Reactivity of Alkyne Insertion and Catalytic Activity of Five- and Six-Membered Cyclometalated Phosphine Complexes of Iridium

Article abstract of DOI:10.1002/ejic.201800412

Reactions of three aryl-substituted phosphines with [Cp*IrCl₂]₂ afforded the corresponding five-membered or six-membered cyclometalated iridium complexes (2 or 5,6) via an intramolecular C(sp²)–H bond activation. Insertion reactions of the five-membered cycloiridated complex 2 with PhC≡CPh and PhC≡CCOPh resulted in the corresponding five-membered and six-membered doubly cycloiridated complexes 7 and 8, the formation of which presumably went through the vinylidene rearrangement of alkynes followed by 1,1-insertion; while the reactions of the six-membered cyclometalated complexes 5, 6 with PhC≡CPh or PhC≡CCOPh gave the corresponding eight-membered cycloiridated complexes 9–12 by 1,2-insertion. The hydrosilylation of imines catalyzed by five- or six-membered P-containing cycloiridated complexes were studied, and the results proved that the six-membered cycloiridated complex 5 can be used as an efficient catalyst, which was applied for the hydrosilylation of various imines, especially aldimines. Molecular structures of complexes 9, 10 and 12 were determined by X-ray diffraction.

Full text of DOI:10.1002/ejic.201800412

A Journal of
Accepted Article
Title: Reactivity of Alkyne-insertion and Catalytic Activity of Five- and
Six-membered Cyclometalated Phosphine Complexes of Iridium
Authors: Tongyu Li, Zhuo Wang, Kai Liu, Siyang Xing, and Bolin Zhu
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201800412
Link to VoR: http://dx.doi.org/10.1002/ejic.201800412

10.1002/ejic.201800412
European Journal of Inorganic Chemistry
FULL PAPER
Reactivity of Alkyne-insertion and Catalytic Activity of Five- and
Six-membered Cyclometalated Phosphine Complexes of Iridium
Tongyu Li,[a] Zhuo Wang,[a] Kai Liu,[a] Siyang Xing,[a] and Bolin Zhu*[a]
Keywords: Iridium complexes / Phosphine ligands / Cyclometalation / Alkyne-insertion / Catalytic
hydrosilylation of imines
___________________________________________________________________________________
Reactions of three aryl-substituted phosphines with [Cp*IrCl2]2 afforded the corresponding
five-membered or six-membered cyclometalated iridium complexes (2 or 5,6) via an intramolecular
C(sp2)–H bond activation. Insertion reactions of the five-membered cycloiridated complex 2 with
PhC≡CPh and PhC≡CCOPh resulted in the corresponding five-membered and six-membered doubly
cycloiridated complexes 7 and 8, the formation of which presumably went through the vinylidene
rearrangement of alkynes followed by 1,1-insertion; while the reactions of the six-membered
cyclometalated complexes 5,6 with PhC≡CPh or PhC≡CCOPh gave the corresponding eight-membered
cycloiridated complexes 9–12 by 1,2-insertion. The hydrosilylation of imines catalyzed by five- or
six-membered P-containing cycloiridated complexes were studied, and the results proved that the
six-membered cycloiridated complex 5 can be used as an efficient catalyst, which was applied for the
hydrosilylation of various imines, especially aldimines. Molecular structures of complexes 9, 10 and 12
were determined by X-ray diffraction.
___________________________________________________________________________________
[a] Tianjin Key Laboratory of Structure and Performance for Functional Molecules; Key Laboratory of
Inorganic-Organic Hybrid Functional Material Chemistry, Ministry of Education; College of
Chemistry, Tianjin Normal University, Tianjin 300387, People’s Republic of China
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http://hxxy.tjnu.edu.cn/info/1057/1414.htm
Fax: +86-22-23766532; Tel: +86-22-23766515
E-mail: hxxyzbl@gmail.com
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Introduction
Pentamethylcyclopentadienyl cyclometalated iridium complexes have attracted increasing interest
in the past years, mainly due to the following facts: (i) cyclometalated iridium complexes have
important photophysical applications, i.e. as organic light-emitting devices (OLEDs)[1] and
photosensitizers,[2] (ii) cycloiridated complexes can be used as antibacterial and anticancer agents in
biology,[3] (iii) cycloiridated complexes show interesting and rich reactivities, like insertion reaction of
alkyne into Ir–C bond,[4] (iv) cycloiridated complexes have demonstrated great potential in
homogenous catalysis, such as water oxidation reaction,[5] alkane C–H oxidation,[6] hydrogenation,[7]
and hydrosilylation.[8] But overall, the cycloiridated complexes described above are mostly
concentrated on the five-membered N-containing metallacycles, the P-containing iridacycles have
been far less studied,[9] especially for the P-containing six-membered ones. Hence, considering the
interest of some of us in the synthesis, reactivity, and catalytic application of the P-containing
six-membered iridacycles, we investigated in this work the reactivity of alkyne-insertion and catalytic
activity in the hydrosilylation of imines of several P-containing five-membered or six-membered
cycloiridated complexes.
Results and Discussion
Reaction of [Cp*IrCl2]2 with benzyldiphenylphosphine (1)
Reaction of [Cp*IrCl2]2 with benzyldiphenylphosphine in the presence of sodium acetate at room
temperature result in the expected five-membered cyclometalated complex 2 in the yield of 62%
(Scheme 1). Obviously, the formation of complex 2 involves an intramolecular C(sp2)–H bond
1
activation. The H NMR spectrum of 2 showed several groups of multiplets in the aromatic region, all
integrating to 14H due to the phenyl rings, two doublets at δ 3.92 and 3.75 assigned to signal for the
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
31
methylene group, and a doublet at δ 1.55 corresponding to five methyl groups of Cp*; the P NMR
spectrum exhibited a peak at δ 32.81, which is consistent with the data (32.1) reported for the
(1-naphthyl)diphenylphosphine analogue Cp*IrClPPh2(η1-C10H6).[10]
Scheme 1. Reaction of [Cp*IrCl2]2 with benzyldiphenylphosphine (1).
