Mononuclear Ni(III) complexes [NiIII(L)(P(C6H 3-3-SiMe3-2-S)3)]0/1- (L = thiolate, selenolate, CH2CN, Cl, PPh3): Relevance to the nickel site of [NiFe] hydrogenases

Article abstract of DOI:10.1021/ic061399g

The stable mononuclear Ni(III)-thiolate complexes [Ni^III(L) (P(C₆H₃-3-SiMe₃-2-S)₃)]^- (L = SePh (2), Cl (3), SEt (4), 2-S-C₄H₃S (5), CH ₂CN (7)) were isolated and characterized by UV-vis, EPR, IR, SQUID, CV, ¹H NMR, and single-crystal X-ray diffraction. The increased basicity (electronic density) of the nickel center of complexes [Ni ^III(L)-(P(C₆H₃-3-SiMe₃-2-S) ₃)]^- modulated by the monodentate ligand L and the substituted groups of the phenylthiolate rings promotes the stability and reactivity. In contrast to the irreversible reduction at -1.17 V (vs Cp ₂Fe/Cp₂Fe⁺) for complex 3, the cyclic voltammograms of complexes [Ni^III(SePh)(P(o-C₆H ₄S)₃)]^-, 2, 4, and 7 display reversible Ni ^III/II redox processes with E_1/2 = -1.20, -1.26, -1.32, and -1.34 V (vs Cp₂Fe/Cp₂Fe⁺), respectively. Compared to complex 2 containing a phenylselenolate-coordinated ligand, complex 4 with a stronger electron-donating ethylthiolate coordinated to the Ni(III) promotes dechlorination of CH₂Cl₂ to yield complex 3 (k_obs = (6.01 ± 0.03) × 10^-4 s^-1 for conversion of complex 4 into 3 vs k_obs = (4.78 ± 0.02) × 10^-5 s^-1 for conversion of complex 2 into 3). Interestingly, addition of CH₃CN into complex 3 in the presence of sodium hydride yielded the stable Ni(III)-cyanomethanide complex 7 with a Ni^III-CH₂CN bond distance of 2.037(3) A. The Ni ^III-SEt bond length of 2.273(1) A in complex 4 is at the upper end of the 2.12-2.28 A range for the Ni^III-S bond lengths of the oxidized-form [NiFe] hydrogenases. In contrast to the inertness of complexes 3 and 7 under CO atmosphere, carbon monoxide triggers the reductive elimination of the monodentate chalcogenolate ligand of complexes 2, 4, and 5 to produce the trigonal bipyramidal complex [Ni^II(CO)(P(C₆H ₃-3-SiMe₃-2-S)₃)]- (6).

Full text of DOI:10.1021/ic061399g

Inorg. Chem. 2006, 45, 10895−10904
/1-
Mononuclear Ni(III) Complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0
(L )
Thiolate, Selenolate, CH2CN, Cl, PPh3): Relevance to the Nickel Site of
[NiFe] Hydrogenases
Chien-Ming Lee,† Ya-Lan Chuang,† Chao-Yi Chiang,† 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 July 26, 2006
The stable mononuclear Ni(III)
−
thiolate complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]- (L
)
SePh (2), Cl (3), SEt (4),
1
2-S-C4H3S (5), CH2CN (7)) were isolated and characterized by UV
−vis, EPR, IR, SQUID, CV, H NMR, and single-
crystal X-ray diffraction. The increased basicity (electronic density) of the nickel center of complexes [NiIII(L)-
(P(C6H3-3-SiMe3-2-S)3)]- modulated by the monodentate ligand L and the substituted groups of the phenylthiolate
rings promotes the stability and reactivity. In contrast to the irreversible reduction at
complex 3, the cyclic voltammograms of complexes [NiIII(SePh)(P(o-C6H4S)3)]-, 2, 4, and 7 display reversible NiIII
redox processes with E1 ) −1.20, 1.26, 1.32, and
1.34 V (vs Cp2Fe/Cp2Fe+), respectively. Compared to
−
1.17 V (vs Cp2Fe/Cp2Fe+) for
/
II
−
−
−
/
2
complex 2 containing a phenylselenolate-coordinated ligand, complex 4 with a stronger electron-donating ethylthiolate
4
1
coordinated to the Ni(III) promotes dechlorination of CH2Cl2 to yield complex 3 (kobs
)
(6.01
±
0.03)
×
10- s-
5
1
for conversion of complex 4 into 3 vs kobs
Interestingly, addition of CH3CN into complex 3 in the presence of sodium hydride yielded the stable Ni(III)
cyanomethanide complex 7 with a NiIII CH2CN bond distance of 2.037(3) Å. The NiIII
SEt bond length of 2.273(1)
Å in complex 4 is at the upper end of the 2.12 S bond lengths of the oxidized-form
2.28 Å range for the NiIII
) (4.78 ± 0.02) ×
10- s- for conversion of complex 2 into 3).
−
−
−
−
−
[NiFe] hydrogenases. In contrast to the inertness of complexes 3 and 7 under CO atmosphere, carbon monoxide
triggers the reductive elimination of the monodentate chalcogenolate ligand of complexes 2, 4, and 5 to produce
the trigonal bipyramidal complex [NiII(CO)(P(C6H3-3-SiMe3-2-S)3)]- (6).
Introduction
have revealed an active site comprised of a hetero-bimetallic
-
(Scys)2Ni(µ-Scys)2(µ-X)Fe(CO)(CN)2 (X ) O2-, HO2 , OH-)
Hydrogenases catalyze the reversible two-electron oxida-
tion of H2 in aerobic and anaerobic micro-organisms.1 Two
classes of hydrogenases, [Fe]-only hydrogenases ([Fe]-only
H2ases) and [NiFe] hydrogenases ([NiFe] H2ases), have been
studied widely.1,2 The X-ray crystallographic studies of the
active-site structure of [NiFe] hydrogenases isolated from
D. gigas, D. Vulgaris, D. fructosoVorans, and D. desulfuri-
cans ATCC27774 in combination with infrared spectroscopy
cluster.3-6 The bridging ligand X was proposed to be an
oxide, hydroxide, or hydro-peroxide in the oxidized state and
was found to be absent in the reduced state. The coordination
(2) (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. (e) Volbeda, A.; Martin, L.; Cavazza,
C.; Matho, M.; Faber, B. W.; Roseboom, W.; Albracht, S. P. J.; Garcin,
E.; Rousset, M.; Fontecilla-Camps, J. C. J. Biol. Inorg. Chem. 2005,
10, 239-249.
* To whom correspondence should be addressed. E-mail: wfliaw@
mx.nthu.edu.tw.
† National Tsing Hua University.
‡ National Taiwan University.
(1) (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) Adams, M. W. W.; Stiefel,
E. I. Curr. Opin. Chem. Biol. 2000, 4, 214-220. (d) 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. (e) Whitehead,
J. P.; Gurbiel, R. J.; Bagyinka, C.; Hoffman, B. M.; Maroney, M. J.
J. Am. Chem. Soc. 1993, 115, 5629-5635.
(3) (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. (e) Ogata, H.; Hirota, S.; Nakahara,
A.; Komori, H.; Shibata, N.; Kato, T.; Kano, K.; Higuchi, Y. Structure
2005, 13, 1635-1642.
