Synthesis and cyclic voltammetric studies of the diiron complexes ER 2[η-C5H4Fe(L2)Me]2 (E = C, Si, Ge, Sn; R = H, alkyl; L2 = diphosphine) and (η5-C5H5)Fe(

Article abstract of DOI:10.1021/om8004004

Cyclic voltammetric studies on ER₂[(η⁵-C ₅H₄)Fe(L₂)Me]₂ (L₂ = dppe; ER₂ = CH₂ (1a), SiMe₂ (2a), GeMe ₂ (3a), SnMe₂ (4a)) re

Full text of DOI:10.1021/om8004004

Organometallics 2008, 27, 4739–4748
4739
Synthesis and Cyclic Voltammetric Studies of the Diiron Complexes
ER2[(η5-C5H4)Fe(L2)Me]2 (E ) C, Si, Ge, Sn; R ) H, alkyl;
L2 ) diphosphine) and (η5-C5H5)Fe(L2)ER2Fc
(Fc ) (η5-C5H4)Fe(η5-C5H5))
Mukesh Kumar,† Francisco Cervantes-Lee,†,‡ Keith H. Pannell,*,† and Jianguo Shao§
Departments of Chemistry, UniVersity of Texas at El Paso, El Paso, Texas 79968-0513, and Midwestern
State UniVersity, 3410 Taft BouleVard, Wichita Falls, Texas 76308-2099
ReceiVed May 5, 2008
Cyclic voltammetric studies on ER2[(η5-C5H4)Fe(L2)Me]2 (L2 ) dppe; ER2 ) CH2 (1a), SiMe2 (2a),
GeMe2 (3a), SnMe2 (4a)) revealed two well-resolved reversible waves (1E1/2 ) -0.33 V, 2E1/2 ) -0.20
V (for 1a); 1E1/2 ) -0.35 V, 2E1/2 ) -0.21 V (for 2a); 1E1/2 ) -0.36 V, 2E1/2 ) -0.23 V (for 3a); 1E1/2
2
) -0.36 V, E1/2 ) -0.22 V (for 4a)) in CH2Cl2, suggesting electronic communication between two
iron centers, which is seen for the first time in this family of organometallic complexes. The resolution
between two reversible waves increases in the order 1a < 2a < 3a < 4a; however, coordinating solvents
such as pyridine, PhCN, DMSO, and DMF decreased these interactions, attributable to the stabilization
of cationic species formed after the first oxidation. UV/vis spectroelectrochemistry of 1a-4a revealed
two distinct absorbance patterns for both redox processes and reflected the stepwise oxidation.
Homobimetallic complexes containing ferrocenyl groups, (η5-C5H5)Fe(L2)ER2Fc (ER2 ) none, L2 )
cis-dppen (5a); ER2 ) SiMe2, L2 ) cis-dppen (6a), dppm (6b); ER2 ) GeMe2, L2 ) cis-dppen (7a),
dppm (7b); ER2 ) SntBu2, L2 ) dmpe (8a); Fc ) (η5-C5H4)Fe(η5-C5H5)), were prepared and studied in
terms of electrochemistry. The cyclic voltammogram of 5a exhibited two well-resolved one-electron
reversible waves at 1E1/2 ) -0.21 V and 2E1/2 ) 0.58 V corresponding to oxidation of the Fe(P-P) and
Fc iron atoms, respectively. Other complexes in this series (6a/6b, 7a/7b, 8a) containing direct Fe-E-Fc
(E ) Si, Ge, Sn) bridging units were not stable under electrochemical conditions, and rupture of the
Fe-E bonds was observed.
Mo¨ssbauer spectroscopy of these mixed-valence systems indi-
cated significant thermal transformations from [FC]+ to [FC]
due to the presence of the [I3]- and [I5]- counteranions.6g
Introduction
Organometallic complexes with two or more redox-active
transition metals linked by specific bridging spacers are of
interest, due to possible electronic communication and mixed-
valence behavior.1 Such materials have potential properties
related to semiconductivity, molecular electronics, photo-/
electroluminescence, magnetism, and nonlinear optics.1,2 For
example, bis(ferrocenyl) complexes3-5 bridged by different
spacers such as (SiMe2)n4 (Figure 1, C), (CHdCH)n,5 etc. exhibit
electronic interactions depending upon the value of n. Similarly,
ferrocenylene-silylene polymers, -[FCSiMe2]m–, have been
investigated in detail in terms of electrochemistry,6 and I2 doping
experiments on thin films of such polymers exhibited mixed-
valence character and conducting properties.6f Furthermore,
(2) (a) Conjugated Polymer Materials: Opportunities in Electronic,
Optoelectronic and Molecular Electronics; Bredas, J. L., Chance, R. R.,
Eds.; Kluwer: Dordrecht, The Netherlands, 1990; NATO ASI Series, Vol.
182. (b) Jortner, J.; Ratner, M. A. Molecular Electronics; Blackwell Science:
Oxford, U.K., 1997. (c) Lehn, J.-M. Supramolecular Chemistry-Concepts
and PerspectiVes; VCH: Weinheim, Germany, 1995. (d) Ward, M. D. Chem.
Soc. ReV. 1995, 121. (e) McCleverty, J. A.; Ward, D. Acc. Chem. Res. 1998,
31, 832. (f) Hoshino, Y.; Higuchi, S.; Fiedler, J.; Su, C.-Y.; Knodler, A.;
Schwederski, B.; Sarkar, B.; Hartmann, H.; Kaim, W. Angew. Chem., Int.
Ed. 2003, 42, 674. (g) Patoux, C.; Launay, J.-P.; Beley, M.; Chodorowski-
Kimmes, S.; Collin, J.-P.; James, S.; Sauvage, J.-P. J. Am. Chem. Soc. 1998,
120, 3717. (h) Laye, R. H.; Couchman, S. M.; Ward, M. D. Inorg. Chem.
2001, 40, 4089. (i) Mosher, P. J.; Yap, G. P. A.; Crutchley, R. J. Inorg.
Chem. 2001, 40, 1189. (j) Cameron, C. C.; Pickup, P. G. J. Am. Chem.
Soc. 1999, 121, 7710. (k) Beck, W.; Niemer, B.; Wieser, M. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 923. (l) Hunter, A. D. Organometallics 1989, 8,
1118. (m) Chukwu, R.; Hunter, A. D.; Santarsiero, B. D. Organometallics
1992, 11, 589.
† University of Texas at El Paso.
‡ Dr. Francisco (Paco) Jose Cervantes-Lee: 11/21/1950-2/15/2007.
§ Midwestern State University.
(1) (a) Mixed-Valence Compounds, Theory and Applications in Chem-
istry, Physics, Geology and Biology; Brown, D. W., Ed.; Reidel: Boston,
MA, 1980. (b) Creutz, C. Prog. Inorg. Chem. 1983, 30, 1. (c) Mixed-Valence
Compounds; Brown, D. B., Ed.; Reidel: Boston, MA, 1980. (d) Astruc, D.
Electron-Transfer and Radical Processes in Transition Metal Chemistry;
VCH: New York, 1995; Chapter 1. (e) Mixed Valency Systems, Applications
in Chemistry, Physics and Biology; Prassides, K., Ed.; Kluwer Academic:
Dordecht, The Netherlands, 1991. (f) Demadis, K. D.; Hartshorn, C. M.;
Meyer, T. J. Chem. ReV. 2001, 101, 2655. (g) Kaim, W.; Klein, A.; Glo¨ ckle,
M. Acc. Chem. Res. 2000, 33, 755. (h) Paul, F.; Lapinte, C. Coord. Chem.
ReV. 1998, 178-180, 431. (i) Ziessel, R.; Hissler, M.; El-ghayoury, A.;
Harriman, A. Coord. Chem. ReV. 1998, 178-180, 1251. (j) Astruc, D. Acc.
