Synthesis, electrochemistry, and reactivity of new iridium(III) and rhodium(III) hydrides

Article abstract of DOI:10.1021/om300398r

Two new iridium hydride complexes, Cp*Ir(2-phenylpyridine)H (Cp* = pentamethylcyclopentadienyl) and Cp*Ir(benzo[h]quinoline)H, and their rhodium analogues Cp*Rh(2-phenylpyridine)H and Cp*Rh(benzo[h]quinoline)H have been prepared from the corresponding chl

Full text of DOI:10.1021/om300398r

Article
pubs.acs.org/Organometallics
Synthesis, Electrochemistry, and Reactivity of New Iridium(III) and
Rhodium(III) Hydrides
§
§,†
‡
Yue Hu, Ling Li, Anthony P. Shaw, Jack R. Norton,* Wesley Sattler, and Yi Rong
Department of Chemistry, Columbia University, New York, New York 10027, United States
*
S Supporting Information
ABSTRACT: Two new iridium hydride complexes, Cp*Ir(2-
phenylpyridine)H (Cp* = pentamethylcyclopentadienyl) and Cp*Ir-
(
benzo[h]quinoline)H, and their rhodium analogues Cp*Rh(2-phenyl-
pyridine)H and Cp*Rh(benzo[h]quinoline)H have been prepared from
the corresponding chlorides. The X-ray structures of Cp*Ir(2-phenyl-
pyridine)H and Cp*Rh(2-phenylpyridine)H have been determined. The
electrochemistry of all four hydride complexes and the corresponding
chlorides has been studied by cyclic voltammetry; all exhibit irreversible
M(III/IV) (M = Ir, Rh) oxidations. The hydride complexes are more easily oxidized than their chloride analogues, and the
rhodium hydrides are more easily oxidized than their iridium analogues. The hydride complexes transfer H− to the N-
carbophenoxypyridinium cation at room temperature, giving mixtures of the 1,2- and 1,4-dihydropyridine products. In CD CN
3
all four hydrides give these products in nearly the same ratio, which results from kinetic control; the thermodynamic ratio of the
products has been calculated, and isomerization in that direction has been observed. In weakly coordinating solvents the cations
−
left after H transfer catalyze this isomerization. Acetonitrile can trap these cations, slowing isomerization substantially. The X-ray
structures of [Cp*Ir(2-phenylpyridine)(CH CN)][PF ] and [Cp*Rh(2-phenylpyridine)(CH CN)][PF ] have also been
3
6
3
6
determined.
the 1,2 product, and (b) a two-step (sequential e− and H•
transfer) process, giving only the 1,4 product.
INTRODUCTION
Ruthenium hydride complexes have been extensively used to
■
7
catalyze “ionic hydrogenations”, in which H is transferred to
2
+
−
1−5
2
the substrate as H and H . The fact that the Shvo hydride
transfers H to CN and CO by an ionic mechanism has
2
3
4
̈
been established in detail by the Casey and Backvall groups.
The Noyori catalyst for the asymmetric hydrogenation of
Relatively few hydrides of the isoelectronic Rh(III) and
Ir(III) have been isolated and characterized, although other
ketonesalthough its resting state is not a hydrideoperates
8
6
by a similar mechanism. The half-sandwich ruthenium hydride
complexes of these metals have been used to catalyze the
complexes 1−4 have been used by the Norton group to effect
9
hydrogenation of alkenes and imines. Pincer hydride
the ionic hydrogenation of iminium cations, aziridinium cations,
5
complexes of Ir(III) have attracted recent interest because of
and the N-acyl pyridinium cation 5 (eq 1). With 5 the ratio of
10
their ability to reduce CO to formate complexes and to serve
2
the 1,2- to the 1,4-dihydropyridine product varied as the
catalyst was changed from 1 to 2, 3, or 4, which led these
authors to suggest competition between two different
as electrocatalysts for the reduction of CO to formate/formic
2
11
acid.
We set out to prepare half-sandwich rhodium(III) and
−
mechanisms: (a) a single-step H transfer, giving principally
iridium(III) hydrides with simpler C−N chelating ligands, i.e.,
2
-phenylpyridine, a, and benzo[h]quinoline, b, from the known
12
chloride complexes (chloride complexes of such ligands have
13
14
also been prepared with Pt and Au ). The planarity of these
ligands should facilitate electron transfer.
