Bis(acetylacetonato)ruthenium(ii) complexes containing alkynyldiphenylphosphines. Formation and redox behaviour of [Ru(acac) 2(Ph2PCCR)2] (R = H, Me, Ph) complexes and the binuclear complex cis-[{Ru(acac)2}2(-Ph 2PCCPPh2)}2]

Article abstract of DOI:10.1039/b618365d

Two equivalents of Ph₂PCCR (R = H, Me, Ph) react with thf solutions of cis-[Ru(acac)₂(η²-alkene)₂] (acac = acetylacetonato; alkene = C₂H₄, 1; C ₈H₁₄, 2) at room temperature to yield the orange, air-stable compounds trans-[Ru(acac)₂(Ph₂PCCR) ₂] (R = H, trans-3; Me = trans-4; Ph, trans-5) in isolated yields of 60-98%. In refluxing chlorobenzene, trans-4 and trans-5 are converted into the yellow, air-stable compounds cis-[Ru(acac)₂(Ph₂PCCR) ₂] (R = Me, cis-4; Ph, cis-5), isolated in yields of ca. 65%. From the reaction of two equivalents of Ph₂PCCPPh₂ with a thf solution of 2 an almost insoluble orange solid is formed, which is believed to be trans-[Ru(acac)₂(-Ph₂PCCPPh₂)]_n (trans-6). In refluxing chlorobenzene, the latter forms the air-stable, yellow, binuclear compound cis-[{Ru(acac)₂(-Ph₂PCCPPh ₂)}₂] (cis-6). Electrochemical studies indicate that cis-4 and cis-5 are harder to oxidise by ca. 300 mV than the corresponding trans-isomers and harder to oxidise by 80-120 mV than cis-[Ru(acac) ₂L₂] (L = PPh₃, PPh₂Me). Electrochemical studies of cis-6 show two reversible Ru^II/III oxidation processes separated by 300 mV, the estimated comproportionation constant (K_c) for the equilibrium cis-6²⁺ + cis-6 2(cis-6⁺) being ca. 10⁵. However, UV-Vis spectra of cis-6⁺ and cis-6²⁺, generated electrochemically at -50 °C, indicate that cis-6⁺ is a Robin-Day Class II mixed-valence system. Addition of one equivalent of AgPF₆ to trans-3 and trans-4 forms the green air-stable complexes trans-3·PF₆ and trans-4·PF₆, respectively, almost quantitatively. The structures of trans-4, cis-4, trans-4·PF₆ and cis-6 have been confirmed by X-ray crystallography. The Royal Society of Chemistry.

Full text of DOI:10.1039/b618365d

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www.rsc.org/dalton | Dalton Transactions
Bis(acetylacetonato)ruthenium(II) complexes containing
alkynyldiphenylphosphines. Formation and redox behaviour of
[Ru(acac)2(Ph2PC≡CR)2] (R = H, Me, Ph) complexes and the binuclear
complex cis-[{Ru(acac)2}2(l-Ph2PC≡CPPh2)}2]
Martin A. Bennett,* Matthew J. Byrnes† and Anthony C. Willis
Received 15th December 2006, Accepted 2nd March 2007
First published as an Advance Article on the web 19th March 2007
DOI: 10.1039/b618365d
2
Two equivalents of Ph2PC≡CR (R = H, Me, Ph) react with thf solutions of cis-[Ru(acac)2(g -alkene)2]
(acac = acetylacetonato; alkene = C2H4, 1; C8H14, 2) at room temperature to yield the orange, air-stable
compounds trans-[Ru(acac)2(Ph2PC≡CR)2] (R = H, trans-3; Me = trans-4; Ph, trans-5) in isolated
yields of 60–98%. In refluxing chlorobenzene, trans-4 and trans-5 are converted into the yellow,
air-stable compounds cis-[Ru(acac)2(Ph2PC≡CR)2] (R = Me, cis-4; Ph, cis-5), isolated in yields of ca.
65%. From the reaction of two equivalents of Ph2PC≡CPPh2 with a thf solution of 2 an almost
insoluble orange solid is formed, which is believed to be trans-[Ru(acac)2(l-Ph2PC≡CPPh2)]n (trans-6).
In refluxing chlorobenzene, the latter forms the air-stable, yellow, binuclear compound
cis-[{Ru(acac)2(l-Ph2PC≡CPPh2)}2] (cis-6). Electrochemical studies indicate that cis-4 and cis-5 are
harder to oxidise by ca. 300 mV than the corresponding trans-isomers and harder to oxidise by
80–120 mV than cis-[Ru(acac)2L2] (L = PPh3, PPh2Me). Electrochemical studies of cis-6 show two
reversible RuII/III oxidation processes separated by 300 mV, the estimated comproportionation constant
(Kc) for the equilibrium cis-62+ + cis-6 ꢀ 2(cis-6+) being ca. 105. However, UV-Vis spectra of cis-6+ and
cis-62+, generated electrochemically at −50 ◦C, indicate that cis-6+ is a Robin–Day Class II
mixed-valence system. Addition of one equivalent of AgPF6 to trans-3 and trans-4 forms the green
air-stable complexes trans-3·PF6 and trans-4·PF6, respectively, almost quantitatively. The structures of
trans-4, cis-4, trans-4·PF6 and cis-6 have been confirmed by X-ray crystallography.
electronic communication between redox-active centres bridged
Introduction
by dppa have been reported.36–38
2
The bifunctionality of alkynyldiphenylphosphines, Ph2PC≡CR,
We have shown that the alkene ligands of cis-[Ru(acac)2(g -
has provided a happy hunting ground for coordination and
alkene)2] [alkene = ethylene (1), cyclooctene (2); acac = 2,4-
organometallic chemists for almost forty years. Although these
compounds behave mainly as P-donors towards most transi-
tion metal centres, there are also many cases in which the
P–C (acetylide) bond is cleaved, leading to complexes con-
pentadionato] are easily displaced by ligands (L), such as tertiary
phosphines, phosphites, pyridine or tert-butyl isocyanide, to give
trans-[Ru(acac)2L2] as the kinetic products, which then usually
isomerise to the more stable cis-products on heating.39 Although
taining l-PPh2 and l-C≡CR ligands. Further, Ph2PC≡CR lig-
the displacements undoubtedly occur stepwise, mono-alkene com-
2
ands can bridge metal centres through the phosphorus and
plexes [Ru(acac)2(g -alkene)(L)] have been isolated only for L =
SbPh3, MeCN, NH3, C5H5N, PPri3 and PCy3.40,41 All of these
complexes undergo reversible one-electron oxidations, without
trans–cis interconversion; the resulting ruthenium(III) cationic
complexes can either be isolated or generated electrochemically
and detected by UV-Vis and ESR spectroscopy.40–42
alkyne functions, the alkyne can coordinate to a pair of metal
atoms while the phosphorus atom remains free, and the alkyne
can also undergo condensation with CO and other unsat-
urated fragments.1–22 Bis(diphenylphosphino)acetylene (dppa),
Ph2PC≡CPPh2, behaves mainly as either a monodentate (j-P)
or a bridging bidentate (l2-P) P-donor,2,23–32 although a few
examples of coordination via the alkyne function have also been
established.1,20,33–35 In the l2-mode, dppa has been widely used
to link metal complexes or clusters, but only a few studies of
We report here on the reactions of various Ph2PC≡CR ligands,
and of dppa, with 1 or 2, and on the redox behaviour of the
resulting complexes. Most previous examples of non-cluster
ruthenium complexes containing Ph2PC≡CR and dppa are
half-sandwhich complexes such as [RuClCp*(Ph2PC≡CPh)2],43
6
[RuCl2(g -arene)(Ph2PC≡CR)] (arene = benzene, para-cymene
6
or mesitylene),44–46 [RuCl(g -p-cym)(Ph2PC≡CR)2]+,46 and
Research School of Chemistry, Australian National University, Canberra,
ACT, 0200, Australia. E-mail: bennett@rsc.anu.edu.au; Fax: +61 2 6125
3216; Tel: +61 2 6125 3639
† Present address: School of Chemistry, Monash University, Box 23, 3800
Clayton, Victoria Australia.
