Pyridine(diimine) Molybdenum-Catalyzed Hydrogenation of Arenes and Hindered Olefins: Insights into Precatalyst Activation and Deactivation Pathways

Article abstract of DOI:10.1021/acscatal.8b00924

Pyridine(diimine) molybdenum bis(olefin) and bis(alkyl) complexes were synthesized, characterized, and examined for their catalytic activity in the hydrogenation of benzene and a selection of substituted arenes. The molybdenum bis(alkyl) complex (4-^tBu-^iPrPDI)Mo(CH₂SiMe₃)₂ (^iPrPDI = 2,6-(2,6-(C(CH₃)₂H)₂C₆H₃N=CMe)₂C₅H₃N) exhibited the highest activity for the hydrogenation of benzene, producing cyclohexane in >98% yield at 23 °C under 4 atm of hydrogen after 48 h. Toluene and o-xylene were similarly hydrogenated to their respective cycloalkanes, with the latter yielding predominantly (79:21 dr) cis-1,2-dimethylcyclohexane. The molybdenum-catalyzed hydrogenation of naphthalene yielded tetralin exclusively, and this selectivity was maintained at higher H₂ pressure. At 32 atm of H₂, more hindered arenes such as monosubstituted benzenes, biphenyl, and m- and p-xylenes underwent hydrogenation with yields ranging between 20 and >98%. (4-^tBu-^iPrPDI)Mo(CH₂SiMe₃)₂ was also a competent alkene hydrogenation catalyst, supporting stepwise reduction of benzene to cyclohexadiene and cyclohexene during molybdenum-catalyzed arene hydrogenation. Deuterium labeling studies for the molybdenum-catalyzed hydrogenation of benzene produced numerous isotopologues and stereoisomers of cyclohexane, indicating reversible hydride (deuteride) insertion/β-H(D) elimination, diene/olefin binding, and allylic C-H(D) activation during the reaction. The resting state of the catalyst under neat conditions was established as the η⁶-benzene complex (^iPrPDI)Mo(η⁶-benzene). Under catalytic conditions, pyridine underwent C-H activation of the 2-position and furan underwent formal C-O oxidative addition to yield a "metallapyran". Both reactions were identified as important catalyst deactivation pathways for the attempted molybdenum-catalyzed hydrogenation of heteroarenes.

Full text of DOI:10.1021/acscatal.8b00924

Subscriber access provided by Kaohsiung Medical University
Article
Pyridine(diimine) Molybdenum-Catalyzed Hydrogenation
of Arenes and Hindered Olefins: Insights into
Precatalyst Activation and Deactivation Pathways
Matthew V. Joannou, Máté J. Bezdek, and Paul J. Chirik
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b00924 • Publication Date (Web): 01 May 2018
Downloaded from http://pubs.acs.org on May 1, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 10
ACS Catalysis
1
2
3
4
5
6
7
8
9
Pyridine(diimine) Molybdenum-Catalyzed Hydrogenation of Arenes
and Hindered Olefins: Insights into Precatalyst Activation and Deac-
tivation Pathways
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Matthew V. Joannou, Máté J. Bezdek, Paul J. Chirik*
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States
Supporting Information Placeholder
ABSTRACT: Pyridine(diimine) molybdenum bis(olefin) and bis(alkyl) complexes were synthesized, characterized, and examined for
their catalytic activity in the hydrogenation of benzene and a selection of substituted arenes. The bis(alkyl) molybdenum complex
(4-tBu-iPrPDI)Mo(CH2SiMe3)2 (iPrPDI = 2,6-(2,6-(C(CH3)2H)2C6H3N=CMe)2C5H3N) exhibited the highest activity for the hydrogenation
of benzene, producing cyclohexane in >98% yield at 23 °C under 4 atm of hydrogen after 48 hours. Toluene and ortho-xylene
were similarly hydrogenated to their respective cycloalkanes with the latter yielding predominantly (79:21 d.r.) of cis-1,2-
dimethylcyclohexane. The molybdenum-catalyzed hydrogenation of naphthalene yielded tetralin exclusively and this selectivity
was maintained at higher H2 pressure. At 32 atm of H2, more hindered arenes such as monosubstituted benzenes, biphenyl, and
m- and p-xylenes underwent hydrogenation with yields ranging between 20 and >98%. (4-tBu-iPrPDI)Mo(CH2SiMe3)2 was also a
competent alkene hydrogenation catalyst, supporting stepwise reduction of benzene to cyclohexadiene and cyclohexene during
molybdenum-catalyzed arene hydrogenation. Deuterium labelling studies for the molybdenum-catalyzed hydrogenation of ben-
zene produced numerous isotopologues and stereoisomers of cyclohexane, indicating reversible hydride (deuteride) insertion/β-
H(D) elimination, diene/olefin binding, and allylic C-H(D) activation during the reaction. The resting state of the catalyst under
neat conditions was established as the η6-benzene complex (iPrPDI)Mo(η6-benzene). Under catalytic conditions, pyridine under-
went C-H activation of the 2-position, and furan underwent formal C-O oxidative addition to yield a “metallapyran”. Both reac-
tions were identified as important catalyst deactivation pathways for the attempted molybdenum-catalyzed hydrogenation of
heteroarenes.
KEYWORDS: Hydrogenation, molybdenum, arene, alkene, mechanism
One of the first purportedly homogeneous arene hydro-
genation catalysts was a tris(phosphite)cobalt allyl developed
INTRODUCTION
by Muetterties and co-workers.8 Catalytic hydrogenation of
arenes was observed under mild conditions (1-3 atm of H2, 24
°C, 1 mol% catalyst) and tolerated substituted arenes such as
xylenes, naphthalene, and mesitylene; in all cases cis cycloal-
kanes were obtained. Based on extensive mechanistic stud-
ies, the origin of the cis selectivity was proposed to result
from successive syn additions of a cobalt-allyl-hydride across
the C – C bonds of the arene and subsequent diene and olefin
reduction products (providing support for homogeneous ca-
talysis1). Rothwell and co-workers observed similar all-cis
selectivity for their tantalum9 and niobium-based10 aryloxide
hydrogenation catalysts. More recently, Glorius and co-
workers disclosed the cis-selective hydrogenation of
fluoroarenes, utilizing a cyclic (alkyl)(amino)carbene rhodium
precursor.11 The selectivity and efficiency of these catalytic
methodologies demonstrate that homogeneous arene hydro-
genation can be highly useful in the selective synthesis of
The catalytic hydrogenation of benzene and other substi-
tuted arenes to cycloalkanes is an important process in both
the fine and petrochemical industries (Figure 1, top).1 Most
notable is the hydrogenation of benzene to cyclohexane,
which is conducted on a >2 million ton/year scale utilizing
Group 10 transition metal-based heterogeneous catalysts.2
These catalysts are highly active and robust, yet are ineffec-
tive for the stereoselective hydrogenation of substituted
1
,
,3 4
arenes.
Development of single-site5 and homogeneous
catalysts for the selective hydrogenation of arenes is highly
desirable, as methods for the stereoselective functionaliza-
tion of cycloalkanes have become more widespread and uti-
lized in the synthesis of pharmaceuticals.6 Chemo- and stere-
oselective hydrogenation of substituted arenes or differential
reactivity in mixtures of different arenes7 would allow for
efficient generation of stereodefined cycloalkanes via well-
defined, organometallic species.
