Carbonylmolybdenum complexes with di(imino)pyridine and related ligands: Reduction of a di(imino)pyridine to an aminoiminopyridine system under mild conditions

Article abstract of DOI:10.1016/j.ica.2006.06.005

The reactions of [Mo(CO)₆] towards a 2,6-di(imino)pyridine L¹ and related ligands were studied. The reaction with L¹ afforded two new complexes, [Mo(CO)₄L¹] (1) and [Mo(CO)₄L²] (2), where L² is the 2-amino-6-iminopyridine ligand arising from the hydrogenation of one imine function of L¹; similar reaction with a 2-acetyl-6-iminopyridine ligand L³ afforded [Mo(CO)₄L³] (3). Compounds 1, 2 and 3 have been fully characterised by IR, ¹H NMR and X-ray crystallography; they present a metal ion in a pseudo-octahedral environment, the three organic ligands acting with bidentate N₂ coordination modes. One of the imine functions in 1, the amine function in 2, and the ketone function in 3 are uncoordinated.

Full text of DOI:10.1016/j.ica.2006.06.005

Inorganica Chimica Acta 359 (2006) 4311–4316
www.elsevier.com/locate/ica
Carbonylmolybdenum complexes with di(imino)pyridine and
related ligands: Reduction of a di(imino)pyridine to an
aminoiminopyridine system under mild conditions
a
a
a,
a
Nathalie Cosquer , Benoˆıt Le Gall , Franc¸oise Conan *, Jean-Michel Kerbaol ,
a
b
b
Jean Sala-Pala , Marek M. Kubicki , Estelle Vigier
a
Laboratoire de Chimie, Electrochimie Mole´culaires et Chimie Analytique, UMR CNRS 6521, Universite´ de Bretagne Occidentale,
CS 93837, 29238 Brest cedex-3, France
` `
´ ´
Laboratoire de Synthese et d’Electrosynthese Organometalliques, UMR CNRS 5188, Universite de Bourgogne, 21000 Dijon, France
b
Received 27 February 2006; accepted 3 June 2006
Available online 10 June 2006
Abstract
The reactions of [Mo(CO)6] towards a 2,6-di(imino)pyridine L1 and related ligands were studied. The reaction with L1 afforded two
new complexes, [Mo(CO)4L1] (1) and [Mo(CO)4L2] (2), where L2 is the 2-amino-6-iminopyridine ligand arising from the hydrogenation
of one imine function of L1; similar reaction with a 2-acetyl-6-iminopyridine ligand L3 afforded [Mo(CO)4L3] (3). Compounds 1, 2 and 3
have been fully characterised by IR, 1H NMR and X-ray crystallography; they present a metal ion in a pseudo-octahedral environment,
the three organic ligands acting with bidentate N2 coordination modes. One of the imine functions in 1, the amine function in 2, and the
ketone function in 3 are uncoordinated.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Carbonyl complexes; Molybdenum complexes; NNN ligands; Crystal structures
1. Introduction
In the course of a general study related to the reactivity of
a 2,6-di(imino)pyridine ligand (see L1 Scheme 1) towards
metal derivatives which could be precursors of magnetic
compounds [6], we were interested in molybdenum carbonyl
complexes. We report here the syntheses, crystal structures
and NMR data of three new compounds resulting in UV-
irradiation or thermal reaction of [Mo(CO)6] with di(imino)
pyridine (L1) or acetyliminopyridine (L2) ligands. An alter-
native synthetic route for a 2-amino-6-iminopyridine ligand
(L2) (without nucleophilic attack or complexation to trim-
ethylaluminium) in complex 2 is presented (Scheme 1).
It has long been known that 2,6-di(imino)pyridine deriv-
atives form a large variety of molecular architectures when
they are coordinated to metals [1]. In the last few years, this
family of ligands has found a renewal of attention since
some of their complexes act as active catalysts for olefin
polymerisation [2]. In these coordination compounds, sub-
tle variations on the ligand result in deep modification of
catalytical activities. In this context, attempts to slightly
modify the 2,6-di(imino)pyridine ligands were done and
two convenient methods were described for 2-amino-6-imi-
nopyridines either by exploiting attack by nucleophilic
reagents at the imine carbon atoms [3] or complexation
to trimethylaluminium and hydrolysis [4,5].
