Syntheses and molecular structures of trans-bis(alkynyl) tetrakis-triethylphosphite ruthenium complexes

Article abstract of DOI:10.1016/j.jorganchem.2017.04.028

A simple synthesis of complexes trans-[Ru(C≡CC₆H₄-4-R)₂{P(OEt)₃}₄] from trans-[RuCl₂{P(OEt)₃}₄] and the terminal alkyne is described. Crystallographically determined molecular structures indicate a range of conformers, with the ethynyl arylene rings differing in their orientation with respect to each other across the Ru{P(OEt)₃}₄ fragment. Electrochemical analysis reveals a well-behaved one-electron oxidation process, which is only some 100 mV more positive that the analogous trans-[Ru(C≡CC₆H₄-4-R)₂(dppe)₂] complexes. Quantum chemical calculations reveal largely delocalised electronic structures and suggest that these compounds may find use as wire-like molecules within single molecule electronics.

Full text of DOI:10.1016/j.jorganchem.2017.04.028

Accepted Manuscript
Syntheses and molecular structures of trans-bis(alkynyl) tetrakis-triethylphosphite
ruthenium complexes
Samantha G. Eaves, Brian W. Skelton, Paul J. Low
PII:
S0022-328X(17)30266-8
10.1016/j.jorganchem.2017.04.028
JOM 19915
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 20 February 2017
Revised Date: 20 April 2017
Accepted Date: 21 April 2017
Please cite this article as: S.G. Eaves, B.W. Skelton, P.J. Low, Syntheses and molecular structures of
trans-bis(alkynyl) tetrakis-triethylphosphite ruthenium complexes, Journal of Organometallic Chemistry
(2017), doi: 10.1016/j.jorganchem.2017.04.028.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Syntheses and molecular structures of trans-bis(alkynyl)
tetrakis-triethylphosphite ruthenium complexes.
Samantha G. Eaves,a,b Brian W. Skelton,a,c Paul J. Lowa*
a School of Molecular Sciences, University of Western Australia, 35 Stirling Highway,
Perth, 6009
b Department of Chemistry, Durham University, South Rd, Durham DH1 3LE, UK
c Centre for Microscopy, Characterisation and Analysis, University of Western
Australia, 35 Stirling Highway, Perth, 6009
Dedicated to Professor John A. Gladysz on the occasion of his 65th birthday and in
celebration of a career of academic achievement.
Abstract
A simple synthesis of complexes trans-[Ru(C≡CC6H4-4-R)2{P(OEt)3}4] from trans-
[RuCl2{P(OEt)3}4] and the terminal alkyne is described. Crystallographically
determined molecular structures indicate a range of conformers, with the ethynyl
arylene rings differing in their orientation with respect to each other across the
Ru{P(OEt)3}4 fragment. Electrochemical analysis reveals a well-behaved one-
electron oxidation process, which is only some 100 mV more positive that the
analogous trans-[Ru(C≡CC6H4-4-R)2(dppe)2] complexes. Quantum chemical
calculations reveal largely delocalised electronic structures and suggest that these
compounds may find use as wire-like molecules within single molecule electronics.
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1. Introduction
The chemistry of trans-bis(alkynyl) complexes of ruthenium has been extensively
developed over the past decades, and whilst the vast majority are supported by
ancillary phosphine ligands,[1-4] examples with other supporting ligand sets,
including, for example, mixed phosphine-carbonyl[5,6] or N-heterocyclic carbene-
carbonyl[7] ligand sets, macrocyclic amines and dioxodiazamacrocyles [8,9] are also
known. In addition to finding extensive application as building blocks and donors for
the construction of NLO active materials,[10,11] including chemically and redox-
switchable examples,[12,13] donor molecules within solar cells[14-16] and
applications as sensors,[17] trans-[Ru(C≡CR)2(dppe)2] [dppe
=
1,2-
bis(diphenylphosphino)ethane] complexes systems commonly feature in designs of
metal-containing molecular wires.[18,19] The development of mechanically
controlled break-junctions and molecular junctions based on the use of a scanning
tunnelling microscope (STM) tip to contact a single molecule now allows the
investigation of molecular compounds and complexes at the molecular level as active
components in prototypical electronic devices.[20,21] In one of the earliest examples
of these investigations, the single-molecule conductance of the organometallic
complex, trans-[Ru(C≡CC6H4-4-SAc)2(dppm)2] was compared with that of the
organic compound, AcSC6H4-4-C≡CC6H4-4-C≡CC6H4-4-SAc in Au|molecule|Au
junctions via the STM break junction.[22] The organometallic complex exhibited a
higher single molecular conductance value (2.45 ± 0.90 × 10-4 G0 vs. 0.46 ± 0.26 × 10-
4
G0), although the β decay constants calculated using the STM apparent height
method[23] of the two wires are comparable (1.01 ± 0.25 Å-1 vs. 1.11 ± 0.18 Å-1).
More recently, it was shown that conductance histograms generated from trans-
[Ru(C≡CC6H4-4-C≡CSiMe3)2(dppe)2] and Me3SiC≡CC6H4-4-C≡CC6H4-4-C≡CC6H4-
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4-C≡CSiMe3, by the I(s) method[24] were simplified in comparison with the thiolate-
contacted compounds, with trimethylsilylethynyl binding groups giving only a single,
narrow conductance peak as the steric bulk of the termini restricts the range of
available, conductive contacts.[25] A higher conductance value was again obtained
for the organometallic complex (5.10 ± 0.99 10-5 G0) compared with the organic
analogue.[26] Efforts are now being expended on the preparation and measurement of
longer, multi-metallic organometallic wires of ruthenium[27-29] and other metals[30-
32] which have clearly demonstrated the potential for organometallic compounds of
this trans-bis(alkynyl) type to find application in molecular electronic platforms.
Excitingly, the results of many years effort are now beginning to show promise within
genuine electronic devices. [21,33,34]
In seeking to optimise the performance of metal complex molecular wires based on
trans-M(C≡CR)2Ln frameworks, attention has been drawn to the role that the ancillary
ligands L might play on tuning alignment of the critical molecular orbitals with the
electrode Fermi levels.[35] Recently, both the Akita group[36] and our own[37] have
been attracted to the potential that trialkylphosphite ligands might play as ancillary
groups in such structures. The majority of synthetic routes to trans-bis(alkynyl)
complexes
bearing
tetrakis-trialkylphosphite
fragments,
trans-
[Ru(C≡CR)2{P(OX)3}4] (where X = Me, Et) involve treatment of trans-
[RuCl2{P(OX)3}4] with alkynyl-lithium reagents and afford the bis(alkynyl) products
in ca. 35-45 % yield.[36,38] Compounds prepared in this manner include trans-
t
[Ru(C≡CR)2{P(OEt)3}4] (R = Ph ([1a]), [38] C6H4-4-Me, [38] Bu, [38]) and trans-
[Ru(C≡CC5H4N-4)2{P(OMe)3}4].[36] Despite being air-stable and obtained in high
isomeric purity, the bis(alkynyl) complexes are sensitive to reactions with
electrophiles, forming alkynyl-vinylidene complexes, which may then undergo further
rearrangement to form η3-butenynyl complexes,[38,39] necessitating care on protic
work-up.
