Infrared spectra of XCIrX3 and CX2IrX2 prepared by reactions of laser-ablated iridium atoms with halomethanes

Article abstract of DOI:10.1039/c002347g

Small iridium high oxidation-state complexes with carbon-iridium multiple bonds are identified in the product matrix infrared spectra from reactions of laser-ablated Ir atoms with tetra-, tri- and dihalomethanes. In contrast to the previously studied Rh case, Ir carbyne complexes (XCIrX₃) are generated in reactions of tetrahalomethanes, and their short Ir-C bond lengths of 1.725-1.736 A are appropriate for the carbon-metal triple bonds. DFT calculations also show that the Ir carbynes with an Ir-F bond have unusual square planar structures, similar to the recently discovered Ru planar complexes. Diminishing preference for the carbyne complexes leads to methylidene product absorptions in the tri- and dihalomethane spectra, marking a limit for generation of small metal carbynes. The insertion complexes, on the other hand, are not observed in this study, suggesting that X migration from C to Ir following initial C-X insertion is swift.

Full text of DOI:10.1039/c002347g

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≡
=
Infrared spectra of XC IrX3 and CX2 IrX2 prepared by reactions of
laser-ablated iridium atoms with halomethanes†
Han-Gook Cho and Lester Andrews*
Received 4th February 2010, Accepted 13th April 2010
First published as an Advance Article on the web 5th May 2010
DOI: 10.1039/c002347g
Small iridium high oxidation-state complexes with carbon–iridium multiple bonds are identified in the
product matrix infrared spectra from reactions of laser-ablated Ir atoms with tetra-, tri- and
≡
dihalomethanes. In contrast to the previously studied Rh case, Ir carbyne complexes (XC IrX3) are
˚
generated in reactions of tetrahalomethanes, and their short Ir–C bond lengths of 1.725–1.736 A are
appropriate for the carbon–metal triple bonds. DFT calculations also show that the Ir carbynes with an
Ir–F bond have unusual square planar structures, similar to the recently discovered Ru planar
complexes. Diminishing preference for the carbyne complexes leads to methylidene product absorptions
in the tri- and dihalomethane spectra, marking a limit for generation of small metal carbynes. The
insertion complexes, on the other hand, are not observed in this study, suggesting that X migration
from C to Ir following initial C–X insertion is swift.
In this study, reactions of iridium with halomethanes have
Introduction
been carried out, and the products are identified in the matrix Ir
spectra through isotopic substitution and with helpful predictions
from DFT calculations for the plausible products. It turns out
that not only iridium carbynes are produced along with the
carbene primary products, but some of the Ir carbynes also bear
unique square planar structures. The gradual decreasing trend in
preference for higher oxidation-state complexes on moving away
from W, Re, and Os is re-confirmed.4–8,10,11
Coordination chemistry has been enriched with numerous transi-
tion metal complexes containing carbon–metal multiple bonds.1
Many of them are reaction intermediates, C–H insertion agents,
and important catalysts for metathesis reactions, and therefore
understanding their synthesis, reactivity, properties, and structures
is ever more important.2 While various transition metal–carbene
complexes and transient species have been introduced through
well established routes, carbyne complexes are relatively rare,
particularly for the early and late transition metals other than
those in Groups 6–8. Only a few Group 9 metal carbynes with
carbon–metal triple bonds have been reported.3
Experimental and computational methods
Laser ablated iridium atoms were reacted with CCl4 (Fisher),
13CCl4 (90% enriched, MSD Isotopes), CFCl3, CF2Cl2 (Dupont),
CHCl3, CH2Cl2, CH2FCl, CH2F2, CDCl3, CD2Cl2 (MSD Iso-
topes), CD2FCl and CD2F2 (synthesized12) in excess argon during
condensation at 10 K using a closed-cycle refrigerator (Air
Products Displex). These methods have been described in detail
in previous publications.3,13 Reagent gas mixtures are typically
0.5% in argon. The Nd:YAG laser fundamental (1064 nm, 10 Hz
repetition rate, 10 ns pulse width) was focused on a rotating
metal target (Ir, 99.99%, Johnson-Matthey) using 5–10 mJ/pulse.
After initial reaction, infrared spectra were recorded at 0.5 cm-1
resolution using a Nicolet 550 spectrometer with a Hg-Cd-Te
range B detector. Then samples were irradiated for 20 min periods
by a mercury arc street lamp (175 W) with the globe removed
using a combination of optical filters and annealed to allow further
reagent diffusion.
To provide support for the assignment of new experimen-
tal frequencies and to correlate with related studies,4–9 density
functional theory (DFT) calculations were performed using the
Gaussian 03 program system,14 the B3LYP density functional,15
the 6-311++G(3df,3pd) basis sets for C, F, Cl16 and the SDD
pseudopotential and basis set17 for Ir to provide vibrational
frequencies for the reaction products. Geometries were fully
relaxed during optimization, and the optimized geometry was
Recently a series of small transition metal complexes, many of
which contain carbon–metal multiple bonds, has been provided
through reactions of metal atoms with small hydrocarbons
and halomethanes, via C–H(X) insertion and subsequent H(X)
migration.4–9 These metal complexes show interesting reactions,
unique structures, photochemistry, and electronic properties and
also offer new model systems to understand the chemistry for
much larger high oxidation-state complexes.10 Like their larger
cousins, small carbenes are more common than carbynes. While
the W, Re, and Os complexes with C–M triple bonds are
preferentially produced,4,6,7 the carbyne products become less
favored on moving left from them in the periodic table.4,5 Small
Group 3–5 metal carbynes have been identified, whereas Group
10 metals do not form products with C–M triple bonds.8 More
recently it has been reported that the Group 9 metal Rh forms
small amounts of carbyne products as well as the primary carbene
complexes.11
Department of Chemistry, University of Incheon, 177 Dohwa-dong, Nam-ku,
Incheon, 402-749, South Korea, and Department of Chemistry, University of
Virginia, P. O. Box 400319, Charlottesville, Virginia, 22904-4319. E-mail:
lsa@virginia.edu
† Electronic supplementary information (ESI) available: Tables S1 to S6 of
calculated product frequencies. See DOI: 10.1039/c002347g
5478 | Dalton Trans., 2010, 39, 5478–5489
This journal is
The Royal Society of Chemistry 2010
©

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confirmed by vibrational analysis. The BPW9118 functional was
also employed to complement the B3LYP results. The vibra-
tional frequencies were calculated analytically, and zero-point
energy is included in the calculation of binding and reaction
energies. Previous investigations have shown that DFT calculated
harmonic frequencies are usually slightly higher than observed
frequencies,4–9,19,20 and they provide useful predictions for infrared
spectra of new molecules.
uv (240 < l < 380 nm) irradiation, and increase back to double
the original intensity on the following visible irradiation. On the
other hand, the weak y absorptions almost disappear on visible
irradiation, but re-emerge on uv irradiation, suggesting that the
products responsible for the m and y absorptions interconvert into
each other on visible and uv irradiations. Both m and y absorptions
sharpen in the early stage of annealing.
