Coordination of LiH Molecules to Mo≡Mo Bonds: Experimental and Computational Studies on Mo2LiH2, Mo2Li2H4, and Mo6Li9H18Clusters

Article abstract of DOI:10.1021/jacs.1c01602

The reactions of LiAlH4 as the source of LiH with complexes that contain (H)Mo≡Mo and (H)Mo≡Mo(H) cores stabilized by the coordination of bulky AdDipp2 ligands result in the respective coordination of one and two molecules of (thf)LiH, with the generation of complexes exhibiting one and two HLi(thf)H ligands extending across the Mo≡Mo bond (AdDipp2 = HC(NDipp)2; Dipp = 2,6-iPr2C6H3; thf = tetrahydrofuran, C4H8O). A theoretical study reveals the formation of Mo-H-Li three-center-two-electron bonds, supplemented by the coordination of the Mo≡Mo bond to the Li ion. Attempts to construct a [Mo2{HLi(thf)H}3(AdDipp2)] molecular architecture led to spontaneous trimerization and the formation of a chiral, hydride-rich Mo6Li9H18 supramolecular organization that is robust enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by pyridine or 4-dimethylaminopyridine.

Full text of DOI:10.1021/jacs.1c01602

pubs.acs.org/JACS
Article
Coordination of LiH Molecules to Mo≣Mo Bonds: Experimental and
Computational Studies on Mo2LiH2, Mo2Li2H4, and Mo6Li9H18
Clusters
Marina Perez-Jimenez, Natalia Curado, Celia Maya, Jesus Campos, Jesus Jover, Santiago Alvarez,*
and Ernesto Carmona*
Cite This: J. Am. Chem. Soc. 2021, 143, 5222−5230
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: The reactions of LiAlH4 as the source of LiH with complexes that contain
(H)Mo≣Mo and (H)Mo≣Mo(H) cores stabilized by the coordination of bulky AdDipp2
ligands result in the respective coordination of one and two molecules of (thf)LiH, with the
generation of complexes exhibiting one and two HLi(thf)H ligands extending across the
Mo≣Mo bond (AdDipp2 = HC(NDipp)2; Dipp = 2,6-iPr2C6H3; thf = tetrahydrofuran, C4H8O).
A theoretical study reveals the formation of Mo−H−Li three-center−two-electron bonds,
supplemented by the coordination of the Mo≣Mo bond to the Li ion. Attempts to construct a
[Mo2{HLi(thf)H}3(AdDipp2)] molecular architecture led to spontaneous trimerization and the
formation of a chiral, hydride-rich Mo6Li9H18 supramolecular organization that is robust
enough to withstand the substitution of lithium-solvating molecules of tetrahydrofuran by
pyridine or 4-dimethylaminopyridine.
LiOtBu agglomerate Li33H17(OtBu)16,24 and the synthesis of a
(LiH)4 cube coordinated to three bis(amido)alane units.25
Transition-metal complexes allegedly containing coordi-
nated monomeric molecules of LiH are sparse. There are,
however, some reports describing M−H−Li systems where a
degree of covalent bonding within the bridging bond can be
proposed on the basis of the observation of one-bond 1H−6,7Li
NMR coupling constants.21,26−35 Despite the scarcity of
complexes of this type, it is conceivable that, like other
main-group metal−hydrogen bonds (e.g., Mg−H, Al−H, and
Zn−H),36−44 a molecule of lithium hydride might bind to a
transition-metal fragment through its Li−H bond, assisted by
an interaction with an adjoining ligand that could compensate
for the unsaturation of the lithium coordination shell and
further heighten the σ-donor strength of the polar Li−H bond.
In this context, we envisioned that quadruply bonded
hydride central units [Mo2(H)n] (n = 1, 2) could be utilized to
build the target molecular architectures. As represented in
structure A of Figure 1, such dimolybdenum dihydride units
possess strong hydride character45 and feature Mo−Mo
separations of close to 2.10 Å, with Mo−H vectors nearly
perpendicular to the Mo−Mo bond.45 Here, we discuss the
INTRODUCTION
■
Along with noble gas helium, hydrogen and lithium are the
simplest, lightest elements and the only ones that existed in the
young universe.1 Helium hydride, HeH+, is a molecule of
astrophysical importance,2 whereas LiH is the lightest metal
hydride and arouses considerable interest due to its many
applications.3−5 In the gas phase, molecules of LiH exist as a
result of the overlap of the singly occupied H 1s and Li 2s
atomic orbitals,6 with an experimentally determined intera-
tomic distance of ca. 1.60 Å.7 In the solid state, LiH adopts a
cubic NaCl-type structure, characterized by long Li···H
contacts of approximately 2.04 Å.3
Molecular hydrides of the s-block elements have been
intensively investigated in recent years. For group 2 metals,
new, uncommon structures and a diversity of useful
applications in hydrometalation, hydrogenation, and other
reactions have been uncovered, thanks in no small part to the
use of sterically encumbered auxiliary ligands.3,8−19 Progress
for the alkali metals has been more limited, although with
notable exceptions. These include Stasch’s hydrocarbon-
soluble lithium hydride cluster [{(DippNPPh2)Li}4(LiH)4],
containing a (LiH)4 central cube (Dipp = 2,6-iPr2C6H3),20 as
well as the generation by Mulvey and co-workers of hexane-
soluble lithium hydride transfer reagents.21,22 Of particular
relevance is the synthesis of the dilithiozincate hydride
[(tmed)Li]2[{iPrNCH2CH2N(iPr)}Zn(tBu)H] that retains
the Li−H bond in solution and undergoes the dynamic
association and dissociation of (tmed)LiH.21 Also noteworthy
are reports on hydride encapsulation by molecular alkali metal
clusters,23 the structural characterization of the LiH and
Received: February 9, 2021
Published: March 23, 2021
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230
© 2021 American Chemical Society
5222

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Figure 1. Simplified representations of the structures of complexes 3·thf-5·thf. The three structural types originate from [Mo2(H)n] cores by the
incorporation of one, two, or three molecules of (thf)LiH (n = 1, complex 3·thf; n = 2, A and complex 4·thf; when n = 3, the unobserved monomer
trimerizes to complex 5·thf with the loss of a molecule of tetrahydrofuran). In the structure of 5·thf, symmetry-related lithium atoms share the same
color.
synthesis and structure of complexes 3·thf and 4·thf (Figure 1)
that contain one and two formally monoanionic, bridging H−
Li(thf)−H ligands, respectively, spanning the Mo≣Mo bond.
