CpCr(CO)3■-initiated N-N bond cleavage in a thiotetrazole ligand in a cyclopentadienylchromium complex

Article abstract of DOI:10.1016/j.jorganchem.2004.11.045

The tetrazolylthiolato complex CpCr(CO)₃(STz) (4a) was obtained from the facile reaction between [CpCr(CO)₃]₂ (Cp = C ₅H₅) (1) and 5,5′-dithiobis(1-phenyl-1H-tetrazole), (abbrev. (PhN₄CS)₂ or (STz)₂). Further reaction of 4a with 1 under thermolytic conditions led to isolation of low yields of the cubane-like complexes Cp₄Cr₄S₃(μ ₃-N₃Ph) (5), Cp₄Cr₄S ₂(μ₃-CO)(μ₃-NC≡CrCp(CO) ₂) (6), Cp₄Cr₄S₂(μ₃- N₃Ph)(μ₃-NC≡CrCp(CO)₂) (7) and Cp ₄Cr₄SO₂(μ₃-NPh) (8), containing μ₃-phenyltriazenido, imidocarbyne and phenylimido groups at the corners of cuboids, in addition to μ₃-sulfide, oxo or carbonyl groups. The predominant products were the decarbonylation derivative of 1, i.e. [CpCr(CO)₂]₂(Cr≡Cr) (9), together with [CpCr(CO)₂]₂S (10) and its thermolytic cuboidal derivatives, mainly Cp₄Cr₄S₂O₂ (11) and Cp₄Cr₄S₄ (13). 1-initiated homolytic fragmentation of the tetrazole ring was proposed to rationalize the formation of the derived cubanes. The structures of the complexes 4a, 6-8 and 11 have been determined by single X-ray diffraction analysis.

Full text of DOI:10.1016/j.jorganchem.2004.11.045

Journal of Organometallic Chemistry 690 (2005) 1157–1165
www.elsevier.com/locate/jorganchem
Å
CpCrðCOÞ -initiated N–N bond cleavage in a thiotetrazole ligand in a
3
cyclopentadienylchromium complex
Victor Wee Lin Ng, Zhiqiang Weng, Jagadese J. Vittal, Lip Lin Koh,
*
Geok Kheng Tan, Lai Yoong Goh
Department of Chemistry, National University of Singapore, Kent Ridge, Singapore 119260, Singapore
Received 23 September 2004; accepted 15 November 2004
Available online 7 February 2005
Abstract
The tetrazolylthiolato complex CpCr(CO)3(STz) (4a) was obtained from the facile reaction between [CpCr(CO)3]2 (Cp = C5H5)
(1) and 5,50-dithiobis(1-phenyl-1H-tetrazole), (abbrev. (PhN4CS)2 or (STz)2). Further reaction of 4a with 1 under thermolytic con-
ditions led to isolation of low yields of the cubane-like complexes Cp4Cr4S3(l3-N3Ph) (5), Cp4Cr4S2(l3-CO)(l3-NC„CrCp(CO)2)
(6), Cp4Cr4S2(l3-N3Ph)(l3-NC„CrCp(CO)2) (7) and Cp4Cr4SO2(l3-NPh) (8), containing l3-phenyltriazenido, imidocarbyne and
phenylimido groups at the corners of cuboids, in addition to l3-sulfide, oxo or carbonyl groups. The predominant products were
the decarbonylation derivative of 1, i.e. [CpCr(CO)2]2(Cr„Cr) (9), together with [CpCr(CO)2]2S (10) and its thermolytic cuboidal
derivatives, mainly Cp4Cr4S2O2 (11) and Cp4Cr4S4 (13). 1-initiated homolytic fragmentation of the tetrazole ring was proposed to
rationalize the formation of the derived cubanes. The structures of the complexes 4a, 6–8 and 11 have been determined by single X-
ray diffraction analysis.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Cyclopentadienylchromium; Thiotetrazole; Phenyltriazenido; Imidocarbyne; Phenylimido; Cubanes
1. Introduction
cleaved C–X (X = C, N, S) and Cr–X (X = N, S)
bonds, giving radical species which are the precursors
of the products. (Schemes 1 and 2) Having observed
1-initiated extensive fragmentation of the metal chelate
rings in 2a and the N-coordinated heterocyclic thiazole
ring of 3, we have extended this investigation to an N-
rich heterocyclic ligand, in order to test the capability
of 1 to also cleave N–N bonds in a coordinated moiety,
which has not been demonstrated before. We have se-
lected for this purpose 5,50-dithiobis(1-phenyl-1H-tetra-
zole) ((STz)2) (see Scheme 3) for various reasons, which
include the special interest in heterocycles on account
of their presence as a component in many bioactive
molecules [7], and in particular, the coordination versa-
tility in mercapto-tetrazole arising from the presence of
at least three potential nitrogen donor sites and an
Our previous studies have shown that the ease with
which [CpCr(CO)3]2 (Cp = g5-C5H5) (1) cleaves non-
metal–nonmetal bonds decreases in the order: X–X
(X = S, Se, Te) > P–X (X = S, Se) > P–P, to form a
variety of complexes of CpCr(CO)n (n = 2, 3) [1–4]. In
recent investigations with C-, N- and S-containing or-
ganic disulfides, in particular with tetraalkylthiuram
disulfanes [5] and dibenzothiazolyl disulfane [6], we
have obtained complexes of different structural geome-
tries belonging to various class types, which indicate
that under thermolytic conditions 1 has efficiently
*
Corresponding author. Tel.: +65 68742677; fax: +65 67791691.