ACS Paragon Plus Environment

ACS Catalysis
Page 2 of 10
molecules of academic, pharmaceutical and fine chemical
interest.
ligand to induce a haptotropic rearrangement of the η6-
benzene ligand and ultimately promote hydrogenation?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Potential for ligand-induced haptotropic rearrange-
ment of η6-arene complex in arene hydrogenation.
Here we describe the development of a molybdenum-
catalyzed method for arene hydrogenation, utilizing both 1,5-
cyclooctadiene (1,5-COD) and bis(neosilyl) molybdenum
precatalysts. Mechanistic investigations establish (PDI)Mo(η6-
benzene) complexes as the catalyst resting states. Hydrogen-
ations with heteroarene substrates were unsuccessful, due to
catalyst deactivation pathways, which were characterized for
pyridine and furan.
Figure 1. Heterogeneous versus Homogeneous Arene Hydro-
genation and their applications.
Arene coordination to a transition metal, the first step in
arene hydrogenation, is known to dramatically alter arene
reactivity and allow for both nucleophilic and electrophilic
reactions at even the most unreactive substrates.12 Ubiqui-
tous η6-arene complexes display classic electrophilic reactivity
at the arene, and have been exploited and broadly utilized in
medicinal, organometallic, and synthetic organic chemistry
for the functionalization and substitution of arenes.12 The
much less common η2-arene binding mode can lead to en-
hanced or Umpolung13 reactivity at the arene. 14
RESULTS AND DISCUSSION
Catalyst Evaluation and Optimization. Our studies com-
menced with evaluation of several different pyridine(diimine)
(PDI) molybdenum precatalysts for the catalytic hydrogena-
tion of benzene to cyclohexane. We previously reported the
robust and scalable synthesis of PDIMo(1,5-COD) complexes,
as well as demonstrated the lability of the bis-olefin ligand
when exposed to donor ligands such as ethylene, which sug-
gested that these complexes may serve as efficient precata-
lysts for arene hydrogenation.19 Initial catalyst optimization
studies demonstrated that (iPrPDI)Mo(1,5-COD) (iPrPDI = 2,6-
(2,6-(C(CH3)2H)2C6H3N=CMe)2C5H3N) was the only precatalyst
capable of producing cyclohexane in meaningful amounts (25
TON, Entry 1, Table 1) under 4 atm of H2 in neat benzene at
60°C. Reducing the size of the imine substituents with MesPDI
and tBuPDI analogues yielded only <1 or 2 equivalents of cy-
clohexane, respectively (Entries 2 and 3, Table 1). Paramag-
netic (iPrPDI)Mo(CH2SiMe3)2 proved to be a more effective
precatalyst, more than doubling the TON to 56 (Entry 5, Table
Taube and co-workers isolated one of the first η2-benzene
compounds: [(NH3)5Os(η2-C6H6)][OTf]2.15 They reported that
this dicationic osmium arene complex could be hydrogenated
with Pd/C under mild conditions to the corresponding cyclo-
hexene complex: [(NH3)5Os(η2-cyclohexene)][OTf]2. While the
hydrogenation could not be accomplished without catalytic
Pd/C, it nonetheless demonstrated that η2-coordination of
benzene to a transition metal center can significantly lower
the barrier for hydrogenation as Pd/C itself is not capable of
hydrogenating benzene.16 This enhanced reactivity likely
stems from ground state destabilization of benzene from loss
3
,17
of aromaticity upon coordination to osmium.
Our laboratory has previously reported that the pyri-
dine(diimine) (PDI) molybdenum(η6-benzene) complex un-
dergoes haptotropic rearrangement of the arene ligand upon
addition of two equivalents of ammonia to yield the corre-
sponding bis(ammonia)(η2-benzene) complex (Figure 2,
top).18 While this molybdenum compound was studied for N-
H bond cleavage by proton coupled electron transfer, we
reasoned that the η2-benzene ligand might display similar
reactivity to [(NH3)5Os(η2-C6H6)][OTf]2. The molybdenum
complex, however, is neutral and supported by a potentially
redox active pyridine(diimine) ligand, which could modulate
π-backdonation from the metal and promote catalytic and
complete arene hydrogenation. A significant fundamental
question therefore arose – is dihydrogen a sufficiently potent
1).
This precatalyst was synthesized by an alkyla-
tion/reduction sequence from (iPrPDI)MoCl3 and 3 equivalents
of neosilyllithium (see SI for details). Substituting the 4-
position of the pyridine ring on the PDI ligand with a tert-
butyl group, known to increase olefin hydrogenation activity
in PDI iron complexes20, further increased the TON to 60.
Increasing the ratio of hydrogen to benzene from approxi-
mately 3:1 to 30:1 (by lowering the amount of substrate used
and including hexanes as an inert solvent), cyclohexane was
obtained in >98% NMR yield at ambient temperature (Entry
6, Table 1).
As with the parent bis(neosilyl) molybdenum compound,
1
(4-tBu-iPrPDI)Mo(CH2SiMe3)2 is paramagnetic and exhibits a H
2
ACS Paragon Plus Environment

Page 3 of 10
ACS Catalysis
NMR spectrum with chemical shifts ranging from δ 16 to -11 Table 2. Substrate Scope of Molybdenum-Catalyzed Arene
1
2
3
4
5
6
7
8
ppm. The solid-state structure, confirmed by X-ray crystallog-
raphy (Figure S1), is distorted trigonal bipyramidal, with the
neosilyl groups and pyridine occupying the equatorial plane.
The Cimine – Nimine and Cipso – Cimine bond lengths of the pyri-
dine(diimine) ligand are consistent with a doubly reduced
chelate, indicating that a Mo(IV) oxidation state assignment is
most appropriate. A solid state magnetic moment (magnetic
susceptibility balance) of 2.5 µB was measured at 23 ºC, con-
sistent with an S = 1 ground state configuration. This meas-
urement is slightly lower than the spin-only value of 2.8 µB,
which has been observed previously for PDI molybdenum (IV)
compounds19 and is likely a result of spin-orbit coupling in the
Hydrogenation
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2
triplet ground state (likely a pseudo e’’ configuration, see SI
for a qualitative molecular orbital diagram).
Table 1. Optimization of the Benzene Hydrogenation with PDI
Molybdenum Precatalysts
Other substituted arenes such as m- and p-xylenes, cy-
mene, ethylbenzene, cumene etc. were unreactive under the
above conditions, as <5% of the corresponding cycloalkane
was detected by NMR spectroscopy after 48 hours at 60 °C.
To promote hydrogenation of more hindered arenes, reac-
tions with higher pressures of H2 were investigated. With 10
mol % (4-tBu-iPrPDI)Mo(CH2SiMe3)2 in cyclohexane at 60 °C
under 32 atm of H2, ethyl-, propyl-, and isopropylbenzene
were hydrogenated to their respective cycloalkanes in >98%,
>98%, and 53% NMR yield. Biphenyl and diphenylmethane
underwent hydrogenation of both arene rings and produced
bicyclohexyl and dicyclohexylmethane in >98% and 69% NMR
yield, respectively. M-xylene was hydrogenated to 1,3-
dimethylcyclohexane, predominately the cis isomer (75:25
d.r.) in 40% NMR yield, while hydrogenation of p-xylene pro-
duced 1,4-dimethylcyclohexane in only 24% NMR yield (50:50
d.r.). Increasing the pressure to 32 atm in the hydrogenation
of naphthalene still produced tetraline exclusively (>98 NMR
yield).
