Activation of H2 and CO by sulfur-rich nickel model complexes for [NiFe] hydrogenases and CO dehydrogenases

Article abstract of DOI:10.1002/ejic.200300786

Reactions of the trinuclear complexes [Ni(^RS₃)] ₃ [^HS₃^2- = bis(2-mercaptophenyl) sulfide(2-) (1a) or ^siS₃^2- = bis(2-mercapto-3-trimethylsilylphenyl)sulfide(

Full text of DOI:10.1002/ejic.200300786

FULL PAPER
Activation of H2 and CO by Sulfur-Rich Nickel Model Complexes for [NiFe]
Hydrogenases and CO Dehydrogenases[‡]
Dieter Sellmann,[a][†] Raju Prakash,*[a] and Frank W. Heinemann[a]
Keywords: Hydrogenases / H2 activation / Nickel / N ligands / S ligands
Reactions of the trinuclear complexes [Ni(RS3)]3 [HS32− = bis(2-
heterolysis is achieved through attack of the Lewis-acidic
nickel centers and the Brönsted-basic sulfur atoms at an η2-
D2 ligand. Complexes 9a and 9b are the first sulfur-only
nickel complexes that enable the modeling of the [NiFe] hy-
drogenase catalyzed D2/H+ exchange reaction. Evidence for
labile five-coordinate [Ni(CO)(L)(RS3)] has been found in the
reaction between [Ni(L)(RS3)] complexes and CO. The CO
adducts of complexes with nitrogenous ligands L such as
N−3, NHPR3 (R = nPr3, Cy3), or NHSPh2 showed rapid consec-
mercaptophenyl)sulfide(2−) (1a) or siS32− = bis(2-mercapto-3-
trimethylsilylphenyl)sulfide(2−) (1b)] with nucleophiles
L
(L = NHPnPr3, NHPCy3, NHSPh2, PnPr3) afforded the corres-
ponding mononuclear complexes [Ni(L)(RS3)] [R = si = SiMe3;
L = NHPnPr3 (2b); L = NHPCy3 (3a,b); L = NHSPh2 (4a,b);
L = PnPr3 (5a)]. X-ray structural determinations showed that
2b, 3a, 3b, 4a, and 5a exhibit tetrahedrally distorted planar
[Ni(L)(RS3)] fragments. Complex 2b dimerizes through inter-
molecular N−H···N hydrogen bonding. In contrast to 2b, com- utive reactions. The reaction between Et4N[Ni(N3)(siS3)] (8b)
plexes 3a and 4a exhibit intramolecular hydrogen bonds be- and CO gave Et4N[Ni(NCO)(siS3)] (10b), whereas reactions
tween thiol groups and NH protons. Complexes 2−4 possess
between 2−4 and CO afforded only 1a or 1b. Mechanisms
weakly acidic NH protons and undergo D+/NH exchange re- are suggested which have the formation of reactive five-co-
actions with D2O or CD3OD. Complexes 2−4 and
[Ni(StBu)(RS3)]− (9a,b) also catalyze D2/H+ exchange in
[D8]THF/H2O under an elevated pressure of D2 (18 bar), as
confirmed by 1H NMR spectroscopy. It is proposed that D2 Germany, 2004)
ordinated [Ni(CO)(L)(RS3)] intermediates in common.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Introduction
(1)
(2)
Modeling active sites in metalloenzymes is the motivation
for the synthesis of low-molecular-weight complexes that
exhibit the structural and reactivity features of the enzyme
centers.[1] A key feature of the active sites of hydrogenases
and CO dehydrogenases are nickel atoms in sulfur-domi-
nated coordination spheres.[1Ϫ5] X-ray structural determi-
nations of several [NiFe] hydrogenases[2,3] and two CO de-
hydrogenases[4,5] have established that the active sites con-
tain four-coordinate nickel atoms in tetrahedrally distorted
planar coordination spheres of sulfur atoms[2Ϫ5] (Figure 1).
These centers are generally accepted to be the location of
Figure 1. Schematic structures of the active centers in fully reduced
[NiFe] hydrogenase from D. vulgaris Miyazaki[2] (left) and the CO
dehydrogenase from C. hydrogenoformans[4,5] (right)
the reactions catalyzed by hydrogenases [Equation (1a),
(1b)] and CO dehydrogenases [Equation (2)].
Catalysis of the reactions in Equations (1) and (2) makes
hydrogenases and CO dehydrogenases essential for energy
metabolism in nature. Low-molecular-weight nickel com-
plexes with sulfur-dominated coordination spheres and re-
activity towards H2, CO, or CO2 thus have considerable sig-
nificance for gaining closer insights into the mechanisms of
the reactions according to Equations (1) and (2), and for
the development of competitive catalysts. Such complexes,
[‡]
Transition Metal Complexes with Sulfur Ligands, 160. Part 159:
D. Sellmann, K. P. Peters, F. W. Heinemann, Eur. J. Inorg.
Chem., 2004, 581Ϫ590.
[a]
Institut für Anorganische Chemie der Universität Erlangen-
Nürnberg,
Egerlandstrasse 1, 91058 Erlangen, Germany
Fax: (internat.) ϩ 49-(0)9131/85-27367
E-mail: prakash@anorganik.chemie.uni-erlangen.de
[†]
Deceased.
Eur. J. Inorg. Chem. 2004, 1847Ϫ1858
DOI: 10.1002/ejic.200300786
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1847

D. Sellmann, R. Prakash, F. W. Heinemann
FULL PAPER
however, are extremely rare. [Ni(L)(RS3)] is one of the very
few examples of complexes of type A, in which RS3 denotes
the
tridentate
sulfur
ligands
HS32Ϫ
[bis(2-
mercaptophenyl)sulfide(2Ϫ)] or S32Ϫ [bis(2-mercapto-3-tri-
methylsilylphenyl)sulfide (2Ϫ)] and L neutral or anionic li-
gands, such as PR3, HNPnPr3, ClϪ, N3Ϫ, or StBuϪ.[6Ϫ9]
si
Recent findings that the neutral phosphorane imine com-
plex [Ni(NHPnPr3)(HS3)] catalyzes the heterolytic activation
of H2 [Equation (1b)][6] and the anionic complex
[Ni(N3)(HS3)]Ϫ reacts with CO to give [Ni(NCO)(HS3)]Ϫ [7]
prompted us to explore this type of complex in greater de-
tail. This paper focuses on the synthesis and characteriz-
ation of [Ni(L)(HS3)] and its analogous [Ni(L)(siS3)] com-
plexes, and their reactivity towards H2. In addition, we ex-
tend our investigation towards the reactivity of [Ni(L)(RS3)]
complexes with CO in an effort to identify the possible five-
coordinate intermediate species by means of spectroscopic
techniques.
Scheme 1. Synthesis of [Ni(L)(RS3)] complexes (R ϭ H Ǟ a; R ϭ
SiMe3 Ǟ b)
[Ni(NHSPh2)(HS3)] (4a) and dark-red [Ni(NHSPh2)(siS3)]
(4b). The X-ray structure determination of 4a proved that
HNSPh2 coordinates to the nickel atom through its N atom
like the phosphorane imines.[8c]
Results and Discussion
Synthesis and Characterization of [Ni(L)(HS3)] and
[Ni(L)(siS3)] Complexes
Red-yellow crystals of [Ni(PnPr3)(HS3)] (5a) formed in-
[Ni(L)(RS3)] complexes containing different ligands L are stantaneously when a black-brown THF suspension of 1a
a prerequisite for probing the influence of L upon the po- was treated with an equivalent amount of PnPr3. The anal-
tential activation of H2 and CO. Scheme 1 summarizes the ogous synthesis of 5b could be carried out in homogeneous
synthesis of such [Ni(L)(RS3)] complexes. The letters a and phase in THF. The chloro complexes Bu4N[Ni(Cl)(HS3)]
b always designate the unsubstituted (R ϭ H) and substi- (Bu4N[7a]) and Bu4N[Ni(Cl)(siS3)] (Bu4N[7b]) were ob-
tuted (R ϭ SiMe3 ϭ si) complexes, respectively. For the tained from 1a and 1b with Bu4NCl. The anions 7a and 7b
sake of completeness, Scheme 1 also includes complexes 2a, were required as precursors for the synthesis of the azido
5b, 6a/6b, Bu4N[7a/7b], and Et4N[8b], which have been re- complexes
Et4N[Ni(N3)(HS3)]
(Et4N[8a])
and
ported previously.[8,9] In most cases, the new complexes Et4N[Ni(N3)(siS3)] (Et4N[8b]), which formed from the reac-
were obtained by cleavage of the trinuclear starting com- tion of 1a and 1b, respectively, with Et4NCl and subsequent
plexes [Ni(RS3)]3 (1a,b) with nucleophiles L.
reaction with Me3SiN3. The sodium derivatives Na-
Treatment of 1b with NHPnPr3 in THF gave purple [Ni(StBu)(HS3)] (Na[9a]) and Na[Ni(StBu)(siS3)] (Na[9b])
[Ni(NHPnPr3)(siS3)] (2b) in analogy to the known synthesis were obtained from 1a and 1b with NaStBu, similar to the
of 2a. The bulkier phosphorane imine HNPCy3 had to be formation of similar Bu4N derivatives reported in the litera-
generated in situ through methanolysis of Me3SiNPCy3 and ture.[8,9]
treated with 1a and 1b to afford [Ni(NHPCy3)(RS3)] (3a,b).