2. Experimental
2.1. General procedures
L1 was prepared according to the literature [7]; a slightly
modified method was followed for L3 preparation. The L1
*
Corresponding author. Tel.: +33 2 98 01 67 08; fax: +33 2 98 01 70 01.
E-mail address: Francoise.Conan@univ-brest.fr (F. Conan).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.06.005

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N. Cosquer et al. / Inorganica Chimica Acta 359 (2006) 4311–4316
N
N
N
N
N
[Mo]
2
H
R
L1
R
R
N
N
N
N
R
[Mo]
R
R
H
1
[Mo(CO)6]
N
O
N
N
L3
R
O
N
[Mo]
R
3
Scheme 1. L1 and/or L3 ligands and syntheses of complexes 1 [Mo(CO)4L1], 2 [Mo(CO)4L2] and 3 [Mo(CO)4L3]. R is the 2,6-diisopropylphenyl group;
[Mo] = Mo(CO)4.
1
purity was carefully checked by H NMR and no trace of
L2 was detected. All complexes were synthesised using stan-
dard Schlenck techniques under purified nitrogen; the sol-
vents were freshly distilled and degassed just before use.
For irradiation experiments, the UV lamp used was a Phi-
lips HPK 125-W mercury vapor lamp. Elemental analyses
were performed by the ‘‘Service Central d’Analyses du
CNRS’’, Gif-sur-Yvette, France. Infrared spectra were
recorded on a Nicolet Nexus FT-IR instrument (KBr pel-
lets). NMR spectra were recorded on a Bruker AMX
400 MHz.
2.2.2. Exclusive synthesis of complex 1
Method A: A mixture of L1 (500 mg; 1.04 mmol) and
[Mo(CO)6] (275 mg; 1.04 mmol) was stirred in THF
(100 mL) under vacuum and left under UV-irradiation
for 48 h. The THF was then removed by evaporation and
the resulting solid treated as described above to give 1 as
a pink crystalline powder (yield: 40%).
Method B: [Mo(CO)6] (137 mg; 0.52 mmol) was heated
for 48 h at 130–140 ꢁC in acetonitrile (120 mL) to displace
some carbonyl groups. After removal of the solvent, the
crude product was suspended in THF (100 mL) and was
then added by small fractions to a hot solution of L1
(250 mg; 0.52 mmol) in THF (80 mL). The mixture was
refluxed for 18 h, then the solvent was evaporated and
the solid treated by chromatography as described above
(yield: 70%).
2.2. Syntheses
2.2.1. Thermal syntheses of complexes 1 and 2
A
stoichiometric mixture of [Mo(CO)6] (548 mg;
2.08 mmol) and L1 (1.00 g; 2.08 mmol) was introduced in
a Schlenck round-flask. THF (120 mL) was poured via
cannulation and the mixture was refluxed for 48 h. THF
was removed under reduced pressure, then the resulting
crude red solid was dissolved into a minimum amount
of diethylether. Chromatography on a column of silica
gel with diethylether/hexane 2:1 as eluent gave, after evap-
oration, 2 as a bright red powder (270 mg; 0.39 mmol;
yield: 19%). Complex 1 was eluted later as a second red
band with the same eluent (140 mg; 0.20 mmol; yield:
10%). Some secondary products were not eluted. Com-
2.2.3. Synthesis of complex 3
L3 (575 mg; 1.78 mmol) and [Mo(CO)6] (472 mg;
1.79 mmol) were poured in a Schlenck round-flask. THF
(80 mL) was added and the solution, which turned to pur-
ple after 15 mn, was refluxed at 80 ꢁC for 48 h. The sol-
vent was then removed under reduced pressure to give a
crude red product which was dissolved into a minimum
amount of dichloromethane. Chromatography on a col-
umn of silica gel with dichloromethane/hexane 4:1 as elu-
ent gave, after evaporation, 3 as a red powder (450 mg;
0.85 mmol; yield: 48%). Anal. Calc. for C25H26MoN2O5:
C, 56.6; H, 4.9; N, 5.3. Found: C, 56.1; H, 5.0; N,
5.0%. IR (KBr, cmꢀ1): 2968 w, 2927 w and 2867 w
(mCH); 2012 s, 1909 vs, 1881 vs and 1819 vs (mC„O); 1708
m (mC@O).
pound 1: Anal. Calc. for C37H43MoN3O4 Æ (CH2Cl2)0.25
:
C, 62.9; H, 6.2; N, 5.9. Found: C, 62.9; H, 6.2; N, 6.1%.
