Potassium Yttrium Ate Complexes: Synergistic Effect Enabled Reversible H2 Activation and Catalytic Hydrogenation

Article abstract of DOI:10.1021/acscatal.9b02899

A potassium yttrium benzyl ate complex was generated simply by mixing an yttrium amide and potassium benzyl. The benzyl ate complex could undergo peripheral deprotonation to produce a cyclometalated complex or hydrogenation to give a hydride ate complex. The latter hydride ate complex features a (KH)₂ structure protected by two yttrium amide complexes. The synergistic effect between potassium hydride and the amide ligand enables the complex to deprotonate a methyl C-H bond. The combination of intramolecular deprotonation of the hydride ate complex and hydrogenation of the cyclometalated complex constitutes a reversible H₂ activation process. Using this process involving formal addition and elimination of H₂, we accomplished the catalytic hydrogenation of alkenes, alkynes, and imines.

Full text of DOI:10.1021/acscatal.9b02899

Letter
Cite This: ACS Catal. 2019, 9, 8766−8771
pubs.acs.org/acscatalysis
Potassium Yttrium Ate Complexes: Synergistic Effect Enabled
Reversible H Activation and Catalytic Hydrogenation
2
Dan-Dan Zhai, Hui-Zhen Du, Xiang-Yu Zhang, Yu-Feng Liu, and Bing-Tao Guan*
State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071,
China
*
S Supporting Information
ABSTRACT: A potassium yttrium benzyl ate complex was
generated simply by mixing an yttrium amide and potassium
benzyl. The benzyl ate complex could undergo peripheral
deprotonation to produce a cyclometalated complex or
hydrogenation to give a hydride ate complex. The latter
hydride ate complex features a (KH) structure protected by
2
two yttrium amide complexes. The synergistic effect between
potassium hydride and the amide ligand enables the complex
to deprotonate a methyl C−H bond. The combination of
intramolecular deprotonation of the hydride ate complex and
hydrogenation of the cyclometalated complex constitutes a reversible H activation process. Using this process involving formal
2
addition and elimination of H , we accomplished the catalytic hydrogenation of alkenes, alkynes, and imines.
2
KEYWORDS: potassium hydride, ate complex, synergistic effect, reversible H activation, hydrogenation
2
3
eversible activation of H is crucial both for energy
storage and for catalytic hydrogenation reactions, which
are among the most fundamental transformations in organic
1, eq 2). In contrast, alkyl early transition-metal catalysts
2
4
R
prefer to undergo σ-bond metathesis reaction between the
M−C bond and H
state and giving an alkane and a metal hydride complex
Scheme 1, eq 3).
important intermediates and catalyst precursors, have been
extensively studied over the past several decades, because of
their versatile structures and reactivities. Some hydride
complexes are reactive enough to undergo intramolecular
, proceeding via a four-centered transition
2
synthesis; various metal-mediated H activation processes have
2
4
−6
1
(
Metal hydride complexes, which are
been reported. Activation of H with late-transition-metal
2
catalysts, either heterogeneous or homogeneous, occurs via a
2
redox process at the metal center (Scheme 1, eq 1). Over the
7
past couple of decades, metal−ligand cooperation in pincer
complexes of late-transition metals has emerged as a powerful
C−H bond activation of their own ligands to give “tuck-in”
cyclometalated complexes and liberate H . The combination
alternative H activation strategy to the redox process (Scheme
2
8
2
of internal deprotonation of a hydride complex and hydro-
genation of the cyclometalated complex constitutes a process
for reversible activation of H , which provide a H activation
Scheme 1. Metal-Mediated H Activation
2
2
2
approach involving early transition metals and even s-block
9
metals. In 1979, Andersen and co-workers reported γ-
metalation reactions of actinide hydride complexes HAn[N-
(
SiMe ) ] (An = Th and U) in which H is reversibly
3 2 3 2
activated via γ-deprotonation of one of the silylamide ligands
and subsequent hydrogenation of a four-membered metal-
9a,b
locycle. The research groups of Evans, Teuben, Chirik, and
Sutton reported the reversible addition and release of H from
2
metallocene hydrides of samarium, yttrium, cerium, and
9c−g
zirconium.
Okuda recently achieved a reversible H release
2
and capture by using a cationic lutetium polyhydride
9h
complex; specifically, a C−H bond of one of the methyl
groups of the neutral Me TACD ligand of the complex is
4
Received: July 11, 2019
Revised: August 20, 2019
©
XXXX American Chemical Society
8766
DOI: 10.1021/acscatal.9b02899
ACS Catal. 2019, 9, 8766−8771

ACS Catalysis
Letter
activated. Despite these achievements, this reversible H2
activation process remains underdeveloped in catalytic trans-
formations.
