Preparation and reactivity of osmium(II) hydride complexes with phosphites and polypyridyls

Article abstract of DOI:10.1016/j.jorganchem.2004.02.019

Chloro-complexes [OsCl(N-N)P₃]BPh₄ (1, 2) [N-N=2,2^′-bipyridine (bpy) and 1,10-phenanthroline (phen); P=P(OEt)₃ and PPh(OEt)₂] were prepared by allowing OsCl₄(N-N) to react with zinc dust in the presence of phosphites. Treatment of the chloro-complexes 1, 2 with NaBH₄ yielded, in the case of bpy, the hydride [OsH(bpy)P₃]BPh₄ (4) derivatives. Mono-phosphite [OsCl(bpy)₂P]BPh₄ (3) complexes were also prepared by reacting the [OsCl₂(bpy)₂]Cl compound with zinc dust in the presence of phosphite. Protonation reaction of the hydride [OsH(bpy)P₃]⁺ (4) cations with Br?nsted acid was studied and led to thermally unstable (above 0 °C) dihydrogen [Os(η²-H₂)(bpy)P₃]²⁺ (4*) derivatives. The presence of the H₂ ligand is supported by variable-temperature NMR spectra and T_1min measurements. Carbonyl [Os(CO)(bpy){P(OEt)₃}₃] (BPh₄)₂ (5), nitrile [Os(CH₃CN)(bpy) {P(OEt)₃}₃](BPh₄)₂ (6), and hydrazine [Os(bpy)(NH₂NH₂){P(OEt)₃} ₃](BPh₄)₂ (7) complexes were prepared by substituting the H₂ ligand in the η²-H₂ (4*) derivatives. Aryldiazene complex [Os(C₆H₅N=NH)(bpy){P(OEt)₃} ₃](BPh₄)₂ (8) was also obtained by allowing the hydride [OsH(bpy)P₃]BPh₄ to react with phenyldiazonium cation.

Full text of DOI:10.1016/j.jorganchem.2004.02.019

Journal of Organometallic Chemistry 689 (2004) 1639–1647
www.elsevier.com/locate/jorganchem
Preparation and reactivity of osmium(II) hydride complexes with
phosphites and polypyridyls
*
Gabriele Albertin , Stefano Antoniutti, Sonia Pizzol
Dipartimento di Chimica, Universitaꢀ Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy
Received 11 December 2003; accepted 17 February 2004
Abstract
Chloro-complexes [OsCl(N–N)P3]BPh4 (1, 2) [N–N ¼ 2,20-bipyridine (bpy) and 1,10-phenanthroline (phen); P ¼ P(OEt)3 and
PPh(OEt)2] were prepared by allowing OsCl4(N–N) to react with zinc dust in the presence of phosphites. Treatment of the chloro-
complexes 1, 2 with NaBH4 yielded, in the case of bpy, the hydride [OsH(bpy)P3]BPh4 (4) derivatives. Mono-phosphite
[OsCl(bpy)2P]BPh4 (3) complexes were also prepared by reacting the [OsCl2(bpy)2]Cl compound with zinc dust in the presence of
phosphite. Protonation reaction of the hydride [OsH(bpy)P3]þ (4) cations with Brønsted acid was studied and led to thermally
unstable (above 0 °C) dihydrogen [Os(g2-H2)(bpy)P3]2þ (4*) derivatives. The presence of the H2 ligand is supported by variable-
temperature NMR spectra and T1 min measurements. Carbonyl [Os(CO)(bpy){P(OEt)3}3](BPh4)2 (5), nitrile [Os(CH3CN)
(bpy){P(OEt)3}3](BPh4)2 (6), and hydrazine [Os(bpy)(NH2NH2){P(OEt)3}3](BPh4)2 (7) complexes were prepared by substituting
the H2 ligand in the g2-H2 (4*) derivatives. Aryldiazene complex [Os(C6H5N@NH)(bpy){P(OEt)3}3](BPh4)2 (8) was also obtained
by allowing the hydride [OsH(bpy)P3]BPh4 to react with phenyldiazonium cation.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Osmium; Hydride; Dihydrogen complexes; Polypyridyl; Phosphite ligands
1. Introduction
with phosphite [P(OR)3, PPh(OR)2, etc.] ligands has
even been prepared.
The chemistry of classical and non-classical osmium
hydride complexes has been developed extensively in the
past 20 years using mainly p-acceptors such as phos-
phine, carbonyl or cyclopentadienyl as supporting li-
gands [1,2]. Less attention has been paid to the use of
nitrogen-donor ligands such as 2,20-bipyridine (bpy) and
1,10-phenanthroline (phen) in stabilizing osmium hy-
drides. A glance through the literature shows that the
only hydride complexes containing polypyridyl ligands
are the carbonyl [3] [OsH(N–N)(CO)(PR3)2]þ and
[OsH(N–N)2(CO)]þ complexes (N–N ¼ bpy, phen) and
the phosphine [3a] [OsH(N–N)(P–P)PR3]þ [P–P ¼ cis-1,
2-bis(diphenylphosphine)ethylene; PR3 ¼ PPh3, PPh2-
Me, PMe3] derivatives (for nitrogen-donor osmium hy-
drides see [4]). No example of such a type of complexes
We have previously reported on the synthesis and
reactivity of classical and non-classical hydride com-
plexes of osmium [5] of the type OsH2P4 and [OsX(g2-
H2)P4]þ (X ¼ H, Cl, Br, I, N3, etc.) containing phosphite
[P ¼ P(OR)3, PPh(OR)2, PPh2OR] as ancillary ligands.
