Synthesis and structure of the first homoleptic 1-Aza-1,3-diene titanium complex: A tightrope walk between ligand coordination and ligand coupling

Article abstract of DOI:10.1021/om0341956

The reaction of TiCl₄(THF)₂ or ZrCl₄(THF)₂ with Mg in the presence of 1-aza-1,3-dienes (1) has been investigated. Reduction of TiCl₄(THF)₂ with 2 equiv of Mg in the presence of 2 equiv of (R¹)N=CHC(R²)=CH(Ph) yields the first homoleptic 1-aza-1,3-diene complex, [Ti-{N(R¹)CH=C(R²)CH(Ph)}₂] (7), but only if the 1-aza-1,3-diene is substituted by a sterically demanding group at the nitrogen atom (1b: R¹ = C₆H₃-2,6-iPr₂, R² = H). X-ray crystallography indicates a σ²,π coordination of the heterodienes, which are reduced to 1-azabut-2-ene-1,4-diyl dianions to form folded 1-aza-2-titanacyclopent-4-ene rings. As a byproduct, the bicyclic complex [{N(R¹)CH=C(R²)CH(Ph)}Ti{N(R¹) CH=C(R²)CH(Ph)CH{C(R²)=CH- (Ph)}N(R¹)] (8) was isolated, which is believed to arise from C=N insertion of 1b into the Ti-C bond of the intermediate [{N(R¹)CH=C(R²)CH(Ph)} TiCl₂], followed by the coordination of a further 1-aza-1,3-diene ligand. The analogous bicyclic zirconium complex [{N(R¹)CH= C(R²)CH(Ph)}ZrN{(R¹)CH=C(R²)CH(Ph) CH{C(R²)=CH(Ph)N(R¹)] (6: R¹ = cyclo-C₆H₁₁, R² = Me) is the only available product when the reduction of ZrCl₄(THF)₂ is performed in the presence of the 1-aza-1,3-diene (cyclo-C₆H₁₁)N=CHC(Me)=CHPh (1a), which is substituted by a sterically less demanding group at the terminal nitrogen atom. Addition of 2 equiv of benzophenone to 7 affords the titanium complex [Ti{OCPh₂CH(Ph)C(R²)=CHN(R¹)}₂] (9). The solid-state structure of 9 shows the titanium in a distorted-tetrahedral environment, being the center of two folded oxazatitanacycloheptene rings.

Full text of DOI:10.1021/om0341956

1594
Organometallics 2004, 23, 1594-1603
Syn th esis a n d Str u ctu r e of th e F ir st Hom olep tic
1-Aza -1,3-d ien e Tita n iu m Com p lex: A Tigh tr op e Wa lk
betw een Liga n d Coor d in a tion a n d Liga n d Cou p lin g†
J oachim Scholz,*,‡ Steffen Kahlert,§ and Helmar Go¨rls|
Institute of Sciences, Department of Chemistry, University of Koblenz-Landau,
Universita¨tsstrasse 1, D-56070 Koblenz, Germany, Bayer AG, CH-P-PSA, Building N60,
D-47812 Krefeld, Germany, and Institute of Inorganic and Analytical Chemistry,
Friedrich-Schiller-Universita¨t J ena, August-Bebel-Strasse 2, D-07743 J ena, Germany
Received September 25, 2003
The reaction of TiCl4(THF)2 or ZrCl4(THF)2 with Mg in the presence of 1-aza-1,3-dienes
(1) has been investigated. Reduction of TiCl4(THF)2 with 2 equiv of Mg in the presence of 2
equiv of (R1)NdCHC(R2)dCH(Ph) yields the first homoleptic 1-aza-1,3-diene complex, [Ti-
{N(R1)CHdC(R2)CH(Ph)}2] (7), but only if the 1-aza-1,3-diene is substituted by a sterically
demanding group at the nitrogen atom (1b: R1 ) C6H3-2,6-iPr2, R2 ) H). X-ray crystal-
lography indicates a σ2,π coordination of the heterodienes, which are reduced to 1-azabut-
2-ene-1,4-diyl dianions to form folded 1-aza-2-titanacyclopent-4-ene rings. As a byproduct,
the bicyclic complex [{N(R1)CHdC(R2)CH(Ph)}Ti{N(R1)CHdC(R2)CH(Ph)CH{C(R2)dCH-
