Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation with a Ni(PS)2 Complex

Article abstract of DOI:10.1002/ejic.201700590

Tetra-coordinate Ni^II and Zn^II complexes employing the PS chelates 2-(diphenylphosphanyl)benzenethiol (HL¹) and 2-(diisopropylphosphanyl)benzenethiol (HL²) have been synthesized and characterized by spectroscopic, structural, and electrochemical methods. All complexes were screened for electrocatalytic activity for hydrogen evolution with acetic acid and hydrochloric acid and hydrogen oxidation in the presence of triethylamine. The nickel complex Ni(L¹)₂ (1) was found to reduce protons from external acids to generate hydrogen with a turnover frequency of 140 s^–1 at an overpotential of 1.1 V and cleave dihydrogen using redox active base triethylamine (Et₃N) with a turnover frequency of 23 s^–1 at an overpotential of 0.33 V. Ni(L²)₂ (3) was also found to be an active catalyst for dihydrogen oxidation, but inefficient for proton reduction due to inaccessible Ni (II/I) reduction in the potential window. Zn(L¹)₂ (2) and Zn(L²)₂ (4) complexes were found to be inadequate for their electrocatalytic behaviour towards both the reactions.

Full text of DOI:10.1002/ejic.201700590

A Journal of
Accepted Article
Title: Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation with
a Ni(PS)2 Complex
Authors: Rahul Jain, Mark S Mashuta, Robert M Buchanan, and Craig
Alan Grapperhaus
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201700590
Link to VoR: http://dx.doi.org/10.1002/ejic.201700590

European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
Electrocatalytic Hydrogen Evolution and Hydrogen Oxidation with
a Ni(PS) Complex
2
[
a]
[a]
[a]
[a]
Rahul Jain, Mark S. Mashuta, Robert M. Buchanan, Craig A. Grapperhaus*
Abstract: Tetra-coordinate Ni(II) and Zn(II) complexes employing the
be attributed in part to the meridional arrangement of the three PS
chelates, which orients two of the sulfur lone-pairs coplanar
1
PS chelates 2-(diphenylphosphino)benzenethiol (HL ) and 2-
2
(
diisopropylphosphino)benzenethiol (HL ) have been synthesized and
2
facilitating the proposed ligand-centered H evolution/oxidation
(Scheme 1).[ Further, the Re center undergoes changes in
redox state with reorganization of spin-density, in conjunction with
the third sulfur donor, to promote S-H bond cleavage in the case
of HER or S-H bond formation during HOR.[9] The role of the metal
center is thus two-fold; serving a structural role by orienting the
ligands and an electronic role as an electron reservoir.
10]
characterized by spectroscopic, structural, and electrochemical
methods. All complexes were screened for electrocatalytic activity for
hydrogen evolution with acetic acid and hydrochloric acid and
hyrdogen oxidation in the presence of triethylamine. The nickel
1
complex Ni(L )
2
(1) was found to reduce protons from external acids
-
1
to generate hydrogen with a turnover frequency of 140 s at an
overpotential of 1.1 V and cleave dihydrogen using redox active base
-
1
Scheme 1. Relative orientation of S lone-pairs in PS chelates of Re, Ni, and Zn.
triethylamine (Et
3
N) with a turnover frequency of 23 s at an
2
overpotential of 0.33 V. Ni(L )
2
(3) was also found to be an active
catalyst for dihydrogen oxidation, but inefficient for proton reduction
1
due to inaccessible Ni (II/I) reduction in the potential window. Zn(L )
2
2
(
2) and Zn(L )
2
(4) complexes were found to be inadequate for their
electrocatalytic behaviour towards both the reactions.
