Preparation of new diazene complexes of ruthenium and osmium

Article abstract of DOI:10.1039/b202888n

The hydrazine complexes [Ru(NH₂NH₂)L₅](BPh₄)₂ 1, 8 or [Ru(NH₂NH₂)L′L₄](BPh₄) ₂ 2 [L=P(OEt)₃, L′=PPh(OEt)₂] were prepared by allowing the corresponding hydride species [RuHL₅]BPh₄ or [RuHL′L₄]BPh₄ to react first with HBF₄ and then with hydrazine. Oxidation of these hydrazine complexes or [Os(NH₂NH₂)L₅](BPh₄)₂ with Pb(OAc)₄ at -30°C led to the corresponding stable and isolable 1,2-diazene complexes [M(NH=NH)L₅](BPh₄)₂ 3, 5 (M=Ru, Os) or [Ru(NH=NH)L′L₄](BPh₄)₂ 4. The phenyldiazene derivatives [M(PhN=NH)L₅](BPh₄)₂ 6, 7 (M=Ru, Os) were also prepared by treating the hydride [MHL₅]BPh₄ species with phenyldiazonium tetrafluoroborate. The aquo-complex, [Ru(H₂O){P(OEt)₃}₅](BPh₄) ₂ 8, was obtained by substitution of the NH=NH ligand in [Ru(NH=NH)L₅](BPh₄)₂ and was characterised by X-ray crystal structure determination. Oxidation reactions of the bis(hydrazine) complexes [Ru(NH₂NH₂)₂L₄](BPh₄) ₂ or [Ru(CH₃NHNH₂)₂L₄](BPh ₄)₂ [L=P(OEt)₃] with Pb(OAc)₄ were reinvestigated and were found to give the diazene complexes [Ru(NH=NH)₂L₄](BPh₄)₂ 9, [Ru(CH₃N=NH)₂L₄](BPh₄) ₂ 11 or [Ru(CH₃N=NH)(CH₃NHNH₂)L₄](BPh ₄)₂ 10.

Full text of DOI:10.1039/b202888n

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Preparation of new diazene complexes of ruthenium and osmium†
Gabriele Albertin,*a Stefano Antoniutti,a Alessia Bacchi,b Mara Boatoa and Giancarlo Pelizzib
a Dipartimento di Chimica, Università Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia,
Italy
b Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica,
Università di Parma, Parco Area delle Scienze 17/a, 43100 Parma, Italy
Received 21st March 2002, Accepted 25th June 2002
First published as an Advance Article on the web 9th August 2002
The hydrazine complexes [Ru(NH2NH2)L5](BPh4)2 1, 8 or [Ru(NH2NH2)LЈL4](BPh4)2 2 [L = P(OEt)3, LЈ = PPh(OEt)2]
were prepared by allowing the corresponding hydride species [RuHL5]BPh4 or [RuHLЈL4]BPh4 to react first with
HBF4 and then with hydrazine. Oxidation of these hydrazine complexes or [Os(NH2NH2)L5](BPh4)2 with Pb(OAc)4 at
Ϫ30 ЊC led to the corresponding stable and isolable 1,2-diazene complexes [M(NH᎐NH)L ](BPh ) 3, 5 (M = Ru, Os)
᎐
5
4 2
or [Ru(NH᎐NH)LЈL ](BPh ) 4. The phenyldiazene derivatives [M(PhN᎐NH)L ](BPh ) 6, 7 (M = Ru, Os) were also
᎐
᎐
4
4
2
5
4 2
prepared by treating the hydride [MHL5]BPh4 species with phenyldiazonium tetrafluoroborate. The aquo-complex,
[Ru(H O){P(OEt) } ](BPh ) 8, was obtained by substitution of the NH᎐NH ligand in [Ru(NH᎐NH)L ](BPh ) and
᎐
᎐
2
3
5
4
2
5
4 2
was characterised by X-ray crystal structure determination. Oxidation reactions of the bis(hydrazine) complexes
[Ru(NH2NH2)2L4](BPh4)2 or [Ru(CH3NHNH2)2L4](BPh4)2 [L = P(OEt)3] with Pb(OAc)4 were reinvestigated and were
found to give the diazene complexes [Ru(NH᎐NH) L ](BPh ) 9, [Ru(CH N᎐NH) L ](BPh ) 11 or [Ru(CH N᎐
᎐
᎐
᎐
2
4
4
2
3
2
4
4
2
3
NH)(CH3NHNH2)L4](BPh4)2 10.
All solvents were dried over appropriate drying agents,
degassed on a vacuum line and distilled into vacuum-tight
storage flasks. The phosphite P(OEt)3 (Aldrich) was purified
by distillation under nitrogen; PPh(OEt)2 was prepared by the
method of Rabinowitz and Pellon.7 Diazonium salts were
obtained in the usual way.8 Hydrazine NH2NH2 was prepared
by decomposition of hydrazine cyanurate (Fluka) following the
reported method.9 RuCl3ؒ3H2O salt was a ChemPur product
and (NH4)2OsCl6 was purchased from Johnson Matthey; both
salts were used as received. High-grade (99.99%) lead()
acetate was purchased from Aldrich. Other reagents were pur-
chased from commercial sources in the highest available purity
and used as received. Infrared spectra were recorded on a
Nicolet Magna 750 FT-IR spectrophotometer. NMR spectra
(1H, 31P) were obtained on a Bruker AC200 spectrometer at
temperatures varying between Ϫ90 and ϩ30 ЊC, unless other-
wise noted. 1H spectra are referred to internal tetramethylsilane.
31P{1H} chemical shifts are reported with respect to 85%
H3PO4, with downfield shifts considered positive. The conduc-
tivity of 10Ϫ3 mol dmϪ3 solutions of the complexes in CH3NO2
at 25 ЊC was measured with a Radiometer CDM 83 instrument.
Introduction
Diazene NH᎐NH is a very reactive molecule in the free state,
᎐
and disproportionates1 at Ϫ150 ЊC into N2 and NH2NH2.
