Low-valent iron complexes stabilised by a bulky guanidinate ligand: Synthesis and reactivity studies

Article abstract of DOI:10.1071/CH14157

A toluene-capped guanidinato iron(i) complex [(Pipiso)Fe(η6-toluene)] (Pipiso≤[(DipN)2C(cis-NC5H8Me2-2,6)]-) was prepared by magnesium metal reduction of {[(Pipiso)FeII(μ-Br)]2} in toluene. The reactivity of the closely related FeI-FeI multiply bonded species, {[Fe(-Pipiso)]2} towards a range of unsaturated small molecule substrates was investigated, and found to be broadly similar to that of low-valent β-diketiminato iron complexes. That is, its reaction with CO yielded the iron(i) carbonyl complex [(Pipiso)Fe(CO)3], whereas reaction with CO2 formed the same product via an apparent reductive disproportionation of the substrate. In contrast, reaction between {[Fe(-Pipiso)]2} and CS2 led to reductive C≤S bond cleavage and the isolation of {[(Pipiso)Fe]2(-S)(-CS)}. Different reactivity was seen with AdN3 (Ad≤1-adamantyl), which was reductively coupled by the iron(i) dimer to give iron(ii) hexaazenyl complex {[(Pipiso)Fe]2(-AdN6Ad)}. CSIRO 2014.

Full text of DOI:10.1071/CH14157

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 1011–1016
Full Paper
http://dx.doi.org/10.1071/CH14157
Low-valent Iron Complexes Stabilised by a Bulky
Guanidinate Ligand: Synthesis and Reactivity Studies*
A
A B
,
Lea Fohlmeister and Cameron Jones
A
School of Chemistry, PO Box 23, Monash University, Melbourne, Vic. 3800, Australia.
Corresponding author. Email: cameron.jones@monash.edu
B
A toluene-capped guanidinato iron(I) complex [(Pipiso)Fe(Z6-toluene)] (Pipiso ¼ [(DipN)2C(cis-NC5H8Me2-2,6)]ꢀ) was
prepared by magnesium metal reduction of {[(Pipiso)FeII(m-Br)]2} in toluene. The reactivity of the closely related FeI–FeI
multiply bonded species, {[Fe(m-Pipiso)]2} towards a range of unsaturated small molecule substrates was investigated,
and found to be broadly similar to that of low-valent b-diketiminato iron complexes. That is, its reaction with CO yielded
the iron(I) carbonyl complex [(Pipiso)Fe(CO)3], whereas reaction with CO2 formed the same product via an
apparent reductive disproportionation of the substrate. In contrast, reaction between {[Fe(m-Pipiso)]2} and CS2 led to
reductive C¼S bond cleavage and the isolation of {[(Pipiso)Fe]2(m-S)(m-CS)}. Different reactivity was seen with AdN3
(Ad ¼ 1-adamantyl), which was reductively coupled by the iron(I) dimer to give iron(II) hexaazenyl complex {[(Pipiso)
Fe]2(m-AdN6Ad)}.
Manuscript received: 17 March 2014.
Manuscript accepted: 9 April 2014.
Published online: 29 May 2014.
Introduction
In recent years, we have developed a range of extremely
bulky amidinate and guanidinate ligands, featuring similar
stabilising properties to those of the related b-diketiminate
The kinetic stabilisation of low-oxidation state/low-coordination
number first row transition metal complexes that are free of
carbonyl ligands is a topic of considerable interest.[1] From a
fundamental standpoint, the appeal of such compounds is
derived from the challenges they pose to existing concepts of
bonding and inherent stability. At the same time, they have been
applied in several areas owing to their high reactivity. As an
example, low-coordinate iron(I) compounds, which have been
stabilised by a variety of bulky mono- and higher-dentate
ligands,[2,3] have recently found roles in catalysis,[4] the chem-
istry of magnetic materials,[5] and bioinorganic chemistry.[6]
A class of ligand that has proved particularly successful
for the stabilisation of iron(I) and quasi-iron(I) complexes are the
b-diketiminates (or Nacnacs). Examples of compounds these
ligands have allowed access to include dinitrogen activated
species 1[7] and arene-coordinated compound 2 (Fig. 1).[7]
Owing to the reducing nature of these systems, these compounds
have been applied in a range of catalytic and stoichiometric
organic transformations,[8] and inorganic synthetic methodolo-
gies.[9] Moreover, compounds such as 1 can be further reduced
by treatment with alkali metals to give, for example, K2[1], in
which the bridging N2 ligand is strongly activated.[7] Com-
pounds related to 1, but incorporating smaller Nacnac ligands
are thought to be intermediates in related reductions of
b-diketiminato iron(II) halides that lead to complete cleavage
of the N2 molecule and formation of iron nitride species such as
3.[10] Treatment of 3 with acids under ambient conditions was
shown to generate NH3, showing potential in the development
of low energy, solution-based alternatives to the Harber–Bosch
process.
