Dinuclear rhodium and iridium complexes with mixed amido/methoxo and amido/hydroxo bridges

Article abstract of DOI:10.1021/ic0109952

The reactions of [{M(μ-OMe)(cod)}₂] (M = Rh, Ir; cod = 1,5-cyclooctadiene) with p-tolylamine, α-naphthylamine, and p-nitroaniline gave complexes with mixed-bridging ligands, [{M(cod)}₂(μ-NHAr)(μ-OMe)]. Similarly, the related complexes [{Rh(cod)}₂(μ-NHAr)(μ-OH)] were prepared from the reactions of [{Rh(μ-OH)(cod)}₂] with p-tolylamine, α-naphthylamine, and p-nitroaniline. The reactions of [{Rh(μ-OR)(cod)}₂] (R = H, Me) with o-nitroaniline gave the mononuclear complex [Rh(o-NO₂C₆H₄NH)(cod)]. The syntheses of the amido complexes involve a proton exchange reaction from the amines to the methoxo or hydroxo ligands and the coordination of the amide ligand. These reactions were found to be reversible for the dinuclear complexes. The structure of [{Rh(cod)}₂(μ-NH{p- NO₂C₆H₄})-(μ-OMe)] shows two edge-shared square-planar rhodium centers folded at the edge with an anti configuration of the bridging ligands. The complex [{Rh(cod)}₂(μ-NH{α-naphthyl})(μ-OH)] cocrystallizes with [{Rh(μ-OH)(cod)}₂] and THF, forming a supramolecular aggregate supported by five hydrogen bridges in the solid state. In the mononuclear [Rh(o-NO₂C₆H₄NH)(cod)] complex the o-nitroamido ligand chelates the rhodium center through the amido nitrogen and an oxygen of the nitro group.

Full text of DOI:10.1021/ic0109952

Inorg. Chem. 2002, 41, 2348−2355
Dinuclear Rhodium and Iridium Complexes with Mixed Amido/Methoxo
and Amido/Hydroxo Bridges
Cristina Tejel, Miguel A. Ciriano,* Marta Bordonaba, Jose´ A. Lo´pez, Fernando J. Lahoz, and
Luis A. Oro*
Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n,
UniVersidad de Zaragoza-CSIC, E-50009 Zaragoza, Spain
Received September 24, 2001
The reactions of [{M(µ-OMe)(cod)}2] (M) Rh, Ir; cod ) 1,5- cyclooctadiene) with p-tolylamine, R-naphthylamine,
and p-nitroaniline gave complexes with mixed-bridging ligands, [{M(cod)}2(µ-NHAr)(µ-OMe)]. Similarly, the related
complexes [{Rh(cod)}2(µ-NHAr)(µ-OH)] were prepared from the reactions of [{Rh(µ-OH)(cod)}2] with p-tolylamine,
R-naphthylamine, and p-nitroaniline. The reactions of [{Rh(µ-OR)(cod)}2] (R) H, Me) with o-nitroaniline gave the
mononuclear complex [Rh(o-NO C H NH)(cod)]. The syntheses of the amido complexes involve a proton exchange
2
6 4
reaction from the amines to the methoxo or hydroxo ligands and the coordination of the amide ligand. These
reactions were found to be reversible for the dinuclear complexes. The structure of [{Rh(cod)}2(µ-NH{p-NO C H })-
2
6 4
(µ-OMe)] shows two edge-shared square-planar rhodium centers folded at the edge with an anti configuration of
the bridging ligands. The complex [{Rh(cod)}2(µ-NH{R-naphthyl})(µ-OH)] cocrystallizes with [{Rh(µ-OH)(cod)}2]
and THF, forming a supramolecular aggregate supported by five hydrogen bridges in the solid state. In the
mononuclear [Rh(o-NO C H NH)(cod)] complex the o-nitroamido ligand chelates the rhodium center through the
2
6 4
amido nitrogen and an oxygen of the nitro group.
Introduction
metallic chemistry and catalysis,3 the relative paucity of their
homologues of late-transition-metals causes the factors
controlling the nature of their M-N and M-O bonds to still
not be well understood.4 A number of palladium amido and
alkoxo complexes have recently been prepared;5 some of
them undergo very unusual reductive elimination reactions
with formation of C-N and C-O bonds.5b,e,6 As a conse-
quence of this type of study, the palladium- and nickel-
catalyzed amination of aryl halides has begun to be mecha-
Late-transition-metal compounds with anionic nitrogen
(amido) and oxygen (alkoxo and hydroxo) ligands are
becoming of increasing interest because of their remarkable
reactivity1 and their potential relevance to catalytic reactions.2
While there is a large body of early-transition-metal chem-
istry based on these groups with applications in organo-
* To whom correspondence should be addressed. E-mail: (L.A.O.)
oro@posta.unizar.es.
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2348 Inorganic Chemistry, Vol. 41, No. 9, 2002
10.1021/ic0109952 CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/20/2002

Dinuclear Rh and Ir Complexes with Mixed Bridges
nistically understood.2b,7 Moreover, palladium and platinum
hydroxide and amido complexes are related by simple acid-
base chemistry with amines and water, which has provided
an easy preparative entry into families of mixed µ-amido/
µ-hydroxo and bis(µ-amido) complexes of these metals.5b,8
Furthermore, this acid-base chemistry has been proved to
be involved in the generation of the active species for the
conversion of aryl halides to arylamido complexes.9
Although there are examples of alkoxy,10 hydroxy,1b,e,11
and amido1h,12 complexes of rhodium, their reactions with
amines and water, similar to those reported for palladium
and platinum, have scarcely been studied.13 As rhodium
compounds of this kind could be of interest for new catalytic
processes such as the amination of olefins,14 we have studied
the reactions of rhodium(I) bis(µ-hydroxo) and bis(µ-
methoxo) complexes with amines. We report herein our
results on this subject leading to a new class of dinuclear
rhodium complexes with mixed-bridging ligands, as well as
on a study of the equilibria involved in their formation.
ligands containing an acidic proton. A rationalization of these
reactions under conventional proton exchange reactions and
coordination of the anionic polydentate ligand accounts for
the preparative results. However, we have found that primary
arylamines (ArNH2), a class of compounds less acidic than
methanol, protonate the methoxo groups in [{M(µ-OMe)-
(cod)}2] to give the complexes [{M(cod)}2(µ-NHAr)(µ-
OMe)] (M ) Rh, Ar ) p-tolyl (1), p-NO2C6H4 (2),
R-naphthyl (3); M ) Ir, Ar ) p-tolyl (4)) with mixed-
bridging ligands. Complexes 1-4 were obtained pure and
in good yields using diethyl ether as the solvent, in which
the products crystallized out as formed. However, mixtures
of complexes were isolated if the reactions were carried out
in solvents such as dichloromethane or benzene. The new
complexes were characterized by analytical and NMR and
mass spectroscopic methods and an X-ray diffraction analysis
of complex 2 (see below).