IR (KBr, cmꢀ1): 2967 m, 2927 m and 2869 w (mCH);
2014 s, 1903 vs, 1883 vs and 1838 vs (mCO); 1648 m (mC@N
imine). Compound 2: Anal. Calc. for C37H45Mo-
N3O4 Æ H2O: C, 62.6; H, 6.7; N, 5.9. Found: C, 62.9; H,
6.7; N, 5.9%. IR (KBr, cmꢀ1): 3367 m (mNH); 2965 s,
2926 m and 2867 w (mCH); 2010 s, 1898 vs, 1870 s and
2.3. X-ray structure analyses
1
1834 vs (mCO); 1608 m and 1587 m (mC@N imine). For H
Suitable crystals for X-ray studies were obtained from
NMR data, see Table 1.
acetone (1 Æ 2(CH3)2CO), pentane for 2 and diethylether/

N. Cosquer et al. / Inorganica Chimica Acta 359 (2006) 4311–4316
4313
Table 1
1H NMR data for complexes 1, 2 and 3 in cCDCl3
c
c
d
d
d
d
d
d'
H
f
N
N
N
N
N
N
N
H
N
O
e
a
a
a
b
b
b
a
a
a
Ligand L1 : C33H43N3
Ligand L2: C33H45N3
Ligand L3: C21H26N2O
[Mo(CO)4L1] (1)
[Mo(CO)4L2] (2)
[Mo(CO)4L3] (3)
da and db
dc
7.30–7.15 m (6H)
8.10 t (1H; JHH = 8.6 Hz)
7.30–7.13 m (6H)
8.05 t (1H; JHH = 8.4 Hz)
7.48–7.27 m (3H)
8.09 t (1H; JHH = 8.0 Hz)
3
3
3
3
3
3
0
dd and dd
7.90 d (2H; JHH = 8.6 Hz)
8.35 d (1H; JHH = 8.4 Hz);
8.01 d (1H; JHH = 8.0 Hz)
3
3
7.88 d (1H; JHH = 8.4 Hz)
7.47 d (1H; JHH = 8.0 Hz)
3
3
3
d CH(CH3)2
d CH(CH3)2
3.00 h (4H; JHH = 9.0 Hz)
3.42 h (2H; JHH = 9.0 Hz)
2.83 h (2H; JHH = 8.0 Hz)
3
2.88 h (2H; JHH = 9.1 Hz)
3
3
3
1.30 d (24H; JHH = 9.0 Hz)
1.20 d (imine) (12H; JHH = 9.1 Hz)
1.36 d (6H; JHH = 8.0 Hz)
3
3
1.36 d (3H; JHH = 9.0 Hz)
1.09 d (6H; JHH = 8.0 Hz)
3
1.33 d (3H; JHH = 9.0 Hz)
3
1.14 d (3H; JHH = 9.0 Hz)
3
1.06 d (3H; JHH = 9.0 Hz)
3
d NCCH3
2.40 s (6H)
–
1.65 d (3H; JHH = 8.9 Hz)
2.29 s (3H)
2.32 s (36H)
Others protons
He 3.26 large (1H)
Hf 5.14 q (1H; JHH = 8.9 Hz)
CH3C@O 2.87 s (3H)
3
Chemical shifts (d) quoted relative to TMS as an internal standard.
s: singlet; d: doublet; t: triplet; q: quadruplet; h: heptuplet; m: multiplet.
hexane 2/1 for 3. X-ray measurements have been carried
out on an Oxford CCD (for 1 and 3) and on a Nonius
Kappa CCD (for 2) diffractometer with Mo Ka radiation
(Table 2).
