Substitution of tetracyanoethene by ethynyl-metal complexes gives tricyanovinylethynyl (tricyanobutenynyl) derivatives: Syntheses, protonation, and addition of metal-ligand fragments

Article abstract of DOI:10.1021/om2007503

A series of complexes containing the new tricyanovinylethynyl (3,4,4-tricyanobut-3-en-1-ynyl) ligand have been obtained by substitution of a CN group in tetracyanoethene upon reaction with the ethynyl complexes M(C≡CH)(PP)Cp′ (M = Ru, Os, (PP)Cp′ = (PPh₃) ₂Cp; M = Ru, PP = dppe, Cp′ = Cp, Cp*). The reactions proceed in higher yield as the metal environment becomes more sterically hindered, the normal [2 + 2]-cycloaddition/ring-opened product M{C[=C(CN) ₂]CH=C(CN)₂}(PP)Cp′ also being formed in some cases. The diynyl complex Ru(C≡CC≡CH)(dppe)Cp* reacts with tcne to give only the ring-opened adduct Ru{C≡CC[=C(CN)₂]CH=C(CN) ₂}(dppe)Cp*. Protonation (HBF₄ or HPF₆) of Ru{C≡CC(CN)=C(CN)₂}(dppe)Cp* afforded the vinylidene cation [Ru{=C=CHC(CN)=C(CN)₂}(dppe)Cp*]⁺. A second transition-metal fragment ML_n (ML_n = Ru(PPh ₃)₂Cp, M′(dppe)Cp* (M′ = Ru, Os), RuCl(dppe)₂) can be added to the CN group trans to the metal center; electrochemical, spectroscopic, and computational studies indicate that there is little ground-state delocalization between the metal centers. In the case of the tricyanovinylethynyl derivatives, an intense MLCT (or ML-LCT) transition can be identified in the visible region, which is responsible for the intense blue to purple color of these species; the analogous transition in the vinylidene-based complexes is significantly blue-shifted. The X-ray crystallographically determined structures of several of these complexes are reported. The cations [{Cp*(dppe)Ru}{μ-(C/N)≡CC(CN)=C(CN) (≡C/N)}{M(dppe)Cp*}]⁺ (M = Ru, Os) show some C≡C/C≡N disorder (and associated Ru/Os disorder in the case of the heterometallic example) in the crystals.

Full text of DOI:10.1021/om2007503

Article
pubs.acs.org/Organometallics
Substitution of Tetracyanoethene by Ethynyl−Metal Complexes
Gives Tricyanovinylethynyl (Tricyanobutenynyl) Derivatives:
Syntheses, Protonation, and Addition of Metal−Ligand Fragments
Michael I. Bruce,*,† Mark A. Fox,‡ Paul J. Low,‡ Brian K. Nicholson,§ Christian R. Parker,†
Wyona C. Patalinghug,⊥,∥ Brian W. Skelton,⊥,# and Allan H. White⊥
†School of Chemistry & Physics, University of Adelaide, Adelaide, South Australia 5005
‡Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, England
§Department of Chemistry, University of Waikato, Hamilton, New Zealand
⊥University of Western Australia, Crawley, Western Australia 6009
∥Department of Chemistry, Delasalle University, Manila, The Philippines 1004
#Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Crawley, Western Australia 6009
S
* Supporting Information
ABSTRACT: A series of complexes containing the new tricyanovinyl-
ethynyl (3,4,4-tricyanobut-3-en-1-ynyl) ligand have been obtained by
substitution of a CN group in tetracyanoethene upon reaction with the
ethynyl complexes M(CCH)(PP)Cp′ (M = Ru, Os, (PP)Cp′ =
(PPh3)2Cp; M = Ru, PP = dppe, Cp′ = Cp, Cp*). The reactions
proceed in higher yield as the metal environment becomes more
sterically hindered, the normal [2 + 2]-cycloaddition/ring-opened
product M{C[C(CN)2]CHC(CN)2}(PP)Cp′ also being formed
in some cases. The diynyl complex Ru(CCCCH)(dppe)Cp*
reacts with tcne to give only the ring-opened adduct Ru{CCC[C-
(CN)2]CHC(CN)2}(dppe)Cp*. Protonation (HBF4 or HPF6) of
Ru{CCC(CN)C(CN)2}(dppe)Cp* afforded the vinylidene cation
[Ru{CCHC(CN)C(CN)2}(dppe)Cp*]+. A second transition-
metal fragment MLn (MLn = Ru(PPh3)2Cp, M′(dppe)Cp* (M′ = Ru,
Os), RuCl(dppe)2) can be added to the CN group trans to the metal center; electrochemical, spectroscopic, and computational
studies indicate that there is little ground-state delocalization between the metal centers. In the case of the tricyanovinylethynyl
derivatives, an intense MLCT (or MLLCT) transition can be identified in the visible region, which is responsible for the
intense blue to purple color of these species; the analogous transition in the vinylidene-based complexes is significantly blue-
shifted. The X-ray crystallographically determined structures of several of these complexes are reported. The cations
[{Cp*(dppe)Ru}{μ-(C/N)CC(CN)C(CN)(C/N)}{M(dppe)Cp*}]+ (M = Ru, Os) show some CC/CN disorder
(and associated Ru/Os disorder in the case of the heterometallic example) in the crystals.
and CC), metal complexes were readily obtained, coordina-
INTRODUCTION
■
Since its discovery,1 the chemistry of tetracyanoethene (tcne),
tion of CN groups to metal centers being the more commonly
observed bonding mode. Recent examples include Ru(η1-
(NC)2CC(CN)2, has provided numerous examples of novel
tcne){NButC(mes)NBut}Cp*,5 trans-[{Ru(PPh3)2Cp}2(μ-
addition and substitution reactions.2 For example, tcne readily
tcne)]2+,6 and [{Fe(CO)2Cp}4(μ4-tcne)]n+ (n = 3, 4).7 Metal
undergoes Diels−Alder reactions with dienes, while one or two
π complexes were first reported by Baddley, who prepared
Pt{η2-C2(CN)4}(PPh3)2 and showed conversion of this
complex to trans-Pt(CN){C(CN)C(CN)2}(PPh3)2.8,9
Many related compounds have since been prepared, especially
for the later transition metals, such as M(CO)5(η2-tcne)
CN groups may be substituted by alcohols, thiols, or aromatic
amines, to give 2,2-dicyanoketene acetals and thioacetals and
tricyanovinylanilines, respectively. The formation of π com-
plexes between tcne and a variety of unsaturated (usually
aromatic) hydrocarbons affords materials with intense charge-
transfer absorptions in their visible−UV spectra. Several
extensive reviews of the chemistry of this remarkable olefin
are available.3,4
Special Issue: F. Gordon A. Stone Commemorative Issue
The transition-metal chemistry of tcne is also rich and has
afforded several surprises. With two potential donor sites (CN
Received: August 11, 2011
Published: November 1, 2011
© 2011 American Chemical Society
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(M = Cr, W),10 Ru(η2-tcne)(NRCR′NR)Cp*,5 and M(η2-
tcne)(L)2 (M = Ni, Pd, Pt, L = CNAr),11 and aspects of the
coordination chemistry of tcne and physical properties of the
resulting complexes have also been reviewed.12−14
[2 + 2]-Cycloaddition of tcne to electron-deficient alkenes to
give cyclobutenes was first described by Hopf and co-workers,15
and more recently, the elegant studies of Diederich and his group
have given a series of compounds with interesting push−pull
electronic properties.16 Similar tetracyanocyclobutenyls were
obtained earlier from reactions of transition-metal alkynyls and
were observed to undergo more or less ready ring-opening
reactions to form tetracyanobutadienyl complexes (Scheme 1),17,18
(1-Ru), the reaction between Ru(CCH)(PPh3)2Cp and tcne
was carried out in tetrahydrofuran at room temperature for
2 h. Conventional workup of the burgundy reaction mixture
afforded red 1-Ru in 64% yield, accompanied by a purple
product, identified as the tricyanovinylethynyl complex
Ru{CCC(CN)C(CN)2}(PPh3)2Cp (2-Ru), which was
isolated in 10% yield. 1-Ru is unstable in solution toward
loss of PPh3: it is likely that the corresponding η3-butadienyl
complex is produced, although we did not isolate this
compound. The facile conversion of η1- to η3-butadienyls
with concomitant loss of one PPh3 ligand is a common reaction
of compounds containing the Ru(PPh3)2Cp fragment.18c,19,25
The analogous osmium complexes 1-Os (which is more stable
than the ruthenium analogue) and 2-Os were obtained similarly
from tcne and Os(CCH)(PPh3)2Cp in 30 and 22% yields,
respectively. Replacement of the PPh3 ligands in the ethynyl−
ruthenium precursor by dppe resulted only in formation of the
corresponding tetracyanobutadienyl complex, Ru{C[C-
(CN)2]CHC(CN)2}(dppe)Cp (3). Of note in the 31P
NMR spectrum of 3 is the appearance of two broad signals
at δP 72.6 and 82.3, which are resolved into two doublets at δP
68.9 and 80.8 (J(PP) = 23 Hz) upon cooling to −57 °C. The
smaller steric bulk of the dppe ligand allows restricted rotation
of the cyanocarbon ligand about the Ru−C bond, this process
being precluded for the analogous PPh3 complex 1.
Scheme 1. [2 + 2]-Cycloaddition of C2(CN)4 to Alkynyl−
Transition Metal Complexes and Subsequent Retro-
Cyclization and Ligand Displacement Reactions18a
Deprotonation of the vinylidenes [Ru(CCH2)(PP)Cp]-
PF6 (PP = (PPh3)2, dppe) with 2 equiv of an alkyllithium base
(both LiMe or LiBu being effective) to give the putative
acetylide salts Li[Ru(CC)(PP)Cp],26 followed by addition of
tcne, gave Ru{CCC(CN)C(CN)2}(PP)Cp (PP = (PPh3)2
2-Ru (37%), dppe 4 (69%)). Given the facile substitution of
CN− by strongly nucleophilic reagents,3,4 such reactions are
perhaps to be expected. In contrast, the complex Ru{C
CC(CN)C(CN)2}(dppe)Cp* (5) was the only product
from the reactions between tcne and Ru(CCH)(dppe)Cp*
(93%). The greater electron-donating properties of the
Ru(dppe)Cp* moiety, and hence greater nucleophilicity of
the Cβ carbon, together with the increased steric congestion of
the alkynyl moiety which limits formation of the intermediate
[2 + 2]-cycloadduct en route to the η1-butadienyl isomer, are
likely to be responsible for this shift in reactivity profile. Similar
results were also obtained from the reaction of [Ru(C
CH2)(dppe)Cp*]PF6/2LiMe with tcne, 5 being formed in
similar yield (95%). The conventional tetracyanobutadienyl-
ethynyl complex Ru{CCC[C(CN)2]CHC(CN)2}-
(dppe)Cp* (6) was obtained from the reaction between tcne
and Ru(CCCCH)(dppe)Cp*, being formed by addition
of the cyanoalkene to the outer CC triple bond, followed by
ring opening. This chemistry is summarized in Scheme 2.