We have recently observed that the complex trans-[Ru(C≡C-cyclo-3-
C4H3S)2{P(OEt)3}4] can be readily obtained from the slow reaction of trans-
[RuCl2{P(OEt)3}4] with 3-ethynyl thiophene, KPF6 and NHiPr2 in ethanol at room
temperature.[37] Here we give further experimental details of this facile synthetic
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route to complexes trans-[Ru(C≡CR)2{P(OEt)3}4] that allows the complexes to be
obtained in moderate to good yield. The crystallographically determined structures of
seven new examples of this class of complex and electrochemical properties are
described. Quantum chemical calculations reveal rather extensively delocalised
frontier orbitals in these wire-like molecules.
2. Results and Discussion
2.1 Syntheses
The key starting material for these studies, trans-[RuCl2{P(OEt)3}4], is readily
obtained from RuCl3.nH2O and P(OEt)3 upon treatment with NaBH4.[40] Reaction of
trans-[RuCl2{P(OEt)3}4] with KPF6 (4 equivalents) and an excess of a terminal
alkyne, HC≡CR, in a mixed EtOH/NHiPr2 solvent resulted in the slow formation of
complexes trans-[Ru(C≡CR)2{P(OEt)3}4] (Scheme 1). Although conversions took
days to weeks to completion, the resulting products were readily isolated from the
reactions mixtures by precipitation and crystallisation and obtained in moderate to
good yields (34 − 85 %), with the exception of the ethynylbenzonitrile complex [1e].
The yield of [1e] (19 %) was considerably lower due to the formation of additional
side products during the reaction and presumably a consequence of competing
coordination reactions of the nitrile group and formation of oligomers of poorly
defined composition. Similar complication are also known in analogous chemistry of
trans-Ru(dppe)2-based complexes.[41] Monitoring of the reactions by in situ 31P{1H}
NMR spectroscopy suggests that the formation of [1] proceeds via an intermediate
mono-alkynyl complex, trans-[RuCl(C≡CR){P(OEt)3}4], with resonances from an
intermediate complex comparable with the mono-alkynyl tetrakis-triethylphosphite
complex trans-[RuCl(C≡CC6H5){P(OEt)3}4] (31P{1H} NMR (CD2Cl2):
δ 132.3 ppm),[42] being observed (Figure S1).
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Scheme 1. The preparation of complexes [1a-h]
Evidence for the formation of [1a-h] includes triplet and quartet resonances in the 1H
NMR spectra corresponding to the -CH3 and -CH2- ethyl fragments (respectively) on
the four equivalent phosphite groups about the ruthenium centre. Resonances occur
between δ 1.18 – 1.21 ppm (CH3) and δ 4.25 – 4.32 ppm (CH2) with mutual 3JHH
couplings of 7 Hz. Singlet resonances in the 31P{1H} NMR spectra, between δ 136.2 –
139.5 ppm, support the trans-arrangement of the alkynyl ligands. In the 13C{1H}
NMR spectra, quintet (or unresolved multiplet) resonances between δ 89.9 –
131.6 ppm for the Ru-C α-carbons coupled to the four cis-phosphorus nuclei
(2JCP = 19 – 21 Hz), and singlet resonances between δ 104.9 – 116.9 ppm for the Ru-
C≡C β-carbons confirmed the presence of the alkynyl ligand. In the IR spectra,
ν(RuC≡C) bands observed between 2055 – 2147 cm-1 further support alkynyl
functionality. Finally, the structures [1b-h] have been determined by single crystal X-
ray diffraction studies (see section 5.3.2), which confirmed the structural assignments
based on spectroscopy.
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The use of alternative halide-abstracting agents in the formation of [1b], by way of
example, was also briefly examined. The analogous reaction sequence to that shown
in Scheme 1 but with NaPF6 rather than KPF6 gave [1b] in lower yield (56 %) after a
13 day reaction (c.f. 86% isolated yield from the reaction in Scheme 1). With TlBF4
as the halide abstracting agent, the reaction sequence is again similar, with slow
generation of [1b] via the mono-alkynyl intermediate. However, in this case, the
conversion from the intermediate mono-alkynyl complex to the product trans-
bis(alkynyl) was not complete, even after the addition of excess TlBF4 and alkyne and
a reaction length of 14 days. Given the extreme toxicity of Tl(I) salts, and subsequent
increased difficulty of work-up procedures, this route is not considered optimal. With
AgOTf, a plethora of unassigned resonances were observed in the in situ 31P NMR
spectrum, evincing a complex mixture of products in solution. The propensity of
Ag(I) salts to coordinate to other species in the reaction mixture (such as chlorides
and alkynes) has been previously demonstrated,[43-45] and similar processes are
likely associated with the range of compounds observed here.
2.2 Molecular Structures
Single crystal X-ray structure determinations have been made for trans-
[Ru(C≡CPh)2{P(OEt)3}4] ([1b]), trans-[Ru(C≡CC6H4-4-C≡CSiMe3)2{P(OEt)3}4]
([1c]) as a CHCl3 solvate, trans-[Ru(C≡CC6H4-4-CO2Me)2{P(OEt)3}4] ([1d]) as a
CH2Cl2 solvate, trans-[Ru(C≡CC6H4-4-C≡N)2{P(OEt)3}4] ([1e]), trans-
[Ru(C≡CC6H4-4-NO2)2{P(OEt)3}4] ([1f]), trans-[Ru(C≡CC6H4-4-C5H11)2{P(OEt)3}4]
([1g]) and trans-[Ru(C≡CC6H4-4-OMe)2{P(OEt)3}4] [1h], with important bond
lengths and bond angles summarised in Table 1 and Table 2. The atom labelling
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scheme is shown in Figure 1, and the definition of the angles θa and θaʹ shown in
Figure 2. Plots of other molecules are given in the Supporting Information.
Figure 1. A plot of a molecule of 1h, with hydrogen atoms and one component of a
disordered ethyl group omitted for clarity, showing the atom labelling scheme.
Ellipsoids are drawn at the 50 % probability level. Crystallographic data for the
structure were collected at 100(2) K on an Oxford Diffraction Gemini diffractometer
with Mo Kα radiation. One ethyl group was modeled as being disordered over two
sets of sites with occupancy factors constrained to 0.5 after trial refinement.
Geometries and displacement parameters of the disordered components were
restrained to reasonable values.
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Figure 2. Representation of angles θa and θaʹ in trans-[Ru(C≡CR)2{P(OEt)3}4]
complexes ([1b-h]), as being the smallest Cortho-Cipso-Ru-P(any) torsion angles
(irrespective of sign) calculated for each of the two aryl rings (depicted as red and
blue lines) on the trans-bis(aryl) alkynyl fragments.
