Reactions of dinuclear carboxylate ruthenium (I) complexes with alcohols. the unexpected oxidation of primary alcohols to carboxylic ligands

Article abstract of DOI:10.1016/S0022-328X(98)01131-0

The dinuclear ruthenium (I) complexes [Ru₂(HCO₂)₂(CO)₄(PPh ₃)₂] react with primary alcohols R′CH₂OH in refluxing toluene, giving rise to [Ru₂(R′CO₂)₂

Full text of DOI:10.1016/S0022-328X(98)01131-0

Journal of Organometallic Chemistry 580 (1999) 108–109
Reactions of dinuclear carboxylate ruthenium (I) complexes with
alcohols. The unexpected oxidation of primary alcohols to carboxylic
ligands
Josep Soler, Isabel Moldes, Esther de la Encarnacio´n, Josep Ros *
Departament de Qu´ımica, Uni6ersitat Auto`noma de Barcelona, E-08193-Bellaterra (Cerdanyola), Barcelona, Spain
Received 14 April 1998
Abstract
The dinuclear ruthenium (I) complexes [Ru2(HCO2)2(CO)4(PPh3)2] react with primary alcohols R%CH2OH in refluxing toluene,
giving rise to [Ru2(R%CO2)2(CO)4(PPh3)2] compounds. Other carboxylate bridging complexes react with alcohols R¦OH to give
very unstable alkoxide compounds [Ru2(R¦O)2(CO)4(PPh3)2]. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Ruthenium; Carboxylate; Formate; Alkoxide
carboxylate bridges [Ru2(RCO2)2(CO)4(PPh3)2] (RꢀCH3
(4) and (CH3)2CꢀCH (5)) with phenol PhOH and alkyl
Dinuclear carbonyl ruthenium (I) complexes bridged
by heteroatom-containing anionic ligands are easy to
prepare [1]. They have shown important catalytic activ-
ity in hydroformylation of olefins [2] and in the addi-
tion of carboxylic acids to alkynes [3]. In this family of
compounds, the carboxylate bridges can easily be re-
placed by other three-electron anionic bridging ligands
such as thiolates, diamides or other carboxylate ligands
[4–6]. During our studies on the substitution of car-
boxylate ligands in complexes such as [Ru2-
(RCO2)2(CO)4(PPh3)2] by other ligands we observed
that they reacted slowly with alcohols in refluxing
toluene. The reaction of the formate compound
[Ru2(HCO2)2(CO)4(PPh3)2] (1) with primary alcohols
R%CH2OH gave rise to carboxylate-bridged complexes
[Ru2(R%CO2)2(CO)4(PPh3)2]. The formation of carboxy-
late bridging ligands was the result of the oxidation of
the alcohols by the formate groups. However, the reac-
tion of dinuclear compounds containing alkyl or alkene
alcohols
R¦OH
(R¦ꢀCH3CH2CH2CH2
and
(CH3)2CHCH2CH2) produced very unstable com-
pounds [Ru2(R¦O)2(CO)4(PPh3)2] bridged by alkoxide
groups.
The reaction of the formate complex [Ru2-
(HCO2)2(CO)4(PPh3)2] (1) with an excess of iso-pen-
tanol or n-butanol in refluxing toluene for 24 h led to
pale-yellow carboxylate-bridged complexes [Ru2
(R%CO2)2(CO)4(PPh3)2] (R%ꢀ(CH3)2CHCH2 (2) and
* Corresponding author. Fax: +34-93-5813101.
E-mail address: ros@cc.uab.es (J. Ros)
Scheme 1.
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01131-0

