Reactions of phenylacetylene with nickel POCOP-pincer hydride complexes resulting in different outcomes from their palladium analogues

Article abstract of DOI:10.1039/c5dt00161g

Nickel POCOP-pincer hydride complexes [2,6-(R₂PO)₂C₆H₃]NiH (R = ⁱPr, 4a; R = ^cPe = cyclopentyl, 4b) react with phenylacetylene to generate [2,6-(R₂PO)₂C₆H₃]NiC(Ph)=CH₂ (5a-b) as the major product and (E)-[2,6-(R₂PO)₂C₆H₃]NiCH=CHPh (6a-b) as the minor product. The 2,1-insertion is more favorable than the 1,2-insertion and both pathways involve cis addition of Ni-H across the C≡C bond. Unlike the palladium case, alkynyl complexes [2,6-(R₂PO)₂C₆H₃]NiC≡CPh (7a-b) and H₂ are not produced in the nickel system. The more bulky hydride complex [2,6-(^tBu₂PO)₂C₆H₃]NiH (4c) shows no reactivity towards phenylacetylene. Catalytic hydrogenation of phenylacetylene with 4a-b takes place at an elevated temperature (70-100 °C) and proves to be heterogeneous. The structures of 5b, 6a, 7a and 7b have been studied by X-ray crystallography.

Full text of DOI:10.1039/c5dt00161g

View Article Online
View Journal
Dalton
Transactions
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: G. L. O. Wilson,
M. Abraha, J. A. Krause and H. Guan, Dalton Trans., 2015, DOI: 10.1039/C5DT00161G.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/dalton

Page 1 of 9
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00161G
Dalton Transactions
RSCPublishing
ARTICLE
Reactions of phenylacetylene with nickel POCOP-
pincer hydride complexes resulting in different
outcomes from their palladium analogues
Cite this: DOI: 10.1039/x0xx00000x
Gleason L. O. Wilson, Medhanei Abraha, Jeanette A. Krause and Hairong Guan∗
Received 00th January 2015,
Accepted 00th January 2015
i
Nickel POCOPꢀpincer hydride complexes [2,6ꢀ(R2PO)2C6H3]NiH (R = Pr, 4a; R = cPe =
DOI: 10.1039/x0xx00000x
cyclopentyl, 4b) react with phenylacetylene to generate [2,6ꢀ(R2PO)2C6H3]NiC(Ph)=CH2 (5a
) as the major product and ( )ꢀ[2,6ꢀ(R2PO)2C6H3]NiCH=CHPh (6a ) as the minor product.
The 2,1ꢀinsertion is more favorable than the 1,2ꢀinsertion and both pathways involve cis
addition of Ni–H across the C C bond. Unlike the palladium case, alkynyl complexes [2,6ꢀ
(R2PO)2C6H3]NiC CPh (7a ) and H2 are not produced in the nickel system. The more bulky
hydride complex [2,6ꢀ(tBu2PO)2C6H3]NiH (4c) shows no reactivity towards phenylacetylene.
Catalytic hydrogenation of phenylacetylene with 4a takes place at an elevated temperature
ꢀ
b
E
ꢀb
www.rsc.org/
≡
≡
ꢀb
ꢀ
b
o
(70ꢀ100 C) and proves to be heterogeneous. The structures of 5b, 6a, 7a and 7b have been
studied by Xꢀray crystallography.
While the importance of utilizing earth abundant metals for
homogeneous catalysis is emphasized in this themed issue, it
would be particularly useful if the reactivity differences
between precious metals and the more abundant firstꢀrow
metals were well understood. As far as the reactions of metal
hydrides with alkynes are concerned, very few reports have
specifically examined how firstꢀrow metals behave differently
from (or similar to) their heavy congeners. Bianchini and coꢀ
Introduction
The reaction between an alkyne and a transition metal hydride
is fundamentally important, and, in many catalytic processes
(e.g., hydrogenation, hydrosilylation, hydroboration and
oligomerization of alkynes), is the key step that determines the
efficiency, regioselectivity and stereoselectivity of the overall
catalytic transformation.1 Understanding the factors governing
the rate and reactivity pattern of metal hydrides towards
alkynes is paramount to the rational design of more efficient
and selective catalysts. The prototypical outcome of the
reaction of a metal hydride with an alkyne involves cis addition
workers have shown that the reaction of (PP3)RhH (PP3
=
P(CH2CH2PPh2)3) with 10 equiv of phenylacetylene at room
temperature generates (PP3)RhC≡CPh and styrene in ~40%
yield after 24 h.5 In contrast, (PP3)CoH does not show any
reactivity under the same reaction conditions.6 The 1 : 1
reaction between (PP3)RhH and ethyl propiolate affords the
2,1ꢀinsertion product (PP3)RhC(CO2Et)=CH2 exclusively,5
whereas a similar reaction with (PP3)CoH gives a mixture of
the unreacted (PP3)CoH, (PP3)CoC(CO2Et)=CH2 and
of M–H across the C≡
C bond.2 Trans addition is also possible,
though far less common than the cis addition, and typically
requires at least one electronꢀwithdrawing substituent such as
CF3 and CO2Me.2c,3 In some cases, the cisꢀ and transꢀaddition
products can interconvert depending on the reaction
conditions.4 When a terminal alkyne is employed (Scheme 1),
three different types of insertion products can be expected.
(PP3)CoC≡
CCO2Et in a 2 : 1 : 1 ratio.6
We have recently reported the reactions of phenylacetylene
with palladium hydride complexes bearing a bis(phosphinite)ꢀ
based pincer ligand, which is better known as a POCOPꢀpincer
ligand.7 When the phosphorus substituents are isopropyl
H
groups, palladium alkynyl complex 2a and (E)ꢀalkenyl complex
M
R
3a are formed in a 13 : 1 ratio (Scheme 2). Replacing the
isopropyl groups with cyclopentyl or tertꢀbutyl groups results in
the alkynyl complex 2b or 2c as the only new palladium
species. In any case, both H2 and styrene can be detected. A
palladium hydride containing a bis(phosphine)ꢀbased pincer (or
PCPꢀpincer) ligand also reacts with phenylacetylene to give an
alkynyl complex and styrene.8
(Z)-alkenyl
trans
1,2-insertion
R
H
M
α
R
R
-substituted
alkenyl
+
cis
M
H
M
cis or trans
2,1-insertion
1,2-insertion
(E)-alkenyl
Scheme 1
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 1-8 | 1

Dalton Transactions
Page 2 of 9
DaltoVnieTwrAartnicsleaOcntliinoens
ARTICLE
DOI: 10.1039/C5DT00161G
O
PR2
Ni
O
O
PR2
Pd
PR2
2,1-insertion
5a (R = iPr)
5b (R = cPe)
+ H2
Ph
O
O
PR2
Ni
2a (R = iPr)
2b (R = cPe)
2c (R = tBu)
Ph
O
O
PR2
Pd
PR2
O
O
PR2
PR2
Ph
H
Ph
+
C6D6
rt, 30 min
H
C6D6, rt
O
PR2
Pd
PR2
Ni
+
4a (R = iPr)
4b (R = cPe)
Ph
cis 1,2-insertion
1a (R = iPr)
1b (R = cPe)
1c (R = tBu)
Ph
(~ 2%)
6a (R = iPr)
6b (R = cPe)
Ph
O
PR2
5a : 6a = 3 : 1
5b : 6b = 5 : 3
O
PR2
3a (R = iPr)
2a : 3a = 13 : 1
Scheme 3
Scheme 2
To confirm the proposed structures, independent syntheses
of the alkenyl and alkynyl complexes were pursued (Scheme 4).
