Organometallics
Article
the possibility of coordination−decoordination of this carbon,
treated with HBMePHI (0.104 g, 0.319 mmol), for 4 h, under reflux.
The resulting dark orange solution was evaporated to dryness. The
residue was treated with diethyl ether (3 × 3 mL, 273 K), to afford an
orange solid, which was dried in vacuo. Yield: 209 mg (86%). Orange
crystals suitable for X-ray diffraction analysis were obtained from slow
diffusion of pentane in a concentrated solution of the solid in toluene.
Anal. Calcd for C H IrN P : C, 54.26; H, 7.19; N, 8.33. Found: C,
as demonstrated by the reactions shown in Scheme 5. Scheme
7
rationalizes the dehydrogenation process through both
metals for the heterobinuclear complex 5. The elemental steps
on the initial iridium center are the same as in the
mononuclear complex 3, whereas according to Scheme 7
alkoxide intermediates E related to A and B should be the key
for the dehydrogenation via the second metal. The β-hydrogen
elimination on the alkoxide group should lead to the hydride F
and the ketone. Thus, a new C−H bond activation of the
position 4 of the isoindoline could close the cycle and release
molecular hydrogen. In addition, it should be pointed out that
the addition of a second metal-hydride fragment to 3 does not
block its relevant nucleophilic centers and therefore the
addition of an external base is not necessary for the bimetallic
catalysis.
3
8
60
5 2
5
4.30; H, 7.22; N, 8.22. HRMS (electrospray, m/z): calcd for
+
1
C H IrN P [M + H] 842.4037, found 842.4028. H NMR (400.13
3
8
61
5 2
3
MHz, CD Cl , 298 K): δ 8.80 (d, J = 7.3, 1 H, CHarom), 8.43 (d,
2
2
H−H
3
3
J
H−H = 7.6, 1 H, CHarom), 7.87 (d, JH−H = 7.3, 1 H, CHarom), 7.55
3
3
(dd, JH−H = 7.6 and 7.6, 1 H, CHarom), 7.53 (dd, JH−H = 7.6 and 7.6,
3
1
H, CHarom), 7.44 (dd, J
= 7.3 and 7.3, 1 H, CHarom), 7.43 (d,
H−H
3
3
JH−H = 7.6, 1 H, CH ), 7.35 (dd, J
= 7.3 and 7.3, 1 H,
H−H
arom
3
3
CHarom), 6.82 (d, J
= 7.6, 1 H, CHarom), 6.78 (d, J
= 7.6, 1 H,
H−H
H−H
CHarom), 2.51 (s, 3 H, py-CH ), 2.39 (s, 3 H, py-CH ), 2.18 (m, 6 H,
3
3
3
PCH(CH ) ), 1.06 (dvt, J
= 6.9, N = 13.0, 18 H, PCH(CH ) ),
3
2
H−H
3 2
3
1
.01 (dvt, J
= 6.9, N = 13.0, 18 H, PCH(CH ) ), −24.22 (td,
H−H
3
2
2
2
2
2
JH−P = 17.3, J
= 8.2, 1 H, Ir−H), −26.35 (td, J
= 16.6, J
H−H
H−P H−H
3
1
1
CONCLUDING REMARKS
=
8.2, 1 H, Ir−H). P{ H} NMR (161.98 MHz, CD Cl , 298 K): δ
■
2
2
13 1
2
1
1
7.2 (s). C{ H} NMR (100.62 MHz, CD Cl , 298 K): δ 171.2,
This study has revealed that the sequential treatment of
HBMePHI with 2 equiv of the pentahydride 1 or with 1 equiv
of the latter and 1 equiv of the hexahydride 2 produces in a
sequential manner the activations of the bonds N−H and C−
H at position 4 of the core isoindoline of the organic molecule,
to give the homobinuclear complex 4 or the heterobinuclear
compound 5, via the mononuclear iridium intermediate 3. The
bonding of the second metal fragment to the intermediate 3
modifies the electronic structure of the polydentate N-donor
ligand, which produces a noticeable perturbation of the
electron density around the initial iridium center. As a
consequence of the mutual electronic influence between the
metals, through the bridge, catalytic synergism between them
in the acceptorless and base-free dehydrogenation of secondary
alcohols is observed. X-ray diffraction analysis data of the
structures of 3−5 and reactivity results on 4 and 5 support a
noninnocent character of the bridging ligand, since its donor
atoms have a direct participation in the formation of the
metal−alkoxide bonds, key for the catalysis, and in the release
of molecular hydrogen.
