Titanium σ-acetylides as building blocks for heterobimetallic transition metal complexes: Synthesis and redox behaviour of π-conjugated organometallic systems

Article abstract of DOI:10.1016/S0022-328X(98)01068-7

A series of related Ti σ-acetylides of the type {Ti}C≡CR ({Ti} = (η⁵-C₅H₅)₂ Ti(CH₂SiMe₃); 2: R = SiMe₃; 3: R = C₆H₃(CH₂NMe₂)₂-3,5; 4: R = C₆H₂I-4-(CH₂NMe₂)₂-3,5; 5: R = C₆H₄CN-4; 6: R = C₅H₄N-4; 7: R = Fc, Fc = (η⁵-C₅H₄)Fe(η⁵-C ₅H₅); 8: R = C₆H₄(C≡C{Ti})-4) have been prepared by reacting the corresponding lithium acetylides with {Ti}Cl (1). The X-ray crystal structure determination of (Ti)C≡CSiMe₃ (2) is reported. This compound exhibits a one-dimensional (1D) arrangement with respect to the Ti-C≡C unit. The reaction of 2 with [CuCl]_n afforded 1 and [CuC≡CSiMe₃]_n (10) and is proposed to occur via prior formation of the dimeric intermediate [(η²-{Ti}C≡CSiMe₃)₂Cu ₂Cl₂]. The chemical oxidation of {Ti}C≡CFc, 7, with Ag[BF₄] yielded HC≡CFc and an undefined Ti species. Treatment of 5 or 6 with {Ru}N≡N{Ru} ({Ru} = mer,trans-[RuCl₂(NN′N)]; NN′N = η³-C₅H₃N(CH₂NMe ₂)₂-2,6) produced intensively coloured heterodinuclear compounds, such as [{Ti}C≡CC₅H₄N-4]{Ru} (16). In contrast, 5 and 6 react with cationic Pt compounds of the type [{Pt}·L][X] ({Pt} = [Pt(C₆H₃{CH₂NMe₂} ₂-2,6]⁺ ; L = H₂O, MeCN; X = BF₄, OTf) to give product mixtures rather than defined compounds. Electrochemical studies on some of the bimetallic compounds show that the Ti(III)/Ti(IV) redox potential appears to be reversible and is shifted to a more negative value upon substitution of the Cl ligand in 1 by C≡CR (compounds 2-8). Whereas the nature of R in {Ti}C≡CR has an influence on the Ti(III)/Ti(IV) redox potential, the attachment of a second metal onto the π-conjugated system has only negligible effect on the electrochemical properties of the Ti centre.

Full text of DOI:10.1016/S0022-328X(98)01068-7

Journal of Organometallic Chemistry 582 (1999) 126–138
Titanium s-acetylides as building blocks for heterobimetallic transition
metal complexes: synthesis and redox behaviour of p-conjugated
organometallic systemsꢀ
Stephan Back a,b, Robert A. Gossage a, Gerd Rheinwald b, Ignacio del R´ıo a, Heinrich Lang b,*,
Gerard van Koten a,1
a Debye Institute, Department of Metal-Mediated Synthesis, Utrecht Uni6ersity, Padualaan 8, NL-3584 CH Utrecht, Netherlands
b Technische Uni6ersita¨t Chemnitz, Institut fu¨r Chemie, Lehrstuhl Anorganische Chemie, Straße der Nationen 62, D-09111 Chemnitz, Germany
Received 4 August 1998
Abstract
A series of related Ti s-acetylides of the type {Ti}CꢀCR ({Ti}=(h5-C5H5)2Ti(CH2SiMe3); 2: R=SiMe3; 3: R=
C6H3(CH2NMe2)2-3,5; 4: R=C6H2I-4-(CH2NMe2)2-3,5; 5: R=C6H4CN-4; 6: R=C5H4N-4; 7: R=Fc, Fc=(h5-C5H4)Fe(h5-
C5H5); 8: R=C6H4(CꢀC{Ti})-4) have been prepared by reacting the corresponding lithium acetylides with {Ti}Cl (1). The X-ray
crystal structure determination of {Ti}CꢀCSiMe3 (2) is reported. This compound exhibits a one-dimensional (1D) arrangement
with respect to the Ti–CꢀC unit. The reaction of 2 with [CuCl]n afforded 1 and [CuCꢀCSiMe3]n (10) and is proposed to occur via
prior formation of the dimeric intermediate [(h2-{Ti}CꢀCSiMe3)2Cu2Cl2]. The chemical oxidation of {Ti}CꢀCFc, 7, with Ag[BF4]
yielded HCꢀCFc and an undefined Ti species. Treatment of 5 or 6 with {Ru}NꢀN{Ru} ({Ru}=mer,trans-[RuCl2(NN%N)];
NN%N=h3-C5H3N(CH2NMe2)2-2,6) produced intensively coloured heterodinuclear compounds, such as [{Ti}CꢀCC5H4N-4]{Ru}
(16). In contrast, 5 and 6 react with cationic Pt compounds of the type [{Pt}·L][X] ({Pt}=[Pt(C6H3{CH2NMe2}2-2,6]+; L=H2O,
MeCN; X=BF4, OTf) to give product mixtures rather than defined compounds. Electrochemical studies on some of the bimetallic
compounds show that the Ti(III)/Ti(IV) redox potential appears to be reversible and is shifted to a more negative value upon
substitution of the Cl ligand in 1 by CꢀCR (compounds 2–8). Whereas the nature of R in {Ti}CꢀCR has an influence on the
Ti(III)/Ti(IV) redox potential, the attachment of a second metal onto the p-conjugated system has only negligible effect on the
electrochemical properties of the Ti centre. © 1998 Elsevier Science S.A. All rights reserved.
Keywords: Metallocenes; Alkynes; Metal–metal interaction; Conjugation; Cyclic voltammetry
possess novel and/or interesting electronic properties
[1]. These conjugated organic systems allow electronic
interaction or communication between attached metal
centres and can impose a one-dimensional (1D) direc-
tionality. Such organometallic complexes resemble clas-
sical organic non-linear optical (NLO) compounds, e.g.
para-nitroaniline [2], in which electron donor and ac-
ceptor units are connected via a conjugated p-system
[3]. The 1D organometallic complexes which are cur-
rently used in NLO studies can be divided into three
main groups: (i) complexes containing a central late
TM complex fragment and one or two conjugated
1. Introduction
Transition metal (TM) complexes in which metal
centers are linked by linear p-conjugated organic sys-
tems (e.g. s-bonded alkynyl ligands) are currently stud-
ied due to their potential as new materials which may
ꢀ Dedicated to Professor Alan Cowley on the occasion of his 65th
birthday.
* Corresponding author. Fax: +49-371-5311833.
1 Also corresponding author. Fax: +31-30-252 3615.
E-mail addresses: heinrich.lang@chemie.tu-chemnitz.de (H. Lang);
g.vankoten@chem.uu.nl (G. van Koten)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(98)01068-7

