Toward a more detailed understanding of oxidative-addition mechanisms: Combined experimental and quantum-chemical study of the insertion of titanium atoms into C-H, Si-H, and Sn-H bonds

Article abstract of DOI:10.1021/om040016o

The reactions between Ti atoms and CH₄, SiH₄, and SnH₄ at a temperature of 12 K in Ar matrixes were studied experimentally by IR spectroscopy, taking in the effect of isotopic substitution, and by quantum-chemical calculations. The experiments show that the reactivity changes considerably from CH₄ to SiH₄ or SnH₄. The reaction between Ti and CH₄ proceeds inefficiently, and only after photolytic activation of the Ti atoms does insertion occur to give HTiCH₃, which features only terminal Ti-H and C-H bonds. On the other hand, reactions with SiH₄ and SnH ₄ occur upon deposition, leading to the products cis- and trans-HTi(μ-H)₂SiH and HTi(μ-H)₃E (E = Si, Sn). Selective photolysis can be used to increase the yields of these products. In agreement with the experimental results, quantum-chemical calculations predict the lowest energy form of a molecule with the overall formula TiEH₄ to be HTiCH₃ with only terminal H atoms for E = C but HTi(μ-H)₃E with three bridging H atoms in the case of E = Si, Sn.

Full text of DOI:10.1021/om040016o

2350
Organometallics 2004, 23, 2350-2361
Tow a r d a Mor e Deta iled Un d er sta n d in g of
Oxid a tive-Ad d ition Mech a n ism s: Com bin ed
Exp er im en ta l a n d Qu a n tu m -Ch em ica l Stu d y of th e
In ser tion of Tita n iu m Atom s in to C-H, Si-H, a n d Sn -H
Bon d s
Angela Bihlmeier,† Tim M. Greene,‡ and Hans-J o¨rg Himmel*,†
Institut fu¨r Anorganische Chemie, Universita¨t Karlsruhe, Engesserstrasse, Geb. 30.45,
76128 Karlsruhe, Germany, and Department of Chemistry, University of Exeter,
Stocker Road, Exeter EX4 4QD, U.K.
Received February 11, 2004
The reactions between Ti atoms and CH4, SiH4, and SnH4 at a temperature of 12 K in Ar
matrixes were studied experimentally by IR spectroscopy, taking in the effect of isotopic
substitution, and by quantum-chemical calculations. The experiments show that the
reactivity changes considerably from CH4 to SiH4 or SnH4. The reaction between Ti and
CH4 proceeds inefficiently, and only after photolytic activation of the Ti atoms does insertion
occur to give HTiCH3, which features only terminal Ti-H and C-H bonds. On the other
hand, reactions with SiH4 and SnH4 occur upon deposition, leading to the products cis- and
trans-HTi(µ-H)2SiH and HTi(µ-H)3E (E ) Si, Sn). Selective photolysis can be used to increase
the yields of these products. In agreement with the experimental results, quantum-chemical
calculations predict the lowest energy form of a molecule with the overall formula TiEH4 to
be HTiCH3 with only terminal H atoms for E ) C but HTi(µ-H)3E with three bridging H
atoms in the case of E ) Si, Sn.
In tr od u ction
Oxidative addition is an important reaction, represen-
ting a key step in many catalytic cycles. However, the
mechanisms of these processes are not fully understood.
The activation of C-H bonds is of particular importance.
It may be expected that oxidative addition proceeds via
a complex, which has in the case of derivatives of silane
or methane (HSiR3 and HCR3) the formulas LnM‚SiHR3
and LnM‚CHR3, respectively, where L represents a
ligand and M the metal center. Several complexes of
SiH4 and even a few of CH4 have been successfully
characterized. Examples include the complex [Mo(η2-
i
SiH4)(CO)(R2PC2H4PR2)2] (R ) Ph, Bu, Et), which is
apparently in thermal equilibrium with the product of
oxidative addition, viz. [Mo(H)SiH3(CO)(R2PC2H4PR2)2].1
Complexes featuring BH4- groups have also been the
-
subject of much study. The BH4 unit is isoelectronic
compound Ti(BH4)3(PMe3)2, for example, features a side-
with CH4, and therefore, it has been argued that the
characterization of the structure, bonding, and confor-
mational variations displayed by derivatives of the BH4
anion may hold vital clues to C-H activation processes.
The compound Ti(BH4)3 has been characterized in the
gas phase via electron diffraction and UV photoelectron
spectroscopy and by IR spectroscopy of the matrix-
isolated molecule.2
on coordination of the Ti center to one of the B-H bonds
-
-
in each of two BH4 groups, while the third BH4
-
group adopts a η2 coordination mode.3 Another example
is the compound Ti(BH4)2(dmpe)2 (dmpe ) (CH3)2-
-
PCH2CH2P(CH3)2), in which two η2-coordinated BH4
units are present.4
There have been numerous previous studies of the
interaction of methane with transition-metal atoms, e.g.
Fe,5 Co,6,7 and Ni,8,9 to name only a few examples (see
also ref 10 and references therein). The reactions of
Several other species with Ti centers show that the
coordination mode of the BH4- unit may vary. Thus, the
* To whom correspondence should be addressed. Fax: +49-721-608-
4854. E-mail: himmel@chemie.uni-karlsruhe.de.
† Universita¨t Karlsruhe.
(2) (a) Dain, C. J .; Downs, A. J .; Rankin, D. W. H. Angew. Chem.
1982, 94, 557. (b) Dain, C. J .; Downs, A. J .; Goode, M. J .; Evans, D.
G.; Nicholls, K. T.; Rankin, D. W. H.; Robertson, H. E. J . Chem. Soc.,
Dalton Trans. 1991, 967.
‡ University of Exeter.
(1) Luo, X.-L.; Kubas, G. J .; Burns, C. J .; Bryan, J . C.; Unkefer, C.
J . J . Am. Chem. Soc. 1995, 117, 1159.
(3) J ensen, J . A.; Girolami, G. S. J . Chem. Soc., Chem. Commun.
1986, 1160.
10.1021/om040016o CCC: $27.50 © 2004 American Chemical Society
Publication on Web 04/15/2004

