Synthesis and characterization of {Ni(NO)}10 and {Co(NO) 2}10 complexes supported by thiolate ligands

Article abstract of DOI:10.1021/ja803992y

Nitric oxide is an important molecule in biology and modulates a variety of physiological and pathophysiological processes. Some of its regulatory functions are exerted through interactions with redox-active elements, including iron, nickel, cobalt, and sulfur. Metalloenzymes containing [nFe-nS] (n = 2 or 4) clusters can be activated or inactivated by reaction with NO, affording dinitrosyl iron complexes. Studies of the NO chemistry of small-molecule iron thiolate complexes have provided insight into these biological processes and suggested probable intermediates. To explore this chemistry from a different perspective, we prepared nickel and cobalt thiolate complexes and investigated their reactions with NO and related compounds. We report here the first examples of anionic complexes containing {Ni(NO)}¹⁰ and {Co(NO) ₂}¹⁰ units, the reactivity of which suggests possible intermediates in the interconversion of iron thiolate nitrosyl compounds. Our results demonstrate new chemistry involving NO and simple complexes of nickel and cobalt supported by thiolates, which have been known for more than 30 years. The use of mass balance methodology was key to their discovery. Among the novel complexes reported are (Et₄N)₂[Ni(NO)(SPh)₃] (2), from (Et₄N)₂[Ni(SPh)₄] (1) and NO, (Et₄N)₂[Ni₂(NO)₂(μ-SPh) ₂(SPh)₂] (3), from 1 and NO⁺ or 2 and Me ₃O⁺, (Et₄N)[Co(NO)₂(SPh) ₂] (5), from (Et₄N)₂[Co(SPh)₄] (4) and NO, and [Co₃(NO)₆(μ-SPh)₃] (6), from 5 and Me₃O⁺. In the syntheses of 2 and 5, NO could be replaced by the convenient solid Ph₃CSNO.

Full text of DOI:10.1021/ja803992y

Published on Web 10/17/2008
Synthesis and Characterization of {Ni(NO)}10 and {Co(NO)2}10
Complexes Supported by Thiolate Ligands
Andrew G. Tennyson, Shanta Dhar, and Stephen J. Lippard*
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
Received May 28, 2008; E-mail: lippard@mit.edu
Abstract: Nitric oxide is an important molecule in biology and modulates a variety of physiological and
pathophysiological processes. Some of its regulatory functions are exerted through interactions with redox-
active elements, including iron, nickel, cobalt, and sulfur. Metalloenzymes containing [nFe-nS] (n ) 2 or 4)
clusters can be activated or inactivated by reaction with NO, affording dinitrosyl iron complexes. Studies of
the NO chemistry of small-molecule iron thiolate complexes have provided insight into these biological
processes and suggested probable intermediates. To explore this chemistry from a different perspective,
we prepared nickel and cobalt thiolate complexes and investigated their reactions with NO and related
compounds. We report here the first examples of anionic complexes containing {Ni(NO)}10 and {Co(NO)2}10
units, the reactivity of which suggests possible intermediates in the interconversion of iron thiolate nitrosyl
compounds. Our results demonstrate new chemistry involving NO and simple complexes of nickel and
cobalt supported by thiolates, which have been known for more than 30 years. The use of mass balance
methodology was key to their discovery. Among the novel complexes reported are (Et4N)2[Ni(NO)(SPh)3]
(2), from (Et4N)2[Ni(SPh)4] (1) and NO, (Et4N)2[Ni2(NO)2(µ-SPh)2(SPh)2] (3), from 1 and NO+ or 2 and Me3O+,
(Et4N)[Co(NO)2(SPh)2] (5), from (Et4N)2[Co(SPh)4] (4) and NO, and [Co3(NO)6(µ-SPh)3] (6), from 5 and
Me3O+. In the syntheses of 2 and 5, NO could be replaced by the convenient solid Ph3CSNO.
the synthetic complexes.11-13 Moreover, the conversion of a
[2Fe-2S] cluster into DNICs could involve intermediate forma-
Introduction
Nitric oxide plays important roles in biology, including
signaling in the central nervous system, activation of immune
response, regulation of protein function, and drug resistance.1-3
In many instances, these activities involve binding to a metal
ion, often a heme. There are a variety of non-heme targets for
NO, however, including iron-sulfur clusters. Mitochondrial
aconitase, for example, houses a [4Fe-4S] cluster in its active
form.4 Reaction of the EPR-silent cluster in this enzyme with
NO shuts down its activity and affords an EPR spectrum
indicative of a [3Fe-4S] cluster having nearly identical geometric
parameters and formation of a dinitrosyl iron complex (DNIC).5
In another example, NO activates the transcription factor SoxR,
which contains a [2Fe-2S] cluster, via DNIC formation.6
In order to elucidate the fundamental chemistry underlying
these processes, we7,8 and others9,10 have undertaken a system-
atic investigation of the nitric oxide chemistry of synthetic iron
thiolate complexes. The conversion of homoleptic [Fe(SR)4]2-
species by NO into DNICs proceeds through mononitrosyl iron
complexes (MNICs). MNICs have not yet been unambiguously
identified in protein regulation, but reactions of non-heme monoiron
enzymes with NO yield EPR spectra similar to those observed for
tion of two monometallic MNICs or a single dimetallic center
containing two mononitrosyl iron units.
In contrast, homoleptic thiolato complexes of nickel and
cobalt have never been observed in biology, and very little is
known about their nitric oxide chemistry. The A cluster of
acetyl-coenzyme A synthase/carbon monoxide dehydroge-
nase contains a [4Fe-4S] cluster bridged by a cysteine to a three-
coordinate nickel thiolate center, which is connected to a four-
coordinate N2S2-bound nickel species. Because iron-sulfur
clusters react with NO and the natural substrate for this enzyme
is CO, it is plausible that nitric oxide interacts with the enzyme
in vivo at iron, nickel, or sulfur. Although lacking a cobalt(II)
thiolate bond, the reduced form of cobalamin binds NO very
rapidly and tightly.14 This cobalt(II) unit is essential for
methionine synthesis and C1 metabolism; treatment of cells with
(7) Harrop, T. C.; Song, D.; Lippard, S. J. J. Am. Chem. Soc. 2006, 128,
3528–3529.
(8) Harrop, T. C.; Song, D.; Lippard, S. J. J. Inorg. Biochem. 2007, 101,
1730–1738.
(9) Lu, T.-T.; Chiou, S.-J.; Chen, C.-Y.; Liaw, W.-F. Inorg. Chem. 2006,
45, 8799–8806.
(10) Chiang, C.-Y.; Miller, M. L.; Reibenspies, J. H.; Darensbourg, M. Y.
J. Am. Chem. Soc. 2004, 126, 10867–10874.
(1) Calabrese, V.; Mancuso, C.; Calvani, M.; Rizzarelli, E.; Butterfield,
D. A.; Stella, A. M. G. Nature ReV. Neurosci. 2007, 8, 766–775.
(2) Turchi, J. J. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 4337–4338.
(3) Bronte, V.; Zanovello, P. Nature ReV. Immunol. 2005, 5, 641–654.
(4) Robbins, A. H.; Stout, C. D. Proc. Natl. Acad. Sci. U.S.A. 1989, 86,
3639–3643.
(11) Chen, V. J.; Orville, A. M.; Harpel, M. R.; Frolik, C. A.; Surerus,
K. K.; Mu¨nck, E.; Lipscomb, J. D. J. Biol. Chem. 1989, 264, 21677–
21681.
(12) Arciero, D. M.; Lipscomb, J. D.; Huynh, B. H.; Kent, T. A.; Mu¨nck,
E. J. Biol. Chem. 1983, 258, 14981–14991.
(5) Kennedy, M. C.; Antholine, W. E.; Beinert, H. J. Biol. Chem. 1997,
272, 20340–20347.
(13) Rich, P. R.; Salerno, J. C.; Leigh, J. S.; Bonner, W. D., Jr. FEBS Lett.
1978, 93, 323–326.
(6) Ding, H.; Demple, B. Proc. Natl. Acad. Sci. U.S.A. 2000, 97, 5146–
5150.
(14) Wolak, M.; Zahl, A.; Schneppensieper, T.; Stochel, G.; van Eldik, R.
J. Am. Chem. Soc. 2001, 123, 9780–9791.
9
10.1021/ja803992y CCC: $40.75
2008 American Chemical Society
J. AM. CHEM. SOC. 2008, 130, 15087–15098 15087

