Diazo complexes of osmium: Preparation of binuclear derivatives with bis(aryldiazene) and bis(aryldiazenido) bridging ligands

Article abstract of DOI:10.1016/j.ica.2003.10.002

Depending on experimental conditions and the nature of the phosphite, the reaction of OsH₂P₄ [P = P(OEt)₃ and PPh(OEt)₂] with bis(aryldiazonium) salts [N₂Ar-ArN ₂](BF₄)₂

Full text of DOI:10.1016/j.ica.2003.10.002

Inorganica Chimica Acta 357 (2004) 1119–1133
www.elsevier.com/locate/ica
Diazo complexes of osmium: preparation of binuclear
derivatives with bis(aryldiazene) and bis(aryldiazenido)
bridging ligands
*
Gabriele Albertin , Stefano Antoniutti, Mara Boato
Dipartimento di Chimica, Universitaꢀ Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy
Received 22 July 2003; received in revised form 24 September 2003; accepted 4 October 2003
Abstract
Depending on experimental conditions and the nature of the phosphite, the reaction of OsH2P4 [P ¼ P(OEt)3 and PPh(OEt)2]
with bis(aryldiazonium) salts [N2Ar–ArN2](BF4)2 [Ar–Ar ¼ 4,40-C6H4–C6H4, 4,40-(2-CH3)C6H3–C6H3(2-CH3), 4,40-C6H4–CH2–
C6H4 and 1,5-C10H6] afford the cis and the trans binuclear [{OsHP4}2(l-HN@NAr–ArN@NH)](BPh4)2 1, 2 aryldiazene derivatives.
These complexes 1, 2 further react with the mono(diazonium) (4-CH3C6H4N2)BF4 salt to give the bis(aryldiazene) [{Os(4-
CH3C6H4N@NH)P4}2(l-HN@NAr–ArN@NH)](BPh4)4 3,
4 derivatives. Binuclear bis(aryldiazenido) [{OsP4}2(l-N2Ar–
ArN2)](BPh4)2 (6) [P ¼ P(OEt)3; Ar–Ar ¼ 4,40-C6H4–C6H4, 4,40-C6H4–CH2–C6H4] complexes were prepared by deprotonating with
NEt3 the nitrile-diazene [{Os(4-CH3C6H4CN)P4}2(l-HN@NAr–ArN@NH)](BPh4)4 (5) derivatives. The aryldiazenido compounds
6 react with HCl to give the new aryldiazene [{OsClP4}2(l-HN@NAr–ArN@NH)](BPh4)2 (7) derivatives. The characterisation of
1
the complexes by IR and H, 31P, 15N NMR data is also discussed. The reaction of the hydride OsH2(PPh2OEt)4 with mono(di-
azonium) salts was also studied and led exclusively to the mono(aryldiazene) [OsH(ArN@ NH)(PPh2OEt)4]BPh4 (8) (Ar ¼ C6H5, 4-
CH3C6H4) derivatives. Spectroscopic data (1H, 31P, 15N NMR) on 15N-labelled derivatives suggest the presence of two isomers with
the N-bonded and the p-bonded ArN@NH ligand, respectively.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Osmium; Aryldiazene; Aryldiazenido; Binuclear complexes
1. Introduction
diazonium) salts [N2Ar–ArN2]2þ of the type of Chart 1,
and no data are reported for the osmium, although these
bis(aryldiazonium) molecule can potentially give rise to
di- or polynuclear compounds, in which the bridging
unit may induce new properties on the same NN group
or on the corresponding complexes.
The chemistry of transition metal complexes con-
taining diazene, ArN@NH, diazenido, ArN2, or other
partially reduced dinitrogen ligands continues to attract
considerable attention, not only for the relationship with
the intermediates of the nitrogen fixation process, but
also for the different coordination modes and chemical
reactivity that this class of complexes may exhibit [1–3].
A number of studies have been reported in the recent
years involving mainly mononuclear complexes ob-
tained from the reaction of common mono(aryldiazo-
nium) salts ArNþ2 with an appropriate precursor [1,2].
Less is known [3d,3e,4,5] on the behaviour of bis(aryl-
We are active in this research area since 1984 [3,5,6]
and have reported the synthesis and reactivity of both
mono- and binuclear diazo complexes of several metals,
such as Mn(I), Re(I), Fe(II), Ru(II), Co(I) and Ir(III).
Also mononuclear aryldiazene and aryldiazenido os-
mium complexes [7] of the type [Os(ArN@NH)2P4]2þ
,
[OsH(ArN@NH)P4]þ and [Os(ArN2)P4]þ [P ¼ P(OEt)3
and PPh(OEt)2] were prepared from the reaction of di-
hydride OsH2P4 with the common mono(aryldiazo-
nium) cations. We have now extended these studies to
the use of bis(aryldiazonium) cations of the type
of Chart 1, with the aim to test whether binuclear
* Corresponding author. Tel.: +39-041-234-8555; fax: +39-041-234-
8917.
E-mail address: albertin@unive.it (G. Albertin).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.10.002

