Syntheses and Molecular Structures of [(thf)4Li] [{(thf)Li}M(C4H8)3] (M = Zr, Hf) and Their Solution Behavior

Article abstract of DOI:10.1002/zaac.202000013

The reaction of MCl₄(thf)₂ (M = Zr, Hf) with 1,4-dilitiobutane in diethyl ether at –25 °C or at 0 °C with a molar ratio of 1 : 3 yields the homoleptic “ate” complexes [(thf)₄Li] [{(thf)Li}M(C₄H₈)₃] 1-Zr (M = Zr) and 1-Hf (M = Hf). The crystalline compounds form ion lattices with solvent-separated [(thf)₄Li]⁺ cations and [{(thf)Li}M(C₄H₈)₃]^– anions. The NMR spectra at –20 °C show magnetic equivalence of the M–CH₂ and of the β-CH₂ groups of the butane-1,4-diide ligands on the NMR time scale. Analogous reactions of MCl₄(thf)₂ with 1,4-dilithiobutane with a molar ratio of 1 : 2 proceed unclear. However, single crystals of [Li(thf)₄] [HfCl₅(thf)] (2) can be isolated with the hafnium atom in a distorted octahedral coordination sphere of five chloro and one thf ligand. NMR spectra allow to elucidate the time-dependent degradation of 1-Hf and 1-Zr in THF and toluene at 25 °C via THF cleavage. Addition of tmeda to a solution of 1-Zr allows the isolation of intermediately formed [{(tmeda)Li}₂Zr(nBu)₂(C₄H₈)₂] (3).

Full text of DOI:10.1002/zaac.202000013

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.202000013
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Syntheses and Molecular Structures of [(thf)4Li]
[{(thf)Li}M(C4H8)3] (M = Zr, Hf) and Their Solution Behavior
Reinald Fischer,[a] Heiner Schmidt,[a] Fadi M. Younis,[a] Helmar Görls,[a] Regina Suxdorf,[a] and
Matthias Westerhausen*[a]
In Memoriam Professor Gerd Becker
Abstract. The reaction of MCl4(thf)2 (M = Zr, Hf) with 1,4-dilitiobut- MCl4(thf)2 with 1,4-dilithiobutane with a molar ratio of 1 : 2 proceed
ane in diethyl ether at –25 °C or at 0 °C with a molar ratio of 1 : 3
unclear. However, single crystals of [Li(thf)4] [HfCl5(thf)] (2) can be
yields the homoleptic “ate” complexes [(thf)4Li] [{(thf)Li}M(C4H8)3] isolated with the hafnium atom in a distorted octahedral coordination
1-Zr (M = Zr) and 1-Hf (M = Hf). The crystalline compounds form sphere of five chloro and one thf ligand. NMR spectra allow to eluci-
ion lattices with solvent-separated [(thf)4Li]+ cations and [{(thf) date the time-dependent degradation of 1-Hf and 1-Zr in THF and
Li}M(C4H8)3]– anions. The NMR spectra at –20 °C show magnetic
toluene at 25 °C via THF cleavage. Addition of tmeda to a solution of
equivalence of the M–CH2 and of the β-CH2 groups of the butane-1,4- 1-Zr allows the isolation of intermediately formed [{(tmeda)
diide ligands on the NMR time scale. Analogous reactions of Li}2Zr(nBu)2(C4H8)2] (3).
been reported for chromium(II),[4] nickel(II),[5] platinum(II),[6]
Introduction
magnesium(II),[7] and zinc(II).[8] In order to study the depen-
Organozirconium compounds are valuable synthons in or-
dency of the molecular structures on the oxidation state of the
ganic synthesis, hydrozirconation processes and as catalysts in
metal we also prepared and investigated the yttrium(III) conge-
hydrofunctionalization and umpolung reactions[1,2] as well as
ner.[9] Homoleptic metalates with central metal(IV) atoms are
in zirconium-catalyzed carbomagnesiation reactions.[3] Haf-
nium-containing organometallics are much more stable and
missing as of yet.
A
zirconium-based complex of the composition
significantly less reactive and therefore, these Hf-based com-
plexes often serve as model compounds to elucidate the reac-
tion mechanisms of catalytic transformations involving group
4 metals.[2] Many of these complexes are based on titanocene,
zirconocene and hafnocene substructures because the side-on
bound cyclopentadienide ligands shield the inner core and their
substitution pattern allows to tune bulkiness and availability of
coordination sites at the metal center and in some cases also
to introduce stereoselective reactivity.
“Li2Zr(C4H8)3(THF)5.5” (1-Zr) has been isolated by Fröhlich
and co-workers.[10] The authors also carboxylated[11] and car-
bonylated[12] the compound and initiated the living anionic po-
lymerization of 1,3-dienes.[13] However, the molecular struc-
ture of this complex remained unknown.
In this investigation we elucidated the crystal structures of
1-Zr and of the thermally more stable homologous hafnium
congener 1-Hf and studied their behavior in solution and in
the presence of a chelating Lewis base.
The formation of metallacycles also stabilizes transition
metal complexes because intramolecular hydride elimination
processes are hindered. The bifunctional synthon 1,4-dili-
thiobutane enables the syntheses of metallacycles and
metalates with the butane-1,4-diide acting as a chelate base.