Insertion of Ti into C-H, Si-H, and Sn-H Bonds
Organometallics, Vol. 23, No. 10, 2004 2351
Zn,11,12 Cd,12 and Hg12,13 atoms with CH4 in Ar and CH4
matrixes have also been studied, as have those between
the main-group atoms Mg,14 B,15 Al,16,17 Ga,18 and In18c
and CH4. In all cases, a species of the form HMCH3 with
a terminal M-H bond and a methyl group featuring
terminal C-H bonds is formed, but the reaction pro-
ceeds only after photoactivation of the metal atom. In
previous studies some of us have explored the reactions
of the group 13 element atoms Al and Ga with SiH4;19,20
in both cases, a spontaneously formed complex featuring
a η2-coordinated metal atom was identified and char-
acterized.
Finally, mechanisms leading to oxidative addition
have also been studied in the gas phase by a variety of
different techniques. The insertion of metal ions was
analyzed, for example, by mass spectrometry, and in
some celebrated cases it has proved possible to deter-
mine dissociation energies for certain of the species that
are generated.22 One important result of these studies
is that most transition metals (charged or uncharged)
cannot easily be persuaded to react with methane. In
the case of some metals, e.g. rhodium,23 not only the
possible reaction of the metal atom cation but also the
reactions of the positively charged dimer and of small
clusters were analyzed. An interesting outcome is that
+
Rh2 reacts spontaneously with CH4 to give the dehy-
+
drogenation product [Rh2CH2]+, but Rh+ and Rhn
clusters (n g 2) do not show this behavior.
Herein we report on the reactions occurring between
Ti atoms and CH4, SiH4, and SnH4. In a future publica-
tion we will report our investigations on the reactions
of Ni atoms with SiH4 and SnH4.24 Hence, it will be
shown that the structures of the products of the
spontaneous and photolytically activated reactions be-
tween Ti atoms and SiH4 or SnH4 differ significantly
from those of other MEH4 species that have been
studied to date.
Exp er im en ta l Section
Evaporation of Ti metal was achieved from a resistively
heated Ti filament. The amount of deposited metal was
monitored by using a microbalance and by UV/vis spectroscopy.
UV/vis and Raman spectroscopy were also used to obtain
information about the amount of metal dimers present in the
matrix.25 The matrix was deposited on a freshly polished Cu
block cooled to 12 K by means of a closed-cycle refrigerator
(Leybold LB 510). Other details of the matrix-isolation tech-
nique can be found elsewhere.26
SiH4 was used as purchased from Linde (purity >99.99%).
SiD4, SnH4, and SnD4 were prepared by the reaction of SiCl4
or SnCl4 with LiAlH4 or LiAlD4 in diglyme and purified by
fractional condensation in vacuo. Argon was used as delivered
from Messer (purity 99.998%).
IR spectra were recorded with a Bruker 113v spectrometer.
An MCT detector was used for the spectral region 4000-650
cm-1. Measurements in the region 700-200 cm-1 were carried
out with a DTGS detector. Additional spectra between 700 and
50 cm-1 were recorded using a liquid He cooled bolometer.
UV/vis spectra were recorded with a Xe arc lamp (Oriel),
an Oriel Multispec spectrograph, and a photodiode-array
detector. The resolution varied between 0.2 and 0.5 nm.
A Hg medium-pressure lamp (Philips LP125) in combination
with interference filters was used for photolysis of the ma-
trixes.
The data allowed for an estimate of the differences in
the bond distances d(Si-H) of the slightly distorted SiH4
unit. On photolytic activation, the metal atoms inserted
into the Si-H bond to give HAlSiH3 and HGaSiH3. In
these products, again only terminal H atoms are present.
The reaction of the photoexcited group 12 metals with
SiH4 yields also the insertion products HMSiH3.21
(4) J ensen, J . A.; Wilson, S. R.; Schultz, A. J .; Girolami, G. S. J .
Am. Chem. Soc. 1987, 109, 8094.
(5) Kauffman, J . W.; Hauge, R. H.; Margrave, J . L. High Temp. Sci.
1984, 17, 237.
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Am. Chem. Soc. 1993, 115, 2039.
(7) Billups, W. E.; Chang, S.-C.; Hauge, R. H.; Margrave, J . L. J .
Am. Chem. Soc. 1995, 117, 1387.
(8) Chang, S.-C.; Hauge, R. H.; Billups, W. E.; Margrave, J . L.;
Kafafi, Z. H. Inorg. Chem. 1988, 27, 205.
(9) Himmel, H.-J . Chem. Eur. J ., in press.
(10) Ozin, G. A.; McCaffrey, J . G.; Parnis, J . M. Angew. Chem., Int.
Ed. 1986, 25, 1072.
(11) Billups, W. E.; Konarski, M. M.; Hauge, R. H.; Margrave, J . L.
J . Am. Chem. Soc. 1980, 102, 7393.
Quantum-chemical calculations were carried out with the
TURBOMOLE program.27 The BP method in combination with
an SVP basis set was used for Ti, Si, and H. In the case of Sn,
(12) Greene, T. M.; Andrews, L.; Downs, A. J . J . Am. Chem. Soc.
1995, 117, 8180.
(13) (a) Legay-Sommaire, N.; Legay, F. Chem. Phys. Lett. 1994, 217,
97. (b) Legay-Sommaire, N.; Legay, F. Chem. Phys. 1996, 211, 367.
(14) McCaffrey, J . G.; Parnis, J . M.; Ozin, G. A.; Breckenridge, W.
H. J . Phys. Chem. 1985, 89, 4945.
(15) (a) Hassanzadeh, P.; Hannachi, Y.; Andrews, L. J . Phys. Chem.
1993, 97, 6418. (b) Hannachi, Y.; Hassanzadeh, P.; Andrews, L. J . Phys.
Chem. 1994, 98, 6950.
(19) Gaertner, B.; Himmel, H.-J . Angew. Chem. 2002, 114, 1602;
Angew. Chem., Int. Ed. 2002, 41, 1538.
(20) Gaertner, B.; Himmel, H.-J .; Macrae, V. A.; Downs, A. J .;
Greene, T. M. Chem. Eur. J ., in press.
(21) (a) Legay-Sommaire, N.; Legay, F. J . Phys. Chem. A 1998, 102,
8759. (b) Macrae, V. A.; Greene, T. M.; Downs, A. J . J . Phys. Chem. A
2004, 108, 1393.
(22) See, for example: Schwarz, H. Angew. Chem. 2003, 42, 4442
and references given therein.
(16) J eong, G.; Klabunde, K. J . J . Am. Chem. Soc. 1986, 108, 7103.
(17) Parnis, J . M.; Ozin, G. A. J . Phys. Chem. 1989, 93, 1204, 1220.
(18) (a) Lafleur, R. D.; Parnis, J . M. J . Phys. Chem. 1992, 96, 2429.
(b) Xiao, Z. L.; Hauge, R. H.; Margrave, J . L. Inorg. Chem. 1993, 32,
642. (c) Himmel, H.-J .; Downs, A. J .; Greene, T. M.; Andrews, L.
Organometallics 2000, 19, 1060.
(23) Albert, G.; Berg, C.; Beyer, M.; Achatz, U.; J oos, S.; Niedner-
Schatteburg, G.; Bondybey, V. E. Chem. Phys. Lett. 1997, 268, 235.
(24) Himmel, H.-J . Unpublished results.
(25) Himmel, H.-J .; Bihlmeier, A. Chem. Eur. J . 2004, 10, 627.
(26) See, for example: Himmel, H.-J .; Downs, A. J .; Greene, T. M.
Chem. Rev. 2002, 102, 4191.

