Infrared spectra of small insertion and methylidene complexes in reactions of laser-ablated nickel atoms with halomethanes

Article abstract of DOI:10.1021/om900498m

Nickel carbene complexes, CX₂=NiX₂, are prepared along with the insertion products, CX₃-NiX, in reactions of laser-ablated Ni atoms with tetrahalomethanes. These reaction products are identified from matrix infrared spectr

Full text of DOI:10.1021/om900498m

Organometallics 2009, 28, 5623–5632 5623
DOI: 10.1021/om900498m
Infrared Spectra of Small Insertion and Methylidene Complexes in
Reactions of Laser-Ablated Nickel Atoms with Halomethanes
Han-Gook Cho,† Lester Andrews,*,‡ Bess Vlaisavljevich,§ and Laura Gagliardi§,^
†Department of Chemistry, University of Incheon, 177 Dohwa-dong, Nam-ku, Incheon, 402-749,
South Korea, ‡Department of Chemistry, University of Virginia, P.O. Box 400319, Charlottesville,
Virginia 22904-4319, §Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis,
Minnesota 55455-0431, and ^Department of Physical Chemistry, University of Geneva, 30, q. E. Ansermet,
ꢀ
1211 Geneve, Switzerland
Received June 12, 2009
Nickel carbene complexes, CX2dNiX2, are prepared along with the insertion products, CX3-NiX,
in reactions of laser-ablated Ni atoms with tetrahalomethanes. These reaction products are identified
from matrix infrared spectra and density functional frequency calculations. In agreement with the
previously studied Pt cases, the carbon-nickel bonds of the Ni carbene complexes are essentially
double bonds with CASPT2-computed effective bond orders of 1.8-1.9. On the other hand, only
insertion complexes are generated from dihalomethane and trihalomethane precursors. The nickel
carbenes have staggered structures, and several insertion complexes containing C-Cl bonds reveal
distinct bridged structures similar to those observed in the corresponding Fe products, which indicate
effective coordination of Cl to the metal center. The unique F-bridged CH2F-NiCl structure is also
observed.
Introduction
actinides with small alkanes and halomethanes via C-H(X)
insertion following H(X) migration.5-9 These complexes
also show distinct structures, particularly due to agostic
interaction and dramatic photochemical reactions including
photoreversibility. Their small sizes make them ideal for
high-level theoretical approaches and, therefore, are consid-
ered as model systems for their much larger cousins. The
higher oxidation-state complexes, however, are expected to
be less favored on going far right among the transition metals
in the periodic table because the d-orbital becomes more
filled.
More recently small Pt carbene complexes, along with the
insertion products, have been identified in reactions with
methane and halomethanes.10 The C-Pt bond orders com-
puted by density functional theory and natural bond order
range from 1.41 to 1.70 as Cl is replaced by F since the
more electronegative halogen evidently supports a stronger
carbon-metal bond. The small Pt methylidenes have a
substantial amount of double bond character from dπ-pπ
bonding, and their C-Pt bonds are considerably shorter
High oxidation-state complexes, first introduced in the
1970s,1 are now considered an essential part of coordination
chemistry and help to understand the nature of carbon-metal
bonds.2 Their rich chemistry includes growing applications in
numeroussynthesesincludingmetathesis, catalytic properties,
and C-H insertion.3 Their distinct structures and photoche-
mical properties have also provided testing grounds for
theoretical applications.4
Recently small high-oxidation-state complexes have been
reported from reactions of group 3-8 transition metals and
*To whom correspondence should be addressed. E-mail: lsa@
virginia.edu.
(1) (a) Fischer, E. O.; Kreis, G.; Kreiter, C. G.; Muller, J.; Huttner,
G.; Lorenz, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 564. (b) Schrock, R.
R. J. Am. Chem. Soc. 1974, 96, 6796.
(2) (a) Herndon, J. W. Coord. Chem. Rev. 2009, 253, 1517.
(b) Herndon, J. W. Coord. Chem. Rev. 2009, 253, 86. (c) Herndon, J. W.
Coord. Chem. Rev. 2007, 251, 1158. (d) Herndon, J. W. Coord. Chem. Rev.
2006, 250, 1889. (e) Herndon, J. W. Coord. Chem. Rev. 2005, 249, 999.
(f) Herndon, J. W. Coord. Chem. Rev. 2004, 248, 3, and earlier review
articles in this series.
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therein. (b) Wada, K.; Craig, B.; Pamplin, C. B.; Legzdins, P; Patrick, B. O.;
Tsyba, I.; Bau, R. J. Am. Chem. Soc. 2003, 125, 7035. (c) Ujaque, G.;
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Rev. 2002, 102, 813, and references therein.
(5) (a) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040, and
references therein (review article, groups 4-6). (b) Lyon, J. T.; Cho, H.-G.;
Andrews, L. Organometallics 2007, 26, 2519 (Ti, Zr, Hf þ CHX3, CX4).
(c) Lyon, J. T.; Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 6373
(Cr, Mo, W þ CHX3, CX4).
(6) (a) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2007, 111, 2480.
(b) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 633. (Group 3).
(7) (a) Cho, H.-G.; Andrews, L. Organometallics 2007, 26, 4096.
(b) Cho, H.-G.; Andrews, L. Inorg. Chem. 2008, 47, 1653. (Re).
(8) (a) Cho, H.-G.; Lyon, J. T.; Andrews, L. Organometallics 2008,
27, 5241. (b) Cho, H.-G.; Andrews, L. Eur. J. Inorg. Chem. 2008, 2537.
(c) Cho, H.-G.; Andrews, L. Organometallics 2008, 27, 1786. (Group 8).
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(Actinides).
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H.-G.; Andrews, L. Organometallics, 2009, 28, 1358. (Pt).
r
2009 American Chemical Society
Published on Web 09/09/2009
pubs.acs.org/Organometallics

5624 Organometallics, Vol. 28, No. 19, 2009
Cho et al.
than those of typical Pt(II) carbene complexes, leading to a
conclusion that the small Pt methylidene complexes have
substantial Pt(IV) character.11
As a continuation of our investigation on the chemistry of
small transition-metal high-oxidation-state complexes, we re-
port reactions of Ni with halomethanes. In contrast to the case
of Pt,10 which is considered as the most effective C-H insertion
agent among group 10 metals,10,12 only tetrahalomethanes
generate Ni methylidenes. Several insertion products have
interesting structures, particularly due to intermolecular inter-
action between X bonded to C and the metal center.
Experimental and Computational Methods
Laser-ablated nickel atoms were reacted with CCl4 (Fisher),
13CCl4 (90% enriched, MSD Isotopes), CFCl3, CF2Cl2
(Dupont), CHCl3, CH2Cl2, CH2FCl, CH2F2 (Dupont), CDCl3,
CD2Cl2 (MSD Isotopes), CD2FCl, and CD2F2 (synthesized13) 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.10,14 Reagent gas
mixtures were in the range 0.2-1.0% in argon. The Nd:YAG
laser fundamental (1064 nm, 10 Hz repetition rate, 10 ns pulse
width) was focused on a rotating metal target (Ni, 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 or annealed to allow further reagent diffusion.
