Spin states and stability of FeIII complexes of ligands with carboxamido nitrogen and phenolato oxygen donors

Article abstract of DOI:10.1002/1099-0682(200203)2002:4<859::AID-EJIC859>3.0.CO;2-Z

As part of our attempts to prepare Fe^III complexes with "tunable" spin states, we have synthesized three novel six-coordinate Fe^III complexes containing both carboxamido nitrogen (N_amido) and phenolato oxygen (O_phen) donors in their ligand framework. Since it has already been shown that carboxamido nitrogen donors usually stabilize Fe^III in a low spin configuration, while phenolato oxygens tend to stabilize Fe^III in a high spin state, we have incorporated both donor groups in our designed ligands. The syntheses and structures of Fe^III complexes with either one or two N_amido and O_phen donors are reported in this paper. The properties of these complexes have been compared with the properties of analogous Fe^III complexes. The competing effects of N_amido and O_phen on the spin state of the Fe^III center are discussed in terms of the stabilities of the overall complexes. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0682(200203)2002:4<859::AID-EJIC859>3.0.CO;2-Z

FULL PAPER
Spin States and Stability of FeIII Complexes of Ligands with Carboxamido
Nitrogen and Phenolato Oxygen Donors
Dana S. Marlin,[a] Marilyn M. Olmstead,[b] and Pradip K. Mascharak*[a]
Keywords: Iron / N ligands / O ligands / Spin states
As part of our attempts to prepare FeIII complexes with ‘‘tun-
able’’ spin states, we have synthesized three novel six-coord- are reported in this paper. The properties of these complexes
inate FeIII complexes containing both carboxamido nitrogen have been compared with the properties of analogous FeIII
complexes with either one or two Namido and Ophen donors
(Namido) and phenolato oxygen (Ophen) donors in their ligand complexes. The competing effects of Namido and Ophen on the
framework. Since it has already been shown that carboxam- spin state of the FeIII center are discussed in terms of the
ido nitrogen donors usually stabilize FeIII in a low spin con- stabilities of the overall complexes.
figuration, while phenolato oxygens tend to stabilize FeIII in
a high spin state, we have incorporated both donor groups
(
Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
in our designed ligands. The syntheses and structures of FeIII 2002)
Introduction
obtaining FeIII complexes with ‘‘tunable’’ spin states. In the
long term, we intend to gain control over (a) the redox po-
tential, (b) stability and (c) the spin state of the FeIII center,
all of which influence its reactivity. Here we report the re-
sults of our initial effort toward this goal.
Monomeric complexes with stable FeIII centers are at-
tractive synthetic targets to inorganic chemists for their use,
among other things, as catalysts, enzyme mimics, or as
model complexes that allow for detailed study of the elec-
tronic properties of the FeIII center.[1Ϫ4] Recent work from
this laboratory in conjunction with the work of others has
shown that coordination of a carboxamido nitrogen (Nam-
ido) to an FeIII center makes it resistant toward hydrolytic
decomposition.[5] Furthermore, the reduction potential of
the FeIII center is shifted toward more negative values by
approximately Ϫ0.5 V per Namido to a maximum of about
Ϫ1.10 V.[5,6] In addition, the majority of the six-coordinate
FeIII complexes with one, two, and four Namido donors pos-
sess low spin (LS) ground states.[3,5,6] Wieghardt and co-
workers have performed extensive studies to evaluate the
electronic and physical properties of mononuclear FeIII
Previously, we have described the structure and chemistry
of FeIII complexes of the pentadentate ligand N,NЈ-bis(2-
hydroxyphenyl)-pyridine-2,6-dicarboxamide
(POPYH4)
(Figure 1).[10] When deprotonated, this ligand becomes
planar and coordinates to the FeIII center in the basal plane
of a pentagonal bipyramid. The HS FeIII complexes of this
ligand namely, [Fe(POPY)(L)2]nϪ (L ϭ SCNϪ, N-methylim-
idazole), were the first examples of structurally character-
ized species in which both Namido and Ophen donors are co-
ordinated to the FeIII center in the same complex. We have
now prepared additional six-coordinate complexes with
similar ligands in order to explore the properties of these
types of complexes in more detail. The two designed ligands