(Ph)}N(R1)] (8) was isolated, which is believed to arise from CdN insertion of 1b into the
Ti-C bond of the intermediate [{N(R1)CHdC(R2)CH(Ph)}TiCl2], followed by the coordination
of a further 1-aza-1,3-diene ligand. The analogous bicyclic zirconium complex [{N(R1)CHd
C(R2)CH(Ph)}Zr{N(R1)CHdC(R2)CH(Ph)CH{C(R2)dCH(Ph)}N(R1)] (6: R1 ) cyclo-C6H11, R2
) Me) is the only available product when the reduction of ZrCl4(THF)2 is performed in the
presence of the 1-aza-1,3-diene (cyclo-C6H11)NdCHC(Me)dCHPh (1a ), which is substituted
by a sterically less demanding group at the terminal nitrogen atom. Addition of 2 equiv of
benzophenone to 7 affords the titanium complex [Ti{OCPh2CH(Ph)C(R2)dCHN(R1)}2] (9).
The solid-state structure of 9 shows the titanium in a distorted-tetrahedral environment,
being the center of two folded oxazatitanacycloheptene rings.
In tr od u ction
complexes the variety of products in these organome-
tallic reactions is even enhanced, as not only the s-cis-
diene complexes but also unsaturated η2-diene com-
plexes often are the actual reacting species.5 These are
intermediates in the isomerization pathway between
s-cis-diene and s-trans-diene complexes.
Increasing development in the chemistry of 1,3-diene
complexes of early transition metals over the last
several years has been due to their potential applicabil-
ity both as synthons in various organic reactions and
as catalysts in polymerization reactions.21-2 The M-C
bonds in metal s-cis-diene complexes mostly exhibit
highly polarized σ-bonding character.3 Therefore, 1,3-
diene complexes of early transition metals undergo a
large number of highly selective carbometalations both
with unsaturated hydrocarbons and with polar electro-
philes containing C-O or C-N multiple bonds.4 Fur-
thermore, in case of the group 4 metallocene diene
(3) (a) Erker, G.; Engel, K.; Kru¨ger, C.; Mu¨ller, G. Organometallics
1984, 3, 128-133. (b) Erker, G.; Kru¨ger, C.; Mu¨ller, G. Adv. Organomet.
Chem. 1985, 24, 1-39. (c) Yasuda, H.; Tatsumi, K.; Okamoto, T.;
Mashima, K.; Lee, K.; Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N.
J . Am. Chem. Soc. 1985, 107, 2410-2422. (d) Kru¨ger, C.; Mu¨ller, G.;
Erker, G.; Dorf, U.; Engel, K. Organometallics 1985, 4, 215-223. (e)
Blenkers, J .; Hessen, B.; van Bolhuis, F.; Wagner, A. J .; Teuben, J . H.
Organometallics 1987, 6, 459-469. (f) Okamoto, T.; Yasuda, H.;
Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N. J . Am. Chem. Soc.
1988, 110, 5008-5017. (g) Okamoto, T.; Yasuda, H.; Nakamura, A.;
Kai, Y.; Kanehisa, N.; Kasai, N. Organometallics 1988, 7, 2266-2273.
(h) Yamamoto, H.; Yasuda, H.; Tatsumi, K.; Lee, K.; Nakamura, A.;
Chen, J .; Kasai, N. Organometallics 1989, 8, 105-119.
(4) (a) Erker, G.; Engel, K.; Atwood, J . L.; Hunter, W. E. Angew.
Chem. 1983, 95, 506-507; Angew. Chem., Int. Ed. Engl. 1983, 22, 494-
495. (b) Akita, M.; Matsuoka, K.; Asami, K.; Yasuda, H.; Nakamura,
A. J . Organomet. Chem. 1987, 327, 193-209. (c) Yasuda, H.; Okamoto,
T.; Matsuoka, Y.; Nakamura, A.; Kai, Y.; Kanehisa, N.; Kasai, N.
