Synthesis and properties of ferrocenyl allenylidene complexes: X-ray structure of [Ru(C=C=CHFc)(PPh3)2(η5-C 5H5)][PF6] CH2Cl2

Article abstract of DOI:10.1021/om9010214

Reactions of the transition metal halide complexes [MXL₂(Cp)] (M = Fe, X = I, L₂ = dppe; M = Ru, X = Cl, L = PPh₃; M = Os, X = Br, L = PPh₃; Cp = 77-C₅H₅) with the alkynol HC=CCH(OH)(Fc) (1) (Fc = ferrocenyl) in the presence of TlBF₄ gave the monosubstituted allenylidene complexes [M(C=C=CHFc)L ₂(Cp)][BF₄] (2a: M = Ru, L = PPh₃; 3: M = Fe, L₂ = dppe; 4: M = Os, L = PPh₃). Similarly, the reaction of 1 with [RuCl(PPh₃)₂(Cp)] and NH₄PF ₆ in methanol gave [Ru(C=C=CHFc)(PPh₃)₂(Cp)] [PF₆] (2b). These highly colored compounds were characterized by spectroscopic and electrochemical techniques and in the case of 2b by a single-crystal X-ray structure determination. Cyclic voltammetry in MeCN in the presence of [ Bu₄N][ClO4] at 100 mV-s_-1 shows a reversible ferrocenyl-based one-electron oxidation, in addition to irreversible oxidation and reduction processes. The NMR spectra of 2b show complex behavior at low temperature, attributed to temperature-dependent chemical shifts and correlated motions of the allenylidene ligand and the ferrocenyl substituent.

Full text of DOI:10.1021/om9010214

Organometallics 2010, 29, 1199–1209 1199
DOI: 10.1021/om9010214
Synthesis and Properties of Ferrocenyl Allenylidene Complexes: X-ray
Structure of [Ru(CdCdCHFc)(PPh3)2(η5-C5H5)][PF6] CH2Cl2
3
Lindsay T. Byrne,† George A. Koutsantonis,*,† Vanessa Sanford,† John P. Selegue,*,‡
Phil A. Schauer,† and Ramnath S. Iyer‡
†Chemistry, M313, School of Biomedical, Biomolecular and Chemical Sciences, University of Western
Australia, Crawley, WA 6009, Australia, and ‡Department of Chemistry, University of Kentucky,
Lexington, Kentucky 40506-0055
Received November 25, 2009
Reactions of the transition metal halide complexes [MXL2(Cp)] (M = Fe, X = I, L2 = dppe;
M = Ru, X = Cl, L = PPh3; M = Os, X = Br, L = PPh3; Cp = η-C5H5) with the alkynol
HCtCCH(OH)(Fc) (1) (Fc = ferrocenyl) in the presence of TlBF4 gave the monosubstituted
allenylidene complexes [M(CdCdCHFc)L2(Cp)][BF4] (2a: M = Ru, L = PPh3; 3: M = Fe, L2 =
dppe; 4: M = Os, L = PPh3). Similarly, the reaction of 1 with [RuCl(PPh3)2(Cp)] and NH4PF6 in
methanol gave [Ru(CdCdCHFc)(PPh3)2(Cp)][PF6] (2b). These highly colored compounds were
characterized by spectroscopic and electrochemical techniques and in the case of 2b by a single-crystal
X-ray structure determination. Cyclic voltammetry in MeCN in the presence of [nBu4N][ClO4] at
100 mV s-1 shows a reversible ferrocenyl-based one-electron oxidation, in addition to irreversible
3
oxidation and reduction processes. The NMR spectra of 2b show complex behavior at low
temperature, attributed to temperature-dependent chemical shifts and correlated motions of the
allenylidene ligand and the ferrocenyl substituent.
Introduction
idene complexes has been comprehensively assessed by
Bruce through 1998,11,12 and Cadierno et al. to date,13,14
with additional reviews appearing in the form of annual
surveys15-19 and metal-specific reviews encompassing chro-
mium and tungsten,20 iridium,21 rhodium,22 manganese,23
and ruthenium.9,24-26 Several comparative density func-
tional theory treatments of cumulenylidene complexes have
also been described.27-30
The vast majority of allenylidene complexes are those
stabilized by cationic ruthenium(II) centers, an observation
predominantly ascribed to the general applicability of the
synthetic methodology developed by us in 1982 for the first
The first transition metal allenylidene complexes, [CpMn-
(CO)2dCdCdC(tBu)2] and [M(CO)5dCdCdC(Ph)NMe2]
(M = Cr, W), were independently isolated by Berke1 and
Fischer,2 respectively, reported in 1976, a decade after the
first carbene3 and vinylidene4 homologues. Research to date
on higher order cumulenylidene complexes has been ham-
pered on account of synthetic challenges and the instability
of products, although a number of butatrienylidene and
pentatetraenylidene complexes have been reported,5-9 and
only very recently have the very first examples of hepta-
hexaenylidene complexes, [(CO)5MdC(dC)5dC(NMe2)2]
(M = Cr, W), been characterized.10 The literature of allenyl-
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selegue@uky.edu.
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r
2010 American Chemical Society
Published on Web 02/08/2010
pubs.acs.org/Organometallics

1200 Organometallics, Vol. 29, No. 5, 2010
Byrne et al.
ruthenium allenylidene complex, [CpRu(PMe3)2dCdC=
CPh2]PF6.31 The mechanism involves dissociation of chlo-
ride from the ruthenium complex and subsequent activation
of the terminal alkyne at the coordinatively unsaturated
metal, followed by rearrangement to a hydroxy-vinylidene
intermediate, from which dehydration affords the alleny-
lidene complex. The stability of the hydroxy-vinylidene
complex is proportional to the electron-releasing properties
of the ruthenium moiety, with dehydration to an allenylidene
complex requiring acid catalysis for very electron-rich metal
centers.32-34
The major exception to the general applicability of this
synthetic route exists in those cases where a hydrogen is present
attheatomRto the hydroxyl carbon of the propargylic alcohol
proligand, in which case competitive Cγ-Cδ dehydration of
the hydroxy-vinylidene intermediate affords a mixture of the
allenylidene and alkenyl-vinylidene complexes.35 Further com-
plications may arise as a consequence, for example in the
reaction of Me2C(OH)CtCH with [CpRuCl(PPh3)2], where
the postulated coupling of an allenylidene and vinyl-vinylidene
complex results in the formation of a dimeric complex.36 In
light of these issues a number of alternate syntheses of alleny-
lidene complexes have been reported, the most pertinent
including addition of a nucleophile to the Cγ atom of a
butatrienylidene complex;25,37 oxidation of a σ-alkynyl com-
plex, such as [CpRu(PPh3)2(CtC-(C5Me4)-η5-RuCp)];38,39
and protonation of a vinyl-σ-alkynyl complex such as
[CpRu(PPh3)2-CtC-C(Me)dCH2].40
One aspect of our long-standing interest in the synthesis,
structure, and reactivity of metallacumulenes31,36,41-45 is the
preparation of new allenylidene complexes. We report here
that it is possible, with judicious choice of the allenylidene
substituents, to stabilize monosubstituted allenylidene com-
plex cations ([LnMdCdCdCHR]þ) by favoring a propargyl
cation resonance form (C and D, Figure 1).
