Nitrido-ruthenium(VI) and -osmium(VI) complexes of multianionic chelating (N, O) ligands. Reactions with nucleophiles, electrophiles and oxidizing agents

Article abstract of DOI:10.1039/b304920p

This account presents the diverse reactivity of nitridoruthenium(VI) complexes with nucleophilic, electrophilic and oxidizing agents. [Ru ^VI(N)(L¹)Cl] (1) [H₂L¹ = 2,6-bis(2,2-diphenyl-2-hydroxyethyl)pyridine] reacted with excess phosphines such as PPh₃, PPhMe₂ and dppe to give [Ru ^III(HL¹)(PPh₃)Cl₂] (2a), [Ru ^III(L¹)(PPhMe₂)₂Cl] (2b) and [Ru^III(L¹)(dppe)Cl] (2c), respectively. In the presence of py or Hpz, 1 was converted to LRu^III(L¹)(py) ₂Cl] (3a) and [Ru^III(L¹)(Hpz)₃]Cl (3b), respectively. A dinuclear μ-nitridoruthenium complex, [Ru ^IV(L¹)Cl₂(μ-N)Ru^VI(L ¹)(C₈H₁₀N)Cl] (4), was obtained by treating 1 with 2,6-dimethylaniline, Based on X-ray crystallographic study, the compound is characterized by an unsymmetrical Ru-Nequiv;Ru moiety with the measured Ru-N distances being 1.661(5) and 1.837(5) A. Complex 1 reacted with dmf to give [Ru^III(HL¹)(dmf)Cl₂] (5) in 17% yield. Excess (Me₃O)BF₄ reacted with 1 to give a dinuclear μ-OH ruthenium complex, [Ru₂(N)₂(L¹) ₂(OH)]PF₆ (6). The measured Ru-O_(OH) distance is 1.984(3) A and the average Ru-O-Ru angle was found to be 100.4(2)°. Other nitrido-metal complexes, [n-Bu₄N][M^VI(N)(L)] [L = L² and L³; M = Os and Ru; H₄L² = 1,2-dichloro-4,5-bis(2-hydroxybenzamido)benzene, H₄L³ = 1,2-bis(2-hydroxybenzamido)benzene], underwent ligand protonation to form [M^VI(N)(HL)] complexes, which have been characterized by X-ray crystallography. Oxidation of [n-Bu₄N][Os^VI(N)(L ²)] by PhI(OAc)₂ produced [n-Bu₄N][Os ^VI(N)(L²O₂)] (8) in 10% yield. X-ray structure analysis of 8 showed that the coordinated phenoxy moiety was converted to a benzoquinone moiety while the Os≡N group remained intact.

Full text of DOI:10.1039/b304920p

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Nitrido-ruthenium(VI) and -osmium(VI) complexes of multianionic
chelating (N, O) ligands. Reactions with nucleophiles,
electrophiles and oxidizing agents†
Ka-Lai Yip, Wing-Yiu Yu, Pui-Ming Chan, Nian-Yong Zhu and Chi-Ming Che*
Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of
Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong,
Pokfulam Road, Hong Kong
Received 1st May 2003, Accepted 10th July 2003
First published as an Advance Article on the web 5th August 2003
This account presents the diverse reactivity of nitridoruthenium() complexes with nucleophilic, electrophilic
and oxidizing agents. [RuVI(N)(L1)Cl] (1) [H2L1 = 2,6-bis(2,2-diphenyl-2-hydroxyethyl)pyridine] reacted with
excess phosphines such as PPh3, PPhMe2 and dppe to give [RuIII(HL1)(PPh3)Cl2] (2a), [RuIII(L1)(PPhMe2)2Cl] (2b)
and [RuIII(L1)(dppe)Cl] (2c), respectively. In the presence of py or Hpz, 1 was converted to [RuIII(L1)(py)2Cl] (3a)
and [RuIII(L1)(Hpz)3]Cl (3b), respectively. A dinuclear µ-nitridoruthenium complex, [RuIV(L1)Cl2(µ-N)RuVI(L1)-
(C8H10N)Cl] (4), was obtained by treating 1 with 2,6-dimethylaniline. Based on X-ray crystallographic study, the
᎐
compound is characterized by an unsymmetrical Ru–N᎐Ru moiety with the measured Ru–N distances being 1.661(5)
᎐
and 1.837(5) Å. Complex 1 reacted with dmf to give [RuIII(HL1)(dmf )Cl2] (5) in 17% yield. Excess (Me3O)BF4 reacted
with 1 to give a dinuclear µ-OH ruthenium complex, [Ru2(N)2(L1)2(OH)]PF6 (6). The measured Ru–O(OH) distance is
1.984(3) Å and the average Ru–O–Ru angle was found to be 100.4(2)Њ. Other nitrido-metal complexes, [n-Bu4N]-
[MVI(N)(L)] [L = L2 and L3; M = Os and Ru; H4L2 = 1,2-dichloro-4,5-bis(2-hydroxybenzamido)benzene, H4L3 =
1,2-bis(2-hydroxybenzamido)benzene], underwent ligand protonation to form [MVI(N)(HL)] complexes, which
have been characterized by X-ray crystallography. Oxidation of [n-Bu4N][OsVI(N)(L2)] by PhI(OAc)2 produced
[n-Bu4N][OsVI(N)(L2O2)] (8) in 10% yield. X-ray structure analysis of 8 showed that the coordinated phenoxy
᎐
moiety was converted to a benzoquinone moiety while the Os᎐N group remained intact.
᎐
Introduction
There is a growing interest in the chemistry of metal-nitrido
complexes, particularly those of late transition metals.1
Recently Meyer,2 Mayer3 and Lau4 have independently
explored some interesting reactivities of [OsVI(N)(terpy)Cl2]ϩ
(terpy = 2,2Ј:6Ј,2Љ-terpyridine), [OsVI(N)(Tp)Cl2]ϩ [Tp = hydro-
tris-(1-pyrazolyl)borate] and [OsVI(N)(salen)]ϩ complexes. Rem-
iniscent of the oxo-metal complexes, these nitridoosmium()
complexes undergo proton-coupled electron transfer5,6 and
atom transfer reactions.2,3,4b Some other reactivity patterns such
as nitrido coupling reactions and electrochemistry had pre-
viously been examined by us and others.7–9 In view of the earlier
works by Groves10 and Carriera11 that nitridomanganese()
complexes can effect alkene aziridination and the rich oxidation
chemistry of high-valent oxo-ruthenium complexes,12 we
investigate the reactivity of nitridoruthenium() complexes for
potential hydrocarbon functionalization.13 To our knowledge,
studies on nitridoruthenium() complexes are sparse in the
Fig. 1 Multi-anionic chelating (N, O) ligands.
literature.13,14 Previously, we reported preparation and struc-
tural characterization of a series of nitrido-ruthenium() and
-osmium() complexes containing multianionic chelating
(N, O) ligands (Fig. 1).14b The reactivities of the complexes
toward triphenylphosphine were found to be affected by the
electron-donating strength of the auxiliary ligands. Herein, we
present a comprehensive account on the reactivity of nitrido-
ruthenium() complexes with respect to their reactions with
nucleophilic and electrophilic reagents.
[OsVI(N)(L2)], [n-Bu4N][RuVI(N)(L3)] and [n-Bu4N][OsVI(N)-
(L3)] were prepared according the previously reported
methods.14b Triphenylphosphine, dimethylphenylphosphine,
1,2-bis(diphenylphosphino)ethane, morpholine, piperidine,
pyridine, pyrazole, 2,6-dimethylaniline, trimethyloxonium
tetrafluoroborate and iodosylbenzene diacetate were obtained
commercially and used as received.
