Werner-Type Complexes of Uranium(III) and (IV)

Werner-Type Complexes of Uranium(III) and (IV)

Article

Judith Riedhammer, J. Rolando Aguilar-Calderon, Matthias Miehlich, Dominik P. Halter, Dominik Munz,

Frank W. Heinemann, Skye Fortier, Karsten Meyer,* and Daniel J. Mindiola*

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.9b03229

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sı Supporting Information

ABSTRACT: Transmetalation of the β-diketiminate salt [M]-

Ph−

−

[

nacnac ] (M = Na or K; nacnac = {PhNC(CH )} CH )

3 2

with UI (THF) resulted in the formation of the homoleptic,

octahedral complex [U( nacnac ) ] (1). Green colored 1 was

fully characterized by a solid-state X-ray diﬀraction analysis and a

combination of UV/vis/NIR, NMR, and EPR spectroscopic

studies as well as solid-state SQUID magnetization studies and

density functional theory calculations. Electrochemical studies of 1

revealed this species to possess two anodic waves for the U(III/IV)

and U(IV/V) redox couples, with the former being chemically

accessible. Using mild oxidants, such as [CoCp ][PF ] or

[

FeCp ][Al{OC(CF ) } ], yields the discrete salts [1][A] (A =

3 3

−

PF , Al{OC(CF ) } ), whereas the anion exchange of [1][PF ] with NaBPh yields [1][BPh ].

3 3

Dipp

INTRODUCTION

UCl (THF)] and [{( nacnac )UCl} (μ -Cl) ]Cl. In

■

Dipp−

some cases, disubstitution of nacnac

generates the

Alfred Werner’s disapproval of the complex ion-chain theory

proposed by Jørgensen and Blomstrand, via the introduction

Dipp

3 Me

Dipp

rearranged species [( nacnac )(η - nacnac )UI],

where one ligand has changed hapticity, most likely due to

steric constraints. It has been found that the reactivity of

[( nacnac )UI (THF) ] allows for halide substitution,

dehydrohalogenation of the β-diketiminate, reduction, and

of coordination complexes and the concept of Nebenvalenz,

resulted in the birth of a ﬁeld we now term coordination

Dipp

2 2

chemistry. Soon after, it was realized that the properties of

these so-called “complexes” are dictated by their electronic

structures. This was understood by an ionic bonding picture

oxidation reactions. Uranyl(VI)- and (V)-based systems have

15−18

also been reported by this ligand scaﬀold.

Whereas the

called crystal-ﬁeld theory and, subsequently, by a more

tBu

use of the more sterically hindered ligand derivative nac-

sophisticated model that is commonly termed ligand-ﬁeld

Dipp− tBu

Dipp−

−

nac

( nacnac

= {DippNC( Bu)} CH ) results in

theory. More than a century after the introduction of

tBu

Dipp

only one ligand being incorporated, namely [( nacnac )-

homoleptic and stereoisomeric complexes by Werner (i.e.,

−

UCl₃]. Lappert’s {Me SiNC(Ph)} CH chelate ensues from

3 2

reactions of ligand cannibalization, forming complexes with

,3-diaza-allyl ligands. Other examples of uranium complexes

using β-diketiminate-like scaﬀolds include a macrocycle

[

Co(en) ]Cl , en = H NCH CH NH or “hexol” forms), we

3 3 2 2 2 2

now wish to report the structural, spectroscopic, magnetic, and

electrochemical properties of Werner-type chiral complexes of

the heaviest naturally abundant metal: uranium. Herein, we

report the ﬁrst examples of homoleptic U(III) and U(IV) ions

0−22

tetramethyltetraazaannulene,

a dianionic and a tridentate

Ph−

N-aryloxy-β-diketiminate, a cyanopentadienyl dianion, and

an aza β-diketiminate ligand 2-(4-tolyl)-1,3-bis(quinolyl)-

supported by the β-diketiminate ligand

nacnac

Ph−

−

(

nacnac

= {PhNC(CH )} CH , nacnac , where R1

malondiiminate).

is the β-carbon substituent and R2 is the α-N group) and

discuss their spectroscopic, magnetic, and electrochemical

properties. Solid-state structural studies for these chiral

uranium ions are also presented.