Introduction
In the current report, we evaluate the related Ni and Zn
Hydrogen, the simplest and lightest molecule, provides an
attractive solution to the challenge of capturing and storing
renewable energy in a carrier that can be used on demand.[1-2]
However, the processes of hydrogen production via hydrogen
evolution reactions (HERs) and hydrogen utilization via hydrogen
oxidation reactions (HORs) require catalysts to mitigate
overpotential. While Pt is the ideal electrocatalyst to perform such
reactions, the scarcity and costs associated with this precious
metal make its application on the global scale problematic.[3-6]
This has led to the development of numerous small molecular
homogeneous catalysts offered as alternatives to Pt. Typically,
these catalysts employ a metal center such as Ni, Fe, and Co
capable of forming a metal hydride intermediate.[7] Ni complexes
with bis(1,5-R′-diphospha-3,7-R′′-diazacyclooctane) reported by
DuBois and Bullock were found to be very efficient catalysts for
complexes 1 – 4 (Scheme 2) as HER/HOR catalysts. Complexes
1
1
and 2 contain the same L ligand that promotes ligand-center
HER/HOR with Re, but in geometrical arrangements more similar
to some planar bis-chelate nickel catalysts of Eisenberg that
[11]
proceed via traditional metal-hydride pathways. Complexes 3
and 4 are derivatives with more electron-donating iso-propyl
groups on the phosphorus donors. Notably, the nickel complex 1
was first isolated by Darensbourg, from a reaction similar to the
2+
3 2
HER, in which the dithioether derivative [Ni(PS-CH ) ] (5) was
reduced by two electrons leading to the formation of ethane and
upon photolysis.[12]
1
Scheme 2. Synthetic pathways to metal complexes 1 – 4.
5
-1
HERs and HORs with higher turnover frequencies (~10 s and 50
-1
[2]
s ) and lower overpotentials (0.5V and 0.4V).
Recently, we reported catalytic HER and HOR using a
system that avoids metal hydride intermediates. The complex
Re(L1) (L1 = 2-(diphenylphosphino)benzenethiolato) catalyzes
3
both hydrogen production and hydrogen oxidation through
proposed ligand-centered processes.[8-9] The atypical activity can
[
a]
Department of Chemistry, University of Louisville,
320 South Brook Street, Louisville, KY, 40292, USA.
2
E-mail: grapperhaus@louisville.edu
Supporting information for this article is given via a link at the end of
the document.
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European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
Results and Discussion
and two sulfur atoms (P
environment (Figure 2). Crystal data and structure refinement
1
, P
2
, S
1
, S
2
) in a pseudo-square planar
Synthesis and Electronic Spectroscopy
details for 3 is listed in Table S1.
2
The M(PS) bis(phosphinothiolato) metal complexes 1 – 4 were
prepared upon addition of simple metal salts to the deprotonated
form of the ligands in ethanol (Scheme 2). Yields range from 81 –
8
8%. Complexes 1 and 2 are the Ni(II) and Zn(II) derivatives of 2-
1
(
diphenylphosphino)benzenethiol, HL . The synthesis of 1 was
previously reported by Darensbourg from an alternate route
employing demethylation of the bis(phosphinothioether)
derivative.[ Complexes 3 and 4 are the analogous Ni(II) and
12]
Zn(II)
derivatives
of
the
related
ligand
2-
2
(
diisopropylphosphino)benzenethiol, HL .
The electronic spectra of
1
–
4 were recorded in
dichloromethane (Figure 1). The nickel complex 1 shows an
intense charge transfer band at 301 nm (18,500 M-1 cm ) with a
shoulder at higher energy and a less intense band at 412 nm
-1
-
1
-1
(
M
1860 M cm ). A weak d-d transition is observed at 615 nm (150
-1
-1
cm ). The data are comparable to a prior report in chloroform
with bands at 298 nm (25,560 M cm ) and 424 nm (2850 M cm-
-1
-1
-1
1
[12]
Figure 2. ORTEP14 representation of 3 with thermal ellipsoids at 50% probability
)
.
Substitution of the phenyl substituents on the phosphine in 1
level. Hydrogen atoms have been omitted.
with electron-donating iso-propyl groups in 3 resolves two,
intense high energy bands at 303 and 284 nm. The lower intensity
charge transfer band and d-d transitions at 408 nm and 610 nm,
respectively, are slightly blue shifted with respect to 1. The zinc
complex 2 displays charge transfer bands similar to 1, but at
higher energies of 272 and 347 nm. Relative to 2, the Zn complex
Table 1. Selected Bond Distances (Å) and Bond Angles (°) for 1, 3, and 4.
1
3
4
4
reveals a red shift of the more intense band to 279 nm and a
blue shift of the less intense band to 326 nm. Protonation of 1with
HCl in dichloromethane shifts the lower intensity charge transfer
band from 412 to 420 nm. This shift is attributed to the protonation
at one of the thiolate donors. Titrations with acetic acid at
concentrations employed in HER studies resulted in no shift in the
charge transfer bands. (Figure S7).