Instrumentation
Experimental
Infrared spectra were recorded as a KBr disc or Nujol mull on a
Nicolet 20 SXC FT-IR spectrophotometer. UV-VIS spectra
were recorded on a HP 8452A diode array spectrophotometer.
FAB-MS spectra were obtained from a Finnigan MAT 95 mass
spectrometer using 3-nitrobenzyl alcohol as matrix. Electro-
spray ionization (ESI) mass spectrometry was performed on a
Finnigan LCQ quadrupole ion trap mass spectrometer. NMR
spectra were obtained using Bruker DPX-300 and -500 pulsed
Materials
All solvents were purified by standard methods before use. The
compounds [RuVI(N)(L1)Cl], [n-Bu4N][RuVI(N)(L2)], [n-Bu4N]-
† Electronic supplementary information (ESI) available: Fig. S1–S6.
See http://www.rsc.org/suppdata/dt/b3/b304920p/
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
3556

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Fourier transform instruments. Elemental analyses were per-
formed by the Institute of Chemistry of the Chinese Academy
of Sciences.
X-Ray crystallography
X-Ray diffraction data were collected on a Enraf-Nonius
CAD-4, Rigaku AFC7R or MAR diffractometer using graph-
ite-monochromatized 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 the Fourier methods (PATTY).15 Structure
refinements were performed by the full-matrix least squares
using the software package TEXSAN16 on a Silicon Graphics
Indy computer. The structures of 2a–c, 3a–b, 4, 5, 6, 7 and 8
were established by X-ray crystallography; the crystal data,
selected bond distances and angles are listed in Tables 1 and 2.
CCDC reference numbers 209727–209736, 213055 and
213056.
See http://www.rsc.org/suppdata/dt/b3/b304920p/ for crystal-
lographic data in CIF or other electronic format.
Syntheses
[RuIII(HL1)(PPh3)Cl2] (2a). To a degassed MeOH solution
(10 cm3) containing 1 (100 mg, 0.16 mmol) was added PPh3
(127 mg, 0.48 mmol) under an argon atmosphere with stirring,
an instantaneous color change from purple to red occurred.
The reaction mixture was stirred for 3 h and the resultant brown
solution was rotary evaporated to dryness to give a brown solid.
The brown residue was recrystallized by slow diffusion of Et2O
to a CH2Cl2 solution to afford a yellow crystalline solid. Yield =
28 mg, 19%. Found: C, 66.23; H, 4.76; N, 1.51. C51H42NO2PCl2-
RuؒH2O requires C, 66.45; H, 4.81; N, 1.52%. IR (KBr, cmϪ1):
3060, 2935, 1438, 1190, 1120 and 1022. FAB-MS (ϩve): m/z 868
(Mϩ Ϫ Cl).
[RuIII(L1)(PPhMe2)2Cl] (2b). To a CH2Cl2 solution (20 cm3)
of 1 (100 mg, 0.16 mmol) was added PPhMe2 (55 mg, 0.48
mmol) under an argon atmosphere. The yellow-orange reaction
mixture was stirred for 2 h at room temperature to give a pale
yellow solution. After removal of solvent by rotary evapor-
ation, the pale yellow residue was recrystallized by slow diffu-
sion of Et2O to a CH2Cl2 solution to give a yellow crystalline
solid. Yield = 117 mg, 83%. Found: C, 66.9; H, 5.75; N, 1.55.
C49H49NO2P2ClRu requires C, 66.7; H, 5.6; N, 1.59%. IR
(Nujol, cmϪ1): 2850, 1600, and 1575. FAB-MS (ϩve): m/z 882
(Mϩ Ϫ Cl).
[RuIII(L1)(dppe)Cl] (2c). To a degassed MeOH solution
(20 cm3) of 1 (100 mg, 0.16 mmol) was added dppe (193 mg,
0.48 mmol) under an argon atmosphere. The purple reaction
mixture was stirred for 3 h at room temperature to give a
yellow-brown solution. Removal of solvent by rotary evapor-
ation afforded a brown residue, which was recrystallized by
slow diffusion of Et2O to a CH2Cl2 solution to give an orange
solid. Yield = 35 mg, 22%. Found: C, 68.0; H, 5.24; N,
1.23. C59H51NO2P2ClRuؒ2H2O requires C, 68.1; H, 5.33; N,
1.35%. IR (KBr, cmϪ1): 3065, 3025, 2932, 1481, 1433 and 1097.
FAB-MS (ϩve): m/z 968 (Mϩ Ϫ Cl).
[RuIII(L1)(py)2Cl] (3a). A mixture of CH2Cl2 (10 cm3) and
pyridine (1 cm3) was degassed by purging with argon for 5 min,
and the solution was added dropwise to 1 (100 mg, 0.16 mmol)
in a 50 cm3 Schlenk flask under an argon atmosphere. The pur-
ple reaction mixture was stirred for 3 h at room temperature
and the resultant yellow-brown solution was rotary evaporated
to dryness to give a yellow-brown residue. The residue was then
recrystallized by slow diffusion of Et2O to a CH2Cl2 solution.
Yield = 43 mg, 40%. Found: C, 63.2; H, 5.23; N, 5.15.
C43H37N3O2ClRuؒ3H2O requires C, 63.1; H, 5.3; N, 5.13%. IR
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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Table 2 Selected bond distances (Å) and angles (Њ) for 2a–c, 3a–b, 4–8
Complex 2a
Complex 5
Ru–N(1)
Ru–O(1)
Ru–O(2)
Ru–O(3)
N(1)–Ru–O(3)
N(1)–Ru–O(1)
N(1)–Ru–O(2)
O(2)–Ru–O(1)
Ru–N
2.17(4)
1.974(3)
2.123(3)
91.86(14)
88.49(13)
179.3(1)
Ru–P
2.348(15)
2.358(12)
2.392(13)
