Investigation and comparison of the mechanistic steps in the [(Cp*MCl2)2] (Cp=C5Me5; M=Rh, Ir)-catalyzed oxidative annulation of isoquinolones with alkynes

Article abstract of DOI:10.1002/chem.201203374

The mechanism of the [(Cp*MCl₂)₂] (M=Rh, Ir)-catalyzed oxidative annulation reaction of isoquinolones with alkynes was investigated in detail. In the first acetate-assisted C-H-activation process (cyclometalated step) and the subsequ

Full text of DOI:10.1002/chem.201203374

DOI: 10.1002/chem.201203374
Investigation and Comparison of the Mechanistic Steps in the [(Cp*MCl2)2]
(Cp*=C5Me5; M=Rh, Ir)-Catalyzed Oxidative Annulation of
Isoquinolones with Alkynes
Nuancheng Wang,[a] Bin Li,*[a] Haibin Song,[a] Shansheng Xu,[a] and Baiquan Wang*[a, b]
Abstract: The mechanism of the
[(Cp*MCl2)2] (M=Rh, Ir)-catalyzed
oxidative annulation reaction of isoqui-
nolones with alkynes was investigated
in detail. In the first acetate-assisted
dibenzo
N
deriva-
formation. The iridium complexes were
found to be inactive in the oxidative
coupling processes. All of the relevant
intermediates were fully characterized
and determined by single-crystal X-ray
diffraction analysis. Based on this
mechanistic study, a RhIII!RhI!RhIII
catalytic cycle was proposed for this re-
action.
tives, were only formed in high yield
when the Rh species participated in the
ꢀ
final oxidative coupling of the C N
bond. Moreover, a RhI sandwich inter-
mediate was isolated during this trans-
ꢀ
C H-activation process (cyclometalat-
ed step) and the subsequent mono-
ꢀ
alkyne insertion into the M C bonds
Keywords: C H activation · iridi-
um · oxidative annulation · reaction
mechanisms · rhodium
of the cyclometalated compounds, both
Rh and Ir complexes participated well.
However, the desired final products,
Introduction
[1]
ꢀ
The catalytic functionalization of C H bonds has become
an increasingly efficient and reliable approach for the con-
struction of nitrogen-containing heterocycles in an atom-
and step-economic fashion that complements traditional
synthetic strategies.[2] During the last few years, [Cp*RhIIILn]
(Cp*=C5Me5)[3,4] complexes were found to be competent
catalysts for the oxidative coupling reactions between
arenes/heteroarenes and alkynes. In this regard, methods to
synthesize indoles,[4b,i,o,u] pyrroles,[4b,i,l] isoquinolines,[4e,g,h,p,q,s,t]
isoquinolones,[4a,j,k,m,r] indenols,[4d,f] and pyridones[4c,n] through
ꢀ
catalytic C H activation have been well-developed. It
should be noted that, amongst these reports, the elegant
report by Jones and co-workers[4v] has described the isola-
tion and characterization of the intermediate compounds in
the [(Cp*RhCl2)2]-mediated synthesis of isoquinoline salts
and a RhIII!RhIV!RhII!RhIII mechanism has been pro-
posed for these stoichiometric reactions (Scheme 1). As far
Scheme 1. Proposed RhIII!RhIV!RhII!RhIII mechanism for the
[(Cp*RhCl2)2]-mediated synthesis of isoquinoline salts reported by Jones
and co-workers.[4v]
as we know, no other related mechanistic studies on the oxi-
dative annulation reaction catalyzed by rhodium
plexes are available in the literature.
ACHTUNGTRENN(UNG III) com-
[a] N. Wang, Prof. Dr. B. Li, Prof. Dr. H. Song, Prof. S. Xu,
Prof. Dr. B. Wang
In our previous study,[5] isoquinolones (1) were found to
be good substrates for the isolation of the reaction inter-
mediates, owing to their rigid structures. In addition, when
[(Cp*MCl2)2] (M=Rh, Ir) were applied as catalysts in the
oxidative annulation reaction between isoquinolones and al-
kynes,[6] the two metal catalysts exhibited great differences
between their catalytic abilities (Table 1), that is, dibenzo-
State Key Laboratory of Elemento-Organic Chemistry
College of Chemistry, Nankai University
Tianjin 300071 (P.R. China)
Fax: (+86)22-2350-4781
E-mail: nklibin@nankai.edu.cn
bqwang@nankai.edu.cn
[b] Prof. Dr. B. Wang
State Key Laboratory of Organometallic Chemistry
Chinese Academy of Sciences
AHCTUNGTREG[NNUN a,g]quinolizin-8-one derivatives 3aa–3da and 3cb were iso-
lated in high yield (86–97%) from the [(Cp*RhCl2)2]-cata-
lyzed reactions, whereas, when [(Cp*IrCl2)2] acted as the
catalyst, compounds 3aa–3da and 3cb were obtained in
Shanghai 200032 (P.R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201203374.
