Synthesis and characterization of triazenide and triazene complexes of ruthenium and osmium

Article abstract of DOI:10.1021/ic052063u

Triazenide [M(η²-1,3-ArNNNAr)P₄]BPh₄ [M = Ru, Os; Ar = Ph, p-tolyl; P = P(OMe)₃, P(OEt)₃, PPh(OEt)₂] complexes were prepared by allowing triflate [M(κ²-OTf)P₄]OTf species to react first with 1,3-ArN=NN(H)Ar triazene and then with an excess of triethylamine. Alternatively, ruthenium triazenide [Ru(η²-1,3-ArNNNAr)P ₄]BPh₄ derivatives were obtained by reacting hydride [RuH(η²-H₂)P₄]⁺ and RuH(κ¹-OTf)P₄ compounds with 1,3-diaryltriazene. The complexes were characterized by spectroscopy and X-ray crystallography of the [Ru(η²-1,3-PhNNNPh){P(OEt)₃}₄]BPh ₄ derivative. Hydride triazene [OsH(η¹-1,3-ArN=NN(H) Ar)P₄]BPh₄ [P = P(OEt)₃, PPh(OEt)₂; Ar = Ph, p-tolyl] and [RuH{η¹-1,3-p-tolyl-N=NN(H)-p-tolyl} {PPh(OEt)₂}₄]BPh₄ derivatives were prepared by allowing κ¹-triflate MH(κ¹-OTf)P₄ to react with 1,3-diaryltriazene. The [Os(κ¹-OTf) {η¹-1,3-PhN=NN(H)Ph}{P(OEt)₃}₄]BPh ₄ intermediate was also obtained. Variable-temperature NMR studies were carried out using ¹⁵N-labeled triazene complexes prepared from the 1,3-Ph¹⁵N=N¹⁵N(H)Ph ligand. Osmium dihydrogen [OsH(η²-H₂)P₄]BPh₄ complexes [P = P(OEt)₃, PPh(OEt)₂] react with 1,3-ArN=NN(H)Ar triazene to give the hydride-diazene [OsH(ArN=NH)P₄]BPh₄ derivatives. The X-ray crystal structure determination of the [OsH(PhN=NH){PPh(OEt)₂}₄]BPh₄ complex is reported. A reaction path to explain the formation of the diazene complexes is also reported.

Full text of DOI:10.1021/ic052063u

Inorg. Chem. 2006, 45, 3816−3825
Synthesis and Characterization of Triazenide and Triazene Complexes
of Ruthenium and Osmium
Gabriele Albertin,*,† Stefano Antoniutti,† Marco Bedin,† Jesu´s Castro,‡ and Soledad Garcia-Fonta´n‡
Dipartimento di Chimica, UniVersita` Ca’ Foscari di Venezia, Dorsoduro 2137, 30123 Venezia,
Italy, and Departamento de Qu´ımica Inorga´nica, UniVersidade de Vigo, Facultade de Qu´ımica,
Edificio de Ciencias Experimentais, 36310 Vigo, Galicia, Spain
Received December 1, 2005
Triazenide [M(
were prepared by allowing triflate [M(
with an excess of triethylamine. Alternatively, ruthenium triazenide [Ru(
obtained by reacting hydride [RuH(
2-H2)P4]+ and RuH( 1-OTf)P4 compounds with 1,3-diaryltriazene. The complexes
were characterized by spectroscopy and X-ray crystallography of the [Ru( P(OEt)3 4]BPh4 derivative.
2-1,3-PhNNNPh)
Hydride triazene [OsH( NN(H)Ar)P4]BPh4 [P P(OEt)3, PPh(OEt)2; Ar
1-1,3-ArN Ph, p-tolyl] and [RuH{η1
1,3-p-tolyl-N NN(H)-p-tolyl}{PPh(OEt)2 4]BPh4 derivatives were prepared by allowing
1-triflate MH( 1-OTf)P4 to
react with 1,3-diaryltriazene. The [Os( NN(H)Ph}{P(OEt)3 4]BPh4 intermediate was also obtained.
1-OTf){η1-1,3-PhN
Variable-temperature NMR studies were carried out using 15N-labeled triazene complexes prepared from the 1,3-
Ph15 N15N(H)Ph ligand. Osmium dihydrogen [OsH( 2-H2)P4]BPh4 complexes [P
P(OEt)3, PPh(OEt)2] react
with 1,3-ArN NN(H)Ar triazene to give the hydride diazene [OsH(ArN NH)P4]BPh4 derivatives. The X-ray crystal
structure determination of the [OsH(PhN NH) PPh(OEt)2
the formation of the diazene complexes is also reported.
η
2-1,3-ArNNNAr)P4]BPh4 [M
2-OTf)P4]OTf species to react first with 1,3-ArN
2-1,3-ArNNNAr)P4]BPh4 derivatives were
)
Ru, Os; Ar
)
Ph, p-tolyl; P
)
P(OMe)3, P(OEt)3, PPh(OEt)2] complexes
κ
dNN(H)Ar triazene and then
η
η
κ
η
{
}
η
d
)
)
-
d
}
κ
κ
κ
d
}
Nd
η
)
d
−
d
d
{
}
4]BPh4 complex is reported. A reaction path to explain
Chart 1
Introduction
The 1,3-diaryltriazenide [ArNNNAr]- anion (Chart 1, A)
is a “small-bite” ligand that can act as a monodentate,1 a
chelate,2 or a bridging ligand,3 giving numerous examples
of transition metal complexes.1-3 Its use in coordination
chemistry, however, is less developed when compared to
* To whom correspondence should be addressed. E-mail:albertin@
unive.it.
† Universita` Ca’ Foscari di Venezia.
‡ Universidade de Vigo.
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Soc. Dalton Trans. 1980, 1098-1100.
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anionic N-C-X-type (X ) N, O, S) ligands,5 even though
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3816 Inorganic Chemistry, Vol. 45, No. 9, 2006
10.1021/ic052063u CCC: $33.50
© 2006 American Chemical Society
Published on Web 04/05/2006

Triazenide and Triazene Complexes of Ru and Os
solvents were dried over appropriate drying agents, degassed on a
vacuum line, and distilled into vacuum-tight storage flasks. RuCl3‚
3H2O and (NH4)2OsCl6 salts were obtained from Pressure Chemical
Co. and were used as received. Phosphite PPh(OEt)2 was prepared
by the method of Rabinowitz and Pellon,9 while P(OEt)3 was an
Aldrich product purified by distillation under nitrogen. 1,3-
Diaryltriazenes, 1,3-ArNdNN(H)Ar (Ar ) Ph, p-tolyl), were
prepared following the literature method.10 The labeled triazene 1,3-
Ph15NdN15N(H)Ph was prepared from labeled aniline Ph15NH2
(99% enriched, CIL) and NaNO2. 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 or Perkin-Elmer Spectrum One FT-IR spectrophotometers.
NMR spectra (1H, 31P, 15N) were obtained on AC 200 or AVANCE
300 Bruker spectrometers at temperatures between -90 and +30
°C, unless otherwise noted. 1H spectra are referred to internal
tetramethylsilane; 31P{1H} chemical shifts are reported with respect
to 85% H3PO4, while 15N is reported with respect to CH315NO2. In
both cases, downfield shifts are considered positive. The COSY,
HMQC, and HMBC NMR experiments were performed using their
standard programs. The SwaN-MR software package11 was used
to treat NMR data. The conductivity of 10-3 mol dm-3 solutions
of the complexes in CH3NO2 at 25 °C were measured with a CDM
83 radiometer.
Synthesis of Complexes. The classical12 MH2P4 and nonclas-
sical13 [MH(η2-H2)P4]Y [M ) Ru, Os; P ) P(OMe)3, P(OEt)3, PPh-
(OEt)2; Y ) BF4, BPh4] hydride complexes were prepared according
to the procedure previously reported. The triflate species, MH-
(κ1-OTf)P4 and [M(κ2-OTf)P4]OTf, were prepared in solution by
reacting hydride MH2P4 complexes with CF3SO3H (HOTf) or CF3-
SO3CH3 (CH3OTf), following the reported method.14
[Ru(η2-1,3-ArNNNAr)P4]BPh4 (1, 2) [P ) P(OMe)3 (1), P-
(OEt)3 (2); Ar ) Ph (a), p-tolyl (b)]. Method 1. An equimolar
amount of HBF4‚Et2O (0.26 mmol, 37 µL) was added to a solution
of the appropriate hydride RuH2P4 (0.26 mmol) complex in 6 mL
of CH2Cl2 cooled to -196 °C. The reaction mixture was brought
to -30 °C and stirred for about 1 h, and then an excess of the
appropriate 1,3-ArNdNN(H)Ar triazene (0.52 mmol) in 2 mL of
CH2Cl2 was added. The solution was brought to room temperature
and then refluxed for about 1 h. The solvent was removed under
reduced pressure yielding an oil which was treated with ethanol (2
mL). The addition of an excess of NaBPh4 (0.78 mmol, 0.27 g) in
2 mL of ethanol caused the separation of a brown solid which was
filtered and crystallized from CH2Cl2 and ethanol: yield from 65
to 80%.