that have been employed in this study are the tridentate
ligand N-(2-hydroxyphenyl)-2-pyridinecarboxamide (Pype-
pOH2) and the pentadentate ligand N,N-bis(2-pyridylme-
thyl)amine-N-ethyl-2-hydroxyphenyl-2-carboxamide (Pap-
y2OH2) (Figure 1). In both PypepOH2 and Papy2OH2, the
H’s represent dissociable phenolic and carboxamide hydro-
gens. In the deprotonated forms, these ligands coordinate
to FeIII to afford stable HS six-coordinate complexes
Na[Fe(PypepO)2] (1), and [Fe(Papy2O)(L)] (2 L ϭ ClϪ; 3
L ϭ SCNϪ). These complexes represent only the second
and third set of examples of structurally characterized com-
plexes with FeIII centers coordinated to both Namido and
Ophen donors. They are also the first such examples of six-
coordinate FeIII complexes. The structural and spectro-
complexes with FeIIIϪOphen (Ophen
ϭ phenolato O)
bonds.[7Ϫ8] They have pointed out that the majority of these
complexes tend to have high spin (HS) FeIII centers (with a
t32geg2 electronic configuration) and that FeIIIϪOphen bonds
are often short, indicating considerable double bond char-
acter with ligand-to-metal dπ-pπ back bonding.[9] We de-
cided to combine both FeIIIϪNamido and FeIIIϪOphen inter-
actions within the same FeIII complex with the intention of
[a]
Department of Chemistry and Biochemistry, University of
California, Santa Cruz,
Santa Cruz, CA 95064, USA
Fax: (internat.) ϩ 1-831/459-2935
E-mail: pradip@chemistry.ucsc.edu
[b]
Department of Chemistry, University of California, Davis
Davis, CA 95616, USA
Eur. J. Inorg. Chem. 2002, 859Ϫ865
WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002 1434Ϫ1948/02/0404Ϫ0859 $ 17.50ϩ.50/0
859

D. S. Marlin, M. M. Olmstead, P. K. Mascharak
FULL PAPER
scopic properties of these complexes (with both ure 2b). This arrangement creates small pockets at the
FeIIIϪNamido and FeIIIϪOphen bonds) have been compared center of each dimer and large pockets by the four-dimer
with FeIII complexes with either FeIIIϪOphen or clusters. Some of the large pockets are occupied by uncoor-
FeIIIϪNamido bonds.
dinated CH3CN molecules (Figure 2b).
It is interesting to note that like complex 1, Na[Fe(PO-
PY)(N-MeIm)2]·3CH3CN also forms an extended structure
in the solid state with Naϩ bonded to phenolate and car-
bonyl oxygen donors from the POPY4Ϫ ligand and lattice
CH3CN molecules.[10] However, in the case of Na[Fe(PO-
PY)(N-MeIm)2]·3CH3CN, polymeric chains form between
monomeric Naϩ···[Fe(POPY)(N-MeIm)2]Ϫ units in the lat-
tice, which differs considerably from the elaborate porous
network seen in 1·2.5CH3CN. Also, the bond lengths for 1
FeIIIϪNamido [av. 2.064(4) A] and FeIIIϪOphen [av. 1.962(4)
˚
Figure 1. Ligands that contain both Namido and Ophen donors used
in previous (POPYH4) and the present study (PypepOH2 and
Papy2OH2); the H’s in POPYH4, PypepOH2 and Papy2OH2
represent dissociable phenolate and carboxamide hydrogens
A] as well as FeIIIϪNpy [av. 2.178(5) A] (py ϭ pyridine)
are substantially shorter than analogous bond lengths in
Na[Fe(POPY)(N-MeIm)2] (av. 2.228 A, 2.045 A, and 2.221
˚
˚
˚
˚
˚
A respectively) due to the ligand strain imposed by the
pentadentate planar POPY4Ϫ ligand in the latter complex.
Results and Discussion
Molecular Structures of [Fe(Papy2O)(Cl)] (2) and
[Fe(Papy2O)(SCN)] (3)
The tridentate ligand PypepOH2 was prepared by re-
acting 2-aminophenol with 2-pyridinecarbonyl chloride (the
latter prepared from 2-picolinic acid and thionyl chloride)
in tetrahydrofuran (THF). The acetate-protected derivative
of the pentadentate ligand Papy2OH2, namely Papy2OC-
OCH3, was synthesized from (2-aminoethyl)bis(2-pyridyl-
methyl)amine and 2-acetylphenylcarbonyl chloride (the lat-
ter prepared from 2-acetylsalicylic acid and oxalyl chlor-
ide). Pure Papy2OH2 was obtained in good yield following
deprotection of Papy2OCOCH3 with NaOH and neutraliza-
tion with HCl. For ease of handling, Papy2OH2 was con-
verted into the mono-sodium salt NaPapy2OH by reaction
of Papy2OH2 with NaOMe in MeOH. Reaction of
[Fe(DMF)6](ClO4)3 with two equiv. of PypepOH2 and four
equiv. of NaH (both relative to iron) in DMF afforded the
FeIII complex Na[Fe(PypepO)2] (1). The dark red complex
[Fe(Papy2O)(Cl)] (2) was synthesized by reacting
(Et4N)[FeCl4] with NaPapy2OH plus one equiv. of NaH in
DMF. Reaction of [Fe(DMF)6](ClO4)3 with one equiv. of
Papy2O2Ϫ in DMF followed by one equiv. of NaSCN re-
sulted in the formation of [Fe(Papy2O)(NCS)] (3) in high
yield.