Analogously, the related µ-hydroxo/µ-amido complexes
[{Rh(cod)}2(µ-NHAr)(µ-OH)] (Ar ) p-tolyl (5), p-NO2C6H4
(6), R-naphthyl (7)) were prepared by reacting equimolar
amounts of [{Rh(µ-OH)(cod)}2] with the corresponding
amines in diethyl ether. Compounds 5 and 6 were isolated
as yellow and red crystalline solids, respectively, whose
elemental analyses agreed with the proposed formulation.
However, attempts to obtain pure samples of complex 7 were
unsuccessful, since it was always contaminated with [{Rh-
(µ-OH)(cod)}2]. In fact, the elemental analyses of the solid
isolated from the reaction corresponded to the formulation
[Rh3(cod)3(NH{R-naphthyl})(OH)2]‚THF. The complete char-
acterization of this solid as the supramolecular entity [{Rh-
(cod)}2(µ-NH{R-naphthyl})(µ-OH)]2‚[{Rh(µ-OH)(cod)}2]‚
2THF (7′) was achieved by a crystallographic X-ray diffraction
study (see below).
Results and Discussion
Syntheses of the Complexes. The methoxo-bridged
complexes [{M(µ-OMe)(cod)}2] (M ) Rh, Ir; cod ) 1,5-
cyclooctadiene) have been shown to be useful starting
materials for the synthesis of a wide range of di- and
polynuclear compounds15 when treated with polydentate
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H.; Kamura, T.; Ariga, K.; Watanabe, Y.; Okubo, T.; Ishii, T.;
Yamashita, M.; Kondo, M.; Kitagawa, S. Organometallics 2000, 19,
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Rodriguez, A.; Terreros, P. Organometallics 1998, 17, 1465. (d)
Dahlenburg, L.; Brunet, J. J.; Daran, J. C.; Neibecker, D.; Rosenberg,
L. J. Organomet. Chem. 1997, 538, 251. (e) Dahlenburg, L.; Herbst,
K. Chem. Ber. 1997, 130, 1693. (f) Brunet, J. J.; Commenges, C.;
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L.; Ahmed, K. J. Inorg. Chem. 1992, 31, 3877. (h) Fernandez, M. J.;
Modrego, J.; Oro, L. A.; Apreda, M. C.; Cano, F. H.; Foces-Foces,
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M. A.; Oro, L. A.; Foces-Foces, C.; Cano, F. H. Inorg. Chim. Acta
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Foces, C.; Cano, F. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 913.
(k) Cetinkaya, B.; Lappert, M. F.; Torroni, S. J. Chem. Soc., Chem.
Commun. 1979, 843. (l) Espinet, P.; Bailey, P. M.; Maitlis, P. M. J.
Chem. Soc., Dalton Trans. 1979, 1542.
A markedly different outcome was observed on treating
[{Rh(µ-OMe)(cod)}2] and [{Rh(µ-OH)(cod)}2] with o-nitro-
aniline, since 2 molar equiv of the amine was required to
achieve the complete consumption of the dinuclear rhodium
precursors. The new complex formed in both cases, [Rh(o-
NO2C6H4NH)(cod)] (8), was isolated as purple needles for
which the mass spectrum indicated a mononuclear nature.
1
The H and 13C{1H} NMR spectra of [Rh(o-NO2C6H4NH)-
(cod)] indicated that the o-NO2C6H4NH ligand chelates the
rhodium center through the amido nitrogen and one oxygen
from the nitro group. To confirm this unusual coordination
of the nitro group, complex 8 was definitively characterized
by an X-ray diffraction study.
Crystal Structures of Complexes 2, 7′ , and 8. A view
of the molecular structure of 2 is shown in Figure 1; selected
bond distances and angles are given in Table 1. Complex 2
has an imposed crystallographic Cs symmetry, with all the
atoms of the methoxo and p-nitrophenylamido bridging
ligands situated on the crystallographic mirror plane. The
(15) (a) Tejel, C.; Villarroya, B. E.; Ciriano, M. A.; Edwards, A. J.; Lahoz,
F. J.; Oro, L. A.; Lanfranchi, M.; Tiripicchio, A.; Tiripicchio-Camellini,
M. Inorg. Chem. 1998, 37, 3954. (b) Tejel, C.; Villarroya, B. E.;
Ciriano, M. A.; Oro, L. A.; Lanfranchi, M.; Tiripicchio, A.; Tiripicchio-
Camellini, M. Inorg. Chem. 1996, 35, 4360. (c) Calvo, M. A.; Manotti-
Lanfredi, A. M.; Oro, L. A.; Pinillos, M. T.; Tejel, C.; Tiripicchio,
A.; Ugozzoli, F. Inorg. Chem. 1993, 32, 1147.
(13) There are only two reports on this topic: (a) Oro, L. A.; Ferna´ndez,
M. J.; Modrego, J.; Lo´pez, J. M. J. Organomet. Chem. 1985, 287,
409. (b) Nutton, A.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1981,
2339.
(14) Mu¨ller, T. E.; Beller, M. Chem. ReV. 1998, 98, 675.
Inorganic Chemistry, Vol. 41, No. 9, 2002 2349

Tejel et al.
Figure 2. A representation of the molecular structure of the mononuclear
complex 8.
Chart 2
Figure 1. A representation of the molecular structure of complex 2
showing the atomic numbering scheme used.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complex 8
Chart 1
Rh-N(1)
Rh-O(1)
Rh-C(7)
Rh-C(8)
Rh-C(11)
Rh-C(12)
O(1)-N(2)
O(2)-N(2)
1.989(5)
2.048(4)
2.107(6)
2.094(6)
2.155(6)
2.150(6)
1.290(6)
1.254(5)
N(1)-C(1)
N(2)-C(6)
C(1)-C(2)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
1.310(7)
1.389(7)
1.444(8)
1.435(7)
1.341(8)
1.423(8)
1.347(8)
1.415(7)
N(1)-Rh-O(1)
O(1)-Rh-M(1)a
O(1)-Rh-M(2)a
Rh-N(1)-C(1)
O(1)-N(2)-O(2)
87.5(2)
178.9(2)
91.6(2)
127.8(4)
116.1(5)
M(1)a-Rh-M(2)a
N(1)-Rh-M(1)a
N(1)-Rh-M(2)a
Rh-O(1)-N(2)
O(1)-N(2)-C(6)
88.1(3)
92.7(2)
177.6(2)
129.0(3)
124.5(5)
Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complex 2a
Rh‚‚‚Rh′
3.0147(8)
2.152(3)
2.116(3)
2.101(4)
2.094(4)
2.130(4)
2.133(4)
1.233(8)
1.452(7)
N(1)-C(11)
C(11)-C(12)
C(11)-C(16)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-C(16)
N(2)-O(3)
1.414(7)
1.404(8)
1.400(7)
1.356(8)
1.396(9)
1.393(8)
1.373(8)
1.219(7)
1.214(9)
Rh-O(1)
Rh-N(1)
Rh-C(1)
Rh-C(2)
Rh-C(5)
Rh-C(6)
N(2)-O(2)
N(2)-C(14)
a M(1) and M(2) are the midpoints between C(7)-C(8) and C(11)-
C(12), respectively.
amido ligand were found in equatorial positions on the open-
book skeleton, while the aryl group was in an axial position.
