Mononuclear [NiII(L)P-(o-C6H4S) 2(o-C6H4SH)]0/1- (L = Thiolate, selenolate, PPh3, and Cl) complexes with intramolecular [Ni...S...H...S]/[Ni...H...S] interactions modulated by the coordinated ligand L: Relevance to the [NiFe] hydrogenases

Article abstract of DOI:10.1021/ic051924w

The shift of the IR ν_S-H frequency to lower wavenumbers for the series of complexes [Ni^II(L)(P-(o-C₆H ₄S)₂(o-C₆H₄-SH))]^0/1- (L = PPh₃ (1), Cl (6), Se-p-C₆H₄-Cl (5), S-C ₄H₃S (7), SePh (4)) indicates that a trend of increasing electronic donation of the L ligands coordinated to the Ni(II) center promotes intramolecular [Ni-S...H-S] interactions. Compared to the Ni...S(H) distance, in the range of 3.609-3.802 A in complexes 1 and 4-7, the Ni...S(CH₃) distances of 2.540 and 2.914 A observed in the [Ni^II(PPh₃)(P(o-C₆H₄S) ₂(o-C₆H₄-SCH₃))] complexes (8a and 8b, two conformational isomers with the chemical shift of the thioether methyl group at δ 1.820 (-60°C) and 2.109 ppm (60°C) (C₄D ₈O)) and the Ni...S(CH₃) distances of 3.258 and 3.229 A found in the [Ni^II(L)(P(o-C₆H₄S) ₂(o-C₆H₄-SCH₃))]^1- complexes (L = SPh (9), SePh (10)) also support the idea that the pendant thiol protons of the Ni(II)-thiol complexes 1/4-7 were attracted by both the sulfur of thiolate and the nickel. The increased basicity (electronic density) of the nickel center regulated by the monodentate ligand attracted the proton of the pendant thiol effectively and caused the weaker S...H bond. In addition, the pendant thiol interaction modes in the solid state (complexes 1a and 1b, Scheme 1) may be controlled by the solvent of crystallization. Compared to complex 1a, the stronger intramolecular [Ni-S...H-S] interaction (or a combination of [Ni-S-H-S]/[Ni...H-S] interactions) found in complexes 4-7 led to the weaker S-H bond strength and accelerated the oxidation (by O ₂) of complexes 4-7 to produce the [Ni^Y(L)(P(o-C ₆H₄S)₃)]^1- (L = Se-p-C ₆H₄-Cl (11), SePh (12), S-C₄H₃S (13)) complexes.

Full text of DOI:10.1021/ic051924w

Inorg. Chem. 2006, 45, 2307−2316
/1-
Mononuclear [NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0
Selenolate, PPh3, and Cl) Complexes with Intramolecular
‚‚‚S] Interactions Modulated by the Coordinated
(L ) Thiolate,
[Ni‚‚‚S‚‚‚H‚‚‚S]/[Ni‚‚‚H
Ligand L: Relevance to the [NiFe] Hydrogenases
Chien-Hong Chen,† Gene-Hsiang Lee,‡ and Wen-Feng Liaw*,†
Department of Chemistry, National Tsing Hua UniVersity, Hsinchu 30043, Taiwan, and
Instrumentation Center, National Taiwan UniVersity, Taipei, Taiwan
Received November 7, 2005
The shift of the IR νS frequency to lower wavenumbers for the series of complexes [NiII(L)(P-(o-C6H4S)2(o-C6H4-
-H
/1-
SH))]0
electronic donation of the L ligands coordinated to the Ni(II) center promotes intramolecular [Ni
Compared to the Ni‚‚‚S(H) distance, in the range of 3.609 3.802 Å in complexes 1 and 4
distances of 2.540 and 2.914 Å observed in the [NiII(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] complexes (8a and 8b, two
conformational isomers with the chemical shift of the thioether methyl group at 1.820 ( 60 C) and 2.109 ppm
(60
C) (C4D8O)) and the Ni‚‚‚S(CH3) distances of 3.258 and 3.229 Å found in the [NiII(L)(P(o-C6H4S)2(o-C6H4-
SCH3))]1 complexes (L
thiol complexes 1/4 7 were attracted by both the sulfur of thiolate and the nickel. The increased basicity (electronic
(L
)
PPh3 (1), Cl (6), Se-p-C6H4-Cl (5), S-C4H3S (7), SePh (4)) indicates that a trend of increasing
S] interactions.
7, the Ni‚‚‚S(CH3)
−S‚‚‚H−
−
−
δ
−
°
°
-
)
SPh (9), SePh (10)) also support the idea that the pendant thiol protons of the Ni(II)−
−
density) of the nickel center regulated by the monodentate ligand attracted the proton of the pendant thiol effectively
and caused the weaker S‚‚‚H bond. In addition, the pendant thiol interaction modes in the solid state (complexes
1a and 1b, Scheme 1) may be controlled by the solvent of crystallization. Compared to complex 1a, the stronger
intramolecular [Ni
−
S
‚‚‚
H
−
−
S] interaction (or a combination of [Ni
H bond strength and accelerated the oxidation (by O2) of complexes 4
Se-p-C6H4 Cl (11), SePh (12), S-C4H3S (13)) complexes.
−
S
‚‚‚
H
−
S]/[Ni‚‚‚
H
−
S] interactions) found in complexes
4
−7 led to the weaker S
−7 to produce the
[NiY(L)(P(o-C6H4S)3)]1 (L
)
−
-
Introduction
drogenases ([NiFe] H2ases), have been studied widely.1,2
[Fe]-only H2ases are usually associated with hydrogen
production, and [NiFe] H2ases are generally involved in
hydrogen uptake.3-7 The X-ray crystallographic studies of
the active-site structure of [NiFe] hydrogenases isolated from
D. gigas, D. Vulgaris, D. fructosoVorans, and D. desulfuri-
Molecular hydrogen plays an important role in the
metabolism of many microorganisms. Hydrogenases catalyze
the reversible two-electron oxidation of H2 in aerobic and
anaerobic microorganisms.1,2 Two classes of hydrogenases,
[Fe]-only hydrogenases ([Fe]-only H2ases) and [NiFe] hy-
(3) (a) Peters, J. W.; Lanzilotta, W. N.; Lemon, B. J.; Seefeldt, L. C.
Science 1998, 282, 1853-1858. (b) Nicolet, Y.; Piras, C.; Legrand,
P.; Hatchikian, C. E.; Fontecilla-Camps, J. C. Structure 1999, 7, 13-
23. (c) Lemon, B. J.; Peters, J. W. J. Am. Chem. Soc. 2000, 122, 3793-
3794. (d) Nicolet, Y.; de Lacey, A. L.; Verne´de, X.; Fernandez, V.
M.; Hatchikian, E. C.; Fontecilla-Camps, J. C. J. Am. Chem. Soc. 2001,
123, 1596-1601.
(4) (a) Volbeda, A.; Charon, M. H.; Piras, C.; Hatchikian, E. C.; Frey,
M.; Fontecilla-Camps, J. C. Nature 1995, 373, 580-587. (b) Garcin,
E.; Vernede, X.; Hatchikian, E. C.; Volbeda, A.; Frey, M.; Fontecilla-
Camps, J.-C. Structure 1999, 7, 557-566. (c) Happe, R. P.; Roseboom,
W.; Pierik, A. J.; Albracht, S. P. J. Nature 1997, 385, 126. (d) Volbeda,
A.; Garcin, E.; Piras, C.; De Lacey, A. L.; Fernandez, V. M.;
Hatchikian, E. C.; Frey, M.; Fontecilla-Camps, J. C. J. Am. Chem.
Soc. 1996, 118, 12989-12996.
* To whom correspondence should be addressed. E-mail: wfliaw@
mx.nthu.edu.tw.
† National Tsing Hua University.
‡ National Taiwan University.
(1) (a) Adams, M. W. W.; Mortenson, L. E.; Chen, J.-S. Biochim. Biophys.
Acta 1981, 594, 105-176. (b) Adams, M. W. W.; Stiefel, E. I. Curr.
Opin. Chem. Biol. 2000, 4, 214-220.
(2) (a) Carepo, M.; Tierney, D. L.; Brondino, C. D.; Yang, T. C.;
Pamplona, A.; Telser, J.; Moura, I.; Moura, J. J. G.; Hoffman, B. M.
J. Am. Chem. Soc. 2002, 124, 281-286. (b) Albracht, S. P. J. Biochim.
Biophys. Acta 1994, 1188, 167-204. (c) van der Zwaan, J. W.;
Coremans, J. M. C. C.; Bouwens, E. C. M.; Albracht, S. J. P. Biochim.
Biophys. Acta 1990, 1041, 101-110. (d) Vignais, P. M.; Billoud, B.;
Meyer, J. FEMS Microbiol. ReV. 2001, 25, 455-501.
