Synthesis and structures of triple-decker complexes with a bridging tetramethylcyclopentadienyl ligand

Article abstract of DOI:10.1021/om301258s

New triple-decker complexes with bridging tetramethylcyclopentadienyl ligands were synthesized by the reaction of electrophilic metal fragments with octamethylferrocene, Cp′₂Fe (Cp′ = C₅Me ₄H). The reaction of coordinatively unsaturated ruthenium cations [(C₅R₅)Ru]⁺ (R = H, CH₃) with Cp′₂Fe afforded purple-colored heterometallic triple-decker complexes [(C₅R₅)Ru(μ-Cp′)FeCp′] ⁺ by direct electrophilic addition. Surprisingly, the analogous reaction with the coordinatively unsaturated manganese cation [Mn(CO) ₃]⁺ and Cp′₂Fe produced a blue homometallic triple-decker complex, [Cp′Fe(μ-Cp′)FeCp′] ⁺, by ring abstraction and subsequent addition of the newly generated cation [Cp′Fe]⁺ to an equivalent of Cp′₂Fe. Three air-stable triple-decker complexes, [Cp′Fe(μ-Cp′) FeCp′]⁺ (2), [CpRu(μ-Cp′)FeCp′]⁺ (3), and [Cp*Ru(μ-Cp′)FeCp′]⁺ (4), have been characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.

Full text of DOI:10.1021/om301258s

Article
pubs.acs.org/Organometallics
Synthesis and Structures of Triple-Decker Complexes with a Bridging
Tetramethylcyclopentadienyl Ligand
Sonam K. Ghag,† Michael L. Tarlton,† Ernst A. Henle,† Elizabeth M. Ochoa,† Alex W. Watson,†
Lev N. Zakharov,‡ and Eric J. Watson*,†
†Department of Chemistry, Seattle University, 901 12th Avenue, Seattle, Washington 98122, United States
‡CAMCOR, University of Oregon, 1443 East 13th Avenue, Eugene, Oregon 97403, United States
S
* Supporting Information
ABSTRACT: New triple-decker complexes with bridging tetrame-
thylcyclopentadienyl ligands were synthesized by the reaction of
electrophilic metal fragments with octamethylferrocene, Cp′2Fe (Cp′
= C5Me4H). The reaction of coordinatively unsaturated ruthenium
cations [(C5R5)Ru]+ (R = H, CH3) with Cp′2Fe afforded purple-
colored heterometallic triple-decker complexes [(C5R5)Ru(μ-Cp′)-
FeCp′]+ by direct electrophilic addition. Surprisingly, the analogous
reaction with the coordinatively unsaturated manganese cation
[Mn(CO)3]+ and Cp′2Fe produced a blue homometallic triple-decker complex, [Cp′Fe(μ-Cp′)FeCp′]+, by ring abstraction
and subsequent addition of the newly generated cation [Cp′Fe]+ to an equivalent of Cp′2Fe. Three air-stable triple-decker
complexes, [Cp′Fe(μ-Cp′)FeCp′]+ (2), [CpRu(μ-Cp′)FeCp′]+ (3), and [Cp*Ru(μ-Cp′)FeCp′]+ (4), have been characterized
by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.
Scheme 1. Synthesis of Cationic Triple-Decker 1 by Stacking
of Decamethylferrocene with a Manganese Tricarbonyl
Fragment
INTRODUCTION
■
Multimetallic complexes possessing π-conjugated ligands
inspire ongoing interest due to their distinctive structural
features and the promise of useful applications in the field of
molecular electronics.1−5 In particular, bimetallic multilayer
complexes incorporating metallocenes (C5R5)2M attract
attention as model systems for the emerging field of bimetallic
organometallic sandwich molecular wires (BOSMW).6−11
Within a BOSMW, electronic communication between the
two metal centers may be mediated by a bridging C5 π-
ligand.12−14 Yet since the discovery of the first triple-decker
complex [Ni2(C5H5)3]+ in 1972, other transition metal
complexes with C5 π-ligands remain relatively rare.15,16
Furthermore among these complexes, only cyclopentadienyl
(Cp = C5H5) and pentamethylcyclopentadienyl (Cp* =
C5Me5) rings have been incorporated as bridging ligands.17−20
As a unique example of the latter, Sweigart et al. prepared
unsymmetrical triple-layer complexes of the iron group by the
electrophilic addition of the [Mn(CO)3]+ moiety to a Cp* ring
of decamethylmetallocenes of Fe, Ru, and Os.21 As shown in
Scheme 1, the electron-rich Cp*2Fe displaced the labile
acenaphthene ligand from [(η6-acenaphthene)Mn(CO)3]BF4,
affording the triple-layer complex [Cp*Fe(μ-Cp*)Mn(CO)3]-
BF4 (1·BF4).22,23
terms of the combination of a 12 valence electron (VE)
manganese complex fragment with an 18 VE metallocene to
produce a 30 VE triple-layer complex.26
RESULTS AND DISCUSSION
■
Although initial attempts to grow crystals of [Cp*Fe(μ-
Cp*)Mn(CO)3]BF4 were not successful, recent experiments
afforded green crystals of 1·PF6 suitable for X-ray analysis.21 As
shown in Figure 1, the structure of 1 confirms the coordination
of the [Mn(CO)3]+ fragment to a Cp* ring of decamethylfer-
rocene and reveals that the manganese tricarbonyl stacked
metallocene contains two perfectly staggered Cp* rings.