Two strong m absorptions at 994.4 and 826.3 cm-1 are observed
in the C–Cl stretching region,21 and the satellites at 991.3 and
824.5 cm-1 with 2/3 of the main band absorption intensities are
believed to arise from chlorine isotopic splitting (one 35Cl and
one 37Cl vs. two 35Cl atoms). Absorptions produced previously
Results and discussion
Reactions of iridium atoms with halomethanes were investigated,
and the infrared spectra (Fig. 1–6) and density functional calcu-
lated frequencies (Tables 1–4) of the products and their structures
(Fig. 7 and 8) will be presented in turn.
through vacuum ultraviolet irradiation at 1036.4 cm-1 (CCl3 ),22
+
1019.3, 926.7, 501.9 cm-1 (Cl2CCl–Cl),23 and 898 cm-1 (CCl3)24
were also observed, which are common to all laser-ablated metal
experiments with CCl4 as a result of ablation plume photolysis.11
A similar experiment with 13CCl4 (90% enriched) shifted the new
absorptions to 958.6 and 800.8 cm-1 (with satellites at 955.5 and
798.7 cm-1) (12/13 isotopic frequency ratios of 1.0363 and 1.0318).
The weak 12C product band at 826.3 cm-1 with about 1/10 of
the 13C product band absorbance suggests single carbon atom
participation in the vibrational mode (the other one at 994.4 cm-1
is believed to be covered by precursor absorption).
Ir + CCl4
Fig. 1 shows the reaction product spectra from laser-ablated Ir
atoms co-deposited with carbon tetrachloride in excess argon
during condensation at 10 K. Two groups of product absorptions
marked “m” and “y” (for methylidene and methylidyne) are
observed. The product absorptions are grouped on the basis of
the intensity variation on photolysis and annealing. The strong m
absorptions double in concert on visible (l > 420 nm) irradiation,
but decrease dramatically to ~70% of the original intensity on
The two strong m product absorptions in the C–Cl stretching
region, parallel to those in the previously studied late transition
metals cases,7,8,11 are strong evidence for formation of a primary
product with a CCl2 moiety generated during co-deposition
of the laser-ablated iridium atoms and CCl4. On the basis
of our previous experience for reactions of metal atoms with
hydrocarbons and halomethanes,4–9,11 they are assigned to the
=
symmetric and antisymmetric CCl2 modes of CCl2 IrCl2. The
DFT computed frequencies and isotopic shifts for the doublet
ground state correlate well with the observed frequencies as shown
in Table 1; for example, the B3LYP frequencies of 987.0 and
803.4 cm-1 and their 13C isotopic shifts of 36.5 and 25.9 cm-1
are compared with the observed frequencies and isotopic shifts
(35.8 and 25.5 cm-1). The slightly lower DFT frequencies than the
experimental values are also observed for the late transition metal
tetrahalomethylidenes in our previous studies, presumably due to
underestimation by the DFT methods for the late transition metal
bond strengths.
Also noticeable are the higher frequency and larger 12/13
isotopic frequency ratio of the symmetric CCl2 stretching band.
The symmetric stretching mode is in fact a combination of CCl2
and C–Ir stretching, where C vibrates back and forth between
heavy Ir and two Cl atoms,8a–c leading to the high frequency and
large 13C shift. The 12/13 frequency ratios of CCl2 symmetric
and antisymmetric stretching bands (1.0363 and 1.0318) are very
close to those of the corresponding Group 10 metal and Rh
methylidenes with the differences less than 0.002 and 0.001.8,11
Another m absorption at 410.7 cm-1 near our observation limit (not
shown in Fig. 1) exhibits a very small 13C shift of 1.0 cm-1 and is
designated to the IrCl2 antisymmetric stretching mode. The other
vibrational bands of the Ir methylidene are all too weak to observe
(Table 1). The observed two strong (symmetric and antisymmetric
CCl2 stretching) absorptions and their 13C counterparts, which
are consistent with the DFT results, substantiate formation of the
Fig. 1 Infrared spectra in the 1400–700 cm-1 region for the reaction
products of the laser-ablated iridium atom with CCl4 isotopomers in excess
argon at 10 K. (a) Ir and CCl4 (0.5% in argon) co-deposited for 1 h. (b) as
(a) after visible (l > 420 nm) irradiation, (c) as (b) after uv (240–380 nm)
irradiation, and (d) as (c) after visible irradiation, and (e) as (d) after
annealing to 28 K. (f) Ir and 13CCl4 reagent (0.5% in argon) co-deposited
for 1 h, (g) as (f) after uv irradiation, (h) as (g) after visible irradiation,
(i) as (h) after uv irradiation, (j) as (i) after visible irradiation, and (k) as
(j) after annealing to 36 K. y and m designate the product absorptions
while P and c stand for the precursor and common precursor product
absorptions. Cl2CCl–Cl is produced in CCl4 reactions due to the ablation
plume irradiation.
=
Ir methylidene, CCl2 IrCl2, via C–Cl bond insertion by Ir and
subsequent Cl migration from C to Ir.
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Dalton Trans., 2010, 39, 5478–5489 | 5479
©

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2
a
=
Table 1 Observed and calculated fundamental frequencies of CCl2 IrCl2 in the ground A2 state
13
=
=
CCl2 IrCl2
CCl2 IrCl2
Approximate description
Obsb
B3LYPc
Intc
BPW91d
Intd
Obsb
B3LYPc
Intc
BPW91d
Intd
A1 CCl2 s. str.
B2 CCl2 as. str.
B1 CCl2Ir deform
A1 C–Ir str.
