Preparation of aryldiazene complexes of rhodium

Article abstract of DOI:10.1016/S0022-328X(01)00720-3

Aryldiazene complexes [Rh(ArN=NH)(CO)(PPh₃)₃]BF₄ (1) and [Rh(ArN=NH)(PPh₃)₄]BF₄ (2) (Ar=C₆H₅ or 4-CH₃C₆H₄) were prepared by allowing h

Full text of DOI:10.1016/S0022-328X(01)00720-3

Journal of Organometallic Chemistry 627 (2001) 99–104
www.elsevier.nl/locate/jorganchem
Preparation of aryldiazene complexes of rhodium
Gabriele Albertin *, Stefano Antoniutti, Emilio Bordignon, Alessandra Tasin
Dipartimento di Chimica, Uni6ersita` Ca’ Foscari di Venezia, Dorsoduro 2137, I-30123 Venice, Italy
Received 18 December 2000; accepted 5 February 2001
Abstract
Aryldiazene complexes [Rh(ArNꢀNH)(CO)(PPh3)3]BF4 (1) and [Rh(ArNꢀNH)(PPh3)4]BF4 (2) (Ar=C6H5 or 4-CH3C6H4) were
prepared by allowing hydride species RhH(CO)(PPh3)3 and RhH(PPh3)4 to react with aryldiazonium cations at low temperature.
1
The complexes were characterised by IR and H-, 31P- and 15N-NMR spectra, using 15N labelled compounds. Free aryldiazene
ArNꢀNH species and [Rh{PPh(OEt)2}4]BF4 were obtained by reacting the hydride RhH[PPh(OEt)2]4 with aryldiazonium cations
in CH2Cl2 at −80°C. Reactions of aryldiazene complexes 1 and 2 with H2 (1 atm) were also studied, but did not lead to
arylhydrazine derivatives. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Rhodium; Aryldiazene complexes; Free aryldiazene
1. Introduction
the first aryldiazenido [4] [Co(RN2){PPh(OEt)2}4]-
(BPh4)2, the reactivity of hydride CoHP4 (P=phos-
phite) towards aryldiazonium salts [5], and the recent
preparation of hydrazine complexes of iridium [6]. As
an extension to these studies, we have now focused our
attention to rhodium as the central metal, the diazo
chemistry of which is less known when compared with
that of other transition metals. In fact, while some
examples of aryldiazenido complexes of the type
[RhCl(PPh3)2(p-N2C6H4OMe)]BF4, [RhC6H5P{(CH2)3-
P(C6H5)2}2Cl(N2C6H5)]PF6 are known [7,8], only one
aryldiazene complex, RhCl3(ArNꢀNH)(PPh3)2, has
been described [9]. This paper reports a study on the
reactivity of rhodium hydride complexes towards aryl-
diazonium cations, which allows the synthesis of a
series of aryldiazene complexes to be obtained.
Currently there is a lot of interest in the chemistry of
transition metal complexes containing aryldiazenido,
ArN2, aryldiazene, ArNꢀNH, or other partially reduced
dinitrogen ligands, NNHx, not only due to possible
relevance in the nitrogen fixation process, but also to
the different coordination modes and to the interesting
properties that this class of ligands may present [1,2].
However, the influence of various factors such as the
nature of the central metal, its oxidation state, and the
nature of the ancillary ligand on the properties of the
complexes has not yet been completely rationalised [1].
Therefore, a systematic study of this class of complexes
is desirable, in order to clarify the factors governing not
only the wide range of coordination geometries adopted
by these diazo ligands, but also their potential proper-
ties towards oxidation, reduction, protonation and de-
protonation reactions.
