Ruthenium(VI) nitrido complexes with a sterically bulky bidentate Schiff base ligand

Article abstract of DOI:10.1016/j.ica.2012.07.025

Ruthenium(VI) complexes with a sterically bulky bidentate Schiff base ligand, 2-[(2,6-diisopropylphenyl)imino]methyl-4,6-dibromophenolate (L ^-), have been synthesized and their reactivity studied. Treatment of [Buⁿ₄N][Ru(N)Cl₄] in tetrahydrofuran with 2 equivalents of NaL afforded cis-[Ru(N)Cl(L)₂] (1) that reacted with Ag(OTf) (OTf^- = triflate) in acetone to give trans-[Ru(N)(H ₂O)L₂][OTf] (2). Reactions of complex 1 with Me ₃NO and elemental sulfur afforded cis-[Ru(NO)(Cl)L₂] (3) and cis-[Ru(NS)(Cl)L₂] (4), respectively. Reaction of complex 1 with Me₃SiN₃ in MeCN afforded [Ru(MeCN)(Cl)L₂], which could alternatively be prepared by photolysis of complex 3 in CH ₂Cl₂-MeCN with UV light. The crystal structures of complexes 1 and 2 have been determined.

Full text of DOI:10.1016/j.ica.2012.07.025

Inorganica Chimica Acta 394 (2013) 171–175
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Ruthenium(VI) nitrido complexes with a sterically bulky bidentate Schiff base ligand
Ho-Yuen Ng a, Ngai-Man Lam a, Min Yang b, Xiao-Yi Yi b, Ian D. Williams a, Wa-Hung Leung a,
⇑
a Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
b School of Chemistry and Chemical Engineering, Central South University, Changsha, Hunan 410083, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Ruthenium(VI) complexes with a sterically bulky bidentate Schiff base ligand, 2-[(2,6-diisopropyl-
phenyl)imino]methyl-4,6-dibromophenolate (Lꢀ), have been synthesized and their reactivity studied.
Treatment of [Bun4N][Ru(N)Cl4] in tetrahydrofuran with 2 equivalents of NaL afforded cis-[Ru(N)Cl(L)2]
(1) that reacted with Ag(OTf) (OTfꢀ = triflate) in acetone to give trans-[Ru(N)(H2O)L2][OTf] (2). Reactions
of complex 1 with Me3NO and elemental sulfur afforded cis-[Ru(NO)(Cl)L2] (3) and cis-[Ru(NS)(Cl)L2] (4),
respectively. Reaction of complex 1 with Me3SiN3 in MeCN afforded [Ru(MeCN)(Cl)L2], which could alter-
natively be prepared by photolysis of complex 3 in CH2Cl2–MeCN with UV light. The crystal structures of
complexes 1 and 2 have been determined.
Received 4 January 2012
Received in revised form 15 June 2012
Accepted 25 July 2012
Available online 17 August 2012
Keywords:
Ruthenium
Nitrido
Bidentate Schiff base ligand
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
Late transition-metal terminal nitrido complexes have attracted
attention due to their potential applications in metal-mediated
nitrogen atom transfer [1–11]. Of special interest are nitrido com-
plexes of ruthenium that are found to exhibit interesting electro-
philic reactivity [7–9,12–16]. Lau and co-workers demonstrated
that RuVI nitrido complexes with tetradentate Schiff base (salen)
ligands are considerably more reactive than the OsVI congeners.
The reactivity of RuVI(salen) nitrido complexes toward phosphine,
isocyanides, thiols and alkenes has been investigated [12]. In polar
solvents, trans-[Ru(N)(MeOH)(salen)]+ undergoes facile intermo-
lecular Nꢁ ꢁ ꢁN coupling to give dinitrogen and RuIII(salen)
complexes [12a]. A synthetic route to trans-[RuIIIL2(salen)]+ com-
plexes based on ligand-accelerated nitrido coupling of trans-
[Ru(N)(MeOH)(salen)]+ has been reported [12b].
In an effort to explore the potential of electrophilic nitrido com-
plexes for nitrogen atom transfer, we sought to synthesize RuVI
nitrido complexes stabilized by sterically bulky coligands, which
can inhibit the intermolecular coupling of the nitrido group. The
sterically bulky bidentate Schiff base ligand 2-[(2,6-diisopropyl-
phenyl)imino]methyl-4,6-dibromophenol (HL, Scheme 1) can form
stable complexes with transition metals [17]. However, to our
knowledge, Ru–L complexes have not been isolated. We herein de-
scribe the synthesis and structures of RuVI nitrido complexes,
which are stable with respect to Nꢁ ꢁ ꢁN coupling, and their reactions
with Me3NO and elemental sulfur.
