cyclo-Hexaphosphane versus cyclo-hexaarsane fragmentation on a sulphur-capped mixed-metal dicobalt-iron skeleton

Article abstract of DOI:10.1016/S0022-328X(01)01280-3

Reaction of the sulphur-capped dicobalt-iron complex [Co₂Fe(μ₃-S)(CO)₉] with cyclo-(PhAs)₆ in toluene at 70 °C gives [Co₂Fe(μ₃-S){μ-cyclo-(PhAs)₆}(CO)₇] (1) as the only product in good yield. Conversely, treatment of [Co₂Fe(μ₃-S)(CO)₉] with cyclo-(PhP)₆ under the same reaction conditions gives two isomers [Co₂Fe(μ₃-S){μ-cyclo-(PhP)₆}(CO)₇] (2) and [Co₂Fe(μ₃-S){μ-cyclo-(PhP)₆}(CO)₇] (3) in ca. 1:1 ratio. Single crystal X-ray analysis shows 1 and 2 to be isostructural with the intact six-membered ring adopting a chair conformation and bridging a cobalt-cobalt edge via either two arsine (1) or two phosphorus (2) atoms in the 1,5 positions of the respective rings. Thermolysis of 2 or of 3 in toluene at 120 °C gives [Co₂Fe(μ₃-SPPh)(μ-η²:η²:η¹-P₅Ph₅)(CO)₅] (4) in moderate yield, while thermolysis of 1 under the same conditions leads to complete decomposition. A single crystal X-ray diffraction study performed on 4 reveals the cyclo-hexaphosphane rings in 2 or 3 to have cleaved to give a P₅Ph₅ chain and a PPh group, the latter of which has additionally undergone coupling with the sulphur cap.

Full text of DOI:10.1016/S0022-328X(01)01280-3

Journal of Organometallic Chemistry 642 (2002) 237–245
www.elsevier.com/locate/jorganchem
cyclo-Hexaphosphane versus cyclo-hexaarsane fragmentation on a
sulphur-capped mixed-metal dicobalt–iron skeleton
Rohini M. De Silva a, Martin J. Mays a,*, Paul R. Raithby a, Gregory A. Solan b
a Department of Chemistry, Lensfield Road, Cambridge CB2 1EW, UK
b Department of Chemistry, Uni6ersity of Leicester, Uni6ersity Road, Leicester LE1 7RH, UK
Received 2 August 2001; received in revised form 19 September 2001; accepted 19 September 2001
Abstract
Reaction of the sulphur-capped dicobalt–iron complex [Co2Fe(m3-S)(CO)9] with cyclo-(PhAs)6 in toluene at 70 °C gives
[Co2Fe(m3-S){m-cyclo-(PhAs)6}(CO)7] (1) as the only product in good yield. Conversely, treatment of [Co2Fe(m3-S)(CO)9] with
cyclo-(PhP)6 under the same reaction conditions gives two isomers [Co2Fe(m3-S){m-cyclo-(PhP)6}(CO)7] (2) and [Co2Fe(m3-S){m-cy-
clo-(PhP)6}(CO)7] (3) in ca. 1:1 ratio. Single crystal X-ray analysis shows 1 and 2 to be isostructural with the intact six-membered
ring adopting a chair conformation and bridging a cobalt–cobalt edge via either two arsine (1) or two phosphorus (2) atoms in
the 1,5 positions of the respective rings. Thermolysis of 2 or of 3 in toluene at 120 °C gives [Co2Fe(m3-SPPh)(m-h2:h2:h1-
P5Ph5)(CO)5] (4) in moderate yield, while thermolysis of 1 under the same conditions leads to complete decomposition. A single
crystal X-ray diffraction study performed on 4 reveals the cyclo-hexaphosphane rings in 2 or 3 to have cleaved to give a P5Ph5
chain and a PPh group, the latter of which has additionally undergone coupling with the sulphur cap. © 2002 Elsevier Science
B.V. All rights reserved.
Keywords: Cobalt; Iron; cyclo-Hexaarsane; cyclo-Hexaphosphane; Fragmentation
CPA or CPP to afford [Co2(m-CRCR){m-cyclo-
(PhX)6}(CO)4], the complexes decompose on further
heating, without any evidence for products containing
fragmented CPAs or CPPs nor species incorporating
the organic fragment [4,5]. Notably, this is a particu-
larly facile process for [Co2(m-CRCR){m-cyclo-
(PhP)6}(CO)4], which decomposes even at room
temperature [5]. In this report, we are concerned with
replacing the acetylenic moiety in [Co2(m-CRCR)(CO)6]
with a (OC)3FeS unit to form [Co2Fe(m3-S)(CO)9] and
examining its reactivity towards both cyclo-hexapheny-
larsane and cyclo-hexaphenylphosphane. To the knowl-
edge of the authors no studies of the reactivity of
heterometallic complexes towards CPAs or CPPs have
been reported.
1. Introduction
The structural diversity exhibited by complexes ob-
tained from the reactions of cyclic main group
molecules of the pnictogen family, such as cyclo-pol-
yarsanes (CPAs) [(RAs)n, R=hydrocarbyl, n=4–6] or
cyclo-polyphosphanes (CPPs) [(RP)n, n=3–6], with
transition metal carbonyl complexes, has been the focus
for considerable research activity [1–3]. Often clusters
are isolated that contain unprecedented transition
metal/main group metal constructions in which the
CPA or the CPP has ring opened and fragmented to
give chains and capping groups (or mixtures of both)
featuring RAs/RP units or the naked Group 15
elements.
