Distorted square planar nickel(II) carbonyl complexes containing terminal thiolate/selenolate ligands

Article abstract of DOI:10.1039/b008902h

Distorted square planar [Ni(CO)(SR)_n(SePh)_3-n]^- (n = 0 (1), 3 (2), 1 (3) or 2 (4); R = Ph or C₄H₃S) complexes, were prepared by unique Cp^-/PhS^- (PhSe^-) exchange reactions and oxidative addition. (SC₄H₃S)₂, [NiCp(CO)]₂ and 2 equivalents of fac-[N(PPh₃)₂][Fe(CO)₃(SC₄ H₃S)₃] in thf led to the isolation of [N(PPh₃)₂][Ni(CO)(SC₄H₃S) ₃] and [FeCp(CO)₂(SC₄H₃S)]. Complex [Ni⁰(CO)₃(SePh)]^- was obtained upon chemical reduction of complex [Ni^II(CO)(SePh)₃]^- with [BH₄]^- under a CO atmosphere in thf. [Ni^II(CO)(SePh)₃]^- was reobtained upon oxidative addition of diphenyl diselenide and benzeneselenol to [Ni⁰(CO)₃(SePh)]^- in thf. The mixed-chalcogenolate nickel(II) carbonyl complexes [Ni(CO)(SPh)_n(SePh)_3-n]^- (n = 1 or 2) were prepared by PhSe^-/PhS^- ligand exchange reaction and oxidative addition of diphenyl disulfide to [Ni(CO)₃(SePh)]^- individually. Complexes [Ni^II(CO)(SePh)₃]^-, [Ni^II(SC₅H₄N)₃]^-, [Ni⁰(CO)₃(SC₅H₄N)]^- and [Ni⁰(CO)₃(SePh)]^- are chemically interconvertible at ambient temperature. Coordinative addition of the metalloanion [Mn(CO)₅]^- ([Fe(CO)₄(SePh)]^-) to complex [Ni(CO) -(SePh)₃]^- and subsequent redox under a CO atmosphere led to formation of cis-[Mn(CO)₄(SePh)₂]^- (fac-[Fe(CO)₃ -(SePh)₃]^-) and [Ni⁰(CO)₃(SePh)]^-. Nickel(IIl)/nickel(0) carbonyl thiolate complexes are more unstable thermally than the corresponding carbonyl selenolate complexes. Isotopic shift experiments demonstrate the lability of carbonyl ligand(s) of complexes 1-4 and [Ni(CO)₃(SePh)]^- species. The vibrational spectroscopy of the Ni^II(CO) fragment (v(CO) ranges from 2023 to 2043 cm^-1) found in 1-4 may be regarded as a spectroscopic reference for the carbonyl binding site of [NiFe] hydrogenases and CO dehydrogenase. The Royal Society of Chemistry 2001.

Full text of DOI:10.1039/b008902h

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Distorted square planar nickel(II) carbonyl complexes containing
terminal thiolate/selenolate ligands
Wen-Feng Liaw,*a Chien-Hong Chen,a Chien-Ming Lee,a Gene-Hsiang Leeb
and Shie-Ming Pengb
a Department of Chemistry, National Changhua University of Education, Changhua 50058,
Taiwan. E-mail: chfeng@cc.ncue.edu.tw
b Instrumentation Center and Department of Chemistry, National Taiwan University,
Taipei 10764, Taiwan
Received 7th November 2000, Accepted 14th November 2000
First published as an Advance Article on the web 21st December 2000
Distorted square planar [Ni(CO)(SR)n(SePh)3 Ϫ n]Ϫ (n = 0 (1), 3 (2), 1 (3) or 2 (4); R = Ph or C4H3S) complexes,
were prepared by unique CpϪ/PhSϪ (PhSeϪ) exchange reactions and oxidative addition. (SC4H3S)2, [NiCp(CO)]2
and 2 equivalents of fac-[N(PPh3)2][Fe(CO)3(SC4H3S)3] in thf led to the isolation of [N(PPh3)2][Ni(CO)(SC4H3S)3]
and [FeCp(CO)2(SC4H3S)]. Complex [Ni0(CO)3(SePh)]Ϫ was obtained upon chemical reduction of complex
[NiII(CO)(SePh)3]Ϫ with [BH4]Ϫ under a CO atmosphere in thf. [NiII(CO)(SePh)3]Ϫ was reobtained upon oxidative
addition of diphenyl diselenide and benzeneselenol to [Ni0(CO)3(SePh)]Ϫ in thf. The mixed-chalcogenolate nickel()
carbonyl complexes [Ni(CO)(SPh)n(SePh)3 Ϫ n]Ϫ (n = 1 or 2) were prepared by PhSeϪ/PhSϪ ligand exchange reaction
and oxidative addition of diphenyl disulfide to [Ni(CO)3(SePh)]Ϫ individually. Complexes [NiII(CO)(SePh)3]Ϫ,
[NiII(SC5H4N)3]Ϫ, [Ni0(CO)3(SC5H4N)]Ϫ and [Ni0(CO)3(SePh)]Ϫ are chemically interconvertible at ambient
temperature. Coordinative addition of the metalloanion [Mn(CO)5]Ϫ ([Fe(CO)4(SePh)]Ϫ) to complex [Ni(CO)-
(SePh)3]Ϫ and subsequent redox under a CO atmosphere led to formation of cis-[Mn(CO)4(SePh)2]Ϫ (fac-[Fe(CO)3-
(SePh)3]Ϫ) and [Ni0(CO)3(SePh)]Ϫ. Nickel()/nickel(0) carbonyl thiolate complexes are more unstable thermally
than the corresponding carbonyl selenolate complexes. Isotopic shift experiments demonstrate the lability of
carbonyl ligand(s) of complexes 1–4 and [Ni(CO)3(SePh)]Ϫ species. The vibrational spectroscopy of the NiII(CO)
fragment (ν(CO) ranges from 2023 to 2043 cmϪ1) found in 1–4 may be regarded as a spectroscopic reference for
the carbonyl binding site of [NiFe] hydrogenases and CO dehydrogenase.