176.9(1)
87.6(1)
2.073(3)
2.127(2)
1.927(2)
2.119(2)
Ru–Cl(1)
Ru–Cl(2)
C(34)–O(3)
C(34)–N(2)
O(2)–Ru–O(3)
Cl(1)–Ru–Cl(2)
O(3)–Ru–C(34)
2.384(10)
2.38(1)
1.234(4)
1.298(5)
177.4(1)
172.66(3)
120.7(2)
Ru–O(1)
Ru–O(2)
N–Ru–O(1)
N–Ru–O(2)
N–Ru–P
Ru–Cl(1)
Ru–Cl(2)
O(1)–Ru–O(2)
O(1)–Ru–P
O(2)–Ru–P
177.4(1)
92.08(9)
92.3(1)
95.33(10)
172.35(9)
Complex 2b
Ru–Cl(1)
Ru–O(1)
Ru–O(2)
Ru–P(1)
Cl(1)–Ru–P(2)
P(1)–Ru–N(1)
O(1)–Ru–O(2)
Cl(1)–Ru–P(1)
Cl(1)–Ru–O(1)
Cl(1)–Ru–N(1)
Cl(1)–Ru–O(2)
P(1)–Ru–P(2)
2.431(4)
2.001(9)
2.008(9)
2.326(5)
174.3(1)
171.5(3)
173.3(4)
84.9(2)
89.0(3)
86.8(3)
94.4(3)
93.5(2)
Ru–P(2)
Ru–N(1)
O(1)–C(17)
O(2)–C37)
P(1)–Ru–O(1)
P(1)–Ru–O(2)
P(2)–Ru–O(1)
P(2)–Ru–N(1)
P(2)–Ru–O(2)
O(1)–Ru–N(1)
O(2)–Ru–N(1)
2.415(4)
2.13(1)
1.39(2)
1.45(2)
89.2(3)
85.3(3)
85.5(3)
94.9(3)
90.9(3)
92.3(5)
93.7(5)
Complex 6
Ru(1)–N(1)
Ru(1)–O(1)
Ru(1)–O(2)
Ru(1)–O(3)
Ru(1)–N(3)
Ru(1)–O(1)–Ru(2)
N(1)–Ru(1)–O(1)
N(2)–Ru(2)–O(1)
N(3)–Ru(1)–O(2)
N(3)–Ru(1)–O(3)
1.603(4)
2.032(3)
1.934(3)
1.928(3)
2.096(4)
136(1)
100.1(2)
100.6(2)
92.4(1)
Ru(2)–N(2)
Ru(2)–O(1)
Ru(2)–O(4)
Ru(2)–O(5)
Ru(2)–N(4)
N(4)–Ru(2)–O(4)
N(4)–Ru(2)–O(5)
N(3)–Ru(1)–O(1) 164.94(12)
O(1)–Ru(2)–N(4) 163.79(12)
1.613(4)
2.040(3)
1.93(3)
1.923(3)
2.086(3)
89.8(1)
92.9(1)
93.66(13)
Complex 2c
Ru–N
Ru–O(1)
Complex 7
Ru–N(1)
Ru–O(1)
Ru–O(2)
Ru–N(2)
2.183(4)
2.020(3)
2.010(3)
88.38(14)
90.97(13)
98.8(1)
Ru–P(1)
Ru–P(2)
Ru–Cl
N–Ru–P(2)
O(1)–Ru–O(2)
P(1)–Ru–P(2)
2.348(13)
2.338(14)
2.447(14)
173.2(1)
170.58(13)
81.89(5)
1.599(4)
1.964(3)
1.975(3)
2.029(4)
1.988(3)
110.4(2)
106.4(2)
102.7(2)
106.9(2)
78.3(1)
O(3)–C(7)
O(4)–C(14)
N(2)–C(7)
N(3)–C(14)
1.296(5)
1.210(6)
1.326(5)
1.395(6)
Ru–O(2)
N–Ru–O(1)
N–Ru–O(2)
N–Ru–P(1)
Ru–N(3)
N(1)–Ru–O(1)
N(1)–Ru–O(2)
N(1)–Ru–N(2)
N(1)–Ru–N(3)
O(1)–Ru–O(2)
O(1)–Ru–N(2)
O(1)–Ru–N(3)
O(2)–Ru–N(2)
O(2)–Ru–N(3)
N(2)–Ru–N(3)
90.8(1)
142.7(1)
150.8(1)
91.6(1)
Complex 3a
Ru–N(1)
Ru–N(2)
2.084(4)
2.103(4)
Ru–O(1)
Ru–O(2)
1.999(3)
1.987(4)
80.8(1)
Ru–N(3)
2.126(4)
Ru–Cl
2.395(14)
92.28(15)
172.88(13)
173.3(1)
N(1)–Ru–N(2)
N(1)–Ru–N(3)
N(1)–Ru–O(1)
175.80(14)
96.55(16)
93.07(15)
N(1)–Ru–O(2)
N(3)–Ru–Cl
O(1)–Ru–O(2)
Complex 8
Os–N(1)
Os–N(2)
1.625(9)
1.974(9)
1.854(13)
2.007(7)
2.014(8)
1.223(13)
1.252(14)
103.7(4)
101.7(4)
93.2(4)
C(14)–C(15)
C(15)–C(16)
C(16)–C(17)
C(17)–C(18)
C(18)–C(19)
C(14)–C(19)
1.350(16)
1.446(16)
1.463(17)
1.350(17)
1.438(18)
1.522(16)
Os–N(3)
Os–O(1)
Os–O(2)
O(5)–C(16)
O(6)–C(19)
N(1)–Os–O(1)
N(1)–Os–O(2)
N(2)–Os–O(1)
Complex 3b
Ru–N(1)
Ru–N(2)
2.073(4)
2.101(3)
2.086(4)
177.05(14)
95.54(14)
94.43(14)
Ru–N(6)
Ru–O(1)
Ru–O(2)
N(1)–Ru–N(6)
N(2)–Ru–N(6)
O(1)–Ru–O(2)
2.089(3)
1.974(3)
2.003(3)
90.73(14)
179.51(16)
169.94(12)
Ru–N(4)
N(1)–Ru–N(4)
N(1)–Ru–O(1)
N(1)–Ru–O(2)
N(2)–Os–O(2)
N(3)–Os–O(1)
N(3)–Os–O(2)
155.9(3)
155.1(3)
94.7(4)
Complex 4
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–N(3)
Ru(1)–O(2)
Ru(1)–O(3)
1.661(5)
2.175(5)
2.077(5)
1.906(5)
1.919(4)
Ru(2)–N(1)
Ru(2)–N(4)
Ru(2)–O(4)
Ru(2)–O(5)
1.837(5)
2.153(5)
1.943(4)
2.003(4)
Ru(1)–N(1)–Ru(2) 170.7(3)
N(2)–Ru(1)–N(3)
O(4)–Ru(2)–O(5)
Cl(11)–Ru(2)–Cl(12) 174.36(7)
177.15(17)
178.59(16)
N(1)–Ru(2)–N(4)
N(1)–Ru(1)–O(2)
N(1)–Ru(1)–O(3)
175.4(2)
114.9(2)
118.6(2)
(KBr, cmϪ1): 3206, 3054, 2956, 1601, 1445 and 1045. ESI-MS
ature, an instantaneous color change from purple to red-brown
occurred. After stirring for 3 h, the reaction mixture was rotary
evaporated to dryness to give a red-brown solid. The solid was
recrystallized by diffusion of Et2O into a CH2Cl2 solution to
give a red-brown crystal. Yield = 20 mg, 9%. UV-VIS (CH2Cl2),
λmax/nm (ε/dm3 molϪ1 cmϪ1): 258 (sh) (56234), 354 (sh) (20417),
523 (11481). Found: C, 64.9; H, 5.06; N, 3.98. C74H65N4O4-
Ru2Cl2ؒH2O requires C, 65.1; H, 4.95; N, 4.1%. IR (KBr, cmϪ1):
3056, 2917, 1606, 1039 and 1008. NMR, δH (500 MHz; 277 K;
solvent CDCl3; standard TMS): 1.86–2.46 (8H, m, 4CH2), 3.75
(6H, s, 2CH3), 6.52–7.84 (49H, m). ESI-MS (ϩve): m/z 1347
(Mϩ Ϫ H).
(ϩve): m/z 650 (Mϩ Ϫ Cl Ϫ py).
[RuIII(L1)(Hpz)3]Cl (3b). A 25 cm3 round-bottom flask was
charged with 1 (100 mg, 0.16 mmol), pyrazole (109 mg, 1.6
mmol) and CH2Cl2 (20 cm3) to give an orange-brown suspen-
sion. The suspension was stirred for 2 h at room temperature to
afford a homogeneous dark brown solution. Complete removal
of solvent by rotary evaporation gave a brown solid, which was
recrystallized by slow diffusion of Et2O to a MeOH solution to
afford a dark brown crystalline solid. Yield = 40 mg, 31%.
Found: C, 60.2; H, 5.32; N, 11.29. C42H39N7O2ClRuؒH2OؒCH3-
OH requires C, 60.03; H, 5.27; N, 11.4%. IR (KBr, cmϪ1): 3324,
3131, 2936, 2850, 1460, 1439 and 1046. FAB-MS (ϩve): m/z 639
(Mϩ Ϫ Cl Ϫ 2Hpz).