Because of the strong coordination ability of the hydride
anion, hydride complexes of early transition metals and s-block
metals usually prefer to form dimers or clusters via bridging
7
,10
coordination of the hydrides to the metals.
In contrast to
the well-developed homometallic hydride complexes, hetero-
metallic hydride complexes have rarely been explored, because
of the shortage of available synthetic methods. Several groups
Figure 1. Solid-state structures of potassium yttrium benzyl ate
complex A (left) and cyclometalated complex B (right) with thermal
ellipsoids set at 50% probability. H atoms (except H19, H19′, H13A,
and H13B) are omitted for clarity. Selected bond lengths for A: Y1−
C19, 2.529(7) Å; K1−C19, 3.238(7) Å; K1−C20, 3.101(7) Å; K1−
C21, 3.334(8) Å; K1−H19, 2.799(2) Å. Selected bond angle for A:
Y1−C19−K1, 154.169(3)°. Selected bond lengths for B: Y1−C13,
1
2
have synthesized hydride complexes containing M −H−M
1
2
moieties (where M = Ti, Zr, Ln, or Al and M = Li, Na, or
1
1
K). However, the reactivity of these heterometallic hydride
complexes remains mostly unknown. Herein, we report the
synthesis and reactions of a potassium yttrium hydride ate
complex featuring a protected (KH) unit. The synergistic
2
2
.452(3) Å; K1−C13, 2.998(3) Å; K1−H13A, 2.814(3) Å; K1−
effect of the potassium yttrium ate complexes can achieve a
H13B, 2.839(3) Å. Selected bond angle for B: Y1−C13−K1,
177.035(1)°.
reversible H activation and affect the hydrogenation of olefins,
2
alkynes, and imines (Scheme 1, eq 4).
Because anionic rare-earth species form readily as by-
products in alkyl lanthanide synthesis, we began our study by
combining an yttrium amide compound with KBn. When KBn,
which is insoluble in benzene, was mixed with a C D solution
6
6
of Y[N(SiMe ) ] , an orange solution formed rapidly (see
3
2 3
Scheme 2). In-situ NMR spectroscopy revealed a doublet at δ
Scheme 2. Potassium Yttrium Ate Complexes
Figure 2. Solid-state structure of potassium yttrium hydride ate
complex C, {KHY[N(SiMe ) ] } , with thermal ellipsoids set at 50%
3
2 3 2
probability. H atoms (except Ha, Hb, H4, H6, H12, H14, H16, and
H18) are omitted for clarity. Selected bond lengths: Y1-Ha, 2.034(2)
Å; K1-Ha, 2.728(2) Å; K1-Hb, 2.643(2) Å; K1−H4, 2.661(4) Å;
K1−H6, 2.823(4) Å; K1−H12, 2.781(4) Å; K1−H14, 3.104(4) Å;
K1−H16, 2.679(3) Å; K1−H18, 2.842(4) Å; K1−N3, 3.029(1) Å.
Selected bond angles: Y1-Ha-K1, 148.89(7)°; Ha−K1−Hb,
76.38(5)°; K1−Ha−K1′, 103.62(5)°.
core of the dimeric hydride ate complex features a (KH)2
parallelogram structure. Remarkably, there were no coordinat-
ing solvent molecules; only a N atom and two hydride atoms
were bonded directly to the K atom. The lack of solvent
molecules may be attributable to six agostic interactions with
the nearby methyl groups, meeting with the high coordination
requirement of the K+ cation. Formally speaking, we
1
2
.22 (J = 4.0 Hz, 2H) in H NMR spectrum and doublet for a
1
3
secondary carbon atom at δ 54.2 (J = 33.3 Hz) in the
NMR spectrum, suggesting the generation of an ate complex
with a newly formed Y−benzyl bond. As shown in Figure 1
left), X-ray diffraction (XRD) analysis indicated that the
complex (A) is composed of contact ion pairs consisting of
C
12
14
(
synthesized a hydrocarbon-soluble (KH) unit protected by
2
two yttrium amide complexes via Y−H and K−N coordinative
−
+
15
{
YBn[N(SiMe ) ] } and [K(THF)] . The potassium cation
interactions. It is important to note that hydride ate complex
3
2 3
3
also coordinates with another molecular unit via an η π-
interaction and an agostic interaction, which extends the
structure supramolecularly (see the Supporting Information).
In its solid state, complex A was stable for months in a
glovebox at −35 °C. However, in benzene solution, the
complex slowly underwent peripheral deprotonation reactions
to produce cyclometalated complex B. XRD analysis of a
single crystal of B revealed a four-membered Y−N−Si−C ring
similar to that described by Niemeyer (Figure 1, right).
C smoothly underwent intramolecular C−H bond activation
upon heating to afford cyclometalated complex B with release
of two H molecules. Thus, by deprotonation of hydride ate
2
complex C and hydrogenation of deprotonated complex B, we
achieved a reversible H activation process.