2.1. General remarks
All manipulations were carried out under nitrogen by standard
Schlenk techniques. Solvents were dried by standard procedures
and distilled prior to use. NMR spectra were recorded on a Bruker
AV 400 spectrometer operating at 400.1, 376.5 and 162.0 MHz for
1H, 19F and 31P, respectively. Chemical shifts (d, ppm) were re-
ported with reference to SiMe4 (1H) and CF3C6H5 19F). IR spectra
(
were recorded on a Perkin-Elmer 16 PC Fourier transform infrared
spectrophotometer. Electrospray ionization mass spectrometry
was recorded on an Applied Bio-system QSTAR mass spectrometer.
Magnetic moments of paramagnetic complexes were determined
by Evans method [18] in CDCl3 solutions at room temperature. Ele-
mental analyses were performed by Medac Ltd., Surrey, UK. The
compound [Bun4N][Ru(N)Cl4] [19] was prepared according to a
literature method. The hydrogen atom labelling scheme for the
ligand Lꢀ is shown in Scheme 1.
2.2. Preparation of the ligand HL
A mixture of 2,6-diisopropylaniline (18 mg, 0.1 mmol) and 3,5-
di-bromo-2-hydroxylbenzaldehyde (28 mg, 0.1 mmol) in methanol
(5 mL) was refluxed for 1.5 h. The solvent was removed in vacuo
and the residue washed with ethanol (3 ꢂ 5 mL). Recrystallization
from methanol–diethyl ether afforded a yellow solid. Yield: 31 mg
(67%). 1H NMR (CDCl3): d = 1.17 (d, J = 7 Hz, 12H, (CH3)2CH), 2.92
(sept, J = 7 Hz, 2H, (CH3)2CH), 7.21 (d, J = 2 Hz, 2H, H3), 7.24 (t,
J = 2 Hz, 1H, H4), 7.44 (d, J = 2 Hz, 1H, H2), 7.80 (d, J = 2 Hz, 1H,
H1), 8.20 (s, 1H, H5, AHC = N) ppm. The sodium salt NaL was
⇑
Corresponding author. Tel.: +852 2358 1594.
E-mail address: chleung@ust.hk (W.-H. Leung).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.07.025

172
H.-Y. Ng et al. / Inorganica Chimica Acta 394 (2013) 171–175
2H, (CH3)2CH), 3.56 (sept, J = 7 Hz, 2H, (CH3)2CH), 7.08 (d,
N
Ru
O
+
N
J = 2 Hz, 2H, H3), 7.14 (d, J = 2 Hz, 2H, H3), 7.28 (t, J = 2 Hz, 1H,
H4), 7.56 (t, J = 2 Hz, 1H, H4), 7.67 (d, J = 2 Hz, 2H, H2) 7.90 (d,
J = 2 Hz, 2H, H1), 7.91 (s, 2H, H5, AHC = N) ppm. 19F{1H} NMR
(CDCl3): d = ꢀ77.47 (s) ppm. MS (ESI): 991.99 (M+ꢀH2O). IR (KBr,
OTf-
Cl
N
N
O
Ag(OTf)
2NaL
S8
[Ru(N)Cl4]-
O
N
N
O
Ru
OH2
Me3SiN3
MeCN/CH2Cl2
cmꢀ1): 1029 [
m(Ru„N)], 1600 [m(C = N)]. Anal. Calc. for C39H42Br4-
Me3NO
ClF3N3O6RuSꢁ1/2 CH2Cl2: C, 39.50; H, 3.61; N, 3.50. Found: C,
39.85; H, 3.86; N, 3.54%.
