An infrared spectroscopic and theoretical study of group 4 transition metal CH2=MCl2 and HC÷MCl3 complexes

Article abstract of DOI:10.1021/om0608399

Laser-ablated group 4 transition metal atoms react with CH ₂Cl₂ and CHCl₃ to yield the singlet CH ₂=MCl₂ and triplet HC÷MCls complexes, respectively. These products are identified by infrared spectra,

Full text of DOI:10.1021/om0608399

332
Organometallics 2007, 26, 332-339
An Infrared Spectroscopic and Theoretical Study of Group 4
Transition Metal CH2dMCl2 and HC÷MCl3 Complexes
Jonathan T. Lyon and Lester Andrews*
Department of Chemistry, UniVersity of Virginia, P.O Box 400319, CharlottesVille, Virginia 22904-4319
ReceiVed September 13, 2006
Laser-ablated group 4 transition metal atoms react with CH2Cl2 and CHCl3 to yield the singlet
CH2dMCl2 and triplet HC÷MCl3 complexes, respectively. These products are identified by infrared
spectra, isotopic substitution of the reactant precursors, and comparison to density functional theoretically
predicted vibrational modes for the lowest energy structures. The computed CH2dMCl2 methylidene
structures show no evidence of agostic distortion, in contrast to the previously investigated CH2dMHCl
complexes. In the triplet HC÷MCl3 complexes, the two unpaired electrons on carbon interact with the
transition metal center and contribute weak π bonding. Comparisons with the analogous fluorinated
complexes are given.
strengths similar to weak hydrogen bonds.18 In addition, titanium
reacted with fluoroform to produce the analogous CHFdTiF2
methylidene, which exhibited no distortion, but zirconium and
hafnium formed the more stable triplet HC÷MF3 complexes.19
In these novel complexes the two unpaired electrons on carbon
are shared with the electron-deficient metal center to give
additional π bonding. We now report on the reaction products
formed between group 4 transition metals and the chlorinated
analogues (CH2Cl2 and CHCl3) for comparison.
1. Introduction
Metal-carbon bonds are fundamentally important, and the
entire organometallic subset of chemistry is devoted to them.
Double-bonded alkylidene complexes in particular are of
considerable interest for their roles in catalysis, and early
transition metal alkylidenes have been proposed as reaction
intermediates.1-3 Carbon-halogen bond activation is also of
considerable interest as a possible means of remediation for
chlorofluorocarbons.4-7
The goals of this study are as follows. In the reactions with
dichloromethane, we wish to investigate whether CH2dMCl2
methylidenes form similarly to the fluorine analogues, or if
chlorine substitution alters the reaction pathway. The C-Cl
bonds are easier to break than C-F bonds, but the bulkier
chlorine atoms are also slower to transfer, and H transfer might
compete. Recall that H transfer produced the CH2dTiHCl
complex from the Ti + CH3Cl reaction.16 If the CH2dMCl2
complexes are formed, will the complex be symmetrical like
CH2dTiF2 or distorted like CH2dTiHCl? As the group 4
transition metals gave different products in the reaction with
CHF3, we now wish to investigate how the chlorine analogues
alter this reaction pathway and to compare the resulting products
with those formed in fluoroform reactions.
Recently our group has investigated the reactions of group 4
transition metals with CH4 and CH3X molecules.8-16 In these
studies, the primary reaction products are double-bonded
methylidene complexes, which show considerable agostic
interactions between the metal center and the bonded C-H
electrons. Methylene fluoride reacted with titanium to form the
CH2dTiF2 methylidene complex.17 However, in this instance
no agostic distortion was observed. Fluorine lone pair repulsions
were suggested to prevent this novel interaction. Recently,
theoretical calculations have predicted that agostic bonds have
* Corresponding author. E-mail: lsa@virginia.edu.
(1) Schrock, R. R. Chem. ReV. 2002, 102, 145.
(2) Wada, K.; Pamplin, C. B.; Legzdins, P.; Patrick, B. O.; Tsyba, I.;
Bau, R. J. Am. Chem. Soc. 2003, 125, 7035.
(3) Bailey, B. C.; Fan, H.; Baum, E. W.; Huffman, J. C.; Baik, M.-H.;
Mindiola, D. J. J. Am. Chem. Soc. 2005, 127, 16016.
(4) Burdeniuc, J.; Jedlicka, B.; Crabtree, R. H. Chem. Ber./Recl. 1997,
130, 145.
(5) Yang, H.; Gao, H.; Angelici, R. J. Organometallics 1999, 18, 2285.
(6) Kraft, B. M.; Lachicotte, R. J.; Jones, W. D. J. Am. Chem. Soc. 2001,
123, 10973.
2. Experimental and Theoretical Methods
Our experimental methods have been described in detail else-
where.20,21 In brief, laser-ablated transition metal atoms, generated
by a Nd:YAG laser (1064 nm), were co-deposited with reagent
gas diluted in argon (0.4-1.0%) onto a CsI window cooled to 8 K
for the duration of 1 h. Infrared spectra were collected at 0.5 cm-1
resolution in the 400-4000 cm-1 region on the matrix-isolated
reaction products by a Nicolet Magna 550 spectrometer with a
HgCdTe type B detector at 77 K. Matrixes were subjected to UV
irradiation for 10 min periods using a medium-pressure mercury
arc lamp (Philips, 175 W) with the globe removed (λ > 220 nm)
and annealings to various temperatures. Infrared spectra were
collected after each procedure.
(7) Scott, V. J.; Celenligil-Cetin, R.; Ozerov, O. V. J. Am. Chem. Soc.
2005, 127, 2852.
(8) Andrews, L.; Cho, H.-G. Organometallics 2006, 25, 4040.
(9) Andrews, L.; Cho, H.-G.; Wang, X. Inorg. Chem. 2005, 44, 4834
(Ti+CH4).
(10) Cho, H.-G.; Wang, X.; Andrews, L. J. Am. Chem. Soc. 2005, 127,
465 (Zr+CH4).
(11) Cho, H.-G.; Wang, X.; Andrews, L. Organometallics 2005, 24, 2854
(Hf+CH4).
(12) Cho, H.-G.; Andrews, L. Inorg. Chem. 2004, 43, 5253 (Ti+CH3F).
(13) Cho, H.-G.; Andrews, L. J. Phys. Chem. A 2004, 108, 6294
(Ti+CH3F).
(18) von Frantzius, G.; Streubel, R.; Brandhorst, K.; Grunenberg, J.
Organometallics 2006, 25, 118.
