Nitrido-ruthenium(VI) and -osmium(VI) complexes containing chelating multianionic (N, O) ligands. Synthesis, crystal structures and reactions with triphenylphosphine

Article abstract of DOI:10.1039/a804204g

A series of nitrido-ruthenium(VI) and -osmium(VI) complexes containing chelating di-, tri- and tetra-anionic ligands was synthesized by ligand substitution reaction in methanol under room conditions in the presence of 2,6-dimethylpyridine. All the newly prepared complexes are air-stable diamagnetic solids. The crystal structures of seven complexes have been established by X-ray crystallography. The Ru≡N (1.615-1.594 A) and the Os≡N (1.612-1.621 A) bond distances are rather insensitive to the electron-donating power of the auxiliary ligands. All the nitridoruthenium(VI) complexes react spontaneously with triphenylphosphine, and the intermediate [Ru^IV(N=PPh₃)-L¹(py)Cl] has been isolated and characterized spectroscopically for the reaction with [Ru^VIN(L¹)Cl]. However, for those nitridoruthenium(VI) complexes bearing the tri- (L²)^3- and tetra-anionic (L^3,4)^4- ligands, the phosphiniminatoruthenium(IV) intermediate undergoes further reaction with pyrazole to generate a bis(pyrazole)ruthenium(IV) complex as the product.

Full text of DOI:10.1039/a804204g

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Nitrido-ruthenium(VI) and -osmium(VI) complexes containing
chelating multianionic (N, O) ligands. Synthesis, crystal structures
and reactions with triphenylphosphine
Pui-Ming Chan, Wing-Yiu Yu, Chi-Ming Che* and Kung-Kai Cheung*
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong
Received 4th June 1998, Accepted 15th July 1998
A series of nitrido-ruthenium() and -osmium() complexes containing chelating di-, tri- and tetra-anionic
ligands was synthesized by ligand substitution reaction in methanol under room conditions in the presence of
2,6-dimethylpyridine. All the newly prepared complexes are air-stable diamagnetic solids. The crystal structures
᎐
᎐
of seven complexes have been established by X-ray crystallography. The Ru᎐N (1.615–1.594 Å) and the Os᎐N
᎐
᎐
(1.612–1.621 Å) bond distances are rather insensitive to the electron-donating power of the auxiliary ligands. All the
nitridoruthenium() complexes react spontaneously with triphenylphosphine, and the intermediate [RuIV(N᎐PPh )-
᎐
3
L1(py)Cl] has been isolated and characterized spectroscopically for the reaction with [RuVIN(L1)Cl]. However, for
those nitridoruthenium() complexes bearing the tri- (L2)3Ϫ and tetra-anionic (L3,4 4Ϫ ligands, the phosphiniminato-
)
ruthenium() intermediate undergoes further reaction with pyrazole to generate a bis(pyrazole)ruthenium()
complex as the product.
Cl
Cl
Introduction
The study of metal–ligand multiple bonded (M᎐X) com-
᎐
plexes has received considerable attention.1 Of our particular
interest is the chemistry of high-valent oxo-, nitrido- and
imido-ruthenium and -osmium complexes, and their reactivities
toward organic substrates.2 While high-valent nitrido-
osmium() complexes of some amine and/or polypyridyl
ligands are known to exhibit interesting photochemistry3 and
electrochemistry,4,5 related studies on the ruthenium()
analogues are sparse in the literature. Electrochemical studies
revealed that high-valent oxoruthenium() complexes are at
least 500 mV more oxidizing than their osmium() counter-
parts;2,6 therefore, it is discernible that high-valent nitrido-
O
O
N
NH HN
HO
Ph
Ph
Ph
Ph
OH HO
tBu
N
H2L1
H3L2
Cl
Cl
ruthenium() complexes could be rather electrophilic and
O
O
O
O
᎐
reactive. Indeed, a N᎐Ru species has been postulated to be the
᎐
NH HN
NH HN
OH HO
active intermediate in the oxidation of bound ammonia to
nitrite.7 Herein we describe synthetic and structural studies of
some nitrido-ruthenium() and -osmium() complexes con-
taining chelating multianionic N, O ligands. Some of them have
been characterized by X-ray crystallography, and their nitrogen
atom transfer reactions to triphenylphosphine have also been
examined.
OH HO
H4L3
H4L4
O
O
NH HN
Experimental
N
N
Materials
H2L5
All solvents were purified by the standard methods before use.
The compounds [NBun ][RuVINCl4],8 2,6-bis(2-hydroxy-2,2-
4
diphenylethyl)pyridine (H2L1)9 and 1,2-bis(2-hydroxybenz-
amido)benzene10 (H4L3) were prepared according to the
reported procedures.
form instruments. Cyclic voltammetric measurements were
conducted using a Princeton Applied Research model 273
potentiostat with a glassy carbon electrode and Ag–AgNO3
(0.1 mol dmϪ3 in MeCN) as the reference electrode, and the
Physical measurements
deaerated dichloromethane solutions in 0.10 M tetra-n-
butylammonium hexafluorophosphate containing the sample
complexes were scanned under an argon atmosphere. Elemental
analyses were performed by Butterworth Co. Ltd., UK.
Infrared spectra were recorded as Nujol mulls on a Nicolet
model 20 FXC FT-IR spectrometer, fast atom bombardment
(FAB) mass spectra on a Finnigan MAT 95 mass spectrometer
using 3-nitrobenzyl alcohol as matrix, electrospray (ES) mass
spectra on a Finnigan LCQ mass spectrometer and NMR
spectra using Bruker DPX 300 and 500 pulsed Fourier trans-
X-Ray crystallography
X-Ray diffraction data were collected on either a Rigaku
J. Chem. Soc., Dalton Trans., 1998, 3183–3190
3183

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AFC7R or MAR diffractometer using graphite-monochrom-
atized Mo-Kα radiation (λ = 0.71073 Å) at 301 K. Intensity
data were corrected for Lorentz-polarization effects, and the
structures were solved by the Patterson method and expanded
by Fourier methods (PATTY).11 Structure refinements were per-
formed by full-matrix least squares using the software package
TEXSAN12 on a Silicon Graphics Indy computer. For com-
plexes 3a, 3b and 4a, disorder in the terminal carbon atoms of
column using diethyl ether–light petroleum (bp 40–60 ЊC) (9:2
v/v) as the eluent. The product was obtained as a white solid.