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G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
cases with downfield shifts considered positive. The
H3C
+N2
SwaN-MR software package [10] was used to treat
NMR data. The conductivities of 10ꢀ3 M solutions of
the complexes in CH3NO2 at 25 °C were measured with
a Radiometer CDM 83.
+N2
N2
N2
+
+
CH3
+
N2
+N2
CH2
N2
2.2. Synthesis of complexes
+
+
N2
The OsH2P4 [P ¼ P(OEt)3,PPh(OEt)2 and PPh2OEt]
compounds were prepared following the method previ-
ously reported [7,11]. To avoid the formation of
byproducts, the reactions with aryldiazonium cations
were carried out starting from very low temperature
()196 °C).
Chart 1.
complexes can be obtained and, in case, to compare the
results with those of mononuclear derivatives. The re-
sults of these studies, which also include the reactivity of
the dihydride OsH2(PPh2OEt)4 with aryldiazonium ca-
tions, are reported here.
2.2.1. cis-[{OsH[P(OEt)3]4}(l-HN@NAr–ArN@NH)]
(BPh4)2 (1) [Ar–Ar ¼ 4,40-C6H4–C6H4 (a), 4,40-(2-
CH3)C6H3–C6H3-(2-CH3) (b), 4,40-C6H4–CH2–C6H4
(c), 1,5-C10H6 (d)]
2. Experimental
In a three-necked 25-ml round-bottomed flask were
placed solid samples of OsH2[P(OEt)3]4 (86 mg, 0.1
mmol) and of the appropriate bis(aryldiazonium) salt
[N2Ar–ArN2](BF4)2 (0.05 mmol) and the flask was
cooled to )196 °C. Acetone (7 ml), or dichloromethane
(7 ml) in the case of 1c and 1d, was added and the re-
action mixture, brought to room temperature, stirred for
4 h. The solvent was removed under reduced pressure to
give an oil which was triturated with ethanol containing
an excess of NaBPh4 (68 mg, 0.2 mmol). A red solid
slowly separated out from the resulting solution which
was filtered and crystallised from CH2Cl2 and ethanol;
yield P 90% (Found: C, 50.50; H, 6.81; N,
2.08C108H172B2N4O24Os2P8 (1a) requires: C, 50.66; H,
6.77; N, 2.19. KM ¼ 125 S cm2 molꢀ1. Found: C, 51.15;
H, 6.98; N, 2.09%. C110H176B2N4O24Os2P8 (1b) requires:
2.1. General considerations and physical measurements
All synthetic work was carried out in an appropriate
atmosphere (Ar, N2) using standard Schlenk techniques
or a vacuum atmosphere drybox. Once isolated, the
complexes were found to be relatively stable in air, but
were stored in an inert atmosphere at )25 °C. All sol-
vents were dried over appropriate drying agents, de-
gassed on a vacuum line, and distilled into vacuum-tight
storage flasks. (NH4)2OsCl6 was a Johnson Matthey
product, used as received. Phosphines, PPh(OEt)2 and
the PPh2OEt, were prepared by the method of Rabi-
nowitz and Pellon [8], while P(OEt)3 was an Aldrich
product purified by distillation under nitrogen. Diazo-
nium salts were prepared in the usual way [9]. The
related bis(diazonium) salts [N2Ar–ArN2](BF4)2
[Ar–Ar ¼ 4,40-C6H4–C6H4, 4,40-(2-CH3)C6H3–C6H3-(2-
CH3), 4,40-C6H4–CH2–C6H4, 1,5-C10H6] were prepared
by treating the amine precursors H2NAr–ArNH2 with
NaNO2, as described in the literature for common
mono(diazonium) salts. The labelled diazonium tet-
rafluoroborates (C6H5NB15N)BF4 and [4,40-15NBN-
C6H4–C6H4NB15N](BF4)2 were prepared from Na-
15NO2 (99% enriched, CIL) and the appropriate amine.
Alternatively, the (C6H515NBN)BF4 salt was prepared
from NaNO2 and C6H515NH2. Other reagents were
purchased from commercial sources in the highest
available purity and used as received. Infrared spectra
were recorded on a Nicolet Magna 750 FTIR spectro-
photometer. NMR spectra (1H, 31P, 15N) were obtained
on a Bruker AC200 spectrometer at temperatures be-
tween )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, while 15N with respect to CH315NO2, in both
C, 51.04; H, 6.85; N, 2.16. KM ¼ 119 S cm2 molꢀ1
.
Found: C, 50.65; H, 6.90; N, 2.11%. KM ¼ 117 S cm2
molꢀ1. C109H174B2N4O24Os2P8 (1c) requires: C, 50.85;
H, 6.81; N, 2.18. Found: C, 50.08; H, 6.85; N, 2.13%.
C
106H170B2N4O24Os2P8 (1d) requires: C, 50.24; H, 6.76;
N, 2.21. KM ¼ 120 S cm2 molꢀ1).
2.2.2.
C6H4N@15NH)](BPh4)2 (1a1)
cis-[{OsH[P(OEt)3]4}(l-4,40-H15N@NC6H4–
This complex was prepared exactly like the related
unlabelled 1a using [4,40-15NBNC6H4–C6H4NB15N]
(BF4)2 diazonium salt; yield P85%.
2.2.3. cis-[{OsH[PPh(OEt)2]4}(l-HN@NAr–ArN@NH)]
(BPh4)2 (2) [Ar–Ar¼4,40-C6H4–C6H4 (a), 4,40-(2-
CH3)C6H3–C6H3(2-CH3) (b), 1,5-C10H6 (d)]
In a 25-ml three-necked round-bottomed flask were
placed solid samples of OsH2[PPh(OEt)2]4 (98 mg, 0.1
mmol) and of the appropriate bis(aryldiazonium) salt
[N2Ar–ArN2](BF4)2 (0.05 mmol) and the flask was
cooled to )196 °C. Dichloromethane (7 ml) was added

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
1121
and the reaction mixture, brought to room temperature,
stirred for about 4 h. The solvent was removed under
reduced pressure to give an oil which was treated with
ethanol containing an excess of NaBPh4 (68 mg, 0.2
mmol). A red solid slowly separated out from the re-
sulting solution which was filtered and crystallised from
CH2Cl2 and ethanol; yield P80% (Found: C, 59.89; H,
6.22; N, 1.85%. C140H172B2N4 O16Os2P8 (2a) requires:
Found: C, 65.45; H, 6.24; N, 2.97%. C202H226B4N8O16
Os2P8 (4a) requires: C, 65.69; H, 6.17; N, 3.03.
KM ¼ 245 S cm2 molꢀ1).
2.2.7. [OsH(4-CH3C6H4CN){P(OEt)3}4]BPh4
An equimolar amount of CF3SO3CH3 (0.3 mmol, 34
ll) was added to a solution of OsH2[P(OEt)3]4 (0.3
mmol, 0.25 g) in 10 ml of toluene cooled to )196 °C.
The reaction mixture was brought to room tempera-
ture, stirred for 1 h and then an excess of 4-
CH3C6H4CN (0.9 mmol, 107 ll) added. After 2 h of
stirring, the solvent was removed under reduced pres-
sure to give an oil which was triturated with ethanol (3
ml) containing an excess of NaBPh4 (0.8 mmol, 0.28 g).
A white solid slowly separated out from the resulting
solution, which was filtered and crystallised from
CH2Cl2 and ethanol; yield P 85% (Found: C, 52.18;
H, 6.93; N, 1.01%. C56H88BNO12OsP4 requires: C,
52.05; H, 6.86; N, 1.08. KM ¼ 54:7 S cm2 molꢀ1. IR
C, 59.70; H, 6.15; N, 1.99. KM ¼ 122 S cm2 molꢀ1
.
Found: C, 59.78; H, 6.29; N, 1.86%. C142H176B2
N4O16Os2P8 (2b) requires: C, 59.95; H, 6.24; N, 1.97.
KM ¼ 124 S cm2 molꢀ1. Found: C, 59.58; H, 6.19; N,
2.05%. C138H170B2N4O16Os2P8 (2d) requires: C, 59.39;
H, 6.14; N, 2.01%. KM ¼ 117 S cm2 molꢀ1).
2.2.4. trans-[{OsH[PPh(OEt)2]4}(l-HN@NAr–ArN@
NH)](BPh4)2 (2-trans) [Ar–Ar ¼ 4,40-C6H4–C6H4 (a),
4,40-C6H4–CH2–C6H4 (c), 1,5-C10H6 (d)]
These complexes were prepared exactly like the related
cis-complexes 2 using acetone as solvent instead of di-
chloromethane; yield P 85% (Found: C, 59.92; H, 6.20;
N, 1.90%. C140H172B2N4O16Os2P8 (2a-trans) requires: C,
59.70; H, 6.15; N, 1.99. KM ¼ 125 S cm2 molꢀ1. Found:
C, 59.66; H, 6.15; N, 1.91C141H174B2N4O16Os2P8 (2c-
trans) requires: C, 59.83; H, 6.20; N, 1.98. KM ¼ 120 S
cm2 molꢀ1. Found: C, 59.23; H, 6.24; N, 1.95%.
(KBr) cmꢀ1: 2262 w mCN, 1958 m mOsH 1H NMR
.
[(CD3)2CO, 25 °C] d: 7.80–6.70 (m, 24H, Ph), 4.40–
4.00 (m, 24H, CH2), 2.43 (s, 3H, CH3 p-tolyl), 1.32,
1.28, 1.25 (t, 36H, CH3), )8.82 to )9.61 (m, 1H, Hꢀ).
31P{H}NMR [(CD3)2CO, 25 °C] d: AB2C spin system,
dA 106.5, dB 104.4, dC 97.4, JAB ¼ 31:4, JAC ¼ 30:0,
JBC ¼ 44:5 Hz.
C
138H170B2N4O16Os2P8 (2d-trans) requires: C, 59.39; H,
6.14; N, 2.01. KM ¼ 116 S cm2 molꢀ1).
2.2.8. [{Os(4-CH3C6H4CN)[P(OEt)3]4}(l-HN@NAr
–ArN@NH)](BPh4)4 (5) [Ar–Ar ¼ 4,40-C6H4–C6H4
(a), 4,40-C6H4–CH2–C6H4 (c)]
2.2.5. trans-[{OsH[PPh(OEt)2]4}(l-4,40-H15N@NC6H4–
C6H4N@15NH)](BPh4)2 (2a1-trans)
This complex was prepared exactly like the related
unlabelled 2a-trans using [4,40-15NBNC6H4–C6H4NB
15N](BF4)2 diazonium salt; yield P 80%.
Solid samples of [OsH(4-CH3C6H4CN){P(OEt)3}4]
BPh4 (0.130 g, 0.1 mmol) and of the appropriate
bis(aryldiazonium) salt [N2Ar–ArN2](BF4)2 (0.05
mmol) were placed in a 25-ml three-necked round-
bottomed flask and, after cooling to )196 °C, acetone
(15 ml) was added. The reaction mixture was brought
to room temperature, stirred for about 20 h and then
the solvent removed under reduced pressure. The oil
obtained was treated with ethanol containing an excess
of NaBPh4 (68 mg, 0.2 mmol). By stirring of the re-
sulting solution, a red-orange solid separated out,
which was filtered and crystallised from CH2Cl2 and
ethanol: yield P 70% (Found: C, 60.00; H, 6.71; N,
2.35. C172H224B4N6 O24Os2P8 (5a) requires: C, 60.21;
H, 6.58; N, 2.45. KM ¼ 239 S cm2 molꢀ1. Found: C,
60.12; H, 6.68; N, 2.29%. C173H226B4N6 O24Os2P8 (5c)
requires: C, 60.31; H, 6.61; N, 2.44. KM ¼ 253 S cm2
molꢀ1).
2.2.6. [{Os(4-CH3C6H4N@NH)P4}2(l-HN@NAr–ArN
@NH)](BPh4)4 (3, 4) [P ¼ P(OEt)3 and Ar–Ar ¼ 1,5-
C10H6 (3d); P ¼ PPh(OEt)2 and Ar–Ar ¼ 4,40-C6H4–
C6H4 (4a)]
In a 25-ml three-necked round-bottomed flask were
placed solid samples of the appropriate binuclear com-
plex [{OsHP4}2(l-NH@NAr–ArN@NH)](BPh4)2 (0.1
mmol) and of a large excess of the aryldiazonium salt [4-
CH3C6H4N2]BF4 (0.206 g, 1 mmol) and the flask was
cooled to )196 °C. Acetone (15 ml) was added and the
reaction mixture, brought to room temperature, stirred
for 20 h. The solvent was removed under reduced
pressure to give an oil which was treated with ethanol (3
ml) containing an excess of NaBPh4 (51 mg, 0.15 mmol).
A red-brown solid slowly separated out from the re-
sulting solution which was filtered and crystallised from
CH2Cl2 and ethanol; yield P60% (Found: C, 59.02; H,
6.70; N, 3.36%. C168H224B4N8O24 Os2P8 (3d) requires:
2.2.9. [{Os(4-CH3C6H4CN)[P(OEt)3]4}2(l-4,40-H15
N@NC6H4–C6H4N@15NH)](BPh4)4 (5a1)
This complex was prepared exactly like the unlabelled
5a using [4,40-15NBNC6H4–C6H4NB15N](BF4)2 diazo-
nium salt; yield P65%.
C, 59.16; H, 6.62; N, 3.28. KM ¼ 238 S cm2 molꢀ1
.