Therefore, complex 2 showed an anti configuration that we
have labeled bent-anti-a (Chart 1) to indicate the axial
position of the aryl group. Within this convention, the anti
conformer with the aryl group at the equatorial position
would be that labeled bent-anti-e in Chart 1.
O(1)-C(9)
O(1)-Rh-N(1)
O(1)-Rh-M(1)b
O(1)-Rh-M(2)b
Rh-O(1)-Rh′
C(9)-O(1)-Rh
80.65(14)
173.88(14)
97.89(14)
88.92(17)
128.9(2)
M(1)b-Rh-M(2)b
N(1)-Rh-M(1)b
N(1)-Rh-M(2)b
Rh-N(1)-Rh′
88.2(2)
93.01(14)
178.00(14)
90.85 (17)
C(11)-N(1)-Rh
a Primed atoms are related to the unprimed ones by a mirror plane. b M(1)
and M(2) are the midpoints between C(1)-C(2) and C(5)-C(6), respec-
tively.
Although dinuclear complexes containing mixed methoxo
and amido bridging ligands are unknown for the late-
transition-metals, this bent-anti-a stereochemistry is similar
to those reported for the related µ-hydroxo/µ-amido com-
plexes [{Pt(PPh3)2}2(µ-NH{p-tolyl})(µ-OH)](BF4)2,8b cis-
[{Pd(C6H5)(PPh3)}2(µ-NHBut)(µ-OH)],9 and trans-[{Pd-
(C6H5)(PPh3)}2(µ-NH{p-OMeC6H4})(µ-OH)],8d which also
showed folded structures.
coordinated oxygen atom of the methoxo group and the
nitrogen atom of the bridging amido, together with a 1,5-
cyclooctadiene ligand on each metal, complete distorted
square-planar coordination for the metal centers. The four-
membered ring “RhNRhO” shows a folded conformation:
the dihedral angle between the coordination planes defined
by O(1)-Rh-N(1) and O(1)-Rh′-N(1) was found to be
135.86(13)°. Accordingly, a relatively short intermetallic
distance (3.0147(9) Å) was observed. While the Rh-N bond
distance, 2.116(3) Å, compares well with those values
observed in other square-planar rhodium cyclooctadiene
complexes (range 2.066-2.200 Å, mean 2.12(3) Å), the
Rh-O bond length, 2.152(3) Å, is in the upper end of those
of related alkoxy-bridged rhodium(I) complexes (range
2.042-2.137 Å, mean 2.08(3) Å).16 The HN-Cipso distance
(N(1)-C(11) ) 1.414(7) Å) indicates a N-C single bond.
The methyl of the methoxo group and the proton of the
The molecular structure of the square-planar complex 8
is shown in Figure 2. Selected bond distances and angles
are given in Table 2. The more striking feature of the
structure involves the inhomogeneous distribution of bond
distances within the amido ligand. Thus, the benzenic ring
of the o-NO2C6H4NH ligand shows two significantly shorter
distances (C(2)-C(3) ) 1.341(8) Å, C(4)-C(5) ) 1.347(8)
Å) than the remaining four C-C bonds (range 1.415(7)-
1.448(8) Å). In addition, the HN-Cipso and O2N-Cipso
distances (N(1)-C(1) ) 1.310(7) Å and N(2)-C(6) ) 1.389-
(7) Å) are clearly shorter than those expected for a single
C-N bond (1.468(14) Å), or than distances reported for a
noncoordinated o-nitroaniline (1.442(7) Å).17 Therefore, the
(16) Allen, F. H.; Kennard, O. Chem. Des. Autom. News 1993, 8, 1.
2350 Inorganic Chemistry, Vol. 41, No. 9, 2002

Dinuclear Rh and Ir Complexes with Mixed Bridges
Figure 4. Hydrogen-bonding scheme established between the two different
dinuclear complexes and the THF solvent molecule in the crystalline
structure of 7′ (see Table 4 for structural parameters).
Figure 3. A drawing of the molecular structure of the heterobridged
complex 7 together with the labeling scheme used.
Table 4. Bond Lengths (Å) and Angles (deg) for the
Hydrogen-Bonding System in 7′
Table 3. Selected Bond Distances (Å) and Angles (deg) for 7
A-H
H‚‚‚B
A‚‚‚B
A-H‚‚‚B
Rh(1)‚‚‚Rh(2)
Rh(1)-O(1)
Rh(1)-N
Rh(1)-C(11)
Rh(1)-C(12)
Rh(1)-C(15)
Rh(1)-C(16)
2.8602(8)
2.078(4)
2.128(5)
2.089(6)
2.117(6)
2.096(7)
2.089(7)
O(1)-H‚‚‚O(4a)
O(1)-H‚‚‚O(4b)
N′ H‚‚‚O(2)a
0.98
0.98
1.08
1.83
1.80
2.24
2.803(14)
2.75(2)
3.305(10)
2.888(10)
2.847(13)
171.4
162.5
168.1
Rh(2)-O(1)
Rh(2)-N
Rh(2)-C(19)
Rh(2)-C(20)
Rh(2)-C(23)
Rh(2)-C(24)
2.068(4)
2.109(5)
2.088(6)
2.098(7)
2.107(7)
2.097(7)
O(2)-H‚‚‚O(1′)b
O(3)-H‚‚‚O(1)b
a Primed atoms are related to the unprimed ones by the symmetry
operation -x + 1, -y, -z. b Hydrogens atoms of O(2) and O(3) were not
located in the X-ray structural analysis.
