Binuclear palladium(I) and palladium(II) complexes of ortho-functionalized 1,3-bis(aryl)triazenido ligands

Article abstract of DOI:10.1021/ic700516p

Three new bis(aryl)triazene ligands, Ar-NNNH-Ar′ [Ar = o-C ₆H₄-CO₂Me, Ar′ = p-C₆H ₄-CH₃ (2); Ar = Ar′ = o-C₆H ₄-CO₂Me (3); Ar = o-C₆H₄-SMe, Ar′ = p-C₆H₄-CH₃) (4)], have been synthesized. The reaction of 1-4 with PdCl₂(NCCH₃) ₂ in the presence of a base afforded a series of binuclear diamagnetic palladium complexes. In these reactions, ligands 1-3 afforded the palladium(I) complexes [Pd^I(o-MeO₂C-C₆H ₄-NNN-o-C₆H₄-CO₂Me)]₂ (5, monoclinic, space group P2₁/c, a = 8.6070(10) A, b = 14.3220(10) A, c = 12.7310(10) A, β = 100.2950(10)°, Z = 2), [Pd^I(o-MeO-C₆H₄-NNN-o-C₆H ₄-OMe)]₂ (6, triclinic, space group P1, a = 6.6288(5) A, b = 10.2631(10) A, c = 11.0246(11) A, α = 85.579(6)°, β = 80.885(6)°, γ = 74.607(6)°, Z = 1), and [Pd^I(o-MeO₂C-C₆H₄-NNN-p-C ₆H₄-CH₃)]₂ (7, tetragonal, space group I41/a, a = 20.866(3) A, b = 20.866(3) A, c = 13.156(2) A, Z = 8). In contrast, the reaction of ligand 4 with PdCl ₂(NCCH₃)₂ resulted in the formation of a palladium(II) dimer, [Pd^II(o-MeS-C₆H₄-NNN-p- C₆H₄-CH₃)Cl]₂ (8, orthorhombic, space group P2₁2₁2, a = 10.4058(5) A, b = 16.2488(8) A, c = 9.9500(5) A, Z = 2).

Full text of DOI:10.1021/ic700516p

Inorg. Chem. 2007, 46, 6182−6189
Binuclear Palladium(I) and Palladium(II) Complexes of
ortho-Functionalized 1,3-Bis(aryl)triazenido Ligands
Juan Jose´ Nuricumbo-Escobar,† Carlos Campos-Alvarado,† Gustavo R´ıos-Moreno,†
David Morales-Morales,‡ Patrick J. Walsh,*,§ and Miguel Parra-Hake*,†,
Centro de Graduados e InVestigacio´n, Instituto Tecnolo´gico de Tijuana, Apartado Postal 1166,
22000 Tijuana, B. C. Me´xico, Instituto de Qu´ımica, UniVersidad Nacional Auto´noma de Me´xico,
Circuito Exterior Cd. UniVersitaria Coyoacan. C.P. 04510 Mexico, D.F., Vagelos Laboratories,
Department of Chemistry, UniVersity of PennsylVania, 231 South 34th Street,
Philadelphia, PennsylVania 19104-6323
Received March 16, 2007
Three new bis(aryl)triazene ligands, Ar-NNNH-Ar
o-C6H4-CO2Me (3); Ar o-C6H4-SMe, Ar′ ) p-C6H4-CH3) (4)], have been synthesized. The reaction of 1
PdCl2(NCCH3)2 in the presence of a base afforded a series of binuclear diamagnetic palladium complexes. In
these reactions, ligands 1
3 afforded the palladium(I) complexes [PdI(o-MeO2C-C6H4-NNN-o-C6H4-CO2Me)]2 (5,
monoclinic, space group P21/c, a
′
[Ar
)
o-C6H4-CO2Me, Ar′ ) p-C6H4-CH3 (2); Ar
)
Ar′ )
)
−4 with
−
)
8.6070(10) Å, b
)
14.3220(10) Å, c
)
, a
)
12.7310(10) Å, â ) 100.2950(10)
6.6288(5) Å, b 10.2631(10) Å,
1), and [PdI(o-MeO2C-C6H4-NNN-p-
13.156(2) Å, Z 8).
°,
Z
c
)
)
2), [PdI(o-MeO-C6H4-NNN-o-C6H4-OMe)]2 (6, triclinic, space group P1
h
)
)
11.0246(11) Å, R ) 85.579(6)
°
,
â ) 80.885(6)
°
,
γ ) 74.607(6)
°
, Z
C6H4-CH3)]2 (7, tetragonal, space group I41/a, a
)
20.866(3) Å, b
)
20.866(3) Å, c
)
)
In contrast, the reaction of ligand 4 with PdCl2(NCCH3)2 resulted in the formation of a palladium(II) dimer,
[PdII(o-MeS-C6H4-NNN-p-C6H4-CH3)Cl]2 (8, orthorhombic, space group P21212, a
)
10.4058(5) Å, b 16.2488(8)
)
Å, c
) 9.9500(5) Å, Z ) 2).
Chart 1. Generic Triazene and Triazenido Binding Modes
Introduction
A fundamental aim of inorganic chemistry is the synthesis
of complexes that exhibit new reactivity. An approach toward
this important goal is the preparation of unique ligands that
impart novel chemistry when incorporated into the metal
coordination sphere. As such, a class of ligands that has
attracted our attention is the triazenido ligands (Chart 1),
because these ligands exhibit a variety of bonding modes
with distinct properties.1,2 Triazenido ligands in monomeric
complexes can bind through a single nitrogen or can form
metallocycles through chelation. They are also well-known
to bridge two metal centers (Chart 1).3,4
Triazenido ligands are isoelectronic with amidinates,5,6
which have been successfully used in transition metal
chemistry. The central nitrogen of the triazene imparts greater
acidity on the N-H7,8 relative to the amidine N-H, making
the triazenido less electron donating and more amenable to
binding to late transition metals. Our initial studies involved
the use of simple 1,3-bis(aryl) triazines to prepare main group
complexes.9,10 More recently, we have turned our attention
* To whom correspondence should be addressed. Tel.: +1-215-573-
2875. Fax: +1-215-573-6743. E-mail: pwalsh@sas.upenn.edu (P.J.W.).
Tel.: +52-664-623-4043.Fax: +52-664-6233772.E-mail: mparra@tectijuana.mx
(M.P.-H.).
(3) Hursthouse, M. B.; Mazid, M. A.; Clark, T.; Robinson, S. D.
Polyhedron 1993, 12, 563-565.
(4) Moore, D. S.; Robinson, S. D. AdV. Inorg. Chem. Radiochem. 1986,
30, 1-68.
† Instituto Tecnolo´gico de Tijuana.
(5) Barker, J.; Kilner, M. Coord. Chem. ReV. 1994, 133, 219-300.
(6) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403-481.
(7) Hansen, L. D.; West, B. D.; Baca, E. J.; Blank, C. L. J. Am. Chem.
Soc. 1968, 90, 6588-6592.
(8) Sawicki, E.; Hauser, T. R.; Stanley, T. W. Anal. Chem. 1959, 31,
2063-2065.
(9) Gantzel, P.; Walsh, P. J. Inorg. Chem. 1998, 37, 3450-3451.
‡ Universidad Nacional Auto´noma de Me´xico.