(19) Lyon, J. T.; Andrews, L. Inorg. Chem., in press [IC061701L] (Ti,
Zr, Hf+CH2F2 and CHF3).
(20) Andrews, L. Chem. Soc. ReV. 2004, 33, 123.
(21) Wang, X.; Andrews, L. Phys. Chem. Chem. Phys. 2005, 7, 3834.
(14) Cho, H.-G.; Andrews, L. J. Am. Chem. Soc. 2004, 126, 10485
(Zr+CH3F).
(15) Cho, H.-G.; Andrews, L. Organometallics 2004, 23, 4357 (Hf+CH3F).
(16) Cho, H.-G.; Andrews, L. Inorg. Chem. 2005, 44, 979 (Ti+CH3Cl).
(17) Lyon, J. T.; Andrews, L. Organometallics 2006, 25, 1341 (Ti+CH2F2).
10.1021/om0608399 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 12/15/2006

Group 4 Transition Metal CH2dMCl2 and HC÷MCl3 Complexes
Organometallics, Vol. 26, No. 2, 2007 333
Figure 2. IR spectra taken in the 710-450 cm-1 region taken after
laser-ablated titanium atoms were reacted with (a) CH2Cl2, (b)
13CH2Cl2, and (c) CD2Cl2 diluted in argon. All spectra were recorded
after full-arc photolysis (λ > 220 nm). Arrows denote product
absorptions.
Figure 1. Infrared spectra taken in the 690-460 cm-1 region after
(a) laser-ablated titanium atoms were reacted with CH2Cl2/Ar, and
the resulting matrix was subjected to (b) irradiation with λ > 290
nm, (c) irradiation with λ > 220 nm, and (d) annealing to 30 K.
Arrows denote product absorptions.
in all figures.) Hence the three observed bands can be assigned
to a single reaction product. The strongest absorption, at 504.3
cm-1, remains nearly unchanged on 13C and D isotopic
substitution (0.5 and 1.9 cm-1 shifts, respectively). This is also
only slightly higher than the 502.6 cm-1 Ti-Cl stretching mode
in TiCl4.26a Hence, the observed product absorption can be
assigned to a Ti-Cl stretching frequency. The next highest peak,
at 675.0 cm-1, shows a modest 5.3 cm-1 carbon-13 shift and a
large 134.5 cm-1 deuterium isotopic shift (frequency ratio 1.249)
(Figure 2). These values are similar to those for the observed
Unless otherwise noted, all theoretical calculations were com-
puted using the Gaussian ’98 package.22 The B3LYP hybrid
functional23 was used with the 6-311++G(2d,p) basis for all atoms
except the transition metal, where the SDD pseudopotential was
employed.24,25 These calculations will enable comparisons with other
methylidene complexes.8-19 Vibrational frequencies were computed
analytically, and all energy values reported include zero-point
vibrational corrections. As a calibration, our calculation for the
stable molecule TiCl4 gave a tetrahedral structure with a strong IR
mode at 499.7 cm-1, which compares favorably with the argon
matrix absorption26a at 502.6 cm-1. Our DFT calculation predicts
TiCl4 to be more stable than Ti and two Cl2 by 285 kcal/mol, which
may be compared to the gas phase thermodynamic value of 295 (
2 kcal/mol.26b
CH2 wagging motion of the CH2dTiF2 complex (695.4 cm-1
;
6.0 and 138.6 cm-1 13C and D shifts, respectively).17 The last
observed vibration at 679.7 cm-1 shows the largest carbon-13
shift (20.1 cm-1) and a modest deuterium shift (71.9 cm-1),
and it can be assigned to a mostly CdTi stretching mode. A
final fourth absorption was observed at 978.9 cm-1 only in
experiments when CD2Cl2 was employed.
3. Results and Discussion
Reactions between group 4 transition metals and CH2Cl2 or
CHCl3 will be investigated, and product infrared spectra and
DFT calculations will be reported in turn.
3.1. Ti + CH2Cl2. When laser-ablated titanium atoms react
with methylene chloride, new product absorptions are observed
at 503.0 with matrix site splitting at 505.5, 675.0, and 679.7
cm-1. All three absorptions increase in unison on all photolysis,
remain nearly unchanged on annealing (Figure 1), and maintain
constant relative intensity in experiments with different precursor
concentrations. (Arrows are used to denote product absorptions
The three identified product modes (Ti-Cl stretch, CH2 wag,
and CdTi stretch) lead to identification of the stable
CH2dTiCl2 complex with confidence. Our computed frequen-
cies for this complex compare favorably with the observed
spectrum (Table 1). Typically DFT-computed frequencies are
a few percent higher than observed values.9-16,26c The fourth
strongest mode predicted for the CH2dTiCl2 complex (Ti-Cl
symmetric stretch; 374.7 cm-1) is below our spectral limits. The
CH2 bending mode was computed to be nearly twice as intense
for the deuterated isotopomer at 1033.1 cm-1 and is in
satisfactory agreement with the fourth peak observed at 978.9
cm-1 when CD2Cl2 was employed. This gain in intensity is due
to increased coupling with the CdTi stretching mode.
Singlet methylidene CH2dTiCl2 is predicted to be 127
kcal/mol more stable than the sum of the individual methylene
chloride and titanium atom reactants and 29 kcal/mol more
stable than the triplet CH2(µ-Cl)TiCl primary insertion product.
Another possible singlet methylidene complex, CHCldTiHCl,
is 62 kcal/mol higher in energy than CH2dTiCl2, and the
computed vibrational spectrum is vastly different (including a
strong Ti-H stretching mode near 1700 cm-1, which is not
observed). Although R-H transfer may be faster than R-Cl
transfer, the latter is much more favorable energetically. The
CH2dTiCl2 complex has been studied theoretically over the last
two decades;27-37 however, this is the first experimental
observation to our knowledge.
(22) 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.; Rega,
N.; Salvador, P.; Dannenberg, J. J.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; J. V. Ortiz,; Baboul, A.
G.; 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.; Challacombe, M.; Gill, P. M. W.; Johnson, B.;
Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian 98, Revision A.11.4; Gaussian, Inc.:
Pittsburgh, PA, 2002.
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Y.; Parr, R. G. Phys. ReV. B 1988, 37, 785.
(24) Frisch, M. J.; Pople, J.A.; Binkley, J.S. J. Chem. Phys. 1984, 80,
3265.
(25) Andrae, D.; Haeussermann, U. Dolg, M.; Stoll, H.; Preuss, H. Theor.