6
[{RuCl2(g -p-cym)}2(l-dppa)].45
Coordination
complexes
[RuCl(bipy)2(j-P-dppa)]+ and [{RuCl(bipy)2}2(l-dppa)]2+ are
also known.47,48
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1
1
Table 1 1H, 13C{ H} and 31P{ H} NMR spectral data for compounds 3–6a,b
acac
1H
13C
Ph2PC≡CR
1H
13C
31P
=
Compound CH3
CH
CH3
CH
C
O
trans-3
1.39
1.42
4.36 27.2
100.3
185.5
7.73–7.26 (20H, m, Ph);
132.7 (t, 2+4JPC = 6.6 Hz, o-C,
22.8
3.49 (2H, t, 3JPH = 2.4 Hz, PPh2); 132.0 (t, 1+3JPC = 20 Hz, i-C,
C≡CH)
PPh2); 129.6 (s, p-C, PPh2); 128.1
(t, 3+5JPC = 4.5 Hz, m-C, PPh2);
97.7 (d, 2+4JPC = 4.2 Hz, C≡CH);
79.0 (t, 1+3JPC = 30 Hz, C≡CH)
trans-4
4.43 27.4
99.9
185.6
7.77–7.30 (20H, m, Ph);
2.20 (6H, s, C≡CCH3)
133.4 (t, 1+3JPC = 20 Hz, i-C, PPh2); 21.9
132.7 (t, 2+4JPC = 6.3 Hz, o-C,
PPh2); 129.2 (s, p-C, PPh2); 127.9
(t, 3+5JPC = 4.1 Hz, m-C, PPh2);
107.5 (s, C≡CCH3); 72.4 (t,
1+3
J
= 35 Hz, C≡CCH3); 6.0 (s,
PC
C≡CCH3)
trans-5
cis-4
1.37
4.50 27.5
100.3
99.5
186.0
7.84–7.30 (30H, m, Ph)
132.9 (t, 2+4JPC = 6.5 Hz, o-C,
PPh2); 132.1 (s, i-C, Ph); 129.6 (s,
p-C, Ph); 129.5 (s, p-C, Ph); 128.8
22.1
(s, o-C, Ph); 128.1 (t, 3+5JPC
=
4.4 Hz, m-C, PPh2); 108.9 (m,
C≡CPh); 83.6 (m, C≡CPh)
1.32, 2.07
5.33 27.2, 28.6
185.4, 187.2
7.90–7.10 (20H, m, Ph);
137.5 (t, 1+3JPC = 26 Hz, i-C, PPh2); 39.8
2.02 (6H, vt, JPH = 1.2 Hz, 136.7 (t, 1+3JPC = 22 Hz, i-C, PPh2);
C≡CCH3)
132.5 and 132.1 (each t, 2+4JPC
5.5 Hz; o-C, PPh2); 128.7 (s, p-C,
PPh2); 127.6 and 127.2 (each t,
=
3+5
J
= 5.0 Hz, m-C, PPh2); 107.9
PC
(t, 2+4JPC = 5.5 Hz, C≡CCH3); 72.8
(m, C≡CCH3); 5.8 (s, C≡CCH3)
137.2 (t, 1+3JPC = 26.2 Hz, i-C,
cis-5
cis-6
1.38, 2.02
5.23 27.3, 28.5
99.5
99.6
184.6, 187.4
7.94–7.08 (30H, m, Ph)
40.3
PPh2); 136.4 (t, 1+3JPC = 22.9 Hz,
i-C, PPh2); 132.5 (t, 2+4JPC = 5.5 Hz;
o-C, PPh2); 132.0 (s, o-C, Ph); 131.9
(t, 2+4JPC = 5.7 Hz; o-C, PPh2);
129.5 (s, i-C, Ph); 128.9 and 128.8
(each s, p-C, Ph); 127.7 (t, 3+5JPC
=
5.0 Hz, m-Ph); 109.1 (d, 2+4JPC
5.0, C≡CPh); 84.3 (m, C≡CPh)
=
1.45, 1.65
5.02 27.6, 27.7
184.5, 187.4
8.16–8.10 (16H, m, o-Ph);
135.9 (t, 1+3JPC = 24 Hz; i-C, PPh2); 43.1
7.25–6.99 (24H, m, m- and 135.4 (t, 2+4JPC = 5.5 Hz; o-C,
p-Ph)
PPh2); 133.9 (t, 1+3JPC = 24 Hz; i-C,
PPh2); 132.0 (t, 2+4JPC = 5.2 Hz;
o-C, PPh2); 129.6 and 128.6 (each s,
p-C, C6H5); 127.6 and 127.5 (each
t, 3+5JPC = 4 Hz; m-C, PPh2); 104.8
(m, C≡CPPh2)
a Measured in CD2Cl2 at room temperature. b Abbreviations: 1+3J = J + 3J, 2+4J = J + 4J, i = ipso, o = ortho, m = meta, p = para.
1
2
Scheme 2
Scheme 1
Ruthenium(II) complexes
Results
Addition of two equivalents of Ph2C≡CR (R = H, Me, Ph) to
2
The preparation of the bis(alkynyldiphenylphosphine) ruthe-
nium(II) complexes is summarised in Schemes 1 and 2. 1H, 13C and
31P NMR data are listed in Table 1; selected infrared bands, mass
spectrometric data, and elemental analyses are given in Table 2.
a thf solution of cis-[Ru(acac)2(g -alkene)2] (alkene = C2H4, 1;40
C8H14, 239) at room temperature gives the orange, air-stable solids
trans-[Ru(acac)2(Ph2PC≡CR)2] (R = H, trans-3; Me = trans-4;
Ph, trans-5), which have been isolated in yields of 60–98%. These
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Table 2 Elemental analyses, selected infrared bands, and mass spectral data for compounds 3–6
IR spectraa
acac
Microanalysis: Found (Calc.)
Compound
trans-3
trans-4
cis-4
Other
%C
%H
%P
m/z (Assignment, % relative intensity)b
1568, 1511
1568, 1512
1574, 1514
1567, 1512
1574, 1515
2035 (C≡C)
2198 (C≡C)
2200 (C≡C)
2172 (C≡C)
2171 (C≡C)
63.31 (63.42)
63.98 (64.25)
64.54 (64.25)
68.67 (68.88)
67.74 (68.88)
4.97 (5.04)
5.61 (5.39)
5.43 (5.39)
5.22 (5.09)
5.08 (5.09)
8.68 (8.61)
8.41 (8.28)
8.33 (8.28)
7.00 (7.10)
—
720.2 (M, 65); 621.3 (M − acac, 10); 510.2
(M − L, 100)
748.4 (M, 50); 649.3 (M − acac, 10); 523.2
(M − L, 100)
748.1 (M, 100); 649.1 (M − acac, 25); 523.2
(M − L, 35]
trans-5
cis-5
872.2 (M, 20); 773.1 (M − acac, 5); 586.1
(M − L, 100)
872.2 (M+, 35); 774.2 (M − acac, 5); 586.1
(M − L, 12)
trans-6
cis-6
trans-3·PF6(0.5CH2Cl2)
1564, 1510
1573, 1514
1538, 1520
—
64.24 (62.33)
61.18 (62.33)
50.52 (50.98)
4.95 (4.94)
4.95 (4.95)
4.11 (4.11)
—
—
—
2131 (C≡C)c
2059 (C≡C)
841 (PF6)
558 (PF6)
2201 (C≡C)
1387.8 (M, 75); 1288.7 (M − acac, 23)
10.40 (10.24)
720.2 (M, 25); 510.2 (M − L, 100)
trans-4·PF6
1520
53.61 (53.82)
4.55 (4.52)
10.71 (10.41)
748.2 (M, 30), 649.1 (M − acac, 10); 524.1
(M − L, 100)
840 (PF6)
558 (PF6)
a Measured as KBr disc. b +ve FAB mass spectrum. c Raman spectrum.
