Synthesis and reactivity of [2]ferrocenophanes with C-Ge and C-Sn bridges

Article abstract of DOI:10.1021/om049650s

The synthesis, characterization and reactivity of carbogerma[2] ferrocenophanes, (η-C₅Me₄)Fe(η-C₅H ₄)CH ₂GeR₂, 11 (a,R=Ph;b, R=Me) and carbostanna[2]ferrocenophanes, (η-C₅Me₄)Fe(η- C₅H₄)CH ₂SnR₂, 12 (a,R=tBu; b, R=Mes; c, R=Me) were investigated. It was found that x-ray diffraction analysis of these species possesses moderate ring-tilt with values in the range α=10.99(2)-11.81(5)° for 11a,b and α=6.64(2)-7.5(1)° for 12a-c. Reactions of 11b and 12a with strong acids resulted in the formation of ring-opened species. Treatment of 12b with HCl resulted in selective Sn-Mes bond cleavage.

Full text of DOI:10.1021/om049650s

6116
Organometallics 2004, 23, 6116-6126
Synthesis and Reactivity of [2]Ferrocenophanes with
C-Ge and C-Sn Bridges
Alexandra Bartole-Scott, Rui Resendes,† Frieder Ja¨kle,‡ Alan J. Lough,
and Ian Manners*
Department of Chemistry, University of Toronto, 80 St. George Street,
Toronto, Ontario, Canada, M5S 3H6
Received May 14, 2004
The synthesis, characterization, and reactivity of novel carbogerma[2]ferrocenophanes,
(η-C5Me4)Fe(η-C5H4)CH2GeR2, 11 (a, R ) Ph; b, R ) Me), and carbostanna[2]ferrocenophanes,
(η-C5Me4)Fe(η-C5H4)CH2SnR2, 12 (a, R ) tBu; b, R ) Mes; c, R ) Me), are reported.
Compounds 11a,b and 12a-c were isolated as orange crystals from the reaction of (η-C5-
Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA with Cl2ER2 (E ) Ge, R ) Ph, Me or E ) Sn, R ) tBu,
1
Mes, Me) and were characterized by H, 13C, and 119Sn NMR, UV/vis, MS, and in repre-
sentative cases elemental analysis. X-ray diffraction analysis of these species revealed
structures possessing moderate ring-tilt with values in the range R ) 10.99(2)-11.81(5)°
for 11a,b and R ) 6.64(2)-7.5(1)° for 12a-c. The presence of a small or moderate degree of
ring-strain was further substantiated through the observation of only a small (ca. 25-30
nm) bathochromic shift in the UV/vis absorption maxima when compared to pentamethyl-
ferrocene. Attempts to induce thermal ring-opening polymerization (ROP) of 11b and 12a-c
proved to be unsuccessful and led only to decomposition at temperatures above 300 °C.
Treatment of 11b and 12a-c with amines such as pyridine and 4-(dimethylamino)pyridine
did not result in ROP of these compounds. In addition, treatment of 11b and 12a-c with
Pt(cod)2, Pt(PEt3)3, PtCl2, Karstedt’s catalyst (a Pt(0)-divinyltetramethyldisiloxane complex),
PtCl2(COD), and nBuLi for 11b and 12c and 2,2′-azobisisobutyronitrile (AIBN) in the
presence of Bu3SnH for 12a,b failed to induce any of the insertion or ring-opening reactions
that are known for the more highly strained [1]ferrocenophane analogues. However, reactions
of 11b and 12a with strong acids such as HCl and 12a with triflic acid (CF3SO3H) resulted
in the formation of the corresponding ring-opened species, (η-C5H5)Fe(η-C5Me4CH2GeMe2-
Cl), 14, (η-C5H5)Fe(η-C5Me4CH2Sn(tBu)2Cl), 15, and (η-C5H5)Fe(η-C5Me4CH2Sn(tBu)2OSO2-
CF3), 16, via selective ipso-Cp-Ge or ipso-Cp-Sn bond cleavage. Treatment of 12b with
HCl resulted in selective Sn-Mes bond cleavage, affording (η-C5H4)Fe(η-C5Me4)CH2SnMesCl,
17.
Introduction
The ROP of strained silicon-bridged [1]ferrocenophanes
such as 1 ((ERx)y ) SiMe2) has been particularly well
studied and provides a well-established route to high
molecular weight polyferrocenylsilanes (e.g., 2, (ERx)y
) SiMe2).3,4 This ROP methodology has also been
extended to a range of other [1]ferrocenophanes (1) with
a variety of p-block elements incorporated in the bridge
(e.g., E ) B, Si, Ge, Sn, P, S)5-7 and has allowed the
synthesis of well-defined homopolymers with interesting
physical and preceramic properties9-16 and also am-
The class of organometallic cyclic species known as
[1]ferrocenophanes has been the focus of much recent
research due to the ring-strain and resulting reactivity
imparted by the presence of a single atom bridge be-
tween the cyclopentadienyl (Cp) ligands.1-7 Molecules
of this type may serve as surface derivatization agents8
and as monomers in ring-opening polymerization (ROP)
reactions.3,4
* Corresponding author. E-mail: imanners@chem.utoronto.ca.
† Present address: Lanxess Inc., 1265 Vidal St. S., Sarnia, Ontario
N7T 7M2, Canada.
(6) (a) Bucaille, A.; Le Borgne, T.; Ephritikhine, M.; Daran, J.-C.
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Ed. Engl. 1995, 34, 1837. (c) Zu¨rcher, S.; Gramlich, V.; Togni, A. Inorg.
Chim. Acta 1999, 291, 355. (d) Brunner, H.; Klankermayer, J.; Zabel,
M. J. Organomet. Chem. 2000, 601, 211. (e) Herberhold, M.; Hertel,
F.; Milius, W.; Wrackmeyer, B. J. Organomet. Chem. 1999, 582, 352.
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Inorg. Chem. 1990, 29, 1817.
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Lough, A. J.; Manners, I. Organometallics 1995, 14, 5503. (c) Mizuta,
T.; Onishi, M.; Miyoshi, K. Organometallics 2000, 19, 5005. (d)
Peckham, T. J.; Massey, J. A.; Honeyman, C. H.; Manners, I.
Macromolecules 1999, 32, 2830. (e) Durfey, D. A.; Kirss, R. U.;
Frommen, C.; Feighery, W. Inorg. Chem. 2000, 39, 3506. (f) Mizuta,
T.; Imamura, Y.; Miyoshi, K. J. Am. Chem. Soc. 2003, 125, 2068.
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‡ Present address: Department of Chemistry, Rutgers University,
73 Warren St., Newark, NJ 07102.
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Am. Chem. Soc. 1979, 101, 6501.
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114, 6246.
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Science 2001, 294, 1664.
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McIntosh, D. F.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 1997,
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10.1021/om049650s CCC: $27.50 © 2004 American Chemical Society
Publication on Web 11/25/2004

Synthesis and Reactivity of [2]Ferrocenophanes
Organometallics, Vol. 23, No. 26, 2004 6117
phiphilic block copolymers with intriguing applications
in supramolecular chemistry.17,18 There has also been
recent interest in the use of polyferrocenylsilanes as
redox-responsive photonic crystals19 and as etch resists
for the nanopatterning of subtrates.20,21
logues. Previous work has shown that highly strained
hydrocarbon-bridged monomers 6 (M ) Fe, R ) H, Me,
E2 ) CH2CH2) and the analogous [2]ruthenocenophane
6 (M ) Ru, R ) H, E2 ) CH2CH2) undergo thermal
ROP,24,25 whereas ring-opening metathesis polymeriza-
tion of [2]ferrocenophane 6 (M ) Fe, R ) H, E2 ) CHd
CH) has also been described.26 In contrast, [2]metallo-
cenophanes with Si-Si bridges such as 6 (M ) Fe or
Ru, E2 ) SiMe2SiMe2) are relatively unstrained and
resist ROP,27 whereas an analogue with a Ge-Ge bridge
(6: M ) Fe, E2 ) GeMe2GeMe2) has been polymerized.28
The reactivity displayed by [1]ferrocenophanes is a
function of not only the ring-strain, as indicated, in part,
by the angle between the planes of the Cp rings (R),22
but also the kinetic lability which is dependent on ipso-
Cp carbon-bridging element bond strength. This is
illustrated by a comparison of the stability of the highly
strained [1]thiaferrocenophane 3 [R ) 31°, ring-strain
(as estimated by DSC) ) 130 ( 5 kJ‚mol-1]5 and the
significantly less strained di-tert-butyl[1]stannaferro-
cenophane 4a (R ) 14°, ring-strain (as estimated by
DSC) ) 36 ( 5 kJ‚mol-1).23 Under inert atmosphere, 3
is stable in solution at ambient temperature, whereas
4 undergoes ROP even in solution at 25 °C, presumably
as a result of the weak Cp-Sn bonds.
Recently, we have synthesized and studied a series
of novel [2]ferrocenophanes, 8-10, with unsymmetrical
C-E bridges in which the covalent radius of E and
hence the ring-strain present are varied.29 The least
strained of these species (8, R ) 11.8(1)°) was found to
be completely resistant to polymerization under all
conditions studied, whereas the significantly more
strained species 9a (R ) 14.9(3)°), 9b (R ) 18.2(2)°), and
10 (R ) 18.5(1)°) were all found to readily undergo ROP
reactions.
