Structure and C-C cross-coupling reactivity of iron(III) complexes of halogenated amine-bis(phenolate) ligands

Article abstract of DOI:10.1016/j.jorganchem.2010.09.076

The preparation of tetradentate amine-bis(phenol) proligands with dichloro and difluoro substituted phenol groups and their reaction with FeX₃ (X = Cl or Br) is described. The compounds, 2-pyridylamino-N,N-bis(2-methylene- 4,6-dichlorophenol), H₂[L₁]; 2-pyridylamino-N,N-bis(2- methylene-4,6-difluorophenol), H₂[L₂]; dimethylaminoethylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H ₂[L₃]; 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4,6- dichlorophenol), H₂[L₄]; and methoxyethylamino-N,N-bis(2- methylene-4,6-dichlorophenol), H₂[L₅] were prepared in aqueous medium and obtained as white powders in good to excellent yield. Ten new iron(III) halide complexes supported by these tetradentate ligands are reported. Representative single crystal X-ray diffraction structures were obtained for H₂[L₁] and a water adduct of the iron(III) complex, aquachloro{2-pyridylamino-N,N-bis(2-methylene-4,6-dichlorophenolato)} iron(III), 2·H₂O. The structure of the proligand H ₂[L₁] shows intramolecular hydrogen bonding. In the solid-state structure, the iron complex exhibits intermolecular hydrogen bonding between the water ligand and the phenolate oxygen of a neighbouring complex. The anhydrous complexes were studied for catalytic activity towards C-C cross-coupling of Grignard reagent nucleophiles with alkyl halide electrophiles.

Full text of DOI:10.1016/j.jorganchem.2010.09.076

Journal of Organometallic Chemistry 696 (2011) 787e794
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structure and CeC cross-coupling reactivity of iron(III) complexes of halogenated
amine-bis(phenolate) ligands
,
Amy M. Reckling a, Dana Martin a, Louise N. Dawe b, Andreas Decken c, Christopher M. Kozak a
*
a Department of Chemistry, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3X7
b C-CART X-ray Diffraction Laboratory, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada A1B 3X7
c X-Ray Crystallography Laboratory, Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3
a r t i c l e i n f o
a b s t r a c t
Article history:
The preparation of tetradentate amine-bis(phenol) proligands with dichloro and difluoro substituted
phenol groups and their reaction with FeX3 (X ¼ Cl or Br) is described. The compounds, 2-pyridylamino-
N,N-bis(2-methylene-4,6-dichlorophenol), H2[L1]; 2-pyridylamino-N,N-bis(2-methylene-4,6-difluor-
ophenol), H2[L2]; dimethylaminoethylamino-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L3]; 2-tetra-
hydrofurfuryl-N,N-bis(2-methylene-4,6-dichlorophenol), H2[L4]; and methoxyethylamino-N,N-bis(2-
methylene-4,6-dichlorophenol), H2[L5] were prepared in aqueous medium and obtained as white
powders in good to excellent yield. Ten new iron(III) halide complexes supported by these tetradentate
ligands are reported. Representative single crystal X-ray diffraction structures were obtained for H2[L1]
and a water adduct of the iron(III) complex, aquachloro{2-pyridylamino-N,N-bis(2-methylene-4,6-
dichlorophenolato)}iron(III), 2$H2O. The structure of the proligand H2[L1] shows intramolecular
hydrogen bonding. In the solid-state structure, the iron complex exhibits intermolecular hydrogen
bonding between the water ligand and the phenolate oxygen of a neighbouring complex. The anhydrous
complexes were studied for catalytic activity towards CeC cross-coupling of Grignard reagent nucleo-
philes with alkyl halide electrophiles.
Received 2 August 2010
Received in revised form
22 September 2010
Accepted 30 September 2010
Available online 14 October 2010
Keywords:
Iron
Cross-coupling
Grignard reagents
Phenolate ligands
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
cleavage of catechol or its derivatives with the incorporation of
molecular oxygen. Indeed, the principal focus of amine-bis
The use of chelating tetradentate amine-bis(phenolate) ligands
has recently played an increasingly important role in transition-
metal catalyst design. They have been predominantly used with
high-valent early transition-metals where they have been
employed as alternative auxiliary ligands to cyclopentadienyl-
based systems. In combination with group 4 and 5 metals they
display high activities towards olefin or cyclic ester polymerization
[1e11]. Also, group 3 and lanthanide metal complexes of these
ligands have been effective as catalysts or initiators for ring-
(phenolate) iron chemistry to-date has been with respect to its use
as a model for redox-active bioinorganic systems [33,34].
While the chemistry of amine-bis(phenolates) is dominated by
examples bearing electron donating alkyl substituents, such as
methyl or tert-butyl groups, electron withdrawing groups such as
nitro substituents have been used as well as asymmetric ligands
bearing mixed substituents [28,35,36]. Ligands bearing chloride- or
bromide-containing phenol units have been reported for use with
early transition metals [6,8,37] and aluminum [38] but there have
been no reports of fluoride-substituted amine-bis(phenolate)
ligands. The use of chloride functionalized ligands of this class with
late transition metals is limited, to our knowledge, to a copper
complex bearing a tridentate amine-bis(phenolate). [39] The elec-
tronic properties of the ligands are easily tuned by varying the
substituents on both the phenol fragments and the pendant donor
group. Therefore, halide functional groups on the phenols should
exhibit a strong influence on the electronic properties of the ligand.
We have previously prepared chromium, cobalt and iron complexes
of amine-bis(phenolate) ligands bearing alkyl substitutents (tert-
butyl and methyl) in the 4- and 6-positions of the phenolic
opening-polymerization of lactide and 3-caprolactone [12e17]. By
comparison, there has been less use of amine-bis(phenolate)
ligands with the late first-row transition-metals [18e22], however,
a growing number of Fe(III) complexes of this class of ligand has
been reported and studied as a result of their close relationship to
phenol-containing ligands found in metalloenzymes containing
non-heme iron [23e32], Particularly interesting is their similarity
to catechol dioxygenases, iron proteins that catalyze the oxidative
* Corresponding author. Tel.: þ1 709 864 8082; fax: þ1 709 864 3702.