Nevertheless, it is an important molecule of possible relevance
as a metal-bound intermediate in inorganic and bioinorganic
N2 fixation processes,2 and useful as a reagent in stereoselec-
tive cis-hydrogenation of unsaturated organic compounds.3
Stabilisation of NH᎐NH in standard conditions has only been
᎐
achieved in a few cases by coordination to transition metals,
mainly in bimetallic complexes containing a µ-NH᎐NH ligand.4
᎐
Stable derivatives containing monodentate diazene have also
been reported.5
We are interested in the chemistry of partially reduced dini-
trogen ligands, and have previously reported6 the synthesis of
both methyldiazene and aryldiazene complexes of ruthenium
and osmium, obtained by oxidation of the related hydrazine
derivatives. However, no evidence of formation of stable
complexes containing coordinated 1,2-diazene was obtained.
We have therefore extended those studies, searching for an
appropriate metal fragment stabilising the diazene NH᎐NH
᎐
molecule by coordination, and results are reported here.
Reinvestigation of our previous reports6a,c on oxidation of
bis(hydrazine) [M(NH2NH2)2L4]2ϩ (M = Ru, Os) derivatives,
which allows bis(1,2-diazene) complexes to be prepared, is also
described here.
Preparation of complexes
Hydrides RuH2L4 [L = P(OEt)3, PPh(OEt)2] and [OsH{P(O-
Et)3}5]BPh4 were prepared following previous methods.6c,10
[RuHL5]BPh4 [L ؍ P(OEt)3 and PPh(OEt)2]. Hydrides
[RuHL5]BPh4 were prepared by a modification of the method
previously reported.11 An equimolar amount of the appropriate
phosphite (0.56 mmol) was added to a solution of RuH2L4
(0.56 mmol) in 5 cm3 of ethanol and the mixture cooled to
Ϫ196 ЊC. A slight excess of HBF4ؒEt2O (0.57 mmol, 82 µL) was
then added and the reaction mixture, brought to room tempera-
ture, stirred for about 2 h. The addition of an excess of NaBPh4
(1.2 mmol, 0.41 g) caused the separation of a white solid, which
was filtered and crystallised from CH2Cl2 and ethanol; yield
≥ 80%. (For [RuH{P(OEt)3}5]BPh4 Found: C, 51.64; H, 7.85.
C54H96BO15P5Ru requires C, 51.80; H, 7.73%. ΛM = 56.2 S cm2
Experimental
All synthetic work was carried out in an inert atmosphere using
standard Schlenk techniques or a Vacuum Atmosphere dry-
box. Once isolated, the complexes were found to be relatively
stable in air, but were stored in an inert atmosphere at Ϫ25 ЊC.
† Electronic supplementary information (ESI) available: observed and
calculated 31P{1H} NMR spectra of compounds [Ru(NH2NH2)-
{PPh(OEt)2}{P(OEt)3}4](BPh4)2 2 (Fig. S1) and [Ru(NH᎐NH){PPh-
(OEt)2}{P(OEt)3}4](BPh4)2
suppdata/dt/b2/b202888n/
᎐
4
(Fig. S2). See http://www.rsc.org/
DOI: 10.1039/b202888n
J. Chem. Soc., Dalton Trans., 2002, 3313–3320
This journal is © The Royal Society of Chemistry 2002
3313

View Article Online
molϪ1. IR (KBr) ν/cmϪ1: 1915 (m) ν(Ru–H). δH [(CD3)2CO, 25
ЊC]: 7.40–6.78 (m, 20 H, Ph), 4.11 (m, 30 H, CH2), 1.31, 1.30
(t, 45 H, CH3), Ϫ9.25 to Ϫ10.03 (m, 1 H, HϪ). δP [(CD3)2CO, 25
ЊC]: A4B spin system, δA 142.0, δB 140.4, JAB = 46.6 Hz).
which was filtered and crystallised by dissolving in CH2Cl2 and,
after filtration and concentration, by fast precipitation with
ethanol; yield ≥ 60%. (Found: C, 58.70; H, 7.47; N, 1.70.
C78H117B2N2O15P5Ru 3 requires C, 58.54; H, 7.37; N, 1.75%.
ΛM = 118.4 S cm2 molϪ1. Found: C, 55.38; H, 7.04; N, 1.75.
C78H117B2N2O15OsP5 5 requires C, 55.45; H, 6.98; N, 1.66%.
ΛM = 120.7 S cm2 molϪ1).
[RuH{PPh(OEt)2}{P(OEt)3}4]BPh4. A slight excess of HBF4ؒ
Et2O (0.42 mmol, 60 µL) was added to a solution of RuH2-
{P(OEt)3}4 (0.4 mmol, 0.31 g) in 10 cm3 of C2H5OH and the
reaction mixture was brought to about Ϫ30 ЊC and stirred for
30 min. A slight excess of PPh(OEt)2 (0.42 mmol, 83 µL) was
added and the resulting solution brought to room temperature.
After 1 h of stirring, an excess of NaBPh4 (0.8 mmol, 0.27 g)
was added and the white solid obtained filtered and crystallised
from CH2Cl2 and ethanol; yield ≥ 80%. (Found: C, 54.34; H,
7.45. C58H96BO14P5Ru requires C, 54.25; H, 7.53%. ΛM = 57.5 S
cm2 molϪ1. IR (KBr) ν/cmϪ1: 1936 (w) ν(Ru–H). δH (CD2Cl2,
25 ЊC): 8.01–6.70 (m, 25 H, Ph), 4.20–3.50 (m, 28 H, CH2), 1.26
(m, 42 H, CH3), Ϫ8.81 to Ϫ9.70 (m, 1 H, HϪ). δP (CD2Cl2,
25 ЊC): ABC2M spin system, δM 166.4, δA 141.0, δB 140.1,
[Ru(NH᎐NH){PPh(OEt) }{P(OEt) } ](BPh ) 4. This com-
᎐
2
3
4
4 2
plex was prepared exactly like the related species 3 and 5 by
oxidation with Pb(OAc)4 of the starting hydrazine compound 2;
yield ≥ 45%. (Found: C, 60.16; H, 7.30; N, 1.61. C82H117B2-
N2O14P5Ru requires C, 60.33; H, 7.22; N, 1.72%. ΛM = 116.9 S
cm2 molϪ1).
