Ruthenocenyl ruthenium bimetallic complexes: Electrospray mass spectrometric study of [RuX(η5-C5H5)(η2-dppr)] n+ (dppr=1,1′-bis(diphenylphosphino)ruthenocene) (X=Cl, n=0; X=CO, CH3CN, C=CHPh, n=1) and

Article abstract of DOI:10.1016/S0022-328X(98)00990-5

[RuCl(Cp)(PPh₃)₂] (Cp=η⁵-C₅H₅) reacts with dppr in refluxing benzene to give [RuCl(Cp)(dppr)], 1, {dppr=[Ru(η⁵-C₅H₄PPh₂) ₂]} in 91% yield. Comple

Full text of DOI:10.1016/S0022-328X(98)00990-5

Journal of Organometallic Chemistry 575 (1999) 171–181
Ruthenocenyl ruthenium bimetallic complexes: electrospray mass
spectrometric study of [RuX(p5-C5H5)(p2-dppr)]n+
(dppr=1,1%-bis(diphenylphosphino)ruthenocene) (X=Cl, n=0;
X=CO, CH3CN, CꢀCHPh, n=1) and the X-ray crystal and
molecular structure of [Ru(p5-C5H5)(CO)(p2-dppr)]PF6
Siew Po Yeo a, William Henderson b, Thomas C.W. Mak c, T.S. Andy Hor a,*
a Department of Chemistry, Faculty of Science, National Uni6ersity of Singapore, Kent Ridge, 119260 Singapore, Singapore
b Department of Chemistry, Uni6ersity of Waikato, Pri6ate Bag 3105, Hamilton, New Zealand
c Department of Chemistry, The Chinese Uni6ersity of Hong Kong, Shatin, NT, Hong Kong
Received 15 July 1998; received in revised form 19 September 1998
Abstract
[RuCl(Cp)(PPh3)2] (Cp=p5-C5H5) reacts with dppr in refluxing benzene to give [RuCl(Cp)(dppr)], 1, {dppr=[Ru(p5-
C5H4PPh2)2]} in 91% yield. Complex ionizes in boiling acetonitrile in the presence of excess NH4PF6 to give
1
[Ru(Cp)(CH3CN)(dppr)]PF6, 2, in 76% yield. Under CO at 60°C, 1 converts to [Ru(Cp)(CO)(dppr)]Cl, 3a, whose derivative
[Ru(Cp)(CO)(dppr)]PF6, 3b, can also be obtained from 2 in 86% with CO. With HCꢁCPh, 2 instantaneously gives a vinylidene
complex, [Ru(CꢀCHPh)(Cp)(dppr)]PF6, 4, quantitatively (98%). The kinetic stability of the p2-coordinated dppr ring is evident in
˚
these reactions. The X-ray molecular structure of 3b [space group P21/c, a=9.990(2), b=19.498(4), c=19.113(4) A and
i=96.21(3)°] reveals a pseudo-octahedral Ru(II) structure with a p5-Cp, a chelated dppr, a terminal CO and an uncoordinated
PF6− anion. It is the first piano-stool dppr structure characterized by X-ray single-crystal diffractometry. The dppr chelate has a
˚
large bite (100.5(1)°) and there is no direct interaction between the two Ru(II) centers (Ru(1)···Ru(2) 4.389 A). The electrospray
mass spectra (ESMS) of 2–4 generally give peaks due to the intact cations at low cone voltages. As the cone voltage increases,
fragmentation commences which inevitably gives [Ru(Cp)(dppr)]+ as the primary fragment ion. In-situ doping of dppr with
AgNO3 gives [Ag(dppr)]+ as the major species plus [Ag(dppr)2]+ (m/z 1307) and other oxidized by-products. Similar treatment
of 4 gives an acetylide complex [Ag{Ru(Cp)(CꢁCPh)(dppr)}2]+ (m/z 1843) at 20 V which ejects one Ru metalloligand to give
[Ag{Ru(Cp)(CꢁCPh)(dppr)}]+ (m/z 975) at higher voltages. Complex 4 is hydrogenated with H2 gas to give ethylbenzene in 55%
yield after 4 h in refluxing THF. It also catalyzes the hydrogenation of HCꢁCPh to give 52% of ethylbenzene in 5 h at 5 mol.%
catalyst level. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Ruthenium; Metallocenyl phosphine; Vinylidene; Electrospray mass spectrometry; Crystal structure
phosphine complexes [1]. The phosphines used include
both monophosphines and diphosphines. In some cases,
the chelate effect of the latter appears to promote the
catalytic efficiency. When the diphosphine is metal-
locene-based such as 1,1%-bis(diphenylphosphino)-
ferrocene (dppf), such catalytic enhancement is further
manifested [2]. Even though in many cases understand-
ing of the role played by the diphosphine
1. Introduction
Many organic reactions, notably cross-coupling,
Grignard-type couplings, Heck reactions, hydroformy-
lations and hydrogenations, are catalyzed by metal
* Corresponding author. Tel.: +65-8742917; fax: +65-7774279;
e-mail: chmandyh@nus.edu.sg.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)00990-5

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S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
Scheme 1. Synthesis of [RuCl(Cp)(dppr)], 1, and its substitution reactions with CO, CH3CN and HCꢁCPh.
