Template synthesis of iron(II) complexes containing tridentate P-N-S, P-N-P, P-N-N, and tetradentate P-N-N-P ligands

Article abstract of DOI:10.1021/ic901945c

A series of mer-tridentate iron(II) complexes bearing P-N-S (3), P-N-P (4), and P-N-N (5) ligands have been prepared via the metal template effect in one pot involving air-stable phosphonium dimers [cyclo-(-PPh₂CH ₂C-(OH)H-)₂](Br)₂ (1) and [cyclo-(-PCy ₂CH₂C(OH)H-)₂](Br)₂ (2), KOtBu, [Fe(H₂O)₆][BF₄]₂ and 2-aminothiolphenol (for 3), 2-(diphenylphosphino)ethylamine (for 4), and 2-(aminomethyl)pyridine (for 5). The new phosphonium dimer 2 was prepared via an S_N2 reaction of PCy₂H with BrCH₂CH(OEt) ₂. The complexes Fe{PR₂CH₂CH=N(2-C ₅H₄)S}₂FeBr₂ (3a, R = Ph; 3b, R = Cy) are paramagnetic, and X-ray diffraction studies revealed that they are bimetallic, in which the S atoms of the bis-tridentate (PNS)₂Fe unit bridge to a FeBr₂ fragment. Complexes [Fe(PR₂CH ₂CH=NC₂H₄PPh₂)(NCMe) ₃]X₂ (4a, R=Ph; 4b, R=Cy; X₂=FeBr₄ or (BF₄)₂) form when 1 equiv of iron is reacted with PPh₂CH₂CH₂NH₂ and 0.5 equiv of the appropriate phosphonium dimer. The evidence for P-N-P coordination is the large ²J_pp coupling constant in the ³¹P { ¹H} NMR spectrum for the trans phosphorus nuclei. If 0.5 equiv of [Fe(H₂O)₆][BF₄]₂ were added in the synthesis, the complex trans-[Fe(NCMe)₂(Ph₂PC ₂H₄NH₂)2][FeBr₄] (4c) formed, and this has been characterized by X-ray diffraction. Complexes [Fe{PR ₂CH₂CH=NCH₂(2-C₅H ₄N)}₂]-(BPh₄)₂ (5) are bis-tridentate iron(II) complexes with pyridyl donors trans to the phosphine donors. Interestingly, addition of the diamines ethylenediamine, (1R, 2R)-(-)-1, 2-diaminocyclohexane, (1R,2R)-(-)-1, 2-diphenylethylenediamine, or o-phenylenediamine, in the template synthesis with 2 led directly to tetradentate P-N-N-P iron(II) complexes trans-[Fe(NCMe)₂(PCy ₂CH₂CH=N-Q-N=CHCH₂PCy₂](BPh ₄)₂ (Q = CH₂CH₂, 6a; Q = (1R, 2R)-cyclo-C₆H₁₀,6b; Q=(1R, 2R)-CHPhCHPh, 6c; Q=C ₆H₄,6d). In contrast, similar reactions under the same conditions with dimer 1 led to complexes mer-[Fe(P-N-N)₂] ²⁺ as reported previously. Complexes 6a and 6b have been characterized by X-ray diffraction and exhibited large P-Fe-P bond angles of 112.92(2) and 111.96(4)°, respectively.

Full text of DOI:10.1021/ic901945c

1094 Inorg. Chem. 2010, 49, 1094–1102
DOI: 10.1021/ic901945c
Template Synthesis of Iron(II) Complexes Containing Tridentate P-N-S, P-N-P,
P-N-N, and Tetradentate P-N-N-P Ligands
Paraskevi O. Lagaditis, Alexandre A. Mikhailine, Alan J. Lough, and Robert H. Morris*
Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6 Canada
Received October 2, 2009
A series of mer-tridentate iron(II) complexes bearing P-N-S (3), P-N-P (4), and P-N-N (5) ligands have been
prepared via the metal template effect in one pot involving air-stable phosphonium dimers [cyclo-(-PPh2CH2C-
(OH)H-)2](Br)2 (1) and [cyclo-(-PCy2CH2C(OH)H-)2](Br)2 (2), KOtBu, [Fe(H2O)6][BF4]2 and 2-aminothiolphenol
(for 3), 2-(diphenylphosphino)ethylamine (for 4), and 2-(aminomethyl)pyridine (for 5). The new phosphonium dimer 2
was prepared via an SN2 reaction of PCy2H with BrCH2CH(OEt)2. The complexes Fe{PR2CH2CHdN(2-
C6H4)S}2FeBr2 (3a, R = Ph; 3b, R = Cy) are paramagnetic, and X-ray diffraction studies revealed that they are
bimetallic, in which the S atoms of the bis-tridentate (PNS)2Fe unit bridge to a FeBr2 fragment. Complexes
[Fe(PR2CH2CHdNC2H4PPh2)(NCMe)3]X2 (4a, R=Ph; 4b, R=Cy; X2=FeBr4 or (BF4)2) form when 1 equiv of iron is
reacted with PPh2CH2CH2NH2 and 0.5 equiv of the appropriate phosphonium dimer. The evidence for P-N-P
coordination is the large 2JPP coupling constant in the 31P {1H} NMR spectrum for the trans phosphorus nuclei. If 0.5
equiv of [Fe(H2O)6][BF4]2 were added in the synthesis, the complex trans-[Fe(NCMe)2(Ph2PC2H4NH2)2][FeBr4] (4c)
formed, and this has been characterized by X-ray diffraction. Complexes [Fe{PR2CH2CHdNCH2(2-C5H4N)}2]-
(BPh4)2 (5) are bis-tridentate iron(II) complexes with pyridyl donors trans to the phosphine donors. Interestingly,
addition of the diamines ethylenediamine, (1R,2R)-(-)-1,2-diaminocyclohexane, (1R,2R)-(-)-1,2-diphenylethyle-
nediamine, or o-phenylenediamine, in the template synthesis with 2 led directly to tetradentate P-N-N-P iron(II)
complexes trans-[Fe(NCMe)2(PCy2CH2CHdN-Q-NdCHCH2PCy2](BPh4)2 (Q = CH2CH2, 6a; Q = (1R,2R)-cyclo-
C6H10, 6b; Q=(1R,2R)-CHPhCHPh, 6c; Q=C6H4, 6d). In contrast, similar reactions under the same conditions with
dimer 1 led to complexes mer-[Fe(P-N-N)2]2þ as reported previously. Complexes 6a and 6b have been chara-
cterized by X-ray diffraction and exhibited large P-Fe-P bond angles of 112.92(2) and 111.96(4)°, respectively.
Introduction
tion,10-12 Michael addition,13 oligiomerization,14,15 and
epoxidation.10,12 Our group has a particular interest in such
complexes with potential activity in the hydrogenation or
transfer hydrogenation of polar bonds. Recently, our interest
has focused on the P-N-N-P ligand system, and we have
reported promising results in the asymmetric transfer hydro-
genation of ketones by use of complexes of iron(II) with the
general structure shown in Figure 1.16-19
Polydentate heteroatom ligands, particularly those con-
taining both phosphorus and nitrogen donors, have garnered
much attention, as they have been demonstrated to create
active catalysts for a multitude of reactions including transfer
hydrogenation,1-6 direct hydrogenation,7-9 cyclopropana-
*To whom correspondence should be addressed. E-mail: rmorris@chem.
utoronto.ca.
(1) Gao, J.-X.; Zhang, H.; Yi, X.-D.; Xu, P.-P.; Tang, C.-L.; Wan, H.-L.;
Tsai, K.-R.; Ikariya, T. Chirality 2000, 12, 383–388.
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J. Mol. Catal. A: Chem. 2004, 218, 153–156.
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A. J.; Abdur-Rashid, K. Organometallics 2006, 25, 4113–4117.
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Morris, R. H. Organometallics 2007, 26, 5940–5949.
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metallics 2000, 19, 4117–4126.
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Dixon, J. T.; Grove, C. Chem. Commun. 2003, 334–335.
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Int. Ed. 2008, 47, 940–943.
€
(17) Sui-Seng, C.; Haque, F. N.; Hadzovic, A.; Putz, A.-M.; Reuss, V.;
Meyer, N.; Lough, A. J.; Zimmer-De Iuliis, M.; Morris, R. H. Inorg. Chem.