10.1021/ic061399g CCC: $33.50
Published on Web 12/06/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 26, 2006 10895

Lee et al.
environment about nickel in the [NiFe] H2ases is pseudo-
tetrahedral in the reduced state and pseudo-square pyramidal
in the oxidized state. The nickel site has been proposed to
be redox-active and changes between Ni(III) and Ni(II), while
the iron site remains as Fe(II) in all spectrally defined redox
states of the enzyme.3-8 The EXAFS/EPR studies indicate
that the formal oxidation state of the Ni center is paramag-
netic Ni(III) in Ni-A, Ni-B, and Ni-C states.1-9 Actually,
the active form Ni-C (the paramagnetic Ni-C intermediate)
of [NiFe] H2ase was proposed to exist as the [(Scys-H)NiIII-
H-Fe] intermediates after an active state Ni-SIa (silent-
active [(Scys-H)NiII(Scys)3]) is passed. Ni-C is believed to
be an intermediate in the catalytic cycle.1-9 Upon illumina-
tion, the Ni-C state is transformed into a fourth paramag-
netic Ni-L state. These conversions are considered to
correspond to photodissociation of proton species from the
[Ni-Fe] center.3d Interestingly, the recent X-ray crystal
structures of CO-inhibited forms and single-crystal EPR
studies of the reduced active site of [NiFe] H2ase isolated
from D. Vulgaris Miyazaki F implicate that the Ni-C
intermediate is a formal Ni(III) oxidation state with a hydride
(H-) bridging between the Ni and the Fe atoms and the sulfur
atom of Cys 546 hydrogenated for the catalytic reaction of
the enzyme.3c Meanwhile, the Ni-C state subsequently
transformed into Ni-CO forms under an exogenous CO
atmosphere.3c
reaction pathways were proposed as involving steps of protic
oxidative addition to Ni(I) to generate NiIII-H-, and electron
transfer to Ni(III) accompanied by protonation of bound
hydride or the bimolecular reaction (2NiIII-H- f 2NiII +
H2) to yield H2.10c,d Complex NiII(BmMe)2 (BmMe ) bis(2-
mercapto-1-methylimidazolyl)borate) with a [NiS4H2] core
and the presence of Ni‚‚‚H - B interaction may provide a
structural model of the nickel site of [NiFe] H2ase.12
Recently, Tatsumi and co-workers reported the isolation of
dithiolato-bridged [Fe(CO)2(CN)2(µ-SCH2CH2CH2S)Ni(S2-
CNR2)]- (R ) Et; R2 ) -(CH2)5-) complexes, displaying
the closely structural feature of the active site of reduced
form [NiFe] H2ase.13
In the previous study of complexes [NiII(L)(P-(o-C6H4S)2-
(o-C6H4SH))]0/1- (L ) PPh3, SePh, SPh, and Cl), the
interaction between the pendent thiol proton and both the
nickel and sulfur atoms (a combination of intramolecular
[Ni-S‚‚‚H-S] and [Ni‚‚‚H-S] interactions) was demon-
strated.14 The extent of interactions between the pendent thiol
proton and both the nickel and sulfur atoms in complexes
[NiII(L)(P-(o-C6H4S)2(o-C6H4SH))]0/1- was modulated by the
monodentate ligand L. Examples of thiolate coordination to
nickel(III) and the spectroscopic signals of nickel(III)-
thiolate complexes are of much interest, particularly in
catalytically active site construction (Ni-A/Ni-B states) of
the nickel active site of [NiFe] hydrogenases. By application
of oxidation, dechlorination, and stepwise ligand exchange,
we have prepared [PPN][NiIII(L)(P(C6H3-3-Si-Me3-2-S)3)]
(L ) SePh (2), Cl (3), SEt (4), 2-S-C4H3S (5), CH2CN (7)),
characterized by UV-vis, EPR, IR, CV, SQUID, and X-ray
crystallography. This study further provides the evidence that
the different monodentate ligands [SePh]-, [Cl]-, [SEt]-,
[2-S-C4H3S]-, [CH2CN]-, and PPh3, rendering the [NiIII-
(P(C6H3-3-Si-Me3-2-S)3)] motif in different electronic en-
vironments, induce different stability and reactivity.
Several mononuclear nickel-thiolate complexes have been
synthesized to afford the information about the structure of
the Ni active state of [NiFe] H2ase.10 An electrochemical
study provided evidence for such a Ni(III)-H species
generated by one-electron reduction of a nickel(II) macro-
cyclic complex accompanied by protonation.11 The mono-
nuclear complex [Ni(psnet)]+ of known structure can stoi-
chiometrically evolve H2 from protic sources.10c,d The
(4) (a) 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. (b) Tye, J. W.; Hall, M.
B.; Darensbourg, M. Y. Proc. Natl. Acad. Sci. U.S.A. 2005, 102,
16911-16912.
(5) 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.
(6) (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. Bond. 1998, 92, 1-65. (c) Bagley, K. A.; Duin, E.
C.; Roseboom, W.; Albracht, S. P. J.; Woodruff, W. H. Biochemistry
1995, 34, 5527-5535. (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.
(7) Niu, S.; Thomson, L. M.; Hall, M. B. J. Am. Chem. Soc. 1999, 121,
4000-4007.
Results and Discussion
Reaction of Complex [NiII(SePh)(P(C6H3-3-SiMe3-2-S)2-
(C6H3-3-SiMe3-2-SH))]- (1) with Dioxygen. In contrast to
[Ni(SePh)(P(o-C6H4S)2(o-C6H4-SH))]-,14a which is slightly
soluble in THF solution, the ligand-modified analogue [Ni-
(SePh)(P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-2-SH))]- (1)
shows significant solubility. Reaction of [Ni(CO)(SePh)3]-
and P(C6H3-3-SiMe3-2-SH)3 in a 1:1 stoichiometry in THF
led to the formation of complex 1 isolated as a dark red-
brown solid.14 Complex 1 reveals the νSH stretching band at
2250 cm-1 (KBr) in IR spectroscopy and the chemical shift
1
of the SH group at δ 8.59 (d) ppm (C4D8O) in H NMR
(8) De Gioia, L.; Fantucci, P.; Guigliarelli, B.; Bertrand, P. Inorg. Chem.
1999, 38, 2658-2662.
(9) Foerster, S.; van Gastel, M.; Brecht, M.; Lubitz, W. J. Biol. Inorg.
Chem. 2005, 10, 51-62.
spectroscopy. These results show the existence of intramo-
lecular [Ni-S‚‚‚H-S] interaction (or a combination of
intramolecular [Ni-S‚‚‚H-S] and [Ni‚‚‚H-S] interactions)
as observed in complex [Ni(SePh)(P(o-C6H4S)2(o-C6H4-
(10) (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.; Mu¨nck, E. J. Am. Chem. Soc. 1996, 118, 8963-8964. (f)
Bouwman, E.; Reedijk, J. Coord. Chem. ReV. 2005, 249, 1555-1581.
(11) Efros, L. L.; Thorp, H. H.; Brudvig, G. W.; Crabtree, R. H. Inorg.
Chem. 1992, 31, 1722-1724.
(12) Alvarez, H. M.; Krawiec, M.; Donovan-Merkert, B. T.; Fouzi, M.;
Rabinovich, D. Inorg. Chem. 2001, 40, 5736-5737.
(13) Li, Z.; Ohki, Y.; Tatsumi, K. J. Am. Chem. Soc. 2005, 127, 8950-
8951.
(14) (a) Lee, C.-M.; Chen, C.-H.; Ke, S.-C.; Lee, G.-H.; Liaw, W.-F. J.
Am. Chem. Soc. 2004, 126, 8406-8412. (b) Chen, C.-H.; Lee, G.-H.;
Liaw, W.-F. Inorg. Chem. 2006, 45, 2307-2316.
10896 Inorganic Chemistry, Vol. 45, No. 26, 2006

Mononuclear Complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1-
Scheme 1
ppm (in CD3CN). Reaction of complex 1 and O2 in THF-
CH3CN (1:1 volume ratio) was also monitored by UV-vis
at ambient temperature. The increase of intensity of absorp-
tion bands 590, 772, and 954 nm with no isosbestic points
indicates the existence of intermediates during the oxidative
transformation of complex 1 to 2 in the first 30 min
(Supporting Information Figure S2(a)). Then the intensity
of absorptions at 590 and 954 nm (complex 2) continuously
increases while the intensity of absorption at 772 nm
decreases with two isosbestic points (Supporting Information
Figure S2(b)). Thus, this spectroscopic evidence may further
support the mechanism proposed in the previous report to
explain the formation of [NiIII(SePh)(P(o-C6H4S)3)]- via O2
oxidation of complex [NiII(SePh)(P(o-C6H4S)2(o-C6H4-
SH))]-.14a However, the intermediate cannot be unambigu-
ously characterized at this moment. In contrast to [NiIII-
(SePh)(P(o-C6H4S)3)]-,14a which is unstable in THF solution,
the ligand-modified analogue complex 2 displays the thermal
stability in THF solution. Presumably, the more electron-
rich functionalities of Ni(III) center (the strongly σ-donating
SiMe3 group acting as an effective promoter of Ni(III) metal
π-donating ability)15 are responsible for the stabilization of
the Ni(III) state to prevent reduction of the Ni(III) by the
monodentate phenylselenolate ligand.