We now report the new Ir and Rh hydride complexes
Cp*M(C−N)H (7a, 7b, 7′a, 7′b). We have examined them,
and their chloride precursors, by cyclic voltammetry. We have
investigated the transfer of H− from 7 and 7′ to the N-
carbophenoxypyridinium cation 5 in different solvents. We have
Received: May 10, 2012
©
XXXX American Chemical Society
A
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Article
determined the structures of 7a, 7′a, and the corresponding
acetonitrile complexes [Cp*Ir(2-phenylpyridine)(CH CN)]-
3
[
PF ] (9) and [Cp*Rh(2-phenylpyridine)(CH CN)][PF ]
6
3
6
(9′) by single-crystal X-ray diffraction.
RESULTS
■
Synthesis and Characteristics of the Hydride Com-
plexes. The chloride complexes 8 and 8′ were prepared from
Cp*MCl ] (M = Ir, Rh) and the imine ligands, in the
[
2
2
presence of NaOAc, by a method that has been previously
1
5
reported. Treating 8a,b and 8′a,b with the appropriate group-
3 hydrides (Scheme 1) gave the hydride complexes 7a,b and
1
Figure 1. Molecular structure of 7a. Hydrogen atoms other than the
hydride ligand have been omitted for clarity. Selected bond distances
(
7
Å) and angles (deg): Ir(1)−H(1) 1.53(4), N(32)−Ir(1)−C(21)
Scheme 1
7.93(13).
7
′a,b. Long reaction times (2−3 days) and high temperatures
(
60−70 °C) were required if the iridium chlorides 8a and 8b
were treated with NaBH in THF, and partial decomposition of
4
the chlorides resulted. However, the use of Red-Al (sodium
bis(2-methoxyethoxy)aluminum hydride), which has good
solubility in THF, gave the hydrides cleanly at 50 °C in 4−6
h. The opposite results were obtained with the rhodium
chlorides 8′a and 8′b: the use of Red-Al under the same
Figure 2. Molecular structure of 7′a. Hydrogen atoms other than the
hydride ligand have been omitted for clarity. Selected bond distances
(
7
Å) and angles (deg): Rh(1)−H(1) 1.51(3), N(21)−Rh(1)−C(32)
9.20(8).
conditions failed, whereas NaBH at 65 °C in THF gave
4
complete conversion to the rhodium hydrides 7′a and 7′b after
coordinated C and N atoms of 2-phenylpyridine was observed
in both 7a and 7′a. The two structures show similar M−H bond
lengths: 1.53(4) Å in the iridium hydride 7a and 1.51(3) Å in
the rhodium hydride 7′a. Structural parameters are listed in
Table 1.
2
days.
The iridium complex 7a is bright yellow, with a hydride
singlet at δ = −15.21; the iridium complex 7b is orange, with a
hydride singlet at δ = −14.98; the rhodium hydride 7′a is
1
yellow-brown, with a hydride doublet at δ = −12.64 ( J
=
Electrochemistry. We chose tetrahydrofuran as the solvent
for our CV studies because of reactivity concerns. The rhodium
hydrides 7′a and 7′b react gradually with CH Cl to give the
H−Rh
3
1.6 Hz); the rhodium hydride 7′b is dark brown, with a
1
hydride doublet at δ = −12.33 ( J
complexes are air sensitive in solution, their crystals are stable
= 29.2 Hz). While these
H−Rh
2
2
16,17
corresponding chlorides, presumably via a radical pathway.
in air for several hours.
CH CN, while generally a good solvent for organometallic
3
X-ray Structures. Crystals of the hydride complexes were
obtained by vapor diffusion of pentane into saturated THF
solutions. The structures of 7a and 7′a were determined by
single-crystal X-ray diffraction (Figures 1 and 2). In both cases
the hydride ligand was located. Disorder between the
electrochemistry, reacts with the radical cations of many
18
hydride complexes, including those from 7 and 7′.
The electrochemical peak potentials of the hydrides 7 and 7′,
the chlorides 8 and 8′, and the N-carbophenoxypyridinium salt
5 in THF are listed in Table 2. All of the anodic oxidations are
B
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Table 1. Crystal, Intensity Collection, and Refinement Data
for 7a and 7′a
of the substrate, suggesting that there is no driving force for
electron transfer.
The iridium chlorides 8a,b appear to be more easily oxidized
7
a
7′a
than the rhodium chlorides 8′a,b. The E values of the iridium
pa
lattice
monoclinic
C H IrN
monoclinic
hydrides 7 are 0.4 V more negative than those of the
corresponding chlorides 8; the difference between the rhodium
hydrides 7′ and the corresponding chlorides is even larger,
around 0.8 V. We have reported similar differences between the
formula
fw
C H NRh
21 24
2
1
24
482.61
393.22
space group
a, Å
P2 /n
P2 /n
1
1
20
13.3885(11)
7.5832(6)
17.8084(14)
90
13.3812(11)
7.5998(7)
17.7777(15)
90
potentials of Ru hydrides and chlorides. These results reflect
b, Å
the fact that hydride ligands are generally better donors than
c, Å
21
chloride ligands.
