Carbonyl rhodium(I) complexes containing (H)PNX (X = O or N) ligands deriving from natural aminoacid-amides. Synthesis, X-ray structure and spectroscopic characterization

Article abstract of DOI:10.1016/j.jorganchem.2009.06.008

The polyfunctional (H)PNX (X = O or N) ligands 1 and 2 react with [Rh(CO)₂Cl]₂ to give the corresponding chloro carbonyl complexes {Rh[κ²-(H)PN](CO)Cl} (1a and 2a), where the neutral ligands coordinate in a κ²-P

Full text of DOI:10.1016/j.jorganchem.2009.06.008

Journal of Organometallic Chemistry 694 (2009) 3281–3286
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Carbonyl rhodium(I) complexes containing (H)PNX (X = O or N) ligands
deriving from natural aminoacid–amides. Synthesis, X-ray structure
and spectroscopic characterization
*
Alessia Bacchi, Marcella Balordi, Paolo Pelagatti , Corrado Pelizzi
Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, University of Parma, Viale G.P. Usberti 17/A, 43100 Parma, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2009
Received in revised form 28 May 2009
Accepted 5 June 2009
Available online 11 June 2009
The polyfunctional (H)PNX (X = O or N) ligands 1 and 2 react with [Rh(CO)2Cl]2 to give the corresponding
chloro carbonyl complexes {Rh[
2-PN bidentate fashion, the square planar coordination being completed by the CO trans to N and the
chloride trans to P. In chloroform solution 1a maintains its original structure, while 2a partially trans-
forms into the cationic species {Rh[
3-(H)PNO](CO)}Cl. The chloroform solutions of 1a and 2a react with
AgPF6 to give the purely cationic species {Rh[
j
2-(H)PN](CO)Cl} (1a and 2a), where the neutral ligands coordinate in a
j
j
j
3-(H)PNO](CO)}PF6 ([1a]+ and [2a]+), while addition of Et3N
Keywords:
Rhodium
PN ligands
Tridentate ligands
Amino amides
Chiral complexes
originates the neutral species {Rh[j3-PNN0](CO)} (1b and 2b). All the complexes have been characterized
by microanalysis, IR, 1H NMR as well as 31P{1H} NMR spectroscopy. The X-ray structures of ligand 1 and
complex 1b are also reported.
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
hyde with the appropriate amino–amide (Scheme 1). For ligand 2
the corresponding hydrochloride amino–amide was neutralized
The chemistry of carbonyl rhodium(I) complexes is of para-
mount importance both in organometallic chemistry [1] and
homogeneous catalysis [2]. As our ongoing research program on
the use of phosphorus-containing potentially tridentate ligands
for the synthesis of organotransition metal complexes [3], here
we report on the synthesis and characterization of new carbonyl
rhodium(I) complexes containing chiral potentially tridentate li-
gands deriving from the condensation of 2-(diphenylphos-
phino)benzaldehyde with two different aminoacid amides, such
with triethylamine prior to condensation. The reactions were con-
ducted in MeOH/CH2Cl2 at 50 °C, isolating white (1) or light yellow
(2) solids in good yields. The completion of the condensation reac-
tion was checked by TLC (SiO2, EtOAc/n-hexane) or by liquid film IR
spectroscopy.
In the IR spectra the stretching bands of the amide group are
centered at 1685 and 1679 cmꢀ1 for 1 and 2, respectively. The
stretching of the amide N–H bonds generates large bands in the re-
gion 3200–3400 cmꢀ1. The 1H NMR spectra of the ligands recorded
in CD2Cl2 show the imine signal in the region 8–9 ppm. Only in the
case of 1 the coupling with the phosphorus nucleus is evident, giv-
ing rise to a doublet with a 4JHP = 5 Hz, while in the spectra of 2 the
same signal gives rise to a broad singlet. The amide protons of 2
give rise to two distinct broad singlets at 6.65 and 5.33 ppm. The
amide proton of 1, where the nitrogen is bound to an o-An ring,
resonates to lower fields, giving rise to a singlet at 9.33 ppm, symp-
tom of a high acidic character. The 31P{1H} NMR spectra of the li-
gands recorded in deuterated dichloromethane show a singlet at
ꢀ13.5 and ꢀ10.6 ppm for 1 and 2, respectively. Ligands 1 and 2
are stable in the solid state towards oxidation of the phosphine
moiety, as evidenced by 31P{1H} NMR spectroscopy. Traces of oxi-
dation become instead visible leaving the solutions of the ligands
in plain air for several days, as indicated by the appearance of a sin-
glet at about 33 ppm in the 31P{1H} NMR spectra. Formation of the
corresponding phosphine oxides can be avoided on storing the
as
dination modes of the ligands towards rhodium, such as neutral
2-PN, neutral 3-PNO and anionic j3-PNN0 have been investi-
L-valine amide and L-valine o-anisidne amide. The different coor-
j
j
gated. The introduction of a stereogenic carbon atom in the ligand
backbone opens the way to the design of enantioselective catalytic
processes promoted by the title complexes.