Introduction
Carbon monoxide dehydrogenase/acetyl-CoA synthase
(CODH/ACS) enzymes catalyse the CO/CO2 interconversion
reaction and the acetyl coenzyme A assembly (thioester acetyl
coenzyme A, CoA–SC(O)CH3).1 Center B is a Fe-S-containing
[Fe4S4]2ϩ/1ϩ cluster which is involved in electron transport
function.1 CO oxidation occurs at a Ni–FeS-containing center
known as center C. Center A responsible for the acetyl-CoA
synthesis was proposed to be a Ni–X–Fe4S4 structure (bridge X
may be a thiolate or sulfide (unidentified)) and the CO adduct
may serve as a precursor of the carbonyl group of acetyl-CoA.1
Center C is believed to have a closely related structure to that of
A.1 The oxidation of CO to CO2 and acetyl-CoA synthesis from
CO, a methyl group, and coenzyme A occur at coupled [Ni–X–
Fe] centers, and both nickel and iron have been proposed as
binding sites of CO.2,3 In combination with EXAFS, EPR, and
Mössbauer studies of the Rhodospirillum rubrum enzyme
it has been proposed that the nickel environment of center C
adopts a distorted tetrahedral or five-coordinate high-spin state
with 2S atoms at 2.23 Å and 2–3 N/O atoms at 1.87 Å,2,4
whereas center A from Clostridium thermoaceticum exhibits
spectroscopic properties that imply a distorted square planar Ni
surrounded by two S donors and two N/O donors.5 A schematic
drawing of the proposed CO binding-site structure of CO
dehydrogenases as deduced from EPR and FTIR studies is
shown in Fig. 1.1a,4,5
Fig. 1 Schematic drawing of the proposed CO binding-site structure
of CO dehydrogenases as deduced from EPR and FTIR studies.1a,4,5
obtained for the SI-CO complex of Chromatium vinosum
hydrogenase revealed the presence of (Scys)2Ni(µ-Scys)2CO
ligation, where the CO is terminally bound to Ni.5c In spite of
the large number of nickel() carbonyl complexes known,6 in
biomimetic chemistry examples of NiI–CO and NiII–CO com-
plexes surrounded by biological thiolate/thioether/selenolate
ligands are limited.7 The five-coordinate nickel() chalcogeno-
late carbonyl complexes [Ni(DAPA)(EPh)2(CO)]Ϫ (E = S or Se;
DAPA = 2, 6-bis[1-(phenylimino)ethyl]pyridine),8 [Ni(NS3t-Bu)-
(CO)][BPh4] (NS3t-Bu = N(CH2CH2S-t-Bu)3),9 [Ni(tpttd)(CO)]Ϫ
(H2tpttd = 1,1,10,10-tetraphenyl-4,7-dithiadecane-1,1-dithiol),10
and the five-coordinate nickel() thiolate carbonyl complex
[Ni(PS3*)(CO)]Ϫ (PS3* = tris(3-phenyl-2-sulfanylphenyl)phos-
phine),11 and [Ni(PhTtt-Bu)(CO)2]Cl (PhTtt-Bu = phenyltris-
(t-butylthiomethyl)borate, ((CH3)3SCH2)3BPh)7h were reported.
In a previous communication we reported the synthesis and
crystal structure of the distorted square planar [NiII(CO)-
(SePh)3]Ϫ prepared by unique CpϪ/PhSeϪ exchange reactions.12
The chemical versatility of sulfur in biology is well estab-
lished.13a A genetic codon for selenocysteine incorporation
There is currently considerable interest in chalcogenolate
carbonyl compounds of NiII/I because of their role as
structural/functional models of nickel-containing CO dehydro-
genase enzymes. Very recently, analysis of the XAS spectra
138
J. Chem. Soc., Dalton Trans., 2001, 138–143
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b008902h

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into proteins has been established in prokaryotes in the past
decade.13b In fact, Böck et al. pronounced selenocysteine as the
21st amino acid in ribosome-mediated protein synthesis.13c
A logical and significant extension of these efforts would be
analogous studies involving exploration of nickel() carbonyl
derivatives in the biologically relevant thiolate/selenolate ligand
field. We have now investigated the reactivity of iron() thiolate
species fac-[Fe(CO)3(SR)3]Ϫ (R = C4H3S) toward [NiCp(SR)]2
and attempted to synthesize nickel() thiolate carbonyl
complexes by employing fac-[Fe(CO)3(SR)3]Ϫ as chelating and
thiolate ligand-transfer reagent.14 Specifically, the syntheses,
structures and reactivities of the distorted square planar [NiII-
(CO)(SR)n(SePh)3 Ϫ n]Ϫ (n = 0 (1), 3 (2), 1 (3) or 2 (4); R = Ph or
C4H3S) complexes are described. This study showed that the
thermal stability of the nickel-()/(0) chalcogenolate carbonyl
complexes is dependent upon the nature of the ligands, and
[NiII(CO)(SePh)3]Ϫ 1, [NiII(SC5H4N)3]Ϫ, [Ni0(CO)3(SC5H4N)]Ϫ
and [Ni0(CO)3(SePh)]Ϫ are chemically interconvertible at
ambient temperature.