2
Given the reversible H2 activation ability of potassium
yttrium ate complexes, we explored their applications for
catalytic hydrogenation. After preliminary condition optimiza-
tion, we achieved complete hydrogenation of 1-octene with 5
mol % of hydride ate complex C as a catalyst in 3 h at 80 °C
under a 6 bar H pressure in C D (Table 1, entry 1).
13
13b
Upon treatment with H , both benzyl ate complex A and
2
cyclometalated complex B smoothly underwent hydrogenation
to produce hydride complex C. X-ray analysis revealed that the
hydride atom coordinates not only with the Y atom but also
with two K atoms, forming a dimer held together by the
interactions between the K and hydride atoms (Figure 2). The
2
6
6
Complete hydrogenation of 1-octene could also be achieved by
using benzyl ate complex A (prepared either in advance or in
situ from the yttrium amide and KBn) as the catalyst (Table 1,
entries 2 and 3). Control reactions that were conducted with
8
767
DOI: 10.1021/acscatal.9b02899
ACS Catal. 2019, 9, 8766−8771

ACS Catalysis
Letter
Table 1. Effects of Hydrogenation Reaction Parameters
Table 2. Catalytic Hydrogenation Reactions*
a
b
entry
variation from standard conditions
conversion (%)
1
2
3
4
5
6
7
8
none
complex A (10 mol %) as catalyst
KBn + Y[N(SiMe ) ] (10 mol %) as catalyst
99
99
99
<5
<5
<5
<5
70
72
17
16
99
3
2 3
Y[N(SiMe ) ] (10 mol %) as catalyst
3
2 3
KBn (10 mol %) as catalyst
KN(SiMe ) (10 mol %) as catalyst
3
2
KH (10 mol %) as catalyst
NaBn + Y[N(SiMe ) ] (10 mol %) as catalyst
3
2 3
c
9
LiBn′ + Y[N(SiMe ) ] (10 mol %) as catalyst
3
2 3
1
1
1
0
1
2
THF (0.5 mL) as additive
18-crown-6 (20 mol %) as additive
{KHY[N(SiMe ) ] } (C, 0.5 mol %), 6 h
d
3
2 3 2
a
Standard conditions: 1-octene 1a (0.3 mmol), C (5 mol %), H (6
2
b
1
bar), 80 °C, C D (0.5 mL), 3 h. Determined by H NMR
6
6
c
d
spectroscopy. LiBn′ = LiCH C H NMe -o. 1-Octene (1a) (3.0
2
6
4
2
*
mmol).
Conditions: 1 (0.3 mmol), C (5 mol %), H (6 bar), 80 °C, C D
2 6 6
1
(
0.5 mL). Conversions were determined by H NMR spectroscopy.
a
b
c
Methylcyclopentane also formed (in 28% yield). 100 °C. H (12
2
d
the yttrium amide, KBn, KN(SiMe ) , or KH as a catalyst
bar). Z/E = 11:1 (determined by inverse gated decoupled
spectroscopy), along with 11% 2-hexene (Z/E = 2.5:1). H (10 bar).
3
2
e
failed to give any of the desired hydrogenation product,
suggesting the synergistic effect between KH and yttrium
amide plays a crucial role for the catalytic hydrogenation
2
Scheme 3. Control Experiments
(Table 1, entries 4−7). Combinations of the yttrium amide
with LiBn′ and with NaBn also catalyzed the hydrogenation,
but with lower conversions (Table 1, entries 8 and 9). The
addition of THF or 18-crown-6 drastically decreased the
conversion (Table 1, entries 10 and 11), probably because
+
coordination of these compounds with the K cation destroyed
the hydride ate structure and prevented the synergistic effect.
The hydrogenation could actually be achieved, even at a much
lower catalyst loading (0.5 mol %), when the reaction time was
prolonged to 6 h (Table 1, entry 12).
We then explored the catalytic activity of the potassium
yttrium hydride ate complex for the hydrogenation of a variety
of alkenes, alkynes, and imines (see Table 2). Trimethylsily-
lethene, 1,5-hexadiene, and 1,9-decadiene smoothly gave the
corresponding alkanes (2b−2d) in high conversions. Interest-
ingly, the reaction of 1,5-hexadiene gave methylcyclopentane
(
28% yield) as an intramolecular cyclization byproduct, in
addition to hexane. The hydrogenation reactions of alkenes
with more sterically bulky alkyl substituents were relatively
slow, requiring a longer reaction time to achieve complete
conversion, they nevertheless afforded the desired alkanes (2e
and 2f). Complete conversion of a disubstituted ethene (2,5-
dimethyl-1,5-hexadiene) to 2g required a reaction temperature
of 100 °C. Norbornene smoothly underwent the catalytic
hydrogenation under the standard conditions to afford 2h,
whereas the hydrogenation of cyclohexene required much
harsher conditions to afford 2i. The reaction of styrene
resulted in the formation of oligomers, but disubstituted
styrenes cleanly afforded catalytic hydrogenation products 2j,
To gain insight into the mechanism of this catalytic
hydrogenation reaction, we performed the hydrogenation of
complex B with H and D under identical conditions at room
2
2
temperature (Scheme 3, eqs 5 and 6). We found that the
reaction of B with H was twice as fast as its reaction with D .