358
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Chem. Eur. J. 2013, 19, 358 – 364

FULL PAPER
Table 1. ACHTUNGTRENNUNG[(Cp*MCl2)2] (M=Rh, Ir)-catalyzed oxidative coupling reaction
between isoquinolones 1 and alkynes 2.
Rh, and 4c-Ir, each of which contained a coordinated pyri-
dine group, were obtained by column chromatography in
moderate-to-excellent yields. It is worth noting that the
yields of the cyclometalated compounds were higher for the
same substrates with [(Cp*IrCl2)2] than with [(Cp*RhCl2)2].
Moreover, metallocycles 4c-Rh and 4c-Ir (R=NO2) were
obtained in much higher yield than compounds 4a-Rh and
4a-Ir (R=H). This result might be attributed to the elec-
tron-withdrawing effect of the nitro substituent, which stabi-
lized the cyclometalated complexes, and is consistent with
R
Yield [%]
M=Rh
M=Ir[a]
R1 =R2 =Ph
H
Cl
NO2
OMe
NO2
3aa
3ba
3ca
3da
3cb
93
97
97
16
12
7
our previous report on the reaction of [{RuCl
2ACHTUNGTRENUN(NG p-cymene)}2]
with isoquinolones.[5]
The structures of compound 4c-Rh and 4b-Ir were con-
firmed by single-crystal X-ray diffraction analysis (Figure 1
93
9
R1 =Ph, R2 =Me
86[b]
8[b]
[a]24 h. [b] With Ag2CO3 (1.5 equiv) and MeCN (2.0 mL) at 1108C.
very low yield (8–16%). These results promoted us to con-
duct experimental investigations to elucidate the mechanism
of the [(Cp*MCl2)2] (M=Rh, Ir)-catalyzed oxidative-cou-
pling/cyclization reaction between isoquinolones and al-
kynes. Herein, we report a detailed investigation and com-
parison of the mechanistic steps in the [(Cp*RhCl2)2] and
[(Cp*IrCl2)2]-catalyzed oxidative annulation reaction by iso-
lating and fully characterizing the relevant intermediate
ꢀ
compounds that are involved in C H activation, alkyne in-
ꢀ
sertion, and oxidative coupling of C N bond, including the
determination of single-crystal X-ray structures.
Results and Discussion
ꢀ
In our mechanistic investigation, the C H-activation process
Figure 1. ORTEP of compound 4c-Rh; thermal ellipsoids are set at 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
to form cyclometalated compounds was studied first. The
direct reaction of an isoquinolone with stoichiometric quan-
tities of [(Cp*MCl2)2] promoted by NaOAc did not afford
any separable complexes. We suspect that, under these reac-
tion conditions, the resulting cyclometalated compound was
a coordinatively unsaturated 16e species that was too reac-
tive to be isolated. Then, the isoquinolones (1a, 1b, and 1c)
were treated with [Cp*MPyCl2] (Py=pyridine, prepared in
situ from [(Cp*MCl2)2] and pyridine) in CH2Cl2 at room
temperature in the presence of NaOAc and Et3N for 12 h
(Table 2). The metallacycles, 4a-Rh, 4a-Ir, 4b-Rh, 4b-Ir, 4c-
ꢀ
ꢀ
lengths [ꢁ] and angles [8]: Rh(1) C(21) 2.028(7), Rh(1) N(1) 2.083(5),
ꢀ
ꢀ
ꢀ
Rh(1) N(2) 2.126(6), C(1) N(1) 1.375(8), C(1) O(1) 1.233(8); C(21)-
Rh(1)-N(1) 78.5(2), C(21)-Rh(1)-N(2) 88.3(3).[7]
and Figure 2). A piano-stool-type geometry that consisted of
a five-membered metallocycle with a coordinated pyridine
was observed in both complexes. The bond lengths and
angles are comparable to those in the reported cyclometalat-
(III).[4v,8] No-
ed Cp* complexes of rhodiumACTHNURTGENN(GU III) and iridiumACHTUNGTRENNUGN
ꢀ
tably, the Ir(1) N(2) bond in complex 4b-Ir (2.109(5) ꢁ)
ꢀ
was, unexpectedly, slightly shorter than the Rh(1) N(2)
bond in 4c-Rh (2.126(6) ꢁ), thus implying stronger s dona-
Table 2. Isolation of the cyclometalated compounds (4).