triazenide is a donor ligand which has shown its ability to
stabilize mono- and dinuclear derivatives.1-3
Triazene 1,3-ArNdNN(H)Ar (Chart 1, C), instead, has
been mainly used as a precursor for the triazenide complexes,
resulting in its very limited use as a ligand. Only two
examples3a,g of IrCl(η4-cod){RNdNN(H)R} (cod ) cyclo-
octa-1,5-diene)- and RhCl{ArNdNN(H)Ar}(CO)2-type com-
plexes, containing triazene as a ligand, are reported in the
literature. This result is somewhat surprising because triazene
may be compared to the substituted-diazene ArNdNH (D),
whose coordination chemistry has been extensively devel-
oped over the past twenty-five years, leading to the synthesis
of several complexes with interesting properties.6
We are interested in the chemistry of “diazo” complexes
of transition metals and have reported on the synthesis and
the reactivity of aryldiazene and aryldiazenido complexes
of manganese and iron triads.7,8 The broadening of these
studies to “triazo” species such as triazene and triazenide
should be of interest not only for a comparison between
“diazo” and “triazo” ligands toward the same metal fragment
but also for extending the knowledge of the chemistry of
triazene and triazenide complexes. A glance through litera-
ture, in fact, shows that, except for the pioneer work of
Robinson et al.2a,f,g on the chemistry of triazenide complexes
of ruthenium(II) and osmium(II), only some cluster com-
pounds3b,c with the triazenide ligand have been reported for
these metals. In this paper, we report some studies on the
reactivity of 1,3-diaryltriazene molecules toward classical and
nonclassical hydride complexes of ruthenium and osmium,
which allow the synthesis of new triazenides and of the first
triazene complexes of Ru and Os to be achieved.
Experimental Section
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
(4) (a) Edelmann, F. T. Coord. Chem. ReV. 1994, 137, 403-481. (b)
Barker, J.; Kilner, M. Coord. Chem. ReV. 1994, 133, 219-300. (c)
Oro, L. A.; Ciriano, M. A.; Perez-Torrente, J. J.; Villaroya, B. E.
Coord. Chem. ReV. 1999, 193-195, 941-975.
(5) Zhang, Z.-Z.; Cheng, H. Coord. Chem. ReV. 1996, 147, 1.
(6) (a) Sutton, D. Chem. ReV. 1993, 93, 995-1022. (b) Kisch, H.;
Holzmeir, P. AdV. Organomet. Chem. 1992, 34, 67-109. (c) Zollinger,
H. In Diazo Chemistry II; VCH: Weinheim, Germany, 1995.
(7) (a) Albertin, G.; Antoniutti, S.; Bortoluzzi, M.; Castro-Fojo, J.; Garcia-
Fonta´n, S. Inorg. Chem. 2004, 43, 4511-4522. (b) Albertin, G.;
Antoniutti, S.; Bacchi, A.; Fregolent, B.; Pelizzi, G. Eur. J. Inorg.
Chem. 2004, 1922-1938. (c) Albertin, G.; Antoniutti, S.; Bacchi, A.;
Boato, M.; Pelizzi, G. J. Chem. Soc., Dalton Trans. 2002, 3313-
3320. (d) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.;
Giorgi, M. T.; Pelizzi, G. Angew. Chem., Int. Ed. 2002, 41, 2192-
2194. (e) Albertin, G.; Antoniutti, S.; Bordignon, E.; Visentin, E. Inorg.
Chem. 2001, 40, 5465-5467. (f) Albertin, G.; Antoniutti, S.; Bordi-
gnon, E.; Perinello, G. J. Organomet. Chem. 2001, 625, 217-230.
(8) (a) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.; Miani, F.;
Pelizzi, G. Inorg. Chem. 2000, 39, 3283-3293. (b) Albertin, G.;
Antoniutti, S.; Bacchi, A.; Ballico, G. B.; Bordignon, E.; Pelizzi, G.;
Ranieri, M.; Ugo, P. Inorg. Chem. 2000, 39, 3265-3279. (c) Albertin,
G.; Antoniutti, S.; Bordignon, E.; Menegazzo, F. J. Chem. Soc., Dalton
Trans. 2000, 1181-1189. (d) Albertin, G.; Antoniutti, S.; Bacchi, A.;
Barbera, D.; Bordignon, E.; Pelizzi, G.; Ugo, P. Inorg. Chem. 1998,
37, 5602-5610. (e) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon,
E.; Busatto, F.; Pelizzi, G. Inorg. Chem. 1997, 36, 1296-1305. (f)
Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.; Pelizzi, G.;
Ugo, P. Inorg. Chem. 1996, 35, 6245-6253.
Method 2. An equimolar amount of CF3SO3H (0.26 mmol, 23
µL) was added to a solution of the appropriate hydride RuH2P4
(0.26 mmol) complex in 6 mL of CH2Cl2 cooled to -196 °C. The
reaction mixture was allowed to reach room temperature, was stirred
for 1 h, and then was cooled again to -196 °C. Triflic acid (0.27
(9) Rabinowitz, R.; Pellon, J. J. Org. Chem. 1961, 26, 4623-4626.
(10) Hartman. W. W.; Dickey, J. B. Org. Synth. 1943, 2, 163-165.
(11) Balacco, G. J. Chem. Inf. Comput. Sci. 1994, 34, 1235-1241.
(12) (a) Gerlach, D. H.; Peet, W. G.; Muetterties, E. L. J. Am. Chem. Soc.
1972, 94, 4545-4549. (b) Peet, W. G.; Gerlach, D. H. Inorg. Synth.
1974, 15, 38-42. (c) Albertin, G.; Antoniutti, S.; Bordignon, E. J.
Chem. Soc., Dalton Trans. 1989, 2353-2358.
(13) (a) Amendola, P.; Antoniutti, S.; Albertin, G.; Bordignon, E. Inorg.
Chem. 1990, 29, 318-324. (b) Albertin, G.; Antoniutti, S.; Baldan,
D.; Bordignon, E. Inorg. Chem. 1995, 34, 6205-6210.
(14) (a) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bordignon, E.; Dolcetti,
P. M.; Pelizzi, G. J. Chem. Soc., Dalton Trans. 1997, 4435-4444.
(b) Albertin, G.; Antoniutti, S.; Bacchi, A.; Bergamo, M.; Bordignon,
E.; Pelizzi, G. Inorg. Chem. 1998, 37, 479-489. (c) Albertin, G.;
Antoniutti, S.; Beraldo, S.; Chimisso, F. Eur. J. Inorg. Chem. 2003,
2845-2854.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3817

Albertin et al.
mmol, 24 µL) was added, and the reaction mixture was stirred for
1 h at room temperature. A solution of the appropriate 1,3-ArNd
NN(H)Ar triazene (0.28 mmol) in 2 mL of CH2Cl2 was added to
the resulting solution, which was stirred for 4 h, and then an excess
of NEt3 (1.04 mmol, 145 µL) was added. The reaction mixture
was stirred for 3 h and filtered to remove the (NHEt3)CF3SO3 salt,
and then the solution was evaporated to dryness under reduced
pressure. The oil obtained was treated with ethanol (2 mL)
containing an excess of NaBPh4 (0.78 mmol, 0.27 g). A brown
solid slowly separated out, and it was filtered and crystallized from
CH2Cl2 and ethanol: yield g 80%.
Anal. Calcd for C48H66BN3O12P4Ru (1a): C, 51.81; H, 5.98; N,
3.78. Found: C, 52.03; H, 6.11; N, 3.67. ΛM: 51.5 Ω-1 mol-1
cm2. 1H NMR (CD2Cl2, 20 °C): δ 7.40-6.87 (m, 30 H, Ph), 3.77
{virtual triplet (vt), JHP ) 5.3 Hz, 18 H, CH3}, 3.51 (vt, JHP ) 5.3
Hz, 18 H, CH3). 31P{1H} NMR (CD2Cl2, 20 °C): δ A2B2 spin syst,
δA 139.0, δB 129.2, JAB ) 57.0 Hz. Anal. Calcd for C50H70-
BN3O12P4Ru (1b): C, 52.64; H, 6.18; N, 3.68. Found: C, 52.48;
H, 6.23; N, 3.56. ΛM: 50.6 Ω-1 mol-1 cm2. 1H NMR (CD2Cl2, 20
°C): δ 7.38-6.86 (m, 28 H, Ph), 3.74 (vt, JHP ) 5.3 Hz, 18 H,
CH3 phos), 3.53 (vt, JHP ) 5.3 Hz, 18 H, CH3 phos), 2.35 (s, 6 H,
CH3 p-tolyl). 31P{1H} NMR (CD2Cl2, 20 °C): δ A2B2 spin syst,
δA 138.8, δB 129.5, JAB ) 57.0 Hz. Anal. Calcd for C60H90-
BN3O12P4Ru (2a): C, 56.25; H, 7.08; N, 3.28. Found: C, 56.36;
H, 7.14; N, 3.20. ΛM: 53.3 Ω-1 mol-1 cm2. 1H NMR (CD2Cl2, 20
°C): δ 7.56-6.87 (m, 30 H, Ph), 4.12, 3.85 (m, 24 H, CH2), 1.33
(t, JHH ) 7 Hz, 18 H, CH3), 1.06 (t, JHH ) 7 Hz, 18 H, CH3).