S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
127
electron donator/acceptor units bonded to it [4], (ii) two
late TM complex fragments linked by a p-conjugated
chain [5] and (iii) three or more late TM complex
fragments incorporated into a p-conjugated system [6].
However, only a few examples of heterobimetallic com-
plexes have been reported in which an early (e.g. Ti, Zr,
Hf) and a late TM unit are connected by a p-conju-
gated organic system [7].
such multimetallic molecules as molecular dipoles and/
or model compounds for ‘nanoconducting’ materials.
2. Results and discussion
2.1. Synthesis of titanium mono-acetylides
The titanocene monochloride {Ti}Cl (1) {{Ti}=(h5-
C5H5)2Ti(CH2SiMe3)} is obtained in high yield by the
reaction of titanocene dichloride with neosilyl magne-
sium chloride [11]. This reaction serves as the basis for
the preparation of a series of titanocene mono-
acetylides, which are virtually 1D with respect to the
Ti-acetylide unit. The synthesis of compounds 2–8 (Eq.
1) was conducted following well-documented proce-
dures for the build-up of titanocene bis(acetylides) [12].
Compounds 2–6 and 8 were obtained as yellow to
orange solids (60–80% yield) which are stable at 25°C if
stored under a nitrogen atmosphere. Compound 7 ex-
hibits an intensively purple colour. Analogous intensive
colours have been obtained for bis(alkynyl) titanocenes
carrying ferrocenyl (Fc) as terminal group of the
acetylide units [7]. The FAB mass spectroscopic investi-
gation of the Ti acetylides 2–8 revealed a peak for the
molecular ion [M]+ at the expected m/z values in
addition to the expected fragmentation patterns.
This latter class of compounds is thought to have the
most interesting electronic properties. One can assume
that an early TM complex fragment with the metal
atom in a high oxidation state, e.g. titanocene deriva-
tives containing a Ti(IV) metal centre, can function as
an electron acceptor unit due to (energetically low
lying) vacant molecular orbitals [8]. A late TM complex
fragment with the metal centre in a low oxidation state
[e.g. Fe(II), Pt(II) or Ru(II)] could therefore act as an
electron donor unit. If both of these entities are con-
nected via a conjugated p-system which supports elec-
tronic communication, e.g. acetylide units, then this
could result in changes in the two metal centres with
respect to their individual electronic behaviour. Previ-
ously, it has been shown by cyclic voltammetric experi-
ments that the electron density of a Ti(IV) centre in
titanocene derivatives can be influenced by the acetylide
substituents [9]. In order to ensure 1D directionality,
one of the two reactive sites of the electron accepting
titanocene fragment should be blocked and this leads to
the {Ti} unit [{Ti}=(h5-C5H5)2TiR; R=blocking an-
ion]. This will permit the synthesis of titanocene mono-
acetylides. The acetylenic units linked to Ti are of two
types: the first class incorporates further potentially
ligating sites, such as 4-pyridyl or 4-benzonitrile groups.
These sites can be used as linkage to a number of
different late TMs, e.g. Pt(II) or Ru(II) containing
fragments. The second class incorporates a late TM
complex fragment directly, i.e. an organometallic
acetylide. A third possibility for the build-up of multi-
metallic systems is offered by the presence of a CꢀC
triple bond of the acetylenic unit itself. Its coordination
chemistry to TM complexes, e.g. Cu(I), is well known
and a number of compounds, in which an acetylide is
h2-coordinated to a Cu(I) centre, has been reported
[10]. This latter approach does not result in a 1D but a
2D arrangement of the respective metal atoms and can
also be used to give some insight into the stability of
the Ti acetylide s-bond. Moreover, this allows for the
possibility to influence an early–late TM interaction
directly via coordination of the bridging CꢀC unit.
These heterometallic compounds will allow the investi-
gation of early–late TM interaction along organic p-
conjugated fragments. Thus, an attempt is made to use
(1)
The CꢀC stretching vibration in the IR spectrum is the
most informative spectroscopic tool for monitoring the
progress of the reaction. While the corresponding free
acetylenes have a wCꢀC vibration in the range of 2100
and 2110 cm−1, compounds 3–8 exhibit wCꢀC vibrations
around 2070 cm−1 (Table 1). In the IR spectrum of 2,
this absorption appears at much lower frequency (2017
cm−1). These values resemble the data obtained for
bis(alkynyl)
titanocenes
of
the
type
(h5-
C5H4SiMe3)2M(CꢀCR)2 (M=Ti, Zr, Hf, e.g. R=

128
S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
Table 1
Representative spectroscopic data (IR, 1H and 13C{1H}-NMR) of the Ti acetylides 2–8 and {Ti}Cl (1) for comparison
{Ti}CꢀCR
R=
IRa
1H-NMRb
13C{1H}-NMRc
C5H5
TiCH2
C5H5
TiCH2
TiCꢀC
TiCꢀC
{Ti}Cl
SiMe3
C6H3(CH2NMe2)2-3,5
C6H2I-4-(CH2NMe2)2-3,5
C6H4CN-4
C5H4N-4
Fc
C6H4CꢀC{Ti}-4
1
2
3
4
5
6
7
8
–
6.31
6.22
6.27
6.27
6.29
6.25
6.25
6.27
2.18
1.60
1.64
1.64
1.75
1.72
1.57
1.65
115.6
113.0
112.9
112.9
113.1
113.2
112.7
112.9
79.7
81.2
81.0
81.0
83.8
83.7
77.7
81.5
–
–
2017
2069
2069
2078
2079
2052
2076
164.6
143.7
143.7
148.8
148.9
140.1
140.1
128.6
123.9
123.8
122.2
121.0
122.8
124.3
a Recorded in KBr (cm−1).
b Relative to SiMe4 (l=0.00 ppm).
c Relative to SiMe4 (l=0.00 ppm). Chemical shifts are reported in l units (ppm) downfield from SiMe4 with the solvent as internal reference
signal.
SiMe3 [13], Ph [14], Fc [7]) and indicate likewise a
given in Fig. 1. Significant structural details are listed in
Table 2. However, the earlier synthesised, analogous
titanocene complex (h5-C5H4SiMe3)2Ti(CH2SiMe3)-
(CꢀCSiMe3) was obtained as a yellow oil [19].
weakening of the CꢀC bond upon binding to Ti [15,16].
1
The comparison of the H-NMR spectrum of 1 with
those of complexes 2–8 reveals that the signals of the
protons of the C5H5 group appear at virtually the same
frequency, while those of the methylene protons of the
neosilyl group are shifted by ca. 0.5 ppm to higher field
(Table 1). The resonance signals of the protons of the
other organic fragments were found in the expected
regions as sharp and well-resolved signals. In the
13C{1H}-NMR spectra of 2–8, the resonance signals of
the C5H5 and CH2Si units are only slightly shifted to
higher field relative to those of the starting material 1
(Table 1). In general, by substitution of the Cl ligand in
1 by organic acetylides other than CꢀCFc, the respec-
tive signal of TiCH2Si is shifted to lower field while the
13C{1H}-NMR spectrum of 7 shows this signal dis-
placed slightly to higher field. The resonance signals of
the acetylenic carbon atoms, which for free acetylenes
are normally found between 80 and 100 ppm [17], are
strongly shifted to lower field. In the 13C{1H}-NMR
spectra of complexes 2–8, the respective signals for
TiCꢀC are found between 140 and 165 ppm while the
signals for TiCꢀC can be found around 125 ppm (Table
1). Similar observations of strong shifts to lower field of
these carbon signals were made for bis(alkynyl) ti-
tanocene and alkynyl titanocene monochlorides. In
these cases, the Ti centred acetylenic carbon atoms
TiCꢀ have been found to exhibit resonance signals
between 145 and 173 ppm [15]. This contrasts the shifts
of the resonance signals of, e.g. Ti=CR2, which were
found between 260 and 360 ppm [18]. Therefore, a
double bond character of the Ti acetylide s-bond can
be excluded.
Complex 2 crystallises in the monoclinic space group
P21/n with one independent molecule per unit cell. A
comparison of the data obtained for 2 to that of {Ti}Cl
(1) [11,20] reveals that the bond lengths and angles of
the {Ti} fragment are virtually unchanged [20]. How-
ever, the main structural features of 2 appear to com-
bine the structural results obtained for alkynyl and
alkyl titanocene derivatives. The Ti–C(sp) distance, i.e.
˚
Ti(1)–C(1) [2.120(4) A], as expected, is significantly
shorter than Ti–C(sp3) bond lengths, e.g. in (h5-
5
˚
˚
C5H5)2TiMe2 [2.181(2) and 2.170(2) A] [21], (h -
C5H5)2Ti(CH2Ph)2 [2.239(6) and 2.210(5) A] [22] or the
one of Ti(1)–C(6) [2.166(4) A] in molecule 2. It resem-
˚
bles rather separations found in, for example, the
monoalkynyl titanocene [(Me2Si)2(h5-C5H2SiMe3)2]-
˚
TiCl(CꢀCSiMe3) [2.10(2) A] [19]. The C(1)–C(2) sepa-
˚
ration of 1.222(5) A resembles values of organic or
organometallic CꢀC distances [17]. The C(2)–Si(1) and
˚
C(6)–Si(2) bond lengths of 1.831(4) and 1.869(4) A,
By cooling a pentane solution of {Ti}CꢀCSiMe3 (2)
to −40°C, yellow crystals have been obtained which
were suitable for a X-ray structural determination. The
solid state structure of the prototypical Ti acetylide 2 is
Fig. 1. ORTEP drawing (50% probability level) of 2 with molecular
geometry and atom numbering scheme.