Most of the new complexes have been characterized by
single-crystal X-ray diffraction structure determinations, as
described earlier for 1 and 2-Os20 and herein for 2-Ru and 3−
5. Plots of single molecules of 2-Ru, 4, and 5 are shown in
Figures 1−3, while selected structural data are collected in
Table 1. The usual pseudo-octahedral M(PP)Cp fragments
(Ru−C(cp) = 2.217(5)−2.292(5) Å (average 2.231(10)−
2.271(16) Å), Ru−P = 2.260(1)−2.3211(3) Å) are attached to
the tricyanovinylethynyl ligand by C(1) (Ru−C(1) =
1.920(1)−1.930(3) Å), although there are considerable differ-
ences contingent upon the change from mono- to bidentate
phosphine(s). The C−C separations along the C4 chain
(C(1)−C(2) = 1.224(5)−1.243(7) Å, C(2)−C(3) =
1.378(2)−1.388(8) Å, C(3)−C(4) = 1.368(8)−1.391(5) Å)
which are sensitive to a range of further reactions.19 In studies
aimed at extending the [2 + 2]-cycloaddition reaction to the
parent ethynyl complexes, such as Ru(CCH)(PPh3)2Cp, we
have now found that a competing reaction is the replacement of
one of the CN groups by the alkynyl group, with elimination of
HCN, to give unprecedented tricyanovinylethynyl (1,1,2-
tricyanobut-1-en-3-yn-4-yl) complexes, such as Ru{CCC-
(CN)C(CN)2}(PPh3)2Cp.20 Previous accounts of tricyanovinyl
complexes are sparse, with MCl{C(CN)C(CN)2}(PP)2 (M =
Fe, Ru, Os; PP = dmpe, dppe),21 Fe{C(CN)C(CN)2}-
(CO)2Cp,22 PdCl{C(CN)C(CN)2}(bpy),23 and PtH{C-
(CN)C(CN)2}(PCy3)224 having been described. However, to
our knowledge, no examples of tricyanovinylethynyl ligands exist.
The CN groups in these complexes are reactive, showing ability to
act as coordinating sites toward other metal−ligand fragments, and
have a propensity for substitution by other nucleophiles. Some of
these results have been described in a preliminary account.20
RESULTS
■
Reactions of tcne with Ethynyl−Ruthenium and −Osmium
Complexes. In seeking to prepare the parent tetracyanobu-
tadienyl complex Ru{C[C(CN)2]CHC(CN)2}(PPh3)2Cp
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Scheme 2. Addition of C2(CN)4 to Ethynyl− and Butadiynyl−Metal Complexes
are consistent with CC triple, C(sp)−C(sp2) single, and
C(sp2)C(sp2) double bonds, respectively, with angles at
C(n) being 169.82(8)−179.5(3)° (n = 1), 172.3(1)−173.5(4)°
(n = 2) and 124.3(1)−126.3(6)° (n = 3). Of interest are the
C(n)−CN bonds, which for n = 4 (1.423(2)−1.449(8) Å) are
generally shorter than those to C(3) (1.443(5)−1.477(8) Å).
In each case the plane containing the tricyanovinyl ligand
approximately bisects the P−Ru−P angle (“vertical” orienta-
tion), although the position of the tricyanovinyl moiety with
respect to the Ru defines two rotamers that can be
differentiated by the Cp′(0)−Ru···C(3)−C(4) bond angle
(Cp′(0) is the centroid of the Cp or Cp* ligand), the
dicyanomethylene being oriented either toward (2-Ru) or away
(4, 5) from the Cp ligand. The barrier to rotation of
substitutents around the ethynyl bond in metal−ethynyl
complexes is usually low, and the different ligand conforma-
tions in the present examples probably arise from packing
effects rather than any significant difference in thermodynamic
stability.
Comparison of the three complexes RuX(dppe)Cp* (X =
27
CCH,27 CCC(CN)C(CN)2 (5), and CCH2
)
(Table 2) shows significant decreases in Ru−Cα (2.015(2),
1.926(6), 1.84(1) Å) and increases in the Cα−Cβ separations
Figure 1. Plot of a molecule of Ru{CCC(CN)C(CN)2}-
(PPh3)2Cp (2-Ru) (isomorphous with its Os counterpart20).
Figure 2. Plot of molecule 1 of Ru{CCC(CN)C(CN)2}(dppe)-
Cp (4).
Figure 3. Plot of a molecule of Ru{CCC(CN)C(CN)2}(dppe)-
Cp* (5).
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Table 2. Comparison of Some Properties of [RuX(dppe)-
Cp*]n+ (n = 0, X = CCH, CCC(CN)C(CN)2 (5);
n = 1, X = CCH2)
bond length/Å
Ru−C(1) C(1)−C(2)
δ(C) δ(P) ν(CC)/
(Ru−C(1)) (dppe)
cm−1
a
compd
b
[Ru*]−CCH
2.015(2) 1.202(3)
1.926(6) 1.243(7)
120.58
215.52
344.21
82.2
80.0
77.3
1925
1979
1621
5
c
[[Ru*]CCH2] 1.84(1)
1.29(2)
b
PF6
a
b
c
[Ru*] = Ru(dppe)Cp*. Reference 27. ν(CC).
(1.202(3), 1.243(7), 1.29(2) Å) in 5, relative to the alkynyl
complex, consistent with a resonance structure for 5 which is
intermediate between the alkynyl and allenylidene tautomers of
the cyanocarbon ligand, the dicyanomethylene fragment
stabilizing the negative charge in the latter (Scheme 3). The
Figure 4. Plot of a molecule of Ru{C[C(CN)2]CHC(CN)2}-
(dppe)Cp (3).
ν(CC) and ν(CN) bands are found between 1975 and 1998
and between 2199 and 2213 cm−1, respectively, with broad
bands at ca. 1500 cm−1 arising from the CC bond. In the 1H,
13C, and 31P NMR spectra, the expected resonances for the Cp′
and phosphine ligands are found, while in the 13C NMR spectra
(Table 3), three resonances for atoms of the carbon chain
(C(1−3) at δ 210.71, 84.76, 118.00 for 2-Ru) are accompanied
by three CN resonances at δ ca. 110−118. The electrospray
mass spectra (ES-MS) contain strong [M + Na]+ ion clusters,
the Na+ coming either from NaOMe added to aid ionization29
or from the glass vial in which the samples were prepared for
analysis.
Scheme 3. Resonance Contributors to the Structure of
Tricyanovinylethynyl Complexes
To examine the effect of adding a second CC triple bond
to the system, the reactivity of Ru(CCCCH)(dppe)Cp*
with tcne was also studied. The only product isolated from this
reaction was blue Ru{CCC[C(CN)2]CHC(CN)2}-
(dppe)Cp* (6), probably formed by retro-cyclization of the
initially formed [2 + 2]-cycloadduct; no evidence for
displacement of a CN group was obtained. This reaction is
analogous to that found for Ru(CCCCFc)(dppe)Cp,28
although in this case only one isomer is formed. Monitoring of
the 31P NMR spectra of the reaction mixture showed formation
of an intermediate, perhaps the [2 + 2] cycloadduct (δ 81.5),
but this had disappeared after 15 min, being replaced by the
signal at δ 81.4 from 6. Spectroscopic properties are consistent
with addition occurring to the outer CC bond, with ν(CN),
ν(CC), and ν(CC) bands at 2209, 1964, and 1450 cm−1,
respectively. In the 13C NMR spectrum, resonances at δ 75.70,
88.95, 138.85, 155.90, and 222.23 arise from the carbon
skeleton, the last signal being assigned to the Ru−C atom and
the sixth carbon of the cyanocarbon ligand not being detected.
Four CN resonances are found at δ ca. 110−117. The ES-MS
of 6 in MeCN contains [M + H]+ at m/z 813.
In MeOH, a rapid change in color of the solution of 6 from
blue to orange occurs and the ES-MS shows the highest mass
ion at m/z 845, corresponding to addition of (MeOH + H+) to
6. Similar changes occurred on silica adsorbents during
chromatography. Earlier related chemistry of tetracyanobuta-
dienyls, such as W{C[C(CN)2]CFcC(CN)2}(CO)3Cp,
which reacts with MeOH to give the orange chelate imino
complex W{C[CC(CN)(OMe)NH}CFcC(CN)2}-
(CO)2Cp,30 suggests that the orange compound formed here
is Ru{CCC[CHC(CN)2]C(CN)C(OMe)NH}-
(dppe)Cp*; similar compounds have also been isolated from
reactions of η3-tetracyanobutadienyl-ruthenium complexes with
methoxide.19
13C chemical shift of Cα (δC 215.52) and the 31P resonances for
the dppe ligands (δP 80.0) for 5 also lie between the values
found for related ethynyl and vinylidene complexes. This
feature has been observed previously in one of the tcne adducts
of Ru(CCCCFc)(dppe)Cp: namely, the tetracyanobuta-
dienyl complex Ru{CCC[C(CN)2]CFcC(CN)2}-
(dppe)Cp, where Ru−Cα = 1.915(4) Å and Cα−Cβ
=
1.230(5) Å, again suggesting a significant contribution from
the allenylidene tautomer Ru+{CCC[C(CN)2 ]CFc
−
C(CN)2}(dppe)Cp.28 Other spectroscopic properties are
consistent with the assigned structures. In particular, the IR
spectra contain unusually strong ν(CC) bands, the increase
in intensity resulting from the strong polarization of the CC
triple bond by the electron-rich metal center (donor) and
cyanocarbon (acceptor) substituents.
The tetracyanobutadienyl 3 described above has also been
structurally characterized (Figure 4, Table 1). The geometries
of the Ru(dppe)Cp fragment and the C[C(CN)2]CH
C(CN)2 ligand closely resemble those found for related
complexes, such as Ru{C[C(CN)2]CPhC(CN)2}(dppe)-
Cp.18 In particular, the CC separations in the C4 chain suggest
only limited electronic delocalization, in contrast to the
situation found for some other adducts of diynyl complexes,
such as Ru{CCC[C(CN)2]CFcC(CN)2}(dppe)Cp
mentioned above.28 There is a considerable difference in the
NC−C−CN angles (Table 1), and these in turn are
considerably different from those in the previously considered
compounds.
Spectroscopic properties of 2-Ru and 3−5 are consistent
with their solid-state structures. In the IR spectra, intense
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Some Reactions of Ru{CCC(CN)C(CN)2}(dppe)Cp*
(5). The virtually quantitative formation of 5 has allowed us to
study some of the chemistry of the novel ligand present in this
complex. The presence of the electron-rich Ru(dppe)Cp* and
electrophilic C(CN)2 groups confers interesting spectro-
scopic properties on this novel “push-pull” (donor−acceptor)
complex (see below). Here we describe the protonation of 5
and the addition of other metal−ligand fragments to CN(42)
(Scheme 4; see Figure 3 for atom labeling); displacement of a
second CN group by other nucleophiles will be described
elsewhere.31
Protonation. We were interested to examine the relative
basicities of the CC and CN parts of the cyanocarbon
ligand in 5. Addition of either HBF4·OEt2 or aqueous HPF6 to
solutions of 5 in CH2Cl2 gave complex salts containing the
corresponding orange vinylidene cation [Ru{CCHC(CN)
C(CN)2}(dppe)Cp*]+ [7]+ in nearly quantitative yield. The
cyanocarbon ligand structure in [7]+ was readily identified from
the characteristic low-field resonance for C(1), which is found
at δC 333.2, together with C(2) at δC 113.9 and its associated
proton at δH 4.54. Three CN resonances are present at δC 110−
113. Other signals are consistent with the ligands present on
the metal center. In the IR spectrum, ν(CN) bands are found at
ca. 2216 cm−1, but no ν(CC) band was observed. Instead, a
strong band at 1612 cm−1 can be assigned to ν(CC) arising
from the vinylidene and cyanoalkene CC bonds. The ES-MS
contains a molecular cation at m/z 762, accompanied by [(M −
H) + Na]+ at m/z 784; loss of HCN affords an ion at m/z 735.
An ion at m/z 1545 corresponds to [(2 M − H) + Na]+,
perhaps formed by clustering of the cyanocarbon around the
Na+ center. We conclude that, in 5, atom Cβ is more basic than
any of the CN groups.
