In situ formation of ligand 2,2′-[(E)-diazene-1,2- diyldicarbonothioyl]diphenol and structural characterization of its binuclear rhodium(v) complex containing RhO2+

Article abstract of DOI:10.1039/c0cc01970d

The ligand 2,2′-[(E)-diazene-1,2-diyldicarbonothioyl]diphenol has been synthesised in situ by aerial oxidation of o-hydroxythiobenzhydrazide [H(htbh)] in presence of rhodium(iii) in DMSO. Each ligand binds two RhO ₂⁺ ions through its

Full text of DOI:10.1039/c0cc01970d

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In situ formation of ligand 2,20-[(E)-diazene-1,2-diyldicarbonothioyl]diphenol
and structural characterization of its binuclear rhodium(V) complex
+
containing RhO2 w
Snigdha Gangopadhyay,*a Prodyut Basak,a Michael Drewb and Pijush Kanti Gangopadhyaya
Received 19th June 2010, Accepted 10th August 2010
DOI: 10.1039/c0cc01970d
The ligand 2,20-[(E)-diazene-1,2-diyldicarbonothioyl]diphenol
has been synthesised in situ by aerial oxidation of o-hydroxy-
thiobenzhydrazide [H(htbh)] in presence of rhodium(III) in
needle-shaped crystals were collected by filtration, washed
with a 1 : 10 DMSO–water mixture and dried under vacuum.
The crystalline compound was found to have the formula
C18H20N2O8Rh2S4 (33 mg, 60% on the basis of rhodium).
Elemental analysis (Found: C, 29.82; H, 2.90; N, 4.02; S,
17.85%. Calc. for C18H20N2O8Rh2S4: C,29.92; H, 2.89; N,
4.08; S, 17.94%).
+
DMSO. Each ligand binds two RhO2 ions through its N and
S atoms and the O atom of its deprotonated hydroxy group.
+
Each RhO2
contains two cis-RhQO bonds. The sixth
coordination site of each rhodium(V) is occupied by the O
of DMSO.
The compound is insoluble in water and most organic
solvents except DMSO and DMF. However, the solubility
of the compound at 25 1C in those two solvents is not high
enough to prepare even a 10ꢀ4 M solution. The low solubility
of the complex did not permit us to undertake the study on the
properties of the compound in solution.
ꢀ
The compounds of rhodium(V) are limited to RhF5, RhF6
and a few less thoroughly characterized oxycations and
oxyanions. A single-crystal X-ray structure shows that RhF5
has a tetrameric structure.1 Various oxycations and oxyanions
of rhodium(V) have been reported to result from the oxidation
of rhodium(III) salts by hypochlorite, hypobromite or
The reaction scheme for the oxidation of H(htbh) by oxygen
from air in the presence of rhodium(III) chloride in DMSO as a
catalyst is shown in Fig. 1. Rhodium(III) chloride in DMSO
bismuthate.1 At pH 2 the hypochlorite oxidation product is
]
(3ꢀn) and its ability to act
+
.
may be regarded as [RhCln(DMSO)6ꢀn
a cationic purple species tentatively identified as RhO2
The oxyanion of rhodium(V), first prepared by Berzelius1 as
a result of the chemical oxidation of rhodium(III) salts,
disproportionates according to the equation
as a catalyst precursor for the oxidation of organic compounds
is not a rare phenomenon. It can catalyze the oxidation of
thioethers to sulfoxides,3 sulfoxides to sulfones4 and the
dehydrogenation of triethylamine.5 The mechanism of activation
of dioxygen by rhodium(III) chloride in DMSO solution
is not yet understood. Isolation and characterization of
[(RhO2)2(C6H4(O)–C(QS)–NQN–C(QS)(O)C6H4)(DMSO)2]
3[RhO3(OH)] 2ꢀ + 2H+ - 2[RhO4] 2ꢀ + Rh(OH)3 + H2O.
+
No stable complex of rhodium(V) containing the RhO2
cation has been reported so far.
In a recent communication2 we reported the synthesis and
may provide an insight into the mechanism of such reactions.
(3ꢀn)
It may be assumed that [RhCln(DMSO)6ꢀn
aerial oxygen to form [RhO2Cln(DMSO)4ꢀn
]
absorbed
(1ꢀn)
as an
structure of
a neutral tris(o-hydroxythiobenzhydrazido)-
]
cobalt(III)ꢁ3DMSO complex where the ligands bind to cobalt(III)
through their N and S atoms as donor sites leaving the –OH
group to form intra and inter molecular H-bonds.
unstable intermediate, which oxidized H(htbh) in situ to the
new ligand 2,20-[(E)-diazene-1,2-diyldicarbonodithioyl]diphenol.
(1ꢀn)
Although the species [RhO2Cln(DMSO)4ꢀn
]
could not
In an attempt to prepare an analogous rhodium(III) complex
from DMSO a new stable complex of rhodium(V) containing
be isolated, the following indirect evidence may support the
proposed mechanism.
+
RhO2 of an entirely new ligand 2,20-[(E)-diazene-1,2-diyldi-
On keeping H(htbh) in DMSO for two weeks the new ligand
2,20-[(E)-diazene-1,2-diyldicarbonodithioyl]diphenol was not
generated. H(htbh) has been characterized by a combination
of spectroscopic methods2 and by X-ray crystallographyz in
order to ascertain that nothing other than the compound was
added to rhodium(III)chloride in DMSO solution. Moreover,
carbonothioyl]diphenol has been obtained.
A proposed
mechanism of the in situ formation of the ligand from
o-hydroxythiobenzhydrazide and the crystal structure of the
rhodium(V) complex are reported here.
To synthesize the complex RhCl3ꢁ3H2O (40 mg) was dissolved
in 10 ml freshly distilled DMSO and to it o-hydroxythio-
benzhydrazide [H(htbh)] (115 mg) was added. The solution
was kept at room temperature for about a week. Dark
a Department of Chemistry, Presidency College, Kolkata 700 073,
India. E-mail: snigdhagangopadhyay@yahoo.com;
Tel: +91-3322413893
b Department of Chemistry, University of Reading Berkshire,
RG6 6AH, United Kingdom. E-mail: m.g.b.drew@reading.ac.uk;
Fax: +44 (0)118 378 8454; Tel: +44 (0)118 378 8454
w CCDC 766983–766984. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/c0cc01970d
Fig.
1
Reaction scheme depicting oxidation of o-hydroxythio-
benzhydrazide to 2,20-[(E)-diazene-1,2-diyldicarbonodithioyl]diphenol.