Similarly, the two Cp* rings in free decamethylferrocene
adopt a staggered conformation in the solid state.27
The chemistry shown in Scheme 1 is an example of an
“electrophilic stacking reaction” in which a coordinatively
unsaturated metal complex fragment adds to a nucleophilic
sandwich complex, producing a cationic triple-decker com-
plex.24,25 In 1976, Hoffmann et al. predicted the stability of
triple-decker complexes possessing 30 or 34 valence electrons,
and thus the stability of monocation 1 may be understood in
Received: December 27, 2012
© XXXX American Chemical Society
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Scheme 2. Proposed Mechanism for the Reaction of
Manganese Tricarbonyl Cation with Octamethylferrocene
ally, Herberich and co-workers reported a ring ligand transfer
reaction in the mechanism for the formation of a diruthenium
triple-decker complex, [Cp*Ru(μ-Cp)RuCp*]+.19,30 In related
chemistry, the formation of [CpNi(μ-Cp)NiCp]+ occurred
through the reaction of nickelocene with electrophilic species
such as HBF4, Ph3CBF4, or C7H7BF4.31,32 However the reaction
of Cp′2Fe with Ph3CBF4 yielded only the oxidation product,
[Cp′2Fe]BF4, suggesting the necessity of electrophilic π-
complexation for triple-decker formation from highly stable
metallocenes. It is noteworthy that Schemes 1 and 2 reveal a
remarkable change in reactivity arising from a relatively minor
difference in the degree of alkylation in the metallocene,
namely, decamethylferrocene or octamethylferrocene.
Blue crystals of 2·BF4 were obtained and X-ray diffraction
analysis confirmed its identity as a homometallic triple-decker
complex containing three parallel Cp′ ligands and two
intercalated iron atoms (Figure 2).
The three Cp′ rings in 2 are almost coplanar: the dihedral tilt
angle between the plane of the bridging ring (C1−C5) and
terminal ring (C10−C14) is 2.86(2)°, while for the bridge and
Figure 1. ORTEP view of the cation 1 with thermal ellipsoids drawn at
the 30% probability level. Selected bond lengths and angles: Mn−C(3)
2.195(4) Å, Mn−C(4) 2.180(3) Å, Mn−C(5) 2.163(3) Å, Fe−C(3)
2.081(4) Å, Fe−C(4) 2.076(3) Å, Fe−C(5) 2.069(3) Å; O(1)−
C(1)−Mn 176.8(4)°, O(2)−C(2)−Mn 175.4(5)°. Hydrogen atoms
are omitted for clarity.
In light of the chemistry shown in Scheme 1, it was
anticipated that the reaction of the same electrophilic reagent
[(η6-acenaphthene)Mn(CO)3]BF4 with octamethylferrocene
might yield [Cp′Fe(μ-Cp′)Mn(CO)3]BF4 by transfer of the
[Mn(CO)3]+ moiety to one of the Cp′ rings of Cp′2Fe. Instead,
the reaction produced a homometallic triple-decker complex,
[Cp′Fe(μ-Cp′)FeCp′]BF4 (2·BF4), and none of the expected
Fe−Mn product. Although [Cp′Fe(μ-Cp′)Mn(CO)3]BF4 was
not observed, it remains a plausible intermediate in the
formation of 2·BF4 since its degradation liberates neutral η5-
Cp′Mn(CO)3 (observed by IR analysis, νCO = 2006, 1918
cm−1) and by mass and charge balance the 12 VE monocation
[η5-Cp′Fe]+. As shown in Scheme 2, this newly generated iron
species then combines with an equivalent of Cp′2Fe to afford
the 30 VE cationic triple-decker complex, 2·BF4.
In support of this mechanism, Chung and co-workers
demonstrated the involvement of triple-layer manganese
tricarbonyl cations in ring abstraction reactions.28,29 Addition-
Figure 2. ORTEP view of the cation 2 with thermal ellipsoids at the
30% level. Hydrogen atoms are omitted for clarity.