M1-S1
2.166(3)
2.166(3)
2.173(3)
2.173(3)
180.0(1)
88.7(1)
91.3(1)
91.3(1)
88.7(1)
180.0(1)
2.1591(3)
2.1641(3)
2.1897(3)
2.1798(3)
177.689(15)
89.503(13)
89.211(13)
91.791(13)
89.573(13)
177.325(15)
2.3066(3)
2.3170(3)
2.3864(3)
2.3711(3)
115.866(13)
88.782(11)
116.169(12)
118.303(12)
89.178(12)
131.031(12)
M1-S2
M1-P1
M1-P2
S1-M1-S2
S1-M1-P1
S1-M1-P2
S2-M1-P1
S2-M1-P2
P1-M1-P2
A comparison of metric parameters for 1, 3, and 4 is
provided in Table 1. The Ni-S distances of 2.1591(3) and
2.1641(3) Å for 3 are statistically equivalent to the symmetric Ni-
S distances, 2.166(3) Å, for 1. The Zn-S1 and Zn-S2 of 2.3066(3)
and 2.3170(3) Å for 4 are slightly longer than the Ni counterparts.
Likewise, the Ni-P distances of 2.1897(3) and 2.1798(3) Å for 3
are similar to the symmetric Ni-P distance of 2.173(3) Å for 1. The
corresponding Zn-P distances of 2.3864(3) and 2.3711(3) Å for 4
are slightly longer. The Ni complexes 1 and 3 are in pseudo-
square planar environment with the two bidentate chelates
oriented in a trans arrangement. For both complexes, all the P-M-
S bond angles are between 88.7(1)° and 91.791(13)°. The
geometry about the Zn center of 4 is best described as distorted
tetrahedral. The S1-Zn-P1 and S2-Zn-P2 bond angles associated
with individual bidentate chelates of 88.782(11)° and 89.178(12)°
Figure 1.Electronic spectra of complexes 1 – 4 in dichloromethane.
Structural Determination
The solid state structure of 3 was determined by single crystal x-
ray diffraction (Table S1, SI). The x-ray crystal structures of 1 and
4
have previously been reported.[12-13] The Ni complex 3
1
crystallizes as orange prisms in the monoclinic shape group P2 /n
upon liquid diffusion of a dichloromethane/ether mixture. The
asymmetric unit contains a single Ni(II) ligated by two phosphorus
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European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
are statistically equivalent to their counterparts in 1. However, the
S1-Zn-P2 and S2-Zn-P1 angles of 116.169(12)° and
Electrocatalytic Hydrogen Evolution Reaction (HER)
The ligands HL and HL and the metal complexes 1 – 4 were
screened for electrocatalytic HER activity in dichloromethane with
118.303(12)°, respectively for
4
are much larger than
1
2
corresponding angles in 1.
3
acetic acid (CH COOH) and hydrochloric acid (HCl) as the acid
Electrochemical Methods
The cyclic voltammograms of
source. Of these systems, only 1 displayed an increase in
cathodic current consistent with catalytic HER activity. Neither the
free ligands nor the zinc complexes 2/4 showed any activity. To
minimize interference from reduction of the dichloromethane
solvent, the window for catalytic evaluation was restricted to -2.5
1
– 4 were recorded in
dichloromethane with tetrabuytlammonium hexafluorophosphate
as a supporting electrolyte (Figure S1). The nickel complexes 1
and 3 display multiple oxidation events upon scanning in the
anodic direction. These processes are assigned to metal- and
ligand-centered oxidations (Table 2), while the zinc complexes 2
and 4 only show ligand-centered events. Complex 1 displays a
+/F 0
V vs F
c
c
.
Addition of acetic acid to solutions of 1 increases cathodic
+/F 0
current at -2.15 V vs F
c
c
(Figure 3), suggesting electrocatalytic
III/II
quasi-reversible oxidation assigned to the Ni couple at +0.25 V
reduction. At relatively low acetic acid concentrations, the current
increases linearly with increased acid concentration consistent
with a first-order acid dependence (Figure 3, inset). The increase
in current is observed with the successive addition of acid, which
when analyzed shows a first-order dependence with respect to 1
+
0
versus ferrocenium/ferrocene (Fc /Fc ), consistent with earlier
reports,[12] and an irreversible oxidation at +1.22 V (v = 200 mV/s)
attributed to ligand-centered oxidation. Substitution of the phenyl
substituents of 1 with isopropyl groups in 3 shifts the NiIII/II
cathodically to +0.13 V consistent with the increased donor ability
of phosphorus. Notably, the ligand-centered oxidation is shifted
anodically to +1.28 V (ν = 200 mV/s). The assignment of the
irreversible oxidation events of 1 and 3 as ligand-centered is
supported by the voltammograms of 2 and 4, which only display
irreversible oxidations at +0.71 and +0.76 V, respectively.