Cp*
Ir
Cl
PPh2
NaOAc
1
PPh2
[Cp*IrCl2]2
+
2
MeOH, RT
-NaCl
-HOAc
1
2
Reactions
of
[Cp*IrCl2]2
with
2-(diphenylphosphino)biphenyl
(3)
and
2-(diisopropylphosphino)biphenyl (4)
First, the phosphines 3 and 4 were chosen as ligands for the reason that they could provide a
C(sp2)−H bond at the appropriate position only for constructing the six-membered metallacycle.
Similarly, reactions of [Cp*IrCl2]2 with ligands 3 and 4 in the presence of sodium acetate at room
temperature resulted in the corresponding six-membered iridacycles 5 and 6 in high yields of 95% and
94% respectively (Scheme 2). The 1H NMR spectrum of 6 showed six groups of peaks in the aromatic
region, all integrating to 8H due to the biphenyl unit, these resonances indicated that one aromatic
C(sp2)–H bond is activated in the reaction to form the six-membered cyclometalated complex 6; the 31P
NMR spectrum exhibited a peak at δ 9.28 ppm, which is significantly low-frequency shifted compared
with the five-membered analogue.
Scheme 2. Reactions of [Cp*IrCl2]2 with 2-(diphenylphosphino)biphenyl (3) and
2-(diisopropylphosphino)biphenyl (4).
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Cp*
PR2
Cl Ir
PR2
NaOAc
1
[Cp*IrCl2]2
+
2
MeOH, RT
-NaCl
-HOAc
3 (R = Ph)
4 (R = iPr)
5
6
Reactions of 2 with PhC≡CPh and PhC≡CCOPh
Recently, insertion reactions of alkynes into transition metal–carbon bonds have attracted
considerable attention in the field of organometallic chemistry, especially for the M–C bond (M = Ir, Rh)
in five-membered N-containing or P-containing cyclometalated complexes.[4] This situation might be
due to the following two factors: firstly, the diversity of insertion mode of alkynes into M–C bond
results in the various products with novel structures and interesting chemistry, including
1,2-insertion,[4,10,11] 1,1-insertion,[4a,b,10,11] and subsequent structural transformation; secondly, in many
alkyne-involved organic reactions catalyzed by transition metal complexes, the step of alkyne insertion
into M–C bond plays an integral part in the catalytic cycle,[12] therefore, detailed study on the reactivity
of alkyne-insertion into different M–C bonds would be very useful for understanding catalytic
mechanism and designing new catalytic processes. Although insertion reactions of alkynes into M–C
bond in five-membered cyclometalated complexes have been intensively studied,[4,10] the similar
reactions with that in six-membered cyclometalated complexes have hardly been reported.[11] Hence,
considering the interests of some of us in the reactivity of six-membered cycloiridated complexes and
the comparative research of others on the reactivity of alkyne-insertion reactions,[4] we investigated the
alkyne-insertion reactions with complexes 2, 5 and 6.
Reactions of 2 with PhC≡CPh and PhC≡CCOPh in methanol at room temperature resulted in
orange solids 7 and 8, which showed low polarity and good solubility in CH2Cl2, benzene, and hexane.
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By careful analysis and comparison of spectral data, 7 and 8 were assigned as the five-membered and
six-membered doubly cyclometalated iridium complexes (Scheme 3). These results are consistent with
those obtained from the reaction of the five-membered cyclometalated analogue Cp*IrClPPh2(η1-C10H6)
with PhC≡CPh in our previous report,[10] so we consider that the plausible pathway for the formation of
7 and 8 is also similar to that we have proposed before, which goes through initial vinylidene
rearrangement of alkyne, 1,1-insertion, and further intramolecular C–H activation (the detailed pathway
for the formation of 7 and 8 was provided in the supporting information).
Scheme 3. Reactions of 2 with PhC≡CPh and PhC≡CCOPh.
Cp*
Ir
Cp*
Ir
Ph2
P
PhC CR
MeOH, RT
-HCl
Cl
PPh2
R
2
7 (R = Ph)
8 (R = COPh)
Reactions of 5 with PhC≡CPh and PhC≡CCOPh
In order to compare with the results obtained from the reactions of alkynes with five-membered
cyclometalated complexes, we similarly performed the reactions of PhC≡CPh and PhC≡CCOPh with
the six-membered cycloiridated complex 5. The reactions of 5 with PhCCPh and PhCCPh in methanol
at room temperature did not afford any characterizable product. Instead when a mixture of 5 with
PhC≡CPh or PhC≡CCOPh in the presence of NaBArF in C2H4Cl2 was stirred at room temperature,[13]
a
4
brown solid 9 or an orange solid 10 was obtained by column chromatography respectively (Scheme 4).
Single crystals of 9 and 10 were obtained by recrystallization in CH2Cl2/n-hexane (1:1), and the X-ray
diffraction studies disclosed their structures, which were shown in Figures 1 and 2, respectively. By
careful analysis of the crystal structure of 9, we found that PhC≡CPh was inserted into Ir–C bond in
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
1,2-mode to form an eight-membered cycloiridated intermediate, and then a geometrically accessible
C=C bond on the biphenyl was coordinated intramolecularly in η2-mode to metal center to give the final
product 9, the flexiblity of eight-membered rings should allow for the intramolecular coordination to
proceed. The involved C=C bond was located at 2,3-position of biphenyl unit, which was reflected by
two Ir–C bond distances (2.526(5) and 2.570(5) Å), both of them are significantly longer than the
normal Ir(1)–C(17) σ bond distance (2.064(5) Å). The dihedral angle between two phenyl rings in
biphenyl unit is 56.8°, and the dihedral angle between two phenyl rings in Ph2C2 unit is 106.0°.
