Synthesis and structural characterization of new phosphinooxazoline complexes of iron

Article abstract of DOI:10.1016/j.jorganchem.2008.06.031

The first phosphinooxazoline chelate complexes of iron were synthesized, and their structural and electronic properties were studied. The known phosphinooxazolines 2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole (7a), 2-(2-(diphenylphosphino)phenyl)-4,

Full text of DOI:10.1016/j.jorganchem.2008.06.031

Journal of Organometallic Chemistry 693 (2008) 3081–3091
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and structural characterization of new phosphinooxazoline complexes
of iron
*
Sergey L. Sedinkin, Nigam P. Rath, Eike B. Bauer
University of Missouri – St. Louis, Department of Chemistry and Biochemistry, One University Boulevard, St. Louis, MO 63121, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2008
Received in revised form 25 June 2008
Accepted 25 June 2008
Available online 2 July 2008
The first phosphinooxazoline chelate complexes of iron were synthesized, and their structural and elec-
tronic properties were studied.
The
known
phosphinooxazolines
2-(2-(diphenylphosphino)phenyl)-4,5-dihydrooxazole
(7a),
2-(2-(diphenylphosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7b), (S)-4-benzyl-2-(2-(diphenyl-
phosphino)phenyl)-4,5-dihydrooxazole (7e) and (R)-2-(2-(diphenylphosphino)phenyl)-4-phenyl-4,5-
dihydrooxazole (7f) were synthesized by a modified three step literature procedure with improved
67–60% overall yields. The new electronically tuned phosphinooxazolines 2-(5-bromo-2-(diphenyl-
phosphino)phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7c), 3-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)-4-
(diphenylphosphino)-N,N-dimethylaniline (7d) and 2-(2-(diphenylphosphino)-3-(trifluoromethyl)-
phenyl)-4,4-dimethyl-4,5-dihydrooxazole (7g) were synthesized in three to six steps with 59–29% overall
yields. Reaction of 7a–f with CpFe(CO)2I (110 °C, 2 h, toluene) gave the iodide salts of the new iron phos-
phinooxazoline complexes [CpFe(CO)(7a–f)]+ in 87–21% yield. The new complexes were characterized by
X-ray and the molecular structures confirm the octahedral coordination geometry and the half-sandwich
structure about the iron center. The impact of different oxazoline ligands on the steric and electronic
Keywords:
Iron
Phosphinooxazolines
X-ray
Carbonyl complexes
Cyclic voltammetry
properties of their iron complexes was determined by analysis of selected bond lengths,
frequency and the oxidation potentials of the ligands and the iron complexes.
mC„O stretching
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Mainly iridium, rhodium, ruthenium and palladium are em-
ployed as metal centers in the catalytic reactions described above.
Iron, however, is typically not the first choice when it comes to
the development of new catalyst systems. However, iron has a
number of advantages over other metals. It is cheap, non-toxic,
environmentally friendly and abundant. Consequently, iron is
increasingly investigated as an alternative for established transi-
tion metal catalyzed reactions such as C–C, C–N and C–O bond
forming as well as oxidation and reduction reactions [14]. Phos-
phines and nitrogen-based ligands are the most prevalent in iron
catalyzed reactions. However, we are not aware of the application
of iron PHOX complexes in catalysis. Braunstein reported hetero-
bimetallic iron copper complexes, where the two metal centers
are bridged by PHOX ligands [15]. These bimetallic complexes
are catalytically active in Diels–Alder and cyclopropanation reac-
tions, but only the phosphorus atom is coordinated to the iron
center.
Phosphinooxazolines (PHOX, 1 in Fig. 1) [1] are an efficient, non-
C2-symmetric, bidentate, P,N chelating ligand class first described
by Pfaltz [2a], Helmchen [2b] and Williams [2c]. Their development
was inspired by Crabtree’s catalyst [(cod)Ir(PCy3)(py)][PF6] (2),
featuring a phosphine and a pyridine ligand in its coordination
sphere (Fig. 1) [3]. Crabtree’s catalyst is highly active in catalytic
hydrogenation reactions, particularly for highly substituted olefins.
PHOX ligands were successfully employed in transition metal
catalyzed asymmetric reactions for such conversions as allylic alky-
lations [2b,4], allylation reactions [5], Heck reactions [6], hydroge-
nations of olefins [7] and ketones [8], transfer hydrogenation of
ketones [9], Diels–Alder reactions [10], and conjugate addition to
enones [11]. The efficiency of the PHOX ligands is in part ascribed
to their ability to create distinguishable coordination sites trans
to the phosphorus and nitrogen donors, enhancing selectivities
[1a,12]. Modifications of the PHOX ligands 1 are mainly undertaken
We were interested to determine if iron can form stable chelate
complexes with PHOX ligands. To the best of our knowledge such
complexes are not known to date. We were also interested
whether the electronic properties of the iron center could be fine
tuned via variation of the substitution pattern of the PHOX ligand.
Insights into the relationship between the structure of the ligand
at the carbon atom
aryl groups on phosphorus [4b,9,13].
a to the oxazoline nitrogen [9,13] and at the two
* Corresponding author.
E-mail address: bauere@umsl.edu (E.B. Bauer).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.06.031

3082
S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
Fig. 1. PHOX ligands (1) and Crabtree’s catalyst (2).
and the properties of the corresponding iron complexes are helpful
in the development of new iron PHOX based catalyst systems.
Herein, we describe the first examples of iron PHOX chelate
complexes. We synthesized a range of PHOX ligands varying in
their electronic and steric properties. Iron complexes of these
PHOX ligands were synthesized and structurally characterized,
and the impact of the ligand structure on the steric and the elec-
tronic properties of the complexes were investigated.
2. Results
2.1. Synthesis of new phosphinooxazoline ligands
First, a set of sterically and electronically tuned phosphinooxaz-
oline ligands was synthesized. We sought electronic tuning by
incorporating different functional groups at the phenyl connected
to the oxazoline, while steric tuning was incorporated with substit-
Scheme 1. Synthesis of sterically and electronically tuned PHOX ligands and overall
yields.
uents at the carbon in the position
line (Fig. 1).
a to the nitrogen of the oxazo-
NO2
F
NO2
Several approaches to oxazoline ring systems are known [16].
They typically utilize aromatic carboxylic acids or their synthetic
equivalents (such as acid chlorides or nitriles) and b-aminoalcohols
as starting materials. One pot syntheses from these reagents cata-
lyzed by ZnCl2 are known [2c,17], but harsh conditions are re-
quired (such as refluxing chlorobenzene) and yields are typically
moderate. However, some two-step procedures from these starting
materials often provide a more efficient pathway to oxazolines,
and one pathway is shown in Scheme 1 [4b,18]. During our studies
we found, that this two-step procedure was indeed more efficient
than the one step processes, leading to higher overall yields of the
corresponding PHOX ligands, which is in agreement with previous
reports [18].
Accordingly, the known PHOX ligands 7a, 7b, (S)-7e and (R)-7f
were synthesized via this standard method following modified lit-
erature procedures [18], as shown in Scheme 1. The benzoic acids
(3) were first converted to the acid chlorides (4), utilizing oxalyl
chloride (COCl)2, which were then reacted with the appropriate
aminoalcohol to give the amides 5a,b,e,f. The amides were cyclized
to the oxazolines 6a,b,e,f with p-toluenesulfonic acid chloride
(TsCl), and finally, in a nucleophilic aromatic substitution, the fluo-
ride substituent was exchanged for PPh2 using commercial KPPh2.
Some of the overall yields were improved over known literature
procedures [18], and full experimental details for these syntheses
may be found in the Supplementary material.
1) (COCl)2
O
2) NH2C(CH3)2CH2OH
3) TsCl
COOH
N
F
8
9 (77%, 3 steps)
Pd/C, H2
EtOAc
N(CH3)2
NH2
(CH3)2SO4
K2CO3, CH3CN
O
O
F
50%
6d
N
F
N
10
97%
Scheme 2. Synthesis of an amine-containing oxazoline.
ð1Þ
Next, electronic tuning via placing substituents at the phenyl
core was accomplished. To obtain information about the influence
of halogen substituents, commercial 2-fluorobenzoic acid was
selectively monobrominated by electrophilic aromatic sub-
stitution.
A
mixture of NaBrO3/H2SO4 was employed as the
To place an electron-donating group on the phenyl ring, the di-
methyl amino PHOX ligand 7d was synthesized as shown in
Scheme 2 for 6d followed by conversion of 6d to 7d as shown in
Scheme 1. Commercial 2-fluoro-5-nitrobenzoic acid (8) first was
converted to the corresponding oxazoline 9 employing the three
step standard procedure described above (Scheme 2). Subse-
bromination agent, and 5-bromo-2-fluorobenzoic acid (3c) was
obtained as white crystals in 88% yield (Eq. (1)). This material
was further elaborated to the corresponding PHOX ligand 7c by
the standard reaction sequence shown in Scheme 1 in 43% overall
yield from 3c.