10.1021/ic051924w CCC: $33.50
Published on Web 02/07/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 5, 2006 2307

Chen et al.
cans ATCC27774 in combination with infrared spectroscopy
have revealed an active site comprised of a heterobimetallic
(Scys)2Ni(µ-Scys)2(µ-X)Fe(CO)(CN)2 (X ) O, OH) cluster.4-7
The bridging ligand, X, was proposed to be an oxide or
hydroxide in the oxidized state and was found to be absent
in the reduced state. The geometry of nickel in the active
site of [NiFe] H2ases is pseudotetrahedral in the reduced state
and pseudosquare-pyramidal in the oxidized state. During
the catalytic cycle of [NiFe] H2ases, the various catalytic
states corresponding to IR vibrations, the EPR g value, and
Em values (vs NHE) were proposed; the formal oxidation
state of the nickel center in the Ni-A, Ni-B, and Ni-C states
is a paramagnetic Ni(III), while it is a Ni(II) in the Ni-R,
Ni-SU, Ni-SI, and Ni-SIa states.8 Hall and De Gioia
suggested that the Ni-R state existed as [(Scys-H)(Scys)NiII(µ-
Several mononuclear nickel-thiolate complexes have been
synthesized to obtain information about the structure of Ni
in the active site of the [NiFe] H2ase.13 Complex NiII(BmMe)2
(BmMe ) bis(2-mercapto-1-methylimidazolyl)borate) with a
[NiS4H2] core and an Ni‚‚‚H-B interaction may provide a
structural model of the nickel site of a [NiFe] H2ase.14 Model
complex [NiII(SC(NH2)NHNCH-C6H4-o-OH)2] with the la-
bile phenolic OH group catalyzes the isotopic exchange of
D2 with the phenol OH proton upon exposure of a DMSO/
ethanol solution of the Ni complex to D2.15 Recent kinetic
studies of the protonation of complexes [Ni(SPh)(triphos)]+,
[Ni(SePh)(triphos)]+, and [Ni(SEt)(triphos)]+ (triphos )
(Ph2PCH2CH2)2PPh) revealed that the sulfur atom’s lone pair
of electrons is the initial site for the protonation of [Ni(SR)-
(triphos)]+.16 However, for the more electron-donating alky-
lthiolate ligand ligated to Ni, interaction of the proton with
both the nickel and sulfur sites (an η2-EtS-H complex) was
proposed.16 Recently, Tatsumi and co-workers reported the
isolation of dithiolato-bridged [NiFe] complexes, [Fe(CO)2-
S
cys)2Fe(CO)(CN)2] and [(Scys-H)(Scys)NiII(µ-H)(µ-Scys)2-
Fe(CO)(CN)2] with a Scys‚‚‚H interacting directly with the
nickel center (a [Ni‚‚‚H-Scys] interaction).9,10 Both of the
proposed mechanisms suggested that the intermediate Ni-C
state existed as [(Scys-H)(Scys)NiIII(µ-H)(µ-Scys)2Fe(CO)-
(CN)2], a hydride bridge. Also, the architecture of the silent-
active Ni-SIa is proposed to be a Cys‚‚‚SH proton directly
interacting with nickel, [(Scys-H)(Scys)NiII(µ-Scys)2Fe(CO)-
(CN)2]. Early electron nuclear double resonance (ENDOR)
studies have provided evidence for the existence of a solvent
exchangeable proton which may coordinate to the Ni atom
as an in-plane hydride form or as a η2-H2 form.11 Recently,
ENDOR and hyperfine sublevel correlation spectroscopy
(HYSCORE) have been applied to study the active site of
the catalytic [NiFe] hydrogenase from D. Vulgaris Miyazaki
F. in the reduced Ni-C state.5c-d,12 These techniques have
provided direct experimental evidence for the hydride
bridging between the nickel and iron atoms. The Ni-C state
was suggested to be either an early product of the heterolytic
cleavage of H2 or a precursor to H2 formation.12
(CN)2(µ-SCH2CH2CH2S)Ni(S2CNR2)]- (R ) Et; R2
)
-(CH2)5-). These complexes display the close structural
feature of the active site of reduced form [NiFe] H2ase.17
In the previous study of the [NiII(L)(P-(o-C6H4S)2(o-C6H4-
SH))] (L ) SePh (4), S-C4H3S (7)) complexes, the interaction
between the thiol proton and both the nickel and sulfur atoms
(a combination of intramolecular [Ni-S‚‚‚H-S] and [Ni‚‚‚H-
S] interactions) was demonstrated.18 The desire to explore
the correlation between the extent of the interactions and
the basicity (electronic density) of nickel has inspired us to
synthesize model complexes [NiII(L)(P-(o-C6H4S)2(o-C6H4-
SH))]0/1- (L ) PPh3 (1), SePh (4), Se-p-C6H4-Cl (5), and Cl
(6)) and [NiII(L′)(P(o-C6H4S)2(o-C6H4-SCH3))]0/1- (L′ ) PPh3
(8), SPh (9), SePh (10)) with various electron-donating
ligands, L/L′, coordinated to the nickel center. This study
further provides evidence that the pendant thiol proton of
the Ni(II) complexes, [NiII(L)(P-(o-C6H4S)2(o-C6H4SH))] 0/1-
,
(5) (a) Higuchi, Y.; Yagi, T.; Yasuoka, N. Structure 1997, 5, 1671-1680.
(b) Higuchi, Y.; Ogata, H.; Miki, K.; Yasuoka, N.; Yagi, T. Structure
1999, 7, 549-556. (c) Ogata, H.; Mizoguchi, Y.; Mizuno, N.; Miki,
K.; Adachi, S.-I.; Yasuoka, N.; Yagi, T.; Yamauchi, O.; Hirota, S.;
Higuchi, Y. J. Am. Chem. Soc. 2002, 124, 11628-11635. (d) Foerster,
S.; Stein, M.; Brecht, M.; Ogata, H.; Higuchi, Y.; Lubitz, W. J. Am.
Chem. Soc. 2003, 125, 83-93.
were “arrested” by both the sulfur of thiolate and nickel
resulting in combinations of intramolecular [Ni-S‚‚‚H-S]
and [Ni‚‚‚H-S] interactions, and the extent of the interac-
tions was modulated by the monodentate ligand.
Results and Discussion
(6) Rousset, M.; Montet, Y.; Guigliarelli, B.; Forget, A.; Asso, M.;
Bertrand, P.; Fontecilla-Camps, J. C.; Hatchikian, E. C. Proc. Natl.
Acad. Sci. U.S.A. 1998, 95, 11625-11630.
Synthesis of Ni(II)-Thiol Complex [NiII(PPh3)(P-(o-
C6H4S)2(o-C6H4SH))] (1). Reaction of NiCl2(PPh3)2 and tris-
(2-phenylthiol)phosphine (P(o-C6H4SH)3) in THF at ambient
temperature led to the isolation of the red-brown four-
(7) Matias, P. M.; Soares, C. M.; Saraiva, L. M.; Coelho, R.; Morais, J.;
Le Gall, J.; Carrondo, M. A. J. Biol. Inorg. Chem. 2001, 6, 63-81.
(8) (a) De Lacey, A. L.; Hatchikian, E. C.; Volbeda, A.; Frey, M.;
Fontecilla-Camps, J. C.; Fernandez, V. M. J. Am. Chem. Soc. 1997,
119, 7181-7189. (b) Maroney, M. J.; Davidson, G.; Allan, C. B.;
Figlar, J. Struct. Bonding 1998, 92, 1-65. (c) Bagley, K. A.; Duin,
E. C.; Roseboom, W.; Albracht S. P. J.; Woodruff, W. H. Biochemistry
1995, 34, 5527. (d) Coremans, J. M. C. C.; van der Zwaan, G. W.;
Albracht, S. P. J. Biochim. Biophys. Acta 1992, 1119, 157-168. (e)
Stein, M.; Lubitz, W. Curr. Opin. Chem. Biol. 2002, 6, 243-249.
(9) Niu, S.; Thomson, L. M.; Hall, M. B. J. Am. Chem. Soc. 1999, 121,
4000-4007.
(10) De Gioia, L.; Fantucci, P.; Guigliarelli, B.; Bertrand, P. Inorg. Chem.
1999, 38, 2658-2662.
(11) (a) Fan, C.; Teixeira, M.; Moura, J.; Moura, I.; Huynh, B. H.; Le
Gall, J.; Peck, H. D., Jr.; Hoffman, B. M. J. Am. Chem. Soc. 1991,
113, 20-24. (b) Whitehead, J. P.; Gurbiel, R. J.; Bagyinka, C.;
Hoffman, B. M.; Maroney, M. J. J. Am. Chem. Soc. 1993, 115, 5629-
5635.
(13) (a) Darensbourg, M. Y.; Lyon, E. J.; Smee, J. Coord. Chem. ReV.
2000, 206, 533-561. (b) Allan, C. B.; Davidson, G.; Choudhury, S.