α, deg
β, deg
Reactivity of the Hydrides with an N-Acyl Pyridinium
Cation. When we treated the N-carbophenoxypyridinium
cation 5 with the new hydride complexes 7 and 7′, we expected
111.5130(10)
90
111.5040(10)
90
γ, deg
V, Å3
1682.1(2)
4
1682.0(3)
4
(
given the E values of 7 and 7′) mixtures of the 1,2- and 1,4-
pa
Z
dihydropyridine products 6a and 6b. This prediction proved
temperature, K
radiation (λ, Å)
150(2)
0.71073
1.906
150(2)
0.71073
1.553
correct. In CD CN (eq 2) the reactions were complete within
3
−
3
ρ (calcd), g cm
−
1
μ (Mo Kα), mm
θmax, deg
7.937
1.014
32.77
32.74
no. of data collected
no. of data
28 339
5921
28 524
5939
no. of params
R1 [I > 2σ(I)]
218
218
0.0308
0.0555
0.0493
0.0612
1.021
0.0340
0.0716
0.0529
0.0782
1.042
wR [I > 2σ(I)]
2
Table 3. Product Ratios from the Reaction of 5 with
R1 [all data]
a
Different Hydride Complexes in CD CN
wR [all data]
2
3
GOF
b
product ratio (6a:6b)
1
0 min
9 h
24 h
Table 2. Peak Potentials as Determined by Cyclic
Voltammetry of the Hydride and the Chloride Complexes
a
7a
40:60
37:63
44:56
37:63
40:60
37:63
40:60
34:66
38:62
34:66
37:63
33:67
7
b
compound
potential (V)
parameter
process
7′a
7′b
b
c
7
7
7
7
8
8
8
8
5
a
−0.09
−0.06
−0.38
−0.39
+0.35
+0.34
+0.45
+0.47
−0.98
Epa
oxidation
oxidation
oxidation
oxidation
oxidation
oxidation
oxidation
oxidation
reduction
b
a
b
′a
′b
a
Epa
Conditions: 0.01 mmol of 5, 0.01 mmol of hydride complex, 700 μL
of CD CN, room temperature. Product ratio determined by H NMR
b
b
1
Epa
3
b
c
Epa
integration. 12 h.
b
Epa
b
b
′a
′b
Epa
10 min, giving only 6a and 6b in the ratios shown in Table 3.
The product ratios remained nearly constant over time. The
product ratios from the iridium hydride complexes 7a and 7b
proved similar to those from the rhodium hydrides 7′a and 7′b,
b
Epa
b
Epa
c
Epc
a
even though the E values of 7 differ from those of 7′ by 0.3 V.
From 1 mM THF solutions, containing 0.1 M [Bu N]PF as the
pa
4
6
b
Apparently the mechanism of hydride transfer is not merely a
function of the redox potential of the hydride complex.
From the related reactions with Ru hydrides we presumed
supporting electrolyte, at a scan rate of 100 mV/s. E , anodic peak
potentials, versus FcH /FcH. E , cathodic peak potentials, versus
FcH /FcH.
pa
+
c
pc
+
7
that the organometallic products of eq 2 were acetonitrile
complexes. We prepared the expected complexes independently
by heating CH CN solutions of the chlorides with NaPF (eq
irreversible, which is expected since hydride cation radicals are
3
6
18,19
quite acidic and undergo rapid deprotonation.
However,
3). The complex [Cp*Ir(2-phenylpyridine)(CH CN)][PF ]
3 6
the compounds have similar structures and have been studied
under the same conditions, so the kinetic potential shifts should
be similar and the Epa values should enable us to make
approximate comparisons. The nature of the C−N ligand does
not have much influence on the electrochemical properties of
the hydride complexes. The E of the iridium hydride 7a, with
pa
a 2-phenylpyridine ligand, is only 0.03 V less than that of its
benzo[h]quinoline analogue 7b, and the difference is even
smaller between the rhodium hydrides 7′a and 7′b. The
rhodium hydrides 7′a and 7′b are more easily oxidized (their Epa
values are around 0.3 V more negative) than their iridium
analogues 7a and 7b. However, all of the hydride complexes
(9) was crystallized by vapor diffusion of pentane into a
saturated THF solution, while the complex [Cp*Rh(2-
phenylpyridine)(CH CN)][PF ] (9′) was crystallized by
3
6
vapor diffusion of diethyl ether into a saturated acetonitrile
have E values that are substantially less negative than the Epc
solution. While other CH CN complexes of Ir and Rh had been
pa
3
C
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Article
2
2
reported, our complexes 9 and 9′ were previously unknown,
Table 4. Product Ratios from the Stoichiometric Reduction
of 5 with Hydride 7′a in Different Solvents
a
so we determined their X-ray structures (Figures 3 and 4).
