Orthometalated amino-carbene derivatives of iridium via anilines and terminal alkynes

Article abstract of DOI:10.1021/om100803g

The reaction of a terminal alkyne (RCCH) and an aniline (R′C ₆H₄NH₂) with the dinuclear species [Cp*IrCl₂]₂ afforded cyclometalated amino-carbene derivatives Cp*Ir(Cl)[=C(CH₂R)NHC₆H ₃R′] via a hydroamination and an orthometalation. The reaction pathway has been examined through deuterium labeling and computational studies.

Full text of DOI:10.1021/om100803g

Organometallics 2010, 29, 6417–6421 6417
DOI: 10.1021/om100803g
Orthometalated Amino-Carbene Derivatives of Iridium via Anilines and
Terminal Alkynes
Elumalai Kumaran,† Venugopal Shanmugham Sridevi,‡ and Weng Kee Leong*,†
†Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link,
Singapore 637371, and ‡Department of Chemistry, National University of Singapore, 3 Science Drive 3,
Singapore 117543
Received August 18, 2010
The reaction of a terminal alkyne (RCCH) and an aniline (R0C6H4NH2) with the dinuclear species
[Cp*IrCl2]2 afforded cyclometalated amino-carbene derivatives Cp*Ir(Cl)[dC(CH2R)NHC6H3R0]
via a hydroamination and an orthometalation. The reaction pathway has been examined through
deuterium labeling and computational studies.
Scheme 1
Introduction
The chemistry of transition metal carbene complexes has
continued unabated from the synthesis of the first carbene
complex,1 through heteroatom-stabilized carbene complexes,2
to their application as reactive intermediates in organic synthesis.3
Fischer-type amino-carbene complexes are well recognized
and have been proven to be useful in C-C bond formation
reactions.4 In the extensive literature on this class of carbene
complexes, those of iridium are relatively rare and less exten-
sively explored.5 Most reports on their syntheses involve
C-H bond activation of N-alkylamines, and although nu-
cleophilic addition of amines onto coordinated alkynes is
well established for a number of metal systems including
those of ruthenium,6 platinum,7 and tungsten,8 to our knowl-
edge, there is no report on the synthesis of iridium amino-
carbene complexes using this methodology.
Earlier studies have shown that some iridium complexes
can add alcohols onto coordinated terminal alkynes or alkyl-
idenes in an intramolecular9 or intermolecular10 fashion. For
example, we have reported that the dinuclear species [Cp*IrCl2]2,1,
reacts with terminal alkynes in the presence of methanol to
afford iridium methoxy-carbene complexes 2 (Scheme 1).
The reaction is believed to proceed via nucleophilic attack at
the R-carbon of a vinylidene intermediate.
In this paper we wish to describe the analogous reaction
involving anilines, which turned out to afford a general route
to orthometalated iridium amino-carbene complexes.
*To whom correspondence should be addressed. E-mail: chmlwk@
ntu.edu.sg.
Results and Discussion
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reaction of 1 with a terminal alkyne (RCCH), and an aniline
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r
2010 American Chemical Society
Published on Web 11/08/2010
pubs.acs.org/Organometallics

6418 Organometallics, Vol. 29, No. 23, 2010
Kumaran et al.
Table 1. Common Atomic Numbering Scheme and Selected Bond
Parameters for 3a and 3b
3a
3b
˚
Bond Lengths (A)
Ir-Cl
2.385(2)
2.047(9)
1.992(9)
1.428(12)
1.291(11)
1.381(12)
1.496(12)
2.4085(14)
2.037(5)
1.991(6)
1.398(8)
1.314(8)
1.386(8)
1.501(9)
Ir-C(1)
Ir-C(3)
N-C(2)
N-C(3)
C(1)-C(2)
C(3)-C(4)
Figure 1. ORTEP plot (50% probability thermal ellipsoids) of 3b.
All but one H atom are omitted.