S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
3083
quently, the nitro group in 9 was reduced to the amine with Pd/C
and H2 to obtain the amine 10 in 97% yield. The amine was then
doubly methylated using dimethyl sulfate ((CH3)2SO4) affording
the dimethyl amino oxazoline 6d in 50% yield. The methylation
is needed, as the amino substituent in 10 is not compatible with
the basic KPPh2 used in the last step to introduce the PPh2 group.
The new PHOX ligand 7d was obtained in 23% overall yield from
8 (6 steps, Schemes 1 and 2).
To place an electron withdrawing group on the ring system,
commercial 2-fluoro-3-(trifluoromethyl)benzoyl chloride (4g)
was subjected to the standard reaction sequence shown in Scheme
1. The new PHOX ligand 7g features a CF3 substituent in position
ortho to the PPh2 group and was obtained in 59% overall yield from
4g.
The new iron complexes are all chiral at the metal. Accordingly,
the achiral PHOX ligands 7a–d gave racemic mixtures of the corre-
sponding metal complexes [11a–d][I]. However, chiral PHOX li-
gands would afford two separable diastereomeric isomers when
employed in the metal complex synthesis shown in Scheme 3.
Thus, (S)-7e was reacted with CpFe(CO)2I under the standard con-
ditions described (Eq. (2)). A 1:1 mixture of the two diastereomeric
complexes [11e][I] and [11e0][I] formed, as assessed by 31P NMR of
the crude reaction mixture. Efforts to separate the stereoisomers
and to obtain diastereomerically pure material have failed so far.
Experimental details and spectroscopic data (including 19F
NMR) for all precursors are given in the Supplementary material.
The final phosphorylation step with KPPh2 leading to the new
PHOX ligands 7c, 7d, and 7g is described in Section 5. The new li-
gands were obtained as oils, some of which solidified over the
course of several weeks and were characterized by NMR (1H, 13C,
31P), mass spectrometry, IR and microanalysis. The substitution
pattern on the oxazoline and on the phenyl ring has some impact
on the chemical shift of the phosphorus atom in the 31P NMR. Typ-
ically, the PHOX ligands described herein give signals between
ꢀ4.0 and ꢀ4.8 ppm. The PHOX ligand 7d bearing the electron-
donating NMe2 group, however, has a 31P NMR chemical shift of
ꢀ6.8 ppm and ligand 7g featuring an electron withdrawing CF3
group has a shift of 0.6 ppm.
ð2Þ
However, the PHOX ligand (R)-7f gave a 85:15 mixture of two dia-
stereomers (31P NMR) when reacted with CpFe((CO)2I (Eq. (3)), and
it was possible to isolate the major diastereomer [11f][I] by frac-
tional crystallization in 63% yield.
2.2. Synthesis of new iron phosphinooxazoline complexes
For incorporation of a PHOX ligand into an iron complex, the
cyclopentadienyl complex CpFe(CO)2I was selected as a precursor
as it is readily available by iodination of commercial iron
carbonyl dimer [CpFe(CO2)]2 [19]. The complex CpFe(CO)2I is
known to give iodide salts of the half-sandwich complexes of the
type [CpFe(CO)2(L)]+ when treated with monodentate donor li-
gands [20]. Reactions with bidentate ligands to give the iodide salts
of the half-sandwich complexes [CpFe(CO)(L–L)]+ are less common
but a few examples have been described in the literature [21]. We
anticipated that the CO ligand would be a sensitive probe for the
electron density at the iron center, which typically impacts the
carbonyl stretching frequency in the IR spectrum.
Accordingly, the PHOX ligands 7a–d were reacted with
CpFe(CO)2I (toluene, 110 °C, 2 h) form which the desired product
precipitated. Recrystallization from CH2Cl2/Et2O provided the
new target compounds [11a–d]+[I]ꢀ as red powders in 87–21%
yields which will subsequently be referred to without charges
(Scheme 3).
I-
+
CpFe(CO)2I
O
Ph
Fe
toluene, 110 °C
recrystallization
PPh2 N
OC
ð3Þ
N
Ph2P
Ph
7f
O
(R)-
11f
, 63%
one diastereomer
Finally, we attempted conversion of the PHOX ligand 7g (featur-
ing a CF3 substituent in position ortho to the PPh2) to the corre-
sponding iron complex (Eq. (4)). After employing the standard
procedure described, complex [11g] could be detected in the crude
reaction mixture by mass spectrometry, IR and 31P NMR. However,
all efforts to isolate the PHOX iron complex [11g][I] have failed to
date (as a result of continuing decomposition during attempts to
separate the desired product).
I-
+
CpFe(CO)2I
I-
+
X
Fe
OC
O
toluene
110 °C
2 h
N
CpFe(CO)2I
Ph2P
F3C
(4)
F3C
R2
Fe
O
ð4Þ
PPh2
N
toluene
110 °C
2 h
R1
O
OC
Y
N
7g
Ph2P
Y
11g
PPh2 N
O
R2
detected in the crude
reaction mixture, not
isolable
R1
7
X
1
2
We assume an intrinsic instability of complex [11g][I], because the
crude reaction mixture contained a major side product, as seen by a
peak in the 31P NMR at ꢀ57.3 ppm, which did not disappear after
purification attempts. Presumably the iodide counter ion under-
takes (aided by the electron withdrawing CF3 group) a nucleophilic
attack on the central aromatic ring, displacing the PPh2 group.
11a
, 66%
X = Y = R = R = H,
1
2
11b
X = Y = H, R = R = CH3,
, 47%
X = Br, Y = H, R1 = R2 = CH3, 11c, 87%
X = NMe2, Y = H, R1 = R2 = CH3, 11d, 21%
Scheme 3. Synthesis of iron PHOX complexes [11a–d][I].

3084
S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
All new iron PHOX complexes [11a–d][I] and [11f][I] were char-
well soluble in CH2Cl2, methanol and acetone. The metal com-
plexes slowly decompose in CH2Cl2 solutions. The decomposition
involves oxidation to paramagnetic iron(III) species, as seen by line
broadening of corresponding aged NMR samples.
acterized by NMR (1H, 13C, 31P), mass spectrometry, IR, and micro-
analysis. All iron complexes except for [11f][I] were isolated as
CH2Cl2 solvates, as seen in the microanalyses and the 1H and 13C
NMR spectra. The solvent could not completely be removed in va-
cuo, even at elevated temperatures. Accordingly, all X-ray struc-
tures (vide infra) except for that of [11f][I] exhibited solvent
molecules in the crystal lattice.
2.3. Further analysis of the phosphinooxazoline iron complexes
2.3.1. X-ray structure analyses
The coordination of the PHOX ligand was best seen by the large
downfield shift of the phosphorus signal in the 31P NMR spectrum.
The free ligands have chemical shifts of around ꢀ4.5 ppm, whereas
the iron complexes exhibited signals between 61.3 and 67.0 ppm.
Due to coordination of the PHOX ligand to the iron center, the
two phenyl rings on phosphorus become diastereotopic, and give
in principle different 13C NMR signals for each carbon atom (but
the peaks are in practice not always resolved). Some of the aro-
matic carbon atoms couple with the phosphorus (JCP = 2–11 Hz).
As a consequence, a complex 13C NMR spectrum in the aromatic re-
gion was observed. However, the number of signals did not reach
the number of diastereomeric aromatic carbons, and some of the
peaks had shoulders (or other non-Gaussian features).
To unequivocally establish the structures of the new iron PHOX
complexes, the crystal structure of selected iodide complexes was
determined (Table 2 and Section 5). Complexes [11a][I], [11c][I],
and [11d][I] crystallized readily, but the other complexes did not
give crystals of X-ray quality. To obtain material that crystallized
more easily, the iodide counter ion in [11b][I] was exchanged by
ClOꢀ4 to give [11b][ClO4] and in [11f][I] by PF6ꢀ to give [11f][PF6] as
described in Section 5.
The molecular structures are depicted in Figs. 2 and 3 and Table
3 lists key structural data.
The bond angles around iron range from 83.2(3)° for the N(1)–
Fe(1)–P(1) angle to 100.00(8)° for the C(1)–Fe–P(1) angle. Thus, the
coordination geometry of the complexes is best described as a
slightly distorted octahedron. The deviations for the C(1)–Fe–
N(1) angles from ideal 90° are the largest for complexes [11b],
[11c] and [11d] (99.2(6)–100.00(8)°, see entry 9 in Table 3). These
The CO ligand was observed in the IR spectra, in the 13C NMR
and in the mass spectra. All new complexes showed one mC„O
stretching frequency in the IR spectrum; they are listed in Table
1 and show some dependency on the ligand structure (vide infra).