Chem. Res. 1997, 30, 383.
(3) (a) Hendrickson, D. N. In Mixed Valency Systems, Applications in
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Dordecht, The Netherlands, 1991; p 67. (b) Barlow, S.; O’Hare, D. Chem.
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Chem. 1975, 14, 2331. (d) Moore, M. F.; Wilson, S. R.; Cohn, M. J.; Dong,
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Cohn, M. J.; Moore, M. F. Comments Inorg. Chem. 1985, 4, 329. (f) Dong,
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10.1021/om8004004 CCC: $40.75
2008 American Chemical Society
Publication on Web 08/27/2008

4740 Organometallics, Vol. 27, No. 18, 2008
Kumar et al.
Figure 1. Representation of group 14 element bridged diiron complexes.
Homo and hetero bi-/trimetallic complexes with conjugated
and rigid spacers such as -Ct C- and -Ct C-aryl-Ct C-
have been utilized with a variety of transition metals and their
electrochemical properties in terms of mixed-valence behavior
and electron delocalization disclosed.7 Furthermore, the elec-
trochemical properties of other metal complexes containing
redox-active ligands, e.g. tetrathiafulvene,8 1,2-dioxalenes,9
catecholate, semiquinone/quinone9 and ferrocene-based
ligands,10 have also been evaluated to create an active area of
modern organometallic materials chemistry.
Recently we reported the electrochemistry of the monoiron
complexes (η5-C5H5)Fe(L2)ER3 (L2 ) bis(diphenylphosphi-
no)methane (dppm); ER3 ) CH3, SiMe3, GeMe3, SnMe3)11 and
the 1-sila-3-ferracyclobutanes, [(η5-C5H4)Fe(L2)CH2SiMe2] (L2
) dppm, dppe, dppp).12 As part of our continuing interest in
such materials, we report the synthesis and electrochemical
characteristics of group 14 element bridged bimetallic iron
complexes involving the ferrocenyl and cyclopentadienyliron-
diphosphine moieties, ER2[(η5-C5H4)Fe(L2)Me]2 (E ) C, Si,
Ge, Sn; R ) H, Me; L2 )
diphosphine) and (η5-
C5H5)Fe(L2)ER2Fc (Fc ) (η5-C5H4)Fe(η5-C5H5)) (Figure 1; A
and B).
Results and Discussion
Group A Compounds: ER2[(η5-C5H4)Fe(L2)Me]2 (L2 )
dppe; ER2 ) CH2 (1a), SiMe2 (2a), GeMe2 (3a), SnMe2
(4a). Synthesis. The dicarbonyl precursors ER2[(η5-C5H4)-
Fe(CO)2Me]2 (ER2 ) CH2 (1), SiMe2 (2)) were prepared from
the reaction between ER2(Fp-Na+)2 (Fp ) η5-C5H4Fe(CO)2)13
and iodomethane at low temperature (eq 1). The corresponding
complexes ER2[(η5-C5H4)Fe(CO)2Me]2 (ER2 ) GeMe2 (3),
SnMe2 (4)) were synthesized by the base-induced double-
migration chemistry outlined in eq 2.14
(4) Dement’ev, V. V.; Cervantes-Lee, F.; Parkanyi, L.; Sharma, H.;
Pannell, K. H.; Nguyen, M. T.; Diaz, A. Organometallics 1993, 12, 1983.
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C. W. Inorg. Chem. 1996, 35, 3735.
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Pannell, K. H. SPIE Proc. 1993, 1910, 230. (b) Nguyen, M. T.; Diaz, A. F.;
Dementiev, V. V.; Pannell, K. H. Chem. Mater. 1993, 5, 1389. (c) Nguyen,
M. T.; Diaz, A. F.; Dementiev, V. V.; Pannell, K. H. Chem. Mater. 1994,
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(b) De Montigny, F.; Argouarch, G.; Costuas, K.; Halet, J.; Roisnel, T.;
Toupet, L.; Lapinte, C. Organometallics 2005, 24, 4558. (c) Chen, J.-L.;
Zhang, L.-Y.; Chen, Z.-N.; Gao, L.-B.; Abe, M.; Sasaki, Y. Inorg. Chem.
2004, 43, 1481. (d) Sato, M.; Hayashi, Y.; Kumakura, S.; Shimizu, N.;
Katada, M.; Kawata, S. Organometallics 1996, 15, 721. (e) Weyland, T.;
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Organometallics 1997, 16, 2024. (f) Weyland, T.; Costuas, K.; Toupet, L.;
Halet, J.-F.; Lapinte, C. Organometallics 2000, 19, 4228. (g) Bruce, M. I.;
De Montigny, F.; Jevric, M.; Lapinte, C.; Skelton, B. W.; Smith, M. E.;
White, A. H. J. Organomet. Chem. 2004, 689, 2860. (h) Coat, F.; Guillemot,
M.; Paul, F.; Lapinte, C. J. Organomet. Chem. 1999, 578, 76. (i) Alberto,
C.; Saverio, S.; Laura, O.; Annalisa, B. Coord. Chem. ReV. 2004, 248, 683.
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Zhu, N. J. Am. Chem. Soc. 2004, 126, 2501.
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J. B.; Lever, A. B. P. Inorg. Chem. 2003, 42, 7887. (b) Pierpont, C. G.;
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361, 1793.
The initial dicarbonyl complexes, 1–4, were treated photo-
chemically (2-3 days) with two equivalent of the appropriate

Electronic Communication in Diiron Complexes
Organometallics, Vol. 27, No. 18, 2008 4741
diphosphine to form the redox-active complexes, 1a-4a, in
60-70% yield, eq 3.
The photochemical reactions were monitored by 31P NMR
and IR spectroscopy and the stepwise CO substitutions could
be observed; however, we made no attempt to isolate the
intermediate complexes formed during this process. The desired
compounds were isolated as red-orange solid materials soluble
in common organic solvents and were characterized by NMR
and elemental analysis.
Spectroscopic Characterization. NMR spectroscopic analy-
ses of 1-4 and 1a-4a are in total accord with their proposed
structures and are presented in the Experimental Section. Thus,
as expected, 13C NMR spectra of 1a-4a exhibited triplets for
the Fe-Me carbon due to heteronuclear coupling with two
equivalent P atoms and appeared in the range of -17.0 to -21.0
ppm. Decoupled 31P NMR spectra exhibited a single resonance
for each compound in the range of 109.0-113 ppm, which is
∼130 ppm downfield as compared to resonances for the
uncoordinated diphosphine and are comparable to that observed
for [(η5-C5H4)Fe(dppe)CH2SiMe2]12 and other diphosphine
derivatives of iron.7b,e,15 29Si and 119Sn NMR resonances for
2a and 4a appeared at δ -5.9 and -27.5 ppm, respectively,
exhibiting the expected chemical shift differences as compared
to resonances for 2 and 4.11
Cyclic Voltammetry. The cyclic voltammograms of the
dicarbonyl derivatives 1-4 showed only one irreversible
oxidation in the range of 1.2-1.4 V (TBAP/dichloromethane,
GCE), typical of the Fp [Fp ) (η5-C5H5)Fe(CO)2] derivatives.11,16
No apparent intramolecular communication between the two
Fe atoms is observed prior to decomposition; however, the
oxidation wave is quite broad compared to those of related
reversible systems and probably contains several distinct
processes. On the other hand, compounds 1a-4a exhibited two
reversible waves (Figure 2). The CH2-bridged complex 1a
showed a weakly resolved pair of reversible waves, and they
Figure 2. Cyclic voltammograms for 1a-4a in CH2Cl2 (left) and
pyridine (right).