To provide support for the assignment of new experimental
frequencies and to correlate with related works,5-10 density func-
tional theory (DFT) calculations were performed using the Gauss-
ian 03 program system,15 the B3LYP and BPW91 density
functionals,16,17 and the 6-311þþG(3df,3pd) basis sets for C, F, Cl,
and Ni atoms.18 Geometries were fully relaxed during optimization,
Figure 1. Infrared spectra in the 1000-800 cm-1 region for the
reaction products of the laser-ablated nickel atom with CCl4 iso-
topomers in excess argon at 10 K. (a) Ni and CCl4 (0.5% in argon)
co-depositedfor1h. (b) As(a) aftervisible(λ> 420 nm) irradiation.
(c) As (b) after ultraviolet (240-380 nm) irradiation. (d) As (c) after
full arc (λ > 220 nm) irradiation. (e) As (d) after annealing to 26 K.
(f) Niand13CCl4 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.
and the optimized geometry was confirmed by vibrational analysis.
The vibrational 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,5-10,19 and they provide useful predictions for infrared
spectra of new molecules. Natural bond orbital (NBO) analysis15,20
was done to help understand the carbon-nickel bonding in the
carbenes, but the results were questionable, and the carbenes were
examined using CASSCF/CASPT2 methods and triple-ζ (ANO-
RCC-VTZP) basis sets.21,22 An active space of (6,6) was chosen for
the active orbitals involved in the C-M bond. A CASPT2
geometry optimization was performed for the carbenes starting
from DFT geometries. The orbitals shown below and the occupa-
tion numbers used to compute the effective bond orders (EBO =
bonding minus antibonding electons divided by two) are from the
final calculation at the optimized geometry. A quadruple-ζ
CASPT2 optimization was performed on Cl2Ni-CCl2 to confirm
that the triple-ζ basis was sufficient.
(11) Prokopchuk, E. M.; Puddephatt, R. J. Organometallics 2003, 22,
563, and references therein. Pt(IV).
(12) (a) Carroll, J. J.; Weisshaar, J. C.; Siegbahn, P. E. M.; Wittborn,
C. A. M.; Blomberg, M. R. A. J. Phys. Chem. 1995, 99, 14388. (b) Low, J.
J.; Goddard, W. A.III. Organometallics 1986, 5, 609. (c) Wang, X.; Andrews,
L. J. Phys. Chem. A 2004, 108, 4838. (d) Cho, H.-G.; Andrews, L. J. Phys.
Chem. A 2004, 108, 6272.
(13) Isotopic modifications synthesized: Andrews, L.; Willner, H.;
Prochaska, F. T. J. Fluorine Chem. 1979, 13, 273.
(14) (a) Andrews, L.; Citra, A. Chem. Rev. 2002, 102, 885, and
references therein. (b) Andrews, L. Chem. Soc. Rev. 2004, 33, 123, and
references therein.
(15) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
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,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo,
C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A.
J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.;
Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.;
Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.;
Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe,
M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT,
2004.
Results and Discussion
Reactions of nickel atoms with halomethanes were inves-
tigated, and infrared spectra (Figures 1-6) and quantum
(19) (a) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.
(b) Andersson, M. P.; Uvdal, P. L. J. Phys. Chem. A 2005, 109, 3937.
(20) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88,
899.
(21) (a) Roos, B. O. The Complete Active Space Self-Consistent Field
Method and its Applications in Electronic Structure Calculations. In
Advances in Chemical Physics; Ab Initio Methods in Quantum Chemis-
try-II; Lawley, K. P., Ed.; John Wiley & Sons Ltd.: New York, 1987;
(16) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
Y.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
(17) (a) Becke, A. D. Phys. Rev. A 1988, 38, 3098. (b) Burke, K.;
Perdew, J. P.; Wang, Y. In Electronic Density Functional Theory: Recent
Progress and New Directions; Dobson, J. F., Vignale, G., Das, M. P. Ed.;
Plenum, 1998.
˚
Chapter 69, p 399. (b) Andersson, K.; Malmqvist, P.-A.; Roos, B. O.
J. Chem. Phys. 1992, 96, 1218 as implemented in Molcas 7.4.
˚
(22) Roos, B.O.;Lindh, R.; Malmqvist, P.-A.; Veryazov, V.; Widmark,
(18) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062.
P.-O. J. Phys. Chem. A, 2005, 109, 6575. (ANO-RCC-VTZP) basis.

Article
Organometallics, Vol. 28, No. 19, 2009 5625
Figure 3. Infrared spectra in the 1000-450 cm-1 region for the
reaction products of the laser-ablated nickel atom with CHCl3
isotopomers in excess argon at 10 K. (a) Ni and CHCl3 (0.5% in
argon) co-deposited for 1 h. (b-e) As (a) spectra taken following
the irradiation and annealing sequence described in Figure 1
caption (visible, UV, and full arc irradiations and annealing to
26 K). (f) Ni and CDCl3 reagent (0.5% in argon) co-deposited
for 1 h. (g-i) As (f) spectra taken following a sequence of visible
and UV irradiation and annealing to 34 K. i, P, and c stand for
product, precursor, and common absorptions, respectively.
Figure 2. Infrared spectra in the 1350-800 and 550-450 cm-1
regions for the reaction products of the laser-ablated nickel
atom with CF2Cl2 and CFCl3 in excess argon at 10 K. (a) Ni
and CF2Cl2 (0.5% in argon) co-deposited for 1 h. (b-e) As
(a) spectra taken following the irradiation and annealing se-
quence described in Figure 1 caption (visible, UV, and full arc
irradiations and annealing to 26 K). (f) Ni and CFCl3 reagent
(0.5% in argon) co-deposited for 1 h. (g-j) As (f) spectra taken
following the same irradiation and annealing sequence. Notice
the photoreversible intensity variation of the m absorptions in
the CFCl3 spectra (decrease and increase on visible and UV
irradiations). i and m designate the product absorption groups,
while P and c stand for the precursor and common absorptions.
chemical frequency calculations of the products and their
structures (Figures 7, 8) will be presented in turn.
