Iron: Vs. ruthenium: Syntheses, structures and IR spectroelectrochemical characterisation of half-sandwich Group 8 acetylide complexes

Article abstract of DOI:10.1039/d0nj03093g

A convenient modification to the established synthetic routes for the preparation of complexes [M(CCR)(dppe)Cp′] (M = Fe, Ru; Cp′ = η5-C5H5 (Cp), η5-C5Me5 (Cp?); R = C6H5, C6H4-p-OMe, C6H4-p-NO2, tBu) and [Ru(CCR)(PPh3)2Cp] from the corresponding [MCl(PP)Cp′] complex and the alkyne HCCR via an intermediate vinylidene is described. The complexes are generally obtained as high quality crystalline samples directly from the reaction mixture. In agreement with previous studies, the iron complexes undergo a predominantly metal-centred oxidation, whilst there is greater involvement of the acetylide ligand in the oxidation processes associated with the ruthenium analogues. Analysis of the redox properties and spectroelectrochemical investigations reveal limited differences in the gross electronic structures of the Cp vs. Cp? derivatives in each of the Fe and Ru series. This journal is

Full text of DOI:10.1039/d0nj03093g

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Iron vs Ruthenium: Syntheses, structures and IR spectroelectrochemicalDOI: 10.1039/D0NJ03093G
characterisation of half-sandwich Group 8 acetylide complexes†
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Daniel P. Harrison,‡ Varshini Jayantha Kumar,‡ Johanna N. Noppers, Josef B.G.
Gluyas, Alexandre N. Sobolev, Stephen A. Moggach, Paul J. Low*
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School of Molecular Sciences, University of Western Australia, 35 Stirling Highway,
Crawley, Western Australia, 6009, Australia
*Corresponding author: paul.low@uwa.edu.au
‡ These authors contributed equally
† Dedicated to Professor Todd B. Marder, colleague, friend, mentor and raconteur, in
recognition of his outstanding contributions to chemistry.
Abstract
A convenient modification to the established synthetic routes for the preparation of
complexes [M(C≡CR)(dppe)Cpʹ] (M = Fe, Ru; Cpʹ = η5-C5H5 (Cp), η5-C5Me5 (Cp*);
R = C6H5, C6H4OMe, C6H4NO2, tBu) and [Ru(C≡CR)(PPh3)2Cp] from the
corresponding [MCl(PP)Cpʹ] complex and the alkyne HC≡CR via an intermediate
vinylidene is described. The complexes are generally obtained as high quality
crystalline samples directly from the reaction mixture. In agreement with previous
studies, the iron complexes undergo a predominantly metal-centred oxidation, whilst
there is greater involvement of the acetylide ligand in the oxidation processes
associated with the ruthenium analogues. Analysis of the redox properties and
spectroelectrochemical investigations reveal limited differences in the gross electronic
structures of the Cp vs Cp* derivatives in each of the Fe and Ru series.
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Introduction
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The isomerization of alkynes to vinylidenes within the coordination sphere of half-
sandwich Group 8 metal acetylide complexes bearing ancillary phosphine ligands has
provided access to a range of fascinating stoichiometric and catalytic organometallic
chemistry.1-7 In turn, deprotonation of terminal vinylidene complexes
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[M{C=C(H)R}(PP)Cp´]+ (M = Fe, Ru, Os; R = H, alkyl, aryl; PP = bis(mono) or
chelating diphosphine; Cp´ = Cp, Cp*) has been identified as the preferred route for
the preparation of metal acetylide complexes of general form [M(C≡CR)(PP)Cp´].8
Complementary to this approach, the in situ desilylation / metallation reactions of
[MCl(PP)Cp´] with trimethylsilyl-protected alkynes (Me3SiC≡CR) in the presence of
a fluoride source have also proven immensely useful.9 In the case of complexes
[Fe(C≡CAr)(dppe)Cp*] (Ar = aryl), Sonogashira-style cross-couplings of aryl halides
with [Fe(C≡CH)(dppe)Cp*] have also been shown to provide a useful synthetic
pathway to these compounds.10
The acetylide species [M(C≡CR)(PP)Cp´] are, in general, readily oxidized at modest
potentials to the radical cations, [M(C≡CR)(PP)Cp´]+. The characteristic shifts in the
ν(C≡C) bands on oxidation provide a clear diagnostic measure for the site of
oxidation, with the larger shifts observed in ruthenium11, 12 and osmium13 complexes
indicating a greater alkynyl ligand based oxidation process than the more metal-
centred processes that take place with the iron analogues.14 These synthetic,
electrochemical and spectroscopic properties have made iron and ruthenium
{M(C≡CR)(PP)Cp´} fragments exceptionally popular building blocks for the
construction and study of ligand-bridged bi- and polymetallic systems, which are
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ideal for the further study of mixed-valence derivatives and associated investigations View Article Online
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of intramolecular electron-transfer processes.15-21
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In this contribution we describe a simple modification to the preparation of iron and
ruthenium acetylide complexes, [M(C≡CR)(PP)Cp´], which allows the one-pot
preparation and isolation of pure material, often as single-crystals suitable for X-ray
diffraction, directly from the reaction vessel. We have taken advantage of the series so
prepared to collect systematic electrochemical, IR spectroelectrochemical and
structural benchmarking data to facilitate further studies of mixed-valence complexes
based on these fragments that are of contemporary interest.
Results and Discussion
Routes to [Fe(C≡CR)(dppe)Cp*] complexes
The synthetic routes reported to date for complexes [Fe(C≡CR)(dppe)Cp*] from the
halide complex [FeCl(dppe)Cp*]22 are illustrative of a range of the potential routes
that have been employed in the preparation of half-sandwich acetylide complexes of
the Group 8 metals. In an early report, the compound [Fe(C≡CPh)(dppe)Cp*] was
prepared in two-steps, with initial reaction of [Fe(NCMe)(dppe)Cp*]PF6 and
HC≡CPh giving the vinylidene [Fe{C=C(H)Ph}(dppe)Cp*]PF6 which could be
isolated (55%) and subsequently deprotonated. Purification of the acetylide complex
was achieved by column chromatography and low temperature crystallization gave
[Fe(C≡CPh)(dppe)Cp*] in 47% yield.23 The reaction of [FeCl(dppe)Cp*] with a
terminal alkyne, HC≡CR, in a polar medium (e.g. methanol) in the presence of a salt
which serves as a halide anion abstractor (e.g. NH4PF6) over periods of typically 12
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hours or more also gives the vinylidene complexes [Fe{C=C(H)R}(dppe)Cp*](PF6)
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(87 – 97%), which can be isolated or deprotonated in situ to give
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[Fe(C≡CR)(dppe)Cp*] (80 – 98%).24
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Photochemical ligand exchange reactions have also been demonstrated to give similar
complexes from [FeCl(CO)2Cp*], dppe, a terminal aryl alkyne and DBU.25 The
reaction likely proceeds via initial carbonyl dissociation and formation of the carbonyl
cation, [Fe(CO)(dppe)Cp*]+ before a second photochemical displacement of the
remaining carbonyl ligand to create the vacant coordination site for binding and
isomerization of the alkyne ligand to give the vinylidene complexes. Subsequent
deprotonation gave the acetylide complexes [Fe(C≡CR)(dppe)Cp*] in moderate to
good yield (28 – 79%) in an overall two-step, one pot process; a higher yield (92%) of
[Fe(C≡CPh)(dppe)Cp*] was obtained when the reaction with HC≡CPh was carried
out in stepwise two-step, two-pot fashion. Alternatively, metalla-Sonogashira
reactions26 of [Fe(C≡CH)(dppe)Cp*] with aryl halides, ArBr, catalyzed by Pd/Cu co-
catalysts in amine solvents have also proven useful;10, 25 indeed many examples of
functionalized arylacetylide complexes [Fe(C≡CAr)(dppe)Cp*] have been prepared
by this route and isolated in yields from 30 – 71%.10 Regardless of the method of
preparation, the oxidation of [Fe(C≡CR)(dppe)Cp*] complexes at low potentials and
the relatively high basicity of the C(β) carbon creates difficulties in isolating pure
samples of these compounds, leading to numerous descriptions of purification
procedures in the literature.
