Routes to titanium tetrazole complexes

Article abstract of DOI:10.1016/j.poly.2003.11.047

The titanium tetrazole coordination complex [TiCl₄ ·(PhCN₄H)₂] has been prepared by treatment of TiCl₄ with two equivalents of 5-phenyltetrazole in dichloromethane and spectroscopically and crystallographically characterised. The solid-state structure of this compound consists of six-coordinate titanium centres with cis ligated tetrazoles. The individual [TiCl₄·(PhCN ₄H)₂] dimerise via intermolecular N?H-N hydrogen bonding interactions and are further organised into 2D supramolecular arrays. Mass spectral evidence indicates that the individual tetrazole ligands are only weakly bound, limiting the potential of this complex as a titanium nitride precursor. 3+2 cycloaddition of tributyltin azide with 2-toluinitrile at 200°C has afforded the tributylstannyl tetrazole[SnBu₃{5-(2- MeC₆H₄)CN₄}]_n. Crystallographic analysis shows that this compound exists as a supramolecular coordination polymer propagated via trigonal bipyramidal tin centres linked by N ¹-Sn-N³ interactions. Preliminary reactivity studies of this tin complex with titanium tetrachloride in an effort to synthesise a covalently bound titanium tetrazolyl complex have thus far yielded incomplete elimination of the expected Bu₃SnCl by-product and intractable titanium-containing products.

Full text of DOI:10.1016/j.poly.2003.11.047

Polyhedron 23 (2004) 801–807
www.elsevier.com/locate/poly
Routes to titanium tetrazole complexes q
a,
b
b
Michael S. Hill *, Peter B. Hitchcock , Nikki Smith
a
Department of Chemistry, Imperial College London, Exhibition Road, South Kensington, London SW7 2AZ, UK
b
The Chemistry Laboratory, University of Sussex, Falmer, Brighton, East Sussex BN1 9QJ, UK
Received 15 October 2003; accepted 12 November 2003
Abstract
The titanium tetrazole coordination complex [TiCl4 ꢀ (PhCN4H)2] has been prepared by treatment of TiCl4 with two equivalents
of 5-phenyltetrazole in dichloromethane and spectroscopically and crystallographically characterised. The solid-state structure of
this compound consists of six-coordinate titanium centres with cis ligated tetrazoles. The individual [TiCl4 ꢀ (PhCN4H)2] dimerise via
intermolecular Nꢀ ꢀ ꢀH–N hydrogen bonding interactions and are further organised into 2D supramolecular arrays. Mass spectral
evidence indicates that the individual tetrazole ligands are only weakly bound, limiting the potential of this complex as a titanium
nitride precursor. 3 + 2 cycloaddition of tributyltin azide with 2-toluinitrile at 200 °C has afforded the tributylstannyl tetrazole
[SnBu3{5-(2-MeC6H4)CN4}]n. Crystallographic analysis shows that this compound exists as a supramolecular coordination polymer
propagated via trigonal bipyramidal tin centres linked by N1–Sn–N3 interactions. Preliminary reactivity studies of this tin complex
with titanium tetrachloride in an effort to synthesise a covalently bound titanium tetrazolyl complex have thus far yielded incomplete
elimination of the expected Bu3SnCl by-product and intractable titanium-containing products.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Titanium; Tin; Tetrazole; Nitride precursor; Cycloaddition
1. Introduction
prompted a search for alternative ÔdesignedÕ or Ôsingle
sourceÕ molecular precursors with more amenable reac-
tion/decomposition characteristics. Although success-
fully attenuating undesirable prereactions, alternative
dual source systems which apply volatile tetrakis(dial-
kyl)amido titanium precursors such as Ti(NMe2)4 and
Ti(NEt2)4 and ammonia and mixed TiCl4/alkyl amine
feedstocks have provided their own additional problems
of carbon contamination and poor step coverage [4–7].