Unlike the complexes [U(acac) ] and [U(N[R]Ar ) ],

along with the latter’s one-electron oxidized counterpart,

On the basis of this precedence, we thought that the use of a

less studied and less sterically encumbered β-diketiminate

nacnac , would provide access to

homoleptic complexes of uranium. Our goal was to

selectively transmetallate three chelating ligands onto the

Ph−

ligand, namely

MeL 3

there are no documented examples of homoleptic Werner-type

complexes of uranium with the ubiquitous β-diketiminate

Received: November 12, 2019

ligand.

For example, using the more traditional β-

Dipp− Me

Dipp−

diketiminate ligand nacnac

( nacnac

= {DippNC-

−

(

CH )} CH , Dipp = 2,6- Pr C H ) results in the formation of

Dipp

monosubstituted complexes, such as [( nacnac )-

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

whereas the ﬁrst anodic wave, assigned to the U(III/IV)

Article

U(III) ion to form D symmetric, enantiomeric pairs. Herein,

we present homoleptic examples of U(III) and U(IV)

complexes using a phenyl-substituted β-diketiminate ligand

and discuss its structural, redox, spectroscopic, and magnetic

properties.

RESULTS AND DISCUSSION

Using a modiﬁed protocol of one reported in the literature,

we developed a convenient entry to the free-base nacnac H

in a 47% yield by slowly adding HCl at low temperatures to a

■

mixture of acetylacetone dissolved in aniline. Upon

completion of the reaction, the solids must be extracted into

CH Cl and neutralized with a saturated aqueous solution of

Na CO , and the organic layer separated and then dried with

MgSO ; the residue (oily material) is then crystallized from

MeOH at −35 °C. The treatment of the crystallized β-

diketimine with a slight excess of K{N(SiMe ) } under an inert

Figure 1. X-band EPR spectrum of 1, recorded in toluene (40 mM) at

9 K (green trace). Simulation (black trace) gives g = 0.37, g = 1.45,

atmosphere and in cold Et O resulted in the immediate

precipitation of a ﬂuﬀy and voluminous yellow solid, which was

and g = 1.20 with W = 130 mT, W = 120 mT, and W = 140 mT.

isolated, washed with cold Et O, dried under vacuum, and

The background cavity is marked with an asterisk (*).

subsequently identiﬁed to be the salt [K][ nacnac ] on the

basis of H and C NMR spectral data. As represented in

Scheme 1, the addition of 3 equiv [K][ nacnac ] (quite

U(III/IV) and U(IV/V) redox couples, respectively (Figure 2,

top). A linear sweep scan also conﬁrmed these two waves to be

oxidations (Figure S33). Figure 2 also shows a cathodic wave

for 1 above −3 V, but such a feature is clearly irreversible,

Scheme 1. Synthesis of Homoleptic and Chiral Complexes 1

and [1][X]

possibly an oligomer containing bridged K-arene units) to

either UI (THF)₄or UI (1,4-dioxane)

and stirring the

1.5

reaction mixture over 2.5 h at room temperature led to the

formation of a dark green solution, from which the complex

[

U( nacnac ) ] (1) was isolated in 71% yield after

recrystallization from a concentrated toluene solution at −35

C. In agreement with its expected D symmetry, the H

NMR spectrum of 1 reveals this species to possess symmetri-

cally equivalent ligands with three aryl resonances in the

aromatic region in addition to one paramagnetically shifted

resonance for the β-methyl at −31.63 ppm. The γ-CH has not

been observed and is likely broadened into the baseline. The

X-band EPR spectrum of 1 (Figure 1), recorded in a frozen

toluene solution at 9 K, reveals a broad feature (W = 130 mT,

W = 120 mT, and W = 140 mT) with rhombic symmetry and

simulated eﬀective g values of g = 0.37, g = 1.20, and g =

Figure 2. Top: cyclic voltammograms of 1 measured in a THF

solution with ∼0.1 M [N(n-Bu) ][PF ] as electrolyte, including the

.45, in accordance with the complexes’ low-temperature

magnetic moment (vide infra).

Fc /Fc redox wave (back trace) and scans of only both oxidations of 1

A potentiodynamic electrochemical study (cyclic voltamme-

(

red trace). Bottom: cyclic voltammograms of 1 scanned with scan

try, CV) of 1, in a THF solution containing [n-NBu ][PF ] as

rates (SR) started from 50 mV/s and ended with 1600 mV/s

an electrolyte, revealed two redox features at −1.69 and 0.15 V

measured in a THF solution with ∼0.1 M [N(n-Bu) ][PF ] as

(

referenced to FeCp₂⁰at 0.0 V), which was suggestive of

electrolyte.