1
2
were identified at Ep,a ) -0.26 V and Ep,a ) -0.17 V in
dichloromethane (Table 1). Surprisingly, the difference between
the two oxidation values 1Ep,a and 2Ep,a (∆Ep,a) changes relatively
little as a consequence of changing the nature of the group 14
bridge, although the resolution between the two increases in
the order C < Si < Ge < Sn. The same is true for the half-wave
potential values (E1/2).
The difference between the two redox processes can be
2
1
expressed as ∆E1/2 (V) ) E1/2 - E1/2, where E1/2 ) (Ep,a
+
Ep,c)/2, and in general this value is similar to the simpler ∆Epa
(2Ep,a - Ep,a). For complexes 1a-4a such values are in the
1
range 0.09-0.14 V with the single-atom bridges. In comparison,
the series of bis(ferrocenyl)polyenes Fc(CHdCH)nFc exhibited
∆E1/2 ) 0.17 V (n ) 1), 0.12 V (n ) 2),5 whereas the class C
compounds Fc(SiMe2)nFc4 had values of ∆Ep,a ) 0.34 V (n )
0), 0.15 V (n ) 1), 0.11 (n ) 2), 0.08 V (n ) 3). These data
reveal that the extent of electronic communication between two
iron atoms is much higher when n ) 0 and quickly decreases
as n increases. Thus, the present complexes compare reasonably
with those noted above. However, in comparison, the 1,1-
ferrocenophanes [(η5-C5H4)Fe(η5-C5H4ER2)]2 were reported to
have larger ∆E1/2 (V) values as compared to those of 1a-4a:
ER2 ) CH2, 0.20;17 SnnBu2, 0.20;18 SiMe2, 0.25;19 SntBu2,
0.27;20 SnMes2, 0.28;20 PbPh2, 0.2.21
The use of the more coordinating solvent pyridine resulted
in both a decrease in the resolution of the waves and a reduction
in the oxidation potentials for the various processes. To
determine the solvent effect on the difference between the two
oxidation potentials, cyclic voltammograms for compound 4a
(12) Kumar, M.; Cervantes-Lee, F.; Sharma, H. K.; Pannell, K. H.
Organometallics 2007, 26, 3005.
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Chem. 2001, 634, 102. (b) Bitterwolf, T. E. J. Organomet. Chem. 1996,
312, 197.
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H. G. Organometallics 1990, 9, 1071.
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1990, 45, 755.

4742 Organometallics, Vol. 27, No. 18, 2008
Kumar et al.
Kc
Table 1. Electrochemical Data of 1a-4a in CH2Cl2 and Pyridine Containing 0.1 M TBAP
a
b
compd
solvent
CH2Cl2
1Ep,a
1Ep,c
1E1/2
2Ep,a
2Ep,c
2E1/2
∆E1/2
∆Ep,a
1a
2a
3a
4a
-0.26
-0.30
-0.32
-0.32
-0.39
-0.40
-0.39
-0.40
-0.33
-0.35
-0.36
-0.36
-0.17
-0.17
-0.19
-0.18
-0.23
-0.25
-0.27
-0.26
-0.20
-0.21
-0.23
-0.22
0.13
0.14
0.13
0.14
0.09
0.13
0.13
0.14
172
256
172
256
1a
2a
3a
4a
pyridine
-0.20
-0.26
-0.27
-0.25
-0.32
-0.32
-0.33
-0.33
-0.26
-0.29
-0.30
-0.29
-0.14
-0.14
-0.15
-0.13
-0.20
-0.20
-0.23
-0.21
-0.17
-0.17
-0.19
-0.17
0.09
0.12
0.11
0.12
0.06
0.12
0.12
0.12
4
116
78
116
2
2
a ∆E1/2 (V) ) E1/2
- . - .
1E1/2 b ∆Ep,a (V) ) Ep,a 1Ep,a
were recorded using the polar solvents PhCN, DMF, and
DMSO. A significant correlation exists between the solvent
dielectric constant and ∆E1/2: the more polar the solvent, the
smaller the separation, e.g. variations from 90 mV in DMF to
140 mV in CH2Cl2 (see the figure in the Supporting Informa-
tion). The better the stabilization of the initially formed charge
by the solvent, the lesser the impact of that charge upon the
neighboring metal center oxidation process.22
observed no well-defined near-IR bands in the region 800-1100
nm but the region 1100-2500 nm was not examined.
Group B compounds: (η5-C5H5)Fe(L2)ER2Fc (ER2 ) none,
L2 ) cis-dppen (5a); ER2 ) SiMe2, L2 ) cis-dppen (6a),
dppm (6b); ER2 ) GeMe2, L2 ) cis-dppen (7a), dppm (7b);
ER2 ) SntBu2, L2 ) dmpe (8a); Fc ) (η5-C5H4)Fe(η5-C5H5)).
Synthesis and Characterization. Compound 5, containing a
direct ferrocenyl-iron bond, was prepared by the salt-elimina-
tion reaction between FcLi and FpI (Fc ) η5-C5H4FeC5H5, Fp
) (η5-C5H5)Fe(CO)2)24 (eq 5). Synthesis of 6-8 involved
quenching Fp-Na+ with FcECl (E ) SiMe2, GeMe2, Sn(tBu)2)25
(eq 6). The synthesis of FcECl was achieved in good yield using
the procedure reported in the literature involving the reaction
The comproportionation associated with the reaction for a
class II system is shown in eq 4.
1
of corresponding 1-ferrocenophane with HCl.26 Infrared, H,
13C, 29Si, and 119Sn NMR spectroscopic analysis were in accord
with their structural formulation, and the data are presented in
the Experimental Section.
The Kc values were calculated by using the e[(2E1/2 - 1E1/2
)
n1n2F]/RT relationship (n1 ) n2 ) 1; F ) Faraday constant, R
) gas constant, T ) 293 K).23 As shown in Table 1, the values
for Kc (CH2Cl2), in the range 170-260, are greater than those
for [{Cp*(dppe)Fe(-Ct C-)}2(1,3-C6H4)] (Kc ) 130) and
[{Cp*(dppe)Fe(-Ct C-)}3(1,3,5-C6H3)] (Kc ) 130).7f These
data suggest that for complexes 1a-4a the equilibrium favors
mixed-valence species.
UV/Vis Spectroelectrochemistry of 1a-4a. A UV/vis
spectroelectrochemical study of 1a-4a was performed in the
region 300-1100 nm. The spectral changes of both 1a and 4a
upon oxidation are available in the Supporting Information.
Compound 1a showed four isosbestic points at 324, 430, 508,
and 578 nm for the first oxidation at -0.20 V, while for the
second oxidation process at 0.0 V three isosbestic points at 326,
426, and 497 nm are observed. Similar behavior was noted for
2a-4a. All spectral variations are reversible, as are the
electrochemical processes. However, due to the small changes
in molar absorptivity of these compounds, no significant
conclusions about the electronic transitions could be made at
this time (see the figure in the Supporting Information). We
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J. E.; Sutton, P. M.; Taube, H. Inorg. Chem. 1979, 18, 1017. (c) Creutz, C.
Prog. Inorg. Chem. 1983, 30, 1.
Ultraviolet irradiation of 5-8 in the presence of a diphosphine
(24-36 h) resulted in the formation of the expected CO-
substituted products (eq 7). These reactions were monitored by

Electronic Communication in Diiron Complexes
Organometallics, Vol. 27, No. 18, 2008 4743
IR and 31P NMR spectroscopy and showed the stepwise
replacement of the CO groups; however, we made no attempt
to isolate the monosubstituted materials. The diphosphine
derivatives 5a, 6a/6b, 7a/7b, and 8a were isolated as orange-
red solid materials and purified by recrystallization from toluene/
hexane mixtures.