orange solids are almost insoluble in thf, benzene or toluene but
readily form air-stable solutions in CH2Cl2 and C6H5Cl. Heating
solutions of trans-4 and trans-5 in C6H5Cl at reflux under an
inert atmosphere causes isomerisation to the yellow, air-stable
complexes cis-[Ru(acac)2(Ph2PC≡CR)2] (R = Me, cis-4; Ph, cis-
5), isolated in yields of ca. 65%. These are much more soluble
than the corresponding trans-isomers in most organic solvents,
giving yellow, air-stable solutions. Heating a solution of trans-3
phosphorus atom lone pair into the C≡C p*-orbitals.5 The Raman
spectrum of cis-6 shows a band of medium intensity at 2131 cm−1
assignable to the symmetric C≡C vibration, which lies in the range
2143–2109 cm−1 found for a range of l-dppa complexes.49–52
As previously noted,39 the geometric isomers of [Ru(acac)2L2]
complexes are easily distinguished by NMR spectroscopy. The
1H NMR spectra of the trans-isomers of 3–5 show singlets at
approximately d 4.5 and 1.4 for the acac CH3 and CH protons,
respectively, whereas the spectra of the cis-isomers of 4 and 5, and
cis-6, contain a pair of singlets for the inequivalent acac CH3
protons, and the singlet due to the acac CH protons appears
characteristically at higher frequency (d ca. 5). Likewise, the
1
gives several unidentified products as shown by 31P{ H} NMR
spectroscopy; this reaction has not been studied further.
Addition of two equivalents of dppa to a thf solution of freshly
prepared 2 initially results in a clear orange solution, which, when
stirred overnight, deposits an orange-red solid that is insoluble in
all common organic solvents. Since its elemental analysis corre-
sponds approximately to the formula [Ru(acac)2(Ph2PC≡CPPh2)],
the solid is probably a polymer or oligomer, trans-6, similar to
the compounds obtained from the reaction of 2 with dppe or
dppp.39 There are no bands in the 2300–1600 cm−1 region of the
IR spectrum assignable to m(C≡C). From a suspension of trans-
6 in refluxing C6H5Cl the yellow, air-stable, binuclear compound
cis-[{Ru(acac)2}2(l-Ph2PC≡CPPh2)2] (cis-6) can be isolated in ca.
40% yield.
1
13C{ H} NMR spectra of the trans-isomers of 3–5 display one
acac CH3 resonance, whereas cis-4, cis-5 and cis-6 show two.
=
In addition, there is one C O resonance at d ca. 185 in the
1
13C{ H} NMR spectra of the trans-isomers, whereas there are
two in the spectra of the cis-isomers. All the complexes show
singlet 31P{ H} NMR resonances, those for the cis-isomers being
1
characteristically ca. 20 ppm to high frequency of those for the
trans-isomers. Although cis-6 could exist in principle as geometric
isomers (DD/KK and DK/KD), the NMR spectra indicate that
only one isomer is present in solution.
The positive ion FAB mass spectra of complexes 3–6 (Table 2)
display the parent molecular ion peak, which, in the case of 6, is
the most abundant peak in the spectrum; generally, however, the
most abundant peak corresponds to the loss of one Ph2PC≡CR
group from the molecular ion and a peak due to the loss of one
acac group is also observed.
The IR spectra exhibit two intense bands at ca. 1570 and
1510 cm−1 characteristic of bidentate O-bonded acac (Table 2).
Except in the case of cis-6, the spectra also show a strong
absorption in the region of 2200–2035 cm−1, corresponding to
m(C≡C) for an uncoordinated alkyne. The small increases in
m(C≡C) relative to the values for the free ligands (Dm(C≡C) = 3,
12, 14, 14 and 5 cm−1 for trans-3, trans-4, cis-4, trans-5 and cis-5,
respectively) are consistent with the reduced delocalisation of the
The resonances due to the alkynyl Ca atoms in 3–5 can be found
(with some difficulty because the complexes tend to crystallise) in
the region of d 80; they are triplets in trans-3 and trans-4, a poorly
resolved multiplet in trans-5, and a six-line multiplet in cis-4 and
cis-5. In the case of cis-6, the six-line multiplet due to ≡C occurs
at d 104.5. In all these compounds Ca represents the X part of an
AAꢀX spin system (A = 31P) and the different patterns probably
reflect the fact that J(AAꢀ) (trans) ꢁ J(AAꢀ) (cis).39 The chemical
shifts of Ca are close to those of the free ligands (Table 3), as is
to be expected if, as indicated by the vibrational data (see above),
the alkynes are not coordinated. The NMR evidence alone is not
decisive, however, because in the chelate alkyne complexes cis-
[Ru(acac)2(o-Me2NC6H4C≡CR)] (R = H, Ph, SiMe3), the chemi-
cal shifts of the alkyne carbon atoms differ only slightly from those
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Table 3 13C Chemical shifts for the acetylenic carbon atoms in com-
pounds 3–5a
are harder to oxidise, by as much as 80 mV, than their counterparts
[Ru(acac)2L2] (L = PPh3, PMePh2). The electron-withdrawing
effect of the alkynyl substituents relative to that of methyl or
phenyl probably causes the ligands Ph2PC≡CR (R = Me, Ph)
to be somewhat stronger p-acceptors than PPh3 or PMePh2, thus
stabilising the oxidation state Ru(II) relative to Ru(III).
Compound
dCa
dCb
97.7
107.5
108.9
107.9
109.1
111.1
106.1
108.1
dCb − dCa
trans-3
79.0
72.4
83.6
72.8
84.3
96.6
76.4
86.6
18.7
35.1
25.3
35.1
24.8
15.5
29.7
21.5
trans-4
trans-5
The cyclic and ac voltammograms of the binuclear complex cis-
6 show two reversible oxidation potentials at +0.60 and +0.90 V
(vs. Ag/AgCl) which are attributed to the sequential oxidation of
cis-4
cis-5
Ph2PC≡CHb
Ph2PC≡CMeb
Ph2PC≡CPhb
both ruthenium metal centres, i.e., RuII/II → RuII/III → RuIII/III
.
Of all of the {Ru(acac)2} compounds containing p-acceptor
ligands studied thus far, only the binuclear dinitrogen complex cis-
[{Ru(acac)2(PiPr3)}2(l-N2)] (+0.30 V and +0.90 V (vs. Ag/AgCl)
at −50 ◦C)41 has shown more than one oxidation potential in the
range between 0.0–1.5 V and none shows evidence for a Ru(III) →
Ru(IV) oxidation process.40–42,54,55 The first oxidation process for cis-
6 is ca. 150 mV higher than the corresponding potentials found for
cis-4 and cis-5, probably as a consquence of the p-acceptor ability
of l-dppa, which stabilises Ru(II).
a Measured in CD2Cl2. b Measured in C6D6 and taken from ref. 20.
of the free ligands.53 The chemical shift difference of the alkynyl
carbon atoms dCb − dCa has been used as a measure of the polari-
sation of the triple bond as a consequence of P-coordination.4,5 The
data in Table 3 indicate that, in the {Ru(acac)2} complexes as in
RuClCp*(Ph2PC≡CPh)2],43 the polarisation is almost unchanged.