31P{1H} NMR (CD2Cl2, 20 °C): δ A2B2 spin syst, δA 134.5, δB
125.2, JAB ) 58.1 Hz.
solution stirred for 1 h at room temperature. An excess of the
appropriate triazene (0.44 mmol) in 2 mL of toluene was added to
the resulting solution which, after the further addition of CH2Cl2
(5 mL), was stirred at room temperature for 4 h. An excess of
triethylamine (0.44 mmol, 61 µL) was added to the reaction mixture,
which was stirred for 3 h, and then the solvent was removed under
reduced pressure. The oil obtained was treated with ethanol (2 mL)
containing an excess of NaBPh4 (0.44 mmol, 0.15 g). A brown
solid slowly separated out which was filtered and crystallized from
CH2Cl2 and ethanol: yield g75%. Anal. Calcd for C60H90BN3O12-
OsP4 (4a): C, 52.59; H, 6.62; N, 3.07. Found: C, 52.42; H, 6.68;
1
N, 3.01. ΛM: 51.5 Ω-1 mol-1 cm2. H NMR (CD2Cl2, 20 °C): δ
7.98-6.87 (m, 30 H, Ph), 4.10, 3.83 (m, 24 H, CH2), 1.34 (t, JHH
) 7 Hz, 18 H, CH3), 1.06 (t, JHH ) 7 Hz, 18 H, CH3). 31P{1H}
NMR (CD2Cl2, 20 °C): δ A2B2 spin syst, δA 91.8, δB 79.1, JAB
)
40.5 Hz. Anal. Calcd for C62H94BN3O12OsP4 (4b): C, 53.25; H,
6.78; N, 3.00. Found: C, 53.41; H, 6.73; N, 2.88. ΛM: 52.7 Ω-1
1
mol-1 cm2. H NMR (CD2Cl2, 20 °C): δ 7.50-6.86 (m, 28 H,
Ph), 4.21, 3.82 (m, 24 H, CH2), 2.33 (s, 6 H, CH3 p-tolyl), 1.31 (t,
JHH ) 7 Hz, 18 H, CH3 phos), 1.04 (t, JHH ) 7 Hz, 18 H, CH3
phos). 31P{1H} NMR (CD2Cl2, 20 °C): δ A2B2 spin syst, δA 92.3,
δB 80.2, JAB ) 41.0 Hz. Anal. Calcd for C76H90BN3O8OsP4 (5a):
C, 60.92; H, 6.05; N, 2.80. Found: C, 60.79; H, 6.16; N, 2.67.
1
ΛM: 50.9 Ω-1 mol-1 cm2. H NMR (CD2Cl2, -30 °C): δ 7.55-
6.86 (m, 50 H, Ph), 4.05, 3.60, 3.35 (m, 16 H, CH2), 1.29, 1.27,
1.17, 1.15, 1.05, 0.84 (t, JHH ) 7 Hz, 24 H, CH3). 31P{1H} NMR
(CD2Cl2, -30 °C): δ ABC2 spin syst, δA 122.7, δB 122.2, δC 111.2,
JAB ) 24.2, JAC ) 26.7, JBC ) 30.5 Hz.
[Os(K1-OTf){η1-1,3-PhNdNN(H)Ph}{P(OEt)3}4]BPh4 (6a).
An equimolar amount of methyltriflate (0.11 mmol, 12 µL) was
added to a solution of OsH2{P(OEt)3}4 (0.12 mmol, 0.10 g) in 6
mL of toluene cooled to -196 °C. The reaction mixture was brought
to room temperature, stirred for 1 h, and then cooled again to -196
°C. A slight excess of CF3SO3H (0.13 mmol, 12 µL) was added,
and the solution was stirred for 1 h at room temperature. An excess
of 1,3-PhNdNN(H)Ph (0.22 mmol, 44 mg) in 2 mL of CH2Cl2
was added, and the reaction mixture, after the addition of 5 mL of
CH2Cl2, was stirred for 2 h. The solvent was removed under reduced
pressure to give an oil which was treated with ethanol containing
an excess of NaBPh4 (0.44 mmol, 0.15 g). A brown solid slowly
separated out which was filtered and crystallized from CH2Cl2 and
ethanol: yield g 45%. Anal. Calcd for C61H91BF3N3O15OsP4S: C,
48.19; H, 6.03; N, 2.76. Found: C, 48.06; H, 6.14; N, 2.63. ΛM:
[Ru(η2-1,3-Ph15NN15NPh){P(OEt)3}4]BPh4 (2a1). This complex
was prepared exactly like the related unlabeled compound 2a
following Method 1 and using the labeled 1,3-Ph15NN15N(H)Ph
triazene ligand: yield g60%. 1H NMR (CD2Cl2, 20 °C): δ 7.55-
6.87 (m, 30 H, Ph), 4.13, 3.87 (m, 24 H, CH2), 1.33 (t, JHH ) 7
Hz, 18 H, CH3), 1.06 (t, JHH ) 7 Hz, 18 H, CH3). 31P{1H} NMR
(CD2Cl2, 20 °C): δ AA′B2XX′ spin syst (X, X′ ) 15N), δA 135.3,
δB 126.0, JAA′ ) 63.5, JAB ) JA′B ) 57.3, JAX ) JA′X′ ) 46.6, JAX′
) JA′X ) 4.95, JBX ) JBX′ ) 5.20, JXX′ ) 4.05 Hz.
[Ru(η2-1,3-PhNNNPh){PPh(OEt)2}4]BPh4 (3a). An equimolar
amount of methyltriflate (CF3SO3CH3, 0.33 mmol, 37 µL) was
added to a solution of RuH2{PPh(OEt)2}4 (0.33 mmol, 0.30 g) in
6 mL of toluene cooled to -196 °C. The reaction mixture was
brought to room temperature and stirred for 1 h, and then an excess
of 1,3-PhNNN(H)Ph (0.70 mmol, 0.138 g) in toluene (2 mL) was
added. Dichloromethane (10 mL) was added to the reaction mixture
which was refluxed for about 30 min. The solvent was removed
under reduced pressure to give an oil which was treated with ethanol
(3 mL) containing an excess of NaBPh4 (0.66 mmol, 0.23 g). A
brown solid separated out which was filtered and crystallized from
CH2Cl2 and ethanol: yield g75%. Anal. Calcd for C76H90BN3O8P4-
Ru: C, 64.77; H, 6.44; N, 2.98. Found: C, 64.55; H, 6.35; N, 3.10.
1
51.2 Ω-1 mol-1 cm2. H NMR (CD2Cl2): δ (-80 °C) 11.65 (s, 1
H, NH); (-50 °C) 11.2 (s, br, 1 H, NH), 7.34-6.90 (m, 30 H, Ph),
4.18 (m, 24 H, CH2), 1.33 (t, JHH ) 7 Hz, 15 H, CH3), 1.12 (t, JHH
) 7 Hz, 21 H, CH3). 31P{1H} NMR (CD2Cl2, -80 °C): δ A2BC
spin syst, δA 84.6, δB 74.2, δC 63.5, JAB ) 41.8, JAC ) 44.9, JBC
) 48.7 Hz. IR (KBr, cm-1): 3327 w (νNH).
[OsH{η1-1,3-ArNdNN(H)Ar}P4]BPh4 (7, 8) [P ) P(OEt)3 (7),
PPh(OEt)2 (8); Ar ) Ph (a), p-tolyl (b)]. A solid sample of the
appropriate OsH2P4 hydride (0.1 mmol) in 6 mL of toluene was
placed in a 25 mL three-necked round-bottomed flask, and the
resulting solution was cooled to -196 °C. An equimolar amount
of methyltriflate (0.11 mmol, 12 µL) was added, and the reaction
mixture was brought to room temperature and stirred for 1 h. An
excess of the appropriate triazene 1,3-ArNdNN(H)Ar (0.20 mmol)
in 2 mL of toluene was added, and the reaction mixture, after the
addition of 5 mL of CH2Cl2, was stirred at room temperature for 4
h. The solvent was removed under reduced pressure to give an oil
which was treated with ethanol containing an excess of NaBPh4
(0.44 mmol, 0.15 g). A dark-green solid slowly separated out which
1
ΛM: 51.9 Ω-1 mol-1 cm2. H NMR (CD2Cl2, 20 °C): δ 8.04-
6.66 (m, 50 H, Ph), 4.30-3.60 (m, 16 H, CH2), 1.50 (t, JHH ) 7
Hz, 6 H, CH3), 1.25 (t, JHH ) 7 Hz, 6 H, CH3), 1.09 (t, JHH ) 7
Hz, 12 H, CH3). 31P{1H} NMR [(CD3)2CO/CDCl3, -100 °C): δ
A2B2 spin syst, δA 163.0, δB 153.8, JAB ) 44.4 Hz.