B1 IrCl2 as. str.
A1 IrCl2 s. str.
A1 CCl2 scis.
B2 CCl2 rock
A1 IrCl2 scis.
B1 IrCl2 rock
B2 IrCl2 wag
A2 CCl2 tort.
994.4, 991.3
826.3, 824.5
987.0
803.4
472.1
428.3
385.5
367.6
230.0
209.2
111.2
79.2
298
182
1
973.5
766.4
454.1
418.4
389.2
371.6
224.7
203.0
112.0
80.7
277
181
1
8
70
9
1
0
0
0
958.6, 955.5
800.8, 798.7
950.5
777.5
454.7
428.1
385.5
367.5
230.0
208.2
111.2
79.2
277
171
1
937.5
741.7
437.4
418.2
389.2
371.6
224.7
202.1
111.9
80.7
257
169
1
7
70
9
1
0
0
0
6
6
89
12
0
0
0
0
1
0
89
12
0
0
0
0
1
0
75.5
19.2
77.8
25.3
0
0
75.5
19.2
77.8
25.3
0
0
a Frequencies and intensities are in cm-1 and km mol-1. b Observed in an argon matrix, and the stronger one in an absorption pair is bold. c Computed
d
=
with B3LYP/6-311++G(3df,3pd). Computed with BPW91/6-311++G(3df,3pd). CCl2 IrCl2(D) has a C2v structure, and the symmetry notations are
based on the structure.
2
a
≡
Table 2 Observed and calculated fundamental frequencies of CCl IrCl3 in the A¢ ground state
13
≡
≡
CCl IrCl3
CCl IrCl3
Approximate description
Obsb
B3LYPc
Intc
BPW91d
Intd
Obsb
B3LYPc
Intc
BPW91d
Intd
A¢ Cl–C–Ir s. str.
A¢ Cl–C–Ir as. str.
A¢¢ IrCl2 as. str.
A¢ IrCl2 s. str.
1289.3, 1283.8
1283.8
476.8
366.4
359.4
342.7
337.8
292.9
136.1
104.4
97.9
320
26
27
9
68
4
23
0
5
1264.0
466.3
354.9
353.7
332.2
331.6
286.2
134.3
95.6
272
31
50
7
38
5
19
0
0
1244.0, 1238.4
1237.4
469.7
359.5
358.7
336.7
336.4
288.1
136.1
104.4
97.8
299
24
53
9
26
21
22
0
5
1
2
1
1218.4
459.5
352.1
353.3
322.6
330.5
281.1
134.2
95.5
254
29
67
7
21
6
18
0
0
A¢¢ ClCIr oop bend
A¢ Ir–Cl str.
A¢ ClCIr ip bend
A¢ IrCl2 wag
A¢ CCl3 deform
A¢¢ IrCl2 rock
1
2
1
88.9
53.2
19.0
7
1
4
88.9
53.2
19.0
7
1
4
A¢ IrCl2 scis.
53.9
43.8
54.0
43.8
A¢¢ CCl3 deform
a Frequencies and intensities are in cm-1 and km mol-1. b Observed in an argon matrix, and the stronger one in an absorption pair is bold. c Computed with
B3LYP/6-311++G(3df,3pd). d Computed with BPW91/6-311++G(3df,3pd). CCl IrCl3(D) has a Cs structure, and the symmetry notations are based on
≡
the structure.
Another product absorption marked “y”, which is considerably
weaker than the m absorptions, is observed at 1283.8 cm-1 (with a
satellite at 1289.3 cm-1), and 13C substitution shifts it to 1238.4 cm-1
(with a satellite at 1244.0 cm-1) (12/13 isotopic frequency ratio
of 1.0367). Our previous results with Group 4–8 metal reactions
with halomethanes show that a higher C–X stretching frequency
normally originate from a higher oxidation-state complex.4–8,11 The
y absorption is assigned to the Cl–C–Ir antisymmetric stretching
fact combinations of the Cl–C and C–M stretching modes, the
higher antisymmetric and lower symmetric stretching frequencies
indicate that the extent of coupling is higher in the Ir carbyne.
This leads to more C participation in the antisymmetric stretching
mode, also giving a larger 13C shift.
Unlike Group 6–8 metal cases,4,6,7 only a few Group 9 metal
complexes with C–M triple bond have been reported,3,11 and
therefore, these small Ir and Rh carbynes provide valuable
opportunities to investigate their chemistry and testing grounds
for theoretical approaches. Generation of small Group 9 carbynes
also re-confirms that reactions of laser-ablated metal atoms with
organic species are efficient routes to provide high oxidation-state
complexes and the matrix Ir spectra allow close examination of
the vibrational characteristics.4–9,11
≡
mode of the Ir methylidyne product, ClC IrCl3. In the vibrational
mode, the carbon atom vibrates back and forth between the
Cl and Ir atoms, leading to the exceptionally high frequency.
The observed frequency and relatively large 13C shift (1283.8 and
45.3 cm-1) match almost perfectly with the B3LYP values of 1283.8
and 45.4 cm-1 as shown in Table 2, supporting formation of the
Ir carbyne complex. The symmetric Cl–C–Ir stretching band is
predicted at 477 cm-1, which is too weak to observe.
In contrast, the tetrachloro Ir insertion complex, CCl3–IrCl,
is not identified in the product matrix spectra, which would
have three strong symmetric and antisymmetric CCl3 stretching
absorptions in the 780–600 cm-1 region. The relatively weak
y absorptions and absence of the insertion product are consistent
≡
Formation of ClC IrCl3 is in line with the recent observation of
≡
ClC RhCl3, whose Cl–C–Rh antisymmetric stretching frequency
and its 13C shift are 1118.4 and 37.8 cm-1, and its Cl–C–Rh
symmetric stretching band is predicted at 539 cm-1. Because the
Cl–C–M antisymmetric and symmetric stretching modes are in
≡
=
with the DFT results; ClC IrCl3, CCl2 IrCl2, and CCl3–IrCl
in the doublet, doublet, and quartet ground states are 96, 113,
5480 | Dalton Trans., 2010, 39, 5478–5489
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and 61 kcal mol-1 more stable than the reactants (Ir(4F) + CCl4).