[Ru(PhN᎐NH){P(OEt) } ](BPh ) 6 and [Os(PhN᎐NH){P-
᎐
᎐
3
5
4 2
(OEt)3}5](BPh4)2 7. In a three-necked 25 cm3 round-bottomed
flask were placed solid samples of the appropriate hydrides
[MHL5]BPh4 (0.1 mmol) and an excess of phenyldiazonium
tetrafluoroborate [PhN2]BF4 (0.5 mmol, 96 mg) and the mixture
was cooled to Ϫ196 ЊC. Acetone (10 cm3) was slowly added and
the reaction mixture, brought to room temperature, stirred for
4 h. The solvent was removed under reduced pressure giving a
brown oil which was treated with ethanol (5 cm3) containing an
excess of NaBPh4 (0.2 mmol, 68 mg). A yellow solid slowly
separated out, which was filtered and crystallised from CH2Cl2
and ethanol; yield ≥ 75%. (Found: C, 60.02; H, 7.35; N, 1.60.
C84H121B2N2O15P5Ru 6 requires C, 60.18; H, 7.27; N, 1.67%.
ΛM = 120.3 S cm2 molϪ1. Found: C, 57.01; H, 6.99; N, 1.67.
C84H121B2N2O15OsP5 7 requires C, 57.14; H, 6.91; N, 1.59%.
ΛM = 117.8 S cm2 molϪ1).
δC 137.6, JAM = Ϫ435.7, JBM = 56.0, JCM = 31.6, JAB = 67.7, JAC
=
38.3, JBC = 55.4 Hz).
[Ru(NH2NH2){P(OEt)3}5](BPh4)2 1. An excess of HBF4ؒEt2O
(0.4 mmol, 57 µL) was added to a solution of hydride
[RuHL5]BPh4 (0.125 g, 0.1 mmol) in 10 cm3 of CH2Cl2 cooled
to Ϫ196 ЊC and placed under a hydrogen atmosphere. The
reaction mixture was brought to room temperature, stirred for
2 h and then, after replacing the H2 atmosphere with argon, an
excess of NH2NH2 (1 mmol, 31 µL) was added. The resulting
solution was stirred for 20 h and then the solvent was removed
under reduced pressure. The oil obtained was triturated with
ethanol containing an excess of NaBPh4 (0.2 mmol, 68 mg)
giving a white solid, which was filtered and crystallised from
CH2Cl2 and ethanol; yield ≥ 60%. (Found: C, 58.35; H, 7.58; N,
1.72. C78H119B2N2O15P5Ru requires C, 58.47; H, 7.49; N, 1.75%.
ΛM = 114.9 S cm2 molϪ1).
[Ru(H2O){P(OEt)3}5](BPh4)2 8. This complex was obtained
in an attempt at crystallisation of the diazene derivative
[Ru(NH᎐NH){P(OEt) } ](BPh ) 3. In fact, by slow cooling to
᎐
3
5
4 2
Ϫ25 ЊC of a saturated solution of 3, prepared by treating the
solid sample (150 mg) with ethanol (8 cm3) and enough CH2Cl2
to obtain a saturated solution at room temperature, white
microcrystals of the aquo-complex 8 were obtained. These
crystals were also suitable for X-ray analysis; yield ≥ 80%.
(Found: C, 59.11; H, 7.49. C78H117B2O16P5Ru requires C, 58.98;
H, 7.42%. ΛM = 118.2 S cm2 molϪ1).
[Ru(NH2NH2){PPh(OEt)2}{P(OEt)3}4](BPh4)2 2. This com-
pound was prepared exactly like the related pentakis(phosphite)
complex 1 by reacting the hydride [RuH{PPh(OEt)2}{P-
(OEt)3}4]BPh4 first with HBF4ؒEt2O and then with NH2NH2;
yield ≥ 65%. (Found: C, 60.39; H, 7.45; N, 1.76. C82H119B2-
N2O14P5Ru requires C, 60.26; H, 7.34; N, 1.71%. ΛM = 115.1 S
cm2 molϪ1).
[Ru(CH N᎐NH)(CH NHNH ){P(OEt) } ](BPh ) 10and[Ru-
᎐
3
3
2
3
4
4 2
(CH N᎐NH) {P(OEt) } ](BPh ) 11. These complexes were
᎐
3
2
3
4
4 2
obtained by oxidation of the [Ru(CH3NHNH2)2{P(OEt)3}4]-
(BPh4)2 complex6a with Pb(OAc)4 in CH2Cl2 at Ϫ30 ЊC follow-
ing the method used for 3 and 5. In this case, by reacting
0.2 mmol (0.300 g) of [Ru(CH3NHNH2)2{P(OEt)3}4](BPh4)2
with 0.4 mmol (0.177 g) of Pb(OAc)4, a mixture of both com-
pounds 10 and 11 was obtained. Their separation involves the
slow cooling to Ϫ25 ЊC of a saturated solution of the mixture
prepared at room temperature using as solvent ethanol and
enough CH2Cl2 to dissolve the solid. The first solid obtained
was the mixed-ligand compound 10 in about 25% yield, while
from the mother liquor, after repeated crystallisation, the bis-
(methyldiazene) 11 was separated in about 10% yield. (Found:
C, 59.31; H, 7.48; N, 3.66. C74H110B2N4O12P4Ru 10 requires C,
59.48; H, 7.42; N, 3.75%. ΛM = 118.5 S cm2 molϪ1. Found:
C, 59.42; H, 7.41; N, 3.63. C74H108B2N4O12P4Ru 11 requires C,
59.56; H, 7.29; N, 3.75%. ΛM = 108.9 S cm2 molϪ1).
[Ru(NH2NH2)2{PPh(OEt)2}4](BPh4)2. This complex was
obtained in an attempt to prepare the pentakis(phosphite)
[Ru(NH2NH2){PPh(OEt)2}5](BPh4)2 following the method
reported for the related compounds 1 and 2. In this case, the
known6a bis(hydrazine) derivative was obtained as the only
isolated product, with a yield of about 75%. (Found: C, 66.12;
H, 6.95; N, 3.45. C88H108B2N4O8P4Ru requires C, 66.21; H, 6.82;
N, 3.51%. ΛM = 114.7 S cm2 molϪ1).
