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Formation of a Methyleneimine Moiety by Reaction of a RuII-Coordinated Azide Ion with Methyl Iodide.

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DOI: 10.1002/ange.200504157
Formation of a Methyleneimine Moiety by
Reaction of a RuII-Coordinated Azide Ion with
Methyl Iodide**
Hirotaka Nagao,* Takehiro Kikuchi, Minako Inukai,
Akihiro Ueda, Takao Oi, Noriyuki Suzuki, and
Mikio Yamasaki
It has been reported that an azide ion coordinated to a metal
center photochemically and thermally decomposes to afford a
nitrogen-containing compound(s), which retain(s) a nitrogen
atom of the azido ligand. The reaction proceeds via a reactive
intermediate such as a nitrene and nitride complex, and N2 is
generated.[1–5] Although azide compounds are explosive as a
result of rapid dinitrogen evolution, azido–metal complexes
can potentially to be converted into various nitrogen-containing complexes such as imido and cycloaddition compounds.[2–6] Di(azido)bis(2,2’-bipyridine) complexes of RuII
and RuIII have been synthesized[1, 7] and investigated in
thermal and photochemical reactions.[1, 8]
Methyleneimine is known to be a reactive molecule and
its existence can be recognized only at low temperatures by
IR spectroscopy.[9] A few metal complexes containing a
methyleneimine moiety (NH=CH2) have been synthesized by
the reaction of a methylhydrazine or methylimido complex.[10]
The NH=CH2 ligand coordinates through two coordination
modes; one is the N-monodentate mode (kN) of a rhenium
complex[10a–c] and another the N,C-bidentate one (k2N,C) of
an osmium complex.[10d] Only one rhenium complex containing an methyleneimine-kN moiety has been characterized by
X-ray crystallography.[10c] Herein, we describe the reaction of
cis-[Ru(N3)2(bpy)2]·H2O (bpy = 2,2’-bipyridine) with CH3I in
CH3CN to give a rare methyleneimine complex of ruthenium(ii) (Ru–NH=CH2) and its characterization by IR and
NMR spectroscopy and X-ray crystallography.
cis-[Ru(NH=CH2)(NCCH3)(bpy)2](PF6)2 was synthesized
by the reaction of cis-[Ru(N3)2(bpy)2]·H2O with CH3I in
CH3CN (Scheme 1). Red needle crystals were obtained by
recrystallization from CH3CN/H2O. The IR spectrum shows
Scheme 1. Reaction of the azido ligand with CH3I.
characteristic bands at ñ = 3283 and 2186 cm 1, which were
assigned to n(NH) and n(CN), respectively, as well as some
bands of bpy ligands and PF6. After the complex was
recrystallized from D2O/CH3CN (1:1 v/v), the band at
3283 cm 1 shifted to 2430 cm 1 (see Supporting Information).
This indicates that the proton of the NH moiety is exchangeable with a solvent proton.
The 1H NMR spectrum in (CD3)2CO shows a broad signal
for the hydrogen atom of the imine function (NH=CH2) at d =
12.14 ppm as a doublet of doublets owing to coupling with two
signals at d = 7.98 and 7.81 ppm (NH=CH2). These two signals
overlap with the bpy signals in the aromatic region and were
characterized by H,H COSY. The d value of the hydrogen
atom of the imine is similar to that of the CH2=NH-kN and
-k2N,C.[10] The 13C NMR spectrum shows a signal at
172.42 ppm, which was assigned to the carbon atoms of the
methyleneimine, analogously to that of the known Os
The structure of the cation, cis-[Ru(NH=CH2)(NCCH3)(bpy)2]2+ is shown in Figure 1. The methyleneimine and the
acetonitrile ligands are positioned cis to each other. The
methyleneimine ligand coordinates to the ruthenium center in
a bent fashion with Ru-N1-C1 = 135.4(7)8 and with Ru N1 =
2.083(10) and N1 C1 = 1.202(16) >. This coordination fashion is similar to that of the reported kN-mode coordination
rhenium complex.[10c] The N1 C1 bond length, 1.202(16) >, is
[*] Prof. Dr. H. Nagao, T. Kikuchi, M. Inukai, A. Ueda, Prof. Dr. T. Oi
Department of Chemistry
Faculty of Science and Technology, Sophia University
7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554 (Japan)
Fax: (+ 81) 3-3238-3361
Dr. N. Suzuki
Wako, Saitama 351-0198 (Japan)
Dr. M. Yamasaki
Application Laboratories, Rigaku Corporation
3-9-12 Matsubara-cho, Akishima, Tokyo 196-8666(Japan)
[**] This work was supported by a Grant-in-Aid for Scientific Research
(no. 14540520) from the Ministry of Education, Culture, Sports,
Science, and Technology, Japan. We thank Professor James M.
Mayer (University of Washington) for his helpful discussion.
Supporting information for this article is available on the WWW
under or from the author.
Angew. Chem. 2006, 118, 3203 –3205
Figure 1. Structure of cis-[Ru(NH=CH2)(NCCH3)(bpy)2]2+ with 50 %
probability for thermal ellipsoids.
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
shorter than those of other structurally characterized imine
moieties coordinated to a metal center (1.25–1.31 >).[10c, 11]
The acetonitrile ligand linearly coordinates to the metal
center, as in previously reported RuII complexes.[11b] The
structural parameters of two bpy ligands are similar to those
of the previously reported ruthenium complexes.[11b, 12]
The cyclic voltammogram (CV) of the complex in CH3CN
containing tetraethylammonium perchlorate (0.1 mol dm 3)
shows irreversible and reversible oxidation waves at Epa =
0.86 and E1/2 = 1.10 V versus Fc/Fc+ at room temperature (see
Supporting Information). The first irreversible oxidation
potential is higher than those of RuII complexes containing
polypyridine ligands and that of the imine complex of RuII,
[Ru(NH=CMe2)(bpy)(trpy)]2+.[13] The first irreversible wave
corresponds to a one-electron process by a controlled
potential electrolysis. After the electrolysis, the CV shows
only one reversible couple at 1.10 V. The profile of the CV
does not change, even at low temperature ( 40 8C). The
oxidized form of this complex is very unstable and decomposes rapidly.