Preparations of Complexes [PPN][NiIII(L)(P(C6H3-3-
Si-Me3-2-S)3)] (L ) Cl (3), SEt (4), 2-S-C4H3S (5)). As
shown in Scheme 1b, addition of CH2Cl2 to complex 2 in
the absence of dioxygen produced [PPN][NiIII(Cl)(P(C6H3-
3-Si-Me3-2-S)3)] (3). The 1H NMR spectrum of the crystal-
line product obtained from diffusion of diethyl ether into a
CH2Cl2 solution of complex 2 at ambient temperature for 1
week exhibits three broadening proton resonances at δ -6.47,
9.59, and 16.20 ppm (CD3CN), also implicating the formation
of complex 3. Upon introduction of complex 2 into CH2Cl2
and monitoring by UV-vis, the UV-vis spectrum showing
four intense absorptions (430, 620, 760, and 990 nm) and
three isosbestic points suggest a straightforward conversion
of complex 2 into complex 3 occurred at ambient temperature
(Supporting Information Figure S3). To our knowledge,
ligand-based reactivity of transition-metal thiolates is well-
documented.16 The formation of nickel-thiolate aggregates
adopting thiolate or methylene group as linkages derived
from CH2Cl2 was reported by Schro¨der and co-workers.17
In particular, Karlin and co-workers reported that copper(I)
complexes with tertiary amine and pyridyl ligands triggered
the dechlorination of CH2Cl2, CHCl3, and benzyl chloride
to yield CuII-Cl complexes.18
SH))]-.14 The H/D exchange reaction occurred between
complex 1 and D2O (excess) in THF solution at room
temperature for 24 h to yield [Ni(SePh)(P(C6H3-3-SiMe3-2-
S)2(C6H3-3-SiMe3-2-SD))]- (1-D) with a νSD stretching band
at 1665 (br) cm-1 (KBr). A 2H NMR resonance that appeared
as a broad peak at δ 8.43 ppm (THF) also supports the
formation of complex 1-D (using natural abundance of D in
C4H8O as internal standard, δ 1.73 and 3.58 ppm).14
Upon injection of 1 equiv of dry O2 into a THF solution
of 4 equiv of complex 1, a pronounced color change from
red-brown to dark green occurs at room temperature. Single-
crystal X-ray diffraction study, UV-vis, and 1H NMR
spectrum confirmed the complete formation of the mono-
nuclear [PPN][NiIII(SePh)(P(C6H3-3-SiMe3-2-S)3)] (2) ac-
companied by byproduct H2O (Scheme 1a).14a To unam-
biguously prove the formation of H2O, the THF solution of
complex 1-D was treated with dry O2 at ambient temperature.
(15) (a) Macgregor, S. A.; Lu, Z.; Eisenstein, O.; Crabtree, R. H. Inorg.
Chem. 1994, 33, 3616-3618. (b) Saint-Joly, C.; Mari, A.; Dart-
iguenave, M.; Dartiguenave, Y.; Galy, J. Inorg. Chem. 1980, 19,
2403-2410. (c) Liaw, W.-F.; Horng, Y.-C.; Ou, D.-S.; Chiang, C.-
Y.; Lee, G.-H.; Peng, S.-M. J. Am. Chem. Soc. 1997, 119, 9299-
9300. (d) Liaw, W.-F.; Chen, C.-H.; Lee, C.-M.; Lee, G.-H.; Peng,
S.-M. J. Chem. Soc., Dalton Trans. 2001, 138-143.
2
A H NMR resonance at δ 8.43 ppm due to SD of 1-D in
C4H8O disappeared along with the formation of the byproduct
D2O with resonance at δ 2.02 ppm in C4H8O (Supporting
Information Figure S1).14a The 1H NMR spectrum of complex
2 at 298 K exhibits the paramagnetic chemical shifts that
appear at δ -4.25 (br), 3.03 (br), 6.50 (br), 10.15 (br), 11.01
(br), 14.77 (br) (SePh, o-C6H3S); 2.13 (s), 2.24 (s) (SiMe3)
(16) Grapperhaus, C. A.; Poturovic, S.; Mashuta, M. S. Inorg. Chem. 2002,
41, 4309-4311.
(17) Wang, Q.; Marr, A. C.; Blake, A. J.; Wilson, C.; Schro¨der, M. Chem.
Commun. 2003, 2776-2777 and references therein.
(18) Lucchese, B.; Humphreys, K. J.; Lee, D.-H.; Incarvito, C. D.; Sommer,
R. D.; Rheingold, A. L.; Karlin, K. D. Inorg. Chem. 2004, 43, 5987-
5998.
Inorganic Chemistry, Vol. 45, No. 26, 2006 10897

Lee et al.
Figure 2. Reaction between complex 2 and CO in CH3CN was monitored
by UV-vis spectra. The measured intervals between two curves are shown
in the diagram.
Figure 1. UV-vis spectra (in CH3CN) of complexes 2 (dotted line ‚‚‚),
3 (dashed line ---), and 4 (solid line s), respectively. Only two intense
absorptions were labeled for comparison.
shown in Scheme 1c, dissolving complex 4 in CH2Cl2 at
room temperature also led to the formation of complex 3.
This result confirms that complexes 2 and 4 containing Ni-
(III)-SePh and Ni(III)-SEt bonds, respectively, serve as a
nucleophile for dechlorination of CH2Cl2. The dechlorination
reaction between complex 2 (or complex 4) and CH2Cl2 was
followed by a UV-vis spectrum with the characteristic
absorption 760 nm of complex 3 at 23 (() °C. The
conversion of complex 4 to 3 is faster than that of complex
2 to 3 in excess CH2Cl2 (kobs ) (6.01 ( 3) × 10-4 s-1 for
conversion of complex 4 into 3 and kobs ) (4.78 ( 0.02) ×
10-5 s-1 for conversion of complex 2 into 3; Supporting
Information Figure S5).
To further examine the effect of electronic modulations
of the monodentate ligand L on the stability of [NiIII(L)-
(P(C6H3-3-SiMe3-2-S)3)]- complexes, complex [PPN][Ni-
(SEt)(P(C6H3-3-SiMe3-2-S)3)] (4) containing coordinated
ethylthiolate was synthesized by adopting complex 3 serving
as a precursor. When a CH3CN-THF (1:3 v/v) solution of
complex 3 and [Na][SEt] were stirred under N2 at ambient
temperature, a rapid reaction ensues over the course of 30
min to give the dark-green [PPN][Ni(SEt)(P(C6H3-3-SiMe3-
2-S)3)] (4) (60% yield) after removal of insoluble NaCl and
recrystallization with CH3CN-THF/diethyl ether (Scheme
1c). It is noticed that the metathesis reaction of complex 3
and [Na][SEt] prefers to follow the dropwise addition of
complex 3 (in CH3CN-THF) to CH3CN solution of [Na]-
[SEt]. If the sequence of addition was reversed, complex 4
was isolated in low yield.19 Complex 4 is soluble in CH3-
CN-THF (1:3 v/v ratio) and shows the dark green color in
solution. A single-crystal X-ray diffraction study confirmed
the formation of complex 4, the first structurally characterized
Ni(III)-alkylthiolate species. In comparison with complexes
2 and 3 dominated by two intense absorption bands at (590,
954) nm and (620, 990) nm, respectively, the electronic
spectrum of complex 4 coordinated by the more electron-
donating ethylthiolate displays blue shifts to (577, 920) nm
(Figure 1). Complex 4 exhibits a diagnostic 1H NMR
spectrum with phenyl and ethyl proton resonances well-
removed from the diamagnetic region. The proton resonances
(δ 40.67 (br), 3.17 (br) ppm and 14.97 (br), 10.27 (br), -3.05
(br) ppm) were assigned to [SEt]- and [P(C6H3-3-SiMe3-2-
S)3]3- ligands, respectively. This result is consistent with the
central NiIII possessing a d7 electronic configuration in a
trigonal bipyramidal ligand field.14a In a similar fashion,
reaction of complex 3 and [Na][2-S-C4H3S] in THF-CH3-
CN solution also led to the formation of [PPN][Ni(2-S-
C4H3S)(P(C6H3-3-SiMe3-2-S)3)] (5) (yield 60%) (Supporting
Information Figure S4).
