Crescent-shaped rhodium(I) complexes with bis(o-carboxymethylphenyl) triazenide

Article abstract of DOI:10.1021/ic049691g

Reaction of [{Rh(μ-Cl)(CO)₂}₂] with the triazene ArNNNHAr (Ar = o-CO₂MeC₆H₄) produced the mononuclear complex [RhCl(ArNNNHAr)(CO)₂] (1). Complex 1 reacted with KOH in methanol to give the dinuclear compound [{Rh(μ-ArNNNAr)(CO) ₂}₂] (2), which showed a "μ-(1κN ¹,2κN³)-ArNNNAr" coordination mode for both bridging ligands. The dinuclear complex [{Rh(μ-ArNNNAr)(CO)₂} ₂] (2) easily undergoes redistribution reactions in which the eight-membered "Rh₂(NNN)₂" core is broken. Thus, reaction of 2 with the anionic complex (NHEt₃)[RhCl ₂(CO)₂] gave the single-bridged complex (NHEt ₃)[Rh₂(μ-ArNNNAr)Cl₂(CO)₄] (4), while the trinuclear complexes [Rh₃(μ-ArNNNAr)-(μ-Cl)(μ-CO) Cl(CO)₄] (5) and [Rh₃(μ-ArNNNAr)₂(μ-Cl) (μ-CO)(CO)₃] (6) were isolated by addition of the neutral compound [{Rh(μ-Cl)(CO)₂}₂] to 2, depending on the molar ratio employed. The formation of 5 and 6 involved the loss of carbonyl groups and the coordination of the oxygen atoms of the CO₂Me groups. The structures of 4, 5, and 6 have been determined by X-ray diffraction methods, which show the ability of bis(o-carboxymethylphenyl)-triazenide to act as bi-, tri-, and tetra-dentate ligand-spanning dinuclear moieties in trinuclear complexes.

Full text of DOI:10.1021/ic049691g

Inorg. Chem. 2004, 43, 4719−4726
Crescent-Shaped Rhodium(I) Complexes with
Bis(o-carboxymethylphenyl)triazenide
,†
Cristina Tejel,* Miguel A. Ciriano,† Gustavo R´ıos-Moreno,† Isabel T. Dobrinovitch,†
Fernando J. Lahoz,† Luis A. Oro,† and Miguel Parra-Hake‡
Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
UniVersidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain, and Centro de Graduados e
InVestigacio´n, Instituto Tecnolo´gico de Tijuana, BlVd. Industrial S/N. Mesa de Otay,
22510 Tijuana, Baja California, Me´xico
Received March 10, 2004
Reaction of [{Rh(µ-Cl)(CO)2}2] with the triazene ArNNNHAr (Ar ) o-CO MeC H ) produced the mononuclear
2
6 4
complex [RhCl(ArNNNHAr)(CO)2] (1). Complex 1 reacted with KOH in methanol to give the dinuclear compound
1
3
[{Rh(µ-ArNNNAr)(CO)2}2] (2), which showed a “µ-(1κN ,2κN )-ArNNNAr” coordination mode for both bridging ligands.
The dinuclear complex [{Rh(µ-ArNNNAr)(CO)2}2] (2) easily undergoes redistribution reactions in which the eight-
membered “Rh2(NNN)2” core is broken. Thus, reaction of 2 with the anionic complex (NHEt3)[RhCl2(CO)2] gave the
single-bridged complex (NHEt3)[Rh2(µ-ArNNNAr)Cl2(CO)4] (4), while the trinuclear complexes [Rh3(µ-ArNNNAr)-
(µ-Cl)(µ-CO)Cl(CO)4] (5) and [Rh3(µ-ArNNNAr)2(µ-Cl)(µ-CO)(CO)3] (6) were isolated by addition of the neutral
compound [{Rh(µ-Cl)(CO)2}2] to 2, depending on the molar ratio employed. The formation of 5 and 6 involved the
loss of carbonyl groups and the coordination of the oxygen atoms of the CO Me groups. The structures of 4, 5,
2
and 6 have been determined by X-ray diffraction methods, which show the ability of bis(o-carboxymethylphenyl)-
triazenide to act as bi-, tri-, and tetra-dentate ligand-spanning dinuclear moieties in trinuclear complexes.
Introduction
chemistry of Rh and Ir with these ligands concerns the
oxidation state I. Although mononuclear complexes of these
d8 ions with terminal5 and chelating6 triazenide ligands are
known, the triazenide anions typically adopt the bridging
mode observed in homodinuclear7-9 and heterodinuclear Rh/
Ir,10 Rh/Hg and Ir/ Hg11 “face-to-face” compounds. The high
stability of the eight-membered “M2(µ-ArNNNAr)2” core in
the homodinuclear complexes has allowed the development
of a rich redox-chemistry involving a combination of
theoretical studies with electrochemistry and ESR spectros-
copy.12 For example, the “face-to-face” dirhodium structure
remained intact after one electron oxidation reaction13,14 to
the corresponding paramagnetic monocations (formally M(I)/
The bis(aryl)triazenide anions (ArNNNAr)- are “short-
bite” ligands understudied when compared with their related
diphosphines, 2-pyridylphosphines,1 and anionic N-C-X
(X ) N, O, S) type ligands,2 although a number of studies
on complexes of these ligands with rhodium and iridium in
different oxidation states have been reported. Derivatives of
Rh and Ir in the oxidation state III are the homoleptic
mononuclear compounds [M(ArNNNAr)3], with the three
ligands acting in an N,N′-chelating mode,3 while the reported
complexes of Rh in the oxidation state II are dinuclear with
a “lantern-type” structure with four triazenide bridges, as
found in [Rh2(µ-ArNNNAr)4].4 However, most of the
(5) Immirzi, A.; Porzio, W.; Bombieri, G.; Toniolo, L. J. Chem. Soc.,
Dalton Trans. 1980, 1098.
(6) Carriedo, C.; Connelly, N. G.; Hettrich, R.; Orpen, A. G.; White, J.
M. J. Chem. Soc., Dalton Trans. 1989, 745.
(7) Knoth, W. H. Inorg. Chem. 1973, 12, 38.
(8) Connelly, N. G.; Daykin, H.; Demidowicz, Z. J. Chem. Soc., Dalton
Trans. 1978, 1532.
(9) Connelly, N. G.; Garc´ıa, G. J. Chem. Soc., Dalton Trans. 1987, 2737.
(10) Connelly, N. G.; Hayward, O. D.; Klangsinsirikul, P.; Orpen, A. G.;
Rieger, P. H. Chem. Commun. 2000, 963.
(11) Van Vliet, P. I.; Kokkes, M.; Van Koten, G.; Vrieze, K. J. Organomet.
Chem. 1980, 187, 413.
* To whom correspondence should be addressed. E-mail: ctejel@
posta.unizar.es. Fax: (+34) 976-761187.
† Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales
de Arago´n, Universidad de Zaragoza-CSIC.
‡ Centro de Graduados e Investigacio´n, Instituto Tecnolo´gico de Tijuana.
(1) Zhang, Z.-Z.; Cheng, H. Coord. Chem. ReV. 1996, 147, 1.
(2) Oro, L. A.; Ciriano, M. A.; Pe´rez-Torrente, J. J.; Villarroya, B. E.
Coord. Chem. ReV. 1999, 195, 941.