S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
129
Table 2
Selected bond lenghts (A) and angles (°) for 2
In contrast, the monoalkynyl titanocene compound 2
lacks this chelating effect. Consequently, for 2 is ex-
pected a coordinative behaviour that is comparable to
that of organic alkynes or metal acetylides [10a,27]. A
mechanism of the complexation reaction of the mono-
and bis(alkynyl) compounds A and B has been sug-
gested earlier, in particular for the reaction of (h5-
C5H4SiMe3)2Ti(CH2SiMe3)(CꢀCSiMe3) with [CuCl]n
[19]. The latter case showed that scrambling of the
s-bonded groups occurred, leading finally to the forma-
tion of stable [(h5-C5H4SiMe3)2Ti(CꢀCSiMe3)2]CuCl
˚
Ti(1)–C(1)
Ti(1)–C(6)
Ti(1)–D(1)a
Ti(1)–D(2)a
2.120(4) Si(1)–C(2)
2.166(4) Si(2)–C(6)
2.0793(7) C(1)–C(2)
2.0749(7)
1.831(4)
1.869(4)
1.222(5)
C(1)–Ti(1)–C(2)
D(1)–Ti(1)–D(2)
C(2)–C(1)–Ti(1)
94.68(15) C(1)–C(2)–Si(1)
167.2(4)
129.2(2)
134.80(4)
174.0(4)
Si(2)–C(6)–Ti(1)
(cf.
B),
(h5-C5H4SiMe3)2Ti(CH2SiMe3)Cl
and
[CuCH2SiMe3]4. In order to further study these reac-
tions and to investigate the use of the CꢀC unit in
mono-(alkynyl) Ti derivatives for the synthesis of het-
erometallic molecules, compound 2 has been reacted
a D(1), D(2): centroids of the cyclopentadienyl ligands.
respectively, are typical values for carbon–silicon dis-
tances in organic or organometallic compounds [23].
The angle enclosed by the s-bound organic ligands
[C(1)–Ti(1)–C(6) 94.68(15)°] is significantly smaller
than these angles found in, for example,
bis(alkynyl)titanocenes (around 100°) [15] but resembles
values obtained for titanocene dichloride derivatives
[24]. The angles C(2)–C(1)–Ti(1) [174.0(4)°] and C(1)–
C(2)–Si(1) [167.2(4)°] exhibit a somewhat stronger devi-
ation from linearity as compared with the
monoacetylide complex [(Me2Si)2(h5-C5H2SiMe3)2]-
TiCl(CꢀCSiMe3) [Ti–C–C: 176(1)°; C–C–Si: 174(1)°]
[19]. The angle Si(2)–C(6)–Ti(1) [129.2(2)°] is clearly
less deviated from the ideal tetrahedral angle as com-
pared with this angle [136.9(1)°] in [(h5-
C5H5)2TiCl(CH2SiMe3)] (1) [20]. This means that the
incoming CꢀCSiMe3 unit modifies the electronic system
of the {Ti} fragment in such a way that a proposed
hyperconjugation in the TiCH2SiMe3 fragment is less
favoured [20].
with
either
[CuCl]n
(1:1
molar
ratio)
or
[Cu(NCMe)4][BF4] (2:1 molar ratio), respectively. These
Cu(I) salts have been chosen because of their well-
known reactivity towards CꢀC triple bonds [12].
(2)
The reaction of 2 with [CuCl]n in THF (−78°C) (Eq. 2)
led to a colour change from orange to red after 10 min.
The course of the reaction was monitored via IR spec-
troscopy. With the red colour intensifying, the appear-
ance of a band at 1920 cm−1 (wCꢀC) was detected while
the band at 2018 cm−1 (wCꢀC of 2) lost intensity. This
new band is assigned to the absorption band arising
from h2-coordination of the CꢀC fragment to Cu(I), i.e.
to the formation of 9. From literature reports, a num-
ber of acetylene complexes with Cu2Cl2 bridging units
The solid state structure of 2 clearly shows that the
desired 1D array is present. Therefore, the formal sub-
stitution of SiMe3 by other ligands should give rise to
similar linear arrangements.
are
known
[12,28],
inter
alia,
[{h2-(h5-
C5H5)Fe(CO)2(CꢀCPh)}2Cu2Cl2] [29a] or the [(CO)5Re]
containing acetylides by Beck et al. [29b,c]. From the
same experiment on laboratory scale, again starting at
−78 °C, it appeared that on rising the temperature a
precipitate begins to appear which was gradually
formed, and subsequently identified as [CuCꢀCSiMe3]n
(10) [30]. After filtration of the reaction mixture
2.2. Reactions of {Ti}CꢀCSiMe3 (2) with Cu(I)
compounds
The coordination chemistry of mono- and
bis(alkynyl) titanocene derivatives has been thoroughly
investigated and a number of stable mixed-metal com-
pounds have been prepared, e.g. with Cu(I) compounds
[12,15]. This led to the formation of heterobimetallic
assemblies such as in compounds A [25] or B [26].
1
through a pad of Celite, H-NMR spectroscopy of the
filtrate showed that the Ti monochloride {Ti}Cl (1) had
been formed. From a second experiment conducted
exclusively at −78°C, an orange solid could be iso-
lated. The IR spectrum of this solid contained again an
intensive absorption band at 1920 cm−1, together with
1
wCꢀC of 10. As the H-NMR spectrum of a solution of
the yellow solid in THF-d8 at −78°C revealed broad
singlets at virtually the same resonance frequencies as
for 2, assignment of the resonance pattern was not

130
S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
Scheme 1.
possible. However, a strong indication for the presence
of 9 was obtained from FAB MS investigations. The
spectra revealed peaks at m/z 922 and 425 with the
correct isotope patterns which can be assigned to the
molecular ion peak of 9 and the fragmentation ion
[({Ti}CꢀCSiMe3)Cu]+, respectively. Complex 9 is ther-
mally unstable and decomposes rapidly in solution at
elevated temperatures while in the solid state it can be
handled for only short periods of time. Due to the
instability of 9, a satisfactory elemental analysis could
not be obtained.
{Pt}Cl and [CuCꢀCSiMe3]n (10) via prior formation of
an intermediate with h2-alkynyl-to-Cu(I) coordination
[33].
2.3. Redox stability of {Ti}CꢀCFc (7)
Compound 7 is comprised of a molecule in which a
reducible group, {Ti}, and an oxidisable group, Fc
(ferrocenyl), are connected via a unit which allows
electronic communication. Therefore, it was of interest
to investigate how this arrangement would influence the
redox behaviour of these two fragments. In general,
reduction of titanocene derivatives is readily achieved by
their reaction with activated Mg metal [34]. However, 7
remains unchanged in the presence of activated Mg
metal, even after prolonged stirring (THF, 25°C) and
can be recovered quantitatively from the reaction mix-
ture. Thus, the reducing power of Mg is not sufficient to
add a single electron to the Ti(IV) centre of complex 7.
The change to a stronger reducing agent such as Na
(THF, 0°C) led to the formation of a complex mixture
of products which could not be identified (IR, NMR).
Similarly, reaction of 7 with Ag[BF4] (THF, 0°C) in an
attempt to oxidise the Fe(II) centre gave a mixture of
products. Extraction of this mixture (pentane, THF)
gave a pentane solution of HCꢀCFc (11) and a THF
solution containing a green compound, which could not
identified unequivocally. Thus, compound 7 is neither
stable to chemical reduction nor to oxidation [8].
In contrast with the well-defined reaction of 2 with
(CuCl)n, the reaction of 2 with[Cu(NCMe)4][BF4] in
THF (−78°C) led solely to the formation of an in-
tractable mixture of reaction products. After evapora-
tion of all volatile material and subsequent work-up at
low temperature, IR spectroscopy revealed the absence
of a band in the typical region of wCN (2200–2300 cm−1
)
[32]. Furthermore, no evidence for h2-coordination of
the CꢀC bond to Cu(I) was obtained neither from IR
1
nor from H-NMR (CH2Cl2, −78°C) spectra of the
resulting yellow residue.
These reactions of 2 with Cu(I) salts indicate that
h2-coordination of the CꢀC unit to Cu(I) occurs, but
that the resulting intermediates are prone to rapid ligand
exchange reactions. These results corroborate the earlier
results
C5H4SiMe3)2Ti(CH2SiMe3)(CꢀCSiMe3)] with [CuCl]n
[31]. However, in the case of
[(h5-
for
the
reaction
of
[(h5-
C5H5)2Ti(CH2SiMe3)(CꢀCSiMe3)], 2, it is solely Ti–
C(acetylide) s-bond cleavage that is observed. The
obvious difference with the reaction discussed above is
the absence of a SiMe3 substituent on the cyclopentadi-
enyl ligands in complex 2.
2.4. Reacti6ity of 5 and 6 towards late transition metal
complexes
Another strategy to obtain ‘early–late’ heterometallic
compounds is the reaction of suitable late TM com-
plexes with the N-ligating site of compounds 5 or 6.
Therefore, these molecules were reacted with the
cationic Pt complexes [{Pt}·H2O][BF4] (12) and
[{Pt}·NCMe][OTf] (13, see Scheme 1) [35] as well as with
the neutral dinitrogen bridged Ru complex 14 [36]. Here,
the Ti acetylide could act as an h1-coordinated ligand
after displacement of H2O, MeCN or N2, respectively
(Scheme 1).
Apparently, also the anion is important, as in the case
of [CuCl]n a selective formation of {Ti}Cl (1) and
[CuCꢀCSiMe3]n (10) is observed. A comparable influ-
ence of the anion on the exchange behaviour of the
alkynyl groups between the Pt(II)–alkynyl compound
{Pt}CꢀCSiMe3
({Pt}=[(h3-NCN)Pt]+;
NCN=
[C6H3(CH2NMe2)2-2,6]−) and Cu(I)-salts has been ob-
served. The reaction of this mono-alkynyl metal
compound with [CuCl]n led to the selective formation of