[Os(NH2NH2)L5](BPh4)2 [L ؍ P(OEt)3]. This complex was
prepared following the method previously reported.6c
[Ru(NH᎐NH){P(OEt) } ](BPh )
4 2
3 and [Os(NH᎐NH){P-
᎐
᎐
3
5
(OEt)3}5](BPh4)2 5. A sample of the appropriate hydrazine
complex [M(NH2NH2)L5](BPh4)2 (0.16 mmol) was placed in a
three-necked 25 cm3 round-bottomed flask fitted with a solid-
addition sidearm containing an equimolar amount of
Pb(OAc)4 (0.16 mmol, 71 mg). Dichloromethane (10 cm3) was
added, the solution cooled to Ϫ30 ЊC and Pb(OAc)4 added
portionwise over 20–30 min to the cold stirring solution. The
solution was then brought to 0 ЊC, stirred for 10 min and the
solvent removed under reduced pressure. The oil obtained was
treated at 0 ЊC with ethanol (2 cm3) containing an excess of
NaBPh4 (0.2 mmol, 68 mg). A white solid slowly separated out,
Oxidation of [Ru(NH2NH2)2L4](BPh4)2 [L ؍ P(OEt)3 and
PPh(OEt)2] and [Os(NH2NH2)2{P(OEt)3}4](BPh4)2
Also the oxidation of the bis(hydrazine) complexes6a,c was
carried out with Pb(OAc)4 at Ϫ30 ЊC, following the method
used for the other hydrazine complexes 1, 2, [Os(NH2-
NH2)L5](BPh4)2 and [Ru(CH3NHNH2)2L4](BPh4)2. A typical
experiment involves the addition of solid Pb(OAc)4 (0.4 mmol,
3314
J. Chem. Soc., Dalton Trans., 2002, 3313–3320

View Article Online
Table 1 Crystal data and structure refinement for [Ru(H2O){P-
(OEt)3}5](BPh4)2 8
Results and discussion
Hydrazine complexes of ruthenium [Ru(NH2NH2){P(O-
Et)3}5](BPh4)2 1 and [Ru(NH2NH2){PPh(OEt)2}{P(OEt)3}4]-
(BPh4)2 2 were prepared by reacting the hydride [RuHLЈ-
L4]BPh4 first with an excess of fluoroboric acid and then with
hydrazine, as shown in Scheme 1.
Empirical formula
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
C78H117B2O16P5Ru
1588.26
293(2)
0.71069
Triclinic
¯
P1
a/Å
b/Å
14.763(5)
16.613(5)
c/Å
18.646(5)
82.05(5)
4529(2)
β/Њ
Volume/Å3
Z
2
Absorption coefficient/mmϪ1
F(000)
0.318
1684
Reflections collected
Independent reflections
Data/restraints/parameters
Final R indices [I > 2σ(I )]
R indices (all data)
26755
18872 [R(int) = 0.0555]
18872/6/845
R1 = 0.0948, wR2 = 0.2383
R1 = 0.1649, wR2 = 0.2968
Scheme 1 LЈ = L = P(OEt)3 1; LЈ = PPh(OEt)2, L = P(OEt)3 2.
Reactions of the pentakis(phosphite)hydride [RuHLЈL4]ϩ
with an excess of HBF4 gives the η2-H2 dihydrogen intermediate
[M(η2-H2)LЈL4]2ϩ (by 1H NMR), which reacts with NH2NH2 to
give final hydrazine complexes 1 or 2. In contrast, the reaction
of the hydride [RuH{PPh(OEt)2}5]BPh4, first with HBF4 and
then with hydrazine, in all conditions afforded the known6a
0.177 g) to a cooled solution (Ϫ30 ЊC) of the appropriate
bis(hydrazine) complex (0.2 mmol) in CH2Cl2. Removal of the
solvent at the end of the reaction gave an oil, which was tri-
turated at 0 ЊC with ethanol (2 cm3) containing an excess of
NaBPh4 (0.4 mmol, 136 mg). The white solid that slowly
separated out was filtered and dried under vacuum. The
bis(hydrazine) complex [Ru(NH2NH2)2{PPh(OEt)2}4]2ϩ
shown in Scheme 2.
, as
samples contained a mixture of bis(diazene) [M(NH᎐NH) -
᎐
2
L4](BPh4)2 and acetate [M(κ2-O2CCH3)L4]BPh4 complexes,
which cannot be separated in pure form. However, in the case
of [Ru(NH᎐NH) {P(OEt) } ](BPh ) 9, the sample contains the
᎐
2
3
4
4 2
bis(diazene) as the major product (about 60–70%), while in
the other cases only little amounts (5–10%) of bis(diazene) are
present in the reaction product. For the mixture containing
Scheme 2 L = PPh(OEt)2.
In the pentakis(phosphite) [Ru(η2-H2)L5]2ϩ intermediate,
hydrazine replaces not only the labile η2-H2 ligand, but also one
phosphite, giving the bis(hydrazine) species. Attempts to pre-
pare other pentakis(phosphite) hydrazine complexes different
from 1 and 2 failed, because the reaction of [RuHLЈL4]ϩ first
with a Brønsted acid and then with an excess of CH3NHNH2 or
C6H5NHNH2 only gave mixtures of solid products not con-
taining the hydrazine ligand. It seems that only the NH2NH2
species can bind to the metal centre in the MLЈL4 fragment to
give stable and isolable derivatives.
[Ru(NH᎐NH) {PPh(OEt) } ](BPh ) δ (CD Cl , 20 ЊC): 16.23,
᎐
2
2
4
3
4
2
H
2
2
15.62 (dm, 2 H, NH᎐NH; J = 32.0 Hz). For the mixture
᎐
HH
containing [Os(NH᎐NH) {P(OEt) } ](BPh ) δH (CD2Cl2,
᎐
2
3
4
4 2
20 ЊC): 16.63, 16.31 (dm, 2 H, NH᎐NH).