We have now extended these studies with the aim of
introducing nitrogen-donor ligands such as 2,20-bipyri-
dine and 1,10-phenanthroline in the osmium hydride
chemistry with phosphite ligands. The results of these
studies, which allow the synthesis and the reactivity of
new mixed-ligand classical and non-classical osmium
hydride complexes, are reported here.
2. Experimental
2.1. General considerations and physical measurements
* Corresponding author. Tel.: +39-041-234-8555; fax: +39-041-234-
All synthetic work was carried out under an appro-
priate atmosphere (Ar, H2) using standard Schlenk
8917.
E-mail address: albertin@unive.it (G. Albertin).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.02.019

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G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
techniques or a Vacuum Atmosphere dry-box. Once
isolated, the complexes were found to be relatively stable
in air, but were stored under an inert atmosphere at )25
°C. All solvents were dried over appropriate drying
agents, degassed on a vacuum line and distilled into
vacuum-tight storage flasks. The (NH4)2OsCl6 was a
Johnson Matthey (USA) product, used as received.
Triethylphosphite P(OEt)3 (Aldrich) was purified by
distillation under nitrogen, while PPh(OEt)2 was pre-
pared by the method of Rabinowitz and Pellon [6]. Di-
azonium salt [C6H5N2]BF4 was obtained in the usual
way, as described in the literature [7]. Labeled diazo-
nium tetrafluoroborate [C6H5NB15N]BF4 was prepared
from Na15NO2 (99% enriched, CIL) and the appropriate
amine. Hydrazine (NH2NH2) was prepared by decom-
position of hydrazine cyanurate (Fluka) following the
reported method [8]. 2,20-Bipyridine (bpy), 1,10-phe-
nanthroline (phen), triflic acid and CF3SO3D were Al-
drich products used without any further purification.
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
FT-IR spectrophotometer. NMR spectra (1H, 31P, 13C,
15N) were obtained on a Bruker AC200 or an AVANCE
300 spectrometers at temperatures varying between )90
and +30 °C, unless otherwise noted. 1H and 13C spectra
are referred to internal tetramethylsilane, while 31P{1H}
chemical shifts are reported with respect to 85% H3PO4,
with downfield shifts considered positive. The 15N
spectra were referred to external CH135NO2 with down-
field shifts considered positive. The COSY, HMQC and
HMBC NMR experiments were performed using stan-
dard Bruker programs. The SwaN-MR software pack-
age [9] has been used in treating the NMR data. The
conductivity of 10ꢀ3 M solutions of the complexes in
CH3NO2 at 25 °C were measured with a Radiometer
CDM 83 instrument.
separated out which was filtered and crystallised from
CH2Cl2 and ethanol; yield P 65%; KM
(S cm2 molꢀ1) ¼ 53.3 for 1a, 49.5 for 1b, 55.1 for 2a.
Found: C, 52.29; H, 6.25; N, 2.20; Cl, 3.17.
C52H73BClN2O9OsP3 (1a) requires C, 52.07; H, 6.13; N,
2.34; Cl, 2.96%. Found: C, 59.08; H, 5.74; N, 1.99; Cl,
2.69. C64H73BClN2O6OsP3 (1b) requires C, 59.33; H,
5.68; N, 2.16; Cl, 2.74%. Found: C, 52.85; H, 6.12; N,
2.16; Cl, 3.11. C54H73BClN2O9OsP3 (2a) requires C,
53.01; H, 6.01; N, 2.29; Cl, 2.90%.
2.3. [OsCl(bpy)2P]BPh4 (3) [P ¼ P(OEt)3 (a),
PPh(OEt)2 (b)]
These complexes were prepared following the method
used for the related tris(phosphite) 1, 2 complexes by
treating the [OsCl2(bpy)2]Cl compound with an excess
of both zinc dust and the appropriate phosphite in re-
fluxing ethanol; yield P 75%; KM (S cm2 molꢀ1) ¼ 50.9
for 3a, 54.2 for 3b. Found: C, 58.56; H, 5.16; N, 5.34; Cl,
3.60. C50H51BClN4O3OsP (3a) requires C, 58.68; H,
5.02; N, 5.47; Cl, 3.46%. Found: C, 61.28; H, 4.72; N,
5.23; Cl, 3.44. C54H51BClN4O2OsP (3b) requires C,
61.45; H, 4.87; N, 5.31; Cl, 3.36%.