2. Experimental
In this context, we have reported several studies on
the diazo chemistry of the iron triad [3], including the
synthesis and reactivity of mono- and bis(aryldi-
azenido), aryldiazene and hydrazine derivatives. Paral-
lel studies on the cobalt family involved the synthesis of
2.1. General considerations and physical measurements
All synthetic work was carried out under an inert
atmosphere using standard Schlenk techniques or a
Vacuum Atmosphere dry-box. Once isolated, the com-
plexes were found to be sufficiently stable in air to
allow characterisation, but were stored under an inert
* Corresponding author. Fax: +39-41-2578517.
E-mail address: albertin@unive.it (G. Albertin).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00720-3

100
G. Albertin et al. / Journal of Organometallic Chemistry 627 (2001) 99–104
atmosphere at −25°C. All solvents were dried over
appropriate drying agents, degassed on a vacuum line,
and distilled into vacuum-tight storage flasks.
RhCl3·3H2O was a CHIMET product, used as received.
Phenyldiethoxyphosphine, PPh(OEt)2, was prepared by
the method of Rabinowitz and Pellon [10] and purified
by distillation under nitrogen. Diazonium salts [ArN2]+
BF−4 were obtained in the usual way [11]. Labelled
diazonium tetrafluoroborate [C6H5Nꢁ15N]BF4 was pre-
pared from Na15NO2 (99% enriched, CIL) and the
appropriate amine. Alternatively, the [C6H515NꢁN]BF4
salt was obtained from NaNO2 and C6H515NH2. Other
reagents were purchased from commercial sources in
the highest available purity and used as received. In-
frared spectra were recorded on a Nicolet Magna 750
FTIR spectrophotometer. NMR spectra (1H, 31P, 15N)
were obtained on a Bruker AC200 spectrometer at
temperatures varying between −90 and +30°C, unless
otherwise noted. 1H spectra are referred to internal
tetramethylsilane. 31P{1H} chemical shifts are reported
with respect to 85% H3PO4, with downfield shifts con-
sidered positive. 15N spectra refer to external CH315NO2,
with downfield shifts considered positive. The SwaN-
MR software package [12] was used to treat NMR
data. The conductivities of 10−3 mol dm−3 solutions of
the complexes in CH3NO2 at 25 or 0°C were measured
with a Radiometer CDM 83 instrument.
lated 1a using labelled (C6H5Nꢁ15N)BF4 and
(C6H155NꢁN)BF4 aryldiazonium salts, respectively; yield
]60%.
2.2.3. [Rh(C6H5NꢀNH)(PPh3)4]BF4 (2a),
[Rh(4-CH3C6H4NꢀNH)(PPh3)4]BF4 (2b)
A solid sample of RhH(PPh3)4 (0.1 g, 0.09 mmol)
and an equimolar amount of the appropriate diazo-
nium salt (ArN2)+BF4− (0.09 mmol) were mixed to-
gether in a 25-cm3 three-necked round-bottomed flask
and cooled to −196°C. CH2Cl2 (10 cm3) was added
and the resulting mixture was brought to −5°C and
stirred at this temperature for 2 h. The solvent was
removed under reduced pressure to give an oil which
was triturated, at −5°C, with Et2O (5 cm3). A yellow
solid slowly separated out which was filtered and crys-
tallised at −10°C from CH2Cl2 and Et2O; yield ]
55%; \M/S cm2 mol−1 at 0°C=79.4 for 2a, 77.7 for 2b.
Anal. Found: C, 69.5; H, 4.8; N, 2.2. Calc. for
C78H66BF4N2P4Rh (2a): C, 69.7; H, 4.9; N, 2.1%. Anal.
Found: C, 69.9; H, 4.9; N, 2.0. Calc. for
C79H68BF4N2P4Rh (2b): C, 69.8; H, 5.0; N, 2.1%.
2.2.4. [Rh(C6H5Nꢀ15NH)(PPh3)4]BF4 (2a1),
[Rh(C6H515NꢀNH)(PPh3)4]BF4 (2a2)
These complexes were prepared like the related 2a
using labelled (C6H5Nꢀ15N)BF4 and (C6H515Nꢀ
N)BF4 aryldiazonium salts, respectively; yield ]55%.