B
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terminal ring (C19−C23) the angle is 1.69(1)°. In addition, the
three Cp′ decks are highly planar with rms (root-mean-square)
deviations of 0.0007 Å (C1−C5), 0.0030 Å (C10−C14), and
0.0003 Å (C19−C23). The methyl groups on the outer Cp′
rings incline away from the Fe atoms by 0.012(5) to 0.079(4)
Å, while the methyl groups on the inner ring deviate from the
plane by only 0.003(4) to 0.024(4) Å. The intramolecular
Fe···Fe distance, 3.3153(5) Å, is considerably longer than the
sum of the covalent radii (estimated at 2.6 to 3.0 Å), and
therefore any direct Fe···Fe interaction is unlikely.33,34 Instead,
electronic communication between the iron atoms may be
mediated by the bridging π-ligand.2,35,36
metal complex fragment, which then coordinated to a Cp′
ligand of the sandwich compound, producing a stable 30 VE
heterometallic triple-decker complex (Scheme 3).
Scheme 3. Synthesis of [Cp(R)Ru(μ-Cp′)FeCp′]+, 3 (R = H)
and 4 (R = Me)
Table 1 shows that for the two terminal Cp′ ligands in 2,
Fe−C bond distances are close to the corresponding distances
Table 1. Selected Bond Lengths (d) in the Complex 2·BF4
Thus an electrophilic stacking reaction of [CpRu]PF6 with
Cp′2Fe afforded purple 3·PF6 in moderate yield, and reaction of
[Cp*Ru]PF6 with Cp′2Fe produced light purple 4·PF6 in
excellent yield. The structure of cation 3 was determined by
single-crystal X-ray diffraction and confirmed that the
ruthenium and iron atoms are located between three parallel
cyclopentadienyl systems. (Figure 3).
M−bridging ligand
bond
M−terminal ligand
bond
d/Å
d/Å
Fe(1)−C(1)
Fe(1)−C(2)
Fe(1)−C(3)
Fe(1)−C(4)
Fe(1)−C(5)
Fe(1)···Cp′
Fe(2)−C(1)
Fe(2)−C(2)
Fe(2)−C(3)
Fe(2)−C(4)
Fe(2)−C(5)
Fe(2)···Cp′
2.054(2)
2.072(2)
2.084(2)
2.078(2)
2.065(2)
1.657(1)
2.055(2)
2.072(2)
2.084(2)
2.077(2)
2.069(2)
1.658(1)
Fe(1)−C(10)
Fe(1)−C(11)
Fe(1)−C(12)
Fe(1)−C(13)
Fe(1)−C(14)
Fe(1)···Cp′
Fe(2)−C(19)
Fe(2)−C(20)
Fe(2)−C(21)
Fe(2)−C(22)
Fe(2)−C(23)
Fe(2)···Cp′
2.026(2)
2.064(2)
2.061(2)
2.056(2)
2.043(2)
1.653(1)
2.039(2)
2.059(2)
2.053(2)
2.049(2)
2.049(2)
1.652(1)
in free octamethylferrocene (Fe−C 2.048 Å, C−C 1.422
Å),37,38 but for the bridging ligand, the average Fe−C bond is
longer (2.071 Å), as are the C−C bonds within the Cp′ ring
(average 1.460 Å). Moreover, the average perpendicular
distance between each Fe and the center of the bridging Cp′
ring is slightly longer (1.658 Å) than the corresponding
distance to the center of the outer rings (1.652 Å). Insofar as
bond length can be correlated with bond strength, these data
suggest weaker Fe−C and C−C interactions for the bifacially
coordinated bridging ring compared with the singly coordi-
nated terminal rings.39,40 Table 1 also shows that the
unsubstituted carbons within each tetramethylcyclopentadienyl
ring (C1, C10, and C19) of 2 are significantly closer to the iron
atom (ca. 0.02 Å) than are the methylated carbons. This same
asymmetry is evident in the parent metallocene Cp′2Fe and its
monocation [Cp′2Fe]BF4, both of which display shorter Fe−C
bonds to the one unsubstituted carbon within each Cp′
ligand.37,41
The two terminal rings in 2 are nearly eclipsed with torsion
angles for C(10−14)−Ct′−Ct″−C(19−23) between 3.8° and
4.4° (Ct = ring centroid), whereas the bridging ring is rotated
by approximately 33° for C(1−5)−Ct−Ct′−C(10−14) and
29° for C(1−5)−Ct−Ct″−C(19−23).20 These cross-orienta-
tion angles differ from the solid-state structure of octamethyl-
ferrocene, in which the two Cp′ rings are staggered perfectly
and the unsubstituted carbon on each Cp′ ring is rotated by
180° from the other.37,38,41
Figure 3. ORTEP view of 3 with displacement ellipsoids at the 30%
level. Hydrogen atoms are omitted for clarity.
