Studies on transition-metal nitrido and oxo complexes. Part 20. Oxoruthenates and oxo-osmates in oxidation catalysis; cis-[Os(OH)2O4]2- as a catalytic oxidant for primary amines and for alcohols

Article abstract of DOI:10.1139/v00-181

cis-[Os(OH)₂O₄]^2- with [Fe(CN)₆]^3- and other co-oxidants has been studied as a catalytic reagent for the oxidative dehydrogenation of primary aromatic and aliphatic amines to nitriles, the oxidation of primary alcohols to carboxylic acids and of secondary alcohols to ketones. Electronic and Raman spectroscopy have been used to elucidate the nature of the oxoruthenates and oxo-osmates present in a number of reported organic oxidations catalyzed by ruthenium and osmium species.

Full text of DOI:10.1139/v00-181

598
Studies on transition-metal nitrido and oxo
complexes. Part 20. Oxoruthenates and oxo-
osmates in oxidation catalysis; cis-[Os(OH)2O4]2–
as a catalytic oxidant for primary amines and for
alcohols
William P. Griffith and Maria Suriaatmaja
Abstract: cis-[Os(OH)2O4]2– with [Fe(CN)6]3– and other co-oxidants has been studied as a catalytic reagent for the oxi-
dative dehydrogenation of primary aromatic and aliphatic amines to nitriles, the oxidation of primary alcohols to
carboxylic acids and of secondary alcohols to ketones. Electronic and Raman spectroscopy have been used to elucidate
the nature of the oxoruthenates and oxo-osmates present in a number of reported organic oxidations catalyzed by ruthe-
nium and osmium species.
Key words: oxidation catalysis, ruthenium, osmium, amine dehydrogenation, alcohol oxidation.
Résumé : On a évalué les possibilités d’utiliser le cis-[Os(OH)2O4]2–, avec le [Fe(CN)6]2– ou d’autres cooxydants,
comme réactif catalytique pour la déshydrogénation oxydante d’amines aromatiques et aliphatiques primaires en nitri-
les, pour l’oxydation d’alcools primaires en acides carboxyliques et d’alcools secondaires en cétones. On a fait appel
aux spectroscopies électronique et Raman pour élucider la nature des oxoruthénates et oxo-osmates présents dans un
certain nombre de réactions d’oxydations connues, catalysées par des espèces contenant du ruthénium et de l’osmium.
Mots clés : oxydation, catalyse, ruthénium, osmium, déshydrogénation d’amine, oxydation d’alcool.
[Traduit par la Rédaction] Griffith and Suriaatmaja 606
Introduction
[Ru(OH)2O3]2– – S2O28− for oxidative amine dehydrogenation,
and is much more effective for the oxidations of secondary
alcohols than we had previously observed (6) in the absence
of CH3CN.
A second purpose of this paper is to use spectroscopic
methods, principally electronic spectroscopy but also Raman
solution studies, to establish the nature of the active catalytic
intermediates, or their precursors, in systems described in a
number of reports of organic oxidations catalyzed by ruthe-
nium and osmim complexes with a variety of co-oxidants.
Since in some cases the procedures are used for organic
preparations a knowledge of the nature of the catalyst (or its
active precursor) is of value.
Homogeneous oxidation reactions catalyzed by transition
metal complexes are a subject of much current interest, and
those catalyzed by ruthenium and osmium complexes have
been much studied in recent years (for Part 19 see ref. 1) (2, 3).
The reagent trans-[RuVI(OH)2O3]2– – S2O28− is effective in
aqueous base for a fairly unusual catalyzed reaction, the oxi-
dative dehydrogenation of primary amines to nitriles at room
temperatures (4), a reaction also studied by the dedicatee of
this paper using ruthenium porphyrinato complexes (5). We
have reported that cis-[OsVIII(OH)2O4]2– – [Fe(CN)6]3– in
aqueous base at room temperatures will oxidize primary al-
cohols and primary alkyl halides to aldehydes (6). Here we
show that cis-[Os(OH)2O4]2– – [Fe(CN)6]3– is, in the pres-
ence of CH3CN, comparable in efficacy with trans-
Results and discussion
Received August 30, 2000. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on May 30, 2001.
I. Oxidations catalyzed by cis-[OsVIII(OH)2O4]2– with
[Fe(CN)6]3– and other co-oxidants
This paper is dedicated to Brian James, a good friend for
many years and a continuing source of inspiration for his
catalytic and ruthenium work in particular, on the occasion
of his 65th birthday.
(i) Oxidative dehydrogenation of primary amines
In earlier work we attempted, with very limited success,
to use cis-[Os(OH)2O4]2– with S2O82−, BrO3−, and [Fe(CN)6]3–
as co-oxidants for the oxidative dehydrogenation of amines
to nitriles (6). Here we examine the utility of cis-
W.P. Griffith1 and M. Suriaatmaja. Department of
Chemistry, Imperial College of Science, Technology and
Medicine, London SW7 2AY, U.K.