2009, 48, 735–743.
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r
pubs.acs.org/IC
Published on Web 12/22/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1095
Figure 2. Diastereomers of 2.
Figure 1. General structure of trans-[Fe(CO)(NCCH3)(Ph2P-R-
HCdN-Q-NdCH-R-PPh2)]2þ
.
Scheme 2. Preparation of the Phosphonium Dimer, 2
Scheme 1. Synthesis of Dimeric Phosphonium Compound 1
We have shown that the dimeric phosphonium compound
[cyclo-(-PPh2CH2C(OH)H-)2](Br)2 (1) is readily prepared
in a two-step process where, first, potassium diphenylpho-
sphide is reacted with the commercially available protected
aldehyde, 2-bromo-1,1-diethoxyethane (BrCH2CH(OEt)2),
and then reacted with HBr(aq) (Scheme 1). It is a useful
precursor for the template synthesis of iron(II) complexes
containing tridentate P-N-N or tetradentate P-N-N-P
ligands.19,20 Depending on which conditions are used, the
iron(II) complexes mer-[Fe(P-N-N)2]2þ containing triden-
tate ligands or trans-[Fe(NCMe)2(P-N-N-P)]2þ contain-
ing tetradentate P-N-N-P ligands are formed. The former
species forms immediately in acetonitrile, while the latter
species either forms slowly in acetonitrile or immediately in
methanol with a stoichiometric amount of acetonitrile. In
particular, the precursor complex trans-(R,R)- [Fe(CO)-
(NCCH3)(PPh2CH2CHdNCHPhCHPhNdCHCH2PPh2)]2þ
is a very active and enantioselective ketone transfer hydrogena-
tion catalyst.19
The template synthesis of these iron(II) complexes is
another example where the metal template effect allowed
for the synthesis of multidentate ligands that would be
otherwise arduous or impossible to obtain using standard
organic techniques.21-27 The results from the template synth-
esis approach prompted us in the current work to explore the
scope and versatility of the use of such phosphonium dimers
in the template synthesis with iron(II) ions. We report here
the convenient synthesis of a new dimeric phosphonium
compound, 2 (Scheme 2). We show the utility of 1 and 2 in
the template synthesis of new iron(II) complexes with bis-
tridentate P-N-S, P-N-P, and P-N-N ligands, as well as
new iron(II) complexes tetradentate P-N-N-P ligands
starting from 2.
Results and Discussion
The new dimeric phosphonium compound [cyclo-(-PCy2-
CH2C(OH)H-)2](Br)2 (2) is synthesized from dicyclohexyl-
phosphine (PCy2H), BrCH2CH(OEt)2, and water in THF in
a one-pot reaction. The white, air-stable solid is obtained in a
high yield of 80% after the reaction mixture was refluxed
overnight (Scheme 2). The synthesis of this dimeric phos-
phonium compound is simpler than the synthesis of its
predecessor, 1. In the synthesis of 1, generation of potassium
diphenylphosphide, KPPh2, from potassium hydride is re-
quired because diphenylphosphine, HPPh2, is not nucleophi-
lic enough to displace the bromo group on the protected
aldehyde. The electron-rich cyclohexyl groups, on the other
hand, make the phosphorus center in HPCy2 more basic and
nucleophilic so that the generation of an anion is not required
for the SN2 reaction to proceed.
Like dimer 1, dimer 2 displays two singlets in the 31P{1H}
NMR spectrum at 27 (major) and 28 (minor) ppm. One of
these is due to the presence of the rac diastereomer while
the other is due to the meso diastereomer, although the
assignment is not certain, as recrystallization attempts did
not separate the two isomers (Figure 2). The 31P NMR
chemical shifts of 2 are more downfield than those of 1,
which appear at 12 (major, rac) and 17 (minor, meso) ppm.28
Furthermore, dimer 2 can be easily cleaved to the phosphine
aldehyde (2a) under basic conditions, similar to dimer 1, in
either CH3CN or toluene. An advantage however to toluene
is that the KBr salt can be filtered off. The phosphine
aldehyde was observed by 31P{1H} NMR as a singlet at
-10 ppm upon the disappearance of the two singlets for 2. In
addition, the 1H NMR spectrum revealed an aldehyde peak
at 9 ppm. The phosphine aldehyde was not isolated
(20) Mikhailine, A. A.; Kim, E.; Dingels, C.; Lough, A. J.; Morris, R. H.
Inorg. Chem. 2008, 47, 6587–6589.
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154.
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2006, 128, 3818–3830.
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metallics 2009, 28, 896–901.
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Newman, P. D.; Hahn, E. J. Am. Chem. Soc. 2009, 131, 306–317.
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1257–1263.

1096 Inorganic Chemistry, Vol. 49, No. 3, 2010
Lagaditis et al.
Scheme 3. Template Synthesis of Novel Bis-Tridentate Iron (II) Com-
plexes with P-N-S, P-N-P, and P-N-N Ligands
Figure 3. ORTEP plot (50% probability ellipsoids) of the X-ray crystal
structure of 3a. Hydrogen atoms are omitted for clarity. Selected bond
˚
lengths (A) and angles (deg): Fe(1)-S(1), 2.3540(10); Fe(2)-S(1),
2.3811(10); Br(1)-Fe(2), 2.4139(6); Fe(1)-P(1), 2.2349(10); Fe(1)-N(1),
1.993(3);N(1)-Fe(1)-N(1), 170.57(17); P(1)-Fe(1)-P(1), 97.98(5); S(1)-
Fe(1)-S(1), 93.13(5); S(1)-Fe(2)-S(1), 91.77(5); Br(1)-Fe(2)-Br(1),
109.24(3); Fe(1)-S(1)-Fe(2), 87.55(3).
but generated in situ for subsequent template synthesis
reactions.
The one-pot template reaction of either dimer 1 or 2 with
KOtBu, [Fe(H2O)6][BF4]2 and 2-aminothiophenol gave the
air-sensitive, neutral, iron(II) complexes with P-N-S li-
gands, mer-Fe{(C6H5)2PCH2CHdN(2-C6H4)S}2FeBr2 (3a)
and mer-Fe{(C6H11)2PCH2HCdN(2-C6H4)S}2FeBr2 (3b),
respectively (Scheme 3). The burgundy-colored complexes
3a and 3b precipitated out of the reaction mixture and were
isolated in yields of 57% and 60%. Both complexes were
insoluble in common organic solvents but were completely
soluble in dimethylsulfoxide (DMSO) or dimethyl forma-
mide (DMF); they were slightly soluble in alcohols but
decompose over time, as noted by the change in color from
burgundy to yellow-brown.
The structures of 3a and 3b were first believed to be mer-
Fe(P-N-S)2, as the corresponding monocationic complexes
were observed in the electrospray ionization (ESIþ) mass
spectra. The growth of crystals of 3a and 3b proved to be
challenging, as the solvent choice was limited. Nonetheless,
crystals of 3a were grown from a reaction mixture by slow
diffusion of 2-aminothiophenol in acetonitrile to an acetoni-
trile mixture of dimer 1, KOtBu, and [Fe(H2O)6][BF4]2
(Figure 3). The X-ray crystal structure of 3a was not just the
Fe(P-N-S)2 complex but a bimetallic species with bridging
thiolate groups. The structure of 3a in Figure 3 is C2-sym-
metric. The iron(II) ion, Fe(1), that is coordinated to the
P-N-S ligands, is pseudo-octahedral, while the second
iron(II) center, Fe(2), is pseudo-tetrahedral. The Br-Fe(2)-Br
bond angle of 109.24° is correct for a perfect tetrahedral
geometry; however, the S-Fe(2)-S bond angle of 91.77°
is smaller due the rigidity of the P-N-S ligand. The bridging
S atoms form almost a perfect Fe2S2 square in which the
imperfection is due to the slight difference in bond lengths
between the two iron centers. In addition, the Fe2S2 unit is
perfectly planar.
in the reaction between o-(diphenylphosphino)benzaldehyde
and 2-aminothiophenol.29-31
A
31P{1H} NMR test sample
containing a mixture of 1 or 2 with a base and 2-aminothio-
phenol revealed a major peak at 50 ppm. The generation of
2-
FeBr4 is crucial since reactions carried out in a toluene/
acetonitrile solvent mixture to exclude bromide salts from the
2-
solution did not produce the same results. Hence, FeBr4
may ring-open the thiazolidine intermediate to give com-
plexes 3a and 3b.