Recently, we have been interested in the reactions of
cyclo-(PhX)6 (X=As, P) with the transverse alkyne–
dicobalt complexes, [Co2(m-CRCR)(CO)6], and have
found that following initial coordination of the intact
2. Results and discussion
The reaction of [Co2Fe(m3-S)(CO)9] with an equimo-
lar amount of cyclo-(PhAs)6 in toluene at 70 °C for 22
h gives [Co2Fe(m3-S){m-cyclo-(PhAs)6}(CO)7] (1) as the
* Corresponding author. Fax: +44-1223-336362.
E-mail address: mjm14@cam.ac.uk (M.J. Mays).
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01280-3

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R.M. De Sil6a et al. / Journal of Organometallic Chemistry 642 (2002) 237–245
Scheme 1. Reagents and conditions: (i) 70 °C, 22 h, cyclo-(PhAs)6, C7H8; (ii) 70 °C, 22 h, cyclo-(PhP)6, C7H8; (iii) 120 °C, 3 h, C7H8.
larger than any AsꢀAsꢀAs angles in the free ligand and
this reflects the significant distortion of the six-mem-
bered arsenic ring on substitution. It appears that, on
substitution, the molecule has undergone a structural
sole product in high yield (Scheme 1). Complex 1 has
been characterised by IR, 1H-, 13C-NMR spectro-
scopies, mass spectrometry and by elemental analysis
(see Table 1). In addition, its structure has been deter-
mined by single crystal X-ray diffraction. The molecu-
lar structure of 1 is shown in Fig. 1 while selected bond
distances and angles are listed in Table 2.
Crystals suitable for the analysis were grown by slow
diffusion of hexane into a dichloromethane solution of
1. The structure of 1 consists of an inner Co2FeS core
having a pseudo-tetrahedral structure in which the tri-
angular Co2Fe moiety is capped by the triply bridging
sulphido group in a manner that has been identified
crystallographically for the parent complex [Co2Fe(m3-
S)(CO)9] [6] and for a range of related structures [7,8].
Two equatorial carbonyl groups in the parent complex,
one on each cobalt atom, are formally replaced in 1 by
the two arsenic atoms in the 1,5 positions of the intact
(PhAs)6 ring. The average AsꢀAsꢀAs angle of 94.79° in
the arsenic ring is close to that in cyclo-(PhAs)6 (91.03°)
[9]. The As(1)ꢀAs(2)ꢀAs(3) angle of 84.51(5)° is smaller
than any angle of the free ligand but comparable with
the corresponding angles of 84.8(6) and 85.74(5)° ob-
served for the complexes [Co2(m-RCCR){m-cyclo-
(PhAs)6}(CO)4] (R=H, Ph) [4], respectively. This angle
contraction allows the two arsenic atoms in the 1,5
positions in the ring to provide better matching to the
CoꢀCo
distance.
The
As(2)ꢀAs(3)ꢀAs(4),
Fig. 1. Molecular structure of [Co2Fe(m3-S){m-cyclo-(PhAs)6}(CO)7]
(1) including the atom numbering scheme. All hydrogen atoms have
been omitted for clarity.
As(3)ꢀAs(4)ꢀAs(5) and As(1)ꢀAs(6)ꢀAs(5) angles of
97.20(6), 101.68(5) and 98.72(6)°, respectively, are

Table 1
Spectroscopic and microanalytical data for the new complexes 1–4
a
Compound w(CO) (cm−1
)
1H-NMR (l) b 13C-NMR (l) c
31P-NMR (l) d
FABMS
Microanalysis (%) e
/
C
H
1
2
3
4
2051vs, 2015s,
8.1–6.4 [m,
30H, Ph]
8.0–6.4 [m,
30H, Ph]
8.2–6.4 [m,
30H, Ph]
8.1–6.7 [m,
30H, Ph]
212.0 [s, CO], 209.0 [br, CO], 200.0 [br,
CO], 137–127 [m, Ph]
213.6 [s, CO], 208.0 [br, CO], 199.0 [br,
CO], 137–128 [m, Ph]
212.0 [s, CO], 210.0 [br, CO], 199.0 [br,
CO], 135–127 [m, Ph]
1314 ([M+] nCO, 40.23 (39.23)
n=1–7)
2.75 (2.30)
3.07 (2.87)
3.01 (2.87)
3.30 (3.04)
2001s, 1948w
2050vs, 2016s,
1997s, 1946w
2050vs, 2017s,
1998s, 1945w
2051w, 2028vs,
1976s
19.2 [br, P(1), P(5)], 17.2 [m, P(6)], −6.8
[m, P(4), P(2)], −41.8 [m, P(3)]
106.2 [m, P(6)], 16.2 [br, P(1), P(5)], 12.2
[m, P(4), P(2)], −40.8 [m, P(3)]
1050 ([M+] nCO, 49.24 (49.13)
n=1–7)
1050 ([M+] nCO, 49.16 (49.13)
n=1–7)
211.0 [s, CO], 206.0 [br, CO], 199.4 [br,
CO], 190.6 [br, CO], 137–128 [m, Ph]
185.2 [br, P(5), 144.0 [br, P(2)], 99.2 [br,
994 ([M+] nCO, 50.15 (49.53)
P(1)], 94.2 [m, P(6)], 60.2 [m, P(4)], −2.8 n=1–5)
[m, P(3)]
a Recorded in dichloromethane solution.
b 1H chemical shifts (l) in ppm relative to SiMe4 (0.0 ppm), coupling constants in Hz in CDCl3 at 293 K.
c Chemical shifts in ppm relative to SiMe4 (0.0), in CDCl3 at 293 K.
