New rhodium-ruthenium heterobimetallic complexes with bridging bi- or tri-dentate phosphine ligands

Article abstract of DOI:10.1016/S0022-328X(99)00459-3

The mononuclear chelated complex [RuCl(Cp)(η²-dppa)] has been synthesised and reacted with [Rh₂Cl₂(CO)₄] to form the heterobimetallic complex [(Cp)Ru(μ-CO)₂{(μ-Ph₂PN(H)PPh₂}RhCl

Full text of DOI:10.1016/S0022-328X(99)00459-3

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 590 (1999) 217–221
New rhodiumꢀruthenium heterobimetallic complexes with bridging
bi- or tri-dentate phosphine ligands
Nagwa Nawar *
Chemistry Department, Faculty of Science, Mansoura Uni6ersity, PO Box 79, Mansoura 35516, Egypt
Received 14 May 1999; accepted 28 July 1999
Abstract
The mononuclear chelated complex [RuCl(Cp)(h2-dppa)] has been synthesised and reacted with [Rh2Cl2(CO)4] to form the
heterobimetallic complex [(Cp)Ru(m-CO)2{(m-Ph2PN(H)PPh2}RhCl2]. Complexes of [RuCl(Cp){(PPh2)2CHCH2PPh2}] have been
reacted with [Rh2Cl2(CO)4] or [RhCl(CO)2(p-toluidene)]. Characterisation of these new ruthenium complexes was carried out
using 31P-NMR, FAB mass spectroscopy, elemental analysis and IR spectrophotometry. © 1999 Elsevier Science S.A. All rights
reserved.
Keywords: Ruthenium; Rhodium; Heterometallic complexes; Tridentate phosphines; Bidentate phosphines
(Cp)(h2-dppa)] 1 and then investigated the extent and
potential of ring-opening reaction to synthesise hetero-
1. Introduction
bimetallic RuꢀRh complexes. It has been reported that
a Michael-type addition occurs across the double bond
of dppen. This addition reaction occurs both on the
uncomplexed dppen [5] and, more readily, on com-
plexed dppen [6]. We have therefore employed this
reaction to synthesise [RuCl(Cp){(PPh2)2CHCH2-
PPh2}] [7] and made use of the dangling phosphine
created in this way to synthesise heterobimetallic com-
plexes. This paper reports the results of the
treatment of [RuCl(Cp)(h2-dppa)] and [RuCl(Cp)-
{(PPh2)2CHCH2PPh2}] with [Rh2Cl2(CO)4].
The use of bidentate phosphine ligands, especially bis-
(diphenylphosphino)ethane, Ph2PCH2CH2PPh2 (dppe),
bis(diphenylphos
phino)methane,
Ph2PCH2PPh2
(dppm), and bis(diphenylphosphino)ethene, Ph2PC-
(ꢁCH2)PPh2 (dppen), has become increasingly frequent
[1–4]. The versatility of dppe, dppm and dppen arises
from their ready coordination to metal centres through
the lone pair of electrons at one or both of the phos-
phorus atoms. Compared with the vast body of data
accumulated on diphosphines in which the phosphorus
nuclei are linked by a carbon atom or chain, less has
appeared on ligands where the backbone of the
molecule comprises a heteroatom or group. In this
respect bis(diphenylphosphino)amine, Ph2PN(H)PPh2
(dppa), has received our attention because dppe, dppm
or dppen and dppa have shared features in the forma-
tion of bimetallic complexes. We have previously re-
ported the ring-opening reaction of [RuCl(Cp)(h2-
dppen)] with [Rh2Cl2(CO)4], which leads to the forma-
tion of the heterobimetallic complex [(Cp)Ru(m-
CO)2{m-Ph2PC(ꢁCH2)PPh2}RhCl2] [3]. We have
therefore employed this reaction to synthesise [RuCl-
2. Results and discussion
The compound Ph2PN(H)PPh2 (dppa) was prepared
by treatment of a diethylether solution of (Me3Si)2NH
with Ph2PCl [8]. It was characterised by elemental
analyses (C-, H- and N-) and NMR spectroscopy. The
31P-NMR spectrum shows a single peak at l +43.1.