All new complexes were isolated in analytically pure
These reactions could be monitored visually by the color form, are soluble in THF, CH2Cl2, acetone, DMF, or
change of the THF suspension (1a) or THF solution (1b) DMSO, and were characterized by IR and NMR spec-
from red-brown to purple-red. Complex 1b reacted much troscopy, and mass spectrometry. The molecular structures
faster than complex 1a.
of 2b, 3a, 3b, 4a, and 5a were determined by X-ray crystal-
Diphenylsulfimine, HNSPh2, can potentially coordinate lography.
through either its nitrogen or sulfur atom. Reactions of 1a
The IR (KBr) spectra of the complexes exhibit absorp-
and 1b in THF with equimolar amounts of diphenylsulfim- tion patterns typical for complexes with [Ni(HS3)] or
ine hydrate, NHSPh2·H2O, afforded the first examples of [Ni(siS3)] fragments. The HNPR3 and HNSPh2 ligands of
sulfimine sulfur-only nickel complexes as red-brown 2Ϫ4 give rise to sharp ν(NH) bands in the region
1848
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Activation of H2 and CO by Sulfur-Rich Nickel Model Complexes
FULL PAPER
3365Ϫ3200 cmϪ1 and ν(NP) or ν(NS) bands in the region lowered to Ϫ80 °C, indicating a free rotation of the PR3
995Ϫ915 cmϪ1. The ν(NH), ν(NP), and ν(NS) bands corre- and SPh2 fragments around the NϪP or NϪS bonds, as
[10]
[11]
spond to those of HNPR3
and HNSPh2
complexes well as of the NH groups around the NiϪN bonds.
reported previously. In comparison to the ν(NH) band of
free HNPnPr3 (3368 cmϪ1), the ν(NH) band in 2b (3298
cmϪ1) is significantly red-shifted. Similarly, the ν(NH) band
of 4a (3202 cmϪ1) and 4b (3210 cmϪ1) appears at lower
wavenumbers than that of free HNSPh2 (3306 cmϪ1).[11b]
The solid-state IR spectra of 3a and 4a also contain weak
bands at 2560 cmϪ1 (3a) and 2559 cmϪ1 (4a), indicating
the existence of NϪH···S(thiolate) bridges. Such hydrogen-
bond bridges were confirmed by the X-ray structure deter-
minations.
X-ray Crystal Structure Determinations
The molecular structures of [Ni(NHPnPr3)(siS3)] (2b),
[Ni(NHPCy3)(HS3)]
(3a),
[Ni(NHPCy3)(siS3)]
(3b),
[Ni(NHSPh2)(HS3)] (4a), and [Ni(PnPr3)(HS3)] (5a) were de-
termined by X-ray structure analysis. Figure 2 depicts the
molecular structures and Table 1 lists selected distances
and angles.
As judged by their well-resolved NMR spectra, the com-
1
plexes are diamagnetic. The H NMR spectra of all com-
plexes show a characteristic splitting pattern for the aro-
matic protons, consisting of either four or three multiplets
depending on the fragment [Ni(HS3)] or [Ni(siS3)]. In 4a and
4b, some of these aromatic multiplets are superimposed by
SPh2 signals. The SiMe3 protons in the [Ni(L)(siS3)] com-
plexes give rise to a sharp singlet in the region between δ ϭ
0.5 and 0.3 ppm. The 1H and 13C NMR spectra are consist-
ent with the Cs symmetry of all complexes in solution. The
NH singlet signals of 2a/b, 3a/b, and 4a/b appear in the
high-field region between δ ϭ 0.9 and Ϫ1.9 ppm, and their
chemical shifts are solvent-dependent. They are always
shifted to higher fields when compared with the NH sing-
lets of free HNPnPr3 (δ ϭ 0.51 ppm) or HNSPh2 (δ ϭ
1.12 ppm), possibly indicating a decrease of NH acidity of
the HNPR3 and HNSPh2 ligands. It should be noted that
the NH protons exhibit slightly lower shifts in the
[Ni(L)(siS3)] complexes 2b, 3b, and 4b than in the corre-
sponding [Ni(L)(HS3)] complexes 2a, 3a, and 4a. This might
indicate a slightly higher NH acidity of the [Ni(L)(siS3)]
complexes, caused by the electron-withdrawing effect of the
SiMe3 groups.
The NH shifts of the HNPR3 and HNSPh2 complexes
allowed us to determine whether the NϪP and NϪS bonds
in HNPR3 and HNSPh2 exhibit single- or double-bond
character. Protons at sp2-hybridized N atoms in HNϭX
compounds (X ϭ NH, NO, CH2, CR2) such as diazene,
nitroxyl, methyleneimines, or ketimines usually exhibit
strong low-field shifts (δ ϭ 10Ϫ20 ppm), both in the free
and coordinated state.[12] The high-field NH shifts of the
HNPR3 and HNSPh2 complexes 2Ϫ4 (δ ϭ 0.9 to
Ϫ1.9 ppm) thus rather resemble the NH shifts in hydrazine
and ammonia complexes and indicate NϪP and NϪS sin-
gle bonds with sp3-hybridized N atoms. These consider-
ations suggest the ylidic structures I and II for the HNPR3
and HNSPh2 ligands.
Figure 2. Thermal ellipsoid plots of [Ni(NHPnPr3)(siS3)] (2b),
[Ni(NHPCy3)(HS3)]
(3a),
[Ni(NHPCy3)(siS3)]
(3b),
[Ni(NHSPh2)(HS3)] (4a), [Ni(PnPr3)(HS3)] (5a) (50% probability el-
lipsoids; H atoms, except for N-bound ones, omitted)
The unit cells of all complexes contain discrete molecules
whose four-coordinate nickel atoms exhibit a tetrahedrally
distorted planar coordination, as evidenced by the non-lin-
ear S1ϪNi1ϪS3 and S2ϪNi1ϪL angles. This tetrahedral
distortion can be traced back to the sp3 hybridization of
the central thioether sulfur atom in the RS3 ligands. It leads
to a butterfly shape of the nickelϪsulfur fragments, the
characteristic topology of which also causes a very short
NiϪS(thioether) distance of 208Ϫ213 pm, which is dis-
tinctly shorter than the NiϪS(thiolate) distances (216Ϫ220
pm).[7Ϫ9]
The NiϪN distances of 2b [190.6(7) pm], 3a [193.1(3)
pm)], 3b [192.3(4) pm], and 4a [189.5(2) pm] are similar to
In agreement with these structures, the 1H and 13C NMR that of [Ni(NHPnPr3)(HS3)] (2a) reported previously,[8c] and
spectra of the HNPR3 and HNSPh2 complexes 2Ϫ4 do not indicate the presence of NiϪN single bonds. They are all
show any splitting of the signals when the temperature was considerably shorter than the NiϪN distances observed in
Eur. J. Inorg. Chem. 2004, 1847Ϫ1858
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1849

D. Sellmann, R. Prakash, F. W. Heinemann
FULL PAPER
Intramolecular NϪH···S(thiolate) bridges are found in
[Ni(NHPCy3)(HS3)] (3a) and [Ni(NHSPh2)(HS3)] (4a). This
can be deduced from the distances H1···S3 in 3a [269(5)
pm] and H1···S1 in 4a [283(3) pm] as well as the distances
N1···S3 in 3a [289.1(3) pm] and N1···S1 in 4a [295.5(2) pm],
which are shorter than the sum of van der Waals radii (N ϭ
155 pm; H ϭ 120 pm; S ϭ 180 pm).[14] No hydrogen bonds
are found in [Ni(NHPCy3)(siS3)] (3b).
Table 1. Selected bond lengths [pm] and angles [°] for
[Ni(NHPnPr3)(siS3)]
[Ni(NHPCy3)(siS3)]
[Ni(PnPr3)(HS3)] (5a)
(2b),
(3b),
[Ni(NHPCy3)(HS3)]
[Ni(NHSPh2)(HS3)]
(3a),
(4a),
Compound
2b
3a
3b
4a
5a
Ni1ϪS1
Ni1ϪS2
Ni1ϪS3
Ni1ϪN1
N1ϪP1
N1ϪH1
216.8(3) 218.7(1) 217.0(2) 221.6(1) 216.3(1)
208.9(3) 210.7(1) 211.0(2) 211.7(1) 214.1(1)
219.9(3) 217.8(1) 217.0(2) 217.7(1) 217.4(1)
190.6(7) 193.1(3) 192.3(4) 189.5(2) 219.0(2)[a]
160.5(7) 160.9(3) 159.8(5) 159.5(2)[b]
Reactions with Molecular Hydrogen
86
73(4)
86
80(3)
The heterolytic cleavage of H2 into Hϩ and HϪ according
to Equation (1b) and formation of HD from H2 and D2O,
respectively, is one of the key reactions catalyzed by hydro-
genases. Such a heterolytic H2 cleavage and H2/Dϩ or D2/
Hϩ exchange reaction could be proved to be catalyzed by
the phosphorane imine and sulfimine complexes. The
NHϪRЈ ligands (RЈ ϭ PnPr3, PCy3, SPh2) in these com-
plexes are excellent probes for unambiguously establishing
the H2 or D2 heterolysis because they have weakly acidic
NH protons that exchange for Dϩ. Such an NH/Dϩ ex-
change was similarly observed for the complexes 2a/b, 3a/b,
and 4a/b according to Equation (3).