A single-crystal X-ray diffraction structure determination of
[7]BF4 (a plot of the cation is shown in Figure 5, and selected
bond parameters are given in Table 1) has confirmed that the
cationic part contains the Ru(dppe)Cp* fragment linked to
vinylidene CCHC(CN)C(CN)2 by a short Ru−C(1)
bond (1.801(2) Å), while C(1)−C(2) has lengthened to
1.342(3) Å; C(2)−C(3) and C(3)−C(4) are 1.419(3) and
1.370(3) Å, respectively. As found for 5, C(3)−CN(31) is
somewhat longer (1.453(3) Å) than C(4)-CN(41,42) (1.437,
1.431(3) Å). Other dimensions are also similar to those found
in 5, although some lengthening of the Ru−C(Cp) (average
2.29(6) Å) and Ru−P bonds (2.3247, 2.3654(6) Å) has
occurred as a result of reduced back-bonding from the cationic
Ru center. The spread in Ru−C(Cp*) compared with that in
Ru−C(Cp) is considerable, consequent upon “tilting” of the
ligand as a result of the increase in steric bulk resulting from the
presence of the five Me substituents. The vinylidene and
tricyanovinyl portions of the ligand are coplanar, suggesting
conjugation throughout the cyanocarbon ligand, which adopts
the usual horizontal position with respect to the Ru(dppe)Cp*
fragment expected of a vinylidene ligand in group 8 complexes
of this type.
Addition of Metal−Ligand Fragments to CN(42) in 5. The
strong donor power of the CN group to metal centers is
well-known, and several groups have described the formation
of polynuclear complexes using a CN group from poly-
cyanometalates as a bridging ligand.32−34 Other complexes are
known in which an organic polynitrile bridges metal centers via
CN group(s).35,36 For example, several mono- or polynuclear
complexes of tcne have been described, some of which
exhibit unusual electronic and magnetic properties.14,37−39
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Scheme 4. Addition of H+ and MLn Moieties to Ru{CCC(CN)C(CN)2}(dppe)Cp* (5)
Accordingly, we investigated the potential of the tricyanovinyl-
ethynyl group of 5 to act as a bridge between the Ru(dppe)Cp*
end cap and a second metal−ligand group.
consequence of packing considerations (see Computational
Studies).
Spectroscopic properties of the bimetallic complexes [8−
11]PF6 resemble those of 5, major differences being found in
the ν(CC) bands, which shift from 1979 cm−1 in 5 to ca.
1963 cm−1 in the bimetallic complexes; the ν(CN) absorptions
are unaffected. In the NMR spectra of [8−10]PF6, the
characteristic resonances for the Cp (or Cp*) groups are
present, while the 13C resonances for the carbons of the
bridging ligand are found at δC ca. 98, 103, 125, and 148; the
CN groups give three signals at δC ca. 112−115. In the case of
[11]PF6, the dppe ligands at each metal center are differ-
entiated, with those for Ru(dppe)Cp* at δH 2.35 and 2.81,
while those for Ru(dppe)2 occur at δH 2.62 and 2.81; the 31P
Reactions of 5 with MCl(PP)Cp′ (M = Ru, (PP)Cp′ =
(PPh3)2Cp, (dppe)Cp*; M = Os, (PP)Cp′ = (dppe)Cp*) and
cis-RuCl2(dppe)2 proceeded in refluxing MeOH in the presence
of [NH4]PF6 to give the corresponding binuclear cationic
complexes [8]+−[11]+ in modest to good yields (43−68%)
(Scheme 4). Three of these were fully characterized by single-
crystal X-ray diffraction studies. Plots of the cations in [9]PF6
and [10]PF6 are shown in Figures 6 and 7, selected bond
parameters being given in Table 1; the structure of [8]+ has
been previously reported.20 From these structures it is clear that
the cyanocarbon ligand forms an almost symmetrical bridge
between the two metal centers, the second metal being attached
to the CN group trans to the Ru(dppe)Cp* group. Indeed, the
similarity between the CC and CN groups, and the Ru/Os
metal atoms in 8, despite the considerable differences in the
Ru−C,N distances (>0.1 Å), results in the cations [8]+ and [9]+
being considerably/completely disordered about crystallo-
graphic inversion centers. This disadvantage is averted in
[10]+ by the use of a completely different terminal component,
confining the disorder to the CC/CN regions only. Other
dimensions are similar to those found for 5. In the solid state,
the Cp′ rings in each of the bimetallic complexes [8]PF6,20
[9]PF6, and [10]PF6 adopt a transoid arragement, likely a
Figure 6. Plot of the centrosymmetric cation of [{Cp*(dppe)Ru}-
{CCC(CN)C(CN)CN}{Os(dppe)Cp*}]PF6 ([9]PF6).
Figure 7. Plot of the cation of [{Cp*(dppe)Ru}{CCC(CN)
C(CN)CN}{Ru(PPh3)2Cp*}]PF6 ([10]PF6).
Figure 5. Plot of the cation in [Ru{CCHC(CN)C(CN)2}-
(dppe)Cp*]BF4 ([7]BF4).
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resonances are at δP 80.1 and 43.2, respectively. The ES-MS
contain molecular cations, which fragment by successive loss of
either of the metal centers; both metal-containing ions [MLn]+
are also present.
UV−Vis Absorption Spectra. The highly polarized
complexes 2-Os, 2-Ru, 3−5, and [7−11]PF6 are all deeply
colored and show solvatochromic behavior, which led us to
investigate the UV−vis spectra of representative examples
(Figure 8 and Table 4). Interestingly, compound 5 did not
nm (ε 10 400 M−1 cm−1) and another broad absorption band at
469 nm (ε 3500 M−1 cm−1); both transitions are likely to have
a degree of MLCT character associated with transitions to the
ethynyl and tricyanovinyl portions of the cyanocarbon ligand.
Consistent with this assignment, dark blue 6, which features a
more extensively delocalized ligand, has an absorption at 365
nm (ε 12 600 M−1 cm−1) and a broad band that extends into
the near -IR at 575 nm (ε 9200 M−1 cm−1). While the spectra
of complexes 3 and 6 have similar profiles, the increased
conjugation in 6 results in the MLCT bands being red-shifted
and having a higher molar absorption.37
Complex 5 gives rise to an intense absorption at λmax 557 nm
(ε 26 200 M−1 cm−1) in dichloromethane, which is responsible
for the characteristic purple color of this complex. This band is
solvatochromic, as expected of a charge transfer transition
(Figure 9 and Table 5). As the solvent polarity increases, λmax
Figure 9. Solvatochromism of 5 in several solvents and the formation
of [7]+ upon addition of CF3CO2H.
a
Table 5. Solvatochromism of 5
solvent
λmax/nm
ε/M‑1 cm‑1
Figure 8. UV−vis absorption spectra: (a) Ru(CCH)(dppe)Cp*, 3,
and 6; (b) 5, [7]BF4, and [8]PF6.
CH2Cl2
CHCl3
MeCN
MeOH
acetone
thf
557
557
557
555
554
548
541
529
527
425
26 200
26 500
24 800
26 700
25 700
25 200
26 300
24 400
26 200
28 000
a
Table 4. UV−Vis Absorption Maxima of [Ru*]CCH, 3,
5, 6, [7]BF4, and [8]PF6
compd
λmax/nm (ε/M−1 cm‑1)
toluene
NEt3
[Ru*]CCH
334 (4200)
Ru{C[C(CN)2]CHC(CN)2}(dppe)Cp
330 (10 400) (sh), 469
(3500)
(3)
CH2Cl2−hexane (1:24)
CH2Cl2−CF3CO2H (24:1)
[Ru*]{CCC(CN)C(CN)2} (5)
557 (26 200)
a
[Ru*]CCCC(CN)2CHC(CN)2 (6)
365 (12 600), 575 (9200)
Solutions in fused quartz cells with a path length of 1 cm.
[[Ru*]CC(H)C(CN)C(CN)2]BF4 ([7] 425 (28 000)
BF4)
shifts by ca. 30 nm (0.08 eV) along the series CH2Cl2−hexane
(1/24) (527 nm), PhMe (541 nm), CH2Cl2 (557 nm). This
behavior results from the “push-pull” polarity conferred on the
molecule by the strongly electron-donating (Ru(dppe)Cp*)
and electron-accepting (C(CN)C(CN)2) substituents. Sim-
ilar properties are found with organic tricyanovinyl compounds
also containing electron-donating substituents, such as
Me2NC6H4CCC(CN)C(CN)2.16c,40 In donor molecules
with dicyanomethylene acceptor groups, this effect has been
attributed to the excited state being more polar than the ground
state, with the former being better stabilized in the more polar
solvents.40−42
{[Ru*]CCC(CN)C(CN)CN[Ru*]}PF6 635 (44 300)
([8]PF6)
a
All solutions in CH2Cl2 in fused quartz cells with a path length of
1 cm. [Ru*] = Ru(dppe)Cp*.
fluoresce, unlike related cyano(ethynyl)ethenes,40 possibly
because the metal center quenches emissions, but the associated
excited-state processes were not investigated in detail.
The spectrum of Ru(CCH)(dppe)Cp* shows a relatively
weak absorption band at 334 nm (ε 4200 M−1 cm−1) which
likely has metal-to-ethynyl MLCT character. The spectrum of
orange 3 (red trace) has a discernible band maximum at ca. 330
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Protonation of 5 with CF3CO2H results in a marked blue
shift of the major absorption to 425 nm (ε 28 000 M−1 cm−1).
While in solvents such as hexane, CH2Cl2, and MeCN yellow
[7]+ persists, a shift in the position of the vinylidene/acetylide
equilibrium, indicated by restoration of the purple color of 5,
occurs in Et2O, acetone, alcohols, and H2O even in the absence
of a base, although upon concentration [7]+ is regenerated.
Facile deprotonation of [7]+ with NEt3 also regenerates 5. This
suggests the basicity/nucleophilicity of Cβ in 5 is much lower
than that in Ru(CCH)(dppe)Cp*, as a result of the presence
of the electron-deficient cyanocarbon moiety. Addition of the
second metal center in [8]+ results in a red shift and almost
doubling of the molar absorption to 635 nm (ε 44 300 M−1 cm−1)
(Figure 8), in comparison with that of 5. In the near-IR region,
[8]+ exhibits a weaker band at 1350 nm (ε 4000 M−1 cm−1).
4. Electrochemistry. The oxidative electrochemistry of
Ru(CCR)(PP)Cp′ complexes is characterized by the non-
innocent behavior of the acetylide ligand.43,44 In the present
case this behavior may be expected to be moderated by the
strongly electron withdrawing tricyanovinyl substituent, which
should additionally offer a reductive electrochemical response.
Complex 2-Ru shows two almost chemically reversible 1e
processes at −0.93 and +0.97 V (in CH2Cl2/0.1 M [NBu4]PF6
vs SCE, referenced to an internal decamethylferrocene/
decamethylferrocenium couple such that FeCp*2/[FeCp*2]+ =
−0.02 V),45 and successive ligand replacement of (PPh3)2Cp
with (dppe)Cp and (dppe)Cp* gives only limited changes in
redox potentials to −0.96, +1.10 V (4) and −1.00, +0.97 V (5),
respectively, despite the increasing electron richness of the metal
center. In the related tetracyanobutadienyl complex Ru{C[
C(CN)2]CHC(CN)2}(dppe)Cp (3), two reduction events
are observed (−1.29, −1.08 V), possibly arising from stepwise
reduction of the two chemically distinct C(CN)2 groups,
while an anodic process gives rise to a wave at +1.05 V.
These redox processes satisfy criteria for electrochemically
reversible processes, with the separation of the anodic and
cathodic waves of each processes being identical with that
observed for the internal decamethylferrocenium reference (ca.
70 mV), ipa/ipc ratios close to unity, and a linear relationship of
peak current vs (scan rate)1/2. The bimetallic complex [8]PF6
shows three 1e events at −0.94, +0.91 and +1.30 V, the last
being chemically irreversible. As with 5, these redox processes
can be assigned to reduction of the tricyanovinylethynyl ligand
and sequential oxidation of the metal fragment ligand at the C
and N termini, albeit with a degree of Ru−CC mixing likely
in the first oxidation. In further support of these assignments,
it is worth noting that the simple phenylethynyl complexes
Ru(CCPh)(PP)Cp′ exhibit two redox events at +0.59
(reversible)/+1.39 (irreversible) (Ru(PP)Cp′ = Ru(PPh3)2Cp)
and +0.34 (reversible)/+1.19 V (irreversible) (Ru(PP)Cp′ =
Ru(dppe)Cp*)43 and [Ru(NCPh)(dppe)Cp*]PF6 exhibits an
irreversible oxidation at +1.10 V,46 while Pri3SiCCC(CN)
C(CN)2 has a single reduction process at −0.72 V associated
with addition of an electron to the dicyanomethylene group to
give a relatively stable anion.40
tricyanovinylethynyl ligand based oxidation. Coordination of a
second metal center to the ligand in 5 results in a modestly
more facile first oxidation process, consistent with the addition
of an electron-donating group to the redox-active ligand, while
the ligand reduction is largely unaffected. Without a broader
range of compounds from which to draw comparisons, the
character of the second anodic process is less clear and better
addressed using spectroscopic and computational methods.
