Expansion of Low- and Mid-Valent Organometallic Uranium Chemistry

Description

<p>A series of uranium benzyl compounds supported by two
hydrotris(3,5-dimethylpyrazolyl) borate (Tp*) ligands has been synthesized and
characterized. In addition to the
previously reported Tp*₂U(CH₂Ph) (<b>2-Bn</b>), examinations of both steric (<i>tert</i>-butyl, <i>iso</i>-propyl)
and electronic (methoxy, picolyl) changes on the aromatic ring led to the
formula Tp*₂U(CH₂Ar) (Ar = 4-<i>tert</i>-butylphenyl (<b>2-<i>^t</i>Bu</b>), 4-isopropyl (<b>2-ⁱPr</b>), 2-picolyl (<b>2-pyr</b>), 3-methoxyphenyl (<b>2-OMe</b>). Treatment of the entire series
of benzyl compounds with azidotrimethylsilane results in the formation of a
neutral, monomeric U(III) compound, Tp*₂U(N₃) (<b>3-N₃</b>), and substituted benzyltrimethylsilane.
While there was no observed change in reactivity among the benzyl compounds and
Me₃SiN₃, treatment of these compounds with
triphenylphosphine oxide saw unique carbon-carbon coupling occur for three of
the substituted benzyl compounds. With a single equivalent of OPPh₃,
the following products were isolated: Tp*₂U[OP(C₆H₅)(C₆H₅CH₂C₆H₅)]
(<b>4-Ph</b>), Tp*₂U[OP(C₆H₅)(C₆H₅-<i>p</i>-<i>i</i>PrC₆H₄)]
(<b>4-ⁱPr</b>), Tp*₂U[OP(C₆H₅)(C₆H₅-<i>p</i>-<i>t</i>BuC₆H₄)]
(<b>4-<i>^t</i>Bu</b>),
Tp*₂U[OP(C₆H₅)(C₆H₅-<i>m</i>-OCH₃C₆H₄)]
(<b>4-OMe</b>). </p>

<p> A family of uranium(IV) imido
complexes of the form Tp*₂U(NR) (R = benzyl (<b>7-Bn</b>), <i>para</i>-tolyl (<b>7-Tol</b>), <i>para</i>-methoxyphenyl (<b>7-OMe</b>),
2,6-diethylphenyl (<b>7-detp</b>),
2,6-diisopropylphenyl (<b>7-dipp</b>)) have
been generated by bibenzyl extrusion from <b>2-Bn</b>.
When <b>7-Bn</b> and <b>7-Tol</b>, along with previously reported Tp*₂U(N-Ph) (<b>7-Ph</b>) and Tp*₂U(N-Ad) (<b>7-Ad</b>), are treated with isocyanates or
isothiocyanates, they readily undergo [2π+2π]-cycloaddition to generate
κ²-ureato and κ²-thioureato derivatives, respectively.
Use of phenylisoselenocyanate with <b>7-Tol</b>
and <b>7-Ph</b> generates a rare κ²-selenoureato
complex. Treating <b>7-Tol</b> and <b>7-OMe</b> with benzonitrile or
4-cyanopryidine results in unusual products of multiple bond metathesis, namely
κ¹-amidinate U(IV) complexes. </p>

<p>A family of
dinuclear bis(Tp*) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) uranium
compounds with conjugated organic linkers was synthesized to explore possible
electronic communication between uranium ions. Trivalent diuranium phenyl alkynyl compounds, Tp*₂UCC(1,3-C₆H₄)CCUTp*₂
(<b>14-<i>meta</i></b>)
or Tp*₂UCC(1,4-C₆H₄)CCUTp*₂ (<b>14-<i>para</i></b>),
and tetravalent diuranium phenylimido compounds, Tp*₂U(N-1,3-C₆H₄-N)UTp*₂
(<b>15-<i>meta</i></b>)
and Tp*₂U(N-1,4-C₆H₄-N)UTp*₂ (<b>15-<i>para</i></b>),
were generated from trivalent Tp*₂UCH₂Ph. All compounds
were fully characterized both spectroscopically and structurally. The
electronic structures of all derivatives were interrogated using magnetic
measurements, electrochemistry, and were the subject of computational analyses.
All of this data combined established that little electronic communication
exists between the uranium centers in these trivalent and tetravalent diuranium
molecules.</p>

<p>Uranium mono(imido) species have been prepared via oxidation of Cp*U(^MesPDI^Me)(THF)
(<b>16-Cp</b>*) and [Cp^PU(^MesPDI^Me)]₂
(<b>16-Cp^P</b>) (Cp* = <i>η</i>⁵-1,2,3,4,5-pentamethylcyclopentadienide;
Cp^P = 1-(7,7-dimethylbenzyl)cyclopentadienide;
^MesPDI^Me = 2,6-((Mes)N=CMe)₂C₅H₃N,
Mes = 2,4,6-trimethylphenyl) with organoazides.
Treating either with N₃DIPP formed uranium(IV) mono(imido)
complexes, Cp^PU(NDIPP)(^MesPDI^Me) (<b>17-Cp^P</b>) and Cp*U(NDIPP)(^MesPDI^Me)
(<b>17-Cp*</b>), featuring reduced [^MesPDI^Me]^1-.
Addition of electron-donating 1-azidoadamantane (N₃Ad) to <b>16-Cp*</b> generated a dimeric product, [Cp*U(NAd)(^MesHPDI^Me)]₂
(<b>18</b>), from radical coupling at the <i>para</i>-pyridine position of the
pyridine(diimine) ligand and H-atom abstraction, formed through a monomeric
intermediate that was observed in solution but could not be isolated. To
support this, Cp*U(<i>^t</i>Bu-^MesPDI^Me)(THF)
(<b>16-<i>^t</i>Bu</b>),
which has a <i>tert</i>-butyl group
protecting the <i>para</i>-position, was
also treated with N₃Ad,
and the monomeric product, Cp*U(NAd)(<i>^t</i>Bu-^MesPDI^Me)
(<b>17-<i>^t</i>Bu</b>),
was isolated. All isolated complexes were analyzed spectroscopically and
structurally, and dynamic solution behavior was examined using electronic
absorption spectroscopy. </p>

Links & Downloads

1. 10.25394/pgs.8244512.v1

Tags

Inorganic Chemistry

Organometallic Chemistry

organometallic

uranium

scorpionate ligand

actinide compounds

f-block elements

Additional Fields

Identifer	oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/8244512
Date	16 August 2019
Creators	Caleb J Tatebe (6812630)
Source Sets	Purdue University
Detected Language	English
Type	Text, Thesis
Rights	CC BY 4.0
Relation	https://figshare.com/articles/Expansion_of_Low-_and_Mid-Valent_Organometallic_Uranium_Chemistry/8244512