E-mail address: ckozak@mun.ca (C.M. Kozak).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.09.076

788
A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
fragments [18,40e42]. The presence of electron withdrawing
halides in these positions is expected to lower the donor ability of
the ligand and generate more electron-poor metal centres. The
increased Lewis acidity of the metal centre was expected to
generate more reactive complexes for use in cross-coupling catal-
ysis of Grignard reagents with alkyl halides.
Transition-metal catalyzed Grignard cross-coupling is an
important class of CeC bond forming reactions [43]. Recently,
following early reports by Kochi [44], and in the interest of
sustainability (lower cost and toxicity), there has been a surge in
the study of iron-based catalysts [45e50]. Iron catalysts are
complementary to Ni and Pd in that they successfully couple alkyl
halides with Grignard reagents, which are not easily achieved using
remaining solid residue was washed with cold methanol to give an
analytically pure white powder. Yield: 20.00 g (70%). Crystalline
product was obtained by slow cooling of a hot diethyl ether solu-
tion. 1H NMR (500 MHz, CDCl3, 298 K):
d
8.69 (d, 3JH1eH2 ¼ 5.8 Hz,
3
3
PyH, 1H); 7.78 (ddd, JH3eH4
¼
8.2 Hz, JH3eH2
1.8 Hz, PyH, 1H); 7.34 (dd, JH2eH1
¼
¼
7.0 Hz,
5.8 Hz,
3
4JH3eH1
3JH2eH3
¼
¼
7.0 Hz, PyH, 1H); 7.28 (s, ArH, 2H); 7.16 (d,
3JH4eH3 ¼ 8.2 Hz, PyH, 1H); 6.94 (s, ArH, 2H); 3.85 (s, CH2, 2H); 3.79
(s, CH2, 4H). 13C{1H} NMR (125 MHz, CDCl3, 298 K):
d 155.1 (Py),
155.5 (ArCeOH), 148.6 (Py), 138.7 (Py), 130.1 (Ar), 128.9 (Ar), 124.3
(Ar), 124.1 (Ar), 123.6 (Py), 123.1 (Py), 122.3 (Ar), 56.5 (CH2), 55.9
(CH2). IR (cmꢀ1): 3350 (OH); 2955 (CeH); 1603 (C]C, phenyl ring).
Anal. Calcd for C20H16Cl4N2O2: C, 52.43; H, 3.52; N, 6.11. Found C,
52.45; H, 3.50; N, 6.10.
Ni or Pd due to competing b-hydride elimination. The breadth of
iron-catalyzed methods used for Kumada-type cross-coupling is
diverse [51e63]. Use of FeCl3, whether on its own or to generate an
active catalyst in situ, is often inconvenient on a large scale because
it is highly hygroscopic and yields vary according to its purity and
commercial origin [57]. Although Fe(acac)3 is a more convenient,
less hygroscopic starting material [51], amine additives are often
employed to achieve high conversions and yields of cross-coupled
products [57,58]. An easy to use, non-hygroscopic single compo-
nent catalyst precursor is, therefore, highly desirable.
We are exploring the catalytic potential of iron complexes
supported by various amine-bis(phenolate) ligands bearing an
additional pendant arm, such as an ether or pyridyl group. For
example, we have recently reported novel iron(III) compounds
bearing amine-bis(phenolate)-ether ligands, which effectively
catalyze the cross-coupling of aromatic Grignard reagents with
2.2. H2[O2NN0]FFPy (H2[L2])
To a solution of 2,4-difluorophenol (4.00 g, 0.031 mol) and 37%
aqueous formaldehyde (2.50 mL, 0.031 mol) in water (50 mL) was
added aminomethylpyridine (1.663 g, 0.015 mol), which formed
a cloudy precipitate and a yellow oil. The mixture was stirred and
heated to reflux for 12 h. Upon cooling, a large quantity of yellow oil
formed. The solvents were decanted and the remaining oily residue
was triturated with cold methanol under ultrasound to give an
analyticallypurewhitepowder. Yield:3.52g(58%).1HNMR(500 MHz,
(CD3)2CO, 298 K):
d
10.72 (s, OH, 1H); 8.68 (d, 3JH1eH2 ¼ 5.8 Hz, PyH,
1H); 7.91 (ddd, 3JH3eH4 ¼ 8.2 Hz, 3JH3eH2 ¼7.0 Hz, 4JH3eH1 ¼1.8 Hz, PyH,
1H); 7.46 (dd, 3JH2eH1 ¼5.8 Hz, 3JH2eH3 ¼ 7.0 Hz, PyH,1H); 7.43 (s, ArH,
2H); 6.93 (d, 3JH4eH3 ¼ 8.2 Hz, PyH,1H); 6.90 (s, ArH, 2H); 4.01 (s, CH2,
2H); 3.91 (s, CH2, 4H). 13C{1H} NMR (125 MHz, (CD3)2CO, 298 K):
alkyl halides possessing b-hydrogens [41]. We decided to investi-
gate the effect of electron withdrawing fluoro and chloro groups on
the phenolate fragments and subsequently the ability of iron
complexes of these ligands to catalyze cross-coupling of aryl
Grignard reagents with alkyl halides. Here we report the synthesis,
structure and catalytic behaviour of these iron(III) complexes.
d 155.1 (Py), 158.5 (ArCeOH), 149.2 (Py), 139.7 (Py), 130.9 (Ar), 123.2
(Ar), 124.9 (Ar), 124.6 (Ar), 124.1 (Py), 123.8 (Py), 122.9 (Ar), 57.0 (CH2),
56.5 (CH2). IR (cmꢀ1): 3350 (OH); 2955 (CeH); 1600 (C]C, phenyl
ring). Anal. Calcd for C20H16F4N2O2: C, 61.22; H, 4.11; N, 7.14. Found C,
61.30; H, 4.15; N, 7.10.
2. Experimental
2.3. H2[O2NN0]ClClNMe2 (H2[L3])
All manipulations and handling of ligands and iron complexes
were performed in air. Cross-coupling experiments were done under
nitrogen using Schlenk technique. Reagents were purchased either
from Aldrich, Alfa Aesar or Strem and used without further purifi-
cation. The syntheses of H2[L3] [37] and H2[L5] [8] were conducted
by modified literature procedure in water [64], as described below.