E-mail address: chmgohly@nus.edu.sg (L.Y. Goh).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.045

1158
Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
Cr
Cr
Cr
S
O
OC
OC
OC
OC
OC
OC
C
C
C
N
R
R
C
N
R
R
HC
N
R
R
N
R
2b
2c
2d
R
S
1
Cr
S
Cr
OC
OC
OC
OC
S
C
S
C
N
R
R
N
OC
R
S
Cr
S
Cr
Cr
S
Cr
S
S
Cr
S
S
Cr
S
S
S
Cr
Cr
S
S
R
S
Cr
Cr
Cr
2a
Cr
Cr
2
S
Cr
Cr
Cr
S
S
S
C
S
S
S
S
C
S
C
N
C
N
N
R
N
R
2e
2f
R
R
R
R
R
R
Scheme 1. Cr–Cr bonds in cubanes 2e and 2f are omitted for clarity.
N
N
S
S
S
S
Cr
Cr
S
Cr
S
C
C
Cr
S
Cr
C
N
H
N
N
S
S
N
Cr
O
1
S
Cr
N
Cr
Cr
N
S
Cr
CO
S
OC
Cr
OC
Cr
Cr
N
S
CO
Cr
S
Cr
S
Cr
OC
OC
S
Cr
C
N
S
N
Cr
C
S
Cr
S
S
3
3b
3a
3d
3c
Scheme 2. Cr–Cr bonds in cubanes 3b and 3c are omitted for clarity.
N
N
N N
N
N
N
N
S
S
N
N
Cr
N
Cr
N
N
N
OC
OC
Insoluble
Purple
Solid
OC
OC
OC
N
S
2
+
2
Cr
N
S
OC
OC
OC
1a
(STz)2
4a
Scheme 3.
4b
exocylic thiolate sulfur atom [8,9], the growing interest
in compounds of tetrazoles for biological, medicinal
and agricultural applications [8,10] and their potential
usage as building blocks in the formation of polymers
and supramolecules for conductivity and optical-related
applications [11]. More importantly in the context of
this aspect of our research is the presence of a poten-
tially aromatic 6p CN4 tetrazole ring in the anticipated
product, chromium 5-mercapto(1-phenyl-1H-tetrazole)
(CpCr(CO)n STz) complexes (4a: n = 3 or 4b: n = 2);
furthermore any forthcoming mechanistic information
on ring-opening of such heterocycles relates to the cur-
rent wider interest of such phenomena in biomolecules
[7e]. This paper describes the reaction of 1 with (STz)2
and the subsequent interaction of the primary product
with 1, resulting in fragmentation of the heterocyclic
ring.
2. Results and discussion
A facile reaction between[CpCr(CO)3]2 (1) with 1 mol
equiv. of 5,50-dithiobis(1-phenyl-1H-tetrazole) (abbrev.
(SCN4Ph)2 or (STz)2) in toluene at ambient temperature
produced a magenta solution, from which a workup at
room temperature gave bright red crystals of
CpCr(CO)3(STz) (4a) in 33% yield, which could be max-
imized to 79% by rapidly cooling and maintaining the
product solution at ꢀ30 ꢁC for 4 days (Scheme 3).