Scheme 4. Reactions of 5 with PhC≡CPh and PhC≡CCOPh.
Cp*
Ir
Cp*
(BArF -
)
NaBArF
4
4
R
PPh2
Cl Ir
PhC CR
PPh2
Ph
C2H4Cl2, RT
-NaCl
5
9 (R = Ph)
10 (R = COPh)
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European Journal of Inorganic Chemistry
Figure 1. Thermal ellipsoid drawing of 9 showing the labeling scheme and 50% probability ellipsoids;
anion BArF - and hydrogens are omitted for clarity. Selected bond lengths [Å] and angles [°] are
4
Ir(1)–P(1) 2.3276(14), Ir(1)–C(17) 2.064(5), Ir(1)–C(25) 2.526(5), Ir(1)–C(26) 2.570(5), C(17)–C(18)
1.357(8), C(18)–C(25) 1.491(7), Cp(centroid)–Ir(1) 1.885, C(17)–Ir(1)–C(25) 59.94(19),
C(17)–Ir(1)–C(26) 77.10(19), C(25)–Ir(1)–C(26) 31.96(17), Ir(1)–C(25)–C(26) 75.7(3),
Ir(1)–C(26)–C(25) 72.3(3), C(11)–C(17)–C(18)–C(19) 21.2(9).
Complex 10 showed the similar crystal structure to 9, PhC≡CCOPh was inserted into Ir–C bond in
1,2-mode, then a geometrically accessible C=C bond on the biphenyl was coordinated intramolecularly
in η2-mode to metal center. The involved C=C bond was also located at 2,3-position of biphenyl unit.
The dihedral angle between two phenyl rings in biphenyl unit is 63.8°. It is worth mentioning that the
insertion of PhC≡CCOPh into Ir–C bond is regioselective, the benzoyl group is found on the carbon
atom adjacent to the metal iridium in 10, while the phenyl group is on the carbon atom adjacent to the
biphenyl unit. This regioselectivity is the same as that observed in the reactions of this alkyne with the
similar six-membered cycloiridated pyridine complex,[11] also the same as that found by Ishii for the
reaction of this alkyne with the similar five-membered cycloiridated pyridine complex.[4a]
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Figure 2. Thermal ellipsoid drawing of 10 showing the labeling scheme and 50% probability ellipsoids;
anion BArF - and hydrogens are omitted for clarity. Selected bond lengths [Å] and angles [°] are
4
Ir(1)–P(1) 2.3349(14), Ir(1)–C(18) 2.072(6), Ir(1)–C(26) 2.584(6), Ir(1)–C(27) 2.604(6), C(18)–C(19)
1.340(8), C(19)–C(26) 1.490(8), Cp(centroid)–Ir(1) 1.867, C(18)–Ir(1)–C(26) 58.9(2),
C(18)–Ir(1)–C(27) 77.2(2), C(26)–Ir(1)–C(27) 31.05(19), Ir(1)–C(26)–C(27) 75.3(3),
Ir(1)–C(27)–C(26) 73.7(3), C(17)–C(18)–C(19)–C(20) −9.2(10).
Reactions of 6 with PhC≡CPh and PhC≡CCOPh
Besides, we also tried the similar alkyne-insertion reactions of the other six-membered
cyclometalated complex 6 and expected the formation of analogues of 9 and 10. When the reaction of 6
with NaBArF and PhC≡CPh or PhC≡CCOPh in C2H4Cl2 was performed under the same conditions
4
described above, similarly, a brown solid 11 or an orange solid 12 was obtained by column
chromatography respectively (Scheme 5). To further confirm the structures of 11 and 12, the single
crystal of 12 was obtained by recrystallization in CH2Cl2/n-hexane (1:1), and the X-ray diffraction
determined the structure of 12, which was shown in Figure 3. Compared with the crystal structures of 9
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
and 10, we found that PhC≡CCOPh was inserted into Ir–C bond in the same way to form an
eight-membered cycloiridated intermediate, and then a geometrically accessible C=C bond on the
biphenyl was coordinated intramolecularly in η2-mode to metal center to form the final compound 12.
The difference between 9–10 and 12 is the position of η2-coordinated C=C bond. For the former, the
involved C=C bond was located at 2,3-position of biphenyl unit, for the latter, the C=C bond was
located at 1,2-position of biphenyl, which was reflected by two Ir–C bond distances (2.408(8) and
2.476(9) Å). We considered that the steric effect of substituents on phosphine affects the position of
coordinated C=C bond. The other difference between 10 and 12 is the regioselectivity of insertion of
PhC≡CCOPh, the phenyl group is found on the carbon atom next to the metal iridium in 11, which is
opposite that usually observed for insertion into the Ir–C bond of cyclometalated complexes. It has been
demonstrated that the regioselectivity of alkyne insertion was affected by the exact palladium precursor
in Davies’ work.[4f] Here we observed that the regioselectivity of insertion of this alkyne may also
depend on the exact substituents on phosphine ligand used. Two phenyl rings in biphenyl unit of 12 are
almost mutually perpendicular, which was reflected by the dihedral angle of 94.90°.
Based on above results, we observed that alkyne-insertion of the six-membered cyclometalated
phosphine complexes of iridium adopted 1,2-insertion mode, then underwent an intramolecular
η2-coordination of a geometrically accessible C=C bond on the biphenyl to give the final products,
while the alkyne-insertion of the five-membered one went through 1,1-insertion and subsequent C–H
activation to give the five- and six-membered doubly cyclometalated product. Therefore, with respect to
the alkyne-insertion reaction, the cyclometalated phosphine complexes of iridium show different
reactivity according to the exact size of iridacycle.