c
7436 Chem. Commun., 2010, 46, 7436–7438
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an attempt to prepare the rhodium(V) complex using the
described method in a nitrogen atmosphere failed while
bubbling oxygen through rhodium(III)chloride in DMSO in
the presence of H(htbh) produced the complex in two days in
powder form (agitation inhibited crystal growth). In addition,
tris(o-hydroxythiobenzhydrazido)rhodium(III) could be prepared
by the reaction between an aqueous solution of rhodium(III)
chloride and H(htbh) at pH 6.5–7.0; the compound is soluble
in most organic solvents.
The newly formed ligand 2,20-[(E)-diazene-1,2-diyldicarbono-
dithioyl]diphenol has two N, S, and O donor sites. All chloride
ions and (3 ꢀ n)DMSO molecules from one molecule of the
compound [RhO2Cln(DMSO)4ꢀn
]
(1ꢀn) were substituted by N, S,
O atoms from each donor site leading to the formation of a
binuclear rhodium(V) complex. The oxygen atom of one DMSO
molecule still remained coordinated to each rhodium(V) creating
an octahedral environment.
That the newly synthesized rhodium(V) complex is a
4
low-spin t2g system is evident from its magnetic moment
Fig. 2 ORTEP views (30% probability thermal ellipsoids) of the
molecular structure of the complex (C18H20N2O8Rh2S4) together with
the atomic numbering scheme. Selected bond lengths (A):
Rh(1)–S(18)$1 = 2.340(3), Rh(1)–N(19) = 2.261(5), Rh(1)–O(11) =
value (magnetic susceptibility was measured with
a
MAGWAY MFG Mk 1, Sherwood Scientific Ltd, UK) of
2.80 BM per rhodium at 300 K. From the magnetic moment
value it may be concluded that there is no significant Rh–Rh
interaction in the complex. In view of the large distance
between two rhodium centers (6.310 A) no such interaction
is expected. The infrared (IR) spectrum of the complex (KBr
disk, using a Unicam SP3-300S) shows a sharp band at
855 cmꢀ1 and the IR spectrum of H(htbh) showed a band at
840 cmꢀ1 which is absent in that of the complex. The sharpness
and high intensity of the band at 855 cmꢀ1 suggests it is due to
the RhQO stretching frequency.
1.953(4), Rh(1)–O(31)
=
2.305(5), Rh(1)–O(1)
=
1.700(5),
Rh(1)–O(2) = 1.712(5), C(18)–S(18) = 1.661(7), C(18)–N(19) =
1.323(9), C(12)–O(11) = 1.365(7), N(19)–N(19)$1 = 1.393(10).
effect of the terminal oxygen atoms O(1) and O(2) in the
coordination sphere. Thus the four atoms in the equatorial
plane, O(2), O(11), N(19) and S(18)$1 show a r.m.s. deviation
of 0.349 A with the metal 0.083 A from the plane in the
direction of O(1).
The structure of C18H20N2Rh2O8S4 was solved using X-ray
crystallographyy and direct methods using the SHELXS97.6 The
non-hydrogen atoms were refined with anisotropic thermal
parameters. The hydrogen atoms bonded to carbon and
nitrogen were included in geometric positions and given
thermal parameters equivalent to 1.2 times those of the atom
to which they were attached. An absorption correction was
carried out using the ABSPACK program.6 The structure was
The C–S, C–N and N–N bond lengths in H(htbh) are
1.6853(15) A, 1.3289(19) and 1.4187(18) Az respectively
compared to 1.661(7), 1.323(9) and 1.393(10) A in the complex.
Both sets of distances are intermediate between formal single-
bond and double-bond lengths and they indicate extensive
electron delocalization.
The NQN covalent bond distance in azenes is 1.252(1) A.7
In the complex it changes to 1.393(2) A indicating extensive
delocalization of double bond on complex formation.
Comparison of the bond lengths in the coordinated ligand
with those in the H(htbh) shows that both the C–S and C–N
bonds suffer contraction. These changes in bond length are
attributable to stabilization of the ligand. The phenolic C–O
length increases a little, signifying the removal of phenolic
hydrogen upon coordination.
6
refined on F2 using SHELXL97 to R1 0.0659, wR2 0.1844 for
2777 reflections with I 4 2s(I).
The structure of the binuclear rhodium(V) complex together
with the atomic numbering scheme is given in Fig. 2.
The structure of the binuclear complex has a crystallo-
graphic centre of symmetry with formula
[(RhO2)2(C6H4(O)–C(QS)– NQN–C(QS)(O)C6H4)(DMSO)2].
The Rh(1)–O(1) and Rh(1)–O(2), metal-to-terminal-oxygen
bond lengths are 1.700(5), 1.712(5) A respectively. These bond
lengths are shorter than that [1.953(4) A] of Rh(1)–O(11) by
more than 0.2 A. The fact signifies the double-bond character
of Rh(1)–O(1) and Rh(1)–O(2) bonds. The most significant
feature in the structure of the complex is the involvement of
the methyl hydrogen of C(33)$1–H in H-bonding with O(1). It
explains the small difference between Rh(1)–O(1) and
Rh(1)–O(2) bond lengths.
Each rhodium(V) ion is six-coordinate with a distorted
octahedral environment, being bonded to two mutually cis
terminal oxygens, nitrogen, sulphur and oxygen from ligand
2,20-[(E)-diazene-1,2-diyldicarbonodithioyl]diphenol together
with one oxygen atom of a DMSO molecule. The ligand thus
has two tridentate donor sites, each site coordinating in a mer
configuration to a RhO2+, forming six and five-membered
rings respectively with bite angles of 81.9(2)1 for
O(11)–Rh(1)–N(19) and 78.6(2)1 for N(19)–Rh(1)-S(18)$1,
$1 = symmetry element 2 ꢀ x, 2 ꢀ y, 1 ꢀ z. The ligand is
significantly distorted from planarity, no doubt because of the
We thank the EPSRC (U.K.) and the University of Reading
for funds for the diffractometer. Financial assistance received
from the Higher Education Department, Government of West
Bengal is gratefully acknowledged.
c
This journal is The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 7436–7438 7437