Initial efforts to address these difficulties by design of
suitable single source precursors containing a pre-
programmed combination of titanium and nitrogen
were prompted by speculation about the nature of in-
termediate products formed by these systems prior to
film growth. Accordingly, a number of titanium amido
and imido species, such as [CpTiCl2{N(SiMe3)2}] and
[{Ti(l-NtBu)(NMe2)2}2], have been prepared and ex-
amined in this context [8–12]. Neither these nor more
recent studies of mono- or bis-azido complexes [for ex-
ample [{Ti(NtBu)Cl(N3)(py)2}2] and [{Ti(NCy)(N3)2-
(py)2}2] (py ¼ pyridine)] have, however, yielded effective
TiN precursors. Film growth in these latter cases is
hampered either by a lack of volatility or unacceptably
The combination of a better conductivity (4698
kS cmꢁ1) than titanium metal (2381 kS cmꢁ1), extreme
hardness (9–10 Moh) and a refractory nature dictate
that titanium nitride (TiN) is perhaps the most exten-
sively applied transition metal nitride in both micro-
electronic (metal/semiconductor interconnects) and
architectural applications (protective coatings) [1,2].
High quality thin films of cubic TiN may be produced
by atmospheric pressure chemical vapour deposition
(APCVD) in a process which conventionally employs
ammonia gas and gaseous titanium tetrachloride trans-
ported in an inert carrier [3]. Although efficient, this
process suffers problems of pre-reaction and requires
removal of the corrosive HCl by-product. These quali-
ties, coupled to inconveniently high substrate tempera-
tures of 600–900 °C required by this process, have
q Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.poly.2003.11.047.
* Corresponding author. Tel.: +44-207-594-5709; fax: +44-207-594-
5804.
E-mail address: mike.hill@imperial.ac.uk (M.S. Hill).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.11.047

802
M.S. Hill et al. / Polyhedron 23 (2004) 801–807
high levels of carbon contamination approaching 35%
[13,14].
vacuum line or in a dinitrogen-filled drybox operating at
less than 1 ppm of O2. Solvents were purified by distil-
lation from an appropriate drying agent (THF from
potassium, CH2Cl2 from CaH2 and hexane from Na/K
alloy). NMR spectra were recorded at 300.13 (1H), 125.8
(13C) and 186.4 MHz (119Sn) from samples in CDCl3 or
Pyrazolate anions derived by deprotonation of parent
pyrazole heterocycles have been shown to provide a
flexible N-donor ligand set in titanium chemistry [15–
17]. The use of titanium pyrazolyl derivatives as mo-
lecular precursors to TiN is likely to be hampered,
however, by similar problems of carbon contamination
to those outlined above due to the presence of direct
carbon to nitrogen bonds in the delocalised heterocycle.
We have turned our attention therefore to the synthesis
of titanium tetrazolato derivatives in the hope that the
high nitrogen content of this latter ligand type will en-
courage clean elimination of thermodynamically stable
small molecule (N2 and nitrile) side products and re-
tention of Ti–N linkages at relatively low temperatures.
Although a number of inorganic and organometallic
tetrazolyl derivatives have been cystallographically
characterised in recent years [18–34], structurally
authenticated titanium derivatives are restricted to
the seven coordinate tris(3,5-di-tert-butylpyrazolato)(5-
phenyltetrazolato)titanium (I) [31]. Although the subject
of a low precision X-ray structural determination and
not reported in detail, g1-N2 coordination of the tet-
razolyl anion to titanium was confirmed. Due to the
multiplicity of potential nitrogen donors, many metal-
coordinated tetrazoles are prone to coordination poly-
merisation. The monodenticity of the tetrazolyl ligand
of I is, most likely, therefore enforced by the g2-coor-
dination of the three bulky pyrazolato co-ligands. As
such co-ligands were reasoned to be of likely detriment
to clean precursor decomposition, our initial studies
have targeted titanium tetrazole complexes with simple
chloride ligands sets. We now report our studies which
have resulted in the high yield synthesis of a simple
Ti(IV) tetrazole coordination complex along with our
initial exploration of an organotin-based strategy that
attempts to effect both clean formation of titanium tet-
razolyl derivatives and a means by which the steric de-
mands at the C5 position of the tetrazole ring may be
readily modulated.
1
d8-THF; Chemical shifts are relative to SiMe4 for H
and 13C NMR. 119Sn NMR were referenced externally
to Me4Sn. Mass spectra were obtained at 70 eV. Trib-
utyltin azide was synthesised by a literature procedure
[35].
Caution! All reactions of azides and tetrazole com-
pounds must be treated as potentially explosive and
conducted behind a rigid safety screen.
