Oxidative dimerization of aryldiynyl-ruthenium complexes

Article abstract of DOI:10.1021/om3005146

Chemical oxidation of Ru(C≡CC≡CR)(dppe)Cp with [FeCp ₂]PF₆ affords the binuclear cations [{Ru(dppe)Cp} ₂C₈R₂]²⁺(PF₆ ^-)₂ (R = Ph, 7²⁺(PF₆ ^-)₂; R = Fc, 8²⁺(PF₆ ^-)₂) by radical coupling at electron-rich sites involving the inner and outer C≡C triple bonds, to give cyclobutenediylidene derivatives. In each case, mixtures of symmetrical and asymmetrical isomers were obtained (2:1 for 7²⁺(PF₆^-)₂, 1:1 for 8²⁺(PF₆^-)₂), shown by single-crystal X-ray diffraction structure determinations of 7 ²⁺-asym(PF₆^-)₂ and 8 ²⁺-sym(AsF₆^-)₂. 8²⁺-sym consists of a central C₄ ring with two =C=C=Ru(dppe)Cp groups in the 1,2-positions and two Fc substituents in the 3,4-positions, whereas for 7 ²⁺-asym the substituent =Ru(dppe)Cp is in the 1-position, =C=C=Ru(dppe)Cp is in the 2-position, Ph is in the 3-position, and -C≡CPh is in the 4-position. DFT calculations reveal that the precursor cationic diynyl complexes show important electron density on C_β and C _δ, suggesting that radical coupling (C_δ + C_δ) or (C_β + C_δ) affords the sym and asym isomers, respectively.

Full text of DOI:10.1021/om3005146

Article
pubs.acs.org/Organometallics
Oxidative Dimerization of Aryldiynyl−Ruthenium Complexes
Michael I. Bruce,*,† Karine Costuas,‡ Frederic Gendron,‡ Jean-Francois Halet,*,‡ Martyn Jevric,†
̧
́
́
and Brian W. Skelton§,∥
†School of Chemistry & Physics, University of Adelaide, South Australia 5005, Australia
‡Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS, Universite
de Rennes 1, 35042 Rennes, France
́
§School of Biomedical, Biomolecular & Chemical Sciences, Chemistry M313, University of Western Australia, Crawley, Western
Australia 6009, Australia
S
* Supporting Information
ABSTRACT: Chemical oxidation of Ru(CCCCR)(dppe)Cp with [FeCp2]PF6 affords the binuclear cations [{Ru(dppe)-
−
−
−
Cp}2C8R2]2+(PF6 )2 (R = Ph, 72+(PF6 )2; R = Fc, 82+(PF6 )2) by radical coupling at electron-rich sites involving the inner and
outer CC triple bonds, to give cyclobutenediylidene derivatives. In each case, mixtures of symmetrical and asymmetrical
isomers were obtained (2:1 for 72+(PF6 )2, 1:1 for 82+(PF6 )2), shown by single-crystal X-ray diffraction structure determinations
−
−
of 72+-asym(PF6 )2 and 82+-sym(AsF6 )2. 82+-sym consists of a central C4 ring with two CCRu(dppe)Cp groups in the
1,2-positions and two Fc substituents in the 3,4-positions, whereas for 72+-asym the substituent Ru(dppe)Cp is in the 1-
position, CCRu(dppe)Cp is in the 2-position, Ph is in the 3-position, and −CCPh is in the 4-position. DFT
calculations reveal that the precursor cationic diynyl complexes show important electron density on Cβ and Cδ, suggesting that
radical coupling (Cδ + Cδ) or (Cβ + Cδ) affords the sym and asym isomers, respectively.
−
−
C6H4X-4, X = CO2Me, CHO, H, Me, OMe, NH2; M = W, R =
Ph, C6H4Me-4),17 Mo(CCR)(CO)(dppe)Cp′, and trans-
Mo(CCR)(CO)(PMe3)2Cp′ (R = Ph, C6H4-4-Me, Cp′ =
Cp, Cp*)18 have shown that ready 1e oxidation of these
complexes occurs to give 17e monocations. Both neutral and
charged species have been investigated by a variety of
spectroscopic (IR, NMR, UV−vis), X-ray structural and
theoretical (DFT) means. In particular, the neutral metal−
ligand fragment, formally containing M(II), is electron-rich and
behaves as an electron-releasing group to the carbon-rich
ligand. It is clear that the properties of σ-alkynyl−metal
complexes are best considered in terms of delocalization of
electron spin density over the metal−alkynyl array.19
Whiteley and co-workers have found that similar oxidation of
Mo(CCPh)(dppe)(η-C7H7) afforded the bis(vinylidene)
[{(η-C7H7)(dppe)Mo}(CCPhCPhC){Mo(dppe)(η-
C7H7)}](PF6)2 by coupling at Cβ.17 Similarly, oxidation of
Mo(CCCCR)(LL)(η-C7H7) (LL = bpy, R = SiMe3; LL =
INTRODUCTION
■
The chemistry of transition-metal complexes containing
conjugated carbon chains continues to intrigue and surprise.1−3
Potential applications as components of electronic,4 magnetic,5
and optical devices6 and as molecular-scale wires7 depend upon
the behavior of unpaired electrons in these systems, and much
research on the redox properties of metal−ligand end-bridged
compounds {LnM}−(CC)x−{MLn} has been carried out.
The series of complexes containing a C4 bridge has been the
subject of many studies with attention being directed toward
the series of oxidized derivatives [{LnM}−(CC)2−{MLn}]m+
(MLn = M(dppe)Cp* (M = Fe,8 Ru,9 Os10), M(dppe)(η-
C7H7) (M = Mo11)).
Extensive studies of the arylethynyl−metal complexes
Fe(CCAr)(dppe)Cp,12 M(CCAr)(dppe)Cp* (M = Fe,13
Ru;14 Ar = C6H4X-4, X = CF3, Br, Me, But (M = Fe), NO2, CN,
F, H, OMe, NH2 (M = Fe, Ru)), Ru(CCAr)(PP)Cp′ (Ar =
Ph, C6H4Me-4, 1-naphthyl, 9-anthryl; (PP)Cp′ = (PPh3)2Cp,
(dppe)Cp*),15 trans-Ru(CCAr)Cl(dppe)2 (Ar = C6H4X-4, X
= NO2, CHO, C(O)Me, F, H, OMe, NMe2),16 M(C
CR)(dppe)(η-C7H7) (M = Mo, R = But, CO2Me, Fc or
Received: June 9, 2012
Published: September 4, 2012
© 2012 American Chemical Society
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Scheme 1. Oxidative Dimerization of Mo(CCCCSiMe3)(dppe)(η-C7H7)
Scheme 2. Reactions of Ru(CCPh)(PPh3)2Cp (1) with [FeCp2]PF6 or Ag[PF6]
dppe, R = H, SiMe3) with [FeCp2]PF6 produces molybdenum-
stabilized diynyl radicals which were characterized by extensive
spectroscopic studies (IR, ESR) and by a structural study of
[Mo(CCCCSiMe3)(bpy)(η-C7H7)]PF6.20 Further oxidation of
Mo(CCCCSiMe3)(dppe)(η-C7H7) afforded a dimeric
product, shown by an X-ray structure to be the bis-vinylidene
[{(η-C7H7)(dppe)Mo}{CC(CCSiMe3)C(C
CSiMe3)CC}{Mo(dppe)(η-C7H7)}](PF6)2 (Scheme 1).
