Complexes comprising 'dangling' phosphorus arms and tri(hetero)metallic butenynyl moieties

Article abstract of DOI:10.1016/j.jorganchem.2016.01.026

Trans-RuCl₂(PP₃)₂ (1a) (PP₃ = tris[2-(diphenylphosphino)ethyl]phosphine) was prepared by reaction of RuCl₂(PPh₃)₃ with 2 eq. PP₃. Through coordination of two potential

Full text of DOI:10.1016/j.jorganchem.2016.01.026

Accepted Manuscript
Complexes comprising ‘dangling’ phosphorus arms and tri(hetero)metallic butenynyl
moieties
Michael S. Inkpen, Andrew J.P. White, Tim Albrecht, Nicholas J. Long
PII:
S0022-328X(16)30026-2
10.1016/j.jorganchem.2016.01.026
JOM 19377
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 5 October 2015
Revised Date: 19 January 2016
Accepted Date: 21 January 2016
Please cite this article as: M.S. Inkpen, A.J.P. White, T. Albrecht, N.J. Long, Complexes comprising
‘dangling’ phosphorus arms and tri(hetero)metallic butenynyl moieties, Journal of Organometallic
Chemistry (2016), doi: 10.1016/j.jorganchem.2016.01.026.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
P' = PPh2
P* = PPh2 or P(O)Ph2

ACCEPTED MANUSCRIPT
Complexes comprising ‘dangling’ phosphorus arms and
tri(hetero)metallic butenynyl moieties
Michael S. Inkpen, Andrew J. P. White, Tim Albrecht* and Nicholas J. Long*
Department of Chemistry, Imperial College London, London, SW7 2AZ, UK
Supporting Information Placeholder
ABSTRACT: Trans-RuCl2(PP3)2 (1a) (PP3 = tris[2-(diphenylphosphino)ethyl]phosphine) was prepared by reaction of
RuCl2(PPh3)3 with 2 eq. PP3. Through coordination of two potentially tetradentate ligands in a bidentate arrangement, four
uncoordinated phosphine moieties remain readily available for subsequent reaction. This is demonstrated through their facile
oxidation with hydrogen peroxide, providing trans-RuCl2(PP[P=O]2)2 (1b) (PP[P=O]2 = bis[2-(diphenylphosphine oxide)ethyl][2-
(diphenylphosphino)ethyl]phosphine). Whilst chloride abstraction reactions from 1a appear slow (typical for trans dichlorides), cis-
RuCl2(PP3) is shown to react rapidly with ethynylferrocene under ‘Dixneuf’ conditions (CH2Cl2, NaPF6, NEt3), providing the
tri(hetero)metallic butenynyl complex [(PP3)Ru(η3–FcC3CHFc)]PF6 (2, Fc = ferrocenyl). The pendant groups of 1a-b offer great
potential for future coordination studies (for example, to prepare mixed transition metal/lanthanide materials), whereby the facile
synthetic route to 2 suggests a path towards examination of complex mixed-valence systems comprising multiple redox-active cen-
tres.
reaction – treatment with H2O2 readily converting the latter to
–P(O)Ph2 (1b) (Scheme 1, right).
1. INTRODUCTION
The functionalization of identical groups within the same mol-
ecule poses a particular synthetic challenge, typically requiring
multi-step processes involving protecting groups, or inelegant
(and often low yielding) stoichiometric control. New strategies
for different substrates are therefore of interest, facilitating the
preparation of asymmetric systems for catalysis and materials
science. For mixed phosphine-phosphine oxides (a hemilabile
ligand class, comprising both ‘hard’ and ‘soft’ nucleophilic
groups),[1] one successful approach has been to coordinate a
multidentate phosphine to a metal centre in such a way so as
one or more of the phosphine groups remain uncoordinated.
The latter can then be selectively oxidized to the phosphine
oxide (or indeed subjected to alternative reactions). The ‘soft’
pendant groups in such materials have been shown to bind to a
range of metal centres, forming discreet or polymeric hetero-
metallics (transition metal-lanthanide).[2-5]
Figure 1. Previously reported mononuclear complexes with
incompletely coordinated tripodal phosphines and a 1:2 metal
to ligand ratio (P' = PPh2; M = Pt, Pd; A = P, N; X = Cl, Br, I,
NO3).
Such a strategy first requires generation of a starting com-
plex with ‘dangling’ arms (NB. the mixed phosphine-
phosphine oxide ligand remains on the same specific metal
centre unless a strategy is devised to displace it). Polydentate
ligands (>3 binding groups) are of particular interest in this
context, finding widespread utility in homogenous catalysis to
enforce specific geometries at a metal centre or confer en-
hanced stability through the chelate effect.[6] However, in the
specific case of incompletely coordinated tripodal phosphines
with a 1:2 metal to ligand ratio, few examples have been re-
ported. These include Mo(PP3)2[7] and MX2(L)2 (M = Pt, Pd;
L = PP3, tris[2-(diphenylphosphino)ethyl]amine; X = Cl, Br, I,
NO3)[8] (Figure 1). A new addition to this select group,
RuCl2(PP3)2 (1a), is reported here. We show that its four un-
coordinated –PPh2 groups may indeed be subjected to further
Scheme 1. Synthesis of RuL2(PP3)n (n = 1, 2) complexes.