Complexes 3 are paramagnetic and could not be charac-
terized by NMR spectroscopy. The solid-state room-tem-
perature magnetic moment was determined to be 5.02 μB for
3a and 5.06 μB for 3b with corrections for diamagnetism.
These valuesare close tothe spin-onlyvalue for four unpaired
electrons (4.9 μB) and imply that there is a high-spin iron(II)
center. It is most likely that the tetrahedral iron center, Fe(2),
is high-spin, while the iron center that is coordinated by the
P-N-S ligands, Fe(1), in an octahedral fashion is low-spin.
The electronic spectrum of a DMSO solution (10-4 M) of 3a
shows two charge transfer transitions at 310 (ε=15933 M-1
cm-1) and 523 nm (ε=762 M-1 cm-1), while that of 3b shows
two transitions at 306 (ε=7558 M-1 cm-1) and 540 nm (ε=
1547 M-1 cm-1).
The cyclic voltammetry of 3a and 3b revealed the non-
innocent behavior of ligands containing S donors.32-34
Figure 4 shows the cyclic voltammogram of 3a and 3b in
DMF; for 3b, two cathodic signals at 0.70 and 0.11 V with
corresponding anodic signals, 0.60 and 0.07 V, respectively,
are assigned to the Fe3þ/Fe2þ redox couple of both iron
centers. The very sharp anodic signal (-0.28 V) and broad
cathodic signal (-0.67 V) are from the redox couple of the
P-N-S ligand. The cyclic voltammogram of 3a shows the
The formation of the complexes 3 may proceed via a
thiazolidine intermediate. A thiazolidine is known to form
~
ꢀ
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Weyhermuller, T.; Wieghardt, K. Angew. Chem., Int. Ed. 2003, 42, 563–567.
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Inorg. Chem. 2003, 42, 3208–3215.
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Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1097
Figure 5. ORTEP plot (30% probability ellipsoids) of the X-ray crystal
structure of 4c as the FeBr4 salt.
Scheme 4. Synthesis of 4c
(II) complexes, then both cis and trans couplings should have
been observed between each inequivalent P center to produce
a second-order AA0XX0 splitting pattern. The IR spectra of
complexes 4a and 4b show an intense stretch at 2203 and
2208 cm-1, respectively. In the case of 4a, an additional, less
intense stretch is present at 2280 cm-1. Typical stretches for
coordinated NCCH3 ligands fall in the range from 2250 to
2290 cm-1; the observed lower frequencies indicated the
strongly Lewis acidic character of the iron center.16,35 Thus,
even without the evidence of X-ray diffraction studies, com-
plexes 4 are concluded to have only one P-N-P and three
NCCH3 ligands coordinated to iron(II), as drawn in
Scheme 3.
Figure 4. Cyclic voltammogram of 3a (top) and 3b (bottom) in DMF
.
solution with 0.1 M [nBu4N][BF4] under Ar, scan rate: 50 mV s-1
same sharp anodic (-0.33 V) and broad cathodic (-0.48 V)
signals of the P-N-S ligand redox couple. However, only
one Fe3þ/Fe2þ redox couple is observed at 0.71 and 0.61 V.
Changing the amine reagent in the template synthesis to
2-(diphenylphosphino)ethylamine (dpea) led to iron(II) com-
plexes featuring a P-N-P ligand, [Fe{(C6H5)2PCH2CHd
NC2H4P(C6H5)2}(NCCH3)3]2þ (4a) and [Fe{(C6H11)2-
PCH2HCdNC2H4P(C6H5)2}(NCCH3)3]2þ (4b) (Scheme 3).
The 31P {1H} NMR spectra of impure samples of com-
plexes 4a and 4b revealed an additional singlet with the same
chemical shift at 66.8 ppm. This corresponded to a secondary
product, a new complex, trans-[Fe(NCMe)2(Ph2PC2H4-
NH2)2][FeBr4] (4c), which was isolated as a crystal from an
NMR sample of crude 4a in acetonitrile-d3 and characterized
by an X-ray diffraction study (Figure 5). This species was
isolated as the FeBr42- salt from experiments where KBr was
not removed. This complex can be obtained as the BF4- salt
by mixing [Fe(H2O)6][BF4]2 with 2 equiv of dpea in acetoni-
trile (Scheme 4). A 31P{1H} NMR spectrum of the reaction
mixture gave the same singlet as previously observed in the
reaction mixture of 4. Since 4c is simply the self-assembly of
Fe2þ and dpea, it will always form in the template synthesis of
complexes 4. In order to avoid or limit 4c, an excess of Fe2þ is
required and a 31P{1H} NMR spectrum of the reaction
mixtures revealed full conversion to complexes 4.
2-
Both counteranions, FeBr4 and BF4-, exist in the crude
product, as observed in the mass spectrum (ESI-), when the
reaction is carried out in acetonitrile. Attempts to isolate 4a
and 4b as the tetraphenylborate (BPh4-) salts failed, as these
complexes decompose in alcohol solvents; thus, they were
simply isolated from CH2Cl2 and Et2O. As a result, com-
plexes 4 were not characterized by elemental analysis since
both BF4- and FeBr42- anions coexist in an unknown ratio.
Complexes 4 were characterized by mass spectrometry
(ESIþ), NMR spectroscopy, and IR spectroscopy. The mass
spectra of complex 4a and 4b both showed peaks with the
mass for the monoprotonated tridentate ligand (440.2 and
452.2 m/z, respectively). The 31P{1H} NMR spectra of both
complexes in acetonitrile-d3 showed two AB doublets at 58.5
and 64.6 ppm for 4a and 56.6 and 66.6 ppm for 4b. The
doublets of both complexes exhibited large 2JPP coupling of
160 and 148 Hz, respectively. The large 2JPP coupling and the
planar geometry of imine bonds strongly support a mer
arrangement of the P-N-P ligand, instead of a fac arrange-
ment, about the iron(II) center. This type of splitting pattern
would support only one P-N-P0 ligand coordinated to the
Fe center. If complexes 4 were bis-tridentate P-N-P0 iron-
By further changing the amine reagent to 2-(amino-
methyl)pyridine, the bis-tridentate iron(II) complexes featuring
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Pollak, M.; Mereiter, K.; Kisala, J.; Kirchner, K. Organometallics 2006, 25,
1900–1913.

1098 Inorganic Chemistry, Vol. 49, No. 3, 2010
Lagaditis et al.
Scheme 5. Template Synthesis of Novel trans-Acetonitrile Tetraden-
tate P-N-N-P Iron(II) Complexes from 2
P-N-N ligands, mer-[Fe{(C6H5)2PCH2HCdNCH2(C5H4-
N)}2]2þ (5a) and mer-[Fe{(C6H11)2PCH2HCdNCH2(C5H5-
N)}2]2þ (5b), are formed (Scheme 3). Unlike the synthesis of
the previous complexes 3 and 4, the template synthesis of 5a
and 5b is carried out in methanol rather than acetonitrile
because the latter solvent gave multiple products as deter-
mined by 31P{1H} NMR spectroscopy. The 31P{1H} NMR
spectra showed only a singlet at 62.5 for 5a and 50.9 for 5b
when the reaction was conducted in methanol. Both com-
plexes were isolated as the BPh4 salt via a counteranion
metathesis with NaBPh4 in methanol in yields of 82 and 62%
for 5a and 5b, respectively. The mass spectrum (ESIþ)
providedsupport for a bis-tridentate iron complex, as clusters
of the dicationic complex were observed (see the Experimen-
tal Section). Crystals of 5a were grown by the slow diffusion
of Et2O into a MeOH/MeCN (1:1 by volume) solution but
were not of good quality for an X-ray diffraction study
because they tended to twin. Nonetheless, the X-ray diffrac-
tion data supported a mer-octahedral arrangement of the
P-N-N ligands about iron, as expected and observed in
similar complexes with P-N-N ligands either involving a
terminal pyridine or amine (-NH2) donor.20,36 Unlike com-
plexes 4, complexes 5 are very stable in solution underan inert
atmosphere and have considerable stability in the solid state
in the air, with minimal decomposition after a week.