Routes to [Fe(C≡CR)(dppe)Cp] complexes
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Synthetic routes to Fe(C≡CR)(dppe)Cp complexes have been amply demonstrated
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from [FeCl(dppe)Cp]27 and [FeI(PP)Cp] (PP = dppe, (R)-(+)-1,2-
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bis(diphenylphosphino)propane ((R)-PROPHOS))28 using a variety of halide
abstracting agents, including NH4PF629 and AgBF4.30 Astruc has described a simple
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visible-light driven photolysis reaction of [FeCp(η6-C6H5Me)]PF6 with terminal
alkynes in the presence of dppe to give [Fe(C≡CR)(dppe)Cp] complexes in near
quantitative yields,31 whilst photolysis of [Fe(CO)(dppe)Cp]BF4 with alkynes gives
the corresponding vinylidenes,32 and photolytic carbonyl-phosphine exchange of
[Fe(C≡CR)(CO)2Cp] gives [Fe(C≡CR)(dppe)Cp] complexes (24% in the case of
[Fe(C≡CCH2CH2CN)(dppe)Cp]).33 Transmetallation of the alkynyl ligand from
[Au(C≡CAr)(PPh3)] to [FeCl(dppe)Cp] (Ar = Ph, C6H5Me) has also provided route to
acetylide complexes [Fe(C≡CAr)(dppe)Cp] in moderate (43 – 54%) yield.34
Routes to [Ru(C≡CR)(dppe)Cp*] complexes
Although early preparations of complexes [Ru(C≡CR)(dppe)Cp*] described the
formation of the intermediate vinylidene from [RuCl(dppe)Cp*] and a terminal
alkyne in methanol without any additional halide abstracting agent affording the
products in 40 – 64% yield,23 the great majority of subsequent reports have utilized
NH4PF6 or similar species as a co-reagent in the preparation of the intermediate
vinylidene.11, 12, 35-48 The effective use of the metallo-Sonogashira reaction in the
preparation of such complexes has also been described, giving complexes in 20-80%
yield,11 whilst transmetallation from [Au(C≡CAr)(PPh)3] to [RuCl(dppe)Cp*] has
also been demonstrated giving [Ru(C≡CAr)(dppe)Cp*] (ca. 50%).34 The in situ
desilylation/metallation reaction has also proven to be effective for a wide variety of
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alkynyl ligand substituents,9 with the complexes often precipitating cleanly as
microcrystalline powders during the course of the reaction.38, 43, 49-60
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Routes to [Ru(C≡CR)(dppe)Cp]
The synthetic chemistry of [Ru(C≡CR)(dppe)Cp] complexes is similar to that of
complexes [Ru(C≡CR)(dppe)Cp*]. Many of the examples of complexes
[Ru(C≡CR)(dppe)Cp] reported to date have been prepared via deprotonation of the
corresponding vinylidene, obtained from [RuCl(dppe)Cp], a halide abstracting agent
and the appropriate terminal alkyne.27, 38, 61, 62 However, the desilylation/metallation
route has also proven effective with the complexes precipitating cleanly from the
methanol reaction solution, and has become a route of choice in recent times.38, 63, 64
Routes to [Ru(C≡CR)(PPh3)2Cp]
Complexes [Ru(C≡CR)(PPh3)2Cp] are perhaps the archetypal members of the family
of half-sandwich Group 8 metal acetylide complexes. These compounds are almost
universally prepared via deprotonation of an intermediate vinylidene complex, formed
from [RuCl(PPh3)2Cp] and the terminal alkyne in a polar solvent such as methanol.
The initial report described the preparation of [Ru(C≡CPh)(PPh3)2Cp], which was
isolated in 87% yield, via deprotonation of the vinylidene
[Ru{C=C(H)Ph}(PPh3)2Cp]Cl formed in situ from [RuCl(PPh3)2Cp] and HC≡CPh in
methanol.65 Analogous procedures were found effective in later studies.66-70 However,
the addition of halide abstracting agents such as NH4PF6, NaBPh4, or other similar
compound within the reaction mixture has become commonplace in many synthetic
schemes.12, 36, 38, 42, 43, 45, 68, 71-86 Desilylation / metallation strategies have also proven
effective9 the complexes generally being isolated by precipitation from the methanol
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reaction medium and purified by column chromatography. Transmetallation reactions
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from gold acetylides have also been demonstrated for this metal ligand group.34
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A simplified synthetic procedure
From the brief summaries above, it is apparent that the rearrangement of terminal
alkynes to vinylidenes within the coordination sphere of half-sandwich metal
complexes {M(PP)Cpʹ}+ fragments provides a convenient entry to the chemistry of
metal acetylide complexes [M(C≡CR)(PP)Cpʹ]. The very early literature indicates that
the formation of [M{C=C(H)R}(PP)Cpʹ]+ complexes can take place directly from
[MCl(PP)Cpʹ] and the alkyne in a polar solvent such as methanol,23, 65 with the
ionization of the M-Cl bond apparently sufficient under such conditions to be
displaced by the alkyne ligand. Over the intervening years, it has become more
common to run these reactions in the presence of a ‘halide abstracting agent’,
although the true importance of such co-reagents is perhaps due for re-consideration.
Certainly if the vinylidene complex is to be isolated then the metathesis of the smaller
–
–
chloride counter ion for a larger PF6 , BPh4 or other example is to be recommended.
However, for the formation of the vinylidene and deprotonation in situ it is less clear
if the co-reagent is necessary.
Here, we have explored the direct reactions of the half-sandwich chloride complexes
[FeCl(dppe)Cp*], [FeCl(dppe)Cp], [RuCl(dppe)Cp*], [RuCl(dppe)Cp] and
[RuCl(PPh3)2Cp] with HC≡CPh, HC≡CC6H4-p-OMe, HC≡CC6H4-p-NO2 and
HC≡CtBu as representative terminal acetylenes. The reactions are typically carried out
in a small volume of laboratory grade methanol, which was degassed by sparging
with nitrogen before use, but not specially dried. The reactions proceeded readily
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under reflux to give solutions containing the appropriate vinylidene over the cDoOuI:r1s0e.10o3f9/D0NJ03093G
ca. 1 – 2 hours, with only the formation of [Ru{C=C(H)tBu}(dppe)Cp] taking
somewhat longer (5h) (Scheme 1). The progress of the reaction was followed by the
dissolution of the [MCl(PP)Cpʹ] reagent, the pronounced colour changes
accompanying vinylidene formation and in situ 31P{1H} NMR monitoring indicating
the clean transformation of the chloride [MCl(PP)Cpʹ] to [M{C=C(H)R}(PP)Cpʹ]Cl
complexes.
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1) HC CR
M Cl
PPh2
M C C R
PPh2
2) DBU
Ph2P
Ph2P
Ph3P
Ph2P
M = Fe (1), Ru(3)
1) HC CR
2) DBU
M Cl
PPh2
M C C R
Ph2P
PPh2
M = Fe (2), Ru(4)
1) HC CR
2) DBU
Ru Cl
PPh3
Ru C C R
Ph3P
PPh3
(5)
R
a
C6H5
b
c
d
C6H4OMe-4
C6H4NO2-4
But
Scheme 1. The preparation of complexes [1a-d] – [5a-d]
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The conversion of the vinylidene to the acetylide and work-up was achieved sDimOI:p1l0y.1039/D0NJ03093G
by stopping the stirring and heating of the reaction mixture, and then allowing a drop
of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) to slowly diffuse into the hot solution.