Anhydrous FeCl3 (97%) was purchased from Aldrich. FeBr3 (99%) was
purchased from Strem. MALDI-TOF MS spectra were recorded on an
Applied Biosystems Voyager DE-PRO equipped with a reflectron,
delayed ion extraction and high performance nitrogen laser
(337 nm). Samples were prepared at a concentration of 0.03 mg Lꢀ1
in methanol. Anthracene was used as the matrix, which was mixed
at a concentration of 0.03 mg Lꢀ1. UVevis spectra were recorded on
an Ocean Optics USB4000þ fiber optic spectrophotometer. Room
temperature magnetic moments were determined in solution by
Evans’ NMR method. Elemental analyses were carried out by
Chemisar Laboratories Inc., Guelph, ON, Canada or Canadian
Microanalytical Service Ltd, Delta, BC, Canada.
To a solution of 2,4-dichlorophenol (20.07 g, 0.123 mol) and 37%
aqueous formaldehyde (10.00 mL, 0.123 mol) in water (50 mL) was
added N,N-dimethylethylenediamine (6.70 mL, 0.062 mol), which
formed a cloudy precipitate and a yellow oil. The mixture was stirred
and heated to reflux for 12 h. Upon cooling, a large quantity of yellow
oil formed. The solvents were decanted and the remaining oily
residue was triturated with cold methanol under ultrasound to give
an analytically pure white powder. Yield: 17.54 g (65%). Spectro-
scopic analysis is identical to that previously reported [37].
2.4. H2[O2NN0]ClClFurf (H2[L4])
To a mixture of 2,4-dichlorophenol (20.00 g, 0.123 mol) and 37%
aqueous formaldehyde (10.00 mL, 0.123 mol) in water (50 mL) was
slowly added tetrahydrofurfurylamine (6.18 g, 0.061 mol), which
resulted in a white precipitate. The mixture was stirred and heated
to reflux for 12 h. Upon cooling, a large quantity of white solid and
yellow oil formed. The solvents were decanted, and the remaining
residues were triturated with cold methanol under ultrasound to
give an analytically pure white powder. Yield: 19.30 g (70%). 1H
NMR (500 MHz, CDCl3, 298 K, labelled resonances correspond to
2.1. H2[O2NN0]ClClPy (H2[L1])
To a mixture of 2,4-dichlorophenol (20.06 g, 0.123 mol) and 37%
aqueous formaldehyde (10.00 mL, 0.123 mol) in water (50 mL) was
slowly added aminomethylpyridine (6.60 g, 0.061 mol), which
resulted in a cloudy suspension. The mixture was stirred and
heated to reflux for 12 h. Upon cooling, a large quantity of pale
orange solid formed. The solvents were decanted and the
diagram below): d
8.29 (s, OHa, 2H); 7.26 (s, ArHb, 2H,); 6.94 (s, ArHc,
2H,); 4.19 (m, CHf, 1H,); 3.98 (m, CH2h, 2H,); 3.73 (s, CHd2, 4H); 2.60
(m, CHe2, 2H,); 1.92 (m, CH2g, 4H). 13C{1H} NMR (125 MHz, CDCl3,
298 K): d 151.6 (ArCOH); 129.6 (ArCCl); 129.0 (ArCCl); 124.8 (ArCH);
124.5 (ArCH); 122.4 (ArC); 78.0 (CH); 69.0 (CH2); 57.1 (CH2); 56.6
(CH2); 30.3 (CH2); 25.6 (CH2). IR (cmꢀ1): 3350 (OH); 2955 (CeH);

A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
789
1603 (C]C, phenyl ring). Anal. Calcd for C19H19Cl4NO3: C, 50.58; H,
4.24; N, 3.10. Found C, 50.45; H, 4.30; N, 3.10.
C20H14BrF4FeN2O2: C, 45.66; H, 2.68; N, 5.32. Found C, 45.65; H,
2.65; N, 5.32. MS (MALDI-TOF) m/z (%, ion): 524.95 (20, [M]þ),
446.03 (100, [MꢀBr]þ). UVevis lmax, nm (
3): (methanol) 480
(8000), 325 (14,500), 280 (16,000). meff (solution, 25 ꢁC) 5.8 mB
.
Cl
Cl
OHa
Hb
Cl
HO
2.8. FeX[L3] (5) and (6)
N
Hd
Hd
Cl
He
Hf
Hd
Hd
To a THF solution of recrystallized H2[O2NN0]ClClNMe2, H2[L3]
(2.86 g, 6.55 mmol) was added a solution of anhydrous FeX3
(6.55 mmol) in THF resulting in an intense violet/blue solution. To
this solution was added triethylamine (1.32 g, 13.0 mmol) and the
resulting mixture was stirred for 2 h. Solvent was removed under
vacuum and the residue was extracted with toluene and filtered
through Celite three times. Removal of solvent under vacuum yiel-
ded analytically pure dark-blue products. Yield 5: 3.11 g (90%); yield
Hc
He
Hg
Hg
O
Hh
Hh
Hg
Hg
2.5. H2[O2NN0]ClClMeth (H2[L5])
6: 3.00
g (80%). Characterization for 5: Anal. Calcd for
C18H18Cl5FeN2O2: C, 40.99; H, 3.44; N, 5.31. Found C, 40.95; H, 3.55;
To a solution of 2,4-dichlorophenol (20.07 g, 0.123 mol) and 37%
aqueous formaldehyde (10.00 mL, 0.123 mol) in water (50 mL) was
added (2-methoxy)ethylamine (5.40 mL, 0.062 mol), which formed
a cloudy precipitate. The mixture was stirred and heated to reflux
for 12 h. Upon cooling, a large quantity of yellow oil formed. The
solvents were decanted and the remaining oily residue was tritu-
rated with cold methanol under ultrasound to give an analytically
pure white powder. Yield: 16.54 g (62%). Spectroscopic analysis is
identical to that previously reported [8].
N, 5.33. MS (MALDI-TOF) m/z (%, ion): 524.92 (20, [M]þ), 489.95 (100,
[MꢀCl]þ). UVevis lmax, nm (
3): (methanol) 480 (8000), 325 (14,500),
280 (16,000). meff (solution, 25ꢁC) 5.9 mB. Characterization for 6: Anal.
