Reversible Formation of a Cerium-Bound Terminal Hydride: Ce(C5Me4SiMe3)2(H)(thf)

Article abstract of DOI:10.1002/ejic.201600737

The use of the bulky cyclopentadienyl ligand Cp′ (Cp′ = C₅Me₄SiMe₃) to stabilize cerium hydrides has resulted in the preparation of two novel tuck-in complexes with C–H activated SiMe₃groups. Subsequent reaction

Full text of DOI:10.1002/ejic.201600737

DOI: 10.1002/ejic.201600737
Communication
f-Block Hydrides
Reversible Formation of a Cerium-Bound Terminal Hydride:
Ce(C Me SiMe ) (H)(thf)
5
4
3 2
[
a]
[b]
[c]
[a]
Owen T. Summerscales, Enrique R. Batista, Brian L. Scott, Marianne P. Wilkerson, and
Andrew D. Sutton*[
a]
Abstract: The use of the bulky cyclopentadienyl ligand Cp′ tained vacuum. This compound is only the second structurally
(
Cp′ = C Me SiMe ) to stabilize cerium hydrides has resulted in characterized terminal cerium hydride. This new hydride is a
5
4
3
3
the preparation of two novel tuck-in complexes with C–H acti- catalyst in H/D exchange reactions between with both sp -CH
vated SiMe groups. Subsequent reaction of these with H in and sp -CH bonds, and for the hydrogenation of unsaturated
2
3
2
thf gives a lanthanide terminal hydride species Ce(Cp′) (H)(thf) alkene bonds.
2
which reversibly regenerates the tuck-in complex under sus-
Introduction
metallocene
salt
with
a
bridging
monohydride
+
[7]
(
[{Ce(C H SiMe tBu) } -(H)] ), and a non-metallocene bridged
5
4
2
3 2
Metal hydride complexes are important species in catalysis and
continue to demand much attention for their complex reactivity
dihydride cluster has also been recently reported by Okuda et
al. ([Ce(Me TACD)(μ-H) ] ; (Me TACD)H 1,4,7-trimethyl-
=
3
2 4
3
[
1]
patterns. In particular, lanthanide hydrides are among the
[8]
1
,4,7,10-tetraazacyclo-dodecane, Me [12]-aneN ).
The only
3
4
[
2]
most reactive coordination compounds known. However,
their high reactivity is also associated with low stability – rela-
tively few well-characterized lanthanide terminal hydride spe-
known terminal cerium hydride, Ce(C H tBu ) H, was reported
by Andersen et al. in 2005 (Scheme 1).
5
2
[3,4]
3 2
[
2–9]
cies are currently known.
We are particularly interested in the chemistry of cerium–
hydrogen bonds: the one cerium species currently known con-
[
3]
taining a terminally-bound hydride (see right) has shown re-
markable reactivity towards the breaking of internal and exter-
nal C–H and C–F bonds (i.e. bonds found in both internal li-
[
4]
gands and added external substrates). Highly Lewis-acidic,
large lanthanide metal centers create a tendency for hydride
species to dimerize, or oligomerize – this propensity is particu-
larly noted for cerium. As the second-largest lanthanide triva-
lent ion, it is essential to use sterically-demanding ligands to
prevent oligomerization. Cyclopentadienyl ligands have been
shown in a few cases to stabilize isolable bridging and terminal
cerium hydrides: the synthesis of a bridging hydride was first
reported in the Cp* complex {Ce(C Me ) H} by Teuben and co-
5
5 2
2
[
5]
workers,
and similarly Bulychev et al. followed with
Ce(C H tBu ) H} in 1992. Lappert et al. reported a dimeric
[
6]
{
5
3
2 2
2
[
a] Chemistry Division, Los Alamos National Laboratory,
Los Alamos, NM 87545, USA
Scheme 1. Synthetic routes to previously known cerium and lanthanide
hydride complexes.[
3,5,9]
E-mail: adsutton@lanl.gov
http://www.lanl.gov/org/padste/adcles/chemistry/inorganic-isotope-actinide/
chemical-energy-storage/index.php
b] Theoretical Division, Los Alamos National Laboratory,
Los Alamos, NM 87545, USA
c] Materials and Physics Applications Division,
Los Alamos National Laboratory,
The bulky Cp′ (Cp′ = C Me SiMe ) ligand meanwhile shows
5
4
3
[
[
promise for stabilizing a new type of cerium terminal hydride
complex, and we have recently utilized the bis-substituted ver-
sion of this ligand to stabilize the first structurally characterized
IV
[10]
bis-cyclopentadiene Ce complex. Hou et al. have also used
this ligand to effectively stabilize terminal lanthanide hydride
Los Alamos, NM 87545, USA
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejic.201600737.