The intermediacy of the 17e diynyl monocation was shown
independently, and this evolved by Cβ coupling to the branched
C8 chain-bridged product.
former species but almost equally distributed on the metal and
the arylalkynyl ligand for the latter.14,17c,24
In the course of these studies, attempts have been made to
isolate the oxidized compounds. Chemical oxidation of Fe(C
CC6H4X-4)(dppe)Cp* with [FeCp2]PF6 has given [Fe-
(CCC6H4X-4)(dppe)Cp*]PF6 (X = NO2, CN, CF3, F, Br, H,
Me, OBut, OMe, NH2, NMe2), and structural determinations of
several of them were completed.13 In the ruthenium series, a
major difference in reactivity is found.14 Electrochemical
oxidation showed that apparently reversible or quasi-reversible
1e processes occur in the range 0.05−0.40 V (vs SCE), the
potential correlating with the electronic properties of the
substituents. However, in attempts to use chemical oxidants it
was not possible to isolate any of the oxidized compounds,
although in one case the vinylidene [Ru{CCH(C6H4NO2-
4)}(dppe)Cp*]PF6 was isolated and characterized.14
In the ruthenium series, the use of [FeCp2]PF6 as the oxidant
has enabled novel dimeric species to be obtained, which had
been formed by radical coupling at sites shown to be electron-
rich, particularly involving the alkynyl Cβ and Ph Cpara atoms
(Scheme 2).24,25 The product from Ru(CCPh)(PPh3)2Cp
(1) is the bis(vinylidene) complex 2, which during workup can
be easily deprotonated to the corresponding alkynyl-
(vinylidene) complex 3.
Related reactions have been reported for the ethynyl
complexes M(CCH)(dppe)Cp* (M = Fe,8,21 Ru,22 Os23),
which gave the bis(vinylidene) dications [{Cp*(dppe)M}(
CCHCHC){M(dppe)Cp*}]2+, from which the neutral
C4-bridged compounds {Cp*(dppe)M}CCCC{M(dppe)-
Cp*} were obtained by deprotonation with KOBut. Repre-
sentative examples of substituted alkynyls were oxidized to 17e
species (formally M(III)), either chemically or electrochemi-
1
cally. Paramagnetic H NMR measurements have allowed the
charge distribution in the aryl group to be determined, while
ionization potential data correlate with electronic substituent
parameters and are related to the effect of the para substituent
on their electronic properties. These data and DFT calculations
indicate a major difference in electronic structures of the Mo
and Fe series on the one hand and the Ru compounds on the
other, with the HOMO heavily weighted on the metal for the
Chemical oxidation of the neutral arylalkynyl−ruthenium
complexes with Ag[OTf] in dichloromethane resulted in rapid
bleaching of the color of the solutions before they turned
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darker, often blue.14 An earlier study described reactions of
Ru(CCPh)(PPh3)2Cp with Ag[PF6] in toluene to give the
silver π complex [Ag{PhC2[Ru(PPh3)2Cp]}2]PF6 (4).25 In
CH2Cl2, the reaction affords the bis(vinylidene) 3 directly.
Related to this chemistry is the earlier report of the
dimerization of the butatrienylidene W{CCCCH-
(C6H4But)}(CO)(dppe)2 to {(dppe)2(OC)W}{CC[CH-
(C6H4But)]C[CH(C6H4But)]CC}{W(CO)(dppe)2} by
coupling at the 3-position.26 It is suggested that this reaction
proceeds via a 1,2-bis(ethynyl)cyclobutenyl diradical inter-
mediate which undergoes retro-electrocyclic ring opening
(Scheme 3).
RESULTS AND DISCUSSION
■
Electrochemical studies reveal a single irreversible oxidation at
+0.46 V for 5 and at +0.32 V for 6 (CH2Cl2, vs SCE, referenced
to internal FeCp2/[FeCp2]+ = +0.46 V). Chemical oxidation of
Ru(CCCCAr)(dppe)Cp (Ar = Ph, Fc) with [FeCp2]PF6
results in the initially orange solutions darkening, eventually to
−
give maroon 72+(PF6 )2 (R = Ph) or intensely purple
82+(PF6 )2 (R = Fc). The 31P NMR spectra of 7 showed two
−
components (in a 2:1 ratio) containing respectively one
resonance at δ 81.0 and two resonances at δ 82.0 and 86.5.
The solid mixture could be precipitated, but after standing for a
few minutes, a d6-acetone solution of 72+(PF6 )2 contained
−
only the two resonances of the minor product. Although
attempts to separate the mixture 72+(PF6 )2 by preparative
Scheme 3. Self-Coupling of W(CCC
−
a
CHAr)(CO)(dppe)2
TLC on silica gel resulted in the separation of two dark blue
bands, the faster moving of which contained multiple 31P NMR
resonances of decomposition products and there was no sign of
the original singlet resonance at δ 81.0. The second fraction had
31P resonances at δ 82.0 and 86.5, suggesting the presence of
two Ru(dppe)Cp groups in different environments. In both
cases, elemental analyses and ES-MS suggested that a dimeric
cation had formed, which afforded the highest ions at m/z
1411, assigned to [M + OMe]+ and confirmed by high-
resolution ES-MS. Crystals satisfactory for X-ray analysis could
be obtained by exchange of PF6 for AsF6 counterion.
−
For 82+(PF6 )2, the products also contained two compo-
nents, in a 1:1:1 ratio (δ 83.1, 84.1, 90.0). These data suggest
that two closely related products were present in each case. In
neither case were the two forms interconvertible. The complex
−
82+(PF6 )2 could not be purified satisfactorily by preparative
TLC, but one product could be fractionally crystallized from
dichloromethane/benzene. This material exhibits a single 31P
resonance at δ 83.1, suggesting that the two Ru(dppe)Cp
−
groups were in identical environments (82+(PF6 )2, symmetric)
and thus allowing assignment of the two other resonances at δ
−
84.1 and 90.0 to a second form (82+(PF6 )2, asymmetric). The
a
[W] = W(CO)(dppe)2; Ar = C6H4But-4.26
ES-MS of the product showed the highest mass ion at m/z
1627, again assigned to [M + MeOH]+.
−
The X-ray structural determinations of 72+(PF6 )2 and
82+(AsF6 )2 revealed that these two compounds have closely
−
This paper describes some chemistry of the diynyl−
ruthenium complexes Ru(CCCCAr)(dppe)Cp (Ar = Ph
(5), Fc (6)), during which binuclear complexes formed by
coupling of electron-rich carbon atoms of the C4 chains give
unusual cyclobutene-centered complexes containing carbene,
vinylidene, and allenylidene ligands.
related structures (Scheme 4).