Figure 6. ORTEP plot (30% probability ellipsoids) of the X-ray crystal
structures of 6a (top) and 6b (bottom). BPh4- and BF4- anions and some
˚
hydrogen atoms are omitted for clarity. Selected bond lengths (A) and
angles (deg): for 6a, Fe(1)-N(1), 1.9643(19); Fe(1)-N(2), 1.966(2); Fe-
(1)-N(3), 1.932(2); Fe(1)-N(4), 1.921(2); Fe(1)-P(1), 2.2699(7); Fe-
(1)-P(2), 2.2781(18); N(1)-Fe(1)-N(2), 82.99(9); N(3)-Fe(1)-N(4),
173.65(8); P(1)-Fe(1)-P(2), 112.92(2); for 6b, Fe(1)-N(1), 1.971(3);
Fe(1)-N(3), 1.928(3); Fe(1)-N(4), 1.911(3); Fe(1)-P(1), 2.2936(11);
Fe(1)-P(2), 2.2752(10); N(1)-Fe(1)-N(2), 82.73(13); N(4)-Fe(1)-N-
(3), 174.44(13); P(2)-Fe(1)-P(1), 111.96(4).
one additional charge transfer absorption at 500 (ε=1483
M
-1 cm-1), while 5b displayed two additional, more intense
charge transfer absorptions at 510 (ε=7930 M-1 cm-1) and
561 (ε=8308 M-1 cm-1) nm.
Although complexes 5 are analogous in structure, a drastic
difference between them is their color, owing to the substit-
uents on the P atoms. Complex 5a is red-pink, while 5bis dark
purple, which indicates that the Phgroups stabilize orbitals of
complex 5a such that the wavelengths of absorbance are
significantly blue-shifted. This effect is the most pronounced
for complexes 5, as the color difference between the Cy and
Phanaloguesof complexes 3 and 4 were merely a differencein
the shade of color they exhibited. The electronic spectra of
complexes 5 (10-4 M) in acetonitrile both display an absorp-
Changing the amine reagent in the template reaction from
2-(aminomethyl)pyridine to a diamine, ethylenediamine (en),
(1R,2R)-(-)-1,2-diaminocyclohexane (dach), (1R,2R)-(-)-
1,2-diphenylethylenediamine (dpen), or o-phenylenediamine
(bn), in acetonitrile, led to a tetradentate ligand complex
instead of the bis-tridentate ligand complex. This leads to the
direct synthesis of the new tetradentate P-N-N-P iron(II)
complexes, trans-[Fe{(C6H11)2PCH2CHdNCH2CH2Nd
CHCH2P(C6H11)2}(CH3CN)2]2þ ( 6a), trans-(R,R)-[Fe{(C6-
H11)2PCH2CHdN(C6H10)NdCHCH2P(C6H11)2}(CH3-
CN)2]2þ ( 6b), trans-(R,R)-[Fe{(C6H11)2PCH2CHdNCH-
tion at 351 (ε=9822 M-1 cm-1) and 358 (ε=6833 M-1 cm-1
)
(Ph)CH(Ph)NdCHCH2P(C6H11)2}(CH3CN)2]2þ
(6c),
nm for 5a and 5b, respectively. However, 5a displayed only
and trans-[Fe{(C6H11)2PCH2HCdN(C6H4)NdCHCH2P-
(C6H11)2}{CH3CN}2]2þ ( 6d) (Scheme 5), as determined by
NMR, mass spectrometry (ESIþ), elemental analysis, and
X-ray diffraction studies.
(36) Pelagatti, P.; Bacchi, A.; Balordi, M.; Caneschi, A.; Giannetto, M.;
Pelizzi, C.; Gonsalvi, L.; Peruzzini, M.; Ugozzoli, F. Eur. J. Inorg. Chem.
2007, 162–171.

Article
A single product was always observed at the end of the
Inorganic Chemistry, Vol. 49, No. 3, 2010 1099
that at -12 ppm to unreacted 2a. The peak at 62.7 ppm
belonged to an intermediate, which fully disappeared after
24 h. This species likely corresponds to a bis-tridentate
iron(II) complex. An intermediate has also been observed
in a 31P{1H} NMR spectrum obtained immediately after the
addition of dach in the synthesis of 6b. The analogous three
peaks were observed at 67.1, 60.2, and -6.7 ppm, where the
singlet at 67.1 ppm was assigned to 6b and -6.7 ppm for 2a.
The peak at 60.2 ppm is again for a similar intermediate
species, a bis-tridentate P-N-N iron(II) complex. However,
this intermediate species disappeared at a faster rate than the
previous intermediate of 6c. The synthesis of 6c was the
slowest of the four reactions shown in Scheme 5, requiring
24 h for complete conversion at room temperature. This may
be a consequence of steric repulsions from the phenyl groups
of dpen rather than an electron-withdrawing effect since the
template synthesis with the least basic of the diamines tested
(bn) was complete after 12 h. Nevertheless, the synthesis of 6c
is still faster than the synthesis of the analogous complex with
Ph substituents on the P atoms when carried out under the
same conditions.
reaction, as the 31P{1H} NMR spectra had only a singlet at
68.5, 68.2, 67.5, and 67.3 ppm for 6a, 6b, 6c, and 6d,
respectively. Initial support for the structure of complexes 6
came from mass spectra (ESIþ) analyses, as only masses of
the tetradentate P-N-N-P ligands were observed and no
masses for bis-tridentate iron(II) complexes ([Fe(P-N-
N)2]2þ) or P-N-N ligands were observed. Even if 2 equiv
of the diamine were added, the reaction always led directly to
complexes 6. This was not expected since previous templating
with 1 in acetonitrile as a solvent immediately led to bis-
tridentate P-N-N iron(II) complexes (except in the case
with bn). Formation of the tetradentate P-N-N-P iron(II)
complexes with 1 was much slower in acetonitrile (24 h with
reflux) but formed faster in the polar, protic solvent, metha-
nol with a stoichiometric amount of acetonitrile. It is believed
that the protic solvent either is involved with the transforma-
tion or stabilizes key intermediates.
We believe that, in the template reaction with 2 to produce
the tetradentate complexes, 6 proceeds via a bis-tridentate
intermediate in a similar fashion to template reactions invol-
ving 1.19,20 Support for this speculation first came from
reaction mixtures observed before complete conversion in
the synthesis of 6c. A 31P {1H} NMR spectrum of the reaction
mixture after 12 h revealed three peaks at 67.5, 62.7, and
-12.8 ppm. The peak at 67.5 ppm corresponded to 6c and
The fact that tetradentate P-N-N-P iron(II) complexes
6a-d are formed faster in the template synthesis with 2
than with 1 is a direct consequence of the Cy groups. The
Cy groups make the P atoms more basic such that tert-
butanol (HOtBu), generated in situ upon cleavage of 2, is
a suitable protic source to aid in the transformation from
a P-N-N iron(II) complex to a P-N-N-P iron(II)
complex.
Complexes 6 were isolated as the BPh4 salt via a counter-
anion metathesis with NaBPh4 in methanol in yields of 80
(6a), 58 (6b), 58 (6c), and 61% (6d). The lower yields of 6b-d
are a consequence of the anion metathesis in methanol, as
these complexes are partially soluble in alcohols.
The structures from X-ray diffraction studies of single
crystals of 6a and 6b are shown in Figure 6. The complexes
are distorted octahedral with the acetonitrile ligands in the
Figure 7. Previous iron(II) complexes with P-N-N-P ligands.