2. Results and discussion
2.1. Synthesis of ligands 1 and 2
The new (H)PNX (X = O, N) ligands 1 and 2 were synthesised by
reacting equimolar amounts of 2-(diphenylphosphino)benzalde-
* Corresponding author. Fax: +39 0521 905557.
E-mail address: paolo.pelagatti@unipr.it (P. Pelagatti).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.06.008

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A. Bacchi et al. / Journal of Organometallic Chemistry 694 (2009) 3281–3286
phorous lone pair have been already characterized in the literature
[4]. Nevertheless, the extended folding adopted by free 1 is evi-
dently electrostatically stabilized by the local arrangement of O2
and N2 around N1–H, that would be disrupted by the entrance of
the phosphine group in the site.
H
R
O
R
CH2Cl2/MeOH
50 °C
N
+ H2N
H2O
+
O
PPh2
N
N
O
PPh2
H
OMe
2.2. Synthesis of the rhodium complexes 1a–2a
1
2
R =
R =
[Rh(CO)2Cl]2 reacts in diethyl ether at room temperature with a
twofold excess of ligands 1 and 2 giving rise to the fast precipita-
tion of orange solids (Scheme 2).
H
Scheme 1. General scheme for the ligands 1 and 2.
The elemental analyses of the isolated products are in agree-
ment with the general formula {Rh[(H)PNX](CO)Cl}. The IR spectra
of the solids show an intense carbonyl stretching band centered at
2003 and 1990 cmꢀ1, for 1a and 2a, respectively, while the v(C@O)
band of the amide group is centered in both cases at values very
close to those of the free ligands, thus indicating its exclusion from
coordination. The stretchings of the N–H bonds give rise to an in-
tense absorption at 3258 cmꢀ1 for 1a and large bands in the region
3200–3400 cmꢀ1 for 2a. The 1H NMR spectra recorded in CDCl3
show the presence of the amide protons with a very broad singlet
at 9.86 ppm for 1a, while for 2a only a proton is visible as a broad
singlet at 7.8 ppm. In order to reduce the chemical exchange the
spectrum of 2a was recorded also in deuterated dmso, where the
amide protons are both visible as broad singlets at 9.49 and
solutions under nitrogen. From a refrigerated methanol solution of
1, crystals suitable for X-ray analysis were collected. The solid
structure of the ligand is reported in Fig. 1 along with the labeling
scheme.
The molecular structure of 1 is potentially highly flexible, due to
the many conformational degrees of freedom around the single
bonds along the molecular skeleton. Namely, six main torsion an-
gles can be evidenced to best represent the overall molecular fold-
ing, indicated as T1–T6 in Fig. 1, besides the potential source of E/Z
isomerism represented by the C@N double bond (the rotation of
the diphenylphosphine aromatic groups is not considered as signif-
icant). Table 1 lists the values of these torsion angles observed in
the solid state for the molecular structure of the free ligand 1.