Because more hindered arenes required increased hydro-
gen pressure to observe turnover, we reasoned that this dif-
ferential reactivity could be exploited for the chemoselective
hydrogenation of mixtures of arenes. To this end, an equimo-
lar mixture of toluene and ethylbenzene was subjected to 4
atm of H2 along with 5 mol % (4-tBu-iPrPDI)Mo(CH2SiMe3)2
(Scheme 1). Methylcyclohexane was obtained exclusively in
>98% NMR yield, along with recovered ethylbenzene,
demonstrating that [(iPrPDI)Mo] is capable of selectively hy-
drogenating arenes with smaller substituents in a mixture.
This also highlights the ability of [(iPrPDI)Mo] to differentiate
subtle changes in substrate sterics (i.e. methyl vs. ethyl or o-
vs. m- and p-xylenes), a distinguishing feature from hetero-
geneous catalysts which typically are selective for more sub-
stituted, electron rich arenes.5c While by no means definitive,
the pressure and ligand dependence, chemoselectivity, and
Arene and Alkene Substrate Scope. The scope of the mo-
lybdenum-catalyzed arene hydrogenation was also investi-
gated and the results are summarized in Table 2. With 5 mol
% (4-tBu-iPrPDI)Mo(CH2SiMe3)2 in cyclohexane at 60 °C under 4
atm of H2, toluene was hydrogenated to methylcyclohexane
in >98% NMR yield. Under identical conditions, ortho-xylene
was hydrogenated to 1,2-dimethylcyclohexane in 81% NMR
yield, predominantly to the cis stereoisomer (79:21 d.r.).
Naphthalene underwent hydrogenation of only one aromatic
ring, selectively producing tetralin in 74% NMR yield. These
conditions are mild compared to other heterogeneous, multi-
site molybdenum catalysts that require elevated tempera-
tures and pressures.21
3
ACS Paragon Plus Environment

ACS Catalysis
Page 4 of 10
stereoselectivity of arene hydrogenation support single site, ported in Table 3. With 5 mol % catalyst, at 23 °C under 4
1
2
3
4
5
6
7
8
soluble pyridine(diimine) molybdenum complexes as the ac-
tive catalysts.
atm of H2, both cyclohexene and 1-methylcyclohexene were
hydrogenated in >98% NMR yield in hydrocarbon solvents
(hexanes
and
cyclohexane,
respectively).
1,2-
Scheme 1. Selective Hydrogenation of Toluene over
Ethylbenzene.
dimethylcyclohex-1-ene23 was hydrogenated to 1,2-
dimethylcyclohexane in 82% NMR yield, 77:23 d.r. (cis:trans),
at 60 °C. The selectivity of this reaction was almost identical
to the hydrogenation of o-xylene, indicating that 1,2-
dimethylcyclohexane is likely an intermediate in the hydro-
genation of o-xylene (vide infra). While molybdenum cata-
lyzed hydrogenation and hydrosilylation of carbonyl com-
pounds is well established,24 the corresponding hydrogena-
tion of alkenes is less developed. There have been several
examples of stoichiometric25, as well as transfer hydrogena-
tion of alkenes using cyclopentadienyl- and phosphine-based
molybdenum complexes/catalysts.26 The scope of molyb-
denum-catalyzed hydrogenation utilizing H2 gas is limited to
linear olefins and requires elevated temperatures (>100 °C)
and pressures (>50 atm of H2).27 To the best of our
knowledge, this is the first instance of a mild (23 °C, 4 atm of
H2) molybdenum-catalyzed alkene hydrogenation that is op-
erative for even tetra-substituted olefins.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The significant drop in arene hydrogenation reactivity with
larger substrates is likely a result of steric crowding around
the molybdenum catalyst, as illustrated in Figure 3. Much like
(PDI) molybdenum bis-olefin complexes, (iPrPDI)Mo(η6-
benzene) is Cs symmetric in the solid state, due to the N-aryl
groups of the ligand being bowed away from the coordinated
benzene.18 This creates an asymmetric pocket around the
molybdenum, where the top face of the molybdenum is
blocked by the 2,6-diisopropyl N-aryl groups. For toluene,
naphthalene, and o-xylene, the arene can coordinate to place
the larger substituents in the more “open” face of the molyb-
denum, which minimizes steric interactions with the isopro-
pyl groups of the ligand (Figure 3, top). For benzenes with
larger substituents, as well as 1,3- and 1,4-disubstituted
arenes, there is no configuration where the substituents of
the arene do not unfavorably interact with the ligand, render-
ing coordination to the molybdenum much more difficult,
ultimately resulting in diminished catalytic activity at 4 atm of
H2 (Figure 3, bottom). This reactivity profile has been ob-
served with other transition metal-catalyzed arene hydrogen-
ations, specifically a cobalt-catalyzed methodology developed
by Muetterties and co-workers. In their report, multi-
substituted and bulky arenes required much longer reaction
times or were completely unreactive.8 Less sterically encum-
bered molybdenum precatalysts (both 1,5-COD and
bis(neosilyl) variants from Table 1) were also screened for the
hydrogenation of larger arenes, but these also produced the
corresponding cycloalkanes in <5% NMR yield. This is likely a
result of weak or unstable arene coordination in MesPDI and
tBuPDI molybdenum complexes.22
Table 3. Substrate Scope of Molybdenum-Catalyzed Alkene
Hydrogenation
To illustrate how the chemoselectivity of molybdenum-
catalyzed hydrogenations can be controlled through H2 pres-
sure, the hydrogenation of styrene was explored (Scheme 2).
With 5 mol % (4-tBu-iPrPDI)Mo(CH2SiMe3)2 and 4 atm of H2,
styrene was quantitatively converted to ethylbenzene after
24 hours at 23 °C. When exposed to 32 atm of H2 at 60 °C
with 10 mol % (4-tBu-iPrPDI)Mo(CH2SiMe3)2, styrene was com-
pletely reduced to ethylcyclohexane in >98% NMR yield. This
demonstrates the versatility and pressure-dependent
chemoselectivity of (PDI) molybdenum hydrogenation cata-
lysts.
Scheme 2. Pressure-Dependent Chemoselective Molyb-
denum-Catalyzed Hydrogenation of Styrene to Ethylbenzene
or Ethylcyclohexane.
Figure 3. Steric interactions between the η6-arene and iPrPDI
ligands: explanation for diminished reactivity.
While neither cyclic olefins nor dienes were detected dur-
ing any of the molybdenum-catalyzed arene hydrogenation
reactions reported here, it is likely that these compounds are
intermediates generated during turnover. To explore this
possibility, (4-tBu-iPrPDI)Mo(CH2SiMe3)2 was employed as an
alkene hydrogenation catalyst, the results of which are re-
4
ACS Paragon Plus Environment

Page 5 of 10
ACS Catalysis
the deuterations of benzene and 1,3-cyclohexadiene, but not
1
2
cyclohexene (Figure 4). Because deuteration of cyclohexene
generates a molybdenum cyclohexyl intermediate, this is less
likely to undergo isomerization than an allylic intermediate
(generated during the benzene and cyclohexadiene deuter-
ations), which explains the observed stereopurity in the deu-
teration of cyclohexene. Representative scrambling path-
ways are summarized in Figure 4. These conclusions explain
the observed diastereoselectivity in the hydrogenation of
both o-xylene and 1,2-dimethylcyclohex-1-ene: since al-
kene/diene coordination is reversible and thermodynamically
controlled, similar selectivity should be observed when any
intermediate along the o-xylene hydrogenation pathway is
exposed to the reaction conditions. This proposal also ex-
plains the >d6 isotopologues observed for the deuteration of
toluene, as the scrambling mechanism via allylic C-H activa-
tion generates a molybdenum hydride, which likely exchang-
es to a deuteride under a D2 atmosphere, which can lead to
further deuterium incorporation.