Plots of the two dications are shown in Figures 1 and 2;
selected bond parameters are collected in Table 1. The dication
72+-asym contains a central four-membered ring which has as
substituents Ph, CCPh, {Ru(dppe)Cp}, and C
C{Ru(dppe)Cp} groups. Of the four ring C−C bonds,
Scheme 4. Oxidation of Ru(CCCCAr)(dppe)Cp (Ar = Ph (5), Fc (6)) with [FeCp2]PF6
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occupying the 3,4-positions. Within the C4 ring, the C-C
separations are 1.392(7) Å (C(4)−C(5)) and 1.452(6),
1.489(6), and 1.464(6) Å, the first value again consistent
with the presence of a CC double bond. The two
{Cp(dppe)Ru}CC fragments are similar, with Ru(1)−
C(1) and Ru(2)−C(8) being 1.913(4) and 1.898(5) Å,
respectively, and CCC separations of 1.244(6),
1.346(6), 1.254(6), and 1.352(7) Å, consistent with the Ru−
vinylidene formulations proposed (cf. Ru−C(1) and C(1)−
C(2) distances of 1.839(7) and 1.30(1) Å in [Ru(C
CMe2)(PPh3)2(η5-C9H7)](OTf)).29
In both complexes, the Ru−P distances (range 2.268(2)−
2.2906(9) Å) are characteristic of cationic ruthenium−carbene
(2.265, 2.266(2) Å),27 −vinylidene (2.352, 2.367(3) Å),29 and
−allenylidene (2.321, 2.358(2) Å)28 complexes mentioned
above, rather than the somewhat shorter distances found in the
neutral Ru−alkynyl species (2.240 and 2.250(1) Å in
Ru(CCPh)(dppe)Cp),30 as a result of weaker back-bonding
from the cationic metal center and electrostatic effects.
Figure 1. Plot of the dication of [C4Ph(CCPh){Ru(dppe)Cp}-
−
{CCCRu(dppe) Cp}](PF6)2 (72+-asym(PF6 )2). Ellipsoids
have been drawn at the 20% probability level, with hydrogen atoms
omitted for clarity.
Other spectroscopic features are in accord with the solid-
state structures. The IR spectra contain ν(CC) bands at 2169,
1933, 1597, and 1563 cm−1 (72+-asym) and at 2139, 1927,
1698, and 1585 cm−1 (82+-sym). For 72+-asym, two CpRu
1
singlet H resonances are at δ 5.50 and 5.74, whereas in 82+-
sym, only a single CpRu signal is found at δ ca. 5.67 (although
this is overlaid by one of the ferrocenyl C5H4 multiplets at δ
5.34). The 31P NMR spectra contain signals at δ 82.0 and 86.5
(for 72+-asym), while 82+-sym has a singlet at δ 83.1. The initial
mixture also shows two 31P resonances at δ 84.1 and 89.95,
which we assign to 82+-asym. As 82+-sym has a single resonance
at δ 83.1, it is reasonable to assign the resonance at δ 84.1 to
the Ru−allenylidene fragment and the signal at δ 90.0 to the
Ru−carbene moiety in 82+-asym. Limited solubility in solvents
suitable for the 13C NMR of these complexes did not allow
observation of the Ru-bonded C atoms.
These data are consistent with the reactions of 5 and 6,
which give isomeric mixtures of 72+ or 82+, respectively,
proceeding in the same way, the two isomers shown to be
present in the original product mixtures by NMR spectroscopy
being the sym and asym isomers in each case. This conclusion is
also supported by noting the less broadened set of signals of
one of the Fc groups, which can be assigned to an Fc group
extended away from the cyclobutenyl system. These signals are
not present in solutions prepared from the crystalline sample.
The IR spectrum of 82+-asym contains a ν(CC) band at 2139
cm−1, which is not present in the spectrum of 82+-sym. We
cannot unequivocally rule out the possibility that the isomers of
which X-ray diffraction structures could not be obtained might
be the open-chain isomers containing butadienyl-based ligands,
analogous to the complex reported by Berke and co-workers,26
but the common features of these two isomer pairs strongly
suggest that, serendipitously, we have determined the structures
of the sym and asym isomers of 72+ and 82+, respectively, the
second isomers being the asym and sym isomers, respectively, of
these complexes.
Figure 2. Plot of the dication of [C4Fc2{CCRu(dppe)Cp}2]-
−
(AsF6)2 (82+-sym(AsF6 )2). Ellipsoids have been drawn at the 30%
probability level, with hydrogen atoms omitted for clarity.
C(4)-C(5) (1.419(13) Å) is shorter than the other three
(1.475(13), 1.468(12), 1.510(12) Å), consistent with its being
a CC double bond. The Ru(2)−C(6) bond is short, at
1.920(9) Å, suggesting the multiple-bond character of a
carbenic interaction (cf. RuC = 1.931(6) Å in [Ru{
C(CH2Ph)(CCPh)}(dppm)(η5-C9H7)](BF4)).27 For
Ru(1)−C(1) (1.891(8) Å) a similar shortening, together with
the C(1)−C(2) and C(2)−C(3) distances of 1.271(11) and
1.341(11) Å, are consistent with an allenylidene ligand (cf. Ru−
C(1), C(1)−C(2), and C(2)−C(3) distances of 1.878(5),
1.260(7), and 1.353(7) Å in [Ru(CCCPh2)(PPh3)2(η5-
C9H7)](PF6)).28 The separation C(7)−C(8) (1.185(12) Å)
shows that the alkynyl nature of the PhCC− group is
preserved.
The reactions described above, which lead to cyclo-
butenylidene derivatives, can be understood in terms of
coupling of radical species in which a significant coefficient of
the spin density is found on the carbon atoms of the C4 chain.