§ University of Pennsylvania.
(1) Vrieze, K.; van Koten, G. ComprehensiVe Coordination Chemistry;
Pergamon Press: Oxford, U.K., 1987; Vol. 2.
(2) Kimball, D. B.; Haley, M. M. Angew. Chem., Int. Ed. 2002, 41, 3338-
3351.
6182 Inorganic Chemistry, Vol. 46, No. 15, 2007
10.1021/ic700516p CCC: $37.00
© 2007 American Chemical Society
Published on Web 06/20/2007

1,3-Bis(aryl)triazenido Ligands
mmol, 3 equiv) at 0 °C. An aqueous solution (15%) of sodium
nitrite (1.997 g, 28.9 mmol, 1.5 equiv) was added dropwise with
stirring. Once the amine was dissolved, a 15% solution of
p-toluidine in ethanol (2.07 g, 19.3 mmol, 1 equiv) was added
at 0 °C and stirred for 30 min. The reaction mixture was neutralized
with a 15% aqueous solution of NaOAc (31.6 mL) to give a yellow
precipitate. The reaction mixture was filtered, and the solid was
dried under vacuum. The product was purified by crystallization
at -4 °C from 9:1 ethyl acetate/hexanes to obtain a yellow
crystalline solid (2.25 g, 8.35 mmol, 87%). mp: 108-110 °C. IR
(KBr): ν 3256, 2951, 1684, 1579, 1496, 1460, 1264, 1152, 1129,
750 cm-1. 1H NMR (CDCl3, 200 MHz, 25 °C): δ 7.92 (d, J ) 5.4
Hz, 1H, Ar), 7.88 (d, J ) 5.2 Hz, 1H, Ar), 7.70 (d, J ) 8.0 Hz,
2H, Ar), 7.14 (t, J ) 5.6 Hz, 1H, Ar), 7.02 (d, J ) 8.6 Hz, 2H,
Ar), 6.67 (t, J ) 7.5 Hz, 1H, Ar), 3.32 (s, 3H, -O-CH3), 2.09 (s,
3H, Ar-CH3). 13C{1H} NMR (CDCl3, 50 MHz, 25 °C): δ 167.7
(CdO), 147.4 (CAr-N), 144.1 (CAr-N), 137.9 (CAr-CdO), 134.4
(CAr-H), 131.1 (CAr-H), 129.7 (2 CAr-H), 121.6 (CAr-H), 120.8
(CAr-H), 114.5 (2 CAr-H), 111.7 (CAr-CH3), 52.1 (-O-CH3),
21.2 (Ar-CH3). MS-EI: m/z [M]+ 269 (23), [M+ - N3(C6H4)-
COOCH3] 91 (100). Anal. Found: C, 66.61; H, 5.43; N, 15.71.
Calcd for C15H15N3O2: C, 66.90; H, 5.61; N, 15.60.
to the application of 1,3-bis(aryl) triazenido ligands bearing
Lewis basic ortho-substituents,11,12 such as esters,13,14 which
can form additional chelating rings and induce novel
coordination environments. The weakly coordinating ester
carbonyl groups can behave as hemilabile ligands15 to open
a coordination site for substrate activation. The ability of
the Lewis basic ortho-substituents to coordinate to soft metals
could be modulated by choice of hard weakly coordinating
groups, such as esters and ethers, or softer more-electron
donating substituents, such as the methylmercapto group. We
have found that the nature of the Lewis basic ortho-
substituent can have a dramatic impact on the chemistry of
these complexes.
In this paper, we examine the synthesis and structure of
palladium complexes bearing 1,3-bis(aryl) triazenido ligands
with Lewis basic substituents in the ortho-positions. Unlike
unfunctionalized 1,3-bis(aryl) triazenido ligands, which give
palladium(II) complexes when palladium(II) is employed as
starting material, we were surprised to find that use of our
ortho-functionalized triazenes gave rise to palladium(I) or
palladium(II) dimers, depending on the characteristics of the
ortho-substituent. We are unaware of previously character-
ized examples of palladium(I) employing triazenido ligands.
These novel palladium(I) complexes have been fully char-
acterized, including by X-ray crystallography.
[1,3-Bis(2-methoxy)benzene]triazene (3). At -5 °C, o-anisidine
(2.0 mL, 17.7 mmol) was mixed with an excess isoamyl nitrite
(2.4 mL, 17.7 mmol, 1 equiv) in toluene (5 mL), and the mixture
was vigorously stirred for 6 h. The reaction mixture was dried over
anhydrous MgSO4 and filtered. The solvent was removed in vacuo
to obtain a red solid. The product was purified by flash chroma-
tography (alumina, ethyl acetate/hexane 9:1), and a red fraction
was collected. The product was crystallized from a 9:1 ethyl acetate/
hexane solution at -4 °C to obtain 2 as a red crystalline solid (784
mg, 3.05 mmol, 34%). mp: 87-90 °C. IR (KBr): ν 3158, 2833,
Experimental Section
All reactions were performed under air. Unless otherwise
specified all chemicals were purchased from Aldrich Chemical Co.
and were used without further purification. Methyl anthranilate
was purchased from Spectrum, while [1,3-bis(2-carboxymethyl)-
benzene]triazene (1)11 and bis(acetonitrile)palladium(II) dichloride16
were synthesized according to literature procedures. NMR spectra
1
1597, 1257, 790 cm-1. H NMR (CDCl3, 200 MHz, 25 °C): δ
10.25 (bs, 1H, NH), 7.66 (dd, J ) 7.9, 1.6 Hz, 2H, Ar), 7.13 (dt,
J ) 7.7, 1.2 Hz, 2H, Ar), 7.01-6.94 (m, 4H, Ar), 3.91 (s, 6H,
-OCH3). 13C NMR (CDCl3, 50 MHz, 25 °C): δ 120.9 (CAr-H),
111.1 (CAr-H), 55.7 (O-CH3) (only observed signals). MS-ESI
(negative mode): m/e [M - H]- 256. Anal. Found: C, 65.45; H,
5.60; N, 16.12. Calcd for C14H15N3O2: C, 65.35; H, 5.88; N, 16.33.
1
were recorded on a Varian Gemini 2000-BB FT. H NMR (200
MHz) and 13C{1H} NMR (50 MHz) are reported in parts per million
relative to Me4Si as an internal standard. Coupling constants, J,
are given in Hertz (Hz). IR spectra were recorded on a Perkin-
Elmer Model 1605 FT-IR spectrometer. UV-vis absorption spectra
were measured on a HP 8452A diode array spectrophotometer. EI
mass spectra were obtained with a HP 5989 MS Engine, and ES
mass spectra were measured with an Agilent 110 MSD ion trap.
Melting points were measured in a Gallenkamp apparatus and are
uncorrected. Elemental analyses were performed at Departamento
de Qu´ımica Inorga´nica, Facultad de Ciencias, Universidad de
Zaragoza, Spain. Samples for elemental analysis were dried at room
temperature under vacuum for at least 24 h.
1-[2-(Thiomethyl)benzene]-3-[4-(methyl)benzene]triazene (4).