Table 1. Selected Crystal Data, Data Collection, and Refinement Parameters for 3a, 4c, 6a, and 6b
compound
3a
4c[FeBr4]
[6a][BF4][BPh4]
[6b][BPh4]2 Et2O
3
empirical formula
fw
C40H34Br2Fe2N2P2S2
940.27
monoclinic
C2/c
150(1)
18.1997(7)
14.2222(4)
15.3805(6)
90
109.704(2)
90
3748.0(2)
4
1.666
3.136
1888
0.10 ꢀ 0.10 ꢀ 0.08
2.56-27.51
15166
C34H41Br4Fe2N5P2
1012.00
monoclinic
P21/c
C58H80B2F4FeN4P2
1048.67
triclinic
P1
150(1)
11.2526(4)
15.1535(5)
16.1638(5)
96.505(2)
90.118(2)
90.360(2)
2738.21(16)
2
1.272
0.389
1116
0.20 ꢀ 0.16 ꢀ 0.09
3.27-27.00
32837
C90H116B2FeN4OP2
1409.28
orthorhombic
P212121
150(1)
12.8806(3)
20.8835(4)
30.1708(7)
90
90
90
8115.7(3)
4
1.153
lattice type
space group
T, K
150(2)
˚
a, A
15.4373(4)
15.6291(5)
18.2926(4)
90
106.2720(15)
90
4236.7(2)
4
1.588
4.562
2008
˚
b, A
˚
c, A
R, deg
β, deg
γ, deg
3
˚
V, A
Z
F
calcd/Mg m-3
μ(Mo, KR), mm-1
F(000)
0.273
3032
0.40 ꢀ 0.35 ꢀ 0.24
2.57-27.50
37207
cryst. size, mm3
range θ collected, deg
reflns collected/unique
abs cor
0.22 ꢀ 0.16 ꢀ 0.12
2.66-27.51
25111
semiempirical from equivalents
max and min transmission coeff
goodness of fit
0.692 and 0.595
1.052
0.0476
0.1236
1.346 and -0.618
0.577 and 0.441
1.032
0.0463
0.1110
0.991 and -0.802
0.7455 and 0.6221
1.054
0.0497
0.1377
1.244 and -0.480
0.888 and 0.740
1.021
0.0654
0.1754
0.677 and -0.455
R1 (I > 2σ(I))a
wR2 (all data)a
peak and hole, e A
-3
˚
P
P
P
P
a Definition of R indices: R1 = (FO - FC)/ (FO); wR2 = [ [w(FO2 - FC2)2]/[ [w(FO2)2]]1/2
.

1100 Inorganic Chemistry, Vol. 49, No. 3, 2010
Lagaditis et al.
axial positions and the P-N-N-P ligand in the equatorial
plane. This mode of coordination has been observed before
in analogous iron structures, in particular for comparison
purposes trans-(R,R)-[Fe(NCCH3)2{PPh2CH2CHdNC6-
H10NdCHCH2PPh2)]2þ (7)20 and trans-(R,R)-[Fe(NCCH3)2-
{PPh2(o-C6H4)CHdNC6H10NdCH(o-C6H4)PPh2}]2þ (8)16
(Figure 7). Overall, the bond lengths and angles are compar-
able; however, the most notable structural feature of com-
plexes 6a and 6b is the large P-Fe-P bond angles of 112.92
and 111.96°, respectively. A large P-Fe-P angle has also been
observed with 7 (109.81°) in comparison to 8 (100.24°). This
large angle is a consequence of the five-, five-, and
five-membered chelate rings of compound 7 compared to
the six-, five-, and six-membered rings of compound 8. This
same geometric constraint exists in complexes 6a and 6b
since their P-N-N-P ligands form five-, five-, and
five-membered chelate rings as well. However, the P-Fe-P
angle of complex 6b is yet slightly larger than 7 due to
additional steric strain imposed by the bulky Cy groups on
both P atoms.
stoichiometric amount of Fe2þ was added; it can be avoided
when an excess of Fe2þ is added after the template reaction
mixture is stirred overnight.
We have demonstrated that, when primary diamines are
used in the template synthesis with 2, trans-acetonitrile
tetradentate P-N-N-P iron(II) complexes 6 are isolated.
Since we have previously shown that mer bis-tridentate
iron(II) complexes form in such templated reactions with 1,
we speculate from NMR studies that such iron(II) species do
form as intermediates in the template synthesis with 2, but
they transform rapidly to the isolated complexes 6.
The results of this report demonstrate the scope and
versatility of the template synthesis. This useful method has
led to active catalysts and novel metal complexes. Explora-
tion of new ligand systems as well as the compatibility of the
template synthesis of multidentate P and N donor ligands
with other metals is currently ongoing.
Experimental Section
General Comments. All procedures and manipulations invol-
ving air-sensitive materials were performed under an argon or
nitrogen atmosphere using Schlenk techniques or a glovebox
with N2(g). Solvents were degassed and dried using standard
procedures prior to all manipulations and reactions. Deuterated
solvents were purchased from Cambridge Isotope Laboratories
and degassed and dried over activated molecular sieves prior to
use. A phosphonium dimer, 1, was synthesized following a
literature procedure.20 All other reagents used were purchased
from commercial sources and utilized without further purifica-
tions. NMR spectra were recorded at ambient temperature and
pressure using a 400 MHz Varian Gemini [1H (400 MHz),
13C{1H} (100 MHz), and 31P{1H} (161 MHz)]. The 31P NMR
spectra were referenced to 85% H3PO4 (0 ppm). Electronic
spectra were recorded on an Aglient 8453 UV-visible photo-
diode array spectrometer in an anaerobic quartz cuvette (d=1
cm) in CH3CN or CH2Cl2 (complexes 4) or DMSO (complexes
3). Magnetic moments were obtained in the solid state with a
Johnson Matthey magnetic susceptibility balance. A Bioanaly-
tical Systems Epsilon electrochemical controller was used for
cyclic voltammetry studies. All manipulations were conducted
in an inert atmosphere. The electrochemical cell was equipped
with a Pt wire working electrode, a tungsten auxiliary electrode,
and an Ag/AgCl reference electrode; dimethylformamide
solutions were 0.1 M in [nBu4N][BF4]. Reported potentials
are referenced to the ferrocenium/ferrocene couple versus the
standard hydrogen electrode, SHE (0.72 V).37 The elemental
analyses were performed at the Department of Chemistry,
University of Toronto, on a Perkin-Elmer 2400 CHN elemental
Regardless of the geometric constraint from the
P-N-N-P ligands or the steric bulkiness from the Cy
substituents, complexes 6 are stable and do not decompose
in the solid state nor in solution under an inert atmosphere.
They can be manipulated in the air for short periods of time.
Complexes 6a-c exhibit analogous electronic spectra, which
is not surprising since there is little variation in the structure
and bonding of the three complexes. Solutions of all three
complexes (10-4 M) displayed a charge transfer transition at
328 nm (ε=3348 (6a), 2952 (6b), and 3397 (6c) M-1 cm-1
and a second, less intense transition at 487 (ε = 302 M-1
cm-1), 478 (ε=268 M-1 cm-1), and 472 (ε=500 M-1 cm-1
)
)
for 6a, 6b, and 6c, respectively. Complex 6d, however,
displayed a very different electronic spectrum even though
it is structurally the same as 6a-c. The added conjugation
from the ortho-phenylene group stabilized molecular orbitals
of 6d such that the second charge transfer transition observed
with complexes 6a-c is gone. As a result, 6d is orange, while
6a-c are all pink. Table 1 gives selected crystal data, data
collection, and refinement parameters for 3a, 4c, 6a, and 6b.
Conclusion
We have presented a new phosphonium dimer (2) that is
conveniently synthesized in a one-pot reaction. We have
demonstrated its usefulness, along with the previous phos-
phonium dimer (1), in the template synthesis of novel bis-
tridentate iron(II) complexes with P-N-S (3a and 3b) and
P-N-N (5a and 5b) as well as monotridentate iron(II)
complexes with P-N-P ligands (4a and 4b). On the basis
of structural evidence and rationale, the ligands of all three
classes form a mer arrangement about the iron center. In the
case of complexes 3, the S donors of the P-N-S ligands
bridge to a second iron center that is coordinated to two
bromine ions in a tetrahedral arrangement. We speculate that
such a species is formed by ring-opening of a thiazolidine
intermediate by FeBr42- to form complexes 3. In the case of
complexes 4, no crystals for X-ray diffraction study were
possible to obtain, but based on a comparison with the other
complexes in this report and in the literature, we deduce a mer
arrangement of these P-N-P ligands about iron. A bypro-
duct, trans-[Fe(NCMe)2(Ph2PC2H4NH2)2][FeBr4] (4c), was
found to form in the reaction mixtures of complexes 4 when a
analyzer. Some complexes gave
a low carbon analysis
but acceptable hydrogen and nitrogen contents because of a
combustion problem. This was not alleviated by the addition of
oxidants such as vanadium pentoxide.
