Binuclear rhodium(III) and iridium(III) monoselenocarboxylates: Synthesis, spectroscopy and structure of an ortho-metallated iridium complex featuring an IrCCC(μ-Se) chelate ring

Article abstract of DOI:10.1016/j.inoche.2010.01.012

Monoselenocarboxylate-bridged binuclear complexes of Rh^III and Ir^III, [(Cp*MCl)₂(μ-SeCOAr)₂] (1) (M = Rh or Ir; Cp* = pentamethylcyclopentadienyl; Ar = Ph, C₆H₄Me-4), have been isolated eit

Full text of DOI:10.1016/j.inoche.2010.01.012

Inorganic Chemistry Communications 13 (2010) 475–478
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Inorganic Chemistry Communications
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Binuclear rhodium(III) and iridium(III) monoselenocarboxylates: Synthesis,
spectroscopy and structure of an ortho-metallated iridium complex featuring
an IrCCC(l-Se) chelate ring
b
b
Liladhar B. Kumbhare a, Amey P. Wadawale a, Vimal K. Jain a, , Monika Sieger , Wolfgang Kaim
*
a Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India
b Institut für Anorganische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569, Stuttgart, Germany
a r t i c l e i n f o
a b s t r a c t
Monoselenocarboxylate–bridged binuclear complexes of RhIII and IrIII
, [(Cp*MCl)2(l-SeCOAr)2] (1)
Article history:
Received 11 December 2009
Accepted 15 January 2010
Available online 22 January 2010
(M = Rh or Ir; Cp* = pentamethylcyclopentadienyl; Ar = Ph, C6H4Me–4), have been isolated either by the
reaction between [Cp*2M2( -Cl)2Cl2] with KSeCOAr in acetonitrile or by treatment of [Cp*MCl(sol-
vent)2][PF6] with KSeCOAr in acetone. The novel binuclear complexes, [Cp*IrCl(
-SeCOAr)(j2
SeCOC6H3R–)IrCp*] (2) (R = H or Me-4) with ortho-metallation at one of the iridium centres have been
isolated following the use of excess AgPF6. The single crystal structure of [Cp*IrCl(
-SeCOC6H5)(j2
l
l
-
Keywords:
Crystal structure
Rhodium
Iridium
Ortho-metallation
NMR
l
-
SeCOC6H4–)IrCp*] (2a) exhibits two phenylcarboselenolate moieties situated in syn fashion with respect
to the ‘‘Ir2Se2” plane, one of which leans towards the metal centre in order to undergo ortho-metallation
after iridium–chlorine bond dissociation.
Ó 2010 Elsevier B.V. All rights reserved.
The organometallic chemistry of group-8 metal complexes with
chalcogen ligands has been progressing rapidly owing to their
intriguing reactivities [1–4] and relevance in catalytic hydrodesul-
furization reactions [5,6]. The chemistry of these complexes has
been dominated by derivatives containing thiolato [7], hydrosulfido
[1,8,9] or sulfido [10] ligands. These ligands invariably yield bi–,
tri–, and tetra–nuclear complexes, whereas 1,1–dithiolates ðRCSꢀ2 ;
ROCSꢀ; R2NCSꢀ; ðROÞ PSꢀÞ give mononuclear compounds [11–13].
contaminated with the starting material, the chloro-bridged dimer,
[Cp*2Ir2( -Cl)2Cl2] which could be separated by recrystallization.
Reaction between [Cp*MCl(solvent)2][PF6] (prepared by treatment
of [Cp*2M2( -Cl)2Cl2] with AgPF6 in 1:2 ratio in acetone) and
KSeCOAr yielded 1 [20]. However, when the AgPF6 amount was in-
creased another binuclear complex was formed. Accordingly, the
l
l
reaction between [Cp*2Ir2(
acetone followed by treatment with KSeCOAr yielded [Cp*IrCl
-SeCOAr)( 2-SeCOC6H3R–)IrCp*] (2) (R = H (2a), Me-4 (2b))
l-Cl)2Cl2] with AgPF6 in 1:3 ratio in
2
2
2
2
Recently, we have investigated metal complexes containing
selenocarboxylate ligands [14–16]. The facile cleavage of the C–Se
bond has led us to develop a convenient synthetic route to sele-
(l
j
[21] (Scheme 1).
IR spectra of 1 and 2 displayed absorptions at ꢁ1650 cmꢀ1, indi-
cating the presence of uncoordinated carbonyl. The high energy
bands of the electronic absorption spectra can be attributed
nide-bridged complexes, [M3(l
-Se)2(PP)3]2+ (M = Pd or Pt) in high
yields and metal selenide (MSe; M = Zn, Cd or Hg) nanoparticles.
However, there is hardly any report dealing with classical or orga-
nometallic complexes of rhodium and iridium with chalcogeno-
carboxylic acids [17]. In view of the above it was considered of
interest to study selenocarboxylate complexes containing Cp*MIII
unit (Cp* = pentamethylcyclopentadienyl).
Treatment of [Cp*2M2(l-Cl)2Cl2] with two equivalents of KSeC-
OAr (prepared according to methods reported [18,19]) afforded
selenocarboxylate-bridged binuclear complexes, [(Cp*MCl)2
to
p?p* transitions whereas the low energy bands (>400 nm for
RhIII complexes) may be assigned to metal-mediated LLCT transi-
tions. The 1H NMR spectra of 1 exhibited the expected resonances
and peak multiplicities. The 1H NMR spectra of 2 showed two clo-
sely spaced Cp* methyl signals due to two different Cp*IrIII moie-
ties. In the 13C{1H} NMR spectra of 1 the resonances due to the
ring carbons of the Cp* are significantly downfield shifted with ref-
erence to the corresponding signals for the chloro-bridged deriva-
(l-SeCOAr)2] (1) (M/Ar = Rh/Ph (1a), Rh/Tol (1b), Ir/Ph (1c) and
tives, [Cp*2M2(l
-Cl)2Cl2]. The 77Se{1H} NMR spectra of 1a and 1b
Ir/Tol (1d), Tol = C6H4Me-4). The iridium complexes were often
showed a triplet (Fig. 1), owing to the coupling with two 103Rh
nuclei which substantiates the presence of bridged selenium in
the complex. The magnitude of 1J(103Rh–77Se) (ꢁ35 Hz) can be
compared with rhodium(III) selenoether complexes (30–52 Hz)
[22–24]. The 77Se NMR resonances are considerably more shielded
* Corresponding author. Tel.: +91 22 2559 5095; fax: +91 22 2550 5151.
E-mail addresses: jainvk@barc.gov.in (V.K. Jain), kaim@iac.uni-stuttgart.de
(W. Kaim).
1387-7003/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.01.012

476
L.B. Kumbhare et al. / Inorganic Chemistry Communications 13 (2010) 475–478
O
Ar
C
Cl
Se
*
M
[Cp2M2(
µ
Cl)2Cl2] + 2 KSeC(O)Ar
M
2 KCl
Se
Cl
C
Ar
O
(1)
i) 2 AgPF6
Ar
ii) 2 KSeCOAr
M
1a
Ph
tol
Ph
Rh
Rh
Ir
1b
1c
1d
Ir tol
3 AgPF6
*
*
µ
[Cp2Ir2Cl(solvent)3](PF6)3
[Cp2Ir2( Cl)2Cl2]
3 AgCl
2 KSeCOAr
O
RH4C6
C
O
R
C
Ir
Se
Se
(2)
Ir
+ 2 KPF6 + HPF6
Cl
R = H (2a); Me (2b)
Scheme 1.
ppm
100
50
0
150
Fig. 1. 77Se{1H} NMR spectrum of [(Cp*RhCl)2(( -SeCOC6H5)2] (1a) in CDCl3, Inset showing triplet with 1J(103Rh–77Se) = 33 Hz.
l
than the signals observed for KSeCOAr and for [M(SeCOAr)2(tme-
da)] (M = Zn, Cd) [16] where the selenolate ligand is monodentate.
An ORTEP drawing with atomic numbering scheme for the crys-
the two bridging Se atoms and to the deprotonated ortho-carbon
atom of a phenyl ring of one SeCOPh ligand. The Ar’CO (Ar0 = C6H4–
and Ph) groups on selenium are mutually syn and adopt an exocy-
clic configuration. Each iridium atom acquires a distorted octahe-
dral configuration with the pentamethylcyclopentadienyl ring at
one face. The Cp* rings are mutually trans.
tallographically
analyzed
[Cp*IrCl(l-SeCOPh)(j
2-SeCOC6H4–)
IrCp*] (2a) [25] is shown in Fig. 2. The molecule consists of two
Cp*IrIII fragments, held together by two bridging selenocarboxylate
groups. One of the Cp*Ir fragment is coordinated to two Se atoms
and a chloride ligand while the other Cp*Ir moiety is bonded to
The cyclometallation-formed five-membered chelate ring
involving the Ir2Se1C28C29C34 atoms is planar and nearly per-

L.B. Kumbhare et al. / Inorganic Chemistry Communications 13 (2010) 475–478
477
Fig. 2. ORTEP (50% probability thermal ellipsoids) diagram of [Cp*IrCl(l-SeCOC6H5)(j
2-SeCOC6H4–)IrCp*] (2a). Selected bond lengths (Å) and bond angles(°): Ir1–Se1 and
Ir2–Se2 2.512(2), Ir1–Se2 2.495(1), Ir2–Se1 2.445(2), Ir2–C34 2.076 (11), Ir1–Cl1 2.408(3), Se1–C28 1.951(14), Se2–C21 1.992(12), Ir1–C15 2.181(12), Ir2–C3 2.261(13),
zIr2–Se2–Ir1 98.16(6), Ir2–Se1–Ir1 90.50(6), Se1–Ir2–Se2 81.30(6), Se1–Ir1–Se2 80.33(6), Ir1–Se2–C21 108.5(4), Ir2–Se1–C28 97.6(5), Ir1–Se1–C28 101.7(4), Ir2–Se2–C21
103.1(4), Se1–Ir1–Cl1 85.19(11), Se2–Ir1–Cl1 80.27(9), Se1–Ir2–C34 84.3(4), Se2–Ir2–C34 91.2(3).
pendicular (86.37°) to the plane formed by the Ir2Se1Se2 atoms.
The planarity is supported by the presence of three sp2 carbon cen-
tres. The four-membered ‘‘Ir2Se2” ring is not quite planar (hinge
angle 171.7°) with alternating long and short Ir–Se distances. The
Ir–Se distances can be compared with the values reported in
uncoordinated carbonyl function), and by one bridging selenola-
to–Se.
Acknowledgements
[Cp*Ir(l-Se4)]2 (2.42–2.50 Å) [26] and [Cp*Ir(Se4)(PMe3)]
(2.468(2)–2.472 (2) Å) [27]. The Ir–Ir separation of 3.784 Å
Authors thank Drs. T. Mukherjee and D. Das for encouragement
of this work.
indicates the absence of any bonding interactions between them;
Ir–Ir single bond distances vary between 2.65 and 3.1 Å. The g5
–
Appendix A. Supplementary material
Cp*–to–Ir bond distances lie in the range between 2.160(12) and
2.261(13) Å with an average value of 2.19 Å. The Ir2–C34 distance
involving the metallated carbon atom (a carbanion) is much smal-
ler at 2.076(11) Å. The Ir–Cl bond length of 2.408(3) Å is well with-
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.inoche.2010.01.012.
in the range reported for IrIII complexes, e.g. [Cp*Ir(
l-SH)Cl]2
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l
-SeCOPh)2Cl2] (1a): Method A, To an acetonitrile
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l
-Cl)2Cl2] (104 mg, 0.17 mmol), solution
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collected on a Rigaku AFC7S diffractometer fitted with Mo K
l-SeCOC6H5)(j
2-SeCOC6H4–)IrCp*] (2a) were
a
(0.71069 Å)
radiation so that hmax = 27.51°. The structures were solved by direct methods
[33] and refinement was on F2 [34] using data which were corrected for
absorption correction effects employing an empirical procedure. The non-
hydrogen atoms were refined with anisotropic displacement parameters and
fitted with hydrogen atoms in their calculated positions. Molecular structures
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details are given in supplementary material. Crystal data and structure
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complexes as mentioned above.
described as follows. To an acetone solution of [Cp*2Rh2(
A
representative procedure has been
-Cl)2Cl2] (110 mg,
l
0.17 mmol), solid AgPF6 (90 mg, 0.36 mmol) was added and mixture was
stirred for 1 h under argon in the dark room. The solution was filtered through
Celite to get rid of AgCl. To the filtrate a methanolic solution of KSeCOPh
(70 mg, 0.31) was added and reaction mixture was stirred for 2 h. Solvents
were stripped off from reaction mixture and contents were extracted with
dichloromethane. The filtrate was concentrated under reduced pressure and to
this few drops of hexane were added to get an oily product which on drying
size 0.3 ꢂ 0.25 ꢂ 0.20 mm, monoclinic, space group P21/n,
20.110, c 12.954 Å, b 105.56(5)°, V 3370 Å3, Z 4, 9.876 mmꢀ1, F(0 0 0) 1992, h
2.55–27.51°, R1[I > 2 (I)] 0.0617, wR2 0.1043, R1 0.1513, wR2 0.1731.
a 13.430(6), b
l
r
gave the title complex. [Cp*2Rh2(
l
-SeCOC6H4Me-4)2Cl2] (1b): Anal. Calc. for
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8.19 (d, 7.8 Hz) [–C6H4–]. 13C{1H} NMR (CDCl3): 9.7 (Me(Cp*)); 21.9 (Me) 98.2
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-SeCOC6H4Me-4)2Cl2] (1d): Anal. Calc. for C36H44Cl2O2Ir2Se2: C, 38.5;
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6.6 Hz), 8.00 (t, 8.1 Hz) [–C6H4–]. 13C{1H} NMR (CDCl3): 9.2 (Me(Cp*)); 21.8
(Me); 100.0 (Cp*); 129.2, 130.2, 144.5 (C6H4); 171.5 (CO).
[21] Preparation of [Cp*IrCl(
l-SeCOC6H5)(
j
2-SeCOC6H4–)IrCp*] (2a): Solid AgPF6
(70 mg, 0.32 mmol) was added to an acetone solution of [Cp*2Ir2(
l-Cl)2Cl2]
(90 mg, 0.11 mmol) and the reaction mixture was stirred for 1 h under argon
in dark. Solution was filtered through Celite. A methanolic solution of KSeCOPh
(60 mg, 0.27 mmol) was added to the above filtrate and reaction mixture was
stirred for additional 2 h. The solvents were evaporated under vacuum and the
residue was extracted with dichloromethane. The filtrate was concentrated
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Oak Ridge TN, 1976.