Calcd for C18H18BrCl4FeN2O2: C, 37.80; H, 3.17; N, 4.90. Found C,
37.85; H, 3.15; N, 4.80. MS (MALDI-TOF) m/z (%, ion): 568.87 (20,
[M]þ), 489.95 (100, [MꢀBr]þ). UVevis lmax, nm (
3): (methanol) 480
(8000), 325 (14,500), 280 (16,000). meff (solution, 25 ꢁC) 5.8 mB
.
2.9. FeX[L4] (7) and (8)
2.6. FeX[L1] (1) and (2)
To a THF solution of recrystallized H2[O2NO]ClClFurf, H2[L4] (2.96 g,
6.55 mmol) was added a solution of anhydrous FeX3 (6.55 mmol) in
THF resulting in an intense violet/blue solution. To this solution was
added triethylamine (1.32 g, 13.0 mmol) and the resulting mixture
was stirred for 2 h. Solvent was removed under vacuum and the
residue was extracted with toluene and filtered through Celite three
times. Removal of solvent under vacuum yielded analytically pure
dark-blue products. Yield 5: 2.48 g (70%); yield 6: 2.68 g (70%).
Characterization for 5: Anal. Calcd for C19H17Cl5FeNO3: C, 42.22; H,
3.17; N, 2.59. Found C, 42.35; H, 3.15; N, 2.53. MS (MALDI-TOF) m/z (%,
To a THF solution of recrystallized H2[O2NN0]ClClPy, H2[L1]
(3.00 g, 6.55 mmol) was added a solution of anhydrous FeX3
(6.55 mmol) in THF resulting in an intense violet/blue solution. To
this solution was added triethylamine (1.32 g, 13.0 mmol) and the
resulting mixture was stirred for 2 h. Solvent was removed under
vacuum and the residue was extracted with toluene and filtered
through Celite three times. Removal of solvent under vacuum
yielded analytically pure dark-blue products. Yield 1: 3.19 g (89%);
yield 2: 3.30 g (85%). Crystals suitable for X-ray diffraction were
obtained by slow evaporation of a solution of 2 in a 1:1 mixture of
hexanes and chloroform to give 2$H2O. Characterization for 1: Anal.
Calcd for C20H14Cl5FeN2O2: C, 43.88; H, 2.58; N, 5.12. Found C,
43.95; H, 2.65; N, 4.93. MS (MALDI-TOF) m/z (%, ion): 544.89 (20,
ion): 537.90 (20, [M]þ), 502.93 (100, [MꢀCl]þ). UVevis lmax, nm (
3):
(methanol) 480 (8000), 325 (14,500), 280 (16,000). meff (solution,
25 ꢁC) 5.9 mB
.
Characterization for 6: Anal. Calcd for
C19H17BrCl4FeNO3: C, 39.02; H, 2.93; N, 2.39. Found C, 38.85; H, 3.10;
N, 2.40. MS (MALDI-TOF) m/z (%, ion): 581.85 (20, [M]þ), 489.95 (100,
[M]þ), 509.92 (100, [MꢀCl]þ). UVevis lmax, nm (
3): (methanol) 480
[MꢀBr]þ). UVevis lmax, nm (
3): (methanol) 480 (8000), 325
(8000), 325 (14,500), 280 (16,000). meff (solution, 25 ꢁC) 5.9 mB
.
(14,500), 280 (16,000). meff (solution, 25 ꢁC) 5.8 mB
.
Characterization for 2: Anal. Calcd for C20H14BrCl4FeN2O2: C, 40.58;
H, 2.38; N, 4.73. Found C, 40.65; H, 2.35; N, 4.80. MS (MALDI-TOF)
2.10. FeX[L5] (9) and (10)
m/z (%, ion): 588.83 (20, [M]þ), 509.92 (100, [MꢀBr]þ). UVevis lmax
,
nm (3): (methanol) 480 (8000), 325 (14,500), 280 (16,000). meff
To a THF solution of recrystallized H2[O2NO]ClClMeth, H2[L4]
(2.78 g, 6.55 mmol) was added a solution of anhydrous FeX3
(6.55 mmol) in THF resulting in an intense violet/blue solution. To
this solution was added triethylamine (1.32 g, 13.0 mmol) and the
resulting mixture was stirred for 2 h. Solvent was removed under
vacuum and the residue was extracted with toluene and filtered
through Celite three times. Removal of solvent under vacuum
yielded analytically pure dark-blue products. Yield 9: 3.03 g (90%);
yield 10: 3.46 g (95%). Characterization for 9: Anal. Calcd for
C17H15Cl5FeNO3: C, 39.69; H, 2.94; N, 2.72. Found C, 39.85; H, 3.11;
N, 2.53. MS (MALDI-TOF) m/z (%, ion): 511.88 (20, [M]þ), 476.92
(solution, 25 ꢁC) 5.8 mB
.
2.7. FeX[L2] (3) and (4)
To a THF solution of recrystallized H2[O2NN0]FFPy, H2[L2] (3.00 g,
6.52 mmol) was added a solution of anhydrous FeX3 (6.52 mmol) in
THF resulting in an intense violet/blue solution. To this solution was
added triethylamine (1.32 g, 13.0 mmol) and the resulting mixture
was stirred for 2 h. Solvent was removed under vacuum and the
residue was extracted with toluene and filtered through Celite
three times. Removal of solvent under vacuum yielded analytically
pure dark-blue products. Yield 3: 2.20 g (70%); yield 4: 2.95 g (86%).
Characterization for 3: Anal. Calcd for C20H14ClF4FeN2O2: C, 49.88;
H, 2.93; N, 5.82. Found C, 49.95; H, 2.95; N, 5.93. MS (MALDI-TOF)
(100, [MꢀCl]þ). UVevis lmax, nm (
3): (methanol) 480 (8000), 325
(14,500), 280 (16,000). meff (solution, 25 ꢁC) 5.9 mB. Characterization
for 10: Anal. Calcd for C17H15BrCl4FeNO3: C, 36.53; H, 2.71; N, 2.51.