DFT studies have shown that this is more likely to occur with
alkynyl− and polyynyl−ruthenium complexes than with the
corresponding iron derivatives.24,31 The spin density is localized
on the Cβ and Cδ atoms, so that coupling would be likely to
In contrast, the dication 82+-sym (Figure 2) contains a C4
ring symmetrically substituted with two CC{Ru(dppe)-
Cp} groups occupying the 1,2-positions and two Fc groups
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Table 1. Selected Bond Parameters for 72+-asym and 82+-sym
distances (Å)
angles (deg)
82+-sym
82+-sym
72+-asym
Ru(dppe)Cp
72+-asym
Ru(1)−P(1)
Ru(1)−P(2)
Ru(1)−C(cp)
av
2.2834(11)
2.2831(12)
2.212−2.236(4)
2.227
2.268(3)
2.280(3)
P(1)−Ru(1)−P(2)
P(1)-Ru(1)−C(1)
P(2)−Ru(1)−C(1)
P(3)−Ru(2)−P(4)
P(3)−Ru(2)−C(6)
P(4)−Ru(2)−C(6)
83.04(3)
81.5(1)
93.1(1)
83.90(4)
87.3(1)
94.6(1)
82.77(11)
84.9(3)
2.226−2.270(9)
2.244
91.3(3)
83.58(10)
94.7(3)
Ru(2)−P(3)
Ru(2)−P(4)
Ru(2)−C(cp)
av
2.2759(12)
2.2908(12)
2.219−2.254(5)
2.237
2.286(3)
2.283(3)
91.5(3)
2.241−2.272(9)
2.260
Ru−Cn Substituents
Ru(1)−C(1)
C(1)−C(2)
C(2)−C(3)
1.913(4)
1.244(6)
1.346(6)
1.891(8)
1.271(11)
1.341(11)
Ru(1)−C(1)−C(2)
C(1)−C(2)−C(3)
C(2)−C(3)−C(4)
C(2)−C(3)−C(6)
Ru(2)−C(8)−C(7)
C(6)−C(7)−C(8)
175.8(3)
179.1(5)
136.5(4)
135.1(4)
171.0(4)
173.3(5)
174.3(9)
174.6(9)
133.5(9)
136.5(9)
Ru(2)−C(8)/C(6)
C(6)−C(7)
C(7)−C(8)
1.898(5)
1.352(7)
1.254(6)
1.920(9)
Exocyclic C−C Bonds
C(4)−C(401)/C(41)
C(5)−C(501)
1.454(7)
1.386(14)
C(3)−C(4)−C(401)/C(41)
C(5)−C(4)−C(401)/C(41)
C(4)−C(5)−C(601)
C(6)−C(5)−C(601)
C(4)−C(5)−C(7)
132.3(4)
134.8(4)
143.3(8)
125.5(8)
132.8(8)
138.6(8)
1.423(16)
132.2(9)
133.9(9)
C(6)−C(5)−C(7)
C(6)−C(7)
C(5)−C(7)
1.352(7)
1.254(6)
C(3)−C(6)−C(7)
C(5)−C(6)−C(7)
C(3)−C(6)−Ru(2)
C(5)−C(6)−Ru(2)
C(5)−C(7)−C(8)
134.9(4)
136.6(4)
1.413(11)
129.0(6)
142.4(6)
177.6(12)
175.7(11)
C(7)−C(8)
C(8)−C(81)
1.185(12)
1.455(12)
C(7)−C(8)−C(81)
Intra-C4 Bonds
C(3)−C(4)
C(3)−C(6)
C(4)−C(5)
C(5)−C(6)
1.452(6)
1.489(6)
1.392(7)
1.464(6)
1.475(13)
1.510(12)
1.419(13)
1.468(12)
C(4)−C(3)−C(6)
C(3)−C(4)−C(5)
C(4)−C(5)−C(6)
C(3)−C(6)−C(5)
87.9(4)
92.6(4)
91.2(4)
88.3(4)
89.9(7)
88.5(8)
93.8(7)
85.4(7)
involve bond formation between these centers. In the case of
the diynyl−molybdenum complex mentioned above, this
occurs at the Cβ atoms of both molecules, although in this
case, only the open-chain bis(vinylidene) is formed. Berke’s
neutral tungsten butatrienylidene complex appears to undergo a
similar Cβ−Cβ coupling, although in this case, the postulated
intermediate cyclobutane intermediate undergoes an internal
redox reaction to a cyclobutene diradical, followed by ring
opening to give the observed diene (Scheme 4).26
We note that oxidation of the diynyl−ruthenium complexes
may form a cumulene, as found with the bis(ruthenium)−C4
species. In the latter instance, steric hindrance around the C4
chains offered by the tertiary phosphine ligands attached to the
ruthenium centers may prevent further reaction to form a cyclic
derivative, such as might be formed by a [2 + 2] cycloaddition
reaction. Such reactions are increasingly common, closely
related examples to the present chemistry being found in the
long-known [2 + 2] cycloadditions of electron-deficient
alkenes, such as tetracyanoethene, to alkynyl−metal species.32
In these reactions, the first-formed (but not always observed)
intermediate has been shown to be a radical salt, thus
facilitating the cycloaddition.
In principle, at least three routes for [2 + 2] cycloaddition are
available for the diynyl complexes studied here: namely, (Cβ +
Cβ), (Cβ + Cδ), and (Cδ + Cδ) coupling (Scheme 5).
Alternatively, dimerization could also occur via the carbon atom
in the para position of the phenyl substituent or via a carbon
atom of the Cp ring, as found in the triphenylphosphine
analogues (see Scheme 2). Nevertheless, no experimental
evidence for these latter possible dimerizations was found.
Reaction might also be expected at the metal center, although
steric protection by the bulky ligands precludes this route.
Similarly, the (Cβ + Cβ) coupling is unfavorable because of
steric hindrance. It can be seen that the observed products
correspond to the (Cβ + Cδ) and (Cδ + Cδ) routes, these
affording the sym and asym isomers, respectively (Scheme 5).
Although the (Cβ + Cβ) route would appear to be the most
favored electronically, again steric protection by the bulky Cp
and PPh2 groups of the dppe ligand precludes this route.
A radical coupling mechanism is favored, initial reaction
taking place at the Cβ or Cδ atoms, as proposed for the
Mo(dppe)(η-C7H7) system mentioned above.20 Electron
transfer from the metal system occurs, generating either
metal−carbene or metal−allenylidene structures on the C4
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Scheme 5. Products of Oxidative Coupling at Cβ and Cδ
ring. The structural parameters confirm the presence of these
unsaturated carbene ligands and further suggest delocalization
of the positive charge over the whole of the C8 ligand.
Table 2. Selected Computed Data Parameters for 5 and
a
[5]+
5
5+
DFT calculations were performed on the precursors Ru(C
CCCPh)(dppe)Cp (5) and Ru(CCCCFc)(dppe)Cp
(6) in order to shed some light on the process of [2 + 2]
cycloaddition which leads to the new binuclear complexes 72+
and 82+. Compounds 5 and 6 were studied in two oxidation
states (0/+) to understand how oxidation affects the spin
density distribution in this diynyl−ruthenium compound. The
geometries of 5 and 6 and their corresponding radical cations
were first geometrically optimized. Pertinent computed metrical
data for the Ph-containing precursors are reported in Table 2
and compared to the available X-ray data measured for the
neutral complex.33 Computed data are in reasonable agreement
with the experimental values, with the largest bond length
deviations found for the Ru−C(Cp) distances (0.11 Å). Upon
oxidation, a substantial contraction of the Ru−Cα bond length
(0.059 Å), a lengthening of the carbon−carbon triple bond, and
a shortening of the carbon−carbon single bond lengths are
computed. These slight differences are commonly observed for
this kind of organometallic compound.14 As expected, ν(C
C) frequencies decrease upon oxidation (see Table 2).
These bond length changes can be interpreted by looking at
the nodal properties of the highest occupied molecular orbitals
HOMO and HOMO-1 of the neutral compound, sketched in
Figure 3. They are π-type in character, antibonding between the
Ru atom and Cα and between Cβ and Cγ, and bonding between
Cα and Cβ and between Cγ and Cδ. These HOMOs are
analogous to those generally computed for arylalkynyl−metal
complexes and result from an antibonding interaction between
the “t2g” orbitals of the metal atom with the π-type orbitals of
Bond Distances (Å)
Ru−C(Cp)
2.350−2.364, av 2.355 [2.238−
2.340−2.374, av
2.251(2), av 2.244 (6)]
2.362
Ru−P1
Ru−P2
Ru−Cα
Cα−Cβ
Cβ−Cγ
Cγ−Cδ
2.297 [2.2515(5)]
2.308 [2.2577(6)]
2.007 [1.988(2)]
1.246 [1.227(3)]
1.353 [1.367(3)]
1.234 [1.147(7)]
1.418 [1.438(7)]
Bond Angles (deg)
83.82 [82.80(2)]
174.12 [174.5(2)]
171.24 [172.5(2)]
176.00 [167.5(3)]
171.22 [172.4(6)]
149.96 [177.73]
2.341
2.348
1.948
1.262
1.333
1.242
1.408
Cδ−C(Ph)
P1−Ru−P2
Ru−Cα-Cβ
Cα−Cβ−Cγ
Cβ−Cγ−Cδ
Cγ−Cδ−C(Ph)
82.92
173.16
172.14
174.84
173.83
162.26
centroid(Cp)−
Ru−Ph
Frequencies (cm−1
2155, 2012 [2156 m, 2017 w]
)
ν(CC)
2085, 1819
Experimental data33 are given in brackets for comparison.