Organometallics 1989, 8, 1139-1152. (d) Erker, G.; Pfaff, R.; Kru¨ger,
C.; Nolte, M.; Goddard, R. Chem. Ber. 1992, 125, 1669-1673. (e) Erker,
G.; Pfaff, R.; Kowalski, D.; Wu¨rthwein, E.-U.; Kru¨ger, C.; Goddard, R.
J . Org. Chem. 1993, 58, 6771-6778. (f) Ho¨ltke, C.; Erker, G.; Kehr,
G.; Fro¨hlich, R.; Kataeva, O. Eur. J . Inorg. Chem. 2002, 2789-2799.
(5) (a) Erker, G.; Engel, K.; Dorf, U.; Atwood, J . L.; Hunter, W. E.
Angew. Chem. 1982, 94, 915-916; Angew. Chem., Int. Ed. Engl. 1982,
21, 913-914. (b) Kai, Y.; Kanehisa, N.; Miki, K.; Kasai, N.; Mashima,
K.; Nagasuna, K.; Yasuda, H.; Nakamura, A. Chem. Lett. 1982, 1979-
1982. (c) Erker, G.; Dorf, U.; Benn, R.; Reinhardt, R.-D. J . Am. Chem.
Soc. 1984, 106, 7649-7649.
* To whom correspondence should be addressed. E-mail: scholz@
uni-koblenz.de.
† Monoazadiene Complexes of Early Transition Metals. 5. Part 4:
ref 1.
‡ University of Koblenz-Landau.
§ Bayer AG, Krefeld.
| University of J ena.
(1) Part 4: Lorenz, V.; Go¨rls, H.; Scholz, J . Angew. Chem. 2003, 115,
2356-2360; Angew. Chem., Int. Ed. Engl. 2003, 42, 2253-2257.
(2) (a) Yasuda, H.; Tatsumi, K.; Nakamura, A. Acc. Chem. Res. 1985,
18, 120-126. (b) Nakamura, A.; Tatsumi, K.; Yasuda, H. In Stereo-
chemistry of Organometallic and Inorganic Compounds; Bernal, I., Ed.;
Elsevier: Amsterdam, 1986; Vol. I, Chapter 1, pp 1-46. (c) Yasuda,
H.; Nakamura, A. Angew. Chem. 1987, 99, 745-764; Angew. Chem.,
Int. Ed. Engl. 1987, 26, 723-742. (d) Nakamura, A.; Mashima, K. J .
Organomet. Chem. 1995, 500, 261-267. (e) Mashima, K.; Fujikawa,
S.; Tanaka, Y.; Urata, H.; Oshiki, T.; Tanaka, E.; Nakamura, A.
Organometallics 1995, 14, 2633-2640.
10.1021/om0341956 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 02/25/2004

The First Homoleptic 1-Aza-1,3-diene Ti Complex
Organometallics, Vol. 23, No. 7, 2004 1595
Ch a r t 1. Str u ctu r es of Cyclop en ta d ien yltita n iu m
1-Aza -1,3-d ien e Com p lexes
the open end of the 1-aza-1,3-diene cup is directed away
from the Cp ligand.11 The preference of the supine
geometry of the most CpTi(1-aza-1,3-diene)Cl complexes
may primarily be due to the severe steric repulsion
between the Cp ligand and substituents on the nitrogen
and inner carbon atoms of the coordinated 1-aza-1,3-
diene in case of the prone geometry.
So far, no reports on the synthesis and structural
analysis of group IV 1-aza-1,3-diene complexes without
stabilizing Cp ligands have been published. The poten-
tial use of 1-aza-1,3-diene complexes in other selective
carbometalation reactions and the catalytic activity
toward olefin polymerization processes,12 together with
the fact that early-transition-metal complexes that
contain more than one 1-aza-1,3-diene ligand are still
unknown, has prompted us to expand our studies with
these ligands. Here we describe the synthesis and
structural characteristics as well as the results of a
typical carbometalation reaction of the first homoleptic
titanium 1-aza-1,3-diene complex.