Chim. Acta 1990, 77, 123.
(26) (a) Ko¨niger, F.; Carter, R. O.; Mu¨ller, A. Spectrochim. Acta 1976,
32A, 891. (b) Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA,
Key Values for Thermodynamics; Hemisphere Publishing Corp: New York,
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(28) Rappe´, A. K.; Goddard, W. A. J. Am. Chem. Soc. 1982, 104, 448.

334 Organometallics, Vol. 26, No. 2, 2007
Lyon and Andrews
a
Table 1. Observed and Calculated Fundamental Frequencies of CH2dTiCl2
CH2dTiCl2
13CH2dTiCl2
calc (int)
CD2dTiCl2
approximate
mode (symmetry)b
obs
calc (int)
obs
obs
calc (int)
HCTiCl dist (a′)
ClTiCl bend (a′)
CTiCl bend (a′′)
CH2 rock (a′′)
54.5 (27)
108.4 (3)
171.2 (2)
54.2 (27)
108.1 (3)
168.8 (2)
52.9 (26)
107.7 (3)
141.2 (0)
273.7 (7)
270.7 (6)
232.6 (6)
Ti-Cl stretch (a′)
CH2 twist (a′′)
Ti-Cl stretch (a′′)
CH2 wag (a′)
CdTi stretch (a′)
CH2 bend (a′)
374.7 (32)
443.6 (0)
374.1 (32)
443.6 (0)
373.2 (31)
314.7 (0)
503.0
675.0
679.7
523.4 (175)c
725.3 (122)c
735.0 (41)c
1308.0 (18)
3056.5 (2)
3151.8 (2)
502.5
669.7
659.6
522.4 (176)
718.5 (118)
718.9 (43)
1298.2 (16)
3051.0 (2)
3139.6 (2)
501.1
540.5
607.8
978.9
518.4 (177)
572.9 (89)
654.2 (28)
1033.1 (28)
2215.9 (4)
2339.0 (1)
CH stretch (a′)
CH stretch (a′′)
b
a B3LYP//6-311++G(2d,p)/SDD level of theory. All frequencies are in cm-1, and computed infrared intensities are in km/mol. Mode symmetries for Cs
c
molecule. B3LYP/6-311++G(3df,3pd) calculated frequencies (intensities) are 517.8 (171), 730.9 (112), and 725.4 cm-1 (48), respectively.
Figure 3. Infrared spectra taken in the 700-400 cm-1 region after
Figure 4. IR spectra taken in the 700-400 cm-1 region taken after
(a) laser-ablated zirconium atoms were reacted with CH2Cl2/Ar,
laser-ablated zirconium atoms were reacted with (a) CH2Cl2, (b)
and the resulting matrix was subjected to (b) irradiation with
13CH2Cl2, and (c) CD2Cl2 diluted in argon. All spectra were recorded
λ > 290 nm, (c) irradiation with λ > 220 nm, and (d) annealing to
after full-arc photolysis (λ > 220 nm).
30 K.
in Table 2. Again, the DFT-computed frequencies are slightly
higher than observed values, and the CH2 wag, which has
considerable anharmonicity based on the H/D frequency ratio,
is predicted least accurately by the harmonic frequency calcula-
tion. Notice that the CD2 scissoring mode, which was observed
only when titanium was reacted with CD2Cl2, was not observed
for the zirconium analogue, as it is predicted to fall underneath
the precursor absorption. Finally, CH2dZrCl2 is computed to
be 163 kcal/mol lower in energy than the sum of the zirconium
atom and methylene chloride precursors.
3.3. Hf + CH2Cl2. Dichloromethane reacts with hafnium
atoms to yield a single product with one strong infrared
absorption at 677.6 cm-1. This absorption shifts 6.0 cm-1 on
13C isotopic substitution and shows a large 131.3 cm-1
deuterium isotopic shift (H/D frequency ratio 1.240), which are
characteristic of a CH2 wagging mode.
The observed absorption matches that predicted for the
strongest absorption of the CH2dHfCl2 complex (Table 3). As
in the case with zirconium, the anharmonic CH2 wagging mode
is predicted about 10% too high, but the isotopic shifts are
predicted extremely well for this complex. The two Hf-Cl
stretching modes are expected to fall below our spectral limits
(B3LYP predicts them at 349.1 and 395.9 cm-1). Hence we
assign the observed band to the CH2dHfCl2 methylidene. This
complex is computed to be 157 kcal/mol lower in energy than
the sum of the two individual reactants.
3.2. Zr + CH2Cl2. Zirconium atoms react with dichlo-
romethane to form a single reaction product with infrared
absorptions at 412.7 and 685.1 cm-1. These absorptions increase
slightly on photolysis and remain nearly unchanged on annealing
(Figure 3). The 685.1 cm-1 absorption shows a modest 5.8 cm-1
13C isotopic shift and a large 139.0 cm-1 deuterium isotopic
shift, as shown from comparison of spectra using CHCl3,
13CHCl3, and CDCl3 in Figure 4. This peak is only 10.1 cm-1
higher than the CH2 wagging mode of the CH2dTiCl2 complex,
and it has a comparable 1.255 H/D isotopic frequency ratio.
The vibration at 412.7 cm-1 is just above our spectral limit. It
shows almost no carbon and hydrogen isotopic dependency (0.1
and 1.5 cm-1 13C and D shifts, respectively) and can be assigned
to a Zr-Cl stretching mode. This absorption is only slightly
below that observed for ZrCl4.38
The identification of these modes (Zr-Cl stretch and CH2
wag) indicate the observed product is CH2dZrCl2. A comparison
of our observed and theoretically predicted vibrations is given
(29) Francl, M. M.; Pietro, W. J.; Hout, R. F.; Hehre, W. J. Organo-
metallics 1983, 2, 281.
(30) Francl, M. M.; Pietro, W. J.; Hout, R. F.; Hehre, W. J. Organo-
metallics 1983, 2, 815.
(31) Gregory, A. R.; Mintz, E. A. J. Am. Chem. Soc. 1985, 107, 2179.
(32) Dobbs, K. D.; Hehre, W. J. J. Am. Chem. Soc. 1986, 108, 4663.
(33) Rappe´, A. K. Organometallics 1987, 6, 354.
(34) Cundari, T. R.; Gordon, M. S. J. Am. Chem. Soc. 1992, 114, 539.
(35) Yamasaki, T.; Goddard, W. A. J. Phys. Chem. A 1998, 102, 2919.