Dicyclohexylphosphinoacetaldehyde Bromide Dimer (2). A
Schlenk flask was charged with dicyclohexylphosphine (2.53 g,
0.013 mol) and dry THF (10 mL). Bromoacetaldehyde diethyl
acetal (2.50 g, 0.013 mol) was added over the course of 15 min.
The mixture was stirred for 1 h, at which time a white precipitate
was evident. An excess amount of degassed water (1 mL) was
added, and the mixture was allowed to reflux overnight to yield a
pristine white sludge. The solid was collected by filtration under
air and washed with water (2 ꢀ 3 mL) and diethyl ether (2 ꢀ
3 mL). Drying in vacuo yielded the phosphonium dimer as an
1
air-stable white powder. Yield: 3.25 g (80%). H NMR (400
MHz, CD3CN): δ 1.42-2.19 (m, HCy), 2.80 (q), 3.08 (m), 5.39
(37) Barrette, W. C.; Johnson, H. W.; Sawyer, D. T. Anal. Chem. 1984, 56,
1890–1898.

Article
Inorganic Chemistry, Vol. 49, No. 3, 2010 1101
(dd, JHP=26 Hz, JHH=4 Hz), 5.23 (dd, JHP=22 Hz, JHH=4
Hz). 31P {H} NMR (121 MHz; CD3CN): 27.2 (s), 28.1 (s). Anal.
Calcd for C28H52O2P2Br2: C, 52.35; H, 8.16. Found: C, 51.93; H,
trans-[Fe(NCMe)2(Ph2PC2H4NH2)2][BF4]2 (4c). To a stirring
solution of [Fe(H2O)6][BF4]2 (80 mg, 0.237 mmol) and CH3CN
(5 mL) was added 2-(diphenylphosphino)ethylamine (109 mg,
0.474 mmol) in CH3CN (1 mL) dropwise. The mixture turned
purple immediately and was allowed to stir further for 30 min.
The solvent was removed, and the residue was dissolved in
CH2Cl2 (1 mL). The addition of Et2O (10 mL) afforded a purple
solid, which was isolated by filtration and dried in vacuo. Yield:
93% (170 mg). 1H NMR (400 MHz, CD3CN): δ 1.96 (s, CH3),
2.93 (m, 4H, H2CP), 3.09 (m, 4H, H2CN), 3.69 (s, 4H, H2N),
6.99 (t, 8H, HAr), 7.29 (t, 8H, HAr), 7.49 (t, 4H, HAr). 13C {1H}
NMR (100 MHz, CD3CN) δ: 31.46 (dd, H2CP, JCP=14, 14.7
Hz), 41.56 (m, H2CN), 129.58 (t, JCP=4.6 Hz, HCArP), 131.29
(m, HCArP), 131.78 (dd, JCP = 16.9, 19.4 Hz, CArP), 132.83
(t, JCP=4.5 Hz, HCArP). 31P {1H} NMR (161 MHz, CD3CN):
δ 64.6 (s). Anal. Calcd for C32H38N4P2FeB2F4: C, 49.91; H,
4.97; N, 7.28. Found: C, 48.67; H, 5.14; N, 6.42. Crystals of
4c as the FeBr4 salt suitable for X-ray diffraction were
obtained from a NMR sample of an incomplete reaction of 4a
in acetonitrile-d3.
8.46. MS (ESI, methanol/water; m/zþ): 241.2 [C28H52O2P2]2þ
.
[Fe{(C6H5)2PCH2CHdN(2-C6H4)S}2FeBr2] (3a). A vial was
charged with 1 (150 mg, 0.243 mmol), KOtBu (54 mg, 0.485
mmol), and CH3CN (2 mL). After stirring for 5 min, [Fe-
(H2O)6][BF4]2 (122 mg, 0.364 mmol) in CH3CN (1 mL) was
added. The reaction mixture was allowed to stir for 20 min. A
solution of 2-aminobenezenethiol (32 mg, 0.249 mmol) in
CH3CN (1 mL) was added to the reaction mixture and stirred
overnight. A burgundy precipitate (3a) was collected via filtra-
tion, washed with acetonitrile (2 ꢀ 3 mL), and dried overnight.
Yield: 57% (135 mg). μeff=5.02 μB. MS (ESI, methanol/water;
m/zþ): 724.2 [C40H34N2P2Fe]þ•
.
[Fe{(C6H11)2PCH2HCdN(2-C6H4)S}2FeBr2] (3b). The synth-
esis of 3b was performed in the same manner as 3a (2 (150 mg,
0.233 mmol), KOtBu (52 mg, 0.467 mmol), [Fe(H2O)6][BF4]2 (118
mg, 0.350 mmol), and 2-aminothiolphenol (59 mg, 0.467 mmol) in
CH3CN (5 mL)). Yield: 65% (150 mg). μeff=5.08 μB. MS (ESI,
methanol/water; m/zþ): 748.3 [C40H59N2P2S2Fe]þ•
.
[Fe{(C6H5)2PCH2CHdNCH2(C5H4N)}2][BPh4]2 (5a). A vial
was charged with 1 (80 mg, 0.129 mmol), KOtBu (29 mg, 0.259
mmol), and MeOH (4 mL). [Fe(H2O)6][BF4]2 (65 mg, 0.194
mmol) in MeOH (1 mL) was added to the colorless reaction
mixture after 5 min. After stirring for 20 min, 0.52 mL of a stock
solution of 2-(aminomethyl)pyridine (215 mg in 4 mL of MeOH)
was added to the colorless mixture. The mixture first turned
yellow, and after stirring overnight, the mixture turned dark
pink. The mixture was filtered through a pad of Celite, concen-
trated (∼2 mL) under reduced pressure, and added to a solution
of NaBPh4 (94 mg, 0.275 mmol) in MeOH (1 mL) to cause the
formation of a dark pink precipitate. The solid was filtered and
washed with MeOH (2 ꢀ 1 mL) and dried under a vacuum.
Yield: 87% (151 mg). 1H NMR (400 MHz, CD3CN): δ 4.05 (d,
2H, HCP), 4.35 (d, 2H, HCP), 5.10 (d, 2H, HC-N), 5.40 (d, 2H,
HC-N), 6.84-7.05 (m, 24H, HPh), 7.22 (t, 4H, Hpy), 7.31 (s,
16H, HPh), 7.44 (t, 2H, Hpy), 7.67 (d, 2H, Hpy), 7.83 (d, 2H,
[Fe{(C6H5)2PCH2CHdNCH2CH2P(C6H5)2}(CH3CN)3]2þ (4a).
A vial was charged with 1 (80 mg, 0.1294 mmol), KOtBu (29 mg,
0.259 mmol), and CH3CN (2 mL). This white slurry was allowed to
stir for 5 min until the slurry turned slightly yellow. To this mixture
was added [Fe(H2O)6][BF4]2 (109 mg, 0.323 mmol) in CH3CN
(5 mL) and the mixture stirred for 20 min. A stock solution of
2-(diphenylphosphino)ethylamine (1.03 mL, 0.257 mmol, 230 mg in
4 mL CH3CN) was added to the solution. The mixture turned purple
immediately and was allowed to stir overnight. An additional 35 mg
of[Fe(H2O)6][BF4]2 was added, and after 3 h the brown-pink mixture
was filtered through a pad of Celite to remove a gray precipitate. The
solvent was removed, the residue was dissolved in CH2Cl2 (1 mL),
and Et2O (10 mL) was added. A pale pink precipitate was collected by
filtrationandwashedwithEt2O(2ꢀ 3 mL). Yield: 130 mg. 1HNMR
(400 MHz, CD3CN): δ 2.95 (m, 2H, CH2N), 3.64 (d, 2H, JHP=3.65
Hz, Ph2PCH2CH2), 4.03 (d, 2H, JHP =4.04 Hz, Ph2PCH2CHN),
7.48-7.79 (m, 20H, HPh), 8.14 (d, 1H, JHP =8.15 Hz, HCdN).