642
(
d 31P chemical shifts (l) in ppm relative to external 85% H3PO4 (0.0 ppm), {1H}-gated decoupled, measured in CDCl3 at 293 K.
e Calculated values in parentheses.
237
245

240
R.M. De Sil6a et al. / Journal of Organometallic Chemistry 642 (2002) 237–245
Table 2
average value for the metal–metal bond lengths of
,
Selected bond lengths (A) and bond angles (°) for 1
,
,
2.554 A while the CoꢀCo bond length of 2.582(2) A is
slightly longer. The two CoꢀS bonds of 2.171(3) and
Bond lengths
,
2.181(3) A are shorter than in the parent complex [MꢀS
Co(1)ꢀCo(2)
Co(2)ꢀFe(1)
Co(2)ꢀS(1)
Co(1)ꢀAs(1)
As(1)ꢀAs(2)
As(2)ꢀAs(3)
As(4)ꢀAs(5)
Mean CoꢀC
(carbonyl)
2.582(2)
2.530(2)
2.181(3)
2.355(2)
2.459(2)
2.453(2)
2.453(2)
1.788
Co(1)ꢀFe(1)
Co(1)ꢀS(1)
Fe(1)ꢀS(1)
Co(2)ꢀAs(3)
As(1)ꢀAs(6)
As(3)ꢀAs(4)
As(5)ꢀAs(6)
Mean FeꢀC
(carbonyl)
2.532(2)
2.171(3)
2.200(3)
2.352(2)
2.475(2)
2.456(2)
2.455(2)
1.78
,
2.158 A (av.)], whereas the FeꢀS bond distance of
,
2.200(3) A is longer. This lengthening of the FeꢀS bond
reflects the displacement of the apical sulphur atom
towards the substituted cobalt atoms. A probable cause
of the observed distortion is the build-up of electron
density on the Co2FeS core as a result of the equatorial
substitution of two cobalt carbonyl groups by cyclo-
(PhAs)6. Relief of the electron density accumulated on
the cobalt–cobalt edge of the metal triangle is achieved
by a more efficient overlap of the appropriate CoꢀFe
and CoꢀS orbitals. This would, therefore, result in the
short FeꢀCo distances and the displacement of the
sulphur atom towards the substituted Co atoms. A
similar effect has been reported for the complex [Co3(m-
CCH3)(m-Ph2PCH2PPh2)(CO)7] [11], in which a dis-
placement of the apical carbon atom towards the
phosphine-substituted cobalt atoms is observed.
Bond angles
Fe(1)ꢀCo(1)ꢀCo(2) 59.29(6)
Co(1)ꢀFe(1)ꢀCo(2) 61.35(6)
Fe(1)ꢀS(1)ꢀCo(2)
S(1)ꢀFe(1)ꢀCo(2)
Fe(1)ꢀCo(1)ꢀS(1)
As(1)ꢀAs(2)ꢀAs(3) 84.51(5)
As(2)ꢀAs(3)ꢀAs(4) 97.20(6)
As(4)ꢀAs(5)ꢀAs(6) 92.55(6)
Fe(1)ꢀCo(2)ꢀCo(1) 59.36(6)
Co(1)ꢀS(1)ꢀCo(2)
Fe(1)ꢀS(1)ꢀCo(1)
S(1)ꢀFe(1)ꢀCo(1)
Fe(1)ꢀCo(2)ꢀS(1)
As(2)ꢀAs(1)ꢀAs(6)
As(5)ꢀAs(4)ꢀAs(3) 101.68(5)
As(5)ꢀAs(6)ꢀAs(1) 98.72(6)
72.81(10)
70.80(10)
54.06(9)
55.08(8)
94.08(5)
70.55(10)
54.37(8)
55.14(8)
Mean AsꢀAsꢀAs
94.79
The spectroscopic properties of 1 are in accord with
the solid-state structure being maintained in solution.
Three strong w(CO) bands and one weak band are
visible in the IR spectrum which is comparable with the
spectra of the structurally related complexes [Co2Fe(m3-
S)(m-Ph2PCH2SR)(CO)7] (R=Me, Ph) [7]. In the
13C{1H}-NMR spectrum at 293 K, the iron-bonded
carbonyl groups exchange rapidly at this temperature
and give rise to a single sharp signal at l 212.0 while
the cobalt-bonded carbonyl groups are seen as two
broad resonances at l 209.0 and 200.0.
The reaction of [Co2Fe(m3-S)(CO)9] with an equimo-
lar amount of cyclo-(PhP)6 in toluene at 70 °C for 22
h, gives two isomers, [Co2Fe(m3-S){m-cyclo-(PhP)6}-
(CO)7] (2) and [Co2Fe(m3-S){m-cyclo-(PhP)6}(CO)7] (3),
in ca. 1:1 yield (Scheme 1). The complexes have been
1
characterised using IR, H-, 13C- and 31P-NMR spec-
troscopies, mass spectrometry and by elemental analysis
(Table 1). In addition, complex 2 has been structurally
characterised using X-ray crystallography. The struc-
ture of 2 is depicted in Fig. 2 and selected bond
distances and angles are collected in Table 3.