2352 Organometallics, Vol. 23, No. 10, 2004
Bihlmeier et al.
F igu r e 1. IR spectra in the region around 1500 cm-1
recorded for the reaction of Ti atoms with CH4: (a)
spectrum upon deposition; (b) difference between the
spectra before and after photolysis at 500 nm; (c) difference
between the spectra before and after UV-vis photolysis
(200 < λ < 800 nm).
F igu r e 2. IR spectra in the regions 2170-2145 and 900-
880 cm-1 of an Ar matrix containing Ti atoms and 0.2%
SiH4: (a) upon deposition; (b) after photolysis at λmax ) 500
nm; (c) after photolysis at λmax ) 410 nm.
all attempts to increase the yield of 1 (e.g. by increasing
the CH4 or Ti concentrations) failed. We conclude that
the reaction between Ti and CH4 needs activation and
proceeds inefficiently under the conditions of our experi-
ments to give a low product yield.
an SVP basis set was used only for the two 5s and the two 5p
electrons; for the remaining 46 electrons a relativistic ECP
(MEFIT, WB)28 was applied.
Resu lts
Ti + SiH4. Unlike the experiments with CH4, the IR
spectrum taken upon deposition of Ti atoms together
with SiH4 gave evidence for spontaneously formed
reaction products. Several experiments showed that not
one but four species are formed immediately upon
deposition. Selective photolysis proved to be extremely
useful to discriminate between these different species.
First, a family of absorptions appeared at 2164.3,
2160.4, 893.8, and 888.7 cm-1. These wavenumbers are
close to those of free SiH4, and thus, low concentrations
of SiH4 (0.2%) in the matrix were necessary in order to
observe all of them (see Figure 2). The bands decrease
sharply upon photolysis at λmax ) 500 nm and were
completely extinguished by photolysis employing broad-
band visible light (400 < λ < 800 nm). The source of
these absorptions is in all probability a complex of the
form Ti‚SiH4.
Some of the bands observed for the remaining three
species have very similar wavenumbers (see Figure 3).
Thus, there should be some similarities in the structures
of these species. Especially close were the bands of two
products, which will be referred to as 2a a and 2a b in
the following discussion. The bands of 2a a and 2a b also
show almost the same response to the various photolysis
cycles. Thus, the bands increase on brief photolysis at
In the following account, the results of the experi-
ments involving codeposition of Ti atoms with CH4,
SiH4, and SnH4 will be reported in turn.
Ti + CH4. The spectrum taken following deposition
of Ti atoms together with 2% CH4 in Ar gave no evidence
for an absorption due to a product of any reaction
between the two reagents (see Figure 1). Subsequently,
the matrix was photolyzed with λmax ) 500 nm light for
a period of 30 min. This wavelength can initiate a z(3D1)
r a(3F2) or a z(3F2) r a(3F2) transition of the Ti
atoms.25,29 The treatment brought about the appearance
of a weak but sharp band at 1513.5 cm-1, which can be
assigned to the product 1, from the reaction between
Ti and CH4. Subsequently, the matrix was subjected to
a period of 10 min of photolysis with λmax ) 410 nm,
resulting in a decrease of the band due to product 1.
No product of the decomposition of 1 was detected. The
spectra gave also evidence for weak absorptions due to
TiO2 and H2TiO.30
The experiment was repeated, but with CD4 in place
of CH4. Again the spectrum taken following deposition
showed no sign of any reaction product. Upon photolysis
at 500 nm, a weak and sharp band was seen to grow in
at 1092.1 cm-1. The absorber responsible for this band
is in all probability the perdeuterated version of 1. The
behavior of the band toward further photolysis at a
different wavelength was similar to that reported for
CH4. Thus, photolysis at λmax ) 410 nm or broad-band
photolysis led to the rapid decay of 1. Unfortunately,
λmax ) 500 (1 min) and decrease on photolysis at λmax
)
410. 2a a has bands centered at 2055.0/2047.4, 1541.5,
1507.2, 1144.5, and 854.0 cm-1 and 2a b at 2042.5/
2040.5, 1514.1, 1120.7, and 937.8/934.2 cm-1
.
The bands belonging to the fourth species, 3a , appear
at 1524.8, 1509.2, 1498.1, and 1129.7 cm-1. They can
easily be distinguished from the bands of 2a a and 2a b
on the basis of their response to photolysis. Thus, the
bands of species 3a were seen to grow upon photolysis
at λmax ) 410 at the expense of those due to 2a a and
2a b. The obvious inference is that 2a a and 2a b are
precursors to 3a .
(27) Ahlrichs, R.; Ba¨r, M.; Ha¨ser, M.; Horn, H.; Ko¨lmel, C. Chem.
Phys. Lett. 1989, 162, 165. Eichkorn, K.; Treutler, O.; O¨ hm, H.; Ha¨ser,
M.; Ahlrichs, R. Chem. Phys. Lett. 1995, 240, 283. Eichkorn, K.;
Treutler, O.; O¨ hm, H.; Ha¨ser, M.; Ahlrichs, R. Chem. Phys. Lett. 1995,
242, 652. Eichkorn, K.; Weigend, F.; Treutler, O.; Ahlrichs, R. Theor.
Chem. Acc. 1997, 97, 119. Weigend, F.; Ha¨ser, M. Theor. Chem. Acc.
1997, 97, 331. Weigend, F.; Ha¨ser, M.; Patzelt, H.; Ahlrichs, R. Chem.
Phys. Lett. 1998, 294, 143.
(28) Bergner, A.; Dolg, M.; Kuechle, W.; Stoll, H.; Preuss, H. Mol.
Phys. 1993, 80, 1431.
(29) Gruen, D. M.; Carstens, D. H. W. J . Chem. Phys. 1971, 54, 5206.
(30) Zhang, L.; Dong, J .; Zhou. M. J . Phys. Chem. A 2000, 104, 8882.
The bands due to 3a decreased slowly upon photolysis
of the matrix with broad-band visible light (400 < λ <

Insertion of Ti into C-H, Si-H, and Sn-H Bonds
Organometallics, Vol. 23, No. 10, 2004 2353
F igu r e 3. IR spectra recorded for the reaction of Ti atoms
with SiH4: (a) upon deposition; (b) after photolysis at λmax
) 500 nm; (c) after photolysis at λmax ) 410 nm; (d) after
broad-band visible photolysis (400 < λ < 800 nm).
F igu r e 5. UV/vis spectra of a matrix containing (a) only
Ti atoms and (b) Ti atoms together with 1% SiH4.
F igu r e 4. IR spectra recorded for the reaction of Ti atoms
with SiD4: (a) upon deposition; (b) after photolysis at λmax
) 500 nm; (c) after photolysis at λmax ) 410 nm; (d) after
broad-band visible photolysis (400 < λ < 800 nm).
F igu r e 6. IR spectra in the regions 1890-1860 and 670-
650 cm-1 of an Ar matrix containing Ti atoms and 0.2%
800 nm). A weak but sharp absorption at 930.2 cm-1
and a broad one around 869 cm-1 appeared upon
prolonged photolysis.
SnH4: (a) upon deposition; (b) after photolysis at λmax
500 nm; (c) after photolysis at λmax ) 410 nm.
)
Finally, bands at 1098.3, 1087.2, 1079.7, and 831.3 cm-1
can be assigned to product 3a in its perdeuterated form.
Again, these absorptions decreased upon photolysis with
broad-band visible light.
In further experiments a bolometer was used to detect
bands in the region 700-50 cm-1. However, no bands
arising from reaction products were observed in these
experiments. Finally, the experiment was repeated with
SiD3H. All absorptions of products 2a a , 2a b, and 3a in
their various isotopic forms together with their response
toward photolysis are included in Table 1.
Figure 5 displays a UV/vis spectrum of a matrix
containing Ti atoms and SiH4 together with that of a
matrix containing only Ti atoms. Unfortunately, it was
not possible to detect an absorption arising from one of
the products. Nevertheless, it can be seen that the half-
width of the absorptions arising from electronic transi-
tions of the Ti atoms slightly increase in the presence
of SiH4. It also can be seen that conditions were chosen
for which the concentration of Ti2 dimers must be very
The experiment was repeated with SiD4 in place of
SiH4. First, experiments were conducted with a low
percentage of SiD4 (0.3%) in the matrix. Here, only one
band at 657.3 cm-1, which could be assigned to a Ti‚SiD4
complex, was observed upon deposition. This band again
decreased sharply upon photolysis at λmax ) 500 nm and
disappeared completely on further photolysis. Figure 4
displays the spectra taken in an experiment involving
a larger concentration of SiD4 (1.5%), following the same
pattern as observed for the reaction with SiH4. However,
the bands due to 2a a and 2a b were more clearly visible
and the relative intensities of the bands due to product
3a appeared to be reduced on deposition and after brief
photolysis at λmax ) 500 nm. All bands were red-shifted
with respect to the corresponding features observed in
the experiments relying on SiH4. Species 2a a appeared
now in absorptions at 1495.5/1490.8, 1125.6, 1085.6,
829.3, and 634.7 cm-1. Unfortunately, only two bands
due to species 2a b in its perdeuterated version were
traced; these appeared at 1480.5 and 1090.5 cm-1
.