2-(Methylthio)aniline (1.10 g, 7.91 mmol) in water (5 mL) was
mixed with 1 M HCl (24.3 mL, 24.3 mmol, 3 equiv) at 0 °C. A
15% NaNO2 aqueous solution (0.838 g, 12.1 mmol, 1.5 equiv) was
then added dropwise with stirring. Once the amine was dissolved,
a 15% solution of p-toluidine in ethanol (0.868 mg, 8.1 mmol, 1
equiv) was added at 0 °C. The reaction mixture was stirred for 30
min, and then it was neutralized with 15% NaOAc (40 mL) to obtain
a yellow solution. The mixture was extracted with ethyl acetate,
and the organic layer was dried over anhydrous MgSO4. The solvent
was removed under reduced pressure to obtain an orange solid,
which was purified by flash chromatography (alumina, 9:1 ethyl
acetate/hexanes). The product was crystallized from ethyl acetate/
hexanes (9:1) at -4 °C to obtain yellow crystals (0.951 g, 3.69
mmol, 93%). mp: 66-68 °C. IR(KBr): ν 3254, 2852, 1522, 1419,
Synthesis of Ligands. 1-[(2-Carboxymethyl)benzene]-3-[(4-
methyl)benzene]triazene (2). Methyl anthranilate (2.5 mL, 19.3
mmol) in water (5 mL) was mixed with 1 M HCl (57.9 mL, 57.9
(10) Westhusin, S.; Gantzel, P.; Walsh, P. J. Inorg. Chem. 1998, 37, 5956-
5959.
1
1256, 1167, 724 cm-1. H NMR (CDCl3, 200 MHz, 25 °C): δ
(11) Vernin, G.; Siv, C.; Metzger, J.; Pa´rka´nyi, C. Syntheses 1977, 10, 691-
10.22 (bs, 1H, NH), 7.68 (dd, J ) 8.1, 1.4 Hz, 1H, Ar), 7.47-7.18
(m, 6H, Ar), 7.04 (dt, J ) 7.5, 1.6 Hz, 1H, Ar), 2.40 (s, 3H,
-SCH3), 2.37 (s, 3H, Ar-CH3). 13C{1H} NMR (CDCl3, 50 MHz,
25 °C): δ 142.1 (CAr-N), 136.4 (CAr-H), 132.3 (CAr-H), 129.4
(2 CAr-H), 128.3 (CAr-Me), 123.3 (CAr-H), 119.7 (CAr-H), 114.6
(2 CAr-H), 21.1 (Ar-CH3), 18.4 (S-CH3) (only observed signals).
Anal. Found: C, 65.14; H, 5.71; N, 16.39; S, 12.41. Calcd for
C14H15N3S: C, 65.34; H, 5.87; N, 16.33; S, 12.46.
693.
(12) Chichibabin, A. E.; Persitz, R. L. J. Russ. Phys. Chem. Soc. 1925, 57,
301-304.
(13) Rodr´ıguez, J. G.; Parra-Hake, M.; Aguirre, G.; Ortega, F.; Walsh, P.
J. Polyhedron 1999, 18, 3051-3055.
(14) R´ıos-Moreno, G.; Aguirre, G.; Parra-Hake, M.; Walsh, P. J. Polyhedron
2003, 22, 563-568.
(15) Braunstein, P.; Naud, F. Angew. Chem, Int. Ed. 2001, 409, 680-699.
(16) Kharasch, M. S.; Seyler, R. C.; Mayo, R. F. J. Am. Chem. Soc. 1938,
60, 882-884.
Inorganic Chemistry, Vol. 46, No. 15, 2007 6183

Nuricumbo-Escobar et al.
Table 1. Crystallographic Data and Refinement Parameters for Compounds 5-8
5
6
7
8
empirical formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
C32H28N6O8Pd2
837.44
monoclinic
P21/c
8.6070(10)
14.3220(10)
12.7310(10)
90
100.2950(10)
90
C30H28N6O4Pd2
749.38
triclinic
P1h
6.6288(5)
10.2631(10)
11.0246(11)
85.579(6)
80.885(6)
74.607(6)
713.51(11)
1
C28H28N6O4Pd2
725.36
tetragonal
I41/a
20.866(3)
20,866(3)
13.156(2)
90
90
90
5728(2)
8
1.62
C29H30N6S2Cl4Pd2
881.31
orthorhombic
P21212
10.4058(5)
16.2488(8)
9.9500(5)
90
90
90
1544.1(2)
2
1.801
1682.36(14)
2
1.740
Z
F
T (K)
calcd (g cm-3
)
1.744
143
293
293
143
λ(Μï ΚR) (Å)
0.71073
1.228
0.0352
0.71069
1.308
0.0190
0.71073
1.300
0.0318
0.0540
0.71069
1.541
0.0424
0.1083
µ (mm-1
)
R1a (%)
wR2b (%)
0.0765
0.0464
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
Synthesis of Complexes. [1,3-Bis(2-carboxymethyl)benzene-
(triazenido)palladium(I)]2 (5). 1,3-Bis(2-carboxymethyl)benzene
triazene (1) (50.0 mg, 0.160 mmol) was dissolved in CH3CN (5
mL), and triethylamine (32.3 mg, 0.319 mmol, 2 equiv) was added
with stirring. To the resulting solution, (CH3CN)2PdCl2 (41.4 mg,
0.160 mmol, 1 equiv) in CH3CN (5 mL) was slowly added, and
the mixture was stirred for 30 min at room temperature, during
which time a red precipitate formed. The reaction mixture was
filtered to obtain a reddish microcrystalline solid, which was
recrystallized by slow evaporation of a solution of 5 in CH2Cl2 to
give dark red crystals (56.5 mg, 0.068 mmol, 85%). mp: 215 °C.
obtain a red microcrystalline solid that was purified by column
chromatography (florisil, CH2Cl2). The resultant product was
crystallized by vapor diffusion of pentane into a concentrated
solution of the product in CHCl3 at room temperature to give red
crystals (28.8 mg, 0.040 mmol, 51%). mp: 160-162 °C. IR
(KBr): ν 2826, 1584, 1489, 1358, 1244, 747, cm-1. UV-vis (CH2-
Cl2, 1.7581 × 10-4 M): λ (ꢀ) 302 (8959.69), 390 (12 084.64), 504
(1398.1), 562 (1030.66), 656 nm (384.51 L cm-1 mol-1). 1H NMR
(CDCl3, 200 MHz, 25 °C): δ 7.28 (dd, J ) 7.4, 2.4 Hz, 2H, Ar),
7.97 (td, J ) 8.2, 1.8 Hz, 2H, Ar), 6.88-6.79 (m, 4H, Ar), 3.64 (s,
6H, O-CH3). 13C{1H} NMR (CDCl3, 50 MHz, 25 °C): δ 151.4
(CAr-O), 138.8 (CAr-N), 124.2 (CAr-H), 121.4 (CAr-H), 120.0
(CAr-H), 111.4 (CAr-H), 57.1 (O-CH3). Anal. Found: C, 46.50;
H, 3.28; N, 11.48. Calcd for C28H28N6O4Pd2: C, 46.36; H, 3.89;
N, 11.59.
IR (KBr): ν 2947, 1713, 1643, 1595, 1562, 1381, 1157, 750 cm-1
.
