Low-valent titanium-pentafulvene complexes - Formation of dinuclear titanium-nitrogen complexes

Article abstract of DOI:10.1002/ejic.200400938

Sodium amalgam reduction of [(η5-C₅Me₅)TiCl ₃] (1) in the presence of the pentafulvenes {C₅H ₄=CR₂, R: p-tol (2), p-FPh (3), CR₂: adamantyl (4)} under nitrogen smoothly produces dark green or dark blue dinuclear low-valent titanium complexes [{(η⁵-C₅Me ₅)Ti(η⁶-C₅H₄=CR ₂)}₂(μ₂,η¹, η¹-N₂)] {R: p-tol (6), p-FPh (7), CR₂: adamantyl (8)}, characterized by a bridging end-on coordinated dinitrogen ligand, in high yield. In the same way, the nitrogen-free, low-coordinated complex [(η⁵-C₅Me₅)Ti(η⁶- C₉H₆=C(p-tol)₂)] (10) is obtained by using the more sterically demanding benzofulvene C₉H₆=C(P-tol) ₂ (5) instead of 2-4. The solid-state structures of the dinitrogen compounds reveal weakly activated end-on bound N₂ ligands with identical N-N distances of 1.160(3) A (6) and 1.160(5) A (8). The dinitrogen complexes 6, 7 and 8 show diamagnetic behaviour, which allowed a complete NMR spectroscopic characterization. So a correlation between the situation in solution, measured by NMR, and in the solid state (X-ray diffraction) becomes possible and shows a congruent picture. A broad range of reactions can be imagined concerning the easily replaceable dinitrogen ligand as well as the known reactivity of fulvene ligands in complexes of early transition metals. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.

Full text of DOI:10.1002/ejic.200400938

FULL PAPER
Low-Valent Titanium–Pentafulvene Complexes − Formation of Dinuclear
Titanium–Nitrogen Complexes
Axel Scherer,[a] Kay Kollak,[a] Arne Lützen,[a] Marion Friedemann,[a] Detlev Haase,[a]
Wolfgang Saak,[a] and Rüdiger Beckhaus*[a]
Dedicated to Prof. Dr. Jan H. Teuben
Keywords: Titanium / Bridging ligands / Nitrogen / Metallocenes / Fulvene ligands
Sodium amalgam reduction of [(η5-C5Me5)TiCl3] (1) in the
presence of the pentafulvenes {C5H4=CR2, R: p-tol (2), p-FPh
(3), CR2: adamantyl (4)} under nitrogen smoothly produces
gands with identical N–N distances of 1.160(3) Å (6) and
1.160(5) Å (8). The dinitrogen complexes 6, 7 and 8 show dia-
magnetic behaviour, which allowed a complete NMR spec-
dark green or dark blue dinuclear low-valent titanium com- troscopic characterization. So a correlation between the situ-
plexes [{(η5-C5Me5)Ti(η6-C5H4=CR2)}2(µ2,η1,η1-N2)] {R: p-tol
(6), p-FPh (7), CR2: adamantyl (8)}, characterized by a bridg-
ing end-on coordinated dinitrogen ligand, in high yield. In
the same way, the nitrogen-free, low-coordinated complex
[(η5-C5Me5)Ti(η6-C9H6=C(p-tol)2)] (10) is obtained by using
the more sterically demanding benzofulvene C9H6=C(p-tol)2
(5) instead of 2–4. The solid-state structures of the dinitrogen
compounds reveal weakly activated end-on bound N2 li-
ation in solution, measured by NMR, and in the solid state
(X-ray diffraction) becomes possible and shows a congruent
picture. A broad range of reactions can be imagined concern-
ing the easily replaceable dinitrogen ligand as well as the
known reactivity of fulvene ligands in complexes of early
transition metals.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
systems, Cp alternatives based on multidentate anionic li-
gands bearing N, O and P donor atoms were successfully
used in order to obtain nitrogen complexes.[17–25] It was also
shown that the introduction of nitrogen into organic sub-
strates becomes possible under reductive conditions.[26–29]
Recently we were able to demonstrate that pentafulvene
complexes of early transition metals are easily available
from the reaction of titanium halides, reducing agents (Mg,
Na/Hg), and free pentafulvenes.[30] Using fulvenes exhibit-
ing asymmetric exocyclic carbon centres, a diastereoselec-
tive complexation of the fulvene ligand at different cyclo-
pentadienyltitanium fragments is possible.[31]
Here we wish to report the one-step formation of dinitro-
gen-containing titanium complexes by reactions of [(η5-
C5Me5)TiCl3] (1) with the pentafulvenes 2, 3, 4 and Na/Hg
as reducing agent in the presence of dinitrogen. Using the
bulky benzofulvene 5, a low-coordinated mononuclear tita-
nium compound is formed.
Introduction
Low-valent titanium complexes are of great importance
in the complexation and activation of molecular nitrogen.
Different bonding modes are found in early transition met-
als, depending on the nature of the other ligands.[1–5] Tita-
nocene- as well as zirconocene-based systems have been and
are still being extensively investigated. It was found that the
cyclopentadienyl substituent patterns have a strong influ-
ence on the N2 coordination and activation modes.[6–11] In
such a way, for example, the permethylated [(η5-C5Me5)2Zr]
fragment coordinates the N2 molecules by end-on bridging
as well as in a terminal mode.[12–14] On the other hand,
using the tetramethylcyclopentadiene ligand instead of the
pentamethyl derivative, a side-on bridging coordination
mode, characterized by an efficient N2 activation, is
found.[15,16] Results like this initiated further studies in or-
der to obtain a detailed understanding of the field of N2
activation reactions. In addition to the metallocene-based
[a] Institut für Reine und Angewandte Chemie, Fakultät für Ma-
thematik und Naturwissenschaften, Carl von Ossietzky Uni-
versität Oldenburg,
Results and Discussion
Treatment of a THF solution of equimolar amounts of
[(η5-C5Me5)TiCl3] (1) [Equation (1)] and 2, 3, or 4 with
three equivalents of Na (20% Na/Hg) under nitrogen leads
to intensely coloured solutions. After removal of
Postfach 2503, 26111 Oldenburg, Germany
Fax: +49-441-798-3581
E-mail: ruediger.beckhaus@uni-oldenburg.de
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2005, 1003–1010
DOI: 10.1002/ejic.200400938
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1003

R. Beckhaus et al.
FULL PAPER
complexes derived from titanium amides are shorter Ti–N
and longer N–N bonds found (Ti–N av. 1.72–1.76 Å, N–N
1.26–1.29 Å[17,24,25]).