2354 Organometallics, Vol. 23, No. 10, 2004
Bihlmeier et al.
Ta ble 1. Obser ved Wa ven u m ber s (cm -1) follow in g th e Rea ction betw een Ti Atom s a n d SiH4, SiD4,
a n d SiD3H
photolysis
SiH4
2164.3
SiD4
SiD3H
2164.0
2160.1
1560.3
deposition
500 nm
410 nm
400-800 nm
absorber
v
v
V
V
V
V
V
V
Ti‚SiH4
Ti‚SiH4
2160.4
2055.0/2047.4
2116.2
2041.7
1479.8
2095.2
v
v
v
v
V
V
V
V
cis-HTi(µ-H)2SiH (2a a )
1480.5
2042.5/2040.5
trans-HTi(µ-H)2SiH (2a b)
1495.5/1490.8
1125.6
1495.9/1491.4
1541.5
1524.8
v
v
v
v
V
v
V
V
cis-HTi(µ-H)2SiH (2a a )
HTi(µ-H)3Si (3a )
1525.5
1098.3
1090.5
1087.2
1102.5/1098.4
1090.5
1514.1
1509.2
1507.2
v
v
v
v
v
v
V
v
V
V
V
V
trans-HTi(µ-H)2SiH (2a b)
HTi(µ-H)3Si (3a )
1508.4
1086.4
1498.3
1079.0
cis-HTi(µ-H)2SiH (2a a )
1085.6
1498.1
v
v
v
V
HTi(µ-H)3Si (3a )
1079.7
829.3
831.3
1144.5
1129.7
1120.7
937.8/934.2
893.8
v
v
v
v
v
v
v
v
v
V
V
v
V
V
V
V
V
V
V
V
cis-HTi(µ-H)2SiH (2a a )
HTi(µ-H)3Si (3a )
trans-HTi(µ-H)2SiH (2a b)
trans-HTi(µ-H)2SiH (2a b)
Ti‚SiH4
1150.5
839.5
838.9
657.7
637.6
888.7
657.3
634.7
v
v
V
V
V
Ti‚SiH4
877.3
854.0
v
v
v
V
V
V
trans-HTi(µ-H)2SiH (2a b)
cis-HTi(µ-H)2SiH (2a a )
F igu r e 7. IR spectra recorded for the reaction of Ti atoms
with SnH4: (a) upon deposition; (b) after photolysis at λmax
) 500 nm; (c) after broad-band visible photolysis (400 < λ
< 800 nm).
F igu r e 8. IR spectra in the regions 1355-1340 and 480-
460 cm-1 of an Ar matrix containing Ti atoms and 0.2%
low. The absorptions characteristic for Ti2 are not
present under these conditions.25 Thus, we can role out
the involvement of Ti2 in the reactions.
SnD4: (a) upon deposition; (b) after photolysis at λmax
)
500 nm; (c) after photolysis at λmax ) 410 nm.
Ti + Sn H4. Upon deposition of an Ar matrix contain-
ing Ti atoms and SnH4, IR bands at 1881.8, 1876.7,
1870.7, 657.0, and 648.0 cm-1 were observed to arise
from the first, spontaneously formed product, which is
most likely to be a complex of the form Ti‚SnH4. The
absorptions of this complex are close to the bands of
SnH4. Therefore, with higher concentrations of SnH4 in
the matrix (1.5%), some of the bands were hidden under
the stronger bands of free SnH4 and could be discerned
only when lower concentrations of SnH4 (0.2%) were
used. The bands of the complex decreased sharply
following photolysis with light having λmax ) 500 nm
and disappeared completely upon broad-band visible
radiation (see Figure 6).
Additional features were observed at 1499.6, 1482.4,
1043.4, 978.5, 385.9, and 249.7 cm-1, and these can be
assigned to the two absorbers 4ba and 4bb. Since all
the absorptions of 4ba are close to those of 4bb (see
Figure 7), it is reasonable to assume that 4ba and 4bb
must have very similar structures. It is therefore
difficult to assign the bands to one or the other of these
two species. However, on the basis of several experi-
ments we have assigned the bands at 1482.4, 1043.4,
and 385.9 cm-1 to species 4ba and those at 1499.6,
978.5, and 249.7 cm-1 to 4bb. We note that the absorp-
tions at 1499.6 and 1482.4 cm-1 have wavenumbers
suggestive of ν(Ti-H) fundamentals. The bands grew

Insertion of Ti into C-H, Si-H, and Sn-H Bonds
Organometallics, Vol. 23, No. 10, 2004 2355
Ta ble 2. Obser ved Wa ven u m ber s (in cm -1) F ollow in g th e Rea ction betw een Ti Atom s a n d Sta n n a n e
(Sn H4 a n d Sn D4)
photolysis
SnH4
SnD4
deposition
500 nm
410 nm
400-800 nm
absorber
1881.8
1876.7
1870.7
1508.1
1499.6
1482.4
1478.4
1043.4
1021.2
1016.5
978.5
1348.5
1345.9
1342.4
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
V
V
V
v
v
v
v
v
v
v
v
v
v
V
V
v
v
v
v
v
V
V
V
v
V
V
v
V
v
v
V
v
v
V
V
v
V
v
V
v
V
V
V
v
V
V
v
V
v
v
V
v
v
V
V
v
V
v
V
v
Ti‚SnH4
Ti‚SnH4
Ti‚SnH4
HTi(µ-H)3Sn (3b)
HTi(µ-H)2(H)Sn (4bb)
HTi(µ-H)2(H)Sn (4ba )
HTi(µ-H)3Sn (3b)
HTi(µ-H)2(H)Sn (4ba )
HTi(µ-H)3Sn (3b)
HTi(µ-H)3Sn (3b)
HTi(µ-H)2(H)Sn (4bb)
HTi(µ-H)3Sn (3b)
HTi(µ-H)3Sn (3b)
Ti‚SnH4
1080.6
1069.0
1065.0
733.5
741.3
939.9
905.5
472.3
466.4
452.0
657.0
648.0
624.8
385.9
255.8
249.7
Ti‚SnH4
HTi(µ-H)3Sn (3b)
HTi(µ-H)2(H)Sn (4ba )
HTi(µ-H)3Sn (3b)
HTi(µ-H)2(H)Sn (4bb)
HTi(µ-H)3Sn (3b)
183.2
were located at 1065.0, 939.9, 905.5, 741.3, 452.0, and
183.2 cm-1. The photolysis behavior of all the species
is the same as that observed in the experiments with
SnH4.
Table 2 includes all the absorptions assignable to the
TiSnH4(SnD4) contact pair and the products 3b, 4ba ,
and 4bb of the reactions of Ti atoms with SnH4 and
SnD4.
Discu ssion
The results clearly show that the product of the
reaction with CH4 differs significantly from those iden-
tified in the reactions with either SiH4 or SnH4. The
observation of at least one absorption in the region
characteristic of the stretching vibrations of terminal
Ti-H bonds suggests that molecules of the form
HTi(µ-H)nEH3-n are formed. On the basis of experi-
ments with several different concentrations of Ti in the
matrix and of the UV/vis spectra (see Figure 5), we can
rule out that more than one Ti atom is present in the
observed reaction products. The spectra also show that
n is different for the three reactants CH4, SiH4, and
SnH4. Several isomers (structures A-E) have to be
considered for a species with this general formula. We
therefore start our discussion with a survey of all the
F igu r e 9. IR spectra recorded for the reaction of Ti atoms
with SnD4: (a) upon deposition; (b) after photolysis at λmax
) 500 nm; (c) after photolysis at λmax ) 410 nm; (d) after
broad-band visible photolysis (400 < λ < 800 nm).
on photolysis at λmax 500 nm and decreased when the
matrix was irradiated with broad-band visible light.
Finally, a family of bands located at 1508.1, 1478.4,
1021.2, 1016.5, 624.8, and 255.8 cm-1 belong to the
species 3b (see Figure 7). The strong band at 1478.4
cm-1 and the weak one at 1508.1 cm-1 again appear in
a region characteristic of ν(Ti-H) fundamentals, whereas
the absorptions at 1021.2 and 1016.5 cm-1 argue for the
presence of bridging H atoms. The behavior of these
bands toward photolysis was distinctly different from
the behavior observed for products 4ba and 4bb. Thus,
the bands grew on λmax ) 500 nm photolysis and
remained almost unchanged when the matrix was
irradiated with broad-band visible light.
Additional experiments were conducted with SnD4. The
bands of the Ti‚SnD4 complex were now observed at
1348.5, 1345.9, 1342.4, 472.3, and 466.4 cm-1 (see
Figure 8). The bands due to products 4ba and 4bb were
red-shifted to 1069.0 cm-1 (4ba ), 1080.6 cm-1 (4bb) and
733.5 cm-1 (4ba ) (see Figure 9). Our experiments gave
evidence of six absorptions due to product 3b . These