[RuIII(HL1)(dmf)Cl2] (5). A dmf solution (10 cm3) of 1 (1 g,
1.6 mmol) was stirred at room temperature for 24 h. The red-
brown solution was concentrated by rotary evaporation to
ca. 5 cm3 and the titled complex was isolated as a crystalline
solid by slow diffusion of Et2O into a dmf solution. Yield =
0.24 g, 17%. Found: C, 55.8; H, 5.78; N, 5.18. C39H41N3O4-
[RuIV(L1)Cl2(ꢀ-N)RuVI(L1)(DMA)] (4) [DMA ؍ 2,6-dimethyl-
aniline]. To a CH2Cl2 solution (20 cm3) of 1 (100 mg 0.16 mmol)
was added DMA (0.059 cm3, 0.48 mmol) at ambient temper-
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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Cl2Ruؒ3H2O requires C, 55.7; H, 5.63; N, 4.99%. IR (KBr,
cmϪ1): 3055, 2917, 1655 (CO) and 1639 (CO). FAB-MS (ϩve):
m/z 606 (Mϩ Ϫ dmf Ϫ Cl).
2964, 2876, 1656 (CO), 1618, and 1096. NMR, δH (300 MHz,
298 K, CD2Cl2, standard TMS): 6.71 [2H, d, (J = 2.5 Hz)], 6.95–
7.01 (1H, m), 7.28 [1H, d, (J = 8.1 Hz)], and 7.38–7.43 [1H, m,
(J = 8.4 Hz)], 8.26 [1H, d, (J = 6.6 Hz)], 8.9 (1H, s) and 9.26 (1H,
s). ESI-MS (Ϫve): m/z 648 (MϪ).
[RuVI2(N)2(L1)2(OH)]PF6 (6). To a CH2Cl2 solution (10 cm3)
of 1 (100 mg, 0.16 mmol) was added excess (Me3O)BF4 (300
mg) under an argon atmosphere. After stirring the mixture for
5 h, the resulting red solution was filtered and the filtrate
was evaporated to dryness by vacuum. The residual solid was
dissolved in MeOH and ammonium hexafluorophosphate
(300 mg) was added. After standing the solution for overnight
at room temperature, a red crystalline solid was formed and was
collected on a frit. Yield = 72 mg, 67%. Found: C, 59.7; H, 4.33;
N, 4.38. C66H55N4O5PF6Ru2 requires C, 59.6; H, 4.16; N, 4.21%.
IR (KBr, cmϪ1): 3498 (OH), 2850, 1610, 1446 1042, and 854.
NMR, δH (300 MHz, 298 K, CDCl3, standard TMS): 4.05 [4H,
d, (J = 15.2 Hz), 2CH2], 4.7 [4H, d, (J = 15.2 Hz), 2CH2], 7.10
(16H, m), 7.38 (24H, m), 7.61 (4H, m), 7.79 (1H, m), 8.13 (1H,
m) and 9.93 (1H, s, 1 OH). FAB-MS (ϩve): m/z 1185 (Mϩ).
Results and discussion
Reactions with phosphines
We previously reported that [RuVI(L1)(N)Cl] (1) reacted with
PPh in a CH Cl –py mixture to give [RuIV(N᎐PPh )(L1)(py)Cl]
᎐
3
2
2
3
based on 31P NMR and FAB-MS analyses. When the reaction
mixture was left standing for > 14 h, [RuIII(L1)(py)3]ϩ complex
was isolated (67 % yield) with the loss of the phosphiniminato
group. In view of steric bulkiness of L1 and PPh3, we studied
the “1 ϩ PPh3” reaction for entry to coordinatively unsaturated
bis(alkoxy)ruthenium complexes (Scheme 1).
[RuVI(N)(HL2)] (7) [H4L2: 1,2-dichloro-4,5-bis(2-hydroxy-
benzamido)benzene]. To a CH2Cl2 solution (10 cm3) of [n-Bu4N]-
[RuVI(N)(L2)] (100 mg, 0.14 mmol) was added excess (Me3O)-
BF4 (300 mg) under an argon atmosphere, and the mixture was
stirred for 1 h at room temperature to give an orange precipi-
tate. The solid was filtered and washed with CH2Cl2. Yield =
62 mg, 83%. Found: C, 45.3; H, 2.02; N, 7.78. C20H11N3O4Cl2Ru
requires C, 45.4; H, 2.09; N, 7.94%. IR (KBr, cmϪ1): 2930, 1600
(CO) and 1460. NMR, δH (300 MHz, 298 K, CD3OD, standard
TMS): 6.95 [2H, t, (J = 7 Hz)], 7.21 [2H, d, (J = 8.3 Hz)], 7.42
[2H, t, (J = 7 Hz)], 8.15 [2H, d, (J = 8.3 Hz)] and 9.17 (2H, s).
FAB-MS (Ϫve): m/z 528 (MϪ).
[OsVI(N)(HL2)]. was prepared in a manner similar to that of
7a. Yield = 62 mg, 83%. Found: C, 38.8; H, 1.71; N, 6.78.
C20H11N3O4Cl2Os requires C, 38.8; H, 1.79; N, 6.79%. IR (KBr,
cmϪ1): 2930, 1600 (CO) and 1460. NMR, δH (300 MHz, 298 K,
CD3OD, standard TMS): 6.91 [2H, t, (J = 8.21 Hz)], 7.2 [2H, d,
(J = 7.51 Hz)], 7.38 [2H, d, (J = 8.2 Hz)], 7.51 [2H, d, (J = 7.51
Hz)] and 9.2 (2H, s). ESI-MS (Ϫve): m/z 617 (MϪ).
[RuVI(N)(HL3)] [H4L3:
1,2-bis(2-hydroxybenzamido)-ben-
zene]. Yield = 43 mg, 67%. Found: C, 52.2; H, 2.77; N, 9.12.
C20H13N3O4Cl2Ru requires C, 52.2; H, 2.85; N, 9.13%. IR (KBr,
cmϪ1): 2945, 1603 (CO) and 1462. NMR, δH (300 MHz, 298 K,
CD3OD, standard TMS): 6.93 (2H, m), 6.99 (2H, m), 7.24 [2H,
d, (J = 6.9 Hz)], 7.34 (2H, m), 8.15 [2H, dd, (J = 7.9 Hz, 1.6 Hz)]
and 8.85 (2H, m). ESI-MS (Ϫve): m/z 459 (MϪ).
Scheme 1 Reactions with phosphines.
When 1 was treated with excess PPh3 (10 equiv.) in degassed
MeOH, [RuIII(HL1)(PPh3)Cl2] (2a) was formed in 19% yield.
Using 20 equiv. of PPh3 afforded 2a exclusively in similar yield,
and any coordinatively unsaturated complexes such as [RuIII-
(HL1)(PPh3)2] were not obtained. Complex 2a in CH2Cl2
exhibits an intense UV-VIS absorption band at λmax/nm (ε/dm3
molϪ1 cmϪ1) = 428 (1300), which is conspicuously absent in the
UV-VIS spectrum of the starting complex. The [RuIII(HL1)-
(PPh3)Cl2] formulation is supported by FAB-MS [(m/z = 868
[OsVI(N)(HL3)]. Yield = 44 mg, 67%. Found: C, 43.3; H, 2.33;
N, 7.67. C20H13N3O4Os requires C, 43.2; H, 2.38; N, 7.65%. IR
(KBr, cmϪ1): 2855, 1600 (CO), 1476 and 1195. NMR, δH (300
MHz, 298 K, CD3OD, standard TMS): 6.95 (4H, m), 7.34 (4H,
m), 8.31 [2H, d, (J = 7.8 Hz)] and 8.97 [2H, dd, (J = 6.3 Hz,
3.5 Hz)]. ESI-MS (Ϫve): m/z 548 (MϪ).
1
(Mϩ)] and elemental analysis. The H NMR spectrum of 2a is
featured by broad absorption bands, indicative of paramagnetic
nature of the complex.