complexes of the type Ln(Cp′) (H)(thf) (Ln = Y, Nd, Sm, Dy and
2
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Communication
Lu, see Scheme 1),[9] but did not report the cerium member of Lu),[9] and similar to a cyclometalated sandwich complex re-
this series, presumably because their synthetic route could not ported by Andersen et al. (Scheme 1).[
be applied to this metal center, owing to the instability of the
3]
analogous starting material.
Here, we have successfully synthesized and structurally char-
acterized a new Ce terminal hydride based on this series.
Results and Discussion
Hydrogenolysis of alkyl complexes has proven to be a success-
ful strategy for synthesizing lanthanide hydrides (Scheme 1).
The syntheses of Ln(Cp′) (H)(thf) use Ln(CH SiMe ) (thf) as the
2
2
3 3
2
[
9]
starting material – however, for cerium, this complex has not
been synthesized as a stable, fully characterizable compound.
5
1
Therefore, we developed an alternative pathway to (η :η -
C Me SiMe CH )Ce(Cp′)(thf) (1) as a precursor for hydride for-
5
4
2
2
mation. Sequential reaction of CeCl with two equivalents of
3
KCp′ and one equivalent of KBz (Bz = benzyl, CH -Ph) gave a
2
red crystalline material that when heated or reacted with H
2
1
5
generated the new tuck-in C–H activated complex (η :η -
C Me SiMe CH )Ce(Cp′)(thf) (1) as a crystalline solid in low yield
Figure 1. Thermal ellipsoid plot of the structure of 1 (hydrogen atoms omit-
5
4
2
2
ted; ellipsoids at 50 % probability).
(
19 % from CeCl ; Scheme 2).
3
Table 1. Selected bond lengths and angles for complexes 1 and 2.
Bond lengths [Å]
1
2
Ce(1)-O(1)
Ce(1)–C(10)
Ce(1)–C(Cp′) av.
Ce(1)–C(1)
Ce(1)–C(2)
Ce(1)–C(3)
Ce(1)–C(4)
Ce(1)–C(5)
2.5207(11)
2.5790(15)
2.8167(14)
2.7016(15)
2.7877(13)
2.8772(13)
2.8363(13)
2.7252(13)
Ce(1)–C(22)
Ce(1)–C(Cp′) av.
Ce(1)–C(13)
Ce(1)–C(14)
Ce(1)–C(15)
Ce(1)–C(16)
Ce(1)–C(17)
2.746(3)
2.8262(19)
2.819(2)
2.868(2)
2.8399(19)
2.7996(19)
2.7643(18)
Bond angles [°]
1
2
Si(1)–C(10)–Ce(1)
C(5)–C(1)–Si(1)
C(2)–C(1)–Si(1)
C(10)–Si(1)–C(1)
97.91(6)
Si(2)–C(22)–Ce(1)′
C(17)–C(16)–Si(2)
C(15)–C(16)–Si(2)
C(22)–Si(2)–C(16)
150.77(12)
124.29(15)
128.72(15)
112.19(11)
125.51(11)
123.89(11)
102.32(7)
3
Scheme 2. Formation of 1 and 2 from CeCl .
Hydrogenation of the red crystalline material obtained from
1
Crystalline samples of 1 gave reproducible fingerprint H and the Cp′/KBz reaction in toluene (as a non-coordinating solvent,
C{ H} NMR spectra, with paramagnetically broadened and rather than thf) gave a new species, identified as {(Cp′)Ce(μ-
1
3
1
5
1
highly shifted resonances, which could not be unambiguously η :η -C Me SiMe CH )} (2) in 17 % yield from CeCl (Scheme 2).