Reductive Elimination of Ni(III)-SePh and Ni(III)-
SEt Bonds under CO Atmosphere. When a THF-CH3-
CN (3:1 v/v) solution of complex 2 (or complexes 4 and 5)
(0.03 mmol) was treated with CO (1 atm) at ambient
temperature for 80 h, complex 2 (or complexes 4 and 5)
completely transformed into complex [PPN][NiII(CO)(P(C6H3-
3-SiMe3-2-S)3)] (6), as monitored by UV-vis (Figure 2) and
IR with a νCO stretching band (2033 cm-1, KBr), ac-
companied by formation of diphenyl diselenide (diethyl
1
disulfide, di(2-thienyl) disulfide) identified by H NMR
spectrum (Scheme 1d,e). Obviously, CO molecule triggers
the reductive elimination of the coordinated phenylselenolate
of complex 2 (or ethylthiolate of complex 4, 2-thienylthiolate
of complex 5) to yield Ni(II)-CO complex 6 (Supporting
Information Figure S6) and byproduct (PhSe)2 (or (SEt)2/
(2-S-C4H3S)2), relevant to the observation that Ni-C state
was converted into the Ni-L form under illumination which
subsequently transformed into Ni-CO state under exogenous
CO condition in [NiFe] hydrogenase isolated from D.
Vulgaris Miyazaki F.3c,d It is presumed that the σ-/π-electron-
donating nature of the coordinated thiolates/selenolate con-
verts Ni(II), a weaker π-donor, into a strong π-donor and
favors Ni-CO bonding.15 Compared to complex 2 (Scheme
1e), the easier reductive elimination of the coordinated
ethylthiolate of complex 4 under CO atmosphere ac-
companied by the formation of Ni(II)-CO complex 6 is
presumably ascribed to the more electron-rich Ni center of
complex 4 which promotes the coordination of CO to Ni-
The influence of the coordinated [SEt]- ligand on the
chemical reactivity of complex 4 was also investigated. As
(19) Rosenfield, S. G.; Armstrong, W. H.; Mascharak, P. K. Inorg. Chem.
1986, 25, 3014-3018.
10898 Inorganic Chemistry, Vol. 45, No. 26, 2006

Mononuclear Complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1-
the most favorable geometries of CO binding to Ni(II) are
trigonal bipyramidal with CO occupying equatorial or square
pyramidal with CO occupying axial.15a Compared to complex
[Ni(CO)Cl2(PMe3)2] (νCO: 2005 cm-1 and Ni-CO bond
distance of 1.730(2) Å),15a,b the CO stretching frequency of
2033 cm-1 (CH3CN) is higher and the Ni-CO bond length
of 1.800(6) Å is longer in complex 6.
Synthesis of Ni(III)-Cyanomethanide Complex. The
unprecedented nickel(III)-thiolate complex containing C-
bonded cyanomethanide [PPN][Ni(CH2CN)(P(C6H3-3-SiMe3-
2-S)3)] (7) was isolated (yield 65%) from reaction of complex
3 and CH3CN in the presence of NaH at ambient temperature
(Scheme 1g).20 The formation of complex 7 is probably
initiated by an anionic deprotonation of CH3CN followed
by a nucleophilic attack by the [CH2CN]- carbanion on Ni
and the precipitation of NaCl.20a In comparisons of complexes
2, 3, and 4 dominated by two intense absorption bands at
(590, 954), (620, 990), and (577, 920) nm in UV-vis spectra,
respectively, the electronic spectrum of complex 7 coordi-
nated by -CH2CN displays blue shifts to 543 and 925 nm.
Carbon monoxide did not trigger the reductive elimination
of Ni(III)-CH2CN bond, even exposing the CH3CN solution
of complex 7 under 1 atm of CO at ambient temperature for
4 days.20a Obviously, the reactivity of complexes [NiIII(L)-
(P(C6H3-3-SiMe3-2-S)3)]- may be tailored by ligand L. To
prove that the Ni(III) complexes containing the monodentate
chalcogenolate ligand undergo reductive elimination of
dialkyl dichalcogenides yielding NiII-CO complex 6 under
CO atmosphere, we repeated the reaction of the neutral [NiIII-
(PPh3)(P(C6H3-3-SiMe3-2-S)3)] (9), synthesized from oxygen
oxidation of complex [NiII(PPh3)(P(C6H3-3-SiMe3-2-S)2-
(C6H3-3-SiMe3-2-SH))]- (8),14b and CO (1 atm). On the basis
of IR νCO and UV-vis spectra, no Ni(II)-CO complex 6
was generated after the reaction solution of complex 9 was
stirred under a CO atmosphere in THF for 4 days.
Figure 3. (a) EPR spectra of complex 2 (dashed line ---), complex 3 (dotted
line ‚‚‚), and complex 4 (solid line s) at 77 K. (b) Plots of µeff vs T for
complexes 2 (triangle up 444) and 3 (circle OOO).
Table 1. Half-wave Potentials (E1/2) (vs Cp2Fe/Cp2Fe+) for Complexes
[NiIII(SePh)(P(o-C6H4S)3)]-, 2, 3, 4, and 7 in CH3CN (Complex 9 in
CH2Cl2) at 100 mV/s Scan Rate
compound
E
1/2 (V)
Ered (V)
[NiIII(SePh)(P(o-C6H4S)3)]-
-1.20
-1.26
2
3
4
7
9
-1.17
EPR and Effective Magnetic Moment. The EPR spectra
of complexes 2, 3, and 4 are identical at 77 K and exhibit
rhombicity with principal g values of 2.31, 2.09, and 2.0
(Figure 3a) (g ) 2.345, 2.093, and 1.99 for complex 7). The
g values (g ) 2.31, 2.09, and 2.0 for complexes 2, 3, and 4)
much higher than the free electron g value 2.0023 implicated
a large orbital contribution, and the unpaired electron is
primarily associated with the nickel ion.14a The effective
magnetic moment in solid state by a SQUID magnetometer
was 1.8 and 2.1 µB for complexes 2 and 3, respectively
-1.32
-1.34
-0.83
(III) center and the subsequent reductive elimination of
ethylthiolate (Supporting Information Figure S7). However,
upon CO bubbled into a THF-CH3CN (1:1 v/v) solution of
complex 3, no νCO stretching band in the IR spectrum and
changes of absorption bands (430, 620, 760, and 990 nm)
in the UV-vis spectrum were observed (Scheme 1f). This
result implies that the Ni(III)sCl bond of complex 3 is
resistant to undergoing reductive elimination, in contrast to
the Ni(III)-SePh and Ni(III)-SEt bonds of complexes 2 and
4, respectively. The Ni(II)-CO of complex 6 is not photo-
labile. THF solution of complex 6 is stable under photolysis
(λ ) 365 nm) for 7 h at ambient temperature.
1
(Figure 3b), consistent with total spin value (ST) of /2.14a
Electrochemistry. Half-wave potentials (E1/2) of com-
plexes [NiIII(SePh)(P(o-C6H4S)3)]-, 2, 3, 4, and 7 (2.0 mM)
were measured in CH3CN with 0.1 M [n-Bu4N][PF6] as
supporting electrolyte at room temperature (scan rate 100
mV/s) and listed in Table 1. In comparisons of complexes
The preferred geometry of complex 6 is a distorted trigonal
bipyramidal with CO occupying an axial position (Supporting
Information Figure S6). This is presumably because the
chelating [P(C6H3-3-SiMe3-2-S)3]3- has to occupy the equa-
torial sites and one of the axial sites.15a CO bonded to Ni(II)
in a square planar geometry has been isolated and character-
ized.15c,d In addition, the computation has demonstrated that
(20) (a) Alburquerque, P. R.; Pinhas, A. R.; Bauer, J. A. K. Inorg. Chim.
Acta 2000, 298, 239-244. (b) Tanaka, K.; Kushi, Y.; Tsuge, K.;
Toyohara, K.; Nishioka, T.; Isobe, K. Inorg. Chem. 1998, 37, 120-
126. (c) Schebler, P. J.; Mandimutsira, B. S.; Riordan, C. G.; Liable-
Sands, L. M.; Incarvito, C. D.; Rheingold, A. L. J. Am. Chem. Soc.