UV-vis (CH2Cl2, 2.2688 × 10-4 M): λ (ꢀ) 242 (5382.98), 340
(15 534.52), 406 (16 012.73), 512 (2637.63), 600 nm (526.75 L
1
cm-1 mol-1). H NMR (CDCl3, 200 MHz, 25 °C): δ 7.79 (dd, J
) 7.8, 1.6 Hz, 2H, Ar), 7.46 (dd, J ) 8.4, 1.4 Hz, 2H, Ar), 7.36
(dt, J ) 7.0, 1.6 Hz, 2H, Ar), 7.06 (dt, J ) 8.4, 1.4 Hz, 2H, Ar),
3.77 (s, 6H, O-CH3). 13C{1H} NMR (CDCl3, 50 MHz, 25 °C): δ
168.5 (CdO), 150.4 (CAr-N), 132.3 (CAr-H), 130.6 (CAr-H),
123.4 (CAr-H), 122.5 (CAr-CdO), 121.3 (CAr-H), 52.8 (-O-
CH3). Anal. Found: C, 45.60; H, 3.12; N, 10.07. Calcd for
C32H28N6O8Pd2: C, 45.89; H, 3.37; N, 10.04.
{1-[2-(Thiomethyl)benzene]-3-[4(methyl)benzene](triazenido)]-
(chloro)palladium(II)}2 (8). Complex 8 was prepared in the same
manner as 5, using ligand 4. The reaction provided a brown
precipitate that was crystallized by vapor diffusion of pentane into
a concentrated solution of the product in CH2Cl2 at room temper-
ature to provide amber crystals (50.6 mg, 0.057 mmol, 59%). mp:
199 °C. IR (KBr): ν 2930, 1575, 1426, 1286, 1164, 819, 768 cm-1
.
{1-[(2-Carboxymethyl)benzene]-3-[(4-methyl)benzene](tria-
zenido)palladium(I)}2 (6). Complex 6 was prepared in the same
manner as 5 using ligand 2 to obtain a reddish microcrystalline
solid that was first purified by column chromatography (florisil,
CH2Cl2). Next, the product crystallized by vapor diffusion of
pentane into a concentrated solution of the product in CH2Cl2 at
room temperature to give dark red crystals (43.8 mg, 0.058 mmol,
45%). mp: 233-235 °C. IR (KBr): ν 3014, 2852, 1642, 1557,
1375, 1151 cm-1. UV-vis (CH2Cl2, 2.9355 × 10-4 M): λ (ꢀ) 220
(4174), 282 (5008.7), 342 (13 256), 396 (13 186), 422 (13 042),
UV-vis (CH2Cl2, 7.375 × 10-4 M): λ (ꢀ) 258 (2154.19), 286
(2370.85), 334 (5580.71), 382 (5577.46), 446 (5510.21), 632 nm
(1263.84 L cm-1 mol-1). H NMR (CDCl3, 200 MHz, 25 °C): δ
1
7.75-7.65 (m, 6H, Ar), 7.56 (dd, J ) 7.8, 1.2 Hz, 2H, Ar), 7.40-
7.03 (m, 8H, Ar), 2.88 (s, 6H, -SCH3), 2.28 (s, 6H, Ar-CH3). 13C-
{1H} NMR (CDCl3, 50 MHz, 25 °C): δ 155.7 (CAr-N), 146.7
(CAr-N), 136.1 (CAr-H), 132.0 (CAr-H), 130.9 (2 CAr-H), 129.3
(CAr-S), 124.7 (CAr-CH3), 122.4 (CAr-H), 121.9 (CAr-H), 118.5
(2 CAr-H), 29.5 (-S-CH3), 20.9 (Ar-CH3). Anal. Found: C,
39.64; H, 3.18; N, 9.91; S, 6.97. Calcd for C29H30N6S2Cl4Pd2: C,
39.52; H, 3.43; N, 9.54; S, 7.28.
1
506 (3312), 598 nm (666 L cm-1 mol-1). H NMR (CDCl3, 200
MHz, 25 °C): δ 7.82 (dd, J ) 8.2, 1.6 Hz, 2H, Ar), 7.57 (dd, J )
8.6, 1.2 Hz, 2H, Ar), 7.35-7.25 (m, 6H, Ar), 7.07 (d, J ) 8.2 Hz,
4H, Ar), 6.89 (dt, J ) 8.2, 1.2 Hz, 2H, Ar), 3.62 (s, 6H, O-CH3),
2.32 (s, 6H, Ar-CH3). 13C{1H} NMR (CDCl3, 50 MHz, 25 °C):
δ 169.1 (CdO), 151.6 (CAr-N), 147.9 (CAr-N), 135.0 (CAr-Cd
O), 133.6 (CAr-H), 131.3 (2CAr-H), 128.1 (CAr-CH3), 122.7
(CAr-H), 121.9 (CAr-H), 119.6 (CAr-H), 116.2 (2CAr-H), 53.5
(-O-CH3), 20.9 (Ar-CH3). Anal. Found: C, 48.18; H, 3.62; N,
11.37. Calcd for C30H28N6O4Pd2: C, 48.08; H, 3.77; N, 11.21.
[1,3-Bis(2-Methoxy)benzene(triazenido)palladium(I)]2 (7). Com-
plex 7 was prepared in the same manner as 5, using ligand 3, to
Structural Determination. A summary of crystal data and
refinement parameters for the structural analyses is given in
Table 1.
Compounds 5 and 7. A deep-red prismlike crystal of complex
5 with approximate dimensions of 0.460 × 0.296 × 0.268 mm
and a red prismlike crystal of 7 with approximate dimensions of
0.278 × 0.232 × 0.086 mm were used for X-ray crystallographic
analysis. The X-ray intensity data were measured at 295 K on a
Bruker SMART CCD-based X-ray diffractometer system equipped
with a Mo-target X-ray tube (λ ) 0.71073 Å). The detector was
placed at a distance of 4.837 cm from the crystal.
6184 Inorganic Chemistry, Vol. 46, No. 15, 2007

1,3-Bis(aryl)triazenido Ligands
Chart 2. Structures of Ligands 1-4
A total of 1200 frames were collected with a scan width of 0.3°
in ω and an exposure time of 10 s/frame. The frames were integrated
with the Bruker SAINT Software package17 using a narrow-frame
integration algorithm. The integration of the data using a monoclinic
unit cell for 5 yielded a total of 20 653 reflections to a maximum
2θ angle of 65.04° (0.66 Å resolution), of which 5571 were
independent (Rint ) 5.65%). The integration of the data using a
tetragonal unit cell for 7 yielded a total of 33 610 reflections to a
maximum 2θ angle of 60.06° (0.70 Å resolution), of which 4183
were independent (Rint ) 5.14%).
The final cell constants for 5 and 7 are based on the refinement
of the XYZ-centroids of 6240 and 5098 reflections, respectively,
above 20σ(I). Analysis of the data showed negligible decay during
data collection; the intensities were corrected for Lorentz and
polarization factors, and an analytical absorption correction was
applied based on the face index.