2 2
69.4, 167.4, 163.7, 157.4, 155.7, 141.7, 140.6 (all s, Carom), 137.9,
36.8, 129.8, 128.7, 123.1, 121.4, 117.4, 117.2, 116.8, 116.1 (all s,
1
CHarom), 27.4 (vt, J
= 26.9, PCH(CH ) ), 24.7, 24.6 (both s, py-
C−P
3 2
CH ), 20.0, 19.7 (both s, PCH(CH ) ).
3
3 2
i
2
-BMePI-κ2-
Preparation of (P Pr ) H Ir{μ-(κ -N ,N
imine
3
2
2
py
4
i
Nimine,C )}IrH (P Pr ) (4). A solution of 3 (0.100 g, 0.119
iso
2
3 2
mmol) in toluene was treated with 1 (0.062 g, 0.119 mmol), for 16
h, under reflux. After this time, the volatiles were removed in vacuo.
Then, pentane (3 × 5 mL, 273 K) was added and the resulting
solution was filtered through Celite. The filtrate was evaporated to
dryness. The residue was treated with cold acetone (3 × 3 mL, 243 K)
to afford a dark red solid, which was dried under vacuum. Yield: 68
mg (42%). Red crystals suitable for X-ray diffraction analysis were
obtained by crystallization from a concentrated solution of the solid in
acetone. Anal. Calcd for C H Ir N P : C, 49.65; H, 7.66; N, 5.17.
5
6
103
2
5 4
Found: C, 49.62; H, 7.67; N, 4.88. HRMS (electrospray, m/z): calcd
+
1
for C H N P Ir [M + H] 1354.6474, found 1354.6510. H NMR
5
6
104
5
4
2
3
(300.13 MHz, C
D
, 298 K): δ 9.14 (d, JH−H = 8.1, 1 H, CHarom),
= 7.1, 1 H, CHarom), 8.31 (d, J
6
6
3
3
8
8
.43 (d, J
.04 (d, J
= 7.1, 1 H, CHarom),
= 7.1 and 7.1, 1 H,
arom H−H
= 7.5, 1 H, CHarom), 6.29
H−H
H−H
H−H
3
3
= 8.1, 1 H, CH ), 7.30 (dd, J
H−H
arom
H−H
3
3
CHarom), 7.25 (dd, J
= 7.5 and 7.5, 1 H, CH ), 7.23 (dd, J
8.1 and 8.1, 1 H, CH ), 6.54 (d, J
H−H
3
=
arom
In summary, an elusive metal-mediated C−H bond
activation of the core isoindoline of a polynitrogenated organic
molecule has been discovered, which generates a noninnocent
bridge ligand, responsible for catalytic synergism between the
bonded metals, in the acceptorless and base-free dehydrogen-
ation of secondary alcohols.