Scheme 2
Bond Angles (deg)
C(1)-Ir-C(3)
C(2)-N-C(3)
C(1)-C(2)-N
N-C(3)-Ir
78.1(4)
78.4(2)
117.2(7)
112.3(8)
117.7(7)
117.0(5)
113.4(5)
116.8(4)
(R0C6H4NH2) in place of methanol, would afford an iridium
amino-carbene complex of the type [Cp*Ir(dC(NHC6H4R0)-
(CH2R))Cl2]. Instead, we obtained orthometalated iridium
amino-carbene complexes in yields from 30% to 80% for a
wide variety of anilines and terminal alkynes; a selected sam-
ple for PhCCH and tBuCCH is shown in Scheme 2.
The reactions required typically a 20 equivalent excess of
the alkyne; use of two equivalents gave incomplete reaction
and the aniline addition product [Cp*IrCl2NH2C6H4R0], 5;11
changing solvents (to DCM, THF, or toluene) or tempera-
ture (to reflux) did not give any improvement. Attempts at
extending the procedure to non-orthometalated carbene com-
plexes, for example, with 2,6-disubstituted anilines such as
2,6-dichloroaniline and 2,6-difluoroaniline and with aliphat-
ic amines such as benzylamine and 1-aminopentane, in the
presence of 3,3-dimethyl-1-butyne were unsuccessful, giving
only the corresponding analogues of 5. In the case of 2,4,6-
trimethylaniline, trace amounts of the CtC triple bond
Figure 2. ORTEP plot (50% probability thermal ellipsoids) of
˚
5b. H atoms are omitted. Selected bond lengths (A) and angles
(deg): Ir(1)-N(11) = 2.169(3); Ir(1)-Cl(2) = 2.4033(7); Ir(1)-
Cl(1) = 2.4315(7); N(11)-C(11) = 1.453(4); N(11)-Ir(1)-Cl(2) =
83.31(8); N(11)-Ir(1)-Cl(1) = 80.67(7); Cl(2)-Ir(1)-Cl(1) =
87.50(3).
6 occurs.10 There were also no indications of alkyne polymer-
ization or hydroamination under these conditions.
t
The products 3-5 have all been characterized spectro-
scopically and analytically, and the structures of 3a, 3b, and
5b have also been confirmed by single-crystal X-ray diffrac-
tion studies. The ORTEP plot for 3b is shown in Figure 1,
while a common atomic numbering scheme and selected
bond parameters for 3a and 3b are given in Table 1; the
ORTEP plot and selected bond parameters for 5b are shown
in Figure 2. Similar carbene complexes that contain an irida-
cycle that have been structurally characterized include TpPh-
Ir(H)(dCHNMepy),13 {Ir(H)2(dCMeNEtpy)(PPh3)2}þ,14 and
{Ir(H)2(dC[CH2CH2CH2Ph]NMepy)(PPh3)2}þ.15 The 1H NMR
cleavage product, viz., [Cp*Ir(Cl)(CO)(CH2 Bu)], 6, were also
formed. Aminolysis of the methoxy-carbene complexes 2, a
well-known synthetic route to amino-carbenes,12 was also
unsuccessful and gave 6 instead. The failure of this route may
be attributed to the deprotonation of adventitious water, thus
favoring hydroxide attack on 2; these are known to decompose
in the presence of aqueous KOH to afford 6. The reaction is
otherwise fairly robust, as it appears unaffected by the presence
of water; in the absence of aniline, CtC triple bond cleavage to
ꢀ
(11) Vicente, J.; Chicote, M. T.; Hernandez, V. H.; Bautista, D. Inorg.
Chem. 2008, 47, 9592–9605.
(12) (a) Gibson, D. H.; Mandal, S. K.; Owens, K.; Richardson, J. F.
Organometallics 1990, 9, 1936–1942. (b) Alvarez, C.; Parlier, A.; Rudler,
H.; Yefsah, R.; Daran, J. C.; Knobler, C. Organometallics 1989, 8, 2253–
2259. (c) Lage, L. L.; Mancheno, M. J.; Alwarez, R. M.; Gallego, M. J.;
Fernandez, I.; Sierra, M. A. Organometallics 2009, 28, 2762–2772.
