Targeting synthetic analogues of the metallo-sulfur active sites of nickel enzymes capable of important catalysis

Article abstract of DOI:10.1039/b307175h

The nickel containing enzymes NiFe-hydrogenase, carbon monoxide dehydrogenase and acetyl-CoA synthase are able to catalyse environmentally, and potentially industrially, important reactions: hydrogen uptake; carbon dioxide/carbon monoxide interconversion; and incorporation of carbon monoxide to form acetyl-CoA, respectively. Progress toward the synthesis of nickel-iron complexes with structural features related to the active sites of these enzymes are described, together with the synthesis, properties and crystal structure of the first methylated-nickel-iron diheterometallic complex, [{Fe(NS₃)(NO)-S} Ni(CH₃)(dppe)] (NS₃ = N(CH₂CH₂S)₃^3-), relevant to a proposed mechanistic intermediate in the acetyl-CoA synthase mechanism.

Full text of DOI:10.1039/b307175h

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Targeting synthetic analogues of the metallo-sulfur active sites of
nickel enzymes capable of important catalysis†
Matt C. Smith, J. Elaine Barclay, Sian C. Davies, David L. Hughes and David J. Evans*
Department of Biological Chemistry, John Innes Centre, Norwich Research Park, Colney,
Norwich, UK NR4 7UH. E-mail: dave.evans@bbsrc.ac.uk
Received 23rd June 2003, Accepted 15th July 2003
First published as an Advance Article on the web 22nd September 2003
The nickel containing enzymes NiFe-hydrogenase, carbon monoxide dehydrogenase and acetyl-CoA synthase are
able to catalyse environmentally, and potentially industrially, important reactions: hydrogen uptake; carbon dioxide/
carbon monoxide interconversion; and incorporation of carbon monoxide to form acetyl-CoA, respectively. Progress
toward the synthesis of nickel–iron complexes with structural features related to the active sites of these enzymes
are described, together with the synthesis, properties and crystal structure of the first methylated-nickel–iron
diheterometallic complex, [{Fe(NS3)(NO)-S}Ni(CH3)(dppe)] (NS3 = N(CH2CH2S)33Ϫ), relevant to a proposed
mechanistic intermediate in the acetyl-CoA synthase mechanism.
to protons and electrons, is a dinuclear thiolate-bridged nickel–
Introduction
iron complex. The nickel atom is coordinated by four cystein-
Enzymes can catalyse reactions which are very relevant to clean
ate-sulfur atoms, two of which bridge to the iron atom. The
technologies. Of particular interest are the hydrogenases and
other ligands to iron, as shown by crystallography and spectro-
nickel-containing carbon monoxide dehydrogenase/acetyl-CoA
scopy,5,6 are cyanide and carbon monoxide. In the aerobically
synthase (CODH/ACS). Hydrogenases catalyse the inter-
isolated crystals there is an additional bridging feature, prob-
conversion of hydrogen and protons/electrons. The bifunctional
ably oxo or hydroxo, which is not present in the active form of
enzyme CODH/ACS converts carbon dioxide through to, even-
the enzyme (Fig. 1b). Several other structures of NiFe-hydro-
tually, cell carbon. Understanding the underlying chemistry at
genase have since been reported.7
the enzyme active sites (which utilise abundant iron and/or
nickel and sulfur) may inform the design of novel, cheaper,
“greener” catalysts for hydrogen production or uptake, for
Recently, crystal structures of a bifunctional CODH/ACS
protein from Moorella thermoacetica have been reported and
they show two distinct active sites: one at which carbon dioxide
carbon dioxide sequestration and for alternative routes for the
and carbon monoxide are interconverted, Cluster C; and one
synthesis of chemical feedstocks.