Scheme 5. Reactions of 6 with PhC≡CPh and PhC≡CCOPh.
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Cp*
Ir
(BArF -
)
Cp*
NaBArF
4
4
Ph
PiPr2
PiPr2
Cl Ir
PhC CR
R
C2H4Cl2, RT
-NaCl
6
11 (R = Ph)
12 (R = COPh)
Figure 3. Thermal ellipsoid drawing of 12 showing the labeling scheme and 30% probability ellipsoids;
anion BArF - and hydrogens are omitted for clarity. Selected bond lengths [Å] and angles [°] are
4
Ir(1)–P(1) 2.312(2), Ir(1)–C(23) 2.408(8), Ir(1)–C(24) 2.476(9), Ir(1)–C(30) 2.102(9), C(29)–C(30)
1.330(12), C(24)–C(29) 1.489(12), Cp(centroid)–Ir(1) 1.915, C(23)–Ir(1)–C(30) 78.3(3),
C(24)–Ir(1)–C(30)
59.8(3),
C(23)–Ir(1)–C(24)
34.7(3),
Ir(1)–C(23)–C(24)
75.2(5),
Ir(1)–C(24)–C(23) 70.1(5), C(31)–C(29)–C(30)–C(38) −3.9(16).
Hydrosilylation of imines catalyzed by the cyclometalated iridium phosphine complexes
Recently, a series of reports have stated the efficiency of cyclometalated iridium complexes for a
range of organic reactions, especially for hydrogenation, transfer hydrogenation, reductive amination,
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European Journal of Inorganic Chemistry
and hydrosilylation.[7a] For example, Michon and co-workers reported a study of the hydrosilylation of
imines employing five-membered cyclometalated pyridine complex of iridium.[8b] General speaking, the
catalysts used in all reported cases are concentrated on the five-membered N-containing cyclometalated
iridium complexes, we considered that the P-containing analogues could be an interesting alternative
catalyst for hydrogenation or hydrosilylation, because phosphine ligands possess rich diversity and
provide more positions to adjust the steric and electronic effects compared with N-containing ligands.
With a series of five- and six-membered cycloiridated complexes in hand, we chose two five-membered
cycloiridated complexes 2 and 13 (Scheme 6, reported in our previous work[10]) and two six-membered
ones 5 and 6 as representatives, and explored their catalytic activities in the hydrosilylation of imines.
Scheme 6. Five-membered cyclometalated iridium phosphine complex 13.
Cp*
Ir
Cl
PPh2
13
Table 1. Screening of catalysts, additives, solvents, times and temperatures.[a]
[Ir]
(mol%)
2 (1)
5 (1)
6 (1)
5 (1)
5 (1)
5 (1)
Additive
(mol%)
none
none
none
NH4PF6 (2)
KPF6 (2)
AgBF4 (2)
Time
(h)
30
30
30
20
20
12
T
(ºC)
40
40
40
40
40
40
Yield
(%)[b]
0
21
0
24
25
47
Entry
Solvent
1
2
3
4
5
6
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
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7
8
9
10
11
12
13
14
15
5 (1)
5 (1)
2 (1)
6 (1)
13 (1)
5 (1)
5 (1)
5 (1)
5 (0.5)
NaBF4 (2)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
MeOH
Toluene
THF
12
2
7
7
7
40
40
40
6
40
40
40
40
40
60
100
80
40
85
98
59
64
56
0
0
0
81
NaBArF (2)
4
NaBArF (2)
4
NaBArF (2)
4
NaBArF (2)
4
NaBArF (2)
4
NaBArF (2)
4
NaBArF (2)
4
NaBArF (1)
CH2Cl2
4
[a] Reactions were carried out with imine (54 mg, 0.3 mmol), silane (70 mg, 0.6 mmol), catalyst
(0.01 equiv), and additive (0.02 equiv) in solvent (3 mL) at 40–100 °C for 2–40 h. [b] Isolated yields
after column chromatography.
For optimization of reaction conditions, N-benzylideneaniline (14a) was chosen as the model
substrate. We observed that an additive is necessary in the catalytic hydrosilylation, which could aid in
removing the iridium chloride ligand and afford an active cationic catalyst (Table 1). By changing the
additives (entries 4–8), we confirmed that NaBArF gave the highest yield as compared to NH4PF6,
4
KPF6, AgBF4, and NaBF4, which might be attributed to the lest coordinating of BArF anion.[14] Among
4
four studied cycloiridated complexes (Scheme 6), the six-membered cyclometalated phosphine complex
of iridium (5) proved to the most active catalyst (entries 8–11). It was interesting to note that only
solvent CH2Cl2 gave good yields, the use of other solvents like MeOH, toluene, and THF resulted in no
catalytic reaction, even at a higher temperature and for a longer reaction time (entries 12–14), which
might be due to the solvent competition with the substrate for the occupation of the free coordination
site at catalytic active center. Based on the economic consideration, the amount of catalyst 5 and
additive was decreased to 0.5 mol% and 1.0 mol% respectively, however, the corresponding reactions
gave the lower yield of 81% for 6 h (entry 15).
Table 2. Screening of the silane reagent.[a]
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Entry
Silane
Time (h)
Yield (%)[b]
1
2
3
Et3SiH
Ph2SiH2
Ph3SiH
2
2
2
98
88
77
[a] Reactions were carried out with imine (54 mg, 0.3 mmol), silane (0.6 mmol), catalyst (0.01
equiv), and additive (0.02 equiv) in solvent (3 mL) at 40 °C for 2 h. [b] Isolated yields after column
chromatography.