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G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
2.2.10. [{Os[P(OEt)3]4}2(l-N2Ar–ArN2)](BPh4)2 (6)
[Ar–Ar ¼ 4,40-C6H4–C6H4 (a), 4,40-C6H4–CH2–C6H4
(c)]
pressure. The oil obtained was treated with ethanol (2
ml) containing an excess of NaBPh4 (68 mg, 0.2 mmol).
An orange solid slowly separated out from the resulting
solution, which was filtered and crystallised from
CH2Cl2 and ethanol; yield P70% (Found: C, 67.05; H,
5.77; N, 1.90%. C86H87BN2O4OsP4 (8e) requires: C,
67.18; H, 5.70; N, 1.82. KM ¼ 50:9 S cm2 molꢀ1. Found:
C, 67.56; H, 6.70; N, 1.77%. C87H89BN2O4OsP4 (8f)
requires: C, 67.35; H, 5.78; N, 1.81. KM ¼ 54:3 S cm2
molꢀ1).
An excess of triethylamine (0.28 ml, 2 mmol) was
added to a solution of the appropriate binuclear [{Os
(4-CH3C6H4CN)[P(OEt)3]4}2(l-HN@NAr–ArN@NH)]
(BPh4)4 complex (0.1 mmol) in 10 ml of CH2Cl2 and the
reaction mixture stirred for 2 h. A white solid
([NHEt3]BPh4) slowly separated out which was filtered
and rejected. The solution was evaporated to dryness
leaving a brown oil which was treated with ethanol (5
ml). By slow cooling of the resulting solution, red-brown
crystals were obtained which were filtered and dried
under vacuum; yield P60% (Found: C, 50.85; H, 6.70;
N, 2.23%. C108H168B2N4 O24Os2P8 (6a) requires: C,
50.74; H, 6.62; N, 2.19. KM ¼ 126 S cm2 molꢀ1. Found:
C, 50.70; H, 6.75; N, 2.29%. C109H170B2N4O24Os2P8
(6c) requires: C, 50.93; H, 6.67; N, 2.18. KM ¼ 118 S cm2
molꢀ1).
2.2.15. [OsH(C6H5N@15NH)(PPh2OEt)4]BPh4 (8e1)
and [OsH(C6H515N@NH)(PPh2OEt)4]BPh4 (8e2)
These complexes were prepared exactly like the re-
lated unlabelled 8e using the [C6H5NB15N]BF4 and
[C6H515NBN]BF4 diazonium salts, respectively; yield
P60%.
3. Results and discussion
2.2.11. [{Os[P(OEt)3]4}2(l-4,40-15NBNC6H4–C6H4N
B15N)](BPh4)2 (6a1)
This complex was prepared exactly like the related
Hydride species OsH2P4 quickly react with bis(aryl-
diazonium) salts [N2Ar–ArN2](BF4) to give the binu-
clear complexes [(OsHP4)2(l-NH@NAr–ArN@NH)]
(BPh4)2 (1), (2), containing the bis(diazene) bridging
unit, as shown in Scheme 1.
unlabelled 6a using 5a1 as precursor; yield P 55%.
2.2.12.
[{OsCl[P(OEt)3]4}2(l-4,40-HN@NC6H4–C6
H4N@NH)](BPh4)2 (7a)
Studies on the reaction course indicate that, both in
acetone and in CH2Cl2 as solvents, the reaction pro-
ceeds, but the nature of the products depends both from
the phosphine and the solvent used. While with P(OEt)3
exclusively the complexes I (Chart 2), containing the
hydride and the diazene in a mutually cis position, were
obtained both in acetone and CH2Cl2 as solvent, with
PPh(OEt)2 the cis complexes I were obtained only in
CH2Cl2. In acetone, instead, complexes with geometry
II (Chart 2) (2-trans), containing the hydride and the
diazene in a mutually trans position, were obtained.
Since the diazene complexes 1, 2 do not isomerise in
solution even after some days, the formation of different
isomers changing the nature of the solvent may suggest
To a solution of the aryldiazenido [{Os[P(OEt)3]4}2
(l-4,40-N2C6H4–C6H4N2)](BPh4)2 (6a) complex (128
mg, 0.05 mmol) in 10 ml of CH2Cl2 cooled to )196 °C
was added a solution of HCl 0.1 M in diethyl ether (1.1
ml, 0.11 mmol). The reaction mixture was brought to
room temperature, stirred for about 4 h and then the
solvent removed under reduced pressure. The oil ob-
tained was treated with ethanol (3 ml) giving a red-
brown solution which was stirred at 0 °C until a solid
separated out, which was filtered and dried under vac-
uum; yield P 70% (Found: C, 49.18; H, 6.45; N, 2.06;
Cl, 2.88%. C108H170B2Cl2N4O24Os2P8 (7a) requires: C,
49.34; H, 6.52; N, 2.13; Cl, 2.70. KM ¼ 124 S cm2
molꢀ1).
þ
that a different mechanism of insertion of –ArN2 into
the OsH bond can take place. This different mechanism
may also explain the formation of the two stereoisomers
A and B (Chart 3) in the case of complexes 2-trans,
obtained in acetone, which will be discussed below. It is
worth to note that the hydride OsH2(PPh2OEt)4, con-
taining the bulky phosphine PPh2OEt, does not give
2.2.13. [{OsCl[P(OEt)3]4}2(l-4,40-H15N@NC6H4–C6
H4N@15NH)](BPh4)2 (7a1)
This complex was prepared exactly like the related
unlabelled 7a by reacting 6a1 with HCl; yield P65%.
2.2.14. [OsH(ArN@NH)(PPh2OEt)4]BPh4 (8) [Ar¼
C6H5 (e), 4-CH3C6H4 (f)]
2OsH2P4
+
[N2Ar-ArN2]2+
In a 25-ml three-necked round-bottomed flask were
placed solid samples of OsH2(PPh2OEt)4 (111 mg, 0.1
mmol) and an excess of the appropriate aryldiazonium
salt [ArN2]BF4 (0.3 mmol). The flask was cooled to
)196 °C and CH2Cl2 (20 ml) was added. The reaction
mixture was brought to room temperature, stirred for
4 h and then the solvent was removed under reduced
[{OsHP4}2(µ-NH=NAr-ArN=NH)]2+
eq.1
1, 2
Scheme 1. P ¼ P(OEt)3 (1), PPh(OEt)2 (2); Ar–Ar ¼ 4,40-C6H4–C6H4
(a), 4,40-(2-CH3)C6H3–C6H3-(2-CH3) (b), 4,40-C6H4–CH2–C6H4 (c),
1,5-C10H6 (d).