2356 Organometallics, Vol. 23, No. 10, 2004
Bihlmeier et al.
Ta ble 3. Ca lcu la ted Dim en sion s (Dista n ces in p m ,
An gles in d eg), IR P r op er ties (Wa ven u m ber s in
cm -1, In ten sities (in k m m ol-1) Given in
tional modes, the ν(Ti-H) stretching fundamental ν3,
to carry most of the intensity. In the case of the singlet
electronic state, the Ti-H bond is significantly shorter
(170.5 pm) and, as a consequence, the ν(Ti-H) stretch-
ing fundamental is predicted to appear at higher wave-
number (1641.3 cm-1). For E ) Si, Sn, no minimum
could be found for such a structure in which none of
the H atoms occupies a bridging position.
HTi(µ-H)EH2 (B; n ) 1). No energy minimum could
be found for this isomer when E ) C. For E ) Si, Sn,
however, isomers of this form were located by our
calculations. Some dimensions and vibrational proper-
ties are summarized in Tables 4 and 5. Both species
possess only C1 symmetry. The Ti-Si and Ti-Sn
distances measure 246.5 and 273.9 pm, respectively.
This isomer has the highest energy of all the calculated
minima. In the case of the Si homologue, the energy
difference from the other forms is relatively small, but
in the case of the Sn-containing compound this species
is already 87.1 kJ mol-1 higher in energy than the global
minimum form.
P a r en th eses). a n d Rela tive En er gies (in k J m ol-1
for th e Sin glet, Tr ip let, a n d Qu in tet Electr on ic
Sta tes of HTiCH3
)
singlet (1A′)
triplet (3A′′)
quintet (5A′)
d(Ti-C)
d(Ti-H)
d(C-H)
201.9
170.5
110.9/111.8/
111.8
207.9
175.2
111.2/111.7/
111.7
230.9
185.1
110.5/110.5/
110.9
(H-Ti-C)
110.2
119.8
178.9
ν1(a′)
ν2(a′)
ν3(a′)
ν4(a′)
ν5(a′)
ν6(a′)
ν7(a′)
ν8(a′)
ν9(a′′)
3068.4 (2)
2889.6 (1)
1641.3 (180)
1300.3 (2)
1031.0 (18)
565.8 (69)
432.1 (9)
208.6 (15)
2991.5 (4)
1334.8 (15)
335.5 (6)
3039.4 (2)
2899.6 (3)
1551.3 (267)
1336.9 (2)
1069.2 (4)
568.0 (118)
467.6 (7)
279.1 (36)
2989.5 (8)
1345.8 (7)
357.6 (19)
194.7 (48)
3107.6 (1)
2945.4 (1)
1337.2 (6)
1227.8 (17)
808.2 (188)
362.0 (16)
293.8 (11)
222.7 (23)
3130.3 (0.001)
1293.9 (1)
389.1 (12)
ν10(a′′)
ν11(a′′)
ν12(a′′)
184.8 (35)
273.8 (0.2)
cis- a n d tr a n s-HTi(µ-H)2EH (C, D; n ) 2). Again,
energy minima of this form were found for E ) Si, Sn
but not for E ) C. The cis and trans forms were found
to have similar energies. The cis form is calculated to
be slightly more stable, but the energy difference from
the trans form amounts to no more than 0.4 and 6.8 kJ
mol-1 for E ) Si, Sn, respectively. In the case of the Si
compound, the Ti-Si distance (242.1 pm in the cis form
and 236.4 pm in the trans form) is slightly shorter than
in the isomer with the structure B. In all cases, the Ti-
Ht distance increases with respect to those found in the
isomers of structure B. In the case of E ) Si, these
isomers are only 24.3 and 24.7 kJ mol-1 higher in energy
than the global minimum structure. For E ) Sn,
however, they are energetically less favored.
HTi(µ-H)3E (E; n ) 3). This isomer, with three
bridging H atoms, represents the global energy mini-
mum for a species of this formula and E ) Si or Sn.
Again, a triplet state is found to be the ground electronic
state. The structure is only slightly distorted from Cs
symmetry. The Ti‚‚‚Si and Ti‚‚‚Sn distances now amount
∆E
92.7
92.0
0
0
232.5
228.3
∆EZPE
possible isomers on the basis of quantum-chemical
calculations. The results of this survey will prove to be
invaluable in the identification and characterization of
the species formed in the course of our experiments.
Qu a n tu m -Ch em ica l Ca lcu la tion s: HTiEH 3 (A; n
) 0). The global energy minimum for a molecule with
the formula TiCH4 is a species exhibiting a triplet
electronic ground state and having one terminal Ti-H
(175.2 pm) bond, three terminal C-H bonds (111.2-
111.7 pm), and a direct Ti-C bond (207.9 pm). The angle
H-Ti-C turns out to be close to 120°. No minimum was
found in which one or more of the H atoms occupy a
bridging position. Table 3 summarizes the calculated
dimensions and IR properties not only for the triplet
ground electronic state but also for the lowest energy
singlet and quintet electronic states, which are 92 and
228 kJ mol-1, respectively, higher in energy than the
ground state. The calculations predict one of the vibra-
Ta ble 4. Ca lcu la ted Dim en sion s (Dista n ces in p m ), IR P r op er ties (Wa ven u m ber s in cm -1, In ten sities
(in k m m ol-1) Given in P a r en th eses), a n d Rela tive En er gies (in k J m ol-1) for HTi(µ-H)n SiH3-n
isomer
B (n ) 1)
175.0
C (n ) 2, cis)
D (n ) 2, trans)
E (n ) 3)
176.1
196.1, 199.1,
199.7
Ti-Ht
Ti-Hb
177.6
194.4, 194.4
177.7
203.3, 203.4
200.6
Ti-Si
Si-Ht
Si-Hb
246.5
151.4, 151.9
163.0
242.1
152.1
162.8, 162.8
236.4
151.1
161.4, 161.4
254.4
160.0, 163.2,
163.2
ν1
2108.6 (99)
2076.7 (117)
1558.1 (232)
1551.3 (218)
1018.6 (153)
896.7 (99)
820.7 (31)
484.9 (2)
414.4 (147)
314.8 (11)
277.5 (68)
214.4 (57)
2075.6 (149)
1575.2 (90)
1564.2 (206)
1522.3 (424)
1171.2 (197)
1105.2 (1)
814.2 (31)
608.3 (0.01)
512.1 (10)
2121.7 (105)
1641.0 (68)
1628.4 (159)
1530.8 (404)
1045.7 (204)
986.3 (2)
849.7 (58)
564.9 (3)
430.5 (6)
1698.2 (79)
1557.3 (222)
1546.5 (158)
1542.3 (148)
1129.8 (398)
1083.8 (54)
1045.0 (19)
743.0 (31)
721.0 (13)
361.8 (51)
256.4 (136)
232.2 (87)
ν2
ν3
ν4
ν5
ν6
ν7
ν8
ν9
ν10
ν11
ν12
317.3 (20)
196.1 (277)
155.0 (137)
336.8 (30)
191.7 (240)
160.4 (130)
∆E
27.5
24.3
24.7
0