and even the catalytic mechanism in general is very
tentative, it does not deter the use of these metallocenyl
diphosphines as ligands in catalytic systems. The com-
mon use of dppf today is such an example [3]. Although
many of the advantages of dppf can in principle be
manifested in its ruthenocene analogue, viz. 1,1%-bis
(diphenylphosphino)ruthenocene (dppr), due to its
larger ring separation and bigger chelate bite, the use of
dppr complexes is still at its infancy. This problem is
partly attributed to the lack of established dppr com-
plexes in the literature. Recently, we reported the syn-
thesis and catalytic behavior of [MCl2(dppr)] (M=Ni,
Pd and Pt) [4] and the chemistry of [RuCl2(dppr)(L)]
(L=PPh3, CO, CH3CN) [5]. We herein extend our
investigations to the synthesis of [RuCl(Cp)(dppr)] and
its reactivity towards some representative small
molecules such as CO, CH3CN and HCꢁCPh. Many of
the complexes isolated are studied by electrospray (ion-
ization) mass spectrometry (ESMS) [6], which is rapidly
gaining recognition as a versatile mass spectrometry
with a soft ionization process. It is particularly useful
for the characterization of organometallic complexes in
solution [7]. The fragmentation patterns at different
cone voltages can often yield invaluable structural in-
sight on the complexes [8]. In this paper, we report the
use of ESMS, assisted by other techniques, in the study
of a series of bimetallic ruthenium ruthenocenyl phos-
phine complexes. We also report the use of AgNO3 as
a doping technique for the ESMS identification of other
species that have not yet been isolated. The catalytic
potential of the Ru–dppr system is also explored. The
reactions described are compared with those of [Ru-
ClCp(L)] (L=2×PPh3, dppm, dppe and dppf
[dppm=bis(diphenylphosphino)methane; dppe=1,2-
bis(diphenylphosphino)ethane]) [9]. Our interest in the
Ru(II) system stems from its potential shown in cataly-
sis especially in chiral synthesis [10] and hydrogenation
[11], for example, Ru(II) diphosphine (binap) (binap=
2,2%-bis(diphenylphosphino)-1,1%-binaphthyl) complexes
in Naproxen® synthesis [12].
2. Results and discussion
Phosphine replacement in [RuCl(Cp)(PPh3)2] with
dppr occurs readily in refluxing benzene to give [Ru-
Cl(Cp)(dppr)], 1 in 91% yield. Complex 1 ionizes in
boiling CH3CN in the presence of excess NH4PF6 to
give the acetonitrile complex [Ru(Cp)(CH3CN)-
(dppr)]PF6, 2 in 76% yield. Chloride displacement of 1
by CO giving [Ru(Cp)(CO)(dppr)]Cl, 3a, occurs at 60°C
in EtOH under an atmospheric pressure of CO gas.
Formation of the PF6− derivative of 3, viz. 3b, can be
effected at room temperature (r.t.) and with high yield
(86%) when 2 is used as the substrate. The advantage in
using a labile solvent complex in ligand substitution
reactions is also evident when 2 absorbs HCꢁCPh
rapidly (within seconds) at r.t. to give [Ru(Cꢀ
CHPh)(Cp)(dppr)]PF6, 4 in near-quantitative (98%)
yield. These reactions are summarized in Scheme 1.

S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
173
Formation of 1 from [RuCl(Cp)(PPh3)2] represents a
facile substitution of PPh3 by dppr. This is somewhat
surprising considering that a bulky ligand such as dppr
is not expected to gain much entropy advantage on the
chelate effect and that a number of dppr complexes are
known to be kinetically labile [13]. The stability of the
p2-coordinated dppr is possibly attributed to the better
y-accepting ability of dppr as a result of the conjuga-
tion of the y* orbitals of C5 rings with the empty
d-orbitals of the phosphorus atoms. The higher acidity
of dppr is expected to contract the 4d orbitals of Ru
which could then overlap better with the filled 3p-or-
bitals of Cl. This proposed strengthening of the Ru–Cl
interaction receives some experimental support as 1 is
insoluble in MeOH in which its PPh3 analogue [14]
readily dissolves by ionization. All the PPh3, PMe3 [15],
dppm ([9]a) and dppe ([9]a) derivatives ionize easily in
acetonitrile through chloride dissociation whereas for 1,
the assistance from NH4PF6 is needed in its chloride
extraction to give 2. There is no evidence that a ring
opening reaction giving [RuCl(Cp)(CH3CN)(p1-dppr)]
would proceed. The integrity of the chelate ring is
maintained even under reflux conditions in a donor
solvent such as CH3CN. The carbonylation of 1 giving
3 reiterates the stability of the bimetallic chelate and the
ability for 1 to accept a 2-electron donor. This absorp-
tion of CO is sluggish at r.t. but proceeds readily at
60°C. However, the labile CH3CN ligand in 2 ex-
changes with CO readily at r.t. The 31P-NMR reso-
nance of 3 is more deshielded compared to 1 or 2. This
is consistent with the incorporation of a strongly y-
acidic CO. Again, there is no evidence for the forma-
tion of [RuCl(Cp)(CO)(p1-dppr)]. This is in sharp
contrast to the analogous reactions of the PPh3 and
dppm derivatives which give [RuCl(Cp)(CO)(PPh3)] [14]
and [RuCl(Cp)(CO)(p1-dppm)] ([9]a), respectively (see
Scheme 1). These differences support the kinetic stabil-
ity of the ring and demonstrate the different behaviors
between dppr and other phosphines. Similar work on
the reaction of CO with [RuCl2(dppr)(PPh3)] also re-
ports a PPh3 substitution to give [RuCl2(CO)(dppr)]
rather than chloride displacement or ring opening of
the chelating phosphine [5].
Fig. 1. An ORTEP drawing of the molecular structure of
[Ru(Cp)(CO)(dppr)]PF6, 3b, (35% thermal ellipsoids)
rhombus with the Ru atoms occupying two opposite
corners and the P atoms sitting at the remaining two.