Noting also the reversible redox behavior of the RuL2P4 (L
= anionic ligand, P = phosphine) family, we characterized 1a
and the related [(PP3)Ru(η3–FcC3CHFc)]PF6 (2) complex

ACCEPTED MANUSCRIPT
3
(Scheme 1, left) using solution voltammetry. Though ferro-
MHz, CDCl3): δ (ppm) -11.79 (t, JPP = ~13 Hz, 4P, free
PPh2), 40.73 (t, |2JPP + JPP| = 24 Hz, 2P, bound PQPh2), 49.54
3
cenyl-terminated butenynyl complexes similar to 2 are known
–
for example, with coordinated (η5-C5Me4H)2Ti[9],
(m, 2P, bridgehead PM). 13C{1H} NMR (100 MHz, CDCl3): δ
(ppm) 20.37-22.55 (m, CH2), 127.44-136.80 (Ph). UV-vis
(CH2Cl2): λmax/nm (ε/M-1 cm-1) 255sh (62078) 305sh (3825).
MS ES+: m/z 1513 ([M+H]+ Calc.: 1513). (Found: C, 66.75;
H, 5.66. Calc. for C84H84Cl2P8Ru: C, 66.67; H, 5.59%).
Cp(PR3)Ru (R = Me, Ph, Cy)[10], Cp2Ti[11] moieties – these
have seldom[11] been subjected to electrochemical studies.
2. EXPERIMENTAL
2.1 Conditions and materials
2.3.2 Trans-RuCl2(PP[P=O]2)2 (1b)
All preparations were carried out using standard Schlenk
line and air-sensitive chemistry techniques under an atmos-
phere of nitrogen. No special precautions were taken to ex-
clude air or moisture during workup, unless otherwise stated.
Solvents used in reactions were sparged with nitrogen and
dried with alumina beads, Q5 Copper catalyst on molecular
sieves, or 3A molecular sieves,[12] where appropriate. Silica
and neutral alumina of Brockmann activity I (0% H2O) or II
(3% H2O) were used for chromatographic separations.
RuCl2(PPh3)3[13] and RuCl2(PP3)[14] (method B) were pre-
pared via literature methods from commercially available
starting materials. All other materials were purchased from
commercial suppliers and used without further purification.
Hydrogen peroxide (0.15 mL, 30 wt. % in H2O) was added to
a solution of 1a (0.027 g, 0.02 mmol) in CHCl3 (5 mL). After
stirring at room temperature in air for 75 min, the mixture was
filtered through a plug of alumina grade II, eluting with addi-
tional CHCl3. Solvent was removed in vacuo and the solid
recrystallized from CH2Cl2/n-hexane to provide 1b as a yellow
1
solid (0.021 g, 72%). H NMR (400 MHz, CDCl3): δ (ppm)
1.79 (br m, 4H, CH2), 2.01 (br m, 12H, CH2), 2.24 (br m, 4H,
CH2), 2.69 (br m, 4H, CH2), 6.74 (m, 8H, Ph–H), 6.81 (m, 4H,
Ph–H), 7.31-7.69 (m, 48H, Ph–H). 31P{1H} NMR (162 MHz,
CDCl3): δ (ppm) 33.00 (t, 4P, 3Jpp = 17 Hz, P=O), 42.50 (t, 2P,
3
|2JPP + JPP| = 22 Hz, bound PQPh2), 52.57 (m, 2P, bridgehead
PM). 13C{1H} NMR (101 MHz, CDCl3): δ (ppm) 17.68-24.43
(m, CH2), 127.53-135.91 (Ph). MS ES+: m/z 1577.2754
([M+H]+ Calc. for C84H85Cl2O4P8Ru: 1577.2769). (Found: C,
63.88; H, 5.26. Calc. for C84H84Cl2O4P8Ru: C, 63.96; H,
5.37%).
2.2 Instrumentation
Unless otherwise stated, 1H, 13C{1H}, 31P{1H} and 19F
NMR spectra were recorded at ambient temperature on Bruker
400 or 500 MHz spectrometers and internally referenced to the
residual solvent peaks of CDCl3 at δ 7.26 (1H) and 77.16 ppm
(13C{1H})[15] or externally to 85% phosphoric acid or CFCl3
(0.00 ppm). 13C{1H} spectra were assigned where possible
using 2D heteronuclear correlation experiments. UV-vis and
IR spectra were recorded on a PerkinElmer LAMBDA 25
UV/vis spectrophotometer or a PerkinElmer Spectrum 100
FT-IR spectrometer, respectively. Mass spectrometry analyses
were conducted by the Mass Spectrometry Service, Imperial
College London. Microanalyses were carried out by Stephen
Boyer of the Science Centre, London Metropolitan University.
Cyclic voltammograms were recorded under an atmosphere of
2.3.3 [(PP3)Ru(η3–FcC3CHFc)]PF6 (2)
Triethylamine (0.12 mL, 0.86 mmol) was added to a mixture
of RuCl2(PP3) (0.088 g, 0.10 mmol), ethynylferrocene (0.090
g, 0.43 mmol), and NaPF6 (0.071 g, 0.42 mmol) in CH2Cl2
(8.5 mL). After stirring for 20 h in the absence of light, the
cherry-red solution was filtered through a short Celite plug.
