Synthesis, characterization, and electrochemistry of a series of iron (ii) complexes containing self-assembled 1,5-diaza-3,7-diphosphabicyclo[3.3.1]nonane ligands

Article abstract of DOI:10.1021/ic900874f

The reaction between PPh(CH₂OH)₂, iron(II) sulfate, ammonium sulfate, and formaldehyde in aqueous solution gives the iron(II) complex [Fe(κ²-O₂SO₂)L₂] (1), where L is the bidentate phosphin

Full text of DOI:10.1021/ic900874f

9924 Inorg. Chem. 2009, 48, 9924–9935
DOI: 10.1021/ic900874f
Synthesis, Characterization, and Electrochemistry of a Series of Iron(II) Complexes
Containing Self-Assembled 1,5-Diaza-3,7-diphosphabicyclo[3.3.1]nonane Ligands
Andrew D. Burrows,*,† Ross W. Harrington,‡ Andrew S. Kirk,† Mary F. Mahon,† Frank Marken,† John E. Warren,§
and Michael K. Whittlesey*,†
†Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, U.K., ‡School of Chemistry,
Newcastle University, Newcastle upon Tyne NE1 7RU, U.K., and §CLRC Daresbury Laboratory, Daresbury,
Warrington WA4 4AD, U.K.
Received May 6, 2009
The reaction between PPh(CH2OH)2, iron(II) sulfate, ammonium sulfate, and formaldehyde in aqueous solution gives
the iron(II) complex [Fe(κ2-O2SO2)L2] (1), where L is the bidentate phosphine ligand 3,7-diphenyl-1,5-diaza-3,
7-diphosphabicyclo[3.3.1]nonane. During the course of the reaction, the ligand L self-assembles on the metal center.
The reaction between PPh(CH2OH)2, iron(II) chloride, ammonium chloride, and formaldehyde under similar
conditions gives cis-[FeCl2L2] (cis-2). The complex cis-2 is converted into trans-2 in Et2O, whereas in water it is
converted into cis-[Fe(OH2)2L2]2þ, though both of these interconversions are reversible. The chloro ligands in cis-2
are readily displaced by reaction with thiocyanate, azide, and carbonate to give cis- and trans-[Fe(NCS)2L2] (cis- and
trans-3), cis- and trans-[Fe(N3)2L2] (cis- and trans-4), and [Fe(κ2-O2CO)L2] (5), respectively. The complex cis-2
reacts with CO in water to give trans-[FeCl(CO)L2]Cl (trans-6), whereas trans-2 reacts with CO in diethyl ether to give
cis-[FeCl(CO)L2]Cl (cis-6), though cis-6 isomerizes in water to form trans-6. The reaction of cis-2 with sodium
borohydride gives the hydride chloride complex trans-[FeCl(H)L2] (7). Electrochemical studies have been undertaken
on complexes 1, cis-2, and 7. These reveal reversible oxidations for cis-2 and 7, with the latter giving rise to an unusual
17-electron iron(III) hydride chloride complex. Crystal structures have been obtained for 1, trans-2, trans-3, 5, and 7.
Introduction
to prepare.2 Use of a metal template, however, allows such
ligands to be prepared in fewer steps and overall higher yields
than might otherwise be possible. For example, Edwards and
co-workers have used coupling reactions between coordi-
nated primary diphosphines and vinylphosphines to prepare
cyclic triphosphines with 9-12 membered rings.3 Stelzer and
co-workers have used a related approach to prepare cyclic
tetraphosphines,4 and also employed the reaction between
coordinated secondary diphosphines and diketones to pre-
pare similar products.5 More recently, Morris and co-work-
ers have shown that template reactions on iron can be used to
convert a dimeric phosphonium salt into tridentate PN2-
donor ligands, and subsequently tetradentate P2N2-donor
ligands.6
Despite the emergence of new classes of ligand, tertiary
phosphines continue to attract attention as the ready varia-
tion of substituents allows these ligands to be tailored to
particular uses. Further control of the properties of a metal
complex can be obtained using a bi- or poly dentate ligand, as
the linkers between the donor atoms affect the bite angle.1
Despite the potential advantages this control can confer,
polydentate and macrocyclic phosphines can be challenging
*To whom correspondence should be addressed. E-mail: a.d.burrows@
bath.ac.uk; m.k.whittlesey@bath.ac.uk.
(1) van Leeuwen, P. W. N. M.; Kamer, P. C. J.; Reek, J. N. H.; Dierkes, P.
Chem. Rev. 2000, 100, 2741–2770.
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Wright, D. S. Chem. Commun. 2005, 3733–3735. Markl, G.; Zollitsch, T.;
Kreitmeier, P.; Prinzhorn, M.; Reithinger, S.; Eibler, E. Chem.;Eur. J. 2000, 6,
3806–3820. Naumov, R. N.; Karasik, A. A.; Sinyashin, O. G.; Lonnecke, P.; Hey-
In 2000 it was reported that an unusual self-assembly reaction
takes place between tetrakis(hydroxymethyl)phosphonium sul-
fate (THPS, [P(CH2OH)4]2SO4), and ammonium sulfate in the
::
::
Hawkins, E. Dalton Trans. 2004, 357–358.
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2000, 39, 2722–2724. Edwards, P. G.; Newman, P. D.; Malik, K. M. A. Angew.
Chem., Int. Ed. 2000, 39, 2922–2924. Edwards, P. G.; Haigh, R.; Li, D.;
Newman, P. D. J. Am. Chem. Soc. 2006, 128, 3818–3830. Battle, A. R.;
Edwards, P. G.; Haigh, R.; Hibbs, D. E.; Li, D.; Liddiard, S. M.; Newman,
P. D. Organometallics 2007, 26, 377–386. Edwards, P. G.; Malik, K. M. A.; Ooi,
L.; Price, A. J. Dalton Trans. 2006, 433–441. Edwards, P. G.; Whatton, M. L.
Dalton Trans. 2006, 442–450.
(4) Brauer, D. J.; Lebbe, T.; Stelzer, O. Angew. Chem., Int. Ed. Engl. 1988,
27, 438–439. Lebbe, T.; Machnitzki, P.; Stelzer, O.; Sheldrick, W. S. Tetrahedron
2000, 56, 157–164.
(5) Bartsch, R.; Hietkamp, S.; Morton, S.; Peters, H.; Stelzer, O. Inorg.
Chem. 1983, 22, 3624–3632.
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r
pubs.acs.org/IC
Published on Web 09/11/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9925
Scheme 1
indicated. PPh(CH2OH)2 was prepared as previously repor-
ted.16 All other chemicals were obtained commercially and
used without further purification. NMR spectra were recorded
at 298 K on Bruker Avance 300, 400, and 500 MHz NMR
spectrometers, and referenced to residual protio solvent signals
1
for H NMR spectra (D2O, δ 4.80; CDCl3, δ 7.24; C6D6,
δ 7.15) and to solvent resonances for 13C{1H} NMR (D2O þ
1% MeOH, δ 49.5; CDCl3 δ 77.2). 31P{1H} NMR chemical
shifts were referenced externally to 85% H3PO4. Microana-
lyses were carried out by Mr. Alan Carver at the University of
Bath. IR spectra were recorded as KBr discs on a Nicolet
Nexus FTIR spectrometer. Mass spectra were recorded on a
Bruker MicrOTOF electrospray time-of-flight (ESI-TOF)
mass spectrometer (Bruker Daltonik GmbH) coupled to an
Agilent 1200 LC system (Agilent Technologies).
presence of iron(II) sulfate to form [Fe(OH2)2(L1)]SO4, which
contains an unusual tetraphosphine ligand (Scheme 1).7 THPS
is used as a biocide in oil wells, and this product was first
detected in the red coloration of water from these systems. In the
oil wells, the source of the metal was iron sulfide deposits, which
are dissolved by THPS. We have previously reported ligand
substitution reactions on [Fe(OH2)2(L1)]SO4 and also the
esterification of the hydroxymethyl groups on reaction with
acetic anhydride which converts [Fe(OH2)2(L1)]SO4 to [Fe(κ2-
O2SO2)(L2)] (Scheme 1).8
Synthesis of [Fe(K2-O2SO2)L2] (1). Iron(II) sulfate heptahy-
drate (0.101 g, 0.363 mmol), ammonium sulfate (0.097 g,
0.734 mmol), and formaldehyde (0.066 g of a 37% aq. solution,
0.813 mmol) were dissolved in water (20 mL) under an atmo-
sphereof N2 togive a pale green solution. PPh(CH2OH)2 (0.247 g,
1.45 mmol) was separately dissolved in degassed water (10 mL),
which was then slowly added dropwise over 30 min to the iron-
containing solution while stirring, taking care to keep the pH
below 5.5. The addition of the aqueous phosphine solution gave
rise to a purple coloration of the solution, which increased in
intensity with further addition of the phosphine solution. As the
solution became darker, a purple solid began to precipitate.
After the addition of PPh(CH2OH)2 was complete, the reaction
mixture was left to stir for 1 h, after which the purple product
was collected by filtration and washed with cold water (2 mL).