As the reaction solution cooled, the acetylide products crystallised, often in a form
suitable for single-crystal X-ray diffraction, and were isolated in 50 – 88% yield by
simple filtration. However, the complex [Ru(C≡CC6H4-p-NO2)(dppe)Cp] (4c)
proved to be rather more soluble in methanol and sensitive to methoxide addition at
C(α) to give the methoxy carbene [Ru{C(OMe)CH2C6H4-p-NO2}(dppe)Cp]+. In this
case, work-up necessitated purification by preparative TLC.
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Each of the complexes was characterised by the usual array of NMR spectroscopies
(1H, 13C{1H}, 31P{1H}), IR spectroscopy and mass spectrometry, with data generally
consistent with that available in the literature. The 31P{1H} NMR data were
particularly diagnostic of the various metal fragments, falling near 99 (1), 106 (2), 81
(3), 86 (4) and 51 (5) ppm. Much more subtle variations were observed as a function
of the acetylide substituent, with the 31P{1H} NMR resonances of the tBu complexes
d falling somewhat downfield of the aryl compounds a – c in each series. The
assignments of the 13C{1H} NMR data were made on the basis of 1H-13C{1H} COSY
spectra and the JCP coupling constants in the case of C(α) (Table S1). The C(α)
resonances of the acetylide ligands in the complexes [M(C≡CR)(PP)Cp´] were more
sensitive to the electronic nature of the R group, falling in sequence δ(C(α)) / ppm c
(R = C6H4-p-NO2) > a (R = C6H5) > b (R = C6H4-p-OMe) > d (R = tBu).
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The 13C{1H} NMR chemical shift of aromatic hydrocarbons can be estimatedDfOroI: m10.1039/D0NJ03093G
simple additive relationships and well-defined, but empirical, substituent specific
parameters, zi (Equation 1, Table 1)
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!! = 128.5 +
!
(1)
!
Table 1. NMR substituent parameters for Equation 1.
R
1
2
3
4
z1
z2
z3
z4
R
H
0
0
0
0
OMe 30.2 -14.7 0.9
NO2 19.6 -5.3 0.8
-8.1
6.0
tBu
22.1 -3.4 -0.4 -3.1
Cp*(dppe)Fe C C
2.1 3.2
1.5 1.9
-1.0 -5.3
-1.0 -5.5
Cp(dppe)Fe C C
Cp*(dppe)Ru C C
Cp(dppe)Ru C C
Cp(Ph3P)2Ru C C
3.0 1.8
1.4 2.0
2.2 2.1
-0.9 -5.9
-1.4 -5.6
-0.7 -5.4
From this expression, the associated substituent parameters, zi, of the metal acetylide
fragments were estimated from the 13C{1H} chemical shifts of complexes 1a, 2a, 3a,
4a and 5a (Table 1). The additive relationship of Equation 1 were found to hold
remarkably well for the metal arylacetylide complexes [1b,c] – [5b,c] (Table 2),
giving further confidence in the assignments proposed (Table S1).
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Table 2. Summary of experimental and estimated 13C{1H} NMR data (C1, C2, C3,
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C4) of compounds [1b,c] – 5b,c].a
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C1
C2
C3
C4
Exp
Calc
Exp
Calc
Exp
Calc
Exp
Calc
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48
49
50
51
52
53
54
55
56
57
58
59
60
1bb
1cc
2bc
2cb
3bc
3cc
4bc
4cc
5bc
5cc
124.8 122.5 131.5 132.6 114.1 112.8 156.7 153.4
137.7 136.6 129.7 132.5 124.0 122.2 141.8 141.8
124.3 121.9 131.7 131.3 113.6 112.8 156.7 153.2
136.8 136.0 130.3 131.2 123.7 122.2 143.4 142.6
124.5 123.4 131.2 131.2 113.3 112.9 155.7 152.8
138.5 137.5 130.0 131.1 123.6 122.3 142.1 142.2
123.1 121.8 131.7 131.4 113.0 112.4 156.0 153.1
137.4 135.9 130.5 131.3 123.3 121.8 142.7 142.7
123.8 122.6 131.5 131.5 113.4 113.1 156.0 153.4
137.7 136.6 130.5 129.7 123.8 122.2 142.8 142.8
a estimated values from Equation 1 and data in Table 1. b experimental data in C6D6
solution. b experimental data in CDCl3 solution.
Molecular Structures
The molecular structures of the compounds 1a-d – 5a-d have been determined, here
or previously (Table 3, Figures S83 – S91). A survey of the key bond lengths give in
Table 1 indicates some important trends across the series and within each sub-group.
The {M(dppe)Cp} (M = Fe, Ru) fragments are rather more compact than the
{M(dppe)Cp*} analogues, and despite the more electron-donating nature of the Cp*
fragment, the average M-P distances are marginally shorter in the Cp systems. This
may suggest that intramolecular steric interactions between the Cp* and dppe ligands
over-ride any increase in the M-P back-bonding contribution arising from the more
electron-rich metal fragment with respect to comparisons of {M(dppe)Cp} and
{M(dppe)Cp*} complexes.
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Metal-acetylide back-bonding is thought to play only a small role in the overall
electronic structure of metal acetylide complexes,87 and direct analyses of electronic
trends in the π-framework as a simple function of bond lengths can be complicated by
underlying effects arising from the σ-system and bond polarization.88 Within the
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relatively precise experimental data set in Table 3 (Figure 1), the M-C(α) and
C(α)≡C(β) bond lengths are essentially insensitive to the nature of the Cp´ ligand in
each pair of complexes [M(C≡CC6H4Y)(dppe)Cp´]. Comparisons of the structural
data from the Y = OMe and NO2 series hints at a degree of increased cumulenic
character along the M-C≡C-C6H4-NO2 backbone. However, the greatest indication of
the variation in electron density at the metal centre induced by the electron-donating
(Y = OMe), electron-neutral (Y = H) or electron-withdrawing (Y = NO2) group comes
from the most precisely determined M-P bond lengths.76 The systematic elongation of
these bonds within each sub-set of complexes (e.g. M-P 1b < 1a < 1c) is consistent
with the overall decrease in electron density at the metal centre and diminished M-P
back-bonding.
M C C C1
C Y
4
α
β
C2
P1
P2
Figure 1. The atom labeling scheme used in Table 3.
12

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Table 3. Selected bond lengths (Å), bond and torsion angles (º) from the crystallographically determined structures of 1a-d – 5a-d.