It can be evidenced that, while the two potential nitrogen donor
sites N1 and N2 are already correctly prepositioned for creating a
virtual chelation site, the phosphorus donor points away, due to
a inconvenient orientation of T5. Actually, a closer approach of
P1 to N1 and N2 in the potential coordination site is not to be ex-
cluded by mere steric considerations, since cases with a similar
pattern of intramolecular NHꢁ ꢁ ꢁPꢁ ꢁ ꢁN distances as well as examples
of intramolecular linear NHꢁ ꢁ ꢁP contacts between a NH and a phos-
9.13 ppm, respectively. The 31P{1H} NMR spectrum of 1a recorded
1
in CDCl3 shows a doublet centered at 45 ppm with a JRh–P
=
142 Hz. Diversely, the 31P{1H} NMR spectrum of 2a shows two
doublets, centered at 52.5 and 43.5 ppm, with JRh–P = 161 and
1
129.5 Hz, respectively. The two doublets are in a 1:0.3 ratio in favor
of the more deshielded signal. The addition of a slight excess of
AgPF6 to the chloroform solutions of 1a and 2a leads to the rapid
precipitation of AgCl. The remaining solutions show a unique dou-
1
blet centered at 53 ppm with a JRh–P = 172 Hz belonging to the
purely cationic complexes {Rh[(H)PNO](CO)}PF6 ([1a]PF6 and
C28
C10
C9
C27
C26
C29
C30
C11
C8
T3
O1
T4
N2
C25
C12
T2
C24
P
N1
C7
C13
C19
T1
C2
C18
T5
C14
T6
C23
C22
C3
C1
C17
C20
C6
O2
C4
C16
C21
C31
C15
C5
Fig. 1. Perspective view of the molecular structure of 1, with thermal ellipsoids at the 50% probability level. Torsion angles discussed in the text are indicated as T1–T6.
Table 1
Comparison of the most relevant torsion angles (°) defining the molecular conformation of 1 and 1b.
T1 (C6–C1–N1–C7)
T2 (C1–N1–C7–C8)
T3 (N1–C7–C8–N2)
T4 (C7–C8–N2–C12)
T5 (N2–C12–C13–C18)
T6 (C13–C18–P1–C19)
1
1b
ꢀ165
173
ꢀ177
ꢀ9
ꢀ121
ꢀ134
170
16
ꢀ176
ꢀ171
60
ꢀ36

A. Bacchi et al. / Journal of Organometallic Chemistry 694 (2009) 3281–3286
3283
In order to test the possibility of forcing the ligands to coordi-
nate rhodium in an anionic tridentate fashion [7], dichloromethane
solutions of the complexes 1a and 2a were treated with an excess
of triethylamine at room temperature. After removal of the ammo-
nium salt the neutral carbonyl complexes 1b and 2b were isolated
(Scheme 4).
H
R
O
N
[Rh(CO)2Cl]2
Et2O, r.t.
Ph
Ph
1 or 2
+
P
N
Rh
OC
Cl
R = o-An 1a
R = H 2a
These are light orange solids, stable in the solid state as well as
in solution. The deprotonation of the ligands forces the amide
nitrogen to coordinate rhodium [8], and this provokes a shift of
the C@O amide stretching band to lower frequencies, from 1686
to 1606 cmꢀ1 for 1b and from 1666 to 1629 cmꢀ1 for 2b, respec-
tively [8,9]. The deprotonation of the amide function is evident in
the 1H NMR spectra of the complexes. For 1b the spectrum re-
corded in CDCl3 does not show any acidic signal, while the spec-
trum of 2b recorded in dmso-d6 shows only a broad singlet at
6.10 ppm, corresponding to the residual NH function. The carbonyl
stretching region contains a unique intense band centered at 1981
and 1982 cmꢀ1 for 1b and 2b, respectively. The shift to lower fre-
quencies of the carbonyl group with respect to the precursors is
attributable to the higher electron density that the anionic triden-
tate ligands place on the metal. This provokes a higher metal to li-
gand back-donation which reduces the bond order of the CO. The
31P{1H} NMR spectra of 1b recorded in CDCl3 shows a singlet at
Scheme 2. General scheme for the synthesis of the chloro–carbonyl complexes 1a
and 2a.
[2a]PF6 in Scheme 3); in both cases the PF6 anion resonates as a
septuplet at ꢀ145 ppm. Chloroform solutions of 1a and 2a have
been analyzed by MS-spectrometry by means of a DEP probe (see
Section 4). The mass spectrum of 1a shows an intense signal at
m/z = 596 corresponding to the loss of HCl and CO, while a second
signal at m/z = 581 originates from the successive loss of the
methyl group from the anisidine moiety. The mass spectrum of
2a shows a signal at m/z = 518 corresponding to the loss of HCl,
while a second, less intense, signal at m/z = 475 originates from
the successive loss of the carbonyl ligand.
