Alkane oxidation catalysed by a self-folded multi-iron complex

Article abstract of DOI:10.1080/10610278.2016.1177184

A preorganised ligand scaffold is capable of coordinating multiple Fe(II) centres to form an electrophilic CH oxidation catalyst. This catalyst oxidises unactivated hydrocarbons including simple, linear alkanes under mild conditions in good yields with selectivity for the oxidation of secondary CH bonds. Control complexes containing a single metal centre are incapable of oxidising unstrained linear hydrocarbons, indicating that participation of multiple centres aids the CH oxidation of challenging substrates.

Full text of DOI:10.1080/10610278.2016.1177184

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Alkane oxidation catalysed by a self-folded multi-
iron complex
Magi Mettry, Melissa Padilla Moehlig, Adam D. Gill & Richard J. Hooley
To cite this article: Magi Mettry, Melissa Padilla Moehlig, Adam D. Gill & Richard J. Hooley
(2016): Alkane oxidation catalysed by a self-folded multi-iron complex, Supramolecular
Chemistry, DOI: 10.1080/10610278.2016.1177184
To link to this article: http://dx.doi.org/10.1080/10610278.2016.1177184
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Date: 03 May 2016, At: 04:28

Supramolecular chemiStry, 2016
http://dx.doi.org/10.1080/10610278.2016.1177184
Alkane oxidation catalysed by a self-folded multi-iron complex
Magi Mettry, Melissa Padilla Moehlig, Adam D. Gill and Richard J. Hooley
Department of chemistry and the ucr center for catalysis, university of california riverside, riverside, ca, uSa
ARTICLE HISTORY
ABSTRACT
received 26 February 2016
accepted 4 april 2016
A preorganised ligand scaffold is capable of coordinating multiple Fe(II) centres to form an
electrophilic CH oxidation catalyst. This catalyst oxidises unactivated hydrocarbons including simple,
linear alkanes under mild conditions in good yields with selectivity for the oxidation of secondary
CH bonds. Control complexes containing a single metal centre are incapable of oxidising unstrained
linear hydrocarbons, indicating that participation of multiple centres aids the CH oxidation of
challenging substrates.
KEYWORDS
alkanes; self-assembly;
catalysis
Fe(II) centre (10). Multi-metal catalysts are more challeng-
ing to synthesise, but have potential for greater catalytic
activity than their mononuclear counterparts (11).
1. Introduction
Biological systems perform hydrocarbon oxidations via
numerous different enzymatic structures (1), from the
porphyrin-derived cytochrome P-450 (2), galactose (3)
and methyl monooxygenases (4), and the Rieske non-
haem iron oxygenases (5). Synthetic systems inspired by
these active biological catalytic motifs have been applied
towards a variety of oxidations including C–H activation
(6) and late stage introduction of functionality to natural
product targets (7). In addition to catalytically active sites
containing one metal species, various biological processes
exploit enzymes that involve multiple metals at the core (4,
8). These systems have inspired a number of ligand struc-
tures that coordinate multiple metal clusters at the interior
(9), and have been applied to water splitting and the oxi-
dation of CH bonds. The application of catalytic systems
that exploit multiple metal coordination to the oxidation
of unactivated hydrocarbons is less common: the majority
of studies employ non-haem oxygenase-inspired ligands
that provide a tetradentate ligand coordinated to a single
One of the challenges in the creation of ligands capable
of complexing multiple metals is the preorganisation of the
coordinating motifs. Self-folding has long been exploited
in the fields of sensors and supramolecular assembly to
confer configurational stability on a flexible system. This
self-folding is generally conferred by hydrogen bonding
(12) or by metal–ligand coordination (13). Inspired by these
motifs, we sought to create a flexible, self-folding ligand
system that could coordinate multiple metals for hydro-
carbon oxidation catalysis. The 2,4,6-trisubstituted-1,3,5-
triethylbenzene scaffold (Figure 1) is an inviting target to
present multiple coordinating motifs in close proximity:
this scaffold is well precedented to orient the three ethyl
groups to the same face of the aromatic ring, allowing
the creation of supramolecular host systems and sensors
for cations (14), anions (15) and saccharides (16), among
other species. The parent triazide 1 is usually reduced to
CONTACT richard J. hooley
richard.hooley@ucr.edu
© 2016 informa uK limited, trading as taylor & Francis Group

2
M. MeTTRy eT Al.
Figure 1. Synthesis of the three Fe-binding ligands used in this study.
the corresponding triamine for further derivatisation, but
1 itself is ideally suited to the introduction of multiple
N-coordinating arms by copper (I) catalysed alkyne-azide
cycloaddition (CuAAC) chemistry: the triazoles formed
upon CuAAC can provide an extra coordination site for
metal binding, simplifying the synthesis of multiply coor-
dinating ligands (13).