Fig. 1. b-diketiminate- and guanidinate-stabilised low-valent iron
complexes.
*This invited submission is associated with the award of the Royal Australian Chemical Institute’s HG Smith Memorial Medal to CJ.
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

1012
L. Fohlmeister and C. Jones
ligand class.[11] These bidentate ligands have been used in
the preparation of low-oxidation state complexes involving
metals from all blocks (s-,[12] p-,[13] d-,[14] and f-[15]) of the
periodic table. For iron(I), these include the toluene-capped
and dinitrogen-bridged amidinato complexes [(Piso)Fe(Z6-
toluene)] and {[(Piso)Fe]2(m-N2)}, respectively where Piso ¼
[(DipN)2CBut]ꢀ and Dip ¼ C6H3Pr2i2,6.[16] Both complexes
have counterparts in the Nacnac chemistry e.g. 1 and 2. More
recently, we have reported the unusual dinuclear, high-spin
guanidinato-iron(I) compound 4, which exhibits the shortest
Scheme 1. Synthesis of compound 5.
[17]
˚
Fe–Fe bond (2.1270(7) A) reported to date in the literature.
This compound was prepared by reduction of the precursor
complex {[(k2-N,N0-Pipiso)Fe(m-Br)]2} (Pipiso ¼ [(DipN)2
C(cis-NC5H8Me2-2,6)]–) with the magnesium(I) reagent
{[(MesNacnac)Mg]2} (MesNacnac ¼ [(MesNCMe)2CH]ꢀ). Given
the rich coordination and redox chemistry of b-diketiminato
iron(I) complexes, e.g. 1 and 2, and the lack of reactivity studies
addressing low-valent, carbonyl-free Fe-Fe bonded systems, it
seemed appealing to investigate further the reactivity of 4 and
related species, and to compare the reactivity with that of
b-diketiminato iron(I) complexes. The results of these studies
are reported herein.
Results and Discussion
In the early stages of this study, attempts were made to prepare
iron(I) compounds, other than 4, incorporating the Pipiso ligand.
The previously reported reduction reaction that gave 4 was
carried out in cyclohexane under an argon atmosphere.[17] In an
attempt to form an analogue of 1 and {[(Piso)Fe]2(m-N2)}, the
reduction process was repeated herein under an N2 atmosphere.
Surprisingly, this did not give the N2 complex, but afforded 4 in
a yield (,50 %) similar to that obtained when the reaction was
carried out under argon. Although 4 is unreactive towards N2, it
was proposed that treatment with toluene would lead to cleavage
of the dimer and formation of a toluene-capped complex com-
parable to 2 and [(Piso)Fe(Z6-toluene)]. However, under these
conditions, 4 remained unreactive, even at temperatures of up to
808C. As an alternative route the toluene-capped iron(I) com-
plex, the reduction of precursor compound{[(k2-N,N0-Pipiso)Fe
(m-Br)]2} was carried out in toluene using activated magnesium
metal as the reducing agent. This yielded the expected complex
5, in a low isolated yield as dark red crystals (Scheme 1).
Although it was not possible to obtain a crystal structure of
publishable quality for this compound, a structure of marginal
quality was obtained, confirming the monomeric nature of the
compound containing N,N0-chelating Pipiso and Z6-coordinated
toluene ligands. Its solution state magnetic moment (Evans
method) was determined as meff ¼ 2.59 mB. Although this
is higher than that expected for a low-spin d7 electron configu-
ration (S ¼ 1/2, mso ¼ 1.73 mB), it is very similar to the
value (meff ¼ 2.5 mB) obtained for the analogous b-diketiminato-
coordinated FeI complex 2.[7]
Scheme 2. Synthesis of compounds 6–8 (Ad ¼ 1-adamantyl).