S1ϪNi1ϪS2 89.3(1) 89.41(3) 89.97(7) 87.46(3) 90.25(5)
S1ϪNi1ϪS3 166.4(2) 162.02(4) 159.50(8) 160.27(3) 164.10(5)
S1ϪNi1ϪN1 91.1(2) 96.60(9) 91.2(2) 91.55(8) 93.05(5)[a]
S2ϪNi1ϪS3 87.2(1) 88.90(4) 89.83(7) 90.71(3) 88.74(4)
S2ϪNi1ϪN1 172.1(2) 165.83(9) 168.5(2) 165.62(8) 170.77(4)[a]
S3ϪNi1ϪN1 94.2(2) 89.23(8) 93.1(2) 94.95(8) 90.42(5)[a]
Ni1ϪN1ϪP1 128.3(4) 128.4(2) 127.3(3) 125.4(2)[b]
Ni1ϪN1ϪH1 116
114(4)
116
122(2)
[a]
[b]
N1ϭP1. P1ϭS4.
other diamagnetic four-coordinate NiII complexes
(201Ϫ203 The NiϪP distances of
pm).[10a,13]
[Ni(PnPr3)(HS3)] (5a) [219.0(2) pm] and previously reported
[Ni(PR3)(RS3)] complexes (R ϭ Me, Ph or Cy) lie in the
same range of 219Ϫ221 pm.[8,9] The NϪP distances (160
pm) of 2b, 3a, and 3b are identical within the limit of the
3σ criterion. Hydrogen bonds are observed for 2b, 3a, and
4a. Figure 3 illustrates that NϪH···N bridges lead to the
formation of dimers of [Ni(NHPnPr3)(siS3)] (2b) which pos-
sesses crystallographically imposed inversion symmetry.
The hydrogen bonds are concluded from the distances
H1···N1a (246 pm) and N1···N1a [322(2) pm], which are
shorter than the sum of the corresponding van der Waals
radii (N ϭ 155 pm; H ϭ 120 pm).[14] With respect to the
hydrogen bonds, complex 2b contrasts with the analogous
complex [Ni(NHPnPr3)(HS3)] (2a) which contains the par-
ent ligand HS32Ϫ. Complex 2a also dimerizes in the solid
state, however through NϪH···S(thiolate) bridges rather
than NϪH···N bridges.[8c]
(3)
A concentrated CD2Cl2/CH2Cl2 solution of the respect-
ive complex was treated with D2O or CD3OD, and the NH/
1
Dϩ exchange was monitored by H/2D NMR spectroscopy.
In the course of 5Ϫ20 min, the NH signals of the starting
complexes (between δ ϭ 0.80 and Ϫ1.96 ppm) disappeared,
while the ND signals of the resulting deuterated product
2
complexes could be observed at the same region in the D
NMR spectrum. After completion of the reactions, the sol-
vents were removed in vacuo; ν(ND) bands in the region of
2480Ϫ2420 cmϪ1 of the IR (KBr) spectra of the residues
further corroborated the formation of the deuterated com-
plexes.
The D2/NH exchange was probed with complexes 2b, 3a/
3b, and 4a/4b and the formation of HD was monitored by
1H NMR spectroscopy. In high-pressure NMR tubes, con-
centrated CD2Cl2 or [D8]THF solutions of 2b, 3a/3b, and
1
4a/4b were pressurized with D2 (18 bar). H NMR spectra
recorded at regular time intervals showed the appearance
of the 1:1:1 triplets of HD (JH,D ϭ 42.5 Hz) formed accord-
ing to Equation (4). The HD triplets in the region of δ ϭ
4.2Ϫ4.8 ppm reached maximum intensity after 80 h in the
case of 2b and 120 h in the case of 4a.
(4)
The reactions in Equations (3) and (4) thus prove that the
[Ni(NHRЈ)(RS3)]complexes 2b, 3a, 3b, 4a, and 4b catalyze
the heterolytic cleavage of D2 and the exchange of molecu-
lar hydrogen with protons that ultimately result from protic
solvents such as H2O or CH3OH. In a further experiment
Figure 3. View of the NϪH···N hydrogen bond dimers of
[Ni(NHPnPr3)(siS3)] (2b) (H atoms, except for N-bound ones, omit-
ted)
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Activation of H2 and CO by Sulfur-Rich Nickel Model Complexes
FULL PAPER
we therefore tried to combine these reactions. Initially, we
chose the complex 3b because it proved to have the highest
stability towards methanolysis leading to [Ni(siS3)]3 and free
NHPCy3. In a high-pressure NMR tube, a concentrated
CD2Cl2 solution of 3b and MeOH (50 µL) was pressurized
1
with D2 (18 bar) and the reaction was monitored by H
NMR spectroscopy. Unfortunately, due to the large signals
of the MeOH protons the HD signal could not be ident-
ified. However, repeating this experiment by changing the
solvent to [D8]THF and the proton source to H2O yielded
a favorable result. A 1H NMR spectrum of 3b recorded
after 4 d showed the appearance of the 1:1:1 triplets
(JH,D ϭ 42.5 Hz) of HD in the region of δ ϭ 4.2Ϫ4.8 ppm.
Interestingly, the intensity of the triplet increases with an
increase in reaction time and nearly triples in size after 15
d. The complexes 2a, 2b, 3a, 4a, and 4b also exhibit the
same behavior.
These positive results prompted us to extend our investi-
gations to complexes Bu4N[9a] and Bu4N[9b] as, like in the
active sites of [NiFe] hydrogenases, they exhibit all-sulfur
nickel coordination. These complexes were investigated first
in the form of their sodium salts Na[9a] and Na[9b]. In a
high-pressure NMR tube, a concentrated solution of Na[9a]
or Na[9b] in a [D8]THF/H2O (50 µL) mixture was pressur-
ized with D2 (18 bar) and the reaction was monitored by
1H NMR spectroscopy at various time intervals. Figure 4
Figure 4. 1H NMR spectra of the HD region of Na[Ni(StBu)(HS3)]
Na[9a] in [D8]THF/H2O under D2 (18 bar), recorded after: (a) 1,
(b) 5, (c) 10, and (d) 15 d
complexes that model the [NiFe] hydrogenase catalyzed D2/
Hϩ exchange reaction.
1
depicts the H NMR spectra of the HD region of Na[9a]
in [D8]THF/H2O with D2 pressure at various time intervals.
1
The H NMR spectrum of Na[9a] recorded after 1 d does
not show any new peaks (Figure 4a), while after 5 d it
shows a small 1:1:1 triplet of HD (JH,D ϭ 42.5 Hz) in the
region between δ ϭ 4.8 and 4.2 ppm (Figure 4b). The con-
comitant formation of HDO could not be identified due to
the large H2O signal. However, the intensity of the HD trip-
let increases with increasing reaction time (Figure 4bϪd).
The reaction was prolonged for 15 d and the intensity of
the HD triplet was enhanced to three times that of the in-
itial one, suggesting that the reaction is catalytic. Com-
pound Na[9b] undergoes an identical reaction but is more
active, giving rise to HD formation in a shorter reaction
time (initial HD triplet showed up after 4 d). It is worth
mentioning that the complexes remain intact even after 15
d of reaction time. Identical experiments performed without
either the complexes Na[9b] and Na[9b] or H2O did not
show any HD signals. These results unambiguously prove
that the reaction is catalytic and the heterolytic cleavage of
D2 must take place at the nickel center via a five-coordi-
nated D2 intermediate species.
Scheme 2. Mechanism of [Ni(L)(RS3)]-catalyzed D2/H2O ex-
change reaction
Reactions with CO
These results suggest that the D2 heterolysis is achieved
Coordination of CO to tetrahedrally distorted planar
through the concerted action of the Lewis-acidic nickel [NiS4] sites is postulated as the primary key step in CO
center and the Brönsted-basic thiol atoms upon η2-D2 li- dehydrogenase reactions[15] and is possibly responsible for
gands. The resulting acidic thiol deuteron exchanges with the inhibition of [NiFe] hydrogenases by CO.[16] Complexes
the H2O proton to give HDO. The thiol proton and nickel exhibiting [Ni(CO)(S4)] cores, however, have never been
deuteride ion combine to give HD. Release of HD in the identified or isolated. Recently, the five-coordinate
consecutive step leaves [Ni(L)(RS3)] intact, which can then carbonylϪNiIϪchalcogenate complexes [Ni(DAPA)(EPh)2-
add another molecule of D2 to complete the reaction cycle (CO)]Ϫ {DAPA ϭ 2,6-bis[1-(phenylimino)ethyl]pyridine;
(Scheme 2). It is worthwhile to note that Na[9a] and Na[9b]
E
ϭ
S
or Se} and the first five-coordinate
are the first completely characterized sulfur-only nickel carbonylϪNiIIϪthiolate complex [Ni(PS3*)(CO)]Ϫ [PS3* ϭ
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D. Sellmann, R. Prakash, F. W. Heinemann
FULL PAPER
tris(3-phenyl-2-thiophenyl)phosphane] were reported.[17]
In the next step, the influence of the phosphane coligands
For this reason, the reaction of the nickel complexes upon CO coordination was probed with [Ni(PCy3)-
[Ni(L)(RS3)] (2Ϫ9) with CO was investigated. They all pos- (siS3)](6b). When CO was bubbled through a THF solution
sess at least [NiS3] cores, and it has been pointed out pre- of 6b according to Equation (6), a ν(CO) band appeared at
viously[8,9] that the characteristic tetrahedral distortion of 2135 cmϪ1 in the IR spectrum. Purging the solution with a
[Ni(L)(RS3)] complexes could be crucial for their capability stream of N2 led to disappearance of the ν(CO) band and
to add a fifth ligand.