We also study the unexpected formation of a unique,
hydrocarbon-soluble, hydride-rich Mo6Li9H18 cluster, 5·thf,
formally resulting from the trimerization of unobserved
monomer [Mo2{μ-HLi(thf)H}3(μ-AdDipp2)], with the loss of
a molecule of tetrahydrofuran. Throughout this article, three-
center−two-electron (3c−2e) interactions implicating Mo−H
and Li−H bonds are represented with the aid of the half-arrow
formalism proposed by Green, Green, and Parkin.46
temperature alkylation of [Mo2(μ-O2CH)2(μ-AdDipp2)2] with
equimolar amounts of LiEt yielded an ethyl-formate inter-
mediate that was reacted in situ with H2 and converted to the
hydride-formate product, 2·thf (Scheme 1), in good isolated
yields (ca. 70%). The coordinated tetrahydrofuran molecule of
2·thf is highly labile, and it was readily replaced by Lewis bases
such as 4-dimethylaminopyridine (dmap), 1,3,4,5-tetramethyl-
imidazol-2-ylidene (IMe4), and PMe3, giving complexes 2·L
(Scheme 1a, top). Similarly, the use of LiAlH4 as a source of
LiH permitted the isolation of complex 3·thf that was obtained
as a yellow solid in yields of around 60%. This reaction was
not, however, simple and also produced related derivative 4·
thf, along with minute amounts of a tetrahydroaluminate
complex to be described elsewhere. Complex 3·thf possesses a
H−Mo≣Mo−H−Li(thf) chelate moiety resulting from the
substitution of the coordinated tetrahydrofuran of 2·thf by a
molecule of (thf)LiH, with the formation of a σ-Li−H
complex, that becomes stabilized by the concomitant
formation of a 3c−2e Mo−H⇀Li bond involving the adjacent
Mo−H terminus.
RESULTS AND DISCUSSION
■
In recent work, we showed that tetrahydrofuran adduct
[Mo2(H)2(μ-AdDipp2)2(thf)2] (1·thf, where AdDipp2 = HC-
(NDipp)2 and Dipp = 2,6-iPrC6H3) is a convenient source of
unsaturated dihydride [Mo2(H)2(μ-AdDipp2)2] containing a
trans-(H)Mo≣Mo(H) core (structure A in Figure 1).45 The
Mo2(H)2 functionality of this complex was engendered by
hydrogenolysis of the Mo−C bonds of the [(Me)Mo≣Mo-
(Me)] homologue,47 a method that continues to be a main
vehicle for the synthesis of transition-metal hydrides. Searching
for a related monohydride [(H)Mo≣Mo] core, we carried out
the two-step transformation shown in Scheme 1a. Low-
Next, 1·thf was utilized as a source of the [Mo2(H)2] center
(Scheme 1b). Mixing a tetrahydrofuran solution of this
complex with a solution of LiAlH4 in the same solvent caused
the immediate precipitation of a bright-yellow solid that was
5223
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
a
Scheme 1. Synthesis of Hydride Complexes with Mo≣Mo Bonds
a
(a) Compounds 2·thf, 2·L, and 3·thf. (b and c) Direct synthesis of complexes 3·thf and 4·thf. [Mo≣Mo] is an abbreviation for Mo2(μ-AdDipp2)2.
L is 4-dimethylaminopyridine (dmap), 1,3,4,5-tetramethylimidazol-2-ylidene, (IMe4), and PMe3.
1
identified as dilithium tetrahydride dimolybdenum complex
[Mo2{μ-HLi(thf)H}2(μ-AdDipp2)2] (4·thf), that is, as a
Mo2Li2H4 cluster. As drawn in Scheme 1b, the compound
contains two trans-[μ-HLi(thf)H] ligands that extend across
the Mo≣Mo bond. Thus, it can be related to 3·thf by means of
formal replacement of the bridging formate of the latter by a
second μ-Li(thf)H2− three-atom chelating ligand. In agreement
with this rationale, complexes 3·thf and 4·thf were generated
in high yields (70−85%) by the more direct method
summarized in Scheme 1c, based on the reaction of readily
available [Mo2(μ-O2CH)2(μ-AdDipp2)2] with LiAlH4, under
appropriate conditions.
spectrum. Moreover, the 4.33 multiplet is absent in the H
NMR spectrum of the DLiD isotopologue of 3·thf, prepared
by the reaction of [Mo2(μ-O2CH)2(μ-AdDipp2)2]48 with
LiAlD4. The Li{1H} NMR spectrum is a somewhat broad
singlet at 3.6 ppm that transforms into a 1:2:1 triplet in the
proton-coupled 7Li NMR experiment, with a one-bond 7Li−1H
coupling constant of 16 Hz.
7
Complex 4·thf is only scarcely soluble in common solvents
such as benzene, toluene, and tetrahydrofuran, but it is just
sufficiently soluble in C6H5F for NMR studies. Pertinent NMR
data are also included in Figure 2. In particular, the Mo2LiH2
moieties exhibit comparable J(7Li−1H) couplings of 17 Hz.
1
Complexes 2·L, 3·thf, and 4·thf were characterized with the
aid of microanalytical, spectroscopic, and X-ray data and were
additionally studied by computational methods. For molecules
of 2·L, the proposed structure is based on IR and NMR data
and was unmistakably confirmed by X-ray crystallography for
2·IMe4 (Figure S1). Regarding complexes 3·thf and 4·thf, their
hydride signals were not readily apparent in the IR spectra,
possibly because of the Mo−H−Li bridging character, so the
unambiguous identification of the three-atom HLiH chains in
3·thf and 4·thf owes much to the 1H and 7Li NMR
experiments developed. Surprisingly more soluble in benzene
and toluene than in tetrahydrofuran, the H atoms of the
HLi(thf)H ligand in 3·thf resonate at δ 4.33 (C6D6), appearing
These observations categorically demonstrate the existence of
HLiH entities coordinated to the Mo−Mo quadruple bond in
the 3·thf and 4·thf molecules. Besides, they attest without a
doubt to the fact that, although probably mainly Coulombic in
nature (vide infra), the Mo−H−Li−H−Mo bonding inter-
actions involve a considerable degree of covalency, that is, of
substantial electron density shared among the molybdenum,
hydrogen, and lithium valence orbitals. It is pertinent to
remark that the observation of scalar coupling in lithium
1
hydride complexes is rare, to the point that few J(6,7Li−1H)
values can be found in the literature.21,29−35 Previously
observed couplings range from approximately 6 to 15 Hz
such that the 16 to 17 Hz values found for 3·thf and 4·thf are
among the highest thus far reported. For the LiH molecule, a
1J(7Li−1H) coupling constant of 159 Hz has been calculated.49
7
as a partially resolved multiplet due to coupling to the Li
(92.6%, I = 3/2) and 6Li (7.4%, I = 1) nuclei. As can be seen in
1
Figure 2, this signal becomes a singlet in the H{7Li} NMR
5224
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Figure 3. Solid-state structure of 4·thf. Some atoms have been
omitted for clarity. Thermal ellipsoids are shown at 50%. Selected
bond distances (Å) and a bond angle (deg): Mo1−Li1, 2.91(2) and
2.97(2); Mo1−Mo1, 2.1006(7); Mo1−N1, 2.10(1); Mo1−N2,
2.20(1); Li1−O1, 1.86(2) Å; and N1−Mo1−Li1, 92.1(5).