d7 electron configuration for the FeI centre. It is noteworthy that
in a previous study, treatment of 1 with an excess of CO affor-
ded an iron(I) tricarbonyl complex, [(DipNacnac)Fe(CO)3]
(meff ¼ 2.0 mB, DipNacnac ¼ [(DipNCMe)2CH]ꢀ),[7] very similar
to 6. Furthermore, the infrared spectrum of compound 6 exhib-
ited strong CO stretching bands at similar wavenumbers to that
of equivalent bands in the infrared spectra of related compounds
[(DipNacnac)Fe(CO)3][7] and [(Piso)Fe(CO)3].[16]
Compound 6 was crystallographically characterised and its
molecular structure is displayed in Fig. 2. The structure is
closely comparable with that of [(Piso)Fe(CO)3][16] i.e. it is
monomeric with a distorted square-based pyramidal Fe coordi-
nation environment. The base of the pyramid encompasses
N(1), N(2), C(33), and C(35) (Sum (S) of the N–Fe–N angles ¼
353.778), with C(34) taking up the apical position. Examination
of the bond lengths within the CN3 fragment of the complex
suggests a degree of electronic delocalisation over the four
atoms. However, given the fact that the dihedral angle between
the CN3 least-squares plane and that of the NC2 unit of the
piperidyl substituent is 22.68, the participation of the C(1)–N(3)
bond in the delocalisation is expected to be lower than that of the
C(1)–N(1) and C(1)–N(2) bonds.
The chemistry of 4 was further explored with respect to its
reactivity towards small unsaturated molecules. Initially, treat-
ment of a toluene solution of the compound with an excess of CO
was carried out and this led to cleavage of the dimer and
generation of the dark green guanidinato iron-tricarbonyl com-
pound 6 in a low isolated yield (Scheme 2). Little useful
The reaction of 4 with an excess of dry CO2 was subsequently
examined. At ꢀ608C, no reaction occurred, but upon warming
the mixture to room temperature and stirring for 16 h, the
solution turned deep green. Infrared and 1H NMR spectroscopic
analyses of the reaction solution revealed a complex mixture of
products that included the iron carbonyl complex 6. All attempts
to separate the product mixture were unsuccessful. Although the
formation mechanism of 6 cannot be ascertained, it is likely that
1
information could be obtained from the H NMR spectrum of
the compound, of which the resonances were very broad because
of the paramagnetic nature of 6. Its solution state magnetic
moment (Evans method) was determined as meff ¼ 1.56 mB,
which is lower than that for 5, but consistent with a low-spin

Iron(I) Guanidinate Chemistry
1013
Fig. 3. ORTEP diagram of 7 (25 % thermal ellipsoids; hydrogen atoms
˚
omitted). Selected bond lengths (A) and angles (8): Fe(1)–C(1) 1.942(3),
Fig. 2. ORTEP diagram of 6 (25 % thermal ellipsoids; hydrogen atoms
˚
omitted). Selected bond lengths (A) and angles (8): Fe(1)–N(1) 1.9672(17),
Fe(1)–N(4) 1.988(2), Fe(1)–N(5) 1.996(2), Fe(1)–S(1) 2.1324(9), Fe(2)–C
(1) 1.935(3), Fe(2)–N(1) 1.976(2), Fe(2)–N(2) 2.008(2), Fe(2)–S(1) 2.1336
(9), N(3)–C(2) 1.361(3), N(1)–C(2) 1.342(4), N(2)–C(2) 1.347(3), N(6)–C
(34) 1.364(3), N(5)–C(34) 1.349(4), N(4)–C(34) 1.337(3), N(4)–Fe(1)–N(5)
66.02(9), C(1)–Fe(1)–S(1) 100.97(9), N(1)–Fe(2)–N(2) 66.13(9), C(1)–Fe
(2)–S(1) 101.17(9), N(1)–C(2)–N(2) 107.9(2), N(4)–C(34)–N(5) 107.8(2).
Fe(1)–N(2) 1.9753(15), Fe(1)–C(35) 1.780(3), Fe(1)–C(33) 1.805(2), Fe
(1)–C(34) 1.852(2), N(1)–C(1) 1.355(2), N(2)–C(1) 1.342(2), N(3)–C(1)
1.358(2), N(1)–Fe(1)–N(2) 66.75(6), N(2)–C(1)–N(1) 107.07(15).
it involves the reductive disproportionation of CO2 by 4, thus
generating CO which reacts with the remaining iron(I) dimer in
the mixture to give the iron carbonyl complex. Although the
generation of iron oxide and/or carbonate by-products would be
expected in such a process, none were identified in the reaction
mixture. Regardless, reductive disproportionations of CO2 to
CO and CO23ꢀ are well known for transition metal com-
plexes,[18] including Nacnac-coordinated iron(I) compounds.[19]
To investigate whether similar chemistry occurs for CS2, two
equivalents of this substrate were reacted with 4 in toluene.