tion from the N atom to the Ir atom.
ꢀ
Subsequently, the insertion of an alkyne into the M C
bond was investigated (Table 3). The alkyne-insertion com-
pounds (5) could be isolated from the reactions between iso-
quinolones, alkynes, and [(Cp*MCl2)2] in MeOH at 408C in
the presence of NaOAc in one step. Again, higher yields of
the alkyne-insertion compounds for the same substrate with
[(Cp*IrCl2)2] than with [(Cp*RhCl2)2] were observed. The
electronic characteristics of the substrate had a tremendous
influence on the reaction. Isoquinolones with an electron-
withdrawing group (R=Cl, 1b; R=NO2, 1c) were found to
R
Yield [%]
M=Rh
M=Ir
H
Cl
NO2
4a-Rh
4b-Rh
4c-Rh
50
69
76
4a-Ir
4b-Ir
4c-Ir
72
78
85
Chem. Eur. J. 2013, 19, 358 – 364
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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359

B. Li, B. Wang et al.
single-crystal X-ray diffraction. Interestingly, two types of
molecular structures were found for these compounds: The
first type was observed in compounds 5ba-Ir, 5da-Rh, 5da-
Ir, and 5cb-Rh. The ORTEPs of compounds 5ba-Ir and
5cb-Rh are shown in Figure 3 and Figure 4, respectively,
Figure 2. ORTEP of compound 4b-Ir; thermal ellipsoids are set at 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
ꢀ
ꢀ
lengths [ꢁ] and angles [8]: Ir(1) C(21) 2.053(6), Ir(1) N(1) 2.092(4),
ꢀ
ꢀ
ꢀ
Ir(1) N(2) 2.109(5), C(1) N(1) 1.378(7), C(1) O(1) 1.235(7); C(21)-
Ir(1)-N(1) 77.04(19), C(21)-Ir(1)-N(2) 88.3(3).[7]
be favored in this reaction, whereas electron-neutral (1a)
and electron-rich isoquinolones (R=OMe, 1d) could not be
efficiently converted. This property resulted in the isolation
of diphenyl-acetylene (2a)-insertion compounds 5ba and
5ca in much higher yields than compounds 5aa and 5da
with both rhodium and iridium complexes. When an unsym-
metrical aryl-alkyl-disubstituted alkyne, 1-phenyl-1-propyne
(2b), was employed, lower yields of the resulting com-
pounds, 5cb-Rh and 5cb-Ir, relative to their diphenyl-acety-
lene counterparts, 5ca-Rh and 5ca-Ir, were found. The in-
sertion of compound 2b occurred with high regioselectivity
for the aryl-substituted carbon center connected onto the
metal center, as confirmed by single-crystal X-ray diffraction
of compound 5cb-Rh (see Figure 4). In addition, in the reac-
tion with [(Cp*RhCl2)2], the final products 3ba-3da and 3cb
were isolated in certain amounts, in addition to the alkyne-
insertion compounds (5-Rh).
