Reactions of trans-[OsO2Cl2L2] (L = PPh3, AsPh3, SbPh3) with acetic acid

Article abstract of DOI:10.1023/A:1023366810613

The possibility of reactions between trans-[OsO₂Cl ₂L₂] (L = PPh₃, AsPh₃, SbPh ₃) osmium(VI) complexes and glacial acetic acid to give osmium(IV) compounds of general formula [Os₂

Full text of DOI:10.1023/A:1023366810613

Russian Journal of Applied Chemistry, Vol. 75, No. 12, 2002, pp. 1907 1910. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 12, 2002,
pp. 1947 1950.
Original Russian Text Copyright
2002 by Belyaev, Eremin, Simanova, Evreinova.
INORGANIC SYNTHESIS
AND INDUSTRIAL INORGANIC CHEMISTRY
Reactions of trans-[OsO2Cl2L2] (L = PPh3, AsPh3, SbPh3)
with Acetic Acid
A. N. Belyaev, A. V. Eremin, S. A. Simanova, and N. V. Evreinova
St. Petersburg State Technological Institute, St. Petersburg, Russia
Received November 15, 2001; in final form, September 2002
Abstract The possibility of reactions between trans-[OsO2Cl2L2] (L = PPh3, AsPh3, SbPh3) osmi-
um(VI) complexes and glacial acetic acid to give osmium(IV) compounds of general formula
[Os2( -O)( -O2CCH3)2Cl4(L)2] was studied.
Dissolution of platinum-containing raw materials is
a labor-consuming and ecologically unsafe process
[1 4]. The creation of safer and less expensive tech-
nologies for breaking-down such concentrates and
the closely related problem of analytical monitoring
of the efficiency of raw material processing can be
regarded as one of important lines of development of
modern chemical technologies for recovery of plat-
inum metals.
containing Os2( -O) core and bidentate coordination
of two bridging acetate groups [6]. If L is Py, then
[(Py)2Cl2(CH3COO)Os( -O)Os(Py)2Cl3] compound
with a linear Os2( -O) core and only one monoden-
tately coordinated acetate group is formed [7].
The present study is concerned with the influence
exerted by the nature of ligand L in trans-[OsO2Cl2L2]
on the formation and spectral characteristics of osmi-
um acetates [OsI2V( -O)( -O2CCH3)Cl4(L)2]. PPh3,
AsPh3, or SbPh3 were selected as ligands L. Their
choice was determined by the fact that, on the one
hand, they behave as donors having a free electron
pair and, on the other, they possess, unlike such a li-
gand as Py, free d-orbitals with rather low energies.
At present, one of ways to dissolve osmium-con-
taining concentrates consists in their fusion with sodi-
um disulfate, leaching of the melt, and its treatment
with chlorine for distilling-off OsO4, which is ab-
sorbed successively, first by HCl solutions with meth-
anol and then by an alcoholic solution of NaOH. Heat-
ing the latter with NH4Cl allows osmium to be pre-
cipitated as [OsO2Cl2(NH3)2 [4].
EXPERIMENTAL
The development of alternative procedures for dis-
solving osmium-containing concentrates is based on
replacement of highly aggressive solutions with etha-
nol acetate mixtures [5]. However, this requires a de-
tailed study of the behavior of trans-[OsO2Cl2L2]
complexes with ligands L of varied nature in acetic
acid media.
The starting trans-OsO2Cl2(PPh3)2 was obtained
using the procedure proposed in [8].
trans-OsO2Cl2(AsPh3)2. A 2-g portion of OsO4
was introduced into a mixture of 30 ml of ethanol and
5 ml of concentrated hydrochloric acid heated to
approximately 90 C. Triphenylphosphine (4.5 g, or
14 mmol per 0.39 mmol of OsO4) was dissolved in
a minimal amount of boiling ethanol and poured into
the first solution. The precipitated light beige complex
was washed on a filter with ethanol and diethyl ether.
Boiling of trans-[OsO2X2L2] (X = Cl, Br; L =
PPh3, PEt2Ph, or Py) in a RCOOH-(RCOO)2O (R =
CH3, C2H5) mixture is known [6, 7] to give binuclear
osmium acetates with a Os2( -O) core.
1
Yield 70%. IR spectrum, cm : 471 s, 693 vs,
X-ray structural data [6, 7] suggest that the for-
mation of a linear or bent binuclear Os O Os frag-
ment is affected by the nature of ligand (L) in
the starting mononuclear trans-[OsO2X2L2] (X =
Cl, Br) compound. If L is PPh3 or PEt2Ph, then
[OsI2V( -O)( -O2CCH3)2Cl4(L)2] (R = CH3, C2H5;
X = Cl, Br) complexes are formed with bent metal-
742 vs, 845 s, 1001 w, 1030 w, 1083 w, 1190 vs,
1460 s, 1510 w.
Found, %: Os 21.1; Cl 8.2.
C36H30As2Cl2Os.
Calculated, %: Os 21.0; Cl 7.8.
1070-4272/02/7512-1907 $27.00 2002 MAIK Nauka/Interperiodica