Figure 1. Resonance forms applicable to a transition metal
allenylidene complex.
resulting ferrocenyl allenylidene cations would be stable
(this work was preliminarily reported).48
A number of ferrocenyl-functionalized allenylidene
complexes derived from tertiary alkynol proligands have
been reported in the literature.49-55 To the best of our
knowledge, the only other analogous mononuclear exam-
ple is the fullerene-substituted complex [(η5-C60Me5)Ru-
(1,2-dppp){C3(H)Fc}]PF6,56 where the crystallographic
characterization is somewhat fraught by problems. Other
salient complexes include a tetranuclear molybdenum com-
plex, derived from [Fe{η5-C5H4C(H)(OH)(CtCH)}2],57 in
which two ferrocenyl allenylidene ligands bridge dimolybde-
num moieties. Monosubstituted vinylidene ruthenocenyl
complexes have also been prepared,38,39 while the oxidation
of [CpRu(PPh3)2-CtC-Fc] leads to a fulvenyl-allenylidene
complex.58
Subsequently, there have been a number of other mono-
substituted allenylidenes prepared and structurally
characterized.59-62
Experimental Section
Since ferrocenyl substituents effectively stabilize carbenium
ions, [FcCR2]þ,46 and carbon-rich metallacumulenes,47 we
have investigated the reactions of the ferrocenyl-functiona-
lized secondary alkynol, HCtCCH(OH)(Fc) (1), with some
group VIII transition metal halides, anticipating that the
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Article
Organometallics, Vol. 29, No. 5, 2010 1201
HE43-2 or Braun MB-120 gloveboxes. Solvents were purified
and dried under nitrogen by using standard techniques and
transferred to reaction vessels via cannula or syringe. Melting
points were measured in sealed capillaries. Microanalyses were
performed by the Canadian Microanalytical Service, Delta,
British Columbia.
Instrumentation. Infrared spectra were recorded as Nujol
mulls on NaCl plates with a Perkin-Elmer 1710 FT-IR spectro-
meter. 1H and 13C NMR spectra were recorded on Varian
Gemini 200 or Varian VXR-400 spectrometers and were refer-
enced to the incompletely deuterated solvent peak. 31P NMR
spectra were recorded on either Varian VXR-400 or VXR-500
spectrometers operating at 162 and 202 MHz, respectively. The
31P{1H} variable-temperature NMR studies were conducted on
a Bruker ARX 500, and 31P chemical shifts are reported in
ppm downfield from external H3PO4. FAB mass spectra were
obtained at the Mass Spectrometry Facility of the Ohio State
University. A drop of the complex dissolved in CH2Cl2 (ca.
0.5 M) was added to a drop of 3-nitrobenzyl alcohol matrix, and
the mixture was applied to the probe tip.
(s, C5,8 and C6,7), 72.7 (s, ring B). {1H}31P NMR (CD2Cl2): δ
(ppm) 47.5. IR (cm-1): 1943 (vs, CdCdC), 1585 (w), 1571 (w),
1435 (s), 1352 (s), 1312 (s), 1282 (m), 1256 (m), 1185 (m), 1159
(m), 1089 (s), 1050 (vs, BF), 998 (m), 923 (w), 834 (w), 744 (w),
722 (w), 696 (s), 618 (w).
Preparation of [Ru(CdCdCHFc)(PPh3)2(Cp)][PF6] (2b). A
mixture of [RuCl(PPh3)2(Cp)] (224 mg, 0.309 mmol), HCt
CCH(OH)(Fc) (135 mg, 0.562 mmol), and NH4PF6 (57 mg,
0.350 mmol) in MeOH (20 mL) was stirred at ambient tempera-
ture for 2.5 h. The resulting emerald-green solution was evapo-
rated to dryness, and the residue was dissolved in CH2Cl2 (ca.
7 mL) and filtered. Addition of Et2O (ca. 100 mL) to the filtrate
and stirring for 2 h resulted in the precipitation of a dark green
powder of 2b (235 mg, 72%). An analytical sample was obtained
by vapor diffusion of isopentane into a CH2Cl2 solution of 2b
and drying in vacuo for 3 days. Anal. Calcd for C54H45F6Fe-
P3Ru: C, 61.31; H, 4.29. Found: C, 61.42; H, 4.29. Mp > 150 °C
1
(dec). H NMR ((CD3)2CO): δ (ppm) 8.79 (s, 1H, H3), 7.20-
6.99 (m, 30H, phenyl), 5.00 (t, 2H, H6,7, 3JH,H = 1.8 Hz), 4.80
(t, 2H, H5,8), 4.73 (s, 5H, ring A), 4.07 (s, 5H, ring B). {1H}13C
NMR (CD2Cl2): δ (ppm) 273.0 (t, C1, 2JP,H = 21 Hz), 183.7 (s,
C2), 153.3 (s, C3), 136.7-128.8 (m, phenyl), 92.4 (s, ring A), 91.2
(s, C4), 79.4 (s, C5,8 and C6,7), 73.1 (s, ring B). {1H}31P NMR
(CD2Cl2): δ (ppm) 47.9. IR (cm-1): 1940 (vs, CdCdC), 1732
(m), 1678 (w), 1651 (w), 1489 (s), 1435 (s), 1435 (s), 1357 (w),
1270 (w), 1258 (m), 874 (m), 839 (vs, br, PF), 758 (w), 741 (m),
723 (w), 699 (s). FAB MS: 913 ([M]þ, 31%); 792 ([M - Fe-
(C5H5)]þ, 26%); 651 ([M - PPh3]þ, 24%); 585 ([M - PPh3 -
C5H6]þ, 12%); 529 ([Ru(C3HC5H4)(PPh3)(C5H5)]þ, 6%); 429
([Ru(PPh3)(C5H5)], 100%).
Electrochemistry. Cyclic voltammetry was performed with a
BAS-100A electrochemical analyzer. The cell consisted of two
compartments separated by a porous glass frit to prevent cross-
contamination of oxidation and reduction products. Platinum
was used for both the working (disk) and auxiliary (wire)
electrodes; a silver wire was used as a pseudoreference electrode.
Each cell compartment was equipped with glass ground joints, a
Teflon stopcock, and septum ports so that samples could be
handled anaerobically. A 1.0 M solution of [nBu4N][ClO4] in
CH3CN was used as supporting electrolyte; sample concentra-
tions were ca. 1 mM. Voltammograms were recorded at 25 °C by
Preparation of [Fe(CdCdCHFc)(dppe)(Cp)][BF4] (3). A mix-
ture of [FeI(dppe)(Cp)] (112 mg, 0.466 mmol), HCtCCH(OH)-
(Fc) (112 mg, 0.466 mmol), and TlBF4 (252 mg, 0.865 mmol) in
CH2Cl2 (30 mL) was stirred at ambient temperature for 12 h.
The resulting deep purple mixture was evaporated to dryness,
and the residue was washed with Et2O (3 ꢀ 20 mL). The residue
was extracted with CHCl3 (ca. 5 mL) and filtered through Celite.
Slow addition of Et2O (ca. 60 mL) to the filtrate precipitated a
deep purple powder of 4 (180 mg, 70%). Anal. Calcd for
C44H39BF4Fe2P2: C, 63.80; H, 4.74. Found: C, 63.00; H, 4.65.
Mp > 150 °C (dec). 1H NMR (CD2Cl2): δ (ppm) 7.90 (t, 1H, H3,
5JP,H = 12 Hz), 7.80-7.30 (m, 20H, phenyl), 5.20 (s, 5H, ring
A), 4.89 (t, 2H, H6,7, 3JH,H = 1.8 Hz), 4.68 (t, 2H, H5,8), 4.06 (s,
using a scan rate of 100 mV s-1. Potentials are reported in mV
3
relative to internal ferrocene(0/þ). The criterion for diffusion
control was ip/v1/2 = constant, with variation of v between 100
and 500 mV s-1. Criteria for reversibility were as follows: (given
3
for an oxidation process) ipa/ipc = 1.0 reversible; ipa/ipc < 1.2
near reversible; ipa/ipc > 1.2 quasi-reversible; no apparent
cathodic peak, irreversible.
Starting Materials. [RuCl(PPh3)2(Cp)],63 [OsBr(PPh3)2-
(Cp)],64,65 and [FeI(dppe)(Cp)]66 were prepared by known
methods. A slight modification of the literature procedure,67
replacing NaCtCH with LiCtCH in THF,68,69 was used to
prepare HCtCCH(OH)(Fc). [nBu4N][ClO4] (Southwestern
Analytical) and NH4PF6 (Ozark-Mahoning) were used as received.