2-pyridylacetylene 3) displays the basic scaffold with fewer
coordinating groups, whereas ligand 6 is a singly coordi-
nating version of 4. These ligands were synthesised in an
analogous, although much simpler manner to 4. Heating
at 100 °C in a 4:1 DMSO:H2O mixture gave good yields
of both 5 and 6 (reaction in BuOH yielded only starting
material), and a single eDTA wash was sufficient to remove
residual copper ions.
t
The strong Cu binding properties of 4 were encourag-
ing, and suggested that ligand 4 would be capable of coor-
dinating metal ions that would confer catalytic activity on
the system, notably Fe salts. ligand 4 was combined with
three equivalents of FeSO4 in a 1:1 mixture of CH2Cl2:MeOH,
and catalyst 4·Fe3(SO4)3 was isolated by simple filtration
after 30 min stirring. The recovered yield of 4·Fe3(SO4)3
was high, indicating that all three Fe(II) ions were coordi-
nated to the ligand. The initial tests of the activity of the
4·Fe3(SO4)3 complex towards hydrocarbon oxidation were
performed on cyclooctane, an unactivated hydrocarbon
that is nonetheless relatively simple to oxidise due to tor-
sional strain release upon reaction. Our previous hydro-
carbon oxidation catalysts had performed adequately in
a CH3CN:H2O solvent mixture, and t-butyl hydroperoxide
(TBHP) was the most effective oxidant (13). As can be seen
in Table 1, 10% 4·Fe3(SO4)3 was an effective catalyst for the
oxidation of cyclooctane to cyclooctanone. Maximal con-
version (84%) was achieved after 24 h at 60 °C, although
the best selectivity was achieved at lower conversions, as
small amounts of over oxidation product 1,4-cyclooctan-
edione were formed upon prolonged oxidation. The pref-
erence for 1,4-cyclooctanedione is due to stereoelectronic
effects (13). Other solvents such as water or anhydrous ace-
tonitrile were less effective, due to the relative insolubility
2. Results and discussion
We initially focused on the application of two core compo-
nents, scaffold 1 (accessed from azidation of commercially
available 1,3,5 tris(bromomethyl)-2,4,6-triethyl-benzene
(17)) and bis-pyridyl alkyne 2. CuAAC coupling of 1 and 2
should give rise to ligand 4, displaying three tetradentate
coordinating groups around the central triethylbenzene
scaffold. The synthetic challenge is to confer complete
derivatisation of 1 under CuAAC conditions: synthesis of
strongly coordinating ligands via metal-catalysed reac-
tions is often complicated by irreversible formation of
metal–ligand complexes with the catalyst. To minimise
leaching of Cu from the catalyst mixture into the prod-
uct, we employed the tetradentate BIm3 as cocatalyst
(Figure 1) (18). even in the presence of the activating BIm3
ligand:CuSO4 system, the reaction required elevated tem-
peratures in a tBuOH:H2O mixture to achieve good yields.
The strong metal-binding properties of the ligand were
evident: complete removal of Cu salts from 4 required four
separate washings with an aqueous solution of NaeDTA,
and purification by column chromatography in neutral alu-
mina, followed by recrystallisation from CH2Cl2. Two other
ligand systems were synthesised as controls: tris-pyridyl
triazine 5 (synthesised by CuAAC coupling between 1 and

SuPRAMOleCulAR CHeMISTRy
3
Table 1. optimisation of oxidation conditions with 4·Fe3(So4)3.a
Oxidant
Time (hr)
eq. AcOH
yield (%)
%A
%B
tBuooh
tBuooh
tBuooh
tBuooh
tBuooh
tBuooh
tBuooh
h2o2
2
6
0
0
0
0
2
5
10
0
29
50
56
84
86
80
80
0
29
50
56
74
73
74
74
0
0
0
0
10
13
6
6
0
0
18
24
24
24
24
24
24
Nmo
0
53
53
a1:1 mecN:h2o as solvent, product yields determined by Gc analysis.
of either reactant or 4·Fe3(SO4)3. The presence of acetic acid
as additive in this system proved unnecessary: although
carboxylic acids have been shown to increase reactivity
or provide directing effects in other tetra-nitrogen ligand:
Fe(II) systems (7), we saw minimal yield enhancement in
the presence of excess AcOH (entries 5–7). The nature of
the stoichiometric oxidant was important: use of fewer
than 10 eq. TBHP led to lower conversions, and 30% H2O2
was an ineffective oxidant. Interestingly, the weaker oxi-
dant N-methylmorpholine N-oxide (NMO) conferred reac-
tivity on the system (entry 9), although less effectively than
TBHP. No reaction was seen with molecular O2 as oxidant.