2.4. [OsH(bpy)P3]BPh4 (4) [P ¼ P(OEt)3 (a),
PPh(OEt)2 (b)]
In a 50-cm3 three-necked round-bottomed flask were
placed 300 mg (0.61 mmol) of OsCl4(bpy), 15 cm3 of
ethanol and an excess of the appropriate phosphite (8
mmol). A solution of NaBH4 (12 mmol, 0.45 g) in 15
cm3 of ethanol was added to the resulting suspension
and the reaction mixture was refluxed for 4 h. The sol-
vent was removed under reduced pressure to give a
brown solid from which the hydride was extracted with
three 10-cm3 portions of CH2Cl2. The extracts were
evaporated to dryness leaving an oil which was treated
with ethanol (2 cm3). The addition of an excess of
NaBPh4 (0.86 g, 2.5 mmol) in 2 cm3 of ethanol caused
the separation of a yellow solid which was filtered and
crystallised from CH2Cl2 and ethanol; yield P60% for
4a and about 20% for 4b; KM (S cm2 molꢀ1) ¼ 55.6 for
4a, 54.6 for 4b. Found: C, 53.49; H, 6.51; N, 2.34.
C52H74BN2O9OsP3 (4a) requires C, 53.61; H, 6.40; N,
2.40%. IR, cmꢀ1 (KBr) 2065 (w), 2026 (w) m(OsH).
Found: C, 60.83; H, 5.80; N, 2.08. C64H74BN2O6OsP3
(4b) requires C, 60.95; H, 5.91; N, 2.22%. IR, cmꢀ1
(KBr) 2025 (w) m(OsH).
2.2. Synthesis of complexes
The OsCl4(N–N) [N–N ¼ 2,20-bipyridine (bpy) and
1,10-phenanthroline (phen)] and [OsCl2(bpy)2]Cl com-
plexes were prepared following the methods previously
reported [10].
2.2.1. [OsCl(N–N)P3]BPh4 (1, 2) [N–N ¼ bpy (1),
phen (2); P ¼ P(OEt)3 (a), PPh(OEt)2 (b)]
In a 25-cm3 three-necked round-bottomed flask were
placed 0.6 mmol of solid OsCl4(N–N) compound, an
excess of zinc dust (0.4 g, 6.1 mmol) and 10 cm3 of
ethanol. An excess of the appropriate phosphite (6
mmol) was added to the resulting suspension which
was refluxed for 4 h and then filtered. The solution was
evaporated to dryness leaving a brown oil which was
triturated with ethanol (2 cm3) containing an excess of
NaBPh4 (1.8 mmol, 0.62 g). A red–brown solid slowly
2.4.1. [Os(g2-H2)(bpy)P3]2þ (4*) [P ¼ P(OEt)3 (a),
PPh(OEt)2 (b)]
These complexes were prepared in solution by react-
ing the [OsH(bpy)P3]BPh4 hydride with an excess of
CF3SO3H or HBF4ꢁEt2O. A typical experiment involves
the preparation of a solution of the appropriate hydride

G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
1641
(0.02 mmol) in 0.5 cm3 of CD2Cl2 in a 5-mm screw-cap
NMR tube. The tube is cooled to )80 °C and an excess
of CF3SO3H (0.03 mmol) added by microsyringe
through the cap. The probe of the NMR instrument was
pre-cooled to )80 °C, the tube introduced and the
spectra were recorded between )80 and +20 °C.
2.4.5.
[Os(C6H5N@NH)(bpy){P(OEt)3}3](BPh4)2
(8a)
In a 25-cm3 three-necked round-bottomed flask were
placed solid samples of [OsH(bpy){P(OEt)3}3]BPh4 (100
mg, 0.086 mmol) and of an excess the phenyldiazonium
tetrafluoroborate (C6H5N2)BF4 (0.26 mmol, 50 mg) and
the flask was cooled to )196 °C. Dichloromethane (10
cm3) was added, the reaction mixture was left to reach
the room temperature and was stirred for 5 h. The sol-
vent was removed under reduced pressure to give an oil
which was triturated with ethanol (2 cm3) containing an
excess of NaBPh4 (60 mg, 0.17 mmol). A yellow solid
slowly separated out which was filtered and crystallised
from CH2Cl2 and ethanol; yield P80%. KM
(S cm2 molꢀ1) ¼ 126. Found: C, 62.16; H, 6.39; N, 3.45.
C82H99B2N4O9OsP3 requires C, 61.97; H, 6.28; N,
3.52%.
2.4.2. [Os(CO)(bpy){P(OEt)3}3](BPh4)2 (5a)
An excess of triflic acid (0.43 mmol, 38 ll) was added
to a solution of [OsH(bpy){P(OEt)3}3]BPh4 (100 mg,
0.086 mmol) in 10 cm3 of CH2Cl2 cooled to )196 °C.
The reaction mixture, brought to room temperature,
was allowed to stand under a CO atmosphere (1 atm)
for about 24 h. The solvent was removed under reduced
pressure to give an oil which was triturated with ethanol
(2 cm3) containing an excess of NaBPh4 (0.060 g, 0.17
mmol). A yellow solid slowly separated out which was
filtered and crystallised from CH2Cl2 and ethanol; yield
P 35%. KM (S cm2 molꢀ1) ¼ 119. Found: C, 61.06; H,
6.33; N, 1.74. C77H93B2N2O10OsP3 requires C, 61.19; H,
6.20; N, 1.85%. IR, cmꢀ1 (KBr) 2025 (s) m(CO).
2.4.6. [Os(C6H5N@15NH)(bpy){P(OEt)3}3](BPh4)2
(8a1)
This complex was prepared exactly like the related
15
unlabelled compound 8a using (C6H5Nꢂ N)BF4 as a
reagent; yield P 75%.