To optimize the silane reagents, we investigated two other silanes Ph2SiH2 and Ph3SiH and
obtained the corresponding hydrogenation product 15a in lower yields of 88% and 77%, respectively
(entries 2–3, Table 2), so Et3SiH proved to be an efficient hydrosilylation agent for a great yield, and the
final optimized conditions were ended up with the combined use of the cycloiradated complex 5 (1
mol%) and NaBArF (2 mol%) as a catalyst in solvent of CH2Cl2 at 40 °C with an excess of Et3SiH.
4
Table 3. Hydrosilylation of imines catalyzed by cycloiridated complex 5.[a]
Entry
Reagent
Time (h)
Yield (%)[b]
1
2
3
4
5
2
4
3
3
3
98
84
58
76
81
3
61
6
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7
8
9
3
3
3
93
82
90
3
75
10
3
3
91
56
11
12
13
14
4
5
35
55
5
76
15
[a] Reactions were carried out with imine (0.3 mmol), silane (70 mg, 0.6 mmol), catalyst (0.01
equiv), and additive (0.02 equiv) in solvent (3 mL) at 40 °C for 2–5 h. [b] Isolated yields after column
chromatography.
Next, we studied the hydrosilylation of a series of aldimines and ketimines under the optimized
conditions (Table 3). The hydrosilylation of N-benzylideneaniline afforded the N-benzylaniline in the
isolated yield of 98%, which was even higher than that (90%) obtained from the similar hydrosilylation
reaction catalyzed by the five-membered N-containing cyclometalated iridium complex. For those
related ortho-, meta-, and para-substituted aldimines (entries 2–11, Table 3), the hydrosilylation still
gave the corresponding amines in good to excellent yields. It was observed that the reactions of those
N-benzylideneanilines containing electron-withdrawing substituent on the benzylidene group were
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
inclined to give higher yields (82–93% in entries 7–9), however, for those N-benzylideneanilines
containing electron-withdrawing substituent on the N-phenyl group, the reactions tended to afford
relatively lower yields (58–81% in entries 3–5). These results could further support the plausible
catalytic mechanism proposed in previous reports,[4c,15] which demonstrated that the real catalyst in
hydrosilylation reaction was the Ir-hydrido intermediate, so the more electropositive the imine carbon
was, the easier the hydritic H was transferred to the polar imine substrates. Regarding the
hydrosilylation of N-Benzylidenebenzylamine, the reaction gave the moderate yield of 61% (entry 6).
Finally, the hydrosilylation of a series of ketimines were performed similarly and afforded the
corresponding amines in relatively low yields (35–76% in entries 12–15).
Conclusion
In summary, insertion reactions of the six-membered cyclometalated phosphine iridium complexes
(5 and 6) with internal aromatic alkynes were firstly reported, which showed different reactivity from
those of the five-membered cyclometalated iridium analogues. For the former, the resulting insertion
products were formed through 1,2-inserion and subsequent intramolecular η2-C=C coordination; while
for the latter, the products were formed via 1,1-inserion and subsequent intramolecular C–H activation,
so the insertion mode of alkyne was found to depend on the exact size of iridacycle. Besides, the
hydrosilylation of imines catalyzed by five- or six-membered P-containing cycloiridated complexes
were studied, and the results proved that the six-membered cycloiridated complex 5 can be used as an
efficient catalyst, which was applied for the hydrosilylation of various imines, especially aldimines.
Experimental Section
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
General Considerations: All reactions were carried out under nitrogen using standard Schlenk and
vacuum line techniques; however, the workup was carried out in air unless stated otherwise. All
1
13
solvents were distilled from appropriate drying agents under nitrogen prior to use. H (400 MHz), C
31
(100 MHz), and P (162 MHz) NMR spectra were recorded on a Bruker AV400 instrument at room
1
temperature with CDCl3 as solvent. Chemical shifts were recorded in ppm, referenced to residual H
and 13C signals of the non-deuterated CDCl3 (δ 7.26 and 77.16) as internal standards or to the 31P signal
of PPh3 (δ −5.65) as an external standard. Elemental analyses were performed on a Perkin–Elmer 240C
analyzer. [Cp*MCl2]2 (M = Ir, Rh) were purchased from Strem, NaBArF was purchased from Alfa
4
Aesar, benzyldiphenylphosphine (1), 2-(diphenylphosphino)biphenyl (3), PhC≡CPh were purchased
from TCI and used as received. 2-(Diisopropylphosphino)biphenyl (4)[16] and PhC≡CCOPh[17] were
synthesized according to the related literatures.
Synthesis of 2: A mixture of [Cp*IrCl2]2 (40 mg, 0.05 mmol), benzyldiphenylphosphine (28 mg, 0.10
mmol) and sodium acetate (17 mg, 0.20 mmol) in methanol (10 mL) was stirred for 2h at room
temperature. The solvent was then removed under vacuum, and the residue was chromatographed on a
silica gel column with a mixture of petrol ether/ethyl acetate (15:1) as the eluent. The products were
recrystallized from n-hexane/CH2Cl2 at −10 °C to afford 1 as orange crystal (62% yield). 1H NMR δ
7.76–7.71 (m, 2H), 7.52 (d, J = 7.2 Hz, 1H), 7.49–7.42 (m, 3H), 7.31–7.22 (m, 4H), 7.12 (m, 2H), 6.95
(m, 1H), 6.90 (m, 1H), 3.92 (dd, J = 16.0, 13.6 Hz, 1H), 3.75 (dd, J = 16.0, 9.2 Hz, 1H), 1.55 (d, J = 2.0
Hz, 15H). 13C NMR: δ 135.1, 134.5, 132.5, 131.9, 131.0, 130.8, 130.7, 130.2, 128.8, 128.2, 127.7,
127.5, 126.1, 120.6, 119.4, 92.1, 35.2, 8.2. 31P NMR δ 32.81. Anal. Calcd for C29H31ClIrP: C, 54.58; H,