In this paper, we will describe the reactions of
phenylacetylene with the analogous nickel hydride complexes, The
which lead to insertion products rather than the alkynyl prepared from the reactions of
complexes and the elimination of H2. We will also compare the from
ꢀbromostyrene and nBuLi) with nickel POCOPꢀpincer
catalytic performance of the nickel complexes with the chloride complexes 8a and 8b, respectively. The 31P{1H}
α
ꢀsubstituted alkenyl complexes 5a and 5b were readily
α
ꢀlithiostyrene (generated in situ
α
palladium analogues in the hydrogenation of phenylacetylene.
NMR spectrum of 5a in C6D6 matches the resonance at 185.6
ppm described above. The vinylic region of the 1H NMR
spectrum shows the resonances with the anticipated chemical
shifts of 5.35 and 6.33 ppm; however, for the purified product,
these resonances are much better resolved as two doublet of
Results and discussion
Reactions of nickel hydrides with phenylacetylene
4
triplets. The small coupling constants (2JHꢀH = 3.2 Hz and JPꢀH
= 2.8 Hz) are consistent with each vinylic resonance being
coupled by its geminal hydrogen and the pincer phosphorus
atoms via a longꢀrange coupling. The NMR data of 5b also
The 1 : 1 reaction of nickel hydride 4a with phenylacetylene in
C6D6 was studied by 1H and 31P{1H} NMR spectroscopy
(Scheme 3). At room temperature, 4a
consumed within 30 min and replaced by two new nickel
species 5a and 6a
(δP = 206.6 ppm) was
support that the
αꢀsubstituted alkenyl complex is the major
product for the reaction between 4b and PhC≡CH.
(
δP = 185.6 and 189.4 ppm) in a 3 : 1 ratio.
Unlike the reaction of phenylacetylene with the palladium
1
hydride 1a, there was neither H2 nor styrene detected by H
NMR. Instead, two broad resonances (5.35 and 6.32 ppm, ꢀν1/2
= 23.7 Hz) with equal intensities emerged from the vinylic
region, suggesting that the PhC
reduced. The reaction of 4b
phenylacetylene was similar to 4a; it went to completion within
≡
CH triple bond had been
(
δP = 199.7 ppm) with
30 min and generated two new pincer complexes 5b and 6b (δP
= 179.5 and 180.5 ppm) in a 5 : 3 ratio. The 1H NMR spectrum
of the reaction was more informative due to somewhat sharper
peaks. In addition to the vinylic resonances found at 5.40 and
6.39 ppm, a doublet was observed at 7.82 ppm with a relatively
large coupling constant of 18.4 Hz. Based on the chemical
shifts and coupling constant, it was hypothesized that the major
species for the NiH/PhC
product and the minor one was an (
≡
CH reaction was a 2,1ꢀinsertion
)ꢀalkenyl complex as a
E
Scheme 4
result of cis 1,2ꢀaddition. The lack of H2 evolution implied that
for the nickel system, the alkynyl complex was probably not
formed. Monitoring the reaction of phenylacetylene with 4c by
1H and 31P{1H} NMR spectroscopy, however, did not show any
new species even when the reaction was carried out for 24 h.
The (
similar fashion from the corresponding nickel chloride complex
and ( )ꢀ ꢀlithiostyrene, which is available from regiospecific
lithiation of ( )ꢀ
ꢀiodostyrene.9 The 31P{1H} NMR spectrum
E)ꢀalkenyl complexes 6a and 6b were prepared in a
E
β
t
E
β
The increased steric crowding caused by the bulky Bu groups
of the pure product in C6D6 has one resonance (189.4 ppm for
6a and 180.5 ppm for 6b), and the chemical shift value
confirms that cisꢀ1,2ꢀinsertion is the pathway leading to the
explains the inactivity of 4c because phenylacetylene is not able
to approach close enough to the Ni–H bond for the reaction to
occur.
minor species (Scheme 3).
In agreement with the E
1
configuration, the H NMR spectrum displays a large coupling
constant (18.8 Hz for 6a, 18.4 Hz for 6b) that is characteristic
of the trans vinylic hydrogens.
To rule out the possibility that an alkynyl complex formed
but coincided with one of the 31P resonances, 7a and 7b were
independently synthesized from the nickel pincer chloride
complexes and PhC≡CLi (generated from the lithiation of
2 | Dalton Trans., 2015, 44, 1-8
This journal is © The Royal Society of Chemistry 2015

Page 3 of 9
Dalton Transactions
Dalton Transactions
View Article Online
ARTICLE
DOI: 10.1039/C5DT00161G
n
1
PhC≡
CH with BuLi). The 31P{1H} and H NMR show peaks
2.1393(11), Ni–P(2) 2.1446(11), C(27)–C(28) 1.267(6), C(27)–
C(29) 1.453(6), P(1)–Ni–P(2) 163.80(5), C(1)–Ni–C(27)
175.77(16).
that are absent from the reactions of nickel hydrides with
phenylacetylene, thus confirming that the alkynyl complexes
are not involved.
The Xꢀray structure of 6a (Fig. 2) confirms the geometry of
the C=C bond for the minor product. As in the case of the
analogous palladium complex 3a,7 the phenyl group in 6a is
coplanar with the CH=CH plane and perpendicular to the pincer
aromatic ring. Interestingly, the C(27)–C(28) bond is shorter
for 6a [1.276(6) Å] than 3a [1.329(5) Å], perhaps due to more
Structures of the alkenyl and alkynyl complexes
The structure of 5b was more unambiguously established by Xꢀ
ray crystallography. As expected, nickel is added to the more
substituted end of the C=C bond (Fig. 1). While the Ni–Cipso
and Ni–P bond lengths of 5b are comparable to those reported
in the literature for nickel POCOPꢀpincer complexes,10ꢀ12 the
Ni–C(27) bond of 2.023(4) Å is noticeably longer. Zargarian
and coꢀworkers have shown that for PCPꢀpincer complexes of
π
ꢀback donation from palladium. This bond length is, however,
almost identical to that of 5b [1.267(6) Å] even though the Ni–
C(27) bond in the latter is longer by 0.10 Å. The elongation of
the Ni–C bond is primarily offset by the shortening of the C–Ph
bond [1.453(6) Å vs. 1.494(5) Å in 6a], which in turn explains
why the C=CH2 plane is not coplanar with the phenyl ring.
the type [(iPr2PCH2CH2)2CH]NiR (R = Me, Ph and C
the Ni–R bond length follows the order of Ni–Csp3 > Ni–Csp2
≡CMe),
>
Ni–Csp.13 Consistent with this trend, the Ni–C(Ph)=CH2 bond
of 5b is significantly longer than the Ni–Csp bond of the alkynyl
complex 7b [1.874(3) Å] (vide infra) and nickel alkynyl and
cyano complexes [1.87ꢀ1.94 Å] bearing a different POCOPꢀ
pincer ligand.11e,g,j It is, however, still longer than the Ni–Csp2
bond of the alkenyl complex 6a [1.924(4) Å] (vide infra) and
[(iPr2PCH2CH2)2CH]Ni–Ph [1.9440(20) Å],13 as well as the Ni–
Csp3 bond of nickel trifluoromethyl complexes [1.93ꢀ1.94 Å]
supported by a POCOPꢀ or PCPꢀpincer ligand.11k,l Only
Zargarian’s [(iPr2PCH2CH2)2CH]Ni–Me [2.0160(20) Å]13 and
our [2,6ꢀ(iPr2PO)2C6H3]Ni–CH2CN [2.0123(19) Å]12g have a
similarly long Ni–C bond distance. This suggests that the
metalꢀcarbon bond length is not solely decided by the
hybridization of the carbon. The elongation of the Ni–C bond
in 5b likely stems from the steric clash between the pincer
periphery and the phenyl ring. To further minimize the
unfavorable steric interactions, the phenyl group adopts a
conformation that is almost perpendicular to the pincer
backbone; the dihedral angle between the two aromatic rings is
measured to be 89.2(1)˚. The phenyl group also orientates itself
towards one side of the pincer arms and the C=CH2 plane is
rotated out of the phenyl plane by 33.1(2)˚ to avoid the steric
repulsion from the ortho hydrogens. Even though the phenyl
group is situated in close proximity to the nickel center, the
closest H…Ni distances [H30…Ni = 3.00 Å; H28B…Ni = 2.87
Å] and the corresponding C–H…Ni angles [C30–H30…Ni =
105˚; C28–H28B…Ni = 80˚] fall outside of the ranges for
agostic and anagostic interactions.14 The chemical shifts of the
phenyl and vinyl groups appear in the normal region for
aromatic and vinylic hydrogens, further arguing against the
possibility of having any Ni–H–C interaction.