O(1)-Rh(1)-N
74.55(18)
O(1)-Rh(2)-N
75.15(18)
174.7(3)
96.7(2)
99.8(3)
171.9(2)
88.4(3)
O(1)-Rh(1)-M(1)a 175.5(3)
O(1)-Rh(2)-M(3)a
O(1)-Rh(2)-M(4)a
N-Rh(2)-M(3)a
N-Rh(2)-M(4)a
M(3)-Rh(2)-M(4)a
Rh(1)-N-Rh(2)
O(1)-Rh(1)-M(2)a
N-Rh(1)-M(1)a
N-Rh(1)-M(2)a
M(1)-Rh(1)-M(2)a
Rh(1)-O(1)-Rh(2)
97.0(3)
100.9(3)
171.6(3)
87.4(3)
planar coordination with a 1,5-cyclooctadiene ligand. The
four-membered ring RhNRhO also shows a folded confor-
mation, with a dihedral angle between the O(1)-Rh(1)-N
and O(1)-Rh(2)-N planes of 118.53(15)°, leading to a
shorter intermetallic distance (2.8602(8) Å) than that ob-
served in 2. The stereochemistry around the central RhNRhO
ring was found to be syn-endo with the aryl group and the
proton of the OH ligand at equatorial positions. This
stereochemistry of the bridging ligands, unusual for related
µ-amido/µ-hydroxo complexes, is probably due to the
H-bonding network established at a supramolecular level in
the crystalline structure of 7′. Figure 4 shows the structure
of this aggregate in which two molecules of 7 and two THF
solvent molecules encapsulate a dinuclear di-µ-hydroxo
complex, [{Rh(µ-OH)(cod)}2]. Five hydrogen bonds involv-
ing the strong H-bond acceptor/donor µ-hydroxo and µ-a-
mido groups18 (see Table 4) are involved in the H-bonding
network established. The hydroxo groups of the two (sym-
metry-related) molecules of 7 behave as H-donors toward
the oxygens of the two THF molecules and H-acceptors for
the two OH groups of the homobridged dinuclear [{Rh(µ-
OH)(cod)}2] complex. Additionally, the amido NH group
acts as a H-donor toward one bridging hydroxo ligand of
[{Rh(µ-OH)(cod)}2] (Figure 4). However, this hydrogen-
bonding system was found to be completely broken on
dissolving the solid, since the individual components, 7,
87.26(15)
84.91(18)
a M(1), M(2), M(3), and M(4) are the midpoints of the olefinic bonds
C(11)-C(12), C(15)-C(16), C(19)-C(20), and C(23)-C(24), respectively.
o-NO2C6H4NH ligand is better represented as a quinodiimide
(b, Chart 2) rather than as an amide ligand (a, Chart 2). It is
interesting to remark that, as a consequence of chelate
coordination of the o-NO2C6H4NH ligand to rhodium in 8,
the benzene ring loses aromaticity. We cannot comment on
the generality of this situation, since complex 8 is the first
example where the o-NO2C6H4NH ligand coordinates in a
chelate fashion. In contrast, the related p-NO2C6H4NH ligand
in 2 appeared close to the amide form. The major difference
between the nitroanilide ligands in complexes 2 and 8 arises
from the presence or absence of a lone electron pair on the
amide nitrogen. In complex 2, this pair is involved in the
formation of a Rh-N dative bond, and the amide nitrogen
was found to be tetrahedral, while the benzene ring was
found almost aromatic. In complex 8, this pair is not involved
in a Rh-N bond; on the contrary, it is supposed to be
delocalized on the benzene ring due to the -I and -M effect
of the nitro group at the ortho position. This bonding situation
leads to the observed short and long distances into the
nitroanilide ligand.
1
The molecular structure of the dinuclear complex 7 is
shown in Figure 3 together with the atom-numbering scheme.
Selected bond distances and angles are given in Table 3. In
7, an R-naphthylamido and a hydroxo group bridge both
rhodium atoms, which complete an approximately square-
[{Rh(µ-OH)(cod)}2], and THF, were observed in the H
NMR spectrum of 7′.
Characterization of Complexes 1-7 in Solution. Ther-
modynamic and Reactivity Considerations. Complexes
(18) (a) Prins, L. J.; Reinhoudt, D. N.; Timmerman, P. Angew. Chem., Int.
Ed. 2001, 40, 2382. (b) Jeffrey, G. A. An Introduction to Hydrogen
Bonding; Oxford University Press: Oxford, 1997.
(17) Huang, S. D.; Lewandowski, B. J.; Liu, C.; Shan, Y. Acta Crystallogr.
1999, C55, 2016.
Inorganic Chemistry, Vol. 41, No. 9, 2002 2351

Tejel et al.
Table 5. KEq Values for the Equilibria Shown in Eq 1
complex amine Keq ∆G298 (kcal/mol)
values, which indicate a small influence of the metal in these
reactions. In addition, the larger Keq value for the reactions
of [{Rh(µ-OMe)(cod)}2] with p-tolylamine versus R-naph-
thylamine is in marked contrast to the reactivity predicted
only by the pKa values of the amines (5.08 and 3.92,
respectively). Since methanol was formed in both reactions,
the observed Keq values indicate a larger affinity of metal
for the p-tolylamido ligand than for the R-naphthylamido
ligand. Moreover, since water is more acidic than methanol,
larger Keq values could be expected for the equilibria of
p-tolylamine with [{Rh(µ-OMe)(cod)}2] versus [{Rh(µ-OH)-
(cod)}2] under a perspective based only on the pKa values
of water and methanol. However, the results were again
opposite to those anticipated, which indicated that the
involved equilibria seem to be much more complex.
From a kinetic point of view, the reaction of [{Rh(µ-
OMe)(cod)}2] with R-naphthylamine was found to go slowly
since 17 h was required to reach equilibrium at room
temperature. In contrast, only 2 h was needed to attain
equilibrium with the less hindered p-tolylamine under
identical conditions.
To test the relative proton-acceptor characteristics of the
coordinated methoxo and amido ligands in 1, we have studied
the reaction of this compound with m-nitrobenzyl alcohol
(HNBA). Just after mixing, the products methanol and the
new complex [{Rh(cod)}2(µ-NH{p-tolyl})(µ-NBA)] along
with the starting materials were observed by 1H NMR
spectroscopy. The concentration of the products increased
with time, but [{Rh(µ-NBA)(cod)}2] and free p-tolylamine
along with unidentified compounds were observed 12 h after
the reaction was started. Therefore, the results at the
beginning of the reaction indicate that HNBA protonates the
methoxo ligand faster than the p-tolylamido ligand in 1. At
first glance, one would expect that p-tolylamine was formed
instead of methanol, assuming that the amido group is a better
proton acceptor than the methoxo group. However, since the
OMe ligand contains lone electron pairs in 1 while the amido
ligand lacks them, the latter is less likely to be protonated.
In other words, the proton easily finds an active site on the
methoxo ligand, while the dissociation of the bridging amido
group is a prerequisite to produce the proton transfer to the
nitrogen.
[{Rh(µ-OMe)(cod)}2] p-tolylamine 1.01,a 9.0b -5.9 × 10-3, -1.30
[{Rh(µ-OMe)(cod)}2] a-naftylamine 0.71a
0.2 × 10-3
[{Ir(µ-OMe)(cod)}2] p-tolylamine 1.03,a 8.5b -17.5 × 10-3, -1.27
[{Rh(µ-OH)(cod)}2] p-tolylamine 5.44a
a In CDCl3. b In benzene-d6.