Table 1. Selected Experimental and Computational Bond
a
Distances (Å) for Complexes 4·thf and 5·thf
1
1
7
7
Figure 2. From bottom to top, H, H{7Li}, Li{1H}, and Li NMR
4·thf
5·thf
spectra of the HLiH moieties of complexes 3·thf (left) and 4·thf
calcd
exp
calcd
exp
1
(right). H resonances at lower frequency relative to Mo−H−Li are
Mo−Mo
Mo−H
Mo−Li
2.134
1.852
2.971
2.968
1.787
1.784
2.1006(7)
2.05
2.97(2)
2.91(2)
1.74
2.14−2.15
2.10 (av.)
1.67−2.04
3.15−3.24
due to methine protons of the AdDipp2 ligands or to tetrahydrofuran.
1.83−1.84 (Mo−Hcent
3.21−3.25 (Mo−Li9)
)
Complexes 3·thf and 4·thf possess good thermal stability.
Their C6D6 and C6D5F solutions appear to be stable for 1 day
at room temperature, though decomposition occurs upon
heating at 70 °C for 3 to 4 h. In the solid state, decomposition
is apparent only at T ≥ 150 °C. The two compounds behave as
soluble LiH carriers, particularly 4·thf, which is the more
reactive of the two. For instance, complex 4·thf reacted with
Ph2C(O) to give the expected alkoxide Ph2C(H)(OLi).20,22
Their molecular structures were investigated by X-ray
crystallography and optimized by means of DFT calculations.
Owing to poor crystal properties, the data collected for the
former do not permit a rigorous structural discussion,
particularly with respect to what concerns the geometric
parameters of H atoms. Nonetheless, they allow us to define
beyond any doubt the connectivity represented in Figure S2.
Figure 3 contains an ORTEP representation of the molecules
of 4·thf, along with selected metrics. A more complete set of
bond distances is collected in Table 1, which contains both
experimental and computational data. When this manuscript
was being prepared, there was no precedent for a structural
motif of this kind in the Cambridge Structural Database
(CSD).50 The two bridging H−Li(thf)−H and AdDipp2 ligands
of complex 4·thf occupy mutually trans positions, originating a
typical paddle-wheel structure51−53 around a Mo−Mo
quadruple bond of length 2.1006(7) Å. The discrepancy
observed between the experimental and calculated Mo−H and
Li−H
1.97−2.07 (Li9−Hcent
)
1.81−2.09
1.85
a
For the latter complex, the Li7/8−Li9 distances are 2.44 and 2.46
(calcd), 2.45 and 2.50 Å (exp), while corresponding values for the
Li7−Li9−Li8 angle are 176.5 and 176.3°.
Li−H distances collected in Table 1 is most likely due to the
incertitude in the localization by X-ray diffraction of hydride
ligands bound to a heavy atom such as molybdenum. The
computed distances are 1.85 and 1.78 Å, respectively. The first
is almost coincident with the average Mo−H−Mo bond
lengths determined by neutron diffraction,54 while the second
is somewhat longer than the 1.60 Å value measured for the
molecule of LiH in the gas phase but significantly shorter than
the interatomic separation of 2.04 Å found for this hydride in
the solid state.3 Regarding the Mo−Li distances, the
experimental values of 2.91(2) and 2.97(2) Å are indistin-
guishable within experimental error, whereas in the optimized
structure this slight asymmetry vanishes, leading to a
separation of ca. 2.97 Å. For comparison, the sum of the
covalent radii of the atoms is 2.82 Å.55
We have carried out geometry optimization and an NBO
analysis of chemical bonding within the Mo−H−Li−H−Mo
rings of 4·thf. For simplicity, we describe here the comparable
5225
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Figure 4. (a) Four NBO orbitals corresponding to the σ component, two π components, and one δ component of the quadruple Mo≣Mo bond in
4·thf′ and one of the Mo−H σ bonding orbitals composed by the δ(Mo−Mo)-type x2−y2 and the hydride 1s orbitals. (b) Coordinate orientation
and composition of the central fragment of the molecule shown in the orbital plots. (c) Some representative interactions between donor (white and
red) and acceptor (light blue and pink) natural orbitals in 4·thf′.
results obtained for monolithiated species 4·thf′, whose
structure (Figure 4b) finds precedent in that of methyl
complex analog [Mo2{μ-MeLi(thf)Me}(μ-Me)(μ-
AdDipp2)2].47,56 The energy for the dissociation of 4·thf′ to
(thf)Li−H and dihydride [Mo2(H)2(μ-AdDipp2)2] given by our
calculations is 27.9 kcal/mol, while the dissociation of two
molecules of (thf)Li−H from 4·thf is 55.1 kcal/mol. The NBO
analysis discloses four orbitals that are responsible for the σ
component, two π components, and one δ component of the
quadruple Mo−Mo bond (Figure 4a). In addition, we find that
the dx2−y2 orbitals, not involved in Mo−Mo bonding, form
spd hybrids directed toward the hydrides47 and combine with
s(H) orbitals to form the two Mo−H bonds (one of which is
shown in Figure 4a).