Preparation of [Ru(CdCdCHFc)(PPh3)2(Cp)][BF4] (2a). A
mixture of [RuCl(PPh3)2(Cp)] (300 mg, 0.413 mmol), HCt
CCH(OH)(Fc) (141 mg, 0.587 mmol), and TlBF4 (173 mg,
0.594 mmol) in THF (20 mL) was stirred at ambient temperature
for 1 h. The resulting dark green solution was filtered through a
Celite pad (1 ꢀ 3 cm), and the pad was eluted with THF until the
eluate was colorless. The filtrate was concentrated to ca. 5 mL,
and Et2O (ca. 60 mL) was added by syringe to precipitate a dark
green powder. The solvent was decanted from the solid by
cannula, and the solid was washed with additional Et2O (2 ꢀ
20 mL) to give 2b (323 mg, 78%). Mp > 150 °C (dec). 1H NMR
(CD2Cl2): δ (ppm) 8.96 (s, 1H, H3), 7.50-7.20 (m, 30H, phenyl),
5.37 (t, 2H, H6,7, 3JH,H = 1.9 Hz), 5.11 (t, 2H, H5,8), 5.08 (s,
5H, ring A), 4.36 (s, 5H, ring B). {1H}13C NMR (CD2Cl2): δ
(ppm) 271.5 (t, C1, 2JP,H = 20 Hz), 182.6 (s, C2), 152.5 (s, C3),
135.8-128.2 (m, phenyl), 91.8 (s, ring A), 90.6 (s, C4), 78.9
2
5H, ring B), 3.18 (vd, 4H, PC2H4P, JP,H = 12 Hz). {1H}13C
NMR (CD2Cl2): δ (ppm) 280.1 (t, C1, 2JP,H = 38 Hz), 198.2 (s,
C2), 146.2 (s, C3), 146.2-128.6 (m, phenyl), 89.6 (s, C4), 88.7 (s,
ring A), 76.6 (s, C5,8 and C6,7), 71.7 (s, ring B), 29.8 (vt,
1
PC2H4P, JP,C = 22 Hz). {1H}31P NMR (CD2Cl2): δ (ppm)
100.8. IR (cm-1): 1934 (vs, CdCdC), 1651 (w), 1586 (w), 1309
(w), 1281 (w), 1261 (w), 1185 (w), 1050 (vs, br, BF), 866 (w),
840 (w), 830 (w), 822 (w), 799 (w), 752 (w), 710 (m), 697 (w).
FAB MS: 741 ([M]þ, 100%); 676 ([M - (C5H5)]þ, 1.5%); 620
([M - Fe(C5H5)]þ, 16%).
Preparation of [Os(CdCdCHFc)(PPh3)2(Cp)][BF4] (4). In a
manner analogous to the preparation of 2b, [OsBr(PPh3)2(Cp)]
(203 mg, 0.236 mmol), HCtCCH(OH)(Fc) (126 mg, 0.525 mmol),
and TlBF4 (340 mg, 1.17 mmol) in CH2Cl2 (20 mL) gave a dark
green powder of 3 (212 mg, 85%). Anal. Calcd for C54H45BF4Fe-
P2Os: C, 59.57; H, 4.17. Found: C, 58.78; H, 4.58. Mp > 150 °C
(dec). 1H NMR (CD2Cl2): δ (ppm) 10.98 (s, 1H, H3), 7.40-7.10 (m,
30H, phenyl), 5.11 (s, 5H, ring A), 5.03 (t, 2H, H6,7, 3JH,H =1.7Hz),
4.86 (t, 2H, H5,8), 4.16 (s, 5H, ring B). {1H}13C NMR (CD2Cl2): δ
(63) Bruce, M. I.; Hameister, C.; Swincer, A. G.; Wallis, R. C. Inorg.
Synth. 1990, 28, 270–272.
2
(ppm) 246.5 (t, C1, JP,H = 13 Hz), 195.1 (s, C2), 150.9 (s, C3),
137.5-128.8 (m, phenyl), 94.1 (s, C4), 90.7 (s, ring A), 77.6 (s, C5,8
and C6,7), 72.6 (s, ring B). {1H}31P NMR (CD2Cl2): δ (ppm) 81.6.
IR (cm-1): 1942 (vs, CdCdC), 1652 (m), 1586 (w), 1573 (w), 1481
(s), 1435 (s), 1352 (sh), 1313 (m), 1259 (m), 1186 (m), 1163 (m), 1080
(vs, br, BF) 925 (w), 836 (m), 823 (m), 747 (m), 697 (s).
(64) Bruce, M. I.; Windsor, N. J. Aust. J. Chem. 1977, 30, 1601–1604.
ꢀ
(65) Benn, R.; Joussen, E.; Lehmkuhl, H.; Lopez Ortiz, F.; Rufinska,
A. J. Am. Chem. Soc. 1989, 111, 8754–8756.
(66) Frank, K. G. Ph.D., University of Kentucky, 1990.
(67) Schlogl, K.; Mohar, A. Monatsh. Chem. 1961, 92, 219–235.
(68) Midland, M. M.; McLoughlin, J. I.; Werley, R. T., Jr. Org.
Synth. 1990, 68, 14–24.
Crystallography. X-ray quality crystals of 2b were obtained by
slow diffusion of isopentane into a dichloromethane solution at
(69) Midland, M. M. J. Org. Chem. 1975, 40, 2250–2252.

1202 Organometallics, Vol. 29, No. 5, 2010
Byrne et al.
Table 1. Summary of the Crystal Data and Details of Intensity
Collection and Refinement for Complex 2b
map and included in least-squares refinement. The remaining hydro-
gen atoms were placed in idealized positions with d(C-H) = 1.0 A
and B = B(attached C) þ 1.0 A2; their positions were adjusted after
each cycle of refinement. Additional details of data collection and
refinement are presented in Table 1.
Crystal Data
color and habit
size (mm3)
formula
dark green, irregular
ca. 0.6 ꢀ 0.4 ꢀ 0.3
C55H47Cl2F6FeP3Ru
1142.714
2
1.521
14.606(3)
15.260(5)
12.654(4)
107.40(3)
108.26(2)
95.83(2)
2495.73
1160
1158.878
Results and Discussion
fw
Z
Synthesis. The reaction of 1 with [RuCl(PPh3)2(Cp)] and
TlBF4 in dichloromethane gave a dark green solution, from
which [Ru(CdCdCHFc)(PPh3)2(Cp)][BF4] (2a, Scheme 1)
was obtained in high yield. Dark green [Ru(CdCdCHFc)-
(PPh3)2(Cp)][PF6] (2b) was conveniently prepared by using
NH4PF6 in methanol. The TlBF4 method was employed
in the preparation of the analogous iron and osmium
complexes [Fe(CdCdCHFc)(dppe)(Cp)][BF4] (3) and
[Os(CdCdCHFc)(PPh3)2(Cp)][BF4] (4).
Dc (g cm-3
a (A)
b (A)
)
c (A)
R (deg)
β (deg)
γ (deg)
volume (A3)
F(000)
F(000) corrected
The TlBF4 reactions are driven by the formation of
insoluble thallium halides, which precipitate as the intense
colors of the allenylidene cations develop. Traces of TlBF4
were carried through the dichloromethane/ethyl ether
recrystallizations; these were removed from microanalytical
samples by filtration of concentrated chloroform solutions
of the complexes. The green ruthenium (2) and osmium (4)
and the deep purple iron (3) allenylidene complexes are
air-stable as solids, but solutions are best handled under
inert atmosphere. The complexes are soluble in polar sol-
vents such as tetrahydrofuran, dichloromethane, and alco-
hols, but insoluble in diethyl ether and hydrocarbons.
A mechanism for the formation of the allenylidene complexes
is shown in Scheme 1. The light-colored solutions encountered in
the synthesis of complexes 2-4 probably contain an intermedi-
ate, either the η2-alkyne complex F or the vinylidene complex G.
