Synthesis and characterization of pentaphosphino zero-valent iron complexes and their corresponding iron(II)-chloride and -hydride complexes

Article abstract of DOI:10.1021/ic1003325

A pentaphosphino iron(II)-chloride species [^tSiP ₃(dmpm)FeCl][Cl] (1-Cl) (^tSiP₃ = ^tBuSi(CH₂PMe₂)₃, dmpm = Me ₂PCH₂PMe₂) was prepared f

Full text of DOI:10.1021/ic1003325

3942 Inorg. Chem. 2010, 49, 3942–3949
DOI: 10.1021/ic1003325
Synthesis and Characterization of Pentaphosphino Zero-Valent Iron Complexes
and Their Corresponding Iron(II)-Chloride and -Hydride Complexes
Kristen A. Thoreson, Angela D. Follett, and Kristopher McNeill*,†
Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455. †Present address:
Department of Environmental Sciences, ETH, Zurich, Switzerland.
Received February 18, 2010
t
A pentaphosphino iron(II)-chloride species [tSiP3(dmpm)FeCl][Cl] (1-Cl) (tSiP3 = BuSi(CH2PMe2)3, dmpm = Me2-
PCH2PMe2) was prepared from [(tSiP3Fe)2(μ-Cl)3][Cl] and dmpm. This species was reduced to give the corresponding
iron(0) complex, tSiP3(dmpm)Fe (3), in near quantitative yield. Analogous complexes [SiP3(dmpe)FeCl][Cl] (2-Cl) and
SiP3(dmpe)Fe (4) (SiP3 = MeSi(CH2PMe2)3, dmpe = Me2PCH2CH2PMe2) were prepared in the same manner as 1 and
3 but withloweryieldsbecauseofcompetitiveligand rearrangementreactionsthat gavebyproduct oftrans-(dmpe)2FeCl2
and (dmpe)5Fe2 (5). [tSiP3(dmpm)FeH][A] (6) was prepared from the reaction of 3 with weak acids (HA), and the pKa of
6 was established to be approximately 25. Attempts to prepare pentaphosphino-iron(0) complexes of the form
SiP3(PR3)2Fe using PPh3 and PMe3 resulted in cyclometalated products, SiP3FeH((o-C6H4)PPh2) (7) and SiP3FeH-
(CH2PMe2) (8). Synthesis and characterization of these complexes, including crystal structures of 1-5, are reported.
Introduction
that occurs in permeable reactive barriers14,15 between bulk
iron(0) and ubiquitous chlorinated solvents.16,17 We have a
strong interest in studying dechlorination reactions through
the use of model complexes,18 thus motivating the work
presented here on the development of a model for iron(0).
Iron-phosphine complexes are promising for modeling the
reactions of iron(0) with chlorinated hydrocarbons. As
opposed to carbonyl and arene ligands, with which one can
argue about the oxidation state of the metal center, phos-
phine ligands have the ability to stabilize low oxidation states
of iron without significant back-bonding. 18-Electron penta-
phosphino iron(0) complexes with dissociable ligands, or
ligand arms, represent relatively stable precursor complexes
with access to the reactive 16-electron, coordinatively un-
saturated intermediate species responsible for activation of
inert C-H bonds, including the C-H bond of methane.8
In this work, we present the synthesis and characterization
of a pentaphosphino zero-valent iron complex, tSiP3(dmpm)-
Fe (tSiP3 = tBuSi(CH2PMe2)3, dmpm = Me2PCH2PMe2) (3),
and a new synthetic route to a similar iron(0) complex
previously reported, SiP3(dmpe)Fe(SiP3 = MeSi(CH2PMe2)3,
dmpe = Me2PCH2CH2PMe2) (4). Preparation and character-
ization of corresponding phosphinoiron-chloride and -hydride
complexes are presented as well, as they are probable products
and intermediates in dechlorination reactions. We also touch
on the propensity of the SiP3Fe0 moiety to cyclometallate with
available C-H donors of monodentate phosphines in the
Iron(0) complexes have been employed in bond activa-
tion processes of C-H,1-9 C-S4,6,10 and to a lesser extent,
C-X11-13 bonds (X = halogen). To the best of our know-
ledge, no studies of well-defined iron(0) complexes reacting
with chlorinated ethylenes have been conducted despite
increasing interest in the groundwater remediation reaction
*To whom correspondence should be addressed. E-mail: kris.mcneill@
env.ethz.ch.
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pubs.acs.org/IC
Published on Web 03/16/2010
2010 American Chemical Society

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3943
Figure 1. Synthetic route to complexes 1-4. Percent yields are given in parentheses.
Figure 2. ORTEP diagrams of 1-BPh4, [tSiP3(dmpm)FeCl][BPh4] (left), and 2-Cl, [SiP3(dmpe)FeCl][Cl] (right), with the thermal ellipsoids drawn at 50%
probability level. The outer sphere anions were removed from both diagrams for clarity. The disorder of the dmpe ligand in 2-Cl is not shown.
preparation and spectroscopic characterization of SiP3FeH((o-
C6H4)PPh2) (7) and SiP3FeH(CH2PMe2) (8).
Characteristic NMR resonances of 1-Cl include the
highly resolved diastereotopic protons of the dmpm-
methylene unit (1H δ ppm 2.8, 3.5) as well as three
complexly coupled peaks in the 31P{1H} NMR spectrum
with an integrated intensity peak ratio of 1:2:2 and
patterns consistent with an AA0BB0C spin system. No
differences between 1-Cl and 1-BPh4 were observed in the
NMR spectra. The elemental composition of 1 (537.1 m/z)
was confirmed via ESI-HRMS using a poly(ethylene
glycol) exact mass internal standard.
Results and Discussion
Iron(II)-Chloride Complexes. Two pentaphosphino iron(0)
complexes, SiP3(dmpm)Fe, 3, and SiP3(dmpe)Fe, 4, were
t
prepared through a two-step synthesis in which the iron(II)-
chloride intermediates were isolated and characterized
(Figure 1). Attempts to perform the reaction in a single step
according to a procedure similar to that described by Bon-
cella19,20 through the reduction of the chloroiron-dimer in the
presence of the desired ligand gave lower yields when com-
pared to our two-step synthesis. Howarth and Wong pre-
viously reported the preparation of 4 through a different
synthetic route starting with (η-C6H6)(PMe3)2Fe.21 How-
ever, because the preparation of (η-C6H6)(PMe3)2Fe is de-
manding, we have found the synthetic method presented
here, from readily available reactants, to be a more facile
route.