Crystals suitable for the analysis were grown by slow
evaporation of hexane into a dichloromethane solution
of 2. The structure of 2 is similar to that of 1 with two
equatorial cobalt-bound carbonyl groups in [Co2Fe(m3-
S)(CO)9] formally replaced by phosphorus atoms in the
1,5 positions of the intact cyclo-hexaphosphane ring.
The average PꢀPꢀP angle of 96.6° in the phosphorus
ring is close to the value of that found in free cyclo-
(PhP)6 (95.5°) [12]. The P(1)ꢀP(2)ꢀP(3) angle 90.5(3)°, is
smaller than any angle of the free ligand, allowing the
two phosphorus atoms in the 1,5 positions of the ring
Fig. 2. Molecular structure of [Co2Fe(m3-S){m-cyclo-(PhP)6}(CO)7] (2)
including the atom numbering scheme. All hydrogen atoms have been
omitted for clarity.
change to minimise the intra-molecular interactions of
the phenyl rings with the sulphur atom and the car-
,
bonyl groups. The average CoꢀAs distance of 2.35 A,
agrees closely with the CoꢀAs distances in the related
species [10]. The replacement of the two equatorial
carbonyl groups by two As atoms causes the following
changes to the Co2FeS cluster core in the parent com-
,
plex. The CoꢀFe distances of 2.532(2) and 2.530(2) A
,
are shorter than in the parent molecule, which has an
to efficiently bridge the CoꢀCo distance [2.570(4) A].

R.M. De Sil6a et al. / Journal of Organometallic Chemistry 642 (2002) 237–245
241
,
The mean CoꢀP distance of 2.292 A in 2 can be
spectroscopy, the signals at l 17.2 and −41.8 have
been assigned to P(6) and P(3), respectively.
compared to the CoꢀP distances found in [Co3(m3-S)(m-
,
Ph2PCH2SPh)(CO)7] [2.207(3) A] [7] and [Co3(m-
CCH3)(m-Ph2PCH2PPh2)(CO)7] [2.23 A (av.)] [11]. As in
The spectroscopic properties of 3 are closely similar
to those of 2, suggesting that they have similar struc-
tures. This poses the question of how the structures of
2 and 3 differ from one another. The unequivocal
identification of 3 by single crystal X-ray diffraction
proved unsuccessful as crystals suitable for the analysis
could not be obtained. However, the four terminal
carbonyl IR bands observed for 3 are located at virtu-
ally identical wavenumbers to those in 2, suggesting
that the bridging of the six-membered ring across the
dicobalt bond and the carbonyl arrangement around
the metal atoms is similar in both cases. The mass
spectrometric data along with the elemental analyses
confirm that the two complexes have the same empiri-
cal formulae and it is clear from these data that they
are isomers.
,
1, the displacement of the apical sulphur atom towards
the CoꢀCo bond is clear in the structure of 2, from the
,
presence of two CoꢀS [2.179(7), 2.176(7) A] and one
,
FeꢀS [2.193(7) A] bond of unequal length. Unlike in 1,
,
however, only the Co(1)ꢀFe(1) [2.553(4) A] distance is
,
significantly shorter than the Co(1)ꢀCo(2) [2.570(4) A]
,
bond with the Co(2)ꢀFe(1) bond [2.574(4) A] being,
within experimental error, the same.
The spectroscopic properties of 2 are consistent with
the solid-state structure being maintained in solution.
Three strong w(CO) bands and one weak band are
visible in the IR spectrum at frequencies similar to
those for [Co2Fe(m3-S)(m-Ph2PCH2SR)(CO)7] (R=Me,
Ph) [7] and isostructural 1. As with 1 the 13C{1H}-
NMR spectrum of 2 displays a sharp downfield signal
(l 212.0) and two more upfield broad signals (l 210.0
and 199.0) in the carbonyl region implying that the
three carbonyl ligands residing on the unsubstituted
iron atom in 2 are fluxional at 293 K.
The 31P{1H}-NMR spectrum of 3 resembles that of
2, although it is noteworthy that one signal in 3 is
considerably more downfield than any in 2. Signifi-
cantly, as for 2, only four signals are observed for 3,
again implying a plane of symmetry passing through
Fe, S, the midpoint of the CoꢀCo bond and two
phosphorus atoms of the cyclo-hexaphosphane ring.
However, the signals at l 106.2, 16.2, 12.2, −40.8 have
an integral ratio of 1:2:2:1, respectively, with the broad
signal at l 16.2 being attributed to the equivalent
coordinated phosphorus atoms and the sharper signal
at l 12.2 to the equivalent non-coordinated phosphorus
atoms. Two possible isomeric structures for 3 are
shown in Scheme 1. Structure (a) differs from 2 in the
orientation adopted by the Co2FeS core relative to the
(PhP)6 ring. In 2 the X-ray diffraction study shows that
the sulphur atom is closest to that part of the (PhP)6
ring which contains three uncoordinated phosphorus
atoms. Therefore, it can be suggested that in 3(a) the
sulphur atom is directed towards that part of the (PhP)6
ring which contains the one uncoordinated phosphorus
atom. Alternatively, we cannot rule out isomer 3(b)
which differs from 2 in the orientations adopted by the
phenyl groups and lone pairs attached to the uncoordi-
nated P atoms. Only one of several such possible inver-
sion isomers for 3 is depicted in Scheme 1. Notably, this
type of inversion isomerism has been observed for
cyclo-(PhP)5 coordinated to a triosmium framework
[13,14]. The spectroscopic data for 1 do not allow us to
rule out the possibility that a similar set of isomers
exists for 1 even though, in contrast to the analogous
phosphorus species, only one product band is observed
on the TLC plates. It is noteworthy that a related set of
isomers has been proposed for [Co2(m-PhCCPh){m-cy-
clo-(PhAs)6}(CO)4] [4].