In the 13C NMR spectra, the CO carbon gave a doublet between
216.9 and 219.2 ppm (JCP = 27.7–29.8 Hz), which is in accordance
with related cyclopentadienyl iron carbonyl complexes [20a]. The
FAB mass spectra showed a strong peak for the cationic portion
of the metal complex, and an equally strong peak arising from loss
of CO.
complexes bear two methyl substituents in the position
a to the
nitrogen in the oxazoline ring. Complex [11a] bears two hydrogen
atoms in this position and [11f] one phenyl ring, and their C(1)–Fe–
N(1) angle is closer to the ideal 90°. Obviously the two methyl
groups in [11b], [11c] and [11d] increase – due to steric interac-
tions – the C(1)–Fe–N(1) angle. In turn, the deviation from linearity
for the CO ligand are the greatest for [11b], [11c] and [11d]
(174.64(19)–170.7(16)°, entry 12 in Table 3), presumably due to
the same steric interaction with the two methyl groups.
The structural differences between [11a] and [11f] on the one
hand and [11b], [11c] and [11d] on the other hand are best seen
in the overlay of the structures of [11a] and [11b] shown in
Fig. 4. In complex [11a], the oxazoline ring plane is oriented almost
parallel to the axis formed by the iron and the Cp centroid; the
phenyl ring attached to the oxazoline points away from the Cp.
In [11b], the oxazoline plane is oriented perpendicular to this axis,
and the phenyl ring points towards the Cp ring.
The Fe–C bond distances between the iron center and the car-
bon atoms of the cyclopentadienyl ring are not all equal (Table 3,
entries 5–7). The Fe–C bond distances trans to the phosphorus
and the CO ligand are slightly longer than the bond distances trans
to the nitrogen. This effect has been previously described and
might be associated with the stronger trans influence of phospho-
rus and CO ligands [10a,b].
Finally, the geminal protons in all complexes [11a–f] and the
geminal methyl groups of the oxazoline rings in [11b–c] are diaste-
reotopic, and consequently give separate signals in the 1H and 13C
NMR, respectively.
Complex [11f] is both chiral at the metal and at the ligand, and
potentially two diastereomers form upon synthesis, which are dis-
tinguishable by NMR. Accordingly, two signals were observed in
the 31P NMR spectra of the crude reaction mixture and also two
signals for the Cp ring in the 13C NMR. Also, some resonances in
the 1H NMR were doubled. After fractional recrystallization, [11f]
was obtained as single diastereomer, as best seen in the NMR spec-
tra. In the 31P NMR, only one signal was observed. The three H
atoms on the oxazoline ring in [11f] are diastereotopic. They gave
three signals in the 1H NMR spectrum, as expected for a diastereo-
pure compound. In the 13C NMR, only one signal for the Cp ligand
was observed.
All metal complexes were obtained as orange-red powders.
They are poorly soluble in hexanes, CHCl3 and diethyl ether, but
The bite angles N(1)–Fe–P(1) (Table 3, entry 10) of the phosph-
inooxazoline ligand vary by only a small amount with the substitu-
ent, being the biggest for the oxazoline with a phenyl substituent
a
to nitrogen in [11f] (86.92(9)°), and the smallest in [11d] (83.2(3)°)
having two methyl substituents in that position.
Table 1
Physical data of iron PHOX complexes
Ec
(V)
ic/
ia
Epa
(V)
Epa (V) Free
c
c
d
Due to coordination of the PHOX ligand to the iron center, a six-
membered chelate ring forms, containing the atoms Fe–N(1)–C(9)–
(C10)–(C15)–P(1). This chelate ring is best described as an enve-
lope conformer and is here analyzed as previously described by
Helmchen and co-workers [22]. All calculations were performed
using MERCURY 1.4.2 software.
Complex mC„O
C„O bond
distance (AÅ)
E1/2
(V)
D
0
c
(cmꢀ1
)
ligand 7
[11a][I]
[11b][I]
[11c][I]
[11d][I]
[11e][I]
[11f][I]
1971
1944
1947
1951
1950
1967
1.138(3)
1.150(3)a
1.159(13)
1.16(2)
1.00
1.28
1.20
1.01
0.43 0.90 1.21 0.92
0.36 1.0 1.46 0.86
0.24 0.95 1.32 1.13
1.18 0.87
1.09
0.35 0.95 1.18 0.82
0.33 1.0
As shown in Fig. 5, five of the six ring atoms – N(1)–C(9)–(C10)–
(C15)–P(1) – nearly form a plane. The involved atoms deviate from
1.142(3)b
1.00
a
[11b][ClO4].
[11f][PF6].
the ideal plane by an average value given in Table 4 and the largest
0
b
c
deviation from planarity was observed for complex [11a] (0.165 ÅA).
The iron center is located above this plane. The ideal N(1)–C(9)–
(C10)–(C15)–P(1) plane and the plane spanned by the iron center
Data from cyclic voltammetry experiments for the first redox couple, referenced
against ferrocene as internal standard (see Section 5). All complexes with [PF6]ꢀ
counter ions.
d
First oxidation potential.
and the two coordinated N(1) and P(1) atoms form an angle
a

S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
3085
Table 2
Crystallographic parameters
[11a][I] ꢁ (CH2Cl2)
28H25Cl2FeINO2P
692.11
566(2)/0.71073
[11b][ClO4] ꢁ (CH3COCH3) [11c][I] ꢁ (CH2Cl2) ꢁ (I2)0.5
[11d][I] ꢁ (CHCl3)4 ꢁ (Et2O)(H2O) [11f][PF6]
Empirical formula
Formula weight
Temperature (K)/
wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
C32H33ClFeNO7P
665.86
C60H56Br2Cl4Fe2I3N2O4P2
1725.03
C70H82Cl12Fe2I2N4O7P2
1944.24
C33H27F6FeNO2P2
701.35
100(2)/0.71073
100(2)/0.71073
100(2)/0.71073
100(2)/0.71073
Monoclinic
P21/c
Monoclinic
P21/c
Triclinic
P1
Monoclinic
Monoclinic
ꢀ
P21/c
P21
14.0012(4)
19.8125(6)
11.1039(3)
90
112.9750(10)
90°
13.7233(9)
13.1971(9)
17.6282(12)
90
110.192(4)
90
13.4019(13)
14.9871(17)
17.2908(19)
112.900(6)
95.131(6)
90.428(6)
3183.0(6)/2
1.800
23.558(2)
13.0156(12)
26.819(2)
90
9.3227(6)
16.4376(11)
9.8896(7)
90
b (Å)
c (Å)
a
(°)
b (°)
97.192(4)
90
96.765(3)
90
c
(°)
Volume (Å3)/Z
2835.87(14)/4
1.621
2996.4(3)/4
1.476
8158.8(12)/4
1.583
1504.96(18)/2
1.548
Dcalc (Mg/m3)
Absorption coefficient
1.891
0.696
3.430
1.596
0.678
(mmꢀ1
)
F(000)
Crystal size (mm)
h Range for data collection 2.87–27.15
1376
0.35 ꢂ 0.28 ꢂ 0.26
1384
1682
3912
716
0.26 ꢂ 0.13 ꢂ 0.12
0.24 ꢂ 0.07 ꢂ 0.06
0.33 ꢂ 0.20 ꢂ 0.18
0.27 ꢂ 0.20 ꢂ 0.11
2.78–26.47
1.53–25.00
1.66–25.00
3.10–26.44
(°)
Index ranges
ꢀ17 6 h 6 17,
ꢀ24 6 k 6 25,
ꢀ13 6 l 6 14
69770
ꢀ17 6 h 6 17,
ꢀ16 6 k 6 16,
ꢀ22 6 l 6 22
73411
ꢀ15 6 h 6 15,
ꢀ17 6 k 6 17,
ꢀ20 6 l 6 20
85151
ꢀ27 6 h 6 25, ꢀ15 6 k 6 14,
ꢀ31 6 l 6 31
ꢀ11 6 h 6 11,
ꢀ20 6 k 6 20,
ꢀ12 6 l 6 12
32208
Reflections collected
75358
Independent reflections
6262 (0.037)
6095 (0.068)
11119 (0.196)
14254 (0.12)
6138 (0.058)
(Rint
)
Completeness to h = 27.15° 99.7
98.2
99.2
99.2
99.2
(%)
Absorption correction
Numerical
0.6877 and 0.6279
Numerical
0.9211 and 0.8398
Semi-empirical from
equivalents
0.8206 and 0.4932
Numerical
0.8382 and 0.7366
Numerical
0.9280 and 0.8376
Maximum and minimum
transmission
Refinement method
Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares Full-matrix least-squares on F2 Full-matrix least-squares
on F2
on F2
on F2
on F2
Data/restraints/
parameters
6262/6/343
6095/0/392
11119/0/658
14254/9/865
6138/55/454
Goodness-of-fit on F2
1.032
1.035
0.991
1.810
1.050
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0337, wR2 = 0.0796 R1 = 0.0347, wR2 = 0.0739 R1 = 0.0728, wR2 = 0.1534 R1 = 0.1304, wR2 = 0.2835
R1 = 0.0522, wR2 = 0.0887 R1 = 0.0500, wR2 = 0.0795 R1 = 0.1546, wR2 = 0.1870 R1 = 0.1948, wR2 = 0.2988
R1 = 0.0387, wR2 = 0.0732
R1 = 0.0512, wR2 = 0.0776
0.346 and ꢀ0.311
Largest difference in peak 0.463 and ꢀ0.394
0.420 and ꢀ0.364
1.964 and ꢀ1.736
5.216 and ꢀ2.146
and hole (e Åꢀ3
)
Absolute structure
parameter
ꢀ0.015(13)
(Fig. 5). The angle
a
depends on the PHOX ligand (Table 4), being
did not give meaningful results. However, the optical rotation of
the ligand 7f employed in metal complex synthesis was close to
the literature value [18]. The enantiomer of [11f] required a change
of the absolute configuration at the ligand. We are not aware of a
mechanism that could largely racemize the ligand. Thus, we as-
sume [11f] is of high optical purity.