a
the alkynyl ligand. As generally observed for arylalkynyl−Ru
compounds, their spatial distribution is rather delocalized over
the whole molecule in 5 (see Figure 3).14,24
The spatial spin distribution calculated for the cationic
diynyl−ruthenium complex 5+ is plotted in Figure 4. As found
in the previous calculations performed on the arylalkynyl−
ruthenium compounds,24 the atomic spin density of 5+ is
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Table 3. Selected Computed Distances (Å) for 72+-asym, 72+-
a
sym, 82+-asym, and 82+-sym
72+-asym
72+-sym 82+-asym
82+-sym
Ru1−P1
Ru1−P2
Ru2−P3
Ru2−P4
2.345 [2.268(3)]
2.366 [2.280(3)]
2.353 [2.286(3)]
2.364 [2.283(3)]
2.340
2.348
2.344
2.347
2.336
2.339
2.339
2.345
2.330 [2.2834(11)]
2.333 [2.2831(12)]
2.334 [2.2759(12)]
2.348 [2.2908(12)]
Figure 3. Plot of the HOMO (left) and HOMO-1 (right) of 5
(isocontour value 0.05 (e/bohr3)1/2). The Ru, Cα, Cβ, Cγ, Cδ, Cortho
and Cpara percentage characters are given.
,
Ru1−
2.354−2.369
2.337−
2.341−
2.346−2.373
C(Cp)
[2.226−2.270(9)]
2.374
2.374
[2.212−2.236(4)]
av 2.362 [2.244]
2.360
2.359
2.363 [2.227]
Ru2−
2.353−2.393
2.337−
2.355−
2.338−2.365
C(Cp)
[2.241−2.272(9)]
2.369
2.380
[2.219−2.254(5)]
av 2.364 [2.260]
2.358
1.935
2.360
1.970
2.355 [2.237]
Ru1−C1
Ru2−Cn
1.952 [1.891(8)]
1.951 [1.913(4)]
1.970 [1.920(6)
C6]
1.933 C8 1.989 C6 1.951 [1.898(5)
C8]
Figure 4. Spatial distributions of computed spin density of 5+ (left)
and 6+ (right) (isocontour value 0.005 e/bohr3). Atomic spin
densities (electrons) are given.
C1−C2
C2−C3
C3−C4
C4−C5
C5−C6
C5−C7
C6−C7
C7−C8
C4−R
1.275 [1.271(11)]
1.355 [1.341(11)]
1.470 [1.475(13)]
1.416 [1.419(13)]
1.484 [1.468(12)]
1.391 [1.413(11)]
1.271
1.349
1.475
1.422
1.472
1.269
1.364
1.462
1.430
1.484
1.380
1.266 [1.244(6)]
1.359 [1.346(6)]
1.467 [1.452(6)]
1.439 [1.392(7)]
1.474 [1.464(6)]
mostly delocalized on the metal−carbon backbone. The largest
part of the spin density is found on the ruthenium atom
(0.33e), which is consistent with the nature of the HOMOs
(see above). However, an important amount of spin density
resides on the Cβ and Cδ atoms (0.22e on each atom) and, to a
lesser extent, on the Cortho and Cpara atoms of the phenyl ring
(0.07e and 0.10e, respectively). Thus, several routes are
electronically possible for radical coupling. However, metal
center and (Cβ + Cβ) couplings are disfavored by the steric
protection of the bulky dppe ligands, and we should expect the
two processes shown in Scheme 5, namely (Cβ + Cδ) and (Cδ +
Cδ) couplings, which lead to the asym and sym isomers,
respectively. A process involving radical coupling between
carbon atoms of the phenyl ring or the Cp ligand might also be
possible, but the smaller spin density computed for these atoms
(maximum of 0.10e), in comparison to those found on the Cβ
and Cδ atoms, suggest that these routes would occur only to a
minor extent if at all. The spatial spin distribution calculated for
6+ slightly differs from that of 5+ (see Figure 4). The largest
atomic spin densities are found on the ferrocenyl group (0.45e)
and on the ruthenium atom (0.21e). However, atomic spin
densities computed on the Cβ and Cδ atoms (0.14e and 0.16e,
respectively) are large enough to get a radical coupling process
involving these atoms.
The two isomers which result from the [2 + 2] cycloaddition
processes of 5+ and 6+, namely 72+-asym and 72+-sym, and 82+-
asym and 82+-sym, respectively, were fully optimized without
any geometrical constraints. These dicationic complexes were
studied in two spin states (singlet and triplet). However, only
results obtained for the singlet spin state, which is energetically
favored over the triplet state by ca. 1 eV for both isomers, are
discussed here. The major computed distances are given in
Table 3 and compared to the data experimentally measured for
72+-asym and 82+-sym. The largest bond length deviations are
again found for the Ru−C(Cp) distances. The computed
distances for the carbon backbone match reasonably well with
the experimental values, except for the −CCPh substituent
of the 72+-asym isomer, which is computed to have a cumulenic
character more extensive than that found in the experimental
compound. Interestingly, mixtures of symmetrical and asym-
metrical isomers of both 72+ and 82+ were obtained in solution,
whereas it is 72+-asym and 82+-sym that crystallize in the solid
state. This indicates that the sym and asym isomers should be
1.349
1.271
1.444
1.448
1.358 [1.352(7)]
1.269 [1.254(6)]
1.429 [1.454(7)]
1.425 [1.423(16)]
1.227 [1.185(12)]
1.439 [1.386(14)]
1.235
1.425
C5−R
C8−R
1.421 [1.455(12)]
1.407
a
Experimental data for 72+-asym and 82+-sym are given in brackets for
comparison.
close in energy. Surprisingly, though, the computed energies for
72+-sym and 72+-asym (in the gas phase) differ somewhat, with
the symmetric isomer being more stable than the asymmetric
isomer by 59 kJ mol−1. A similar energy gap (54 kJ mol−1 in
favor of 82+-sym) is also computed for the two isomers of 82+.
At first sight, such energy differences may appear important,
but remember that (i) the cations 72+ and 82+ are large (156
atoms for the former (R = Ph) and 174 atoms for the latter (R
= Fc)), (ii) several energy minima with respect to rotation of
the metal end groups along the potential energy surface of
these species might exist with some of them deeper in energy
than others, especially for asymmetric isomers where steric
hindrance might be more important than in symmetric ones,
and (iii) interactions of such charged and heavy molecules
(very large dipole moments are computed) with counterions
and the solvent may be important (taking into account solvent
effects using the COSMO formalism diminishes the energy
difference between the two isomers of 72+, for instance, by ca.