2001, 123, 331-332. (d) Schenker, R.; Mock, M. T.; Kieber-Emmons,
M. T.; Riordan, C. G.; Brunold, T. C. Inorg. Chem. 2005, 44, 3605-
3617.
Inorganic Chemistry, Vol. 45, No. 26, 2006 10899

Lee et al.
Figure 4. Cyclic voltammograms of [Ni(SePh)(P(o-C6H4S)3)]- (solid line
s), complex 2 (dashed line ---), and complex 4 (dotted line ‚‚‚) (condi-
tions: CH3CN, scan rate 0.1 V/s, room temperature, and referenced to
ferrocinium/ferrocene).
Figure 5. Cyclic voltammogram of complex 7 (conditions: CH3CN, scan
rate 0.1 V/s, room temperature, and referenced to ferrocinium/ferrocene).
[NiIII(SePh)(P(o-C6H4S)3)]- and 2, the induction of trimeth-
ylsilyl substituents in the meta positions of the phenyl rings
causes the E1/2 of complex 2 to shift more negative values
(∆E1/2 ) 0.06 V; E1/2 ) -1.20 V for complex [NiIII(SePh)-
(P(o-C6H4S)3)]- (vs Cp2Fe/Cp2Fe+)), as shown in Figure 4.
Similar effects are observed for complexes 2 and 4. Complex
4 with a coordinated [SEt]- ligand reveals one reversible
NiIII/II redox process at -1.32 V (E1/2), as compared to -1.26
V (E1/2) for complex 2 (vs Cp2Fe/Cp2Fe+, Figure 4). In
comparisons of complexes 2 and 4, the more positive redox
potential of Ni center in complex 2 presumably was caused
by the weaker electron-donating ability of the coordinated
[SePh]- ligand compared to [SEt]-. Complex 9 with a
coordinated PPh3 revealing one reversible NiIII/II redox
process at -0.83 V (E1/2) (vs Cp2Fe/Cp2Fe+) further cor-
roborates this rationalization (Table 1 and Supporting
Information Figure S8). In contrast to complexes 2 and 4
displaying a reversible Ni(III)-Ni(II) process, the cyclic
voltammogram of complex 3 with a coordinated chloride
ligand displays an irreversible reduction at -1.17 V (vs Cp2-
Fe/Cp2Fe+, Supporting Information Figure S9). Although
carbon monoxide did not promote the reductive elimination
of Ni(III)-CH2CN bond of complex 7, electrochemistry of
complex 7 also reveals one reversible redox process at -1.34
V (vs Cp2Fe/Cp2Fe+), as shown in Figure 5.
Structures. The X-ray single-crystal structures of com-
plexes 2, 3, 4, and 7 are displayed in Figures 6, 7, 8, and 9,
respectively, and selected bond distances and angles are
presented in the figure captions. Complexes 2-4 and 7 are
isostructural mononuclear Ni(III)-thiolate complexes. The
strain effect of the chelating ligand ([P(C6H3-3-SiMe3-2-
S)3]3-) in the coordination sphere of complexes 2-4 and 7
explains the geometry of Ni is a distorted trigonal bipyra-
midal with three thiolates locating equatorial positions and
the phosphorus occupying an axial position trans to [SePh]-
in 2, [Cl]- in 3, [SEt]- in 4, and [CH2CN]- in 7. The Ni
metal was displaced from the mean three sulfur-atoms plane
toward [SePh]-, [Cl]-, and [SEt]- ligands (0.1344(11) Å for
2, 0.1446(8) Å for 3, and 0.1353(14) Å for 4), respectively.
The average Ni-S bond lengths (bond lengths between the
sulfur of chelating [P(C6H3-3-SiMe3-2-S)3]3- ligand and NiIII)
Figure 6. ORTEP drawing and labeling scheme of [NiIII(SePh)(P(C6H3-
3-SiMe3-2-S)3)]- (2) anion with thermal ellipsoids drawn at 50% probability.
Selected bond distances (Å) and angles (deg): Ni-Se(1) 2.3473(8); Ni-
S(1) 2.2853(12); Ni-S(2) 2.2927(12); Ni-S(3) 2.2122(12); Ni-P(1)
2.1318(12); S(1)-Ni-S(2) 106.58(5); S(1)-Ni-S(3) 119.39(5); S(2)-Ni-
S(3) 132.94(5); S(1)-Ni-Se(1) 93.67(4); S(2)-Ni-Se(1) 91.75(4); S(3)-
Ni-Se(1) 94.72(4); P(1)-Ni-Se(1)176.55(4); P(1)-Ni-S(1) 87.19(4);
P(1)-Ni-S(2) 84.80(4); P(1)-Ni-S(3) 87.76(4).
in complexes 2, 3, and 4 do not show dramatic differences
(2.263(1) Å for 2, 2.258(1) Å for 3, 2.253 (1) Å for 4, and
2.254(1) Å for 7). Compared to [NiIII(SePh)(P(o-C6H4S)3)]-,14a
the mean Ni-S bond lengths (bond lengths between the
sulfur of chelating [P(o-C6H4S)3]3- ligand and NiIII) have
increased by 0.014 Å and the NiIII-Se bond distance has
decreased by 0.024 Å in complexes 2. The NiIII-S(4) bond
length of 2.273(1) Å (the distance between the monodentate
ethylthiolate and NiIII) in complex 4, comparable to the NiIII-
S(4) bond length of 2.2554(9) Å in complex 5 (Supporting
Information Figure S4), is shorter than the average NiII-S
bond length of 2.281(1) Å in [Ni(S-p-C6H4Cl)4].2-19 It is
noticed that the NiIII-C(28) (CH2CN) bond distance of
2.037(3) Å in complex 7 is longer than the NiII-C bond
lengths of 1.94(2), 1.921(8), and 1.918(5) Å observed in
complexes [Ni(NS3iPr)Me][BPh4],21 [(2.2′-bipyridine)Ni-
(O(CH2)3CH2)],22 and [bis(pyridine)Ni(CH3)2],23 respectively.
10900 Inorganic Chemistry, Vol. 45, No. 26, 2006

Mononuclear Complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1-
Figure 7. ORTEP drawing and labeling scheme of [NiIII(Cl)(P(C6H3-3-
SiMe3-2-S)3)]- (3) anion with thermal ellipsoids drawn at 50% probability.
Selected bond distances (Å) and angles (deg): Ni-Cl(1) 2.2338(5); Ni-
S(1) 2.2191(6); Ni-S(2) 2.2673(6); Ni-S(3) 2.2867(6); Ni-P(1) 2.1203-
(6); S(1)-Ni-S(2) 115.09(2); S(1)-Ni-S(3) 136.19(2); S(2)-Ni-S(3)
107.44(2); S(1)-Ni-Cl(1) 91.25(2); S(2)-Ni-Cl(1) 94.33(2); S(3)-Ni-
Cl(1) 95.74(2); P(1)-Ni-Cl(1) 178.21(3); P(1)-Ni-S(1) 87.58(2); P(1)-
Ni-S(2) 87.39(2); P(1)-Ni-S(3) 84.19(2).
Figure 9. ORTEP drawing and labeling scheme of [NiIII(CH2CN)(P(C6H3-
3-SiMe3-2-S)3)]- (7) anion with thermal ellipsoids drawn at 50% probability.
Selected bond distances (Å) and angles (deg): Ni-S(1) 2.2795(8); Ni-
S(2) 2.2259(9); Ni-S(3) 2.2580(9); Ni-P(1) 2.1362(8); Ni-C(28) 2.037-
(3); C(28)-C(29) 1.390(5); N(1)-C(29) 1.167(4); S(1)-Ni-S(2) 109.92(3);
S(1)-Ni-S(3) 110.66(3); S(2)-Ni-S(3) 138.45(3); P(1)-Ni-S(1) 87.18-
(3); P(1)-Ni-S(2) 88.00(3); P(1)-Ni-S(3) 85.40(3); Ni-C(28)-C(29)
114.6(2); C(28)-Ni-P(1) 179.03(9); C(28)-Ni-S(2) 92.78(9); C(28)-
Ni-S(3) 94.39(9); C(28)-Ni-S(1) 92.01(9).