The purple solid of 1 was then dried in a desiccator under
reduced pressure overnight. Yield 0.093 g (33%). 1H NMR
(500 MHz, CDCl3): δ 7.4-7.1 (m, 20H, Ar), 5.27 (d, 2H, PCH2N
AB1, Δν 821 Hz, 2JHH 13.9 Hz), 4.92 (d, 2H, PCH2N AB2, Δν
736 Hz, 2JHH 12.9 Hz), 4.17 (d, 2H, NCH2N AB, Δν 76 Hz, 2JHH
Reactions between bis(hydroxymethyl)phosphines and
amines have been studied in the absence of templates. In
::
1980, Markl and co-workers showed that reactions between
an alkyl or aryl bis(hydroxymethyl)phosphine, PR-
(CH2OH)2, and a primary amine led to 1,5-diaza-3,7-dipho-
sphacyclooctanes.9 Subsequently, these eight-membered
rings have been prepared with a wide range of substituents,
including chiral centers,10 ferrocenyl groups,11 and amino
acids.12,13 The amine used in the synthesis is crucial to
determining the nature of the product formed. Karasik,
Hey-Hawkins, and co-workers found that they could obtain
linear bis(arylaminomethyl)phosphines, six-membered 1,3-dia-
za-5-phosphacyclohexanes and 1,5-diaza-3,7-diphosphacyclooc-
tanes from aryl bis(hydroxymethyl)phosphines.14 Katti and co-
workers have also investigated the reactions of a number of
hydroxymethyl phosphines with primary amines. They showed
that the reactions between 1,2-bis(bis(hydroxymethyl)phosph-
ino)ethane and amino acids gave 3,7-diaza-1,5-diphosphabicy-
clo[3.3.2]decanes.12,15
2
13.9 Hz), 4.01 (d, 2H, NCH2N AB, Δν 76 Hz, JHH 13.9 Hz),
2
4.03 (d, 2H, PCH2N AB3, Δν 228 Hz, JHH 13.9 Hz), 3.63 (d,
2
2H, PCH2N AB1, Δν 821 Hz, JHH 13.9 Hz), 3.53 (d, 2H,
PCH2N AB4, Δν 411 Hz, 2JHH 13.9 Hz), 3.53 (d, 2H, PCH2N
AB3, Δν 228 Hz, 2JHH 13.9 Hz), 3.45 (d, 2H PCH2N AB2, Δν
736 Hz, 2JHH 12.9 Hz), 2.71 (d, 2H, PCH2N AB4, Δν 411 Hz,
2JHH 13.9 Hz). 31P{1H} (122 MHz, CDCl3):δ-26.4(t,2JPP=72 Hz),
Our objective in this work was to assess the generality of
the self-assembly reaction that produces [Fe(OH2)2(L1)]SO4
by changing the phosphorus source from tetrakis(hydroxy-
methyl)phosphonium to a bis(hydroxymethyl)phosphine. In
this paper, we report our results using PPh(CH2OH)2.
2
-51.2 (t, JPP = 72 Hz). Found: C, 50.7; H, 5.25; N, 6.28%.
Calcd for C34H40N4O4FeP4S H2O: C, 51.1; H, 5.30; N, 6.99%.
3
MS (ESI): m/z=803.1 [M þ Na]þ.
Synthesis of cis-[FeCl2L2] (cis-2) and trans-[FeCl2L2] (trans-2).
Iron(II) chloride tetrahydrate (0.335 g, 1.69 mmol), NH4Cl
(0.362 g, 6.77 mmol), and formaldehyde (0.281 g of a 37% aq.
solution, 3.46 mmol) were dissolved in water (25 mL). PPh-
(CH2OH)2 (1.150 g, 6.76 mmol) was dissolved in degassed water
(9 mL), then added dropwise over 45 min to the iron-containing
solution while stirring, taking care to keep the pH below 5. The
reaction mixture was stirred for 2 h, then the purple product was
collected by filtration and washed with cold water (2 mL). The
purple solid of cis-2 was dried in a desiccator under reduced
pressure overnight. Yield 1.01 g (79%). 31P{1H} NMR (122 MHz,
CDCl3): δ -32.4 (br t), -46.5 (br t). 31P{1H} NMR (122 MHz,
D2O): δ -17.9 (m, 2JPP 74 Hz), -38.2 (m, 2JPP 74 Hz). A sample
of cis-2 was placed in a cellulose extraction thimble inserted into
a Soxhlet extractor fitted with a condenser and round-bottomed
flask. Diethyl ether was placed in the round-bottomed flask and
heated to reflux for 24 h. This gave a yellow solution, which
yielded yellow crystals of trans-2 upon evaporation of the diethyl
ether solution at room temperature. Found: C, 53.4; H, 5.33; N,
7.23%. Calcd for C34H40N4FeP4Cl2: C, 54.0; H, 5.34; N, 7.42%.
MS (ESI): m/z 684.2 [M - 2Cl]þ.
Experimental Section
Reactionswere typicallycarriedout in air, thoughmanipu-
lations on a Schlenk line under dinitrogen were used as
(7) Jeffery, J. C.; Odell, B.; Stevens, N.; Talbot, R. E. Chem. Commun.
2000, 101–102.
(8) Burrows, A. D.; Dodds, D.; Kirk, A. S.; Lowe, J. P.; Mahon, M. F.;
Warren, J. E.; Whittlesey, M. K. Dalton Trans. 2007, 570–580.
::
(9) Markl, G.; Jin, G. Y.; Schoerner, C. Tetrahedron Lett. 1980, 21, 1409–
1412.
(10) Karasik, A. A.; Naumov, R. N.; Sinyashin, O. G.; Belov, G. P.;
::
Novikova, H. V.; Lonnecke, P.; Hey-Hawkins, E. Dalton Trans. 2003, 2209–
2214.
(11) Karasik, A. A.; Spiridonova, Y. S.; Yakhvarov, D. G.; Sinyashin,
::
O. G.; Lonnecke, P.; Sommer, R.; Hey-Hawkins, E. Mendeleev Commun.
2005, 89–90.
(12) Berning, D. E.; Katti, K. V.; Barnes, C. L.; Volkert, W. A. J. Am.
Chem. Soc. 1999, 121, 1658–1664.
(13) Karasik, A. A.; Sinyashin, O. G.; Heinicke, J.; Hey-Hawkins, E.
Phosphorus, Sulfur Silicon Relat. Elem. 2002, 177, 1469–1471.
(14) Karasik, A. A.; Naumov, R. N.; Sommer, R.; Sinyashin, O. G.; Hey-
Hawkins, E. Polyhedron 2002, 21, 2251–2256.
(15) Katti, K. V.; Kannan, R.; Katti, K. K.; Pillarsetty, N.; Barnes, C. L.
Phosphorus, Sulfur Silicon Relat. Elem. 2002, 177, 1587–1589.
(16) Higham, L. J.; Whittlesey, M. K.; Wood, P. T. Dalton Trans. 2004,
4202–4208.

9926 Inorganic Chemistry, Vol. 48, No. 20, 2009
Burrows et al.
2
2
Synthesis of cis-[Fe(NCS)2L2] (cis-3) and trans-[Fe(NCS)2L2]
(trans-3). Compound cis-2 (0.050 g, 0.66 mmol) was added to
EtOH (10 mL) giving a purple suspension. Excess potassium
thiocyanate (0.129 g, 1.33 mmol) was added to the reaction
mixture giving an orange precipitate of cis-3. The orange solid
was collected by filtration and washed with cold water (5 mL).
Yield 0.043 g (78%). Single crystals of trans-3 suitable for X-ray
diffraction were grown from a CDCl3 solution over 48 h. 31P{1H}
and 1H NMR spectroscopy showed a mixture of cis-3 and trans-
3 in an 4:1 ratio after 20 min in solution, which changed to a 2:3
ratio after 48 h. 1H NMR (cis-3) (300 MHz, CDCl3): δ 7.8-6.6
(m, 20H, Ar), 4.6 (d, 2H, PCH2N AB1, Δν 391 Hz, 2JHH 13.9 Hz),
4.3 (d, 2H, PCH2N AB2, Δν 387 Hz, 2JHH 13.4 Hz), 4.0 (d, 2H,
(t, JPP 72 Hz), -41.4 (t, JPP 72 Hz). 13C{1H} (125 MHz,
CDCl3): δ 163.7 (s, O2CO), 131-128 (m, Ar), 72.8 (s, NCH2N),
53.3 (m, PCH2N), 51.2 (m, PCH2N), 50.9 (s, PCH2N), 48.0
(s, PCH2N). Calcd for C35H40N4O3FeP4: C, 56.5; H, 5.42;
N, 7.53%. Found: C, 56.1; H, 5.29; N, 7.46%. IR (cm-1): 1556
(νCO ). MS (ESI): m/z 744.1678. (Calcd for [M]þ, m/z 744.1400).
3
Synthesis of trans-[FeCl(CO)L2]Cl (trans-6). Compound cis-2
(0.100 g, 0.133 mmol) was dissolved in H2O (20 mL) and CO
bubbled through the solution for 20 min. The reaction was
stirred for 2 h, resulting in a yellow solution. A yellow solid was
precipitated from solution by the addition of acetone. The
yellow solid of trans-6 was washed with additional acetone
(5 mL) and dried in a desiccator. Yield 0.087 g (83%). 1H
NMR (400 MHz, D2O): δ 7.1-6.9 (m, 20H, Ar), 4.9 (d, 4H,
2
PCH2N AB3, Δν 161 Hz, JHH 13.8 Hz), 3.9 (d, 2H, NCH2N
2
AB, Δν 24 Hz, 2JHH 13.9 Hz), 3.8 (d, 2H, NCH2N AB, Δν 24 Hz,
2JHH 13.9 Hz), 3.5 (d, 2H, PCH2N AB4, Δν 309 Hz, 2JHH 13.8 Hz),
3.5 (d, 2H, PCH2N AB3, Δν 161 Hz, 2JHH 13.8 Hz), 3.3 (d, 2H,
PCH2N AB1, Δν 423 Hz, JHH 13.5 Hz), 4.4 (d, 4H, PCH2N
AB2, Δν 156 Hz, 2JHH 14.5 Hz), 3.9 (s, 4H, NCH2N), 3.8 (d, 4H,
2
PCH2N AB2, Δν 156 Hz, JHH 14.5 Hz), 3.5 (d, 4H, PCH2N
AB1, Δν 423 Hz, JHH 13.5 Hz). 31P{1H} (122 MHz, D2O):
2
2
PCH2N AB1, Δν 391 Hz, JHH 13.9 Hz), 3.0 (d, 2H PCH2N
δ -51.0 (s). 13C{1H} (trans-[FeCl(13CO)L2]Cl, 126 MHz, D2O):
2
AB2, Δν 387 Hz, JHH 13.4 Hz), 2.4 (d, 2H, PCH2N AB4, Δν
δ 214.7 (quintet, 13CO, JCP 25.8 Hz), 132-129 (m, Ar), 72.2
(s, NCH2N), 52.3 (s, PCH2N), 49.1 (s, PCH2N). Calcd for
2
2
309 Hz, JHH 13.8 Hz). 31P{1H} (cis-3) (122 MHz, CDCl3):
δ -31.0 (m, 2JPP 77 Hz), -38.6 (m, 2JPP 77 Hz). 1H NMR (trans-3)
(300 MHz, CDCl3): δ 7.8-6.6 (m, 20H, Ar), 4.3 (d, 8H, PCH2N
AB, Δν 221 Hz, 2JHH 13.4 Hz), 4.0 (s, 4H, NCH2N), 3.5 (d, 8H,
PCH2NAB, Δν221 Hz, 2JHH 13.4 Hz). 31P{1H} (trans-3) (122MHz,
CDCl3): δ -42.2 (s). IR (cm-1): 2098 (νNCS). MS (ESI): m/z
742.1304 (Calcd for [M - NCS]þ, m/z 742.1304).