The latter seems more likely, since [Ru(η2-HCtCR)(L2)(Cp)]þ
complexes are detectable or isolable only for phosphine or
phosphite ligands (L) of small cone angle and very small alkyne
substituents (R = H or Me).42,66,72 Rearrangement of F to G
should be very rapid; the mechanism by which this occurs
has been extensively studied and thought to occur by a 1,2-H
shift42,66,72 or via intra- or intermolecular proton transfer in an
alkynyl-hydride intermediate.73 Spontaneous loss of H2O from
G gives the allenylidene complexes, E, in high yield. Acid-
promoted hydroxide loss to give ferrocenyl-stabilized vinyl and
allenyl cations is well-precedented.46,74-78 The intermediacy of
hydroxyvinylidene complexes leading to allenylidene complexes
is consistent with many previous observations.13,31,32,36,49,50,79-90
Data Collection
radiation
λ
temperature
Mo KR
0.710703 A
23 °C
25
3° to 20°
90 s
sets of setting angles refined
θ range for Cell
maximum counting time
θ limits for data
h, k, l ranges
2° to 22.5°
0 to 15, -16 to16, -13 to 13
scan type
scan range
number of standards
maximum variation
unique data
data with Ι g 3σ(Ι)
μ
absorp corr
ω-2θ
0.70 þ 0.35 tan θ
3
5.2%
6819
5527
8.479 cm-1
none
Structure Solution and Refinement
space group
final number of variables
P1 (No. 2)
617
0.02
0.08 (β1,2 of C9)
3.8%
4.9%
p factor
max. shift/error in last cycle
R
Rw
error in observation of unit weight
largest peak in final diff Fourier
2.9037
0.091 e/A3 near C12
room temperature. A crystal was mounted on a glass fiber and
coated withepoxy resin. All X-ray diffraction measurementswere
made by using an Enraf-Nonius CAD4 diffractometer. The unit
cell was determined from 25 randomly selected reflections, which
were recentered to obtain refined cell dimensions. Data were
corrected for Lorentz and polarization effects. Corrections for
extinction or absorption (ν = 8.479 cm-1) were not needed.
(72) Bullock, R. M. J. Chem. Soc., Chem. Commun. 1989, 165–167.
(73) Bustelo, E.; Carbo, J. J.; Lledos, A.; Mereiter, K.; Puerta, M. C.;
Valerga, P. J. Am. Chem. Soc. 2003, 125, 3311–3321.
(74) Behrens, U. J. Organomet. Chem. 1979, 182, 89–98.
(75) Watts, W. E. J. Organomet. Chem. 1981, 220, 165–172.
(76) Cais, M.; Dani, S.; Herbstein, F. H.; Kapon, M. J. Am. Chem.
Soc. 1978, 100, 5554–5558.
(77) Sime, R. L.; Sime, R. J. J. Am. Chem. Soc. 1974, 96, 892–896.
(78) Watts, W. E. J. Organomet. Chem. Libr. 1979, 7, 401–452.
(79) Selegue, J. P.; Young, B. A.; Logan, S. L. Organometallics 1991,
10, 1972–1980.
(80) Le Bozec, H.; Dixneuf, P. H. Russ. Chem. Bull. 1995, 44, 801–
812.
(81) Le Bozec, H.; Devanne, D.; Dixneuf, P. H. NATO ASI Ser., Ser.
C 1989, 269, 107–121.
(82) Picquet, M.; Touchard, D.; Bruneau, C.; Dixneuf, P. H. New J.
Chem. 1999, 23, 141–143.
The ruthenium and iron atoms were located from
a
Patterson map, and the remaining non-hydrogen atoms were located
by using DIRDIF70 and difference Fourier methods. Data with Ι g
3σ(Ι) were used for the subsequent refinement of the structure using
local versions of Ibers’ NUCLS least-squares program (based on the
Busing-Levy ORFLS), Zalkin’s FORDAP Fourier program, and
Johnson’s ORTEP thermal ellipsoid plotting program.71 Non-
hydrogen atoms were refined by using anisotropic thermal para-
meters. Anomalous dispersion corrections were included for the
scattering of Ru, Fe, P, and F. Least-squares refinements minimized
the function hklw(Fo - Fc)2, where the weighting factor was w =
1/σ(Fo)2. The hydrogen atom H3 was located in a difference Fourier
P
(70) Beurskens, P. T.; Bosman, W. P.; Doesburg, H. M.; Van den Hark,
T. E. M.; Prick, P. A. J.; Noordik, J. H.; Beurskens, G.; Gould, R. O.;
Parthasarathi, V. Conform. Biol. 1983, 389–406.
(71) Johnson, C. K. Report ORNL 5138; Oak Ridge National Labora-
tory, 1976.
(83) Trost, B. M. Chem. Ber. 1996, 129, 1313–1322.
(84) Trost, B. M.; Flygare, J. A. J. Am. Chem. Soc. 1992, 114, 5476–
5477.
(85) Trost, B. M.; Martinez, J. A.; Kulawiec, R. J.; Indolese, A. F.
J. Am. Chem. Soc. 1993, 115, 10402–10403.

Article
Organometallics, Vol. 29, No. 5, 2010 1203
Scheme 1. Reaction of 1 to Form the Allenylidene Complexes 2-4a
a Fc = 1-ferrocenyl; dppe = 1,2-bis(diphenylphosphino)ethane.
In contrast, [OsCl(PiPr3)2(Cp)] reacts with alkynols to give
[OsCl{η2-HCtCC(OH)R2}(PiPr3)(Cp)] (R = Ph, Me), which
rearrange and dehydrate in toluene to give allenylidene
[OsCl{CdCdCPh2}(PiPr3)(Cp)] or vinylvinylidene [OsCl{Cd
CHCMedCH2}(PiPr3)(Cp)] complexes or react with TlPF6
to give stable, cationic complexes with four-electron alkyne
ligands, [Os{η2-HCtCC(OH)R2}(PiPr3)(Cp)][PF6].91
was calculated to have a singlet ground state. Comparison of
computed vibrational frequencies with experimentally derived
IR intensities suggested that the intense band at ca. 2000 cm-1 is
an antisymmetric CC stretching mode. The intensity of the band
was ascribed to a large change in dipole moment as a result of
oscillation between limiting structures H2CdCdC: and H2Cþ-
CtC:-, respectively. Such arguments may explain the intensity
of the bands at ca. 1900 cm-1 in the infrared spectra of
complexes 2-4.
We were not able to isolate pure ruthenium allenylidene
complexes containing PMe3 or dppe ligands. In the latter case,
the presence of relatively large amounts of impurities prevented
the complete characterization of the dark green complex ob-
tained; FAB mass spectrometry suggested that [Ru(CdCd
CHFc)(dppe)(Cp)][BF4] was the principal product. Cadierno
et al. similarly reported that [RuCl(PPh3)2(η5-indenyl)] reacts
with HCtCH(OH)(Ph) and NaPF6 to give stable [Ru(CdCd
CHPh)(PPh3)2(η5-indenyl)][PF6], whereas the allenylidene
complexes derived similarly from [RuClL2(η5-indenyl)] (L2 =
dppm, dppe) are unstable toward MeOH.87 The reaction of
[RuCl(PMe3)2(Cp)] and TlBF4 or NH4PF6 with 1 in THF or
In the 1H NMR spectra of complexes 2, 3, and 4 (Table 2),
the allenylidene hydrogen (H3, [MdCdCdCHFc]þ) reso-
nates downfield (δ 8-11) in the region typical of hydrogen
atoms on carbenium ions or metal alkylidene ligands.93,94
The allenylidene hydrogen resonates furthest downfield for
osmium compound 4 and furthest upfield for iron compound
3. This trend may reflect the decreasing π-donating ability of
the [ML2(Cp)] fragments on descending the group, suggest-
ing that the propargyl cation resonance form B decreases in
importance from osmium to iron. Cadierno et al. reported a
similar 1H NMR shift of δ 9.09 for the allenylidene hydrogen
of [Ru(CdCdCHPh)(PPh3)2(η5-indenyl)][PF6].87
The [ML2(Cp)] cyclopentadienyl resonance is downfield
of the ferrocenyl cyclopentadienyl resonance, reflecting the
substantial positive charge localized at [ML2(Cp)]. Only for
iron complex 3 does the cyclopentadienyl resonance show
1H-31P coupling to the phosphine ligands; phosphorus-to-
ligand J coupling is typically larger for Fe than for Ru or Os.