6b was regained. This result suggests that [Ni(PR3)(RS3)]
The distances and angles in the [Ni(RS3)] cores of all the complexes can also reversibly add CO. In addition, the
complexes investigated are almost identical, although the ν(CO) frequency of [Ni(CO)(PCy3)(siS3)] at 2135 cmϪ1 is
reactivity of the individual [Ni(L)(RS3)] complexes towards similar to that of [Ni(CO)(StBu)(HS3)]Ϫ (2131 cmϪ1), indi-
CO proved to be extremely different, clearly showing the cating that the electron density at the nickel atom is a little
decisive influence of the coligands L. The influence of the lower in the neutral phosphane than in the anionic StBuϪ
R substituents of the RS3 ligands is evidenced by the fact complex. However, the relatively high wavenumbers indicate
that the [Ni(L)(siS3)] complexes always reacted faster than a weak binding of the CO ligands, rationalizing their revers-
their [Ni(L)(HS3)] counterparts.
ible coordination.
Because the StBuϪ complex [Ni(StBu)(HS3)]Ϫ (9a) has an
all-sulfur coordination sphere, it was investigated first in
form of its sodium salt Na[9a]. Bubbling CO gas through a
THF solution of Na[9a] for 3Ϫ5 min gave rise to a ν(CO)
band in the IR spectrum at 2131 cmϪ1. When this solution
was stored under CO for 24 h, a second ν(CO) band ap-
peared at 2040 cmϪ1. These bands were assigned to
[Ni(CO)(StBu)(HS3)]Ϫ (2131 cmϪ1) and [Ni(CO)4] (2040
cmϪ1) which form according to Equation (5).
(6)
The coligands StBuϪ or PCy3 in the [Ni(L)(RS3)] com-
plexes [Ni(StBu)(HS3)]Ϫ (9a) and [Ni(PCy3)(SiS3)] (6b) do
not react with CO, either in the free or complexed state,
whereas the nitrogen-containing ligands NHPR3, NHSPh2,
and N3Ϫ show a distinctly different behavior. In the free state
they, too, do not react with CO, however, when functioning
as ligands in the [Ni(L)(RS3)] complexes 2Ϫ4 and 8b, they
undergo rapid reactions with equimolar amounts of CO.
This demonstrates that the reactions are mediated by the
[Ni(RS3)] fragments, and indicates that both CO and nitro-
genous ligands can be activated.
From the mechanistic point of view, the reaction between
Et4N[Ni(N3)(siS3)] (8b) and CO can be rationalized best. In
THF solution, complex 8b is thermally stable and resistant
to UV photolysis (150 W Hg lamp) over extended periods
of time (3 d). When treated with equimolar amounts of CO
gas in the dark, however, it rapidly transforms into the
NCO complex Et4N[Ni(NCO)(siS3)] (10b) and N2, and
complex 10b could be isolated in nearly quantitative yield
(92%). Monitoring the reaction by IR spectroscopy demon-
strated that the ν(N3) band of 8b at 2037 cmϪ1 continuously
decreases in intensity while the ν(NCO) band of 10b at
2227 cmϪ1 increases.
(5)
The reduction of NiII to Ni0 is possibly initiated by the
reductive elimination of the (labile) StBuϪ ligand. This is
suggested by the observation that the substitutionally inert
phosphane complex [Ni(PCy3)(siS3)] does not yield
[Ni(CO)4] when treated with CO (vide infra).
The ν(CO) assignment was corroborated by the following
experiments. Purging the solutions with N2 for 10 min led
to complete disappearance of the ν(CO) bands. This indi-
cated that the first step yielding [Ni(CO)(StBu)(HS3)]Ϫ is
reversible. Carrying out the experiment [according to Equa-
tion (5)] with 13CO gave rise to ν(CO) bands at 2085 cmϪ1
([Ni(13CO)(StBu)(HS3)]Ϫ) and 1995 cmϪ1 ([Ni(13CO)4]).
The isotopic shifts of 45 cmϪ1 agree with theoretical expec-
tations. Formation of the five-coordinate intermediate
[Ni(CO)(StBu)(HS3)]Ϫ was further corroborated by moni-
toring the reaction by 13C NMR spectroscopy. The 13C
NMR spectrum shows that treatment of a [D8]THF solu-
tion of Na[9a] with 13CO (5 bar) in a medium-pressure
NMR tube gave rise to 13C NMR signals at δ ϭ 198.5,
192.1, and 184.7 ppm, which could be assigned to
[Ni(13CO)(StBu)(HS3)]Ϫ, [Ni(13CO)4], and free 13CO,
respectively. This assignment was checked by recording the
13C NMR spectra of 13CO and [Ni(CO)4] in [D8]THF. In
summary, these results suggest that nickel thiolate com-
plexes with a tetrahedrally distorted planar [NiS4] core can
The analogous reaction of the HS3 complex Bu4N-
[Ni(N3)(HS3)] (Bu4N[8a]) with CO afforded Bu4N-
[Ni(NCO)(HS3)][7] and enabled us to detect a short-lived
[Ni(CO)(N3)(HS3)]Ϫ intermediate, with a ν(CO) band at
2129 cmϪ1 by IR spectroscopy. Such an intermediate could
not be found in the reaction between Et4N[8b] and CO,
probably owing to the greater reactivity of 8b and its inter-
mediates. However, the close analogy between Bu4N[8a]
and Et4N[8b] suggests identical mechanisms for their reac-
tion with CO [Equation (7)].
Coordination of CO to the [Ni(N3)(RS3)]Ϫ anion leads to
reversibly coordinate CO, but afford [Ni(CO)4] when activation of CO and N3Ϫ, release of N2 and formation of
treated with an excess of CO for longer periods of time.
the NCO complex. Related mechanisms have previously
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Activation of H2 and CO by Sulfur-Rich Nickel Model Complexes
FULL PAPER
1
The H NMR spectrum of 2a in CD2Cl2 shows the NH
signal at δ ϭ Ϫ1.82 ppm. After injecting an equimolar
amount of CO, this NH signal gradually broadens and dis-
appears and a new doublet appears at δ ϭ 4.85 ppm (JP,H ϭ
550 Hz). Similarly, in the 31P NMR spectrum of 2a, the
signal at δ ϭ 50.8 ppm disappears gradually in the presence
of CO and a new peak appears at δ ϭ 55.1 ppm. This new
peak, in turn, vanishes over the course of 30 h to give a new
low-intensity doublet at δ ϭ 34.2 ppm (JP,H ϭ 527 Hz). All
1H and 31P NMR signals disappear when [Ni(HS3)]3 (1a)
precipitates from the solution. These findings can be inter-
preted as follows: the initial step is the coordination of CO
to give a five-coordinate [Ni(CO)(NHPnPr3)(HS3)] inter-
mediate showing a ν(CO) band at 2146 cmϪ1 (31P NMR:
δ ϭ 55.1 ppm). As above, the high frequency of this band
indicates that the CO is only weakly bound. Subsequently,
the intramolecular nucleophilic addition of the N atom of
NHPnPr3 to CO is followed by the removal of PnPr3 to give
an unstable acylimide species. Then, the deprotonation of
the NϪH bond by the free PnPr3 gives [HPnPr3]ϩ (doublet
been suggested for four-coordinate azido(phosphane) com-
plexes of PdII, PtII, RhI and IrI.[18] The phosphorane im-
ine complexes 2a/2b, 3a/3b, and the sulfimine complexes 4a/
4b also react quickly with CO under standard conditions (1
bar, 20 °C). However, the mechanisms of the reactions are
less obvious. When a stream of CO was bubbled through
CH2Cl2 solutions of 2a/2b, 3a/3b, or 4a/4b, the parent com-
plexes [Ni(RS3)]3 (1a or 1b) formed and could be isolated in
high yields. When the CH2Cl2 solutions were each treated
with 1 equiv. of CO gas, the reactions proceeded more
slowly, and monitoring of the reactions by IR and NMR
spectroscopy, and mass spectrometry, yielded hints as to the
nature of the intermediates. Experiments with the respective
[Ni(L)(HS3)] and [Ni(L)(siS3)] complexes complemented
each other. For example, after addition of 1 equiv. of CO,
the IR spectrum of the CH2Cl2 solution of the phosphorane
imine complex [Ni(NHPnPr3)(HS3)] (2a) shows a weak band
at 2146 cmϪ1. This band disappeared in the course of 25 h,
and a new band at 2227 cmϪ1 developed simultaneously; its
intensity increased over 45 h and then decreased again,
while [Ni(HS3)]3 (1a) started precipitating from the solution
(Figure 5). The weak band at 2040 cmϪ1 corresponds to the
side product [Ni(CO)4] that forms and disappears during
the reaction. The same IR spectroscopic behavior was
found for CH2Cl2 solutions of [Ni(NHPnPr3)(siS3)] (2b).