Yield: 0.85 g, 60%. IR (Nujol, cmϪ1) 3100 (νNH), 3000, 2890,
1680 (νC O). 1H NMR (300 MHz, 298 K, CDCl3) δ 1.69 (s, 12 H),
᎐
᎐
7.39 (t, 2 H, J = 6.1), 7.82 (t, 2 H, J = 7.7), 8.18 (d, 2 H, J = 7.7),
8.57 (d, 2 H, J = 3.8 Hz) and 8.91 (s, 2 H). 13C NMR (75.47
MHz, 298 K, CDCl3) δ 22.34, 60.68, 121.80, 124.61, 125.82,
137.19, 147.96, 150.91 and 164.25. MS m/z 326 (Mϩ) (Found:
C, 66.31; H, 6.82; N, 17.12. Calc. for C18H22N4O2: C, 66.24; H,
6.79; N, 17.17%).
one of the n-butyl groups of the [NBun ]ϩ cation was treated by
4
assigning occupation numbers of ca. 0.5 to the disordered
carbon atoms: 0.5 each to C(36) and C(37) in 3a, as well as to
C(36) and C(36Ј) in 3b; 0.55 and 0.45 to C(36) and C(36Ј) in 4a,
where the thermal parameters of these disordered carbon
atoms are comparable. For structures 5a and 5b the NH protons
were located in the Fourier difference syntheses and their
positional parameters included in the least squares refinement.
CCDC reference number 186/1097.
Syntheses of nitrido-ruthenium(VI) and -osmium(VI) complexes
[RuVIN(L1)Cl] 1. To a stirred solution of H2L1 (1 g, 2.1 mmol)
and 2,6-dimethylpyridine (0.5 cm3) in anhydrous chloroform
(10 cm3) was added a methanolic solution (30 cm3) of [NBun ]-
4
[RuVINCl4] (1 g, 2.0 mmol) and the mixture stirred for 2 h. The
purple precipitate formed was collected by filtration, and
washed first with chloroform then with diethyl ether. The
product was dried on a frit by vacuum suction. Yield: 0.46 g,
37% (Found: C, 63.70; H, 4.25; N, 4.45. Calc. for C33H27-
See http://www.rsc.org/suppdata/dt/1998/3183/ for crystallo-
graphic files in .cif format.
Ligand syntheses
ClN2O2Ru: C, 63.92; H, 4.39; N, 4.52%); IR (Nujol, cmϪ1
)
1
1-(4-tert-Butylpyridine-2-carboxamido)-4,5-dichloro-2-(2-
hydroxybenzamido)benzene (H3L2).10 To a stirred anhydrous 1,4-
dioxane (60 cm3) solution of N-(2-amino-4,5-dichlorophenyl)-
4-tert-butylpyridine-2-carboxamide (3.0 g, 8.9 mmol) was
slowly added O-acetylsalicyloyl chloride (1.8 g, 9.0 mmol). After
the mixture was stirred for 12 h water (ca. 100 cm3) was added
cautiously to the solution with stirring, and the resulting white
precipitate was collected by filtration and washed with water.
The solid was redissolved in 1,4-dioxane (50 cm3), and concen-
trated hydrochloric acid (15 cm3) added; the mixture was stirred
for 12 h. The reaction mixture was treated by dropwise addition
of water (ca. 100 cm3) to induce precipitation of the product,
and the solid was then collected on a frit and washed with
water. The crude product was recrystallized from acetone.
Yield: 2.4 g, 59%. IR (Nujol, cmϪ1) 3275 (νOH), 3111 (νNH), 2846,
1667 (νC O) and 1645 (νC O). 1H NMR (300 MHz, 298 K, CDCl3)
3060, 2922, 1600, 1573 and 1025. H NMR (300 MHz, 298 K,
CDCl3) δ 3.75 (d, 2 H, J = 14.8), 4.55 (d, 2 H, J = 14.8 Hz)
and 6.9–8.2 (m, 23 H). FAB MS m/z 585 (Mϩ Ϫ Cl) and 570
(Mϩ Ϫ Cl Ϫ N).
[MVIN(L2)] 2 (M ؍ Ru a or Os b). To a methanolic solution
(30 cm3) of [NBun ][MVI(N)Cl4] (0.2 g, 0.4 mmol) were added
4
H3L2 (0.13 g, 0.4 mmol) in chloroform (10 cm3) and 2,6-
dimethylpyridine (ca. 0.5 cmϪ3). The mixture was stirred for 2 h
and a brown precipitate gradually deposited. The brown solid
was collected, washed with acetone, and then dried in vacuo.
For 2a: yield 0.10 g (56%) (Found: C, 48.36; H, 3.04; N, 9.76.
Calc. for C23H18Cl2N4O3Ru: C, 48.43; H, 3.18; N, 9.82%); IR
(Nujol, cmϪ1) 2890, 1680 (νC O), 1620 (νC O) and 1102; 1H NMR
᎐
᎐
᎐
[300 MHz, 298 K, (CD3)2SO] δ 1.51 (᎐s, 9 H), 6.94 (t, 1 H,
J = 7.2), 7.24 (d, 1 H, J = 7.5), 7.42 (t, 1 H, J = 6.7), 8.29 (m,
3 H), 8.69 (s, 1 H) and 9.30 (d, 2 H, J = 5.7 Hz); FAB MS m/z
571 (Mϩ ϩ 1) and 558 (Mϩ Ϫ N). For 2b: yield 0.19 g (72%)
(Found: C, 41.66; H, 2.65; N, 8.44. Calc. for C23H18Cl2N4O3Os:
᎐
᎐
᎐
᎐
δ 1.38 (s, 9 H), 6.92 (m, 1 H), 7.00 (dd, 1 H, J = 8.4, 1.0), 7.43
(m, 1 H), 7.5 (dd, 1 H, J = 5.2, 1.9), 7.54 (s, 1 H), 7.75 (dd, 1 H,
J = 8.0, 1.3), 8.02 (s, 1 H), 8.31 (d, 1 H, J = 1.6), 8.50 (dd, 1 H,
J = 5.2, 0.5 Hz), 10.12 (s, 1 H), 10.32 (s, 1 H) and 12.05 (s, 1 H).
13C NMR (75.47 MHz, 298 K, CDCl3) δ 30.49, 35.24, 114.24,
118.67, 119.02, 119.90, 124.37, 124.61, 125.37, 126.38, 127.93,
129.32, 129.73, 130.32, 134.78, 147.93, 148.45, 162.19, 162.70,
164.28 and 168.72. MS m/z 458 (Mϩ) (Found: C, 60.18; H,
4.58; N, 9.23. Calc. for C23H21Cl2N3O3: C, 60.27; H, 4.62; N,
9.17%).
