2-Ethyl-1-phenylindazolium hexafluorophosphate. N-heterocyclic carbene formation, rearrangement, ring-cleavage reactions, and rhodium complex formation

Article abstract of DOI:10.1515/znb-2014-0188

2-Ethyl-1-phenylindazolium hexafluorophosphate was deprotonated by potassium 2-methylbutan-2-olate to give the N-heterocyclic carbene of indazole, i.e., indazol-3-ylidene. This N-heterocyclic carbene undergoes a ring transformation to 9-ethylaminoacridine

Full text of DOI:10.1515/znb-2014-0188

Z. Naturforsch. 2015; 70(1)b: 83–89
Z2o-ngEGtuhany, Ml-im1o-zpa hGjiekanj ayndliAnnddreaaszSochlmiiudtm* hexafluorophosphate.
N-heterocyclic carbene formation, rearrangement,
ring-cleavage reactions, and rhodium complex
formation
Abstract: 2-Ethyl-1-phenylindazolium hexafluoropho- structures [5], metalations [6, 7], and biological activities
sphate was deprotonated by potassium 2-methyl- [8–11] has been summarized in recent review articles and
butan-2-olate to give the N-heterocyclic carbene of book chapters. To date, only very few examples of natural
indazole, i.e., indazol-3-ylidene. This N-heterocyclic products possessing the indazole ring have been discov-
carbene undergoes a ring transformation to 9-ethyl- ered [12–14]. Among those, nigellicin (1) has been isolated
aminoacridine. Trapping of the carbene with sulfur, from Nigella sativa (Scheme 1) [14]. This alkaloid belongs
silver(I) oxide, and carbonylbis(triphenylphosphane) to the class of pseudo-cross-conjugated heterocyclic meso-
rhodium(I) chloride resulted in the formation of inda- meric betaines known to provide versatile starting materi-
zolethione, indazolone (X-ray structure analysis), and als for the generation of N-heterocyclic carbenes (NHC).
carbonylbis(triphenylphosphane)(2-ethyl-1-phenyl-1H-in- Indeed, indazol-3-ylidenes 4 are formed on thermal decar-
dazol-3-ylidene)rhodium(I) hexafluorophosphate (X-ray boxylations of indazolium-3-carboxylates 2, when stabi-
structure analysis), respectively. Reaction of the inda- lizing effects such as hydrogen bonds to protic solvents or
zolium salt with phenolate and thiophenolate gave an water of crystallization are absent [15]. The pseudo-cross-
N-ethyl-2-(phenylamino)benzimidate and benzimidothio- conjugated mesomeric betaines, pyrazolium-3-carboxy-
ate, respectively.
lates [16] and imidazolium-2-carboxylates [17–22], behave
similarly, and normal N-heterocyclic carbenes (nNHC)
Keywords: carbene–Rh Complex; indazol-3-ylidene; inda- are formed effectively under relatively mild conditions.
zolone; indazolthione.
By contrast, decarboxylations of imidazolium-4-carboxy-
lates, which are members of the class of cross-conjugated
heterocyclic mesomeric betaines, to the abnormal N-heter-
ocyclic carbene (aNHC) imidazole-4-ylidene require harsh
conditions [22]. The relationship between N-heterocyclic
carbenes and mesomeric betaines has been the subject of
recent review articles [23, 24]. The deprotonation of inda-
zolium salts 3 is an alternative pathway for the genera-
tion of indazol-3-ylidenes 4. In general, indazol-3-ylidenes
(and pyrazol-3-ylidenes) have a chemistry of their own
that sets them apart from the chemistry of N-heterocy-
clic carbenes of other ring systems [25–29]. Whereas the
majority of N-heterocyclic carbenes are strong σ donors in
transition metal-catalyzed cross-coupling reactions, inda-
zol-3-ylidenes can be applied in coordination chemistry
[30] and heterocycle synthesis [23–26]. In continuation of
our studies of N-heterocyclic carbenes in synthesis [27–29]
and catalysis [31], we describe here an indazolethione,
an indazolone, and the formation of a rhodium complex
as well as an indazole-acridine rearrangement of 2-ethyl-
1-phenyl-indazol-3-ylidene. In addition, we report a ring-
opening reaction of the indazole ring to a benzamide and
a benzothioamide.