1
In complexes cis-4, cis-5 and cis-6, the 13C{ H} NMR spectra
Since the potentials for the stepwise oxidation of cis-6 differ
by more than 250 mV,56 the difference of E1/2 values obtained
from cyclic voltammetry or ac voltammetry can be related to the
comproportionation constant Kc, as shown in eqn (1). The derived
value of ca. 105 indicates that the mono-cationic species cis-6+ is
either a Class II or Class III mixed-valence system according to
the Robin–Day classification.
show that the PPh2 phenyl groups are inequivalent, as would be
expected because they are diastereotopic (cf. the methyl groups
of cis-[Ru(acac)2(PMe2Ph)2]39). A similar observation has been
made for the complexes [MClCp*(PPh2C≡CR)2]n+ (n = 0, R =
Ph, M = Ru; n = 1, R = Ph, M = Rh, Ir)43 and [RuCl(p-
cym)(Ph2PC≡CR)2]+ (R = But and various aryl groups)46 but
incorrectly ascribed to restricted rotation about the Ru–P bonds.
The structural conclusions drawn from spectroscopic data have
been confirmed by X-ray crystallography in the cases of trans-4,
cis-4 and cis-6 (see below).
2 RuII/III
RuII/II + RuIII/III
K
c
−−−−−→
←−−−−−
(1)
Kc = exp(DE1/225.69)
Electrochemistry
Electrochemical studies of the two-electron reduction of
[{Ru3(CO)11}2(l-dppa)] suggest that there is little, if any, elec-
tronic communication between the {Ru3(CO)11} groups, although
the fast reactions that occur after reduction prevent a precise
estimate.37 Similar studies of the bridged complex [{Ru3O(OAc)6-
(py)}2(l-Ph2PC≡CPPh2)][PF6]2 show two [Ru3II,III,III] oxidation
processes separated by 130 mV and two [Ru3II,III,III] reduction
processes separated by 95 mV, corresponding to Kc values of
158 and 40, respectively.38 The bridged bis(dithiolene) cobalt
complex [nBu4N]2[{(R2C2S2)2Co}2(l-dppa)] (R = CF3) (140 mV)
also has two reversible one-electron oxidation processes separated
by 140 mV corresponding to a Kc value of 233.36 The greater
electronic communication mediated by dppa between the metal
centres in cis-6+ may be a consequence of the pronounced p-donor
ability of RuII when it is surrounded by non p-acceptor ligands such
as NH3, H2O and acac.57
The electronic spectra (UV-Vis) of complexes trans-4, cis-4 and
cis-6 in CH2Cl2 containing 0.5 M [nBu4N]PF6 show characteristic
bands assigned to the RuII → acac p* transition (MLCT) as well
as the acac p → p* transitions (Table 5). These spectra are similar
to those previously reported for other {Ru(acac)2} compounds
containing p-acceptor ligands.40,41,53,58 Above ca. 30 000 cm−1 the
p → p* transitions of the phenyl rings overlap the acac transitions.
When a potential of ca. +0.40 V (vs. Ag/AgCl) is applied to
a solution of trans-4 at ca. −50 ◦C, the characteristic bands
gradually disappear and are replaced by bands at 14 900 (e ∼
1300 M−1 cm−1), 32 100 (e ∼ 21 700 M−1 cm−1) and 34 200 (e ∼
19 500 M−1 cm−1) cm−1. After the solution has been exhaustively
The cyclic and ac voltammograms of compounds 3–5 each show
one fully reversible E1/2(RuII/III) couple between +0.0 and +0.5 V
(vs. Ag/AgCl) at room temperature. The E1/2 values are listed
and compared with the potentials of the corresponding isomers of
[Ru(acac)2L2] [L = PMe3, PMePh2, PPh3 and P(OMe)3] in Table 4.
As in the latter series,42 the cis-isomers of 4 and 5 are harder to
oxidise than the corresponding trans-isomers by about 300 mV.
Further, both cis- and trans-alkynyldiphenylphosphine complexes
Table 4 Reduction potentials E1/2(Ru3+/2+) for complexes 3–6a
Complex
E
1/2(Ru3+/2+)/V
DE1/2(cis)−(trans)b/V
trans-3
+0.16
+0.09
+0.45
+0.12
+0.49
+0.60 and +0.90
+0.07
+0.37
+0.04
+0.37
+0.00
+0.26
+0.22
—
0.36
trans-4
cis-4
trans-5
0.37
cis-5
cis-6
—
0.30
trans-[Ru(acac)2(PPh3)2]c
cis-[Ru(acac)2(PPh3)2]c
trans-[Ru(acac)2(PMePh2)2]c
cis-[Ru(acac)2(PMePh2)2]c
trans-[Ru(acac)2(PMe3)2]c
cis-[Ru(acac)2(PMe3)2]c
trans-[Ru(acac)2(P{OMe}3)2]c
cis-[Ru(acac)2(P{OMe}3)2]c
0.33
0.26
0.48
+0.70
a Measured in 0.5M nBu4NPF6/CH2Cl2 at room temperature vs. Ag/AgCl.
b DE1/2 = E1/2 (cis) − E1/2(trans). c Values from ref. 54.
1680 | Dalton Trans., 2007, 1677–1686
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a
Table 5 Principal electronic band maxima (cm−1) and molar absorp-
tivities (M−1 cm−1) for ruthenium(II) and in situ electrogenerated ruthe-
nium(III) complexesa
Table 6 g-Values for compounds trans-3·PF6 and trans-4·PF6
Compound
g1
g2
g3
Compound
MLCT or LMCT
acac p → p*
trans-3·PF6
2.27
2.26
2.28
2.40
2.23
2.22
2.23
2.08
1.86
1.86
1.84
1.84
trans-4·PF6
b
trans-4
cis-4
28 100 (∼5900), 27 000 (sh)
30 000 (∼6900)
35 900 (∼15 500)
36 700 (∼14 400)
36 300 (∼23 400)
34 200 (∼19 500)
33 500 (∼8500)
33 300 (∼16 500)
trans-[Ru(acac)2(PPh3)2]PF6
cis-[Ru(acac)2(PPh3)2]PF6
b
cis-6
31 700 (∼12 700)
a Recorded in 0.5 M nBu4NPF6/CH2Cl2 at 4.7 K. b Recorded in 1 : 1
CH2Cl2–toluene at 120 K, taken from ref. 54.
trans-4+
cis-4+
cis-62+
14 900 (∼1300), 32 100 (∼21 700)
15 000 (∼2300)
13 800 (∼4400), 16 200 (∼4400)
a Measured in CH2Cl2 at ca. −60 ◦C.
The positive FAB mass spectra of trans-3·PF6 and trans-4·PF6
both display the molecular ion peak (Table 2) though in each
case the most abundant ion is associated with the loss of one
phosphine ligand. The IR spectra of both solids show either two
bands or one strong band with a shoulder on the high energy
side between 1560–1510 cm−1, due to bidentate O-bonded acac,
and bands at ca. 840 cm−1 and ca. 558 cm−1 due to PF6. A
strong absorption assigned to m(C≡C) (uncoordinated) is found
at 2059 cm−1 and 2201 cm−1 for trans-3·PF6 and trans-4·PF6,
respectively, representing an increase of 24 cm−1 for trans-3·PF6
and only 3 cm−1 for trans-3·PF6 from the values in the parent
Ru(II) complexes.
oxidised, the original spectrum can be regenerated by application
of a potential of ca. −0.20 V (vs. Ag/AgCl). During both the
oxidation and reduction processes, isosbestic points are observed,
indicating the presence of only two absorbing species in solution.