Insertion of Ti into C-H, Si-H, and Sn-H Bonds
Organometallics, Vol. 23, No. 10, 2004 2357
Ta ble 5. Ca lcu la ted Dim en sion s (Dista n ces in p m ), IR P r op er ties (Wa ven u m ber s in cm -1, In ten sities
(in k m m ol-1) Given in P a r en th eses), a n d Rela tive En er gies (in k J m ol-1) for HTi(µ-H)n Sn H3-n
isomer
B (n ) 1)
C (n ) 2, cis)
Cs
D (n ) 2, trans)
E (n ) 3)
sym
C1
Cs
C1
Ti-Ht
Ti-Hb
Ti-Sn
Sn-Ht
Sn-Hb
176.9
193.4
273.9
176.7, 177.5
199.0
177.5
192.5
279.3
178.8
196.4
178.5
193.5
276.4
178.9
199.5
179.2
195.8, 199.0, 199.3
278.0
191.3, 196.8, 196.9
ν1
1727.1 (a, 262)
1704.0 (a, 270)
1542.1 (a, 376)
1188.7 (a, 191)
968.4 (a, 223)
701.3 (a, 82)
618.7 (a, 34)
441.7 (a, 5)
345.5 (a, 175)
272.3 (a, 92)
196.3 (a, 10)
182.8 (a, 28)
1667.5 (a′, 302)
1534.2 (a′, 442)
1222.7 (a′, 123)
1105.6 (a′, 320)
685.5 (a′, 55)
409.4 (a′, 78)
272.8 (a′, 182)
126.8 (a′, 15)
1661.1 (a′, 310)
1529.9 (a′, 454)
1217.1 (a′, 151)
952.1 (a′, 69)
680.3 (a′, 77)
310.9 (a′, 18)
261.3 (a′, 196)
83.9 (a′, 5)
1159.9 (a′′, 246)
960.6 (a′′, 51)
478.9 (a′′, 19)
241.9 (a′′, 336)
1520.0 (a, 484)
1302.6 (a, 97)
1207.2 (a, 104)
1166.0 (a, 168)
1063.3 (a, 457)
940.5 (a, 154)
917.5 (a, 47)
656.1 (a, 41)
559.4 (a, 89)
254.7 (a, 87)
195.5 (a, 94)
192.0 (a, 141)
ν2
ν3
ν4
ν5
ν6
ν7
ν8
ν9
1171.2 (a′′, 219)
1043.1 (a′′, 137)
540.7 (a′′, 1)
ν10
ν11
ν12
276.7 (a′′, 95)
∆E
87.1
50.5
57.3
0
F igu r e 11. Plot showing the isomers of TiSnH4 and their
relative energies.
Tables 4 and 5 summarize some of the important
dimensions, IR properties, and relative energies calcu-
lated for isomers B-E and for E ) Si, Sn. Figure 11
shows the minima as calculated by quantum-chemical
means in the order of energies for E ) Sn.
It is noteworthy, then, that here is an example of a
change in structure that occurs between homologues of
the first and subsequent rows (in this case from C to Si
and Sn). This change of structure is caused by several
effects. Certainly the trend in the polarization of the
F igu r e 10. Frontier orbitals of HTi(µ-H)3Si.
to 254.4 and 278.0 pm, respectively. The Ti-Ht distance
is slightly shorter in HTi(µ-H)3Si (176.1 pm) than it is
in HTi(µ-H)3Sn (179.2 pm). Figure 10 displays the
frontier orbitals of HTi(µ-H)3Si. It can be seen very
clearly that the two orbitals that are each occupied by
only one electron (SOMO’s) are centered at the Ti
atom.

2358 Organometallics, Vol. 23, No. 10, 2004
Bihlmeier et al.
Ti‚SiH4 a n d Ti‚Sn H4. The bands at 2164.3, 2160.4,
893.8, and 888.7 cm-1 in the experiments with SiH4 and
at 1881.8, 1876.7, 1870.7, 657.0, and 648.0 cm-1 in the
experiments with SnH4 can be assigned to a complex of
the form Ti‚EH4. Unfortunately, it proved difficult to
obtain information about the possible structures of such
complexes Ti‚SiH4 and Ti‚SnH4 on the basis of quantum-
chemical calculations. All attempts to model these
species resulted in insertion of the Ti atom into one of
the E-H bonds (E ) Si, Sn). Thus, it appears that the
barrier for insertion is very small. A detailed analysis
of the energy hypersurface is difficult, because several
electronic states have to be considered in these calcula-
tions. Possibly a tridentate complex is formed, such as
that which is observed for the formally valence isoelec-
tronic BH4- anion in the case of Ti(III) complexes.2 The
adoption of such a structure is also suggested by our
proposed reaction pathway (see below).
E-H bonds from CH4 to SiH4 and SnH4 is of importance
in this context. The more negatively polarized the H
atoms become, the larger the inclination of the Ti atom
(acceptor) to establish bonds to them. Another factor is
clearly the strength of a possible Ti-E bond.
Oth er P ossible Isom er s. An isomer of the form
H2TiSiH2, containing only terminal Ti-H and Si-H
bonds, is calculated to have an energy which is 89.3 kJ
mol-1 higher than that calculated for HTi(µ-H)3Si. In
the case of H2TiSnH2, the energy difference amounts
to 115.5 kJ mol-1 in favor of the isomer with three H
bridges. The decreasing strength of the Ti-E bond down
the group is probably responsible for the increasing
energy of the H2TiEH2 isomer. The IR spectra recorded
for the products of the reactions between Ti atoms and
CH4, SiH4, or SnH4 gave no evidence for the formation
of these species.
The wavenumbers observed for Ti‚SiH4 are close to
those reported previously for Al‚SiH4.19,20 In the case
of Al‚SiH4, the binding energy of the complex was
estimated to be not more than 10 kJ mol-1 on the basis
of quantum-chemical calculations. The IR spectrum
measured for Ti‚SiH4 thus indicates that this complex
is also only weakly bound.
cis- a n d tr a n s-HTi(µ-H)2SiH (2a a a n d 2a b). Our
experiments clearly show that Ti atoms are much more
reactive toward SiH4 and SnH4 than toward CH4.
Already, upon deposition, the IR spectra give evidence
not only for the formation of the complex Ti‚SiH4 or
Ti‚SnH4 but also for some degree of spontaneous inser-
tion of the Ti atoms into the Si-H and Sn-H bonds,
respectively.
Assign m en t of th e Ma tr ix P r od u cts. The combi-
nation of experimental and quantum-chemical results
can now be used to identify and characterize most of
the species formed in the course of our experiments.
HTiCH3 (1). Photolysis is necessary to initiate a
limited reaction between Ti and CH4. The product yield
is relatively small. Nevertheless, the appearance of a
ν(Ti-H) band in the product spectrum indicates that
some of the Ti atoms have indeed inserted into a C-H
bond, leading in all probability to a species of the general
formula HTiCH3. The wavenumber argues for a Ti(II)
species. The IR spectrum shows no absorption in the
region between 1400 and 900 cm-1 that is characteristic
of the ν(C-Hb) and ν(Ti-Hb) stretching modes of bridg-
ing H atoms (Hb). The obvious inference then is that
product 1 contains only terminal H atoms. Our quantum-
chemical calculations (see above) are in excellent agree-
ment with these results. According to the calculations,
HTiCH3 features no bridging H atom. The calculations
also agree that one vibrational mode carries most of the
IR intensity. The wavenumber of this mode is calculated
to be 1551.3 cm-1, a value which compares well with
the value of 1513.5 cm-1 that we observe. From a
comparison with the measured IR spectrum, it is clear
that HTiCH3 is formed in its triplet electronic state in
a spin-allowed reaction between Ti atoms and CH4.
On the basis of the IR spectra, both 2a a and 2a b are
likely to have one terminal Ti-H bond and Ti-H-Si
bridges. The spectra also indicate the presence of one
terminal Si-H bond. The obvious inference is that 2a a
and 2a b are cis- and trans-HTi(µ-H)2SiH.