b
product ratio (6a:6b)
solvent
10 min
9 h
24 h
CD CN
44:56
25:75
24:76
40:60
10:90
13:87
37:63
<5:95
10:90
3
THF-d8
C D
6
6
a
Conditions: 0.01 mmol of 5, 0.01 mmol of 7′a, 700 μL of solvent,
b
1
room temperature. Product ratio determined by H NMR integration.
Scheme 2
+
demonstrating the ability of “[Cp*M(C−N)] ” to catalyze the
6
a → 6b isomerization.
Both the literature and other experiments are consistent with
Figure 3. Molecular structure of 9. The counteranion and the
hydrogens have been omitted for clarity. Selected bond distances (Å)
and angles (deg): Ir(1)−N(1) 2.068(4), C(11)−Ir(1)−N(2)
the implication that the 1,4-dihydropyridine 6b is more stable
23
than its 1,2 isomer 6a. Fowler measured in 1972 a positive
ΔG, 2.3 kcal/mol, for the equilibrium (established by base in
DMSO at 91.6 °C) between the N-methyl dihydropyridines
8
6.85(12).
24
1
0a and 10b in eq 4. Eisner and Sadeghi reported catalysis by
Disorder between the coordinated C and N atoms of 2-
phenylpyridine was observed in both 9 and 9′. The structural
parameters of 9 and 9′ are given in the Supporting Information.
some rhodium complexes of the isomerization of the 1,2-
25
dihydropyridine 11a to its 1,4 analogue 11b (eq 5). We have
treated the 1,2-dihydropyridine 6a with Rh(PPh ) (CO)H in
3
3
THF-d at room temperature and obtained a 6a:6b ratio of
8
26
1
3:87 after three weeks (eq 6). Calculations using Spartan′10
imply that the gas-phase equilibrium ratio of 6a to 6b is 7:93 at
room temperature.
Figure 4. Molecular structure of 9′. The counteranion and the
hydrogens have been omitted for clarity. Selected bond distances (Å)
and angles (deg): Rh(1)−N(1) 2.064(2), C(11)−Rh(1)−N(2)
7
8.51(8).
In the absence of CH CN the Ir or Rh complex remaining
3
after hydride transfer catalyzed the isomerization of the 1,2-
dihydropyridine 6a to the 1,4-dihydropyridine 6b. The effect
was most obvious with Rh hydride 7′a: in THF-d or C D the
Even 4 equiv of CH
stop) the isomerization of 6a → 6b during a hydride transfer
experiment in THF-d , CD Cl , or C (Table 5). It is clear
that the product ratios in CD CN (Table 3) are the result of
kinetic control. It is also clear that under other conditions (no
CH CN, Table 4, or a small amount of CH CN, Table 5) the
3
CN proved enough to slow (but not
D
6 6
8
2
2
8
6
6
6
a:6b ratio was 1:3 after 10 min, but decreased substantially
3
over 24 h (Table 4). The hydride peak of 7′a disappeared
completely within 10 min, so isomerization was slower than
hydride transfer. Isomerization was also observed when excess
3
3
product ratios reflect the slow isomerization of 6a → 6b.
1
,2-dihydropyridine 6a (about 3 equiv) was added24 h after
DISCUSSION
hydride transfer was completeto an NMR tube in which 5
■
had been treated with 7′a in THF-d (the experiment is
Table 3 shows that the kinetic product ratios from these
hydride transfer reactions are not much affected by the nature
of the C−N ligand (2-phenylpyridine, a, or benzo[h]quinoline,
8
summarized in Scheme 2). After 24 h at room temperature the
6
a:6b ratio in the tube decreased from 77:23 to 62:38, again
D
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+
0.24 V with respect to our reference electrode. All samples were
Table 5. Product Ratios from the Stoichiometric Reduction
prepared under an N /Ar atmosphere and further purged with N
before measurement. Analyte concentrations were 0.001 M. The scan
rate was 100 mV/s. All potentials are reported in volts (V) vs FcH /
FcH.