Similar changes occur during the anodic bulk electrolysis of a
solution of cis-4 under an applied potential of ca. +0.75 V (vs.
Ag/AgCl) (see Table 5). The original spectrum is again regenerated
after cathodic bulk electrolysis of the electrogenerated solution of
cis-4+, indicating that this process also is fully reversible.
The electronic spectra (UV-Vis) of cis-6 is very similar to that
of cis-4, the absorptions at 31 700 cm−1 (e ∼ 12 700 M−1cm−1)
and 36 300 cm−1 (e ∼ 23 400 M−1cm−1) being assigned to the RuII
MLCT and acac p → p* transitions respectively. Bulk anodic
electrolysis of a solution of cis–6 at −50 ◦C under a potential
of +0.75 V (vs. Ag/AgCl), results in the gradual loss of these
bands and the formation of bands associated with cis-6+, which
displays the characteristic RuIII → acac p* transitions (MLCT) at
13 800 (e ∼ 2100 M−1 cm−1) and 16 200 (e ∼ 2100 M−1 cm−1) cm−1.
However, no intervalence charge transfer (IVCT) band could
be detected between 6000–10 000 cm−1, either because its molar
absorption coefficent is very small or because it lies outside the
spectral window used here (< 6000 cm−1). These observations,
together with the electrochemical data, suggest that cis-6+ has a
localised structure i.e., it is a Robin–Day Class II mixed valence
compound. Application of a potential of +1.10 V (vs. Ag/AgCl)
to the electrogenerated solution of cis-6+ formed in situ doubles
the intensity of the RuIII → acac p* transitions. The band positions
above 30 000 cm−1 also change presumably because there is now
only one chromophore viz. RuIII/III instead of RuII/III. The changes
in the electronic spectrum after both anodic electrolytic processes
are fully reversible upon reduction. Isosbestic points occur for
each electro-oxidation and subsequent reduction, suggesting that
only two absorbing species are present during each process.
Cyclic and ac voltammograms show that the E1/2 (RuIII/II
)
potentials of complexes trans-3·PF6 and trans-4·PF6 do not differ
from those of the parent Ru(II) complexes, hence the chemical
oxidation is not accompanied by geometrical rearrangement.
Further, the ESR spectra of trans-3·PF6 and trans-4·PF6 in a frozen
glass in 0.5 M [nBu4N][PF6]/CH2Cl2 at 4.7 K show three g values,
shown in Table 6 and may be considered as pseudo-axial with
two relatively close resonances (g1 and g2). Not surprisingly, the
g-values for trans-3+ and trans-4+ do not differ significantly from
those reported for trans-[Ru(acac)2(PPh3)2]+, but are significantly
different from those of cis-[Ru(acac)2(PPh3)2]+.54
Molecular structures
The structures of complexes trans-4, cis-4, trans-4·PF6 and cis-
6 have been confirmed by single crystal X-ray crystallography;
the molecular structures and selected metrical data are presented
in Fig. 1–4 and Tables 7–10, respectively. The ruthenium atoms
Ru(1) in trans-4 and trans-4·PF6 lie on an inversion centre. There
are two pairs of independent molecules in the unit cell for cis-4,
one of which shows some disorder in its alkynyl groups. In all the
complexes, the coordination geometry about the metal centre is
close to octahedral. The Ru–O distances in trans-4, cis-4 and cis-6
˚
lie within the narrow range of 2.051(3) to 2.104(4) A observed in
other Ru(II)–acac complexes;39–41,53,58 the Ru–O distances trans to
Chemical oxidation
˚
the P atoms are ca. 0.03 A longer than those trans to the acac
From the addition of a slight excess of AgPF6 to an orange solution
of trans-3 or trans-4 in CH2Cl2 at room temperature the green
complexes trans-[Ru(acac)2(PPh2C≡CR)2][PF6] (R = H, trans-
3·PF6; Me, trans-4·PF6) can be isolated in yields of ca. 90%. These
have been fully characterised and the structure of trans-4·PF6 has
been confirmed by a single crystal X-ray study. Addition of ca. one
equivalent of AgPF6 to cis-3 or cis-4 in CH2Cl2 gives deep blue
solutions but we have been unable to isolate the resulting oxidation
products, presumably cis-3·PF6 and cis-4·PF6, as pure crystalline
solids.
O atoms corresponding to the expected trans-influences. The Ru–
O distances characterising the coordination of the acac groups
in trans-4·PF6 are similar to those reported in the orthorhombic
and monoclinic forms of [Ru(acac)3].59, 60 These distances are ca.
˚
0.05 A shorter than those in trans-4, which confirms the expected
stronger coordination of the acac− anion in the higher oxidation
state.
˚
The Ru–P distances in cis-4 (2.26 A, av.) are significantly less
than that in trans-4 (2.3330 (7) A), again reflecting the expected
˚
trans-influences of P and acac O. Similar bond lengths were
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Fig. 1 Molecular structure of trans-4. Ellipsoids represent 30% probabil-
ity levels. Hydrogen atoms have been omitted for clarity. Asterisked atom
labels indicate atoms that have been generated by the symmetry operation
(1 − x, 1 − y, 1 − z).
Fig. 3 Molecular structure of trans-4·PF6. Ellipsoids represent 30%
probability levels. Hydrogen atoms and the PF6 anion have been omitted
for clarity. Asterisked atom labels indicate atoms that have been generated
by the symmetry operation (1 − x, 1 − y, 1 − z).
Fig. 4 Molecular structure of cis-6. Ellipsoids represent 30% probability
levels. Hydrogen atoms have been omitted for clarity.
Fig. 2 Molecular structure of one of the molecules of cis-4. Ellipsoids
represent 30% probability levels. Hydrogen atoms have been omitted for
clarity.
◦
˚
Table 7 Selected bond distances (A) and angles ( ) for compound trans-4
Ru(1)–P(1)
Ru(1)–O(1)
2.3330(7)
2.060(2)
180.0
91.27(6)
88.73(6)
90.22(6)
89.78(6)
179.6(4)
Ru(1)–O(2)
C(6)–C(7)
2.063(2)
1.185(4)
180.0
93.34(7)
86.66(7)
180.0
observed in cis- and trans-[Ru(acac)2(PMePh2)2].39 The Ru–P
distance in trans-4·PF6, 2.393(1) A, is 0.06 A greater than in trans-
4, perhaps indicating of the smaller p-back-bonding ability of
RuIII.
P(1)–Ru(1)–P(1)a
P(1)–Ru(1)–O(1)a
P(1)–Ru(1)–O(1)
P(1)–Ru(1)–O(2)
P(1)–Ru(1)–O(2)a
C(6)–C(7)–C(8)
O(1)–Ru(1)–O(1)a
O(1)–Ru(1)–O(2)
O(1)–Ru(1)–O(2)a
O(2)–Ru(1)–O(2)a
P(1)–C(6)–C(7)
˚
˚
˚
The C≡C bond lengths in all four structures are close to 1.18 A.
174.5(3)
They are similar tothose found inmanyalkynyldiphenylphosphine
complexes and significantly less than that found in free dppa
a Atoms generated by the symmetry operation (1 − x, 1 − y, 1 − z).