[Os(η2-1,3-ArNNNAr)P4]BPh4 (4, 5) [P ) P(OEt)3 (4), PPh-
(OEt)2 (5); Ar ) Ph (a), p-tolyl (b)]. An equimolar amount of
methyltriflate (0.11 mmol, 12 µL) was added to a solution of the
appropriate hydride OsH2P4 (0.11 mmol) in 6 mL of toluene cooled
to -196 °C. The reaction mixture was brought to room temperature,
stirred for 1 h, and then cooled again to -196 °C. An equimolar
amount of triflic acid (0.11 mmol, 10 µL) was added, and the
3818 Inorganic Chemistry, Vol. 45, No. 9, 2006

Triazenide and Triazene Complexes of Ru and Os
was filtered and crystallized from CH2Cl2 and ethanol: yield from
60 to 75%. Anal. Calcd for C60H92BN3O12OsP4 (7a): C, 52.51; H,
6.76; N, 3.06. Found: C, 52.42; H, 6.88; N, 3.14. ΛM: 52.6 Ω-1
mol-1 cm2. 1H NMR (CD2Cl2, -90 °C): δ 10.84 (s, br, 1 H, NH),
7.90-6.67 (m, 30 H, Ph), 4.12-3.60 (m, 24 H, CH2), 1.24 (t, JHH
[OsH(PhNdNH)P4]BPh4 (10a, 11a) [P ) P(OEt)3 (10), PPh-
(OEt)2 (11)]. An equimolar amount of CF3SO3H (0.1 mmol, 9 µL)
was added to a solution of the appropriate OsH2P4 hydride (0.1
mmol) in 5 mL of dichloromethane cooled to -196 °C. The reaction
mixture was stirred for 1 h at room temperature, and then an excess
of 1,3-PhNdNN(H)Ph (0.3 mmol, 59 mg) was added. The resulting
solution was stirred at room temperature for 10 h, and then the
solvent removed under reduced pressure to give a brown oil which
was treated with ethanol containing an excess of NaBPh4 (0.2 mmol,
68 mg). An orange solid slowly separated out which was filtered
and crystallized from CH2Cl2 and ethanol: yield g 45%. Anal.
Calcd for C54H87BN2O12OsP4 (10a): C, 50.62; H, 6.84; N, 2.19.
Found: C, 50.54; H, 6.96; N, 2.05. ΛM: 54.7 Ω-1 mol-1 cm2. 1H
NMR (CD2Cl2, 20 °C): δ 14.47 (s, br, 1 H, NH), 7.30-6.97 (m,
25 H, Ph), 4.02 (m, 24 H, CH2), 1.27 (t, JHH ) 7 Hz, 9 H, CH3),
1.24 (t, JHH ) 7 Hz, 9 H, CH3), 1.18 (t, JHH ) 7 Hz, 18 H, CH3),
-8.28 to -8.68 (m, 1 H, OsH). 31P{1H} NMR (CD2Cl2, -90 °C):
) 7 Hz, 9 H, CH3), 1.17 (t, JHH ) 7 Hz, 9 H, CH3), 1.15 (t, JHH
)
7 Hz, 18 H, CH3), -8.19 to -8.66 (m, 1 H, OsH). 31P{1H} NMR
(CD2Cl2, -90 °C): δ A2BC spin syst, δA 107.0, δB 102.5, δC 100.2,
JAB ) 32.3, JAC ) 44.4, JBC ) 29.0 Hz. IR (KBr, cm-1): 3345 w
(νNH). Anal. Calcd for C76H92BN3O8OsP4 (8a): C, 60.84; H, 6.18;
N, 2.80. Found: C, 60.67; H, 6.28; N, 2.72. ΛM: 55.8 Ω-1 mol-1
cm2. 1H NMR (CD2Cl2, -90 °C): δ 11.04 (s, br, 1 H, NH), 7.90-
6.55 (m, 50 H, Ph), 4.10-3.34 (m, 16 H, CH2), 1.27 (t, JHH ) 7
Hz, 3 H, CH3), 1.20 (t, JHH ) 7 Hz, 6 H, CH3), 1.14 (t, JHH ) 7
Hz, 9 H, CH3), 1.04 (t, JHH ) 7 Hz, 6 H, CH3), -7.92 to -8.36
(m, 1 H, OsH). 31P{1H} NMR (CD2Cl2, -90 °C): δ AB2C spin
syst, δA 124.6, δB 123.5, δC 120.4, JAB ) 19.3, JAC ) 29.7, JBC
)
20.4 Hz. IR (KBr, cm-1): 3358 w (νNH), 1975 w (νOsH). Anal.
Calcd for C78H96BN3O8OsP4 (8b): C, 61.29; H, 6.33; N, 2.75.
Found: C, 61.44; H, 6.26; N, 2.69. ΛM: 55.3 Ω-1 mol-1 cm2. 1H
NMR (CD2Cl2, -80 °C): δ 10.12 (s, br, 1 H, NH), 7.46-6.47 (m,
48 H, Ph), 4.05-3.40 (m, 16 H, CH2), 2.35 (s, 6 H, CH3 p-tolyl),
1.23 (t, JHH ) 7 Hz, 6 H, CH3 phos), 1.19 (t, JHH ) 7 Hz, 6 H,
CH3 phos), 1.10 (t, JHH ) 7 Hz, 12 H, CH3 phos), -7.83 to -8.46
(m, 1 H, OsH). 31P{1H} NMR (CD2Cl2, -80 °C): δ AB2C spin
δ AB2C spin syst, δA 102.4, δB 100.5, δC 99.5, JAB ) 32.5, JAC
)
42.8, JBC ) 31.7 Hz. Anal. Calcd for C70H87BN2O8OsP4 (11a): C,
59.66; H, 6.22; N, 1.99. Found: C, 59.84; H, 6.30; N, 1.91. ΛM:
50.4 Ω-1 mol-1 cm2. 1H NMR (CD2Cl2, 20 °C): δ 13.42 (s, br, 1
H, NH), 8.05-6.67 (m, 45 H, Ph), 4.02-3.20 (m, 16 H, CH2),
1.30 (t, JHH ) 7 Hz, 6 H, CH3), 1.12 (t, JHH ) 7 Hz, 6 H, CH3),
1.08 (t, JHH ) 7 Hz, 12 H, CH3), -7.78 to -8.45 (m, 1 H, OsH).
31P{1H} NMR (CD2Cl2, -90 °C): δ AB2C spin syst, δA 125.8, δB
123.7, δC 119.8, JAB ) 19.2, JAC ) 22.7, JBC ) 30.0 Hz.
[OsH(Ph15NdNH){PPh(OEt)2}4]BPh4 (11a1). This compound
was prepared exactly like the related unlabeled 11a complex, using
1,3-Ph15NdN15N(H)Ph as a reagent: yield g 45%. 1H NMR (CD2-
Cl2, 20 °C): δ 13.40 (s, br, 1 H, NH), 8.04-6.67 (m, 45 H, Ph),
4.00-3.20 (m, 16 H, CH2), 1.30 (t, JHH ) 7 Hz, 6 H, CH3), 1.14
(t, JHH ) 7 Hz, 6 H, CH3), 1.08 (t, JHH ) 7 Hz, 12 H, CH3), -7.78
to -8.45 (m, 1 H, OsH). 31P{1H} NMR (CD2Cl2, -90 °C): δ AB2C
spin syst, δA 125.9, δB 123.6, δC 119.8, JAB ) 19.2, JAC ) 22.7,
JBC ) 30.2 Hz.
syst, δA 126.7, δB 121.6, δC 121.2, JAB ) 20.1, JAC ) 29.6, JBC
)
22.1 Hz. IR (KBr, cm-1): 3359 w (νNH), 1990 w (νOsH).
[OsH{η1-1,3-Ph15NdN15N(H)Ph}{PPh(OEt)2}4]BPh4 (8a1). This
complex was prepared exactly like the related unlabeled compound
1
8a using the 1,3-Ph15NN15NPh triazene ligand: yield g65%. H
15NH
NMR (CD2Cl2, -80 °C): δ 11.05 (d, 1 H, NH, J
) 92 Hz),
7.90-6.58 (m, 50 H, Ph), 4.11-3.34 (m, 16 H, CH2), 1.27 (t, JHH
) 7 Hz, 3 H, CH3), 1.20 (t, JHH ) 7 Hz, 6 H, CH3), 1.14 (t, JHH
)
7 Hz, 9 H, CH3), 1.04 (t, JHH ) 7 Hz, 6 H, CH3), -7.91 to -8.38
(m, 1 H, OsH). 31P{1H} NMR (CD2Cl2, -80 °C): δ AB2CX spin
syst (X ) 15N), δA 124.7, δB 123.7, δC 120.4, JAB ) 19.2, JAC
)
X-ray Crystal Structure Determinations. The data collection
was taken on a SIEMENS Smart CCD area-detector diffractometer
with graphite-monochromated Mo KR radiation at room temperature
for 2a and at -100 °C for 11a. Absorption corrections were carried
out using SADABS.15
29.7, JAX ) 1.0, JBC ) 20.6, JBX ) 1.0, JCX ) 6.30 Hz. IR (KBr,
cm-1): 3347 w (νNH), 1972 w (νOsH).
[RuH{η1-1,3-p-tolyl-NdNN(H)-p-tolyl}{PPh(OEt)2}4]BPh4 (9b).
An equimolar amount of methyltriflate (CF3SO3CH3, 0.33 mmol,
37 µL) was added to a solution of RuH2{PPh(OEt)2}4 (0.33 mmol,
0.30 g) in 6 mL of toluene cooled to -196 °C. The reaction mixture
was brought to room temperature and stirred for 1 h, and then an
excess of 1,3-p-tolyl-NdNN(H)-p-tolyl (0.70 mmol, 0.158 g) in
toluene (2 mL) was added. Dichloromethane (10 mL) was added,
and the reaction mixture was stirred at room temperature for 3 h.