of 5 with Hydrides 7 and 7′ in the Presence of 4 equiv of
2
2
a
CH CN in Different Solvents
3
+
b
product ratio (6a:6b)
Cp*Ir(2-phenylpyridine)H (7a). Under a nitrogen atmosphere,
complex
solvent
10 min
9 h
24 h
1
10 μL of Red-Al (3.5 M toluene solution, 0.39 mmol) was added
7a
THF-d8
21:79
19:81
20:80
27:73
20:80
25:75
40:60
43:57
28:72
35:65
16:84
18:82
15:85
19:81
17:83
24:76
19:81
39:61
16:84
28:72
15:85
17:83
14:86
15:85
15:85
20:80
13:87
35:65
11:89
24:76
dropwise to a suspension of 200 mg of Cp*Ir(2-phenylpyridine)Cl
(8a) (0.39 mmol) in 40 mL of THF. Heating the resulting mixture at
50 °C for 5 h gave a bright yellow solution and a white precipitate,
which was removed by filtration after the mixture was cooled to room
temperature. The solvent was removed under vacuum, and the yellow
solid was washed with n-hexane three times, then dried under vacuum
to give the bright yellow powder 7a (121 mg, 64% yield). IR (KBr):
CD Cl
2
2
C D
6
6
7
b
′a
THF-d8
CD Cl
2
2
C D
6
6
c
7
7
THF-d8
−1
1
2
053 cm (Ir−H). H NMR (400 MHz, THF-d ): δ −15.21 (s, 1H,
C D
6
8
6
c
IrH), 1.89 (s, 15H, Cp*), 6.85 (dd, J = 7.2, 5.6 Hz, 2H), 6.92 (t, J =
.2 Hz, 1H), 7.52 (t, J = 7.8 Hz, 1H), 7.64 (d, J = 7.6 Hz, 1H), 7.71 (d,
J = 7.6 Hz, 1H), 7.81 (d, J = 8.4 Hz, 1H), 8.77 (d, J = 5.6 Hz, 1H).
′b
THF-d8
7
C D
6
6
a
Conditions: 0.01 mmol of 5, 0.01 mmol of hydride complex, 0.04
mmol of CH CN, 700 μL of solvent, room temperature. Product
13
1
C{ H} NMR (100 MHz, THF-d ): δ 9.67 (Cp*), 89.72 (Cp*),
8
b
3
118.53, 119.34, 120.79, 124.25, 129.11, 134.49, 136.14, 143.97, 152.77
1
c
ratio determined by H NMR integration. The hydride complexes 7′a
and 7′b are converted back to the corresponding chloride complexes in
CD Cl
+
(
HCN), 163.71, 168.61 (Ir−C). The LRMS (FAB ) showed peaks
191
+
193
+
for Ir (m/e = 480.2, [M − 1] ) and Ir (m/e = 482.2, [M − 1] )
191
2
2.
with the appropriate isotopic distribution; calculated Ir (m/e =
80.14, [M − 1] ) and Ir (m/e = 482.15, [M − 1] ).
Cp*Ir(benzo[h]quinoline)H (7b). The synthesis was analogous to
+
193
+
4
b), a result that is consistent with the “outer-sphere”
mechanism proposed previously: hydride transfer to an
uncoordinated substrate. Table 3 also shows little difference in
kinetic product ratio between the iridium hydrides 7 and the
rhodium hydrides 7′. Although the potentials of 7 and 7′ differ
significantly in Table 2, all of the hydride complexes have Epa
values that are substantially less negative than the Epc of the
substrate, implying that there is little driving force for electron
transfer. The e /H mechanism may not be important for
either the Ir hydrides 7 or the Rh hydrides 7′.
Finally, the left-hand column of Table 5 shows that the
kinetic product ratios are little affected by the nature of the
solvent. The isomerization of 6a to 6b must be catalyzed by
coordinatively unsaturated species in equilibrium with acetoni-
that of 7a, using Red-Al (3.5 M toluene solution, 106 μL, 0.37 mmol)
and Cp*Ir(benzo[h]quinoline)Cl (8b) (200 mg, 0.37 mmol) in 60
mL of THF at 50 °C for 5 h. The hydride complex 7b was isolated as
−
1
1
an orange solid (143 mg, 76% yield). IR (KBr): 2043 cm (Ir−H). H
NMR (400 MHz, THF-d ): δ −14.98 (s, 1H, IrH), 1.94 (s, 15H,
Cp*), 7.27 (br, 1H), 7.38 (br, 2H), 7.49 (d, J = 7.6 Hz, 1H), 7.71 (d, J
= 7.6 Hz, 1H), 7.92 (br, 1H), 8.03 (d, J = 5.6 Hz, 1H), 9.02 (br, 1H).