Attempts for optimization of the insertion complex in the doublet
electronic state all end up with the allene-type staggered structure
of CCl2 IrFCl, where C vibrates back and forth between Cl2 and
Ir. While the strong CCl2 antisymmetric stretching band expected
at ~790 cm-1 is believed to be covered by precursor absorption,
another m¢ absorption at 611.5 cm-1 is assigned to the Ir–F
stretching mode. They again correlate excellently with the DFT
values (e.g. B3LYP frequencies of 990.3 and 614.5 cm-1) as shown
in Table 4, supporting production of the Ir–F bond containing
=
=
of CCl2 IrCl2 shown in Fig. 8. These results indicate that initial C–
Cl bond insertion by Ir is instantaneously followed by Cl migration
=
from C to Ir, forming more stable CCl2 IrCl2, and another Cl
≡
migration eventually leads to ClC IrCl3.
=
methylidene, CCl2 IrFCl.
=
=
Formation of both CFCl IrCl2 and CCl2 IrFCl reflects their
relatively close energies (107 and 91 kcal mol-1 more stable than
the reactants (Ir(4F) + CFCl3)). Normally the high oxidation-state
complexes with a smaller number of M–F bonds are more favored
because of the higher dissociation energy of the C–F bond than
that of the C–Cl bond (117 vs. 63 kcal mol-1).25 The present result
reveals that the Ir–F bond is substantially stronger than the Ir–Cl
bond, compensating the energy difference between the C–F and
C–Cl bonds. Computations show that IrF2 and IrCl2 are 162
and 107 kcal mol-1 more stable than the reactants (Ir(4F) + F2
and Ir(4F) + Cl2) with B3LYP/6-311++G(3df,3pd).
Both y and y¢ absorptions are also observed in the Ir + CFCl3
spectra, both of which almost disappear on visible irradiation
(as the m and m¢ absorptions increase 40%), increase to about
twice the original intensities (as the m and m¢ absorption decrease
to the original intensity), and slightly decrease in the following
Ir + CFCl3 and Ir + CF2Cl2
Fig. 2 shows infrared spectra from reactions of Ir atoms with the
chlorofluorocarbones (CFC). In the CFCl3 spectra, two groups of
m absorptions (m and m¢) are observed, both of which increase in
concert ~40% on visible irradiation, decrease back to the original
intensity on uv, and increase ~15% on full arc irradiation. Parallel
to the CCl4 case, the m absorptions at 1204.0 and 958.4 cm-1 in
the C–F and C–Cl stretching regions21 suggest that a primary
product with a CFCl moiety is formed in reaction of Ir with
=
CFCl3, which is most probably CFCl IrCl2. The C–F and C–
Cl stretching bands are the two observably strong bands for the Ir
carbene complex as shown in Table 3, and they are also in good
agreement with the DFT computed values (e.g. B3LYP values of
1211.2 and 946.4 cm-1). In contrast, the m¢ absorption observed
at 999.0 cm-1 is assigned to the CCl2 symmetric stretching mode
Fig. 2 Infrared spectra in the 1700–900 and 700–500 cm-1 regions for the reaction products of the laser-ablated iridium atom with CF2Cl2 and CFCl3
in excess argon at 10 K. (a) Ir and CFCl3 (0.5% in argon) co-deposited for 1 h, (b) as (a) after visible irradiation, (c) as (b) after uv irradiation, (d) as (c)
after full arc (l > 220 nm) irradiation, and (e) as (d) after annealing to 28 K. (f) Ir and CF2Cl2 reagent (0.5% in argon) co-deposited for 1 h, (g)–(j) as
(f) spectra taken following the same irradiation and annealing sequence. y and m designates the product absorption groups while P and c stand for the
precursor and common absorptions. “w” and “CH4” indicate the water and methane absorptions. Methane is produced due to cracking of vacuum oil
vapor.
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Dalton Trans., 2010, 39, 5478–5489 | 5481
©

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2
2
a
=
=
Table 3 Observed and calculated fundamental frequencies of CFCl IrCl2 and CF2 IrCl2 in the ground A2 and A¢¢ state
=
=
CFCl IrCl2
CF2 IrCl2
Approximate description Obsb B3LYPc Intc
BPW91d
Intd
Approximate description Obsb
B3LYPc Intc
BPW91d
Intd
A¢ C–F str.
1204.0
958.4
1211.2
946.4
526.5
525.6
350.1
385.5
371.2
224.6
113.6
85.9
392
297
6
0
0
90
11
0
0
0
1165.1
910.1
513.6
505.0
343.3
387.9
372.9
219.4
114.0
88.4
374
258
9
0
2
71
8
0
0
0
A1 CF2 s. str.
B2 CF2 as. str.
A1 CF2 scis.
B1 CF2Ir deform
A1 C–Ir str.
B1 IrCl2 as. str.
A1 IrCl2 s. str.
B2 CF2 rock
A1 IrCl2 scis.
B1 IrCl2 rock
B2 IrCl2 wag
A2 CF2 tort.
1292.7
covered
1299.3
1205.1
720.3
595.4
394.6
386.0
367.4
320.4
115.7
88.5
724
199
2
3
4
92
2
0
0
0
1255.0
1128.3
692.6
568.6
390.5
389.4
370.1
313.7
117.2
92.1
654
186
0
1
7
72
0
0
0
0
A¢ C–Cl str.
A¢ C–Ir str.
A¢¢ CFCl wag
A¢¢ IrCl2 as. str.
A¢ IrCl2 s. str.
A¢ FCIr bend
A¢ ClCIr bend
A¢ IrCl2 bend
A¢¢ IrCl2 rock
A¢ IrCl2 wag
A¢¢ CFCl tort
77.7
4.2
1
0
80.4
20.7
0
0
80.3
30.6
1
0
83.1
18.2
0
0
a Frequencies and intensities are in cm-1 and km mol-1. b Observed in an argon matrix. c Computed with B3LYP/6-311++G(3df,3pd). d Computed with
=
=
BPW91/6-311++G(3df,3pd). CF2 IrCl2(D) and CFCl IrCl2(D) have C2v and Cs structures.
2
2
a
=
=
Table 4 Observed and calculated fundamental frequencies of CCl2 IrFCl and CFCl IrFCl in the ground A and A¢¢ states
Approximate
description
Approximate
description
=
=
CCl2 IrFCl
CFCl IrFCl
Obsb
B3LYPc
Intc
BPW91d
Intd
Obsb
B3LYPc
Intc
BPW91d
Intd
A¢ CCl2 s. str.