4.90. Found: C, 54.37; H, 4.82.
Synthesis of 5: A mixture of [Cp*IrCl2]2 (40 mg, 0.05 mmol), 2-(diphenylphosphino)biphenyl (34 mg,
0.10 mmol) and sodium acetate (17 mg, 0.20 mmol) in methanol (10 mL) was stirred for 2h at room
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
temperature. The solvent was then removed under vacuum, and the residue was chromatographed on a
silica gel column with a mixture of petrol ether/ethyl acetate (5:1) as the eluent. The product was
1
recrystallized from n-hexane/CH2Cl2 at −10 °C to afford 5 as orange crystal (95%yield). H NMR δ
7.88–7.83 (m, 3H), 7.65 (d, J = 7.2 Hz, 1H), 7.55–7.42 (m, 6H), 7.28 (d, J = 7.6 Hz, 1H), 7.20–7.16 (m,
2H), 6.97–6.83 (m, 5H), 1.26 (d, J = 2.0 Hz, 15H). 13C NMR: δ 151.4, 143.2, 141.7, 136.5, 133.7, 131.0,
31
130.4, 130.0, 128.9, 128.7, 128.4, 126.8, 126.6, 126.2, 124.9, 123.7, 94.3, 8.5. P NMR δ 5.12. Anal.
Calcd for C34H33ClIrP: C, 58.32; H, 4.75. Found: C, 58.55; H, 4.63.
Synthesis of 6: A mixture of [Cp*IrCl2]2 (40 mg, 0.05 mmol), 2-(diisopropylphosphino)biphenyl (27
mg, 0.10 mmol) and sodium acetate (17 mg, 0.20 mmol) in methanol (10 mL) was stirred for 2h at room
temperature. The solvent was then removed under vacuum, and the residue was chromatographed on a
silica gel column with a mixture of petrol ether/ethyl acetate (5:1) as the eluent. The product was
1
recrystallized from n-hexane/CH2Cl2 at −10 °C to afford 6 as yellow crystal (94%yield). H NMR δ
7.78 (d, J = 7.6 Hz, 1H), 7.60 (dd, J = 7.4, 3.4 Hz, 1H), 7.47–7.41 (m, 2H), 7.31 (t, J = 7.6 Hz, 1H),
7.23 (t, J = 7.6 Hz, 1H), 7.07–6.97 (m, 2H), 2.72 (m, 1H), 2.05 (m, 1H), 1.75–1.63 (m, 6H), 1.37 (dd,
13
J = 15.6, 7.6 Hz, 3H), 1.24 (d, J = 1.6 Hz, 15H), 0.64 (dd, J = 14.4, 7.6 Hz, 3H). C NMR: δ 150.8,
143.6, 143.0, 141.1, 131.3, 129.3, 128.2, 125.8, 124.5, 123.5, 93.1, 27.1, 24.4, 22.6, 21.5, 21.1, 19.3, 8.3.
31P NMR δ 9.28. Anal. Calcd for C28H37ClIrP: C, 53.19; H, 5.90. Found: C, 52.98; H, 5.67.
Synthesis of 7 and 8: A mixture of cyclometalated complex 2 (15.0 mg, 0.02 mmol) and alkyne (4.0
equiv) was stirred in methanol (5 mL) at 60ºC for 1h. Then cool to room temperature. The solvent was
then removed under vacuum, and the residue was chromatographed on a silica gel column with a
mixture of petrol ether/ethyl acetate (10:1) as the eluent. The products were recrystallized from
n-hexane/CH2Cl2 at −10 °C to afford 7 and 8.
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European Journal of Inorganic Chemistry
7: orange solid (38% yield). 1H NMR δ 7.63–7.59 (m, 4H), 7.45 (m, 2H), 7.35 (m, 4H), 7.06 (m, 6H),
7.00 (m, 1H), 6.92 (m, 2H), 6.82 (m, 2H), 6.78 (m, 1H), 6.50 (d, J = 8.0 Hz, 1H), 4.20 (d, J = 10.4 Hz,
13
2H), 1.30 (d, J = 2.4 Hz, 15H). C NMR: δ 146.0, 142.7, 142.0, 139.7, 138.9, 137.7, 135.0, 134.0,
131.6, 131.5, 131.2, 131.1, 131.0, 130.8, 130.1, 129.7, 129.4, 128.9, 128.5, 128.3, 128.1, 127.9, 127.8,
127.7, 127.2, 126.6, 126.4, 126.2, 92.0, 31.8, 8.3. 31P NMR δ 17.74. Anal. Calcd for C43H40IrP: C, 66.22;
H, 5.17. Found: C, 66.35; H, 5.42.
8: orange solid (35% yield). 1H NMR δ 7.7 (m, 2H), 7.59 (t, J = 7.2 Hz, 2H), 7.50 (t, J = 7.2 Hz, 1H),
7.35–7.22 (m, 7H), 7.18 (d, J = 7.2 Hz, 1H), 7.13 (t, J = 7.2 Hz, 1H), 7.03 (m, 2H), 6.92 (d, J = 7.6 Hz,
1H), 6.86 (m, 2H), 6.72 (m, 3H), 6.59 (t, J = 7.2 Hz, 1H), 3.88 (m, 1H), 3.75 (m, 1H), 1.13 (s, 15H). 13C
NMR: δ 200.6, 152.0, 147.4, 143.1, 140.6, 139.3, 136.4, 136.0, 135.6, 134.7, 134.6, 134.5, 133.8, 133.1,
132.6, 132.3, 132.1, 131.3, 131.2, 130.2, 130.0, 129.7, 129.4, 129.2, 128.4, 128.0, 127.8, 127.4, 126.9,
31
126.4, 125.9, 125.2, 96.7, 37.6, 8.4. P NMR δ 11.41. Anal. Calcd for C44H40IrOP: C, 65.41; H, 4.99.