2.2. [TiCl4 ꢀ (PhCN4H)2] (1)
A solution of titanium tetrachloride (1.97 g, 10.4
mmol) in dichloromethane (30 cm3) was added at room
temperature to a stirred slurry of PhCN4H (3.04 g, 20.8
mmol) in dichloromethane (40 cm3). This resulted in the
formation of a dense pale yellow precipitate and a yel-
low solution. The yellow solid, 1 (4.70 g, 94%), was
isolated by filtration and dried under vacuum. Cooling
of the filtrate to )30 °C resulted in the formation of a
small number of yellow crystals suitable for X-ray dif-
fraction after 3 days. Elemental and spectroscopic
analysis of the bulk powder was consistent with an un-
solvated form. Anal. Calc. for C14H12Cl4N8Ti: C, 34.87;
H, 2.51; N, 23.25. Found: C, 34.71; H, 2.36; N, 23.00%.
1H NMR [d8-THF, 298 K] d: 7.49 (m, 6H, m, p-C6H5),
8.01 (m, 4H, o-C6H5), 15.1 (br.s, 2H, N–H). 13C{1H}
NMR [d8-THF, 298 K] d: 126.3 (i-C6H5), 127.4 (o-
C6H5), 129.3 (m-C6H5), 131.2 (p-C6H5). MS (EIþ, 70
eV), 190 (55%, TiCl4), 153 (100, TiCl3), 118 (70, TiCl2),
103 (25, PhCN), 83 (45, TiCl).
2.3. [SnBu3{5-(2-MeC6H4)CN4}]n (2)
Bu3SnN3 (3.17 g, 9.75 mmol) and 2-toluinitrile (1.25
g, 9.75 mmol) were heated at 200 °C for 2 h under ni-
trogen to yield a pale amber glass. This was washed with
hexane (30 cm3) and dried in vacuo. Storage of the re-
sultant colourless glass at room temperature for 3 days
induced crystallisation to produce compound 2 in
effectively stoichiometric yield. Anal. Calc. for
C20H34N4Sn: C, 53.47; H, 7.64; N, 12.48. Found: C,
1
53.56; H, 7.64; N, 12.48%. H NMR [CDCl3, 298 K] d:
0.71 (t, 9H, (CH2)3CH3), 1.05–1.34 (m, 18H, (CH2)3
CH3), 2.17 (s, 3H, Ar–Me), 7.15–7.29 (m, 4H, Ar–H).
13C{1H} NMR [CDCl3, 298 K] d: 13.6 (CH2)3CH3, 18.2
(CH2(CH2)2CH3, 1J117;119 Sn=C ¼ 457 Hz), 20.2 (Ar–Me),
2. Experimental
3
2.1. General
27.0 ((CH2)2CH2CH3, J117;119 Sn=C ¼ 70.9 Hz), 28.0
2
(CH2CH2CH2CH3 J117;119 Sn=C ¼ 27.9 Hz), 125.6, 128.6,
129.8, 130.5, 137.7 (Ar–C), 161.5 (CN4). 119Sn{1H}
All reactions were conducted under an atmosphere of
dry argon and manipulated either on a double manifold
NMR [CDCl3, 298 K] d: )17.9 (Dm1=2 )2 kHz).

M.S. Hill et al. / Polyhedron 23 (2004) 801–807
803
2.4. Attempted reaction of 2 and TiCl4
To a solution of compound 2 (2.37 g, 5.26 mmol) in
dichloromethane (120 cm3) was added a solution of ti-
tanium tetrachloride (1.0 g, 5.26 mmol) in dichlorome-
thane (20 cm3). This resulted in the immediate
formation of an orange solution which darkened to a
vivid red over the subsequent 48 h. In vacuo removal of
the solvent produced a dark red sticky solid, which was
washed with hexane (2 ꢂ 30 cm3) to produce a yellow
solid. The 1H NMR spectrum of this material in d8-
THF displayed resonances corresponding to both Bu3Sn
and the tetrazole ligand. Crystals which formed in the
NMR tube were suitable for X-ray analysis and proved
to be a hydrolysis product, the oxo-bridged species
(THF)2Cl3Ti–O–TiCl3(THF)2.
Fig. 1. The asymmetric unit of 1 with thermal ellipsoids drawn at the
30% probability level. All hydrogen atoms apart from H4a, H4b re-
moved for clarity.
for an X-ray diffraction analysis. The asymmetric unit
resulting from this analysis is illustrated in Fig. 1. Se-
lected bond lengths and angles are provided in Table 1,
while details of the X-ray analysis are listed in Table 2.