61
˚
(1.207(5) A). In trans-4, cis-4 and trans-4·PF6 the alkynyl
groups are slightly distorted from linearity, the P–C≡C bond
angles being in the range 173 to 179◦. A similar bending has
been observed in other alkynyldiphenylphosphine complexes, e.g.,
trans-[Pd(SCN)2(Ph2PC≡CtBu)2] (174◦)62 and cis-[Pt(SCN)(NCS)
(Ph2PC≡CtBu)2] (168◦, 176◦),63 and in free dppa.61
The crystal of cis-6 contains only the homochiral (DD/KK)
isomer, which is presumably the only isomer present in solution.
The Ru–P distances are close to those in cis-4. The two octahe-
dra have different orientations, the dihedral angle between the
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◦
◦
˚
˚
Table 10 Selected bond distances (A) and angles ( ) for compound cis-6
Table 8 Selected distances (A) and angles ( ) for compound cis-4
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–O(3)
Ru(1)–O(4)
C(11)–C(12)
C(26)–C(27)
2.249(1) Ru(2)–P(3)
2.265(1) Ru(2)–P(4)
2.063(3) Ru(2)–O(5)
2.088(3) Ru(2)–O(6)
2.059(3) Ru(2)–O(7)
2.098(3) Ru(2)–O(8)
1.183(6) C(66)–C(67)
1.180(6) C(511)–C(521)
C(522)(C(532)
2.259(1)
2.254(2)
2.056(3)
2.095(3)
2.069(3)
2.104(4)
1.177(6)
1.18(2)
1.20(2)
94.30(5)
90.6(1)
176.8(1)
92.0(1)
92.6(1)
92.4(1)
88.8(1)
91.8(1)
172.8(1)
90.0(1)
174.9(1)
85.5(1)
87.2(1)
84.3(1)
89.9(1)
173(1)
Ru(1)–P(1)
Ru(1)–P(2)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–O(3)
Ru(1)–O(4)
C(11)–C(12)
P(1)–Ru(1)–P(2)
P(1)–Ru(1)–O(1)
P(1)–Ru(1)–O(2)
P(1)–Ru(1)–O(3)
P(1)–Ru(1)–O(4)
P(2)–Ru(1)–O(1)
P(2)–Ru(1)–O(2)
P(2)–Ru(1)–O(3)
P(2)–Ru(1)–O(4)
O(1)–Ru(1)–O(2)
O(1)–Ru(1)–O(3)
O(1)–Ru(1)–O(4)
O(2)–Ru(1)–O(3)
O(2)–Ru(1)–O(4)
O(3)–Ru(1)–O(4)
2.265(1) Ru(2)–P(3)
2.253(1) Ru(2)–P(4)
2.051(3) Ru(2)–O(5)
2.090(3) Ru(2)–O(6)
2.068(3) Ru(2)–O(7)
2.091(3) Ru(2)–O(8)
1.179(6) C(25)–C(26)
2.269(1)
2.261(1)
2.065(3)
2.088(3)
2.056(3)
2.097(3)
1.190(6)
94.43(4)
91.61(9)
172.26(9)
90.7(1)
91.93(9)
92.06(9)
92.64(9)
91.15(9)
173.51(9)
91.3(1)
175.9(1)
86.5(1)
86.0(1)
81.1(1)
90.1(1)
121.9(1)
114.1(1)
170.1(4)
169.7(4)
92.04(4)
91.82(9)
173.97(9)
91.10(9)
95.85(9)
88.94(9)
92.60(9)
95.36(9)
170.26(9)
92.1(1)
P(3)–Ru(2)–P(4)
P(3)–Ru(2)–O(5)
P(3)–Ru(2)–O(6)
P(3)–Ru(2)–O(7)
P(3)–Ru(2)–O(8)
P(4)–Ru(2)–O(5)
P(4)–Ru(2)–O(6)
P(4)–Ru(2)–O(7)
P(4)–Ru(2)–O(8)
O(5)–Ru(2)–O(6)
O(5)–Ru(2)–O(7)
O(5)–Ru(2)–O(8)
O(6)–Ru(2)–O(7)
O(6)–Ru(2)–O(8)
O(7)–Ru(2)–O(8)
Ru(2)–P(3)–C(12)
Ru(2)–P(4)–C(26)
P(2)–C(25)–C(26)
P(4)–C(26)–C(25)
P(1)–Ru(1)–P(2)
P(1)–Ru(1)–O(1)
P(1)–Ru(1)–O(2)
P(1)–Ru(1)–O(3)
P(1)–Ru(1)–O(4)
P(2)–Ru(1)–O(1)
P(2)–Ru(1)–O(2)
P(2)–Ru(1)–O(3)
P(2)–Ru(1)–O(4)
O(1)–Ru(1)–O(2)
O(1)–Ru(1)–O(3)
O(1)–Ru(1)–O(4)
O(2)–Ru(1)–O(3)
O(2)–Ru(1)–O(4)
O(3)–Ru(1)–O(4)
P(1)–C(11)–C(12)
94.20(5) P(3)–Ru(2)–P(4)
91.3(1)
174.3(1)
93.5(1)
90.1(1)
P(3)–Ru(2)–O(5)
P(3)–Ru(2)–O(6)
P(3)–Ru(2)–O(7)
P(3)–Ru(2)–O(8)
89.91(9) P(4)–Ru(2)–O(5)
91.0(1) P(4)–Ru(2)–O(6)
92.82(9) P(4)–Ru(2)–O(7)
174.2(1)
91.2(1)
174.3(1)
86.0(1)
83.8(1)
85.0(1)
90.9(1)
175.8(5)
P(4)–Ru(2)–O(8)
174.7(1)
85.1(1)
84.6(1)
O(5)–Ru(2)–O(6)
O(5)–Ru(2)–O(7)
O(5)–Ru(2)–O(8)
O(6)–Ru(2)–O(7)
O(6)–Ru(2)–O(8)
O(7)–Ru(2)–O(8)
P(3)–C(511)–C(521)
P(3)–C(512)–C(522)
P(4)–C(66)–C(67)
C(511)–C(521)–C(531)
C(512)–C(522)–C(532)
C(66)–C(67)–C(68)
79.9(1)
90.2(1)
Ru(1)–P(1)–C(11) 119.7(1)
Ru(1)–P(2)–C(25) 112.4(2)
P(1)–C(22)–C(12) 178.3(4)
P(3)–C(12)–C(11) 177.9(4)
173(2)
177.2(5)
177(2)
180(2)
179.4(7)
P(2)–C(26)–C(27)
C(11)–C(12)–C(13)
176.4(5)
178.8(6)
Conclusions
C(26)–C(27)–C(28)
178.9(6)
We have reported in this paper P-donor alkynyldiphenylphos-
phine complexes of ruthenium(II) containing acetylacetonate as
co-ligand, [Ru(acac)2L2] (L = Ph2PC≡CH, Ph2PC≡CCH3, or
Ph2PC≡CPh), which can be isolated in trans- or cis-isomeric
forms. The trans-isomers undergo reversible one-electron oxida-
tion to the RuIII level more easily than the cis-isomers. A compar-
ison of the metrical data for trans-[Ru(acac)2(Ph2PC≡CCH3)2]0,+
(trans-4, 4+) shows the effect of one-electron redox on the metal–
ligand bond lengths. In cis-[{Ru(acac)2(l-dppa)}2], cis-6, two
molecules of the dppa bridge a pair of cis-{Ru(acac)2} fragments,
only the homochiral DD/KK isomer being present. cis-6 undergoes
two, successive one-electron oxidations; cis-6+ is classed as a
Robin–Day Class II mixed valence system, showing that electron
delocalisation via dppa can occur.