[n-Bu4N][OsVI(N)(L2O2)] (8). A MeOH solution (15 cm3) of
[n-Bu4N][OsVI(N)(L2)] (100 mg, 0.12 mmol) and PhI(OAc)2
(112 mg, 0.35 mmol) was stirred for 3 h at room temperature, an
orange solution was obtained. Excess Hpz (ca. 500 mg) was
added to the reaction mixture, which was stirred for another
24 h. Removal of solvent by rotary evaporation gave an orange
solid, which was dissolved in CH2Cl2 (1 cm3) and loaded onto
an alumina column (activity 90, neutral) for chromatographic
purification using CHCl3 as eluant. An orange band was col-
lected and complete removal of solvent by rotary evaporation
gave an orange solid. The crude product was recrystallized by
diffusion of Et2O to a CH2Cl2 solution to give orange crystals.
Yield = 5 mg, 10%. Found: C, 48.5; H, 4.98; N, 6.52. C36H44N4-
O6Cl2Os requires C, 48.6; H, 4.98; N, 6.30%. IR (KBr, cmϪ1):
The molecular structure of 2a was established by X-ray crys-
tallography. As shown in Fig. 2, the Ru atom adopts a distorted
octahedral coordination. A notable feature is the unsym-
metrical Ru–O distances. The Ru–O(1) distance is 1.974(3) Å,
which is close to the corresponding distances of 1.902(3) and
1.921(3) Å in 1. However, the Ru–O(2) distance [2.123(3) Å] is
significantly longer than the Ru–O(1) distance. Compared to
the Ru–OH2 distances in both [RuII(Me3tacn)(bpy)(OH2)]2ϩ
[2.168(3) Å; Me3tacn = trimethyl-1,4,7-triazacyclononane, bpy
= 2,2Ј-bipyridine]17 and [RuIII(N2O2)(OH)(OH2)]2ϩ [2.199(3) Å;
N2O2 = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxa-
cyclopentadecane],18 the Ru–O(2) value is comparable to a
Ru–OH2 distance, suggesting that O(2) is protonated. The PPh3
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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Fig. 3 Perspective view of [RuIII(L1)(PPhMe2)2Cl] (2b) with atom
labelling scheme (50% probability ellipsoids).
Fig. 2 Perspective view of [RuIII(HL1)(PPh3)Cl2] (2a) with atom
labelling scheme (50% probability ellipsoids).
species at m/z = 672 and 656, which did not correspond to
[RuVI(N)(L1)]ϩ (m/z = 584) or [RuIII(L1)(C4H9NO)2]ϩ (m/z = 744)
species. Based on the agreement of the experimental and calcu-
lated isotopic patterns, the two species are designated to [RuIII-
(N)(L1)(C4H9NO)]ϩ (m/z = 672) and [RuIII(L1)(C4H9NO)]ϩ (m/z
ligand is located trans to the pyridyl group with the Ru–P and
Ru–N distances being 2.348(15) and 2.17(4) Å, respectively.
The failure to obtain coordinatively unsaturated complexes
can be ascribed to steric repulsion between the bulky L1 and
PPh3 ligands. This prompted us to employ PPhMe2 as a less
bulky phosphine derivative for the “1 ϩ phosphine” reaction.
When 1 was treated with PPhMe2 (3 equiv.) in degassed CH2Cl2,
[RuIII(L1)(PPhMe2)2Cl] (2b) was produced as a yellow solid in
83% yield. The molecular structure of 2b is depicted in Fig. 3.
The six-coordinated Ru atom adopts a distorted octahedral
structure. Unlike 2a, both the Ru–O distances [Ru–O(1) =
2.001(9) Å; Ru–O(2) = 2.008(9) Å] are comparable to the corre-
sponding values [Ru–O(1) = 1.902(3) Å; Ru–O(2) = 1.921(3) Å]
in 1, suggesting that the O(1) and O(2) atoms remain in a
deprotonated form. The two PPhMe2 ligands are cis-co-
ordinating to the Ru atom, and the Ru–P(1) distance [2.326(5)
Å] is considerably shorter than the Ru–P(2) one [2.415(4) Å].
The difference in the Ru–P distances between the equatorial
and axial coordinating PPhMe2 ligands is discernible since the
axial PPhMe2 ligand would experience unfavorable steric
interaction with the nearby phenyl groups (Fig. 3).
=
656) formulations. The expected ruthenium-hydrazido
complex was not obtained.
Interestingly, we obtained [RuIII(L1)(py)2Cl] (3a) as a yellow
crystalline solid (37% yield) when treating 1 with excess pyrid-
ine (py) [CH2Cl2 : py = 20 : 1 (v/v)]. Infra-red spectral analysis
Ϫ1
᎐
of 3a revealed the absence of a Ru᎐N stretch at 1000–1100 cm
᎐
(Ru᎐N stretch for 1 is at 1025 cmϪ1), indicative of the loss of the
᎐
᎐
nitrido ligand after the reaction. The 1H NMR spectrum
featured broad resonances, suggesting a paramagnetic nature
for the complex. By means of ESI-MS analysis, we observed a
prominent ionic species with m/z = 650, which was assigned to a
[RuIII(L1)(py)]ϩ complex based on excellent agreement between
the calculated and experimental isotopic distribution patterns
(Scheme 2).
Likewise, 1 would react with pyrazole (Hpz) to furnish [RuIII-
(L1)(Hpz)3]Cl (3b) in 31% isolated yield. The molecular struc-
tures of 3a–b have been established by X-ray crystallography
(see later section).
Analogous to 2b, [RuIII(L1)(dppe)Cl] (2c) was prepared by
reacting 1 with excess dppe in MeOH. As expected, 2c is
structurally similar to 2b based on crystallographic studies;
the Ru–O(1) and Ru–O(2) distances are compatible with Ru–O-
(alkoxide) linkages. The Ru–P(1) and Ru–P(2) distances are
2.348(13) and 2.338(14) Å, respectively.
In contrast to the analogous reaction of [OsVI(N)(terpy)Cl2]ϩ
complex, the reaction of 1 with morpholine is characterized by
the loss of the nitrido ligand accompanied with ligand substi-
tution. In this case, no hydrazido-ruthenium complex was
obtained. For the less electrophilic osmium complexes, [OsVI-
(N)(L1)Cl] reacted with morpholine and piperidine to give the
adduct complexes [OsVI(N)(L1)Cl(morpholine)] and [OsVI(N)-
(L1)Cl(piperidine)], which have been structurally characterized
by X-ray crystallography.
Reaction with amines
᎐
It is known that M᎐N complexes would react with amines by
᎐
nucleophilic addition. For example, Meyer2e and co-workers
previously showed that the [OsVI(N)(terpy)Cl2]ϩ complex [terpy
= 2,2Ј,6Ј,2Љ-terpyridine] would react with morpholine and
piperidine to form a hydrazido-osmium() species. In this
work, when 1 was treated with morpholine in CH2Cl2, only a
gummy solid was obtained by Et2O induced precipitation.