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Article
Organometallics, Vol. 29, No. 23, 2010 6419
Scheme 3a
a Ir = blue; Cl = green; N = pink; C = large, gray; H = small, gray.
spectra of the amino-carbene complexes were characterized by
the two doublet resonances arising from the two diastereotopic
protons and the broad NH singlet resonance at ∼10 ppm.
The carbene carbon exhibited a resonance at 220-233 ppm in
the 13C{1H} NMR spectra, as is typical for a transition metal
carbene. The carbene nature of C(3) is indicated by the signifi-
cantly longer Ir-C(1) bond length compared to the Ir-C(3)
bond length, a difference of ∼8σin both 3a and 3b. Interestingly,
both these bonds are longer than the corresponding bonds
formed 5a almost immediately and in good yields, and
subsequent reaction of it with excess alkynes afforded 3 or 4
in similar yields to the one-pot reaction. This latter reaction
t
proceeded more slowly; monitoring the reaction of BuCCH
with 5a showed complete consumption of 5a after about 12 h.
Addition of tBuCCH and an equivalent of 4-methoxyaniline to
a sample of 5a afforded 3a and 3d in a 1:3 ratio, pointing to the
easy dissociation of the aniline ligand from 5a and suggesting
that it acts as an intermediary for the cleavage of 1. A proposed
reaction pathway is shown in Scheme 3. The energetics for this
has also been examined computationally with DFT at the
B3LYP/LANL2DZ level, as for the earlier study, and the
˚
(2.015(3) and 1.930(3) A, respectively) in the most similar
iridacycle, TpPhIr(H)(dCHNMepy). These are presumably a
result of the different bonding nature (soft vs hard) of Cp* vs
TpPh.16 There also appears to be significant double-bond
character in the C-N bonds, however, as the N-C(3) and
computed energies (ΔGo) from B onward (in kJ mol-1) are
9
given.10
˚
Although no kinetic barriers were computed, the negative
or small computed energies involved in the steps suggest that
the reaction pathway is reasonable. With the exception of the
formation of A (or 5) and the final orthometalation step, the
pathway is similar to that proposed earlier for the CtC triple
bond cleavage reaction. Presumably, in the presence of an
excess of the appropriate alkyne, the coordinated aniline is
replaced, and the alkyne species B rapidly rearranges to the
vinylidene complex C. Step III was believed to involve
deprotonation-protonation for the 1,2-shift, and in accord
with that,10 the reaction of 1 with PhCCD and aniline
showed no deuterium incorporation in the product 4a. Step
N-C(2) bond lengths (1.314(8) and 1.398(8) A, and 1.291(11)
˚
and 1.428(12) A, in 3a and 3b, respectively) are significantly
˚
shorter than the N(11)-C(11) bond (1.453(4) A) in 5b. This is
also consistent with the ∼117° C(2)-N-C(3) bond angle,
which is indicative of sp2 hybridization at the N atom.
Mechanistic Considerations. That the reactions afforded 5
in the absence of a large excess of the alkynes suggested that it
may be involved in the reaction pathway. This was shown to
be the case when it was found that the reaction of aniline with 1
(16) Pettinari, C.Scorpionates II: Chelating Borate Ligands; Imperial
College Press: London, 2008.

6420 Organometallics, Vol. 29, No. 23, 2010
Kumaran et al.