Preliminary reports have shown that the substitution
of one of the terminal diene carbon atoms by a nitrogen
atom may offer a number of interesting options to the
organic chemistry of these heterodiene complexes.6
However, early-transition-metal complexes bearing 1-aza-
1,3-diene ligands have attracted less attention. This can
probably be ascribed to the fact that, so far, no general
method for the preparation of these heterodiene com-
plexes has been developed.
The utility of the magnesium-butadiene adduct
7
[(C4H6)Mg(THF)2]n or its derivatives as a synthon of
Resu lts a n d Discu ssion
the diene dianion has been widely accepted in the
synthesis of diene complexes of early transition metals.
Dilithium but-2-ene-1,4-diyl derivatives such as [{C4H4-
(SiMe3)2}{Li(THF)2}2]8 can also be used for transferring
dianionic diene ligands to transition metals. However,
to our knowledge no efforts have been made so far to
explore the preparation of magnesium 1-aza-1,3-diene
compounds, and only recently we reported for the first
time the reaction of the 1-aza-1,3-diene (iPr)NdCHC-
(Me)dCH(Ph) with lithium.1,9 Thus, most of the 1-aza-
1,3-diene complexes of early transition metals known
up to now have been prepared by simple reduction of
transition-metal halides by magnesium or lithium in the
presence of 1-aza-1,3-dienes.10
The results of NMR and X-ray structural analyses of
1-aza-1,3-diene group 4 metallocenes (2) prepared in
this way demonstrate that these complexes prefer the
σ2,π-1-metalla-2-azacyclopent-3-ene structure (Chart 1;
3a ).10a,b In the case of the monocyclopentadienyltita-
nium 1-aza-1,3-diene complexes CpTi(1-aza-1,3-diene)-
Cl (3) two orientations of the heterodiene are possible.10b
The supine structure shows the opening of the hetero-
diene cup pointing toward the Cp ring (Chart 1; 3a ).11
The alternative prone isomer (Chart 1; 3b) is present if
Syn th eses a n d Molecu la r Str u ctu r es of 1-Aza -
1,3-d ien e Com p lexes. The metallocene 1-aza-1,3-diene
complexes Cp2M(1-aza-1,3-diene) (2) and the monocy-
clopentadienyl 1-aza-1,3-diene complexes CpTi(1-aza-
1,3-diene)Cl (3) were prepared by a “one-pot syn-
thesis”.10a,b Application of this method to the simple
group 4 metal chlorides, i.e., reduction of TiCl4(THF)2
with 2 equiv of Mg in the presence of 2 equiv of various
1-aza-1,3-dienes (R1)NdCHC(R2)dCH(Ph) (1: R1 ) cy-
clo-C6H11, Ph, C6H4-2-Me, C6H4-4-Me; R2 ) H, Me) in
THF at room temperature as well as at low tempera-
tures, always yielded complex mixtures that were
almost insoluble even in THF and were not separable
into pure products. Only the attempt to run this reaction
with ZrCl4(THF)2 and (cyclo-C6H11)NdCHC(Me)dCH-
(Ph) (1a ) generated a brown solution from which small
amounts of dark yellow crystals could be separated
(Scheme 1).
The 1H NMR spectrum (THF-d8) of this zirconium
complex 6 reveals three different resonances for olefinic
protons (δ 6.34, 6.26, and 5.94), each integrated to one
hydrogen, as well as three singlets for three different
methyl resonances (δ 1.97, 1.62, and 1.55). These
surprising spectroscopic data demonstrate that at least
three 1-aza-1,3-diene ligands are bonded to the zirco-
nium atom. However, a singlet at δ 2.42 integrated to
one hydrogen which can be assigned to a methine group
attached to the zirconium suggests that only one of the
1-aza-1,3-dienes is σ2,π-coordinated to the zirconium,
forming an 1-aza-2-zirconacyclopent-4-ene ring. No
other ZrCH methine proton resonance was observed.