Crystals of 1-BPh4 suitable for X-ray diffraction were
obtained from slow evaporation of acetonitrile at ambi-
ent temperature. The structure determination confirmed
a distorted octahedral geometry about iron because of the
small (<90°) chelate angle of dmpm (Figure 2). A slightly
˚
elongated Fe-Cl bond length in 1-BPh4 (0.2 to 0.7 A)
compared to other P5FeClþ complexes, [P(CH2CH2-
PMe2)3PPh3FeCl][BPh4]22 and [(PF2Ph)5FeCl][FeCl4],23
suggests an enhanced electron donating ability from the
t
Compound 1-Cl, [tSiP3(dmpm)FeCl][Cl], was prepared
quantitatively from the reaction of [(tSiP3Fe)2(μ-Cl)3][Cl]
with dmpm at 60 °C and was isolated as a dark pink solid
that is relatively stable in air and thermally stable to at
alkyl phosphines of the dmpm and SiP3 ligands. Select
crystallographic parameters, bond lengths, and angles are
presented in Tables 1 and 2.
The electrochemical behavior of 1-BPh4 (0.5 mM) was
evaluated by CV using a glassy carbon working electrode
at room temperature in N,N-dimethylformamide (DMF).
The collected CV data showed a reversible one-electron
Fe3þ/Fe2þ couple at þ0.58 V (versus Agþ/AgCl) and an
irreversible two-electron Fe2þ/Fe0 peak at a potential
of -1.64 V. A small anodic peak that is related to the
irreversible peak was also observed at 0.31 V, although
only after reduction (Figure 3). The electrochemically
generated iron(0) species (3) has independently been
found to react with any solvent that was suitable for CV
-
least 110 °C. Metathesis of the Cl- for BPh4 in the
reaction of 1-Cl with NaBPh4 to give 1-BPh4 was carried
out to aid in characterization. Compound 1-Cl was
1
characterized by H, 13C, and 31P NMR spectroscopy
and electrospray ionization high-resolution mass spectro-
metry (ESI-HRMS) and 1-BPh4 by X-ray crystallo-
graphy and cyclic voltammetry (CV).
(19) Boncella, J. M.; Green, M. L. H. J. Organomet. Chem. 1987, 325,
217–231.
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Commun. 1986, 618–619.
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1385–1391.
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Turner, P. Inorg. Chem. 1997, 36, 2884–2892.
(23) Sheldrick, W. S.; Stelzer, O. Chem. Ber. 1977, 110, 3421–3429.

3944 Inorganic Chemistry, Vol. 49, No. 8, 2010
Table 1. X-ray Crystallographic Data for Complexes 1-5
1-BPh4
Thoreson et al.
2-Cl
3
4
5
empirical formula
fw, g mol-1
color/habit
C42H67BClFeP5Si
857.01
C16H43Cl2FeP5Si
545.19
pink/block
monoclinic
C2/c
33.776(2)
9.5076(7)
18.121(1)
90
115.254(1)
90
5262.9(6)
8
1.376
2304
30228
6043
0.0314, 0.0680
0.0429, 0.0721
1.033
C18H47FeP5Si
502.35
red/plate
triclinic
P1
13.515(1)
14.039(1)
15.150(2)
76.833(2)
77.260(2)
87.623(2)
2729.9(5)
4
1.222
1080
23515
11448
0.0343, 0.0849
0.0448, 0.0926
1.026
C16H43FeP5Si
474.29
red/block
orthorhombic
Pna21
17.790(9)
14.919(7)
9.317(4)
90
90
90
2473(2)
4
1.274
1016
28300
5651
0.0339, 0.0620
0.0432, 0.0645
1.027
C15H40FeP5
430.17
orange/plate
triclinic
P1
9.075(1)
9.224(1)
15.328(2)
101.020(2)
98.323(2)
113.373(2)
1120.9(2)
2
1.278
462
12929
4986
0.0298, 0.0696
00447, 0.756
1.091
red/block
orthorhombic
P212121
12.058(2)
12.668(2)
29.658(6)
90
90
90
4530(1)
4
1.257
1824
53740
10386
0.0426, 0.0890
0.0537, 0.0927
1.054
crystal system
space group
˚
a, A
˚
b, A
˚
c, A
R, degrees
β, degrees
γ, degrees
3
˚
V, A
Z
Dcalc, g cm-3
F(000)
reflns collect
ind. reflns
R1, wR2 (I>2σ(I))
R1, wR2, all data
GOF
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) of Complexes 1-5
bond/angle
1-BPh4
2-Cl
3
4
5
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
˚
Fe-P1
Fe-P2
Fe-P3
Fe-P4
Fe-P5
Fe-Cl
2.2309(9)A
2.2550(6)A
2.1453(7)A
2.159(1)A
2.1736(6)A
2.2706(9)A
2.2889(6)A
2.1564(6)A
2.198(1)A
2.1580(6)A
˚
2.179(1)A
2.1954(9)A
2.2496(9)A
2.2982(5)A
2.1624(7)A
2.1655(6)A
˚
˚
˚
˚
˚
2.3029(9)A
2.2962(6)A
2.1826(7)A
2.1625(6)A
˚
˚
˚
2.1798(7)A
˚
2.1751(9)A
˚
2.1811(6)A
2.3063(9)A
2.3059(6)A
˚
2.3749(9)A
˚
2.3800(5)A
P4-Fe-P5
P3-Fe-P5
P2-Fe-P4
P1-Fe-Cl
72.61(3)°
166.40(3)°
164.44(3)°
174.35(3)°
83.58(2)°
172.58(2)°
169.28(2)°
176.36(2)°
72.66(3)°
149.83(3)°
154.08(3)°
82.35(4)°
140.67(4)°
166.28(4)°
82.14(2)°
154.23(3)°
151.12(3)°
analysis, including DMF; this reactivity may explain the
irreversibility of the peak associated with the iron(0)
species, and the related anodic peak can then be attrib-
uted to an oxidative process of the resulting product.
While both Fe2þ/Feþ and Fe4þ/Fe3þ couples have pre-
viously been reported with phosphine-stabilized iron(II)
complexes, neither were observed electrochemically with
1-BPh4.24,25
A signal for [SiP3(dmpe)FeCl]þ was observed at 509.0 m/z
with an isotope pattern consistent with an iron and chlorine
containing species. The molecular structure of 2-Cl was
determined by X-ray crystallography with crystals grown
from CH2Cl2 at room temperature. Disorder in the dmpe
ligand required modeling of the methylene moieties over
two positions. Structural features similar to those discussed
for 1-BPh4 were also observed for 2-Cl, including a distorted
octahedral geometry and a longer Fe-Cl bond than pre-
viously observed for complexes with a phosphorus atom
trans to the chloride. See Figure 2 for the Oak Ridge thermal
ellipsoid plot (ORTEP) diagram of 2-Cl and Tables 1 and 2
for crystal and structural data of interest.