8
13
1
C{ H} NMR (100 MHz, THF-d ): δ 10.04 (Cp*), 89.83 (Cp*),
8
−
•
117.62, 120.73, 123.63, 127.23, 129.43, 130.17, 132.95, 133.67, 135.04,
+
1
42.36, 151.09 (HCN), 159.15, 161.08 (Ir−C). The LRMS (FAB )
1
91
+
193
showed peaks for Ir (m/e = 504.2, [M − 1] ) and Ir (m/e =
+
5
06.2, [M − 1] ) with the appropriate isotopic distribution; calculated
+ 193 +
191
Ir (m/e = 504.14, [M − 1] ) and Ir (m/e = 506.15, [M − 1] ).
Cp*Rh(2-phenylpyridine)H (7′a). Under a nitrogen atmosphere,
8
(
0 mL of THF was added to a mixture of Cp*Rh(2-phenylpyridine)Cl
+
trile complexes. ([Cp*Rh(2-phenylpridine)] from 9′ is a
particularly effective catalyst.) Large amounts of acetonitrile
inhibit isomerization by trapping the catalytically active metal
complex cation “[Cp*M(C−N)] ”.
8′a) (400 mg, 0.94 mmol) and NaBH (80 mg, 2.16 mmol), giving a
4
yellow-orange suspension. Heating the mixture at 65 °C for 2 d
resulted in a brownish mixture. The precipitate was removed by
filtration after the mixture was cooled to room temperature. The
volume of the brownish filtrate was reduced to around 3 mL; then
pentane was added to cause precipitation. The solvent was removed by
cannula, and the solid was washed with pentane three times, then dried
under vacuum to give 162.5 mg of the yellow-brown solid 7′a (42%
+
EXPERIMENTAL SECTION
General Procedures. All air-sensitive compounds were prepared
and handled under an N /Ar atmosphere using standard Schlenk and
inert-atmosphere box techniques. CD Cl2 and CD CN were
■
2
−
1
1
yield). IR (KBr): 1935 cm (Rh−H). H NMR (400 MHz, THF-d ):
8
2
3
δ −12.64 (d, J = 31.6 Hz, 1H, RhH), 1.85 (s, 15H, Cp*), 6.88 (t, J =
.2 Hz, 1H), 7.00 (m, 2H), 7.63 (d, J = 7.6 Hz, 2H), 7.68 (d, J = 7.2
Hz, 1H), 7.81 (d, J = 8.4 Hz, 1H), 8.61 (d, J = 5.6 Hz, 1H). C{ H}
deoxygenated and stored over 3 Å molecular sieves. THF-d and
8
7
C D were dried over CaH2 and purified by vacuum transfer. n-
6
6
1
3
1
Hexane, Et O, and CH Cl were deoxygenated and dried by two
successive columns (Q-5, activated alumina). THF and pentane were
distilled from sodium/benzophenone under an N atmosphere. N-
Carbophenoxypyridinium tetraphenylborate (5) was prepared by the
method of King and recrystallized from CH Cl −Et O. Cp*Ir(2-
phenylpyridine)Cl (8a),
2
2
2
NMR (100 MHz, THF-d ): δ 10.03 (s, Cp*), 95.61 (d, J = 17.6 Hz,
8
Cp*), 118.71, 120.62, 120.71, 123.67, 128.38, 135.24, 137.52, 143.24,
2
1
52.45 (HCN), 165.75, 179.54 (d, J = 141.2 Hz, Rh−C). The
27
+
103
+
LRMS (FAB ) showed a peak for Rh (m/e = 392.1, [M − 1] ) with
2
2
2
1
5a
15a
103
the appropriate isotopic distribution; calculated Rh (m/e = 392.09,
Cp*Ir(benzo[h]quinoline)Cl (8b),
15a
+
[
M − 1] ).
Cp*Rh(2-phenylpyridine)Cl (8′a),
Cp*Rh(benzo[h]quinoline)
1
5a
28
Cp*Rh(benzo[h]quinoline)H (7′b). The synthesis was analogous
(
8′b),
Rh(PPh ) (CO)H, and N-carbophenoxy-1,2-dihydropyr-
3 3
29
idine (6a) were prepared by literature methods.
to that of 7′a, using Cp*Rh(benzo[h]quinoline)Cl (8′b) (400 mg, 0.89
Electrochemical Procedures. Cyclic voltammetry was performed
with a BAS CV-50W potentiostat. The supporting electrolyte for all
solutions except the reference electrode was 0.10 M [Bu N]PF in
THF. The cell consisted of a 1.6 mm diameter platinum disk working
electrode, a platinum wire auxiliary electrode, and a silver wire
reference electrode (0.01 M AgNO + 0.10 M [Bu N]PF in CH CN).