B.; Gu, Z.; Bose, K.; Day, R. O.; Maroney, M. J. Inorg. Chem. 1998,
37, 4166-4167. (c) James, T. L.; Cai, L.; Mutterties, M. C.; Holm,
R. H. Inorg. Chem. 1996, 35, 4148-4161. (d) Cha, M.; Shoner, S.
C.; Kovacs, J. A. Inorg. Chem. 1993, 32, 1860-1863. (e) Nguyen,
D. H.; Hsu, H.-F.; Millar, M.; Koch, S. A.; Achim, C.; Bominaar, E.
L.; Munck, E. J. Am. Chem. Soc. 1996, 118, 8963-8964. (f)
Bouwman, E.; Reedijk, J. Coord. Chem. ReV. 2005, 249, 1555-1581.
(14) Alvarez, H. M.; Krawiec, M.; Donovan-Merkert, B. T.; Fouzi, M.;
Rabinovich, D. Inorg. Chem. 2001, 40, 5736-5737.
(15) Zimmer, M.; Schulte, G.; Luo, X.-L.; Crabtree, R. H. Angew. Chem.,
Int. Ed. Engl. 1991, 30, 193-194.
(16) Clegg, W.; Henderson, R. A. Inorg. Chem. 2002, 41, 1128-1135.
(17) Li, Z.; Ohki, Y.; Tatsumi, K. J. Am. Chem. Soc. 2005, 127, 8950-
8951.
(12) Foerster, S.; van Gastel, M.; Brecht, M.; Lubitz, W. J. Biol. Inorg.
Chem. 2005, 10, 51-62.
2308 Inorganic Chemistry, Vol. 45, No. 5, 2006

[NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- Complexes
Scheme 1
planar ligand field. The chemical shift (5.91 ppm (S-H)
(CDCl3)) of the pendant thiol of complex 1 is shifted ca.
1.84 ppm downfield from that of the free thiol P(o-C6H4-
SH)3 (δ 4.07 (d)).19 Treatment of complex 1 with D2O in a
THF solution at 5 °C led to the H/D exchange product
[NiII(PPh3)(P(o-C6H4S)2(o-C6H4SD))] (1-D), identified by IR
and 2H NMR. The IR νS-D stretching frequency of 1752 (br)
cm-1 (νS-D, KBr) for complex 1-D is consistent with the
calculated position, based only on the difference in masses
between S-H and S-D. The 2H NMR spectrum of complex
1-D (using the natural abundance of D in C4H8O solvent,
two singlet peaks at 1.73 and 3.57 ppm, as internal standard)
displaying the signal at 6.175 (br) ppm (C4H8O) was assigned
to the S-D resonance. When a THF solution of complex 1
was recrystallized with THF-hexane, complex 1a, displaying
a broad νS-H stretching band at 2393 cm-1 (KBr), was
isolated and characterized by X-ray crystallography (Scheme
1). In contrast, the diffusion of hexane into a CH2Cl2 solution
of complex 1 yielded complex 1b with a broad νS-H
stretching band at 2240 cm-1 (KBr), characterized by single-
crystal diffraction (Scheme 1). The IR spectra of complexes
1a and 1b display broad νS-H stretching bands at 2393 and
2240 cm-1 (KBr), which are ∼90 and ∼250 cm-1, respec-
tively, lower than the free ligand, 2488 cm-1 (KBr). This
lower νS-H stretching frequency may imply the existence of
intramolecular [Ni-S‚‚‚H-S]/[Ni‚‚‚H-S] interactions.18
The ORTEP diagrams of complexes 1a and 1b are shown
in Figure 1. The selected bond distances and angles are given
in the figure caption. Complexes 1a and 1b consist of a four-
coordinate nickel(II) center in a distorted square planar
geometry with two thiolate sulfur atoms and two phosphorus
atoms, respectively, in the trans positions. In complex 1a,
the acute (C(14)-S(3)-H(3A)) bond angle of 95.04° and
the similar distances of Ni‚‚‚S(3) (3.802 Å) and S(2)‚‚‚S(3)
(3.743 Å) suggested that the proton of S(3)-H(3A) points
toward the middle, between the Ni and S(2) atoms, and
interacts with both the sulfur (S(2)) and nickel atoms (i.e., a
combination of the intramolecular [Ni-S‚‚‚H-S] and
coordinated Ni(II) complex, 1, in a high yield (79%) (Scheme
1).18,19 Complex 1 is soluble in CH2Cl2/THF and displays
air sensitivity in organic solvents. However, in the solid state,
complex 1 is air-stable for minutes. The 1H NMR spectrum
of complex 1 displays the benzene proton resonances at 6.993
(t), 7.181 (t), 7.293-7.424 (m), 7.708 (t) ppm, and the 31P
NMR spectrum shows two nonequivalent phosphorus atoms
31P-31
P
at 76.57 (d) (J
and 24.65 (d) (J
(CDCl3). Both the H and 31P NMR spectra are consistent
) 695 Hz, (P-(o-C6H4S)2(o-C6H4SH))
31P-31
1
P
) 695 Hz, PPh3) ppm (vs H3PO4)
with a low-spin d8 Ni(II) electronic configuration in a square-
Figure 1. ORTEP drawing and labeling scheme of [NiII(PPh3)(P(o-C6H4S)2(o-C6H4SH))] (1a and 1b). Selected bond distances (Å) and angles (deg):
complex 1a Ni-S(1) ) 2.1892(9), Ni-S(2) ) 2.1751(9), Ni-P(1) ) 2.1318(8), Ni-P(2) ) 2.2452(8), S(1)-Ni-S(2) ) 156.68(4), P(1)-Ni-P(2) )
171.64, S(1)-Ni-P(2) ) 94.66(3), S(2)-Ni-P(2) ) 93.85(3), C(1)-P(1)-Ni ) 106.37(10), C(7)-P(1)-Ni ) 110.05(11), C(13)-P(1)-Ni ) 117.02(9);
complex 1b Ni-S(1) ) 2.1782(5), Ni-S(2) ) 2.1916(5), Ni-P(1) ) 2.1224(5), Ni-P(2) ) 2.2340(5), S(1)-Ni-S(2) ) 156.01(2), P(1)-Ni-P(2) )
169.75(2), S(1)-Ni-P(2) ) 94.88(2), S(2)-Ni-P(2) ) 94.82(2), C(1)-P(1)-Ni ) 110.33(7), C(7)-P(1)-Ni ) 106.60(6), C(13)-P(1)-Ni ) 116.50(6).
Inorganic Chemistry, Vol. 45, No. 5, 2006 2309

Chen et al.
Scheme 2
[Ni‚‚‚H-S] interactions, Scheme 1). In contrast, the Ni‚‚‚S(3)
distance of 3.248 Å is significantly shorter than the S(1)‚‚‚S(3)
distance of 3.966 Å in complex 1b. Also, the Ni-P(1)-
C(13)-C(14) torsion angle of 35.2° observed in complex
1b is significantly smaller than the Ni-P(1)-C(13)-C(14)
torsion angle of 62.6° observed in complex 1a (Scheme 1).
Compared to complex 1a, the acute C(14)-S(3)-H(3A)
bond angle of 99.64°, the smaller Ni-P(1)-C(13)-C(14)
torsion angle of 35.2°, and a lower νS-H stretching band
(2240 cm-1 (KBr)) may indicate that the thiol proton tends
to interact directly with the nickel atom in complex 1b (i.e.,
a [Ni‚‚‚H-S] interaction). We noticed that the most probable
Ni‚‚‚H(3A)-S distance of 2.182 Å in complex 1b is roughly
consistent with the Ni‚‚‚H-B distance of 1.863 Å in complex
NiII(BmMe)2.14 The pendant thiol interaction modes in the
solid state (complexes 1a and 1b, Scheme 1) may be
controlled by the solvent of crystallization.
(br) for the byproduct D2O, and the UV-vis spectra display
the characteristic absorption bands (610, 672, and 1152 nm
(CH2Cl2)) of complex 2. Complex 2 is soluble in CH2Cl2/
THF and displays air and thermal sensitivity. The 1H NMR
spectrum of complex 2 displays the paramagnetic chemical
shifts at -3.99 (br), 5.48 (br), 8.42 (br), 9.70 (br), 11.82
(br), 12.62 (br), and 13.67 (br) ppm (CDCl3) at 298 K, and
the effective magnetic moment in the solid state, found using
the the SQUID magnetometer, is 1.71 µB. These results sup-
port the idea that complex 2 adopts a low-spin d7 Ni(III)
electronic configuration in a distorted trigonal bipyramidal
ligand field. The cyclic voltammogram of complex 2 (mea-
sured in a 2 mM CH2Cl2 solution of complex 2, with 0.1 M
[n-Bu4N][PF6] as the supporting electrolyte at room tem-
perature, scan rate 100 mV/s) reveals one reversible reduc-
tion-oxidation process (i.e., reversible Ni(III)-Ni(II) redox
process) at E1/2 ) -0.865 V (vs Cp2Fe/Cp2Fe+) (Figure 2).