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M-P1
M-P2
C(4)-Y
P1-M-P2
85.92(4)
86.80(6)
83.73(4)
83.3(1)
100.9(1)
86.50(2)
86.88(4)
83.01(2)
84.03(4)
99.18(2)
86.56(3)
Ref
M-C(α)
1.894(3)
C(α)-C(β) C(β)-C(1)
10
1a 2.1857(10) 2.1745(9)
2a 2.1618(17) 2.1577(16) 1.908(6)
3a 2.2622(12) 2.2563(12) 2.011(4)
4a 2.240(1)
5a 2.307(1)
1b 2.1789(6)
2b 2.1611(11) 2.1752(11) 1.900(4)
3b 2.2652(6) 2.2643(6) 2.015(2)
4b 2.2461(12) 2.2599(12) 2.023(5)
5b 2.2922(6)
1c 2.1911(8)
2c 2.158(2)
3c 2.2639(6)
4c 2.2525(8)
5c 2.297(2)
1.210(4)
1.205(8)
1.215(5)
1.204(5)
1.214(7)
1.215(3)
1.217(6)
1.216(3)
1.203(6)
1.212(3)
1.220(4)
1.430(4)
1.443(8)
1.431(5)
1.444(5)
1.462(8)
1.437(3)
1.446(6)
1.433(3)
1.444(6)
1.442(3)
1.419(4)
[Fe(C≡CPh)(dppe)Cp*]
[Fe(C≡CPh)(dppe)Cp]a
this work
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11
[Ru(C≡CPh)(dppe)Cp*]
[Ru(C≡CPh)(dppe)Cp]
[Ru(C≡CPh)(PPh3)2Cp]
89
89
90
2.250(1)
2.294(1)
2.1884(6)
2.009(3)
2.017(5)
1.899(2)
1.382(3)
1.369(5)
1.379(3)
1.378(5)
1.378(3)
1.455(4)
[Fe(C≡CC6H4OMe-4)(dppe)Cp*]
[Fe(C≡CC6H4OMe-4)(dppe)Cp]
[Ru(C≡CC6H4OMe-4)(dppe)Cp*]
[Ru(C≡CC6H4OMe-4)(dppe)Cp]
[Ru(C≡CC6H4OMe-4)(PPh3)2Cp]b
[Fe(C≡CC6H4NO2-4)(dppe)Cp*]
[Fe(C≡CC6H4NO2-4)(dppe)Cp]
[Ru(C≡CC6H4NO2-4)(dppe)Cp*]
[Ru(C≡CC6H4NO2-4)(dppe)Cp]
[Ru(C≡CC6H4NO2-4)(PPh3)2Cp]
[Fe(C≡CBut)(dppe)Cp*]
this work
11
this work
81
2.2902(5)
2.1857(8)
2.157(2)
2.2721(6)
2.2463(8)
2.301(2)
2.019(2)
1.876(3)
1.856(8)
2.001(3)
1.993(3)
1.994(5)
10
28
1.216(10) 1.442(11) 1.450(13) 85.15(8)
1.218(4)
1.214(4)
1.202(8)
1.208(7)
1.123(3)
1.215(6)
1.198(3)
1.424(4)
1.424(4)
1.432(7)
1.490(7)
1.483(3)
1.482(6)
1.478(3)
1.478(2)
1.452(3)
1.451(4)
1.468(6)
83.77(2)
84.91(3)
101.17(7)
85.96(6)
86.94(2)
82.13(4)
83.53(2)
this work
61
66
1d 2.1557(15) 2.1762(15) 1.912(5)
this work
this work
this work
this work
[Fe(C≡CBut)(dppe)Cp]b
2d 2.1472(7)
3d 2.2440(9)
4d 2.2463(6)
5d 2.2807(4)
2.1557(7)
2.2527(11) 2.015(4)
2.2528(6)
2.2815(4)
1.920(2)
[Ru(C≡CBut)(dppe)Cp*]
[Ru(C≡CBut)(dppe)Cp]
2.019(2)
2.0224(18) 1.207(2)
[Ru(C≡CBut)(PPh3)2Cp]
102.57(2) this work
a data from one of four molecules in the unit cell data from one of two molecules in the unit cell
b
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Electrochemistry and Spectroelectrochemistry
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A number of previous studies have explored trends in electrochemical potential of
complexes [M(C≡CR)(PP)Cpʹ] as a function of the alkynyl group substituent, R.10, 11
However, fewer studies have looked at the comparative redox potentials of such
complexes as a function of the different {M(PP)Cpʹ} fragments. Here, the family of
complexes 1a-d – 5a-d offer an opportunity to benchmark the electrochemical
potentials of the five readily available half-sandwich complex types over a range of
alkynyl substituents and permit comparisons of the relative behavior (Table 4)
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Table 4. Electrochemical potentials (E1/2 / V vs Fc/Fc+) for complexes 1a-d – 5a-d
(CH2Cl2 / 0.1 M NBu4PF6)
tBu
C6H4-p-OMe Ph
C6H4-p-NO2
–0.46
Fe(dppe)Cp*
Fe(dppe)Cp
–0.76
–0.54
–0.67
–0.46
–0.31
–0.17
–0.12
–0.63
–0.40
–0.24
–0.09
–0.03
–0.27
Ru(dppe)Cp* –0.35
–0.08
Ru(dppe)Cp
Ru(PPh3)2Cp
–0.19
–0.10
+0.08
+0.14
Each complex undergoes a largely electrochemically and chemically reversible one-
electron oxidation process in room temperature solution (CH2Cl2 / 0.1 M NBu4PF6) at
moderate potential vs ferrocene/ferricenium [E1/2(Fc/Fc+) = 0 V] at a platinum
working electrode (Table 2, Figure S1). The anodic and cathodic current ratios of the
{Ru(PPh3)2Cp} series (5) indicates some degree of chemical instability in the
oxidized products, but linear plots of peak currents against ν1/2 are consistent with the
electrochemical reversibility (diffusion controlled) of these processes. The other
14

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complexes display almost ideal electrochemical behavior. The data in Table 2DaOlIs: o10.1039/D0NJ03093G
reveals that for both iron and ruthenium examples of {M(dppe)Cpʹ} complexes, the
introduction of a Cp* ligand causes a decrease in oxidation by ca. –0.2 V relative to
the Cp analogue. Similarly, the iron examples {Fe(dppe)Cpʹ} undergo oxidation
approximately some 0.3 – 0.4 V lower (less positive) than the isostructural
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{Ru(dppe)Cpʹ} examples. Comparisons of the oxidation potentials of complexes
[Ru(C≡CR)(dppe)Cp] (4a-d) and [Ru(C≡CR)(PPh3)2Cp] (5a-d) clearly indicate the
more electron-donating nature of the dppe vs (PPh3)2 ancillary ligands, with the
complexes 4 undergoing oxidation some 0.05 – 0.09 V lower (less positive) than the
analogous compounds 5 (Table 4).
The characteristic shifts in the ν(C≡C) frequencies of metal acetylide complexes on
oxidation have proven useful as indirect reporters on the nature of the redox processes
in such systems (i.e. ligand vs metal character),11, 12, 15, 91-97 and in this regard
spectroelectrochemistry has proven to be an especially useful technique to assess such
changes.98 Although the complex types described here are well-known, there have
been few direct comparisons of the spectroscopic behavior of the
[M(C≡CC6H4Y)(dppe)Cp] complexes with their better investigated Cp* analogues.
Infra-red spectoelectrochemical data from the complexes in sub-series b – d are given
in Table 5, and spectra illustrated in Figure S2. Given the propensity for
phenylacetylide complexes to dimerize on oxidation,97 the series of complexes
[M(C≡CPh)(PP)Cp´] (a) were not investigated within the spectroelectrochemical cell.
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Table 5. Summary of IR spectroelectrochemical data (from 0.1 M NBu4PF6 / CH2Cl2 solutions) for complexes [1b-d] – [5b-d].