The 31P{1H}-NMR spectrum of 2 shows four signals
at l 19.2, 17.2, −6.8, −41.8, with an integral ratio of
2:1:2:1, respectively, and consistent with 2 possessing an
approximate mirror plane of symmetry passing through
Fe, S, the midpoint of the CoꢀCo bond, P(3) and P(6)
(see Fig. 2). The broad signal at l 19.2 can be at-
tributed to the two equivalent phosphorus atoms P(1)
and P(5) coordinated to the quadrupolar cobalt atoms
and the signal at l −6.8, to the two non-coordinated
equivalent phosphorus atoms P(2) and P(4). Through
the use of two-dimensional COSY-90 31P{1H}-NMR
Table 3
,
Selected bond lengths (A) and bond angles (°) for 2
Bond lengths
Co(1)ꢀCo(2)
Co(2)ꢀFe(1)
Co(2)ꢀS(1)
Co(1)ꢀP(1)
P(1)ꢀP(2)
P(2)ꢀP(3)
P(4)ꢀP(5)
2.570(4)
2.574(4)
2.179(7)
2.235(6)
2.250(8)
2.225(8)
2.250(8)
1.76
Co(1)ꢀFe(1)
Co(1)ꢀS(1)
Fe(1)ꢀS(1)
Co(2)ꢀP(5)
P(1)ꢀP(6)
P(3)ꢀP(4)
P(5)ꢀP(6)
2.553(4)
2.176(7)
2.193(7)
2.249(7)
2.225(8)
2.243(8)
2.237(8)
1.77
Mean CoꢀC
(carbonyl)
Mean FeꢀC
(carbonyl)
Bond angles
Fe(1)ꢀCo(1)ꢀCo(2)
Co(1)ꢀFe(1)ꢀCo(2)
Fe(1)ꢀS(1)ꢀCo(2)
S(1)ꢀFe(1)ꢀCo(2)
Fe(1)ꢀCo(1)ꢀS(1)
P(1)ꢀP(2)ꢀP(3)
P(2)ꢀP(3)ꢀP(4)
P(4)ꢀP(5)ꢀP(6)
Mean PꢀPꢀP
60.3(1)
60.2(1)
72.1(2)
53.7(2)
54.6(2)
103.3(3)
96.4(3)
94.7(3)
96.6
Fe(1)ꢀCo(2)ꢀCo(1)
Co(1)ꢀS(1)ꢀCo(2)
Fe(1)ꢀS(1)ꢀCo(1)
S(1)ꢀFe(1)ꢀCo(1)
Fe(1)ꢀCo(2)ꢀS(1)
P(2)ꢀP(1)ꢀP(6)
59.51(1)
72.3(2)
71.5(2)
53.9(2)
54.2(2)
94.1(3)
100.7(3)
90.5(3)
P(5)ꢀP(4)ꢀP(3)
P(5)ꢀP(6)ꢀP(1)
The thermolysis of 1–3, containing intact rings of
arsenic and phosphorus atoms, was carried out with the
intention of breaking AsꢀAs and PꢀP bonds in order to

242
R.M. De Sil6a et al. / Journal of Organometallic Chemistry 642 (2002) 237–245
m-RPS ligands have been structurally identified and the
,
PꢀS bond distance [2.081(2) A] in 4 lies in the mid-
,
range [15]. The average PꢀP bond length of 2.208 A
within the chain, may be compared with the average
,
PꢀP distance of 2.23 A in free cyclo-(PhP)6 [12]. The
average CoꢀP distances for the bridging phosphorus
atom P(5) are comparable with values obtained for
other phosphido-bridged cobalt complexes [16]. The
phosphorus atoms bridging the FeꢀCo metal centres
[P(6) and P(1)] also have metal–phosphorus distances
similar to other phosphido-bridged FeꢀCo complexes
[17] with the Fe(1)ꢀP(6)ꢀCo(2) angle larger than
Fe(1)ꢀP(1)ꢀCo(1) angle [115.34(9) vs. 76.09(7)°] and
consistent with the absence of a metal–metal bond
between Fe(1) and Co(2). Interestingly, the large
,
Fe(1)ꢀP(6)ꢀCo(2) angle means the P(6) atom is 2.636 A
away from Co(1), suggesting there is a very weak
interaction between the two atoms. The two CoꢀS bond
,
distances of 2.288(3) and 2.261(3) A fall at the top end
of the range reported for CoꢀS distances [18] in SR-
bridged dicobalt–carbonyl complexes. The average
PꢀPꢀP bond angle of 103.45°, is larger than any of the
Fig. 3. Molecular structure of [Co2Fe(m3-SPPh)(m-h2:h2:h1-
P5Ph5)(CO)5] (4) including the atom numbering scheme. All hydrogen
atoms have been omitted for clarity.
Table 4
examine the effect of having exchanged the acetylenic
fragment in [Co2(m-CRCR)(CO)6] for the (OC)3FeS
unit. Thermolysis of 2 and of 3 in toluene at 120 °C for
3 h gives [Co2Fe(m3-SPPh)(m-h2:h2:h1-P5Ph5)(CO)5] (4)
as a brown crystalline complex in 40% yield (Scheme 1).