Syntheses of Complexes [NiIII(PPh3)(P(o-C6H4S)3)] (2)
and [PPN][NiII(PPh3)(P(o-C6H4S)3)] (3). When dry O2 was
added to the THF solution of complex 1 at 0 °C, a color
change from red-brown to dark green was observed (Scheme
2a). As observed in the previous study,18 the reaction led to
the formation of complex 2 accompanied by the byproduct
When a CH3CN-THF (1:3 volume ratio) solution of
complex 1 and [SPh]- (or [SEt]-) was stirred at ambient
temperature for 3 h (Scheme 2b), a deprotonation reaction
occurred yielding mononuclear complex 3 accompanied by
the liberation of thiophenol (or ethanethiol), identified by
1H NMR spectra; protonation of complex 3 in THF at 0 °C
by HClO4 produced complex 1 (Scheme 2b′), characterized
by IR and 1H NMR spectra. Instead of ligand displacement,
treatment of complex 2 with 1 equiv of [SEt]- in CH3CN-
THF solutions (1:3 volume ratio) for 1.5 h at ambient
temperature led to the reduction of complex 2 to produce
1
H2O, characterized by UV-vis, H NMR, SQUID, and
single-crystal X-ray diffraction. The formation of the byprod-
uct, H2O, was confirmed again by treating a dry THF solution
of complex 1-D with dry O2 at ambient temperature. The
2H NMR spectrum shows the expected signal at 2.783 ppm
1
(18) Lee, C.-M.; Chen, C.-H.; Ke, S.-C.; Lee, G.-H.; Liaw, W.-F. J. Am.
Chem. Soc. 2004, 126, 8406-8412.
(19) Block, E.; Ofori-Okai, G.; Zubieta, J. J. Am. Chem. Soc. 1989, 111,
2327-2329.
complex 3 and diethyl disulfide, identified by H NMR
(Scheme 2c). Complex 3 is soluble in CH2Cl2 or CH3CN-
THF (1:3 volume ratio), but it is significantly less soluble
2310 Inorganic Chemistry, Vol. 45, No. 5, 2006

[NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- Complexes
Figure 2. Cyclic voltammogram of [NiIII(PPh3)(P(o-C6H4S)3)] (2) (mea-
sured in a 2 mM CH2Cl2 solution with 0.1 M [n-Bu4N][PF6] as the
supporting electrolyte at room temperature, scan rate 100 mV/s) vs Cp2Fe/
Cp2Fe+ (∆Ep ) 0.087 V).
Figure 4. ORTEP drawing and labeling scheme of [NiII(PPh3)(P(o-
C6H4S)3)]- anion (3). Selected bond distances (Å) and angles (deg): Ni-
P(1) ) 2.0995(7), Ni-P(2) ) 2.1978(7), Ni-S(1) ) 2.2801(7), Ni-S(2)
) 2.3729(8), Ni-S(3) ) 2.3056(8), P(1)-Ni-P(2) ) 177.00(3), P(1)-
Ni-S(1) ) 85.12(3), P(2)-Ni-S(1) ) 92.19(3), S(1)-Ni-S(2) ) 121.17(3),
S(1)-Ni-S(3) ) 120.77(3), S(2)-Ni-S(3) ) 115.62(3).
with three thiolate sulfurs in the equatorial positions and two
phosphorus atoms in the axial positions for both complexes
2 and 3. The strained effect of the chelating ligand from the
tridentate mode in complex 1 to the tetradentate mode in
complex 3 results in an increase of mean Ni-S bond dis-
tances of 0.137 Å. Compared to Ni(II) complex 1, the mean
Ni-S distance in Ni(III) complex 2 increased by 0.082 Å.
Obviously, the longer Ni-S bond distances in complex 2
indicate that the influence of the strained effect of the chela-
ting ligand overwhelms the contraction effect resulting from
the oxidation of Ni(II) (complexes 1/3) to Ni(III) (complex 2).
Reduction of complex 2 to 3 (Ni(III) to Ni(II)) was believed
to cause the elongation of the mean Ni-S bond distances
(mean Ni-S bond distances: 2.266 Å for 2, 2.320 Å for 3).
In complex 2, the nickel atom lies 0.174 Å under the mean
plane defined by three sulfur atoms toward the axial triphenyl
phosphine. The displaced distance (0.2102 Å) of the nickel
atom from the mean three sulfur atom plane toward the axial
triphenyl phosphine was observed in complex 3.
Preparation of Ni(II)-Thiol Derivatives by Ligand
Displacement. In contrast to the deprotonation of complex
1 by addition of the anionic thiolates [PhS]-/[SEt]-, the
addition of [SePh]- (or [Cl]-/[Se-p-C6H4-Cl]-) to the
CH3CN-THF solution (1:3 volume ratio) of complex 1 at
0 °C for 4 h yielded ligand-displacement complexes, [NiII-
(L)(P-(o-C6H4S)2(o-C6H4SH))]- (L ) SePh (4), Se-p-C6H4-
Cl (5), Cl (6)), isolated as red-brown solids and identified
by IR, NMR, UV-vis, and single-crystal X-ray diffraction
(Scheme 2d and 2e).18 Reaction of complex 1 and stronger
(hard) Lewis base ligands ([PhS]- and [SEt]-) triggers
deprotonation of complex 1 to yield complex 3. However,
the reaction of complex 1 and weaker (soft) Lewis base
ligands ([SePh]-, [Se-p-C6H4-Cl]-, [Cl]-) preferred the
ligand-displacement reaction to produce complexes 4-6.
Complex 6 is soluble in CH2Cl2 and CH3CN-THF (1:3
volume ratio) and is air sensitive. The IR spectrum of
complex 6 displays the νS-H stretching band at 2300
cm-1(KBr) which is ∼150 cm-1 lower than that of the free
Figure 3. ORTEP drawing and labeling scheme of [NiIII(PPh3)(P(o-
C6H4S)3)] (2). Selected bond distances (Å) and angles (deg): Ni-P(1) )
2.1270(10), Ni-P(2) ) 2.2519(10), Ni-S(1) ) 2.2392(11), Ni-S(2) )
2.3010(12), Ni-S(3) ) 2.2564(11), P(1)-Ni-P(2) ) 178.73(4), P(1)-
Ni-S(1) ) 86.36(4), P(2)-Ni-S(1) ) 94.64(4), S(1)-Ni-S(2) ) 117.66(5),
S(1)-Ni-S(3) ) 126.01(5), S(2)-Ni-S(3) ) 114.57(5).
in pure THF or pure CH3CN. The CH2Cl2 solution of com-
plex 3 is air sensitive. The 1H NMR spectrum of complex 3
is consistent with low-spin d8 Ni(II). Complex 2 was regen-
erated upon addition of [Cp2Fe][PF6] to complex 3 in CH3CN
at 0 °C, based on the disappearance of the 801 nm absorption
band (CH2Cl2) and the concomitant formation of 611 and 671
nm absorption bands of complex 2 (Scheme 2c′). Apparently,
complexes 2 and 3 are chemically interconvertible without
decomposition. During the reversible reduction/oxidation of
complexes 2/3, the retention of the coordination number and
geometry of the nickel ion and the prevention of a potential
dimerization from removing the triphenylphosphine ligand
suggest that the one phosphine and three thiolate ligands
coordinated to Ni(III)/Ni(II) may optimize the electronic
structure of the nickel ion to stabilize complexes 2 and 3.
X-ray crystal structures of complexes 2 and 3 are depicted
in Figures 3 and 4, respectively, and selected bond coordi-
nates for complexes 2 and 3 are presented in the figure
captions. Complex 2 is essentially isostructural with complex
3. The geometry of the Ni center is a trigonal bipyramidal
Inorganic Chemistry, Vol. 45, No. 5, 2006 2311

Chen et al.
proton interacting with both Ni(II) and thiolate sulfur to result
in the weaker S-H bond strength. The above results unam-
biguously illustrate one aspect of how a coordinated ligand
functions to promote [Ni-S‚‚‚H-S] interactions (or a
combination of [Ni-S‚‚‚H-S] and [Ni‚‚‚H-S] interactions).
Syntheses of Ni(II)-Thioether Complexes. To further
corroborate the pendant thiol proton interacting with the
sulfur atom (or presumably, both the sulfur and nickel atoms)
in 1a, 1b, and 4-7, where the proton is bound to sulfur and
“attracted” by the second sulfur atom to yield an intramo-
lecular [Ni-S‚‚‚H-S] interaction, the neutral [NiII(PPh3)-
(P(o-C6H4S)2(o-C6H4-SCH3))] (8) complex was synthesized.
As shown in Scheme 2f, treatment of [Me3O][BF4] and
complex 3 in a CH3CN-THF solution (1:3 volume ratio) at
0 °C for 4 h yielded the green solid, [NiII(PPh3)(P(o-C6H4S)2-
(o-C6H4-SCH3))] (8), identified by NMR, UV-vis, and
single-crystal X-ray diffraction. Complex 8 is soluble in THF
and CH2Cl2, but it is insoluble in hexane, CH3CN, and
Figure 5. ORTEP drawing and labeling scheme of the [NiIICl(P(o-C6H4S)2-
(o-C6H4SH))]- anion (6). Selected bond distances (Å) and angles (deg):
Ni-S(1) ) 2.1783(7), Ni-S(3) ) 2.2111(8), Ni-P(1) ) 2.0891(7), Ni-
Cl(1) ) 2.2243(7), S(1)-Ni-S(3) ) 161.36(3), P(1)-Ni-Cl(1) )
170.89(3), S(1)-Ni-Cl(1) ) 91.93(3), S(3)-Ni-Cl(1) ) 95.74(3), C(18)-
P(1)-Ni ) 106.63(9), C(6)-P(1)-Ni ) 110.44(9), C(12)-P(1)-Ni )
116.20(10).