Ni þ CX4. Laser-ablated Ni atoms co-deposited with
carbon tetrachloride in excess argon during condensation at
10 K produced two strong new absorptions at 953.3 cm-1
(944.0 cm-1 satellite for matrix site splitting) and 912.2 cm-1
(909.9 cm-1 shoulder for chlorine isotopic splitting) (labeled
m for methylidene). Previously reported bands at 1036.4 cm-1
(CCl3þ),23 1019.3 and 926.7 cm-1 (Cl2CCl-Cl),24 and 898 cm-1
(CCl3)25 were also observed: these are common to all laser-
ablated metal experiments with CCl4 as produced by ablation
plume photolysis, and their identification follows from earlier
work using vacuum ultraviolet irradiation.23
The product absorptions increased in concert 5, 20, and a few
% on sequential irradiations in the visible (λ > 420 nm),
ultraviolet (240-380 nm), and full arc (λ > 220 nm) regions,
respectively. A similar experiment with 13CCl4 (90% enriched)
shifted the new absorptions to 920.5 cm-1 (912.6 cm-1 satellite)
(12/13 isotopic frequency ratio of 1.0356) and to 883.2 cm-1
(880.8 cm-1 shoulder) (12/13 ratio of 1.0328). The appearance
of a weak 12C product band at 953.3 cm-1 with about 1/10 of
the 13C product band absorbance (Figure 1) confirms that a
Figure 4. Infrared spectra in the 1100-410 cm-1 region for the
reaction products of the laser-ablated nickel atom with CH2Cl2
isotopomers in excess argon at 10 K. (a) Ni and CH2Cl2 (0.5% in
argon) co-deposited for 1 h. (b-e) As (a) spectra taken following
the irradiation and annealing sequence described in Figure 1
caption (visible, UV, and full arc irradiations and annealing to
26 K). (f) Ni and CD2Cl2 reagent (0.5% in argon) co-deposited
for 1 h. (g-i) As (f) spectra taken following a sequence of visible
and UV irradiation and annealing to 28 K.
single carbon atom participates in these vibrational modes. The
909.9 and 880.8 cm-1 shoulders on the 912.2 and 883.2 cm-1
bands are 6/9 of the main band absorbances, which is appro-
priate for natural abundance chlorine isotopes in a species
containing two equivalent chlorine atoms (statistical popula-
tion of one 35Cl and one 37Cl vs two 35Cl atoms).
(23) (a) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1971, 54, 3935.
(b) Jacox, M. E. Chem. Phys. 1976, 12,þ51. (c) Prochaska, F. T.; Andrews, L.
J. Chem. Phys. 1977, 67, 1091. (CCl3
(24) Maier, G.; Reisenauer, H. P.; Hu, J.; Hess, B. A., Jr.; Schaad,
)
L. J. Tetrahedron Lett. 1989, 30, 4105. (Cl2CCl-Cl).
(25) Andrews, L. J. Chem. Phys. 1968, 48, 972. (CCl3).

5626 Organometallics, Vol. 28, No. 19, 2009
Cho et al.
Figure 5. Infrared spectra in the 1200-500 cm-1 region for the
reaction products of the laser-ablated nickel atom with CH2FCl
isotopomers in excess argon at 10 K. (a) Ni and CH2FCl (0.5%
in argon) co-deposited for 1 h. (b-e) As (a) spectra taken
following the irradiation and annealing sequence described in
Figure 1 caption (visible, UV, and full arc irradiations and
annealing to 26 K). (f) Ni and CD2FCl reagent (0.5% in argon)
co-deposited for 1 h. (g-j) As (f) spectra taken following the
same sequence. i, P, and c stand for product, precursor, and
common absorptions, respectively.
Figure 7. Structures calculated for the identified reaction pro-
ducts of nickel with halomethanes at the B3LYP level of theory
using the 6-311þþG(3df,3pd) basis sets for H, C, F, Cl, and Ni.
˚
Bond distances and angles are in A and deg. Notice the staggered
allene-type structures of the Ni methylidenes and the bridged
structures of the insertion complexes [the bridged halogen-metal
distance is given in brackets]. Molecular symmetries are given
under each structure.
Figure 6. Infrared spectra in the 1000-450 cm-1 region for the
reaction products of the laser-ablated nickel atom with CH2F2
isotopomers in excess argon at 10 K. (a) Ni and CH2F2 (0.5% in
argon) co-deposited for 1 h. (b-e) As (a) spectra taken following
the irradiation and annealing sequence described in Figure 1
caption (visible, UV, and full arc irradiations and annealing to
26 K). (f) Ni and CD2F2 reagent (0.5% in argon) co-deposited
for 1 h. (g-j) As (f) spectra taken following the same sequence. i,
P, and c stand for product, precursor, and common absorptions,
respectively.
Figure 8. Calculated CASPT2 structures for the nickel carbenes.
and halomethanes,5-10 they are assigned to the symmetric
and antisymmetric CCl2 stretching modes of CCl2-NiCl2.
The carbon 12/13 isotopic frequency ratio for a pure sym-
metric CCl2 stretching mode is smaller than that for an
antisymmetric stretching mode, but mixing with the Ni-C
stretching mode increases the carbon participation and the
12/13 isotopic frequency ratio, as found for the CCl2-PtCl2
molecule.10a This mode is in fact C vibrating back and
forth between Ni and two Cl atoms in an antisymmetric
fashion. The totally symmetric counterpart calculated at
451.9 cm-1 (Table 1) has a very small carbon-13 shift, as
The two strong m product absorptions in the C-Cl
stretching region suggest that a primary product with a
CCl2 moiety is generated during co-deposition of the laser-
ablated nickel atoms and CCl4. On the basis of our previous
experience for reactions of metal atoms with hydrocarbons

Article
Table 1. Observed and Calculated Fundamental Frequencies of CCl2-NiCl2 Isotopomers in the 1A1 Ground State in C2v Symmetrya
12C35Cl2-Ni35Cl2 13C35Cl2-Ni35Cl2
Organometallics, Vol. 28, No. 19, 2009 5627
approximate
description
obsb
B3LYPc
intc
BPW91c
intc
obsb
B3LYPc
intc
BPW91c
intc
A1 C-Cl2, Ni-C str.
B2 CCl2 str.
B1 NiCCl2 deform
A1 Ni-C, C-Cl2 str.
B1 NiCl2 str.
953.3
912.2
945.2
899.9
452.4
451.9
443.4
343.3
244.6
194.9
106.6
92.1
248
233
6
1
70
3
0
0
4
3
958.2
863.0
453.7
425.5
453.6
348.9
241.3
191.4
103.5
96.5
196
209
7
4
57
4
1
0
2
0
920.5
883.2
912.7
871.0
431.8
451.5
447.7
343.2
244.5
194.3
106.5
92.0
231
218
24
1
52
3
0
0
4
3
925.0
835.3
410.2
453.6
453.3
348.6
241.1
190.8
103.4
96.4
182
196
2
7
58
4
1
0
2
0
A1 NiCl2 str.
A1 NiCl2, CCl2 bend
B2 Cl2NiCCl2 def
B2 CNiCl2 def
A1 NiCl2 bend
B1 NiCl2 rock
A2 CCl2 twist
57.6
14.5
1
0
69.1
19.2
1
0
57.6
14.5
1
0
69.1
19.2
1
0
a Frequencies and intensities are in cm-1 and km/mol. Approximate mode descriptions as considerable mixing is involved. The first and fourth modes
differ by phasing of the C motion, antisymmetric for the first and symmetric for the fourth mode. b Observed in an argon matrix. Chlorine isotopic
splitting listed. c Harmonic frequencies and intensities computed with B3LYP or BPW91/6-311þG(3df).
Table 2. Observed and Calculated Fundamental Frequencies of
CCl3-NiCl Isotopomers in the 1A Ground Statea
triplet state is energetically comparable (0.6 kcal/mol lower)
to the singlet state; however, the CCl2 frequencies calculated
for the triplet state are much lower (e.g., the B3LYP fre-
quencies of 862.5 and 839.9 cm-1 are 90.8 and 72.3 cm-1
lower than the observed values) and the predicted isotopic
shifts (27.3 and 27.4 cm-1) are not in good agreement as well.