Figure 3. ORTEP of compound 5ba-Ir; thermal ellipsoids are set at 30%
probability. Hydrogen atoms are omitted for clarity. Selected bond
ꢀ
ꢀ
lengths [ꢁ] and angles [8]: Ir(1) C(29) 2.068(4), Ir(1) N(1) 2.086(3),
ꢀ
ꢀ
ꢀ
Ir(1) O(1) 2.250(3), C(1) N(1) 1.336(5), C(1) O(1) 1.293(4); C(29)-
Ir(1)-N(1) 79.63(13), O(1)-Ir(1)-N(1) 60.46(11).[7]
and those for compounds 5da-Rh and 5da-Ir are provided
in the Supporting Information. The structures of compounds
5ba-Ir, 5da-Rh, 5da-Ir, and 5cb-Rh contain a seven-mem-
ꢀ
ꢀ
bered metallocycle with the formation of M C(alkyne), M N,
ꢀ
and M O bonds. To satisfy the 18e rule around the center
metal atom, electron delocalization of the amide moiety
ꢀ
takes place in these compounds. Therefore, the C(1) N(1)
bond lengths in compounds 5ba-Ir (1.336(5) ꢁ) and 5cb-Rh
(1.334(6) ꢁ) are much shorter than those in compounds 4b-
Ir and 4c-Rh (1.378(7) and 1.375(8) ꢁ, respectively), where-
ꢀ
as the C(1) O(1) distances (1.293(4) ꢁ for 5ba-Ir and
The molecular structures of compounds 5ba-Ir, 5ca-Rh,
5ca-Ir, 5da-Rh, 5da-Ir, and 5cb-Rh were determined by
1.278(6) ꢁ for 5cb-Rh) are much longer than before the in-
sertion (1.235(7) ꢁ for 4b-Ir and 1.233(8) ꢁ for 4c-Rh, re-
spectively).
The molecular structures of
Table 3. Isolation of the alkyne-insertion compounds (5).
compounds 5ca-Rh and 5ca-Ir
belong to the second type. The
ORTEP of compound 5ca-Rh
is shown in Figure 5 and that
of compound 5ca-Ir is provid-
ed in the Supporting Informa-
tion. The structures of com-
pounds 5ca-Rh and 5ca-Ir
R
Yield [%]
contain
a
seven-membered
M=Rh
M=Ir
metallocycle with the forma-
R1 =R2 =Ph
R1 =Ph, R2 =Me
360
H
Cl
NO2
OMe
NO2
5aa-Rh (39)+3aa (trace)
5ba-Rh(64)+3ba (6)
5ca-Rh(89)+3ca (5)
5da-Rh(21)+3da (25)
5cb-Rh(35)+3cb (22)
5aa-Ir(56)+3aa (trace)
5ba-Ir(80)+3ba (trace)
5ca-Ir(92)+3ca (trace)
5da-Ir(67)+3da (trace)
5cb-Ir(69)+3cb (trace)
ꢀ
ꢀ
tion of M C(alkyne) and M N
bonds. The difference between
these two sets molecule struc-
tures is the formation of a h2-
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Chem. Eur. J. 2013, 19, 358 – 364

Oxidative Annulation of Isoquinolones with Alkynes
FULL PAPER
reactions between cyclometalated complexes 4a–4c and di-
phenyl acetylene or 1-phenyl-1-propyne for both rhodium
and iridium complexes (Table 4).
Table 4. Transformation of the cyclometalated complexes (4) into the
alkyne-insertion compounds (5).
R
Yield [%]
M=Rh
5aa-Rh
5ba-Rh
5ca-Rh
5cb-Rh
M=Ir
R1 =R2 =Ph
H
Cl
NO2
NO2
69
5aa-Rh
81
92
97
71
90
95
70
5ba-Rh
5ca-Rh
5cb-Rh
Figure 4. ORTEP of compound 5cb-Rh; thermal ellipsoids are set at
30% probability. Hydrogen atoms are omitted for clarity. Selected bond
R1 =Ph, R2 =Me
ꢀ
ꢀ
lengths [ꢁ] and angles [8]: Rh(1) C(29) 2.068(5), Rh(1) N(1) 2.087(4),
ꢀ
ꢀ
ꢀ
Rh(1) O(1) 2.318(4), C(1) N(1) 1.334(6), C(1) O(1) 1.278(6); C(29)-
Rh(1)-N(1) 82.63(18), O(1)-Rh(1)-N(1) 59.87(14).[7]
The final products, compounds 3ba and 3ca, were formed
in almost-quantitative yields upon heating compounds 5ba-
Rh and 5ca-Rh with CuACHTNUTRGNE(UNG OAc)2·H2O as an oxidant in o-
xylene at 1208C (Scheme 2). However, when their corre-
Scheme 2. Transformation of alkyne-insertion compounds 5-Rh and 6-Rh
into compound 3.[a] Results: X=Cl, 6ba-Rh (85%)+3ba (5%); X=NO2,
6ca-Rh (93%)+3ca (trace).