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

couple, is fully reversible at various scan rates from 50 to 1600

mV/s (Figure 2, bottom). The more positive scan at 0.15 V is

only quasi-reversible, especially at a higher scan rate of 1600

mV/s (Figure 2, bottom).

Chemical oxidation of 1 with a relatively weak oxidant, such

as [CoCp ][PF ], resulted in the precipitation of the U(IV)

species [U( nacnac ) ][PF ] [1][PF ] in an 87% yield with

concomitant formation of CoCp (Scheme 1). Strangely, for a

symmetrical U(IV) ion, the H NMR spectrum of 1 , recorded

in methylene chloride at 293 K, shows four very broad signals

Figure S6 ). Similar to 1, one-electron oxidized 1 features

three aryl resonances in the aromatic region and one

paramagnetically shifted resonance for the β-methyl at −1.87

ppm; a resonance for the methine-CH could not be detected

and assigned.

Complementary to 1, complex [1][PF ] shows a reversible

cathodic and a quasi-reversible anodic wave at −1.82 and 0.23

V (ΔE = 2.05 V), respectively, which were corroborated by a

linear sweep scan, showing both anodic and cathodic responses

Figure S39). More soluble variants to [1][PF ], namely

[

1][Al{OC(CF ) } ] (69% yield) and [1][BPh ] (95% yield),

could be readily achieved via the oxidation of 1 with

[

FeCp ][Al{OC(CF ) } ] or alternatively by anion exchange

2 3 3 4

of [1][PF ] with NaBPh , respectively (Scheme 1). Despite

the CV data suggesting the presence of a second and

chemically accessible electrochemical oxidation wave for 1,

numerous eﬀorts to chemically access a U(V) salt remained

unsuccessful, often resulting in the formation of the free base

Ph 27

nacnac H, which is most likely due to the vulnerability of

Ph−

the

nacnac

ligand to oxidation and subsequent

Figure 3. Molecular representation of complexes Λ-1 (ORTEP, top)

and cationic Δ-[1][BPh ] (ORTEP, bottom) in crystals of solvate-

free 1 and [1][BPh ] with their ﬁrst coordination spheres (inserts).

demetalation. In fact, as shown in Figures S31 and S32, an

examination of the scan rate dependence for the second anodic

wave of 1 shows the irreversibility in the wave at a scan rate of

All hydrogen atoms and the BPh anion are omitted for clarity. All

thermal ellipsoids are shown at the 50% probability level. Only one of

the two enantiomers in the unit cell is shown for each complex for the

purpose of clarity.

0 mV/s, and it is quasi-reversible at much higher scan rates

(

1600 mV/s). Likewise, the CV data of [K][ nacnac ] reveal

an irreversible oxidation wave at −0.4 V, thus arguing for

ligand oxidation likely being the locus of reactivity for the

second quasi-reversible anodic wave (Figure S34 ). Given the

broad H NMR spectral features of both [1][PF ] and

Table 1. Selected Interatomic Distances (Å) and Angles

(

^d^e^g⁾ⁱⁿ¹^aⁿ^d^[¹^]^[^B^P^h4^]

[

1][BPh ] at room temperature, we conducted variable

[1]

[1][BPh₄]

temperature H NMR spectroscopic studies for these two

species in the range of 125 to −35 °C (Figures S10 −S16).

Interestingly, it was found that 1 , regardless of the counter

anion, exhibited sharpened signals at higher and at lower

temperatures. It is presently unclear why these signals are

rather broad at room temperatures.