Having optimised the reaction conditions, the scope of
the process was tested with more challenging hydrocar-
bon substrates (Table 2). The 4·Fe3(SO4)3 complex was an
effective oxidant for a variety of unstrained, unactivated
cyclic hydrocarbons: adamantane, methylcyclohexane
and cis- and trans-decalin were all oxidised in moderate
to good yields. The reactions were clean, and only the oxi-
dation products and reactants were observed: the yields
described in Table 2 also correspond to conversions. Most
excitingly, linear alkanes such as n-octane were suscepti-
ble to oxidation by 4·Fe3(SO4)3, challenging targets that
are unreactive to other self-folded multi-metal oxidation
catalysts (13). The reaction was not highly selective, but
did show some unusual regiochemical outcomes. Most
C–H activations show strong selectivity for 3º substrates
(6), although there are examples of systems that favour
2º oxidation (19). Here, the 4·Fe3(SO4)3 complex shows
selectivity (albeit moderate) for 2º C–H bonds. Oxidation
of methylcyclohexane (entry 4) gives a 5:1 selectivity for
the various ketone isomers over 3º oxidation, with little
selectivity between the 1,2-, 1,3- and 1,4-methylcyclohex-
anone products seen.
conversion was high (88%), but a greater proportion of sec-
ondary oxidation occurred (2°:3° ratio = 4.4:1). Five major
oxidation products were formed (in similar yields): the
expected ketone and tertiary alcohol products, plus small
amounts of 2° alcohol products were observed. essentially,
no selectivity between the 2° oxidation products was
observed, as would be expected. This lack of positional
selectivity was also observed for the oxidation of n-octane:
2-, 3- and 4-octanone were all formed in essentially iden-
tical yields. Only adamantane-carboxylic acid (entry 9)
showed significant selectivity for 3° over 2° C–H oxida-
tions, an observation attributed to the increase in ring
strain upon incorporation of the ketone into the tricyclic
scaffold. No appreciable directing effect is observed from
the COOH group, and the oxidation selectivity appears
to be dominated by substitution. Other substrates were
applied to test the functional group tolerance of catalyst
4·Fe3(SO4)3. Activated C–H bonds were very easily oxidised:
4-ethyltoluene was rapidly oxidised in excellent yield, and
complete selectivity was observed for ketone formation.
Dibutyl ether provided the corresponding ester in 43%
yield, along with a small amount of hydrolysis product.
The observed (moderate) selectivity in hydrocarbon
oxidation is consistent with a sterically bulky multi-Fe cat-
alyst. 3° C–H bonds are weaker and more easily oxidised:
even moderate selectivity for 2° C–H oxidation requires
limited access to the more crowded 3° sites, something
enhanced by bulky ligands around the active metal sites.
In addition, the selectivity for the distal oxidation product
of cis-decalin corroborates this theory. Interestingly, no
isomerisation was observed in the bridgehead 3º oxidation
product of cis-decalin. The radical rebound mechanism
usually present in non-haem Fe-catalysed oxygenations
forms radical intermediates (6), which leads to isomerisa-
tions of strained bridgehead C–H bonds (20). This is not
observed here: no trans-decalin products are observed
from cis-decalin reactants (see Supporting Information for
Cis-decalin (entry 5) displays a 2:1 selectivity towards
2º oxidations, with the terminal ketone product most
favoured. In the case of trans-decalin (entry 6), the overall

4
M. MeTTRy eT Al.
Table 2. Scope of unactivated hydrocarbon oxidation with 4·Fe3(So4)3.
areaction performed in 1:1 mecN: h2o.
breaction performed in 1:1 etcN: h2o.
comparison between the GC traces). We have no reason
to suggest a different mechanism in this case: presumably
recombination merely happens before isomerisation.