The solvent was removed under reduced pressure giving an oil
which was triturated with ethanol (2 mL) containing an excess of
NaBPh4 (0.60 mmol, 0.21 g). A green solid slowly separated out
which was filtered and crystallized from CH2Cl2 and ethanol: yield
g70%. Anal. Calcd for C78H96BN3O8P4Ru: C, 65.09; H, 6.72; N,
2.92. Found: C, 65.31; H, 6.85; N, 2.79. ΛM: 49.5 Ω-1 mol-1
The structure of [Ru(η2-1,3-PhNNNPh){P(OEt)3}4]BPh4 (2a) was
solved by the Patterson method, and the structure of [OsH(PhNd
NH){PPh(OEt)2}4]BPh4 (11a) was solved by direct methods. Both
were refined by a full-matrix least-squares methods based on F2.16
Non-hydrogen atoms were refined with anisotropic displacement
parameters. Hydrogen atoms were included in idealized positions
and refined with isotropic displacement parameters, except for those
labeled as H1, bonded to the Os atom, and H11, bonded to a
nitrogen atom, in [OsH(PhNdNH){PPh(OEt)2}4]BPh4 (11a). H1
and H11 were located on a difference electron-density map. H11
was refined with isotropic displacement parameters, but for H1,
the positions were not refined. Atomic-scattering factors and
anomalous dispersion corrections for all atoms were taken from
International Tables for X-ray Crystallography.17 Details of the
crystal data and structural refinement are given in Table 1.
1
cm2. H NMR (CD2Cl2): δ (20 °C) 9.84 (s, br, 1 H, NH), 8.10-
6.85 (m, 48 H, Ph), 4.15-3.50 (m, 16 H, CH2), 2.43 (s, 3 H, CH3
p-tolyl), 2.40 (s, 3 H, CH3 p-tolyl), 1.51 (t, JHH ) 7 Hz, 3 H, CH3
phos), 1.35 (t, JHH ) 7 Hz, 6 H, CH3 phos), 1.27 (t, JHH ) 7 Hz,
9 H, CH3 phos), 1.10 (t, JHH ) 7 Hz, 6 H, CH3), -6.70 to -7.30
(m, 1 H, RuH); (-90 °C) 11.97 (s, 1 H, NH), 8.00-6.60 (m, 48
H, Ph), 4.10-3.50 (m, 16 H, CH2), 2.41 (s, 3 H, CH3 p-tolyl),
2.38 (s, 3 H, CH3 p-tolyl), 1.35-1.15 (m, 24 H, CH3 phos), -6.78
to -7.15 (m, 1 H, RuH). 31P{1H} NMR (CD2Cl2, -90 °C): δ AB2C
spin syst, δA 172.2, δB 165.2, δC 160.4, JAB ) 44.5, JAC ) 29.5,
JBC ) 27.9 Hz. IR (KBr, cm-1): 3331 m (νNH).
(15) Sheldrick, G. M. SADABS. An empirical absorption correction
program for area detector data; University of Go¨ttingen: Go¨ttingen,
Germany, 1996.
(16) Sheldrick, G. M. SHELX-97. Program for the solution and refinement
of crystal structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(17) International Tables for X-ray Crystallography; Kluwer: Dordrecht,
The Netherlands, 1992; Vol. C.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3819

Albertin et al.
Scheme 2
Table 1. Crystal Data and Structure Refinement
2a
11a
empirical formula
fw
C60H90BN3O12P4Ru
1281.11
C70H87BN2O8OsP4
1409.31
temp
293(2) K
0.71073 Å
triclinic
173(2) K
0.71073 Å
triclinic
P1h
wavelength
cryst syst
space group
P1h
unit cell dimensions a ) 12.5801(13) Å
b ) 14.8211(16) Å
c ) 18.7249(19) Å
a ) 12.5264(6) Å
b ) 15.1969(7) Å
c ) 18.0865(8) Å
R ) 87.1340(10)°
â ) 83.7010(10)°
γ ) 82.9620(10)°
3394.1(3) Å3
2
R ) 88.894(2)°
â ) 85.266(2)°
γ ) 75.550(2)°
vol
Z
3369.3(6) Å3
2
density (calcd)
abs coeff
F(000)
1.263 Mg/m3
0.385 mm-1
1352
1.379 Mg/m3
2.027 mm-1
1452
cryst size
θ range
index ranges
0.42 × 0.39 × 0.20 mm 0.36 × 0.32 × 0.27 mm
P ) P(OMe)3 (1), P(OEt)3 (2), PPh(OEt)2 (3); Ar ) Ph (a), p-tolyl (b).
1.42-28.03°
-16 e h e 16
-17 e k e 19
-19 e l e 24
19 562
1.65-28.01°
-16 e h e 13
-19 e k e 16
-19 e l e 23
21 481
The reaction of the κ2-triflate [M(κ2-OTf)P4]+ cations with
1,3-diaryltriazene (Scheme 1) proceeds with the initial
coordination of the triazene to give the [M(κ1-OTf){η1-1,3-
ArNdNN(H)Ar}P4]+ (A) intermediate which, in the case of
the [Os(κ1-OTf){η1-1,3-PhNdNN(H)Ph}{P(OEt)3}4]+ cation,
was isolated in the solid state and characterized (6a).
Treatment of these η1-triazenes (A) with an excess of NEt3
gives the final triazenide derivatives (1-5). Triethylamine,
in fact, deprotonates the η1-triazene allowing η2-coordination
of the 1,3-ArNNNAr triazenide ligand.
reflns collected
independent reflns
13 683
14 976
[R(int) ) 0.0293]
6917
[R(int) ) 0.0291]
12 163
reflns obsd (>2σ)
data completeness
max. and min.
transmission
data/restraints/
params
0.839
0.912
1.000 and 0.883
1.000 and 0.900
13 683/0/742
14 976/0/788
GOF on F2
final R indices
[I > 2σ(I)]
0.821
0.864
R1 ) 0.0506
R1 ) 0.0351
The reaction of the ruthenium hydrides (Scheme 2) was
followed by NMR spectroscopy and showed that the addition
of triazene to both the [RuH(η2-H2]P4]+ and RuH(κ1-OTf)-
P4 hydride precursors causes the substitution of the labile18
η2-H2 or κ1-OTf ligand and the formation of a new complex
formulated as the hydride-triazene intermediate (B). This
complex was not isolated in pure form, but its formulation
is supported both by the NMR data and by the separation,
as solids, of the related hydride-triazene [MH{η1-1,3-ArNd
NN(H)Ar}P4]BPh4 complexes of both ruthenium (9b) and
wR2 ) 0.0945
R1 ) 0.1088
wR2 ) 0.0567
R1 ) 0.0481
R indices
(all data)
wR2 ) 0.1078
wR2 ) 0.0591
largest diff. peak
and hole
0.572 and -0.381 e Å-3 2.025 and -1.254 e Å-3
Results and Discussion
Triazenide Complexes. Triazenide [M(η2-1,3-ArNNNAr)-
P4]BPh4 complexes of ruthenium (1-3) and osmium (4 and
5) were easily prepared by reacting triflate [M(κ2-OTf)P4]+
cations with 1,3-diaryltriazene and then with an excess of
NEt3, as shown in Scheme 1.
1
osmium (7-8) (see below). In fact, the H NMR spectrum
of the reaction mixture shows, starting from the triflate
complex, the disappearance of the signals of the RuH(κ1-
OTf)P4 precursors and the appearance of a new hydride
multiplet at -8.10 to -8.60 ppm. Furthermore, at -40 °C
a broad signal near +9.2 ppm also appears and is attributable
to the NH proton of the η1-coordinate triazene ligand. Finally,
the 31P NMR spectra show a nonsymmetric AB2C type
multiplet, in agreement with the presence of an intermediate-
type (B) compound. As the reaction proceeds, the 31P spectra
show the appearance of the A2B2 multiplet of the final
triazenide [Ru(η2-1,3-ArNNNAr)P4]+ (1-2) derivatives. At
room temperature, however, the formation of the triazenide
complex is slow and needs higher temperatures (40 °C) to
be completed in a reasonable time. The formation of the final
complexes (1-2) from the hydride-triazene intermediate (B)
is not surprising and can be explained by taking into account
Scheme 1
M ) Ru (1, 2, 3), Os (4, 5); P ) P(OMe)3 (1), P(OEt)3 (2, 4, 6),
PPh(OEt)2 (3, 5); Ar ) Ph (a), p-tolyl (b); OTf- ) CF3SO3- and when M
) Os, P ) P(OEt)3, Ar ) Ph, [A] ) 6a.
Furthermore, in the case of ruthenium, the reactions of
both [RuH(η2-H2)P4]+ and RuH(κ1-OTf)P4 hydride com-
plexes with 1,3-diaryltriazene give the triazenide [Ru(η2-
1,3-ArNNNAr)P4]+ (1 and 2) derivatives, which were
isolated as BPh4 salts and characterized (Scheme 2).
(18) In the case of the [RuH(η2-H2){PPh(OEt)2}4]OTf complex, the known
stability13a to the loss of the H2 ligand prevented the preparation of
triazenide 3a in pure form, which was obtained as a byproduct in a
mixture of compounds.
3820 Inorganic Chemistry, Vol. 45, No. 9, 2006

Triazenide and Triazene Complexes of Ru and Os
the increased acidity of the triazene N-H hydrogen atom
caused by the η1-coordination of the 1,3-ArNdNN(H)Ar
group19 and the protonation of the hydride [Ru]-H ligand
to give a H2 molecule. Thus, an intramolecular acid-base
reaction between the triazene NH proton of η1-1,3-ArNd
NN(H)Ar ligand and the Ru-H hydride group in the
intermediate species (B) may result in evolution of H2 and
formation of the chelate η2-triazenide ligand. Support for this
hypothesis comes from the 1H NMR spectra of the reaction
mixture of RuH(κ1-OTf)P4 with 1,3-PhNdNN(H)Ph in CD2-
Cl2, which show a weak signal at 4.6 ppm characteristic20
of the presence of free dihydrogen, in agreement with the
path proposed in Scheme 2.