C35H40N4OFeP4Cl2 6H2O: C, 46.6; H, 5.81; N, 6.21%. Found:
C, 46.3; H, 5.47; N, 6.06%. IR (cm-1): 1939 (ν12CO), 1895 (ν13CO).
MS (ESI): m/z 747.1165. (Calcd for [M]þ, m/z 747.1191).
3
Synthesis of cis-[FeCl(CO)L2]Cl (cis-6). Compound trans-2
(0.010 g, 0.013 mmol) was dissolved in diethyl ether (20 mL)
giving a pale yellow solution. CO was bubbled through the
reaction mixture for 20 min, and the reaction mixture was stirred
for a further 4 h, after which time a pale orange precipitate began
to form. cis-6 was separated by filtration after a further 7 days of
stirring, then washed with Et2O (5 mL) and dried in air. Yield
0.005 g (48%). Alternatively, cis-6 could be also prepared by
addition of 1 atm CO to a CDCl3 solution of cis-2. 31P{1H}
Synthesis of cis-[Fe(N3)2L2] (cis-4) and trans-[Fe(N3)2L2]
(trans-4). Compound cis-2 (0.050 g, 0.066 mmol) was added to
EtOH (10 mL) giving a purple suspension. Excess NaN3 (0.086 g,
1.32 mmol) was added to the reaction mixture, to give a red
suspension of cis-4. The red solid was collected by filtration and
washed with cold water (5 mL). Repeated recrystallizations
from various solvent combinations failed to give a satisfactory
microanalysis because of the difficulty in removing excess
2
NMR (122 MHz, CDCl3): δ -39.4 (ddd, JPP 91, 38, 45 Hz),
-55.3 (ddd, 2JPP 91, 61, 48 Hz), -59.4 (ddd, 2JPP 38, 61, 120 Hz),
-69.0 (ddd, 2JPP 45, 48, 120 Hz). Selected 13C{1H} (126 MHz,
CDCl3): δ 214.2 (m, 13CO, J 20.6 Hz). IR (cm-1): 1974 (νCO).
MS (ESI): m/z 747.1 [M]þ.
1
sodium azide from the product. 31P{1H} and H NMR spec-
troscopy showed a mixture of cis-4 and trans-4 in an 11:1 ratio,
which did not change over time. H NMR (cis-4) (300 MHz,
1
CDCl3):δ7.5-7.1 (m, 20H, Ar), 4.7 (d, 2H, PCH2NAB1, Δν30 Hz,
2
2JHH 13.6 Hz), 4.6 (d, 2H, PCH2N AB2, Δν 473 Hz, JHH
Synthesis of trans-[FeCl(H)L2] (7). Compound cis-2 (0.200 g,
0.265 mmol) and NaBH4 (0.020 g, 0.529 mmol) were placed in a
Schlenk tube under dinitrogen, to which was added degassed
EtOH (10 mL), dissolving the starting materials to give an
orange solution. Upon stirring for 1 h, an orange suspension
of 7 formed. The solution was filtered by cannula under
dinitrogen, and the solid washed with degassed ethanol (5 mL)
then recrystallized from degassed benzene. Yield 0.128 g (67%).
1H NMR (400 MHz, C6D6): δ 7.0-6.8 (m, 20H, Ar), 5.5 (d, 4H,
PCH2N AB1, Δν 806 Hz, 2JHH 12.9 Hz), 3.9 (s, 4H, NCH2N),
3.9 (d, 4H, PCH2N AB2, Δν 107 Hz, 2JHH 13.3 Hz), 3.6 (d, 4H,
13.6 Hz), 3.9 (d, 2H, PCH2N AB3, Δν 155 Hz, 2JHH 13.6 Hz), 3.9
2
(d, 2H, NCH2N AB, Δν 25 Hz, JHH 13.6 Hz,), 3.9 (d, 2H,
NCH2N AB, Δν 25 Hz, 2JHH 13.6 Hz,), 3.5 (d, 2H, PCH2N AB4,
Δν 293 Hz, 2JHH 13.6 Hz), 3.4 (d, 2H, PCH2N AB3, Δν 155 Hz,
2JHH 13.6 Hz), 3.4 (d, 2H, PCH2N AB1, Δν 30 Hz, 2JHH 13.6 Hz),
3.0 (d, 2H, PCH2N AB2, Δν 473 Hz, 2JHH 13.6 Hz), 2.5 (d, 2H,
PCH2N AB4, Δν 293 Hz, 2JHH 13.6 Hz). 31P{1H} (cis-4) (122 MHz,
2
2
1
CDCl3): δ -27.4 (m, JPP 75 Hz), -36.9 (m, JPP 75 Hz). H
NMR (trans-4) (300 MHz, CDCl3): δ 7.5-7.1 (m, 20H, Ar), 4.3
(d, 8H, PCH2N AB, Δν 186 Hz, JHH 14.1 Hz), 4.2 (s, 4H,
2
2
2
NCH2N), 3.6 (d, 8H, PCH2N AB, Δν 186 Hz, JHH 14.1 Hz).
PCH2N AB2, Δν 107 Hz, JHH 13.3 Hz), 3.5 (d, 4H, PCH2N
31P{1H} (trans-4) (122 MHz, CDCl3): δ -43.2 (s). IR (cm-1):
2043 (νN3). MS (ESI): m/z 684.2 [M - 2N3]þ.
AB1, Δν 806 Hz, 2JHH 12.9 Hz), -28.6 (quintet, FeH, 2JHP 49 Hz).
31P (162 MHz, C6D6): δ -27.5 (d, 2JPH=49 Hz). MS (ESI): m/z
685.1632. (Calcd for [M - Cl]þ, m/z 685.1632).
Synthesis of [Fe(K2-O2CO)L2] (5). Compound cis-2 (0.107 g,
0.142 mmol) was added to ethanol (20 mL) giving a purple
suspension. Excess sodium carbonate (0.170 g, 1.60 mmol) in
water (5 mL) was added, to give a pink suspension. The resulting
pink solid was separated by filtration and recrystallized from
chloroform. Yield 0.061 g (59%). Single crystals of 5 suitable for
X-ray diffraction grew from an aqueous solution over 8 weeks.
1H NMR (500 MHz, CDCl3): δ 7.6-7.1 (m, 20H, Ar), 5.16 (d, 2H,
PCH2N AB1, Δν 918 Hz, 2JHH 12.9 Hz,), 4.76 (d, 2H, PCH2N
AB2, Δν 680 Hz, 2JHH 12.9 Hz), 4.03 (d, 2H, PCH2N AB3, Δν
Electrochemistry. All reagents used for electrochemical ana-
lyses were of analytical or electrochemical grade purity. The
supporting electrolyte was tetrabutylammonium hexafluoropho-
sphate in acetonitrile and 1,2-dichloroethane solutions. The sol-
vents were purged with argon prior to use. All experiments were
conducted at 295 ( 2 K. Voltammetric experiments were per-
formed using an Ecochemie Autolab potentiostat. For the purpose
of these experiments a three electrode cell setup was used, com-
posed of working, counter, and reference electrodes. The working
electrode used was a 3 mm diameter platinum electrode unless
otherwise stated. The counter electrode consisted of a spiral of
platinum wire. All potentials were referenced to internal cobalto-
cenium hexafluorophosphate, which was referenced to ferrocene
(E1/2=0.00 V) but were measured using a platinum wire pseudo
reference (a platinum wire which was immersed and equilibrated in
the electrolyte containing solvent used for the experiment).