2
2
A similar kinetic isotope effect (1.9) was also measured for the
B-catalyzed hydrogenation of 1,1-diphenylethylene (1j) with
H and D (Scheme 3, eqs 7 and 8). For the reaction between
2
2
C and D , we observed the emergence of a signal for a
2
2
k, and 2l. 3-Hexyne was also a suitable substrate, undergoing
selective semihydrogenation to afford (Z)-3-hexene (2m) in
1% yield (see the Supporting Information). Finally, we found
deuterated methyl group (see the Supporting Information).
However, the reaction of 1j with D gave 2j-d with a lower
2
8
deuterium content than expected (Scheme 3, eq 8). This result
that several imines also underwent hydrogenation to provide
suggests that an H−D exchange reaction between D and the
2
the corresponding amines (2n−2q) under the increased H
C−H of the methyl group occurred both in the hydrogenation
of complex B and in the catalytic hydrogenation of the alkene.
2
pressure conditions.
8
768
DOI: 10.1021/acscatal.9b02899
ACS Catal. 2019, 9, 8766−8771

ACS Catalysis
Letter
To investigate product formation in more detail, we allowed 1j
to react with hydride ate complex C (Scheme 3, eq 9). After
heating at 80 °C for 3 h, the hydrogenated product 2j was
obtained in 84% yield, and C was completely transformed to
complex B. Notably, the hydrogenation reaction even occurred
AUTHOR INFORMATION
Corresponding Author
E-mail: guan@nankai.edu.cn.
■
*
ORCID
Bing-Tao Guan: 0000-0003-0686-4945
Notes
The authors declare no competing financial interest.
in the absence of H ; that is, hydride ate complex C, in effect,
2
released the H , which added across the double bond of the
2
alkene. Based on the above-described observations, we propose
the reaction mechanism shown in Scheme 4 for alkene 1j.
ACKNOWLEDGMENTS
■
Scheme 4. A Possible Mechanism
We gratefully acknowledge the support from the State Key
Laboratory of Elemento-Organic Chemistry National Program
for Support of Top-notch Young Professionals. This project
was supported by the National Natural Science Foundation of
China (No. 21372123) and the National Natural Science
Foundation of Tianjin (No. 19JCYBJC20100).
DEDICATION
Dedicated to the 100th anniversary of Nankai University.
■
REFERENCES
■
(
1) (a) Blaser, H. U.; Pugin, B.; Spindler, F.; Saudan, L. A.
Hydrogenation. In Applied Homogeneous Catalysis with Organometallic
Compounds; Cornils, B., Herrmann, W. A., Beller, M., Paciello, R.,
Eds.; Wiley−VCH: Weinheim, Germany, 2017. (b) Pettinari, C.;
Marchetti, F.; Martini, D. Metal Complexes as Hydrogenation Catalysts
in Comprehensive Coordination Chemistry II; McCleverty, J. A., Meyer,
T. J., Eds.; Pergamon: Oxford, U.K., 2003; pp 75−139. (c) Li, Y.;
Coordination of the unsaturated bond of the alkene to dimeric
potassium yttrium hydride ate complex C results in
deaggregation of the dimeric complex and a hydride insertion
reaction to give an alkyl ate intermediate D. Subsequent
peripheral deprotonation of a methyl group by the alkyl anion
gives the hydrogenation product and four-membered ring
complex B, which then undergoes a formal H2 addition
reaction to regenerate hydride ate complex C, completing the
catalytic cycle.
In conclusion, we prepared a potassium yttrium benzyl ate
complex A that can undergo peripheral deprotonation of the
methyl group to afford four-membered cyclometalated
complex B. The subsequent hydrogenation of B with H2
provides dimeric potassium yttrium hydride ate complex C,
Hou, C.; Jiang, J.; Zhang, Z.; Zhao, C.; Page, A. J.; Ke, Z. General H
2
Activation Modes for Lewis Acid−Transition Metal Bifunctional
Catalysts. ACS Catal. 2016, 6, 1655−1662. Frustrated Lewis pairs
(
FLPs) achieved a great breakthough on reversible H activation with
2
main group element compounds; see: (d) Welch, G. C.; Juan, R. R. S.;
Masuda, J. D.; Stephan, D. W. Reversible, Metal-Free Hydrogen
Activation. Science 2006, 314, 1124−1126. (e) Stephan, D. W. The
broadening reach of frustrated Lewis pair chemistry. Science 2016,
354, aaf7229. (f) Lam, J.; Szkop, K. M.; Mosaferi, E.; Stephan, D. W.