Found C, 36.55; H, 2.83; N, 2.50. MS (MALDI-TOF) m/z (%, ion):
m/z (%, ion): 481.00 (20, [M]þ), 446.03 (100, [MꢀCl]þ). UVevis lmax
,
555.83 (20, [M]þ), 489.95 (100, [MꢀBr]þ). UVevis lmax, nm (
3):
nm (
3
): (methanol) 480 (8000), 325 (14,500), 280 (16,000). meff
(methanol) 480 (8000), 325 (14,500), 280 (16,000). meff (solution,
(solution, 25 ꢁC) 5.9 mB. Characterization for 4: Anal. Calcd for
25 ꢁC) 5.8 mB
.

790
A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
2.11. Cross-coupling catalysis general procedure
coated with Paratone-N oil, mounted using a polyimide MicroMount
and frozen in the cold nitrogen stream of the goniometer. A hemi-
sphere of data was collected on a Bruker AXS P4/SMART 1000
Catalyst (0.1 mmol, 5.0 mol%) in CH2Cl2 (3 mL) was added to
a Schlenk flask followed by removal of the solvent in vacuo. To the
catalyst were added Et2O (5 mL), alkyl halide (2.0 mmol) and
dodecane (2.0 mmol as internal standard) and the solution was
stirred at room temperature. Grignard (4.0 mmol) was added and
the resulting mixture was stirred for 30 min. The reaction was
quenched with HCl (aq., 2 M, 5 mL) and the organic phase was
extracted with Et2O (1 ꢂ 5 mL) and dried over MgSO4. The mixture
was analyzed by GCeMS and quantified using 1H NMR and/or GC.
NMR samples were prepared by careful removal of solvent under
vacuum and dissolving the residue in CDCl3.
diffractometer using
u and q
scans with a scan width of 0.3ꢁ and 30 s
exposure times. The detector distance was 5 cm. The data were
reduced (SAINT) [76] and corrected for absorption (SADABS) [77].
The structure was solved by direct methods and refined by full-
matrix least squares on F2(SHELXTL) [78]. All non-hydrogen atoms
were refined using anisotropic displacement parameters. Hydrogen
atoms were included in calculated positions and refined using
a riding model except those for the water molecule which were
found in Fourier difference maps and refined using isotropic thermal
parameters. Structural illustrations were created using ORTEP-III for
Windows [79].
2.12. X-ray crystallography experimental
3. Results and discussion
Crystallographic data for compounds H2[L1] and 2$H2O are
summarized in Table 1. Data collections for H2[L1] were performed
on a Rigaku AFC8-Saturn 70 equipped with a CCD area detector and
an X-Stream 2000 low temperature system, using graphite mono-
3.1. Synthesis of ligands and metal complexes
The amine-bis(phenolate)-ether ligands, H2[L1] to H2[L5] (Fig. 1)
were prepared by modified literature procedures [64] employing
Mannich condensation of 2,4-dichlorophenol or 2,4-difluor-
ophenol, formaldehyde and the corresponding primary amine in
water. Ligands H2[L3], H2[L5] and related ligands bearing halide-
containing phenol units have been reported for use with early
transition metals [6,8,37] and aluminum [38] for polymerization
catalysis.
The overall yields of halide-containing amine-bis(phenolate)
ligands are generally much lower than the alkyl substituted
analogs. We find that by performing the reaction in water as
opposed to alchohol solvents traditionally used can give moder-
ately improved yields of the desired compounds, which are often
obtained as viscous oils. Solids can be obtained, but purification is
slow and often requires sonication to obtain the compounds as
analytically pure white powders.
chromated Mo K
a
radiation (
l
¼ 0.71073 Å). Suitable crystals were
selected and mounted on glass fibers using Paratone-N oil and
freezing to ꢀ135 ꢃ1 ꢁC. The data were processed [65] and corrected
for Lorentz and polarization effects and absorption [66]. Neutral
atom scattering factors for all non-hydrogen atoms were taken from
the International Tables for X-ray Crystallography [67]. The structure
was solved by direct methods using SIR92 [68] and expanded using
Fourier techniques (DIRDIF99) [69]. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were included in calculated
positions, with the exception of two hydroxyl hydrogens that were
found in the difference map, with isotropic parameters set twenty
percent greater than those of their bonding partners. Anomalous
dispersion effects were included in Fcalc [70]; the values for
D
f0 and
D
f00 were those of Creagh and McAuley [71]. The values for the mass
attenuation coefficients are those of Creagh and Hubbell [72]. All
calculations were performed using the Crystal Structure [73,74]
crystallographic software package except for refinement, which
was performed using SHELXL-97 [75]. Single crystals of 2$H2O were
Single crystals of H2[L1] suitable for X-ray diffraction were
obtained from a saturated chloroform or acetone solution. The
structure of H2[L1] (obtained at 138 K) is shown in Fig. 2, crystal-
lographic data are given in Table 1 and selected bond lengths and
Table 1
Crystallographic and structure refinement data for H2[L1] and 2$H2O.
H2[L1]
20H16Cl4N2O2
458.15
2$H2O
Chemical formula
Formula weight
T/K
C
C20H16BrCl4FeN2O3
609.91
198(1)
138(2)
Colour, habit
Crystal dimensions/mm
Crystal system
Space group
a/Å
Colourless, prism
0.52 ꢂ 0.40 ꢂ 0.20
Orthorhombic
Pbcn (#60)
21.947(4)
12.2012(17)
14.936(2)
90
Black, plate
0.225 ꢂ 0.100 ꢂ 0.025
Monoclinic
P21/c (#14)
8.4415(8)
25.301(3)
11.2053(12)
90
109.5510(10)
90
2255.2(4)
4
1.796
2.941
1212.00
27.49e1.61
15603
b/Å
c/Å
ꢁ
ꢁ
a
/
b
/
90
90
ꢁ
g
/
V/Å3
3999.5(10)
8
1.522
Z
Dc/g cmꢀ3
m
(Mo K
F(000)
Range for collection/ꢁ
a
)/cmꢀ1
6.104
1872.00
26.49e2.35
26306
4149
254/0
q
Reflections collected
Independent reflections
Parameters/restraints
R(int)
5002
288/0
0.0479
0.027
R, wR2 (all)
0.0414, 0.1027
0.0408, 0.1023
1.173
0.0753, 0.1182
0.0422, 0.0991
1.083
R, wR2 [I > 2
s(I)]
GOF on F2
Fig. 1. Amine-bis(phenolate)-donor ligands used in this study.