2
277 Hz, JHH 12.9 Hz,), 4.00 (d, 2H, NCH2N AB, Δν 33 Hz,
2JHH 14.5Hz), 3.94 (d, 2H, NCH2N AB, Δν 33 Hz, 2JHH 13.9 Hz),
2
3.48 (d, 2H, PCH2N AB4, Δν 401 Hz, JHH 13.9 Hz), 3.48
2
(d, 2H, PCH2N AB3, Δν 277 Hz, JHH 12.9 Hz), 3.40 (d, 2H,
PCH2N AB2, Δν 680 Hz, 2JHH 12.9 Hz), 3.32 (d, 2H, PCH2N
AB1, Δν 918 Hz, 2JHH 12.9 Hz), 2.68 (d, 2H, PCH2N AB4, Δν
2
401 Hz, JHH 13.9 Hz). 31P{1H} (122 MHz, CDCl3): δ -20.2

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9927
Table 1. Crystal Data and Structure Refinement for Compounds 1 2H2O, trans-2, trans-3, 5 7H2O, and 7 1.5C6H6
3
trans-2
C34H40Cl2FeN4P4
755.37
150(2)
3
trans-3
C36H40FeN6P4S2
800.59
150(2)
3
compound
empirical formula
formula weight
T/K
1 2H2O
3
5 7H2O
3
7 1.5C6H6
3
C34H44FeN4O6P4S
816.52
150(2)
C35H54FeN4O10P4
870.55
150(2)
C43H50ClFeN4P4
838.05
150(2)
wavelength/A
crystal system
space group
a/A
b/A
c/A
0.69040
monoclinic
C2/c
15.422(3)
9.5514(18)
24.333(5)
90
100.469(2)
90
3524.5(11)
4
1.539
0.71073
monoclinic
P21/c
21.9030(2)
10.3800(1)
22.1870(2)
90
97.990(1)
90
4995.32(8)
6
1.507
0.69070
orthorhombic
Pbcn
15.0527(9)
14.9361(9)
16.0794(9)
90
90
90
3615.1(4)
4
1.471
0.71073
triclinic
P1
0.68840
monoclinic
C2/c
26.873(3)
14.5374(17)
22.100(3)
90
111.244(1)
90
8047.0(17)
8
1.383
9.4170(2)
10.5490(2)
22.2750(6)
87.925(1)
79.223(1)
65.600(1)
1977.53(8)
2
R/deg
β/deg
γ/deg
U/A3
Z
Dc/g cm-3
1.462
0.604
916
μ/mm-1
F(000)
0.721
1704
0.838
2352
0.747
1664
0.637
3512
crystal size/mm
θ min., max for data
index ranges
0.03 ꢀ 0.03 ꢀ 0.01
3.65,22.55.
-16 e h e 17;
-10 e k e 9;
-21 e l e 26
7752
0.45 ꢀ 0.30 ꢀ 0.25
3.58, 27.49
-27 e h e 28;
-13 e k e 13;
-28 e l e 28
63320
0.07 ꢀ 0.01 ꢀ 0.01
3.09, 29.56
-21 e h e 21;
-17 e k e 21;
-22 e l e 22
28014
0.25 ꢀ 0.15 ꢀ 0.05
3.97, 27.54 .
-12 e h e 12;
-13 e k e 12;
-28 e l e 28
23946
0.02 ꢀ 0.01 ꢀ 0.01
3.44, 23.91
-31 e h e 31;
-17 e k e 17;
-26 e l e 26
27709
reflections collected
independent reflections, Rint
reflections observed (>2σ)
absorption correction
max., min transmission
data/restraints/parameters
goodness-of-fit (F2)
2513, 0.0981
1549
multiscan
0.991, 0.975
2513/3/233
0.977
11444, 0.0482
9117
multiscan
0.80, 0.94
11444/0/604
1.044
5481, 0.0564
4240
multiscan
0.981, 0.923
5481/0/222
1.014
8787, 0.0707
6814
multiscan
0.9704, 0.8637
8787/21/529
1.128
6833, 0.1122
3746
multiscan
0.995, 0.978
6833/1/516
0.958
final R1, wR2 [I > 2σ(I)]
final R1, wR2 (all data)
largest diff. peak, hole/e A-3
0.0525, 0.1130
0.1067, 0.1327
0.347, -0.364
0.0328, 0.0713
0.0501, 0.0784
0.472, -0.427
0.0343, 0.0792
0.0525, 0.0868
0.468, -0.402
0.0618, 0.1406
0.0835, 0.1517
0.784, -0.691
0.0562, 0.1229
0.1217, 0.1530
0.690, -0.312
Crystallography. Single crystals of compounds trans-2 and 5
were analyzed using a Nonius Kappa CCD diffractometer, while
the data sets for 1, trans-3, and 7 were obtained at Daresbury
(Station 9.8 or 16.2 SMX). Details of the data collections, solutions
and refinements are given in Table 1. The structures were solved
using SHELXS-97 and refined using full-matrix least-squares in
SHELXL-97.17 Refinements were generally straightforward with
the following exceptions and points of note. The crystals for 1and 7
were small, even by Daresbury standards, and this is reflected in the
upper Bragg limits for these data collections. Solvent water
hydrogens were located in both 1 and 5, and refined at a distance
of 0.9 A from the relevant parent oxygen in addition to restraining
Results and Discussion
To assess the effects of the phosphine substituents on the
self-assembly of the tetraphosphine ligand around the iron
center, we sought to þundertake analogous reactions to that
between P(CH2OH)4 and NH4þ, but using phosphonium
þ
cations of the type PR(CH2OH)3 (R= aryl, alkyl). Since
[Fe(OH2)2(L1)]SO4 can also be prepared from P(CH2OH)3,7
we reasoned it would be possible to use a bis(hydroxy-
methyl)phosphine such as PPh(CH2OH)2 rather than the
phosphonium PPh(CH2OH)3þ, which would be prepared
from it. In addition, since PPh(CH2OH)3þ would be present
in solution in equilibrium with PPh(CH2OH)2 and HCHO,
we decided to investigate the reactions of iron(II) salts with
PPh(CH2OH)2 in the presence of formaldehyde.
the H H distances therein to a value of 1.5 A. In 1, the
3 3 3
asymmetric unit was seen to comprise half of one molecule (with
the central metal and sulfur atoms located on a crystallographic
2-fold rotation axis) plus one full water molecule. The asymmetric
unit in trans-2, on the other hand, consists of one full molecule of
the iron complex plus half of an additional complex molecule. The
central metal in the latter is located on a crystallographic inversion
center. Carbons 6-11 were refined after accounting for disorder
over two positions in 60:40 ratio. As observed in 1, the asymmetric
unit in trans-3 was also seen to be half of a molecule, with the iron
located on a 2-fold rotation axis implicit in the space group.
Finally, in 7, H1 and H2 were located and refined subject to being
similar distances from the iron centers to which they respectively
bond. The asymmetric unit in this structure contains two crystal-
lographically independent halves of the iron complex (wherein the
iron, chloride, and hydride in each are located on a 2-fold rotation
axis), one-half of a benzene molecule with full occupancy
(proximate to an inversion center) plus an additional molecule of
benzene exhibiting 1:1 disorder. The disordered portions of the
latter fragments were treated as rigid hexagons in the final least-
squares cycles.
Synthesis of [Fe(K2-O2SO2)L2] (1). Bis(hydroxyme-
thyl)phenylphosphine, PPh(CH2OH)2, was prepared via
the reaction of phenylphosphine and formaldehyde.16 An
aqueous solution of PPh(CH2OH)2 was slowly added to
an aqueous solution containing iron(II) sulfate, ammo-
nium sulfate, and formaldehyde. The pale green solution
rapidly turned purple, and subsequently yielded a purple
precipitate. The pH of the reaction solution was moni-
tored and kept below pH 5.5 by adding the phosphine
slowly to prevent base-induced decomposition of the
products. The purple material 1 was found to be soluble
in chloroform, dichloromethane, and acetone, but inso-
luble in THF and benzene.
Single crystals suitable for X-ray analysis were grown
from the slow evaporation of a dichloromethane solution
of 1. The crystallographic analysis showed that 1 does not
contain a ligand analogous to that in [Fe(OH2)2(L1)]SO4,
but instead 1 has the formula [Fe(κ2-O2SO2)L2], where L
is the new bidentate phosphine ligand 3,7-diphenyl-1,
(17) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467–473.
Sheldrick, G. M. SHELXL-97, Computer Program for Crystal Structure
::
::
Refinement; University of Gottingen: Gottingen, Germany, 1997.

9928 Inorganic Chemistry, Vol. 48, No. 20, 2009
Burrows et al.
Scheme 2
Table 2. Selected Bond Lengths (A) and Angles (deg) for 1 2H2Oa
3
Fe(1)-P(1)
Fe(1)-P(2)
Fe(1)-O(1)
2.2831(16)
2.1837(18)
2.061(4)
S(1)-O(1)
S(1)-O(2)
1.501(4)
1.451(4)
P(2)-Fe(1)-P(1)
P(2)0-Fe(1)-P(1)
P(1)-Fe(1)-P(1)0
83.42(6)
98.54(6)
176.99(11)
P(2)-Fe(1)-P(2)0
O(1)0-Fe(1)-O(1)
99.55(10)
68.4(2)
1
a Primed atoms generated by the symmetry operation -x, y, -z þ /2.
5-diaza-3,7-diphosphabicyclo[3.3.1]nonane (Scheme 2). The
diphosphine contains two fused six-membered PN2C3
rings, with the rings sharing the two nitrogen atoms and
the interlinking methylene group. Details of the crystal
structure are given below. Following the X-ray structural
analysis, the ratio of PPh(CH2OH)2/FeSO4/(NH4)2SO4/
HCHO in the synthesis was adjusted to 4:1:2:2 to match
the stoichiometry of the product and give an optimal
yield.
Figure 1. Molecular structure of [Fe(κ2-O2SO2)L2] (1), from the crystal
structure of 1 2H2O. Ellipsoids are represented at 30% probability.
Hydrogen atoms have been omitted for clarity. Primed labels are related
tothose inthe asymmetric unit bythe -x, y, -z þ /2 symmetry operation.
3
1
The 31P{1H} NMR spectrum of 1 showed two triplet
resonances at δ -26.4 and δ -51.2, with a coupling
constant of JPP 72 Hz. This pattern is characteristic of
in Figure 1. The diphosphine ligands contain a backbone
of two fused 1-aza-3,5-diphosphacyclohexane rings, with
the rings sharing the two nitrogen atoms and the con-
necting carbon atom. Each phosphorus atom is also
bonded to a phenyl ring.