Removal of solvent provided a dark red solid, which was elut-
ed through a CH2Cl2 packed SiO2 column using CH2Cl2-ethyl
acetate (1:0→6:4 v/v). Selected fractions from the second half
1
of the primary orange band yielded 2 (~95% purity by H
NMR) as a dark red solid (0.028 g, 20%). 1H NMR (500 MHz,
CDCl3): δ (ppm) 1.63 (br m, 2H, CH2), 2.51 (br m, 4H, CH2),
2.85 (br m, 2H, CH2), 3.07 (br m, 2H, CH2), 3.24 (br m, 2H,
CH2), 3.90 (br s, 5H, C5H5), 4.01-4.37 (br m, 4H, C5H4), 4.46
(s, 5H, C5H5), 4.74 (pseudo-t, 2H, C5H4), 5.01 (pseudo-t, 2H,
C5H4), 5.56 (br s, 1H, C=CH), 6.7-7.2 (m, 30H, Ph–H).
31P{1H} NMR (162 MHz, CDCl3): δ (ppm) -144.29 (sept, JP-F
= 713 Hz, 1P, PF6), 42.90 (m, 2P, PM), 70.59 (m, 1P, PQ),
150.78 (m, 1P, PA). 19F NMR (376.56 MHz, CDCl3): -72.66
(d, JF-P = 715 Hz, PF6). 13C{1H} NMR (126 MHz, CDCl3): δ
28.16-29.16 (m, CH2), 31.84-32.17 (m, CH2), 66.80-72.69 (m,
Cp), 70.35 (2C, Cp, CH), 70.55 (5C, Cp, CH), 72.56 (2C, Cp,
CH), 128.04-138.84 (Ph). MS ES+: m/z 1336.1340 ([M]+ Calc.
for C66H61F6Fe2P5Ru: 1336.1108), 1191.1299 ([M-PF6]+ Calc.
for C66H61Fe2P4Ru: 1191.1466), 595.5543 ([M-PF6]2+ Calc. for
C66H61Fe2P4Ru: 595.5733). (Found: C, 63.88; H, 5.26. Calc.
for C66H61F6Fe2P5Ru: C, 59.34; H, 4.60%).
n
argon in CH2Cl2/0.1 M Bu4NPF6 on a CHI760C potentiostat
(CH Instruments, Austin, Texas) with a glassy carbon disc as
working electrode (diameter = 2.5 mm), and Pt-wire as refer-
ence and counter electrodes respectively. Analyte solutions
were between 0.1-1 mM. Potentials are reported relative to
[FeCp2]+/[FeCp2],
measured
against
an
internal
[FeCp*2]+/[FeCp*2] reference.
2.3 Synthetic Details
2.3.1 Trans-RuCl2(PP3)2 (1a)
A solution of RuCl2(PPh3)3 (0.150 g, 0.123 mmol) and PP3
(0.214 g, 0.319 mmol) in toluene (1 mL) was heated in an oil
bath at 120°C for 2 h. After cooling, the toluene solution was
filtered through cotton wool into a clean glass vial, using
CH2Cl2 (3 mL) to extract residual material from the reaction
flask. Diethyl ether (20 mL) was layered above the tolu-
ene/CH2Cl2 solution, forming yellow crystals after 6 d. The
solution was decanted, the solid material washed with diethyl
ether (1 x 15 mL) and acetone (1 x 15 mL) and dried in vacuo
to provide 1 as a yellow-orange powder (0.133 g, 71%). Crys-
tals suitable for X-ray diffraction were obtained by slow diffu-
3. RESULTS AND DISCUSSION
3.1 Synthesis
Our interest in ruthenium complexes comprising the PP3 lig-
and was sparked by the possibility of forcing octahedral di-
chlorides of the form RuX2P4 (X = halide, P = phosphine) into
a cis geometry. Such materials are known to undergo rapid
substitution to form the corresponding σ-alkynyl
species,[13,16] which are of substantial current interest as
1
sion of diethyl ether into a CH2Cl2 solution. H NMR (400
MHz, CDCl3): δ (ppm) 1.45 (br m, 4H, CH2), 1.77 (br m, 12H,
CH2), 1.94 (br m, 4H, CH2), 2.53 (br m, 4H, CH2), 6.98 (t, J =
7.6 Hz, 8H, Ph–H), 7.12 (t, J = 7.4 Hz, 4H, Ph–H), 7.15-7.30
(m, 40H, Ph–H), 7.56 (m, 8H, Ph–H). 31P{1H} NMR (162

ACCEPTED MANUSCRIPT
conducting materials.[17-21] Following Bianchini et al.,[14]
1119 cm-1 may be attributable to the P=O functionality (not
our initial attempts to prepare cis-RuCl2(PP3) from
RuCl2(PPh3)3 and 1.1 eq. PP3 provided the expected material
plus an additional, unexpected side product which was isolated
following addition of EtOH to the product mixture in toluene.
The latter was ultimately identified as RuCl2(PP3)2 (1a), and
could be prepared as the sole product under the same condi-
tions by using 2 eq. PP3. Attempts to prepare the iron and os-
mium congeners using conditions analogous to those used to
synthesize their mono-ligated complexes (for example, heating
being present in the spectrum of 1a).