S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
131
Reaction of 5 or 6, respectively, with the cationic Pt
complexes 12 or 13 in the temperature range −40“
25°C led to the formation of a mixture of compounds.
After concentration of the reaction mixtures, a yellow
and poorly soluble residue remained. Further purifica-
tion of this residue was not successful. These results
mirror the behaviour of 2 against [Cu(NCMe)4][BF4]
(see above).
Interestingly, the blocking of one reactive site with a
s-bonded neosilyl group as in {Ti}Cl (1) leads to the
observation of an irreversible reductive process at
E
red= −1.85 V. Nevertheless, compared with (h5-
C5H5)2TiCl2 the reduction of Ti(IV) to Ti(III) in com-
pound 1 is shifted by ca. 0.4 V to a more negative
potential. When the chloride ligand of 1 is substituted
by either CꢀCSiMe3 (compound 2) or CꢀCFc (com-
pound 7), the cyclic voltammogram reveals again a
reversible reduction wave for the Ti(III)/Ti(IV) couple
[2: E1/2= −2.26 V (DE=100 mV); 7: E1/2= −2.25 V
(DE=70 mV)] which is again shifted by ca. 0.4 V to a
more negative potential. Upon substitution of the
acetylide bridge with aromatic units, as in compounds 3
or 6, the shift induced by the second substitution is not
as large as for 2 or 7 (as compared with the E1/2 of 1).
As can be observed from Table 3, the cyclic voltam-
mogram of 3 exhibits the reversible reduction of Ti(IV)
at E1/2= −2.08 V (DE=70 mV) and for compound 6
at E1/2= −1.97 V (DE=100 mV). With compound 2
taken as standard, this can be interpreted by means of
the aromatic system in C6H3(CH2NMe2)2-3,5 being a
weak and the electron poor aromatic system C5H4N-4
(compound 6) as being a stronger electron withdrawing
group. In total, the stepwise substitution of the two Cl
ligands of (h5-C5H5)2TiCl2 by s-bonded organic ligands
leads to an increase in electron density of the Ti core,
which manifests itself in the large shift (by almost 1 V)
of E1/2 to a more negative potential. The formal substi-
tution of SiMe3 in 2 by a ferrocenyl group (compound
7) does not affect the value of the reversible reductive
process. This contrasts results which have been ob-
tained with ferrocenyl-substituted bis(alkynyl) ti-
Nevertheless, well-defined early–late heterobimetallic
compounds were obtained when either 5 or 6 are
reacted with {Ru}NꢀN{Ru} (14), yielding the Ti–Ru
compounds 15 or 16, respectively (Scheme 1). The
course of the reaction can be followed visually by a
colour change of the reaction mixture from brown to
an intensive violet. The pure compounds are dark red
colored solids. The FAB mass spectra of 15 and 16
exhibit a peak for the molecular ion [M]+ at the
calculated m/z values as well as the expected fragmenta-
tion patterns (i.e. m/z at 329: [{Ru}–Cl]+; 295: [{Ru}–
2Cl]+). In the IR spectrum of 15, wCN appears at 2197
cm−1. In the coordination chemistry of nitriles, this is
a rather unusual shift [32] which points to CꢀN bond
weakening due to the backbonding properties of the
coordinated {Ru} fragment. This displacement to lower
wavenumbers is also observed with {Ru}NCPh (17,
wCN: 2214 cm−1) but for this compound is not as strong
as with 15. This indicates a significant influence of the
titanocene fragment on the electronic properties of the
1
nitrile system present in 15. The H-NMR spectra of 15
and 16 in CDCl3 consist of sharp and well resolved
signals. The absence of an AB pattern for the
CH2NMe2 protons indicates that the coordination of 5
or 6 to {Ru} gives rise to an apparent molecular
symmetry plane containing the C- and N-centres of the
–CH2NMe2 ortho-substituents, i.e. that a linear ar-
rangement of the metal centres is obtained.
Table 3
Comparison of electrochemical data for (h5-C5H5)2TiCl2 and com-
pounds 1–3, 6–8 and 15–17
2.5. Electrochemical beha6iour
Compound
Reduction
Oxidation
A number of representative mono- and bimetallic Ti
acetylides have been subjected to cyclovoltammetric
investigation. The objectives of this work were to study
the influence of both the nature of the organic groups
and the effect of the proximity of a second metal atom
on the Ti(IV)/Ti(III) redox properties and, indirectly,
the role of connecting the metal centers. Table 3 depicts
the cyclovoltammetric data of representative examples
and, for comparative purposes, the data of both (h5-
C5H5)2TiCl2 [37] and [(h5-C5H5)2TiCl(CH2SiMe3)] (1)
have been included.
E1/2 (V) DE (mV)
E1/2 (V) DE (mV)
(h5-C5H5)2TiCl2 −1.45
190
1
2
3
6
7
8
15
16
17
−1.85a
−2.26
−2.08
−1.97
−2.25
−2.12
−2.15
−1.98
100
70
100
70
100
60
80
−0.08b
−0.42
−0.46
−0.32
90
100
70
a Irreversible reductive process.
b Irreversible oxidative process and immediately appearance of a
reversible wave at E1/2=0.01 V, DE=130 mV (10). The cyclic
voltammograms have been recorded at c=1×10−3 M in a THF
solution in the presence of [n-Bu4N][PF6] (c=0.1 M) at 25°C under
N2; scan-rate 100 mV s−1; potentials are referenced to FcH/FcH+
(E1/2=0.00 V).
The cyclic voltammogram of neat (h5-C5H5)2TiCl2
exhibits a (chemically) reversible reductive process at
E1/2= −1.45 V (DE=190 mV) which can be assigned
to the Ti(III)/Ti(IV) redox couple [37]. This behaviour
contrasts results obtained in acetonitrile solution, where
this process has been shown to be irreversible [9].