10 kJ mol−1). These results suggest that the sym forms of each
complex are the thermodynamic isomers.
The DFT diagrams of the first molecular frontier orbitals for
the two isomers of 72+ bearing phenyl groups are shown in
Figure 5 (left). The computed HOMO−LUMO energy gaps
are substantial for both isomers (ca. 1.4 eV), confirming the
stability of these complexes in their singlet spin states. Indeed,
the nature of the HOMOs is similar to those found for the
precursor 5. The HOMO (215a) and HOMO-1 (214a) of both
isomers are plotted in Figure 6. The frontier orbitals are
delocalized over the entire Ru2C8 array, and it is not possible to
draw a meaningful VB representation of the structure. They are
π-type in character, being antibonding between ruthenium
atoms and adjacent carbon atoms and bonding between C(1)
and C(2), C(4) and C(5), and C(7) and C(8). The LUMO
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Figure 5. MO energy diagram of the frontier molecular orbitals of 72+-sym, 72+-asym, 82+-sym, and 82+-asym.
and LUMO+1 (216a and 217a) are not metal−ligand
antibonding in character but rather are found delocalized
over the carbon chain with an important character on the four
carbon atoms of the square (see Figure 6 (top)). They are
reminiscent of the π-MOs of the cyclobutadiene dication
[C4H4]2+, with the LUMO having a bonding character between
C(3) and C(4) and C(5) and C(6) and antibonding character
between C(3) and C(6) and C(4) and C(5).
The energy and nature of the first LUMOs (244a and 245a)
of 82+-sym and 82+-asym are hardly affected by the replacement
of phenyl groups by ferrocenyl groups, and they remain
delocalized over the carbon chain (compare the right and left
sides in Figure 5, and see also Figure 7). On the other hand, the
HOMO and HOMO-1 of the 82+-sym complex, plotted in
Figure 7, are not delocalized over the ruthenium−carbon
skeleton as described for the 72+-sym complex. Rather, they are
mainly localized on the iron atoms of the Fc donor groups and
are consequently higher in energy compared to those of the
72+-sym and 72+-asym isomers. Thus, smaller HOMO−LUMO
energy gaps of ca. 1 eV are computed for the former species,
which should thus be easier to oxidize than the 72+-sym and
72+-asym isomers. This ferrocenyl character is computed for the
first six HOMOs (“t2g” d-type orbitals of the two Fc fragments).
The MOs analogous to the HOMOs of the 72+ isomers, which
are antibonding in character between the ruthenium atoms and
first adjacent carbon atoms, are HOMO-6 and HOMO-7 (236a
and 237a).
C{Ru(dppe)Cp} groups in the 1,2-positions and Ar and
−CCAr substituents in the 3,4-positions (for Ar = Ph, 72+-
asym), or symmetrically, with two CC{Ru(dppe)Cp}
groups in the 1,2-positions and two Ar substituents in the 3,4-
positions (for Ar = Fc, 82+-sym), disposed as indicated in
Scheme 4. NMR data for the second products in each case
suggest that they are respectively 72+-sym and 82+-asym,
although we cannot conclusively rule out the formation of
open-chain isomers similar to Berke’s W2 complex (Scheme 2).
In agreement with experiment, DFT calculations reveal that the
precursor diynyl cationic complexes show important electron
density on Cβ and Cδ, suggesting that radical coupling (Cδ +
Cδ) or (Cβ + Cδ) can afford the sym and asym isomers,
respectively, which are analogues of the cyclobutadiene
dication. The sym forms are computed to be the thermody-
namic isomers.
EXPERIMENTAL SECTION
■
General Considerations. 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. Nujol mull spectra were
obtained from samples mounted between NaCl disks. 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 d6-acetone 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. 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 ionization were used as required.34 Electro-
chemical samples (1 mM) were dissolved in CH2Cl2 containing 0.5 M
[NBu4]BF4 as the supporting electrolyte. Cyclic voltammograms were
CONCLUSION
■
In conclusion, we have demonstrated that chemical oxidation of
Ru(CCCCAr)(dppe)Cp (Ar = Ph (5), Fc (6)) with
[FeCp2]PF6 affords binuclear cations [{Ru(dppe)Cp}2C8Ar2]-
(PF6)2 by radical coupling at electron-rich sites involving the
inner and outer CC triple bonds, to give cyclobutenediyli-
dene derivatives. In each case, isomeric mixtures (non-
interconvertible) were obtained. X-ray structural studies have
shown that a central C4 ring (cyclobutenylidene) is substituted
either asymmetrically, with {Ru(dppe)Cp} and C
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Figure 6. Plots of the first HOMOs and LUMOs of 72+-sym (left) and
72+-asym (right) (isocontour value 0.03 [e/bohr3]1/2).
recorded using a PAR Model 263 apparatus, with a saturated calomel
Figure 7. Plots of the first HOMOs and LUMOs of 82+-sym (left) and
82+-asym (right) (isocontour value 0.03 [e/bohr3]1/2).
electrode, with ferrocene as internal calibrant (FeCp2/[FeCp2]+
=
+0.46 V vs SCE). A 1 mm path length cell was used with a Pt-mesh
working electrode and Pt-wire counter and pseudo reference
electrodes. Elemental analyses were carried out by Campbell
Microanalytical Laboratory, University of Otago, Dunedin, New
Zealand.
Reagents. The compounds Ru(CCCCPh)(dppe)Cp and
[FeCp2]PF6 were prepared as described in the literature.33,35
Preparation of Ru(CCCCFc)(dppe)Cp (6). A mixture of
RuCl(dppe)Cp (1000 mg, 2.67 mmol), KF (127 mg, 2.19 mmol), and
FcCCCCSiMe3 (550 mg, 1.80 mmol) in MeOH (50 mL,
containing 1 drop of DBU, 0.10 mL of water) was heated under reflux
for 1 h. After cooling, the mixture was filtered and the precipitate was
washed with cold MeOH and dried under vacuum. The solid was
taken up in a small amount of benzene and chromatographed (50%
ether/50% hexane, basic alumina) to give Ru(CCCCFc)(dppe)-
Cp (6; 430 mg, 32%) as a yellow-orange solid. FcCCCCH (170
mg, 0.73 mmol) was recovered from the filtrate. Anal. Calcd for
C45H38FeP2Ru: C, 67.85; H, 4.68; M, 798. Found: C, 67.02; H, 4.55.
1
IR (Nujol, cm−1): 2174 (m), 2024 (m), 1653 (broad w). H NMR: δ
1.93−2.00 (m, 2H), 2.40−2.50 (m, 2H), 3.80 (t, J = 1.8 Hz, 2H), 4.03
(s, 5H), 4.28 (t, J = 1.6 Hz, 2H), 4.65 (s, 5H), 6.95−7.00 (m, 6H),
7.07−7.14 (m, 4H), 7.23−7.35 (m, 5H), 7.91−8.00 (m, 5H). 13C
NMR (d6-benzene): δ 28.13−28.74 (m), 60.86, 67.93, 69.81, 70.13,
71.78, 77.77, 83.33, 95.19, 115.75 (t, J(CP) = 99 Hz), 128.89, 129.81,
131.80−131.94 (m), 134.14−134.28 (m), 136.96−137.63 (m),
142.29−142.91 (m). 31P NMR: δ 86.0. ES-MS (m/z): 798, M+.