The 31P{1H} NMR spectrum of complex 2 shows three
well separated yet somewhat broadened resonances (certainly
in comparison to the spectrum of RuCl2[PP3]), having relative
intensities 1:1:2 (an AMQ2 splitting pattern, typical of analo-
gous octahedral Ru materials[14]). Though the splitting of
each resonance cannot be clearly observed, it is straightfor-
ward from related studies to assign the resonance at 150.78
ppm to PA (unresolved doublet of triplets), and those at 70.59
and 42.90 ppm to PM (unresolved triplet of doublets) and PQ
2
eq. PP3 with OsCl2(PPh3)3/FeCl2 at reflux in 2-
–
methoxyethanol/ethanol, respectively),[22,23] proved unsuc-
cessful, producing only multiple product mixtures with no
clear evidence for MCl2(PP3)2.
(unresolved doublet of doublets), respectively. The single PF6
counterion is also represented by a septet at –144.29 ppm with
relative intensity 1.
1
Noting that pendant –PPh2 moieties in related complexes
had been shown amenable to further modification,[24] we
reacted 1a with an excess of hydrogen peroxide and observed
that it readily forms an analogous complex with pendant –
P(O)Ph2 arms (1b, Scheme 1). In contrast, attempts to substi-
tute the chloride groups, forming vinylidene or σ-alkynyl
complexes, by reacting 1a in CH2Cl2 with ethynylben-
zene/ethynylferrocene under ‘Dixneuf’ conditions (NaPF6
followed by filtration through an alumina plug, or NaPF6 and
Et3N together)[16,25,26] did not yield the desired products in
appreciable yields. Under similar conditions we found that cis-
RuCl2(PP3) (bright yellow) reacts with ethynylferrocene to
provide the tri(hetero)metallic complex 2 (dark red; Scheme
1). This butenynyl complex is analogous to a family of previ-
ously reported materials – [(PP3)M(η3–RC3CHR)]BF4 (M =
Ru, Os; R = Ph, SiMe3) – normally isolated as a mixture of
isomers, and prepared from MH2(PP3).[27-29]
Whilst the H NMR spectra of 1a and 1b are straightfor-
ward (SI, Figures S1 and S3), that of 2 (SI, Figure S7) war-
rants further discussion. Two separate sets of ferrocenyl reso-
nances are observed, and – along with a peak assigned to the
vinylic proton at 5.56 ppm – appear broadened (with the up-
field shifted ferrocenyl set extremely so). At present, the
origin of broadening for these features remains uncertain. At-
tempts to sharpen the features using heteronuclear (1H{31P})
decoupling experiments proved unsuccessful, although this did
import additional detail to the CH2 peaks (SI, Figure S10). At
elevated temperature (328 K; SI, Figure S11) most resonances
appear slightly sharpened, whereas various peaks become
broader at low temperature (213 K; SI, Figure S12). It is pos-
sible that the broadened features at room temperature could
result from local paramagnetic effects, for example if one of
the ferrocene centres had been oxidized to Fe3+. However,
–
only one PF6 counter ion is observed in the 31P{1H} NMR
spectrum, and no readily assignable peaks above [M]+ were
observed in mass spectra.
3.2 Spectroscopy
The 31P{1H} NMR spectra of complexes 1a, 1b and 2 are par-
ticularly interesting (see Figure 2 and 3 for labeling scheme
and representative spectra, respectively). In 1a, three reso-
nances are observed with relative intensities 1:1:2 and a rather
complicated splitting pattern. We consider that the pendant –
PPh2 moieties of each ligand are chemically non-equivalent
(PA/B) as they cannot be interchanged by any symmetry opera-
tion (point group = Ci), and the bound PM/PM' and PQ/PQ' nuclei
are magnetically non-equivalent as JMQ ≠ JMQ' (an ABMQ-
ABM'Q' system). The resonance at δ 49.57 ppm can thus be
attributed to the apical phosphorus atoms, PM (PM'), appearing
as a broad multiplet (unresolved dddd) due to 2J coupling with
The stereochemistry of the butenynyl ligand was assigned
based on NOESY experiments at 213 K which exhibited
cross-peaks between the vinylic proton and a CH2 resonance.
Additional cross-peaks were observed between the substituted
ring Cp–H (sharper set) and Ph–H resonances. As the vinylic
proton appears directed towards the PP3 ligand backbone (re-
quiring the other substituent at that carbon to be directed away
from the PP3 backbone), and given that no cross-peaks were
observed between the substituted Cp ring Cp–H (broader set)
and Ph–H resonances, we suggest the extremely broadened set
of ferrocenyl resonances are associated with the ferrocenyl
group bound at the vinylic alkene. Assignment of the relative
orientation of the butenynyl ligand with respect to the PP3
ligand (vinylic alkene trans to PA or PM) was not attempted.
Most 13C{1H} resonances were also not easily individually
assigned as a result of the low solubility of complexes, multi-
ple overlapping environments and 13C-31P coupling for peaks
associated with the PP3 ligand. Ranges for different nuclei
environments are provided in the experimental section, with
all observed peak values detailed in the SI (Figures S2, S5,
and S8).