1
in the H and 31P NMR spectra) and the acyl azide com-
plexes. A similar reactivity has already been reported in
coordinated phosphanylamine complexes of NiII and free
PMe3 to give [HPMe3]ϩ.[10a] These acyl azides can
rearrange to give [HPnPr3][Ni(NCO)(HS3)] [ν(NCO) ϭ
2227 cmϪ1
]
according
to
Equation (8).
Unlike
Et4N[Ni(NCO)(siS3)] (10b), [HPnPr3][Ni(NCO)(HS3)] is un-
stable and undergoes further reactions to give 1a as the final
product. Monitoring the reactions of the siS3 complex 2b
by 1H and 31P NMR spectroscopy only showed the replace-
ment of the signals of 2b by those of 1b, but did not allow
us to draw further conclusions. All attempts to isolate the
intermediate species were unsuccessful, even at Ϫ78 °C.
After addition of 1 equiv. of CO, the IR spectrum
of the CH2Cl2 solution of the sulfimine complex
[Ni(NHSPh2)(HS3)] (4a) shows a weak band at 2148 cmϪ1
.
This band disappeared over the course of 1 h, and simul-
taneously a new band appeared at 2185 cmϪ1, whose inten-
sity increased over 5 h and then decreased again, while
[Ni(HS3)]3 (1a) started precipitating from the solution. The
same IR spectroscopic behavior was found for CH2Cl2 solu-
tions of [Ni(NHSPh2)(siS3)] (4b). The SiMe3 substituents of
1
4b were also used as a spectroscopic probe. The H NMR
spectra of the reactions in CD2Cl2 show that the SiMe3 sin-
glet of 4b at δ ϭ 0.36 ppm broadens slightly and is replaced
by the two singlets of [Ni(siS3)]3 (1b) at δ ϭ 0.55 and
0.08 ppm.
These findings are interpreted in the following way. The
primary step is again the coordination of CO to give a five-
coordinate [Ni(CO)(NHSPh2)(RS3)] intermediate showing a
ν(CO) band at 2148 cmϪ1. Subsequent reaction between
CO and the HNSPh2 ligands leads to deoxygenation of CO
resulting in OSPh2 and coordinated HCϭN or HNϭC li-
gands, which give rise to the band at 2185 cmϪ1. Transition
metal complexes with HCN or HNC ligands show ν(CN)
bands in the region of 2200Ϫ2100 cm
coordination of the HCN ligands results in the formation
.
Ϫ1 [19] Subsequent de-
Figure 5. IR spectroscopic monitoring of the reaction between
equimolar amounts of [Ni(NHPnPr3)(HS3)] (2a) and CO in CH2Cl2
solution; the spectra were recorded after (a) 3, (b) 20, and (c) 48 h of [Ni(RS3)]3 [Equation (9)].
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D. Sellmann, R. Prakash, F. W. Heinemann
FULL PAPER
Table 2. ν(CO) frequencies of the primary five-coordinate species
[Ni(CO)(L)(RS3)] resulting from [Ni(L)(RS3)] and CO (1 bar) at
20 °C
The mass spectra of the reaction solutions recorded when
the band at 2185 cmϪ1 had attained maximum intensity
support this interpretation. These spectra exhibit peaks at
m/z ϭ 202 assignable to OSPh2 and at 335 (4a) or 479 (4b),
which are compatible with the formation of
[Ni(HCN)(RS3)] complexes.
Complex
ν(CO) [cmϪ1
]
Reaction type
Bu4N[Ni(N3)(HS3)] (Bu4N[8a])[a] 2129[b]
irr.
Ϫ
Et4N[Ni(N3)(siS3)] (Et4N[8b])
Na[Ni(StBu)(HS3) (Na[9a])
Ni(PCy3)(siS3)] (6b)
Ϫ
Table 2 summarizes the ν(CO) frequencies of the CO ad-
ducts initially formed and demonstrates that complexes
with HS3 and SiS3 ligands show identical ν(CO) frequencies.
Therefore, the sometimes remarkably different reaction
rates of HS3 and siS3 complexes might be caused by differ-
ences in solubility rather than by changes in the electronic
properties. Anionic complexes give rise to lower ν(CO) fre-
quencies than neutral complexes. This trend of ν(CO) fre-
quencies is well known from classical carbonylmetal com-
plexes, and it strongly suggests that structurally similar five-
coordinate [Ni(CO)(L)(RS3)] species form in all cases. These
five-coordinate species can reversibly dissociate CO or un-
dergo rapid consecutive reactions if L is a nitrogenous spec-
ies having lone-pairs at the N donor such as azide or the
ylidic HNPR3 and HNSPh2 ligands. The subsequent reac-
tions lead to conversion of CO and the nitrogenous ligand.
The final products, which could be isolated, depend on the
nitrogenous ligands. If they release inert species such as N2
in the case of azide, the resulting NCOϪ complexes
[Ni(NCO)(RS3)]Ϫ can be isolated in good yields. In the case
of the phosphorane imine or sulfimine complexes, an anal-
ogous cleavage of NϪP or NϪS bonds yields species that
are still highly reactive and go on reacting until the stable
trinuclear [Ni(RS3)]3 complexes form.
2131[b]
2135[b]
2146[c]
2146[c]
2146[c]
2146[c]
2148[c]
2148[c]
rev.
rev.
irr.
irr.
irr.
irr.
irr.
irr.
Ni(NHPnPr3)(HS3)] (2a)
Ni(NHPnPr3)(siS3)] (2b)
Ni(NHPCy3)(HS3)] (3a)
Ni(NHPCy3)(siS3)] (3b)
Ni(NHSPh2)(HS3)] (4a)
Ni(NHSPh2)(siS3)] (4b)
[a]
[c]
Ref.[7] [b] In THF. In CH2Cl2.
of up to 2280 cm .
Ϫ1 [20] The high ν(CO) frequencies of these
complexes are rationalized by a subtle interplay of σ-donor,
π-acceptor and semipolar contributions in the MϪCO
bonds.[21] In accordance with this rationalization, the results
obtained here show that binding CO to [Ni(L)(RS3)] com-
plexes not only enhances the polarity of the CO bond but
also increases the susceptibility of CO towards attack by
nucleophiles. This may be a reason why coordination of CO
to the [NiS4] core of CO dehydrogenase centers can enable
the CO/CO2 conversion according to Equation (2) (vide in-
fra).
Conclusion
It should be noted that the ν(CO) frequencies of all five-
coordinate intermediates (Table 2) are relatively high and,
in some cases, even slightly higher than that of free CO in
the gas phase (2143 cmϪ1). Additional measurements cor-
roborated that these bands do not result from dissolved CO.
In the quest for sulfurϪnickel complexes that enable us
to model the reactivity features and key intermediates of
[NiFe] hydrogenases and CO dehydrogenases, [Ni(L)(RS3)]
complexes were synthesized, completely characterized, and
The CO adducts of the phosphorane imine and sulfimine investigated with regard to their reactivity towards H2 and
complexes thus belong to the class of ‘‘non-classical’’ car- CO. All [Ni(L)(RS3)] complexes exhibit sulfur-dominated
bonylmetal complexes which can exhibit ν(CO) frequencies and tetrahedrally distorted square-planar coordination
1854
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Activation of H2 and CO by Sulfur-Rich Nickel Model Complexes
FULL PAPER
(10 mL), and the color changed from black-brown to purple-red in
the course of about 6 h. The solution was filtered after 15 h, the
purple-red filtrate was reduced in volume to 3 mL and layered with
CH3CN (20 mL). Pink crystals precipitated at Ϫ25 °C which were
separated after 10 d, washed with cold CH3CN and dried in vacuo.
Yield: 765 mg (69%). C27H46NNiPS3Si2 (626.71): calcd. C 51.75, H
7.40, N 2.23, S 15.35; found C 51.88, H 7.53, N 2.10, S 15.21. IR
(KBr): ν˜ ϭ 3298 [ν(NH)], 995 [ν(NP)] cmϪ1. 1H NMR (269.7 MHz,
[D8]THF): δ ϭ 7.57 (d, JH,H ϭ 7.9 Hz, 2 H, C6H3), 7.19 (d, JH,H ϭ
6.8 Hz, 2 H, C6H3), 6.84 (t, JH,H ϭ 7.6 Hz, 2 H, C6H3), 2.04 (m, 6
spheres. Complexes 4a and 4b are rare examples of sulfim-
ine complexes and are the first sulfimine complexes with
only sulfur as ancillary coligands. Introduction of the siS3
ligand enabled us to overcome the solubility problems fre-
quently encountered with nickel complexes of the HS3 par-
ent ligand.