A R T I C L E S
Tennyson et al.
NO donors disrupts these functions,15 suggesting a role for NO
in regulating C1 metabolism.
X-ray Crystallographic Studies. Single crystals were mounted
at room temperature within microfiber loops immersed in Para-
tone-N oil and cooled to 110 K under a stream of cold nitrogen.
Intensity data were collected on a Bruker APEX CCD diffractometer
running the SMART software package, with Mo KR radiation (λ
) 0.71073 Å). The structures were solved by direct methods and
refined by using the SHELXTL20,21 software package. Empirical
absorption corrections were applied with SADABS,22 part of the
SHELXTL program package, and the structures were checked for
higher symmetry by the program PLATON.23 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were placed
at calculated positions and assigned thermal parameters equal to
either 1.5 (methyl hydrogen atoms) or 1.2 (non-methyl hydrogen
atoms) times the thermal parameters of the atoms to which they
were attached. Complex 3 crystallizes with one CH3CN molecule
in the asymmetric unit, and the nitrogen atom was refined in two
positions, each with half-occupancy. Parameters for 2, 3, 5, and 6
are listed in the Supporting Information (Tables S1-S4).
General Procedure for Mass Balance Analyses. Reactions were
quenched by addition to 10 volume equiv of Et2O and cooled to
-30 °C for 2 h, after which the precipitate and supernatant were
separated by filtration. The filtrate was transferred to a Schlenk
flask, cycled out of the drybox, and stripped on a vacuum line
without heating (room-temperature water bath). The residue from
the filtrate was washed three times with 3 mL of solvents with
increasing polarity, Et2O < THF < CH3CN, to extract separately
the components present. Each wash was filtered into a separate tared
vial, the solvent removed, and the mass recorded. GC-MS was
performed on the white solid isolated from the Et2O fraction and
the result compared with that of authentic Ph2S2. When Ph3CSNO
rather than NO was used as the NO-donating reagent, a statistical
mixture of Ph2S2, PhSSCPh3, and Ph3CSSCPh3 was observed. To
calculate the percent yield of disulfide in this case, the average
molecular weight was computed from the relative contribution of
each disulfide to the total mixture; e.g., for a 1:2:1 mixture,
0.25(Ph2S2) + 0.5(PhSSCPh3) + 0.25(Ph3CSSCPh3) ) 0.25(218.34)
+ 0.5(384.56) + 0.25(550.77) ) 384.56 g mol-1. The THF and
CH3CN extracts from the filtrate residue and precipitate were
analyzed separately by IR and 1H NMR spectroscopy and combined
only after their identities were confirmed.
Syntheses. (Et4N)2[Ni(NO)(SPh)3] (2). From 1 + NO(g). In 5
mL of CH3CN was dissolved 75.1 mg of 1 (99.4 µmol), and into
the resulting dark red solution was bubbled 2.5 mL of NO(g) (102
µmol), affording a gradual color change to blue-green. This solution
was allowed to stir for 30 min at room temperature and was then
added to 100 mL of Et2O, causing the formation of a white-green
suspension. After this mixture was cooled to -30 °C for 2 h, a
blue-green microcrystalline product had formed along with a light
green supernatant. The precipitate was collected by filtration, and
the filtrate was stripped to afford a mixture of white and blue-
green solids. Mass balance analysis was performed, and from this
reaction were isolated 9.0 mg of Ph2S2 (41 µmol, 82%) and 65 mg
of 2 (96 µmol, 97%).
From 1 + Ph3CSNO. In 5 mL of CH3CN was dissolved 77.8
mg of 1 (103 µmol), and to the resulting dark red solution was
added 32.4 mg of Ph3CSNO (106 µmol) in 5 mL of CH3CN,
affording a gradual color change to blue-green. This solution was
allowed to stir for 30 min at room temperature and was then added
to 100 mL of Et2O, causing the formation of a white-green
suspension. After this mixture was cooled to -30 °C for 2 h, a
blue-green microcrystalline product had formed along with a light
green supernatant. The precipitate was collected by filtration, and
Previous reactivity studies of simple iron thiolate complexes
with NO suggest that intermediates exist in the formation of
multimetallic iron nitrosyl species that have not yet been
observed. Low-temperature in situ spectroscopy might reveal
their existence but would not yield as much information as
isolation and characterization of discrete complexes. An alterna-
tive is to study the nitric oxide chemistry of analogous thiolate
complexes of the adjacent transition metals cobalt and nickel.
Electronic configurations or geometries that are transient or
unstable for iron may be more robust when these other metals
are employed. Furthermore, by studying the reactivity of simple
thiolate complexes of nickel and cobalt with NO, we might gain
insight into how nitric oxide could interact with complexes of
these metals in vivo and guide potential future enzymatic
investigations. We therefore extended our studies to include
reactions of nickel(II) and cobalt(II) thiolate complexes with
NO(g), NOBF4, and Ph3CSNO, beginning with the homoleptic
[M(SPh)4]2- ions. Despite the simplicity of this system and the
availability of the reactants for more than a decade, their
chemistry remained unexplored. Herein we report the first results
of our investigation.
Experimental Section
Materials and Methods. Metal salts and porphyrinato complexes
were purchased from Strem Chemicals and organic reagents from
Aldrich Chemical Co. or Alfa Aesar and used as received. Solvents
were dried and purified by passage through alumina columns under
an argon atmosphere. (Et4N)2[Ni(SPh)4] (1) and (Et4N)2[Co(SPh)4]
(4) were prepared by literature methods.16,17 Ph3CSNO was
prepared by a modification of an established procedure.18 Air- and
water-sensitive manipulations were carried out under a dry nitrogen
or argon atmosphere using standard Schlenk or glovebox techniques.
Nitric oxide gas was purified following a reported procedure19 by
passage first through a 2 m stainless steel coil packed with silica
and cooled to -78 °C, then through an Ascarite column. Manipula-
tions and transfers of purified NO(g) were performed with gas-
tight syringes under an inert atmosphere.
General Spectroscopic Considerations. NMR spectra were
recorded at 22 °C on a 400 MHz Bruker Avance spectrometer.
Chemical shifts for 1H and 13C NMR spectra are expressed in ppm
relative to residual solvent (CD2HCN in CD3CN, 1.94 and 1.24
1
ppm for H and 13C, respectively). FT-IR spectra were recorded
on a ThermoNicolet Avatar 360 spectrophotometer running the
OMNIC software. Solid samples were examined as KBr discs.
Solution FT-IR spectra were acquired in a gas-tight Graseby-Specac
solution cell equipped with CaF2 windows and 0.1 mm Teflon
spacers. UV-visible absorption spectra were recorded on a Cary
50 spectrophotometer at 25 °C. Stirring and temperature control
were performed with a Quantum Northwest TC125 Peltier device.
All measurements were made with a matched pair (blank and
sample) of 6Q Spectrosil quartz cuvettes (Starna) with 1 cm path
lengths and 3.0 mL sample solution volumes. The sample cuvette
was sealed with a gas-tight Teflon-lined screw cap equipped with
a septum.
(15) Danishpajooh, I. O.; Gudi, T.; Chen, Y.; Kharitonov, V. G.; Sharma,
V. S.; Boss, G. R. J. Biol. Chem. 2001, 276, 27296–27303.
(16) Yamamura, T.; Miyamae, H.; Katayama, Y.; Sasaki, Y. Chem. Lett.
1985, 269–272.
(17) Dance, I. G. J. Am. Chem. Soc. 1979, 101, 6264–6273.
(18) (a) Josephy, P. D.; Rehorek, D.; Janzen, E. G. Tetrahedron Lett. 1984,
25, 1685–1688. (b) Arulsamy, N.; Bohle, D. S.; Butt, J. A.; Irvine,
G. J.; Jordan, P. A.; Sagan, E. J. Am. Chem. Soc. 1999, 121, 7115–
7123. (c) Harrop, T. C.; Tonzetich, Z. J.; Reisner, E.; Lippard, S. J.
J. Am. Chem. Soc. 2008, 130, in press (http://dx.doi.org/ja8054996).
(19) Tran, D.; Skelton, B. W.; White, A. H.; Laverman, L. E.; Ford, P. C.
Inorg. Chem. 1998, 37, 2505–2511.
(20) Sheldrick, G. M. SHELXTL; University of Go¨ttingen: Go¨ttingen,
Germany, 2000.
(21) Sheldrick, G. M. SHELXTL, v 6.10; Bruker AXS: Madison, WI, 2001.
(22) Sheldrick, G. M. SADABS; University of Go¨ttingen: Go¨ttingen,
Germany, 2001.
(23) Spek, A. L. PLATON; Utrecht University: Utrecht, The Netherlands,
2000.
9
15088 J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008

