5
24
H.-C. Böttcher et al. / Inorganica Chimica Acta 370 (2011) 523–525
are given in ppm relative to TMS. Mass spectra were recorded
using a Jeol Mstation JMS 700. Elemental analyses (C, H, N and
Cl) were performed by the Microanalytical Laboratory of the
Department of Chemistry, LMU Munich, using a Heraeus Elementar
Vario El instrument.
3. Results and discussion
The compound [Rh(acac)(coe) ] (2) was described in the litera-
ture [8] and prepared by the reaction of [{Rh(l-Cl)(coe) } ] (1)
2 2
with Na(acac) in toluene at 40 °C during 3 h. We have slightly mod-
ified this procedure by using THF as the solvent. Thus a very short
reaction time of about 20 min is only necessary. Recently we de-
2
2
2.2. Synthesis of [Rh(acac)(ppy) ] (3) from in situ prepared
[
Rh(acac)(coe) ] (2)
2
scribed an analogous synthesis for [Ir(acac)(coe) ] [1]. Because of
2
the successful use of the latter species in the preparation of irid-
To a solution of 1 (359 mg, 0.50 mmol) in 20 mL of THF solid
O (140 mg, 1 mmol) was added. Immediately a clear
deep orange solution resulted which was stirred for 30 min at
room temperature. Then the solvent was removed in vacuo. At this
point the residue contained only [Rh(acac)(coe) ] (2) in nearly
2
quantitative yield as checked by NMR spectroscopy. To remove
the sodium chloride, the remaining residue was treated with
ium(III) complexes containing cyclometalated C^N ligands, we
developed a similar procedure for the synthesis of the analogous
rhodium(III) complexes (Scheme 1).
Na(acac)ÁH
2
In accordance with the known higher stability of iridium(III)
complexes in ligand substitution processes compared to the analo-
gous rhodium species, we found that the synthesis of the rhodium
compounds could be realized in shorter reaction times and under
milder reaction conditions. Thus the treatment of 1 with two
equivalents of hydrated Na(acac) in THF at room temperature re-
sulted immediately in a clear orange solution. After a short reac-
tion period, complex 2 was obtained after evaporation of the
solvent in nearly quantitative yield as yellow powder. The purity
of 2 was checked by NMR spectroscopy and the data agreed well
with the reported ones [8]. As illustrated in Scheme 1, the in situ
prepared complex 2 reacts with two equivalents of Hppy in reflux-
ing toluene during 1 h under oxidative addition to [Rh(acac)(ppy)2]
(3) in high yield. The latter compound is known from the literature
1
5 mL of cold hexane, the solution filtered and the solvent evapo-
rated to dryness in vacuo. The residue was dissolved in 15 mL of
toluene and 2-phenylpyridine (620 mg, 4 mmol) was added and
the mixture was refluxed with stirring for 1 h. During this time a
yellow powder precipitated from the solution. After cooling to
room temperature the solid was filtered off, washed three times
with 10 mL portions of hexane and dried in vacuo. Yield: 439 mg
(
86%). Anal. Calc. for C27
Found: C, 63.73; H, 4.51; N, 5.63%. C{ H} NMR (100 MHz, CD
d 187.4 (CO-acac), 168.3 (d, JRh–C = 35.5 Hz, C, metalated), 165.1,
49.0, 144.5, 137.3, 133.8, 128.7, 123.6, 122.1 (2 singlets over-
23 2 2
H N O Rh: C, 63.54; H, 4.54; N, 5.49.
13
1
2
2
Cl ):
1
1
and was unambiguously identified by its known H NMR data [4].
-acac). The 1H NMR data
13
1
lapped), 118.9, 97.9 (CH-acac), 28.6 (CH
3
Additionally we collected the C{ H} NMR data of 3 (see Section
agreed with the reported ones [4].
2).