There is a progressive shift upfield, therefore, from
dppm (l −22.1) to dppen (l −3.1) to dppa.
Treatment of [RuCl(Cp)(PPh3)2] in toluene with one
equivalent of dppa gave an orange complex, microana-
lytical data for which were consistent with the formula
* Fax: +20-50-346781.
E-mail address: sinfac@mum.mans.eun.eg (N. Nawar)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00459-3

218
N. Nawar / Journal of Organometallic Chemistry 590 (1999) 217–221
[RuCl(Cp)(h2-dppa)] 1. The 31P-NMR spectrum of 1
shows a single sharp peak at l +71.95 due to the
equivalence of the coordinated phosphine groups.
difference of 35 amu, indicating the loss of chlorine as
seen for the previous complex 1. The spectrum also
shows a peak at m/z=690, a difference of 56 amu,
corresponding to the loss of the two bridging carbonyl
groups. As with the complex 1 an impurity peak at
m/z=814 was observed due to [RuCl(Cp)PPh3(dppa-
p)] complex. No reaction had occurred between [Ru-
Cl(Cp)PPh3(dppa-p)] and [Rh2Cl2(CO)4]. This is
probably due to the fact that [RuCl(Cp)PPh3(dppa-p)]
complex has no chelate ring and, therefore, is less likely
to undergo the metal insertion reaction. Elemental
analysis of [(Cp)Ru(m-CO)2{(m-Ph2PN(H)PPh2}RhCl2]
complex 2 shows good agreement between theoretical
and obtained values. The infrared spectrum shows a
single metalꢀcarbonyl band in the bridging region (1825
cm−1) and a strong band at 300 cm−1 due to RhꢀCl
bond. A crystallisation was set up as with complex 1. A
suitable yellow crystal was selected and mounted in a
Lindemann tube. However, as data collection pro-
ceeded the crystal lost solvent, rendering it useless for
X-ray purposes.
Analysis by FAB mass spectroscopy gave the molec-
ular ion at the desired position, m/z=587. The next
significant peak appears at m/z=552, indicating a loss
of 35 amu. This suggests the loss of chlorine from the
ruthenium centre. An impurity peak at m/z=814 was
observed; this is suggested to be due to the loss of
chlorine from the singly substituted molecule [Ru-
Cl(Cp)PPh3(dppa-p)] 2, although there was no 31P-
NMR evidence for this complex.
On treatment of [RuCl(Cp)(h2-dppa)] 1 with 0.5
equivalent of [Rh2Cl2(CO)4] in dichloromethane, the
yellow heterobimetallic product [(Cp)Ru(m-CO)2{(m-
Ph2PN(H)PPh2}RhCl2] 2 is formed as shown in Fig. 1.
This preparation involves the ring-opening reaction of
[RuCl(Cp)(h2-dppa)] with [Rh2Cl2(CO)4]. This is a
common preparative route for the synthesis of ligand-
bridged heterobimetallics and similar reactions have
been carried out successfully using [RuCl(Cp)(h2-
dppen)] [6] and [RuCl(Cp)(h2-dppm)] [9].
The heterobimetallic complex 2 has been confirmed
by the microanalytical data and the presence of bridg-
ing carbonyl in the infrared spectrum (w(CO) 1825
cm−1) and, further, by the fact that the 31P-NMR
spectrum shows a doublet and a doublet of doublets.
This pattern arises from two different phosphorus
atoms, PA and PB. The doublet at 102.3 ppm is formed
by coupling of PA–PB, with a coupling constant (JPP of
70 Hz, consistent with the analogous dppm bridged
bimetallic complex. The doublet of doublets at l 85.2 is
formed by coupling of PB–PA to form a doublet, then
further coupling of PB to rhodium giving a doublet of
doublets with coupling constants 2JPP=70 Hz and
1JPRh 128 Hz, both are consistent with the dppm
bridged bimetallic. Analysis by FAB mass spectroscopy
of the heterobimetallic complex 2 did not gave a molec-
ular ion peak at the desired position of m/z=781. A
peak at m/z=746, however, was observed. There is a
A Michael-type addition of the NꢀH bond of [Ru-
Cl(Cp)(h2-dppa)] across both coordinated and uncoor-
dinated dppen was examined. The results for
uncoordinated dppen showed no reaction had occurred.