was demonstrated by exposing a thf solution of 2 to 13CO. The
IR ν(CO) band at 2043 cmϪ1 shifted to a single absorbance at
1997 cmϪ1. Following extended periods of stirring in thf at
room temperature overnight the dark green thf solution of 2
converted into an insoluble solid. Further to add credibility to
the proposed mechanism shown in Scheme 1 a similar reaction
was conducted. The addition of fac-[Fe(CO)3(SePh)3]Ϫ to
[NiCp(SePh)(PPh3)] in thf at room temperature led to the
formation of complex 1, [FeCp(CO)2(SePh)] (major products),
and cis-[Ni(CO)2(PPh3)2], [Ni(CO)3(PPh3)] (minor products)
identified by IR.19
In order to synthesize nickel() mixed-chalcogenolate
carbonyl complexes and evaluate the influence of the chalco-
genolate (RSeϪ/RSϪ) ligands on the stability and reactivity of
the [Ni(CO)(ER)3]Ϫ complexes (E = S or Se), a straightforward
synthetic reaction of complex 1 with 1 equivalent of (PhS)2
in thf was conducted. This resulted in the formation of air-
sensitive dark green [Ni(CO)(SPh)(SePh)2]Ϫ 3 under N2 at
25 ЊC. In addition to the X-ray analysis and the UV-visible
spectrum, a higher ν(CO) (2029 cmϪ1) compared to that of 1
(2023 cmϪ1) also supports the formation of complex 3. From
these results it can be concluded that replacement of benzene-
selenolate with thiolate ligand in complex 1 has a significant
effect on its thermal stability and sensitivity toward air.
Results and discussion
The synthesis of [NiII(CO)(SC4H3S)3]Ϫ 2 in a manner analogous
to that of [NiII(CO)(SePh)3]Ϫ 1 by reaction of fac-[Fe(CO)3-
(SC4H3S)3]Ϫ, [NiCp(CO)]2, and (SC4H3S)2 in 2:1:1 stoichio-
metry was investigated in thf under a nitrogen atmosphere at
room temperature. The reaction mixture finally led to the
isolation of dark green oily compound 2 and the known diethyl
ether-soluble green [FeCp(CO)2(SC4H3S)] on addition of diethyl
ether.12,15 This result may be accounted for by the following
sequences of reaction (Scheme 1); the oxidative addition of
The complex [Ni0(CO)3(SePh)]Ϫ was obtained upon chemical
reduction of 1 with [N(PPh3)2][BH4] ([sodium–benzophenone–
LiMeؒOEt2) under CO in thf (MeCN) at ambient temperature
(Scheme 2a). IR ((thf): ν(CO) 1944vs, 2031w cmϪ1) and 13C
Scheme 2
NMR (δ 199.72 (s) (CO) (CD3CN)) studies confirmed the
formation of dark green oily [Ni0(CO)3(SePh)]Ϫ.19,20 The [BH4]Ϫ
and LiMeؒOEt2 serve as reductants in these reactions. Binding
HϪ/RϪ groups to NiII–CO was not observed spectrally (by IR)
at 0 ЊC. Following extended periods of stirring at room tem-
perature, a thf solution of [Ni0(CO)3(SePh)]Ϫ converted into
Ni(CO)4 and, presumably, [N(PPh3)2][SePh]. Ni(CO)4 was iden-
tified by its IR ν(CO) band at 2043 cmϪ1 (thf).7c Alkylation of
[Ni(CO)3(SePh)]Ϫ by [Et3O][BF4] led to formation of Ni(CO)4
and PhSeEt identified by 1H NMR. Indeed the complex
[Ni(CO)3(SePh)]Ϫ undergoes a clean ligand exchange process
with 13C-labeled carbon monoxide in thf to afford 13C-enriched
derivatives [Ni(13CO)3(SePh)]Ϫ (ν(CO) 1900vs, 1984m cmϪ1
close to 1944vs, 2031m cmϪ1 for [Ni(12CO)3(SePh)]Ϫ as expected
on the basis of the difference in mass between 12C and 13C).
Oxidative addition of diphenyl disulfide to coordinatively
unsaturated, low-valent, anionic [Ni0(CO)3(SePh)]Ϫ results in
formation of [NiII(CO)(SPh)2(SePh)]Ϫ 4 (Scheme 2b). Com-
plexes 3 and 4, individually, exhibit a one-band pattern in the
νCO region of the infrared, but different positions, νCO 2029
cmϪ1 (thf) for 3 and 2034 cmϪ1 (thf) for 4, which is consistent
with the distinct electronic effects of benzene-selenolate and
-thiolate ligands. Complex 4 was formed as a crystalline solid in
Scheme 1
(SC4H3S)2 across the Ni–Ni bond (Scheme 1a),16 nucleophilic
attack of an incoming chelating metallo ligand fac-[Fe(CO)3-
(SC4H3S)3]Ϫ accompanied by cyclopentadienyl shift from NiII to
FeII,17 concomitant carbonyl ligand shift from FeII to NiII,18 and
subsequent FeII–S bond cleavage to give complex 2 and [FeCp-
(CO)2(SC4H3S)] (Scheme 1b, c). Complex 2 exhibits a IR ν(CO)
band at 2043 cmϪ1 (for [N(PPh3)2]ϩ cation and 2050 cmϪ1 for
Et4Nϩ cation) which compares well to that (2023 cmϪ1) of com-
plex 1. The IR spectra of 1 and 2 in the aprotic solvent thf
reveal a strong absorption band for the CO group at 2023
and 2043 cmϪ1 respectively, within the range observed for the
CODH–CO complex formed upon incubation of the C. thermo-
aceticum enzyme with 12CO (1995 cmϪ1).1d Also, the CO ligand
lability of complex 2, as observed in the CODH–CO complex,1d
J. Chem. Soc., Dalton Trans., 2001, 138–143
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good yield after recrystallization from thf–hexane. Its structure
determined by X-ray crystallography shows that it is isostruc-
tural with complexes 1 and 3.