◦
˚
Table 9 Selected bond distances (A) and angles ( ) for compound trans-
4·PF6
Ru(1)–P(1)
Ru(1)–O(1)
2.393(1)
2.011(3)
Ru(1)–O(2)
2.003(3)
1.185(6)
C(6)–C(7)
P(1)–Ru(1)–P(1)a
P(1)–Ru(1)–O(1)a
P(1)–Ru(1)–O(1)
P(1)–Ru(1)–O(2)
P(1)–Ru(1)–O(2)a
C(6)–C(7)–C(8)
180.0
O(1)–Ru(1)–O(1)a
O(1)–Ru(1)–O(2)
O(1)–Ru(1)–O(2)a
O(2)–Ru(1)–O(2)a
P(1)–C(6)–C(7)
180.0
90.36(8)
89.64(8)
88.88(9)
91.12(9)
179.3(6)
90.3(1)
89.7(1)
180.0
178.9(5)
a Atoms generated by the symmetry operation (1 − x, 1 − y, 1 − z).
Experimental
planes defined by the atoms Ru(1), P(1) and P(2), and Ru(2),
P(3) and P(4), being ca. 46◦. A similar arrangement is found
in the complexes [Pt2X4(l-dppa)2] (X = Cl,29 I,29 C6F532) and
[{Mo(CO)4}2(l-dppa)2],25 which gives the complex a characteristic
“bow-tie” appearance, whereas in [Pd2Cl4(l-dppa)2]29 the ten-
membered ring is planar. Viewed along the Ru–Ru axis, the two
octahedra are essentially eclipsed and the l-dppa ligand defined
by atoms P(1) and P(3) is almost linear [angles P(1)–C(11)–C(12)
and P(3)–C(12)–C(11) are both 178◦], whereas the second l-dppa
ligand shows a slight concave bowing, the angles P(2)–C(25)–C(26)
and P(4)–C(26)–C(25) each being 170◦. However, the linear l-
dppa shows the greater strain at its phosphorus atoms as judged
by the departure of the Ru–P–C valence angles from the ideal
tetrahedral value [Ru(1)–P(1)–C(11) 119.7(1)◦; Ru(2)–P(3)–C(12)
121.9(1)◦] cf the values for the concave l-dppa [Ru(1)–P(3)–C(25)
112.4(2)◦; Ru(2)–P(4)–C(26) 114.1(1)◦].
All operations were carried out under a dry argon atmosphere
using standard Schlenk techniques unless otherwise stated. All
solvents were dried by standard methods and distilled under
nitrogen. The starting ruthenium(II) complexes 1,40 239 and the
alkynyldiphenylphosphines Ph2PC≡CR (R = H, Me, Ph)64 were
prepared according to the literature procedures; Ph2PC≡CPPh2
(dppa) was obtained from Fluka and used as received.
NMR spectra were recorded at 20.5 ◦C on either a Varian
Gemini 300 BB or a Varian VXR 300 spectrometer (1H at
1
1
300 MHz, 13C{ H} at 75.4 MHz and 31P{ H} at 121.4 MHz). The
chemical shifts (d) for 1H and 13C are given in ppm referenced to the
residual protons and the carbon atoms of the deuterated solvents;
31P chemical shifts are referenced to external 85% H3PO4. Coupling
constants (J) are given in Hertz. IR spectra were recorded on either
Perkin-Elmer 1800 FT or Perkin-Elmer Spectrum One instru-
ments as KBr disks. The Raman spectrum of cis-6 was collected
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on a Renishaw Raman system 2000 with a HeNe laser (Spectra-
Physics, model 127) emitting at 632.8 nm or a Renishaw NIR laser
diode emitting at 780 nm. Fast atom bombardment (FAB) mass
spectra were measured on a VG ZAB2-SEQ mass spectrometer us-
ing either 3-nitrobenzyl alcohol or (3-nitrophenyl)octyl ether as the
matrix. Microanalyses were performed in-house. Electrochemical
measurements in CH2Cl2 and electronic spectra were recorded in
(6) trans-[{Ru(acac)2(l-dppa)}n]
(trans-6). Solid
dppa
(400 mg, 1.01 mmol) was added to a THF solution of 2 prepared
from [Ru(acac)3] (200 mg, 0.51 mmol) and the mixture was stirred
overnight. The initially orange clear solution deposited an orange
solid trans-6 (325 mg, 90%), which was isolated by filtration and
washed several times with n-hexane. Free Ph2PC≡CPPh2 was
1
detected in the washings by 31P{ H} NMR spectroscopy but no
the range 6000–45 000 cm−1 as previously described;40,41,58 the E1/2
-
attempt was made to quantify it.
value for the ferrocenium/ferrocene couple on the electrochemical
set-up was +0.55 V vs. Ag/AgCl. Continuous wave X-band ESR
spectra were collected on a Bruker ESP 300e spectrometer with a
rectangular TE102 cavity and a frequency counter for accurate g-
value measurements. The following settings were used: modulation
frequency 50–100 kHz, microwave power 2.0 mW (sufficiently
low to avoid sample saturation), modulation amplitude 5 G, time
constant 0.33 s, and sweep time 330 s. The temperature was lowered
to 4.7 K with liquid helium and an Oxford Instrument cryostat.
(7) cis-[{Ru(acac)2(l-Ph2PC≡CPPh2)}2] (cis-6). A suspen-
sion of trans-6 (157 mg, 0.23 mmol) in C6H5Cl (20 ml) was heated
to 150 ◦C for 3 h, giving a clear yellow solution. The solvent was
removed in vacuo at room temperature and the yellow residue was
dissolved in a small amount of CH2Cl2; the solution was then
layered with n-hexane (20 ml). The yellow solid cis-6(63 mg, 40%)
was isolated by filtration and washed with n-hexane. It is air-stable
and readily forms air-stable solutions in CH2Cl2 and C6H5Cl.
(8) trans-[Ru(acac)2(Ph2PC≡CH)2][PF6] (trans-3·PF6). Ad-
dition of AgPF6 (50 mg, 0.20 mmol) to a solution of trans-3
(100 mg, 0.14 mmol) in CH2Cl2 (10 ml) resulted in an immediate
colour change from orange to blue-green, and a grey metallic
mirror deposited on the flask wall. The solution was stirred for
30 min and filtered through Celite. Solvent was removed in vacuo
leaving a green solid, which was dissolved in a small amount of
CH2Cl2 and carefully layered with n-pentane. The green crystalline
solid trans-3·PF6 (98 mg, 89%) was isolated by filtration.
Preparations
(1) trans-[Ru(acac)2(Ph2PC≡CH)2] (trans-3). A clear solu-
tion of 1 prepared from [Ru(acac)3] (260 mg, 0.65 mmol) in THF
(20 ml) was stirred with Ph2PC≡CH (275 mg, 1.31 mmol) for 1 h;
within 5 min of mixing a fine orange precipitate had formed. An
orange solid was isolated after evaporating the mixture to dryness
and washing with n-hexane (3 × 10 ml). 357 mg (79%) of trans-
3 was isolated by filtration and air-dried. A small amount of the
orange solid was recrystallised from CH2Cl2 and n-pentane vapour
was allowed to diffuse into the solution resulting in large orange
crystals.
(9) trans-[Ru(acac)2(Ph2PC≡CMe)2][PF6]
(trans-4·PF6).
This was prepared similarly to trans-3·PF6 from AgPF6 (52 mg,
0.21 mmol) and trans-4 (65 mg, 0.09 mmol). 70 mg (90%) of the
green crystalline solid trans-4·PF6 was isolated containing some
X-ray quality crystals.