Figure 3. ORTEP diagram of [(η5-C5H5)Fe(Ph2PCH2Ph2P)SiMe2Fc]
(6b). Thermal ellipsoids are drawn at the 50% probability level,
and hydrogen atoms are deleted for clarity.
Table 2. Summary of Crystallographic Data of 6b and 9
6b
9
source
synthesis
red
red chunk
synthesis
red
red chunk
0.40 × 0.40 × 0.34
12.3242(12)
12.3981(12)
19.5110(19)
90
98.403(2)
90
cryst color
cryst habit
cryst size/mm3
a/Å
b/Å
c/Å
0.20 × 0.16 × 0.16
10.1001(7)
14.4739(9)
15.7609(11)
77.5740(10)
80.2480(10)
76.3780(10)
2169.6(3)
monoclinic
C2/c
R/deg
ꢀ/deg
γ/deg
volume/Å3
cryst syst
space group
Z
2949.2(5)
monoclinic
P21/c
The 1H and 13C NMR spectral properties of the new
complexes are in accord with their proposed structures. The 29Si
NMR spectra of both 6a and 6b showed a triplet due to two-
bond heteronuclear coupling for the SiFeP2 moiety (26.0 ppm,
2
4
Dc/g cm-3
1.325
0.805
1.303
0.681
µ/mm-1
abs cor
Bruker SADABS V2.05
2
2JSi-P ) 45.7 Hz (6a); 26.7 ppm, JSi-P ) 44.5 Hz (6b)),
temp/K
296(2)
0.710 73
graphite
wavelength (Å)
monochromator
diffractometer
no. of rflns collected 13 475
no. of indep rflns
structure solun
technique
structure solution
program
reflecting the expected moderate upfield shift when compared
to 6 (36.2 ppm).25 Similarly, a triplet (2JSn-P ) 409 Hz) in the
119Sn NMR spectrum of 8a was observed at 105.2 ppm. 31P
NMR spectra of all these compounds showed a downfield shift
as compared to free phosphine ligands.
Crystal Structure of 6b. There is apparently only a single
literature report concerning the structures of Fp(L2)R complexes,
that of Fp(dppm)Ph.27 The structural data reveal a piano-stool
arrangement at the Fe atom with Fe-P1 and Fe-P2 bond
distances of 2.199(1) and 2.174(1) Å, respectively, with a
P1-Fe-P2 bite angle of 73.8(0)°.
The molecular structure of 6b, as determined by single-crystal
X-ray analysis of a crystal formed from a benzene/hexane
solvent mixture, also exhibits a piano-stool arrangement at Fe,
as shown in Figure 3. The crystallographic data and selected
bond lengths and angles are summarized in Tables 2 and 3,
respectively. Compound 6b crystallizes in a monoclinic crystal
system with the C2/c space group, and each molecule in the
unit cell crystallizes with 1.5 molecules of C6H6; however, the
benzene molecule has no apparent interactions with the iron
complex.
Bruker APEX CCD area detector
33 312
9341 (R(int) ) 0.0206) 7029 (R(int) ) 0.0353)
direct methods
SHELXS-97 (Sheldrick, 1990)
refinement technique
refinement program
function minimized
goodness of fit on F2 1.047
R1, wR2 (I > 2σ(I)) R1 ) 0.0486,
wR2 ) 0.1068
full-matrix least squares on F2
SHELXL-97 (Sheldrick, 1997)
2
2 2
∑w(Fo - Fc )
1.155
R1 ) 0.0682,
wR2 ) 0.1586
R1 ) 0.0769,
wR2 ) 0.1643
R1, wR2 (all data)
R1 ) 0.0557,
wR2 ) 0.1112
Fe(CO)2]2Si2Me4 (Fe-Si ) 2.375(2) Å),28 (η5-C5H5)Fe(CO)2-
SiMe2SiPh3 (Fe-Si ) 2.346(1) Å),29 and (η5-C5H5)Fe-
(CO)2SiMe2GePh3 (Fe-Si ) 2.328(1) Å).30 The geometry
around the Si atom is that of a slightly distorted tetrahedron
(C41-Si-C42 ) 103.22(12), C42-Si-C2 ) 100.66(12),
C41-Si-C2 ) 103.75(12)°). The Fe-P bond distances are
2.1921(7) and 2.1872(7) Å, and the P2-Fe2-P1 bite angle is
found to be 74.44(3)°. Such values are almost identical with
those noted above for Fp(dppm)Ph27 and also those observed
The Fe2-Si distance of 2.3786(8) Å is reminiscent of
distances in the related dicarbonyl complexes [(η5-C5H5)-
(24) Pannell, K. H.; Cassias, J. B.; Crawford, G. M.; Flores, A. Inorg.
Chem. 1976, 15, 2671.
(25) Pannell, K. H.; Sharma, H. Organometallics 1991, 10, 954.
(26) MacLachlan, M. J.; Ginzburg, M.; Zheng, J.; Knoll, O.; Lough,
A. J.; Manners, I. New J. Chem. 1998, 22, 1409.
(27) Scott, F.; Kruger, G. J.; Cronje, S.; Lombard, A.; Raubenheimer,
H. G. Organometallics 1990, 9, 1071.
(28) Pannell, K. H.; Cervantes, J.; Parkanyi, L.; Cervantes-Lee, F.
Organometallics 1990, 9, 859.

4744 Organometallics, Vol. 27, No. 18, 2008
Kumar et al.
Table 3. Selected Bond Lengths (Å) and Angles (deg) of
(η5-C5H5)Fe(dppm)SiMe2Fc (6b) and (η5-C5H5)Fe(dppm)SiMe3 (9)
Bond Lengths (Å)
Compound 6b
Fe2-Si
Si-C2
2.3786(8)
1.924(3)
Fe2-C12 2.114 (3)
Fe2-P1
2.1921(7) Fe2-P2
2.1872 (7)
1.921(3)
Si-C41
1.920 (3) Si-C42
Fe2-C13 2.102 (3) Fe2-C14 2.126 (3)
Fe2-C15 2.128(3)
Fe2-C16 2.128 (3)
Compound 9
Fe-Si
2.4756(10) Fe-P1
2.2789(9) Fe-P2
2.0878(9)
1.929(4)
2.126(3)
Si-C31
Fe-C1
Fe-C4
1.952(4)
1.987(4)
2.038(3)
Si-C32
Fe-C2
Fe-C5
1.812(4)
2.263(3)
1.837(3)
Si-C33
Fe-C3
Bond Angles (deg)
Compound 6b
P2-Fe2-P1
P2-Fe2-Si
C42-Si-C2
74.44(3)
P1-Fe2-Si
C41-Si-C2
C41-Si-C42
93.76(3)
103.75(12)
103.22(12)
94.06(3)
100.66(12)
Compound 9
P2-Fe-P1
P2-Fe-Si
C32-Si-C31
C32-Si-Fe
C31-Si-Fe
67.35(3)
105.30(3)
99.0(2)
P1-Fe-Si
100.18(3)
110.0(2)
90.1(2)
116.74(15)
85.27(13)
C32-Si-C33
C33-Si-C31
C33-Si-Fe
P1-C6-P2
112.11(15)
125.97(13)
Figure 4. ORTEP diagram of [(η5-C5H5)Fe(Ph2PCH2Ph2P)SiMe3]
(9). Thermal ellipsoids are drawn at the 50% probability level, and
hydrogen atoms are deleted for clarity.
in Fe(CO)3dppm31 (P1-Fe-P2 ) 73.5(1)°; Fe-P1 ) 2.209(4)
Å, Fe-P2 ) 2.225(3) Å). Related bidentate phosphine com-
plexes with larger chelate rings do, as expected, have much
larger bite angles: e.g., Cp*(dppe)Fe-Ct C-9,10-ant-Ct C-
FeCp*(dppe)7b (85.42(5)°), [Cp*Fe(dppe)]3(Ct C)3(µ-1,3,5-
C6H3)7e (84.7(1), 83.7(4), 85.7(1)°), and Fc-Ct C-CpFe-
(dppe)7d (86.7(2)°) (ant ) anthracene, dppe ) bis(diphe-
nylphosphino)ethane).