DOI 10.1515/znb-2014-0188
Received August 11, 2014; accepted September 3, 2014
1 Introduction
The number of publications dealing with indazoles has
increased considerably during the last decade. Progress in
the field of indazole chemistry concerning syntheses [1–4],
*Corresponding author: Andreas Schmidt, Institute of Organic
Chemistry, Clausthal University of Technology, Leibnizstrasse 6,
D-38678 Clausthal-Zellerfeld, Germany,
e-mail: schmidt@ioc.tu-clausthal.de
Zong Guan: Institute of Organic Chemistry, Clausthal University
of Technology, Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld,
Germany
Mimoza Gjikaj: Institute of Inorganic and Analytical Chemistry,
Clausthal University of Technology, Walter-Nernst-Strasse 4,
D-38678 Clausthal-Zellerfeld, Germany
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ꢀZ. Guan et al.: 2-Ethyl-1-phenylindazolium hexafluorophosphate
O
S
O
O
S8, t-BuOK,
OH
O
toluene, reflux, 3 h
N
Et
5
N
N
N
R
N
N
Me
Ph
R
2
7 (20 %)
1
X
Scheme 3ꢀTrapping of the NHC derived from 5 by sulfur.
N
R
N
R
N R
N
N
R
N
R
R
presence of sulfur gave indazole-3-thione 7, although
in low yield (Scheme 3). Thione formations are sup-
posed to be typical trapping reactions of N-heterocyclic
carbenes.
3
4
Scheme 1ꢀBetaines, salts and N-heterocyclic carbenes of indazole.
The corresponding oxygen analogue of thione 7,
2-ethyl-1-phenylindazolone 8, could be obtained on
treatment of 5 with silver(I) oxide in anhydrous dichlo-
romethane in excellent yields (Scheme 4). On examina-
tion of the reaction mixture by electrospray ionization
mass spectrometry (ESIMS), the silver adduct of indazol-
3-ylidene was unambiguously detected at m/zꢀꢀ= ꢀꢀ551.0 (2
carbene + Ag+) when a sample was sprayed from MeOH
at 0 V fragmentor voltage. A similar reaction, but in the
presence of copper(I) chloride, has been observed with
a triazolylidene that reacted with CsOH to give the corre-
sponding triazolium-olates [32].
The indazolone 8 dissolved in THF displays a strong,
broad but structureless fluorescence emission in the range
378–570 nm with a maximum at 425 nm (excitation wave-
length 317 nm). Upon excitation at 248 nm, an additional
broad, slightly structured fluorescence peak centered at
330 nm appears. This weaker emission can probably be
attributed to the phenyl substituent. Single crystals of
indazolone 8 suitable for an X-ray structure determination
(Fig. 1) were obtained by slow evaporation of a concen-
trated solution in diethyl ether. The compound crystal-
lizes in the monoclinic space group P21/c (no. 14) with
Zꢀꢀ= ꢀꢀ4. The phenyl ring is twisted with respect to the plane
of the indazolone by 79.3ꢀ° (torsion angle C2–N5–C6–C7;
crystallographic numbering). The C–O bond length (C3
and O17; crystallographic numbering) was determined to
be 123.5(4) pm.
2 Results and discussion
2-Ethyl-1-phenylindazolium hexafluorophosphate 5, pre-
pared by ethylation of 1-phenylindazole using diethyl
sulfate, was deprotonated with t-BuOK in toluene to give
the 9-ethylaminoacridine 6 (Scheme 2). The mechanism
of this reaction can be formulated in analogy to related
transformations starting from indazol-3-ylidenes [26] as
well as pyrazole-3-ylidenes [16] as follows: Deprotonation
of the indazolium salt 5 gives the indazol-3-ylidene 5A,
which undergoes a ring opening by N–N bond cleavage to
ketenimine 5B. Subsequent ring–closure results in the for-
mation of 5C, which tautomerizes to yield the acridine 6.