1
MeOH. The H NMR spectrum of complex 8 exhibits the
methyl (CH3) proton resonance at 2.021 ppm, and the 31P
NMR spectrum shows two nonequivalent phosphorus atoms
31P-31
31P-31
P
at 84.423 (d) (J
P ) 649 Hz) and 26.639 ppm (d) (J
) 649 Hz, PPh3) (vs H3PO4) (CDCl3) at room temperature.
Both the 1H NMR and 31P NMR spectra are consistent with
a low-spin d8 Ni(II) complex in a square planar ligand field.
However, the temperature dependence of the 1H NMR
spectrum of complex 8 revealed that the chemical shifts of
the methyl group change from 1.820 ppm at -60 °C to 2.109
ppm at 60 °C (C4D8O) (Supporting Information). On the basis
of the single-crystal X-ray diffraction, two different confor-
mational isomers were isolated. The green crystals of
complex 8a were obtained by diffusion of hexane into the
THF solution of complex 8 at 0 °C. Interestingly, the
diffusion of hexane into the THF solution of complex 8 at
30 °C produced green crystals (complex 8a) and red crystals
which were identified by single-crystal X-ray diffraction as
Table 1. IR νS-H Stretching Frequencies for Complexes 1a, 1b, 4, 5,
6, and 7
complex
ν(S-H), cm-1 (KBr)
L ) PPh3 (1a)
L ) Cl (6)
2393
2300
2288
2283
2273
2240
L ) Se-p-C6H4-Cl (5)
L ) S-C4H3S (7)
L ) SePh (4)
L ) PPh3 (1b)
ligand P(o-C6H4SH)3, and the 1H NMR spectrum of complex
6 shows the downfield chemical shift of the SH group at
5.808 (s) ppm (CDCl3), suggesting the existence of an
intramolecular [Ni-S‚‚‚H-S] interaction (or presumably, a
combination of [NiS‚‚‚H-S] and [Ni‚‚‚H-S] interactions).
Figure 5 displays an ORTEP plot of the anionic mono-
nuclear complex 6, and the selected bond distances and angles
are presented in figure caption. The single-crystal X-ray
structural analysis of complex 6, isostructural with complex
5, reveals that the geometry of Ni(II) in complex 6 is a
distorted square planar with a phosphorus, a chloride and
two trans thiolate ligands. The large C(12)-P(1)-Ni angle
of 116.20(10)° differs from the C(6)-P(1)-Ni and C(18)-
P(1)-Ni angles of 110.44(9)° and 106.63(9)° in complex 6.
The acute (C(12)-S(2)-H(2S)) bond angle of 99.89° and
the similar distances of Ni‚‚‚S(2) (3.642 Å) and S(1)‚‚‚S(2)
(3.698 Å) also suggested that the specific intramolecular
[Ni-S‚‚‚H-S] interaction exists in complex 6.
As shown in Table 1, the IR νS-H stretching frequencies
for complexes 1a, 4, 5, 6, and [NiII(S-C4H3S)(P-(o-C6H4S)2-
(o-C6H4SH))]- (7) reflect the expected changes as the
electron-donating abilities of the monodentate ligands [SePh]-,
[S-C4H3S]-, [Se-p-C6H4-Cl]-, [Cl]-, and PPh3 are varied.18
The IR νS-H stretching frequencies of complexes 1a, 4, 5,
6, and 7 clearly revealed that the stronger electron-donating
monodentate ligands enriched the electronic density of the
Ni(II) and sulfur centers triggering the stronger pendant thiol
1
complex 8b. Each crystal form shows identical H NMR
spectroscopic properties (methyl (CH3) proton resonance at
2.021 ppm) (CDCl3)) when complexes 8a and 8b were
redissolved in CDCl3 at room temperature. Obviously, these
two conformational isomers (8a and 8b) are in equilibrium
with one another via intramolecular rearrangement controlled
by the temperature in solution.
Figure 6 displays ORTEP plots of complexes 8a and 8b,
respectively. The nickel center is best described as existing
in a distorted square planar coordination environment sur-
rounded by two trans thiolate sulfur atoms and two phos-
phorus atoms. The selected bond distances and angles are
given in the caption of Figure 6. The increase in the Ni‚‚‚S(3)
distance of ca. 0.37 Å from complex 8a to 8b has several
consequences. The torsion angles of Ni-P(1)-C(13)-C(18)
are 6.5 and 24.9° in complexes 8a and 8b, respectively. The
C(13)-P(1)-Ni angle of 115.76(11)° differs from the C(1)-
P(1)-Ni and C(7)-P(1)-Ni angles of 110.65(11)° and
107.38(10)° in complex 8b. In contrast, complex 8a shows
similar bond angles, C(7)-P(1)-Ni ) 110.82(11), C(1)-
P(1)-Ni ) 111.19(12), and C(13)-P(1)-Ni ) 111.09(12)°.
The Ni-S(3)-C(19) bond angles of 109° in complex 8a
2312 Inorganic Chemistry, Vol. 45, No. 5, 2006

[NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- Complexes
Figure 6. ORTEP drawing and labeling scheme of [NiII(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] (8a) and [NiII(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] (8b). Selected
bond distances (Å) and angles (deg): complex 8a Ni-S(1) ) 2.2150(11), Ni-S(2) ) 2.2281(10), Ni-P(1) ) 2.1209(10), Ni-P(2) ) 2.2323(10), Ni‚‚‚S(3)
) 2.5397(10), S(1)-Ni-S(2) ) 147.99(4), P(1)-Ni-P(2) ) 177.31(4), S(1)-Ni-P(2) ) 90.01(4), S(2)-Ni-P(2) ) 94.39(4), C(7)-P(1)-Ni ) 110.82(12),
C(1)-P(1)-Ni ) 111.19(12), C(13)-P(1)-Ni ) 111.09(12), C(18)-S(3)-C(19) ) 99.30(19), Ni-S(3)-C(19) ) 109.00(17); complex 8b Ni-S(1) )
2.1828(9), Ni-S(2) ) 2.2044(8), Ni-P(1) ) 2.1160(8), Ni-P(2) ) 2.2343(8), Ni‚‚‚S(3) ) 2.9135(11), S(1)-Ni-S(2) ) 153.42(4), P(1)-Ni-P(2) )
173.33, S(1)-Ni-P(2) ) 93.22(3), S(2)-Ni-P(2) ) 95.55(3), C(1)-P(1)-Ni ) 110.65(11), C(7)-P(1)-Ni ) 107.38(10), C(13)-P(1)-Ni ) 115.76(11),
Ni-S(3)-C(19) ) 158.18(19), C(18)-S(3)-C(19) ) 103.7(2).
Scheme 3
and 158.18° in complex 8b demonstrate that the methyl groups
of these Ni(II) complexes, 8a/8b, do not point directly to the
Ni or S atoms. These results further support that the pendant
thiol proton of the Ni(II)-thiol complexes, 1a/4-7, locates
in the position attracted by both nickel and the sulfur of thio-
late to stabilize the thiol proton. Compared to the Ni‚‚‚S(3)
Figure 7. ORTEP drawing and labeling scheme of the [NiII(SPh)(P(o-
C6H4S)2(o-C6H4-SCH3))]- anion (9). Selected bond distances (Å) and
angles (deg): Ni-S(1) ) 2.1664(7), Ni-S(2) ) 2.2187(7), Ni-P(1) )
2.0998(7), Ni-S(4) ) 2.2322(7), Ni‚‚‚S(3) ) 3.258(7), S(1)-Ni-S(2) )
159.61(3), P(1)-Ni-S(4) ) 176.97(3), S(1)-Ni-S(4) ) 93.79(3), S(2)-
Ni-S(4) ) 91.82(3), C(7)-P(1)-Ni ) 106.73(9), C(1)-P(1)-Ni )
110.53(9), C(13)-P(1)-Ni ) 119.48(9), C(18)-S(3)-C(19) ) 100.66(15),
Ni-S(3)-C(19) ) 102.47(15).
complexes 9 and 10 are consistent with the diamagnetic d8
square planar Ni(II) complexes, and the chemical shifts at
2.528 (s) and 2.553 (s) ppm (CDCl3) were assigned to the
methyl groups of complexes 9 and 10, respectively. Presum-
ably, there is no interaction between Ni(II) and the thioether
sulfur atom (Ni‚‚‚S(3) distance of 3.258(7) and 3.229 (5) Å
in complexes 9 and 10, respectively); therefore, the absence
of electron back-donation of Ni(II) to the π-accepting
thioether sulfur may explain the downfield chemical shift
of the methyl groups in complexes 9 and 10, as compared
to complexes 8a and 8b.
distances of 3.802 and 3.248 Å observed in complexes 1a
and 1b (Scheme 1), the single-crystal X-ray structure reveal-
ed that a thioether sulfur semibonding to Ni(II) (Ni‚‚‚S(3)
distances of 2.5397 Å) may exist in complex 8a, and there
is no interaction between Ni and S(3) (Ni‚‚‚S(3) distances
of 2.9135 Å) in complex 8b. The electron back-donation of
Ni(II) to the π-accepting thioether sulfur may be adopted to
rationalize the upfield chemical shift of the methyl group in
complex 8a (green crystals obtained at 0 °C or lower),20 as
compared to complex 8b (red crystals obtained at 30 °C).