A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
791
characteristic fragment ions, but in all complexes the parent ion
corresponding to FeX[Ln] is relatively weak. The halide ion is only
weakly coordinated to the metal [25] and therefore the reference
peak corresponds to the loss of halide, [MꢀX]þ, namely Fe[L1]þ. The
identity of the fragments was further confirmed by matching the
isotopic patterns of the relevant peaks.
Single crystals suitable for X-ray diffraction were obtained by
slow evaporation of a solution of 2 in a mixture of hexanes and
chloroform in air at room temperature. The structure is shown in
Fig. 3 and selected bond lengths and angles are given in Table 3.
Unlike our previously reported iron complexes of alkyl-function-
alized amine-bis(phenolate) ligands, which display five-coordinate
trigonal bipyramidal geometries [42], the coordination geometry
around the iron atom is distorted octahedral as a result of the
addition of a water ligand. This aquo ligand results from adventi-
tious water present in the solvent of recrystallization or atmo-
spheric moisture. Combustion analysis of the amorphous powder
obtained prior to recrystallization, however, confirms the forma-
tion of complexes that can be formulated as FeX[Ln]. Microcrys-
talline samples of these materials were used for further
characterization and catalysis studies discussed below. Crystals of
the presumably five-coordinate water-free complex unfortunately
could not be obtained, although based upon similarities between
the spectroscopic characterization of complexes 1e10 and those we
have previously reported [41,42], it is reasonable to expect the
newly prepared complexes exhibit trigonal bipyramidal metal ions
as proposed in Scheme 1.
Complex 2$H2O exhibits a six-coordinate geometry constituted
by two cis-coordinated phenolate oxygen atoms (O(1), O(2)) and
the cis-coordinated amine and pyridine nitrogen donors (N(1) and
N(2)). The bromide ion and aquo ligand reside in cis positions, with
the bromide residing trans to the central amine nitrogen and the
aquo oxygen occupying a position trans to one of the phenolate
oxygen donors. The molecule therefore possesses C1 symmetry. The
cis-disposed FeeO(phenolate) bonds are significantly different
(FeeO(1), 1.879(3); FeeO(2), 1.970(3) Å), with the longer bond
being found for the phenolate oxygen located trans to the water
ligand. The FeeBr bond distance is 2.4241(7) Å, and FeeN distances
are 2.261(3) and 2.179(3) Å for Fe(1)eN(1) and Fe(1)eN(2),
respectively. The FeeO bond distance of the water ligand is 2.148
(3) Å and is consistent with bond lengths observed in related
octahedral iron(III) complexes bearing non-bridging aquo ligands
[25]. The FeeOeC bond angles are asymmetric, namely C(1)eO(1)e
Fe(1) is 134.1(3)ꢁ and C(8)eO(2)eFe(1) is 122.5(2)ꢁ. The smaller
Fig. 2. Molecular structure (ORTEP) and numbering scheme of H2[L1]. Ellipsoids are
shown at 50% probability and only phenolic hydrogen atoms H(16) and H(15) are
shown.
angles are given in Table 2. Ligand precursor, H2[L1], displays
intramolecular hydrogen bonding between the phenolic hydroxyl
group O(1)eH and the pyridyl nitrogen N(2), and between the
second phenolic hydroxyl group, O(2)eH, and the amine nitrogen N
(1) [O(1)/N(2) 2.699 Å and O(2)/N(1) 2.720 Å], which gives the
molecule an orientation similar to that observed in metal
complexes of this class of ligand. No intermolecular hydrogen
bonding is observed. 1H and 13C{1H} NMR analyses of H2[L1] are
consistent with the solid-state structure but show that in solution
the hydrogen bonding interactions are easily broken allowing free
rotation of the phenol fragments. The methylene protons located
between the amine nitrogen and the phenol groups appear as
singlets in CDCl3 or acetone-d6, whereas restricted rotation of the
methylene group would lead to diastereotopic protons. The bond
lengths and angles around each atom are consistent with those
found in the structures of related ligands [9,23,41,80].
The desired iron(III) complexes were obtained by dropwise
addition of a THF solution of FeX3 (X ¼Cl, Br) to a THF solution of the
ligand at room temperature to yield a dark-blue mixture (Scheme 1).
NEt3 in methanol is added to neutralize the resulting solution. The
complexes FeX[L1] (1, X ¼ Cl; 2, X ¼ Br), FeX[L2] (3, X ¼ Cl; 4, X ¼ Br),
FeX[L3] (5, X ¼ Cl; 6, X ¼ Br), FeX[L4] (7, X ¼ Cl; 8, X ¼ Br) and FeX[L5]
(9, X ¼ Cl; 10, X ¼ Br) are obtained as paramagnetic dark indigo
powders that give analytically pure products upon recrystallization
from methanol or acetone. The 1H NMR spectra of these compounds
show shifted and broadened resonances as a result of their para-
magnetic nature. All the iron(III) complexes have magnetic
moments in solution in the range of 5.8e5.9 mB obtained by Evans’
method at room temperature, consistent with high-spin d5 ions.
MALDI-TOF mass spectrometry was useful in characterizing these
paramagnetic complexes. When prepared using an anthracene
matrix, masses were observed corresponding to the parent and
Table 2
Selected bond lengths (Å) and angles (ꢁ) for H2[L1].
Cl(1)eC(4)
Cl(2)eC(6)
Cl(3)eC(19)
Cl(4)eC(17)
O(1)eC(3)
O(2)eC(20)
N(1)eC(8)
N(1)eC(1)
N(1)eC(14)
N(2)eC(9)
N(2)eC(13)
1.742(2)
1.740(2)
1.734(2)
1.748(2)
1.346(2)
1.355(2)
1.469(2)
1.480(2)
1.482(2)
1.339(2)
1.345(3)
O(2)eC(20)eC(19)
O(2)eC(20)eC(15)
N(2)eC(13)eC(12)
N(1)eC(14)eC(15)
N(1)eC(1)eC(2)
N(1)eC(8)eC(9)
N(2)eC(9)eC(10)
N(2)eC(9)eC(8)
C(8)eN(1)eC(1)
C(8)eN(1)eC(14)
C(1)eN(1)eC(14)
C(9)eN(2)eC(13)
119.40(17)
121.77(17)
123.15(19)
110.71(15)
111.99(15)
113.89(15)
121.58(18)
119.25(16)
111.24(15)
110.36(14)
109.89(14)
118.38(17)
Fig. 3. Molecular structure (ORTEP) and numbering scheme of FeBr(H2O)[L1] (2$H2O).
