Triplet XC÷TiX3 Methylidyne Complexes
Figure 1. Infrared spectra in the 1480-1400, 780-680, and 500-440 cm-1 regions taken after (a) laser-ablated titanium atoms were reacted with 1%
CF4/Ar during condensation at 8 K for 1 h, and the resulting matrix was subjected to (b) irradiation with light λ > 290 nm, (c) irradiation with λ > 220 nm,
(d) annealing to 30 K, and (e) irradiation with λ > 220 nm.
well documented by calculations.18-21 Likewise, gaseous Tit
CH has been investigated in neutral and ionic forms both
theoretically and experimentally.22-26 Most recently, a ter-
minal titanium alkylidyne intermediate has been proposed
for C-H activation reactions.27 We now present the first
experimental observation of a titanium alkylidyne complex
with an electron-deficient or partially occupied triple bond
(σ2ππ) from the reactions of Ti and CX4 molecules.
slight increases upon irradiation by mercury arc light passing
through a Pyrex filter (λ > 290 nm), substantial growth on
full arc photolysis (λ > 220 nm), no change on annealing to
30 K, and slight growth on a subsequent full arc irradiation
(Figure 1). These four absorptions exhibit constant relative
intensities in experiments with different reagent concentra-
tions, and they can be assigned to a common reaction
product. The two lower strong peaks are above and below
the 740 cm-1 antisymmetric Ti-F stretching frequency of
TiF2,34 whereas the upper product band is 179 cm-1 higher
Experimental and Theoretical Methods
Our experimental apparatus has been described in detail else-
where.10,11,28 In brief, laser-ablated (Nd:YAG laser; 1064 nm)
titanium atoms were reacted with CF4, CCl4, or 13CCl4 at a 0.1-
1.0% concentration in argon during condensation at 8 K. Low laser
energy was employed to minimize any contribution from Ti cluster
species. In previous work, a major product exhibited resolved
natural Ti isotopic splittings for a vibration involving one Ti atom.11
Infrared spectra of the products were collected on a Nicolet Magna
550 spectrometer with a mercury cadmium telluride type B detector
cooled to 77 K. Reaction products were subjected to irradiation
from a mercury arc lamp with the globe removed (λ > 220 nm)
using select filters and to sample annealings. Additional IR spectra
were recorded after each procedure.
(18) Gutsev, G. L.; Andrews, L.; Bauschlicher, C. W. Theor. Chem. Acc.
2003, 109, 298.
(19) Pyykko¨, P.; Riedel, S.; Patzschke, M. Chem.sEur. J. 2005, 11, 3511.
(20) Clemmer, D. E.; Elkind, J. L.; Aristov, N.; Armentrout, P. B. J. Chem.
Phys. 1991, 95, 3387.
(21) Kerkines, I. S. K.; Mavridis, A. J. Phys. Chem. A 2000, 104, 11777.
(22) Mavridis, A.; Alvarado-Swaisgood, A. E.; Harrison, J. F. J. Phys.
Chem. 1986, 90, 2584.
(23) Kalemos, A.; Dunning, T. H.; Harrison, J. F.; Mavridis, A. J. Chem.
Phys. 2003, 119, 3745.
(24) Zhang, R. Q.; Lu, W. C.; Cheung, H. F.; Lee S. T. J. Phys. Chem. B
2002, 106, 625.
(25) Barnes, M.; Merer, A. J.; Metha, G. F. J. Mol. Spectrosc. 1997, 181,
168.
(26) Vidal, I.; Melchor, S.; Dobado, J. A. J. Phys. Chem. A 2005, 109,
7500.
All theoretical computations were performed using the Gaussian
98 package with the B3LYP hybrid density functional.29,30 The
6-311+G(3df) basis was used to represent the electronic density
of the carbon, halogen, and titanium atoms.31 Frequencies were
computed analytically, and all energy values reported include zero-
point vibrational corrections. The calculation of vibrational frequen-
cies is not an exact science, and density functional theory (DFT)
provides a very good approximation for observed frequencies.
Calculated frequencies are usually a few percent higher than the
observed values,32,33 but that is not always the case. Relevant
comparisons can be made to CH2dTiF2, where two strong Ti-F
stretching modes were calculated 23.6 and 24.5 cm-1 (3.2 and 3.5%)
too high,12 and to TiCl4, where the strong 502.6 cm-1 antisymmetric
Ti-Cl fundamental is calculated 0.8% lower at 499.8 cm-1 by using
the above methods.
(27) Bailey, B. C.; Fan, H.; Baum, E. W.; Huffman, J. C.; Baik, M.-H.;
Mindiola, D. J. J. Am. Chem. Soc. 2005, 127, 16016.
(28) (a) Andrews, L. Chem. Soc. ReV. 2004, 33, 123. (b) Andrews, L.;
Cho, H.-G. Organometallics 2006, 25, 4040 (review article).
(29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B. G.;
Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon, M.; Replogle,
E. S.; Pople, J. A. Gaussian 98, revision A.11.4; Gaussian, Inc.:
Pittsburgh, PA, 1998.
(30) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.; Yang,
Y.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(31) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80,
3265.
Results and Discussion
(32) Scott, A. P.; Radom, L. J. Phys. Chem. 1996, 100, 16502.
(33) Andersson, M. P.; Uvdal, P. J. Phys. Chem. A 2005, 109, 2937.
(34) Hastie, J. W.; Hauge, R. H.; Margrave, J. L. J. Chem. Phys. 1969, 51,
2648.
Laser-ablated titanium atoms react with CF4 to produce
one weak 481.7 cm-1 band and three strong absorptions at
686.1, 752.8, and 1453.1 cm-1. All four absorptions showed
Inorganic Chemistry, Vol. 45, No. 24, 2006 9859