2.2. Synthesis of complexes
2.2.5. [Rh{PPh(OEt)2}4]BF4 (3)
Hydride complexes RhH(CO)(PPh3)3, RhH[P-
Ph(OEt)2]4, RhH(PPh3)4 were prepared following the
methods previously reported [13–15].
In a 25-cm3 three-necked round-bottomed flask were
placed solid samples of RhH[PPh(OEt)2]4 (0.1 g, 0.11
mmol) and of an equimolar amount (0.11 mmol) of
(C6H5N2)BF4 or (4-CH3C6H4N2)BF4 aryldiazonium
salts and the flask was cooled to −196°C. CH2Cl2 (10
cm3) was added and the reaction mixture brought to
−5°C and stirred for 1 h. The solvent was removed
under reduced pressure giving an oil which was tritu-
rated with EtOH (5 cm3). A yellow solid slowly sepa-
rated out from the resulting solution, which was filtered
and crystallised from ethanol; yield ]70%; \M/
S cm2 mol−1 at 25°C=84.3. Anal. Found: C, 48.7; H,
6.3. Calc. for C40H60BF4O8P4Rh: C, 48.9; H, 6.2%.
2.2.1. [Rh(C6H5NꢀNH)(CO)(PPh3)3]BF4 (1a),
[Rh(4-CH3C6H4NꢀNH)(CO)(PPh3)3]BF4 (1b)
In a 25-cm3 three-necked round-bottomed flask were
placed 0.1 g (0.11 mmol) of RhH(CO)(PPh3)3 and an
equimolar amount of the appropriate aryldiazonium
tetrafluoroborate (ArN2)BF4 (0.11 mmol). The flask
was cooled to −196°C and 10 cm3 of CH2Cl2 added.
The reaction mixture was brought to −5°C and stirred
at this temperature for 50 min. The solvent was re-
moved under reduced pressure, giving an oil which was
treated, at −5°C, with 2 cm3 of EtOH. By cooling of
the resulting solution to −25°C yellow microcrystals
were obtained which were filtered and dried under
vacuum; yield ]60%; \M/S cm2 mol−1 at 25°C=87.3
for 1a, 91.5 for 1b. Anal. Found: C, 66.1; H, 4.5; N,
2.4. Calc. for C61H51BF4N2OP3Rh (1a): C, 66.0; H, 4.6;
N, 2.5%. Anal. Found: C, 66.4; H, 4.6; N, 2.6. Calc. for
C62H53BF4N2OP3Rh (1b): C, 66.2; H, 4.8; N, 2.5%.
2.2.6. Hydrogenation reactions
A solid sample of aryldiazene complex 1 or 2 (0.1
mmol) was placed in a 25-cm3 three-necked round-bot-
tomed flask cooled to −10°C and treated with 10 cm3
of the appropriate solvent (CH2Cl2, THF). The result-
ing solution was allowed to stir under a hydrogen
atmosphere (1 atm) for several hours (from 4 to 10) at
−10°C, and the solvent was then removed under re-
duced pressure. The oil thus obtained was treated with
EtOH (2 cm3), giving a yellow solid which was filtered
and dried under vacuum.
2.2.2. [Rh(C6H5Nꢀ15NH)(CO)(PPh3)3]BF4 (1a1),
[Rh(C6H515NꢀNH)(CO)(PPh3)3]BF4 (1a2)
These complexes were prepared exactly like the re-

G. Albertin et al. / Journal of Organometallic Chemistry 627 (2001) 99–104
101
Scheme 1. Ar=C6H5 (a) or 4-CH3C6H4 (b).
For the product obtained from 1a: IR (KBr, cm−1):
3277 (m), 3209 (m) [2008 (m), 1965 (s) w(CO)]. 1H-
NMR (CD2Cl2-d2, 293 K, l ppm): 7.90–6.82 (m, Ph);
5.71 (br); 5.14 (br). 31P{1H}-NMR (CD2Cl2-d2, 293 K,
l ppm): 39–22 (m).