(36) Cundari, T. R.; Klinckman, T. R. Inorg. Chem. 1998, 37, 5399.
(37) Bo¨hme, U.; Beckhaus, R. J. Organomet. Chem. 1999, 585, 179.
(38) (a) Bu¨chler, A.; Berkowitz-Mattuck, J. B.; Dugre, D. H. J. Chem.
Phys. 1961, 34, 2202. (b) Godnev, I. N.; Aleksandrovskaia, A. M.; Rigina,
I. V. Opt. Spectrosc. 1959, 7, 172.
3.4. Ti + CHCl3. The reaction between laser-ablated titanium
atoms and CHCl3 yielded a single product with two infrared
absorptions at 498.3 and 700.4 cm-1 (Figure 5). The lower
absorption at 498.3 cm-1 showed 0.3 and 2.0 cm-1 shifts upon

Group 4 Transition Metal CH2dMCl2 and HC÷MCl3 Complexes
Organometallics, Vol. 26, No. 2, 2007 335
a
Table 2. Observed and Calculated Fundamental Frequencies of CH2dZrCl2
CH2dZrCl2
13CH2dZrCl2
calc (int) calc (int)
CD2dZrCl2
approximate
mode (symmetry)b
obs
obs
obs
calc (int)
HCZrCl dist (a′)
ClZrCl bend (a′)
CZrCl bend (a′′)
CH2 rock (a′′)
30.8 (30)
92.7 (3)
126.7 (0)
30.6 (29)
92.5 (3)
125.6 (0)
30.0 (28)
92.1 (3)
99.0 (0)
249.8 (4)
245.6 (3)
224.0 (2)
Zr-Cl stretch (a′)
Zr-Cl stretch (a′′)
CH2 twist (a′′)
CdZr stretch (a′)
CH2 wag (a′)
CH2 bend (a′)
CH stretch (a′)
CH stretch (a′′)
348.6 (29)
426.4 (147)
470.0 (0)
703.7 (59)
745.4 (132)
1318.6 (15)
3044.7 (0)
3127.2 (5)
348.4 (29)
425.3 (147)
470.0 (0)
685.1 (58)
738.6 (128)
1310.1 (13)
3039.0 (0)
3115.4 (5)
348.3 (29)
421.7 (147)
333.1 (0)
632.0 (44)
585.9 (97)
1023.5 (29)
2209.5 (3)
2318.4 (2)
412.7
685.1
412.6
679.3
411.2
546.1
c
b
a B3LYP//6-311++G(2d,p)/SDD level of theory. All frequencies are in cm-1, and computed infrared intensities are in km/mol. Mode symmetries for Cs
c
molecule. Peak hidden behind precursor absorptions.
a
Table 3. Observed and Calculated Fundamental Frequencies of CH2dHfCl2
CH2dHfCl2
calc (int)
13CH2dHfCl2
CD2dHfCl2
calc (int)
approximate
mode (symmetry)b
obs
obs
calc (int)
obs
HCHfCl dist (a′)
ClHfCl bend (a′)
CHfCl bend (a′′)
CH2 rock (a′′)
43.2 (20)
91.2 (3)
138.5 (0)
42.7 (20)
90.8 (3)
136.8 (0)
41.3 (19)
90.0 (3)
111.3 (0)
281.1 (7)
277.5 (6)
247.2 (2)
Hf-Cl stretch (a′)
Hf-Cl stretch (a′′)
CH2 twist (a′′)
CdHf stretch (a′)
CH2 wag (a′)
CH2 bend (a′)
CH stretch (a′)
CH stretch (a′′)
349.1 (25)
395.9 (105)
462.3 (0)
699.2 (45)
747.1 (103)
1323.2 (12)
3053.2 (0)
3130.1 (5)
349.1 (25)
394.2 (105)
462.3 (0)
678.7 (44)
740.3 (99)
1315.5 (10)
3047.4 (0)
3118.3 (5)
349.0 (25)
386.1 (108)
328.5 (0)
630.1 (33)
587.8 (77)
1018.6 (23)
2216.3 (2)
2320.0 (1)
677.6
671.6
546.3
c
b
a B3LYP//6-311++G(2d,p)/SDD level of theory. All frequencies are in cm-1, and computed infrared intensities are in km/mol. Mode symmetries for Cs
c
molecule. Peak hidden behind precursor absorptions.
Figure 5. Infrared spectra taken in the 720-470 cm-1 region after
(a) laser-ablated titanium atoms were reacted with CHCl3/Ar, and
the resulting matrix was subjected to (b) irradiation with λ > 290
nm, (c) irradiation with λ > 220 nm, (d) annealing to 30 K, and
(e) a second irradiation with λ > 220 nm.
Figure 6. IR spectra taken in the 720-480 cm-1 region taken after
laser-ablated titanium atoms were reacted with (a) CHCl3, (c)
13CHCl3, and (e) CDCl3 diluted in argon, and (b, d, and f) after
the resulting matrixes were subjected to full-arc photolysis (λ >
220 nm).
13C and D isotopic substitution, respectively, indicating a
Ti-Cl stretching mode, which is 4.7 cm-1 below this mode for
CH2dTiCl2. The second absorption at 700.4 cm-1 shifted 18.3
cm-1 on carbon-13 substitution and 17.5 cm-1 on deuterium
substitution (Figure 6) and must be assigned to a mostly
carbon-titanium stretching mode.39 Finally, the shoulder ab-
sorption near 503 cm-1 is probably due to TiCl4.26a
the individual reactants.40 When titanium was reacted with
CHF3, the CHFdTiF2 complex was the lone observed product.19
However, for the CHCldTiCl2 complex, three strong infrared
absorptions are predicted at 487.7 (147 km/mol), 532.6 (96
km/mol), and 624.2 cm-1 (77 km/mol, C-H wagging mode),
which does not match the observed spectrum. Next we computed
the singlet HC-TiCl3 complex, which converged to a bridge-
bonded HC(µ-Cl)TiCl2 complex that is about 1 kcal/mol higher
Computations on the possible singlet CHCldTiCl2 complex
led to a product 134 kcal/mol lower in energy than the sum of
(40) Optimized CHCldTiCl2 structure: Ti-Cl: 2.222 and 2.219 Å,
CdTi: 1.869 Å, C-Cl: 1.738 Å, C-H 1.094 Å, ClTiCl: 132.2°,
ClTiC: 111.7 and 116.0°, ClCTi: 131.2°, HCTi: 118.1°, ClCH:
110.7°.