Although it has not been possible to grow X-ray quality crystals
for the complexes 1a and 2a, their structures in solution can be in-
ferred by the aforementioned characterization data. The most
likely structure for chloro–carbonyl complexes of Rh(I) with phos-
phine–imine ligands is represented by the square planar coordina-
tion, with the four positions occupied by the P and N donors of
ligands 1 and 2 and by the CO and chloride ligands trans to N
and P, respectively. This represents the most thermodynamic sta-
ble ligand disposition around the metal. The microanalysis and IR
data indicate that this is the case for both complexes in the solid
state [5]. In solution, however, two different situations are found.
With 1a only one species is observed, while with 2a there is the
coexistence of two different species. The square planar geometry
is expected to create a steric repulsion between the isopropyl
group of the tridentate ligands with the chloride one, repulsion
which could be removed by changing the coordination mode of
1
45 ppm, with a JRhP = 143 Hz, values very similar to those found
for 1a in the same solvent. This is not a totally unexpected behav-
ior, which has already been observed by us with chloro–carbonyl
rhodium(I) complexes containing tridentate acyl-hydrazones on
passing from a
j j
2-(H)PN coordination to a 3-PNO one [3c]. The
31P{1H} NMR spectrum of 2b recorded in dmso-d6 shows a doublet
1
at 47.7 ppm with a JRh–P = 133 Hz.
The solid structure of 1b has been definitively established by X-
ray diffraction analysis on a single crystal grown by slow diffusion
of diethyl ether into a dichloromethane solution of the complex.
The crystalline structure of 1b is reported in Fig. 2.
Upon complexation, 1 is deprotonated and changes remarkably
its conformation in order to adopt a tridentate PNN0 chelation
mode in 1b, with a CO ligand trans to the imine nitrogen complet-
ing a square planar coordination around rhodium. The major con-
formational alterations due to coordination are evidenced by the
comparison of torsion angles along the molecular backbones of 1
and 1b listed in Table 2, and involve a 180° rotation of the trip-
henylphosphino group around T5 aimed to bring the phosphorus
donor in the chelation site, and a parallel rotation by 100° of the
o-methoxy-phenyl ring around T1 in order to bring the methoxy
substituent away from the coordination core. Two remarkably
puckered chelation systems are thus created, namely a six-mem-
bered ring comprising P1 and N2, presenting an envelope confor-
mation with the metal deviating by 0.92 Å from the mean plane
defined by P1, C18, C12, C13, N2, and a five-membered ring con-
taining N1 and N2, presenting a twisted conformation with C7
and C8 displaced from the plane defined by Rh1, N1 and N2, in a
k absolute configuration. The combination of the deformations of
the two chelation rings fused at the common Rh1–N2 bond influ-
ences the overall geometry of the coordination site of 1b, that
can be regarded as a butterfly configuration hinged on the P1–N2
the chelating from
j j
2-PN to 3-PNO (Scheme 3). For neutral amide
ligands the coordination through oxygen is certainly more fa-
voured than that through nitrogen [6]. This change in the hapticity
of the ligand is not observed with 1a which in fact shows a unique
doublet at 45 ppm in its 31P{1H} NMR spectrum. This signal is then
assigned to the neutral species {Rh[
2a instead, the doublet at 43.5 ppm is attributed to the neutral spe-
cies {Rh[
2-(H)PN](CO)Cl} (2a), while the doublet at 52.5 ppm is
attributed to the cationic species {Rh[
3-(H)PNO](CO)}Cl ([2a]Cl
j
2-(H)PN](CO)Cl}. For complex
j
j
in Scheme 3), where 2 behaves as a neutral tridentate PNO ligand.
The replacement of an amide proton with a o-An function seems
then to block the rotation around the C*AC(O)N bond of the ligand,
rotation necessary in order to pass from 1a to [1a]+, likely because
of steric reasons. This rotation occurs only after removal of the hal-
ogen ligand by a halogen scavenger or a base (vide infra).
+
NHR
CDCl3
Ph
Ph
X-
Ph
Ph
P
N
O
P
N
O
Rh
or
AgPF6
Rh
H
R
O
OC
solid
(κ2-PN) 1a, 2a
Cl
N
OC
Ph
Ph
Ph
Ph
CH2Cl2
NHR
P
N
P
N
Et3N/r.t.