A¢¢ CCl2 as. str.
A¢ Ir–F str.
999.0
covered
611.5
990.3
804.9
614.5
477.0
428.5
384.4
232.3
213.2
150.0
107.2
87.7
267
181
130
1
6
38
0
0
0
2
0
976.8
770.6
605.8
459.4
419.1
388.0
227.0
207.7
145.8
106.3
88.7
251
179
108
1
7
29
1
0
0
1
0
C–F str.
C–Cl str.
covered
962.1
612.6
1218.2
950.9
615.6
535.7
524.7
387.1
353.4
228.2
157.5
107.1
94.4
361
292
127
1
5
38
2
1
1
3
0
1168.3
913.6
606.0
516.0
508.1
390.6
345.5
222.9
144.2
108.7
94.7
351
249
107
5
3
29
3
1
0
1
0
CFCl scis.
CFClIr deform
C–Ir str.
IrFCl as. str.
IrFCl s. str.
CFCl rock
IrFCl scis.
IrFCl rock
IrFCl wag
CFCl tort.
A¢ CCl2 wag
A¢ C–Ir s. str.
A¢ Ir–Cl str.
A¢ CCl2 scis.
A¢¢ CCl2 rock
A¢ IrFCl bend
A¢¢ IrFCl wag
A¢ IrFCl rock
A¢¢ CCl2 tort
11.1
0
20.6
0
9.1
0
20.1
0
a Frequencies and intensities are in cm-1 and km mol-1. b Observed in an argon matrix. c Computed with B3LYP/6-311++G(3df,3pd). d Computed with
=
=
BPW91/6-311++G(3df,3pd). CFCl IrFCl(D) and CFCl IrCl2(D) have C1 and Cs structures.
=
≡
≡
full arc irradiation. The unusually high frequencies of the y and y¢
absorptions (1545.4 and 1316.7 cm-1) indicate that parallel to the
Ir + CCl4 case, higher oxidation-state complexes are generated
in reaction of CFCl3 as well. We assign them to the F–C–Ir
CCl2 IrFCl, FC IrCl3, and ClC IrFCl2 in their doublet ground
states are 107, 91, 84, and 88 kcal mol-1 more stable than the
reactants (Ir(4F) + CFCl3), respectively, whereas CFCl2–IrCl in
the quartet ground state, which is not observed, is 55 kcal mol-1
more stable. Geometry optimization of the Ir insertion complexes
in the doublet state all lead to those of the methylidenes.
≡
and Cl–C–Ir antisymmetric stretching modes of FC IrCl3 and
≡
ClC IrFCl2 in their doublet ground states, whose frequencies
are remarkably higher than normal C–F and C–Cl stretching
frequencies.
Fig. 2 also shows the product spectra of Ir + CF2Cl2, a strong
m absorption at 1292.7 cm-1 is observed along with the weaker m¢
absorptions at 962.1 and 612.6 cm-1. The m absorption in the C–F
stretching region shows a slight increases on visible irradiation but
increases ~ 40% on uv irradiation and further increase to twice
the original intensity on full arc irradiation. The m absorption at
1292.7 cm-1 is assigned to the CF2 symmetric stretching mode of
The low X–C–Ir symmetric stretching frequencies are also
observed. The weak y and y¢ absorptions at 629.4 and 607.3 cm-1
are designated to the X–C–Ir symmetric stretching modes of
≡
≡
FC IrCl3 and ClC IrFCl2. The observed frequencies of y and
y¢ absorptions are in good agreement with the B3LYP computed
-1
≡
≡
=
values for FC IrCl3 (1573.8 and 630.3 cm ) and ClC IrFCl2
(1332.5 and 595.8 cm-1) as shown in Tables S1 and S2 [ESI†],
substantiating formation of the Ir fluorochloromethylidynes. The
CF2 IrCl2 on the basis of the almost exact match with the B3LYP
value of 1299.3 cm-1 (Table 3). The strong CF2 antisymmetric
stretching band expected at ~1190 cm-1 is unfortunately covered
=
observed F–C–M antisymmetric and symmetric stretching fre-
by precursor absorption, and other CF2 IrCl2 absorptions are all
-1
≡
quency of FC IrCl3 (1545.4 and 629.4 cm ) is also compared with
too weak to observe. The weak m¢ absorptions increase ~30% on
visible irradiation but decrease to half the original intensities on
uv irradiation and slightly recover on full arc irradiation. They
are assigned to the C–Cl stretching and CFCl scissoring modes
≡
the previously reported values for FC RhCl3 (1482.0 (observed)
and 663.1 (predicted) cm-1). These Ir carbynes are energetically
=
slightly higher than the corresponding carbenes; CFCl IrCl2,
5482 | Dalton Trans., 2010, 39, 5478–5489
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=
of CFCl IrFCl while stronger C–F stretching band expected at
are assigned to the F–C–Ir and C–Ir–F antisymmetric stretching
~1200 cm-1 is covered by precursor absorption. The observed
frequencies are compared with the B3LYP computed values of
950.9 and 615.6 cm-1 as shown in Table 4.
modes of FC IrFCl2 on the basis of the excellent agreement with
≡
the B3LYP values of 1662.9 and 610.8 cm-1 as shown in Table S1.†
The y¢ absorptions are designated to the Cl–C–Ir antisymmetric
≡
Parallel to the CCl4 and CFCl3 cases, y absorptions are also
observed at 1635.4 and 619.4 cm-1, and y¢ absorptions at 1318.0
and 629.2 cm-1. The y absorptions almost disappear on visible
photolysis but recover the original intensities on uv photolysis
and halve on full arc photolysis, whereas the y¢ absorptions remain
unchanged on visible irradiation, but nearly double on uv irradia-
tion, and stay unchanged on full arc photolysis. The y absorptions
stretching and IrF2 symmetric stretching mode of CCl IrF2Cl,
whose B3LYP frequencies are 1331.1 and 623.6 cm-1 as shown in
Table S2.† The high frequency y and y¢ absorptions in the CCl4,
CFCl3, and CF2Cl2 spectra showing good agreement with the DFT
≡
values substantiate generation of these Ir methylidynes (XC IrX3)
in reaction with tetrahalocarbons. The insertion products (CF2Cl–
IrCl and CFCl2–IrF) are not identified most probably due to their
Fig. 3 Infrared spectra in the 1250–550 cm-1 region for the reaction products of the laser-ablated iridium atom with CHCl3 isotopomers in excess argon
at 10 K. (a) Ir and CHCl3 (0.5% in argon) co-deposited for 1 h, (b) as (a) after visible irradiation, (c) as (b) after uv irradiation, (d) as (c) after visible
irradiation, and (e) as (d) after annealing to 28 K. (f) Ir and CDCl3 reagent (0.5% in argon) co-deposited for 1 h, (g)–(j) as (f) spectra taken following
the sequence of visible and uv irradiations and annealing to 28 K. (k) Ir and 13CHCl3 reagent (0.5% in argon) co-deposited for 1 h, (l) as (k) after visible
irradiation, (m) as (l) after uv irradiation, and (n) as (m) after annealing to 28 K. m designates a product absorption while P and c stand for the precursor
and common absorptions.