IR ν(CO) spectra revealed that [Ni0(CO)3(SePh)]Ϫ was re-
obtained when adding 2 equivalents of [N(PPh3)2][BH4] to
complex 4 under a CO atmosphere in thf (MeCN) solution
(Scheme 2c). Apparently, the metal-centered reduction of 4
labilizes the [SPh]Ϫ ligands and results in formation of
[Ni0(CO)3(SePh)]Ϫ. The loss of the [SPh]Ϫ ligands from the Ni0
may be due to the rich electron density around the nickel(0)
center and the more stable nickel(0) carbonyl selenolate
compound.21
Complex 1 was reobtained upon oxidative addition of di-
phenyl diselenide and benzeneselenol to [Ni(CO)3(SePh)]Ϫ in
thf respectively (Scheme 2d). The reaction presumably involved
oxidative addition of PhSe–H to [Ni0(CO)3(SePh)]Ϫ to yield the
nickel() hydride intermediate [NiII(H)(CO)2(SePh)2]Ϫ, and
subsequent acid–base reaction (PhSe–H and [NiII(H)(CO)2-
(SePh)2]Ϫ) to form complex 1 with evolution of H2 gas.22
Attempts to trap the potential intermediate spectrally (by IR
and 1H NMR) were unsuccessful.
Fig. 2 An ORTEP26 drawing and labeling scheme of the [Ni(CO)-
(SPh)(SePh)2]Ϫ anion with thermal ellipsoids drawn at 30% probability
(X2 = 0.605 Se ϩ 0.395 S; X3 = 0.395 Se ϩ 0.605 S).
In a similar fashion, the ligand-displacement reaction was
also displayed by complex 1 and bis(2-pyridyl) disulfide. When
a thf solution of 1 was treated with 2 equivalents of bis(2-
pyridyl) disulfide an immediate change from dark green to dark
1
brown was observed. The H NMR spectrum (δ 96.47 (br),
70.10 (br), 53.73 (br), 12.27 (br)) indicated formation of the
known d8 paramagnetic tris-chelate complex [NiII(SC5H4N)3]Ϫ
(Scheme 3a).23
Scheme 4
reported in this paper for [Ni(CO)3(SePh)]Ϫ and earlier (IR and
X-ray diffraction) for cis-[Mn(CO)4(SePh)2]Ϫ (Scheme 4a,b).18
This result can be interpreted as coordinative addition of the
metalloanion [Mn(CO)5]Ϫ to 1 and subsequent redox ligand
transfer to give cis-[Mn(CO)4(SePh)2]Ϫ and [Ni0(CO)3(SePh)]Ϫ,18
since the [Mn(CO)5]Ϫ anion has been shown to serve as a lone-
pair-electron donor.24 The presumed intermediate A was not
detected spectrally.
ϩ
Scheme 3 PPN = N(PPh3)2
.
Under similar reaction conditions, addition of [Fe(CO)4-
(SePh)]Ϫ to complex 1 under a CO atmosphere in thf also
resulted in formation of fac-[Fe(CO)3(SePh)3]Ϫ and [Ni0(CO)3-
(SePh)]Ϫ.25 The ligands [SePh]Ϫ were not observed to undergo
oxidation and decomposition in the above two redox processes,
and consequently the redox processes were assigned to the
NiIIMnϪI–Ni0MnI and NiIIFe0–Ni0FeII couples respectively.
The molecular structure of complex 3 is depicted in Fig. 2.
Selected bond distances and angles for 3 and 4 are given in
Table 1. The complexes 3 and 4 consist of discrete [N(PPh3)2]ϩ
cations and [Ni(CO)(SPh)(SePh)2]Ϫ/[Ni(CO)(SPh)2(SePh)]Ϫ
anions individually. Disorder in the structure of 3 prevents
detailed determinations of NiII–S and NiII–Se bond distances.
Bond angles (Se(1)–Ni–X(2) 174.65(12), Se(1)–Ni–C(1)
94.8(4)Њ, X(3)–Ni–C(1) 171.6(5)Њ, and Se(1)–Ni–X(3)
93.01(12)Њ) around the NiII define a distorted square planar
coordination sphere. The NiII–Se(1) bond length of 2.270(3) Å
is significantly shorter than the NiII–Se bond length of 2.317(2)
Å (average) in 1.12 The anionic complex 4 is isostructural with 3
(Fig. 3). Owing to disorder, the exact Ni–S, Ni–Se bond
distances are poorly determined in 4. The NiII–X bond length
of 2.264(1) Å (average) is comparable to the NiII–S bond
The ring-opened complex [Ni0(CO)3(SC5H4N)]Ϫ (IR (thf):
ν(CO) 2037w, 1951s cmϪ1; monodentate, S-bonded) was
obtained upon chemical reduction of [NiII(SC5H4N)3]Ϫ with
sodium–benzophenone under a CO atomosphere in thf at
room temperature (Scheme 3b).20 Here the metal-centered
reduction of [NiII(SC5H4N)3]Ϫ labilizes the chelating ligands
[SC5H4N]Ϫ and results in formation of the four-coordinate
species [Ni0(CO)3(SC5H4N)]Ϫ. Upon addition of 1 equivalent
of diphenyl diselenide to [Ni0(CO)3(SC5H4N)]Ϫ the bands at
2037w, 1951s cmϪ1 disappeared, with concomitant formation
of a spectrum (ν(CO) 2031w, 1944s cmϪ1) assigned to
[Ni(CO)3(SePh)]Ϫ (Scheme 3c). The results suggest that the
selenolate ligand enhances the stability of nickel(0) complexes.