{Ni(NO)}10 and {Co(NO)2}10 Thiolate Complexes
A R T I C L E S
the filtrate was stripped to afford a mixture of white and blue-
green solids. Mass balance analysis was performed, and from this
reaction were isolated 37 mg of disulfide (96 µmol, 93%) and 66
mg of 2 (98 µmol, 95%).
and from this reaction were isolated 10 mg of disulfide (46 µmol,
92%), 24 mg of Et4NSPh (100 µmol, 100%), and 41 mg of 5 (88
µmol, 88%).
From 4 + Ph3CSNO. In 5 mL of CH3CN was dissolved 76.1
mg of 4 (101 µmol), and to the resulting dark green solution was
added 62.0 mg of Ph3CSNO (204 µmol) in 5 mL of CH3CN,
affording a gradual color change to dark brown. This solution was
allowed to stir for 30 min at room temperature and was then added
to 100 mL of Et2O, causing the formation of a white-brown
suspension. While this mixture was being cooled to -30 °C for
2 h, we observed formation of a dark brown microcrystalline
product along with a dark brown supernatant. The precipitate was
collected by filtration, and the filtrate was stripped to afford a
mixture of white and dark brown solids. Mass balance analysis was
performed, and from this reaction were isolated 56 mg of disulfide
(85 µmol, 84%), 19 mg of Et4NSPh (79 µmol, 77%), and 44 mg
of 5 (93 µmol, 92%).
From 4 + NOBF4. In 5 mL of CH3CN was dissolved 76.8 mg
of 4 (102 µmol), and to the resulting dark green solution was added
11.8 mg of NOBF4 (101 µmol) in 5 mL of CH3CN, affording a
color change to dark brown with a purple colloid. This mixture
was allowed to stir for 30 min at room temperature and was then
added to 100 mL of Et2O, causing the formation of a white-brown
suspension. After this mixture was cooled to -30 °C for 2 h, a
dark brown microcrystalline product had formed along with a dark
brown supernatant. Mass balance analysis was performed, and from
this reaction were isolated 11 mg of Ph2S2 (50 µmol, 100%), 22
mg of Et4NBF4 (101 µmol, 100%), 21 mg of 5 (45 µmol, 90%),
and an intractable dark purple solid.
1
Characterization of 2. H NMR (CD3CN): δ 7.62 (d, o-C6H5,
6H); 6.99 (t, m-C6H5, 6H); 6.79 (s, p-C6H5, 3H); 3.15 (q, NCH2CH3,
16H); 1.20 (tt, NCH2CH3, 24H) ppm. 13C NMR (CD3CN): δ 133.7,
128.1, 120.9, 120.8, 52.9 (t, NCH2CH3), 7.59 (NCH2CH3) ppm.
FT-IR (KBr): 1655 (vs, νNO), 1570 (vs), 1481 (s), 1468 (vs), 1450
(s), 1437 (m), 1390 (s), 1365 (w), 1336 (w), 1304 (w), 1261 (w),
1182 (w), 1173 (m), 1151 (w), 1126 (w), 1082 (s), 1063 (m), 1024
(m), 1003 (m), 993 (m), 964 (w), 904 (vw), 885 (w), 839 (vw),
783 (m), 739 (vs), 694 (vs), 617 (vw), 548 (w), 482 (m), 428 (w)
cm-1. FT-IR (CH3CN, CaF2): νNO ) 1756 (vs) cm-1. UV-vis in
CH3CN, λ (ꢀ) in nm (M-1 cm-1): 372 (6260), 423 (sh, 2930), 812
(1380). Anal. Calcd for C34H55N3OS3Ni: C, 60.35; H, 8.19; N, 6.21.
Found: C, 59.54; H, 8.13; N, 6.09. Blue-green plates (0.14 × 0.09
× 0.04 mm) suitable for X-ray diffraction were grown by cooling
a saturated solution of 2 in CH3CN from room temperature to -30
°C over 2 weeks.
(Et4N)2[Ni2(NO)2(µ-SPh)2(SPh)2] (3). From 1 + NOBF4. In 5
mL of CH3CN was dissolved 156 mg of 1 (206 µmol), and to the
resulting dark red solution was added 23.1 mg of NOBF4 (198
µmol) in 5 mL of CH3CN, affording a gradual color change to
dark brown-green. This solution was allowed to stir for 30 min at
room temperature and was then added to 100 mL of Et2O, causing
the formation of a white-brown suspension. After this mixture was
cooled to -30 °C for 2 h, a dark brown microcrystalline product
had formed along with a dark green supernatant. Mass balance
analysis was performed, and from this reaction were isolated 41
mg of Ph2S2 (188 µmol, 95%), 40 mg of Et4NBF4 (184 µmol, 93%),
and 86 mg of 3 (98 µmol, 99%).
From 2 + Me3OBF4. In 5 mL of CH3CN was dissolved 67.7
mg of 2 (100 µmol), and to the resulting dark blue-green solution
was added 14.7 mg of Me3OBF4 (99.4 µmol) in 3 mL of CH3CN,
affording a gradual color change to dark green. This solution was
allowed to stir for 30 min at room temperature and was then added
to 100 mL of Et2O, causing the formation of a white-green
suspension. After this mixture was cooled to -30 °C for 2 h, a
white solid had formed along with a dark green supernatant. Mass
balance analysis was performed, and from this reaction were isolated
21 mg of Et4NBF4 (97 µmol, 98%) and 43 mg of 3 (49 µmol, 98%).
Characterization of 3. 1H NMR (CD3CN): δ 7.83 (br, o-C6H5,
8H); 7.13 (br, m-C6H5, 8H); 6.98 (br, p-C6H5, 4H); 3.12 (q,
NCH2CH3, 16H); 1.17 (tt, NCH2CH3, 24H) ppm. 13C NMR
(CD3CN): δ 134.1, 137.8, 128.5, 123.1, 53.0 (t, NCH2CH3), 7.62
(NCH2CH3) ppm. FT-IR (KBr): 1709 (vs, νNO), 1574 (s), 1471 (s),
1433 (m), 1392 (m), 1367 (w), 1338 (vw), 1302 (w), 1265 (w),
1182 (w), 1171 (m), 1082 (s), 1065 (m), 1055 (m), 1024 (m), 1001
(m), 976 (w), 895 (w), 854 (w), 789 (m), 742 (vs), 694 (vs), 671
(vw), 615 (vw), 569 (w), 482 (m), 426 (w). FT-IR (THF, CaF2):
νNO ) 1751 (vs), 1721 (vs) cm-1. UV-vis in CH3CN, λ (ꢀ) in nm
(M-1 cm-1): 365 (7990), 431 (sh, 3360), 639 (sh, 989), 808 (1650).
Anal. Calcd for C41H61.5N4.5O2S4Ni2: C, 55.01; H, 6.93; N, 7.04.
Found: C, 54.64; H, 6.60; N, 7.34. Dark green blocks (0.20 × 0.20
× 0.05 mm) suitable for X-ray diffraction were grown by vapor
diffusion of Et2O into a solution of 3 in CH3CN at -30 °C over 3
days.
(Et4N)[Co(NO)2(SPh)2] (5). From 4 + NO(g). In 5 mL of
CH3CN was dissolved 75.6 mg of 4 (100 µmol), and into the
resulting dark green solution was bubbled 10.0 mL of NO (406
µmol), affording a gradual color change to dark brown. This solution
was allowed to stir for 30 min at room temperature and was then
added to 100 mL of Et2O, causing the formation of a white-brown
suspension. After this mixture was cooled to -30 °C for 2 h, a
dark brown microcrystalline product had formed along with a white
precipitate and a dark brown supernatant. The solids were collected
by filtration, and the filtrate was stripped to afford a mixture of
white and dark brown solids. Mass balance analysis was performed,
Characterization of 5. 1H NMR (CD3CN): δ 7.30 (dd, o-C6H5,
4H); 7.00 (tt, m-C6H5, 4H); 6.84 (tt, p-C6H5, 2H); 3.14 (br q,
NCH2CH3, 8H); 1.18 (br t, NCH2CH3, 12H) ppm. 13C NMR
(CD3CN): δ 148.9, 133.2, 128.3, 122.5, 53.0 (t, NCH2CH3), 7.68
(NCH2CH3) ppm. FT-IR (KBr): 1756 (vs, νNO), 1678 (vs, νNO),
1573 (s), 1558 (m), 1479 (s), 1473 (s), 1460 (s), 1433 (s), 1390
(s), 1374 (w), 1366 (m), 1335 (w), 1311 (w), 1295 (w), 1265 (w),
1170 (s), 1083 (s), 1067 (m), 1056 (m), 1020 (m), 998 (m), 895
(w), 844 (w), 781 (m), 753 (s), 749 (s), 696 (s), 480 (w), 421 (w)
cm-1. FT-IR (THF, CaF2): νNO ) 1769 (vs), 1699 (vs) cm-1
.
UV-vis in CH3CN, λ (ꢀ) in nm (M-1 cm-1): 346 (sh, 6060). Anal.
Calcd for C20H30N3O2S2Co: C, 51.38; H, 6.47; N, 8.99. Found: C,
51.65; H, 6.58; N, 8.79. Dark brown-black needles (0.25 × 0.08
× 0.03 mm) suitable for X-ray diffraction were grown by vapor
diffusion of Et2O into a solution of 5 in THF at -30 °C overnight.
[Co3(NO)6(µ-SPh)3] (6). In 5 mL of CH3CN was dissolved 70.0
mg of 5 (150 µmol), and to the resulting dark brown solution was
added 22.7 mg of Me3OBF4 (153 µmol) in 3 mL of CH3CN,
affording a gradual color change to dark red-orange. This solution
was allowed to stir for 30 min at room temperature and was then
added to 100 mL of Et2O, causing the formation of cloudy red-
orange solution. After this mixture was cooled to -30 °C for 2 h,
a light gray precipitate had formed along with a red-orange
supernatant. Mass balance analysis was performed, and from this
reaction were isolated 32 mg of Et4NBF4 (147 µmol, 98%) and 33
mg of 6 (48 µmol, 96%).
1
Characterization of 6. H NMR (CD3CN): δ 7.53 (d, o-C6H5,
6H); 7.28 (t, m-C6H5, 6H); 7.19 (t, p-C6H5, 3H) ppm. 13C NMR
(CD3CN): δ ) 134.4, 130.5, 128.3 ppm. FT-IR (KBr): 1840 (s,
νNO), 1817 (s, νNO), 1779 (s, νNO), 1744 (s, νNO), 1575 (vw), 1473
(w), 1435 (w), 1385 (vw), 1295 (vw), 1261 (w), 1152 (vw), 1011
(vw), 1080 (vw), 1066 (w), 1021 (w), 999 (vw), 800 (w), 740 (vs),
687 (s), 479 (m) cm-1. FT-IR (THF, CaF2): νNO ) 1844 (m sh),
1819 (vs), 1780 (vs), 1764 (s sh) cm-1. UV-vis in CH3CN, λ (ꢀ)
in nm (M-1 cm-1): 325 (sh, 12 500), 421 (br sh, 6670), 656 (sh,
757). Anal. Calcd for C18H15N6O6S3Co3: C; 31.59; H, 2.21; N,
12.28. Found: C, 31.28; H, 2.25; N, 12.20. Dark brown-red plates
(0.20 × 0.20 × 0.02 mm) suitable for X-ray diffraction were grown
by cooling a saturated solution of 6 in Et2O at room temperature
to -30 °C for 1 week.
9
J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008 15089

A R T I C L E S
Tennyson et al.
Scheme 1. Syntheses of 2 and 3
Table 1. 1H NMR Chemical Shifts for PhS- Ligands and Ratio of
Et4N+:PhS- Integrals for 1-6
NO Transfer Reactions. UV-Vis Spectroscopic Parameters.
Using the Cary 50 scanning kinetics software, the scan window
range was set to 800-200 nm, with 50 ms averaging time, 1.00
nm resolution, and 1200 nm/min scan rate; scans were acquired
every 60 s for 2 h. The first scan in each experiment measured the
metalloporphyrin alone. An aliquot of metal nitrosyl was added,
and the solution was vigorously shaken for 3 s and then allowed to
stand for an additional 7 s before beginning the second scan. Thus,
a total of 10 s elapsed between injection of the metal nitrosyl and
the beginning of the second scan.
ortho
meta
para
Et4N+:PhS-
1
2
3
4
5
6
1.91
7.62
7.83
17.3
7.30
7.54
21.7
-12.5
1:2
2:3
1:2a
1:2
1:2
s
6.99
7.13
-24.5
6.79
6.98
-33.0
7.00
7.28
6.84
7.19
a Terminal and bridging PhS- ligands are in rapid exchange (see text
and Figure S1, Supporting Information).
Metal Nitrosyl Reactions with [Fe(TPP)Cl]. A 762 µM stock
solution of [Fe(TPP)Cl] in THF was prepared, from which a 7.62
µM working solution in THF was obtained. A 2.3 mM stock
solution of metal nitrosyl (2 in CH3CN, 3 or 5 in THF) was
prepared. After a blank was acquired in THF, the spectrum of a 3
mL aliquot of the working solution of [Fe(TPP)Cl] was obtained
to verify the concentration by measuring the absorption of the Soret
band (λ ) 417 nm, ꢀ ) 1.11 × 105 M-1 cm-1). Simple NO
coordination would afford [Fe(TPP)(NO)Cl], a process that does
not significantly alter the UV-vis spectrum in the 400-1000 nm
concomitant bathochromic shift in the Soret band and increase in
absorptivity (λ ) 411 nm, ꢀ ) 1.77 × 106 M-1 cm-1).27 In
comparison, the Soret band for cobalt-reconstituted guanylyl cyclase
[Co(sGC)] (λ ) 401 nm, ꢀ ) 1.14 × 105 M-1 cm-1) shifts
hypsochromically with a decrease in absorptivity upon binding NO
(λ ) 390 nm, ꢀ ) 1.07 × 105 M-1 cm-1).28
Results and Discussion
region.24
A reductive nitrosylation reaction would afford
[Fe(TPP)(NO)] with a concomitant hypsochromic shift in the Soret
Synthesis and Properties of the First Mononuclear {Ni(NO)}10
Anion (2). Addition of a stoichiometric amount of Ph3CSNO to
a solution of 1 in CH3CN caused an immediate color change
from dark red to dark blue-green. Mass balance analysis
band (λ ) 405 nm, ꢀ ) 1.00 × 105 M-1 cm-1).25
Reaction of 2 with [Fe(TPP)Cl]. In 5 mL of THF was dissolved
70.9 mg of [Fe(TPP)Cl] (101 µmol), and to the resulting dark red
solution was added 67.1 mg of 2 (99.2 µmol) in 3 mL of CH3CN,
affording no perceptible color change. This solution was allowed
to stir for 30 min at room temperature and was then added to 100
mL of Et2O, causing the formation of a red-brown solution. After
this mixture was cooled to -30 °C for 2 h, a sticky dark green
precipitate had formed along with a red-brown supernatant. No
Ph2S2 was isolated from the supernatant, and the IR spectrum of
the dark green precipitate was identical to that of authentic 3, with
an NO stretch at 1709 cm-1. Mass balance analysis could not be
performed because of the similar solubilities of 3 and the porphyrin-
containing product.
indicated that
1 equiv of disulfide and 1 equiv of
(Et4N)2[Ni(NO)(SPh)3] (2) were produced per equiv of 1
1
consumed (Scheme 1). Compound 2 is diamagnetic, and H
NMR spectroscopy reveals a 2:3 ratio of Et4N+ to PhS- protons
(Table 1). The NO stretch for 2 occurs at 1655 cm-1 in the
solid state (KBr) but shifts to 1756 cm-1 in solution (CH3CN).
Monometallic {Ni(NO)}10 complexes can exhibit solvent-
dependent variations in νNO by up to 50 cm-1 from the value
measured in the solid state.29 This behavior is believed to be a
result of a Lewis acid-base interaction between the nitrosyl
and solvent,30 but the limited solubility of 2 precludes a study
of νNO dependence on solvent acceptor number. Dissolving 2
in CH3CN, removing the solvent in vacuo, and acquiring the
IR spectrum in a KBr pellet or Nujol mull reveals the same
NO Transfer to [Co(TPP)]. A 2.01 mM stock solution of
[Co(TPP)] in THF was prepared, from which a 5.03 µM working
solution in THF was obtained. A 2.0 mM stock solution of 2 in
CH3CN was prepared. After a blank was acquired in THF, the
spectrum of a 3 mL aliquot of the working solution of [Co(TPP)]
was obtained to verify the concentration by measuring the absorp-
tion of the Soret band (λ ) 409 nm, ꢀ ) 2.05 × 105 M-1 cm-1).26
Simple NO coordination would afford [Co(TPP)(NO)] with a
(27) Richter-Addo, G. B.; Hodge, S. J.; Yi, G.-B.; Khan, M. A.; Ma, T.;
Van Caemelbecke, E.; Guo, N.; Kadish, K. M. Inorg. Chem. 1996,
35, 6530–6538.
(28) Dierks, E. A.; Hu, S.; Vogel, K. M.; Yu, A. E.; Spiro, T. G.; Burstyn,
J. N. J. Am. Chem. Soc. 1997, 119, 7316–7323.
(24) Wayland, B. B.; Olson, L. W. J. Am. Chem. Soc. 1974, 96, 6037–
6041.
(25) Scheidt, W. R.; Frisse, M. E. J. Am. Chem. Soc. 1975, 97, 17–21.
(26) Cruz, F. D.; Driaf, K.; Berthier, C.; Lameille, J.-M.; Armand, F. Thin
Solid Films 1999, 349, 155–161.
(29) Darensbourg, D. J.; Decuir, T. J.; Stafford, N. W.; Robertson, J. B.;
Draper, J. D.; Reibenspies, J. H.; Katho´, A.; Joo´, F. Inorg. Chem.
1997, 36, 4218–4226.
(30) Hunter, A. D.; Legzdins, P. Organometallics 1986, 5, 1001–1009.
9
15090 J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008

