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H.J. Breunig et al. / Journal of Organometallic Chemistry 696 (2011) 523e526
(1.4 Å) the protection by Me3Si groups is sufficient to prevent the
phosphorus monomer from dimerization but not a [Cp2TiSb
(SiMe3)2] monomer.
The new complexes are orange (1) or red (2) air sensitive
compounds. Their characterization is based mainly on single
crystal X-ray crystallography. Meaningful NMR spectra were not
observed and mass spectra showed only ions corresponding to
decomposition products. Elemental analyses were not carried out
because of the sensitivity of the samples. 2 was isolated as crys-
talline solid only in reduced quantities. Nevertheless, it is possible
that in solution the amount of 2 could have been larger but the
identification of the compounds was hindered by its magnetic
properties. The molecular structures of 1 and 2 are shown in the
Figs. 1 and 2.
The structures of 1 and 2 consist of R2Sb units between two
Cp2Ti groups forming a planar (SbTi)2 heterocycle. The Sb atoms
adopt a distorted tetrahedral geometry with wider TieSbeTi angles
(1: 105.32(5), 2: 103.384(13)ꢁ) and smaller C(2)eSb(1)eC(1) 93.8
(6) or SieSbeSi (94.51(2)ꢁ) angles. Related structural parameters
were reported for [Cp2TiSbR2]2 (R ¼ Et). The transannular Sb/Sb
distances (1: 3.4991(11), 2: 3.7145(4) Å) are shorter than the sum of
the van-der-Waals radii of two antimony atoms [Sr.v.d.W (Sb,
Sb) ¼ 4.4 Å]. The SbeTi-bond lengths in 2 (2.999(4) Å) are larger
than in 1 (2.8800(17), 2.8890(18) Å) or [Cp2TiSbEt2]2 (molecule 1:
2.8797(11), 2.8917(11); molecule 2: 2.9046(11), 2.9105(11) Å).
The inspection of the 1H NMR spectra during the synthesis of 1
revealed that the signals of the starting materials [Cp2Ti(btmsa)]
Fig. 2. Thermal ellipsoid (20%) representation of 2. The hydrogen atoms were omitted
for clarity. Selected bond lengths (Å) and bond angles (ꢁ): Ti(1)eSb(1) 2.9994(4),
Ti(10)eSb(10) 2.9927(5), Si(1)eSb(1) 2.5842(6), Si(2)eSb(1) 2.5824(6), Sb(1)/Sb(10)
3.7145(4), Ti(1)eSb(1)eTi(10) 103.384(13), Si(1)eSb(1)eSi(2) 94.51(2), Si(1)eSb(1)eTi
(1) 114.779(16), Si(2)eSb(1)eTi(1) 114.870(16), Sb(1)eTi(1)eSb(10) 76.616(13).
molecular ion of Cp2Ti (m/z ¼ 178, 100%) were observed. The
spectra contain also signals for CpnTi6 (n ¼ 4e8) clusters. These
results indicate that 1 and 2 decompose under the conditions of
mass spectrometry with the formation of the parent distibanes and
titanocene monomers and oligomers.
In an attempt to synthesize analogues of 1 and 2 containing
dimesitylantimony units we reacted [Cp2Ti(btmsa)] with Mes2SbH
(Mes ¼ 2,4,6-Me3C6H2) in benzene at ambient temperature. After
working up the product mixture several crystals of [(Cp2TiCl)2]$2
(Mes2Sb)2 (3) were obtained. The source of the chlorine atoms is
probably ammonium chloride used during the preparation of
Mes2SbH. In related reactions (Ph2P)2 and [(Cp2TiCl)2] were formed
from Cp2Ti(btmsa) and Ph2PCl [13]. The crystal structure of 3 was
determined by single crystal X-ray diffraction. The structure is
shown in Fig. 3.
Crystals of 3 contain the complex [(Cp2TiCl)2] and tetramesi-
tyldistibane in the ratio 1: 2. The structures of the components of 3
were determined independently several years ago. The geometrical
parameters of 3 and the pure compounds [(Cp2TiCl)2] [15] and
(Mes2Sb)2 [16,17] are similar. Future work will concentrate on
obtaining the analogue of 1 and 2 containing dimesitylantimony
unit by the reaction of pure Mes2SbH with [Cp2Ti(btmsa)].
[
d
¼ 6.40 (C5H5), 0.33 (CH3)] and Me4Sb2
intensity during the reaction whereas the signal for non coordi-
nated btmsa (
¼ 0.14) increased. However no new signals
(
d
¼ 0.82) decreased in
d
appeared in the spectra. Also when crystals of 1 or 2 were solved in
C6D6 no characteristic NMR signals were observed. This absence of
NMR signals is not surprising because also the analogous ethyl
derivative was found NMR silent and DFT calculations on
[Cp2TiSbR2]2 (R ¼ Et) had shown that indeed the paramagnetic
state with two unpaired electrons at the Ti(III) centers with d1
configuration is lower in energy than the diamagnetic state with
coupled electrons [2]. It can be concluded that 1 and 2 are para-
magnetic at room temperature as well.
Mass spectra were measured from crystalline samples of 1 or 2
with the EI technique. The spectra showed no signals of the intact
SbeTi complexes. Instead intense signals of the distibanes,
(Me4Sb2, m/z ¼ 304, Mþ; (Me3Si)4Sb2, m/z ¼ 534, Mþ) and of the
3. Conclusion
Reactions between [Cp2Ti(btmsa)] and substituted distibanes
offer a feasible access to dimeric complexes between titanocene
and diorganoantimony units. In contrast distibane formation is
favoured in reactions between Cp2Ti(btmsa) and Mes2SbH with
NH4Cl traces.
4. Experimental
Crystals suitable for X-ray diffraction of 1e3 were grown from
concentrated benzene solutions in case of 2 and 3 or deuterated
benzene solution in case of 1 Table 1. Data were collected at 173
(2) K on a Siemens P4 diffractometer using a 0.71073 Å MoK
a
radiation and corrected for absorption effects using DIFABS [18].
The structures were solved by direct or Patterson methods [19].
Structure solutions and refinements were performed using WinGX
software package [20]. The representations of the X-ray structures
Fig. 1. Thermal ellipsoid (20%) representation of 1. The hydrogen atoms were omitted
for clarity. Selected bond lengths (Å) and bond angles (ꢁ): Sb(1)eTi(1) 2.881(2), Sb(1)e
Ti(10), 2.889(2), C(1)eSb(1) 2.163(12), C(2)eSb(1) 2.154(12), C(2)eSb(1)eC(1) 94.3(7),
Sb(1)eTi(1)eSb(10), 74.66(5) Ti(1)eSb(1)eTi(10) 105.34(5).