The significantly different steric requirements of dppr
and CO forces some distortions among the legs of the
stool (C(16)–Ru(1)–P(1) 92.3(3)°, C(16)–Ru(1)–P(2)
91.6(3)° and P(1)–Ru(1)–P(2) 100.5(1)°). The chelate
angle (100.5(1)°) is larger than those reported in the
piano-stool M–dppf structures ([(Ru(Cp)H(dppf)]
([9]b) 95.5(1) and 99.1(1)°; [Mn(MeCp)(CO)(dppf)] [16]
99.3(12)°). Such a large chelate bite however does not
destabilize the metal chelate ring. In agreement with the
Table 1
Crystallographic data and refinement details for [Ru(p5-
C5H5)(CO)(dppr)][PF6] 3b
Chemical formula
M
C40H33OF6P3Ru2
938.7
Crystal system
Space group
Monoclinic
P21/c
˚
a (A)
9.990(2)
19.498(4)
19.113(4)
96.21(3)
3701(2)
4
˚
b (A)
˚
c (A)
Among the few dppr complexes reported in the liter-
ature, the only one which was crystallographically char-
acterized was [PtCl2(dppr)] [4]. We intended to study
the X-ray structure of 3b and establish the bimetallic
chelate ring characteristics of dppr in an expected pi-
ano-stool environment in 3. The X-ray molecular struc-
ture of 3b confirms such a structure with a tetrahedral
ruthenium bearing a p5-Cp, a dppr chelate and a
terminal CO with an uncoordinated PF6− anion (see
Fig. 1 and Tables 1–3). The dppr chelate forms a
closed loop with the central ruthenium with no direct
interactions between the two Ru(II) centers
i (°)
V (A )
3
˚
Z
F(000)
1872
1.685
1.01
0.09
0.574–1.000
0.055
0.075
Dcalc. (g cm−3
)
v (mm−1
Mean mr
)
Transmission factors
a
RF
b
Rw
Sc
1.13
a RF=SꢀFoꢁ−ꢁFcꢀ/SꢁFoꢁ.
2 0.5
b Rw=[Sw(ꢁFoꢁ−ꢁFcꢁ)2/SwꢁFoꢁ ]
.
(Ru(1)···Ru(2) 4.389 A). This loop can be viewed as a
c S (goodness-of-fit)=[Sw(ꢁFo−ꢁFcꢁ)2/(n−p)]0.5
.
˚

174
S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
Table 2
To accommodate the large bite angle, both C5 rings
5
˚
Selected bond lengths (A) for [Ru(p -C5H5)(CO)(dppr)][PF6] 3b
are tilted inwards towards Ru(1). This causes a slight
distortion from linearity on the angle subtended by
Ru(2) to the two centroids of the C5 rings (177.4(4)°).
The large chelate bite could force stronger interactions
among the co-ligands. It also helps to stabilize the
unsaturated complex upon departure of the third lig-
and, Cl, CO or CH3CN. With these in mind, the
catalytic study of the hydrogenation of HCꢁCPh with 4
becomes meaningful.
The rapid formation of 4 from 2 demonstrates the
ability of the latter to activate unsaturated organic
substrates at r.t. The identification of a vinylidene
complex as opposed to a y-bonded alkyne complex
[Ru(Cp)(HCꢁCPh)(dppr)]PF6 or |-bonded acetylide
complex [Ru(Cp)(CꢁCPh)(dppr)] is based on the IR1
and NMR data and the related PPh3 and dppf com-
plexes [17]. Weak coupling between the vinylic proton
and phosphorus [4J(P–H) 1.9 Hz] is observed. Conclu-
sive evidence comes from the exceedingly low field shift
of the Ch atom (carbon bonded to Ru) (354.0 ppm),
which has been explained based on the paramagnetic
contribution of nuclear shielding [18]. Similar p2-alkyne
complexes would give 13C shifts which are at signifi-
cantly higher field (ꢀ50 ppm) [19]. It is interesting to
note that a similar addition of HCꢁCPh to [Ru-
Cl(Cp*)(P–P)] (P–P=diop (diop={[(2,2-dimethyl-
1,3-dioxolan-4,5-diyl)bis(methylene)]
˚
˚
Atoms
Length (A)
Atoms
Length (A)
Ru(1)–C(16)
Ru(1)–P(2)
Ru(2)–X(1B)
C(16)–O(1)
C(1)–C(5)
C(3)–C(4)
C(6)–C(7)
C(7)–C(8)
C(9)–C(10)
C(11)–C(12)
C(12)–C(13)
C(14)–C(15)
1.84(1)
2.351(2)
1.799(9)
1.16(1)
1.39(2)
1.42(2)
1.41(2)
1.39(2)
1.44(1)
1.39(1)
1.40(1)
1.40(1)
Ru(1)–P(1)
Ru(1)–X(1A)a
Ru(2)–X(1C)
C(1)–C(2)
C(2)–C(3)
C(4)–C(5)
C(6)–C(10)
C(8)–C(9)
C(10)–P(2)
C(11)–C(15)
C(13)–C(14)
C(15)–P(1)
2.361(3)
1.897(8)
1.804(9)
1.41(2)
1.39(2)
1.37(2)
1.43(1)
1.41(2)
1.823(9)
1.41(1)
1.43(1)
1.845(9)
a X(1A), X(1B) and X(1C) represent centroids of the rings of (C1,
C2, C3, C4, C5), (C6, C7, C8, C9, C10) and (C11, C12, C13, C14,
C15), respectively.
NMR data that support dppr as a good y-acid charac-
ter, the Ru–P bonds strengthen from 2.43 A in [Ru-
Cl(Cp)(PPh3)2] [15] to 2.356(3)
competition for y electrons weakens the Ru–Cp bonds
from 1.846(6) A in [RuCl(Cp)(PPh3)2] to 1.897(8) A in
3b. The terminal CO is slightly bent (Ru(1)–C(16)–
O(1) 173.3(8)°) in order to avoid extending into the
ruthenocenyl region. Coordination of dppr expectedly
weakens the phosphorus link to the C5 ring from
1.808(4) A in the free ligand [4] to an average of
1.834(9) A in 3b. The substitutionally-induced C–C
bond variations among the C5 rings are less obvious in
3b (Cp–Ch 1.42(1), Ch–Ci 1.41(2), Ci–Ck 1.40(2) A)
than in the free ligand (1.432(5), 1.413(6), and 1.402(6)
A, respectively). The coordination of the dppr ligand
imposes some differences between the two C5 rings and
their PPh2 residues.