5
4
2
2
2
3
assigned. Variable temperature (VT) NMR measurements Complex 2 crystallized in orthorhombic space group Pcan; the
–50 to 100 °C (dec.), d -toluene] showed a complex pattern of structure shows a dimeric sandwich species containing one in-
[
8
coalescence and subsequent decoalescence of the spectra and tact Cp′ ligand and one cyclometalated ligand, similar to that
failed to enable full assignment (see supporting information).
found in 1, but as a “tuck-over” bridging ligand between two
Primary characterization of 1 was obtained via single crystal cerium centers (Figure 2).
X-ray diffraction, as for most of the other members of the series The complex forms an asymmetric bridging structure, with
[
9]
previously reported, using a single crystal grown from hexane the cyclometalated ligands found adjacent to one another, pre-
at –30 °C. The structure was solved in triclinic space group P 1¯ , sumably due to crystal packing forces. Ce–C distances are typi-
and shows a monomeric sandwich complex with one internally cal for this type of complex (Table 1).[
3,11]
VT NMR (–50 to
C–H activated SiMe3 group forming a metallacycle with the 100 °C) of concentrated solutions of crystalline material showed
1
13
1
C Me SiMe CH ligand (Figure 1). Ce–C distances are typical for only residual protio solvent resonance in the H and C{ H}
5
4
2
2
[
3]
this type of complex (Table 1). This structure is analogous to NMR spectra. Presumably this is because of severe paramag-
η :η -C Me SiMe CH )Ln(Cp′)(thf) (Ln = Y, Nd, Sm, Dy and netic broadening similar to other 4f-element complexes.
5
1
(
5
4
2
2
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Communication
bis-cyclopentadienyl lanthanide alkyl and hydride complexes,
[
12–14]
e.g. for {Cp* M(H)(thf)} (M = Y, Sc).
In the latter cases, a
2
x
monomeric (terminal) hydride is speculated as the active spe-
[
13]
2
cies,
although never directly isolated. An identical H NMR
3
experiment performed using thf also showed sp -C–H/D scram-
bling; in this case the 2,5-CH bonds were, on average, ex-
changed five times more than the 3,4-CH bonds, as determined
by the relative integration of the peaks.
Recrystallization of 1 under a H atmosphere resulted in the
2
new crystallographically characterized terminal hydride species
Ce(Cp′) (H)(thf) (3). The structure of 3 was solved in monoclinic
2
P 2 /n and shows a sandwich complex, with intact SiMe3
1
groups, isostructural to the series described previously (Fig-
[
9]
ure 3). The terminal hydride could be located and isotropically
refined, giving a Ce–H distance of 2.264(4) Å (Table 2), signifi-
cantly longer than the Ce–H bond found in Ce(C H tBu ) H
5
2
3 2
[
3]
[1.90(5) Å],
the only previously known cerium terminal
Figure 2. Thermal ellipsoid plot of the structure of 2 (hydrogen atoms omit-
ted; ellipsoids at 50 % probability).
hydride. Bridging cerium hydrides meanwhile have been re-
[6–8]
ported in the range 2.327–2.678 Å.
Presumably, the longer
bond is due to a more congested steric environment at the
Addition of thf to 2 results in thf coordination and monomer cerium center in 3. Although crystals of 3 could be obtained,
formation to give 1 as evidenced by 1H NMR spectroscopy elemental analysis data was not reliable as solid samples of the
(
Scheme 2). Complexes analogous to 1 will react with H to compound slowly revert back to 3 when the H atmosphere is
2
2
[
9]
form terminal hydrides (Scheme 1). For the smaller lanthan- removed or rapidly when under vacuum.
ides Y, Dy and Lu the reaction was irreversible, however for the
larger metals Nd and Sm, the process was found to be reversi-
ble under the application of vacuum (Scheme 3).
Scheme 3. Formation of 3 from 1.