Compound 2-Cl, [SiP3(dmpe)FeCl][Cl], was synthe-
sized in 97% yield from the reaction of [(SiP3Fe)2(μ-
1
Cl)3][Cl] with dmpe and characterized by H, 13C, and
31P NMR spectroscopy, ESI-HRMS, and X-ray crystallo-
graphy. Room temperature 31P{1H} NMR spectra of this
compound showed three highly coupled peaks in a pat-
tern consistent with an AA0BB0C spin system of inte-
grated intensity ratio 2:1:2. A simulation of the spectrum
using Varian software confirmed this spin system and
allowed for determination of the distinguishable P-P
coupling constants (Figure 4). The sign and magnitude
of the calculated constants follow the trends expected for
two-bond phosphorus-phosphorus coupling across a
metal center.26
Iron(0) Complexes. Compound 3, tSiP3(dmpm)Fe, was
prepared in 98% yield from the reduction of 1-Cl with
sodium amalgam at room temperature. The isolated oily
product readily decomposed upon exposure to trace
oxygen but was thermally stable to at least 100 °C in
toluene. Compound 3 was characterized by 1H, 13C, and
31P NMR spectroscopy, electron-impact high-resolution
mass spectra (EI-HRMS) and X-ray crystallography. The
reduction potential characterization of 3 was determined
from CV on 1-BPh4 (Figure 3).
EI-HRMS of 3 resulted in a signal with an isotope
pattern consistent with an iron-containing complex at
502.1 m/z and the elemental composition was confirmed
with perfluorokerosene internal standard. The ambient
temperature 31P{1H} NMR of 3 showed two resonances,
a quartet and a triplet for the dmpm and tSiP3 phosphorus
nuclei, respectively, that are consistent with fluxional
ESI-HRMS was used to verify the elemental composi-
tion of 2 with poly(ethylene glycol) internal standard.
(24) Field, L. D.; George, A. V.; Laschi, F.; Malouf, E. Y.; Zanello, P.
J. Organomet. Chem. 1992, 435, 347–356.
(25) Bianchini, C.; Laschi, F.; Masi, D.; Ottaviani, F. M.; Pastor, A.;
Peruzzini, M.; Zanello, P.; Zanobini, F. J. Am. Chem. Soc. 1993, 115,
2723–2730.
(26) Baker, M. V.; Field, L. D. Inorg. Chem. 1987, 26, 2010–2011.

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3945
Figure 3. Cyclic voltammograms of complex 1-BPh4 (0.5 mM in DMF) recorded at a glassy carbon electrode and referenced to Agþ/AgCl (sweep rate:
100 mV/s, supporting electrolyte: 0.1 M TBAPF6). The anodic (left) and cathodic (right) directional traces are shown.
31
32
byproducts trans-(dmpe)2FeCl2 and (dmpe)5Fe2 (5).
Both contaminants could be removed through recrystal-
lization to give a pure solution of 4. It was also possible
to structurally characterize one of the impurities, penta-
phosphino-iron(0) dimer, (dmpe)5Fe2 (5) (τ = 0.05, see
Figure 6 and Tables 1 and 2 for structural information).
The elemental composition of 4 (474.1 m/z) was con-
firmed by EI-HRMS with perflourokerosene internal
standard. X-ray characterization of 4 demonstrates an
intermediate distortion between square pyramidal and
trigonal bipyramidal geometries with a τ value of 0.43
(Figure 5). The larger bite angle of dmpe and the flexi-
bility acquired with an extra methylene unit account for
the enhanced distortion when compared to 3. See Tables 1
and 2 for crystal data and structural metrics.
dmpe vs dmpm. Through the synthesis of two analogous
Fe(0) complexes, 3 and 4, it was found that the dmpm-
containing complex (3) had enhanced stability over the
dmpe-containing complex (4) as evidenced by the lack of
byproduct formation and near quantitative yields. Of the
slight structural differences in these complexes, the
Figure 4. 31P{1H} NMR simulation of 2-Cl. The experimental spectrum
is shown on top and the simulated spectrum using an AA0BB0C spin
system on the bottom. The coupling constants were determined from the
simulation.
behavior on the NMR time scale. No decoalescence of the
resonances was detectable at temperatures down to -85 °C.
The X-ray structure of 3 exhibits a slight distor-
tion from square pyramidal about the iron center with
τ = 0.07 (on a τ scale from 0 to 1, with 0 and 1 corres-
ponding to idealized square pyramidal and trigonal bi-
pyramidal geometries, respectively27). This is consistent
with other five coordinate phosphine-ligated complexes
containing small bite angle diphosphines (e.g., dmpm and
dmpe) that have previously been observed to favor a sq-
uare pyramidal geometry over trigonal bipyramidal.28-30
The vacant site created by the square pyramidal geometry
is desirable for a model of bulk iron, as it gives an open
reactive site similar to an iron surface.
t
change from SiP3 to SiP3 has been found to enhance
solubility and crystallinity33 but was not expected to
create the stability divergences observed. Instead, the
choice of bidentate ligand (dmpe or dmpm) is suggested
to account for the difference by influencing the binding
ability of the tripodal ligand because the byproduct
identified in the preparation of 4, trans-Fe(dmpe)2Cl2
and (dmpe)5Fe2 (5), require the dissociation of the tripo-
dal ligand, yet these types of products are not observed in
the preparation of dmpm-containing 3. The more
strained bite angle of dmpm (72.66°) results in a dimini-
shed trans-effect, allowing for the tripodal ligand to bind
more tightly than when dmpe (82.35°) is used. This
hypothesis is supported by X-ray crystallographic data
Compound 4, SiP3(dmpe)Fe, was synthesized in 52%
yield from the reduction of 2-Cl using sodium amalgam in
t
in which the SiP3Fe-P bonds trans to dmpm are on
average 0.025 A shorter in 3 than the identical bonds in 4.
1
toluene and characterized by H, 13C, and 31P NMR
˚
spectroscopy, EI-HRMS, and X-ray crystallography.