Figure S4). With acetic acid, a turnover frequency (TOF) of 51 s-
(
1
is recorded at higher scan rates for 1. An overpotential of 1.1 V
was determined from the open circuit potential.[15] Catalytic
reduction of deuterated acetic acid (CD COOD) reveals a kinetic
isotope effect (KIE) of 0.82 for 1. The inverse value of KIE (k /k
3
H
D
<
1) value is consistent with a metal hydride intermediate based
on previous reports by Gray and Fukuzumi.[
16-17]
In contrast, the
Table 2. Electrochemical data for complexes 1 – 5 in dichloromethane.[a]
inverse KIE for 1 is distinct from the value of 10 observed for
Re(L1) , which operates via ligand centered HER.[8-9] In the strong
acid HCl, an increased TOF of 140 s-1 is observed. (Figure S5).
3
♦
Compound
ML /ML [V]
+1.22 (i)
+0.71 (i)
+1.28 (i)
+0.76 (i)
-
Ni(III/II) [V]
Ni(II/I) [V]
-2.15 (q)
-
Ni(I/0) [V]
1
2
3
4
5
+0.25 (q)
-2.71 (i)
-
-
+0.12 (q)
-2.48 (q)
-
-
-
-
-
-0.54 (q)
-1.23 (i)
+
0
[
a] Data recorded in 0.1 M Bu
4
NPF
6
with potentials versus Fc /Fc . (i) and
(q) denote irreversible and quasi-reversible process, respectively. For
irreversible events, the potential of maximum current at a scan rate of 200
mV/s is reported. For quasi-reversible events, the E1/2 value is reported. Data
for 5 is taken from reference 12.
Both of the nickel complexes display reduction events in
addition to the oxidation events noted above. The nickel complex
Figure 3. Electrocatalytic H
the presence of 0.1 M Bu NPF
(red), 1.4 mM [CH COOH] (green), 2.8 mM [CH
p
[CH COOH] (black) at a scan rate of 200 mV/s. (Inset) Plot of icat/i vs [AcOH] .
2
evolution. Cyclic voltammograms of 0.50 mM 1 in
in dichloromethane solution with no [CH COOH]
COOH] (blue), 3.5 mM
4
6
3
1
displays a quasi-reversible reduction at -2.15 V (Figure 3) and
3
3
1/2
+
0
3
an irreversible reduction at -2.71 V versus Fc /Fc , respectively,
in dichloromethane. Prior reports noted that no reduction events
were observed within the solvent window (-1.5 V to -3.0 V vs
Fc /Fc ). However, in dry dichloromethane, subtraction of the
background current associated with solvent reduction reveals the
+
0
Control experiments with acetic acid and hydrochloric acid
in the absence of 1 shows no significant current beyond the
background (Figure S9). To probe for the formation of any
adsorbed species on the electrode that may be responsible for
HER activity, the working electrode was removed from the
solution following catalytic HER measurements, washed with
dichloromethane solvent, and then placed in fresh acidic solution
without the catalyst. No catalytic current was observed. This
excludes the possibility of catalyst degradation or film formation
two reduction events (Figure S2). The quasi-reversible reduction
at -2.15 V is assigned to the NiII/I couple and the irreversible
I/0
reduction at -2.71 V is assigned to Ni . Notably, these events for
1
are shifted by 1.61 and 1.48 V, respectively, with respect to the
]2+ (5), reported by
dithioether derivative of 1, [Ni(PS-CH
Darensbourg, consistent with the displacement of two CH
groups.[ Substitution of the phenyl groups of 1 with isopropyl in
3
)
2
+
3
12]
[18-
II/I
+
0
on the electrode surface that is responsible for catalytic activity.
3
shifts the reversible Ni couple by -0.33 V to -2.48 V vs. Fc /Fc .
1
9]
I/0
The expected Ni event of 3 is shifted out of the solvent window.
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European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
The robustness of the catalyst 1 was demonstrated in
complexes 2 and 4 were found to be be minimally active for
controlled potential bulk electrolysis experiments carried out for
hydrogen oxidation.