X-ray quality crystals of 2·2CH3CN were grown from
CH3CN at Ϫ20 °C while a toluene/CH2Cl2 (3:1) mixture
was used to obtain single crystals of 3·toluene. Both 2 and
3 are monomeric and the coordination geometry is octahed-
ral with the deprotonated Papy2O2Ϫ ligand coordinated to
five of the six sites of the FeIII center in both complexes. In
2, a ClϪ ion occupies the sixth site (Figure 3) while in 3, the
sixth site is occupied by a SCNϪ ion (Figure 4).
Since these complexes are neutral, there is no extended
structure in solid state. The bond lengths of 2 and 3 are
similar (Table 1). The FeIIIϪNamido [av. 2.0157(14) A] and
˚
FeIIIϪNpy [av. 2.1511(15) A] bond lengths of 2 and 3 com-
˚
pare well with those noted for 1 while the FeIIIϪOphen dis-
˚
tance [av. 1.8781(12) A] is slightly shorter. The
N
amidoϪFeϪOphen angles in both 2 and 3 are larger (91°,
six-membered rings) than the same angles in 1 (av. 80°, five-
membered rings, Table 1).
Stability and Spectroscopic Properties
The EPR spectra of 1, 2, and 3 in DMF glass clearly
indicate that the FeIII centers in these complexes exist as
HS. During the past few years, we have synthesized several
Molecular Structure of Na[Fe(PypepO)2] (1)
X-ray quality crystals of 1·2.5CH3CN were grown from similar FeIII complexes that contain one, two or four
a saturated solution of 1 in CH3CN, upon cooling to Ϫ20 FeIIIϪNamido bonds in addition to FeIIIϪNpy and/or
°C. The structure of the complex shows two deprotonated FeIIIϪSthio (thio ϭ thiophenolato) bonds.[5,11Ϫ14] All these
PypepO2Ϫ ligands coordinated to an FeIII center in a mer complexes are consistently LS (Table 2). The obvious differ-
geometry (Figure 2a). In the solid state, 1·2.5CH3CN forms ence between the present set of complexes (1, 2, and 3) and
an elaborate network of [Fe(Pypep)2]Ϫ and Naϩ ions the rest of the entries in Table 2 is the fact that complexes
bridged through carbonyl and phenolato oxygens with ad- 1, 2, and 3 contain FeIIIϪOphen bonds. In general, mononu-
ditional coordination of CH3CN to the Naϩ center. The clear FeIII complexes with either one,[7,15,16] two,[17]
lattice
structure
is
built
up
of
dimeric three[8,18] or four[10,19] FeIIIϪOphen bonds all tend to possess
[Fe(PypepO)2]Ϫ···Naϩ···[Fe(PypepO)2]Ϫ···Naϩ units which HS (t32geg2) FeIII centers. The FeIIIϪOphen bond in the major-
in turn are connected together into an extended network ity of these complexes has been described as more than a
with large pockets formed by four such dimeric units (Fig- single bond with additional dπ-pπ back-bonding.[9] Wiegh-
860
Eur. J. Inorg. Chem. 2002, 859Ϫ865

FeIII Complexes of Ligands with Carboxamido Nitrogen and Phenolato Oxygen Donors
FULL PAPER
Figure 2. (a) Thermal ellipsoid plot of [Fe(PypepO)2]ϩ (at the 35% probability level); (b) extended structure of
Na[Fe(PypepO)2]·2.5CH3CN showing the small and large pockets formed in the solid state
ardt and co-workers have suggested that the HS configura- FeIIIϪOphen interaction dominates and the resultant com-
tion of the FeIII center facilitates such a dπ-pπ interaction.[9] plexes are HS.