[Os(OH)2O4]2– as
a
catalyst for the oxidative
1Corresponding author (telephone: +0207 594 475 9;
fax: +0207 594 580 4; e-mail: w.griffith@ic.ac.uk).
dehydrogenation of primary amines to nitriles with a variety
of co-oxidants in the presence of CH3CN. Acetonitrile is
Can. J. Chem. 79: 598–606 (2001)
© 2001 NRC Canada
DOI: 10.1139/cjc-79-5/6-598

Griffith and Suriaatmaja
599
Table 1. Oxidative dehydrogenation of primary amines to nitriles by cis-[OsVIII(OH)2O4]2– – [Fe(CN)6]3–.
Yield (%)
[Turnover]
Time
(h)
Substrate
Product
Benzylamine
Benzonitrile
94 [24]
81 [21]
75 [19]
74 [19]
82 [21]
80 [20]
80 [20]
84 [22]
2
4-Methoxybenzylamine
2-Chlorobenzylamine
4-Chlorobenzylamine
2-Bromobenzylamine·HCl
3-Bromobenzylamine·HCl
4-Bromobenzylamine·HCl
Octylamine
4-Methoxybenzonitrile
2-Chlorobenzonitrile
4-Chlorobenzonitrile
2-Bromobenzonitrile
3-Bromobenzonitrile
4-Bromobenzonitrile
Octanenitrile
1.5
1.5
1.5
1.5
1.5
1.5
1.5
With BrO−3 co-oxidant the following were obtained:
Benzylamine
Octylamine
Benzonitrile
Octanenitrile
51 [13]
63 [16]
2
2
Note: Conditions: 2 mmol of the amine in 25 cm3 of the cis-[OsVIII(OH)2O4]2– – [Fe(CN)6]3– or the cis-
[OsVIII(OH)2O4]2– – BrO−3 reagent, each with 5 cm3 of CH3CN at room temperature.
known to improve yields in a number of ruthenium-
catalyzed reactions (7, 8).
conclude that this is the effective catalyst precursor in the
system.
As indicated above the yields of nitriles are much im-
proved by addition of CH3CN. It has long been known that
acetonitrile substantially improves yields, selectivities, and
catalytic turnovers in ruthenium-catalyzed reactions (7), and
We tried the three co-oxidants used previously with cis-
[Os(OH)2O4]2–, viz. S2O82−, BrO3−, and [Fe(CN)6]3–. Persul-
fate gave rather poor yields of nitriles (ca. 15%) as was the
case with trans-[Ru(OH)2O3]2– with S2O28− (4). Ferricyanide
gave the best results while bromate was of intermediate effi-
ciency (Table 1). The success of [Fe(CN)6]3– is perhaps not
surprising since with cis-[OsVIII(OH)2O4]2– for oxidation of
alcohols, aldehydes, and alkyl halides it was the most effec-
tive co-oxidant (6) (and the related trans-[OSVIO2(OH)4]2– is
widely used in the asymmetric cis-hydroxylation of alkenes
(3, 9)). Results in terms of product yields, turnovers and
we have recently observed
a similar effect in the
RuCl3.nH2O–IO(OH)5 system for alkene and alkyne cleav-
age (8). The action of CH3CN is not clear; Sharpless and co-
workers (7) have suggested, in the case of ruthenium com-
plexes, that CH3CN, itself resistant to oxidation, may stabi-
lize intermediate lower oxidation states of ruthenium
involved in the catalytic cycle, and it is possible that there is
a similar effect with osmium.
times for amine dehydrogenations by cis-[Os(OH)2O4]2–
[Fe(CN)6]3– are comparable with those found (4) for trans-
[Ru(OH)2O3]2– – S2O82−
–
Attempts were made to use N-methylmorpholine-N-oxide
(nmo) as a co-oxidant since this is very effective in
nonaqueous solutions for alcohol oxidations with [RuO4]–
(10, 11). Although some oxidation of 4-methoxybenzyl-
amine to the nitrile was observed, black OsO2 was formed
during the reaction, so such dehydrogenation as did occur
was probably via a heterogeneously catalyzed route. With
hypochlorite as co-oxidant primary aromatic amines gave
only ca. 15% of nitriles. GC–MS studies on the oxidation
products of benzylamine, 2-methoxy-, 2-methyl-, 4-methyl-
benzylamine, and octylamine showed in all cases a clean
conversion to the nitrile. For benzylamine no formation of
the imine (PhCH2N=CHPh) was observed, though this was a
significant side-product (4) in the oxidation of benzylamine
.
In the absence of [Fe(CN)6]3–, addition of benzylamine to
the orange cis-[Os(OH)2O4]2– in base gives an immediate
purple colour of trans-[OsO2(OH)4]2–, identified by its elec-
tronic spectrum. Reaction of trans-[Ru(OH)2O3]2– with
benzylamine gave a transient green amine complex (4), but
there is no evidence of such a species being formed with cis-
[Os(OH)2O4]2– or trans-[OsO2(OH)4]2–. In the presence of
excess [Fe(CN)6]3– with cis-[Os(OH)2O4]2– in base the col-
our darkens on addition of amine, but when the reaction is
complete the original orange returns, so the reagent is self-
indicating. Comparisons of the electronic spectra of [Fe(CN)6]3–
and of a mixture of [Fe(CN)6]3– with cis-[Os(OH)2O4]2– in
molar NaOH show, in addition to bands due to [Fe(CN)6]3–,
maxima at 225, 325, and 380 nm due to cis-[Os(OH)2O4]2–.