absorption bands of carbonyl ligands and coordinated imi-
nopyridine ligand. For 2, a supplementary absorption was
pointed out at 3367 cmꢀ1. It was assigned to a mNH vibra-
tion in agreement with the 1H NMR spectrum which exhib-
ited a large signal at d = 3.26 ppm (Table 1); associated
with the presence on the NMR spectrum of a signal at
d = 5.14 ppm (Table 1), these features indicate that one
imine function of the di(imino)pyridine L1 ligand is hydro-
genated to a secondary amine group generating a modified
ligand L2 (Scheme 1). On the contrary, the IR and 1H
NMR data for 1 (Table 1) are consistent with the presence
of the starting di(imino)pyridine L1 ligand with a bidentate
coordination mode. In agreement with the elemental anal-
yses, 2 was formulated as the tetracarbonyl complex
The measured intensities were reduced with CrysAlis
RED [8] (for 1 and 3) and with DENZO [9] (for 2) programs.
The structures were solved by direct methods with SIR92
[10] for 1 and 3 and SHELXS97 [11] for 2; refinements with
full-matrix least-squares with SHELXL97 [11] based on F2.
All non-hydrogen atoms were refined with anisotropic
thermal parameters. Both hydrogen atoms responsible for
imine bond reduction in 2 were found on difference Fourier
map and isotropically refined. Other not chemically signif-
icant hydrogens were placed in calculated positions and
included in final refinements in a riding model. Crystallo-
graphic data and final discrepancy factors are gathered in
Table 1. Molecular graphics were obtained from ORTEP-
3 [12].
[Mo(CO)4L2] and
1
as the unreduced complex
[Mo(CO)4L1]; these formulations were corroborated by
the crystal structure determinations. It is worthy to note
that derivative 1 was exclusively produced using either
the thermal or the photochemical procedures described in
the experimental part.
3. Results and discussion
With the asymmetric acetyliminopyridine ligand L3
(Scheme 1), reaction towards [Mo(CO)6] afforded the
new compound 3 for which 1H NMR data (Table 1)
clearly showed the presence of the starting ligand and
not the corresponding acetylaminopyridine one. The spec-
troscopic data and the elemental analyses agreed with
3.1. Syntheses
The stoichiometric reaction of hexacarbonylmolybde-
num with L1 in refluxed THF afforded, after chromatogra-
phy, two new compounds 1 and 2. Both IR spectra display

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N. Cosquer et al. / Inorganica Chimica Acta 359 (2006) 4311–4316
Table 2
Crystal data and structure refinement for compounds 1 Æ 2(CH3)2CO, 2 and 3
1 Æ 2(CH3)2CO
2
3
Empirical formula
M (g Æ molꢀ1
C
805.84
43H55MoN3O6
C37H45MoN3O4
691.70
C25H26MoN2O5
530.42
)
Temperature (K)
170(2)
120(2)
170(2)
Crystal system, space group
monoclinic, P21/c (14)
14.321(5)
10.645(5)
monoclinic, P21/c (14)
11.1880(2)
16.5765(3)
monoclinic, P21/c (14)
12.089(5)
14.140(5)
˚
a (A)
˚
b (A)
˚
c (A)
28.393(5)
18.8410(4)
15.859(5)
b (ꢁ)
V (A )
98.002(5)
4286(3)
95.592(1)
3477.6(2)
115.427(5)
2448(2)
3
˚
Z
4
4
4
Dcalc (Mg mꢀ3
)
1.249
0.353
1.321
0.419
1.439
0.573
Absorption coefficient (mmꢀ1
)
F(000)
1696
0.78 · 0.39 · 0.10
3.36–29.18
ꢀ18 + 18, ꢀ13 + 9, ꢀ37 + 36
27070/8804 (0.0326)
8804/0/492
R1 = 0.0358, wR2 = 0.0756
0.939
1448
1088
0.24 · 0.05 · 0.05
3.19–23.25
ꢀ13 + 13, ꢀ15 + 15, ꢀ13 + 17
13662/3504 (0.058)
3504/0/298
R1 = 0.0378, wR2 = 0.0586
0.925
Crystal size (mmꢀ3
)
0.18 · 0.13 · 0.08
1.018–30.508
ꢀ15 + 15, ꢀ20 + 23, ꢀ25 + 25
14656/9056 (0.0411)
9056/0/414
R1 = 0.0518, wR2 = 0.1034
1.042
0.613, ꢀ1.175
h Range (ꢁ) for collection
hkl Ranges
Reflections collected/unique (Rint
Data/restraints/parameters
Final R indices [I > 2r(I)]a,b
Goodness-of-fit on F2
)
ꢀ3
˚
Largest difference peak, hole (e A
)
1.002, ꢀ0.268
0.427, ꢀ0.326
2
2 1=2
a
R(F) = RjjFoj ꢀ jFcjj/RjFoj, RwðF 2Þ ¼ ½RwðF o2 ꢀ F 2c Þ =R½wðF o2Þ ꢁ
.