Deuterium Labelling Studies. To gain further insight into
the regio- and stereoselectivity of the molybdenum-catalyzed
arene hydrogenation, catalytic deuteration experiments were
conducted with benzene, 1,3-cyclohexadiene, and cyclohex-
ene (Scheme 3). Exposure of benzene to 4 atm of D2 under
the conditions detailed in Entry 5, Table 1, produced cyclo-
hexane-dn in 10 turnovers after 24 hours. The reaction mix-
ture was analyzed by quantitative 13C NMR spectroscopy and
was found to be a complex mixture of different stereoisomers
and isotopologues of cyclohexane (Scheme 1). While no sin-
gle compound can be precisely identified, meaningful infor-
mation about specific carbon environments can be extracted
from the NMR spectrum: both cis and trans relationships
between deuteria are present; carbons with two deuteria
attached are present; and carbons with no deuterium incor-
poration are present (Scheme 2). 1,3-cyclohexadiene was
also deuterated under the conditions detailed in Table 3 and
a similar mixture of stereoisomers and isotopologues to the
benzene deuteration was observed. Finally, cyclohexene was
exposed to 4 atm of D2 under the conditions detailed in Table
3. Cyclohexane-d2 was produced in >98% NMR yield and
found to be only the cis isomer by quantitative 13C NMR spec-
troscopy.28
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Investigations into Catalyst Generation and Resting State.
To determine the identity of the active molybdenum catalyst
and/or the catalyst resting state, several stoichiometric and
catalytic experiments were performed on (iPrPDI)Mo(1,5-COD)
and (iPrPDI)Mo(η6-benzene). As depicted in Scheme 4 (top),
heating a benzene-d6 solution of (iPrPDI)Mo(1,5-COD) to 60 °C
for 18 hours under 4 atm of H2 produced (iPrPDI)Mo(η6-
benzene-d6) in >98% conversion. Cyclooctane, as well as cy-
Toluene was similarly deuterated under the conditions in
Entry 5, Table 1, which produced methylcyclohexane-dn in
34% NMR yield. The methylcyclohexane-dn that was formed
was found to also be a complex mixture of stereoisomers and
isotopologues, similar to the benzene deuteration. Im-
portantly, no deuterium incorporation into the methyl group
of methylcyclohexane-dn was observed (see SI for details).
Mass spectrometry was used to determine the composition
of the isotopologues formed from the catalytic deuteration.
Methylcyclohexane-d6 accounted for only 35% of the product
mixture with the balance of the material comprised of
isotopologues ranging from d4 to d11 (see SI for details and full
list of ratios).
1
clohexane-dn, were observed by H NMR spectroscopy, indi-
cating that the NMR solvent had been hydrogenated. To de-
termine whether the η6-benzene complex was still an active
arene hydrogenation catalyst, (iPrPDI)Mo(η6-benzene) was
heated to 60 °C in benzene-d6 under 4 atm of H2 and moni-
tored over the course of 18 hours (Scheme 4, middle). Cyclo-
hexane-dn steadily grew in over the course of the reaction,
accompanied by disappearance of the coordinated benzene
resonance of the molybdenum complex (located at δ 3.56
ppm), reaching 87% conversion to (iPrPDI)Mo(η6-benzene-d6)
after 18 hours. It is important to note that no such arene
exchange was observed without added H2: heating a ben-
zene-d6 solution of (iPrPDI)Mo(η6-benzene) to 60 °C for 24 h
under an atmosphere of N2 produced no detectable arene
exchange or decomposition of the starting material. This sup-
ports the assertion that dihydrogen can induce a haptotropic
rearrangement of coordinated benzene to allow for arene
hydrogenation in analogy to the isolable ammine derivatives
(Figure 2). Under the catalytic conditions described in Table
1, 0.2 mol % of (iPrPDI)Mo(η6-benzene) in benzene produced
cyclohexane in 19 TON, again, confirming that the η6-benzene
complex is catalytically active. These data suggest that the
resting state of the molybdenum catalyst in benzene is
(iPrPDI)Mo(η6-benzene).
Scheme 3. Deuterium Labelling Experiments
These data support a pathway involving reversible insertion
of the arene into a Mo-H followed by β-H elimination where
coordination of benzene, and its hydrogenation intermedi-
ates (cyclohexadiene and cyclohexene) is reversible. PDI mo-
lybdenum complexes have been shown to undergo facile
allylic C-H activation at ambient temperature, which is a likely
pathway for H/D scrambling.19 This would account for the
numerous stereoisomers and isotopologues observed from
5
ACS Paragon Plus Environment

ACS Catalysis
Page 6 of 10
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Summary of H/D scrambling and isomerization mechanisms for molybdenum-catalyzed deuteration of benzene and its
intermediates
molybdenum catalyst at ambient temperature, unlike the 1,5-
COD precatalysts. The alkyl groups of (4-tBu-
iPrPDI)Mo(CH2SiMe3)2 are readily cleaved by H2 at ambient
temperature to generate a highly active molybdenum hy-
dride, which then converts to an η6-benzene complex, a much
slower arene hydrogenation catalyst (vide supra). By compar-
ison, (iPrPDI)Mo(1,5-COD) has a longer induction period than
(4-tBu-iPrPDI)Mo(CH2SiMe3)2, as it takes heating to 60 °C for 18
hours just to hydrogenate the 1,5-COD ligand and activate
the catalyst.
Scheme 4. Fate of (iPrPDI)Mo(1,5-COD) Precatalyst and Ac-
tivity of (iPrPDI)Mo(η6-benzene) as a Hydrogenation Catalyst
Attempts to observe a molybdenum hydride in cyclohexane
(without added arene or other coordinating ligands) have
been unsuccessful. Exposure of any of the molybdenum
precatalysts listed in Table 1 to hydrogen in cyclohexane-d12
led to decomposition of the starting material and produced
1
an intractable mixture of compounds as judged by H NMR
spectroscopy. Interestingly, exposure of (iPrPDI)Mo(η6-
benzene) to 4 atm of H2 in cyclohexane-d12 produced one
equivalent of cyclohexane, but led to decomposition of the
molybdenum complex. These results suggest that a single
turnover of arene hydrogenation had taken place and that
dihydrogen appears to induce a haptotropic rearrangement
of the η6-benzene ligand and facilitate benzene hydrogena-
tion. The resulting PDI molybdenum hydride is likely only
stable in the presence of other coordinating ligands (i.e.
arene or olefin, vide supra).
