Reactions of 7,7,8,8-tetracyanoquinodimethane with poly-ynyl ruthenium and iron complexes

Article abstract of DOI:10.1021/om3006728

The reaction of tetracyanoquinodimethane (TCNQ) with Ru(C≡CC≡ CH)(dppe)Cp* (5) at the outer (from Ru) C≡C triple bond gives η¹-(butadienyl)ethynyl Ru{C≡CC[CH=C(CN)₂]=C ₆H₄=C(CN)₂}(dppe)Cp (8), which reacts with a second equivalent of diynyl-Ru complex to give {Ru(dppe)Cp*}{C≡CC[= C₆H₄=C(CN)₂]CH=CHC[=C(CN)₂] C≡C}{Ru(dppe)Cp*} (9). The Ph-substituted complexes M{C≡CC≡CPh}(dppe)Cp* (M = Fe 6-Fe, Ru 6-Ru) and Ru{(C≡C)₃Ph}(PPh₃)₂Cp (7) react with TCNQ to give the η¹-(butadienyl)ethynyls M{C≡CC[CPh=C(CN) ₂]=C₆H₄=C(CN)₂}(dppe)Cp (10-Fe, 10-Ru) and Ru{C≡CC[C(C≡CPh)=C(CN)₂]=C₆H ₄=C(CN)₂}(PPh₃)₂Cp (11), respectively. Single-crystal X-ray diffraction molecular structure determinations for 8-11 have been carried out. In the Fe series, we suggest that the initial step of the mechanism involves electron transfer to form the [TCNQ]^-? salt of the diynyl-iron cation, followed by C-C bond formation to give a zwitterionic intermediate. Isolated products can be rationalized by further reaction involving [2 + 2]-cycloaddition of one of the C=C(CN)₂ groups of TCNQ to a C≡C triple bond of the metal poly-ynyl complex and a subsequent ring-opening reaction of the resulting (unobserved) cyclobutenyl intermediate. On the basis of X-ray diffraction data, redox potential determinations, and ⁵⁷Fe Moessbauer and UV-vis spectroscopies, the electronic structures of the new compounds contain significant contributions from polarized mesomers involving charge transfer from the electron-rich metal-ligand fragment to the cyanocarbon ligand via the conjugated unsaturated carbon linker.

Full text of DOI:10.1021/om3006728

Article
pubs.acs.org/Organometallics
Reactions of 7,7,8,8-Tetracyanoquinodimethane with Poly-ynyl
Ruthenium and Iron Complexes
Michael I. Bruce,*,† Alexandre Burgun,†,‡ Guillaume Grelaud,† Claude Lapinte,*,‡ Christian R. Parker,†
Thierry Roisnel,‡ Brian W. Skelton,§ and Natasha N. Zaitseva†
†School of Chemistry & Physics, University of Adelaide, South Australia 5005
‡Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite
́
de Rennes 1, Campus de Beaulieu, F-35042 Rennes, France
§Centre for Microscopy, Characterisation and Analysis M313, University of Western Australia, Crawley, Western Australia 6009
S
* Supporting Information
ABSTRACT: The reaction of tetracyanoquinodimethane (TCNQ) with
Ru(CCCCH)(dppe)Cp* (5) at the outer (from Ru) CC triple bond
gives η1-(butadienyl)ethynyl Ru{CCC[CHC(CN)2]C6H4C-
(CN)2}(dppe)Cp (8), which reacts with a second equivalent of diynyl-Ru
complex to give {Ru(dppe)Cp*}{CCC[C6H4C(CN)2]CH
CHC[C(CN)2]CC}{Ru(dppe)Cp*} (9). The Ph-substituted com-
plexes M{CCCCPh}(dppe)Cp* (M = Fe 6-Fe, Ru 6-Ru) and
Ru{(CC)3Ph}(PPh3)2Cp (7) react with TCNQ to give the η1-
(butadienyl)ethynyls M{CCC[CPhC(CN)2]C6H4C(CN)2}-
(dppe)Cp (10-Fe, 10-Ru) and Ru{CCC[C(CCPh)C(CN)2]
C6H4C(CN)2}(PPh3)2Cp (11), respectively. Single-crystal X-ray diffrac-
tion molecular structure determinations for 8−11 have been carried out. In
the Fe series, we suggest that the initial step of the mechanism involves
electron transfer to form the [TCNQ]−• salt of the diynyl-iron cation,
followed by C−C bond formation to give a zwitterionic intermediate. Isolated products can be rationalized by further reaction
involving [2 + 2]-cycloaddition of one of the CC(CN)2 groups of TCNQ to a CC triple bond of the metal poly-ynyl
complex and a subsequent ring-opening reaction of the resulting (unobserved) cyclobutenyl intermediate. On the basis of X-ray
diffraction data, redox potential determinations, and 57Fe Mossbauer and UV−vis spectroscopies, the electronic structures of the
̈
new compounds contain significant contributions from polarized mesomers involving charge transfer from the electron-rich
metal−ligand fragment to the cyanocarbon ligand via the conjugated unsaturated carbon linker.
by ring-opening (retro-electrocyclic reactions) to give sub-
stituted butadienes. Similar chemistry of alkynyl-metal com-
plexes was first described in 1972 (for TCNQ) and 1979 (for
TCNE), with completely regioselective [2 + 2]-cycloaddition of
TCNQ being found. The butadienes formed by subsequent
ring-opening reactions contain nonplanar chromophores that
have unusual redox and opto-electronic properties.6
Studies of homo- and hetero-organobimetallics with various
carbon bridges have also been the subject of intense efforts over
recent years. These multifunctional molecular arrays have been
extensively investigated in order to establish variations in their
electronic, magnetic, and optical properties as a function of
differing metal oxidation states.7−11 More recently, hybrid
systems containing both metallic and organic electrophores
have shown properties that, like the organic D-π-A systems
mentioned above, may make these materials suitable for
incorporation into components for molecular electronic and
NLO assemblies.12,13
INTRODUCTION
■
There is considerable current interest in the synthesis and
properties of molecules containing an electron-rich center
linked by a bridge containing a conjugated π-system to an
electron-accepting fragment (D-π-A systems). These com-
pounds are strongly polarized and consequently, among other
features, show efficient nonlinear optical properties.1−4 Popular
electron-accepting molecules are the cyano-alkenes, for example
but not limited to tetracyanoethene [(NC)2CC(CN)2,
TCNE] and tetracyanoquinodimethane [(NC)2CC6H4
C(CN)2, TCNQ]. The strong electron-accepting properties of
these molecules have been known for more than half a century,
with the formation of a large range of charge-transfer (CT)
adducts, and their opto-electronic, magnetic, and conduction
properties have resulted in applications as p-dopants for solar
cells and light-emitting diodes.
Studies of their addition to donor-substituted alkynes,
particularly N,N-dialkylanilino derivatives, are of more recent
origin.5 Reactions between the cyano-alkenes and these donor-
substituted alkynes commonly proceed via [2 + 2]-cyclo-
addition reactions to give cyclobutenes, which may react further
Received: July 19, 2012
Published: September 10, 2012
© 2012 American Chemical Society
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Reactions of electron-deficient alkenes, such as TCNE, with
transition metal complexes have attracted interest for many
years, those with alkynyl and poly-ynyl derivatives affording an
extensive chemistry that again originates from the donor−
acceptor interactions.14,15 As shown in Scheme 1, initial
several years later for some arylalkynyl-nickel systems and for
a mixed-metal Co3{C(CC)3}Ru complex.19,20
In a more detailed study, we have recently described
reactions of TCNQ with alkynyl-iron or -ruthenium complexes
(Scheme 2).21 These follow pathways similar to those found for
Scheme 1. Reactions of TCNE with Alkynyl-Transition
Metal Complexes
Scheme 2. Reactions of Alkynyl-Metal Complexes with
TCNQ
a
a
a
Key: (i) [2 + 2]-cycloaddition; (ii) R = H: CN displacement (−
HCN).
a
Key: (i) [2 + 2]-cycloaddition; (ii) ring-opening; (iii) chelation by
loss of a 2-e donor ligand; (iv) R = H: CN-displacement.
formation of a radical anion salt of the oxidized alkynyl-metal
complex A (CT complex) is followed by C−C bond formation
to give B, which undergoes intramolecular [2 + 2]-cyclo-
addition to give cyclobutene C and subsequent ring-opening
reactions affording D and E, the latter being formed by
displacement of a 2-e donor ligand from the metal center.