DFT calculations have revealed that the ring–closure from
5B to 5C is predominantely pericyclic in nature [16, 26].
In the present studies, we investigated some inter-
ception reactions. Thus, reaction of indazolium salt
5 with t-BuOK in toluene at reflux temperature in the
PF6
t-BuOK
N
Et
N
Et
N
N
toluene,
reflux, 3 h
Ph
Ph
5A
5
Et
Et
N
N
Reactionoftheindazoliumsalt5withsodiumhydrogen
sulfide hydrate gave a mixture of N-ethyl-2-(phenylamino)
Ph
Ph
N
N
5B
O
Et
Et
H
HN
N
Ag2O, CH2Cl2 abs.
40 °C, 24 h
N
Et
N
5
N
N
5C
6
(41 %)
8 (90 %)
Scheme 4ꢀIndazolone formation starting from indazolium salt 5.
Scheme 2ꢀRing transformation of indazolium salt 5 to acridine 6
via the N-heterocyclic carbene of an indazole.
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Z. Guan et al.: 2-Ethyl-1-phenylindazolium hexafluorophosphateꢀ
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N-ethyl-2-(phenylamino)benzimidothioate (11) and phenyl
N-ethyl-2-(phenylamino)benzimidate (12) (Scheme 7).
Finally, we trapped the N-heterocyclic carbene inda-
zol-3-ylidene as a rhodium complex. Deprotonation of
2-ethyl-1-phenyl-indazolium hexafluorophosphate (5)
with potassium 2-methyl-butan-2-olate in anhydrous THF
at –80ꢀ°C resulted in the formation of indazol-3-ylidene
which was trapped by carbonylbis(triphenylphosphane)
rhodium(I) chloride to give the rhodium complex 13 in
54ꢀ% yield as yellow crystals (Scheme 8).
In the 13C NMR spectra of 13, measured in CDCl3, the
signal of the former carbene carbon atom of the inda-
zole ligand appears at δꢀ=ꢀ186.6 ppm. The signal of the
CO ligand was detected at 191.3 ppm. In comparison to
Fig. 1ꢀMolecular structure of indazolone 8 in the solid state.
Displacement ellipsoids are drawn at the 50 % probability level, H
atoms as spheres with arbitrary radius.
1
salt 5, in the H NMR spectrum, the resonance of 5-H is
shifted upfield by Δδꢀ=ꢀ0.54 ppm on complex formation.
However, this value is also influenced by a solvent change
from CDCl3 to [D6]DMSO, in which the salt is soluble.
The CO frequency can be seen in the IR spectrum at
1974 cm–1. A comparison with the stretching frequencies
of the CO ligands in comparable complexes (2009 and
1994 cm–1) [25] indicates very strong donor strengths of
these indazol-3-ylidenes as already postulated earlier on
benzamide (9) as the main product and the corresponding
thioamide 10 as a result of two competing nucleophiles
(Scheme 5).
The formation of the products 9 and 10 can either
be explained by the nucleophilic attack of hydroxide or
hydrogen sulfide, respectively, to the iminium bond of the
indazolium salt 5, or by interception of the ketenimine 5B
(Scheme 6). An interception of a ketenimine intermediate,
although formed under inert conditions, with water has
been reported [33]. Its formation as a byproduct was also
observed on treatment of an N-ethyl indazolium-carboxy-
late with lithium silylcuprate [34]. Benzothioamide 10 is
a known compound. It has been prepared before by treat-
ment of a 3,1,2-benzothiazaphosphorine-4-thione with
ethylamine [35].