the greatest for [11b], [11c], and [11d] (52.35–55.32°, with two
methyl substituents on the oxazoline ring), somewhat smaller for
[11a] (42.66°, no substituent on the oxazoline ring) and the small-
est for [11f] (41.02°, one phenyl on the oxazoline ring). The two
phenyl groups on phosphorus occupy pseudoaxial and pseudoequ-
atorial positions and are thus diastereotopic.
The angle between the best fit planes of the oxazoline ring and
the phenyl ring, to which it is connected, was also calculated (Table
4). The angle is the smallest for [11a] and [11f] (13.19–14.99°) and
larger for the oxazoline ring bearing two methyl groups in [11b],
[11c] and [11d] (21.95–27.96°). Finally, the distance between the
iron center and the centroid of the cyclopentadienyl ring was cal-
culated (Table 4). These values only range between 1.714 and
1.729 Å and depend very little on the ligand structure.
Complex [11f] is chiral at the metal. According to the priority
order C5H5 > P > N > C [10,23], the absolute configuration of this
complex is (R), as determined from the X-ray structure. However,
a racemic crystal of [11f] was also found in the crystallized mate-
rial. Attempts were made to determine the optical purity of the
bulk sample, but solutions of [11f] are intensely colored, making
the determination of optical rotations difficult, even at different
wavelengths [24]. NMR experiments with chiral shift reagents
2.3.2. Cyclic voltammetry
In order to obtain preliminary insight into the electronic prop-
erties of the new metal complexes, cyclic voltammograms of the
PHOX ligands and the iron PHOX complexes were recorded as de-
scribed in Section 5. Key data are listed in Table 1 and the traces are
given in the Supplementary material.
The cyclic voltammograms of the ligands suggest complex and
irreversible chemical reactions taking place [25]. Scans towards
increasing positive potential show a varying number of irreversible
oxidation waves without reduction waves on the reverse scan. No
signs of greater reversibility were observed at higher scan rates up
to 2 V sꢀ1 and faster scans further impeded the electron transfer.
The potentials of the free PHOX ligands for the first oxidation dif-
fered between 0.82 and 1.13 V. The oxidation potentials show a
slight dependency on the substituents. For example, ligand 7b
has an oxidation potential Ea of 0.86 V, whereas ligand 7c – bearing

3086
S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
Fig. 2. Molecular structures of iron PHOX complexes [11a][I], [11b][ClO4] (top) and [11c][I], [11d][I] (bottom). Counter ions and solvent molecules are omitted for clarity.
sluggish electron transfer. At higher potentials, additional irrevers-
ible oxidation waves were observed for almost all complexes. The
complex electrochemical reactions taking place at higher oxidation
states remain as a subject of future study.
Whereas the ligands alone show irreversible electrochemical
behavior, the formation of the complex yields much greater signs
of reversibility. This suggests that a one-electron oxidation and
reduction is occurring that involves a highest occupied molecular
orbital found only for the complex and not for the ligand alone.
The relationship between Ea and the mC„O stretching frequency will
be discussed in the next section.
3. Discussion
This study shows for the first time the isolation and character-
ization of a series of stable PHOX chelate complexes of iron. Steric
and electronic properties are influenced by the structure of the
PHOX ligand.
Fig. 3. Molecular structures of iron PHOX complex [11f][PF6]. Counter ion omitted
for clarity.
a bromo substituent – has an oxidation potential of 1.13 V. As ex-
pected, the electron withdrawing bromo substituent increases the
oxidation potential of the PHOX ligand.
The steric properties of the new the iron complexes described
above are basically governed by the substituents
atom on the oxazoline ring as shown by the crystallographic data.
Complex [11a] bearing no substituent to the nitrogen in the
a to the nitrogen
The cyclic voltammograms for the corresponding metal com-
plexes show a fair degree of reversibility in that a reduction wave
is seen for each complex that appears similar in size and is of com-
plimentary shape to the first oxidation wave. The E1/2 values for the
first oxidation range from 1.00 to 1.28 V and the peak current ra-
tios ic/ia are P0.9. While the ideal separation between the oxida-
tion and reduction peaks for a diffusing species undergoing a
one-electron oxidation–reduction cycle is 59 mV, the peak-to-peak
a
oxazoline ring system crystallographically resembles [11f], bearing
one phenyl substituent in that position. Complexes [11b], [11c]
and [11c] bear two methyl groups in this position and are structur-
ally related as well. The geminal methyl groups cause changes in
the structure of the corresponding complexes, as shown in Fig. 4.
The properties of the new iron complexes were further analyzed
by means of X-ray structure analysis, oxidation potentials deter-
mined by cyclic voltammetry and by evaluation of the IR spectra
separations
DE seen here are between 0.24 and 0.43 V suggesting

S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
3087
Table 3
Selected bond lengths, angles and torsion angles for iron PHOX complexes
Entry
Complex
[11a][I]
[11b][ClO4]
[11c][I]
[11d][I]
[11f][PF6]
0
Bond lengths (ÅA)
1
2
3
4
5
6
7
8
Fe–C(1)
Fe–N(1)
Fe–P(1)
N(1)–C(9)
Fe–C(X) (trans to CO)
Fe–C(Y) (trans to N)
Fe–C(Z) (trans to P)
C(1)–O(1)
1.753(3)
1.980(2)
2.1891(7)
1.274(4)
2.110(3)a
2.088(3)a
2.103(3)a
1.138(3)
1.754(2)
1.9788(17)
2.1950(6)
1.285(2)
2.100(2)b
2.080(2)b
2.112(2)b
1.150(3)
1.755(13)
1.989(9)
2.192(4)
1.271(14)
2.103(12)c
2.068(11)c
2.137(12)c
1.159(13)
1.75(3)
1.763(3)
1.988(3)
2.1868(9)
1.292(5)
2.122(3)e
2.079(3)e
2.096(3)e
1.142(3)
1.983(11)
2.197(4)
1.277(18)
2.082(16)d
2.078(13)d
2.111(14)d
1.16(2)
Bond angles (°)
9
C(1)–Fe–N(1)
N(1)–Fe–P(1)
C(1)–Fe–P(1)
O(1)–C(1)–Fe
92.62(12)
85.23(7)
92.32(9)
176.6(3)
100.00(8)
83.38(5)
93.58(7)
99.4(4)
84.2(3)
96.2(4)
173.6(10)
99.2(6)
83.2(3)
96.5(5)
170.7(16)
91.57(14)
86.92(9)
92.90(11)
176.2(3)
10
11
12
174.64(19)
Torsion angles (°)
13
N(1)–C(9)–C(10)–C(15)
ꢀ17.8(4)
ꢀ31.8(3)
25.1(18)
33(2)
20.1(6)
a
X = 2, Y = 4, Z = 6.
X = 6, Y = 3, Z = 4.
X = 4, Y = 6, Z = 2.
X = 5, Y = 2, Z = 3.
b
c
d
e
X = 3, Y = 6, Z = 5.