Table 2. Amount of Reagent Used, Product Formed, and Elemental Analyses and HRMS Data for Productsa
aniline
C6H5NH2
(9 μL, 100 μmol)
4-MeC6H4NH2
(10.7 mg, 100 μmol)
4-ClC6H4NH2
(12.8 mg, 100 μmol)
4-MeOC6H4NH2
(12.4 mg, 100 μmol)
4-O2NC6H4NH2
(13.8 mg, 100 μmol)
C6H5NH2
(9 μL, 100 μmol)
4-MeC6H4NH2
(10.7 mg, 100 μmol)
4-ClC6H4NH2
alkyne
product (mg, %)
elemental analysis
HRMS
tBuCCH
C22H31ClIrN, 3a (43.7, 81)
Found: C, 48.95; H, 6.08; N, 2.98
Calc: C, 49.19; H, 5.82; N, 2.61
Found: C, 50.23; H, 6.35; N, 2.75
Calc: C, 50.12; H, 6.03; N, 2.54
Found: C, 45.97; H, 5.03; N, 2.12
Calc: C, 46.23; H, 5.29; N, 2.45
Found: C, 48.96; H, 6.05; N, 2.61
Calc: C, 48.70; H, 5.86; N, 2.47
Found: C, 45.09; H, 5.04; N, 4.61
Calc: C, 45.39; H, 5.19; N, 4.81
Found: C, 52.05; H, 4.91; N, 2.64
Calc: C, 51.74; H, 4.88; N, 2.51
Found: C, 52.16; H, 5.41; N, 2.53
Calc: C, 52.57; H, 5.12; N, 2.45
Found: C, 48.91; H, 4.56; N, 2.35
Calc: C, 48.73; H, 4.43; N, 2.37
Found: C, 51.16; H, 4.98; N, 2.51
Calc: C, 51.14; H, 5.05; N, 2.39
Found: C, 48.05; H, 4.25; N, 4.76
Calc: C, 47.87; H, 4.35; N, 4.65
Found: 502.2074
Calc [M - Cl]þ: 502.2087
Found: 516.2247
tBuCCH
tBuCCH
tBuCCH
tBuCCH
PhCCH
PhCCH
PhCCH
PhCCH
PhCCH
C23H33ClIrN, 3b (43.7, 79)
C22H30Cl2IrN, 3c (57.3, 72)
C23H33ClIrNO, 3d (56.9, 81)
C22H30ClIrN2O2, 3e (44.4, 76)
Calc [M - Cl]þ: 516.2243
Found: 536.1682
Calc [M - Cl]þ: 536.1688
Found: 532.2186
Calc [M - Cl]þ: 532.2192
Found: 547.1923
Calc [M - Cl]þ: 547.1937
Found: 522.1765
C
C
C
C
C
24H27ClIrN, 4a (35.8, 64)
25H29ClIrN, 4b (40.7, 71)
24H26Cl2IrN, 4c (40.9, 69)
25H29ClIrNO, 4d (43.0, 73)
24H26ClIrN2O2, 4e (39.3, 65)
Calc [M - Cl]þ: 522.1774
Found: 536.1927
Calc [M - Cl]þ: 536.1931
Found: 556.1362
(12.8 mg, 100 μmol)
4-MeOC6H4NH2
(12.4 mg, 100 μmol)
4-O2NC6H4NH2
(13.8 mg, 100 μmol)
Calc [M - Cl]þ: 556.1376
Found: 552.1872
Calc [M - Cl]þ: 552.1879
Found: 567.1620
Calc [M - Cl]þ: 567.1625
a In all experiments, amounts of reagents used are: 1 (40 mg, 50 μmol), tBuCCH (125 μL, 100 μmol), or PhCCH (110 μL, 100 μmol).