(3) Colson, S. F.; Robinson, S. D. Polyhedron 1990, 9, 1737.
(4) Hursthouse, M. B.; Mazid, M. A.; Clark, T.; Robinson, D. Polyhedron
1993, 12, 563.
10.1021/ic049691g CCC: $27.50 © 2004 American Chemical Society
Published on Web 06/24/2004
Inorganic Chemistry, Vol. 43, No. 15, 2004 4719

Tejel et al.
M(II) complexes), and a recent study15 on dinuclear com-
plexes with a family of triazenide ligands of the type (p-
XC6H4)NNN(p-X′C6H4) showed the marked influence of the
X and X′ groups on the oxidation potential Eo′. Moreover,
the geometrically asymmetric triazenido-bridged complex
[(CO)2Rh(µ-ArNNNAr)2Rh(bipy)]16 was found to be a
precursor to a wide range of redox-active species,17 allowing
the observation of processes such as the redox-isomerization
of a triazenide bridge “µ-(1κN1,2κN3)-ArNNNAr” into “µ-
(1κN1,1:2κN3)-ArNNNAr”18 and the equilibrium between the
cores “Rh(II)(µ-ArNNNAr)2Rh(II)(CO)” and “Rh(III)-
(µ-ArNNNAr)2(µ-CO)Rh(III)”.19,20 In addition, the triply
bridged paramagnetic Rh(I)/Rh(II) complex [Rh2(µ-
ArNNNAr)3(CO)2] has been recently reported.21 A notewor-
thy point is that the bis(aryl)triazenide ligands involved on
the Rh and Ir chemistry overviewed here are the simplest
PhNNNPh- anion and its para-substituted derivatives.
The incorporation of different groups (X) at the ortho
position of the aryl ring of the bis(aryl)triazenide ligand with
donor properties could produce a markedly different coor-
dination chemistry. For example, these functionalized aryl-
triazenides could span a dinuclear unit to form cavity shaped
ligands, as reported for 2,7-bis(2′-pyridyl)-1,8-naphthyri-
dine.22,23 Moreover, a hemilabile behavior could be observed
if the X groups were poorly coordinating donors toward soft
metal centers, such as the oxygen from an ester group.
Therefore, it seemed to us that the scarcely studied bis-
(o-carboxymethylphenyl)triazene24 would be a useful ligand
to test the above-mentioned properties with rhodium com-
plexes, and we report here our results on this topic.
were dried and distilled under argon before use by standard
methods. Carbon, hydrogen, and nitrogen analyses were performed
with a Perkin-Elmer 2400 microanalyzer. IR spectra were recorded
with a Nicolet 550 spectrophotometer. Mass spectra were recorded
in a VG Autospec double-focusing mass spectrometer operating in
the FAB+ mode. Ions were produced with the standard Cs+ gun at
1
ca. 30 kV, 3-nitrobenzyl alcohol (NBA) was used as matrix. H
and 13C{1H} NMR spectra were recorded on a Bruker ARX 300
and on a Varian UNITY 300 spectrometers operating at 300.13
and 299.95 MHz for 1H, respectively. Chemical shifts are reported
in parts per million and referenced to SiMe4 using the residual signal
of the deuterated solvent as reference. Conductivities were measured
in acetone solutions using a Philips PW 9501/01 conductimeter.
Synthesis of the Complexes. [RhCl(ArNNNHAr)(CO)2] (1).
A saturated solution of ArNNNHAr (163.0 mg, 0.52 mmol) in
diethyl ether (3 mL) was added dropwise to a solution of [{Rh(µ-
Cl)(CO)2}2] (101.0 mg, 0.26 mmol) in hexane (15 mL). A yellow
microcrystalline solid precipitated almost immediately. The suspen-
sion was concentrated to ca. 5 mL and the solution was decanted.
The solid was washed with hexane (5 mL) and vacuum-dried.
Yield: 216 mg (82%). Anal. Calcd for C18H15N3ClO6Rh: C, 42.58;
H, 2.98; N, 8.28. Found: C, 42.65; H, 3.14; N, 8.39. IR (KBr,
cm-1): ν(CO) 2089 (s), 2025 (s); ν(CdO) 1721 (s), 1702 (m). 1H
NMR (-73 °C, CD2Cl2) δ: 14.36 (s, 1H, NH); 8.09 (d, JHH ) 7.9
Hz, 1H), 8.07 (d, JHH ) 7.9 Hz, 1H), 7.76 (d, JHH ) 7.5 Hz,
1H), 7.63 (t, JHH ) 7.7 Hz, 1H), 7.56 (m, 2H), 7.49 (t, JHH )
7.7 Hz, 1H) and 7.26 (td, JHH ) 8.1, 2.1 Hz, 1H) (C6H4); 4.00 (s,
3H) and 3.63 (s, 3H) (CO2Me). 13C{1H} NMR (-73 °C, CD2Cl2)
δ: 183.9 (d, JCRh ) 67 Hz) and 179.2 (d, JCRh ) 73 Hz) (Rh-
CO); 168.3 and 168.2 (CO2Me); 147.6, 141.0, 135.9, 132.8, 131.9,
131.2, 129.4, 126.8, 126.0, 125.6, 115.4 and 114.8 (C6H4); 54.0
and 53.5 (CO2Me). MS (FAB+, CH2Cl2, m/z): 472, 100% (M+
Cl), 444, 45% (M+ - Cl - CO).
-
Experimental Section
[{Rh(µ-ArNNNAr)(CO)2}2] (2). To a solution of [RhCl-
(ArNNNHAr)(CO)2] (1) (264.0 mg, 0.52 mmol) in diethyl ether
(10 mL) was added dropwise a solution of KOH in methanol (0.52
mmol in 2.0 mL). The initial yellow solution turned purple
immediately. The solution was stirred for 10 min and evaporated
to dryness. The residue was extracted with several portions of
hexane (10 mL), filtered over Celite, and evaporated to dryness.
The purple microcrystalline material was vacuum-dried. Yield: 218
mg (89%). Anal. Calcd for C36H28N6O12Rh2: C, 45.88; H, 2.99; N,
8.92. Found: C, 45.76; H, 3.11; N, 8.93. IR (hexane, cm-1): ν-
Starting Materials and Physical Methods. All reactions were
carried out under argon using standard Schlenk techniques. The
compounds [{Rh(µ-Cl)(CO)2}2]25 and bis(o-carboxymethylphenyl)-
triazene26 were prepared according to literature methods. Solvents
(12) Boyd, D. C.; Connelly, N. G.; Garc´ıa Herbosa, G.; Hill, M. G.; Mann,
K. R.; Mealli, C.; Orpen, A. G.; Richardson, K. E.; Rieger, P. H. Inorg.
Chem. 1994, 33, 960.
(13) Connelly, N. G.; Finn, C. J.; Freeman, M. J.; Orpen, A. G.; Stirling,
J. J. Chem. Soc., Chem. Commun. 1984, 1025.
(14) Connelly, N. G.; Garc´ıa, G.; Gilbert, M.; Stirling, J. S. J. Chem. Soc.,
Dalton Trans. 1987, 1403.
(15) Connelly, N. G.; Davis, P. R. G.; Harry, E. E.; Klangsinsirikul, P.;
Venter, M. J. Chem. Soc., Dalton Trans. 2000, 2273.