The two fused six-membered PN2C3 rings both possess
chair conformations, which enables the lone pairs of the
phosphorus atoms to chelate to the metal center. The
crystallographic bite angle of the diphosphine in 1 is
83.42(6)°, which is close to the average values for bis-
(diphenylphosphino)ethane (dppe) (85(3)°) and 1,2-bis-
(diphenylphosphino)benzene (83(3)°).1 The bite angle of
the coordinated sulfate in 1 is 68.4(2)°.
The structure of 1 shows some similarities to that
of [Fe(κ2-O2SO2)(L2)], with two bidentate diphosphine
ligands present instead of a tetradentate L2 ligand.8 The
Fe-P bond lengths in 1 are 2.1837(18) A (equatorial) and
2.2831(16) A (axial), which compares with equivalent
values of 2.1803(17)/2.1776(17) A (equatorial) and
2.2256(16)/2.2362(16) A (axial) for [Fe(κ2-O2SO2)(L2)].
The lengthening of the axial Fe-P bonds with respect to
the equatorial Fe-P bonds in these complexes is due to
the phosphine donors having a greater trans influence
than sulfate.
2
1
the cis arrangement of the diphosphine ligands. The H
NMR spectrum showed five different AB patterns arising
from the five methylene proton environments, four from
the P-CH2-N groups and one from the N-CH2-N
group. This means that all 10 methylene protons on the
ligand backbone are inequivalent. The N-CH2-N
methylene protons give rise to the AB system centered
at δ 4.1, though it is difficult to unambiguously assign the
four remaining AB systems to particular methylene
groups. The ESI mass spectrum of 1 shows a major peak
at m/z 803.1, which corresponds to [M þ Na]þ.
The diphosphine ligand L can be thought of as a 1,
5-diaza-3,7-diphosphacyclooctane with
a methylene
bridge between the two nitrogen atoms. This bridging
CH2 moiety is formed from the condensation of a for-
maldehyde molecule with an N-H bond on each side of
the eight-membered ring, which means that the formal-
dehyde plays two roles in the self-assembly of the dipho-
sphine ligand;it acts as a catalyst in the Mannich
reaction involved in the self-assembly process, as well as
a reagent which is an essential part of the final ligand
structure.
X-ray Crystal Structure of [Fe(K2-O2SO2)L2] 2H2O
The two phenyl rings on each L ligand are almost
perpendicular to one another, as quantified by the mean
3
(1 2H2O). The crystallographic analysis revealed that
the crystals were of the dihydrate, 1 2H2O. The asym-
3
C-C C-C torsion angle between the rings of 84°. This
3
3 3 3
metric unit contains one-half of the complex molecule
and a molecule of H2O, with the remainder of the formula
unit generated by symmetry. Selected bond lengths and
gives each ligand a staggered conformation, and this
minimizes the steric interactions between aromatic rings
of the two L ligands. One of the methylene groups on each
L ligand is directed toward a ring on the other L ligand,
and a distance of 2.54 A between the hydrogen atom and
angles for 1 2H2O are given in Table 2. The iron(II)
3
center has a distorted octahedral geometry and is coordi-
nated to two bidentate L ligands, arranged in a cis
configuration, and a bidentate sulfato ligand, as shown
the ring plane is suggestive of a C-H π interaction.
The included water molecules form hydrogen bonds to a
3 3 3

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9929
sulfate oxygen atom (O O 2.866, H O 2.01 A,
O-H O 163°) and a nitrogen atom (O N 3.047,
3 3 3
3 3 3
3 3 3 3 3 3
H
molecules into chains.
N 2.20 A, O-H N 159°), and these link the
3 3 3
3 3 3
Synthesis of cis-[FeCl2L2] (cis-2). Initial attempts to
displace the coordinated sulfato ligand in 1 were unsuc-
cessful. When [PPN]Cl (bis(triphenylphosphoranylid-
ene)ammonium chloride) was added to a dichlorometh-
ane solution of 1, no reaction occurred. This is in contrast
to [Fe(κ2-O2SO2)(L2)], which reacts with chloride under
similar conditions to form [FeCl2(L2)].8
To synthesize the dichloride complex [FeCl2L2], iron-
(II) chloride and ammonium chloride (rather than the
equivalent sulfate salts) were reacted with PPh(CH2OH)2
and formaldehyde. Using the same stoichiometry as with
the sulfate salts, the reaction gave a similar purple pre-
cipitate as in the formation of 1. The 31P{1H} NMR
spectrum of the purple solid in CDCl3 showed two triplet
resonances at δ -32.4 and δ -46.5 as would be expected
for a complex with the same geometry as 1, consistent
with formation of the dichloride complex cis-[FeCl2L2]
(cis-2). However, the resonances in CDCl3 were broad
suggesting the complex is fluxional, although cooling to
232 K failed to either sharpen the signals or resolve any
additional resonances, making it unclear what fluxional
processes are in operation.
Figure 2. Molecular structure oftrans-[FeCl2L2] (trans-2), showing only
the full occupancy molecule. Ellipsoids are represented at 30% prob-
ability, and hydrogen atoms have been omitted for clarity.
Complex cis-2 partially dissolves in aqueous solution to
give a purple solution. When the 31P{1H} NMR spectrum
was recorded in D2O, two sharp resonances were observed
at δ -17.9 and δ -38.2, although these were now obser-
ved as second order multiplets rather than triplets. The
large chemical shift difference between CDCl3 and D2O is
consistent with a change in the coordination sphere, and
the solubility of cis-2 in water at neutral pH suggests that
the chloro ligands are being displaced by aqua ligands to
give the dicationic complex cis-[Fe(OH2)2L2]Cl2. Com-
plex cis-2 is increasingly soluble in water with decreasing
pH, possibly because of protonation of the nitrogen
groups. If an excess of sodium chloride is added to the
aqueous solution of cis-[Fe(OH2)2L2]Cl2, cis-2 precipi-
tates from solution.
Attempts to grow crystals of cis-2 proved unsuccessful,
though it was observed that despite the complex being largely
insoluble in diethyl ether, washings of the purple solid gave a
very dilute pale yellow solution. Slow evaporation of this
diethyl ether solution gave yellow crystals suitable for X-ray
crystallography. The resulting structure showed that this
complex was trans-[FeCl2L2] (trans-2). Because of the very
low solubility of trans-2 in diethyl ether, a good 31P{1H}
NMR spectrum of this compound proved difficult to
obtain. When dissolved in other organic solvents such
as dichloromethane, chloroform, and acetone, the yellow
crystals of trans-2 dissolved to give a purple solution. The
31P{1H} NMR spectrum of this solution showed broad
triplet resonances at δ -32.4 and δ -46.5, demonstrating
that cis-2 had been reformed. Dissolving trans-2 in D2O
also gave a purple solution, the 31P{1H} NMR spectrum
of which displayed the two multiplet resonances at
δ -17.9 and δ -38.2. This suggests that the diaqua
complex cis-[Fe(OH2)2L2]Cl2 had formed, in a similar
manner to when cis-2 is dissolved in aqueous solution.
The interconversions between cis-2, trans-2, and cis-
[Fe(OH2)2L2]Cl2 are summarized in Scheme 3.
Scheme 3
Table 3. Selected Bond Lengths (A) and Angles (deg) for trans-2a
Fe(1)-P(1)
Fe(1)-P(2)
Fe(1)-Cl(1)
Fe(2)-P(3)
Fe(2)-P(4)
2.2674(5)
2.2954(5)
2.3600(4)
2.2469(5)
2.2474(5)
Fe(2)-P(5)
Fe(2)-P(6)
Fe(2)-Cl(2)
Fe(2)-Cl(3)
2.2614(5)
2.2506(5)
2.3676(5)
2.3610(5)
P(1)-Fe(1)-P(2)
P(1)-Fe(1)-P(2)0
P(3)-Fe(2)-P(4)
P(3)-Fe(2)-P(5)
P(3)-Fe(2)-P(6)
80.839(17)
99.161(17)
82.007(19)
168.17(2)
99.98(2)
P(4)-Fe(2)-P(5)
P(4)-Fe(2)-P(6)
P(6)-Fe(2)-P(5)
Cl(3)-Fe(2)-Cl(2)
98.60(2)
169.13(2)
81.669(19)
177.47(2)
a Primed atoms generated by the symmetry operation -x, -y, -z þ 1.
X-ray Crystal Structure of trans-[FeCl2L2] (trans-2).
The X-ray crystallographic analysis of trans-2 revealed
the asymmetric unit contains 1.5 molecules of the com-
plex, with one full molecule and one-half molecule resid-
ing on a mirror plane. The full occupancy molecule is
shown in Figure 2, and selected bond lengths and angles
are given in Table 3. The three independent crystallo-
graphic bite angles for the diphosphine L ligand in the
structure are 82.007(19) and 81.669(19)° for the full
molecule, and 80.839(17)° for the half molecule. These
are all notably lower than the value for 1 (83.42(6)°). The
geometry around the metal center in trans-2 is distorted
from a regular octahedron, with the cis equatorial
P-Fe-P bond angles ranging from 81.669(19) and
99.98(2)° for the full molecule and from 80.838(17) to
99.162(17)° for the half molecule. The geometry is less
regular for the full molecule, with a tetrahedral distortion

9930 Inorganic Chemistry, Vol. 48, No. 20, 2009
Burrows et al.
present, as illustrated by a 20° angle between the two FeP2
planes.
In the full molecule, the two phenyl rings on each of the
independent L ligands are orientated in staggered con-
formations, as quantified by mean C-C C-C torsion
3 3 3
angles between the rings of 53° and 47°. In contrast, in the
half molecule, the two phenyl rings on each ligand are
almost coplanar, with a mean C-C C-C torsion angle
3 3 3
of 6°; hence this ligand adopts an eclipsed conformation.
In both independent molecules, the phenyl groups face
one another with closest C C distances between 3.22
3 3 3
and 3.64 A, consistent with the presence of intramolecular
π
π interactions.