the solvent, addition of n-hexane to the residue and separa-
tion from the insoluble NaCl and mercury by filtration, 6,
7, and 8 can be isolated as dark green (6, 7) or dark blue
(8) crystals showing a fascinating cupric lustre. All com-
plexes were isolated in high yields (6, 8 90%; 7 80%). It is
also possible to use magnesium as the reducing agent, but
the products could only be isolated in lower yields (40%),
because the formation of MgCl2 containing adducts with
the dinitrogen complexes made it difficult to separate
MgCl2 quantitatively. All three dinitrogen complexes are
thermally stable; melting points are found at 125 °C (6),
138–140 °C (7), and 175 °C (8). They are easily soluble in
inert solvents like ethers and saturated or aromatic hydro-
carbons.
Figure 1. Solid state structure of 6 (50% probability ellipsoids). Se-
lected bond lengths [Å] and angles [°]: Ti(1)–C(1) 2.195(3), Ti(1)–
C(2) 2.253(3), Ti(1)–C(5) 2.303(3), Ti(1)–C(3) 2.375(3), Ti(1)–C(4)
2.409(3), Ti(1)–C(6) 2.601(3), C(1)–C(6) 1.436(4), C(1)–C(2)
1.439(4), C(1)–C(5) 1.434(4), C(2)–C(3) 1.416(5), C(4)–C(5)
1.412(4), C(3)–C(4) 1.393(5), Ti(1)–N(1) 1.997(3), N(1)–N(2)
1.160(3), Ti(1)–Ct(1) 2.056(3), Ti(1)–Ct(2) 1.968(3), Θ 28.4, Ct(1)–
Ti(1)–Ct(2) 139.0 [Ct(1) = Centroid of Cp*, Ct(2) = centroid of the
fulvene ring, Θ = tilt of C(6) out of the plane of C(11)–C(15)].
Suitable crystals for X-ray diffraction were obtained from
n-hexane/toluene (1:1) (6) or n-hexane (8) solutions at ambi-
ent temperature. In the case of 6 the asymmetric unit con-
tains a disordered n-hexane molecule, which was refined on
3 positions (1/3, 1/3, 1/3) in idealised geometry; 8 shows two
independent molecules in the asymmetric unit. Figure 1 and
Figure 2 show ORTEP plots of the molecules with 50%
probability ellipsoids, the hydrogen atoms, solvent mole-
cules and the second molecule in the asymmetric unit (8)
are omitted for clarity. Due to similarities of the structural
values, we will limit our discussion mainly on the data of
molecule one (Ti1, Ti2). Selected structural data are given
in Table 1 and Table 2. The dinuclear structures consist of
two [(η5-C5Me5)(η6-C5H4=CR2)Ti] moieties bridged by N2
in an almost linear Ti–NϵN–Ti arrangement. However, a
deviation from linearity of about 9–10° was found (6 Ti1–
Ti2–N2 9.4°, Ti2–Ti1–N1 9.0°; 8 Ti1–Ti2–N2 9.9°, Ti2–
Ti1–N1 10°). In accordance with this observation, the Ti–
N–N angles were found to be slightly smaller than 180°
[6 171.0(2)°, 169.1(2)°; 8 170.0(4)°, 169.6(4)°]. These values
correspond well to the lower range of values found in com-
parable µ2,η1,η1-N2 titanium complexes (168–180°,
Table 1). The N–N bond lengths of 1.160(3) Å (6) and
1.160(5) Å (8) are also consistent with a just slightly acti-
vated N2 molecule, since the N–N distance is not signifi-
cantly different from that of free N2 (1.0976 Å[32]). Thus,
these values are in good agreement with metallocene type
Figure 2. Solid state structure of 8 (50% probability ellipsoids). Se-
lected bond lengths [Å] and angles [°]: Ti(1)–C(1) 2.179(5), Ti(1)–
C(2) 2.301(5), Ti(1)–C(5) 2.291(5), Ti(1)–C(3) 2.424(5), Ti(1)–C(4)
2.426(5), Ti(1)–C(6) 2.511(5), C(1)–C(6) 1.441(6), C(1)–C(2)
1.437(6), C(1)–C(5) 1.448(7), C(2)–C(3) 1.413(8), C(4)–C(5)
1.419(7), C(3)–C(4) 1.397(7), Ti(1)–N(1) 2.012(4), N(1)–N(2)
1.160(5), Ti(1)–Ct(1) 2.061(4), Ti(1)–Ct(2) 1.986(4), Θ 30.4, Ct(1)–
Ti(1)–Ct(2) 138.8 [Ct(1) = Centroid of Cp*, Ct(2) = centroid of the
fulvene ring, Θ = tilt of C(6) out of the plane of C(1)–C(5)].