During the preparation of 4, ligand rearrangement reac-
tions involving loss of SiP3 produced previously reported
The Fe-P bond lengths of the bidentate ligand in 3 and 4
remain constant near 2.18 A in both complexes, a length
˚
comparable to other iron(0) complexes with phosphine
ligands.34-36 The same trends in bond lengths were also
observed in the precursor Fe(II)-Cl complexes where the
(27) Addison, A. W.; Rao, T. N.; Reedijk, J.; Van Rijn, J.; Verschoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
(28) Battaglia, L. P.; Delledonne, D.; Nardelli, M.; Pelizzi, C.; Predieri, G.
J. Organomet. Chem. 1987, 330, 101–113.
(29) Cotton, F. A.; Hardcastle, K. I.; Rusholme, G. A. J. Coord. Chem.
1973, 2, 217–223.
(30) Wong, W. K.; Chiu, K. W.; Wilkinson, G.; Howes, A. J.; Motevalli,
M.; Hursthouse, M. B. Polyhedron 1985, 4, 603–614.
(32) Tolman, C. A.; Ittel, S. D.; English, A. D.; Jesson, J. P. J. Am. Chem.
Soc. 1978, 100, 4080–4089.
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metallics 2004, 23, 2053–2068.
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Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1985, 1339–1348.
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4240–4251.

3946 Inorganic Chemistry, Vol. 49, No. 8, 2010
Thoreson et al.
t
Figure 5. ORTEP diagrams of 3, SiP3(dmpm)Fe (left), and 4, SiP3(dmpe)Fe (right), with the thermal ellipsoids drawn at 50% probability level.
One molecule of 3 in the asymmetric unit and the disorder of the methylene units on tSiP3 were removed for clarity.
Figure 6. ORTEP diagram of 5, (dmpe)5Fe2, with the thermal ellipsoids
drawn at 50% probability level.
Figure 7. 31P{1H} NMR comparison of the tSiP3 resonance from tSiP3-
4 (A) and 3 (B) in C6D6.
˚
Fe-P bonds in the tripodal ligand of 1-BPh4 are 0.034 A
shorter than in 2-Cl.
Further support for the more tightly bound tripodal
ligand in dmpm-containing complexes comes from the
t
analysis of 31P{1H} NMR spectra of 3 and SiP3-4
t
(tSiP3(dmpe)Fe, the analogous SiP3 version of 4, see
Supporting Information for synthesis and full NMR
characterization of this complex). A 6 ppm downfield
shift of the tSiP3 ligand (16.4 to 22.5 ppm, δ of free tSiP3:
-54.21 ppm) is observed from the dmpe complex to the
Figure 8. [tSiP3(dmpm)FeH][A], 6, is observed from the reaction of
3 with weak acids (HA, pKa e 25). The isolated form was prepared with
HA = NH4PF6.
dmpm complex (Figure 7). The JPP coupling constants
also increased from 11.7 Hz (tSiP3-4) to 17.5 Hz (3). A
similar comparison between other dmpm- and dmpe-
containing species, [(MeC(CH2PMe2)3)(dmpm/dmpe)-
MCl]2þ (M=Rh, Co), revealed the same trends in bond
length decrease and downfield 31P NMR shift of the
tripodal ligand with the replacement of dmpe with
dmpm.37
Iron(II)-Hydride Complexes. The preparation of iron(II)-
hydride complexes, [tSiP3(dmpm)FeH][A] (6), was achie-
ved through reaction of 3 with weak acids (HA) in toluene
or C6D6 at room temperature (Figure 8). Characteriza-
1
tion of 6, including H and 31P NMR, IR, and ESI-
HRMS, was performed on the iron-hydride complex
isolated from reaction of 3 with ammonium hexafluoro-
phosphate (NH4PF6) according to the procedure de-
scribed by Howarth and Wong.21 1H NMR spectroscopy
Figure 9. Characteristic iron-hydride peak of 6 observed in the 1H
NMR spectrum (CD3CN, JHP = 13, 51 Hz).
(36) Paul, F.; da Costa, G.; Bondon, A.; Gauthier, N.; Sinbandhit, S.;
Toupet, L.; Costuas, K.; Halet, J.; Lapinte, C. Organometallics 2007, 26,
reveals a characteristic quintet of doublets hydride reso-
nance (δ ppm -11.3, C6D6, -10.9, CD3CN) that col-
874–896.
(37) Suzuki, T.; Tsukuda, T.; Kiki, M.; Kaizaki, S.; Isobe, K.; Takagi,
H. D.; Kashiwabara, K. Inorg. Chim. Acta 2005, 358, 2501–2512.
lapses to a singlet in the 1H{31P} spectrum (Figure 9). A

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3947
Figure 10. Preparation of the cyclometalated complexes 7, SiP3FeH((o-C6H4)PPh2), and 8, SiP3FeH(CH2PMe2).
similar hydride peak for the analogous complex
[SiP3(dmpe)FeH][PF6] prepared from the reaction of 4
with NH4PF6 has also been reported.21 An upfield shift
from the corresponding chloride complex is observed in
the 31P{1H} NMR resonance for the phosphorus trans to
the hydride, consistent with a hydride complex. IR spectro-
scopy also revealed an absorbance attributed to an
Fe-H stretch at 1831 cm-1, similar to that reported for
the pentaphosphino-iron hydride complex, [(dmpm)3-
FeH][BF4].30 A signal at 503.1 m/z in the ESI-HRMS
corresponding to [tSiP3(dmpm)FeH]þ was observed and
matched the exact mass within 2 ppm.
The reactivity of 3 with weak acids demonstrated the
basic nature of the iron(0) complex. This characteristic
may be attributed to the strong electron donating ability
of 3 as quantified by the negative reduction potential
(-1.64 V). To quantify the basicity of 3, the pKa of the
conjugate acid, 6, was determined. Titration or equili-
brium experiments could not be used to establish the pKa
because a non-reactive solvent in which both 3 and 6 were
completely soluble was not found.
basis of these observations, the pKa of 6 is estimated to be
approximately 25.
Cyclometalated Complexes. Attempts were made to
prepare additional pentaphosphino iron(0) complexes
of the type SiP3(PR3)2Fe, similar to those reported by
Karsch,43,44 using a modification of the method described
by Boncella.19 In each case cyclometalation of the mono-
dentate phosphine was observed. Complexes SiP3FeH((o-
C6H4)PPh2) (7) and SiP3FeH(CH2PMe2) (8) were pre-
pared by reduction of [(SiP3Fe)2(μ-Cl)3][Cl] in toluene
with excess sodium amalgam in the presence of PPh3 or
PMe3, respectively (Figure 10). These complexes were
characterized by 1H and 31P NMR spectroscopy. A highly
1
coupled H resonance (δ ppm -7.01, 7, and -12.90, 8)
corresponding to an iron-hydride in addition to an up-
field shifted resonance in the 31P{1H} NMR (δ ppm 10.06,
7, and -17.36, 8) are consistent with a phosphorus atom
trans to a hydride. The cyclometalated products were
found to be quite stable to thermolysis, with 7 showing no
decomposition up to 100 °C in C6D6.