The six independent Fe-P bond lengths in the structure
3 3 3
of trans-2 range from 2.2469(5) to 2.2954(5) A, and these
are closer to the axial rather than the equatorial Fe-P
bond lengths in the structure of 1, as all of the Fe-P
bonds in trans-2 are trans to another phosphine. The
Fe-P bond lengths in trans-2 are significantly longer than
those in the related bis(1,2-bis(dialkylphosphino)ethane
complexes trans-[FeCl2L2], where L = 1,2-bis(dimethyl-
phosphino)ethane (2.241(1) and 2.230(1) A),18 1,2-bis-
(diethylphosphino)ethane (2.256(2) and 2.264(2) A), and
1,2-bis(di-n-propylphosphino)ethane (2.261(2) and
2.275(2) A).19 This is a consequence of the steric require-
ment of the phosphine substituents, and also the greater
σ-donor ability of the trialkylphosphine donors over the
dialkylarylphosphine donors in trans-2.
Reactions of cis-2 with Thiocyanate and Azide. Potas-
sium thiocyanate was added to cis-2 in ethanol to give an
orange suspension of cis-[Fe(NCS)2L2] (cis-3). The 31P{1H}
NMR spectrum of this complex in CDCl3 showed two
second order resonances at δ -31.0 and δ -38.6, as
expected for a cis isomer, plus a singlet at δ -42.2 which
was assigned to trans-3. From the integrals, the cis and
trans isomers are present in a 4:1 ratio. Over time, the
ratio of cis to trans isomers changes, and the 31P{1H}
NMR spectrum recorded after 48 h shows a cis/trans ratio
of 2:3. Orange crystals suitable for X-ray crystallography
also grew over time, and these were shown to be of trans-3
(see below).
Figure 3. Molecular structure of trans-[Fe(NCS)2L2] (trans-3). Ellip-
soids are represented at 30% probability, and hydrogen atoms have been
omitted for clarity. Primed labels are related to those in the asymmetric
unit by the -x, y, -z þ /2 symmetry operation.
1
Table 4. Selected Bond Lengths (A) and Angles (deg) for trans-3a
Fe(1)-P(1)
Fe(1)-P(2)
Fe(1)-N(1)
2.2453(4)
2.2592(4)
1.9387(14)
N(1)-C(1)
S(1)-C(1)
1.165(2)
1.6339(16)
P(1)-Fe(1)-P(2)
P(1)-Fe(1)-P(1)0
P(1)0-Fe(1)-P(2)
P(2)-Fe(1)-P(2)0
82.469(15)
98.24(2)
166.572(15)
99.97(2)
N(1)0-Fe(1)-N(1)
C(1)-N(1)-Fe(1)
N(1)-C(1)-S(1)
179.20(8)
177.58(12)
179.50(16)
1
a Primed atoms generated by the symmetry operation -x, y, -z þ /2.
process is less favorable for cis-4 and trans-4 than it is for the
thiocyanate analogues. The observation of both cis and trans
isomers of 4is in contrast to the synthesis of [Fe(N3)2(dmpe)2]
(dmpe = 1,2-bis(dimethylphosphino)ethane, which showed
no evidence for the cis isomer, with only the trans isomer
observed in the 31P{1H} NMR spectrum.20
The 1H NMR spectrum of a mixture of the cis and trans
isomers showed five separate AB resonances for cis-3,
arising from the four inequivalent P-CH2-N methylene
groups and the N-CH2-N group, and a single AB
system and a singlet for trans-3. In this case the
N-CH2-N methylene protons are equivalent, while each
of the four P-CH2-N methylene groups is in a similar
environment, with one proton axial and the other equa-
torial in the PN2 six-membered rings of the diphosphine
ligand.
Sodium azide was added to an ethanol solution of cis-2,
resulting in a red precipitate of cis-[Fe(N3)2L2] (cis-4). The
31P{1H} NMR spectrum in CDCl3 showed two second
order resonances at δ -27.4 and δ -36.9, assigned to cis-
4, as well as a singlet at δ -43.2, assigned to trans-4, with
the compounds present in an 11:1 ratio. The spectrum was
unchanged after 48 h, showing that the isomerization
1
The H NMR spectrum of the mixture of cis-4 and
trans-4 showed a similar series of resonances to that of cis-
3 and trans-3. Therefore, one AB system and a singlet
were observed for trans-4, and five AB resonances obser-
ved for cis-4. IR spectroscopy of the mixture showed only
one peak for ν(N3) at 2043 cm-1, which given the ratio of
isomers observed is likely to be due to cis-4. This isomer
might be expected to show both symmetric and antisym-
metric stretches, though only one peak was observed for
the tetraphosphine complex [Fe(N3)2(L1)], whereas the
two peaks in the cis diazido complex [Fe(N3)2-
{P(CH2CH2PMe2)3}] were separated by only 6 cm-1 21
.
X-ray Crystal Structure of trans-[Fe(NCS)2L2] (trans-3).
The X-ray analysis of the orange crystals isolated from
(18) Di Vaira, M.; Midollini, S.; Sacconi, L. Inorg. Chem. 1981, 20, 3430–
3435.
(20) Field, L. D.; George, A. V.; Pike, S. R.; Buys, I. E.; Hambley, T. W.
Polyhedron 1995, 14, 3133–3137.
(19) Baker, M. V.; Field, L. D.; Hambley, T. W. Inorg. Chem. 1988, 27,
2872–2876.
(21) Field, L. D.; Messerle, B. A.; Smernik, R. J. Inorg. Chem. 1997, 36,
5984–5990.

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9931
Figure 4. (a) Molecular structure of [Fe(κ2-O2CO)L2] (5), from the crystal structure of 5 7H2O. Ellipsoids are represented at 30% probability. Hydrogen
atoms have been omitted for clarity. (b) The hydrogen-bonded tapes of water molecules present in the structure of 5 7H2O.
3
3
the CDCl3 solution containing cis- and trans-3 showed
the structure to be of trans-3, as shown in Figure 3. The
asymmetric unit of the structure contains one-half mole-
cule of trans-3, with the other generated by symmetry
inherent to the space group. Selected bond lengths and
angles for trans-3 are given in Table 4. The thiocyanato
ligands are coordinated to the iron center by the nitrogen
atoms, in a similar manner to that observed in the
tetraphosphine complex [Fe(NCS)2(L1)].8 The thiocya-
nato ligands in trans-3 are almost linear, with the
Fe-N-C angle 177.58(12)°.
The conformation adopted by trans-3 is similar to that of
the full molecule in the crystal structure of trans-2. There is a
tetrahedral distortion around the iron center, with the angle
between the two FeP2 planes being 20°. The two phenyl
rings within each L ligand are staggered with respect to each
O2CO)L2] (5). The 31P{1H} NMR spectrum of 5 in CDCl3
showed two triplet resonances at δ -20.2 and δ -41.4
with 2JPP 72 Hz. The 1H NMR spectrum of 5 showed the
expected pattern for a bis(diphosphine) complex posses-
sing cis geometry, that is, four AB systems for the
P-CH2-N methylene protons and one AB system for
the N-CH2-N methylene protons. The N-CH2-N
protons give rise to the second order AB system centered
at δ 3.9, with the four remaining P-CH2-N methylene
proton groups giving four sets of AB systems between
δ 5.2 and δ 2.6, some of which overlap.
X-ray Crystal Structure of [Fe(K2-O2CO)L2] 7H2O
3
(5 7H2O). Purple crystals were grown from the slow
3
evaporation of an aqueous solution of 5 over 8 weeks,
and were shown by a single crystal X-ray analysis to be the
heptahydrate. The structure confirms that the two chloro
ligands have been replaced with a bidentate carbonate,
giving a cis octahedral geometry as shown in Figure 4a.
Selected bond lengths and angles are given in Table 5. The
chelating carbonato ligand has a small bite angle, which
results in a structure that is far from a regular octahedral
geometry. The cis equatorial bond angles range between
65.00(9)° and 100.98(4)°. The crystallographic bite angles
of the diphosphine ligand in the structure are 82.62(3)° and
82.88(4)°, which are similar tothose incomplexes 1, trans-2
and trans-3. In comparison with the X-ray structure of
[Fe(κ2-O2CO)(L1)],8 the Fe-O bonds are similar (2.030(2)
other (mean C-C C-C torsion angle 46°), and face the
3 3 3
equivalent phenyl group on the other L ligand. The shortest
distance between the phenyl rings of the two L ligands is
3.3 A, suggesting the presence of π π interactions. Phenyl
3 3 3
rings on adjacent molecules also interdigitate parallel to
each other, but the longer distance between them suggests
this occurs for packing reasons rather than as the conse-
quence of any significant π π interactions.
3 3 3
Reaction of cis-2 with Carbonate. The reaction of an
ethanol solution of cis-2 with an aqueous solution of
sodium carbonate gave a pink suspension of [Fe(κ2-

9932 Inorganic Chemistry, Vol. 48, No. 20, 2009
Burrows et al.
Table 5. Selected Bond Lengths (A) and Angles (deg) for 5 7H2O
Scheme 4
3
Fe-P(1)
Fe-P(2)
Fe-P(3)
Fe-P(4)
Fe-O(1)
2.2045(9)
2.2630(10)
2.2572(10)
2.1911(9)
2.030(2)
Fe-O(2)
2.016(2)
1.316(4)
1.315(4)
1.247(4)
C(20)-O(1)
C(20)-O(2)
C(20)-O(3)
P(1)-Fe-P(2)
P(4)-Fe-P(3)
P(1)-Fe-P(3)
P(4)-Fe-P(1)
P(3)-Fe-P(2)
82.62(3)
82.88(4)
99.25(4)
100.98(4)
176.45(4)
P(4)-Fe-P(2)
99.77(4)
65.00(9)
124.8(3)
123.8(3)
111.5(3)
O(2)-Fe-O(1)
O(3)-C(20)-O(1)
O(3)-C(20)-O(2)
O(2)-C(20)-O(1)
is bound to the iron center. The 13C{1H} NMR spectrum
is consistent with this, showing a quintet 13CO resonance
at δ 214.7. The IR spectrum of trans-6 showed a single
12CO stretching frequency at 1939 cm-1, which would be
expected for a monocarbonyl complex. The IR spectrum
of the corresponding 13CO complex showed the equiva-
lent 13CO stretching frequency with the expected isotopic
shift at 1895 cm-1. The ESI mass spectrum showed the
major peak to be at m/z 747.1, which can be assigned to
the chloride carbonyl complex cation [FeCl(CO)L2]þ. As
a result of the combined spectroscopic evidence, trans-6
has been identified as trans-[FeCl(CO)L2]Cl.