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
1123
On the basis of these data, a geometry of type I with
the hydride and the aryldiazene ligand in a mutually
cis position can be proposed for these binuclear com-
plexes.
Surprisingly, the H NMR spectra of the trans com-
plexes 2-trans show two NH signals between 14 and 15
2+
P
P
P
H
H
N
H
N
H
P
P
P
P
Os
N
N
Os
P
Ar Ar
1
I
ppm, each of which are split into a doublet in the la-
1
1, 2
belled 2a1-trans complex, with a J
value for both
15NH
2+
signals of 62 Hz. Furthermore, in the low-frequency
region of the proton spectra are also present two quin-
tets near )13 ppm, which are attributed to two hydride
ligands, each coupled with four magnetically equivalent
phosphorus nuclei. Finally, in the temperature range
between +20 and )80 °C, the 31P{1H} NMR spectra of
the trans complexes show two singlets with close values
of chemical shift, each of which is split into one doublet
in the labelled 2a1-trans complex, due to the coupling
with the 15N nuclei of the diazene. It can be also noted
that the ratio between the two diazene signals is similar
to those between the two hydride and the two 31P sig-
nals, and that close chemical shift values were observed
for each couple of signals. These results may be inter-
preted on the basis of the existence of two isomers, each
of which must contain the diazene and the hydride li-
gands in a mutually trans position, with four equivalent
phosphite ligands. Two stereoisomers of the types A and
B (Chart 3), with the H and the aryl substituent mutu-
ally in trans and in cis positions with respect to the N@N
moiety, should give two different NH signals, as ob-
served in our complexes.
P
P
H
P
P
H
Os
P
N
Ar Ar
N
Os
P
P
N
H
N
H
P
II
2-trans
Chart 2.
H
N
H
Os
N
Os
N
Ar
N
Ar
A (cis)
B (trans)
2-trans
Chart 3.
binuclear complexes in the reaction with bis(aryldiazo-
nium) salt, but only an intractable mixture of products
which was not separated.
Since the complexes are binuclear, the existence of
both isomers A and B bonded to the osmium centre
should give four isomers, i.e. cis–cis, trans–trans, cis–
trans and trans–cis, with the last two equivalent, as
shown in Chart 4.
The complexes 1, 2, which were isolated as BPh4
salts, are stable both as solids and in solution of polar
organic solvents, where they behave as 2:1 electrolytes
[12]. Analytical and spectroscopic data (Table 1) sup-
port the proposed formulation, and the geometries I
and II (Chart 2) in solution were also established. The
IR spectra of the cis complexes 1, 2 show a weak band
at 2030–1965 cmꢀ1 attributed to the stretching of the
The presence of these isomers for the 2-trans com-
1
plexes is in agreement with both the H and 31P NMR
spectra and finds a precedent [3d] in the rhenium diazo-
diazene [Re(CO)5ꢀnPn(HN@NAr–ArNBN)]2þ (n ¼ 1; 2;
P ¼ phosphite) complexes, which were obtained using,
also in this case, acetone as solvent. This precedent and
the spectroscopic data support the hypothesis of the
stereoisomers A and B affording the mixture of Chart 4.
The binuclear complexes 1 and 2 still contain a hy-
dride ligand which can potentially further react with
aryldiazonium cations to afford bis(aryldiazene) deriv-
atives. We therefore studied the reaction of mono(dia-
zene) 1, 2 with p-tolyldiazonium salt and observed that
the reaction slowly takes place to give the bis(aryldia-
1
OsH bond. The H NMR spectra confirm the presence
of the hydride ligand, showing a complicated multiplet
between 7 and 9 ppm due to the coupling with the
phosphorus nuclei. In the spectra also appears a
slightly broad signal in the high-frequency region, at
13–15 ppm, attributed to the NH diazene proton.
Support for this assignment comes from the spectra of
the labelled 1a1 complex, which show a doublet of
multiplets centered at the same value (14.73 ppm)
zene)
complexes
[{Os(4-CH3C6H4N@NH)P4}2(l-
of the broad signal of the unlabelled 1a compound,
1
HN@NAr–ArN@NH)](BPh4)4 3, 4, which were isolated
and characterised (Scheme 2).
with J
of 66 Hz, in agreement [1a,13,14] with the
15NH
presence of a diazene ligand. In the temperature range
between 20 and )80 °C, the 31P NMR spectra appear
as a multiplet which can be simulated using an A2BC
or AB2C model, with the parameters reported in Table 1.
However, in the case of the PPh(OEt)2 ligand, al-
though both the cis and trans complexes 2 react with the
aryldiazonium cation, only with the cis were stable and
isolable bis(aryldiazene) derivatives obtained.