{Ni(NO)}10 and {Co(NO)2}10 Thiolate Complexes
A R T I C L E S
νNO band at 1655 cm-1. According to the Enemark-Feltham
convention,31 2 has a {Ni(NO)}10 core, and complexes of this
type are well-known. Other four-coordinate, monometallic
{Ni(NO)}10 complexes are diamagnetic and display a range of
NO stretching frequencies from 1558 to 1867 cm-1 (avg ) 1742
( 68 cm-1).29,32-43 Possibly, the solid-state νNO value is
significantly below average because the {Ni(NO)}10 core is
supported by three thiolates in a dianionic molecule, whereas
the other complexes are cationic or charge neutral. Complex 2
contains the first reported example of a {Ni(NO)}10 species
contained within an anionic molecule.
A preliminary reactivity study of 1 with S-nitroso-N-acetyl-
penicillamine (SNAP) also afforded 2, judging by FT-IR
spectroscopy, but the insolubility of SNAP in CH3CN prevented
reaction homogeneity and accurate mass balance analysis.
S-Nitrosothiols (RSNOs), like SNAP, are prevalent in biology
and believed by some to be the predominant carriers of NO.
Nevertheless, the mechanism by which an RSNO delivers NO
is controversial.44-49 The two limiting cases are RSNO delivery
of NO, termed nitrosylation, and delivery of NO+, termed
nitrosation.50 To determine whether the RSNO species were
behaving as NO or NO+ donors, we compared the reactivity of
Ph3CSNO and SNAP with that of NO(g). Addition of stoichio-
metric NO(g) to 1 afforded slow conversion to 0.5 equiv of
Ph2S2 and 1 equiv of 2 (Scheme 1). Because the reaction of 1
with either Ph3CSNO or SNAP yielded 2, we conclude that these
S-nitrosothiols are functioning as NO donors, and such behavior
has been observed previously by us8 and others.9 Slow vapor
diffusion of Et2O into a solution of 2 in CH3CN at -30 °C
over 2 weeks afforded crystals suitable for X-ray diffraction,
which confirmed the structural assignment of 2 (Figure 1). The
average nickel nitrosyl structural parameters for 2 (Ni-N-O
) 156.6°, N-O ) 1.171 Å, Ni-N ) 1.663 Å, Table 2s) fall
within the range of reported values for other four-coordinate,
monometallic{Ni(NO)}10 complexes(Ni-N-O)149.1-180.0°,
Figure 1. ORTEP diagram showing 50% probability thermal ellipsoids
and selected atom labels for one of the two crystallographically distinct
molecules of 2 in the crystal lattice. The Et4N+ cations and H atoms are
omitted for clarity. Selected bond distances (Å) and angles (deg): N1-O1,
1.178(9); Ni1-N1, 1.651(7); Ni1-S1, 2.339(2); Ni1-S2, 2.307(2); Ni1-S3,
2.279(2); Ni1-N1-O1, 159.0(6); S1-Ni1-N1, 121.6(2); S2-Ni1-N1,
119.9(2); S3-Ni1-N1, 105.5(2); S1-Ni1-S2, 99.67(7); S1-Ni1-S3,
106.82(7); S2-Ni1-S3, 101.14(7); N2-O2, 1.164(8); Ni2-N2, 1.674(7);
Ni2-S4, 2.295(2); Ni2-S5, 2.270(2); Ni2-S6, 2.317(2); Ni2-N2-O2,
154.2(6); S4-Ni2-N2, 126.0(2); S5-Ni2-N2, 103.0(2); S6-Ni2-N2,
118.2(2); S4-Ni2-S5, 98.71(8); S4-Ni2-S6, 99.19(8); S5-Ni2-S6,
109.80(8).
Table 2. List of Bond Lengths (Å), Angles (deg), and νNO (cm-1
Values for 2 and IIa-c
)
2a
IIa
IIb
IIc
N-O
M-N
M-S
1.171(10)
1.663(16)
2.328(16)
2.301(8)
2.275(6)
156.6(34)
123.8(31)
119.1(12)
104.3(18)
108.3(21)
100.2(14)
99.19(7)
1655
1.131(4)
1.665(3)
2.3503(11)
2.3432(11)
2.3190(10)
173.9(4)
121.34(11)
114.47(10)
114.01(11)
103.87(4)
101.34(4)
99.30(4)
s
1.173(2)
1.683(2)
2.2915(5)
2.2838(5)
2.2775(5)
167.0(2)
130.48(7)
117.99(6)
117.48(8)
95.67(2)
94.54(2)
92.99(2)
1785
1.169(6)
1.682(5)
2.2780(13)
2.2696(12)
2.2670(14)
164.6(5)
116.52(16)
109.19(18)
108.69(18)
109.47(5)
108.35(5)
103.87(5)
s
M-N-O
S-M-N
S-M-S
(31) Enemark, J. H.; Feltham, R. D. J. Am. Chem. Soc. 1974, 96, 5002–
5004.
νNO (solid)
νNO (soln)
(32) Schebler, P. J.; Riordan, C. G.; Guzei, I. A.; Rheingold, A. L. Inorg.
Chem. 1998, 37, 4754–4755.
1756
1752
s
1732
(33) Fullmer, B. C.; Pink, M.; Fan, H.; Yang, X.; Baik, M.-H.; Caulton,
K. G. Inorg. Chem. 2008, 47, 3888–3892.
a Structural parameters are averaged from the two crystallographically
distinct molecules. Numbers in parentheses represent standard deviation
from mean, not ESD values.
(34) Landry, V. K.; Pang, K.; Quan, S. M.; Parkin, G. Dalton Trans. 2007,
820–824.
(35) Landry, V. K.; Parkin, G. Polyhedron 2007, 26, 4751–4757.
(36) Maffett, L. S.; Gunter, K. L.; Kreisel, K. A.; Yap, G. P. A.; Rabinovich,
D. Polyhedron 2007, 26, 4758–4764.
Chart 1
(37) MacBeth, C. E.; Thomas, J. C.; Betley, T. A.; Peters, J. C. Inorg.
Chem. 2004, 43, 4645–4662.
(38) Rahman, A. F. M. M.; Salem, G.; Stephens, F. S.; Wild, S. B. Inorg.
Chem. 1990, 29, 5225–5230.
(39) Kriege-Simondsen, J.; Elbaze, G.; Dartiguenave, M.; Feltham, R. D.;
Dartiguenave, Y. Inorg. Chem. 1982, 21, 230–236.
(40) Chong, K. S.; Rettig, S. J.; Storr, A.; Trotter, J. Can. J. Chem. 1979,
57, 3107–3112.
(41) Di Vaira, M.; Ghilardi, C. A.; Sacconi, L. Inorg. Chem. 1976, 15,
1555–1561.
(42) Meiners, J. H.; Rix, C. J.; Clardy, J. C.; Verkade, J. G. Inorg. Chem.
1975, 14, 705–710.
avg ) 165.8 ( 11.1°; N-O ) 1.120-1.185 Å, avg ) 1.160 (
0.017 Å; Ni-N ) 1.581-1.692 Å, avg ) 1.645 ( 0.032
Å).29,32-43 Because the mean Ni-N-O angle for 2 is more
acute than average and the N-O and Ni-N distances are longer,
we conclude that the nickel atom in 2 provides greater
π-backbonding to the nitrosyl. This result is consistent with the
anionic environment and ligand donation ability in the nickel
nitrosyl fragment of 2, whereas other reported {Ni(NO)}10
complexes are neutral or cationic and are not bound by thiolates.
Of the structurally characterized, four-coordinate, monome-
tallic {Ni(NO)}10 complexes, only two are supported by sulfur
(43) Enemark, J. H. Inorg. Chem. 1971, 10, 1952–1957.
(44) Chen, Y.; Irie, Y.; Keung, W. M.; Maret, W. Biochemistry 2002, 41,
8360–8367.
(45) Dicks, A. P.; Williams, D. L. H. Chem. Biol. 1996, 3, 655–659.
(46) Kelm, M. Biochim. Biophys. Acta 1999, 1411, 273–289.
(47) Singh, S. P.; Wishnok, J. S.; Keshive, M.; Deen, W. M.; Tannenbaum,
S. R. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 14428–14433.
(48) Tsikas, D.; Fro¨lich, J. C. Nitric Oxide 2004, 11, 209–213.
(49) Vanin, A. F.; Papina, A. A.; Serezhenkov, V. A.; Koppenol, W. H.
Nitric Oxide 2004, 10, 60–73.
(50) Bonner, L.; Stedman, G. In Methods in Nitric Oxide Research;
Feelisch, M., Stamler, J. S., Eds.; Wiley: London, 1996; pp 4-18.
9
J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008 15091