Complex 1 was reobtained upon addition of diphenyl di-
selenide to [Ni(CO)3(SePh)]Ϫ in thf (Scheme 3d). Apparently,
anionic 1, [NiII(SC5H4N)3]Ϫ, [Ni0(CO)3(SC5H4N)]Ϫ and [Ni0-
(CO)3(SePh)]Ϫ are chemically interconvertible at ambient tem-
perature.
Additionally, when a thf solution of 1 equivalent of
[N(PPh3)2][Mn(CO)5] and
1 equivalent of complex 1 is
stirred under CO a rapid reaction ensues over the course of 5
min at ambient temperature to give [Ni(CO)3(SePh)]Ϫ and cis-
[Mn(CO)4(SePh)2]Ϫ, as evident from their IR and NMR spectra
length of 2.281(1) Å in [Ni(SC6H4Cl-p)4]2Ϫ 27 The NiII–CO
.
bond lengths 1.80(2) and 1.737(5) Å in 3 and 4 respectively,
well within the range observed for other nickel() carbonyl
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J. Chem. Soc., Dalton Trans., 2001, 138–143

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4 Complexes 1–4 are easily reduced to the nickel(0) tricarb-
onyl chalcogenolate species with reductants like [BH4]Ϫ/
sodium–benzophenone in thf.
5 [NiII(CO)(SePh)3]Ϫ, [NiII(SC5H4N)3]Ϫ, [Ni0(CO)3(SC5H4-
N)]Ϫ and [Ni0(CO)3(SePh)]Ϫ are chemically interconvertible at
ambient temperature.
6 Redox and subsequent ligand transfer lead to the formation
of [Ni0(CO)3(SePh)]Ϫ and cis-[Mn(CO)4(SePh)2]Ϫ (fac-[Fe(CO)3-
(SePh)3]Ϫ) from [NiII(CO)(SePh)3]Ϫ and [Mn(CO)5]Ϫ ([Fe(CO)4-
(SePh)]Ϫ) individually.
7 The vibrational spectra of the NiII(CO) fragment (ν(CO)
ranges from 2023 to 2043 cmϪ1) found for complexes 1–4
may be regarded as a spectroscopic reference for the carbonyl
binding site of CO dehydrogenase.1d
8 All attempts to bind both R (H or Me) and CO ligands to
NiII simultaneously were not observed spectrally (by IR). This
may support the existence of two binding sites for transient
binding of both CO and the alkyl ligands in CODH/ACS.1–4,8,9
Fig. 3 An ORTEP drawing and labeling scheme of the [Ni(CO)(SPh)2-
(SePh)]Ϫ anion with thermal ellipsoids drawn at 30% probability
(X1 = 0.46 Se ϩ 0.54 S; X2 = 0.40 Se ϩ 0.60 S; X3 = 0.14 Se ϩ 0.86 S).
Experimental
Manipulations, reactions, and transfers of samples were con-
ducted under nitrogen according to standard Schlenk tech-
niques or in a glove-box (argon gas). Solvents were distilled
under nitrogen from appropriate drying agents (diethyl ether
from CaH2; acetonitrile from CaH2–P2O5; methylene chloride
from P2O5; hexane and tetrahydrofuran (thf) from sodium–
benzophenone) and stored in dried, N2-filled flasks over 4 Å
molecular sieves. Nitrogen purge was used on these solvents
before use and transfers to reaction vessels were via stainless
steel cannula under a positive pressure of N2. The reagents iron
Table 1 Selected bond distances (Å) and angles (Њ) for complexes 3
and 4
Complex 3
Ni–Se(1)
Ni–X(3)
C(1)–O(1)
2.270(3)
2.237(3)
1.09(2)
Ni–X(2)
Ni–C(1)
2.304(3)
1.80(2)
Se(1)–Ni–X(2)
Se(1)–Ni–C(1)
X(2)–Ni–C(1)
Ni–C(1)–O(1)
174.65(12)
94.8(4)
87.8(4)
Se(1)–Ni–X(3)
X(2)–Ni–X(3)
X(3)–Ni–C(1)
93.01(12)
84.62(11)
171.6(5)
pentacarbonyl,
bis(triphenylphosphoranylidene)ammonium
chloride, diphenyl diselenide, di(2-thienyl) disulfide, diphenyl
disulfide, bis(2-pyridyl) disulfide (Aldrich/Lancaster) were used
as received. ν(CO) Infrared spectra were recorded on a Bio-Rad
Model FTS-185 spectrophotometer with sealed solution cells
(0.1 mm) and KBr windows, NMR spectra on a Bruker AC 200
spectrometer (1H and 13C relative to tetramethylsilane) and
UV/VIS spectra on a GBC 918 spectrophotometer. Analyses of
carbon, hydrogen and nitrogen contents were obtained with a
Heraeus CHN analyzer.