˚
˚
A
in 3b. The
˚
˚
˚
˚
bis(diphenylphosphine)}) or binap) in the presence of
NH4PF6 and Al2O3 gives an acetylide complex [20]
whereas many of the others, including 4, result in
vinylidene complexes. Formation of 4 from 2 likely
takes place by an established mechanism which involves
ethyne addition, followed by a slippage with a con-
certed 1,2-hydrogen shift [21]. An alternative pathway
involving oxidative addition giving rise to a hydride
acetylide intermediate [22] is more feasible only for
metals such as Co(I) [23] and Rh(I) [24]. The signifi-
cance of similar vinylidene complexes in a reconstitutive
condensation of allylic alcohols and terminal alkynes
has been described elsewhere [25].
Metallocenes that have been previously studied by
ESMS display two ionization pathways, namely oxida-
tion and protonation. The former route depends on the
redox potential of the metallocene whereas the latter is
promoted by the presence of basic substituents. In
many cases, both pathways can be observed. Although
˚
˚
Table 3
Selected bond angles (°) for [Ru(p5-C5H5)(CO)(dppr)][PF6] 3b
Atoms
Angle (°) Atoms
Angle (°)
C(16)–Ru(1)–X(1A)a 121.6(5) C(16)–Ru(1)–P(1)
92.3(3)
121.0(3)
100.5(1)
C(16)−Ru(1)–P(2)
P(2)–Ru(1)–X(1A)
Ru(1)–C(16)−O(1)
C(15)–P(1)–C(28)
C(22)–P(1)–C(28)
C(10)–P(2)–C(40)
Ru(1)–P(1)–C(15)
Ru(1)–P(1)–C(28)
Ru(1)–P(2)–C(34)
91.6(3) P(1)–Ru(1)–X(1A)
122.1(4) P(1)–Ru(1)–P(2)
173.3(8) X(1B)–Ru(2)–X(1C) 177.4(4)
99.1(4) C(15)–P(1)–C(22)
102.2(4) C(10)–P(2)–C(34)
103.6(4) C(40)–P(2)–C(34)
125.2(3) Ru(1)–P(1)–C(22)
112.5(3) Ru(1)–P(2)–C(10)
112.4(3) Ru(1)–P(2)–C(40)
101.0(4)
102.7(4)
100.2(4)
113.7(3)
117.8(3)
117.7(3)
1 The presence of two n(CꢀC) bands both in the solid KBr mull and
solution could suggest the presence of two isomers. For related
compounds with similar IR observations, see: (a) R.M. Bullock, J.
Chem. Soc. Chem. Commun. (1989) 165. (b) M.I. Bruce, F.S. Wong,
B.W. Skelton, A.H. White, J. Chem. Soc. Dalton Trans. (1982) 2203.
For isomers of vinylidene complexes, see: (c) Y. Wakatsuki, N. Koga,
H. Yamazaki, K. Morokuma, J. Am. Chem. Soc. 116 (1994) 8105.
a X(1A), X(1B) and X(1C) represent centroids of the rings of (C1,
C2, C3, C4, C5), (C6, C7, C8, C9, C10) and (C11, C12, C13, C14,
C15), respectively.

S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
175
fragmentation is almost complete at 40 V (Fig. 2 and
Scheme 3). These studies suggest that the most labile
ligand is ejected at the lowest voltage whilst the
stronger ones would depart as the cone voltage in-
creases. These spectra confirm the solution results in
suggesting that CH3CN is preferentially dissociated
over dppr. Similar behavior is seen for [Ru-
Cl(Cp)(PPh3)2] which gives [Ru(Cp)(CH3CN)(PPh3)2]+
(IX) (m/z 732) at low cone voltages. The acetonitrile
ligand is lost to give [Ru(Cp)(PPh3)2]+ (X) (m/z 691)
when the voltage is increased to 40 V. The observed
isotope patterns compare well with the calculated ones.
The spectra of the carbonyl complex 3 lead to a similar
conclusion in that the molecular ion (VIII) is observed
at low cone voltages. However, there is no evidence for
decarbonylation when the voltage is raised to 40 V.
Only when the voltage is further increased to 60 V does
[Ru(Cp)(dppr)]+ (VII) begin to appear. This is consis-
tent with our earlier deduction that CO binds much
stronger to Ru(II) than CH3CN. Although an alterna-
tive pathway involving cyclometalation is seen in other
PPh3 complexes [27], no such phenomenon is observed
for 3. The most likely explanation is that cyclometala-
tion of a chelated ligand would experience greater
difficulty. The fragmentation pathways of 1, 2 and 3 are
summarized in Scheme 3.
The positive-ion ESMS spectrum of 4 at 20 V (Fig.
3a) shows the parent ion [Ru(ꢀCꢀCHPh)(Cp)(dppr)]+
(XI) as the main species at m/z 867. The negative-ion
spectrum at 20 V also shows a single intense ion at m/z
146 for the PF6− counter-ion. These support the Ru–
vinylidene formulation. A weak peak at m/z 433 is
identified as the doubly charged molecular cation
[Ru(ꢀCꢀCHPh)(Cp)(dppr)]2+ (XII) formed by the oxi-
dation of the sandwiched ruthenium (Scheme 4). Such
oxidation gives two different oxidation states (II, III)
for both Ru centers and opens an opportunity for the
study of their cooperative effects by tuning their elec-
tronic states. A weak ion at m/z 793 is tentatively
Scheme 2. ESMS fragmentation pattern of dppr and its addition to
AgNO3.
dppr in CH3CN does not show any peak corresponding
to the parent ion [dppr]+, its oxidation product,
{Ru[(p5-C5H4)P(O)Ph2]2} (dpprO2), (I), (m/z 632) is
detected as its [M+H]+ ion. Doping with a drop of
AgNO3 to the analyte solution gives [Ag(dppr)]+ (II)
(m/z 709) as the major species and [Ag(dppr)2]+ (III)
(m/z 1307) and other oxidized products such as
[Ag(dppr)(dpprO)]+ (IV) (m/z 1323) and [Ag(dp-
prO)2]+ (V) (m/z 1339) and proposed structures are
given in Scheme 2. Formation of these species illus-
trates the ability for Ag+ to give linear, trigonal planar
and tetrahedral phosphine complexes with dppr and
dpprO. In the latter case, the ligand is most likely
P-bonded due to the soft character of Ag(I). A similar
finding was reported in a recent study of dppf with
Ag+ by ESMS [26].
assigned
as
the
parent
vinylidene
species
[Ru(Cp)(CꢀCH2)(dppr)]+. On increasing the cone
voltage to 50 V (Fig. 3b), fragmentation occurs, result-
ing in loss of the vinylidene ligand to give
[Ru(Cp)(dppr)]+ at m/z 766.