Low temperature slowed down considerably the facile
decomposition of 4a to an insoluble purple amorphous
non-characterizable solid, via an unstable intermediate
1
derivative 4b, identified on the basis of its H NMR
and IR spectral characteristics (Scheme 3). Precedents
of such four-membered CrSCN rings are complexes 3
[6], A and B [12], which we have recently synthesized

Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
1159
CO
OC
OC
Cr
Cr
OC
CO
CO
S
N
S
2
1
HSPym
OC
SPy
N
2
Cr
N
Cr
OC
OC
N
S
S
N
OC
Cr
S
OC
OC
3
B
S
δ(Cp) 4.51
v(CO) 1949s, 1878s (cm-1
δ(Cp) 4.36
v(CO) 1960s, 1875s (cm-1
A
)
)
δ(Cp) 4.44
v(CO) 1950s, 1878s (cm-1
)
Scheme 4.
(Scheme 4) and the Cp* analogue of A from the work of
Hoff and co-workers [13].
As proposed previously for the reactions of 1 with
available for 4a; for the others the low yields rendered
this non-feasible even after repeat reactions. The struc-
ture of 5 was not available, but its elemental composi-
tion was supported by its microanalytical data and
mass spectrum which shows the mother ion, while its
proposed structural formulation is consistent with the
1H and 13C NMR spectra which show the presence of
two pairs of equivalent Cp rings, and with the presence
of m(N–N@N) in the IR spectrum at a frequency very
close to that in complex 7.
disulfanes [1,2], it is proposed that this reaction is also
Å
initiated by the homolytic attack of fCpCrðCOÞ g
3
(1a), the incumbent 17-electron organometallic radical
from the facile dissociation of 1 [14], on the S–S bond
of (STz)2, generating complex 4a (Scheme 3).
The thermal interaction of 4a and 1 in refluxing tolu-
ene for 2 h produced a brown-black mixture, which
upon concentration gave a fine dark green solid (14),
accounting for ca. 24% of total weight of the reactants
(the proton NMR spectrum of this species indicated
the presence of four CpCr groups with three of them
in equivalent environments, while the mass spectrum
also supported a multinuclear species, but unfortunately
an X-ray crystal structure could not be obtained). Chro-
matographic workup of the supernatant gave an isolated
mixture of deep green crystals of [CpCr(CO)2]2 (9) and
[CpCr(CO)2]2S (10) in estimated yields of 34% and 8%,
respectively, the triazenido cubane Cp4Cr4S3(l3-N3Ph)
(5) as brown microcrystals (7%), the imidocarbyne cu-
bane Cp4Cr4S2(l3-CO)(l3-NCCrCp(CO)2) (6) as an
olive-green crystalline solid (2%), the phenyltriazenido-
disulfido-imidocarbyne cubane Cp4Cr4S2(l3-N3Ph)-
(l3-NCCrCp(CO)2) (7) as a brown crystalline solid
(4%), the phenylimidodioxosulfido cubane complex
Cp4Cr4SO2(l3-NPh) (8) as a dirty-green crystalline solid
(2%), the dioxodisulfido cubane Cp4Cr4S2O2 (11) (9%)
as dark greenish crystals, the dicarbonyldisulfido cubane
Cp4Cr4S2(CO)2 (12) (5%) as dark greenish crystals and
the tetrasulfido cubane Cp4Cr4S4 (13) (17%), as pre-
sented in Scheme 5.
The molecular structure of CpCr(CO)3(SCN4Ph) (4a)
is shown in Fig. 1. The Cr center achieves a four-legged
piano-stool 18e configuration with coordination to g5-
Cp, the thiolate sulfur of STz and three terminal CO
˚
ligands. The S(1)–C(4) bond length of 1.730(2) A is
˚
within the range (1.6822(19)–1.7568(18) A) of the single
C–S bonds, that we have found for complexes CpCr
(CO)3(g1-S2CNMe2) (2) and CpCr(CO)2(g2-S2CNMe2)
(R = Me, Et, Pr) (2a) [5a]. The N–N distances (N(1)–
i
˚
N(2), 1.364(3) A; N(2)–N(3), 1.287(3) A; and N(3)–
˚
˚
N(4), 1.370(3) A) lie between PaulingÕs values for a sin-
˚
gle bond (1.48 A) and a double bond (1.22 A); likewise,
˚
the C(4)–N(1) and C(4)–N(4) bond lengths (1.3321(3)
˚
and 1.348(3) A, respectively) are between values for a
˚
˚
single bond (1.512 A) and a double bond (1.287 A)
[15]. These findings are indicative of p-electron delocal-
ization in the ring. The Cr(5)–S(1) distance of 2.4485(7)
˚
˚
A is very close to the value of 2.4406(5) A found in 2
[5a].