᎐
Crystallography
Crystals were air sensitive, a white irregular prism single crystal
was sealed in a glass capillary along with some drops of
solution. X-Ray diffraction data were collected on a Bruker-
Siemens SMART AXS 1000 equipped with a CCD detector,
using graphite monochromated Mo-Kα radiation (λ = 0.71069
Å). Data collection details are: crystal to detector distance =
5.0 cm, hemisphere mode, time per frame = 30 s, oscillation
∆ω = 0.300Њ. Data reduction was performed up to θ = 28Њ by the
SAINT package12 and data were corrected for absorption
effects by the SADABS13 procedure. Data collection and
refinement results are summarised in Table 1. The crystal
suffered a severe merohedral twinning expressed by a mirror
plane perpendicular to b, which simulated a 2/m Laue sym-
Hydrazine complexes 1 and 2 were isolated as white [BPh4]
salts, stable in air and in solutions of polar organic solvents, in
which they behave as 2 : 1 electrolytes. Analytical and spectro-
scopic data (Table 2) support the proposed formulation. The
presence of the hydrazine ligand was supported by infrared
spectroscopy, which showed the characteristic νNH medium-
intensity bands of NH2NH2 between 3387 and 3266 cmϪ1
.
1
Further support for the presence of NH2NH2 came from H
NMR spectra, which showed two broad signals at 4.37 and
3.36 ppm (1) or at 4.41 and 3.46 ppm (2), due to the two NH2
proton resonances. Integration measurements and homo-
decoupling experiments confirmed the proposed assignment.
In the temperature range between ϩ30 and Ϫ80 ЊC, the 31P{1H}
NMR spectrum of [M(NH2NH2)L5]2ϩ 1 appeared as an AB4
multiplet, fitting the proposed formulation (geometry I, Fig. 1).
In contrast, the spectra of [Ru(NH2NH2){PPh(OEt)2}{P-
(OEt)3}4](BPh4)2 2 showed a rather complicated pattern, simu-
lated as a set of two systems of types AB4 and ABC2M, partly
overlapping, and with the parameters listed in Table 2. This
result may be interpreted as due to two geometries in solution
of the type shown in Fig. 1, with the hydrazine and PPh(OEt)2
ligands in mutually trans (II) or cis (III) positions, respectively.
Pentakis(phosphite)hydrazine complexes of both ruthenium
1, 2 and osmium6c [Os(NH2NH2)L5](BPh4)2 reacted with
Pb(OAc)4 at low temperature (Ϫ30 ЊC) with the selective oxida-
tion of the NH2NH2 ligand to give 1,2-diazene complexes
[M(NH᎐NH)L ]2ϩ (M = Ru 3, Os 5) and [Ru(NH᎐NH){PPh-
¯
metry, whilst the actual structure is described in P1, with α and
β close to 90Њ. The phase problem was solved by direct
methods14 and the structure was refined by full matrix least
squares on all F 2 by taking into account the twinning as imple-
mented in Shelxl 97,15 using the WinGX package.16 The refine-
ment without considering the twinning was unsuccessful.
Anisotropic displacement parameters were refined for all non-
hydrogen atoms, while hydrogen atoms were introduced in
calculated positions, except for those belonging to the water,
located on the Fourier maps. Phenyls were treated as rigid
bodies. Use of the Cambridge Crystallographic Database17
facilities was made for structure discussion. Meaningless
electron density residues were left around the metal in the final
map.
CCDC reference number 182442.
See http://www.rsc.org/suppdata/dt/b2/b202888n/ for crystal-
lographic data in CIF or other electronic format.
᎐
᎐
5
J. Chem. Soc., Dalton Trans., 2002, 3313–3320
3315

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Table 2 IR and NMR data for ruthenium and osmium complexes
IRa
1H NMRb, c
31P-{1H} NMRb, d
Compound
ν/cmϪ1
Assignment
δ(J/Hz)
Assignment
Spin system
AB4
δ(J/Hz)
1
[Ru(NH2NH2)-
{P(OEt)3}5](BPh4)2
3368 m
3328 m
3275 w
3267 w
ν(NH)
4.37 s, br
4.07 m
3.97 qnt
3.36 s, br
1.32 t
RuNH2
CH2
δA 131.9
δAB 120.9
JAB = 58.3
NH2
CH3
1.27 t
2
[Ru(NH2NH2){PPh(OEt)2}-
{P(OEt)3}4](BPh4)2
3387 w
3340 w
3327 w
3266 w
ν(NH)
4.41 s, br
4.15–3.70 m
3.46 q, br
1.36 t
RuNH2
CH2
NH2
AB4
δA 160.7
δB 120.4
JAB = 50.5
δA 131.5
CH3
ABC2M
1.35 t
1.33 t
δB 122.0
δC 120.5
1.32 t
1.29 t
δM 150.4
JAB = 55.5
JAC = 61.7
JAM = 48.6
JBC = 63.2
JBM = Ϫ475.5
JCM = 54.0
δA 129.1
3
[Ru(NH᎐NH){P(OEt)3}5]-
(BPh4)2
AB4XY spin syst.
δX 16.76
δY 15.36
JAX = 12.4
JAY = 9.2
JBX = 1.5
JBY = 2.6
JXY = 32.5
4.06 m
᎐NH
AB4
᎐
᎐
δB 118.3
JAB = 59.3
CH2
CH3
1.37 t
1.32 t
4
[Ru(NH᎐NH){PPh(OEt)2}-
{P(OEt)3}4](BPh4)2
16.74 m
15.38 m
3.93 m
᎐NH
AB4
δA 158.8
δB 120.5
JAB = 51.1
δA 128.8
᎐
᎐
CH2
CH3
1.34 t
ABC2M
1.32 t
1.31 t
δB 119.0
δC 118.2
1.27 t
1.25 t
δM 147.3
JAB = 53.8
JAC = 65.2
JAM = 45.8
JBC = 61.2
JBM = Ϫ460.5
JCM = 52.7
δA 84.2
5
[Os(NH᎐NH){P(OEt)3}5]-
(BPh4)2
A4BXY spin syst.