The shifts of the C5H4 group proved difficult to assign. The
H3,4 protons of [Fe(η5-C5H4CH2)(η5-C5H5)]þ (5, Scheme 2)
and related R-ferrocenylcarbenium ions are found at lower
field than the H2,5 protons.46 However, Connor assigned the
H2,5 protons at lower field than the H3,4 protons in neutral,
ferrocenyl Fischer-type carbene complexes of group VI metals
(6),95 in which the carbene carbon bears a partial positive
charge. The C5H4 shifts of complexes 6 were assigned by
analogy to other Fischer-type carbene complexes containing
electron-withdrawing groups.95 The H2,5 and H3,4 reso-
nances were not specifically assigned in the ferrocenyl carbyne
complexes (7).96 We were not able to unequivocally assign the
1
CH2Cl2 gave a complex mixture of products (by H NMR).
Perhaps the PMe3 ancillary ligands are too small to effectively
shield the allenylidene ligand from nucleophilic attack in puta-
tive [Ru(CdCdCHFc)(PMe3)2(Cp)]þ.
Spectroscopic Characterization. Ferrocenyl allenylidene
complexes 2, 3, and 4 were unambiguously characterized
by spectroscopic methods. In fast atom bombardment
(FAB) mass spectra of complexes 2b and 3, molecular cations
were found at m/z 913 and 741, respectively, which fragment
by loss of [Fe(C5H5)]. The infrared spectra of complexes 2-4
show intense bands at ca. 1940 cm-1, confirming the pre-
sence of the allenylidene moiety.12
There has been theoretical and experimental interest in the
properties of C3H2 species.14,92 Vinylidenecarbene, H2CdCdC:,
(86) Trost, B. M.; Rhee, Y. H. J. Am. Chem. Soc. 2003, 125, 7482–
7483.
(87) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Gonzalez-Cueva, M.;
Lastra, E.; Borge, J.; Garcia-Granda, S.; Perez-Carreno, E. Organome-
tallics 1996, 15, 2137–2147.
(88) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J. Orga-
nometallics 2002, 21, 3837–3840.
(89) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J.; Rodriguez,
M. A. Organometallics 2002, 21, 203–209.
(90) Cadierno, V.; Gamasa, M. P.; Gimeno, J.; Borge, J.; Garcia-
(93) Vinyl Cations; Stang, P. J., Rappoport, Z., Hanack, M., Subramanian,
L. R., Eds.; Academic Press: New York, 1979.
Granda, S. Organometallics 1997, 16, 3178–3187.
(94) Carbonium Ions; Olah, G. A., Schleyer, P. v. R., Eds.; Wiley-
Interscience: New York, 1968; Vol. 1.
(95) Connor, J. A. J. Chem. Soc., Dalton Trans. 1972, 1470–1476.
(96) Fischer, E. O.; Schluge, M.; Besenhard, J. O.; Friedrich, P.;
Huttner, G.; Kreissl, F. R. Chem. Ber. 1978, 111, 3530.
(91) Carbo, J. J.; Crochet, P.; Esteruelas, M. A.; Jean, Y.; Lledos, A.;
Lopez, A. M.; Onate, E. Organometallics 2002, 21, 305–314.
(92) Maier, G.; Reisenauer, H. P.; Schwab, W.; Carsky, P.; Hess,
B. A., Jr.; Schaad, L. J. J. Am. Chem. Soc. 1987, 109, 5183–5188.

1204 Organometallics, Vol. 29, No. 5, 2010
Table 2. 1H and 31P NMR Data for the Allenylidene Complexes
Byrne et al.
1H
31P
ppm (multiplicity, 3JH,H (Hz))
H3
H5,8
H6,7
ring A
ring B
phenyl
2aa
2bb
3a,c
4b
8.96 (s)
8.79 (s)
5.11 (t, 1.9)
4.80 (t, 1.8)
4.68 (t, 1.8)
4.86 (t, 1.7)
5.37 (t, 1.9)
5.00 (t, 1.8)
4.89 (t, 1.8)
5.03 (t, 1.7)
5.08 (s)
4.73 (s)
5.20 (s)
5.11 (s)
4.36 (s)
4.07 (s)
4.06 (s)
4.16 (s)
7.20-7.50 (m)
6.99-7.20 (m)
7.30-7.80 (m)
7.10-7.40 (m)
47.5
47.9
100.8
81.6
7.90 (t, 2.4)d
10.98 (s)
5
a CD2Cl2. b (CD3)2CO. c dppe CH2 δ 3.18 (vd), 2JP,H = 12 Hz. d JP,H = 12 Hz.
ferrocenyl resonances of 2-4, even with the extensive applica-
tion of 2-D NMR techniques. We favor the assignment of the
lower field triplets of 2-4 to protons H5,8 and the higher field
signal to H6,7, based on analogy to the R-ferrocenylcarbe-
nium ion 5. Connor and Lloyd used empirical linear relation-
ships between (a) the Hammett substituent constant, σP, and
Scheme 2
Δ2,5 and also between (b) the resonance substituent constant,
σR, and the value of (Δ3,4 - Δ1) as an indication of the overall
and the resonance electron-withdrawing abilities of the alky-
lidene substituent in compounds 6.95 Fischer and co-workers
derived similar Hammett σ values from NMR and electro-
chemical data for compounds 7.96 By using Connor’s empiri-
cal relationships, we find σP values of þ0.75, þ0.52, þ0.46,
and þ0.49 and σR values of þ1.00, þ1.16, þ1.03, and þ1.06
for the [M(C3H)(L)2(Cp)]þ substituents in compounds 2a, 2b,
3, and 4, respectively.97 Both the 1H shifts themselves and the
derived Hammett
σ values make it clear that the
[M(C3H)(L)2(Cp)]þ substituents are strongly electron-with-
drawing, especially through the delocalized π-system rather
than through inductive effects. However, the large solvent
dependence of the 1H NMR shifts of 2a in CD2Cl2 and 2b in
(CD3)2CO, and the uncertainty in the H5,8 versus H6,7
assignments, make the derived σ values quantitatively worth-
less. Clearly, the [M(C3H)(L)2(Cp)]þ substituents are more
strongly electron-withdrawing than either the alkylidene sub-
stituents in 6 or the alkylidyne substituents in 7, probably
because of the overall positive charge of compounds 2-4.
In the 13C NMR spectra of complexes 2-4 (Table 3),
phosphorus-coupled triplets assigned to C1 are found at low
field (δ 245 to 280 ppm). C1 of the iron complex 3 resonates
at lowest field, and C1 of the osmium complex 4 at the
highest field. Carbon atoms C2 resonate between δ 180 and
200 ppm, characteristic of the internal, sp-hybridized carbon
atoms of allenes98 and other allenylidene complexes.11,31,99
Carbon atoms C3 resonate between δ 145 and 155 ppm,
downfield of the usual δ 75 to 120 ppm range for terminal
allene carbons.98 This is evidence for cationic character, or a
significant contribution of the paramagnetic chemical shift
term due to a small HOMO-LUMO gap, at C3.100,101 The
13C{1H} NMR spectra of complexes 2-4 (Table 3) showed
only two singlets of relative intensity ca. 1:4 at ca. 90 and
ca. 78 ppm for the substituted ferrocenyl cyclopentadienyl
ring. These peaks are assigned to C4 and the superimposition
of C5,8 and C6,7, respectively. The shifts of C2,5 and C3,4 in
complexes 7 are found at ca. 71 ppm, differing by only ca.
1 ppm.96 The remaining cyclopentadienyl and phenyl reso-
nances of complexes 2-4 are found at predictable shifts.
31P NMR Spectra. The 31P NMR spectra of the allenyli-
dene complexes 2-4 (Table 2) each display a singlet for the
phosphine ligands at room temperature. The 31P NMR
spectrum of [Ru(CdCdCHFc)(PPh3)2(Cp)][PF6] (2b) shows
complex temperature dependence. The 31P NMR spectrum
in CD2Cl2 shows one singlet (δ 47.9) at room temperature.