6 as well as 8 show similarities but also some marked
dinitrogen–titanium complexes (Table 1). Also, the Ti–N differences compared with titanocene complexes. Probably
bond lengths are in the range of end-on coordinated dini- the most striking point is the well-defined arrangement of
trogen–titanocene complexes [6 1.997(3), 2.001(3) Å; 8 the pentafulvene ligands which are located on the same side
2.012(4), 2.003(4) Å]. Only in non-titanocene–nitrogen of the molecule. In general, a selective trans orientation of
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Low-Valent Titanium–Pentafulvene Complexes
FULL PAPER
Table 1. Selected bond lengths [Å] and angles [°] of 6 and 8, compared with related dinitrogen complexes.
Compound
N–N
Ti–N
Ti–N–N
Ref.
6
1.160(3)
1.160(5)
1.165(14)
1.170(4)
1.191(8)
1.162(12)
1.164(5)
1.289(9)
1.263(7)
1.280(8)
1.997(3), 2.001(3)
2.012(4), 2.003(4)
2.005(10), 2.016(10)
1.987(3)
1.920(6), 1.921(5)
1.962(6)
171.0(2), 169.1(2)
170.0(4), 169.6(4)
176.8(4), 178.1(4)
178.5(3)
169.0(5), 172.6(5)
176.5(5)
8
[{(η5-C5Me5)2Ti}2(µ2,η1,η1-N2)]
[{(η5-C5Me4 H)2Ti}2(µ2,η1,η1-N2)]
[{(η5-C5H5)2Ti(PMe3)}2(µ2,η1,η1-N2)]
[{(η5-C5H5)2Ti(p-Tol)}2(µ2,η1,η1-N2)]
[{(η5-C5H3(SiMe3)2)2Ti}2(µ2,η1,η1-N2)]
[{((Me3Si)2N)TiCl(TMEDA)}2(µ2,η1,η1-N2)]
[{((Me3Si)2N)TiCl(Py)2}2(µ2,η1,η1-N2)]
[{((Me2N)C(NiPr)2)2Ti}2(µ2,η1,η1-N2)]
[33]
[8]
[9]
[11]
[7]
1.991(4)
1.762(5)
1.759(3)
176.0(3)
168.5(2)
175.5(3)
180.0
[25]
[24]
[17]
1.723(8), 1.744(8)
the non-Cp-type ligands is found in dinuclear, µ2,η1,η1-dini-
trogen-bridged titanocene complexes with tetrahedral coor-
dinated titanium centres like [{(η5-C5H5)2Ti(p-tol)}2-
(µ2,η1,η1-N2)][11] and [{(η5-C5H5)2Ti(PMe3)}2(µ2,η1,η1-
N2)].[9] In the case of 6 and 8, in principle, four different
stereoisomers are possible with respect to the position of
the exocyclic fulvene carbon atoms (Ce) to each other
(Scheme 1). Again, the formation of the “cis isomers” A
and B was not observed, whereas of the two possible “trans
isomers” C was found to be formed exclusively. This was
confirmed not only in the solid state but also in solution
(vide infra).
Table 2. Selected bond lengths [Å] and angles [°] of 6, 8, 10 com-
pared with 2,[30] 4[35] and 5.
6
2
8
4
10
5
Ti–Ci
2.195(3)
2.195(2)
2.601(3)
2.612(3)
2.253(3)
2.258(3)
2.303(3)
2.296(3)
2.375(3)
2.362(3)
2.409(3)
2.399(3)
2.056(3)
2.056(3)
1.968(3)
1.963(3)
2.179(5)
2.188(4)
2.511(5)
2.471(5)
2.291(5)
2.282(5)
2.301(5)
2.310(4)
2.426(5)
2.428(6)
2.424(5)
2.424(5)
2.061(4)
2.068(4)
1.986(4)
1.986(4)
2.116(2)
Ti–Ce
2.351(2)
2.220(2)
2.350(3)
2.360(2)
2.461(2)
2.006(2)
1.956(2)
Ti–Ca
Ti–CЈa
Ti–Cb
Ti–CЈb
Ti–Ct* [a]
Ti–CtFv [a]
Ci–Ce
1.436(4) 1.359(2) 1.441(6) 1.342(2) 1.465(3) 1.359(2)
1.435(4) 1.427(8)
1.439(4) 1.465(2) 1.448(7) 1.459(2) 1.449(4) 1.467(2)
1.441(4) 1.459(8)
1.434(4) 1.458(3) 1.437(6) 1.459(2) 1.465(3) 1.488(2)
1.430(4) 1.454(7)
1.416(5) 1.340(3) 1.419(7) 1.327(3) 1.401(3) 1.340(3)
1.406(5) 1.411(8)
1.412(4) 1.344(3) 1.413(8) 1.337(3) 1.437(4) 1.416(2)
1.412(4) 1.404(8)
1.393(5) 1.445(3) 1.397(7) 1.451(3) 1.414(4) 1.454(2)
Ci–Ca
Ci–C’a
Ca–Cb
Scheme 1. Possible isomers of [{(η5-C5Me5)(η6-C5H4=CR2)-
Ti}2(µ2,η1,η1-N2)] complexes (Ct*: ring centroid of C5Me5; CtFv
:
CЈa–CЈb
Cb–CЈb
Θ[b]
ring centroid of Ci, Ca, CЈa, Cb, CЈb; Ce exo-cyclic carbon of the
fulvene ligand, see also Table 2).
1.396(5)
28.4
1.416(8)
30.4
The formal titanocene moieties [(η5-C5Me5)Ti(η6-
C5H4=CR2)] are canted towards each other, forming a dihe-
dral angle of 3.2° in 6 and 19.1° in 8 between the planes
defined by the metallocene wedges, respectively (a value of
20.0° was found for the second molecule of 8 in the asym-
metric unit). This is again in the same range as it was ob-
served for similar complexes as, for example, in the case
of [{(η5-C5H3(SiMe3)2)2Ti}2(µ2,η1,η1-N2)] where a dihedral
angle of 9.6° was found.[7]
0
0
34.9
0
28.2
139.0
138.7
32.8
138.8
138.8
Ct*–Ti–CtFv [a]
150.9
[a] Ct*: ring centroid of C5Me5 ligand; CtFv: ring centroid of Ci,
Ca, CЈa, Cb, CЈb.