C, 41.89; H, 2.75; N, 8.49%). IR (Nujol, cmϪ1) 2890, 1690 (νC O),
᎐
᎐
1
1620 (νC O) and 1068; H NMR [300 MHz, 298 K, (CD3)2SO]
᎐
δ 1.45 (s᎐, 9 H), 6.93 (m, 1 H), 7.23 (d, 1 H, J = 8.1), 7.43 (m,
1 H), 8.23 (dd, 1 H, J = 8.1, 1.5), 8.29 (d, 2 H, J = 2.6 Hz), 8.66
(s, 1 H), 9.21 (s, 1 H) and 9.27 (m, 1 H); FAB MS m/z 661
(Mϩ ϩ 1).
[NBun4][MVIN(L3)] 3 (M ؍ Ru a or Os b). To a stirred meth-
1,2-Dichloro-4,5-bis(2-hydroxybenzamido)benzene (H4L4). A
anolic solution (10 cm3) of [NBun ][MVINCl4] (0.5 g, 1.0 mmol)
4
similar procedure was employed as for the preparation of H3L2.
was added H4L3 (0.35 g, 1.0 mmol) and 2,6-dimethylpyridine
(ca. 0.5 cm3), and the mixture was stirred for 1 d. Solvent evap-
oration by vacuum left an oily residue, which was chromato-
graphed on an alumina column (activity 90, neutral) using
chloroform as the eluent. The orange (Ru) or yellow (Os) band
was collected in one portion and concentrated to ca. 2 cm3 by
rotary evaporation. Addition of diethyl ether to the red solu-
tion led to isolation of the complex as orange or yellow prism-
shaped crystals. The crystalline solid was collected on a frit and
dried in vacuo. For 3a: yield 0.3 g (43%) (Found: C, 61.52; H,
6.76; N, 7.76. Calc. for C36H48N4O4Ru: C, 61.61; H, 6.89; N,
Yield: 1.8 g, 76%. IR (Nujol, cmϪ1) 3280 (νOH), 3100 (νNH), 2880,
1
1650 (νC O). H NMR [300 MHz, 298 K, (CD3)2CO] δ 6.96 (d,
᎐
4 H, J =᎐7.9), 7.47 (dt, 2 H, J = 7.9, 1.4), 8.02 (dd, 2 H, J = 8.4,
1.6 Hz), 8.14 (m, 2 H), 10.15 (s, 2 H) and 11.49 (s, 2 H). 13C
NMR [75.47 MHz, 298 K, (CD3)2CO] δ 116.61, 118.46, 120.37,
127.74, 129.19, 129.63, 131.76, 135.45, 160.65 and 168.62. MS
m/z 417 (Mϩ) (Found: C, 57.49; H, 3.29; N, 6.81. Calc. for
C20H14Cl2N2O4: C, 57.57; H, 3.38; N, 6.71%).
2,3-Dimethyl-2,3-bis(pyridine-2-carboxamido)butane (H2L5).
Pyridine-2-carboxylic acid (1.06 g, 8.17 mmol) was added to
neat SOCl2 (ca. 10 cm3), and the mixture refluxed for 3 h. An
excess of SOCl2 was removed by vacuum evaporation. The solid
residue was redissolved in dichloromethane (30 cm3), and the
solution added dropwise to another dichloromethane solution
(30 cm3) of 2,3-diamino-2,3-dimethylbutane (0.5 g, 4.31 mmol)
and triethylamine (ca. 3 cm3). The mixture was allowed to stand
overnight with stirring. Removal of solvent under vacuum left
an oily substance. The crude product was purified on a silica gel
7.98%); IR (Nujol, cmϪ1) 3066, 2850, 1615 (νC O), 1580 and
᎐
᎐
1
1073; H NMR (300 MHz, 298 K, CDCl3) δ 0.78 (t, 12 H,
J = 7.0), 1.13 (m, 16 H), 2.63 (m, 8 H), 6.91 (m, 2 H), 6.99 (m,
2 H), 7.27 (d, 2 H, J = 6.9), 7.36 (m, 2 H), 8.20 (dd, 2 H, J = 7.9,
1.6 Hz) and 8.89 (m, 2 H); FAB MS (negative) m/z 460 (MϪ).
For 3b: yield 0.54 g (68%) (Found: C, 54.48; H, 6.19; N, 7.22.
Calc. for C36H48N4O4Os: C, 54.66; H, 6.12; N, 7.08%); IR
(Nujol, cmϪ1) 3064, 2580, 1625 (νC O), 1595 and 1108; 1H
᎐
᎐
NMR (300 MHz, 298 K, CDCl3) δ 0.80 (t, 12 H, J = 7.0), 1.15
3184
J. Chem. Soc., Dalton Trans., 1998, 3183–3190

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(m, 16 H), 2.63 (m, 8 H), 6.97 (m, 4 H), 7.36 (m, 4 H), 8.27 (d, 2
H, J = 7.8) and 8.97 (dd, 2 H, J = 6.3, 3.5 Hz); FAB MS (nega-
tive) m/z 548 (MϪ).
diethyl ether into its acetonitrile solution, and a dark green
microcrystalline solid was collected by filtration. For [NBun ]-
4
[RuIVL3(Hpz)(pz)]: yield 80 mg (76%) (Found: C, 61.11; H,
6.66; N, 11.89. Calc. for C42H55N7O4Ru: C, 61.29; H, 6.74; N,
[NBun ][MVIN(L4)] 4 (M ؍ Ru a or Os b). The complexes were
synthesized in a manner similar to that for 3. For 4a: yield 0.14
11.91%); IR (Nujol, cmϪ1) 2925, 1595 (νC O) and 1460; ES MS
4
᎐
᎐
(negative) m/z 581 (MϪ). For [NBun ][RuIVL4(Hpz)(pz)]: yield
4
g, 53% (Found: C, 56.03; H, 6.06; N, 7.32. Calc. for C36H46-
96 mg (83%) (Found: C, 56.45; H, 5.88; N, 10.78. Calc. for
C42H53Cl2N7O4Ru: C, 56.56; H, 5.99; N, 10.99%); IR (Nujol,
Cl2N4O4Ru: C, 56.10; H, 6.02; N, 7.27%); IR (Nujol, cmϪ1
)
1
cmϪ1) 2930, 1600 (νC O) and 1460; ES MS (negative) m/z 649
3020, 2965, 2870, 1600 and 1010; H NMR (300 MHz, 298 K,
CDCl3) δ 0.84 (t, 12 H, J = 7.1), 1.18 (m, 8 H), 1.32 (m, 8 H),
2.80 (m, 8 H), 6.93 (m, 2 H), 7.28 (d, 2 H, J = 9.2), 7.35 (m, 2 H),
8.19 (d, 2 H, J = 7.9 Hz) and 9.21 (s, 2 H); FAB MS (negative)
m/z 528 (MϪ). For 4b: yield 0.66 g (77%) (Found: C, 50.33; H,
5.23; N, 6.67. Calc. for C36H46Cl2N4O4Os: C, 50.28; H, 5.39; N,
᎐
᎐
(MϪ).