To further explore the factors that govern the reactiv-
ity and polymerizability of the [2]ferrocenophanes, we
report here our studies of analogues of 8-10 with C-Ge
and C-Sn bridges (11a,b, 12a-c). The impact of the
presence of weak C-E (E ) Sn or Ge) bonds on the
significantly less strained [2]ferrocenophane structure
was envisaged to be a focal point of this work.
While considerable work has focused on the study of
the reactivity of [1]ferrocenophanes, comparatively less
attention has been devoted to [2]ferrocenophane ana-
(9) Kulbaba, K.; Manners, I. Macromol. Rapid. Commun. 2001, 22,
711.
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S.; Sokolov, I.; Lam, C. N. C.; Neumann, A. W.; Manners, I.; Ozin, G.
A. Langmuir 2000, 16, 9609.
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Raju, N. P.; Greedan, J. E.; Ozin, G. A.; Manners, I. Science 2000, 287,
1460.
(12) Hmyene, M.; Yassar, A.; Escorne, M.; Percheronguegan, A.;
Garnier, F. Adv. Mater. 1994, 6, 564.
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Am. Chem. Soc. 1996, 118, 7578.
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Dementiev, V. V.; Pannell, K. H. Macromolecules 2000, 33, 7107.
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Inorg. Organomet. Polym. 2000, 10, 169.
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7669.
(17) Massey, J. A.; Winnik, M. A.; Manners, I.; Chan, V. Z.-H.;
Ostermann, J. M.; Enchelmaier, R.; Spatz, J. P.; Mo¨ller, M. J. Am.
Chem. Soc. 2001, 123, 3147.
(22) For theoretical calculations on strained metallocenophanes,
see: (a) Ref 5a. (b) Barlow, S.; Drewitt, M. J.; Dijkstra, T.; Green, J.
C.; O’Hare, D.; Whittingham, C.; Wynn, H. H.; Gates, D. P.; Manners,
I.; Nelson, J. M.; Pudelski, J. K. Organometallics 1998, 17, 2113. (c)
Green, J. C. Chem. Soc. Rev. 1998, 263.
(18) Wang, X.-S.; Arsenault, A.; Ozin, G. A.; Winnik, M. A.; Manners,
I. J. Am. Chem. Soc. 2003, 125, 12686.
(19) Arsenault, A.; Miguez, H.; Kitaev, V.; Ozin, G. A.; Manners, I.
Adv. Mater. 2003, 15, 503.
(20) (a) Clendenning, S. B.; Han, S.; Coombs, N.; Paquet, C.; Rayat,
M. S.; Grozea, D.; Broderson, P. M.; Sodhi, R. N. S.; Yip, C. M.; Lu,
Z.-H.; Manners, I. Adv. Mater. 2004, 16, 291. (b) Clendenning, S. B.;
Aouba, S.; Rayat, M. S.; Grozea, D.; Sorge, J. B.; Broderson, P. M.;
Sodhi, R. N. S.; Lu, Z.-H.; Yip, C. M.; Freeman, M. R.; Ruda, H. E.;
Manners, I. Adv. Mater. 2004, 16, 215. (c) Cheng, A. Y.; Clendenning,
S. B.; Yang, G.; Lu, Z.-H.; Yip, C. M.; Manners, I. Chem. Commun.
2004, 780.
(23) (a) Ja¨kle, F.; Rulkens, R.; Zech, G.; Massey, J. A.; Manners, I.
J. Am. Chem. Soc. 2000, 122, 4231. (b) Baumgartner, T.; Ja¨kle, F.;
Rulkens, R.; Zech, G.; Lough, A. J.; Manners, I. J. Am. Chem. Soc.
2002, 124, 10062. (c) Rulkens, R.; Lough, A. J.; Manners, I. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1805.
(24) Nelson, J. M.; Rengel, H.; Manners, I. J. Am. Chem. Soc. 1993,
115, 7035.
(25) Nelson, J. M.; Nguyen, P.; Petersen, R.; Rengel, H.; Macdonald,
P. M.; Lough, A. J.; Manners, I.; Raju, N. P.; Greedan, J. E.; Barlow,
S.; O’Hare, D. Chem. Eur. J. 1997, 3, 573.
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Chem. Mater. 2003, 15, 3663. (b) Cheng, J. Y.; Ross, C. A.; Thomas, E.
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6118 Organometallics, Vol. 23, No. 26, 2004
Bartole-Scott et al.
Results and Discussion
1. Synthesis and Characterization of C-Sn and
C-Ge Bridged [2]Ferrocenophanes, 11a,b and
12a-c. The C-E bridged [2]ferrocenophanes (11a,b,
12a-c) targeted in this study were obtained as crystal-
line solids through the reaction of (η-C5Me4)Fe(η-C5H4-
Li)CH2Li‚xTMEDA (TMEDA ) N,N,N′,N′-tetramethyl-
ethylenediamine) with the corresponding organoelement
dihalides Cl2R2E (E ) Sn or Ge) in yields ranging from
26% to 49%. The former species is readily formed by
the deprotonation of pentamethylferrocene [(η-C5Me5)-
Fe(η-C5H5) ) Cp*FeCp] in a preparation modified from
literature.30 1H, 13C, and 119Sn NMR analysis of the
resulting products confirmed the proposed structures.
Of note in the 13C NMR spectra of 11a,b and 12a-c
are the ipso-Cp and ipso-Cp′ (Cp′ ) C5Me4) 13C reso-
nances, which range from 72.8 to 86.9 ppm and 86.2 to
92.1 ppm, respectively. In the moderately strained [1]-
ferrocenophane analogues, such as 4a, the resonances
for the ipso-Cp carbons are found at 34.9 ppm,23c con-
sistent with a deviation from planar sp2 hybridization
at the ipso-Cp carbon atom.1,31,32 The ipso-Cp 13C reson-
ances found in 11a,b and 12a-c are consistent with
those found in the nonbridged compounds fc(SnMe2Cl)2
(δ ) 70.7 ppm) (fc ) (η-C5H4)Fe(η-C5H4)), fc(SnMe2H)2
(δ ) 65.8 ppm),33 and Fc(GeMe2Cl) (δ ) 72.4 ppm) (Fc
) (η-C5H5)Fe(η-C5H4)).34 In addition, 119Sn NMR reso-
nances for 12a-c were consistent with the assigned
structures. By comparing the NMR characterization
data with that for the analogous [1]ferrocenophanes, it
would appear that the [2]ferrocenophanes 11a,b and
12a-c possess relatively nonstrained structures. How-
ever, it is important to note that the corresponding ipso-
Cp 13C resonances for the significantly strained [2]-
ferrocenophanes, 8-10, also possess similar chemical
shifts.29 This suggests that the ring-strain present
within this [2]ferrocenophane framework cannot be com-
pletely inferred from the ipso-Cp 13C resonances alone
and thus requires examination via other techniques.
Figure 1. UV/visible spectra (hexanes) of Cp*FeCp, 11a,b,
and 12a-c.
to the lowest energy d-d transition is shifted to a longer
wavelength by up to 60 nm when compared to analogous
nonbridged ferrocenes.5a,32 The UV/visible spectra in
hexanes revealed absorptions at 462 nm (ꢀ ) 173 M-1
cm-1) for 11a and 461 nm (ꢀ ) 203 M-1 cm-1) for 11b,
which have been assigned to the lowest energy d-d
transitions (Figure 1) and which are similar to the
absorptions observed for the C-Si bridged [2]ferro-
cenophane, 8 (R ) 11.8(1)°, λmax ) 458, ꢀ ) 120 M-1
cm-1). Similarly, the absorptions observed for 12a-c
were observed in the range from 453 to 462 nm. These
values are significantly but not dramatically red-shifted
by ca. 25-30 nm from that of Cp*FeCp (λmax ) 430 nm,
ꢀ ) 120 M-1 cm-1, in hexanes). This indicates that an
appreciable but not high degree of strain is present in
structures 11 and 12.
2. X-ray Structural Analysis of [2]Ferro-
cenophanes 11a,b and 12a-c. To further investigate
the amount of ring-strain present in 11a,b and 12a-c,
single-crystal X-ray diffraction studies were undertaken.
Suitable single crystals were obtained through low-
temperature (ca. -30 °C) recrystallization of 11a,b and
12c from minimal hexanes and of 12a,b from minimal
Et2O/MeCN (50/50 v/v). In all cases, only one molecule
was found in the unit cell. The molecular structure of
11a is shown in Figure 2, and selected bond lengths and
angles are given in Table S1 (see Supporting Informa-
tion). Of note in the structure of 11a is the relatively
moderate R angle (ca. 11.81(5)°) found between the
planes of the Cp and Cp′ rings. This R angle in addition
to the staggering angle (σ ) 11.5(8)°) (σ ) angle with
which the Cp rings deviate from an eclipsed confirma-
tion) and torsional angle (τ ) 16.5(3)°) (τ ) angle
between the CH2-GeR2 bond and the plane containing
the Cp centroids and iron atom) would suggest that 11a
possesses some degree of ring-strain (cf. 10, R ) 18.5-
Previous studies on [1]- and [2]ferrocenophanes have
demonstrated that the absorption maximum attributed
(30) Chao, S.; Robbins, J. L.; Wrighton, M. S. J. Am. Chem. Soc.
1983, 105, 181.