The protonated compound [7]+ does not display any
oxidation events when first scanning in the anodic direction,
which further supports the assignment of the first oxidation
event in 2-Ru, 4, and 5 to an ethynyl ligand based process;
oxidation of the analogous vinylidene is expected to fall at much
higher potentials and probably lies outside the observable
electrochemical window. However, complex [7]+ does show a
chemically irreversible reduction at Epc = −0.53 V. Given the
relative potentials of this reduction observed in the vinylidene
[7]+ and the considerably more negative reduction processes
associated with the dicyanomethylene portions of 2-Ru, 4, and
5, reduction of [7]+ is proposed to occur on the vinylidene
portion of the ligand.47 Further scanning in the cathodic
direction reveals a fully reversible reduction at −1.00 V, which is
at the same potential as for the deprotonated compound 5. The
molecule may lose H• upon gaining an electron, generating 5.48
COMPUTATIONAL STUDIES
■
As has been noted elsewhere, the acetylide ligand in complexes
Ru(CCR)(PP)Cp′ and closely related systems is redox
noninnocent, being heavily involved in the oxidation processes
of these complexes, and in radical cations [Ru(CCR)(PP)-
Cp′]+ the acetylide moiety supports a substantial fraction of the
unpaired electron spin density.43,44,49 In the present case, the
strongly electron-withdrawing nature of the tricyanovinyl
substituent on the acetylide moiety renders the site of oxidation
in 2-Ru, 2-Os, 4, and 5 decidedly unclear. To better understand
the structural, spectroscopic, and electrochemical properties of
this family of complexes, electronic structure calculations were
undertaken on 5, [7]+, and [8]+, supported by UV−vis−near-
IR spectroelectrochemical studies. To ensure the most reliable
comparisons, full ligand sets were included in the computa-
tional model, with no symmetry constraints applied. The
computational models are denoted 5′, [7′]+, and [8′]+ to
distinguish them from the experimental systems. For both
mono- and bimetallic complexes, geometry optimizations
revealed a series of closely lying minima distinguished by the
relative orientation of the Ru(dppe)Cp* fragment(s) with
respect to the plane of the tricyanovinylethynyl moiety, the
relative energies of which were sensitive to the functional
employed. The best agreement with the crystallographically
determined structures was obtained with the MPW1K
functional and the 3-21G* basis set. However, the low barrier
to rotation around the Ru−C(1)/N bond implied by these
results indicates that the different conformations adopted by
the tricyanovinylethynyl ligand in the solid-state structures of
2-Ru and 5 is likely a consequence of packing effects rather
than a result of any significant electronic factors. Table 6
compares the bond lengths and angles of the crystallo-
graphically observed and optimized structures, and the good
agreement of these metric parameters and of the observed and
calculated IR frequencies (Table 7) give confidence in the
accuracy of the computational models.
The limited variation in the redox potentials in the series of
mononuclear complexes 2-Ru, 4, and 5 is consistent with
ligand-centered redox processes in which the metal center is
not appreciably involved. This suggestion is consistent with the
noninnocent redox behavior of the phenylethynyl ligand in
Ru(CCPh)(PP)Cp′ systems.43,44 The first oxidation poten-
tials of 2-Ru, 4 ,and 5, which are much more positive than those
of the phenylethynyl systems, are also consistent with a largely
The electronic structure of the alkynylmetal complexes
Ru(CCR)(L2)Cp′ has been described in a wide range of
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Table 6. Comparison of Selected Bond Lengths (Å) and Angles (deg) from the Crystallographically Determined Structures of 5
and [7]+ (as the BF4 Salt) and the Optimized Geometries of 5′, [7′]+, and [8′]+
−
5
5′
[7]BF4
Bond Distances (Å)
[7′]+
[8′]+
a
a
M−P(1)
M−P(2)
2.274(2)
2.305(2)
2.2705
2.2808
2.3247(6)
2.3375
2.3179
2.2888; 2.2930
2.2802; 2.3072
2.3654(6)
a
M−C(cp)
M−C (av)
M-C(1)
2.254−2.292(5)
2.271(16)
2.243−2.306
2.239−2.353(2)
2.29(6)
2.258 - 2.329
2.249−2.306; 2.237−2.273
2.278, 2.257
a
a
1.926(6)
1.944
1.801(2)
1.825
1.919 (C(1)); 2.048 (N(1))
a
C(1)−C(2)
C(2)−C(3)
C(3)−C(4)
C(3)−C(31)
C(4)−C(41,42)
C−N
1.243(7)
1.233
1.342(3)
1.325
1.243 (C(1)); 1.160 (N(42))
1.388(8)
1.378
1.419(3)
1.439
1.360
1.368(8)
1.376
1.370(3)
1.362
1.395
1.477(8)
1.427
1.453(3)
1.418
1.428
1.441, 1.449(8)
1.152, 1.128, 1.136(8)
1.406, 1.407
1.155, 1.158, 1.158
1.437, 1.431(3)
1.138; 1.142, 1.145(3)
1.413, 1.411
1.155, 1.156, 1.157
1.403; 1.396
1.159; 1.156
Bond Angles (deg)
a
P(1)−M−P(2)
P(1)−M−C(1)
84.58(5)
86.0(2)
83.38
82.78(2)
85.93(7)
88.49(7)
175.4(2)
126.4(2)
124.0(2)
117.7(2)
118.2(2)
121.4, 123.4(2)
82.49
82.23; 83.09
a
83.43
96.64
90.23; 84.29
a
P(2)−M−C(1)
83.9(2)
90.35
83.61
83.03; 91.62
M−C(1)−C(2)
174.2(5)
173.4(6)
126.3(6)
117.6(5)
116.0(5)
120.4, 120.7(6)
173.42
176.4
166.7
175.94 (C(1)); 173.47 (N(42))
C(1)−C(2)−C(3)
C(2)−C(3)−C(4)
C(2)−C(3)−C(31)
C(4)−C(3)−C(31)
C(3)−C(4)−C(41,42)
128.9
176.88 (C(1)); 178.80 (N(42))
124.4
121.9
125.1
116.6
119.0
117.2
119.09
118.4, 122.4
118.9
118.7
119.6, 122.0
119.3, 121.9
a
Equivalent data from Ru(2).
contexts from calculations at various different levels of theory
on several previous occasions.43,44,50−52 A qualitative analysis of
the pseudo-octahedral [RuCCR(L2)Cp′] fragment reveals a
lifting of the degeneracy of the t2g type orbitals by interactions
with the Cp′ ligand. Of this set, two are of the correct symmetry
to interact with the π orbitals of the alkynyl ligand, and in the
case of 5′ the antibonding combinations of these dπ orbitals
feature in the HOMO and HOMO-2. Furthermore, the
orthogonal nature of these orbital fragments results in different
degrees of spatial distribution of the HOMO and HOMO-2
over the Ru{CCC(CN)C(CN)2} backbone (Table 8),
with greater participation of the cyanocarbon fragment in the
HOMO than in the HOMO-2 (Figure 10). The HOMO-1 is
derived from the third orbital of the t2g-like set and is more
localized on the Ru(dppe)Cp* fragment.
the metal fragment (Table C1). The partial spatial overlap of the
HOMO and LUMO permits a facile HOMO−LUMO optical
transition with a degree of MLCT character. Indeed, the
solvatochromic absorption band observed in the solution-phase
spectra of 5 between 527 and 557 nm (Table 5) is reproduced by
TD DFT calculations from 5′ as the HOMO−LUMO transition,
which is found at 409 nm in the gas-phase calculations.
The computational model of the vinylidene [7′]+ reproduced
the crystallographically observed ‘horizontal’ ligand conforma-
tion, with the C(4)−C(3)···Ru−C(0) angle in the optimized
structure of [7′]+ calculated to be −81.37°. An examination of
the frontier orbital composition (Table 9, Figure 11) reveals
that the vinylidene ligand serves to decouple the metal
fragment from the tricyanovinyl moiety in the HOMO. The
LUMO retains considerable tricyanovinyl character, while the
vinylidene ligand contributes strongly to the LUMO+1, which
is only some +0.73 eV higher in energy than the LUMO, and
the LUMO+2 is strongly metal in character and δ symmetry
with respect to the vinylidene ligand; the relative order of these
orbitals may be sensitive to the level of theory employed, and
we note that reorganization of the orbital manifold may take
place upon reduction; for comparison, the LUMOs of mono-
and dicyanovinylidene complexes of the Ru(dppe)Cp* moiety
are weighted heavily on Cα.46 The HOMO-2 has π character
and is extensively delocalized over the CC(H)−C(CN)
C(CN)2 portion of the molecule. The nodes between Ru−
C(1) and C(2)−C(3) are consistent with the valence bond
description of the ligand. In the case of [7′]+, TD DFT
calculations indicate that the lowest energy electronic transition
has HOMO−LUMO (MLCT) character but that this transition
is blue-shifted (349 nm) with respect to the analogous MLCT
transition in 5′, in good agreement with the observed spectra
(Figure 8b).
The LUMO of 5′ is well removed from the HOMO
(|ΔEHOMO−LUMO| = 4.3 eV) and other unoccupied (metal- and
phosphine-based) orbitals and essentially comprises the C
CC(CN)C(CN)2 π* system, with a limited contribution from
Table 7. Selected Observed (CH2Cl2/cm−1) and Calculated
(vacuum/cm−1 with Oscillator Strength Given in
a
Parentheses) IR Bands in 5, [7]+, and [8]+ (as the [PF6]−
Salts) and from the Optimized Geometries of 5′, [7′]+, and
[8′]+
ν(CC)
1979 vs
ν(CC)
ν(CN)
2209 m; 2199 w
5
1463 s
5′
2024 (2579)
1612 s
1450 (454)
1612 s
2242 (6); 2230 (55); 2216 (26)
2216 m
[7]PF6
[7′]+
[8]PF6
[8′]+
b
1588 (1234)
1963 vs
1503 (111)
1448 s
2252 (27); 2243 (2); 2236 (10)
2209 w
1984 (5878)
1400 (846)
2233 (10); 2215 (82); 2193 (45)
The bimetallic complex model [8′]+ gave rise to a series of
closely lying minima with the cisoid conformer lying only
a
At the MPW1K/3-21G* level with a frequency correction of 0.92.49c
ν(CCHC).
b
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Table 8. Energy (eV) and Composition (%) of Selected Frontier Orbitals in 5′ (MPW1K/3-21G*)
composition
MO
energy
Ru
Cp*
dppe
C1C2
C3C4
CN31
CN41
CN42
201 LUMO+4
200 LUMO+3
199 LUMO+2
198 LUMO+1
197 LUMO
−0.02
−0.07
−0.30
−0.41
−1.92
−6.22
−6.49
−7.27
−7.35
−7.97
−8.16
4
4
2
1
93
94
94
76
2
0
0
0
0
0
0
0
0
0
0
0
0
8
5
0
1
3
0
1
4
2
0
0
0
0
15
5
9
0
0
0
0
1
16
18
7
45
13
0
14
0
10
4
196 HOMO
30
37
36
12
42
9
19
42
18
37
12
3
11
14
7
195 HOMO-1
194 HOMO-2
193 HOMO-3
192 HOMO-4
191 HOMO-5
0
0
34
15
1
2
1
0
23
46
84
8
1
2
0
0
0
1
1
0
1
Figure 10. Plots of selected frontier orbitals from 5′ (isocontour value ±0.04 (e/bohr3)1/2).