The structures were solved and refined on F2 values by full-
matrix least-squares with anisotropic thermal parameters for non-
hydrogen atoms, using the Bruker SHELXTL (version 5.1) Software
Package.18 Positions of hydrogen atoms H atoms in these structures
were introduced at calculated positions as riding atoms, with C-H
) 0.96 (CH2) or 0.93 Å (aromatic) and Uiso(H) ) 1.2 Ueq(C) or
Uiso(H) ) 10.08 Å.2
Compounds 6 and 8. A deep-red prismlike crystal of complex
6 with approximate dimensions of 0.44 × 0.11 × 0.05 mm and a
reddish-black prismlike crystal of 8 with approximate dimensions
of 0.32 × 0.27 × 0.10 mm were used for X-ray crystallographic
analysis. X-ray intensity data were collected on a Rigaku Mercury
CCD area detector employing graphite-monochromated Mo KR
radiation (λ ) 0.71069 Å) at a temperature of 143 K. Preliminary
indexing was performed from a series of four 0.5° rotation images
with exposures of 30 s. A total of 830 (for 6) and 440 (for 8) rotation
images were collected with a crystal-to-detector distance of 36 mm,
2θ swing angles of -12° for 6 and -10° (for 8), a rotation width
of 0.5°, and exposures of 30 (6) and 10 s (8): scan 1 was a φ-scan
from 225 to 405° at ω ) 0° and ø ) 0° (for 6) and a φ-scan from
-90 to 90° at ω ) 0° and ø ) 0°; scan 2 was a φ-scan from 270
to 450° at ω ) 0° and ø ) -30° (for 6) and a ω-scan from -20
to 20° at ø ) -90° and φ ) 0-30° (for 8); scan 3 was an ω-scan
from -20 to 4° at ø) -90° and φ ) 315° (for 6); scan 4 was an
ω-scan from -20 to 11° at ø ) -90° and φ ) 135° (for 6). Rotation
images were processed using CrystalClear,19 producing a listing
of unaveraged F2 and σ(F2) values which were then passed to the
CrystalStructure20 program package for further processing and
structure solution on a Dell Pentium 111 computer. For 6, a total
of 8129 reflections were measured over the ranges of 5.46 e 2θ e
54.96°, -8 e h e 6, -13 e k e 10, -14 e 1 e 14, yielding 3063
unique reflections (Rint ) 0.0160). The intensity data were corrected
for Lorentz and polarization effects and for absorption using
REQAB21 (min and max transmission, 0.733 and 1.000). For 8,
subsequent inspection of the rotation images indicated that there
were a large number of diffraction spots that did not fit the
orientation matrix from CrystalClear. The crystal was found to be
twinned by a rotation of 2.4° about the normal to 5.9, 5.5-1 (it
can be surmised that the crystal was cracked or split into two
components or that there was a misalignment of the stacking of
crystal plates). Twin indexing and processing of twinned data was
performed by the TwinSolve22 module of CrystalClear. A total of
18 491 reflections were measured over the ranges of 5.02 e 2θ e
55.08°, -12 e h e 12, -12 e k e 20, -9 e l e 12, yielding
18 491 unique reflections (Rint ) 0.0000). The intensity data were
corrected for Lorentz and polarization effects and for absorption
using REQAB21 (min and max transmission, 0.688 and 1.000). The
structures were solved by direct methods (SIR97).23 Refinement
was by full-matrix least-squares based on F2 using SHELXL-97.24
All reflections were used during refinement (F2 values that were
experimentally negative were replaced by F2 ) O). For 6, the
2
weighting scheme used was W ) 1/[σ2(Fo ) + 0.0172P2
+
0.5506P], where P ) (Fo + 2Fc2)/3. Non-hydrogen atoms were
refined anisotropically, and hydrogen atoms were refined using a
“riding” model. Refinement converged to R1 ) 0.0190 and
wRr2)0.0464 for 2994 reflections for which F > 4σ(F) and R1 )
0.0196, wRr2 ) 0.0470, and GOF ) 1.097 for all 3063 unique,
nonzero reflections and 192 variables.25 The maximum ∆/σ in the
final cycle of least-squares was 0.005, and the two most prominent
2
peaks in the final difference Fourier were +0.396 and 0.656 e Å-3
.
2
For 8, the weighting scheme used was w ) 1/[σ2(Fo ) + 0.0512P2
+ 5.8696P], where P ) (Fo2 + 2Fc2)/3. Non-hydrogen atoms were
refined anisotropically, and hydrogen atoms were refined using a
“riding” model. Refinement converged to R1 ) 0.0424 and wR2 )
0.1083 for 17 763 reflections for which F > 4σ(F) and R1 ) 0.0462,
wRr2 ) 1129, and GOF ) 1.129 for all 18 491 unique, nonzero
reflections and 198 variables.25 The maximum ∆/σ in the final cycle
of least-squares was 0.001, and the two most prominent peaks in
the final difference Fourier were +0.788 and 0.849 e Å-3
.
Results and Discussion
Ligand Syntheses. Triazenes 1-4 (Chart 2) were syn-
thesized following modified literature procedures. Ligands
1 and 3 were obtained in one step by coupling of methyl
anthranilate and o-anisidine, respectively, in toluene using
isoamyl nitrite.11 Synthesis of triazenes 2 and 4 was
performed by diazotization of the corresponding function-
alized aniline with sodium nitrite, followed by coupling with
p-toluidine.12 The triazenes were isolated by crystallization
from 9:1 ethyl acetate/hexanes at -4 °C with yields in the
range of 34-93%.
(22) TwinSolve: Christer Swensson, MaxLab, Lund, Sweden, Private
communication.
(23) SIR97: Altomare, A.; Burla, M.; Camalli, M.; Cascarazo, G.;
Giacovazzo, A.; Guagliardi, A.; Moliterni, A.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115-119.
(17) Saint-plus, version 6.04; Bruker AXS Inc.: Madison, WI, 2000.
(18) Sheldrick, G. M. SHELXTL, version 6.10; Bruker AXS Inc.: Madison,
WI, 2000.
(19) CrystalClear; Rigaku Corp.: The Woodlands, TX, 1999.
(20) CrystalStructure: Crystal Structure Analysis Package; Rigaku
Corp.: The Woodlands, TX, 2002.
(24) Sheldrick, G. M. SHELXL-97: Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.
2
2
(25) R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2) {∑[w(Fo2 - Fc )2]/∑[w(Fo )2]}1/2
,
2
2
GOF){∑[w(Fo - Fc )2/(n - p)}1/2, where n ) the number of
(21) REQAB4: Jacobsen, R. A. Private communication, 1994.
reflections and p ) the number of parameters refined.
Inorganic Chemistry, Vol. 46, No. 15, 2007 6185

Nuricumbo-Escobar et al.
Synthesis of Palladium(I) Complexes. Palladium com-
plexes of 1-3 were prepared by combination of bis-
(acetonitrile)palladium(II) dichloride in acetonitrile with a
mixture of the corresponding triazenes and triethylamine to
obtain reddish microcrystalline compounds 5-7 (eq 1). The
products were isolated by filtration and purified by recrys-
tallization (5) or column chromatography on florisil in
dichloromethane, followed by crystallization (6, 7). The
palladium triazenido complexes were isolated as analytically
pure solids 5, 6, and 7 in 85, 45, and 51% yield, respectively.
We were surprised to find that elemental analyses of the
crystalline solids 5-7 were not consistent with simple
substitution of a chloride or a chloride and acetonitrile by
the triazenido ligand. Instead, the analyses were consistent
with palladium(I) bearing a single triazenido, as outlined in
eq 1.