Fig. 2 ORTEP drawing of (
6a) at the 50 % probability level. Selected bond lengths (Å)
and angles (˚): Ni–C(1) 1.903(4), Ni–C(27) 1.924(4), Ni–P(1)
and Ni–P(1A) 2.1270(8), C(27)–C(28) 1.276(6), C(28)–C(29)
E
)ꢀ[2,6ꢀ(iPr2PO)2C6H3]NiCH=CHPh
(
1.494(5),
P(1)–Ni–P(1A)
164.40(5),
C(1)–Ni–C(27)
179.55(18).
Complexes 7a and 7b crystallize readily from pentane or
methanol, providing a good opportunity for crystallography
study.
Unlike the solidꢀstate structures of the alkenyl
complexes, the phenyl ring in the alkynyl complexes is not
perpendicular to the pincer aromatic backbone (Figs 3 and 4),
presumably because the phenyl ring is further extended out
from the pincer core so that its rotation is not restricted. In fact,
the dihedral angle between the two aromatic rings is scattered
between 0˚ and 90˚ for nickel and palladium POCOPꢀpincer
phenylacetylide complexes (Table 1). On the other hand, the
C≡
C bond length is consistently measured within the narrow
range of 1.198ꢀ1.214 Å regardless of the metal and pincer
ligand used. The C
C stretching frequency of 7a (2089 cmꢀ1)
or 7b (2082 cmꢀ1) is substantially lower than that of [2,6ꢀ
(Ph2PO)2C6H3]NiC CPh
(2105 cmꢀ1),11g which can be
explained by less ꢀback donation from nickel when supported
≡
≡
π
by the lessꢀdonating phenylꢀsubstituted POCOPꢀpincer ligand.
Using this electronic argument to rationalize the difference
between 7a and 7b is however challenging, as the opposite
trend of ν(C≡C) was observed in the palladium case (Table 1).
Fig. 1 ORTEP drawing of [2,6ꢀ(cPe2PO)2C6H3]NiC(Ph)=CH2
Given the fact that tertꢀbutylꢀsubstituted phosphines are more
basic than other alkylꢀsubstituted phosphines,15 one might have
anticipated that among the palladium series, 2c should have the
(
5b) at the 50 % probability level. Selected bond lengths (Å)
and angles (˚): Ni–C(1) 1.909(4), Ni–C(27) 2.023(4), Ni–P(1)
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 1-8 | 3

Dalton Transactions
Page 4 of 9
DaltoVnieTwrAartnicsleaOcntliinoens
ARTICLE
DOI: 10.1039/C5DT00161G
lowest wavenumber for the C≡ ≡CPh (7a)
C stretch. On the contrary, the Fig. 3 ORTEP drawing of [2,6ꢀ(iPr2PO)2C6H3]NiC
at the 50 % probability level. Selected bond lengths (Å) and
angles (˚): Ni–C(1) 1.895(4), Ni–C(27) 1.871(5), Ni–P(1)
2.1226(14), Ni–P(2) 2.1309(14), C(27)–C(28) 1.198(6), P(1)–
Ni–P(2) 164.85(6), C(1)–Ni–C(27) 176.2(2).
C≡C stretching frequency of 2c is higher than that of 2b and 2a
by 5 cmꢀ1 and 15 cmꢀ1, respectively. It is possible that the
phosphorus donor ability in 2c is compromised by slightly
longer Pd–P bonds. In other words, steric effects may also play
an important role in determining the strength of the C
The electrochemistry study of nickel PCPꢀpincer complexes
also shows that [(iPr2PCH2CH2)2CH]NiBr bears
more
electronꢀrich metal center than [(tBu2PCH2CH2)2CH]NiBr.13
≡C bond.
a
Fig. 4 ORTEP drawing of [2,6ꢀ(cPe2PO)2C6H3]NiC
≡CPh (7b)
at the 50 % probability level. Selected bond lengths (Å) and
angles (˚): Ni–C(1) 1.889(3), Ni–C(27) 1.874(3), Ni–P(1) and
Ni–P(1A) 2.1374(6), C(27)–C(28) 1.213(5), P(1)–Ni–P(1A)
164.42(4), C(1)–Ni–C(27) 180.0.
Table 1 IR and Xꢀray data for nickel and palladium POCOPꢀpincer phenylacetylide complexes
complex
dihedral angle (˚)d
42.3(2)
M–P (Å)
2.1226(14), 2.1309(14)
2.1374(6)
C≡C (Å)
1.198(6)
1.213(5)
1.204(2)
ν(C≡C) (cmꢀ1)
2089
[2,6ꢀ(iPr2PO)2C6H3]NiC≡CPh (7a)
[2,6ꢀ(cPe2PO)2C6H3]NiC≡CPh (7b)
[2,6ꢀ(Ph2PO)2C6H3]NiC≡CPha
[2,6ꢀ(iPr2PO)2C6H3]PdC≡CPh (2a)
[2,6ꢀ(cPe2PO)2C6H3]PdC≡CPh (2b)b
[2,6ꢀ(tBu2PO)2C6H3]PdC≡CPh (2c)b,c
63.6(1)
2082
16.39, 29.02
85.66
2.1343(4), 2.1283(4)
2.2597(7), 2.2614(7)
N/A
2105
1.214(3)
N/A
2085
2095
2100
N/A
18.66
21.40
8.81
1.213(6)
1.211(5)
1.210(6)
2.2720(10), 2.2745(11)
2.2753(10), 2.2802(10)
2.2664(10), 2.2750(10)
aReported in ref. 11g. bReported in ref. 7. cThree sets of data are listed because three independent molecules of 2c crystallize in
the lattice. dDihedral angle between the phenyl ring and the pincer aromatic backbone.
hexyne, the major product remains to be the
alkenyl complex.
αꢀsubstituted
The mechanism for the insertion reactions
Another possible explanation involves hydrogen atom (H•)
transfer from metal to phenylacetylene,18 resulting in selective
formation of a radical on the more substituted carbon
(H2C=CPh•). Combining this radical with the metalloradical
The preference of 2,1ꢀ over 1,2ꢀinsertion of phenylacetylene
was unexpected. From the steric point of view, the
substituted alkenyl complexes 5a should be less favored than
the ( )ꢀalkenyl complexes 6a , as inferred by the crystal
αꢀ
ꢀ
b
E
ꢀb
would yield an
mechanism is operating, the reaction of a metal hydride with
PhC CD should lead to 50% of D for the vinylic hydrogens
because the vinyl radical H(D)C=CPh• is linear.19 The reaction
of 4a and PhC CD, however, showed that for the resulting 5a
the hydrogen trans to the nickel was all D (eq 1). The product
ratio for the 4a/PhC CH reaction was also unaffected by the
αꢀsubstituted alkenyl complex.