A R T I C L E S
Tennyson et al.
donor ligands (Chart 1).32,36 For comparison, the structural
parameters for these complexes and their νNO values are reported
in Table 2. Complexes IIa,b both contain {Ni(NO)}10 cores
supported by monoanionic, κ3-S3 ligands and are arranged
according to increasing νNO. Unfortunately, no clear trends are
apparent in this comparison. Complex 2 most closely resembles
IIa on the basis of the M-N bond length and the S-M-N
and S-M-S angles. However, the N-O and M-S distances
in 2 are most similar to those in IIb, whereas the Ni-N-O
angle and solid-state NO stretching energy are substantially
different from those of the other complexes with {Ni(NO)}10
cores bound to three sulfur atoms. A similar lack of any
straightforward trend in structural parameters is also observed
for manganese nitrosyls,51 for which the νNO is recommended
as the most reliable measure of the {M(NO)} electron count.
Complexes containing {Cu(NO)}11 cores are very rare, and the
structurally characterized examples with C3V geometries exhibit
νNO values ranging from 1698 to 1742 cm-1 (avg ) 1712 (
18 cm-1).52,53 Because {Cu(NO)}11 formally contains one more
electron in the metal nitrosyl unit than {Ni(NO)}10, complexes
with this unit should display lower νNO values. This behavior
is observed for the average NO stretching energies for
{Cu(NO)}11 and {Ni(NO)}10 complexes with similar geometries
(1712 vs 1742 cm-1). However, complex 2 exhibits a νNO value
in KBr nearly 50 cm-1 lower than the lowest measured value
for a {Cu(NO)}11 complex, despite the latter having greater
electron density within the metal nitrosyl unit. These results
suggest that the electronic properties of a {M(NO)} core depend
heavily on the electron-donating ability of the ligands and the
overall charge of the molecule.
those of 2 and 3 (Figure S1), equal to the weighted average of
their values in 2 and 3, confirming that intermolecular thiolate
exchange is occurring. The presence of only one set of
broadened aryl peaks in the spectrum of 3 therefore results from
a similar intermolecular exchange. Presumably, this process
allows for isolation of crystalline 2 from a cooled THF solution
of 3 and accounts for the interconversion of 2 and 3 by loss or
gain of Et4NSPh (vide infra).
In the solid state (KBr), only one NO stretch is observed for
3 at 1709 cm-1, but in THF solution, 3 displays two NO
stretching modes at 1751 and 1721 cm-1. Like 2, complex 3
contains a {Ni(NO)}10 core, and dimetallic complexes of this
unit have been previously reported. There are examples of
structurally characterized diamagnetic complexes comprising
two {Ni(NO)}10 moieties bridged by anionic54-56 or neutral57
ligands with NO stretching frequencies ranging from 1718 to
1817 cm-1 (avg ) 1771 ( 29 cm-1). Furthermore, some of
these complexes display one νNO value in the solid state and
two in solution.56 For example, the [Ni2(NO)2(µ-N2C5H7)2-
(PPh3)2] dimer, consisting of two {Ni(NO)}10 units bridged by
3,5-dimethylpyrazolates, exhibits one NO stretching mode at
1728 cm-1 in a Nujol mull and two at 1804 and 1758 cm-1 in
cyclohexane solution. The solid-state IR spectrum of 3 suggests
a Ci geometric configuration with anti nitrosyls and trans
bridging thiolates. Only this arrangement of nitrosyl and thiolate
ligands would afford an IR spectrum with one NO stretching
band, of Au symmetry. The other possible arrangements, anti
nitrosyls and cis thiolates (Cs), syn nitrosyls and cis thiolates
(C2V), or syn nitrosyls and trans thiolates (Cs), are expected to
display two IR-active NO stretching modes. Dipole-dipole
interaction between solvent and 3 may allow the symmetric (Ag)
stretching mode to become IR-active, or a different nitrosyl/
thiolate geometric arrangement may be preferred in solution.
Reaction of 2 with 1 equiv of Me3OBF4 in CH3CN yielded
0.5 equiv of 3 and 1 equiv of Et4NBF4 (Scheme 1). Because no
Ph2S2 is formed, we presume that Me3OBF4 converts one PhS-
ligand to MeSPh, which cannot not be isolated or quantified
due to its volatility. Additionally, cooling a saturated solution
of 3 in THF to -30 °C afforded 2. This result is not surprising,
given that 2 is THF-insoluble and could be formed by simple
association of Et4NSPh with 3. Complex 2 could be formed in
this manner by disproportionation of 3 into 1 equiv of 2 and 1
equiv of a molecule with the empirical formula [Ni(NO)(SPh)].
Even if the equilibrium favors 3, 2 will selectively crystallize
from THF solution, and its generation will be irreversible.
Qualitative IR analysis of the reaction of 3 with Et4NSPh
similarly indicated formation of 2.
Interestingly, 2 has structural characteristics similar to those
of the MNIC (Et4N)[Fe(NO)(SPh)3] (IIc, Table 2).9 The most
notable differences between the two structures are a more acute
M-N-O angle in 2, a greater average M-S distance (2.301
vs 2.271 Å), and a more acute average S-M-S angle (102.7°
vs 107.2°). These differences are consistent with the fact that 2
contains a {Ni(NO)}10 core and IIc a {Fe(NO)}7 core; greater
electron density in the {M(NO)} unit will result in more
π-backbonding. As the backbonding increases, the nitrosyl will
become more reduced and adopt a more bent geometry.
Furthermore, as the M-N bond develops multiple bonding
character, its length will decrease, and the thiolates will be pulled
closer together and lie farther away from the metal atom.
Synthesis and Properties of 3. Treatment of a solution of 1
in CH3CN with 1 equiv of NOBF4 produced an immediate color
change from dark red to brown-green. Product and mass balance
analysis revealed that 1 equiv of Ph2S2, 1 equiv of Et4NBF4,
and 0.5 equiv of (Et4N)2[Ni2(NO)2(µ-SPh)2(SPh)2] (3) were
produced per equiv of 1 consumed (Scheme 1). Complex 3 is
also diamagnetic, and 1H NMR spectroscopy revealed a 1:2 ratio
of Et4N+ to PhS- protons. Despite the presence of both terminal
and bridging thiolate ligands in 3, only one set of broadened
aryl peaks was observed, presumably due to rapid exchange
Crystals suitable for X-ray diffraction were grown from vapor
diffusion of Et2O into a solution of 3 in CH3CN at -30 °C
over 3 days. The structure confirms the assignment of 3 as
containing a thiolate-bridged dimer of two {Ni(NO)}10 units
(Figure 2). The nickel nitrosyl structural parameters for 3,
Ni-N-O ) 161.5(2)°, N-O ) 1.168(3) Å, Ni-N ) 1.657(2)
Å (Table 3), fall close to or within the range of values reported
for analogous complexes containing two {Ni(NO)}10 cores
bridged by anionic or neutral ligands (Ni-N-O ) 166.4-178.9°,
1
(Table 1). To test this hypothesis, the H NMR spectrum of a
1:1 mixture of 2 and 3 was acquired, which revealed a single
set of sharp aryl resonances at chemical shift values between
(51) Ghosh, K.; Eroy-Reveles, A. A.; Avila, B.; Holman, T. R.; Olmstead,
M. M.; Mascharak, P. K. Inorg. Chem. 2004, 43, 2988–2997.
(52) Fujisawa, K.; Tateda, A.; Miyashita, Y.; Okamoto, K.-i.; Paulat, F.;
Praneeth, V. K. K.; Merkle, A.; Lehnert, N. J. Am. Chem. Soc. 2008,
1205–1213.
(54) Heinemann, F. W.; Pritzkow, H.; Zeller, M.; Zenneck, U. Organo-
metallics 2000, 19, 4283–4288.
(55) Chong, K. S.; Rettig, S. J.; Storr, A.; Trotter, J. Can. J. Chem. 1979,
57, 3099–3106.
(56) Chong, K. S.; Rettig, S. J.; Storr, A.; Trotter, J. Can. J. Chem. 1979,
57, 3090–3098.
(53) Ruggiero, C. E.; Carrier, S. M.; Antholine, W. E.; Whittaker, J. W.;
Cramer, C. J.; Tolman, W. B. J. Am. Chem. Soc. 1993, 115, 11285–
11298.
(57) Del Zotto, A.; Mezzetti, A.; Novelli, V.; Rigo, P.; Lanfranchi, M.;
Tiripicchio, A. J. Chem. Soc., Dalton Trans. 1990, 1035–1042.
9
15092 J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008

{Ni(NO)}10 and {Co(NO)2}10 Thiolate Complexes
A R T I C L E S
Figure 2. ORTEP diagram showing 50% probability thermal ellipsoids
and selected atom labels for 3. The Et4N+ cations, H atoms, and disordered
CH3CN have been omitted for clarity. Selected bond distances (Å) and
angles (deg): N1-O1, 1.168(3); Ni1-N1, 1.657(2); Ni1-S1, 2.2923(9);
Ni1-S1A, 2.3320(10); Ni1-S2, 2.2733(11); Ni1-N1-O1, 161.5(2);
S1-Ni1-N1, 118.56(8); S1A-Ni1-N1, 127.12(9); S2-Ni1-N1, 116.58(8);
S1-Ni1-S1A, 89.24(4); S1-Ni1-S2, 100.80(3); S1A-Ni1-S2, 98.65(3).
Figure 3. ORTEP diagram showing 50% probability thermal ellipsoids
and selected atom labels for 5. The Et4N+ cation and H atoms have
been omitted for clarity. Selected bond distances (Å) and angles (deg):
N1-O1, 1.106(3); N2-O2, 1.126(3); Co1-N1, 1.684(3); Co1-N2,
1.651(3); Co1-S1, 2.2478(8); Co1-S2, 2.2565(8); Co1-N1-O1,
161.4(3); Co1-N2-O2, 174.9(2); N1-Co-N2, 110.35(14); S1-Co1-N1,
111.56(9);S1-Co1-N2,118.38(9);S2-Co1-N1,116.26(9);S2-Co1-N2,
111.67(10); S1-Co1-S2, 87.14(3).
Table 3. List of Bond Lengths (Å), Angles (deg), and νNO (cm-1
Values for 3 and IIIa,ba
)
Scheme 2. Proposed Conversion of a [2Fe-2S] Cluster into DNICs
3
IIIa
IIIb
N-O
1.168(3)
1.657(2)
2.2733(11)
2.3320(10)
2.2923(9)
161.5(2)
116.58(8)
127.12(9)
118.56(8)
100.80(3)
98.65(3)
89.24(4)
1709
1.169(5)
1.662(3)
2.3304(11)
2.2874(11)
2.2626(11)
166.4(3)
124.56(12)
111.67(12)
107.44(12)
105.50(4)
103.54(4)
101.74(4)
1751
1.161(2)
1.6725(16)
s
2.2569(5)
2.2527(5)
167.0(2)
s
108.91(6)
107.73(8)
s
M-N
M-At
M-Ab
M-N-O
At-M-N
Ab-M-N
(96.23° vs 103.6°). Although both 3 and IIIa contain dimers of
{Ni(NO)}10 cores, complex 3 has an overall 2- charge and is
supported by thiolate ligands. As a result, the nickel atom in 3
will be more electron-rich than in IIIa, resulting in greater
π-backbonding.
Ab-M-At
s
Ab-M-Ab
νNO (solid)
νNO (soln)
106.060(17)
1775, 1749
1783, 1765, 1722
Although no iron analogue of 3 is known, the structure of 3
suggests a possible intermediate in the conversion of 1 equiv
of [Fe2S2(SR)2]2- to 2 equiv of the DNIC [Fe(NO)2(SR)2]-.
This process requires a net gain of 4 equiv of NO and a net
loss of 2 equiv of sulfur, of unknown allotropic form. Coordina-
tion of 2 equiv of NO followed by extrusion of sulfur might
afford [Fe2(NO)2(µ-SR)2(SR)2]2-, the iron analogue of 3,
composed of two {Fe(NO)}8 units stabilized by π-donating
thiolate ligands (Scheme 2). Subsequent binding of 1 equiv of
NO to each metal could break apart the dimer to yield 2 equiv
of DNIC. Preliminary experiments performed in our laboratory
have suggested that such an intermediate exists.58 This observa-
tion suggests a possible intermediate in the breakdown of
[2Fe-2S] clusters into DNICs in vivo.
1751, 1721
s
a At ) atom coordinated to metal from terminal, non-nitrosyl ligand.
Ab ) atom coordinated to metal from bridging, non-nitrosyl ligand.
Chart 2
Crystal structures of Roussin red ester (RRE) complexes of
the general formula [Fe2(NO)4(µ-SR)2] have been known for
decades.59 For comparison, we have juxtaposed the structural
parameters of 3 with those previously obtained for the RRE
[Fe2(NO)4(µ-SBz)2] (IIIb) in Table 3.8 The M-N and N-O
bond lengths are nearly identical, whereas the bridging
thiolate-metal bonds are slightly longer in 3 than in IIIb
(2.3122 vs 2.2548 Å). Unsurprisingly, the M-N-O angle is
more acute in 3 than in IIIb. Because 3 contains a {Ni(NO)}10
avg ) 172.6 ( 5.4°; N-O ) 1.13-1.183 Å, avg ) 1.154 (
0.024 Å; Ni-N ) 1.591-1.670 Å, avg ) 1.638 ( 0.033
Å).54-57 There are no examples of dimers of {Ni(NO)}10 units
supported by terminal or bridging thiolates. The closest analogue
of 3 that has been structurally characterized (IIIa, Chart 2)
contains two {Ni(NO)}10 cores bridged by two triphospholyl
ligands (Table 3).54 Although the bridging and terminal ligands
are different and 3 is dianionic whereas IIIa is neutral, the av-
erage bond lengths are nearly identical. However, the average
S-Ni-N angle in 3 (120.8°) is more obtuse than the average
P-Ni-N angle in IIIa (114.6°), and the average S-Ni-S angle
in 3 is more acute than the average P-Ni-P angle in IIIa
(58) Harrop, T. C.; Lippard, S. J., unpublished results.
(59) Thomas, J. T.; Robertson, J. H.; Cox, E. G. Acta Crystallogr. 1958,
11, 599–604.
9
J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008 15093