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=
=
≡
high energy. CF2 IrCl2(D), CFCl IrFCl(D), FC IrFCl2(D),
Ir + CHCl3
≡
ClC IrF2Cl(D), CF2Cl–IrCl(Q), and CFCl2–IrF(Q) are 102, 84,
78, 67, 52, and 32 kcal mol-1 more stable than the reactants.
Attempts for geometry optimization for the insertion complexes
in the doublet states all lead to the structure of the corresponding
methylidenes.
The earlier studies show that methylidyne complexes are ex-
clusively produced in reactions of Re and Os with small alkanes
and halomethanes. While the preference for the high oxidation-
state product gradually decreases with moving away from Re
and Os in the periodic table, the second and third row metal
carbynes of Group 4–8 metals have been identified in the matrix
IR spectra from reactions with halomethanes.4–7 Recent studies
reveal that Group 10 metals forms only insertion and methylidene
complexes being consistent with the computation results; while
ClC PtCl3 is estimated to be 27 kcal mol-1 higher in energy
than CCl2 PtCl2, and attempts for optimization of the Ni and
Pd methylidyne complexes end up with the structures of the
corresponding methylidene complexes. Therefore, the Group 9
metals (Ir and Rh) mark a limit where transition metal carbynes
are no longer produced in reactions with halomethanes.
Fig. 3 shows the product absorptions in the infrared spectra
from reactions of Ir with CHCl3 isotopomers. The product
absorptions (all marked with “m”), which are weaker relative to
the tetrahalomethane cases, increase ~30% on visible irradiation,
but they almost disappear on the following uv photolysis. They
slightly recover (~30% increase) on the following visible irradiation
and sharpen up in the early stage of annealing. Therefore, the
relatively weak absorptions in the original spectra are at least
partly due to dissociation by ablation plume uv radiation. The
product absorptions are believed to arise from the methylidene
complex, CHCl IrCl2 on the basis of the stability relative to
other plausible products and good agreement with the predicted
frequencies and isotopic shifts as shown in Table S3.†
The m absorption at 1174.8 cm-1 (with site absorptions at 1185.7
and 1182.2 cm-1) has its D counterpart at 1000.1 cm-1 (H/D
ratio of 1.1747) and 13C counterpart at 1166.2 cm-1 (with site
absorptions at 1177.2 and 1173.9 cm-1) (12/13 ratio of 1.0074).
It is designated to the H–C–Ir bending mode on the basis of the
relatively large D and small 13C shifts. The stronger m absorption
=
≡
=
Fig. 4 Infrared spectra in the 1500–800 cm-1 region for the reaction products of the laser-ablated iridium atom with CH2Cl2 isotopomers in excess argon
at 10 K. (a) Ir and CH2Cl2 (0.5% in argon) co-deposited for 1 h, (b)–(e) as (a) spectra taken following a sequence of visible, uv, and visible irradiations
and annealing to 28 K. (f) Ir and CD2Cl2 reagent (0.5% in argon) co-deposited for 1 h, (g)–(j) as (f) after spectra taken following a sequence of visible,
uv, and visible irradiations and annealing to 36 K. (k) Ir and 13CH2Cl2 reagent (0.5% in argon) co-deposited for 1 h, (l)–(o) as (k) spectra taken following
a sequence of visible, uv, and full arc irradiations and annealing to 28 K. m designates a product absorption while P and c stand for the precursor and
common absorptions. H2CCl–Cl absorption28 is also designated.
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at 914.9 cm-1 (with site absorption at 909.9 cm-1) has its D
counterpart at 775.6 cm-1 (H/D ratio of 1.180) and 13C counterpart
at 888.3 cm-1 (with site absorption at 884.0 cm-1) (12/13 ratio
of 1.030). It is assigned to the Ir–C–Cl antisymmetric stretching
mode, where C vibrates back and forth between Ir and Cl, resulting
in the relatively large 12/13 isotopic frequency ratio. Another
product absorption is observed at 730.3 cm-1 along with the D
counterpart at 601.0 cm-1 (with a site absorption at 604.3 cm-1)
(H/D ratio of 1.215), and on the basis of its frequency and large
H/D ratio, it is assigned to the C–H out-of-plane bending mode.
The 13C counterpart expected at ~720 cm-1 is probably covered by
precursor absorption.
IrCl in the doublet state leads to the structure of CHCl IrCl2,
which shows a possibility that system crossing (quartet → doublet)
=
leads to spontaneous Cl migration from C to Ir from the C–Cl
insertion product. The energy difference of 25 kcal mol-1 between
CHCl IrCl2 and HC IrCl3 is compared with that of 17 kcal mol
between CCl2 IrCl2 and ClC IrCl3. Introduction of C–H bond
makes the carbyne complex more unstable and Cl migration from
C to Ir more difficult as well.