Table 3. 1H and 13C{1H} NMR Data for 3 and 4
compound
1H NMR data
13C{1H} NMR data
3a
1.16 (s, 9H, tBu), 1.77 (s, 15H, Cp*), 2.77 (d, 2JHH = 12.6, 1H,
CH2), 3.64 (d, 1H, CH2), 6.91 (m, 1H, aromatic), 6.99
(m, 1H, aromatic), 7.18 (m, 1H, aromatic), 7.56 (m, 1H,
aromatic), 9.93 (s, 1H, NH)
9.68 (CH3, Cp*), 30.99 (CH3, tBu), 35.36 (C, tBu),
60.00 (CH2), 95.04 (C, Cp*), 112.38, 122.58, 125.35 and
135.53, (aromatic CH), 144.89 and 151.00 (aromatic C),
227.44 (IrdC)
3b
3c
3d
1.15 (s, 9H, tBu), 1.77 (s, 15H, Cp*), 2.34 (s, Me), 2.75
(d, 2JHH = 12.6 Hz, 1H, CH2), 3.61 (d, 1H, CH2), 6.72
(m, 1H, aromatic), 7.07 (m, 1H, aromatic), 7.36 (m, 1H,
aromatic), 9.90 (s, 1H, NH)
9.68(CH3, Cp*), 21.68 (CH3, Ar), 30.98 (CH3, tBu),
35.30 (C, tBu), 59.81(CH2), 94.78 (C, Cp*), 112.09,
123.16, and 136.16 (CH, aromatic), 134.57, 144.92,
and 148.76 (C, aromatic), 225.77 (IrdC)
1.15 (s, 9H, tBu), 1.77 (s, 15H, Cp*), 2.77 (d, 2JHH = 12.8 Hz,
1H, CH2), 3.63 (d, 1H, CH2), 6.90 (m, 1H, aromatic), 7.11
(m, 1H, aromatic), 7.47 (m, 1H, aromatic), 9.91 (s, 1H, NH)
9.66 (CH3, Cp*), 31.00 (CH3, tBu), 35.44 (C, tBu), 60.05
(CH2), 95.30 (C, Cp*), 113.20, 122.43, and 134.81
(CH, aromatic), 129.77, 146.97, and 149.70 (C, aromatic),
227.73 (IrdC)
1.15 (s, 9H, tBu), 1.77 (s, 15H, Cp*), 2.75 (d, 2JHH = 12.6 Hz,
1H, CH2), 3.58 (d, 1H, CH2), 3.82 (s, OMe), 6.48 (m, 1H,
aromatic), 7.11 (m, 1H, aromatic), 7.14 (m, 1H, aromatic),
9.89 (s, 1H, NH)
9.65 (CH3, Cp*), 30.97 (CH3, tBu), 35.19 (C, tBu), 55.56 (OMe),
59.70 (CH2), 94.66 (C, Cp*), 107.29, 112.91, and 120.90
(CH, aromatic), 145.10, 146.92, and 156.88 (C, aromatic),
223.91 (IrdC)
3e
4a
1.17 (s, 9H, tBu), 1.80 (s, 15H, Cp*), 2.80 (d, 2JHH = 12.8 Hz,
1H, CH2), 3.70 (d, 1H, CH2), 7.26 (m, 1H, aromatic), 7.85
(m, 1H, aromatic), 8.41 (m, 1H, aromatic), 10.04 (s, 1H, NH)
1.87 (s, 15H, Cp*), 4.58 (d, 2JHH = 18.8 Hz, 1H, CH2), 4.76
(d, 1H, CH2), 6.84-6.87 (m, 1H, aromatic), 6.95-6.99
(m, 2H, aromatic), 7.27 (m, 2H, aromatic), 7.39-7.46
(m, 3H, aromatic), 7.68 (m, 1H, aromatic), 9.50 (s, 1H, NH)
1.87 (s, 15H, Cp*), 2.34 (s, Me), 4.55 (d, 2JHH = 19.0 Hz,
1H, CH2), 4.73 (d, 1H, CH2), 6.65 (m, 1H, aromatic), 6.87
(m, 1H, aromatic), 7.25-7.27 (m, 2H, aromatic), 7.38-7.48
(m, 4H, aromatic), 9.47 (s, 1H, NH)
9.73 (CH3, Cp*), 31.06 (CH3, tBu), 35.96 (C, tBu), 60.56 (CH2),
96.48 (C, Cp*), 111.53, 120.02, and 130.26 (CH, aromatic),
144.32, 145.49, and 156.62 (C, aromatic), 233.64 (IrdC)
9.65 (CH3, Cp*), 52.80 (CH2), 94.07 (C, Cp*), 113.40,
122.41, 125.60, 128.12, 129.75, 130.39, and 135.28
(CH, aromatic), 134.48, 144.50, and 151.10
(C, aromatic), 224.22 (IrdC)
9.65 (CH3, Cp*), 21.66 (CH3, Ar), 52.75 (CH2),