In 3, the dihedral tilt angle between Cp(C1−C5) and
Cp′(C6−C10) is 2.11(3)°, and between Cp′(C6−C10) and
Cp′(C11−C15) the angle is 2.45(3)°. The Cp ring is highly
planar (rms deviation of 0.0028 Å), as are the two Cp′ rings
(rms deviations of 0.0010 and 0.0012 Å). The four methyl
groups deviate from the plane of the middle deck by 0.0012(8)
to 0.020(8) Å, while those on the outer Cp′ ring incline away
from the iron atom by 0.021(8) to 0.071(8) Å. The
intramolecular Fe···Ru distance is 3.4700(6) Å, which exceeds
the sum of Ru···Fe covalent radii (2.98 Å), indicating the
absence of a direct metal−metal bond.1,4,34
In contrast with the manganese chemistry, reaction of
ruthenium cations [CpRu(NCMe)3]+ and [Cp*Ru(NCMe)3]+
with Cp′2Fe did not bring about ring abstraction. Rather each
ruthenium complex eliminated acetonitrile to generate a 12 VE
As shown in Table 2, the average distance between the Fe
atom and its terminal ring carbons is 2.057 Å, while the
distance to the bridging ring carbons is 2.077 Å. Similarly, the
average Ru−C(Cp) distance is 2.160 Å, while the Ru−C(Cp′)
C
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Table 2. Selected Bond Lengths (d) in the Complex 3·PF6
M−bridging ligand
bond
M−terminal ligands
d/Å
bond
d/Å
Ru(1)−C(6)
Ru(1)−C(7)
Ru(1)−C(8)
Ru(1)−C(9)
Ru(1)−C(10)
Ru(1)···Cp′
Fe(1)−C(6)
Fe(1)−C(7)
Fe(1)−C(8)
Fe(1)−C(9)
Fe(1)−C(10)
Fe(1)···Cp′
2.187(4)
2.186(4)
2.193(4)
2.204(4)
2.215(4)
1.809(2)
2.057(4)
2.078(4)
2.091(4)
2.086(4)
2.075(4)
1.661(2)
Ru(1)−C(1)
Ru(1)−C(2)
Ru(1)−C(3)
Ru(1)−C(4)
Ru(1)−C(5)
Ru(1)···Cp
Fe(1)−C(11)
Fe(1)−C(12)
Fe(1)−C(13)
Fe(1)−C(14)
Fe(1)−C(15)
Fe(1)···Cp′
2.180(5)
2.160(5)
2.151(4)
2.153(4)
2.155(5)
1.792(2)
2.054(4)
2.062(4)
2.065(4)
2.057(4)
2.045(4)
1.660(2)
distance is almost 0.04 Å longer (average 2.197 Å). The average
C−C bond in the central ring is 1.467 Å but only 1.428 Å for
the outer Cp′. Therefore as with bimetallic complex 2,
formation of 3 from Cp′2Fe elongated the Fe−C and C−C
bonds for the bridging Cp′ ligand relative to the terminal Cp′
ligand.
In 3 none of the rings is staggered as in free
octamethylferrocene, but instead the cross-orientation for the
two Cp′ rings, C(6−10)−Ct′−Ct″(C11−C15), ranges from
19.0° to 19.7° (average 19.3°). The Cp ring and bridging Cp′
ring are almost eclipsed, with torsion angles of only 1.9° to 4.0°
(average 3.1°) for C(1−5)−Ct−Ct′−C(6−10), while the Cp
ring and the terminal Cp′(C11−C15) are rotated by an average
of 22.4°.
For Ru−Fe complex 4, X-ray diffraction analysis revealed two
symmetrically independent triple-decker complexes in the unit
cell (Figure 4). The three parallel carbocyclic ligands are nearly
coplanar in both conformations: in 4A, the dihedral tilt angle
between Cp*(C1−C5) and Cp′(C6−C10) is 0.60(5)° and
between Cp′(C6−C10) and Cp′(C11−C15) the angle is
2.85(5)°; in 4B, the dihedral tilt angle between Cp*(C1−C5)
and Cp′(C6′−C10′) is 1.85(5)° and between Cp′(C6′−C10′)
and Cp′(C11′−C15′) the angle is 3.44(5)°. The intramolecular
distances between the iron and ruthenium atoms are similar in
both conformations: 3.4703(9) Å for 4A and 3.4762(9) Å for
4B. In both rotamers of 4, the methyl groups of the terminal
Cp′ rings incline away from the Fe atom by 0.004(1) to
0.090(1) Å, and the five methyl groups on the Cp* ring bend
away from the Ru atom by 0.005(1) to 0.053(1) Å. The methyl
groups of the bridging Cp′ rings are more planar, deviating
from the plane of the central ring by 0.004(1) to 0.039(1) Å.
Comparison of selected bond lengths in 4A and 4B reveals
close similarities between the two rotational conformers. As
shown in Table 3, the Fe−C bonds to the bridging ring are
longer for conformer 4A (average 2.053 Å) than 4B (average
2.046 Å), whereas the Fe−C bonds for the terminal ring are
longer for conformer 4B (average 2.064 Å) than 4A (average
2.058 Å). Thus unlike 2 and 3, complex 4 has shorter Fe−C
bonds for the bridging ligand than for the terminal ligand.