Addition of a trace amount of AgNO3 to a solution
of 4 surprisingly gives [Ag{Ru(Cp)(CꢁCPh)(dppr)}2]+
(XIII) as a small peak at m/z 1842 at 20 V. (Fig. 3c)
This is possibly an [AgRu2]+ complex bridged by two
acetylide ligands |-bonded to Ru(II) and y-bonded to
Ag(I). A similar [AgW2]+ complex has recently been
observed in the ESMS of a W2 tetrayne complex [28].
This follows an earlier work in the use of Ag+ as an
agent to promote ionization and hence spectral detec-
tion [29]. Although this [AgRu2]+ complex has not
been isolated in solution, it is nevertheless significant
that such acetylide-bridged complex can be detected
The spectrum of 2 in a CH3CN/H2O solution at a
low cone voltage (5 V) (Fig. 2) gives the parent ion
[Ru(Cp)(CH3CN)(dppr)]+ (VI). Upon increasing to 20
V, fragmentation begins to occur by which the CH3CN
ligand is lost to give [Ru(Cp)(dppr)]+ (VII). Such

176
S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
Fig. 2. Positive-ion ESMS spectra (CH3CN–H2O solvent) of the complex [Ru(Cp)(CH3CN)(dppr)]PF6, 2 recorded at cone voltages of 5 V (left)
and 40 V (right), showing the relatively facile loss of the CH3CN ligand. The insets show the experimental (upper) and calculated (lower) isotope
patterns for the parent ion [Ru(Cp)(CH3CN)(dppr)]+. The cation of the related carbonyl complex 3b showed similar behavior, although the CO
ligand did not begin to be lost until a cone voltage of 60 V.
under the ESMS conditions. Loss of the acetylide lig-
and from [Ag{Ru(Cp)(CꢁCPh)(dppr)}2]+ (XIII) occurs
at a higher cone voltage (50 V) although XIII is still
observed. Under these conditions, a major species,
[Ag{Ru(Cp)(CꢁCPh)(dppr)}]+ (XIV) (m/z 975) is
formed, which can be explained by the cleavage of one
those of the known phosphines and diphosphines. We
are especially interested in the activation of unsaturated
inorganic and organic molecules and their catalytic
implications. The mechanistic significance of the forma-
tion of a vinylidene complex from a terminal acetylene
has been elegantly described by Caulton et al. [30].
Although our vinylidene complex (4) cannot be formed
from the proposed Ru–H insertion into the acetylene
(since our substrates are not hydrides and there is no
obvious hydride source), the mechanism proposed by
Caulton et al. may have some implications in the
catalytic and stoichiometric hydrogenation capability
shown by 4. Research work in this direction is currently
in progress.
metalloligand
from
XIII,
together
with
[Ru(Cp)(dppr)]+ (VII). Generation of the latter frag-
ment is also inferred from the thermal degradation
profile of 3b. Thermogravimetric analysis (TGA) of 3b
gives a weight loss of 5.9% in the region of 50–150°C.
This corresponds to the loss of solvent of crystallization
and the CO ligand and gives [Ru(Cp)(dppr)]+. Heating
beyond 170°C would cause further decomposition to
give RuO2.
Complex 4 readily yields ethylbenzene (55%) when it
is refluxed (for 4 h) in THF under an atmospheric
pressure of H2 gas. There is no evidence for the forma-
tion of styrene. This reaction becomes catalytic when a
THF solution of HCꢁCPh is refluxed under H2 in the
presence of 5 mol% of 4. It gives a 52% yield of
ethylbenzene after 5 h. The catalytic mechanism is
presently being investigated.
3. Experimental section
3.1. General comments
All reactions were routinely carried out under pure
dry argon using standard Schlenk techniques [31]. All
solvents for the reactions were vacuum degassed before
use. The solvents were of reagent grade and were
freshly purified and dried by published procedures [32].
Chemical reagents, unless otherwise stated, were com-
The kinetic stability of the ruthenocenyl ruthenium
chelate ring is unexpected. It enables the development
of some new chemistry parallel to but different from

S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
177
Scheme 3. ESMS fragmentation pattern of [RuCl(Cp)(PPh3)2], [RuCl(Cp)(dppr)], 1, [Ru(Cp)(CH3CN)(dppr)]PF6, 2 and [Ru(Cp)(CO)(dppr)]PF6,
3b.
spectra were recorded in samples pulverized with KBr.
Elemental analyses were conducted at the Microana-
lytical Laboratory, Department of Chemistry, National
University of Singapore. Some data of selected com-
pounds are unsatisfactory despite repeated purification
and analysis. We attribute this to problems faced in the
acid digestion of these bimetallic compounds. The iden-
tification and purity of these compounds are supported
by spectroscopy (NMR) and thermal analyses (TG &
DSC). Thermogravimetry (TG) and derivative ther-
mogravimetry analysis (DTG) were conducted using
the DuPont Instruments 910 DSC and 951 TGA. All
catalytic results were analyzed by gas chromatography
(Hewlett-Packard 5890 series II) using a HP/I/cross-
linked methyl silicone gum column (25 m×0.32 mm×
0.52 mm film thickness). Results were plotted by the HP
3396 Series II integrator. Analysis was performed by
injecting 1.0 ml of a sample of filtered reaction mixture
into the gas chromatogram. The initial temperature of
30°C was maintained for 1 min, thereafter increasing at
a rate of 10°C min−1 before reaching the maximum
temperature of 180°C and holding it for another
minute. Standards of phenylacetylene, styrene, ethyl-
benzene, toluene and THF were checked for their reten-
tion times. Toluene was used as the internal standard
for the calibration of standards. Calibration using mix-
tures of toluene and ethylbenzene were carried out.
mercial products and were used without further
purification.