Figure 5. ORTEP of compound 5ca-Rh; thermal ellipsoids are set at
30% probability. Hydrogen atoms are omitted for clarity. Selected bond
ꢀ
ꢀ
lengths [ꢁ] and angles [8]: Rh(1) C(7) 2.064(3), Rh(1) N(1) 2.094(2),
ꢀ
ꢀ
ꢀ
Rh(1) C(15) 2.481(3), Rh(1) C(20) 2.557(3), N(1) C(35) 1.370(3),
[7]
ꢀ
C(35) O(1) 1.262(3); C(7)-Rh(1)-N(1) 83.88(10).
sponding iridium complexes (5-Ir) were treated under the
same reaction conditions, the final products (3) were only
isolated in low yields. Intriguingly, in the absence of Cu-
coordinated phenyl group on the isoquinolone moiety
ꢀ
through atoms C(15) and C(20), instead of a M O bond in
the latter type. Under such an arrangement, the metal
ACHTUNGTREN(UNNG OAc)2·H2O, the reactions of compounds 5ba-Rh and 5ca-
Rh led to the formation of RhI sandwich complexes 6ba-Rh
and 6ca-Rh, respectively. No complexes 6-Ir were isolated
from similar reactions with iridium and most of the starting
materials (5-Ir) were recovered. Sandwich complexes 6ba-
Rh and 6ca-Rh were not stable in MeOH and decomposed
into the final products. Thus, no analogues of compounds 6-
Rh were observed in the reactions described in Table 3. As
shown in Scheme 2, when complexes 6ba-Rh and 6ca-Rh
center also has 18e. In all cases, the insertion of an alkyne
ꢀ
ꢀ
into the Rh C bond, rather than the Rh N bond, was ob-
served. Moreover, only a single alkyne-insertion complex
was isolated, instead of multiple insertions, which have been
observed in palladium and nickel analogues.[9] This result is
consistent with that found by Jones and co-workers.[4v]
As expected, the alkyne-insertion compounds 5aa–5ca
and 5cb were formed in good-to-excellent yields from the
were heated with CuACHTNUTRGNE(UGN OAc)2·H2O in o-xylene at 1208C,
Chem. Eur. J. 2013, 19, 358 – 364
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361

B. Li, B. Wang et al.
products 3ba and 3ca were isolated in almost-quantitative
yield. This fact indicated that complex 6-Rh might be an in-
termediate between the alkyne-insertion compounds (5-Rh)
and the final products (3).
The molecular structure of compound 6ca-Rh was deter-
mined by single-crystal X-ray diffraction. Figure 6 shows
that complex 6ca-Rh adopts a sandwich structure, with an
Scheme 3. Proposed mechanism of the oxidative coupling reaction
(another structure type of compound 5 is omitted).
(6), with the reduction of the rhodium center from RhIII into
RhI. Finally, complex 6 is transformed into the desired prod-
uct (3) and the RhI center undergoes oxidation to regener-
ate the catalytically active RhIII complex with the aid of a
copper oxidant. For [(Cp*IrCl2)2], this catalyst participated
ꢀ
well in the first C H-activation step and subsequent mono-
Figure 6. ORTEP of compound 6ca-Rh; thermal ellipsoids are set at
30% probability. Hydrogen atoms are omitted for clarity. Selected bond
ꢀ
alkyne insertion into the Ir C bonds of the cyclometalated
ꢀ
compounds. But, in the oxidative coupling of the C N bond,
ꢀ
ꢀ
ꢀ
lengths [ꢁ]: Rh(1) C(11) 2.141(4), Rh(1) C(18) 2.134(4), Rh(1) C(25)
[7]
the iridium complex exhibited low reactivity. This result can
explain why [(Cp*IrCl2)2] failed to catalyze this oxidative
annulation reaction.