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Ziembinski, R.; Lough, A. J.; Manners, I. Organometallics 1993, 12,
823. (b) Peckham, T. J.; Foucher, D. A.; Lough, A. J.; Manners, I. Can.
J. Chem. 1995, 73, 2069. (c) Nelson, J. M.; Lough, A. J.; Manners, I.
Organometallics 1994, 13, 3703.
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(29) Resendes, R.; Nelson, J. M.; Fischer, A. B.; Ja¨kle, F.; Bartole,
A.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2001, 123, 2116.
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Chem. 1980, 193, 345.
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A. J.; Manners, I. New J. Chem. 1998, 1409.

Synthesis and Reactivity of [2]Ferrocenophanes
Organometallics, Vol. 23, No. 26, 2004 6119
Figure 4. Molecular structure of 12a showing 30%
thermal ellipsoids. Hydrogen atoms are omitted for clarity.
Figure 2. Molecular structure of 11a showing 30%
thermal ellipsoids. Hydrogen atoms are omitted for clarity.
Figure 5. Molecular structure of 12b showing 30%
thermal ellipsoids. Hydrogen atoms are omitted for clarity.
Figure 3. Molecular structure of 11b showing 30%
thermal ellipsoids. Hydrogen atoms are omitted for clarity.
(1)°, ∆HROP ) -13 ( 5 kJ mol-1). In addition, careful
examination of the structure of 11a revealed a â(Ge)
(angle between Cp plane and ipso-Cp-Ge bond) angle
of 17.6(2)° and a â(CH2) (angle between Cp′ plane and
ipso-Cp′-CH2 bond) angle of 7.2(3)°. Given that in a
nonbridged system â angles approach zero, these values
suggest again that ring-strain may be present in 11a.
The molecular structure of 11b shown in Figure 3 has
very similar characteristics to 11a. As was seen in the
structure of 11a, the structure of 11b suggests a small
degree of ring-strain, as evidenced by the relatively
moderate R angle (R ) 10.99(2)°). As expected, the R
angle of compound 11b is slightly smaller compared
with structure 8 (R ) 11.8(1)°) due to the larger covalent
radius of germanium versus silicon (Ge: rcov ) 1.22 Å;
Si: rcov ) 1.17 Å).35 In addition, the bond lengths of the
CH2-E bridge for structures 11a,b are larger than that
of 8, ranging from 1.983(3) to 1.985(5) Å (cf. 8: CH2-Si
) 1.914(3) Å).29
The molecular structures of 12a-c are similar to
those of 11a,b and are shown in Figures 4-6. The larger
covalent radius of tin compared with germanium (Sn:
rcov ) 1.40 Å)35 is demonstrated by the smaller R angle
values observed for species 12a-c ranging from R )
Figure 6. Molecular structure of 12c showing 30%
thermal ellipsoids. Hydrogen atoms are omitted for clarity.
6.64(2)° for 12a to R ) 7.5(1)° for 12c. The CH2-Sn
bridge bond length values for 12a-c range from 2.184-
(3) to 2.191(2) Å, which are longer than the correspond-
ing CH2-Ge bond lengths of 11a,b, as expected. For
comparison, selected angles for the more highly strained
species 8 and 10 along with the corresponding values
for 11a,b and 12a-c are given in Table 1. Selected bond
lengths and angles for 11b and 12a-c are given in
Tables S2-S5 (see Supporting Information).
3. Electrochemical Studies of [2]Ferroceno-
phanes, 11b and 12a-c. The [2]ferrocenophanes 11b
and 12a-c were also characterized by cyclic voltam-
metry. Previous studies of the electrochemical properties
of [1]- and [2]ferrocenophanes have identified one-
electron oxidation processes that are reversible except
for the most strained examples.5a,29,36 It was also found
(35) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Oxford
University Press: New York, 1984.

6120 Organometallics, Vol. 23, No. 26, 2004
Table 1. Comparison of Structural Data for 8, 10, 11a,b, and 12a-ca
Bartole-Scott et al.
bridging moiety
R [deg]
â1 [deg]
â2 [deg]
σ [deg]
τ [deg]
λmax [nm]c (ꢀ, M-1cm-1
)
8b
CH2-SiMe2
CH2-S
CH2-GePh2
CH2-GeMe2
CH2-Sn(tBu)2
CH2-SnMes2
CH2-SnMe2
11.8(1)
18.5(1)
11.81(5)
10.99(2)
6.64(2)
7.1(1)
7.3(3)
9.3(2)
7.2(3)
6.1(2)
4.1(2)
3.8(2)
3.3(2)
17.9(3)
10.6(2)
17.6(2)
17.4(2)
18.5(1)
17.3(1)
19.1(1)
0.1(2)
10.0(2)
11.5(8)
0.2(5)
3.0(4)
2.8(3)
4.3(3)
0.5(2)
17.9(3)
16.5(3)
4.4(2)
3.6(2)
3.9(2)
4.9(2)
458 (120)
475 (243)
462 (173)
461 (203)
462 (153)
454 (131)
453 (221)
10b
11a
11b
12a
12b
12c
7.5(1)
a â1 ) â(CH2), â2 ) â(E), where E ) Si, S, Ge, Sn. b See ref 29. c In hexanes.
that cyclic voltammetric analysis of a 0.005 M solutionof
11b in CH2Cl2 (with 0.1 M [Bu4N][PF6] as the support-
ing electrolyte) revealed the presence of a chemically
reversible redox wave centered at -274 mV versus the
ferrocene/ferrocenium redox couple. Compounds 12a-c
demonstrated similar reversible redox waves in the
range E1/2 ) -279 to -332 mV. The observed redox
couples were found centered at more negative potentials
than that observed for ferrocene, consistent with the
more electron-rich iron center in these species arising
from the presence of a tetramethylated-Cp ligand.29
4. Attempted Thermal Polymerization of [2]-
Ferrocenophanes, 11a,b and 12a-c. The thermal
polymerization behavior of 11b was explored by heating
a sample in an evacuated tube at temperatures up to
250 °C for up to 72 h. 1H NMR analysis of the contents
of the tube resulted in unreacted 11b as well as peaks
corresponding to decomposition to small quantities of
free pentamethylferrocene. These observations suggest
that there is inadequate ring-strain to induce thermal
ROP of 11b.
To investigate the thermal polymerization behavior
of 12a,b, differential scanning calorimetry studies were
undertaken. In the temperature range of 25-300 °C,
no exothermic transitions attributable to ROP were
detected. For 12a, a melt transition was found at 77 °C,
while for 12b, a similar transition was observed at 114
°C. When attempts were made to heat samples of 12a,b
beyond 300 °C, decomposition was observed in every
case, which led to the formation of an insoluble black
material. These observations again suggest that there
is little ring-strain present in 12a,b. Despite the pres-
ence of a bridging moiety possessing weak Cp-Sn
bonds, the amount of ring-strain present appears to be
insufficient to facilitate ROP at a temperature below
that at which decomposition occurs.37
resulting product resulted in very broad peaks, perhaps
due to the formation of trace amounts of magnetic
species such as Fe metal; however only unreacted 12c
could be isolated.
5. Ring-Opening and Insertion Reactions of [2]-
Ferrocenophanes 11a,b and 12a-c. To gain insight
into the ring-strain dependence of the reactivity of Ge-
Cp and Sn-Cp bonds, a series of ring-opening reactions
with 11b and 12a-c were attempted.
(a) Attempted Ring-Opening Reactions with 11b
and 12a,c with Amine Nucleophiles and Radical
Initiators. Recently it has been shown that reaction of
the [1]stannaferrocenophane, 4, with amines such as
pyridine leads to ROP.23 However, when samples of 12a
were treated with pyridine at either 25 or 60 °C, no
reaction was detected by 1H NMR even after 72 h.
Similarly, no reaction was observed at 25 °C or at
elevated temperatures in the presence of the much
stronger nucleophile 4-(dimethylamino)pyridine for 11b,
12a, and 12c. In an attempt to generate a ring-opened
species through a radical pathway as previously de-
tected for tin-bridged [1]ferrocenophanes,23 samples of
12a were treated with AIBN at 25 and 60 °C in the
presence of Bu3SnH. After 72 h, no ring-opening was
detected by 1H NMR. This is in contrast to the reactions
of 4 with AIBN and Bu3SnH, in which ring-opening
reactions do occur.23
(b) Attempted Reactions of 11b, 12a, and 12c
with Platinum(0) Complexes and ROP Precata-
lysts. Compound 4a reacts with equimolar amounts of
Pt(cod)2 to form the corresponding platinastanna[2]-
ferrocenophane insertion compound, 13.31
In a manner analogous to 11b, the thermal poly-
merization of 12c was also attempted by heating a
sample in an evacuated tube at temperatures up to 250
°C for up to 72 h. 1H NMR characterization of the
(36) Pudelski, J. K.; Foucher, D. A.; Honeyman, C. H.; Lough, A. J.;
Manners, I.; Barlow, S.; O’Hare, D. Organometallics 1995, 14, 2470.