Moreover, the perpendicular distance from the iron atom to the
center of the bridging ring is shorter than the distance to the
outer ring for both conformations. The average C−C bonds in
the three rings do not differ significantly between 4A and 4B:
the average C−C bonds in 4A are 1.423 Å (Cp*), 1.421 Å
(Cp′, terminal), and 1.451 Å (Cp′, bridge); the average C−C
Figure 4. ORTEP views of complexes 4A (top) and 4B (bottom) with
displacement ellipsoids at the 30% level. Hydrogen atoms are omitted
for clarity.
bonds in 4B are 1.416 Å (Cp*), 1.424 Å (Cp′, terminal), and
1.448 Å(Cp′, bridge).
While the two rotational conformers are neither fully eclipsed
nor staggered, Figure 5 shows that the cross orientation of the
two Cp′ rings and Cp* ring is closer to an eclipsed
conformation in 4B than in 4A. In the rotational conformer
4A, the average torsion angle between Cp* and the bridging
Cp′ is 20.7°, while the two Cp′ rings are rotated by 23.9°. For
4B, the average torsion angle between the Cp* ring and the
bridging Cp′ is 18.9°, while the two Cp′ rings are rotated by
19.9°. Therefore for 4B, the two terminal rings are nearly
eclipsed (average torsion angle 1.0°) compared with a more
staggered geometry of 44.5° for the terminal rings in 4A.
1
Table 4 presents results from H NMR, 13C NMR, and 2-D
HMQC experiments for the three 30 VE monocations 2−4. 1H
NMR data reveal that the signals for protons on the terminal
D
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a
ring and δ 1.69 (s, 12H) and 1.73 (s, 12H) for hydrogens on
the methyl group. In contrast, signals for the 12 methyl protons
and one ring proton on the bridging Cp′ are shifted downfield
of these values by 0.6 to 1.3 ppm. Similarly 13C resonances for
the terminal ligands of the triple-deckers are near those for free
Cp′2Fe (δ 71.0 (2C), 80.3 (4C), 80.5 (4C) and δ 9.8 (4C),
11.8 (4C)). However, for the bridging position, signals for
methyl carbons are shifted downfield of these by 1.1 to 4.0
ppm, and ring carbons are shifted upfield by 9.5 to 12.7 ppm.
HMQC experiments confirmed the assignment of the signals
for the Cp′ methyl carbons in 3 and 4, whereas in 2 their
assignment was unambiguous since [Cp′Fe(μ-Cp′)FeCp′]+
possesses two identical terminal Cp′ rings. Within each
tetramethylcyclopentadienyl ring, the 13C resonance of the
unsubstituted carbon is upfield of the resonance for the
methylated ring carbons by 7.4 to 12.2 ppm. These
spectroscopic data correlate with structural information (Tables
1, 2, and 3) that shows that in the solid state the unsubstituted
carbon on each Cp′ ring is typically closer to the iron atom
than are the methylated ring carbons.
Table 3. Selected Bond Lengths (d) in 4A·PF6 and 4B·PF6
M−bridging ligand
M−terminal ligands
bond
d/Å
bond
d/Å
Ru(1)−C(6)
Ru(1)−C(7)
Ru(1)−C(8)
Ru(1)−C(9)
Ru(1)−C(10)
Ru(1)···Cp′
Fe(1)−C(6)
Fe(1)−C(7)
Fe(1)−C(8)
Fe(1)−C(9)
Fe(1)−C(10)
Fe(1)···Cp′
Ru(1′)−C(6′)
Ru(1′)−C(7′)
Ru(1′)−C(8′)
Ru(1′)−C(9′)
Ru(1′)−C(10′)
Ru(1′)···Cp′
Fe(1′)−C(6′)
Fe(1′)−C(7′)
Fe(1′)−C(8′)
Fe(1′)−C(9′)
Fe(1′)−C(10′)
Fe(1′)···Cp′
2.195(6)
2.204(5)
2.203(5)
2.217(6)
2.216(6)
1.829(3)
2.034(6)
2.049(6)
2.070(6)
2.065(6)
2.049(6)
1.641(3)
2.200(6)
2.210(5)
2.215(5)
2.235(6)
2.032(6)
1.843(3)
2.029(6)
2.044(5)
2.069(5)
2.054(6)
2.032(6)
1.633(3)
Ru(1)−C(1)
Ru(1)−C(2)
Ru(1)−C(3)
Ru(1)−C(4)
Ru(1)−C(5)
Ru(1)···Cp*
Fe(1)−C(11)
Fe(1)−C(12)
Fe(1)−C(13)
Fe(1)−C(14)
Fe(1)−C(15)
Fe(1)···Cp′
Ru(1′)−C(1′)
Ru(1′)−C(2′)
Ru(1′)-C(3′)
Ru(1′)−C(4′)
Ru(1′)−C(5′)
Ru(1′)···Cp*
Fe(1′)−C(11′)
Fe(1′)−C(12′)
Fe(1′)−C(13′)
Fe(1′)−C(14′)
Fe(1′)−C(15′)
Fe(1′)···Cp′
2.161(6)
2.161(6)
2.168(6)
2.148(6)
2.145(6)
1.785(3)
2.051(6)
2.058(6)
2.068(5)
2.056(5)
2.057(5)
1.666(3)
2.143(6)
2.147(6)
2.146(6)
2.138(6)
2.143(6)
1.773(3)
2.066(6)
2.074(6)
2.072(5)
2.065(5)
2.045(5)
1.671(3)
The NMR spectroscopy of 2−4 shares key features with the
other bimetallic triple-decker complexes. In their pioneering
research with iron group complexes, Rybinskaya and Kudinov
and co-workers reported a downfield shift for protons on Cp*
ligands in the bridging position and an upfield shift of their ring
carbons (Table 5).17−19 Similarly for complexes 2−4, bifacial
1
Table 5. H and 13C NMR Data for [CpFe(μ-
a
Atom labels for complex 4B are designated with primes.