Reaction occurred with coordinated dppen but analysis
of the products gave inconclusive results.
The complex [RuCl(Cp)(h2-dppen)] 3 was prepared
in high yield by treatment of [RuCl(Cp)(PPh3)2] with
dppen [3]. The complex [RuCl(Cp){(PPh2)2CHCH2-
PPh2}] 4, is formed in quantitative yield by the base
(KOBut)-catalysed addition of diphenylphosphine to
[RuCl(Cp)(h2-dppen)] solution in tetrahydrofuran [4].
The presence of a dangling phosphine in complex 4
provides an opportunity for further reactions with dif-
ferent metal centres. The treatment of the uncoordi-
nated phosphine group of complex 4 with [Rh2Cl2-
(CO)4] in THF at ambient temperature gave an un-
stable heterobimetallic [RuCl(Cp){(PPh2)2CHCH2-
PPh2}Rh(CO)2Cl] 5, characterised on the basis of its
infrared spectrum and by 31P-NMR spectroscopy and
microanalysis. The infrared spectrum of complex 5
shows bands due to the LRh(CO)2Cl [10] moiety at
2078, 2010 and 1975 cm−1. The 31P-NMR spectrum of
complex 5 shows a resonance at l 41.5 ppm (t, JPP 2.44)
due to two phosphorus atoms coordinated to Ru, and a
resonance centred at l 22.1 ppm (d of t, JPRh 125.7, JPP
2.44 Hz) due to the phosphorus atom coordinated to
Rh, in the ratio 2:1, as expected (Table 1). Complex 5
transforms slowly in solution over a period of 48 h, or
immediately on addition of Me3NO, into [(Cp)Cl-
¸¹¹¹¹¹¹¹¹¹¹¹¹¹q
{Ru(PPh2)2CHCH2PPh2Rh(CO)2Cl] complex 6. Again,
this complex has been characterised by spectroscopic
methods. The infrared spectrum of complex 6 shows
two CO bands due to the LRh(CO)2Cl moiety,
Fig. 1.

N. Nawar / Journal of Organometallic Chemistry 590 (1999) 217–221
219
Table 1
Spectroscopic data
a
b
Compound
31P-NMR
IR (cm−1
)
[RuCl(Cp)(h2-dppa)] 1
71.95 [s]
–
[(Cp)Ru(m-CO)2{(m-Ph2PN(H)PPh2}RhCl2] 2
102.3 [d, JPP 70], 85.2 [dd, JPP 70; JPRh 128]
31.77 [s]
36.8 [d, JPP 9.8, PA], −22.0 [t, PX]
2140, 2108, 2040, 1985, 1825
–
–
[RuCl(Cp)(h2-dppen)] 3
[RuCl(Cp){(PPh2)2CHCH2PPh2}] 4
[RuCl(Cp){(PPh2)2CHCH2PPh2}Rh(CO)2Cl] 5 41.5 [d, JPP 2.44], 22.1 [d of t, JPP 2.44; JPRh 125.7]
2078, 2010, 1975
[(Cp)Cl{R¸u¹(P¹P¹h2¹)2¹C¹H¹C¹H¹2P¹P¹hq2Rh(CO)2Cl}] 6 39.8 [d, JPP 9.8], 26.2 [d of t, JPP 9.8; JPRh 111.1]
2023, 1962
a In THF/C6D6; coupling constants in Hz; PA refers to two equivalent P atoms bound to Ru, PX refers to the unique P atom.
b w(CO), in CH2Cl2.