(37) A reviewer made the suggestion that the replacement of a weak
E-Cp bond in a [1]ferrocenophane with a bridging atom E (E ) Ge or
Sn) by a stronger E-CH2 bond may decrease polymerizability if this
bond is cleaved in the polymerization mechanism. However, all the
current evidence from studies to date indicate that during thermal
polymerizations of ferrocenophanes it is the E-Cp bond that breaks,
and such a bond is also present in the [2]ferrocenophanes 11 and 12
reported in this study. In addition, previous work on analogous, but
more tilted and hence more strained [2]ferrocenophanes containing
C-S and C-P bridges has demonstrated that these species do
polymerize, even though one can similarly argue that weak E-Cp
bonds (E ) S or P) have been replaced by stronger E-CH2 bonds
relative to [1]ferrocenophane analogues. This indicates that the
replacement of E-Cp by a E-CH2 bond is unlikely to be mechanisti-
cally significant. For relevant discussions see: (a) Pudelski, J. K.;
Manners, I. J. Am. Chem. Soc. 1995, 117, 7265. (b) Sheridan, J. B.;
Lough, A. J.; Manners, I. Organometallics 1996, 15, 2195. (c) Ref 29.
In addition to work by Tanaka et al. and ourselves
concerning the transition metal-catalyzed ROP of germa-
[1]ferrocenophanes,38,39 Mochida and co-workers have
recently reported platinum- and palladium-catalyzed
ROP of a digerma[2]ferrocenophane to yield high mo-
lecular weight polymer.28 In contrast, the reaction of 12a
with Pt(cod)2, at 25 and 60 °C, resulted only in the
formation of colloidal Pt(0), with no evidence for Pt(0)
insertion into the ipso-Cp-Sn bond. Treatment of 11b
and 12c with PtCl2, Karstedt’s catalyst (Pt(0)), and
(38) Reddy, N. P.; Yamashita, H.; Tanaka, M. J. Chem. Soc., Chem.
Commun. 1995, 2263.
(39) Peckham, T. J.; Massey, J. A.; Edwards, M.; Foucher, D. A.;
Manners, I. Macromolecules 1996, 29, 2396.

Synthesis and Reactivity of [2]Ferrocenophanes
Organometallics, Vol. 23, No. 26, 2004 6121
PtCl2(COD) yielded only starting material, as evidenced
by H NMR. Similarly, treatment of 11b and 12a with
equimolar amounts of Pt(PEt3)3 at 25 °C as well as at
elevated temperatures failed to induce insertion reac-
tions.
with equimolar amounts of HCl, the corresponding
CH2-SnMesCl-bridged [2]ferrocenophane, 17, was ob-
tained in 50% yield. As a result of the difficulty
encountered in recrystallizing 17, the proposed struc-
ture was verified through the reaction of 17 with excess
CuMes, after which complete retroconversion to 12b was
1
(c) Attempted Photolytic Ring-Opening of 11b.
We have shown very recently that the ROP of [1]-
silaferrocenophanes can be achieved photolytically in
the presence of an initiator such as Na[η-C5H5] via
cleavage of the Fe-Cp bond.40 The ring-opening of 11b
was attempted using photolysis in the presence of an
initiator using analogous procedures. Solutions of 11b
in THF were treated with catalytic and equimolar
amounts of Na[η-C5H5] and irradiated for 3-6 h. In each
case, only unreacted 11b was detected by 1H NMR.
Similarly, there was no reaction under analogous condi-
tions with a 5-fold excess of Na[η-C5H5]. In addition,
treatment of a solution of 11b with bis(diphenylphos-
phino)ethane and irradiation for 6 h yielded no change
1
confirmed by H, 13C, and 119Sn NMR.
(e) Attempted Reaction of 11b and 12c with an
Anionic Ring-Opening Initiator. The anionic ROP
of [1]silaferrocenophanes is a useful route to monodis-
perse polyferrocenylsilanes which allows molecular
weight control and access to block copolymer architec-
tures.17,43 In the presence of 0.01 equiv of n-butyllithium
(nBuLi), no indication of ring-opening of compound 11b
1
as observed by H NMR.
(d) Reaction of 11a,b and 12a-c with Strong
Protic Acids. The reaction of strained [1]ferroceno-
phanes with strong acids generally results in the
formation of ring-opened products possessing a proto-
nated Cp ring.2,41 In addition, the cleavage of Sn-aryl
bonds and sp2-C-Sn bonds (such as the ipso-Cp-Sn
bond of 12a-c) with protic acids is well known in both
strained and unstrained systems.42 Thus, despite the
moderate degree of ring-strain in 12a-c, the presence
of sp2-C-Sn bonds would be expected to still allow ipso-
Cp-Sn bond cleavage reactions. The reactivity of the
ipso-Cp-Ge bond of 11a,b is expected to be similar.
Indeed, when samples of 11b and 12a were treated with
an equimolar amount of HCl (in Et2O), quantitative
cleavage of the E-Cp bond (E ) Ge, Sn) occurred,
resulting in the corresponding ring-opened species, 14
and 15. Similarly, when a sample of 12a was treated
with an equimolar amount of triflic acid (CF3SO3H), the
corresponding ring-opened species, 16, was isolated.
In addition, when 12c was treated with 1 equiv of
HCl, the corresponding product (η-C5Me4)Fe(η-C5H5)CH2-
SnMe2Cl was detected by 1H NMR after 10 min.
However, after the solvent was removed, the only
product that could be isolated was free Cp*FeCp.
1
or 12c was detected by H NMR after 2 h. Similarily,
when compounds 11b and 12c were treated with
equimolar amounts of nBuLi, followed by quenching of
any potential lithiated product with Me3SiCl, only
unreacted starting material was isolated.
6. X-ray Structural Analysis of Ring-Opened
Species 15 and 16. Previous work has shown that
certain ferrocenyl derivatives, 18a-c, possess Fe‚‚‚E
interactions whose magnitude (as indicated by the â
angle; angle with which the ipso-Cp-E bond bends
toward the Fe atom) depends on the degree of Lewis
acidity at E.44-47
To probe the possible existence of an Fe‚‚‚Sn interac-
tion, X-ray structural analyses of compounds 15 and 16
were undertaken. The structure of 15 is shown in Figure
7, and selected bond lengths and angles are given in
Table S6 (see Supporting Information). Examination of
the structure of 15 reveals that the CH2-Sn(tBu)2Cl
moiety is located above the plane of the Cp′ ligand,
thereby resulting in no significant Fe‚‚‚Sn interaction.
The structure of 16 is shown in Figure 8, and selected
bond lengths and angles are given in Table S7 (see
Supporting Information). As was observed in the struc-
ture of 15, the CH2-Sn(tBu)2OSO2CF3 moiety of 16 is
also above the plane of the Cp′ ring, and thus no
Unlike 12a, which possesses only one sp2-C-Sn bond,
12b possesses both a Cp-Sn bond and two Sn-aryl-C
bonds. Interestingly, when a sample of 12b was treated
(40) Tanabe, M.; Manners, I. J. Am. Chem. Soc. 2004, 126, 11434.
For previous work on phosphorus-bridged [1]ferrocenophanes see ref
7f.
(43) Ni, Y.; Rulkens, R.; Manners, I. J. Am. Chem. Soc. 1996, 118,
4102.
(44) Foucher, D. A.; Edwards, M.; Burrow, R. A.; Lough, A. J.;
Manners, I. Organometallics 1994, 13, 4959.
(41) MacLachlan, M.; Bourke, S. C.; Lough, A. J.; Manners, I. J.
Am. Chem. Soc. 2000, 122, 2126.
(45) Behrens, U. J. Organomet. Chem. 1979, 182, 89.
(46) Koridze, A. A. Russ. Chem. Rev. 1986, 55, 113.
(47) (a) Appel, A.; Ja¨kle, F.; Priermeier, T.; Schmid, R.; Wagner, M.
Organometallics 1996, 15, 1188. (b) Scheibitz, M.; Bats, J. W.; Bolte,
M.; Lerner, H.-W.; Wagner, M. Organometallics 2004, 23, 940.
(42) (a) Bhattacharya, S. N.; Raj, P.; Husain, I. Indian J. Chem.,
Sect. A 1978, 16A, 1108. (b) Olszowy, H. A.; Kitching, W. Organome-
tallics 1984, 3, 1670. (c) Uhlig, W. J. Organomet. Chem. 1991, 409,
377.

6122 Organometallics, Vol. 23, No. 26, 2004
Bartole-Scott et al.
inherently relatively high ring-strain present in those
species. The intriguing ability of 6 (M ) Fe, E2 ) GeMe2-
GeMe2) to undergo ROP28 despite the presence of a very
low degree of strain (R ) ca. 4°) appears to be a
consequence of the relatively labile Ge-Ge bond, whereas
11a,b, which are clearly more strained, are unreactive
under similar reaction conditions.
Experimental Section
Materials. All reagents, unless otherwise specified, were
purchased from Aldrich Chemical Co. and were used as
received. Solvents were dried by standard procedures and
distilled immediately prior to use. Cl2SnMes2,48 pentamethyl-
ferrocene,49 and CuMes50 were prepared according to standard
literature procedures.
Equipment. All reactions and manipulations were per-
formed under an inert atmosphere (prepurified N2) using
either standard Schlenk techniques or an inert-atmosphere
Figure 7. Molecular structure of 15 showing 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
1
glovebox (MBraun). H (400 MHz) and 13C NMR (100.5 and
75.5 MHz) spectra were recorded on Varian Unity 400 or
Varian XL 300 spectrometers. The 111.8 MHz 119Sn NMR
spectra were recorded on a Varian XL 300 spectrometer. All
1
solution H and 13C NMR spectra were referenced internally
to residual protonated solvent shifts. 119Sn NMR spectra were
referenced externally to SnMe4. UV/visible spectra were
obtained using a Perkin-Elmer Lambda 900 UV/vis/near-IR
spectrophotometer in hexanes at concentrations of 1.0 mmol‚L-1
.