On cooling, the line initially broadens, and below 255 K two
broad signals become apparent. These two signals sharpen to
a clear AB pattern below 233 K (Figure 2). The 31P NMR
chemical shift of each of the components of the AB system
shows a nearly linear temperature dependence between 238
and 190 K. In addition, the higher field 31P signal at 233 K
moves to a lower field position relative to its partner below
206 K, presumably due to changes in the phosphorus shifts,
possibly via slight movements of phenyl rings affecting
angles at phosphorus.
Each of the spectra that showed a clear AB pattern was
simulated, initially by line assignment and subsequently by
complete line-shape analysis,102 in order to determine accu-
rate chemical shifts, the 31P-31P coupling constant of
29.5 Hz, and the pseudo-first-order rate constants for the
exchange process in the temperature range 210-233 K. The
linearity of the change in chemical shift with temperature
allowed the determination of 31P NMR chemical shifts in
(97) Δ2,5 = -147σp þ 13; (Δ3,4 - Δ1) = -81σR þ 0.8; where Δi,j =
δ(FcH) - δ(Hi,j of complex) and Δ1 = δ(FcH) - δ(H unsubstituted Cp
of complex). For comparison with Connor’s values, Δi,j values are
corrected to Hz for a 100 MHz 1H spectrum.
(98) Levy, G. C.; Lichter, R. L.; Nelson, G. L. In Carbon-13 Nuclear
Magnetic Resonance Spectroscopy; Wiley: New York, 1980; pp 85-89.
(99) Bruce, M. I.; Swincer, A. G. Adv. Organomet. Chem. 1983, 22,
59–128.
(100) Czech, P. T.; Ye, X.-Q.; Fenske, R. F. Organometallics 1990, 9,
2016–2022.
(101) Fenske, R. F. In Organometallic Compounds: Synthesis, Struc-
ture and Theory; Shapiro, B. L., Ed.; Texas A&M University Press: College
Station, TX, 1983; pp 305-333.
(102) Adams, C. J.; Bruce, M. I.; Skelton, B. W.; White, A. H. Chem.
Commun. 1996, 7, 2663–2664.

Article
Organometallics, Vol. 29, No. 5, 2010 1205
Table 3. 13C NMR Data for the Allenylidene Complexes (CD2Cl2 solution)
ppm (multiplicity, 2JP,C (Hz))
C5,8
and C6,7
C1
C2
C3
C4
ring A
ring B
phenyls
2a
2b
3a
4
271.5 (t, 20)
273.0 (t, 21)
280.1 (t, 38)
246.5 (t, 13)
182.6 (s)
183.7 (s)
198.2 (s)
195.1 (s)
152.5 (s)
153.3 (s)
146.2 (s)
150.9 (s)
90.6 (s)
91.2 (s)
89.6 (s)
94.1 (s)
78.9 (s)
79.4 (s)
76.6 (s)
77.6 (s)
91.8 (s)
92.4 (s)
88.7 (s)
90.7 (s)
72.7 (s)
73.1 (s)
71.7 (s)
72.6 (s)
128.2-135.8 (m)
128.8-136.7 (m)
128.6-146.2 (m)
128.8-137.5 (m)
a dppe CH2 δ 29.8 (vt), 1JP,C = 22 Hz.
Figure 2. Stacked plot of 31P NMR variable-temperature experiment on compound 2b (202 MHz, CD2Cl2).
We attribute this 31P NMR temperature dependence to
slow rotation of the allenylidene ligand about the RuC3 axis,
whereby the anti isomer exchanges with the corresponding
syn isomer (kRu, Figure 4). Rotation of the ferrocenyl sub-
stituent with respect to the allenylidene plane, kFe, is appar-
ently rapid, although some line broadening at low temp-
erature may be due to slowing of ferrocenyl rotation.
each of the broadened spectra (238-263 K) by extrapola-
tion. The extrapolated chemical shifts were employed as
starting values in the simulation of each of the spectra,
leading to pseudo-first-order rate constants. Some of the
simulated and experimental spectra are depicted in Figure 3.
The rate constant (kC) at the coalescence temperature
(TC = 255 K) was also calculated by using eq 1.103
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Solid-State Structure of [Ru(CdCdCHFc)(PPh3)2(Cp)]-
[PF6] CH2Cl2 (2b). The molecular structure of the cation of
kC ¼ 2:22 Δv2 þ 6JA2 Bs-1
ð1Þ
3
2b is shown in Figure 5. The ruthenium atom displays
a typical “three-legged piano stool” (pseudo-octahedral)
coordination geometry, and structural parameters within
the [Ru(PPh3)2(Cp)] moiety are typical. The C1-C2-C3
chain of the allenylidene ligand is roughly linear, adopting a
“vertical” conformation with a dihedral angle of 8.90°
This equation gives a kC of 440 s-1, which is in good
agreement with 430 s-1 obtained from line-shape analysis.
The barrier for the exchange process (ΔGqC) was calculated to
be 49.0(8) kJ mol-1 by using eq 2.103
ꢀ
ꢁ
TC
kC
ΔGqC ¼ 19:14TC 10:32 þ log
kJ mol-1
ð2Þ
between the molecular pseudosymmetry plane (Cpcentroid
-
Ru-C1) and the allenylidene plane (Ru-C1-C2-C3-
C4-H3) (Figure 6). This orientation of the allenylidene
ligandis consistentwiththeoretical expectations thatπ-orbital
overlap should be maximized by this geometry.105-107 The
ferrocenyl substituent and cyclopentadienyl ring on ruthe-
nium adopt a cisoid conformation, with a Cpcentroid-Ru-
C3-C4 torsion angle of 11.7°. The ferrocenyl C5H4 ring is
Alternatively, ΔGqC was calculated to be 49.1(8) kJ mol-1
by using eq 3.104
ꢀ
ꢁ
TC
ΔGq ¼ 19:14TC 9:97 þ log
kJ mol-1
ð3Þ
δν
The parameters ΔHq = 50(3) kJ mol-1 and ΔSq = 3 (
13 J K-1 mol-1 were determined by plotting log k/T vs
1/T according to eq 4.103,104
nearly coplanar with the allenylidene plane, with
a
(C4-C5-C6-C7-C8)-(Ru-C1-C2-C3-C4-H3) dihe-
dral angle of 13.9°. This orientation maximizes π-orbital
overlap between the ferrocenyl C5H4 ring and the attached
unsaturated ligand, structurally resembling several ferrocenyl-
stabilized carbocations.46 The structural characteristics of this
k
ΔHq
ΔSq
ð4Þ
log ¼ 10:32 -
þ
19:14T 19:14
T
(105) Schilling, B. E. R.; Hoffmann, R.; Faller, J. W. J. Am. Chem.
Soc. 1979, 101, 592–598.
(106) Schilling, B. E. R.; Hoffmann, R.; Lichtenberger, D. L. J. Am.
(103) Friebolin, H. Basic One- and Two-Dimensional NMR Spectro-
scopy; VCH: Weinheim, 1993.
(104) Gunther, H. NMR Spectroscopy; Wiley: New York, 1980;
Chapter 6.
Chem. Soc. 1979, 101, 585–591.
(107) Kostic, N. M.; Fenske, R. F. Organometallics 1982, 1, 974–982.

1206 Organometallics, Vol. 29, No. 5, 2010
Byrne et al.
Figure 4. Schematic depicting rotation of the allenylidene ligand
with respect to the ruthenium moiety (kRu) and of the ferrocenyl
group about the axis of the allenylidene moiety (kFe).
