Organometallics
Article
synthetic pathway could yet be another alternative method for
the preparation of heterobimetallic complexes. In this approach,
a metal complex is prepared and a ditopic bridging ligand (a
donor ligand possessing two binding sites for the coordination to
metal atoms) is bound to the first metal, which is followed by
0.23 mmol) was added to a solution of [Cp*Rh(ppy)Cl] (100 mg, 0.23
mmol) in CH Cl (10 mL). The resulting mixture was stirred at room
2
2
temperature for 1 h. The reaction mixture was filtered on Celite to
separate the AgCl precipitate. The solvent of the orange solution was
reduced to a small volume, and 3 mL of n-hexane was added; afterward
1 was precipitated as a light orange solid. Yield: 93%. The NMR spectral
27
coordination of the second metal complex. Among these linker
ligands, 1,1-bis(diphenylphosphino)methane (dppm) is a
suitable candidate for the coordination of various metals to
51
data agree with those reported in the literature.
[
{Cp*Rh(ppy)(μ-dppm)PtMe(Obpy)}PF ] (3a). Under an Ar atmos-
6
phere, 1 (58 mg, 0.1 mmol) and 2a (77 mg, 0.1 mmol) were dissolved in
28
form homo- and heterobimetallic complexes. This ligand has a
short chain between its two phosphine moieties which can hold
the metal centers close to each other. Sometimes this proximity
leads to metal−metal bond formation. Also, we have widely
engaged the dppm ligand as a bridging ligand for the formation
of homo- and hetero-organoplatinum complexes with different
CH Cl (10 mL) to give an orange solution that was stirred at room
2
2
temperature for 2 h. The solvent was reduced to a small volume, and 3
mL of n-pentane was added; afterward 3a was precipitated as an orange
solid. Yield: 86%. Anal. Calcd for C H F N OP PtRh (MW =
5
7
55
6
3
3
1302.96): C, 52.54; H, 4.25; N, 3.22. Found: C, 52.19; H, 4.34; N, 3.46.
+
HR ESI-MS(+): m/z calcd for C H NP Rh [4 − PF ] 776.2; found
46 45
2
6
1
2
3
2
9−33
7
76.2. NMR in CD CN: δ ( H, 400 MHz) 0.94 (d, J = 77.8 Hz, J
applications.
3 PtH PH
3
=
7.0 Hz, 3H, PtMe), 1.62 (s, 15H, MeCp*), 3.67 (t, J = 26.1 Hz,
PtH
3
Tandem catalysis refers to the combination of two steps in
one, which makes the process shorter and saves energy, as the
2
JPH = 10.6 Hz, 2H, CH of dppm), 6.84 (t, J = 5.9 Hz, 1H), 7.20 (t,
2
HH
3
34
JHH = 7.5 Hz, 1H), 7.23−7.45 (m, 17 H), 7.48−7.54 (m, 4H), 7.56−
interim purification is avoided. Additionally, the usage of one-
3
7
.66 (m, 4H), 7.75−7.86 (m, 2H), 7.94−8.03 (m, 3H), 8.09 (d, J
=
=
PtH
pot multistep reactions has been reported as an important and
3
3
3
3
5,36
21.7 Hz, J = 6.1 Hz, 1H), 8.76 (d, J = 5.6 Hz, 1H), 9.90 (d, J
HH HH HH
1 1 2
effective pathway for the construction of C−N
and C−C
3
1
1
1
2
2
0,37
38,39
38,40
8.1 Hz, 1H); δ ( P{ H}, 162 MHz) 25.0 (d, JPtP = 2209 Hz, JP P = 96
bonds
or activation of C−F,
and C−H bonds
organic synthesis. Heterobimetallic compounds can be an
option for tandem catalytic processes. In this regard, several
in
1
1
3
2
2
2
1
2
Hz, P ), 0.3 and −3.6 (dd, J
≈ 46 Hz, J ≈ 312 Hz, J = 96 Hz,
RhP
PtP
P P
2
1
195 1
3
P ), −144.6 (septet, J = 707 Hz, PF ); δ ( Pt{ H}, 85 MHz)
5
P F
6
1
1
1
2
−
3986.2 (dt, J = 2212 Hz, J = 314 Hz).