Since the FeIIIϪOphen distances in complexes 1, 2, and 3
A change in spin state occurs when the ClϪ ligand of
(Table 1) compare well with the ‘‘short’’ FeIIIϪOphen dis- [Fe(Papy2O)(Cl)] (2) is replaced with CNϪ. The HS com-
[7Ϫ10,15Ϫ19]
˚
tances reported so far (range ϭ 1.85Ϫ1.97 A),
it plex 2 is converted into a LS cyanide adduct [Fe(Papy2-
is evident that the FeIIIϪOphen bonds in 1, 2, and 3 are of O)(CN)] upon addition of one equiv. of (Et4N)(CN) to a
a similar nature, and hence these complexes prefer a HS solution of 2 in DMF (EPR data, Figure 5). This change in
configuration. Taken together, these facts indicate that spin state on going from 2 to [Fe(Papy2O)(CN)] supports
when the FeIII center is coordinated to both carboxamido the notion that the spin state of the FeIII center is controlled
nitrogen(s) and phenolato oxygen(s) (like 1, 2, and 3), the by the FeIIIϪNamido and FeIIIϪOphen interactions which
Eur. J. Inorg. Chem. 2002, 859Ϫ865
861

D. S. Marlin, M. M. Olmstead, P. K. Mascharak
FULL PAPER
˚
Table 1. Selected bond lengths [A] and angles[°] for complexes 1, 2
and 3
Complex 1
FeϪN(1)
FeϪN(2)
FeϪN(3)
C(19)ϪN(3)
2.069(4)
2.192(5)
2.059(4)
1.311(7)
FeϪN(4)
FeϪO(1)
FeϪO(3)
C(19)ϪO(4)
2.164(5)
1.964(4)
1.959(4)
1.243(7)
1.229(7)
79.79(17)
107.98(18)
164.22(19)
92.40(18)
96.6(2)
C(7)ϪN(1)
1.307(7)
C(7)ϪO(2)
O(3)ϪFeϪO(1)
O(1)ϪFeϪN(3)
O(1)ϪFeϪN(1)
O(3)ϪFeϪN(4)
N(3)ϪFeϪN(4)
O(3)ϪFeϪN(2)
N(3)ϪFeϪN(2)
N(4)ϪFeϪN(2)
92.91(16)
113.73(17)
80.15(17)
155.35(18)
76.04(19)
94.06(18)
91.23(18)
91.23(19)
O(3)ϪFeϪN(3)
O(3)ϪFeϪN(1)
N(3)ϪFeϪN(1)
O(1)ϪFeϪN(4)
N(1)ϪFeϪN(4)
O(1)ϪFeϪN(2)
N(1)ϪFeϪN(2)
154.92(17)
74.77(18)
Complex 2
Figure 3. Thermal ellipsoid plot of 2 (at the 50% probability level)
FeϪN(1)
FeϪN(2)
FeϪN(3)
C(9)ϪN(3)
O(2)ϪFeϪN(3)
O(2)ϪFeϪN(1)
N(3)ϪFeϪN(1)
O(2)ϪFeϪN(4)
N(3)ϪFeϪN(4)
N(1)ϪFeϪN(4)
O(2)ϪFeϪN(2)
N(3)ϪFeϪN(2)
2.1449(12)
2.2065(11)
2.0172(12)
1.3472(17)
91.08(4)
104.91(4)
85.98(5)
102.47(4)
94.65(5)
152.60(5)
172.92(4)
82.45(4)
FeϪN(4)
FeϪO(2)
FeϪCl
C(9)ϪO(1)
N(1)ϪFeϪN(2)
N(4)ϪFeϪN(2)
O(2)ϪFeϪCl
N(3)ϪFeϪCl
N(1)ϪFeϪCl
N(4)ϪFeϪCl
N(2)ϪFeϪCl
2.1489(12)
1.8745(9)
2.3822(4)
1.2532(17)
77.61(4)
75.33(4)
95.99(3)
171.52(4)
87.68(3)
88.40(3)
90.70(3)
Complex 3
FeϪN(1)
FeϪN(2)
FeϪN(3)
2.0142(14)
2.2171(14)
2.1551(15)
90.29(6)
FeϪN(4)
FeϪN(5)
FeϪO(1)
2.1553(15)
2.0478(16)
1.8816(12)
152.41(6)
170.35(5)
81.01(5)
92.18(6)
76.93(5)
76.01(5)
89.49(6)
O(1)ϪFeϪN(1)
O(1)ϪFeϪN(5)
N(1)ϪFeϪN(5)
O(1)ϪFeϪN(3)
N(1)ϪFeϪN(3)
N(5)ϪFeϪN(3)
O(1)ϪFeϪN(4)
N(1)ϪFeϪN(4)
N(3)ϪFeϪN(4)
O(1)ϪFeϪN(2)
N(1)ϪFeϪN(2)
N(5)ϪFeϪN(2)
N(3)ϪFeϪN(2)
N(4)ϪFeϪN(2)
N(5)ϪFeϪN(4)
FeϪN(5)ϪC(22)
96.87(6)
171.20(6)
106.93(6)
86.78(6)
86.23(6)
100.64(6)
94.23(6)
Figure 4. Thermal ellipsoid plot of 3 (at the 50% probability level)
169.33(15)
compete against each other. The competing effect of these
two interactions appears to be similar enough so that
addition of a strong sixth ligand like CNϪ results in a
switch in the spin state during the [Fe(Papy2O)(Cl)] Ǟ complexes with phenolate ligands in which the t62g config-
[Fe(Papy2O)(CN)] transformation.
uration of the CoIII center eliminates any dπ-pπ bonding.[9]
At this point it is also important to note that the LS Our work thus far indicates that LS complexes with
species [Fe(Papy2O)(CN)] is quite unstable and can only be FeIIIϪNamido and FeIIIϪOphen bonds are inherently un-
studied by low temperature spectroscopy. All attempts to stable. We must comment here that our conclusion regard-
isolate this complex as a solid product have failed so far. In ing weakening of the FeIIIϪOphen interaction in LS com-
contrast, the analogous CNϪ adduct [Fe(Papy3)(CN)]ϩ (a plexes is preliminary and the final word on the stability of
similar complex with no FeIIIϪOphen bond) is LS and very LS versus HS FeIII complexes with both FeIIIϪNamido and
stable.[6] Clearly, the change in spin state converts a stable FeIIIϪOphen coordination will require more in-depth stud-
complex 2 into an unstable species [Fe(Papy2O)(CN)]. Since ies. Such studies are in progress in this laboratory at the
HS complexes with FeIIIϪOphen bonds are usually very present time.