Crystallographically authenticated homoleptic metalates have
Results and Discussion
1 Molecular Structures of [(thf)4Li][{(thf)Li}M(C4H8)3] with
M = Zr (1-Zr), Hf (1-Hf)
* Prof. Dr. M. Westerhausen
E-Mail: m.we@uni-jena.de
The complex [(thf)4Li][{(thf)Li}Zr(C4H8)3] (1-Zr) was syn-
thesized according to the procedure of Fröhlich and Göbel[10]
via the metathesis reaction of ZrCl4(thf)2 with Li2(CH2)4 in the
molar ratio of 1:3.1 in diethyl ether at –25 °C (Scheme 1). Af-
ter recrystallization of the crude product from THF solution
colorless and thermally highly sensitive single crystals were
isolated allowing the determination of the crystal structure.
Molecular structure and numbering scheme of the anion of
[(thf)4Li][{(thf)Li}Zr(C4H8)3] (1-Zr) are depicted in Figure 1,
the whole molecule is shown in the Supporting Information.
[a] Chair of Inorganic Chemistry I
Friedrich-Schiller-University Jena
Humboldtstr. 8
07743 Jena, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.202000013 or from the au-
thor.
© 2020 The Authors. Published by Wiley-VCH Verlag GmbH &
Co. KGaA. · This is an open access article under the terms of the
Creative Commons Attribution-NonCommercial License, which
permits use, distribution and reproduction in any medium, provided
the original work is properly cited and is not used for commercial
purposes.
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Zr–C values between the carbanionic sites that also bind to
lithium are larger than 90° [93.86(17)–98.63(18)°]. The in-
teratomic Zr1···Li1 distance of 267.7(7) pm clearly excludes
bonding interactions.
The homologous hafnium(IV) complex [(thf)4Li][{thf)
Li}Hf(C4H8)3] (1-Hf) was obtained with good yields via the
metathetical approach of HfCl4(thf)2 with an ethereal 1,4-dili-
thiobutane solution in the molar ratio of 1:3.2 at 0 °C in diethyl
ether. After removal of precipitated lithium chloride and ad-
dition of THF the product crystallized in the centrosymmetric
space group P21/n as a colorless and thermally moderately sen-
sitive compound. Contrary to 1-Zr, the asymmetric unit con-
tains two molecules A and B which differ by the orientation
of the thf ligands at O1A and O1B; however, the influence on
the structural parameters is negligible. The structure of the
anion of 1-Hf and the atom labeling scheme of molecule A
are depicted in Figure 2, molecule B and the whole molecule
including the cation are shown in the Supporting Information.
Scheme 1. Synthesis of [(thf)4Li][{(thf)Li}M(C4H8)3] with M = Zr (1-
Zr) and Hf (1-Hf) in diethyl ether and formation of the thf adduct
after addition of tetrahydrofuran. The bold semicycles symbolize the
butane-1,4-diide ligands at the octahedral coordination spheres of M.
Figure 1. Molecular structure and atom labeling scheme of the anion
of [Li(thf)4][Zr(C4H8)3{Li(thf)}] (1-Zr). The hydrogen atoms are
omitted for clarity reasons. The ellipsoids represent a probability of
30%. Selected bond lengths /pm: Zr1–C1 243.1(4), Zr1–C4 231.6(4),
Zr1–C5 241.2(4), Zr1–C8 231.7(5), Zr1–C9 242.7(5), Zr1–C12
233.1(4), Li1–O1 191.2(7), Li1–C1 218.9(7), Li1–C5 221.2(7), Li1–
C9 221.2(7); non-bonding interatomic distance/pm: Zr1···Li1 267.7(7);
selected bond angles/°: C1–Zr1–C4 73.18(14), C5–Zr1–C8 72.68(17),
C9–Zr1–C12 72.40(16), C1–Zr1–C5 88.11(14), C1–Zr1–C9 84.59(14),
C4–Zr1–C8 93.86(17), C5–Zr1–C9 85.81(17), C8–Zr1–C12
98.63(18), C4–Zr–C12 97.65(16), O1–Li1–C1 119.8(5), O1–Li1–C5
121.2(5), O1–Li1–C9 123.2(5), C1–Li1–C5 93.8(5), C1–Li1–C9
96.0(5), C1–Li1–C9 96.2(5).