Ellipsoids are shown at 50% probability and only the water hydrogen atoms are shown
for clarity.

792
A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
Table 3
Selected bond lengths (Å) and angles (ꢁ) for 2$H2O.
Fe(1)eO(1)
Fe(1)eO(2)
Fe(1)eO(3)
Fe(1)eN(2)
Fe(1)eN(1)
Fe(1)eBr(1)
Cl(1)eC(4)
Cl(2)eC(2)
Cl(3)eC(9)
Cl(4)eC(11)
N(1)eC(20)
N(1)eC(14)
N(1)eC(7)
N(2)eC(15)
N(2)eC(19)
O(1)eC(1)
O(2)eC(8)
1.879(3)
1.970(3)
2.148(3)
2.179(3)
2.261(3)
2.4241(7)
1.744(4)
1.745(4)
1.731(5)
1.731(5)
1.482(5)
1.489(5)
1.493(5)
1.341(5)
1.348(5)
1.321(5)
1.339(5)
O(1)eFe(1)eO(2)
99.52(13)
89.27(13)
167.49(13)
163.16(13)
87.68(12)
81.56(13)
88.31(12)
86.08(12)
85.30(13)
76.94(12)
97.43(9)
96.96(9)
90.64(10)
96.77(9)
172.95(9)
134.1(3)
122.5(2)
O(1)eFe(1)eO(3)
O(2)eFe(1)eO(3)
O(1)eFe(1)eN(2)
O(2)eFe(1)eN(2)
O(3)eFe(1)eN(2)
O(1)eFe(1)eN(1)
O(2)eFe(1)eN(1)
O(3)eFe(1)eN(1)
N(2)eFe(1)eN(1)
O(1)eFe(1)eBr(1)
O(2)eFe(1)eBr(1)
O(3)eFe(1)eBr(1)
N(2)eFe(1)eBr(1)
N(1)eFe(1)eBr(1)
C(1)eO(1)eFe(1)
C(8)eO(2)eFe(1)
bond angle at O(2) (and possibly the slightly longer Fe(1)eO(2)
bond) may be a result of intramolecular stacking between the
pep
pyridine ring the phenolate ring. The distance between centroids is
3.519 Å with an angle of 26.04ꢁ between the planes of the two
aromatic rings. Furthermore, the structure exhibits intermolecular
pep stacking as well as intermolecular hydrogen bonding (Fig. 4).
The interplanar distance between stacked phenolate rings in a pair
of complexes is approximately 3.55 Å (found between the centroid
Fig. 4. Molecular structure (ORTEP) of FeBr(H2O)[L1] (2$H2O) showing intermolecular
hydrogen bonding. Ellipsoids are shown at 50% probability and only the water
hydrogen atoms are shown for clarity.
of ring A and the ipso carbon of ring B) and the two rings display an
offset orientation. In addition to this intermolecular phenyl stack-
ing, there exists a hydrogen bonding interaction between the water
ligand of one molecule (the H-bond donor) and the phenolate
oxygen (the H-bond acceptor) of a “partner” molecule giving an
O/O interatomic distance of 2.688 Å between oxygen atoms. This
results in the formation of hydrogen bonded linear “chains” in the
solid-state. In comparison, we have recently reported
a bis
(phenolate)aminopyridyl manganese acetate complex possessing
2,4-di(tert-butyl) substituted phenolate groups, MnIII(H2O)(OAc)
[O2NN0]BuBuPy [81]. The manganese complex is also six-coordinate
with the Mn(III) ion in a distorted octahedral geometry and an
acetate ligand bonded to the metal in monodentate fashion occu-
pying the analogous site to the bromide ion in complex 2$H2O.
Unlike complex 2$H2O, the manganese analog does not exhibit
intramolecular or intermolecular
pep stacking between the
phenolate arene ring and the pyridine ring. Also, unlike 2$H2O, the
phenolate rings in the Mn complex are orientated trans to one
another and it is the pyridine nitrogen donor that occupies the
position trans to the aquo ligand. Interestingly, a related octahedral
iron(III) choride complex possessing tetradentate diamine-bis
(phenolate) and aquo ligands also shows the phenolate oxygen
donors to be trans orientated [25]. Despite the absence of bulky
groups in the 2-position in this reported complex (the phenolate
groups possess para-nitro substituents), the pendant donor is
a dimethylaminoethyl group, which occupies a sterically larger
volume of space around the metal ion than the planar pyridine ring
found in 2$H2O. On the other hand, a related six-coordinate iron(III)
aminepyridyl-bis(phenolate)(acac) complex also exhibits cis-
orientated phenolate donors [82]. In this complex, the phenolate
donors are unsubstituted 2-hydroxybenzyl groups and the distance
between centroids of adjacent phenolate and pyridine rings is
3.878 Å.
Scheme 1.

A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
793
Table 4
Cross-coupling catalysis data.
3.2. Electronic spectroscopy
Electronic absorption spectra of all complexes in methanol show
multiple intense bands in the UV and visible regions. In complexes
1e10, the absorption maxima observed in the near-UV regions
(below 300 nm) are caused by
phenolate unitsdabsorptions in this region are observed in the
Entry
Grignard,
RMgBr R¼
Alkyl halide
Cat.