Room temperature one-dimensional H-NMR spec-
1
tra were recorded on either a JEOL FX 90Q Fourier
transformation NMR spectrometer or a Bruker AC
300F spectrometer, at 89.55 or 299.96 MHz, respec-
tively, with (CH3)4Si as internal standard. 31P-NMR
spectra were also recorded on these instruments at
36.23 or 121.49 MHz, respectively. The phosphorus
chemical shifts were quoted from the proton-decoupled
spectra, and are reported in ppm to the higher fre-
quency of external 85% H3PO4. 13C-NMR spectra were
recorded only on a Bruker AC 300F spectrometer. The
carbon chemical shifts were quoted from the proton-de-
coupled spectra, with (CH3)4Si as internal standard. Air
sensitive samples were prepared inside a Schlenk tube
under argon.
Fourier transform IR spectra were recorded with
either a Perkin-Elmer 1725X or a Bio-rad FTS-165
FT-IR spectrometer. All spectra were recorded at r.t.
either in the solution or solid phase. For the solution
phase IR, liquid cells with NaCl windows were used.
The cells were equipped with PTFE spacers giving a
pathlength of 0.1 mm. Air-sensitive solutions were in-
troduced into the cell via a syringe after the cell was
flushed with argon gas. The openings of the cell were
then sealed with 5 mm red rubber septa. Solid phase IR

178
S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
ml) was refluxed for 16 h. The solution was evaporated
to dryness under reduced pressure and this crude
product was suspended in CH2Cl2 (5 ml) to which
absolute alcohol (15 ml) was added with rapid stirring.
The supernatant liquid was removed using a syringe.
This process of suspension, alcohol addition and sol-
vent removal was repeated. The residue was recrystal-
lized in CH2Cl2–hexane (1:3) to give yellow–orange
crystals of 1·0.5C6H14. Yield: 0.14 g, 91%. The same
product was obtained when a two molar excess of dppr
was used. Anal. Calc. for C42H40P2ClRu2: C, 59.7; H,
4.8; P, 7.3; Cl, 4.2; Ru, 23.9%. Found: C, 59.2; H, 4.2;
P, 7.8; Cl, 5.5; Ru, 22.0%. lH (CDCl3): 3.97 (s, Cp, 5H);
4.44 (m, C5H4, 2H); 4.65 (m, C5H4, 2H); 4.80 (m, C5H4,
2H); 5.46 (m, C5H4, 2H); 7.26−7.87 (m, C6H5, 20H)
ppm. lP: 42.2 (s) ppm.
3.2. Synthesis of [1,1%-bis(diphenylphosphino)-
ruthenocene]chlorocyclopentadienyl-ruthenium(II)
[RuCl(p5-C5H5)(dppr)] (1) from dppr
A solution of [RuCl(p5-C5H5)(PPh3)] (0.140 g, 0.193
mmol) and dppr (0.17 g, 0.284 mmol) in benzene (25
3.3. Synthesis of [Ru(p5-C5H5)(CH3CN)(dppr)][PF6] ·
C6H14 (2) from [RuCl(p5-C5H5)(dppr)] (1) and NH4PF6
in refluxing acetonitrile
A solution of NH4PF6 (0.07 g, 0.43 mmol) in dry
acetonitrile (40 ml) was added to [RuCl(p5-
C5H5)(dppr)] (0.20 g, 0.250 mmol) in a Schlenk tube
equipped with a reflux condenser topped with a nitro-
gen bypass. The solution was refluxed for 4 h. After
evaporation under vacuum, the residue was extracted
with CH2Cl2 (5 ml). The extract was filtered through
Celite to remove excess NH4PF6 and evaporated under
reduced pressure. This residue was recrystallized from
CH3CN−hexane (1:4) to give a yellow solid. Yield:
0.18 g, 76%. Anal. Calc. for C47H50F6NP3Ru2: C, 54.4;
H, 4.9; F, 11.0; N, 1.4; P, 9.0; Ru, 19.5%. Found: C,
54.0; H, 4.00; F, 9.4; N, 1.2; P, 9.6; Ru, 17.1%. lH
(CDCl3): 2.22 (s, CH3, 3H); 4.31 (s, Cp, 5H); 4.65
(m, C5H4, 2H); 4.72 (m, C5H4, 2H); 4.74 (m, C5H4, 2H);
4.83 (m, C5H4, 2H); 7.26−7.54 (m, C6H5, 20H)
ppm. lP: −144.2 (septet, J(PF)=712.1 Hz); 43.4 (s)
ppm.
3.4. Synthesis of [Ru(p5-C5H5)(CO)(dppr)]Cl (3a) from
[RuCl(p5-C5H5)(dppr)] (1) and carbon monoxide at
60°C
CO was bubbled into a solution of [RuCl(p5-
C5H5)(dppr)] (0.02 g, 0.02 mmol) in absolute alcohol
(10 ml) at 60°C for 2 h. The reaction mixture was
filtered into a Schlenk tube at 0°C, and the solution
evaporated to dryness under reduced pressure to give a
light-yellow solid (3a). wmax: 1968s (CO), 3385s (br),
3050s, 1624w, 1479m, 1433m, 1157m, 1090m, 823w
cm−1 (CH2Cl2). lH (CDCl3): 4.83 (s, C5H4, 2H); 4.86
(m, C5H4, 2H); 4.88 (s, Cp, 5H); 5.10 (m, C5H4, 4H);
7.26−7.61 (m, C6H5, 20H) ppm. lP: 48.9 (s) ppm.