S)3]3- and [P(o-C6H4S)3)]3- ligands. In brief, the SiMe3
group, a strongly σ-donating group, serves as an effective
promoter of Ni(III) metal π-donating ability to stabilize the
Ni(III)-thiolate complexes.15a As reflected in the shift of
the half-wave potentials (E1/2), the cyclic voltammograms
of complexes [NiIII(SePh)(P(o-C6H4S)3)]-, 2, 4, and 7 display
reversible NiIII/II process with E1/2 ) -1.20, -1.26, -1.32,
and -1.34 V (vs Cp2Fe/Cp2Fe+), respectively. However, the
cyclic voltammogram of complex 3 with a coordinated
chloride ligand displays an irreversible reduction at -1.17
V (vs Cp2Fe/Cp2Fe+).
Figure 8. ORTEP drawing and labeling scheme of [NiIII(SC2H5)(P(C6H3-
3-SiMe3-2-S)3)]- (4) anion with thermal ellipsoids drawn at 50% probability.
Selected bond distances (Å) and angles (deg): Ni-S(1) 2.2791(12); Ni-
S(2) 2.2639(13); Ni-S(3) 2.2169(13); Ni-S(4) 2.2734(12); Ni-P(1)
2.1345(12); C(1)-S(4) 1.760(9); C(1)-C(2) 1.524(10); S(1)-Ni-S(2)
109.65(5); S(1)-Ni-S(3) 111.26(5); S(2)-Ni-S(3) 137.95(6); S(1)-Ni-
S(4) 92.88(5); S(2)-Ni-S(4) 93.13(5); S(3)-Ni-S(4) 94.16(5); P(1)-Ni-
S(4) 177.78(5); P(1)-Ni-S(1) 87.30(5); P(1)-Ni-S(2) 84.73(5); P(1)-
Ni-S(3) 87.84(5); Ni-S(4)-C(1) 109.1(6).
(2) The thermally stable complex 4 with a monodentate
ethylthiolate coordinated to the Ni(III) was isolated. The
single-crystal X-ray structure shows a NiIII-S(4) (ethylthi-
olate) bond length of 2.273(1) Å in complex 4 is in the range
of 2.12-2.28 Å for the NiIII-S bond lengths of the oxidized
D. gigas hydrogenases.2
(3) In contrast to the inertness of complexes 3, 7, and 9
under a CO atmosphere, carbon monoxide did trigger the
reductive elimination of the monodentate chalcogenolate
ligand of complexes 2, 4, and 5 to yield NiII-CO complex
6 accompanied by the formation of diphenyl/dialkyl dichal-
cogenides. This result may provide some clues to the
transformation mechanism between the Ni-L form and Ni-
CO form of [NiFe] hydrogenase isolated from D. Vulgaris
Miyazaki F and CO acting as an inhibitor for catalytic
activity of [NiFe] hydrogenases.3c,d
Conclusion and Comments
Studies on the mononuclear Ni(III)-thiolate complexes
(2-5, 7, 9) have led to the following results related to the
structure, reactivity, and spectroscopic properties of the nickel
center of bimetallic Ni-Fe active site of the oxidized-state
[NiFe] hydrogenase.
(1) The mononuclear Ni(III)-thiolate complex 2 is more
stable thermally than the corresponding Ni(III) complex [NiIII-
(SePh)(P(o-C6H4S)3)]-. This result may be rationalized by
the distinct electronic effects between [P(C6H3-3-SiMe3-2-
It is anticipated that the Ni(III)-alkylthiolate complexes
containing an optimum electronic condition around Ni center
may trigger heterolytic H2 cleavage via the cooperation of
Ni(III) and [SR]-. However, no heterolytic H2 cleavage
reaction was observed in the THF solution of complex 4
under an atmosphere of hydrogen. The synthesis of oxygen-
containing Ni(III)-thiolate complexes is ongoing.
(21) Holm, R. H.; Carrie, M.; Muetterties, M. C.; Stavropoulos, P. J. Am.
Chem. Soc. 1991, 113, 8485-8492.
(22) Hillhouse, G. L.; Matsunaga, P. T. J. Am. Chem. Soc. 1993, 115,
2075-2077.
(23) Nelkenbaum, E; Kapon, M.; Eisen, M. S. Organometallics 2005, 24,
2645-2659.
Inorganic Chemistry, Vol. 45, No. 26, 2006 10901

Lee et al.
precipitate the dark-green solid [PPN][Ni(SePh)(P(C6H3-3-SiMe3-
2-S)3)] (2) (0.118 g, 90%). Diffusion of diethyl ether into a THF-
MeCN (3:1 volume ratio) solution of complex 2 at -15 °C for 4
weeks yielded dark-green crystals suitable for X-ray crystallography.
1H NMR (CD3CN): δ -4.25 (br), 3.03 (br), 6.50 (br), 10.15 (br),
11.01 (br), 14.77 (br) (SePh, o-C6H3S); 2.13 (s), 2.24 (s) (SiMe3)
ppm. Absorption spectrum (CH3CN) [λmax, nm (ꢀ, M-1 cm-1)]: 304
(21000), 356 (13000), 590 (2500), 771 (800), 954 (970). Anal. Calcd
for C69H71NP3Si3S3SeNi: C, 62.53; H, 5.40; N, 1.06. Found: C,
62.41; H, 5.10; N, 0.81.
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, sodium ethylthiolate, 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(C6H3-3-SiMe3-2-SH)3) was synthe-
sized by published procedures.24 Infrared spectra of the ν(SH)
stretching frequencies were recorded on a Perkin-Elmer model
spectrum One B spectrophotometer with KBr solid. UV-vis spectra
were recorded on a GBC Cintra 10e and Jusco V-570. H and H
NMR spectra were obtained on a Varian Unity-500 spectrometer.
Electrochemical measurements were performed with CHI model
421 potentionstat (CH Instrument) instrumentation. Cyclic volta-
mmograms were obtained from 2.0 mM analyte concentration in
O2-free CH3CN using 0.1 M [n-Bu4N][PF6] as a supporting
electrolyte. Potentials were measured at 298 K vs a Ag/AgCl
reference electrode by using a glassy carbon working electrode.
Analyses of carbon, hydrogen, and nitrogen were obtained with a
CHN analyzer (Heraeus).
Preparation of [PPN][Ni(SePh)(P(C6H3-3-SiMe3-2-S)2(C6H3-
3-SiMe3-2-SH))] (1). Complexes [PPN][Ni(CO)(SePh)3] (0.2 mmol,
0.218 g) and P(C6H3-3-SiMe3-2-SH)3 (0.2 mmol, 0.115 g) were
loaded into a 50-mL flask and 15 mL of THF was added by cannula.
The reaction mixture was stirred at ambient temperature for 1 h,
and then hexane (20 mL) was added to precipitate the red-brown
solid [PPN][Ni(SePh)(P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-2-SH))]
(1) (yield 0.225 g, 85%).14 Diffusion of diethyl ether into THF
solution of complex 1 at room temperature for 1 week yielded
layered brown-red crystals of complex 1 (yield 0.212 g, 80%). IR:
2250 w (νSH) cm-1 (KBr).14 1H NMR (C4D8O): δ 8.59 (d) (SH),
6.65-6.77 (m), 6.87 (t), 7.15-7.33 (m) (PhSe, P(C6H3-3-SiMe3-
2-S)3); 0.20 (s), 0.30 (s) (SiMe3) ppm. Absorption spectrum (THF)
[λmax, nm (ꢀ, M-1 cm-1)]: 420 (2700), 500 (1150). Anal. Calcd
for C69H72NNiP3S3SeSi3: C, 62.48; H, 5.47; N, 1.06. Found: C,
62.18; H, 5.12; N, 0.98.
Preparation of [PPN][Ni(Cl)(P(C6H3-3-SiMe3-2-S)3)] (3). A
portion 15 mL of CH2Cl2 was added into a 50-mL flask loaded
with complex 2 (0.132 g, 0.1 mmol), and the reaction mixture was
allowed to stir at ambient temperature for 48 h. A change in color
from dark green to light green occurred, and 20 mL of hexane was
then added to precipitate the green solid complex [PPN][Ni(Cl)-
(P(C6H3-3-SiMe3-2-S)3)] (3) (0.102 g, 85%). Diffusion of hexane
into a CH2Cl2 solution of complex 3 at room temperature for 1
week led to dark-green crystals suitable for X-ray crystallography.