The NBO approach results in limited participation of the
lithium atomic orbitals in occupied MOs. However, this does
not mean that its interactions with the hydrides and the
molybdenum atoms are strictly ionic, since the calculated
charge on Li is +0.67, indicative of a non-negligible covalent
Figure 5. (a) Relative energy contributions of natural orbital donor−
acceptor interactions between [Mo2(H)2(μ-H)(μ-AdDipp2)2]− and
(thf)Li+ fragments in 4·thf′. (b) Share of the Li valence electron
density at each of its atomic orbitals, resulting from σ(Mo−H) → Li,
Mo≣Mo → Li, and thf → Li donor−acceptor interactions.
contribution. The reduced charge of the lithium “ion” is thus
associated, in addition to thf → Li donation, with two sets of
donor−acceptor interactions: (i) donation from σ(Mo−H) to
Li and (ii) donation from the components of the Mo≣Mo
bond to Li (Figure 4c).
From the energy point of view, there are two sets of
dominant interactions (Figure 5a) that imply donations from
the σ(Mo−H) and σ(Mo’−H) bonds to both s(Li) and pz(Li)
and from the σ component of the Mo≣Mo bond to the atomic
orbitals of Li. In the first set, we find donation from σ(Mo−H)
to both s(Li) and pz(Li), which are responsible for 84% of the
interaction energy. Among the second set of interactions,
donation from σ(Mo−Mo) to s(Li) (Figure 4c) makes a
significant contribution of 12%; smaller contributions come
from the donations of δ(Mo−Mo) to px(Li) and of σ(Mo−
Mo) to py(Li), while almost negligible contributions appear for
π(Mo−Mo) and for py and s(Li).
0.33 valence electron held by the Li atomic orbitals (Figure
5b) reflects the major role played by the 2s and 2pz Li AOs as
acceptors. The high population of the lithium py orbital
compared to its minor acceptor role toward the Mo≣Mo
group is undoubtedly due to the donation from its thf ligand.
Finally, the lowest atomic orbital population in px results from
the interesting donation from the δ(Mo≣Mo) bonding orbital
(Figure 4c).
We can therefore conclude that the stability of the Mo−H−
Li−H−Mo ring results mainly from the formation of two 3c−
2e Mo−H−Li bonds, supplemented by σ coordination of the
Mo≣Mo bond to the Li atom. The latter bonding component
is consistent with a short distance between Li and the Mo≣Mo
centroid of 2.77 Å (Mo−Li = 2.97 Å), to be compared with a
As a result of all of these donor−acceptor interactions from
the Mo2H2 moiety to the lithium ion, the distribution of the
5226
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
covalent radii sum of 2.82 Å.55 Although of lesser quantitative
importance, the existence of non-negligible electron donation
from the bonding π and δ(Mo≣Mo) orbitals is worth being
stressed. The fact that the calculated dissociation energy of 4·
thf′ into (thf)Li−H and dihydride [Mo2(H)2(μ-AdDipp2)2] is
27.9 kcal/mol, smaller than the sum of NBO interaction
energies shown in Figure 5a (98.7 kcal/mol), is explained by
the high energy required to deform the (thf)Li−H group from
linear in the free molecule to a highly bent (120°) geometry in
4·thf′ as well as to modify the second coordination sphere of
the Mo atoms to make room for the Li−thf moiety.
Having successfully built Mo2LiH2 and Mo2Li2H4 platforms
based on Mo≣Mo bonds coordinated to one and two H−
Li(thf)−H units, respectively, our next goal was to explore the
possibility of reaching a Mo2Li3H6 organization in a purported
[Mo2{HLi(thf)H}3(μ-AdDipp2)] complex. To this end and
taking into account the successful synthesis of complexes 3·thf
and 4·thf by the procedure shown in Scheme 1c, we prepared
tris(acetate) precursor [Mo2(μ-O2CMe)3(μ-AdDipp2)] and
performed its reaction with an excess of LiAlH4. Although
the above Mo2Li3H6 complex could not be observed, the
transformation led to complex 5·thf, identified as a
polymetallic hydride cluster Mo6Li9H18 (Scheme 2), that
molecular skeleton. Notwithstanding the foregoing, complex 5·
thf acted as an efficient source of LiH in the hydrolithiation of
Ph2C(O) to give Ph2C(H)(OLi).20,22 Somewhat unexpectedly,
solutions of 5·thf decomposed gradually upon stirring at room
temperature under an atmosphere of H2, generating LiAdDipp2
as a byproduct. Dideuterium acted similarly and showed that
H/D exchange took place, as attested to by NMR detection of
HD along with H2. The H2-promoted cluster breakup was not
investigated any further. Nevertheless, it seems plausible that
H2 may disrupt the cluster structure by displacing LiH
molecules from the [Li9H18]9− linker, eliminating LiAdDipp2. As
an extension of these studies, various attempts were made to
produce an alleged {Mo2(H)8[Li(thf)]4} complex (i.e., the
hydride analogue of known methyl compound
{Mo2(CH3)8[Li(OEt2)]4}).59 As detailed in the SI, all essayed
trials were unsuccessful.
1
The room-temperature H NMR spectra of complexes 5·L
in C6D6 or thf-d8 solution show two septets and four doublets
for the 12 isopropyl groups of the amidinate spectator ligands,
in accordance with the proposed D3 molecular symmetry
(details in Supporting Information). The 18 H atoms that
make up the [Li9H18] linker are expected to give rise to three
resonances of equal relative intensity. Whereas for 5·thf one of
these signals seems to be hidden underneath other resonances,
the three are clearly observed for complex 5·py with chemical
shifts of 2.04, 5.21, and 5.41 ppm. They appear as broad
multiplets, but while the 2.04 peak becomes a singlet in the
1H{7Li} NMR spectrum, the other two are converted to
Scheme 2. Formation of Hexamolybdenum Nonalithium
Dodecaoctahydride Cluster 5·thf
2
7
doublets with JHH = 4 Hz. The Li NMR spectrum contains
three resonances centered at 5.4, 4.7, and 2.7 ppm, with
relative intensities approaching roughly 6:2:1, once more in
agreement with the proposed structure.
The molecular structure of complex 5·thf was determined by
X-ray crystallography (Figure 6) and computational studies.
Since the calculated and experimental structures are very
probably results from spontaneous trimerization of the targeted
Mo2Li3H6 monomer, with the loss of a molecule of
tetrahydrofuran. The reaction was, however, complex and
gave in addition compound [Mo2(μ-O2CMe)2(μ-AdDipp2)2]
through an undisclosed reaction path. Like the bis(formate)
analogue (Scheme 1c), the latter may react further with
LiAlH4, justifying that isolated yields of 5·thf are about 25%.