(2023, 1962 cm−1). The 31P-N¸M¹R¹¹sp¹e¹ct¹ru¹m¹¹is¹i¹de¹nqtical
3.1. Preparation of [RuCl(Cp)(p2-dppa)] 1
to that obtained for [{(CO)3Fe(Ph2P)2CHCH2PPh2Rh-
(CO)2Cl}] [11]. It shows a resonance at l 39.8 ppm due
to two phosphorus atoms coordinated to Ru, and a
resonance centred at l 26.2 ppm (d of t, JPRh 111.1, JPP
9.8 Hz) due to the phosphorus atom coordinated to Rh.
The high-frequency wCO band (at ca. 2023 cm−1) in
the infrared spectrum of RuꢀRh complex, and the
A solution of [RuCl(Cp)(PPh3)2] (0.2g, 0.28 mmol) in
toluene (70 cm3) was added to the dppa (0.11 g, 0.28
mmol) in toluene (30 cm3) with stirring. The solution
was refluxed for 4 h, giving a red–orange coloured
solution. This was evaporated to dryness. The remain-
ing solid was purified by adding heptane to dissolve the
liberated PPh3. The pure product was collected by
filtration and dried in vacuo. The remaining solid was
recrystallised from toluene to give complex 1 as an
orange solid (0.11g, 67%). Anal. Found: C, 59.17; H,
4.64; N, 2.09%. RuC29H26NClP2 requires C, 59.34; H,
4.46; N, 2.39%.
phosphorusꢀphosphorus coupling constant of 9.8 Hz
¸¹¹¹¹¹¹¹¹¹¹¹¹¹q
similar to that of [(CO)3Fe{(PPh2)2CHCH2PPh2Rh-
(CO)2Cl}] [11], and larger than that of [(CO)3-
Fe{(PPh2)2CHCH2PPh2Rh(CO)3Cl2}] [12] suggest that
a donor Ru“Rh bond is present (Scheme 1). The
uncoordiated phosphine group of complex 4 also reacts
with [RhCl(CO)2(p-toluidene)] to give the hetero-
bimetallic complex 5. The infrared spectrum of this
complex and 31P-NMR spectrum is typically identical
to that previously described for complex 5, suggesting
that the tppe ligand ((PPh2)2CHCH2PPh2) bridges the
Ru and Rh atoms, and p-toluidene has not remained
coordinated to the rhodium. Again, the transformation
of 5 to complex 6 occurred by addition of Me3NO.
3.2. Preparation of [(Cp)Ru(v-CO)2{(v-Ph2PN(H)-
PPh2}RhCl2] 2
[RuCl(Cp)(h2-dppa)] (0.1 g, 0.17 mmol) and
[Rh2Cl2(CO)4] (0.033g, 0.09 mmol) were added to de-
gassed dichloromethane (50 cm3) in the strict absence of
air. The reaction mixture was stirred for 1 h. The
yellow product was collected by slowly blowing off the
solvent (0.073 g, 54.8%). Anal. Found: C, 47.29; H,
3.39; N, 1.73%. RuRhC31H26NCl2P2O2 requires C,
47.63; H, 3.36; N, 1.79%.
3. Experimental
All reactions were carried out under nitrogen unless
otherwise stated, using dry, degassed solvents and stan-
dard Schlenk-line techniques. IR spectra were recorded
as dichloromethane solutions in 0.5 mm NaCl cells on
a Perkin–Elmer 681 spectrophotometer; NMR spectra
were recorded on Jeol FX-60 or Bruker WM250 instru-
ments. Chemical shifts are relative to 85% H3PO4 for
31P-NMR spectra. Microanalyses were carried out in
the Department of Chemistry, University of Liverpool.
FAB atom bombardment mass spectroscopy was used
to run all the samples in 3-nitrobenzyl alcohol for a
duration of 16 min.
3.3. Preparation of [RuCl(Cp)(p2-dppen)] 3
A solution of [RuCl(Cp)(PPh3)2] (0.362 g, 0.48 mmol)
and dppen (0.203 g, 0.52 mmol) in toluene (100 cm3)
was refluxed for 5 h. The volume of the solution was
reduced to 15 cm3 by evaporation under vacuum, and
hexane (50 cm3) was added. On standing for 24 h at
−20°C, the solution gave dark red crystals of [Ru-
Cl(Cp)(h2-dppen)] (0.24 g, 85%). Anal. Found: C, 62.0;
H, 4.4%. RuC31H27ClP2 requires C, 62.26; H, 4.55%;
M+ at m/z 598. M+ based on 101Ru and 35Cl, 598.
The compounds PPh2N(H)PPh2 [8], Ph2PC(ꢁCH2)-
PPh2 [13], [RuCl(Cp)(h2-dppen)] [3], [RuCl(Cp)(PPh3)2]
[14], [RhCl(CO)2(p-toluidene)] [15] and [Rh2Cl2(CO)4]
[16] were prepared according to published proce-
dures.