Others have also observed these types of metallocycles
formed through intramolecular C-H activation of avail-
able alkyl groups by coordinatively unsaturated iron(0)
species.45-49 A three-membered metallocyclic ring with
PMe3, similar to 8, has also been observed in other iron
and ruthenium complexes.50,51 The reaction depicted in
Figure 10 is presumed to go through an unsaturated
intermediate that is responsible for the metallocycle
products.49
Instead, to estimate the pKa a series of increasingly
weaker acids were reacted in 1:1 ratios (21 mM) with 3 in
C6D6. The reactions were analyzed by H NMR spec-
1
troscopy within 10 min of mixing. If no hydride resonance
was observed, the reactions were kept at room tempera-
ture and reanalyzed after 24 h. In the event of precipitate
formation, reaction mixtures were concentrated to a solid
and redissolved in CD3CN for NMR analysis. It should
be noted that some of these hydride-anion complexes
were not stable and went on to form other products;
however, any evidence of hydride formation was deemed
a deprotonation by 3. The following acids were used, with
their aqueous pKa values given in parentheses: NH4PF6
(9.338), BHT (>10, the pKa of phenol39), diethyl malonate
(13.340), methanol (15.241), tert-butyl alcohol (16.541), in-
dene (19.042), fluorene (22.742), ethyl acetate (24.540), acet-
onitrile (2540) and triphenylmethane (31.542). For all acids
with pKa e 23, the hydride resonance indicative of 6 was
observed upon initial analysis. A small hydride peak was
observed with ethyl acetate and acetonitrile after 24 h, and
no reaction was observed with triphenylmethane. On the
Conclusions
A new phosphine-ligated iron(0) complex, tSiP3(dmpm)Fe,
was prepared from the reduction of [tSiP3(dmpm)FeCl][Cl]. It
was shown that the identity of the bidentate ligand is im-
portant to the stability of this type of complex, as the
analogous dmpe-containing species was prone to rearrange-
ment reactions during synthesis. Similarly, monodentate
ligands paired with SiP3 were not suitable for preparation of
iron(0) complexes as cyclometalation occurred. tSiP3(dmpm)-
Fe exhibits square pyramidal geometry (τ = 0.07), is strongly
(43) Karsch, H. H. Angew. Chem. 1982, 94, 322.
(44) Karsch, H. H. Chem. Ber. 1983, 116, 1643–1655.
(45) Ittel, S. D.; Tolman, C. A.; Krusic, P. J.; English, A. D.; Jesson, J. P.
Inorg. Chem. 1978, 17, 3432–3438.
(38) Ross, S. A.; Pitie, M.; Meunier, B. Eur. J. Inorg. Chem. 1999,
557–563.
(39) Krasowska, A.; Rosiak, D.; Szkapiak, K.; Oswiecimska, M.; Witek,
S.; Lukaszewicz, M. Cell. Mol. Biol. Lett. 2001, 6, 71–81.
(40) Pearson, R. G.; Dillon, R. L. J. Am. Chem. Soc. 1953, 75, 2439–2443.
(41) Reeve, W.; Erikson, C. M.; Aluotto, P. F. Can. J. Chem. 1979, 57,
2747–2754.
(46) Karsch, H. H. Chem. Ber. 1984, 117, 3123–3133.
(47) Hirano, M.; Akita, M.; Morikita, T.; Kubo, H.; Fukuoka, A.;
Komiya, S. J. Chem. Soc., Dalton Trans. 1997, 3453–3458.
(48) Baker, M. V.; Field, L. D. Organometallics 1986, 5, 821–823.
(49) Baker, M. V.; Field, L. D. Aust. J. Chem. 1999, 52, 1005–1011.
(50) Rathke, J. W.; Muetterties, E. L. J. Am. Chem. Soc. 1975, 97,
3272–3273.
(42) Streitwieser, A., Jr.; Ciuffarin, E.; Hammons, J. H. J. Am. Chem.
Soc. 1967, 89, 63–67.
(51) Mainz, V. V.; Andersen, R. A. Organometallics 1984, 3, 675–678.

3948 Inorganic Chemistry, Vol. 49, No. 8, 2010
Thoreson et al.
reducing (-1.64 V), and basic in nature with the ability to
deprotonate weak acids with a pKa e 25. These characteristics
of tSiP3(dmpm)Fe, in addition to the capability of preparing
the related hydride and chloride species, are promising for the
use of this complex in the study of Fe(0)-mediated dechlori-
nation reactions. Reactivity studies of SiP3(dmpm)Fe with
C-Cl bonds will be reported in due course.
opposite enantiomer, respectively. Complex 2-Cl showed dis-
order in the dmpe-CH2 moieties and was modeled over two
positions (52.5:47.5).
t
Complex 3 displayed a twisting disorder about the SiP3
ligand requiring the CH2 components to be modeled over two
positions (73:27 and 87:13 for the two asymmetric units, re-
spectively). A warning for close atom contact between a PMe2
hydrogen and a CH2 hydrogen, both on tSiP3, exists in check-
CIF/PLATON for 3. The methyl group could not be modeled
over two positions, so the hydrogen close atom contact, insig-
nificant to reactivity and structural features of interest, remains
as an artifact of the disorder.
t
Experimental Section
General Considerations. All experiments were conducted
under anhydrous and anaerobic (dinitrogen) conditions using
a glovebox or Schlenk line. Chemicals were purchased from
chemical suppliers and used as received unless noted. Toluene,
diethyl ether, hexanes, pentane, and petroleum ether were
distilled from sodium metal. Dichloromethane, acetonitrile,
d6-benzene, d3-acetonitrile, and d1-chloroform were dried over
calcium hydride and distilled. Tetrahydrofuran was distilled
from sodium-benzophenone ketyl, N,N-dimethylformamide was
distilled under reduced pressure from calcium sulfate, and mercury
was degassed prior to use. Small volumes of methanol, tert-butyl
alcohol, indene, and ethyl acetate were degassed and stored over
tBuSi(CH2PMe2)3 (tSiP3). Procedures for the preparation of
tris(dimethylphosphinomethyl)-tertbutylsilane (or “trimpsi”)
have previously been published.55,56 The procedure used for
the synthesis of SiP3 ligand was employed for the preparation
t
t
of SiP3.54 In brief, BuSiCl3 (12.4 g, 64.7 mmol) dissolved in
100 mL of Et2O was added to the highly pyrophoric solid
LiCH2PMe257 (18.0 g, 219 mmol) at -78 °C as described. The
final colorless oil was passed through a silica column and
dried in vacuo before collection. The oil was distilled at 140 °C
under active vacuum (5.27 g, 16.9 mmol, 26.2% yield). Product
decomposition was observed above 150 °C. 1H NMR (300
MHz, C6D6, 25 °C): δ 0.81 (br s, 6H, CH2-tSiP3); 1.01 (br s,
˚
4 A molecular sieves. Tris(dimethylphosphinomethyl)-methylsi-
lane (SiP3)52 and [(SiP3Fe)2(μ-Cl)3][Cl]19 were prepared according
to literature procedures.
t
18H, PMe2); 1.16 (s, 9H, Bu-Si). 31P{1H} (121 MHz, C6D6,
25 °C): δ -54.21 (s, tSiP3).