Raman spectra of a similar mixture show the symmetric
Os=O stretch (νs (OsO4)) of cis-[Os(OH)2O4]2– known2 to lie
at 915 cm–1 in addition to bands from [Fe(CN)6]3–. Elec-
tronic spectra also show that excess [Fe(CN)6]3– with trans-
[OsVIO2(OH)4]2– gives cis-[OsVIII(OH)2O4]2–, as shown by
appearance of bands due to the latter at 325 and 380 nm, and
again Raman spectra confirm this by the appearance of the
same 915 cm–1 band. It thus seems clear that [Fe(CN)6]3–
oxidizes trans-[OsO2(OH)4]2– to cis-[Os(OH)2O4]2–, and we
by trans-[Ru(OH)2O3]2– – S2O82−
.
(ii) Oxidation of primary and secondary alcohols
Our earlier use of cis-[Os(OH)2O4]2– as a catalyst for al-
2–
cohol oxidations with [Fe(CN)6]3–, BrO3−, and S2O8 as co-
oxidants showed that Fe(CN)6]3– was the most efficient co-
oxidant, but no acetonitrile was added to the reaction mix-
ture (6). In the presence of CH3CN (Table 2) we again find
that [Fe(CN)6]3– is the most effective co-oxidant, and sec-
ondary alcohols (found to give relatively poor yields of ke-
tones in our earlier work in the absence of acetonitrile (6))
2 A.M. El-Hendawy, W.P. Griffith, M. Suriaatmaja. To be submitted.
© 2001 NRC Canada

600
Can. J. Chem. Vol. 79, 2001
Table 2. Oxidations of alcohols by cis-[OsVIII(OH)2O4]2– – [Fe(CN)6]3–.
Yield (%)
[Turnover]
Time
(h)
Substrate
Product
Benzyl alcohol
1-Hexanol
Benzoic acid
1-Hexanoic acid
Cyclopentanone
Cyclohexanone
Cyclohexanone
Cyclohexanone
Cycloheptanone
Cyclooctanone
2-Hexanone
2-Octanone
2-Octanone
4-Methylcyclohexanone
Citronellal
Citral
81 [21]
70 [18]
>99 [25]
66 [17]
69 [18]
>99 [25]
>99 [25]
>99 [25]
>99 [25]
90 [23]
>99 [25]
>99[25]
90 [24]
91 [24]
2
2
2
0.5
1
2
2
2
2
0.5
2
2
2
2
Cyclopentanol
Cylohexanol
Cylohexanol
Cylohexanol
Cycloheptanol
Cyclooctanol
2-Hexanol
2-Octanol
2-Octanol
4-Methylcyclohexanol
Citronellol
Geraniol
Note: Conditions: 2 mmol of the alcohol in 25 cm3 of the cis-[OsVIII(OH)2O4]2– – [Fe(CN)6]3 reagent with 25 cm3 of
CH3CN at room temperature.
gave good yields and turnovers if CH3CN is used. Thus
cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, 2-
methyl-cyclohexanol, 2-hexanol, and 2-octanol give the cor-
responding ketones in >99% yield with catalytic turnovers
of ca. 25 over a two-hour period. With primary alcohols
however, the yields and turnovers of carboxylic acids are
only slightly improved by addition of acetonitrile. Unsatu-
rated alcohols (citronellol, geraniol) do not suffer competing
double bond cleavage and give the corresponding unsatu-
rated aldehydes in good yield. The same colour changes as
with amines are observed when alcohols are added to orange
cis-[Os(OH)2O4]2– in base, without and with [Fe(CN)6]3–.
(cis-[OsVIII(OH)2O4]2–), or osmate (trans-[OsVIO2(OH)4]2–).
These can be distinguished by their electronic (17–19) or
Raman2 (6, 15) spectra, and here again we use electronic
spectra to help in the identification of such species in pub-
lished procedures. An earlier paper of ours (20) covered
some literature for oxoruthenate but not oxo-osmate species
up to 1994.
A. Oxidations with ruthenium catalysts
(i) Electronic spectra of oxoruthenates
In Fig. 1 we reproduce the electronic spectra of: (a) RuO4,
(b) [RuO4]–, and (c) of trans-[Ru(OH)2O3]2– in aqueous me-
dia; they are close to those reported earlier for all three spe-
cies (12), for [RuO4]– (13), and of trans-[Ru(OH)2O3]2– (13,
14).
II. Identification of ruthenium and osmium catalyst
precursors in published oxidation procedures
Over the past 20 years there have been numerous reports
on oxidations catalyzed by ruthenium and, in a smaller num-
ber of cases, osmium complexes. Usually RuCl3·nH2O or
OsO4 are the reagents initially used, but there is often doubt
about the nature of the species involved in the catalysis. We
have tried (Table 3) to establish the nature of such species
by measuring the electronic and, in some cases, Raman
spectra of the solutions used in typical literature reports. Of-
ten, particularly in kinetic studies, a range of concentrations
was used by the original investigators. We have used condi-
tions typical of these and they are listed (catalyst and its
concentration, co-oxidant, substrate, solvent and solutes,
pH). In the last two columns of Table 3 the active catalyst
precursor is given as suggested by the literature and that
which we favour from spectra which we have measured of
the reaction solutions. Occasionally our catalyst concentra-
tions differ from those in the cited publications to be able to
obtain reasonable spectra.