(39) The “mostly CdTi” and “mostly C÷Ti” stretching modes in these
two product molecules are not strictly comparable, as the former is mixed
with the CH2 bend and the latter carries H.

336 Organometallics, Vol. 26, No. 2, 2007
Lyon and Andrews
a
Table 4. Observed and Calculated Fundamental Frequencies of HC÷TiCl3
HC÷TiCl3
H13C÷TiCl3
DC÷TiCl3
approximate
mode (symmetry)b
obs
calc (int)
obs
calc (int)
obs
calc (int)
ClTiCl bend (e)
TiCl3 umbrella (a1)
CTiCl bend (e)
113.7 (0)
130.5 (3)
147.8 (6)
113.5 (0)
129.9 (3)
145.1 (6)
113.3 (2)
129.9 (3)
134.6 (6)
Ti-Cl stretch (a1)
393.4 (20)
431.6 (6)
494.6 (330)
713.4 (62)
3169.1 (14)
392.7 (19)
428.1 (8)
494.1 (328)
694.4 (61)
3158.8 (13)
392.7 (19)
345.4 (10)
491.3 (296)
691.1 (59)
2337.5 (15)
HCTi def (e)c
Ti-Cl stretch (e)c
C-Ti stretch (a1)
C-H stretch (a1)
498.3
700.4
498.0
682.1
496.3
682.9
b
a B3LYP//6-311++G(2d,p)/SDD level of theory. All frequencies are in cm-1, and computed infrared intensities are in km/mol. Mode symmetries for
c
C3V molecule. Mixed modes.
Figure 8. IR spectra taken in the 660-400 cm-1 region taken after
Figure 7. Infrared spectra taken in the 660-430 cm-1 region after
laser-ablated zirconium atoms were reacted with (a) CHCl3, (c)
(a) laser-ablated zirconium atoms were reacted with CHCl3/Ar, and
13CHCl3, and (e) CDCl3 diluted in argon, and (b, d, and f) after
the resulting matrixes were subjected to full-arc photolysis (λ >
220 nm).
the resulting matrix was subjected to (b) irradiation with λ > 290
nm, (c) irradiation with λ > 220 nm, (d) annealing to 30 K, and
(e) a second irradiation with λ > 220 nm.
for this structure the two Zr-Cl stretching modes are predicted
in energy than the CHCldTiCl2 methylidene. The triplet com-
to be at or below our spectral limit (353.1 and 412.7 cm-1),
plex is 9 kcal/mol lower in energy than the bridged HC(µ-Cl)-
TiCl2 singlet species and 142 kcal/mol lower than the sum of
the individual reactants. In related investigations, zirconium and
but the strongest observable absorption is predicted at 651.2
cm-1, corresponding to the C-H wagging mode. No absorption
was observed that showed a significant deuterium shift (the
hafnium metal atom reactions with CHF3 formed triplet
CHCl wagging mode of the CHCldZrCl2 complex was pre-
HC÷MF3 complexes,19 and the chlorinated analogues must be
dicted to show a 139.8 cm-1 shift upon D substitution). Next,
considered. Our theoretical computations predict the strongest
the very stable triplet HC÷ZrCl3 complex is 23 kcal/mol lower
infrared absorption (antisymmetric Ti-Cl stretch) of the triplet
in energy than the methylidene species. For this complex, the
HC÷TiCl3 complex to fall at 494.6 cm-1, in good agreement
mostly C-Zr stretching mode is predicted at 640.7 cm-1 with
19.9 and 22.6 cm-1 13C and D isotopic shifts, respectively (Table
5), which reproduce the observed absorptions with the ex-
pected accuracy. Our computations predict the Zr-Cl antisym-
metric stretch (406.6 cm-1) and the H-C-Zr deformation
(449.9 cm-1) modes to be highly mixed. The observed band at
439.2 cm-1 shows a 2.6 cm-1 13C isotopic shift, which agrees
well with the predicted shift of the H-C-Zr deformation (3.3
cm-1). However, the observed deuterated species absorption
agrees better with the Zr-Cl stretching mode prediction as the
D-C-Zr deformation shifts to lower frequency. Hence, the
observed absorption is a mixture of the two modes, and the
hydrogen counterpart is mostly H-C-Zr deformation and the
deuterium counterpart mostly Zr-Cl antisymmetric stretch. The
observed spectrum is assigned to the triplet HC÷ZrCl3 complex,
which is supported by comparison between calculated and
observed frequencies in Table 5.
with the observed Ti-Cl stretching mode at 498.3 cm-1 (Table
4). The second strongest mode (mostly C-Ti stretch) is
predicted at 713.4 cm-1 with 19.0 cm-1 carbon-13 isotopic shift
and 22.3 cm-1 D shift, which agrees well with the second
observed product absorption (700.4 cm-1; 18.3 cm-1 13C shift,
17.5 cm-1 D shift). The next strongest mode (Ti-Cl symmetric
stretch) is predicted to fall below our spectral limits (393.4
cm-1). Hence the two observed absorption peaks can be assigned
to the triplet HC÷TiCl3 complex.
3.5. Zr + CHCl3. Laser-ablated zirconium atoms react with
trichloromethane to yield infrared absorptions at 439.2 and 639.8
cm-1. Both absorptions are characterized by the same behavior
on photolysis and annealing and can be assigned to a single
reaction product (Figure 7). The lower absorption at 439.2 cm-1
shows 2.6 and 16.8 cm-1 carbon-13 and deuterium isotopic
shifts, respectively (Figure 8). This appears to be a predominant-
ly Zr-Cl stretching mode, but must be mixed with another mode
involving H(D). The upper absorption at 639.8 cm-1 shows a
large 20.2 cm-1 13C isotopic shift and a 22.7 cm-1 D shift, which
is appropriate for a strong mostly C-Zr stretching mode.
Computations on the possible singlet CHCldZrCl2 meth-
ylidene complex converged to a structure lying 168 kcal/mol
lower in energy than the sum of the initial reactants.41 However,
3.6. Hf + CHCl3. Diluted chloroform in argon reacts with
hafnium atoms to produce a single product with infrared
(41) Optimized CHCldZrCl2 structure: Zr-Cl: 2.386 and 2.383 Å,
CdZr: 2.011 Å, C-Cl: 1.764 Å, C-H 1.093 Å, ClZrCl: 130.9°,
ClZrC: 111.2 and 116.1°, ClCZr: 127.3°, HCZr: 122.8°, ClCH:
109.8°.