2
b
w ¼ 1=½r2ðF 2oÞ þ ðaPÞ þ bPꢁ with P ¼ ðF o2 þ 2F 2c Þ=3.
the formulation of 3 as the tetracarbonyl complex
general positions. ORTEP drawing and selected bond
lengths and angles are displayed in Figs. 1–3 and Table 3.
In compounds 1–3, the molybdenum cores exhibit
pseudo-octahedral environments, the organic ligand acting
with a bidentate N2 coordination mode. Distortions of the
octahedral environment mainly arise from (i) the usual
trans influence induced by the donor nitrogen atoms of
the L ligand (the MoC bond lengths in trans of L are ca
[Mo(CO)4L3].
3.2. Crystal structures
Compounds 1, 2 and 3 crystallise in the monoclinic
space group P21/c (Table 2). In the three cases, the asym-
metric unit contains one molybdenum atom, four carbonyl
groups and one organic ligand located on general posi-
tions; that of 1 also contains two molecules of acetone in
˚
0.05–0.10 A shorter than those in trans of a CO ligand)[13]
and (ii) the usual bite of this ligand (NpyridineMoNimine
Fig. 1. Perspective drawing of the compound [Mo(CO)4L1] (1) showing the atom numbering. Thermal ellipsoids are drawn at the 40% probability level.
˚
Carbonyl bond lengths (A): Mo–C(34) 2.058(3); C(34)–O(1) 1.138(3); Mo–C(35) 1.961(2); C(35)–O(2) 1.165(3); Mo–C(36) 2.012(3); C(36)–O(3) 1.154(3);
Mo–C(37) 1.958(3); C(37)–O(5) 1.163(3).

N. Cosquer et al. / Inorganica Chimica Acta 359 (2006) 4311–4316
4315
O1
C16
C15
C14
C3
C34
C2
C4
C5
C21
C1
C7
N2
C6
C10
C9
N1
C35
C20
C8
H
N3
Mo
O2
H20
C28
C37
O4
C11
C22
C30
C31
C27
C13
C18
C36
C33
C12
C29
C17
C23
C24
C32
O3
C19
C26
C25
Fig. 2. ORTEP representation of the asymmetric unit for compound [Mo(CO)4L2] (2). Thermal ellipsoids are drawn at the 30% probability level.
˚
Carbonyl bond lengths (A): Mo–C(34) 2.018(3); C(34)–O(1) 1.157(4); Mo–C(35) 1.969(3); C(35)–O(2) 1.161(4); Mo–C(36) 2.057(3); C(36)–O(3) 1.141(4);
Mo–C(37) 1.950(3); C(37)–O(4) 1.164(4).
Fig. 3. ORTEP representation of the asymmetric unit for compound [Mo(CO)4L3] (3). Thermal ellipsoids are drawn at the 40% probability level.
˚
Carbonyl bond lengths (A): Mo–C(22) 2.027(5); C(22)–O(1) 1.142(4); Mo–C(23) 1.948(5); C(23)–O(2) 1.158(5); Mo–C(24) 1.933(5); C(24)–O(3) 1.164(4);
Mo–C(25) 2.027(5); C(25)–O(4) 1.144(4).