However, the thermolysis of 1 under similar reaction
conditions leads to complete decomposition of 1. Com-
plex 4 has been characterised by IR, 1H-, 13C-, 31P-
NMR spectroscopies, mass spectrometry and elemental
analysis. Complex 4 has also been the subject of a
single crystal X-ray diffraction study. A view of the
structure of 4 is illustrated in Fig. 3 and selected bond
distances and angles are listed in Table 4.
Suitable crystals of 4 were grown by the slow diffu-
sion of hexane into a dichloromethane solution of 4.
The molecule is constructed around a distorted tetrahe-
dral core, containing two cobalt atoms, a phosphorus
atom and a sulphur atom. The edges Co(1)ꢀP(6) and
Co(1)ꢀCo(2) of the tetrahedron, are bridged by a
Fe(CO)3 group and a phosphorus atom, P(5), respec-
tively. Both cobalt atoms, Co(1) and Co(2), are coordi-
nated by atoms S(1), P(5) and one carbonyl ligand. In
addition, Co(1) is coordinated by the Fe(1) atom and
P(1) while Co(2) is coordinated by P(2) and P(6). In this
reaction the cyclo-(PhP)6 ring has undergone ring open-
ing and breaking to form a P5Ph5 chain and a PPh unit.
The end phosphorus atoms of the P5 chain, P(1) and
P(5), act as three-electron donors; P(1) bridges the
Co(1) and Fe(1) atoms, while P(5) bridges Co(1) and
Co(2). The PPh unit formed in the ring cleavage during
thermolysis of 2 and 3 has undergone coupling with the
sulphur cap to the bridging PhPS ligand in 4. Related
,
Selected bond lengths (A) and bond angles (°) for 4
Bond lengths
Fe(1)ꢀP(6)
Fe(1)ꢀCo(1)
Co(1)ꢀP(5)
Co(1)ꢀCo(2)
Co(2)ꢀP(2)
Co(2)ꢀP(5)
S(1)ꢀP(6)
2.225(3)
2.706(1)
2.200(2)
2.430(3)
2.163(2)
2.187(2)
2.081(2)
2.225(2)
2.457(3)
Fe(1)ꢀP(1)
Co(1)ꢀP(1)
Co(1)ꢀS(1)
Co(1)ꢀP(6)
Co(2)ꢀP(6)
Co(2)ꢀS(1)
P(1)ꢀP(2)
2.228(2)
2.162(2)
2.288(3)
2.636(3)
2.177(2)
2.261(3)
2.190(3)
2.201(3)
P(2)ꢀP(3)
P(4)ꢀP(5)
P(3)ꢀP(4)
Bond angles
P(6)ꢀFe(1)ꢀP(1)
P(1)ꢀFe(1)ꢀCo(1)
P(1)ꢀCo(1)ꢀS(1)
P(1)ꢀCo(1)ꢀCo(2)
S(1)ꢀCo(1)ꢀCo(2)
P(5)ꢀCo(1)ꢀP(6)
Co(2)ꢀCo(1)ꢀP(6)
P(5)ꢀCo(1)ꢀFe(1)
87.81(9)
50.86(5)
127.88(8)
84.90(10)
57.17(7)
106.57(9)
50.72(6)
142.99(6)
P(6)ꢀFe(1)ꢀCo(1)
P(1)ꢀCo(1)ꢀP(5)
P(5)ꢀCo(1)ꢀS(1)
P(5)ꢀCo(1)ꢀCo(2)
P(1)ꢀCo(1)ꢀP(6)
S(1)ꢀCo(1)ꢀP(6)
P(1)ꢀCo(1)ꢀFe(1)
S(1)ꢀCo(1)ꢀFe(1)
P(6)ꢀCo(1)ꢀFe(1)
P(2)ꢀCo(2)ꢀP(5)
P(2)ꢀCo(2)ꢀS(1)
P(5)ꢀCo(2)ꢀS(1)
P(6)ꢀCo(2)ꢀCo(1)
S(1)ꢀCo(2)ꢀCo(1)
P(6)ꢀS(1)ꢀCo(1)
Co(1)ꢀP(1)ꢀP(2)
P(2)ꢀP(1)ꢀFe(1)
Co(2)ꢀP(2)ꢀP(3)
P(4)ꢀP(3)ꢀP(2)
63.75(7)
100.40(8)
87.36(9)
56.11(8)
79.45(8)
49.39(6)
53.05(5)
91.25(7)
49.21(7)
89.66(8)
138.76(7)
88.35(9)
69.53(8)
58.24(8)
74.04(8)
93.29(10)
111.70(9)
114.62(8)
100.36(9)
67.26(9)
123.73(9)
112.49(10)
56.57(7)
67.04(7)
Co(2)ꢀCo(1)ꢀFe(1) 92.67(8)
P(2)ꢀCo(1)ꢀP(6)
P(6)ꢀCo(2)ꢀP(5)
P(6)ꢀCo(2)ꢀS(1)
P(2)ꢀCo(2)ꢀCo(1)
P(5)ꢀCo(2)ꢀCo(1)
P(6)ꢀS(1)ꢀCo(2)
Co(2)ꢀS(1)ꢀCo(1)
Co(1)ꢀP(1)ꢀFe(1)
Co(2)ꢀP(2)ꢀP(1)
P(1)ꢀP(2)ꢀP(3)
93.62(7)
125.78(9)
55.89(7)
86.89(10)
56.62(7)
60.03(7)
64.59(8)
76.09(7)
91.05(10)
108.98(10)
101.03(9)
117.89(10)
64.08(7)
115.34(9)
59.75(8)
P(3)ꢀP(4)ꢀP(5)
Co(2)ꢀP(5)ꢀCo(1)
Co(1)ꢀP(5)ꢀP(4)
S(1)ꢀP(6)ꢀFe(1)
S(1)ꢀP(6)ꢀCo(1)
Fe(1)ꢀP(6)ꢀCo(1)
Co(2)ꢀP(5)ꢀP(4)
S(1)ꢀP(6)ꢀCo(2)
Co(2)ꢀP(6)ꢀFe(1)
Co(2)ꢀP(6)ꢀCo(1)

R.M. De Sil6a et al. / Journal of Organometallic Chemistry 642 (2002) 237–245
243
bond angles in cyclo-(PhP)6 reflecting a considerable
strain in the P5 chain.