ꢀ
2.179(4), Rh(1) C(30) 2.206(4).
h5-coordinated Cp* ligand and an h4-coordinated heterocy-
cle (through atoms C(11) and C(18) of the former alkyne
group and atoms C(25) and C(30) of the isoquinolone
group) to a univalent rhodium center. From the structure of
compound 6ca-Rh, it is apparent that the oxidative coupling
Conclusion
In conclusion, we have reported a detailed study of the
mechanism of the RhIII-catalyzed oxidative annulation of
isoquinolones with alkynes. All of the key intermediates, in-
ꢀ
of the C N bond is concomitant with the reduction of the
rhodium center from RhIII into RhI. An analogous sandwich
structure for a Rh complex that also involved a combination
of h5- and h4-bonded ligands, [6-hydro-2,7-dimethyl-as-inda-
ꢀ
cluding acetate-assisted C H activation (4), alkyne insertion
ꢀ
ꢀ
of the Rh C bond (5), and oxidative coupling of C N bond
(6), were isolated and determined by single-crystal X-ray
diffraction. Based on our study, a RhIII!RhI!RhIII catalytic
cycle was proposed for the reaction. This mechanism insight
will be helpful for the development of more-efficient RhIII-
cenide-RhACHTUNGTRENNUNG
(h4-cod)], has been reported.[10]
Based on these above experiments, a plausible mechanism
for the [(Cp*RhCl2)2]-catalyzed oxidative coupling of isoqui-
nolones with alkynes is proposed in Scheme 3. The dimeric
rhodium pre-catalyst presumably dissociates into the coordi-
natively unsaturated monomer in solution, which can ex-
ꢀ
catalyzed C H functionalization with alkyne reaction sys-
tems. Meanwhile, similar mechanistic experiments were car-
ried out with [(Cp*IrCl2)2]. We found that the low reactivity
change ligands with CuACHTNUTRGNEUNG(OAc)2·H2O to form an acetate-ligat-
ꢀ
ꢀ
ꢀ
ed species. Then, a N H/C H bond-cleavage process occurs
to afford a five-membered metallocycle (4) with the con-
comitant formation of acetic acid through an acetate-assist-
ed mechanism.[8d] According to the kinetic study, an inter-
of the iridium complex in the oxidative coupling of the C N
bond resulted in the low catalytic activity of [(Cp*IrCl2)2] in
this reaction.
ꢀ
molecular deprotonation process for C H activation was
proposed by Dixneuf, Jutand, and co-workers.[11] After the
Experimental Section
ꢀ
insertion of an alkyne into the Rh C bond of compound 4,
a seven-membered rhodacycle intermediate (5) is formed.
General procedures: All of the reactions were carried out under an
argon atmosphere by using standard Schlenk techniques. 1H NMR
(300 MHz or 400 MHz), 19F NMR (376MHz), and 13C NMR spectroscopy
ꢀ
Subsequent oxidative coupling of the C N bond in com-
pound 5 takes place to form a rhodium sandwich species
362
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Chem. Eur. J. 2013, 19, 358 – 364

Oxidative Annulation of Isoquinolones with Alkynes
FULL PAPER
(75 MHz or 100 MHz) were performed on Bruker AV300 and AV400
NMR spectrometers in CDCl3. Chemical shifts are reported in parts per
million (ppm); residual solvent signals were used as references and the
chemical shifts were converted onto the TMS scale (CDCl3: dH =
7.26 ppm). All of the coupling constants (J) are reported in Hertz (Hz).
Multiplicities are reported as follows: singlet (s), doublet (d), doublet of
doublets (dd), doublet of doublet of doublets (ddd), doublet of triplets
(dt), triplet (t), triplet of doublets (td), quartet (q), and multiplet (m).
Column chromatography was performed on silica gel (200–300 mesh). IR
spectra were recorded as KBr disks on a Nicolet 380 FTIR spectrometer.
MS (EI) and HRMS (EI) were performed on Thermo Finnigan TRACE
DSQ and Varian 7.0 T FTICR-mass spectrometers, respectively.
pressure. Purification was performed by flash column chromatography on
silica gel.
X-ray crystallography: Data collection was performed on
a Rigaku
Saturn 70 diffractometer that was equipped with a rotating anode system
by using graphite-monochromated MoKa radiation (wꢀ2q scans). Semi-
empirical absorption corrections were applied for all complexes.[12] The
structures were solved by using direct methods and refined by full-matrix
least-squares. All calculations were performed by using the SHELXL-97
program system.[13] All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were assigned idealized positions and were included in
the structure-factor calculations. The crystal data and a summary of the
X-ray data are presented in the Supporting Information, Tables S2 and
S3.