Further studies have revealed that highly nucleophilic ethynyl-
metal complexes can also react by substitution of a CN group
of TCNE, with concomitant elimination of HCN, to give the
ethynyl-tricyanovinyl complexes {MLn}CCC(CN)C-
(CN)2, F. These are further examples of D-π-A systems, in
which an organometallic donor is linked via a σ-ethyndiyl (C
C) connector to an organic acceptor ligand.16 Unusual
electronic properties of Ru{CCC(CN)C(CN)2}(dppe)-
Cp*, which can be obtained in nearly quantitative yield from
Ru(CCH)(dppe)Cp* and TCNE, are evidenced by its
intense purple color arising from an intramolecular CT band at
ca. 557 nm in CH2Cl2, which shows pronounced solvatochrom-
ism.16
The competition between (i) [2 + 2]-cycloaddition and (ii)
CN-displacement, as depicted in Scheme 1, depends on the
nature of the R group (H vs Ph) and also on the electronic and
steric properties of the alkynyl-metal fragment. In this case, the
use of more sterically hindered alkynyl-metal derivatives favors
route (ii) and allows access to hybrid molecules containing an
electron-rich MLn fragment linked to a strongly electrophilic
organic acceptor by the CC moiety. In these complexes, this
arrangement favors the π−d interaction between the two
electrophores. The resulting tricyanovinylethynyl (tricyanobu-
tenynyl) complexes are examples of polarized D-π-A systems.
Although the chemistry with TCNE is well-established,15
related studies of TCNQ are still somewhat limited in scope.
The deep red-purple complexes obtained from trans-Pt(C
CR)2(PR′3)2 (R = H, Me, Et; R′ = Me, Et) and TCNQ were
initially considered to be the CT adducts,17 but were later
shown by an X-ray study to be the butadienyl-platinum(II)
derivatives, trans-Pt(CCR){C[C6H4C(CN)2]CRC-
(CN)2}(PR′3)2, formed by [2 + 2]-cycloaddition of TCNQ
to one CC triple bond, followed by ring-opening of the
resulting cyclobutenyls.18 Similar chemistry was described
TCNE, although it has also been possible to isolate and
structurally characterize examples of the radical ion pair G
(formed by 1-e oxidation) and the zwitterionic intermediate H
(assumed but not previously isolated during related studies
with TCNE), as well as the spiro-cyclobutenyl I and the η1- and
η3-butadienyls (J and K, respectively). The synthesis and the
characterization of the CN-substituted product L, exemplified
by the new hybrid complex 1 (see Chart 1), from TCNQ and
Ru(CCH)(PPh3)2Cp (2), was also achieved. Compound 1
contains the electron-rich organometallic donor Ru(PPh3)2Cp
linked via a σ-ethyndiyl bridge to an organic acceptor fragment
(a D-π-A system). The ultimate products again depend on the
nature of the metal−ligand combinations, but extensive studies
have shown that the reactions proceed by initial formation of a
radical ion pair G or zwitterion H (the charge transfer is driven
by accommodation of electronic charge on the dicyano-
methylene group), followed by regiospecific formation of a
cyclobutenyl I, which may undergo ring-opening to afford a
butadienyl complex J. In some cases, where an easily
displaceable 2-e donor ligand is present, further reaction can
occur to give a η3-butadienyl K.
Double addition of TCNE to anilinobuta-1,3-diynes affords
octacyano[4]dendralenes,22 while addition of 4-Me2NC6H4C
CH to the TCNE adduct of 4-Me2NC6H4CCCN gave a
diaryl-tetracyanopentafulvene.23 Extension of the reactions of
TCNE to poly-ynyl-metal complexes has shown that steric
protection of the CC triple bond adjacent to the metal center
by the associated phosphine ligands usually results in
cycloaddition of TCNE to the outer CC triple bond of
diynyl and to the central triple bond of the triynyl, to give
ethynylbutadienyl ligands (as in 4A, Scheme 3).24,25 In only
one case so far, namely, Ru(CCCCFc)(dppe)Cp, has
addition to each of the CC triple bonds been found, to give
Ru{C[C(CN)2]C[C(CN)2]CCFc}(dppe)Cp (3) and
Ru{CCC[C(CN)2]CFcC(CN)2}(dppe)Cp (4).25b
This behavior may result from the smaller size of Cp vs Cp*,
but can also result from the presence of the weaker electron-
donor Fc group, leading to competitive cycloaddition reactions
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Chart 1. Compounds Discussed in This Work
to each CC triple bond. The ethynylbutadiene 4 shows a
distinct structural distortion toward the zwitterionic (or
vinylidene) formulation 4B shown in Scheme 3. Interestingly,
an analogous situation occurs with the regioselective addition of
TCNE to the CC triple bonds of the diyne FcCCC
CC6H4NMe2-4, which is directed by the strong anilino electron
donor to its adjacent CC triple bond. Protonation (HBF4) of
the NMe2 group reduces its donor power sufficiently so that the
Fc donor could activate the CC triple bond adjacent to this
group.12b
Scheme 3. Two Sites of Addition of TCNE to a Diynyl-Metal
Complex
With the dual intent of gaining additional insight into the
reactivity of TCNQ with alkynyl-metal complexes and access to
further examples of hybrid donor−acceptor compounds, we
have now reacted some poly-ynyl-metal derivatives with
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TCNQ. This paper reports the rich chemistry found in
reactions between this cyanocarbon and the group 8 derivatives
Ru(CCCCH)(dppe)Cp* (5) and M{(CC)2+nPh}(PP)-
Cp′ [n = 0, M = Fe, Ru, (PP)Cp′ = (dppe)Cp* (6-Fe and 6-
Ru); n = 1, M(PP)Cp′ = Ru(PPh3)2Cp (7)], from which we
have prepared compounds 8−11 (Chart 1). Interestingly,
compound 9 resulted from the unprecedented addition of two
metal fragments to a single cyanocarbon molecule.
RESULTS
■
1. Preparation of the New Complexes. The reactions of
TCNQ with 5, 6-Fe, 6-Ru, and 7 are summarized in Schemes
4− and 5. The molecular structures of five complexes have been
Scheme 4. Formation of 8 and 9 from Ru(CCC
CH)(dppe)Cp* with TCNQ
Figure 1. Plot of molecule 1 of Ru{CCC[C6H4C(CN)2]-
CHC(CN)2}(dppe)Cp* (8). Molecules 2−4 are similar. Hydrogen
atoms have been omitted for clarity.
Scheme 5. Reactions of TCNQ with M{(C
C)2+nPh}(PP)Cp′ [n = 0, (PP)Cp′ = (dppe)Cp*, M = Fe 6-
Fe, Ru 6-Ru; n = 1, M(PP)Cp′ = Ru(PPh3)2Cp 7]
Figure 2. Plot of a molecule of {Cp*(dppe)Ru}{CCC[C6H4
C(CN)2]CHCHC[C(CN)2]CC}{Ru(dppe)Cp*} (9). Hy-
drogen atoms have been omitted for clarity.
determined by single-crystal X-ray diffraction studies (Figures
1−4 and Table 1) and confirmed by elemental microanalyses
and from their spectroscopic properties. In the case of the iron
compound 10-Fe, the nature of the iron−carbon bonding has
aromatic (7.01−7.42) resonances are accompanied by a singlet
at δH 6.72 assigned to the CHC(CN)2 proton. In the 13C
NMR spectrum, resonances occur at δC 9.79, 96.61 (Cp*),
29.42−30.30 (CH2), 124.75−138.22 (Ph + C6H4), and 218.70
(Ru−C, t), together with four CN signals between δC 111.73
and 120.89. In addition, resonances at δC 86.13, 145.01, 152.70,
and 155.26 arise from the cyanocarbon skeleton.