1908
BELYAEV et al.
trans-OsO2Cl2(SbPh3)2. The synthesis was similar
Electronic absorption spectra of solutions of the
complexes were recorded on an SF-56 spectrophotom-
eter in the range 200 1100 nm in quartz cells with
l = 1 cm. The IR spectra were recorded in the range
to that of trans-OsO2Cl2(AsPh3)2. Owing to the low
solubility of triphenylantimony in ethanol, the alcohol
was replaced with an EtOH Et2O mixture (1 : 1 by
volume). The precipitated light green complex was
filtered off and carefully washed with ether, in which
it is partially soluble. Slow evaporation of the filtrate
gave an additional amount of the finely crystalline
precipitate of the complex. Total yield 80%. IR
1
4000 400 cm on a Nicolet FT-360 spectrophotom-
eter in KBr pellets, and X-ray-photoelectron spectra
(XPS), on a Perkin Elmer PHI 5400 spectrophotom-
eter with excitation by X-ray emission of Mg. Pow-
dered samples were compacted with indium and
placed, after preliminary evacuation of the chamber,
on a manipulator cooled with liquid nitrogen. The
working residual pressure in the spectrophotometer
1
spectrum, cm : 454 s, 683 vs, 729 vs, 836 s, 993 s,
1019 s, 1061 w, 1179 w, 1301 w, 1329 w, 1433 s,
1475 s, 1571 w, 1637 wide, 1871 wide.
8
was 10 mm Hg.
Found, %: Os 18.9, Cl 7.2.
C36H30Cl2OsSb2.
The X-ray structural analysis was carried out on
a SYNTEX P21 diffractometer with CuK emission
Calculated, %: Os 19.0, Cl 7.1.
(
= 1.54178 ) at 20 1 C.
The experimental data obtained suggest that bi-
[Os2( -O)( -O2CCH3)2(PPh3)2Cl4] (I). A sus-
pension of 1 g of trans-[OsO2(PPh3)2Cl2] in 20 ml of
glacial acetic acid was boiled until the starting com-
plex dissolved completely. In the process, the color-
less solution turned dark brown. The dry residue
formed upon evaporation of the solution on an air bath
was dissolved in 40 ml of chloroform and a minor
amount of pentane or hexane was added to the result-
ing solution. The precipitated complex was filtered
off, washed with ether, and kept in a desiccator over
KOH to constant weight.1 Yield 95%. IR spectrum,
nuclear oxygen-bridged osmium acetates [OsI2V( -O)
( -O2CCH3)2Cl4(L)2] (L = PPh3 or AsPh3) can be
formed in the reaction of trans-[OsO2Cl2L2] with
CH3CO2H in the absence of (CH3CO)2O, too. Heating
of the trans-[OsO2Cl2L2] complexes with glacial acetic
acid gives dark brown binuclear osmium(IV) compounds
of general formula [OsI2V( -O)( -O2CCH3)2Cl4(L)2] in
high yield. However, [OsI2V( -O)( -O2CCH3)2Cl4(L)2]
complexes can only be isolated for L = PPh3 (I) or
AsPh3 (II). According to XPS data, the Os (4f 7/2)
bond energies are 53.0 and 53.1 eV for complexes I
and II, respectively, which corresponds to a formal
oxidation state of osmium atoms in these compounds
equal to +4, in good agreement with the data of [5].
1
cm : 443 w, 523 vs, 619 w, 691 vs, 720 s, 744 s,
997 w, 1028 w, 1091 s, 1159 w, 1220 w, 1408 w,
1435 vs, 1482 s, 1697 wide, 2927 w, 2964 w, 3059 w,
3440 wide.
Compounds I and II are stable in air, poorly sol-
uble in water, ethanol, ether, and saturated hydrocar-
bons, but readily soluble in such solvents as chloro-
form, dichloromethane, or benzene.
Found, %: Os 32.0, Cl 12.5.
C40H36Cl4O5Os2P2.
Calculated, %: Os 32.2, Cl 12.0.
The electronic absorption spectra of [OsI2V( -O)
( -O2CCH3)2Cl4(L)2] solutions in chloroform con-
[Os2( -O)( -O2CCH3)2(AsPh3)2Cl4] (II). The syn-
thesis was similar to that of complex I. The yield of
the dark brown complex was about 70%. IR spectrum,
cm : 472 s, 690 s, 740 s, 778 w, 860 wide, 1000 w,
1028 w, 1085 s, 1163 wide, 1187 wide, 1440 s,
1490 w, 1630 s, 3420 wide.
tain absorption bands with
= 456.0 nm (
=
=
max
1
10134 l mol 1 cm ) for compound I and
1
max
426.0 nm ( = 7362 l mol 1 cm ), and a shoulder at
533.0 nm for complex II (Fig. 1). It is seen from
Fig. 1 that the most intense band in the electronic
absorption spectrum of complex II, which can be
1
Found, %: Os 29.8, Cl 11.4.
C40H36As2Cl4O5Os2.
unbonding
*
assigned to the
transition within
the Os2( -O) [7], is shifted by 30 nm to higher en-
ergies. It is most likely that the shoulder in the low-
energy region of the spectrum is related to charge
*
Calculated, %: Os 30.0, Cl 11.2.
1
IV
An X-ray structural analysis of
a similar [Os ( -O)
2
transfer from the core to
The band related to the
-orbitals of AsPh3.
( -O CCCl ) Cl (PPh ) ] complex, obtained recently by
2
2 2
4
3 2
unbonding
*
transition
the authors, confirmed the bent structure of the Os ( -O) core
2
and the presence of two bridging carboxylate ions.
within the Os2( -O) core shifts to higher energies
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 12 2002