[RuIVL2(Hpz)(pz)]. A round-bottom flask (25 cm3) was
charged with complex 2a (100 mg, 0.17 mmol), pyrazole (198
mg, 0.35 mmol), triphenylphosphine (46 mg, 0.17 mmol) and
dichloromethane (10 cm3). The orange-brown suspension was
stirred for 0.5 h, and a homogeneous dark brown solution
resulted. After complete removal of solvent by rotary evapor-
ation a brown solid was isolated. The solid residue was
extracted by diethyl ether (3 × 20 cm3), and the combined
6.52%); IR (Nujol, cmϪ1) 3020, 2990, 2850, 1600(νC O) and 1110;
᎐
᎐
1H NMR (300 MHz, 298 K, CDCl3) δ 0.85 (t, 12 H, J = 7.1),
1.19 (m, 8 H), 1.32 (m, 8 H), 2.76 (m, 8 H), 6.95 (m, 2 H), 7.37
(m, 4 H), 8.26 (dd, 2 H, J = 8.0, 1.5 Hz) and 9.28 (s, 2 H); FAB
MS (negative) m/z 617 (MϪ).
organic extracts were evaporated to dryness to leave HN᎐PPh
᎐
3
[MVIN(H2L5)Cl3] 5 (M ؍ Ru a or Os b]. To a stirred solution
as a white residue [EI MS m/z = 277 (Mϩ); 31P NMR δ ϩ30.1].
The remaining brown solid was recrystallized by slow diffusion
of diethyl ether into its chloroform solution, and a brown
microcrystalline solid was isolated by filtration. Yield: 100 mg,
88% (Found: C, 50.25; H, 3.45; N, 14.32. Calc. for C29H25-
of [NBun ][MVI(N)Cl4] (0.5 g, 1.0 mmol) in methanol (10 cm3)
4
were added H2L5 (0.326 g, 1.0 mmol) in chloroform (5 cm3) and
a few drops of 2,6-dimethylpyridine and stirred for 3 h. The
pink solid formed was collected, washed with methanol and
dried in vacuo. For 5a: yield 0.21 g (38%) (Found: C, 39.36; H,
4.22; N, 12.62. Calc. for C18H22Cl3N5O2Ru: C, 39.46; H, 4.05;
Cl2N7O3Ru: C, 50.37; H, 3.64; N, 14.18%); IR (Nujol, cmϪ1
)
2850, 1680 (νC O), 1630 (νC O) and 1460. FAB MS m/z 693
᎐
᎐
᎐
᎐
N, 12.78%); IR (Nujol, cmϪ1) 3320 (νNH), 2950, 1650 (νC O), 1640
(Mϩ ϩ 1).
᎐
᎐
(νC O) and 1067; 1H NMR (300 MHz, 298 K, CDCl3) δ 1.53 (s,
᎐
᎐
6 H), 1.61 (s, 6 H), 7.53 (t, 1 H, J = 6.0), 7.92 (m, 2 H), 8.20 (d,
1 H, J = 7.9), 8.42 (t, 1 H, J = 7.3), 8.54 (s, 1 H), 8.59 (d, 1 H,
J = 4.4), 8.78 (d, 1 H, J = 7.9), 9.27 (d, 1 H, J = 7.1 Hz) and
11.40 (s, 1 H); FAB MS m/z 512 (Mϩ Ϫ Cl). For 5b: yield 0.35 g
(55%) (Found: C, 33.77; H, 3.55; N, 10.83. Calc. for C18H22Cl3-
Results and discussion
Synthesis and spectral characterization
Multianionic chelating ligands are strong σ donors capable
of stabilizing metal ions in high oxidation states. Notable
examples are complexes of CuIII, MnV and FeIV which are
readily attainable by using tetraanionic amide ligands.13 In this
work we have prepared a series of auxiliary (N, O) ligands,
H2L1, H3L2 and H4L3,4, with different electronic charges upon
deprotonation of the amide and hydroxyl groups. The H2L1
ligand was first reported by Berg and Holm,9 and its high-valent
dioxo- and nitrido-osmium(),14 oxo-9 and bis(imido)-molyb-
denum()15 derivatives have been prepared and structurally
characterized. On the contrary, the use of tetradentate tri-
anionic ligands to support high-valent metal centres has
received relatively less attention, a noteworthy example being
the preparation of an iron() metallocorrole complex by Vogel
et al.16 The H3L2 ligand was prepared by the method developed
by Kabanos and co-workers.10,17 The presence of a tert-butyl
substituent rendered the ligand more soluble in organic sol-
vents. We are interested to examine the effect of the electron-
donating strength (in terms of formal anionic charge) of the
N5O2Os: C, 33.94; H, 3.48; N, 10.99%); IR (Nujol, cmϪ1
)
3320(νNH), 2950, 1660(νC O), 1640(νC O)and1112;1HNMR(300
᎐
᎐
᎐
᎐
MHz, 298 K, CDCl3) δ 1.52 (s, 6 H), 1.62 (s, 6 H), 7.54 (dd, 1 H,
J = 7.1, 4.7), 7.87 (t, 1 H, J = 6.5), 7.95 (dt, 1 H, J = 7.8, 1.4),
8.21 (d, 1 H, J = 7.8), 8.31 (t, 1 H, J = 7.8), 8.57 (s, 1 H), 8.60 (d,
1 H, J = 4.4), 8.82 (d, 1 H, J = 8.0), 9.15 (d, 1 H, J = 5.4 Hz) and
11.63 (s, 1 H); FAB MS m/z 637 (Mϩ) and 602 (Mϩ Ϫ Cl).