3
(d, J
= 7.5, 1 H, CHarom), 2.51 (s, 3 H, py-CH ), 2.45 (m, 6 H,
H−H 3
PCH(CH ) ), 2.18 (s, 3 H, py-CH ), 2.13 (m, 6 H, PCH(CH ) ),
3
2
3
3
2
3
3
1
.27 (dvt, J
= 6.4, N = 12.5, 18 H, PCH(CH ) ), 1.24 (dvt, J
H−H
3
2
H−H
3
= 6.4, N = 12.5, 18 H, PCH(CH ) ), 1.04 (dvt, J
18 H, PCH(CH ) ), 0.96 (dvt, JH−H = 6.9, N = 13.1, 18 H,
= 6.9, N = 13.1,
3
2
H−H
3
3
2
2
2
PCH(CH
)
), −12.94 (td, JH−P = 19.6, JH−H = 5.9, 1 H, Ir−H),
3
2
2
2
2
−
=
24.33 (td, J
= 17.6, J
= 8.1, 1 H, Ir−H), −25.48 (td, J
H−P
H−H
H−P
2
2
2
17.4, J
= 5.9, 1 H, Ir−H), −25.55 (td, J
= 16.5, J = 8.1,
H−H
H−P
H−H
EXPERIMENTAL SECTION
All reactions were carried out with rigorous exclusion of air using
Schlenk-tube techniques. Solvents were obtained oxygen and water
3
1
1
■
1 H, Ir−H). P{ H} NMR (121.49 MHz, C D , 298 K): δ 32.5 (s),
6
6
13 1
27.0 (s). C{ H} NMR (75.48 MHz, C D , 298 K): δ 185.0, 179.2,
6 6
2
169.9 (all s, Carom), 169.6 (t, J
= 8.0, Ir−C ), 163.6, 160.9, 156.7,
C−P
iso
1
31
1
free from an MBraun solvent purification apparatus. H, P{ H}, and
154.8 (all s, Carom), 144.4, 137.5 (both s, CHarom), 135.9 (s, Carom),
135.5, 127.1, 118.6, 117.8, 117.6, 116.3, 114.1 (all s, CHarom), 27.2
(vt, N = 13.3, PCH(CH ) ), 26.5 (vt, N = 13.1, PCH(CH ) ), 24.5 (s,
13
1
C{ H} NMR spectra were recorded on a Bruker ARX 300 MHz,
Bruker Avance 300 MHz, or Bruker Avance 400 MHz instrument.
Chemical shifts (expressed in parts per million) are referenced to
3
2
3 2
py-CH ), 24.4 (s, py-CH ), 20.8, 20.3, 20.2, 19.7 (all s, PCH(CH ) ).
3
3
3 2
1
1
31
13
1
i
2
2
residual solvent peaks ( H, H{ P}, C{ H}) or an external standard
Preparation of (P Pr ) H Ir{μ-(κ -N ,N
imine,C iso)}OsH
-BMePI-κ -
(5). A solution of 3 (0.200 g, 0.238
3
2
2
py
imine
31
1
4
i
(
P{ H} to 85% H PO ). Coupling constants J and N (N = J
+
N
3
(P Pr
3
)
2
3
4
H−P
1
13
JH−P′ for H; N = J
+ JC−P′ for C) are given in hertz. C, H, and N
mmol) in toluene was treated with 2 (0.122 g, 0.238 mmol), for 4 h,
under reflux. After this time, the volatiles were removed in vacuo.
Then, cold pentane (10 mL, 273 K) was added and the resulting
solution was filtered through Celite. The filtrate was evaporated to
dryness. The residue was treated with cold acetone (3 × 3 mL, 273 K)
to afford a dark purple solid, which was dried under vacuum. Yield:
150 mg (46%). Purple crystals suitable for X-ray diffraction analysis
were obtained from a concentrated solution of the solid in acetone at
−20 °C. Anal. Calcd for C H N P IrOs: C, 49.68; H, 7.74; N, 5.17.
C−P
analyses were carried out with a PerkinElmer 2400 CHNS/O
analyzer. High-resolution electrospray mass spectra (HRMS) were
acquired using a MicroTOF-Q hybrid quadrupole time-of-flight
i
spectrometer (Bruker Daltonics, Bremen, Germany). IrH (P Pr )
5
3
2
25
i
26
(
1), OsH (P Pr ) (2), and 1,3-bis(6′-methylpyridyl-2′-imino)-
6
3 2
27
isoindoline (HBMePHI) were prepared according to the published
methods.
2
i
Preparation of IrH {κ -N ,N
(BMePHI)}(P Pr ) (3). A
2
py imine
3 2
56 104
5 4
solution of 1 (0.150 g, 0.290 mmol) in 2-propanol (5 mL) was
found: C, 49.39; H, 8.08; N, 4.93. HRMS (electrospray, m/z): calcd
I
Organometallics XXXX, XXX, XXX−XXX