Figure 2. Molecular structure and atom labeling scheme of the anion
of molecule A of [Li(thf)4][Hf(C4H8)3{Li(thf)}] (1-Hf). The hydrogen
atoms are neglected for the sake of clarity (see Figure S1, Supporting
Information, for molecule B.) Selected bond lengths of molecule A
[molecule B]/pm: Hf1–C1 241.4(3) [240.8(3)], Hf1–C4 230.2(3)
[229.7(3)], Hf1–C5 230.3(3) [230.0(3)], Hf1–C8 239.4(3) [240.7(3)],
Hf1–C9 229.6(3) [229.9(3)], Hf1–C12 240.5(3) [239.1(3)], Li1–O1
190.1(5) [192.1(6)], Li1–C1 220.2(6) [220.5(6)], Li1–C8 222.8(6)
[221.8(6)], Li1–C12 221.5(6) [221.5(6)]; non-bonding interatomic dis-
tances /pm: Hf1···Li1 265.8(5) [267.0(5)]; selected bond angles/°: C1–
Hf1–C4 74.32(11) [73.50(10)], C5–Hf1–C8 73.58(11) [73.83(10)],
C9–Hf1–C12 74.32(11) [73.65(12)], C1–Hf1–C5 108.72(12)
[112.27(12)], C1–Hf1–C8 84.55(11) [85.11(11)], C1–Hf1–C9
152.92(12) [153.18(12)], C1–Hf1–C12 84.62(11) [85.80(12)], C4–
Hf1–C5 93.53(11) [96.44(12)], C4–Hf1–C8 149.98(12) [151.27(12)],
C4–Hf1–C9 98.83(12) [97.98(12)], C4–Hf1–C12 110.49(11)
[111.80(12)], C5–Hf1–C9 97.71(12) [93.72(12)], C5–Hf1–C12
155.17(11) [150.17(12)], C8–Hf1–C9 109.56(12) [109.41(12)], C8–
Hf1–C12 87.55(11) [84.86(11)].
Crystalline 1-Zr forms a 1–1 ion lattice. The cations are
[(thf)4Li]+ ions with a distorted tetrahedral environment of the
lithium atoms. In the anion [Zr(C4H8)3{Li(thf)}]– the zirconi-
um(IV) center is in a distorted octahedral coordination sphere
of three chelating butane-1,4-diide ligands. In the crystalline
state both enantiomers of the octahedral complexes form a ra-
cemate of Δ and Λ isomers due to the centrosymmetric space
group P21/c. The bite angles of the hydrocarbyl chelate ligands
are significantly smaller than 90° [C–Zr–C of the zir-
conacycles: 72.40(16)–73.18(14)°]. From each butane-1,4-di-
ide ligand one α-methylene group also binds to the Li1 atom
of the Li(thf) unit via Li–C–Zr three-center two-electron
bonds. These bridging positions of the methylene groups cause
additional distortion of the octahedral environment of Zr1 and
The ion lattice consists of two crystallographically indepen-
elongation of the respective Zr–C bonds by approx. 10 pm dent units A and B. The ionic radii of Zr4+ (86 pm) and Hf4+
compared to the Zr–C bonds without interaction to the lithium (85 pm) are very similar due to the lanthanoide contraction of
atom. The C–Zr–C bond angles between carbanionic methyl- the radii in the 5d row of the Periodic Table of the elements.[14]
ene groups of the butane-1,4-diide moieties with Li contacts As a consequence the structural parameters of 1-Zr and 1-Hf
are smaller than 90° [84.59(14)–88.11(14)°] whereas the C– are very similar with the Hf–C bonds even being slightly
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shorter by approx. 2 pm. Despite the far-reaching structural uene: α-C 47.9 ppm, β-C 33.9 ppm; 1-Hf in [D8]THF: α-C
similarity between the zirconiate and hafniate anions chemical 56.1 ppm, β-C 36.2 ppm; in [D8]toluene: α-C 57.2 ppm, β-C
stability and reactivity differ significantly (see Section 2.2).
34.9 ppm). Such shifts of the α-carbon atoms to lower field
Selected structural parameters of homoleptic 1-Zr and 1-Hf have also been observed earlier for zircona-[17–22] and hafna-
are compared with heteroleptic complexes LLЈMC4H8 of the cyclo-pentane[23] congeners and was explained with the heavy
1
group 4 metals, containing saturated metalla-cyclo-pentane atom effect induced by these metal atoms. The H NMR reso-
fragments. Most commonly these compounds have been pre- nances of the butane-1,4-diide ligands lie in the expected ran-
pared via the cyclization reaction of the “LLЈM” precursor ges (1-Zr in [D8]THF: α-CH2 0.08 ppm, β-CH2 1.78 ppm; in
with two equivalents of ethylene. For the sake of completeness [D8]toluene: α-CH2 0.83 ppm, β-CH2 2.76 ppm; 1-Hf in
also the very rare structures of titanium complexes containing [D8]THF: α-CH2 0.05 ppm, β-CH2 1.96 ppm; in [D8]toluene:
the titana-cyclo-pentane fragment are included.
α-CH2 0.86 ppm, β-CH2 2.89 ppm). Obviously these com-
The Zr–C and Hf–C bond lengths in 1-Zr and 1-Hf, respec- plexes show symmetric structures in solution and/or exchange
tively, lie at the upper range of metal-carbon single bonds. On processes that are fast on the NMR time scale. Hence, the fol-
the one hand, intramolecular steric repulsion between the li- lowing three possible solution structures are proposed in
gands plays a significant role. On the other hand, this elong- Scheme 2: solvent-separated ion pairs, contact ion pairs and
ation is effectuated by intramolecular electrostatic repulsion fast exchange of the Li(thf) unit from one octahedral face to
between six carbanions bound at the metal center. The forma- the opposite face. In Scheme 2 the fluxionality in solution is
tion of Li–C–M three-center two-electron bonds via coordina- depicted at a Δ isomer; these equilibria are equally operative
tion of the Li(thf) moiety additionally stretches the M–C in the Λ isomers; in addition Δ/Λ enantiomer interconversion
bonds. Due to ring strain, the C–M–C bond angles are in all is very likely, too.
compounds significantly smaller than 90°. The narrowest
angles are observed for 1-Zr and 1-Hf, which is a consequence
of the large Zr–C and Hf–C distances (Table 1).