Group 4 Transition Metal CH2dMCl2 and HC÷MCl3 Complexes
Organometallics, Vol. 26, No. 2, 2007 337
a
Table 5. Observed and Calculated Fundamental Frequencies of HC÷ZrCl3
HC÷ZrCl3
calc (int)
H13C÷ZrCl3
DC÷ZrCl3
approximate
mode (symmetry)b
obs
obs
calc (int)
obs
calc (int)
ClZrCl bend (e)
ZrCl3 umbrella (a1)
CZrCl bend (e)
Zr-Cl stretch (a1)
Zr-Cl stretch (e)c
HCZr def (e)c
95.3 (1)
101.8 (6)
132.9 (0)
367.6 (20)
406.6 (71)
449.9 (79)
640.7 (75)
3169.3 (5)
95.2 (1)
101.6 (6)
130.0 (0)
367.4 (20)
406.4 (68)
446.6 (81)
620.8 (72)
3159.1 (4)
95.2 (1)
101.6 (6)
122.8 (0)
367.4 (20)
413.6 (131)
344.9 (5)
618.1 (71)
2336.4 (9)
422.4
617.1
439.2
639.8
436.6
C-Zr stretch (a1)
C-H stretch (a1)
619.6d
b
a B3LYP//6-311++G(2d,p)/SDD level of theory. All frequencies are in cm-1, and computed infrared intensities are in km/mol. Mode symmetries for
c
d
C3V molecule. Mixed modes. Peak mixed with weak precursor absorption.
our experimental results. Hence the product spectrum cannot
be assigned to the CHCldHfCl2 species. However, once this
complex is formed, the third chlorine atom can transfer to the
hafnium metal center, which is predicted to be 4 kcal/mol lower
in energy, conserving the singlet spin multiplicity, followed by
spin relaxation to the triplet HC÷HfCl3 complex, which is 32
kcal/mol lower in energy than the methylidene. The C-Hf
stretching mode of this complex is predicted at 625.1 cm-1 with
20.9 and 23.6 cm-1 13C and D isotopic shifts, respectively, in
excellent agreement with experiment (Table 6). The only other
absorption predicted to be observed is the H-C-Hf deformation
mode at 451.0 cm-1, which is mixed with some Hf-Cl
stretching character. A 3.4 cm-1 carbon-13 shift is computed
for this absorption, in good agreement with the peak observed
at 437.8 cm-1 showing a 3.4 cm-1 13C isotopic shift. This is an
acetylenic-like C-H deformation mode. Hence, the observed
vibrational spectrum is assigned to the triplet HC÷HfCl3
complex.
Figure 9. Infrared spectra taken in the 670-410 cm-1 region after
(a) laser-ablated hafnium atoms were reacted with CHCl3/Ar, and
the resulting matrix was subjected to (b) irradiation with λ > 290
nm, (c) irradiation with λ > 220 nm, (d) annealing to 30 K, and
(e) a second irradiation with λ > 220 nm.
3.7. Reaction Mechanisms. Following our investigations of
the group 4 metal atom reactions with CH4, CH3X, and CH2F2
molecules,8-17,19 these reactions with CH2Cl2 most likely
proceed first through the triplet C-Cl insertion product.
M (3F) + CH2Cl2
f CH2(µ-Cl)MCl (T)
(1a)
fCH2-MCl2 (T) f CH2dMCl2 (S) (1b)
Alternative insertion into a C-H bond gives a higher energy
CHCl2-MH metal hydride product,14 for which we find no
evidence. Reaction 1a is predicted to be sufficiently exothermic
(98, 91, and 102 kcal/mol lower in energy than the reactants
for Ti, Zr, and Hf, respectively) to activate further R-Cl transfer
rearrangement to the triplet CH2-MCl2 intermediate, which
relaxes in the matrix to the lower energy singlet methylidene
dichloride product (T and S denote triplet and singlet electronic
states, respectively). The final Ti, Zr, and Hf methylidene
dichloride products are 127, 163, and 157 kcal/mol, respectively,
lower in energy than the precursors. Although R-H transfer
might be faster, the alternative CHCldTiHCl methylidene
complex is 62 kcal/mol higher in energy and is not observed in
these experiments.
Figure 10. IR spectra taken in the 650-400 cm-1 region taken
after laser-ablated hafnium atoms were reacted with (a) CHCl3, (c)
13CHCl3, and (e) CDCl3 diluted in argon, and (b, d, and f) after
the resulting matrixes were subjected to full-arc photolysis (λ >
220 nm).
absorptions at 437.8 and 636.3 cm-1 (Figure 9). The upper
absorption shows 21.2 and 23.8 cm-1 13C and D isotopic shifts,
respectively, which is characteristic of a strong mostly C-Hf
stretching mode. The second observed absorption at 437.8 cm-1
shows a 3.4 cm-1 carbon-13 isotopic shift (Figure 10).
The reaction with CHCl3 begins in like fashion with C-Cl
insertion.
The potential singlet methylidene CHCldHfCl2 is predicted
to be 162 kcal/mol more stable than the sum of the reactants.42
However, our computations on this complex predict the strongest
M (3F) + CHCl3
infrared active mode within our spectral limits at 665.2 cm-1
,
f CHCl(µ-Cl)MCl (T)
(2a)
(2b)
corresponding to the C-H wagging mode, which does not match
f CHCl-MCl2 (T) f CHCldMCl2 (S)
(42) Optimized CHCldHfCl2 structure: Hf-Cl: 2.374 and 2.368 Å,
CdHf: 2.020 Å, C-Cl: 1.777 Å, C-H 1.090 Å, ClHfCl: 125.6°,
ClHfC: 110.3 and 114.6°, ClCHf: 123.0°, HCHf: 127.3°, ClCH:
109.5°.
f HC-MCl3 (S) f HC÷MCl3 (T)
f CHCl-MCl2 (T) f HC÷MCl3 (T)
(2c)
(2b′)

338 Organometallics, Vol. 26, No. 2, 2007
Lyon and Andrews
a
Table 6. Observed and Calculated Fundamental Frequencies of HC÷HfCl3
HC÷HfCl3
H13C÷HfCl3
DC÷HfCl3
approximate
mode (symmetry)b
obs
calc (int)
obs
calc (int)
obs
calc (int)
HfCl3 umbrella (a1)
ClHfCl bend (e)
CHfCl bend (e)
Hf-Cl stretch (a1)
Hf-Cl stretch (e)c
HCHf def (e)c
92.8 (5)
93.3 (4)
134.2 (0)
364.3 (18)
375.7 (144)
451.0 (82)
625.1 (61)
3183.0 (5)
92.7 (5)
93.3 (4)
131.0 (0)
364.3 (18)
375.7 (144)
447.6 (82)
604.2 (58)
3172.8 (4)
92.7 (5)
93.3 (4)
124.2 (0)
364.3 (18)
378.4 (206)
348.1 (6)
601.5 (57)
2346.8 (9)
437.8
636.3
434.4
615.1
C-Hf stretch (a1)
C-H stretch (a1)
612.5
b
a B3LYP//6-311++G(2d,p)/SDD level of theory. All frequencies are in cm-1, and computed infrared intensities are in km/mol. Mode symmetries for
c
C3V molecule. Mixed modes.