4
5
6
7
E1/2 / Va
ν(C≡C) / cm-1
2059
ν(C≡C) / cm-1 Δν(C≡C) / cm-1
1b
[1b]+ 1988
[Fe(C≡CC6H4OMe-4)(dppe)Cp*]
–0.67
–71
ATR 2059
8
9
2b
3b
4b
5b
1c
2c
3c
2065
ATR 2064
2074
ATR 2074
2079
ATR 2080
2072
ATR 2065
2036s, 2008s
ATR 2026, 1999
2044s, 2010w
ATR 2042, 2010
2047s, 2015m
ATR 2044, 2003
2056s, 2014w
ATR 2053, 2017
2052s, 2011w
ATR 2031, 2004
2069
ATR 2062
2069
ATR 2078
2087
ATR 2083
2084
ATR 2084
2089
[2b]+ 1978
[3b]+ 1929
[4b]+ 1938
[5b]+ 1930
[1c]+ N/Ac
[2c]+ N/A e
[3c]+ N/A
[Fe(C≡CC6H4OMe-4)(dppe)Cp]
[Ru(C≡CC6H4OMe-4)(dppe)Cp*]
[Ru(C≡CC6H4OMe-4)(dppe)Cp]
[Ru(C≡CC6H4OMe-4)(PPh3)2Cp]
[Fe(C≡CC6H4NO2-4)(dppe)Cp*]
[Fe(C≡CC6H4NO2-4)(dppe)Cp]
[Ru(C≡CC6H4NO2-4)(dppe)Cp*]
[Ru(C≡CC6H4NO2-4)(dppe)Cp]
[Ru(C≡CC6H4NO2-4)(PPh3)2Cp]
[Fe(C≡CBut)(dppe)Cp*]
–0.46
–0.31
–0.17
–0.12
–0.46
–0.27
–0.08
–87
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46
–145
–141
–142
4c +0.08
5c +0.14
[4c]+ N/A
[5c]+ N/A
1d
2d
3d
4d
5d
[1d]+ 2034
[2d]+ 2025
[3d]+ 1984, 1967
[4d]+ 1982, 1963
[5d]+ 1977, 1957
–0.76
–0.54
–0.35
–0.19
–0.10
–35
[Fe(C≡CBut)(dppe)Cp]
–44
[Ru(C≡CBut)(dppe)Cp*]
–103, –120
–102, –121
–112, –132
[Ru(C≡CBut)(dppe)Cp]
[Ru(C≡CBut)(PPh3)2Cp]
ATR 2081
a vs ferrocene / ferricenium
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The smaller shift in the ν(C≡C) band (Δν(C≡C)) of the iron complexes 1b and 2b on View Article Online
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oxidation in comparison with the ruthenium examples 3b, 4b and 5b is consistent
with the greater metal character in the iron oxidation events,14, 90, 99 and the more
ligand-centred oxidation of the ruthenium compounds (Table 3).11, 12, 43 However, for
each metal, the spectroelectrochemical response is almost independent of the nature
of the ancillary ligands.
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The IR spectra of the nitro-substituted complexes c present a range of features worthy
of comment. The neutral complexes 1c – 5c are characterized by two ν(C≡C) bands
separated by ca. 30 – 40 cm-1 in both the solid state and CH2Cl2 solution (Table 3).
These features arise from the stabilization of two conformers of the nitroaromatic
moiety with respect to the {M(PP)Cp´} fragment stabilized by the enhanced donor-
acceptor interaction through the alkynyl moiety. These conclusions are readily
mapped to the results of frequency calculations carried out on DFT optimized
geometries (BLYP35, LANL2DZ (Ru) / 6-31G** (all other atoms), CPCM(CH2Cl2))
chosen to sample two points on the ground-state potential energy surfaces of 4c and
[4c]+, as representative examples. The geometries of the neutral system were
optimized from initial structures in which the nitrobenzene ring was positioned
approximately bisecting the P-Ru-P angle (4c´) or rotated around the Ru-C≡C axis by
ca. 90º (4c´´) (Figure 2). These two representative geometries, which differ in energy
only by ca. 2 kJ/mol (4c´ being more stable at this level of theory), give rise to
ν(C≡C) bands at 2028 cm-1 (4c´) and 2043 cm-1 (4c´´), in good agreement with the
two band envelopes observed in the experimental spectrum (2014, 2056 cm-1;
Table 3).
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(b)
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4c”
(a)
4c’
Figure 2. Plots of the computational model complexes 4c´ and 4c´´, illustrating the
different conformation of the aryl ring and the associated distribution of the HOMO in
each case (HOMO % composition Ru / C≡C / C6H4-p-NO2: 4c´ 36/28/20; 4c´´
46/29/2)
In contrast, the one-electron oxidised complexes [1c – 5c]+ do not display an IR active
ν(C≡C) band; this is likely due the diminished dipole moment over the alkynyl
moiety and reflects a degree of metal character in the oxidation event for both the iron
and ruthenium systems.
In the case of the tBu terminated complexes 1d – 5d the average shift in the ν(C≡C)
band was smaller than the aryl-capped complexes. This reflects the diminished
delocalization of the radical cation and the greater metal character in the oxidation
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event for both iron and ruthenium complexes. The IR spectra of the ruthenium
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complexes [3d]+, [4d]+ and [5d]+ were characterized by two distinct ν(C≡C) bands
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separated by ca. 20 cm-1, in this case likely due to Fermi coupling.
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Conclusions
A convenient one-pot procedure for the preparation of the half-sandwich metal
acetylide complexes [M(C≡CR)(dppe)Cpʹ] (M = Fe, Ru; Cpʹ = Cp, Cp*; R = C6H5,
C6H4OMe, C6H4NO2, tBu) and [Ru(C≡CR)(PPh3)2Cp] has been described. These
complexes, which are usually obtained as high-quality crystalline samples directly
from the reaction vessel, have been characterized by a combination of spectroscopic,
spectrometric and electrochemical methods. Whilst electrochemical and IR
spectroelectrochemical studies confirm the anticipated distinction in the predominant
redox character of the iron (more metal centred) and ruthenium (more acetylide ligand
centred), the systematic study also reveals little change in the nature of these
processes as a function of the Cp vs Cp* ancillary ligand. The relative expense of
pentamethylcyclopentadiene vs cyclopentadiene and the lower computational expense
involved in DFT investigations of the Cp derivatives, suggests that {M(dppe)Cp}
based complexes are viable substitutes for the more thoroughly investigated
{M(dppe)Cp*} systems in future studies.
Experimental
General information
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All reactions were carried out under nitrogen using standard Schlenk procedures, but
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8
no special methods were used during work up. Reaction solvents were used as
received, and degassed by sparging with nitrogen before use. The compounds
[FeCl(dppe)Cp*],22 [FeCl(dppe)Cp],22 [RuCl(dppe)Cp*],22 [RuCl(dppe)Cp],22 and
[RuCl(PPh3)2Cp],8 and the alkynes 4-ethynyl anisole (HC≡CC6H4-p-OMe)100 and 4-
ethynyl nitrobenzene (HC≡CC6H4NO2)100 were prepared by literature routes. Other
compounds were purchased and used as received.
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NMR data were collected on 400 MHz Varian, 500 MHz Bruker and 600 MHz
1
Bruker machines. H and 13C{1H} NMR spectra were referenced to CDCl3 solvent
signals (δ 7.26 ppm and δ 77.16 ppm respectively) and C6D6 solvent signals (δ 7.16
13
ppm and δ 128.06 ppm respectively). A summary of C{1H} NMR data is given in
Table S1. IR spectra were recorded on a Cary 630 FTIR Spectrometer with an ATR
method. Electrospray Ionisation, positive mode (ESI+) Mass Spectra were collected
on a Waters Liquid Chromatograph Premier Mass Spectrometer.
Cyclic voltammetry was conducted in a standard three-electrode cell, with Pt disc
working electrode, Pt wire counter and Pt wire pseudo-reference electrodes, from
solutions in 0.1 M NBu4PF6 / CH2Cl2, with data collected from an EmStat3+
potentiostat.
The
decamethylferrocene/decamethylferrocinium
or
ferrocene/ferrocinium couples were used as internal references for potential
measurements (Fc*H/Fc*H+ = –0.48 V; FcH/FcH+ = 0.00 V). Spectroelectrochemical
studies were conducted in a transmission cell of Hartl design fitted with CaF2
widows,101 and controlled by the EmStat3+ from solutions of the analyte (ca. 1 mM)
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in 0.1 M NBu4PF6 / CH2Cl2. Data were recorded on Cary 5000 UV-vis-NIR and Cary
5
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660 FT-IR/NIR spectrometers.
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Synthetic details
Preparation of [Fe(C≡CC6H5)(dppe)Cp*] (1a) 23
A solution of [FeCl(dppe)Cp*] (0.100 g, 0.160 mmol) and HC≡CC6H5 (19.4 µL,
0.177 mmol) in MeOH (5 mL) was heated at reflux for 1.25h to give a red-brown
coloured solution of the vinylidene [Fe{C=C(H)C6H5}(dppe)Cp*]Cl. After this time,
heating and stirring were discontinued and DBU (1 drop) was carefully added to the
hot solution by allowing the base to run along the inner wall of the Schlenk flask.