The molecular structure of 8 was determined from a single-
crystal X-ray diffraction study, and a plot of the molecule is
given in Figure 1. Selected structural data are presented in
Table 1. The structure is that expected from ring-opening of
the [2 + 2]-cycloadduct of one of the C(CN)2 double bonds
with the outer CC triple bond of the precursor diynyl
complex. Thus, the Ru center is attached to the remaining C
C triple bond [Ru−C(11) 1.939(12), C(11)−C(12) 1.207(18)
Å; values for molecule 1 cited], which in turn is a substituent on
the dienyl system C(131)C(13)−C(14)C(15). As found
both with similar products from reactions of TCNE and for
organic adducts of cyanocarbons with donor-substituted
alkynes,5b there is a marked dihedral [50.6(6)°] between the
been investigated by Mossbauer spectroscopy of a powdered
̈
sample. In addition, the redox properties and the UV−vis
spectroscopy of 8, 9, 10-Fe, 10-Ru, and 11 were determined in
solution.
i. Reaction of TCNQ with Ru(CCCCH)(dppe)Cp* (5).
The two complexes 8 and 9 have been obtained from reactions
between TCNQ and this diynyl-ruthenium complex (Scheme
4). If the reaction is carried out in THF with an excess of
TCNQ, an instantaneous color change from yellow to dark
green occurs, and subsequent purification of the product by
preparative TLC affords a low yield of Ru{CCC[C6H4
C(CN)2]CHC(CN)2}(dppe)Cp* (8), which is obtained as
a dark green solid. The composition was confirmed by a high-
resolution ES-MS of M+. The IR spectrum contains ν(CN)
(2193), ν(CC) (1940), and ν(CC) bands (1586 cm−1). In
1
the H NMR spectrum, Cp* (δH 1.38), CH2 (1.94, 2.57), and
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Figure 3. Plots of single molecules of M{CCC[C6H4C(CN)2]CPhC(CN)2}(dppe)Cp* [M = Fe 10-Fe (left) and M = Ru 10-Ru (right)].
Hydrogen atoms have been omitted for clarity.
1.51 and 1.53; the two dppe CH2 signals are found at δH 1.99−
2.12 (4H) and 2.68, 2.82 (2 × 2H). In the 13C NMR spectrum,
the two Cp* groups give Me resonances at δC 10.28, 10.41 and
ring C signals at δC 95.56 and 96.62. There are also two broad
Ru−C triplet resonances at δC 191.89 and 210.57. Other signals
include four CN signals between δC 114.43 and 118.95, with
two cyanocarbon skeleton resonances at δC 77.10 and 121.17.
Two 31P signals at δP 80.7 and 81.8 arise from the two dppe
ligands. The IR spectrum was similar to that of 8, with ν(CN)
(2186), two ν(CC) (1983, 1947), and ν(CC) (1579
cm−1) bands.
Figure 2 is a plot of a molecule of 9; selected structural data
are presented in Table 1. This shows that two Ru(dppe)Cp*
groups at each end of a C8 chain bear the C(CN)2 and 
C6H4C(CN)2 components of the TCNQ molecule attached
to C(3) and C(6), respectively [C(6)−C(61) 1.398(5), C(3)−
C(31) 1.425(5) Å]. The C(4)C(5) fragment [1.339(5) Å]
carries one H atom on each carbon, with angles C(3)−C(4)−
C(5) and C(4)−C(5)−C(6) of 125.1(4)° and 121.6(4)°,
respectively. The Ru atoms are attached to C(1) and C(8) of
the two end CC triple bonds [Ru(1)−C(1) 1.952(4),
Ru(2)−C(8) 1.943(4), C(1)−C(2) 1.233(5), C(7)−C(8)
Figure 4. Plot of a molecule of Ru{CCC[C6H4C(CN)2]C[
1.227(5) Å].
C(CN)2]CCPh}(PPh3)2Cp (11). Hydrogen atoms have been
omitted for clarity.
The formation of 9 is notable in that the second addition
occurs to the dienyl-bonded CC(CN)2 group of 8 rather
than to the other CC(CN)2 moiety of the TCNQ. We note
that the two components of the original TCNQ reactant are
now separated by a −CHCH− fragment, so that it is unlikely
that 9 was formed by addition of TCNQ to an Ru-(CC)4-Ru
precursor, which might have been formed by oxidative coupling
of the diynyl complex.26 Instead, we favor a route whereby a
molecule of 8 reacts with a second molecule of the diynyl-
ruthenium complex, with a [2 + 2]-cycloaddition to the
C(14)C(CN)2 fragment, followed by the usual ring-opening
step (as shown in Scheme 4). Indeed, the reaction between 8
and a second equivalent of 5 afforded 9 in 56% yield. It is also
likely that charge separation within the metal−cyanocarbon
array, facilitated by both the electron-richness of the former and
the electrophilic properties of the latter, and the steric influence
of the diphosphine ligand play roles in the course of this
reaction.
two CC double bonds. The structure determination reveals
that the C6 quinoid group is attached to C(13), i.e., nearer to
the electron-rich metal center, with the C(CN)2 group being
attached to C(14). This mode of addition was previously found
in reactions of TCNQ with Ni(CCR)(PPh3)Cp,19 Ru(C
CR)(dppe)Cp* (R = H, Ph),21 and Ru{CCCCC
C[CCo3(μ-dppm)(CO)7]}(dppe)Cp*.20 In all of these reac-
tions, cycloaddition of TCNQ is stereospecific, the C(CN)2
group residing further from the metal center; no evidence was
found for the formation of any isomeric product resulting from
the alternative mode of addition.
When the reaction between TCNQ and Ru(CCC
CH)(dppe)Cp* was carried out in benzene, a different product
was obtained in low yield, namely, dark brown {Cp*(dppe)-
Ru}{μ-CCC[C6H4C(CN)2]CHCHC[C(CN)2]-
CC}{Ru(dppe)Cp*} (9). The dimeric formulation was
confirmed by high-resolution ES-MS, and the two Ru(dppe)-
Cp* groups could be distinguished in the NMR spectra. Thus,
ii. Reaction of TCNQ with M(CCCCPh)(dppe)Cp* (M
= Fe, 6-Fe; M = Ru, 6-Ru). A rapid color change from orange
to dark purple (Fe) or from yellow to dark blue (Ru) followed
1
in the H NMR spectrum, the two Cp* resonances are at δH
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Table 1. Selected Bond Parameters for TCNQ Complexes
a
8 (molecule 1)
9
10-Fe
10-Ru
2.287(2)
11
Bond Distances (Å)
Ru−P(1)
Ru−P(2)
2.294(4)
2.274(1); 2.290(1)
2.277(1); 2.298(1)
2.232−2.285(4);
2.235−2.286(4)
2.249;
2.2186(8)
2.2160(8)
2.3059(3)
2.3100(3)
2.287(4)
2.292(2)
Ru−C(cp)
2.229−2.301(15)
2.122−2.156(3)
2.230−2.281(6)
2.235−2.266(1)
(av)
2.260
2.141
2.259
2.249
2.261
Ru−C(1)
C(1)−C(2)
C(2)−C(3)
C(3)−C(4)
C(3)−C(31, 32)
C(n)−C(41)
C(4)−C(5)
1.939(12)
1.21(2)
1.45(2)
1.45(2)
1.42(2)
1.952(4)
1.811(3)
1.943(6)
1.931(1)
1.248(2)
1.379(2)
1.497(2)
1.412(2)
1.233(5)
1.251(4)
1.223(9)
1.388(5)
1.383(4)
1.370(9)
1.457(5)
1.494(4)
1.497(9)
1.425(5)
1.423(4)
1.430(9)
1.480(4) [C(4)]
1.359(4)
1.480(10) [C(4)]
1.341(9)
1.35(2)
1.339(5)
1.464(5)
1.416(2)
1.208(2)
C(5)−C(6)
C(5)−C(51, 52)
C(6)−C(61)
1.47, 1.43(2)
1.433, 1.439(4)
1.452, 1.450(10)
1.398(5)
1.429(2)
C(34)−C(340)
C(340)−C(341, 342)
Bond Angles (deg)
P(1)−Ru−P(2)
1.418(4)
1.410(10)
1.416, 1.426(4)
1.419, 1.400(10)
1.420, 1.422(2)
102.91(1)
89.68(4)
83.5(1)
79.2(4)
88.6(4)
85.10(4);
83.63(4)
85.7(1);
82.2(1)
85.97(3)
89.59(9)
82.96(8)
82.69(6)
84.5(2)
89.8(2)
P(1)−Ru−C(1)
P(2)−Ru−C(1)
82.6(1);
85.5(1);
176.0(4)
173.1(4)
119.7(2)
119.6(4)
125.1(4)
89.21(4)
Ru−C(1)−C(2)
C(1)−C(2)−C(3)
C(2)−C(3)−C(4)
C(2)−C(3)−C(31, 32)
C(3)−C(4)−C(5)
166.9(12)
178.8(17)
116.8(13)
120.2(13)
126.8(14)
174.3(2)
172.3(5)
174.7(1)
172.6(3)
169.0(6)
169.9(1)
112.7(2)
113.2(6)
114.1(1)
125.3(3)
127.0(6)
125.7(1)
120.4(2)
120.3(6)
120.0(1)
C(3)−C(4)−C(n)
C(4)−C(5)−C(6)
116.4(2) [C(41)]
115.1(6) [C(41)]
120.4(1) [C(40)]
174.8(1)
121.6(4)
119.9(4)
C(5)−C(6)−C(61)
C(34)−C(340)−C(341, 342)
C(341)−C(340)−C(342)
C(4)−C(5)−C(51, 52)
C(51)−C(5)−C(52)
175.3(2)
121.3, 118.4(3)
121.8, 115.5(3)
121.2, 121.3(7)
117.4(7)
121.8, 120.7(1)
117.5(1)
123.4, 120.9(13)
120.5(6), 124.2(7)
115.3(6)
a
For Ru, read Fe. For 8: C(34)−C(37) 1.39(2), C(37)−C(38,39) 1.39, 1.42(2) Å; C(34)−C(37)−C(38,39) 124.6, 115.7(14)°. For 9: Ru(2)−C(8)
1.943(4), C(6)−C(7) 1.396(5), C(7)−C(8) 1.227(5), C(34)−C(340) 1.409(5) Å; C(5)−C(6)−C(7) 119.5(4), C(4)−C(3)−C(31) 120.7(3),
C(6)−C(7)−C(8) 177.1(4), C(7)−C(8)−Ru(2) 178.8(3)°. For 11: C(4)−C(40) 1.361(2), C(40)−C(41,42) 1.430, 1.431(2) Å; C(4)−C(40)−
C(41,42) 122.9, 120.8(1), C(41)−C(40)−C(42) 116.2(1)°.