The hydrogenases can be classified into three main groups:
all-iron hydrogenases which are bidirectional; nickel–iron
where carbon monoxide is utilised in the acetylation of
coenzyme A to acetyl-CoA, Cluster A.8,9 In the structure at
2.2 Å resolution by Drennan et al.,8 Cluster C is an asymmetric
hydrogenases which are generally involved in hydrogen uptake;
NiFe4S5 assembly. The nickel is approximately four-coordinate
and transition metal free hydrogenases. X-ray crystallographic
square planar and one of the iron atoms is extraneous to the
structures of all-iron hydrogenases from Desulfovibrio desulfu-
cuboidal-like core (Fig. 2a). This assembly has been previously
observed in the 1.6 Å resolution structure of the dithionite-
ricans and Clostridium pasteurianum,1,2 together with spectro-
scopic data on all-iron hydrogenase from D. vulgaris,3 show that
reduced state of CODH from Carboxydothermus hydro-
the active site is an Fe4S4-cluster linked by a bridging cysteinyl
genoformans.10 Cluster C of CODH from Rhodospirillum
sulfur to an “organometallic” Fe2S3 sub-site (Fig. 1a). Recently,
considerable advances have been made in the synthesis of
synthetic analogues of the Fe2S3 sub-site.4
Fig. 1 (a) Composite representation of the “organometallic” Fe2S3
sub-site of all-iron hydrogenase; (b) The structure of the NiFe-site in
inactive, as-isolated NiFe-hydrogenase.
The nickel–iron hydrogenase from D. gigas, as aerobically
isolated in the inactive form, has been characterised by X-ray
crystallography.5 The active site, where dihydrogen is converted
Fig. 2 The metal–sulfur assemblies of (a) reduced Cluster C of
CODH from M. thermoacetica;10 (b) CO-preincubated Cluster C of
CODH from R. rubrum, X is an unidentified ligand, possibly non-
† Based on the presentation given at Dalton Discussion No. 6, 9–11th
September 2003, University of York, UK.
substrate CO;11 (c) Cluster A of ACS from M. thermoacetica from
Drennan et al.8
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 4 1 4 7 – 4 1 5 1
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rubrum preincubated with carbon monoxide has a similar struc-
ture,11 Fig. 2b, except that the cuboidal fragment is “closed”
and the nickel is five-coordinate in approximately a trigonal
bipyramidal pattern. The fifth ligand, X, is, possibly, non-
substrate carbon monoxide. This structure has some similarity
to that of Cluster C observed by Fontecilla-Camps et al. in the
1.9 Å resolution structure of CO-treated CODH/ACS.9
Results and discussion
Nickel in an all-sulfur environment
To improve the structural analogy of complexes 1 and 2 to the
active site of NiFe-hydrogenase it is desirable to replace the
diphosphine ligation by sulfur ligation. An alternative, higher
yield, preparation of the trinuclear complex [Ni{Fe(NS3)(CO)-
S,SЈ}2] 3 is by reaction of [Fe(NS3)(CO)]Ϫ with [NiCl2(PPh3)2].
Both the chloride and monophosphine ligands to nickel are
labile in this system. Subsequent to isolation of 3 from this
reaction mixture other products could be isolated: [NEt4]-
[NiCl3(PPh3)], the structure of which we have reported else-
where,21 triphenylphosphine and tetraethylammonium chloride.
The overall stoichiometry of the reaction is represented in
eqn. (1).
Cluster A has a totally unexpected structure and is a remark-
able assembly of an Fe4S4 cubane-cluster bridged through
cysteinyl sulfur to a binuclear metal subsite.8,9 In the structure
of Drennan et al.8 this subsite comprises copper and nickel
(Fig. 2c). In the structure by Fontecilla-Camps et al.9 the copper
is substituted by either a zinc or nickel. The physiologically
important combination of metal atoms at this active site
remains controversial.8,9,12,13 Previously, it had been proposed
that both Cluster A and C were far simpler assemblies based on
a Fe4S4-cluster linked through cysteinyl sulfur to a nickel–iron14
or nickel based fragment,15 respectively. The ACS reaction (the
synthesis of acetyl-CoA by the non-redox condensation of a
methyl group, a carbonyl group and an organic thiol) parallels
the industrial Monsanto modification of the Reppe process for
the production of acetic acid, both apparently involving metal
carbonyl, methyl-metal and acyl-metal intermediates.