For the product obtained from 2a: IR (KBr, cm−1):
3285 (m), 3217 (m). 1H-NMR (CD2Cl2-d2, 293 K, l
ppm): 7.80–6.77 (m, Ph), 5.53 (m), 4.74 (m). 31P{1H}-
NMR (CD2Cl2-d2, 293 K, l ppm): 52–23 (m).
The synthesis of aryldiazene complexes 1 prompted
us to extend the study on aryldiazonium cations to
other rhodium hydrides of the type RhHP4. The results
obtained are summarised in Scheme 2.
3. Results and discussion
The hydride–carbonyl complex RhH(CO)(PPh3)3
quickly reacts with aryldiazonium cations to give aryl-
diazene derivatives [Rh(ArNꢀNH)(CO)(PPh3)3]BF4 1,
which were isolated in good yield and characterised
(Scheme 1).
Aryldiazene complexes 1 are rather unstable and only
the use of low temperature at the start and during the
reaction course allows stable compounds to be ob-
tained. Furthermore, crucial for successful preparation
of ArNꢀNH species is the use of an exact stoichiometric
ratio between the reagents; otherwise, a large amount
of decomposition substances are found in the final
reaction product.
Analytical and spectroscopic data (Table 1) support
the formulation of complexes 1, which are air-stable
yellow solids, thermally unstable in solution, and 1:1
electrolyte [16]. In particular, diagnostic for the pres-
ence of the diazene ligand was the high-frequency H-
NMR signal of the NH proton at 12.66–12.47 ppm,
Hydride RhH(PPh3)4 quickly reacts with aryldiazo-
nium cations to give aryldiazene complexes
[Rh(ArNꢀNH)P4]BF4 2, which were isolated in the
solid state and characterised. Also in this case, crucial
for the success of the synthesis was the use of stoichio-
metric amounts of the reagents and keeping tempera-
ture below −5°C during the reaction course. In fact,
the use of a higher temperature yields decomposition
products with only traces of aryldiazene complex.
In contrast, the hydride RhHP4 containing the
PPh(OEt)2 ligand reacts in all conditions with aryldia-
zonium cations to give, instead of an aryldiazene com-
plex, the tetrakis(phosphite) [Rh{PPh(OEt)2}4]BF4
3
derivative, which was isolated in high yield and charac-
terised. The formation of a complex of type 3 suggested
studying the reaction course extensively, starting from
low temperature (−80°C), in order to detect the prob-
able intermediate and to propose a path for the reac-
1
1
tion. The H-NMR spectrum of the solution containing
which is split into a sharp doublet in labelled com-
RhH[PPh(OEt)2]4 and an equimolar amount of the
1
pounds 1a1 and 1a2. The values for both the J15 and
NH
aryldiazonium salt ArN+2 BF4− salt in CD2Cl2-d2 at
2J15
of 62 and 4.5 Hz, respectively, were also deter-
minNedH and agreed [1,3,9,17] with the proposed
formulation.
The IR spectra show only one w(CO) band at 1965
cm−1. At room temperature, the 31P{1H}-NMR spectra
of 1 appear as rather broad multiplets, suggesting flux-
ionality of the complexes. In fact, lowering the sample
temperature causes a change in the spectra, until at
−90°C a well-resolved multiplet appears (Fig. 1),
which may be simulated as the A2B part of an AB2X
system (X=rhodium) with the parameters listed in
Table 1. The structure of the complexes may be dis-
cussed in terms of a trigonal bipyramidal TBP or a
square pyramidal SP geometry, but the spectroscopic
data do not allow us to decide between them. However,
a type I geometry, fitting both literature data [1,2] and
IR and NMR spectra, may be tentatively proposed.
Fig. 1. 31P{1H}-NMR spectra of complex [Rh(4-CH3C6H4NꢀNH)-
(CO)(PPh3)3]BF4 (1b) in CD2Cl2 at 203 K. Top: simulated (see
parameters in Table 1); bottom: experimental. The peak indicated by
an asterisk is due to an impurity.