-1.0
1-7 were found to be dinuclear by observation of the
molecular ions (M+) via mass spectra (FAB+). A general
trend in these mass spectra was the detection of the “[{Rh-
(cod)}2(µ-NHR)]+” ions coming from the loss of the methoxo
or hydroxo groups. The 1H NMR data indicated that
complexes 1-7 were single species in solution with a Cs
symmetry plane, as found for 2 in the solid state. The
structure of the complexes is evident from the number of
resonances (i.e., four for the olefinic protons of the cod
1
ligand), and was confirmed by the H,1H-COSY spectra of
1-7 (see the Supporting Information). A rapid rotation of
the aryl groups around the HN-Cipso bond was found to be
operative for complexes 1, 2, and 4-6 even at 193 K, since
the ortho and meta protons of the amido ligands remained
equivalent even at this temperature in CD2Cl2. It is interesting
to note that the possible interconversion of the bent-anti-e
into the bent-anti-a conformation, through an inversion of
the four-membered RhNRhO ring, was not detected by NMR
spectroscopy.
The reactions of complexes [{M(µ-OR)(cod)}2] (R ) Me,
H) with p-tolylamine, R-naphthylamine, and p-NO2C6H4NH2
stop at the complexes with mixed-bridging ligands, 1-7.
Thus, the bis(amido) compounds [{M(µ-NHAr)(cod)}2] were
not detected upon addition of 1 molar equiv of the respective
amine to 1-7. However, we have observed the formation
of the complexes [{M(µ-NH{p-tolyl})(CO)2}2] (M ) Rh,
Ir)12g by adding p-tolylamine to complexes 1, 4, and 5 under
an atmosphere of carbon monoxide, which indicates the
strong influence of the ancillary ligands on the products of
these reactions. In addition, the reactions leading to com-
plexes 1-7 were found to be reversible. Thus, addition of
methanol to solutions of 1-4 in CDCl3 gave [{M(µ-OMe)-
(cod)}2] and free amine, while the addition of water to
solutions of 5-7 in CDCl3 resulted in the formation of [{Rh-
(µ-OH)(cod)}2] and free amine. The equilibrium shown in
eq 1
Finally, the deprotonation reactions of o-NO2C6H4NH2 by
[{Rh(µ-OMe)(cod)}2] and by [{Rh(µ-OH)(cod)}2] leading
to the mononuclear 8 rather than complexes with mixed-
bridging ligands are easily explained considering the chelat-
ing effect. Assuming that the hypothetical intermediates
[{Rh(cod)}2(µ-NH{o-NO2C6H4})(µ-OR)], analogous to [{Rh-
(cod)}2(µ-NH{p-NO2C6H4})(µ-OR)] (2, 6), were formed in
the first steps of the reaction, the interaction of an oxygen
atom of the nitro group with one of the metal centers provides
an easy pathway to split the bridges in these intermediates
to give 8.
Keq
[{M(µ-OR)(cod)}2] + ArNH2 y z
[{M(cod)}2(µ-NHAr)(µ-OR)] + ROH (1)
was established by mixing equimolecular amounts of [{M-
(µ-OR)(cod)}2] (R ) Me, H) and the amines in solvents such
as CDCl3 or benzene-d6 for which different Keq values were
observed. After the reaction reached equilibrium, the con-
1
centrations of the complexes were measured by H NMR
spectroscopy. Table 5 summarizes the equilibrium constant
(Keq) and the corresponding free enthalpy (∆G298) for the
reactions amenable to study.
The reactions of the rhodium and iridium (M) complexes
[{M(µ-OMe)(cod)}2] with p-tolylamine gave similar Keq
Experimental Section
Starting Materials and Physical Methods. All reactions were
carried out under argon using standard Schlenk techniques. The
complexes [{M(µ-OMe)(cod)}2]11b (M ) Rh, Ir,) and [{Rh(µ-OH)-
2352 Inorganic Chemistry, Vol. 41, No. 9, 2002

Dinuclear Rh and Ir Complexes with Mixed Bridges
(cod)}2]11b were prepared according to literature methods. p-
Tolylamine, R-naphthylamine, p-NO2C6H4NH2, and o-NO2C6H4-
NH2 were purified by sublimation prior to use. Solvents were dried
and distilled under argon before use by standard methods. Carbon,
hydrogen, and nitrogen analyses were performed in 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 ca. 30 kV;
2-nitrophenyl octyl ether (NPOE) was used as matrix. 1H and 13C-
{1H} NMR spectra were recorded on Bruker ARX 300 and Varian
UNITY 300 spectrometers operating at 299.95 and 300.13 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.
Equilibrium Constants. Solutions (0.0066 mol‚L-1) of the
complexes [{M(µ-OMe)(cod)}2] (M ) Rh, Ir) or [{Rh(µ-OH)-
(cod)}2] with an equimolar amount of the amine (p-tolylamine,
R-naphthylamine) were prepared in CDCl3 and in C6D6. The
evolution of the reactions was monitored by 1H NMR spectroscopy
until no changes in the concentrations were observed for 1 h. At
this stage, the equilibrium was considered to be reached.
6.01; N, 2.20. 1H NMR (298 K, benzene-d6): δ 8.77 (m, 1H), 7.62
(d, J ) 8.1 Hz, 1H), 7.39 (m, 1H), 7.21 (m, 3H), 6.93 (m, 1H)
(C10H7NH); 3.95 (m, 2H), 3.84 (m, 2H), 3.30 (m, 2H), 2.84 (m,
2H) (dCH cod); 3.07 (s, 3H, OMe); 2.62 (m, 2H), 2.33 (m, 2H),
exo
1.99 (m, 2H), 1.87 (m, 2H) (CH2 cod); 2.39 (s, 1H, NH); 1.81
endo
(m, 2H), 1.53 (m, 2H), 1.29 (m, 2H), 1.08 (m, 2H) (CH2
cod).
13C {1H} NMR (298 K, benzene-d6): δ 149.8, 135.0, 129.1, 128.6,
125.8, 124.6, 122.6, 120.3, 116.8, 109.8 (C10H7NH); 80.1 (d, JC-Rh
) 12 Hz), 78.8 (d, JC-Rh ) 13 Hz), 74.1 (d, JC-Rh ) 14 Hz), 71.5
(d, JC-Rh ) 14 Hz) (dCH cod); 53.6 (OMe); 32.7, 32.2, 29.6, 29.1
(CH2 cod). MS (FAB+, CH2Cl2; m/z (rel intens, %)): 595 (32) (M+);
564 (100) (M+ - OMe).