If this
structures. Regioselective 2,1ꢀinsertion of phenylacetylene has
been reported for other metal hydrides,2i,16 although the origin
for the regioselectivity is not fully understood. Huggins and
Bergman have proposed that sterics control the regioselectivity
for the insertion of unsymmetrical alkynes into (acac)(PPh3)Ni–
CH3, in which case nickel is added to the sterically more
demanding side of the triple bond.17 One could argue that for
the current system, the transition state for 2,1ꢀinsertion could be
≡
≡
,
≡
radical inhibitor TEMPO. The insertion of phenylacetylene
into 4a or 4b most likely proceeds via a concerted addition of
Ni–H across the triple bond, which is primarily controlled by
electronic effects.
stabilized by
π,πꢀstacking between the aromatic rings of
phenylacetylene and the pincer backbone. However, for the
reaction between 4a (or 4b) and an aliphatic alkyne such as 1ꢀ
4 | Dalton Trans., 2015, 44, 1-8
This journal is © The Royal Society of Chemistry 2015

Page 5 of 9
Dalton Transactions
Dalton Transactions
View Article Online
ARTICLE
DOI: 10.1039/C5DT00161G
phenylacetylene to styrene under 1 atm of H2 pressure. In
contrast, nickel complexes 4a and 4b showed practically no
catalytic activity at room temperature even under a much higher
H2 pressure (entries 1 and 2, Table 2). Raising the temperature
to 70 oC resulted in up to 3 catalytic turnovers, and 4a exhibited
better activity than 4b (entries 3 and 4). Using the highꢀboiling
toluene as the solvent allowed the temperature to be raised
o
further to 100 C without significant pressure build up. Under
The reason why phenylacetylene does not prefer the
insertion into the palladiumꢀhydrogen bond remains unclear.
Perhaps with a more electron rich metal, the oxidative addition
of Csp–H bond of phenylacetylene becomes more favorable, and
the subsequent reductive elimination of H2 generates the
observed palladium alkynyl complexes.
this condition (pH2 = 5 atm) for 24 h, 67% of phenylacetylene
was converted to styrene and 31% was reduced fully to
ethylbenzene (entry 5). Apparently, the hydrogenation process
is pressure dependent; under 2 atm of H2 pressure with 10
mol% catalyst, only 10% of phenylacetylene was hydrogenated
to styrene after 24 h (entry 6). The catalytic reaction with 4b
was less effective than that with 4a, and produced a lesser
amount of styrene when lowering the H2 pressure (entry 8) or
the temperature (entry 9).
Catalytic hydrogenation of phenylacetylene
In our previous study,7 palladium complexes 2a
were shown to catalyze room temperature hydrogenation of
ꢀc (or 1aꢀc)
Table 2 Nickelꢀcatalyzed hydrogenation of phenylacetylenea
entry
catalyst catalyst loading solvent temperature
H2 pressure
conversionb
1
2
3
4
5
6
7
8
9
5 mol%
5 mol%
5 mol%
5 mol%
5 mol%
10 mol%
5 mol%
5 mol%
5 mol%
THF
THF
22 oC
22 oC
70 oC
5 atm
5 atm
5 atm
5 atm
5 atm
2 atm
5 atm
4 atm
5 atm
< 1%
< 1%
4a
4b
4a
4b
4a
4a
4b
4b
4b
THF
15%
THF
70 oC
1%
toluene
toluene
toluene
toluene
toluene
100 oC
100 oC
100 oC
100 oC
80 oC
67% (31%)
10% (1%)
9%
4%
3%
aReaction conditions: phenylacetylene (0.5 or 1.0 mmol) and nickel catalyst (50 ꢁmol) in 0.60 mL of solvent for 24 h. bThe conversion of
phenylacetylene to styrene was determined by NMR; the conversion to ethylbenzene is listed in parenthesis.
Our previous mechanistic investigation on the palladium
system confirms that the hydrogenation of alkynes is
catalyzed by palladium particles rather than a molecular
catalyst.7 The release of particles from the palladium pincer
complexes is made possible by oxidative addition of H2 to
the Pd(II) species followed by reductive elimination of the
pincer ligand. Such a process is expected to be more
difficult for Ni(II), which is likely the reason why 4a and 4b
Conclusions
are inactive at room temperature. Nevertheless, both
compounds catalyze the hydrogenation of phenylacetylene
at elevated temperatures, probably via a completely different
decomposition pathway from metal complexes to particles.
An attempt to hydrogenate 5a did not yield 4a and styrene
(eq 2), suggesting that oxidative addition of H2 followed by
reductive elimination of styrene is not a viable pathway.
During the catalytic hydrogenation reaction, darkening of
the solution was noted. Consistent with a heterogeneous
mechanism, adding elemental mercury (200 equiv with
Through this study, we have shown distinctively different
reactivity of nickel from palladium for the reaction between
a POCOPꢀpincer hydride complex and phenylacetylene.
The nickel system generates (E)ꢀalkenyl and αꢀsubstituted
complexes through cis 1,2ꢀ and 2,1ꢀinsertion, with the latter
being the major pathway. In contrast, the palladium system
yields an alkynyl complex and H2 with little or no insertion
products. We have attributed these differences to the
tendency of palladium to undergo oxidative addition of the
Csp–H bond of phenylacetylene to a M(II) center, which,
following reductive elimination of H2, gives the alkynyl
complex. Similarly, oxidative addition of H2 to a Pd(II)
pincer complex is more facile, creating a unique pathway for
the formation of palladium particles that can catalyze
respect to PhC≡CH) to the reaction in entry 5 poisoned the
catalyst, resulting in <5% of phenylacetylene converted to
styrene.
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 1-8 | 5

Dalton Transactions
Page 6 of 9
ARTICLE
DaltoVnieTwrAartnicsleaOcntliinoens
DOI: 10.1039/C5DT00161G
heterogeneous hydrogenation of phenylacetylene. Nickelꢀ
catalyzed hydrogenation is possible and also heterogeneous,
but the reaction conditions are harsher, requiring higher
temperature to decompose the metal complexes to particles.
Our future direction will be focused on the assessment of
M–H and M–C bond strengths for a better understanding of
nickel vs. palladium in reduction reactions.
were obtained from an acetonitrile solution that was kept at
o
–5 C. 1H NMR (400 MHz, C6D6,
δ): 1.27ꢀ1.37 (m, CH2
,
8H), 1.47ꢀ1.51 (m, CH2, 4H), 1.60ꢀ1.65 (m, CH2, 4H), 1.75ꢀ
1.88 (m, CH2, 12H), 2.01ꢀ2.07 (m, CH2, 4H), 2.22ꢀ2.29 (m,
PC
JHꢀH = 3.6 Hz, CPh=CH2, 1H), 6.80 (d, JHꢀH = 8.0 Hz, Ar
2H), 7.02ꢀ7.08 (m, Ar , 2H), 7.15ꢀ7.20 (m, Ar , 2H), 7.77
(d, JHꢀH = 7.6 Hz, Ar
, 2H). 13C{1H} NMR (101 MHz,
C6D6, ): 26.3 (t, JPꢀC = 4.0 Hz, H2), 26.7 (t, JPꢀC = 4.0 Hz,
H2), 28.2 (t, JPꢀC = 3.0 Hz, H2), 28.5 (s, H2), 39.2 (t, JPꢀC
= 12.6 Hz, H), 104.7 (t, JPꢀC = 5.6 Hz, Ar ), 118.2 (t, JPꢀC
= 5.6 Hz, C= H2), 125.6 (s, Ar ), 128.4 (s, Ar ), 128.6 (s,
Ar ), 129.1 (s, Ar ), 151.7 (s, Ar ), 167.2 (t, JPꢀC = 22.2
Hz, =CH2), 168.0 (t, JPꢀC = 10.1 Hz, Ar ); one resonance
was obscured by the solvent resonances. 31P{1H} NMR
(162 MHz, C6D6, ): 179.5 (s). Anal. Calcd for
C34H46O2P2Ni: C, 67.23; H, 7.63. Found: C, 67.03; H, 7.44.