FLP catalysis: main group hydrogenations of organic unsaturated
substrates. Chem. Soc. Rev. 2019, 48, 3592−3612.
(
2) Kubas, G. J. Fundamentals of H Binding and Reactivity on
2
Transition Metals Underlying Hydrogenase Function and H2
Production and Storage. Chem. Rev. 2007, 107, 4152−4205.
(3) (a) Karvembu, R.; Prabhakaran, R.; Natarajan, K. Shvo’s
which features a formal (KH) structure protected by two
2
diruthenium complex: a robust catalyst. Coord. Chem. Rev. 2005, 249,
yttrium amides. For the synergistic effect between the
potassium hydride and the amide ligand, complexes B and C
exist in equilibrium and can be interconverted by reversible
9
11−918. (b) Gunanathan, C.; Milstein, D. Applications of
Acceptorless Dehydrogenation and Related Transformations in
Chemical Synthesis. Science 2013, 341, 1229712. (c) Gunanathan,
C.; Milstein, D. Bond Activation and Catalysis by Ruthenium Pincer
Complexes. Chem. Rev. 2014, 114, 12024−12087.
formal addition or elimination of a molecule of H . Using this
2
process, we accomplished the catalytic hydrogenation of
alkenes, alkyne, and imines. Considering the ready availability
and good activity of the catalyst, this reaction constitutes a
(4) (a) Watson, P. L. Methane exchange reactions of lanthanide and
early-transition-metal methyl complexes. J. Am. Chem. Soc. 1983, 105,
6491−6493. (b) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger,
practical approach to H activation and catalytic hydrogenation
2
B. J.; Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. σ-
Bond metathesis for carbon-hydrogen bonds of hydrocarbons and Sc-
R (R = H, alkyl, aryl) bonds of permethylscandocene derivatives. J.
Am. Chem. Soc. 1987, 109, 203−219. (c) Lin, Z. Current
reactions. Exploration of applications of the potassium yttrium
ate complex and a search for additional ate complex systems
are underway in our laboratory.
understanding of the σ-bond metathesis reactions of L MR. Coord.
n
ASSOCIATED CONTENT
Supporting Information
■
Chem. Rev. 2007, 251, 2280−2291. (d) Waterman, R. σ-Bond
Metathesis: A 30-Year Retrospective. Organometallics 2013, 32,
7249−7263.
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acscatal.9b02899.
(5) For selected reviews, see: (a) Anwander, R. Rare earth metals in
homogeneous catalysis. In Applied Homogeneous Catalysis with
Organometallic Compounds, 2nd Edition; Herrmann, W. A., Cornils,
B., Eds.; Wiley−VCH: Weinheim, Germany, 2002; pp 974−1014.
1
13
Experimental details, H, C NMR and other character-
ization data, single-crystal X-ray analysis (PDF)
Crystallographic data for Complex A (CIF)
Crystallographic data for Complex B (CIF)
Crystallographic data for Complex C (CIF)
(
b) Coperet, C. Hydrogenation with Early Transition Metal,
́
Lanthanide and Actinide Complexes. In The Handbook of
Homogeneous Hydrogenation; de Vries, J. G., Elsevier, C. J., Eds.;
8
769
DOI: 10.1021/acscatal.9b02899
ACS Catal. 2019, 9, 8766−8771

ACS Catalysis
Letter
Wiley−VCH: Weinheim, Germany, 2008; pp 111−151. For selected
examples, see: (c) Jeske, G.; Lauke, H.; Mauermann, H.; Schumann,
H.; Marks, T. J. Highly reactive organolanthanides. A mechanistic
study of catalytic olefin hydrogenation by bis-
Activation by f-Block Complexes. Angew. Chem., Int. Ed. 2015, 54,
82−100.
(9) (a) Simpson, S. J.; Turner, H. W.; Andersen, R. A. Hydrogen-
d e u t e r i u m e x c h a n g e : p e r d e u t e r i o h y d r i d o t r i s -
(hexamethyldisilylamido)thorium(IV) and -uranium(IV). J. Am.
Chem. Soc. 1979, 101, 7728−7729. (b) Simpson, S. J.; Turner, H.
W.; Andersen, R. A. Preparation and hydrogen-deuterium exchange of
alkyl and hydride bis(trimethylsilyl)amido derivatives of the actinide
elements. Inorg. Chem. 1981, 20, 2991−2995. (c) Evans, W. J.;
Ulibarri, T. A.; Ziller, J. W. Reactivity of samarium complex
[(C Me ) Sm(μ-H)] in ether and arene solvents. X-ray crystal
(pentamethylcyclopentadienyl) and related 4f complexes. J. Am.