The molecular structures illustrated in Figs. 2–4 show
that the thermolytic products 6–8 all possess cubane
cores, which may be considered to be S-substituted
derivatives of the parent Cp4Cr4S4 cubane (13), the ther-
modynamic sink from degradation of [CpCr(CO)2]2S
(10) [1,16]; thus there exists cuboidal cores of Cr4S2NC
in 6, Cr4S2N2 in 7 and Cr4SNO2 in 8, and by inference
from elemental and spectroscopic data a core of Cr4S3N
The complexes 4a, 6–8 and 11, were structurally char-
acterized by X-ray diffraction analysis. Their formula-
tion was also supported by NMR, IR and mass
spectral data; however, microanalytical data were only

1160
Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
CO
OC
OC
Cr
Cr
Cr
N
N
OC
OC
OC
CO
CO
S
C
N
OC
N
1
4a
∆
Cr
Cr
S
Cr
Cr
S
Cr
OC
OC
C
S
N
Cr
Cr
S
S
Cr
S
Cr
Cr
Cr
S
Cr
O
OC
OC
Cr
N
N
C
Cr
N
N
O
Cr
N
+
N
+
+
N
S
Cr
Cr
N
Cr
C
O
6 (2%)
7 (4%)
8 (2%)
5 (7%)
OC
OC
OC
OC
Cr
Cr
S
X = O: 11 (9%)
X = CO: 12 (5%)
X = S: 13 (17%)
Unknown
14 (24%)
Cr Cr
+
Cr
S
Cr
+
X
+
S
Cr
CO
CO
CO
CO
Cr
X
9
(34%)
10 (8%)
Scheme 5. The four Cr–Cr bonds in the cubanes of 5–8 and 11–13 are omitted for clarity. Yields of all are given in mol% (based on 1), except that of
14 which is given as wt.% of total reactants, since its structural composition is unknown. Values for 9 and 10 were estimated.
Fig. 1. Molecular structure of CpCr(CO)3(SCN4Ph) (4a). Selected
˚
metric data: Cr(5)–S(1) 2.4485(7) A, S(1)–C(4) 1.730(2) A, N(1)–N(2)
˚
˚
˚
1.364(3) A, N(2)–N(3) 1.287(3) A, N(3)–N(4) 1.370(3) A, C(4)–N(1)
˚
˚
˚
˚
1.332(3) A, C(4)-N(4) 1.348(3) A, N(4)–C(5) 1.425(3) A, Cr(5)–S(1)–
C(4) 109.37(8)ꢁ, N(3)–N(4)–C(5) 120.58(18)ꢁ.
Fig. 2. Molecular structure of Cp4Cr4S3(l3-CO)(l3-NC„CrCp(CO)2)
(6). Selected metric data: in the cuboid, Cr–Cr 2.6320(11)–2.8092(12)
in 5. Selected metric data are given in the figure cap-
tions. A brief comparison is given here of notable fea-
tures. Both 6 and 7 possess a CpCr carbyne moiety
linked to a cuboidal imido vertex, with Cr„C distances
of 1.750(5) and 1.746(4) A, respectively; these values
compare favourably with the distances of 1.735(4)–
˚
A, Cr–S 2.2340(15)–2.2526(15) A, Cr–C(3) 2.041(6)–2.266(5) A and
˚
˚
˚
˚
Cr–N(1) 1.978(4)–1.997(4) A. Cr(5)„C(4) 1.750(5) A, C(4)–N(1)
˚
1.283(7) A, Cr(5)–C(4)–N(1) 178.2(4)ꢁ.
˚
˚
1.283(7) and 1.296(4) A, respectively, very close to ob-
˚
˚
served values of 1.278(5)–1.300(4) A [17] and 1.290(9)
1.745(3) A in the half-sandwich aminocarbyne com-
t
plexes CpCr(CNR2)(tBuNC)2X (X = Br, BuNC) [17],
A in 3a [6]. The Cr–C–N linkages are almost linear
(Cr(5)–C(4)–N(1) 178.2(4) and 178.9(3)ꢁ, respectively).