Complex 1 is revealed to exist as a six-coordinate
adduct with cis tetrazole ligands. The coordination
sphere exhibits significant deviations from ideal octa-
hedral geometry, with cis angles ranging from 81.94(14)o
[N(6)–TiCl(3)] to 99.30(8)o [Cl(4)–Ti–Cl(1)] and the
trans angles between 160.92(8)o [Cl(3)–TiCl(2)] and
3. Results and discussion
Winter [36] has studied the treatment of titanium
tetrachloride with two equivalents of a variety of
substituted pyrazoles. Reaction with 3,5-di-tert-buty-
lpyrazole resulted in HCl elimination and the formation
of
a
mixture of molecular L2TiCl4 and ionic
]
2ꢁ
[LHþ]2[TiCl6
(where L ¼ 3,5-di-tert-butylpyrazole)
products. Conversely, reaction with less sterically
demanding heterocycles produced a series of six-coor-
174.06(14)o [Cl(4)–Ti–N(6)]. The Ti–Cl(1) [2.231(2) A]
ꢀ
dinate TiCl4. L0 adducts (where L0 ¼ 3,5-dimethylpy-
ꢀ
and Ti–Cl(4) [2.216(2) A] bonds that are trans to the
tetrazole N-donor atoms are significantly shorter than
2
razole, 3-methylpyrazole, 4-iodopyrazole), where the
adoption of either a cis or trans coordination geometry
was reasoned to be largely dependent upon the steric
profile of the pyrazole ligand. Prompted by these ob-
servations, and intrigued by the possible divergent re-
activity that may be induced by the increased acidity of
the tetrazole heterocycle [37], we carried out the analo-
gous reaction between two equivalents of commercially
available 5-phenyltetrazole and TiCl4 in dichlorome-
thane. This resulted in the immediate precipitation of
compound 1 as a pale yellow powder, which was iso-
lated by filtration. Elemental analysis indicated that a
2:1 adduct had been formed, while the presence of a
tetrazole N–H functionality was confirmed by the ob-
servation of weak absorptions at 3340 and 3390 cmꢁ1 in
the infra-red spectrum. Although 1 was not soluble in
non-donor solvents, 1H NMR data collected in THF-d8
displayed resonances similar to those of the free neutral
tetrazole. Although these data do not preclude the
presence of compound 1 in solution, we tentatively
conclude that the tetrazole ligands are displaced from
the titanium coordination sphere by the donor solvent.
Despite this problematic insolubility, storage of the pale
yellow, dilute but saturated supernatant dichlorome-
thane solution from the original reaction at )30 °C for
one week produced a small number of yellow single
crystals of 1 as a bis-dichloromethane solvate suitable
ꢀ
the mutually trans Ti–Cl(2) [2.275(2) A] and Ti–Cl(3)
Table 1
ꢀ
Selected bond lengths (A) and angles (°) for compound 1
Bond lengths
Ti–Cl(4)
Ti–N(6)
Ti–Cl(2)
2.216(2)
2.265(5)
2.275(2)
1.326(7)
1.294(6)
1.340(7)
1.365(7)
1.329(7)
Ti–Cl(1)
Ti–Cl(3)
Ti–N(2)
2.231(2)
2.271(2)
2.279(5)
1.357(6)
1.344(7)
1.324(7)
1.290(6)
1.336(8)
N(1)–C(1)
N(2)–N(3)
N(4)–C(1)
N(5)–N(6)
N(7)–N(8)
N(1)–N(2)
N(3)–N(4)
N(5)–C(8)
N(6)–N(7)
N(8)–C(8)