Table 7. Geometrical Parameters and Physical Constants of
Ground State CH2dMCl2 (M ) Ti, Zr, Hf)a
e
parameter
CH2dTiCl2
CH2dZrCl2
CH2dHfCl2
r(CsH)
r(CdM)
r(M-Cl)
(HCH)
(CMCl)
(ClMCl)
(HCM)
Φ(HCMCl)
q(C)b
1.092
1.835
2.226
114.2
113.0
134.0
122.9
0.0, 180.0
-0.56
0.15
1.093
1.983
2.393
112.3
112.3
133.4
123.8
5.4, 171.7
-0.76
0.13
1.092
1.995
2.381
111.7
111.6
130.8
124.1
9.0, 165.0
-0.77
0.09
q(H)b
q(M)b
0.81
1.37
1.62
q(Cl)b
-0.27
0.957
127
-0.43
1.020
163
-0.51
1.772
157
µc
∆Ed
a Bond lengths and angles are in Å and deg. All calculations were
b
performed at the B3LYP//6-311++G(2d,p)/SDD level. Mulliken atomic
c
d
charge. Molecular dipole moment in D. Binding energy in kcal/mol.
eDimensions for the B3LYP//6-311++G(2d,p) all-electron calculation are
1.092, 1.840, 2.234, 114.2, 113.7, 132.5, 122.9, 0.6, and 178.8, respectively.
pares well with our B3LYP result and other computations re-
ported for the CH2dTiCl2 complex,27,29,30,32-34 although previ-
ous workers assumed a coplanar molecule. We find that the
CH2dTiCl2 complex has one plane of symmetry (Cs) bisecting
the Cl-Ti-Cl angle, and the Ti-Cl bonds are slightly out of
the CH2dTi plane using the all-electron basis set for Ti. This
nonplanarity increases for the Zr and Hf complexes. Hence we
believe the B3LYP method is accurate for describing these
complexes.
It is of interest to reflect on the prevalence of agostic distortion
in the simple group 4 methylidenes. The CH2dMH2 and
CH2dMHX complexes all possess agostic interactions.9-16
However, it is important to note that the agostic bonds in the
CH2dMHX methylidenes are trans to the M-X bond. The
CH2dMF2 and CHFdMF2 complexes17,19 (as well as the
CH2dMCl2 species reported here) do not show any evidence
of agostic interactions in the DFT-calculated structures. Clearly
this is due to the presence of the second halogen atom on the
metal center. One possible explanation is that halogen lone pair
Figure 11. Optimized geometries (Å and deg) for the singlet
CH2dMCl2 (Cs) and triplet HC÷MCl3 (C3V) complexes at the
B3LYP//6-311++G(2d,p)/SDD level of theory. Atomic spin densi-
ties in parentheses are given by each atom in the triplet complexes.
The initial insertion product undergoes R-Cl transfer to form
the triplet CHCl-MCl2 species. Here, the reaction pathway can
go one of two ways. First (reactions 2b and 2c), spin relaxation
to the singlet CHCldMCl2 methylidene forms a stable species
similar to the reactions with CH2Cl2. From here, the third R-Cl
transfers to the metal center followed by spin relaxation to the
very stable triplet HC÷MCl3 complex. Alternatively, the
HC÷MCl3 complex could form directly via chlorine transfer
in the triplet CHCl-MCl2 complex (reaction 2b′), which is
predicted to be only 2 kcal/mol higher in energy than the singlet
CHCldMCl2 complex for titanium. Reactions with group 4
metals and CHF3 follow the former reaction pathway, but C-Cl
bonds are weaker than C-F bonds, and we cannot rule out the
latter reaction pathway. Hence, we are unable to determine the
reaction pathway from M + CHCl3 to HC÷MCl3 at this time.
3.8. Group Trends and Comparison to Fluorine Ana-
logues. The geometries of the group 4 CH2dMCl2 complexes
at the B3LYP level of theory are shown in Figure 11, and the
structural parameters are summarized in Table 7. For compari-
son, a CCSD calculation of the CH2dTiCl2 complex with similar
basis sets (SDD pseudopotential and 6-311++G(2d,2p)) was
done using the NWChem Program.43,44 This geometry45 com-
(44) Apra`, E.; Windus, T. L.; Straatsma, T. P.; Bylaska, E. J.; de Jong,
W.; Hirata, S.; Valiev, M.; Hackler, M.; Pollack, L.; Kowalski, K.; Harrison,
R.; Dupuis, M.; Smith, D. M. A; Nieplocha, J.; Tipparaju V.; Krishnan,
M.; Auer, A. A.; Brown, E.; Cisneros, G.; Fann, G.; Fru¨chtl, H.; Garza, J.;
Hirao, K.; Kendall, R.; Nichols, J.; Tsemekhman, K.; Wolinski, K.; Anchell,
J.; Bernholdt, D.; Borowski, P.; Clark, T.; Clerc, D.; Dachsel, H.; Deegan,
M.; Dyall, K.; Elwood, D.; Glendening, E.; Gutowski, M.; Hess, A.; Jaffe,
J.; Johnson, B.; Ju, J.; Kobayashi, R.; Kutteh, R.; Lin, Z.; Littlefield, R.;
Long, X.; Meng, B.; Nakajima, T.; Niu, S.; Rosing, M.; Sandrone, G.; Stave,
M.; Taylor, H.; Thomas, G.; van Lenthe, J.; Wong, A.; Zhang, Z. NWChem,
A Computational Chemistry Package for Parallel Computers, Version 4.6;
Pacific Northwest National Laboratory: Richland, WA, 2004.
(45) Optimized CH2dTiCl2 structure at CCSD//6-311++G(2d,2p)/
SDD: Ti-Cl: 2.232 Å, CdTi: 1.869 Å, C-H 1.088 Å, ClTiCl: 135.8°,
ClTiC: 112.1°, HCTi: 123.9°, HCH: 112.3°.