A R T I C L E S
Tennyson et al.
Scheme 3. Syntheses of 5 and 6a
a (i) +2 equiv of Ph3CSNO, -1.5 equiv of R2S2 and 1 equiv of Et4NSPh; (ii) +excess NO(g), -0.5 equiv of Ph2S2 and 1 equiv of Et4NSPh; (iii) +1 equiv
of NOBF4, -0.5 equiv of Ph2S2 and 1 equiv of Et4NBF4 (to afford 0.5 equiv of 5).
Table 4. List of Bond Lengths (Å), Angles (deg), and νNO (cm-1
Values for 5 and Va-c
)
dark green to dark brown. Mass balance analysis revealed that
1.5 equiv of disulfide, 1 equiv of Et4NSPh, and 1 equiv of
(Et4N)[Co(NO)2(SPh)2] (5) were produced per equiv of 4
consumed (Scheme 3, route i). Complex 5 is diamagnetic, and
5
Vaa
Vb
Vc
N-O
1.126(3)
1.106(3)
1.684(3)
1.651(3)
2.2565(8)
2.2478(8)
174.9(2)
1.120(5)
s
1.650(6)
s
2.224(2)
2.217(2)
168.9(5)
s
115.5(3)
111.1(2)
109.1(2)
s
1.181(2)
1.179(2)
1.680(2)
1.678(2)
2.288(1)
2.272(1)
169.4(2)
168.5(2)
117.36(9)
111.47(6)
110.81(6)
103.88(6)
103.61(6)
109.73(2)
1743, 1683
1737, 1693
1.189(3)
1.188(4)
1.650(3)
1.648(3)
s
1
its H NMR spectrum displays a 1:2 ratio of Et4N+ to PhS-
M-N
protons (Table 1). The asymmetric and symmetric NO stretching
modes for 5 occur at 1678 and 1756 cm-1 in the solid state
(KBr) and shift to 1699 and 1769 cm-1 in solution (THF),
respectively.
M-S
s
M-N-O
170.1(3)
167.5(3)
117.33b
s
s
s
s
s
s
161.4(3)
Complex 5 contains a {Co(NO)2}10 core, and other four-
coordinate, monometallic complexes with this configuration
have asymmetric νNO values ranging from 1730 to 1798 cm-1
(avg ) 1766 ( 20 cm-1) and symmetric νNO values ranging
from 1809 to 1870 (avg ) 1837 ( 18 cm-1).60-66 Presumably,
the asymmetric and symmetric νNO modes for 5 are nearly 100
cm-1 lower than the average values observed with other
{Co(NO)2}10 complexes because the previously reported com-
plexes of this configuration have been overall charge neutral or
cationic. Complex 5 represents the first example of a
{Co(NO)2}10 species contained within an anion. The formation
of 5 from 4 may proceed through a cobalt mononitrosyl
intermediate, but attempts to observe such a species by IR or
UV-vis spectroscopy were unsuccessful. Addition of fewer than
2 equiv of NO(g) or Ph3CSNO yields incomplete conversion
to 5.
N-M-N
S-M-N
110.35(14)
118.38(9)
116.26(9)
111.67(10)
111.56(9)
87.14(3)
s
S-M-S
νNO (solid)
νNO (soln)
100.0(1)
s
1820, 1750
1756, 1678
1769, 1699
1673, 1617
a Structural parameters averaged for metal nitrosyl moieties in
original report with errors propagated. b For the nitrosyl nitrogens.
Chart 3
As with the Ph3CSNO reactivity, addition of excess NO(g)
to 4 yielded 0.5 equiv of Ph2S2, 1 equiv of Et4NSPh, and 1
equiv of 5 (Scheme 3, route ii). Surprisingly, addition of 1 equiv
of NOBF4 to a solution of 4 in CH3CN yielded 0.5 equiv of
Ph2S2, 1 equiv of Et4NBF4, and 0.5 equiv of 5, as well as an
intractable plum-colored solid, the IR spectrum of which showed
bands only for the Et4N+ and PhS- moieties (Scheme 3, route
iii). The combination of mass balance analysis and the IR
spectrum of this material suggests it could have the formula
(Et4N)[Co(SPh)4]. Such a product would be consistent with a
possible mechanism by which 5 might form. Oxidation of 4 by
NOBF4 would yield 0.5 equiv of Ph2S2, 1 equiv of Et4NBF4, 1
equiv of NO, and 1 equiv of “(Et4N)[Co(SPh)3]”. Presumably,
this cobalt(II) thiolate complex would rapidly bind NO to
produce a cobalt(II) nitrosyl. Previous studies have demonstrated
core, there are more electrons spread over fewer NO moieties
than in the {Fe(NO)2}9 complex, and therefore π-backbonding
is better. The greater multiple-bond character between the metal
and nitrosyl in 3 shortens the M-N bond with concomitant
lengthening of the M-S bonds. One nitrosyl will cause the three
other ligands in a pseudotetrahedral configuration to draw closer
together; two nitrosyls will prefer a wider separating angle and
cause the bridging thiolates to spread farther apart. An additional
difference between 3 and IIIb is the ability of the two
{Fe(NO)2}9 units in the latter to interact via an Fe-Fe bond,
which is not possible for two {Ni(NO)}10 units.
Attempts to prepare a nickel dinitrosyl complex by reacting
2 with NO(g) or Ph3CSNO failed, yielding only slow conversion
to 3. This result is consistent with the fact that there are no
structurally characterized complexes containing a {Ni(NO)2}n
fragment of any electron count. As n increases above 10
electrons, M-NO antibonding orbitals would become filled and
cause dissociation of one of the nitrosyl ligands. For n to be
less than or equal to 10 electrons with nickel, the metal would
need to be in a 2+ oxidation state, an electronic configuration
not conducive to supporting two nitrosyl ligands. Other metals,
such as iron and cobalt, can support two nitrosyl ligands in a
1+ oxidation state without exceeding n ) 10.
(60) Lim, M. H.; Kuang, C.; Lippard, S. J. ChemBioChem 2006, 7, 1571–
1576.
(61) Franz, K. J.; Singh, N.; Spingler, B.; Lippard, S. J. Inorg. Chem. 2000,
39, 4081–4092.
(62) Gerbase, A. E.; Vichi, E. J. S.; Stein, E.; Amaral, L.; Vasquez, A.;
Ho¨rner, M.; Maichle-Mo¨ssmer, C. Inorg. Chim. Acta 1997, 266, 19–
27.
(63) Roustan, J.-L.; Ansari, N.; Le Page, Y.; Charland, J.-P. Can. J. Chem.
1992, 70, 1650–1657.
(64) Aresta, M.; Ballivet-Tkatchenko, D.; Bonnet, M. C.; Faure, R.;
Loiseleur, H. J. Am. Chem. Soc. 1985, 107, 2994–2995.
(65) Haymore, B. L.; Huffman, J. C.; Butler, N. E. Inorg. Chem. 1983,
22, 168–170.
Synthesis and Properties of the First Mononuclear {Co(NO)2}10
Anion (5). Upon addition of 2 equiv of Ph3CSNO to a solution
of 4 in CH3CN, the solution color immediately changed from
(66) Kaduk, J. A.; Ibers, J. A. Inorg. Chem. 1977, 16, 3283–3287.
9
15094 J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008