132
S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
tanocenes, where an additional shift to more negative
potentials was observed ([7]c, [9]). In the homo-bimetal-
lic compound [{Ti}CꢀCC6H4CꢀC{Ti}], 8, one could
predict that the presence of two metal centres that are
connected by a conjugated p-system would lead to the
appearance of two distinct reduction waves. However,
this is not the case. As shown in Table 3, both ti-
tanocene fragments have the same reversible reduction
potential, which manifests itself in a concerted two-elec-
tron process at E1/2= −2.12 V (DE=100 mV). An
explanation can be given by the fact that the intermetal-
lic distance imposed by the 1,4-di(ethynyl)benzene frag-
ment is too large and therefore, despite the presence of
a conjugated p-system, the two metals are electrochem-
ically isolated from each other [38]. The Ti(III)/Ti(IV)
redox potential of the mixed-metal complexes 15 [E1/2
= −2.15 V (DE=60 mV)] and 16 [E1/2= −1.98 V
(DE=80 mV)] indicate that the h1-coordinated Ru
complex fragment {Ru} does not add electrochemically
relevant additional electron density on the Ti(IV) cen-
tre. This fact has already been observed with compound
7. This interpretation is supported by a comparison of
the Ti(III)/Ti(IV) redox potentials of [{Ti}CꢀCC6H4N-
4] 6 and its {Ru}-adduct, 16. Both of these data reveal
that the concerned reversible Ti redox couples remain
virtually unaffected.
Fig. 2. Cyclic voltammogram of compound 16 in THF solution in the
presence of [n-Bu4N][PF6] (c=0.1 M) at 25°C under N2 at a scan
rate of 100 mV s−1. Potentials are referenced to FcH/FcH+ as
internal standard (E1/2=0.00 V).
tion in this range. However, the oxidation potential
Ru(II)/Ru(III) is shifted slightly to a more negative
value. This indicates that the presence of the {Ti}CꢀC
unit in a position para to {Ru} influences the latter in
such a way that the oxidation of Ru(II) to Ru(III) is
facilitated.
As expected, compounds 1 and 2 do not exhibit
oxidation processes under these conditions. The hetero-
bimetallic complex 7 reveals an irreversible one-electron
oxidation at Eox= −0.08 V. Immediately after this first
irreversible oxidative step, a second and then reversible
oxidation wave at E1/2=0.01 V (DE=130 mV) ap-
pears. The latter persists in multi cycle experiments. It
is also a one-electron process and can be assigned to the
ferrocene derivative HCꢀCFc, 11 (see above), which is
formed instantaneously under the conditions of the
measurement. Taking into account the observations
made for complexes such as (h5-C5H4SiMe3)2-
Ti(CꢀCFc)2 [7c] or (h5-C5H4SiMe3)2Ti(CꢀCCꢀCFc)2
[7b] the conclusion can be drawn that the oxidation of
the ferrocenyl unit leads immediately to the cleavage of
the Ti–Cꢀ s-bond. By removal of an electron from this
bond, the electrochemically generated Fe(III) centre is
then reduced to Fe(II) via single electron transfer from
the Ti–Cꢀ s-bond through the C2 unit and the conju-
gated p-system of the C5H4 ring inducing formation of
HCꢀCFc (11). Nevertheless, the Ru containing com-
plexes 15 and 16 behave differently. As exemplified in
Fig. 2 for compound 16, the Ru(II)/Ru(III) oxidation is
like the Ti(III)/Ti(IV) redox couple a reversible one-
electron process [15: E1/2= −0.42 V (DE=90 mV); 16:
3. Conclusions
Ti mono-acetylides 2–8 have been prepared and
characterised. They have been connected successfully to
a second metal centre via the alkynyl system. The X-ray
crystal structure of prototypical {Ti}CꢀCSiMe3 showed
clearly the 1D arrangement with respect to the Ti–
CꢀC–R fragment. The CꢀC unit of 2 exhibited the
expected h2-coordinative behaviour with [CuCl]n. This
led to the formation of [(h2-{Ti}CꢀCSiMe3)2Cu2Cl2] (9)
at low temperature. However, this complex decom-
posed at temperatures above −78°C to yield {Ti}Cl, 1,
and [CuCꢀCSiMe3]n, exclusively. This is a different
behaviour than presented for the system (h5-
C5H4SiMe3)2Ti(CH2SiMe3)(CꢀCSiMe3)/[CuCl]n
and
suggests an influence of the type of cyclopentadienyl
substituents on the reactivity of the Ti centre. Gener-
ally, the reaction of the Ti acetylides presented in this
work with cationic complexes leads to the formation of
product mixtures, which can not be separated into pure
compounds. The behaviour of the {Ti}CꢀCFc complex
7 has been investigated. It reveals that 7 is not stable
against chemical oxidation with Ag[BF4] or reduction
with Na metal. However, the use of activated Mg metal
does not lead to a reduction of 7 at all and 7 can be
recovered from the reaction mixture. Bimetallic com-
E1/2= −0.46 V (DE=100 mV)]. This Ru(II)/Ru(III)
redox couple could be assigned unequivocally by com-
parison with the electrochemical data of the new Ru
benzonitrile complex {Ru}NCPh (17) [E1/2= −0.32 V
(DE=70 mV)] which exhibits the one-electron oxida-

S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
133
plexes have been obtained via (i) incorporation of a
4.2. General remarks
metal complex fragment into the acetylide (compounds
7 and 8) and (ii) coordination of the appropriate Ti
acetylides, i.e. 5 and 6, to {Ru} (compounds 15 and
16). The cyclic voltammetric investigation of represen-
tative examples shows an anodic shift of the Ti(III)/
Ti(IV) redox potential upon substitution of Cl in 1 by
CꢀCR groups in compounds 2–8. The size of the shift
has been found to be dependent on the electronic
properties of the group R. Electron donating groups R
give larger shifts while with electron withdrawing
groups such as 4-pyridyl only a small shift is obtained.
The incorporation or attachment of a second metal
centre (cf. 7, 15 and 16) does not influence the redox
behaviour of the Ti centre. However, the oxidation of
Ru(II) to Ru(III) is facilitated by the presence of the
{Ti} unit in the system. This may be due to a lowering
of the energy of the transition state of the oxidation of
Ru(II) to Ru(III). The intensive colours of these early–
late TM complexes indicate that their electronic system
is strongly influenced by having joined two distinct
metal centres via p-conjugated groups. Further investi-
gations on these complexes regarding their electronic
structure are in progress.
The starting materials {Ti}Cl (1) [11,20], C6H3-
(CH2NMe2)2-1,3-(CꢀCH)-5 [39], IC6H2(CH2NMe2)2-
2,6-(CꢀCH)-4 [33] HCꢀCC6H4CN-4 [40], HCꢀCC5H4-
N-4 [41], HCꢀCFc [42], [Cu(NCMe)4][BF4] [43],
[{Pt}·H2O][BF4] (12) [35], [{Pt}·NCMe][OTf] (13) [35]
and {Ru}NꢀN{Ru} (14) [36] were prepared following
published procedures. All other chemicals were pur-
chased from commercial sources.
4.3. Synthesis of {Ti}CꢀCSiMe3 (2)
At −78°C, 330 mg (1.2 mmol) of 1 were added to a
solution of LiCꢀCSiMe3 (125 mg, 1.2 mmol) in Et2O
(100 ml). After stirring (5 h; 25°C), the reaction mixture
was evaporated. The resulting brown residue was then
extracted with pentane (3×20 ml) and filtered through
a pad of Celite. The obtained orange solution was
concentrated to ca. 5 ml and crystallisation at −20°C
yielded 2 (260 mg, 70% based on 1) as orange needles.
M.p.: [°C] 96. IR (KBr): [cm−1] 2017 (s) [wCꢀC], 1253
1
(s) [wCSi], 1245 (s) [wCSi]. H-NMR (CDCl3): [l] −0.05
(s, 9 H, SiMe3), 0.08 (s, 9 H, SiMe3), 1.60 (s, 2 H,
TiCH2), 6.22 (s, 10 H, C5H5). 13C{1H}-NMR (CDCl3):
[l] 0.6 (SiMe3), 2.9 (SiMe3), 81.2 (TiCH2), 113.0
(C5H5), 128.6 (ꢀCSi), 164.6 (ꢀCTi). FAB-MS [m/z (rel.
int.)]: 361 (20) [M−H]+, 347 (30) [M−Me]+, 275
(100) [C15H19SiTi]+, 178 (90) [C10H10Ti]+, 73 (20)
[C3H9Si]+. Anal. Calc. for C19H30Si2Ti (362.53): C,
62.95; H, 8.34; Si, 15.50. Found: C, 62.85; H, 8.31; Si,
15.68.
4. Experimental
4.1. General methods
All reactions were carried out under an atmosphere
of dry nitrogen using standard Schlenk techniques.
Tetrahydrofuran (THF) and diethyl ether (Et2O) were
purified by distillation from sodium/benzophenone
ketyl and pentane was purified by distillation from
calcium hydride. Infrared spectra were obtained with a
Mattson Galaxy Series FTIR 5000. The 1H- and
13C{1H}-NMR spectra were recorded on a Bruker AC
300 spectrometer. Chemical shifts are reported in l
units (parts per million) downfield from tetramethylsi-
lane with the solvent as the internal reference signal.
FAB mass spectra were recorded at the Department of
Mass Spectrometry, Bijvoet Center, Utrecht University
on a JEOL JMS SX/SX 102A four sector mass spec-
trometer operating at 10 kV accelerating voltage. Melt-
ing points were determined on a Bu¨chi melting point
apparatus. Microanalyses were performed by H. Kolbe,
Mikroanalytisches Laboratorium, Mu¨lheim/Ruhr, Ger-
many. Electrochemical measurements were carried out
by cyclic voltammetry in a solution of [n-Bu4N][PF6]
(c=0.1 M) in THF at 25°C, using a standard three-
electrode cell on a Princeton Applied Research EG&G
263A analyzer. All potentials were referenced to the
ferrocene/ferrocenium redox couple which was used as
internal reference with E1/2=0.00 V.
4.4. X-ray structure determination of 2
The structure of 2 was determined from single crystal
X-ray diffraction, which were collected on a Bruker
SMART CCD diffractometer using Mo–Ka radiation.
Crystallographic data of 2 are given in Table 4. The
structure was solved by direct methods (SHELX 97;
G.M. Sheldrick, University of Go¨ttingen: Go¨ttingen,
Germany, 1997). An empirical absorption correction
was applied. The structure was refined by the least-
squares method based on F2 with all reflections. All
non-hydrogen atoms were refined anisotropically; the
hydrogen atoms were placed in calculated positions.
4.5. Synthesis of {Ti}CꢀCC6H3(CH2NMe2)2-3,5 (3)
Experimental conditions and work-up were the same
as described for the synthesis of 2. Experimental details:
200 mg (0.9 mmol) 1-(LiCꢀC)-3,5-(Me2NCH2)2C6H3,
270 mg (0.9 mmol) 1, 100 ml Et2O. Yield: 260 mg, 60%
based on 1.