Cyclic voltammetry (CV) was performed using an Epsilon EC
instrument equipped with a Au electrode and an Ag/AgCl
reference electrode. The solutions were prepared using CH2-
Cl2 (previously dried over CaH2 and distilled under N2) and
[NBu4][PF6]. The concentration of [NBu4][PF6] was 0.1 M, and
the solutions were prepared in concentrations of 0.001-0.005
M. All measurements were made under N2 atmosphere at a
scan rate of 100 mV/s, and ferrocene was used as an internal
standard. Potentials are reported versus the ferrocene/ferro-
cenium couple. Mass spectra were obtained with the use of a
VG 70-250S mass spectrometer operating in electron impact
(EI) mode. The calculated isotopic distribution for each ion was
in agreement with experimental values. The photoirradiation
experiments were performed by placing the reaction flask next
to a 125 W high-pressure Hg arc lamp (Philips). The emission
was filtered by Pyrex glass (λ > ca. 300 nm). The thermal
behavior of the CH2-Sn-bridged monomers, 12a,b, was stud-
ied using a Perkin-Elmer DSC-7 differential scanning calo-
rimeter equipped with a TAC-7 instrument controller. Ther-
mograms were calibrated with the melt transitions of hexane
and indium and were obtained at a heating rate of 10 °C/min
under a nitrogen atmosphere. Elemental analyses were per-
formed by Quantitative Technologies, Inc., Whitehouse, NJ.
In addition, elemental analyses were obtained using a Perkin-
Elmer Series II 2400 CHNS analyzer maintained by the
Analest facility at the University of Toronto.
Figure 8. Molecular structure of 16 showing 30% thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
significant Fe‚‚‚Sn interaction is present in this case
either. These observations suggest that the Sn centers
present in compounds 15 and 16 do not possess the
degree of Lewis acidity necessary to induce an electro-
philic interaction with the electron-rich iron center.
Summary
The synthesis of novel carbogerma[2]ferrocenophanes
11a,b and carbostanna[2]ferrocenophanes 12a-c was
accomplished via the reaction of (η-C5Me4)Fe(η-C5H4-
Li)CH2Li‚xTMEDA with the appropriate dichlorodior-
ganogermanes and dichlorodiorganostannanes. The struc-
tures of 11a,b and 12a-c, as determined by X-ray
structural analysis, revealed the presence of very mod-
erate R angles with values ranging from R ) 10.99(2)°
to 11.81(5)° for the C-Ge-bridged species 11a,b and
from R ) 6.64(2)° to 7.5(1)° for the C-Sn-bridged
analogues 12a-c, which is indicative of a small to
moderate degree of ring-strain. The results of this study
suggest that the presence of diminished ring-strain
renders these species much less reactive than their [1]-
ferrocenophane counterparts (4, 5) or [2]ferrocenophanes
such as 6, 9a,b, and 10 to ring-opening reactions.
Furthermore, it can be concluded that the high reactiv-
ity displayed by the Sn-bridged and Ge-bridged [1]-
ferrocenophanes, 4a,b and 5, is a consequence of the
presence of weak Cp-E (E ) Sn or Ge) bonds and the
Synthesis of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA.
Note: Reaction stoichiometries were calculated based on (η-
1
C5Me4)Fe(η-C5H4Li)CH2Li‚0.66TMEDA. H NMR analysis of
reactions of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA with Me3-
SiCl suggests that x ) 2; however, it was found that by
employing a coefficient of x ) 0.66 the overall yields were
improved.
To a suspension of pentamethylferrocene (30 g) in hexanes
(500 mL) were added 2.0 equiv of TMEDA (35 mL) and 4.0
equiv of nBuLi (1.6 M in hexanes). The reaction mixture was
allowed to stir at 25 °C for 48 h, after which the brick red
(48) Ja¨kle, F.; Manners, I. Organometallics 1999, 18, 2628.
(49) Bunel, E. E.; Valle, L.; Manriquez, J. M. Organometallics 1985,
4, 1680.
(50) Tsuda, T.; Yazawa, T.; Watanabe, K.; Fujii, T.; Saegusa, T. J.
Org. Chem. 1981, 46, 192.

Synthesis and Reactivity of [2]Ferrocenophanes
Organometallics, Vol. 23, No. 26, 2004 6123
precipitate was collected by filtration under N2. The resulting
pyrophoric red-orange material was washed with 3 × 200 mL
aliquots of hexanes and dried under vacuum. Yield: 35 g (86%)
Synthesis of (η-C5Me4)Fe(η-C5H4)CH2GePh2, 11a. To a
suspension of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA (1.0 g, 2.9
mmol) in Et2O (200 mL) kept at -78 °C was added slowly with
stirring a solution of Cl2GePh2 (1.03 g, 3.5 mmol) in 50 mL of
Et2O. The resulting solution was allowed to warm to 25 °C, at
which point the reaction mixture was filtered under N2,
resulting in the isolation of a clear orange solution. Solvent
removal under vacuum (for 24 h to ensure removal of any trace
amounts of TMEDA) resulted in the isolation of a light orange
gummy material. Recrystallization of this material from
hexanes at -30 °C yielded 11a as orange crystals. Yield: 0.51
g (37%). 1H NMR (400 MHz, C6D6, 25 °C): δ 7.76-7.74 (m,
4H, C6H5-Ge), 7.25-7.20 (m, 4H, C6H5-Ge), 7.10-7.00 (m,
2H, C6H5-Ge), 4.38 (ps t, 2H, C5H4), 3.87 (ps t, 2H, C5H4),
2.95 (s, 2H, CH2-Ge), 2.16 (s, 6H, C5Me4), 1.74 (s, 6H, C5Me4)
ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ 140.0 (ipso-C6H5),
134.4 (o-C6H5), 129.5 (p-C6H5), 129.1 (m-C6H5), 86.2 (ipso-C5-
Me4), 81.5 (C5Me4), 81.3 (C5Me4), 80.6 (C5H4), 75.0 (C5H4), 72.8
(ipso-C5H4), 19.2 (CH2), 13.1 (C5Me4), 12.0 (C5Me4). UV-vis
(hexanes): λmax 462 nm (ꢀ ) 173 M-1 cm-1). MS (70 eV, EI):
m/z (%) 482 (56) [M+], 256 (100) [M+] - GePh2. HR-MS: calcd
mV vs Fc/Fc+ couple. MS (70 eV, EI): m/z (%) 488 (50) [M+],
374 (100) [M+] - 2 C(CH3)3, 254 (51) [M+] - Sn(tBu)2. HR-
MS: calcd for C23H3656Fe120Sn 488.1188 g‚mol-1, found 488.1186
g‚mol-1
.
Synthesis of (η-C5Me4)Fe(η-C5H4)CH2SnMes2, 12b. To
a suspension of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA (1.0 g,
2.9 mmol) in Et2O (100 mL) kept at -78 °C was added slowly
with stirring a suspension of Cl2Sn(Mes)2 (1.36 g, 3.2 mmol)
in 50 mL of Et2O. The resulting solution was allowed to warm
to 25 °C, at which point the reaction mixture was filtered under
N2, resulting in the isolation of a clear orange solution. Solvent
removal under vacuum (for 24 h to ensure removal of any trace
amounts of TMEDA) resulted in the isolation of a light orange
powder. Recrystallization of this material at -30 °C from a
concentrated Et2O/MeCN (50/50 v/v) solution afforded 12b as
orange crystals. Yield: 0.80 g (45%). 1H NMR (400 MHz, C6D6,
25 °C): δ 6.80 (s/d, J(117/119Sn/H) ) 20 Hz, 4H; m-Mes), 4.29
(ps t, J(H/H) ) 3 Hz, 2H; C5H4), 3.79 (ps t, J(H/H) ) 3 Hz,
2H; C5H4), 3.04 (s/d, J(117/119Sn/H) ) 64 Hz, 2H, CH2-Sn), 2.61
(s, 12H; o-Mes), 2.21 (s, 6H; C5Me4), 2.14 (s, 6H; p-Mes), 1.78
(s, 6H, C5Me4) ppm. 13C NMR (75.5 MHz, C6D6, 25 °C): δ 144.4
(J(117/119Sn/13C) ) 35 Hz; o-Mes), 141.0 (p-Mes), 138.4 (J(117/119Sn/
13C) ) 15 Hz; ipso-Mes), 128.9 (J(117/119Sn/13C) ) 30 Hz, m-Mes),
90.3 (ipso-C5Me4), 86.9 (ipso-C5H4), 81.4 (J(117/119Sn/13C) ) 56
Hz; C5H4), 80.4 (C5Me4), 79.9 (C5Me4), 72.1 (J(117/119Sn/13C) )
47 Hz; C5H4), 26.0 (CH2-Sn), 25.6 (J(117/119Sn/13C) ) 50 Hz;
o-Mes), 21.0 (p-Mes), 12.8 (C5Me4), 11.7 (C5Me4) ppm. 119Sn
NMR (111.8 MHz, C6D6, 25 °C): δ -60.4 (CH2-Sn) ppm. UV/
vis (hexanes): λmax 454 nm (ꢀ ) 131 M-1 cm-1). CV (1 mM):
E1/2 ) -280 mV, Eox ) -162 mV, Ered ) -398 mV vs Fc/Fc+
couple. MS (70 eV, EI): m/z (%) 612 (100) [M+], 493 (8) [M+]
- Mes, 254 (54) [M+] - Sn(Mes)2. Anal. Calcd for C33H40FeSn
(611): C 64.85, H 6.60. Found: C 64.62, H 6.53.
for C27H2856FeGe 482.0752 g‚mol-1, found 482.0760 g‚mol-1
.