stable, it is quite evident that forcing the HS complex 2
Finally, we like to point out that complexes 2 and 3 are
(with FeIIIϪOphen bond) into a LS (t25geg0) configuration in quite stable toward hydrolysis and do not give rise to species
[Fe(Papy2O)(CN)] reduces its stability, presumably by min- with a (µ-oxo)diiron(III) core. For some time now we have
imizing the dπ-pπ bonding interaction. Reduction of the maintained that the presence of an FeIIIϪNamido bond sta-
MIIIϪOphen bonding interaction has been noted for CoIII bilizes the FeIII center to a great extent and prevents both
862
Eur. J. Inorg. Chem. 2002, 859Ϫ865

FeIII Complexes of Ligands with Carboxamido Nitrogen and Phenolato Oxygen Donors
FULL PAPER
Table 2. Comparison of FeIIIϪNamido and FeIIIϪOphen (or Sthio) bond lengths, with spin state (on FeIII) and half wave reduction potential
(vs. SCE) for six coordinate FeIII complexes
Complex
No. of FeIIIϪNamido
bonds
FeIIIϪNamido
(A)
FeIIIϪOphen
Spin state of FeIII
E1/2 (V)
(DMF)
Reference
[a]
[a]
˚
˚
(or Sthio
)
(A)
[Fe(Papy3)(Cl)]ϩ
[Fe(Papy3)(CN)]ϩ
[Fe(Papy2O)(Cl)] (2)
[Fe(Papy2O)(NCS)] (3)
[Fe(Prpep)2]ϩ
1
1
1
1
2
2
2
2
4
4
1.8559(17)
1.858(2)
2.0172(12)
2.0142(14)
1.955(2)
1.957(4)
1.954(2)
2.064(4)
1.962(2)
1.955(3)
LS
LS
HS
HS
LS
LS
LS
HS
LS
LS
Ϫ0.03
Ϫ0.01
Ϫ0.51
6
6
1.8745(9)
1.8816(12)
this work
this work
12
11
Ϫ0.10
Ϫ0.31
Ϫ1.12
Ϫ1.08
Ϫ0.95
Ϫ1.05
[Fe(Pypep)2]ϩ
[Fe(PypepS)2]Ϫ
2.2291(11)
1.962(4)
14
[Fe(PypepO)2]Ϫ (1)
[Fe(Py3P)2]Ϫ
this work
13
13
[Fe(MePy3P)2]Ϫ
[a]
Average bond length when more than one bond is present.
Conclusion
In conclusion, we have prepared and structurally charac-
terized three stable complexes that contain both
FeIIIϪNamido and FeIIIϪOphen bonds. In previous studies, it
has been shown that carboxamido nitrogens (Namido) are
strong donors and their coordination to iron usually results
in LS FeIII complexes. Previous studies have also shown
that complexes with Ophen comprise HS FeIII centers. The
complexes reported herein now indicate that these two
donor atoms in the same molecule influence the spin state
of the FeIII center in the opposite sense. Overall, the re-
sulting complexes are HS and so far, no LS complex with
both FeIIIϪNamido and FeIIIϪOphen bonds has been isol-
ated. It thus appears that the effect of the phenolato oxygen
to afford HS FeIII species overrides the spin-pairing trend
of the carboxamido nitrogen in FeIII complexes. In the case
of FeIII complexes of the Papy2O2Ϫ ligand (which has one
Namido and one Ophen donor), the overriding effect of Ophen
can just be compensated by adding a strong sixth ligand
(like CNϪ). The resulting LS complex [Fe(Papy2O)(CN)] is,
however, unstable. Since similar LS FeIII complexes with no
FeIIIϪOphen bond(s) are stable entities, it now appears that
FeIIIϪOphen bonds impart instability to LS FeIII complexes.
Figure 5. Conversion of HS [Fe(Papy2O)(Cl)] (2) to LS [Fe(Papy2-
O)(CN)] upon addition of (Et4N)(CN); EPR settings: DMF/
MeOH (10:1) glass, T ϭ 80 K, microwave power 13 mW, microwave
frequency 9.43 GHz, modulation frequency 100 KHz, modulation
amplitude 2 G; the g values for 2 are 9.05, 4.22 and 4.17, and for
[Fe(Papy2O)(CN)] g ϭ 2.39, 2.27 and 1.87
Experimental Section
hydrolytic decomposition and formation of oxo- or hy-
droxo-bridged iron species which are often the thermodyn-
amic end products in iron chemistry.[10,13] Since the com-
plexes with the Papy2O2Ϫ ligand contain only one
FeIIIϪNamido bond, we have attempted to synthesize dir-
ectly the corresponding (µ-oxo)diiron(III) complex. How-
ever, addition of 2 equiv. of Papy2O2Ϫ to (Et4N)2[Fe2OCl6]
[a pre-formed (µ-oxo)diiron(III) synthon] resulted in the
isolation of complex 2 rather than the expected µ-oxo spe-
cies [{Fe(Papy2O)}2O]. This further supports our previous
remarks that complexes with FeIIIϪNamido bonds do not
form oxo-bridged dimers (or polymers), which translates
into an enhanced stability of these complexes towards hy-
drolytic decomposition.