In contrast to the temperature-dependent interconversion
of the conformational isomers 8a and 8b, the temperature-
independent four-coordinated Ni(II)-thioether complexes
[NiII(L)(P(o-C6H4S)2(o-C6H4-SCH3))]- (L ) SPh (9), SePh
(10)) were isolated when complex 8 was reacted with [SPh]-/
[SePh]- in THF at room temperature overnight, respectively
(Scheme 3). The red brown complexes 9 and 10 are soluble
1
in THF, CH2Cl2, and CH3CN. The H NMR spectra of
Figures 7 shows the thermal ellipsoid plot of the anionic
complex 9, and the selected bond distances and angles of
complex 9 are given in the figures caption, respectively.
Complexes 9 and 10 are isostructural Ni(II) complexes with
the monodentate thiolate/selenolate ligands. The Ni‚‚‚S(thioether)
distances of 3.258(7) and 3.229 (5) Å found in complexes 9
(20) (a) Ashby, M. T.; Enemark, J. H.; Lichtenberger, D. L. Inorg. Chem.
1988, 27, 191-197. (b) Jacobsen, H.; Kraatz, H.-B.; Ziegler, T.;
Booran, P. M. J. Am. Chem. Soc. 1992, 114, 7851-7860. (c) Kraatz,
H.-B.; Jacobsen, H.; Ziegler, T.; Boorman, P. M. Organometallics
1993, 12, 76-80. (d) McGuire, D. G.; Khan, M. A.; Ashby, M. T.
Inorg. Chem. 2002, 41, 2202-2208.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2313

Chen et al.
and 10, respectively, indicated that no interaction exists
between Ni(II) and the thioether sulfur atom (Supplementary
information).
(3) The extent of the intramolecular [Ni-S‚‚‚H-S]
interaction (or a combination of intramolecular [Ni-S‚‚‚H-
S] and [Ni‚‚‚H-S] interactions) was modulated by the dis-
tinct monodentate ligands PPh3, [Se-p-C6H4-Cl]-, [S-C4H3S]-,
[Cl]-, and [SePh]- in complexes 1a and 4-7. The IR νS-H
stretching frequency reflects that an increase in the Ni
basicity (electronic density) regulated by the monodentate
ligand arrests the proton of the pendant thiol effectively and
causes the weaker S-H bond.
(4) Compared to the Ni‚‚‚S(3) distances of 3.802 and 3.248
Å observed in complexes 1a and 1b (Scheme 1), the single-
crystal X-ray structure revealed that thioether sulfur semi-
bonding to Ni(II) (Ni‚‚‚S(3) distance of 2.5397 Å) may exist
in complex 8a and that there is no interaction between Ni
and S(3) (Ni‚‚‚S(3) distance of 2.9135 Å) in complex 8b.
On the basis of the 1H NMR spectra and single-crystal X-ray
diffractions, the intramolecular interaction between NiII and
the thioether sulfur atom became weaker when the temper-
ature is increased or the more electron-donating monodentate
ligand is ligated to the NiII center as observed in the
mononuclear NiII-thioether complexes 8a, 8b, 9, and 10.
Obviously, increasing the electron density on Ni should have
the opposite effect on the interaction with RSH and RSR′.
Increasing the electron density on Ni favors the interaction
with S-H (Ni acts as a hydrogen-bond acceptor) and
disfavors the interaction with S in SRS′ (RSR′ is an electron
pair donor).
(5) Complexes 1 and 4-7 are sensitive toward O2 to
yield mononuclear Ni(III) thiolate complexes [NiIII(L)(P(o-
C6H4S)3)]0/1- (L ) PPh3 (2), Se-p-C6H4-Cl (11), SePh (12),
S-C4H3S (13)).18 [NiII(L′)(P(o-C6H4S)2(o-C6H4-SH))]0/1-
(L′ ) Se-p-C6H4-Cl, SePh, S-C4H3S) and [NiII(L′)(P(o-
C6H4S)2(o-C6H4-SH))]0/1-, with the monodentate selenolate/
thiolate ligands L′, show more O2 sensitivity than complex
1. It is presumed that the stronger intramolecular [Ni-
S‚‚‚H-S] interaction found in the [NiII(L′)(P(o-C6H4S)2(o-
C6H4-SH))]0/1- complexes led to the weaker S-H bond
strength and accelerated the oxidation of the [NiII(L′)(P(o-
C6H4S)2(o-C6H4-SH))]0/1- complexes to produce complexes
11-13.18 A detailed study is underway. The isolation of
complexes 1a and 1b-10 may support the proposed proton-
bonding type of the active site of the Ni-R and Ni-SI states
in the catalytic cycle of [NiFe] hydrogenases.
Conclusion and Comments
Studies on the mononuclear Ni(II)-thiol complexes (1,
4-7), Ni(III, II)-thiolate complexes (2, 3), and Ni(II)-
thioether complexes (8a, 8b, 9, 10) have produced the
following results.
(1) Neutral NiII-thiol complex 1 was synthesized and
1
characterized by IR, H NMR, UV-vis, and single-crystal
X-ray diffraction. Complex 1 serves as a precursor for the
syntheses of the anionic mononuclear NiII-thiol complexes
4-7 via a ligand-displacement reaction. On the basis of 2H
NMR and IR νS-D studies, the pendant thiol proton of
complexes 1/4-7 is D2O exchangeable.
(2) In complexes 1a, 1b, and 4-7, the presence (strength)
of the intramolecular [Ni-S‚‚‚H-S] interaction (or a com-
bination of intramolecular [Ni-S‚‚‚H-S] and [Ni‚‚‚H-S]
interactions) was verified in the solid state by the observation
of a lower IR νS-H stretching frequency compared to that of
the free ligand P(o-C6H4SH)3 (Table 1)18 and was subse-
quently confirmed by a single-crystal X-ray diffraction.
Single-crystal X-ray diffraction studies reveal that the
Ni‚‚‚S(1) distance falls into the range of 3.609-3.802 Å in
Ni(II)-thiol complexes 1a and 4-7 (type A), compared to
those of 2.540 and 2.914 Å in the Ni(II)-thioether complexes
8a and 8b (type C). In contrast, the long Ni‚‚‚S(1) distances
(3.258 and 3.229 Å) found in complexes 9 and 10 indicated
the absence of interaction between the Ni and S(1) atoms
(type D). These results rule out the existence of an intramo-
lecular Ni‚‚‚S(1) interaction (Ni‚‚‚S(1) distance of 3.609-
3.802 Å) in complexes 1a/4-7 (type B) and may support
the idea that the pendant thiol protons of Ni(II)-thiol
complexes 1/4-7 were attracted by both nickel and the sulfur
of thiolate, resulting in combinations of intramolecular [Ni-
S‚‚‚H-S] and [Ni‚‚‚H-S] interactions (type A).
Experimental Section
Manipulations, reactions, and transfers were conducted under
nitrogen according to Schlenk techniques or in a glovebox (argon
gas). Solvents were distilled under nitrogen from appropriate drying
agents (diethyl ether from CaH2; acetonitrile from CaH2-P2O5;
methylene chloride from CaH2; hexane and tetrahydrofuran (THF)
from sodium benzophenone) and stored in dried, N2-filled flasks
over 4 Å molecular sieves. Nitrogen was purged through these
solvents before use. Solvent was transferred to the reaction vessel
via stainless cannula under positive pressure of N2. The reagents
bis(triphenylphosphoranylidene)ammonium chloride ([PPN][Cl])
(Fluka), diphenyl diselenide, bis(4-chlorophenyl) diselenide, di(2-
thienyl) disulfide, (triphenylphosphine) nickel(II) dichloride, and
deuterium oxide, 99.9 atom % D (Aldrich) were used as received.
Compound tris(2-thiophenyl)phosphine (P-(o-C6H4SH)3) was syn-
2314 Inorganic Chemistry, Vol. 45, No. 5, 2006

[NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- Complexes
thesized by published procedures.19 Infrared spectra of the ν(SH)
stretching frequencies were recorded on a Perkin Elmer model
Spectrum One B spectrophotometer with sealed solution cells (0.1
mm, KBr windows) or KBr solid. UV-vis spectra were recorded
spectrum (CH2Cl2) [λmax, nm (ꢀ, M-1 cm-1)]: 801 (533).