Instead, two doublets at δ 4.95 and 4.82 (3J H,H ) 10 Hz)
assigned to two vicinal aliphatic protons indicate that
a new ligand system had formed by C-C coupling of
two other 1-aza-1,3-dienes. This remarkable structural
feature has been confirmed by an X-ray structural
analysis.
(6) (a) Davis, J . M.; Whitby, R. J .; J axa-Chamiec, A. J . Chem. Soc.,
Chem. Commun. 1991, 1743-1745. (b) Enders, D.; Kroll, M.; Raabe,
G.; Runsink, J . Angew. Chem. 1998, 110, 1770-1773; Angew. Chem.,
Int. Ed. Engl. 1998, 37, 1673-1675.
(7) Fujita, K.; Ohnuma, Y.; Yasuda, H.; Tani, H. J . Organomet.
Chem. 1976, 113, 201-213.
(8) (a) Field, L. D.; Gardiner, M. G.; Messerle, B. A.; Raston, C. L.
Organometallics 1992, 11, 3566-3570. (b) Gardiner, M. G.; Raston,
C. L.; Cloke, F. G. N.; Hitchcock, P. B. Organometallics 1995, 14, 1339-
1353.
(9) The first isolable intermediate produced during the reduction
reaction of the 1-aza-1,3-diene (iPr)NdCHC(Me)dCH(Ph) with lithium
is the N,N′-dilithium hexa-1,5-diene-1,6-diamide {[Li(OEt2)]2[N(iPr)-
CHdC(Me)CH(Ph)CH(Ph)C(Me)dCHN(iPr)]}. This C-C coupling prod-
uct is probably formed by dimerization of the initially generated radical
anion of the 1-aza-1,3-diene. However, finally the reduction results in
the formation of the desired dilithium 1-azabut-2-ene-1,4-diyl com-
pound {[Li(OEt2)]2[N(iPr)CHdC(Me)CH(Ph)]}.
(10) (a) Scholz, J .; Nolte, M.; Kru¨ger, C. Chem. Ber. 1993, 126, 803-
809. (b) Scholz, J .; Kahlert, S.; Go¨rls, H. Organometallics 1998, 17,
2876-2884. (c) Mashima, K.; Matsuo, Y.; Nakahara, S.; Tani, K. J .
Organomet. Chem. 2000, 593-594, 69-76.
(11) (a) Chen, J .; Kai, Y.; Kasai, N.; Yamamoto, H.; Yasuda, H.;
Nakamura, A. Chem. Lett. 1987, 1545-1548. (b) For the definitions of
prone and supine designations, see also refs 2c and 3h.
Molecu la r St r u ct u r e of 6. Recrystallization of
complex 6 from pentane afforded suitable orange crys-
(12) Becke, S.; Windisch, H.; Scholz, J .; Kahlert, St. (Bayer AG) U.S.
Patent 5 965 678, 1999; Chem. Abstr. 1999, 130, P125529p.

1596 Organometallics, Vol. 23, No. 7, 2004
Sch em e 1. P r op osed Rea ction P a th w a y of th e F or m a tion of 6
Scholz et al.
tals. The molecular structure is provided in Figure 1
with the appropriate atom-labeling scheme for the non-
hydrogen atoms. Data collection parameters and se-
lected important bond lengths and bond angles are
summarized in Tables 1 and 2.
) 10 Hz of the vicinal protons at C19 and C33 (δ 4.95
and 4.82) places the phenyl group and the substituted
vinyl group in a gauche orientation, similar to the solid-
state structure.