The 1,3-triazenide complexes of ruthenium and osmium
can be isolated with both the 1,3-diphenyl and 1,3-di-p-tolyl
ligands. However, complexes 1a-5a can only be prepared
with the 1,3-PhNNNPh group with all the phosphites used.
With the 1,3-p-tolyl-NNN-p-tolyl ligand, instead, triazenide
complexes 1b and 4b were obtained only with the good
π-accepting21 P(OMe)3 and P(OEt)3 phosphite ligands. The
use of the less π-acidic21 PPh(OEt)2 ligand probably makes
the NH hydrogen atom of the [RuH{η1-p-tolyl-NdNN(H)-
p-tolyl}P4]+ and the [M(κ1-OTf){η1-p-tolyl-NdNN(H)-p-
tolyl}P4]+ intermediates less acidic, preventing the intra-
molecular acid-base reaction between RuH and the triazene
NH hydrogen atom, in one case, and the deprotonation by
NEt3 in the other. As a result, samples of pure hydride-
triazene [RuH{η1-p-tolyl-NdNN(H)-p-tolyl}{PPh(OEt)2}4]-
BPh4 (9b) complex can be isolated (see below). We have
also used LiOH as a base, instead of NEt3, in the reaction of
the triflate-triazene intermediate (A) (Scheme 1), but with
both the PPh(OEt)2 and the p-tolyltriazene ligands, only
intractable mixtures were obtained.
The triazenide [M(η2-1,3-ArNNNAr)P4]BPh4 (1-5) com-
plexes are red-brown microcrystalline solids stable in air and
in a solution of polar organic solvents where they behave
like 1:1 electrolytes.22 Their formulation is supported by
analytical and spectroscopic data and by the X-ray crystal
structure determination of [Ru(η2-1,3-PhNNNPh){P(OEt)3}4]-
BPh4 (2a) for which the ORTEP diagram of the cation is
shown in Figure 1.
Figure 1. Cation [Ru(η2-1,3-PhNNNPh){P(OEt)3}4]BPh4 (2a) (30%
probability level), where the carbon atoms have been drawn as small spheres.
Hydrogen atoms have been omitted.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 2a
Ru(1)-N(3)
Ru(1)-P(4)
Ru(1)-P(1)
N(1)-N(2)
2.163(3)
Ru(1)-N(1)
Ru(1)-P(2)
Ru(1)-P(3)
N(2)-N(3)
2.170(3)
2.2538(10)
2.3363(11)
1.319(4)
2.2621(11)
2.3392(12)
1.312(4)
N(3)-Ru(1)-N(1)
N(1)-Ru(1)-P(4)
N(1)-Ru(1)-P(2)
N(3)-Ru(1)-P(1)
P(4)-Ru(1)-P(1)
N(3)-Ru(1)-P(3)
P(4)-Ru(1)-P(3)
P(1)-Ru(1)-P(3)
58.43(11)
105.71(9)
161.14(9)
90.30(8)
95.06(4)
82.01(8)
91.06(4)
171.14(4)
N(3)-Ru(1)-P(4)
N(3)-Ru(1)-P(2)
P(4)-Ru(1)-P(2)
N(1)-Ru(1)-P(1)
P(2)-Ru(1)-P(1)
N(1)-Ru(1)-P(3)
P(2)-Ru(1)-P(3)
N(1)-N(2)-N(3)
162.35(9)
104.47(9)
92.24(4)
81.59(8)
91.25(4)
90.59(8)
94.91(4)
107.0(3)
107.0(3)°, similar to that of previously reported complexes
with triazenide ligands3b,c,e but slightly larger than that for
the Ru(II) complex [Ru(PhNNNPh)2(PPh3)2]2i with an aver-
age value of 104.0(4)°. The N-N distances, 1.319(4) and
1.312(4) Å, are well within the range expected for this ligand
and, together with the Ru-N distances of 2.163(3) and
2.170(3) Å, show an important delocalization over the ring
and its strained nature. The Ru-P distances are in two
different sets, since those in the equatorial plane are shorter
than those in axial positions. This could be an effect of the
electron withdrawal of the triazenide ligand added to the
mutually trans effect of the phosphites in the axial positions.
Those last values are not very different from those found in
the already mentioned complex [Ru(PhNNNPh)2(PPh3)2],2i
in which the phosphine ligands are also mutually in trans
positions.
In the temperature range between +20 and -80 °C, the
31P{1H} NMR spectra of the P(OMe)3 and P(OEt)3 com-
plexes 1a, 1b, 2a, 4a, and 4b appear as an A2B2 multiplet,
in agreement with a geometry of type I (Schemes 1 and 2),
like that observed in the solid state. We have also prepared
the labeled [Ru(η2-1,3-Ph15NN15NPh){P(OEt)3}4]BPh4 (2a1)
complex using the 1,3-Ph15NdN15N(H)Ph ligand and ob-
Selected bond distances and angles for 2a are in Table 2.
The cation complex contains the Ru(II) atom in a distorted
octahedral environment which is coordinated to N1 and N3
of the triazenide ligand [RuNN bite angle of 58.4(1)°] and
to four phosphorus atoms of four monodentated phosphite
ligands P(OEt)3. The octahedron can be described as having
the nitrogen atoms in the distorted equatorial plane, with the
dihedral angle between the RuPP and the RuNN planes
being 11.5(2)°. The N1-N2-N3 angle takes a value of
(19) (a) Sutherland, J. W. J. Phys. Chem. 1979, 83, 789-795. (b) Sawicki,
E.; Hauser, T. R.; Stanley, T. W. Anal. Chem. 1959, 31, 2063-2065.
(c) Hansen, L. D.; West, B. D.; Baca, E. J.; Black, C. L. J. Am. Chem.
Soc. 1968, 90, 6588-6592.
(20) Crabtree, R. H.; Lavin, M.; Bonneviot, L. J. Am. Chem. Soc. 1986,
108, 4032.
(21) (a) Tolman, C. A. Chem. ReV. 1977, 77, 313-348. (b) Rahaman, M.
M.; Liu, H.-Y.; Eriks, K.; Prock, A.; Giering, W. P. Organometallics
1989, 8, 1-7.
(22) Geary, W. J. Coord. Chem. ReV. 1971, 7, 81-122.
Inorganic Chemistry, Vol. 45, No. 9, 2006 3821

Albertin et al.
Table 3. 15N NMR Data for Selected Triazene and Triazenide
Complexes
Triazenide complexes of ruthenium(II) and osmium(II)
have been reported with carbonyl and triphenylphosphine
ligands and are neutral species of the MX(ArNNNAr)(CO)-
(PPh3)2 (X ) H, Cl) and M(ArNNNAr)2(PPh3)2 types.2a,i The
use of both the dihydrogen [RuH(η2-H2)P4]+ and the triflate
[M(κ2-O2SOCF3)P4]+ (M ) Ru, Os) cations as precursors
allows new cationic [M(η2-ArNNNAr)P4]+ triazenide com-
plexes stabilized by phosphite ligands to be prepared.
Triazene Complexes. Hydride-triflate OsH(κ1-OTf)P4
complexes react with an excess of 1,3-diaryltriazene to give
the hydride-triazene [OsH{η1-1,3-ArNdNN(H)Ar}P4]+ de-
rivatives, which were isolated as BPh4 salts and characterized
(Scheme 3).
15N NMRa,b
compound
δ (J/Hz)
assignment
Ph15NdN-15N(H)Ph
-20.5 sc
Ph15N)15NH
-198.0 d
15
J
NH ) 92
2a1
[Ru(η2-1,3-Ph15NN15NPh)
{P(OEt)3}4]BPh4
AA′B2XX′
spin syst
X ) X′ ) 15N
δX -140.0
JAX ) JA′X′
) 46.6
JBX ) JBX′
) 5.20
JAX′ ) JA′X
) 4.95
JXX′ ) 4.05
-10.7 s
Scheme 3
11a1 [OsH{Ph15NdNH)
{PPh(OEt)2}4]BPh4
Ph15N)
8a1
[OsH{η1-1,3-Ph15NdN15N(H)Ph} -15.6 mc
Ph15N)15NH
{PPh(OEt)2}4]BPh4
-199.2 d
15
J
NH ) 92
a From CH315NO2. b In CD2Cl2 at 20 °C unless otherwise noted. c At
-90 °C.
served a complicated multiplet in the 31P spectra. A simula-
tion using an AA′B2XX′ (X, X′ ) 15N) model, however, gave
an excellent agreement between the simulated and the
experimental spectra, allowing the NMR parameters to be
calculated. The 15N NMR spectrum of 2a1 was also recorded
and appears as an AA′B2XX′ (X, X′ ) 15N) multiplet at
-140.0 ppm whose parameters are reported in Table 3.
The 31P{1H} NMR spectra of the PPh(OEt)2 derivatives
3a and 5a are temperature-dependent and result partially
different from those of the related compounds 1, 2, and 4.