1H nuclear magnetic resonance (NMR) spectra were obtained
on Varian Inova 300 MHz and Varian Unity Plus 400 MHz
instruments. 13C{1H} NMR and 31P{1H} NMR spectra were
[(tSiP3Fe)2(μ-Cl)3][Cl]. The procedure described by Boncel-
la19 was employed to synthesize the tSiP3-analogue of
[(SiP3Fe)2(μ-Cl)3][Cl]) (>95% yield). 1H NMR (300 MHz,
CD3CN, 25 °C): δ ppm 0.63 (m, 12H, CH2-tSiP3); 0.80 (s,
1
obtained at 75 MHz and 121, respectively. H and 13C NMR
spectra were referenced to the residual solvent peak while 31P
spectra were referenced to external 85% H3PO4. ESI-HRMS, in
positive polarity, were collected on a Bruker II BioTOF mass
spectrometer. A Finnigan MAT 95 double-focusing mass spectro-
meter with BE-geometry was used to collect EI-HRMS with
sample introduction using a solids probe. Infrared (IR) spectra
were collected with a Midac M series spectrometer.
t
18H, Bu-Si); 1.53 (m, 36H, Me-tSiP3). 31P{1H} NMR (121
MHz, CD3CN, 25 °C): δ ppm 44.15 (s, tSiP3).
[tSiP3(dmpm)FeCl][X] (1-Cl, 1-BPh4). [(tSiP3Fe)2(μ-Cl)3][Cl]
(0.698 g, 0.798 mmol) was combined with bis(dimethyl-
phophino)methane (dmpm) (275 μL, 1.74 mmol) in CH2Cl2
(40 mL) and placed into a 100 mL sealed reaction flask. The
reaction was heated to 60 °C overnight. The reaction solu-
tion was filtered, concentrated to a solid, washed with CH2Cl2
(20 mL), and filtered again. The filtrate was concentrated to
yield a clean dark pink solid (0.917 g, 1.59 mmol, 99% yield).
The anion was exchanged from Cl- to BPh4- by adding 1 equiv
of NaBPh4 to a solution of [tSiP3(dmpm)FeCl][Cl] in aceto-
nitrile. The solution was filtered and concentrated to a solid. X-ray
quality crystals were obtained from slow evaporation in aceto-
Electrochemistry. CV experiments were performed with a
BAS 100B electrochemical analyzer consisting of a Pt auxiliary
electrode, a glassy carbon working electrode (A = 0.07 cm-1),
and a Agþ/AgCl reference electrode containing 1.0 M KCl. The
three-compartment cell was filled with dry DMF containing 0.1
M tetrabutylammonium hexafluorophosphate (TBAPF6) as the
supporting electrolyte. The 5 mL working compartment, sepa-
rated from the reference compartment by a modified Luggin
capillary, was bubbled with argon prior to all experiments to
deoxygenate the solution. Background cyclic voltammograms
of the electrolyte solution were recorded prior to addition of the
sample. Potentials were reported versus Agþ/AgCl without
correction for the junction potential. The E°0 value for the
ferrocenium/ferrocene couple under the stated conditions was
þ0.42 V. A scan rate of 100 mV/s and sample concentration of
0.5 mM were used.
1
nitrile at ambient temperature. H NMR (300 MHz, CD3CN,
25 °C): δ ppm 0.72 (d, JHP = 2.3 Hz, 2H, CH2-tSiP3); 0.91 (s, 9H,
tBu-Si); 1.0 (m, 4H, CH2-tSiP3); 1.41 (d, JHP = 5.1 Hz, 6H,
Me-tSiP3); 1.49 (m, 12H, Me-tSiP3); 1.56 (m, 6H, Me-dmpm);
1.67 (m, 6H, Me-dmpm); 2.84 (q, JHP = 11.2 Hz, 1H, CH2-
dmpm); 3.58 (q, JHP =12.8 Hz, 1H, CH2-dmpm). 13C{1H}
NMR (75 MHz, CD3CN, 25 °C): δ ppm 5.04 (s, 2C, CH2-tSiP3);
9.02 (m, 1C, C-Si); 9.97 (m, 1C, CH2-tSiP3); 12.31 (t, JCP = 14
Hz, 2C, PMe2); 15.00 (t, JCP = 13 Hz, 2C, PMe2); 21.25 (m, 2C,
PMe2); 27.72 (br s, 5C, (CH3)3C-Si, PMe2); 27.17 (d, JCP = 23
Hz, 2C, PMe2); 41.04 (t, JCP = 25 Hz, 1C, CH2-dmpe). 31P{1H}
NMR (121 MHz, CD3CN, 25 °C): δ ppm -10.23 (m, 2P, dmpm);
25.05 (m, 2P, tSiP3); 35.27 (tt, JPP = 43, 56 Hz, 1P, tSiP3). ESI-
HRMS-TOF (m/z): [M - Cl]þ calcd for C18H47ClFeP5Si,
537.1173; found, 537.1197.
X-ray Crystallography. Crystal structures of 1-BPh4, 2-Cl, 3,
4, and 5 were collected using a Siemens or Bruker SMART
Platform CCD diffractometer at 173(2) K using a graphite
monochromator and Mo KR radiation. Structures were solved
using SHELXS-9753 or SIR-9754 and refined with SHELXL-
97.53 Crystallographic data for these complexes are given in
Table 1.
[SiP3(dmpe)FeCl][Cl] (2-Cl). This complex was prepared as
described above for 1-Cl, using [(SiP3Fe)2(μ-Cl)3][Cl] (0.240 g,
0.31 mmol) and dmpe (100 μL, 0.60 mmol) in CH2Cl2 (20 mL) to
Complexes 1-BPh4 and 4 were each modeled as a racemic twin
using a SHELXL TWIN command as 29.7% and 18.6% of the
(52) McNeill, K.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1997, 119, 11244–11254.