REACTIONS OF trans-[OsO2Cl2L2] (L = PPh3, AsPh3, SbPh3) WITH ACETIC ACID
1909
when osmium complexes react with HClO4 (Fig. 2).
The appearance of a shoulder with
580 nm
seems to be attributable to charge transfmearxfrom d
p
*
orbitals of the core to
orbitals of PPh3. This pro-
cess seems to be due to protonation of the bridging
oxygen atom in the metal-containing core:
[OsI2V( -O)( -O2CCH3)2Cl4(L)2] + H+
[OsI2V( -OH)( -O2CCH3)2Cl4(L)2]+.
It is necessary to note that protonation of bridging
oxygen atoms in similar binuclear ruthenium com-
plexes Ru2( -O)( -O2-CCH3)22+ is well known [9, 10].
The study demonstrated that the formation of com-
plexes I and II can be described by the scheme:
Fig. 1. Electronic absorption spectra of solutions of
(1) [Os ( -O)( -O CCH ) (PPh ) Cl ] and (2) [Os ( -O)
2
2
3 2
3 2
4
2
( -O CCH ) (AsPh ) Cl ] complexes in CHCl . ( ) ex-
2[OsO2Cl2L2] + 2RCO2H
[OsI2V( -O)( -O2CR)2Cl4L2] + 2O = L + H2O,
2
3 2
3 2
4
3
tinction coefficient related to 1 mol of a complex and
( ) wavelength.
where L = PPh3 or AsPh3.
The presence of triphenylphosphinoxide (POPh3)
or triphenylarsinoxide (AsOPh3) in the reaction prod-
ucts is indicated by the results of elemental analysis
and also by IR spectral data and melting points of
these compounds, which are in good agreement with
published data [11, 12].
Found for PO(C6H5)3, %: P 11.0, C 78.1, H 5.0.
Calculated for C18H15OP, %: P 11.1, C 77.7, H 5.43.
1
IR spectrum, cm : 420 w, 452 wide, 500 s, 542 s,
695 s, 722 vs, 759 s, 950 s, 998 w, 1030 s, 1077 s,
1123 s, 1195 ws ( P=O), 1440 s, 1490 s, 1590 s;
mp 156 C.
Fig. 2. Electronic absorption spectra of acetonitrile so-
lutions of (1) [Os ( -O)( -O CCH ) (PPh ) Cl ] and
2
2
3 2
3 2
4
Found for C18H15AsO, %: C 67.0, H 3.2.
Calculated for AsOC18H15, %: C 67.1, H 4.7.
+
(2) [Os ( -OP)( -O CCH ) (AsPh ) Cl ] complexes.
2
2
3 2
3 2
4
(D) optical density and ( ) wavelength.
1
IR spectrum, cm : 418 w, 461 s, 690 vs, 742 vs,
812 vs, 998 w, 1026 w, 1086 s (As=O), 1162 w,
1190 w, 1450 s, 1490 s; mp 184 C.
attributable to vibrations of acetate groups [8, 9, 11].
However, these bands are too broad and have too low
intensity to be used in determining the coordination
of the CH3CO2 ion.
Triphenyldichloroantimony and a poorly soluble
osmium-containing light brown compound are always
formed in the reaction of trans-[OsO2Cl2(SbPh3)2]
with acetic acid. The composition of the osmium-con-
taining product could not be determined; however,
according to the elemental analysis it contains 59.2%
Os and 16.4% C, and also trace amounts of chlorine.
The Os : C ratio of about 1 : 4.4 shows that this prod-
uct contains acetate ions CH3CO2. This is also indirect-
ly confirmed by IR spectral data. Characteristic bands
The formation of SbCl2Ph3 is confirmed by the el-
emental and X-ray analyses2 (Fig. 3).
Crystallographic data for SbCl2Ph3: the complex
is crystallized from ether as colorless needles char-
acterized by the orthorhombic space group Pbca,
a = 13.122(2)
,
= 90 , b = 23.885(3)
,
= 90 ,
2
The X-ray structure analysis was carried out at the Karpov
Physicochemical Institute (Moscow).
1
present in the frequency range 1400 1700 cm are
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 12 2002