Reactions with triphenylphosphine
[RuIV(NPPh3)L1(py)Cl]. Triphenylphosphine (42 mg, 0.16
mmol) was added under an argon atmosphere to a dichloro-
methane solution (20 cm3) of complex 1 (100 mg, 0.16 mmol)
and pyridine (1 cm3) with stirring. An instantaneous change
from yellow-orange to a dark green solution occurred; this was
stirred for 1 h and the solvent removed by rotary evaporation.
The green residue was then loaded on an alumina column and
eluted with chloroform, the green band being collected in one
fraction. After solvent evaporation a green solid was obtained.
Yield: 90 mg (58%) (Found: C, 69.88; H, 4.75; N, 4.55. Calc. for
C56H47ClN3O2PRu: C, 69.95; H, 4.93; N, 4.37%); IR (Nujol,
᎐
auxiliary ligands on the M᎐N functions, especially on its
᎐
electrophilicity. We envisaged that the increase in σ donation
from the ligand would promote the electron density at the metal
centre; as a result the electrophilicity of the nitrido ligand
would be reduced.1
1
cmϪ1) 2850, 1650 (νC O), 1605 and 1160 (νN P). H NMR (300
᎐
᎐
MHz, 298 K, CDCl3᎐) δ 3.32 (d, 2 H, J = 1᎐4.6), 4.90 (d, 2 H,
J = 14.6 Hz) and 6.90–7.90 (m, 38 H). 31P NMR (202.48 MHz,
298 K, CDCl3) δ ϩ66.41. FAB MS m/z 926 (Mϩ).
Several methods are known for the preparation of high-
valent terminal nitrido-ruthenium() and -osmium() com-
plexes: (1) oxidative deprotonation of co-ordinated amines,3a
(2) thermal decomposition of azidoosmium complexes,8,18 and
recently (3) reduction of nitrosyl complexes.19 A synthetic route
based on the ligand substitution reactions of [MVINCl4]Ϫ pro-
vides the easiest entry to our target complexes, and similar
methods had previously been exploited by Shapley and co-
workers20 for the preparation of nitrido-ruthenium() and
-osmium() bearing anionic N, S, O or carboxylate ligands.
[NBun4][RuIVL(Hpz)(pz)] (L ؍ L3 or L4). A light orange
acetonitrile solution containing the nitridoruthenium complex
3a or 4a (100 mg, 0.13 mmol) and pyrazole (Hpz, 198 mg, 0.26
mmol) was treated with triphenylphosphine (34 mg, 0.13 mmol)
under an argon atmosphere; an instantaneous change to dark
green occurred. The reaction mixture was stirred for 15 min and
then rotary evaporated to dryness to leave a dark green solid.
The solid was extracted by diethyl ether (3 × 20 cm3), and the
combined organic extracts were evaporated to dryness to leave
HN᎐PPh as a white solid [EI MS 277 (Mϩ); 31P NMR δ ϩ30.1].
Treatment of [NBun ][MVINCl4] with HnL1–4 (n = 1–4) in
4
methanol–chloroform (5:1 v/v) with a few drops of 2,6-
᎐
3
The dark green residue was recrystallized by slow diffusion of
dimethylpyridine (acting as a base) affords the desired nitrido-
J. Chem. Soc., Dalton Trans., 1998, 3183–3190
3185

View Article Online
N
[NBun
]
4
Cl
Cl
Cl
Cl
MVI
M = Ru, Os
(i)
(ii)
N
N
O
N
O
VI
VI
M
O
O
M
Cl
N
N
Fig. 1 Perspective view of [RuVIN(L4)]Ϫ 4a.
1
3
N
Cl
Cl
N
ligand absorptions in the same spectral region. Their UV/VIS
spectra are featureless and dominated by intense absorption(s)
at λ < 250 nm. Complexes 1, 3a, 3b and 4a, 4b show similar 1H
NMR spectral patterns to those of their respective unbound
ligands, suggesting that the mirror symmetry of the chelating
ligands is retained after co-ordination. For 3 and 4 the aromatic
protons on the ligands are downfield-shifted relative to the
unbound states probably due to inductive withdrawal of elec-
trons by the electrophilic metal centre. All the 1H NMR spectra
of the nitridometal complexes show no amido and phenolic
proton absorptions, consistent with the infrared results that the
MVI
N
O
N
But
N
O
N
O
VI
2
M
N
4
Scheme 1 (i) For H2L1 and H3L2, 2,6-dimethylpyridine, MeOH–CHCl3,
room temperature (r.t.); (ii) for H4L3 and H4L4, 2,6-dimethylpyridine,
MeOH, r.t.
1
ligands are in their deprotonated forms. The H NMR spectra
of the ruthenium and the analogous osmium complexes
revealed similar patterns implying an isostructural relationship.
N
[NBun
]
4
Cl
Cl
M = Ru, Os
Cl
MVI
Structural studies of the nitrido-ruthenium and -osmium
complexes
Cl
The crystal structures of some nitrido-ruthenium() (1, 3a,
4a and 5a) and -osmium() (2b, 3b and 5b) complexes were
determined by single-crystal X-ray diffraction method. The
crystal data, selected bond distances and angles are listed in
Tables 1 and 2 respectively. All the nitridometal complexes pre-
pared in this work are five-co-ordinated (except 5a and 5b); this
can be ascribed to the strong trans effect exerted by the nitride
(N3Ϫ) ligand.
H2L5
MeOH, r.t.