H, 4H), 5.40 (d, JHꢀH = 3.6 Hz, CPh=CH2, 1H), 6.39 (d,
H
,
H
H
H
δ
C
Experimental
C
C
C
C
C
Materials and methods
C
C
C
C
C
C
Unless otherwise mentioned, all the organometallic
compounds were prepared and handled under an argon
atmosphere using standard glovebox and Schlenk
techniques. Dry and oxygenꢀfree solvents for carrying out
syntheses (pentane, THF and toluene) were collected from
an Innovative Technology solvent purification system.
Acetonitrile, anhydrous methanol (packed in a Sure/SealTM
C
C
δ
Synthesis of
(
E
)-[2,6-(iPr2PO)2C6H3]NiCH=CHPh
(6a). At –78 oC under an argon atmosphere, a 2.5 M
solution of nBuLi in hexanes (184
L, 0.46 mmol) was
added slowly to a solution of ꢀiodostyrene (100 mg, 0.43
bottle), PhC≡CD and αꢀbromostyrene (95% purity) were
used as received without purification. Phenylacetylene was
freshly distilled prior to the stoichiometric reduction and
catalytic hydrogenation studies; however, for the synthesis
of alkynyl complexes, it was used as received without
ꢁ
E
mmol) in pentane (10 mL). The reaction mixture was
o
warmed to 22 C and stirred at this temperature for 15 min.
purification.
Benzeneꢀd6 was distilled from Na and
The resulting colorless suspension was transferred via
a
cannula to a cold (–78 ˚C) solution of 8a (100 mg, 0.23
benzophenone under an argon atmosphere.
(
E)ꢀβꢀ
iodostyrene,9 4a 12a 4b 12d [2,6ꢀ(tBu2PO)2C6H3]NiH (4c),12a
,
,
mmol) in THF (10 mL). The orange colored reaction
o
8a11b and 8b12d were prepared as described in the literature.
mixture was stirred at 22 C for 45 min, after which the
volatiles were removed under vacuum. Extraction of the
Synthesis of [2,6-(iPr2PO)2C6H3]NiCPh=CH2 (5a). At
yellow residue with toluene (10 mL
× 3) followed by
–78 oC under an argon atmosphere, a 2.5 M solution of
filtration through a short plug of Celite gave a yellow
solution. Removal of the solvent under vacuum yielded the
product as a yellow powder (46 mg, 40% yield). Xꢀray
nBuLi in hexanes (485
ꢁL, 1.21 mmol) was added slowly to
a solution of
αꢀbromostyrene (175 ꢁL, 1.35 mmol) in
quality crystals were obtained from a methanol solution that
pentane (10 mL). The reaction mixture was warmed to 22
oC and stirred at this temperature for 15 min. The resulting
colorless suspension was transferred via a cannula to a cold
(–78 ˚C) solution of 8a (295 mg, 0.68 mmol) in THF (10
mL). The orange colored reaction mixture was stirred at 22
oC for 3 h, after which the volatiles were removed under
vacuum. Extraction of the orange residue with toluene (10
o
was kept at –5 C. 1H NMR (400 MHz, C6D6,
δ
): 1.09ꢀ1.18
, 4H), 6.78 (d, JHꢀH = 8.0
=CHPh + Ar , 3H), 7.28
, 2H), 7.45 (d, JHꢀH = 7.6 Hz, Ar
2H), 7.75 (d, JHꢀH = 18.8 Hz, NiCH=C
Ph, 1H). 13C{1H}
NMR (101 MHz, C6D6, ): 17.0 (s, H3), 17.7 (s, H3), 27.8
(t, JPꢀC = 12.1 Hz, H), 105.0 (t, JPꢀC = 6.1 Hz, Ar ), 128.8
), 129.2 (s, Ar ), 138.1 (t, JPꢀC = 6.1 Hz, Ar ), 142.0
), 152.4 (t, JPꢀC = 24.8 Hz, H=CHPh), 168.4 (t, JPꢀC
); other resonances were obscured by the
solvent resonances. 31P{1H} NMR (162 MHz, C6D6,
):
(m, CH3, 24H), 2.07ꢀ2.14 (m, PC
Hz, Ar , 2H), 6.95ꢀ7.07 (m, NiC
(t, JHꢀH = 7.6 Hz, Ar
H
H
H
H
H
H,
H
δ
C
C
C
C
C
mL
× 3) followed by filtration through a short plug of Celite
(s, Ar
(s, Ar
C
C
C
gave a yellow solution. Removal of the solvent under
vacuum yielded a light orange oil. The pure product was
obtained as yellow crystals from a concentrated solution in
acetonitrile or methanol kept at –30 ˚C (55 mg, 16 % yield).
C
= 10.1 Hz, Ar
C
δ
1H NMR (400 MHz, C6D6
δ
): 1.07ꢀ1.15 (m, CH3, 24H),
, 4H), 5.35 (dt, JHꢀH = 3.2 Hz, JPꢀH = 2.8
Hz, CPh=CH2, 1H), 6.32 (dt, JHꢀH = 3.2 Hz, JPꢀH = 2.8 Hz,
CPh=CH2, 1H), 6.75 (d, JHꢀH = 8.0 Hz, Ar , 2H), 6.99 (t, JHꢀ
H = 8.0 Hz, Ar , 1H), 7.07 (t, JHꢀH = 7.6 Hz, Ar , 1H), 7.22
(t, JHꢀH = 7.6 Hz, Ar , 2H), 7.72 (d, JHꢀH = 7.6 Hz, Ar
2H). 13C{1H} NMR (101 MHz, C6D6,
): 16.5 (s, H3),
17.4 (t, JPꢀC = 3.0 Hz, H3), 27.6 (t, JPꢀC = 11.6 Hz, H),
104.6 (t, JPꢀC = 6.1 Hz, Ar ), 119.1 (t, JPꢀC = 5.1 Hz,
C= H2), 125.6 (s, Ar ), 129.2 (s, Ar ), 137.3 (t, JPꢀC = 9.1
Hz, Ar ), 152.3 (s, Ar ), 165.8 (t, JPꢀC = 22.2 Hz, =CH2),
168.1 (t, JPꢀC = 10.1 Hz, Ar ); other resonances were
obscured by the solvent resonances. 31P{1H} NMR (162
MHz, C6D6, ): 185.6 (s). Anal. Calcd for C26H38O2P2Ni: C,
189.4 (s). Anal. Calcd for C26H38O2P2Ni: C, 62.06; H, 7.61.
Found: C, 62.33; H, 7.57.