(16) Connelly, N. G.; Garc´ıa, G. J. Chem. Soc., Chem. Commun. 1987,
246.
(17) Brauns, T.; Carriedo, C.; Goekayne, J. S.; Connelly, N. G.; Garc´ıa-
Herbosa, G.; Orpen, A. G. J. Chem. Soc., Dalton Trans. 1989, 2049.
(18) Connelly, N. G.; Hopkins, P. M.; Orpen, A. G.; Rosair, G. M.; Viguri,
F. J. Chem. Soc., Dalton Trans. 1992, 2907.
(19) Connelly, N. G.; Einig, T.; Garc´ıa Herbosa, G.; Hopkins, P. M.; Mealli,
C.; Orpen, A. G.; Rosair, G. M. J. Chem. Soc., Chem. Commun. 1992,
143.
(20) Connelly, N. G.; Einig, T.; Garc´ıa Herbosa, G.; Hopkins, P. M.; Mealli,
C.; Orpen, A. G.; Rosair, G. M.; Viguri, F. J. Chem. Soc., Dalton
Trans. 1994, 2025.
(21) Connelly, N. G.; Hayward, O. D.; Klangsinsirikul, P.; Orpen, A. G.
J. Chem. Soc., Dalton Trans. 2002, 305.
1
(CO) 2094 (s), 2067 (m), 2031 (s); ν(CdO) 1735 (s). H NMR
(25 °C, C6D6) δ: 7.80 (d, JHH ) 8.1 Hz, 4H), 7.50 (d, JHH ) 7.7
Hz, 4H), 7.00 (t, JHH ) 7.7 Hz, 4H) and 6.76 (t, JHH ) 7.5 Hz,
4H) (C6H4); 3.29 (s, 12H) (CO2Me). 13C{1H} NMR (25 °C, C6D6)
δ: 184.7 (d, JCRh ) 67 Hz) (Rh-CO); 167.8 (CO2Me); 150.5,
130.9, 130.3, 127.2, 127.0 and 125.6 (C6H4); 51.6 (CO2Me). MS
(FAB+, CH2Cl2, m/z): 886, 10% (M+ - 2CO), 858, 100% (M+
-
3CO).
(NHEt3)[RhCl2(CO)2] (3). Solid NHEt3Cl (71.5 mg, 0.52 mmol)
was added to a solution of [{Rh(µ-Cl)(CO)2}2] (101.0 mg, 0.26
mmol) in diethyl ether (5 mL) to give a pale yellow solution in 10
min. The solution was evaporated to dryness, and the yellow residue
was washed with hexane (2 × 5 mL) and vacuum-dried. Yield:
155 mg (90%). Anal. Calcd for C8H16NCl2O2Rh: C, 28.94; H, 4.86;
N, 4.22. Found: C, 29.12; H, 5.12; N, 4.37. IR (diethyl ether, cm-1):
ν(CO) 2073 (s), 1999 (s). 1H NMR (-73 °C, CD2Cl2) δ: 7.82 (br
s, 1H, NH); 3.12 (m, 6H, CH2); 1.25 (t, JHH ) 7.2 Hz, 9H, CH3).
(22) Campos-Ferna´ndez, C. S.; Thomson, L. M.; Gala´n-Mascaro´s, J. R.;
Ouyang, X.; Dunbar, K. R. Inorg. Chem. 2002, 41, 1523.
(23) Tikkanen, W. R.; Binamira-Soriaga, E.; Kaska, W. C.; Ford, P. C.
Inorg. Chem. 1983, 22, 1147.
(24) R´ıos-Moreno, G.; Aguirre, G.; Parra-Hake, M.; Walsh, P. J. Polyhedron
2003, 22, 563.
(25) McCleverty, J. A.; Wilkinson, G. Inorg. Synth. 1966, 8, 211.
(26) Vernin, G.; Siv, C.; Metzger, Y. J. Synthesis 1977, 10, 691.
4720 Inorganic Chemistry, Vol. 43, No. 15, 2004

Crescent-Shaped Rhodium(I) Complexes
Table 1. Crystal Data and Refinement Parameters for Complexes 4, 5, and 6
4
5
6
empirical formula
fw
C26H30Cl2N4O8Rh2
803.26
C21H14Cl2N3O9Rh3
831.98
C36H28ClN6O12Rh3
1080.82
space group
a, Å
b, Å
P21/c (No. 14)
19.5308(13)
9.9136(7)
33.023(2)
90.0
98.3400(10)
90.0
6326.3(7)/8
1.687
P1h (No. 2)
P1h (No. 2)
9.5760(6)
9.0715(7)
9.7734(6)
11.2733(9)
20.0489(16)
84.2820(10)
83.1200(10)
68.8380(10)
1894.8(3)/2
1.894
c, Å
14.6622(9)
94.9420(10)
92.9820(10)
108.7770(10)
1289.74(14)/2
2.142
R, deg
â, deg
γ, deg
V, Å3/Z
D
calcd, g‚cm-3
µ, mm-1
1.264
2.160
1.434
no data/restraints/params
GOF (all data)a
R1(F)
11172/0/769
1.033
0.0492 (7556 reflns)
5997/0/357
0.973
0.0303 (4941 reflns)
8662/0/550
1.024
0.0463 (6752 reflns)
(only for F2 > 2σ(F2))b
wR2(F2) (all data)c
0.1102
0.0561
0.1019
2
a GOF ) (∑[w(Fo2 - Fc )2]/(n - p))1/2, where n and p are the number of data and parameters. b R1(F) ) ∑||Fo| - |Fc||/∑|Fo| only for observed reflections
2
2
2
2
2
2
(in parentheses). c wR2(F2) ) (∑[w(Fo - Fc )2]/∑[w(Fo )2])1/2 where w ) 1/[σ2(Fo ) + (aP)2] and P ) [max(0, Fo ) + 2Fc ]/3.
13C{1H} NMR (-73 °C, CD2Cl2) δ: 181.3 (d, JCRh ) 73 Hz, Rh-
CO); 46.2 (CH2); 9.97 (CH3).
7.4 Hz, 1H), 7.88 (t, JHH ) 7.4 Hz, 1H), 7.82 (d, JHH ) 7.8 Hz,
1H), 7.75 (d, JHH ) 7.0 Hz, 1H), 7.65 (d, JHH ) 7.2 Hz, 1H),
7.74-7.22 (m, 8H), 7.18 (t, JHH ) 7.5 Hz, 1H), 7.10 (d, JHH )
7.9 Hz, 1H), 7.02 (d, JHH ) 7.5 Hz, 1H) (C6H4); 4.03 (s, 3H),
3.95 (s, 3H), 3.70 (s, 3H) and 3.54 (s, 3H) (CO2Me). MS (FAB+,
CH2Cl2, m/z): 1017, 26% (M+ - Cl - CO), 989, 55% (M+ - Cl
- 2CO), 961, 100% (M+ - Cl - 3CO).