Synthesis of (η-C5Me4)Fe(η-C5H4)CH2GeMe2, 11b. To a
suspension of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA (3.0 g, 8.7
mmol) in Et2O (250 mL) kept at -78 °C was added slowly with
stirring a solution of Cl2GeMe2 (1.51 mg, 8.7 mmol) in 100 mL
of Et2O. The resulting solution was allowed to warm to 25 °C,
at which point the reaction mixture was filtered under N2,
resulting in the isolation of a clear orange solution. Solvent
removal under vacuum (for 24 h to ensure removal of any trace
amounts of TMEDA) resulted in the isolation of a light orange
gummy material. Recrystallization of this material from
hexanes at -30 °C yielded 11b as orange crystals. Yield: 0.98
Synthesis of (η-C5Me4)Fe(η-C5H4)CH2SnMe2, 12c. To a
suspension of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA (5.0 g,
14.5 mmol) in Et2O (200 mL) kept at -78 °C was added slowly
with stirring a solution of Cl2SnMe2 (3.8 g, 17.4 mmol) in 100
mL of Et2O. The resulting solution was allowed to warm to 25
°C, at which point the reaction mixture was filtered under N2,
resulting in the isolation of a clear orange solution. Solvent
removal under vacuum (for 24 h to ensure removal of any trace
amounts of TMEDA) resulted in the isolation of a light orange
powder. Recrystallization of this material at -30 °C from a
concentrated hexanes solution afforded 12c as orange crystals.
1
g (33%). H NMR (400 MHz, C6D6, 25 °C): δ 4.20 (ps t, 2H,
C5H4), 3.82 (ps t, 2H, C5H4), 2.22 (s, 6H, C5Me4), 2.20 (s, 2H,
CH2-Ge), 1.81 (s, 6H, C5Me4), 0.50 (s, 6H, Me2-Ge) ppm. 13
C
NMR (400 MHz, C6D6, 25 °C): δ 87.9 (ipso-C5Me4), 80.8 (C5-
Me4), 80.4 (C5Me4), 80.4 (C5H4), 78.9 (ipso-C5H4), 72.4 (C5H4),
22.4 (CH2-Ge), 13.2 (C5Me4), 12.4 (C5Me4), 0.9 (Me2-Ge) ppm.
UV-vis (hexanes): λmax 461 nm (ꢀ ) 203 M-1 cm-1), CV (5
mM): E1/2 ) -274 mV, Eox ) -93 mV, Ered ) -454 mV vs Fc/
Fc+ couple. MS (70 eV, EI): m/z (%) 358 (100) [M+], 254 (22)
[M+] - GeMe2. Anal. Calcd for C17H24FeGe (357): C 57.22, H
6.77. Found: C 57.22, H 6.73.
1
Yield: 1.5 g (26%). H NMR (400 MHz, C6D6, 25 °C): δ 4.16
(ps t, J(H/H) ) 2 Hz, 2H; C5H4), 3.83 (ps t, J(H/H) ) 3 Hz,
2H; C5H4), 2.22 (s, 6H, C5Me4), 2.19 (s, 2H; CH2-Sn), 1.82 (s,
6H; C5Me4), 0.36 (s, 6H; SnMe2) ppm. 13C NMR (100 MHz,
C6D6, 25 °C): δ 92.1 (ipso-C5Me4), 80.7 (J(117/119Sn/13C) ) 35
Hz; C5H4), 79.4 (C5Me4), 78.9 (ipso-C5H4), 75.2 (C5Me4), 72.3
(J(117/119Sn/13C) ) 40 Hz; C5H4), 17.5 (CH2-Sn), 12.6 (C5Me4),
11.7 (C5Me4), -6.5 (SnMe2) ppm. 119Sn NMR (111.8 MHz, C6D6,
25 °C): δ 32.9 ppm (CH2-Sn) ppm. UV/vis (hexanes): λmax
453 nm (ꢀ ) 221 M-1 cm-1). CV (5 mM): E1/2 ) -279 mV, Eox
) -107 mV, Ered ) -450 mV vs Fc/Fc+ couple. MS (70 eV,
EI): m/z (%); 404 (78) [M+], 374 (49) [M+] - 2 Me, 254 (100)
[M+] - SnMe2. HR-MS: calcd for C17H2456Fe120Sn 404.0249
Synthesis of (η-C5Me4)Fe(η-C5H4)CH2Sn(tBu)2, 12a. To
a suspension of (η-C5Me4)Fe(η-C5H4Li)CH2Li‚xTMEDA (5.0 g,
14.5 mmol) in Et2O (200 mL) kept at -78 °C was added slowly
with stirring a solution of Cl2Sn(tBu)2 (4.85 g, 16 mmol) in
100 mL of Et2O. The resulting solution was allowed to warm
to 25 °C, at which point the reaction mixture was filtered under
N2, resulting in the isolation of a clear orange solution. Solvent
removal under vacuum (for 24 h to ensure removal of any trace
amounts of TMEDA) resulted in the isolation of a light orange
powder. Recrystallization of this material at -30 °C from a
concentrated Et2O/MeCN (50/50 v/v) solution afforded 12a as
orange crystals. Yield: 3.5 g (49%). 1H NMR (400 MHz, C6D6,
25 °C): δ 4.30 (ps t, J(H/H) ) 1 Hz, 2H; C5H4), 3.82 (ps t, J(H/
H) ) 3 Hz, 2H; C5H4), 2.34 (s/d, J(117/119Sn/H) ) 40 Hz, 2H;
CH2-Sn), 2.28 (s/d, J(117/119Sn/H) ) 48 Hz, 6H, C5Me4), 1.82
(s/d, J(117/119Sn/H) ) 40 Hz, 6H; C5Me4), 1.42 (s/d, J(117/119Sn/
H) ) 62 Hz, 18H; CMe3) ppm. 13C NMR (100 MHz, C6D6, 25
°C): δ 90.2 (ipso-C5Me4), 80.9 (J(117/119Sn/13C) ) 40 Hz; C5H4),
79.9 (C5Me4), 78.8 (ipso-C5H4), 78.7 (C5Me4), 72.2 (J(117/119Sn/
g‚mol-1, found 404.0235 g‚mol-1
.
Attempted Thermal Polymerization of 11b. A sample
of 11b (ca. 0.1 g) was sealed in an evacuated Pyrex tube and
heated at temperatures of 130, 150, 180, and 250 °C for
approximately 24 h at each temperature. The melt changed
color from an orange to red, but there was no observable
increase in viscosity. The resulting material was characterized
by 1H NMR and contained unreacted 11b as well as (η-C5Me5)-
Fe(η-C5H5).
Attempted Ring-Opening Reactions of 11b. A sample
of 11b (ca. 0.05 g, 0.14 mmol) was dissolved in minimal toluene
(5 mL). To this solution was added (a) 1 vol % Karstedt’s
catalyst (Pt(0)), (b) 1 wt % PtCl2, (c) 4 mol % PtCl2(COD), (d)
1 equiv (0.09 g) of Pt(PEt3)3, (e) 1 equiv (17.1 mg) of (dimethyl-
13C) ) 40 Hz; C5H4), 31.9 (CMe3), 30.8 (CMe3), 14.2 (J(117/119
-
Sn/13C) ) 280 Hz; CH2-Sn), 12.8 (C5Me4), 11.8 (C5Me4) ppm.
119Sn NMR (111.8 MHz, C6D6, 25 °C): δ -24.9 ppm (CH2-
Sn) ppm. UV/vis (hexanes): λmax 462 nm (ꢀ ) 153 M-1 cm-1).
CV (1 mM): E1/2 ) -332 mV, Eox ) -247 mV, Ered ) -418

6124 Organometallics, Vol. 23, No. 26, 2004
Bartole-Scott et al.
Table 2. Selected Crystal, Data Collection, and
Refinement Parameters for 11a,b
amino)pyridine (DMAP), and (f) excess DMAP (0.15 g). The
solution was stirred for 24 h at room temperature and
alternatively at 120 °C for each sample, after which the solvent
was removed under vacuum. In the cases of Pt(0) and PtCl2,
a slight broadening of the peaks was observed in the 1H NMR;
however only unreacted 11b could be isolated. In all other
11a
11b
empirical formula
fw
C
27H28FeGe
C17H24FeGe
356.80
480.93
temperature, K
wavelength, Å
cryst syst
space group
a, Å
150(1)
150(1)
0.71073
triclinic
P1h
0.71073
triclinic
P1h
1
cases, only unreacted 11b was detected by H NMR.