mmol) and NaBH
4
(80 mg, 2.16 mmol) in 80 mL of THF at 65 °C for
2 d. The hydride complex 7′b was isolated as a dark brown solid
−
1
1
(252.3 mg, 68% yield). IR (KBr): 1923 cm (Rh−H). H NMR (400
MHz, THF-d ): δ −12.33 (d, J = 29.2 Hz, 1H, RhH), 1.87 (s, 15H,
Cp*), 7.34−7.70 (m, 5H), 7.88 (d, J = 5.2 Hz, 1H), 8.11 (d, J = 7.2
4
6
8
Hz, 1H), 8.86 (br, 1H). 13C{ H} NMR (100 MHz, THF-d
1
): δ 9.85
3
4
6
3
8
The reference electrode was separated from the sample solutions with
(s, Cp*), 95.22 (s, Cp*), 118.62, 120.16, 122.90, 126.74, 128.07,
129.50, 133.53, 133.81, 134.22, 140.04, 150.46 (HCN), 155.52,
a porous Vycor tip (Bioanalytical Systems, MF-2042). Ferrocene
+
+
(
FcH /FcH) was used as an external reference and was found to be
176.51 (d, J = 142.0 Hz, Rh−C). The LRMS (FAB ) showed a peak
E
dx.doi.org/10.1021/om300398r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
for 103Rh (m/e = 416.1, [M − 1] ) with the appropriate isotopic
+
X-ray Structure Determinations. X-ray diffraction data were
collected on a Bruker Apex II diffractometer. Crystal data, data
collection, and refinement parameters are summarized in Table 1 and
in the Supporting Information. The structures were solved using direct
methods and standard difference map techniques and were refined by
103
+
distribution; calculated Rh (m/e = 416.09, [M − 1] ).
[
Cp*Ir(2-phenylpyridine)(CH CN)][PF ] (9). Under a nitrogen
3 6
atmosphere, 30 mL of CH CN was added to a mixture of Cp*Ir(2-
3
phenylpyridine)Cl (8a) (200 mg, 0.39 mmol) and NaPF (100 mg,
.60 mmol), giving an orange solution. The solution was heated at 50
C overnight, a white precipitate formed, and the solution became
6
2
0
°
full-matrix least-squares procedures on F with SHELXTL (version
6.10).
light yellow. The precipitate (NaCl) was removed by filtration after the
mixture was cooled to room temperature. The solvent was pumped off,
leaving a sticky material. n-Hexane was added, and the resulting
mixture was stirred for several hours to give a light orange solid. The
solid was washed with n-hexane three times and then dried under
Computational Methods. Calculations were done with Spar-
tan’10. The structures were minimized using the B3LYP functional in
conjunction with the 6-311++G** basis set. For the N-methylated 1,2
to 1,4 ratio, single-point energy calculations were performed with a
variety of basis sets, and the results compared to those in ref 24.
(
Calculated entropies were negligible.) The best results were obtained
vacuum. Excess NaPF was not removed from the product. IR (KBr):
6
−1
with the triple-ζ (cc-PVTZ) basis set, and this method was used for
single-point calculations on compounds 6a and 6b, which were used to
determine the equilibrium ratio. For computational details see ref 31.
2
345, 2322 cm (NC); two peaks for one coordinated CH CN
3
30
1
were also observed in some Zr complexes. H NMR (400 MHz,
CD Cl ): δ 1.71 (s, 15H, Cp*), 2.31 (s, 3H, CH CN), 7.20 (m, 1H),
2
2
3
7
.30 (m, 2H), 7.77 (m, 2H), 7.93 (m, 2H), 8.73 (d, J = 4.8 Hz, 1H).
+
191
ASSOCIATED CONTENT
The LRMS (FAB ) showed peaks for Ir (m/e = 480.2, [M −
CH CN] ) and
■
+
193
+
Ir (m/e = 482.2, [M − CH CN] ) with the
3
3
*
S
Supporting Information
191
appropriate isotopic distribution; calculated Ir (m/e = 480.14, [M −
1
13
1
Lists of H NMR and C{ H} NMR spectra of 7a,b, 7′a,b, 9,
and 9′, cyclic voltammograms of 7a,b, 7′a,b, 8a,b, 8′a,b, and 5,
and complete details of the crystallographic study (PDF and
CIF). This material is available free of charge via the Internet at
http://pubs.acs.org.