Cl
M
N
Cl
Cl
O
N
H
N
N
N
H
O
As revealed by X-ray crystal analysis, complexes 3a and 4a
are isostructural, and for illustration a perspective view of 4a
is shown in Fig. 1. Both complexes adopt a distorted square
pyramidal co-ordination with the terminal nitride ligand in the
apical position. The metal centre is slightly elevated by ≈0.58 Å
from the mean equatorial plane consisting of the four N- and
O-donor atoms; a similar structural feature has been found for
some other nitridometal complexes.21 The RuVI᎐N (amide)
bond distances for 3a and 4a are in a range of 1.991(6)–2.006(3)
Å, significantly shorter than the RuII᎐N(sp3) {2.144(4) Å in
[Ru(NH3)6]I2},22 RuIII᎐N(sp3) {2.104–2.117 Å in cis-[RuIII-
5
Scheme 2
metal complexes in moderate to good yields (Scheme 1). How-
ever, this method is apparently limited to those ligands bearing
OH groups, for example a pyridine amide ligand (H2L5) lacking
any OH groups failed to effect metal encapsulations, instead
pyridyl nitrido-ruthenium() and -osmium() adducts
[MVIN(H2L5)Cl3] 5a and 5b were produced (Scheme 2). Com-
plexes 1, 2a, 2b and 5a, 5b were isolated as insoluble solids in
([14]aneN4)Cl2]Cl}23 and RuIV᎐N(sp3) {2.085–2.141(5)
Å
1
good purities as revealed by H NMR spectroscopy. Analytic-
in trans-[RuIV(tmc)O(MeCN)][PF6]2}24 ([14]aneN4 = 1,4,8,11-
tetraazacyclotetradecane, tmc = 1,4,8,11-tetramethyl-1,4,8,11-
tetraazacyclotetradecane) distances involving saturated amine
ligands, but the values are close to those [1.987(5)–2.044(5) Å]
of [RuIV(chbae)(PPh3)(py)]25 [chbae = 1,2-bis(3,5-dichloro-2-
hydroxybenzamido)ethane tetraanion].
ally pure samples of 3a, 3b and 4a, 4b were obtained after
purification by column chromatography on alumina using
chloroform as the eluent. Good quality crystals were grown by
slow diffusion of diethyl ether into dichloromethane or chloro-
form solutions.
All the nitrido complexes prepared in this work are dia-
magnetic solids, consistent with the formulation of a singlet
Complexes 5a and 5b are six-co-ordinated and isostructural;
the metal atoms adopt a distorted octahedral co-ordination
2
5
᎐
᎐
(d ) electronic ground state (taking the M᎐N axis as the z
where the pyridine amide ligand (H L ) binds to the M᎐N
᎐
᎐
xy
2
direction). Their infrared spectra do not show any NH and/or
OH stretches, suggesting that the chelating ligands are in com-
moiety in a bidentate fashion via the pyridyl nitrogen and the
carbonyl oxygen atoms. The carbonyl oxygen atom is opposite
to the N3Ϫ ligand. The Ru᎐N and Os᎐N distances are found to
᎐
᎐
᎐
pletely deprotonated forms. However the M᎐N stretches cannot
᎐
᎐
᎐
be unequivocally assigned because of extensive overlap with the
be 1.598(3) and 1.612(5) Å respectively.
3186
J. Chem. Soc., Dalton Trans., 1998, 3183–3190

View Article Online
O
VI
N
Ru
N
PPh3
Cl
O
py/CH2Cl2
PPh3
N
O
O
O
O
N
RuIII(py)3 Cl
prolonged reaction
py
N
RuIV
Fig. 2 Perspective view of [RuVIN(L1)Cl] 1.
Cl
structure
determined
Scheme 3
unsaturation in, equatorial macrocyclic amine ligands.24 The
Os–O(1) (2.010 Å) and Os–N (amide) (2.004 and 1.962 Å) dis-
tances are comparable to those for [NBun ][OsVIN(L3)] 3b [Os–
4
O 1.97 Å, Os–N (amide) 2.010 and 2.011 Å]. The Os–N (py)
distance (2.088 Å) is also close to the reported value (2.119 Å)
for [OsVIN(L1)Cl].14
Nitrogen-atom transfer reactions of nitridoruthenium to PPh3
To examine the possible influence of the electron-donating
power of the auxiliary ligands on the electrophilicity of the
᎐
Ru᎐N function, triphenylphosphine was used as a nucleophile
᎐
to effect a series of nitrogen atom transfer reactions. When
[RuVIN(L1)Cl] was treated with a stoichiometric amount of
PPh3 in dry dichloromethane–pyridine (20:1) an instantaneous
change from a yellow orange to dark green solution occurred
(Scheme 3). After column chromatography on alumina a green
solid was isolated. The IR spectrum of the green compound
revealed a strong absorption peak at 1106 cmϪ1 which is con-
spicuously absent from the spectrum of complex 1. According
Fig. 3 Perspective view of [OsVIN(L3)] 2b.
The structure of complex 1 (Fig. 2) is again isostructural to
the osmium() analogue [OsVIN(L1)Cl] reported earlier,14 and
the co-ordination polyhedron around the metal atom can be
described as distorted trigonal bipyramidal with the N(1), O(1)
and O(2) atoms on the trigonal plane. The N(2)᎐Ru᎐Cl(1) axis
significantly deviates from linearity [167.0(1)Њ]. The respective
N(1)᎐Ru᎐O(1), O(1)᎐Ru᎐O(2) and N(1)᎐Ru᎐O(2) bond angles
are 117.7(2), 129.2(1) and 112.4(2)Њ, and the two six-membered
chelate rings are in a gauche conformation. The trigonal plane
defined by the Ru, N(1), O(1) and O(2) atoms is a near isosceles
triangle. The Ru᎐O(1) and the Ru᎐O(2) bond distances are
1.902(3) and 1.921(3) Å respectively, comparable to those
[2.007(3) and 1.897(3) Å] found in [NPr4][RuVO(phab)]26
to related studies this could be assigned as a N᎐P stretch.29
᎐
The 31P NMR spectrum of the compound showed a singlet at δ
ϩ66.4 vs. 85% H3PO4, which is close to other reported values
for a phosphiniminate co-ordinated to a metal centre.30 With
1
the aid of mass spectroscopy (Mϩ Ϫ Cl m/z = 926), H NMR
and elemental analysis, the green solid can be formulated as
[RuIV(N᎐PPh )L1(py)Cl]. When the triphenylphosphine reduc-
᎐
3
tion was monitored by 31P NMR spectroscopy in a CD2Cl2–
C D N mixture [RuIV(N᎐PPh )L1(py)Cl] (31P = δ ϩ66.4) was
᎐
5
5
3
formed instantaneously upon mixing the reactants, no absorp-
tion (δ Ϫ3.5) corresponding to free PPh3 being detected indi-
cates that all PPh3 was consumed on the NMR timescale.