174.2(14)
Complex 4
Ni–X(3)
Ni–X(2)
C(1)–O(1)
2.228(1)
2.300(1)
1.137(5)
Ni–X(1)
Ni–C(1)
2.265(1)
1.737(5)
X(3)–Ni–X(1)
X(3)–Ni–C(1)
X(1)–Ni–C(1)
Ni–C(1)–O(1)
92.75(4)
170.51(14)
96.20(14)
178.2(4)
X(3)–Ni–X(2)
X(1)–Ni–X(2)
X(2)–Ni–C(1)
84.65(4)
174.47(3)
86.7(2)
Preparations
[N(PPh3)2][Ni(CO)(SePh)3] 1. Complex 1 was prepared and
complexes (1.73–1.83 Å),6 are comparable to the value 1.75(3) Å
in [Ni(PS3*)(CO)]Ϫ,11 and shorter than the NiI–CO bond dis-
tance (1.81(1) Å) observed for [Ni(NS3t-Bu)(CO)][BPh4].9 The
longer NiII–CO bond distances (in 3 and 4) compared with that
(1.729 Å) in 1 are ascribed to the weaker σ-donating ability of
benzenethiolate.
characterized according to the method reported earlier.12
[N(PPh3)2][Ni(CO)(2-SC4H3S)3] 2. A solution containing
0.230 g (1 mmol) of di(2-thienyl) disulfide and 0.283 g (0.4
mmol) of [N(PPh3)2][HFe(CO)4] in thf (5 mL) was stirred at
15 ЊC for 20 min. The reaction was monitored immediately by
IR. The spectrum ((thf): ν(CO) 2053s, 1994s cmϪ1) was assigned
to the formation of fac-[N(PPh3)2][Fe(CO)3(2-SC4H3S)3].24 In
the same flask 0.2 mmol of [NiCp(CO)]2 (0.061 g) were added,
followed by stirring at room temperature for 6 h, and then
diethyl ether (10 mL) was added to precipitate the dark green
oily product. The reaction mixture was filtered, and the
dark green oily product dried under N2 purge to afford
[N(PPh3)2][Ni(CO)(2-SC4H3S)3] 2 at 0 ЊC (yield 48%, 0.19 g).
The filtrate was dried under vacuum to afford [FeCp(CO)2-
(2-SC4H3S)]. When a thf solution of complex 2 is purged with
13CO the IR ν(CO) peak at 2043 cmϪ1 immediately shifts to 1997
cmϪ1. The magnitude ≈ 46 cmϪ1 of the isotopic shift (∆ν(CO))
is consistent with the calculated position, based only on the
difference in masses between 12CO and 13CO. 1H NMR
(CD3CN): δ 6.62 (t), 6.85 (d) and 6.99 (d) (C4H3S). UV/VIS
(thf): λmax/nm (ε/MϪ1 cmϪ1) 363(6500) and 429(3747). Complex
[FeCp(CO)2(2-S–C4H3S)]: IR ν(CO) 2029s, 1982s (thf); 2035s,
1994s cmϪ1 (hexane); 1H NMR (CD2Cl2) δ 5.23 (s) (Cp); Found
C 60.35, H 4.18, N 1.60; Calc. for C49H39NNiOP2S6 C 59.62, H
4.05, N, 1.44%. The elemental analysis did not show good
Conclusion
The following are the principal results of this study.
1 The distorted square planar complex [NiII(CO)(SR)3]Ϫ
(R = C4H3S) with a NiII–CO bond has been prepared by
reaction of 2fac-[Fe(CO)3(SR)3]Ϫ, (RS)2, and [NiCp(CO)]2. The
mixed-chalcogenolate nickel() carbonyl complexes [Ni(CO)-
Ϫ
(SePh)n(SPh)3 Ϫ n
]
(n = 2 or 1) are prepared by PhSeϪ/PhSϪ
ligand exchange reaction and oxidative addition of diphenyl
disulfide to [Ni(CO)3(SePh)]Ϫ respectively.
2 Nickel()/nickel(0) carbonyl thiolate complexes are more
unstable thermally than the corresponding carbonyl selenolate
complexes. This result may be accounted for by the distinct
electronic effects of selenolate and thiolate ligands. In brief,
the electronic effect plays an important role in stabilizing the
nickel() carbonyl chalcogenolate complexes.
3 Isotopic shift experiments demonstrate the lability of
carbonyl ligand(s) of [Ni(CO)(SePh)n(SR)3 Ϫ n]Ϫ (n = 3, 2, 1 or 0)
and [Ni(CO)3(SePh)]Ϫ species.
J. Chem. Soc., Dalton Trans., 2001, 138–143
141

View Article Online
Table 2 Crystallographic data of complexes 3 and 4
agreement with the calculated values because of the extreme
thermal unstability.