Complex 5·thf is very air-sensitive and decomposes instantly in
the presence of oxygen and water, both in solution and in the
solid state. Under strict anaerobic conditions, solutions in
tetrahydrofuran or aromatic hydrocarbons remain unchanged
at 25 °C for at least 24 h, although decomposition is fast above
50 °C.
The new supramolecular entity can be understood as a
triangular array of [Mo2(μ-AdDipp2)]3+ components51,57,58
connected by a [Li9H18]9− linker in a fairly robust manner.
The Li-coordinated molecules of tetrahydrofuran were readily
substituted by pyridine and 4-dimethylaminopyridine, giving
complexes 5·py and 5·dmap without the alteration of the
Figure 6. Solid-state structure of 5·thf as determined by X-ray
diffraction. Thermal ellipsoids are shown at 30%. Hydrogen atoms
(except the hydride ligands) are omitted for clarity, as are thf
molecules. Selected bond lengths (Å) and a bond angle (deg): Mo−
Mo, 2.10 av.; Mo−Li9, 3.20 av.; Mo−N, 2.13 av.; Li9−Li7, 2.45(2);
Li9−Li8, 2.50(2); Li7−Li9−Li8, 176.3(9).
5227
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
similar (Table 1), all of the features that are discussed here
based on the X-ray data also apply to the optimized geometry.
The whole cluster is built up by successive concentric groups
around a central Li3 unit (Figure 7, left) formed by Li7, Li9,
= 3, trimerization of the purported [Mo2{μ-HLi(thf)H}3(μ-
AdDipp2)] monomer occurs spontaneously, leading to a
hydride-rich Mo6Li9H18 supramolecular organization that
features an uncommon linear Li3 group around which are
organized Mo6, Li6, and two H6 polyhedra with shapes
intermediate between an octahedron and compressed trigonal
prisms.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/jacs.1c01602.
Relevant experimental and calculated bonding parame-
ters for 3·thf, 4·thf and 5·thf; computational details; and
atomic coordinates for the optimized geometries of the
same compounds; synthesis and characterization of
compounds (PDF)
Figure 7. Li9 polyhedron present in the molecules of complex 5·thf
(left) and the distribution of H and Li atoms in the vicinity of central
lithium atom Li9 (right).
Olex2 1.3 data (PDF)
Accession Codes
and Li8 with a nearly linear arrangement (176(1)°) and
distances of 2.50(2) and 2.45(2) Å, which are slightly shorter
than twice the lithium covalent radius (2.56 Å).55 We have
been unable to locate a solid-state or gas-phase structure in
which such a Li3 rod is present. The only Li3 group whose
structure we are aware of appears in the crystal structure of
Li3[IrD6], with Li−Li distances of 2.58 and 2.76 Å and a Li−
Li−Li angle of 75.7°.60 The first concentric group around the
central axis is composed of six Hcent atoms that provide a nearly
octahedral coordination sphere to the central Li9 atom (Figure
7, right) and act as bridging atoms with the terminal atoms of
the Li3 rod, with Li−H separations in the 1.70−2.20 Å interval.
These hydrides are connected to the molybdenum atoms of
the three Mo2 units that constitute the second concentric ring,
with the shape of a slightly twisted trigonal prism and Mo−H
distances in the range of 1.67−2.05 Å. The Mo−Mo bond
length of 2.1020(7) Å is coherent with 4-fold bonding.51
Leaving aside the Li atoms, an ionic description of the
cluster leaves us with three [Mo2(μ-AdDipp2)H6]3− blocks, in
which each Mo atom bears two cis hydrides and one trans
hydride relative to the N atoms of the μ-AdDipp2 ligand. The
latter have just been described as forming an H6 octahedron
around the inner Li3 rod and being bonded to the three Mo2
units as well. The 12 cis hydrides can be described as distorted
trigonal prisms, one with the trigonal faces roughly at the
CCDC 2059184−2059187 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
̀
Santiago Alvarez − Department de Química Inorganica i
̀
̀
Organica, Secció de Química Inorganica, and Institut de
̀
Química Teorica i Computacional, Universitat de Barcelona,
08028 Barcelona, Spain; Email: santiago.alvarez@qi.ub.es
Ernesto Carmona − Instituto de Investigaciones Químicas
(IIQ), Departamento de Química Inorgánica and Centro de
Innovación en Química Avanzada (ORFEO-CINQA),
Consejo Superior de Investigaciones Científicas (CSIC),
University of Sevilla, 41092 Sevilla, Spain; orcid.org/
0000-0003-2449-5848; Email: guzman@us.es
Authors
Marina Perez-Jimenez − Instituto de Investigaciones Químicas
(IIQ), Departamento de Química Inorgánica and Centro de
Innovación en Química Avanzada (ORFEO-CINQA),
Consejo Superior de Investigaciones Científicas (CSIC),
University of Sevilla, 41092 Sevilla, Spain
Natalia Curado − Instituto de Investigaciones Químicas (IIQ),
Departamento de Química Inorgánica and Centro de
Innovación en Química Avanzada (ORFEO-CINQA),
Consejo Superior de Investigaciones Científicas (CSIC),
University of Sevilla, 41092 Sevilla, Spain
Celia Maya − Instituto de Investigaciones Químicas (IIQ),
Departamento de Química Inorgánica and Centro de
Innovación en Química Avanzada (ORFEO-CINQA),
Consejo Superior de Investigaciones Científicas (CSIC),
University of Sevilla, 41092 Sevilla, Spain
Jesus Campos − Instituto de Investigaciones Químicas (IIQ),
Departamento de Química Inorgánica and Centro de
Innovación en Química Avanzada (ORFEO-CINQA),
Consejo Superior de Investigaciones Científicas (CSIC),
University of Sevilla, 41092 Sevilla, Spain; orcid.org/
0000-0002-5155-1262
ext
height of the external atoms of the central Li3 rod, or H6
group, and the other with the trigonal faces very close to the
central Li9 atom, or H6int. Finally, the six peripheral Li atoms
form another trigonal prism (Figure 7, left) with one of the
triangular faces (Li1, Li3, and Li5) rotated ca. 13° relative to
the other (Li2, Li4, and Li6). Those Li atoms form three Li2
dumbbells with Li···Li distances of 2.83−2.90 Å and are
supported by hydride bridges to neighboring Li and Mo atoms,
with Li−H separations in the range of 1.74−2.29 Å (section 5
in the Supporting Information).