However, on prolonged standing (14 h) of the reaction mixture
the 31P NMR spectrum revealed only a singlet at δ ϩ30.1
[phab = 1,2-bis(2-hydroxy-2,2-diphenylethanamido)benzene
᎐
tetraanion]. The Ru᎐N distance of 1.615(4) Å is close to that
᎐
found in the tetraanionic (L3)4Ϫ [1.594(4) Å] and (L4)4Ϫ [1.609(6)
Å] analogues. On the other hand the alkoxide (OϪ) and amide
(NϪ) donor atoms of the L3 and L4 tetraanions are regarded as
considerably more basic than the chloride ligand; notwithstand-
(Ph P᎐NH) and the complex [RuIIIL1(py) ]Cl was isolated and
᎐
3
3
characterized by spectroscopic as well as X-ray crystallographic
᎐
ing, these Ru᎐N distances are comparable to those found for
means.31
᎐
VI
5
VI
Ϫ
᎐
᎐
[Ru N(H L )Cl ] 5a [Ru᎐N 1.598(3) Å], [Ru NCl ] (Ru᎐N
Likewise complexes 2a, 3a and 4a undergo facile reactions
with triphenylphosphine, however we were unable to isolate
analytically pure ruthenium() phosphiniminato complexes
when CH2Cl2–pyridine (20:1) was employed as the reaction
medium (Scheme 4). The 31P NMR spectra recorded for their
reactions with PPh3 in CD2Cl2–C5D5N mixture revealed a weak
᎐
᎐
2
3
4
1.570 Å)22 and [Ru NMe ] (Ru᎐N 1.58 Å).
VI
Ϫ
27
᎐
᎐
4
Although we could not obtain crystals of [RuVIN(L2)] 2a
suitable for X-ray crystal analysis, the molecular structure of
the osmium() analogue 2b has been determined. As shown in
Fig. 3, complex 2b is five-co-ordinated and exhibits distorted
square pyramidal co-ordination at the osmium centre; the
singlet absorption at δ ϩ30.1 (Ph P᎐NH) only, and yet no free
᎐
3
᎐
Os᎐N bond distance was found to be 1.621(4) Å. Similar
PPh3 was detected. When the triphenylphosphine reductions
were carried out using CH2Cl2 (2a) or MeCN (3a and 4a) as
solvent in the presence of an excess of pyrazole (Hpz) (10
᎐
᎐
insensitivity of the Os᎐N bond distances to the number of
᎐
anionic donor atoms is also observed for the isostructural
nitridoosmium() analogues [OsVIN(L1)Cl] [1.634(5) Å],22
equivalents vs. Ru᎐N) some green crystalline solids were
᎐
᎐
[NBun ][OsVIN(L3)] 3b [1.618(7) Å], [OsVIN(H2L5)Cl3] 5b
obtained by addition of diethyl ether (>76% isolated yield).
The product complexes are paramagnetic solids with µeff = 2.9
µB (µB = 9.27 × 10Ϫ24 J TϪ1) consistent with a ground state
electronic configuration with two unpaired electrons (S = 1)
4
[1.612(5) Å] and [OsVINCl5]2Ϫ (1.614 Å).28 Unlike the oxoruthe-
nium() systems, the O᎐Ru bond strength is sensitive to the
᎐
electron-donating power of, as well as the presence of π
J. Chem. Soc., Dalton Trans., 1998, 3183–3190
3187

Table 1 Crystallographic data for the nitrido-ruthenium(VI) and -osmium(VI) complexes
1
2b
3a
4aؒCHCl3
3b
5a
5b
Formula
M
C33H27ClN2O2Ru
620.11
C23H18Cl2N4O3Os
659.53
C36H48N4O4Ru
701.87
C37H47Cl5N4O4Ru
890.14
C36H48N4O4Os
791
C18H22Cl3N5O2Ru
546.83
C18H22Cl3N5O2Os
635.96
Crystal symmetry
Space group
a/Å
b/Å
c/Å
α/Њ
β/Њ
Monoclinic
P21/n (no. 14)
9.609(7)
18.444(7)
16.099(8)
Monoclinic
P21/n (no. 14)
14.107(2)
10.225(1)
15.216(9)
Orthorhombic
Pbca (no. 61)
15.346(3)
19.721(3)
22.744(4)
Triclinic
P1 (no. 2)
Orthorhombic
Pbca (no. 61)
19.816(2)
22.746(4)
15.430(2)
Monoclinic
P21/n (no. 14)
11.817(2)
10.165(2)
19.091(3)
Monoclinic
P21/n (no. 14)
11.825(2)
10.276(4)
19.011(1)
¯
12.074(2)
13.118(2)
13.648(2)
75.65(2)
84.14(2)
86.46(2)
2081.8(6)
2
104.56(5)
91.581(7)
100.72(2)
100.952(7)
γ/Њ
U/Å3
2761(2)
4
2194.0(4)
4
6883(1)
8
6955(1)
8
2254.3(8)
4
2267.9(8)
4
Z
Diffractometer
Dc/g cmϪ3
No. collected data
No. unique data
No. data used
No. parameters
µ(Mo-Kα)/cmϪ1
F(000)
Rigaku AFC7R
1.491
5355
5040
3454
352
6.98
1264
Rigaku AFC7R
1.997
4051
3884
3223
298
60.87
1272
0.020
0.028
1.39
MAR
1.354
53014
7048
3902
405
MAR
1.420
28929
5737
3695
458
7.39
916
0.056
0.076
Rigaku AFC7R
1.511
6753
6753
3047
405
37.08
3200
0.031
0.041
1.29
MAR
1.611
20165
4128
2986
265
10.74
1100
0.032
0.046
2.24
Rigaku AFC7R
1.862
4464
4247
2944
265
59.96
1228
0.028
0.030
1.33
4.99
2944
0.042
0.056
2.14
R
RЈ
0.041
0.046
1.80
Goodness of fit
1.52
¹
R = Σ||Fo| Ϫ |Fc||/Σ|Fo|; RЈ = [Σw(|Fo| Ϫ |Fc|)2/ΣwFo ]² where w = 4Fo /σ2(Fo ).