[{Ir(cod)}2(µ-NH{p-tolyl})(µ-OMe)] (4). Solid p-tolylamine
(12.9 mg, 0.12 mmol) was added to a yellow suspension of [{Ir-
(µ-OMe)(cod)}2] (80.0 mg; 0.12 mmol) in diethyl ether (10 mL).
After being stirred for 2 h, the yellow solution was concentrated to
ca. 2 mL, carefully layered with pentane (10 mL), and left in the
freezer for 3 days. The resulting yellow microcrystals were isolated
by filtration, washed with 5 mL of pentane, and vacuum-dried.
Yield: 52.0 mg (58%). Anal. Calcd for C24H35NOIr2: C, 39.06;
1
H, 4.78; N, 1.90. Found: C, 39.09; H, 4.76; N, 1.85. H NMR
(298 K, benzene-d6): δ 6.80 (δΑ, 4H), 6.58 (δΒ, JA-B ) 7.8 Hz,
4H) (p-MeC6H4); 3.90 (m, 2H), 3.69 (m, 4H), 3.24 (m, 2H) (dCH
cod); 3.47 (s, 3H, OMe); 2.85 (s, 1H, NH); 2.52 (m, 2H), 2.26 (m,
Synthesis of Complexes. [{Rh(cod)}2(µ-NH{p-tolyl})(µ-OMe)]
(1). Solid p-tolylamine (15.5 mg, 0.14 mmol) was added to a yellow
solution of [{Rh(µ-OMe)(cod)}2] (70.0 mg, 0.14 mmol) in diethyl
ether (10 mL). After 4 h, the yellow solution was concentrated to
ca. 5 mL, carefully layered with pentane (10 mL), and left for 3
days at room temperature to give yellow microcrystals. The liquid
phase was decanted, and the solid was washed with pentane (5
mL) and vacuum-dried. Yield: 49.0 mg (61%). Anal. Calcd for
C24H35NORh2: C, 51.53; H, 6.31; N, 2.50. Found: C, 51.51; H,
2H), 1.97 (m, 4H) (CH2exo cod); 2.08 (s, 3H, p-MeC6H4); 1.97 (m,
endo
2H), 1.80 (m, 2H), 1.11(m, 2H), 0.98 (m, 2H) (CH2
cod). 13C
{1H} NMR (298 K, benzene-d6): δ 147.3, 130.8, 128.7, 121.5 (p-
MeC6H4); 63.5, 61.6, 57.5, 52.2 (dCH cod); 55.2 (OMe); 34.2,
33.8, 29.4, 29.2 (CH2 cod); 20.3 (p-MeC6H4). MS (FAB+, CH2-
Cl2; m/z (rel intens, %)): 738 (15) (M+); 707 (100) (M+ - OMe).
[{Rh(cod)}2(µ-NH{p-tolyl})(µ-OH)] (5). Solid p-tolylamine
(23.5 mg, 0.22 mmol) was added to a yellow suspension of [{Rh-
(µ-OH)(cod)}2] (100.0 mg, 0.22 mmol) in diethyl ether (8 mL).
After being stirred for 2 h, the yellow suspension was concentrated
to ca. 2 mL, carefully layered with pentane (20 mL), and left in
the refrigerator for 2 days. The liquid phase was decanted, and the
solid was washed with pentane (5 mL) and vacuum-dried. Yield:
80.0 mg (67%). Anal. Calcd for C23H33NORh2: C, 50.66; H, 6.10;
N, 2.57. Found: 49.93; H, 5.63; N, 2.64. 1H NMR (298 K, benzene-
d6): δ 6.82 (δA, 2H), 6.70 (δB, JA-B ) 8.1 Hz, 2H) (p-MeC6H4);
3.75 (m, 6H), 3.26 (m, 2H) (dCH cod); 2.61 (m, 2H), 2.40 (m,
1
6.11; N, 2.43. H NMR (298 K, benzene-d6): δ 6.80 (δA, 4H),
6.66 (δΒ, JAB ) 8.4 Hz, 4H) (p-MeC6H4); 3.93 (m, 2H), 3.80 (m,
2H), 3.69 (m, 2H), 3.24 (m, 2H) (dCH cod); 3.07 (s, 3H, OMe);
exo
2.66 (m, 2H), 2.36 (m, 2H), 2.03 (m, 4H) (CH2 cod); 2.10 (s,
3H, p-MeC6H4); 1.74 (s, 1H, NH); 1.92 (m, 2H), 1.67 (m, 2H),
endo
1.30 (m, 4H) (CH2
cod). 13C{1H} NMR (298 K, benzene-d6):
δ 150.7, 129.5, 122.0, 121.0 (p-MeC6H4); 80.1 (d, JC-Rh ) 12 Hz),
78.6 (d, JC-Rh ) 13 Hz), 73.9 (d, JC-Rh ) 14 Hz), 70.2 (d, JC-Rh
) 15 Hz) (dCH cod); 53.7 (OMe); 32.7, 32.2, 29.4, 29.0 (CH2
cod); 20.4 (p-MeC6H4). MS (FAB+, CH2Cl2; m/z (rel intens, %)):
559 (52) (M+); 528 (100) (M+ - OMe).
exo
2H), 2.10 (m, 4H) (CH2 cod); 2.07 (s, 3H, p-MeC6H4); 1.86 (s,
1H, NH); 1.80 (m, 2H), 1.75 (m, 2H), 1.36 (m, 4H) (CH2endo cod);
-0.90 (s, 1H, OH). 13C {1H} NMR (298 K, benzene-d6): δ 151.0,
129.9, 129.1, 120.8 (MeC6H4); 78.4 (d, JC-Rh ) 12 Hz), 77.1 (JC-Rh
) 13 Hz), 74.0 (JC-Rh ) 14 Hz), 71.1 (JC-Rh ) 14 Hz) (dCH
cod); 33.0, 32.0, 30.0, 29.1 (CH2 cod); 20.6 (p-MeC6H4). MS
(FAB+, CH2Cl2; m/z (rel intens, %)): 545 (90) (M+); 528 (100)
(M+ - OH).