(ii) Hypochlorite as co-oxidant
Recently Mills and Holland (21) studied the oxidation of
2-octanol to 2-octanone by RuO4 using ClO– as co-oxidant,
and gave a speciation diagram for the oxoruthenates pro-
duced from RuO4 at different pH. From pH 5–7 RuO4 is the
predominant species, [RuO4]– from pH 7.5–10.5, and trans-
[Ru(OH)2O3]2– at higher pH, essentially in agreement with
the classic work of Connick and Hurley (12)). They noted
for oxoruthenates in hypochlorite solutions that, although at
pH 11–14 the orange trans-[Ru(OH)2O3]2– might be ex-
pected to be present, in fact the yellow-green [RuO4]– is the
predominant species. This was ascribed to a kinetic effect,
the oxidation of trans-[RuVI(OH)2O3]2– to [RuVIIO4]– by
ClO– being much more rapid than the reduction of RuO4 to
trans-[RuVI(OH)2O3]2– by OH–, unless the pH is very high
(>5 M OH–). However, they did not show spectroscopically
that [RuO4]– is present in such hypochlorite solutions. Here
we demonstrate both with electronic and Raman
spectroscopies that this is the case.
In most cases the ruthenium precursors are likely to be the
oxo species ruthenium tetroxide (RuVIIIO4), perruthenate
([RuVIIO4]–), or ruthenate (trans-[RuVI(OH)2O3]2–); these are
easily distinguished by their electronic (13–15) or Raman2
(15, 16) spectra. For the osmium-catalyzed reactions, likely
intermediates are osmium tetroxide (OsVIIIO4), perosmate
In Table 3 (entries 1–7 (22–26)) we list a number of ru-
thenium-catalyzed oxidations with hypochlorite, all used as
preparative methods and thus of particular interest. The elec-
tronic spectra of both aqueous and organic layers were mea-
© 2001 NRC Canada

Table 3. Oxidation reactions catalyzed by ruthenium and osmium complexes.
Aqueous solute pH
Claimed
No. Precursor (mmol dm–3)
Co-oxidant (mol dm–3)
Substrate
Solventa
(mol dm–3)
measured catalyst
Actual catalystb
Ref.
1
2
3
4
5
6
7
8
RuCl3·nH2O (0.4)
RuCl3·nH2O (3.4)
RuCl3·nH2O (1.0)
RuCl3·nH2O (0.4)
RuCl3·nH2O (2.5)c
RuCl3·nH2O (5.2)
RuCl3·nH2O (0.4)
RuCl3·nH2O (1.1)
RuCl3·nH2O (0.4)
RuCl3·nH2O (0.4)
RuCl3·nH2O (0.05)
RuCl3·nH2O (0.4)
NaOCl (0.3)
NaOCl (0.3)
NaOCl (0.3)
NaOCl (0.3)
NaOCl (0.3)
NaOCl (0.3)
Ca(OCl)2 (0.3)
NaIO4 (0.2)
NaIO4 (0.3)
NaIO4 (0.04)
NaIO4 (0.1)
KBrO3 (0.1)
1-Pentadecene
Methylbenzenes
Epoxybornane
1-Decanol
1-Decanol
Cyclopentene
Alcohols
Epoxybornane
Alcohols
DMF
Acetaldehyde
Bordeaux
aq–CH2Cl2
aq–DCE
aq–CH3CN–CCl4
aq–CCl4
aq–CCl4
aq–CCl4
aq–CH3CN
aq–CH3CN–CCl4
aq–CH3CN
aq
NaOH (0.8)
—
—
—
—
NaOH (1)
—
—
14
13
13
13
13
14
13
7
RuO4
RuO4
RuO4
[RuO4]–
[RuO4]–
[RuO4]2–
—
RuO4
—
RuI/RuIII
RuI/RuIII
—
[RuO4]–
[RuO4]–
[RuO4]–
[RuO4]–
[RuO4]–
[RuO4]–
[RuO4]–
RuO4
(22)
(23)
(24)
(25)
(25)
(26)
(27)
(24)
(27)
(31)
9
—
7
RuO4
RuO4
10
11
12
NaOH (0.02)
NaOH (0.1)
H2SO4 (1) –
K2SO4 (0.5)
NaOH (0.4)
NaOH (3)
NaOH (0.2)
NaOH (0.1)
H2SO4 (1)
H2SO4 (0.8)
NaOH (0.1)
NaOH(0.8)
NaOH (1)
NaOH (2)
NaOH (1)
NaOH (1)
NaOH (3.3)
NaOH (0.5)
12
13
3
aq
aq
[RuO2(HIO6)2]6– (32)
RuO4
(33)
13
14
15
16
17
18
19
20
21
22
23
24
25
26
[Ru(OH)2O3]2– (0.2)
RuCl3·nH2O (0.24)
RuCl3·nH2O (0.3)
RuCl3·nH2O (0.3)
RuCl3·nH2O (0.06)
RuCl3·nH2O (1.78)
OsO4 (0.8)
OsO4 (6)
OsO4 (0.45)
OsO4 (0.35)
KBrO3 (0.014)
K3(Fe(CN)6) (0.2)
K3(Fe(CN)6) (1)
K3(Fe(CN)6) (1)
Ce(SO4)2 (0.04)
Ce(SO4)2 (0.01)
—
Cyclopentanol
Ethanediol
Propan-2-ol
Hexyleneglycol
Butyric acid
DMSO
Sugars
Oleate
Acetaldehyde
DMF
Allylalcohol
aq
aq
aq
aq
aq
aq
aq
aq
aq
aq
aq
13
14
13
13
1
[RuO4]2–
RuIII
[Ru(OH)2O3]2–
RuIII
RuIII
RuIII
See text
See text
(34)
(36)
(37)
(38)
(39)
(40)
(43)
(44)
(27)
(46)
(47)
(48)
(49)
(47)
RuIII
RuIII
RuIII-complex
RuIII-complex
1
13
13
14
14
14
14
14
14
[Os(OH)2O4]2– [Os(OH)2O4]2–
NaOCl (0.3)
—
??