Analysis of the solid by FAB-MS revealed two prominent ionic
The molecular structure of [RuIII(L1)(py)2Cl] (3a) is depicted
in Fig. 4. As shown in the figure, the ruthenium atom adopts a
distorted octahedral coordination geometry. The two measured
Ru–O(1) [1.999(3) Å] and Ru–O(2) [1.987(4) Å] distances are
comparable to the corresponding distances for [RuIII(L1)-
(dppe)Cl] [Ru–O(1) = 1.999(3) and Ru–O(2) = 1.987(4) Å]. This
finding suggests that the coordinated L1 ligand is in a doubly
Scheme 2 Reactions in the py–CH2Cl2 and Hpz–CH2Cl2 solutions.
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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Scheme 3 Reactions with 2,6-dimethylaniline and dimethylformamide.
to morpholine. When 1 was reacted with 2,6-dimethylaniline
(DMA; 3 equiv.) in CH2Cl2, the red-brown [RuIV(L1)Cl2-
(µ-N)RuVI(L1)(C8H10N)Cl] complex (4) was produced in 10%
yield (Scheme 3). Based on X-ray crystallographic studies, 4
was found to be a dinuclear µ-nitridoruthenium complex as
depicted in Fig. 6. The structure is characterized by an unsym-
metrical linear Ru(1)–N(1)–Ru(2) configuration [170.7(3)Њ]; the
measured Ru(1)–N(1) and Ru(2)–N(1) distances are 1.661(5)
and 1.837(5) Å, respectively. The short Ru(1)–N(1) distance is
᎐
characteristic of a Ru᎐N bond, which is slightly longer than the
᎐
corresponding distance of 1.605(4) Å in 1. Compared to a
Ru–N single bond (ca. 2.0–2.1 Å), the Ru(2)–N(1) distance
[1.837(5) Å] is apparently shorter, suggesting multiple bond-
ing character. Therefore, coordination of Ru(2) atom to
᎐
Ru(1)᎐N(1) causes delocalization of some π-electron density to
᎐
᎐
the Ru(2)–N(1) bond, leading to weakening of the Ru(1)᎐N(1)
᎐
linkage.
Fig. 4 Perspective view of [RuIII(L1)(py)2Cl] (3a) with atom labelling
scheme (50% probability ellipsoids).
deprotonated form (i.e., bis-alkoxides). The Ru, O(1), C(1),
C(2), C(3) and N(1) atoms, as well as the Ru, O(2), C(9), C(8),
C(7) and N(1) atoms, constitute a pair of six-membered rings;
both of them adopt a boat conformation. The two pyridine
ligands are cis-coordinating and the Ru–N(2) and Ru–N(3)
bond distances [Ru–N(2) = 2.103(4) and Ru–N(3) = 2.126(4) Å]
are comparable to the corresponding values in [Ru(bpy)2-
(py)2][(ϩ)-O,OЈ-dibenzoyl--tartrate] [Ru–N(41) = 2.114(5) and
Ru–N(31) = 2.122(5) Å].19
Analogous to 3a, [RuIII(L1)(Hpz)3]Cl (3b) has a similar
molecular structure (Fig. 5). The six-coordinated ruthenium
atom is bound to L1 and the three Hpz molecules are arranged
in a meridional configuration. The O(1)–Ru–O(2) angle is
169.94(12)Њ, which is close to the corresponding angle of
173.3(1)Њ in [RuIII(L1)(py)2Cl]. The three Ru–N (Hpz) distances
of 2.073(4), 2.086(4) and 2.089(3) Å are similar.
We have also examined the reactions of 1 with aromatic
amines such as aniline, which is a weaker nucleophile compared
Fig. 6 Perspective view of [RuIV(L1)Cl2(µ-N)RuVI(L1)(C8H10N)Cl] (4)
with atom labelling scheme (50% probability ellipsoids). The atom
labelling for non-esssential bonding atoms is omitted for clarity.
Notably, the dinuclear complex is constituted by two struc-
turally distinct Ru fragments, which exhibit different co-
ordination geometries. The five-coordinated Ru(1) atom
exhibits a distorted trigonal bipyrimidal configuration, which is
isostructural to the starting ruthenium complex 1. The N(2)–
Ru(1)–N(3) axis [177.15(17)Њ] is close to linearity, and the tri-
gonal plane is defined by the Ru(1), N(1), O(2) and O(3) atoms.
The respective Ru(1)–O(2) and Ru(1)–O(3) distances are
1.906(5) and 1.919(4) Å, which are close to the corresponding
distances of [Ru–O(1) = 1.902(3) Å; Ru–O(2) = 1.921(3) Å] in 1.
The respective Ru(1)–N(2) and Ru(1)–N(3) distances are
2.175(5) and 2.077(5) Å, which are compatible with a Ru–N
single bond distance.
Fig. 5 Perspective view of the complex cation of [RuIII(L1)(Hpz)3]-
Cl (3b) with atom labelling scheme (50% probability ellipsoids).
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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The six-coordinated Ru(2) atom adopts a distorted octa-
hedral configuration. The N(1)–Ru(2)–N(4) [175.4(2)Њ], O(4)–
Ru(2)–O(5) [178.59(16)Њ] and Cl(11)–Ru(2)–Cl(12) axes
[174.36(7)Њ] are close to linearity, and the Ru(2)–O(4) [1.943(4)
Å] and Ru(2)–O(5) [2.003(4) Å] distances are comparable to the
corresponding distances in 1.
Analogous to the reactions with amines and anilines, 1 was
found to be transformed to [RuIII(HL1)(dmf )Cl2] (5) in a dmf
(10 cm3) solution. Complex 5 was isolated as a red-brown solid
in 17% yield. The IR spectrum of 5 revealed the absence of
᎐
Ru᎐N stretch, and there are two intense absorptions at 1639
᎐
and 1655 cmϪ1 characteristic of C᎐O stretches of the co-
᎐
ordinated and free dmf molecules, respectively. The FAB-MS
spectrum is featured by a prominent ion peak at a m/z = 606
assignable to a [RuIII(HL1)Cl]ϩ species. The 1H NMR spectrum
shows broad signals revealing that the complex is para-
magnetic. In CH2Cl2, the complex shows several intense UV-
VIS absorption bands at λmax/nm (ε/dm3 molϪ1 cmϪ1) at 266 (br,
10000), 330 (sh, 3400), and 420 (sh, 2050). The 420 nm band is
Fig.
7
Perspective view of [RuIII(HL1)(dmf )Cl2] (5) with atom
tentatively assigned to a pπ(ClϪ)
transition.
Ru() charge transfer
labelling scheme (50% probability ellipsoids).
The molecular structure of 5 has been determined by X-ray
crystal analysis. As depicted in Fig. 7, the ruthenium atom co-
ordinates to the tridendate L1, the dmf and the two trans-chloro
ligands, which together adopt a distorted octahedral geometry.
The Ru–N(1) distance of 2.073(3) Å is close to the corre-
sponding distances [2.085(5)–2.141(5) Å] found in 1 and some
[RuIII(N4)Cl2]ϩ complexes (N4 = macrocyclic tertiary amines).20
The two Ru–O distances are unsymmetrical with Ru–O(1) and
Ru–O(2) distances being 2.127(2) and 1.927(2) Å, respectively.