the addition of TCNQ to solutions of M(CCCCPh)-
(dppe)Cp* (6, M = Fe, Ru) in THF at rt. Purification by
preparative TLC afforded dark blue M{CCC[C6H4
C(CN)2]CPhC(CN)2}(dppe)Cp* (10-Fe, 10-Ru) in mod-
erate yields (Scheme 5). In the IR spectrum, ν(CN), ν(CC),
and ν(CC) bands are found at 2223, 1914, and 1579 (Fe) or
at 2194, 1946, and 1585 cm−1 (Ru).
to CN groups, and a downfield triplet at δ 244.90 (217.10),
arising from the M-bonded carbon.
The single-crystal X-ray diffraction molecular structure
determinations of 10-Fe and 10-Ru (Figure 3; selected
structural data are presented in Table 1) showed that the
products are butadienyls, likely formed by ring-opening of the
undetected cyclobutenyls formed by [2 + 2]-cycloaddition of
one C(CN)2 moiety to the outer CC triple bond, in a
fashion similar to the formation of 8. Cleavage of the TCNQ
molecule into C6H4C(CN)2 and C(CN) fragments has
occurred, the former being attached to C(3) [C(3)−C(31)
1.423(4) [1.430(9)] Å; values for 10-Fe (10-Ru) given], and
the C(CN)2 group is attached to C(4) [C(4)−C(5)
1.359(4) [1.341(9) Å]], the resulting diene again being
nonplanar [73.0(3)°, (73.6(2)°)].
The 1H, 13C, and 31P NMR spectra of 10 contain the
expected resonances [values for the Fe (Ru) complexes given]
for the Cp* [δH 1.21 (1.53), δC 9.52, 96.54 (10.24, 98.17)],
dppe [δH 1.76−2.42 (2.22), δC 30.87 (30.01−30.62), δP 94.3
(80.5 br)], and Ph + C6H4 [δH 6.85−7.60 (6.96−7.50), δC
127.86−136.97 (128.38−137.47)] groups. In addition, the 13C
NMR spectrum contains four resonances between δC 58.28 and
171.56 assigned to carbons of the butadienyl skeleton, four
resonances (in two pairs) between 113.03 and 123.20, assigned
In 10, the usual M(dppe)Cp* moieties are attached to C(1)
[M−C(1) 1.811(3) [1.943(6)], C(1)−C(2) 1.251(4)
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[1.223(9) Å]; values for Fe [Ru]]. Of interest is the contraction
of the M−C bond from the ca. 1.90 (2.00) Å expected for an
M−C(sp) bond [cf. 1.894(3) in Fe(CCPh)(dppe)Cp*,27
2.015(2) Å in Ru(CCH)(dppe)Cp*28], supporting a
contribution to the structure from the zwitterionic formulation
(see structures A, B in Scheme 5), with the positive charge
centered on the metal center, resulting in some multiple-bond
character for the M−C(1) link. The localization of negative
charge on the remote C(CN)2 group is also indicated by the
elongation of the C−CN bonds, compared with the values
found for the C−CN bonds in the C6H4C(CN)2 group. The
M−C(1)−C(2)−C(3) arrays are nearly linear, with angles at
C(1) and C(2) of 174.3(2)° [172.3(5)°] and 172.6(3)°
[169.0(6)°], respectively.
Figure 5. 57Fe Mossbauer spectrum of 10-Fe at 80 K.
̈
iii. Reaction of TCNQ with Ru{(CC)3Ph}(PPh3)2Cp, 7.
Addition of TCNQ to a solution of the triynyl complex
Ru{(CC)3Ph}(PPh3)2Cp (7) in dichloromethane resulted in
an immediate change of color from yellow to dark blue, the
complex Ru{CCC[C6H4C(CN)2]C[C(CN)2]C
CPh}(PPh3)2Cp (11) (Scheme 5) being precipitated by
addition of hexanes to the concentrated reaction mixture.
The composition was confirmed by a high-resolution ES-MS on
[M + H]+. In the IR spectrum, ν(CN), ν(CC), and ν(C
C) bands are found at 2198, 1956, and 1590 cm−1, respectively.
but not exceptional, for compounds containing the Fe(dppe)-
Cp* moiety.32
However, the isomeric shift [IS = 0.187(3) mm s−1 vs Fe ] is
particularly small for a neutral compound. This parameter
reflects the electron density at the iron nucleus and decreases as
charge is progressively removed from the metal atom or less
and less stabilized by electrostatic interaction between cations
and anions.33 In the case of compound 10-Fe the value
compares well with data obtained for iron carbene, vinylidene,
or allenylidene complexes, in which the positive charge is
localized on the metal center.34
1
The usual signals are present in the H and 31P NMR spectra
[at δH 4.64 (Cp), 7.01−7.52 (Ph + C6H4), δP 48.0], while the
13C NMR spectrum has resonances at δC 61.77 (CC), 88.86
(Cp), 127.98−136.80 (Ph + C6H4), and 217.99 (Ru−C, t),
together with several other cyanocarbon skeleton signals
between δC 86.75 and 154.05 and two pairs of CN resonances
between δ 112.90 and 123.55.
The quadrupole splitting parameter [QS = 1.367(6) mm s−1]
also does not match with the alkynyl-iron(II) structure depicted
for 10-Fe as structure A in Scheme 5. Indeed, for such a
structure the expected QS value is close to 2.0
0.1 mm
s−1.32,34,35 In this series, QS values ranging between 1.0 and 1.5
are characteristic of cationic metallacumulenylidene complexes
with the general structure [Cp*(dppe)Fe{C(C)nR2}]X
and consistent with a major contribution from Lewis structure
B (Scheme 5) to the electronic structure of 10-Fe.34
Figure 4 is a plot of a molecule of 11 (selected structural data
are presented in Table 1), from which it can be seen that the 
C6H4C(CN)2 fragment is attached to C(3) [C(3)−C(31)
1.412(2) Å] and the C(CN)2 group to C(4) [C(4)−C(40)
1.361(2) Å], i.e., the central two carbons of the C6 chain in the
triynyl precursor. Consequently, it is the Ru(PPh3)2Cp and Ph
groups that are attached to the CC groups at the ends of the
chain [Ru−C(1) 1.931(1), C(1)−C(2) 1.248(2), C(5)−C(6)
1.208(2), C(6)−C(61) 1.429(2) Å]. Some lengthening of the
inner CC bond to 1.248(2) Å is notable and is consistent
with a significant contribution from structure 11B (Scheme 5).