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References
z The compound H(htbh) (C14H20N4O4S2) crystallizes in the mono-
clinic, space group P21/n with a = 9.2078(4) A, b = 7.9309(4) A,
c = 11.4536(4) A, a = 90.001, b = 91.796(4)1, g = 90.001, V =
836.00(6) A3, M = 372.46, Z = 2, Dc = 1.480 g cmꢀ3. A Oxford
Diffraction X-Calibur CCD system with graphite monochromatized
Mo Ka radiation (l = 0.71073 A) was used to collect 5426 reflections
(2337 unique) in the range 2.88 o y o 29.99 at 150(2) K giving a final
residual value of R1 = 0.0522 (all data) and wR2
=
0.0939
([I 4 2s(I)]). Full diffraction data collection, refinement, and structural
details are given in the ESI.w
6 (a) CrysAlis, Oxford Diffraction Ltd, Abingdon, UK, 2006;
(b) G. M. Sheldrick, SHELXL-97, Program for refinement of crystal
structures, University of Gottingen, Germany, 1997G. M. Sheldrick,
¨
SHELXS-97, Program for solution of crystal structures, University
y The compound C18H20N2Rh2O8S4 crystallizes in the triclinic space
group P1 with M = 726.42, Z = 1, a = 7.2911(6), b = 8.9330(8),
ꢀ
c = 10.6189(9) A, a = 68.437(8)1, b = 87.346(7)1, g = 71.086(8)1,
V = 606.40 A3, Dc = 1.752 g cmꢀ3. 4289 independent reflections were
collected with Mo Ka (l = 0.71073 A) radiation at 150(2) K using the
Oxford Diffraction X-Calibur CCD system. The crystal was positioned at
50 mm from the CCD. 321 frames were measured with a counting time of
10 s. Data analysis was carried out using the CrysAlis program.6
of Gottingen, Germany, 1997; (c) ABSPACK, Oxford Diffraction
¨
Ltd, Oxford UK, 2005.
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¨
413–414, 447–456; (b) S. Dutta, S.-M. Peng and S. Bhattacharya,
J. Chem. Soc., Dalton Trans., 2000, 4623–4627.
c
7438 Chem. Commun., 2010, 46, 7436–7438
This journal is The Royal Society of Chemistry 2010