93.83 (C, Cp*), 113.04, 123.01, 128.13, 129.71,
130.38, 134.72, 134.86, 135.93, 144.58, and
148.92 (aromatic), 222.76 (IrdC)
9.61 (CH3, Cp*), 52.88 (CH2), 94.30 (C, Cp*),
114.26, 122.19, 128.29, 129.79, 130.20, 130.35,
134.32, 134.56, 146.79, and 149.76 (aromatic),
225.14 (IrdC)
9.61 (CH3, Cp*), 52.53 (CH2), 55.48 (OMe), 93.75
(C, Cp*), 107.09, 113.91, 120.63, 128.12, 129.69,
and 130.39 (CH, aromatic), 134.67, 145.21, 146.57,
and 157.00 (C, aromatic), 220.88 (IrdC)
4b
4c
4d
4e
1.86 (s, 15H, Cp*), 4.55 (d, 2JHH = 19.2 Hz, 1H, CH2), 4.72
(d, 1H, CH2), 6.82 (m, 1H, aromatic), 6.91 (m, 1H, aromatic),
7.25 (m, 2H, aromatic), 7.39-7.46 (m, 3H, aromatic), 7.58
(m, 1H aromatic), 9.53 (s, 1H, NH)
1.87 (s, 15H, Cp*), 3.82 (s, OMe), 4.54 (d, 2JHH = 19.0 Hz,
1H, CH2), 4.70 (d, 1H, CH2), 6.41 (m, 1H, aromatic), 6.91
(m, 1H, aromatic), 7.24-7.27 (m, 3H, aromatic), 7.38-7.45
(m, 3H, aromatic), 9.46 (s, 1H, NH)
1.89 (s, 15H, Cp*), 4.58 (d, 2JHH = 19.0 Hz, 1H, CH2), 4.78
(d, 1H, CH2), 7.08 (m, 1H, aromatic), 7.25-7.27 (m, 2H,
aromatic), 7.40-7.48 (m, 3H, aromatic), 7.76 (m, 1H, aromatic),
8.51 (m, 1H, aromatic), 9.78 (s, 1H, NH)
9.65 (CH3, Cp*), 53.58 (CH2), 95.35 (C, Cp*),
113.01, 113.51, 119.48, 126.51, 128.52, 129.92,
130.31, 133.94, 144.47, 145.53, and 156.73
(aromatic), 231.29 (IrdC)
IV, from C to the proposed amino-carbene complex inter-
mediate D, is a hydroamination step and also has an analogue
for this step: A nucleophilic attack by aniline at the vinylidene
R-carbon atom (to a zwitterions) followed by proton transfer
(may be intramolecular or intermolecular)6g or via a concerted
process involving a four-membered transition state.6b That the
reaction solvent is rather nonpolar tends to disfavor the first
alternative, although it cannot be ruled out at this point.
in the CtC triple bond cleavage reaction. The ΔGoassociated
with this step in both reactions (an alkyne hydroamination
9
vs a hydration) are also comparable: -36 and -69 kJ mol-1
respectively. There are at least two alternative mechanisms
,

Article
Organometallics, Vol. 29, No. 23, 2010 6421
Isotopic labeling experiments employing (a) aniline and
tBuCCH in the presence of D2O, (b) d7-aniline and tBuCCH,
and (c) d5-aniline and tBuCCH afforded 3a with both, one, or
none, respectively, of the diastereotopic CH2 protons being
deuterated. These results are consistent with the source for
each of these protons being water and aniline; an intermolec-
ular proton transfer for step IV is therefore unlikely, as that
would be expected to involve water or free aniline.
Similar procedures were used with the other alkynes and
anilines, and these are summarized in Tables 2 and 3.