Chem. Soc. 1985, 107, 8111−8118. (d) Molander, G. A.; Winterfeld, J.
Organolanthanide catalyzed hydrogenation and hydrosilylation of
substituted methylenecycloalkanes. J. Organomet. Chem. 1996, 524,
2
75−279. (e) Obora, Y.; Ohta, T.; Stern, C. L.; Marks, T. J.
Organolanthanide-Catalyzed Imine Hydrogenation. Scope, Selectivity,
Mechanistic Observations, and Unusual Byproducts. J. Am. Chem. Soc.
5
5
2
2
1
997, 119, 3745−3755. (f) Getsoian, A. G. B.; Hu, B.; Miller, J. T.;
structures of the internally metalated complex (C Me ) Sm(μ-H)(μ-
5 5 2
Hock, A. S. Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic
CH C Me )Sm(C Me ), the benzyl complex (C Me ) Sm-
2
5
4
5
5
5
5 2
Hydrogenation of Propylene. Organometallics 2017, 36, 3677−3685.
(
(
(
CH C H )(THF), and the siloxide complex [(C Me ) Sm-
2 6 5 5 5 2
(
6) Recently, s-block metals complexes, including calcium,
THF)] (μ-OSiMe OSiMe O). Organometallics 1991, 10, 134−142.
2
2
2
strontium, barium, and potassium, have made great progress in
d) Evans, W. J.; Champagne, T. M.; Ziller, J. W. Organolutetium
catalytic hydrogenation reactions. In this process, activation of H by
2
Vinyl and Tuck-Over Complexes via C-H Bond Activation. J. Am.
Chem. Soc. 2006, 128, 14270−14271. (e) Booij, M.; Deelman, B. J.;
Duchateau, R.; Postma, D. S.; Meetsma, A.; Teuben, J. H. Carbon-
hydrogen activation of arenes and substituted arenes by the yttrium
hydride (Cp* YH) : competition between Cp* ligand metalation,
the s-block metal complexes probably also occurs by means of σ-bond
metathesis. See: (a) Spielmann, J.; Buch, F.; Harder, S. Early Main-
Group Metal Catalysts for the Hydrogenation of Alkenes with H2.
Angew. Chem., Int. Ed. 2008, 47, 9434−9438. (b) Jochmann, P.;
2
2
Davin, J. P.; Spaniol, T. P.; Maron, L.; Okuda, J. A Cationic Calcium
Hydride Cluster Stabilized by Cyclen-Derived Macrocyclic N,N,N,N
Ligands. Angew. Chem., Int. Ed. 2012, 51, 4452−4455. (c) Leich, V.;
Spaniol, T. P.; Maron, L.; Okuda, J. Molecular Calcium Hydride:
Dicalcium Trihydride Cation Stabilized by a Neutral NNNN-Type
Macrocyclic Ligand. Angew. Chem., Int. Ed. 2016, 55, 4794−4797.
arene metalation, and hydrogen/deuterium exchange. Molecular
1
5
structures of Cp* Y(μ-H)(μ-η ,η -CH C Me )YCp* and Cp* Y(o-
2
2
5
4
2
C H PPh CH ). Organometallics 1993, 12, 3531−3540. (f) Pool, J.
6
4
2
2
A.; Bradley, C. A.; Chirik, P. J. A Convenient Method for the
Synthesis of Zirconocene Hydrido Chloride, Isobutyl Hydride, and
Dihydride Complexes Using tert-Butyl Lithium. Organometallics 2002,
(d) Schuhknecht, D.; Lhotzky, C.; Spaniol, T. P.; Maron, L.; Okuda, J.
2
1, 1271−1277. (g) Summerscales, O. T.; Batista, E. R.; Scott, B. L.;
Calcium Hydride Cation [CaH]+ Stabilized by an NNNN-type
Macrocyclic Ligand: A Selective Catalyst for Olefin Hydrogenation.
Angew. Chem., Int. Ed. 2017, 56, 12367−12371. (e) Bauer, H.; Alonso,
Wilkerson, M. P.; Sutton, A. D. Reversible Formation of a Cerium-
Bound Terminal Hydride: Ce(C Me SiMe ) (H)(thf). Eur. J. Inorg.
5
4
3 2
Chem. 2016, 2016, 4551−4556. (h) Fegler, W.; Venugopal, A.;
Spaniol, T. P.; Maron, L.; Okuda, J. Reversible Dihydrogen Activation
in Cationic Rare-Earth-Metal Polyhydride Complexes. Angew. Chem.,
Int. Ed. 2013, 52, 7976−7980.