The differential Ru–O distances suggests that L1 is in a
mono-protonated form. The respective Ru–Cl(1) and Ru–Cl(2)
distances are 2.384 (1) and 2.38(1) Å. The dmf molecule co-
ordinates to the Ru atom through the carbonyl oxygen atom
with a Ru–O(3)–C(34) angle of 120.7(2)Њ; a similar coordin-
ation mode for dmf can be found in [RuII(dmf )6](CF3SO3)2
X(dppe)2]23 and [Re(N)Y2(PEt2Ph)3]24 (Y = Cl and Br)] are
known to react with electrophilies such as Hϩ, (Me3O)BF4 and
BX3 (X = F, Cl, Br). Previously, Shapley and co-workers
reported that a series of Os() nitrido-alkyl complexes,
[n-Bu4N][OsVI(N)R4] (R = Me, CH2SiMe3, CH2CMe3 and
CH2Ph2), reacts with (Me3O)BF4 by electrophilic alkylation
of the nitrido ligand to generate imido-osmium() com-
plexes.25
In this work, we are interested to explore the reactivity of
nitridoruthenium() complexes toward electrophilic reagents
(Scheme 4). When 1 was treated with excess (Me3O)BF4 in
CH2Cl2, a red crystalline solid was isolated and characterized
by X-ray crystal analysis to be [RuVI2(N)2(L1)2(OH)]PF6 (6),
᎐
which contains two Ru᎐N groups and the two ruthenium atoms
᎐
are bridged by a hydroxyl group.
(Ru–O᎐C
121.75Њ)].21 The C(34)–O(3) [1.234(4) Å] and
᎐
average
The IR spectrum of 6 shows an absorption band at 3498
C(34)–N(2) [1.298(5) Å] distances of the coordinated dmf are
comparable to the corresponding values found in [RuII(dmf )6]-
(CF3SO3)2.
cmϪ1, assignable to a νOH stretch. The Ru᎐N stretch could not
᎐
᎐
be located because of extensive overlapping peaks due to the
ligand absorptions at the 1200–800 cmϪ1 region. As 6 is dia-
magnetic, the bridging hydroxyl proton can also be found in the
1H NMR spectrum (δH = 10.0 ppm).
Electrophilic attack on metal-nitrido complex
Reactions of nitrido ligand in late transition metal-nitrido
complexes toward electrophilies are sparse in the literature.22 In
contrast, the nitrido ligand in some early transition metal-
nitrido complexes [e.g. [Mo(N)(S2CNR2)3] and trans-[Mo(N)-
As shown in Scheme 5 the formation of 6 was believed to be
initiated by electrophilic attack of a “CH3ϩ” cation on the
chloride ligand, followed by the loss of CH3Cl and generation
ϩ
᎐
of a coordinately unsaturated [Ru᎐N] species. A similar
᎐
Scheme 4 Reaction with trimethyloxonium tetrafluoroborate.
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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Scheme 5 Proposed reaction sequence for the formation of 6.
᎐
reaction was reported earlier by Shapley and co-workers show-
ing that nitridoruthenium() alkyl complexes readily under-
went dealkylation in the presence of HCl.26 The vacant site
would be taken up by a H2O molecule; the µ-OH complex was
formed upon reaction with another molecule of coordinatively
in the figure, the two Ru᎐N moieties are connected through a
᎐
bridging OH ligand, and the N(1)–Ru(1)–O(1) and N(2)–
Ru(2)–O(1) angles are 100.1(2) and 100.6(2)Њ, respectively. The
coordination geometries of the ruthenium atoms are similar to
that of 1. The Ru᎐N distances are 1.603(4) Å [Ru(1)–N(1)] and
1.613(4) Å [Ru(2)–N(2)], which are similar to the corresponding
᎐
᎐
ϩ
᎐
unsaturated [Ru᎐N] species. It should be noted that treatment
᎐
of 1 with silver trifluoromethanesulfonate in acetone or
acetonitrile in room temperature did not give AgCl.
distance of [Ru(1)–N(1) = 1.615(4) Å] in 1. Yet, the observed
᎐
Ru᎐N distances in 6 are substantially shorter than 1.66(1) Å
᎐
It is widely believed that oxidation of cationic ruthenium-
amine complexes would proceed through a highly reactive
nitridoruthenium intermediate, which reacts with water to give
found in the related [(RuVI(N)(heda)2)2(µ-O)]ClO4 complex.28
Each Ru complex fragment can be described as a distorted tri-
gonal bipyramid, and the N(1), O(2), O(3) and N(2), O(4), O(5)
atoms are situated on two distorted trigonal planes. Structurally
analogous to 1, the O(1)–Ru(1)–N(3) [164.94(12)Њ] and O(1)–
Ru(2)–N(4) [163.79(12)Њ] axes deviate significantly from linear-
ity. The two trigonal planes defined by the Ru(1), N(1), O(2),
O(3) and Ru(2), N(2), O(4), O(5) atoms are nearly isosceles
triangles. The respective Ru(1)–O(2), Ru(1)–O(3), Ru(2)–O(4)
and Ru(2)–O(5) distances are 1.934(3), 1.928(3), 1.93(3), and
1.923(3) Å, which are typical values of a Ru–O single bond
formulation. The Ru(1)–O(1)–Ru(2) moiety in 6 is not linear
with an angle of 136(1)Њ, unlike the corresponding bond angle
[180(2)Њ] in [(RuVI(N)(heda)2)2(µ-O)]ClO4.28
a
nitrosyl-ruthenium complex as the isolated product.27
Examples of structurally characterized cationic nitridoruthe-
nium complexes are sparse in the literature. In 1995, we
reported the first structurally characterized nitridoruthenium
complex, [(RuVI(N)(heda)2)2(µ-O)]ClO4 (heda = 2,5-dimethyl-
2,5-hexanediamine).28
Fig. 8 depicts the molecular structure of [RuVI(N)(L1)(µ-OH)-
RuVI(N)(L1)]ϩ, which represents the second example of struc-
turally defined cationic nitridoruthenium complexes. As shown
It has been documented that electrophilic alkylation (N vs.
S-alkylation) of [n-Bu4N][Os(NCPh3)(S2C6H4)2] can preferen-
tially take place at the nitrido ligand by employing encumbered
electrophilic reagents such as (Ph3C)PF6.29 However, when
[RuVI(N)(L1)Cl] (1) was treated with an excess of (Ph3C)PF6 in
CH2Cl2, the dimeric nitrido complex 6 was formed exclusively,
albeit in lower yield (30%). No N-alkylated nitridoruthenium
complex was obtained.
Reports from various groups showed that nitrido-
manganese()-porphyrins and -Schiff base complexes can effect
alkene aziridination in the presence of trifluoroacetic anhydride
and pyridine.
A highly reactive N-trifluoroacetylimido-
manganese species has widely been invoked as the active inter-
mediate in such reactions.10,11,30 In this work, reaction of
[RuVI(N)(L1)Cl] with (CF3CO)2O (3 equiv.)/cyclooctene (excess)
in CH2Cl2 under an argon atmosphere did not afford any azirid-
ine products. However, [RuVI2(N)2(L1)2(µ-OH)]PF6 was isolated
in less than 10% yield. We postulate that the acid anhydride
would attack the alkoxide oxygen atom resulting in extensive
demetallation.
Fig. 8 Perspective view of the complex cation of [RuVI2(N)2(L1)2-
(OH)]PF6 (6) with atom labelling scheme (50% probability ellipsoids).