Table 9. Energy (eV) and Composition (%) of Selected Frontier Orbitals in [7′]+ (MPW1K/3-21G*)
composition
MO
energy
Ru
Cp*
dppe
C1C2H
C3C4
CN31
CN41
CN42
201 LUMO+4
200 LUMO+3
199 LUMO+2
198 LUMO+1
197 LUMO
−2.88
−3.06
−3.53
−4.30
−5.03
11
12
30
26
5
6
6
78
80
49
7
4
2
0
0
0
0
0
0
0
0
0
1
8
1
2
6
0
0
0
21
7
0
0
0
0
52
15
11
12
21
0
5
1
1
1
1
47
3
13
0
10
1
196 HOMO
−9.91
29
10
15
1
43
42
20
2
12
30
19
96
97
90
195 HOMO-1
194 HOMO-2
193 HOMO-3
192 HOMO-4
191 HOMO-5
−10.07
−10.27
−10.65
−10.84
−10.86
4
0
1
14
0
1
4
0
0
1
1
0
0
0
0
6
3
1
0
0
0
+7.5 kJ mol−1 higher than the transoid structure, the transoid
conformer being the more closely related to the crystallo-
graphically observed structure. The energies and composition
of selected frontier orbitals from the transoid conformer of
[8′]+, summarized in Table 10 and illustrated in Figure 12, are
well described in terms of the addition of a [Ru(dppe)Cp*]+
fragment to the metallo ligand 5′, with limited mixing of
the orbital character of the two fragments (Table 10).
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Figure 11. Plots of selected frontier orbitals from [7′]+ (isocontour value ±0.04 (e/bohr3)1/2), with hydrogen atoms omitted for clarity.
Table 10. Energy (eV) and Composition (%) of Selected Frontier Orbitals in [8′]+ (MPW1K/3-21G*)
composition
MO
energy
Ru1
Cp-1
dppe-1
C1C2
C3C4
CN31
CN41
CN42
Ru2
Cp-2
dppe-2
365 LUMO+4
364 LUMO+3
363 LUMO+2
362 LUMO+1
361 LUMO
−1.90
−1.96
−2.03
−2.15
−4.11
−7.90
−8.25
−8.39
−8.66
−9.05
−9.06
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
6
4
0
0
0
0
2
1
0
0
0
8
5
0
4
2
0
3
6
7
3
4
87
88
1
18
0
12
0
69
0
0
0
0
0
0
0
0
0
19
1
10
0
70
0
9
2
2
19
12
6
38
12
0
14
0
360 HOMO
22
32
4
17
48
8
10
14
4
11
0
5
3
359 HOMO-1
358 HOMO-2
357 HOMO-3
356 HOMO-4
355 HOMO-5
0
0
0
1
2
0
26
43
1
31
37
1
19
15
0
0
1
1
0
0
0
41
11
13
28
6
33
12
2
2
20
7
0
6
6
4
The Ru(dppe)Cp* fragment orbitals from the N ligand moiety
interleave with the orbitals derived from 5′ in the frontier region
and comprise the HOMO-3, HOMO-2, and LUMO+1 in the
bimetallic system [8′]+. The HOMO−LUMO gap in [8′]+
(|ΔEHOMO−LUMO| = 3.79 eV) is somewhat smaller than in 5 as a
result of the stabilization of the LUMO by the cationic charge, and
consequently the HOMO−LUMO transition in the bimetallic
complex is red-shifted relative to the mononuclear precursor.
DISCUSSION
■
Over 20 years ago, the formal [2 + 2]-cycloaddition of
tetracyanoethene to σ-alkynyl−transition-metal complexes to
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Figure 12. Plots of selected frontier orbitals from [8′]+ (isocontour value ±0.04 (e/bohr3)1/2), with hydrogen atoms omitted for clarity.
give labile tetracyanocyclobutenyl−metal derivatives, followed
by their retro-electrocyclic ring opening to the corresponding
tetracyanobutadienyl−metal complexes, was described.17,18 In
the intervening years, similar reactions have been described
with several other electron-deficient alkenes, such as
(CF3)2CC(CN)2, R1CHCR2(CN) (R1 = Ph, C6H4NO2-
4; R2 = CN, CO2Et, C6H4NO2-4), and (MeO2C)CH
C(CN)(CO2Me).30,53 In several cases, the intermediate
cyclobutenyls were not isolated or even observed. More
recently, similar reactions of purely organic alkynes have been
studied, first by Hopf and co-workers15 and later by Diederich
and his group.16 The latter group has recently extended these
studies to the addition of 2,2-dicyanovinylalkenes to alkynes
containing donor substituents.40
The present work arose out of an attempt to obtain similar
tetracyanobutadienyl derivatives from the parent ethynyl−
ruthenium complexes, Ru(CCH)(PP)Cp′ ((PP)Cp′ =
(PPh3)2Cp, (dppe)Cp, (dppe)Cp*). We were surprised to
find that instead of the well-established [2 + 2]-cyclo-addition
reaction, displacement of a CN group from the cyanoalkene by
the ethynyl−metal group had occurred. The alkynyl complexes
were thus acting as significant nucleophiles, attacking at an
olefinic carbon, with elimination of HCN. In this, the chemistry
resembled much more the characteristic chemistry of tcne with
more conventional nucleophiles, such as alcohols, thiols and
amines, which had been detailed in the early studies of the du
Pont group.2 Substitution of tcne by alkynyllithiums or
-coppers has been described.40,54,55
The formation of the tricyanovinylethynyl complexes described
above results from the strong steric protection afforded to the
ethynyl groups in the precursors, the metal−ligand fragment
becoming more bulky along the series Ru(dppe)Cp < Ru-
(PPh3)2Cp < Ru(dppe)Cp*. In addition, the electronic changes
on proceeding along this series cannot be discounted, Cp* being
more basic (a stronger electron donor) than Cp. We recall a
similar effect upon the reactions of MeOH with the related
vinylidenes [Ru(CCH2)(PP)Cp′]+, where rapid attack on
Cα to give the corresponding carbenes [Ru{CMe(OMe)}-
(PP)Cp′]+ occurs with (PP)Cp′ = (PPh3)2Cp, (dppe)Cp, but
the (dppe)Cp* complex is unreactive (cf. the synthesis of
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Ru(CCH)(dppe)Cp* described below). Space-filling models
of the ethynyl complexes also show that Cα is well shielded by the
(PP)Cp′ ligands, particularly in Ru(CCH)(dppe)Cp*, while
Cβ is slightly exposed, allowing it to attack the olefinic carbon of
tcne.
significant increase in the energy of the MLCT transition with
concomitant change in the color of the solution to yellow. The
vinylidene ligand adopts the usual “horizontal” orientation in
the solid state. In contrast, however, a second MLn fragment
(here we have used M′(PP)Cp′ (M′ = Ru, (PP)Cp′ = (PPh3)2Cp,
(dppe)Cp, (dppe)Cp*; M′ = Os, (PP)Cp′ = (dppe)Cp′)) and
trans-[RuCl(dppe)2] adds to the CN group trans to the −CC-
Ru(dppe)Cp* group. Steric effects may dictate this result, a
second bulky MLn fragment not being able to add to Cα,
although four Fp moieties (less bulky than the Ru(dppe)Cp*
group employed here) are found N-bonded to tcne in
[{Fe(CO)2Cp}4(μ4-tcne)]n+ (n = 3, 4).7 These monocations
have the expected solid-state structures, although the similarity
between CC and CN results in disorder in the structures of
8 and 9, making these two groups experimentally indistinguish-
able. DFT studies, supported by the electrochemical results,
suggest that there is only limited delocalization between the two
metal centers in 8, with the HOMO and HOMO-1 being
localized on the C-ligated metal atom and the HOMO-2 and
HOMO-3 being more closely associated with the N-ligated metal
center.
There are several examples of the replacement of one or
more CN groups of tcne in its reactions with organometallic
compounds. At high temperatures in polar solvents, ferrocene
reacts with tcne to give a mixture of FcCN and FcC(CN)
C(CN)2,56,57 while TlCp gives Tl{C5H4C(CN)C(CN)2}.58
Similar reactions have been observed with the Ir(CH2CMe2-
C6H4)(C6H4But-2)(But2-bpy) complex, where substitution
occurred on the aryl ring to give Ir{CH2CMe2C6H3[C-
(CN)C(CN)2]-4}(C6H4But-2)(But2-bpy),59 while the for-
mation of cyano complexes indicates similar reactions occur
60
with [fac-Re(CO)3(bpy)MeOH)]+ and {Fe(CO)2Cp}2.61
The monometallic tricyanovinylethynyl (1,1,2-tricyanobut-1-
en-3-yn-4-yl) complexes described herein are deep purple
solids, which crystallize readily and were originally characterized
by single-crystal X-ray diffraction structure determinations,
supported by elemental microanalyses and mass spectrometric
studies. Their IR and NMR spectra contain absorptions or
resonances characteristic of the CC triple bond and CN
groups, as well as of the M(PP)Cp′ (M = Ru, Os) fragments. In
the 13C NMR spectra, only three resonances between δ 114
and 120 are found for the CN groups, in contrast to the four
signals usually obtained for the tetracyanobutadienyl com-
plexes. In the 31P NMR spectra, the tricyanovinylethynyl
complexes give singlet resonances, while the phosphine ligand
resonances are found as AB quartets for the η1-tetracyanobu-
tadienyls, as a result of the asymmetry of the cyanocarbon
ligand. The observation of different conformations of the
tricyanovinylethynyl ligand (being “up” or “down” with respect
to the Cp′ ligand) in the crystallographically determined
structures of 2-Ru, 4, and 5 is consistent with the flat potential
energy surface associated with ligand rotation determined by
DFT calculations.
The presence of the tricyanovinyl substituent significantly
alters the electronic structure of the complexes M{C
CC(CN)C(CN)2}(PP)Cp′ relative to the phenylacetylide
analogues M(CCPh)(PP)Cp′. The low-lying cyanocarbon
π* system which comprises the LUMO of these systems has
appreciable special overlap with the HOMO, which is largely
associated with the M−CC portion of the molecule. This
effective overlap leads to an intense, solvatochromic MLCT
band that in turn gives rise to the characteristic purple color of
these donor−acceptor (“push-pull”) complexes. Some electro-
chemical studies have been carried out, which incorporate
comparative studies with analogous cyanocarbon derivatives.
The tricyanovinylethynyl complexes are reduced at much less
negative potentials (ca. −1.0 V vs SCE) than the phenylacetylide
derivatives, for which reduction is not usually observed within
the normal solvent window, and reduction likely is associated
with the population of the cyanocarbon ligand based LUMO.
The complexes also exhibit an oxidation process at ca. +0.9 V
which is more closely associated with oxidation of the C-ligated
ruthenium center and CC group. The much more positive
potential of this oxidation relative to that of the phenylacetylide
examples is consistent with the strongly electron withdrawing
nature of the tricyanovinyl moiety.
CONCLUSIONS
■
This work has demonstrated the ready displacement of one of
the CN groups of tcne by ethynyl−ruthenium or −osmium
groups, which behave as strong nucleophiles akin to alkoxide,
thiolate, or amines. The resulting tricyanovinylethynyl com-
plexes are novel examples of donor−acceptor molecular arrays
and show the expected solvatochromism. Addition of a second
metal−ligand fragment to a CN group trans to the metal center
has given further examples of binuclear complexes containing
carbon-rich polynitriles as bridging groups.
The chemistry of tcne contains many examples of the
replacement of a second CN group on the same carbon atom
(gem disubstitution), these reactions being driven by the
excellent leaving properties of the CN group(s) and the
stabilization of the negative charge on the C(CN)2 group.3,4
Disubstitution by a second -CCRu(PP)Cp′ group is not
found in the present study, no doubt because of the strong
steric interactions which would occur if two such MLn groups
were on the same carbon atom. However, as we have briefly
reported,20 the use of smaller nucleophiles has indeed resulted
in the formation of a range of dicyanoethene derivatives, which
will be described in detail elsewhere.31
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), or by flash
chromatography on silica gel (Davisil 40−63 μm).
