. Suslick

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
• Chemistry, Nuclear

Language

eng

Abstract

• The first bis(porphyrin)actinide complexes have been prepared by reaction of M(NEt$\sb2$)$\sb4$ (where M = Th, U) with H$\sb2$TPP or H$\sb2$OEP. The coordination geometry of (TPP)$\sb2$Th is a distorted square-prism where the thorium center is displaced 1.47 A from each of the porphyrin N$\sb4$ planes; the porphyrin planes are separated by 2.94 A. The porphyrin macrocycles, held in such close proximity, interact electronically as shown by a shift in the porphyrin Soret band to higher energy and unusually facile oxidation processes relative to related monoporphyrin complexes.
• Oxidation of (TPP)$\sb2$M yields porphyrin-based radical cation complexes ((TPP)$\sb2$M$\sp+$) (SbCl$\sb6\sp-$) and dicationic complexes, ((TPP)$\sb2$M$\sp{2+}$) (SbCl$\sb6\sp-$) $\sb2$. The porphyrin planes of ((TPP)$\sb2$Th$\sp+$) (SbCl$\sb6\sp-$) are separated by 2.89 A, this separation is slightly less than that of (TPP)$\sb2$Th.
• The EPR spectrum of ((TPP)$\sb2$Th$\sp+$) (SbCl$\sb6\sp-$) is that of a simple organic radical (g = 2.0016) while the uranium complex shows unusual signals at g$\sb{\rm para}$ = 3.175 and g$\sb{\rm perp}$ = 1.343. SQUID measurements on ((TPP)$\sb2$Th$\sp+$) (SbCl$\sb6\sp-$) suggest that above 70 K there are thermally populated excited state(s) with f-orbital character. Above 200 K, ((TPP)$\sb2$U$\sp+$) (SbCl$\sb6\sp-$) apparently adopts S = 3/2 spin state(s), but below 70 K the spin state appears to be S = 1/2. This behavior may be due to antiferromagnetic coupling of the porphyrin radical to the f$\sp2$ U$\sp{\rm IV}$ center.
• The dicationic complex ((TPP)$\sb2$Th$\sp{2+}$) (SbCl$\sb6\sp-$) $\sb2$ is essentially diamagnetic. This suggests that there is a direct porphyrin-porphyrin interaction that results in a new set of molecular orbitals composed of both porphyrin ligands and perhaps some metal contribution. All of the oxidized complexes have near-IR absorptions due to transitions between these molecular orbitals.
• Mono(porphyrin)actinide complexes may be prepared directly from UCl$\sb4$ or ThCl$\sb4$. The uranium center of (TPP)UCl$\sb2$(thf) is displaced 1.29 A from the porphyrin macrocycle. Reaction of Na (OCH(CF$\sb3$)$\sb2$) with (TPP)UCl$\sb2$ in 1,2-dimethoxyethane (dme) yields $\{$Na(dme)$\sb3\sp+\}\{$(TPP)U (OCH(CF$\sb3$)$\sb2$) $\sb3\sp-\}$. The uranium center of this complex is displaced 1.43 A from the porphyrin macrocycle plane. Reaction of KOC$\sb6$H$\sb3$Cl$\sb2$ with (TPP)UCl$\sb2$ yields (TPP)U(OC$\sb6$H$\sb3$Cl$\sb2$)$\sb2$, which has an available coordination site and binds Lewis bases. (TPP)U(OC$\sb6$H$\sb3$Cl$\sb2$)$\sb2$ reacts with O$\sb2$ to form the first U$\sp{\rm VI}$ porphyrin complex (TPP)U(O)(OC$\sb6$H$\sb3$Cl$\sb2$)$\sb2$. This oxo complex cannot oxidize PPh$\sb3$ to OPPh$\sb3$.

Type of Resource

text

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Copyright and License Information

Copyright 1989 Milam, Stanley Nemec

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