Physical Measurements: A PerkinϪElmer 1600 FTIR spectropho-
tometer was used to monitor the IR spectra. 1H NMR spectra were
recorded on a Bruker 250 MHz spectrometer. EPR spectra were
monitored at X-band frequencies on a Bruker ESP-300 spectro-
meter. Electrochemical measurements were performed with stand-
ard Princeton Applied Research instrumentation and a Pt inlay
electrode. Potentials were measured at 25 °C versus an aqueous
saturated calomel electrode (SCE) as reference.
Materials and Methods: All manipulations were carried out in air.
(2-Aminoethyl)bis(2-pyridylmethyl)amine was prepared following a
published procedure.[20] 2-Aminophenol, 2-picolinic acid, 2-acetyl-
salicyclic acid, thionyl chloride (SOCl2), oxalyl chloride, sodium
hydroxide (NaOH), sodium hydride (NaH), and sodium thiocyan-
ate (NaSCN) were purchased from Aldrich Chemical Company
Eur. J. Inorg. Chem. 2002, 859Ϫ865
863

D. S. Marlin, M. M. Olmstead, P. K. Mascharak
FULL PAPER
and used without further purification. (Et4N)[FeCl4][21] and were dried over MgSO4 and volatiles were removed under vacuum
[22]
[Fe(DMF)6](ClO4)3
were prepared by following published pro-
to yield a gummy yellow residue (crude Papy2OH2: 2.30 g,
cedures. N,NЈ-dimethylformamide (DMF) was distilled from BaO 6.2 mmol). Sodium metal (0.14 g, 6.2 mmol) was dissolved in meth-
while tetrahydrofuran (THF) and toluene were distilled from Na/ anol (10 mL) and added to the residue. The solution was stirred
benzophenone prior to use. Dichloromethane (CH2Cl2) and ace-
tonitrile (CH3CN) were distilled from CaH2 prior to use.
for 1 h and then the solvent was removed under vacuum. The re-
maining yellow solid, NaPapy2OH, was used without further puri-
fication (2.40 g, 83% yield). 1H NMR (250 MHz, [D6]DMSO): δ ϭ
2.56 (t, 2 H, CH2), 3.40 (m, 2 H, CH2), 3.78 (s, 4 H, CH2), 6.08 (t,
1 H, ArH), 6.36 (d, 1 H, ArH), 6.87 (t, 1 H, ArH), 7.19 (t, 2 H,
ArH), 7.63 (m, 5 H, ArH), 8.44 (d, 2 H, ArH). Selected FTIR
Preparation of PypepOH2: 2-picolinic acid (5.00 g, 41 mmol) was
dissolved in neat SOCl2 (10Ϫ20 mL) and warmed to 50 °C until a
clear deep purple solution remained (approx. 1 h). The excess
SOCl2 was removed under vacuum and the purple residue was trit-
urated twice with THF to remove traces of HCl. The purple solid
was then redissolved in THF (30 mL) and added to a solution of
2-aminophenol (4.40 g, 41 mmol) and Et3N (6.30 g, 62 mmol) in
THF (50 mL) at 0 °C. The mixture was then heated to reflux for
5 h. Following a brief cooling period, triethylamine hydrochloride
˜
absorption bands (KBr pellet): ν ϭ 3051 (w), 2933 (w), 1625 (s),
1594 (s), 1466 (s), 1438 (s), 1390 (m), 1342 (m), 1256 (m), 1150 (m),
860 (w), 758 (s), 704 (m), 567 (w), 543 (w) cmϪ1
.