1H NMR (CD3CN): δ -6.47 (br), 9.59 (br), 16.20 (br) (o-C6H3S);
1
2
2.12 (s), 2.31 (s) (SiMe3) ppm. Absorption spectrum (CH3CN) [λmax
,
nm (ꢀ, M-1 cm-1)]: 430 (6000), 620 (2200), 760 (1650), 990
(1000). Anal. Calcd for C63H66NP3Si3S3ClNi: C, 62.81; H, 5.52;
N, 1.16. Found: C, 62.24; H, 5.03; N, 1.49.
Preparation of [PPN][Ni(SC2H5)(P(C6H3-3-SiMe3-2-S)3)] (4).
A CH3CN-THF solution (5:15 mL) of complex 3 (0.242 g, 0.2
mmol) was added to a CH3CN solution of [Na][SC2H5] (0.034 g,
0.4 mmol) by cannula under positive N2. The resulting mixture
was stirred at room temperature for 2 h and then filtered through
Celite to remove [Na][Cl]. Diethyl ether (20 mL) was added to
precipitate the dark green solid [PPN][Ni(SC2H5)(P(C6H3-3-SiMe3-
2-S)3)] (4) (0.147 g, 60%) after the solution was concentrated to 8
mL. Diffusion of diethyl ether into CH3CN-THF solution of
complex 4 at -15 °C for 4 weeks led to dark green crystals suitable
1
for X-ray crystallography. H NMR (CD3CN): δ 40.67 (br), 3.17
(br) (SEt); -3.05 (br), 10.27 (br), 14.97 (br) (o-C6H3S); 2.10 (s),
2.34 (s) (SiMe3) ppm. Absorption spectrum (CH3CN) [λmax, nm
(ꢀ, M-1 cm-1)]: 360 (11285), 500 (1760), 579 (2435), 724 (885),
922 (960), 1123(615). Anal. Calcd for C65H66NP3Si3S4Ni: C, 63.71;
H, 5.43; N, 1.14. Found: C, 63.71; H, 5.51; N, 1.34.
Preparation of [PPN][NiIII(2-S-C4H3S)(P(C6H3-3-SiMe3-2-
S)3)] (5). Method (a): A THF-CH3CN solution (10:5 mL) of
complex 3 (0.242 g, 0.2 mmol) was added to a CH3CN solution of
[Na][2-S-C4H3S] (0.028 g, 0.2 mmol). The resulting mixture was
stirred at room temperature for 3 h and then filtered through Celite
to remove [Na][Cl]. Diethyl ether (20 mL) was added to precipitate
the green solid [PPN][NiIII(2-S-C4H3S)(P(C6H3-3-SiMe3-2-S)3)] (5)
(yield 0.154 g, 60%). Method (b): Di(2-thienyl) disulfide (0.23 g,
1 mmol) and [PPN][HFe(CO)4] (0.283 g, 0.4 mmol) were loaded
into a 20-mL Schlenk tube and dissolved in THF (5 mL). After
the reaction solution was stirred for 15 min at ambient temperature,
the solution was transferred to another Schlenk flask containing
[NiCp(CO)]2 (0.061 g, 0.2 mmol) by cannula under a positive
pressure of N2. The reaction mixture was stirred for 6 h at ambient
temperature, and hexane (10 mL) was added to precipitate the brown
oily product [PPN][Ni(CO)(2-S-C4H3S)3].15c,d The brown oily
product was dried under N2 purge and redissolved in THF. The
THF solution of [PPN][Ni(CO)(2-S-C4H3S)3] was then transferred
to another Schlenk flask containing P(C6H3-3-SiMe3-2-SH)3 (0.23
g, 0.4 mmol) by cannula under positive N2. After the reaction
mixture was stirred for 30 min under N2, degassed hexane (25 mL)
was added to precipitate the red-brown solid [PPN][NiII(2-S-
C4H3S)(P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-2-SH))] (yield 0.324
D/H Exchange for Reaction of Complex 1 and D2O. To a THF
(10 mL) solution of complex 1 (0.133 g, 0.1 mmol) at 5 °C, a
100-fold excess of D2O (0.18 mL, 10 mmol) was added. The
reaction solution containing the mixture solution of complex 1 and
D2O was stirred for 24 h at 5 °C. Hexane (15 mL) was then added
slowly to layer above the mixture solution. The flask was tightly
sealed and kept at room temperature for 1 week. Red-brown crystals
[PPN][Ni(SePh)(P(C6H3-3- SiMe3-2-S)2(C6H3-3-SiMe3-2-SD))] (1-
D) were isolated (0.08 g, 60%). IR (KBr): 1665 (νSD) cm-1. H
NMR (C4H8O): δ 8.43 (br) ppm (SD) vs C4H8O (natural abundance
of D in C4H8O solvent, δ 1.73 and 3.58 ppm).
Preparation of [PPN][Ni(SePh)(P(C6H3-3-SiMe3-2-S)3)] (2).
Pure oxygen gas (0.62 mL) was injected through a red-brown THF
solution (10 mL) of complex 1 (0.133 g, 0.1 mmol) at room
temperature. The resulting deep-green solution was reduced in
volume under vacuum, and diethyl ether was then added to
2
(24) Block, E.; Ofori-Okai, G; Zubieta, J. J. Am. Chem. Soc. 1989, 111,
2327-2329.
10902 Inorganic Chemistry, Vol. 45, No. 26, 2006

Mononuclear Complexes [NiIII(L)(P(C6H3-3-SiMe3-2-S)3)]0/1-
1
g, 63%) characterized by EA (Anal. Calcd for C67H70NP3Si3S5Ni:
C, 62.60; H, 5.49; N, 1.09. Found: C, 62.43; H, 5.56; N, 0.94),
IR, and single-crystal X-ray diffraction.14a Pure oxygen gas (10 mL)
was injected into the red-brown THF solution (20 mL) of complex
[NiII(2-S-C4H3S)(P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-2-SH))]-
and stirred for 1 h at room temperature. The resulting green solution
was reduced in volume under vacuum, and then hexane was added
to precipitate the green solid [PPN][NiIII(2-S-C4H3S)(P(C6H3-3-
SiMe3-2-S)3)] (5). Diffusion of hexane into a THF solution of
complex 5 at 4 °C for 1 week led to green crystals suitable for
X-ray crystallography (Supporting Information Figure S5). 1H NMR
(CD3CN): δ -6.44 (br), 9.58 (br), 16.20 (br) (o-C6H3S); 0.37 (s),
0.60 (s) (SiMe3) ppm. Absorption spectrum (THF) [λmax, nm (ꢀ,
M-1 cm-1)]: 372 (2336), 435 (1612), 598 (686), 973 (242). Anal.
Calcd for C67H69NP3Si3S5Ni: C, 62.60; H, 5.41; N, 1.09. Found:
C, 62.39; H, 5.10; N, 0.88.
Information Figure S10). H NMR (CD3Cl): δ 0.11 (s) (SiMe3);
6.26 (s) (SH); 6.92 (br), 7.2 (br), 7.4 (br), 7.68 (br) (PPh3, o-C6H3S)
ppm. IR (KBr): 2192 (νSH) cm-1 14
Absorption spectrum (THF)
.
[λmax, nm (ꢀ, M-1 cm-1)]: 385 (1221), 623 (245). Anal. Calcd
for C45H52P2Si3S3Ni: C, 60.46; H, 5.86. Found: C, 59.84; H,
5.66.
Preparation of [NiIII(PPh3)(P(C6H3-3-SiMe3-2-S)3)] (9). Dry
oxygen gas (2.48 mL) was purged through a red THF solution (10
mL) of complex 8 (0.388 g, 0.4 mmol) at room temperature. The
reaction solution was stirred for 1 h and a significant change in
color of the reaction solution from red to deep green was observed.
After the solution was concentrated to 5 mL, hexane (15 mL) was
then added to precipitate the dark green solid [NiIII(PPh3)(P(C6H3-
3-SiMe3-2-S)3)] (9) (yield 0.207 g, 58%).14b Diffusion of hexane
into a THF solution of complex 9 at 0 °C for 3 weeks led to dark
green crystals. 1H NMR (CD3Cl): δ -10.71 (br), 11.29 (br), 15.85
(br) (o-C6H3S); 7.24 (br), 7.76 (br) (PPh3); 2.76 (s) (SiMe3) ppm.