U−N_a_v_g

U−N1

U−N2

U−N3

U−N4

U−N5

U−N6

2.458

2.404

2.458(2)

2.469(2)

2.450(2)

2.458(2)

2.457(2)

73.75(6)

74.98(6)

74.79(7)

174.07(6)

171.90(6)

170.81(6)

2.405(2)

2.390(2)

2.405(2)

2.413(2)

2.393(2)

2.420(2)

76.03(7)

75.02(7)

74.79(6)

172.98(7)

172.08(7)

172.88(7)

Solid-state structures of 1, [1][BPh ], and [1][Al{OC-

(

CF ) } ] were collected by single-crystal X-ray diﬀraction

∠_b_i_t_eN1−U−N2

∠_b_i_t_eN3−U−N4

∠_b_i_t_eN5−U−N6

∠N1−U1−N5 and ∠N2−U1−N5

∠N2−U1−N4 and ∠N1−U1−N3

∠N3−U1−N6 and ∠N4−U1−N5

3 4

studies with the ﬁrst two being displayed in Figure 3. Metrical

parameters for [1][BPh ] are quite similar to [1][Al{OC-

(

CF ) } ] (Table 1), and thus, we omit discussion of the latter

3 3 4

complex in the text. Each uranium ion is virtually conﬁned to

an octahedral geometry with an overall local D symmetry. As a

result of this geometry, the uranium complexes are chiral, with

the pair of enantiomers (Λ and Δ) being present in the unit

cell, given the centrosymmetric nature of the space group

surprising given the smaller size of the U(IV) ion versus the

U(III) ion, but this argues for the oxidation being metal-

centered, involving a nonbonding f-orbital. Indeed, density

(

P2 /c and P2 /n). Figure 1 (top) shows only the Λ isomer of

with the other enantiomer excluded for clarity, in which the

U(III) ion is slightly more distorted from that observed for 1

functional theory (DFT) calculations indicate an f electron

(

Figure 1, bottom) when judged by the U−N distances and

conﬁguration for the cation 1 (vide infra and Figure S44 ).

N−U−N angles (Table 1). As expected, the oxidation of

trivalent 1 to tetravalent 1 results in a slight shortening of the

To further support the uranium ions’ formal oxidation states,

1 and [1][PF ] were subjected to spectroscopic and magnetic

U−N_a_v_gdistances from 2.458 to 2.404 Å. This feature is not

studies. The UV/vis/NIR electronic absorption spectra of 1

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

and [1][PF ] were recorded in a spectral range from 250 to

500 nm. The UV/vis region of 1 and [1][PF ] (Figure 4 ) are

Figure 5. Averaged temperature-dependent magnetic susceptibility

data of three independently synthesized samples of 1 (green trace)

and [1][PF ] (red trace), plotted as μ vs T (right).

eff

properties for tri- and tetravalent coordination complexes of

uranium. The average eﬀective magnetic moment (μ ) for

eff

trivalent 1 is temperature-dependent and varies from 2.35 μ at

00 K to 0.80 μ_Bat 2 K. The low-temperature value is

33−36

unusually low for an f complex.

the relation 4μ_e_f_f= (g₁+ g₂+ g ) with the experimentally

However, by applying

determined eﬀective g values (Figure 1), the resulting value for

μ is calculated to be 0.96 μ , which is in excellent agreement

eff

with the experimentally determined magnetic moment of μ =

eff

.95 μ at 9 K. Notably, while characteristic for U(IV) f

complexes, even in nearly the same ligand environments, the

magnetic moment of 1 at 300 K is higher than that of its f

Figure 4. UV/vis/NIR electronic absorption spectra for 1 in toluene

analogue and was determined to be 2.81 μ . Also, typical for

U(IV) complexes, the temperature dependence is markedly

stronger, which is characteristic of temperature-independent

(

green trace) and [1][PF ] in methylene chloride (red trace) at 25

°C. Breaks in the NIR spectra are due to cutouts of the solvent

absorptions.

paramagnetism (TIP), with a typical μ_e_f_fof 0.52 μ at 2 K or

even lower; this is in agreement with the complex’s

dominated by intense absorption bands, and due to their

unusually large molar extinction coeﬃcients (ε), these bands

are assigned to metal−ligand charge-transfer transitions (either

metal-to-ligand or vice versa). Notably, trivalent 1 possesses a

well-resolved absorption band centered at 344 nm (ε = 61200

nonmagnetic H ground state.