Fig. 3. Positive-ion ESMS spectrum of complex 4 recorded in
methanol solution at cone voltages of (a) 20, (b) 50 , and (c) 20 V
after the addition of AgNO3. Inset to (b): this shows the isotope
pattern for the m/z 434 ion recorded at 50 V; the 0.5 m/z separation
of adjacent peaks is the signature of a doubly-charged ion, in this case
caused by oxidation of the ruthenocene moiety.

S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
179
Scheme 4. ESMS fragmentation pattern of [Ru(CꢀCHPh)(Cp)dppr)]PF6, 4, and its addition to AgNO3.
3.5. Synthesis of [Ru(p5-C5H5)(CO)(dppr)][PF6] (3b)
from [Ru(p5-C5H5)(CH3CN)(dppr)][PF6] (2) and carbon
monoxide at r.t.
10.4; P, 8.5; Ru, 18.4%. Found: C, 57.7; H, 4.5; F, 10.6;
P, 8.1; Ru, 14.4%. wmax: 1699s (CꢀC), 1645s (CꢀC),
838m (br) (PF6), 1436m, 1080w cm−1 (KBr). lH
(CDCl3): 4.86 (m, C5H4, 2H); 4.96 (m, C5H4, 2H); 5.06
(m, C5H4, 2H); 5.08 (m, C5H4, 2H); 5.23 (s, Cp, 5H);
5.64 (t, CH, 1H, J(HP)=1.9 Hz); 6.84−7.50 (m,
C6H5, 25H) ppm. lP: −144.2 (septet), 50.0 (s) ppm. lC:
74.65 (s, k-C5H4); 74.95 (s, k-C5H4); 77.7 (t, i-C5H4,
J(CP)=5.7 Hz); 78.5 (t, i-C5H4, J(CP)=4.6 Hz); 88.5
(m, h-C5H4); 94.13 (s, Cp); 119.58 (s, ꢀCHPh);
126.78−137.85 (m, C6H5); 354.00 (t, RuꢀC) ppm.
CO was bubbled into
a
solution of [Ru(p5-
C5H5)(CH3CN)(dppr)][PF6] (0.02 g, 0.02 mmol) in ab-
solute alcohol (10 ml) at r.t. for 15 min. The
light-yellow solid of 3b·H2O (yield 86%; m.p. 164–
166°C) was isolated similarly to 3a. Anal. Calc. for
C40H35F6OP3Ru2: C, 50.2; H, 3.7; F, 11.9; P, 9.7; Ru,
21.1%. Found: C, 49.9; H, 4.1; F, 7.3; P, 9.3; Ru,
15.5%. wmax: 1968s (CO), 831vs (b) (PF6), 1429m,
1094m cm−1 (KBr). lH (CDCl3): 4.82 (s, Cp, 5H); 4.82
(m, C5H4, 2H); 4.84 (m, C5H4, 2H); 5.08 (m, C5H4, 4H);
7.26−7.57 (m, C6H5, 20H) ppm. lP: −144.2 (septet,
J(PF)=712.5 Hz); 48.7 (s) ppm.
3.7. Electrospray mass spectrometry
Spectra were recorded in positive-ion mode using a
VG Platform II instrument employing nitrogen as both
the drying and nebulizing gas. The negative-ion spec-
trum of complex 4 was also recorded, to confirm the
presence of the PF6− anion. Spectra were an average of
ten to 12 scans. A range of cone voltages, from 5 to 50
V were typically used for each sample, to investigate
fragmentation pathways. The analyte solution, of ap-
proximate concentration 0.1 mM, was delivered to the
mass spectrometer source using a Spectra System P1000
HPLC pump, at a flow rate of 0.01 ml min−1. Spectra
of dppr were recorded in MeCN solution, to which a
small quantity of aqueous AgNO3 solution had been
added to generate in situ dppr–Ag+ complexes. Com-
plexes 2 and 3b were recorded in 1:1 MeCN–H2O
3.6. Synthesis of [Ru(CꢀCHPh)(p5-C5H5)(dppr)][PF6] ·
C6H14 (4) from [Ru(p5-C5H5)(CH3CN)(dppr)][PF6] (2)
Excess phenylacetylene was added to [Ru(p5-
C5H5)(CH3CN)(dppr)][PF6] (0.02 g, 0.02 mmol) in
CH2Cl2 (10 ml) at r.t. under nitrogen. The solution
turned from chrome-yellow to deep red after a few
seconds of stirring. It was evaporated to dryness under
reduced pressure and the crude solid was recrystallized
from CH2Cl2–hexane (1:3) to give the reddish–pink
product (Yield: 0.02 g, 98%; m.p. 229–232°C). Anal.
Calc. for C53H53F6P3Ru2: requires C, 57.9; H, 4.9; F,

180
S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
solution, while the ESMS sample of complex 4
was prepared by dissolving a small crystal of the
complex in a drop of CH2Cl2, followed by dilution
to 1 ml with MeOH. Pure methanol was used as
the mobile phase solvent for this complex. Assign-
ment of major ions was aided by a comparison of the
experimental and calculated isotope distribution pat-
terns, the latter obtained using the Isotope program
[33].