Table 1. Comparison of M–C bond lengths /pm and C–M–C bond
angles /° of metallacycles with saturated MC4H8 rings in complexes
of the type LLЈMC4H8 of titanium, zirconium, and hafnium.
a)
M
Ti
L/LЈ
M–C
C–M–C
Reference
2 ϫO-C6H3-2,6-Ph2 208.6
85.6
86.2
[15]
[16]
This work
[17]
[18]
[19]
[20]
[21]
[22]
Cp/N=PtBu3
2ϫC4H8 (1-Zr)
2ϫCpMent
Cp’-C2H4-CpЈ
2ϫC5H3-1,3-tBu2
Ind-C2H4-Ind
2ϫIndR4
214.3
232.1 / 242.3 72.8
Zr
230.4
229.8
230.2
229.4
230.1
82.6
84.0
81.2
84.8
81.0
76.4
2ϫ(Me3Si-N)2C-Ph 224.8
Hf
2ϫC4H8 (1-Hf)
CpЈ-C2H4-CpЈ
230.0 / 240.3 73.7
225.7 84.6
This work
[23]
a) Bu = butyl, CpЈ = 4,5,6,7-tetrahydroindenyl, Ind = indenyl, Ment =
menthyl, Ph = phenyl.
Scheme 2. Molecular dynamics of 1-Zr (M = Zr] and 1-Hf (M = Hf]
depending on the polarity of the solvents THF and toluene. The bold
hemicycles symbolize the butane-1,4-diide ligands. The metal-bound
carbon atoms form a distorted octahedron, which is drawn with thin
solid and broken lines. The Li–C bonds are shown with red broken
lines.
2 Solution Behavior of [(thf)4Li][{(thf)Li}M(C4H8)3] [M =
Zr (1-Zr), Hf (1-Hf)]
2.1 Fluxionality in Solution
1-Zr and 1-Hf are highly soluble at –20 °C in THF and
toluene. The excellent solubility in hydrocarbons was not ex-
In the 13C{1H} NMR spectrum of 1-Hf in [D8]THF solution
pected based on the ionic composition of both complexes. At at –20 °C the signal of the Hf-bound methylene units is signifi-
temperatures above –20 °C these compounds slowly degrade cantly broader than the resonance of the β-CH2 fragments. At
and the solutions turned increasingly dark brown.
the lower temperature of –50 °C this effect is getting stronger,
In the 1H and 13C NMR spectra one would expect four reso- however, the coalescence could not be realized. The 13C{1H}
nance sets of equal intensity for the butane-1,4-diide frag- NMR spectrum of 1-Zr in [D8]toluene shows no such effects
ments. However, in all these spectra only two signal sets were down to –45 °C. A slight broadening of the Zr-bound methyl-
observed. The assignment succeeded with HSQC experiments. ene group is observed below this temperature and at –50 °C
It is noteworthy that in the 13C{1H} NMR spectra the α-carbon crystallization of 1-Zr is observed.
atoms were found at lower field than the β-carbon atoms
If a molar ratio of 1:2 is applied for the metathesis reaction
(1-Zr in [D8]THF: α-C 49.9 ppm, β-C 36.2 ppm; in [D8]tol- of [ZrCl4(thf)2] with ethereal 1,4-dilithiobutane a yellow,
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sticky and thermally very sensitive product formed that con- proaches of [MCl4(thf)2] with 1,4-dilithiobutane with molar ra-
tained at least two different zirconium-containing compounds. tios of 1:2 or 1:1.
The NMR spectroscopic data of a [D8]toluene solution at
–40 °C shows two sets of resonances for 1-Zr and a yet un-
2.2 Stability of [(thf)4Li][{(thf)Li}M(C4H8)3] [M = Zr (1-Zr),
Hf (1-Hf)] in Solution
known second component [1H NMR: 1.11 ppm (CH2Zr),
3.20 ppm (β-CH2); 13C{1H} NMR: 16.6 ppm (β-CH2),
66.0 ppm (CH2Zr)]. Nevertheless, the reaction proceeded quite
unclear and we were unable to solve the reaction mechanism.
The use of homologous [HfCl4(thf)2] allowed the isolation of
a hafniate derivative without butane-1,4-diide ligands, namely
[(thf)4Li][HfCl5(thf)] (2). Molecular structure and atom label-
ing scheme are depicted in Figure 3. This hafniate ion has al-
ready been structurally authenticated with other counter cat-
ions.[24]
In the crystalline state the complexes 1-Zr and 1-Hf could
be stored at –20 °C. In THF and toluene solutions these com-
plexes already started to slowly degrade already at –20 °C. At
room temperature the degradation was significantly ac-
celerated which could be monitored by NMR spectroscopy.
The intensity of new signals increased in equal measure as
the resonances of 1-Zr and 1-Hf vanished. The decomposition
process could be observed by 1H NMR experiments (Figure 4).