A rapid reaction occurred at ꢀ408C, yielding a dark brown
solution that was then warmed to ambient temperature. Subse-
quent workup afforded a moderate isolated yield of the thermal-
ly stable iron(II) complex 7 (Scheme 2). It is apparent that the
reaction proceeds via the reductive cleavage of a C¼S bond of
CS2 to give 7, which is unreactive towards excess substrate.
Although the reductive disproportionation of CS2 to CS and
CS23ꢀ did not occur under these conditions, compound 7 could be
considered as an intermediate of this hypothetical reaction
pathway. It is worth noting that the cleavage of a C¼S bond in
CS2, facilitated by low-valent iron centres, has precedent in the
literature. For example, Lewis et al. showed that the reaction
between [Fe3(CO)12] and excess CS2 at 808C in a CO atmo-
sphere affords the tetra-nuclear cluster compound
[Fe4(CO)12(CS)S] as one of the reaction products.[20] Although
related to 7, both the CS and S ligands in [Fe4(CO)12(CS)S]
m3ꢀcap a Fe3 triangular unit in that cluster.
Square planar iron(II) complexes, though not rare, are atypi-
cal. Regardless, this geometry has been reported to be sterically
enforced on iron when it is coordinated to amidinate ligands
of a similar steric bulk to that of Pipiso, e.g. in [Fe(Phiso)2]
(Phiso ¼ [(DipN)2CPh]ꢀ).[23] Moreover, square planar iron(II)
complexes often adopt intermediate spin (S ¼ 1) electronic
configurations.[24] A combination of intermediate spin iron(II)
centres in 7 and significant antiferromagnetic coupling between
those centres would provide an explanation for the rather low
solution state magnetic moment (meff ¼ 2.6 mB, Evans method)
determined for the compound. However, confirmation of this
hypothesis via a detailed variable temperature solid state mag-
netic moment analysis of 7 is beyond the scope of this prelimi-
nary reactivity study.
Holland and co-workers reported that the low-valent
b-diketiminato iron complex 1 was able to reductively couple
1-adamantyl azide, AdN3, producing the first reported metal
hexaazenyl complex, {[(DipNacnac)Fe]2(m-AdN6Ad)}.[25] For
comparison, reaction of 4 with two equivalents of AdN3 was
conducted. This led to the cleavage of the Fe–Fe bond in 4 and
the low-yield formation of the analogous dark brown crystalline
hexaazenyl complex 8 (Scheme 2). The major product of this
reaction precipitated as a poorly soluble paramagnetic yellow
solid. Crystals of this compound suitable for X-ray diffraction
analysis could not be grown, and the spectroscopic data shed
little light on its formulation. Similarly, the paramagnetic
complex 8 is NMR inactive in solution. Given the very low
yield of the complex, and the fact that it consistently co-
crystallised with significant amounts (,10 %) of the free amine
PipisoH, no meaningful magnetic data could be obtained. It is
noteworthy, however, that magnetic and Mo¨ssbauer spectrosco-
pic measurements of the closely related complex {[(DipNacnac)
Fe]2(m-AdN6Ad)} revealed that it possessed two high-spin FeII
centres that are antiferromagnetically coupled.[25]
The crystal structure of 7 contains one full and one half
molecule (sitting on a crystallographic inversion centre) in the
asymmetric unit; the molecular structure of the full molecule is
displayed in Fig. 3. Both iron centres of the compound display
distorted square planar coordination environments, with an
average dihedral angle of 18.18 between the CN2Fe and Fe2CS
least-squares planes. The Fe atoms are chelated by delocalised
Pipiso ligands, and are symmetrically bridged by sulfide and
thiocarbonyl units. All of the Fe–N, Fe–S, Fe–C and C¼S
distances in the complex are all well within the known ranges
for such interactions.[21] Although the FeꢁꢁꢁFe separation in the
Despite the lack of spectroscopic data for 8, an X-ray crystal
analysis revealed the hexaazenyl-bridged diiron structure of
the complex to be essentially isostructural to {[(DipNacnac)Fe]2
(m-AdN6Ad)} (see Fig. 4). Each N–C–N-delocalised Pipiso
ligand chelates an iron(II) centre with similar Fe–N bond lengths.