[Os(OH)2O4]2–
[Os(OH)2O4]2–
NaIO4 (0.01)
NaIO4 (0.04)
NaIO4 (0.04)
K3(Fe(CN)6) (0.2)
[Os(OH)2O4]2– [Os(OH)2O4]2–
[Os(OH)2O4]2– [Os(OH)2O4]2–
OsO4 (0.45)
OsO4 (4.7 × 10–4)
OsO4 (0.7)
2-Bromopropionate aq
OsVIII
OsVI-complex
See text
[Os(OH)2O4]2–
[Os(OH)2O4]2–
See text
K3(Fe(CN)6) (0.01) (0.2) Tartrate
aq
aq
RuCl3·nH2O (0.45) + OsO4 NaIO4 (0.1)
Allyalcohol
(0.45)
27
RuCl3·nH2O (0.7) + OsO4
NaIO4 (0.1)
Acetaldehyde
aq
NaOH (0.1)
13
See text
See text
(50)
(0.7)
aElectronic spectra of aqueous layer measured at 60°C.
bSpecies present in aqueous layer according to electronic spectra.
cElectronic spectra of aqueous layer measured at room temperature.

602
Can. J. Chem. Vol. 79, 2001
Fig. 1. Electronic spectra in aqueous solutions of: (a) RuO4 in
water at pH 7 (ca. 2.6 × 10–4 M RuO4); (b) [RuVIIO4]– in water
at pH 10; 0.09 g dm–3 (3.5 × 10–4 M) RuCl3·3H2O in 0.2 M
NaBrO3 and molar Na2CO3; (c) trans-[RuVI(OH)2(O3]2– in water
at pH 14; 0.15 g dm–3 (6 × 10–4 M) RuCl3·3H2O in 0.05 M
K2S2O8 and molar KOH.
tional fine structure particularly for the 385 nm band. The
aqueous layer could contain RuO4, [RuO4]– or trans-
[Ru(OH)2O3]2–, depending on the pH. Unfortunately for
such layers the electronic spectrum of ClO– obscures
the 315 nm band and part of the 385 nm band of [RuO4]–.
Nevertheless the latter is visible as a shoulder without the
fine structure always observed on this band for RuO4, as
well as the weak shoulder near 480 nm present in the spec-
trum of [RuO4]– but not RuO4. Study of the Raman spectra
of more concentrated solutions of RuCl3·nH2O (0.01 M) in
0.3 M hypochlorite clearly show the νs (RuO4) band of
[RuO4]– at 853 cm–1, close to the literature values for this
mode in the perruthenate ion (15, 16).
For entries 1 and 2, RuO4 was suggested as the oxidant
(22, 23), but certainly for the aqueous layers our electronic
spectra showed [RuO4]– to be present, although no phase-
transfer reagent was used in our measurements. For entries 3
(24), 4, and 5 (25) the pH of the aqueous layers are 13 and
our electronic spectra show that they contain [RuO4]– rather
than the RuO4 which we had earlier suggested (20). For the
solution at 60°C this is still the case for entry 5. For entry 6
(26) [RuO4]– is clearly present rather than the claimed
“[RuO4]2–”.
In entry 7 Ca(OCl)2 is used in a small quantity of concen-
trated water – CH3CN (27). Little of the co-oxidant dis-
solves under the conditions described and the mixture
separates into two layers. The upper, predominantly
acetonitrile, layer contains RuO4 and the lower, predomi-
nantly aqueous layer [RuO4]–.
Thus in all the solutions studied with hypochlorite as the
co-oxidant we observe [RuO4]– in the aqueous layer and
RuO4 in the organic layer ([RuO4]–, being a charged species,
does not extract into the organic layer in the absence of a
phase-transfer agent).