3
PQ' (PQ) and J coupling with PA, PB and PQ (PQ'). Further up-
field at δ 40.70 ppm appears a pseudo-triplet (unresolved dd)
assigned to the coordinated –PPh2 group, PQ/PQ', coupling to
PM and PM'. Finally, at δ –11.83 ppm there is another reso-
nance, corresponding to the uncoordinated phosphorus atoms,
PA and PB. As these have similar but non-identical chemical
shifts (also notably comparable to that of –PPh2 in the free
ligand, at approximately δ –13 ppm), their overlapping dou-
blets (from 3J coupling to PM/PM') appear as a triplet. It was not
possible to run homonuclear (31P{31P}) decoupling NMR ex-
periments with available spectrometers, but these could be
used to verify our explanation of the observed spectral charac-
teristics. The spectrum of 1b is similar to that of 1a, with the
notable exception that the resonance attributable to PA/B envi-
ronments have been shifted downfield by ~45 ppm due to oxi-
dation (other environments exhibit downfield shifts a factor of
ten smaller). A comparison of IR spectra for complexes 1a and
1b (SI, Figure S13) suggest that an absorption at 2212 cm-1
and two sets of overlapping peaks with maxima at 1170 and

ACCEPTED MANUSCRIPT
PA
PB
3.3 Electrochemistry
Cl
Ru
Cl
PQ
PM
All materials were studied by solution voltammetry in
CH2Cl2/0.1 M NBu4PF6, and exhibited reversible behaviour
under the described conditions (ipa/ipc ~ 1, ip ∝ Vs1/2; data
summarized in Table 1 and 2). Both 1a and 1b show only a
single redox wave within the observable potential window,
assigned to the Ru2+/Ru3+ couple. It is apparent that oxidation
of the pendant PPh2 groups to P(=O)Ph2 makes the Ru centre
of 1b harder to oxidize than that of 1a by ~0.1 V. These values
are similar to equilibrium potentials measured for analogous
PM'
PQ'
PA
PB
Figure 2. Labeling schemes used in 31P{1H} NMR assign-
ments.
(a)
species such as trans-RuCl2(dppe)2,[30] (0.04
V
vs.
FcH/[FcH]+). The multi-nuclear complex 2, demonstrates two
redox waves which are reversible if the potential range is set
appropriately (Figure 4a). Extension to higher oxidation poten-
tials reveals an additional, irreversible redox wave which also
negatively impacts the reversible events previously observed
(Figure 4b).
Table 1. Equilibrium potentials (E1/2) and the difference in
equilibrium potentials (ꢀE1/2) for complexes 1a, 1b and 2.a
Fe1
Fe2
Ru
PM
PQ
PA/B
compound
E1/2
E1/2
ꢀE1/2 E1/2
RuCl2(PP'3)2 (1a)
RuCl2(PP'P''2)2 (1b)
[(PP3)Ru(η3–
-
-
-
-
-
-
0.116
0.221
-
(b)
–0.057 0.275 0.332
FcC3CHFc)]PF6 (2)
a
Scan rate 0.1 V s−1. All potentials in V, reported relative to
[Cp2Fe]+/[Cp2Fe]. Measured with internal Cp*2Fe (-0.495 V
vs. Cp2Fe/[Cp2Fe]+).
Table 2. Additional electrochemical data for complexes 1a, 1b
and 2.a
redox
PM
PQ
PA/B
compound
transition Epa
Epc
ꢀE
ipa/ipc
RuCl2(PP'3)2
0→1+
0.152
0.080
0.072 1.10
(1a)
RuCl2(PP'P''2)2
(1b)
0→1+
0.254
0.189
0.065 1.03
(c)
[(PP3)Ru(η3–
FcC3CHFc)]PF6
(2)
0→1+
1+→2+
2+→4+
–0.023
0.308
0.961b
–0.092 0.069 1.05
0.242 0.066 0.91
a
For conditions see Table 1. b Estimated Epa value obtained at
a scan rate of 1 V s-1, corrected for Ru.
PA
PM
PQ
Figure 3. 31P{1H} NMR spectra of (a) 1a, (b) 1b and (c) 2 in
CDCl3.

ACCEPTED MANUSCRIPT
(a)
expected at E1/2 ≥ 0.97 V. This is remarkably close to the
measured Epa of the irreversible wave (≈ 0.96 V vs.
FcH/[FcH]+). The high value likely reflects the difficulty in
removing 2e– from [2]2+. We thus tentatively assign the irre-
versible, 2e– process to the Ru2+/Ru4+ couple, and the reversi-
ble 1e– processes to Fe2+/Fe3+. It is of further note that the
ꢀE1/2 of 0.332 V measured for 2 is ~0.222 V larger than for
Fc–C≡C–HC=CH–Fc (ꢀE1/2 ~ 0.11 V).[33,34] The latter has a
similar connectivity between each Fe2+ centre, but no associa-
tion with a Ru centre.
Before applying a potential externally, the measured open
circuit potential for an electrolyte solution containing 2 ranged
between –0.288 and –0.224 V vs. Pt, where E1/2Fe1 = 0.055 V
vs. Pt. These values offer further support to the conclusion that
both ferrocene centres exist in the reduced state prior to volt-
ammetry measurements (and so also in NMR experiments). If
one ferrocene centre was already oxidized, the measured open
Fe2
circuit potential would be expected between E1/2Fe1 and E1/2
.