The X-ray structure determination of the monoiron analogue
(η5-C5H5)Fe(dppm)SiMe3 (9) (see ref 11 for the synthesis of
9) was also performed in order to compare the variations in
structural pattern of Fe-Si/Fe-P bond distances and P-Fe-P
bite angles (Figure 4, Tables 2 and 3). The differences between
the structures of 6b and 9 are associated with the Fe-Si/Fe-P
bond distances and P-Fe-P bite angles. The Fe-Si bond
distance observed for 9 (Fe-Si ) 2.4756(10) Å) is significantly
longer than other reported Fe-Si bond lengths and obviously
that found in 6b, 2.3786(8) Å. Similarly, the two Fe-P bond
distances Fe-P1 ) 2.2789(9) Å and Fe-P2 ) 2.0878(9) Å
exhibit a distinct variation from those in 6b and Fp(dppm)Ph27
and exhibit a greater Fe-P bond distance difference. It may
also be noted that the P1-Fe-P2 bite angle in this complex is
sharply reduced to 67.35(3)°. The replacement of one methyl
by a ferrocenyl on the trimethylsilyl group gives rise to a large
variation in the crystal structure parameters. The extra crowding
around the Fe atom of the Fp group results in shorter Fe-Si
bond length, an increased bite angle, and a general increase in
asymmetry at the Fe center, as noted by two differing Fe-P
bond distances.
Figure 5. Cyclic voltammogram of (η5-C5H5)Fe(cis-dppen)Fc (5a)
in CH2Cl2 containing 0.1 M TBAP.
processes were assigned to the iron centers in the Fp and Fc
moieties, respectively (Figure 5). The first oxidation of the Fp
moiety makes the ferrocenyl group more difficult to oxidize,
as found by comparison with the oxidation potential of the pure
ferrocene, 0.54 V (vs SCE). This can be accounted for by either
a weak communication between the two metal centers or an
electronic effect of the Fp substituent on the Fc center.
Complex 5a exhibited a clean UV/vis spectroelectrochemistry,
as illustrated in Figure 6. The first oxidation at 0.20 V revealed
two isosbestic points at 314 and 402 nm. A broad and intense
band is formed between 402 and 700 nm. The magnitude of
the absorbance associated with the low-energy band in the
spectra is strongly suggestive of a charge transfer between the
Fc and Fp(P-P) groups that occurs after the first oxidation of
the Fp(P-P) moiety. These low-energy bands may be best
described as LMCT bands.7b The second oxidation at 0.80 V
(Figure 6b) also exhibited two isosbestic points at 480 and 750
nm; however, the spectral pattern is different from that expected
for a simple Fc/Fc+ transformation. Interestingly, after the
second oxidation, there is a significant reduction in the absor-
bance in the region of the CT bands.
Cyclic Voltammetry and UV/Vis Spectroelectrochemistry
of (η5-C5H5)Fe(cis-dppen)Fc (5a). The cyclic voltammogram of
(η5-C5H5)Fe(cis-dppen)Fc (5a) in dichloromethane containing
0.1 M TBAP from -0.5 to 1.0 V (vs SCE) revealed two well-
separated one-electron reversible redox processes at E1/2
-0.21 and 0.58 V with an ip,a/ip,c current ratio of 1.0. These
)
Cyclic Voltammetry of 6a/6b, 7a/7b, and 8a. Cyclic
voltammograms of compounds 6a and 6b, containing a di-
methylsilyl bridging group between the Fp(P-P) and Fc
moieties, were obtained in dichloromethane/TBAP solution. The
results for 6a are illustrated in Figure 7 and reveal three
oxidations, and that of 6b is similar (Table 4). A first reversible
oxidation at ∼0.0 V is reminiscent of those noted above for
(29) Parkanyi, L.; Pannell, K. H.; Hernandez, C. J. Organomet. Chem.
1983, 252, 127.
(30) Parkanyi, L.; Hernandez, C.; Pannell, K. H. J. Organomet. Chem.
1986, 301, 145.
(31) Cotton, F. A.; Hardcastle, K. I.; Rusholme, G. A. J. Coord. Chem.
1973, 2, 217.

Electronic Communication in Diiron Complexes
Organometallics, Vol. 27, No. 18, 2008 4745
Figure 6. UV/vis spectral changes for (η5-C5H5)Fe(cis-dppen)Fc (5a) upon the first (a) and the second (b) oxidations in CH2Cl2 containing
0.2 M TBAP.
changes observed with the first redox processes for 6a/6b and
7a/7b at ∼0.0.V are essentially identical, and a representative
spectroelectrogram of 6b is shown in Figure 8a. Maintaining
the oxidation potential in the experiment at 0.25 V, i.e. well
below the potential where the subsequent oxidations become
significant, results in a well-defined reversible optical change
(Figure 8a). Two isosbestic points are observed at 320 and 375
nm, a pattern similar to those in the related Fp(dppm)SiMe3
complex (isosbestic points at 340 and 395 nm, Figure 8c). The
maximum wavelengths of the low-energy bands in 6a/6b and
7a/7b are at ∼500 nm, compared to those of the Fp(P-P)EMe3
complexes at ∼430 nm, presumably an effect associated with
the Fc substituent. The ferrocenyl-type redox process observed
for 6a and 7a at ∼0.5 V exhibits a typical spectral property for
an Fc/Fc+ process, as may be observed for 6b in Figure 8b.
The typical UV/vis spectral changes of Fc/Fc+ are shown in
Figure 8d.
Attempted Chemical Oxidation of 6a and 7a. To investigate
this reactivity, we treated complexes 6a and 7a to a chemical
oxidation reaction using AgPF6. From the reaction mixture we
Figure 7. Cyclic voltammograms of (η5-C5H5)Fe(cis-dppen)-
were able to isolate FcSiMe2F (or FcGeMe2F) in good yield,
SiMe2Fc (6a) in CH2Cl2 containing 0.1 M TBAP.
thereby confirming the facile oxidative cleavage of the Fe-Si/
Fe-Ge bonds. FcSiMe2F (from 6a)32 and FcGeMe2F (from 7a)
the Fp(P-P) part of the molecule, and the third reversible
were isolated as hexane-soluble products, while the iron
oxidation in the region of ∼0.5 V is typical of those associated
compound [CpFe(Ph2PCHdCHPPh2)]PF6 was isolated as an
with a ferrocenyl group. However, the system is neither simple
acetone-soluble product from the residue of both reactions
nor clean. Recycling the electrochemistry process illustrates that
(Scheme 1).
the initial Fp(P-P) reversible oxidation disappears. After the
NMR spectroscopy and elemental analysis confirmed the
initial oxidation of the Fp(P-P) group, there appears to be a
formation of these products, and ESI mass spectroscopy of
cleavage of the Fe-Si bond in these complexes under these
FcGeMe2F revealed [M]+ at m/z 306 and [M+ - F] at m/z 287.
conditions. The chemical decomposition is slow compared
Stable 17e- Cp*Fe(dppe) and its 16e- oxidized complex
to the electrochemical reversibility, but continued spectral
-
[Cp*Fe(dppe)]+PF6 have been reported in the literature, and
observation of the initially formed oxidation product il-
analysis by X-ray crystallography revealed their structures.33
lustrates the slow decomposition.