Bond angles
Cl(4)–Ti–Cl(1)
Cl(1)–Ti–N(6)
Cl(1)–Ti–Cl(3)
Cl(4)–Ti–Cl(2)
N(6)–Ti–Cl(2)
Cl(4)–Ti–N(2)
N(6)–Ti–N(2)
Cl(2)–Ti–N(2)
99.30(8)
86.43(14)
96.86(8)
96.32(8)
84.62(14)
89.82(14)
84.48(18)
82.37(14)
Cl(4)–Ti–N(6)
Cl(4)–Ti–Cl(3)
N(6)–Ti–Cl(3)
Cl(1)–Ti–Cl(2)
Cl(3)–Ti–Cl(2)
Cl(1)–Ti–N(2)
Cl(3)–Ti–N(2)
C(1)–N(1)–N(2)
N(3)–N(2)–Ti
174.06(14)
95.71(8)
81.94(14)
95.72(8)
160.93(8)
170.84(15)
82.93(14)
105.4(5)
N(3)–N(2)–N(1) 112.0(5)
120.5(4)
N(1)–N(2)–Ti
127.0(4)
109.9(5)
N(7)–N(6)–N(5) 111.1(5)
N(2)–N(3)–N(4) 105.1(5)
C(8)–N(5)–N(6)
N(7)–N(6)–Ti
C(1)–N(4)–N(3)
105.8(5)
123.0(4)
N(5)–N(6)–Ti
N(7)–N(8)–C(8)
125.9(4)
110.6(5)
N(6)–N(7)–N(8) 105.5(5)
N(1)–C(1)–N(4) 107.6(5)

804
M.S. Hill et al. / Polyhedron 23 (2004) 801–807
Table 2
Selected crystallographic and data collection parameters for compounds 1 and 2
1
2
Chemical formula
Formula weight
T (K)
C
14H12Cl4N8Ti ꢀ 2(CH2Cl2)
C20H34N4Sn
449.20
173(2)
651.87
173(2)
Crystal size (mm)
Crystal system
Space group
0.2 ꢂ 0.2 ꢂ 0.1
monoclinic
P21=n (No. 14)
12.4934(14)
14.1217(19)
16.0886(17)
90
0.4 ꢂ 0.2 ꢂ 0.4
orthorhombic
Fdd2 (No. 43)
21.2292(10)
33.379(3)
12.8979(11)
90
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
a (°)
b (°)
c (°)
Z
105.519(5)
90
90
90
4
16
9140(1)
3
ꢀ
V (A )
2735.0(6)
1.58
1.12
Dcalc (Mg mꢁ3
)
1.31
1.13
l (mmꢁ1
h range (°)
)
3.76–21.96
0.059; 0.108
0.100; 0.122
10 987/3310/0.092
2277
3.76–25.04
0.050, 0.101
0.073; 0.110
10 141/3559/0.068
2755
R1; wR2½I > 2rðIÞꢃ
R1; wR2 all data
Measured/independent reflections/Rint
Reflections with I > 2rðIÞ
variation of the tetrazole C5 substituent steric demands.
A very wide range of tetrazole derivatives may be ac-
cessed by the straightforward 3 + 2 cycloaddition reac-
tion of organotin azides and RCN dipolarophiles
(Scheme 1) [22–27,39]. The ready availability of a great
number of substituted nitriles allows facile variation of
the resultant tetrazole substituent and provides the
heterocycle in a synthetically convenient deprotonated
form for subsequent metathesis with TiCl4 (Scheme 1).
A similar strategy involving Me3SiCl elimination has
previously been successfully applied to the synthesis of
sterically encumbered pyrazolatotrichlotitanium deriv-
atives [16], while R3SnX elimination from reaction be-
tween triorganostannyltetrazoles and alkyl halides has
been demonstrated as a straightforward means to tet-
razole N-alkylation [40]. Although a great number of
potential nitrile precursors are available, our initial
ꢀ
[2.271(2) A] bonds. These observations and bond
lengths are similar to those in other TiCl4 ꢀ L2 cis ad-
ducted structures including the bis-pyrazole adduct
[TiCl4(4-IC3H2N2)2] [36]. The Ti–N bond distances
ꢀ
[2.279(5), 2.265(5) A] of 1 are, however, significantly
longer than those reported for this analogous pyrazole
ꢀ
adduct [2.235(7) A] and possibly result from the reduced
basicity of the tetrazole moiety [37].