J. Soler et al. / Journal of Organometallic Chemistry 580 (1999) 108–109
109
CH3CH2CH2 (3)) (Scheme 1)1. The IR spectra of com-
pounds 2 and 3 show three w(CꢁO) bands with the pattern
expected for the Ru2(CO)4 fragment with a C26 symmetry.
The w(OCO) bands are observed at 1565 and 1413–1415
cm−1 with D=w(OCO)asym−w(OCO)sym=152–150
cm−1, which are normal values for h2-carboxylate-bridg-
ing ligands [7]. The 1H-NMR of complexes 2 and 3 display
the expected signals of the hydrocarbon chain of the
carboxylate ligand, and their 31P{1H}-NMR spectra show
a singlet at 14.8 and 12.5 ppm respectively, in accordance
with two equivalent PPh3 ligands bonded to ruthenium
atoms in a trans arrangement [6]. A gas chromatography
(GC) analysis of the crude of reaction revealed the
formation of methanol, which is the product of the
reduction of the formate group.
Carboxylate dinuclear complexes [Ru2(RCO2)2(CO)4
(PPh3)2] (RꢀCH3 (4) and (CH3)2CꢀCH (5)) reacted slowly
with alcohols R¦OH in refluxing toluene to give dark
solutions that contained alkoxide dinuclear compounds
[Ru2(R%O)2(CO)4(PPh3)2] (R%ꢀC6H5 (6), CH3CH2CH2
CH2 (7) and (CH3)2CHCH2CH2 (8)) (Scheme 2)2. These
green products are very unstable and we have so far been
unable to isolate them as pure solids. When the crude
products of these reactions were chromatographed in
columns containing florisil using a dichloromethane-ethy-
lacetate mixture as eluant we obtained yellow solutions
of alkoxide complexes 6–8.The IR spectra of solutions
containing complexes 6–8 showed three w(CꢁO) bands
with different intensity patterns. The IR spectrum of 6
in the w(CꢁO) region suggested an anti configuration of
alkoxide bridges, whereas the IR spectrum of (7) is
consistent with a syn arrangement of alkoxide bridges.
Complex 8 showed a w(CꢀO) pattern that suggested the
presence of two stereoisomers with syn (8a) and anti (8b)
configurations, respectively. The 31P{1H}-NMR spectra
Scheme 2.
of these complexes supported the IR data showing a
singlet at 26.5 and 27.6 ppm for compounds 6 and 7
respectively and two singlets at 25.5 ppm for 8a and 12.4
ppm for 8b. Both syn–endo and syn–exo structures are
possible for complexes 7 and 8a but we assign syn–endo
configurations for them because of the bulk of alkoxide
substituents. These spectroscopic data are consistent with
the formation of [Ru2(R¦O)2(CO)4(PPh3)2] complexes
and those found for the bis(methoxi)ruthenium com-
pound [Ru2(MeO)2(CO)4(PtBu)2], which was prepared by
reacting [Ru(CO)3(PtBu3)2] with methanol [8]. On the
other hand, the proposed geometries for alkoxides are
concordant with those found for the thiolate bridged
[Ru2(RS)2(CO)4(PPh3)2] compounds, which were previ-
ously reported by our group of research [5].
Acknowledgements
We thank the Direccio´n General de Investigacio´n
Cient´ıfica y Te´cnica for the financial support (Projects
PB92-0628 and PB96-1146).
1 Analytical and spectroscopic data for 2 and 3: (2) 40% yield.
Anal. Calc. for C50H48O8P2Ru2: C, 57.69; H, 4.65. Found: C, 56.87;
H, 4.69%. IR (CH2Cl2, cm−1): w(CꢁO) 2022 s, 1978 m, 1949 s. IR
(KBr, cm−1): w(OCO) 1565 m, 1413 m. 1H-NMR (CDCl3, 250
MHz): l 0.6 (d, J=6.8 Hz, 12 H), 1.5 (m, 2 H), 1.8 (d, J=6.8 Hz,
4 H), 7.2–7.6 (m, 30 H) ppm. 13C{1H}-NMR (CDCl3, 62 MHz): l
22.3 (CH3), 26.1 (CH), 46.5 (CH2), 127.9, 133.7, 133.8, 133.9 (C6H5),
188.3 (CO2), 205.4(CO) ppm. 31P{1H}-NMR (CDCl3, 102 MHz): l
14.8 ppm. (3) 30% yield. Anal. Calc. for C48H44O8P2Ru2: C, 56.92; H,
4.38. Found: C, 56.87; H, 4.35%. IR (CH2Cl2, cm−1): w(CꢁO) 2022 s,
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