It has been demonstrated that the phosphorane imine
and sulfimine complexes 2Ϫ4 possess weakly acidic NH
protons and catalyze D2/NH exchange reactions through
heterolysis of D2. The D2/Hϩ exchange reaction between H, PCH2), 1.73 (m, 6 H, PCH2CH2), 1.08 (t, JH,H ϭ 6.9 Hz, 9 H,
PCH2CH2CH3), 0.38 (s, 18 H, SiMe3), Ϫ1.06 (s, 1 H, NH) ppm.
D2 and protons from H2O is also catalyzed by complexes
2Ϫ4 and 9. These reactions unambiguously prove that the
D2/Hϩ exchange is catalytic in nature. The D2 heterolysis
most likely proceeds through attack of the Lewis-acidic
nickel and Brönsted-basic sulfur atoms at η2-D2 ligands. It
is worthwhile to note that 9a and 9b are the first completely
characterized sulfur-only nickel complexes that enable us to
model the [NiFe] hydrogenase catalyzed D2 heterolysis and
D2/Hϩ exchange reactions.
Coordination of CO to four-coordinate nickel centers in
sulfur coordination spheres is assumed to be the decisive
step in the activation of CO catalyzed by CO dehydrogen-
ases. Evidence for labile five-coordinate [Ni(CO)(L)(RS3)]
has been found in the reactions of CO with [Ni(L)(RS3)]
complexes containing neutral and anionic ligands L. The
13C NMR (67.8 MHz, [D8]THF): δ ϭ 159.9, 139.6, 134.8, 134.3,
1
129.0, 121.3 (C6H3), 29.7 (d, JP,C ϭ 62.9 Hz), 15.7 (d, JP,C
ϭ
3.3 Hz), 15.5 (d, JP,C ϭ 16.1 Hz, PnPr3), Ϫ0.7 (SiMe3) ppm. 31P
NMR (161.8 MHz, [D8]THF): δ ϭ 50.3 (PnPr3) ppm. MS (FD,
THF): m/z ϭ 626 [Ni(NHPnPr3)(siS3)]ϩ.
[Ni(NHPCy3)(HS3)] (3a): A solution of Me3SiNPCy3 (825 mg,
2.24 mmol) in THF (5 mL) and MeOH (1 mL) was added to a
black-brown suspension of [Ni(HS3)]3 (1a; 525 mg, 0.57 mmol) in
THF (15 mL). A purple-red solution formed which was concen-
trated to dryness after 15 h. The purple-red residue was redissolved
in THF (10 mL), and traces of undissolved materials were removed
by filtration. The filtrate was reduced in volume to 3 mL, layered
with CH3CN (30 mL) and stored at Ϫ25 °C. Pink microcrystals
precipitated which were separated after 3 days, washed with cold
CH3CN and Et2O, and dried in vacuo. Yield: 815 mg (79%).
CO adducts of complexes with nitrogenous ligands L such C30H42NNiPS3 (602.54): calcd. C 59.80, H 7.03, N 2.32, S 15.96;
as N3Ϫ, NHPR3, or NHSPh2 showed rapid consecutive reac-
tions demonstrating the activation of CO and ligands L. In
found C 59.82, H 7.19, N 2.35, S 15.58. IR (KBr): ν˜ ϭ 3364
1
[ν(NH)], 978 [ν(NP)] cmϪ1. H NMR (269.7 MHz, [D8]THF): δ ϭ
7.58 (d, JH,H ϭ 7.6 Hz, 2 H, C6H4), 7.20 (d, JH,H ϭ 7.9 Hz, 2 H,
C6H4), 6.97 (t, JH,H ϭ 7.1 Hz, 2 H, C6H4), 6.83 (t, JH,H ϭ 7.1 Hz,
extrapolation of these findings it can be hypothesized that
simultaneous coordination of CO and H2O to [Ni(RS3)]
2 H, C6H4), 2.23Ϫ1.32 (m, 33 H, PCy3), Ϫ1.88 (s, 1 H, NH) ppm.
fragments possibly enables the biological CO dehydrogen-
ase reaction.
13C NMR (67.8 MHz, [D8]THF): δ ϭ 154.2, 134.2, 129.6, 128.5,
128.0, 121.9 (C6H4), 35.3 (d, 1JP,C ϭ 55.3 Hz), 27.8, 27.5 (d, 3JP,C ϭ
15 Hz), 26.9 (PCy3) ppm. 31P NMR (161.8 MHz, [D8]THF): δ ϭ
59.2 (PCy3) ppm. MS (FD, THF): m/z ϭ 602 [Ni(NHPCy3)(HS3)]ϩ.
Experimental Section
[Ni(NHPCy3)(siS3)] (3b): A solution of Me3SiNPCy3 (272 mg,
0.74 mmol) in THF (5 mL) and MeOH (1 mL) was added to a
solution of [Ni(siS3)]3 (1b; 300 mg, 0.22 mmol) in THF (15 mL),
and the color changed from black-brown to purple-red in the co-
urse of about 3 h. After 15 h, the solution was concentrated to dry-
ness to give a purple-red residue, which was redissolved in THF
(10 mL). Undissolved material was removed by filtration. The fil-
trate was reduced in volume to 3 mL, layered with CH3CN (30 mL)
and stored at Ϫ25 °C. Pink microcrystals precipitated which were
separated after 4 d, washed with cold CH3CN and Et2O, and dried
in vacuo. Yield: 412 mg (83%). C36H58NNiPS3Si2 (746.90): calcd.
C 57.89, H 7.83, N 1.87, S 12.88; found C 57.47, H 7.44, N 1.80,
S 12.63. IR (KBr): ν˜ ϭ 3364 [ν(NH)], 985 [ν(NP)] cmϪ1. 1H NMR
(269.7 MHz, [D8]THF): δ ϭ 7.56 (d, JH,H ϭ 7.9 Hz, 2 H, C6H3),
7.18 (d, JH,H ϭ 7.1 Hz, 2 H, C6H3), 6.82 (t, JH,H ϭ 7.5 Hz, 2 H,
C6H3), 2.35Ϫ1.30 (m, 33 H, PCy3), 0.38 (s, 18 H, SiMe3), Ϫ1.62
(s, 1 H, NH) ppm. 13C NMR (67.8 MHz, CDCl3): δ ϭ 158.0, 139.5,
General Methods: Unless noted otherwise, all reactions and ma-
nipulations were carried out under nitrogen at room temperature
using standard Schlenk techniques. Reaction solutions were stirred
continuously. Solvents were freshly dried and distilled before use.
As far as possible, reactions were monitored by IR or NMR spec-
troscopy. Physical measurements were carried out with the follow-
ing instruments: IR (KBr discs or CaF2 cuvettes, solvent bands
were compensated for): PerkinϪElmer 983, 1620 FT-IR and 16PC
FT-IR. NMR: Jeol JMM-GX 270, Jeol JMM-EX 270, and
Lambda LA 400 with the residual protio-solvent signal used as an
internal reference. Chemical shifts are quoted in the δ scale (down-
field shifts are positive) relative to tetramethylsilane (1H, 13C{1H}
NMR) or 85% H3PO4 (31P{1H} NMR). MS: Jeol MSTATION 700
spectrometer. Elemental analysis: Carlo Erba EA 1106 or 1108 ana-
lyzer. Me3SiCl, HNSPh2·H2O, Et4NCl, and Bu4NCl were pur-
chased from either Aldrich or Fluka. HNPnPr3, Me3SiNPCy3,[22]
[Ni(HS3)]3 (1a), [Ni(NHPnPr3)(HS3)] (2a), [Ni(PCy3)(HS3)] (6a),
Bu4N[Ni(Cl)(HS3)] (Bu4N[7a]), and Bu4N[Ni(N3)(HS3)] (Bu4N[8b])
were prepared as described in the literature.[8] The syntheses of
[Ni(siS3)]3 (1b), Et4N[Ni(N3)(siS3)] (Et4N[8b]), [Ni(PnPr3)(siS3)] (5b),
[Ni(PCy3)(siS3)] (6b), and Bu4N[Ni(Cl)(siS3)] (Bu4N[7b]) were de-
scribed in our previous paper.[9]
1
134.2, 133.2, 127.9, 126.8 (C6H3), 34.3 (d, JP,C ϭ 49.5 Hz), 27.0
2
3
(d, JP,C ϭ 6.8 Hz), 26.7 (d, JP,C ϭ 2.7 Hz), 25.9 (PCy3), Ϫ0.5
(SiMe3) ppm. 31P NMR (161.8 MHz, [D8]THF): δ ϭ 54.5 (PCy3)
ppm. MS (FD, THF): m/z ϭ 746 [Ni(NHPCy3)(siS3)]ϩ.