A computational analysis by DFT was performed in order to

further elucidate the electronic structure of 1. Optimizations

of the structural parameters were subsequently performed,

where the aryl substituents were truncated by methyl groups

(BP86/DKH-def2-SVP). The obtained U−N bond lengths as

well as the nacnac N−U−N bond angles were in good

agreement with the structural parameters from the solid-state

structure; the mean deviation from the solid-state, single-

crystal XRD structure was 0.006 Å and 2.2° for the bond

lengths and angles, respectively. Molecular orbitals were then

obtained from single-point calculations at the B3PW91/DKH-

def2-TZVPP//BP86/DKH-def2-SVP level of theory. The

−

−1

cm ) with a shoulder at 429 nm (Figure 4, top, green

trace). The spectral region between 600 and 2100 nm (Figure

, bottom) shows a broad band of relatively high intensity

centered at 770 nm (ε_m_a_x= 1060 M⁻cm ), which is often

−1

seen for trivalent uranium complexes, albeit at slightly higher

4,27−30

energy (500−700 nm),

and this band could be assigned

to Laporte-allowed f → d transitions. A number of less-

intense, less-resolved Laporte-forbidden f → f transitions are

observed on the band’s bathochromic ﬂank. The UV/vis

calculations suggest an f electron conﬁguration with moderate

spectrum of [1][PF ] (Figure 4, top, red trace) shows multiple

overlapping charge-transfer transitions between 280 and 600

(Lowdin spin population at uranium of 2.6 electrons)

delocalization of the spin density onto the nacnac ligands

(Figure 6, top). Very little, if any, discrepancy was observed in

the spin densities using various levels of theory, but the BP86-

D3/DKH-def2-TZVPP//BP86-D3/DKH-def2-SVP and

BP86/DKH-def2-TZVPP//BP86/DKH-def2-SVP levels of

theory showed the least di ﬀ erence for truncated and

nontruncated models (Table S2). The molecular orbitals

obtained from the truncated model system were essentially

equivalent to those obtained without truncation. Plotting the

three singly occupied molecular orbitals associated with the f-

nm, with molar extinction coeﬃcients of ε = 49000 to 18000

−

−1

cm . Characteristic for tetravalent uranium complexes,

the NIR region features several sharp f → f transitions with

−

−1

molar extinction coeﬃcients up to ε = 55 M cm (Figure 4,

middle, red trace).

30,31

The magnetic properties of 1 and [1][PF ] were determined

by SQUID magnetization measurements in the temperature

range from 2 to 300 K and with an applied magnetic ﬁeld of 1

T. For reproducibility, the data were collected on three

independently synthesized samples (Figures S19 and S20), and

orbitals indicates the mixing of one orbital, namely f

y(3x ‑y )

the averaged data plotted as μ vs T are shown in Figure 5.

The pair of complexes 1/1 shows characteristic magnetic

with some π-orbitals derived from the β-diketiminate ligands.

The other two orbitals are essentially metal centered f_y_zand

eff

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Information is available free of charge at https://pubs.ac-

Article

CONCLUSION

■

In summary, we reported the ﬁrst examples of tris-homoleptic

β-diketiminate complexes of uranium. The reduction of steric-

bulk by using phenyl groups allows three chelating ligands to

coordinate to uranium in a propeller-like fashion, thus

rendering these compounds chiral. We also demonstrate how

precursor 1 can be smoothly oxidized to 1 with minimal

geometrical rearrangement, when judged by single-crystal

solid-state structural studies. Consistent with electrochemical

data of complex 1 or 1 , we have been unable to chemically

access a hypothetical U(V) complex [U( nacnac ) ] . We

have shown how complexes 1 and 1⁺exist as a pair of

enantiomers Λ and Δ, which are observed in the unit cell and

are comparable with the ﬁndings reported in the literature,

namely the complex [U{MeC(NCy) } ] by Ephritikhine et

al. Spectroscopic and magnetic data for 1 and 1 are

unarguably consistent with f and f ions, which are conﬁned

to an idealized D symmetry. Frequency-dependent measure-

ments of the out-of-phase susceptibility χ″M of 1, collected

with various applied magnetic ﬁelds (0.1, 1, and 2 kOe) at AC

frequencies of ν = 1−950 Hz from 2 −10 K, reveal no single

molecular magnetic behavior (Figures S21 and S22). The

U(III/IV) complex pair 1⁰presented here compliments the

/−

U(V/VI) homoleptic hexakisamide complexes [U(dbabh) ]

(

−

dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-

diene), which have been shown to have a reversible U(V/

VI) redox couple at −1.01 V.