On the basis of the observed frequencies and their isotopic
shifts, which are in excellent agreement with the predicted
values, the Ni methylidene product has a singlet ground
state.
Recently small Pt carbenes have been formed in reactions
with methane and halomethanes and observed in the matrix
infrared spectra. The C-Pt bond is clearly a double bond
and apparently much stronger than those in larger Pt com-
plexes.10,11 Previous studies reveal that higher oxidation-
state transition-metal complexes are favored on going down
the family,5-8,12 and therefore, Ni is normally considered a
weaker C-H(X) insertion agent than Pt. Our identification
of CCl2-NiCl2 from reactions of CCl4 isotopomers, how-
ever, confirms that Ni also undergoes C-X insertion and
following X migration from C to Ni.
12CCl3-NiCl
13CCl3-NiCl
approximate
description
obsb B3LYPc intc obsb B3LYPc intc
A0 CCl2 s. str.
A00 CCl2 as. str.
A0 NiCCl2 deform
A0 C-Ni str.
851.3 862.9
798.0
143 824.2 833.0
132
156
27
96
27
4
d
d
166
29
110
20
5
772.2
458.9
426.9
378.4
290.3
235.6
229.2
164.8
148.5
78.2
463.2
432.0
383.7
290.4
236.3
229.3
165.4
148.6
78.2
A0 NiCl2 as. str.
A0 NiCl2 s. str.
A00 CCl2 scis.
0
0
A0 Cl2NiC deform
A0 NiCl2 wag
A00 NiCl2 bend
A00 NiCl2 rock
A0 CCl2 twist
13
33
1
13
33
1
2
4
2
76.4
4
76.4
a Frequencies and intensities are in cm-1 and km/mol. b Observed in
an argon matrix. c Frequencies and intensities computed with B3LYP/
6-311þG(3df) are for harmonic calculations. d Covered by precursor
absorption. CCl3-NiCl has a bridged Cs structure. Attempts to opti-
mize with BPW91/6-311þG(3df) end up with the methylidene structure
(CCl2-NiCl2).
Another weak product absorption marked “i” (i for
insertion) is observed at 851.3 cm-1 and its 13C counterpart
at 824.2 cm-1 (12/13 ratio of 1.0329). They decrease slightly
on visible irradiation, but increase slightly on UV irradia-
tion. The frequency and 13C shift indicate that it is a C-Cl
stretching band of another product formed in the reaction of
Ni and CCl4. The previous studies5-10 and computational
results suggest that the most plausible product along with the
methylidene complex is the insertion complex, CCl3-NiCl.
The insertion complex is expected to have a bridged structure
(Figure 7) and to be energetically comparable to the methy-
lidene complex (1.8 kcal/mol lower). The observed frequency
and 13C shift are in good agreement with the predicted values
for the CCl2 symmetric stretching mode of the insertion
complex (862.9 and 27.1 cm-1) as shown in Table 2. Un-
fortunately the antisymmetric CCl2 stretching band and its
13C counterpart are believed to be covered by precursor
absorption, and other bands are calculated to be too weak
to observe. We tentatively assign the weak i absorption to the
CCl2 symmetric stretching mode of the insertion complex in
the singlet ground state. The singlet and triplet states are
energetically close again (66.0 and 63.5 kcal/mol more stable
than the reactants), but the triplet insertion complex would
have the CCl2 symmetric and strongest antisymmetric
the carbon atom hardly moves in this mode. The 912.2 cm-1
band is due to the antisymmetric C-Cl2 stretching mode,
and the 1.0328 isotopic 12/13 frequency ratio is virtually the
same as found for the CCl2-PtCl2 molecule.10a
The observed CCl2 stretching frequencies correlate well
with the predicted values for CCl2-NiCl2 in its singlet
ground state as shown in Table 1, and the carbon-13 isotopic
shifts are also well reproduced (observed 32.8 and 29.0 cm-1
vs predicted 32.5 and 28.9 cm-1). The observed frequencies
are, however, slightly higher than the predicted values, and
similar reversals are also observed from the C-X stretching
frequencies in the previously studied halogenated late transi-
tion-metal carbene and carbynes.8,10 The two strong ob-
served (antisymmetric and symmetric) CCl2 stretching
absorptions and their 13C counterparts are consistent with
the DFT results and substantiate formation of the Ni
methylidene, CCl2-NiCl2, via C-Cl bond insertion by Ni
and subsequent Cl migration from C to Ni.
Unfortunately the weaker NiCl2 antisymmetric stretching
band is predicted too close to our observation limit, and all
the other vibrational bands of the Ni methylidene are too
weak to be observed (Table 1). It is also notable that the

5628 Organometallics, Vol. 28, No. 19, 2009
Cho et al.
Table 3. Observed and Calculated Fundamental Frequencies of CF2-NiCl2 and CFCl-NiCl2 in the 1A2 and 1A00 Ground Statesa
CF2-NiCl2
CFCl-NiCl2
approximate
description
approximate
description
obsb
B3LYPc
intc
BPW91c
intc
528
obsb
B3LYPc
intc
BPW91c
intc
A1 CF2 s. str.
B2 CF2 as. str.
A1 CF2 bend
B1 CF2 wag
B1 NiCl2 as. str.
A1 NiCl2 s. str.
A1 C-Ni str.
B2 CF2 rock
A1 NiCl2 bend
B2 NiCl2 wag
A2 CCl2 twist
B1 NiCl2 rock
1310.0
1294.5
1328.1
1302.8
726.4
579.5
451.9
387.2
334.6
274.1
117.8
88.4
501
242
15
59
69
1
0
0
5
7
1279.1
1213.7
705.7
546.7
453.9
416.6
336.3
277.9
116.4
93.4
A0 C-F str.
1251.9
974.8
1269.1
966.2
540.3
508.1
448.9
360.8
324.8
214.4
112.5
88.5
274
363
2
25
69
3
0
0
4
5
1207.6
946.1
538.7
480.2
453.1
372.2
324.7
214.0
111.1
94.2
283
295
6
7
58
5
0
0
2
1
217.5
A00 C-Cl str.
4
24
55
3
0
0
3
2
1
0
A CFCl bend
A00 NiCFCl deform
A00 NiCl2 as. str.
A0 C-Ni str.
520.8
474.5
A0 NiCl2 s. str.
A0 CFCl rock
A0 NiCl2 wag
A0 NiCl2 bend
A00 NiCl2 rock
A00 CFCl twist
21.4
-8.0
2
0
56.9
-36.6
42.5
-9.5
2
0
64.5
-13.7
0
0
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/
6-311þG(3df) are for harmonic calculations. CF2-NiCl2 and CFCl-NiCl2 have staggered allene-type C2v and Cs structures.