In general, this structure has features similar to those of 10-Ru
already described. Notable here, however, is the bending of the
C6 chain. Angles at C(1), C(2), C(5), and C(6) range between
169.9(1)° and 175.3(1)° (as expected for slightly distorted
C(sp) atoms), whereas those at C(3) and C(4) are 114.1(1)°
and 120.0(1)°, respectively, typical of C(sp2) atoms. Angles at
individual C(sp) [C(1,2,5,6)] and at C(sp2) atoms [C(3,4)]
sum to 151.2° from linear in a cumulative sense, so that the
C(6)−C(61) vector is inclined at 55.0(2)° to the C(1)−C(2)
vector.
3. Redox Properties. The initial scans of the CVs of
complexes 8, 9, 10-Fe, 10-Ru, and 11 were run from −1.5 to
+1.5 V vs SCE. The redox potentials and, when the redox
processes are reversible, the peak-to-peak separations (ΔEp) are
collected in Table 2, and the CV of 10-Ru is shown in Figure 6
as a representative example. For the four mononuclear
compounds 8, 10-Fe, 10-Ru, and 11, the CVs display a single
oxidation wave (E0/1+) corresponding to the formation of the
Table 2. Electrochemical Data for 8, 9, 10-Fe, 10-Ru, 11, and
a
Selected Compounds
compd
E2−/1− (ΔEp)
E1−/0 (ΔEp)
E0/1+ (ΔEp)
E1+/2+ (ΔEp)
b
6-Fe
−0.02 (0.06)
b
c
6-Ru
0.44
c
c
1
−1.40
−0.50 (0.05)
−0.34
−0.52 (0.05)
−0.49 (0.15)
−0.41 (0.05)
−0.27 (0.05)
0.20 (0.05)
0.76
c
8
−0.72
0.44
c
c
9
−0.85 (0.05)
−0.82 (0.15)
−0.62 (0.05)
−0.45 (0.05)
−0.35 (0.05)
0.57
0.80
2. Investigation of the Iron−Carbon Bonding by
Mossbauer Spectroscopy. 57Fe Mossbauer spectroscopy is
a very sensitive probe for identifying the oxidation state of the
10-Fe
10-Ru
11
0.42 (0.07)
̈
̈
c
0.67
b
iron and the nature of the Fe−C bond.29,30 The zero-field 57Fe
Mossbauer spectrum of a microcrystalline sample of the
0.79
TCNQ
̈
complex 10-Fe was obtained at 80 K and least-squares fitted
with Lorentzian line shapes.31 The spectrum displays a unique
doublet (Figure 5), proving the purity and the thermal stability
of the sample. The half-widths at half-height [Γ = 0.209(4) mm
s−1] of the two components of the doublet are relatively large,
a
Potentials in CH2Cl2 (0.1 M [n-Bu4N][PF6], 20 °C, platinum
electrode, sweep rate 0.100 V s−1) are given in V vs SCE; the
ferrocene−ferrocenium couple (0.46 V vs SCE) was used as an
b
internal calibrant for the potential measurements. From ref 36.
c
Irreversible.
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complexes are very similar. Besides intense absorptions below
300 nm, which are assignable to intraligand transitions
involving the C5 ring and the phosphine ligands, the electronic
spectra of the neutral species exhibit two absorptions each of
medium intensity between 300 and 600 nm. By comparison
with the related iron and ruthenium complexes bearing σ-
acetylides substituents, these bands are tentatively assigned to
dπ(M) → π*(CC) metal-to-ligand charge transfer tran-
sitions.36,38b Additional broad and very intense bands that are
responsible for the intense colors of these complexes were also
found on the low-energy side of the spectra and extend into the
near-IR. These bands are characteristic of CT transitions, and in
the case of complex 1, it has been shown that these bands are
solvatochromic.21
Figure 6. Cyclic voltammogram of 10-Ru (V vs SCE). Experimental
conditions are given below Table 2.
DISCUSSION
■
Previous studies of the reactions of TCNQ with alkynyl−group
8 complexes have resulted in complexes that may reasonably be
expected to be formed by reactions summarized in Scheme 2.
The adduct 8 has been identified here as the initial product
from the reaction between TCNQ and Ru(CCCCH)-
(dppe)Cp*, but this complex is accompanied by the binuclear
adduct 9. The latter is the product of addition of two ethynyl-
ruthenium groups to one TCNQ molecule, and we suggest that
it has been formed by cycloaddition of a second molecule of
Ru(CCCCH)(dppe)Cp* to 8 followed by ring-opening.
Indeed, reaction of pure 8 with Ru(CCCCH)(dppe)Cp*
gives 9 in high yield. Formally, this reaction corresponds to
insertion of the CCH triple bond into the C−H bond
present in 8. Double addition of TCNE has been observed
previously for {Ru(PPh3)2Cp}2(μ-C8) to give {Cp(Ph3P)2Ru}-
CC{C[C(CN)2]}4CC{Ru(PPh3)2Cp},37 but this is the
first occasion on which addition of two metal fragments to a
single cyanocarbon molecule has been demonstrated. In
principle, this mode of action should be available to other
tetracyanobutadiene complexes. As mentioned above, various
octacyano[4]dendralenes were formed by double addition of
TCNE to anilino-capped buta-1,3-diynes,22 and cascade
additions of TCNE and tetrathiafulvene to 4-Me2NC6H4(C
C)4Ph have been described.23 Reactions of Ph-diynyl- or Ph-
triynyl-ruthenium complexes with TCNQ afford products 10-
Ru and 11, in which the cyanocarbon has added to the CC
triple bond one removed from the metal center; the iron
analogue 10-Fe has been obtained from a similar reaction with
6-Fe.
The molecular structures of the new complexes described
above have been confirmed by single-crystal X-ray diffraction
studies. Of note is the twisting of the butadiene moiety, with
dihedrals between the two CC double bonds ranging
between 12.6(4)° (for 9) and 73.6(2)° (for 10-Ru). In
analogous tricyanovinyl organics this feature has been related to
a preference for π conjugation with other substituents rather
than with the second CC double bond in the usual diene
structure.5c In the present cases (and those found with TCNE
earlier),15a this may be related to charge transfer from the
electron-rich metal center to give a stable zwitterionic
vinylidene mesomer of the complex, the formation of which
would be encouraged by delocalization of electron density onto
the C(CN)2 groups.
corresponding radical cations at the platinum electrode. In the
case of complex 10-Fe, the process found for the FeII/FeIII
redox couple is chemically reversible, indicating that the radical
cation [10-Fe]+ is thermally stable at the electrode. In contrast,
the reverse reduction wave cannot be detected for the
ruthenium complexes, indicating that the oxidized species
rapidly decompose at the electrode. In the particular case of the
binuclear complex 9, two irreversible oxidation waves were
observed corresponding to the sequential oxidation of the two
metal centers. The two different ruthenium ethynyl moieties of
9 oxidize independently at 0.57 and 0.80 V, and both give rise
to chemically reactive species. In the case of the ruthenium
complexes, the 1-e oxidation products are labile and rapidly
decompose; the signatures of the resulting materials are found
in the CVs during the back reduction. Indeed, the CVs of the
ruthenium complexes 8, 9, 10-Ru, and 11 display reduction
waves of weak intensity at 0.14, 0.78, 0.18, and 0.39 V,
respectively, at potentials distinct from those of the 0/1+ redox
couples.