[Ni(NHSPh2)(HS3)] (4a): HNSPh2·H2O (425 mg, 1.93 mmol) was
added to a black-brown suspension of 1a (500 mg, 0.54 mmol) in
THF (10 mL). The resulting suspension was stirred for 12 h, in the
course of which it became red-brown. The solution was filtered,
[Ni(NHPnPr3)(siS3)] (2b): HNPnPr3 (0.52 mL, 2.35 mmol) was ad-
ded to a solution of [Ni(siS3)]3 (1b; 800 mg, 0.59 mmol) in THF
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1855

D. Sellmann, R. Prakash, F. W. Heinemann
the filtrate reduced in volume to about 3 mL and layered with Et2O D2/H2O Exchange Reaction of 2a/2b, 3a/3b, 4a/4b, and Na[9a]/
FULL PAPER
(20 mL). Dark red crystals precipitated at Ϫ25 °C, which were
separated after 7 d, washed with Et2O and dried in vacuo. Yield:
680 mg (82%). C24H19NNiS4 (508.38): calcd. C 56.70, H 3.77, N
2.75, S 25.23; found C 56.82, H 3.91, N 2.71, S 25.07. IR (KBr):
Na[9b]: In a high-pressure NMR tube, a concentrated solution of
the respective complex (ca. 50 mg) in [D8]THF, after addition of
H2O (50 µL), was pressurized with D2 (18 bar). The reactions were
1
monitored by recording H NMR spectra at regular time intervals
ν˜ ϭ 3202 [ν(NH)], 924 [ν(NS)] cmϪ1 1H NMR (269.7 MHz, for 15 d. The formation of HD gave rise to a 1:1:1 triplet (JH,D
. ϭ
[D8]THF): δ ϭ 7.75Ϫ7.40 (m, 12 H, C6H4, SPh2), 7.21 (d, JH,H
ϭ
42.5 Hz) in the region of δ ϭ 4Ϫ5 ppm.
7.5 Hz, 2 H, C6H4), 7.00 (t, JH,H ϭ 6.5 Hz, 2 H, C6H4), 6.85 (t,
JH,H ϭ 6.4 Hz, 2 H, C6H4), 0.89 (s, 1 H, NH) ppm. 13C NMR
(67.8 MHz, [D8]THF): δ ϭ 153.0, 134.6, 132.4, 131.8, 130.4, 130.0,
128.9, 128.4, 127.8, 122.4 (C6H4, SPh2) ppm. MS (FD, THF):
m/z ϭ 508 [Ni(NHSPh2)(HS3)]ϩ.
Et4N[Ni(NCO)(siS3)] (10b) from Et4N[Ni(N3)(siS3)] (8b) and CO:
CO gas (16.5 mL, 0.74 mmol) was injected into a Schlenk tube in
the dark containing a solution of 8b (450 mg, 0.72 mmol) in THF
(10 mL) and fitted with a septum. The color of the solution
changed from purple to dark-red in the course of ca 15 h. The
solution was filtered after 24 h, reduced in volume to ca. 2 mL and
layered with pentane (20 mL). Dark-red microcrystals precipitated
at Ϫ25 °C which were separated after 4 d, washed with pentane
and dried in vacuo. Yield: 412 mg (92%). C27H44N2NiOS3Si2
(623.73): calcd. C 51.99, H 7.11, N 4.49, S 15.42; found C 52.41,
[Ni(NHSPh2)(siS3)] (4b): A solution of HNSPh2·H2O (128 mg,
0.58 mmol) in THF (5 mL) was added to a solution of 1b (250 mg,
0.18 mmol) in THF (10 mL) and the color changed from black-
brown to brown-red in the course of about 6 h. The solution was
filtered after 12 h, reduced in volume to 3 mL and layered with
pentane (20 mL). Dark-red microcrystals precipitated at Ϫ25 °C
which were separated after 7 d, washed with pentane and dried in
vacuo. Yield: 282 mg (78%). C30H35NNiS4Si2 (652.75): calcd. C
55.20, H 5.40, N 2.15, S 19.65; found C 55.91, H 5.90, N 2.28, S
1
H 7.43, N 4.27, S 15.38. IR (KBr): ν˜ ϭ 2227 [ν(NCO)] cmϪ1. H
NMR (269.7 MHz, [D8]acetone): δ ϭ 7.63 (d, JH,H ϭ 7.9 Hz, 2 H,
C6H3), 7.20 (d, JH,H ϭ 7.1 Hz, 2 H, C6H3), 6.89 (t, JH,H ϭ 7.9 Hz,
2 H, C6H3), 3.42 (m, 8 H, NCH2), 1.29 (t, JH,H ϭ 7.3 Hz, 12 H,
NCH2CH3), 0.35 (s, 18 H, SiMe3) ppm. 13C NMR (67.8 MHz,
[D8]acetone): δ ϭ 160.4, 139.7, 135.0, 133.9 (C6H3), 132.0 (NCO),
129.1, 121.4 (C6H3), 53.1, 7.7 (Et4N), Ϫ0.5 (SiMe3) ppm.
19.02. IR (KBr): ν˜ ϭ 3210 [ν(NH)], 916 [ν(NS)] cmϪ1 1H NMR
.
(269.7 MHz, [D8]THF): δ ϭ 7.75Ϫ7.40 (m, 12 H, C6H3, SPh2),
7.19 (d, JH,H ϭ 6.1 Hz, 2 H, C6H3), 6.84 (t, JH,H ϭ 6.8 Hz, 2 H,
C6H3), 0.83 (s, 1 H, NH), 0.36 (s, 18 H, SiMe3) ppm. 13C NMR
(67.8 MHz, [D8]THF): δ ϭ 159.2, 139.8, 134.9, 134.8, 132.3, 131.8,
130.4, 129.3, 128.4, 121.6 (C6H3, SPh2), Ϫ0.4 (SiMe3) ppm.
MS(FD, THF): m/z ϭ 653 [Ni(NHSPh2)(siS3)]ϩ.
[Ni(HS3)]3 (1a) from [Ni(NHR)(HS3)] [R ؍ PnPr3 (2a), PCy3 (3a),
SPh2 (4a)] and CO. General Procedure: An equimolar amount of
CO was injected into a Schlenk tube containing a CH2Cl2 solution
(ca. 10 mL) of the respective complex and fitted with a septum. In
the course of several hours, depending on the complex, the color
of the CH2Cl2 solution changed from purple or yellow-red to dark-
red. Subsequently, dark-brown microcrystals of 1a precipitated,
which were separated, washed with MeOH and/or pentane and
dried in vacuo.
[Ni(PnPr3)(HS3)] (5a): PnPr3 (0.3 mL, 1.49 mmol) was added to a
black-brown suspension of 1a (445 mg, 0.48 mmol) in THF
(10 mL). In the course of about 10 min, a red-yellow solution
formed which was filtered after 1 h. The filtrate was reduced in
volume to 2 mL, layered with hexane (20 mL) and stored at Ϫ25
°C. Dark red crystals precipitated which were separated after 2 d,
washed with hexane and dried in vacuo. Yield: 645 mg (95%).
C21H29NiPS3 (467.33): calcd. C 53.97, H 6.26, S 20.58; found C
54.06, H 6.38, S 20.37. 1H NMR (269.7 MHz, CDCl3): δ ϭ 7.66
(dd, JH,H ϭ 1.2, 8.1 Hz, 2 H, C6H4), 7.39 (d, JH,H ϭ 1.3, 7.9 Hz,
2 H, C6H4), 7.09 (dt, JH,H ϭ 1.3, 7.9 Hz, 2 H, C6H4), 6.98 (dt,
JH,H ϭ 1.4, 7.3 Hz, 2 H, C6H4), 1.72 (m, 6 H, PCH2), 1.65 (m, 6
H, PCH2CH2), 1.04 (t, JH,H ϭ 6.6 Hz, 9 H, PCH2CH2CH3) ppm.
[Ni(HS3)]3 (1a) from 2a and CO: From 215 mg (0.445 mmol) of 2a
and 10.0 mL (0.446 mmol) of CO. The reaction was complete after
50 h. Yield: 93 mg (67%). C36H24Ni3S9 (921.25): calcd. C 46.94, H
2.63, S 31.33; found C 46.81, H 2.56, S 30.83. MS (FD, DMF):
m/z ϭ 921 [Ni(HS3)]3ϩ, 614 [Ni(HS3)]2ϩ.
[Ni(HS3)]3 (1a) from 3a and CO: From 210 mg (0.348 mmol) of 3a
and 7.85 mL (0.350 mmol) of CO gas. Reaction time 78 h. Yield:
79 mg (74%).
3
13C NMR (100.4 MHz, CDCl3): δ ϭ 152.1(d, JP,C ϭ 12.5 Hz),
1
132.4, 129.8, 128.5, 127.4, 122.5 (C6H4), 25.4 (d, JP,C ϭ 26.4 Hz),
[Ni(HS3)]3 (1a) from 4a and CO: From 200 mg (0.393 mmol) of 4a
and 8.9 mL (0.397 mmol) of CO gas. Reaction time 5 h. Yield:
94 mg (78%).
17.8 (d, JP,C ϭ 1.7 Hz), 16.0 (d, JP,C ϭ 14.0 Hz) (PnPr3) ppm. 31P
NMR (161.8 MHz, CDCl3): δ ϭ 13.5 (PnPr3) ppm. MS (FD,
THF): m/z ϭ 467 [Ni(PnPr3)(HS3)]ϩ.