2[NEt4][Fe(NS3)(CO)] ϩ 2[NiCl2(PPh3)2]
[Ni{Fe(NS3)(CO)-S,SЈ}2] ϩ [NEt4][NiCl3(PPh3)] ϩ
[NEt4]Cl ϩ 3PPh3 (1)
When the reaction is performed in the presence of one equiv-
alent of ethanedithiol, under an atmosphere of carbon mon-
oxide, a dark red solution, consistent with 3, is formed immedi-
ately but on stirring this quickly turns brown. From the reaction
mixture can be isolated a brown, insoluble, solid which has
an elemental analysis consistent with the formulation [{Fe-
(NS3)(CO)-S,SЈ}Ni(SCH2CH2S)] 4. The Mössbauer parameters
are consistent with the iron remaining iron() and are similar to
those found for the trigonal pyramidal, low-spin iron() in the
series of complexes [M{Fe(NS3)(CO)-S,SЈ}2] (M = Fe, Co,
Ni).19 Due to its insolubility we have been unable to characterise
this material further and cannot eliminate the possibility that
the material is polymeric. A similar approach, utilising the labil-
ity of monophosphines on nickel(), has been independently
developed by Sellmann et al.22 They have reacted the dinuclear
iron complex [Fe(‘S3’)(CO)2]2 (‘S3’2Ϫ = bis(mercaptophenyl)-
sulfide(2Ϫ)) with [Ni(PMe3)2(S2C6H4)] to give, in low yield, the
crystallographically characterised complex [Fe(CO)(PMe3)2-
(µ-‘S3’)Ni(S2C6H4)]. In this complex nickel sits in an all-sulfur,
square planar coordination environment. The Ni ؒ ؒ ؒ Fe dis-
tance of 3.323(1) Å is very close to that found for complexes 1
and 2 (3.308(2) and 3.0216(5) Å, respectively).
We have utilised the anions [Fe(NS3)(CO)]Ϫ and [Fe(NS3)-
3Ϫ 16,17
(NO)]Ϫ {NS3 = N(CH2CH2S)3
}
as chelate ligands to
nickel to generate materials with structural features of
relevance to the active sites of these nickel enzymes. For
example, the crystallographically characterised NiFe-dinuclear
complexes [{Fe(NS3)(CO)2-S,SЈ}NiCl(dppe)]18 1 and [{Fe-
(NS3)(NO)-S,SЈ}NiCl(dppe)]19 2, Fig. 3, have a core structure
similar to that of the active site of the NiFe-hydrogenase,
Fig. 4. The core of each is dinuclear with nickel bound to iron by
a bis(thiolate-bridge) and the iron atom is also bound by
diatomic molecules. The trinuclear complex [Ni{Fe(NS3)(CO)-
S,SЈ}2]19,20 3, that unusually possesses nickel() coordinated in
an almost regular tetrahedral geometry by thiolate-sulfur, has
some structural features relevant to the active site structures
of CODH/ACS. Here we report progress toward improved
structural analogues of the active site of NiFe-hydrogenase, in
which nickel is in an all-sulfur environment, and the prepar-
ation and crystal structure of [{Fe(NS3)(NO)-S}Ni(CH3)-
(dppe)]. This complex can be considered a chemical model of a
proposed9,13,14 nickel-methyl intermediate in the catalytic cycle
of ACS and is the first example of a methylated-nickel in a
heterodimetallic assembly.
An alternative route to NiFe-complexes with nickel in an all-
sulfur environment is to react the iron-carbonyl chelate, [Fe-
(NS3)(CO)]Ϫ, with a nickel dithiocarbamate possessing labile
co-ligands, [NiCl(PPh3)(S2CNiPr2)]. The product has an ele-
mental analysis consistent with the formulation [{Fe(NS3)(CO)-
S,SЈ}Ni(S2CNiPr2)] 5, the labile chloride and phosphine ligands
again being lost from the nickel. Infra-red peaks, in addition to
the carbonyl stretch at 1935 cmϪ1, are observed at 800, 1022
(characteristic of a delocalised C–S bond in dithiocarb-
amates)23 and 1099 cmϪ1; these bands are also present in the
nickel-dithiocarbamate precursor (802, 1020, 1099 cmϪ1).