MeCN
NS
Ru
O
Cl
N
N
Cl
N
N
O
NO
Ru
2.3.3. Preparation of cis-[Ru(NO)(Cl)L2] (3)
O
Cl
N
N
O
Ru
O
O
To a solution of complex 1 (103 mg, 0.1 mmol) in THF (10 mL)
was added 1 equivalent Me3NO (8 mg, 0.1 mmol), and the mixture
was stirred at room temperature for 12 h, during which the color of
solution changed from red to yellow. The solvent was removed in
vacuo and the residual solid was extracted with Et2O–hexane (v/v,
1:1, 3 ꢂ 10 ml). Concentration and cooling at ꢀ18 °C to give yellow
crystals which were suitable for the X-ray diffraction study. Yield:
94 mg (90%). 1H NMR (C6D6): d = 0.79 (d, J = 7 Hz, 3H, (CH3)2CH),
0.95 (d, J = 7 Hz, 3H, (CH3)2CH), 0.97 (d, J = 7 Hz, 3H, (CH3)2CH),
1.10 (d, J = 7 Hz, 3H, (CH3)2CH), 1.13 (d, J = 7 Hz, 3H, (CH3)2CH),
1.21 (d, J = 7 Hz, 3H, (CH3)2CH), 1.23 (d, J = 7 Hz, 3H, (CH3)2CH),
1.29 (d, J = 7 Hz, 3H, (CH3)2CH), 2.99 (sept, J = 7 Hz, 1H, (CH3)2CH),
3.48 (sept, J = 7 Hz, 1H, (CH3)2CH), 3.65 (sept, J = 7 Hz, 1H, (CH3)2-
CH), 4.43 (sept, J = 7 Hz, 1H, (CH3)2CH), 7.06 (d, J = 2 Hz, 1H, H3),
7.09 (d, J = 2 Hz, 1H, H3), 7.10 (d, J = 2 Hz, 1H, H3), 7.14 (d,
J = 2 Hz, 1H, H3), 7.23 (t, J = 2 Hz, 1H, H4), 7.28 (t, J = 2 Hz, 1H,
H4), 7.31 (d, J = 2 Hz, 1H, H2), 7.33 (d, J = 2 Hz, 1H, H2), 7.40 (d,
J = 2 Hz, 1H, H1), 7.42 (d, J = 2 Hz, 1H, H1), 7.64 (s, 1H, H5, AHC = N),
hν
MeCN/CH2Cl2
3
4
N
O
=
5
N
2
Br
O
1
Br
Scheme 1. Synthesis and reactivity of RuVI nitrido complexes.
prepared by reaction of HL (44 mg, 0.1 mmol) with 60% NaH (4 mg,
0.17 mmol) in tetrahydrofuran (THF) (10 mL) at room temperature
for 1.5 h and recrystallized from THF–hexane.
7.95 (s, 1H, H5, AHC@N) ppm. IR (KBr, cmꢀ1): 1859 [
m(N„O)], 1618
2.3. Synthesis of complexes
[
m
(C = N)]. Anal. Calc. for C38H40Br4ClN3O3Ruꢁ1/2 C6H14: C, 45.35; H,
4.36; N, 3.87. Found C, 44.87; H, 4.15; N, 3.53%. Despite two at-
tempts, we have not been able to obtain satisfactory carbon anal-
ysis for complex 3. However, the identity of complex 3 has been
established by spectroscopic methods and X-ray diffraction.
2.3.1. Preparation of cis-[Ru(N)Cl(L)2] (1)
To a solution of [Bun4N][Ru(N)Cl4] (50 mg, 0.1 mmol) in THF
(10 mL) was added 2 equivalents of NaL (92 mg, 0.2 mmol) in
THF (10 mL) dropwise. The mixture was stirred at room tempera-
ture for 12 h. The solvent was removed in vacuo and the residual
solid was extracted by Et2O-hexane (v/v, 1:1, 3 ꢂ 10 mL). The ex-
tract was concentrated to 3 mL and cooled at ꢀ18 °C to give block
red crystals which were suitable for the X-ray diffraction study.