2
2
2

View Article Online
Table 2 Selected bond distances (Å) and angles (Њ) for the ruthenium(VI) and osmium(VI) nitrido complexes
Complex 1
Complex 2b
Ru᎐N(1)
Ru᎐N(2)
Ru᎐O(1)
Ru᎐O(2)
Ru᎐Cl
1.615(4)
2.125(4)
1.902(3)
1.921(3)
2.366(1)
N(1)᎐Ru᎐N(2)
O(1)᎐Ru᎐O(2)
N(1)᎐Ru᎐O(1)
N(1)᎐Ru᎐O(2)
O(1)᎐Ru᎐O(2)
N(2)᎐Ru᎐Cl
95.3(2)
129.2(1)
117.7(2)
112.4(2)
129.2(1)
167.0(1)
Os᎐N(1)
Os᎐N(2)
Os᎐N(3)
Os᎐N(4)
Os᎐O(1)
1.621(4)
2.004(3)
1.962(3)
2.088(3)
2.010(3)
N(1)᎐Os᎐N(2)
N(1)᎐Os᎐N(3)
N(1)᎐Os᎐N(4)
N(1)᎐Os᎐O(1)
N(2)᎐Os᎐N(4)
O(1)᎐Os᎐N(3)
104.0(2)
107.4(2)
98.2(1)
105.4(2)
154.7(1)
147.2(1)
Complex 3aa
Complex 4a
Ru᎐N(1)
Ru᎐N(2)
Ru᎐N(3)
Ru᎐O(1)
Ru᎐O(2)
1.594(4)
N(1)᎐Ru᎐N(2)
N(1)᎐Ru᎐N(3)
N(1)᎐Ru᎐O(1)
N(1)᎐Ru᎐O(2)
N(2)᎐Ru᎐O(2)
O(1)᎐Ru᎐N(3)
105.8(2)
106.0(2)
108.4(2)
108.0(1)
146.2(1)
145.6(1)
Ru᎐N(1)
Ru᎐N(2)
Ru᎐N(3)
Ru᎐O(1)
Ru᎐O(2)
1.609(6)
1.991(5)
1.992(6)
1.960(4)
1.955(5)
N(1)᎐Ru᎐N(2)
N(1)᎐Ru᎐N(3)
N(1)᎐Ru᎐O(1)
N(1)᎐Ru᎐O(2)
N(2)᎐Ru᎐O(2)
O(1)᎐Ru᎐N(3)
105.8(3)
106.8(3)
108.3(3)
107.3(3)
146.9(2)
144.9(2)
2.006(3)
1.992(4)
1.956(3)
1.957(3)
Complex 3ba
Os᎐N(1)
Os᎐N(2)
Os᎐N(3)
Os᎐O(1)
Os᎐O(2)
1.618(7)
N(1)᎐Os᎐N(2)
N(1)᎐Os᎐N(3)
N(1)᎐Os᎐O(1)
N(1)᎐Os᎐O(2)
N(2)᎐Os᎐O(2)
O(1)᎐Os᎐N(3)
107.0(3)
106.1(3)
109.0(3)
107.4(3)
145.5(2)
144.9(2)
2.011(6)
2.010(6)
1.969(5)
1.977(5)
a Same atom labelling scheme is adopted.
observe the ruthenium() intermediate by 31P NMR spectro-
scopy could be ascribed to the paramagnetic nature of the
molecule.
Hpz
n
N
n
+
PPh3 / Hpz (excess)
CH2Cl2 or MeCN
RuIVL
HN PPh3
RuVIL
Despite previous reports that [OsVIN(terpy)Cl2]Cl will also
pz
react with PPh3 to give [OsIV(N᎐PPh )(terpy)Cl ]Cl (terpy =
᎐
3
2
2,2Ј:6Ј,2Љ-terpyridine),32 the analogous reaction of [NBun ]-
4
[OsVIN(L4)] was found to be sluggish. This observation is
consistent with the findings from related studies on the oxo-
ruthenium() and -osmium() complexes that high-valent
ruthenium is a stronger oxidant than its osmium counterpart.2,6
PPh3
≠
N
RuIV
L
A
31P NMR spectrum recorded after 12 h of reaction
revealed that the mixture contained largely unchanged PPh3
(δ Ϫ3.5).
N
N
O
(L2)3-
n = 0; when L =
N
Conclusion
But
A series of nitrido-ruthenium() and -osmium() complexes
containing di-, tri- and tetra-anionic ligands was prepared via
Cl
Cl
᎐
ligand substitution reactions. The M᎐N bond distance is invari-
᎐
ant to the electron-donating power of the auxiliary ligands. All
the nitridoruthenium() complexes react readily with tri-
phenylphosphine, and the intermediate [RuIV(N᎐PPh )(L1)-
n = –1; when L =
N
O
N
N
O
N
O
or
᎐
3
(py)Cl] can be isolated and characterized spectroscopically for
the reaction with [RuVIN(L1)Cl]. However, for those nitrido-
ruthenium complexes bearing the tri- (L2)3Ϫ and tetra-anionic
O
(L3)4-
(L4)4-
Scheme 4
(L3,4 4Ϫ ligands the phosphiniminatoruthenium() intermediate
)
undergoes further reaction with pyrazole to generate a bis-
(pyrazole)ruthenium() complex as the product.
indicating that the ruthenium centre is in the ϩ4 oxidation
state. According to the mass spectroscopic analyses, molecular
ion peaks at m/z = 693 (Mϩ ϩ 1), 581 (MϪ) and 649 (MϪ), these
green solids could be formulated as [RuIVL2(Hpz)(pz)], [RuIV-
L3(Hpz)(pz)]Ϫ and [RuIVL4(Hpz)(pz)]Ϫ respectively. The cyclic
voltammogram of [NBu4][RuIVL4(Hpz)(pz)] in 0.1 mol dmϪ3
NBu4PF4 (CH2Cl2) showed three quasi-reversible couples at
ϩ0.8, ϩ0.04 and Ϫ1.24 V vs. Ag–AgNO3.
Acknowledgements
We gratefully acknowledge support from The University of
Hong Kong and The Hong Kong Research Grants Council.
References
All the triphenylphosphine reductions of the nitrido-
ruthenium complexes take place spontaneously. When the
1 W. A. Nugent and J. M. Mayer, Metal–Ligand Multiple Bonds,
Wiley, New York, 1988.
2 C.-M. Che, Pure Appl. Chem., 1994, 67, 225.
reaction with [NBun ][RuVIN(L4)] was monitored by UV/VIS
4
3 (a) C.-M. Che, T.-C. Lau, H.-W. Lam and C.-K. Poon, J. Chem.
Soc., Chem. Commun., 1989, 114; (b) H.-W. Lam, C.-M. Che and
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spectroscopy immediately after mixing of the reactants a new
species exhibiting an absorption band at 551 nm was generated.
This species slowly converted into [NBun ][RuIVL4(Hpz)(pz)]
4
(over 12 h) manifested by the gradual decay of the 551 nm
band, suggesting that the putative RuIV(N᎐PPh ) species is
᎐
3
unstable toward subsequent ligand substitution. The failure to
J. Chem. Soc., Dalton Trans., 1998, 3183–3190
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