In the l3-(N–N@NPh) triazenido ligand of 7, the
˚
˚
1.740(2) A in CpCr(CO)2 (CNMe2) (2c) [5c] and
˚
1.733(7) A in 3a [6]. The C(4)–N(1) distances are

Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
1161
Fig. 4. Molecular structure of Cp4Cr4SO2(l3-NPh) (8). Selected metric
Fig. 3. Molecular structure of Cp4Cr4S3(l3-N3Ph)(l3-NC„CrCp-
(CO)2) (7). Selected metric data: in the cuboid, Cr–Cr 2.7031(9)–
˚
data: in the cuboid, Cr–Cr 2.6862(7)–2.7829(7) A, Cr–S 2.2802(9)–
˚
2.2880(10) A, Cr–O 1.898(2)–1.914(2) A and Cr–N 1.989(3)–1.992(3)
˚
˚
˚
2.8123(10) A, Cr–S 2.2388(13)–2.2532(13) A, and Cr–N 1.953(3)–
˚
A, N(4)–C(5) 1.421(4) A.
˚
˚
˚
˚
2.012(3) A, Cr(5)„C(4) 1.746(4) A, C(4)–N(1) 1.296(4) A, N(2)–N(3)
˚
˚
1.372(5) A, N(3)–N(4) 1.237(5) A, N(4)–C(5) 1.438(6) A, Cr(5)–C(4)–
˚
N(1) 178.9(3)ꢁ, N(2)–N(3)–N(4) 128.1(5)ꢁ, N(3)–N(4)–C(5) 119.9(5)ꢁ.
industrial chemical processes, and in the oxidation of
ammonia [19].
The nature of the groups at the corners of the cu-
boids, viz. l3-N–N„N–Ph found in 5 and 7, l3-N–
C„CrCp(CO)2 found in 6 and 7, l3-N–Ph in 8 and
additionally l3-CO and l3-O in 6 and 8, respectively,
are suggestive of extensive cleavage of the tetrazole ring,
as well as the C–S and the metal–ligand Cr–S bonds in
4a, leading to the formation of radical fragments, either
discrete or quasi-associated, illustrated in Chart 1. Sub-
sequent or concomitant aggregation of these will form
the isolated products; for instance the structure of 7
shows the presence of fragments M, 1A, IIIA and IIIB.
We have previously postulated such pathways for the
formation of complex molecular structures from similar
reactions of compounds of CpCr(dithiocarbamate) [5]
˚
distance between Cr-bound N(2) and N(3) (1.372(5) A)
˚
is longer than N(3)–N(4) (1.237(5) A); these are similar
to values reported for a series of group 10 metal triazen-
ido complexes [18], though the NNN angle in 7
(128.1(5)ꢁ) is much larger than those in the Group 10
metal complexes (111(2)ꢁ–116(2)ꢁ). Complex 8 possesses
a l3-NPh imido vertex, with N(4)–C(5) distance of
˚
1.421(4) A, which is similar to the distances (1.406(9),
˚
1.407(9) and 1.411(4) A) of similar bonds of benzothio-
latonitrido units in 3b and 3c [6]. Imido- or nitrene-
capped clusters such as 8 are of considerable interest,
because of the perceived role of adsorbed nitrogen
atoms as intermediates in the Haber process and other
N
N
N
N
C
C
M
M
C
N
N
N
M
M
N
IIIA
S
C
N
C
S
C
N
N
N
N
S
+
+
N
N
N
N
IA
IIA
4a
N
N
IIIB
= CpCr(CO)n
M
M
M
M
S
N
+
N
N
= bond cleavage
- N2
IVA
Chart 1. Proposed fragmentation pathways of the thiotetrazole ligand in 4a.

1162
Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
and CpCr(benzothiazole) [6] and of CpCr systems con-
taining P,S-ligands [20]. Complexes 9–13 have all been
previously characterized [1,16,21–23]. The high yield of
[CpCr(CO)2]2 (9), the decarbonylation derivative of 1
[21] is indicative of the relative difficulty of N–N bond
scission in this complex. Cubane complexes 12 and 13
are isolated thermolytic derivatives of [CpCr(CO)2]2S
(10) [16]; Cp4Cr4S2O2 (11) [23] is also in all likelihood
one of the thermolysis products of 10, by inference from
the formation of its Se analogue from thermal degrada-
tion of the Se analogue of 10 [24]. The combined sub-
stantial yield (ca. 39%) of 10–13 is consistent with the
frequently manifested thiophilicity of 1a in all its reac-
tions with S-containing CpCr compounds [2].
Manning [25] from chromium hexacarbonyl (98% purity
from Fluka). 5,50-Dithiobis(1-phenyl-1H-tetrazole) was
obtained from Sigma–Aldrich. All solvents were dried
over sodium-benzophenone and distilled before use.
Celite (Fluka AG) and silica gel (Merck Kieselgel 60,
230–400 mesh) were dried at 140 ꢁC overnight before
chromatographic use.