134
S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
M.p.: [°C] 75. IR (KBr): [cm−1] 2069 (s) [wCꢀC].
220 mg (0.7 mmol) 1, 100 ml Et2O. Yield: 310 mg, 50%
based on 1.
1H-NMR (CDCl3): [l] −0.03 (s, 9 H, SiMe3), 1.64 (s,
2 H, TiCH2), 2.22 (s, 12 H, NMe2), 3.34 (s, 4 H, CH2),
6.27 (s, 10 H, C5H5), 7.06 (s, 1 H, C6H3), 7.10 (s, 2 H,
C6H3). 13C{1H}-NMR (CDCl3): [l] 3.0 (SiMe3), 45.4
(NMe2), 64.2 (CH2), 81.0 (TiCH2), 123.9 (TiCꢀC),
125.4 (iC/C6H3), 128.3 (CH/C6H3), 130.2 (CH/C6H3),
138.7 (iC/C6H3), 143.7 (TiCꢀC). FAB-MS [m/z (rel.
M.p.: [°C] dec. IR (NaCl): [cm−1] 2069 (s) [wCꢀC].
1H-NMR (CDCl3): [l] −0.03 (s, 9 H, SiMe3), 1.64 (s,
2 H, TiCH2), 2.22 (s, 12 H, NMe2), 7.10 (s, 2 H, C6H2).
13C{1H}-NMR (CDCl3): [l] 3.0 (SiMe3), 45.4 (NMe2),
63.9 (CH2), 81.0 (TiCH2), 112.9 (C5H5), 123.8 (TiCꢀC),
125.4 (iC/C6H2), 130.2 (CH/C6H2), 131.0 (iC/C6H2),
138.6 (iC/C6H2), 143.7 (TiCꢀC). Anal. Calc. for
C28H39IN2SiTi (606.52): C, 55.45; H, 6.48; N, 4.62; Si,
4.63. A satisfying elemental analysis could not be
obtained.
int.)]: 481 (50) [M+H]+, 394 (40) [M+H]+
−
C4H11Si, 217 (20) [C14H17N2]+. Anal. Calc. for
C28H40N2SiTi (480.63): C, 69.97; H, 8.39; N, 5.83; Si,
5.88. Found: C, 69.86; H, 8.33; N, 5.95; Si, 5.88.
4.6. Synthesis of {Ti}CꢀCC6H2I-4-(CH2NMe2)2-3,5
(4)
4.7. Synthesis of {Ti}CꢀCC6H4CN-4 (5)
To
a
stirring Et2O solution (150 ml) of
Experimental conditions and work-up were the same
as described for the synthesis of 2. Experimental details:
250 mg (0.7 mmol) 1-(LiCꢀC)-2,6-(Me2NCH2)2C6H2I,
LiCꢀCC6H4CN-4 (150 mg, 1.1 mmol) was added 1 (340
mg, 1.1 mmol) at −78°C. After stirring for 12 h
(25°C), the reaction mixture was evaporated. The re-
sulting residue was extracted with pentane (3×10 ml)
and Et2O (4×20 ml) and filtered through a pad of
Celite. Evaporation of the combined Et2O extracts
yielded 5 (300 mg, 70% yield based on 1) as a dark
orange solid.
Table 4
Crystal and intensity collection data for 2
Empirical formula
Molecular mass
Crystal system
Space group
C19H30Si2Ti
362.51
Monoclinic
P21/n
M.p.: [°C] 153 (dec). IR (KBr): [cm−1] 2224 (s) [wCN],
2078 (s) [wCꢀC]. H-NMR (CDCl3): [l] −0.02 (s, 9 H,
1
˚
a (A)
6.6618(1)
˚
b (A)
21.1906(3)
14.2395(1)
91.360(1)
2009.59(4)
1.198
SiMe3), 1.75 (s, 2 H, CH2), 6.29 (s, 10 H, C5H5),
7.2–7.6 (m, 4 H, C6H4). 13C{1H}-NMR (CDCl3): [l]
3.0 (SiMe3), 83.8 (CH2), 109.1 (CN), 113.1 (C5H5),
122.2 (TiCꢀC), 130.4 (iC/C6H4), 130.7 (iC/C6H4), 130.8
(CH/C6H4), 131.8 (CH/C6H4), 148.8 (TiCꢀC). FAB-
MS [m/z (rel. int.)]: 304 (60) [M−C4H11Si]+, 265 (70)
[M−C9H4N]+, 178 (100) [C10H10Ti]+, 73 (50)
[C3H9Si]+. Anal. Calc. for C23H25NSiTi (391.45): C,
70.57; H, 6.44; N, 3.58. Found: C, 70.39; H, 6.36; N,
3.52.
˚
c (A)
i (°)
3
˚
V (A )
zcalc (g cm−3
)
F(000)
776
Z
4
Crystal dimensions (mm)
Diffractometer model
0.4×0.04×0.04
Bruker SMART CCD
0.541
Empirical using SADABS
0.927996 and 0.719564
Mo–Ka (0.71073)
173(2)
Linear absorption coefficient (mm−1
Absorption correction
)
Max. and min. transmission
˚
Radiation (u, A)
Temperature (K)
Scan mode
4.8. Synthesis of {Ti}CꢀCC5H4N-4 (6)
ꢀ-scan
Scan range (°)
Index ranges
1.72B2qB29.07
−85h58, −275k528,
−185l514
15026
Experimental procedures and work-up are the same
as described for the synthesis of 5. Experimental details:
LiCꢀCC5H4N-4 (100 mg, 0.9 mmol), 1 (270 mg, 0.9
mmol), 150 ml Et2O. Yield: 240 mg, 75% based on 1.
M.p.: [°C] 128. IR (KBr): [cm−1] 2079 (s) [wCꢀC].
1H-NMR (CDCl3): [l] −0.01 (s, 9 H, SiMe3), 1.72 (s,
2 H, CH2), 6.25 (s, 10 H, C5H5), 7.0–7.1 (m, 2 H,
C5H4N), 8.3–8.5 (m, 2 H, C5H4N). 13C{1H}-NMR
(CDCl3): [l] 3.0 (SiMe3), 87.2 (CH2), 113.2 (C5H5),
121.0 (TiCꢀC), 124.5 (CH/C5H4N), 133.4 (iC/C5H4N),
148.9 (TiCꢀC), 149.4 (CH/C5H4N). FAB-MS [m/z (rel.
int.)]: 368 (20) [M+H]+, 280 (40) [M+H−
C4H12Si]+, 178 (30) [C10H10Ti]+, 73 (80) [C3H9Si]+.
Anal. Calc. for C21H25NSiTi (369.43): C, 68.65; H, 6.86;
N, 3.68; Si, 7.65. Found: C, 68.53; H, 6.44; N, 3.81; Si,
7.22.
Total reflections
Unique reflections
4702
Observed reflections [I]2|(I)]
Refinement method
2778
Full-matrix, least-squares
(F2)
Refined parameters
202
Rint
0.1135
a,b
R1a, wR2 [I]2|(I)]
0.0782, 0.1078
0.1512, 0.1305
1.043
R1a, wR2 (all data)
a,b
GOF (S)c
Max. and min. peaks in final Fourier 0.387 and −0.553
−3
˚
map (e A
)
a R1=[S(ꢀꢀFoꢀ−ꢀFcꢀ)/SꢀFoꢀ)]; wR2=[S(w(Fo2−Fc2)2)/S(wF4o)]0.5
b w=1/[s2(F2o)+(0.0083P)2+3.3243P] with P=[Fo2+2F2c]/3.
.
c S=[Sw(F2o−Fc2)2]/(n−p)0.5
; n=number of reflections, p=
parameters used.