Table 4. Observed and Calculated Fundamental Frequencies of
CFCl2-NiCl in the 1A Ground Statesa
with the B3LYP frequency of 1181.0 cm-1 for the C-F
stretching mode of the insertion complex, CFCl2-NiCl
(Table 4). Another i absorption at 868.6 cm-1 (with a
shoulder at 866.5 cm-1) is assigned to the C-Cl stretching
mode. The products from C-Cl insertion are much more
stable than those via C-F insertion; CFCl-NiCl2,
CCl2-NiFCl, CFCl2-NiCl, and CCl3-NiF are 63, 48, 62,
and 49 kcal more stable than the reactants, respectively.
CFCl2-NiCl has a C1 structure with a bridging Cl atom
similar to CCl3-NiCl as shown in Figure 7.
Again the triplet states are energetically comparable; the
singlet and triplet states for the Ni methylidenes are 63 and
64 kcal/mol more stable than the reactant (Ni(3F) þ CFCl3).
Optimization attempts for the triplet insertion complex also
end up with the triplet methylidene. However, the triplet
methylidene would have its C-Cl stretching and NiCFCl
deformation bands at ∼850 and ∼410 cm-1, which are not
observed in this study. Most probably the F-containing Ni
methylidene is in its singlet ground state (Table 3).
CFCl2-NiCl
approximate
description
obsb
B3LYPc
intc
BPW91c
intc
C-F str.
1119.8
868.6, 866.5
1181.0
892.9
533.4
474.6
441.0
330.2
291.0
245.7
166.3
140.3
90.1
225
242
52
93
53
6
10
5
1
1210.0
945.3
537.8
479.8
453.7
371.6
325.1
213.3
113.3
96.1
279
294
6
6
59
6
0
0
2
1
C-Cl str.
CFCl bend
NiCFCl deform
NiCl2 as. str.
C-Ni str.
NiCl2 s. str.
CFCl rock
NiCl2 wag
NiCl2 bend
NiCl2 rock
CFCl twist
47
4
4
68.5
19.0
0
0
77.2
a Frequencies and intensities are in cm-1 and km/mol. b Observed in
an argon matrix. c Frequencies and intensities computed with B3LYP or
BPW91/6-311þG(3df) are for harmonic calculations. CFCl2-NiCl has
a bridged C1 structure.
In the CF2Cl2 spectra the m absorptions remain unchanged
onvisibleirradiationbut increase ∼15% andanother ∼5%on
UV and full arc photolysis. The two strong m absorptions at
1310.0 cm-1 (with a satellite at 1315.1 cm-1) and 1294.5 cm-1
(with a satellite at 1297.9 cm-1) in the C-F stretching region26
reflectformation of a primaryproductwitha CF2 group, most
probably CF2-NiCl2. The observed CF2 stretching bands are
assigned to the symmetric and antisymmetric modes of the Ni
methylidene, and the frequencies are well reproduced as
shown in Table 3. A weak m absorption is also observed at
520.8 cm-1 and assigned to the CF2 wagging mode. The
tetrahalomethanes (CCl4, CFCl3, and CF2Cl2) used in this
study all produce the Ni carbene complexes via C-Cl inser-
tion following Cl migration from C to Ni. The observed
vibrational characteristics show that CF2-NiCl2 is also in
the singlet ground state because the triplet state would have
the symmetric and antisymmetric CF2 stretching bands
at ∼1250 and ∼1200 cm-1 and the CF2 wagging band at
∼420 cm-1, while the singlet and triplet states are 60 and
63 kcal/mol, respectively, more stable than the reactants.
No i absorption is observed in the CF2Cl2 spectra, unlike
the CCl4 and CFCl3 cases. It is, however, in line with the fact
that attempts to optimize the structure of the insertion
complex all end up with that of CF2-NiCl2, suggesting that
the original C-Cl bond insertion directly leads to Cl migra-
tion from C to Ni to form the methylidene complex in
reaction of Ni with CF2Cl2. The products with Ni-Cl bonds
stretching band at ∼790 and ∼720 cm-1, which are not
observed from the spectra.
Ni þ CFCl3 and CF2Cl2. Infrared spectra from the reaction
of Ni atoms with the chlorofluoromethanes are shown in
Figure 2. In the CFCl3 spectra three m absorptions are
observed, which decrease one-third and double on visible and
UV irradiations reversibly. The two strong product absorp-
tions, one at 1251.9 cm-1 (with a satellite at 1244.3 cm-1) in the
C-F stretching region26 and the other one at 974.8 cm-1 in the
C-Cl stretching region, indicate that a primary product with a
CFCl group is generated in the process of co-deposition and
subsequent UV photolysis. It is most likely CFCl-NiCl2, and
the observed C-F and C-Cl stretching frequencies are well
reproduced by computation as shown in Table 3. The weak
absorption at 474.5 cm-1 is assigned to the NiCFCl deforma-
tion mode. All other bands are either too weak to observe or
beyond our observation limit. The observed bands and good
correlation with the predicted values support formation of the
F-containing Ni methylidene.
Parallel to the Ni þ CCl4 case, weak i absorptions are also
observed, which increase ∼20% on UV photolysis. The one
at 1119.8 cm-1 in the C-F stretching region is compared
(26) Pavia, D. L.; Lampman, G. M.; George, S. K. Introduction to
Spectroscopy, 3rd ed.; Brooks Cole: New York, 2000.

Article
Organometallics, Vol. 28, No. 19, 2009 5629
Table 5. Calculated Fundamental Frequencies of CHCl2-NiCl Isotopomers in the 1A0 Ground Statea
CHCl2-NiCl
CDCl2-NiCl
approximate
description
obsb
B3LYPc
intc
BPW91c
intc
obsb
B3LYPc
intc
BPW91c
intc
C-H str.
3162.8
1233.0
995.1
805.3
601.5
471.7
428.8
290.3
223.3
186.8
97.9
3
22
33
128
19
63
67
2
2
6
3
3
3084.5
1180.5
945.2
779.0
606.5
440.0
421.0
285.9
225.0
179.2
98.6
2
20
49
163
16
12
102
2
2
5
2
3
2327.2
931.9
819.2
727.2
560.1
457.2
426.3
288.9
222.9
185.0
97.1
2
90
45
46
35
40
71
2
2
5
3
3
2269.4
892.1
788.9
698.2
559.8
436.8
409.6
284.7
224.5
177.6
97.7
1
111
69
49
26
13
87
2
2
4
2
3
C-H ip. bend
C-H oop. bend
C-Cl str.
882.3
763.8
671.3
935.1
803.1
CNiCl s. str.
CNiCl as. str.
Ni-Cl str.
CClNi s. str.
CClNi as. str.
CNiCl ip. bend
Ni-Cl oop. bend
Ni-Cl ip. bend
472.9
422
420
77.9
76.0
77.8
75.9
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/
6-311þþG(3df, 3pd) are for harmonic calculations. CHCl2-NiCl has a bridged C1 structure.
Table 6. Observed and Calculated Fundamental Frequencies of CH2Cl-NiCl Isotopomers in the 1A Ground Statesa
.