This further proves that after oxidation the Fe-E bond was not
Related cyclic voltammetric studies on the germyl-bridged
stable and ruptured to form [FcEMe2]+ species, which takes a
bimetallic complexes 7a/7b showed four oxidations (TBAP,
fluoride ion from PF6- to form FcEMe2F. We have not further
GCE, PtE), the first three of which resemble those observed
studied this aspect of the chemistry, but it is clear that a series
for 6a and 6b. The reason for the appearance of a fourth
of complex processes take place during the electrochemical
oxidation is unclear and further illustrates the facile cleavage
voltammetry experiments. The second irreversible oxidation
and decomposition of Fe-metalloid bonds, as observed for the
observable at ∼0.4 V (6a, 6b, 7a, and 7b) presumably belongs
silyl complexes discussed above. The organotin analogue 8a
to one such material, but we are unable/unwilling to speculate
revealed two irreversible redox in the Fp(P-P) region and one
upon its formulation.
reversible wave observed in the Fc region, all of which are of
uncertain provenance but seem to indicate a lesser stability of
the particular Fe-Sn bond upon oxidation.
The spectroelectrochemical UV/vis data associated with the
above processes confirm the above analysis. The spectral
(32) Bourke, S. C.; MacLachlan, M. J.; Lough, A. J.; Manners, I. Chem.
Eur. J. 2005, 11, 1989.
(33) Hamon, P.; Toupet, L.; Hamon, J.-R.; Lapinte, C. Organometallics
1996, 15, 10.

4746 Organometallics, Vol. 27, No. 18, 2008
Kumar et al.
Table 4. Cyclic Voltammetric Data of 5-8a and 5a, 6a/b, 7a/b, and
8ab
compd
Ep,a
Ep,c
E1/2
5
0.70
1.65
-0.17
0.62
0.69
1.70
0.06
0.38
0.53
0.00
0.39
0.53
0.74
1.60
0.08
0.39
0.53
0.63
-0.01
0.38
0.57
0.72
1.75
-0.20
0.03
0.60
0.54
0.41
0.55
5a
6
-0.25
0.54
0.39
-0.21
0.58
0.54
6a
-0.02
0.02
0.41
-0.07
0.47
-0.04
6b
0.45
0.40
0.49
0.57
7
7a
0.00
0.04
0.44
0.55
-0.08
0.49
0.59
-0.05
7b
0.47
0.43
0.52
0.57
8
8a
0.42
0.46
0.51
0.50
ferrocene
a Oxidation potentials (V vs Ag/AgCl, CH2Cl2, 0.1
b Oxidation potentials (V vs SCE, CH2Cl2, 0.1 M TBAP).
M TBAB).
Figure 8. UV/vis spectral changes upon oxidations for (η5-
C5H5)Fe(dppm)SiMe2Fc (a and b), (η5-C5H5)Fe(dppm)SiMe3 (c),
and Fc (d) in CH2Cl2 and 0.2 M TBAP.
Experimental Section
All experiments were performed under an atmosphere of dry N2
using Schlenk techniques. THF and hexanes were freshly distilled
from sodium benzophenone ketyl immediately prior to use;
CH2[CpFe(CO)2Me]2 (1)13b and SiMe2[(η5-C5H4)Fe(CO)2Me]2 (2)
were synthesized by following the procedure reported for SiMe2-
[(η5-C5H4)Fe(CO)2SiMe2SiMe3]2.13 GeMe2[(η5-C5H4)Fe(CO)2Me]2
(3),14 SnMe2[(η5-C5H4)Fe(CO)2Me]2 (4),14 (η5-C5H5)Fe(CO)2-
SiMe2Fc (6),25 and (η5-C5H5)Fe(dppm)SiMe3 (9)11 were prepared
according to literature methods. FcSntBu2Cl was prepared by
following the procedure reported for FcSiMe2Cl.26 1,2-Bis(diphe-
nylphosphino)ethane, cis-1,2-bis(diphenylphosphino)ethylene, 1,2-
bis(diphenylphosphino)methane, and bis(dimethylphosphino)ethane
were purchased from Strem Chemicals and used as received. Tetra-
n-butylammonium perchlorate (TBAP) and dichloromethane
(CH2Cl2, 99.5%) were obtained from Fluka Chemical Company
and used as received. Other solvents for cyclic voltammetry
included benzonitrile (PhCN, 99.0%), dimethyl sulfoxide (DMSO,
99.9%), N,N-dimethylformamide (DMF, 99.9%), and pyridine
(99.9%); these were purchased from Sigma-Aldrich and used
without further purification. Cyclic voltammetry was carried out
at room temperature under an atmosphere of dry N2 using a Pine
Instrument Co. AFCBP1 potentiostat. A three-electrode system was
used and consisted of a platinum-disk or glassy-carbon-disk working
electrode, a platinum-wire counter electrode, and a saturated calomel
reference electrode (SCE). The SCE was separated from the bulk
of the solution by a fritted-glass bridge of low porosity that
contained the solvent/supporting electrolyte mixture. UV-vis
spectroelectrochemical experiments were performed with an opti-
cally transparent platinum thin-layer electrode of the type described
in the literature,34 and the UV-vis spectra were recorded with a
HP 8453 diode array spectrophotometer. Infrared spectra were
obtained in THF/hexane solution using an ATI Mattson Infinity
series FTIR spectrometer; 1H, 13C, 29Si, and 31P NMR were
recorded in C6D6 on a Bruker DPX-300 spectrometer at 300, 75.4,
Scheme 1. Oxidative Cleavage of the Fe-Si Bond
59.6, and 121.5 MHz, respectively, and the values are reported in
ppm. Elemental analysis was performed at Galbraith Laboratories.
Synthesis of CH2[(η5-C5H4)Fe(dppe)Me]2 (1a). To a 40 mL
THF solution of 1 (0.64 g, 1.62 mmol) in a quartz tube was added
1.28 g (3.24 mmol) of dppe, and the tube was degassed twice. The
solution was then irradiated by a Hanovia 450 W medium pressure
lamp at a distance of 4 cm for 2-3 days. After completion of the
reaction, THF was evaporated under vacuum. The solid material
obtained was washed with hexanes and filtered. The hexane-
insoluble orange material was collected, dried, and characterized
as 1a (70%). Mp: 138-140 °C. Anal. Calcd for C65H64P4Fe2: C,
72.23; H, 5.97. Found: C, 72.11; H, 5.90. 1H NMR: δ -0.50 (6H,
FeMe), 1.92 (s, 2H, CH2), 2.28 (s, 8H, P(CH2)2P), 3.92 (s, 4H,
C5H4), 4.37 (s, 4H, C5H4), 7.09-7.63 (40H, Ph). 13C NMR: δ -17.0
(34) Lin, X. Q.; Kadish, K. M. Anal. Chem. 1985, 57, 1498.