2.4.3. [Os(CH3CN)(bpy){P(OEt)3}3](BPh4)2 (6a)
To a solution of [OsH(bpy){P(OEt)3}3]BPh4 (100 mg,
0.086 mmol) in 5 cm3 of CH2Cl2 was added an excess of
CH3CN (2 cm3, 38 mmol) and the mixture cooled to
)196 °C. An excess of CF3SO3H (38 ll, 0.43 mmol) was
added and the solution, brought to room temperature,
was stirred for 3 h. The solvent was removed under re-
duced pressure to give an oil which was triturated with
ethanol (2 cm3) containing an excess of NaBPh4 (0.17
mmol, 0.060 g). A yellow solid slowly separated out
which was filtered and crystallised from CH2Cl2 and
ethanol; yield P55%. KM (S cm2 molꢀ1) ¼ 124. Found:
C, 61.38; H, 6.45; N, 2.71. C78H96B2N3O9OsP3 requires
C, 61.46; H, 6.35; N, 2.76%.
3. Results and discussion
Zinc dust reduction of OsCl4(N–N) (N–N ¼ bpy and
phen) complexes in the presence of the phosphite
P(OEt)3 or PPh(OEt)2 gives the mixed-ligand chloro
cations [OsCl(N–N)P3]þ (1, 2) which were isolated as
BPh4 salts and characterised (Scheme 1).
Treatment of the chloro-complexes 1, 2 with NaBH4
in ethanol gives the hydride [OsH(bpy)P3]þ (4) cations
only in the case of the 2,20-bipyridine ligand (Scheme 2)
while with the 1,10-phenanthroline no reaction was
observed and the chloro-complex 2 was recovered in
almost quantitative yield.
The hydride derivatives [OsH(bpy)P3]þ (4) were also
obtained by one-pot synthesis by reacting OsCl4(bpy)
2.4.4. [Os(bpy)(NH2NH2){P(OEt)3}3](BPh4)2 (7a)
An excess of CF3SO3H (122 ll, 1.38 mmol) was ad-
ded to a solution of [OsH(bpy){P(OEt)3}3]BPh4 (200
mg, 0.172 mmol) in 10 cm3 of CH2Cl2 cooled to )196
°C. The reaction mixture was brought to room tem-
perature, stirred for 3 h and then again cooled to )196
°C. An excess of NH2NH2 (82 ll, 2.6 mmol) was added
and the reaction mixture, brought to room temperature,
was stirred for about 18 h. The solvent was removed
under reduced pressure to give an oil which was tritu-
rated with ethanol (3 cm3) containing an excess of
NaBPh4 (0.35 mmol, 0.12 g). A pale-yellow solid slowly
separated out which was filtered and crystallised from
Zn dust
exc. P, EtOH
OsCl4(N-N)
[OsCl(N-N)P3]+
1, 2
Scheme 1. N–N ¼ bpy 1, phen 2; P ¼ P(OEt)3 (a), PPh(OEt)2 (b).
exc. NaBH4
EtOH, reflux
[OsCl(bpy)P3]+
[OsH(bpy)P3]+
1
4
CH2Cl2
and
ethanol;
yield
P 35%.
KM
(S cm2 molꢀ1) ¼ 118. Found: C, 59.98; H, 6.52; N, 3.57.
C72H72BN3O4P3Re requires C, 60.24; H, 6.45; N,
3.70%. IR, cmꢀ1 (KBr) 3354 (w), 3310 (w), 3269 (w),
3231 (w) m(NH).
exc. NaBH4
EtOH, reflux
[OsCl(phen)P3]+
2
Scheme 2. P ¼ P(OEt)3 (a), PPh(OEt)2 (b).

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G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
The reaction of [OsCl2(bpy)2]Cl with phosphites was
NaBH4
OsCl4(bpy)
[OsH(bpy)P3]+
also studied in the presence of NaBH4, but exclusively
the chloro-complexes 3 were obtained (Scheme 4). The
absence of any hydride species in this reaction prompted
us to extend the studies of both the chloro-cations
[OsCl2(bpy)2]þ and [OsCl(bpy)2P]þ (3) towards other
reagents such as LiAlH4, LiBHEt3 and KH in an at-
tempt to prepare hydride complexes. Unfortunately, no
complex containing the Hꢀ ligand was separated from
the reaction and either the chloro-complexes 3 or de-
composition products were the only obtained products.
It seems, therefore, that osmium hydride species with
bis(bipyridine) and phosphites as supporting ligands
cannot be obtained using the [OsCl2(bpy)2]Cl as a pre-
cursor.
These results contrast with those previously obtained
[3] with carbon monoxide, which allows the easy syn-
thesis of bis(bipyridine) hydride [OsH(bpy)2(CO)]þ
derivatives. Differences were also observed by a com-
parison with the related ruthenium complexes [11],
whose [RuH(bpy)2P]þ (P ¼ phosphite) hydride deriva-
tives can be prepared by reacting RuCl2(bpy)2 with
NaBH4 in the presence of phosphites.
exc. P, EtOH
4
NaBH4
exc. P, EtOH
OsCl4(phen)
decomp. products
Scheme 3. P ¼ P(OEt)3 (a), PPh(OEt)2 (b).
with NaBH4 in refluxing ethanol in the presence of an
excess of phosphite, as shown in Scheme 3.