When the reaction between cis-2 and CO was carried out
in CDCl3, the 31P{1H} NMR spectrum showed four main
resonances at δ -39.4, δ -55.3, δ -59.4, and δ -69.0,
which are all doublets of doublets of doublets, though the
resonance at δ -69.0 appears simpler because of two of the
2JPP values being coincidently similar. The coupling pat-
tern shows that all four phosphorus donors in the complex
are inequivalent, strongly suggesting that the product is
cis-[FeCl(CO)L2]Cl (cis-6). This formulation was strongly
supported by the 13C{1H} NMR spectrum recorded upon
reaction with 13CO rather than 12CO, the spectrum dis-
playing a single multiplet carbonyl resonance at δ 214.1.
On leaving this solution to stand at room temperature, a
small quantity of trans-6 appeared, as witnessed by a
doublet 31P resonance (δ -51.0) and quintet 13CO reso-
nance, but this remained a minor product, with no evi-
dence for an equilibrium between the isomers.
and 2.016(2) A for 5 7H2O compared to 2.044(5) and
3
2.073(5) A for [Fe(κ2-O2CO)(L1)]). The O-Fe-O bite
angle in 5 7H2O (65.00(9) A) is larger than that of
3
[Fe(κ2-O2CO)(L1)] (63.8(2) A). In contrast to 1, the two
independent L ligands adopt conformations in which the
two phenyl rings are almost coplanar, as quantified by
mean C-C C-C torsion angles of 7° and 13° for the
two ligands.
3 3 3
The related complex [Fe(κ2-O2CO)(dmpe)2] has been
recently reported from the reaction between trans-[FeMe2-
(dmpe)2] and CO2, probably in the presence of adventi-
tious water.22 This compound crystallizes as a H2CO3
adduct, with a pair of hydrogen bonds between the carbo-
nic acid molecule and the coordinated carbonate. The
Fe-O distances are comparable with those in 5 7H2O
3
(2.039(2), 2.041(2) A), whereas the O-Fe-O bite angle is
slightly lower (64.48(9)°).
Unsurprisingly, the included water molecules in the
structure of 5 7H2O are involved in hydrogen bonding,
3
with the carbonate oxygen atoms and the L nitrogen
atoms both acting as acceptors. In addition, there are
tapes formed by hydrogen-bonded water molecules run-
ning through the lattice. These tapes contain alternating
eight- and four-membered rings (T4(2)8(2)),23 as shown
in Figure 4b. Water molecules can adopt a multitude of
hydrogen-bonding arrangements within crystal struc-
tures, but this motif is relatively unusual with only a few
previous examples.24
Reaction of cis-2 with CO. When CO was bubbled
through an aqueous solution of cis-2, the color changed
over an hour from purple to yellow. The 31P{1H} NMR
spectrum of the yellow solution showed a singlet reso-
nance at δ -51.0, consistent with formation of a trans
bis(diphosphine) complex, trans-6. 1H NMR spectrosco-
py showed two sets of AB doublets at δ 4.9 and δ 4.4, and
δ 3.8 and δ 3.5, as well as a singlet at δ 3.9. This indicates
When trans-2 was reacted with CO in diethyl ether
solution, a pale orange precipitate was formed. The 31P{1H}
NMR spectrum of the orange solid dissolved in CDCl3
showed the product to be cis-6. When cis-6 was dissolved in
D2O, it gave a yellow solution and the 31P{1H} NMR
spectrum showed a singlet resonance at δ -51.0. This is
similar to the spectrum observed for trans-6, suggesting that
cis-6 isomerizes in water.
The syntheses and interconversions of 6 are summar-
ized in Scheme 4. While the formation of cis-6 in Et2O is
likely to be driven by solubility, it is noteworthy that the
majority of reactions in water lead to isomerization. It is
likely that these processes occur via initial coordination of
H2O, though the reactions are too fast to obtain spectro-
scopic evidence to validate this.
1
that trans-6 is unsymmetrically substituted, since the H
NMR spectrum of a symmetrical product such as
trans-[Fe(CO)2L2]2þ would give a single AB system and
a singlet in a 4:1 ratio because the four P-CH2-N
methylene groups on each L ligand would be equivalent.
When the reaction was repeated with 13CO a similar
yellow solution was produced, but now the 31P{1H}
2
NMR spectrum showed a doublet at δ -51.1 with JPC
Another example of how the geometrical isomer iso-
lated is influenced by reaction conditions is provided by
Mays and co-workers.25 When trans-[FeCl2(dmpe)2] was
reacted with CO in an acetone solution in the presence of
NaBPh4, cis-[FeCl(CO)(dmpe)2]BPh4 was formed as the
major product. In contrast, when trans-[FeCl2(dmpe)2]
25.8 Hz. The doublet indicates that only one 13CO ligand
(22) Allen, O. R.; Dalgarno, S. J.; Field, L. D.; Jensen, P.; Turnbull, A. J.;
Willis, A. C. Organometallics 2008, 27, 2092–2098.
(23) Infantes, L.; Chisholm, J.; Motherwell, S. CrystEngComm 2003, 5,
480–486. Mascal, M.; Infantes, L.; Chisholm, J. Angew. Chem., Int. Ed. 2006,
45, 32–36.
(24) Wang, J.; Hu, S.; Tong, M.-L. Eur. J. Inorg. Chem. 2006, 2069–2077.
Fan, G.; Xie, G.; Chen, S.; Gao, S. J. Coord. Chem. 2007, 60, 1093–1099.
(25) Bellerby, J. M.; Mays, M. J.; Sears, P. L. J. Chem. Soc., Dalton Trans.
1976, 1232–1236.

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9933
a
Table 6. Selected Bond Lengths (A) and Angles (deg) for 7 1.5C6H6
3
Fe(1)-P(1)
Fe(1)-P(2)
Fe(2)-P(3)
2.2050(14)
2.1595(13)
2.1708(14)
Fe(2)-P(4)
Fe(1)-Cl(1)
Fe(2)-Cl(2)
2.2075(15)
2.461(2)
2.454(2)
P(2)-Fe(1)-P(1)
P(3)-Fe(2)-P(4)
P(1)-Fe(1)-P(1)0
P(2)-Fe(1)-P(2)0
P(3)-Fe(2)-P(3)0
P(4)0-Fe(2)-P(4)
83.59(5)
83.13(5)
172.16(9)
153.72(9)
154.44(10)
173.99(9)
P(2)0-Fe(1)-P(1)
P(3)-Fe(2)-P(4)0
P(1)-Fe(1)-Cl(1)
P(2)-Fe(1)-Cl(1)
P(3)-Fe(2)-Cl(2)
P(4)-Fe(2)-Cl(2)
98.20(5)
98.22(5)
86.08(4)
103.14(5)
102.78(5)
86.99(5)
1
a Primed atoms generated by the symmetry operation -x, y, -z þ /2.
2JPH values of 45-46 Hz.26 Complex 7 proved to be
relatively air-stable in the solid-state, showing no change
after 24 h. In contrast, ethanolic solutions of 7 turned
brown and decomposed upon exposure to air after a few
minutes.
X-ray Crystal Structure of trans-[FeCl(H)L2] 1.5C6H6
3
(7 1.5C6H6). Orange crystals from the recrystallization of
3
7 in benzene were suitable for single crystal analysis. The
asymmetric unit contains two independent half molecules
of trans-[FeCl(H)L2] along with one-half molecule of
benzene with full occupancy and one whole molecule of
benzene exhibiting 1:1 disorder. One of independent
complex molecules is shown in Figure 5. Selected bond
lengths and angles are given in Table 6.
The two Fe-Cl bond lengths in the structure are
2.461(2) and 2.454(2) A for the Fe(1)-Cl(1) and Fe-
(1)-Cl(2) bonds, respectively, which are significantly
longer than those observed in trans-2 because of increased
trans influence of hydride relative to chloride. Only two
other X-ray crystal structures of similar complexes of the
formula trans-[FeCl(H)L2] (where L = any bidentate
phosphine ligand) have been reported in the literature
to date. Both of these have slightly shorter Fe-Cl bond
lengths than 7, 2.404(2) A for trans-[FeCl(H)(dppe)2]27
and 2.4044(12) A for trans-[FeCl(H)(depe)2] (depe=bis-
(diethylphosphino)ethane).28
Figure 5. Molecular structure of trans-[FeCl(H)L2] (7), from the crystal
structure of 7 1.5C6H6. Only one ofthe independent complex molecules is
3
shown. Ellipsoids are represented at 30% probability. With the exception
of the hydride ligand, hydrogen atoms have been omitted for clarity.
Primed labels are related to those in the asymmetric unit by the -x, y,
1
-z þ /2 symmetry operation.
was reacted with CO in a refluxing acetone solution for 5 h,
followed by addition of NaBPh4, the major product was
trans-[FeCl(CO)(dmpe)2]BPh4. In both cases, the other
isomer was observed as a minor product, but in this system
no evidence was observed for the interconversion of the
isomers in solution.
Reaction of cis-2 with Sodium Borohydride. When cis-2
and 2 equiv of sodium borohydride were dissolved in
ethanol under a nitrogen atmosphere, an orange solution
formed, which produced an orange precipitate after 1 h.