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dppe), 4.21 (s, 5H, FeCp), 4.32 (br s, 17H, FeCp + C5H4 of Fc), 4.64,
4.70 (2s, 4H, C5H4 of Fc), 5.31 and 5.70 (2s br, 30H, CpRu and C5H4
of Fc), 7.30−8.08 (m br, 80H, Ph). 13C NMR: δ 63.06, 69.71, 71.38,
71.69, 72.66, 73.11, 73.39, 77.91 (br, FeCp), 89.42, 91.49 (RuCp),
91.90 (RuCp), 92.98 (br, RuCp), 129.52−130.09 (br m), 130.90 (br),
131.03, 131.61 (br), 131−96−132.61 (br m), 134.04−134.22 (br m),
135.09−135.17 (m). ES-MS (MeOH + NaOMe, m/z (calcd)):
1643.156 (1643.182), [M + O + OMe]+; 1627.196 (1627.191), [M +
OMe]+; 1475.202 (1475.198), [M − FeCp]+; 798.068 (798.086), M2+;
593.074 (593.074), [Ru(CO)(dppe)Cp]+; 565.079 (565.079), [Ru-
(dppe)Cp]+. 31P NMR (d6-acetone, 121.5 MHz): δ −142.3 (septet,
J(PF) = 706 Hz, PF6), 83.1 (PRuCCC), 84.1 (PRuCC
C), 89.95 (PRuC). UV−vis (acetone): 737 (ε = 15 800), 520 (27
000), 464 nm (25 400).
Oxidative Coupling of Ru(CCCCR)(dppe)Cp (R = Ph (7),
−
Fc (8)). Preparation of [{Ru(dppe)Cp}2C8Ph2](PF6)2 (72+(PF6 )2).
(a) [FeCp2]PF6 (78 mg, 0.23 mmol) was added to a stirred
solution of Ru(CCCCPh)(dppe)Cp (104 mg, 0.15
mmol) in CH2Cl2 (10 mL), and the contents were stirred at
ambient temperature for 5 min. The solvent was removed in
vacuo and the residue separated by preparative TLC (3%
acetone/97% dichloromethane) to give two main purple bands.
The lower band (Rf = 0.25) was isolated and crystallized
(CH2Cl2/C6H6) to give the asymmetric complex 72+-
−
asym(PF6 )2 as a maroon solid (71 mg, 57%). Anal. Calcd
for C82H68F12P6Ru2: C, 59.00; H, 4.08; M (dication), 1398.
Found: C, 59.32; H, 4.25. IR (nujol, cm−1): 1933s ν(CC
−
82+-sym(PF6 )2. Anal. Calcd for C90H76F12Fe2P6Ru2: C, 57.34; H,
1
C), 1597w, 1563 w ν(CC), 839 s ν(PF). H NMR: δ 3.27,
4.06. Found: C, 58.72; H, 4.14. IR (Nujol, cm−1): 1933 s ν(CC
3.28, 3.59 and 3.85 (4 × br s, 8H, CH2 of dppe), 5.55 and 5.75
(2 × br s, 10H, CpRu), 7.35−7.99 (broad m, 50H, Ph). 13C
NMR: δ 86.76, 92.97 (br s, RuCp), 93.49 (br, RuCp), 129−
53−129.61 (m), 129.72−129.80 (m), 130.02−130.20 (m),
130.51, 130.93 (br), 131.75 (br), 131.84, 131.98, 132.21,
132.33, 134.05−134.13 (m), 134.72 (br), 140.26−140.77 (m).
31P NMR: δ −142.3 (septet, J(PF) = 706 Hz), 82.0, 86.5 (Ru−
P). ES-MS (MeOH, m/z): 1411, [M + OMe]+; 565,
[Ru(dppe)Cp]+. UV−vis (acetone): 515 nm (ε = 19 300). X-
ray-quality crystals were obtained from dichloromethane/
benzene.
1
C), 1590 s ν(CC), 839 ν(PF). H NMR: δ 3.28 (s br, 8H, CH2 of
dppe), 4.06, 4.31 (2s br, 13H, 2C5H4 + FeCp), 5.32 and 5.67 (2s br,
15H, FeCp, RuCp), 7.20−8.00 (m, 40H, Ph). 13C NMR: δ 70.57,
71.34, 71.65, 72.63, 73.04, 73.40, 77.77, 91.38, 91.87, 92.22, 100.80,
129.31−129.97 (m), 130.76−130.85 (m), 131.50−132.41 (m),
133.60−134.40 (m), 134.96 (t, J(CP) = 5.4 Hz). 31P NMR: δ
−142.3 (septet, J(PF) = 706 Hz, PF6), 83.1 (Ru(dppe)). ES-MS
(MeOH + NaOMe, m/z): 1628, [M + OMe]+. UV−vis (acetone):
509 nm (ε = 26 400), 728 (20 600).
The anion could be exchanged for AsF6 by treatment of the
complex with an excess of K[AsF6] in acetone. Removal of the solvent
in vacuo followed by extraction and filtration gave sym-[{Ru(dppe)-
Cp}2C8Fc2](AsF6)2, which afforded X-ray-quality crystals from
CH2Cl2/C6H6. The amount obtained was too small to allow elemental
microanalyses.
(b) [FeCp2]PF6 (20 mg, 0.060 mmol) was added to a stirred
solution of Ru(CCCCPh)(dppe)Cp (50 mg, 0.072
mmol) in CH2Cl2 (10 mL), resulting in a color change to
bright red. The mixture was stirred at ambient temperature for
5 min. The solution was filtered though a cotton-wool plug into
stirred diethyl ether to give a precipitate which was collected on
a sinter and washed several times with both Et2O and C6H6 to
−
Structure Determinations. Crystal data for 72+-asym(PF6 )2 and
−
82+-sym(AsF6 )2 are summarized in Table 1, with the structures being
−
afford the isomeric mixture 72+(PF6 )2 as a maroon solid (41
depicted in Figures 1 and 2. Selected coordination geometries are
shown in Table 2. Crystallographic data for the structures were
collected at 100(2) K on an Oxford Diffraction Gemini diffractometer
fitted with Cu Kα radiation (λ = 1.541 78 Å). Following analytical
absorption corrections and solution by direct methods, the structures
were refined against F2 with full-matrix least squares using the program
SHELXL-97.36
mg, 82%). Anal. Calcd for C82H68F12P6Ru2: C, 59.00; H, 4.08;
M (dication), 1398. Found: C, 58.61; H, 4.07. IR (Nujol,
cm−1): 2164 w ν(CC), 1929 s ν(CCC), 1595 w, 1573
w ν(CC), 838 s ν(PF). 1H NMR: δ 3.28, 3.59 and 3.86 (3 ×
br s, 8H, CH2 of dppe), 5.51 and 5.74 (2 × br s, 10H, CpRu),
7.37−7.98 (broad m, 50H, Ph). 31P NMR: δ −142.3 (septet,
J(PF) = 706 Hz), 81.0, 82.1, 86.5 (3 × Ru−P). ES-MS
(MeOH−NaOMe, m/z (calcd)): 1411.256 (1411.257), [M +
OMe]+; 690.108 (690.119), M2+; 593.087 (593.074), [Ru-
(CO)(dppe)Cp]+; 565.084 (565.079), [Ru(dppe)Cp]+. UV−
vis (acetone): 464 nm (ε = 25 400), 520 (27 000).