δX 16.82
δY 15.73
JAX = 1.65
JAY = 3.85
JBX = 11.0
JBY = 7.65
JXY = 32.2
4.11 m
᎐NH
A4Be
᎐
᎐
δB 63.3
JAB = 40.3
CH2
CH3
4.00 qnt
1.37 t
1.35 t
e
6
7
[Ru(C6H5N᎐NH){P(OEt)3}5]-
(BPh4)2
13.72 me
4.30 m
᎐NH
CH2
AB4
δA 133.0
δB 121.3
JAB = 60.4
᎐
᎐
4.19 qnt
1.40 t
CH3
1.32 t
[Os(C6H5N᎐NH){P(OEt)3}5]-
14.15 me
4.35 m
᎐NH
A4Be
δA 86.6
δB 69.7
᎐
᎐
(BPh4)2
CH2
4.11 qnt
1.40 t
JAB = 41.0
CH3
1.34 t
4.07 m
2.65 s, br
1.36 t
1.32 t
16.71 dm
15.83 dm
JHH = 32
4.07 m
8
9
[Ru(H2O){P(OEt)3}5](BPh4)2
CH2
H2O
CH3
AB4
δA 131.7
δB 119.1
JAB = 59.5
[Ru(NH᎐NH)2{P(OEt)3}4]-
᎐NH
᎐
A2B2
δA 128.2
δB 118.1
JAB = 60.0
᎐
f
(BPh4)2
CH2
CH3
1.37 t
1.32 t
3316
J. Chem. Soc., Dalton Trans., 2002, 3313–3320

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Table 2 IR and NMR data for ruthenium and osmium complexes
IRa
1H NMRb, c
31P-{1H} NMRb, d
Compound
ν/cmϪ1
Assignment
δ(J/Hz)
Assignment
Spin system
δ(J/Hz)
e
10
[Ru(CH3N᎐NH)(CH3NHNH2)-
{P(OEt)3}4](BPh4)2
3347 w
3304 m
3295 w
ν(NH)
13.74 m, br
4.64 s, br
4.10 m
3.76 s
3.45 m, br
2.65 d
᎐NH
RuNH2
CH2
ABC2
δA 128.9
δB 127.4
δC 118.5
JAB = 68.7
JAC = 61.2
JBC = 60.1
᎐
᎐
CH3N᎐
᎐
NHhydrazine
CH3 hydrazine
CH3
1.37 t
1.34 t
1.32 t
11
[Ru(CH3N᎐NH)2{P(OEt)3}4]-
(BPh4)2
13.58 m, br
4.10 m
3.81 s
᎐NH
CH2
CH3N᎐
CH3
A2B2
δA 129.8
δB 119.8
JAB = 61.6
᎐
᎐
᎐
1.39 t
1.35 t
a In KBr pellets. b In CD2Cl2 at 25 ЊC, unless otherwise noted. c Phenyl proton resonances are omitted. d Positive shift downfield from 85% H3PO4.
e In (CD3)2CO. f The sample contains the acetate complex [Ru(κ2-O2CCH3){P(OEt)3}4]BPh4.
which was isolated and characterised. The H2O molecule prob-
ably comes from the traces of water always present in the com-
mon “anhydrous” solvents. In the solution the presence of
hydrazine was also detected and confirms the decomposition
of free NH᎐NH.
᎐
Diazene complexes 3–5 are 2 : 1 electrolytes, and their ana-
lytical and spectroscopic data (Table 2) support the proposed
1
formulation. In the low-field region of the H NMR spectrum
of complex [Ru(NH᎐NH)L ]2ϩ 3, two multiplets (Fig. 2) at
᎐
5
Fig. 1 L = P(OEt)3.
1
Fig. 2 Observed (bottom) and calculated (top) H NMR spectra, in
the diazene region, of [Ru(NH᎐NH){P(OEt)3}5](BPh4)2 3, in CD2Cl2 at
᎐
25 ЊC. The simulated spectrum was obtained using the parameters
reported in Table 2.
16.76 and 15.36 ppm appeared, which were attributed to the
two NH protons of a monohapto NH᎐NH ligand. This pattern
᎐
is due to coupling with 31P nuclei (AB4 multiplet), as confirmed
by simulation of the spectrum using an AB4XY model (X =
Scheme 3 M = Ru 3, Os 5; L = P(OEt)3.
(OEt)2}L4]2ϩ 4, which were isolated as white solids and charac-
terised (Scheme 3).
HA, Y = HB), with the parameters listed in Table 2. The JHH
3
value of 32.5 Hz (JXY) also suggested4d,5 a probable trans-NH᎐
᎐
It was essential for the successful synthesis of diazene deriva-
tives 3–5 to carry out reactions at low temperature (Ϫ30 ЊC) and
to use high-purity Pb(OAc)4 (99.99%) in equimolar amounts.
Otherwise, mixtures of products not containing the 1,2-diazene
complex were obtained. In particular, the use of common
Pb(OAc)4 (95%) did not yield pure samples of 3–5, but only
mixtures containing small amounts (10–15%) of the diazene
complex.
NH geometry. The related osmium complex [Os(NH᎐NH)L ]2ϩ
᎐
5
5, in the low-field region of the proton spectra, also showed the
characteristic A4BXY multiplet of the diazene ligands. In the
temperature range between Ϫ80 and ϩ30 ЊC, the 31P{1H} NMR
spectra of both complexes 3 and 5 appeared as AB4 or A4B
multiplets, fitting geometry IV (Fig. 3).
The presence of the diazene ligand was also confirmed in the
mixed-phosphite derivative [Ru(NH᎐NH){PPh(OEt) }{P-
᎐
2
All NH᎐NH derivatives 3–5 are stable as solids, but slowly
(OEt)3}4](BPh4)2 4, the 1H NMR spectrum of which showed the
᎐
decompose in solution, losing the diazene ligand. An attempt to
crystallise 3 in a mixture of ethanol and dichloromethane as
solvent gave aquo-complex [Ru(H2O){P(OEt)3}5](BPh4)2 8,
characteristic ᎐NH multiplet between 17 and 15 ppm (Table 2).