Me
Me
SH
S
N
t-BuOK, toluene, 60 °C, N2, 2 h
Et
NH
Ph
11 (87 %)
Correspondingly,
4-methylthiophenol
and
5
phenol converted the indazolium salt 5 into p-tolyl
OH
O
S
O
NaSH H2O, t-BuOK
toluene, reflux, 3 h
t-BuOK, toluene, 60 °C, N2, 2 h
Et
Et
N
H
N
H
+
5
N
Et
NH
NH
NH
Ph
Ph
Ph
9 (57 %)
10 (10 %)
12 (51 %)
Scheme 5ꢀCompeting ring-opening reactions on treatment of inda-
zolium salt 5 with NaSH·H2O.
Scheme 7ꢀRing cleavage of indazolium salt 5 to form a benzimidate
(12) and a benzthioimidate (11).
HX
HX
Et
N
Et
N
XH
N
H
N
Et
9/10
Et
N
N
Ph
Ph
Ph
Ph
N
N
5
X = O, S
5B
Scheme 6ꢀProposed mechanisms for the formation of 9 and 10.
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ꢀZ. Guan et al.: 2-Ethyl-1-phenylindazolium hexafluorophosphate
PPh3
and 186.9(3) pm, respectively. The phenyl substituent is
rotated by 71.5(4)° out of the plane of the indazole ring
(C4–N7–C10–C15).
Rh CO
PPh3
1. Cl
CO
Rh
Ph3P
PPh3
Et
OK
In summary, we generated the N-heterocyclic carbene
of 2-ethyl-1-phenylindazole by deprotonation of the corre-
sponding indazolium salt. The carbene can be trapped as
thione, oxide, or rhodium complex. It rearranges to 9-ami-
noethylacridine upon warming. Treatment of the indazo-
lium salt with phenolate and thiophenolate resulted in a
ring cleavage of the indazole ring to give a benzimidate
and a benzthioimidate, respectively.
N
THFabs., N ,
−80 °C
2
N
5
2. r. t., overnight
PF6
13 (54 %)
Scheme 8ꢀSynthesis of the rhodium complex 13.
comparing different stretching frequencies of selected
5-membered NHCs [30] or 13C NMR resonance frequen- 3 Experimental section
cies of several palladium carbene complexes [36]. ESIMS
were taken in MeOH solution. Samples were also sprayed Nuclear magnetic resonance (NMR) spectra were meas-
from MeOH at fragmentor voltages between 0 and 150 V at ured with Bruker Avance 400 MHz and Bruker Avance
300ꢀ°C drying gas temperature. At 0 V fragmentor voltage, III 600 MHz instruments. 1H NMR spectra were recorded
the base peak corresponds to the molecular ion at at 400 or 600 MHz, 13C NMR spectra at 100 or 150 MHz,
m/zꢀ=ꢀ877.2. The peak at m/zꢀ=ꢀ849.2 at voltages above 100 with the solvent peak or tetramethylsilane used as the
V is due to the loss of CO, and the peak at m/zꢀ=ꢀ615.0 is internal reference. Multiplicities are described by using
due to the loss of one molecule of PPh3. Additional peaks the following abbreviations: sꢀ=ꢀsinglet, dꢀ=ꢀdoublet,
were detected at m/zꢀ=ꢀ587.0 (–CO, –PPh3) and m/zꢀ=ꢀ223.1, tꢀ=ꢀtriplet, qꢀ=ꢀquartet, and mꢀ=ꢀmultiplet. The mass
which corresponds to the carbene.
spectra were measured with a Varian 320 MS Triple Quad
Single crystals of 13 were obtained by slow evapo- GC/MS/MS instrument. The ESIMS were measured with
ration of a concentrated solution in CH2Cl2-i-PrOH, an Agilent LCMSD instrument series HP 1100. Samples
which allowed the determination of the solid-state for ESI mass spectrometry were sprayed from metha-
structure (Fig. 2). The complex crystallizes in the tri- nol at 30 V fragmentor voltage unless otherwise noted.
clinic space group P (no. 2) with Zꢀ=ꢀ2. The Rh–Ccarbene Melting points are uncorrected and were determined in
1
and Rh–CCO bond lengths (Rh–C9 and Rh–C17; crystal- an apparatus according to Dr. Tottoli (Büchi). Yields are
lographic numbering) were determined to be 208.3(2) not optimized.