Figure 1. ORTEP of 5. Bond distances and angles are given in Table 2.
cm-1.13 Compound 5 (KBr) exhibits two absorptions at 1713
and 1643 cm-1. From the IR spectrum of 5, we believe that
one of the carbonyl oxygens is coordinated to palladium and
the other is unbound. The IR spectrum of unbound monoester
2 (KBr) shows a single absorption for the carbonyl group at
1684 cm-1, which is shifted to 1642 cm-1 in compound 6
(KBr). This shift is indicative of coordination of the ester
carbonyl to palladium.
Structures of Pd(I) Complexes. X-ray quality crystals
of 5 were grown from dichloromethane by slow evaporation
of the solvent, while crystals of 6 and 7 formed upon vapor-
phase diffusion of pentane into concentrated solutions of the
complexes in dichloromethane. ORTEP diagrams for com-
plexes 5, 6, and 7 are illustrated in Figures 1, 2, and 3,
respectively. Crystallographic data and refinement parameters
are located in Table 1, and the bond distances and angles
for 5-7 are displayed in Table 2. The gross structural
features of 5-7 consist of two palladium centers bridged
by two triazenido ligands with one pendent Lewis basic ester
carbonyl oxygen (5, 6) or methoxy oxygen (7) coordinated
to each palladium center. The absence of counterions
indicates that the palladium(II) starting material has been
reduced to palladium(I) during the syntheses.
Palladium(I), which has the d9 configuration, is expected
to exhibit paramagnetic behavior. Compounds 5, 6, and 7,
however, are diamagnetic and amenable to NMR analysis.
1
The H and 13C{1H} NMR spectra of all three complexes
are indicative of a single-ligand environment. 1H resonances
are found in the range of 7.8-6.8 ppm for the aromatic
protons, 3.8-3.6 ppm for the methoxy groups in 5-7, and
2.3 ppm for the tolyl methyl protons in 6. A single 13C
resonance at 168.5 ppm was observed for the esters of 5,
which is virtually unchanged from that of the unbound ligand
(168.2 ppm). Similarly, the ester carbonyl resonance of 6
was located at 169.1 ppm, only slightly downfield from the
unbound ligand 2 (167.7 ppm). The equivalence of the two
ester substituents in 5 and methoxy groups in 7 on the NMR
time scale can be explained by rapid exchange of bound and
free carbonyl groups. Analogous behavior has been observed
for the [Cu(Ar-NNN-Ar)]2 and [Ag(Ar-NNN-Ar)]2 com-
plexes of ligand 1.14 On the basis of the NMR behavior, it
is assumed that the d9 Pd(I) centers are spin-coupled through
a Pd-Pd bond, as observed in other dinuclear Pd(I)
complexes.26
The positions of IR absorptions of pendent carbonyl groups
in 5 and 6 can provide insight into their interaction with
palladium. Interpretation of changes in ester νCO absorptions
of unbound 1 and 2 versus their adducts 5 and 6 is not
straightforward. First, the triazenes must be deprotonated to
bind to the metals in these complexes, which will cause a
change in the CdO stretching frequency. Second, each ligand
binds to two metal centers compared to a single proton in
the triazenes. The IR spectrum of unbound diester 1 (KBr)
shows absorptions for the carbonyl groups at 1714 and 1698
The Pd(I) structures are similar to those of the Cu(I) and
Ag(I) dimeric complexes [Cu(Ph-NNN-Ph)]2,27 [Cu(Ar-
NNN-Ar)]2, and [Ag(Ar-NNN-Ar)]2 (Ar
) o-C6H4-
COOCH3)14 and the related amidinato complexes [Ag(R-
NCPhN-R)]2 (R ) o-C6H4-COOCH3, o-C6H4-SCH3).28 In
these complexes, each ligand bridges two metal centers, as
observed in the structures of 5-7. Complexes 5-7 have
nearly planar bicyclic cores formed by the two N3 units and
the palladium centers (Figures 1-3). The trans nitrogens
(27) Brown, I. D.; Dunita, J. D. Acta Crystallogr. 1961, 14, 480-485.
(28) Archibald, S. J.; Alcock, N. W.; Busch, D. H.; Whitcomb, D. R. Inorg.
Chem. 1999, 38, 5571-5578.
(26) Lord, P.; Olmstead, M. M.; Balch, A. L. Angew. Chem., Int. Ed. 1999,
38, 2761-2763.
6186 Inorganic Chemistry, Vol. 46, No. 15, 2007

1,3-Bis(aryl)triazenido Ligands
Table 2. Bond Distances (Å) and Angles (deg) for Compounds 5-7
5
6
7
Pd(1)-Pd(1a)
Pd(1)-N(1)
Pd(1)-N(3a)
Pd(1)-O(1a)
Pd(1)-O(1)
C(15/14)-O(1)
C(2)-O(1)
2.4309(3)
2.0341(17)
2.0177(17)
2.1631(16)
2.4202(3)
2.0302(14)
2.0264(15)
2.1641(13)
2.4158(4)
2.0069(19)
2.024(2)
2.4464(17)
1.219(2)
1.217(2)
1.380(3)
1.398(3)
1.356(3)
1.420(3)
C(7)-O(1)
C(9)-O(2)
C(14)-O(2)
C(7)-O(3)
1.195(3)
1.286(2)
1.318(2)
N(1)-N(2)
N(2)-N(3)
1.289(2)
1.321(2)
1.303(2)
1.305(2)
N(1)-N(2)-N(3)
116.76(16)
173.95(7)
89.63(5)
121.72(13)
127.41(14)
116.05(14)
173.25(6)
89.39(4)
121.68(11)
125.66(12)
114.47(19)
173.61(7)
87.21(5)
N(3a)-Pd(1)-N(1)
N(3a)-Pd(1)-Pd(1a)
N(2)-N(3)-Pd(1a)
C(15/14)-O(1)-Pd(1a)
C(2)-O(1)-Pd(1)
N(3a)-Pd(1)-O(1a)
N(3a)-Pd(1)-O(1)
N(1)-Pd(1)-Pd(1a)
N(2)-N(1)-Pd(1)
N(1)-Pd(1)-O(1a)
N(1)-Pd(1)-O(1)
O(1a)-Pd(1)-Pd(1a)
O(1)-Pd(1)-Pd(1a)
125.01(15)
108.06(14)
88.33(6)
88.55(5)
114.37(7)
86.45(5)
126.82(15)
84.34(5)
127.54(13)
97.70(6)
84.68(4)
127.70(12)
97.56(5)
Figure 2. ORTEP of 6. Bond distances and angles are given in Table 2.
71.89(7)
177.88(4)
175.95(4)
151.12(5)
Table 3. Pd-Pd Bond Distances in Some Bridged Dinuclear Pd(I)
Complexes
dPd-Pd
complex
(Å)
ref
Pd2(µ-Me2PCH2PMe2)2Br2
2.603(1)
2.6597(4)
2.617(2)
2.644(2)
2.670(2)
2.699(5)
2.701(3)
34
35
36
37
38
39
40
[(i-Pr)3Pd]2(µ-allyl)(µ-CCH)
[Pd2(µ-Ph2P(CH2)3PPh2)2(2,4,6-Me3C6H2NC)2]2+
Pd2(µ-Ph2PCH2PPh2)2(SnCl3)Cl
Pd2(µ-Ph2PCH2PPh2)2(C6Cl5)2
Pd2(µ-Ph2PCH2PPh2)2Br2
[Pd2{Ph2P(CH2)3PPh2}2]2+
similar at 2.0341(17) and 2.0177(17) Å in 5, 2.0302(14) and
2.026(2) Å in 6, and 2.0069(19) and 2.024(2) in 7.