,
2.05ꢀ2.10 (m, PC
H
(E
)-[2,6-(cPe2PO)2C6H3]NiCH=CHPh
H
Synthesis of
(6b). This compound was prepared in 17 % yield using a
procedure similar to that used for 6a
1H NMR (400 MHz,
C6D6, ): 1.36ꢀ1.40 (m, CH2, 8H), 1.52ꢀ1.75 (m, CH2, 16H),
1.85ꢀ1.98 (m, CH2, 4H), 2.00ꢀ2.12 (m, CH2, 4H), 2.32ꢀ2.38
(m, PC , 4H), 6.79 (d, JHꢀH = 8.0 Hz, Ar , 2H), 6.85 (dt, JHꢀ
= 18.8 Hz, JPꢀH = 3.2 Hz, NiC =CHPh, 1H), 7.00 (t, JHꢀH
, 2H), 7.27 (t, JHꢀH = 8.0 Hz, Ar , 2H), 7.47
(d, JHꢀH = 8.0 Hz, Ar , 2H), 7.83 (dt, JHꢀH = 18.8 Hz, JPꢀH
2.8 Hz, NiCH=C
Ph, 1H). 13C{1H} NMR (101 MHz,
C6D6, ): 26.9 (t, JPꢀC = 4.5 Hz, H2), 27.0 (t, JPꢀC = 3.0 Hz,
H2), 28.0 (t, JPꢀC = 3.5 Hz, H2), 28.7 (s, H2), 38.5 (t, JPꢀC
= 13.1 Hz, H), 105.0 (t, JPꢀC = 6.0 Hz, Ar ), 124.6 (s,
Ar ), 124.7 (s, CH= HPh), 128.7 (s, Ar ), 128.9 (s, Ar
129.2 (s, Ar ), 137.6 (t, JPꢀC = 5.5 Hz, Ar ), 154.5 (t, JPꢀC
24.7 Hz, H=CHPh), 168.3 (t, JPꢀC = 10.1 Hz, Ar
H
H
H
H
,
.
δ
C
δ
C
C
C
H
H
C
C
C
H
H
C
C
C
= 8.0 Hz, Ar
H
H
C
H
=
H
δ
δ
C
62.06; H, 7.61. Found C, 61.91; H, 7.73.
C
C
C
C
C
Synthesis of [2,6-(cPe2PO)2C6H3]NiCPh=CH2 (5b).
This compound was prepared in 31 % yield using a
procedure similar to that used for 5a. Xꢀray quality crystals
C
C
C
C),
C
C
=
C
C); one
6 | Dalton Trans., 2015, 44, 1-8
This journal is © The Royal Society of Chemistry 2015

Page 7 of 9
Dalton Transactions
Dalton Transactions
View Article Online
ARTICLE
DOI: 10.1039/C5DT00161G
resonance was obscured by the solvent resonances. 13C{1H}
JPꢀC = 5.1 Hz,
C
C
H2), 27.8 (t, JPꢀC = 3.0 Hz,
H2), 39.4 (t, JPꢀC = 13.1 Hz, H), 104.4 (t, JPꢀC = 6.1 Hz,
CPh), 124.66 (s, C Ph),
), 128.7 (s, Ar ), 128.8 (s,
), 135.8 (t, JPꢀC = 20.2 Hz, Ar ), 168.2
(t, JPꢀC = 10.1 Hz, Ar
). 31P{1H} NMR (162 MHz, C6D6,
): 186.4 (s). ATRꢀIR (solid): (C
C) = 2082 cmꢀ1. Anal.
CH2), 28.6 (s,
NMR (101 MHz, CDCl3,
26.9 (t, JPꢀC = 3.5 Hz, H2), 27.7 (t, JPꢀC = 3.0 Hz,
28.6 (s, H2), 38.3 (t, JPꢀC = 13.1 Hz,
6.1 Hz, Ar
(s, Ar ), 128.5 (s, Ar
Hz, Ar
H=CHPh), 167.6 (t, JPꢀC = 10.5 Hz, Ar
(162 MHz, C6D6, ): 180.5 (s).
C34H46O2P2Ni: C, 67.23; H, 7.63. Found: C, 66.74; H, 7.70.
δ
): 26.7 (t, JPꢀC = 4.0 Hz,
CH2),
C
C
C
C
C
H2),
Ar
C
), 110.1 (t, JPꢀC = 28.8 Hz,
), 127.9 (s, Ar
), 130.3 (s, Ar
≡
≡C
C
CH), 104.3 (t, JPꢀC
=
124.73 (s, Ar
Ar
C
C
C), 124.0 (s, CH=
CHPh), 124.3 (s, Ar
C), 128.3
C
C
C
C
C), 129.3 (s, ArC), 136.6 (t, JPꢀC = 5.0
C
C
), 141.5 (s, Ar
C
), 154.9 (t, JPꢀC = 25.8 Hz,
). 31P{1H} NMR
Anal. Calcd for
δ
ν
≡
C
C
Calcd for C34H44O2P2Ni: C, 67.46; H, 7.33. Found: C,
67.52; H, 7.34.
δ
Procedures for catalytic hydrogenation of phenylacetylene
(a) Hydrogenation in THF: At room temperature under an
argon atmosphere, phenylacetylene (0.5 or 1.0 mmol), nickel
Synthesis of [2,6-(iPr2PO)2C6H3]NiC
78 oC under an argon atmosphere, a 2.5 M solution of nBuLi
in hexanes (276 L, 0.69 mmol) was added slowly to a
solution of phenylacetylene (83 L, 0.76 mmol) in pentane
(10 mL). The reaction mixture was warmed to 22 C and
stirred at this temperature for 15 min. The resulting
colorless suspension was transferred via a cannula to a cold
(–78 ˚C) solution of 8a (150 mg, 0.34 mmol) in THF (10
mL). The orange colored reaction mixture was stirred at 22
oC for 3 h, after which the volatiles were removed under
vacuum. Extraction of the yellow residue with pentane (10
≡CPh (7a). At –
ꢁ
catalyst 4a or 4b (50 ꢁmol) and 0.6 mL of THF were mixed
ꢁ
in a FisherꢀPorter bottle. The reaction vessel was then
exposed to a dihydrogen atmosphere (2 atm), after which the
system was flushed with H2 three times before being placed
under the appropriate pressure and temperature. For the
reaction at 70 oC, after 24 h, the color of the reaction
mixture changed from yellow to red with some particle
formation, which were removed by filtration. The solvent
was removed under vacuum and the residue was dissolved in
CDCl3 for NMR analysis. The conversion of
phenylacetylene to styrene was calculated based on NMR
o
mL
× 3) followed by filtration through a short plug of Celite
gave a yellow solution. Removal of the solvent under
vacuum yielded the product as a yellow powder (85 mg,
49% yield). Xꢀray quality crystals were obtained from a
integrations.
For the reactions catalyzed by 4b, the
resonances of ethylbenzene were overlapped with those of
4b and therefore, to ensure accuracy, 1,4ꢀdioxane (0.11
mmol) was added as an NMR internal standard. (b)
Hydrogenation in toluene: The procedure was the same as
described above except that the reaction was carried out in
tolueneꢀd8 and analyzed by NMR directly without filtration
and removal of the solvent.
o
methanol solution that was kept at –5 C. 1H NMR (400
MHz, C6D6,
C
δ
): 1.14ꢀ1.19 (m, CH3, 12H), 1.33ꢀ1.39 (m,
H3, 12H), 2.26ꢀ2.29 (m, PC , 4H), 6.73 (d, JHꢀH = 8.0 Hz,
, 2H), 7.13 (t, JHꢀH = 8.0 Hz,
, 2H), 7.54 (d, JHꢀH = 8.0 Hz, Ar
, 2H). 13C{1H} NMR
H
Ar
Ar
H
H
, 2H), 6.93ꢀ6.99 (m, ArH
H
(101 MHz, C6D6,
δ
): 16.8 (s,
C
C
H3), 17.7 (t, JPꢀC = 3.0 Hz,
H), 105.0 (t, JPꢀC = 6.1 Hz,
CH3), 28.5 (t, JPꢀC = 12.1 Hz,
Ar
H
), 108.2 (t, JPꢀC = 28.8 Hz,
), 129.4 (s, Ar ), 130.6 (s, Ar
= 20.2 Hz, Ar ), 168.8 (t, JPꢀC = 10.1 Hz, Ar
resonances were obscured by the solvent resonances.