4.2. Reaction of [CpCr(CO)3]2 (1) with (SCN4Ph)2-
((STz)2)
(a) A deep green solution of 1 (40 mg, 0.10 mmol) in 2
mL THF was mixed with a solution of (STz)2 (35 mg,
0.10 mmol) in 2 mL THF in a test tube; the magenta
mixture was immediately kept at ꢀ30 ꢁC. After 4 days,
bright red rhombic-shaped crystals of CpCr(CO)3(g1-
SCN4Ph) (4a) (60 mg, 0.16 mmol, 79%) were obtained.
(b) In a repeat reaction in toluene (5 mL) for 30 min
at RT, the resultant dark brown product solution was
concentrated to 2 mL and layered with n-hexane (2
mL). Standing 1 day at ꢀ30 ꢁC gave a mixture of micro-
3. Conclusion
The homolytic S–S bond cleavage in 5,50-dithiobis(1-
phenyl-1H-tetrazole) (C6H5N4CS)2 by {CpCr(CO)3}
(1a) has provided a facile route to the cyclopentadienyl
5-mercapto(1-phenyl-1H-tetrazole) chromium complex
CpCr(CO)3(SCN4Ph) (4a). Further reaction of 4a with
[CpCr(CO)3]2 (1) resulted in extensive fragmentation
of the tetrazole ring leading to a variety of cuboidal
complexes, viz. Cp4Cr4S3(l3-N3Ph) (5), Cp4Cr4S2(l3-
CO)(l3-NC„CrCp(CO)2) (6), Cp4Cr4S2(l3-N3Ph)(l3-
NC„CrCp(CO)2) (7) and Cp4Cr4SO2(l3-NPh) (8).
Notably this study led to the first instance of N–N bond
cleavage by 1; though the low yields of products from
aggregation of radical fragments, relative to the Cr„Cr
bonded complex 9 and the Cr„S„Cr complex 10 and
its thermolytic derivatives 11–13, indicates that scission
of N–N bonds in the tetrazole ring is a high energy pro-
cess and is not competitive with decarbonylation of 1 to
give 9, nor cleavage of Cr–S and C–S bonds in 4a, which
are the precursor steps to 10 and its incumbent thermo-
lytic derivatives.
1
crystalline solids (total 57 mg), the H NMR spectrum
of which indicated
a
1:15 molar mixture of
CpCr(CO)3(g1-SCN4Ph) (4a) and CpCr(CO)2(g2-
SCN4Ph) (4b). However, it was not possible to obtain
4b in a pure form unmixed with a fine purple solid,
the ultimate degradation product (69 mg, 92% by weight
of total reactants from a 2 h reaction at RT). The purple
solid was insoluble in all common organic solvents,
including DMSO and DMF, and in water. Its IR spec-
trum does not possess any CO stretches.
An attempt was made to obtain some spectroscopic
data of 4b as follows:
(i) NMR tube reaction. A mixture of 1 (4 mg, 0.01
mmol) and (STz)2 (3.5 mg, 0.01 mmol) was dissolved
in benzene-d6 (0.5 mL) in a 5-mm NMR tube, and the
1H NMR spectrum of the magenta product solution
immediately scanned and subsequently monitored at
intervals (5, 10, 30, 60, 120 min). Initially, the Cp signal
(d 4.32) of 4a was observed and was increasingly re-
placed over a period of 30 min by d 4.58, which was as-
signed to the Cp signal of 4b; this subsequently
disappeared as purple solids totally precipitated out of
solution after ca. 2 h.
4. Experimental
4.1. General procedures
All reactions were carried out using conventional
Schlenk techniques under an inert atmosphere of nitro-
gen or under argon in an M. Braun Labmaster 130 Inert
Gas System. NMR spectra were measured on a Bruker
(ii) IR spectrum. To obtain a sample for an IR spec-
trum, a product solution was concentrated to dryness
at the point of total disappearance of the signal of 4a.
1
300 MHz FT NMR spectrometer; H and 13C chemical
4.3. Data for 4a
shifts were referenced to residual C6H6 in C6D6. IR spec-
tra in KBr discs were measured in the range of 4000–600
cmꢀ1 by means of a BioRad FTS-165 FTIR instrument.