Absorption spectrum (THF) [λmax, nm (ꢀ, M-1 cm-1)]: 381 (4770),
620 (1700), 682 (1620), 1167 (1000). Anal. Calcd for C45H51P2-
Si3S3Ni: C, 60.53; H, 5.76. Found: C, 59.95; H, 5.26.
Kinetic Measurements. The reaction between complex 2 (or
4) and CH2Cl2 was followed by UV-vis with the intensity increase
of the characteristic absorption at 760 nm due to the formation of
complex 3 at 23 ((1) °C. Complex 2 (0.0014 g, 0.001 mmol) was
loaded into a 4-mL UV Precision cell (Hellma, 10.00-mm light
path) and then CH2Cl2 (4.0 mL) was injected to dissolve it. The
reaction was monitored by UV-vis using time scan model with
the integration time (2 s) and the internal time (10 min) for 20 h.
This reaction obeyed pseudo-first-order kinetics in the presence of
an excess amount of CH2Cl2 over 20 h, and the rate constant (kobs
) (4.78 ( 0.02) × 10-5 s-1) (R2 ) 0.9990) was determined by fits
of data using the Sigmaplot2001 software. The kinetics of the
reaction of complex 4 (0.0012 g, 0.001 mmol) and CH2Cl2 (4.0
mL) were monitored by UV-vis spectrometer using time scan
model with the following parameters: the integration time (2 s),
the internal time (1 min), and reaction time (2 h). This reaction
also obeyed pseudo-first-order kinetics with the rate constant (kobs
) (6.01 ( 0.03) × 10-4 s-1) (R2 ) 0.9990).
Reaction of Complex 2 (or 4 and 5) and CO. The 50-mL flask
containing a THF-CH3CN solution (10:5 mL, v/v) of complex 2
(0.067 g, 0.05 mmol) (or complex 4/5 (0.05 mmol)) was filled with
pure CO gas (28 psi, at 293 K) and tightly sealed. After the reaction
solution was stirred at ambient temperature for 1 week, the color
of solution gradually turned from dark green to light green
accompanied by trace of white solid precipitate. The resulting
mixture was filtered and solvent was removed from the filtrate under
vacuum to leave the dark green solid. Hexane (10 mL) was added
to extract the (PhSe)2 (0.007 g, 80%) identified by EI-MS and the
left dark green solid [PPN][Ni(CO)(P(C6H3-3-SiMe3-2-S)3)] (6)
characterized by IR, UV-vis, and single-crystal X-ray diffrac-
tion. Diffusion of diethyl ether into a THF-CH3CN (2:1 v/v) of
complex 6 at room temperature for 1 week led to dark green
crystals suitable for X-ray crystallography (0.036 g, 60%).10e IR
1
(νCO): 2033 vs (CH3CN), 2033 vs cm-1 (KBr). H NMR (CD2-
Cl2): δ 6.77 (td), 7.10 (td), 7.23 (dd), (P(C6H3-3-SiMe3-2-S)3); 0.06
(s), 0.35 (s) (SiMe3) ppm. Absorption spectrum (CH3CN) [λmax
,
nm (ꢀ, M-1 cm-1)]: 711 (1350). Anal. Calcd for C64H61NOP3Si3S3-
Ni: C, 64.47; H, 5.16; N, 1.17. Found: C, 65.07; H, 4.33; N,
1.26.
Preparation of [PPN][Ni(CH2CN)(P(C6H3-3-SiMe3-2-S)3)] (7).
A portion of CH3CN (15 mL) was added into a 50-mL flask loaded
with complex 3 (0.242 g, 0.2 mmol) and NaH (0.015 g, ∼0.6
mmol). The resulting mixture was stirred at ambient temperature
for 1 h and then filtered through Celite to remove [Na][Cl]. The
purple solution was concentrated under vacuum, and diethyl ether
was added to precipitate the dark purple solid [PPN][Ni(CH2CN)-
(P(C6H3-3-SiMe3-2-S)3)] (7) (0.167 g, 65%). Diffusion of diethyl
ether into CH3CN solution of complex 7 at -15 °C for 4 weeks
led to dark purple crystals suitable for X-ray crystallography. IR:
EPR Measurements. EPR measurements were performed at
X-band using a Bruker EMX spectrometer equipped with a Bruker
TE102 cavity and a Bruker VT2000 temperature control unit (120-
300 K). The microwave frequency was measured with a Hewlett-
Packard 5246L electronic counter. X-band EPR spectra of com-
plexes 2-4 in CH3CN were obtained with a microwave power of
20.0, 20.3, and 19.9 mW, frequency at 9.602, 9.602, and 9.606
GHz, and modulation amplitude of 1.6, 1.6, and 0.4 G at 100 kHz,
respectively.
Magnetic Measurements. The magnetization data were recorded
on a SQUID magnetometer (MPMS5 Quantum Design company)
with an external 0.5 T magnetic field for complexes 2 and 3 in the
temperature range 2-300 K. The magnetic susceptibility of the
experimental data was corrected for diamagnetism by the tabulated
Pascal’s constants.
Crystallography. The crystals chosen for X-ray diffraction
studies measured 0.32 × 0.21 × 0.20 mm for complex 2, 0.40 ×
0.30 × 0.20 mm for complex 3, 0.40 × 0.35 × 0.25 mm for
complex 4, and 0.45 × 0.35 × 0.15 mm for complex 7, respectively.
Each crystal was mounted on a glass fiber and quickly coated in
epoxy resin. Unit-cell parameters were obtained by least-squares
refinement. Diffraction measurements for complexes 2, 3, 4, and 7
were carried out on a SMART CCD (Nonius Kappa CCD)
diffractometer with graphite-monochromated Mo KR radiation (λ
) 0.7107 Å) and between 1.41 and 27.50° for complex 2, between
1
2192 m (νCN) cm-1 (KBr, CH3CN). H NMR (CD3CN): δ 84.50
(br) (-CH2CN); -4.71 (br), 12.10 (br), 14.30 (br) (o-C6H3S); 2.17
(s) (SiMe3) ppm. Absorption spectrum (CH3CN) [λmax, nm (ꢀ, M-1
cm-1)]: 356 (12720), 543 (3490), 648 (1500), 925 (1700). Anal.
Calcd for C65H68N2P3Si3S3Ni: C, 64.56; H, 5.67; N, 2.32. Found:
C, 64.69; H, 5.55; N, 2.09.
Preparation of [NiII(PPh3)(P(C6H3-3-SiMe3-2-S)2(C6H3-3-
SiMe3-2-SH))] (8). NiCl2(PPh3)2 (0.131 g, 0.2 mmol) and P(C6H3-
3-SiMe3-2-SH)3 (0.115 g, 0.2 mmol) were dissolved in THF (10
mL) and stirred under N2 atmosphere for 30 min at ambient
temperature. Hexane (20 mL) was then added to precipitate the
brown solid [PPN][NiII(PPh3)(P(C6H3-3-SiMe3-2-S)2(C6H3-3-SiMe3-
2-SH))] (8) (yield 0.114 g, 64%). Diffusion of hexane into the THF
solution of complex 8 at room temperature for 4 days led to red-
brown crystals suitable for X-ray crystallography (Supporting
Inorganic Chemistry, Vol. 45, No. 26, 2006 10903

Lee et al.
1.42 and 27.50° for complex 3, between 1.45 and 27.50° for
complex 4, and between 1.64 and 27.50° for complex 7. Least-
squares refinement of the positional and anisotropic thermal
parameters of all non-hydrogen atoms and fixed hydrogen atoms
was based on F2. A SADABS absorption correction was made.25
The SHELXTL structure refinement program was employed.26
Acknowledgment. We gratefully acknowledge fin-
ancial support from the National Science Council of
Taiwan.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structural determinations of complexes 2-8,
crystallographic data and refinement parameters, and bond distances
and angles. This material is available free of charge via the Internet
at http://pubs.acs.org.
(25) Sheldrick, G. M. SADABS, Siemens Area Detector Absorption Cor-
rection Program; University of Go¨ttingen: Germany, 1996.
(26) Sheldrick, G. M. SHELXTL, Program for Crystal Structure Determi-
nation; Siemens Analytical X-ray Instruments Inc.: Madison, WI,
1994.
IC061399G
10904 Inorganic Chemistry, Vol. 45, No. 26, 2006