CONCLUSIONS
■
We have demonstrated that a monomeric molecule of LiH can
bind to the unsaturated molybdenum atom of [(H)Mo≣Mo]
entities by means of a 3c−2e Mo−H⇀Li interaction
combined with a σ-Li−H⇀Mo bond. [Mo2{μ-HLi(thf)H}n]
skeletons containing five-membered H−Mo≣Mo−H−Li rings
have been constructed in this manner for n = 1 and 2. When n
5228
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
and Magnesium(II) Hydride Complexes: Synthesis, Characterization,
Adduct Formation, and Reactivity Studies. Chem. - Eur. J. 2010, 16,
938−955.
(12) Bonyhady, S.; Green, S.; Jones, C.; Nembenna, S.; Stasch, A. A
dimeric magnesium(I) compound as a facile two-centre/two-electron
reductant. Angew. Chem., Int. Ed. 2009, 48, 2973−2977.
(13) Green, S.; Jones, C.; Stasch, A. Stable Adducts of a Dimeric
Magnesium(I) Compound. Angew. Chem., Int. Ed. 2008, 47, 9079−
9083.
̀
̀
Jesus Jover − Department de Química Inorganica i Organica,
̀
Secció de Química Inorganica, and Institut de Química
̀
Teorica i Computacional, Universitat de Barcelona, 08028
Barcelona, Spain; orcid.org/0000-0003-3383-4573
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.1c01602
Notes
(14) Arrowsmith, M.; Hill, M. S.; Hadlington, H.; Kociok-Köhn, G.;
Weetman, C. Magnesium-Catalyzed Hydroboration of Pyridines.
Organometallics 2011, 30, 5556−5559.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(15) Spielmann, J.; Harder, S. Hydrocarbon-Soluble Calcium
Hydride: A “Worker-Bee” in Calcium Chemistry. Chem. - Eur. J.
2007, 13, 8928−8938.
This work has been supported by the Spanish Ministry of
Economy and Competitiveness (PID2019-110856GA-I00 and
PGC2018-093863-B-C21), the Spanish Structures of Excel-
lence María de Maeztu program (grant MDM-2017-0767), and
the Generalitat de Catalunya - AGAUR (grant 2017-SGR-
1289). M.P.-J. thanks the Spanish Ministry of Education and
Ministry of Science, Innovation and Universities for an FPU
Ph.D. fellowship.
(16) Schuhknecht, D.; Spaniol, T. P.; Maron, L.; Okuda, J.
Regioselective Hydrosilylation of Olefins Catalyzed by a Molecular
Calcium Hydride Cation. Angew. Chem., Int. Ed. 2020, 59, 310−314.
(17) Schnitzler, S.; Spaniol, T. P.; Okuda, J. Reactivity of a
Molecular Magnesium Hydride Featuring a Terminal Magnesium−
Hydrogen Bond. Inorg. Chem. 2016, 55, 12997−13006.
(18) Schnitzler, S.; Spaniol, T. P.; Maron, L.; Okuda, J. Formation
and Reactivity of a Molecular Magnesium Hydride with a Terminal
Mg-H Bond. Chem. - Eur. J. 2015, 21, 11330−11334.
(19) Arrowsmith, M.; Hill, M.; MacDougall, D.; Mahon, M. A
Hydride-Rich Magnesium Cluster. Angew. Chem., Int. Ed. 2009, 48,
4013−4016.
(20) Stasch, A. A Hydrocarbon-Soluble Lithium Hydride Complex.
Angew. Chem., Int. Ed. 2012, 51, 1930−1933.
(21) Campbell, R.; Cannon, D.; García-Alvarez, P.; Kennedy, A. R.;
Mulvey, R. E.; Robertson, S. D.; Saßmannshausen, J.; Tuttle, T. Main
Group Multiple C−H/N−H Bond Activation of a Diamine and
Isolation of A Molecular Dilithium Zincate Hydride: Experimental
and DFT Evidence for Alkali Metal−Zinc Synergistic Effects. J. Am.
Chem. Soc. 2011, 133, 13706−13717.
DEDICATION
■
This paper is dedicated to the memory of our esteemed
colleague and friend Professor Malcolm L. H. Green, in
recognition of his monumental contributions to inorganic
chemistry, organometallic chemistry, and catalysis.
REFERENCES
■
(1) Johnson, J. A. Populating the periodic table: Nucleosynthesis of
the elements. Science 2019, 363, 474−478.
(2) Gusten, R.; Wiesemeyer, H.; Neufeld, D.; Menten, K. M.; Graf,
̈
U. U.; Jacobs, K.; Klein, B.; Ricken, O.; Risacher, C.; Stutzki, J.
Astrophysical detection of the helium hydride ion HeH. Nature 2019,
568, 357−359.
(3) Aldridge, S.; Downs, T. Hydrides of the Main-Group Metals:
New Variations on an Old Theme. Chem. Rev. 2001, 101, 3366 and
references therein.
(22) Robertson, S. D.; Kennedy, A. R.; Liggat, J. J.; Mulvey, R. E.
Facile synthesis of a genuinely alkane-soluble but isolable lithium
hydride transfer reagent. Chem. Commun. 2015, 51, 5452−5455.
(23) Haywood, J.; Wheatley, A. E. H. Hydride encapsulation by
molecular alkali-metal clusters. Dalton Trans. 2008, 3378−3397.
(24) Hoffmann, D.; Kottke, T.; Lagow, R. J.; Thomas, R. D. X-Ray
Structural Analysis of a Novel Lithium Hydride/Lithium tert-Butoxide
Superaggregate: Li33H17(OtBu)16. Angew. Chem., Int. Ed. 1998, 37,
1537−1539.
(4) Kelly, M. T. In Structure and Bonding 141; Bocarsly, A., Mingos,
D. M. P., Eds.; Springer: Berlin, 2011; pp 169−201.
(5) Klusener, P. A. A.; Brandsma, L.; Verkruijsse, H. D.; Schleyer, P.
v. R.; Friedl, T.; Pi, R. Superactive Alkali Metal Hydride Metalation
Reagents: LiH, NaH, and KH. Angew. Chem., Int. Ed. Engl. 1986, 25,
465−466.
(25) Veith, M.; König, P.; Rammo, A.; Huch, V. Cubane-Like Li4H4
and Li3H3Li(OH): Stabilized in Molecular Adducts with Alanes.