Instead, the reaction of the related phenanthroline
OsCl4(phen) complex does not give any hydridic species,
but only decomposition products.
The different behaviour of the two nitrogenous li-
gands bpy and phen in the chemistry of mixed-ligand
complexes with phosphites and polypyridyls is rather
unexpected in light of the comparable properties shown
by bpy and phen as ligands in related [RuH(N–N)P3]þ
complexes [11] which can be obtained with both bpy and
phen as supporting groups. The absence of reactivity of
both the phenanthroline complexes OsCl4(phen) and
[OsCl(phen)P3]þ towards the formation of hydride with
NaBH4 prompted us to extend the studies to other re-
agents such as LiAlH4, NaBH3CN, LiBHEt3, KH or H2
in the presence of base in an attempt to prepare the
related Hꢀ species. In any case, no formation of hydride
complexes was observed and therefore it seems that only
with bpy can mixed-ligand hydrides with phosphites and
polypyridyls be prepared. With phenanthroline, instead,
substitution of the Cl ligand with hydride does not take
place.
We have also studied the reaction of OsCl4(bpy) with
phosphite and NaBH4 in different conditions, i.e.
changing the ratio between the reagents and the reaction
time, in an attempt to prepare hydride species with a
different stoichiometry of the type OsH2(bpy)2P2 or
OsHCl(bpy)2P2. The only obtained result, however, was
a decrease of the yield of [OsH(bpy)P3]þ (4a) complex
which seems to be the only hydride containing phosphite
and polypyridyl ligands obtained from the OsCl4(bpy)
used as a precursor.
The coordination of any hydride ligand to mixed-li-
gand osmium(II) complexes with polypyridyls and
phosphites seems therefore to be rather difficult and only
the tris(phosphite) [OsH(bpy)P3]BPh4 (4) derivatives
can be obtained.
Good analytical data were obtained for all the os-
mium complexes, which are stable in air and in solution
of polar organic solvents in which they behave as 1:1
electrolytes [12]. The IR and NMR data (Table 1) sup-
port the proposed formulation. The 1H NMR spectra of
the [OsCl(N–N)P3]BPh4 (1, 2) complexes show the
characteristic signals of both the phosphite and the ni-
trogenous ligands (bpy and phen) beside those of the
BPh4 anion. The 31P{1H} NMR spectra appear as AB2
multiplets suggesting the magnetic equivalence of two
phosphines, different from the third. These data do not
allow to unambiguously distinguish between a mer or a
fac geometry for the complexes (Chart 1). However, the
methylene proton signals of the P(OEt)3 ligands in 1a
and 2a appear as one quintet and one multiplet between
4.36 and 3.65 ppm. The presence of the multiplet should
be due to the coupling [13] of two phosphites in a mu-
tually trans position. On this basis a mer geometry (I)
can be reasonably proposed.
Bis(bipyridine) [OsCl2(bpy)2]Cl react with zinc dust
in the presence of phosphite to give the chloro-cations
[OsCl(bpy)2P]þ (3) which were isolated as BPh4 salts
and characterised (Scheme 4).
The 1H NMR spectra confirm the presence of the
ligands in the bis(bipyridine) [OsCl(bpy)2P]þ (3) com-
plex whose 31P spectra appear as one sharp singlet at
67.5 (3a) and 97.6 (3b) ppm. The spectroscopic data,
however, do not allow to distinguish between a cis or a
trans geometry (Chart 1) of the complexes.
The IR spectra of the hydride [OsH(bpy){PPh
(OEt)2}3]BPh4 (4b) show a weak band at 2025 cmꢀ1
attributed to mOsH of the hydride ligand. The presence of
Zn dust
exc. P
[OsCl2(bpy)2]+
[OsCl(bpy)2P]+
3
NaBH4
exc. P
Scheme 4. P ¼ P(OEt)3 (a), PPh(OEt)2 (b).