The reaction mixture was stirred at room temperature for
a further 1 h to complete the reaction, then the crude
material was separated by filtration and recrystallized
from degassed benzene to give trans-[FeCl(H)L2] (7) as a
dark orange microcrystalline solid.
The conformations of the two independent molecules
in the structure of 7 are similar to the full molecule of
complex trans-2. Within each L ligand, the two phenyl
rings are staggered with respect to each other, as quanti-
fied by C-C C-C torsion angles of 47-50°. The iron
3 3 3
centers are distorted octahedral, with two of the phos-
phorus centers on each molecule pushed toward the
hydride, giving trans P-Fe-P angles of 154°. The pairs
of phenyl rings on the two L ligands within each complex
The 31P{1H} NMR spectrum of 7 in C6D6 showed a
singlet at δ -27.5 consistent with a trans complex. When
the same 31P NMR experiment was run without proton
decoupling, the singlet split into a doublet with 2JPH 49 Hz,
suggesting the phosphorus resonance is coupling to a
molecule are approximately parallel, and closest C
C
3 3 3
contacts of 3.3 A suggest the presence of π π interac-
3 3 3
tions. In the supramolecular structure, the molecules are
aligned into chains, with the chloride of one complex
directed to the hydride of a neighbor, though this is likely
to be the consequence of packing as opposed to any
interaction.
1
single hydride nucleus. The H NMR spectrum of the
solid dissolved in C6D6 showed a quintet at δ -28.6
because of the coupling of the hydride with the four
equivalent phosphorus nuclei, confirming the presence
of the hydride in the complex and the trans geometry.
These observations are similar to those reported by the
groups of Tyler and Holah for the related compounds
trans-[FeCl(H)(bmppe)2] (bmppe=1,2-bis(bis-(methoxy-
propyl)phosphino)ethane) and trans-[FeCl(H)(dppm)2]
(dppm=bis(diphenylphosphino)methane). These comp-
ounds both displayed low frequency quintet hydride
resonances (δ -31.8 and δ -21.2, respectively), with
Electrochemistry. Cyclic voltammetry studies were car-
ried out on 1, cis-2, and 7 to determine their redox
(26) Gao, Y.; Holah, D. G.; Hughes, A. N.; Spivak, G. J.; Havighurst,
M. D.; Magnuson, V. R.; Polyakov, V. Polyhedron 1997, 16, 2797–2807.
Gilbertson, J. D.; Szymczak, N. K.; Crossland, J. L.; Miller, W. K.; Lyon, D. K.;
Foxman, B. M.; Davis, J.; Tyler, D. R. Inorg. Chem. 2007, 46, 1205–1214.
(27) Lee, J.-G.; Jung, G.-S.; Lee, S. W. Bull. Korean Chem. Soc. 1998, 19,
267–269.
::
(28) Wiesler, B.; Tuczek, F.; Nather, C.; Bensch, W. Acta Crystallogr.,
Sect. C 1998, 54, 44–46.

9934 Inorganic Chemistry, Vol. 48, No. 20, 2009
Burrows et al.
Figure 6. Cyclic voltammograms for the oxidation of 1 mM [Fe(κ2-
O2SO2)L2] (1) at a 1 mm diameter Pt electrode in 1,2-dichloroethane/0.1
M NBu4PF6 at scan rates of (i) 20 mV s-1, (ii) 50 mV s-1, (iii) 100 mV s-1
,
Figure 7. Cyclic voltammograms for the oxidation of
trans-[FeCl(H)L2] (7) at a 1 mm diameter Pt electrode in 1,2-dichloro-
ethane/0.1 M NBu4PF6 at scan rates of (i) 10 mV s-1, (ii) 20 mV s-1
(iii) 50 mV s-1, (iv) 100 mV s-1, and (v) 200 mV s-1
1 mM
and (iv) 200 mV s-1
.
,
.
properties, as well as to establish whether the related
iron(III) complexes were stable and potentially isolable.
Cyclic voltammograms were recorded using a 1 mm
platinum electrode and employed 1 mM 1,2-dichloro-
ethane solutions of the complexes with 0.1 M tetrabu-
tylammonium hexafluorophosphate as the electrolyte. In
the case of 1, the voltammogram recorded with an initial
scan rate of 20 mV s-1 showed a chemically irreversible
peak at about 0 V versus Fcþ/Fc (see Figure 6), which
suggests that the complex is reactive upon oxidation.
Voltammograms were then recorded at 50, 100, and 200 mV
appeared to be no appearance of trans-2. This suggests
that the complex stays as the cis isomer in acetonitrile
solution, which is consistent with the greater polarity of
acetonitrile than 1,2-dichloroethane.
The voltammogram obtained for 7 showed one main
oxidation process occurring at -0.85 V versus Fcþ/Fc,
which can be assigned to the Fe(II)/Fe(III) redox process
for the trans hydride chloride complex 7. The experiment
was repeated at scan rates of 20, 50, 100, and 200 mV s-1
(Figure 7), indicating fully reversible characteristics.
Therefore, the iron(III) complex [FeCl(H)L2]þ is stable
even at low scan rates, making it a rare example of a stable
17-electron metal(III) hydride complex formed from the
oxidation of the corresponding neutral 18-electron spe-
cies.29 After leaving the 1,2-dichloroethane solution of 7
for 30 min under argon, the color of the solution changed
from bright orange to a darker orange/purple, and the
voltammogram showed two new processes at -1.25 and
-0.35 V versus Fcþ/Fc. Both processes appear reversible,
but were not fully identified. The process at -0.35 V
versus Fcþ/Fc occurs at the same potential as cis-2 in 1,
2-dichloroethane, suggesting the process could be caused
by this complex, which may be present as a decomposi-
tion product. The observed darkening of the solution
supports this interpretation. Additionally, the more ne-
gative potential of the hydride complex 7 compared to
that of cis-2 shows that 7 is far easier to oxidize than cis-2,
which would be expected for a hydride complex.
s
-1, and the Fe(II)/Fe(III) redox process was seen to
become more reversible with increasing scan rate. The
small redox process at -0.4 V versus Fcþ/Fc is believed to
be a result of either a minor impurity or a new species
resulting from the decomposition of 1. Insolubility of 1
in acetonitrile prevented the cyclic voltammetry being
investigated in that solvent.
The voltammogram for cis-2 in 1,2-dichloroethane was
first recorded at 200 mV s-1, which showed the main
reversible process at -0.35 V versus Fcþ/Fc. A second but
minor process was observed at -0.05 V versus Fcþ/Fc.
When the voltammogram of cis-2 was obtained at lower
scan rates, both reversible redox processes were still
observed in the same ratio, suggesting that two isomers
may be present in solution. Unlike the sulfate complex 1,
the dichloride complex [FeCl2L2] can switch between cis
and trans isomers. As the purple cis-2 was used in the
experiment and the 1,2-dichloroethane solution was pur-
ple, it seems highly likely that the main Fe(II)/Fe(III)
redox process at -0.35 V versus Fcþ/Fc is associated with
cis-2. As the Fe(II)/Fe(III) redox process for cis-2 occurs
at a more negative potential than for 1, it can be con-
cluded that the dichloride complex cis-2 is easier to
oxidize than the sulfate complex 1. The minor redox
process at 0.05 V versus Fcþ/Fc can be tentatively as-
signed as arising from complex trans-2. Cyclic voltamme-
try of trans-2 in 1,2-dichloroethane would be ideal for
comparison, but the complex converted rapidly to cis-2 in
this solvent, as indicated by the deep purple coloration of
the solution when yellow crystals of trans-2 were dissolved.
Cyclic voltammetry studies of cis-2 were also carried out in
acetonitrile. The CV (scan rate=100 mV s-1) now showed
only one reversibleredox processat-0.35V versusFcþ/Fc
due to cis-2. No redox process at about -0.1 V versus Fcþ/
Fc was observed in the voltammogram, that is, there
Conclusions
The reaction between PPh(CH2OH)2, NH4þ, and formal-
dehyde in the presence of iron(II) salts has led to the
formation of the iron(II) complexes [Fe(κ2-O2SO2)L2] (1)
and cis-[FeCl2L2] (cis-2) which contain the novel self-as-
sembled 3,7-diphenyl-1,5-diaza-3,7-diphosphabicyclo[3.3.1]-
nonane ligand L. This is the first observation of a dipho-
sphine containing the 1,5-diaza-3,7-diphosphabicyclo-
[3.3.1]nonane backbone, and the product is in marked
contrast to that observed from the related reaction between
P(CH2OH)4þ, NH4þ, and iron(II). This demonstrates how
the use of hydroxymethylphosphines can give rise to unusual
(29) Hamon, P.; Toupet, L.; Hamon, J.-R.; Lapinte, C. Organometallics
1992, 11, 1429–1431.

Article
Inorganic Chemistry, Vol. 48, No. 20, 2009 9935
and unprecedented structural types through self-assembly
reactions. The iron(II) center isnecessaryfor theformation of
L, and the reaction of PPh(CH2OH)2, NH4þ, and formalde-
hyde without iron(II) gives multiple products that could not
be unambiguously characterized. The chloro ligands in the
complex cis-[FeCl2L2] can readily be substituted, and both cis
and trans isomers of compounds of the general formula
[FeX2L2] have been observed and in some cases can be
interconverted. Current work is focused on removing L from
the metal template for reaction with other metal centers and
studying the 17-electron iron(III) complexes.
Acknowledgment. We thank the EPSRC for financial
support (Doctoral Training Award to A.S.K.).
Supporting Information Available: Crystallographic informa-
tion files (CIF) for the structures of 1 2H2O, trans-2, trans-3,
3
5 7H2O, and 7 1.5C6H6. This material is available free of
charge via the Internet at http://pubs.acs.org.
3
3