Table 1
IR and NMR data for the rhodium complexes
a
Compound
IR
1H-NMR b,c
Assignment l (J Hz)
Spin system 31P{1H}-NMR b,d
w¯ (cm−1
)
Assignment
l (J Hz)
1a [Rh(C6H5NꢀNH)(CO)(PPh3)3]BF4
1965s
1966s
w(CO)
w(CO)
12.66 (s)
12.66 (d) J15 =62 NH
NH
A2BX e
lA 26.9; lB=25.9; JAB=38.3; JAX=122.2; JBX=128.3
lA=26.9;lB=25.9; JAB=38.3; JAX=122.2; JBX=128.0;
AY=B0.5; JBY=B0.5
dA=26.9; lB=25.9; JAB=38.3; JAX=122.2; JBX=128.0;
AY=B0.5; JBY=B0.5
f
1
1a1 [Rh(C6H5Nꢀ15NH)(CO)(PPh3)]BF4
A2BXY e
NH
/
J
1a2 [Rh(C6H155NꢀNH)(CO)(PPh3)3]BF4
1965s
w(CO)
w(CO)
12.67 (d) J15 =4.5 NH
A2BXY e
A2BX e
2
NH
J
1b [Rh(4-CH3C6H4NꢀNH)(CO)(PPh3)3]BF4 1966s
2a [Rh(C6H5NꢀNH)(PPh3)4]BF4
12.47 (s)
2.28 (s)
NH
CH3
NH
NH
lA=26.9; lB=25.9; JAB=38.5; JAX=122.5; JBX=128.0
12.15 (m, br) g
12.17 (dm) g,
1J15 =60
12.1N7H(m, br) g
11.8 (m, br) g
2.32 (s)
29.6 (s, br) g; 50–21 (m, br) e
50–21 (m, br) e
2a1 [Rh(C6H5Nꢀ15NH)(PPh3]4BF4
h
2a2 [Rh(C6H155NꢀNH)(PPh3]4BF4
2b [Rh(4-CH3C6H4NꢀNH)(PPh3]4BF4
NH
NH
CH3
CH2
CH3
28.3 (s, br) g
28.5 (s, br) g; 50–20 me
3
[Rh{PPh(OEt)2}4]BF4
3.56 (m), 3.27 (m),
1.04 (t)
A4X
lA 145.0; JAX=180
627
a In KBr pellets.
b In CD2Cl2 at 25°C.
(
c Phenyl proton resonances are omitted.
d Positive shift downfield from 85% H3PO4.
e At −80°C.
104
f 15N-NMR, l: 3.9 (dd), J15NRh=12 Hz, J15NH=62 Hz.
g At −5°C.
h 15N-NMR, d: −20 (s, br).

G. Albertin et al. / Journal of Organometallic Chemistry 627 (2001) 99–104
103
Scheme 2.
−80°C shows a diazene proton signal at 15.29 ppm,
which is split into a doublet (1J15NH=49.9 Hz) using
the labelled ArNꢀ15N+BF−4 salt, and may suggest the
presence of an aryldiazene complex. However, the
31P{1H}-NMR spectra of this reaction mixture do not,
in any conditions, show the presence of new signals
beside the two doublets due to the final
[Rh{PPh(OEt)2}4]+ cations 3 (at 145.2 ppm) and the
starting RhH[PPh(OEt)2]4 derivative at 166.9 ppm.