Attempted Anionic ROP of 11b. To solutions of 11b (0.05
g, 0.14 mmol) in THF (0.5 mL) were added n-BuLi (1.6 M in
hexanes) [(i) 1 equiv (87.5 µL), (ii) 10 mol % (8.75 µL)], and
the mixtures were stirred for 2 h. A slight excess of TMSCl
(1.1 equiv, 19.5 µL) was added to each reaction, and all solvent
was removed under vacuum. In each case, only unreacted 11b
7.7235(9)
11.7744(16)
12.8300(18)
88.313(6)
79.831(7)
72.316(7)
1093.8(2)
2
7.3330(4)
8.5260(5)
14.2880(10)
74.826(4)
89.732(4)
66.607(4)
786.31(8)
2
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
1
was detected by H NMR.
F
calc, g cm-3
1.460
2.048
1.507
2.818
Attempted Photolytic Ring-Opening of 11b. To solu-
tions of 11b (0.05 g, 0.14 mmol) in THF (1 mL) were added (i)
4 mol % (2.8 µL) of Na[η-C5H5] (2.0 M in THF), (ii) 1 equiv (70
µL) of Na[η-C5H5], (iii) 5 equiv (0.35 mL) of Na[η-C5H5], and
(iv) 1 equiv (56 mg) of bis(diphenylphosphino)ethane. The
solution was irradiated for up to 6 h and kept at a temperature
of 5 °C in a water bath. In each case, only unreacted 11b could
abs coeff µ(Mo KR),
mm-1
F(000)
496
368
cryst size, mm3
θ range for data
collection, deg
index ranges
0.20 × 0.12 × 0.12
0.35 × 0.30 × 0.28
2.81 to 25.12
2.70 to 27.50
0 e h e 9
12 e k e 14
-15 e l e 15
0 e h e 9
-9 e k e 11
-18 e l e 18
8124
1
be detected by H NMR.
no. of reflns collected 7946
Attempted Thermal Polymerization of 12a. Samples of
12a (ca. 0.1 g) were sealed in an evacuated Pyrex tube and
heated at temperatures of 200, 250, and 300 °C for 48 h. For
polymerization attempts carried out at 200 and 250 °C, only
no. of indep reflns
completeness to
θ ) 27.50°
3834 [R(int) ) 0.09] 3562 [R(int) ) 0.059]
98.3%
98.4%
abs corr
multiscan
0.7912 and 0.6849
multiscan
0.5058 and 0.4387
max. and min.
transmn
1
unreacted 12a was detected by H NMR. At 300 °C, decom-
refinement method
full matrix least-
full matrix least-
squares on F2
3562/0/179
position to an intractable black material was observed.
squares on F2
no. of data/restraints/ 3834/0/267
params
Attempted Ring-Opening Reactions with 12a. To a
solution of 12a (0.02 g, 0.04 mmol) in 0.6 mL of C6D6 was added
(a) 1 equiv (3.3 µL) of pyridine, (b) 1 equiv (0.005 g) of DMAP,
(c) 1 equiv of AIBN (0.0067 g) and Bu3SnH (0.012 g), (d) 1 equiv
(0.017 g) of Pt(cod)2, and (e) 1 equiv (0.027 g) of Pt(PEt3)3. The
reaction solutions were allowed to stir at (i) 25 °C for 72 h
and (ii) 60 °C for 72 h. In each case, only unreacted 12a was
GoF on F2
0.972
1.035
R1a [I>2σ(I)]
wR2b (all data)
extinction coeff
largest diff peak and
hole, e Å-3
R1 ) 0.0586
wR2 ) 0.1456
0.0062(18)
R1 ) 0.0396
wR2 ) 0.1041
0.019(3)
0.815 and -0.793
0.859 and -1.011
a R1 ) ∑||Fo| - |Fo||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
1
detected by H NMR.
Table 3. Selected Crystal, Data Collection, and Refined Parameters for 12a-c
12a
12b
12c
empirical formula
fw
C
23H36FeSn
C33H40FeSn
611.19
100.0(1)
0.71073
triclinic
P1h
C17H24FeSn
402.90
150(1)
0.71073
monoclinic
P21/n
487.06
173(2)
temperature, K
wavelength, Å
cryst syst
space group
a, Å
0.71073
monoclinic
P21/n
12.138(3)
11.4142(8)
16.3104(14)
90
7.9662(2)
12.5838(2)
14.0272(4)
93.573(15)
91.389(14)
101.775(15)
1372.91(6)
2
9.0434(4)
13.9146(5)
13.0246(6)
90
b, Å
c, Å
R, deg
â, deg
100.666(11)
90
97.815(2)
90
γ, deg
volume, Å3
Z
2220.6(6)
4
1623.73(12)
4
F
calc, g cm-3
1.457
1.478
1.648
abs coeff µ(Mo KR), mm-1
F(000)
1.781
1.457
2.417
1000
628
808
cryst size, mm3
θ range for data collection,
deg
0.46 × 0.45 × 0.43
0.25 × 0.25 × 0.23
0.26 × 0.22 × 0.05
2.54 to 27.00
2.94 to 27.47
2.59 to 27.51
index ranges
0 e h e 15
0 e h e 10
-11 e h e 11
0 e k e 14
-16 e k e 15
-17 e k e 17
-20 e l e 20
5080
-18 e l e 18
-14 e l e 16
no. of reflns collected
no. of indep reflns
completeness to θ ) 27.50°
abs corr
19 947
11 426
4853 [R(int) ) 0.0231]
6239 [R(int) ) 0.025]
99.1%
3696 [R(int) ) 0.0416]
99.1%
empirical
multiscan (Denzo-SMN)
0.7304 and 0.7121
full-matrix least-squares on F2
6239/0/327
semiempirical from equivalents
0.892 and 0.686
full-matrix least-squares on F2
3696/0/179
max. and min. transmn
refinement method
no. of data/restraints/
params
full-matrix least-squares on F2
4853/0/237
GoF on F2
1.052
1.047
1.044
R1a [I>2σ(I)]
R1 ) 0.0259
wR2 ) 0.0685
0.0009(2)
R1 ) 0.0233
wR2 ) 0.0603
0.0023(4)
R1 ) 0.0349
wR2 ) 0.0927
0.0018(5)
wR2b (all data)
extinction coeff
largest diff peak and hole, e Å-3
0.427 and -0.380
0.815 and -0.538
1.063 and -1.473
a R1 ) ∑||Fo| - |Fo||/∑|Fo|. b wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2
.
2
2

Synthesis and Reactivity of [2]Ferrocenophanes
Organometallics, Vol. 23, No. 26, 2004 6125
Table 4. Selected Crystal, Data Collection, and
Refined Parameters for 15 and 16
Attempted Thermal Polymerization of 12c. A sample
of 12c (ca 0.1 g) was sealed in an evacuated Pyrex tube and
heated at temperatures of 150, 180, and 250 °C for ap-
proximately 24 h at each temperature. Additionally, the
sample was kept at 250 °C for 72 h. The melt changed color
slightly to dark orange; however there was no observable
increase in viscosity. Very broad peaks were observed in the
1H NMR of the resulting material; however only unreacted 12c
could be isolated.
15
16
empirical formula
fw
temperature, K
wavelength, Å
cryst syst
space group
a, Å
C
23H37ClFeSn
C24H37F3FeO3SSn
637.14
523.52
100(2)
100(2)
0.71073
triclinic
P1h
0.71073
monoclinic
P21/c
9.1561(3)
13.8154(5)
21.3416(6)
90
96.483(2)
90
2682.35(15)
4
9.9871(6)
11.5504(7)
12.4486(5)
66.703(3)
75.478(3)
69.329(2)
1223.65(12)
2
Attempted Ring-Opening Reactions with 12c. To a
solution of 12c (0.04 g, 0.1 mmol) in 1 mL of C6D6 was added
(a) 0.1 wt % Karstedt’s catalyst, (b) 4 mol % PtCl2(COD), (c) 1
wt % PtCl2, (d) 2 equiv (24 mg) of DMAP, and (e) 10 mol %
(1.2 mg) DMAP. The solutions were allowed to stir for (a) 72
h at 25 °C and heated for (b) 72 h at 60-80 °C. In each case,
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
1
only unreacted 12c was detected by H NMR.
Attempted Anionic ROP of 12c. To solutions of 12c (0.04
g, 0.10 mmol) in THF (0.5 mL) were added n-BuLi (1.6 M in
hexanes) [(i) 1 equiv (61.8 µL), (ii) 10 mol % (6.18 µL)], and
the mixtures were stirred for 2 h. A slight excess of TMSCl
(1.1 equiv, 13.8 µL) was added to each reaction, and all solvent
was removed under vacuum. In each case, only unreacted 12c
F
calc, g cm-3
1.421
1.727
1.578
1.593
abs coeff µ(Mo KR),
mm-1
F(000)
536
1296
cryst size, mm3
θ range for data
collection, deg
index ranges
0.25 × 0.12 × 0.10 0.20 × 0.15 × 0.15
2.65 to 27.45
2.68 to 27.50
1
was isolated and characterized by H NMR.