Electronic Communication in Diiron Complexes
Organometallics, Vol. 27, No. 18, 2008 4747
(t, FeMe, 2JP-C ) 26.4 Hz), 22.9 (CH2), 27.6 (t, P(CH2)2P, JP-C
)
Synthesis of (η5-C5H5)Fe(CO)2GeMe2Fc (7). To a 50 mL THF
solution of [(η5-C5H5)Fe(CO)2]-Na+ (prepared from 2.0 g (0.011
mol) of [(η5-C5H5)Fe(CO)2]2) was added, via syringe, 3.6 g (0.011
mol) of FcGeMe2Cl at 0 °C. The solution was stirred at this
temperature for 1 h and then warmed to room temperature and
further stirred overnight. The solvent was removed under vacuum,
and the residue was extracted with 50 mL of hexanes. The solution
was filtered and dried. The residue that was obtained was placed
upon a silica column, and elution with hexanes developed a yellow
band that was collected, dried, and characterized as 7. Recrystal-
lization from hexanes afforded pure material in 75% yield. Mp:
114 °C. Anal. Calcd for C19H20Fe2GeO2: C, 49.11; H, 4.34. Found:
C, 49.02; H, 4.35. IR (THF, cm-1): 1987, 1934 (νCO). 1H NMR: δ
0.92 (s, 6H, GeMe2), 4.05 4.31(m, 14H, C5H5 + Fc). 13C NMR: δ
5.21 (GeMe2), 68.5, 70.0, 71.5 (Fc), 83.2 (C5H5), 216.2 (CO).
(η5-C5H5)Fe(cis-dppen)GeMe2Fc (7a). Mp: 203 °C dec. Anal.
Calcd for C43H42Fe2GeP2: C, 64.15; H, 5.26. Found: C, 64.02; H,
5.30. 1H NMR: δ 0.19 (s, 6H, GeMe2), 4.01-4.39 (m, 14H, C5H5
+ Fc), 6.90 (2H, CHdCH), 6.98-7.58 (20H, Ph). 13C NMR: δ
5.85 (GeMe2), 68.0, 68.2, 72.3, (Fc), 77.2 (C5H5), 129.2, 131.7,
133.0, 138.1 (Ph), 147.9 (t, CHdCH, JP-C ) 33.7 Hz). 31P NMR:
δ 100.9.
21.5 Hz), 67.7, 75.5, 79.3 (C5H4), 129.2, 132.6, 139.1, 144.0 (Ph).
31P NMR: δ 112.3.
2a-4a were prepared by a similar procedure and isolated in
65-70% yield. All these compounds were purified by recrystalli-
zation from a mixture of benzene and hexanes.
SiMe2[(η5-C5H4)Fe(CO)2Me]2 (2).13 Orange oil. Anal. Calcd
for C18H20Fe2O4Si: C, 49.12; H, 4.58. Found: C, 49.01; H, 4.50.
IR (THF, cm-1): 2010, 1956 (νCO). 1H NMR: δ 0.38 (s, 6H, FeMe),
0.40 (s, 6H, SiMe2), 4.34 (s, 4H, C5H4), 4.41 (s, 4H, C5H4). 13C
NMR: δ -22.5 (FeMe), -0.29 (SiMe2), 84.1, 86.9, 92.1 (C5H4).
29Si NMR: δ -10.6.
SiMe2[(η5-C5H4)Fe(dppe)Me]2 (2a). Mp: 148 °C dec. Anal.
Calcd for C66H68Fe2P4Si: C, 70.47; H, 6.09. Found: C, 69.95; H,
1
6.10. H NMR: δ -0.4 (6H, FeMe), 0.22 (s, 6H, SiMe2), 2.08 (s,
8H, P(CH2)2P), 4.05 (s, 4H, C5H4), 4.75 (s, 4H, C5H4), 7.10-7.68
(40H, Ph). 13C NMR: δ -20.3 (t, FeMe, 2JP-C ) 26.8 Hz), -0.61
(SiMe2), 27.6 (t, P(CH2)2P, JP-C ) 21.0 Hz), 78.4, 84.3, 87.1
(C5H4), 129.3, 131.1, 133.3, 142.0 (Ph). 29Si NMR: δ -5.9; 31P
NMR: δ 110.3.
GeMe2[(η5-C5H4)Fe(dppe)Me]2 (3a). Mp: 150 °C dec. Anal.
Calcd for C66H68Fe2GeP4: C, 67.79; H, 5.86. Found: C, 67.71; H,
5.68. 1H NMR: δ -0.5 (6 H, FeMe), 0.43 (s, 6H, GeMe2), 2.12 (s,
8H, P(CH2)2P), 4.05 (s, 4H, C5H4), 4.74 (s, 4H, C5H4), 7.12-7.70
(40H, Ph). 13C NMR: δ -20.2 (t, FeMe, 2JP-C ) 27.1 Hz), -1.30
(GeMe2), 27.5 (t, P(CH2)2P, JP-C ) 20.3 Hz), 77.9, 84.5, 89.5
(C5H4), 128.7, 132.2, 138.6, 144.4 (Ph). 31P NMR: δ 109.0.
SnMe2[(η5-C5H4)Fe(dppe)Me]2 (4a). Mp: 162 °C dec. Anal.
Calcd for C66H68Fe2P4Sn: C, 65.21; H, 5.64. Found: C, 65.01; H,
5.51. 1H NMR: δ -0.4 (6H, FeMe), 0.22 (s, 6H, SnMe2), 2.08 (s,
8H, (CH2)2), 4.05 (s, 4H, C5H4), 4.75 (s, 4H, C5H4), 7.10-7.68
(40 H, Ph). 13C NMR: δ -19.2 (t, FeMe, 2JP-C ) 27.1 Hz), -8.10
(SnMe2), 27.5 (t, (CH2)2, JP-C ) 20.3 Hz), 78.3, 86.5, 87.1 (C5H4),
132.2, 132.9, 138.6, 144.5.0 (Ph). 119Sn NMR: δ -27.5. 31P NMR:
δ 113.0.
(η5-C5H5)Fe(dppm)GeMe2Fc (7b). Mp: 194 °C dec. Anal.
Calcd for C42H42Fe2GeP2: C, 63.61; H, 5.34. Found: C, 63.52; H,
5.41. 1H NMR: δ 0.76 (s, 6H, GeMe2), 3.23 (2H, PCH2P),
4.15-4.51(m, 14H, C5H5 + Fc), 6.90-7.41(20H, Ph). 13C NMR:
δ 7.54 (GeMe2), 43.3 (t, PCH2P, JP-C ) 20.3 Hz), 68.2, 68.5, 73.2,
(Fc), 75.4 (C5H5), 129.2, 131.3, 133.2, 138.9 (Ph). 31P NMR: δ
39.3.
FcSntBu2Cl. Anal. Calcd for C18H27ClFeSn: C, 47.68; H, 6.00.
t
Found: C, 57.10; H, 5.92. 1H NMR: δ 143 (s, 18H, Bu), 4.02,
4.11, 4.30 (9H, Fc). 13C NMR: δ 30.2 (tBu), 31.9 (ipso-tBu), 68.7,
69.2, 71.4, 74.8, (Fc). 119Sn NMR: δ 72.3.
(η5-C5H5)Fe(CO)2SntBu2Fc (8). 8 was synthesized by a pro-
cedure similar to that described for 7. Mp: 122-123 °C. Anal. Calcd
for C25H32Fe2O2Sn: C, 50.47; H, 5.42. Found: C, 50.13; H, 5.19.
IR (THF, νCO, cm-1): 1990, 1935. 1H NMR: δ 1.55 (s, 18H, tBu),
4.10, 4.28, 4.37 (14H, C5H5 + Fc). 13C NMR: δ 32.7 (tBu), 33.3
(ipso-tBu), 68.7, 70.1, 74.9, 75.2 (Fc), 81.3 (C5H5), 216 (CO). 119Sn
NMR, 167.0.