Insertion of Ti into C-H, Si-H, and Sn-H Bonds
Organometallics, Vol. 23, No. 10, 2004 2359
Ta ble 6. Com p a r ison betw een Obser ved a n d Ca lcu la ted Wa ven u m ber s (in cm -1, w ith In ten sities
(in k m m ol-1) Given in P a r en th eses) for HTi(µ-H)2SiH a n d DTi(µ-D)2SiD (2a a (Cis) a n d 2a b (Tr a n s)]
approx descripn
of molecular
motion
HTi(µ-H)2SiH (cis)
DTi(µ-D)2SiD (cis)
obsd
calcd
obsd
calcd
2055.0/2047.4
2075.6 (149)
1575.2 (90)
1564.2 (206)
1522.3 (424)
1171.2 (197)
1105.2 (1)
814.2 (31)
608.3 (0.01)
512.1 (10)
1480.5
1499.2 (78)
1132.8 (46)
1127.5 (106)
1091.3 (227)
839.8 (97)
787.2 (0.2)
593.1 (14)
445.2 (0.2)
401.0 (9)
ν(Si-Ht)
νs(Si-Hb)
1541.5
1507.2
1144.5
1125.6
1085.6
829.3
νas(Si-Hb)
ν(Ti-Ht)
νs(Ti-Hb)
ν
as(Ti-Hb)
854.0
634.7
δ(Ht-Si-Hb)
317.3 (20)
196.1 (277)
155.0 (137)
290.6 (12)
142.7 (146)
113.0 (72)
ν(Si-Ti)
torsion
approx descripn
of molecular
motion
HTi(µ-H)2SiH (trans)
DTi(µ-D)2SiD (trans)
obsd
calcd
obsd
calcd
2042.5/2040.5
2121.7 (105)
1641.0 (68)
1628.4 (159)
1530.8 (404)
1045.7 (204)
986.3 (2)
1495.5/1490.8
1533.4 (56)
1179.8 (37)
1173.3 (82)
1096.9 (215)
753.6 (95)
702.8 (1)
ν(Si-Ht)
νs(Si-Hb)
ν
as(Si-Hb)
1514.1
1120.7
1090.5
ν(Ti-Ht)
νs(Ti-Hb)
νas(Ti-Hb)
937.8/934.2
849.7 (58)
564.9 (3)
614.8 (29)
415.8 (2)
δ(Ht-Si-Hb)
430.5 (6)
375.9 (19)
276.1 (11)
140.7 (125)
115.2 (67)
336.8 (30)
191.7 (240)
160.4 (130)
ν(Si-Ti)
torsion
Table 6 compares the experimentally observed wave-
numbers with those forecast by our DFT calculations.
The mode which can roughly be described as ν(Si-Ht)
is calculated to occur at 2075.6 cm-1 in the case of cis-
HTi(µ-H)2SiH and at 2121.7 cm-1 in the case of the
trans isomer. These values compare well with the
experimentally obtained values of ca. 2052 and ca. 2042
cm-1, respectively. The ν(H):ν(D) ratios are also in
agreement with this assignment (calculated 1.3845:1
and observed 1.3855:1 for the cis form and calculated
1.3837:1 and observed 1.3672:1 for the trans form). The
next two modes calculated at 1575.2 and 1564.2 cm-1
for the cis form and at 1641.0 and 1628.4 cm-1 for the
trans form are strongly associated with the symmetric
and antisymmetric Si-Hb stretching modes, νs(Si-Hb)
and νas(Si-Hb). Unfortunately, our experiments found
only one of these modes, νas(Si-Hb), of the cis form. This
mode should have the highest intensity of the three
ν(Si-H) modes, according to the calculations. Moving
to lower wavenumber, the next vibrational mode has a
high contribution from ν(Ti-Ht). This mode is calculated
to have a wavenumber of 1522.3 cm-1 for the cis form
and 1530.8 cm-1 for the trans form. The experimental
values of 1507.2 and 1514.1 cm-1 are in excellent
agreement with the calculated values. As expected, the
ν(H)/ν(D) ratios are close to 1.4:1 for this mode (cis,
calculated 1.3949:1, experimental 1.3884; trans, calcu-
lated 1.3956, experimental 1.3884). The symmetric and
antisymmetric ν(Ti-Hb) modes contribute to the next
two modes, which are predicted to appear at 1171.2 and
1105.2 cm-1 for cis-HTi(µ-H)2SiH and at 1045.7 and
986.3 cm-1 for the trans form. One of these modes is
calculated to have a very low intensity, and therefore,
it is not surprising that the experiments gave evidence
for only one of the two transitions. This was located at
1144.5 and 1120.7 cm-1 for the cis and trans forms,
respectively.
We strictly cannot rule out the possibility that the
presence of the bands assigned to 2a a and 2a b results
from a matrix splitting. This would imply that only one
of the two isomers (cis- or trans-HTi(µ-H)2SiH) is
formed. However, because of the similar energies, we
believe that it is more likely that 2a a and 2a b are the
cis and trans isomers.
In the case of the Sn homologues, the experiments
failed to find any evidence for a ν(Sn-H) stretching
fundamental, which is calculated to occur at 1667.3 and
1661.1 cm-1 for cis- and trans-HTi(µ-H)2SnH, respec-
tively, and should carry sufficient intensity. Thus, we
conclude that HTi(µ-H)2SnH is not formed. According
to the calculations, the energy difference between the
global energy minimum form of TiSnH4, HTi(µ-H)3Sn
(see below), and cis- and trans-HTi(µ-H)2SnH amounts
to more than 50 kJ mol-1. In the case of the Si
homologue, the difference was less than half this value
(24-25 kJ mol-1). The relative destabilization of HTi-
(µ-H)2SnH might explain the fact that HTi(µ-H)2SiH but
not HTi(µ-H)2SnH can be found in our experiments.
HTi(µ-H)3Si a n d HTi(µ-H)3Sn (3a a n d 3b). Accord-
ing to our calculations, these species define the global
energy minima for molecules with the overall formula
TiSiH4 and TiSnH4. The measured IR spectra leave no
doubt that both are formed in our experiments. They
are already present upon deposition but can be formed
in higher concentrations following appropriate photoly-
sis. While HTi(µ-H)3Si can be decomposed upon pho-
tolysis with broad-band visible light (a possible decom-
position product being TiSiH2), HTi(µ-H)3Sn is photo-
stable. As already mentioned, both species exhibit a
triplet ground electronic state.