-1
=
≡
=
≡
Ir + CH2X2
Product absorptions from reactions of Ir with CH2Cl2, CH2FCl,
and CH2F2 isotopomers are shown Fig. 4–6, where only carbene
products are observed. The carbene products are also the most
stable among the plausible products from Ir reactions with the
dihalomethanes. In the CH2Cl2 isotopomer spectra (Fig. 4), the
product absorptions (m) increase ~30% on visible irradiation but
decrease to ~50% of the original intensity on uv irradiation and
slightly recover on subsequent visible irradiation. The relatively
weak product absorptions are probably due to dissociation of
Parallel to the previously studied Rh case,11 the insertion and
≡
methylidyne products (CHCl2–IrCl and HC IrCl3) are not iden-
tified in the product spectra, indicating that a tetrahalomethane
is necessary to form a Group 9 metal complex with carbon–
metal triple bond. The present results are also in line with the
=
relative product energies; CHCl IrCl2(D), CHCl2–IrCl(Q), and
-1
≡
HC IrCl3(D) are 101, 54, and 76 kcal mol more stable than the
reactants (Ir(4F) + CHCl3). Geometry optimization for CHCl2–
Fig. 5 Infrared spectra in the 1100–600 cm-1 region for the reaction products of the laser-ablated iridium atom with CH2FCl isotopomers in excess argon
at 10 K. (a) Ir and CH2FCl (0.5% in argon) co-deposited for 1 h, (b)–(e) as (a) spectra taken following a sequence of visible, uv, and full arc irradiations
and annealing to 28 K. (f) Ir and CD2FCl reagent (0.5% in argon) co-deposited for 1 h, (g)–(j) as (f) spectra taken following the same irradiation and
annealing sequence. i and m designate the product absorption groups while P and c stand for the precursor and common absorptions.
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at 918.5 cm-1 on the side of a precursor band is assigned to the
CH2 wagging mode while the D counterpart, which is expected
near 720 cm-1, is probably covered by precursor absorption. The
frequency and negligible D shift of the strong Ir–F stretching
=
band is well reproduced for CH2 IrFCl as shown in Table S5.†
Again the Ir methylidene is the most stable among the plausible
=
≡
products; CH2 IrFCl(D), CH2F–IrCl(Q), and HC IrHFCl(D)
are 73, 44, and 49 kcal mol-1 more stable than the reactants, and
CH2F–IrCl(D) with a bridged structure is 57 kcal mol-1.
The product absorptions from Ir reactions with CH2F2 iso-
topomers are shown in Fig. 6. The m absorptions show no
variation in intensity on visible irradiation, but double on uv irra-
diation, increase another 50% on subsequent full arc irradiation
(150% increase in total), and sharpen up in the early stage of
annealing. The strong m absorption at 642.3 cm-1 (with a satellite
at 643.7 cm-1) in the Ir–F stretching region has its D counterpart
at 642.6 cm-1 (with a satellite at 643.6 cm-1) and is assigned to the
=
IrF2 antisymmetric stretching mode of CH2 IrF2 on the basis of
its frequency and negligible isotopic shift (see Table S6†). The Ir–F
=
≡
stretching band of CHF IrHF, CH2F–IrF, and HC IrHF2 would
appear at ~550, ~550, and ~590 cm-1, which are not observed.
The weaker m absorption at 602.3 cm-1 shows no D shift and is
assigned to the IrF2 symmetric stretching mode. [Note that the
Fig. 6 Infrared spectra in the 720–520 cm-1 region for the reaction
products of the laser-ablated iridium atom with CH2F2 isotopomers in
excess argon at 10 K. (a) Ir and CH2F2 (0.5% in argon) co-deposited for
1 h, (b)–(e) as (a) spectra taken following a sequence of visible, uv, and full
arc irradiations and annealing to 28 K. (f) Ir and CD2F2 reagent (0.5% in
argon) co-deposited for 1 h, (g)–(j) as (f) spectra taken following the same
irradiation and annealing sequence. m designates a product absorption
while P and c stand for the precursor and common precursor product
absorptions.
622.3 cm-1 average of the Ir–F stretching modes in CH2 IrF2
is slightly higher than the 615.7 cm-1 Ir–F stretching mode in
CH2 IrFCl.] The observably strong CH2 wagging absorption
expected at ~920 cm-1 is probably covered by product absorption
=
=
in the congested region. The insertion and methylidyne products
=
are observed in the CH2F2 isotopomer spectra; CH2 IrF2(D),
-1
≡
the primary product by plume uv radiation during co-deposition,
similar to the CHCl3 case. The m absorption at 1350.8 cm-1 has
its D and 13C counterparts at 1067.6 and 1342.5 cm-1 (H/D and
12/13 ratios of 1.2653 and 1.0062) and are assigned to the CH2
scissoring mode due to the frequency and relatively large and
small D and 13C shifts. Another m absorption at 890.4 cm-1 has is
its 13C counterpart at 882.4 cm-1 (12/13 ratio of 1.009) while the D
counterpart is believed to be covered by precursor absorption. It is
designated as the CH2 wagging mode on the basis of the frequency,
small 13C shift, and correlation with the DFT values.
CH2F–IrF(Q), and HC IrHF2(D) are 57, 25, 30 kcal mol more
stable than the reactants, and CH2F–IrF(D), which is 51 kcal mol-1
more stable, has a bridged structure (with bridging H). Despite the
comparable energy, CH2F-IrF(D) is not identified in the spectra.
Structures of Ir complexes
The structures of the small Ir carbyne and carbene complexes
identified in this study are illustrated in Fig. 7 and 8. The
˚
C–Ir bond lengths of the carbyne complexes (1.725–1.736 A)
+
-
≡
are compared with that of [(Cp¢)(PMe3)Ir CPh] BArf (Cp¢ =
5 3
The calculated frequencies in Table S4† also show that the
observed absorptions are the strongest bands predicted for
˚
h -C5Me4Et; Barf = B[C5H3(3,5-CF3)2]4) (1.734(6) A). They are
=
CH2 IrCl2, and the predicted frequencies for the methylidene
also considerably shorter than those of the corresponding carbene
˚
=
product (CH2 IrCl2) correlate well with the observed values. The
complexes (1.809–1.815 A), being appropriate for the triple bonds.
≡
≡
observed product is consistent with its stability over other plausible
While ClC IrCl3 and FC IrIrCl3 have Cs structures similar
=
≡
ones; CH2 IrCl2(D), CH2Cl–IrCl(Q), and CH IrHCl2(D) are
87.9, 51.7, and 64.5 kcal mol-1 more stable than the reactants
(Ir(4F) + CH2Cl2). On the other hand, the insertion complex in the
doublet state, which is 70.6 kcal mol-1 more stable, has a bridged
structure (with a bridging Cl atom).
to those for Group 7 and 8 metal carbynes,6,7 introduction of
≡
Ir–F bond leads to the square planar structure of ClC IrFCl2,
≡
≡
ClC IrF2Cl, and FC IrFCl2 as shown in Fig. 7.