Absent from the infra-red spectrum of 5 is a peak at 1504 cmϪ1
,
characteristic of a dithiosemicarbazone and associated with
delocalisation of an electron over the C–N bond, consistent
with this electron in 5 residing between the carbon, two sulfur
and nickel atoms. The Mössbauer parameters of 5 are consist-
ent with the iron atom remaining low-spin iron(). Unfortu-
nately, the insolubility again precludes further spectroscopic
characterisation or crystal growth for structural analysis.
Fig. 3 The structures of NiFe-dinuclear complexes [{Fe(NS3)(CO)2-
S,SЈ}NiCl(dppe)]
1 (left) and [{Fe(NS3)(NO)-S,SЈ}NiCl(dppe)] 2
(right). The phenyl groups of the dppe ligand and all hydrogen atoms
have been omitted for clarity.
An iron–nickel-methyl assembly relevant to ACS
The mechanism for the synthesis of acetyl-CoA by the enzyme
ACS is yet to be defined unequivocally.8,9,12,13 However, metal
carbonyl, methyl-nickel and acyl-metal intermediates are still
implicated.
Reaction of the iron-nitrosyl chelate, [Fe(NS3)(NO)]Ϫ, with
[NiCl(CH3)(dppe)] in acetonitrile gave, in good yield, the
Fig. 4 A schematic comparison of the proposed, active NiFe-
hydrogenase active centre (left) and the core of complex 1 (right).
D a l t o n T r a n s . , 2 0 0 3 , 4 1 4 7 – 4 1 5 1
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Table 1 Selected molecular dimensions (bond lengths in Å, angles and
methylated-nickel dinuclear complex [{Fe(NS3)(NO)-S}Ni-
(CH3)(dppe)] 6 in which the iron moiety is linked to nickel
through a single bridging thiolate.‡ Compound 6 is insoluble in
most solvents but will dissolve in N-dimethylformamide. The
structure of 6 is shown in Fig. 5 and selected bond lengths and
angles are listed in Table 1. Examination of the crystal structure
of 6ؒ0.2MeCN shows that the nickel and methyl carbon are
displaced 0.004(3) and 0.107(13) Å respectively from the SP2
plane, whilst the trigonal bipyramidal iron is displaced 0.242(2)
Å towards the apical nitrosyl from the plane of three sulfur
ligands. The S3 and SP2 planes are twisted with respect to each
other about S(1) with an angle between their normals of
74.82(9)Њ. The angle about the bridging sulfur, 101.62(12)Њ, is
similar to that in other monothiolate bridged NS3 complexes,17
and substantially greater than the mean 80.59Њ in the dithiolate
bridged 2. As expected in 6 there is a concomitant increase in
the Ni ؒ ؒ ؒ Fe distance to 3.596(2) Å compared with 3.0216(5)
Å in 2. In contrast to [NEt4][Fe(NS3)(NO)]17 and compound 219
no disorder is observed in the N-methylene groups of the NS3
ligand in 6.
torsion angles in Њ) in complex 6
(a) Bond lengths
Ni(1)–C(1)
Ni(1)–S(1)
Ni(1)–P(1)
Ni(1)–P(2)
Ni(1)–Fe(1)
1.969(10)
2.206(3)
2.120(3)
2.243(3)
3.596(2)
Fe(1)–N(1)
S(1)–Fe(1)
Fe(1)–S(2)
Fe(1)–S(3)
Fe(1)–N(4)
1.754(10)
2.429(3)
2.284(3)
2.286(3)
2.265(8)
(b) Bond angles
C(1)–Ni(1)–S(1)
C(1)–Ni(1)–P(1)
C(1)–Ni(1)–P(2)
P(1)–Ni(1)–S(1)
S(1)–Ni(1)–P(2)
P(1)–Ni(1)–P(2)
93.3(4)
85.4(4)