In contrast to the effective oxidation performance of the
multi-iron complex 4·Fe3(SO4)3, the two control complexes
5·FeSO4 and 6·FeSO4 were less active (Table 3). There was
little difference between complexes 5·FeSO4 and 6·FeSO4
for relatively simple substrates: the obtained yields for
cyclooctane and trans-decalin oxidation were similar for
the two catalysts, and only slightly lower than those for
the folded 4·Fe3(SO4)3. The catalytic power of 4·Fe3(SO4)3
is illustrated by the more challenging substrates, however:
no products were observed at all for the oxidation of n-oc-
tane with either 5·FeSO4 or 6·FeSO4. Whereas, simple, cyclic
substrates can be oxidised by single Fe centres, only the
self-folded, multi-metal catalyst 4·Fe3(SO4)3 is capable of
oxidising linear, unactivated hydrocarbons. This behaviour
is not simply due to a greater concentration of Fe in the sys-
tem: the complete lack of reactivity of 5·FeSO4 or 6·FeSO4
towards n-octane indicates that 4·Fe3(SO4)3 is greater than
the sum of its parts, and that participation between the Fe
centres is necessary for optimal catalytic activity for chal-
lenging substrates.
The improved reactivity of the multi-metal coordinating
ligand 4 led us to investigate the structure of the pre-cat-
alyst complex formed upon addition of FeSO4 to ligand
4. Accurate analysis of the 4·Fe3(SO4)3 complex structure
was challenging, however. We were unable to access X-ray
quality crystals of 4·Fe3(SO4)3, or indeed of any complexes
−
between 4 and other Fe(II) salts (e.g. ClO4 , Cl− or OAc−). The
4·Fe3(SO4)3 complex was weakly paramagnetic and gave
rise to broad NMR spectra, but determination of the coor-
dination stoichiometry was possible by MS analysis (see
Figure 2(a) and Supporting Information). The parent ion
[4·Fe3(SO4)2·H2O·OH]+ is the largest m/z species observed,
and the other major ionic species correspond to the loss
of one or more sulfate ions and formation of iron-oxo spe-
cies under the ionisation/injection conditions. The weakly
coordinated sulfate ions and associated water molecules
are easily lost upon ionisation, but the 4·Fe3 core with

SuPRAMOleCulAR CHeMISTRy
5
Table 3. Scope of unactivated hydrocarbon oxidation with monometal complexes 5·FeSo4 and 6·FeSo4.a
a1:1 mecN:h2o solvent.
Figure 2. metal coordination properties of ligand 4. (a) eSi-mS spectrum of the 4·Fe3(So4)3 complex; 1h Nmr spectra (298 K, DmSo-d6) of
the titration of Zn(otf)2 into 4, (b) ligand 4 alone, (c) 4 + 1 equiv. Zn(otf)2, and (d) 4 + 3 equiv. Zn(otf)2.
attached anions is detectable, and the isotope pattern
matches that of a three Fe-containing system. elemental
analysis explains some of the issues with crystal growth:
ICP analysis of a microcrystalline sample of 4·Fe3(SO4)3 was
performed, and corroborated the proposed stoichiometry
4·Fe3, but the microcrystalline samples contained a mix of
three and four Fe centres (see Supporting Information).
C–H–N combustion analysis was also consistent with this
mixture of two stoichiometries, and traces of a four Fe
complex were observed. No evidence of a four Fe species
was observed in the MS analysis, however, suggesting
that weak coordination is possible in the solid state with
a fourth Fe centre, but the most stable structure in solution
(and upon ionisation in MS) is 4·Fe3(SO4)3.
Further evidence for the favoured binding stoichiom-
etry containing three metal ions was obtained by 1H NMR
analysis of an analogous 4·Zn3 complex (Figure 2(b)–(d)).
While the coordination modes of ZnII and FeII can obviously

6
M. MeTTRy eT Al.
Figure 3. (colour online) minimised models of the Fe-ligand catalyst complex structures: (a) 4 + 3 x FeSo4, (b) 5 + FeSo4, (c) 6 + FeSo4
(SpartaN, hartree-Fock forcefield, counterions in (b) and (c) omitted for clarity).
vary, ZnII can act as a suitable diamagnetic surrogate of FeII,
to shed light on the complex structure formed. upon addi-
tion of one equiv. Zn(OTf)2 to a solution of 4 in DMSO-d6,
multiple species can be seen in the NMR spectrum: after
addition of three equivalents, only a single species is pres-
ent, displaying reduced symmetry and diastereotopic
methylene protons between 4.0 and 4.5 ppm, suggesting
that all six pyridyl groups are coordinated to the Zn (II)
ions. No further change is observed upon adding excess
Zn (II). MAlDI-MS analysis of the 4·Zn3 complex was also
performed (see Supporting Information), and the parent
[4·Zn3·(OTf)5]+ ion was the only species observed.