The Pd-Pd distances of 2.4309(3) Å in 5, 2.4202(3) Å in
6, and 2.4158(4) in 7 are consistent with Pd-Pd bonds. These
distances are considerably shorter than most of the Pd-Pd
bonds reported for dinuclear Pd(I)-Pd(I) complexes (see
Table 3 for examples).29-36 A comparison of the M-M
distances in dimeric complexes prepared from ligand 1 is
informative. The metal-metal distances in the Pd(I) [2.4309-
(3) Å] and Cu(I) [2.439(12) Å] dimers are in close contact;
however, in the Ag(I) dimer, the Ag-Ag distances is quite
long [2.704(2) Å].14 This observation leads us to conclude
Figure 3. ORTEP of 7. Bond distances and angles are given in Table 2.
exhibit N-Pd-N bond angles of 173.95, 173.25, and
173.61° in 5-7, respectively, indicating a small distortion
from planarity of the Pd-triazenido framework resulting from
the coordination of the ester carbonyl (5 and 6) or methoxy
groups (7). Like the Cu(I) and Ag(I) analogs, the coordinated
carbonyl oxygens in 5 and 6 lie slightly above and below
the planar core with Pd-Pd-O bond angles of 177.88 and
175.95°, respectively. In 7, a greater deviation from planarity
with the Pd-triazenido core is observed with a Pd-Pd-O
angle of 151.12°. The difference is attributed to the reduced
size of the metallocycle. The C-O distances of the coordi-
nated carbonyl oxygens in 5 and 6 are slightly elongated
[1.2119(16) and 1.217(13) Å, respectively] with respect to
the carbonyl group in the unbound ligand 1 [1.183(6) Å].13
The Pd-N(1) and Pd-N(3) bond lengths in 5-7 are very
(29) Kulberg, M.; Lemke, L. F. R.; Powel, D. R.; Kubiak, C. P. Inorg.
Chem. 1985, 24, 3589-3593.
(30) Tanase, T.; Kawahara, K.; Ukaji, H.; Kobayashi, K.; Yamazaki, H.;
Yamamoto, Y. Inorg. Chem. 1993, 32, 3682-3688.
(31) Olmstead, M. M.; Benner, L. S.; Hope, H.; Balsh, A. L. Inorg. Chim.
Acta 1979, 32, 193-198.
(32) Espinet, P.; Fornies, J.; Fortun˜o, C.; Hidalgo, G.; Mart´ınez, F.; Tomas,
M.; Welch, A. J. J. Organomet. Chem. 1986, 317, 105-119.
(33) Holloway, R. G.; Penfold, B. R.; Colton, R.; McCornick, M. J. J.
Chem. Soc., Chem. Commun. 1976, 485-486.
(34) Budzelaar, P. H. M.; van Leeuwen, P. W. N. M.; Roobeek, C. F.;
Orpen, A. G. Organometallics 1992, 11, 23-25.
(35) Krause, J.; Goddard, R.; Mynott, R.; Porschke, K.-R. Organometallics
2001, 20, 1992-1999.
(36) Lu, C. C.; Peters, J. C. J. Am. Chem. Soc. 2002, 124, 5272-5273.
Inorganic Chemistry, Vol. 46, No. 15, 2007 6187

Nuricumbo-Escobar et al.
that the triazenide ligands are not solely responsible for the
short M-M contacts observed in the Pd(I) complexes
reported herein. It is noteworthy that the Pd(I) oxidation state
is rare, whereas Cu(I) and Ag(I) complexes are common.
We hypothesize that the triazenido ligands derived from 1-3
facilitate the reduction of the Pd(II) to Pd(I) and stabilize
the Pd(I) oxidation state.
During the course of the synthesis of the dimeric Pd(I)
complexes outlined above, the Pd(II) is reduced by one
electron. At this time, we do not have experimental data
concerning this process. It is well-known, however, that the
reduction of Pd(II) starting materials to Pd(0) is common in
cross-coupling reactions initiated with Pd(II).37 Trzeciak,
Ciunik, and Ziolkowski38 have reported that tertiary amines
can reduce Pd(II) to Pd(0) in the presence of trace amounts
of water with formation of the corresponding secondary
amine and aldehyde oxidation products (eq 2). The mech-
anism is proposed to begin with amine coordination to Pd-
(II), followed by C-H activation. The observation of
aldehyde formation and labeling experiments support their
proposed mechanism.
Figure 4. ORTEP of 8‚CH2Cl2. Bond distances and angles are given in
Table 4. CH2Cl2 is omitted for clarity.
etonitrile with triazene 4 and triethylamine resulted in the
formation of brown microcrystalline 8. Filtration of 8 was
followed by recrystallization to provide analytically pure
amber crystals in 59% yield (eq 3). Unlike 5-7, elemental
analysis of 8 was not consistent with formation of reduced
Pd(I) dimers. The analysis was in line with our initial
expectations for the substitution product, [(triazenido)PdCl]2.
The 1H and 13C{1H} NMR spectra of 8 indicated a
In a detailed study of a related process, Lu and Peters
found that a Pd(II) complex bearing an anionic bis(phos-
phine) ligand undergoes reduction to Pd(I) in approximately
70% yield when exposed to 3 equiv of tertiary amine
(Scheme 1). In THF, however, the cyclometallation product
is observed quantitatively when the same Pd(II) complex is
exposed to a large excess of tertiary amine. In this case, a
mechanism involving binding of the amine, â-hydride
elimination, and deprotonation of the resulting palladium
hydride by free amine is favored.39 The cyclometalated
amine, of course, has a second resonance form in which the
palladium is formally Pd(0). Dissociation of the iminium
would lead to Pd(0). Iminium hydrolysis would generate a
secondary amine and an aldehyde, as observed in eq 2.
symmetric complex with a single triazenido ligand environ-
1
ment. In the H NMR, resonances for the aromatic protons
were found between 7.0 and 7.7 ppm. The methyl mercapto
protons resonated at 2.88 ppm, and a signal for the tolyl
methyl protons was observed at 2.28 ppm. A shift from 2.40
ppm for the S-Me group in the unbound ligand 4 to 2.88
ppm for the S-Me in 8 suggests that the sulfur is coordinated
to palladium. The IR spectrum (KBr) of 8 exhibits an
absorption at 1575 cm-1 assigned to the N-N-N linkage,
which is shifted to shorter wavelength compared to that of
the free ligand (1522 cm-1).
Scheme 1. Reactions of a Pd(II) Complex with Amine in Different
Solvents
Structure of 8. X-ray quality crystals of 8 were grown
by vapor-phase diffusion of pentane into a concentrated
solution of the complex in dichloromethane. The structure
of 8 was determined, and an ORTEP diagram is illustrated
in Figure 4. Bond distances and angles are displayed in Table
4. The complex cocrystallizes with one molecule of CH2-
Cl2, which is not included in Figure 4. The structure consists
of a dimeric palladium complex with two bridging tridentate
triazenide ligands. The S-Me of each ligand is bonded to a
palladium, and the remaining coordination sites are occupied
by chlorides.