˚
compound (2.5800(6) A) is also within the sum of the covalent
radii of the two iron centres (2.64 A),[22] it is unlikely that there is
˚
any significant bonding interaction between the atoms.

1014
L. Fohlmeister and C. Jones
N3
N1
N5Ј N4Ј
N6Ј
C1
Fe1
N2
N4
N6
N5
C33
˚
Fig. 4. ORTEP diagram of 8 (25 % thermal ellipsoids; hydrogen atoms omitted). Selected bond lengths (A) and
angles (8): Fe(1)–N(6)0 2.013(4), Fe(1)–N(2) 2.019(5), Fe(1)–N(4) 2.027(4), Fe(1)–N(1) 2.053(5), N(1)–C(1) 1.342
(6), N(2)–C(1), 1.322(7), N(3)–C(1) 1.392(6), N(4)–N(5) 1.300(6), N(5)–N(6) 1.308(6), N(6)–N(6)0 1.416(8),
N(2)–Fe(1)–N(1) 65.14(18), N(6)0–Fe(1)–N(4) 75.63(16), N(2)–C(1)–N(1) 110.7(4), N(4)–N(5)–N(6) 117.5(4),
N(5)–N(6)–N(6)0 113.5(5). Symmetry operation: 0ꢀx þ 2, ꢀy þ 1, ꢀz.
The distorted tetrahedral iron coordination spheres are completed
by chelation with two N centres of the hexaazenyl unit. Exami-
nation of the N–N distances in that unit suggests that the central
N(6)–N(6)0 bond is single, whereas the other four N–N inter-
actions are delocalised double bonds. In that respect, the N6
fragment is best viewed as two triazaallyl moieties bridged by an
N–N bond, similar to the AdN6Ad fragment in {[(DipNacnac)
Fe]2(m-AdN6Ad)}[25] and other recently reported iron[26] and
magnesium[27] hexaazenyl complexes.
potassium, whereas diethyl ether was distilled from Na/K alloy.
Melting points were determined in sealed glass capillaries under
dinitrogen and are uncorrected. Mass spectra were recorded at
the EPSRC National Mass Spectrometric Service at Swansea
University. The microanalysis was carried out at London Met-
ropolitan University. Suitable microanalyses could not be
obtained for compounds 6–8 because of their very high sensi-
tivity to moisture and oxygen. In addition, recrystallisation of 8
consistently led to co-crystallisation with PipisoH, which could
not be completely separated from the compound. Infrared (IR)
spectra were recorded using a Perkin–Elmer RX1 FT-IR spec-
trometer as Nujol mulls between NaCl plates. 1H NMR spectra
were recorded on a Bruker Avance III 400 spectrometer and
were referenced to the residual proton resonance of the solvent
used. Solution state magnetic moments were determined by the
Evans method. {[(Pipiso)Fe(m-Br)]2} and {[Fe(Pipiso)]2} were
prepared according to literature procedures.[17] All other
reagents were used as received.
Conclusion
A new monomeric, toluene-capped guanidinato iron(I) complex
[(Pipiso)Fe(Z6-toluene)] (5) was formed upon reduction of
iron(II) precursor complex {[(k2-N,N0-Pipiso)Fe(m-Br)]2} in
toluene. In addition, the reactivity of the related Fe–Fe multiply
bonded species {[Fe(m-Pipiso)]2} (4) towards a range of unsat-
urated small molecule substrates was investigated. The reaction
with CO yielded the iron(I) carbonyl complex [(Pipiso)Fe(CO)3]
(6), whereas that with CO2 proceeded via an apparent reductive
disproportionation of the gas, ultimately generating 6. In con-
trast, reaction between 4 and CS2 led to reductive C¼S bond
cleavage and isolation of the iron(II) sulfide/thiocarbonyl-
bridged system {[(Pipiso)Fe]2(m-S)(m-CS)} (7). Differing
reactivity was seen with AdN3, which underwent reductive
coupling upon treatment with 4 to give iron(II) hexaazenyl
complex {[(Pipiso)Fe]2(m-AdN6Ad)} (8). All reactions with 4
involved cleavage of the Fe–Fe bond of the compound, and its
reactivity was shown to be broadly similar to that of low-valent
b-diketiminato iron complexes, e.g. 1 and 2. We continue to
explore the reactivity of 4 towards the activation of small
molecules and will report on this work in due course.