8

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Table 1: Selected bond distances (Å), Cortho-Cipso-Ru-P(any) torsion angles (θa, θaʹ / °) and angles between planes containing the aryl-ring
fragments (θp / °) for trans-[Ru(C≡CR)2{P(OEt)3}4] complexes [1b − h].
Complex
[1b]a
R
Ru-C1
2.066(3)
2.056(3)
Ru-C3
C1≡C2
C3≡C4
Ru-P
Ru-Pavg
2.323
θa , θaʹ
θp
C6H5
-
1.207(4)
-
2.3166(9), 2.3245(9)
2.327(1), 2.328(1),
2.316(1), 2.309(1)
2.292(3), 2.300(3),
2.322(3), 2.331(3)
− 12.2, 40.8
23.8, 42.0
61.2
22.2
[1c]
C6H4-4-
C≡CSiMe3
2.062(4)
1.218(5) 1.214(5)
2.320
[1d]
[1e]
C6H4-4-CO2Me 2.050(5)
-
1.217(7)
-
2.311
2.316
16.3, − 22.6
9.4, − 27.2
83.6
79.7
26.0
69.7
13.9
3.9
C6H4-4-C≡N
C6H4-4-NO2
C6H4-4-C5H11
C6H4-4-OMe
C6H4-4-OMe
C6H4-4-OMe
2.053(3)
2.059(2)
2.072(2)
2.078(2)
2.089
2.052(3)
2.063(2)
2.075(2)
2.066(2)
2.089
1.213(4) 1.213(4) 2.3155(7), 2.3156(7),
2.3161(7), 2.3170(7)
[1f]
1.214(3) 1.214(3) 2.3161(6), 2.3167(6),
2.3176(6), 2.3199(6)
2.318 − 39.1, 22.9
[1g]
1.210(3) 1.218(3) 2.3129(6), 2.3133(6),
2.3175(6), 2.3178(5)
2.315
2.309
2.353
2.352
16.4, 22.6
29.3, − 18.2
21.9, -18.6
23.3, -23.1
[1h]
1.207(3) 1.204(3) 2.3041(6), 2.3061(6),
2.3123(6), 2.3138(6)
planar-[1h’]
perp-[1h’]
1.223
1.223
2.351, 2.352,
2.354, 2.355,
2.351, 2.352,
2.353, 2.353
2.089
2.089
1.223
1.223
-89.9
a From one component of the disorder model.
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Table 2: Selected bond angles (°) for trans-[Ru(C≡CR)2{P(OEt)3}4], [1b − h].
Complex
R
C3-Ru-C1 Ru-C1-C2 Ru-C3-C4
P-Ru-P (cis)
P-Ru-P (trans)
179.93(6),
171.46(5)
172.17(4),
174.39(4)
172.25(10),
167.90(10)
173.03(3),
172.13(3)
173.39(2),
172.87(2)
174.43(2),
172.44(2)
168.56(2),
170.81(2)
173.88,
[1b]
C6H5
180.0
180.0
178.5(3)
178.8(6)
175.2(2)
176.3(2)
177.7(2)
178.8(2)
179.3
180.0
90.27(4), 89.74(4)
[1c]
[1d]
C6H4-4-C≡CSiMe3 178.8(1)
179.6(3)
89.99(3), 91.56(4),
89.97(4), 89.23(4)
C6H4-4-CO2Me
C6H4-4-C≡N
C6H4-4-NO2
C6H4-4-C5H11
C6H4-4-OMe
C6H4-4-OMe
C6H4-4-OMe
179.8(4)
179.5(1)
178.7(1)
178.3(1)
177.7(2)
179.7
179.8(4) 90.36(12), 89.69(10),
89.37(11), 92.17(11)
[1e]
178.6(2)
178.7(2)
176.5(2)
175.7(2)
179.22
89.76 (3), 90.29(3),
89.80(3), 91.09(3)
88.87(2), 89.89(2),
91.33(2), 90.70(2)
89.31(2), 91.91(2),
90.68(2), 88.83(2)
89.25(2), 89.34(2),
90.75(2), 92.44(2)
89.97, 90.10,
[1f]
[1g]
[1h]
planar-[1h’]
perp-[1h’]
90.27, 90.30
174.07
179.9
179.6
180.0
90.18, 90.18,
173.44,
90.18, 90.20,
173.43
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Although
the
mixed
alkynyl-vinylidene
has
complex,
been
trans-
[Ru(C≡CC6H5)(=C=CMeC6H5){P(OEt)3}4]OTf,
structurally
characterised,[38] the series of complexes [1b - h] represents the first structurally
characterised trans-bis(alkynyl) derivatives of the type trans-[Ru(C≡CR)2{P(OR)3}4].
For all cases, [1b - h], the P-Ru-P bond angles between cis-phosphines (ca. 90 °) and
those between trans-phosphines (ca. 180 °) in addition to ≡C-Ru-C≡ angles (ca.
180 °), indicate the octahedral geometry about the ruthenium centre, in agreement
with the previously published alkynyl-vinylidene complex.[38]
Orpen and Connelly have summarised geometric variations in a series of metal-
phosphine and phosphite complexes, and similar trends are observed here.[46] In
general, the M-PX3 (X = R, OR; R = alkyl, aryl) bond length increases upon oxidation
of the metal centre, evincing M-PX3 π-back-bonding. The P-X bonds are
correspondingly shortened on oxidation, implicating P(σ*), the predominantly anti-
bonding combination of P(3px,y) with X(σ), as the acceptor orbital in the back-
bonding model. The P(σ*) orbital is lowered in energy when X is more
electronegative and the PX3 fragment is made more pyramidal as stabilising overlap
between P(3px,y) and X(σ) decreases when the X atoms move out of the xy plane. As a
result, the π-accepting character of P(OEt)3 (Tolman cone angle 109 °)[47] is
expected to be far superior than PPh3 (Tolman cone angle 145 °) and other related
ligands bearing aromatic fragments, such as dppe and dppm. Hence for the
crystallographically determined complexes [1b-h], variations in Ru-P bond lengths
are anticipated to reflect the degree of Ru-P π-back-bonding.
The angles θa and θaʹ (Figure 2, Table 1) provide a convenient proxy measure for the
alignment of the aryl π-systems, Ar(π), with Ru(d) on geometric grounds. Given the
difficulty in defining a unique value for θ, with two indistinguishable aryl rings and
four indistinguishable phosphite groups, θa and θaʹ values reported here represent the
smallest Cortho-Cipso-Ru-P(any) torsion angles (irrespective of sign) measured for each
of the two ring fragments (Figure 2). Therefore, in this case, angles close to 0 °
represent the most effective M(d)-C≡C-Ar(π) overlaps and hence greatest correlation
of structural and electronic properties.[48] As an indication of the extent of
11

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delocalisation, θp values, representing the angle between planes containing the aryl
ring fragments, are also given in Table 1. Angles with a higher deviation from 0 °
(perfectly ‘aligned’ ring systems) reflect more twisted conformations.