(b)
3.4 X-ray crystallography
The crystal structure of 1a (Figure 5) shows the complex to
possess two bidentate phosphine ligands with the octahedral
coordination sphere completed by a pair of trans chlorides; as
a result of the ruthenium atom being situated on a centre of
symmetry, the RuP4 plane is perfectly flat. The phosphine
ligand binds using the central phosphorus atom P1 and one of
the three –CH2CH2PPh2 arms (that based on P4), the other two
being non-coordinating. These latter P–CH2–CH2–P arms
adopt anti conformations (torsion angles of 166.70(11) and
174.41(14)° for the P1-P7 and P1-P10 arms respectively)
whilst the bound arm has the expected gauche conformation
(torsion angle 58.12(17)°).
Figure 4. Cyclic voltammograms of 2 (V vs. FcH/[FcH]+,
corrected for Ru). (a) Reversible 1e– waves attributed to sepa-
rated Fe2+/Fe3+ transitions (scan rate = 0.1 v s-1). (b) Extension
of potential window results in an irreversible process, attribut-
ed to Ru2+/Ru4+. Voltammograms shown are cycles 1 (solid
blue curves), cycles 2, 5, 10 (dotted black curves) and 50 (sol-
id red curves) (scan rate = 1 V s-1).
We subjected a voltammogram of 2 comprising all three
redox waves to further analysis (measured at 1 V s-1; Figure
4b). For Nernstian waves, the difference between Epa and Epa/2
(the potential at ipa/2) is 56.5/n mV at 25°C (where n is the
stoichiometric number of electrons involved in the electrode
process).[31] During our first cycle of measurement, succes-
sive oxidation waves exhibited ipa (Epa/2) values of 30.9 (-
0.078), 27.0 (0.255) and 100.0 (0.922) ꢁA (V), respectively.
Figure 5. The crystal structure of the Ci-symmetric complex
1a.
Taking these values and data from Table 2, we find |Epa – Epa/2
|
for each wave as 55, 53, and 39 mV. Taken together (and ac-
counting for difficulties associated with defining the baseline
for each wave), this analysis suggests that the observed redox
waves are sequential 2 x 1e- (reversible), and 1 x 2e– (irre-
versible) processes.
In this context, it is notable that the 4+ state is accessible
in analogous ruthenium complexes – typically observed as an
irreversible Ru3+/Ru4+ process occurring >0.80 V positive of
redox waves associated with Ru2+/Ru3+.[13,32] If E1/2 for 1a
and 1b are taken as a reference point for where Ru2+/Ru3+
might occur in 2 (average E1/2 ≈ 0.17 V), Ru3+/Ru4+ might be
4. CONCLUSION
We have demonstrated how a simple change in reagent stoi-
chiometry can provide Ru complexes comprising PP3 ligands
with unusual coordination geometries. The reactivity of pen-
dant PPh2 moieties towards H2O2 demonstrates a synthetic
route to novel, metal-bound mixed phosphine-phosphine oxide
ligands, and in general a new strategy (using the Ru centre as a
blocking group) for the preparation of any number of unusual

ACCEPTED MANUSCRIPT
(6) A. Phanopoulos, P.W. Miller, N.J. Long, Beyond Triphos –
new hinges for a classical chelating ligand, Coord. Chem. Rev.
299 (2015) 39-60.
mixed ligand motifs based on PP3. Furthermore, solution volt-
ammetry studies of complex 2 indicates that interaction be-
tween ferrocene centres across a butenynyl bridge may be
accentuated when the latter is coordinated to Ru(PP3). Our
work lays the foundation for additional investigations into
both Ru-PP3 based transition metal-lanthanide, and functional-
ized butenynyl complexes within catalysis and materials
chemistry.
(7) M. Garcìa-Basallote, P. Valerga, M.C. Puerta-Vizcaíno, A.
Romero, A. Vegas, M. Martínez-Ripoll, An unexpected
molybdenum(0) complex with "MoP6" coordination: Crystal
structure of [Mo{P(CH2CH2PPh2)3}2]·C5H10, J. Organomet.
Chem. 420 (1991) 371-377.
(8) D. Fernández-Anca, M.I. García-Seijo, M.E. García-
Fernández, Tripodal polyphosphine ligands as inductors of chelate
ring-opening processes in mononuclear palladium(II) and
platinum(II) compounds. The X-ray crystal structure of two
derivatives containing dangling phosphorus, Dalton Trans. 39
(2010) 2327-2336.
(9) P. Štěpnička, R. Gyepes, I. Císařová, M. Horáček, J.
Kubišta, K. Mach, Photoinduced generation of catalytic
complexes from substituted-titanocene−bis(trimethylsilyl)ethyne
complexes: Contribution to the mechanism of the catalytic head-
to-tail dimerization of terminal alkynes, Organometallics 18
(1999) 4869-4880.
(10) E. Rüba, K. Mereiter, R. Schmid, K. Kirchner, H.
Schottenberger, The reaction of ferrocenyl acetylene with
[RuCp(PR3)(CH3CN)2]PF6 (R=Me, Ph, Cy). Formation of the first
allenyl carbene complexes, J. Organomet. Chem. 637–639 (2001)
70-74.
ASSOCIATED CONTENT
Supporting Information
NMR, IR spectra and additional crystallographic information.