3.1 2-Ethyl-1-phenyl-1H-indazole-3(2H)-
thione (7)
A solution of 1 mmol of the indazolium salt 5 [26], 2 mmol
of sulfur and 1.2 mmol of potassium t-butoxide in 20 mL
of toluene was stirred for 3 h at reflux temperature. After
evaporation of the solvent in vacuo, the crude reaction
product was purified by flash column chromatography
(petroleum ether-ethyl acetateꢀ=ꢀ5:1) and dried in vacuo.
Yield: 50 mg of a yellow solid (20 %); m.p.: 90–92ꢀ°C.
1
– H NMR (CDCl3 + TMS): δꢀ=ꢀ8.12 (dt, Jꢀ=ꢀ8.0, 1.0 Hz, 1H,
Ar-H), 7.59–7.47 (m, 4H, Ar-H), 7.32–7.24 (m, 3H, Ar-H), 7.00
(dt, Jꢀ=ꢀ8.3, 0.7 Hz, 1H, Ar-H), 4.38 (q, Jꢀ=ꢀ7.1 Hz, 2H, CH2-
H), 1.25 (t, Jꢀ=ꢀ7.1 Hz, 3H, CH3-H) ppm. – 13C NMR (CDCl3 +
TMS): δꢀ=ꢀ172.8, 145.7, 137.7, 132.3, 130.3, 129.9, 127.3, 127.2,
Fig. 2ꢀMolecular structure of complex 13 in the solid state.
Displacement ellipsoids are drawn at the 50 % probability level, H
atoms as spheres with arbitrary radius.
125.2, 123.2, 110.9, 41.1, 12.9 ppm. – IR (ATR): νꢀ=ꢀ3045, 3031,
2978, 2950, 2932, 1612, 1588, 1491, 1457, 1306, 1276, 1150,
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1033, 977, 840, 748, 698, 609, 490 cm–1. – MS ((+)-ESI): m/z 1.0 Hz, 1H, Ar-H), 6.76 (ddd, Jꢀ=ꢀ7.7, 7.4, 1.0 Hz, 1H, Ar-H),
(%)ꢀ=ꢀ255.0 (100) [M+H]+. – HRMS ((+)-ESI): m/zꢀ=ꢀ255.0958 3.71 (dq, Jꢀ=ꢀ5.4, 7.3 Hz, 2H, CH2-H), 1.23 (t, Jꢀ=ꢀ7.3 Hz, 3H,
(calcd. 255.0956 for [C15H15N2S]+).
CH3-H) ppm. – 13C NMR (CDCl3 + TMS): δꢀ=ꢀ198.0, 142.1,
141.7, 130.7, 130.4, 129.4, 126.9, 121.9, 119.7, 119.4, 117.1, 40.9,
13.2 ppm. – IR (ATR): νꢀ=ꢀ3166, 3036, 3014, 2978, 2929,
1588, 1505, 1463, 1418, 1372, 1307, 1251, 1210, 1150, 1088,
1023, 967, 742, 696, 486 cm–1. – MS ((+)-ESI): m/zꢀ=ꢀ279.0
3.2 2-Ethyl-1-phenyl-indazol-3-one (8)
A solution of 0.2 mmol of the indazolium salt 5 [26] and [M+Na+]. – HRMS ((+)-ESI): m/zꢀ=ꢀ257.1110 (calcd. 257.1112
0.4 mmol of silver(I) oxide in 5 mL of dichloromethane was for [C15H17N2S]+).