The CVs of 8, 9, 10-Fe, 10-Ru, and 11 also show also two
reversible or quasi-reversible reduction waves in the reduction
range (E1−/0 and E2−/1− in Table 2). These redox events are
centered on the TCNQ side of the complexes, and the redox
potentials are significantly more negative than that of TCNQ,
showing that a strong electronic interaction between the
electron-donor metal centers and the electron-withdrawing
organic ligands occurs through the bridge. Similarly, one can
also note that the oxidation potentials of the iron and
ruthenium centers are both located at more positive potentials
than those of 6-Fe and 6-Ru, consistent with the zwitterionic
formulations indicated by the structural results.36
UV−Vis Spectroscopy. The UV−vis spectra of 10-Fe, 10-
Ru, and 11, chosen as representative of this series, were
investigated at 20 °C in CH2Cl2, and the data are collected in
Table 3 together with those obtained previously for 1 for
purposes of comparison.21 The spectra of these deeply colored
Table 3. UV−Vis Absorption Data for 10-Fe, 10-Ru, 11, and
the Related Complex 1 in CH2Cl2 at 298 K
cmpd
absorption λ/nm (ε/dm3 mol−1 cm−1
)
a
1
260 (87.9), 332 (15.9), 488 (5.1), 748 (66.7), 814 (73.6)
265 (46.2), 367 (8.9), 520 (9.8), 830 (35.9)
10-Fe
10-Ru
11
There is an interesting contrast between the reactions of
TCNQ with similar iron complexes, which afford the oxidized
(1-e) compounds, and a richer chemistry found with the
ruthenium systems. These results further highlight the
256 (32,3), 296 (20.0), 468 (6.9), 725 (32.6), 782 (56.3)
b
354 (18.4), 587 (13.9), 706 (29.6, 761 (40.9)
a
b
From ref 21. Measurement started at 350 nm.
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differences in electronic structures of the two series of
complexes. DFT calculations have shown that the Fe complexes
have a high tendency for electron density in the HOMOs to be
centered on the metal atom. In the Ru analogues, higher
coefficients are found on the carbon atoms of the chain.38
Evidently, for the phenylethynyl complex, loss of an electron
from the iron center to generate the related 17-e cation is
preferred over extended conjugation with the unsaturated
chain, which leads to formation of more electron-rich centers
that can attack the cyanocarbon at the C(CN)2 groups. On
the other hand, lengthening of the C(sp) chain allows the iron
and ruthenium systems to display similar chemistry, as found
here for M(CCCCPh)(dppe)Cp* (M = Fe, Ru).25
In conclusion, the first step in all of these reactions appears
to be electron transfer from the metal to the cyanocarbon,
generating structure G (Scheme 2). If the steric protection
within the radical is large enough, the cationic complex is stable
enough to isolate. This is particularly the case when there is a
single CC bond. With poly-ynyl derivatives, delocalization of
the spin density on the poly-ynyl ligand is larger and C−C
bond formation can ensue. When this occurs, formation of
cyclobutenyl and butadienyl derivatives is found.
δr = (((a + a′)/2 − (b + b′)/2)
+ ((c + c′)/2 − (b + b′)/2))/2
For benzene δr is 0 Å, but increases to ca. 0.08−0.10 Å for
quinoid rings; for TCNQ itself, δr is 0.102 Å.38a The detailed
results are given in Table S1 (Supporting Information), which
includes values for δr. Only in 13 (Chart 1) does this value
(0.093 Å) approach that of TCNQ itself, while in 12, in which
the C6 ring originating in TCNQ has become fully aromatic, δr
is 0.012 Å. In the other complexes listed in Table S1 (1, 8, 9,
10-Fe, 10-Ru, and 11), the values range between 0.031 and
0.066 Å. For 8, the low value of 0.031 Å relates to short C−C
bond average (c + c′)/2 of 1.398(0) Å, the value for (a + a′)
being 1.444(0) Å. The decrease in δr is the result of replacing
the strong acceptor CC(CN)2 group by the electron-rich
group 8 metal center, which acts as a strong donor. Values of δr
can in turn be related to the Ru−P and RuC bond lengths,
thus giving a second estimate of the contribution of the quinoid
character to the structure. Further, in CT salts, the apparent
charge per TCNQ anion can be determined from the exocyclic
double-bond lengths.40,41 As summarized in Table S1, the
single exocyclic CC lengths range from 1.39(2) Å (for 8) to
1.454(15) Å (for 1).
Detailed examination of the structural parameters of
complexes described above and related systems reported
elsewhere points to significant contributions from zwitterionic
forms of the molecules. Of interest in this discussion are (a) the
lengths of the M−P, M−C(1), and C(1)−C(2) bonds and (b)
the degree of quinoid character possessed by the C6H4
C(CN)2 fragment. Characteristic lengths for Ru−C(sp) bonds
in alkynyl complexes are ca. 2.000 Å [cf. 2.015(2) Å in Ru(C
CH)(dppe)Cp*28], while for RuC(sp) bonds in vinylidenes,
distances of ca. 1.85 Å [cf. 1.85(1) Å in [Ru(C
CH2)(dppe)Cp*]+38b] are found. In the molecules derived
from TCNQ whose structures are reported here and else-
where,21 the Ru−C distances range between 1.855(6) Å in 12
(Chart 1) and 1.943(4) Å in 9 and 10-Ru. All are considerably
shorter than the Ru−C(sp) single bond, but approach the value
expected for a RuC(sp) double bond in vinylidenes. The
Ru−P distances fall within the range 2.26 Å (found for neutral
Ru-alkynyl complexes)28 to 2.36 Å (found in cationic Ru-
vinylidene complexes).38b These data suggest that there is a
considerable contribution from the mesomeric zwitterionic
structure, with charge separation between the positively
charged metal center and the anion stabilized by the distant
cyanocarbon group (Scheme 5). This will have a further effect
upon the geometry of the C6H4C(CN)2 group, which will
tend toward the fully aromatic structure. Further, in the case of
10-Fe, Fe−P bond distances also support a zwitterionic
CONCLUSIONS
■
In this paper we have extended our earlier study of the
reactions of TCNQ with alkynyl-iron and -ruthenium
complexes21 to those of analogous diynyl and triynyl systems.
In the case of Ru(CCCCH)(dppe)Cp*, the product
Ru{CCC[C6H4C(CN)2]CHC(CN)2}(dppe)Cp*
(8) is formed by ring-opening of the initial [2 + 2]-adduct of
TCNQ to the outer CC triple bond. A second equivalent of
the diynyl-Ru complex adds to a CC double bond of 8
(possibly via initial formation of charge-transfer and zwitter-
ionic intermediates) to give binuclear {Ru(dppe)Cp*}{C
CC[C6H4C(CN)2]CHCHC[C(CN)2]CC}{Ru-
(dppe)Cp*} (9). The latter reaction is unprecedented in the
otherwise similar chemistry of TCNE. Iron and ruthenium
complexes M(CCCCPh)(dppe)Cp* react to give analo-
gous η1-(butadienyl)ethynyls {CCC[C6H4C(CN)2]-
CPhC(CN)2}(dppe)Cp* (10-M); a similar reaction with
the analogous triynyl-Ru precursor affords Ru{CCC[
C6H4C(CN)2]C(CCPh)C(CN)2}(PPh3)2Cp (11).
The molecular structures of the new complexes have been
determined by single-crystal X-ray diffraction studies. The
structural parameters give information about the degree of
charge transfer from the electron-rich M(PP)Cp′ group to the
TCNQ-derived ligands. In this process, the alkynylmetal moiety
takes on some vinylidene character (shorter M−C, longer M−
P, and CC bonds), while the quinodimethane portion, of
which the C(CN)2 group can accept charge, becomes more
aromatic, as measured by the endocyclic CC distances. The
chromophores in all complexes described show interesting CT
behavior, the complexes themselves being further examples of
interesting donor−acceptor molecular arrays.
structure, while Mossbauer spectroscopy clearly confirms that
̈
this structure is strongly dominant.
Comparison of the structural parameters of TCNQ itself39
with those of the various fragments found in these complexes is
instructive. In TCNQ, the two exocyclic CC(CN)2 groups
have CC, C−CN, and CN bond lengths of 1.374(3),
1.440(3), and 1.141(3) Å, respectively.42 Within the C6 ring,
the CC and C−C bonds are 1.346(3) and 1.450(3) Å. As
charge accumulates on the C6H4C(CN)2 group, trans-
formation of the C6H4 moiety toward a fully aromatic structure
occurs. The quinoid character of C6 rings, δr, can be expressed
by
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c. Independent Synthesis of 9. When THF was added to a Schlenk
flask containing Ru(CCCCH)(dppe)Cp* (5) (5 mg, 0.007
mmol) and Ru{CCC[C6H4C(CN)2]CHC(CN)2}(dppe)-
Cp* (8) (6 mg, 0.007 mmol), a dark brown solution was formed
immediately. After 1 h at room temperature, solvent was removed and
the residue was purified by preparative TLC (acetone/hexane, 3/7).