1124
G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
2+
H
P
N
P
Ar Ar
P
Os
P
2+
P
H
P
P
P
P
H
N
H
N
P
P
P
P
H
Os
N
N
Os
H
N
N
Ar Ar
H
N
P
P
H
P
Os
trans-trans
cis-cis
2+
2+
P
P
P
P
H
N
H
N
P
P
P
P
H
Os
N
N
Os
H
Ar Ar
N
N
Ar Ar
P
N
H
H
N
P
P
Os
P
P
Os
P
H
P
P
H
cis-trans
trans-cis
2-trans
Chart 4.
+
4+
exc. ArN2
H
P
CH3
[{OsHP4}2(µ-NH=NAr-ArN=NH)]2+
H
P
Os
P
P
N
N
N
P
Os
[{Os(ArN=NH)P4}2(µ-NH=NAr-ArN=NH)]4+
N
Ar Ar
H3C
N
P
N
N
N
P
P
3, 4
H
H
Scheme 2. P ¼ P(OEt)3 (3), PPh(OEt)2 (4); Ar ¼ 4-CH3C6H4; Ar–
Ar ¼ 4,40-C6H4– C6H4 (a), 1,5-C10H6 (d).
III
3, 4
The complexes are yellow-orange solids stable in the
air and in solution of polar organic solvents, where they
behave as 4:1 electrolytes [12]. Analytical and spectro-
Chart 5.
1
scopic data support the proposed formulation. The H
NMR spectra confirm the presence of two diazene li-
gands, showing two slightly broad signals between 15
and 13 ppm. Furthermore, the 31P{1H }NMR spectra
show a complicated multiplet which, in the case of 4a,
can be simulated using an A2BC model with the pa-
rameters reported in Table 1. On the basis of these data
a geometry of type III (Chart 5) can be reasonably
proposed for the bis(aryldiazene) derivatives 3 and 4.
A comparison between the reactivity of both mono-
ArNþ2 and the bis-[N2Ar–ArN2]2þ aryldiazonium ca-
tions toward the osmium dihydride OsH2P4 shows that
in both cases the facile insertion of one ArNþ2 group
takes place giving mononuclear hydride-diazene com-
plexes [OsH(ArN@NH)P4]þ in one case [7], and binu-
clear species with di-diazene as bridging unit of type 1
and 2 in the other. Difference was observed, instead, in
the geometry of the complexes which result, with the
P(OEt)3 ligand, always cis in both mono- [7] and binu-
clear complexes 1, while with the PPh(OEt)2 both the cis
and trans geometries were obtained in the binuclear
derivatives 2. Furthermore, the formation of two ste-
reoisomers of the type A and B with a cis or trans ar-
rangement of the substituents on the N@N group was
also observed in binuclear complexes 2-trans. Finally,
the second insertion of an ArNþ2 group into the OsH
bond of hydride-diazene species was observed in both
mono- [7] and binuclear complexes affording, in every
case, bis(aryldiazene) derivatives.

Table 1
IR and NMR spectroscopic data for osmium complexes
Compound
IRa
Assignment
1H NMRb;c
(ppm)/J (Hz)
d
Assignment
Spin system
A2BCe
31P{1H} NMRb;d
d
(ppm)/J (Hz)
(cmꢀ1
)
(1a)
cis-[{OsH[P(OEt)3]4}2(l-4,40-HN@NC6H4–
C6H4N@NH)](BPh4)2
1973 w
mOsH
14.75 m, br
4.32–3.98 m
1.34 t
NH
CH2
CH3
dA ¼ 106:8
dB ¼ 103:3
dC ¼ 101:4
JAB ¼ 45:3
JAC ¼ 31:5
JBC ¼ ꢀ29:4
1.31 t
1.23 t
)7.95 to )8.70 m
Hꢀ
(1a1)
cis-[{OsH[P(OEt)3]4}2(l-4,40-H15N@NC6H4–
C6H4N@15NH)](BPh4)2
1971 w
mOsH
14.73 dm
1J
4.30–4.00 m
NH
CH2
CH3
A2BCYe
dA ¼ 106:8
dB ¼ 103:3
dC ¼ 101:4
JAB ¼ 46:4
JAC ¼ 31:5
JAY ¼ 3:5
¼ 66
15NH
1.33 t
1.30 t
1.22 t
)7.95 to )8.70 m
Hꢀ
JBC ¼ ꢀ29:4
JBY ¼ 49:4
JCY ¼ 2:5
(1b)
cis-[{OsH[P(OEt)3]4}2l-4,40-HN@N-4,40-(2-
CH3)C6H3–C6H3(2-CH3)N@NH](BPh4)2
1978 w
mOsH
14.66 m
4.33–3.98 m
2.64 s
NH
CH2
A2BCe
dA ¼ 107:8
dB ¼ 103:0
dC ¼ 100:4
JAB ¼ 45:0
JAC ¼ 31:5
JBC ¼ ꢀ29:4
CH3
CH3 phos
1.34 t
1.30 t
1.21 t
)7.93 to )8.73 m
Hꢀ
(1c)
(1d)
(2a)
cis-[{OsH[P(OEt)3]4}2(l-4,40-HN@NC6H4–CH2–
C6H4N@NH)](BPh4)2
1980 w
1965 w
2013 w
mOsH
mOsH
mOsH
14.54 m
NH
CH2
CH3
A2BC
A2BCe
AB2C
dA ¼ 104:4
dB ¼ 102:5
dC ¼ 101:8
JAB ¼ 32:7
JAC ¼ 44:7
JBC ¼ 29:5
4.20–3.95 m
1.28 t
1.26 t
1.18 t
)8.16 to )8.75 m
Hꢀ
cis-[{OsH[P(OEt)3]4}2(l-1,5-HN@
NC10H6N@NH)](BPh4)2
15.08 m, br
4.15 m
1.32 t
NH
CH2
CH3
dA ¼ 107:0
dB ¼ 102:7
dC ¼ 100:9
JAB ¼ 46:1
JAC ¼ 31:2
JBC ¼ ꢀ29:4
1.31 t
1.18 t
)8.03 to )8.63 m
Hꢀ
cis-[{OsH[PPh(OEt)2]4}2(l-4,40-HN@NC6H4–
C6H4N@NH)](BPh4)2
13.60 m, br
4.20–3.45 m
1.33 t
NH
CH2
CH3
dA ¼ 125:8
dB ¼ 123:7
dC ¼ 120:1
JAB ¼ 18:9
JAC ¼ 23:6
JBC ¼ 31:1
1.20 t
1.15 t
1.11 t
)7.63 to )8.36 m
Hꢀ