171.7(4)
178.68(13)
94.41(12)
86.89(12)
N(1)–Fe(1)–S(1)
N(1)–Fe(1)–S(3)
N(1)–Fe(1)–S(2)
N(1)–Fe(1)–N(4)
S(2)–Fe(1)–S(1)
S(3)–Fe(1)–S(1)
N(4)–Fe(1)–S(1)
S(2)–Fe(1)–S(3)
N(4)–Fe(1)–S(2)
N(4)–Fe(1)–S(3)
101.5(3)
91.2(3)
95.9(3)
175.4(4)
109.26(12)
122.71(13)
82.2(2)
124.78(14)
85.3(2)
84.5(2)
Ni(1)–S(1)–Fe(1)
C(14)–S(1)–Ni(1)
C(14)–S(1)–Fe(1)
C(24)–S(2)–Fe(1)
C(34)–S(3)–Fe(1)
O(1)–N(1)–Fe(1)
101.62(12)
117.0(4)
99.8(4)
101.2(4)
101.8(4)
152.5(9)
(c) Torsion angles
Ni(1)–P(1)–C(12)–C(21)
P(1)–C(12)–C(21)–P(2)
C(12)–C(21)–P(2)–Ni(1)
Ni(1)–S(1)–C(14)–C(41)
Fe(1)–S(1)–C(14)–C(41)
S(1)–C(14)–C(41)–N(4)
Fe(1)–N(4)–C(41)–C(14)
Fe(1)–S(2)–C(24)–C(42)
S(2)–C(24)–C(42)–N(4)
Fe(1)–N(4)–C(42)–C(24)
Fe(1)–S(3)–C(34)–C(43)
S(3)–C(34)–C(43)–N(4)
Fe(1)–N(4)–C(43)–C(34)
Ϫ38.2(8)
50.2(9)
Ϫ42.3(8)
Ϫ145.5(7)
Ϫ37.1(8)
57.3(11)
Ϫ46.0(11)
Ϫ23.7(9)
50.6(13)
Ϫ49.6(11)
Ϫ29.6(8)
50.1(12)
Fig. 5 A molecule of [{Fe(NS3)(NO)-S}Ni(CH3)(dppe)] 6 showing
principal atoms. The phenyl groups of the dppe ligand and all hydrogen
atoms have been omitted for clarity.
Ϫ43.2(11)
(d) Mean planes
The nitrosyl ligand is bent at 152.5(9)Њ about the nitrogen,
consistent with NOϪ, which compares favourably with the
mean angle of 147.9Њ in 2, as does the nitrosyl infra-red stretch
for 6 at 1666 cmϪ1 and for 2 at 1667 cmϪ1. These values are
similar to those of other Fe(NS3)-nitrosyl complexes.17 This
limited difference suggests that the change from one bridging
thiolate to two bridging thiolates has little effect upon the
nitrosyl environment and, from Mössbauer parameters, there is
also little effect on the iron environment (6, isomer shift (i.s.)
0.40, quadrupole splitting (q.s.) 1.26; 2, i.s. 0.40, q.s. 1.19
mmsϪ1). These values, and the temperature independent q.s.
between 77–298 K, correspond to a formal high-spin iron()
oxidation state. The Mössbauer parameters are in line with
those of other reported five-coordinate high-spin iron() com-
Atoms in plane 1: S(1), S(2), S(3)
Distance from plane 1 to Fe(1): 0.242(2) displaced towards the NO
ligand
Atoms in plane 2: S(1), P(1), P(2)
Distance from plane 2 to Ni(1): 0.004(3)
Distance from plane 2 to C(1): 0.107(13)
Angles between the normals to planes 1 and 2: 74.82(9)
Complex 6 is a first generation analogue of a proposed
nickel-methyl intermediate in the enzymatic cycle of ACS.9,13,14
It is the first example of a methylated nickel in a hetero-
dimetallic assembly. Mononuclear nickel-methyl complexes
such as [NMe4][Ni(CH3)(‘MeS2’)2] (where ‘MeS2’Ϫ = o-(methyl-
thio)-thiophenolate(1Ϫ))29 and [Ni(N(CH2CH2SR)3)(CH3)]
(where R = iPr, tBu)30 can be reacted with carbon monoxide to
form nickel-acetyl species whose occurrence can be monitored
through the formation of characteristic acetyl bands in the
infra-red spectrum. Complex 6 has low solubility and under our
conditions does not react with carbon monoxide. We are cur-
rently investigating routes to related, more soluble compounds,
which are expected to be more reactive.