The brown band (Rf = 0.38) contained {Ru(dppe)Cp*}{CCC[
C6H4C(CN)2]CHCHC[C(CN)2]CC}{Ru(dppe)Cp*} (9)
(6 mg, 56%).
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out under dry
nitrogen, although normally no special precautions to exclude air were
taken during subsequent workup. Common solvents were dried,
distilled under nitrogen, and degassed before use. Separations were
carried out by preparative thin-layer chromatography on glass plates
(20 × 20 cm2) coated with silica gel (Merck, 0.5 mm thick).
Instruments. IR spectra were obtained on a Bruker IFS28 FT-IR
spectrometer. Spectra in CH2Cl2 were obtained using a 0.5 mm path-
length solution cell with NaCl windows. NMR spectra were recorded
on a Varian Gemini 2000 instrument (1H at 300.145 MHz, 13C at
75.479 MHz, 31P at 121.501 MHz). Unless otherwise stated, samples
were dissolved in CDCl3 contained in 5 mm sample tubes. Chemical
shifts are given in ppm relative to internal tetramethylsilane for 1H and
13C NMR spectra and external H3PO4 for 31P NMR spectra. UV−vis
spectra were recorded on a Varian Cary 5 UV−vis/NIR spectrometer.
Electrospray mass spectra (ES-MS) were obtained from samples
dissolved in MeOH unless otherwise indicated. Solutions were injected
into a Varian Platform II spectrometer via a 10 mL injection loop.
Nitrogen was used as the drying and nebulizing gas. Chemical aids to
ii. With Fe(CCCCPh)(dppe)Cp*. THF (15 mL) was added to a
Schlenk flask containing Fe(CCCCPh)(dppe)Cp* (6-Fe) (200
mg, 0.280 mmol) and TCNQ (57 mg, 0.280 mmol) at −78 °C to give
a dark purple solution. After 1 h at −78 °C, the solution was allowed
to warm to room temperature over 4 h. Pentane (50 mL) was then
added to the solution, and the purple precipitate was filtered off and
washed with pentane (3 × 10 mL) to afford Fe{CC−C[C6H4
C(CN)2]CPhC(CN)2}(dppe)Cp* (10-Fe) (184 mg, 71%) as a
dark purple solid. X-ray quality crystals were obtained from CH2Cl2/
pentane. Anal. Calcd (C58H48N4P2Fe·0.33CH2Cl2): C, 73.97; H, 5.18;
N, 5.92; M, 918. Found: C, 74.28; H, 5.18; N, 5.83. IR (KBr): ν(C
N) 2223w, 2183w, ν(CC) 1914s, ν(CC) 1579 m cm−1. 1H
NMR: δ 1.21 (s, 15H, Cp*), 1.76−2.42 (m, 4H, PCH2), 6.85−7.60
ionization were used as required.43 The 57Fe Mossbauer spectra were
̈
recorded with a 2.5 × 10−2 C (9.25 × 108 Bq) 57Co source using a
1
(m, 29H, Ph). 13C NMR: δ 9.52 (s, C5Me5), 30.87 [t, JPC = 22 Hz,
symmetric triangular sweep mode. Computer fitting of the Mossbauer
̈
dppe], 82.39 (s), 96.54 (s, C5Me5), 112.85, 113.01, 120.30, 121.14 (4s,
CN), 127.86−136.97 (m, Ph), 150.95 (s), 170.97 (s), 178.01 (s),
244.90 [t, 2JPC = 35 Hz, Ru-C]. 31P NMR: δ 94.3 (s). ES-MS (m/z):
found 919.2786, [M + H]+ (calcd 919.2782).
data to Lorentzian line shapes was carried out with a previously
reported computer program.31 The isomer shift values are reported
relative to iron foil at 298 K. Elemental analyses were by Campbell
Microanalytical Laboratory, University of Otago, Dunedin, New
Zealand.
iii. With Ru(CCCCPh)(dppe)Cp*. When THF (8 mL) was
added to a Schlenk flask containing Ru(CCCCPh)(dppe)Cp*
(6-Ru) (53 mg, 0.070 mmol) and TCNQ (16 mg, 0.077 mmol), the
solution became dark blue instantaneously. After 1 h at rt, solvent was
removed and the residue was taken up in a small amount of CH2Cl2
and purified by chromatography (acetone/hexane, 3/7, silica gel) to
afford Ru{CCC[C6H4C(CN)2]CPhC(CN)2}(dppe)Cp*
(10-Ru) (49 mg, 73%) as a dark blue solid (Rf = 0.11). X-ray quality
crystals were obtained from CH2Cl2/C6H6. Anal. Calcd
(C58H48N4P2Ru): C, 72.26; H, 5.02; N, 5.81; M, 964. Found: C,
71.74; H, 5.11; N, 5.63. IR (CH2Cl2/cm−1): ν(CN) 2194w, ν(C
C) 1946s, ν(CC) 1585 m. 1H NMR: δ 1.53 (s, 15H, Cp*); 2.22 (m,
4H, CH2); 6.96−7.50 (m, 29H, Ph). 13C NMR: δ 10.24 (s, C5Me5),
30.01−30.62 (m, dppe), 58.28 (s), 83.18 (s), 98.17 (s, C5Me5), 113.03,
113.50, 121.33, 123.20 (4s, CN), 128.38−137.47 (m, Ph), 150.24 (s),
153.81 (s), 171.56 (s), 217.10 (br, Ru-C). 31P NMR: δ 80.5 [br d,
JPP = 113.5 Hz]. ES-MS (MeOH/NaOMe, m/z): 965, [M + H]+; 987,
[M + Na]+.
Reagents. Ru(CCCCH)(dppe)Cp*,44 M(CCCCPh)-
(dppe)Cp* (M = Fe, Ru),36 and Ru(CCCCCCPh)-
(PPh3)2Cp36 were made by the literature methods. TCNQ was a
commercial sample (Aldrich).
Reactions of TCNQ. i. With Ru(CCCCH)(dppe)Cp*. a. In
THF. THF (8 mL) was added to a Schlenk flask containing Ru(C
CCCH)(dppe)Cp* (5) (50 mg, 0.073 mmol) and TCNQ (18 mg,
0.088 mmol) to give a dark green solution. After 2 h at room
temperature, solvent was removed and the residue was purified by
preparative TLC (acetone/hexane, 3/7). The green band (Rf = 0.41)
was collected to afford Ru{CCC[C6H4C(CN)2]CHC-
(CN)2]}(dppe)Cp* (8) (6 mg, 9%) as a dark green solid. X-ray
quality crystals were obtained from benzene/hexane. Anal. Calcd
(C52H44N4P2Ru): C, 70.34; H, 4.99; N, 6.31; M, 888. Found: C, 70.74;
H, 5.16; N, 6.50. IR (CH2Cl2, cm−1): ν(CN) 2193w, ν(CC)
1
1940s, ν(CC) 1586 m. H NMR (C6D6): δ 1.38 (s, 15H, Cp*),
1.94, 2.57 (2m, 4H, CH2), 6.72 [s, 1H, CHC(CN)2], 7.01−7.42
(m, 24H, Ph). 13C NMR (C6D6): δ 9.79 (s, C5Me5), 29.42−30.30 (m,
dppe), 86.13 (s), 96.61 (s, C5Me5), 111.73, 113.89, 117.53, 120.89 (4s,
CN), 124.75−138.22 (m, Ph), 145.01 (s), 152.70 (s), 155.26 (s),
iv. With Ru(CCCCCCPh)(PPh3)2Cp. TCNQ (41 mg, 0.2
mmol) was added to a solution of Ru(CCCCCCPh)-
(PPh3)2Cp (7) (168 mg, 0.2 mmol) in CH2Cl2 (20 mL), resulting
in an instantaneous darkening of the solution. After 1 h solvent was
reduced to approximately 1 mL and hexane (50 mL) was added to give
a dark blue precipitate. The precipitate was collected and then washed
with diethyl ether (10 mL) to afford Ru{CCC[C6H4
C(CN)2]C(CCPh)C(CN)2}(PPh3)2Cp (11) (183 mg, 88%) as
a dark blue solid. X-ray quality crystals were grown from dichloro-
methane/MeCN. Anal. Calcd (C65H44N4P2Ru): C, 74.77; H, 4.25; N,
5.37; M, 1044. Found: C, 74.18; H, 4.86; N, 5.19. IR (CH2Cl2, cm−1):
2
218.70 [t, JCP = 23 Hz, Ru-C]. 31P NMR (C6D6): δ 80.4 (s). ES-
MS (MeOH/NaOMe, m/z): found 888.2128, M+ (calcd 888.2085).