With the exception of [1h] (θp = 13.9 °), and perhaps [1c] (θp = 22.2 °) and [1f] (θp =
26.0 °), the phenylene rings in these bis-aryl acetylide complexes [1] do not lie in the
same plane (with θp values within the range 61.2 – 87.6 °). In addition, complexes [1]
generally display θa and θaʹ values between ca. 20 – 40 °, and hence the Ar(π) systems
and Ru(d) orbitals are not aligned for optimal overlap through the alkynyl π-system.
In addition, whilst [1e] shows alignment of one Ar(π) system with Ru(d) (θa / θaʹ =
9.4 °), the second ring is not aligned, (θa / θaʹ = − 27.2 °, θp = 79.7). For these reasons,
it is unsurprising to find that a definitive trend between Ru-Pavg and the electronic
character of the aryl substituent does not exist. For example, the un-substituted
complex [1b] has the longest Ru-Pavg bond length (2.321 Å) of the series. For all
structures [1b-h], the Ru-C(1, 3) bond lengths are consistent with single bond
character, although complexes containing electron withdrawing para-substituents on
the aromatic ring ([1c, 1d, 1e, 1f]) are found to have generally shorter lengths
(2.050(5) – 2.059(2) Å) than those bearing electron donating para-substituents ([1g,
h] 2.072(2) – 2.078(2) Å), evincing an electronic substituent effect, possibly
propagated through the σ-framework. In this case, the un-substituted complex, [1b],
has a Ru-C(1) bond length between these two ranges (2.066(3) Å). For all cases, the
C≡C bond lengths are consistent with triple bond character. Differences in C≡C bond
lengths as a result of the R substituent are found to be within statistical error.
2.3 Electrochemistry
The electrochemical responses of trans-bis(alkynyl) tetrakis-triethylphosphite
complexes [1a-h] in CH2Cl2 solutions containing 0.1 M [NnBu4]PF6 were examined
by cyclic voltammetry (Table 3). Potentials are quoted against the ferrocene /
ferrocenium couple ([Fe{η5-C5H5}2] / [Fe{η5-C5H5}2]+ = 0.00 V) using an internal
decamethylferrocene / decamethylferrocenium reference ([Fe{η5-C5Me5}2] / [Fe{η5-
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C5Me5}2]+ = − 0.48 V).[49,50] These data represent the first electrochemical
exploration of trans-bis(alkynyl) complexes containing the trans-
[Ru(C≡CR)2{P(OEt)3}4] motif.
Electrochemical reversibility describes the experiment where the rate of electron
transfer is mass transport limited, and characterised by ipa / ipc ≈ 1, ∆Ep ≈ 60 mV and
ip ∝
ν
1/2 (where ipa = anodic peak current; ipc = cathodic peak current; ΔEp = |Epc –
ν = scan rate. The trans-bis(alkynyl) complexes [1a-g] exhibit two oxidation
Epa|,
events. In addition, the nitro-phenyl complex [1f] exhibits a reduction wave, assigned
to the closely occurring independent reductions of the two nitro groups on the basis of
the higher peak current, and large ∆Ep value (220 mV) in comparison with the
internal standard (60 mV). The complex [1h], which contains the most electron
donating substituent, exhibits three oxidation events. There was evidence of
electrochemical-chemical (EC) behavior in the first oxidation process of [1a] with ipa
> ipc at room temperature, and additional electrochemical processes indicative of new
chemical species being observed on the reverse scan when conducting the experiment.
At reduced temperatures (ca. –20 °C), current ratios approached unity, indicating
improvements to the chemical reversibility. The second oxidation processes (and third
for [1h]) are irreversible at all temperatures.
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Table 3. Selected electrochemical data (V) of [1a-h] from solutions in 0.1 M
[NBu4][PF6] / CH2Cl2 at room temperature.
Complex R
E1/2(1) E1/2(2) E1/2(3) E1/2(red) ∆E1-2 ∆E2-3
[1a]
[1b]
C4H9
− 0.09b 0.83c
-
-
-
-
0.92
0.76
-
-
C6H5
0.09a
0.85c
C6H4-4-
C≡CSiMe3
C6H4-4-
CO2Me
[1c]
[1d]
0.14a
0.89c
-
-
-
-
0.75
0.69
-
-
0.19a
0.30a
0.88c
[1e]
[1f]
C6H4-4-CN
0.83c
0.93c
-
-
-
0.53
0.55
-
-
C6H4-4-NO2 0.38a
− 1.73d
C6H4-4-
0.02a
C5H11
[1g]
[1h]
0.74c
-
-
-
0.72
0.50
-
C6H4-4-OMe − 0.11a 0.39c
0.81c
0.42
areversible; breversibility improves at lower temperatures (-20°C) ; cirreversible;
dtwo-electron redox event
The electronic effects of the R group on molecular properties are expected to be more
apparent in the solution state over the solid state, as a result of greater conformational
freedom, which permits better overlap and conjugation through the molecular
backbone. The first oxidation potentials (E1/2(1)) span a 500 mV range (Table 3), and
display a clear dependence on the electronic characteristics of the aryl substituent. As
with other ruthenium alkynyl complexes,[51] the oxidation processes are presumably
largely centered on the alkynyl ligand(s). Similar trends in redox potentials are also
displayed in trans-bis(alkynyl) complexes containing the {Ru(dppe)2} motif.[48]
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These {Ru{P(OEt)3}4} containing complexes have higher (more positive) oxidation
potentials (by ca. + 0.10 V), than the analogous {Ru(dppe)2} complexes reflecting the
increased π-accepting character of phosphite ligands.[46,48] In contrast, E1/2(2) is less
sensitive to the nature of the R group, where values fall within a narrower 150 mV
range. The additional anodic redox event observed for [1h] is thought to arise as a
result of the strongly electron donating alkynyl fragments and {Ru{P(OEt)3}4}
although assignment to a ligand or metal based process is not obvious.
The plots of E1/2(1) vs Hammett parameter (σp)[52] are decidedly non-linear as is
found for other parameters arising from organometallic metal acetylide
complexes.[53,54] This likely arises from the decidedly mixed (M(d)-C≡C-Ar(π))
electronic character of the metal alkynyl complexes and non-additive effects of trans-
disposed ligands,[3,55] in addition to the effects of solvation and ion-pairing on
electrode potentials that are not well captured by the Hammett parameters. Various
attempts have been made arrive at more ‘electrochemically relevant’ parameters, most
notably those by Lever [56] and Pickett. [57] However, these schemes assume metal-
based oxidation and whilst excellent in the case of Werner-style coordination
complexes and organometallic complexes with well-defined metal-based oxidation
processes, [58] they are largely ill-suited to the ligand-based oxidation processes
associated with complexes such as those described here. [48,59]
2.4 Quantum Chemical Calculations
To better understand the electronic structure of complexes trans-
[Ru(CCR)2{P(OEt)3}4] we turned to quantum chemical calculations of a simplified
model of [1h], in which the ethyl groups of the phosphite ligands were replaced by
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methyl groups. The simplified computational model complex, trans-[Ru(C≡CC6H4-4-
OMe)2{P(OMe)3}4] is denoted [1h’] for clarity. Geometry optimisation (CAM-
B3LYP/LAN2DZ (Ru), 6-31G** all other atoms/COSMO(CH2Cl2) solvent model)
was undertaken with two close lying minima being identified. One of these minima,
denoted planar-[1h’] is remarkably similar to the crystallographically determined
structure (Table 1), with the anisole rings being close to co-planar (θp = 3.9°) and
almost aligned with a Ru-P bond (θa , θaʹ = 21.9, -18.6°). A second minimum, only some
0.99 kJ/mol lower in energy features anisole rings that are essentially orthogonal (θp =
89.9°) and hence denoted perp-[1h’]. Geometries similar to perp-[1h’] are found in the
crystallographic structures of [1d] and [1e] and it is very likely that the structures adopted
in the crystal state owe more to crystal packing then any significant electronic effect.