Rh
Rh
OC
OC
(κ 3-PNO)
N
R
O
Cl
X = Cl [2a]Cl
R = o-An 1b
R = H
X = PF6 [1a]PF6, [2a]PF6
2b
Scheme 3. From
j
2-PN to
j
3-PNO hapticity.
Scheme 4. Synthesis of the carbonyl complexes 1b and 2b.

3284
A. Bacchi et al. / Journal of Organometallic Chemistry 694 (2009) 3281–3286
C10
C22
C11
C9
C23
C12
C21
C20
C24
C8
N1
C14
O1
C7
C31
C19
C15
N2
C13
C18
P1
C16
O3
C6
Rh1
C1
C17
C25
C26
C27
C32
O2
C2
C5
C30
C4
C3
C28
C29
Fig. 2. Perspective view of the molecular structure of 1b, with thermal ellipsoids at the 50% probability level. Relevant coordination parameters with e.s.d.’s in parentheses
(Å,°): Rh1–P1 2.207(1), Rh1–N1 2.061(3), Rh1–N2 2.062(3), Rh1–C32 1.811(4); P1–Rh1–N1 167.42(9), P1–Rh1–N2 87.32(9), P1–Rh1–C32 93.8(1), N1–Rh1–N2 80.1(1), N1–
Rh1–C32 98.8(2), N2–Rh1–C32 177.8(2).
Table 2
chiral ligands behave as neutral
In chloroform solution this behavior is retained with 1, while 2
tends to involve also the amide function in a neutral
3-(H)PNO
j
2-(H)PN chelatings (1a and 2a).
Crystal data and structure refinement for 1 and 1b.
1
1b
j
fashion. A neutral tridentate behavior is observed upon addition
of AgPF6, leading to the cationic species [1a]+ and [2a]+. The addi-
tion of an excess of triethylamine to chloroform solutions of 1a and
2a leads to the clean deprotonation of the amide function with iso-
lation of neutral carbonyl complexes where both ligands exert a
anionic j3-PNN0 behavior (1b and 2b).
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
C31H31N2O2P
494.55
293(2)
C32H30N2O3PRh
624.46
293(2)
1.54178
0.71073
orthorhombic
P 21 21 21
a = 26.112(8)
b = 15.256(6)
c = 7.002(2)
2789.3(16)
4
orthorhombic
P 21 21 21
a = 11.8359(7)
b = 15.3258(9)
c = 16.491(1)
2991.4(3)
4
Space group
Unit cell dimensions (Å)
The study of the complexes as potential chiral catalysts is cur-
rently under investigation in our laboratory.
Volume (Å3)
Z
Density (calculated) (Mg/m3) 1.178
1.387
0.658
4. Experimental
Absorption coefficient
(mmꢀ1
F(0 0 0)
1.096
1048
)
4.1. General methods
1280
h range for data collection (°) 3.36–70.81
1.81–23.29
24 726
4304 [Rint = 0.0546]
4304/0/406
0.861
R1 = 0.0277,
wR2 = 0.0443
R1 = 0.0402,
wR2 = 0.0466
0.02(2)
All reactions were performed under an atmosphere of dry nitro-
gen, employing standard Schlenk techniques. Solvents were dried
prior to use and stored over molecular sieves and under nitrogen.
Elemental analysis (C, H, N) were performed by using a Carlo Erba
Mod. EA1108apparatus. InfraredspectrawererecordedwithaNico-
let 5PCFT-IR spectrophotometer in the range 4000–400 cmꢀ1 by
using KBr disks. 1H NMR spectra were obtained at 300 K on a Bruker
300 FT spectrometer, while 31P{1H}-NMR spectra were collectedon a
Bruker AMX 400 FT by using H3PO4 85% as external standard. The
FAB(+)-MS spectra were collected by an EVG Autospec M, using m-
nitrobenzyl alcohol as matrix. The EI(+)-MS spectra were collected
with a DSQ-II Thermo Scientific mass-spectrometer equipped with
a single quadrupole mass-analyzer, by means of a direct exposure
probe (DEP) mounting a rhenium filament. The analyses were con-
ducted applying a ramp of 100 mA/s from 30 to 1000 mA, with an
electron potential of 70 eV. The enantiomerically pure Boc-pro-
tected amino acids and the commercially available amino acid
amides have been used as received without further purifications.