The control ligands 5 and 6 were simpler in their
coordination motifs, and MS/NMR analysis showed the
presence of only a single Fe ion when either 4 or 5 were
complexed with FeSO4, as expected. Interestingly, loss of
the anthracenyl group via C–C cleavage was observed in
eSI-MS analysis of 6·FeSO4, which did not occur for the mul-
timetal 4·Fe3(SO4)3 complex. ICP analysis was consistent
with a monomeric coordination of FeSO4 (see Supporting
Information).
are positioned in close proximity to each other, with two
vacant (or weakly sulfate/solvent coordinated) cis sites
present on each metal that can be easily displaced by
stoichiometric oxidant. This structure (especially the plan
view in Figure 3(a)) also suggests the possibility of a coor-
dinating a fourth FeII ion atop the bridging sulfates, which
would explain the presence of a small excess of FeSO4 in
the solid state analysis. Single-arm ligand 6 forms a sim-
ilar coordination environment around a single Fe(II) ion,
maintaining the weakly coordinated cis positions at the
metal centre. ligand 5 appears more restricted, however,
and all six coordinating nitrogens can access the Fe centre,
presumably limiting its catalytic ability.
3. Conclusions
A new preorganized ligand scaffold has been shown to
coordinate multiple Fe(II) centres, forming an electro-
philic C–H oxidation catalyst. This catalyst is capable of
oxidising unactivated C–H bonds including simple, linear
alkanes under mild conditions in good yields. The catalyst
shows selectivity for the oxidation of secondary over ter-
tiary CH bonds. Maximal activity is only obtained for the
multi-iron complex: control complexes containing single
metal centres are incapable of oxidising unstrained linear
hydrocarbons, indicating that participation of multiple
centres is required for the oxidation of challenging sub-
strates. Further investigations into self-folding scaffolds for
multi-metal coordination are underway in our laboratory.
The expected complex structures of 4–6 with FeSO4
were analysed by molecular modelling, and the structures
shown in Figure 3. The minimised structure of 4·Fe3(SO4)3
shows the possibility of sulfate templation of the struc-
ture. The difficulty in crystallisation of the 4·Fe3(SO4)3 com-
plex indicates that this is not a static structure in solution,
and there will be an appreciable amount of flexing of the
three ‘arms’ when dissolved, but the three Fe(II) centres

SuPRAMOleCulAR CHeMISTRy
7
was separated, dried with Na2SO4, filtered and the solvent
removed under reduced pressure to yield 9-anthracenyl-
methyl azide as a yellow solid (1.70 g, 97% yield). CAuTION:
organic azides are explosive, and should be handled
4. Experimental section
4.1. General information
1H and 13C NMR spectra were recorded on a Varian Inova
300 or Inova 400 spectrometer. Proton (1H) chemical
shifts are reported in parts per million (δ) with respect to
tetramethylsilane (Si(CH3)4, δ = 0), and referenced inter-
nally with respect to the protio solvent impurity. Carbon
(13C) chemical shifts are reported in parts per million (δ)
with respect to tetramethylsilane (Si(CH3)4, δ = 0), and
referenced internally with respect to the solvent 13C sig-
nal (either CDCl3 or DMSO-d6). Deuterated NMR solvents
were obtained from Cambridge Isotope laboratories,
Inc., Andover, MA, and used without further purification.
All other materials were obtained from Aldrich Chemical
Company, St. louis, MO and were used as received.
Solvents were dried through a commercial solvent puri-
fication system (SG Water, Inc.). electrospray mass spectra
were recorded on an Agilent 6210 lC TOF mass spectrom-
eter using electrospray ionisation and processed with an
Agilent MassHunter Operating System. MAlDI mass spec-
tra were obtained using a Pe Biosystems De-STR MAlDI
TOF spectrometer operating in refractive mode at 2100 eV.
Molecular minimisations were performed using Hartree-
Fock calculations of equilibrium geometry at ground state
with basis set 3–21G using SPARTAN. The minimisations
started from initial geometry with total charge neutral.
1
carefully. H NMR (400 MHz, CDCl3) δ 8.50 (1H, s), 8.28
(d, J = 8.4 Hz, 2H), 8.06 (d, J = 8.4 Hz, 2H), 7.59 (t, J = 8.0 Hz,
2H), 7.50 (t, J = 8.0 Hz, 2H), 5.33 (2H, s); 13C NMR (100 MHz,
CDCl3) δ 131.4, 130.7, 129.3, 129.0, 126.9, 125.2, 123.5, 46.4;
eIMS: found 233.1 [M+] calculated for C15H11N3: 233.1.