The UV/Vis spectrum of the starting diazido complex of
RuII in CH3CN shows two bands at l = 560 and 387 nm. The
spectrum in the presence of CH3I in CH3CN changes to show
new bands at l = 496 and 356 nm. The band at l = 496 nm
then decreases in intensity and a new band appears at l =
442 nm (see Supporting Information). However, in absence of
CH3I, the spectrum does not change for at least 4 days. The
spectral change in CH3NO2 is the same as that in CH3CN at
the first stage, but no further change is observed for at least a
few hours. A reaction intermediate like [Ru(NH=CH2)(N3)(bpy)2]+ and [Ru(NH=CH2)2(bpy)2]2+, which shows a characteristic band at 496 nm, develops during the formation of the
methyleneimine complex. Attempts to isolate the product in
CH3NO2 were all unsuccessful. We believe that the methyleneimine ligand is formed by the reaction of CH3I with the
negatively charged nitrogen atom of the azido ligand on RuII
via a methylimido intermediate with N2 evolution and proton
transfer from the methyl group to the imido nitrogen atom, as
in the formation of a methyleneimine-k2N,C osmium complex
from a methylimido-kN analogue.[10d]
In this reaction of the azido complex, the nitrogen atom of
the coordinated azide ion remains on the ruthenium center.
The reaction of azido complexes will be useful in the synthesis
of nitrogen-containing ligands for metal complexes. Detailed
studies on the reaction of the azido complex and further
reactions and properties of the methyleneimine ligand on the
ruthenium complex are in progress.
Experimental Section
cis-[Ru(NH=CH2)(NCCH3)(bpy)2](PF6)2 : A suspension of cis[Ru(N3)2(bpy)2]·H2O (200 mg, 0.388 mmol) and CH3I (3 cm3) in
CH3CN (100 cm3) was stirred in the dark until the starting complex
dissolved to form a dark red solution. A red oily reaction product was
obtained after addition of KPF6 (200 mg, 1.09 mmol) as a precipitant
and concentration of the resultant solution. The red product obtained
was recrystallized from CH3CN/H2O (1:1, 100 cm3) through concentration by slow evaporation to form red needles (138 mg, 46 %).
Elemental analysis: calcd for C23H22N6P2F12Ru (%): C 35.72, H 2.87,
N 10.87; found: C 35.64, H 2.70, N 10.72; FAB MS: 629(M-PF6); 1H
and 13C NMR spectra were recorded on JEOL EX-270, AL-400 and
ECP-500 spectrometers. The signals of the complex were characterized by 1H, 1H{1H}, 13C{1H}, DEPT, COSY, C,H-COSY NMR
spectroscopy (see Supporting Information). 1H NMR (400 MHz,
[D6]acetone, TMS): d = 2.50 (s, 3 H; CH3CN), 7.41–7.44 (m, 2 H;
bpy), 7.81 (d, J = 21 Hz, 1 H; CH2), 7.89–7.94 (m, 4 H; bpy), 7.98 (d,
J = 13 Hz, 1 H; CH2), 8.04–8.09 (m, 2 H; bpy), 8.32–8.36 (m, 2 H; bpy),
8.61–8.70 (m, 2 H; bpy), 8.74–8.81 (m, 2 H; bpy), 9.15–9.17 (m, 1 H;
bpy), 9.52–9.54 (m, 1 H; bpy), 12.14 ppm (br dd, J = 13 Hz, J = 21 Hz,
1 H; NH); 13C NMR (67.8 MHz, [D6]acetone, TMS): d = 4.04
(CH3CN), 124.49, 124.71, 124.90, 124.98, 127.82 (CH3CN, overlapped
with 2,2’-bipyridyl), 127.98, 128.46, 128.77, 138.73 (2C), 139.00, 139.27,
152.89, 153.16, 153.41, 154.09, 158.00 (q), 158.28 (q), 158.49 (q), 159.07
(q), 172.42 ppm (CH2).
Crystal structure determination: Intensity data were collected on
a Rigaku RAXIS RAPID imaging plate area detector, using graphitemonochromated MoKa radiation (0.71075 >). All the calculations
were carried out with the Crystal Structure software package.
Structures were solved by SHELXL, expanded by using Fourier
techniques, and refined by using full-matrix least-squares techniques
on F2. Crystallographic data: C23H22F12N6P2Ru, Mw = 773.47, monoclinic, P21/c, a = 17.078(6) >, b = 17.847(5) >, c = 11.825(3) >, b =
127.266(14)8, V = 2868.3(15) >3, Z = 4, 1calcd = 1.791 g cm 3, m(MoKa) = 7.63 cm 1, T = 103 K, 26 072 reflections collected, 6523
unique (Rint = 0.0330), R1{I>2s(I)} = 0.0909, wR2 (all data) =
0.2458, GOF = 1.052; two PF6 ions are disordered: P F bonds and
F-P-F angles of each PF6 ion were restrained and refined. CCDC289 365 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
Received: November 22, 2005
Published online: April 4, 2006
Keywords: azides · imines · N ligands · ruthenium ·
synthetic methods
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methyl, ion, moiety, reaction, azido, methyleneimine, formation, coordinated, iodide, ruii
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