+
24 hours. At an applied potential of -1.9 V vs Fc /Fc, 1 catalytically
evolved H
based on total charge of 15 C. The gas evolved during electrolysis
was confirmed as H by gas chromatography thermal conductivity
GC-TCD) analysis of headspace.
The HER mechanism is proposed to follow an ECEC
2 2 2
from CH Cl with a turnover number (TON) of 3.4
Conclusions
2
(
In summary, we have synthesized four Ni(II) and Zn(II) complexes
with (dialkyl/diarylphosphino)benzenethiol ligands and screened
their electrocatalytic activity for HER and HOR. Of these only the
nickel complex 1 catalyzed both reactions, while 3 showed activity
mechanism. Initial reduction of 1 is followed by metal-centered
protonation. Further reduction of the resulting metal-hydride leads
+
to an anionic intermediate that can react with H in solution to form
for HOR in the presence of Et
3
N. Notably, complex 1 contains the
H
2
. The mechanism is similar to other proposed HER routes for
1
same ligand, HL , that supports ligand-centered HER/HOR in the
related Ni(II) complexes.[20-21]
related Re(L1)
3
system. The lack of HER or HOR activity with the
Zn complexes 2 and 4 confirm that the ligand-centered catalytic
Electrocatalytic Hydrogen Oxidation Reaction (HOR)
1
activity of Re(L )
3
relies on contributions from the metal center.
In addition to electrocatalytic proton reduction, 1 also serves as
an electrocatalyst for the hydrogen oxidation reaction (HOR).
Under one atmosphere of hydrogen gas, addition of triethylamine
For the nickel complex 1, the HER TOF with acetic acid or HCl is
similar to that reported for Re(L1)
3
, although the latter operates at
a lower overpotential. Despite similar activities, the mechanisms
of the Ni and Re systems are different as reflected in the inverse
KIE of 0.82 measured for 1 as compared to the KIE of 10 for
(
Et
anodic current at 0.77 V (Figure 4), which can be attributed to the
oxidation of H . A maximum anodic current is obtained at Et
concentrations of 1.68 mM. Under these base saturated
3
N) to the solutions of 1 leads to the steady increase in the
3
N
Re(L1)
.[8] This is further observed in the HOR results. Again, the
are similar. However, 1 and
are only catalytically active for HOR in the presence of redox
2
3
catalytic activities for 1, 3 and Re(L1)
3
-1
conditions, 1 displays a TOF of 23 s with an overpotential of 0.33
V. Complex 3 also catalyzes the hydrogen oxidation reaction
3
1
3
active bases, whereas Re(L ) functions with a variety of bases.
(
s
HOR) with Et
3
N. Under base saturated conditions, a TOF of 19
is obtained at an overpotential of 0.49 V (Figure S8). No
N under H atmosphere in
the absence of 1 or 3. Also, control experiments with 1 or 3 in the
presence of Et N under N atmosphere gives no catalytic current.
-1
significant current is observed with Et
3
2
Experimental Section
3
2
Physical Methods
Elemental analyses were obtained from Midwest Microlab (Indianapolis,
IN). Infrared spectra were recorded on a Thermo Nicolet Avatar 360
spectrometer with ATR attachment (4 cm-1 resolution). Mass spectrometry
(+ESI-MS) was performed by the Laboratory for Biological Mass
Spectrometry at Texas A&M University. All electrochemical measurements
were performed using a Gamry Interface potentiostat/galvanostat with a
three-electrode cell (glassy carbon working electrode, platinum wire
counter electrode, and Ag/Ag ion reference electrode). Reported potentials
+
are scaled versus a ferrocenium/ferrocene (Fc /Fc) standard (0.00 V),
which was determined using ferrocene as an internal standard. 1H NMR
and 31P NMR spectra were recorded on a Varian 400 MHz spectrometer.
Electronic absorption spectra were recorded with an Agilent 8453 diode
array spectrometer with a 1 cm path length quartz cell.
Figure 4. Electrocatalytic H
the presence of 0.1 M [Bu NPF
atm. of H with no added base (blue), 1.12 mM (CH
CH CH N (red) at a scan rate of 200 mV/s.