(NHEt3)[Rh2(µ-ArNNNAr)Cl2(CO)4] (4). The addition of neat
triethylamine (36.2 µL, 0.26 mmol) to a mixture of [{Rh(µ-Cl)-
(CO)2}2] (101.0 mg, 0.26 mmol) and ArNNNHAr (81.5 mg, 0.26
mmol) in diethyl ether (6 mL) caused the immediate formation of
a purple solution, from which an orange solid crystallized in 10
min. This mixture was evaporated to dryness and then the residue
was stirred with hexane (5 mL) to give an orange solid and a pale-
orange solution. The solution was decanted and the solid was
washed with hexane (6 mL) and vacuum-dried. Yield: 205 mg
(98%). Single crystals of 4 were obtained by layering a purple
solution of the compound in diethyl ether with hexane. Anal. Calcd
for C26H30N4Cl2O8Rh2: C, 38.87; H, 3.76; N, 6.97. Found: C, 38.89;
H, 3.35; N, 7.20. IR (KBr, cm-1): ν(CO) 2074 (s), 2058 (s), 1996
(s); ν(CdO) 1732 (m), 1707 (m).
Structural Determination of compounds 4, 5, and 6. A
summary of crystal data and refinement parameters for the structural
analyses is given in Table 1. The crystals used in the analyses
(orange block 0.20 × 0.11 × 0.07 mm (4), red block 0.17 × 0.17
× 0.12 (5), and a red lamina 0.16 × 0.13 × 0.06 mm (6)) were
glued to a glass fiber and mounted on Bruker SMART APEX
diffractometer. The instrument was equipped with CCD area
detector and data were collected using graphite-monochromated Mo
KR radiation (λ ) 0.71073 Å) at low temperature (100 K). Cell
constants were obtained from the least-squares refinement of three-
dimensional centroids (6643 reflns, 2.3° e θ e 28.2° for 4; 4971
reflns, 2.3° e θ e 28.0° for 5 and 4531 reflns, 2.3° e θ e 27.9°
for 6). Data were measured (61739 reflns, 1.1° e θ e 25.0° (4);
15845 reflns, 1.4° e θ e 28.6° (5); 22599 reflns, 1.9° e θ e 28.4°
(6)) through the use of CCD recording of narrow ω rotation frames
(0.3° each), completing almost all reciprocal space in the stated θ
range. All data were integrated with the Bruker SAINT program,
which includes Lorentz and polarization corrections. Absorption
correction was applied by using the SADABS routine (min. max.
transmission factors 0.731 and 0.914 (4), 0.708 and 0.789 (5), and
0.889 and 0.915 (6)).27
[Rh3(µ-ArNNNAr)(µ-Cl)(µ-CO)Cl(CO)4] (5). A solution of
[{Rh(µ-ArNNNAr)(CO)2}2] (2) (47.1 mg, 0.05 mmol) in hexane
(10 mL) was added dropwise to a solution of [{Rh(µ-Cl)(CO)2}2]
(38.9 mg, 0.10 mmol) in the same solvent (5 mL). The resulting
dark-red solution was maintained undisturbed for 12 h to render
the title compound as red-violet crystals. The solution was decanted
and the crystals were washed with hexane and vacuum-dried.
Yield: 71 mg (85%). Anal. Calcd for C21H14N3Cl2O9Rh3: C, 30.32;
H, 1.70; N, 5.05. Found: C, 30.18; H, 1.56; N, 4.95. IR (KBr,
cm-1): ν(CO) 2072 (s), 2038 (m), 2003 (s); ν(µ-CO) 1849 (m),
1839 (m); ν(CdO) 1651 (m), 1624 (m). 1H NMR (25 °C, CDCl3)
δ: 8.04 (d, JHH ) 8.1 Hz, 2H), 7.53 (td, JHH ) 6.6, 1.5 Hz, 2H),
7.37 (d, JHH ) 8.4 Hz, 2H) and 7.29 (t, JHH ) 7.2 Hz, 2H) (C6H4);
4.13 (s, 6H, CO2Me). MS (FAB+, CH2Cl2, m/z): 602, 70% ({Rh2-
(µ-ArNNNAr)(µ-CO)(CO)2}+), 577, 90% ({Rh2(µ-ArNNNAr)(µ-
The structures were solved by Patterson methods, completed by
subsequent difference Fourier techniques and refined by full-matrix
least-squares on F2 (SHELXL-97)28 with initial isotropic, but
subsequent anisotropic, thermal parameters for all non-hydrogen
atoms. Hydrogen atoms were included in the model from observed
(5 and 6) or calculated (4) positions, but were refined in all cases
with riding positional and free displacement parameters. Atomic
scattering factors were used as implemented in the program.28
CO)(CO)}+). ΛM (3.45 10-4 M in acetone) ) 20 S cm2 mol-1
.
[Rh3(µ-ArNNNAr)2(µ-Cl)(µ-CO)(CO)3] (6). A solution of
[{Rh(µ-Cl)(CO)2}2] (11.6 mg, 0.03 mmol) in hexane (5 mL) was
dropwise added to a solution of [{Rh(µ-ArNNNAr)(CO)2}2] (2)
(56.5 mg, 0.06 mmol) in the same solvent (10 mL). After 3 h, a
brown solid started to crystallize and the suspension was left at
-30 °C overnight. The solution was decanted and the crystals were
washed with hexane and vacuum-dried. Yield: 58 mg (89%). Anal.
Calcd for C36H28N6ClO12Rh3: C, 40.01; H, 2.61; N, 7.78. Found:
C, 39.96; H, 2.49; N, 7.53. IR (CH2Cl2, cm-1): ν(CO) 2070 (s),
2011 (s), 1992 (s); ν(µ-CO) 1826 (s); ν(CdO) 1723 (m), 1712 (m),
(27) SAINTPLUS program, v. 6.28; Bruker AXS: Madison, WI 2001.
Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33; implemented
in SADABS: Area-detector absorption correction, v. 2.03; Bruker-
AXS: Madison, WI, 2002.
(28) SHELXTL Package, v. 6.10; Bruker-AXS: Madison, WI, 2000.
Sheldrick, G. M. SHELXS-86 and SHELXL-97; University of Go´ttin-
gen: Go¨ttingen, Germany, 1997.
1
1652 (m), 1630 (s). H NMR (25 °C, CDCl3) δ: 8.00 (d, JHH )
Inorganic Chemistry, Vol. 43, No. 15, 2004 4721

Tejel et al.
Results and Discussion
Reaction of [{Rh(µ-Cl)(CO)2}2] with the triazene ligand
(o-CO2MeC6H4)NNNH(o-CO2MeC6H4), ArNNNHAr in the
following discussion, produced the mononuclear compound
[RhCl(ArNNNHAr)(CO)2] (1), isolated as a yellow micro-
crystalline material. Analytical and spectroscopic data of 1
agreed with the proposed formulation. Thus, two strong ν-
(CO) bands in the IR spectrum (at 2089 and 2025 cm-1)
indicated a cis-dicarbonyl moiety in 1, while the CO2Me
groups remained uncoordinated since there is no shift of the
ν(CdO) bands relative to the free ligand. In addition, the
1H NMR spectrum showed, along with the NH resonance
(at 14.36 ppm), two inequivalent o-CO2MeC6H4 groups, also
detected in the 13C{1H} NMR spectrum, that agreed with
the monocoordination of the triazene ligand through the N3
atom to the rhodium center.
Figure 1. Molecular structure of the dinuclear anionic complex [Rh2(µ-
ArNNNAr)Cl2(CO)4]- (from 4) (only one independent molecule is repre-
sented).