The broad multiplet observed at room temperature for both
3a and 5a changes as the temperature is lowered and, for
the ruthenium complex (3a), resolves at -100 °C into an
A2B2 multiplet, in agreement with a type-I geometry. In the
case of the osmium compound 5a, instead, a well-resolved
multiplet appears at -30 °C which remains unchanged until
-100 °C and was simulated using an ABC2 model with the
parameters reported in the Experimental Section. A 31P
spectrum of this type is not in agreement with the proposed
formulation of the compound, which should give a symmetric
A2B2-type spectrum. However, taking into account that the
values of the chemical shifts of A and B are very close and
that the PPh(OEt)2 ligand can give rotational isomers,23 the
VT 31P spectra of 5a may be explained on the basis of the
restricted rotation of the phosphine ligand around the Os-P
bond. At -30 °C, two PPh(OEt)2 phosphites are magnetically
equivalent, while the other two can be made virtually
inequivalent by the different arrangement of the phenyl and
ethoxy groups of one phosphite with respect to the other.
The steric requirements of the PPh(OEt)2, as compared to
the P(OEt)3 phosphite ligand in our η2-triazenide complexes,
probably lead to the asymmetric ABC2 31P spectra in the
[Os(η2-1,3-PhNNNPh){PPh(OEt)2}4]BPh4 (5a) derivative.
P ) P(OEt)3 (7), PPh(OEt)2 (8); Ar ) Ph (a), p-tolyl (b)
Scheme 4
P ) PPh(OEt)2
Related ruthenium triazene complexes were also prepared
in only one case, using both the 1,3-di-p-tolyltriazene and
the PPh(OEt)2 phosphite ligands, as shown in Scheme 4.
The hydride-triazene [OsH{η2-1,3-ArNdNN(H)Ar}P4]+
(7, 8) cations are very stable and do not give rise to evolution
of H2 nor to formation of the related triazenide [Os(η2-1,3-
ArNNNAr)P4]+ cations under any conditions. This unreac-
tivity of the osmium species is rather surprising (see Scheme
2) and may be attributed to a different reactivity of the Os-H
as compared to that of Ru-H toward the NH of the
coordinate η1-1,3-triazene.
The hydrogen atom in the [Os]-H group probably has
less hydridic character13a,27 than the related [Ru]-H and
needs a stronger acid than the NH of the η1-triazene for its
protonation. The absence of this acid-base reaction between
the hydride and the triazenic NH group prevents the
(24) Albertin, G.; Antoniutti, S.; Bordignon, E. J. Organomet. Chem. 1996,
513, 147-153.
(25) Deeming, A. J.; Doherty, S.; Marshall, J. E.; Powell, N. I. J. Chem.
Soc., Chem. Commun. 1989, 1351.
(26) Albertin, G.; Antoniutti, S.; Bettiol, M.; Bordignon, E.; Busatto, F.
Organometallics 1997, 16, 4959-4969.
(27) (a) Dedieu, A. Transition Metal Hydrides; Wiley-VCH: New York,
1992. (b) Peruzzini, M.; Poli, R. Recent AdVances in Hydride
Chemistry; Elsevier: Amsterdam, 2001.
(23) Examples of inequivalent phosphorus nuclei in octahedral complexes
containing four PPh(OEt)2 or PPhMe2 ligands in a plane have recently
been reported for FeHCl{PPh(OEt)2}4,24 [IrCl2(PPhMe2)4]ClO4,25 and
26
MnH(CO){PPh(OEt)2}4 derivatives.
3822 Inorganic Chemistry, Vol. 45, No. 9, 2006

Triazenide and Triazene Complexes of Ru and Os
Scheme 5
formation of the triazenide complexes and, for the first time,
allows the preparation of 1,3-diaryltriazene complexes.
The absence of the acid-base reaction is also observed
in ruthenium complex 9b, in which the nature of both the
phosphite and the triazene ligands prevents the formation of
the η2-triazenide derivative.
The hydride-triazene [MH{η1-1,3-ArNdNN(H)Ar}P4]-
BPh4 (7-9) compounds are green or yellow-green solids
stable both as solids and in solutions of polar organic
solvents, where they behave like 1:1 electrolytes.22 The
infrared spectra show a weak band at 3359-3331 cm-1
attributed to the NH of the triazene and, for 7 and 8, a weak
band at 1990-1975 cm-1 from νM-H. The presence of both
the triazene and the hydride ligands is confirmed by the 1H
NMR spectra, which also indicate that the complexes are
fluxional (see Figure S1). The broad signals that appear at
room temperature in the proton spectra of complexes 7-9
change as the temperature is lowered, and at -90 °C, a
slightly broad singlet attributed to the NH of the triazene
ligand appears at 11.97-10.12 ppm. At this temperature, a
well-resolved multiplet of the hydride ligand between -6.70
and -8.66 ppm is also present, as well as the signal of the
phosphite groups. At -90 °C, the 31P NMR spectra also
resolve into an AB2C or A2BC pattern, which was simulated
with the parameters reported in the Experimental Section.
Further information on the behavior in solution of the
hydride-triazene complexes come from VT-NMR studies
of the labeled [OsH{1,3-Ph15NdN15N(H)Ph}{PPh(OEt)2}4]-
BPh4 (8a1) derivative (see Figure S2). The broad signal at
10.5 ppm that appears at -30 °C in the proton spectra of
the [OsH{1,3-PhNdNN(H)Ph}P4]+ (8a) cation is now a
multiplet and was simulated using the parameters reported
in the Experimental Section, thus confirming the proposed
geometry (II) for the hydride-triazene derivative 8a1.
Further support for geometry II comes from a comparison
of the 15N NMR spectra of 8a1 with those of the free 1,3-
Ph15NdN15N(H)Ph ligand (Table 3), which shows that, while
the chemical shift of the diazenic Ph15Nd nitrogen atom
changes by about 5 ppm upon coordination, that of the NH
group remains practically the same, in agreement with a type-
II coordination.
The fluxional behavior shown by triazene complexes 7-9
may be explained by an intermolecular process involving,
as suggested by a reviewer, the dissociation of the triazene
ligand, as shown in Scheme 5. This dynamic process, which
involves both dissociation of the 1,3-triazene and hydrogen
exchange between the two N atoms of the free 1,3-ArNd
NN(H)Ar species,30 may explain the VT NMR spectra
observed.
Strong support for such a dissociation equilibrium of the
triazene ligand in the complexes has been obtained by adding
the 15N-labeled free triazene to the unlabeled 7a, 8a, and 9b
compounds in a NMR tube and observing that exchange
between the labeled and unlabeled triazene does take place.
On the basis of these results, the dissociation process of
Scheme 5, which slows at -80 °C, can reasonably be
proposed to explain the VT behavior of our triazene
derivatives.
broad doublet in the spectra of the labeled compound 8a1
1
15
and resolves into a sharp doublet (11.05 ppm) with J NH of
92 Hz at -80 °C. These results strongly support the
formulation proposed for the triazene complexes 7-9 and
suggest that a geometry of the type II, with the hydride and
the triazene ligands in a mutually cis position, is also present
at -80 °C. The AB2C or A2BC pattern of the 31P spectra, in
fact, and the complicated multiplet of the hydride ligand
The IR spectrum of the triflate-triazene [Os(κ1-OTf)-
{η1-1,3-PhNdNN(H)Ph}{P(OEt)3}4]BPh4 (6a) complex shows
a weak band at 3327 cm-1 attributed to the νNH of the
1
triazene ligand. The H NMR spectra confirm the presence
1
of this ligand and also indicate that the compound is
fluxional. The NH signal of the triazene, in fact, begins to
appear at -40 °C as a very broad signal near 11 ppm, which
sharpens as the temperature is lowered and becomes a slightly
broad signal at 11.6 ppm at -80 °C. The 31P{1H} NMR
spectrum also changes as the temperature is lowered, and
the broad multiplet that appears at room temperature resolves
into an A2BC multiplet at -80 °C. On the basis of these
data, a dissociation equilibrium of the type shown in Scheme
5 probably also occurs for this complex containing the η1-
triazene and the triflate ligand in a mutually cis position.
observed in the H NMR spectra, with one large JPH value
and three small ones, agree with this arrangement.
Furthermore, the absence of a detectable coupling28
between the NH proton and the 31P nuclei of the phosphine
seems to suggest that structure II, with the diazene nitrogen
atom bonded to the central metal, is present in the low
exchange-limit conditions. The proton coupled 15N NMR
spectrum (Table 3) supports this hypothesis showing, at -80
1
15
°C, a doublet at -199.2 ppm with a J NH value of of 92 Hz
from the 15NH triazene nitrogen atom and a multiplet at
-15.6 ppm attributed to the Ar15NdN-15N diazenic atom
coupling with the phosphorus nuclei of the phosphine, in
agreement with a geometry of type II. The coupling between
the 15N and the 31P nuclei is also observed in the spectra of
the 31P NMR which appears as an AB2CX (X ) 15N)
(29) Albertin, G.; Antoniutti S.; Giorgi, M. T. Eur. J. Inorg. Chem. 2003,
2855-2866.