᎐
In the temperature range between Ϫ80 and ϩ30 ЊC, the 31P{1H}
NMR spectrum appeared as a complicated pattern, simulated
J. Chem. Soc., Dalton Trans., 2002, 3313–3320
3317

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Table 3 Selected bond lengths (Å) and angles (Њ) for [Ru(H2O){P(O-
Et)3}5](BPh4)2 8, with s.u.s in parentheses
Ru–O16
Ru–P4
Ru–P1
2.219(7)
2.238(3)
2.348(3)
Ru–P3
Ru–P2
Ru–P5
2.352(3)
2.356(3)
2.372(3)
O16–Ru–P4
O16–Ru–P1
P4–Ru–P1
O16–Ru–P3
P4–Ru–P3
P1–Ru–P3
O16–Ru–P2
P4–Ru–P2
178.3(2)
89.9(2)
91.1(1)
80.7(2)
98.0(1)
91.81(9)
87.0(2)
94.3(1)
P1–Ru–P2
P3–Ru–P2
O16–Ru–P5
P4–Ru–P5
P1–Ru–P5
P3–Ru–P5
P2–Ru–P5
88.2(1)
167.7(1)
86.8(2)
92.1(1)
176.6(1)
88.7(1)
90.6(1)
Fig. 3 L = P(OEt)3.
as a set of one AB4 and one ABC2M multiplets, partially over-
lapping. On this basis, and taking into account the 31P spectra
of hydrazine precursor 2, we propose the existence of two iso-
mers of the type shown in Fig. 4 for our complex 4, containing
the NH᎐NH and PPh(OEt) ligands in mutually cis (V) or
᎐
2
trans (VI) positions, respectively.
Scheme 5 L = P(OEt)3, M = Ru.
Although aryldiazenes 6 and 7 were stable in solution, related
1,2-diazene complexes 3–5 slowly decomposed giving aquo-
complex [M(H2O)L5]2ϩ, probably by substitution of the labile
Fig. 4 L = P(OEt)3, LЈ = PPh(OEt)2.
NH᎐NH ligand with traces of water present in the solvent. In
᎐
Complexes containing the monodentate 1,2-diazene ligand
are very rare,5 and only one example5c of isolable species has
been reported for ruthenium and osmium metal centres. Using
the pentakis(phosphite) ML5 (or MLЈL4) fragment stabilises
the case of ruthenium, compound [Ru(H2O)L5](BPh4)2
8
(Scheme 5) was isolated as white microcrystals and charac-
terised spectroscopically (Table 2) and crystallographically
(Table 1). The presence of H2O as a ligand in the complex was
indicated by the proton NMR signal at 2.65 ppm, and the
31P{1H} spectra confirmed the ML5 fragment.
the NH᎐NH molecule through coordination, affording stable
᎐
and isolable species for both Ru() and Os().
Unfortunately, no other [M(RN᎐NH)L ]2ϩ diazene com-
The structure and atom labelling of [Ru(H2O){P(OEt)3}5]2ϩ
is shown in Fig. 5, and the coordination geometry is summarised
in Table 3. The metal coordination is octahedral, with ligand
᎐
5
plexes besides 3 and 5 could be prepared by oxidation of
coordinated hydrazine, owing to the absence of the correspond-
ing precursors. In our hands, hydrazines RNHNH2 different
from NH2NH2 could not be coordinated to the ML5 fragment
to give stable species. However, taking into account that aryl-
diazene can also be prepared by insertion of aryldiazonium
cations into a M–H bond, we treated the [MHL5]ϩ (M = Ru, Os)
Ϫ
hydrides with the phenyldiazonium cation PhN2ϩBF4 and
observed the formation of aryldiazene derivatives [M(PhN᎐
᎐
NH)L5]2ϩ (M = Ru 6, Os 7) which were isolated as BPh4Ϫ salts
and characterised (Scheme 4).
Scheme 4 M = Ru 6, Os 7; L = P(OEt)3.
The formation of complexes 6 and 7 may indicate that the
Fig. 5 Perspective view of the solid-state molecular structure of cation
[Ru(H2O){P(OEt)3}5]2ϩ 82ϩ. Anisotropic displacement parameters are
at the 50% probability level. Ethoxy groups are omitted for clarity.
steric requirement of aryldiazene PhN᎐NH is lower than that
᎐
of arylhydrazine PhNHNH2, whose coordination on the ML5
fragment did not take place. Aryldiazene [M(PhN᎐NH)L ]-
᎐
5
(BPh4)2 derivatives 6 and 7 are stable as solids and in solutions
of polar organic solvents, in which they behave as 2 : 1 electro-
lytes. The presence of the diazene ligand was confirmed by the
1H NMR spectra, which displayed the characteristic high-
frequency NH proton resonances at 13.72 (6) and 14.15 (7)
ppm. In the temperature range between Ϫ90 and ϩ30 ЊC, the
31P{1H} NMR spectrum appeared as an AB4 multiplet, fitting
the proposed formulation.
at P4 located trans to the water molecule, the remaining phos-
phites being sterically equivalent to each other. The steric
crowding of the bulky phosphite ligands is partly relieved by
pushing them towards the water position, thus reducing the
width of the cis O–Ru–P bond angles, which range between
80.7(2) and 89.9(2)Њ. The presence of the water ligand also
affects the Ru–P4 bond trans to it [2.238(3) Å], which is far
shorter than the remaining cis ones [2.348(3)–2.372(3) Å]. The
3318
J. Chem. Soc., Dalton Trans., 2002, 3313–3320

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large trans influence of the unique P(OEt)3 ligand is evidenced
by the fact that the Ru–O bond is among the longest found in
Ru2ϩ water complexes (e.g. Ru–O = 2.139 Å in the hexa-aquo
cation18). There are no intermolecular interactions among
non-hydrogen atoms below 3.55 Å in the structure.
Results from oxidation reactions of hydrazine complexes [M-
(NH2NH2)L5]2ϩ using the new high-purity Pb(OAc)4 (99.99%)
prompted us to reinvestigate the oxidation of the bis(hydrazine)
complexes [M(NH2NH2)2L4]2ϩ, that were previously studied by
us,6a,c using low-purity Pb(OAc)4 (95%) as oxidising agent.