b. In C6H6. To a solution of Ru(CCCCH)(dppe)Cp* (5) (50
mg, 0.073 mmol) in benzene was added TCNQ (15 mg, 0.073 mmol);
the solution turned slowly from yellow to dark green. After 2 h at
room temperature, solvent was removed and the residue was purified
by preparative TLC (acetone/hexane, 3/7). The brown band (Rf =
0.38) was collected to afford {Ru(dppe)Cp*}{CCC[C6H4
C(CN)2]CHCHC[C(CN)2]CC}{Ru(dppe)Cp*} (9) (6 mg,
10%) as a dark brown solid. X-ray quality crystals were obtained from
benzene/diethyl ether. Anal. Calcd (C92H84N4P4Ru2): C, 70.30; H,
5.39; N, 3.56; M, 1572. Found: C, 70.01; H, 5.59; N, 3.52. IR
(CH2Cl2, cm−1): ν(CN) 2186w, ν(CC) 1983s, 1947s, ν(CC)
1579 m. 1H NMR (C6D6): δ 1.51 (s, 15H, Cp*), 1.53 (s, 15H, Cp*),
1.99−2.12 (m, 4H, 2 × CH2), 2.68, 2.82 (2 m, 4H, 2 × CH2), 6.88−
7.63 (m, 46H, Ph and HCCH). 13C NMR (C6D6): δ 10.28 (s,
C5Me5), 10.41 (s, C5Me5), 29.31−30.91 (m, dppe), 77.10 (s), 95.56 (s,
C5Me5), 96.62 (s, C5Me5), 114.43, 117.49, 118.05, 118.95 (4s, CN),
121.17 (s), 127.52−153.58 (m, Ph), 191.89, 210.57 [2 × t(br), Ru-
C]. 31P NMR (C6D6): δ 80.7 (s), 81.8 (s). ES-MS (MeOH/
NaOMe, m/z): found 1573.3752, [M + H]+ (calcd 1573.3812).
1
ν(CN) 2198w, ν(CC) 1956s, ν(CC) 1590 m. H NMR: δ
4.64 (s, 5H, Cp); 7.01−7.52 (m, 39H, Ph). 13C NMR: δ 61.77 (s),
86.75 (s), 88.86 (s, Cp), 90.32 (s), 111.86 (s), 112.90, 113.46 (2s,
CN), 117.69 (s), 119.91 (s), 121.49, 123.55 (2s, CN), 127.98−136.80
2
(m, Ph), 146.99 (s), 153.86 (s), 154.05 (s), 217.99 [t, JCP = 23 Hz,
Ru-C]. 31P NMR: δ 48.0 (s). ES-MS (MeOH/NaOMe, m/z):
found 1045.2221, [M + H]+ (calcd 1045.2163).
Structure Determinations. Diffraction data were measured using
Oxford Diffraction Xcalibur CCD diffractometers (Oxford Diffraction
Gemini for 8, Bruker-AXS APEXII for 10-Fe) at 100 K with Mo Kα
radiation, λ = 0.71073 Å (Cu Kα, λ = 1.54184 Å for 8). Following
multiscan absorption corrections and solution by direct methods, the
structures were refined using full-matrix least-squares refinements on
F2 using the SHELXL-97 program.45−47 Except where stated below,
6632
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Organometallics
Article
Table 4. Crystal Data and Refinement Details
8
9
10-Fe
10-Ru
11
CCDC #
835455
835456
892450
835457
835458
formula
C52H44N4P2 Ru·0.25C6H6 C92H84N4P4
C58H48N4P2 Fe·CH2Cl2 C58H48N4P2 Ru·3C6H6 C65H44N4P2 Ru·1.5CH2Cl2
Ru2·C4H10O·C6H6
1723.88
MW
907.45
1003.72
triclinic
1198.34
1171.44
triclinic
cryst syst
space group
a/Å
triclinic
triclinic
monoclinic
P21
P1
̅
P1
P1
̅
P1
̅
̅
12.5353(6)
25.7160(10)
29.3469(15)
76.344(4)
81.617(4)
80.015(4)
8999.0(7)
1.34
10.9127(5)
16.6873(6)
24.4436(11)
94.234(3)
94.875(4)
105.793(3)
4245.9(3)
1.348
13.0027(6)
13.5494(6)
15.2633(8)
69.676(2)
84.497(2)
88.105(2)
2510.0(2)
1.328
14.0764(10)
12.1829(8)
18.9165(14)
14.1999(3)
14.9393(3)
15.1754(3)
65.886(2)
80.367(2)
69.633(2)
2753.4(1)
1.413
b/Å
c/Å
α/deg
β/deg
100.112(7)
γ/deg
V/Å3
ρc/g cm−3
Z (f.u.)
2θmax/deg
μ(Mo Kα)/mm−1
3193.6(4)
1.246
8
2
2
2
2
134
56
55
50
78
3.80 (Cu Kα)
0.48
0.51
0.34
0.54
transmn (min./max.) 0.29/0.71
0.96/0.99
0.15 × 0.06 × 0.05
34 953
0.83/0.97
0.20 × 0.18 × 0.07
34 753
0.78/0.95
0.49 × 0.33 × 0.14
21 911
0.85/0.87
0.32 × 0.31 × 0.27
76 060
cryst dimens/mm3
0.27 × 0.04 × 0.03
reflns measd
67 492
unique reflns (Rint)
reflns (I > 2σ(I)]
R1 [I > 2σ(I)]
28728 (0.233)
12 545
20508 (0.050)
15 480
11445 (0.064)
8652
10555 (0.036)
9667
31399 (0.033)
23 425
0.165
0.072
0.059
0.067
0.043
wR2 (all data)
0.426
0.136
0.121
0.149
0.115
anisotropic displacement parameter forms were refined for the non-
hydrogen atoms; hydrogen atoms were treated with a riding model.
Pertinent results are given in Figures 1−4 (which show non-hydrogen
atoms with 50% probability amplitude displacement ellipsoids, with
hydrogen atoms removed for clarity) and in Tables 1 and 4.
8: Crystals of 8 were thin needles that diffracted very poorly. Even
though the data were collected over several days using the intense
Enhance Ultra Copper tube of the Oxford Diffraction diffractometer,
the resultant data set was weak and of limited resolution. This resulted
in a low fraction of “observed” reflections (12 545 out of 28 728 with I
> 2σ(I)) and a high R(int). Only the Ru and P atoms were refined
with anisotropic displacement parameters. The crystal structure
nevertheless does identify the molecule unambiguously, albeit with
high uncertainties in the geometries.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge financial support of this work by the ARC
(Australia) and the CNRS (France). A.B. gratefully acknowl-
̀ ́
edges le Ministere de l'Enseignement Superieur et de la
Recherche (France) for a Ph.D. grant. M.I.B. thanks Johnson
Matthey plc for a generous loan of RuCl3·nH2O. L'Universite
́
́
Europeenne de Bretagne is acknowledged for a travel grant to
A.B.
9: One Ph ring and its associated CH2 atoms of one dppe ligand
were modeled as being disordered over two sets of sites with
occupancies constrained to 0.5 after trial refinement.
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̈
AUTHOR INFORMATION
Corresponding Author
■
*(M.I.B.) Fax: + 61 8 8303 4358. E-mail: michael.bruce@
adelaide.edu.au. (C.L.) Phone: +33(0)2-2323-5963. Fax:
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