Yield: 52 mg (50%). 1H NMR (C6D6): d = 0.74 (d, J = 7 Hz, 3H, (CH3)2-
CH), 0.87 (d, J = 7 Hz, 3H, (CH3)2CH), 0.88 (d, J = 7 Hz, 3H, (CH3)2CH),
1.08 (d, J = 7 Hz, 3H, (CH3)2CH), 1.27 (d, J = 7 Hz, 3H, (CH3)2CH),
1.40 (d, J = 7 Hz, 3H, (CH3)2CH), 1.41 (d, J = 7 Hz 3H, (CH3)2CH),
1.54 (d, J = 7 Hz, 3H, (CH3)2CH), 3.12 (sept, J = 7 Hz, 1H, (CH3)2CH),
3.80 (sept, J = 7 Hz, 1H, (CH3)2CH), 3.99 (sept, J = 7 Hz, 1H, (CH3)2-
CH), 4.78 (sept, J = 7 Hz, 1H, (CH3)2CH), 6.83 (d, J = 2 Hz, 1H, H3),
6.94 (d, J = 2 Hz, 2H, H3), 6.97 (d, J = 2 Hz, 1H, H3), 7.05 (t,
J = 2 Hz, 1H, H4), 7.12 (t, J = 2 Hz, 1H, H4), 7.20 (d, J = 2 Hz, 1H,
H2), 7.22 (d, J = 2 Hz, 1H, H2), 7.37 (d, J = 2 Hz, 1H, H1), 7.40 (d,
J = 2 Hz, 1H, H1), 7.51 (s, 1H, H5, AHC = N), 7.85 (s, 1H, H5, AHC = N)
2.3.4. Preparation of cis-[Ru(NS)(Cl)L2] (4)
A mixture of complex 1 (103 mg, 0.1 mmol) and elemental sul-
fur (3.2 mg, 0.1 mmol) in THF (10 mL) was heated at reflux for 12 h,
during which the color of solution changed from red to orange. The
solvent was removed in vacuo and the residue was extracted by
Et2O–hexane (v/v, 1:1, 3 ꢂ 10 ml). Concentration and cooling at
ꢀ18 °C afforded an orange crystalline solid. Yield: 92 mg (87%).
1H NMR (C6D6): d = 0.79 (d, J = 7 Hz, 3H, (CH3)2CH), 0.83 (d,
J = 7 Hz, 3H, (CH3)2CH), 0.87 (d, J = 7 Hz, 3H, (CH3)2CH), 0.90 (d,
J = 7 Hz, 3H, (CH3)2CH), 1.08 (d, J = 7 Hz, 3H, (CH3)2CH), 1.10 (d,
J = 7 Hz, 3H, (CH3)2CH), 1.40 (d, J = 7 Hz, 3H, (CH3)2CH), 1.42 (d,
J = 7 Hz, 3H, (CH3)2CH), 1.65 (d, J = 7 Hz, 3H, (CH3)2CH), 2.88 (sept,
J = 7 Hz, 1H, (CH3)2CH), 3.86 (sept, J = 7 Hz, 1H, (CH3)2CH), 4.07
(sept, J = 7 Hz, 1H, (CH3)2CH), 4.21 (sept, J = 7 Hz, 1H, (CH3)2CH),
7.05 (d, J = 2 Hz, 1H, H3), 7.09 (d, J = 2 Hz, 2H, H3), 7.11 (d,
J = 2 Hz, 2H, H3), 7.12 (d, J = 2 Hz, 1H, H3), 7.20 (t, J = 2 Hz, 1H,
H4), 7.27 (t, J = 2 Hz, 1H, H4), 7.32 (d, J = 2 Hz, 1H, H2), 7.35 (d,
J = 2 Hz, 1H, H2), 7.40 (d, J = 2 Hz, 1H, H1), 7.42 (d, J = 2 Hz, 1H,
H1), 7.63 (s, 1H, H5, ꢀHC = N), 7.92 (s, 1H, H5, AHC@N) ppm. MS
(ESI): 1058.76 (M+), 1023.69 (M+ꢀCl). IR (KBr, cmꢀ1): 1613
ppm. IR (KBr, cmꢀ1): 1025 [
m(Ru„N)], 1611 [m(C@N)]. Anal. Calc.
for C38H40Br4ClN3O2Ruꢁ1.5Et2O: C, 46.44; H, 4.87; N, 3.69. Found:
C, 46.74; H, 4.97; N, 3.72%.
2.3.2. Preparation of trans-[Ru(N)(H2O)L2][OTf] (2)
To a solution of complex 1 (103 mg, 0.1 mmol) in CH2Cl2
(10 mL) was added 1 equivalent of AgOTf (26 mg, 0.1 mmol), and
the mixture was stirred at room temperature for 6 h and filtered.