(53) SHELXTL, V6.14; Bruker Analytical X-Ray Systems: Madison, WI,
2000.
(54) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1998, 32, 115.
(55) Gardner, T. G. Low-valent early transition metal complexes stabi-
lized by the chelating tripod phosphine ligand (t-butyl)tris[(dimethylphos-
phino)methyl]silane (“trimpsi”). Ph.D. Thesis, University of Illinois,
Urbana-Champaign, IL, 1989.
(56) Karsch, H. H.; Appelt, A. Z. Naturforsch. B 1983, 38B, 1399–1405.
(57) Karsch, H. H.; Schmidbaur, H. Z. Naturforsch. B 1977, 32B,
762–767.

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3949
1
give a pink solid (0.320 g, 0.587 mmol, 97% yield). H NMR
3.3 Hz, 2H, CH2-tSiP3); 0.86 (s, 9H, tBu-Si); 0.88 (m, 4H,
CH2-tSiP3); 1.33 (m, 6H, Me-tSiP3); 1.47 (t, JHP = 3.7 Hz, 6H,
Me-dmpm), 1.57-1.64 (18H, overlapping m, Me-tSiP3, Me-
dmpm); 3.04 (m, 2H, CH2-dmpm). 31P{1H} NMR (121 MHz,
CD3CN, 25 °C): δ ppm -0.5 (m, 2P, dmpm); 20.7 (tt, JPP = 33, 39
(300 MHz, CDCl3, 25 °C): δ ppm -0.35 (s, 3H, Me-Si); 0.88 (d,
JHP = 12 Hz, 2H, CH2-SiP3); 1.14 (m, 4H, CH2-SiP3); 1.44 (d,
JHP = 7.2 Hz, 6H, Me-SiP3); 1.52 (d, JHP = 7.5 Hz, 6H, Me-
SiP3); 1.58 (d, JHP = 6.0 Hz, 6H, Me-SiP3); 1.69 (d, JHP = 5.4
Hz, 6H, Me-dmpe); 1.74 (m, 6H, Me-dmpe); 2.06 (m, 4H, CH2-
dmpe). 13C{1H} NMR (75 MHz, CDCl3, 25 °C): δ ppm -0.98 (s,
1C, Me-Si); 14.54 (s, 1C, CH2-SiP3); 15.50 (t, JCP = 13.7 Hz,
2C, CH2-SiP3); 17.34 (s, 2C, PMe2); 19.54 (t, JCP = 13.2 Hz,
2C, PMe2); 21.33 (t, JCP = 8.6 Hz, 2C, PMe2); 25.44 (m, 2C,
PMe2); 28.72 (d, JCP = 21 Hz, 2C, PMe2); 30.82 (t, JCP = 19.4
Hz, 2C, CH2-dmpe). 31P{1H} NMR (121 MHz, CDCl3, 25 °C):
δ ppm 17.46 (m, see Results for coupling constants, 2P,
SiP3); 27.33 (tt, JPP = -53, -41 Hz, 1P, SiP3); 41.98 (m, see
Results for coupling constants, 2P, dmpe). ESI-HRMS-TOF
(m/z): [M - Cl]þ calcd for C16H43ClFeP5Si, 509.0855; found,
509.0858.
t
Hz, 1P, SiP3); 33.7 (m, 2P, tSiP3). ESI-HRMS-TOF (m/z):
[M - PF6]þ calcd for C18H48FeP5Si, 503.1563; found, 503.1555.
IR (Nujol mull, cm-1) 1831, Fe-H stretch.
SiP3FeH((o-C6H4)PPh2) (7). To a solution of [(SiP3Fe)2(μ-
Cl)3][Cl] (0.34 g, 0.44 mmol) and PPh3 (0.30 g, 1.13 mmol) in
toluene (20 mL) in a 30 mL sealed flask were added an excess of
sodium and a drop of metallic mercury. The solution was
sonicated for 10 min and then stirred 4 days until red-brown
in color. The reaction solution was filtered and washed with
petroleum ether (20 mL). The filtrate was then concentrated to a
solid. The solid was extracted into pentane, the resultant solu-
tion filtered, and the filtrate concentrated to approximately 4
mL. This solution was placed in the freezer (-35 °C) overnight
yielding a brown solid (0.14 g, 0.24 mmol, 27% yield). 1H NMR
(300 MHz, C6D6, 25 °C): δ ppm -7.01 (dddd, JHP = 27, 51, 51,
63 Hz, 1H, Fe-H); -0.07 (s, 3H, Me-Si); 0.20 (dd, JHP = 6.9,
13.2 Hz, 1H, CH2-SiP3); 0.27 (m, 1H, CH2-SiP3); 0.36-0.52
(overlapping m, 3H, CH2-SiP3); 0.67 (dd, JHP = 7.8, 14.4 Hz,
1H, CH2-SiP3); 1.18 (d, JHP = 4.8 Hz, 3H, Me-SiP3); 1.34 (d,
JHP = 6.0 Hz, 3H, Me-SiP3); 1.52 (d, JHP = 6.0 Hz, 3H, Me-
SiP3); 1.65 (d, JHP = 7.5 Hz, 3H, Me-SiP3); 6.60 (dd, JHP = 6.6,
11.4 Hz, 1H, C6H4); 6.86 (t, JHP = 6.6 Hz, 1H, C6H4); 7.0-7.7
(overlapping m, 8H, PPh2); 7.66 (t, JHP = 6.3 Hz, 2H, PPh2);
8.53 (t, JHP = 8.1 Hz, 2H, PPh2). 31P{1H} NMR (121 MHz,
C6D6, 25 °C): δ ppm 10.1 (m, 1P, PMe2); 22.6 (m, 1P, PPh2);
31.87 (m, 1P, PMe2); 41.6 (m, 1P, PMe2).
tSiP3(dmpm)Fe (3). To a suspension of 1-Cl (0.456 g, 0.795
mmol) in toluene (50 mL) in a 100 mL round-bottom flask were
added an excess of sodium metal and a drop of metallic mercury.