[{Rh(cod)}2(µ-NH{p-NO2C6H4})(µ-OMe)] (2). A diethyl ether
solution (10 mL) of [{Rh(µ-OMe)(cod)}2] (70.0 mg, 0.14 mmol)
was allowed to diffuse into a solution of p-NO2C6H4NH2 (20.0 mg,
0.14 mmol) in the same solvent (5 mL). Red crystals suitable for
diffraction studies formed after 3 days. The solution was decanted,
and the solid was washed with 2 × 5 mL of pentane and vacuum-
dried. Yield: 65.0 mg (76%). Anal. Calcd for C23H32N2O3Rh2: C,
46.80; H, 5.46; N, 4.74. Found: 46.40; H, 4.81; N, 4.69. 1H NMR
(298 K, CDCl3): δ 7.88 (δA, 4H), 6.78 (δB, JA-B ) 9.0 Hz, 4H)
(p-NO2C6H4); 3.90 (m, 4H), 3.27 (m, 2H), 3.05 (m, 2H) (dCH
[{Rh(cod)}2(µ-NH{p-NO2C6H4})(µ-OH)] (6). The addition of
solid p-NO2C6H4NH2 (15.2 mg, 0.11 mmol) to a suspension of
[{Rh(µ-OH)(cod)}2] (50.0 mg, 0.11 mmol) in diethyl ether (10 mL)
gave a red microcrystalline solid. After being stirred for 30 min,
the suspension was left in the refrigerator overnight. The solution
was decanted, and the solid was washed with diethyl ether (5 mL)
and vacuum-dried. Yield: 45.0 mg (71%). Anal. Calcd for
C22H30N2O3Rh2: C, 45.85; H, 5.25; N, 4.86. Found: 45.37; H, 4.82;
exo
cod); 2.92 (s, 3H, OMe); 2.41 (m, 8H, CH2 cod); 2.15 (m, 8H,
endo
CH2
cod). MS (FAB+, CH2Cl2; m/z (rel intens, %)): 590 (40)
(M+); 559 (100) (M+ - OMe).
[{Rh(cod)}2(µ-NH{r-naphthyl})(µ-OMe)] (3). Solid R-naph-
thylamine (17.7 mg, 0.12 mmol) was added to a diethyl ether
solution (10 mL) of [{Rh(µ-OMe)(cod)}2] (60.0 mg, 0.12 mmol).
After being stirred for 1 h, the yellow suspension was concentrated
to ca. 2 mL and left in the freezer. The yellow microcrystalline
solid was isolated by filtration, washed with 5 mL of cold diethyl
ether, and vacuum-dried. Yield: 40.0 mg (54%). Anal. Calcd for
C27H35NORh2: C, 54.47; H, 5.92; N, 2.35. Found: C, 54.32; H,
1
N, 4.49. H NMR (298 K, CDCl3): δ 7.89 (δA, 2H), 6.82 (δB,
JA-B ) 9.0 Hz, 2H) (p-NO2C6H4); 3.84 (m, 4H), 3.35 (m, 2H),
3.16 (m, 2H) (dCH cod); 2.50 (m, 4H), 2.30 (m, 4H) (CH2exo cod);
1.83 (m, 2H), 1.58 (m, 6H) (CH2endo cod); 1.82 (s, 1H, NH); -0.89
(s, 1H, OH). MS (FAB+, CH2Cl2; m/z (rel intens, %)): 576 (40)
(M+); 559 (100) (M+ - OH).
Inorganic Chemistry, Vol. 41, No. 9, 2002 2353

Tejel et al.
Table 6. Crystallographic Data for the Structural Analyses of
Complexes 2, 7′, and 8
8), with graphite-monochromated Mo KR radiation (λ ) 0.71073
Å). Corrections for Lorentz and polarization effects were applied.
The structures were solved by the Patterson method (SHELXS97)19
and difference Fourier techniques and refined by full-matrix least-
squares on F2 (SHELXL97).19 Scattering factors, corrected for
anomalous dispersion, were used as implemented in the refinement
program.
2
7′
8
empirical formula
C23H32N2O3Rh2 C38H54NO3Rh3 C14H17N2O2Rh
fw
590.33
881.55
348.21
temp, K
space group
a, Å
b, Å
c, Å
293(2)
173(2)
173(2)
Pnma (no. 62)
12.639(2)
15.733(3)
11.309(2)
P?1 (no. 2)
10.1587(11)
11.4766(12)
16.4380(17)
105.480(2)
90.307(2)
109.288(2)
1734.0(3)
2
1.688
1.448
0.0546
0.1143
P21/n (no. 14)
9.4419(14)
12.0801(17)
12.2334(17)
Crystal Data for [{Rh(cod)}2(µ-NH{p-NO2C6H4})(µ-OMe)]
(2). A red irregular block of approximate dimensions 0.09 × 0.14
× 0.34 mm was used for data collection. Of 4734 measured
reflections in the range 2θ ) 4-50° (ω/2θ scans), 2056 were unique
(Rint ) 0.0318); a ψ scan absorption correction was applied,20 with
minimum/maximum transmission factors of 0.617/0.843. All non-
hydrogen atoms were refined with anisotropic displacement pa-
rameters. Hydrogens of the sp3 carbons were calculated and refined
riding on the corresponding atoms; those bonded to the nitrogen
or to sp2 carbons were located in a difference Fourier map and
refined with free positional and isotropic displacement parameters.
Final agreement factors were obtained (Table 6) for 185 parameters
with no restraints; GOF ) 1.005. The largest peak and hole in the
R, deg
â, deg
110.573(3)
γ, deg
V, Å3
2248.8(7)
4
1.744
1.494
1306.3(3)
4
1.770
1.306
0.0533
0.1063
Z
F(calcd), g cm-3
µ(Mo KR), mm-1
R(F) [F2 > 2σ(F2)]a 0.0288
Rw(F2) (all data)b
0.0615
a R(F) ) ∑||Fo| - |Fc||/∑|Fo|, for 1476, 4438, and 1829 observed
2
2
reflections for 2, 7′, and 8, respectively. b Rw(F2) ) (∑[w(Fo - Fc )2]/
2
∑[w(Fo )2])1/2
.
final difference map were 0.46 and -0.66 e Å-3
.
[{Rh(cod)}2(µ-NH{r-naphthyl})(µ-OH)]2‚[{Rh(µ-OH)(cod)}2]‚
2THF (7′). Solid R-naphthylamine (18.8 mg, 0.13 mmol) was added
to a yellow suspension of [{Rh(µ-OH)(cod)}2] (60.0 mg, 0.13
mmol) in diethyl ether (5 mL). After being stirred for 1 h, the
suspension was evaporated to dryness. The residue was dissolved
in THF (3 mL), and the solution was carefully layered with pentane
(15 mL). Cubic yellow crystals suitable for diffraction studies were
formed after 4 days. The solution was decanted, and the solid was
washed with pentane (2 mL) and vacuum-dried. Yield: 83.0 mg
(72%). Anal. Calcd for C38H54NO3Rh3: C, 51.77; H, 6.17; N, 1.59.