Crystallographic Studies. Diffraction quality crystals were
grown by slow cooling from dichloromethane and then mounted
ontoquartz fibres. X-ray data were collected at 223 K on a Bruker
X8 APEX system, using Mo KR radiation, with the SMART
suite of programs.19 Data were processed and corrected for
Lorentz and polarization effects with SAINT,20 and for absorp-
tion effects with SADABS.21 Structural solution and refinement
were carried out with the SHELXTL suite of programs.22
The structures were solved by direct methods to locate the
heavy atoms, followed by difference maps for the light, non-
hydrogen atoms. The amine hydrogens were located via low-
angle difference maps and refined, while the organic hydrogen
atoms were placed in calculated positions and refined with a
riding model. A disordered dichloromethane solvate was found
in 3b, which was modeled over two symmetry-related sites with a
total occupancy of 0.25 and appropriate restraints placed. All
non-hydrogen atoms were given anisotropic displacement param-
eters in the final model.
Computational Studies. The reaction energetics were studied
using DFT theory utilizing Becke’s three-parameter hybrid
function23 and Lee-Yang-Parr’s gradient-corrected correla-
tion function24 (B3LYP), together with the LanL2DZ (Los
Alamos effective core potential double-ζ) basis set. Spin-re-
stricted calculations were used for geometry optimization, and
harmonic frequencies were then calculated to characterize the
stationary points as equilibrium structures with all real frequen-
cies and to evaluate zero-point energy (ZPE) corrections. All
calculations were performed using the Gaussian 03 suite of
programs.25
The final step is an orthometalation,6a and the ΔG9ohas been
computed to be þ1.9 kJ mol-1; this would most certainly
become considerably negative in the presence of moisture
(ΔG298 for formation of hydrochloric acid is about -96 kJ
mol )
-1 17 and is probably the driving force for the reaction.
Concluding Remarks
In this study, we have reported a facile synthetic route to
amino-carbene derivatives of iridium(III) from the reaction
of anilines and terminal alkynes with the readily available
dinuclear species [Cp*IrCl2]2. Deuteration and computa-
tional studies suggest that the reaction pathway is very
similar to that followed in the CtC triple bond cleavage
reaction with water and involves a hydroamination step.
Further work to examine the extension of this synthetic
methodology to other heteroatom-substituted carbenes, as
well as cleavage of the carbene fragment, is underway.
Experimental Section
General Procedures. All reactions and manipulations, except
for TLC separations, were performed under argon by using
standard Schlenk techniques. The starting material 1 was pre-
Acknowledgment. This work was supported by Nanyang
Technological University and the Ministry of Education
(Research Grant No. T208B1111), and one of us (E.K.)
thanks the University for a Research Scholarship.
pared according to the published method.18 All other chemicals
were from commercial sources and used as supplied without
further purification. 1H and 13C{1H} NMR spectra were re-
corded in CDCl3 on a JEOL ECA400 or ECA400SL spectrom-
eter and were referenced to residual solvent resonances. High-
resolution mass spectra (HRMS) were recorded in ESI mode on
a Waters UPLC-Q-TOF mass spectrometer. Elemental analyses
were performed by the microanalytical laboratory in NTU.
Reaction of 1 with Alkyne and Aniline. In a typical reaction, to
a solution of 1 (40 mg, 50 μmol) and 3,3-dimethyl-1-butyne (125
μL, 20-fold excess) in 1,2-dichloroethane (4 mL) was added
aniline (9 μL, 100 μmol). There was an immediate color change
from bright orange to yellow, and upon overnight stirring, it
turned orange. The solvent was then removed under reduced
pressure, and the residue obtained was dissolved in the mini-
mum amount of dichloromethane for chromatographic separa-
tion on silica gel TLC plates. Elution with hexane/ethylacetate
(3:2, v/v) yielded 3a as a yellow solid.
Supporting Information Available: Crystallographic data in
CIF format, experimental details and characterization for other
amino-carbene complexes, and details of deuterium labeling
experiments. This material is available free of charge via the
Internet at http://pubs.acs.org.
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Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
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€
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