Table 4
Structural parameters calculated from X-ray data
Complex
[11a]
[11b]
[11c]
[11d]
[11f]
Envelope angle aa (°)
42.66
0.165
14.99
1.729
55.32
0.116
27.96
1.725
52.35
0.107
21.95
1.714
53.91
0.107
24.86
1.723
41.02
0.087
13.19
1.723
0
Deviation from planarityb (ÅA)
Oxazoline–Ph anglec (°)
0
Fe–Cp distanced (AÅ)
a
The angle between an idealized plane formed by N(1)–C(9)–C(10)–C(15)–P(1)
and the N(1)–Fe–P(1) plane, see Fig. 5.
b
Average distance of the involved atoms from the ideal N(1)–C(9)–C(10)–C(15)–
P(1) plane.
c
The angle between an idealized plane formed by the oxazoline ring and the
plane of the phenyl to which it is attached.
d
Distance between the Cp centroid and Fe.
(Table 1). In general, strongly electron-donating ligands increase
the electron density at the metal center. As a consequence, the oxi-
dation potential of the metal complex should decrease. In addition,
electron rich metal centers increase back bonding into the p
* orbi-
tals of the carbonyl ligand. This weakens the C„O bond, resulting
in increased bond lengths and lowered IR mC„O stretching
frequencies.
Fig. 4. Overlay of the molecular structures of [11a][I] (thin lines) and [11b][ClO4]
(thick lines). For the overlay, the inverted structure of [11b][ClO4] was used.
Some dependency of the ligand structure on the oxidation po-
tential of the corresponding iron complex was observed. For most
of the cases, the oxidation potentials of the iron complexes do not
follow a clear trend (Table 1). For example, complex [11d] with the
PHOX ligand bearing an electron-donating dimethyl amino group
has about the same oxidation potential (1.01 V) as complex [11f]
without the dimethyl amino group but with one phenyl substitu-
Fe
ent
a to the oxazoline nitrogen (1.00 V). Strictly speaking, the Ea
N
P
C
C
C
values for the free ligands and the E1/2 values for the metal com-
plexes cannot be compared. However, the potentials of the ligands
seem to be generally similar to those of their respective metal com-
plexes, suggesting a ligand-centered HOMO.
The mC„O stretching frequencies, which range from 1944 to
1971 cmꢀ1, vary only little with the PHOX ligand. Complex [11a],
which bears substituents neither on the phenyl core nor on the
oxazoline ring, shows the highest stretching frequency of
1971 cmꢀ1. Complex [11f] (
ring
For all other complexes, the ligand has only a small influence on
m
C„O = 1967 cmꢀ1), bearing one phenyl
to the oxazoline nitrogen, closely resembles complex [11a].
Fig. 5. Geometry of the six-membered metallacycle formed upon coordination and
a corresponding part of the molecular structure of [11b] (whose inverted structure
was used for this representation).
a

3088
S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
the IR stretching frequencies, which range from 1944 to
1951 cmꢀ1. If at all, it seems that the substituent
to the nitrogen
C„O stretch-
5.2. Synthesis of the ligands
a
in the oxazoline ring has the biggest influence on the
m
5.2.1. Synthesis of 2-[5-bromo-2-(diphenylphosphino)phenyl]-4,4-
dimethyl-4,5-dihydro-1,3-oxazole (7c)
ing frequencies.
Similarly, the CO bond distances for the structurally character-
ized metal complexes range from 1.138(3) to 1.159(13) and show
only little dependency on the ligand structure.
The relationship between E° and mC„O has been discussed by
Eriks and Giering [26]. They established a linear dependency of
the stretching frequency mC„O on the reduction potential E° for
A Schlenk flask was charged with the aryl fluoride 6c (0.552 g,
2.029 mmol) and KPPh2 (0.5 M in THF, 4.5 mL, 2.3 mmol) was
added dropwisely with stirring. The resulting reddish solution
was refluxed for 1 h. The reaction mixture was diluted with CH2Cl2
(50 mL) and poured into a saturated aqueous solution of NaHCO3
(25 mL). The organic layer was separated, washed with H2O and
dried over MgSO4. The solution was concentrated in vacuo and
the crude product purified by flash column chromatography on
silica (1 ꢂ 15 cm column; eluted with 1:0 v/v toluene/EtOAc ? 7:3
v/v toluene/EtOAc) to obtain the product (0.540 g, 1.23 mmol, 61%)
as an oil which solidified over the course of several weeks to give a
white solid. Anal. Calc. for C23H21BrNOP: C, 63.03; H, 4.83. Found:
C, 62.75; H, 4.86%.
structurally related iron carbonyl complexes bearing a purely
r
-
donating phosphine ligand. But ligands with both -donor/
r
p
-
acceptor capability exhibited considerable scatter of linearity in
this study. The PHOX ligands described herein feature in the oxaz-
oline ring a sp2 hybridized nitrogen atom capable of backbonding.
Furthermore, the electrochemical data point towards a ligand-cen-
tered HOMO, whereas the mC„O reflects the electron density at the
metal. These might be the reasons why a linear dependency of the
electron density of the ligand and the oxidation potential of its cor-
responding metal complex could not be observed.
Furthermore, analysis and comparison of trends described
above are, strictly speaking, possible only for structurally related
complexes. The X-ray analysis data show that the complexes differ
somewhat in their geometry (see e.g. Fig. 4 or the Fe–C(1)–(O) an-
gles which show noticeable deviation from linearity, as seen in en-
try 12 in Table 2), which also might explain deviations from
idealized trends.
NMR (d, CDCl3) 1H 8.02 (t, 4JHH = 2.6 Hz, 1H, H-6 aromatic), 7.38
(dd, 3JHH = 8.4, 4JHH = 2.2 Hz, 1H, H-4 aromatic), 7.29–7.34 (m, 10 H,
P(C6H5)2), 6.67 (dd, 3JHH = 8.3, 3JHP = 4.0 Hz, 1H, H-3 aromatic), 3.74
3
(s, 2H, CH2O), 1.04 (s, 6H, 2CH3); 13C{1H} 161.1 (d, JCP = 2.7 Hz,
C@N), 138.0 (d, JCP = 26. 9 Hz, Ph), 137.2 (d, JCP = 11.0 Hz, Ph),
134.9 (d, JCP = 2.7 Hz, Ph), 134.1 (d, JCP = 21.4 Hz, Ph), 133.4 (d,
JCP = 18.1 Hz, Ph), 133.3 (s, Ph), 132.8 (d, JCP = 2.2 Hz, Ph), 128.9
(s, Ph), 128.6 (d, JCP = 7.7 Hz, Ph), 122.3 (d, JCP = 1.1 Hz, Ph), 78.9
(s, CH2O), 67.7 (s, C(CH3)2), 27.9 (s, 2CH3); 31P{1H} – 4.7 (s).
MS (FAB, 3-NBA, m/z) [27] 476 ([7c+O+Na]+, 100%), 454
([7c+O]+, 7%); IR (cmꢀ1, neat) mC@N 1643 (s).
4. Conclusion
5.2.2. Synthesis of 3-(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)-4-
(diphenylphosphino)-N,N-dimethylaniline (7d)
Aryl fluoride 6d (0.122 g, 0.515 mmol) was converted as de-
scribed above for 7c to obtain 7d (0.162 g, 0.403 mmol, 78%) as
white crystals. Anal. Calc. for C25H27N2OP: C, 74.61; H, 6.76. Found:
In conclusion, we have for the first time synthesized a series of
chelating PHOX complexes of iron, which were structurally and
spectroscopically analyzed. The crystallographically determined
bond lengths of the CO ligand and its mC„O stretching frequencies
vary only slightly with the ligand, but some dependence of the oxi-
dation potential of the complexes on the ligand structure was ob-
served. The novel PHOX complexes established herein potentially
allow for applications of iron catalysts in organic syntheses and
such studies are currently underway.
C, 74.56; H, 6.75%.
4
NMR (d, CDCl3) 1H 7.24–7.38 (m, 10H, P(C6H5)2), 7.18 (t, JHH
=
3
3
2.9 Hz, 1H, H-2 aromatic), 6.69 (dd, JHH = 8.7, JHP = 4.3 Hz, 1H,
H-5 aromatic), 6.59 (dd, 3JHH = 8.7, 4JHH = 2.8 Hz, 1H, H-6 aromatic),
3.78 (s, 2H, CH2O), 2.93 (s, 6H, N(CH3)2), 1.11 (s, 6H, 2CH3); 13C{1H}
3
163.2 (d, JCP = 1.7 Hz, C@N), 149.9 (s, Ph), 139.0 (d, JCP = 12.1 Hz),
134.7 (d, JCP = 1.7 Hz, Ph), 133.8 (d, JCP = 20.3 Hz, Ph), 133.4 (d,
JCP = 22.0 Hz, Ph), 128.2 (d, JCP = 5.4 Hz, Ph), 128.1 (s, Ph), 122.6
(d, JCP = 18.1 Hz, Ph), 114.0 (s, Ph), 113.5 (d, JCP = 4.4 Hz, Ph), 78.7
(s, CH2O), 67.5 (s, C(CH3)2), 40.1 (s, N(CH3)2), 28.0 (s, C(CH3)2);
31P{1H} – 6.8 (s).