This material is available free of charge via the Internet at
http://www.sciencedirect.com.
AUTHOR INFORMATION
Corresponding Author
* E-mail for T.A.: t.albrecht@imperial.ac.uk
.
* E-mail for N.J.L.: n.long@imperial.ac.uk
.
Notes
The authors declare no competing financial interest.
(11) K. Kaleta, A. Hildebrandt, F. Strehler, P. Arndt, H. Jiao, A.
Spannenberg, H. Lang, U. Rosenthal, Ferrocenyl-substituted
metallacycles of titanocenes: Oligocyclopentadienyl complexes
with promising properties, Angew. Chem., Int. Ed. 50 (2011)
11248-11252.
(12) D.B.G. Williams, M. Lawton, Drying of organic solvents:
Quantitative evaluation of the efficiency of several desiccants, J.
Org. Chem. 75 (2010) 8351-8354.
ACKNOWLEDGMENT
The authors thank Phillip Miller and Andreas Phanopoulos
(Imperial College London, UK) for useful discussions and
Peter Haycock for conducting NMR experiments. M.S.I., T.A.
and N.J.L thank the EPSRC and the Leverhulme Trust (RPG
2012-754) for funding.
(13) M.A. Fox, J.E. Harris, S. Heider, V. Pérez-Gregorio, M.E.
Zakrzewska, J.D. Farmer, D.S. Yufit, J.A.K. Howard, P.J. Low, A
simple synthesis of trans-RuCl(CCR)(dppe)2 complexes and
representative molecular structures, J. Organomet. Chem. 694
(2009) 2350-2358.
DEDICATION
Dedicated to Professor, the Lord Lewis (Jack) – a true gentle-
man and a leading light in inorganic and organometallic chem-
istry.
(14) C. Bianchini, P. Perez, M. Peruzzini, F. Zanobini, A.
Vacca, Classical and nonclassical polyhydride ruthenium(II)
complexes stabilized by the tetraphosphine P(CH2CH2PPh2)3,
Inorg. Chem. 30 (1991) 279-287.
(15) G.R. Fulmer, A.J.M. Miller, N.H. Sherden, H.E. Gottlieb,
A. Nudelman, B.M. Stoltz, J.E. Bercaw, K.I. Goldberg, NMR
chemical shifts of trace impurities: Common laboratory solvents,
organics, and gases in deuterated solvents relevant to the
organometallic chemist, Organometallics 29 (2010) 2176-2179.
(16) P. Haquette, N. Pirio, D. Touchard, L. Toupet, P.H.
Dixneuf, Activation of terminal alkynes with cis-
KEYWORDS
Ferrocenes, phosphines, multi-metallic, butenynyl, electro-
chemistry
REFERENCES
(1) V.V. Grushin, Mixed phosphine−phosphine oxide ligands,
Chem. Rev. 104 (2004) 1629-1662.
(2) M. Nakamura, S. Yoshida, T. Katayama, A. Taninaka, Y.
Mera, S. Okada, O. Takeuchi, H. Shigekawa, Mechanically
activated switching of Si-based single-molecule junction as
imaged with three-dimensional dynamic probe, Nat. Commun. 6
(2015)
[RuCl2(Ph2PCH2PPh2)2]
acetylide-ruthenium complexes and crystal-structures of
[(Ph2PCH2PPh2)2(Cl)RuCCH2]PF6 and
-
new vinylidene-ruthenium and
[(Ph2PCH2PPh2)2(Cl)RuCCH] complexes, J. Chem. Soc., Chem.
Commun. (1993) 163-165.
(17) L. Luo, A. Benameur, P. Brignou, S.H. Choi, S. Rigaut,
C.D. Frisbie, Length and temperature dependent conduction of
ruthenium-containing redox-active molecular wires, J. Phys.
Chem. C 115 (2011) 19955-19961.
(18) B. Kim, J.M. Beebe, C. Olivier, S. Rigaut, D. Touchard,
J.G. Kushmerick, X.-Y. Zhu, C.D. Frisbie, Temperature and
length dependence of charge transport in redox-active molecular
wires incorporating ruthenium(II) bis(sigma-arylacetylide)
complexes, J. Phys. Chem. C 111 (2007) 7521-7526.
(19) K. Liu, X. Wang, F. Wang, Probing charge transport of
ruthenium-complex-based molecular wires at the single-molecule
level, ACS Nano 2 (2008) 2315–2323.
(3) S. Al-Jibori, Z. Kalay, T.K. Al-Allaf, Synthesis of novel
heterobimetallic complexes of platinum(II) bridged by the mixed
phosphine-phosphine
oxide
ligands
Ph2P(CH2)2P(O)Ph2,
Transition. Met. Chem. 19 (1994) 293-295.
(4) L.V. Koplitz, D.S. McClure, D.A. Crerar, Spectroscopic
study of chloroiron(II) complexes in lithium chloride-deuterium
chloride-deuterium oxide solutions, Inorg. Chem. 26 (1987) 308-
313.
(5) V.A. Petrov, W.J. Marshall, V.V. Grushin, The first
perfluoroacetylacetonate metal complexes: As unexpectedly
robust as tricky to make, Chem. Commun. (2002) 520-521.

ACCEPTED MANUSCRIPT
(20) S. Marques-Gonzalez, D.S. Yufit, J.A.K. Howard, S.