G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
1643
Table 1
IR and NMR data for the osmium complexes
Compound
1H NMRa;bd (J, Hz)
Assignment
Spin system 31P{1H}NMRa d (J, Hz)
1a
1b
[OsCl(bpy){P(OEt)3}3]BPh4
[OsCl(bpy){PPh(OEt)2}3]BPh4
9.78–6.88 m
4.30 m
3.76 m
1.36 t
bpy + Ph
CH2
AB2
dA 81.2
dB 77.5
JAB ¼ 47
CH3
0.91 t
9.27–6.70 m
4.11 m
3.72 m
1.42 t
bpy + Ph
CH2
AB2
dA 111.5
dB 104.4
JAB ¼ 36
CH3
1.07 t
0.98 t
2a
[OsCl(phen){P(OEt)3}3]BPh4
10.0–6.84 m
4.36 qnt
3.65 m
phen + Ph
CH2
AB2
dA 81.0
dB 77.2
JAB ¼ 44
1.40 t
0.75 t
CH3
3a
3b
4a
[OsCl(bpy)2{P(OEt)3}]BPh4
[OsCl(bpy)2{PPh(OEt)2}]BPh4
9.65–6.83 m
3.87 qnt
1.01 t
bpy + Ph
CH2
CH3
A
67.5 s
97.6 s
9.90–6.57 m
3.89 m
1.28 t
bpy + Ph
CH2
CH3
A
c
[OsH(bpy){P(OEt)3}3]BPh4
9.75–6.83 m
4.03 qnt
3.65 m
bpy + Ph
CH2
AB2
dA 103.9
dB 101.4
JAB ¼ 26
1.31 t
1.27 t
CH3
Hꢀ
A2B
dA 105.5
0.93 t
AB2X spin system
dB 97.2
dX )6.76
JAB ¼ 45
JAX ¼ 112
JBX ¼ 22
A2BX spin system
dX )15.87
JAX ¼ JBX ¼ 22
Hꢀ
4*a
[Os(g2-H2)(bpy){P(OEt)3}3]2þd
9.30–6.81 m
3.76 m
3.37 m
1.36 t
bpy + Ph
CH2
A2B
A2B
dA 84.9
dB 79.2
JAB ¼ 41
CH3
H2
1.12 t
0.34 m
)9.17 br
dA 81.6
dB 80.2
JAB ¼ 20
4b
[OsH(bpy){PPh(OEt)2}3]BPh4
8.84–6.38 m
3.80–3.26 m
1.29 t
bpy + Ph
CH2
CH3
A2B
dA 125.7
dB 123.3
JAB ¼ 30
1.21 t
1.15 t
A2BX spin system
dX )15.35
JAX ¼ JBX ¼ 20
Hꢀ
4*b
[Os(g2-H2)(bpy){PPh(OEt)2}3]2þ
9.30–6.85 me
bpy + Ph
CH2
CH3
A2Be
dA 113.0
dB 103.6
JAB ¼ 32
3.74 m
1.09 m
)9.34 br
H2
f
5a
[Os(bpy)(CO){P(OEt)3}3](BPh4)2
9.37–6.85 m
4.18 m
bpy + Ph
CH2
AB2
dA 83.7
dB 75.5

1644
G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
Table 1 (continued)
Compound
1H NMRa;bd (J, Hz)
Assignment
CH3
Spin system 31P{1H}NMRa d (J, Hz)
JAB ¼ 42
3.60 qnt
1.41 t
0.94 t
6a
7a
[Os(CH3CN)(bpy){P(OEt)3}3](BPh4)2
9.37–6.85 m
4.12 m
3.61 qnt
1.28 s
bpy + Ph
CH2
A2B
dA 76.9
dB 72.4
JAB ¼ 49
CH3CN
CH3
1.37 t
0.94 t
[Os(bpy)(NH2NH2){P(OEt)3}3](BPh4)2
9.26-6.81 m
4.18 m
3.51 qnt
4.02 br
1.69 br
1.38 t
bpy + Ph
CH2
AB2
dA 79.5
dB 77.8
JAB ¼ 46
OsNH2
NH2
CH3
0.92 t
8a
[Os(C6H5N@NH)(bpy){P(OEt)3}3](BPh4)2
15.24 s, br
14.04 s, br
9.12–6.83 m
4.20 m
NH
AB2
A2B
dA 81.6
dB 75.7
JAB ¼ 46
bpy + Ph
CH2
3.68 m
1.36 m
0.99 m
dA 78.4
CH3
dB 75.5
JAB ¼ 45
8a1
[Os(C6H5N@15NH)(bpy){P(OEt)3}3](BPh4)2
15.25 dm
J15NH ¼ 66
14.06 dm
J15NH ¼ 66
9.12–6.83 m
4.20 m
NH
AB2
A2B
dA 81.6
dB 75.8
JAB ¼ 46
bpy + Ph
CH2
dA 78.4
3.67 m
1.36 m
0.98 m
dB 75.5
JAB ¼ 45
CH3
a In CD2Cl2 at 25 °C.
b Positive shift downfield from 85% H3PO4.
c T1 min (200 MHz) at 213 K: 181 ms.
d At )30 °C.
e At )70 °C.
f
13C{1H} NMR (CD2Cl2, 25 °C) d: 232.5 (dt, CO, JCPcis ¼ JCPtrans ¼ 30 Hz), 165–122 (m, Ph + bpy), 65.2 (m, CH2), 16.1 (m, CH3).
this ligand, however, is confirmed by the 1H NMR
+
+
+
spectra, which show a quartet at )15.35 ppm attributed
to the hydride ligand coupled with the phosphorus nu-
clei. Taking into account that in the temperature range
between +30 and )80 °C the 31P{1H} NMR spectra
appear as an A2B multiplet, this hydridic quartet can be
simulated using an A2BX (X ¼ H) model with the pa-
rameters reported in Table 1. These parameters high-
light how the two JPH have the same value of 20 Hz, in
agreement with the same mutual cis position of the hy-
dride with all the phosphite ligands. On the basis of
these data, a mer geometry (II, Chart 2) can reasonably
be proposed for the hydride 4b.
P
P
Os
P
P
P
N
N
Os
P
Cl
N
N
Cl
fac
( I ) mer
+
Cl
N
N
Os
N
N
N
Os
N
Cl
N
N
P
P
The 1H NMR spectra of the related [OsH(bpy)
{P(OEt)3}3]BPh4 (4a) show, in contrast with 4b, two
multiplets in the hydride region at )6.76 and at )15.87
trans
cis
Chart 1.