13C{1H} NMR (100 MHz, CD3CN): δ 26.3 (d, JCP = 24.0 Hz,
CH2N), 38.8 (d, JCP=25.0 Hz, CH2CHN), 60.8 (d, JCP=5.6 Hz,
HCdN). 13C {1H} NMR (100 MHz, CD3CN): δ 40.53 (dd, JCP
=
15, 10 Hz CH2P), 64.81 (CH2N), 122.09 (Cpy), 122.80 (CPhB),
125.61 (Cpy), 126.62 (q, CPhB), 129.56 (CPhP), 130.09 (CPhP),
130.46 (CPhP), 130.66 (CPhP), 131.89 (CPhP), 132.02 (CPhP),
136.75 (q, JCB=1.3 Hz, CPhB), 138.56 (Cpy), 151.21 (Cpy), 162.01
(Cpy), 164.81 (m, JCB 49 Hz, CPhB), 180.36 (t, JCP = 3.5 Hz,
CHN). 31P{1H} NMR (161 MHz, CD3CN): δ 62.51. Anal.
Calcd for C88H78N4P2FeB2: C, 79.41; H, 5.91; N, 4.21. Found:
C, 71.97; H, 5.37; N, 4.37. MS (ESI, methanol/water; m/zþ):
Ph2PCH2CH2), 129.5 (dd, JCP=2.2, 4.4 Hz, CPh), 129.9 (dd, JCP
=
2.2, 3.4 Hz, CPh), 130.8 (d, JCP=2.4 Hz, CPh), 130.7 (d, JCP=2.4,
CPh), 131.7 (d, JCP=9.4 Hz, CPh), 132.2 (d, JCP=10.1 Hz, CPh), 179.5
(dd,JCP=2.6, 6.8 Hz, HC=N). 31P{1H} NMR (161 MHz, CD3CN):
δ 57.0 (JPP=160 Hz), 63.3 (JPP=160 Hz). IR (KBr, cm-1) 2203 (s,
ν
CtꢁN), 2280 (m, νCtN). MS (ESI, methanol/water; m/zþ): 440.2
[C28H28NP2]þ.
346.1 [C40H38N4P2Fe]2þ
.
[Fe{(C6H11)2PCH2HCdNCH2CH2P(C6H5)2}(CH3CN)3]2þ
(4b). The synthesis of 4b was performed in the same manner as
4a (2 (80 mg, 0.125 mmol), KOtBu (28 mg, 0.250 mmol),
[Fe(H2O)6][BF4]2 (105 mg, 0.311 mmol), and 2-(diphenylphos-
phino)ethylamine (0.99 mL of stock solution)). After stirring
overnight, an additional 35 mg of Fe(H2O)6][BF4]2 was added,
and the reaction mixture was allowed to stir for 3 h. Upon
filtering the solution and removing the solvent, a brick-pink
solid was isolated and washed with Et2O (2 ꢀ 3 mL). Yield: 130
mg. 1H NMR (400 MHz, CD3CN): δ 1.35-2.40 (m, HCy), 2.93
(m, 2H, CH2N), 3.28 (d, 2H, JHP=3.51 Hz, Cy2PCH2), 3.76 (d,
2H, JHP=3.26 Hz, Ph2PCH2), 7.58-7.86 (m, 10H, HPh), 8.08
(d, 1H, JHP = 8.06 Hz, HCdN). 13C{1H} NMR (100 MHz,
CD3CN): δ 25.8 (CCy), 27.3 (d, JCP = 11.3 Hz, CCy), 28.4
(d, JCP=23.9 Hz, CH2N), 29.0 (CCy), 34.5 (d, JCP=20.6 Hz,
CH2CHN), 35.4 (d, JCP=15.2 Hz, HCCyP), 62.2 (d, JCP=6.3
[Fe{(C6H11)2PCH2CHdNCH2(C4H4N)}2][BPh4]2 (5b). Fol-
lowing the same procedure as for 5a (2 (80 mg, 0.125 mmol),
KOtBu (28 mg, 0.249 mmol), and [Fe(H2O)6][BF4]2 (63 mg,
0.187 mmol) in MeOH (5 mL)), a solution of 2-(amino-
methyl)pyridine (0.50 mL from a stock solution of 215 mg in
4 mL of MeOH) was added to the colorless mixture. The mixture
first turned red, and after stirring overnight, the mixture turned
purple-black. The mixture was filtered through a pad of Celite,
concentrated (∼2 mL) under reduced pressure, and added to a
solution of NaBPh4 (94 mg, 0.274 mmol) in MeOH (1 mL) to
cause the formation of a purple precipitate. The solid was
filtered and washed with MeOH (2 ꢀ 1 mL) and dried under a
vacuum. Yield: 62% (105 mg). 1H NMR (400 MHz, CD2Cl2): δ
0.91-2.06 (m, HCy), 2.31 (m, 2H, HCP), 3.06 (m, 2H, HC-N),
3.99 (m, 2H, HC-N), 6.77 (s, 2H, Hpy), 6.87 (t, 8H, HPh), 6.96
(d, 2H, Hpy), 7.08 (m, 16H, HPh), 7.27 (t, 2H, Hpy), 7.35 (d,
2H, Hpy), 7.59 (s, 16H, HPh), 7.73 (t, 2H, HCdN). 13C {1H}
NMR (100 MHz, CD2Cl2): δ 26.46 (CCy), 28.51 (CCy), 30.24
(CCy), 30.93 (CCy), 31.36 (CCy), 37.88 (CCy), 41.23 (CH2P), 57.53
(CH2N), 122.66 (CPhB), 126.57 (CPhB), 126.98 (Cpy), 129.21
(Cpy), 136.21 (CPhB), 138.21 (Cpy), 149.77 (Cpy), 158.44 (Cpy),
164.86 (CPhB), 171.23 (HCdN). 31P {1H} NMR (161 MHz,
Hz, Ph2PCH2CH2), 129.5 (d, JCP=9.3 Hz, CPh), 130.2 (d, JCP
35.9 Hz, CPh), 130.8 (d, JCP=2.3 Hz, CPh), 132.3 (d, JCP=9.3,
Ph), 180.8 (dd, JCP=2.3, 6.0 Hz, HC=N). 31P{1H} NMR (161
=
C
MHz, CD3CN): δ 55.8 (JPP=148 Hz), 65.5 (JPP=148 Hz). IR
(KBr, cm-1) 2208 (s, νCtN). MS (ESI, methanol/water; m/zþ):
452.2 m/z [C28H40NP2]þ.

1102 Inorganic Chemistry, Vol. 49, No. 3, 2010
Lagaditis et al.
CD2Cl2): δ 50.03. Anal. Calcd for C88H102N4P2FeB2: C, 77.99;
H, 7.59; N, 4.13. Found: C, 76.74; H, 7.02; N, 4.88. MS (ESI,
C86H106N4P2FeB2: C, 77.36; H, 8.00; N, 4.20. Found: C, 72.68;
H, 7.85; N, 4.11. MS (ESI, methanol/water; m/zþ): 559.4
[C34H61N2P2]þ.
methanol/water; m/zþ): 358.2 [C40H62N4P2Fe]2þ
.
Precursor Solution A. A vial was charged with 2 (200 mg,
0.311 mmol), KOtBu (70 mg, 0.623 mmol), and CH3CN (4 mL).
After stirring for 5 min, [Fe(H2O)6][BF4]2 (158 mg, 0.467 mmol)
in CH3CN (2 mL) was added to the white slurry. The solution
turned gray-yellow after 5 min.
trans-(R,R)-[Fe{(C6H11)2PCH2CHdNCH(Ph)CH(Ph)NdCH-
CH2P(C6H11)2}(CH3CN)2][BPh4]2 (6c).Asolutionof(1R,2R)-(-)-
1,2-diphenylethylenediamine (66 mg, 0.311 mmol) in CH3CN
(1 mL) was added to precursor solution A. The mixture slowly
turned pink, and after stirring for 48 h, the mixture was filtered
through a pad of Celite to remove a gray-white precipitate. The
solvent was removed under reduced pressure to give a red-pink
residue. The solid was dissolved in MeOH (2 mL) and added to a
solution of NaBPh4 (266mg,0.778mmol) inMeOH(1mL) tocause
the formation of a dark pink precipitate. The solid was filtered and
washed with MeOH (2 ꢀ 1 mL) and dried under a vacuum. Yield:
trans-[Fe{(C6H11)2PCH2CHdNCH2CH2NdCHCH2P(C6-
H11)2}(CH3CN)2][BPh4]2 (6a). To precursor solution A was
added ethylenediamine (0.34 mL from a stock solution of 200
mg in 4 mL of CH3CN). The mixture turned pink immediately.