Synthesis
of
N,N-bis(2-pyridylmethyl)-N-
propargylamine
2.
N,N-bis(2-pyridylmethyl)-N-
propargylamine was synthesised according to literature
procedures (23). Di-(2-picolyl)amine (10.0 mmol, 1.08 ml)
was dissolved in MeCN (20 ml). K2CO3 (40 mmol, 5.4 g) was
added to the solution followed by dropwise addition of
propargyl bromide (80% in toluene, 10 mmol, 1.09 ml). The
reaction mixture was stirred for 24 h before being diluted
with dichloromethane. The diluted reaction mixture was
filtered to remove K2CO3, and then washed with dichlo-
romethane before being concentrated under vacuum.
N,N-bis(2-pyridylmethyl)-N-propargylamine was isolated
as yellow oily solid (2.28 g, 96%) from an alumina column
eluted by etOAc in dichloromethane (0% - 40%). After
purification, the solvent was rapidly removed by rotary
evaporation and the product was stored under nitrogen.
1H NMR (300 MHz, CDCl3): δ 8.57 (d, J = 4.2 Hz, 2H), 7.66
(td, J = 1.2, 7.8 Hz, 2H), 7.52 (d, J = 7.8 Hz, 2H), 7.17 (td,
J = 5.4, 7.2 Hz, 2H), 3.93 (4H, s), 3.43 (d, J = 2.4 Hz, 2H), 2.30
(t, J = 2.4 Hz, 1H); 13C NMR (75 MHz, CDCl3): δ 159.0, 149.5,
136.7, 123.4, 122.3, 73.9, 59.7, 42.79; HRMS (eSI): calcd.
(M + Na+) 260.1164, found 260.1159.
4.2. Synthesis of new compounds
Synthesis of 1,3,5-tris(azidomethyl)-2,4,6-triethylben-
zene 1. Adapted from a literature procedure (21): In a 25-ml
round bottom flask equipped with a stir bar 1,3,5-trisbro-
momethyl-2,4,6-trimethyl-benzene (1.0 g, 2.3 mmol) and
sodium azide (18 ml, 0.5 M in DMSO, 9.0 mmol) were com-
bined. The reaction mixture was stirred for 24 h at room
temperature. The solution was then diluted in 100 ml H2O
and extracted with dichloromethane. The organic layer
was dried with Na2SO4, filtered, and the solvent removed
under reduced pressure to yield 1 as a white solid (621 mg,
Synthesis of hexapicolyl ligand 4. In a sealed
tube flushed with nitrogen, 1,3,5-tris(azidomethyl)-2,
4,6-triethylbenzene 1 (50 mg, 0.15 mmol), N,N-bis(2-
pyridylmethyl)-N-propargylamine 2 (180 mg, 0.76 mmol),
CuSO4·5H2O (12 mg, 0.05 mmol), sodium ascorbate (18 mg,
0.09 mmol), BIm3 co-catalyst (19 mg, 0.05 mmol), and 2 ml
t
of 1:1 BuOH:H2O were added. The reaction mixture was
stirred for 24 h at 80 °C. The solvent was removed under
vacuum, redissolved in dichloromethane (20 ml) and
added to an aqueous solution of Na2eDTA (15 ml). This
mixture was stirred for 1 h to remove any bound copper
from the ligand. The organic layer was separated, dried
with Na2SO4, filtered and the solvent removed under
reduced pressure to yield a brown, tar-like substance
(130 mg, 82% yield). The ligand was purified via rapid
flash chromatography with an alumina column eluted by
etOAc in dichloromethane (0–40%). The product was then
recrystallized from CH2Cl2 under a nitrogen atmosphere.
After purification, the product was stored under nitrogen.
CAuTION: organic azides are explosive, and should be han-
dled carefully. 1H NMR (300 MHz, CDCl3): δ 8.46 (dt, J = 4.7,
1.4 Hz, 6H), 7.61(td, J = 7.6, 1.8 Hz, 6H), 7.51 (td, J = 7.8,
1
84%) H NMR (300 MHz, CDCl3): δ 4.50 (6H, s), 3.86 (q,
J = 7.7 Hz, 6H), 1.25 (t, J = 7.7 Hz, 9H); 13C NMR (100 MHz,
CDCl3): δ 144.9, 130.0, 47.9, 23.2, 15.7.