CD2Cl-NiCl
intc
approximate
description
obsb
B3LYPc
intc
BPW91c
intc
obsb
B3LYPc
BPW91c
intc
A00 CH2 as. str.
A0 CH2 s. str.
A0 CH2 scis.
3211.8
3106.3
1426.3
1080.8
988.8
696.0
680.1
511.4
426.2
240.2
104.4
101.9
0
2
2
11
0
28
6
25
58
1
3
5
3136.9
3029.8
1373.7
1031.3
946.9
709.7
658.9
493.1
426.4
244.1
103.6
97.6
0
3
2
12
0
24
5
19
51
1
1
4
2392.6
2246.4
1059.5
851.3
728.2
639.8
502.9
489.8
424.4
239.3
103.1
100.1
0
2
4
8
0
39
3
11
59
1
2337.5
2189.6
1022.1
816.3
700.2
648.2
485.6
473.9
423.2
243.3
102.6
95.9
0
3
4
8
0
33
2
6
52
1
1
A0 CH2 wag
1031.1
700.0
813.1
645.0
A000 CH2 twist
A CClNi s. str.
A00 CH2 rock
A0 CClNi as. str.
A0 NiCl str.
A0 CClNi bend
A00 CNiCl oop bend
A0 CNiCl ip bend
496.8
425
477.3
422
3
5
4
a Frequencies and intensities are in cm-1 and km/mol. b Observed (i absorption) in an argon matrix. c Frequencies and intensities computed with
B3LYP or BPW91/6-311þþG(3df, 3pd) are for harmonic calculations. CH2Cl-NiCl has a bridged Cs structure in its triplet ground state.
are far more stablethanthosewithNi-F bonds. For example,
CF2-NiCl2 and CFCl-NiFCl are 60 and 42 kcal/mol more
stable than the reactants. It is consistent with the fact that the
Ni-F stretching absorptions, which would be strong and near
650 cm-1, are not observed in the CFCl3 and CF2Cl2 spectra.
Ni þ CHCl3. Figure 3 shows the infrared spectra from
reactions of Ni with CHCl3 and CDCl3, where the product
absorptions are weaker relative to the tetrahalomethane cases.
The product absorptions (all marked with “i”) arise from the
insertion complex, based on comparison with computed
frequencies (Table 5). These bands increase ∼50% on visible
irradiation but decrease ∼20 and ∼10% on the following UV
and full arc photolysis. The i absorption at 935.1 cm-1 and D
counterpart at 793.6 cm-1 (H/D ratio of 1.178) are assigned to
the C-H(C-D) out-of-plane bending mode. The relatively
strong i absorption at 803.1 cm-1 has its D counterpart at
671.3 cm-1 (H/D ratio of 1.196) and is designated as the C-Cl
stretching mode. The weak absorption at 472.9 cm-1 with its
D counterpart at 450.1 cm-1 (H/D ratio of 1.051) is assigned
to the CNiCl antisymmetric stretching mode. The one at
882.3 cm-1 from the deuterated product is assigned to the
C-D in-plane bending mode, while its H counterpart expec-
ted at ∼1180 cm-1 is probably covered by precursor absorp-
tion. The observed i absorptions substantiate formation of the
Ni insertion complex in reaction with CHCl3.
methylidenes are the primary products. Chlorine migration
from C to Ni in the insertion complex is evidently more
difficult than the tetrahalomethane cases, and the insertion
complex is also marginally more stable than the methylidene
product: CHCl2-NiCl and CHCl-NiCl2 in their singlet
ground states are 60 and 53 kcal/mol more stable than the
reactants (Ni(3F) þ CHCl3). Triplet CHCl2-NiCl is again
energetically comparable (2.6 kcal/mol higher) to the sing-
let insertion product, but its CNiCl2 deformation bands
would appear with similar intensities at ∼720, ∼520, and
∼480 cm-1, which are not observed in this study.
Ni þ CH2X2. Figures 4-6 are the spectra from reactions of
Ni with CH2Cl2, CH2FCl, and CH2F2 and their deuterated
isotopomers. Parallel to the CHCl3 case, the insertion com-
plexes are the primary products, and no m absorptions are
observed, correlating well with the stability of the insertion
complex relative to the carbene product in each case.
CH2Cl-NiCl(S), CH2F-NiCl(T), and CH2F-NiF(T) are
18, 2, and 11 kcal/mol more stable than the Ni carbene
counterparts, respectively.
Figure 4 shows the product spectra from reactions of Ni
and CH2Cl2 isotopomers, where the i absorptions remain
unchanged on visible irradiation but increase ∼5% on UV
irradiation and increase slightly further on full arc photo-
lysis. The insertion complex is believed to have a Cs structure
with a bridging Cl atom (Figure 7), and the weakened C-Cl
bond, due to coordination to the metal center, leads to a low
The absence of the m absorptions in the CHCl3 spectra is
in contrast to the tetrahalomethane cases, where the Ni

5630 Organometallics, Vol. 28, No. 19, 2009
Cho et al.
Table 7. Observed and Calculated Fundamental Frequencies of CH2F-NiCl Isotopomers in the 1A Ground Statesa
CH2F-NiCl
B3LYP int
CD2F-NiCl
approximate
description
obs
BPW91
int
obs
B3LYP
int
BPW91
int
CH2 as. str.
CH2 s. str.
CH2 scis.
CH2 wag
CH2 twist
C-F str.
CH2 rock
C-Ni str.
Ni-Cl str.
NiCF bend
CH2F tort
CNiCl bend
3197.3
3086.0
1456.0
1177.2
1137.1
889.7
678.9
629.8
434.0
242.3
122.5
105.1
1
6
0
29
3
131
7
12
44
6
5
10
3117.6
3004.2
1402.8
1127.0
1093.4
874.4
657.0
614.2
435.2
223.2
117.9
101.4
1
7
0
31
3
119
6
20
31
5
4
9
2384.1
2229.9
1087.2
949.8
856.2
848.9
571.0
501.4
433.4
241.5
118.8
102.2
1
5
10
17
2
132
3
4
44
6
5
10
2325.3
2169.2
1049.1
917.2
825.3
824.7
557.1
485.0
434.7
222.4
113.9
98.7
1
7
9
20
2
126
5
3
31
6
3
9
1122.0
884.2
797.7
844.9
605.3, 598.4
425.3
a Frequencies and intensities are in cm-1 and km/mol. b Observed (i0 absorption) in an argon matrix. c Frequencies and intensities computed with
B3LYP or BPW91/6-311þþG(3df, 3pd) are for harmonic calculations. CH2F-NiCl has a bridged C1 structure in its triplet ground state.
Table 8. Observed and Calculated Fundamental Frequencies of CH2F-NiCl Isotopomers in the 3A Ground Statesa
CH2F--NiCl
CD2F-NiCl
approximate
description
obsb
B3LYPc
intc
BPW91c
intc
obsb
B3LYPc
intc
BPW91c
intc
CH2 as. str.
CH2 s. str.
CH2 scis.