plexes, e.g. [Fe(salen)Cl]ؒ2MeNO2 (i.s. = 0.40, q.s. = 1.33 mmsϪ1
,
80 K).24 The NOϪ ligand (S = 1) enforces spin pairing to give an
S = 3/2 state arising from antiferromagnetic coupling with a
high-spin ferric state (S = 5/2)25 giving an {FeNO}7 complex
under the Enemark and Feltham notation.26
The 1H-NMR signal for Ni-methyl (δH = 1.3) is in accord with
those of [Ni(CH3)2(dppe)] (δH = 0.8)27 and [NiCl(CH3)(dppe)]
1
(δH = 0.1).28 The NMR shifts for the ethylene (δH = 2.2) and
phenyl protons (δH = 7.3–8.0 ppm) of dppe are the same in
[NiCl(CH3)(dppe)], dithiolate-bridged 2 and 6. Complexes 2
and 6 exhibit 31P NMR signals (referenced to TMP) at Ϫ113
and Ϫ112 ppm, respectively, which are upfield from dppe (δP =
Experimental
General
All manipulations were performed under a dinitrogen atmos-
phere, unless otherwise stated, using either Schlenk or vacuum
line techniques. Solvents were dried over appropriate drying
agents and distilled under dinitrogen prior to use. [NEt4]-
[Fe(NS3)(CO)],16 [NEt4][Fe(NO)(NS3)],17 [NiCl2(PPh3)2]31 and
Ϫ150) and downfield from those of [NiCl(CH3)(dppe)] (δP
Ϫ79 and Ϫ102).
=
‡ Previously, in the absence of a crystal structure, we proposed a
dithiolate-bridge between the nickel and iron.19
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[NiCl2(dppe)]32 were prepared by published procedures. [NiCl-
(PPh3)(S2CNiPr2)] was prepared by adaptation of the syn-
thesis of [NiCl(PPh3){S2CN(BziPr)2}] (where BziPr = benzyl-
isopropyl).33 An improved synthesis of [NiCl(CH3)(dppe)]28 is
described below. IR spectra were recorded on Shimadzu FTIR-
8000 spectrophotometer. 1H and 31P NMR were obtained on a
Jeol Lambda 400 spectrometer. Mössbauer spectra were
recorded on an ES-Technology MS-105 spectrometer with a
925 MBq 57Co source in a rhodium matrix at ambient temper-
ature. Spectra were referenced to a 25 µm iron foil at 298 K
and fitted with Lorentzian lines. Elemental analyses were by
Mr A. W. L. Saunders at the University of East Anglia (CHN),
or by Southern Science, Falmer Laboratories, East Sussex
(metals).
reduced pressure and ethanol (100 cm3) added. Honey-brown
rhombic crystals precipitated over two days at Ϫ20 ЊC, these
were collected by filtration and dried (0.45g, 33.0%) (Found: C,
64.1; H, 5.6. Expected for C27H27ClNiP2 requires: C, 63.9; H,
5.4%); δH(Me) (400 MHz, dmf-d7, standard SiMe4) 0.1.
[{Fe(NS3)(NO)-S}Ni(CH3)(dppe)]ؒ0.2MeCN 6ؒ0.2MeCN. A
solution of [NiCl(CH3)(dppe)] (0.13 g, 0.26 mmol) in MeCN
(40 cm3) was layered onto the surface of a solution of [NEt4]-
[Fe(NO)(NS3)] (0.11 g, 0.23 mmol) in MeCN (20 cm3). Black
square plates formed after two days that were collected by fil-
tration, washed repeatedly with diethyl ether and then dried
(0.14 g, 69%) (Found: C, 52.2; H, 5.2; N, 4.5; Fe, 6.9; Ni, 7.7.