General Synthetic Procedure for Diphosphine Derivatives
5a, 6a/6b, 7a/7b, and 8a. To a 30 mL THF solution of 5 (0.25 g,
0.69 mmol) in a quartz tube was added 0.28 g (0.69 mmol) of cis-
dppen, and the tube was degassed twice. The solution was then
irradiated by a Hanovia 450 W medium-pressure lamp at a distance
of 4 cm for 40-45 h. After completion of the reaction, THF was
evaporated under vacuum. The solid material obtained was washed
with hexanes and filtered. The hexane-insoluble red material was
collected, dried, and characterized as 5a. Recrystallization from
benzene and hexanes (1:2) afforded the pure compound in 68%
yield. 6a/6b, 7a/7b, and 8a were prepared by following the identical
procedure as described above for 5a in 65-70% yields.
(η5-C5H5)Fe(dmpe)SntBu2Fc (8a). Mp: 166 °C dec. Anal. Calcd
for C29H48Fe2P2Sn: C, 50.55; H, 7.02. Found: C, 50.20; H, 6.87.
1H NMR: δ 0.95 (6H, PMe2), 1.46 (4H, P(CH2)P), 1.75 (s, 18H,
tBu), 4.09, 4.19, 4.34 (14H, C5H5 + Fc). 13C NMR: δ 24.5 (PCH3),
26.0 (t, P(CH2)2P, JP-C ) 12 Hz), 30.2 (ipso-tBu), 35.1 (tBu), 69.0,
69.1, 72.9 (Fc), 76.0 (C5H5). 119Sn NMR: δ 105.2 (t, 2JSn-P ) 409
Hz). 31P NMR, 69.3.
(η5-C5H5)Fe(cis-dppen)Fc (5a). Mp: 175-178 °C dec. Anal.
Calcd for C41H36Fe2P2: C, 70.11; H, 5.17. Found: C, 70.01; H, 5.08.
1H NMR: δ 3.77 (s, 2H, Fc), 3.67 (s, 2H, Fc), 4.21 (5H, Fc), 4.54
(5H, C5H5), 7.00 (2H, CHdCH), 7.10-7.62 (20H, Ph). 13C NMR:
δ 68.3, 70.0, 73.1 (Fc), 80.7 (C5H5), 129.1, 132.6, 133.0, 133.3
(Ph), 148.0 (CHdCH). 31P NMR: δ 109.0.
Reaction of 6a/7a with AgPF6. To a 30 mL dichloromethane
solution of 6a (0.1 g, 0.13 mmol) was added AgPF6 (0.033 g, 0.13
mmol or 0.065 g, 0.26 mmol) at 0 °C. The formation of black
precipitate was observed during the addition of the AgPF6 in each
case. The contents were then stirred for 1 h, and dichloromethane
was evaporated under vacuum. Extraction of the residue with hexane
yielded the previously reported (η5-C5H5)Fe(η5-C5H4SiMe2F)31 as
a yellow solid product purified via a small silica column and
characterized by NMR spectroscopy. The remaining residue was
dissolved in acetone and filtered; removal of the acetone from the
(η5-C5H5)Fe(cis-dppen)SiMe2Fc (6a). Mp: 192-195 °C dec.
Anal. Calcd for C43H42Fe2P2Si: C, 67.91; H, 5.57. Found: C, 67.80;
1
H, 5.43. H NMR: δ 0.16 (s, 6H, SiMe2), 3.40, 4.05, 4.08, 4.29
(14H, C5H5 + Fc), 6.92 (2H, CHdCH), 7.11-7.53 (20H, Ph). 13
C
NMR: δ 7.88 (SiMe2), 68.5, 68.7, 73.4 (Fc), 78.7 (C5H5), 128.7,
-
filtrate yielded [(η5-C5H5)Fe(Ph2PCHdCHPPh2)]+PF6 as a dark
1
129.2, 132.1, 143.1 (Ph), 148.0 (t, CHdCH, JP-C ) 33.7 Hz).
2
29Si NMR: δ 26.0 (t, JSi-P ) 45.7 Hz). 31P NMR: δ 100.4.
red solid. This compound was purified by washing with benzene
until the unreacted 6a was washed away. The reaction of 7a with
AgPF6 was performed in a similar way and yielded (η5-C5H5)Fe-
(η5-C5H4GeMe2F) and [CpFe(Ph2PCHdCHPPh2)]+PF6.
(η5-C5H5)Fe(dppm)SiMe2Fc (6b). Mp: 180 °C dec. Anal. Calcd
for C42H42Fe2P2Si: C, 67.39; H, 5.66; Found: C, 67.01; H, 5.51.
1H NMR: δ 0.73 (s, 6H, SiMe2), 3.20 (2H, PCH2P), 3.95, 4.08,
4.26 (14H, C5H5 + Fc), 6.91-7.94 (20H, Ph). 13C NMR: δ 8.69
(GeMe2), 43.4 (t, PCH2P, 1JP-C ) 20.1 Hz), 68.4, 68.6, 73.8 (Fc),
76.4 (C5H5), 129.1, 131.3, 133.5, 143.0 (Ph). 29Si NMR: δ 26.7 (t,
2JSi-P ) 44.5 Hz). 31P NMR: δ 39.0.
(η5-C5H5)Fe(η5-C5H4GeMe2F). Mp: 66-67 °C. Anal. Calcd for
C12H15FFeGe: C, 46.99; H, 4.93. Found: C, 46.95; H, 4.85. 1H NMR
3
(C6D6): δ 0.62 (d, 6H, GeMe2, JH-F ) 6.0 Hz), 4.03 (5H, Cp,
Fc), 4.15 (2H, C5H4), 4.22 (2H, C5H4). 13C NMR (C6D6): δ 0.39

4748 Organometallics, Vol. 27, No. 18, 2008
Kumar et al.
(d, GeMe2, 2JC-F ) 16.0 Hz), 68.6 (C5H5), 71.5 (C5H4), 72.6 (C5H4).
ESI (MS): m/z 306.0 (M+), 287.0 (M+ - F).
squares on F2 values for all reflections using the SHELXL-97
program. All non-hydrogen atoms were assigned anisotropic
displacement parameters, and hydrogen atoms were constrained
to ideal geometries with fixed isotropic displacement parameters.
(η5-C5H5)Fe(Ph2PCHdCHPPh2)]+PF6-. Mp: 178-182 °C dec.
Anal. Calcd for C31H27F6FeP3: C, 56.22; H, 4.11. Found: C, 55.45;
1
H, 4.01. H NMR (acetone-d6): δ 4.93 (s, 5H, C5H5), 7.18 (2H,
CHdCH), 7.26-7.80 (20H, Ph). 13C NMR (acetone-d6): 90.6
Acknowledgment. Financial support from the Welch
Foundation (Grant Nos. AH-546 and A0-0001) and an NIH
SCORE grant are gratefully acknowledged.
(C5H5), 134.6, 136.5, 137.7, 138.6 (Ph), 150.8 (CHdCH). 31P NMR
-
(acetone-d6): -137.0 (septet, PF6
(PCHdCHP).
,
1JP-F ) 710.0 Hz), 105.0
Supporting Information Available: CIF files giving crystal-
lographic data for 6b and 9 and figures detailing the UV/vis
spectroelectrochemistry of 1a and 4a and a correlation between
the dielectric constant. This material is available free of charge via
the Internet at http://pubs.acs.org. Crystal data are also available
from the Cambridge Crystallographic Database as file numbers
CCDC 661327 (for 6b) and 661328 (for 9).
X-ray Crystallography
Crystals of 6b and 9 suitable for X-ray analysis were mounted
in a Bruker APEX CCD diffractometer equipped with mono-
chromated Mo KR radiation. Crystallographic measurements
were carried out at 296(2) K. Details of the crystal data and
refinement parameters are described in Table 1. The structure
was solved by direct methods and refined by full-matrix least
OM8004004