Plots of the HOMO and LUMO of each conformer are given in Figure 3, and the energy
and composition (%) of key frontier orbitals are given in Table 4. For the lowest energy
conformer, perp-[1h’] a degenerate pair of orbitals that mix the ethynyl ligand π and
Ru(d) orbitals and are distributed over the molecular framework form the HOMO and
HOMO-1. Thus, despite the orthogonal arrangement of the anisole rings, the cosine-like
dependence of the overlap of the anisole π, ethynyl π and Ru(d) orbitals mediates the
extended delocalisation. In the case of planar-[1h’], the HOMO is well removed from the
other orbitals in the occupied manifold, but also delocalised across the molecular
backbone. In each conformer the LUMO is comprised of the ethynyl anisole π* system.
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LUMO
HOMO
Figure 3. Plots of the HOMO and LUMO of planar-[1h’] (left) and perp-[1h’] (right)
with surfaces shown at 0.02 (e/bohr3)1/2.
Table 4. The energy (e / eV) and composition (%) of selected molecular orbitals of
planar-[1h’] and perp-[1h’]
eV
Ru C(1)C(2) C6H4OMe-1a C(3)C(4) C6H4OMe-2b POMe3
planar-[1h’]
LUMO+2
LUMO+1
LUMO
HOMO
HOMO-1
HOMO-2
1.35
1.29
1.14
-6.02 20
-6.49
-6.67 39
0
1
2
1
3
9
21
18
23
49
50
38
21
24
1
0
4
9
18
21
30
48
40
39
18
30
2
1
2
2
2
7
5
0
perp-[1h’]
LUMO+2
LUMO+1
LUMO
HOMO
HOMO-1
HOMO-2
1.35
1.23
1.22
-6.15 18
-6.15 18
-7.16 17
1
2
2
1
12
3
14
26
31
14
67
15
12
25
10
3
3
12
26
14
24
80
15
67
25
12
7
2
2
2
4
4
11
a the anisole group bonded to C(2). b the anisole group bonded to C(4)
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Given the significant contribution of the ethynyl aromatic ligands to the HOMO(s) of
these conformers of [1h’] it is very likely that the one-electron oxidation products of
complexes [1] can be better described in terms of oxidation of the organic ligands,
rather than in terms of Ru(II/III) couples.
3. Conclusion
Complexes of the general form trans-[Ru(C≡CR)2{P(OEt)3}4] are readily obtained
from trans-[RuCl2{P(OEt)3}4], the terminal alkyne HC≡CR and KPF6 in moderate to
good yield, albeit over long reaction times; work-up is simple and the complexes
obtained in good purity, and are readily crystallised. The compounds [1a – h] undergo
a well-behaved one-electron oxidation at potentials only some 100 mV more positive
than the well-known trans-[Ru(C≡CR)2(dppe)2] analogues. Quantum chemical
calculations indicate extended delocalisation of π-type orbitals across the molecular
backbone, which when coupled with the ability to introduce a range of surface
binding groups through the mild synthetic methods described here, makes these
complexes attractive candidates for the further development of metal-containing
molecular wires.
4. Experimental
4.1 General considerations
All reactions were carried out under a dry, high-purity, nitrogen environment using
oven dried (119 °C) glassware and standard Schlenk techniques, although no special
precautions were taken in order to exclude air or moisture during work-up. The
reaction solvent EtOH was dried over dry magnesium turnings and iodine whilst
NHiPr2 was dried over KOH and CH2Cl2 was dried over CaH2. All other solvents
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were reagent grade and used without further purification. The compounds
HC≡CC6H4-4-NO2,[60] HC≡CC6H4-4-CN, HC≡CC6H4-4-CO2Me,[60] HC≡CC6H4-4-
C≡CSiMe3,[26] TlBF4,[61] and trans-[RuCl2{P(OEt)3}4][40] were synthesized by
literature methods. All other reagents were commercially available and used as
received.
NMR spectra were recorded at 25 ° C on Varian Inova 300 (1H, 300.2 MHz; 31P,
121.5 MHz) or Bruker Avance 600 (1H, 600.1 MHz; 13C, 150.9 MHz; 31P, 242.9
MHz) spectrometers. Chemical shifts were determined relative to internal residual
solvent signals (1H, δ = 7.26 ppm; 13C, δ = 77.2 ppm) or external 85% H3PO4 (31P,
δ = 0.0 ppm). [62,63] FT-IR spectra were measured on a Nicolet Avatar 6700 or an
Agilent Technologies Cary 660 spectrophotometer from solutions in CH2Cl2 in a thin
layer cell fitted with CaF2 windows. ESI-MS and APCI-MS were recorded on a
Waters LCT Premier XE mass spectrometer in positive ion mode from solutions in
methanol. Elemental analyses were carried out at London Metropolitan University.
Cyclic voltammetry was carried out using a Versastat 3 potentiostat with a platinum
disc working electrode, a platinum wire counter electrode, and a platinum wire
pseudo-reference electrode, from solutions in CH2Cl2 containing 0.1 M [NnBu4]PF6 as
the electrolyte. Potentials are reported vs. the ferrocene / ferrocenium couple ([Fe(η5-