(2) trans-[Ru(acac)2(Ph2PC≡CMe)2] (trans-4). This was pre-
pared as outlined above for trans-3 from [Ru(acac)3] (260 mg,
0.65 mmol) and Ph2PC≡CMe (305 mg, 1.36 mmol). The yield of
the orange, air-stable solid trans-4 was 482 mg (98%). Its physical
properties were similar to those of trans-3. X-Ray quality crystals
were grown by vapour diffusion of n-pentane into an orange
CH2Cl2 solution.
X-Ray crystallography
Measurements for trans-4, trans-4·PF6 and cis-6 were made on
a Rigaku AFC6R diffractometer with graphite-monochromated
˚
Cu-Ka radiation (k = 1.54178 A); those for cis-4 were made on
a Rigaku AFC6S diffractometer with graphite-monochromated
˚
Mo-Ka radiation (k = 0.71069 A). Selected crystal data and
(3) trans-[Ru(acac)2(Ph2PC≡CPh)2] (trans-5). This was pre-
pared similarly to trans-3 from [Ru(acac)3] (208 mg, 0.52 mmol)
and Ph2PC≡CPh (1.05 mmol). The yield of the orange, air-stable
solid trans-5 was 278 mg (61%).
details of data collection are in Table 11. The structures were
solved by direct methods (SIR 92)65 and expanded by use of
Fourier techniques (DIRDIF94).66 Non-hydrogen atoms were
refined anisotropically by full-matrix least squares. Hydrogen
atom coordinates were refined but their isotropic B-values were
held fixed. Difference maps obtained before hydrogen atoms had
been included did not give clear evidence for a single preferred
orientation for the acac methyl groups in every case. The H-
atoms were therefore added in the same orientation as in the
other structures, but CHECKCIF revealed some very short
intermolecular H · · · H contacts between some of these atoms.
These methyl groups were therefore reorientated, thereby reducing
the problems. The changes therefore seemed to be warranted.
The CH2Cl2 molecule in cis-4 was disordered over two unequally
populated orientations. The carbon atom and one of the chlorine
atoms of the major orientation were refined with anisotropic
displacement factors, while the corresponding chlorine atom of
the minor orientation was assigned an isotropic B-value equal to
(4) cis-[Ru(acac)2(Ph2PC≡CMe)2] (cis-4). An orange solu-
tion of trans-4 (232 mg, 0.31 mmol) in C6H5Cl (5 ml) was refluxed
for 1 h, during which time the colour changed from orange to
yellow. The yellow residue obtained after the solvent had been
removed in vacuo was dissolved in CH2Cl2 (2 ml) forming a yellow
solution to which n-hexane (25 ml) was carefully added. The
bright yellow, micro-crystalline solid that deposited overnight was
separated by filtration, washed with n-hexane (ca. 5 ml) and air-
dried to give 151 mg (65%) of cis-4. It is stable towards air and
forms yellow, air-stable solutions in benzene, toluene, CH2Cl2 and
C6H5Cl.
(5) cis-[Ru(acac)2(Ph2PC≡CPh)2] (cis-5). This was prepared
as outlined above for cis-4 from trans-5 (120 mg, 0.14 mmol). The
yield of bright yellow cis-5 was 80 mg (67%). The compound has
similar physical properties to those reported for cis-4.
B
eq of the chlorine atom in the major orientation; the carbon atom
in the minor orientation could not be be located. Disorder was
1684 | Dalton Trans., 2007, 1677–1686
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Table 11 Crystal and refinement data for trans-4, cis-4, trans-4·PF6 and cis-6a
trans-4
cis-4
trans-4·PF6
cis-6
Empirical formula
Formula weight
Crystal system
C40H40O4P2Ru.2CH2Cl2 C80H80O8P4Ru2.CH2Cl2
C42H44Cl4F6O4P3Ru.2CH2Cl2
C72H68O8P4Ru2.0.5CH2Cl2.0.5C6H14
1472.9
917.64
1580.48
Triclinic
P1 (no. 2)
1062.60
Triclinic
Triclinic
Monoclinic
¯
¯
¯
¯
Space group
P1 (no. 2)
P1 (no. 2)
P2/n (no. 14)
Crystal colour, habit
Orange, block
10.247(1)
11.045(3)
11.720(2)
117.21(2)
94.27(2)
107.61(1)
1088.3(5)
1
Yellow, hexagonal prism Green, rhomboid
Yellow, cuboid
12.096(4)
22.508(4)
27.778(3)
90
˚
a/A
16.317(4)
16.469(6)
18.975(4)
65.46(2)
66.17(2)
60.76(2)
3915(2)
2
9.7900(9)
11.1192(8)
11.1518(9)
104.946(6)
93.248(7)
97.520(7)
1157.6(2)
1
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
102.41(2)
90
7386(3)
4
1.324
48.76 (CuKa)
193
3
˚
V/A
Z
D
calc/g cm−3
1.400
1.340
1.524
64.07 (CuKa)
193
l/cm−1
63.16 (CuKa)
193
5.88 (MoKa)
296
T/K
Crystal dimensions/mm
0.20 × 0.12 × 0.10
0.52 × 0.24 × 0.16
0.08 × 0.07 × 0.07
0.25 × 0.18 × 0.15
F(000)
470
1628
539
3032
◦
2hmax
/
120.0
55.1
120.1
120.0
Number of reflections
measured
Number of unique
3425
18715
3678
11280
3241 (0.039)
18081 (0.030)
3443 (0.031)
10940
reflections (Rint
)
Used reflections
R; RW
3026 [I > 2r(I)]
0.028; 0.035
1.63
9045 [I > 2r(I)]
0.042, 0.044
1.54
0.70, −0.54
2737 [I > 2r(I)]
0.036, 0.041
1.36
0.55, −0.46
8826 [I > 3r(I)]
0.039, 0.044
1.15
Goodness of fit
−3
˚
qmax, qmin/e A
0.49, −0.43
1.07, −0.61
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
a Definitions: R = ꢂFo| − |Fcꢂ/ |Fo|; Rw = [ w(|Fo| − |Fc|)2/ w|Fo
|
1/2; w = [r2(Fo) + 0.25p2Fo
]
−1; GOF = [ w(|Fo| − |Fc|)2/(No
−
2
2
Nv)1/2; No = used reflections, Nv = number of variables.
also evident from the anisotropy of the carbon atoms in one of
the C≡CCH3 units of cis-4; each atom was split over two sites
and the relative occupancy of the two orientations was refined.
All the calculations were carried out with the TEXSAN software
package,67 except for the refinement of cis-6, which was carried out
with the use of CRYSTALS.68 Neutral atom scattering factors,69
the values of Df and Df ꢀꢀ, and mass attenuation coefficients70 were
taken from standard compilations.
7 I. Ara, L. R. Falvello, S. Ferna´ndez, J. Fornie´s, E. Lalinde, A. Mart´ın
and M. T. Moreno, Organometallics, 1997, 16, 5923–5937.
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11 G. Hogarth and S. P. Redmond, J. Organomet. Chem., 1997, 534, 221–
227.
CCDC reference numbers 631384–631387.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b618365d
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101, 5422–5424.
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Acknowledgements
We thank Dr C. Cobley (ANU) for synthesising Ph2PC≡CR (R =
H, Me, Ph), Dr V. Otieno-Alego (University of Canberra) for the
measurement of the Raman spectrum of cis-6, and Dr R. Webster
(ANU) for the ESR measurements.
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1686 | Dalton Trans., 2007, 1677–1686
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©