0 e h e 12
-13 e k e 14
-15 e l e 16
30 906
5404 [R(int) )
0.038]
97.1%
0 e h e 11
0 e k e 17
-27 e l e 27
20 254
6039 [R(int) )
0.038]
98.1%
Synthesis of (η-C5Me4)Fe(η-C5H5)CH2GeMe2Cl, 14. One
equivalent of HCl‚Et2O (0.11 mL, 1 M in Et2O) was added to
a solution of 11b (0.04 g, 0.11 mmol) in C6D6. Upon addition,
the solution became yellow. This mixture was stirred for an
additional 24 h and yielded a slightly greenish solution. The
solvent was removed under vacuum, and the resulting powder,
no. of reflns collected
no. of indep reflns
completeness to
θ ) 27.50°
abs corr
1
14, was recrystallized from hexanes. Yield: 35 mg (80%). H
multiscan
(Denzo-SMN)
0.8463 and 0.6721 0.7961 and 0.7412
multiscan
(Denzo-SMN)
NMR (400 MHz, C6D6, 25 °C): δ 3.58 (s, 5H, C5H5), 2.29 (s,
2H, CH2-Ge), 1.78 (s, 6H, C5Me4), 1.76 (s, 6H, C5Me4), 0.35
(s, 6H, Me2GeCl) ppm. 13C NMR (100 MHz, C6D6, 25 °C): δ
81.4 (ipso-C5Me4), 79.6 (C5Me4), 79.4 (C5Me4), 73.4 (C5H5), 21.6
(CH2-Ge), 12.4 (C5Me4), 11.8 (C5Me4), 3.8 (-Ge(Me2)Cl) ppm.
MS (70 eV, EI): m/z (%) 394 (40) [M+], 255 (100) [M+] - GeMe2-
Cl.
max. and min.
transmn
refinement method
full-matrix least-
full-matrix least-
squares on F2
6039/0/298
squares on F2
no. of data/restraints/ 5404/30/265
params
GoF on F2
1.040
1.051
R1 ) 0.0267
wR2 ) 0.0605
Synthesis of (η-C5Me4)Fe(η-C5H5)CH2Sn(tBu)2Cl, 15. To
a solution of 12a (0.20 g, 0.41 mmol) in 10 mL of toluene was
added at 25 °C 1 equiv (410 µL) of HCl (1.0 M in Et2O). The
reaction solution was allowed to stir at 25 °C for 6 h, at which
point the solvent was removed under vacuum. Compound 15
was obtained almost quantitatively as an orange powder.
Crystals for X-ray structural analysis were obtained through
low-temperature (-30 °C) recrystallization from minimal CH3-
R1a [I>2σ(I)]
wR2b (all data)
extinction coeff
largest diff peak and
hole, e Å-3
R1 ) 0.0431
wR2 ) 0.1004
0.0013(6)
1.054 and -0.935
0.642 and -0.537
a R1 ) ∑||Fo| - |Fo||/∑|Fo|. b wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2
.
1
CN. Yield: 0.21 g (96%). H NMR (400 MHz, C6D6, 25 °C): δ
3.59 (s, 5H; C5H5), 2.54 (s/d, J(117/119Sn/H) ) 44 Hz, 2H; CH2-
Sn), 1.96 (s, 6H; C5Me4), 1.81 (s, 6H; C5Me4), 1.15 (s/d,
J(117/119Sn/H) ) 76 Hz, 18H; CMe3) ppm. 13C NMR (100.5 MHz,
C6D6, 25 °C): δ 84.3 (ipso-C5Me4), 80.3 (C5Me4), 78.1 (C5Me4),
71.9 (C5H5), 35.6 (CMe3), 29.0 (CMe3), 16.3 (CH2-Sn), 12.3
(C5Me4), 11.5 (C5Me4) ppm. 119Sn NMR (111.8 MHz, C6D6, 25
°C): δ 53.9 (CH2-Sn) ppm. MS (70 eV, EI): m/z (%); 524 (13)
[M+], 255 (100) [M+] - Sn(tBu)2Cl.
Synthesis of (η-C5Me4)Fe(η-C5H5)CH2Sn(tBu)2OSO2CF3,
16. To a solution of 12a (0.10 g, 0.20 mmol) in 10 mL of toluene
was added at 25 °C 1 equiv (18.1 µL) of CF3SO3H. The reaction
solution was allowed to stir at 25 °C for 6 h, at which point
the solvent was removed under vacuum. Compound 16 was
obtained almost quantitatively as an orange powder. Crystals
for X-ray structural analysis were obtained through low-
temperature (-30 °C) recrystallization from minimal CH3CN.
Yield: 0.12 g (92%). 1H NMR (400 MHz, C6D6, 25 °C): δ 3.58
(br, 5H; C5H5), 2.83 (br, 2H; CH2-Sn), 1.88 (br, 6H; C5Me4),
1.75 (br, 6H; C5Me4), 1.09 (s/br, J(117/119Sn/H) ) 109 Hz, 18H;
CMe3) ppm. 119Sn NMR (111.8 MHz, C6D6, 25 °C): δ 118.2 (br,
CH2-Sn) ppm. MS (70 eV, EI): m/z (%) 638 (6) [M+], 255 (100)
[M+] - Sn(tBu2)OSO2CF3. Anal. Calcd for C24H37F3FeO3SSn
(638): C 45.24, H 5.85. Found: C 45.68, H 5.94.
added at 25 °C 1 equiv (82 µL) of HCl (1.0 M in Et2O). The
reaction solution was allowed to stir at 25 °C for 6 h, at which
point the solvent was removed under vacuum. Compound 17
was obtained as an orange oil in 50% yield, as determined by
1H NMR. Attempts to recrystallize 17 proved to be unsuccess-
ful. Therefore, the identity of 17 was confirmed through the
reaction of 17 with excess CuMes in order to regenerate the
starting material, 12b. For 17: 1H NMR (400 MHz, C6D6, 25
°C): δ 6.71 (br, 1H; m-Mes), 6.81 (br, 1H; m-Mes), 4.88 (br,
C5H4), 4.10 (br, C5H4), 3.81 (br, C5H4), 3.73 (br, C5H4), 3.12 (d,
J(H/H) ) 16 Hz, 1H; CH2-Sn), 3.72 (d, J(H/H) ) 16 Hz, 1H,
CH2-Sn), 2.44 (br, o-Mes), 2.40 (br, C5Me4), 2.15 (br, o-Mes),
2.05 (br, p-Mes), 1.92 (br, C5Me4), 1.72 (br, C5Me4), 1.70 (br,
C5Me4) ppm. 119Sn NMR (111.8 MHz, C6D6, 25 °C): δ 36.3
(CH2-Sn) ppm.
Stoichometric Ring-Opening Reactions of 12c. One
equivalent of HCl‚Et2O (99 µL, 1 M in Et2O) was added to a
solution of 12c (0.04 g, 0.099 mmol) in C6D6. Upon addition,
the solution became yellow. Within 10 min, ring-opened
product was observed in 90% yield by 1H NMR. 1H NMR (400
MHz, C6D6, 25 °C): δ 3.62 (s, C5H5), 2.01 (br, CH2-Sn), 1.79
(br, C5Me4), 0.37 (s, -SnMe2Cl) ppm. The solvent was removed
under vacuum; however the product could not be isolated. After
24 h, only (η-C5Me5)Fe(η-C5H5) could be observed by 1H NMR.
Synthesis of (η-C5Me4)Fe(η-C5H4)CH2SnMesCl, 17. To
a solution of 12b (0.05 g, 0.08 mmol) in 5 mL of toluene was

6126 Organometallics, Vol. 23, No. 26, 2004
Bartole-Scott et al.
X-ray Crystallography. Selected crystal, data collection,
and refinement parameters for 11a,b, 12a-c, 15, and 16 are
given in Tables 2, 3, and 4. Selected angles are given in Table
1, and selected bond lengths and bond angles are given in
Tables S1 (11a), S2 (11b), S3 (12a), S4 (12b), S5 (12c), S6
(15), and S7 (16) (see Supporting Information). Single-crystal
X-ray diffraction data were collected at low temperature (see
Tables 2-4) using a Nonius Kappa-CCD diffractometer and
monochromated Mo KR radiation (λ ) 0.71073 Å). The data
were integrated and scaled using the Denzo-SMN package.51
The SHELXTL/PC package was used to solve and refine the
structures.52 Refinement was by full-matrix least-squares on
F2 using all data (negative intensities included). Hydrogen
atoms were placed in calculated positions and included in the
refinement in riding motion approximations.
the Cp ring and the tert-butyl group refined to 79:21 and 74:
26, respectively.
Acknowledgment. We thank the Natural Science
and Engineering Research Council of Canada (NSERC)
for funding this research. A.B. is grateful to the Ontario
Government for an OGSST scholarship. R.R. is grateful
to NSERC for a postgraduate scholarship. In addition,
I.M. is grateful to the Government of Canada for a CRC
award (2001-2008), the Ontario Government for a
PREA award (1999-2004), and the University of Tor-
onto for a McLean Fellowship (1997-2003). We also
wish to thank Dr. Cory Jaska for supplying [Pt(PEt3)4].
Supporting Information Available: Tables of atomic
coordinates, bond lengths, and bond angles, anisotropic dis-
placement parameters, and hydrogen coordinates for com-
pounds 11a,b, 12a-c, 15, and 16. This material is available
free of charge via the Internet at http://pubs.acs.org.
In the case of 15, the Cp ring (η-C5H5) and the tert-butyl
group are both disordered. Each group was modeled over two
static sites. The occupancies of the disorder components for
(51) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(52) Sheldrick, G. M. SHELXTL/PC V5.1; Bruker Analytical X-ray
Systems: Madison, WI, 1997.
OM049650S