5. Experimental
5.1. General methods
MS (FAB, 3-NBA, m/z) [27] 425 ([7d+Na]+, 68%), 441
([7c+O+Na]+, 48%); IR (cmꢀ1, neat) mC@N 1598 (s).
Chemicals were treated as follows: THF, toluene, diethyl
ether, distilled from Na/benzophenone; CH2Cl2, distilled from
CaH2; KPPh2, (Aldrich, 0.5 M in THF), NaPF6 (Aldrich) used as
received. The syntheses of 2-(5-bromo-2-fluorophenyl)-4,
4-dimethyl-4,5-dihydro-1,3-oxazole (6c), 3-(4,4-dimethyl-4,5-
dihydro-1,3-oxazol-2-yl)-4-fluoro-N,N-dimethylaniline (6d), and
2-[2-fluoro-3-(trifluoromethyl)phenyl]-4,4-dimethyl-4,5-dihydro-
1,3-oxazole (6g) and intermediates (if required) are described in
the Supplementary material. CpFe(CO)2I was synthesized accord-
ing to the literature [19].
5.2.3. Synthesis of 2-[2-(diphenylphosphino)-3-
(trifluoromethyl)phenyl]-4,4-dimethyl-4,5-dihydro-1,3-oxazole (7g)
Aryl fluoride 6g (1.562 g, 5.98 mmol) was converted and
worked up as described above for 7c to obtain 7g (2.07 g,
4.84 mmol, 81%) as slightly yellowish crystals. Anal. Calc. for
C
24H21F3NOP: C, 67.44; H, 4.95. Found: C, 67.42; H, 5.02%.
NMR (d, CDCl3) 1H 7.85–7.98 (m, 2 H, H-4, H-6 aromatic), 7.57
3
NMR spectra were obtained at room temperature on a Bruker
Avance 300 MHz or a Varian Unity Plus 300 MHz instrument and
referenced to a residual solvent signal; all assignments are tenta-
tive. GC/MS spectra were recorded on a Hewlett Packard GC/MS
System Model 5988A. Exact masses were obtained on a JEOL MSta-
tion [JMS-700] Mass Spectrometer. Melting points are uncorrected
and were taken on an Electrothermal 9100 instrument. IR spectra
were recorded on a Thermo Nicolet 360 FT-IR spectrometer. UV–
Vis spectra were recorded on a Varian Cary 100 UV–Vis spectro-
photometer. Elemental analyses were performed by Atlantic
Microlab Inc., Norcross, GA, USA.
(t, JHH = 7.8 Hz, 1H, H-5 aromatic), 7.24–7.39 (m, 10H, 2C6H5),
3.46 (s, 2H, CH2O), 1.01 (s, 6H, 2CH3); 13C{1H} 163.1 (d,
3JCP = 2.2 Hz, C@N), 137.6 (d, J = 8.8 Hz, Ph), 137.6–136.1 (m, C-3
aromatic), 135.6 (s, Ph), 135.3 (dd, J = 13.5, 1.4 Hz, Ph), 135.2 (d,
J = 41.7 Hz, Ph), 132.6 (d, J = 20.3 Hz, Ph), 129.5 (s, C-6 aromatic),
129.4–129.0 (m, Ph), 128.04 (d, J = 6.6 Hz, Ph), 128.03 (s, Ph),
1
123.8 (q, JCF = 275.5 Hz, CF3), 78.3 (s, CH2O), 67.1 (s, C(CH3)2),
4
27.8 (s, C(CH3)2); 31P{1H} 0.6 (q, JPF = 46.4 Hz); 19F{1H} ꢀ 55.7 (d,
4JFP = 46.4 Hz, CF3).
MS (FAB, 3-NBA, m/z) [27] 466 ([7g+O+Na]+, 100%), 450
([7c+Na]+, 19%); IR (cmꢀ1, neat) mC@N 1644 (s).

S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
3089
5.3. Synthesis of the iron complexes
(d, JCP = 8.3 Hz, Ph), 136.1 (br, Ph), 135.1 (d, JCP = 10.5 Hz, Ph), 133.0
(br, Ph), 132.3 (s, Ph), 132.2 (s, Ph), 131.9 (d, JCP = 10.8 Hz, Ph), 131.5
(d, JCP = 2.5 Hz, Ph), 131.0 (s, Ph), 130.5 (s, Ph), 130.0 (d, JCP = 10.0 Hz,
Ph), 129.6 (d, JCP = 10.8 Hz, Ph), 128.4 (s, Ph), 127.8 (s, Ph), 127.0 (d,
JCP = 2.5 Hz, Ph), 84.3 (s, Cp), 80.8 (s, CH2), 72.2 (s, CH2), 26.0 (s, CH3),
24.7 (s, CH03); 31P{1H} 64.4 (s).
5.3.1. Synthesis of ‘‘[CpFe(CO)(7a)][I] ꢁ (CH2Cl2)0.5”,
[11a][I] ꢁ (CH2Cl2)0.5
To a Schlenk flask containing PHOX 7a (0.200 g, 0.604 mmol),
CpFe(CO)2I (0.166 g, 0.546 mmol) was added followed by toluene
(2 mL) to obtain a dark suspension. The flask was immersed in
an oil bath preheated to 110 °C, and the mixture was allowed to
stir under nitrogen atmosphere at room temperature for 2.5 h. A
red precipitate formed. The solvent was removed by high vacuum
and the residue taken up in CH2Cl2 (2 mL) and filtered through a
short pad of CeliteÒ (rinsed with CH2Cl2). The red filtrate was con-
centrated to ca. 2 mL, layered with diethyl ether, and stored at
ꢀ18 °C for 18 h. A red precipitate formed. The solvent was dec-
anted, and the red residue dried under vacuum to obtain
[11a][I] ꢁ (CH2Cl2)0.5 as a red solid (0.235 g, 0.361 mmol, 66%),
m.p. 196–198 °C dec. (capillary). Anal. Calc. for C27H23FeI-
NO2P ꢁ (CH2Cl2)0.5: C, 50.84; H, 3.72. Found: C, 50.76; H, 3.79%.
NMR (d, CD2Cl2) [28]] 1H 8.03–7.88 (m, 1H, Ph), 7.79–7.45 (m,
13H, Ph), 7.45–7.30 (s, 1H, Ph), 5.03–4.90 (s, 5H, Cp), 4.70–4.34
(m, 3H, CH2 + CHH0), 4.01–3.84 (m, 1H, CHH0); 13C{1H} 167.5 (d,
JCP = 5.6 Hz, C@N), 133.6 (d, JCP = 6.9 Hz, Ph), 133.1 (d, JCP = 9.7 Hz,
Ph), 132.6 (d, JCP = 10.3 Hz, Ph), 132.3 (br, Ph), 132.1 (s, Ph), 131.8
(d, JCP = 7.4 Hz, Ph), 131.6 (d, JCP = 5.1 Hz, Ph), 130.6 (d,
JCP = 15.5 Hz, Ph), 130.4 (s, Ph), 130.2 (d, JCP = 10.3 Hz, Ph), 129.9
(s, Ph), 129.8 (d, JCP = 10.3 Hz, Ph), 128.0 (d, JCP = 12.0 Hz, Ph),
83.9 (s, Cp), 68.7 (s, CH2), 64.3 (s, CH2); 31P{1H} 66.8 (s).
HRMS calc. for C29H2679BrNO2P56Fe 586.0233, found 586.0253;
MS (FAB, 3-NBA, m/z) [27] 586 ([11c]+, 60%), 558 ([11cꢀCO]+,
100%); IR (cmꢀ1, neat) mC„O 1947 (s), mC@N 1613 (m); UV–Vis
(nm (e
, Mꢀ1 cmꢀ1), CH2Cl2, 0.05 mM) 230 (40280), 368 (1320).
5.3.4. Synthesis of ‘‘[CpFe(CO)(7d)][I] ꢁ (CH2Cl2)”, [11d][I] ꢁ (CH2Cl2)
PHOX 7d (0.151 g, 0.375 mmol), CpFe(CO)2I (0.126 g,
0.415 mmol) in toluene (1 mL) were reacted and worked up as
described above for [11a][I]. Complex [11d][I] ꢁ (CH2Cl2) was iso-
lated as a red solid (0.065 g, 0.0853 mmol, 21%), m.p. 187–189 °C
dec. (capillary). Anal. Calc. for
50.36; H, 4.49. Found: C, 50.94; H, 4.75%.