13C{1H} NMR (101 MHz, CDCl3,
): 17.0 (s, H3), 17.9 (t,
JPꢀC = 3.0 Hz, H3), 28.6 (t, JPꢀC = 12.1 Hz, H), 104.5 (t,
JPꢀC = 6.6 Hz, Ar ), 108.1 (t, JPꢀC = 28.8 Hz, CPh), 125.0
(s, Ar ), 126.2 (s, C Ph), 127.9 (s, Ar ), 128.6 (s, Ar ),
128.8 (s, Ar ), 130.6 (s, Ar ), 135.5 (t, JPꢀC = 20.2 Hz,
Ar ), 168.4 (t, JPꢀC = 10.6 Hz, Ar
). 31P{1H} NMR (162
MHz, C6D6, ): 195.7. ATRꢀIR (solid): ν(C≡
C) = 2089 cmꢀ
C
≡
CPh), 125.0 (s, Ar
), 135.9 (t, JPꢀC
); other
C),
X-ray structure determinations
129.3 (s, Ar
C
C
C
Crystal data collection and refinement parameters can be
found in ESI. Intensity data were collected at 150K on a
Bruker SMART6000 CCD diffractometer using graphiteꢀ
monochromated Cu Kα radiation, λ = 1.54178Å. The data
frames were processed using the program SAINT. The data
were corrected for decay, Lorentz, and polarization effects
as well as absorption and beam corrections based on the
multiꢀscan technique. The structures were solved by a
combination of direct methods in SHELXTL and the
difference Fourier technique and refined by fullꢀmatrix leastꢀ
squares procedures. Nonꢀhydrogen atoms were refined with
C
C
δ
C
C
C≡
C
H
C
≡
C
C
C
C
C
C
C
δ
1. Anal. Calcd for C26H36O2P2Ni: C, 62.31; H, 7.24. Found:
C, 62.60; H, 7.34.
anisotropic displacement parameters.
calculated and treated with a riding model. No solvent of
crystallization is present in the lattice for any of the
Hꢀatoms were
Synthesis of [2,6-(cPe2PO)2C6H3]NiC
compound was prepared in 64 % yield using a procedure
similar to that used for 7a Xꢀray quality crystals were
obtained from a pentane solution that was kept at –5 C. 1H
NMR (400 MHz, C6D6, ): 1.38ꢀ1.42 (m, CH2, 8H), 1.73ꢀ
1.80 (m, CH2, 12H), 1.85ꢀ1.95 (m, CH2, 4H), 2.04ꢀ2.13 (m,
H2, 4H), 2.31ꢀ2.40 (m, CH2, 4H), 2.46ꢀ2.55 (m, PC , 4H),
6.75 (d, JHꢀH = 7.6 Hz, Ar , 2H), 6.92ꢀ6.99 (m, Ar , 2H),
7.13 (t, JHꢀH = 7.6 Hz, Ar , 2H), 7.53 (d, JHꢀH = 7.6 Hz,
Ar ): 26.7ꢀ26.8
, 2H). 13C{1H} NMR (101 MHz, C6D6,
(m, two H2 overlapped), 28.0 (t, JPꢀC = 3.0 Hz, H2), 28.8
H2), 39.6 (t, JPꢀC = 13.1 Hz, H), 105.1 (t, JPꢀC = 6.1 Hz,
), 110.4 (t, JPꢀC = 28.3 Hz, CPh), 125.0 (s, Ar ),
Ph), 129.5 (s, Ar ), 129.6 (s, Ar ), 130.5 (s,
), 136.1 (t, JPꢀC = 20.2 Hz, Ar ), 168.8 (t, JPꢀC = 10.1
≡CPh (7b). This
structures.
cyclopentyl rings of 5b and 7b; twoꢀcomponent disorder
models were applied. The crystal structures for 5b 6a 7a
Typical disorder was observed for the
.
o
,
,
and 7b have been deposited at the Cambridge
Crystallographic Data Centre (CCDC) and allocated the
deposition numbers CCDC 1043222ꢀ1043225.
δ
C
H
H
H
Acknowledgements
H
H
δ
We thank the U.S. National Science Foundation (CHEꢀ
0952083) and the Alfred P. Sloan Foundation (research
fellowship to H.G.) for supporting this research.
C
C
(s,
Ar
C
C
C
Crystallographic data were collected on
SMART6000 diffractometer which was funded by an NSFꢀ
MRI grant (CHEꢀ0215950).
a
Bruker
C≡
C
125.8 (s, C
Ar
Hz, Ar
≡
C
C
C
C
C
C); one resonance was obscured by the solvent
resonances. 13C{1H} NMR (101 MHz, CDCl3,
δ): 26.6 (t,
Notes and references
This journal is © The Royal Society of Chemistry 2015
Dalton Trans., 2015, 44, 1-8 | 7

Dalton Transactions
Page 8 of 9
DaltoVnieTwrAartnicsleaOcntliinoens
ARTICLE
DOI: 10.1039/C5DT00161G
Mol. Catal. A: Chem., 2011, 335, 1ꢀ7; (e) X. Lefèvre, D. M.
Spasyuk and D. Zargarian, J. Organomet. Chem., 2011, 696, 864ꢀ
870; (f) A. B. Salah, C. Offenstein and D. Zargarian,
Organometallics, 2011, 30, 5352ꢀ5364; (g) A. B. Salah and D.
Zargarian, Dalton Trans., 2011, 40, 8977ꢀ8985; (h) B. Vabre, D. M.
Spasyuk and D. Zargarian, Organometallics, 2012, 31, 8561ꢀ8570;
(i) B. Vabre, F. Lindeperg and D. Zargarian, Green Chem., 2013,
15, 3188ꢀ3194; (j) J. Hao, B. MougangꢀSoumé, B. Vabre and D.
Zargarian, Angew. Chem. Int. Ed., 2014, 53, 3218ꢀ3222; (k) B.
Vabre, P. Petiot, R. Declercq and D. Zargarian, Organometallics,
2014, 33, 5173ꢀ5184; (l) J. Hao, B. Vabre and D. Zargarian,
Organometallics, 2014, 33, 6568ꢀ6576.
Department of Chemistry, University of Cincinnati, P. O. Box 210172,
Cincinnati, Ohio 45221ꢀ0172, USA. Eꢀmail: hairong.guan@uc.edu;
Fax: (+1)513ꢀ556ꢀ9239; Tel: (+1)513ꢀ556ꢀ6377
† Electronic supplementary information (ESI) available: CCDC
1043222ꢀ1043225 for 5b
,
6a,
7a and 7b
.
For ESI and
crystallographic data in CIF or other electronic format see
DOI: 10.1039/b000000x/
1. J. F. Hartwig, Organotransition Metal Chemistry: From
Bonding to Catalysis, University Science Books: Sausalito, CA,
2010; pp. 368ꢀ370.
2. (a) H. C. Clark and C. R. Milne, J. Organomet. Chem., 1978,
161, 51ꢀ59; (b) H. Werner, M. A. Esteruelas and H. Otto,
12. (a) S. Chakraborty, J. A. Krause and H. Guan, Organometallics,
2009, 28, 582ꢀ586; (b) S. Chakraborty, J. Zhang, J. A. Krause and
H. Guan, J. Am. Chem. Soc., 2010, 132, 8872ꢀ8873; (c) J. Zhang, C.
M. Medley, J. A. Krause and H. Guan, Organometallics, 2010, 29,
6393ꢀ6401; (d) S. Chakraborty, Y. J. Patel, J. A. Krause and H.
Guan, Polyhedron, 2012, 32, 30ꢀ34; (e) J. Zhang, A. Adhikary, K.
M. King, J. A. Krause and H. Guan, Dalton Trans., 2012, 41, 7959ꢀ
7968; (f) S. Chakraborty, J. Zhang, Y. J. Patel, J. A. Krause and H.