stirred for 24 h at 40ꢀ°C. After evaporation of the solvent
in vacuo, the crude reaction product was purified by flash
column chromatography (silica gel; dichloromethane) 3.6 p-Tolyl-N-ethyl-2-(phenylamino)benzi-
and dried in vacuo. Yield: 43 mg (90 %) of a colorless solid;
midothioate (11)
m.p.: 80–82ꢀ°C. – 1H NMR ([D6]DMSO): δꢀ=ꢀ7.78 (ddd, Jꢀ=ꢀ7.6 ,
0.9, 0.8 Hz, 1H, Ar-H), 7.58–7.53 (m, 3H, Ar-H), 7.46–7.38 (m, A solution of 0.5 mmol of indazolium salt 5 [26], 0.5 mmol
3H, Ar-H), 7.24 (ddd, Jꢀ=ꢀ7.6, 7.0, 0.8 Hz, 1H, Ar-H), 7.14 (d, of 4-methylbenzenethiol and 0.6 mmol of potassium
Jꢀ=ꢀ8.4 Hz, 1H, Ar-H), 3.70 (q, Jꢀ=ꢀ7.1 Hz, 2H, CH2-H), 1.04 (t, t-butoxide in 20 mL of toluene was stirred for 2 h at 60ꢀ°C.
Jꢀ=ꢀ7.1 Hz, 3H, CH3-H) ppm. – 13C NMR ([D6]DMSO): δꢀ=ꢀ162.6, After evaporation of the solvent in vacuo, the crude reac-
149.3, 140.3, 132.7, 130.0, 128.0, 124.8, 123.2, 122.7, 117.5, tion product was purified by flash column chromatog-
112.0, 37.3, 12.9 ppm. – IR (ATR): νꢀ=ꢀ2915, 2848, 1472, 1462, raphy (petroleum ether-ethyl acetateꢀ=ꢀ5:1) and dried
1
1021, 958, 887, 843, 718, 557, 492, 473 cm–1. – MS (70 eV): in vacuo. Yield: 150 mg of a yellow oil (87 %). – H NMR
m/zꢀ=ꢀ238.2 [M]+. – HRMS ((+)-ESI): m/zꢀ=ꢀ239.1183 (calcd. (CDCl3 + TMS): δꢀ=ꢀ9.11 (s, 1H, PhNH-H), 7.56 (dd, Jꢀ=ꢀ7.9, 1 . 5
239.1184 for [C15H15N2O]+).
Hz, 1H, Ar-H), 7.30–7.25 (m, 3H, Ar-H), 7.10–7.07 (m, 4H,
Ar-H), 7.03 (ddd, Jꢀ=ꢀ8.0, 7.0, 1.5 Hz, 1H, Ar-H), 6.97–6.92
(m, 3H, Ar-H), 6.61 (ddd, Jꢀ=ꢀ7.9, 7.0, 1.2 Hz, 1H, Ar-H), 3.80
(q, Jꢀ=ꢀ7.3 Hz, 2H, CH2-H), 2.24 (s, 3H, PhMe-H), 1.41 (t,
Jꢀ=ꢀ7.3 Hz, 3H, CH2CH3-H) ppm. – 13C NMR (CDCl3 + TMS):
δꢀ=ꢀ161.1, 142.8, 142.4, 137.3, 132.1, 132.0, 129.8, 129.7, 129.4,
129.3, 124.0, 121.4, 119.1, 118.6, 115.9, 49.3, 21.1, 16.0 ppm.
3.3 N-Ethyl-2-(phenylamino)benzamide (9)
and N-ethyl-2-(phenylamino)benzthio-
amide (10)
A solution of 1 mmol of the indazolium salt 5 [26], 1 mmol – IR (ATR): νꢀ=ꢀ3019, 2967, 2929, 2867, 1588, 1510, 1449,
of sodium hydrogensulfide hydrate, and 1.2 mmol of 1313, 1197, 1017, 926, 804, 745, 694, 491 cm–1. – MS ((+)-
potassium t-butoxide in 20 mL of toluene was stirred ESI): m/zꢀ=ꢀ347.2. – HRMS ((+)-ESI): m/zꢀ=ꢀ347.1583 (calcd.
for 3 h at reflux temperature. After evaporation of the 347.1582 for [C22H23N2S]+).
solvent in vacuo, the crude reaction product was purified
by flash column chromatography (petroleum ether-ethyl
acetateꢀ=ꢀ5:1) and dried in vacuo.