The newly formed hydrocarbons were n-butane and toward the
end of the degradation also ethylene was detected. Under these
conditions the half-life time of the decomposition of 1-Hf in
[D8]toluene at 25 °C was approx. 15 hours. If THF was re-
placed by [D8]THF (deuteration of 99.5%) the degradation at
room temperature was significantly decelerated and a half-life
time of 105 hours was observed. Expectedly, the solution of
1-Zr in [D8]THF was much more thermolabile and a half-life
time of approx. 2 hours was determined. Due to this finding a
reliable time dependency of the very fast degradation of 1-Zr
in toluene could not be elucidated.
Figure 3. Molecular structure of [Li(thf)4]+[HfCl5(thf)]– (2). Hydrogen
atoms are omitted for clarity reasons. The ellipsoids represent a prob-
ability of 30%. Selected bond lengths /pm: Hf1–Cl1 243.11(16), Hf1–
Cl2 238.6(2), Hf1–Cl3 242.11(19), Hf1–Cl4 242.0(2), Hf1–Cl5
243.39(16), Hf1–O1 222.1(5), Li1–O2 193.4(12), Li1–O3 190.3(12),
Li1–O4 189.2(12), Li1–O5 190.3(12); selected bond angles /°: O1–
Hf1–Cl1 85.70(12), O1–Hf1–Cl2 179.87(15), O1–Hf1–Cl3 85.87(14),
O1–Hf1–Cl4 85.36(14), O1–Hf1–Cl5 84.89(12), Cl1–Hf–Cl5
170.58(7), Cl3–Hf–Cl4 171.23(8), Cl1–Hf–Cl2 94.31(7), Cl2–Hf–C3
94.26(8), Cl2–Hf–C4 94.51(8), Cl2–Hf–C5 95.11(7).
The hafnium center in 2 has a distorted octahedral coordina-
tion sphere. All Cl2–Hf1–Cl bond angles are larger than 90°
and the O1–Hf1–Cl values to the cisoid chloride ligands are
smaller than 90°. This finding is caused by the electrostatic
repulsion between the halide anions whereas the oxygen
atom is electroneutral. The Hf1–Cl2 bond length is
approx. 4 pm smaller than the distances to the cisoid chloride
atoms. These Hf–Cl distances of the hafniate 2 are in agree-
Figure 4. Time depending decomposition of 1-Zr (black) and 1-Hf
(red and blue) at 25 °C in [D8]THF and [D8]toluene solutions.
The fact that 1-Hf degrades much faster in [D8]toluene than
ment with values of other six-coordinate hafnium derivatives in [D8]THF supports a fast ligand exchange of coordinated thf
like [cis-HfCl4(thf)2],[25] [Ph4P]2[HfCl6]·2solv,[26] and ligands by deuterated THF solvent molecules which were pres-
[Et4N]2[HfCl6][27] with increasing number of chloro ligands ent with large excess during the NMR experiments. Tetra-
(see Table S1, Supporting Information). The lithium atom Li1 hydrofuran acts as a weak Brønsted base toward the highly
is in a distorted tetrahedral environment.
nucleophilic butane-1,4-diide.[29] The rate of degradation de-
The formation of 2 hints toward a side reaction of pends on the deprotonation of the methylene groups CH2O in
[HfCl4(thf)2] with lithium chloride that forms during the me- [D8]toluene and CD2O in [D8]THF after ligand substitution of
tathesis reaction or might already be present in the ethereal the ether bases. The quotient kD/kH (kinetic isotope effect of
solution of starting [(Et2O)4Li][Li12(C4H8)6(@Cl)].[28] This 2D/1H) of this reaction has a value of 7. A similarly stabilizing
complex 2 can also act as starting material for the metathesis solvent effect of [D8]THF has been observed earlier for solu-
reaction with 1,4-dilithiobutane. The significantly more tions of related [{(thf)2Li}3Y(C4H8)3].[9] Initially the butane-
thermolabile neutral compounds “M(C4H8)2(thf)2” and 1,4-diide ions form n-butyl groups. A second deprotonation
“MCl2(C4H8)(thf)2” are not accessible via metathetical ap- of THF or [D8]THF yields n-butane (or 1-[D]butane and 1,4-
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[D2]butane) which have been authenticated by NMR spec-
troscopy. Pure 1,4-[D2]butane is not accessible due to met-
alation reactions also with [D7]THF and THF from the original
complex. The decomposition end products of THF are the vi-
nylate as well as ethylene and [D4]ethylene, which are authen-
ticated by NMR spectroscopy. The vinylate species are only
sparingly soluble and hence, trapped in the white precipitate
which forms during the decomposition process. This main de-
gradation cascade is depicted in Scheme 3.
Figure 5. Structural motif and atom labeling scheme of [{(tmeda)
Li}2Zr(nBu)2(C4H8)2] (3). Symmetry-related atoms are marked with
the letter “A”. Hydrogen atoms are omitted for clarity reasons, heavy
atoms are drawn with arbitrary radii.
tmeda ligands prevents coordination to the butyl groups. Isola-
tion of this complex supports the degradation pathway which
is discussed above.
Scheme 3. Proposed initial decomposition steps of 1-Zr and 1-Hf at
room temperature via deprotonation of THF molecules.