(iii) With periodate as co-oxidant
We have isolated salts of trans-[RuVIO2{I(OH)O5}2]6–
from reaction of RuCl3·nH2O with periodates and persulfate
(28, 29) and have shown that with excess periodate these
function as catalysts for the oxidation of primary alcohols
and alkyl halides to carboxylic acids, and for secondary al-
cohols and halides to ketones (29). The X-ray crystal struc-
ture
of
trans-NaK5[RuVIO2{I(OH)O5}2]·8H2O
was
determined (28), and the electronic spectrum of trans-
[RuO2{I(OH)O5}2]6– in aqueous base has bands at 221 and
389 nm (29). Rozovskii et al. (30) have proposed the forma-
tion of a ruthenium(VII) periodato complex from trans-
[Ru(OH)2O3]2– and periodate in base (0.04–2 M KOH) and
such a species, possibly trans-[RuVIIO2{I(OHO)O5}2]5–,
seems to be associated with a band near 380 nm.
For those oxidations effected in neutral solution (entries 8,
9 (24, 27)) it is clear that RuO4 is produced, as expected. At
60°C, at which some of these oxidations (entry 8) were con-
ducted (24), electronic spectra show that there is surprisingly
still some RuO4 remaining in both layers. Raman spectra
also show, in addition to bands due to (IO4)–, the νs (RuO4)
and νas (RuO4) bands at 883 and 915 cm–1, in agreement
with the literature data (15).
At high pH (entries 10 and 11 (31, 32)) problems arise
from the very low solubilities of NaIO4 or KIO4 at such pH.
We observe inflections in the electronic spectra of the
sured. In the organic solvent RuO4 is always present, clearly
shown by its bands at 315 and 385 nm with attendant vibra-
© 2001 NRC Canada

Griffith and Suriaatmaja
603
Fig. 2. Electronic spectra in aqueous solutions of: (a) OsVIIIO4 in
water at pH 7 (0.13 g dm–3 (5.2 × 10–4 M) OsO4); (b) cis-
[OsVIII(OH)2O4]2– (0.11 g dm–3 (4.5 × 10–4 M) OsO4 in molar
NaOH); (c) trans-[OsVIO2(OH)4]2– (0.165 g dm–3 (4.5 × 10–4 M)
trans-K2[OsO2(OH)4 in 0.1 M NaOH).
solutions near 380 nm which could well arise from trans-
[RuO2{I(OH)O5}2]6– which has a band near this wavelength
and is an effective catalytic oxidant with periodate as co-
oxidant (29). Unfortunately, Raman spectra could not be re-
corded owing to the low concentrations at this pH. We
believe the effective oxidation precursor to be the periodato
species abbreviated as [RuO2(HIO6)2]6– in Table 3.
(iv) With bromate and iodate as co-oxidant
Aqueous bromate is an effective co-oxidant at pH 10 for
[RuO4]– and trans-[Ru(OH)2O3]2– at pH 14 (13). For entry
12 our electronic spectra show that RuO4 is produced, as
expected, since the pH
7. The substrate was “Bordeaux”
(disodium-2-hydroxy-4-(1-naphthylazo)-naphthalen-3,6-disul-
phonate) being oxidized to an unspecified product; the effec-
tive oxidant was not identified (33). Raman spectra also
show the νs (RuO4) and νas (RuO4) bands of RuO4 at 883
and 915 cm–1 in addition to those due to bromate. Entry 13
involves the initial use of trans-[Ru(OH)2O3]2– (incorrectly
formulated in (34) as [RuO4]2–) with BrO3− in 0.01 M OH–.
Bands in the electronic spectra at 385 and 460 nm show that
trans-[Ru(OH)2O3]2– is indeed the effective oxidant precursor.
There are references to the use of iodate (IO−3) as a co-
oxidant with RuCl3·nH2O as the catalyst for kinetic data on
certain oxidations (35). However, under the conditions re-
ported, we found no evidence of electronic spectral change
on addition of iodate to RuCl3·nH2O.
(v) With ferricyanide as co-oxidant
We have shown the viability of using [Fe(CN)6]3– on a
preparative scale for the oxidation of primary alcohols to al-
dehydes and carboxylic acids and for secondary alcohols to
ketones with trans-[Ru(OH)2O3]2– as the catalyst (20) and,
above (section I), with cis-[Os(OH)2O4]2–. Three recent re-
ports concern oxidations with RuCl3·nH2O with [Fe(CN)6]3–
as co-oxidant (entries 14–16). As before (20), there is no ev-
idence of formation of oxoruthenates in such mixtures in the
absence of organic substrate. It is likely, as the authors sug-
gest (36–38), that a ruthenium(III) species is responsible for
the catalysis.
(vi) With cerium(IV) sulfate
With cerium(IV) sulfate as co-oxidant and RuCl3·nH2O
(entries 17, 18 (39, 40)) a strong electronic absorption at
315 nm in the aqueous layer is observed, but extraction of
the solutions with CCl4 shows RuO4 to be present in the or-
ganic layer. It may be that the band at 315 nm arises from a
ruthenium(IV) chloro-aquo complex, the existence of which
was suggested by Giddings and Mills (41) from their studies
on cerium(IV) sulfate at pH 5 with RuO2·nH2O.