3.7 Phenyl-N-ethyl-2-(phenylamino)benzi-
midate (12)
3.4 N-Ethyl-2-(phenylamino)benzamide (9)
A solution of 0.5 mmol of the indazolium salt 5 [26],
0.6 mmol of phenol and 0.6 mmol of potassium t-butox-
Yield: 137 mg (57 %), all spectroscopic data are identically ide in 20 mL of toluene was stirred for 2 h at 60ꢀ°C. After
with the literature values [33].
evaporation of the solvent in vacuo, the crude reaction
product was purified by flash column chromatography
(petroleum ether-ethyl acetateꢀ=ꢀ3:1) and dried in vacuo.
Yield: 80 mg of a colorless solid (51 %); m.p.: 68–70ꢀ°C.
3.5 N-Ethyl-2-(phenylamino)benzothio-
amide (10)
1
– H NMR (CDCl3 + TMS): δꢀ=ꢀ11.10 (s, 1H, PhNH-H), 7.57 (dd,
Jꢀ=ꢀ8.1, 1.5 Hz, 1H, Ar-H), 7.39 (dd, Jꢀ=ꢀ8.5, 1.0 Hz, 1H, Ar-H),
Yield: 26 mg of a yellow solid (10 %); m.p.: 107–109ꢀ°C. 7.36–7.32 (m, 2H, Ar-H), 7.29–7.25 (m, 4H, Ar-H), 7.19 (ddd,
1
ref. [37]: 116ꢀ°C. – H NMR (CDCl3 + TMS): δꢀ=ꢀ8.23 (s, Jꢀ=ꢀ8.5, 7.0, 1.5 Hz, 1H, Ar-H), 7.06–6.98 (m, 2H, Ar-H), 6.92–
1H, PhNH-H), 7.86 (bs, 1H, EtNH-H), 7.24–7.11 (m, 5H, 6.89 (m, 2H, Ar-H), 6.62 (ddd, Jꢀ=ꢀ8.1, 7.0, 1.0 Hz, 1H, Ar-H),
Ar-H), 7.02 (dd, Jꢀ=ꢀ8.5, 1.0 Hz, 2H, Ar-H), 6.88 (tt, Jꢀ=ꢀ7.3, 3.53 (q, Jꢀ=ꢀ7.3 Hz, 2H, CH2-H), 1.27 (t, Jꢀ=ꢀ7.3 Hz, 3H, CH3-H)
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88ꢀ
ppm. – 13C NMR (CDCl3 + TMS): δꢀ=ꢀ155.9, 154.1, 146.2, 141.7, C15H14N2O (8)ꢀMonoclinic space group P21/c (no. 14).
131.5, 130.4, 130.0, 129.4, 122.6, 122.4, 121.2, 117.2, 115.4, Cell parameters: aꢀ=ꢀ10.476(3), bꢀ=ꢀ9.250(2), cꢀ=ꢀ15.742(4)
114.7, 113.9, 42.5, 16.1 ppm. – IR (ATR): νꢀ=ꢀ3021, 2968, 2931, Å, βꢀ=ꢀ121.95(2)°, Vꢀ=ꢀ1294.4(5) Å3, Zꢀ=ꢀ 4, dcalcd.ꢀ=ꢀ1.22 g cm–
1634, 1588, 1575, 1488, 1455, 1376, 1287, 1201, 1161, 1129, 3, F(000)ꢀ=ꢀ504 e. The structure refinement using 2449
1047, 893, 744, 690, 641 cm–1. – MS ((+)-ESI): m/zꢀ=ꢀ317.2 independent reflections and 219 parameters converged
[M+H]+. – HRMS ((+)-ESI): m/zꢀ=ꢀ317.1656 (calcd. 317.1654 at R1ꢀ=ꢀ0.0639, wR2ꢀ=ꢀ0.1012 [Iꢀ>ꢀ2 σ(I)], goodness of fit on
for [C21H21N2O]+).