Reflections collected
10 639
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
5335 [Rint = 0.0305]
5335/0/449
0.942
Final R indices [I>2
r
(I)]
R1 = 0.0412,
wR2 = 0.0800
R1 = 0.0713,
wR2 = 0.0910
ꢀ0.03(2)
R indices (all data)
Absolute structure
parameters
Largest
D
F residuals (e Åꢀ3
)
0.100/ꢀ0.179
0.355 and ꢀ0.177
direction. The two planes constituting the butterfly wings consist
respectively of (Rh1, C32, O2, N1, C7, C8, N2, P1) and (N2, P1,
C12–C18), and make a dihedral angle of 39°.
3. Conclusions
In the present work we have shown the synthesis and charac-
terization of two new chiral polyfunctional ligands obtained by
condensation of 2-(diphenylphosphino)benzaldehyde with two
different types of amino acid amides (ligands 1 and 2). These give
rise to square planar carbonyl rhodium(I) complexes where the
N-(tert-Butoxycarbonyl)-(L)-valyne o-anisidine amide was synthes-
ised as already reported [8b]. 2-(diphenylphosphino)benzaldehyde
was purchased by Aldrich and purified by chromatographic column
prior condensation. [Rh2(CO)4Cl2] was purchased by Aldrich.

A. Bacchi et al. / Journal of Organometallic Chemistry 694 (2009) 3281–3286
3285
4.2. Synthesis of the ligands
3258 (NH), 2005 (C„O), 1685 (C@O). EI(+)-MS (DEP): m/z = 596
[1a-HCl–CO]+, 581 [596-CH3]+.
4.2.1. Ligand 1
Five hundred and seventy milligrams (1.8 mmol) of N-(tert-
butoxycarbonyl)-(L)-valyne o-anisidine amide were dissolved in
4.3.1.2. Complex 2a. As for 1 but starting from 2. Yield: 180 mg
(72%). M.p.: 210 °C (dec.). Anal. Calc. for C25H25ClN2O2PRhꢁ1/
2H2O: C, 58.28; H, 4.44; N, 4.97. Found: C, 53.03; H, 4.48; N,
4.68%. 1H NMR (CDCl3): d 8.52 (s, 1H, C(H)@N), 7.80 (sbr, 1H,
15 ml of dichloromethane. The resulting solution was treated with
10 equivalents of trifluoroacetic acid and stirred for two hours at
room temperature. The solvent was then removed under vacuum
and the residue dissolved in 10 ml of a 0.2 M KOH solution and ex-
tracted with 40 ml of dichloromethane. The solution was concen-
trated under vacuum before adding 510 mg (1.8 mmol) of 2-
(diphenylphosphino)benzaldehyde and anhydrous Na2SO4. The
yellow solution was heated at 50 °C for 12 h under stirring, then fil-
tered and dried under vacuum. The resulting whitish sticky residue
was dissolved in methanol and the solution refrigerated at ꢀ18 °C
obtaining a white powder. From a methanol solution of the ligand
refrigerated at ꢀ18 °C crystals suitable for X-ray analysis were col-
lected. Yield: 560 mg (63%). M.p.: 138.4–139.1 °C. Anal. Calc. for
C31H31N2O2P: C, 75.30; H, 6.28; N, 5.67. Found: C, 75.21; H, 6.33;
N, 5.49%. 1H NMR (CD2Cl2): d 9.33 (s, 1H, NH), 8.86 (d, 1H, CH@N,
*
NH), 7.70-7.42 (m, 13H, Ph), 7.04 (tbr, 1H, Ph), 5.32 (d, 1H, C H,
3JHH = 9.9 Hz), 2.29 (m, 1H, CH(CH3)2), 1.88 (sbr, 1H, NH), 0.92 (d,
3
3
3H, CH(CH3)2, JHH = 5.9 Hz), 0.62 (d, 3H, CH(CH3)2, JHH = 5.9 Hz).
31P{1H}-NMR (CDCl3): major signal: d 52.5 (d, 1JRhP = 161 Hz); min-
1
or signal: d 43.5 (d, JRhP = 129.5 Hz). IR: 3250 (NH), 2076 (C„O),
1666 (C@O). EI(+)-MS (DEP): m/z = 518 [2a-HCl]+, 475 [518-CO]+.