Synthesis of Palladium(II) Triazenido Complex. Com-
bination of bis(acetonitrile)palladium(II) dichloride in ac-
(37) Beletskaya, I. P.; Cheprakov, A. V. Chem. ReV. 2000, 100, 3009-
3066.
(38) Trzeciak, A. M.; Ziokowski, J. J.; Monatshefte, F. Organometallics
2002, 21, 132-137.
(39) Lu, C. C.; Peters, J. C. J. Am. Chem. Soc. 2004, 126, 15818-15832.
The central eight-membered core formed by the two N3
units and the palladium centers are found in an “open book”
6188 Inorganic Chemistry, Vol. 46, No. 15, 2007

1,3-Bis(aryl)triazenido Ligands
Table 4. Bond Distances (Å) and Angles (deg) for 8‚CH2Cl2
We propose that the electron-donating S-Me group of 8
results in a more electron-rich palladium center. The S-Me
group increases the stability of the complex toward reduction
more than the weakly donating ester carbonyl groups in 5
and 6 or the methoxy group in 7.
Pd(1)-Pd(1a)
Pd(1)-N(1)
Pd(1)-N(3a)
N(1)-N(2)
N(2)-N(3)
Pd(1)-S(1)
Pd(1)-Cl(1)
2.9077(4)
2.010(2)
2.087(2)
1.313(3)
1.293(3)
2.2707(7)
2.3108(7)
Concluding Remarks
N(3)-N(2)-N(1)
114.3(2)
93.70(9)
84.26(7)
89.29(7)
92.13(3)
113.16(2)
76.24(7)
75.44(7)
108.32(2)
113.16(2)
Reported herein are the structures of three novel Pd(I)
dimers (5-7) supported by 1,3-bis(aryl) triazenido ligands
bearing Lewis basic groups in the ortho-positions. The Lewis
basic ester and methoxy groups coordinate to the palladium-
(I) centers. These ligands appear to facilitate reduction of
Pd(II) to the uncommon Pd(I) and to stabilize metals in the
+1 oxidation state. Previous studies from our group have
shown that ligand 1 forms similar complexes with Cu(I) and
Ag(I).
N(1)-Pd(1)-N(3a)
N(1)-Pd(1)-S(1)
N(3a)-Pd(1)-Cl(1)
S(1)-Pd(1)-Cl(1)
S(1)-Pd(1)-Pd(1a)
N(1)-Pd(1)-Pd(1#1)
N(3a)-Pd(1)-Pd(1a)
Cl(1)-Pd(1)-Pd(1a)
S(1)-Pd(1)-Pd(1a)
geometry, which has been previously observed in some
palladium(II)-triazenido complexes.15,40,41 The geometry
about each palladium is only slightly distorted from idealized
square planar, as seen in the bond angles around palladium
(Table 4). The angle N(1)-N(2)-N(3) of the triazenide
ligand is 114.3°, and the Pd-N(1) and Pd-N(3) bond lengths
are 2.010(2) and 2.087(2) Å. The Pd-N distances in this
dimer can be compared to the Pd-N lengths in [Pd(C6F5)-
(CN-t-Bu)(µ-Ph-NNN-Ph)]2 [2.073(4) and 2.098(4) Å],35 as
well as those of the amidinate dimer Pd2Cl2{µ-PhNC(Me)-
NPh}2(PMe2Ph)2 [2.097(5) and 2.059(5) Å].36 The Pd-S
distance of 2.2707(7) Å in 8 is within the range found in
other mercapto-palladium complexes (2.2716-2.2661 Å).42
The Pd-Pd distance in 8 is 2.9077(4) Å. This distance is
comparable to that found in other triazenido complexes of
Pd(II): [Pd(C6F5)(CN-t-Bu)(µ-PhNNNPh)]2 [2.9007(8) Å],36
[Pd(C6H4NdNC6H5)(µ-p-tol-NNN-p-tol)]2 [2.895(2) Å],43
and the related amidinate complex [Pd2Cl2{µ-Ph-NC-
(Me)N-Ph}2(PMe2Ph)2] [2.9014(2) Å].36 Although a shorter
Pd-Pd distance, 2.747(1) Å, has been reported for [Pd2(µ-
Ar-NNN-Ar)2]2(µ-Cl)4,44 both are nonbonding, as expected
for 16-electron square-planar Pd(II) complexes.
In contrast to reactions with triazenes 1-3, the reaction
of ligand 4, containing a pendent S-Me group, with Cl2-
Pd(NCCH3)2 does not yield reduced Pd(I), but rather a
dimeric Pd(II) with bridging tridentate ligands. We speculate
that the greater donating ability of the S-Me group, with
respect to that of the CO2Me and OMe groups, results in a
more electron-rich palladium center that is more stable to
reduction than complexes prepared from ligands 1-3. These
studies illustrate how pendent Lewis basic groups of the 1,3-
bis(aryl) triazenido ligands can enable the synthesis of novel
palladium complexes in the rare Pd(I) oxidation state. The
next step in these studies will be to determine how our
ligands impact the reactivity of the resulting Pd(I) complexes.
Acknowledgment. This work was supported by Consejo
Nacional de Ciencia y Tecnolog´ıa (CONACyT) Grant
36435-E and Consejo del Sistema Nacional de Educacio´n
Tecnolo´gica (COSNET) Grant 486-02-P. The authors are
indebted to Rube´n A. Toscano of Instituto de Qu´ımica,
UNAM, and Patrick J. Carroll of University of Pennsylvania
for the X-ray analysis. Analytical support from Jesu´s Pe´rez-
Torrente at Universidad de Zaragoza and Ignacio Rivero at
Instituto Tecnolo´gico de Tijuana is gratefully acknowledged.
J.J.N.-E., G.R.-M, and C.C.-A. thank CONACyT for gradu-
ate fellowships. P.J.W. thanks the NSF and NIH for support.
(40) Ruiz, J.; Javier Lo´pez, J. F.; Rodr´ıguez, V.; Pe´rez, J; Ram´ırez de
Arellano, M. C.; Lo´pez, G. J. Chem. Soc., Dalton Trans. 2001, 2683-
2689.
(41) Singhal, A.; Jain, V. K.; Nethaji, M.; Samuelson, A. G.; Jayaprakash,
D.; Butcher, R. J. Polyhedron 1998, 17, 3531-3540.
(42) Grotjahn, D. B.; Combs, D.; Van, S.; Aguirre, G.; Ortega, F. Inorg.
Chem. 2000, 39, 2080-2086.
(43) Garc´ıa Herbosa, G.; Connelly, N. G.; Mun˜oz, A.; Cuevas, J. V.; Orpen,
A. G.; Politzer, S. D. Organometallics 2001, 20, 3223-3229.
(44) Cuevas, J. V.; Garc´ıa-Herbosa, G.; Mun˜oz, A.; Hickman, S. W.; Orpen,
A. G.; Connelly, N. G. J. Chem. Soc., Dalton Trans. 1995, 4127-
4128.
Supporting Information Available: Structural data for 5-8.
This material is available free of charge via the Internet at
http://pubs.acs.org.
IC700516P
Inorganic Chemistry, Vol. 46, No. 15, 2007 6189