To explore why molybdenum bis(neosilyl) precatalysts
were more active than their 1,5-COD counterparts, (4-tBu-
iPrPDI)Mo(CH2SiMe3)2 was exposed to 4 atm of H2 in benzene-
1
d6 and analyzed by H NMR spectroscopy. After 10 minutes,
>98% conversion to a C1 symmetric, diamagnetic PDI molyb-
denum hydride was observed, with a diagnostic hydride sig-
nal centered at δ -3.40 ppm.29 The precise structure of this
complex has yet to be determined as it is too reactive to iso-
late and rapidly converts to (4-tBu-iPrPDI)Mo(η6-benzene-d6),
reaching >95% conversion after 3 hours at 23 °C. Cyclohex-
ane-dn was observed in the NMR spectrum after 10 minutes
of reaction, indicating this molybdenum hydride intermediate
is an active arene hydrogenation catalyst. These experiments
indicate that bis(neosilyl) precatalysts rapidly form the active
Identification of Catalyst Deactivation Pathways from the
Attempted Hydrogenation of Heteroarenes. Several differ-
ent nitrogen- and oxygen-containing heteroarenes were test-
ed in the molybdenum-catalyzed arene hydrogenation, but
under the conditions detailed in Table 2 (both 4 and 32 atm
of H2), only unreacted starting material was observed in the
crude 1H NMR spectrum of the unpurified mixture. To identi-
fy any potential deactivation pathways that may occur with
molybdenum precatalysts in the presence of heteroarenes
6
ACS Paragon Plus Environment

Page 7 of 10
ACS Catalysis
and hydrogen, several stoichiometric reactions were con-
ducted.
(iPrPDI)Mo(1,5-COD) was mixed with 2.1 equivalents of pyr-
1
2
3
idine and heated to 60 °C in benzene-d6 under 4 atm of H2,
and after 18 hours, all the starting material was consumed
and cyclooctane was observed. The resulting purple organo-
metallic complex was identified as the 2-pyridinyl molyb-
denum pyridine-hydride (iPrPDI)Mo(H)(η2-C5H4N)(pyridine),
which was obtained in >98% conversion (Scheme 5). The
compound was characterized by multinuclear NMR spectros-
copy and its structure confirmed by X-ray crystallography.
Crystals for the diffraction study were obtained from inde-
pendent synthesis by sodium amalgam reduction of
(iPrPDI)MoCl3 in the presence of pyridine (see SI for details).
The ambient temperature 1H NMR spectrum of
(iPrPDI)Mo(H)(η2-C5H4N)(pyridine) in benzene-d6 exhibits the
expected number of signals for a Cs symmetric compound and
also supports a diamagnetic ground state. Most of the aro-
matic pyridine signals are well resolved and were assigned,
ranging from δ 6.73 to 5.72 ppm. The hydride signal appears
as a singlet at δ -8.84 ppm, a chemical shift within the range
of molybdenum hydrides with other nitrogen- and oxygen-
based ligands.30 C-H activation of this type has been previ-
ously observed with molybdenum(0) complexes, as Parkin
and co-workers observed C-H activation of pyridine in the 2-
position by Mo(PMe3)6.30 While (PMe3)4Mo(H)(η2-C5H4N) con-
verts to the η6-pyridine analogue upon heating, this was not
observed for (iPrPDI)Mo(H)(η2-C5H4N)(pyridine), which is sta-
ble at 80 °C under 4 atm of H2, 1 atm of N2, or vacuum.
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. Representation of the solid-state structure of
(iPrPDI)Mo(H)(η2-C5H4N)(pyridine) at 30% probability thermal
ellipsoids. Hydrogen atoms and co-crystallized thf molecule
are omitted for clarity. Selected bond distances (Å) and an-
gles (deg): Mo1 – N1 2.117(3), Mo1 – N2 2.043(3), Mo1 – N3
2.106(3), Mo1 – N4 2.334(3), Mo1 – N5 2.095(3), Mo1 – C39
2.101(3), N1 – C2 1.335(4), N3 – C8 1.350(4), C2 – C3
1.403(5), C7 – C8 1.407(5), N5 – C39 1.329(5); N1 – Mo1 – N3
146.2(1), N1 – Mo1 – N2 73.4(1), N2 – Mo1 – N3 73.3 (1), N1
– Mo1 – N4 94.5(1), N1 – Mo1 – N5 125.7(1), N1 – Mo1 – C39
88.8(1).
To determine if there was a similar catalyst deactivation
pathway
with
oxygen-containing
heterocycles,
(iPrPDI)Mo(CH2SiMe3)2 was treated with 5 equivalents of furan
under 1 atm of H2 in benzene-d6 (Scheme 6). After 10
minutes at 23 °C, the starting material was consumed and
Scheme 5. Isolation of Catalyst Deactivation Species with
Pyridine – C-H Activation of Pyridine (2-position)
1
tetramethylsilane was detected by H NMR spectroscopy. A
new, maroon molybdenum complex had formed in >98%
conversion, which was identified as the C-O bond cleaved
species (iPrPDI)Mo[κ2-O(CH)4], a “metallapyran”. Its composi-
tion and structure were determined by a combination of mul-
tinuclear NMR spectroscopy and X-ray crystallography, and
independently prepared from sodium amalgam reduction of
(iPrPDI)MoCl3 in the presence of furan (see SI for details).
(iPrPDI)Mo[κ2-O(CH)4] was also obtained from addition of fu-
ran to a benzene-d6 solution of (iPrPDI)Mo(1,5-COD) in the
presence of hydrogen, but this route required heating to 60
°C for 24 hours, and (iPrPDI)Mo(η6-benzene) was also ob-
served.31 This is a unique instance of oxidative addition into
the C–O bond of furan by molybdenum. Aluminum(II) 1,3-
diketimidate complexes have been shown to undergo oxida-
tive addition into the more reactive C–O bond of benzofu-
ran32, while iridium metallapyrans have been synthesized by
alkylation with enolates and C-H activation of enal iridium
complexes.33 Group 434 and Group 1035 metallapyrans have
also been observed when the respective metal-furanyl com-
pounds are exposed to nucleophiles such as phenyl, methyl,
or furanyl lithium. This suggests that C-H activation of furan
(analogous to pyridine) may occur en route to (iPrPDI)Mo[κ2-
O(CH)4], where the resulting molybdenum-hydride-furanyl
undergoes a hydride-induced, migratory ring enlargement to
yield the metallapyran.34a
Single crystals of (iPrPDI)Mo(H)(η2-C5H4N)(py) suitable for X-
ray diffraction were obtained from slow diffusion of pentane
into a concentrated thf solution at -35 °C over a period of 18
hours. The solid-state structure is presented in Figure 5,
along with selected bond distances and angles.
(iPrPDI)Mo(H)(η2-C5H4N)(py) has a distorted pentagonal bi-
pyramidal geometry, a 7-coordinate molybdenum center with
the hydride (which could not be located) and N-bound pyri-
dine ligand occupying the apical positions, and the C-H acti-
vated pyridine and iPrPDI ligands occupying the equatorial
positions. The Cimine – Nimine and Cipso – Cimine bond lengths of
the pyridine(diimine) chelate are consistent with a doubly
reduced chelate, indicating that a Mo(IV) oxidation state is
most appropriate.
Scheme 6. Isolation of Catalyst Deactivation Species with
Furan – C-O Oxidative Addition into a Metallapyran
7
ACS Paragon Plus Environment

ACS Catalysis
Page 8 of 10
es (Å) and angles (deg): Mo1 – N1 2.062(1), Mo1 – N2
1
2
3
4
5
6
2.052(1), Mo1 – N3 2.073(1), Mo1 – O1 1.921(1), Mo1 – C34
2.030(2), N1 – C2 1.347(2), N3 – C8 1.336(2), C2 – C3
1.406(2), C7 – C8 1.414(2); N1 – Mo1 – N3 143.00(5), N1 –
Mo1 – N2 72.45(5), N2 – Mo1 – N3 72.51(5), N2 – Mo1 – O1
172.04(5), N2 – Mo1 – C34 96.57(6), O1 – Mo1 – C34
88.71(6).