General procedure A: Rhodium/iridium-catalyzed oxidative coupling of
isoquinolones with alkynes. Isoquinolone 1 (0.20 mmol, 1.0 equiv), alkyne
(if solid) 2 (0.40 mmol, 2.0 equiv), [(Cp*MCl2)2] (0.008 mmol, 4.0 mol%,
CCDC-900548 (4b-Ir), CCDC-900549 (4c-Rh), CCDC-900550 (5ba-Ir),
CCDC-900551 (5ca-Rh), CCDC-900552 (5ca-Ir), CCDC-900553 (5da-
Rh), CCDC-900554 (5da-Ir), CCDC-900556 (5cb-Rh), and CCDC-
900556 (6ca-Rh) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
M=Rh (4.9 mg), M=Ir (6.4 mg)), and CuACHTUNGRTENUNG(OAc)2·H2O (87.8 mg,
0.44 mmol, 2.2 equiv) were weighed into a Schlenk tube that was equip-
ped with a stirrer bar. Dry o-xylene was added (2.0 mL) (immediately
followed by the alkyne if it was a liquid) and the mixture was stirred at
1208C for 12 h (for Rh)/24 h (for Ir) under an Ar atmosphere. After-
wards, the mixture was diluted with CH2Cl2 and transferred into a round-
bottomed flask. Silica was added to the flask and the volatile compounds
were evaporated under reduced pressure. Purification was performed by
flash column chromatography on silica gel.
Acknowledgements
Support of this work by the NSFC (21072097 and 21072101) and the
SRFDP (20110031110009) is gratefully acknowledged.
Typical procedure for the preparation of cyclometalated complex 4: Pyri-
dine (15.8 mg, 0.20 mmol) was added to a solution of [(Cp*MCl2)2]
(0.10 mmol) in CH2Cl2 (8 mL) at RT. After vigorous stirring for 4 h,
NaOAc (41.0 mg, 0.50 mmol) and isoquinolone 1 (0.2 mmol) were added
to the solution, along with triethylamine (TEA, 0.4 mL), and vigorous
stirring was continued for a further 12 h. After the reaction was com-
plete, the solution was transferred into a round-bottomed flask. Silica
was added to the flask and the volatile compounds were evaporated
under reduced pressure. The crude product was purified by column chro-
matography on silica gel to afford complex 4.
ꢀ
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Typical procedure for the preparation of alkyne-insertion complex 5: Iso-
quinolone
1 (0.20 mmol, 1.0 equiv), alkyne 2 (0.3 mmol, 1.5 equiv),
[(Cp*MCl2)2] (0.12 mmol, 0.6 equiv, M=Rh (74.2 mg), M=Ir (95.5 mg)),
and NaOAc (32.8 mg, 0.40 mmol, 2.0 equiv) were weighed into a Schlenk
tube that was equipped with a stirrer bar. Dry MeOH (4.0 mL) was
added and the mixture was stirred at 408C for 48 h under an Ar atmos-
phere. Afterwards, the mixture was diluted with CH2Cl2 and transferred
into a round-bottomed flask. Silica was added to the flask and the vola-
tile compounds were evaporated under reduced pressure. Purification
was performed by flash column chromatography on silica gel.
Transformation of complex 4 into complex 5 through alkyne insertion:
Compound 4 (0.10 mmol, 1.0 equiv) and alkyne 2 (0.15 mmol, 1.5 equiv)
were weighed into a Schlenk tube that was equipped with a stirrer bar.
Dry MeOH (2.0 mL) was added and the mixture was stirred at 408C for
8 h under an Ar atmosphere. Afterwards, the mixture was diluted with
CH2Cl2 and transferred into a round-bottomed flask. Silica was added to
the flask and the volatile compounds were evaporated under reduced
pressure. Purification was performed by flash column chromatography on
silica gel.
Preparation of rhodium(I) complex 6-Rh: Compound 5-Rh (0.1 mmol)
was weighed into a Schlenk tube that was equipped with a stirrer bar.
Dry o-xylene (2.0 mL) was added and the mixture was stirred at 1208C
for 10 h under an Ar atmosphere. Afterwards, the mixture was diluted
with CH2Cl2 and transferred into a round-bottomed flask. Silica was
added to the flask and the volatile compounds were evaporated under re-
duced pressure. Purification was performed by flash column chromatog-
raphy on silica gel.
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Received: September 20, 2012
Published online: November 21, 2012
364
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Chem. Eur. J. 2013, 19, 358 – 364