B. Oxidations reported catalyzed by osmium complexes
There is an early but comprehensive review of reactions
catalyzed by OsO4 in base by a variety of co-oxidants (42).
(i) Electronic spectra of oxo-osmates
In Fig. 2 we give the spectra of: (a) OsO4, (b) cis-
[OsVIII(OH)2O4]2–, and (c) trans-[OsVIO2(OH)4]2–; again
these are close to those reported for these species (17–19).
No molar extinction coefficients (ε) values have been given
in the literature (17) for OsO4 in aqueous solution, but for
the 251 and 288 nm bands we measured the ε values to be
1905 and 1048 mol–1 cm–1, respectively. For trans-
[OsVIO2(OH)4]2– we measured the spectrum of a known
© 2001 NRC Canada

604
Can. J. Chem. Vol. 79, 2001
amount of trans-K2[OsVIO2(OH)4]2– dissolved in 0.1 M NaOH.
Essentially identical spectra were obtained by reduction of
cis-[OsVIII(OH)2O4]2– in molar KOH with 2-propanol.
Experimental
Materials
Chemicals were purchased from Aldrich (hydrated ruthe-
nium trichloride and osmium tetroxide were obtained from
Johnson, Matthey) and used without further purification.
The use of cis-[OsVIII(OH)2O4]2– as a catalyst for oxida-
tive amine dehydrogenation and alcohol oxidations.
(ii) Oxidations by OsO4 with no co-oxidant
Entry 19 concerns stoichiometric oxidations by OsO4 in
base. cis-[Os(OH)2O4]2– was suggested as the catalyst
precursor (43) and our spectra, showing bands at 325 and
375 nm, confirm this.
Preparation of the cis-[Os(OH)2O4]2– – [Fe(CN)6]3– reagent
OsO4 (0.02 g, 0.08 mmol) was dissolved in 25 cm3 of
aqueous molar NaOH and excess K3[Fe(CN)6] (9.9 g,
30 mmol) was added to give an orange solution.
(iii) Oxidations with hypochlorite as co-oxidant
Foglia et al. (44) report oxidations with OsO4 in alkaline
hypochlorite (entry 20) and implied that OsO4 is the active
species. We observe a shoulder at 380 nm which probably
arises from cis-[Os(OH)2O4]2– which has a band here (its
300 nm band would be obscured by absorption from
hypochlorite).
Preparation of cis-[Os(OH)2O4]2– – S2O82− and cis-
[OsO4(OH)2]2– – BrO3−
OsO4 (0.02 g, 0.08 mmol) was dissolved in 25 cm3 of
aqueous molar NaOH to give an orange solution of cis-
[OsO4(OH)2]2–. Excess K2S2O8 (9.9 g, 30 mmol) or 1.5 g
(10 mmol) of NaBrO3 was then added.
(iv) With periodate as co-oxidant
The complex trans-Na6[OsVIO2{I(OH)O5}2]·18H2O is
made from trans-K2[OsO2(OH)4] and NaIO4 in NaOH (45).
Its electronic spectrum in aqueous base shows bands at 325
and 385 nm and it functions as a catalyst, with periodate as
co-oxidant, for the oxidation of primary alcohols and alkyl
halides to carboxylic acids and of secondary alcohols to ke-
tones (29).
Catalytic dehydrogenation of amines to nitriles
The reactions (Table 1) were performed at room tempera-
ture by dropwise addition of the amines (RCH2NH2,
2 mmol) over a period of 5 min to a vigorously stirred solu-
tion (25 cm3) of the cis-[Os(OH)2O4]2– – [Fe(CN)6]3– re-
agent and acetonitrile (25 cm3). Subsequent work with
benzylamine and 2-chlorobenzylamine shows that the same
results were obtained with only 5 cm3 of CH3CN. The initial
colour of the reaction mixture is orange; on addition of
amine the solution darkens and some pale-yellow
K4[Fe(CN)6] is deposited. When the reaction is complete the
original orange colour of the mixture reappears. The mixture
was then extracted with chloroform (3 × 25 cm3), these ex-
tracts dried over anhyd MgSO4, and the chloroform re-
moved. Products were characterized by 1H NMR, IR spectra,
and melting points of solids; liquids were characterized by
GC–MS.
For entries 21–23 (27, 46, 47) in which oxidations are car-
ried out at high pH our electronic spectra show a clearly pro-
nounced shoulder at 380 nm which could arise either from
trans-[OsVIO2{I(OH)O5}2]6– or cis-[Os(OH)2O4]2–. We think
it likely that, from the known ease of oxidation of os-
mium(VI) to (VIII), that the latter is the more likely effec-
tive catalyst precursor. Again, as was the case with the
analogous ruthenium system, low solubilities prevent Raman
spectra being obtained.
(v) With ferricyanide as co-oxidant
The use of [Fe(CN)6]3– with trans-[OsVIO2(OH)4]2– at
pH 10 is common in organic synthesis for the cis-
hydroxylation of alkenes (3, 9); in our earlier work (6) we
showed that cis-[OsVIII(OH)2O4]2– is not present in such
mixtures at that pH. In entries 24 and 25 (48, 49) the oxida-
tions were carried out at high pH, and our electronic spectra
show a band at 325 nm in addition to bands due to
[Fe(CN)6]3–. We ascribe this (as discussed above in section
I) to cis-[Os(OH)2O4]2–; the 380 nm band of the latter is ob-
scured by the broad 425 nm band of [Fe(CN)6]3–. The
Raman data alluded to above also suggest that that cis-
[Os(OH)2O4]2– is present in these mixtures.