Crystal Data and Refinement Details. 72+-asym(PF6−)2:
[C4Ph(CCPh){=Ru(dppe)Cp}{CCRu(dppe)Cp}]-
(PF6)2·C6H6 = C82H68P4Ru2·2F6P·C6H6, MW = 1747.43, triclinic,
space group P1, a = 11.7963(4) Å, b = 16.7726(9) Å, c = 20.4211(7)
̅
Å, α = 94.253(4)°, β = 105.569(3)°, γ = 97.765(4)°, V = 3830.6(3) Å3,
Z = 2, ρcalcd = 1.515 g cm−3, μ = 5.02, absorption correction (min/
max) 0.80, crystal 0.22 × 0.09 × 0.04 mm3, 43 395 reflections
measured, 13 463 unique reflections (Rint = 0.063), R1 = 0.080 (I >
2σ(I)), wR2 = 0.233 (all data). One solvent benzene molecule located
adjacent to an inversion center was refined with isotropic displacement
parameters; site occupancies were set at 0.5 and geometries
−
Preparation of [{Ru(dppe)Cp}2C8Fc2](PF6)2 (82+(PF6 )2).
(a) A solution of Ru(CCCCFc)(dppe)Cp (68.5 mg, 0.086
mmol) and [FeCp2]PF6 (27.8 mg, 0.084 mmol) were stirred in
THF (20 mL) at room temperature for 1 h. An excess of
hexane was added, and the resulting precipitate was filtered off
−
and washed with hexane to afford the oxidized product
constrained to ideal values. One PF6 anion was modeled as
−
82+(PF6
)
as a dark purple solid (48 mg, 61%). A
2
rotationally disordered over two sets of sites with occupancies
microanalytical sample was crystallized from MeCN/benzene.
(b) Addition of [FeCp2]PF6 (85 mg, 0.257 mmol) to a solution of
Ru(CCCCFc)(dppe)Cp (205 mg, 0.257 mmol) in THF
(20 mL) resulted in an instantaneous color change to an
intense purple. The mixture was stirred at ambient temperature
for 5 min. Solvent was removed in vacuo and the residue
purified by preparative TLC (5% acetone/95% dichloro-
methane; Rf = 0.50) to afford [{Ru(dppe)Cp}2C8Fc2](PF6)2
constrained to 0.5 after trial refinement.
8
2 + -sym(AsF6 − )2 : [C4 Fc2 {CCRu(dppe)Cp}2 ]-
(AsF6)2·4C6H6 = C90H76Fe2P4Ru2·2AsF6·4C6H6, MW = 2285.5,
monoclinic, space group Pc, a = 15.9391(1) Å, b = 11.7641(1) Å, c
= 26.1975(2) Å, β = 95.270(1)°, V = 4891.51(6) Å3, Z = 2, ρcalcd
=
1.552 g cm−3, μ = 6.76, absorption correction (min/max) = 0.62,
crystal 0.21 × 0.09 × 0.015 mm3, 56 958 reflections measured, 16 616
unique reflections (Rint = 0.050), R1 = 0.034 (I > 2σ(I)), wR2 = 0.075
(all data).
−
(82+(PF6 )2; an inseparable 1:1 mixture of symmetric and
asymmetric isomers) as a dark purple solid (210 mg, 87%). It
Computational Details. DFT calculations were carried out with
the Amsterdam Density Functional (ADF) package37,38 without any
symmetry constraints on the precursor complexes Ru(CCC
CR)(dppe)Cp (R = Ph, 5; R = Fc, 6) and their cations, as well as on
[{Ru(dppe)Cp}2C8R2]2+ isomers (R = Ph, 72+; R = Fc, 82+). Electron
correlation was treated within the local density approximation (LDA)
in the Vosko−Wilk−Nusair parametrization.39 The nonlocal correc-
tions of Becke and Perdew were added to the exchange and correlation
was possible to partially separate small amounts of 82+-
−
sym(PF6 )2 from the mixture by slow fractional crystallization
from CH2Cl2/C6H6 at 4 °C.
−
82+(PF6 )2 (Mixture). Anal. Calcd for C90H76F12Fe2P6Ru2: C, 57.34;
H, 4.06. Found: C, 57.99; H, 4.34. IR (Nujol, cm−1) 2139 w ν(CC),
1927 s ν(CCC), 1698 w ν(CC), 1585 m ν(CC), 839 s
1
ν(PF). H NMR: δ 2.83, 3.27, 3.35, 3.73 (4 × br s, 16H, CH2 of
6564
dx.doi.org/10.1021/om3005146 | Organometallics 2012, 31, 6555−6566

Organometallics
Article
energies, respectively.40 The analytical gradient method implemented
by Versluis and Ziegler was used.41 The standard ADF TZP basis set
was used: i.e., a triple-ζ STO basis set for the valence core augmented
with a 2p polarization function for H, a 3d polarization function for C
and P, and a 5p polarization function for Ru, respectively. Orbitals up
to 1s, 2p, and 4p were kept frozen for C, P, and Ru, respectively.
Geometry optimization convergence criteria were more drastic than
default criteria (energy change <0.0005 hartree and atomic position
displacement <0.005 Å). Harmonic vibrational frequency calculations
were performed on the precursors (5 and 5+) to check that the
geometries are stationary points. Molecular orbitals were plotted with
the ADF-GUI package,42 and representations of the spin density were
done using MOLEKEL4.1.43
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ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving full details of the structure determinations for
−
−
72+-asym(PF6 )2 and 82+-sym(AsF6 )2 and tables containing
atomic coordinates of the optimized geometries of complexes
50 /+, 60/+, 72+, and 82+. 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 been
deposited with the Cambridge Crystallographic Data Centre as
CCDC 881590 (72+-asym(PF6 )2) and 881591 (82+-sy-
−
−
m(AsF6 )2). Copies of this information may be obtained free
of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, + 44 1223 336 033; e-mail,
deposit@ccdc.cam.ac.uk; web, http://www.ccdc.cam.ac.uk).
AUTHOR INFORMATION
Corresponding Author
*M.I.B.: tel, +61 8 8313 5939; fax, +61 8 8303 4358; e-mail,
michael.bruce@adelaide.edu.au. J.-F.H.: tel, +33 2 2323 6778;
fax, +33 2 2323 6840; e-mail, halet@univ-rennes1.fr.
■
Present Address
∥CMCA, University of Western Australia, Crawley, Western
Australia 6009, Australia
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Professor B. K. Nicholson, University of Waikato,
Hamilton, New Zealand, for measuring mass spectra. We
acknowledge financial support of this work by the ARC and
Johnson Matthey plc for a generous loan of RuCl3·nH2O. F.G.
and J.-F.H. acknowledge the CNRS (France) for travel grants
to Australia. K.C., F.G., and J.-F.H. thank the French GENCI-
CINES and GENCI-IDRIS centres for high-performance
computing resources (Grant 2010-80649).
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