These results are rather surprising and may be ex-
plained by the formation of an aryldiazene intermediate
[Rh(ArNꢀNH)P4]+ [A], in which the ArNꢀNH ligand is
so labile even at −80°C so as to give
[Rh{PPh(OEt)2}4]+ and the free ArNꢀNH ligand
(Scheme 2). Comparison of the value of the chemical
shift of the NH diazene proton signal with those of
already known examples of free aryldiazene molecules
[18] supports its formation and shows that also the
hydrides containing the phosphonite PPh(OEt)2 un-
dergo an insertion reaction of ArN+2 cation into the
RhꢂH bond giving an aryldiazene complex. The lability
of the ligand, however, makes this reaction useful as a
new method for the easy synthesis, even at very low
temperatures, of aryldiazene molecules. The reaction
was also followed at temperature higher than −80°C
and observed a slow decomposition of free aryldiazene
(upon 0°C) giving N2 and the corresponding hydrocar-
bon CH3C6H5.
allow comparisons with the reactivity of the related
cobalt complexes CoH[PPh(OEt)2]4, previously re-
ported by us [5]. Reactivity with ArN+2 is completely
different in the two cases, with the oxidation of CoH[P-
Ph(OEt)2]4 to give cationic paramagnetic [CoH{PPh-
(OEt)2}4]+ species for cobalt, and insertion of ArN2+
into the RhꢂH bond to give an aryldiazene for
rhodium. This different behaviour in the reactivity of
the two hydrides towards ArN+2 is difficult to explain,
also taking into account that it is very rare [1,19] for
aryldiazonium salt to act as an oxidant on a metal
complex. Probably, the unreactivity toward insertion of
the CoHP4 is due to the low hydridic character of the
H− ligand in cobalt complexes, which prevents reduc-
tion of ArN+2 to aryldiazene. Instead, oxidation of the
central metal from +1 to +2 was observed, which is
probably peculiar to this metal, but does not involve all
the hydrides in the triad, for which the classical inser-
tion reaction to give aryldiazene complexes predomi-
nates [1,2,6].
The yellow–orange [Rh(ArNꢀNH)(PPh3)4]BF4
2
complexes are stable as solids, but decompose in solu-
tion even at 0°C, with loss of the aryldiazene ligand.
Therefore, spectroscopic measurements for characteri-
sation (1H- and 31P-NMR) were carried out at tempera-
tures below 0°C. Conductivity measurements were also
carried out at 0°C and indicated the presence of 1:1
1
electrolytes [16]. The H-NMR spectra are consistent
Previously reported methods [18] for the synthesis of
these thermally unstable ArNꢀNH molecules often in-
volve substitution reactions of coordinate ArNꢀNH
species at a temperature (between −5 and +5°C) at
which the free aryldiazene is only marginally stable.
The use of the reaction of RhH[PPh(OEt)2]4 with ArN2+
allows the easy synthesis of ArNꢀNH in good yield at
low temperature, and it can be used as a reagent for
peculiar organic reactions.
with the presence of the aryldiazene ligand, showing in
the high frequency region a broad NH signal at 12.15
ppm for 2a (at 11.8 ppm for 2b), split into a sharp
doublet (1J15NH=60 Hz) in the labelled [Rh-
(PhNꢀ15NH)(PPh3)4]BF4 2a1 compound, in agreement
with the proposed formulation. At −5°C, the 31P{1H}-
NMR spectra appear as a broad signal which changes
as the temperature is lowered. However, even at
−90°C the spectra are still too broad to give a fine
structure, thus preventing geometric assignment in solu-
tion for these complexes.
Results on the reactivity of phosphite-containing
rhodium(I) hydrides RhHP4 with aryldiazonium cations

104
G. Albertin et al. / Journal of Organometallic Chemistry 627 (2001) 99–104
The tetracoordinate [Rh{PPh(OEt)2}4]BF4 is a yellow
Acknowledgements
diamagnetic solid, stable in the air, and 1:1 electrolyte
[16]. The analytical and spectroscopic data (Table 1)
confirm its formulation, which is similar to other
known [20] tetrakis(phosphite) Rh(I) complexes.
The financial support of the Ministero della Ricerca
Scientifica e Tecnologica, Rome — Programmi di
Ricerca Scientifica di Rilevante Interesse Nazionale,
Cofinanziamento 2000–2001 — is gratefully acknowl-
edged. We thank Daniela Baldan for technical
assistance.