Found: C, 65.25; H, 5.04.
Synthesis of 9 and 10: A mixture of cyclometalated complex 5 (15.0 mg, 0.02 mmol), alkyne (4.0
equiv) and NaBArF (1.2 eq) in 1,2-dichloroethane (5 mL) was stirred for 1 h at room temperature. The
4
solvent was then removed under vacuum, and the residue was chromatographed on a silica gel column
with ethyl acetate as the eluent. The products were recrystallized from n-hexane/CH2Cl2 at −10 °C to
afford 9 and 10.
9: brown solid (45% yield). 1H NMR δ 7.78 (t, J = 7.6 Hz, 1H), 7.72 (m, 8H), 7.64–7.53 (m, 3H), 7.52
(m, 6H), 7.47–7.35 (m, 3H), 7.26–7.20 (m, 3H), 7.14 (m, 3H), 7.11 (d, J = 6.4 Hz, 1H), 7.05 (t, J = 7.6
Hz, 1H), 6.92–6.84 (m, 5H), 6.66–6.58 (m, 3H), 6.48 (dd, J = 7.4, 4.1 Hz, 1H), 6.13 (d, J = 7.1 Hz, 2H),
13
1.22 (d, J = 2.0 Hz, 15H). C NMR: δ 162.6, 162.1, 161.6, 161.1, 144.0, 143.0, 141.3, 140.8, 139.5,
135.0, 134.8, 133.4, 132.3, 132.2, 131.9, 131.3, 129.8, 129.3, 129.1, 129.0, 128.9, 128.8, 128.6, 128.5,
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European Journal of Inorganic Chemistry
128.3, 128.0, 127.7, 127.6, 126.7, 126.6, 126.1, 123.4, 120.6, 117.6, 108.0, 98.1, 9.1. 31P NMR δ 24.83.
Anal. Calcd for C80H55BF24IrP: C, 56.31; H, 3.25. Found: C, 56.14; H, 3.33.
10: orange solid (39% yield). 1H NMR δ 7.92 (m, 1H), 7.70 (m, 8H), 7.67 (m, 3H), 7.60 (t, J = 8.4 Hz,
2H), 7.51 (s, 4H), 7.45–7.35 (m, 3H), 7.26 (m, 1H), 7.20 (d, J = 6.8 Hz, 1H), 7.15–7.06 (m, 2H),
7.00–6.95 (m, 3H), 6.88 (t, J = 8.0 Hz, 3H), 6.77 (t, J = 8.2 Hz, 5H), 6.62–6.58 (m, 2H), 6.53 (d, J = 6.8
13
Hz, 1H), 6.14 (d, J = 7.6 Hz, 1H), 1.13 (d, J = 2.0 Hz, 15H). C NMR: δ 198.9, 162.6, 162.1, 161.6,
161.1, 148.0, 143.6, 142.2, 139.7, 138.4, 137.5, 135.4, 135.3, 135.2, 135.0, 134.0, 133.1, 132.4, 132.2,
131.3, 129.5, 129.4, 129.3, 129.2, 129.0, 128.9, 128.8, 128.6, 128.5, 128.1, 127.8, 126.4, 126.1, 123.4,
31
120.6, 117.6, 103.1, 98.0, 9.4. P NMR δ 28.14. Anal. Calcd for C81H55BF24IrOP: C, 56.10; H, 3.20.
Found: C, 55,84; H, 3.38.
Synthesis of 11 and 12: A mixture of cyclometalated complex (5) (15.0 mg, 0.02 mmol), alkyne (4.0
equiv) and NaBArF (1.2eq) in 1,2-dichloroethane (5 mL) was stirred for 1 h at room temperature. The
4
solvent was then removed under vacuum, and the residue was chromatographed on a silica gel column
with ethyl acetate as the eluent. The products were recrystallized from n-hexane/CH2Cl2 at −10 °C to
afford 11 and 12.
1
11: brown solid (41% yield). H NMR δ 7.94 (m, 1H), 7.70 (m, 8H), 7.59 (t, J = 6.4 Hz, 1H), 7.52 (s,
4H), 7.39 (m, 1H), 7.33 (m, 1H), 7.29–7.23 (m, 2H), 7.08–6.98 (m, 6H), 6.96 (d, J = 8.0 Hz, 1H), 6.72
(m 1H), 6.41 (m, 4H), 2.58 (m, 1H), 2.45 (m, 1H), 1.43 (d, J = 1.6 Hz, 15H), 1.28–1.20 (m, 6H), 0.95
13
(dd, J = 14.0, 7.6 Hz, 3H), 0.73 (dd, J = 18.0, 7.2 Hz, 3H). C NMR: δ 162.6, 162.1, 161.6, 161.1,
147.7, 144.4, 142.6, 141.7, 141.0, 135.0, 134.5, 134.3, 133.8, 132.6, 131.8, 130.1, 129.2, 128.9, 128.7,
128.1, 128.0, 127.8, 127.5, 127.0, 126.1, 123.4,122.6, 120.6, 117.6, 110.3, 108.6, 97.9, 28.6, 22.8, 22.5,
31
20.2, 18.4, 18.0, 9.3. P NMR δ 35.24. Anal. Calcd for C74H59BF24IrP: C, 54.25; H, 3.63. Found: C,
54.29; H, 3.44.