C72H57NP4S3Ni: C, 71.17; H, 4.73; N, 1.15. Found: C, 70.54; H,
4.93; N, 1.64.
Protonation of Complex 3 by HClO4. HClO4 (28 µL, 0.2 mmol)
was added dropwise to complex 3 (0.243 g, 0.2 mmol) in THF (5
mL) at 0 °C under a N2 atmosphere. The reaction mixture was
stirred for 30 min and then filtered through Celite to remove
[PPN][ClO4]. Hexane (10 mL) was added to precipitate the red
solid, identified as complex 1 (0.076 g, 56%) by FTIR, UV-vis,
1
2
on a GBC Cintra 10e. H and H NMR spectra were obtained on
a Varian Unity-500 spectrometer. Electrochemical measurements
were performed with a CHI model 421 potentionstat (CH Instru-
ment). Cyclic voltammograms were obtained from a 2.0 mM analyte
concentration in CH2Cl2 using 0.1 M [n-Bu4N][PF6] as a supporting
electrolyte. Potentials were measured at 298 K versus a Ag/AgCl
reference electrode using a glassy carbon working electrode. Under
the conditions employed, the potential (V) of the ferrocinium/
ferrocene couple was 0.39 (CH2Cl2). Analyses of carbon, hydrogen,
and nitrogen were obtained with a CHN analyzer (Heraeus).
Preparation of [NiII(PPh3)(P(o-C6H4S)2(o-C6H4SH))] (1). NiCl2-
(PPh3)2 (0.195 g, 0.3 mmol) and P(o-C6H4SH)3 (0.108 g, 0.3 mmol)
were dissolved in 5 mL of THF and stirred at ambient temperature
for 20 min. Hexane (20 mL) was then added to precipitate the red
solid [NiII(PPh3)(P(o-C6H4S)2(o-C6H4SH))] (1) (yield 0.160 g, 79%).
Diffusion of hexane into the THF solution of complex 1 at room
temperature for 5 days led to red-brown needle crystals identified
by single-crystal X-ray diffraction as complex 1a. In contrast,
diffusion of hexane into the CH2Cl2 solution of complex 1 afforded
dark red crystals characterized by single-crystal diffraction as
complex 1b. IR (KBr): complex 1a 2393 (νSH) cm-1; complex 1b
1
and H NMR spectra.
Reaction of Complex 3 and [Cp2Fe][PF6]. [Cp2Fe][PF6] (0.067
g, 0.2 mmol) dissolved in CH3CN (5 mL) was added dropwise to
the THF-CH3CN (3:1 volume ratio) solution of complex 3 at 0
°C under a N2 atmosphere. After the mixture was stirred for 30
min, it was dried under vacuum to produce a green-yellow solid,
and then the green-yellow solid was redissolved in THF (5 mL).
The THF solution was then filtered through Celite to remove
[PPN][PF6], and diethyl ether (20 mL) was added to precipitate
the green solid. The green solid was washed twice with 20 mL
diethyl ether and dried under vacuum to yield complex 2 (0.061 g,
1
45%) characterized by UV-vis and H NMR spectra.
Reaction of Complex 1 and [PPN][SePh]/[PPN][Se-p-C6H4-
Cl]. Complex 1 (0.067 g, 0.1 mmol) and [PPN][SePh] (0.069 g,
0.1 mmol) (or [PPN][Se-p-C6H4-Cl] (0.073 g, 0.1 mmol)) were
dissolved in THF (4 mL) and stirred overnight under nitrogen at
ambient temperature. Diethyl ether (10 mL) was then added to
precipitate the red-brown solid, identified as [PPN][NiII(SePh)P-
((o-C6H4S)2(o-C6H4SH))] (4) (0.071 g, 61%) and [PPN][NiII(Se-
C6H4-p-Cl)(P(o-C6H4S)2(o-C6H4SH))] (5) (0.080 g, 70%) by FTIR,
1
2240 (νSH) cm-1. H NMR (CDCl3): δ 5.908 (s) (SH), 6.992 (s),
7.180 (t), 7.297-7.421 (m), 7.708 (t). 31P NMR (CDCl3): δ 76.57
31P-31 31P-31
(d) (J P ) 695 Hz, (P-(o-C6H4S)2(o-C6H4SH)), 24.65 (d) (J
P
) 695 Hz, PPh3) (vs H3PO4). Absorption spectrum (CH2Cl2) [λmax
,
nm (ꢀ, M-1 cm-1)]: 606 (181). Anal. Calcd for C36H28P2S3Ni: C,
63.83; H, 4.17. Found: C, 63.51; H, 3.73.
1
UV-vis, H NMR spectra, and single-crystal X-ray diffraction.18
1
Complex 5. IR (KBr): 2283 (νSH) cm-1. H NMR (C4H8O): δ
Preparation of [NiIII(PPh3)(P(o-C6H4S)3)] (2). Dry oxygen gas
(9 mL) was purged into a red THF solution (7 mL) of complex 1
(0.203 g, 0.3 mmol) at 0 °C. The reaction solution was stirred at 0
°C for an additional 30 min, and a significant change in color of
the reaction solution from red to deep green was observed. Hexane
(25 mL) was then added to precipitate the dark green solid
[NiIII(PPh3)(P(o-C6H4S)3)] (2) (yield 0.155 g, 76%). Diffusion of
hexane into a CH2Cl2 solution of complex 2 at -15 °C for three
weeks led to dark green crystals suitable for X-ray crystallography.
1H NMR (CDCl3): δ -3.99 (br), 5.48 (br), 8.42 (br), 9.70 (br),
11.82 (br), 12.62 (br), 13.67 (br). Absorption spectrum (CH2Cl2)
[λmax, nm (ꢀ, M-1 cm-1)]: 611 (1777), 671 (1596), 1150 (1031).
Anal. Calcd for C36H27P2S3Ni: C, 63.92; H, 4.02. Found: C, 63.71;
H, 3.61.
Preparation of [PPN][NiII(PPh3)(P(o-C6H4S)3)] (3). Method
A. [PPN][SPh] (0.323 g, 0.5 mmol) dissolved in CH3CN (5 mL)
was added to a stirred solution of complex 1 (0.339 g, 0.5 mmol)
in THF (5 mL) under N2 at ambient temperature. The reaction
mixture was stirred for 3 h, and diethyl ether (25 mL) was added
to precipitate the orange solid. The orange solid was dried under
vacuum to give [PPN][NiII(PPh3)(P(o-C6H4S)3)] (3). Yield: 0.384
g, 63%.
Method B. A solution containing complex 2 (0.338 g, 0.5 mmol)
and [PPN][SEt] (0.300 g, 0.5 mmol) in THF-CH3CN (volume ratio
5:5 mL) was stirred at ambient temperature under N2 for 3 h. Diethyl
ether (25 mL) was then added to precipitate the orange solid. After
the orange solid was dried under vacuum, complex 3 was isolated.
Yield: 0.330 g, 54%. Red-orange crystals suitable for X-ray
diffraction analysis were obtained by the diffusion of diethyl ether
into a THF-CH3CN (3:1 volume ratio) solution of complex 3 at 0
°C for one week. 1H NMR (CD3CN): δ 6.748 (t), 6.925 (t), 7.270-
7.481 (m), 7.539-7.580 (m), 7.648 (t), 7.777 (t). Absorption
8.39 (d) (S-H). Absorption spectrum (CH2Cl2) [λmax, nm (ꢀ, M-1
cm-1)]: 440 (4320). Anal. Calcd for C58H46NP3S5Ni: C, 65.17;
H, 4.34; N, 1.31. Found: C, 65.04; H, 4.46; N, 1.01.
D/H Exchange for Reaction of Complexes 1/5 and D2O. A
100-fold excess of D2O (0.8 mL, 40 mmol) was added to a THF
solution of complex 1 (THF-CH3CN solution, 3:1 mL, volume
ratio) or complex 5 (0.458 g, 0.4 mmol)) at 0 °C. The reaction
solution containing complex 1 (or complex 5) and D2O was stirred
for 30 min at 0 °C. Diethyl ether (3 mL) was then added to layer
above the mixture. The flask was tightly sealed and kept in the
refrigerator at -15 °C for one week. Red-brown crystals [NiII(PPh3)-
(P(o-C6H4S)2(o-C6H4SD))] (1-D) were isolated. Yield: 0.155 g,
77%. IR (KBr): 1752 (νSD) cm-1. 2H NMR (CDCl3): δ 6.175 (br)
(SD) (using the natural abundance of D in C4H8O solvent, two
singlet peaks at 1.73 and 3.57 ppm, as the internal standard). Red-
brown crystals of [PPN][Ni(Se-p-C6H4-Cl)(P(o-C6H4S)2(o-C6H4-
SD))] (5-D) were isolated (0.398 g, 86.9%). IR (KBr): 1676 (νSD
cm-1 2H NMR (CH2Cl2): δ 7.833 (br) (vs CHDCl2, natural
abundance of D in CH2Cl2 solvent, 5.32 ppm).