C5H5)2] / [Fe(η5-C5H5)2]+ = 0 V) using a decamethylferrocene /
decamethylferrocenium internal standard ([Fe(η5-C5Me5)2] / [Fe(η5-C5Me5)2]+ = −
0.48 V).
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4.2 Syntheses of {Ru{P(OEt)3}4} complexes and characterisation data
4.2.1 Synthesis of trans-[Ru(C≡CC4H9)2{P(OEt)3}4], [1a]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.21 g, 0.25 mmol), KPF6 (0.25 g, 1.3 mmol)
and HC≡CC4H9 (0.18 ml, 1.6 mmol) in EtOH (5 ml) and NHiPr2 (2.5 ml) was stirred
under N2 for 15 days (or until all mono-alkynyl was converted to the bis-alkynyl
complex in solution, monitored by unlocked 31P{1H} NMR spectroscopy). The
solution colour changed from yellow to orange / brown over the reaction period and a
white solid precipitated. The reaction solvents were removed under high vacuum,
yielding a brown oily residue. A minimum amount of MeOH (ca. 3 ml) was added to
the residue and solution stirred until a white solid separated out (ca. 5 minutes). The
solution was left in an ice bath for ca. 20 minutes, to complete precipitation, before
filtering. The collected white solid was washed with minimum cold MeOH (3 × 8 ml)
and vacuum dried (0.10 g, 45 %). IR (CH2Cl2, cm-1): 2098 ν(RuC≡C). 1H NMR
(CDCl3, 300 MHz) δ / ppm: 0.83 (t, J = 7 Hz, 6H, H6), 1.19 (t, J = 7 Hz, 36H, CH3,
P(OEt)3), 1.26 (quin., J = 7 Hz, 4H, H4), 1.36 (sex., J = 7 Hz, 4H, H5), 2.10 (t,
J = 7 Hz, 4H, H3), 4.27 (quar., J = 7 Hz, 24H, CH2, P(OEt)3). 31P{1H} NMR (CDCl3,
300 MHz) δ / ppm: 139.5 (s, Ru{P(OEt)3}4). 13C{1H} NMR (CDCl3, 600 MHz)
δ / ppm: 14.2 (s, C6), 16.5 (s, CH3, P(OEt)3), 22.3 (s, C5), 22.4 (s, C3), 33.4 (s, C4),
60.8 (s, CH2, P(OEt)3), 89.9 (quin., J = 20 Hz, C1), 109.3 (s, C2). ESI(+)-MS (m/z):
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929 [Ru(C≡CC4H9)2{P(OEt)3}4 + H]+, 888 [Ru(C≡CC4H9){P(OEt)3}4 + MeCN]+, 879
[Ru(C≡CC4H9){P(OEt)3}4 + MeOH]+, 847 [Ru(C≡CC4H9){P(OEt)3}4]+.
4.2.2 Synthesis of trans-[Ru(C≡CC6H5)2{P(OEt)3}4], [1b]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.15 g, 0.18 mmol), KPF6 (0.13 g, 0.73 mmol)
and HC≡CC6H5 (0.2 ml, excess) in EtOH (5 ml) and NHiPr2 (2 ml) was stirred under
N2 for 11 days (or until all mono-alkynyl converted to the bis-alkynyl complex in
solution, monitored by unlocked 31P{1H} NMR spectroscopy). The solution colour
changed from yellow to orange over the reaction period and a white solid precipitated.
The reaction solvents were removed under high vacuum, yielding an orange / brown
residue. The residue was extracted with minimum CH2Cl2, filtered through Celite to
remove reaction salts and concentrated to dryness by rotary evaporation, yielding an
orange / brown residue. A minimum amount of MeOH (3 ml) was added to the
residue and solution left in the fridge for ca. two hours to aid precipitation of a white
solid. The solid was collected by filtration, washed with cold MeOH (3 × 10 ml) and
air-dried (0.15 g, 85 %). The precipitate may be further purified by recrystallisation
from CH2Cl2 / MeOH layer diffusion, yielding large white crystals suitable for X-ray
crystallography. IR (CH2Cl2, cm-1): 2076 ν(RuC≡C). 1H NMR (CDCl3, 600 MHz)
δ / ppm: 1.21 (t, J = 7 Hz, 36H, CH3, P(OEt)3), 4.31 (quar., J = 7 Hz, 24H, CH2,
P(OEt)3), 6.94 (t, J = 7 Hz, 2H, H6), 7.03 (d, J = 8 Hz, 4H, H4), 7.11 (t, J = 7 Hz, 4H,
H5). 31P{1H} NMR (CDCl3, 300 MHz) δ / ppm: 138.2 (s, Ru{P(OEt)3}4). 13C{1H}
NMR (CDCl3, 600 MHz) δ / ppm: 16.6 (s, CH3, P(OEt)3), 61.0 (s, CH2, P(OEt)3),
113.8 (s, C2), 116.7 (quin., J = 20 Hz, C1), 122.5 (s, C6), 130.1 (s, C4), 131.5 (s, C3).
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ESI(+)-MS (m/z): 969 [Ru(C≡CC6H5)2{P(OEt)3}4]+, 868 [Ru(C≡CC6H5){P(OEt)3}4]+.
Anal. Found: C, 49.37; H, 7.16. Calc for C40H70O12P4Ru: C, 49.57; H, 7.29 %.
4.2.3 Synthesis of trans-[Ru(C≡CC6H4-4-C≡CSiMe3)2{P(OEt)3}4], [1c]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.12 g, 0.15 mmol), KPF6 (0.12 g, 0.65 mmol)
and HC≡CC6H4-4-C≡CSiMe3 (0.089 g, 0.45 mmol) in EtOH (4 ml) and NHiPr2
(1.5 ml) was stirred under N2 for 17 days (or until all mono-alkynyl converted to the
bis-alkynyl complex in solution, monitored by unlocked 31P{1H} NMR spectroscopy).
The solution colour changed from yellow to orange over the reaction period and a
white solid precipitated. The reaction solvents were removed under high vacuum,
yielding a brown oily residue. The residue was extracted with minimum CH2Cl2,
filtered through Celite to removed reaction salts and concentrated to dryness by rotary
evaporation, yielding a brown oily residue. The residue was re-extracted with hexanes
and filtered until extracts ran clear. The hexanes extracts were concentrated to
dryness, yielding an orange solid. The orange solid was extracted a final time with
minimum CH2Cl2 and filtered through a small alumina plug (basic, oven-dried). The
first orange / yellow fraction was collected, concentrated to dryness yielding an
orange solid, washed with minimum cold MeOH (3 × 3 ml) and air-dried (0.072 g,
43 %). Crystals suitable for single crystal X-ray crystallography were grown from a
CHCl3 / MeOH layer diffusion at reduced temperature (− 18 °C). IR (CH2Cl2, cm-1):
2147 ν(C≡CSiMe3), 2068 ν(RuC≡C). 1H NMR (CDCl3, 600 MHz) δ / ppm: 0.22 (s,
18H, SiMe3), 1.18 (t, J = 7 Hz, 36H, CH3, P(OEt)3), 4.27 (quar., J = 7 Hz, 24H, CH2,
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P(OEt)3), 6.91 (d, J = 8 Hz, 4H, H4), 7.21 (d, J = 8 Hz, 4H, H5). 31P{1H}
NMR (CDCl3, 300 MHz) δ / ppm: 137.6 (s, Ru{P(OEt)3}4). 13C{1H} NMR (CDCl3,
600 MHz) δ / ppm: 0.3 (s, SiMe3), 16.6 (s, CH3, P(OEt)3), 61.0 (s, CH2, P(OEt)3),
93.5 (s, C8), 106.5 (s, C7), 114.8 (s, C3), 116.4 (s, C2), 123.3 (quin., J = 20 Hz, C1),
129.8 (s, C4), 131.7 (s, C5). APCI(+)-MS (m/z): 1161 [Ru(C≡CC6H4-4-
C≡CSiMe3)2{P(OEt)3}4 + H]+, 963 [Ru(C≡CC6H4-4-C≡CSiMe3){P(OEt)3}4]+. Anal.