3
4
[N(PPh3)2][Ni(CO)(SPh)(SePh)2] 3. The compounds
1
(0.2 mmol, 0.218 g) and diphenyl disulfide (0.2 mmol, 0.044 g)
dissolved in 4 mL of thf were stirred under N2 at ambient tem-
perature for 4 h. The dark green brown solution was then
filtered through Celite and hexane (5 mL) added to precipitate
the air-sensitive, dark green solid [N(PPh3)2][Ni(CO)(SPh)-
(SePh)2] 3. Yield 0.190 g (87%). Diffusion of hexane into a
solution of complex 3 in thf at Ϫ15 ЊC for 4 weeks led to
dark green crystals suitable for X-ray crystallography. IR (thf):
Formula
M
Crystal system
Space group
a/Å
b/Å
c/Å
α/Њ
C55H45NNiOP2SSe2
1046.55
C55H45NNiOP2S2Se
999.65
Triclinic
Triclinic
¯
¯
P1
P1
10.114(3)
15.504(3)
16.402(3)
73.35(2)
87.06(2)
87.50(2)
2459.8(10)
2
2.021
22
0.0968
0.1619
6413
10.133(4)
15.499(3)
16.426(5)
73.39(2)
87.07(3)
87.51(3)
2467.7(13)
2
1.319
22
0.039
0.0895
8672
β/Њ
1
ν(CO) 2029s cmϪ1. H NMR (CD3CN): δ 7.02–7.65 (m) (Ph).
γ/Њ
V/Å3
13C NMR (CD3CN): δ 134.6, 134.5, 133.4, 133.3, 133.2, 133.0,
132.9, 130.5, 130.4,130.3, 130.2 and 130.1 (Ph). UV/VIS (thf):
λmax /nm (ε/MϪ1 cmϪ1) 555(1060), 416(2605) (sh), 354(9433) (sh)
and 320(18719). Found: C, 63.03; H, 4.48; N, 1.46. Calc. for
C55H45NNiOP2SSe2: C, 63.12; H, 4.33; N, 1.34%.
Z
µ/mmϪ1
T/ЊC
R
RWF
Independent
reflections
Reaction of [N(PPh3)2][Ni(CO)(SePh)3] with [N(PPh3)2]-
[BH4] (and [N(PPh3)2][Ni(CO)(SePh)3] with sodium–benzo-
phenone). A solution containing 0.218 g (0.2 mmol) of complex
1 and 0.222 g (0.4 mmol) of [N(PPh3)2][BH4] (the same stoichio-
metry is used for sodium–benzophenone) in thf (10 mL) was
stirred under a CO atmosphere overnight (half hour for
sodium–benzophenone) at room temperature. The solution
was filtered to remove [N(PPh3)2][SePh] (or [Na][SePh]). The
volume of the filtrate was then reduced to 3 mL and the dark
green oily product [N(PPh3)2][Ni(CO)3(SePh)] precipitated by
addition of hexane (6 mL). The thermally unstable product
[N(PPh3)2][Ni(CO)3(SePh)] was isolated by removing the
solvent (since decomposition occurred after prolonged vacuum
the yield of the oily [N(PPh3)2][Ni(CO)3(SePh)] was difficult
Reactions of sodium–benzophenone with [N(PPh3)2][Ni(2-
SC5H4N)3] and [N(PPh3)2][Ni(CO)3(2-SC5H4N)] with diphenyl
diselenide. [N(PPh3)2][Ni(2-SC5H4N)3] (0.186 g, 0.2 mmol) dis-
solved in thf (3 mL) was stirred under a CO atmosphere, and a
solution of sodium–benzophenone (0.4 mmol) in thf added
dropwise by cannula under a positive CO gas pressure at room
temperature. [N(PPh3)2][Cl] (0.23 g, 0.4 mmol) was then added.
After stirring for 1 h, the dark green solution was filtered to
remove NaCl and the oily product [N(PPh3)2][Ni(CO)3(2-
SC5H4N)] precipitated by addition of hexane. The IR spectrum
((thf): ν(CO) 2037w and 1951s cmϪ1) was identical to that of
[N(PPh3)2][Ni(CO)3(2-SC5H4N)].19,20 The [N(PPh3)2][Ni(CO)3-
(2-SC5H4N)] was then redissolved in thf (3 mL). In the same
flask 0.2 mmol of diphenyl diselenide (0.062 g) was added,
followed by stirring at room temperature for 10 min, and then
hexane (5 mL) was added to precipitate the dark green oily
product [N(PPh3)2][Ni(CO)3(SePh)] (by ligand exchange)
identified by IR ((thf): ν(CO) 2031w and 1944s cmϪ1). Addition
of more diphenyl diselenide (0.2 mmol, 0.062 g) to the same
flask at room temperature results in the formation of [N(PPh3)2]-
[Ni(CO)(SePh)3] (by oxidative addition) identified by IR, which
was precipitated as a dark green solid on addition of hexane.
to determine). IR (thf): ν(CO) 2031w and 1944s cmϪ1 13C
.
NMR (CD3CN): δ 199.72 (s) (CO), 134.52, 133.14, 133.03,
130.65, 130.44, 130.18, 129.28 and 127.79 (Ph).18,19 [N(PPh3)2]-
[Ni(CO)3(2,4,6-Me3C6H2Se)]: IR (thf): ν(CO) 2028w and
1938s cmϪ1
.