However, this behaviour is different from that of the
Ti(II) dinitrogen complexes showing twisted metallocene
units [{(η5-C5Me5)2Ti}2(µ2,η1,η1-N2)] (av. 90°)[33] and [{(η5-
C5H5)2Ti(PMe3)}2(µ2,η1,η1-N2)] (P–Ti–Ti–P 109°).[9] A ne-
arly perpendicular twist was found also for tantalum–dini-
trogen
complexes
[{(η5-C5Me5)2TaCl}2(µ2,η1,η1-N2)]
(90.8°).[34] Nevertheless, structural parameters that are com-
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1005

R. Beckhaus et al.
FULL PAPER
parable to those of 6 and 8 were found in the case of the
diamagnetic TiIII derivative [{(η5-C5H5)2Ti(p-Tol)}2-
(µ2,η1,η1-N2)][11] exhibiting a coplanar arrangement of
both aryl groups and the centrosymmetric titanocene com-
plex [{(η5-C5Me4 H)2Ti}2(µ2,η1,η1-N2)].[8]
Indeed, the N2 coordination in our complexes is compar-
atively weak, and nitrogen is thus released quantitatively
under reduced pressure or vacuum (0.49 moles per mole of
Ti), forming the paramagnetic fulvene complex 9 [Equa-
tion (2)], characterized by elementary analysis (C30H33Ti
(Mτ = 441.47 gmol–1): calcd. C 81.62, H 7.53; found: C
81.46, H 7.42). This observation is confirmed by MS analy-
sis (EI, 70 eV) of 6, 7, and 8, where only the monomeric
[(η5-C5Me5)Ti(η6-C5H4=CR2)] units are detectable.
Figure 3. Solid-state structure of 10 (50% probability ellipsoids).
Selected bond lengths [Å] and angles [°]: Ti(1)–C(1) 2.116(2), Ti(1)–
C(2) 2.220(2), Ti(1)–C(9) 2.350(3), Ti(1)–C(3) 2.360(3), Ti(1)–C(4)
2.461(2), Ti(1)–C(10) 2.351(2), C(1)–C(10) 1.465(3), C(1)–C(2)
1.449(4), C(1)–C(9) 1.465(3), C(2)–C(3) 1.401(3), C(4)–C(9)
1.437(4), C(3)–C(4) 1.414(4), C(5)–C(6) 1.355(4), C(6)–C(7)
1.415(4), C(7)–C(8) 1.367(4), C(8)–C(9) 1.408(4), Ti(1)–Ct(1)
2.006(3), Ti(1)–Ct(2) 1.956(3), Θ 34.9, Ct(1)–Ti(1)–Ct(2) 150.9
[Ct(1) = Centroid of Cp*, Ct(2) = centroid of the fulvene ring, Θ
= tilt of C(10) out of the plane of C(1)–C(9)].
(2)
Unfortunately, crystals of 9 suitable for X-ray diffraction
were not available up to now. However, using 5 instead of
2 under the reaction conditions described in Equation (1),
the nitrogen-free fulvene complex 10 became available in a
one-step synthesis. The low-coordinated complex 10 [Equa-
tion (3)] was isolated in the form of black, needle-shaped
crystals (85%). In the mass spectrum, the peak of the mol-
ecular ion (m/z 491) was observed as the base peak. Suitable
crystals for X-ray structure determination were obtained
from n-hexane solutions at –20 °C. Due to the paramag-
netic behaviour of the complex caused by the odd number
of electrons at the titanium, it was not possible to record
NMR spectra with distinct signals.
Figure 4. Solid-state structure of 5 (50% probability ellipsoids). Se-
lected bond lengths [Å] and angles [°]: C(1)–C(10) 1.359(2), C(1)–
C(2) 1.467(2), C(1)–C(9) 1.488(2), C(2)–C(3) 1.340(3), C(3)–C(4)
1.454(2), C(4)–C(5) 1.390(3), C(4)–C(9) 1.416(2), C(5)–C(6)
1.382(3), C(6)–C(7) 1.387(3), C(7)–C(8) 1.390(3), C(8)–C(9)
1.387(2).
(3)
The molecular structure of 10 is given in Figure 3. The
structure of the free ligand 5 was determined for compari- by the formation of a dianionic fulvene ligand coordinated
son by X-ray diffraction (Figure 4). Selected structural in a π-η5:σ-η1 manner.[31,30] Thus, the five-membered ring
parameters are summarized in Table 2.
of the pentafulvene becomes aromatic, the Ci–Ce bond is
Due to the two quite different π-ligands, (η5-C5Me5) and elongated, and the Ce atom is bent out of the ring plane (Θ,
(η6-C5H4=CR2), in 6 and 8 the bonding situation is remark- see footnote Table 2). A comparison of the structural data
ably different compared to bent-titanocene-derived dinitro- of the free ligands 2,[30] 4[35] and 5 with the titanium com-
gen complexes. The complexation of pentafulvenes to low- plexes 6, 8 and 10 is given in Table 2. The exocyclicCi–Ce
valent titanium fragments is generally assumed to be ac- distances in
2 [1.359(2) Å], 4 5
[1.342(2) Å][35] and
companied by electron transfer to the π-acceptor ligand. [1.359(2) Å] are elongated to av. 1.436 Å (6), av. 1.434 Å
This leads to a situation that can probably be best described (8) and 1.465(3) Å (10) after complexation. The strongest
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Low-Valent Titanium–Pentafulvene Complexes
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elongation and, simultaneously, the shortest Ti–Ce bond Table 3. Selected 1H- (C6D6, 500 MHz, 300 K) and 13C NMR spec-
troscopic data (C6D6, 125 MHz, 300 K) of 6, 7 and 8, compared
lengths [2.351(2) Å] were observed in the mononuclear tita-
with 2,[30] 3 and 4[47] (assignment of the proton and carbon signals
nium complex 10. On the other hand, the Ti–Ce distances
in accordance with footnote[b] in Table 2).