ASSOCIATED CONTENT

sı Supporting Information

■

The Supporting Information is available free of charge on the

ACS Publications Web site at DOI: The Supporting

s.org/doi/10.1021/acs.inorgchem.9b03229.

Figure 6. Singly occupied molecular orbitals of 1 (without

truncation). Phenyl groups have been omitted for clarity; see Table

S2 for calculations without truncation.

General considerations, synthetic and spectroscopic

details, SQUID magnetization data, UV/Vis/NIR

electronic absorption spectroscopy, EPR measurements,

electrochemical details, references, X-ray crystal struc-

ture determinations, references for X-ray structure

orbitals (Figure 6). Conversely, for the U(IV) compound

, the B3PW91/DKH-def2-TZVPP//BP86/def2-SVP (U:

DKH-def2-TZVP) level of theory was used, and the phenyl

groups were not truncated; the mean deviation from the solid-

state, single-crystal XRD structure was 0.02 Å and 0.4° for the

bond lengths and angles, respectively. It was found that the f

electron conﬁguration found in 1 , with f and f_x_zmagnetic

orbitals (both with some f character), has considerable ligand

contributions (Figure 7). The greater degree of ligand mixing

in the SOMOs of 1 might help explain why attempts to

oxidize this complex result in demetalation.

determination of 1 and [1][BPh ], computational

details, and references for computations (PDF )

Accession Codes

CCDC 1943494 for [U( nacnac ) ] 1, CCDC 1943495 for

[U( nacnac ) ][BPh ] [1][BPh ], and CCDC 1946325 for

3 4 4

[

U( nacnac ) ][Al{OC(CF ) } ] [1][Al{OC(CF ) } ]

3 3 3 4 3 3 4

contain the supplementary crystallographic data for this

paper. These data can be obtained free of charge via

www.ccdc.cam.ac.uk/data_request/cif, by e-mailing data_

request@ccdc.cam.ac.uk, or by contacting the Cambridge

Crystallographic Data Centre, 12 Union Road, Cambridge

CB2 1EZ, U.K. (fax: +44 1223 336033).

AUTHOR INFORMATION

Corresponding Authors

■

Karsten Meyer − Inorganic Chemistry, Department of

Chemistry and Pharmacy, Friedrich-Alexander-University

Erlangen-Nu

orcid.org/0000-0002-7844-2998; Email: karsten.meyer@

fau.de

rnberg (FAU), Erlangen 91058, Germany;

Daniel J. Mindiola − Inorganic Chemistry, Department of

Figure 7. SOMO orbitals for the computed structure of the cation

Chemistry and Pharmacy, Friedrich-Alexander-University

[1] (nontruncated).

Erlangen-Nu

rnberg (FAU), Erlangen 91058, Germany;

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Philadelphia, Pennsylvania 19104, United States; orcid.org/

Article

Department of Chemistry, University of Pennsylvania,

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scientific legacy of Alfred Werner. Chem. Soc. Rev. 2013, 42, 1429−

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000-0001-8205-7868 ; Email: mindiola@sas.upenn.edu

(

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(

Authors

Judith Riedhammer − Inorganic Chemistry, Department of

Chemistry and Pharmacy, Friedrich-Alexander-University

Erlangen-Nurnberg (FAU), Erlangen 91058, Germany

J. Rolando Aguilar-Calderon − Department of Chemistry and

Biochemistry, University of Texas at El Paso, El Paso, Texas

9968, United States; Department of Chemistry, University of

(

Fallab, S. The rediscovery of Alfred Werner ’s second hexol. Chem.

Commun. 2004, 2322−2323.

Pennsylvania, Philadelphia, Pennsylvania 19104, United

States; orcid.org/0000-0002-3113-3629

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Chem. Soc., Dalton Trans. 1990, 921−924.

Matthias Miehlich − Inorganic Chemistry, Department of

Chemistry and Pharmacy, Friedrich-Alexander-University

(10) Fox, A. R.; Silvia, J. S.; Townsend, E. M.; Cummins, C. C. Six-

coordinate uranium complexes featuring a bidentate anilide ligand. C.

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Erlangen-Nurnberg (FAU), Erlangen 91058, Germany

Dominik P. Halter − Inorganic Chemistry, Department of

(11) A homoleptic tris-phopshinodiboranate complex was recently

Chemistry and Pharmacy, Friedrich-Alexander-University

reported to exist as a mixture of monomer and dimer in solution:

Blake, A. V.; Fetrow, T. V.; Theiler, Z. J.; Vlaisavljevich, B.; Daly, S. R.