Slow cooling upon standing gave 1a as red crystals (0.056 g, 0.081 mmol, 51 %; lit.
1
47%). H NMR (CDCl3): δ/ppm 7.88, 7.27-7.38 (m, 20H, PPh2), 7.14, 6.74 (m, 5H,
Ph), 2.73 (bs, 2H, CH2 (dppe)), 1.88 (bs, 2H, CH2 (dppe)), 1.54 (s, 15H, Cp*).
31P{1H} NMR (C6D6): δ/ppm 100.39 (s, PPh2). IR (solid, ATR): ν(C≡C) 2048s cm-1.
ESI(+)-MS (m/z): Calculated for [M]+ ([C44H44P2Fe]+) 691.2272 amu; Observed:
691.2274 amu.
Preparation of [Fe(C≡CC6H5-p-OMe)(dppe)Cp*] (1b) 25
A solution of [FeCl(dppe)Cp*] (0.102 g, 0.163 mmol) and HC≡CC6H4-p-OMe (22.8
µL, 0.176 mmol) in MeOH (5 mL) was heated at reflux for 1.25h to give a dark green
coloured solution of the vinylidene [Fe(C=C(H)C6H4-p-OMe)(dppe)Cp*]Cl. Heating
and stirring were discontinued before careful addition of 1 drop of DBU to the hot
solution via the inside wall of the reaction vessel. On slow cooling, crimson coloured
crystals of 1b were deposited (0.078 g, 0.108 mmol, 66 %; lit 56%). 1H NMR (C6D6):
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δ/ppm 8.06, (m, 4H, Ph), 6.80-7.32 (m, 20H, PPh2), 3.34 (s, 3H, OMe), 2.67D(ObI:s1,02.10H39,/D0NJ03093G
CH2 (dppe)), 1.84 (bs, 2H, CH2 (dppe)), 1.56 (s, 15H, Cp*). 31P{1H} NMR (C6D6):
δ/ppm 100.53 (s, PPh2). IR (solid, ATR): ν(C≡C) 2059s cm-1. Calculated for [M]+
([C45H46OP2Fe]+) 721.2378 amu; Observed: 721.2375 amu.
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Preparation of [Fe(C≡CC6H4-p-NO2)(dppe)Cp*] (1c) 10
A solution of [FeCl(dppe)Cp*] (0.102 g, 0.163 mmol) and HC≡CC6H4-p-NO2 (0.031
g, 0.211 mmol) in MeOH (10 mL) was heated at reflux for 50min to give a green
coloured solution of the vinylidene [Fe{C=C(H)C6H4-p-NO2}(dppe)Cp*]Cl. Heating
and stirring were discontinued before a drop of DBU was added to the hot reaction
solution via the inside wall of the reaction vessel. Upon slow cooling the solution
1
deposited 1c as a purple powder (0.069 g, 0.094 mmol, 57 %; lit. 64%). H NMR
(CDCl3): δ/ppm 7.93, 6.73 (d, JHH = 8.8 Hz, 4H, Ph), 7.77, 7.26 (m, 20H, PPh2), 2.60
(m, 2H, CH2 (dppe)), 2.01 (m, 2H, CH2 (dppe)), 1.42 (s, 15H, Cp*). 31P{1H} NMR
(CDCl3): δ/ppm 99.13 (s, PPh2). IR (solid, ATR): ν(C≡C) 2026s, 1999s; ν(NO2)
1569s, 1312s cm-1. ESI(+)-MS (m/z): Calculated for [M]+ ([C44H43FeNO2P2Fe]+)
736.2123 amu; Observed: 736.2112 amu.
Preparation of [Fe(C≡CtBu)(dppe)Cp*] (1d) 24
A solution of [FeCl(dppe)Cp*] (0.102 g, 0.163 mmol) and HC≡CtBu (100 µL, 0.812
mmol) in MeOH (5 mL) was heated at reflux for 1h to give a red coloured solution of
the vinylidene [Fe{C=C(H)tBu}(dppe)Cp*]Cl. Heating and stirring were ceased, and
addition of a drop of DBU to the reaction mixture via the inside wall of the reaction
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vessel and slow cooling gave 1d as crimson crystals (0.055 g, 0.0813 mmol, 50 %; lit.
5
6
80 – 87%). 1H NMR (C6D6): δ/ppm 8.09, 7.0-7.30 (m, 20H, PPh2), 2.77 (bs, 2H, CH2
7
8
9
t
(dppe)), 1.94 (bs, 2H, CH2 (dppe)), 1.54 (s, 15H, Cp*), 1.31 (s, 9H, Bu). 31P{1H}
NMR (C6D6): δ/ppm 101.07 (s, PPh2). IR (solid, ATR): ν(C≡C) 2062s cm-1. ESI(+)-
MS (m/z): Calculated for [M+H]+ ([C42H49FeP2]+) 671.2659 amu; Observed:
671.2653 amu.
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Preparation of [Fe(C≡CC6H5)(dppe)Cp] (2a)34
A solution of [FeCl(dppe)Cp] (0.102 g, 0.183 mmol) and HC≡CC6H5 (30.2 µL, 0.275
mmol) in MeOH (5 mL) was heated at reflux for 1h to give a red-brown coloured
solution of the vinylidene [Fe{C=C(H)C6H5}(dppe)Cp]Cl. Heating and stirring was
discontinued, and a drop of DBU introduced to the hot solution via the inner wall of
the flask. On standing and slow cooling, maroon coloured crystals of 2a were
1
deposited (0.057 g, 0.092 mmol, 50 %; lit. 43%). H NMR (CDCl3): δ/ppm 7.94,
7.41-7.30, 6.92-6.48 (m, 25H, PPh2, Ph), 4.25 (s, 5H, Cp), 2.61 (m, 2H, CH2 (dppe)),
2.22 (m, 2H, CH2 (dppe)). 31P{1H} NMR (CDCl3): δ/ppm 106.45 (s, PPh2). IR (solid,
ATR): ν(C≡C) 2057s cm-1. ESI(+)-MS (m/z): Calculated for [M]+ ([C39H34P2Fe]+)
621.1490 amu; Observed: 621.1488 amu.
Preparation of [Fe(C≡CC6H4-p-OMe)(dppe)Cp] (2b)
A solution of [FeCl(dppe)Cp] (0.104 g, 0.188 mmol) and HC≡CC6H4-p-OMe (100 µL
0.910 mmol) in MeOH (5 mL) was heated at reflux for 1.5h to give a brown-red
coloured solution of the vinylidene [Fe(C=C(H)C6H4-p-OMe)(dppe)Cp]Cl, which
was treated with 1 drop of DBU in the manner described before. The solution was
allowed to cool to room temperature and then chilled to give red crystals of 2b
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(0.0824 g, 0.126 mmol, 67 %). H NMR (C6D6): δ/ppm 8.04 (m, 4H, Ho), 7.41 (m,
5
6
6H, Hm, para), 7.32 (m, 2H, Hpara’), 7.26 (bs, 4H, Hm’), 7.21 (m, 4H, Ho’), 6.9, 6.6 (d,
7
8
9
JHH = 7.8 Hz, 4H, Ph), 4.31 (s, 5H, Cp), 3.25 (s, 3H, OMe), 2.57 (bs, 2H, CH2
31
(dppe)), 1.97 (bs, 2H, CH2 (dppe)). P{1H} NMR (C6D6): δ/ppm 106.75 (s, PPh2).