Similarly we proceeded to examine the reactions of
[n-Bu4N][RuVI(N)(L2)] toward electrophilic reagents under
D a l t o n T r a n s . , 2 0 0 3 , 3 5 5 6 – 3 5 6 6
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Scheme 6 Oxidation by iodosylbenzene diacetate.
similar conditions. Again, treating [n-Bu4N][RuVI(N)(L2)] with
(Me3O)BF4 in CH2Cl2 did not result in N-alkylation. However,
[n-Bu N][RuVI(N)(L2)] underwent protonation at the C᎐O
double bond (cf. average 1.22 Å in [n-Bu4N][RuVI(N)(L2)]). In
the literature, amide-to-iminol tautomerism is known,32 for
example, [Co(η4-bpb)(η2-Hbpb)]33 has two different C–N
᎐
4
group of the ligand to form [RuVI(N)(HL2)] (7), which was iso-
lated as a yellow precipitate (>90% yield) (Scheme 6). Similar
observation was obtained when HBF4 was used as the electro-
bonds [1.332(8) and 1.408(8) Å] assignable to an imine (C᎐N)
᎐
and an amide [–C(᎐O)–N] linkage, respectively.
᎐
The hydroxyl proton was located in the difference Fourier
map and its positional parameters were included in the least
squares refinement. The O(3)–H bond distance is 1.18 Å; the
C(7)–O(3)–H angle is estimated to be 116.7Њ.
1
philic reagent. The H and 13C NMR spectra of the yellow
product revealed identical spectral features as that of the start-
ing nitridoruthenium() complexes, except that the signals
corresponding to the [n-Bu4N]ϩ protons were completely
Similarly, (Me3O)BF4 reacted with [n-Bu4N][RuVI(N)(L3)],
[n-Bu4N][OsVI(N)(L2)], and [n-Bu4N][OsVI(N)(L3)] to afford the
ligand-protonated nitrido-metal complexes which have been
characterized by spectroscopic means. The slow hydrolysis of
(Me3O)BF4 due to moisture in CH2Cl2 would produce HBF4,
which would protonate the carbonyl group of the auxiliary
ligand.
1
absent. Moreover, the H NMR spectrum did not show any
᎐
extra resonance corresponding to a methylimido (Ru᎐NMe)
᎐
moiety, nor any methoxy group arising from O-alkylation of
the ligand. The IR and Raman spectra showed a sharp and
strong absorption at 3125 cmϪ1, which could either be a N–H or
O–H stretch. This absorption is conspicuously absent in the
corresponding spectrum of the starting complex.
The molecular structure of 7 was determined by X-ray
Oxidation by PhI(OAc)2
crystallography (Fig. 9). The complex is isostructural to
Reactions of the nitrido-metal complexes with PhI(OAc)2
(iodosylbenzene diacetate) have been examined. In MeOH,
[n-Bu4N][OsVI(N)(L2)] was found to undergo ligand-oxidation
upon treatment with PhI(OAc)2 (3 equiv.) in the presence of
Hpz (10 equiv.) to give [n-Bu4N][OsVI(N)(L2O2)] (8), which was
isolated as an orange crystalline solid in <10% yield after chro-
matographic purification (Scheme 6). Complex 8 was analyzed
by ESI-MS, and a prominent ion cluster peak at m/z = 648
was observed. Based on the agreement of the experimental
and calculated isotopic distribution patterns, an oxygenated
derivative of [OsVI(N)(L2)]Ϫ, i.e., [OsVI(N)(L2O2)]Ϫ, was form-
ulated. The IR spectrum of 8 revealed an intense absorp-
[RuVI(N)(L2)]Ϫ with similar Ru᎐N distance of 1.599(4) Å
᎐
᎐
(cf. 1.609(6) Å for [n-Bu4N][RuVI(N)(L2)]). By careful inspec-
tion of the difference Fourier map, we did not find significant
electron density that can be attributed to a H atom in the
vicinity of the N3Ϫ ligand. Therefore, N-protonation is unlikely.
The coordination geometry of [RuVI(N)(HL2)] (7) at the
ruthenium atom is a distorted square pyramid, with the nitrido
ligand at the apical position. The Ru atom is slightly lifted out
of the mean plane defined by O(1), O(2), N(2) and N(3) by
∼ 0.57 Å. The Ru–N(2), Ru–N(3), Ru–O(1) and Ru–O(2),
distances are 2.029(4), 1.988(3), 1.964(3) and 1.975(3) Å,
respectively. However, it is noteworthy that the auxiliary L2
tion band at 1656 cmϪ1 characteristic of a C᎐O stretch, along
᎐
ligand displays a structural asymmetry in the C᎐O distance, i.e.,
᎐
with all the major spectral features of the starting complex. The
UV-VIS absorption spectrum recorded in CH2Cl2 shows two
intense absorption bands at λmax/nm (ε/dm3 molϪ1 cmϪ1) = 245
(49000) and 305 (23500) presumably due to intraligand
transitions.
With regard to the low product yield, most of the starting
complex (ca. 70%) was recovered during Et2O induced crystal-
lization. Analysis of the residual mother liquor by ESI-MS
revealed several ion species with molecular ion peaks at m/z =
738, 716, 686, 678 and 604, which can be assigned to [OsIV-
(L2)(Hpz)(pz)]Ϫ, [OsVI(N)(L2O2)(Hpz)]Ϫ, [OsVI(N)(L2) (Hpz)]Ϫ,
[OsVI(N)(L2)(AcOH)]Ϫ and [OsIII(L2)]Ϫ, respectively, based on
the agreement of the experimental and calculated isotopic
distribution patterns.
the O(3)–C(7) distance [1.296(5) Å] is significantly longer than
the O(4)–C(14) distance [1.210(6) Å]. A similar differential
in bond distances was observed for the amide groups, i.e.,
N(2)–C(7) [1.326(5) Å] bond distance is close to a N᎐C bond
᎐
length (ca. 1.31 Å in [OsIV(salch-tBu)Cl2]31 [salch-tBu = trans-
1,2-bis(di-tert-butylsalicyliminato)cyclohexane]), whereas the
N(3)–C(14) has a distance of 1.395(6) Å compatible with an
amide bond (cf. 1.391 Å in [n-Bu4N][RuVI(N)(L2)]). Moreover,
the O(3)–C(7) distance [1.296(5) Å] is significantly longer than
the O(4)–C(14) distance [1.210(6)Å], which is a typical C᎐O
᎐
The molecular structure of 8 has been established by X-ray
crystallography and is depicted in Fig. 10. One of the phenoxy
moieties was oxygenated to give a 1,4-benzoquinone structure,
᎐
whereas the Os᎐N moiety [1.625(9) Å] remained unchanged
᎐
after the reaction. The osmium atom adopts distorted square
pyramidal coordination, isostructural to the starting complex
[OsVI(N)(L2)]Ϫ. For the benzoquinone moiety, the C(16)–O(5)
and C(19)–O(6) bond distances are 1.223(13) and 1.252(14) Å,
which is a typical C᎐O double bond [cf. average 1.22 Å] in
᎐
[n-Bu4N][OsVI(N)(L2)]. Moreover, the C(14)–C(15) [1.350(16)
Å] and C(17)–C(18) [1.350(17) Å] distances are slightly shorter
Fig. 9 Perspective view of [RuVI(N)(HL2)] (7) with atom labelling
scheme (50% probability ellipsoids).
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Conclusion
In this work, we examined a series of nucleophilic and electro-
philic additions and oxidative reactions of some nitrido-
ruthenium() and -osmium() complexes containing di- and
tetra-anionic ligands. The high-valent nitrido-ruthenium()
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Acknowledgements
This work is supported by the Areas of Excellence Scheme
established under the University Grants Committee of the
Hong Kong Special Administrative Region, China (Project
AoE/P-10/01), The University of Hong Kong (University
Development Fund) and the Hong Kong Research Grants
Council (HKU7099/00P). We thank Prof. S.-M. Peng (National
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