Table 1 (continued)
Compound
IRa
(cmꢀ1
Assignment
1H NMRb;c
(ppm)/J (Hz)
d
Assignment
Spin system
31P{1H} NMRb;d
d
(ppm)/J (Hz)
)
(2a-trans)
trans-[{OsH[PPh(OEt)2]4}2(l-4,40-
HN@NC6H4–C6H4N@NH)](BPh4)2
2038 w
mOsH
14.83 br
14.75 br
3.82 m
NH
CH2
CH3
Hꢀ
A4
A4
122.5 s
122.3 s
3.68 m
1.20 t
1.08 t
)13.29 qnt
JPH ¼ 20
)13.47 qnt
JPH ¼ 20
(2a1-trans)
trans-[{OsH[PPh(OEt)2]4}2(l-4,40-
H
2040 w
mOsH
14.83 d
1J
NH
A4Y
A4Y
122.5 d
JAY ¼ 2
122.2 d
JAY ¼ 2
f
15N@NC6H4–C6H4-N@ 15NH)](BPh4)2
¼ 62
15NH
14.75 d
1J
3.82 m
¼ 62
15NH
CH2
CH3
Hꢀ
3.67 m
1.20 t
1.08 t
)13.28 qnt
JPH ¼ 20
)13.48 qnt
JPH ¼ 20
(2b)
cis-[{OsH[PPh(OEt)2]4}2(l-4,40-HN@N-
(2CH3)C6H3–C6H3-(2CH3)N@NH)](BPh4)2
1973 w
mOsH
13.53 m
4.10–3.40 m
2.67 s
NH
CH2
AB2C
dA ¼ 128:0
dB ¼ 126:1
dC ¼ 122:1
JAB ¼ 19:6
JAC ¼ 21:3
JBC ¼ 30:5
CH3
CH3 phos
1.35 t
1.19 t
1.12 t
1.08 t
)7.59 to )8.33 m
Hꢀ
(2c-trans)
trans-[{OsH[PPh(OEt)2]4}2(l-4,40-
HN@NC6H4–CH2–C6H4N@NH)](BPh4)2
2038 w
mOsH
14.65 m
4.03 s
NH
CH2
A4
122.6 s
3.80 m
3.67 m
1.17 t
CH2 phos
CH3
Hꢀ
)13.57 qnt
(2d)
cis-[{OsH[PPh(OEt)2]4}2(l-1,5-HN@
NC10H6N@NH)](BPh4)2
2030 w
mOsH
14.01 s, br
4.10–3.50 m
1.33 t
NH
CH2
CH3
AB2C
dA ¼ 125:0
dB ¼ 123:3
dC ¼ 119:7
JAB ¼ 19:2
JAC ¼ 23:1
JBC ¼ 31:0
1.11 t
1.08 t
)7.55 to )8.28 m
Hꢀ

(2d-trans)
trans-[{OsH[PPh(OEt)2]4}2(l-1,5-
HN@NC10H6N@NH)](BPh4)2
2029 w
mOsH
15.25 s, br
15.11 s, br
4.00–3.30 m
1.21 t
NH
A4
A4
122.4 s
121.5 s
CH2
CH3
1.20 t
)13.02 qnt
JPH ¼ 20
)13.42 qnt
JPH ¼ 20
Hꢀ
(3d)
cis-[{Os(4-CH3C6H4N@NH) [P(OEt)3]4}2(l-1,5-
HN@NC10H6N@NH)](BPh4)4
15.02 m, br
14.67 s, br
4.40–4.00 m
2.44 s
NH
95–70 m
CH2
CH3
1.43 t
1.35 t
1.15 t
CH3 phos
(4a)
cis-[{Os(4-CH3C6H4N@NH) [PPh(OEt)2]4}2(l-
4,40-HN@NC6H4–C6H4N@NH)](BPh4)4
13.71 s, br
13.59 s, br
4.21 m
3.84 m
3.70 m
2.42 s
NH
A2BC
dA ¼ 109:8
dB ¼ 107:3
dC ¼ 107:0
JAB ¼ 33:7
JAC ¼ 36:0
JBC ¼ 33:1
CH2
CH3
CH3 phos
1.54 t
1.13 t
1.09 t
(5a)
cis-[{Os(4-CH3C6H4CN)[P(OEt)3]4}2(l-4,40-
HN@NC6H4–C6H4N@NH)](BPh4)4
2264 m
mCN
14.56 s, br
4.30 m
2.45 s
NH
CH2
A2BC
dA ¼ 85:0
dB ¼ 83:1
dC ¼ 72:4
JAB ¼ 41:8
JAC ¼ 45:8
JBC ¼ 44:1
CH3
CH3 phos
1.43 t
1.38 t
1.29 t
(5a1)
cis-[{Os(4-CH3C6H4CN)[P(OEt)3]4}2(l-4,40-
H15N@NC6H4-C6H4N@15NH)](BPh4)4
2266 w
mCN
14.58 dm
1J
NH
83–71 m
¼ 66
15NH
4.30 m
2.46 s
1.43 t
1.38 t
1.28 t
CH2
CH3
CH3 phos
(5c)
cis-[{Os(4-CH3C6H4CN)[P(OEt)3]4}2(l-4,40-
HN@NC6H4-CH2–C6H4N@NH)](BPh4)4
2264 w
mCN
14.10 brg
4.20–3.95 m
2.45 s
NH
CH2
82–70 m
CH3
CH3 phos
1.37 t
1.33 t
1.14 t

Table 1 (continued)
Compound
IRa
(cmꢀ1
Assignment
1H NMRb;c
(ppm)/J (Hz)
d
Assignment
Spin system
31P{1H} NMRb;d
d
(ppm)/J (Hz)
)
g;h
(6a)
[{Os[P(OEt)3]4}2(l-4,40-NBNC6H4–
C6H4NBN)](BPh4)2
1642 m
mN2
4.43–4.01 mg;h
1.38 t
1.37 t
CH2
CH3
ABC2
dA ¼ 105:2
dB ¼ 101:4
dC ¼ 92:6
JAB ¼ 47:7
JAC ¼ 40:6
JBC ¼ 37:2
dA ¼ 105:2
dB ¼ 101:4
dC ¼ 92:6
JAB ¼ 47:8
JAC ¼ 40:6
JAY ¼ 39:0
JBC ¼ 37:2
JBY ¼ 27:0
JCY ¼ 10:2
dA ¼ 104:6
dB ¼ 100:8
dC ¼ 94:1
JAB ¼ 48:0
JAC ¼ 40:5
JBC ¼ 36:4
1.35 t
1.21 t
(6a1)
[{Os[P(OEt)3]4}2(l-4,40-15NBNC6H4–
C6H4NB15N)](BPh4)2
1617 m
m15
NBN
4.43–4.00 mg;h
4.06 m
1.38 t
CH2
CH3
ABC2Yg;h
1.37 t
1.35 t
1.21 t
g;h
(6c)
[{Os[P(OEt)3]4}2(l-4,40-NBNC6H4–CH2–
C6H4NBN)](BPh4)2
1643 m
mN2
4.05 mg;h
1.32 t
1.29 t
CH2
CH3
ABC2
(7a)
[{OsCl[P(OEt)3]4}2(l-4,40-HN@NC6H4-
C6H4N@NH)](BPh4)2
14.55 m, brg
4.13 m
1.34 t
NH
CH2
CH3
AB2Cg
dA ¼ 85:1
dB ¼ 83:4
dC ¼ 72:1
JAB ¼ 45:9
JAC ¼ 42:7
JBC ¼ 41:0
1.30 t
1.21 t
(7a1)
[{OsCl[P(OEt)3]4}2(l-4,40-H15N@NC6H4–
C6H4N@15NH)](BPh4)2
14.55 dmg
NH
AB2CYg
dA ¼ 85:1
dB ¼ 83:4
dC ¼ 72:0
JAB ¼ 45:9
JAC ¼ 42:7
JAY ¼ 46:0
JBC ¼ 41:0
JBY ¼ 4:0
JCY ¼ 2:3
1J
¼ 65
15NH
4.13 m
1.33 t
1.30 t
1.20 t
CH2
CH3
e
(8e)
[OsH(C6H5N@NH)(PPh2OEt)4]BPh4
2048 w
mOsH
14.29 s
13.52 s
3.36 m
3.05 m
0.46 t
NH
CH2
CH3
Hꢀ
A4
A4
109.6 s
96.7 s
0.26 t
)3.10 qnt
JPH ¼ 20