Found: C, 51.90; H, 7.46. Calc. for C50H86O12P4RuSi2: C, 51.71; H, 7.47.
4.2.4 Synthesis of trans-[Ru(C≡CC6H4-4-CO2Me)2{P(OEt)3}4], [1d]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.17 g, 0.20 mmol), KPF6 (0.23 g, 1.2 mmol)
and HC≡CC6H4-4-COOMe (0.21 g, 1.3 mmol) in EtOH (5 ml) and NHiPr2 (2 ml) was
stirred under N2 for 20 days (or until all mono-alkynyl was converted to the bis-
alkynyl complex in solution, monitored by unlocked 31P{1H} NMR spectroscopy).
The solution colour changed from yellow to orange / brown over the reaction period
and a white solid precipitated. The reaction solvents were removed under high
vacuum, yielding a brown oily residue. The residue was extracted with minimum
CH2Cl2, filtered through Celite to remove reaction salts and concentrated to dryness
by rotary evaporation, yielding an orange / brown oily residue. A minimum amount of
MeOH (2.5 ml) was added to the residue and solution left in an ice bath to aid
precipitation of a yellow solid (ca. 30 minutes). The solid was collected by filtration,
washed with minimum cold MeOH (3 × 10 ml) and air-dried (0.12 g, 56 %). Large,
yellow, needle-like crystals, suitable for X-ray crystallography, were grown from a
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CH2Cl2 / MeOH layer diffusion. IR (CH2Cl2, cm-1): 2066 ν(RuC≡C), 1706 ν(C=O),
1594 ν(C=C). 1H NMR (CDCl3, 300 MHz) δ / ppm: 1.19 (t, J = 7 Hz, 36H, CH3,
P(OEt)3), 3.86 (s, 6H, OCH3), 4.28 (quar., J = 7 Hz, 24H, CH2, P(OEt)3), 7.02 (d,
J = 8 Hz, 4H, H4), 7.80 (d, J = 8 Hz, 4H, H5). 31P{1H} NMR (CDCl3, 300 MHz)
δ / ppm: 137.3 (s, Ru{P(OEt)3}4). 13C{1H} NMR (CDCl3, 600 MHz) δ / ppm: 16.5 (s,
CH3, P(OEt)3), 51.9 (s, OCH3), 61.1 (s, CH2, P(OEt)3), 115.4 (s, C2), 123.7 (s, C3),
127.9 (quin., J = 20 Hz, C1), 129.4 (s, C5), 130.0 (s, C4), 136.0 (s, C6), 167.7 (s, C=O).
APCI(+)-MS (m/z): 1085 [Ru(C≡CC6H4-4-COOMe)2{P(OEt)3}4 + H]+, 925
[Ru(C≡CC6H4-4-COOMe){P(OEt)3}4]+. Anal. Found: C, 48.64; H, 6.86. Calc. for
C44H74O16P4Ru: C, 48.70; H, 6.88 %.
4.2.5 Synthesis of trans-[Ru(C≡CC6H4-4-CN)2{P(OEt)3}4], [1e]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.21 g, 0.25 mmol), KPF6 (0.11 g, 0.59 mmol)
and HC≡CC6H4-4-C≡N (0.076 g, 0.60 mmol) in EtOH (4 ml) and NHiPr2 (2 ml) was
stirred under N2 for 1 month. The solution colour changed from yellow to
orange / brown over the reaction period and a white solid precipitated. The reaction
solvents were removed under high vacuum, yielding a brown oily residue. The
residue was extracted with minimum CH2Cl2, filtered through a cotton wool pipette to
remove reaction salts and concentrated to dryness by rotary evaporation, yielding an
orange / brown oily residue. A minimum amount of MeOH (ca. 3 ml) was added to
the residue and solution left to in the fridge for 24 hours to aid precipitation of an
24

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orange solid. The orange solid was collected by filtration, washed with minimum cold
MeOH (3 × 3 ml) and air-dried (0.040 g, 19 %). The precipitate may be further
purified by recrystallisation from CHCl3 / MeOH layer diffusion, yielding yellow
needles suitable for X-ray crystallography. IR (CH2Cl2, cm-1): 2234 ν(C≡N), 2219
ν(C≡N), 2065 ν(RuC≡C), 1606 ν(C=C), 1591 ν(C=C). 1H NMR (CDCl3, 300 MHz)
δ / ppm: 1.19 (t, J = 7 Hz, 36H, CH3, P(OEt)3), 4.25 (quar., J = 7 Hz, 24H, CH2,
P(OEt)3), 7.01 (d, J = 8 Hz, 4H, H4), 7.37 (d, J = 8 Hz, 4H, H5). 31P{1H}
NMR (CDCl3, 300 MHz) δ / ppm: 136.8 (s, Ru{P(OEt)3}4). 13C{1H} NMR (CDCl3,
600 MHz) δ / ppm: 16.5 (s, CH3, P(OEt)3), 61.1 (s, CH2, P(OEt)3), 104.9 (s, C2), 115.1
(s, C3), 120.4 (s, CN), 130.2 (s, C4), 131.6 (quin., J = 20 Hz, C1), 131.9 (s, C5), 135.5
(s, C6). ESI(+)-MS (m/z): 1019 [Ru(C≡CC6H4-4-C≡N)2{P(OEt)3}4 + H]+.
4.2.6 Synthesis of trans-[Ru(C≡CC6H4NO2)2{P(OEt)3}4], [1f]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.10 g, 0.12 mmol), KPF6 (0.086 g,
0.47 mmol) and HC≡CC6H4-4-NO2 (0.044 g, 0.30 mmol) in EtOH (5 ml) and NHiPr2
(2 ml) was stirred under N2 for 24 days. The solution colour changed from orange to
brown over the reaction period and a white solid precipitated. The reaction solvents
were removed under high vacuum, yielding a dark red oily residue, which was
purified by column chromatography (silica, 90 : 10, hexanes : acetone). The first
bright red / orange band was collected and solvent removed to yield the product as a
bright red precipitate (0.075 g, 59 %). Crystals suitable for single crystal X-ray
crystallography were obtained by slow evaporation from CH2Cl2 at reduced
25

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temperature (− 18 °C). IR (CH2Cl2, cm-1): 2054 ν(RuC≡C), 1584 ν(N=O), 1324 ν(N-
O). 1H NMR (CDCl3, 600 MHz) δ / ppm: 1.21 (t, J = 7 Hz, 36H, CH3, P(OEt)3), 4.25
(quar., J = 7 Hz, 24H, CH2, P(OEt)3), 7.03 (d, J = 9 Hz, 4H, H4), 8.02 (d, J = 9 Hz,
4H, H5). 31P{1H} NMR (CDCl3, 600 MHz) δ / ppm: 136.2 (s, Ru{P(OEt)3}4).