We find that when 1 is exposed to H (1 atm) in situ, new
2
1
peaks are observed in the H NMR spectrum of 1 (C D ; δ =
6
6
7
9.6, 13.2 ppm), although no noticeable color change is ob-
Figure 3. Thermal ellipsoid plot of the structure of 3 (H atoms omitted; ellip-
soids at 50 % probability).
served. Some peaks of any new hydride product may be miss-
ing due to paramagnetic broadening, or due to CH/CD scram-
bling with the solvent (see below). These new peaks disappear
after taking the solution to dryness and holding under vacuum
Table 2. Selected bond lengths and angles for complex 3.
for 30 min, but reappear when H is added back to the NMR
tube indicating a reversible process on addition or removal of
2
Bond lengths [Å]
Bond angles [°]
Ce(1)–H(1)
Ce(1)-O(1)
Ce(1)–C(Cp′)
av. (C1–5)
Ce(1)–C(Cp′)
av. (C13–17)
2.264(4)
2.530(4)
C(1)–Si(1)–C(10)
C(1)–Si(1)–C(11)
C(1)–Si(1)–C(12)
110.34(8)
112.2(3)
110.34(8)
H .
2
2
The H NMR spectrum of the reaction between 1 and D in
2
(
protio) toluene gave two broadened resonances at δ = –0.38
2.779(5)
2.797(5)
and –6.71 ppm, which were presumably owing to a deuterated
ligand bound to cerium, in addition to a more distinct set of
resonances for d -toluene. Resonances for both the aromatic
8
and aliphatic C–H groups of the toluene were observed. This
data indicate that both sp - and sp -C–H activation of the sol-
Addition of H to 2 meanwhile produced no change in the
2
2
3
1
H NMR spectrum (C D ). Crystals were again grown under an
6
6
vent is occurring, presumably via exchange at the Ce–H moiety. atmosphere of H2 and gave the same unit cell as 2, i.e. no
This behavior has been documented previously for analogous reaction was observed.
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Figure 4. Calculated IR spectra of 3 and 3-D.
–1
The values for cerium–hydrogen bond stretches in the infra- Two main normal modes, at 478 and 598 cm , were seen as
red spectrum for Ce(C H tBu ) H could not be assigned by An- the most dominated by the Ce–H vibration modes. Replacing
5
2
3 2
[
3]
dersen et al. Likewise, Hou et al. did not report the identifica- hydride for deuteride shifts the vibrational frequency by the
tion of any Ln–H stretches for Ln(Cp′) (H)(thf) (Ln = Y, Nd, Sm, change in effective mass i.e. square root of 2. The new stretch-
2
[
9]
–1
Dy and Lu).
ing mode is therefore calculated at 876 cm . The low frequency
Comparison of the IR spectrum of 3 with a sample prepared bend band also moves to lower frequencies of 332 and
–1
using D2 (3-D) did not show any obvious peaks that could 438 cm . We observe a strong absorption centered around
be expected for Ce–H or Ce–D vibrational resonances: the Ln– 800 cm– in the spectra of both 3 and 3-D, possibly due to the
H (Ln = lanthanide) absorption is known to be located in the bound thf, which apparently obscure this new Ce-D peak in 3-
1
–
1
1
100–1350 cm
range for bridging hydrides [e.g. D (see Supporting Information.
[
2,12]
(Cp*LnH)2]
but which is often obscured by bands attributed
Given the unique reversibility of the formation of the
[
2]
to metal-bound thf (terminal transition metal hydride bonds hydride, we were curious to test for possible olefin hydrogen-
are meanwhile observed in the region of 1600 to 2250 cm– ). ation reactivity, which is well-known for a variety of metal
1[1]
[
1]
1
In order to guide us in peak assignment, we used density hydride species. Initial H NMR (C D ) screening showed that
6 6
functional calculations to predict the frequency of the Ce–H 1 was a functional pre-catalyst for the hydrogenation of cis-
stretching mode. 3 was first optimized in gas phase and very stilbene, tert-butylethylene and styrene (ambient temperatures
good agreement between the experimental and optimized and pressures, 5 % catalyst). This behavior would be expected
structures was obtained for the metal ligand distances, e.g. for cyclopentadienyl lanthanide hydrides, which have known as
Ce–thf 2.557 Å (1 % error), and Ce–Cp′(centroid) 2.529 and hydrogenation catalysts since the 1980s, when they were
.505 Å (0.1 and 0.2 % error). The Ce–H distance optimized to amongst the most active known at the time.[15] In this case,
.135 Å, which is 6 % shorter than the experimental value, we demonstrate that in solution, the hydride functionality is
2
2
which we believe is due to our model not taking into account accessible and active, likely part of an equilibrium between
an interaction with a thf molecule on an adjacent molecule. cyclometalated 1 and hydride 3.