C33H39FeN2NiOP2S3.C0.2H0.6N0.2 requires: C, 52.7; H, 5.2; N,
4.1; Fe, 7.3; Ni, 7.7%); λmax/nm (dmf ) 265 (ε/dm3 molϪ1 cmϪ1
30053), 318 (9309), 375 (5053), 464 (2394); νmax/cmϪ1 (NO) 1666
(KBr); δH(Me) (400 MHz; dmf-d7; standard SiMe4) 1.3; δP(162
MHz; dmf-d7; standard P(OMe)3) Ϫ112; Mössbauer, i.s. = 0.40,
Preparations
[Ni{Fe(NS3)(CO)-S,SЈ}2] 3. To
a solution of [NEt4]-
[Fe(NS3)(CO)] (0.59 g, 1.44 mmol) in MeCN (25 cm3) was
added a solution of [NiCl2(PPh3)2] (1.17 g, 1.79 mmol) in
MeCN (100 cm3). The dark red solution that immediately
formed was stirred for 90 min under an atmosphere of CO, with
no signs of CO uptake. Upon standing overnight, dark crystals
formed which were collected by filtration, washed with diethyl
ether and dried (0.25 g, 56%). This material showed identical
infra-red and Mössbauer spectra to those reported pre-
viously.19,20 The retained filtrate, over a period of three days
under a dinitrogen atmosphere, slowly changed to a dark blue
colour whilst giving a crystalline precipitate of PPh3. The solu-
tion was reduced to a volume of ∼15 cm3 in vacuo and filtered
to remove PPh3. Diethyl ether (5 cm3) was added to the blue
filtrate leading to the formation of large royal blue crystals of
[NEt4][NiCl3(PPh3)] and white crystals of [NEt4]Cl. These were
collected by filtration, washed with diethyl ether and dried in
vacuo.
q.s. = 1.19, Γ = 0.17 mmsϪ1
.
½
Crystal structure analysis of complex 6
Crystals of [{Fe(NO)(NS3)-S}Ni(CH3)dppe]ؒ0.2MeCN were
black square plates. A single crystal of size 0.24 × 0.17 × 0.06
mm (corresponding to the c, a and b axes of the unit cell) was
selected and mounted on a glass fibre for photographic examin-
ation and the data collection. Diffraction data were measured
on an Nonius CAD4 diffractometer with monochromated
Mo-Kα radiation. The data were collected at 140 K, with the
temperature being lowered slowly to avoid shocking the crystal.
Cell parameters were refined using least-squares methods from
the settings of 24 reflections in the range 10 to 11Њ in θ centred
in 4 orientations. 4173 Unique reflections were collected to θ of
22Њ the limit of observable intensities, with 1854 having inten-
sities greater than 2σI. There were no change in orientations or
decay of intensities during data collection.
[{Fe(NS3)(CO)-S,SЈ}Ni(SCH2CH2S)] 4. Under an atmos-
phere of carbon monoxide, a solution of [NiCl2(PPh3)2] (0.79 g,
1.50 mmol) in MeCN (80 cm3) containing ethanedithiol (0.10
cm3, 1.19 mmol) was added to a solution of [NEt4][Fe(NS3)-
(CO)] (0.49 g, 1.20 mmol) in MeCN (30 cm3). The solution
immediately turned a dark red colour associated with the form-
ation of [Ni{Fe(NS3)(CO)-S,SЈ}2] but quickly turned brown
upon stirring. No CO gas uptake was observed. After stirring
for two hours the reaction mixture was left to stand overnight.
A dark brown solid was collected by filtration, washed repeat-
edly with diethyl ether and dried (0.23 g, 45.0%) (Found: C,
25.3; H, 3.7; N, 2.8; Fe, 13.2; Ni, 14.7. C9H16FeNNiOS5
requires: C, 25.2; H, 3.8; N, 3.3; Fe, 13.0; Ni, 13.7%); νmax/cmϪ1
The data were corrected for Lorentz-polarisation effects, for
absorption by semi-empirical psi-scan methods, and for
negative intensities by Bayesian statistical methods. The struc-
ture was solved using direct methods in the SHELXS-86
program34 and refined on F 2 using full-matrix least-squares
procedures in SHELXL-97.35 All non-hydrogen atoms were
refined with anisotropic displacement parameters, except some
unresolved solvent atoms, which were all refined isotropically as
carbon atoms. Hydrogen coordinates were of idealised positions
and set to ride on the parent atoms in the complex molecule, with
thermal displacement parameters refined isotropically. Con-
vergence was reached with R1 = 0.148 and wR2 = 0.138 for all data
2
weighted w = 1/[σ2(Fo ) ϩ (0.013P)2] where P = (Fo2 ϩ 2Fc2)/3; for
(CO) 1935 (KBr); Mössbauer, i.s. = 0.20, q.s. = 1.34 mms, Γ =
½
the 1854 observed data R1 = 0.067 and wR2 = 0.100.