in 6 and 8 were found to be av. 2.606 Å and av. 2.491 Å. A
comparable value was found for [(η5-C5Me5)Ti(η6-
6
2
7
3
8
4
C5H4=C(p-tol)2)Cl] [2.535(5) Å].[30] In fulvene complexes 1H NMR data
substituted with one or two protons at the Ce-atom of the
fulvene ligand, Ti–Ce distances close to typical bond
lengths between titanium and sp3-hybridized C-atoms were
found as in [(η5-C5Me5)Ti(η6-C5Me4=CH2)] [2.281(14) Å][36]
and [(η5-C5Me5)Ti(η6-C5H4=CH(tBu))Cl] [2.355(2) Å].[31]
The fulvene ligands in 6, 8 and 10 show characteristic devia-
tions (Θ) of the Ce-atom from the plane of the five-mem-
bered ring (6 av. 28.3°, 8 av. 31.6°, 10 34.9°). The Ct*–Ti–
CtFv angles of 6 (av. 138.8°) and 8 (138.8°) were found in a
typical range of bent-titanocene derivatives[37] {TiIV: [(η5-
C5Me5)(η5-C5H5)TiCl2] 132.0°,[38] TiIII: [(η5-C5Me4H)2-
TiCl] 139.1°,[39] [(η5-C5Me5)2TiCl] 143.6°[40]}. In contrast,
the Ct*–Ti–Ct* angles in permethylated titanium() com-
plexes are usually significantly larger {[{(η5-C5Me5)2-
Ha
4.38
6.57
4.17
6.29
3.64
6.66
(m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H)
3.98 6.57 3.87 6.29 4.20 6.66
(m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H)
4.79 6.65 4.86 6.58 5.10 6.61
(m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H)
4.07 6.65 4.17 6.58 5.69 6.61
(m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H) (m, 2 H) (m, 1 H)
HЈa
Hb
HЈb
13C NMR data
Ce
Ca
CЈa
Cb
CЈb
108.5
104.0
106.5
111.9
108.4
152.2
124.8
124.8
132.4
132.4
105.7
104.1
105.9
112.3
108.0
149.0
124.4
124.4
133.2
133.2
107.9
103.2
104.5
113.3
103.7
164.8
119.8
119.8
131.0
131.0
Ti}2(µ2,η1,η1-N2)]
145.7(3)°,[33]
[(η5-C5Me5)2Ti(CO)2]
[(η5-C5Me5)Ti(η6-C5H4=C(p-tol)2)Cl][30] and [(η5-C5Me5)-
Ti(η6-C5H4=C(p-C6H4F)2)Cl][46], where a fast rotation of
the fulvene ligand was observed under similar conditions.
Obviously, a free rotation of the fulvene ligand is hindered
by the dimeric structure, although the Ti–Ce distances are
in a similar range. NOE measurements at room temperature
indicate that the favoured isomer C (Scheme 1) in the solid
state is also found in benzene solution because strong NOE
contacts were observed between fulvene ring protons HЈb–
HЈa of 8 which do not only result from the interaction of
these protons attached to one fulvene ring but also from
the interaction of protons attached to different fulvenes.
147.9°[41]}. Also, in the case of the bulky fulvene complex
10 a larger value of 150.9° was found. Compared to free
fulvene 5, the two double bonds of the six-membered ring
are significantly shortened from av. 1.39 Å to av. 1.36 Å in
10 and therefore seem to be more localised, indicating a loss
of aromaticity. This is in agreement with an η5 complex-
ation mode of the five-membered ring, thus no hints for a
typical indenyl effect are found.[42,43]
The isolated dinitrogen complexes 6, 7, and 8 showed
diamagnetic behaviour, which allowed a complete NMR
spectroscopic characterization (Table 3). The magnetic be-
haviour is comparable to the titanium()–dinitrogen com-
plex [{(η5-C5H5)2Ti(p-tol)}2(µ2,η1,η1-N2)].[44] On the other
hand the titanium()–dinitrogen complexes like [{(η5-
C5Me5)2Ti}2(µ2,η1,η1-N2)] are often paramagnetic com-
pounds (µeff = 2.18 BM per titanium atom[33]), showing
broad downfield-shifted signals at room temperature[45] and
Conclusion
An efficient type of one-step synthesis of end-on bridged
dinuclear cyclopentadienyltitaniumfulvene complexes was
presented. These complexes are formed in high yields from
[(η5-C5Me5)TiCl3], bulky substituted pentafulvenes, and so-
dium amalgam as reducing agent under nitrogen. Along the
Ti–NϵN–Ti axis the C5Me5 as well as the fulvene ligands
are arranged in a stereoregular manner. The weak acti-
vation of the dinitrogen ligand suggests that the dinuclear
[(η5-C5Me5)Ti(η6-C5H4=CR2)] dinitrogen complexes serve
as synthons for interesting titanocenes, derived from the
displacement of the nitrogen molecule in combination with
the known possibilities to functionalize the strongly nucleo-
philic exocyclic carbon atom of the fulvene ligand by elec-
trophilic attack.