Conclusions
This degradation proceeds primarily via deprotonation of
THF and [D7]THF und only secondarily via dedeuteration of
After the structural characterization of homoleptic butane-
[D8]THF (and [D7]THF]). In the solution of 1-Hf in hydro- 1,4-diide complexes with metal(II) and metal(III) centers we
carbons like toluene the thf ligands are not substituted and report here for the first time the structures of metal(IV) deriva-
hence, they remain in the vicinity of the carbanions. Therefore, tives which are accessible via the metathetical approach of
degradation of 1-Hf in toluene is significantly accelerated in [MCl4(thf)2] (M = Zr, Hf) with 1,4-dilitiobutane with a molar
comparison to this reaction in [D8]THF solutions. Expectedly, ratio of 1:3.1 in diethyl ether. After addition of THF thermally
the solution of the hafnium complex is much more stable than highly sensitive Li2M(C4H8)3(thf)5 [M = Zr (1-Zr) and Hf (1-
of the zirconium congener due to stronger Hf–C σ-bonds.[30]
Hf)] can be isolated that form ion lattices with solvent-sepa-
According to Fröhlich and Göbel[10] the ligated thf bases rated [(thf)4Li]+ cations and [{(thf)Li}M(C4H8)3]– anions. De-
can be substituted by N,N,NЈ,NЈ-tetramethylethylenediamine spite the ionic composition these complexes are highly soluble
(tmeda) ligands yielding “Li2Zr(C4H8)3(tmeda)3”, which in ethereal and aromatic hydrocarbon solvents. In THF and
should be more stable than the thf adduct. We reinvested the toluene solutions these compounds show a dynamic behavior
reaction and added 1,4-dilithiobutane to [ZrCl4(thf)2] with a with only two resonances caused by the α-CH2 and β-CH2
molar ratio of 1:3.1 in diethyl ether. Thereafter we removed fragments of the butane-1,4-diide ligands. This finding can be
precipitated lithium chloride and added a stoichiometric explained by the formation of solvent-separated ions
amount of tmeda. At –40 °C a colorless sticky substance pre- [(thf)4Li+]2 [M(C4H8)3]2– in Lewis donor solvents and by a
cipitated which was isolated. After recrystallization at –40 °C contact ion pair of the type [{(thf)Li}2M(C4H8)3] in hydro-
only a few crystals of [{(tmeda)Li}2Zr(nBu)2(C4H8)2] (3) were carbons. At room temperature these complexes degrade via α-
obtained. The crystal structure determination verified the pro- deprotonation of (ligated) thf molecules followed by the char-
posed composition, however due to poor crystal quality we acteristic degradation pathway yielding ethylene and sparingly
were only able to refine a structural motif. The molecular soluble vinylate species. In the presence of tmeda a complex
structure and atom labeling scheme of C2 symmetric 3 is de- of the composition of “Li2Zr(C4H8)3(tmeda)3” forms which
picted in Figure 5.
slowly decomposes already at –40 °C via ether cleavage with
Despite the substandard data set the molecular structure formation of [{(tmeda)Li}2Zr(nBu)2(C4H8)2] (3), which crys-
verifies the formation of a heteroleptic zirconiate complex as tallizes as a contact ion pair.
contact ion pair. The zirconium center binds to six carbanions.
The metathesis reactions with different stoichiometric ratios
The Li(tmeda) fragments bind to the carbanionic sites of the of 1:2 and 1:1 for [MCl4(thf)2] and 1,4-dilitiobutane yield dif-
different butane-1,4-diide ligands leading to a coordination ferent species which cannot be separated and isolated. During
number of four for the lithium atoms and a distorted tetrahedral these experiments using the substrate [HfCl4(thf)2] the solvent
environment. The shielding of the lithium center by the chelate separated hafniate [(thf)4Li][HfCl5(thf)] (2) crystallizes. Com-
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The mother liquor was decanted and layered with 10 mL of diethyl
plexes of the types [M(C4H8)2(thf)2] and [MCl2(C4H8)(thf)2]
ether. At –78 °C a yellow sticky substance formed which was isolated
by decanting the mother liquor. Then this substance was dried in
vacuo. A [D8]THF solution was studied at –40 °C by NMR spec-
troscopy. This solution is highly temperature sensitive and quickly
turned brownish black already at –20 °C. The product is a mixture of
1-Zr and an unknown organozirconium compound. 1-Zr: 1H NMR
(400 MHz, [D8]toluene, –40 °C): δ = 0.71 (12 H, br, α-CH2-Zr), 1.59
(20 H, br, THF), 2.46 (12 H, br, β-CH2), 3.46 (20 H, br, THF). 13C{1H}
NMR (100.6 MHz, [D8]toluene, –40 °C): δ = 25.6 (THF), 36.1 (β-C),
(or LiCl adducts thereof) are not accessible using this meta-
thetical procedure.
The compounds 1-Zr, 1-Hf, and 3 are complexes with six
very reactive M–C σ-bonds allowing the application in multi-
level syntheses or catalyses.
Experimental Section
1
50.0 (α-C-Zr), 68,3 (THF). H NMR (400 MHz, [D8]THF, –40 °C): δ
General: All manipulations were carried out under anaerobic condi-
tions in an argon atmosphere using standard Schlenk techniques. The
solvents were dried according to common procedures and distilled in
an argon atmosphere; deuterated solvents were dried with sodium, de-
gassed, and saturated with argon. The yields given are not optimized.