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IR (solid, ATR): ν(C≡C): 2064s cm-1. ESI(+)-MS (m/z): Calculated for [M]+
([C40H36OP2Fe]+) m/z 651.1595 amu; Observed: 650.1600 amu
Preparation of [Fe(C≡CC6H4-p-NO2)(dppe)Cp] (2c) 28, 102
A solution of [FeCl(dppe)Cp] (0.104 g, 0.181 mmol) and HC≡CC6H4-p-NO2 (0.0647
g, 0.439 mmol) in MeOH (5 mL) was heated at reflux for 2h to give a ruby-purple
coloured solution of the vinylidene [Fe{C=C(H)C6H4-p-NO2}(dppe)Cp]Cl. After
heating was stopped, addition of a drop of DBU via the inside wall of the reaction
vessel and slow cooling resulted in formation of dark purple crystals of 2c (0.0580 g,
1
0.087 mmol, 48 %; lit. 68, 31%). H NMR (C6D6): δ/ppm 7.86-6.97 (m, 20H, PPh2),
7.0, 6.5 (d, JHH = 8.7 Hz, 4H, Ph), 4.25 (s, 5H, Cp), 2.40 (m, 2H, CH2 (dppe)), 1.95
(m, 2H, CH2 (dppe)). 31P{1H} NMR (C6D6): δ/ppm 105.77 (s, PPh2). IR (solid, ATR):
ν(C≡C) 2042s, 2010m; ν(NO2) 1573s, 1303s cm-1. ESI(+)-MS (m/z): Calculated for
[M]+ ([C39H33FeNO2P2Fe]+) 666.1341 amu; Observed: 666.1342 amu.
Preparation of [Fe(C≡CtBu)(dppe)Cp] (2d)23
A solution of [FeCl(dppe)Cp] (0.105 g, 0.189 mmol) and HC≡CtBu (100 µL, 0.812
mmol) in MeOH (5 mL) was heated at reflux for 1h to give a red-orange coloured
solution of the vinylidene [Fe{C=C(H)tBu}(dppe)Cp]Cl. After heating and stirring
was ceased, addition of DBU and slow cooling in the manner described above gave
1
gave 2d as red crystals (0.047 g, 0.078 mmol, 41 %; lit. 23%). H NMR (C6D6):
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δ/ppm 8.15-7.05 (m, 20H, PPh2), 4.32 (s, 5H, Cp), 2.71 (m, 2H, CH2 (dppe)),D2O.1I: 810.(10m39,/D0NJ03093G
2H, CH2 (dppe)), 1.08 (s, 9H, H4). 31P{1H} NMR (C6D6): δ/ppm 107.85 (s, PPh2). IR
(solid, ATR): ν(C≡C) 2078s cm-1. ESI(+)-MS (m/z): Calculated for [M]+
([C37H38FeP2]+) 601.1803 amu; Observed: 601.1797 amu.
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Preparation of [Ru(C≡CC6H5)(dppe)Cp*] (3a)23
A solution of [RuCl(dppe)Cp*] (0.101 g, 0.151 mmol) and HC≡CC6H5 (18 µL, 0.164
mmol) was allowed to react in refluxing MeOH (10 mL) for 1h to give a pink-orange
solution of the vinylidene [Ru{C=C(H)C6H5}(dppe)Cp*]Cl. After this time, heating
and stirring was discontinued, and a drop of DBU introduced to the hot solution via
the inner wall of the flask. On standing and slow cooling, yellow crystals of 3a were
deposited (0.073 g, 0.099 mmol, 66 %; lit. 40%). 1H NMR (CDCl3): δ/ppm 7.61-7.82,
6.78-7.35 (m, 25H, PPh2, Ph), 2.68 (m, 2H, CH2 (dppe)), 2.05 (m, 2H, CH2 (dppe)),
31
1.56 (s, 15H, Cp*). P{1H} NMR (CDCl3): δ/ppm 81.45 (s, PPh2). IR (solid, ATR):
ν(C≡C) 2064s cm-1. ESI(+)-MS (m/z): Calculated for [M+H]+ ([C44H45P2Ru]+)
737.2040 amu; Observed: 737.2040 amu.
Preparation of [Ru(C≡CC6H4-p-OMe)(dppe)Cp*] (3b)11
A solution of [RuCl(dppe)Cp*] (0.101 g, 0.151 mmol) and HC≡CC6H4-p-OMe (100
µL, 0.771 mmol) in MeOH (5 mL) was heated at reflux for 2h to give a pink-red
solution of the vinylidene [Ru{C=C(H)C6H4-p-OMe}(dppe)Cp*]Cl. Heating was
stopped and a drop of DBU added via the inside wall of the Schlenk flask and the
solution allowed to stand. On slow cooling, yellow crystals of 3b were deposited
1
(0.0831 g, 0.108 mmol, 72 %; lit. 68%). H NMR (CDCl3): δ/ppm 7.77-7.81, 7.05-
7.19 (m, 20H, PPh2), 6.61, 6.72 (d, JHH = 8.8 Hz, 4H, Ph), 3.73 (s, 3H, OMe), 2.68
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(m, 2H, CH2 (dppe)), 2.04 (m, 2H, CH2 (dppe)), 1.56 (s, 15H, Cp*). P{ H} NMR
5
6
7
8
(CDCl3): δ/ppm 80.99 (s, PPh2). IR (solid, ATR): ν(C≡C) 2074s cm-1. ESI(+)-MS
(m/z): Calculated for [M+H]+ ([C45H47OP2Ru]+) 767.2146 amu; Observed: 767.2145
amu.
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Preparation of [Ru(C≡CC6H4-p-NO2)(dppe)Cp*] (3c)11
A solution of [RuCl(dppe)Cp*] (0.109 g, 0.163 mmol) and HC≡CC6H4-p-NO2 (0.026
g, 0.183 mmol) in MeOH (5 mL) was heated at reflux for 1h to give a red coloured
solution of the vinylidene [Ru{C=C(H)C6H4-p-NO2}(dppe)Cp*]Cl. After heating was
stopped, a drop of DBU was allowed to run into the hot solution via the inside wall of
the reaction vessel. On slow cooling, purple crystals of 3c were deposited (0.09 g,
0.115 mmol, 71 %; lit. 80%). 1H NMR (CDCl3): δ/ppm 7.88, 6.65 (d, JHH = 9 Hz, 4H,
Ph), 7.15-7.40, 7.67-7.70 (m, 20H, PPh2), 2.63 (m, 2H, CH2 (dppe)), 2.07 (m, 2H,
31
CH2 (dppe)), 1.56 (s, 15H, Cp*). P{1H} NMR (CDCl3): δ/ppm 80.42 (s, PPh2). IR
(solid, ATR): ν(C≡C) 2044s, 2003m; ν(NO2) 1573s, 1318s cm-1. ESI(+)-MS (m/z):
Calculated for [M+H]+ ([C44H44NO2P2Ru]+) 782.1891 amu; Observed 782.1894 amu.
Preparation of [Ru(C≡CtBu)(dppe)Cp*] (3d)23
A solution of [RuCl(dppe)Cp*] (0.102 g, 0.152 mmol) and HC≡CtBu (20.2 µL, 0.164
mmol) in MeOH (5 mL) was heated at reflux for 50 min to give an orange coloured
solution of the vinylidene [Ru{C=C(H)tBu}(dppe)Cp*]Cl. After heating and stirring
were ceased, addition of DBU and slow cooling in the manner described above gave
1
2d as a yellow powder (0.076 g, 0.106 mmol, 65 %; lit. 64%). H NMR (CDCl3):
δ/ppm 7.13-7.82 (m, 20H, PPh2), 2.73 (m, 2H, CH2 (dppe)), 2.08 (m, 2H, CH2
t
(dppe)), 1.53 (s, 15H, Cp*), 0.89 (s, 9H, Bu). 31P{1H} NMR (CDCl3): δ/ppm 81.20
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(s, PPh2). IR (solid, ATR): ν(C≡C) 2083s cm-1. ESI(+)-MS (m/z): Calculated foVriew Article Online
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5
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[M+H]+ ([C42H49RuP2]+) 717.2353 amu; Observed: 717.2371 amu.