The reaction was allowed to stir for 3 days, until the solution was
dark red-brown in color. The solution was concentrated to a
solid, extracted with hexanes, filtered (2ꢀ), and the solvent
removed in vacuo to a yield a pure red solid (0.393 g, 0.782
mmol, 98% yield). X-ray quality crystals were obtained from
1
toluene at -40 °C. H NMR (300 MHz, C6D6, 25 °C): δ ppm
0.65 (m, 6H, CH2-tSiP3); 0.88 (s, 9H, tBu-Si); 1.46 (t, JHP = 3.9
Hz, 12H, Me-dmpm); 1.49 (br s, 18H, Me-tSiP3); 2.88 (t, JHP
=
10.5 Hz, 2H, CH2-dmpm). 13C{1H} NMR (75 MHz, C6D6,
25 °C): δ ppm 15.51 (br s, 3C, CH2-tSiP3); 26.69 (m, 1C, C-Si);
27.09 (s, 4C, PMe2); 29.98 (m, 3C, (CH3)3C-Si); 32.75 (m, 6C,
PMe2); 52.07 (m, 1C, CH2-dmpm). 31P{1H} NMR (121 MHz,
C6D6, 25 °C): δ ppm -21.01 (q, JPP = 17.5 Hz, 2P, dmpm);
22.46 (t, JPP = 17.5 Hz, 3P, tSiP3). EI-HRMS (70 eV) m/z: Mþ
calcd for C18H47FeP5Si, 502.1485; found, 502.1509.
SiP3FeH(CH2PMe2) (8). To a solution of [(SiP3Fe)2(μ-Cl)3]-
[Cl] (0.33 g, 0.42 mmol) in toluene (40 mL) in a 100 mL sealed
flask were added an excess of sodium and a drop of mercury.
Under a flow of N2, PMe3 (100 μL, 97 mmol) was added and the
flask sealed. The reaction was stirred for 3 days until green-
brown in color, concentrated to a solid, and extracted into
hexanes. The resultant solution was filtered, and the filtrate
concentrated to a solid. The solid was extracted into pentane
and placed in the freezer (-35 °C). Attempts to purify the
product through crystallization were unsuccessful. The 31P{1H}
NMR spectrum was consistent with 8 as the major product. An
internal standard (diethylphenylphosphine) was used to esti-
mate the percent conversion to 8 as 37%. 1H NMR (300 MHz,
C6D6, 25 °C): δ ppm -12.78 (dq, JHP = 26, 60 Hz, 1H, Fe-H);
-0.98 (m, 1H, PCH2-Fe); -0.42 (m, 1H, PCH2-Fe); 0.04
(s, 3H, Me-Si); 0.51 (m, 4H, CH2-SiP3); 0.61 (m, 2H,
SiP3(dmpe)Fe (4). Complex 4 was prepared according to the
method described for 3 except utilizing 2 (0.14 g, 0.26 mmol) in
toluene (20 mL). Recrystallization in toluene produced crystals
of the contaminant, (dmpe)5Fe2 (5), and a clean supernatant
containing the desired material (0.065 g, 0.14 mmol, 52% yield).
Red X-ray quality crystals of SiP3(dmpe)Fe were isolated from
1
toluene at -35 °C. H NMR (300 MHz, C6D6, 25 °C): δ ppm
0.07 (s, 3H, Me-Si); 0.72 (m, 6H, CH2-SiP3); 1.39 (pseudo t,
“JHP” = 3 Hz, 12H, Me-dmpe); 1.44 (br s, 18H, Me-SiP3); 1.51
(m, 4H, CH2-dmpe). 13C{1H} NMR (75 MHz, C6D6, 25 °C):
δ ppm 0.60 (pseudo q, “JCP” = 6 Hz, 1C, Me-Si); 24.98 (s, 3C,
CH2-SiP3); 28.37 (m, 2C, PMe2); 30.18 (t, JCP = 27 Hz, 2C,
PMe2); 32.82 (m, 6C, PMe2); 36.31 (td, JCP = 26, 3.5 Hz, 2C,
CH2-dmpe). 31P{1H} NMR (121 MHz, C6D6, 25 °C): δ ppm
15.8 (t, JPP = 11.6 Hz, 3P, SiP3); 58.4 (q, JPP = 11.6 Hz, 2P,
dmpe). EI-HRMS (70 eV) m/z: Mþ calcd for C16H43FeP5Si,
474.1172; found, 474.1200.
CH2-SiP3); 1.15 (d, JHP = 5.4 Hz, 3H, PMe2); 1.19 (d, JHP
=
5.1 Hz, 3H, PMe2); 1.42 (m, 12H, Me-SiP3); 1.54 (m, 6H, Me-
SiP3). 31P{1H} NMR (121 MHz, C6D6, 25 °C): δ ppm -17.36
(m, 1P, PMe2); 27.5 (m, 1P, SiP3-PMe2); 37.6 (m, 1P,
SiP3-PMe2); 43.8 (m, 1P, SiP3-PMe2).
(dmpe)5Fe2 (5). This previously characterized complex32 was
isolated as a byproduct in the preparation of 4. X-ray quality
crystals were obtained from toluene. See preparation of 4 above.
1H NMR (300 MHz, C6D6, 25 °C): δ ppm 1.03 (d, JHP = 3 Hz,
12H, Me-dmpe); 1.28 (br s, 24H, Me-dmpe); 1.54 (m, 4H, CH2-
dmpe); 1.57 (br s, 24H, Me-dmpe); 1.75 (m, 16H, CH2-dmpe).
31P{1H} NMR (121 MHz, C6D6, 25 °C): δ ppm 8.39 (t, JPP = 9.4
Hz, 2P, bridging dmpe); 61.44 (d, JPP = 9.4 Hz, 4P).
Acknowledgment. This work was funded by the National
Science Foundation (CHEM-0239461, CHE-0809575). We
thank the Prof. Kent Mann group for use of their CV equip-
ment, and we acknowledge Dr. Victor Young from the X-ray
Crystallographic Laboratory, Elodie Marlier, and Dr. Alicia A.
Peterson for help in solving crystal structures.
[tSiP3(dmpm)FeH][PF6] (6). Prepared according the procedure
described by Howarth21 for the preparation of [SiP3(dmpe)-
FeH][PF6] using 3 and NH4PF6 to give a orange solid (0.062 g,
0.123 mmol, 82% yield). 1H NMR (300 MHz, CD3CN, 25 °C): δ
Supporting Information Available: Synthesis and NMR char-
t
t
acterization of complexes SiP3-2 and SiP3-4, ORTEP dia-
grams (showing disorder with methyl groups removed) for
complexes 1-5 and CIF files for complexes 1-5. This material
is available free of charge via the Internet at http://pubs.acs.org.
ppm -10.93 (dtt, JHP = 13, 51, 51 Hz, 1H, Fe-H); 0.75 (d, JHP
=