Angew. Chem., Int. Ed. 2005, 44, 5968−5971.
̀
(6) Bickelhaupt, F. M.; Sola, M.; Fonseca Guerra, C. Highly polar
bonds and the meaning of covalency and ionicity-structure and
bonding of alkali metal hydride oligomers. Faraday Discuss. 2007, 135,
451−468.
(26) Fischer, K.; Jonas, K.; Misbach, P.; Stabba, R.; Wilke, G. The
“Nickel Effect. Angew. Chem., Int. Ed. Engl. 1973, 12, 943−953.
(27) Goddard, R.; Kruger, C.; Pörschke, K. R.; Wilke, G.
̈
(7) Bellini, M.; De Natale, P.; Inguscio, M.; Varberg, T. D.; Brown, J.
M. Precise experimental test of models for the breakdown of the
Born-Oppenheimer separation: The rotational spectra of isotopic
variants of lithium hydride. Phys. Rev. A: At., Mol., Opt. Phys. 1995, 52,
1954−1960.
Elektronendichte-verteilungen in metallorganischen verbindungen.
̈
Wechselnde struktur- und bindungsverhaltnisse in dimeren metal-
lorganischen nickel-hydriden mit ionenpaar-beziehungen zu den
hauptgruppen-metallen natrium und lithium. J. Organomet. Chem.
1986, 308, 85−103.
(8) Maitland, B.; Wiesinger, M.; Langer, J.; Ballmann, G.; Pahl, J.;
Elsen, H.; Färber, C.; Harder, S. A Simple Route to Calcium and
Strontium Hydride Clusters. Angew. Chem., Int. Ed. 2017, 56, 11880−
11884.
(9) Rauch, M.; Ruccolo, S.; Parkin, G. Synthesis, Structure, and
Reactivity of a Terminal Magnesium Hydride Compound with a
Carbatrane Motif, [TismPriBenz]MgH: A Multifunctional Catalyst
for Hydrosilylation and Hydroboration. J. Am. Chem. Soc. 2017, 139,
13264−13267.
(10) Arrowsmith, M.; Hill, M. S.; Kociok-Köhn, G.; MacDougall, D.
J.; Mahon, M. F. Beryllium-Induced C-N Bond Activation and Ring
Opening of an N-Heterocyclic Carbene. Angew. Chem., Int. Ed. 2012,
51, 2098−2100.
(11) Bonyhady, S. J.; Jones, C.; Nembenna, S.; Stasch, A.; Edwards,
A. J.; McIntyre, G. J. β-Diketiminate-Stabilized Magnesium(I) Dimers
̈
(28) Pörschke, K. R.; Wilke, G. Zur Lewisaciditat von Nickel(0):
VII. Alkalimetall-μ3-hydrido-tetrakis(ethen)diniccolat(0)-Komplexe:
(pmdta) Li(μ3-H)Ni2(C2H4)4 und (pmdta)Na(μ3-H)Ni2(C2H4)4. J.
Organomet. Chem. 1988, 349, 257−261.
(29) Gilbert, T. M.; Bergman, R. G. NMR spectra of (C5(CH3)-
5)IrH2SiMe3Li(pmdeta) and (C5(CH3)5)IrH3Li(pmdeta): the first
direct observation of resolved lithium-7-proton coupling. J. Am. Chem.
Soc. 1985, 107, 6391−6393.
(30) Heine, A.; Stalke, D. Structures of Two Highly Reactive
Intermediates upon LiAlH4 Reduction in the Solid State and in
Solution: [(Me3Si)2NAlH3Li·2Et2O]2 and [(Me3Si)2N]2AlH2Li·
2Et2O. Angew. Chem., Int. Ed. Engl. 1992, 31, 854−855.
(31) Liu, H.-J.; Ziegler, M. S.; Tilley, T. D. Ring-opening and
double-metallation reactions of the N-Heterocyclic carbene ligand in
5229
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230

Journal of the American Chemical Society
pubs.acs.org/JACS
Article
Cp*(IXy)Ru (IXy = 1,3-bis(2,6-dimethylphenyl)imidazol-2-ylidene)
complexes. Access to an anionic fischer-type carbene complex of
ruthenium. Polyhedron 2014, 84, 203−208.
(32) Berry, A.; Green, M. H. L.; Bandy, J. A.; Prout, K. J. Chem. Soc.,
Transition metal−hydrogen−alkali metal bonds: synthesis and crystal
structures of [K(18-crown-6)][W(PMe3)3H5], [Na(15-crown-5)][W-
(PMe3)3H5] and [{W(PMe3)3H5Li}4] and related studies. J. Chem.
Soc., Dalton Trans. 1991, 2185−2206.
and LiH: Energetics and Spin−Spin Coupling Constants across
Intermolecular Bonds. J. Phys. Chem. A 2010, 114, 8463−8473.
(50) The Cambridge Structural Database; Groom, C. R.; Bruno, I. J.;
Lightfoot, M. P.; Ward, S. C. The Cambridge Structural Database.
Acta Crystallogr. 2016, B72, 171−179.
(51) Cotton, F. A.; Murillo, L. A.; Walton, R. A. Multiple Bonds
Between Metal Atoms; Springer: New York, 2005.
(52) Liddle, S. T. Molecular Metal-Metal Bonds: Compounds,
Synthesis, Properties; Wiley-VCH, 2015.
(33) Bohra, R.; Hitchcock, P. B.; Lappert, M. F.; Au-Yeung, S. C. F.;
Leung, W.-P. Group 6 metallocene(IV)−main group metal com-
plexes: synthesis and structures of a Mo−B−Li compound and of
[W(η-C5H5)2H{SnCl2CH(SiMe3)2}]. J. Chem. Soc., Dalton Trans.
1995, 2999−3005.
(53) Krogman, J. P.; Thomas, C. M. Metal-metal multiple bonding
in C3-symmetric bimetallic complexes of the first row transition
metals. Chem. Commun. 2014, 50, 5115−5127.
(54) Bau, R.; Drabnis, M. H. Structures of transition metal hydrides
determined by neutron diffraction. Inorg. Chim. Acta 1997, 259, 27−
50.
(55) Cordero, B.; Gómez, V.; Platero-Prats, A. E.; Revés, M.;
Echeverría, J.; Cremades, E.; Barragán, F.; Alvarez, S. Covalent radii
revisited. Dalton Trans. 2008, 2832−2838.