Table 3
˚
Selected bond lengths (A) and bond angles (ꢁ) in 1 Æ 2(CH3)2CO, 2 and 3
1 Æ 2(CH3)2CO
2
3
Mo–N(1)
Mo–N(2)
C(6)–N(2)
C(20)–N(3)
2.304(2)
2.234(2)
1.291(3)
1.273(3)
Mo–N(1)
Mo–N(2)
C(6)–N(2)
C(20)–N(3)
2.314(2)
2.232(2)
1.289(4)
1.465(4)
Mo–N(1)
Mo–N(2)
C(6)–N(2)
C(8)–O(5)
2.279(3)
2.239(3)
1.292(4)
1.188(4)
C(34)–Mo–N(1)
C(35)–Mo–N(1)
C(36)–Mo–N(1)
C(37)–Mo–N(1)
N(2)–Mo–N(1)
94.26(8)
107.23(8)
92.15(7)
166.30(8)
72.02(6)
C(34)–Mo–N(1)
C(35)–Mo–N(1)
C(36)–Mo–N(1)
C(37)–Mo–N(1)
N(2)–Mo–N(1)
91.5(1)
109.6(1)
92.9(1)
164.7(1)
71.58(8)
C(22)–Mo–N(1)
C(23)–Mo–N(1)
C(24)–Mo–N(1)
C(25)–Mo–N(1)
N(2)–Mo–N(1)
93.9(2)
168.2(2)
103.8(2)
91.8(2)
71.8(2)

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N. Cosquer et al. / Inorganica Chimica Acta 359 (2006) 4311–4316
angles ca 72ꢁ) [6]. The Mo–Npyridine bond lengths are
Acknowledgements
˚
slightly longer (0.03–0.08 A) than the Mo–Nimine ones. In
´
compounds 1–3, the coordinated imine groups present
CNRS and Universite de Bretagne Occidentale are
acknowledged for financial support and the ‘‘MENRT’’
for a doctoral fellowship (BLG). We thank Drs F.
Michaud and M. Marchivie for stimulating discussion
and help in the structure resolutions.
essentially similar CN bond lengths (from 1.289(4) to
˚
1.292(4) A); it is worthy to note that coordination of the
imine nitrogen atom does not deeply affect the CNimine
˚
bond length (1.273(3) A for the uncoordinated imine func-
tion in 1). On the contrary, structural data for 2 clearly
show a strong difference between the CNimine (C(6)–N(2)
Appendix A. Supplementary material
˚
˚
1.289(4) A) and the C(20)–N(3) (1.465(4) A) bond lengths.
The later, which is in good agreement with those usually
observed for Csp3–Nsp3 bonds [14], indicates the change
of the imine function into an amine function; examination
of bond angles around C(20) (from 108 to 112ꢁ) corrobo-
rates this result.
In the three compounds, the system containing the pyr-
idine ring and the coordinated imine group is essentially
planar; the distance from the molybdenum atom to the
mean plane is significantly greater in compounds 2 and 3
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC Nos. 299799–299801. Copies of this infor-
mation may be obtained free of charge from the Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax
+44 1223 336 003; e-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk). Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.ica.2006.06.005.
˚
˚
(0.50 and 0.43 A, respectively) than in 1 (0.14 A). In con-
trast to the essentially in-plane conformation of the coordi-
nated iminopyridine systems, there is a marked deviation
of the no co-ordinated groups from co-planarity with the
pyridyl ring (the N1–C5–C20–N3 torsion angles are,
respectively, 113.4 and 136.4ꢁ for 1 and 2) [5].
References
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(b) R.F. Carina, G. Bernardelli, A.F. Williams, Angew. Chem. Int.
Ed. Engl. 32 (1993) 1463.
[2] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169.
[3] G. Van Koten, J.T.B.H. Jastrzebski, K. Vrieze, J. Organomet. Chem.
250 (1983) 49.
[4] M. Bruce, V.C. Gibson, C. Redshaw, G.A. Solan, A.J.P. White, D.J.
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Redshaw, G.A. Solan, A.J.P. White, D.J. Williams, Eur. J. Inorg.
Chem. (2001) 431.
These features indicate that in complex 2 the bidentate
L2 ligand possesses a transoid relationship between the
imine and the amine groups similar to that observed in
the free L2 unit [5] and therefore very different from the
cisoid conformation associated with the tridentate coordi-
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Formation of compound 1 is in agreement with previous
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hexacarbonylmolybdenum to afford tetracarbonyl com-
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of examples of imine hydrogenation without CN bond
cleavage. It corroborates the possibility of reduction of
such ligand in mild conditions and it is likely that the sol-
vent is the source of hydrogen. Such situation was clearly
demonstrated in the cases of rhodium (I) complexes for
which reduction of the two imine functions occurred when
the reaction was carried out in acetonitrile/ethanol mix-
tures but was not observed in pure acetonitrile [18].
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