M.; Farber, C.; Elsen, H.; Pahl, J.; Causero, A.; Ballmann, G.; De
̈
Proft, F.; Harder, S. Imine hydrogenation with simple alkaline earth
metal catalysts. Nat. Catal. 2018, 1, 40−47. (f) Shi, X.; Qin, G.; Wang,
Y.; Zhao, L.; Liu, Z.; Cheng, J. Super-Bulky Penta-arylcyclopenta-
dienyl Ligands: Isolation of the Full Range of Half-Sandwich Heavy
Alkaline-Earth Metal Hydrides. Angew. Chem., Int. Ed. 2019, 58,
(
10) (a) Harder, S. Molecular early main group metal hydrides:
synthetic challenge, structures and applications. Chem. Commun.
012, 48, 11165−11177. (b) Mukherjee, D.; Okuda, J. Molecular
Magnesium Hydrides. Angew. Chem., Int. Ed. 2018, 57, 1458−1473.
11) (a) Jacoby, D.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
2
4
356−4360. (g) Bauer, H.; Alonso, M.; Fischer, C.; Rosch, B.; Elsen,
̈
H.; Harder, S. Simple Alkaline-Earth Metal Catalysts for Effective
(
Alkene Hydrogenation. Angew. Chem., Int. Ed. 2018, 57, 15177−
Zirconium meso-octaethylporphyrinogen as a carrier for sodium
hydride in toluene: zirconium-sodium bimetallic hydride and alkyls. J.
Am. Chem. Soc. 1993, 115, 3595−3602. (b) Lukens, W. W.;
Matsunaga, P. T.; Andersen, R. A. Synthesis and Structure of
Cp* TiH, Cp* TiH Li(tmed), and [Cp* TiOLi(THF)] . Organo-
1
5182. (h) Elsen, H.; Farber, C.; Ballmann, G.; Harder, S. LiAlH :
̈
4
From Stoichiometric Reduction to Imine Hydrogenation Catalysis.
Angew. Chem., Int. Ed. 2018, 57, 7156−7160. (i) Xu, M.; Jupp, A. R.;
Qu, Z.; Stephan, D. W. Alkali Metal Species in the Reversible
2
2
2
2
2
Activation of H . Angew. Chem., Int. Ed. 2018, 57, 11050−11054.
2
metallics 1998, 17, 5240−5247. (c) Hou, Z.; Zhang, Y.; Tardif, O.;
Wakatsuki, Y. (Pentamethylcyclopentadienyl)samarium(II) Alkyl
Complex with the Neutral “C Me K” Ligand: A Precursor to the
(7) (a) Ephritikhine, M. Synthesis, Structure, and Reactions of
Hydride, Borohydride, and Aluminohydride Compounds of the f-
Elements. Chem. Rev. 1997, 97, 2193−2242. (b) Hou, Z.; Nishiura,
M.; Shima, T. Synthesis and Reactions of Polynuclear Polyhydrido
Rare Earth Metal Complexes Containing “(C Me SiMe )LnH ”
5
5
First Dihydrido Lanthanide(III) Complex and a Precatalyst for
Hydrosilylation of Olefins. J. Am. Chem. Soc. 2001, 123, 9216−9217.
5
4
3
2
(
d) Veith, M.; Konig, P.; Rammo, A.; Huch, V. Cubane-Like Li H
̈
Units: A New Frontier in Rare Earth Metal Hydride Chemistry.
Eur. J. Inorg. Chem. 2007, 2007, 2535−2545. (c) Konkol, M.; Okuda,
J. Non-metallocene hydride complexes of the rare-earth metals. Coord.
Chem. Rev. 2008, 252, 1577−1591. (d) Trifonov, A. A. Guanidinate
and amidopyridinate rare-earth complexes: Towards highly reactive
alkyl and hydrido species. Coord. Chem. Rev. 2010, 254, 1327−1347.
4 4
and Li H Li(OH): Stabilized in Molecular Adducts with Alanes.
3
3
Angew. Chem., Int. Ed. 2005, 44, 5968−5971. (e) Conroy, K. D.; Piers,
W. E.; Parvez, M. Nucleophilic Degradation of a β-Diketiminato
Ancillary by a Transient Scandium Hydride Intermediate. Organo-
metallics 2009, 28, 6228−6233. (f) Liptrot, D. J.; Hill, M. S.; Mahon,
M. F. Heterobimetallic s-Block Hydrides by σ-Bond Metathesis.
(
e) Nishiura, M.; Hou, Z. Novel polymerization catalysts and hydride
clusters from rare-earth metal dialkyls. Nat. Chem. 2010, 2, 257−268.
f) Cheng, J.; Saliu, K.; Ferguson, M. J.; McDonald, R.; Takats, J.