C
31H32FeIN2O2P ꢁ (CH2Cl2): C,
NMR (d, CD2Cl2) [28] 1H 7.55–7.11 (m, 12 H, Ph), 6.77 (br s, 1H,
Ph), 4.83 (br s, 6H, Cp + CHH0), 4.68 (d, JHH = 8.1 Hz, 1H, CHH’), 4.10
(br s, 1H, CHH’), 3.17 (s, 6H, N(CH3)2), 1.48 (s, 3H, CCH3), 0.05 (s, 3H,
CCH03); 13C{1H} 219.1 (d, JCP = 28.4 Hz, CO), 167.6 (d, JCP = 6.5 Hz,
C@N), 151.4 (s, C–N), 134.4 (s, Ph), 134.1 (d, JCP = 11.2 Hz, Ph),
133.8 (s, Ph), 131.7 (s, Ph), 131.2 (d, JCP = 10.0 Hz, Ph), 130.9 (s,
Ph), 130.2 (s, Ph), 129.5 (s, Ph), 129.1 (d, JCP = 10.0 Hz, Ph), 128.5
(d, JCP = 10.5 Hz, Ph), 116.9 (br m, Ph), 113.7 (d, JCP = 7.6 Hz, Ph),
113.5 (s, Ph), 112.9 (s, Ph), 84.1 (s, Cp), 79.5 (s, CH2), 70.8 (s,
C(CH3)2), 40.3 (s, N(CH3)2), 26.1 (s, CH3), 24.1 (s, CH03); 31P{1H}
61.3 (s).
HRMS calc. for C27H23NO2P56Fe 480.8015, found 480.8023; MS
(FAB, 3-NBA, m/z) [27] 480 ([11a]+, 45%), 452 ([11aꢀCO]+, 55%);
IR (cmꢀ1, neat) mC„O 1971 (s), mC@N 1610 (m).
HRMS calc. for C31H32N2O2P56Fe 551.1551, found 551.1561; MS
(FAB, 3-NBA, m/z) [27] 551 ([11d]+, 40%), 523 ([11dꢀCO]+, 100%);
IR (cmꢀ1, neat) mC„O 1951 (s), mC@N 1583 (m); UV–Vis (nm (
e,
5.3.2. Synthesis of ‘‘[CpFe(CO)(7b)][I] ꢁ (CH2Cl2)”, [11b][I] ꢁ (CH2Cl2)
PHOX 7b (0.117 g, 0.327 mmol), CpFe(CO)2I (0.090 g, 0.296
mmol) in toluene (1.5 mL) were reacted and worked up as de-
scribed above for [11a][I]. Complex [11b][I] ꢁ (CH2Cl2) was isolated
as a red solid (0.100 g, 0.139 mmol, 47%), m.p. 180–182 °C dec.
(capillary). Anal. Calc. for C29H27FeINO2P ꢁ (CH2Cl2): C, 50.03; H,
4.06. Found: C, 50.09; H, 4.04%.
Mꢀ1 cmꢀ1), CH2Cl2, 0.025 mM) 245 (49280), 231 (48840), 296
(19520), 361 (7280).
5.3.5. Synthesis of ‘‘[CpFe(CO)(7e)][I]”, [11e+11e0][I]
PHOX 7e (0.200 g, 0.474 mmol) and CpFe(CO)2I (0.159 g,
0.524 mmol) in toluene (2 mL) were reacted and worked up as de-
scribed above for [11a][I]. [11e+11e0][I] was isolated as mixture of
diastereomers as a red solid (0.250 g, 0.359 mmol, 76%).
NMR (d, CDCl3) 1H 8.52–8.35 (m, 1H, Ph), 7.88–7.19 (m, 11H,
Ph), 7.17–6.98 (m, 2H, Ph), 5.27 (CH2Cl2), 4.89 (s, 6 H, Cp + CHH0),
4.07 (d, JHH = 8.4 Hz, 1H, CHH0), 1.34 (s, 3H, CH3), 0.10 (s, 3H, CCH03);
13C{1H} 219.2 (d, JCP = 29.4 Hz, CO), 167.4 (d, JCP = 7.0 Hz, C=N),
134.7 (d, JCP = 11.5 Hz, Ph), 133.6 (d, JCP = 7.2 Hz, Ph), 133.3 (d,
JCP = 7.2 Hz, Ph), 132.7 (s, Ph), 132.5 (s, Ph), 132.5 (s, Ph), 132.3
(s, Ph), 131.8 (s, Ph), 131.6 (d, JCP = 11 Hz, Ph), 131.3 (s, Ph), 130.9
(d, JCP = 2.2 Hz, Ph), 130.5 (d, JCP = 11.0 Hz, Ph), 129.6 (d,
JCP = 11.0 Hz, Ph), 129.1 (d, JCP = 10.5 Hz, Ph), 128.7 (s, Ph), 128.2
(s, Ph), 128.0 (s, Ph), 84.1 (s, Cp), 79.6 (s, CH2), 71.3 (s, CH2), 53.4
(CH2Cl2), 25.7 (s, CH3), 24.4 (s, CH03); 31P{1H} 64.3 (s).
NMR (d, CDCl3) 1H 8.09 (m, 1H, Ph), 7.70–7.48 (m, 8H, Ph), 7.37–
7.21 (m, 5H, Ph), 7.06–6.94 (m, 3H, Ph), 6.85 (d, JHH = 10.5 Hz, 1H,
Ph), 5.86–5.81 (m, 1H, CH), 5.00–4.98 (m, 1H, CH), 4.61 (s, 5H,
13
Cp), 4.19–4.14 (m, CH); C{1H}(partial) 84.8 (s, Cp), 84.0 (s, Cp0);
31P{1H} 66.5 (s), 65.2 (s).
HRMS calc. for C34H29NO2P56Fe 570.1284, found 570.1271; MS
(FAB, 3-NBA, m/z) [27] 570 ([11e]+, 60%), 542 ([11eꢀCO]+, 100%);
IR (cmꢀ1, neat) mC„O 1950 (s), mC@N 1608 (m).
HRMS calc. for C29H27NO2P56Fe 508.1129, found 508.1125; MS
(FAB, 3-NBA, m/z) [27] 508 ([11b]+, 95%), 480 ([11bꢀCO]+, 100%);
5.3.6. Synthesis of ‘‘[CpFe(CO)((R)-7f)][I]”, [11f][I]
IR (cmꢀ1, neat) mC„O 1944 (s), mC@N 1610 (m); UV–Vis (nm (
e,
PHOX (R)-7f (0.344 g, 0.844 mmol) and CpFe(CO)2I (0.230 g,
0.757 mmol) in toluene (2 mL) were reacted and worked up as de-
scribed above for [11a][I]. Complex [11f][I] was isolated as a red
solid (0.325 g, 0.476 mmol, 63%), m.p. 201–202 °C dec. (capillary).
Anal. Calc. for C33H27FeINO2P: C, 58.01; H, 3.98. Found: C, 57.74;
H, 3.99%.
Mꢀ1 cmꢀ1), CH2Cl2, 0.05 mM) 230 (36080), 368 (2940).
5.3.3. Synthesis of ‘‘[CpFe(CO)(7c)][I] ꢁ (CH2Cl2)0.5”, [11c][I] (CH2Cl2)0.5
PHOX 7c (0.200 g, 0.456 mmol), CpFe(CO)2I (0.125 g,
0.411 mmol) in toluene (1 mL) were reacted and worked up as de-
scribed above for [11a][I]. Complex [11c][I] ꢁ (CH2Cl2)0.5 was iso-
lated as a red solid (0.271 g, 0.358 mmol, 87%), m.p. 180–182 °C
dec. (capillary). Anal. Calc. for C29H26BrFeINO2P(CH2Cl2)0.5, 46.83;
H, 3.60. Found: C, 47.10; H, 3.73%.