13C{1H} NMR (CDCl3, 600 MHz) δ / ppm: 16.5 (s, CH3, P(OEt)3), 61.1 (s, CH2,
P(OEt)3), 102.2 (quin., J = 21 Hz, C1), 116.9 (s, C2), 124.0 (s, C5), 129.9 (s, C4), 137.9
(s, C3), 142.8 (s, C6). ESI(+)-MS (m/z): 1058 [Ru(C≡CC6H4-4-NO2)2{P(OEt)3}4]+,
953 [Ru(C≡CC6H4-4-NO2){P(OEt)3}4 + MeCN]+, 912 [Ru(C≡CC6H4-4-
NO2){P(OEt)3}4]+. Anal. Found: C, 45.46; H, 6.50; N, 2.67. Calc. for
C40H68N2O16P4Ru: C, 45.36; H, 6.48; N, 2.65 %.
4.2.7 Synthesis of trans-[Ru(C≡CC6H4-4-C5H11)2{P(OEt)3}4], [1g]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.19 g, 0.22 mmol), KPF6 (0.14 g, 0.75 mmol)
and HC≡CC6H4-4-C5H11 (0.22 ml, 1.13 mmol) in EtOH (5 ml) and NHiPr2 (2 ml) was
stirred under N2 for 17 days (or until all mono-alkynyl converted to the bis-alkynyl
complex in solution, monitored by unlocked 31P{1H} NMR spectroscopy). The
solution colour changed from yellow to orange over the reaction period and a white
solid precipitated. The reaction solvents were removed under high vacuum, yielding a
brown residue. The residue was extracted with minimum CH2Cl2, filtered through
Celite to remove reaction salts and concentrated to dryness by rotary evaporation,
yielding a brown residue. A minimum amount of EtOH (2.5 ml) was added to the
26

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residue and solution stirred in an ice bath until a yellow solid separated out (ca. 30
minutes). The solid was collected by filtration, washed with minimum cold EtOH
(3 × 5 ml) and vacuum dried (0.083 g, 34 %). Large white crystals, suitable for X-ray
crystallography, were grown from CDCl3 / EtOH layer diffusion. IR (CH2Cl2, cm-1):
2076 ν(RuC≡C), 1602 ν(C=C). 1H NMR (CDCl3, 600 MHz) δ / ppm: 0.89 (t,
J = 7 Hz, 6H, H11), 1.20 (t, J = 7 Hz, 36H, CH3, P(OEt)3), 1.29 − 1.37 (m, 8H, H8 and
H10), 1.58 (quin., J = 7 Hz, 4H, H9), 2.51 (t, J = 7 Hz, 4H, H7), 4.32 (quar., J = 7 Hz,
24H, CH2, P(OEt)3), 6.92 (d, J = 8 Hz, 4H, H5), 6.94 (d, J = 8 Hz, 4H, H4). 31P{1H}
NMR (CDCl3, 300 MHz) δ / ppm: 138.4 (s, Ru{P(OEt)3}4). 13C{1H} NMR (CDCl3,
600 MHz) δ / ppm: 14.2 (s, C11), 16.6 (s, CH3, P(OEt)3), 23.0 (s, C8 or C10), 31.3 (s,
C9), 31.9 (s, C8 or C10), 35.9 (s, C7), 61.0 (s, CH2, P(OEt)3), 113.5 (s, C2), 114.2 (quin.
J = 21 Hz, C1) 127.8 (s, C5), 128.9 (s, C3), 129.9 (s, C4), 136.9 (s, C6). APCI(+)-MS
(m/z): 1109 [Ru(C≡CC6H4-4-C5H11)2{P(OEt)3}4 + H]+, 937 [Ru(C≡CC6H4-4-
C5H11){P(OEt)3}4]+, 771 [Ru(C≡CC6H4-4-C5H11){P(OEt)3}3]+, 605 [Ru(C≡CC6H4-4-
C5H11){P(OEt)3}2 + H]+. Anal. Found: C, 54.23; H, 8.09. Calc. for C50H90O12P4Ru: C,
54.13; H, 8.18 %.
4.2.8 Synthesis of trans-[Ru(C≡CC6H4-4-OMe)2{P(OEt)3}4], [1h]
A mixture of trans-[RuCl2{P(OEt)3}4] (0.11 g, 0.13 mmol), KPF6 (0.087 g,
0.47 mmol) and HC≡CC6H4-4-OMe (0.3 ml, excess) in EtOH (5 ml) and NHiPr2
(2 ml) was stirred under N2 for 14 days (or until all mono-alkynyl was converted to
the bis-alkynyl complex in solution, monitored by unlocked 31P{1H} NMR
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spectroscopy). The solution colour changed from yellow to orange over the reaction
period and a white solid precipitated. The reaction solvents were removed under high
vacuum, yielding a brown oily residue. The residue was extracted with minimum
CH2Cl2, filtered through Celite to remove reaction salts and concentrated to dryness
by rotary evaporation, yielding a brown oil. A minimum amount of MeOH (3 ml) was
added to the oily residue, solution stirred for ca. two minutes and left in the fridge for
ca. 1 hour, where a white solid was formed. The solid was collected by filtration,
washed with cold MeOH (3 × 10 ml) and air-dried (0.095 g, 72 %). Crystals suitable
for single crystal X-ray crystallography were grown via slow evaporation of a
CH2Cl2 / hexanes solution. IR (CH2Cl2, cm-1): 2077 ν(RuC≡C), 1501 ν(C-O). 1H
NMR (CDCl3, 600 MHz) δ / ppm: 1.20 (t, J = 7 Hz, 36H, CH3, P(OEt)3), 3.75 (s, 6H,
OCH3), 4.32 (quar., J = 7 Hz, 24H, CH2, P(OEt)3), 6.68 (d, J = 8 Hz, 4H, H4), 6.96 (d,
J = 8 Hz, 4H, H5). 31P{1H} NMR (CDCl3, 300 MHz) δ / ppm: 138.4 (s,
Ru{P(OEt)3}4). 13C{1H} NMR (CDCl3, 600 MHz) δ / ppm: 16.6 (s, CH3, P(OEt)3),
55.3 (s, OCH3), 61.0 (s, CH2, P(OEt)3), 112.1 (quin., J = 19 Hz, C1), 112.5 (s, C2),
113.4 (s, C4), 124.6 (s, C3), 130.8 (s, C5), 155.5 (s, C6). ESI(+)-MS (m/z): 1028
[Ru(C≡CC6H4-4-OMe)2{P(OEt)3}4]+, 938 [Ru(C≡CC6H4-4-OMe){P(OEt)3}4 +
MeCN]+, 897 [Ru(C≡CC6H4-4-OMe){P(OEt)3}4]+. Anal. Found: C, 48.94; H, 7.32.
Calc. for C42H74O14P4Ru: C, 49.01; H, 7.25 %.
4.3 Crystallography
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[64] ([1b] and [1h]) or SHELXL-2014.[65] All hydrogen atoms were
added at calculated positions and refined by use of a riding model with isotropic
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