Addition of one molar-equiv of KOH in methanol to a
solution of 1 in diethyl ether caused the deprotonation of
the triazene ligand with formation of the dinuclear complex
[{Rh(µ-ArNNNAr)(CO)2}2] (2), which was isolated as a
purple-red microcrystalline material. The mutually cis dis-
position of the two triazenide ligands in the face-to-face
complex 2 was established from the observation of equivalent
carbonyl and aryl groups in the 1H and 13C{1H} NMR spectra
and the typical pattern of three ν(CO) bands for a dinuclear
tetracarbonyl complex under C2V symmetry in the IR
spectrum.
Å) are in the normal range. The relative conformation of
the two square-planar rhodium atoms is slightly staggered,
26.6° approximately. The intramolecular rhodium-rhodium
nonbonding distances, 2.9718(7) and 2.9628(7) Å, were
observed to be similar to those found in related binuclear
rhodium and iridium (I) neutral complexes bridged by two
triazenide ligands (2.960(4) Å in [Rh2(µ-RNNNR)2(CO)2-
(PPh3)2] (R ) p-tolyl),13 or 2.8462(8) Å in [Rh(cod)(µ-
RNNNR)2Ir(CO)2]10).
While the mononuclear complex [RhCl(ArNNNHAr)-
(CO)2] reacted with KOH in methanol to cleanly give the
dinuclear compound [{Rh(µ-ArNNNAr)(CO)2}2] (2), the
result from the apparently similar reaction of 1 with NEt3
was found to be quite different. Thus, addition of one molar-
equiv of NEt3 to a diethyl ether solution of 1 gave a purple
solution whose IR spectrum showed the partial formation
of 2 along with a new species (3) having two strong ν(CO)
absorptions at 2073 and 1999 cm-1. From these solutions,
an orange microcrystalline material (4) separated after stirring
for 10 min. The IR spectrum of 4 in KBr pellets again
showed three ν(CO) absorptions, but shifted ca. 20 cm-1 to
low frequencies relative to those of 2 and uncoordinated CO2-
Me groups, while solutions of 4 in toluene are purple and
contain complexes 2 and 3. Since 4 evolved in solution to 2
and 3, the elucidation of the structure of 4 in the solid state
was achieved from a X-ray diffraction study.
The structure shown in complex 4 is noteworthy since no
previous reports on dinuclear anionic complexes of formula
[Rh2(µ-L)Cl2(CO)4]- (L ) anionic ligand) have been de-
scribed.29 The closer dinuclear compounds were the neutral
complexes derived from bridging hydrazine ligands [Rh2(µ-
L)Cl2(CO)4] (L ) RHNNHMe, R ) H, Me) showing a
slightly longer Rh-Rh distance of 3.208 Å.30
Since 4 contains one single bridging ligand in the solid
state and transforms into the dinuclear compound [{Rh(µ-
ArNNNAr)(CO)2}2] (2) together with compound 3 in solu-
tion, the cis-dicarbonyl species 3 should be the Vallarino’s-
type compound (NHEt3)[RhCl2(CO)2] (3). To ensure this
point, complex 3 was independently prepared by addition
of two molar-equiv of NHEt3Cl to a diethyl ether solution
of [{Rh(µ-Cl)(CO)2}2]. Analytical and spectroscopic data of
3 agreed with the proposed formulation (see Experimental
Section). One relevant property of 3 is its high solubility in
nonpolar solvents that could be explained assuming a
zwitterionic character due to the formation of hydrogen bonds
between the HN proton from the cation and the chloride
ligands from the anion. In fact, the NHEt3+ cation was found
to be able to form such bonds in related anionic mononuclear
rhodium complexes.31
Compound 4 was found to contain the anionic dinuclear
complex [Rh2(µ-ArNNNAr)Cl2(CO)4]-. Two crystallograph-
ically independent, formally enantiomeric, dinuclear com-
plexes were detected in the crystal structure. Figure 1 shows
the molecular structure of one of these anionic complexes
together with the atomic numbering scheme; the most
relevant bond distances and angles are collected in Table 2.
In this dinuclear complex, one bis(o-carboxymethylphenyl)-
triazenide group bridges the two rhodium atoms through the
triazenide moiety, acting as a 3-electron donor ligand. Both
rhodium atoms complete square-planar coordination spheres
with two cis CO groups and a chloride ligand, the Rh-N
(2.099(3) Å), Rh-C (1.850(3) Å), and Rh-Cl (2.3481(8)
Once complexes 2, 3, and 4 were identified, the formation
of 4 by addition of NEt3 to 1 could be explained according
(29) Allen. F. H. Acta Crystallogr. 2002, B58, 380.
(30) Barkley, J. V.; Heaton, B. T.; Jacob, C.; Mageswaran, R.; Sampanthar,
J. T. J. Chem. Soc., Dalton Trans. 1998, 697.
(31) Elduque, A.; Garce´s, Y.; Lahoz, F. J.; Lo´pez, J. A.; Oro, L. A.; Pinillos,
T.; Tejel, C. Inorg. Chem. Commun. 1999, 2, 414.
4722 Inorganic Chemistry, Vol. 43, No. 15, 2004

Crescent-Shaped Rhodium(I) Complexes
Table 2. Selected Bond Distances (Å) and Angles (deg) for the Compound (NHEt3)[Rh2(µ-ArNNNAr)Cl2(CO)4] (4)a
Rh(1)-Cl(1)
Rh(1)-N(1)
Rh(1)-C(17)
Rh(1)-C(18)
C(17)-O(5)
C(18)-O(6)
N(1)-N(2)
N(1)-C(8)
2.3529(16)
2.094(5)
1.847(7)
1.859(7)
1.125(7)
1.124(8)
1.308(6)
1.413(7)
1.209(7)
2.3507(16)
2.096(5)
1.844(7)
1.848(7)
1.130(7)
1.140(7)
1.297(6)
1.426(7)
1.207(7)
Rh(2)-Cl(2)
Rh(2)-N(3)
Rh(2)-C(19)
Rh(2)-C(20)
C(19)-O(7)
C(20)-O(8)
N(2)-N(3)
N(3)-C(9)
2.3489(16)
2.099(5)
1.858(7)
1.840(7)
1.123(7)
1.143(7)
1.293(7)
1.421(7)
1.197(8)
2.3401(17)
2.105(5)
1.863(7)
1.842(7)
1.129(8)
1.140(7)
1.294(7)
1.430(7)
1.192(7)
C(1)-O(1)
C(15-O(3)
Cl(1)-Rh(1)-N(1)
Cl(1)-Rh(1)-C(17)
Cl(1)-Rh(1)-C(18)
N(1)-Rh(1)-C(17)
N(1)-Rh(1)-C(18)
C(17)-Rh(1)-C(18)
Rh(1)-N(1)-N(2)
Rh(1)-N(1)-C(8)
N(2)-N(1)-C(8)
90.80(14)
173.01(19)
88.9(2)
89.6(2)
175.7(2)
90.1(3)
126.3(4)
120.7(4)
111.9(5)
116.8(5)
90.31(14)
173.3(2)
89.6(2)
89.9(2)
175.3(2)
89.6(3)
126.1(4)
121.5(4)
111.4(5)
117.1(5)
Cl(2)-Rh(2)-N(3)
Cl(2)-Rh(2)-C(19)
Cl(2)-Rh(2)-C(20)
N(3)-Rh(2)-C(19)
N(3)-Rh(2)-C(20)
C(19)-Rh(2)-C(20)
Rh(2)-N(3)-N(2)
Rh(2)-N(3)-C(9)
N(2)-N(3)-C(9)
90.11(14)
174.10(19)
88.4(2)
90.4(2)
172.6(2)
90.3(3)
125.9(4)
121.1(4)
111.2(5)
89.95(14)
173.8(2)
88.6(2)
91.0(2)
174.0(2)
89.8(3)
125.3(4)
120.8(4)
112.4(5)
N(1)-N(2)-N(3)
a The two figures stated correspond to the two crystallographically independent molecules. Values consigned for the second molecule are organized
according to the enantiomeric relationship existent between the two independent anions.