Na[Fe(PypepO)2] (1): PypepOH2 (0.24 g, 1.1 mmol) was dissolved
in DMF (25 mL) and to this was added solid NaH (0.05 g,
was filtered off, and the volatiles were removed by rotary evapora- 2.2 mmol). The mixture was stirred for 2 h and then a batch of
tion. The remaining residue was triturated twice with THF and
[Fe(DMF)6](ClO4)3 (0.43 g, 0.55 mmol) dissolved in DMF (5 mL)
was added to it. The resultant deep green solution was allowed to
recrystallized from MeOH/H2O (1:10 v/v) (6.90 g, 78% yield). 1H
NMR (250 MHz, CDCl3): δ ϭ 6.85 (t, 1 H, ArH), 7.00 (d, 1 H, stir for 2 h at 25 °C. Next, the solvent was removed under vacuum
ArH), 7.08 (t, 2 H, ArH), 7.47 (t, 1 H, ArH), 7.87 (t, 1 H, ArH), and the residue was dissolved in CH3CN (10 mL). The solution
8.23 (d, 1 H, ArH), 8.58 (d, 1 H, ArH), 10.16 (s, 1 H, NH). Selected was then stored at Ϫ20 °C for 3 days. The dark green microcrystal-
˜
FTIR absorption bands (KBr pellet): ν ϭ 3308 (m, NϪH), 3072
line solid thus obtained was collected by filtration (0.27 g, 42%
(m, OϪH), 1653 (s, CϭO), 1593 (s), 1543 (s), 1458 (s), 1434 (m), yield). C29H23.5FeN6.5NaO4 (605.58 for Na[Fe(PypepO)2]·2.5
1370 (m), 1284 (m), 1230 (m), 1098 (w), 1038 (w), 932 (w), 852 (w), CH3CN): calcd. C 57.47, H 3.91, N 15.03; found C 57.21, H 3.85,
757 (s), 738 (s), 691 (s), 618 (w), 594 (w) cmϪ1
.
N 15.21. Selected FTIR absorption bands (KBr pellet): ν ϭ 1670
˜
(s), 1614 (s), 1593 (s, CϭO), 1567 (s), 1464 (s), 1388 (m), 1274 (s),
NaPapy2OH: 2-Acetylsalicyclic acid (1.40 g, 7.5 mmol) was dis-
solved in neat oxalyl chloride (10Ϫ20 mL) and warmed to 40 °C
until a clear solution remained (approx. 1 h). Excess oxalyl chloride
1248 (m), 1098 (m), 1020 (w), 937 (w), 863 (w), 803 (w), 754 (m),
742 (m), 692 (w), 642 (w), 611 (w), 575 (w), 562 (w), 501 (w) cmϪ1
.
was removed under vacuum and the clear oil was triturated twice [Fe(Papy2O)(Cl)] (2): A portion of solid NaH (0.01 g, 0.43 mmol)
with THF to remove traces of HCl. The residue was then redis- was added to NaPapy2OH (0.16 g, 0.43 mmol) dissolved in DMF
solved in THF (10 mL) and added dropwise to a solution of (2- (10 mL) and the mixture was stirred for 2 h. To this solution was
aminoethyl)bis(2-pyridylmethyl)amine (1.80 g, 7.5 mmol) and trie- added a solution of (Et4N)[FeCl4] (0.14 g, 0.43 mmol) dissolved in
thylamine (0.90 g, 9.0 mmol) in THF (25 mL) at 0 °C. The mixture DMF (5 mL) and the resultant deep red solution was allowed to
was warmed to room temperature and allowed to stir for 12 h, at stir for an additional 1 h. The DMF solvent was then removed
which point 6  NaOH (20 mL) was added. Volatiles were removed under vacuum and the residue was dissolved in CH3CN (20 mL).
by rotary evaporation, the residue was made neutral with 12  HCl,
and extracted with CH2Cl2 (3 ϫ 20 mL). The combined extracts
The red solution was stored at Ϫ20 °C overnight. The resultant
deep red microcrystalline solid was then filtered off and dried under
Table 3. Crystallographic data for Na[Fe(PypepO)2]·2.5CH3CN (1·2.5CH3CN), [Fe(PapyO)(Cl)]·2CH3CN (2·2CH3CN), and
[Fe(PapyO)(NCS)]·toluene (3·toluene)
1·2.5CH3CN
2·2CH3CN
3·toluene
Empirical formula
Molecular weight
C29H23.5FeN6.5NaO4
605.88
C25H26ClFeN6O2
533.82
C29H28FeN5O2S
566.47
˚
a [A]
10.7660(10)
13.0305(12)
20.5973(19)
95.239(2)
2877.4(5)
4
15.3649(7)
11.3058(5)
15.8124(8)
115.7740(10)
2473.5(2)
4
9.4884(4)
22.1746(10)
12.9277(6)
94.1370(10)
2712.9(2)
4
˚
b [A]
˚
c [A]
β [°]
V [A ]
3
˚
Z
Crystal system
Space group
monoclinic
P21/n
1.399
90(2)
0.585
0.961
6.23
15.26
monoclinic
P21/c
1.433
90(2)
0.753
0.960
3.26
7.77
monoclinic
P21/n
1.387
90(2)
0.669
1.019
4.12
9.13
ρ [g·cmϪ3
T [K]
]
abs coeff, µ, mmϪ1
GOF[a] on F2
[b]
R1
[c]
Rw2
[a]
2
2 2
[b]
[c]
GOF ϭ [Σ[w(F0 Ϫ Fc ) ][M Ϫ N]]1/2 (M ϭ number of reflections, N ϭ number of parameters refined).
R1 ϭ Σ||Fo Ϫ Fc||/Σ|Fo|.