Instrumentation. IR spectra were obtained using a Bruker IFS28
FT-IR spectrometer. Spectra in CH2Cl2 were obtained using a 0.5 mm
path length solution cell with NaCl windows. Nujol mull spectra were
obtained from samples mounted between NaCl disks. UV−vis−near-IR
spectra were obtained with a Varian Cary 5000 spectrometer: sample
solutions were in fused quartz cells, path length 1 cm. NMR spectra
were recorded on a Varian Gemini 2000 instrument (1H at 300.145
MHz, 13C at 75.479 MHz, 19F at 282.388 MHz, 31P at 121.501 MHz) or
Varian Unity Inova 600 instrument equipped with a cryoprobe (1H at
599.653 MHz, 13C at 150.796 MHz). Unless otherwise stated, samples
were dissolved in CDCl3 contained in 5 mm sample tubes. Chemical
Addition of the proton to the ethynyl Cβ is notable and
suggests that Cβ is more electron rich than the N atoms of the
CN groups. Protonation of 5 to give vinylidene [7]+ results in a
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1
shifts are given in ppm relative to internal tetramethylsilane for H and
13C NMR spectra and external H3PO4 for 31P NMR spectra. Unless
otherwise stated, electrospray (ES-MS) or high-resolution (HR-MS)
mass spectra were obtained from samples dissolved in MeOH which
contained NaOMe as an aid to ionization.29 Solutions were injected into
a Finnegan LCG (ES-MS, Adelaide) or Bruker MicrOTOF (HR-MS,
Waikato) spectrometer via a 10 mL injection loop. Nitrogen was used
as the drying and nebulizing gas. Peaks listed are the most intense of the
isotopic clusters. Elemental analyses were by the CMAS, Belmont,
Victoria 3216, Australia, and Campbell Microanalytical Centre,
University of Otago, Dunedin, New Zealand.
Os(CCH)(PPh3)2Cp. A reaction similar to that for Ru(C
CH)(PPh3)2Cp, using Os(CCH)(PPh3)2Cp (32 mg, 0.04 mmol)
and tcne (6 mg, 0.044 mmol), gave the following products.
Os{C[C(CN)2]CHC(CN)2}(PPh3)2Cp (1-Os; 11 mg, 30%)
(Rf = 0.4) was obtained as a dark red solid. X-ray-quality crystals were
grown from C6H6/MeOH. Anal. Calcd (C49H36N4OsP2): C, 63.08; H,
3.89; N, 6.00; M, 934. Found: C, 62.56; H, 3.86; N, 5.91. IR (CH2Cl2,
cm−1): ν(CN) 2228 w, 2204 m, ν(CC) 1605 w, 1480 m, 1435 s,
1414 w. 1H NMR (CDCl3): δ 4.98 (s, 5H, Cp), 5.82 (s, 1H, CCH),
7.05−7.45 (m, 30 H, Ph). 13C NMR (CD2Cl2): δ 76.26, 92.82 (s, C),
84.69 (s, Cp), 113.23, 113.65, 118.46, 122.05 (4s, CN), 128.86−
135.24 (m, Ph), 169.57 (d, J(CP) = 4.8 Hz, CH), 192.42 (m, Os−
Cα). 31P NMR (CDCl3): δ −0.1, −5.2 (AB q, J(PP) = 17 Hz, 2P,
Os(PPh3)2). ES-MS (m/z): 1889, [2 M + Na]+; 957, [M + Na]+; 935,
[M + H]+; 781, [Os(PPh3)2Cp]+.
Os{CCC(CN)C(CN)2}(PPh3)2Cp (2-Os; 8 mg, 22%) (Rf =
0.5) was obtained as a dark purple solid. X-ray-quality crystals were
grown from CH2Cl2/hexane. Anal. Calcd (C48H35N3OsP2): C, 63.65;
H, 3.89; N, 4.64; M, 907. Found: C, 63.90; H, 3.90; N, 4.62. IR
(CH2Cl2, cm−1): ν(CN) 2210 w, ν(CC) 1998 (sh), 1975 vs,
ν(CC) 1481 w, 1457 m, 1435 w. 1H NMR (CDCl3): δ 4.78 (s, 5H,
Cp) 7.14−7.28 (m, 30 H, Ph). 13C NMR (CDCl3): δ 86.69 (s, Cp),
111.87, 140.21 (2s, C), 116.03, 116.89, 117.59 (3s, CN) 128.12−
137.32 (Ph). 31P NMR (CDCl3): δ 2.8 (s, 2P, Os(PPh3)2). ES-MS
(m/z): 930, [M + Na]+.
Reagents. The compounds RuCl(dppe)Cp*,62 RuCl(PPh3)2Cp,63
Ru(CCH)(PPh3)2Cp,64 Ru(CCCCH)(dppe)Cp*,65 [M(
CCH2)(dppe)Cp′]PF6 (Cp′ = Cp, Cp*; M = Ru,27 Os50b), cis-
67
RuCl2(dppe)2,66 and HCCSiMe3 were all prepared by the cited
literature procedures. Os(CCH)(PPh3)2Cp was prepared by
deprotonation of [Os(CCH2)(PPh3)2Cp]PF6 with KOBut.68 All
other reagents were obtained from Sigma-Aldrich or Fluka and used as
received without further purification.
Ru(CCH)(dppe)Cp*. A degassed solution of Me3SiCCH
(2.1 mL, 14.90 mmol) in MeOH (20 mL) was added to a mixture
of RuCl(dppe)Cp* (2.0 g, 2.98 mmmol) and [NH4]PF6 (0.971 g,
5.96 mmol) in a Schlenk flask. The mixture was heated to reflux for 2 h
and cooled to room temperature, and then sodium metal (0.343 g,
14.90 mmol) was added to give a yellow precipitate. After 1 h, this was
collected and washed with MeOH (2 × 5 mL) and hexane (5 mL) to
give Ru(CCH)(dppe)Cp* as a yellow powder (1.91 g, 95%).
Reactions of Ethynyl or Vinylidene Complexes with tcne.
Caution! Extremely toxic HCN is produced in these reactions!
Appropriate care should be taken, working in a well-ventilated area.
HCN and accompanying solvent were collected in a trap cooled in
liquid N2. After it was warmed to room temperature, the condensate
was treated with KMnO4 solution.
Ru(CCH)(PPh3)2Cp. To a solution of Ru(CCH)(PPh3)2Cp (70
mg, 0.098 mmol) in thf (12 mL) was added tcne (13 mg, 0.102 mmol).
The color of the solution changed from yellow to yellow-brown to red
to burgundy over a 30 min period. After 2 h, no further color change
was observed and solvent was removed. The residue was purified by
preparative TLC (acetone−hexane, 3:7) affording two bands.
Extraction of the lower red band (Rf = 0.4) gave Ru{C[
C(CN)2]CHC(CN)2}(PPh3)2Cp (1-Ru; 53 mg, 64%). Anal. Calcd
(C49H36N4P2Ru): C, 69.74; H, 4.30; N, 6.64; M, 844. Found: C, 68.83;
H, 4.54; N, 6.47. IR (CH2Cl2, cm−1): ν(CN) 2226 w, 2207 m,
ν(CC) 1605 m, 1480 m, 1433 s, 1414 w. 1H NMR (CDCl3): δ 4.78
(s, 5H, Cp), 5.90 (s, 1H, CCH), 7.10−7.49 (m, 30 H, Ph). 31P
NMR (CDCl3): δ 45.2, 42.2 (AB q, J(PP) = 33 Hz, 2P, Ru(PPh3)2).
ES-MS (m/z): 867, [M + Na]+.
Ru(CCH)(dppe)Cp. To a stirred thf solution (10 mL) of Ru(C
CH)(dppe)Cp (57 mg, 0.097 mmol) in thf (10 mL) was added tcne
(14 mg, 0.106 mmol). The solution slowly turned from yellow to
transparent dark red and then to orange after 5 h. The reaction was
monitored by spot TLC: the initial upper burgundy band was replaced
by an orange band. After 7 h, solvent was removed and the residue was
purified by column chromatography (flash silica, acetone−petroleum
spirit, 3:7). An orange fraction contained Ru{C[C(CN)2]CH
C(CN)2]}(dppe)Cp (3) as an orange solid (55 mg, 79%). X-ray-
quality crystals were grown from CH2Cl2−hexane. Anal. Calcd
(C39H30N4P2Ru): C, 65.27; H, 4.21; N, 7.81; M, 718. Found: C,
65.30; H, 4.25; N, 7.78. IR (CH2Cl2, cm−1): ν(CN) 2228 m, 2213 s,
1
ν(CC) 1605 m, 1556 m. H NMR (CDCl3): δ 2.36, 2.80 (2m, 2 ×
CH2, dppe), 4.94 (s, 5H, Cp), 6.76 (s, 1H, CCH), 6.83−7.69 (m,
Ph). 13C NMR (CDCl3): δ 27.65−31.79 (m, PCH2CH2P), 86.43 (s,
Cp), 112.38, 112.85, 113.07, 117.91 (4s, CN), 128.51−135.92 (m,
Ph), 140.37 (s, CC(CN)2), 165.25 (d, J(CP) = 4 Hz, CC(CN)2).
31P NMR (CDCl3): at room temperature, δ 82.3 (br s, P, Ru(dppe)),
72.6 (vbr s, P, Ru(dppe)); at −57 °C, δ 80.8 (d, J(PP) = 23 Hz, 1P,
dppe), 68.9 (d, J(PP) = 23 Hz, 1P, dppe). ES-MS (m/z): 740, [M −
H + Na]+; 565, [Ru(dppe)Cp]+.
With [Ru(CCH2)(dppe)Cp]PF6/LiMe. A solution of [Ru(
CCH2)(dppe)Cp]PF6 (150 mg, 0.204 mmol) in thf (15 mL) at
−78 °C was treated with MeLi (0.27 mL, 1.5 M in hexane, 0.408
mmol). After 40 min tcne (29 mg, 0.224 mmol) was added to the
mixture. After the mixture was warmed to room temperature, the color
changed from yellow to purple. After the mixture was stirred for 1 h,
solvent was removed and the residue was purified by preparative TLC
(CH2Cl2), giving Ru{CCC(CN)C(CN)2}(dppe)Cp (4) as a
purple solid (97 mg, 69%). X-ray-quality crystals were grown from
CDCl3−MeOH. Anal. Calcd (C38H29N3P2Ru): C, 66.08; H, 4.23; N,
6.08; M, 691. Found: C, 66.08; H, 4.35; N, 6.02. IR (CH2Cl2, cm−1):
The upper purple band (Rf = 0.6) contained Ru{CCC(CN)
C(CN)2}(PPh3)2Cp (2-Ru; 8 mg, 10%) as a dark purple solid. X-ray-
quality crystals were grown from CDCl3/MeOH. Anal. Calcd
(C48H35N3P2Ru·CDCl3): C, 62.86; H, 3.88; N, 4.49; M, 817.
Found: C, 62.98; H, 3.93; N, 4.44. IR (CH2Cl2, cm−1): ν(CN)
2213 w, 2204 w, ν(CC) 1991 vs, ν(CC) 1605 m, 1481 m, 1462 s,
1
1434 m. H NMR (CDCl3): δ 4.62 (s, 5H, Cp) 7.16−7.30 (m, 30 H,
Ph). 13C NMR (CDCl3): δ 84.76 (t, J(CP) = 2.5 Hz, Cβ), 89.32 (s,
Cp), 113.33, 115.35, 115.96 (3s, CN), 118.00 (s, C), 128.11−137.15
(Ph), 210.71 (t, J(CP) = 22 Hz, Cα); in C6D6, δ 77.73 (t, J = 32 Hz,
CDCl3). 31P NMR (CDCl3): δ 48.6 (s, 2P, Ru(PPh3)2). ES-MS
(m/z): 840, [M + Na]+.