Furthermore we examined the subsequent reaction pathway to
2
.3. Synthesis of fac-[Rh(ppy)
3
] (4) from in situ prepared
the tris-cyclometalated complex [Rh(ppy)
respectively, with an excess of Hppy (reflux conditions). Recently
we could show that the complex mer-[Ir(ppy) ] can be prepared
by reaction of [Ir(acac)(ppy) ] with a slight excess of Hppy in
refluxing ethoxyethanol during 3 h [1]. Adapting this method to
the rhodium species 3 as the precursor to generate the complex
3
] by reacting 2 and 3,
[Rh(acac)(coe) ] (2)
2
3
To a solution of 1 (359 mg, 0.50 mmol) in 20 mL of THF solid
Na(acac)ÁH O (140 mg, 1 mmol) was added and the mixture stirred
2
2
at room temperature for 30 min. Then the solvent was removed in
vacuo. The remaining residue was treated with 10 mL of cold hex-
ane, the solution filtered and the solvent evaporated to dryness in
vacuo. The residue was dissolved in 5 mL of 2-phenylpyridine and
the mixture refluxed for 20 min. The solution was cooled to room
temperature and the product precipitated by adding 30 mL of hex-
ane. The powder was filtered off, washed three times with 10 mL
portions of hexane and dried in vacuo. The raw product was puri-
fied by filtration over alumina using dichloromethane as the elu-
mer-[Rh(ppy)
unable to detect signals belonging to mer-[Rh(ppy)
3
] failed in numerous attempts. In all cases we were
] by 1H NMR
3
spectroscopy. A distinction between the fac and mer isomers in
1
the H NMR spectra is easy to realize. Because of the lower symme-
try of the mer isomer in comparison with the fac configured spe-
1
cies, more complex H NMR spectra should be usually observed
for the mer isomers. In comparison with an octahedral complex
with facial arrangement of ligands, which exhibit a set of eight cou-
pled protons due to the threefold symmetry of the molecule, in a
meridional configuration of ligands the protons are magnetically
inequivalent resulting in a set of 24 coupled protons. Thus the
treatment of 3 with Hppy in excess under various reaction condi-
tions, e.g. in ethoxyethanol (3 h, reflux) or treatment in an open
vessel to remove the Hacac by distillation, or treatment in Hppy
ent. Yield: 360 mg (64%). Anal. Calc. for C33
.28; N, 7.43. Found: C, 69.93; H, 4.41; N, 7.61%. C{ H} NMR
100 MHz, CD Cl ): d 178.9 (d, JRh–C = 38.4 Hz, C, metalated),
63.9, 147.4, 143.6, 137.2, 136.5, 129.0, 123.5, 121.8, 120.8, 118.7
24 3
H N Rh: C, 70.09; H,
13
1
4
(
1
2
2
+
+
1
MS (FAB ): m/z = 565 [M ]. The H NMR data agreed well with
the reported ones [5]. The excess of 2-phenylpyridine could be
recovered by distillation and reused in further preparations.
at 180 °C in an oil bath for 2 h, resulted not in the formation of
1
mer-[Rh(ppy)
3
]. By H NMR spectroscopy only the unreacted
2
.4. Synthesis of [{Rh(
l
-Cl)(ppy)
2
}
2
] (5) from [{Rh(
l
-Cl)(coe)
2
}
2
] (1)
precursor 3 could be detected in each case. This was somewhat
surprising and frustrating because we were able to isolate the cor-
responding two iridium isomers [1]. Otherwise the synthesis of the
To a solution of 1 (359 mg, 0.50 mmol) in 25 mL of toluene 2-
phenylpyridine (310 mg, 2 mmol) was added and the mixture stir-
red under reflux for 1 h. During this period the color of the solution
changed from deep orange to pale yellow and a yellow powder
precipitated from the solution. After cooling to room temperature
the solvent was reduced in vacuo to 10 mL. The crystals were fil-
tered off, washed three times with 10 mL portions of hexane and
3
isomer fac-[Rh(ppy) ] (4) was possible in our hands by treatment
of in situ prepared 2 which was dissolved in a small amount of
2-phenylpyridine and refluxed for 20 min at 260 °C (Scheme 1). It
should be noted that a longer reaction time resulted in a markedly
decomposition accompanied with separation of some rhodium me-
tal from the solution. The crude product 4 was precipitated with
hexane as a powder, which was filtered over alumina with dichlo-
romethane as the solvent. Compound 4 was obtained as yellow
crystals in yields of 65%. The NMR data agreed well with the re-
dried in vacuo. Yield: 438 mg (98%). Anal. Calc. for C44
2 4 2
H32Cl N Rh :
C, 59.15; H, 3.61; Cl, 7.94; N, 6.27. Found: C, 58.93; H, 3.41; Cl, 7.89;
1
13
N, 6.42%. The NMR data ( H and C) agreed with the literature data
9].
[
3
ported ones [5] and showed that only the isomer fac-[Rh(ppy) ]
B?ttcher, Hans-Christian