2360 Organometallics, Vol. 23, No. 10, 2004
Bihlmeier et al.
Ta ble 7. Com p a r ison betw een Obser ved a n d Ca lcu la ted Wa ven u m ber s (in cm -1, w ith In ten sity
(in k m m ol-1) Given in P a r en th eses) for HTi(µ-H)3Si a n d DTi(µ-D)3Si (3a )
approx descripn
of molecular
motion
HTi(µ-H)3Si
DTi(µ-D)3Si
obsd
calcd
obsd
calcd
1698.2 (79)
1557.3 (222)
1546.5 (158)
1542.3 (148)
1129.8 (398)
1083.8 (54)
1045.0 (19)
743.0 (31)
721.0 (13)
361.8 (51)
256.4 (136)
232.2 (87)
1222.0 (44)
1120.0 (86)
1110.1 (88)
1108.4 (106)
818.2 (211)
775.3 (19)
747.6 (8)
535.6 (17)
518.2 (6)
345.6 (16)
192.1 (83)
167.2 (47)
νs(Si-Hb)
ν(Ti-Ht) (+νs(Si-Hb))
1524.8
1509.2
1498.1
1129.7
1098.3
1087.2
1079.7
831.3
νas(Si-Hb)
νs(Si-Hb) (+ν(Ti-Ht))
ν(Ti-Hb)
ν(Ti-Hb)
ν(Ti-Hb)
Ti(µ-H)3Si def
Ti(µ-H)3Si def
ν(Ti-Si)
δ(Si-Ti-Ht)
torsion
Ta ble 8. Com p a r ison betw een Obser ved a n d
Ca lcu la ted Wa ven u m ber s (in cm -1, w ith In ten sity
(in k m m ol-1) Given in P a r en th eses) for
HTi(µ-H)3Sn a n d DTi(µ-D)3Sn (3b)
bution from the three ν(Ti-Hb) stretching fundamen-
tals, which results in extensive and complicated mode
coupling.
Next in order of decreasing wavenumber follow the
three vibrations with high ν(Ti-Hb) character. For both
the Si- and Sn-containing compounds, one of these three
modes dominates in intensity. This mode is calculated
to occur at 1129.8 and 1063.3 cm-1, respectively. The
experiments give evidence for intense absorptions at
1129.7 and 1016.5 cm-1. The ν(H):ν(D) ratios of 1.3808:1
and 1.3996:1 derived from the quantum-chemical cal-
culations compare well with the values of 1.3590:1 and
1.3712:1 afforded by experiment.
approx descripn
of molecular
motion
HTi(µ-H)3Sn
DTi(µ-D)3Sn
obsd calcd
obsd calcd
1478.4 1520.0 (484) 1065.0 1089.9 (256) ν(Ti-Ht)
1302.6 (97)
1207.2 (104)
1021.2 1166.0 (168)
1016.5 1063.3 (457)
940.5 (154)
939.9
905.5
928.0 (50)
860.2 (50)
831.2 (87)
νs(Sn-Hb)
as(Sn-Hb)
νs(Sn-Hb)
ν
741.3
452.0
183.2
759.7 (239) ν(Ti-Hb)
672.2 (73)
656.4 (22)
468.9 (21)
402.2 (48)
238.4 (11)
ν(Ti-Hb)
ν(Ti-Hb)
Ti(µ-H)3Sn def
Ti(µ-H)3Sn def
ν(Ti-Sn)
917.5 (47)
624.8
255.8
656.1 (41)
559.4 (89)
254.7 (87)
195.5 (94)
192.0 (141)
The modes that can be described as ν(Ti‚‚‚Si) and ν-
(Ti‚‚‚Sn) vibrations are calculated to give rise to rela-
tively weak features at 361.8 and 254.7 cm-1. Unfortu-
nately, our experiments fail to detect these bands.
148.3 (109) δ(Sn-Ti-Ht)
139.7 (46) torsion
In Tables 7 and 8, the calculated IR properties are
compared with the observed ones for HTi(µ-H)3E and
DTi(µ-D)3E. The tables also contain attempts to describe
the modes responsible for the absorptions. Obviously,
in the absence of symmetry higher than Cs, there is a
high degree of coupling. The mode coupling is especially
strong between ν(Ti-Ht) and some of the ν(Si-Hb)
vibrations. The mode with the highest contribution from
Ti-Ht stretching is located at 1557.3 and 1520.0 cm-1
for HTi(µ-H)3Si and HTi(µ-H)3Sn, respectively. The
HTi(µ-H)2(H)Sn (4ba a n d 4bb). These species are
clearly precursors to HTi(µ-H)3Sn. Their absorptions lie
close to those of HTi(µ-H)3Sn and, hence, indicate that
4ba and 4bb feature a terminal Ti-H bond and one or
more bridging H atoms. From the absence of an absorp-
tion with a high degree of Sn-Ht stretching, we can
conclude that 4ba and 4bb probably do not contain any
terminal Sn-H bonds. The best explanation in our view
is that 4ba and 4bb are species with a structure that
lies between those of cis- or trans-HTi(µ-H)3SnH and
HTi(µ-H)3Sn, in which the three H atoms are already
in more or less bridging positions, but the terminal
Ti-H bond has not relaxed to its optimal position. It is
certainly not easy to calculate the detailed structure of
such a species, and more sophisticated methods are
definitely required for any future attempt.
observed wavenumbers of 1524.8 and 1478.4 cm-1
,
respectively, are in pleasing agreement with the calcu-
lated values. The ν(H):ν(D) ratios amount to 1.3904:1
and 1.3946:1 for the calculated wavenumbers and
1.3883:1 and 1.3882:1 for the observed values.
The wavenumbers of the three fundamentals with
high Si-Hb stretching character are located at 1698.2,
1546.5, and 1542.3 cm-1. The band at 1698.2 cm-1 is
calculated to be much weaker than the other two, and
unfortunately, our experiments have failed to detect it.
However, the other two modes appear clearly in the
experimental IR spectra at 1509.2 and 1498.1 cm-1. The
strong, sharp band at 1498.1 cm-1 in the observed
spectrum and 1542.3 cm-1 in the calculated spectrum
belongs to a mode which also includes a very high
contribution from Ti-Hb stretching (almost as high as
in the mode calculated to occur at 1557.3 cm-1). In
the case of the Sn homologue, the modes with high
ν(Sn-Hb) stretching character occur at significantly
lower wavenumbers and, consequently, the coupling
with ν(Ti-Ht) is reduced. These modes are, however,
in close proximity to fundamentals with a high contri-
Rea ction P a th w a ys. The experiments clearly show
that the reactions between Ti atoms and SiH4 or SnH4
proceed spontaneously, while the reaction between Ti
and CH4 requires the action of photolysis and even then
proceeds inefficiently. Thus, SiH4 and SnH4 appear
much more reactive toward Ti atoms than does CH4.
The reaction with SiH4 proceeds first to the weakly
bound complex Ti‚SiH4, in which the SiH4 is possibly
η3 coordinated (see eq 1). This complex can be converted
with almost no activation energy into cis- and trans-
HTi(µ-H)2SiH and subsequently to HTi(µ-H)3Si, all of
which are observed in the infrared spectrum of the
matrix following deposition. cis- and trans-HTi(µ-H)2SiH
may also be converted to HTi(µ-H)3Si by the action of

Insertion of Ti into C-H, Si-H, and Sn-H Bonds
Organometallics, Vol. 23, No. 10, 2004 2361
The experiments show that visible light leads to the
slow decomposition of HTi(µ-H)3Si. Unfortunately, it
was not possible to identify the decomposition products.
One possible product is TiSiH2. We also cannot rule out
the possibility of decomposition back to Ti atoms and
SiH4. Finally, hydrides such as TiH2 and SiH2 might
be possible decomposition products. However, no ab-
sorptions which had previously been assigned to these
two species31,32 were detected in the experiments.
Con clu sion s
This account describes studies of the spontaneous and
photolytically activated reactions of Ti atoms with CH4,
SiH4, and SnH4 in Ar matrixes at 12 K. The results show
that the reactivities of Ti atoms toward the three
reactants are very different. In the case of CH4, the
reaction requires photolytic activation of the Ti atoms
and then proceeds to give HTiCH3, a species featuring
only terminal Ti-H and C-H bonds. With SiH4 and
SnH4, spontaneous reactions were observed. For SiH4,
the products of these reactions are the weakly
bound complex Ti‚SiH4, the species cis- and trans-
HTi(µ-H)2SiH with two bridging
H
atoms, and
HTi(µ-H)3Si with three bridging H atoms. TiSiH4 can
be converted into cis- and trans-HTi(µ-H)2SiH by the
action of photolysis at λmax ) 500 nm. On photolysis at
λmax ) 410 nm, cis- and trans-HTi(µ-H)2SiH are them-
selves photolabile and undergo conversion into HTi(µ-
H)3Si. According to quantum-chemical calculations,
HTi(µ-H)3Si defines the global energy minimum for all
molecules of the general formula TiSiH4. The reaction
of Ti atoms with SnH4 leads spontaneously to the
complex Ti‚SnH4 and HTi(µ-H)3Sn with three H bridges.
Again, photolysis at λmax ) 500 and 410 nm can be used
to increase the yield of HTi(µ-H)3Sn at the expense of
Ti‚SnH4. The mechanisms of the reactions and the
structures of the products identified and characterized
in this work may have wider significance in improving
the understanding of oxidative-addition processes in
catalytic cycles.
photolysis at λmax ) 410 nm. Such a reaction is calcu-
lated to be exothermic by 24.3 kJ mol-1 (cis) and 24.7
kJ mol-1 (trans).
According to our calculations, the overall reaction
between Ti and SiH4 to give HTi(µ-H)3Si is exothermic
by -154.6 kJ mol-1, while the reaction between Ti
atoms and SnH4 proceeds with a reaction energy of
-266.0 kJ mol-1. In contrast, the reaction between Ti
atoms and CH4 to give HTiCH3 (eq 2) is exothermic by
only -92.3 kJ mol-1. All these values have to be treated
with caution, however, since they clearly depend on the
method and basis set used in the calculations. All the
reactions are spin allowed.
The reaction of Ti with SnH4 leads to an end product
analogous to that delivered by the reaction with SiH4.
However, cis- and trans-HTi(µ-H)2SnH appear not to be
formed. Instead, the IR spectra point to intermediates
which should have structures featuring both fully
established Ti-H-Sn bridges and Ti‚‚‚H-Sn interac-
tions.
Ack n ow led gm en t. We thank (i) the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen
Industrie for financial support and (ii) Dr. Ingo Krossing
for fruitful discussions.
OM040016O
(31) Chertihin, G. V.; Andrews, L. J . Am. Chem. Soc. 1994, 116,
8322.
(32) Andrews, L.; Wang, X. J . Phys. Chem. A 2002, 106, 7696.