Synthesisof9-anthracenylmethylazide.Adaptedfrom
a literature procedure (22), 9-Anthracenemethanol (1.50 g,
7.40 mmol) was dissolved in dichloromethane (30 ml).
SOCl2 (810 μl, 11.1 mmol) was then added at 0 °C. After
mixing for 2 h, the solvent was removed under vacuum.
The resultant residue was redissolved in DMF (10 ml), and
sodium azide (0.77 g, 12.0 mmol) was added. The reac-
tion mixture was heated for 4 h at 60 °C, cooled to room
temperature and diluted with 50 ml water. The mixture
was then extracted with ethyl acetate. The organic layer

8
M. MeTTRy eT Al.
1.2 Hz, 6H), 7.45 (s, 3H), 7.11 (ddd, J = 7.4, 4.9, 1.4 Hz, 6H),
5.62 (s, 6H), 3.76 (s, 6H), 3.75 (s, 12H), 2.80 (q, J = 7.4 Hz,
6H), 0.92 (t, J = 7.3 Hz, 9H). 13C NMR (75 MHz, CDCl3): δ
158.9, 148.8, 146.2, 144.2, 136.4, 129.6, 123.2, 122.7, 121.9,
59.3, 48.4, 47.8, 23.5, 15.2. eSI-TOF [MNa+] calcd 1061.5616,
found 1061.5734.
Synthesis of dipicolyl ligand 6. In a sealed tube
was combined with 9-anthracenylmethyl azide (100 mg,
0.43 mmol), N,N-bis(2-pyridylmethyl)-N-propargylamine
(160 mg, 0.64 mmol), CuSO4·5H2O (32 mg, 0.13 mmol),
sodium ascorbate (42 mg, 0.25 mmol), BIm3 co-catalyst
(52 mg, 0.13 mmol), and 10 ml of 4:1 DMSO:H2O. The reac-
tion mixture was stirred for 24 h at 110 °C before removing
the solvent and redissolving in dichloromethane (20 ml)
and adding an aqueous solution of Na2eDTA (15 ml). This
mixture was stirred for 1 h to remove any bound copper
from the ligand. The organic layer was separated, dried
with Na2SO4, filtered and the solvent removed under
reduced pressure to yield a brown solid (90 mg, 53%). 1H
NMR (400 MHz, CDCl3): δ 8.56 (s, 1H), 8.34 (d, J = 4.5 Hz,
2H), 8.28 (d, J = 8.7 Hz, 2H), 8.05 (d, J = 8.0 Hz, 2H), 7.61
(m, 2H), 7.40 (m, 2H), 7.45 (td, J = 7.6, 1.6 Hz, 2H), 7.30 (d,
J = 7.6 Hz, 2H), 7.07 (d, J = 5.9 Hz, 1H), 6.97 (dd, J = 6.4,
5.2 Hz, 2H), 6.47 (s, 2H), 5.30 (s, 1H), 3.69 (d, 4H), 2.58 (s,
2H).13C NMR (125 MHz, CDCl3): δ 158.19, 148.7, 136.6, 131.4,
131.2, 130.8, 129.7, 129.4, 129.3, 127.6, 125.7, 125.4, 124.0,
123.5, 123.1, 122.9, 122.1, 59.4, 48.8, 46.4, 41.0. eSI/APCI
[MH+] calcd 470.22, found 471.0.
Synthesis of 4·Fe3(SO4)3. In a dry two-dram vial
flushed with nitrogen, 4 (100 mg, 0.16 mmol) was dis-
solved in dichloromethane (1 ml). In a separate two-
dram vial FeSO4·7H2O (48 mg, 0.17 mmol) was dissolved
in MeOH (1 ml). The two solutions were combined and
sonicated for 5 min before collecting a brown precipitate
(221 mg, 92%). mp:>250 °C (decomp). eSI-TOF [4·Fe3(SO4)
2·H2O·OH]+ calcd 1061.5616, found 1061.5734. elemental
Analysis: Theoretical (C60H66Fe4N18O16S4): C: 43.76, H: 4.04,
N: 14.31. Theoretical (C60H66Fe3N18O12S3): C: 48.20, H: 4.45,
N: 16.86. Found: C: 45.07, H: 4.39, N: 15.22. ICP analysis
1
(Fe): 3.76%. NMR analysis: The broadness of the H NMR
spectrum limited accurate spectral assignments due to the
paramagnetic nature of the complex, and so the peaks
are not transcribed here. See Supporting Information for
spectral data.