in commercial Merck plates with a 0.25 mm layer of
silica, or in 1 mm silica plates prepared at the Depart-
ment of Chemistry, Cambridge. Column chromatogra-
phy was performed on Kieselgel 60 (70–230 or
230–400 mesh). Products are given in order of decreas-
ing Rf values. Elemental analyses were performed at the
Department of Chemistry, Cambridge.
Unless otherwise stated all reagents were obtained
from commercial suppliers and used without further
purification. The syntheses of [Co2Fe(m3-S)(CO)9] [20],
cyclo-(PhAs)6 [9] and cyclo-(PhP)6 [12] have been re-
ported previously.
The spectroscopic properties of 4 are consistent with
the solid-state structure being maintained in solution.
The IR spectrum shows two strong and broad carbonyl
bands in the terminal carbonyl region which can be
attributed to the three iron- and two cobalt-bound
carbonyl groups. The 13C{1H}-NMR spectrum shows,
in addition to resonances corresponding to phenyl
groups, four terminal carbonyl resonances. Two sharp
peaks at l 211.0 and 190.6 can be assigned to the three
carbonyls bound to the iron and the two broad signals
at l 206.0 and 199.4 to the two carbonyls bound to the
quadrupolar cobalt atoms. The 31P{1H}-NMR spec-
trum of 4 displays six signals corresponding to the six
unique environments for the phosphorus atoms. The
three broad signals at low field (l 185.2, 144.0, 99.2)
can undoubtedly be assigned to the cobalt-bound phos-
phorus atoms. The assignment of the fourth cobalt-
bound phosphorus atom was established using
two-dimensional COSY-90 31P{1H}-NMR as P(6) (l
94.2) while the uncoordinated phosphorus centres P(3)
and P(4) correspond to the signals at l −2.8 and 60.2,
respectively.
In conclusion, the reaction of [Co2Fe(m3-S)(CO)9]
with cyclo-(PhX)6 (X=As, P) leads in the first instance
to complexes 1, 2 and 3, in which an intact CPA or
CPP ring bridges the dicobalt vector in a manner that
has previously been observed for the transverse
alkyne–dicobalt complexes [Co2(m-CRCR){m-cyclo-
(PhX)6}(CO)4]. Unlike the thermolytic reactions of
[Co2(m-CRCR){m-cyclo-(PhX)6}(CO)4], the well charac-
terised complex 4 is identified on thermolysis of 2 and
3, resulting from fragmentation of the CPP to give a
P5Ph5 chain and PPh unit (which additionally under-
goes coupling with the sulphur cap). Notably, thermol-
ysis of 1 yields only uncharacterised decomposition
products.
3.1. Reaction of [Co2Fe(v3-S)(CO)9] with cyclo-(PhAs)6
The complex [Co2Fe(m3-S)(CO)9] (0.114 g, 0.25
mmol) and cyclo-(PhAs)6 (0.228 g, 0.25 mmol) were
dissolved in toluene (10 ml) in a Schlenk flask. The
Schlenk flask was evacuated with three freeze-pump-
thaw cycles and closed under vacuum. The mixture was
stirred at 70 °C for 23 h. After cooling the reaction
mixture was opened to the air and the solution filtered.
The filtrate was then concentrated under reduced pres-
sure and the residue dissolved in the minimum CH2Cl2,
absorbed onto silica and added to the top of a chro-
matography column. Elution using hexane–CH2Cl2
(4:1) gave dark brown crystalline [Co2Fe(m3-S){m-cyclo-
(PhAs)6}(CO)7] (1) (0.30 g, 91%).
3.2. Reaction of [Co2Fe(v3-S)(CO)9] with cyclo-(PhP)6
The complex [Co2Fe(m3-S)(CO)9] (0.114 g, 0.25
mmol) and cyclo-(PhP)6 (0.162 g, 0.25 mmol) were
dissolved in toluene (10 ml) in a Schlenk flask. The
Schlenk flask was evacuated with three freeze-pump-
thaw cycles and closed under vacuum. The mixture was
stirred at 70 °C for 23 h. After cooling the reaction
mixture was opened to the air and the solution filtered.
The filtrate was then concentrated under reduced pres-
sure, the residue dissolved in the minimum CH2Cl2 and
the solution applied to the base of silica TLC plates.
Elution with hexane–CH2Cl2 (4:1) gave the green solid
[Co2Fe(m3-S){m-cyclo-(PhP)6}(CO)7] (2) (0.05 g, 20%)
followed by dark green crystalline [Co2Fe(m3-S){m-cy-
clo-(PhP)6}(CO)7] (3) (0.06 g, 24%).