1
ν(CN) 2212 w, ν(CC) 1990 vs, ν(CC) 1462 m, 1410 w. H
NMR (CDCl3): δ 2.46, 2.88 (2m, 2 × CH2, dppe), 5.02 (s, 5H, Cp),
7.19−7.76 (m, Ph). 13C NMR (CDCl3): δ 28.34 (m, PCH2CH2P),
86.84 (s, Cp), 113.51, 115.40, 115.55 (3s, CN), 117.55 (s, C),
128.38−138.83 (m, Ph). 31P NMR (CDCl3): δ 84.6 (s, 2P, Ru(dppe)).
ES-MS (m/z): 714, [M + Na]+.
Ru(CCH2)(PPh3)2Cp/LiBu. A solution of [Ru(CCH2)-
(PPh3)2Cp]PF6 (175 mg, 0.20 mmol) in thf (15 mL) at −78 °C was
treated with LiBu (0.23 mL of a 1.8 M solution in hexane, 0.41 mmol).
After 30 min, tcne (52 mg, 0.41 mmol) was added to the reaction
mixture and was warmed to room temperature. The color changed from
yellow to dark purple, and after 2 h hexane (15 mL) was added and the
mixture was passed through a small column (silica, acetone−petroleum
spirit, 3:7). Further purification by flash chromatography (silica,
CH2Cl2−hexane, 3:1) gave 2-Ru as a purple solid (61 mg, 37%).
With Ru(CCH)(dppe)Cp*. A stirred solution of Ru(CCH)-
(dppe)Cp* (500 mg, 0.758 mmol) in thf (20 mL) was treated with tcne
(102 mg, 0.796 mmol). The solution instantaneously turned from yellow
to purple and was stirred at room temperature for a further 30 min
before the solvent was removed under reduced pressure. The residue
was taken up in a minimal amount of CH2Cl2 and purified by flash
chromatography (silica, CH2Cl2−hexanes, 3:1). The first purple fraction
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afforded Ru{CCC(CN)C(CN)2}(dppe)Cp* (5) as a purple solid
(538 mg, 93%). X-ray-quality crystals were grown from CH2Cl2−hexane.
Anal. Calcd (C43H39N3P2Ru): C, 67.88; H, 5.17; N, 5.52; M, 761.
Found: C, 67.90; H, 5.25; N, 5.60. IR (CH2Cl2, cm−1): ν(CN) 2199
0.079 mmol), RuCl(dppe)Cp* (53 mg, 0.079 mmol), and
[NH4]PF6 (51 mg, 0.315 mmol) in MeOH (8 mL, 90 min),
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{Ru(dppe)Cp*}]-
PF6 ([8]PF6; 82 mg, 68%) was obtained as dark blue crystals. X-ray-
quality crystals were grown from CDCl3−hexane. Anal. Calcd
(C79H78F6N3P5Ru2): C, 61.59; H, 5.10; N, 2.73; M (cation), 1396.
Found: C, 61.36; H, 5.17; N, 2.72. IR (CH2Cl2, cm−1): ν(CN) 2209
w, ν(CC) 1963 vs, ν(Ph−CH) coupled with ν(Cp* C−H) 1604 w,
1
w, 2209 m; ν(CC) 1979 vs; ν(CC) 1463 s, 1435 w. H NMR
(CDCl3): δ 1.58 (s, 15H, Cp*), 2.23, 2.82 (2m, 2 × CH2, dppe), 7.16−
7.44 (m, Ph). 13C NMR: in CDCl3, δ 10.29 (C5Me5), 29.03−29.65 (m,
PCH2CH2P), 97.75 (s, C5Me5), 116.55, 138.22 (2s, C), 113.72, 116.12,
116.46 (3s, CN), 128.04−135.55 (m, Ph) 221.30 (t, J(CP) = 21 Hz,
Ru−C); in C6D6, δ 9.91 (C5Me5), 28.70−34.29 (m, PCH2CH2P), 80.41,
118.48 (2s, C), 97.44 (s, C5Me5), 114.56, 116.09, 116.50 (3s, CN),
128.07−136.77 (m, Ph), 215.52 (m, C−Ru). 31P NMR (CDCl3): δ 80.0
(s, 2P, Ru(dppe)). ES-MS (m/z): 784, [M + Na]+.
1
ν(CC) 1448 s, 1436 s. H NMR (CDCl3): δ 1.55, 1.46 (2s, 15H,
Cp*), 2.24−2.52 (br m, 3 × CH2, dppe), 2.71−2.79 (m, 1 × CH2,
dppe), 7.09−7.50 (m, Ph). 13C NMR (CDCl3): δ 9.82 (C5Me5 (Ru−
NC)), 10.10 (C5Me5 (Ru−CC)) 28.21−29.97 (m, 2 ×
PCH2CH2P), 93.51 (s, C5Me5 (Ru−NC)), 98.71 (s, C5Me5 (Ru−
CC)), 102.61, 124.23, 145.61 (3s, C), 113.92, 115.22 (2s, CN),
128.22−136.01 (m, Ph). 31P NMR (CDCl3): δ 79.8 (s, 2P,
Cp*(dppe)Ru(CC)), 75.0 (s, 2P, Cp*(dppe)Ru(NC)), −142.9
(sept, J(PF) = 711 Hz, 1P, PF6). ES-MS (MeOH, m/z): 1396, M+;
635, [Ru(dppe)Cp*]+.
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{Os(dppe)Cp*}]PF6
([9]PF6). From Ru{CCC(CN)C(CN)2}(dppe)Cp* (52 mg,
0.072 mmol), OsCl(dppe)Cp* (52 mg, 0.072 mmol), and
[NH4]PF6 (47 mg, 0.287 mmol) in MeOH (7 mL, 24 h),
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{Os(dppe)Cp*}]-
PF6 ([9]PF6; 58 mg, 50%) was obtained as dark blue microcrystals.
Single crystals suitable for X-ray diffraction were grown from CH2Cl2−
hexane. Anal. Calcd (C79H78F6N3P5OsRu): C, 58.22; H, 4.82; N, 2.58;
M (cation), 1486. Found: C, 58.24; H, 4.84; N, 2.61. IR (CH2Cl2,
cm−1): ν(CN) 2206 w, 2158 w, ν(CC) 1964 vs, ν(CC) 1445
w, 1436 m. 1H NMR (CDCl3): δ 1.55 (s, 30H, 2 × Cp*), 2.30 (br m,
1 × CH2, dppe), 2.44−2.49 (br m, 2 × CH2, dppe), 2.74 (m, 1 × CH2,
dppe), 7.12−7.48 (m, Ph). 13C NMR (CDCl3): δ 9.54 (C5Me5 (Os−
NC)), 10.13 (C5Me5 (Ru−CC)), 29.47−31.06 (m, 2 ×
PCH2CH2P), 90.84 (s, C5Me5 (Os−NC)), 98.50 (s, C5Me5 (Ru−
CC)), 128.22−136.01 (m, Ph). 31P NMR (CDCl3): δ 79.7 (s, 2P,
Cp*(dppe)Ru−(CC)), 41.3 (s, 2P, Cp*(dppe)Os−(NC)),
−142.5 (sept, J(PF) = 710 Hz, 1P, PF6). ES-MS (MeOH, m/z):
1486, M+; 725, [Os(dppe)Cp*]+; 635, [Ru(dppe)Cp*]+.
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{Ru(PPh3)2Cp}]PF6
([10]PF6). From Ru{CCC(CN)C(CN)2}(dppe)Cp* (55 mg,
0.072 mmol), RuCl(PPh3)2Cp (52 mg, 0.072 mmol), and [NH4]PF6
(47 mg, 0.288 mmol) in MeOH (8 mL, 30 min), [{Cp*(dppe)Ru}{μ-
CCC(CN)C(CN)CN}{Ru(PPh3)2Cp}]PF6 ([10]PF6; 59 mg,
51%) was obtained as dark blue crystals. X-ray-quality crystals were
grown from CDCl3−hexane. Anal. Calcd (C84H74F6N3P5Ru2): C,
63.19; H, 4.76; N, 2.63; M (cation), 1451. Found: C, 62.82; H, 4.76;
N, 2.66. IR (CH2Cl2, cm−1): ν(CN) 2210 w, 2165 w, ν(CC)
1961 vs, ν(CC) 1481 w, 1436 s. 1H NMR (CDCl3): δ 1.60 (s, 15H,
Cp*), 2.37, 2.88 (2m, 2 × CH2, dppe), 4.48 (s, 5H, Cp), 7.04−7.50
(m, Ph). 13C NMR (CDCl3): δ 10.23 (C5Me5), 29.43 (m,
PCH2CH2P), 84.36 (s, C5H5), 99.19 (s, C5Me5), 97.83, 104.42,
149.68 (3s, C), 113.69, 114.66, 115.25 (3s, CN), 127.63−136.45 (m,
Ph). 31P NMR (CDCl3): δ 79.5 (s, 2P, Ru(dppe)Cp*), 41.3 (s, 2P,
Ru(PPh3)2Cp), −142.5 (sept, J(PF) = 709 Hz, 1P, PF6). ES-MS
(MeOH, m/z): 1451, M+; 691, [Ru(PPh3)2Cp]+.
With [Ru(CCH2)(dppe)Cp*]PF6 /LiMe. A solution of [Ru(
CCH2)(dppe)Cp*]PF6 (90 mg, 0.113 mmol) in thf (15 mL) at −78
°C was treated with LiMe (0.09 mL, 2.5 M in hexane, 0.225 mmol).
After 25 min tcne (14 mg, 0.113 mmol) was added to the mixture. The
solution changed through orange-brown (5 min) to maroon (10 min).
After it was stirred overnight, the solution was purple. The solvent was
removed, and purification by preparative TLC (CH2Cl2) gave Ru{C
CC(CN)C(CN)2}(dppe)Cp* (5; 72 mg, 95%).
With Ru(CCCCH)(dppe)Cp*. A stirred solution of Ru(C
CCCH)(dppe)Cp* (53 mg, 0.077 mmol) in thf (12 mL) was
cooled to −78 °C, and tcne (11 mg, 0.086 mmol) was added. After
30 min the yellow solution had turned blue. The reaction mixture was
left overnight with no further color change. Solvent was removed, and
the residue was purified by preparative TLC (CH2Cl2). The major
blue band afforded Ru{CCC[C(CN)2]CHC(CN)2}(dppe)-
Cp* (6) as a dark blue solid (30 mg, 48%). Anal. Calcd
(C46H40N4P2Ru): C, 68.05; H, 4.97; N, 6.90; M, 812. Found: C,
68.09; H, 5.03; N, 6.79. IR (CH2Cl2, cm−1): ν(CN) 2209 m, ν(C
1
C) 1964 vs, ν(CC) 1450 br. H NMR (C6D6): δ 1.42 (s, 15H,
Cp*), 1.93−2.17, 2.76−2.94 (2m, 2 × CH2, dppe), 6.37 (s, 1H,
CCH), 7.00−7.57 (m, Ph). 13C NMR (CDCl3): δ 10.27 (C5Me5),
29.21−30.47 (m, PCH2CH2P), 75.70, 88.95, 138.85 (3s, C),
95.57 (s, C5Me5), 110.70, 112.81, 116.79, 116.81 (4s, CN), 128.29−
138.45 (m, Ph), 155.90 (s, CCH), 222.23 (m, Ru−Cα). 31P
NMR (C6D6): δ 81.4 (s, 2P, Ru(dppe)). ES-MS (MeCN, m/z): 813,
[M + H]+.