Cat.
loading (%)
Yield
(%)
1
2
3
4
5
6
7
8
p-Tolyl
p-Tolyl
p-Tolyl
p-Tolyl
p-Tolyl
p-Tolyl
p-Tolyl
Allyl
Allyl
Allyl
Allyl
Allyl
Bromocyclohexane
Bromocyclohexane
Bromocyclohexane
Bromocyclohexane
Bromocyclohexane
Bromocyclohexane
Bromocyclohexane
Bromocyclohexane
Chlorocyclohexane
Iodocyclohexane
2-Bromobutane
1
1
1
1
3
5
6
1
1
1
1
1
1
5
10
15
20
5
5
5
5
5
5
5
5
5
28
31
25
23
29
47
57
3
5
7
5
2
p /
p* transitions involving the
spectra of the unmetallated ligand precursors. Intense bands
(which appear as shoulders on the
the region between 300 and 375 nm and are assigned to charge
transfer transitions from the out-of-plane p orbital (HOMO) of the
p /
p* bands) are observed in
p
9
phenolate oxygen to the half-filled dx2ꢀy2 =dz2 orbital of high-spin Fe
(III). Intense, lower energy bands between 450 and 700 nm in the
visible region are proposed to arise from charge-transfer transitions
10
11
12
13
2-Bromopentane
Benzylbromide
from the in-plane pp
orbital of the phenolate to the half-filled dp*
Allyl
13
orbital of Fe(III) and account for the intense indigo blue/purple
colour of the complexes. The halide ligands are anticipated to be
labile in solution [25], hence a coordinating solvent such as
methanol would clearly interact with the iron(III) centres influ-
encing the ligand fields and, therefore, the electronic spectra.
yield (entry 7). Therefore, while there is a mild influence of the
ligand in cross-coupling ability, none of the complexes studied
exhibited the high activity shown by our previously reported tet-
radentate amine-bis(phenolate) ligands possessing alkyl groups on
the phenolate fragments.
3.3. Cross-coupling catalysis
Since sp2-nucleophiles are generally weaker than sp3-carbon
containing reactants in terms of cross-coupling ability, we next
investigated whether these complexes would prove competent for
sp3esp3 CeC cross-coupling (entries 8 to 13). Disappointingly, using
5 mol% catalyst loading of complex 1 gave very poor yields of cross-
coupled products for the reaction of allyl Grignard reagent with
cyclic and acyclic secondary alkyl halides as well as benzyl bromide.
There are several possible reasons why the halogenated ligands
gave poorer catalysts for these cross-coupling reactions. Previously,
we found decreasing the Grignard reagent stoichiometry decreased
the yield of the desired cross-coupled product, but increasing the
amount of Grignard reagent was only found to generate more biaryl
product, C [41]. It has been proposed that excess Grignard is
required to reduce the Fe(III) precatalyst, thus generating the active
catalyst [57,54]. During these screenings, the presence of products
D, E and F was only detected in trace amounts by GCeMS, and the
yield of homo-coupled biaryl products was low to negligible. A
likely reason is that the halide-functionalized phenolate fragments
may themselves be attacked by the nucleophile. Also, although care
was taken to keep exposure to moisture minimal during the
handling of the iron complexes, these compounds are considerably
more hygroscopic than those bearing alkyl-substituted phenolate
ligands. Clearly, adventitious water would be detrimental to the
Grignard reagents during the reaction.
Based on our previous work with FeIII compounds supported by
tetradentate amine-bis(phenolate)-ether ligands, we employed
similar reaction conditions for our preliminary investigations using
complex 1 (Table 4). We previously found that diethyl ether was
superior to THF as a solvent for cross-coupling of Grignard reagents
with alkyl halides [41], therefore it was the solvent chosen for the
current study. Also, we previously found that reactions performed
at room temperature gave superior results to those conducted at
lower temperatures. For the preliminary screening of catalyst
performance, the reaction shown in Scheme 2 was chosen. In
addition to the desired cross-coupled product, by-products may
include the elimination product (cyclohexene), the hydro-
dehalogenated product (cyclohexane), and two possible homo-
coupled products (dicyclohexane and bitoluene). Initially, complex
1 was examined for its catalytic cross-coupling activity and the
effect of catalyst loading. Varying catalyst loading from 5 to 20%
versus alkyl halide showed little effect on the yield of the cross-
coupled product, 1-cyclohexyl-4-methylbenzene (entries 1 to 4). In
all cases a poor yield was obtained, significantly lower than our
previously reported systems. The effect of varying ligand was
investigated (entries 5 to 7) while maintaining catalyst loading at
5 mol% versus alkyl halide. Fluoro-phenolate complex 3 gave
a similar yield of product to its chloro-substituted phenolate con-
taining analog, 1 (entry 5). Slightly better yields were obtained
using complex 5 (entry 6). Changing the monodentate chloride
ligand to bromide in complex 6 gave in turn a moderately better
4. Conclusions
A series of iron(III) complexes supported by chloro- and fluoro-
functionalized amine-bis(phenolate) ligands has been prepared.
Representative complex 2$H2O has been structurally characterized
by single crystal X-ray diffraction and shows a six-coordinate, dis-
torted octahedral iron(III) ion. Additionally, all of the paramagnetic
complexes have been analytically verified by elemental analysis
and MALDI-TOF mass spectrometry. Magnetic moment measure-
ments confirm high-spin d5 electronic configurations. Electronic
absorption spectra in the UVevis range exhibit strong charge
transfer bands. The catalytic activity of these complexes for CeC
cross-coupling of aryl and allyl Grignard reagents with alkyl halides
was investigated. Unfortunately, the complexes studied were
inferior to those previously reported by us and others and only gave
poor to modest yields of cross-coupled products. The presence of
halide-functional groups on the phenolate arms and the increased
hygroscopic behaviour of the complexes are likely causes for the
Scheme 2.

794
A.M. Reckling et al. / Journal of Organometallic Chemistry 696 (2011) 787e794
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This research was supported by Memorial University of
Newfoundland, the Natural Sciences and Engineering Research
Council (NSERC) of Canada, the Canada Foundation for Innovation
and the Provincial Government of Newfoundland and Labrador in
the form of research grants and student research awards. A. M. R.
thanks NSERC for an Undergraduate Student Research Award. We
are grateful to Prof. Francesca M. Kerton for use of the GC-MS
instrument, acquired through a CFI Leaders Opportunity Fund
Award.
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Appendix. Supplementary data
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CCDC-794213 (H2[L1]) and CCDC-794214 (2$H2O) contain the
crystallographic data for the structures reported in this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
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