Scanning of the Ce–H potential energy including a second mol-
ecule (albeit constrained at the crystal structure) yields a mini-
mum at 2.28 Å, which is in close agreement with experiment.
However, for calculation of vibrational modes one needs to be
Conclusions
at a potential energy minimum which forces us to use the opti- 3 is the second known example of a terminal cerium hydride
mized structure with Ce–H at 2.135 Å, and accepting an error complex, which has proved challenging to synthesize and ne-
in the absolute frequency. From the calculated spectrum, the cessitated a different preparative route than reported for the
[
9]
Ce–H mode is cleanly identified as the normal mode at analogues based on Y, Nd, Sm, Dy and Lu. In the same man-
–
1
1
213 cm (Figure 4). The transverse modes of the Ce–H couple ner, we obtained a cyclometaled “tuck-in” species 1 as a precur-
with the ligand bending modes, which leads to a broader band sor to the hydride 3, however isolation of synthetic intermedi-
–1
at low frequencies in the range between 350 and 600 cm . ates to 1 (e.g. the presumed benzyl compound) was not possi-
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Communication
ble. The dimeric “tuck-over” analog 2 was obtained by exclusion (br.), –6.98 (br., two peaks overlapping), –13.69 (s, br.), –23.27 (br.),
1
–
33.97 (br.) ppm. 13C{ H} NMR (C D ): δ = 4.6, 6.4, 11.6, 13.8, 14.3,
of thf; such “tuck-in” and “tuck-over” complexes are common
6 6
[
16]
23.0, 32.0, 242.3 (* some peaks not observed presumably due to
amongst f-element metallocenes.
species 3 reversibly reforms the cyclometalated parent species
upon prolonged exposure to vacuum. This behavior, which
is notably different from the Andersen hydride Ce(C H tBu ) H
The new terminal hydride
paramagnetism) ppm. 1H NMR (d -toluene): δ = 18.45 (br.), 11.14
8
(
–
(
7
br.), 8.27 (br.), 6.30 (br.), 2.16 (br.), –0.49 (br.), –2.61 (br.), –5.09 (br.),
7.51 (br., two peaks overlapping), –13.74 (br.), –22.91 (br.), –34.49
br.) ppm. 1H NMR ([D ]thf): δ = 19.70 (br.), 12.02 (br.), 9.38 (br.),
1
5
2
3 2
8
(
which forms the hydride from the cyclometalated precursor
.11 (br.), 4.97 (br.), 3.80 (br.), 0.46 (br.), –0.58 (br.), –3.11 (br.), –5.65
br.), –11.98 (br.), –32.76 (br.), –33.65 (br., two peaks overlapping)
towards external substrates. Indeed, we have found that 3 ppm. Elemental analysis for C H CeSi (1 – thf) calcd. % (found)
[
3]
irreversibly ), is likely to indicate a unique reactivity profile of
(
3
24
41
2
facilitates C–H/D exchange between D and benzene, toluene C 54.82 (54.47) H 7.86 (7.89). IR (KBr disc): ν˜ = 2723 (w), 2139 (w),
2
or thf, catalytically. We currently are exploring more reactivity 1571 (w), 1445 (br., s), 1382 (m), 1323 (s), 1245 (s), 1188 (w), 1124
(
5
m), 1020 (s), 951 (w), 921 (w), 837 (br., s), 753 (s), 679 (s), 628 (s),
65 (w) cm .
modes of this compound.