S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
135
4.9. Synthesis of {Ti}CꢀCFc (7)
of the evaporated (in vacuo) residue revealed the pres-
ence of 1.
Experimental procedures and work-up are the same
as described for the synthesis of 5. Experimental details:
200 mg (0.9 mmol) LiCꢀCFc, 270 mg (0.9 mmol) 1, 150
ml Et2O. Yield: 260 mg, 60% based on 1.
4.11.2. Method B
Then, the THF was removed (in vacuo, −78°C) and
the orange residue was extracted with pentane (−78°C,
3×10 ml), Et2O (−78°C, 3×10 ml) and THF (−
78°C, 3×10 ml) and filtered through a pad of Celite.
The combined THF extracts were evaporated (in vacuo,
−78°C) to yield an orange residue (30 mg).
M.p.: [°C] dec. IR (KBr): [cm−1] 1920 (s) [wCꢀC], 1894
(s) [wCꢀC]. 1H-NMR (d8-THF): [l] 0.11 (SiMe3), 0.22
(SiMe3), 1.55 (CH2), 6.17 (C5H5). FAB-MS [m/z (rel.
int.)]: 922 (5) [M+], 425 (15) [C19H30CuSi2Ti]+, 178
(100) [C10H10Ti]+.
M.p.: [°C] 139. IR (KBr): [cm−1] 2052 (s) [wCꢀC].
1H-NMR (CDCl3): [l] −0.2 (s, 9 H, SiMe3), 1.57 (s, 2
3
H, CH2), 4.12 (t, JHH=1.8 Hz, 2 H, C5H4), 4.16 (s, 5
H, C5H5), 4.24 (t, 3JHH=1.8 Hz, 2 H, C5H4), 6.25 (s, 10
H, C5H5). 13C{1H}-NMR (CDCl3): [l] 3.0 (SiMe3), 68.2
(CH/C5H4), 69.6 (C5H5), 70.1 (iC/C5H4), 70.8 (CH/
C5H4), 77.7 (TiCH2), 112.7 (C5H5), 122.8 (TiCꢀC),
144.1 (TiCꢀC). FAB-MS [m/z (rel. int.)]: 476 (10)
[M]+, 460 (10) [M−Me]+, 418 (90) [M−SiMe2]+,
296 (100) [M−SiMe2−C5H5Fe]+, 266 (100) [M−
C12H9Fe]+, 210 [C12H9Fe]+, 178 (60) [C10H10Ti]+.
Anal. Calc. for C26H30FeSiTi (474.37): C, 65.83; H,
6.37. Found: C, 65.72; H, 6.34.
4.12. Reaction of {Ti}CꢀCSiMe3 (2) with
[Cu(NCMe)4][BF4]
Experimental conditions were the same as for the
reaction of 2 with 9—see Method B above. Experimen-
tal details: 10 (30 mg, 0.1 mmol), 2 (70 mg, 0.2 mmol),
THF (10 ml).
4.10. Synthesis of {Ti}CꢀCC6H4CꢀC{Ti}-4 (8)
To a Et2O solution (150 ml) of 1,4-(LiCꢀC)2C6H4
(130 mg, 0.9 mmol) was added 1 (540 mg, 1.8 mmol) at
−78°C. After stirring for 12 h (25°C), the solvent was
removed in vacuo. The resulting residue was then ex-
tracted with pentane (3×10 ml), Et2O (3×10 ml) and
then with CH2Cl2 (3×20 ml) and filtered through a
pad of Celite. The combined CH2Cl2 extracts were
evaporated to dryness to yield 8 (310 mg, 50% yield
based on 1) as yellow solid.
After stirring (2 h), the suspension was evaporated in
vacuo. The yellow residue was extracted (−78°C) with
pentane (3×10 ml), Et2O (3×10 ml), THF (3×10 ml)
and CH2Cl2 (3×10 ml). After filtration through pad of
Celite and evaporation (−78°C) of the combined
CH2Cl2 extracts, a yellow solid (10 mg) was obtained.
IR spectroscopy carried out on the yellow residue
revealed no characteristic bands in the region typical
for wCꢀC and the 1H-NMR spectrum exhibited a number
of uncharacteristic signals.
M.p.: [°C] \200. IR (KBr): [cm−1] 2076 (s) [wCꢀC].
1H-NMR (CDCl3): [l] −0.04 (s, 18 H, SiMe3), 1.65 (s,
4 H, CH2), 6.27 (s, 20 H, C5H5), 7.10 (s, 4 H, C6H4).
13C{1H}-NMR (CDCl3): [l] 3.0 (SiMe3), 81.5 (CH2),
112.9 (C5H5), 124.3 (TiCꢀC), 130.5 (CH/C6H4), 140.1
(TiCꢀC). FAB-MS [m/z (rel. int.)]: 265 (80)
[C14H21SiTi]+, 178 (100) [C10H10Ti]+. Anal. Calc. for
C38H46Si2Ti2 (654.77): C, 69.71; H, 6.81; Si, 8.58.
Found: C, 69.56; H, 6.81; Si, 8.36.
4.13. Reaction of {Ti}CꢀCFc (7) with Mg
Activated Mg (30 mg, 1.3 mmol) and 7 (50 mg, 0.1
mmol) were mixed. Then, THF (20 ml) was added and
the solution stirred (10 h, 25°C). No colour change was
observed. After filtration of the reaction mixture
through a pad of Celite, the red solution was evapo-
rated to dryness (in vacuo) to yield a red brown solid
1
4.11. Reaction of {Ti}CꢀCSiMe3 (2) with [CuCl]n
(45 mg). IR and H-NMR revealed the presence of 7
solely.
[CuCl]n (15 mg, 0.15 mmol) and 2 (60 mg, 0.15
mmol) were mixed and cooled to −78°C. Cooled THF
(−78°C, 10 ml) was then added via a syringe. While
the reaction mixture was stirred (−78°C, 2 h) it
changed colour from orange to red and became clear.
4.14. Reaction of {Ti}CꢀCFc (7) with Na
To Na metal (10 mg, 0.4 mmol) was added a solution
of 7 (150 mg, 0.3 mmol) in THF (20 ml, 0°C). During
the course of the reaction a precipitate formed. After
stirring (0°C, 6 h) the mixture was evaporated (in
vacuo). The residue was then extracted with pentane
(3×10 ml), Et2O (3×20 ml) and THF (3×10 ml) and
filtered through a pad of Celite. The Et2O and THF
extracts were removed in vacuo to yield a brown solid.
1H-NMR investigation of the Et2O and THF residues
revealed a signal pattern which could not be assigned
4.11.1. Method A
Then, the reaction mixture was allowed to warm to
25°C. Monitoring the reaction mixture (IR), the devel-
opment of an absorption band assigned to
[CuCꢀCSiMe3]n was observed and the band at 1920
cm−1 (9) disappeared. After extraction of the resulting
1
solid with pentane (3×10 ml), the H-NMR spectrum