Guan, Inorg. Chem., 2013, 52, 37ꢀ47; (g) S. Chakraborty, Y. J.
Patel, J. A. Krause and H. Guan, Angew. Chem. Int. Ed., 2013, 52,
7523ꢀ7526.
Organometallics, 1986,
Mawby, J. Chem. Soc. Dalton Trans., 1989, 589ꢀ594; (d) M. A.
Esteruelas, L. A. Oro and C. Valero, Organometallics, 1995, 14
5, 2295ꢀ2299; (c) J. M. Bray and R. J.
,
3596ꢀ3599; (e) M. Bassetti, P. Casellato, M. P. Gamasa, J.
Gimeno, C. GonzálezꢀBernardo and B. MartínꢀVaca,
Organometallics, 1997, 16, 5470ꢀ5477; (f) D. S. Frohnapfel, P.
S. White and J. L. Templeton, Organometallics, 2000, 19, 1497ꢀ
1506; (g) A. V. Marchenko, H. Gérard, O. Eisenstein and K. G.
Caulton, New J. Chem., 2001, 25, 1244ꢀ1255; (h) M. Bassetti, S.
Marini, J. Díaz, M. P. Gamasa, J. Gimeno, Y. Rodríguezꢀ
13. A. Castonguay, A. L. Beauchamp and D. Zargarian,
Organometallics, 2008, 27, 5723ꢀ5732.
14. M. Brookhart, M. L. H. Green and G. Parkin, Proc. Natl. Acad. Sci.
U.S.A., 2007, 104, 6908ꢀ6914.
15. R. C. Bush and R. J. Angelici, Inorg. Chem., 1988, 27, 681ꢀ686.
Álvarez and S. GarcíaꢀGranda, Organometallics, 2002, 21
,
4815ꢀ4822; (i) J. Navarro, E. Sola, M. Martín, I. T.
Dobrinovitch, F. J. Lahoz and L. A. Oro, Organometallics, 2004,
23, 1908ꢀ1917; (j) H. Xia, T. B. Wen, Q. Y. Hu, X. Wang, X.
Chen, L. Y. Shek, I. D. Williams, K. S. Wong, G. K. L. Wong
and G. Jia, Organometallics, 2005, 24, 562ꢀ569; (k) Y. Jiang, O.
Blacque, T. Fox, C. M. Frech and H. Berke, Organometallics
2009, 28, 4670ꢀ4680; (l) J. S. Merola, T. L. Husebo and K. E.
Matthews, Organometallics, 2012, 31, 3920ꢀ3929.
16. (a) Y. Gao, M. C. Jennings and R. J. Puddephatt, Dalton Trans.
,
2003, 261ꢀ265; (b) W. Weng, S. Parkin and O. V. Ozerov,
Organometallics, 2006, 25, 5345ꢀ5354; (c) L. She, X. Li, H.
Sun, J. Ding, M. Frey and H.ꢀF. Klein, Organometallics, 2007,
26, 566ꢀ570.
,
17. J. M. Huggins and R. G. Bergman, J. Am. Chem. Soc., 1981,
103, 3002ꢀ3011.
3. (a) A. Nakamura and S. Otsuka, J. Mol. Catal., 1975/76,
1, 285ꢀ
18. (a) T. M. Bockman, J. F. Garst and F. Ungváry, J. Organomet.
Chem., 1999, 586, 41ꢀ47; (b) D. P. Estes, J. R. Norton, S. Jockusch
and W. Sattler, J. Am. Chem. Soc., 2012, 134, 15512ꢀ15518.
19. C. J. Rhodes and E. Roduner, J. Chem. Soc. Perkin Trans. 2, 1990,
1729ꢀ1733.
307; (b) S. Otsuka and A. Nakamura, Adv. Organomet. Chem.
,
1976, 14, 245ꢀ283; (c) H. C. Clark and C. S. Wong, J. Am.
Chem. Soc., 1977, 99, 7073ꢀ7074; (d) H. C. Clark, G. Ferguson,
A. B. Goel, E. G. Janzen, H. Ruegger, P. Y. Siew and C. S.
Wong, J. Am. Chem. Soc., 1986, 108, 6961ꢀ6972; (e) A. A. H.
van der Zeijden, H. W. Bosch and H. Berke, Organometallics
,
1992, 11, 563ꢀ573; (f) A. D. Selmeczy and W. D. Jones, Inorg.
Chim. Acta, 2000, 300-302, 138ꢀ150.
4. (a) G. E. Herberich and W. Barlage, Organometallics, 1987,
1924ꢀ1930; (b) M. A. Esteruelas, F. J. Lahoz, J. A. Lopez, L. A.
Oro, C. Schlünken, C. Valero and H. Werner, Organometallics
6,
,
1992, 11, 2034ꢀ2043; (c) R. Shen, T. Chen, Y. Zhao, R. Qiu, Y.
Zhou, S. Yin, X. Wang, M. Goto and L.ꢀB. Han, J. Am. Chem.
Soc., 2011, 133, 17037ꢀ17044.
5. C. Bianchini, A. Meli, M. Peruzzini and F. Vizza, Organometallics,
1990, 9, 1146ꢀ1155.
6. C. Bianchini, P. Innocenti, A. Meli, M. Peruzzini and F. Zanobini,
Organometallics, 1990, 9, 2514ꢀ2522.
7. A. Adhikary, J. R. Schwartz, L. M. Meadows, J. A. Krause and H.
Guan, Inorg. Chem. Front., 2014, 1, 71ꢀ82.
8. R. Johansson and O. F. Wendt, Organometallics, 2007, 26, 2426ꢀ
2430.
9. J. A. Bull, J. J. Mousseau and A. B. Charette, Org. Lett., 2008, 10,
5485ꢀ5488.
10. (a) V. GómezꢀBenítez, O. BaldovinoꢀPantaleón, C. Herreraꢀ
Álvarez, R. A. Toscano and D. MoralesꢀMorales, Tetrahedron Lett.,
2006, 47, 5059ꢀ5062; (b) F. EstudianteꢀNegrete, S. Hernándezꢀ
Ortega and D. MoralesꢀMorales, Inorg. Chim. Acta, 2012, 387, 58ꢀ
63; (c) T. Chen, L. Yang, L. Li and K.ꢀW. Huang, Tetrahedron,
2012, 68, 6152ꢀ6257; (d) N. Á. EspinosaꢀJalapa, S. Hernándezꢀ
Ortega, X.ꢀF. Le Goff, D. MoralesꢀMorales, J.ꢀP. Djukic and R. Le
Lagadec, Organometallics, 2013, 32, 2661ꢀ2673.
11. (a) V. Pandarus and D. Zargarian, Chem. Commun., 2007, 978ꢀ980;
(b) V. Pandarus and D. Zargarian, Organometallics, 2007, 26,
4321ꢀ4334; (c) A. Castonguay, D. M. Spasyuk, N, Madern, A. L.
Beauchamp and D. Zargarian, Organometallics, 2009, 28, 2134ꢀ
2141; (d) X. Lefèvre, G. Durieux, S. Lesturgez and D. Zargarian, J.
8 | Dalton Trans., 2015, 44, 1-8
This journal is © The Royal Society of Chemistry 2015

Page 9 of 9
Dalton Transactions
View Article Online
DOI: 10.1039/C5DT00161G
For Table of Contents use only
O
PR2
Ni
O
O
PR2
Ph
O
O
PR2
Pd
PR2
O
PR2
M
H
(major)
-H2
Ph
O
PR2
PR2
Ph
+
Ni
Pd favors H2 elimination
Ph
Ni favors insertion
O
PR2
(minor)
Nickel POCOP-pincer hydride complexes react with phenylacetylene to afford alkenyl
complexes whereas the palladium analogs give alkynyl complexes.