–
1
5
1
{
(C Me SiMe )Ce(μ-η :η -C Me SiMe CH )} (2). Method 1: Hy-
5 4 3 5 4 2 2 2
drogenolysis. Hydrogen (1 atm) was added to a degassed solution
of 1 (0.100 g, 0.16 mmol) in toluene (20 mL) with stirring, where-
upon the green color immediately turned to pink. After stirring for
Experimental Section
30 min, the solvent was removed by vacuum and the product re-
General: Unless noted otherwise, all operations were performed
under a purified argon atmosphere in a standard MBraun UniLab
drybox or under an argon atmosphere using high-vacuum and
crystallized from a minimum quantity of hexane at –30 °C (m =
1
13
1
0.056 g, 0.05 mmol, 67 % yield). H and C{ H}NMR (C ): no ob-
servable signals. Elemental analysis for C48 82Ce Si calcd. %
2 4
D
6 6
H
Schlenk techniques. Hydrocarbon solvents were purchased anhy- (found) C 53.81 (53.37) H 7.86 (7.95). IR (KBr disc): ν˜ = 1621 (br., w),
drous from Sigma–Aldrich, and further dried with activated molec-
1441 (m), 1326 (m), 1248 (s), 1026 (s), 942 (s), 837 (s), 753 (m), 687
–
1
ular sieves (4 Å). Deuterated solvents were purchased from Cam- (w), 629 (w), 628 (w), 553 (w) cm .
bridge Isotope Laboratory, and dried with molecular sieves (4 Å).
Method 2: Thermolysis. A solution of 1 (0.100 g, 0.16 mmol) in
Unless noted, chemicals were purchased from commercial sources
and used without further purification. K(CH C H ) was prepared by
hexane (20 mL) was heated to 60 °C in a sealed ampule with a
Teflon® stopcock for one hour, whereupon the green color turned
to pink. the solvent was removed by vacuum and the product re-
crystallized from a minimum quantity of hexane at –30 °C (m =
2
6 5
deprotonation of toluene by KOtBu/nBuLi. K(C Me SiMe ) was pre-
5
4
3
pared by deprotonation of C Me (H)SiMe by K[N(SiMe ) ] in tolu-
5
4
3
3 2
ene. C Me (H)SiMe , K[N(SiMe ) ], nBuLi (1.6
M
in hexanes) and
5
4
3
3 2
0
.060 g, 0.06 mmol, 72 % yield).
Ce(C Me SiMe ) (H)(thf) (3): A sample of 1 was exposed to H
2
KOtBu were purchased from Sigma–Aldrich and used as received.
H2 gas was provided by the LANL in-house gas facility at 99.9 %
grade. CeCl3 was purchased anhydrous from Strem and used as
5
4
3 2
(1 atm; no color change observed) which formed 3 quantitatively
1
received. All NMR spectra were recorded using a Bruker 400 Ultra
by H NMR spectroscopy. 3 could be recrystallized under a H at-
2
1
Shield spectrometer. H NMR spectra were referenced to solvent mosphere (hexane) however was not stable as a solid due to loss
1
residual peaks (δ = 7.15 ppm for C D ). Infrared spectra were meas-
of H and formation of 1 under vacuum. H NMR (C D ): δ = 80.2
6
6
2
6 6
ured as KBr discs using a Perkin–Elmer Spectrum Two FTIR spec-
trometer. Elemental analyses were performed by Midwest Microlab
(s, br.), 19.14 (s, br.), 11.66 (s, br.), 8.61 (s, br.), 6.51 (s, br.), –3.07 (s,
br.), –5.44 (s, br.), –7.43 (s, br.), –8.16 (s, br.), –14.15 (s, br.), –23.88 to
–24.83 (m, br.), –35.01 to –36.79 (m, br.) ppm. 13C{ H} NMR (C D :
1
(Indianapolis, IN).
6
6
δ = 4.6, 6.4, 11.6, 13.8, 14.3, 23.0, 32.0, 242.3 ppm (* some peaks
not observed presumably due to paramagnetism).