(56) Curado, N.; Carrasco, M.; Alvarez, E.; Maya, C.; Peloso, R.;
Rodriguez, A.; Lopez-Serrano, J.; Carmona, E. Lithium Di- and
Trimethyl Dimolybdenum(II) Complexes with Mo−Mo Quadruple
Bonds and Bridging Methyl Groups. J. Am. Chem. Soc. 2015, 137,
12378−12387.
(57) Cotton, F. A.; Liu, C. Y.; Murillo, C. A.; Wang, X.
Dimolybdenum-Containing Molecular Triangles and Squares with
Diamidate Linkers: Structural Diversity and Complexity. Inorg. Chem.
2006, 45, 2619−2626.
(58) Li, J.-R.; Yakovenko, A. A.; Lu, W.; Timmons, D. J.; Zhuang,
W.; Yuan, D.; Zhou, H.-C. Ligand Bridging-Angle-Driven Assembly of
Molecular Architectures Based on Quadruply Bonded Mo−Mo
Dimers. J. Am. Chem. Soc. 2010, 132, 17599−17610.
(59) Cotton, F. A.; Troup, J. M.; Webb, T. R.; Williamson, D. H.;
Wilkinson, G. Preparation, chemistry, and structure of the lithium salt
of the octamethyldimolybdate (II) ion. J. Am. Chem. Soc. 1974, 96,
3824−3828.
(60) Gehlen, W.; Bronger, M.; Auffermann, G. Na3RhH6, Na3IrH6
und Li3IrH6, neue komplexe Hydride mit isolierten [RhH6]3‑ und
[IrH6]3‑ Oktaedern. J. Alloys Compd. 1991, 176, 255−262.
(34) Plois, M.; Wiegand, T.; Wolf, R. Novel Ruthenium(II)
Aluminate Anions: Building Blocks of Unique Cage Structures.
Organometallics 2012, 31, 8469−8477.
(35) Schmidt, J. A. R.; Arnold, J. Alkyl and Alkylidene Tantalum−
Lithium Complexes Supported by an Anionic Triazacyclononane
Ligand. Organometallics 2002, 21, 3426−3433.
(36) Riddlestone, I. M.; Abdalla, J. A. B.; Aldridge, S. Coordination
and Activation of E-H Bonds (E = B, Al, Ga) at Transition Metal
Centers. Adv. Organomet. Chem. 2015, 63, 1−38.
(37) Abdalla, J. A. B.; Riddlestone, I. M.; Tirfoin, R.; Phillips, N.;
Bates, J. I.; Aldridge, S. Al−H σ-bond coordination: expanded ring
carbene adducts of AlH3 as neutral bi- and tri-functional donor
ligands. Chem. Commun. 2013, 49, 5547−5549.
(38) Turner, J.; Abdalla, J. A. B.; Bates, J. I.; Tirfoin, R.; Kelly, M. J.;
Phillips, N.; Aldridge, S. Formation of sub-valent carbenoid ligands by
metal-mediated dehydrogenation chemistry: coordination and
activation of H2Ga{(NDippCMe)2CH}. Chem. Sci. 2013, 4, 4245−
4250.
(39) Riddlestone, I. M.; Edmonds, S.; Kaufman, P. A.; Urbano, J.;
Bates, J. I.; Kelly, M. J.; Thompson, A. L.; Taylor, R.; Aldridge, S. σ-
Alane Complexes of Chromium, Tungsten, and Manganese. J. Am.
Chem. Soc. 2012, 134, 2551−2554.
(40) Ekkert, O.; White, A. J. P.; Crimmin, M. R. Trajectory of
Approach of a Zinc-Hydrogen Bond to Transition Metals. Angew.
Chem., Int. Ed. 2016, 55, 16031−16034.
(41) Ekkert, O.; White, A. J. P.; Tomsb, H.; Crimmin, M. R.
Addition of aluminium, zinc and magnesium hydrides to rhodium-
(III). Chem. Sci. 2015, 6, 5617−5622.
(42) Garco̧ n, M.; Bakewell, C.; Sackman, G.; White, A. J. P.; Cooper,
R. I.; Edwards, A. J.; Crimmin, M. R. A hexagonal planar transition-
metal complex. Nature 2019, 574, 390−393.
(43) Riddlestone, I. M.; Rajabi, N. A.; Lowe, J. P.; Mahon, M. F.;
Macgregor, S. A.; Whittlesey, M. K. Activation of H2 over the Ru−Zn
Bond in the Transition Metal−Lewis Acid Heterobimetallic Species
[Ru(IPr)2(CO)ZnEt]. J. Am. Chem. Soc. 2016, 138, 11081−11084.
(44) Butler, M. J.; Crimmin, M. R. Magnesium, zinc, aluminium and
gallium hydride complexes of the transition metals. Chem. Commun.
2017, 53, 1348−1365.
(45) Perez-Jimenez, M.; Curado, N.; Maya, C.; Campos, J.; Ruiz, E.;
́
Alvarez, S.; Carmona, E. Experimental and Computational Studies on
Quadruply Bonded Dimolybdenum Complexes with Terminal and
Bridging Hydride Ligands. Chem. - Eur. J. 2021, DOI: 10.1002/
chem.202004948.
(46) Green, J.; Green, M. L. H.; Parkin, G. The occurrence and
representation of three-centre two-electron bonds in covalent
inorganic compounds. Chem. Commun. 2012, 48, 11481−11503.
(47) Curado, N.; Carrasco, M.; Maya, C.; Peloso, R.; Rodríguez, A.;
́
Ruiz, E.; Alvarez, S.; Carmona, E. An Unsaturated Four-Coordinate
Dimethyl Dimolybdenum Complex with a Molybdenum−Molybde-
num Quadruple Bond. Chem. - Eur. J. 2017, 23, 194−205.
́
(48) Mendoza, I.; Curado, N.; Carrasco, M.; Alvarez, E.; Peloso, R.;
Rodríguez, A.; Carmona, E. Synthesis and structure of mixed
carboxylate-aminopyridinate and -amidinate complexes of dimolybde-
num and ditungsten. Inorg. Chim. Acta 2015, 424, 120−128.
(49) Del Bene, J. E.; Alkorta, I.; Elguero, J. Ab Initio Study of
Ternary Complexes A···NCH···C with A, C = HCN, HF, HCl, ClF,
5230
https://doi.org/10.1021/jacs.1c01602
J. Am. Chem. Soc. 2021, 143, 5222−5230