Rw2 ϭ [Σ[w(F0 Ϫ Fc ) ]/ Σ[w(F0 ) ]]1/2
.
2
2 2
2 2
864
Eur. J. Inorg. Chem. 2002, 859Ϫ865

FeIII Complexes of Ligands with Carboxamido Nitrogen and Phenolato Oxygen Donors
FULL PAPER
vacuum (0.16 g, 70% yield). C25H26ClFeN6O2 (533.55 for [Fe-
[1]
(Papy2O)(Cl)]·2CH3CN): calcd. C 56.23, H 4.91, N 15.75; found C
56.19, H 4.96, N 15.28. Selected FTIR absorption bands (KBr pel-
let): ν˜ ϭ 1597 (m, CϭO), 1571 (s), 1533 (s), 1444 (s), 1360 (s), 1290
(w), 1244 (w), 1102 (w), 1024 (w), 895 (w), 768 (s,), 704 (w), 658
E. I. Solomon, T. C. Brunold, M. I. Davis, J. N. Kemsley, S. -
K. Lee, N. Lehnert, F. Neese, A. J. Skulan, Y. -S. Yang, J. Zhou,
Chem. Rev. 2000, 100, 235Ϫ350.
Biomimetic Oxidations Catalyzed by Transition Metal Com-
plexes (Ed.: B. Meunier), Imperial College Press, London,
1999.
[2]
[3]
(w) cmϪ1
.
D. S. Marlin, P. K. Mascharak, in Encyclopedia of Catalysis:
Biomimetic Catalysis by Models of Non-Heme Iron Enzymes
(Ed.: I. T. Horvath), John Wiley & Sons, Inc. New York, in
[Fe(Papy2O)(NCS)] (3): To a solution of NaPapy2OH (0.21 g,
0.55 mmol) in DMF (10 mL) was added a batch of solid NaH
(0.013 g, 0.55 mmol) and the mixture was allowed to stir for 2 h. To
this solution was then added a batch of [Fe(DMF)6](ClO4)3 (0.43 g,
0.55 mmol) dissolved in DMF (5 mL) and the purple/red solution
was stirred for an additional 1 h. At this point, a solution of
NaSCN (0.067 g, 0.83 mmol) in DMF (1 mL) was added and the
color of the solution changed to red/brown. The DMF solvent was
removed under vacuum and the residue was dissolved in THF
(30 mL). The solution was stored at Ϫ20 °C overnight. The deep
red needles were collected by filtration (0.15 g, 50% yield).
C26H28FeN5O3S (546.17 for [Fe(Papy2O)(NCS)]·THF): calcd. C
57.13, H 5.17, N 12.82; found C 57.27, H 5.19, N 12.74. Selected
´
press.
[4]
T. J. Collins, S. W. Gordon-Wylie, M. J. Bartos, C. P. Horwitz,
C. G. Woomer, S. A. Williams, R. E. Patterson, L. D. Vuocolo,
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Green Chemistry: Frontiers in Benign Chemical Syntheses and
Processes (Eds.: P. T. Anastas and T. C. Williamson), Oxford
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˜
FTIR absorption bands (KBr pellet): ν ϭ 2046 (s, SCN), 1594 (m,
CϭO), 1570 (m), 1534 (m), 1445 (m), 1352 (m), 1103 (w), 1024 (w),
763 (m,) cmϪ1
.
Crystal Structure Analysis: Deep black/green crystals of
Na[Fe(PypepO)2]·2.5CH3CN (1·2.5CH3CN) and dark red crystals
of [Fe(Papy2O)(Cl)]·2CH3CN (2·2CH3CN) were each grown from
CH3CN at Ϫ20 °C. Black/red X-ray quality plates of
[Fe(Papy2O)(NCS)]·toluene (3·toluene) were grown from toluene/
CH2Cl2 (3:1). Diffraction data for all complexes were collected at
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
˚
90 K on Bruker SMART 1000 diffractometer. Mo-Kα (0.71073 A)
radiation was used in all cases and the data were corrected for
absorption. The structures were solved using the standard
SHELXS-97 package. Machine parameters, crystal data, and data
collection parameters for 1·2.5CH3CN, 2·2CH3CN, and 3·toluene
are summarized in Table 3, while selected bond lengths and angles
are listed in Table 1.
CCDC-166560, -166561 and -166552 contain the supplementary
crystallographic data for complexes 1·2.5CH3CN, 2·2CH3CN, and
3·toluene, respectively. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; Fax: (internat.) ϩ44-1223/336-033; E-mail:
deposit@ccdc.cam.ac.uk].
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Acknowledgments
[21]
[22]
Financial support from NSF (CHE-9818492) and NIH (GM
61636) is gratefully acknowledged. The Bruker SMART 1000 dif-
fractometer was funded in part by an NSF Instrumentation Grant
CHE-9808259.
Received July 18, 2001
[I01267]
Eur. J. Inorg. Chem. 2002, 859Ϫ865
865