The solvent was removed in vacuo and the residual solid was ex-
tracted with Et2O–CH2Cl2 (v/v, 1:1, 3 ꢂ 10 mL). Concentration (to
ca. 8 mL) and cooling at ꢀ18 °C afforded reddish-brown blocks
which were suitable for the X-ray diffraction study. Yield: 87 mg
(83%). 1H NMR (CDCl3): d = 1.23 (d, J = 7 Hz, 6H, (CH3)2CH), 1.43
(d, J = 7 Hz, 6H, (CH3)2CH), 1.66 (d, J = 7 Hz, 6H, (CH3)2CH), 1.83
(d, J = 7 Hz, 6H, (CH3)2CH), 2.35 (br, 2H, H2O), 3.29 (sept, J = 7 Hz,
[
m
(C@N)], 1284 [
m
(N„S)]. Anal. Calc. for C38H40Br4ClN3O2RuSꢁ1/
2C6H14: C, 44.68 H, 4.30; N, 3.81; S, 2.91: Found C, 45.57; H,
4.18; N, 3.71; S, 3.29%. Despite two attempts, we have not been
able to obtain satisfactory carbon analysis for complex 4. However,
complex 4 has been well characterized by spectroscopic methods.
2.3.5. Preparation of cis-[Ru(MeCN)(Cl)L2] (5)
Method A: a solution of complex 1 (104 mg, 0.1 mmol) in CH2-
Cl2–MeCN (100 mL, v/v, 9:1) was irradiated with UV light (Hg

H.-Y. Ng et al. / Inorganica Chimica Acta 394 (2013) 171–175
173
lamp, 9 W) for 2 h, during which the color of solution changed from
red to green. The solvent was removed in vacuo and the residue
was extracted by Et2O (10 mL). Concentration and cooling of the
extract at ꢀ18 °C gave a green crystalline solid. Yield: 72 mg
(68%). leff (Evans method) = 1.7
l
B. MS (ESI): 1052.91 (M+ꢀ1),
1018.42 (M+ꢀCl). Anal. Calc. for C40H43Br4ClN3O2Ru: C, 45.58; H,
4.11; N, 3.99. Found: C, 45.74; H, 4.23; N, 3.78%.
Method B: to a solution of complex 1 (104 mg, 0.1 mmol) in CH2-
Cl2–MeCN (10 mL, v/v, 9:1) was added 1 equivalent of Me3SiN3
(1.3 lL, 0.1 mmol). The mixture was stirred for 12 h. The solvent
was removed in vacuo and the residue was extracted by Et2O
(5 mL). Concentration and cooling of the extract at ꢀ18 °C gave a
green crystalline solid characterized as complex 5. Yield: 59 mg
(56%).
2.4. X-ray crystallography
Fig. 1. Structure of the complex cation in trans-[Ru(N)(H2O)(L)2][OTf] (2). Hydrogen
atoms are omitted for clarity. The ellipsoids are drawn at 30% probability level.
Selected bond lengths [Å]: Ru(1)AO(1) 1.983(5), Ru(1)AO(2) 1.960(5), Ru(1)AO(3)
2.225(5), Ru(1)AN(1) 2.129(6), Ru(1)AN(2) 2.070(6), Ru(1)AN(3) 1.651(6).
Complexes 2 and 3 have been characterized by X-ray diffrac-
tion. However, due to the positional disorder problem of the li-
gands (vide infra), the bond distances and angles of complex 3
have not been analyzed. Intensity data were collected on a Bruker
1000 or APEX 1000 CCD diffractometer using graphite-monochro-
geometry of the molecule. The IR spectrum displayed the m(Ru„N)
band at 1029 cmꢀ1. Unlike trans-[Ru(N)(MeOH)(salen)]+, complex
2 is stable in polar solvents such as acetonitrile and dimethylsulf-
oxide. No nitrido coupling was found even when 2 was reacted
with pyridine in C6D6 at 50 °C. This result indicates that the inter-
molecular Nꢁ ꢁ ꢁN coupling of the Ru nitride can be inhibited by the
bulky, electron-deficient Schiff base coligand.
mated Mo-Ka radiation (k = 0.71073 Å). The collected frames were
processed with the software SAINT [20]. Structures were solved by
the direct methods and refined by full-matrix least-squares on F2
using the SHELXTL software package [21]. Atomic positions of non-
hydrogen atoms were refined with anisotropic parameters and
with suitable restraints. However, disordered atoms were refined
isotropically. Hydrogen atoms were generated geometrically and
allowed to ride on their respective parent carbon atoms before
the final cycle of least-squares refinement.