Figure 5. ORTEP depiction of the cation (H and solvent atoms
omitted for clarity, 20% probability ellipsoids).
longer than most Ru-C (vinylidene) bond lengths
(1.83-1.85 A).11,31,99 The C1-C2 bond lengths in 2b, 8,
and 9 are nearly as short as typical carbon-carbon triple
bonds, close to that obtained for the CtC bond in 10
(1.215(4) A). The C2-C3 lengths are about 0.03 A longer
than a typical allene C(sp)-C(sp2) double bond (average
1.307 A).110 The geometry of the allenylidene ligand suggests
substantial contributions from both allenylidene and pro-
pargyl cation resonance forms.31 The ferrocenyl substituent
of complex 2b apparently does not promote the propargyl
form any more than the two phenyl substituents of com-
plexes 8 and 9. The ferrocenyl to C3 distance in 2b (C3-C4,
1.429(7) A) is similar to those previously reported for the
ferrocenyl substituents in the complexes [Cr(tCFc)(Br)-
(CO)4] (7b) (1.40(2) A)96 and [W(E)-{C(NMe2)CHdCH-
(Fc)}(CO)5] (11) (1.63(3), 1.48(2) A).111 Since this work
Figure 3. Simulated (upper) and observed (lower) 31P NMR
spectra of complex 2b.
ligand can be considered in comparison with those obtained
for disubstituted complexes [Ru(CdCdCPh2)(PMe3)2(Cp)]-
[PF6] (8)31 and [Ru(CdCdCPh2){P(OMe3)}2(Cp)][PF6] (9)108
(Table 4).
The distances of interest differ little among the complexes,
despite the difference in basicity of the phosphorus ligands.
The Ru1-C1 bonds in complexes 2b, 8, 9, 12, and 13 are
significantly shorter than the Ru-C (sp) bond in
[Ru(CtCPh)(PPh3)2(Cp)] (10) (2.016(3) A),109 but slightly
(108) Brodsky, R.; McAdoo, E. J.; Selegue, J. P., unpublished results,
1989.
(109) Manna, J.; John, K. D.; Hopkins, M. D. Adv. Organomet.
Chem. 1995, 38, 78–154.
(110) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1–S19.
(111) Macomber, D. W.; Madhukar, P.; Rogers, R. D. Organome-
tallics 1989, 8, 1275–1282.

Article
Organometallics, Vol. 29, No. 5, 2010 1207
Table 4. Selected Bond Lengths and Angles for Some Allenylidene Complexes
[MdCdCdCR1R2]PF6
bond length (A)
bond angle (deg)
[M]
R1
R2
Ru-C1
C1-C2
C2-C3
Ru-C1-C2
C1-C2-C3
ref
CpRu(PPh3)2 2b
CpRu(PMe3)2 8
CpRu{P(OMe)3}2 9
Cp*Ru(dippe) 12a
RuCl(dppm)2 13
H
Fc
Ph
Ph
Ph
Ph
1.901(5)
1.884(5)
1.895(7)
1.865(8)
1.89(1)
1.258(6)
1.255(8)
1.248(9)
1.25(1)
1.328(7)
1.329(9)
1.344(9)
1.32(1)
172.7(4)
179.5(5)
174.4(6)
172.8(7)
177.0(8)
175.1(5)
175.1(7)
166.6(8)
177.5(9)
174(1)
this work
31
108
61
Ph
Ph
H
H
1.25(1)
1.34(2)
59
a BPh4 salt.
The triphenylphosphine ligands of 2b adopt a geometry in
which two phenyl rings effectively shield the ferrocenylallenylidene
ligand (Figure 6). Several short nonbonding distances are
found between the allenylidene chain and the adjacent phenyl
rings (C1-C31, 3.200(6) A; C1-C32, 3.523(6) A; C2-C32,
3.385(6) A; C1-C61, 3.396(6) A; C1-C62, 3.512(6) A; C2-
C62, 3.599(7) A). This steric shielding probably accounts for the
lack of reactivity of compounds 2-4toward nucleophiles. There is
a close contact between the allenylidene hydrogen and a PF6- ion
(H3-F6, 2.83(5) A).
Electrochemistry. The results of the cyclic voltammetric
studies on allenylidene complexes 2b, 3, and 4 are summari-
zed in Table 5, quoted versus internal ferrocene(0/þ). The
complexes all exhibit similar voltammetric features. Each
undergoes a diffusion-controlled, one-electron oxidation,
with the separation between anodic and cathodic peak
potentials in good agreement with those measured for ferro-
cene under identical conditions.112 This first anodic feature
appears to be chemically reversible on the electrochemical
time scale if the switching potential remains less than ca.
1000 mV, where ipc/ipa ratios calculated graphically over the
scan range 100 to 1000 mV are unity. At more positive
switching potentials, ca. 1800 mV, a second anodic feature
is observed with Epa ≈ 1100 mV. In the return scan and
subsequent scans the chemical reversibility of the first anodic
feature is destroyed at scan rates between 100 and 1000 mV
with a reduction peak current, ipc, considerably depressed.
When the switching potential is maintained at 1000 mV, an
additional feature of interest, at ca. 450 mV, is consistent with
adsorption or precipitation of the electroactive species on the
electrode surface.113 A totally irreversible cathodic feature was
observed for each complex. Associated with this feature is an
anodic return wave (at ca. 0 mV), which is not observed at slow
scan rates and is presumably the result of an ECE process.
Clearly, the origin of the anodic wave observed for all the
complexes at ca. 300 mV is the ferrocenyl substituent of the
allenylidene ligand. The anodic peak potentials observed for this
process in complexes 2b, 3, and 4 differ by only ca. 70 mV, with
the E1/2 values increasing in the order 2b > 3 > 4 (typically,
[Ru(R)(L)2(Cp)] (R = alkyl114,115 or alkynyl116-119) complexes
Figure 6. ORTEP depiction highlighting the ferrocenyl substi-
tuent. The phenyl groups on the ligands are omitted for clarity
(H, phenyl and solvent atoms omitted for clarity, 20% prob-
ability ellipsoids).
was completed, there have been a number of complexes
structurally characterized that contain the [MC3(H)(R)]
moiety. The most pertinent are [(Cp*)Ru(dippe)(CdCd
CHPh)][BPh4] (12),61 [RuCl(dppm)2(CdCdCHPh)][PF6]
(13),59 and [(η5-C60Me5)Ru(R-prophos)(CdCdCHPh)]-
[PF6] (14).56 The last report is somewhat problematic, as
very little information appears in the body of the paper, and
on inspection of the CIF file, one finds that the structure
contains a second poorly refined molecule in the asymmetric
unit, rendering the bond lengths and angles unreliable for
comparison. The geometry of the ferrocenyl substituent in 2b
is similar to that of 7b and 11. The C-C distances in the
substituted cyclopentadienyl ring (C4 to C8, dh = 1.419(8) A)
are slightly longer than the C-C distances in the unsubsti-
tuted ring (C91 to C95, dh = 1.36(1) A). Although the
alternation of C-C bond distances in the substituted cyclo-
pentadienyl ring suggests some contribution of a fulvene
resonance form to the structure of 2b, other parameters
indicate that this is a very minor contributor. The exo carbon
C3 is displaced from the mean cyclopentadienyl plane to-
ward the iron atom by 0.184 A (Fe-C3, 2.984(7) A), with
the angle Cpcentroid-C4-C3 = 171.6(5)° (usually expressed
as R = 8.4(5)°).46,74-78 For [FcCPh2]þ[BF4]-, in which the
fulvene resonance form is significant, the out-of-plane dis-
placement = 0.50 A, d(Fe-exo C) = 2.715(6) A and R =
20.7°.74 The ferrocenyl rings of 2b are nearly parallel, with a
(C4-C5-C6-C7-C8) to (C91-C92-C93-C94-C95) di-
hedral angle of 2.09°, and eclipsed, with torsion angles of
opposite carbon atoms ranging from 0.1° to 1.4°, averaging 0.7°.
(112) Hupp, J. T. Inorg. Chem. 1990, 29, 5010–5012.
(113) Bard, A. J.; Faulkner, L. R. In Electrochemical Methods; Wiley:
New York, 1980; pp 488-552.
(114) Rogers, W.; Page, J. A.; Baird, M. C. J. Organomet. Chem.
1978, 156, C37–C42.
(115) Joseph, M. F.; Page, J. A.; Baird, M. C. Inorg. Chim. Acta 1982,
64, L121–L122.
(116) Bitcon,C.;Whiteley,M.W.J. Organomet. Chem. 1987,336, 385–392.
(117) Beddoes, R. L.; Bitcon, C.; Ricalton, A.; Whiteley, M. W.
J. Organomet. Chem. 1989, 367, C21–C24.
(118) Wong, W.-Y.; Lu, G.-L.; Ng, K.-F.; Wong, C.-K.; Choi, K.-H.