Martin, H.M. Osorio, V.M. Garcia-Suarez, R.J. Nichols, S.J.
Higgins, P. Cea, P.J. Low, Simplifying the conductance profiles
of molecular junctions: The use of the trimethylsilylethynyl
moiety as a molecule-gold contact, Dalton Trans. 42 (2013) 338-
341.
(21) F. Meng, Y.-M. Hervault, Q. Shao, B. Hu, L. Norel, S.
Rigaut, X. Chen, Orthogonally modulated molecular transport
junctions for resettable electronic logic gates, Nat. Commun. 5
(2014)
(22) C. Bianchini, K. Linn, D. Masi, M. Peruzzini, A. Polo, A.
Vacca, F. Zanobini, Classical, nonclassical, and mixed-metal
osmium(II) polyhydrides stabilized by the tetraphosphine
P(CH2CH2PPh2)3. Hydrogen/deuterium isotope exchange
reactions promoted by a strongly bound dihydrogen ligand, Inorg.
Chem. 32 (1993) 2366-2376.
(23) R. King, R. Kapoor, M. Saran, P. Kapoor, Polytertiary
phosphines and arsines. IV. Metal complexes of two isomeric
tetratertiary phosphines, Inorg. Chem. 10 (1971) 1851-1860.
(24) D. Fernandez-Anca, M.I. Garcia-Seijo, M.E. Garcia-
Fernandez, Transition of trigonal-bipyramidal to square-planar
geometries by oxidation of a coordinated tripodal polyphosphine
in Pd(II) and Pt(II) complexes, RSC Adv. 2 (2012) 1404-1415.
(25) S. Ingham, M. Khan, J. Lewis, N. Long, P. Raithby, C.
Faulkner, Ruthenium(II) sigma-acetylide complexes - monomers,
dimers and polymers, J. Organomet. Chem. 482 (1994) 139-145.
(26) D. Touchard, P. Haquette, S. Guesmi, L.L. Pichon, A.
Daridor, L. Toupet, P.H. Dixneuf, Vinylidene-, alkynyl-, and
trans-bis(alkynyl)ruthenium complexes. Crystal structure of
trans-[Ru(NH3)(C≡C-Ph)(Ph2PCH2CH2PPh2)2]PF6,
Organometallics 16 (1997) 3640-3648.
(27) C. Bianchini, C. Bohanna, M.A. Esteruelas, P. Frediani, A.
Meli, L.A. Oro, M. Peruzzini, A deceptively simple case of
selective hydrogenation of phenylacetylene to styrene catalyzed
by
a
cis-hydrido(.eta.2-dihydrogen)ruthenium(II) complex,
Organometallics 11 (1992) 3837-3844.
(28) C. Bianchini, M. Peruzzini, F. Zanobini, P. Frediani, A.
Albinati, A ruthenium(II) enynyl complex mediates the catalytic
dimerization of 1-alkynes to Z-1,4-disubstituted enynes, J. Am.
Chem. Soc. 113 (1991) 5453-5454.
(29) P. Barbaro, C. Bianchini, M. Peruzzini, A. Polo, F.
Zanobini, P. Frediani, Regio- and stereoselective dimerization of
1-alkynes catalyzed by an Os(II) complex, Inorg. Chim. Acta 220
(1994) 5-19.
(30) C.E. Powell, M.P. Cifuentes, J.P. Morrall, R. Stranger,
M.G. Humphrey, M. Samoc, B. Luther-Davies, G.A. Heath,
Organometallic complexes for nonlinear optics. 30.
Electrochromic linear and nonlinear optical properties of
alkynylbis(diphosphine)ruthenium complexes, J. Am. Chem. Soc.
125 (2002) 602-610.
(31) A.J. Bard, L.Y. Faulkner, Electrochemical Methods, second
ed., Wiley, 2004.
(32) F.E. Kühn, J.-L. Zuo, F.F. de Biani, A.M. Santos, Y. Zhang,
J. Zhao, A. Sandulache, E. Herdtweck, 4-Ethynylpyridine as
bridging moiety in mixed Ru/Re complexes, New J. Chem. 28
(2004) 43-51.
(33) D. Courtney, C. John McAdam, A.R. Manning, H. Müller-
Bunz, Y. Ortin, J. Simpson, The preparation, spectroscopy,
structure and electrochemistry of some [Co(η4-C4Ph4)(η5-
C5H4C=C–CH=Y)], [Fe(η5-C5H5)(η5-C5H4C=C–CH=Y)], and
related complexes, J. Organomet. Chem. 705 (2012) 7-22.
(34) A. Donoli, A. Bisello, R. Cardena, A. Ceccon, M. Bassetti,
A. D’Annibale, C. Pasquini, A. Raneri, S. Santi, Electron transfer
within C4 unsaturated spacers between terminal ferrocenyl
moieties, Inorg. Chim. Acta 374 (2011) 442-446.

ACCEPTED MANUSCRIPT
Highlights
-
-
-
-
RuCl2(diphos)2 family extended to include coordinatively unsaturated PP3 ligands.
Pendant –PPh2 moieties available for further synthetic modification.
cis-RuCl2(PP3) can react with ethynylferrocene to form butenylnyl species.
Characterization includes solution voltammetry studies and X-ray crystallography.