Cp)FeCp]PF6,18 [CpFe(μ-Cp*)FeCp*]PF6,17 [CpFe(μ-
42
Cp*)RuCp*]PF6,17 and [Cp*Ru(μ-Cp*)FeCp*]PF6 in
CD2Cl2
1H NMR, δ (ppm)
η5-
13C NMR, δ (ppm)
η5-
Cp(R) μ-η5:η5-
Fe Cp(R)
Cp(R) μ-η5:η5-
η5-
η5-
Cp(R)
complex
Fe
Cp(R) Cp(R)
CpFe(μ-Cp)
4.37
4.37
2.69
2.56
2.32
4.37 69.2 52.5
69.2
FeCp
CpFe(μ-Cp*)
FeCp*
CpFe(μ-Cp*)
RuCp*
Cp*Fe(μ-
Cp*)RuCp*
3.87
4.09
1.65
1.51 71.9
8.3, 69.1 13.3,
79.2
1.43 72.4
1.44 8.4,
9.2, 71.1 13.7,
84.9
11.4,
69.9
9.1,
84.6
79.4
Figure 5. ORTEP views of complexes 4A (left) and 4B (right) along
the Fe···Ru line with displacement ellipsoids at the 30% level.
Hydrogen atoms are omitted for clarity.
coordination to the bridging Cp′ ring brought about a
downfield shift of its proton signals and an upfield shift for
its ring carbon signals (Table 4). Thus for this class of
compounds, coordination of two transition metals to opposing
Cp′ rings in the triple-decker complexes are close to those of
free octamethylferrocene: δ 3.33 (s, 2H) for hydrogens on the
1
Table 4. H and 13C NMR Data for 2−4 and Octamethylferrocene in CD2Cl2
1H NMR, δ (ppm)
13C NMR, δ (ppm)
μ-η5:η5-Cp′
complex
η5-Cp(R)
μ-η5:η5-Cp′
η5-Cp′
η5-Cp(R)
8.5, 10.4
η5-Cp′
8.5, 10.4
a
2
methyl
ring
1.59, 1.69
3.45
2.53, 2.54
3.99
1.59, 1.69
3.45
11.5, 13.1
69.4, 80.8, 81.6
58.7, 67.6, 69.0
13.8, 15.2
69.4, 80.8, 81.6
8.6, 10.4
b
3
methyl
ring
2.57, 2.69
4.65
1.68, 1.79
3.63
4.37
1.53
73.3
9.6
59.5, 69.4, 71.0
11.3, 12.9
73.7, 81.0, 81.7
8.8, 10.6
c
4
methyl
ring
2.31, 2.33
4.05
1.70,1.79
3.62
85.3
60.2, 69.1, 69.8
71.0, 81.2, 81.9
9.8, 11.8
Cp′2Fe
methyl
ring
1.69,1.73
3.33
71.0, 80.3, 80.5
a
b
c
Cp(R) = C5Me4H. Cp(R) = C5H5. Cp(R) = C5Me5.
E
dx.doi.org/10.1021/om301258s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
from brown to dark purple. After cooling to room temperature, the
solution was concentrated under N2 flow to about 2 mL. Addition of
50 mL of diethyl ether precipitated a purple solid. The solid was
washed with diethyl ether (2 × 10 mL) and then placed on a
deactivated neutral alumina column (10% H2O) prepared with
CH2Cl2. The product was eluted with CH2Cl2, and the solvent was
faces of a bridging ligand almost always distinguishes its NMR
signals from those of the singly coordinated terminal ligands.
However this difference is less pronounced in some triple-
decker complexes,43 and indeed for [CpFe(μ-Cp)FeCp], H
1
NMR spectroscopy revealed a single resonance for all three
rings.18
1
removed in vacuo to yield a purple solid. Yield: 0.088 g (42%). H
NMR (CD2Cl2): δ 4.65 (s, 1H, μ-C5(CH3)4H), 4.37 (s, 5H, C5H5),
3.63 (s, 1H, C5(CH3)4H), 2.69 (s, 6H, μ-C5(CH3)4H), 2.57 (s, 6H, μ-
C5(CH3)4H), 1.79 (s, 6H, C5(CH3)4H), 1.68 (s, 6H, C5(CH3)4H).