Variable nuclearity scorpionate-supported lanthanide polyhydrides:
(TpR,R’)LnH ]n (n = 3, 4 and 6). J. Organomet. Chem. 2010, 695,
Chem. - Eur. J. 2014, 20, 9871−9874. (g) Dube, T.; Gambarotta, S.;
́
(
Yap, G. P. A. Dinuclear Complexes of Di-, Tri-, and Mixed-Valent
Samarium Supported by the Calix-tetrapyrrole Ligand. Organo-
metallics 2000, 19, 817−823. (h) Cui, P.; Spaniol, T. P.; Okuda, J.
Heterometallic Potassium Rare-Earth-Metal Allyl and Hydrido
Complexes Stabilized by a Dianionic (NNNN)-Type Macrocyclic
Ancillary Ligand. Organometallics 2013, 32, 1176−1182.
[
2
2
696−2702. (g) Fegler, W.; Venugopal, A.; Kramer, M.; Okuda, J.
Molecular Rare-Earth-Metal Hydrides in Non-Cyclopentadienyl
Environments. Angew. Chem., Int. Ed. 2015, 54, 1724−1736.
(8) For a report of internal deprotonative metalation to form “tuck-
(12) Similar NMR reactions and observations were reported
recently. See: Rachor, S. G.; Cleaves, P. A.; Robertson, S. D.;
Mansell, S. M. NMR spectroscopic study of the adduct formation and
reactivity of homoleptic rare earth amides with alkali metal benzyl
in” and “tuck-over” metallocycle complexes, see: (a) Johnson, K. R.
D.; Hayes, P. G. Cyclometalative C-H bond activation in rare earth
and actinide metal complexes. Chem. Soc. Rev. 2013, 42, 1947−1960.
(
b) Arnold, P. L.; McMullon, M. W.; Rieb, J.; Ku
̈
hn, F. E. C-H Bond
compounds, and the crystal structures of [Li(TMEDA) ][Nd{N-
2
8
770
DOI: 10.1021/acscatal.9b02899
ACS Catal. 2019, 9, 8766−8771

ACS Catalysis
Letter
(
SiMe ) } (CH Ph)] and [{Li(TMP)} {Li(Ph)}] . J. Organomet.
3 2 3 2 2 2
Chem. 2018, 857, 101−109.
(13) (a) Karl, M.; Harms, K.; Seybert, G.; Massa, W.; Fau, S.;
Frenking, G.; Dehnicke, K. Die Deprotonierung silylierter Amido-
Komplexe von Seltenerdelementen. Z. Anorg. Allg. Chem. 1999, 625,
2
055−2063. (b) Niemeyer, M. Reactions of Hypersilyl Potassium
with Rare-Earth Metal Bis(Trimethylsilylamides): Addition versus
Peripheral Deprotonation. Inorg. Chem. 2006, 45, 9085−9095.
(14) (a) Moore, M.; Gambarotta, S.; Bensimon, C. Serendipitous
Formation of a Dinuclear Vanadium(III) Amide Complex Containing
a Vanadaazacyclobutane Ring. Potassium−Hydrogen Agostic Inter-
actions Holding Together a V2K2 Tetrametallic Framework.
Organometallics 1997, 16, 1086−1088. (b) Clegg, W.; Kleditzsch,
S.; Mulvey, R. E.; O’Shaughnessy, P. Crystal structure of a heavier
alkali metal diisopropylamide complex: a discrete (KN) ring dimer
2
with TMEDA chelation and short intramolecular K···H(C) contacts.
J. Organomet. Chem. 1998, 558, 193−196.
(
15) (a) Knizek, J.; Noth, H. Hydridoborates and hydridoborato
̈
metallates: Part 26. Preparation and structures of dihydridoborates of
lithium and potassium. J. Organomet. Chem. 2000, 614−615, 168−
1
87. (b) Chen, X.; Liu, S.; Du, B.; Meyers, E. A.; Shore, S. G. The
Structure of Potassium and Tetramethylammonium Salts of the Cyclic
Organohydroborate Anion [H BC H ] with Different Solvent
−
2
8
14
Ligands. Eur. J. Inorg. Chem. 2007, 2007, 5563−5570. (c) Izod, K.;
Wills, C.; Clegg, W.; Harrington, R. W. Influence of aromatic ring
substituents and co-ligand on the binding mode of a phosphine-
borane-stabilized carbanion. J. Organomet. Chem. 2007, 692, 5060−
5
064. (d) Ding, K.; Brennessel, W. W.; Holland, P. L. Three-
Coordinate and Four-Coordinate Cobalt Hydride Complexes That
React with Dinitrogen. J. Am. Chem. Soc. 2009, 131, 10804−10805.
(
e) Haywood, J.; Wheatley, A. E. H. Metal-Hydride Bonding in
Higher Alkali Metal Boron Monohydrides. Eur. J. Inorg. Chem. 2009,
2009, 5010−5016.
8
771
DOI: 10.1021/acscatal.9b02899
ACS Catal. 2019, 9, 8766−8771