2
oxidation. Cyclic voltammograms of 0.50 mM 1 in
] in dichloromethane solution of under N (grey),
CH N (green), 1.68 mM
4
6
2
Materials and methods
1
(
2
3
2 3
)
3
2 3
)
All reagents were obtained from commercially available sources and used
as received unless otherwise noted. The ligands 2-(diphenylphosphino)-
1
2
benzenethiol (HL ) and 2-(diisopropylphosphino)benzenethiol (HL ) have
1
[29-
Notably, unlike the Re analogue of HL , both 1 and 3 require
N or other redox active bases, such as tributylamine (Bu N), to
been prepared by slight modifications of previously reported methods.
31]
Et
3
3
The synthesis and characterization of 1 and 4 has previously been
reported,[12-13] herein we report an alternate synthesis. Solvents were dried
and purified using an MBraun solvent purification system unless otherwise
noted. The complexes in this study are air and water stable as solids and
were handled on the benchtop with no required protection from the
atmosphere.
catalyze the HOR. No catalytic current is observed with 2,6-
lutidine [(CH N] which is redox inactive base in
dichloromethane. This suggests that Et
mediator in addition to its role as a base in these reactions. Such
3 2 5 3
) C H
[
22]
3
N serves as redox
[
23-26]
behavior has previously been noted.
3
Oxidation of Et N initally
+
results in the formation of [NEt
3
•] , which rapidly abstracts an H-
3 3
N to form [HNEt
]+ and the
atom from a second equivalent of Et
radical species Et
N•=CHMe.[27-28] The exact nature of the NEt
intermediate in the HOR mechanism remains unresolved. The Zn
2
3
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European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
-
1
Metal Complexes
for absorption (transmission min./max. = 0.916 /1.000; µ = 1.083 mm )
using SCALE3 ABSPACK[33]. The structure was solved by Direct methods
bis[2-(diphenylphosphino)benzenethiolato]nickel(II), Ni(L1)
in the space group P2
1
/n using SHELXS[34] and refined by least squares
2
(1). A
methods on F using SHELXL[34]. Non-hydrogen atoms were refined with
anisotropic atomic displacement parameters. All hydrogen atoms were
located by difference maps and refined isotropically. For all 6105 unique
reflections (R(int) 0.026) the final anisotropic full matrix least-squares
refinement on F2 for 406 variables converged at R1 = 0.029 and wR2 =
2
solution of sodium ethoxide (0.11 g, 1.60 mmol) in degassed ethanol (10
mL) was prepared in a Schlenk flask under a nitrogen atmosphere. Solid
1
HL (0.40 g, 1.50 mmol) was added under a nitrogen purge and the mixture
was stirred until all ligand dissolved. To the resulting ligand solution,
NiCl ·6H O (0.15g, 0.75 mmol) dissolved in degassed ethanol (10 mL) was
2 2
0
.064 with a GOF of 1.04.
added via cannula. The mixture was stirred for 10 minutes, resulting in
color change from light green to dark green. Filtration of the reaction
product yielded a Ni(L1)
as a dark green solid. The product was washed
with ethanol (20 mL) and diethyl ether (20 mL) and dried under vacuum.
Yield: 0.31 g, 81%. +ESI-MS, m/z calcd. for C36 Ni 645.39; Found
Ni: C, 66.99; H, 4.37; Found: C, 64.33;
) δ 7.66 (dd, J = 12.7, 5.9 Hz, 8H), 7.49
CCDC 1549464 (for 3) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre.
2
28 2 2
H P S
6
45.04. Anal. Calcd. for C36
H
28
P
2
S
2
1
H, 4.16. H NMR (400 MHz, CD
2
Cl
2
(
6
t, J = 7.4 Hz, 4H), 7.40 (m, 10H), 7.18 (t, J = 7.8 Hz, 3H), 7.07 (m, 2H),
Acknowledgements
.92 (t, J = 7.5 Hz, 2H).31P { H} (400 MHz, CD
1
2 2
Cl ): δ 55.69 ppm.
bis[2-(diphenylphosphino)benzenethiolato]zinc(II), Zn(L1)
This research was supported in part by the National Science
Foundation (CHE-1361728) and a Competitive Enhancement and
Internal Research Initiation Grants from the Office of the
Executive Vice President for Research and Innovation (U of L).
MSM thanks the Department of Energy (DEFG02-08CH11538)
and the Kentucky Research Challenge Trust Fund for upgrade of
our X-ray facilities.