Aryldiazene complexes of rhodium 1 and 2 were
reacted with H2 (1 atm) in order to test the possibility
of reduction of the ArNꢀNH moiety to hydrazine. We
carried out the reaction of 1 and 2 with H2 in various
solvents and at low temperature (−10 to 0°C) to avoid
decomposition of the starting complexes. A yellow–or-
ange solid was obtained from the reduction of both
complexes 1 and 2, whose IR spectra show two medium
intensity bands at 3277 and 3209 cm−1 for reduction of
1 and at 3285 and 3217 cm−1 for reduction of 2,
probably attributable to w(NH) of a coordinated aryl-
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[10] R. Rabinowitz, J. Pellon, J. Org. Chem. 26 (1961) 4623.
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mans, Green and Co, New York, 1956.
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Synth. 15 (1974) 45.
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1
hydrazine ligand. The H-NMR spectra of this reduc-
tion product show the presence of two broad signals
between 5.71 and 4.74 ppm, attributable to NH and
NH2 signals of an arylhydrazine ligand. On this basis, it
seems reasonable to hypothesise that the reaction pro-
ceeds with reduction of the aryldiazene ligand to aryl-
hydrazine in mild conditions. In order to confirm the
formulation of the reduction product, we treated the
labelled complex [Rh(PhNꢀ15NH)(CO)P3]BF4 1a1 with
1
H2 and recorded the H-NMR spectra of the resulting
solid. Surprisingly, the spectra were exactly like those of
the unlabelled complex, and no splitting due to cou-
pling with 15N of the signals attributable to NH and
NH2 was observed. We repeated the reaction with the
other labelled complexes 1a2, 2a1 and 2a2 and observed
no variations in the proton spectra, in comparison with
those of the unlabelled ones, indicating that the broad
signals at 5.71–4.74 ppm are not attributable to the
NH proton of hydrazine complexes. We also attempted
to purify the complexes, and observed that crystallisa-
tion from CH2Cl2 and EtOH gives a product with
1
identical H-NMR spectra, but whose IR spectra show
the disappearance of the 3285–3209 cm−1 band at-
tributed to the w(NH) group. On this basis, and taking
into account that elemental analyses indicate the ab-
sence of N2, we can exclude the possibility that the
reaction of rhodium(I) aryldiazene 1 and 2 with H2
proceeds with the reduction of the ArNꢀNH group, to
give an arylhydrazine complex. These results contrast
with previous studies [21] on the diazo chemistry of
rhodium, which reported that aryldiazene and aryldi-
azenido complexes may be reduced to arylhydrazine
complexes in the presence of H2 in mild conditions (1
atm, 20°C). We also attempted to assign a formula to
our reduction product, but the 31P spectra indicate the
presence of more than one product, and we can there-
fore only conclude that, in the presence of H2, the
aryldiazene complexes of rhodium 1 and 2 react with
loss of the nitrogen ligand and formation of uncharac-
terised products.
[16] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[17] J.A. Carroll, D. Sutton, Z. Xiaoheng, J. Organomet. Chem. 244
(1982) 73.
[18] (a) M.R. Smith III, T.-Y. Cheng, G.L. Hillhouse, Inorg. Chem.
31 (1992) 1535. (b) M.R. Smith III, G.L. Hillhouse, J. Am.
Chem. Soc. 110 (1988) 4066.
[19] W.L. Bowden, G.M. Brown, E.M. Gupton, W.F. Little, T.J.
Meyer, Inorg. Chem. 16 (1977) 213.
[20] L.M. Haines, Inorg. Chem. 10 (1971) 1685 (see also p. 1693).
[21] (a) L. Toniolo, Inorg. Chim. Acta 4 (1972) 660. (b) L. Toniolo,
G. De Luca, C. Panattoni, G. Deganello, Gazz. Chim. Ital. 104
(1974) 961.