{Ni(NO)}10 and {Co(NO)2}10 Thiolate Complexes
A R T I C L E S
that [CoII(NO)(L)] complexes disproportionate to form 0.5 equiv
of [CoI(NO)2] and 0.5 equiv of [CoIII(L)2].67,68
Crystals suitable for X-ray diffraction were grown by cooling
a saturated solution of 5 in THF to -30 °C overnight. The
structure confirms the assignment of 5 as containing a
{Co(NO)2}10 fragment supported by two thiolates (Figure 3).
The cobalt nitrosyl structural parameters for 5 (Co-N-O )
161.4(3)° and 174.9(2)°, N-Co-N ) 110.35(14)°, N-O )
1.106(3) and 1.126(3) Å, Co-N ) 1.651(3) and 1.684(3) Å,
Table 4) fall close to or within the range of reported values
for four-coordinate, monometallic {Co(NO)2}10 complexes
(Co-N-O ) 162.2-176.6°, avg ) 169.2 ( 4.9°; N-Co-N
) 115.6-131.7°, avg ) 121.7 ( 6.6°; N-O ) 1.12-1.156 Å,
avg ) 1.142 ( 0.011 Å; Co-N ) 1.641-1.671 Å, avg ) 1.654
( 0.010 Å). The cobalt dinitrosyl complex (Va) is the only
structurally characterized, monometallic {Co(NO)2}10 unit
coordinated by sulfur atoms (Chart 3).69 A summary of its bond
lengths and angles is presented in Table 4. The average cobalt
nitrosyl structural parameters for 5 are similar to those for Va,
but the Co-S bonds are longer and the S-M-S angle is more
acute. Presumably, the greater Co-S distances in 5 are due to
increased electron density at the metal compared to Va.
Although the smaller S-M-S angle in 5 may reflect greater
π-backbonding from the metal to the nitrosyls compared to Va,
the ligand supporting the latter complex is bidentate, and its
geometry is dictated by the delocalized π-system. An idealized
five-membered chelate ring would exhibit an S-M-S angle
of 108°, and an idealized six-membered chelate ring would
display an angle of 120°. Because five of the six atoms in the
chelate ring for Va are sp2-hybridized, whereas the cobalt atom
in 5 contains only monodentate ligands, the S-M-S angle in
Va will be necessarily greater, independent of any electronic
effects.
Although the NO stretching bands in 5 are well below the
range of those reported for other complexes, the IR spectrum
for the DNIC (Et4N)[Fe(NO)2(SPh)2] (Vb) strongly resembles
that of 5. The average M-N distance in 5 is shorter than that
in Vb, consistent with greater π-backbonding, but the N-O
lengths are significantly shorter. A DNIC containing a
{Fe(NO)2}10 core supported by 1-methylimidazole ligands
(Vc)70 should be a better molecule for comparison to 5 because
it has the same number of electrons in its {M(NO)2} framework.
However, the M-N bonds in Vc are shorter and the N-O
distances are greater, suggesting more π-backbonding in Vc than
5. Consistent with this speculation, the symmetric and asym-
metric νNO values in Vc are nearly 100 cm-1 lower in energy
than those observed in 5. Discussion of the electronic config-
uration of metal nitrosyl complexes based solely on structural
parameters can be counterproductive, but the νNO values should
be consistent with the Enemark-Feltham configuration of the
complex. Perhaps the use of σ,π-donor thiolates negates the
validity of considering the metal nitrosyl core as an independent
moiety.
Figure 4. ORTEP diagram showing 50% probability thermal ellipsoids
and selected atom labels for 6. The H atoms have been omitted for clarity.
Selected bond distances (Å) and angles (deg): N1-O1, 1.139(4); N2-O2,
1.131(4); N3-O3, 1.135(4); N4-O4, 1.127(4); N5-O5, 1.154(4); N6-O6,
1.147(4); Co1-N1, 1.663(3); Co1-N2, 1.675(3); Co2-N3, 1.672(3);
Co2-N4, 1.668(3); Co3-N5, 1.674(3); Co3-N6, 1.669(3); Co1-S1,
2.3093(9); Co1-S2, 2.2814(9); Co2-S1, 2.2832(9); Co2-S3, 2.2811(10);
Co3-S2, 2.2984(9); Co3-S3, 2.3027(9); Co1-N1-O1, 170.2(3);
Co1-N2-O2, 171.1(3); Co2-N3-O3, 170.1(3); Co2-N4-O4, 175.8(3);
Co3-N5-O5, 164.3(3); Co3-N6-O6, 173.0(3); N1-Co1-N2, 119.30(5);
N3-Co2-N4, 118.05(16); N5-Co3-N6, 119.60(14); S1-Co1-N1,
114.97(10); S1-Co1-N2, 110.72(10); S1-Co2-N3, 111.86(11); S1-
Co2-N4, 112.51(11); S2-Co1-N1, 106.97(10); S2-Co1-N2, 106.88(10);
S2-Co3-N5, 102.13(10); S2-Co3-N6, 107.40(10); S3-Co2-N3,
102.36(11); S3-Co2-N4, 111.66(11); S3-Co3-N5, 121.29(10); S3-Co3-
N6, 105.12(10); S1-Co1-S2, 94.59(3); S1-Co2-S3, 98.07(4); S2-Co3-S3,
98.22(3).
mass balance analyses indicated that 1 equiv of Et4NBF4 and
1/3 equiv of [Co3(NO)6(µ-SPh)3] (6) were formed per equiv of
1
5 consumed (Scheme 3). Compound 6 is diamagnetic, and H
NMR spectroscopy reveals only PhS- protons (Table 1). The
NO stretches of 6 occur at 1840, 1817, 1779, and 1744 cm-1
in the solid state (KBr). The νNO values in THF solution do not
shift significantly and appear at 1844, 1819, 1780, and 1764
cm-1. Both solid-state and solution νNO values for 6 lie within
the range of values previously observed for complexes compris-
ing one {Co(NO)2}10 unit (vide supra) or multiple ligand-
bridged {Co(NO)2}10 units (1750-1878 cm-1, avg ) 1815 (
41 cm-1).71-74 Synthesis of a dimetallic [Co2(NO)4(µ-SPh)2]
compound from [Co2(NO)4(µ-Cl)2] and LiSPh has been re-
ported.75 Although the NO stretches at 1842, 1820, 1783, and
1767 cm-1 in this complex are nearly identical to those observed
for 6, the only other characterization provided was its mass
spectrum. In the solid state, 6 displays C3V symmetry (Figure
4, see below), and its six nitrosyls should give rise to four IR-
active modes (2A1 + 2E), as we observe. If 6 were a dimetallic
species with the same solid-state structure as RRE (C2h), only
two NO stretching modes would be IR-active (Au + Bu). Because
four overlapping NO stretching bands are observed in the solid-
state and solution IR, we conclude that the trimetallic formula-
tion is retained in solution. The νNO values for 6 are in excellent
agreement with those reported for the purported [Co(NO)2(µ-
SR)]n complexes.75
Synthesis and Properties of 6. Addition of stoichiometric
Me3OBF4 to a solution of 5 in CH3CN caused an immediate
color change from dark brown to dark red-orange. Product and
Crystals suitable for X-ray diffraction were grown by cooling
a saturated solution of 6 in Et2O to -30 °C overnight. The
(71) Hilderbrand, S. A.; Lippard, S. J. Inorg. Chem. 2004, 43, 5294–5301.
(72) Chong, K. S.; Rettig, S. J.; Storr, A.; Trotter, J. Can. J. Chem. 1979,
57, 3119–3125.
(67) Del Zotto, A.; Mezzetti, A.; Rigo, P. Inorg. Chim. Acta 1990, 171,
61–69.
(68) Hendrickson, A. R.; Ho, R. K. Y.; Martin, R. L. Inorg. Chem. 1974,
13, 1279–1281.
(73) Strouse, C. E.; Swanson, B. I. J. Chem. Soc., Chem. Commun. 1971,
55–56.
(69) Martin, R. L.; Taylor, D. Inorg. Chem. 1976, 15, 2970–2976.
(70) Reginato, N.; McCrory, C. T. C.; Pervitsky, D.; Li, L. J. Am. Chem.
Soc. 1999, 121, 10217–10218.
(74) Dahl, L. F.; de Gil, E. R.; Feltham, R. D. J. Am. Chem. Soc. 1969,
91, 1653–1664.
(75) Bitterwolf, T. E.; Pal, P. Inorg. Chim. Acta 2006, 359, 1501–1503.
9
J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008 15095

A R T I C L E S
Tennyson et al.
Table 5. List of Bond Lengths (Å), Angles (deg), and νNO (cm-1
Values for 6 and VIa-e
)
S-M-S angle; the greater average M-S length in VIb is most
likely a consequence of the greater ionic radius of iridium (0.69
vs 0.82 Å for Co(III) vs Ir(III) in octahedral, high-spin
configurations).78 The M3S3 core of VIb also more closely
resembles the cyclohexane-like configuration of 6 than does VIa.
Although no iron analogue of 6 has been reported, (Et4N)3-
[Fe3Cl6(µ-SPh)3] (VIc) shares its M3S3 core configuration.79
Despite having an average S-M-S angle similar to that in 6,
VIc exhibits a much longer M-S distance and a planar M3S3
core. An iron nitrosyl complex with structural parameters and
6a
VIaa
VIba
VIca
VIda,b
1.162
1.669
2.292 2.369 2.356 2.256
VIea
N-O
M-N
M-S
1.139
1.670
2.293
s
s
s
s
s
s
1.19
1.650
s
M-N-O 170.8
s
s
s
s
s
s
s
s
s
166.4
115.3
110.4
171.7
116.9
s
s
s
N-M-N 119.0
S-M-N
S-M-S
109.49
96.96
132.61 94.8 100.5 104.07
s
νNO (solid) 1840, 1817,
s
s
s
1779, 1744
νNO (soln) 1844, 1819,
1780, 1764
s
s
s
1795, 1743 1733, 1721
1708 1687, 1668
νNO values similar to those in 6 is the Roussin black salt (RBS),
(Et4N)[Fe4S3(NO)7] (VId).80 The greater average N-O distance
in VId compared to 6, the more acute average M-N-O angle
and more obtuse S-M-S angle in VId, and the lower νNO
values suggest that there is greater M-NO π-backbonding in
VId than in 6. Although 6 contains three {Co(NO)2}10 units
and VId three equatorial {Fe(NO)2}9 units, the latter are bridged
by sulfides and the complex is overall anionic, thus providing
a more electron-rich environment for the metal centers in VId.
An analogue of RRE containing {Fe(NO)2}10 units bridged by
two bis(diphenylphosphino)methane ligands (VIe)81 displays
nearly identical metal nitrosyl angles, but the average M-N
distance is shorter and the average N-O length is greater than
in 6, indicating better π-backbonding in VIe.
a Bond lengths and angles are averaged for all similar occurrences.
b Excluding apical {Fe(NO)}7 unit.
Chart 4
In support of this observation, the NO stretching energies in
VIe are nearly 100 cm-1 lower in energy than those in 6.
Although 6 and VIe both contain {M(NO)2}10 cores and the
cobalt complex is supported by σ,π-donor ligands, the iron
complex exhibits structural and spectroscopic parameters con-
sistent with greater electron density residing within the M-NO
units. Because 6 and VIe have the same Enemark-Feltham
configuration, the iron must be in a more reduced state and will
thus be more electron-releasing than the cobalt.
The results for the nickel and cobalt nitrosyls supported by
thiolates, especially in comparison with similar metal nitrosyl
thiolate complexes, suggest that the nature of the metal and
supporting ligands can have a nontrivial influence on the
structural and vibrational properties of the “independent”
{M(NO)x}n core. Comparison to other complexes containing
similar metal nitrosyl units has revealed the importance of the
electron-donating ability of the ligand and the overall charge
of the molecule in influencing the electronic properties of the
metal nitrosyl core. These relationships are currently being
explored via computational methods and will be reported at a
later date.
structure reveals that 6 contains a trimer of thiolate-bridged
{Co(NO)2}10 fragments (Figure 4). The average bond lengths
and angles for the {Co(NO)2}10 units in 6 (N-Co-N ) 119.0°,
Co-N-O ) 170.8°, N-O ) 1.139 Å, Co-N ) 1.670 Å, Table
5) fall within the range of reported values for four-coordinate,
monometallic (vide supra) or multimetallic {Co(NO)2}10 com-
plexes (Co-N-O ) 161.6-173.5°, avg ) 168.2 ( 5.1°;
N-Co-N ) 109.8-118.3°, avg ) 112.5 ( 3.2°; N-O )
1.11-1.19 Å, avg ) 1.146 ( 0.022 Å; Co-N ) 1.60-1.68 Å,
avg ) 1.648 ( 0.030 Å).71-74
Although there are no structurally characterized complexes
with three ligand-bridged {Co(NO)2}10 units, dimers71,72 and
infinite chains73,74 are known. Only one thiolate-bridged trime-
tallic complex containing four-coordinate cobalt centers (VIa)
has been structurally characterized (Chart 4). Although the
average Co-S lengths are similar, the average S-Co-S angle
is wider in VIa, most likely due to the geometric constraints
imposed by the ligand (Table 5).76 A trimer of {Ir(CO)2} units
bridged by alkyl thiolates (VIb)77 is a better structural analogue
of the metal thiolate core in 6 and displays a comparable average
NO Transfer to [Fe(TPP)Cl]. The metalloporphyrin [Fe-
(TPP)Cl] can be used to measure the ability of a metal nitrosyl
complex to donate or transfer NO by monitoring the response
of the Soret band at 417 nm.8,82 The reaction between [Fe-
(76) Shearer, J.; Kaminsky, W.; Kovacs, J. A. Acta Crystallogr. C 2003,
59, m379–m380.
(77) Maisonnat, A.; Devillers, J.; Poilblanc, R. Inorg. Chem. 1987, 26,
1502–1507.
(78) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; John Wiley & Sons, Inc.: New York,
1999.
(79) Whitener, M. A.; Bashkin, J. K.; Hagen, K. S.; Girerd, J.-J.; Gamp,
E.; Edelstein, N.; Holm, R. H. J. Am. Chem. Soc. 1986, 108, 5607–
5620.
(80) D’Addario, S.; Demartin, F.; Grossi, L.; Iapalucci, M. C.; Laschi, F.;
Longoni, G.; Zanello, P. Inorg. Chem. 1993, 32, 1153–1160.
(81) Li, L.; Reginato, N.; Urschey, M.; Stradiotto, M.; Liarakos, J. D. Can.
J. Chem. 2003, 81, 468–475.
(82) Chiang, C.-Y.; Darensbourg, M. Y. J. Biol. Inorg. Chem. 2006, 11,
359–370.
9
15096 J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008