G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
1645
presence of only one proton g2-H2 signal may be due ei-
ther to overlapping of the signals of the two isomers due to
their broadness, or to decomposition of one isomer giv-
ing, by loss of g2-H2, the triflate complex.
+
+
P
Os
P
P
P
P
N
N
Os
H
P
N
N
We have also prepared the isotopomer [Os(g2-
HD)(bpy)P3]þ by protonation of the hydride 4 with
H
( II ) mer
fac
CF3SO3D in an attempt to determine the values of JHD
.
Unfortunately, the g2-HD signal of the isotopomers
results rather broad and does not allow a reasonable
value of JHD to be measured. The values of the T1 min
measurements on the broad signal near )9 ppm, how-
ever, strongly support [14,15] the presence of an g2-H2
ligand. From the T1 min values the H–H distances were
Chart 2.
ppm, respectively, suggesting the presence of two iso-
mers. This is confirmed by the 31P{1H} NMR spectra
which show two multiplets simulated using one AB2 and
one A2B model with the parameters reported in Table 1.
1
Also the two hydride multiplets of the H NMR spec-
ꢁ
calculated [16] and fall in the range 0.88 (4*a)–0.84 A
(4*b) for a fast rotation model and in the range 1.11
trum can be simulated using an AB2X (X ¼ H) model in
one case, and an A2BX model in the other. The values
for the two JPH are the same (22 Hz) for the multiplet at
)15.87 ppm of one isomer in which the hydride should
be in the same cis position with all the phosphite ligands,
as in a mer geometry (II). In the other isomer the JPH
show two different values of 22 and 112 Hz, respectively,
suggesting that the hydride should be trans to one
phosphite and cis with respect to the other two, as in a
fac geometry. On the basis of these data, the presence of
two isomers with a mer and a fac geometry (Chart 2) can
be reasonably proposed for the hydride 4a.
ꢁ
(4*a)–1.06 A (4*b) for a static one. These values, which
do not seem to be influenced by the nature of the
phosphite ligands, are comparable with those calculated
for known [17] dicationic dihydrogen complexes and
very similar to those of the related osmium [Os(g2-
H2)(bpy)(CO)(PPh3)2]2þ derivative [3c].
The influence of the three phosphite ligands bonded to
the Os(bpy)P3 fragment (4*) on the g2-H2 seems therefore
to be very similar to that of one carbonyl and two PPh3
ligands in the [Os(g2-H2)(bpy)(CO)(PPh3)2]2þ derivative.
The new dihydrogen complexes 4* are thermally un-
The mixed-ligand phosphite-bipyridine osmium
[OsH(N–N)P3]þ complexes can be protonated with
CF3SO3H to give the dihydrogen [Os(g2-H2)(bpy)P3]2þ
(4*) derivatives, as shown in Scheme 5.
1
stable and the H NMR spectra showed that the evo-
lution of H2 began above 0 °C. This prevented the
isolation of the compounds in the solid state. The
thermal instability of 4* is somewhat unexpected, be-
cause the dihydrogen complexes of osmium are usually
more stable than the related ruthenium derivatives [11].
Probably, this trend is not followed in dicationic mixed-
ligand g2-H2 complexes with phosphites and polypy-
ridyls and a comparable thermal instability is expected
for all the iron triad derivatives.
The reaction was followed by NMR spectra and
showed that, in the case of the [OsH(bpy){PPh (OEt)2}3]þ
(4b) cation, the addition of CF3SO3H caused the disap-
pearance of the hydride multiplet at )15.35 ppm in the
proton spectra and the appearance of one broad signal at
)9.1 ppm attributed to the g2-H2 ligand of the [Os(g2-
H2)(bpy)P3]2þ dication. Measurements of T1 (200 MHz)
on these signals gave values of T1 min of 7.5 ms, in agree-
ment [14] with the presence of the dihydrogen ligand.
The protonation of the related [OsH (bpy)
{P(OEt)3}3]þ (4b) cation, which contains two hydride
multiplets due to both the fac and the mer isomers, pro-
ceeds with the formation of only one broad signal at )9.0
ppm in the 1H NMR spectra. T1 measurements (200 MHz)
on the broad proton signal at )9.0 ppm give a value of 9.5
ms, in agreement with the existence of a dihydrogen
complex. The 31P{1H} NMR spectra, however, show the
presence of two multiplets simulable using AB2 and A2B
spin systems (Table 1) and suggesting that the proton-
ation should afford two different g2-H2 isomers, probably
with fac and mer geometry, as the hydride precursor. The
3.1. Reactivity
The lability of the g2-H2 ligand in the [Os(g2-
H2)(bpy)P3]2þ derivatives prompted us to test these
complexes as precursors for the synthesis of new os-
mium derivatives. The results show that the substitution
of g2-H2 proceeds with several types of ligands affording
the corresponding complexes. Some examples are shown
in Scheme 6.