1H and 13C NMR spectra and two dimensional spectra were recorded
on Bruker AC 400 and AC 500 spectrometers. Chemical shifts are
reported in parts per million (ppm, δ scale) relative to the residual
signal of the solvent.[31] Anhydrous zirconium tetrachloride, hafnium
tetrachloride, and 1,4-dichlorobutane were supplied by Alfa Aesar.
MCl4(thf)2 with M = Zr, Hf were prepared by recrystallization of MCl4
from a THF solution.[32] The 1,4-dilithiobutane solution was prepared
according to a literature procedure from lithium sand (Ø ≈ 50 μm) and
1,4-dichlorobutane in diethyl ether.[28] The concentration of the solu-
tion was determined by acidimetric titrations of an aliquot with N/10
hydrochloric acid against phenolphthalein. 1-Zr was prepared accord-
ing to a protocol of Fröhlich and Göbel.[10] The elemental analyses
gave no reliable data due to the enormous reactivity toward moisture
and air as well as due to loss of thf ligands during handling, weighing
and combustion analyses.
= 0.08 (12 H, br, α-CH2-Zr), 1.78 (32 H, br, β-CH2, THF), 3.62 (20
H, br, THF). 13C{1H} NMR (100.6 MHz, [D8]THF, –40 °C): δ = 25.3
(CH2, THF), 36.2 (β-C), 50.1 (α-C-Zr), 68.1 (THF). Unknown organ-
ozirconium compound: 1H NMR (400 MHz, [D8]toluene, –40 °C): δ
= 1.11 (α-CH2Zr), 3.20 (β-CH2). 13C{1H} NMR (100.6 MHz, [D8]tol-
uene, –40 °C): δ = 16.6 (β-C), 66.0 (α-C-Zr).
NMR Control of the Solvolysis of 1-Zr and 1-Hf: Approx. 0.1 g of
1-Zr and 1-Hf were dissolved at –20 °C in approx. 0.7 mL of [D8]THF
or [D8]toluene (approx. 0.2 m solutions) and transferred into NMR
tubes. Immediately thereafter the NMR spectra were recorded at 25 °C.
The NMR sample remained in the tempered NMR spectrometer and
spectra were recorded in regular intervals (1H NMR of 1-Zr in
1
[D8]THF: 0 h, 4 h, 5.5 h. H NMR of 1-Hf in [D8]THF: 0 h, 4 h, 24
1
h, 49 h, 142 h, 310 h. H NMR of 1-Hf in [D8]toluene: 0 h, 5.5 h, 24
h, 49 h). The residual solvent signals were used as standard to deter-
mine the intensity of the resonances (see Figure 4).
Single Crystal Preparation of [(thf)4Li][HfCl5(thf)] (2): HfCl4(thf)2
(4.04 g, 8.70 mmol) was suspended in 30 mL of diethyl ether and
cooled to –40 °C. 1,4-Dilithiobutane (30 mL of a 0.58 m diethyl ether
solution, 17.4 mmol) was added to this suspension. The reaction mix-
ture was stirred at this temperature for 4 h. Then the precipitated lith-
ium chloride was removed with a precooled frit covered with diato-
maceous earth. At –40 °C THF was slowly added dropwise to the fil-
trate till the light brown precipitate redissolved again. After filtration
the clear filtrate was stored at –78 °C. A brown solid crystallized and
was recrystallized several times from THF solution until colorless
crystals of [(thf)4Li] [HfCl5(thf)] (2) were isolated.
Synthesis of [(thf)4Li][{(thf)Li}Hf(C4H8)3] (1-Hf): HfCl4(thf)2
(2.52 g, 5.42 mmol) was suspended in 20 mL of diethyl ether at
–78 °C. Thereafter 30 mL (17.4 mmol) of a 1,4-dilithiobutane solution
in diethyl ether (0.58 m) was added dropwise. The suspension was
slowly warmed to 0 °C. At this temperature the stirring was continued
for 4 h until all the starting compounds were consumed. The color of
the solution turned red and lithium chloride precipitated. The pre-
cipitate was removed by filtration with a Schlenk frit (G4). Then 5 mL
of THF were added to the clear filtrate. At –40 °C white crystals of 1-
Hf grew. Yield of 1-Hf: 3.49 g (89% with respect to starting
Single Crystal Preparation of [{(tmeda)Li}2(nBu)2Zr(C4H8)2] (3):
A solution of 1,4-dilithiobutane (19.0 mL of a 1.5 m diethyl ether solu-
tion, 28.5 mmol) was diluted with 50 mL of diethyl ether and cooled
to –40 °C. ZrCl4(thf)2 (3.3 g, 8.75 mmol) were added in small portions.
After 2 h of stirring at –40 °C the reaction was finished. The lithium
chloride precipitate was removed by filtration with a precooled Schlenk
frit. Then 3.9 mL of TMEDA (3.0 g, 26.0 mmol) were added dropwise
at –40 °C to the stirred solution. During this time a clumpy white
precipitate formed, which was collected on a cooled frit and dried in
vacuo. The solid was washed from the frit with 60 mL of diethyl ether
and this suspension was stirred for 3 h at –50 °C. Remaining solid
materials were removed by filtration and the clear filtrate was stored
at –40 °C. After 3 d a few slightly orange crystals of [{(tmeda)
Li}2(nBu)2Zr(C4H8)2] (3) precipitated besides an amorphous white so-
lid.