13C{1H} NMR (CD2Cl2): δ 81.7, 81.0, 73.7, 73.3, 71.0, 69.4, 59.5,
15.2, 13.8, 10.4, 8.6. Anal. Calcd for C23H31FeRuPF6: C, 45.33; H,
5.13. Found: C, 45.47; H, 5.12.
CONCLUSION
■
In 2001, Sweigart et al. demonstrated that the manganese
tricarbonyl transfer reagent [(η6-acenaphthene)Mn(CO)3]BF4
reacted with electron-rich decamethylferrocene to produce the
triple-layer complex 1·BF4. Extending this methodology to
octamethylferrocene did not afford the analogous Fe−Mn
stacking product, but instead produced 2·BF4, a novel diiron
triple-decker by a more complicated mechanism involving ring
abstraction and subsequent electrophilic addition. Comparison
of the chemistry of complexes 1 and 2 points to a dramatic
change in reactivity based on a relatively subtle difference in the
degree of alkylation of the bridging ligand, namely, C5Me5 vs
C5Me4H. In contrast with the manganese chemistry, two
ruthenium cations, [CpRu]+ and [Cp*Ru]+, produced stable
coordination products with octamethylferrocene by an electro-
philic stacking mechanism and yielded two heterometallic
triple-decker complexes, 3·PF6 and 4·PF6.
[(C5(CH3)5)Ru(μ-C5(CH3)4H)Fe(C5(CH3)4H)]PF6 (4·PF6). Cp*Ru-
(NCMe)3]PF6 (0.150 g, 0.297 mmol), Cp′2Fe (0.098 g, 0.327
mmol), and 40 mL of CH2Cl2 were mixed under N2. The solution was
refluxed for 2 h, during which time the solution changed quickly from
brown to light purple. After cooling to room temperature, the solution
was concentrated under N2 flow to about 2 mL. Addition of 50 mL of
diethyl ether precipitated a light purple solid. The solid was washed
with diethyl ether (2 × 10 mL) and then placed on a deactivated
neutral alumina column (10% H2O) prepared with CH2Cl2. The
product was eluted with CH2Cl2, and the solvent was removed in
1
vacuo to yield a light purple solid. Yield: 0.175 g, (87%). H NMR
(CD2Cl2): δ 4.05 (s, 1H, μ-C5(CH3)4H), 3.62 (s, 1H, C5(CH3)4H),
2.33 (s, 6H, μ-C5(CH3)4H), 2.31 (s, 6H, μ-C5(CH3)4H), 1.79 (s, 6H,
C5(CH3)4H), 1.70 (s, 6H, C5(CH3)4H), 1.53 (s, 15H, C5(CH3)5).
13C{1H} NMR (CD2Cl2): δ 85.3, 81.9, 81.2, 71.0, 69.8, 69.1, 60.2,
12.9, 11.3, 10.6, 9.6, 8.8. Anal. Calcd for C28H41FeRuPF6: C, 49.47; H,
6.08. Found: C, 49.56; H, 6.06.
EXPERIMENTAL SECTION
■
General Experimental Methods. All reactions were carried out
under an atmosphere of dry nitrogen. Dichloromethane was collected
from a Braun MBS-800 solvent purification system immediately before
use. All other solvents were purchased from commercial sources and
used without further purification. [CpRu(NCMe)3]PF6,44 [Cp*Ru-
(NCMe)3]PF6,45 and octamethylferrocene or bis(tetramethyl)-
cyclopentadienyl iron(II) were synthesized according to literature
methods or purchased from Strem Chemicals Inc. [(η6-
Acenaphthene)Mn(CO)3]BF4 was prepared according to literature
methods.46 1H and 13C{1H} NMR spectra were recorded at 400.1 and
100.6 MHz, respectively, and at ambient temperatures. All chemical
shifts are reported in δ units referenced to the internal standards for
the deuterated solvents. Elemental analyses were carried out by
Atlantic Microlab Inc.
X-ray Crystallography. Crystals for 2·BF4, 3·PF6, and 4·PF6 were
obtained by the slow vapor diffusion of diethyl ether into CH2Cl2
solutions at −20 °C. Crystals for complex 1·PF6 were obtained by the
addition of an excess of NH4PF6 prior to vapor diffusion of diethyl
ether into a CH2Cl2 solution of 1·BF4 at −20 °C. Table 6 (Supporting
Information) presents the key crystallographic and structure refine-
ment data. X-ray diffraction experiments were carried out on a Bruker
Smart Apex diffractometer at 193 K (1·PF6 and 2·BF4), 173 K (3·PF6),
and 110 K (4·PF6) using Mo Kα radiation (λ = 0.71073 Å).