These earlier reactions did not give diazene complexes, but
only acetate derivative [M(κ2-O2CCH3)L4]ϩ. The reaction was
studied in CH2Cl2 at Ϫ30 ЊC using high-purity Pb(OAc)4 in a
Ru : Pb ratio 1 : 2, and showed that, in the case of [Ru(NH2-
NH2)2{P(OEt)3}4]2ϩ it does give a white solid containing a
On this basis, we extended the oxidation reaction to methyl-
hydrazine complexes [Ru(CH3NHNH2)2L4]2ϩ and found that,
using high-purity Pb(OAc)4 (99.99%), the reaction gives a
mixture of bis(methyldiazene) [Ru(CH N᎐NH) L ]2ϩ 11 and
᎐
3
2
4
methyldiazene–methylhydrazine
[Ru(CH N᎐NH)(CH NH-
᎐
3 3
NH2)L4]2ϩ 10 complexes, which were isolated as BPh4Ϫ salts and
characterised (Scheme 7).
Complexes 10 and 11 were separated by fractional crystallis-
ation into two pale yellow solids, stable in air and in solutions
of polar organic solvents, in which they behave as 2 : 1 electro-
lytes. Analytical and spectroscopic data (Table 2) support the
1
proposed formulation. The H NMR spectrum of bis(methyl-
mixture of bis(diazene) [Ru(NH᎐NH) L ](BPh ) 9 and acetate
᎐
2
4
4 2
[Ru(κ2-O2CCH3)L4]BPh4 derivatives, as shown in Scheme 6.
Scheme 7 L = P(OEt)3.
diazene) complex 11 shows a slightly broad multiplet at 13.58
ppm, characteristic of the diazene ligand. Beside the signals of
phosphite and BPh4 ion, the spectrum also contains, a singlet at
3.81 ppm, due to the methyl–proton resonance of the methyl-
diazene group. In the temperature range between Ϫ80 and
ϩ30 ЊC, the 31P{1H} NMR spectra appear as an A2B2 multiplet,
fitting the presence of two diazene ligands in a mutual cis
position (IX).
Scheme 6 L = P(OEt)3.
From this mixture, we attempted to separate the diazene
complex by fractional crystallisation at low temperature, but
the instability in solution of [Ru(NH᎐NH) L ]2ϩ on the one
᎐
2
4
hand, and the comparable solubility of the two complexes on
the other, always gave samples containing more products. How-
ever, the H NMR spectra of the mixture strongly supports
In mixed-ligand complex [Ru(CH N᎐NH)(CH NHNH )-
᎐
3
3
2
L4](BPh4)2 10, the 1H NMR spectra show the presence of both
nitrogenous ligands. The broad multiplet at 13.74 ppm of the
NH proton and the singlet at 3.76 ppm of the methyl reson-
1
the formation of bis(diazene) 9, showing two doublets of
multiplets at 16.71 and 15.83 ppm, attributed to the two NH
ances confirm the presence of the CH N᎐NH ligand, whereas
᎐
3
3
protons of the two diazene ligands. The JHH value of 32 Hz
the broad signals at 4.64 and 3.45 ppm, due to NH2 and NH
resonances respectively, and the doublet at 2.65 ppm are
diagnostic of the hydrazine group. The ABC2 multiplet present
in the 31P{1H} spectra also suggests mutual cis position of the
hydrazine and diazene ligands in the complex (X).
The RuL4 fragment is therefore able to stabilise both 1,2-
diazene and methyldiazene by coordination, affording the
related bis(diazene) species, which are very stable, in the case
also suggests4d,5 a trans-NH᎐NH geometry. The 31P{1H} NMR
᎐
spectra of the oxidation product also shows two A2B2 multi-
plets, due to acetate compound6a [Ru(κ2-O2CCH3)L4]ϩ and
bis(diazene) complex 9, fitting the proposed formulation. The
A2B2 pattern also suggests the mutually cis positions of the
two diazene ligands, as in geometry VIII, Scheme 6.
Oxidation of the related [Ru(NH2NH2)2{PPh(OEt)2}4]-
(BPh4)2 and [Os(NH2NH2)2{P(OEt)3}4](BPh4)2 derivatives
of CH N᎐NH. Partial substitution was observed with the
᎐
3
1
afforded white solids, with H NMR spectra showing diazene
NH᎐NH ligand, affording a mixture of diazene (9) and acetate
᎐
[Ru(κ2-O2CCH3)L4]ϩ derivatives. However, isolation of solid
samples containing diazene complexes of ruthenium was only
achieved by using high-purity Pb(OAc)4 (99.99%), and the
absence in previous studies6 of any evidence of these diazene
species is probably due to the fact that standard-grade
Pb(OAc)4 (95%) was used, which leads to decomposition of
diazene derivatives (see ESI).
signals, probably attributable to bis(diazene) [M(NH᎐NH) -
᎐
2
L4](BPh4)2 (M = Ru, Os) complexes. In these cases, however, the
predominant species is acetate compound [M(κ2-O2CCH3)L4]ϩ,
with the diazene complex present only in a small amount (from
5 to 10%).
These studies on the oxidation of bis(hydrazine) complexes
with high-purity Pb(OAc)4 (99.99%) show that 1,2-diazene
complexes can also be formed in these cases, but their stabilisa-
tion on the ML4 fragment is restricted, as compared with
related [M(NH᎐NH)L ]2ϩ derivatives, and does not allow
Acknowledgements
᎐
5
separation of the samples in pure form. However, although
The financial support of MURST (Rome)—Programmi di
Ricerca Scientifica di Rilevante Interesse Nazionale, Cofinan-
ziamento 2000–2001—is gratefully acknowledged. We thank
Daniela Baldan for technical assistance.
substitution of the NH᎐NH ligand by the acetate ion also takes
᎐
place using high-purity Pb(OAc)4, a solid sample containing the
coordinated 1,2-diazene (9) as the predominant species was
isolated. In addition, these results confirm our previous
hypothesis6a,c on the formation of a diazene complex in
the oxidation of [M(NH2NH2)2L4]2ϩ cations, and highlight the
importance of the purity of Pb(OAc)4 in determining the nature
of the final oxidation products.
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