(43) Scuseria, G. E.; Schaefer, H. F., III. J. Chem. Phys. 1989, 90, 3700,
and references therein.

Group 4 Transition Metal CH2dMCl2 and HC÷MCl3 Complexes
Organometallics, Vol. 26, No. 2, 2007 339
Table 8. Geometrical Parameters and Physical Constants of
We find one difference in structural preference for group 4
metal reaction products with CHF3 and CHCl3. In the case of
Ti the products trapped are the methylidene CHFdTiF2 and the
electron-deficient methylidyne HC÷MCl3, respectively. In the
cases of Zr and Hf, both haloforms form the latter complex.
Finally, we find no evidence for any higher energy R-H transfer
products in these di- and trihalomethane systems.
Ground State HC÷MCl3 (M ) Ti, Zr, Hf)a
e
parameter
HC÷TiCl3
HC÷ZrCl3
HC÷HfCl3
r(C-H)
r(C÷M)
r(M-Cl)
(CMCl)
(ClMCl)
q(C)b
1.088
1.949
2.192
106.2
112.5
-0.28
0.18
1.088
2.127
2.359
106.8
112.0
-0.42
0.16
1.086
2.131
2.357
107.2
111.7
-0.39
0.21
For the three triplet state HC÷MCl3 complexes, the
Cl-M-Cl angles again become smaller with increasing metal
size (Figure 11 and Table 8). It appears that halogen substitution
for hydrogen in these complexes strengthens the C÷M bond.
The C÷Ti bond length in HC÷TiCl3 is only 0.003 Å longer
than in the ClC÷TiCl3 species,46 indicating a similar bond
strength in the two electron-deficient methylidyne complexes.
However, the computed C÷Zr and C÷Hf bond lengths are 0.029
and 0.024 Å shorter in the trichloride than in the trifluoride
species. The HC÷MCl3 complexes are well-defined triplet
species ( s2 values near 2.0, Table 8). The atomic spin densities
total 2.00 (Figure 11) and show carbon 2p electron sharing
with the metal center, which decreases with metal size as the
C(2p)-M(nd) overlap decreases. Hence, two weak degenerate
π bonds are formed to augment the single C-M bond in these
electron-deficient methylidyne systems. This additional π bond-
ing appears to be greater in the ClC÷TiCl3 complex because
of contribution from the single chlorine. The spin densities of
Cl (0.22), C (1.29), Ti (0.34), and 3Cl (0.05) suggest a stronger
π interaction in the latter complex.46
q(H)b
q(M)b
q(Cl)b
µc
0.71
1.27
1.31
-0.20
2.214
142
-0.34
1.970
191
-0.38
1.872
194
∆Ed
s2
2.0104
2.0081
2.0076
a Bond lengths and angles are in Å and deg. All calculations were
performed at the B3LYP//6-311++G(2d,p)/SDD level on the triplet
b
c
HC÷MCl3 species in C3V symmetry. Mulliken atomic charge. Molecular
d
e
dipole moment in D. Binding energy in kcal/mol. Dimensions for the
B3LYP//6-311++G(3df,3pd) all-electron calculation are 1.087, 1.955,
2.199, 106.1, and 112.7, respectively.
repulsions are significantly strong to prohibit agostic distor-
tion. This would also explain why the agostic bonds18 in the
CH2dMHX complexes are trans to the M-X bond. We note
here that the CdTi bond is 0.015 Å shorter in the CH2dTiCl2
than in the CH2dTiF2 complex, where fluorine lone pairs have
been suggested to prevent agostic distortion.17
Also, as the group 4 metal atom gets heavier, the Cl-M-Cl
and H-C-H angles both decrease, and the Cl atoms are more
out of the CH2dM plane. However, they are all larger angles
than found for the fluorine analogues.19 Similar to the fluorine
analogues, the HCMCl dihedral angles deviate more from
0°/180° moving down the group 4 transition series (Table 7), a
trend discussed in more detail.19 The CH2dMCl2 complexes
are lower in energy than the individual reactants by 127, 163,
and 157 kcal/mol for Ti, Zr, and Hf, respectively (Table 7).
This is the same order observed for the fluorine analogues, but
the CH2dMCl2 molecules are slightly less stable.19 As the metal
atom becomes larger, it is easier for the chlorine atoms to
withdraw electron density from the metal atom. Hence, the
Mulliken charges on the chlorine atoms become more negative,
while the charges on the metal centers become more positive.
The CH2dMF2 and CH2dMCl2 complexes are symmetrical
and isostructural. The CdM bond lengths are 0.015, 0.015, and
0.013 Å longer in the group 4 difluoride series, respectively.17,19
The stronger inductive effect of fluorine relative to chlorine
appears to weaken slightly the CdM bond. The CH2 wagging
modes in the CH2dMCl2 complexes discussed here are 20, 14,
and 30 cm-1 lower than their CH2dMF2 counterpart values,19
and they exhibit comparable anharmonicities (observed H/D iso-
topic frequency ratios 1.249, 1.255, 1.240, respectively, in the
dichloride series). In contrast the harmonic frequency ratios cal-
culated here for the mode are 1.266, 1.272, and 1.271,
respectively.
4. Conclusions
Laser-ablated group 4 transition metals react with CH2Cl2
and CHCl3 to form CH2dMCl2 and HC÷MCl3 complexes,
respectively, which are trapped in solid argon. The CH2dMCl2
methylidenes show no agostic distortions and have slightly
shorter computed carbondmetal bonds than the fluorine ana-
logues. The triplet HC÷MCl3 complexes have C3V molecular
symmetry. The two lone electrons on carbon are partially
donated to the electron-deficient metal center, forming electron-
deficient methyldyne complexes, and this π bonding interaction
decreases with increasing metal size.
Acknowledgment is made to the Donors of the American
Chemical Society Petroleum Research Fund for support of this
research. This research was performed in part using the
Molecular Science Computing Facility (MSCF) in the William
R. Wiley Environmental Molecular Sciences Laboratory, a
national scientific user facility sponsored by the U.S. Department
of Energy’s Office of Biological and Environmental Research
and located at the Pacific Northwest National Laboratory. Pacific
Northwest is operated for the Department of Energy by Battelle.
OM0608399
(46) The ClC÷TiCl3 structure was optimized at the same theoretical level
as that employed here (Cl-C: 1.630 Å, C÷Ti: 1.946 Å, Ti-Cl: 2.198 Å,
CTiCl: 106.3°, ClTiCl: 112.4°).