)
.
Preparation of [PPN][NiIICl(P(o-C6H4S)2(o-C6H4SH))] (6).
Complex 1 (0.068 g, 0.1 mmol) and [PPN][Cl] (0.057 g, 0.1 mmol)
were loaded into a 20 mL Schlenk tube. After THF (3 mL) was
added to give a red solution, the solution mixture was stirred at
ambient temperature overnight. Diethyl ether (12 mL) was then
added to precipitate the red-brown solid, [PPN][NiIICl(P(o-C6H4S)2-
(o-C6H4SH))] (6). Yield: 0.068 g, 69%. Red-brown crystals suitable
for X-ray crystallography were obtained by the diffusion of diethyl
ether into a THF-CH3CN (3:1 volume ratio) solution of complex
1
6 at 0 °C for one week. IR (KBr): 2300 (νSH) cm-1. H NMR
(CDCl3): δ 5.808 (s) (SH), 6.818 (t), 6.905 (t), 7.025 (t), 7.188-
7.298 (m), 7.403-7.488 (m), 7.637-7.666 (t). Absorption spectrum
(CH2Cl2) [λmax, nm (ꢀ, M-1 cm-1)]: 605 (453), 876 (137). Anal.
Inorganic Chemistry, Vol. 45, No. 5, 2006 2315

Chen et al.
Calcd for C54H43P3S3ClNNi: C, 65.57; H, 4.38; N, 1.42. Found:
C, 64.80; H, 4.38; N, 1.19.
Magnetic Measurements. The magnetization data were recorded
on a SQUID magnetometer (MPMS5 Quantum Design company)
with an external 1 T magnetic field for complex 2 in the temperature
range of 2-300 K. The magnetic susceptibility of the experimental
data was corrected for diamagnetism by the tabulated Pascal’s
constants.
Preparation of [NiII(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] (8).
A CH3CN solution (3 mL) containing [Me3O][BF4] (0.030 g, 0.2
mmol) was added dropwise to the THF-CH3CN (3:1 volume ratio)
solution of complex 3 at 0 °C under a N2 atmosphere. After the
mixture was stirred for 1 h, the volume of the reaction mixture
was reduced under vacuum, and then methanol (10 mL) was added
to precipitate the green solid. The green solid was washed twice
with another 10 mL of methanol and dried under vacuum to produce
green solid [NiII(PPh3)(P(o-C6H4S)2(o-C6H4-SCH3))] (8). Yield:
0.162 g, 78%. Diffusion of hexane into a THF solution of complex
8 at 0 °C for three weeks led to dark green crystals characterized
by X-ray crystallography as complex 8a. However, diffusion of
hexane into a THF solution of complex 8 at 30 °C for one week
yielded dark green crystals (complex 8a) and some red crystals
which were characterized by single-crystal X-ray diffraction as
complex 8b. The X-ray diffraction analyses revealed the subtle
Crystallography. The crystals chosen for the X-ray diffraction
studies measured 0.40 × 0.35 × 0.20 mm for complex 1a, 0.40 ×
0.30 × 0.30 mm for complex 1b, 0.25 × 0.20 × 0.10 mm for
complex 2, 0.32 × 0.20 × 0.20 mm for complex 3, 0.50 × 0.45×
0.40 mm for complex 5, 0.20 × 0.15 × 0.15 mm for complex 6,
0.35 × 0.33 × 0.15 mm for complex 8a, 0.30 × 0.15 × 0.15 mm
for complex 8b, 0.4 × 0.32 × 0.27 mm for complex 9, and 0.30 ×
0.25 × 0.25 mm for complex 10. Each crystal was mounted on a
glass fiber and quickly coated in epoxy resin. Unit-cell parameters
were obtained by least-squares refinement. Diffraction measure-
ments for complexes 1a, 1b, 2, 3, 5, 6, 8a, 8b, 9, and 10 were
carried out on a SMART CCD (Nonius Kappa CCD) diffractometer
with graphite-monochromated Mo KR radiation (λ ) 0.7107 Å)
between 2.07 and 27.50° for complex 1a, 1.45 and 27.50° for
complex 1b, 1.35 and 27.50° for complex 2, 1.33 and 27.50° for
complex 3, 1.24 and 27.50° for complex 5, 1.26 and 27.50° for
complex 6, 1.25 and 27.50° for complex 8a, 1.48 and 27.50° for
complex 8b, 1.23 and 27.50° for complex 9, and 1.23 and 28.31°
for complex 10. Least-squares refinement of the positional and
anisotropic thermal parameters of all non-hydrogen atoms and fixed
hydrogen atoms (H(3A) in complex 1 and H(2S) in complex 6)
was based on F2. A SADABS absorption correction was made.21
The SHELXTL structure refinement program was employed.22
1
differences between the red and green crystals. H NMR (25 °C)
(CDCl3): δ 2.012 (s) (S-CH3), 6.914 (t), 7.072 (t), 7.230-7.441
1
(m), 7.596-7.659 (m), 7.735-7.772 (m). VT H NMR (C4D8O):
δ 1.820 (-60 °C), ∼2.109 (60 °C) (s) (S-CH3). Absorption spectrum
(CH2Cl2) [λmax, nm (ꢀ, M-1 cm-1)]: 393 (3367), 609 (374). Anal.
Calcd for C37H30P2S3Ni: C, 64.27; H, 4.37. Found: C, 64.56; H,
4.93.
Preparation of [PPN][NiII(L)(P(o-C6H4S)2(o-C6H4-SCH3))] (L
) SPh (9), SePh (10)). Complex 8 (0.1 mmol, 0.069 g) and [PPN]-
[SPh] (0.1 mmol, 0.065 g) (or [PPN][SePh], 0.1 mmol, 0.070 g)
were loaded into a 20 mL Schlenk tube, and then 5 mL of THF
was added to the tube via cannula under a positive pressure of
nitrogen. After the reaction mixture was stirred overnight under
N2 at room temperature, the green solution completely converted
into a red-brown solution. Hexane (10 mL) was then added to
precipitate the red-brown solid. The red-brown solid was washed
twice with 10 mL of diethyl ether and dried under vacuum to afford
[PPN][NiII(SPh)(P(o-C6H4S)2(o-C6H4-SCH3))] (9) (0.074 g, 68%)
(or [PPN][NiII(SePh)(P(o-C6H4S)2(o-C6H4-SCH3))] (10), 0.088 g,
78%). Suitable red crystals of complexes 9 and 10 for single-crystal
X-ray diffraction were obtained by diffusion of diethyl ether into
the THF solution of complexes 9 and 10, respectively. Complex 9.
1H NMR (CDCl3): δ 2.553 (s) (SCH3), 6.684 (t), 6.750 (t), 6.862-
6.904 (m), 6.990 (t), 7.194-7.454 (m), 7.587-7.619 (m), 7.708-
7.725 (m). Absorption spectrum (CH2Cl2) [λmax, nm (ꢀ, M-1 cm-1)]:
445 (2015). Anal. Calcd for C61H50NP3S4Ni: C, 68.03; H, 4.68;
N, 1.30. Found: C, 68.03; H, 4.44; N, 1.29. Complex 10. 1H NMR
(CDCl3): δ 2.528 (s) (SCH3), 6.684 (t), 6.843-6.900 (m), 6.992
(t), 7.182-7.453 (m), 7.584-7.616 (m), 7.837-7.856 (m). Absorp-
tion spectrum (CH2Cl2) [λmax, nm (ꢀ, M-1 cm-1)]: 478 (1816). Anal.
Calcd for C61H50NNiP3S3Se: C, 65.19; H, 4.48; N, 1.25. Found:
C, 64.55; H, 5.02; N, 0.95.
Acknowledgment. We gratefully acknowledge financial
support from the National Science Council (Taiwan).
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determinations of [NiII(PPh3)(P-(o-
C6H4S)2(o-C6H4SH))], [NiIII(PPh3)(P(o-C6H4S)3)], [PPN][NiII(PPh3)-
(P(o-C6H4S)3)], [PPN][Ni(Se-p-C6H4-Cl)(P(o-C6H4S)2(o-C6H4SH))],
[PPN][Ni(Cl)P((o-C6H4S)2(o-C6H4SH))], [NiII(PPh3)(P(o-C6H4S)2-
(o-C6H4-SCH3))], [PPN][NiII(SPh)(P(o-C6H4S)2(o-C6H4-SCH3))],
and [PPN][NiII(SePh)(P(o-C6H4S)2(o-C6H4-SCH3))] and figures
1
showing H NMR spectra of 8 and an ORTEP drawing of 10.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC051924W
(21) Sheldrick, G. M. SADABS, Siemens Area Detector Absorption Cor-
rection Program; University of Go¨ttingen: Go¨ttingen, Germany, 1996.
(22) Sheldrick, G. M. SHELXTL, Program for Crystal Structure Determi-
nation; Siemens Analytical X-ray Instruments Inc.: Madison, WI,
1994.
2316 Inorganic Chemistry, Vol. 45, No. 5, 2006