1910
BELYAEV et al.
(2) In glacial acetic acid, trans-[OsO2Cl2(SbPh3)2]
undergoes an intramolecular redox conversion to
SbCl2Ph3.
(3) It is suggested that the increase in the size of
ligands L in the order SbPh3 > AsPh3 > PPh3 is one
of the main reasons for the decrease in the stability
of oxygen-bridged osmium acetates [OsI2V( -O)
( -O2CCH3)2Cl4(L)2] in acetic acid medium.
ACKNOWLEDGMENTS
The study was supported financially by the Rus-
sian Foundation for Basic Research (grant nos. 00-03-
32659 and 01-03-06119) and by the program of
the Ministry of Education of the Russian Federation
Research in Higher School in the Field of Chemistry
and Chemical Products (Section 003).
Fig. 3. Structure of SbCl Ph .
2
3
REFERENCES
c = 43.823(8)
R = 0.0353.
,
= 90 , V = 13735(4) 3, z = 16,
1. Maslenitskii, I.N., Chugaev, L.V., Borbat, V.F., et al.,
Metallurgiya blagorodnykh metallov (Metallurgy of
Noble Metals), Moscow: Metallurgiya, 1987.
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Found for SbCl2(C6H5)3, %: Cl 16.5, C 51.0, H 3.3.
Calculated for C18H15Cl2Sb, %: Cl 16.72, C 50.99, H 3.57.
1
IR spectrum, cm : 450 vs, 681 s, 727 s, 993 wide,
1018 w, 1055 w, 1430 s, 1480 s.
Since the starting trans-[OsO2Cl2(SbPh3)2] com-
plex is isolated from the reaction mixture containing
hydrochloric acid, it is unlikely that its reaction with
acetic acid may lead to an intramolecular redox reac-
tion yielding SbCl2Ph3. Presumably, the first stage of
the reaction between trans-[OsO2Cl2(SbPh3)2] and ace-
tic acid results in an unstable binuclear osmium acetate
[OsI2V( -O)( -O2CCH3)2Cl4(SbPh3)2], which further
decomposes to give SbCl2Ph3 and an osmium-contain-
ing compound, possibly of polymer composition.
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Abstracts of Papers, XIV Vsesoyuznoe Chernyaevskoe
soveshchanie po khimii, analizu i tekhnologii platino-
vykh metallov (XIV All-Union Chernyaev Symp. on
Chemistry, Analysis, and Technology of Platinum
Metals), Novosibirsk, 1990, vol. 2, p. 76.
In conclusion, it should be noted that the ionization
energies I (eV) of ligands L increase in the order
7.85 (PPh3) < 8.03 (AsPh3) < 8.08 (SbPh3). However,
small differences between these energies suggest that
the ligands have similar donor acceptor properties.
Therefore, it is most probable that the instability of
the [OsI2V( -O)( -O2CCH3)2Cl4(SbPh3)2] complex is
caused by steric effects: SbPh3 is larger in size than
PPh3 or AsPh3.
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CONCLUSIONS
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(1) Binuclear oxygen-bridged osmium acetates
[OsI2V( -O)( -O2CCH3)2Cl4(L)2] (L = PPh3 or AsPh3)
can be formed in high yield (95 to 70%) in the reac-
tion of trans-[OsO2Cl2L2] complexes with glacial
acetic acid.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 75 No. 12 2002