1
dynamic properties in solutions. In such a way, detailed H
NMR measurements of [{(η5-C5Me5)2Ti(N2)}2(µ2,η1,η1-
N2)] in [D8]toluene at low temperatures (–78 to –42 °C) are
in full accord with an η5-C5Me5 ring site exchange.[13]
However, strong upfield shifts of proton and carbon sig-
nals, e.g. of up to 3 ppm for Ha of 8, clearly show the pres-
ence of low-valent titanium complexes. This is especially
pronounced for the exocyclic fulvene carbon atoms of all
titanium complexes compared to the free ligands. Interest-
ingly, the signals for these carbons were found at almost
the same chemical shifts in all complexes although the free
fulvenes do show significant differences. Furthermore, a
complete loss of symmetry indicated by separated signals
for all protons and carbons of the fulvenes in the dinuclear
titanium complexes compared to the highly symmetrical
fulvenes themselves and the absence of saturation transfer
phenomena clearly show the formation of conformationally
rigid dinitrogen complexes in benzene solution at room
temperature. This is in sharp contrast to the conformational
behaviour found for the mononuclear fulvene complexes
Experimental Section
General Remarks: All operations were performed under nitrogen
with rigorous exclusion of oxygen and moisture by using glove box
or Schlenk techniques. Solvents were thoroughly dried and satu-
rated with nitrogen. 1H- and 13C NMR spectra were recorded with
a
Bruker AVANCE 500 spectrometer (1H, 500.1 MHz; 13C
Eur. J. Inorg. Chem. 2005, 1003–1010
www.eurjic.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1007

R. Beckhaus et al.
FULL PAPER
125.8 MHz) or a Bruker AVANCE 300 spectrometer for 19F-
= 12.4 [C5(CH3)5], 104.1 (Ca), 105.7 (Cexo), 105.9 (CЈa), 108.0 (CЈb),
112.3 (Cb), 114.0 [C5(CH3)5], 114.6 (outer C4H6F, d, 2JC,F = 21 Hz),
114.7 (inner C4H6F, d, JC,F = 21 Hz), 125.4 (Ci), 133.5 (outer
(282.4 MHz) and H- or 13C nuclei. The H NMR chemical shifts
were referenced to residual protons of the solvent. The 13C NMR
spectra were referenced to the signals of the solvent. The 19F NMR
spectra were referenced externally to CFCl3. Assignment of the sig-
nals was done on the basis of 1H, 13C, H,H-COSY, HMQC,
HMBC, and sel-1D NOESY NMR experiments.[48] Electron im-
pact (EI) mass spectra were taken with a Finnigan-MAT 95 Spec-
trometer. IR spectra were recorded with a BIO-RAD FTS-7 Spec-
trometer by using KBr pellets. Elemental analyses were carried out
by the Analytischen Laboratorien in Lindlar (Germany). [(η5-
C5Me5)TiCl3] (1) was prepared according to the literature.[49] So-
dium amalgam was purchased as 20% pellets from Aldrich. The
fulvenes 2 and 3 were prepared according to general literature pro-
cedures.[48,50] 5[48,51] was obtained in a similar way under only
slightly modified conditions. Compound 4 was prepared according
to the literature.[47,48]
1
1
2
3
3
C4H6F, d, JC,F = 8 Hz), 133.5 (inner C4H6F, d, JC,F = 8 Hz),
4
140.4 (outer i-C6H4-C6, d, JC,F = 3 Hz), 142.8 (inner i-C6H4-C6,
4
1
d, JC,F = 3 Hz), 159.9 (outer i-C6H4-F, d, JC,F = 244 Hz), 162.2
(inner i-C6H4-F, d, JC,F = 244 Hz) ppm. 19F NMR (282.4 MHz,
1
C6D6, 303 K): δ = –115.8 (2F) ppm.- MS (CI, isobutane): m/z (%)
= 938 (65) [469 × 2], 469 (100) [M+ – N2 – Cp*Ti(p-Ffv) + HF],
450 (20) [M+ – N2 – Cp*Ti(p-Ffv) + H]. C56H54F4N2Ti2 (926.81):
calcd. C 72.57, H 5.87, N 3.02; found C 72.16, H 6.11, N 2.37.
[Bis{(η6-adamantylidenepentafulvene)(η5-pentamethylcyclo-
pentadienyl)titanium}-µ2-η1,η1-dinitrogen] (8): Sodium amalgam
(2.38 g, 20% Na, 20.73 mmol Na), adamantylidenepentafulvene 4
(1.37 g, 6.91 mmol) and [(η5-C5Me5)TiCl3] (1) (2.00 g, 6.91 mmol)
were placed in a Schlenk tube. At a temperature of 0 °C (ice bath)
THF (100 mL) was added under an excess nitrogen pressure of
200 mbar. The reaction mixture was stirred for 16 h. A colour
change from red to dark blue occurred. The reaction mixture was
filtered twice (first P4/Celite, then P5). Removing the solvent under
vacuum led to a turquoise residue, which became dark blue again
after adding N2. After recrystallisation from n-hexane (20 mL) at
–20 °C, 8 could be isolated as dark blue crystals with a cupric lus-
tre. Yield: 2.46 g (90%). M.p. 175 °C. 1H NMR (500.1 MHz, C6D6,
300 K):[48] δ = 1.75 (s, 30 H, C5(CH3)5), 1.48–2.53 (m, 28 H,
HAdamantyl), 3.64 (m, 2 H, Ha), 4.20, (m, 2 H, HЈa), 5.10 (m, 2 H,
Hb), 5.69 (m, 2 H, HЈb) ppm. 13C NMR (125.8 MHz, C6D6,
300 K):[48] δ = 12.3 [C5(CH3)5], 29.2, 30.2, 34.1, 34.9, 38.2, 38.8,
39.0, 43.4, 45.4 (CAdamantyl), 103.2 (Ca), 103.7 (CЈb), 104.5 (CЈa),
113.3 (Cb), 107.9 (Ce), 112.8 [C5(CH3)5], 125.2 (Ci) ppm. MS
(70 eV): m/z (%) = 381 (100) [M+ – N2 – Cp*Ti{C5H4(C10H14)}].
C50H66N2Ti2 (790.85): calcd. C 75.94, H 8.41, N 3.54; found C
75.76, H 8.45, N 3.47.