Mass spectra were run on a Finnigan Mat 95XL-T spec-
trometer. Elemental analyses were carried out by the
microanalytical laboratory in-house. [CpCr(CO)3]2
(Cp = g5-C5H5) (1) was synthesized as described by
Anal. Found: C, 47.9; H, 2.9; N, 14.6; S, 8.5. Calcd.
for C15H10CrN4O3S: C, 47.6; H, 2.7; N, 14.8; S, 8.5.
IR (KBr, cmꢀ1): m(CO) 2044s, 1937s and 1894s; m(N–
N@N) 1275m; m(C–S) 696s, 685s and 627s. FAB+-MS:
m/z 379 [M+ + H, CpCr(CO)3(SCN4Ph)], 351 [M+ ꢀ
CO, CpCr(CO)2(SCN4Ph)], 294 [M+ ꢀ 3CO CpCr-

Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
1163
(SCN4Ph)], 219 [CpCr(SCN4)], 136 [(CN4)2], 69 [CN4].
1H NMR (300 MHz, 300 K, C6D6): d 4.32 (s, 5H,
C5H5); d 7.63, 7.66 (m, 5H, C6H5). The 13C NMR spec-
trum could not be obtained, owing to the instability of
the complex in solution.
the observed and calculated isotropic distribution pat-
tern of the mother ions in the mass spectra were found
to match.
5. Anal. Found: C, 46.1; H, 4.0; N, 6.5; S, 13.5. Calc.
for C26H25Cr4N3S3: C, 45.7; H, 3.7; N, 6.1; S, 14.1. IR
[KBr, cmꢀ1] m(N–N@N) 1431m, 1278w and 1175s;
m(C–N) 1009mbr. FAB+-MS: m/z 683 [M+, Cp4Cr4S3
(N3Ph)], 617 [M+ ꢀ Cp], 513 [M+ ꢀ Cp ꢀ N2Ph]. HR-
FAB+-MS: for [M+] 682.8845 (found), 682.8831 (calcd).
1H NMR (300 MHz, 300 K, C6D6): d 5.08 (s, 15H,
C5H5), 4.87 (s, 5H, C5H5); 7.42–7.72 (m, 5H, C6H5).
13C NMR (75 MHz, 300 K, C6D6): d 91.0, 94.0
(C5H5); 127.9, 130.0, 130.9, 132.7 (C6H5).
4.4. Data for 4b
1
IR (KBr, cmꢀ1): m(CO) 1964s and 1891s. H NMR
(300 MHz, 300 K, C6D6): d 4.58 (s, 5H, C5H5); d 7.84,
7.82 (d, J = 6 Hz, 2H, C6H5), 6.81–6.97 (m, 3H, C6H5).
4.5. Cothermolysis of CpCr(CO)3(SCN4Ph) with
[CpCr(CO)3]2 at 90 ꢁC
6. IR [KBr, cmꢀ1] m(CO) 1924s and 1853s, m(l3-CO)
1655s; m(C–N) 1066sbr. FAB+-MS: m/z 759 [M+,
Cp4Cr4S2(CO)(NCCrCp(CO)2)].
A typical reaction was performed as follows: A dark
brown mixture of [CpCr(CO)3]2 (1) (80 mg, 0.20 mmol)
and CpCr(CO)3(SCN4Ph) (4a) (76 mg, 0.20 mmol) in tol-
uene (7 mL) was stirred at 90 ꢁC for 2 h. The resultant
blackish-brown reaction mixture was concentrated to
ca. 3 mL and filtered to remove some blackish-green pre-
cipitate (14) (38 mg). The filtrate was then loaded onto a
silica gel column (2.5 · 15 cm) prepared in n-hexane. Elu-
tion gave eight fractions: (i) a bright green eluate in n-hex-
7. IR [KBr, cmꢀ1] m(CO) 1923s and 1854s; m(N–
1
N@N) 1401m, 1203m and 1167m; m(C–N) 1030sb. H
NMR (300 MHz, 300 K, C6D6): d 4.64 (s, 5H, C5H5),
4.93 (s, 5H, C5H5), 5.13 (s, 10H, C5H5), 5.48 (s, 5H,
C5H5); 7.42–7.72 (m, 5H, C6H5). FAB+-MS: m/z 850
[M+, Cp4Cr4S2(N3Ph)(NCCrCp(CO)2)].
1
8. H NMR: no peaks in the normal region, possibly
due to paramagnetism. FAB+-MS: m/z 623 [M+,
Cp4Cr4SO2(NPh)].