Catalytic oxidation of alcohols
Reactions (Table 2) were carried out at room temperature,
and the oxidation of cyclohexanol is typical. To 25 cm3 of
the cis-[Os(OH)2O4]2– – [Fe(CN)6]3– reagent made as de-
scribed above was added 0.22 g (2 mmol) of cyclohexanol
and 25 cm3 of acetonitrile, and the mixture stirred for the
stated time. The colour changes are similar to those ob-
served for the amine dehydrogenations. The mixture was
then extracted with chloroform (3 × 25 cm3), the extracts
combined and dried over anhyd MgSO4, the chloroform
evaporated off, and the product characterized by GC or, in
the cases of carboxylic acids, by isolation.
C. Oxidations reported catalyzed by osmium and
ruthenium complexes
The nature of oxoruthenates or oxo-osmates present in
solutions
The last entries in Table 3 (26, 27 (47, 50)) concern oxi-
dations with a mixture of OsO4 and RuCl3·nH2O with
periodate in base. The mixtures show electronic spectral
bands at 325 and 385 nm; it is possible that a mixture of
trans-[RuO2{I(OH)O5}2]6– (which has a band at 389 nm
(29)) and cis-[Os(OH)2O4]2– (bands at 325 and 385 nm (6))
is present in both cases. Unfortunately, low solubilities pre-
vented the collection of Raman data.
In all cases (Table 3) the cited literature procedure was
followed but no substrate added. The solvent after mixture
of the ruthenium or osmium precursor, co-oxidant and buffer
(if appropriate) was diluted if necessary, using the same sol-
vent or solvent mixture at the same pH as in the literature so
that good quality electronic spectra could be obtained.
© 2001 NRC Canada

Griffith and Suriaatmaja
605
3. H.C. Kolb, M.S. van Nieuwenzhe, and K.B. Sharpless. Chem.
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Spectroscopic data
In general the optimum ruthenium or osmium concentra-
tions for measurements of electronic spectra were ca. 4 ×
10–4 M (see also legends for Figs. 1 and 2. Note that for
Fig. 1(a) the concentration of RuO4 given is approximate
since the solution was made by passing RuO4 vapour into
water). For the less sensitive Raman technique the ruthenium
or osmium concentrations had to be substantially higher: for
cis-[Os(OH)2O4]2– in [Fe(CN)6]3– 0.02 M of the former and
0.6 M of the latter in molar NaOH was used, while for
Raman spectral demonstration of the oxidation of trans-
[OsO2(OH)4]2– to cis-[OsO4(OH)2]2– by [Fe(CN)6]3– in base
the same concentrations were used. For detection of [RuO4]–
in hypochlorite 0.01 M RuCl3·nH2O was used in aqueous
0.3 M hypochlorite. For detection of RuO4 in periodate and
also in bromate, 0.25 M RuCl3·nH2O was used in molar aq
NaIO4 and in 2 M aq NaBrO3, respectively.
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Instrumentation
Electronic spectra were measured in 1 cm quartz cuvettes
on a PerkinElmer Lambda 2 instrument. Raman spectra were
measured on a PerkinElmer 1760X Fourier Transform
Raman instrument with 1064 nm Nd-YAG excitation with a
power of 2 W, and on a Dilor LabRam Infinity instrument
with 632 nm. He–Ne excitation and 532 nm frequency-
doubled Nd-YAG excitations, as appropriate, each at 5 mW.
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Mass spectra were measured on
a
PerkinElmer
Autosystem instrument with a PerkinElmer stainless-steel
column packed with 5% Carbowax 20M on Chromosorb
(DCMS treated). GC–MS characterization was carried out
on a Micromass Autospec with a Hewlett–Packard 5890 gas
chromatograph and an SGE BPX5 column.
Conclusions
The cis-[Os(OH)2O4]2– – [Fe(CN)6]3– reagent will, in the
presence of acetonitrile, oxidatively dehydrogenate primary
amines to nitriles and oxidise primary alcohols to carboxylic
acids and secondary alcohols to ketones at room tempera-
tures. Ferricyanide is the best co-oxidant while others (per-
sulfate, bromate, hypochlorite) are less effective.
Studies by electronic and Raman spectroscopies of solu-
tions in a wide variety of procedures in the literature using
ruthenium or osmium catalysts with a number of co-oxidants
(hypochlorite, periodate, bromate, iodate, ferricyanide, and
cerium(IV)) were made to identify the nature of the catalyst
or catalyst precursor.
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Acknowledgements
We thank the University of London Intercollegiate Re-
search Service (ULIRS) for the Raman facilities, Mr. John
Barton for the GC–MS studies, and Johnson Matthey for
loan of ruthenium trichoride and osmium tetroxide.
32. L. Timmanagoudar, G.A. Hiremath, and S.T. Nandibewoor. J.
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