Mass spectral analysis of compound 1 displayed a
highest mass fragment at 190 corresponding to the
molecular ion [TiCl4]þ. This is an indication that the
tetrazole ligands are only weakly bound and most likely
inhibits the practical potential of 1 as a nitride precur-
sor. For this reason, we turned our attention to the
synthesis of titanium tetrazolyl derivatives containing
more robust covalent Ti–N bonds. Winter [31] has re-
ported previously that reactions of the 5-phenyltetraz-
olyl anion with titanium tetrahalides resulted in
intractable mixtures of products, an observation that
was confirmed by the present study. Ab initio calcula-
tions undertaken as part of the same study highlighted
the small energy difference (ca. 5 kcal/mol) that exists
between g1- and g2-ligated titanium tetrazolyl deriva-
tives while older quantum mechanical calculations have
shown that N1 and N2 binding are energetically equiv-
alent [38]. The mixture of species that likely results from
such facile isomer interconversion, as well as the po-
tential for the formation of complex extended network
structures, mitigates therefore against the isolation of
simple homo- and heteroleptic titanium tetrazolyl
complexes unless the reaction conditions are very care-
fully controlled. In an attempt to address this issue, we
reasoned that enhanced product solubility may result by
Scheme 1.

M.S. Hill et al. / Polyhedron 23 (2004) 801–807
805
efforts identified 2-toluinitrile as a suitable candidate due
to the small incremental increase in steric demands over
5-phenyltetrazole and the spectroscopic simplicity of the
ortho-substituted aryl tetrazolyl product.
Tributyltin azide was synthesised by literature meth-
ods [35] while [SnBu3{5-(2-MeC6H4)CN4}] (2) was
synthesised using the well established methodology in
which the neat triorganotin azide is heated with a slight
excess of the chosen nitrile [39]. The reaction was
monitored by the disappearance of the IR bands due to
m(CN) at ca. 2250 cmꢁ1 and masym(N3) at ca. 2060 cmꢁ1
.
The glassy, crude solid product that was produced upon
cooling was washed with hexane to remove excess nitrile
and crystallised upon standing at room temperature for
three days to produce analytically pure compound 2.
Compound 2 was sufficiently soluble in CDCl3 to
enable the collection of good quality NMR data. The 1H
and 13C NMR spectra were consistent with the proposed
structure. The 1J(13C–119Sn) coupling constant of 457
Hz implied a coordination number of >4 about tin,
while use of the semiempirical relationship derived by
Fig. 2. The asymmetric unit of 2 with thermal ellipsoids drawn at the
50% probability level. All hydrogen atoms removed for clarity.
The solid-state structure of 2 has been crystallo-
graphically confirmed. Details of the analysis are listed
in Table 2, while selected bond lengths and angles are
produced in Table 3. Although the asymmetric unit
(Fig. 2) contains only one nitrogen donor, the geometry
at tin is best described as trigonal bipyramidal and is
defined by trans-N2SnC3 coordination. The additional
tetrazole coordination is provided by a nitrogen atom of
an adjacent tetrazole unit. This structural feature is
similar to that found in all previously characterised or-
ganotin tetrazoles, while both inter- and intramolecular
bonding parameters are typical of molecules of this type
[22–24]. Within the accuracy of the data, the two Sn–N
bonds are identical and serve to propagate a 1D, helical
polymeric array along 21 screw axes parallel to c. This
occurs via the N1 + N3 (N(1)/N(3)) bridging mode,
which has previously been observed in a number of
related triorganostannyl tetrazole derivatives (Fig. 3)
1
Holecek and Lycka for correlating J data and coordi-
nation geometry yielded a value of 123.2° for the C–Sn–
C bond angles, consistent with a trans-trigonal bipyra-
midal N2SnC3 geometry about tin [41]. These observa-
tions are similar to those of previous solution NMR
studies of triorganostannyl tetrazoles that have deduced
the formation of concentration- and temperature-
dependent N,N0-bridged oligomeric species in solution
[22,23,42]. The fluxionality of these systems and similar
dynamic behaviour deduced for certain platinum and
cobalt tetrazoles [43,44] may also be used to rationalise
the broad 119Sn{1H} NMR signal (Dm1=2; ca. 2 kHz)
observed at )17.9 ppm.