(30) It can be noted that the labeled 1,3-Ph15NdN15N(H)Ph free diazene
molecule is fluxional (see Figure S3), and at room temperature, no
NH signal was observed in the proton NMR spectra. At -30 °C a
broad signal appears which splits into two humps at -70 °C, and at
(28) Values between 2 and 10 Hz for the 3JHP were observed both in diazene
[Ru(ArNdNH)2P4](BPh4)2 and [Re(NHdNH)(CO)P4]BPh4 complexes
and in hydroxylamine [M(NH2OH)2P4](BPh4)2 (M ) Ru, Os)
derivatives.14c,29,31b
-90 °C, a well-resolved doublet with J
1
15NH
of 92 Hz appears. This
behavior may be explained on the basis of a proton exchange between
the two 15N nitrogen atoms in the molecule, which is fast at room
1
15
temperature and prevents the observation of the J
.
NH
Inorganic Chemistry, Vol. 45, No. 9, 2006 3823

Albertin et al.
Scheme 6
P ) P(OEt)3 (10), PPh(OEt)2 (11); Y- ) OTf-, BPh4-; Ar ) Ph (a)
Scheme 7
Figure 2. Cation of [OsH(PhNdNH){PPh(OEt)2}4]BPh4 (11a) (30%
probability level). Hydrogen atoms, except for two, were omitted for clarity.
analytical data have been obtained for the two complexes,
which were characterized spectroscopically (IR and NMR
data) and by the X-ray crystal structure determination of
[OsH(PhNdNH){PPh(OEt)2}4]BPh4 (11a). The ORTEP
diagram of the cation of 11a is shown in Figure 2.
[Os] ) OsP4
Aryldiazene Derivatives. Dihydrogen [OsH(η2-H2)P4]Y
-
The osmium atom in the cationic complex is coordinated
by four phosphonite ligands, a phenyl diazene group, and a
hydride ligand, which is cis to the diazene ligand. Unfortu-
nately, the position of the hydride ligand was not refined,
so its geometrical parameters are not precise. The coordina-
tion polyhedron can be described as a distorted octahedron
where the hydride and the diazene ligands are in the
equatorial positions. The other two equatorial position and
the axial positions are occupied by four PPh(OEt)2 phos-
phonite ligands. The main source of the distortion is the usual
bend of the ligand toward the position occupied by the
hydride ligand, as is shown by the value of the axial
P-Os-P angle of 166.70(3)° or the N11-Os-P1 angle of
165.91(9)°. The Os-P distances show that the phosphonite
trans to the diazene ligand is about 0.04 Å shorter than the
other three. The Os-N and C-N distances are as expected
for single bonds, although there are not any structural studies
on Os(II) complexes with diazene ligands to our knowledge.
The N(11)-N(12) distance, 1.241(4) Å, is typical for a
double bond and is within the range expected for aryldiazene
complexes.8b,e,31,32
(Y ) OTf-, BPh4 ) complexes slowly react with 1,3-
diaryltriazene to give the aryldiazene [OsH(ArNdNH)P4]-
BPh4 (10a and 11a) derivatives which were isolated in about
a 60% yield and characterized (Scheme 6).
The formation of an aryldiazene complex from the reaction
of a 1,3-triazene species is rather surprising because coor-
dinate aryldiazenes are generally obtained6-8 from the
+
insertion reaction of an aryldiazonium cation, ArN2 , into
the M-H bond of a hydride derivative. However, when the
properties of both the osmium η2-H2 complexes13 and of the
1,3-diaryltriazene molecule are taken into account, a reaction
path to explain the synthesis of hydride-diazene complexes
10 and 11 can be proposed (Scheme 7). Although the η2-H2
ligand in the osmium [OsH(η2-H2)P4]+ cations is stable to
the substitution by other ligands, such as triazene, it is
sufficiently acidic13a to be able to protonate the aminic
nitrogen atom of the 1,3-ArNdNN(H)Ar molecule. The
protonation of the triazene to the amine nitrogen atom can
result in cleavage of the N-N bond with formation of both
the amine, ArNH2, and the aryldiazonium cation, ArN2+. The
reaction of ArN2+ with the dihydride OsH2P4, formed from
the deprotonation of the [OsH(η2-H2)P4]+ cation, can give
the final aryldiazene derivatives 10a and 11a.
The phosphonite ligand being trans to the hydride ligand
allows a hydrogen bond to be established between the NH
group of the diazene ligand and the π-cloud of the phenyl
ring bond to the phosphorus atom, with parameters N-Ct
The presence of free ArNH2 amine (detected by 1H NMR)
in the reaction mixture and the known reactivity12c of the
dihydride OsH2P4 complexes toward aryldiazonium cations
+
ArN2 , which gives the same [OsH(ArNdNH)P4]+ deriva-
(31) (a) Albertin, G.; Antoniutti, S.; Pelizzi, G.; Vitali, F.; Bordignon, E.
J. Am. Chem. Soc. 1986, 108, 6627-6634. (b) Albertin, G.; Antoniutti,
S.; Pelizzi, G.; Vitali, F.; Bordignon, E. Inorg. Chem. 1988, 27, 829-
835.
(32) Melenkivitz, R.; Southern, J. S.; Hillhouse, G. L.; Concolino, T. E.;
Liable-Sands, L. M.; Rheingold, A. L. J. Am. Chem. Soc. 2002, 124,
12068-12069.
tives, support the path proposed in Scheme 7.
The osmium aryldiazene complexes, 10 and 11, were
isolated as stable diamagnatic yellow solids, soluble in polar
organic solvents, where behave like 1:1 electrolytes.22 Good
3824 Inorganic Chemistry, Vol. 45, No. 9, 2006

Triazenide and Triazene Complexes of Ru and Os
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 11a
with the path proposed in Scheme 7 for the formation of the
diazene derivative.
Os-N(11)
Os-P(3)
2.104(3)
2.3296(9)
2.3382(9)
1.423(4)
Os-P(1)
2.2716(9)
2.3297(9)
1.7848(2)
1.241(4)
Os-P(4)
Os-P(2)
Os-H(1)
N(11)-N(12)
Conclusions
N(12)-C(51)
In this paper we report the synthesis of unprecedented
complexes of ruthenium and osmium containing 1,3-diaryl-
triazene as a monodentate ligand. The complexes are
fluxional, and at -90 °C, a geometry with the diazene
nitrogen atom of the 1,3-ArNdNN(H)Ar ligand bonded to
the metal was proposed. The hydride-triazene [MH{η1-1,3-
ArNdNN(H)Ar}P4]+ species are unstable in some cases and
lead to the η2-triazenide [M(η2-1,3-ArNNNAr)P4]BPh4 de-
rivatives. However, a route for the facile synthesis of this
type of triazenide complexes of ruthenium and osmium can
be achieved using the κ2-triflate [M(κ2-O2SOCF3)P4]+ cation
as a precursor. The structural parameters for the chelate
triazenide [Ru(η2-1,3-PhNNNPh){P(OEt)3}4]BPh4 complex
were also obtained. Finally, we also report a new reaction
shown by the dihydrogen [OsH(η2-H2)P4]+ cation which
yields the aryldiazene [OsH(ArNdNH)P4]+ derivative when
treated with diaryltriazene 1,3-ArNdNN(H)Ar molecules.
A reaction path for this reaction, involving a N-N cleavage
of the triazene, is also proposed.
N(11)-Os-P(1)
P(1)-Os-P(3)
P(1)-Os-P(4)
N(11)-Os-P(2)
P(3)-Os-P(2)
165.91(9)
103.01(3)
90.67(3)
86.35(8)
92.13(3)
N(11)-Os-P(3)
N(11)-Os-P(4)
P(3)-Os-P(4)
P(1)-Os-P(2)
P(4)-Os-P(2)
90.91(9)
85.08(8)
98.15(3)
95.24(3)
166.70(3)
) 2.90(4) Å, H-Ct ) 3.694(3) Å, and N-H‚‚‚Ct )
149(4)°, where Ct represents the centroid of the ring.
1
The H NMR spectra of the aryldiazene complexes, 10
and 11 show, in addition to the signals of the phosphite and
the BPh4 anion, slightly broad signals at 14.47 (10a) and
13.42 (11a) ppm, attributed to the NH diazene proton, and
a multiplet between -7.78 and -8.68 ppm from the hydride
ligand. In the temperature range between +20 and -80 °C,
the 31P NMR data appear, for both compounds 10a and 11a,
as an AB2C multiplet, in agreement with a mutually cis
position of the hydride and the diazene ligand. On the basis
of these data, a geometry of type III (Scheme 6) like that
observed in the solid state can be reasonably proposed for
diazene complexes 10a and 11a. We have also prepared the
labeled [OsH(Ph15NdNH)P4]BPh4 (11a1) complex from the
reaction of Ph15NdN15N(H)Ph with [OsH(η2-H2)P4]+ and
recorded both the 1H and 15N NMR spectrum. In the proton
spectra, only one signal of the diazene 15NH proton is present
in the high region of the spectra at 13.4 ppm, and although
the broadness of this signal prevents the determination of
Acknowledgment. The financial support of MIUR (Rome),
PRIN 2004, is gratefully acknowledged. We thank Daniela
Baldan for technical assistance.
Supporting Information Available: Crystallographic data in
CIF format for complexes 2a and 11a and NMR data in Figures
S1, S2, and S3. This material is available free of charge via the
Internet at http://pubs.acs.org.
15
the J NH, the spectrum indicates that a value lower than 7-8
15NH
Hz for J
can be estimated. These data confirm that the
15N-labeled atom is in the â position, in further agreement
IC052063U
Inorganic Chemistry, Vol. 45, No. 9, 2006 3825