These are the first small square planar complexes with carbon–
metal triple bond generated from transition metal reactions with
halomethanes.4–8,11 It is also notable that their distinct planar
structures are comparable to the recently discovered square planar
carbyne complexes with C–M triple bond (Ru halocarbynes).26
These Ir complexes with C–Ir triple bond are not only the small
version of the rare Ir high oxidation-state complexes but possess
interesting structures as well. Geometry optimizations of the
Ir carbyne from various starting points all lead to the planar
structure, indicating that the planar structure is most probably
the true energy minimum. Altering location of F (from opposite
In the products spectra from reactions of Ir with CH2FCl
isotopomers in Fig. 5, the m absorptions remain almost the same
on visible irradiation but more than double on uv irradiation
and increase slightly further on full arc irradiation. The strong
m absorption at 615.7 cm-1 (with a site absorption at 620.8 cm-1)
shows a D shift of only 0.3 cm-1, leading to an assignment to the
=
Ir–F stretching mode of CH2 IrFCl. The insertion complex,
CH2F–IrCl, would not have a strong absorption in the 600 cm-1 re-
gion. The observed frequency and small D shift are compared with
the calculated values of 620.7 and 0.1 cm-1. Another m absorption
≡
to right angle with respect to the Ir C bond or visa versa)
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Fig. 7 The Ir methylidyne structures in the doublet ground states calculated at the B3LYP level of theory using the 6-311++G(3df,3pd) basis sets for
◦
˚
≡
≡
H, C, F, and Cl and the SDD pseudo potential and basis for Ir. Bond distances and angles are in A and . ClC IrCl3 and FC IrCl3 have Cs structures
≡
≡
≡
similar to the Groups 7 and 8 carbynes, whereas ClC IrFCl2, ClC IrF2Cl, and FC IrFCl2 have distinct planar structures, suggesting that F substitution
to Ir leads to the stability of the planar structure.
hardly changes the energy and frequencies. It is not clear at this
point what determines the structure of the Ir complexes while
molecular orbital analysis shows that the non-bonding electrons
of Ir are mostly located above and below the molecular plane.
Close theoretical examination is needed to understand the role of
the ligands in the high oxidation-state complex.
carbene complexes, probably due to the higher energies of the
carbyne complexes.
M* + CX4 → CX3–MX* → CX2–MX2* ↔ CX–MX3
(1)
X migration from C to Ir is believed to be fast enough to leave
an undetectable amount of the insertion complex. Formation of
TheIr carbenecomplexes, ontheother hand, allhaveallene-type
staggered structures as shown in Fig. 8, which are similar to those
of previously reported Group 7–10 metal halomethylidenes.4–8,11
≡
≡
=
=
ClC IrF2Cl, ClC IrFCl2, CFCl IrFCl and CCl2 IrFCl along
≡
≡
=
=
with FC IrFCl2, FC IrCl3, CF2 IrCl2, and CFCl IrCl2 also
indicates that F migration is as competitive as Cl migration
along with the comparable stabilities between the corresponding
products. The reversible intensity variation of m and y absorptions
in the tetrahalomethane spectra indicate that the Ir methylidenes
and methylidynes are inter-convertible in the process of photolysis.
The methylidyne undergoes rearrangement (X migration) to the
methylidene on visible (l > 420 nm) irradiation, and vice versa on
uv (240 < l < 380 nm) irradiation.
The Ir–C bond lengths are relatively shorter than the typical values
27
˚
of 1.86–1.97 A for the larger Ir complexes.
Reactions
The earlier studies reveal that laser ablated transition metal
atoms undergoes C–X insertion and the excess reaction energy
leads to X migration from C to M, producing high oxidation-
state complexes.4 In the iridium system, reactions with tetra-
halomethanes proceed to the carbene and carbyne complexes,
whereas those with the tri- and dihalomethanes stops at the
(2)
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Fig. 8 The Ir methylidene structures calculated in the doublet ground states at the B3LYP level of theory using the 6-311++G(3df,3pd) basis sets for
H, C, F, and Cl and the SDD pseudo potential and basis for Ir. Bond distances and angles are in A and ◦. The methylidenes have staggered allene-type
˚
structures, consistent with their stabilities over the planar structures. CHF(H)–IrCl also in the doublet ground state has a bridged structure.
In between Groups 8 and 10, the Ir and Rh11 tetrahalocarbynes
are energetically reachable from the carbene complexes and X
migration is also swift enough. Generation of the Ir complexes
with C–Ir triple bond, which are rare, demonstrates that direct
reaction of laser-ablated transition metal atoms with small organic
species and subsequent photolysis are an effective route to provide
high oxidation-state complexes.
similar to those of the previously studied Group 7–10 metal
carbenes.6–8 The identified products are consistent with their DFT
energies. Absence of the insertion product absorptions indicates
that X migration from C to Ir is swift. Along with the previous
results that no Group 10 metal carbynes are observed in the
matrix spectra,8 Group 9 metals (Ir and recently studied Rh) are
most probably the last late transition metals that produce the
methylidyne complexes with C–M triple bond in reactions with
halomethanes.
Conclusions
Acknowledgements
Reactions of laser-ablated Ir atoms with halomethanes have been
carried out, and the products are identified from the matrix Ir
spectra on the basis of frequencies, isotopic shifts, and correlation
with the DFT results. Ir methylidyne complexes are identified
only in the tetrahalomethane reactions, and the calculated bond
We gratefully acknowledge financial support from National
Science Foundation (U. S.) Grant CHE 03-52487 to L. A., and
support from the Korea Research Foundation (KRF) grant funded
by the Korean government (MEST) (No 2009-0075428).
˚
lengths of 1.725–1.736 A are appropriate for the carbon–metal
triple bonds. It is interesting that the carbyne complexes with Ir–F
bond have square planar structures, in contrast to the previously
studied the non-planar C3v or Cs carbyne structures.4–7,11 The
planar structure is similar to those of the recently discovered
square planar Ru complexes with Ru–X bonds.26 On the other
hand, reactions of tetra-, tri-, and dihalomethanes all generate the
methylidene products, which have allene-type staggered structures
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The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 5478–5489 | 5489
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