Table 3
ꢀ
Selected bond lengths (A) and angles (°) for compound 2
Bond lengths
Sn–C(13)
Sn–C(9)
Sn–N(1)
2.131(9)
2.138(9)
2.406(7)
1.354(16)
1.365(8)
1.492(12)
Sn–C(17)
Sn–N(3)0
2.134(8)
2.368(7)
1.336(9)
1.294(19)
1.315(9)
N(1)–C(1)
N(2)–N(3)
N(4)–C(1)
N(1)–N(2)
N(3)–N(4)
C(1)–C(2)
Bond angles
C(13)–Sn–C(17)
C(17)–Sn–C(9)
C(17)–Sn–N(3)0
C(13)–Sn–N(1)
C(9)–Sn–N(1)
C(1)–N(1)–N(2)
N(2)–N(1)–Sn
N(2)–N(3)–N(4)
N(4)–N(3)–Sn00
N(4)–C(1)–N(1)
N(1)–C(1)–C(2)
125.8(4)
C(13)–Sn–C(9)
C(13)–Sn–N(3)0
C(9)–Sn–N(3)0
C(17)–Sn–N(1)
N(3)0 –Sn–N(1)
C(1)–N(1)–Sn
N(3)–N(2)–N(1)
N(2)–N(3)–Sn00
C(1)–N(4)–N(3)
N(4)–C(1)–C(2)
115.9(3)
118.3(3)
89.9(3)
89.5(3)
89.0(3)
89.6(3)
89.4(3)
92.9(3)
177.5(3)
141.5(5)
108.5(7)
125.1(6)
103.4(6)
124.9(7)
104.6(8)
113.7(7)
110.7(8)
123.7(5)
112.8(6)
121.8(7)
0
Symmetry elements: , ꢁx; 0:5 ꢁ y; ꢁ0:5 þ z; 00, ꢁx; 0:5 ꢁ y; 0:5 þ z.

806
M.S. Hill et al. / Polyhedron 23 (2004) 801–807
4. Crystallography
Crystals of 1 and 2 were covered in oil and suitable
single crystals were selected under a microscope and
mounted on a KappaCCD diffractometer. Data were
ꢀ
collected at 173 K; k(Mo KaÞ ¼ 0.71073 A; details are
given in Table 2. The structures were solved by direct
methods (SHELXS 97) [46] and refined by full matrix
least squares (SHELXL 97) [47] with non-H atoms an-
isotropic and H atoms included in riding mode. No
absorption correction was applied.
Fig. 3. The 1D polymeric structure of 2. All hydrogen atoms and butyl
carbon atoms except Sn-aC removed for clarity.
[22–24]. Although the thermal parameters of for several
of the carbon atoms after refinement were large relative
to the rest of the structure, this in no way negates our
analysis of the overall lattice structure. The thermal
parameters of the C4H9 units are ascribed to disorder
inherent in the packing of the flexible butyl chains. This
feature is common to many structures containing the
Bu3Sn fragment and has been commented upon previ-
ously with specific reference to organotin tetrazole
compounds [22a].
5. Crystal structure data
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 221843 and 221844 for
compounds 1 and 2, respectively. Copies may be
obtained free of charge from the director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-
336033; email: deposit@ccdc.cam.ac.uk or http://www.
ccdc.cam.ac.uk).
Although attempts to apply 2 to the synthesis of ti-
tanium tetrazolyl derivatives have, thus far, met with
only limited success, our initial observations are suffi-
ciently encouraging to prompt further study and also
serve to illustrate the difficulties inherent in the appli-
cation of this class of ligand. Reaction of equimolar
quantities of 2 and TiCl4 in dichloromethane at room
temperature produced a deep red solution which, upon
removal of solvent, yielded a sticky red solid. This ma-
terial was washed with dry hexane to remove eliminated
Bu3SnCl (confirmed by NMR analysis of the hexane
filtrate) and the yellow solid produced by this procedure
was analysed by 1H NMR and 70 eV mass spectrometry.
This analysis revealed the presence of both the tetrazole
ligand and residual Bu3Sn-, which persisted even upon
repeated hexane washing. This observation is suggestive
of either incomplete reaction or inclusion of Bu3SnCl by
adduct formation with the Lewis basic tetrazole nitrogen
atoms. Indirect evidence for the formation of a titanium
tetrazolyl linkage were provided by an X-ray study of a
small quantity of yellow crystals obtained from the
NMR tube prepared for the analysis of these reaction
products in d8-THF. These were identified as the known
l-oxo complex (THF)2Cl3Ti–O–TiCl3(THF)2 (II) [45],
and are tentatively suggested as a result of preferential
hydrolysis of the Ti–N bond of the target trichloroam-
ido species.
Acknowledgements
The Royal Society is thanked for the provision of a
University Research Fellowship (M.S.H.).
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