5
1
(
η :η -C Me SiMe CH )Ce(C Me SiMe )(thf) (1): A mixture of
5 4 2 2 5 4 3
CeCl (0.392 g, 1.59 mmol) and K(C Me SiMe ) (0.74 g, 3.18 mmol)
3
5
4
3
Computational Methodology: The calculations of minimum-en-
ergy geometries, vibrational modes and frequencies, and infrared
spectra of all of the compounds in this paper were computed at
the density functional theory level, using the hybrid functional from
were stirred in thf (50 mL) overnight, resulting in the formation of
a yellow solution. Filtration through celite and removal of volatiles
gave a bright yellow solid, assumed to be “Ce(C Me SiMe ) -
5
4
3 2
Cl K(thf) ”, which was subsequently de-solvated at 150 °C for 6 h
2
x
[
17]
the Truhlar group M06.
The Ce ion was represented by the SDD
under vacuum (m = 0.828 g). This process resulted in a subtle color
change from bright- to straw-yellow. This material {assumed to be
[
18]
pseudopotential whereas for the light elements all-electron basis
sets were employed. The C, O, and Si centers were represented by
Pople's 6-31+g* basis set. The smaller 6-31g was used for all the
hydrogen atoms as they are removed from the metal center. One
exception was made for the hydride center where we used the
larger 6-311+g* basis set in an effort to best describe the electronic
structure of the region of interest. All the calculations were carried
“
Ce(C Me SiMe ) Cl K”}, was combined with K(CH C H ) (0.169 g,
5 4 3 2 2 2 6 5
1
.30 mmol) in toluene and stirred overnight to yield a green solu-
tion. This was filtered through celite, leaving yellow solids, and then
reduced to dryness in vacuo. The solids were subsequently ex-
tracted into hexane (50 mL) and filtered again through celite. The
subsequent green-red dichroic solution was reduced in volume to
[
19]
out with the Gaussian09 rev. D.01 package.
1
0 mL and a dark red crystalline material was obtained after cooling
to –30 °C. Finally, this material was re-dissolved in thf (20 mL) and
hydrogen (1 atm) was added to the degassed solution with stirring,
whereupon the green color turned to pink. After stirring for 30 min,
the solvent was removed by vacuum and the product recrystallized
CCDC 1056189 (for 1), 1056190 (for 2), and 1056191 (for 3) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre.
from a minimum quantity of hexane at –30 °C (m = 0.069 g,
1
0
.12 mmol, 17 % yield from CeCl ). H NMR (C D ): δ = 18.75 (br.),
Supporting Information: Crystallographic tables cif files for 1–3,
3
6 6
1
1.37 (br.), 8.44 (br.), 6.45 (br.), 2.13 (br.), –0.46 (br.), –2.66 (br.), –5.05 experimental procedures and characterizing data for 1–3.
Eur. J. Inorg. Chem. 0000, 0–0
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Communication
[
7] Y. K. Gun'ko, P. B. Hitchcock, M. F. Lappert, Organometallics 2000, 19,
Acknowledgments
2
832.
This work was funded by Los Alamos National Laboratory
LDRD-DR (Laboratory Directed Research and Development – Di-
rected Research). Los Alamos National Laboratory is operated
by Los Alamos National Security, LLC, for the National Nuclear
Security Administration of the U.S. Department of Energy under
contract DE-AC5206NA25396.
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[
Keywords: Hydrides · C–H activation · Lanthanides ·
Cerium
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Received: June 20, 2016
Published Online: ■
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
f-Block Hydrides
The cerium tuck-in metallocene Ce-
(
C H SiMe )(C H SiMe CH -)(thf) was
5 4 3 5 4 2 2
O. T. Summerscales, E. R. Batista,
B. L. Scott, M. P. Wilkerson,
A. D. Sutton* ........................................ 1–7
synthesized and shown to reversibly
form terminal hydride species
Ce(C H SiMe ) (H)(thf) upon reaction
a
5
4
3 2
Reversible Formation of a Cerium-
Bound Terminal Hydride: Ce(C Me -
with H . This new hydride is a catalyst
2
5
4
in H/D exchange reactions between
SiMe ) (H)(thf)
3
2
3
2
with both sp -CH and sp -CH bonds,
and for the hydrogenation of unsatu-
rated alkene bonds.
DOI: 10.1002/ejic.201600737
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim