Palladium nitrosyl carboxylate complexes X-ray structures of Pd 4(μ-NO)2(μ-OCOCMe3)6

Article abstract of DOI:10.1016/S0020-1693(02)01575-X

Two types of palladium nitrosyl carboxylate complexes were synthesized and their structures were characterized by several methods including an X-ray diffraction analysis. The tetranuclear complexes Pd₄(μ-NO) ₂(OCOR)₆ (R=CMe₃, Me, Ph, CHMe₂, CH₂Cl, IIa-e, respectively) were synthesized by the reaction of Pd(NO)Cl with silver carboxylates Ag(OCOR). The structure of IIa was determined by a single crystal X-ray diffractometry. Crystals of IIa are monoclinic, space group P2₁/n, a=12.104(7), b=23.970(8), c=15.495(4) A?, β=90.30(4)°, V=4496(4) A?³. The least-square structure refinement on F² was converged to R=0.0714 for 6228 reflections [I>2σ(I)]. In IIa the palladium atoms form near regular rectangle Pd₄, with the edges bridged by the ligands. Two bridging NO groups occupying the opposite sides of the rectangle are in the cis-positions with respect to the Pd₄ plane. These groups are symmetric, with the Pd-N-O angles ranging from 120.4(5) to 121.8(5)°. The coordination polyhedrons of the Pd atoms are close to square planar ones. The reaction of the Pd₄(CO)₄(OCOCF₃)₄ clusters with nitrogen monoxide leads to a substitution of the carbonyl groups and formation of the low stable complex Pd₄(NO)₄(OCOCF₃) ₄ (III) that was characterized by the spectroscopic and analytical data. The transformation of III during slow recrystallization from toluene gives Pd₃(NO)₂(OCOCF₃) ₄·2C₆H₅Me (IV) and palladium black. The structure of IV was determined by an X-ray diffraction analysis. Crystals of IV are monoclinic, space group P2₁/n, a=9.2340(2), b=9.2859(2), c=18.0460(4) A?, β=92.339(1)°, V=1546.08(6) A?³. The least-square refinement on F² was converged to R=0.0205 for 3209 reflections [I>2σ(I)]. In the linear tri-nuclear molecule of IV, any adjacent metal atoms are linked with a couple of the CF₃CO ₂ ligands and are separated by 3.0755(2) A?. Additionally, the terminal Pd atoms bear the NO and the η²-toluene ligands. The configuration of the N atoms corresponds to the ideal sp²- hybridization. The Pd-N-O angle is 117.2(2)°. The N atoms form short contacts with the aromatic rings. The distance between the center of the ring and the nitrogen atom is 2.70 A?. Complex IV is the first example of the Pd complex with the terminal nitrosyl ligand. The scheme of transformation of complex III to complex IV was proposed.

Full text of DOI:10.1016/S0020-1693(02)01575-X

Inorganica Chimica Acta 350 (2003) 283ꢁ288
/
www.elsevier.com/locate/ica
Palladium nitrosyl carboxylate complexes X-ray structures of Pd4(m-
NO)2(m-OCOCMe3)6 and Pd3(NO)2(m-OCOCF3)4×2C6H5Me
/
Tatiana A. Stromnova a,*, Denis V. Paschenko a, Lyubov’ I. Boganova a,
Mikhail V. Daineko a, Sergei B. Katser a, Andrei V. Churakov a,
Lyudmila G. Kuz’mina a, Judith A.K. Howard b
a Institute of General and Inorganic Chemistry, Russian Academy of Science, 31, Leninsky Pr. GSP-1, 119991 Moscow, Russia
b Department of Chemistry, University of Durham, South Road, Durham DH1 3LE, UK
Received 26 June 2002; accepted 24 October 2002
This paper is dedicated to Professor Pierre Braunstein in honor of his celebrated career
Abstract
Two types of palladium nitrosyl carboxylate complexes were synthesized and their structures were characterized by several
methods including an X-ray diffraction analysis. The tetranuclear complexes Pd4(m-NO)2(OCOR)6 (RꢀCMe3, Me, Ph, CHMe2,
CH2Cl, IIaꢁe, respectively) were synthesized by the reaction of Pd(NO)Cl with silver carboxylates Ag(OCOR). The structure of IIa
was determined by a single crystal X-ray diffractometry. Crystals of IIa are monoclinic, space group P21/n, aꢀ12.104(7), bꢀ
4496(4) A . The least-square structure refinement on F was converged to Rꢀ0.0714
2s(I)]. In IIa the palladium atoms form near regular rectangle Pd4, with the edges bridged by the ligands.
Two bridging NO groups occupying the opposite sides of the rectangle are in the cis-positions with respect to the Pd4 plane. These
O angles ranging from 120.4(5) to 121.8(5)8. The coordination polyhedrons of the Pd atoms
/
/
/
/
3
2
˚
˚
23.970(8), cꢀ
/
15.495(4) A, bꢀ
/
90.30(4)8, Vꢀ
/
/
for 6228 reflections [I ꢀ
/
groups are symmetric, with the Pdꢀ
/
Nꢀ
/
are close to square planar ones. The reaction of the Pd4(CO)4(OCOCF3)4 clusters with nitrogen monoxide leads to a substitution of
the carbonyl groups and formation of the low stable complex Pd4(NO)4(OCOCF3)4 (III) that was characterized by the spectroscopic
and analytical data. The transformation of III during slow recrystallization from toluene gives Pd3(NO)2(OCOCF3)4×
/
2C6H5Me (IV)
and palladium black. The structure of IV was determined by an X-ray diffraction analysis. Crystals of IV are monoclinic, space
3
2
˚
˚
1546.08(6) A . The least-square refinement on F
group P21/n, aꢀ
was converged to Rꢀ
linked with a couple of the CF3CO2 ligands and are separated by 3.0755(2) A. Additionally, the terminal Pd atoms bear the NO and
O angle is
/
9.2340(2), bꢀ
/
9.2859(2), cꢀ
/
18.0460(4) A, bꢀ
/
92.339(1)8, Vꢀ
/
/
0.0205 for 3209 reflections [I ꢀ
/
2s(I)]. In the linear tri-nuclear molecule of IV, any adjacent metal atoms are
˚
the h2-toluene ligands. The configuration of the N atoms corresponds to the ideal sp2-hybridization. The Pdꢀ
/
Nꢀ
/
117.2(2)8. The N atoms form short contacts with the aromatic rings. The distance between the center of the ring and the nitrogen
˚
atom is 2.70 A. Complex IV is the first example of the Pd complex with the terminal nitrosyl ligand. The scheme of transformation
of complex III to complex IV was proposed.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Palladium complexes; Nitrosyl; Carboxylate; Crystal structures
1. Introduction
identified as intermediates in some reactions where
nitrate ions, nitrite ions or nitrogen oxide participate
as reactants or co-catalysts. For example, the complex
Pd4(NO)2(OAc)6 (I) was obtained as a by-product upon
oxidation of ethylene by dioxygen in acetic acid to
ethylene glycol monoacetate in the presence of the
Pd(OAc)2/LiNO3 catalyst [1]. The formation of the
palladium nitrosyl complex was detected mainly by the
spectroscopic data in allylic acetoxylation of alkenes in
The palladium complexes containing the coordinated
nitrosyl groups are very rare. Such compounds were
* Corresponding author. Tel.:
9541279.
E-mail address: strom@igic.ras.ru (T.A. Stromnova).
ꢂ
/
7-095-9554805; fax:
ꢂ/7-095-
0020-1693/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0020-1693(02)01575-X

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T.A. Stromnova et al. / Inorganica Chimica Acta 350 (2003) 283ꢁ288
/
the presence of Pd(OAc)2ꢁ
in the reduction of NO to N2O on the PdCl2ꢁ
catalyst [3].
/
Fe(NO3)3 as a catalyst [2], or
small portions of water, methanol, and hexane and dried
in vacuum. Yield is 90ꢁ92%.
/
CuCl
/
Thus, the palladium and platinum nitrosyl complexes
are of high interest not only as traditional objects of
coordination chemistry of noble metals but also as
possible intermediates (or their models) of industrially
important catalytic processes.
2.2.2. AgOCOCHMe2
A solution of NaOH (0.72 g, 18 mmol) in small excess
of iso-butiric acid was added to a saturated aqueous
solution of AgNO3 (2.55 g, 15 mmol). White (or light
gray) residue was filtered off, washed with water,
This paper describes new methods for the synthesis of
palladium nitrosyl carboxylate complexes and study
their structures by several methods including an X-ray
diffraction analysis.
MeOH, and hexane and dried in vacuum. Yield is 85ꢁ
90%.
/
2.2.3. AgOCOCM3, AgOCOCH2Cl, AgOCOPh
NaOH (0.72 g, 18 mmol) was dissolved in minimum
amount of water, the solution was acidified by several
drops of acetic acid, and 20 mmol of the corresponding
acid (pivalic, monochloroacetic, or benzoic) was added.
The solution was added to a saturated aqueous solution
of AgNO3 (2.55 g, 15 mmol). The residue was filtered
2. Experimental
All organic solvents and liquid organic reagents were
purified and dried according to the standard procedures
[4].
off, washed and dried in vacuum. Yields is 80ꢁ95%.
/
PdCl2, AgNO3, NaNO2, and pivalic, benzoic, mono-
chloroacetic, and trichloroacetic acids were commer-
cially supplied by Reakhim (Russia), Aldrich, and
Merck.
Note: all the operations should be conducted in the
darkness to avoid the decomposition of silver carbox-
ylates.
The elemental C, H, N analysis were conducted on an
Analyzer CHNS-OEA 1108 (Carlo Erba Instruments,
Italy).
2.3. Synthesis of palladium nitrosyl carboxylates from
Pd(NO)Cl
The IR spectra were obtained with Spectrometer
SPECORD M-80 in Nujol.
All the reactions with Pd(NO)Cl were carried out
under inert atmosphere.
The X-ray structural data were collected on NONIUS
CAD-4 and Bruker SMART CCD diffractometers.
2.3.1. Synthesis of Pd4(NO)2(OCOCMe3)6 (IIa)
In two-neck flask, Pd(NO)Cl (0.17 g, 1 mmol),
AgOCOCMe3 (0.31 g, 1.5 mmol), and THF (10 ml)
2.1. Pd(NO)Cl
were stirred during ꢁ1 h. The initial uncolored solution
/
Pd(NO)Cl was prepared by the modified method [5].
In a two-neck flask, PdCl2 (1.77 g, 10 mmol) and
NaNO2 (0.69 g, 10 mmol) were dissolved in 100 ml of
H2O containing 2 ml of concentrated H2SO4 The flask
was evacuated and filled with propene; the later was
bubbled until the color of the solution changed from
bright-orange to dark-brown and a lustrous-black pre-
cipitate formed. The precipitate was filtrated off and
washed by water, dried in vacuum, and kept under inert
atmosphere. Yield of Pd(NO)Cl is equal 1.63 g (83% per
Pd). IRS: nNO 1712, 1764 cmꢃ1. Anal. Calc. for
NOClPd: N, 8.14. Found: N, 8.27%.
acquired dark-red color. The reaction mixture was
filtered, and washed by THF. Than the filtrate was
evaporated to dryness and recrystallized from mixture
CH2Cl2ꢁhexene.
/
Reddish-brown powder, soluble in THF, benzene,
toluene, CHCl3, CH2Cl2, and ethanol, insoluble in
hexane. Yield: 0.25 g (92% on Pd). IRS: nNO 1568
cmꢃ1. Anal. Calc. for Pd2C6H9O7N: C, 32.98; H, 4.95;
N, 2.57. Found: C, 33.35; H, 5.35; N, 2.67%.
2.3.2. Synthesis of Pd4(NO)2(OCOCH3)6 (IIb)
Synthesis of Pd4(NO)2(OCOCH3)6 (IIb) was provided
analogously to the synthesis of Pd4(NO)2(OCOCMe3)6,
using Pd(NO)Cl (0.35 g, 0.2 mmol), AgOCOMe (0.60 g,
3 mmol), and THF (20 ml). Reaction time was 1.5 h.
The product is insoluble in THF, benzene, toluene
and CH2Cl2, soluble in HCl.
Yield: 0.35 g (85% based on Pd). IRS: nNO 1616 cmꢃ1
.
Anal. Calc. for Pd2C6H9O7N: C, 17.15; H, 2.14; N, 3.34.
Found: C, 17.63; H, 2.50; N, 3.74%.
2.2. Preparation of silver carboxylates
2.2.1. AgOCOMe
To saturated solution of AgNO3 (2.55 g, 15 mmol) in
water acidified with several drops of HOAc was added a
saturated water solution of NaOAc (1.47 g, 18 mmol).
White residue that formed was filtered off, washed with
2.3.3. Synthesis of Pd4(NO)2(OCOPh)6 (IIc)
Synthesis of Pd4(NO)2(OCOPh)6 (IIc) was provided
analogously to the synthesis of Pd4(NO)2(OCOMe3)6,

T.A. Stromnova et al. / Inorganica Chimica Acta 350 (2003) 283ꢁ
/288
285
using Pd(NO)Cl (0.17 g, 0.1 mmol), AgOCOPh (0.34 g,
1.5 mmol), and THF (10 ml). Reaction time was1 h.
After evaporation a solution by half, several drops of
hexane was added to avoid the formation of oil and the
evaporation was continued to dryness. Yield: 0.19 g
(86% based on Pd). IRS: nNO 1544 cmꢃ1. Anal. Calc. for
Pd2C21H15O7N: C, 41.39; H, 2.47; N, 2.31. Found: C,
40.97; H, 2.96; N, 2.45%.
Table 1
Crystal data, data collection, structure solution and refinement
parameters for IIa and IV
Empirical formula
Formula weight
Color, habit
C30H54N2O14Pd4 IIa C22H16F12N2O10Pd3 IV
1092.35
Brown block
1015.57
Dark brown block
Crystal size (mm)
Crystal system
Space group
0.20ꢄ
monoclinic
P21/n
/
0.10ꢄ
/0.10
0.20ꢄ
monoclinic
P21/n
/
0.20ꢄ0.10
/
Analogously the complexes Pd4(NO)2(OCOCHMe2)6
(IId) and Pd4(NO)2(OCOCH2Cl)6 (IIe) were prepared
with good yields:
Unit cell dimensions
˚
a (A)
˚
12.104(7)
23.970(8)
15.495(4)
90.30(4)
4496(3)
4
9.2340(2)
9.2859(2)
18.0460(4)
92.339(1)
1546.08(6)
2
b (A)
˚
c (A)
b (8)
IId: Anal. Calc. for C12H21NO7Pd2: C, 28.38; H, 4.17;
N, 2.87. Found: C, 27.95; H, 3.89; N, 3.14%. IRS: nNO
3
V (A )
˚
Z
1572 cmꢃ1
.
Dcalc (g cmꢃ3
Absorption coeffi-
)
1.614
1.629
2.182
1.853
IIe: Anal. Calc. for C6H6NO7Cl3Pd2: C, 13.76; H, 1.15;
N 2.67. Found: C, 14.28; H, 1.11; N, 2.82%. IRS: nNO
cient (mmꢃ1
F(000)
)
2176
976
1588 cmꢃ1
.
Diffractometer
Temperature (K)
˚
Radiation (l/A)
Enraf-Nonius CAD4 Bruker SMART CCD
293(2) 120.0(2)
Graphite-monochromated Mo Ka (0.71073)
2.13ꢁ29.96 2.26ꢁ27.50
115h 5 115h 5
335k 5 105k 5
215l 521 235l 522
8757 8872
u Range (8)
Index ranges
/
/
2.4. Synthesis of Pd4(NO)4(OCOCF3)4 (III)
ꢃ/
/
/
0,
32,
ꢃ/
/
/
11,
ꢃ/
/
/
ꢃ/
/
/
12,
Complex Pd4(CO)4(OCOCF3)4 (0.8 g, 0.81 mmol)
prepared according to [6] was dissolved in 50 ml of
toluene and solution was stirred under NO during 1.5 h
at room temperature (r.t.). The color of the solution was
changed from light-yellow to dark-red. The solution was
evaporated, and reddish-brown residue was recrystal-
ꢃ/
/
/
ꢃ/
/
/
Reflections
collected
Independent
reflections
Absorbtion
correction
Min./max.
transmission
Solution
8054 [Rint
ꢀ
/
0.0629]
3518 [Rint
empirical [7]
0.7082 and 0.8364
Direct methods (SHELX-86) [8]
ꢀ0.0154]
/
none
lized from a mixture CH2Cl2ꢁhexane. Yield: 0.75 g (93%
/
on Pd). IRS: nNO 1516 cmꢃ1. Anal. Calc. for
C2NO3F3Pd: C, 19.82; H, 0.00; N, 5.61. Found: C,
10.31; H, 0.00; N, 5.59%.
method
Refinement method full-matrix least-squares on F2
(SHELXL-93) [9]
Data/restraints/
parameters
Reflections with
8054/0/389
3518/0/255
2.5. Synthesis of Pd3(NO)2(OCOCF3)4×
/
2TolH (IV)
6228
3209
I ꢀ2s(I)
/
Goodness-of-fit
on F2
1.067
1.068
During slow recrystallization of Pd4(NO)4(OCOF3)4
from toluene solution the lustrous black crystals were
formed. The composition and structure of this substance
were determined from the X-ray structure data.
Final R indices
R1ꢀ
wR2ꢀ
R1ꢀ0.0714,
wR2ꢀ0.1570
Extinction coefficient 0.0009(2)
/0.0507,
R1ꢀ
wR2ꢀ
R1ꢀ0.0233,
wR2ꢀ0.0547
/0.0205,
[I ꢀ
/
2s(I)]
/
0.1478
/
0.0535
R indices (all data)
/
/
/
/
Largest difference
peak and hole
1.005 and ꢃ
/
0.719
0.688 and ꢃ0.620
/
2.6. X-ray diffraction study
ꢃ3
˚
(e A
)
The crystal data, data collection, and structure
solution and refinement parameters for compounds IIa
and IV are presented in Table 1. In the structure of IIa,
all the methyl carbon atoms were refined isotropically.
The t-Butyl group attached to C(26) was found to be
disordered over two positions with approximately equal
occupancies. All hydrogen atoms were placed in the
calculated positions and refined using a riding model. As
for the structure of IV, all non-hydrogen atoms were
refined with the anisotropic thermal parameters. All
hydrogen atoms were found from the difference Fourier
synthesis and refined isotropically.
3. Results and discussion
The first palladium nitrosyl complex Pd(NO)Cl (V)
has been synthesized more than 40 years ago by the
reaction of PdCl2 with NaNO2 in water in the presence
of alkene [5]. The dissolution of Pd(NO)Cl in concen-
trated HCl followed by the addition of phosphonium or
arsonium salts produces the anionic complex
[Pd2Cl4(NO)2]2ꢃ [10]. Later, the palladium nitrosyl
?
ƒ
complexes (C5R2R3)Pd(NO) (VI), where R?ꢀ
/
Rƒꢀ/H,

286
T.A. Stromnova et al. / Inorganica Chimica Acta 350 (2003) 283ꢁ288
/
Fig. 1. Molecular structure of complex IIa. Hydrogen atoms are omitted for clarity.
Ph or p-tolyl; or R?ꢀ
/
Et, Rƒꢀ
/
Ph, have been prepared
solution. The analytical and spectroscopic data for the
products isolated from THF as a brown or reddish-
brown powder or oil allow us to formulate these
complexes as Pd2(NO)(OCOR)3 (II). The IR spectra of
complexes II contain a middle-intensity band in the
by the treatment of initial salts with NO gaseous [11].
It is essential that none of the complexes under
consideration have been characterized by an X-ray
diffraction analysis and their structures are not clear
up-to-date. For example, complexes VI were proposed
[12,13] to have a geometry of ‘one-legged piano-stool’ by
analogy to the corresponding nickel compounds. How-
ever, the frequency nNO (around 1750 cmꢃ1) in the IR
spectra of complexes VI also allows one to assume the
bridging coordination of the nitrosyl groups and a dimer
structure of the complexes.
region of 1560ꢁ
the bridging nitrosyl group. The stability of complexes
II decreases in the series CMe3ꢁCHMe2ꢀPhꢁMeꢀ
CH2ClꢂCCl3ꢀCF3. Therefore, we have managed to
/
1620 cmꢃ1, which can be attributed to
/
/
/
/
/
/
characterize the complexes II except those containing
CCl3COO and CF3COO groups.
We solved the structures of complexes II (IIa, Rꢀ
/
Two palladium nitrosyl complexes have been char-
acterized by an X-ray diffractometry. The first com-
pound, Pd4(m-NO)2(m-OCOCH3)6 (I), was isolated as an
intermediate (or by-product) with a very low yield in the
process of ethylene oxidation [see above, [1]]. The
second complex, Pd6(m-NO)2(m-OAc)8 (VII), was iso-
lated in a low yield from the reaction of palladium(II)
acetate with carbon monoxide in the nitric acid medium
[14]. Hence, no efficient methods for the preparation of
palladium nitrosyl complexes were available up-to-date.
In our search for feasible methods for the preparation
of palladium nitrosyl complexes, we studied the reac-
tions of Pd(NO)Cl with potential acceptors of Cl anions.
Our experiments showed that the reaction of
CMe3; IIb, RꢀMe) using an X-ray diffraction analysis.
/
The structure of complex IIa is shown in Fig. 1. The
selected geometrical parameters for IIa are given in
Table 2. In the molecule of IIa, the palladium atoms
Table 2
˚
Selected bond lengths (A) and angles (8) for complex IIa
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
N(1)ꢀ
/
Pd(4)
N(1)
O(2)
O(14)
O(12)
N(1)
O(3)
O(4)
O(6)
2.994(1) Pd(2)ꢀ
1.903(6) Pd(3)ꢀ
2.009(6) Pd(3)ꢀ
2.019(6) Pd(3)ꢀ
2.043(6) Pd(3)ꢀ
1.909(6) Pd(4)ꢀ
2.011(6) Pd(4)ꢀ
2.016(5) Pd(4)ꢀ
2.029(5) Pd(4)ꢀ
1.184(8) N(2)ꢀ
/
Pd(3)
N(2)
O(9)
3.000(1)
1.916(5)
2.008(5)
2.021(5)
2.063(5)
1.917(6)
1.999(6)
2.021(5)
2.056(5)
1.188(7)
/
/
/
/
/
/O(5)
/
/O(7)
/
/
N(2)
O(10)
O(13)
O(11)
/
/
/
/
Pd(NO)Cl with silver carboxylates AgOCOR (Rꢀ
CMe3, Me, Ph, CHMe2, CH2Cl, CCl3, CF3) (THF,
room temperature, molar ratio PdꢁAgꢀ1/1.5) occurs
almost completely in 0.5ꢁ3.0 h (depending on the nature
/
/
/
/
O(1)
/
O(8)
/
/
O(1)ꢀ
O(1)ꢀ
Pd(1)ꢀ
/
N(1)ꢀ
N(1)ꢀ
/
Pd(1)
120.4(5) O(8)ꢀ
120.7(5) O(8)ꢀ
118.9(3) Pd(3)ꢀ
/
N(2)ꢀ
/
Pd(3)
Pd(4)
121.8(5)
121.0(5)
117.2(3)
/
/
/Pd(2)
/
N(2)ꢀ
/
of silver carboxylate) and leads to the formation of
dirty-white precipitate of AgCl and a dark-brown
/
N(1)ꢀ
/Pd(2)
/
N(2)ꢀPd(4)
/

T.A. Stromnova et al. / Inorganica Chimica Acta 350 (2003) 283ꢁ
/288
287
form almost rectangular Pd4 skeleton with the pair of
bridging ligands on each side of the rectangle. Two
opposite shortest sides of the rectangle are bridged by
two pairs of the carboxylate ligands. Another two sides
are linked by the carboxylate and the nitrosyl bridges
each. The two NO groups have cis-arrangement with
close to that of the initial Pd complex. During the
reaction, the replacement of the CO groups to the NO
groups was accompanied by the oxidation of Pd(ꢂ
/
1) to
Pd(ꢂ
/
2) and the reduction of the neutral NO molecules
to anions NOꢃ. Complex III is unstable. Our attempts
to grow the single crystals of III suitable for an X-ray
Structural Analysis from toluene solution resulted in
respect to the Pd4 plane. The Pd(1)ꢀ
Pd(3) bond lengths are 2.994(1) and 3.000(1) A, while
Pd(1)ꢀPd(2) and Pd(3)ꢀPd(4) distances are longer than
/
Pd(4) and Pd(2)ꢀ
/
˚
complex Pd3(NO)2(OCOCF3)4×/2C6H5CH3 (IV) together
/
/
with palladium black. The structure of complex IV was
characterized by the X-ray diffraction data (see Fig. 2).
Selected geometrical parameters for complex IV is given
in Table 3.
˚
3.27 A and they may be considered as non-bonded. The
coordination polyhedrons of all Pd atoms are close to
the square-planar ones. The NO bridges are approxi-
mately symmetric, with the Pdꢀ
/
Nꢀ
/
O angles ranging
The linear tri-nuclear molecule of IV lies on the center
of symmetry. The Pd(1) and Pd(2) atoms are linked by
the two CF3CO2 bridging ligands and they are separated
within 120.4(5)ꢁ121.8(5)8.
/
We found that complexes IIa and IIb have the
analogous structure, which turned out to be close to
the structure of complex I [1]. In complex I, the
palladium atoms form the tetrahedron strongly dis-
torted towards the parallelogram; the deviations from
˚
by 3.0755(2) A. Additionally, Pd(1) and Pd(1A) atoms
bear the NO and the h2-toluene substituents. The
configuration of the N(1) atom corresponds to the
almost ideal sp2-hybridization; the Pd(1)ꢀ
/
N(1)ꢀ
/
O(5)
˚
the Pd4 plane do not exceed 0.17 A). The angles in the
angle is 117.2(2)8. To the best of our knowledge, IV is
the first example of the Pd complex with the terminal
nitrosyl ligand. The N(1) atom forms a short contact
with the aromatic ring. The distance between the center
parallelogram are close to 908. All other peculiarities of
the structures under consideration are identical. It is of
interest that the platinum analog Pt4(NO)2(OCOCH3)6
(VIII) is of almost the same structure, that is, four metal
atoms form a rectangle with the bridging nitrosyl and
acetate groups [15]. Complex VIII was isolated as a by-
product in the synthesis of Pt4(OCOCH3)8 from plati-
num(II) salts in the presence of nitric acid [16]. These
facts suggest that as in the case of complex I, the NO
ligands originates from nitric acid.
˚
of the ring and the nitrogen atom is 2.70 A.
One can assume that the unusual transformation of
tetranuclear complex III containing bridging NO groups
It is noteworthy that three complexes, I, II, and VIII,
prepared by different methods, have almost the same
structures. It is possible to suggest that, in each case, the
source of the NO ligands ([Pd(NO)Cl] or the product of
NO3ꢃ reduction) supplies the nitrosyl groups in the
form of NOꢃ.
We also found another method for preparation of
palladium nitrosyl complexes, which includes replace-
ment of the coordinated CO ligands to the NO ones.
The reaction of the Pd4(m-CO)4(m-OCOR)4 tetranuclear
clusters with nitrogen monoxide was found to afford the
palladium nitrosyl carboxylate complexes. The struc-
tures of the prepared nitrosyl carboxylate complexes is
similar to those of the initial Pd carbonyl carboxylate
clusters that have a rectangular metal core and bridging
carbonyl and carboxylate ligands.
Fig. 2. Molecular structure of complex IV. Hydrogen atoms are
omitted for clarity.
Complex Pd4(NO)4(OCOCF3)4 (III) was synthesized
by the reaction of Pd4(m-CO)4(m-OCOCF3)4 with NO in
benzene solution. Comparative analysis of the IR
spectra of the initial and the prepared complexes showed
no changes in the bands related to the carboxylate
groups. The absence of IR absorption in the region of
Table 3
˚
Selected bond lengths (A) and angles (8) for complex IV
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
Pd(1)ꢀ
/
N(1)
O(1)
O(4)
C(7)
C(8)
1.896(2)
2.229(2)
2.237(2)
2.405(2)
2.428(2)
Pd(1)ꢀ
Pd(2)ꢀ
Pd(2)ꢀ
N(1)ꢀ
O(5)ꢀ
/
Pd(2)
O(3)
O(2)
3.0755(2)
2.005(1)
2.009(1)
1.150(3)
117.2(2)
/
/
2000ꢁ
1900 cmꢃ1 (nCO bridging) and the appearance of a
/
/
/
new band at 1516 cmꢃ1 (nNO bridging) indicate full
replacement of the m-CO groups to the m-NO groups.
Therefore, the structure of complex III seems to be very
/
/
O(5)
/
/
N(1)ꢀPd(1)
/

288
T.A. Stromnova et al. / Inorganica Chimica Acta 350 (2003) 283ꢁ288
/
into trinuclear complex IV with terminal nitrosyl ligands
includes an intramolecular migration of the bridging
nitrosyl and trifluoroacetate groups through the metal
core. Such a ligand migration is the well-known process
in cluster chemistry [17,18].
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
Acknowledgements
It seems that complex III can exist in solution as a
mixture of isomers with different arrangement of the
ligands:
Support from the Russian Foundation for Basic
Research for LGK (grant number 01-03-32474) is
gratefully acknowledged. A.V.C. thanks the Royal
Society of Chemistry for the RSC Journal Grant for
International Authors.
References
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The crystallographic data (excluding structure fac-
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