+
193
+
CH CN] ) and Ir (m/e = 482.15, [M − CH CN] ). The analogous
3
3
CD CN complex, 9-d , is prepared by heating 0.01 mmol of 8a and
3
3
0
.02 mmol of NaPF in 700 μL of CD CN at 50 °C. The reaction was
6 3
1
monitored over time by H NMR. After 2 h, the reaction was finished
and the NMR data of the product were recorded. IR (KBr): 2254,
−1
1
2
110 cm (NC). H NMR (400 MHz, CD CN): δ 1.69 (s, 15H,
3
Cp*), 7.18 (t, J = 7.6 Hz, 1H), 7.27 (dd, J = 7.2, 7.6 Hz, 1H), 7.35
AUTHOR INFORMATION
Corresponding Author
E-mail: jrn11@columbia.edu.
■
*
(
ddd, J = 1.2, 6.0, 7.4 Hz, 1H), 7.82 (d, J = 7.6 Hz, 2H), 7.95 (ddd, J =
1
1
.6, 8.0, 8.4 Hz, 1H), 8.04 (d, J = 8.0 Hz, 1H), 8.74 (d, J = 5.6 Hz,
H). 13C{ H} NMR (100 MHz, CD CN): δ 8.73 (Cp*), 92.03
1
3
Present Addresses
Department of Chemistry, City University of New York, New
York, New York 10031, United States.
Pyrotechnics Technology and Prototyping Division, U.S.
Army RDECOM-ARDEC, Bldg 1515, Picatinny Arsenal, New
Jersey 07806, United States.
(
1
Cp*), 120.48, 124.50, 124.66, 125.19, 131.94, 136.65, 140.14, 145.98,
53.26 (HCN), 157.45, 167.92 (Ir−C).
Cp*Rh(2-phenylpyridine)(CH CN)][PF ] (9′). The synthesis was
†
[
3
6
‡
analogous to that of 9, except using Cp*Rh(2-phenylpyridine)Cl (8′a)
(
200 mg, 0.47 mmol) and NaPF (110 mg, 0.66 mmol) in 30 mL of
6
CH CN at 50 °C overnight. The complex 9′ is a light orange solid.
The excess NaPF was not removed from the product. IR (KBr): 2318,
2
observed in some Zr complexes. When the title complex was
dissolved in CD CN, the coordinated CH CN exchanged with solvent
to give the CD CN complex and free CH CN. H NMR (400 MHz,
3
6
−1
Author Contributions
These authors contributed equally to this work.
289 cm (NC); two peaks for one coordinated CH CN were also
3
§
30
3
3
Notes
1
3
3
The authors declare no competing financial interest.
CD CN): δ 1.61 (s, 15H, Cp*), 7.18 (dd, J = 7.2, 7.6 Hz, 1H), 7.30
3
(
dd, J = 7.2, 7.6 Hz, 1H), 7.39 (td, J = 2.4, 6.0 Hz, 1H), 7.76 (d, J = 7.6
ACKNOWLEDGMENTS
■
Hz, 1H), 7.81 (d, J = 7.6 Hz, 1H), 7.97 (m, 2H), 8.77 (d, J = 5.6 Hz,
1
=
1
H). 13C{ H} NMR (100 MHz, CD CN): δ 8.96 (s, Cp*), 98.96 (d, J
1
This research was supported by NSF grant CHE-0749537 and
by Boulder Scientific and OFS Fitel. The National Science
Foundation is thanked for acquisition of an X-ray diffrac-
tometer (CHE-0619638) and a 400 MHz NMR spectrometer
(CHE-0840451). We thank Prof. G. Parkin for assistance with
the X-ray structure determinations, and Jim Yang for
synthesizing compound 5. We thank Deven P. Estes for the
calculations.
3
25.2 Hz, Cp*), 120.54, 124.29, 124.84, 125.00, 131.44, 137.29,
39.86, 145.38, 152.79 (HCN), 165.83, 174.50 (d, J = 119.2 Hz,
+
103
Rh−C). The LRMS (FAB ) showed a peak for Rh (m/e = 392.1,
+
[
M − CH CN] ) with the appropriate isotopic distribution; calculated
3
1
03
+
Rh (m/e = 392.09, [M − CH CN] ).
3
Stoichiometric Hydride Transfer from Metal Hydrides to 5 in
CD CN. The Ir or Rh hydride (0.01 mmol) and 5 (0.01 mmol) were
dissolved in 700 μL of CD CN at room temperature, and the product
ratio was measured by H NMR integration.
3
3
1
REFERENCES
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■
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by H NMR integration. The hydrides are sparingly soluble in C D ,
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F
dx.doi.org/10.1021/om300398r | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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dx.doi.org/10.1021/om300398r | Organometallics XXXX, XXX, XXX−XXX