)11.89 qnt
JPH ¼ 20
14.30 d
(8e1)
[OsH(C6H5N@15NH) (PPh2OEt)4]BPhi4
2048 w
mOsH
NH
A4
A4Y
106.0 s, br
94.9 d, br
JPY ¼ 1:7
1J
13.51 d
1J
3.35 m
¼ 62
15NH
¼ 62
15NH
CH2
CH3
Hꢀ
3.06 m
0.46 t
0.25 t
)3.10 qnt
JPH ¼ 20
)11.90 qnt
JPH ¼ 20
(8e2)
[OsH(C6H155N@NH)(PPh2OEt)4]BPh4
2050 w
mOsH
14.29 s
13.52 s
NH
CH2
CH3
Hꢀ
A4
A4
109.3 s
96.6 s
3.36 m
3.04 m
0.46 t
0.27 t
)3.10 qnt
JPH ¼ 20
)11.90 qnt
JPH ¼ 20
j
(8f)
[OsH(4-CH3C6H4N@NH)(PPh2OEt)4]BPh4
2048 w
mOsH
14.18 s
13.32 s
3.37 m
3.07 m
2.66 s
NH
A4
A4
108.4 s, br
96.9 s, br
CH2
CH3
2.37 s
0.46 t
CH3 phos
Hꢀ
0.29 t
)3.11 qnt
)12.10 qnt
a In KBr pellets.
b In (CD2)2CO at 25 °C, unless otherwise noted.
c Phenyl proton resonances are omitted.
d Positive shift downfield from 85% H3PO4.
e At )70 °C.
f
15N{1H}NMR, d: )24.1 qnt, )25.5 qnt, 2J
¼ 2:0 Hz.
15NP
g In CD2CI2.
h At )30 °C.
i
15N{1H}NMR, d: )19.5 br, )22.3 qnt, 2J
¼ 1:7 Hz.
15NP
j At )90 °.

1130
G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
The synthesis of binuclear complexes 1, 2 with
4+
P
Os
P
CR
N
RC
N
P
Os
P
bis(diazene) bridging ligand prompted us to extend the
studies to the preparation of binuclear complexes [Os]–
N2Ar–ArN2–[Os] with the bis(aryldiazenido) bridging
unit. The strategy we have employed (Scheme 3) in-
volves the synthesis of binuclear bis(aryldiazene)
P
P
N
N
P
P
Ar Ar
N
H
N
H
IV
complexes
[{Os(RCN)P4}2(l-HN@NAr–ArN@NH)]
(BPh4)4 5, containing a labile ligand such as the nitrile
RCN bonded to each central metal. By deprotonation of
the diazene ligands followed by the dissociation of the
nitrile group, the expected binuclear bis(aryldiazenido) 6
derivatives can be obtained.
5
Chart 6.
NMR spectra confirm the presence of the diazene
groups showing a slightly broad signal near 14 ppm,
which is split into a doublet with J
labelled compounds 5a1. In the temperature range be-
tween +20 and )80 °C the 31P spectra appear as a
complicated multiplet which, in the case of 5a, can be
simulated using an A2BC model with the parameters
reported in Table 1. On these bases, a geometry of type
IV (Chart 6) can reasonably be proposed for the binu-
clear derivatives 5.
The hydride-nitrile precursor [OsH(RCN)P4]BPh4
was prepared by reacting the dihydride OsH2P4 first
with methyltriflate [15] and then with an excess of nitrile.
Reaction of the [OsH(RCN)P4]þ cation with bis(aryl-
diazonium) salt proceeds to give binuclear complexes
[{Os(RCN)P4)2(l-HN@NAr–ArN@NH)]4þ 5, which
were isolated as BPh4 salts and characterised. Treatment
of these nitrile-bis(aryldiazene) complexes 5 with an
excess of triethylamine in CH2Cl2 gives a white solid of
[NHEt3]BPh4 and a red-orange solution, from which the
binuclear bis(aryldiazenido) complexes 6 was isolated.
The formation of free nitrile and the separation of the
ammonium salt in about quantitative yield also support
for the reaction the stoichiometry reported in eq. 3. On
the basis of these data it can be hypothesised [5a] that
the deprotonation of the two diazene moieties in binu-
clear complexes 5, giving the diazenido N2Ar–ArN2
group, is followed by the dissociation of the nitrile li-
gand affording 6 as final product.
1
of 66 Hz in the
15NH
The
bis(aryldiazenido)
[{OsP4}(l-N2Ar–ArN2)]
(BPh4)2 (6) complexes are yellow-orange solid stable in
the air and in solution of polar organic solvents, where
they behave as 2:1 electrolytes [12]. The IR spectra show
a medium-intensity band at 1643–1642 cmꢀ1 attributed
to mN2 of the aryldiazenido ligand. In the labelled 6a1
compound this band falls at 1617 cmꢀ1, in agreement
with the proposed attribution. Furthermore, a compar-
ison of our mN2 values with the literature data [1,5,6,16]
suggests a singly bent arrangement of the aryldiazenido
ligand, which can be considered present as þN2Ar–
ArNþ2 , with a formal oxidation number of zero [Os(0)]
for the two metal centres in the complexes.
The 31P{1H}NMR spectra of the bis(aryldiazenido)
compounds 6 change with the temperature and the
broad signal observed at room temperature resolves into
an ABC2 multiplet already at )30 °C, which can be
simulated with the parameters reported in Table 1. Such
spectra seem to exclude, in first approximation, a regular
TBP geometry of the type of Chart 7, for which a
symmetric A2B2 spectrum should be expected.
Both the nitrile-diazene precursors
5 and the
bis(aryldiazenido) complexes 6 were isolated in the solid
state and characterised in the usual way by analytical
and spectroscopic data (Table 1). The infrared spectra of
nitrile compounds 5 show a medium-intensity band at
1
2264 cmꢀ1 due to the mCN of the RCN ligand. The H
– CH4
1
OsH2P4 + CF3SO3CH3
OsH(κ -OSO2CF3)P4
RCN
[OsH(RCN)P4]+
2[OsH(RCN)P4]+
+
[N2Ar-ArN2]2+
P
Os
P
2+
[{Os(RCN)P4}2(µ-NH=NAr-ArN=NH)]4+
P
P
eq. 2
eq. 3
N
N
5
[{Os(RCN)P4}2(µ-NH=NAr-ArN=NH)]4+
+ 2NEt3
P
Os
P
P
P
N
N
+
2NHEt3
+
2RCN + [{OsP4}2(µ-N2Ar-ArN2)]2+
6
6
Scheme 3. P ¼ P(OEt)3; R ¼ 4-CH3C6H4; Ar–Ar ¼ 4,40-C6H4– C6H4
(a), 4,40-C6H4– CH2–C6H4 (c).
Chart 7.