Complex 2 has been characterized by X-ray diffraction.1 Fig. 1
shows the molecular structure of complex 2. Unlike complex 1, the
nitrido and aqua ligands complex 2 are trans to each other. The
two imino groups of Lꢀ are trans to each other in order to minimize
the repulsion between the sterically demanding 2,6-diisopropyl-
phenyl groups. The Ru-nitrido distance of 1.651(6) Å in 2 is longer
than that in [Ru(N)(MeOH)(salchda)]+ (salchda = N,N0-bis(salicylid-
ene)-o-cyclohexyldamine dianion, 1.592(4) Å) [12a], possibly due
to steric effects. The RuAO(H2O) distance of 2.225(5) Å in 2 is consis-
tent with the formulation of an aqua ligand. The RuAO [1.972(5) Å]
and RuAN [2.100(6) Å] distances for the Schiff base ligands are
normal.
3. Results and discussion
3.1. Ruthenium nitrido complexes
The synthesis and reactivity of RuVI nitrido complexes with the
bidentate Schiff base ligand Lꢀ are summarized in Scheme 1. Treat-
ment of [Bun4N][Ru(N)Cl4] (1) with 2 equivalents of NaL in tetrahy-
drofuran (THF) afforded cis-[Ru(N)(Cl)L2] (1). A preliminary X-ray
diffraction study confirmed the cis arrangement between the ni-
tride and chloride ligands in complex 1. Unfortunately, the struc-
ture has not been refined satisfactorily because the nitrido ligand
is disordered. Nevertheless, the identity of complex 1 has been
fully confirmed. It may be noted a similar disorder problem has
been observed in a related CrV nitrido chloride complex [22]. Com-
plex 1 is soluble in common organic solvents including hexane, and
air stable in both the solid state and solution. The imine protons of
Lꢀ in 1 appeared as two singlets at d = 7.51 and 7.85 ppm in the 1H
NMR spectrum, consistent with the solid-state structure. This is in
contrast with analogous Ru(N)(X)(salen)-type complexes contain-
ing quadridentate Schiff base ligands, which usually exhibit trans
geometry. The IR spectrum of complex 1 displayed a peak at
1025 cmꢀ1, which is absent in the related nitrosyl complex (see la-
ter section). This peak is tentatively assigned as the RuAN stretch.
Similar RuAN stretching frequencies have been found in related
salen complexes.
3.2. Reactivity of complex 1
Unlike the salen analogue, no reactions were found between 1
and nucleophiles such as triphenylphosphine, tricyclohexylphos-
phine and morpholine. However, complex 1 reacted readily with
PMe3 to give an unidentified paramagnetic species. Reaction of
complex 1 with Me3NO led to formation of the nitrosyl complex
cis-[Ru(NO)(Cl)L2] (3). The IR spectrum of complex 3 is similar to
that of
1 except that an intense N-O band was found at
1859 cmꢀ1. The NAO stretching frequency of complex 3 is lower
than those of related salen-type complexes, e.g. 1830 cmꢀ1 for
trans-[Ru(L1)(NO)C]
(L1 = (R,R)-(ꢀ)-cyclohexanebis(3,5-di-tert-
butylsalicylidene aminate)) [23], indicating that the Ru center in
complex 3 is less electron-rich than those in the salen analogues.
Such an electronic difference together with the steric factors may
lead to the lower reactivity of complex 3 (e.g. NAN coupling and
reactions with nucleophiles) compared with the salen analogues.
The 1H NMR spectrum displayed two imine proton signals at
The treatment of complex 1 with Ag(OTf) (OTf = triflate) affor-
ded the cationic aqua complex trans-[Ru(N)(H2O)L2][OTf] (2). Un-
like 1, complex 2 exhibits a trans geometry with the nitrido and
aqua ligand opposite to each other. The reason (steric and/or elec-
tronic) for the difference in geometry between complexes 1 and 2
is not clear. Complex 2 is soluble in common organic solvents ex-
cept Et2O and hexane. The 1H NMR spectrum of 2 showed a singlet
at d = 7.91 ppm for the imine proton, consistent with the trans
1
Crystal data for complex 2ꢁ0.75CH2Cl2: C39
.75H43.5Br4Cl1.5F3N3O6RuS,
Mr = 1222.22, T = 100(2) K, monoclinic, space group P21/n, a = 11.3057(6),
b = 13.2964(7), c = 31.8107(16) Å, b = 97.747(1)°, V = 4738.3(4) Å3, Z = 4,
calc = 1.481
Mg mꢀ3
(Mo ) = 3.794; 23349 reflections collected, and 8140 unique
q
,
l
Ka
(Rint = 0.0416). The final R1 = 0.0458 and wR2 = 0.1077 [I > 2.0
wR2 = 0.1127 (all data).