[Bis{[η6-6,6-bis(p-tolyl)pentafulvene](η5-pentamethylcyclopentadi-
enyl)titanium}-µ2,η1,η1-dinitrogen] (6): Sodium amalgam (2.38 g,
20 % Na, 20.73 mmol Na), di-para-tolylfulvene (2) (1.78 g,
6.91 mmol) and [(η5-C5Me5)TiCl3] (1) (2.00 g, 6.91 mmol) were
placed in a Schlenk tube. At a temperature of 0 °C (ice bath) of
THF (100 mL) was added under an excess nitrogen pressure of
200 mbar. The reaction mixture was stirred for 16 h. A colour
change from red to dark green occurred. The reaction mixture was
filtered twice (first P4/Celite, then P5). Removing the solvent under
vacuum led to a brown residue, which became dark green again
after adding N2. After recrystallisation from of n-hexane (50 mL)
at –20 °C, complex 6 could be isolated as dark green crystals show-
ing a cupric lustre. Yield: 2.83 g (90%). M.p. 125 °C. 1H NMR
(500.1 MHz, C6D6, 300 K):[48] δ = 1.69 [s, 30 H, C5(CH3)5], 2.14 (s,
6 H, outer CH3), 2.16 (s, 6 H, inner CH3), 3.98 (m, 2 H, HЈa), 4.07
(m, 2 H, HЈb), 4.38 (m, 2 H, Ha), 4.79 (m, 2 H, Hb), 6.83 (m, 4 H,
inner C6H4), 6.92 (m, 4 H, outer C6H4), 6.98 (m, 4 H, inner C6H4),
7.28 (m, 4 H, outer C6H4) ppm. 13C NMR (125.8 MHz, C6D6,
300 K):[48] δ = 12.5 [C5(CH3)5], 21.0 (each C6H4-CH3), 104.0 (Ca),
106.5 (CЈa), 108.4 (CЈb), 108.5 (Ce), 111.9 (Cb), 113.5 [C5(CH3)5],
125.6 (Ci), 126.3 (outer C6H4), 128.5 (outer C6H4), 128.8 (inner
C6H4), 132.0 (outer i-C6H4-C6), 132.2 (inner C6H4), 133.9 (inner i-
C6H4-CH3), 141.7 (outer i-C6H4-C6), 144.1 (inner i-C6H4-C6) ppm.
[{η6-10,10-Bis(p-tolyl)benzofulvene}(η5-pentamethylcyclopentadi-
enyl)titanium] (10): Sodium amalgam (2.38 g, 20% Na, 20.73 mmol
Na), di-p-tolylbenzofulvene (5) (2.13g, 6.91 mmol) and [(η5-C5Me5)
TiCl3] (1) (2.00 g, 6.91 mmol) were placed in a Schlenk tube. At a
temperature of 0 °C (ice bath) THF (100 mL) was added under an
excess nitrogen pressure of 200 mbar. The reaction mixture was
stirred for 16 h. A colour change from red to brownish green oc-
curred. The reaction mixture was filtered twice (first P4/Celite, then
P5). Removing the solvent under vacuum led to a brown residue,
which was recrystallised from n-hexane (20 mL) at –20 °C. Com-
pound 10 could be isolated as black needle-shaped crystals. Yield:
2.8 g (85%). M.p. 115 °C. MS (70 eV): m/z (%) = 491 (100) [M+],
308 (80) [di-para-tolylbenzofulvene+]. C34H35Ti (491.51): calcd. C
83.08, H 7.18; found C 83.04, H 7.21.
IR (KBr): ν = 2915 (m), 2859 (m), 2745 (m), 1894 (w), 1746, 1605,
˜
1505 (s), 1460 (s), 1375 (s), 1296, 1260 (w), 1159, 1103, 1067, 1020
(m), 905, 804, 731 cm–1. MS (70 eV): m/z (%) = 441 (100) [M+
–
N2 – Cp*Ti(p-Tolfv)], 307 (28). C60H66N2Ti2 (910.56): calcd. C
79.11, H 7.30, N 3.08; found C 78.93, H 7.42, N 3.05.
[Bis{[η6-6,6-bis(p-fluorophenyl)pentafulvene](η5-pentamethylcyclo-
pentadienyl)titanium}-µ2-η1,η1-dinitrogen] (7): Sodium amalgam
(2.38 g, 20% Na, 20.73 mmol Na), di-para-fluorofulvene 3 (1.84 g,
6.91 mmol) and [(η5-C5Me5)TiCl3] (1) (2.00 g, 6.91 mmol) were
placed in a Schlenk tube. At a temperature of 0 °C (ice bath) THF
(100 mL) was added under an excess nitrogen pressure of 200 mbar.