Protonation of Ru{CCC(CN)C(CN)2}(dppe)Cp* (5). A
solution of Ru{CCC(CN)C(CN)2}(dppe)Cp* (5; 116 mg,
0.152 mmol) in CH2Cl2 (10 mL) was protonated using either
HBF4·OEt2 (1.05 equiv) or HPF6 (aqueous, 60%, 0.022 mL, 0.16
mmol). The stirred solution changed from dark purple to orange after
3 min. Solvent was removed, and the residue was taken up in CH2Cl2
and added to hexane (60 mL) to give an orange-red precipitate of
[Ru{CCHC(CN)C(CN)2}(dppe)Cp*]X ([7]X; X = BF4,
PF6) (89−92%). X-ray-quality crystals of the BF4 salt were grown from
CH2Cl2−hexane. Anal. Calcd (C43H40F6N3P3Ru): C, 56.96; H, 4.45;
N, 4.63; M (cation), 762. Found: C, 56.87; H, 4.51; N, 4.60. IR
(Nujol, cm−1): ν(CN) 2216 m, ν(CC) 1612 s. 1H NMR
(CD2Cl2): δ 1.72 (s, 15H, Cp*), 2.61, 2.97 (2m, 2 x CH2, dppe), 4.54
(s, 1H, CCH), 7.12−7.70 (m, 20H, Ph). 13C NMR (CD2Cl2): δ
10.89 (C5Me5), 27.84−28.76 (m, PCH2CH2P), 78.92 (s, C), 107.67 (s,
C5Me5), 110.84, 112.04, 113.04 (3s, CN) 113.92 (s, CCH, shown
by DEPT NMR), 127.67−133.54 (m, Ph), 333.20 (t, J(CP) = 15 Hz,
RuC). 31P NMR (CD2Cl2): δ 67.4 (s, 2P, Ru(dppe)). ES-MS
(MeCN, m/z) 635, [Ru(dppe)Cp*]+; 676, [Ru(NCMe)(dppe)-
Cp*]+; 1545, [2(M − H) + Na]+; 784, [M − H + Na]+; 762, M+;
735, [M − HCN]+.
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{trans-RuCl(dppe)2}]PF6
([11]PF6). The product from Ru{CCC(CN)C(CN)2}(dppe)-
Cp* (80 mg, 0.105 mmol), cis-RuCl2(dppe)2 (51 mg, 0.053 mmol),
and [NH4]PF6 (68 mg, 0.420 mmol) in MeOH (10 mL, 24 h) was
purified by column chromatography (silica). Unreacted purple
Ru{CCC(CN)C(CN)2}(dppe)Cp* first eluted with CH2Cl2,
while with acetone−hexane (1:1), a blue fraction containing
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{trans-RuCl-
(dppe)2}]PF6 ([11]PF6; 42 mg, 43%) was obtained. Anal. Calcd
(C95H89F6N3P7Ru2): C, 61.97; H, 4.87; N, 2.28; M (cation), 1696.
Found: C, 61.84; H, 4.90; N, 2.35. IR (CH2Cl2, cm−1): ν(CN) 2207
Reactions of Ru{CCC(CN)C(CN)2}(dppe)Cp* (5) with
MClLn. General Conditions. A mixture of Ru{CCC(CN)
C(CN)2}(dppe)Cp* (5; 1 equiv), MClLn (1 equiv), and [NH4]PF6
(4 equiv) was heated in refluxing MeOH. In all cases, the solution
changed from deep purple to dark blue. The solution was cooled to
room temperature, and the blue crystalline material was collected upon
a sinter and washed with methanol (2 × 3 mL) and hexane (5 mL) to
give the product.
1
w, ν(CC) 1964 vs, ν(CC) 1605 w, 1484 w, 1436 m. H NMR
(CDCl3): δ 1.57 (s, 15H, Cp*), 2.35 (br m, 1 × CH2, dppe) 2.62 (br
m, 2 × CH2, dppe), 2.81 (m, 3 × CH2, dppe), 7.01−7.58 (m, Ph). 13
C
NMR (CDCl3, 50 MHz): δ 10.10 (C5Me5), 29.26−29.91 (m, 3 ×
[{Cp*(dppe)Ru}{μ-CCC(CN)C(CN)CN}{Ru(dppe)Cp*}]PF6
([8]PF6). From Ru{CCC(CN)C(CN)2}(dppe)Cp* (60 mg,
PCH2CH2P), 98.73, 102.66, 124.62, 148.11 (4s, C), 99.16 (s, C5Me5),
2654
dx.doi.org/10.1021/om2007503|Organometallics 2012, 31, 2639−2657

Organometallics
Article
Table 11. Crystal Data and Refinement Details for 2-Ru, 3−5, [7]BF4, [9]PF6, and [10]PF6
2-Ru
3
4
5
formula
MW
C48H35N3P2Ru
816.80
C39H30N4P2Ru·CH2Cl2
802.61
C38H29N3P2Ru
690.65
C43H39N3P2Ru
760.78
cryst syst
space group
a/Å
monoclinic
P21/n
triclinic
orthorhombic
Pca21
monoclinic
P21/n
P1
̅
11.4978(7)
17.5630(9)
19.605(1)
11.7459(5)
11.9723(5)
13.2917(6)
82.087(4)
89.623(4)
75.665(4)
1793
21.433(2)
16.439(1)
17.989(2)
13.362(3)
17.193(4)
16.114(4)
b/Å
c/Å
α/deg
β/deg
100.135(1)
98.964(4)
γ/deg
V/Å3
ρc/g cm−3
3897
6338
3657
1.392
1.487
1.448
1.382
Z
4
2
8
4
2θmax/deg
μ(Mo Kα)/mm−1
Tmin/max
cryst dimens/mm3
Ntot
75
60
67
50
0.52
0.71
0.63
0.55
0.82
0.94
0.86
0.62
0.45 × 0.38 × 0.35
81 052
0.20 × 0.18 × 0.13
19 495
0.48 × 0.16 × 0.10
89 975
0.52 × 0.18 × 0.03
35 617
N (Rint)
No
20 404 (0.022)
17 661
9313 (0.038)
5735
23 867 (0.054)
17 574
6472 (0.109)
4584
a
R1
0.027
0.040
0.048
0.057
wR2 (a (,b))
T/K
0.075 (0.036, 1.4)
150
0.088 (0.038)
100
0.117 (0.052, 5.4)
150
0.148 (0.079, 2.5)
100
[7]BF4
[9]PF6
[10]PF6
formula
MW
C43H40N3P2Ru·BF4
848.60
C79H78N3OsP4Ru·F6P
1629.56
C84H74N3P4Ru2·F6P
1596.45
cryst syst
space group
a/Å
monoclinic
P21/n
monoclinic
C2/c
orthorhombic
Fdd2
11.1286(2)
17.4916(3)
20.1481(4)
103.473(2)
3814
20.9050(10)
14.7607(8)
23.7010(10)
100.138(5)
7199
36.72(2)
b/Å
68.84(3)
c/Å
11.415(5)
β/deg
V/Å3
ρc/g cm−3
28 857
1.478
1.502
1.470
Z
4
4
16
2θmax/deg
μ(Mo Kα)/mm−1
Tmin/max
cryst dimens/mm3
Ntot
68
62
55
0.55
2.15
0.59
0.80
0.81
0.85
0.34 × 0.24 × 0.03
75 979
0.23 × 0.20 × 0.10
51 366
0.60 × 0.12 × 0.10
47 047
N (Rint)
No
15 394 (0.072)
8061
10 772 (0.077)
5503
15 861 (0.072)
10 929
b
R1
0.042
0.075
0.062
wR2 (a (,b))
T/K
0.097 (0.043)
100
0.204 (0.075, 43)
100
0.16 (0.056, 243)
150
a
b
xabs = −0.02(10). xabs = 0.02(4).
112.01, 113.73, 115.62 (3s, CN), 127.22−136.00 (m, Ph). 31P NMR
(CDCl3): δ 80.1 (s, 2P, Cp*(dppe)Ru), 43.2 (s, 4P, RuCl(dppe)2),
−142.5 (sept, J(PF) = 710 Hz, 1P, PF6). ES-MS (MeOH, m/z): 1696,
M+; 933, [RuCl(dppe)2]+; 635, [Ru(dppe)Cp*]+.
Structure Determinations. Full spheres of diffraction data were
measured using CCD area-detector instrumentation. Ntot reflections
were merged to N unique (Rint cited) after “empirical”/multiscan
absorption correction (proprietary software), No with F > 4σ(F) being
considered “observed”; all data were used in the full matrix least-
squares refinements on F2. All data were measured using
monochromatic Mo Kα radiation (λ = 0.710 73 Å). Anisotropic
displacement parameter forms were refined for the non-hydrogen
atoms, (x, y, z, Uiso)H being included following a “riding” model
(reflection weights (σ2(F2) + (aP)2 (+ bP))−1 (P = (Fo2 + 2Fc2)/3)).
Neutral atom complex scattering factors were used; computation used
the SHELXL 97 program.69 Pertinent results are given in the figures
(which show non-hydrogen atoms with 50% probability amplitude
displacement ellipsoids) and in Tables 1 and 11.
Variata. [8]PF6. As refined in space group C2/c, with a
centrosymmetric cation, three of the four phenyl rings were modeled
as disordered over pairs of sites, with occupancies 0.5, as were also the
fluorine atoms. In the isomorphous [9]PF6, all phenyl rings were
modeled as disordered, with isotropic adp forms; the metal atom was
modeled as a Ru/Os composite. The pendant ligand atom at the metal
was modeled as a C/N composite.
2655
dx.doi.org/10.1021/om2007503|Organometallics 2012, 31, 2639−2657

Organometallics
Article
(11) Tsuchiya, K.; Kondo, H.; Nagashima, H. Organometallics 2007,
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ASSOCIATED CONTENT
* Supporting Information
■
S
Text giving details of the computational work, tables giving the
energy and Cartesian coordinates of the optimized geometries
of 5′, 7′, and 8′, and CIF files giving all crystallographic data for
2-Ru, 3−5, [7]BF4, [9]PF6, and [10]PF6. This material is
available free of charge via the Internet at http://pubs.acs.org.
Full details of the structure determinations (except structure
factors) have also been deposited with the Cambridge
Crystallographic Data Centre as CCDC 705431−705435,
707491, and 707492. Copies of this information may be
obtained free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ (Fax: + 44 1223 336 033; e-mail:
deposit@ ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
(13) Kohler, H. Z. Chem. 1973, 13, 401.
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148; Angew. Chem., Int. Ed. Engl. 1991, 30, 1127.
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P.; Frank, B.; Moonen, N. N. P.; Gross, M.; Diederich, F. Chem. Eur. J.
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P.; Gross, M.; Diederich, F. Chem. Commun. 2007, 4731.
(e) Retenauer, P.; Kivala, M.; Jarowski, P. D.; Boudon, C.;
Gisselbrecht, J.-P.; Gross, M.; Diederich, F. Chem. Commun. 2007,
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Rodgers, J. R.; Snow, M. R.; Swincer, A. G. J. Chem. Soc., Chem.
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(19) Bruce, M. I.; Fox, M. A.; Low, P. J.; Skelton, B. W.; Zaitseva,
N. N. Dalton Trans. 2010, 39, 3759.
(20) Bruce, M. I.; Burgun, A.; Kramarczuk, K. A.; Nicholson, B. K.;
Parker, C. R.; Skelton, B. W.; White, A. H.; Zaitseva, N. N. Dalton
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AUTHOR INFORMATION
Corresponding Author
*Fax: 61 8 8303 4358. E-mail: michael.bruce@adelaide.edu.au.
■
ACKNOWLEDGMENTS
■
We thank the Australian Research Council for support of this
work and Johnson Matthey Ltd, Reading, U.K., for generous
loans of RuCl3·nH2O and OsO4. P.J.L. holds an EPSRC
Leadership Fellowship. Ms. K. A. Kramarczuk performed some
initial experiments with the Os system, Ms. Wing Y. Man
assisted with some of the spectroscopic data collection and
presentation, and we are grateful to Dr. G. J. Perkins for a
sample of Os(CCH)(PPh3)2Cp.
DEDICATION
■
Chem. 1974, 73, C17.
(24) Anderson, G. K.; Clark, H. C.; Davies, J. A. Organometallics
1982, 1, 550.
Dedicated to the memory of Professor F. G. A. Stone,
organometallic chemist extraordinaire, respected mentor, and
valued friend of M.I.B.
(25) Bruce, M. I.; Low, P. J.; Skelton, B. W.; White, A. H. New J.
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́
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