CH2 twist
CH2 wag
3110.7
3022.1
1446.4
1209.1
1207.1
969.2
602.7
537.2
388.8
164.9
78.6
9
13
5
3046.9
2943.4
1391.1
1167.1
1146.7
952.8
573.3
506.4
388.7
176.0
83.8
7
11
3
2308.4
2188.1
1073.6
901.1
949.2
942.6
507.5
455.5
378.4
163.2
74.7
5
9
22
2
48
203
17
35
36
6
2260.8
2130.1
1036.2
872.0
899.7
926.4
490.2
431.8
371.6
173.5
80.2
4
8
33
2
88
138
7
26
15
3
8
3
1158.2
982.6
70
239
11
24
54
6
48
238
8
13
32
3
900.6
956.7
C-F str.
C-Ni str.
CH2 rock
Ni-Cl str.
FCNi bend
CNiF bend
CH2F tort
5
8
3
5
5
8
4
5
30.1
39.6
29.5
38.6
a Frequencies and intensities are in cm-1 and km/mol. b Observed in an argon matrix. c Frequencies and intensities computed with B3LYP or BPW91/
6-311þþG(3df, 3pd) are for harmonic calculations. CH2F-NiCl has a bridged C1 structure in its triplet ground state.
stretching frequency. The i absorption at 1031.1 cm-1 along
with the D counterpart at 813.1 cm-1 (H/D ratio of 1.268) is
assigned to the CH2 wagging mode. Another one at 700.0
cm-1 shows a D shift of -55.0 cm-1 (H/D ratio of 1.085) and
are observed. The i absorptions remain unchanged upon
visible and UV irradiation, but decrease ∼20% on full arc
irradiation, whereas the i0 absorptions increase ∼20% on
visible irradiation, remain almost the same on UV irradia-
tion, and decrease slightly on full arc irradiation. The
observed frequencies are compared with the DFT frequen-
cies in Tables 7 and 8. The i absorption at 1122.0 cm-1 along
with its D counterpart at 884.2 cm-1 (H/D ratio of 1.268) is
assigned to the CH2 wagging mode of singlet CH2F-NiCl on
the basis of the frequency and small D shift. The strong i
absorption at 844.9 cm-1 has its D counterpart at 797.7 cm-1
(H/D ratio of 1.059) and is assigned to the C-F stretching
is assigned to the C-Cl Ni symmetric stretching mode on
3 3 3
the basis of the frequency and relatively small D shift. The
one at 496.8 cm-1 has its D counterpart at 477.3 cm-1 (H/D
ratio of 1.041) and is assigned to the C-Cl Ni antisym-
3 3 3
metric stretching mode. The strong absorption at 425 cm-1
near our observation limit shows its D counterpart at 422
cm-1 and is assigned to the Ni-Cl stretching mode. The four
observed i absorptions and their D counterparts have good
correlations with the DFT frequencies and substantiate
formation of CH2Cl-NiCl.
mode of the bridged (C-F Ni) complex in the singlet state
3 3 3
(Figure 7). Another i absorption at 605.3 cm-1 (with a
shoulder at 598.4 cm-1) is assigned to the C-Ni stretching
mode without observation of the D counterpart. The weak
absorption at 425 cm-1 (not shown) is tentatively assigned to
the Ni-Cl stretching mode. The observed absorptions all
support formation of singlet, F-bridged CH2F-NiCl
(Table 7). The strongest Ni-F stretching absorption for
the Ni methylidene, CH2-NiFCl, would be expected at
∼650 cm-1 in both singlet and triplet states, which is not
observed in this study.
In addition, isolated NiCl2 is observed at 520.9, 517.5, and
513.1 cm-1 (Figure 4) for chlorine and nickel isotopic splittings,
in good agreement with previous observations.27 Such NiCl2
bands were detected with CCl4 but not with CHCl3. The
observation of NiCl2 suggests that CH2-NiCl2 may be formed
in these experiments, but if so, it decomposes. The strong
425 cm-1 band is not appropriate for assignment to either
singlet- or triplet-state carbene based on calculated frequencies.
The spectra from reactions of CH2FCl and its deuterated
isotopomer are shown in Figure 5, where i and i0 absorptions
The i0 absorption at 1158.2 cm-1 has its D counterpart at
900.6 cm-1 (H/D ratio of 1.286), and we assign it to the CH2
wagging mode of the insertion complex in the triplet state
(CH2F-NiCl(T)) on the basis of the frequency, H/D ratio,
(27) Jacox, M. E.; Milligan, D. E. J. Chem. Phys. 1969, 51, 4143.
(NiCl2).

Article
Organometallics, Vol. 28, No. 19, 2009 5631
and computational results. The strong i0 absorption at
982.6 cm-1 with its D counterpart at 956.7 cm-1 (H/D ratio
of 1.027) is assigned to the C-F stretching mode (Table 8).
The structure of the insertion complex in the triplet state
substantially differs from that in the singlet state, while the
singlet and triplet states are almost isoergic (42 and 43 kcal
lower than the reactants (Ni(3F) þ CH2FCl)). Unlike the
F-bridged structure in the singlet state, it does not bear a
bridged structure and the C-Ni-Cl moiety is more linear
(—CNiCl = 145.0ꢀ), and therefore, the large structural
difference is retained by trapping in the matrix and so is
the electronic state. Unfortunately all other bands for
CH2F-NiCl(T) are expected to be too weak to observe as
shown in Table 8.
Figure 6 illustrates spectra from reaction of Ni with
CH2F2 and CD2F2, where only one type of absorption
marked “i0” is observed. The product absorptions decrease
slightly on visible irradiation, increase ∼30% on UV photo-
lysis, and increase slightly further on full arc photolysis.
We attribute these product absorptions to the insertion
product in its triplet ground state (i0 for triplet insertion
complex). The i0 absorption at 958.3 cm-1 (with a shoulder at
955.8 cm-1) has its D counterpart at 927.1 cm-1 (H/D ratio
of 1.034) and is assigned to the C-F stretching mode on the
basis of the frequency and small D shift. The strong absorp-
tion at 663.7 cm-1 along with its D counterpart at 657.0 cm-1
(H/D ratio of 1.010) is assigned to the Ni-F stretching mode.
The weaker i0 absorption at 573.2 cm-1 has its D counterpart
at 484.0 cm-1 (H/D ratio of 1.184) and is assigned to the
CH2 rocking mode. Another i0 absorption is observed at
927.0 cm-1 in the CD2F2 spectra, and its H counterpart is
believed covered by precursor absorption. It is assigned to
the CH2 wagging mode. The carbene complex (CH2-NiF2)
is 15 and 11 kcal/mol higher in the singlet and triplet states
than the insertion complex and would show the strong NiF2
antisymmetric stretching band at ∼750 cm-1, which is not
observed. The singlet insertion complex (4.5 kcal/mol higher
than that in the triplet state) would have the strong C-F
stretching band at ∼830 cm-1 and its D counterpart at
∼790 cm-1, which are not observed in the spectra.
Structures of Ni Complexes. The calculated structures of
the Ni complexes identified here are illustrated in Figure 7.