1
ane (15 mL), the H NMR spectrum of which showed a
1
4:1 molar mixture (total ca. 30 mg) of [CpCr(CO)2]2 (9)
and [CpCr(CO)2]2S (10) which were not separated, but
identified by their well-documented Cp resonances (d
4.23 [4b] and d 4.36 [1,22]) and mass spectral characteris-
tics [4b,22b], and estimated to be present in 0.07 mmol
(34%) and 0.02 mmol (8%) yields, respectively; (ii) a grey-
ish-green eluate in n-hexane/toluene (2:1, 5 mL), which
on concentration gave Cp4Cr4S4 (13) (10 mg, 0.02 mmol,
17%); (iii) a dark brown eluate in n-hexane/toluene (1:1, 5
mL), which yielded brown crystals of Cp4Cr4S3(l3-N3Ph)
(5) (5 mg, 7.3 lmol, 7%); (iv) a dirty-green eluate in n-hex-
ane/toluene (1:2, 5 mL), which yielded greyish-green crys-
tals of Cp4Cr4S2(l3-CO)(l3-NC„CrCp(CO)2) (6) (ꢁ1
mg, 1.3 lmol, 2%). (v) a brown eluate in n-hexane/toluene
(1:2, 5 mL), which yielded brown crystals of Cp4Cr4S2(l3-
N3 Ph)(l3-NC„CrCp(CO)2) (7) (3 mg, 3.5 lmol, 4%) (vi)
a greyish-green eluate in toluene/THF (1:1, 5 mL), which
on concentration gave greyish-green crystals of
Cp4Cr4SO2(l3-NPh) (8) (ꢁ1 mg, 1.6 lmol, 2%); (vii) a
dirty green eluate in THF (5 mL), which on concentration
gave black-green crystals of Cp4Cr4S2O2 (11) (5 mg, 8.8
lmol, 9%); (viii) a pale green eluate in THF (10 mL),
which yielded greyish microcrystalline solids of
Cp4Cr4S2(CO)2 (12) (3 mg, 1.6 lmol, 5%). A pale pur-
plish-blue band remained unmoved on top of the column.
14. H NMR (300 MHz, 300 K, C6D6): d 5.10 (s,
15H, 3· C5H5), 4.84 (s, 5H, C5H5); 7.42–7.72 (m, 5H,
C6H5). Elemental analyses: C, 44.8; H, 3.6; N, 13.1; S,
9.9, could not be rationalized. FAB+-MS shows the
highest mass fragment at 914, followed by 698, indica-
tive of a multinuclear species.
9–13. These complexes were identified by comparison
of their 1H NMR and mass spectral data with published
values [16,21–23].
4.7. Structure determinations
Diffraction-quality single crystals were obtained from
solutions in n-hexane–toluene after 2–3 days at ꢀ30 ꢁC
as follows: 4a as bright red rhombus, 6 as olive-green
crystals, 7 as reddish-brown rhombus and 8 as dark-
green crystals; 11 was similarly obtained as dirty dark
green crystals from hexane–THF.
The crystals were mounted on quartz fibres. The
intensity data were collected on a Bruker AXS APEX
CCD diffractometer, equipped with a CCD detector,
˚
using Mo Ka radiation (k 0.71073 A). The data was cor-
rected for Lorentz and polarization effects with the
SMART suite of programs [26] and for absorption effects
with SADABS [27]. Structure solution and refinement
were carried out with the SHELXTL suite of programs.
[28] The structure was solved by direct methods to locate
the heavy atoms, followed by difference maps for the
light non-hydrogen atoms. The Cp and Ph hydrogens
were placed in calculated positions. The crystallographic
data together with data collection details are given in
4.6. Data
Elemental analyses for 6–8 are incomplete or unavail-
able, owing to extremely low yields of compounds. Like-
wise also for the NMR spectra of 6 and 7. In all cases,

1164
Victor Wee Lin Ng et al. / Journal of Organometallic Chemistry 690 (2005) 1157–1165
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Table S1. In the diagrams for the molecular structures,
H atoms have been omitted for clarity.
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Acknowledgements
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621;
Support from the National University of Singapore
for Academic Research Grant No. R143-000-135-112
(L.Y.G.) and research scholarship (V.W.L.N.) is grate-
fully acknowledged.
Appendix A. Supplementary data
(b) V.A. Ostrovskii, A.O. Koren, Heterocycles 53 (2000) 1421.
´
´
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S2, giving IR spectral data of the new compounds.
Structure of 11. Figure S1 for the molecular structure
of 11. Crystallographic data for the structural analysis
have been deposited with the Cambridge Crystallo-
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compounds 4a, 6–8 and 11, 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). Sup-
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