G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
1131
However, a restricted rotation at low temperature of
2+
P
Os
P
P
Os
P
the ArNN group placed in the equatorial plane of a
regular TBP (Chart 7) may cause either the two apical or
the two equatorial phosphorus nuclei to be mutually
Cl
Cl
P
P
N
Ar Ar
N
N
H
P
N
H
P
magnetically inequivalent, resulting in an ABC2-type 31
P
spectra. An alternative explanation for the presence of
an ABC2 spectra, which does not agree with none reg-
ular TBP geometry, may involve a distorted TBP toward
SP geometry. An ABC2-type 31P spectrum could be
expected in this case, as previously proposed for related
mono-nuclear complexes [7].
V
7
Chart 8.
plexes were not obtained. The results show that the
hydride OsH2(PPh2OEt)4 reacts with an excess of aryl-
diazonium cation to give, after work-up, a red-orange
solid characterised as the hydride-aryldiazene
The bis(aryldiazenido) complexes [{OsP4}2(l-N2Ar–
ArN2)](BPh4)2 (6a) react with HCl in CH2Cl2 to give the
bis(aryldiazene) complexes [{OsClP4}(l-HN@NAr–
ArN@NH)](BPh4)2 (7), which can be isolated in the
solid state and characterised (Scheme 4).
[OsH(ArN ¼ NH)(PPh2OEt)4]BPh4
(8)
derivatives
(Scheme 5).
The reaction proceeds with the protonation of the
aryldiazenido group to give the aryldiazene and the
concurrent addition of the Clꢀ ligand to the metal centre
to give the final binuclear octahedral derivative 7. Fur-
thermore, in order to determine the nitrogen site of the
protonation, we treated the labelled [{OsP4}(l-
15NBNAr–ArNB15N)]2þ cation (6a1) with HCl and
observed that the protonation takes place at the N1
nitrogen atom, affording [{OsClP4}(l-H15N@NAr–
ArN@15NH)]2þ (7a1) as the final compound.
Studies on the reaction course showed that the for-
mation of the aryldiazene 8 is very slow as compared
with the formation of the related [OsH(ArN@NH)P4]þ
cations containing P(OEt)3 and PPh(OEt)2 ligand [7],
and therefore an excess of ligand must be used for the
synthesis of 8. This slow rate for the insertion reaction of
ArNþ2 unit into the Os–H bond of OsH2(PPh2OEt)4 may
explain why the syntheses of binuclear bis(aryldiazene)
complexes like 1, 2 failed in this case, yielding only
mixtures of intractable products. Furthermore, the fur-
ther insertion of ArNþ2 into the Os–H bond of
[OsH(ArN@NH)P4]þ (8) cation to give bis(aryldiazene)
[Os(ArN@NH)2P4]2þ species was not observed, even in
the presence of a large excess of ArNþ2 , being the mono-
diazene 8 the only isolated product.
The new bis(aryldiazene) complex 7a is an orange
solid stable in the air and in solution of polar organic
solvents, where it behaves as a 2:1 electrolyte [12]. The
1H NMR spectra confirm the presence of the diazene
ligand showing a slightly broad signal at 14.55 ppm due
to the NH protons, which is split into a doublet with
Good analytical data were obtained for complexes 8,
which are stable as solids and in solution of polar or-
ganic solvents where they behave as 1:1 electrolytes [12].
The spectroscopic data (Table 1) confirm the proposed
formulation and seem also to suggest the presence of
two isomers. In fact, the 1H NMR spectra show two NH
signals at 14.29–14.18 and 13.52–13.31 ppm, respec-
1J
of 65 Hz in the labelled 7a1 complex. In the
15NH
temperature range between +20 and )80 °C the
31P{1H}NMR spectra appear as an AB2C multiplet
suggesting the mutually cis position of the diazene and
the halogenide ligand. On this basis, a geometry of type
V (Chart 8) can reasonably be proposed for the binu-
clear complex 7.
As reported before, the hydride OsH2(PPh2OEt)4
containing the PPh2OEt phosphine ligand does not give
binuclear complexes with bridging bis(diazene) ligand
like 1 and 2. Since the behaviour of this hydride complex
toward the common monoaryldiazonium cations ArN2þ
had not been reported [7], we thought to begin this study
with the aim to compare the data with those obtained
with the related OsH2P4 [P ¼ P(OEt)3 and PPh(OEt)2]
complexes [7] and to understand why binuclear com-
tively, each of which is split into a doublet with 1J
of
15NH
62 Hz in the labelled 8e1 complex. In the spectra are also
present two quintets at 11.90 to 12.10 and at 3.11 to 3.10
ppm, respectively, attributed to two hydride ligands,
each coupled with four equivalent phosphorus nuclei. In
the temperature range between +20 and )80 °C the
31P{1H}NMR spectra show two singlets suggesting the
existence of two isomers, each containing four equiva-
lent phosphite ligands. These data may be interpreted,
as for the above-discussed trans bis(diazene) 2-trans, on
the basis of the existence of two stereoisomers of the
HCl
[{OsP4}2(µ-N2Ar-ArN2)]2+
6a
+
exc. ArN2
[{OsClP4}2(µ-NH=NAr-ArN=NH)]2+
OsH2P4
[OsH(ArN=NH)P4]+
8
7a
Scheme 4. P ¼ P(OEt)3; Ar–Ar ¼ 4,40-C6H4–C6H4 (a).
Scheme 5. P ¼ PPh2OEt; Ar ¼ C6H5 (e), 4-CH3C6H4 (f).

1132
G. Albertin et al. / Inorganica Chimica Acta 357 (2004) 1119–1133
type A and B (Chart 9), with the substituents to the
N@N group in a mutually cis and trans positions, re-
spectively.
+
H
P
P
P
P
This hypothesis, however, cannot be applied to this
case, because the 31P{1H}NMR spectrum of the labelled
[OsH(C6H5N@15NH)P4]BPh4 (8e1) compound shows
that only one signal of the two present is coupled with
the 15N of the diazene ligand, giving a doublet with
N
N
H
Os
Ar
E
2J
of 1.7 Hz. The 15N{1H}NMR spectra confirm
15N31
P
these data showing a slightly broad singlet at 19.5 ppm
and a quintet at 22.3 ppm, due to the coupling with four
8
2
equivalent phosphorus nuclei, with J
of 1.7 Hz.
P
15N31
Chart 11.
One explanation of these data may involve the existence
always of two isomers, one containing a N1-bonded and
the other containing a N2-bonded diazene ligand, as
shown in geometries C and D (Chart 10).
In order to verify this hypothesis, we prepared the
labelled [OsH(C6H515N@NH)P4]BPh4 (8e2) complex
and recorded both the 31P and 15N spectra. In every
case, no coupling between the 15N of the diazene ligand
and the 31P nuclei was observed for the two isomers in
this complex, whose NMR spectra show two sharp
singlets in both 31P and 15N, so excluding the existence
of an isomer of type D.
A further hypothesis to explain the whole of spec-
troscopic data may involve the presence of two isomers,
one of which containing a usual N-bonded diazene li-
gand such as C and the other containing a p-bonded
ArN@NH group of the type E (Chart 11).
[17]. Although an X-ray crystal structure was not de-
termined due to the poor quality of the obtained crys-
tals, these precedents support the existence of a
geometry E, which agrees with all the spectroscopic data
of the complex.
The presence of two isomers, probably of types C and
E, for the aryldiazene [OsH(ArN@NH)(PPh2OEt)4]þ (8)
derivatives is not, however, the only difference observed
with the PPh2OEt ligand as compared with the related
P(OEt)3 and PPh(OEt)2 in the reaction of the dihydride
OsH2P4 with ArNþ2 cations. The absence of binuclear
complexes as well as the formation of exclusively mono-
diazenic species highlight once more the peculiar influ-
ence of the ancillary ligand in the chemistry of ‘‘diazo’’
derivatives.
The p-coordination of a diazene ligand is known but
rather rare [1b], and generally involves di-substituted
1,2-diazene bonded to a poor r-acceptor metal fragment
Acknowledgements
The financial support of MIUR (Rome), PRIN 2002,
is gratefully acknowledged. We thank Daniela Baldan
for technical assistance.
+
+
P
P
P
P
H
N
P
P
P
P
H
N
H
Os
N
H
Os
N
Ar
Ar
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