Preparation of [(Pipiso)Fe(Z6-toluene)] (5)
1,2-Dibromoethane (5 drops) and one crystal of I2 were added
to a suspension of Mg filings (50 mg, 2.0 mmol) in diethylether
(15 mL). The mixture was stirred until the orange–brown iodine
colour disappeared. The solvent was filtered off, the activated
Mg filings were washed with toluene (15 mL), then dried
under vacuum. A solution of {[(Pipiso)Fe(m-Br)]2} (222 mg,
0.18 mmol) in toluene (25 mL) was then added to the filings at
ambient temperature. The reaction vessel was subsequently
placed in an ultrasonic bath for 1 h, during which time the colour
of the solution changed from yellow to brown. The solution was
stirred for 3 days at room temperature before being filtered, and
the filtrate was evaporated to dryness. The residue was extracted
with hexane (20 mL); the extract was concentrated to ,5 mL,
then stored at ꢀ308C to yield compound 5 as dark red crystals
(59 mg, 26 %), mp 180–1878C. meff (C6D6) ¼ 2.59 mB. nmax
(Nujol)/cmꢀ1 1614 (vs), 1583 (s), 1079 (m), 1056 (w), 1024 (s),
986 (w), 973 (w), 924 (m), 789 (s), 769 (m). dH (C6D6, 400 MHz,
Experimental
General Considerations
All manipulations were carried out using standard Schlenk and
glove box techniques under a high-purity dinitrogen atmo-
sphere. Toluene and hexane were distilled over molten

Iron(I) Guanidinate Chemistry
1015
298 K) ꢀ1.10, ꢀ0.14, 1.21, 2.47, 2.78, 4.63, 6.44, 11.30
(all broad). m/z (EI) 530.3 (1 %, Mþ–toluene). Anal. Calc.
for C39H56FeN3: C 75.22, H 9.06, N 6.75. Found: C 75.39,
H 9.15, N 6.86 %.
All hydrogen atoms were included in calculated positions
(riding model). Crystal data, details of data collection and
refinement are given in Table S1 (Supplementary Material).
Crystallographic data (CIF files) for all structures have been
deposited with the Cambridge Crystallographic Data Centre
(CCDC no. 991289–991291).
Preparation of [(Pipiso)Fe(CO)3] (6)
Compound 4 (118 mg, 111 mmol) was dissolved in toluene
(15 mL) and the solution cooled to ꢀ788C. The headspace of the
reaction flask was then purged with CO for 2 min and the flask
was sealed. The solution was warmed to room temperature
during which time a slow colour change from dark red to green
was observed. After stirring for a further 1.5 h, all volatiles were
removed under vacuum and the residue was extracted with
hexane (10 mL). The extract was concentrated to ,5 mL and
stored at ꢀ308C for several weeks, after which dark green
crystals of 6 were isolated (22 mg, 16 %), mp 125–1408C. meff
(C6D6) ¼ 1.56 mB. nmax (Nujol)/cmꢀ1 2043 (s, CO str.), 1967
(m, CO str.), 1957 (v., CO str.), 1180 (m), 1111 (m), 1010 (w),
935 (m), 797 (m). dH (C6D6, 400 MHz, 303 K) ꢀ0.9, 0.97, 1.87,
3.87, 5.89, 9.25 (all broad). m/z (EI) 530.3 (13 %, Mþ–3CO).
Supplementary Material
Crystal data, and details of data collection and refinement for all
structures are available on the Journal’s website.
Acknowledgements
The authors gratefully acknowledge financial support from the Australian
Research Council. LF thanks the Monash Institute of Graduate Research for
financial support in the form of a Postgraduate Publications Award. The
EPSRC Mass Spectrometry Service (Swansea University) is also thanked.
Part of this research was undertaken on the MX1 beamline at the Australian
Synchrotron, Victoria, Australia.
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ꢀ408C, leading to an immediate colour change from dark red to
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added to a solution of 4 (80 mg, 70 mmol) in hexane (15 mL) at
ꢀ808C. The resultant dark brown reaction mixture was warmed
to room temperature and stirred for 2 h, after which a yellow
precipitate was filtered off. The filtrate was concentrated to
,2 mL and stored at 58C for three days to give an inseparable
mixture of dark brown crystals of 8 and colourless crystals of
PipisoH in an approximate ratio of 9 : 1 (,15 mg, 16 %), mp
116–1258C. nmax (Nujol)/cmꢀ1 1612 (vs), 1582 (s), 1099 (w),
1079 (m), 1058 (m), 1022 (s), 973 (w), 934 (m), 855 (w), 801
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˚
radiation (l 0.71073 A) or the MX1 beamline at the Australian
˚
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