7
8
CONCLUSIONS
9
In summary, a molybdenum-catalyzed arene and alkene
hydrogenation method has been developed. Benzene, along
with several substituted arenes were fully hydrogenated and
demonstrate that the barrier to arene hydrogenation can be
significantly lowered through coordination to a transition
metal. Deuterium labeling studies reveal the formation of
multiple isotopologues and stereoisomers, indicating reversi-
ble insertion/β-H elimination, substrate coordination, and
allylic C-H activation all taking place during the reaction. The
catalyst resting state in benzene was determined to be the
η6-benzene complex, while attempts to observe a molyb-
denum hydride in hydrocarbon solvents were unsuccessful.
Catalyst deactivation pathways for selected heteroarene sub-
strates were also identified: C-H activation of pyridine and C-
O bond cleavage of furan were observed and their resulting
organomolybdenum complexes characterized.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
The H NMR spectrum of (iPrPDI)Mo[κ2-O(CH)4] in benzene-
d6 is consistent with a diamagnetic ground state and Cs sym-
metric structure. There are 4 distinct resonances correspond-
ing to the metallapyranyl protons, ranging from δ 7.53 to 6.20
ppm. Crystals of (iPrPDI)Mo[κ2-O(CH)4] suitable for X-ray dif-
fraction were obtained by slow evaporation of a concentrat-
ed pentane solution at -35 °C over a period of 24 hours. The
solid-state structure is presented in Figure 6, along with se-
lected bond lengths and angles. The coordination geometry
of (iPrPDI)Mo[κ2-O(CH)4] is best described as a distorted
square-based pyramid, which is consistent with the NMR
spectroscopic data. The oxygen of the metallapyran is trans
to the pyridine nitrogen of PDI and in an equatorial position,
while the C-terminus of the metallacycle bound to the metal
occupies the apical position of the square-based pyramid.
The C–C bond lengths of the metallapyran are statistically
distinguishable: the C-terminus C – C bond (C34 – C35) has a
length of 1.365(2) Å and the O-terminus C – C bond (C36 –
C37) has a length of 1.348(3) Å, indicating double bond char-
acter for both. The C – C (C35 – C36) and C – O (C37 – O1)
single bonds have lengths only slightly contracted from nor-
mal values, 1.425(3) Å and 1.334(2) Å, respectively. The Cimine
– Nimine and Cipso – Cimine bond lengths of (iPrPDI)Mo[κ2-O(CH)4]
are consistent with a closed-shell, doubly reduced PDI ligand,
ASSOCIATED CONTENT
Supporting Information
Complete experimental details and procedures including metal
complex syntheses, hydrogenation procedures, and characteriza-
tion data for all compounds. The materials may be downloaded
free of charge at pubs.acs.org
AUTHOR INFORMATION
Corresponding Author
* Email for P.J.C. pchirik@princeton.edu
ORCID
analogous
to
(iPrPDI)Mo(H)(η2-C5H4N)(py)
and
(iPrPDI)Mo(CH2SiMe3)2, and supports a Mo(IV) oxidation state.
Paul J. Chirik: 0000-0001-8473-2898
Matthew V. Joannou: 0000-0002-0079-7107
Máté J. Bezdek: 0000-0001-7860-2894
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
We thank Dr. Ilia Korobkov for helpful discussions and Dr. Zöe
Turner for the X-ray structure of (iPrPDI)Mo(CH2SiMe3)2. We also
thank Dr. John Eng for assistance with mass spectrometry. Fi-
nancial support was provided by the National Science Foundation
(NSF) Grant Opportunities for Academic Liaison with Industry
(GOALI) grant (CHE-1265988).
REFERENCES
1
Dyson, P. J. Arene Hydrogenation by Homogeneous Catalysts: Fact
Figure 6. Representation of the solid-state structure of
(iPrPDI)Mo[O(CH)4] at 30% probability thermal ellipsoids. Hy-
drogen atoms are omitted for clarity. Selected bond distanc-
or Fiction? Dalton Trans. 2003, 15, 2964–2974.
8
ACS Paragon Plus Environment

Page 9 of 10
1
ACS Catalysis
2
3
4
5
6
7
8
9
2
cloalkanes.” Science 2017, 357, 908–912. (b) Wei, Y.; Rao, B.; Cong,
Campbell, M. L. Cyclohexane. In Ullmann’s Encyclopedia of Indus-
X.; Zeng, X. Highly Selective Hydrogenation of Aromatic Ketones and
Phenols Enabled by Cyclic (Amino)(Alkyl)Carbene Rhodium Complex-
es. J. Am. Chem. Soc. 2015, 137, 9250–9253.
trial Chemistry; Wiley-VCH Verlag GmbH & Co. KGaA, 2000.
3
Giustra, Z. X.; Ishibashi, J. S. A.; Liu, S.-Y. Homogeneous metal catal-
ysis for conversion between aromatic and saturated compounds.
12
Transition Metal Arene π-Complexes in Organic Synthesis and Ca-
Coord. Chem. Rev. 2016, 314, 134–181.
4
talysis; Kündig, E. P., Ed.; Brown, J. M., Fürstner, A., Hofmann, P., van
Koten, G., Kündig, E. P., Reetz, M., Dixneuf, P. H., Hegedus, L. S.,
Knochel, P., Murai, S., Abe, A., Series Eds.; Topics in Organometallic
Chemistry; Springer Berlin Heidelberg: Berlin, Heidelberg, 2004; Vol.
7.
(a) Taylor, P.D.; Orchin, M. Hydrogenation of 9,10-
dimethylanthracene with cobalt hydrocarbonyl J. Org. Chem. 1972,
37, 3913. (b) Weil, T. A.; Friedman, S.; Wender, I. Reactions catalyzed
by di-.mu.-carbonylhexacarbonyldicobalt. Selective deuterium incor-
poration into some polycyclic hydrocarbons. J. Org. Chem. 1974, 39,
48.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
13
Meiere, S. H.; Keane, J. M.; Gunnoe, T. B.; Sabat, M.; Harman, W.
5
D. “Binding and Activation of Aromatic Molecules by a Molybdenum
(a) Stalzer, M. M.; Nicholas, C. P.; Bhattacharyya, A.; Motta, A.;
π-Base” J. Am. Chem. Soc. 2003, 125, 2024–2025.
Delferro, M.; Marks, T. J. Single-Face/All-Cis Arene Hydrogenation by
a Supported Single-Site d0 Organozirconium Catalyst. Angew. Chem.
Int. Ed. 2016, 55, 5263–5267. (b) Gu, W.; Stalzer, M. M.; Nicholas, C.
P.; Bhattacharyya, A.; Motta, A.; Gallagher, J. R.; Zhang, G.; Miller, J.
T.; Kobayashi, T.; Pruski, M.; Delferro, M.; Marks, T. J. Benzene Selec-
tivity in Competitive Arene Hydrogenation: Effects of Single-Site
Catalyst···Acidic Oxide Surface Binding Geometry. J. Am. Chem. Soc.