r(I)]; R1 = 0.0571 and

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H.-Y. Ng et al. / Inorganica Chimica Acta 394 (2013) 171–175
4. Conclusions
In summary, we have synthesized a RuVI nitrido complex
containing sterically bulky bidentate Schiff base ligand,
a
cis-[Ru(N)(Cl)L2] (1). Chloride abstraction of complex 1 afforded a
cationic aqua complex, trans-[Ru(N)(H2O)L2]+ (2), which has a trans
geometry. In contrast with the salen analogues, complex 2 is stable
with respect to intermolecular nitrido coupling in solutions. No
reactions were found between complex 1 and nucleophiles includ-
ing triphenylphosphine and morpholine. This result demonstrates
that the steric and electronic factors of the coligand have an influ-
ence on the stability/reactivity of RuVI nitrido complexes. Complex
1 reacts with Me3NO, S8 and Me3SiN3–MeCN to give the nitrosyl,
thionitrosyl and acetonitrile complexes, respectively. The investi-
gation of reactivity of RuVI nitrido complexes with bulky, elec-
tron-deficient Schiff base ligands is underway.
Acknowledgements
We thank Dr. Herman H.Y. Sung for solving the crystal struc-
tures. The financial support from the Hong Kong Research Grants
Council (Project Nos. 602209 and 603111) is gratefully acknowl-
edged. X.-Y. Yi thanks support from the National Natural Science
Foundation of China (Project No. 21001118).
Fig. 2. Structure of [Ru(NO)Cl(L)2] (3). The chloride and nitrosyl ligands are 50:50
disordered. Hydrogen atoms are omitted for clarity. The ellipsoids are drawn at 30%
probability level.
Appendix A. Supplementary material
d = 7.64 and 7.95 ppm, consistent with the cis geometry. The iden-
tity of complex 3 has been established by an X-ray diffraction
study (Fig. 2)2. Unfortunately, the metal–ligand distances in 3 have
not been analyzed due to the positional disorder found for the chlo-
ride and nitrosyl ligands.
CCDC 838645 and 838646 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.07.025.
Refluxing complex 1 with elemental sulfur led to formation of
the thionitrosyl complex [Ru(NS)(Cl)L2] (4). It may be noted that
ꢀ
a
[Co(
related Ru thionitrosyl complex, [Ru(LOEt)(NS)Cl2] (LOEt
=
5-C5H5)(P(O)Et)3]ꢀ) has been prepared by reaction of
References
g
[Ru(LOEt)(N)Cl2] with S2O3 [14b]. Similar to complex 3, the 1H
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7.92 ppm for the imine protons, indicative of the cis geometry of
the molecule. The IR spectrum of complex 4 displayed the NAS
stretch at 1284 cmꢀ1, which is similar to that for [Ru(LOEt)(NS)Cl2]
(1307 cmꢀ1) [14b]. An attempt to prepare a selenonitrosyl complex
by refluxing complex 1 with elemental selenium failed.
2ꢀ
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2
Crystal data for complex 3: C41H40Br4ClN4O2Ru, Mr = 1076.93, T = 173(2) K,
ꢀ
triclinic, space group P1, a = 9.0029(2) Å, b = 15.4893(4) Å, c = 15.8688(4) Å,
a
= 87.688(2)°, b = 80.721(2)°, calc = 1.670 -
c
= 78.804(2)°, V = 2142.27(9) Å3, Z = 2,
q
Mg mꢀ3 ) = 8.211 mmꢀ1
,
l
(Mo , 11587 reflections collected, and 7412 unique
K
a
(Rint = 0.0400). The final R1 = 0.0433 and wR2 = 0.1156 [I > 2.0
wR2 = 0.1169 (all data).
r(I)]; R1 = 0.0448 and

H.-Y. Ng et al. / Inorganica Chimica Acta 394 (2013) 171–175
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