4.3.2. Synthesis of the complexes {Rh[j3-PNN0](CO)} (1b–2b)
4.3.2.1. Complex 1b. Hundred milligrams of complex 1a
(0.150 mmol) were dissolved in 15 ml of dichloromethane and 5
equivalents of Et3N were added to the resulting solution. After a
prolonged stirring at room temperature (12 h) the solvent was re-
moved under vacuum and the resulting solid was treated with tol-
uene. After filtration over a plug of celite the solution was
concentrated under vacuum, treated with n-hexane and refriger-
ated at ꢀ18 °C. A light orange powder was filtered off and washed
with n-hexane and finally dried under vacuum. Yield: 90 mg
(56%). M.p.: 167.6–168.1 °C. Anal. Calc. for C32H30N2O3PRh: C,
61.53; H, 4.81; N, 4.49. Found: C, 60.83; H, 4.92; N, 4.32%. 1H
NMR (CD2Cl2): d 7.87 (s, 1H, C(H)@N), 7.61–6.87 (m, 18 H, Ph),
3
4
4JHP = 5 Hz), 8.34 (dd, 1H, An, JHH = 7.8 Hz, JHH = 1.3 Hz), 8.18 (m,
3
1H, Ph), 7.49 (t, 1H, Ph, JHH = 7 Hz), 7.42–7.26 (m, 11H, Ph), 7.07
(td, 1H, An, JHH = 7.7 Hz, JHH = 1.5 Hz), 6.96 (m, 3H, Ph + An)
3.90 (s, 3H, OCH3), 3.62 (d, 1H, C H, JHH = 4.5 Hz), 2.19 (m, 1H,
3
4
3
*
3
CH(CH3)2), 0.73 (d, 3H, CH(CH3)2, JHH = 5.9 Hz), 0.68 (d, 3H,
CH(CH3)2, JHH = 5.9 Hz). 31P{1H}-NMR (CD2Cl2): d-13.5 (s). IR:
3
3324 (NH), 1685 (C@O). FAB(+)-MS: m/z = 495 [1+H+]+.
3
*
3.99 (d, 1H, C H, JHH = 3.9 Hz), 3.87 (s, 3H, OCH3), 2.47 (mbr,
3
1H, CH(CH3)2), 0.94 (d, 3H, CH(CH3)2, JHH = 5.9 Hz), 0.75 (d, 3H,
4.2.2. Ligand 2
CH(CH3)2, JHH = 5.9 Hz). 31P{1H} NMR (CD2Cl2):
d 45.0 (d,
3
Two hundred and sixty milligrams (1.7 mmol) of (L)-valinea-
1JRhP = 143 Hz). IR: 1983 v(C„O), 1606 v(C@O), 1454 v(P–Ph). By
slow diffusion of diethyl ether into a dichloromethane solution
of 1b, X-ray quality crystals were collected.
mide hydrochloride were dissolved in 15 ml of methanol and
0.28 ml (1.2 mmol) of triethylamine were added. After 2 h of stir-
ring at room temperature 490 mg (1.7 mmole) of 2-(diphenylphos-
phino)benzaldehyde dissolved in 10 ml of dichloromethane were
added, and the solution was stirred at 50 °C for 24 h in the pres-
ence of anhydrous Na2SO4. After filtration, the solvent was re-
moved under vacuum and the residue dissolved in toluene,
passed through a silica pad and the resulting clear solution dried
under vacuum. The solid is again dissolved in methanol and the
solution refrigerated at ꢀ18 °C, obtaining a yellow powder. Yield:
460 mg (67%). M.p.: 106.4–107.1 °C. Anal. Calc. for C24H25N2OP:
C, 74.23; H, 6.44; N, 7.22. Found: C, 74.08; H, 6.80; N, 6.52%. 1H
NMR (CD2Cl2): d 8.47 (sbr, 1H, CH@N), 7.80 (m, 1H, Ph), 7.49 (t,
4.3.2.2. Complex 2b. As for 1b but starting from 2a. Yield: 69 mg
(77%). M.p.: 112.4–113 °C. Anal. Calc. for C25H24N2O2PRh: C,
57.93; H, 4.63; N, 5.40. Found: C, 57.51; H, 4.58; N, 5.22%. 1H
NMR (dmso-d6): d 8.36 (s, 1H, C(H)@N), 7.80–7.06 (m, 14H, Ph),
3
*
6.10 (s, 1H, NH), 3.73 (d, 1H, C H, JHH = 4.9 Hz), 2.18 (m, 1H,
3
CH(CH3)2), 0.77 (d, 3H, CH(CH3)2, JHH = 5.9 Hz), 0.55 (d, 3H,
CH(CH3)2, JHH = 5.9 Hz). 31P{1H} NMR (dmso-d6):
d 47.7 (d,
3
1JRhP = 133 Hz). IR: 1983 v(C„O); 1629 v(C@O); 1435 v(P–Ph).