Absorption corrections were applied by SADABS.47 The structures
were solved using direct methods and refined with full-matrix least-
squares methods based on F2. All non-H atoms were refined with
anisotropic thermal parameters. The H atoms in all structures were
refined in calculated positions using a rigid group model. The structure
of 2·BF4 was determined in non-centrosymmetrical space group Cc.
The found Flack parameter is 0.500(12), indicating possible space
group C2/c. The structure of 2·BF4 could be obtained in space group
C2/c but with disordered C5Me4H groups in the Fe2(C5Me4H)3
cation. The symmetry of the Fe2(C5Me4H)3 cation is close to but not
exactly C2. On this basis, it is thought that the correct space group for
2·BF4 is Cc, and in this space group there is no disorder for the
C5Me4H groups. The PF6 anion in 3·PF6 is disordered over two
positions with the ratio 1:1. The structure of 4·PF6 consists of two
symmetrically independents units. Attempts to solve the structure in
the range of temperatures from 173 K up to ambient temperature
failed. At these temperatures, the structure of 4·PF6 had triclinic
symmetry with disordered molecules; the Fe and Ru atoms shared the
same positions, and terminal methyl groups were disordered as well.
At 110 K, the structure of 4·PF6 was determined to be monoclinic with
two symmetrically independent units and without any disorder for the
Fe and Ru atoms or the terminal methyl groups. One of three PF6
anions in 4·PF6 is in a general position, and two others are on a 2-fold
axis. All calculations were performed using the SHELXTL package.48
[(C5(CH3)4H)Fe(μ-C5(CH3)4H)Fe(C5(CH3)4H)]BF4 (2·BF4). [(η6-
acenaphthene)Mn(CO)3]BF4 (0.200 g, 0.526 mmol), Cp′2Fe (0.330
g, 1.105 mmol), and 40 mL of CH2Cl2 were mixed under N2 and
heated to reflux for 2 h. During the course of the reaction, the solution
color changed from orange to blue. The reaction may be monitored
for completion by IR since the neutral side product η5-Cp′Mn(CO)3
has bands at νCO = 2006 (s), 1918 (s, br) cm−1 distinct from the
starting cation [(η6-acenaphthene)Mn(CO)3]BF4 at νCO = 2072 (s),
2012 (s, br) cm−1. The solution was cooled to room temperature and
concentrated to about 2 mL under N2 flow. Addition of 70 mL of
diethyl ether precipitated a blue powder. The solid was washed with
diethyl ether (2 × 10 mL) and then placed on a short silica gel column
prepared with CH2Cl2. The deep blue product eluted with a 1:5
mixture of CH3NO2/CH2Cl2, and the solvent was removed in vacuo to
yield 2·BF4 as a blue solid. In some instances, a small amount of green
[Cp′2Fe]BF4 eluted with the product. This could be separated cleanly
from 2·BF4 on a silica gel TLC plate with a 1:10 mixture of acetone/
1
CH2Cl2. Yield: 0.136 g (46%). H NMR (CD2Cl2): δ 3.99 (s, 1H, μ-
C5(CH3)4H), 3.45 (s, 2H, C5(CH3)4H), 2.53 (s, 6H, μ-C5(CH3)4H),
2.54 (s, 6H, μ-C5(CH3)4H), 1.69 (s, 12H, C5(CH3)4H), 1.59 (s, 12H,
C5(CH3)4H). 13C{1H} NMR (CD2Cl2): δ 81.6, 80.8, 69.4, 69.0, 67.6,
58.7, 13.1, 11.5, 10.4, 8.5. Anal. Calcd for C27H39Fe2BF4: C, 57.65; H,
6.99. Found: C, 57.60; H, 7.02.
[(C5H5)Ru(μ-C5(CH3)4H)Fe(C5(CH3)4H)]PF6 (3·PF6). [CpRu-
(NCMe)3]PF6 (0.150 g, 0.345 mmol), Cp′2Fe (0.115 g, 0.386
mmol), and 40 mL of CH2Cl2 were mixed under N2. The solution was
refluxed for 4 h, during which time the solution changed gradually
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic and structure refinement data for complexes
1−4, 1H, 13C{H}, and HMQC NMR spectra for complexes 2−
4, and X-ray crystallographic data in CIF format for the
F
dx.doi.org/10.1021/om301258s | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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AUTHOR INFORMATION
Corresponding Author
*E-mail: watsone1@seattleu.edu.
Notes
■
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ACKNOWLEDGMENTS
■
This research was supported by an award from Research
Corporation for Science Advancement (Award # 20904). We
thank the Peach Foundation (S.K.G. and E.M.O), the Murdock
College Science Research Program (M.L.T. and E.J.W.), and
Seattle University for financial support.
DEDICATION
■
This article is dedicated in memoriam to Professor Dwight A.
Sweigart.
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