F2ꢀ=ꢀ1.040, residual electron density 0.219 and –0.196 e Å–3.
C54H48Cl4F6N2OP3Rh (13)ꢀTriclinic space group P1 (no.
2). Cell parameters: aꢀ=ꢀ12.183(1), bꢀ=ꢀ14.658(1), cꢀ=ꢀ15.803(2)
Å, αꢀ=ꢀ100.71(1), βꢀ=ꢀ103.32(1), γꢀ=ꢀ91.90(1)°; Vꢀ=ꢀ2689.6(5)
Å3, Zꢀ=ꢀ2, dcalcd.ꢀ=ꢀ1.47 g cm–3, F(000)ꢀ=ꢀ1212 e. The structure
refinement using 9879 independent reflections and 816
3.8 Carbonylbis(triphenylphosphane)
(2-ethyl-1-phenyl-1H-indazole-3-ylidene)
rhodium(I) hexafluorophosphate (13)
A solution of 0.5 mmol of indazolium salt 5 [26] and parameters converged at R1ꢀ=ꢀ0.0584, wR2ꢀ=ꢀ0.1135 [Iꢀ>ꢀ2
0.5 mmol of carbonylbis(triphenylphosphane)rhodium(I) σ(I)], goodness of fit on F2ꢀ=ꢀ1.015, residual electron density
chloride in 20 mL of THF was cooled to –80ꢀ°C. Then, 1.19 and –0.79 e Å–3.
0.3 mL of a 2-m solution of potassium 2-methylbutan-
CCDC 1002044 (compound 8) and CCDC 1002043
2-olate in THF was added dropwise. The reaction mixture (compound 13) contain the supplementary crystallo-
was stirred overnight at room temperature. Yellow solids graphic data for this paper. These data can be obtained
formed were filtered off, washed with 2 mL of ethyl acetate free of charge from The Cambridge Crystallographic Data
and dried in vacuo. Yield: 277 mg (54 %); m.p.: 212ꢀ°C Centre via www.ccdc.cam.ac.uk/data_request/cif.
(dec.) – 1H NMR (CDCl3 + TMS): δꢀ=ꢀ7.54–7.52 (m, 3H, Ar-H),
7.49–7.42 (m, 19H, Ar-H), 7.37–7.34 (m, 13H, Ar-H), 6.92 (t, Acknowledgments: Dr. Gerald Dräger, University of Han-
Jꢀ=ꢀ7.5 Hz, 1H, Ar-H), 6.76–6.71 (m, 3H, Ar-H), 3.93 (q, Jꢀ=ꢀ7. 3 nover, Hannover, Germany, is greatfully acknowledged
Hz, 2H, CH2-H), 0.57 (t, Jꢀ=ꢀ7.3 Hz, 3H, CH3-H) ppm. – 13C for measuring the high-resolution mass spectra. We thank
NMR (CDCl3 + TMS): δꢀ=ꢀ191.3, 186.6, 140.5, 133.8 (dd, Jꢀ=ꢀ7.4 , PD Dr. Jörg Adams, Clausthal University of Technology, for
6.6 Hz), 133.3, 132.5 (dd, Jꢀ=ꢀ24.0, 23.0 Hz), 132.1, 131.4, 131.0, measuring the fluorescence spectra.
130.6, 129.5, 128.8 (dd, Jꢀ=ꢀ5.9, 5.0 Hz), 128.1, 126.9, 122.6,
109.5, 49.2, 13.8 ppm. – IR (ATR): νꢀ=ꢀ3058, 1974, 1497, 1437,
1306, 1119, 1091, 829, 744, 721, 693, 556, 514, 496 cm–1. – MS
References
((+)-ESI): m/zꢀ=ꢀ877.2 [M]+. – HRMS ((+)-ESI): m/zꢀ=ꢀ877.1984
(calcd. 877.1984 for [C52H44N2OP2Rh]+).
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