3. Experimental
All reactions were carried out under an atmosphere
of dry, oxygen-free nitrogen, using standard Schlenk
techniques. Solvents were distilled under nitrogen from
appropriate drying agents and degassed prior to use
[19]. Infrared spectra were recorded in hexane solution
in 0.5 mm NaCl cells, using a Perkin–Elmer 1710
Fourier-transform spectrometer. Fast atom bombard-
ment mass spectra (FABMS) were recorded in a Kratos
MS 890 instrument using 3-nitrobenzyl alcohol as a
matrix. Proton (reference to SiMe4), 31P-NMR and
13C-NMR spectra were recorded in either a Bruker
WM250 or AM400 spectrometer; 31P-NMR chemical
shifts are referenced to external 85% H3PO4. Prepara-
tive thin-layer chromatography (TLC) was carried out
3.3. Thermolysis of complexes 1–3
(i) Thermolysis of a solution of [Co2Fe(m3-S){m-cyclo-
(PhAs)6}(CO)7] (1) (0.10 g, 0.076 mmol) in toluene (50
ml) at 120 °C for 3 h led to complete decomposition as
indicated by TLC.
(ii) A solution of [Co2Fe(m3-S){m-cyclo-(PhP)6}(CO)7]
(2) or [Co2Fe(m3-S){m-cyclo-(PhP)6}(CO)7] (3) (0.05 g,
0.05 mmol) in toluene (25 ml) was thermolysed at
120 °C for 3 h. The solvent was removed under re-

244
R.M. De Sil6a et al. / Journal of Organometallic Chemistry 642 (2002) 237–245
Table 5
Crystal data and structure refinement parameters for complexes 1, 2 and 4
Complex
1
2
4
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
Unit cell dimensions
C43H30As6Co2FeSO7
1313.96
150(2)
Monoclinic
P21/n
C
43H30P6Co2FeSO7
C41H30P6Co2FeSO5
994.24
180(2)
1050.26
293(2)
Orthorhombic
Pna21
Triclinic
(
P1
,
a (A)
15.089(4)
16.322(5)
18.613(7)
90
96.97(3)
90
4550(3)
4
21.326(6)
17.569(4)
13.678(6)
90
90
90
5125(3)
4
11.830(9)
18.423(7)
10.701(12)
97.35(6)
116.01(6)
94.83(5)
2053(3)
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
2
Dcalc (mg m−3
F(000)
)
1.918
2552
1.361
2120
1.608
1004
Crystal size (mm)
0.30×0.30×0.18
5.459
0.20×0.20×0.15
1.190
0.30×0.20×0.20
1.476
v (Mo–Ka) (mm−1
)
Reflections collected
Independent reflections
Rint
20 337
7276
0.0862
7009
4995
0.0996
11 486
9422
0.0674
Parameters/restraints
Final R indices [I\2|(I)]
541/0
327/1
505/0
R1=0.0856, wR2=0.1267
R1=0.1195, wR2=0.2454
R1=0.0596,
wR2=0.1422
R1=0.1010,
wR2=0.1664
All data
R1=0.1079, wR2=0.1664
R1=0.1421, wR2=0.2795
1
2
2
2 2
2 2
−1
,
Data in common: graphite-monochromated Mo–Ka radiation, u=0.71073 A; R1=ꢀꢁ ꢁFoꢁ−ꢁFcꢁ ꢁ/ꢀꢁFoꢁ, wR2=[ꢀw(Fo−Fc) /ꢀw(Fo) ] , w
=
[|2(Fo)2+(aP)2], P=[max(Fo2,0)+2(Fc2)]/3, where a is a constant adjusted by the program; goodness-of-fit=[ꢀ(Fo2−F2c)2/(n−p)]1/2 where n is the
number of reflections and p the number of parameters.
4. Supplementary material
duced pressure, the residue dissolved in the minimum
quantity of CH2Cl2 and the solution applied to the base
of preparative TLC plates. Elution using hexane–
CH2Cl2 (4:1) gave brown crystalline [Co2Fe(m3-
SPPh)(m-h2:h2:h1-P5Ph5)(CO)5] (4) (0.02 g, 40%).
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC nos. 167868–167870 for com-
pounds 1, 2, 3 and 4, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
3.4. Crystallography
X-ray intensity data was collected using Rigaku
RAXIS-IIC image plate (1 and 2) and AFC7R diffrac-
tometers (4). Both systems were equipped with an Ox-
ford Cryosystems Cryostream. Details of data
collection, refinement and crystal data are listed in
Table 5. Semiempirical absorption corrections based on
€-scan data were applied [21,22] to the data for 4; no
absorption correction was applied to the data for 1 and
2. The structures were solved by direct methods
Acknowledgements
We gratefully acknowledge the financial support of
the Cambridge Commonwealth Trust and the United
Kingdom Committee of Vice Chancellors and Princi-
pals (to R.M.D.S.). Thanks are also due to Dr J.E.
Davies for collection of the X-ray data.
(SHELXS 86 [23]) and subsequent Fourier-difference syn-
theses and refined anisotropically on all ordered non-
hydrogen atoms by full-matrix least-squares on F2
References
(SHELXL 93 [24]). Hydrogen atoms were placed in geo-
metrically idealised positions and refined using a riding
model. In the final cycles of refinement a weighting
scheme was introduced which produced a flat analysis
of variance.
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