The reaction mixture was stirred for 16 h. A colour change from
red to dark green occurred. The reaction mixture was filtered twice
(first P4/Celite, then P5). Removing the solvent under vacuum led
to a brown residue, which became dark green again after adding
N2. After recrystallisation from n-hexane (20 mL) at –20 °C, 7
could be isolated as dark green crystals with a cupric lustre. Yield:
Di-p-tolylbenzofulvene (5): During 30 minutes, nBuLi (40.5 mL,
1.6 ) was added dropwise to a cooled solution (0 °C) of freshly
distilled indene (9.8 mL, 0.082 mol) in THF (170 mL). The mixture
was cooled to –60 °C, and 4,4Ј-dimethylbenzophenone (17.24 g,
0.082 mol) dissolved in THF (120 mL) was added. The reaction
mixture was stirred overnight at room temperature. Then, water
and diethyl ether were added, and the ether phase was extracted
with water until pH 7 was reached. The ether phase was dried with
MgSO4, and the solvent was evaporated. After that the residue was
2.56 g (80 %). M.p. 138–140 °C. 1H NMR (500.1 MHz, C6D6, dissolved in n-hexane (200 mL) and cooled rapidly. The precipi-
300 K):[48] δ = 1.56 [s, 30 H, C5(CH3)5], 3.87 (m, 2 H, HЈa), 4.17 tated crystalline solid was filtered and dried. Finally, the product
(m, 4 H, Ha and HЈb), 4.86 (m, 2 H, Hb), 6.68 [m, J = 8.1 Hz, 4 could be isolated as orange crystals after recrystallisation from n-
H, 3J(H,F) = 8.5 Hz, inner C4H6F], 6.75 (m, J = 8.4 Hz, 4 H, 3JH,F
= 8.5 Hz, outer C4H6F), 6.81 (m, 4 H, inner C4H6F), 7.05 (m, 4
hexane/dichloromethane (2:1). Yield: 19.0 g (75 %). M.p. 130–
1
131 °C. H NMR (500 MHz, CDCl3, 300 K):[48] δ = 2.46 (s, 3 H,
H, outer C4H6F) ppm. 13C NMR (125.8 MHz, C6D6, 300 K):[48]
δ
H-20), 2.52 (s, 3 H, H-15), 6.75 (m, 1 H, H-2), 6.79 (m, 1 H, H-8),
1008
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2005, 1003–1010

Low-Valent Titanium–Pentafulvene Complexes
FULL PAPER
Table 4. Crystal structure data for compounds 6, 8, 10 and 5.
6
8
10
5
Empirical formula
Formula mass
C66 H80 N2 Ti2
997.12
C50 H66 N2 Ti2
790.85
C34 H35 Ti
491.52
C24 H20
308.40
Diffractometer
Crystal dimensions [mm]
Colour, habit
Crystal system
a [Å]
b [Å]
c [Å]
α [°]
STOE IPDS
0.45×0.38×0.36
dark green, red
triclinic
11.0985(6)
12.9268(5)
19.5985(10)
86.095(5)
STOE IPDS
0.52×0.04×0.04
dark blue, red
monoclinic
29.2685(18)
10.0234(4)
29.713(2)
90
104.619(8)
90
8434.7(9)
P21/n
STOE IPDS
0.30×0.16×0.13
black
STOE IPDS
0.21×0.19×0.18
orange
triclinic
triclinic
8.1648(5)
12.5378(9)
13.9286(10)
74.338(8)
74.302(8)
77.604(8)
1306.19(15)
9.2556(10)
9.3584(12)
11.0345(14)
71.141(14)
67.960(13)
85.793(14)
837.12(18)
β [°]
87.996(6)
81.364(5)
γ [°]
V [Å]3
2772.6(2)
¯
¯
P1
¯
P1
Space group
P1
Z
2
8
2
2
Dcalcd [Mg·m–3]
1.194
0.330
1.246
0.415
1.250
0.348
1.224
0.069
µ [mm–1]
F(000)
λ (Mo-Kα, graphite) [Å]
Temperature [K]
θ range for data collection [°]
Number of reflections collected
Number of observed reflections [I Ͼ
2σ(I)]
1068
3392
0.71073
193(2)
2.09 to 26.06
69268
5786
522
328
0.71073
193(2)
2.11 to 25.90
33979
6285
0.71073
193(2)
2.62 to 25.97
16076
3308
0.71073
193(2)
2.30 to 26.02
10252
1760
Number of independent reflections
Absorption correction method
Max. and min. transmission
Number of data/restraints/parameters
R indices (all data)
10040
none
15703
none
4750
none
3057
None
0.8906 and 0.8659
10040/27/634
R1 = 0.0868,
wR2 = 0.1370
R1 = 0.0510,
wR2 = 0.1245
0.908
0.9836 and 0.8131
15703/0/973
R1 = 0.1626,
wR2 = 0.1392
R1 = 0.0494,
wR2 = 0.0946
0.601
0.9562 and 0.9028
4750/0/316
R1 = 0.0693,
wR2 = 0.1131
R1 = 0.0427,
wR2 = 0.1047
0.958
0.9877 and 0.9857
3057/0/297
R1 = 0.0824,
wR2 = 0.0770
R1 = 0.0374,
wR2 = 0.0680
0.816
Final R indices [I Ͼ 2σ(I)]
GoF on F2
Largest difference peak and hole
0.556 and –0.383
0.307 and –0.280
0.414 and –0.424
0.160 and –0.161
[e·Å–3]
6.94 (m, 1 H, H-3), 6.94 (m, 1 H, H-7), 7.20 (m, 1 H, H-6) 7.24
(m, 2 H, H-18), 7.27 (m, 2 H, H-17), 7.30 (m, 2 H, H-13), 7.34 (m, 2
H, H-12), 7.35 (m, 1 H, H-5) ppm. 13C NMR (125.8 MHz, CDCl3,
300 K):[48] δ = 21.3 (C-20), 21.4 (C-15), 120.7 (C-5), 123.4 (C-8),
124.3 (C-7), 126.8 (C-6), 128.5 (C-18), 129.2 (C-13), 130.4 (C-12),
130.7 (C-2, C-3), 131.7 (C-17), 136.0 (C-4), 138.1 (C-19*), 138.2
(C-9*), 138.4 (C-14), 138.7 (C-11), 139.7 (C-16), 144.3 (Ci), 147.4
(Ce) ppm (*assignment might be interchanged).
Acknowledgments
We thank the Fonds der Chemischen Industrie for a kindly granted
scholarship (A. S.).
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5 were collected on a STOE-IPDS diffractometer with graphite-
monochromated Mo-Kα radiation (λ = 0.71073 Å). A summary of
crystal data and intensity collection and refinement parameters is
reported in Table 4. Intensity measurements were performed at
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page of this article).
Eur. J. Inorg. Chem. 2005, 1003–1010
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1009

R. Beckhaus et al.
FULL PAPER
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