PtP PtP
III
II 35,37,41
III
II 37,41
II
catalytic systems such as Ir −Pd ,
Rh −Pd ,
Ru −
[
{Cp*Rh(ppy)(μ-dppm)Pt(p-MeC H )(ppy)}PF ] (3b). This com-
6 4 6
II 13,41 III
I
42
III
I
42
II
I
43,44
Pd ,
Ir −Au , Rh −Au , Pd −Au ,
etc. have been
pound was made similarly to 3a using 2b. Yield: 74%. Anal. Calcd for
described and their catalytic activities investigated in various
tandem transformations (Chart 1).
We have synthesized and characterized new Rh −Pt and
Rh −Pd complexes supported by a dppm bridging ligand. The
Rh −Pd complex showed good catalytic activity in three
tandem reactions: (i) transfer hydrogenation (TH) and
dehalogenation (DH), (ii) TH and Suzuki−Miyaura coupling,
and (iii) nitro reduction and imine preparation. Interestingly, in
our tandem reactions ethanol (having abundance, sustainability,
and a safe nature) was used as a powerful and efficient hydrogen
C H F N P PtRh (MW = 1362.07): C, 56.44; H, 4.44; N, 2.06.
6
4
60
6
2 3
Found: C, 56.71; H, 4.47; N, 2.24. HR ESI-MS(+): m/z calcd for
III
II
+
1
C
4
H
45NP
Rh [4 − PF
] 776.2; found 776.2. NMR in CD CN: δ ( H,
46
2
6
3
III
II
00 MHz) 1.62 (s, 15H, MeCp*), 1.99 (s, 3H, Me of p-MeC H ), 2.94
6
4
3
2
3
III
II
(t, J = 21.8 Hz, J = 9.8 Hz, 2H, CH of dppm), 6.27 (d, J = 7.7
PtH PH 2 HH
3
4
Hz, 2H), 6.78 (td, J = 7.1, J = 1.7 Hz, 1H) 7.16−7.27 (m, 18H),
HH
HH
3
4
7
.31−7.38 (m, 5H), 7.40 (td, J = 7.3, J = 2.1 Hz, 1H), 7.55−7.68
HH
HH
3
(
m, 4H), 7.71−7.85 (m, 4H), 7.95−8.00 (m, 3H), 8.12 (d, J = 19.2,
PtH
3
3 31 1
J
HH
= 5.5 Hz, 1H), 8.76 (d, J = 5.6 Hz, 1H); δ ( P{ H}, 162 MHz)
HH
1
1
2
1
1
1
2
2
2
≈
3.9 (d, J = 1896 Hz, J = 93 Hz, P ), − 2.2 and −6.1 (dd, J
PtP
P P
RhP
3
2
2
1
2
1
2
3
39 Hz, J ≈ 291 Hz, J = 93 Hz, P ), − 144.6 (septet, J = 707
i
PtP
P P
P F
source for the tandem reactions. Although formic acid or PrOH
195
1
1
1
1
2
Hz, PF ); δ ( Pt{ H}, 85 MHz) −3831.2 (dt, J = 1892 Hz, J
=
6
PtP
PtP
3
7,41
have been mainly used for TH reactions,
been applied for tandem processes.
ethanol has rarely
This difficulty can be
attributed to the fact that EtOH causes catalyst deactivation.
294 Hz).
4
5−48
[{Cp*Rh(ppy)(μ-dppm)Pd(TSC)}PF ] (3c). This compound was
6
46,47
made similarly to 3a using 2c. Yield: 81%. Anal. Calcd for
C H ClF N P PdRhS (MW = 1267.82): C, 53.05; H, 4.37; N,
5
6
55
6
4 3
4
.42; S, 2.53. Found: C, 53.21; H, 4.31; N, 4.57; S, 2.62. HR ESI-
EXPERIMENTAL SECTION
General Information. All chemicals were purchased from Sigma-
Aldrich or Merck and were used without any further purification. NMR
■
+
MS(+): m/z calcd for C H NP Rh [4 − PF ] 776.2; found 776.2.