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Preparation of [Ru(C≡CC6H5)(dppe)Cp] (4a)65
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A solution of [RuCl(dppe)Cp] (0.11 g, 0.18 mmol) in methanol (5 ml) was treated
with phenylacetylene (100 µL, 0.91 mmol) and the mixture heated at reflux for 2 h to
give a cherry-red solution of the vinylidene [Ru{C=C(H)C6H5}(dppe)Cp]Cl. The
solution volume was reduced to ca. 2 ml in vacuo before a drop of DBU was added
via the inside wall of the reaction vessel and allowed to stand to afford 4a as a yellow
microcrystalline solid which was collected by filtration, washed with hexanes and
1
dried (0.060 g, 0.090 mmol, 50 %; lit. 75%). H NMR (CDCl3): δ/ppm 7.93 (m, 4H,
Ho), 7.40 (m, 6H, Hpara/m), 7.27 (m, 10H, Ho/para/m), 6.88 (dd, JHH = 7.1 Hz, 2H, H5),
6.80 (t, JHH = 7.1 Hz, 1H, H6), 6.41 (d, JHH = 7.5 Hz, 2H, H4), 4.78 (s, 5H, Cp), 2.66
(m, 2H, CH2 (dppe)), 2.29 (m, 2H, CH2 (dppe)). 31P{1H} NMR (CDCl3): δ /ppm
86.14 (s, PPh2). IR (solid, ATR): ν(C≡C) 2076s cm-1. ESI(+)-MS (m/z): Calculated
for [M+H]+ ([C39H35RuP2]+) 667.1258 amu; Observed: 667.1265 amu.
Preparation of [Ru(C≡CC6H4-p-OMe)(dppe)Cp] (4b)
A solution of [RuCl(dppe)Cp] (0.11 g, 0.18 mmol) and 4-ethynylanisole (100 µL,
0.77 mmol) was heated at reflux in 5 ml of methanol for 1hr to give a dark-red
coloured solution of the vinylidene [Ru{C=C(H)C6H4-p-OMe}(dppe)Cp]Cl. The
solvent volume was reduced and DBU added in the manner described for 4a above to
give a yellow crystalline sample of 4b (0.077 g, 0.11 mmol, 61 %). 1H NMR (CDCl3)
δ/ppm 7.92 (m, 4H, Ho), 7.40 (m, 6H, Hpara/m), 7.26-7.24 (m, 10H, Ho/para/m), 6.45 (d,
JHH = 8.8 Hz, 2H, H5), 6.32 (d, JHH = 8.8 Hz, 2H, H4), 4.77 (s, 5H, Cp), 3.65 (s, 3H,
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H7), 2.66 (m, 2H, CH2 (dppe)), 2.26 (m, 2H, CH2 (dppe)). P{ H} NMR (CDCl3):
5
6
δ/ppm 86.20 (s, PPh2). IR (solid, ATR): ν(C≡C) 2080s cm-1. ESI(+)-MS (m/z):
7
8
9
Calculated for [M+H]+ ([C40H37OP2Ru]+) 697.1363 amu; Observed: 697.1375 amu.
10
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Preparation of [Ru(C≡CC6H4-p-NO2)(dppe)Cp] (4c) 61
The reaction of [RuCl(dppe)Cp] (0.11 g, 0.18 mmol) with 4-ethynylnitrobenzene
(0.030, 0.21 mmol) in dry, degassed methanol (5 ml) was allowed to proceed at reflux
for 3 h to give a dark-red coloured solution of the vinylidene [Ru{C=C(H)C6H4-p-
NO2}(dppe)Cp]Cl. After this time, a solution of DBU (1 drop) in 1 mL of dry
methanol was added to the stirred reaction mixture. The resulting precipitate was
purified by preparative TLC (3:7 acetone: hexanes) to afford 7c as a dark red solid
1
(0.060 g, 0.084 mmol, 77 %; lit. 30%). H NMR (CDCl3): δ/ppm 7.87 (m, 4H, Ho),
7.75 (d, JHH = 8.8 Hz, 2H, H5), 7.40 (m, 6H, Hpara/m), 7.29 (m, 10H, Ho/p/m), 6.33 (d,
JHH = 8.8 Hz, 2H, H4), 4.81 (s, 5H, Cp), 2.61 (m, 2H, CH2 (dppe)), 2.32 (m, 2H, CH2
(dppe)). 31P{1H} NMR (CDCl3): δ/ppm 85.39 (s, PPh2). IR (solid, ATR): ν(C≡C)
2053s, 2017m; ν(NO2) 1580s, 1306s cm-1. ESI(+)-MS (m/z): Calculated for [M+H]+
([C39H34NO2P2Ru]+) 712.1108 amu; Observed: 712.1144 amu.
Preparation of [Ru(C≡CtBu)(dppe)Cp] (4d)
A solution of [RuCl(dppe)Cp] (0.12, 0.19 mmol) and 3,3-dimethylbut-1-yne (100 µL,
0.81 mmol) was allowed to react in refluxing methanol (5 ml) for 5h to give a red-
orange solution of the vinylidene [Ru{C=C(H)tBu}(dppe)Cp]Cl. Reduction of the
solvent volume to ca. 2 ml and addition of DBU to the standing solution resulted in
the crystallisation of 4d, with further reduction of solvent volume yielding additional
1
product as a yellow precipitate (total yield 0.065 g, 0.10 mmol, 53 %). H NMR
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(CDCl3): δ /ppm 7.92 (m, 4H, Ho), 7.34 (m, 6H, Hpara/m), 7.22 (m, 10H, Ho/p/m), 4.67
5
6
7
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(s, 5H, Cp), 2.72 (m, 2H, CH2 (dppe)), 2.31 (m, 2H, CH2 (dppe)), 0.53 (s, 9H, H4).
31P{1H} NMR (CDCl3): δ/ppm 87.36 (s, PPh2). IR (solid ATR): ν(C≡C) 2084s cm-1.
ESI(+)-MS (m/z): Calculated for [M+H]+ ([C37H39RuP2]+) 647.1571 amu; Observed:
647.1577 amu.
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Preparation of [Ru(C≡CC6H5)(PPh3)2Cp] (5a) 8
A solution of [RuCl(PPh3)2Cp] (0.101 g, 0.139 mmol) and HC≡CC6H5 (24 µL, 0.219
mmol) was heated in refluxing MeOH (5 mL) for 1h to give a cherry red solution of
the vinylidene [Ru{C=C(H)C6H5}(PPh3)2Cp]Cl. After this time, heating and stirring
were discontinued and DBU (1 drop) was carefully added to the hot solution by
allowing the base to run along the inner wall of the Schlenk flask. Slow cooling gave
1a as yellow crystals (0.097 g, 0.123 mmol, 88 %; lit. 96%), which could be collected
1
via vacuum filtration, washed with MeOH (2 × 5 mL) and air-dried. H NMR
(CDCl3): δ/ppm 7.52-7.47, 7.21-7.06 (m, 35H, PPh3, Ph), 4.32 (s, 5H, Cp). 31P{1H}
NMR (CDCl3): δ/ppm 50.38 (s, PPh3). IR (solid, ATR): ν(C≡C) 2064s cm-1. ESI(+)-
MS (m/z): Calculated for [M+H]+ ([C49H41P2Ru]+) 793.1727 amu; Observed:
793.1721 amu.
Preparation of [Ru(C≡CC6H4-p-OMe)(PPh3)2Cp] (5b) 81
A solution of [RuCl(PPh3)2Cp] (0.106 g, 0.146 mmol) and HC≡CC6H4-p-OMe (20
µL, 0.154 mmol) in MeOH (10 mL) was heated at reflux for 1h to give a dark red
coloured solution of the vinylidene [Ru{C=C(H)C6H4-p-OMe}(PPh3)2Cp]Cl. Heating
and stirring was discontinued, a drop of DBU added via the inside wall of the Schlenk
flask and the solution allowed to stand where upon yellow crystals of 5b were
29