a
Scheme 1
a The b symbol denotes a CO group.
to Scheme 1. The deprotonation of the triazenide ligand in
1 caused the formation of 2 along with NHEt3Cl. This
ammonium salt reacted with the mononuclear 1 to give the
Vallarino’s-type compound (NHEt3)[RhCl2(CO)2] (3), and
finally, complex 3 reacted with the dinuclear 2 to give the
complex 4, insoluble in diethyl ether.
Furthermore, the difference in the reactions of 1 with NEt3
and KOH could be attributed to the low solubility in the
reaction medium of the KCl formed in the second case that
prevents the formation of the Vallarino’s-type com-
pound.
Once the ability of [{Rh(µ-ArNNNAr)(CO)2}2] (2) to
undergo redistribution reactions was established, we focused
our attention on the reactions of complex 2 with [{Rh(µ-
Cl)(CO)2}2]. Addition of [{Rh(µ-ArNNNAr)(CO)2}2] (2) to
[{Rh(µ-Cl)(CO)2}2] (1:2 molar ratio) gave a red solution
from which red-violet crystals of [Rh3(µ-ArNNNAr)(µ-Cl)-
(µ-CO)Cl(CO)4] (5) (Scheme 2) deposited overnight and
were characterized by X-ray diffraction methods.
The molecular structure of complex 5 is represented in
Figure 2; relevant bond distances and angles are given in
Table 3. The complex can be described as the result of
binding of the anionic [RhCl2(CO)2]- species to the cationic
dinuclear framework [Rh2(µ-ArNNNAr)(µ-CO)(CO)2]+
through a highly asymmetric chloride bridge. In this frame-
work, one bis(o-carboxymethylphenyl)triazenide group bridges
the two rhodium atoms, Rh(1) and Rh(2), through the N(1)
and N(3) atoms, and chelates both metals through the oxygen
atoms from the two carboxymethyl substituents (O(1) and
O(3)). In this way, the bis(o-carboxymethylphenyl)triazenide
behaves as a cavity-shaped 7-electron donor ligand spanning
both metal centers. In this dinuclear framework, the rhodium
atoms complete a distorted square-pyramidal coordination
We have verified this picture with three independent
experiments: (i) no changes were observed by reacting the
dinuclear complex [{Rh(µ-ArNNNAr)(CO)2}2] (2) with
NHEt3Cl in diethyl ether; (ii) the mononuclear complex 1
evolved quantitatively to the Vallarinos’s-type compound 3
upon addition of NHEt3Cl in diethyl ether, and more
interesting, (iii) by mixing the dinuclear complex [{Rh(µ-
ArNNNAr)(CO)2}2] (2) with two molar-equivalent of (NHEt3)-
[RhCl2(CO)2] (3) the quantitative precipitation of 4 occurs.
This particular behavior seems to be related to the
incorporation of the CO2Me groups at the ortho position of
the phenyl groups in the triazenide ligand, since our attempts
to reproduce these reactions with the triazene ligands
RNNNHR (R ) Ph, p-tolyl) were unsuccessful. Moreover,
the complexes [{Rh(µ-RNNNR)(CO)2}2] (R ) Ph, p-XC6H4)
can be prepared cleanly by addition of NEt3 to a mixture of
[{Rh(µ-Cl)(CO)2}2] and the corresponding triazene, as previ-
ously reported.15 In our particular case, the lability of the
triazenide ligand in 1, that favors the transformation of 1
into 3, along with the facility of 2 to undergo redistribution
reactions are, probably, the origin of the observed reactions.
Inorganic Chemistry, Vol. 43, No. 15, 2004 4723

Tejel et al.
Table 3. Selected Bond Distances (Å) and Angles (deg) for the
Trinuclear Complex [Rh3(µ-ArNNNAr)(µ-Cl)(µ-CO)Cl(CO)4] (5)
Rh(1)-Rh(2)
Rh(1)-O(1)
Rh(1)-N(1)
Rh(1)-C(17)
Rh(1)-C(18)
C(17)-O(5)
C(18)-O(6)
N(1)-N(2)
2.5544(4)
2.110(2)
2.048(3)
2.014(4)
1.860(4)
1.166(4)
1.132(4)
1.313(3)
1.423(4)
1.226(4)
2.3772(9)
1.836(4)
1.139(4)
Rh(1)‚‚‚Rh(3)
Rh(2)-O(3)
Rh(2)-N(3)
Rh(2)-C(17)
Rh(2)-C(19)
Rh(2)-Cl(1)
C(19)-O(7)
N(2)-N(3)
3.0482(4)
2.173(2)
2.040(3)
1.953(4)
1.883(4)
2.5458(9)
1.131(4)
1.294(4)
1.435(4)
1.231(4)
2.3421(10)
1.829(4)
1.147(4)
N(1)-C(8)
N(3)-C(9)
C(1)-O(1)
C(15)-O(3)
Rh(3)-Cl(2)
Rh(3)-C(21)
C(21)-O(9)
Rh(3)-Cl(1)
Rh(3)-C(20)
C(20)-O(8)
Rh(2)-Rh(1)-O(1)
Rh(2)-Rh(1)-N(1)
Rh(2)-Rh(1)-C(18)
O(1)-Rh(1)-N(1)
O(1)-Rh(1)-C(17)
O(1)-Rh(1)-C(18)
N(1)-Rh(1)-C(17)
N(1)-Rh(1)-C(18)
C(17)-Rh(1)-C(18)
Rh(2)-Cl(1)-Rh(3)
Rh(1)-C(17)-Rh(2)
Rh(1)-C(17)-O(5)
Rh(2)-C(17)-O(5)
N(1)-N(2)-N(3)
165.51(7)
85.93(7)
Rh(1)-Rh(2)-Cl(1) 105.12(2)
Rh(1)-Rh(2)-O(3)
157.78(6)
84.43(8)
98.18(10)
94.74(6)
85.19(8)
95.64(11) Rh(1)-Rh(2)-N(3)
87.58(10) Rh(1)-Rh(2)-C(19)
143.80(12) Cl(1)-Rh(2)-O(3)
91.76(12) Cl(1)-Rh(2)-N(3)
Figure 2. Molecular drawing of the trinuclear complex [Rh3(µ-ArNNNAr)-
(µ-Cl)(µ-CO)Cl(CO)4] (5).