{Ni(NO)}10 and {Co(NO)2}10 Thiolate Complexes
A R T I C L E S
have been extensively studied, and coordination of a sixth ligand
to [Fe(TPP)(NO)] can cause a significant change in the optical
spectrum.
The six-coordinate [Fe(TPP)(NO)(MeIm)] complex, where
MeIm is 1-methylimidazole, has a Soret band at 425 nm with
ꢀ ) 1.54 × 106 M-1 cm-1 83
.
However, product analysis from
a preparative-scale reaction of 2 with [Fe(TPP)Cl] revealed an
IR spectrum identical to that of 3 and no evidence for formation
of Ph2S2. We therefore conclude that 2 transfers PhS- to
[Fe(TPP)Cl] with concomitant formation of 3 and Et4NCl.
Because 3 and 5 have the same optical response, we propose
that these complexes also undergo thiolate-chloride ligand
exchange.
NO Transfer to [Co(TPP)]. To avoid the mechanistic com-
plications of [Fe(TPP)Cl], we studied the ability of one of our
nitrosyl complexes to transfer NO to [Co(TPP)]. Addition of 2
to [Co(TPP)] in THF did not significantly alter the optical
spectrum when shielded from light. A small increase in intensity
of the Soret band was noted due to the absorption of 2 at this
wavelength. Exposure of the [Co(TPP)] + 2 solution to ambient
fluorescent lighting after 60 s and at 5 min intervals thereafter
produced a rapid decrease in absorption along with a slight
hypsochromic shift (Figure 6). The final spectrum obtained from
this reaction matched that for [Co(TPP)] + NO(g) or Ph3CSNO
but not the previously reported values for the Soret band
wavelength and absorptivity of [Co(TPP)(NO)].27 As a control,
the reaction of [Co(TPP)] with Ph3CSNO was performed on a
Figure 5. Reaction of [Fe(TPP)Cl] with 2 in THF without illumination.
The Soret band for [Fe(TPP)Cl] (purple trace) shifts hypsochromically and
increases in intensity upon addition of 2 (green trace). Scans every 60 s
thereafter (black traces) show increasing absorptivity that is complete within
10 min.
preparative scale, and the νNO value observed was 1697 cm-1
.
This value is in good agreement with that previously observed
for [Co(TPP)(NO)]. The cause of the disparity between the
results from IR and UV-vis spectroscopy is unclear, but the
optical spectrum of [Co(TPP)(NO)] may depend on solvent,
since our measurements were performed in THF and the
literature values27 were acquired in CH2Cl2. By comparison,
cobalt(II)-reconstituted soluble guanylyl cyclase displays a slight
hypsochromic shift in the Soret band upon coordination of NO
with a decrease in absorptivity to 1.07 × 105 M-1 cm-1 28
.
Figure 6. Reaction of [Co(TPP)] with 2 in THF with illumination. The
Soret band for [Co(TPP)] (purple trace) is unaffected by the addition of 2
(green trace). After 60 s of exposure to ambient lighting, the intensity had
decreased (blue trace). Scans every 5 min thereafter (black traces) show
decreasing absorptivity that is complete within 30 min.
Conclusions and Speculations
Reaction of 1 with Ph3CSNO or NO(g) yielded the mono-
metallic {Ni(NO)}10 species 2, which displays one of the lowest
recorded νNO values and shares similar structural parameters
with MNIC IIc. Compound 2 is the first example of an anionic
complex containing a {Ni(NO)}10 moiety. Although IIc is light-
and temperature-sensitive and readily converts to a DNIC, 2 is
stable, and our efforts to prepare the corresponding nickel
dinitrosyl complex have been unsuccessful. The similarity in
reactivity of Ph3CSNO and NO(g) indicates that Ph3CSNO
functions as an NO donor under these reaction conditions. In
contrast, addition of NOBF4 to 1 produced a dimetallic
{Ni(NO)}10 species that exhibited 1H NMR and IR spectra
different from those of 2. The resulting thiolate-bridged dimer
3 suggests a possible intermediate in the conversion of one
[2Fe-2S] cluster into two DNICs that has not yet been observed.
Complex 3 was also prepared by addition of Me3OBF4 to 2,
demonstrating the ability of these two {Ni(NO)}10 species to
interconvert by simple ligand dissociation or association reactions.
The {Co(NO)2}10 complex 5 can be obtained by reaction of
4 with Ph3CSNO, NO(g), or NOBF4 and displays the lowest
recorded νNO values for any dinitrosylcobalt complex with this
(TPP)Cl] and the MNIC (Et4N)[Fe(NO)(StBu)3] under ambient
fluorescent lighting afforded [Fe(TPP)(NO)] with the expected
hypsochromic shift to 405 nm and small decrease in absorptivity.
However, [Fe(TPP)(NO)] is only obtained by reductive nitros-
ylation of [Fe(TPP)Cl] s an exogenous electron must be sup-
plied, with the displaced chloride being trapped by the NO
donor.24 In the absence of a reducing agent, reaction of a
stoichiometric amount of NO(g) with [Fe(TPP)Cl] in aprotic
solvent affords [Fe(TPP)(NO)Cl], a complex that is optically
indistinguishable from [Fe(TPP)Cl].24 When solutions of this
six-coordinate nitrosyl are allowed to stand, they gradually lose
NO and the spectrum of the original [Fe(TPP)Cl] is restored,
and this process is greatly accelerated upon exposure to a
vacuum.
Contrary to our expectations, addition of 1 equiv of 2, 0.5
equiv of 3, or 1 equiv of 5 to [Fe(TPP)Cl] in THF produced a
bathochromic shift in the Soret band from 417 to 426 nm with
dramatic increases in absorption in the dark (Figure 5). Because
the Soret band moves to lower energy and the absorptivity
increases, we can exclude the formation of either [Fe(TPP)-
(NO)Cl] or [Fe(TPP)(NO)]. Iron porphyrin nitrosyl complexes
(83) Praneeth, V. K. K.; Neese, F.; Lehnert, N. Inorg. Chem. 2005, 44,
2570–2572.
9
J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008 15097

A R T I C L E S
Tennyson et al.
electron count. Furthermore, 5 is the first example of an anionic
complex containing a {Co(NO)2}10 moiety. Attempts to isolate
or observe a cobalt mononitrosyl were unsuccessful, presumably
due to rapid disproportionation into a cobalt(I) dinitrosyl and a
cobalt(III) species. Reaction of 5 with Me3OBF4 afforded a
trinuclear analogue of RRE 6 composed of three {Co(NO)2}10
units. The existence of this complex suggests a pathway by
which RRE might be converted into RBS. RRE might be in
equilibrium among various [Fe(NO)2(µ-SPh)]n species, where
the predominant form has n ) 2, followed by n ) 3, etc. The
trimeric form of RRE could react with one molecule of MNIC
to produce RBS and three molecules of thioether. Such
chemistry may seem improbable, but iron persulfide complexes
can be prepared by insertion of a thiolate into an iron-sulfur
bond,84 and sulfur can be extruded from iron persulfide
complexes.85,86 Conversion of RRE into RBS could occur by
insertion of a thiolate into an iron-sulfur bond followed by
alkyl or aryl transfer within the coordinated disulfide and
dissociation of the resultant thioether.
ity for the analogous iron(II) complexes. Syntheses of alkyl
variants of 2, 3, 5, and 6 will be interesting to pursue for
comparison, as will iron analogues of 3, together with attempts
to convert RRE-type complexes to RBS.
Acknowledgment. This work was supported by NSF Grant
CHE-0611944. The MIT DCIF NMR spectrometer used was funded
through NIH Grant 1S10RR113886-01. A.G.T. is grateful for an
NSF predoctoral fellowship, and S.D. is the recipient of an Anna
Fuller Fellowship in Molecular Oncology. We thank Dr. Z.
Tonzetich for a gift of Ph3CSNO, experimental assistance, and
helpful discussions. We also appreciate helpful comments from Prof.
W. D. Jones.
Supporting Information Available: 1H NMR spectra of 2, 3,
and an equimolar mixture of the two; X-ray crystallographic
data, including tables, ORTEP diagrams, and CIF files, for 2,
3, 5, and 6. This material is available free of charge via the
Internet at http://pubs.acs.org.
The exploration of the nitric oxide reactivity of homoleptic
nickel(II) and cobalt(II) thiolate complexes has yielded interest-
ing coordination compounds and suggests undiscovered reactiv-
JA803992Y
(85) Schweitzer, D.; Shearer, J.; Rittenberg, D. K.; Shoner, S. C.; Ellison,
J. J.; Loloee, R.; Lovell, S.; Barnhart, D.; Kovacs, J. A. Inorg. Chem.
2002, 41, 3128–3136.
(86) Coucouvanis, D.; Lippard, S. J. J. Am. Chem. Soc. 1968, 90, 3281–
3282.
(84) Wu, X.; Bose, K. S.; Sinn, E.; Averill, B. A. Organometallics 1989,
8, 251–253.
9
15098 J. AM. CHEM. SOC. VOL. 130, NO. 45, 2008