[Ni(siS3)]3 (1b) from [Ni(NHR)(siS3)] [R ؍ PnPr3 (2b), PCy3 (2b),
SPh2 (4b)] and CO. General Procedure: An equimolar amount of
CO was injected into a Schlenk tube containing a CH2Cl2 solution
(ca. 10 mL) of the respective complex and fitted with a septum. In
the course of several hours, depending on the complex, the color
of the CH2Cl2 solution changed from purple or yellow-red to red-
brown. The solution was filtered, reduced in volume to ca. 2 mL
and layered with MeOH (20 mL). Dark-red crystals of 1b precipi-
tated at Ϫ25 °C, which were separated after 3Ϫ7 d, washed with
MeOH and dried in vacuo.
D؉/NH Exchange Reactions of 2a/2b, 3a/3b, and 4a/4b with D2O or
CD3OD: In an NMR tube, D2O or CD3OD (50 µL) was added to
a saturated solution of the respective complex (ca. 50 mg) in
CD2Cl2 or CH2Cl2. The reactions were monitored by recording the
1H/2D NMR spectra and measuring the intensity of the NH or ND
signals. After completion of the reactions (5Ϫ20 min), the solvents
were removed in vacuo and the resulting residue was identified by
IR (KBr) spectroscopy. The deuterated complexes each exhibited a
ν(ND) band in the region 2480Ϫ2420 cmϪ1
.
D2/NH Exchange Reactions of 2b, 3a/3b, and 4a/4b with D2 and
Identification of HD: In a high-pressure NMR tube (524-PV-1,
Wilmad, USA), a concentrated solution of the respective complex
(ca. 50 mg) in CD2Cl2 or [D8]THF was pressurized with D2 (18
bar). The reactions were monitored by recording 1H NMR spectra.
The formation of HD gave rise to a 1:1:1 triplet (JH,D ϭ 42.5 Hz)
in the region of δ ϭ 4Ϫ5 ppm after 80Ϫ120 h.
[Ni(siS3)]3 (1b) from 2b and CO: From 185 mg (0.295 mmol) of 2b
and 6.7 mL (0.299 mmol) of CO gas. Reaction time 40 h. Yield:
81 mg (61%).
[Ni(siS3)]3 (1b) from 3b and CO: From 224 mg (0.300 mmol) of 3b
and 6.8 mL (0.304 mmol) of CO gas. Reaction time 65 h. Yield:
87 mg (64%).
1856
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Eur. J. Inorg. Chem. 2004, 1847Ϫ1858

Activation of H2 and CO by Sulfur-Rich Nickel Model Complexes
FULL PAPER
Table 3. Selected crystallographic data for [Ni(NHPnPr3)(siS3)] (2b), [Ni(NHPCy3)(HS3)] (3a), [Ni(NHPCy3)(siS3)] (3b), [Ni(NHSPh2)(HS3)]
(4a), and [Ni(PnPr3)(HS3)] (5a)
2b
3a
3b
4a
5a
Empirical formula
Mr (g molϪ1
C27H46NNiPS3Si2
626.69
C30H42NNiPS3
602.51
monoclinic
P21/c
1084.2(1)
1452.1(1)
1937.8(1)
90
105.40(1)
90
C36H58NNiPS3Si2
746.87
C24H19NNiS4
508.35
monoclinic
P21/c
1295.2(1)
1536.0(2)
1126.8(1)
90
101.08(1)
90
2.1999(4)
4
C21H29NiPS3
467.30
orthorhombic
Pbca
1231.9(1)
1640.8(1)
2295.4(2)
90
90
90
4.6397(6)
8
1.338
)
Crystal system
Space group
a [pm]
b [pm]
c [pm]
α [°]
triclinic
orthorhombic
P212121
1107.4(1)
1532.1(2)
2383.9(2)
90
90
90
4.0446(7)
4
1.227
¯
P1
1154.8(2)
1659.7(2)
1913.2(3)
73.43(1)
84.60(1)
76.20(1)
3.4118(9)
4
β [°]
γ [°]
V [nm3]
Z
2.9413(4)
4
1.361
ρcalcd. [g cmϪ3
]
1.220
0.886
1.535
1.274
µ [mmϪ1
]
0.947
0.758
1.179
Crystal size [mm]
2θ range [°]
Tmin/Tmax
Measd. refl.
Indep. refl.
0.30 ϫ 0.18 ϫ 0.06 0.60 ϫ 0.55 ϫ 0.42 0.70 ϫ 0.50 ϫ 0.10 0.60 ϫ 0.55 ϫ 0.42 0.70 ϫ 0.62 ϫ 0.44
3.6Ϫ50.0
Ϫ
12546
10615
4824
3.5Ϫ56.0
0.321/0.360
8815
3.4Ϫ52.0
0.385/0.441
8876
4.1Ϫ58.0
0.189/0.250
7153
3.5Ϫ54.0
0.168/0.222
6197
7086
4806
7956
5464
5846
4241
5067
3487
Obsd. refl.
Ref. parameters
649
451
397/Ϫ328
403
342/Ϫ452
347
390/Ϫ311
266
482/Ϫ756
Max/min resid. density 462/Ϫ446
[e·nmϪ3
]
R1;[a] wR2[b][%]
7.63; 17.80
Ϫ
4.88; 11.32
Ϫ
6.48; 16.30
0.03(2)
3.88; 8.49
Ϫ
4.87; 12.15
Ϫ
Abs. struct. parameter
[a]
[b]
[I Ͼ 2σ(I)]. All data.
[Ni(siS3)]3 (1b) from 4b and CO: From 112 mg (0.172 mmol) of 4b
and 3.9 mL (0.174 mmol) of CO gas. Reaction time 3 h. Yield: or were refined isotropically (4a). In all other compounds, the H
refined with a fixed common isotropic displacement parameter (3a)
62 mg (80%).
atoms were geometrically positioned with isotropic displacement
parameters being 1.5-times U(eq) of the corresponding C or N
atom. One of the n-propyl groups of 5a is disordered. Two alterna-
tive sites were refined giving site-occupancy factors of 0.711(8) (site
A) and 0.289(8) (site B). The unit cell of 2b contains two symmetri-
cally independent molecules. Selected crystallographic data are
summarized in Table 3.[24]
Monitoring the Reactions of 2a/2b, 3a/3b, and 4a/4b with CO by
1H and 31P NMR Spectroscopy: An equimolar amount of CO was
injected into an NMR tube containing the solution of the respect-
ive complex (ca. 50 mg) in CD2Cl2 (ca. 0.6 mL) and fitted with a
septum. 1H and 31P NMR spectra were recorded at regular time in-
tervals.
X-ray Structure Determination of [Ni(NHPnPr3)(siS3)] (2b), Acknowledgments
[Ni(NHPCy3)(HS3)] (3a), [Ni(NHPCy3)(siS3)] (3b), [Ni(NHSPh2)-
Support of these investigations by the Deutsche Forschungsgemein-
(HS3)] (4a), and [Ni(PnPr3)(HS3)] (5a): In the course of 10 d, red-
brown blocks of 2b crystallized at Ϫ25 °C from a saturated THF
solution of 2b layered with CH3CN. In an NMR tube at Ϫ25 °C,
in the course of 3 d dark-red blocks of 3a crystallized from a CDCl3
solution of 3a layered with Et2O. Red-violet plates of 3b crys-
tallized from a hot CH3CN solution (65 °C) of 3b, which was slowly
cooled to Ϫ30 °C. Red-brown crystals of 4a were grown in the
course of 7 d from a saturated CH2Cl2 solution of 4a that was
layered with hexane at Ϫ30 °C. Red-brown blocks of 5a crystallized
from a concentrated THF solution of 5a, which was layered with
hexane at Ϫ30 °C. Suitable single crystals were either embedded in
protective perfluoro polyether oil or sealed in glass capillaries un-
der N2. Data were collected at 210 K (2b and 5a), 220 K (3a and
4a), or 295 K (3b) with a Siemens P4 diffractometer using Mo-Kα
radiation (λ ϭ 71.073 pm), a graphite monochromator, and the ω-
scan technique. With the exception of 2b, semiempirical absorption
corrections using ψ-scans were performed. All structures were
solved by direct methods, and full-matrix least-squares refinement
was carried out on F2 using SHELXTL NT 5.1.[23] All non-hydro-
gen atoms were refined anisotropically. The hydrogen atoms of 3a
and 4a were located in a difference Fourier map and were either
schaft (SFB 583: ‘‘Redoxaktive Metallkomplexe’’) and the Fonds
der Chemischen Industrie is gratefully acknowledged. We thank
Prof. Dr. Horst Kisch for his fruitful discussions.
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Eur. J. Inorg. Chem. 2004, 1847Ϫ1858
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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D. Sellmann, R. Prakash, F. W. Heinemann
FULL PAPER
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Received October 22, 2003
Early View Article
Published Online March 18, 2004
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C.
1858
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Eur. J. Inorg. Chem. 2004, 1847Ϫ1858