NMR in CDCl : δ ( H, 400 MHz) 1.74 (s, 15H, MeCp*), 2.73 (s, 3H,
4
6
45
2
6
1
3
3
2
MeCN), 2.94 (d, J = 4.9 Hz, 3H, NHMe), 4.15 (t, J = 9.2 Hz,
HH
PH
spectra were recorded on a Bruker Avance DPX 400 MHz spectrometer
3
2
6
1
H, CH of dppm), 3.98 (br, 1H, NHMe), 6.73 (t, J = 7.6 Hz, 1H),
2 HH
.80 (t, J = 7.7 Hz, 1H), 7.11−7.20 (m, 15H), 7.38 (d, J = 7.5 Hz,
H), 7.43−7.51 (m, 8H), 7.63 (d, J = 8.0 Hz, 1H), 7.76−7.84 (m,
1
at room temperature; frequencies are referenced to Me Si ( H and
3
3
4
13
1
31
1
195
1
HH
HH
C{ H}), 85% H PO ( P{ H}), and Na PtCl ( Pt{ H}). The
3
3
4
2
6
HH
chemical shifts and coupling constants are given in ppm and Hz,
respectively. Microanalyses were done using a Thermo Finnigan Flash
EA-1112 CHNSO rapid elemental analyzer. Mass data were obtained
by a time-of-flight mass spectrometer equipped with an electrospray ion
source (Bruker micrOTOF II). UV−vis absorption spectra were
recorded on a PerkinElmer Lambda 25 spectrophotometer using a
cuvette with 1.00 cm path length. Powder X-ray diffraction (PXRD)
spectra were recorded on a Bruker AXS D8-Advance X-ray
diffractometer with Cu Kα radiation (λ = 1.5418 Å). All yields refer
to the isolated products. The known precursor complexes [{Ag-
3
31
1
3
H), 8.69 (d, J = 5.2 Hz, 1H); δ ( P{ H}, 162 MHz) 30.7 (dd,
HH
1
2
1
3
2
1
1
2
2
1
2
JRhP = 151 Hz, J = 28 Hz, P ), 22.0 (dd, J
= 4 Hz with J
=
P P
RhP
P P
2
1
3
2
8 Hz, P ), − 144.1 (septet, J = 711 Hz, PF6).
{Cp*Rh(ppy)(μ-dppm)}PF ] (4). Under an Ar atmosphere, 1 (58
P F
[
6
mg, 0.1 mmol) and the dppm ligand (39 mg, 0.1 mmol), in a 1:1 molar
ratio, were dissolved in CH Cl (10 mL) to give a dark orange solution
that was stirred at room temperature for 1 h. The solvent was reduced to
a small volume, and 3 mL of n-pentane was added; afterward 4 was
precipitated as an orange solid. Yield: 94%. Anal. Calcd for
C H F NP Rh (MW = 921.67): C, 59.94; H, 4.92; N, 1.52. Found:
2
2
4
9
50
(
CH CN) }PF ], [Cp*Rh(ppy)Cl] (Cp* = pentamethylcyclopen-
46 45
6
3
3
4
6
C, 59.83; H, 4.93; N, 1.61. HR ESI-MS(+): m/z calcd for
tadienyl; ppy = 2-phenylpyridnate), [Cp*{Rh(ppy)(CH CN)}PF ]
3
6
+
51
1
52
C H NP Rh [4 − PF ] 776.2; found 776.2. NMR in CDCl : δ
(
1), [PtMe(Obpy)(κ -dppm)] (2a; Obpy = 2,2′-bipyridine N-
46 45
2
6
3
1
1
1
31
1
( H, 400 MHz) 1.43 (s, 15H, MeCp*), 2.08 ppm (dd, J = 14.6 Hz,
oxide), [Pt(p-MeC H )(ppy)(κ -dppm)] (2b), and [Pd(TSC)(κ -
HH
6
4
53
2
1
2
JPH = 8.6 Hz, 1H, CH of dppm), 2.27 (dd, J = 14.6 Hz, J = 10.2
dppm)] (2c; TSC = 2-chlorophenyl thiosemicarbazone) were
prepared by literature methods.
2
HH
PH
3
3
Hz, 1H, CH
of dppm), 6.69 (t, JHH = 7.6 Hz, 1H), 6.77 (t, JHH = 7.7
2
3
3
Synthesis of Complexes. [{Cp*Rh(ppy)(CH CN)}PF ] (1). This
complex was prepared by a modified procedure. Under dark
conditions and an Ar atmosphere, [{Ag(CH CN) }PF ] (97 mg,
Hz, 1H), 7.04 (t, JHH = 7.8 Hz, 1H), 7.09−7.20 (m, 20H), 7.39 (d, JHH
= 7.7 Hz, 1H), 7.47 (d, J = 7.8 Hz, 1H), 7.64 (d, J = 8.0 Hz, 1H),
HH HH
7.79 (t, J = 7.7 Hz, 1H), 8.69 (d, J = 5.4 Hz, 1H); δ ( P{ H},
3
6
5
1
3
3
3
3
31
1
3
4
6
HH HH
B
Organometallics XXXX, XXX, XXX−XXX
Mandegani, Zeinab