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
12: orange solid (38% yield). 1H NMR δ 8.00 (t, J = 7.6 Hz, 1H), 7.70 (s, 8H), 7.52 (s, 4H), 7.48 (t, J =
6.8 Hz, 1H), 7.44–7.38 (m, 2H), 7.34 (m, 1H), 7.22 (m, 3H), 7.15–7.11 (m, 2H), 6.95 (t, J = 7.6 Hz, 2H),
6.85 (m, 4H), 6.20 (m, 2H), 2.59 (m, 1H), 2.49 (m, 1H), 1.46 (d, J = 1.3 Hz, 15H), 1.28–1.19 (m, 6H),
0.86–0.72 (m, 6H). 198.7, 150.3, 147.9, 147.1, 144.7, 142.4, 141.4, 140.1, 137.1, 135.0, 134.7, 134.1,
133.5, 132.4, 131.9, 129.5, 129.3, 128.9, 128.8, 128.6, 128.4, 128.3, 128.0, 127.8, 127.5, 126.1, 124.1,
31
123.4, 122.3, 120.7, 117.6, 98.3, 29.2, 22.8, 21.6, 20.3, 18.4, 18.2, 9.3. P NMR δ 32.29. Anal. Calcd
for C75H59BF24IrOP: C, 54.06; H, 3.57. Found: C, 54.36; H, 3.35.
General procedure for catalytic hydrosilylation reactions: The imine reagent (0.3 mmol), the
selected iridium catalyst (0.01 equiv), and the additive (0.02 equiv) were introduced in a Schlenk tube.
Under nitrogen, the solvent (3ml) was added followed by the silane reagent (2.0 equiv). The reaction
mixture was then heated at 40 ºC under stirring. Then volatiles were removed under reduced pressure,
and the residue was chromatographed on a silica column. Elution with ether acetate/petroleum ether
(1:5) developed a colorless band. After vacuum removal of the solvents from the above eluate, the
residue was obtained as white solid or colorless oil.
Crystallographic Studies: Single crystals of complexes 9, 10, and 12 suitable for X-ray diffraction
were obtained by crystallization from n-hexane/CH2Cl2 (1:1). Data collection was performed on a
Bruker SMART 1000, using graphite-monochromated Mo Kα radiation (ω–2θ scans, λ = 0.71073 Å).
Semiempirical absorption corrections were applied for all complexes. The structures were solved by
direct methods and refined by full-matrix least squares. All calculations were using the SHELXTL-97
program system. The crystal data and summary of X-ray data collection are presented in Table 4.
CCDC 1826034 (9), 1829299 (10), 1826035 (12) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre,
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
12 Union Road, Cambridge CB2 1EZ, UK (fax: (+44) 1223-336-033; e-mail: deposit@ccdc.cam.ac.uk)
or awww.ccdc.cam.ac.uk/data request.cif.
Supporting Information: CIF files and Check CIF files giving crystallographic details for complexes 9,
10, and 12.
Acknowledgments
We gratefully acknowledge financial support from the National Natural Science Foundation of China
(21572160) and the Program for Innovative Research Team in University of Tianjin (TD13-5074).
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
Table 3. Crystal Data and Summary of X-ray Data Collection for 9, 10 and 12
9
10
12
formula
fw
C80H55BF24IrP
1706.22
145(1)
C81H55BF24IrOP
1734.23
100.01(10)
Monoclinic
P21/n
C151H120B2Cl2F48Ir2O2P2
3417.32
292.85(17)
Monoclinic
I2/a
T (K)
cryst syst
space group
a (Å)
Triclinic
P-1
13.3627(3)
13.8611(3)
19.7514(5)
78.305(2)
83.644(2)
84.052(2)
3548.00(15)
2
19.4959(6)
16.0811(4)
23.1672(7)
90
26.1362(6)
14.7274(6)
38.3462(10)
90
b (Å)
c (Å)
 (deg)
 (deg)
 (deg)
97.171(3)
90
97.196(2)
90
V (Å3)
7206.4(4)
4
14643.9(8)
4
Z
Dcalc (gcm−3)
 (mm−1)
F(000)
1.597
1.598
1.550
2.013
1.984
1.987
1696.0
3448.0
6808.0
cryst size (mm)
max. 2 (deg)
0.25× 0.22 × 0.20 0.25 × 0.24 × 0.22 0.25 × 0.22 × 0.20
50.246
50.018
50.02
no. of reflns collected 31228
32614
33019
no. of indep reflns/Rint 12630/0.0448
12661/0.0362
1002
12871/0.0370
1014
no. of params
989
goodness-of-fit on F2 1.043
1.063
1.021
R1, wR2 [I > 2(I)]
R1, wR2 (all data)
0.0487, 0.1158
0.0569, 0.1217
0.0508, 0.1059
0.0600, 0.1110
1.85, −1.39
0.0730, 0.1931
0.0959, 0.2132
4.85, −1.21
largest diff peak and 2.03, −1.10
hole (e Å−3)
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10.1002/ejic.201800412
European Journal of Inorganic Chemistry
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European Journal of Inorganic Chemistry
For table of contents use only:
Reactivity of Alkyne-insertion and Catalytic Activity of Five- and
Six-membered Cyclometalated Phosphine Complexes of Iridium
Key Topic: Iridium Complexes
T. Li, Z. Wang, K. Liu, S. Xing, and B. Zhu*
Keywords: Iridium complexes / Phosphine ligands / Cyclometalation / Alkyne-insertion / Catalytic
hydrosilylation of imines
Insertion reactions of aromatic alkyne with the five-membered and six-membered cyclometalated
iridium complexes (2 and 5,6) were studied, which exhibited the different insertion modes. Besides, the
six-membered cycloiridated complex 5 can be used as a highly efficient catalyst in the hydrosilylation
of various imines, especially aldimines.
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