Table 4
Atomic coordinates of [Ru(p5-C5H5)(CO)(dppr)][PF6], 3b; (×105 for
Ru atoms, and ×104 for others) and equivalent isotropic temperature
2
4
2
3
˚
˚
factors (A ×10 for Ru; A ×10 for others)
a
Atom
x
y
z
Ueq
Ru(1)
Ru(2)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
20321(7)
−4353(7)
1311(14)
2642(12)
2666(11)
1317(12)
517(12)
−648(10)
−1521(11)
−757(12)
616(10)
6246(4)
14596(4)
323(6)
17110(3)
32758(3)
609(5)
503(2)
519(2)
81(5)
88(5)
81(4)
79(4)
79(4)
63(3)
76(4)
79(4)
64(3)
52(3)
54(3)
68(4)
64(3)
59(3)
54(3)
66(4)
95(3)
49(1)
76(4)
88(5)
93(5)
91(5)
68(4)
59(3)
70(4)
88(5)
98(5)
76(4)
65(3)
58(3)
47(1)
71(4)
85(5)
88(5)
88(5)
69(4)
56(3)
69(4)
78(4)
71(4)
68(4)
54(3)
51(3)
87(1)
208(7)
215(7)
119(5)
146(7)
264(17)
243(14)
270(16)
164(8)
108(5)
125(6)
84(7)
768(6)
−386(6)
−454(6)
−19(6)
378(5)
552(6)
806(6)
1317(6)
1473(6)
1047(5)
3073(5)
3580(6)
4175(6)
4072(4)
3373(4)
2982(4)
3426(5)
3101(40
2446(4)
2373(4)
1799(4)
1798(4)
1635(1)
745(5)
3.8. X-ray crystallography
Single crystals of [Ru(p5-C5H5)(CO)(dppr)][PF6],
3b, were grown by a diffusion method with n-
hexane layered on a concentrated solution of the
complex in CH2Cl2 at r.t. Good crystals could also
be obtained by a similar method using Et2O on a
concentrated solution of the complex in CH2Cl2.
C(8)
C(9)
799(5)
536(4)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
O(1)
690(9)
676(9)
2321(4)
2570(5)
2439(5)
2103(5)
2038(5)
1102(5)
1368(4)
1637(1)
2266(6)
2819(8)
3463(8)
3577(6)
3037(5)
2376(5)
1962(6)
1919(7)
1499(8)
1103(6)
1142(5)
1561(5)
420(1)
−218(10)
−1517(10)
−1404(9)
−30(9)
3632(11)
4673(8)
A
well-formed colorless crystal (0.16×0.18×
0.20 mm3) was mounted inside a thin-walled Linde-
mann glass capillary under an atmosphere of nitro-
gen. Preliminary characterization and intensity data
P(1)
728(2)
collection was performed on
a Rigaku AFC7R
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
P(2)
C(29)
C(30)
C(31)
C(32)
C(33)
C(34)
C(35)
C(36)
C(37)
C(38)
C(39)
C(40)
P(3)
2424(11)
2966(11)
2757(13)
2000(14)
1407(11)
1586(9)
−949(11)
−2099(13)
−3146(13)
−3015(10)
−1821(9)
−788(10)
2199(2)
3886(11)
4302(13)
3538(15)
2310(14)
1890(10)
2685(9)
4181(10)
5196(11)
5540(10)
4881(10)
3874(9)
diffractometer at r.t. using graphite-monochromatized
418(6)
648(7)
˚
Mo–Kh radiation (u=0.71073 A) powered at 50 kV
and 90 mA. Intensity data were collected using
ꢀ scans of width (0.68+0.35 tan q)° in q at a rate
of 8.0–32.0° min−1. Data for the structure were
corrected for Lorentz-polarization factors. An empiri-
cal absorption correction based on a series of c-scans
was applied to the data. A total of 10781 unique
reflections, of which 4113, with ꢁFoꢁ\6|ꢁFoꢁ were
treated as observed reflections, n, and having
465 number of variables, p. Atomic coordinates data
for [Ru(p5-C5H5)(CO)(dppr)][PF6], 3b are listed in
Table 4.
The structure was solved with the Patterson super-
position method, and refinement was carried out by
full-matrix least-squares using the SHELXTL package
on a IBM compatible PC computer [34]. All hydro-
gen atoms were fixed as isotropic ellipsoids in ideal-
ized positions in the final cycles of least-squares
refinement. The non-hydrogen atoms were allowed
anisotropic motion. Refinement on F gave the R val-
1181(6)
1496(5)
1287(4)
380(4)
−77(5)
76(6)
679(6)
1139(5)
1006(4)
2929(1)
2963(5)
3187(6)
3582(6)
3751(6)
3542(5)
3154(4)
4078(5)
4479(5)
4320(5)
3761(5)
3340(4)
3490(4)
3589(2)
4019(5)
3117(7)
3536(10)
4281(7)
3741(22)
2882(10)
4017(20)
4119(12)
3159(8)
3006(8)
−723(5)
−1385(6)
−1770(6)
−1528(6)
−873(5)
−463(5)
579(5)
920(6)
1574(6)
1884(15)
1541(5)
887(5)
3498(9)
3182(3)
3972(2)
3353(5)
4558(6)
3673(8)
4291(10)
4451(17)
3669(16)
3934(21)
4507(10)
4003(8)
3401(8)
ues shown in Table 1 with the weighting scheme
F(1)
F(2)
F(3)
F(4)
F(5)
F(6)
F(3%)
F(4%)
F(5%)
F(6%)
2760(15)
3645(15)
4636(11)
3932(24)
1991(30)
2514(37)
4605(21)
2705(30)
1724(11)
3336(20)
2
w
−1=[|2ꢁFoꢁ+0.0025ꢁFoꢁ ] and maximum and mini-
mum heights in the final difference map of +0.75
−3
˚
and −0.59 e A
.
4. Supplementary material available
Lists of thermal parameters and of observed and
calculated structure factors for [Ru(p5-C5H5)-
(CO)(dppr)][PF6], 3b are available from the authors
upon request.
a Ueq defined as one third of the trace of the orthogonalized Uij
tensor.

S. Po Yeo et al. / Journal of Organometallic Chemistry 575 (1999) 171–181
181
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Acknowledgements
The authors acknowledge the National University of
Singapore (NUS) and Hong Kong Research Grants
Council (Ref. CUHK 311/94P) for financial support.
W.H. thanks the University of Waikato and the New
Zealand Lottery Grants Board for funding of the mass
spectrometer. Experimental assistance from A.S.W.
Fong and stenographic help from Y.P. Leong are
appreciated.
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