Synthesis of trispyridyl ligand 5. In a 10-ml round
bottom flask equipped with a stir bar was combined with
CuSO4·5H2O (23 mg, 0.09 mmol), sodium ascorbate (36 mg,
0.18 mmol) and 1,3,5-tris(azidomethyl)-2,4,6-triethylben-
zene 1 (100 mg, 0.31 mmol) in 4 ml of 4:1 DMSO:H2O.
To this mixture was added 2-ethynyl pyridine 3 (97 μl,
0.92 mmol) and the reaction mixture was stirred for 24 h
at 100 °C. After being cooled to room temperature, 15 ml
of water was added and the resulting grey precipitate
was collected by vacuum filtration. The crude precipi-
tate was dissolved in dichloromethane and washed with
an aqueous solution of Na2eDTA. The organic layer was
dried with Na2SO4, filtered, and the solvent removed under
reduced pressure to yield 5 as a grey solid (175 mg, 90%).
1H NMR (400 MHz, CDCl3): δ 8.46 (d, J = 4.5 Hz, 3H), 8.18 (d,
J = 7.9 Hz, 3H), 8.08 (s, 3H), 7.76 (td, J = 7.8, 1.5 Hz, 3H), 7.21
(dd, J = 6.8, 5.2 Hz, 3H), 5.73 (s, 6H), 2.84 (q, J = 7.4 Hz, 6H),
1.00 (t, J = 7.5 Hz, 9H). 13C NMR (101 MHz, CDCl3): δ 150.1,
149.0, 148.2, 146.9, 137.3, 129.8, 123.1, 121.8, 120.6, 48.2,
23.8, 15.5. eSI-TOF [MH+] calcd 637.3259, found 637.3227.
Synthesis of 5·FeSO4. In a dry two-dram vial flushed
with nitrogen, 5 (25 mg, 0.04 mmol) was dissolved in
MeOH (1.5 ml). In a separate 2-dram vial FeSO4·7H2O
(65 mg, 0.24 mmol) was dissolved in MeOH (1 ml). The
two solutions were combined and sonicated for 5 min
before collecting a brown precipitate (30 mg, 97%). eSI-
TOF [5·Fe(HSO4)]+ calcd 881.2, found 881.4. NMR analysis:
The broadness of the 1H NMR spectrum limited accurate
spectral assignments due to the paramagnetic nature of
the complex, and so the peaks are not transcribed here.
See Supporting Information for spectral data.
Synthesis of 6·FeSO4. In a dry two-dram vial flushed
with nitrogen, 6 (40.0 mg, 0.038 mmol) was dissolved
in MeOH (1.5 ml). In a separate 2-dram vial FeSO4·7H2O
(30 mg, 0.192 mmol) was dissolved in MeOH (1 ml). The
two solutions were combined and sonicated for 5 min
before collecting a brown precipitate (21 mg, 90% yield).
eSI-TOF [6·Fe(SO4)·H2O·H]+ calcd 643.13, found 643.48. ICP
1
analysis (Fe): 1.64%. The broadness of the H NMR spec-
trum limited accurate spectral assignments due to the
paramagnetic nature of the complex, and so the peaks
are not transcribed here. See Supporting Information for
spectral data.
General procedure for oxidation reactions. In a 0.3-
ml conical vial, catalyst (4 μmol, 10 mol%) was dissolved
t
in 0.25 ml solvent (1:1 MeCN:H2O). BuOOH (0.40 mmol,
10 equiv.), and substrate (0.04 mmol, 1 equiv.) were added.
The reaction mixture was stirred for 24 h at 60 °C. Aliquots
were taken and passed through a silica gel pipet plug with
ether before being analysed by GCMS. All yields are based
on GCMS analysis via integrative comparison to an internal
standard. Product identification was determined by com-
parison to authentic samples via fragmentation pattern
matching in MS.
Acknowledgements
The authors would like to thank the National Science Founda-
tion (CHe-1151773), the uCR Center for Catalysis and the uCR
Office for Research and economic Development for support.
M.P.M. acknowledges support through the uS Department of
education GAANN Award #P200A120170. The authors would
like to acknowledge lauren R. Holloway for some preparative

SuPRAMOleCulAR CHeMISTRy
9
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Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Science Foundation
[CHe-1151773]; the uCR Center for Catalysis; and the uCR Office
for Research and economic Development.
Supplemental material
Supplemental data for this article can be accessed online here:
http://dx.doi.org/10.1080/10610278.2016.1177184
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