3
4.4. X-ray diffraction analysis
1H, Ph, JHH = 7.5 Hz), 7.37–7.27 (m, 7H, Ph), 7.26–7.19 (m, 4H,
Ph), 6.94 (m, 1H, Ph), 6.65 (sbr, 1H, NH2), 5.33 (sbr, 1H, NH2),
3
*
CuK
fractometer equipped with scintillation detector was employed for
1, while MoK radiation (k = 0.71073 Å), T = 293 K, on a SMART AXS
a radiation (k = 1.54178 Å), T = 293 K, on a Siemens AED dif-
3.53 (d, 1H, C H, JHH = 4.3 Hz), 2.12 (m, 1H, CH(CH3)2), 0.74
3
3
(d, 3H, CH3, JHH = 6.8 Hz), 0.63 (d, 3H, CH3, JHH = 6.8 Hz).
31P{1H}-NMR (CD2Cl2): d-10.6 (s). IR: 3400–3275 (NH2), 1679
(C@O). FAB(+)-MS: m/z = 389 [2+H+]+.
a
1000 diffractometer equipped with CCD detector was used for
compound 1b. Lorentz, polarization, and absorption corrections
were applied [10]. Structures were solved by direct methods using
SIR97 [11] and refined by full-matrix least-squares on all F2 using
SHELXL97 [12] implemented in the WINGX package [13]. Hydrogen
atoms were partly located on Fourier difference maps and refined
isotropically, partly introduced in calculated positions. Anisotropic
displacement parameters were refined for all non-hydrogen atoms.
Final geometries have been analyzed with SHELXL97 [12] and PARST97
[14], and extensive use was made of the Cambridge Crystallo-
graphic Data Centre packages [15]. Table 2 summarizes crystal
data and structure determination results.
4.3. Synthesis of the complexes
4.3.1. Complexes {Rh[j
2-(H)PN](CO)Cl} (1a–2a)
4.3.1.1. Complex 1a. One hundred and fifty milligrams (0.3 mmol) of
1 were dissolved in 20 ml of diethyl ether and 60 mg (0.15 mmol) of
[Rh(CO2)Cl]2 were added. The orange solution was stirred at room
temperature for 5 h. The shiny orange solid formed was filtered off,
washed with diethyl ether and n-hexane and finally dried under vac-
uum. Yield: 160 mg (80%). M.p.: 179 °C (dec.). Anal. Calc. for
C32H31ClN2O3PRh: C, 58.18; H, 4.97; N, 4.24. Found: C, 58.42; H,
4.71; N, 4.33%. 1H NMR (CDCl3): d 9.86 (sbr, 1H, NH), 8.69 (s, 1H,
C(H)@N), 8.18 (br, 1H, An), 7.62–6.87 (m, 20H, Ph + An), 5.64 (d,
Supplementary material
3
*
1H, C H, JHH = 9.9 Hz), 3.94 (s, 3H, OCH3), 2.17 (m, 1H, CH(CH3)2),
3
0.94 (d, 3H, CH(CH3)2, JHH = 5.9 Hz), 0.52 (d, 3H, CH(CH3)2,
CCDC 733396 and 733397 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
1
3JHH = 5.9 Hz). 31P{1H}-NMR (CD2Cl2): d 45.0 (d, JRhP = 142 Hz). IR:

3286
A. Bacchi et al. / Journal of Organometallic Chemistry 694 (2009) 3281–3286
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Acknowledgments
The authors thank Prof. María C. Rodríguez Argüelles (Univer-
sity of Vigo, Spain) for the FAB-MS analyses, and Centro Interdipar-
timentale ‘‘G. Casnati” of the University of Parma for the
instrument facilities.
(b) M.R.J. Elsegood, A.J. Lake, M.B. Smith, Eur. J. Inorg. Chem. (2009)
1068–1078.
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