136
S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
unambiguously. Also, the IR spectra revealed non-diag-
nostic absorption bands.
details: 6 (50 mg, 0.14 mmol), 13 (75 mg, 0.13 mmol),
THF (20 ml).
In each experiment, the IR and 1H-NMR spec-
troscopy revealed an uncharacteristic signal pattern of
the yellow residue obtained which could not be as-
signed unequivocally.
4.15. Reaction of {Ti}CꢀCFc (7) with Ag[BF4]
To a light protected Schlenk flask containing Ag[BF4]
(40 mg, 0.2 mmol) was added a THF solution (30 ml,
0°C) of 7 (97 mg, 0.2 mmol). The reaction mixture was
stirred (5 h, 0°C) and then the solvent is removed (in
vacuo). The green residue was extracted with pentane
(3×10 ml), Et2O (3×10 ml) and THF (3×20 ml) and
then filtered through a pad of Celite. Then, the extracts
were evaporated to dryness (in vacuo). The residue of
the pentane extracts contained HCꢀFc, identified by its
IR and 1H-NMR spectra. After evaporation of the
THF extracts, a green solid was obtained. 1H-NMR
spectroscopic investigation showed paramagnetism and
the IR spectrum exhibited uncharacteristic absorption
bands.
4.20. Synthesis of [{Ti}CꢀCC6H4CN-4]{Ru} (15)
Compound
5
(105 mg, 0.3 mmol) and
{Ru}NꢀN{Ru} (14) (106 mg, 0.15 mmol) were mixed.
Addition of THF (50 ml, 0°C) resulted in a brown
solution which turned intensively red after ca. 15 min.
The mixture was stirred at 0°C (3 h) and then concen-
trated to ca. 5 ml. Then 20 ml of pentane were added,
the precipitate washed twice with pentane and then
dried in vacuo. Product 15 (100 mg, 90% yield based on
5) was thus obtained as dark red solid.
M.p.: [°C] 123 (dec). IR (KBr): [cm−1] 2197 (s) [wCN],
1
2077 (s) [wCꢀC]. H-NMR (CDCl3): [l] −0.3 (s, 9 H,
4.16. Reaction of {Ti}CꢀCC6H4CN-4 (5) with
[{Pt}·H2O][BF4] (12)
SiMe3), 1.73 (s, 2 H, CH2), 2.63 (s, 12 H, NMe2), 4.09
(s, 4 H, CH2), 6.29 (s, 10 H, C5H5), 7.1–7.7 (m, 3 H,
C6H3), 7.2–7.5 (m,
4
H, C6H4). 13C{1H}-NMR
Compound 5 (50 mg, 0.13 mmol) was mixed with 12
(63 mg, 0.13 mmol) and dissolved in THF (−40°C, 20
ml). In the course of the reaction, a yellow precipitate
formed. After stirring (−40°C, 3 h) the solution was
allowed to warm up (25°C) and evaporated. The
residue was then extracted with Et2O (2×20 ml), THF
(3×10 ml) and CH2Cl2 (2×10 ml) and filtered
through a pad of Celite. The combined CH2Cl2 extracts
were then concentrated to ca. 5 ml and 15 ml pentane
was added. The supernatant solution was removed and
the yellow residue dried in vacuo.
(CDCl3): [l] 3.0 (SiMe3), 54.5 (NMe2), 71.2 (CH2), 83.3
(TiCH2), 110.8 (CN), 113.1 (C5H5), 118.9 (CH/
C5H3N), 122.7 (iC/C6H4), 125.3 (TiCꢀC), 129.2 (iC/
C6H4), 130.8 (CH/C6H4), 132.0 (iC/C5H3N), 132.4
(CH/C6H4), 149.0 (TiCꢀC), 163.2 (CH/C5H3N). FAB-
MS [m/z (rel. int.)]: 756 (5) [M]+, 721 (5) [M−Cl]+,
365
(60)
[C11H19Cl2N3Ru]+,
329
(100)
[C11H19ClN3Ru]+. Anal. Calc. for C34H44Cl2N4RuSiTi
(756.75): C, 53.96; H, 5.86; N, 7.40; Si, 3.71. Found: C,
54.15; H, 5.76; N, 7.26; Si, 3.84.
4.17. Reaction of {Ti}CꢀCC6H4CN-4 (5) with
[{Pt}·NCMe][OTf] (13)
4.21. Synthesis of [{Ti}CꢀCC5H4N-4]{Ru} (16)
Experimental procedures and work-up are the same
as described for the synthesis of 5. Experimental details:
6 (45 mg, 0.12 mmol), {Ru}NꢀN{Ru} (14) (45 mg, 0.06
mmol), 20 ml THF. Yield: 80 mg, 90% based on 6.
M.p.: [°C] 125 (dec). IR (KBr): [cm−1] 2083 (s)
Experimental conditions and work-up were the same
as described for the reaction of 5 with 13. Experimental
details: 5 (150 mg, 0.4 mmol), 13 (150 mg, 0.3 mmol),
THF (40 ml).
1
[wCꢀC]. H-NMR (CDCl3): [l] −0.3 (s, 9 H, SiMe3),
4.18. Reaction of {Ti}CꢀCC5H4N-4 (6) with
[{Pt}·H2O][BF4] (12)
1.79 (s, 2 H, CH2), 2.39 (s, 12 H, NMe2), 4.04 (s, 4 H,
CH2), 6.31 (s, 10 H, C5H5), 7.0–7.1 (m, 2 H, C5H4N),
7.1–7.3 (m, 3 H, C5H3N), 9.5–9.6 (m, 2 H, C5H4N).
13C{1H}-NMR (CDCl3): [l] 3.0 (SiMe3), 53.7 (NMe2),
72.3 (CH2), 83.8 (TiCH2), 113.2 (C5H5), 118.4 (CH/
C5H3N), 123.5 (TiCꢀC), 124.5 (CH/C5H4N), 130.5 (iC/
C5H3N), 134.1 (iC/C5H4N), 151.1 (TiCꢀC), 156.0
(CH/C5H4N), 163.6 (CH/C5H3N). FAB-MS [m/z (rel.
int.)]: 734 (10) [M+H]+, 697 (10) [M−Cl]+, 365 (5)
[C11H19Cl2N3Ru]+, 329 (100) [C11H19ClN3Ru]+. Anal.
Calc. for C32H44Cl2N4RuSiTi (732.73): C, 52.45; H,
6.05; N, 7.65; Si, 3.83. A satisfying elemental analysis
could not be obtained.
Experimental conditions and work-up were the same
as described for the reaction of 5 with 12. Experimental
details: 6 (100 mg, 0.3 mmol), 12 (120 mg, 0.3 mmol),
THF (50 ml).
4.19. Reaction of {Ti}CꢀCC5H4N-4 (6) with
[{Pt}·NCMe][OTf] (13)
Experimental conditions and work-up were the same
as described for the reaction of 6 with 13. Experimental

S. Back et al. / Journal of Organometallic Chemistry 582 (1999) 126–138
137
Lou, K.K. Chang, Organometallics 14 (1995) 2749. (e) A.M.
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B.W. Skelton, A.H. White, J. Organomet. Chem. 523 (1996) 33.
(f) S. Houbrechts, K. Clay, A. Persoons, V. Cardiero, M.P.
Gamasa, J. Gimeno, Organometallics 15 (1996) 5266. (g) I.R.
Whitall, M.G. Humphrey, M. Samroc, B. Luther-Davies,
D.C.R. Hockless, J. Organomet. Chem. 544 (1997) 189. (h) I.R.
Whitall, M.G. Humphrey, S. Houbrechts, J. Maes, A. Persoons,
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277. (i) P. Nguyen, G. Lesley, T.B. Marder, I. Ledaux, J. Zyss,
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4.22. Synthesis of {Ru}NCPh (17)
A solution of {Ru}NꢀN{Ru} (14) (128 mg, 0.2
mmol) and PhCN (40 mg, 0.4 mmol) in THF (30 ml)
was stirred for 1 h. During the course of the reaction
the colour of the solution turned from brown to red
and the turbidity disappeared. The reaction mixture
was then concentrated to ca. 5 ml and pentane (50 ml)
added. The supernatant liquid was carefully decanted
and the residue dried in vacuo to yield 17 (150 mg, 95%
yield based on 14) as brown solid.
M.p.: [°C] 148. IR (KBr): [cm−1] 2214 (s) [wCN].
1H-NMR (CDCl3): [l] 2.68 (s, 12 H, NMe2), 4.09 (s, 4
H, CH2), 7.1–7.7 (m, 3 H, C6H3). 13C{1H}-NMR
(CDCl3): [l] 54.5 (NMe2), 71.2 (CH2), 110.8 (CN),
118.9 (CH/C5H3N), (iC/C6H4), 130.8 (CH/C6H4), 132.0
(iC/C5H3N), 132.4 (CH/C6H4), 163.2 (CH/C5H3N).
FAB-MS [m/z (rel. int.)]: 467 (15) [M]+, 433 (10)
[M−Cl]+, 365 (10) [M−C7H5N]+, 329 (20)
[C11H19ClN3Ru]+. Anal. Calc. for C18H24Cl2N4Ru
(468.42): C, 46.15; H, 5.16; N, 11.96. A satisfying
elemental analysis could not be obtained.
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Acknowledgements
The authors would like to thank the Volkswagens-
tiftung, the Fonds der Chemischen Industrie and
Utrecht University (a 1.5 year stay of S. Back) for
financial support. The authors are grateful to the De-
partment of Mass Spectrometry for the recording of the
mass spectra. The authors also thank B. Richter for
helpful discussions.
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