1
HfCl4(thf)2). H NMR (400 MHz, [D8]THF, –30 °C): δ = 0.05 (12 H,
br, α-CH2-Hf), 1.85 (m, 20 H, THF), 1.96 (12 H, br, β-CH2), 3.69 (m,
20 H, THF). 13C{1H} NMR (100.6 MHz, [D8]THF, –30 C): δ = 26.4
(THF), 36.2 (β-CH2), 56.1 (br., α-CH2-Hf), 68.3 (THF). 1H NMR
(400 MHz, [D8]toluene, –20 °C): δ = 0.86 (12 H, br, α-CH2-Hf), 1.31
(m, 20 H, THF), 2.89 (12 H, br, β-CH2), 3.50 (m, 20 H, THF). 13C{1H}
NMR (100.6 MHz, [D8]toluene, –20 C): δ = 25.3 (THF), 34.9 (β-
CH2), 57.2 (α-CH2-Hf), 67.6 (THF).
Reaction of ZrCl4(thf)2 with 1,4-Dilithiobutane in the 1:2 Molar
Ratio: ZrCl4(thf)2 (1.3 g, 3.45 mmol) was suspended in a solvent mix-
ture of 5 mL of diethyl ether and 10 mL of THF. At –78 °C 15 mL of
an ethereal 1,4-dilithiobutane solution (7.35 mmol, 0.49 m) was added
in small portions. Thereafter the cooling bath was warmed to –40 °C.
During this time the fast depositing ZrCl4(thf)2 disappeared and slowly
depositing white lithium chloride formed. At the moment when resid-
Crystal Structure Determination: The intensity data for the com-
ual substrate started to combine with the fine precipitate with forma- pounds were collected on a Nonius KappaCCD diffractometer using
tion of an creme-colored oil, the reaction mixture was cooled again to graphite-monochromated Mo-Kα radiation. Data were corrected for
–55 °C and additional 5 mL of THF were added. Now the oil dissolved
Lorentz and polarization effects; absorption was taken into account on
and a yellow solution formed containing a fine white precipitate. The a semi-empirical basis using multiple-scans.[34–36] The structures were
solid was removed by filtration and was collected in a cooled flask
and stored overnight at –78 °C. Crystals of [LiCl(thf)2]2 formed.[33] least-squares techniques against Fo .
solved by Direct Methods (SHELXS)[37] and refined by full-matrix
2 [38]
All hydrogen atoms were in-
Z. Anorg. Allg. Chem. 2020, 207–214
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Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Spessard, G. L. Miessler: Organometallic Chemistry, 2nd ed., Ox-
cluded at calculated positions with fixed thermal parameters. All non-
hydrogen atoms were refined anisotropically.[38] The crystal of 3 was
extremely thin and of low quality, resulting in a substandard data set;
however, the structure is sufficient to show connectivity and geometry
despite the high final R values. We only publish the conformation of
the molecule and the crystallographic data. We will not deposit the
data at the Cambridge Crystallographic Data Centre. Crystallographic
data as well as structure solution and refinement details are summa-
rized in Table S2 (Supporting Information). XP[39] and POV-Ray[40]
were used for the structure representations.
ford University Press, Oxford, 2010; h) D. Steinborn: Fundamen-
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[8] [{(tmeda)Li}2Zn(C4H8)2]: H.-O. Fröhlich, B. Kosan, B. Un-
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[9] [{(dme)Li}3Y(C4H8)3]: R. Fischer, S. Bode, M. Köhler, J. Langer,
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[10] a) H.-O. Fröhlich, A. Göbel, Z. Anorg. Allg. Chem. 1989, 577,
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[11] H. Schreer, A. Göbel, H.-O. Fröhlich, V. Griehl, E. Anton, Hy-
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A5 19910508.
[12] H. Schreer, A. Göbel, H.-O. Fröhlich, V. Griehl, E. Anton, Prepa-
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Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-1975946 for 1-Hf, CCDC-1975947 for 1-Zr, and
CCDC-1975948 for 2 (Fax: +44-1223-336-033; E-Mail: deposit@
ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk).
Supporting Information (see footnote on the first page of this article):
Representation of the complete molecular structures of 1-Zr and 1-Hf,
crystal and refinement data, NMR spectra.
Acknowledgements
We acknowledge the valuable support of the NMR service platform
(www.nmr.uni-jena.de/) of the Faculty of Chemistry and Earth Sci-
ences of the Friedrich Schiller University Jena, Germany.
Keywords: Zirconium; Hafnium; Organohafniate complexes;
Organozirconiate complexes; α,ω-Alkanediides
[13] H.-O. Fröhlich, E. Anton, V. Griehl, A. Göbel, Catalysts for Liv-
ing Polymerisation of 1,3-Diens, patent 1990 DD 278808, Ger-
many (East) A1 19900516.
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Received: January 10, 2020
Published Online: February 13, 2020
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