Titanium, Zirconium, and Hafnium Metal Atom Reactions with CF 4 , CCl 4 , and CF 2 Cl 2 : A Matrix Isolation Spectroscopic and DFT Investigation of Triplet XC÷MX 3 Complexes Jonathan T. Lyon and Lester Andrews* Department of Chemistry, UniVersity of Virginia, P.O. Box 400319, CharlottesVille, Virginia 22904-4319 ReceiVed February 6, 2007 Laser-ablated group 4 transition metal atoms react with CF 4 to form triplet state electron-deficient FC÷MF 3 methylidyne complexes, which are identified by their infrared spectra and comparison to density functional vibrational frequency calculations of stable possible products. Of particular interest in these complexes are the strong C-X bonds and carbon-metal π bonding. The two unpaired electrons on carbon are drawn to the electron-deficient transition metal center, forming a partially filled triple bond, which is approximately equal in length to a classical CdM double bond. Reactions with carbon tetrachloride form the analogous ClC÷MCl 3 complexes, whereas reactions with CF 2 Cl 2 form a mixture of FC÷MFCl 2 and ClC÷MF 2 Cl species. The FC÷MFCl 2 complexes involving more R-Cl transfer are favored in the reaction of excited metal atoms during sample deposition, but UV irradiation photoisomerizes FC÷MFCl 2 to the lower energy ClC÷MF 2 Cl complexes with more R-F transfer to the metal center. Introduction Transition metal compounds are important for their roles in catalysis. In particular, the study of organotitanium compounds has been an active field of research. 1-3 Recently, nanostructural carbon has been synthesized by the reaction of titanium carbide with chlorine gas, with TiCl 4 as a byproduct of the reaction. 4-6 Freon compounds are hazardous to the ozone layer, and the activation of C-X bonds is a necessary process in their remediation. 7 However, C-F bonds are the strongest known carbon single bond, 8 and their activation is not always trivial. We have recently reacted group 4 transition metal atoms with CH 3 X precursors (X ) H, F, Cl, and Br). 9 In these experiments, the primary reaction products are the double-bonded CH 2 dMHX methylidene complexes, which show considerable agostic interactions between the transition metal center and one set of C-H-bonding electrons. Titanium, zirconium, and hafnium all combined with CH 2 X 2 (X ) F and Cl) to yield the very stable CH 2 dMX 2 methylidenes, which showed no agostic distortions, 10-12 but reactions with CHX 3 (X ) F and Cl) yielded triplet HC÷MX 3 species (except for Ti + CHF 3 , where the reaction stopped at the CHFdTiF 2 intermediate). 11,12 These complexes are unique in that the two unpaired electrons on carbon are shared partially with the transition metal center. The formation of this novel electron-deficient C÷M triple bond is more prevalent in the FC÷TiF 3 and ClC÷TiCl 3 complexes in the reaction between laser-ablated titanium atoms and CX 4 (X ) F and Cl). 13 We now report on reactions of the entire group 4 transition metal series with CF 4 and CCl 4 , and the mixed chlorofluorocarbon CF 2 Cl 2 for comparison. A particular question we want to answer in this investigation is whether FC÷MFCl 2 , ClC÷MF 2 Cl, neither complex, or both complexes are formed and how this distortion of symmetry effects the partially filled C÷M triple bonds. Experimental and Theoretical Methods Our experimental design has been described in detail previ- ously. 14 In brief, metal atoms, produced by laser ablation with a Nd:YAG laser, were co-deposited with a dilute mixture (0.25- 1.0%) of reagent vapor (CF 4 , CCl 4 , CF 2 Cl 2 , 13 CCl 4 , or 13 CF 2 Cl 2 ) 15 in argon onto a CsI window cooled to 8 K. The resulting reaction products were frozen in the inert matrix, and the infrared spectrum was recorded on a Nicolet Magna 550 spectrometer. Matrix samples were irradiated for 10 min periods by a medium-pressure mercury arc lamp with the globe removed (λ > 220 nm) with or without a Pyrex (λ > 290 nm) filter and subsequently annealed to various temperatures. Additional infrared spectra were recorded following each procedure. * Corresponding author. E-mail: lsa@virginia.edu. (1) Bini, F.; Rosier, C.; Saint-Arroman, R. P.; Neumann, E.; Dadlemont, C.; de Mallmann, A.; Lefebvre, F.; Niccolai, G. P.; Basset, J.-M.; Crocker, M.; Buijink, J.-K. Organometallics 2006, 25, 3743. (2) Zhang, Y.; Mu, Y. Organometallics 2006, 25, 631. (3) Anthis, J. W.; Filippov, I.; Wigley, D. E. Inorg. Chem. 2004, 43, 716. (4) Leis, J.; Perkson, A.; Arulepp, M.; Nigu, P.; Svensson, G. Carbon 2002, 40, 1559. (5) Zetterstro ¨m, P.; Urbonaite, S.; Lindberg, F.; Delaplane, R. G.; Leis, J.; Svensson, G. J. Phys.: Condens. Matter 2005, 17, 3509. (6) Permann, L.; La ¨tt, M.; Leis, J.; Arulepp, M. Electrochim. Acta 2006, 51, 1274. (7) Molina, M. J.; Rowland, F. S. Nature 1974, 249, 810. (8) Strauss, S. H. Chem. ReV. 1993, 93, 927. (9) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040, and references therein. (10) Lyon, J. T.; Andrews, L. Organometallics 2006, 25, 1341 (Ti + CH 2F2). (11) Lyon, J. T.; Andrews, L. Inorg. Chem. 2007, 46, ASAP 12/19/06 (Ti, Zr, and Hf + CH 2F2 and CHF3). (12) Lyon, J. T.; Andrews, L. Organometallics 2007, 26, 332 (Ti, Zr, and Hf + CH2Cl2 and CHCl3). (13) Lyon, J. T.; Andrews, L. Inorg. Chem. 2006, 45, 9858 (Ti + CF4 and CCl4). (14) (a) Andrews, L. Chem. Soc. ReV. 2004, 33, 123. (b) Andrews, L.; Citra, A. Chem. ReV. 2002, 102, 885, and references therein. (15) (a) Prochaska, F. T.; Andrews, L. J. Chem. Phys. 1978, 68, 5568. (b) Prochaska, F. T.; Andrews, L. J. Chem. Phys. 1978, 68, 5577. (c) Milligan, D. E.; Jacox, M. E.; McAuley, J. H.; Smith, C. E. J. Mol. Spectrosc. 1973, 45, 377. 2519 Organometallics 2007, 26, 2519-2527 10.1021/om070120g CCC: $37.00 © 2007 American Chemical Society Publication on Web 04/06/2007