[N(PPh3)2][Ni(CO)(SPh)2(SePh)] 4. A solution containing
0.218 g (0.2 mmol) of complex 1 and 0.222 g (0.4 mmol) of
[N(PPh3)2][BH4] in MeCN (3 mL) was stirred under CO at
ambient temperature for 5 h and then diethyl ether was added
to precipitate the dark green oily product. The dark green oily
product that was obtained upon removal of solvent from the
resulting solution was extracted with 5 mL of degassed thf. The
IR ν(CO) and 13C NMR spectra ((thf): ν(CO) 1944vs and
2031w cmϪ1; δ (CD3CN): 199.72 (s) (CO)) were assigned to the
formation of [N(PPh3)2][Ni(CO)3(SePh)].20 To the same flask a
thf solution of 0.2 mmol of (PhS)2 (0.044 g) was added slowly,
followed by stirring at 5 ЊC for 3 h. The dark green solution was
then filtered and hexane added to precipitate the air-sensitive
solid [N(PPh3)2][Ni(CO)(SPh)2(SePh)]. Recrystallization from
saturated thf solution with hexane diffusion gave dark green
crystals of complex 4 at Ϫ15 ЊC. IR (thf): ν(CO) 2034s cmϪ1. 1H
NMR (CD3CN): δ 6.99–7.61 (m) (Ph). 13C NMR (CD3CN):
δ 134.5, 133.3, 133.1, 133.0, 130.5, 130.4, 130.3, 130.1 and 130.0
(Ph). UV/VIS (thf): λmax /nm (ε/MϪ1 cmϪ1) 537(1250) and
423(3837). Found: C, 65.62; H, 4.66; N, 1.53. Calc. for
C55H45NNiOP2S2Se: C, 66.08; H, 4.54; N, 1.40%. Elemental
analysis for S does not give good agreement with the calculated
value because of extreme air-sensitivity.
Reaction of [N(PPh3)2][Mn(CO)5] and [N(PPh3)2][Ni(CO)-
(SePh)3].
A solution of [N(PPh3)2][Mn(CO)5] (0.147 g,
0.2 mmol) in thf (2 mL) was added dropwise to complex 1
(0.218 g, 0.2 mmol) in thf solution under a CO atmosphere at
ambient temperature. The mixture was stirred overnight at
room temperature. The IR spectrum showed six new bands
attributed to the well known carbonyl stretching modes of
[Ni(CO)3(SePh)]Ϫ ((thf): ν(CO) 2031w and 1944s cmϪ1) and
cis-[Mn(CO)4(SePh)2]Ϫ ((thf): ν(CO) 2041m, 1969s, 1950m
and 1908m cmϪ1).18 No attempts were made to separate the
complexes [Ni(CO)3(SePh)]Ϫ and cis-[Mn(CO)4(SePh)2]Ϫ.
Crystallography
Crystallographic data of complexes 3 and 4 are summarized in
Table 2. The crystals of 3 and 4 are chunky. Each was mounted
on a glass fiber and quickly coated in epoxy resin. Unit-cell
parameters were obtained by least-squares refinement from 25
reflections. Diffraction measurements were carried out on a
Nonius CAD 4 diffractometer with graphite-monochromated
Mo-Kα radiation.28 Least-squares refinement of the positional
and anisotropic thermal parameters for all non-hydrogen atoms
and fixed hydrogen atom contributions was based on F2. A
φ scan absorption correction was made. The SHELXTL29
package of programs was employed, and atomic scattering
factors were from ref. 30. In the case of complex 3 one sulfur
and one selenium atom (X(2) and X(3) as shown in Fig. 2) are
Reaction of [N(PPh3)2][Ni(CO)(SePh)3] with bis(2-pyridyl)
disulfide. Complex 1 (0.218 g, 0.2 mmol) was added to bis-
(2-pyridyl) disulfide (0.088 g, 0.4 mmol) in MeCN (6 mL) at
ambient temperature. After 3 h of stirring the green product
[N(PPh3)2][Ni(2-SC5H4N)3] precipitated upon addition of
diethyl ether. It was recrystallized from acetonitrile–diethyl
1
ether.23 Yield 0.166 g (89%). H NMR (CD3CN): δ 12.27 (br),
53.73 (br), 70.10 (br) and 96.47 (br) (SC5H4N).
142
J. Chem. Soc., Dalton Trans., 2001, 138–143

View Article Online
8 C. A. Marganian, H. Vazir, N. Baidya, M. M. Olmstead and P. K.
found at disordered positions; in the case of 4 two sulfur atoms
and one selenium atom are found at disordered positions and
were refined by partial occupancies.
CCDC reference numbers 152484 and 152485.
See http://www.rsc.org/suppdata/dt/b0/b008902h/ for crystal-
lographic data in CIF or other electronic format.
Mascharak, J. Am. Chem. Soc., 1995, 117, 1584.
9 P. Stavropoulos, M. C. Muetterties, M. Carrie and R. H. Holm,
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10 T. Yamamura, S. Sakurai, H. Arai and H. Miyamae, J. Chem. Soc.,
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11 D. H. Nguyen, H.-F. Hsu, M. Millar, S. A. Koch, C. Achim,
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12 W.-F. Liaw, Y.-C. Horng, D.-S. Ou, C.-Y. Chiang, G.-H. Lee and
S.-M. Peng, J. Am. Chem. Soc., 1997, 119, 9299.
Acknowledgement
13 (a) R. H. Holm, P. Kennepohl and E. I. Solomon, Chem. Rev. 1996,
96, 2239; (b) T. C. Stadtman, Annu. Rev. Biochem., 1996, 65, 83; (c)
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Lee and S.-M. Peng, J. Chem. Soc., Dalton Trans., 1998, 353; W.-F.
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Organometallics, 1999, 18, 782.
15 E. D. Schermer and W. H. Baddley, J. Organomet. Chem., 1971, 27,
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18 W.-F. Liaw, C.-Y. Chuang, W.-Z. Lee, C.-K. Lee, G.-H. Lee and
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19 G.-M. Bodner, Inorg. Chem., 1975, 14, 1932; C. A. Tolman, J. Am.
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22 T. L. James, L. Cai, M. C. Muetterties and R. H. Holm, Inorg.
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We gratefully acknowledge financial support from the National
Science Council (Taiwan).
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