88.00(12) Cl(1)-Rh(2)-C(17) 156.10(10)
175.75(14) Cl(1)-Rh(2)-C(19)
90.06(14) O(3)-Rh(2)-N(3)
91.88(11)
87.44(10)
108.80(12)
90.92(12)
91.61(13)
176.52(14)
91.83(15)
127.5(2)
a
Scheme 2
85.67(3)
80.14(14) O(3)-Rh(2)-C(19)
O(3)-Rh(2)-C(17)
134.5(3)
145.3(3)
116.7(3)
124.7(2)
125.6(2)
109.6(3)
89.76(3)
N(3)-Rh(2)-C(17)
N(3)-Rh(2)-C(19)
C(17)-Rh(2)-C(19)
Rh(2)-N(3)-N(2)
Rh(2)-N(3)-C(9)
N(2)-N(3)-C(9)
Rh(1)-N(1)-N(2)
Rh(1)-N(1)-C(8)
N(2)-N(1)-C(8)
121.7(2)
110.4(3)
87.36(12)
Cl(1)-Rh(3)-Cl(2)
Cl(2)-Rh(3)-C(20)
Cl(1)-Rh(3)-C(20) 173.92(12) Cl(2)-Rh(3)-C(21) 177.39(11)
Cl(1)-Rh(3)-C(21)
91.86(11) C(20)-Rh(3)-C(21)
90.83(16)
means of a Cl(1) to Rh(2) dative bond (2.5458(9) Å) and,
with regard to the short Rh(1)‚‚‚Rh(3) separation
(3.0482(4) Å), a metal-metal interaction. Considering all
the above commented interactions, the metal coordination
spheres in the binuclear fragment can be described as
distorted octahedral environments. Even in the absence of
geometric constrains forcing the close proximity between Rh-
(3) and Rh(1), the latter interaction seems to be preferred
over a second dative chloride bond from Cl(2) to Rh(1).34
However, the long Rh(2)-Cl(1) bond distance and the Rh-
(1)‚‚‚Rh(3) separation suggest that the [RhCl2(CO)2]- group
is only weakly bound to the binuclear cationic species.
In agreement with this description, the [RhCl2(CO)2]-
group dissociates readily in solution. Thus, complex 5 was
found to be slightly conductive in acetone solutions (ΛM )
20 S cm2 mol-1), and the cationic fragment [Rh2(µ-
ArNNNAr)(µ-CO)(CO)2]+ is observed as the ion of higher
m/z in the MS (FAB+) spectrum of 5. Moreover, complex 5
is fluxional in solution, since the o-carboxymethylphenyl
groups were found to be equivalent in the 1H NMR spectrum
of fresh solutions of complex 5 in CDCl3 and in HDA. This
fluxional behavior could be explained as due to the dissocia-
tion equilibrium of the [RhCl2(CO)2]- fragment, while the
coordination of the CO2Me groups to the metals remains in
the cationic fragment [Rh2(µ-ArNNNAr)(µ-CO)(CO)2]+. This
binding is evident from the shift in ca. 80 cm-1 to lower
a The b symbol denotes a CO group.
with one terminal carbonyl ligand, the second metal center,
and with a bridging CO group at the apical position. The
nonketonic character of bridging carbonyl was established
from the observation of ν(µ-CO) at ca. 1845 cm-1 in the IR
spectrum.
Electron counting for the cationic [Rh2(µ-ArNNNAr)(µ-
CO)(CO)2]+ fragment gave 30 v.e. and, therefore, a single
metal-metal bond is required. Accordingly, the short Rh-
(1)-Rh(2) bond separation (2.5544(4) Å) agrees with this
picture. This intermetallic distance is slightly shorter than
those found in the related, but neutral, complexes [Rh2(µ-
PPyPh2)2(µ-CO)Cl2] (2.612(1) Å)32 and [{Rh2(µ-aza)(µ-CO)-
Cl(nbd)}2] (2.686(2) Å).33 The Rh(3) atom in the [RhCl2-
(CO)2] moiety shows a nearly square-planar coordination
with Rh(3)-Cl bond distances of 2.3421(10) and 2.3772(9)
Å. The two idealized fragments are maintained together by
(32) Farr, J. P.; Olmstead, M. M.; Hunt, C. H.; Balch, A. L. Inorg. Chem.
1981, 20, 1182.
(33) Oro, L. A.; Ciriano, M. A.; Villarroya, B. E.; Tiripicchio, A.; Lahoz,
F. J. J. Chem. Soc., Dalton Trans. 1985, 1891.
(34) A related situation stabilized only by chloride bridges has been reported
for the trinuclear complex [Rh3(µ-Cl)3(µ-L)(CO)4] (L ) bis(diphen-
oxyphosphino)methane). Kumar, R.; Puddephatt, R. J.; Fronczek, F.
R. Inorg. Chem. 1990, 29, 4850.
4724 Inorganic Chemistry, Vol. 43, No. 15, 2004

Crescent-Shaped Rhodium(I) Complexes
Table 4. Selected Bond Distances (Å) and Angles (deg) for the
Trinuclear Complex [Rh3(µ-ArNNNAr)2(µ-Cl)(µ-CO)(CO)3] (6)
Rh(1)-Rh(2)
Rh(1)-O(1)
Rh(1)-N(1)
Rh(1)-C(17)
Rh(1)-C(18)
C(17)-O(5)
C(18)-O(6)
N(1)-N(2)
N(1)-C(8)
N(2)-N(3)
N(3)-C(9)
C(1)-O(1)
C(15)-O(3)
Rh(3)-Cl
2.5538(5)
2.103(3)
2.070(4)
2.082(5)
1.834(5)
1.168(5)
1.144(6)
1.324(5)
1.417(6)
1.280(5)
1.432(6)
1.216(5)
1.197(6)
2.3703(12)
1.854(6)
1.134(6)
Rh(1)‚‚‚Rh(3)
Rh(2)-O(7)
Rh(2)-N(3)
Rh(2)-C(17)
Rh(2)-N(4)
Rh(2)-Cl
C(19)-O(7)
N(4)-N(5)
N(4)-C(26)
N(5)-N(6)
N(6)-C(27)
C(19)-O(7)
C(33)-O(9)
Rh(3)-N(6)
Rh(3)-C(36)
C(36)-O(12)
3.0136(5)
2.243(3)
2.029(4)
1.895(5)
2.044(4)
2.5223(12)
1.228(6)
1.293(5)
1.423(6)
1.295(5)
1.442(6)
1.228(6)
1.200(6)
2.097(4)
1.862(6)
1.127(6)
Rh(3)-C(35)
C(35)-O(11)
Rh(2)-Rh(1)-O(1)
Rh(2)-Rh(1)-N(1)
Rh(2)-Rh(1)-C(17)
Rh(2)-Rh(1)-C(18)
O(1)-Rh(1)-N(1)
O(1)-Rh(1)-C(17)
O(1)-Rh(1)-C(18)
N(1)-Rh(1)-C(17)
N(1)-Rh(1)-C(18)
C(17)-Rh(1)-C(18)
Rh(1)-Cl-Rh(2)
Rh(1)-C(17)-Rh(2)
Rh(1)-C(17)-O(5)
Rh(2)-C(17)-O(5)
N(1)-N(2)-N(3)
Rh(1)-N(1)-N(2)
Rh(1)-N(1)-C(8)
N(2)-N(1)-C(8)
Rh(2)-N(3)-N(2)
Rh(2)-N(3)-C(9)
N(2)-N(3)-C(9)
Cl-Rh(3)-N(6)
172.00(9)
Rh(1)-Rh(2)-Cl
107.97(3)
167.28(8)
84.17(11)
97.61(10)
84.74(9)
88.70(11)
161.33(14)
91.51(11)
96.17(14)
113.93(16)
81.92(14)
88.97(17)
178.05(16)
91.45(17)
119.5(4)
132.6(3)
116.3(3)
110.9(4)
131.1(3)
118.7(3)
109.1(4)
88.5(2)
84.48(10) Rh(1)-Rh(2)-O(7)
46.91(13) Rh(1)-Rh(2)-N(3)
98.17(15) Rh(1)-Rh(2)-N(4)
87.81(13) Cl-Rh(2)-O(7)
137.11(16) Cl-Rh(2)-N(3)
89.38(17) Cl-Rh(2)-C(17)
99.16(16) Cl-Rh(2)-N(4)
175.40(18) O(7)-Rh(2)-N(3)
85.37(19) O(7)-Rh(2)-C(17)
Figure 3. Molecular structure of the trinuclear complex [Rh3(µ-ArNN-
NAr)2(µ-Cl)(µ-CO)(CO)3] (6).