NMR (d, CDCl3) 1H 8.09 (m, 1H, Ph), 7.70–7.48 (m, 8H, Ph), 7.37–
7.21 (m, 5H, Ph), 7.06–6.94 (m, 3H, Ph), 6.85 (d, JHH = 10.5 Hz, 1H,
Ph), 5.86–5.81 (m, 1H, CH), 5.00–4.98 (m, 1H, CH), 4.61 (s, 5H,
Cp), 4.19–4.14 (m, 1H, CH); 13C{1H} 216.9 (d, JCP = 27.3 Hz, CO),
167.7 (d, JCP = 4.7 Hz, C@N), 139.9 (s, Ph), 133.7 (d, JCP = 6.5 Hz,
Ph), 132.9 (s, Ph), 132.72 (s, Ph), 132.68 (s, Ph), 132.5 (s, Ph),
132.2 (s, Ph), 132.14 (s, Ph), 132.11 (s, Ph), 131.9 (d, JCP = 3.0 Hz,
Ph), 131.2 (s, Ph), 130.9 (s, Ph), 130.6 (s, Ph), 130.4 (d, JCP = 6.2 Hz,
Ph), 129.8 (d, JCP = 10.0 Hz, Ph), 129.6 (d, JCP = 10.6 Hz, Ph), 129.1 (s,
NMR (d, CD2Cl2) [28] 1H 8.49 (s, 1H, Ph), 7.85–7.95 (m, 1H, Ph),
7.69–7.65 (m, 3H, Ph), 7.46–7.34 (m, 6H, Ph), 7.18–7.14 (m, 2H,
Ph), 5.27 (CH2Cl2), 4.91 (s, 5H, Cp), 4.68 (d, JHH = 8.1 Hz, 1H, CHH0),
4.20 (d, JHH = 8.4 Hz, 1H, CHH’), 1.51 (s, 3H, CH3), 0.09 (s, 3H, CH03);
13C{1H} 219.0 (d, JCP = 28.7 Hz, CO), 166.5 (d, JCP = 6.8 Hz, C=N), 136.8

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S.L. Sedinkin et al. / Journal of Organometallic Chemistry 693 (2008) 3081–3091
Ph), 128.4 (s, Ph), 127.5 (d, JCP = 10.8 Hz, Ph), 126.6 (s, Ph), 82.7 (s,
Cp), 76.5 (s, CH2), 75.5 (s, CH2); 31P{1H} 67.0.
(NPD) anisotropic thermal parameters. These were refined with
EADP (SHELX-TL) restraints. Complex [11d][I]: There are two unique
molecules in the asymmetric unit for this compound. The lattice
contains several solvent molecules. A total of four molecules of
CHCl3, a molecule of Et2O and two molecules of H2O (one full
and two half molecules) were located and refined. Of the four
CHCl3, Cl atom disorders were resolved with partial occupancies
for two solvates. Complex [11f][PF6]: The molecule exhibits large
amount of disorder. Several phenyl motifs have more than one
orientations. These were modeled using SAME and EADP
HRMS calc. for C33H27NO2P56Fe 556.1128, found 556.1125; MS
(FAB, 3-NBA, m/z) [27] 556 ([11f]+, 60%), 528 ([11fꢀCO]+, 100%);
IR (cmꢀ1, neat) mC„O 1967 (s), mC@N 1603 (s).
5.4. General procedures for counter ion exchanges
5.4.1. Synthesis of ‘‘[CpFe(CO)(7b)][ClO4]”, [11b][ClO4]
A solution of NaClO4 (0.144 g, 1.183 mmol) in MeOH (1.5 mL)
was added dropwisely to a solution of complex [11b][I] (0.150 g,
0.237 mmol) in MeOH (1.5 mL) with stirring. The reaction mixture
was stirred for 30 min. A precipitate formed. The solvent was dec-
anted, and the red solid residue washed with MeOH (3 ꢂ 1 mL).
The residue was dried in high vacuum to obtain [11b][ClO4] as
red powder (0.085 g, 0.140 mmol, 59%).
(SHELX-TL) restraints.
5.6. Cyclic voltammetry
The voltammograms were recorded with a Princeton Applied
Research Parstat 2273 Electrochemical System and analyzed with
POWERSUITE 2.58 software. Cells were fitted with a glassy carbon
working electrode, and an Ag wire pseudoreference electrode and
a platinum wire as auxiliary electrode. All CH2Cl2 solutions were
2 ꢂ 10ꢀ3 M in substrate and 0.05 M in n-Bu4N+PFꢀ6 and degassed
with argon. All cyclic voltammograms were recorded with a scan
rate of 100 mV sꢀ1. Ferrocene was subsequently added, and calibra-
tion voltammograms recorded. All potentials are references to the
observed E1/2 value for the ferrocene/ferrocenium couple. The ambi-
ent laboratory temperature was 22 1 °C.
NMR (d, CD2Cl2) 1H 8.17–8.11 (m, 1H, Ph), 7.82–7.46 (m, 7H,
Ph), 7.41–7.20 (m, 6H, Ph), 7.12–7.02 (m, 2H, Ph), 4.71 (5H, Cp),
4.31 (d, JHH = 8.5 Hz, 1H, CHH0), 4.11 (d, JHH = 8.5 Hz, 1H, CHH0),
1.38 (s, 3H, CH3), 0.01 (s, 3H, CCH03); 13C{1H}167.8 (br, C@N),
135.3 (d, JCP = 11.3 Hz, Ph), 134.1 (d, JCP = 7.0 Hz, Ph), 133.6 (s, Ph),
133.0 (d, JCP = 2.5 Hz, Ph), 132.7 (s, Ph), 132.67 (s, Ph), 132.62 (s,
Ph), 132.60 (s, Ph), 132.58 (s, Ph), 132.0 (d, JCP = 10.7 Hz, Ph), 131.4
(d, JCP = 3.0 Hz, Ph), 130.6 (s, Ph), 130.0 (s, Ph), 129.9 (s, Ph), 129.6
(d, JCP = 10.4 Hz, Ph), 129.2 (d, JCP = 1.0 Hz, Ph), 128.8 (s, Ph), 84.2
(s, Cp), 80.0 (s, CH2), 71.9 (s, CH2), 26.3 (s, CH3), 24.6 (s, CH03);
31P{1H} 64.6 (s).
HRMS calc. for C29H27NO2P56Fe 508.1129, found 508.1115; MS
(FAB, 3-NBA, m/z) [27] 508 ([11b]+, 50%), 480 ([11bꢀCO]+, 100%);
IR (cmꢀ1, neat) mC„O 1958 (s), mC@N 1622 (m).
Acknowledgments
We thank Dr. Keith Stine and Dr. Olga Shulga (University of Mis-
souri – St. Louis) for assistance with the cyclic voltammograms. We
thank the University of Missouri – St. Louis for support. Funding
from the National Science Foundation for the purchase of the Apex-
II diffractometer (MRI, CHE-0420497), the purchase of the NMR
spectrometer (CHE-9974801) and the purchase of the mass spec-
trometer (CHE-9708640) is acknowledged.
5.4.2. Synthesis of ‘‘[CpFe(CO)(7f)][PF6]”, [11f][PF6]
NaPF6 (0.037 g, 0.219 mmol) in MeOH (1.5 mL) was reacted
with [CpFe(CO)(7e)][I] (0.030 g, 0.044 mmol) in MeOH (1.5 mL)
and worked up as described above for [11b][ClO4] to obtain
[11f][PF6] as red powder (0.025 g, 0.036 mmol, 81%).
NMR (d, CD2Cl2) 1H 8.09–8.01 (m, 1H, Ph), 7.72–6.91 (m, 16H,
Ph), 6.68–6.54 (m, 1H, Ph), 4.97–4.80 (m, 1H, CH), 4.80–4.70 (m,
1H, CH), 4.41 (s, 5H, Cp), 4.27–4.12 (m, 1H, CH); 31P{1H} 65.7 (s,
PPh2); ꢀ143.7 (qintet, JPF = 710 Hz, PF6).
Appendix A. Supplementary material
CCDC 689550, 689549, 689547, 689546 and 689548 contain the
supplementary crystallographic for [11a][I], [11b][ClO4], [11c][I],
[11d][I] and [11f][PF6]. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
HRMS calc. for C33H27NO2P56Fe 556.1128, found 556.1125; MS
(FAB, 3-NBA, m/z) [27] 556 ([11f]+, 60%), 528 ([11fꢀCO]+, 100%);
IR (cmꢀ1, neat) mC„O 1967 (s), mC@N 1604 (m).
5.5. X-ray structure determination of [11a][I], [11b][ClO4], [11c][I],
[11d][I] and [11f][PF6]
Supplementary data (experimental details and NMR data (1H,
13C, 19F) for compounds 3, 4, 5, 6, 8, 9, and 10; cyclic voltammo-
grams) associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.jorganchem.2008.06.031.
To obtain X-ray quality crystals, CH2Cl2 solutions of [11a][I],
[11c][I], and [11f][PF6], an acetone solution of [11b][ClO4] and a
CHCl3 solution of [11d][I] were layered with Et2O and stored for
18 h at ꢀ18 °C.
References
Data collections were performed as outlined in Table 2 using a
Bruker Kappa Apex II Charge Coupled Device (CCD) Detector sys-
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