J. Organomet. Chem. 2001, 637-639, 159–166.
(119) Powell, C. E.; Cifuentes, M. P.; Morrall, J. P.; Stranger, R.;
Humphrey, M. G.; Samoc, M.; Luther-Davies, B.; Heath, G. A. J. Am.
Chem. Soc. 2003, 125, 602–610.

1208 Organometallics, Vol. 29, No. 5, 2010
Byrne et al.
Table 5. Electrochemical Data for the Allenylidene Complexes
Scheme 4. Products of Reaction after Coupling at Cβ of
Example Alkynyl Complexesa
redn
oxn
oxn
2
1
Epc
E1/2 (ΔEp)
σp
Epa
2b
3
4
-1275
-1149
-1222
258 (75)
313 (120)
324 (74)
þ0.54
þ0.67
þ0.69
1123
1068
a tren# = κ4-N,N0,N00,N000-N(CH2CH2NSiR03)3; SiR03 = SiMe3,
SiPhMe2.
Scheme 3. Proposed Mechanisms for Oxidation and Reduction
of the Allenylidene Complexes
an observable process for the iron analogue 3 is not readily
explained.
We suggest that the irreversibility of the cathodic process
may be the result of a ligand-centered coupling of the radicals
[M(CtCCHFc)(PR3)2(Cp)] produced by reduction of 2-4
(Scheme 3b). Disubstituted allenylidenes, [Ru(dCdCdCR2)-
(dppe)2Cl]þ (R = Me and Ph), have been shown to undergo
one-electron reduction to give propargyl radicals that can be
trapped by reaction withnBu3SnH, giving [Ru(-CtC-CHR2)-
(dppe)2Cl].122 Subsequently Rigaut and co-workers were able
to show an unprecedented coupling of an allenylidene com-
plex with a diynyl complex.123 Related redox couplings have
been reported. Upon reduction and oxidative workup,
[Cr(CtCPh)(CO)3(Cp)] couples at the β-carbon of the alky-
nyl ligand, giving neutral complex 15 (Scheme 4).124 [Mo-
(CtCH){N(CH2CH2NSiR3)3}] spontaneously couples at Cβ
to give 16.125 Oxidation of the anionic vinylidene complex
[Mo(dCdCHCMe3){P(OMe)3}2(Cp)]- gives the bis-carbyne
17.126 Several examples of oxidative Cβ-Cβcouplings of neutral
metal alkynyls (or their conjugate acids, vinylidene cations) to
give dicationic bis(vinylidene) complexes,43,117,127,128 as well as
Cβ-Cβ couplings of metal carbene or vinyl complexes,129,130
have been reported.
are more difficult to oxidize than the analogous iron complexes
by ca. 300 mV). The potential of this ferrocenyl-based redox
couple is close to that reported for the related allenylidene
complexes [TpRu(L)C3PhFc] (L = 2PPh3, 360 mV; L = dppf,
370 mV),53 ca. 30-40 mV lower than that of the chromium
carbyne complexes 7, and ca. 15-45 mV higher than that of the
tungsten analogues of 7 (Scheme 2).96 The electronic commu-
nication between the allenylidene metal headgroup and ferro-
cenyl moiety is evident in comparison to the related complexes
Conclusions
We have demonstrated that the reaction of a ferrocenyl
propargylic alcohol has given exceptionally stable mono-
substituted allenylidene complexes. The ferrocenyl substitu-
ents do not apparently favor either possible resonance form,
except perhaps in Os complex 4, and the stability of the
allenylidene complexes almost certainly arises from the steric
shielding afforded by the phosphine phenyl substituents. The
electrochemical results suggest that these allenylidene com-
plexes are easily oxidized, initially at the ferrocenyl substi-
tuent and further oxidized to give an unidentified trication.
The most likely reduction product is a propargyl radical that
is very reactive. The reactivity of allenylidene complexes is
[MC3(NMe2)(CH2CH2Fc)]þ
and
[MC3(CH2CH2-
CHdCH2)(SeFc)]þ (M = [RuCl(dppm)2]),51,54 for which the
ferrocenyl redox couple is observed at E1/2 20 and 50 mV,
respectively, practically unchanged from that of unsubstituted
ferrocene. Fischer et al. have used an empirical relationship120,121
to derive σp substituent values from E1/2 data for alkylidyne
complexes 7.96 These σp values are probably more reliable than
the NMR-based σ values (vide supra). They are generally
consistent with the observation that [Os(PPh3)2(Cp)]þ is the
least effective π-electron donor of the three iron-group substit-
uents used here, leading to the most carbenium character
(propargyl resonance form B in Figure 1) and the furthest
downfield 1H NMR shift of H3.
(122) Rigaut, S.; Maury, O.; Touchard, D.; Dixneuf, P. H. Chem.
Commun. 2001, 373–374.
(123) Rigaut, S.; Massue, J.; Touchard, D.; Fillaut, J.-L.; Golhen, S.;
Dixneuf, P. H. Angew. Chem. 2002, 41, 4513–4517.
(124) Ustynyuk, N. A.; Vinogradova, V. N.; Andrianov, V. G.;
Struchkov, Y. T. J. Organomet. Chem. 1984, 268, 73–78.
(125) Shih, K.-Y.; Schrock, R. R.; Kempe, R. J. Am. Chem. Soc.
1994, 116, 8804–8805.
(126) Beevor, R. G.; Freeman, M. J.; Green, M.; Morton, C. E.;
Orpen, A. G. J. Chem. Soc., Chem. Commun. 1985, 68–70.
(127) Le Narvor, N.; Lapinte, C. J. Chem. Soc., Chem. Commun.
1993, 357–359.
The ferrocenyl-based reversible oxidation gives rise to a
dication that slowly precipitates or adsorbs onto the elec-
trode surface, as evinced by an additional feature observable
at ca. 450 mV,113 an effect accelerating with increasing
switching potential. The irreversible anodic process at ca.
1100 mV is logically attributed to a RuII/RuIII and OsII/OsIII
redox couple for 2b and 4, respectively,12 although the lack of
(128) Brady, M.; Weng, W.; Gladysz, J. A. J. Chem. Soc., Chem.
Commun. 1994, 2655–2656.
(120) Hoh, G. L. K.; McEwen, W. E.; Kleinberg, J. J. Am. Chem. Soc.
1961, 83, 3949–3953.
(121) Hall, D. W.; Russell, C. D. J. Am. Chem. Soc. 1967, 89, 2316–
(129) Cron, S.; Morvan, V.; Lapinte, C. J. Chem. Soc., Chem.
Commun. 1993, 1611–1612.
(130) Rabier, A.; Lugan, N.; Mathieu, R.; Geoffroy, G. L. Organo-
2322.
metallics 1994, 13, 4676–4678.

Article
Organometallics, Vol. 29, No. 5, 2010 1209
clearly dominated by the reaction with nucleophiles at C1
and C3 of the three-carbon chain and with electrophiles at
C2. These sites of reactivity are now being developed in
methodologies for the formation of carbon-carbon bonds
and in alkene metathesis.
University of Kentucky Major Research Instrumentation
Bond Program (ID 7E48-25) for equipment, David
Chang of the Ohio State University Mass Spectrometry
Center for FAB mass spectra, Claude Dungan for assis-
tance with NMR spectra, Johnson-Matthey Inc. for the
loan of RuCl3, Thomas Guarr for helpful discussions,
and Brian Skelton for the production of a figure.
Acknowledgment. We are grateful to the U.S. Depart-
ment of Energy (DE- FG05-85ER13432 and DE-FG02-
00ER45847) and the NSF EPSCoR (RII-8610671) and
MRSEC (DMR-9809686) programs for financial sup-
port, the University of Kentucky Center for Computa-
tional Science for computing time and facilities, the
Supporting Information Available: Selected bond lengths and
angles for the structure of [Ru(CdCdCHFc)(PPh3)2(Cp)]-
[PF6] CH2Cl2, 2b. This material is available free of charge via
3
the Internet at http://pubs.acs.org.