Homoleptic uranium and lanthanide phosphinodiboranates. Chem.

Commun. 2018, 54, 5602−5605.

Erlangen-Nurnberg (FAU), Erlangen 91058, Germany

Dominik Munz − Inorganic Chemistry, Department of

Chemistry and Pharmacy, Friedrich-Alexander-University

Erlangen-Nu

orcid.org/0000-0003-3412-651X

rnberg (FAU), Erlangen 91058, Germany;

(12) Monreal, M. J.; Wright, R. J.; Morris, D. E.; Scott, B. L.;

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Uranium(IV) Halide Complexes Supported by Bulky β -Diketiminate

Ligands. Organometallics 2013, 32, 1423−1434.

Frank W. Heinemann − Inorganic Chemistry, Department of

Chemistry and Pharmacy, Friedrich-Alexander-University

Erlangen-Nurnberg (FAU), Erlangen 91058, Germany;

orcid.org/0000-0002-9007-8404

Skye Fortier − Department of Chemistry and Biochemistry,

University of Texas at El Paso, El Paso, Texas 79968, United

States; orcid.org/0000-0002-0502-5229

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tetrahydrofuran and the development of a new thorium starting

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.9b03229

material: preparation and chemistry of ThI

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4 2

(DME) . Dalton Trans.

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Diketiminate Derivatives of Alkali Metals and Uranium. Organo-

Author Contributions

metallics 2013, 32, 5058−5070.

The manuscript was written through contributions of all

authors. All authors have given approval to the ﬁnal version of

the manuscript.

Reactivity of a Uranyl β -Diketiminate Complex. J. Am. Chem. Soc.

2008, 130, 2005−2014.

16) Wu, G.; Hayton, T. W. Mixed-Ligand Uranyl(V) β -

Funding

Diketiminate/β -Diketonate Complexes: Synthesis and Character-

For funding, we thank the Friedrich-Alexander-University

Erlangen-Nurnberg (FAU), the University of Pennsylvania,

ization. Inorg. Chem. 2008, 47, 7415−7423.

(17) Schettini, M. F.; Wu, G.; Hayton, T. W. Coordination of N-

the US National Science Foundation (CHE-0848248 and

CHE-1152123 to D.J.M. and CHE-1827875 to S.F.), and the

Welch Foundation (AH-1922-20170325 to S.F). D.J.M. also

acknowledges support from the Alexander von Humboldt

Foundation. D.M. thanks the “Fonds der chemischen Industrie

im Verband der chemischen Industrie” for a Liebig fellowship

and the RRZE for computation time.

Donor Ligands to a Uranyl(V) β -Diketiminate Complex. Inorg. Chem.

2009, 48, 11799−11808.

(18) Schettini, M. F.; Wu, G.; Hayton, T. W. Synthesis and reactivity

of a uranyl-imidazolyl complex. Chem. Commun. 2012, 48, 1484−

1486.

(19) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. Transformation of

the bis(trimethylsilyl)methyl into a 1,3-diaza-allyl ligand. Synthesis

and crystal structures of [cyclic] [K{N(R)C(Ar)NC(Ar)CHR}-

Notes

NCAr)]₂ and [{UCl(μ -Cl)(L)(NR)} ][UCl (L)(L ′)] [R =

The authors declare no competing ﬁnancial interest.

SiMe ; Ar = C H Me -2,5; L = [cyclic] N(R)C(Ph)C(H)C(Ph)NR;

3 6 3 2

L ′ = [cyclic] N(R)C(Ph)NC(Ph)CHR]. J. Organomet. Chem. 1995,

88, 241−248.

ACKNOWLEDGMENTS

■

(20) Hohloch, S.; Garner, M. E.; Parker, B. F.; Arnold, J. New

supporting ligands in actinide chemistry: tetramethyltetraazaannulene

complexes with thorium and uranium. Dalton Trans. 2017, 46,

We thank Drs. John C. Huﬀman and Falguni Basuli for

insightful discussions.

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3768−13782.

21) Hohloch, S.; Garner, M. E.; Booth, C. H.; Lukens, W. W.;

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