2
(2). The
was prepared using a similar methodology as described
complex Zn(L1)
2
for 1 except that the solution of zinc acetate dihydrate (0.16 g, 0.75 mmol)
in degassed ethanol (10mL) was added as the metal source. The Zn(L1)
product was isolated by filtration as a white solid. The solid was washed
with ethanol (20 mL) and diethyl ether (20 mL) and dried under vacuum.
2
Yield 0.42 g, 86%. +ESI-MS, m/z calcd. for C36
H
28
P
2
S
2
Zn 652.09; Found
Zn: C, 66.30; H, 4.32; Found: C, 64.32;
) δ 7.65 (m, 4H), 7.44 (m, 6H), 7.33 (m,
6
52.06. Anal. Calcd. for C36
H
28
P
2
S
2
1
H, 5.44. H NMR (400 MHz, CD
2
Cl
2
31
1
10H), 7.20 (m, 4H), 7.02 (m, 2H), 6.93 (t, J = 7.5 Hz, 2H). P { H} (400
Keywords: Hydrogen • Electrocatalysis • Redox active ligands •
MHz, CD Cl ): δ -9.77 ppm.
2
2
PS ligands
bis[2-(diisopropylphosphino)benzenethiolato]nickel(II), Ni(L2)
2
was prepared using a similar methodology as
described for 1 except that the solution of HL2 (0.30 g, 1.50 mmol) in
2
(3).
References
The complex Ni(L2)
degassed ethanol (10mL) was used as the ligand source. The brown-red
3
product was washed with ethanol (20 mL) and diethyl ether (20 mL) and
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[
[
2]
3]
36
H P
S
2 2
Ni 509.30; Found 509.09.
Ni: C, 56.59; H, 7.12; Found: C, 53.51; H, 7.67.
2 2
Cl ) δ 7.45 (m, 2H), 7.30 (m, 2H), 7.20 (m, 2H),
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H P S
36 2 2
1
[4]
H NMR (400 MHz, CD
.96 (m, 2H), 2.50 (m, 4H), 1.24 (d, J = 7.2 Hz, 24H). P { H} (400 MHz,
CD Cl ): δ 75.62 ppm.
31
1
6
[
[
5]
6]
2
2
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bis[2-(diisopropylphosphino)benzenethiolato]zinc(II) Zn(L2)
complex Zn(L2)
was prepared using a similar methodology as described
for 2 except that the solution of HL2 (0.30 g, 0.75 mmol) in degassed
ethanol (10mL) was used as the ligand source. The white precipitate was
washed with ethanol (20mL) and diethyl ether (20mL) and dried under
(4). The
2
16954.
2
[
[
7]
8]
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9238-9241.
vacuum. Yield: 0.34 g, 88%. +ESI-MS, m/z calcd. for C24
H
36
P
2
S
2
Zn
Zn: C, 55.86; H, 7.03;
Cl ) δ 7.89 (m, 2H), 7.47
[
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36
H P
2
S
2
1
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2
2
[
[
[
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2
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3
An orange prism 0.38 x 0.30 x 0.10 mm crystal of 3 grown from a solution
of dichloromethane/ether was mounted on a glass fiber for collection of x-
ray data on an Agilent Technologies/Oxford Diffraction Gemini CCD
diffractometer. The CrysAlisPro32 CCD software package (v 1.171.36.32)
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[
[
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32
CrysAlisPro RED to determine final unit cell parameters: a = 8.23199(17)
Å, b = 20.1632(3) Å, c = 15.2322(4) Å, β = 99.355(3)°, V = 2494.67(9) Å ,
D
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3
calc = 1.356 Mg/m , Z = 4 to produce raw hkl data that were then corrected
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
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2
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.201700590
FULL PAPER
Entry for the Table of Contents
FULL PAPER
A series of Ni(PS)
2
and Zn(PS)
2
Hydrogen evolution/oxidation
complexes were synthesized,
Rahul Jain, Mark S. Mashuta, Robert M.
Buchanan, Craig A. Grapperhaus*
characterized, and screened for
electrocatalytic activity for hydrogen
evolution and hydrogen oxidation. The
nickel complex of 2-(diphenylphos-
phino)benzenethiol catalytically
reduces protons upon reduction and
catalytically oxidizes dihydrogen in the
presence of triethylamine.
Page No. – Page No.
Electrocatalytic Hydrogen Evolution
and Hydrogen Oxidation with a
Ni(PS) Complex
2
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