0.17 mmsϪ1
.
In the final difference map the residual electron density was
0.52 eϪ
Å
Ϫ3 for the largest peak, which lay between the Ni and
[{Fe(NS3)(CO)-S,SЈ}Ni(S2CNiPr2)] 5. [NiCl(PPh3)(S2C-
NiPr2)] (0.14 g, 0.26 mmol) dissolved in MeCN (30 cm3) was
layered by syringe on to the surface of a solution of [NEt4]-
[Fe(NS3)(CO)] (0.11 g, 0.27 mmol) in MeCN (20 cm3). Over-
night, crystals of [Fe{Fe(NS3)(CO)-S,SЈ}2] (<0.01 g) formed
and were removed by filtration. Stirring the filtrate again over-
night gave a dark brown solid that was collected by filtration,
washed repeatedly with MeCN and then diethyl ether before
being dried. (0.03 g, 22.3%) (Found: C, 32.1; H, 5.3; N, 5.7; Fe,
10.2; Ni, 10.7. C9H16FeNNiOS5 requires: C, 32.8; H, 4.9; N, 5.5;
Fe, 10.9; Ni, 11.5%); νmax/cmϪ1 (CO) 1935 (KBr); Mössbauer,
the methyl carbon. Scattering factors were taken from ref. 36.
Computer programs used in the analysis have been noted above
and/or in Table 4 of ref. 37, and were run on a DEC-Alpha-
Station 200 4/100 in the Department of Biological Chemistry,
John Innes Centre.
Crystal data: C33H39FeN2NiOP2S3,0.2(C2H3N), M = 760.5,
monoclinic, space group P21/c (no. 14), a = 11.410(3), b =
19.361(3), c = 15.633(2) Å, α = 90Њ, β = 98.64(2)Њ, γ = 90Њ,
V = 3414.3(17) Å3. Z = 4, Dc = 1.480 g cmϪ3, F(000) = 1582, T =
140(1) K, µ(Mo-Kα) = 1.284 mmϪ1, λ(Mo-Kα) = 0.71069 Å.
CCDC reference number 192738.
i.s. = 0.21, q.s. = 1.16 mms, Γ = 0.20 mmsϪ1
.
½
See http://www.rsc.org/suppdata/dt/b3/b307175h/ for crystal-
lographic data in CIF or other electronic format.
[NiCl(CH3)(dppe)]. MeMgI (12 cm3 of a 3.0 M diethyl ether
solution, 36 mmol) was added to [NiCl2(dppe)] (1.42 g, 2.69
mmol) in tetrahydrofuran (65 cm3). After stirring for 2 days the
solution was concentrated to ∼ 40 cm3 and filtered through
approx. 1 cm of Celite. Ethanol (5 cm3) was added to the filtrate
which was then refiltered. The filtrate volume was halved under
Acknowledgements
The Biotechnology and Biological Sciences Research Council
are thanked for funding. Dr J. R. Sanders of the Dept. of
D a l t o n T r a n s . , 2 0 0 3 , 4 1 4 7 – 4 1 5 1
4150

View Article Online
16 S. C. Davies, D. L. Hughes, M. C. Durrant, R. L. Richards and
Biological Chemistry, John Innes Centre is thanked for the
supply of NS3H3.
J. R. Sanders, J. Chem. Soc., Dalton Trans., 2000, 4694.
17 S. C. Davies, D. J. Evans, D. L. Hughes, M. Konkol, R. L. Richards,
J. R. Sanders and P. Sobota, J. Chem. Soc., Dalton Trans., 2002,
2473.
18 S. C. Davies, D. J. Evans, D. L. Hughes, S. Longhurst and J. R.
Sanders, Chem. Commun., 1999, 1935.
19 M. C. Smith, J. E. Barclay, S. P. Cramer, S. C. Davies, W.-W. Gu,
D. L. Hughes, S. Longhurst and D. J. Evans, J. Chem. Soc., Dalton
Trans., 2002, 2641.
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