2015, 137, 6770–6780.
14
Liebov, B. K.; Harman, W. D. “Group 6 Dihapto-Coordinate
Dearomatization Agents for Organic Synthesis” Chem. Rev. 2017,
117, 13721–13755. And the references therein.
15
Harman, W. D.; Taube, H. “Reactivity of pentaammineosmium(II)
with benzene” J. Am. Chem. Soc. 1987, 109, 1883–1885.
16 (a) Harman, W. D.; Taube, H. “The selective hydrogenation of ben-
zene to cyclohexene on pentaammineosmium (II)” J. Am. Chem. Soc.
1988, 110, 7906–7907. (b) Harman, W. D.; Sekine, M.; Taube, H.
“Substituent effects on. eta. 2-coordinated arene complexes of pen-
taammineosmium (II)” J. Am. Chem. Soc. 1988, 110, 5725–5731.
6
(a) White, M. C. Adding Aliphatic C-H Bond Oxidations to Synthesis.
Science 2012, 335, 807–809 and the references therein.
(b) Serrano-Plana, J.; Oloo, W. N.; Acosta-Rueda, L.; Meier, K. K.;
Verdejo, B.; García-España, E.; Basallote, M. G.; Münck, E.; Que, L.;
Company, A.; Costas, M. Trapping a Highly Reactive Nonheme Iron
Intermediate That Oxygenates Strong C—H Bonds with Stereoreten-
tion. J. Am. Chem. Soc. 2015, 137, 15833–15842.
17
(a) Kistiakowsky, G.B. Ruhoff, J.R. Smith, H.A. Vaughan, W.E.
“Heats of Organic Reactions III. Hydrogenation of Some Higher Ole-
fins” J. Am. Chem. Soc. 1936, 58, 137. (b) Kistiakowsky, G.B. Ruhoff,
J.R. Smith, H.A. Vaughan, W.E. “Heats of Organic Reactions. IV. Hy-
drogenation of Some Dienes and of Benzene” J. Am. Chem. Soc.,
1936, 58, 146. (c) Slayden, S.W. Liebman, J.F. “The Energetics of
Aromatic Hydrocarbons:ꢀ An Experimental Thermochemical Perspec-
tive“ Chem. Rev., 2001, 101, 1541.
7
Gu, W.; Stalzer, M. M.; Nicholas, C. P.; Bhattacharyya, A.; Motta, A.;
Gallagher, J. R.; Zhang, G.; Miller, J. T.; Kobayashi, T.; Pruski, M.;
Delferro, M. Marks, T. J. Benzene Selectivity in Competitive Arene
Hydrogenation: Effects of Single-Site Catalyst···Acidic Oxide Surface
Binding Geometry. J. Am. Chem. Soc. 2015, 137, 6770–6780.
18
Margulieux, G. W.; Bezdek, M. J.; Turner, Z. R.; Chirik, P. J. Ammo-
nia Activation, H2 Evolution and Nitride Formation from a Molyb-
denum Complex with a Chemically and Redox Noninnocent Ligand. J.
Am. Chem. Soc. 2017, 139, 6110–6113.
8
(a) Muetterties, E. L.; Hirsekorn, F. J. “Homogenous catalysis of
aromatic hydrocarbon hydrogenation reactions” J. Am. Chem. Soc.
1974, 96, 4063–4064. (b) Rakowski, M. C.; Hirsekorn, F. J.; Stuhl, L. S.;
Muetterties, E. L. “Catalytic homogeneous hydrogenation of arenes.
4. Characterization of the basic reaction and the catalysts” Inorg.
Chem. 1976, 15, 2379–2382. (c) Bleeke, J. R.; Muetterties, E. L. “Cata-
lytic hydrogenation of aromatic hydrocarbons. Stereochemical defi-
nition of the catalytic cycle for .eta.3-C3H5Co(P(OCH3)3)3” J. Am.
Chem. Soc. 1981, 103, 556–564. (d) Thompson, M. R.; Day, V. W.;
Tau, K. D.; Muetterties, E. L. “Catalytic hydrogenation of aromatic
hydrocarbons. 7. Chemistry and crystal structure of (.eta.3-
cyclooctenyl)cobalt(I) tris(trimethyl phosphite)” Inorg. Chem. 1981,
20, 1237–1241.
19
Joannou, M. V.; Bezdek, M. J.; Al-Bahily, K.; Korobkov, I.; Chirik, P.
J. Synthesis and Reactivity of Pyridine(diimine) Molybdenum Olefin
Complexes: Ethylene Dimerization and Alkene Dehydrogenation.
Organometallics 2017, 36, 4215–4223.
20
Darmon, J. M.; Turner, Z. R.; Lobkovsky, E.; Chirik, P. J. Electronic
Effects in 4-Substituted Bis(imino)pyridines and the Corresponding
Reduced Iron Compounds. Organometallics 2012, 31, 2275–2285.
21
(a) Wang, S.; Ge, H.; Sun, S.; Zhang, J.; Liu, F.; Wen, X.; Yu, X.;
Wang, L.; Zhang, Y.; Xu, H.; Neuefeind, J. C.; Qin, Z.; Chen, C.; Jin, C.;
Li, Y.; He, D.; Zhao, Y. A New Molybdenum Nitride Catalyst with
Rhombohedral MoS2 Structure for Hydrogenation Applications. J.
Am. Chem. Soc. 2015, 137, 4815–4822. (b) Quincy, R. B.; Houalla, M.;
Proctor, A.; Hercules, D. M. Distribution of Molybdenum Oxidation
States in Reduced Molybdenum/Titania Catalysts: Correlation with
Benzene Hydrogenation Activity. Journal of Physical Chemistry 1990,
94, 1520–1526. (c) Rocha, Â. S.; Silva, V. L. T. da; Leitão, A. A.;
Herbst, M. H.; Jr, A. C. F. Low Temperature Low Pressure Benzene
Hydrogenation on Y Zeolite-Supported Carbided Molybdenum. Catal.
Today 2004, 98, 281–288.
9
(a) Ankianiec, B. C.; Fanwick, P. E.; Rothwell, I. P. “Isolation of a
New Series of Seven-Coordinate Hydride Compounds of Tantalum(V)
and Their Involvement in the Catalytic Hydrogenation of Arene
Rings.” J. Am. Chem. Soc. 1991, 113, 4710–4712. (b) Rothwell, I. P. A
New Generation of Homogeneous Arene Hydrogenationcatalysts.
Chem. Commun. 1997, 0, 1331–1338.
10 (a) Chesnut, R. W.; Jacob, G. G.; Yu, J. S.; Fanwick, P. E.; Rothwell, I.
P. “Mechanistic Study of the Cyclometalation of O-Arylphenoxide
Ligands at Group 5 Metal Centers.” Organometallics 1991, 10, 321–
328. (b) Visciglio, V. M.; Clark, J. R.; Nguyen, M. T.; Mulford, D. R.;
Fanwick, P. E.; Rothwell, I. P. “Coordination and Hydrogenation of
1,3-Cyclohexadiene by Niobium and Tantalum Aryl Oxide Com-
pounds: Relevance to Catalytic Arene Hydrogenation.” J. Am. Chem.
Soc. 1997, 119, 3490–3499. (c) Yu, J. S.; Ankianiec, B. C.; Rothwell, I.