The carbene complexes, CCl2-NiCl2, CFCl-NiCl2, and
CF2-NiCl2, have staggered structures, parallel to the corre-
sponding group 8 metal and Pt complexes.8,10 The B3LYP-
computed C-Ni bond lengths of the small Ni carbenes of
˚
1.733, 1.738, and 1.748 A are slightly longer than CASPT2
˚
values, 1.673, 1.663, and 1.658 A, which may be compared
28
˚
with those of 1.83-1.92 A for typical Ni carbenes. The
CASPT2 structures for the carbenes are shown in Figure 8.
New CASSCF/CASPT2 calculations were performed on
the carbenes in order to characterize the nickel-carbon
bonds. The molecular orbitals involved in the C-Ni bonds
are illustrated in Figure 9. The EBO, effective bond orders
(bonding minus antibonding occupancy divided by two), of
CCl2-NiCl2, CFCl-NiCl2, and CF2-NiCl2 are 1.81, 1.84,
and 1.87 as shown. Analogous calculations reveal 1.89, 1.90,
and 1.91 EBO values for the corresponding Pt complexes.
In agreement with the previously characterized group 3-8
Figure 9. Calculated CASPT2 orbitals involved in the carbon-
nickel double bonds. Occupation numbers given in parentheses.
metal, actinide, and Pt carbenes,5-10 the methylidene C-Ni
bond is essentially a double bond. The increasing effective
bond order with the number of F atoms is also observed in
previously studied Pt systems,10 suggesting that the more
electronegative F substituent on carbon contracts the C 2p
orbitals and thus enhances the C 2p-Ni 3d orbital overlap.
(28) (a) Miki, K.; Taniguchi, H.; Kai, Y.; Kasai, N.; Nishiwaki, K.;
Wada, M. J. Chem. Soc., Chem. Commun. 1982, 1180. (b) Hou, H.;
Gantzel, P. K.; Kubiak, C. P. J. Am. Chem. Soc. 2003, 125, 9564.
(c) Normand, A. T.; Hawkes, K. J.; Clement, N. D.; Cavell, K. J.; Yates,
B. F. Organometallics 2007, 26, 5352 (C-Ni length).

5632 Organometallics, Vol. 28, No. 19, 2009
Cho et al.
The Ni insertion complexes with X (particularly Cl)
bonded to C have bridged structures as shown in Figure 7,
and similar bridged structures (with bridging Cl) are ob-
served in the Fe insertion complexes CH2Cl-FeCl and
CHCl2-FeCl.8 Coordination of Cl electrons to the metal
center is evidently more efficient than that of F, and
CH2F-NiCl is believed to be the first F-bridged complex
between C and M to the best of our knowledge. Coordina-
tion of F electrons to Ni is, however, not as effective as that of
Cl; the —FCNi (79.3ꢀ) is larger than those of the Cl-bridging
complexes (—ClCNi = 71.9-76.7), and vibrational analysis
through C-X bond activation/insertion followed by R-X
transfer,8-10 reaction 1.
ꢀ
ꢀ
ꢀ
M þCX4 f CX3-MX f CX2-MX2 f CX-MX3
ð1Þ
The present results reveal that C-X bond insertion by
group 10 metal atoms occurs readily in reactions with
halomethanes, and in the case of tetrahalomethanes,
X migration from C to M also follows. However, further
X migration to form the carbyne product has not been
observed, probably due to the much higher energy of the
product. For example, CCl-PtCl3 is 27 kcal/mol higher in
energy than CCl2dPtCl2,10 and geometry optimization for
CCl-NiCl3 and CCl-PdCl3 results in the corresponding
carbene complexes.
shows that the contribution of the Ni F stretching motion
3 3 3
to the C-F stretching mode is insignificant.
As described above, the singlet and triplet states of the
identified products except CH2F-NiF are almost isoergic;
however, the observed vibrational characteristics correlate
with those predicted for the singlet states. In the case of
CH2F-NiCl, evidence shows that both the singlet and triplet
states are trapped in a matrix as described above. It is not
clear at the moment why the singlet Ni products are more
favored in the matrix. The singlet Ni products are in line with
the identified singlet Pt complexes.10 Unlike the Ni cases, the
singlet states of the Pt products are substantially more stable
than the triplet states.
Conclusions
Laser-ablated Ni atoms react with halomethanes, and the
products are identified on the basis of isotopic shifts and
correlation with the DFT results. The CX2-NiX2 molecules
are produced by reactions with tetrahalomethanes, revealing
that group 10 metals all form carbenes, while the reaction is
more exothermic and the yield much higher for X = Cl than
X = F, parallel to the previously studied Pt case.10 On the
other hand, only insertion complexes are identified from
reactions with precursors containing H substituents, indicat-
ing that X migration from C to M following initial C-X bond
insertion becomes much more difficult. This also suggests that
group 10 metals are close to the limit where the carbene
complex is no longer produced in transition-metal reactions
with halomethanes. In agreement with the Pt case, the car-
bon-metal bonds of the Ni carbenes are essentially double
bonds with effective bond orders in the range 1.8-1.9.
Although singlet states are clearly the most stable for the
corresponding Pt complexes,10 DFT calculations show that
the singlet and triplet states are often nearly isoergic for the
Ni complexes. However, the observed vibrational character-
istics show that most of the Ni products also have singlet
ground states. The identified Ni carbene complexes all have
staggered structures, whereas the insertion products with a
C-Cl bond have bridged structures, indicative of efficient Cl
electron donation to the metal center. CH2F-NiCl reveals a
unique F-bridged structure.
Reactions. Previous studies and the present results reveal
that high-oxidation-state complexes are generated from
reactions of group 3-10 transition metals and actinides with
small alkanes and halomethanes.5-10,29 However, the pre-
ference for methylidene products in reactions of group 10
metals varies substantially. Pt, which is regarded in general
as the strongest insertion agent among group 10 metals,12
forms carbenes not only with haloalkanes but with less
reactive methane as well.10 Analogous Ni carbene complexes
are, on the other hand, far less favored. They are produced
only in reactions with tetrahalomethanes, thanks to the
preference for reaction of the M-X bond (particularly the
M-Cl bond) over the M-H bond. Only the insertion
complex is formed with chloroform and dihalomethane
precursors. It is possible that repulsion between halogen
atoms on the carbon center in the insertion product increases
the rate of R-X transfer. Overall these results suggest that
group 10 metals are near the limit of carbene complex
formation in reactions with small alkanes and halomethanes,
which is consistent with the fact that Ni carbene complexes
are rare.2 The observation of NiCl2 in the CH2Cl2 experi-
ments suggests that the CH2-NiCl2 carbene may be formed
but decomposes.
Acknowledgment. We gratefully acknowledge financial
support from National Science Foundation (U.S.) Grant
CHE 03-52487 to L.A., and support from Korea Institute
of Science and Technology Information (KISTI) by Grant
No. KSC-2008-S02-0001 and from the Swiss National
Science Foundation (grant 200020-120007).
Investigations in our laboratory have shown that laser-
ablated transition-metal atoms react with halomethanes
(29) Cho, H.-G.; Andrews, L. Reactions of group 9 metals with
halomethanes, unpublished data.