After the reaction has gone to completion overnight, the
mixture was filtered through a pad of Celite to remove a
gray-white precipitate. Solvent was removed under reduced
pressure to give a red-pink residue. The solid was dissolved in
MeOH (2 mL) and added to a solution of NaBPh4 (234 mg,
0.685 mmol) in MeOH (1 mL) to cause precipitation of a pale
pink solid. The solid was filtered and washed with MeOH (2 ꢀ
1 mL) and dried under a vacuum. Yield: 80% (319 mg). Single
crystals suitable for an X-ray diffraction study were obtained
by the slow diffusion of pentane into CH3CN/CH2Cl2 (1:1 by
1
58% (260 mg). H NMR (400 MHz, CD3CN): δ 1.13-2.16 (m,
HCy, CH3), 3.21 (d, 2H, H2CP), 3.42 (m, 2H, H2CP), 5.30 (s, 2H,
HCPh), 6.86-7.40 (m, HAr), 7.88 (m, 2H, HCdN). 13C {1H}
NMR (100 MHz, CD3CN): δ 26.50 (CCyP), 26.82 (CCyP), 27.77 (q,
JCP=5.1 Hz CCyP), 27.91 (q, JCP=4.8 Hz, CCyP), 29.23 (CCy), 29.75
(CCy), 30.56 (CCy), 35.81 (t), 36.00(t), 36.59(dd, JCP=10.1, 14.7 Hz,
CH2P), 78.58 (HC-N), 122.64 (CPhB), 126.47 (q, JCB =2.7 Hz,
CPhB), 130.26 (CPh), 130.43 (CPh), 130.74 (CPh), 134.41 (CPh),
136.62 (q, JCB=1.3 Hz, CPhB), 163.94-165.41 (m, JCB=49 Hz),
178.15 (s, HCdN). 31P {1H} NMR (161 MHz, CD3CN): δ 67.5 (s).
Anal. Calcd for C94H105N4P2FeB2: C, 78.77; H, 7.59; N, 3.91.
Found: C, 74.92; H, 7.53; N, 3.74. MS (ESI, methanol/water;
m/zþ): 657.4 [C42H63N2P2]þ.
1
volume) at -40 °C. H NMR (400 MHz, CD3CN): δ 1.11-
1.95 (m, HCy, CH3), 3.31 (d, 4H, H2CP), 3.95 (s, 4H, H2C-N),
6.8-7.3 (m, HAr), 8.41 (m, 2H, HCdN). 13C {1H} NMR (100
MHz, CD3CN): δ 26.58 (CCy), 27.63 (t, JCP =5.1 Hz, CCy),
27.82 (t, JCP=5.1 Hz, CCy), 29.87 (CCy), 30.04 (CCy), 35.72 (t,
JCP=6.9 Hz, CCyP), 36.92 (dd, JCP=15, 10 Hz, CH2P), 61.10
(CH2N), 122.61 (CPhB), 126.43 (q, JCB=2.7 Hz, CPhB), 136.58
(q, JCB=1.4 Hz, CPhB), 164.62 (m, JCB=49 Hz, CPhB), 177.86
(HCdN). 31P {1H} NMR (161 MHz, CD3CN): δ 68.5 (s).
Anal. Calcd for C82H100N4P2FeB2: C, 76.88; H, 7.87; N, 4.37.
Found: C, 71.23; H, 7.51; N, 4.47. MS (ESI, methanol/water;
m/zþ): 505.4 [C30H55N2P2]þ.
trans-[Fe{(C6H11)2PCH2HCdN(C6H4)NdCHCH2P(C6-
11)2}(CH3CN)2][BPh4]2 (6d). A solution of o-phenylene-
H
diamine (14 mg, 0.125 mmol) in CH3CN (1 mL) was added
to precursor solution A. The mixture first turned brown,
and after stirring overnight, the mixture became orange.
The solvent was removed under reduced pressure to give a
red-orange solid. The solid was dissolved in MeOH (2 mL)
and added to a solution of NaBPh4 (94 mg, 0.274 mmol) in
MeOH (1 mL) to cause precipitation of an orange solid. The
solid was filtered and washed with MeOH (2 ꢀ 1 mL) and
dried under a vacuum. Yield: 61% (252 mg). 1H NMR (400
MHz, CD3CN): δ 1.24-1.95 (m, HCy, CH3), 3.66 (d, 4H,
H2CP), 6.82-7.28 (m, HAr), 7.54 (m, 2H, HAr), 7.99 (m,
2H, HAr), 9.07 (m, 2H, HCdN). 13C {1H} NMR (100 MHz,
CD3CN): δ 26.64 (CCyP), 27.93 (t, JCP=4.9 Hz CCyP), 28.07
(t, JCP=5.2 Hz, CCyP), 29.96 (CCyP), 30.23 (CCyP), 36.32 (t,
trans-(R,R)-[Fe{(C6H11)2PCH2CHdN(C6H10)NdCHCH2P-
(C6H11)2}(CH3CN)2][BPh4]2 (6b). A solution of (1R,2R)-(-)-
1,2-diaminocyclohexane (36 mg, 0.311 mmol) in CH3CN (1 mL)
was added to precursor solution A. The color of the reaction
mixture turned pink within 5 min. After stirring overnight, the
reaction mixture was filtered through a pad of Celite to remove a
gray-white precipitate, and the solvent was removed under
reduced pressure to give a red-pink residue. The solid was
dissolved in MeOH (2 mL) and added to a solution of NaBPh4
(266 mg, 0.778 mmol) in MeOH (1 mL) to cause precipitation of
a pale pink solid. The solid was filtered and washed with MeOH
(2 ꢀ 1 mL) and dried under a vacuum. Yield: 58% (242 mg).
Single crystals suitable for an X-ray diffraction study were
obtained by the slow diffusion of Et2O into MeOH/CH3CN
(1:1 by volume). 1H NMR (400 MHz, CD3CN): δ 1.24-1.95 (m,
HCy, CH3), 2.53 (d, 2H, HCyP), 3.12 (d, 2H, HCP), 3.36 (m, 2H,
HC-N), 3.49 (m, 2H, HCP), 6.8-7.2 (m, HAr), 8.35 (m, 2H,
HCdN). 13C {1H} NMR (100 MHz, CD3CN): δ 24.42 (CCy),
26.31 (CCy), 26.63 (CCyP), 27.48 (t, JCP=5.1 Hz, CCyP), 27.66 (q,
J
CP =7 Hz, CCyP), 37.95 (dd, JCP =10.1, 14.7 Hz, CH2P),
122.65 (CPhB), 126.47 (q, JCB=2.7 Hz, CPhB), 130.83 (CPh),
136.61 (m, CPhB), 145.28 (CPh), 164.67 (m, JCB = 49 Hz,
CPhB), 175.11 (HCdN). 31P {1H} NMR (161 MHz,
CD3CN):
δ
67.3 (s). Anal. Calcd for C86H100-
N4P2FeB2: C, 77.71; H, 7.58; N, 4.22. Found: C, 66.88; H,
6.98; N, 3.50. MS (ESI, methanol/water; m/zþ): 553.4
[C34H55N2P2]þ.
Acknowledgment. R.H.M. thanks NSERC for a Discovery
Grant and the PRF, as administered by the ACS, for an ACgrant.
JCP = 5.1 Hz, CCyP), 28.86 (CCy), 29.58 (CCyP), 30.35 (CCy),
30.40 (d, JCP =4.6 Hz, CCyP), 35.50 (q, JCP =2.9 Hz, CCyP),
36.56 (dd, JCP=10.1, 14.7 Hz, CH2P), 71.94 (HC-N), 122.48
(CPhB), 126.30 (q, JCB=2.8 Hz, CPhB), 136.44 (q, JCB=1.4 Hz,
Supporting Information Available: Complete crystallographic
data in CIF format for complexes 3a, 4c[FeBr4], 6a[BPh4][BF4],
and 6b[BPh4] Et2O. This material is available free of charge via
C
PhB), 163.75-165.22 (m, JCB=49 Hz, CPhB), 173.87 (HCdN).
3
31P {1H} NMR (161 MHz, CD3CN): δ 68.2 (s). Anal. Calcd for
the Internet at http://pubs.acs.org.