CO
[Os(bpy)(CO)P3]2+
5a
CH3CN
[Os(η2-H2)(bpy)P3]2+
[Os(CH3CN)(bpy)P3]2+
6a
4*
H+
NH2NH2
[OsH(bpy)P3]+
[Os(η2-H2)(bpy)P3]2+
[Os(bpy)(NH2NH2)P3]2+
4
4*
7a
Scheme 5. P ¼ P(OEt)3 (a), PPh(OEt)2 (b).
Scheme 6. P ¼ P(OEt)3.

1646
G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
The new carbonyl 5a, nitrile 6a and hydrazine 7a
at 4.02 and 1.69 ppm, attributed to the hydrogen of the
NH2 groups of hydrazine. The 1H COSY confirms these
attributions. The proton spectrum also shows the signals
of the other ligands, while the 31P spectrum appears as
an AB2 multiplet. Also in this case, however, any ge-
ometry in solution cannot be unambiguously proposed.
Insertion reaction into the Os–H bond of the hydride
[OsH(bpy)P3]þ was studied with several unsaturated
molecules such as terminal alkynes RCBCH, heteroal-
lenes (CO2, CS2) and aryldiazonium cations ArNþ2 . The
results showed that at room temperature only the aryl-
diazonium cations react with the hydride 4 to give the
corresponding aryldiazene complex 8a, which was iso-
lated as an orange solid and characterised (Scheme 7).
In the high-frequency region, the 1H NMR spectra of
8a show two slightly broad signals at 15.24 and 14.04
ppm, each of which is split into one doublet of multiplets
(J15NH ¼ 66 Hz) in the spectra of the labelled [Os
(C6H5N@15NH)(bpy)P3]2þ (8a1) derivative, in agree-
ment [20,21] with the presence of two different diazene
ligands. The 31P{1H} NMR spectra show two multiplets
which can be simulated using one AB2 and one A2B
model with the parameters reported in Table 1. The el-
emental analysis agrees with the presence of only one
aryldiazene ligand in the complex, so the two diazene
signals in the proton spectra and the two multiplets in
the 31P ones can be interpreted on the basis of the
presence of two isomers of the type reported in Chart 4.
The insertion of ArNþ2 into the Os-H bond of the two
isomers of 4 is not followed by any isomerisation reac-
tion affording, as in the hydride precursor, the fac and
mer isomers of the aryldiazene derivatives.
complexes were isolated as yellow or orange solids stable
in air and in solution of polar organic solvents, where
they behave as 2:1 electrolytes [12]. Analytical and
spectroscopic data (Table 1) support the proposed for-
mulations.
The IR spectra of the carbonyl compound 5a show,
beside the absorptions of the bpy, the phosphites and the
BPh4, a strong absorption at 2025 cmꢀ1 due to mCO of the
carbonyl ligand. The 13C spectra confirm the presence of
CO showing a doublet of triplets at 232.5 ppm, attrib-
uted to the carbonyl carbon resonances coupled with the
phophorus nuclei of the phosphines. The two JPC show
the same value of 30 Hz, suggesting that the CO is in a
mutual cis position with all the phosphite ligands. Tak-
ing into account that, in the temperature range between
+20 and )80 °C, the 31P spectrum is an AB2 multiplet, a
mer-type geometry (III, Chart 3) can be reasonably
proposed for the carbonyl derivative.
The IR spectra of the nitrile [Os(CH3CN)(bpy)
P3](BPh4)2 (6a) complex do not show any band attrib-
utable to mCN, probably owing to its very low intensity
[18]. However, the presence of this ligand is confirmed
1
by the H NMR spectra which show the singlet at 1.28
ppm of the methyl group of the CH3CN. In the tem-
perature range between +20 and )80 °C the 31P{1H}
NMR spectrum of the nitrile complex 6a appears as an
A2B multiplet which was simulated with the parameters
reported in Table 1. These data, however, do not allow
to unambiguously assign a geometry in solution to the
complex.
The presence of the hydrazine ligand in [Os
(NH2NH2)(bpy)P3]2þ (7a) derivative is confirmed by the
IR spectra which show the characteristic [19] medium-
intensity bands at 3354–3231 cmꢀ1 due to the mNH of the
Aryldiazene complexes of osmium(II) are known [21],
but contain only phosphine or carbonyl as supporting
ligands. The preparation of the complex 8a shows that
also bipyridyl is able to stabilise aryldiazene derivatives
of osmium(II).
1
NH2NH2 ligand. Further support comes from the H
NMR spectrum which shows two slightly broad signals
2+
P
2+
2+
P
Os
P
P
Os
N
P
P
P
N
Ar
N
N
N
Os
CO
N
N
P
N
N
P
H
H
N
Ar
III
mer
fac
Chart 3.
Chart 4.
+
exc. C6H5N2
[OsH(bpy)P3]+
[Os(C6H5N=NH)(bpy)P3]2+
4
8a
Scheme 7. P ¼ P(OEt)3.

G. Albertin et al. / Journal of Organometallic Chemistry 689 (2004) 1639–1647
1647
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Acknowledgements
The financial support of MIUR (Rome) – Programmi
di Ricerca Scientifica di Rilevante Interesse Nazionale,
Cofinanziamento 2002–2003 – is gratefully acknowl-
edged. We thank Daniela Baldan for technical assis-
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Available from <http://qobrue.usc.es/jsgroup/Swan/index.html>,
for current updates.