Crystal Data for [{Rh(cod)}2(µ-NH{r-naphthyl})(µ-OH)]2-
[{Rh(µ-OH)(cod)}2]‚2THF (7′). A yellow irregular block of
approximate dimensions 0.06 × 0.12 × 0.18 mm was used for data
collection. Of 20410 measured reflections in the range 2.6-54° in
2θ (ω scans), 7512 were unique (Rint ) 0.0791); a multiscan
absorption correction based on this multiplicity was performed,21
with minimum/maximum transmission factors of 0.724/0.929. All
non-hydrogen atoms were refined with anisotropic displacement
parameters, except the carbon atoms of the cod ligands of the [{Rh-
(µ-OH)(cod)}2] complex. This dinuclear molecule sits on an
inversion center located in the midpoint of the intermetallic vector;
this symmetry constraint imposes the presence of a static disorder
for the ligands (bridging hydroxides and terminal cyclooctadienes),
with 2-folded dinuclear complexes of equal occupancy at both sides
of the center of symmetry. Bond restraints in the C-C bond
distances were necessary to make the refinement to converge; no
hydrogens were included for this complex. The THF solvent was
also partially disordered, with two oxygens in the model (comple-
mentary occupancy factors of 0.63(5) and 0.37(5)), and refined
without hydrogens and with restraints in the C-O bond lengths.
The positions of the remaining hydrogen atoms were geometrically
calculated, except those bonded to nitrogen, oxygen, and the sp2
carbons of the cod ligands in the [Rh2(cod)2(µ-NH{R-naphthyl})-
(µ-OH)] complex, which were located in a difference Fourier map;
all of them were refined riding on the corresponding atoms. Final
agreement factors were obtained (Table 6) for 431 parameters and
63 restraints; GOF ) 0.888. The largest peak and hole in the final
1
Found C, 51.46; H, 6.43; N, 1.70. H NMR (298 K, benzene-d6)
for 7: δ 8.65 (m, 1H), 7.62 (d, J ) 8.4 Hz, 1H), 7.38 (t, J ) 7.2
Hz, 1H), 7.20 (m, 2H), 7.15 (m, 1H), 7.05 (d, J ) 6.9 Hz, 1H)
(C10H7NH); 3.83 (m, 2H), 3.73 (m, 2H), 3.10 (m, 2H), 2.66 (m,
exo
2H) (dCH cod); 2.00 (m, 6H), 1.83 (m, 2H) (CH2 cod); 1.50
endo
(m, 2H), 1.34 (m, 4H), 1.11 (m, 2H) (CH2
cod); 2.58 (s, 1H,
NH); -1.01 (s, 1H, OH). 13C{1H} NMR (298 K, benzene-d6) for
7: δ 150.2, 153.1, 129.1, 128.0, 125.9, 125.8, 124.8, 122.6, 120.2,
116.6 (C10H7NH); 78.4 (d, JC-Rh ) 11 Hz), 77.2 (d, JC-Rh ) 9
Hz), 74.1 (d, JC-Rh ) 15 Hz), 72.1 (d, JC-Rh ) 11 Hz) (dCH cod);
32.9, 31.9, 29.8, 29.0 (CH2 cod). MS (FAB+, CH2Cl2; m/z (rel
intens, %)) for 7: 581 (100) (M+); 564 (85) (M+ - OH).
[Rh(o-NO2C6H4NH)(cod)] (8). The addition of solid o-NO2C6H4-
NH2 (57.1 mg, 0.42 mmol) to a solution of [{Rh(µ-OMe)(cod)}2]
(100.0 mg, 0.21 mmol) in THF (10 mL) produced immediately a
purple solution. This solution was concentrated to ca. 2 mL,
carefully layered with pentane (20 mL), and left undisturbed for 3
days at room temperature. The resulting dark-purple needles were
separated by decantation, washed with pentane (2 × 5 mL), and
vacuum-dried. Yield: 132.0 mg (92%). Anal. Calcd for C14H17N2O2-
Rh: C, 48.29; H, 4.92; N, 8.04. Found C, 47.89; H, 5.00; N, 7.89.
1H NMR (298 K, CDCl3): δ 7.87 (d, J ) 9.1 Hz, 1H), 7.00 (m,
1H), 6.58 (d, J ) 9.0 Hz, 1H), 6.39 (m, 1H) (o-NO2C6H4); 6.08 (s,
1H, NH); 4.46 (m, 2H), 3.87 (m, 2H) (dCH cod); 2.44 (m, 4H,
difference map were 0.798 and -0.802 e Å-3
.
Crystal Data for [Rh(o-NO2C6H4NH)(cod)] (8). A purple
needle of approximate dimensions 0.02 × 0.04 × 0.34 mm was
used for data collection. Of 8167 reflections integrated in the range
2θ ) 4.7-54° (ω scans), 2824 were unique (Rint ) 0.1068); a
multiscan absorption correction was performed,21 with minimum/
maximum transmission factors of 0.536/0.925. All non-hydrogen
atoms were refined with anisotropic displacement parameters;
exo
endo
CH2 cod), 2.00 (m, 4H, CH2
cod). 13C{1H} NMR (298 K,
CDCl3): δ 155.4, 135.6, 133.0, 126.5, 126.0 (d, JC-Rh ) 2 Hz),
117.6 (o-NO2C6H4); 84.4 (d, JC-Rh ) 11 Hz), 71.8 (d, JC-Rh ) 11
Hz) (dCH cod); 31.1, 29.4 (CH2 cod). MS (FAB+, CH2Cl2; m/z
(rel intens, %)) for 7: 348 (100) (M+).
Crystal Structure Determination of Compounds 2, 7′, and 8.
A summary of crystal data and refinement parameters is given in
Table 6. Data were collected on a Siemens P4 diffractometer at
room temperature (2) or on a Bruker Smart APEX at 173 K (7′,
(19) Programs for Crystal Structure Analysis (release 97-2): G. M.
Sheldrick, Institu¨t fu¨r Anorganische Chemie der Universita¨t, Go¨ttingen,
Germany, 1998.
(20) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr.
1968, A24, 351.
(21) SADABS: Area-Detector Absorption Correction; Siemens Industrial
Automation, Inc.: Madison, WI, 1996.
2354 Inorganic Chemistry, Vol. 41, No. 9, 2002

Dinuclear Rh and Ir Complexes with Mixed Bridges
hydrogens were introduced in calculated positions and refined riding
on the corresponding atoms. Final agreement factors were obtained
(Table 6) for 175 parameters with no restraints; GOF ) 0.866. The
largest peak and hole in the final difference map were 0.973 and
PNI) (Projects PB 98-641 and BQU2000-1170) is gratefully
acknowledged.
Supporting Information Available: An X-ray crystallographic
file in CIF format for the structure determination of complexes 2,
7′, and 8 and the 1H,1H-COSY spectrum of complex 4. This material
is available free of charge via the Internet at http://pubs.acs.org.
-0.910 e Å-3
.
Acknowledgment. The generous financial support from
the Direccio´n General de Ensen˜anza Superior e Investigacio´n
(DGES) and Ministerio de Ciencia y Tecnolog´ıa (MCyT-
IC0109952
Inorganic Chemistry, Vol. 41, No. 9, 2002 2355