P.; Nguyen, M. T. “All-Cis Catalytic Hydrogenation of Polynuclear
Aromatic Hydrocarbons by Group 5 Metal Aryl Oxide Compounds.” J.
Am. Chem. Soc. 1992, 114, 1927–1929.
22
Attempts to synthesize and isolate (MesPDI)Mo(η6-benzene) and
(
tBuPDI)Mo(η6-benzene) were unsuccessful.
23 Isolated with 17% 2,3-dimethylcyclohex-1-ene
24
Molybdenum and Tungsten Catalysts for Hydrogenation, Hydrosi-
lylation, and Hydrolysis. Bullock, R. M. 2010. Wiley-VCH Verlag
GmbH & Co. KGaA, Weinheim, Germany.
25
(a) Nakamaura, A.; Otsuka, S. Reaction of Transition Metal Dihy-
drides. I. Insertion and Substitution at the Metal-Hydride Bonds in
Dihydridobis(.Pi.-Cyclopentadienyl)Molybdenum. J. Am. Chem. Soc.
1972, 94, 1886–1894. (b) Nakamura, A.; Otsuka, S. Reaction of Tran-
sition Metal Dihydrides. III. Stereochemistry and Mechanism of
11 (a) Wiesenfeldt, M. P.; Nairoukh, Z.; Li, W.; Glorius, F. “Hydrogena-
tion of Fluoroarenes: Direct Access to All-Cis-(Multi)Fluorinated Cy-
9
ACS Paragon Plus Environment

ACS Catalysis
Page 10 of 10
1
2
3
4
5
6
7
8
9
35
Stoichiometric Hydrogenation of Olefins by Dihydrobis (.Pi.-
García-Ventura, I.; Flores-Alamo, M.; J. García, J. “Carbon–carbon
Cyclopentadienyl) Molybdenum. J. Am. Chem. Soc. 1973, 95, 7262–
7272. (c) Bullock, R. M.; Rappoli, B. J. Ionic Hydrogenations Using
Transition Metal Hydrides. Rapid Hydrogenation of Hindered Alkenes
at Low Temperature. J. Chem. Soc., Chem. Commun. 1989, 0, 1447–
1448. (d) Bullock, R. M.; Song, J.-S. Ionic Hydrogenations of Hindered
Olefins at Low Temperature. Hydride Transfer Reactions of Transi-
tion Metal Hydrides. J. Am. Chem. Soc. 1994, 116, 8602–8612.
vs. carbon–oxygen bond activation in 2- and 3-furonitriles with nick-
el” RSC Adv. 2016, 6, 101259–101266.
TOC Graphic
26
Tatsumi, T.; Shibagaki, M.; Tominaga, H. Hydrogen Transfer from
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Alcohols to Ketones and Olefins Catalyzed by Molybdenum Com-
plexes. J. Mol. Catal. 1981, 13, 331–338.
27
(a) Chakraborty, S.; Blacque, O.; Fox, T.; Berke, H. Trisphosphine-
Chelate-Substituted Molybdenum and Tungsten Nitrosyl Hydrides as
Highly Active Catalysts for Olefin Hydrogenations. Chem. Eur. J. 2014,
20 (39), 12641–12654. (b) Fuchikami, T.; Ubukata, Y.; Tanaka, Y.
Group 6 Anionic μ-Hydride Complexes [HM2(CO)10]− (M = Cr, Mo,
W): New Catalysts for Hydrogenation and Hydrosilylation. Tetrahe-
dron Lett. 1991, 32, 1199–1202.
(c) Baricelli, P. J.; Melean, L. G.; Ricardes, S.; Guanipa, V.; Rodriguez,
M.; Romero, C.; Pardey, A. J.; Moya, S.; Rosales, M.
Mo(CO)3(NCMe)(PPh3)2: Synthesis, X-Ray Structure and Evaluation
of Its Catalytic Activity for the Homogeneous Hydrogenation of Ole-
fins and Their Mixtures. J. Organomet. Chem. 2009, 694, 3381–3385.
28
Jeske, G.; Lauke, H.; Mauermann, H.; Schumann, H.; Marks, T. J.
“Highly reactive organolanthanides. A mechanistic study of catalytic
olefin hydrogenation by bis(pentamethylcyclopentadienyl) and relat-
ed 4f complexes” J. Am. Chem. Soc. 1985, 107, 8111–8118.
29 Zhang, Y.; Hanna, B. S.; Dineen, A.; Williard, P. G.; Bernskoetter, W.
H. “Functionalization of Carbon Dioxide with Ethylene at Molyb-
denum Hydride Complexes” Organometallics 2013, 32, 3969–3979.
30
(a) Zhu, G.; Tanski, J. M.; Churchill, D. G.; Janak, K. E.; Parkin, G.
“The Reactivity of Mo(PMe3)6 towards Heterocyclic Nitrogen Com-
pounds:ꢀ Transformations Relevant to Hydrodenitrogenation” J. Am.
Chem. Soc. 2002, 124, 13658–13659. (b) Zhu, G.; Pang, K.; Parkin, G.
“Coordination chemistry of molybdenum relevant to hydrodenitro-
genation: Reactivity of Mo(PMe3)6 towards 6-membered heterocy-
clic aromatic nitrogen compounds involving C–H bond cleavage and
η6-coordination” Inorg. Chim. Acta 2008, 361, 3221–3229.
31
The metallapyran is resistant to hydrogenation; after heating a
benzene-d6 solution of (iPrPDI)Mo[O(CH)4] to 80 °C under 4 atm of H2
for 48 hours, only 30% conversion to a diamagnetic hydride-
containing species was observed.
32
Crimmin, M. R.; Butler, M. J.; White, A. J. P. “Oxidative addition of
carbon–fluorine and carbon–oxygen bonds to Al(I)” Chem. Commun.
2015, 51, 15994–15996.
33
(a) Bleeke, J. R.; Haile, T.; Chiang, M. Y. “Pentadienyl-metal-
phosphine
chemistry.
22.
Metallacyclohexadiene
and
metallabenzene chemistry. 4. Synthesis of iridaoxacyclohexadiene
and iridacyclopentenone complexes via C-H bond activation” Organ-
ometallics 1991, 10, 19–21. (b) Bleeke, J. R.; Blanchard, J. M. B.; Don-
nay, E. “Synthesis, Spectroscopy, and Reactivity of a Metallapy-
rylium“ Organometallics 2001, 20, 324–336. (c) Frogley, B. J.; Wright,
L. J. “Recent Advances in Metallaaromatic Chemistry” Chem. Eur. J.
2018, 24, 2025-2038.
34 (a) Erker, G.; Petrenz, R. “Formation of a conjugated oxametallacy-
clohexadiene by dyotropic rearrangement of bis(2-furyl)zirconocene”
Journal of the Chemical Society, Chem. Commun. 1989, 6, 345–346.
(b) Erker, G.; Petrenz, R.; Krueger, C.; Lutz, F.; Weiss, A.; Werner, S.
“Chalcogenametallacyclohexadienes by thermally induced migratory
ring enlargement of furyl-and thienylzirconocene complexes” Or-
ganometallics 1992, 11, 1646–1655. (c) Yow, S.; Nako, A. E.; Neveu,
L.; White, A. J. P.; Crimmin, M. R. “A Highly Chemoselective, Zr-
Catalyzed C–O Bond Functionalization of Benzofuran” Organometal-
lics 2013, 32, 5260–5262.
10
ACS Paragon Plus Environment