3.4. Reaction of [RuCl(Cp)(p2-dppa)] with dppen
A solution of [RuCl(Cp)(h2-dppa)] (0.06 g, 0.10
mmol) and dppen (0.04 g, 0.10 mmol) in toluene (100

220
N. Nawar / Journal of Organometallic Chemistry 590 (1999) 217–221
cm3) was stirred at room temperature (r.t.) until a
colour change was observed. The volume of the solu-
tion was reduced to 15 cm3 by evaporation under
vacuum. Analysis was carried out by 31P-NMR. This
reaction failed as shown by 31P-NMR. There was sin-
glets at 71.95 and −3.1 ppm corresponding to [Ru-
Cl(Cp)(h2-dppa)] and dppen, respectively.
3.6. Preparation of [RuCl(Cp){(PPh2)2CHCH2PPh2}-
Rh(CO)2Cl] 5
The freshly prepared [RuCl(Cp){(PPh2)2CHCH2-
PPh2}] (0.058 g, 0.074 mmol) in THF (10 cm3) was
stirred at r.t. with [Rh2Cl2(CO)4] (0.019 g, 0.037 mmol)
in THF. After 10 min, the solution was evaporated to
dryness. The remaining solid was recrystallised from
3.5. Reaction of [RuCl(Cp)(p2-dppa)] with
[RuCl(Cp)(p2-dppen)]
THF–benzene to give complex
5 as a yellow
solid (0.059 g, 87.6%). Anal. Found: C, 55.28; H,
3.7%. RuRhC45H38Cl2P3O2 requires C, 55.23; H,
3.91%.
[RuCl(Cp)(h2-dppa)] (0.1 g, 0.17 mmol) and [Ru-
Cl(Cp)(h2-dppen)] (0.1 g, 0.17 mmol) were added to a
flask containing degassed toluene (50 cm3). A catalytic
amount of potassium tert-butoxide (KOBut) was added
and the reaction mixture was stirred overnight under a
nitrogen atmosphere at r.t. The solvent was removed by
evaporation under vacuum. Analysis of the product
was carried out by 31P-NMR. The reaction was show-
ing several products with 31P-NMR. These products
were dissolved in chloroform and thin-layer chromatog-
raphy (TLC) using 1:3 dichloromethane–acetone was
carried out on the solution. The separation produced
four bands ranging from brown to pale yellow. Unfor-
tunately, extraction of these bands failed to give any
products. It is assumed that the products had decom-
posed on the TLC plate.
¸¹¹¹¹¹¹¹¹¹¹¹¹¹q
3.7. [(Cp)Cl{Ru(PPh2)2CHCH2PPh2Rh(CO)2Cl}] 6
Complex 5 was dissolved in THF (10 cm3) and
stirred at 40°C for 48 h, after which time NMR spec-
troscopy showed reaction had occurred. Me3NO·2H2O
(0.009 g, 0.074 mmol) in methanol (2 cm3) was added to
complex 5 dropwise and the mixture stirred at 40°C for
10 min. Spectroscopic analysis showed complete con-
¸¹¹¹¹¹¹¹¹q
version to [(Cp)Cl{Ru(PPh2)2CHCH2PPh2Rh(CO)2Cl}]
complex 6 had occurred. The yellowish–brown solution
was evaporated to dryness and the residue was recrys-
tallised by slow evaporation from THF–benzene. Anal.
Found: C, 54.9; H, 3.81%. RuRhC45H38Cl2P3O2 re-
quires C, 55.23; H, 3.91%.
Scheme 1.

N. Nawar / Journal of Organometallic Chemistry 590 (1999) 217–221
221
3.8. Reaction of [RhCl(CO)2(p-toluidene)] with
References
[RuCl(Cp){(PPh2)2CHCH2PPh2}]
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mmol), with stirring. Infrared monitoring confirmed
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yellow solid (0.06 g, 53.6%). Anal. Found: C, 54.98;
H, 3.8; 1.43%. RuRhC45H38Cl2P3O2 requires C, 55.23;
H, 3.91%.
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Acknowledgements
We thank Professor A.K. Smith (CPE Lyon,
France) for his kind support and interest.
.