78.26(3)
79.74(18) N(3)-Rh(2)-C(17)
O(7)-Rh(2)-N(4)
131.0(4)
148.8(4)
116.4(4)
123.0(3)
126.7(3)
110.1(4)
127.1(3)
121.6(3)
111.2(4)
N(3)-Rh(2)-N(4)
C(17)-Rh(2)-N(4)
N(4)-N(5)-N(6)
Rh(2)-N(4)-N(5)
Rh(2)-N(4)-C(26)
N(5)-N(4)-C(26)
Rh(3)-N(6)-N(5)
Rh(3)-N(6)-C(27)
N(5)-N(6)-C(27)
frequencies of the ν(CdO) bands, relative to the uncoordi-
nated CO2Me groups in complexes 2 and 4, in the IR
spectrum of 5 in solution.
Solutions of complex 5 in CDCl3 were found to be
unstable, evolving to new compounds, whose signals in the
1H NMR spectrum start to appear in 20 min. One of them,
showing four resonances for the OMe groups, was found to
be the complex [Rh3(µ-ArNNNAr)2(µ-Cl)(µ-CO)(CO)3] (6)
(Scheme 2). According to the formulation, complex 6 was
prepared straightforwardly by reacting [{Rh(µ-ArNNNAr)-
(CO)2}2] (2) and [{Rh(µ-Cl)(CO)2}2] in a 1:0.5 molar ratio
in hexane. From these solutions, single crystals of the brown-
red complex 6 deposited in 2 days. The structure of 6 is
represented in Figure 3 together with the atomic numbering
scheme; the relevant bond distances and angles are given in
Table 4. In complex 6 one bis(o-carboxymethylphenyl)-
triazenide bridges two rhodium atoms, Rh(1) and Rh(2), and
chelates Rh(1) through the oxygen from one CO2Me group.
The other bis(o-carboxymethylphenyl)triazenide ligand bridges
the Rh(2) and Rh(3) atoms and also chelates Rh(2) through
one oxygen atom, O(7). Therefore, both triazenide groups
are acting in the molecule as five electron donor ligands.
This compound could be considered formally as derived from
the previously described complex 5, in which a second bis-
(o-carboxymethylphenyl)triazenide ligand was incorporated
into the molecule. Thus, the CO2Me group bonded to
Rh(2), the terminal CO ligand bonded to Rh(2), and the
chloride ligand coordinated to Rh(3) in 5 are replaced by
one CO2Me group and the nitrogen atoms N(4) and N(6),
respectively, of the new bis(o-carboxymethylphenyl)tri-
azenide ligand. This formal exchange maintains complex 6
electronically similar to 5.
89.30(11) N(6)-Rh(3)-C(35)
176.09(16) N(6)-Rh(3)-C(36)
91.16(17) C(35)-Rh(3)-C(36)
Cl-Rh(3)-C(35)
Cl-Rh(3)-C(36)
173.37(19)
90.7(2)
Å). In this case, the two moieties: the dinuclear formed by
Rh(1) and Rh(2), and the mononuclear “Rh(3)ClN(CO)2”,
are maintained together by the 5-electron-donor bridging
ligand. As described for 5, a long dative Cl-Rh(2) bond
(2.5223(12) Å), and a feeble Rh(1)‚‚‚Rh(3) interaction
(3.0136(5) Å) can be also proposed for 6.
The coordination of the Rh(3) center to the second
triazenide bridge ligand prevents the dissociation of this
moiety in 6. In fact, trinuclear species were observed in the
MS spectrum of this compound (see Experimental Section),
in contrast with the lack of trinuclear species in the MS
spectrum of 5. According to the structure found in the solid
state for 6, four inequivalent o-CO2MeC6H4 groups were
observed in the 1H NMR spectrum, and the coordination to
the metal of one CO2Me group per triazenide ligand was
detected in the IR spectrum of 6.
Attempts to prepare new derivatives by reacting [{Rh(µ-
ArNNNAr)(CO)2}2] (2) with [{Rh(µ-Cl)(CO)2}2] in molar
ratios from 1:0.5 to 1:2 led to mixtures of the complexes 5
and 6. Finally, attempts to prepare the cationic complex [Rh2-
(µ-ArNNNAr)(µ-CO)(CO)2]PF6, proposed as a moiety in 5,
by the reaction of [{Rh(µ-ArNNNAr)(CO)2}2] (2) with [Rh-
(CO)2(MeCN)2]PF6 in a 1:2 molar ratio were unsuccessful.
Consequently, we believe the Rh-Cl dative bond and the
Rh-Rh interaction found in complexes 5 and 6 were the
Accordingly, the bonding between Rh(1) and Rh(2) was
clearly deduced from the short Rh-Rh distance (2.5538(5)
Inorganic Chemistry, Vol. 43, No. 15, 2004 4725

Tejel et al.
key for the stabilization of the “Rh2(µ-ArNNNAr)(µ-CO)”
moiety.
the complex [Rh3(µ-ArNNNAr)2(µ-Cl)(µ-CO)(CO)3] (6),
where one carboxymethyl group from each ligand remains
uncoordinated. To the best of our knowledge crescent-shaped
complexes are quite uncommon in dinuclear rhodium(I)
chemistry.
Concluding Remarks
The incorporation of carboxymethyl groups at the ortho
position of the phenyl groups of the triazene PhNNNHPh
ligand provides new coordination possibilities to these
ligands, leading to structures with interesting features
disclosed herein. Besides the typical “µ-(1κN1,2κN3)” co-
ordination mode for triazenides, the bis(o-carboxymethyl-
phenyl)triazenide ligand is able to occupy three and four
coordination positions spanning a binuclear unity. The
tetradentate mode has been identified in the crescent-shaped
complex [Rh3(µ-ArNNNAr)(µ-Cl)(µ-CO)Cl(CO)4] (5), while
the tridentate mode is found for both triazenide ligands in
Acknowledgment. The financial support from Ministerio
de Ciencia y Tecnolog´ıa (MCyT(DGI)/FEDER) Project
BQU2002-0074 is gratefully acknowledged. G.R.-M. thanks
Programa CYTED for a fellowship.
Supporting Information Available: An X-ray crystallographic
file, in CIF format, containing full details of the structural analyses
of 4, 5, and 6. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC049691G
4726 Inorganic Chemistry, Vol. 43, No. 15, 2004