An interesting feature of the seven-membered met-
allacyclic ring of 6 is the significant difference in the
Zr-N bonding distances. Thus, the Zr-N3 bond length
(2.069(4) Å) is comparatively short, indicating a π-dona-
tion from the nearly sp2-hybridized nitrogen atom
(summation of bonding angles at N3 359.3(3)°) to the
electron-deficient zirconium center. The Zr-N2 distance
is noticeably longer (2.120(4) Å), which is certainly a
consequence of the formation of a σ,π-distorted η3-
azaallyl unit comprising N2 and the adjacent carbon
atoms C17 and C18 (N2-C17 ) 1.359(6) Å, C17-C18
) 1.342(7) Å) and its concerted interaction with the
zirconium (Zr-C17 ) 2.505(5) Å, Zr-C18 ) 2.753(5) Å).
Unfortunately, to date only few structurally character-
ized η3-azaallyl zirconium complexes have been pub-
lished, but their bonding parameters are largely com-
parable with those of 6.13
As suggested from NMR data only one of the 1-aza-
1,3-dienes is σ2,π-coordinated to the zirconium, forming
a five-membered zirconacycle which is comparable to
that of the zirconocene 1-aza-1,3-diene complex Cp2Zr-
[N(C6H4-2-Me)CHdC(Me)CH(Ph)].10a Thus, the Zr-N1
(2.089(5) Å) and the Zr-C3 distances (2.253(6) Å) as
well as the inner C1dC2 bond length (1.380(8) Å) are
analogous to those of the zirconocene complex. With
respect to the bonding mode of the 1-aza-1,3-diene
ligand the characteristic folding of the five-membered
chelate ring along the N1-C3 axis by 126.4(2)°, too, is
of particular relevance. However, the nitrogen atom N1
is only slightly pyramidalized, as evidenced by the
summation of the bond angles about N1 (351.3(3)°).
Until now we have had no mechanistic information
about the individual events leading to the zirconium
The new complex contains a metallabicyclic frame-
work which is made up of a five-membered ring com-
prising the zirconium atom and a s-cis-configured 1-aza-
1,3-diene unit and of a seven-membered ring which
consists of two 1-aza-1,3-diene molecules that have
coupled to form a but-1-ene-1,4-diamide ligand and
which is N,N-coordinated to the zirconium. Interest-
ingly, the structure shows that the new single bond
between the carbon atoms C19 and C33 (C19-C33 )
1.533(7) Å) has changed these atoms to chiral centers
of the molecule. Hence, two diastereoisomers could have
been formed; however, only one has been observed in
the crystal. It is characterized by a gauche conformation
of the phenyl group and the substituted vinyl group at
the novel bond (C26-C19-C33-C34 ) -54.9(3)°). In
solution, too, only a single diastereoisomer of 5 was
3
observed. The large (anti-periplanar) coupling of J H,H
F igu r e 1. ORTEP drawing of complex 6 (50% probability
level) with the atom-labeling scheme (hydrogen atoms have
been omitted for clarity).
(13) (a) Lappert, M. F.; Liu, D.-Sh. J . Organomet. Chem. 1995, 500,
203-217. (b) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-Sh.; Ryan, E. J .
Polyhedron 1995, 14, 2745-2752.

The First Homoleptic 1-Aza-1,3-diene Ti Complex
Organometallics, Vol. 23, No. 7, 2004 1597
Ta ble 1. Su m m a r y of X-r a y Diffr a ction Da ta a n d Over a ll Refin em en t P a r a m eter s for 1b a n d 6-9
1b
6
7
8
9
chem formula
mol wt
C
21H25
N
C48H63N3Zr
733.23
C42H50N2Ti
630.74
C63H75N3Ti‚C4H10
O
C68H70N2O2Ti‚1/2C4H10
1032.22
0.28 × 0.22 × 0.12
pale yellow prism
triclinic
P1h (No. 2)
-90
O
291.42
959.22
cryst dimens (mm3)
cryst color, shape
cryst syst
0.36 × 0.32 × 0.20 0.40 × 0.38 × 0.32 0.38 × 0.34 × 0.30 0.34 × 0.32 × 0.28
yellow prism
monoclinic
orange prism
triclinic
P1h (No. 2)
-90
black-brown prism brown prism
monoclinic
P21/c (No. 14)
-90
triclinic
P1h (No. 2)
-90
space group
temp (°C)
cell params
a (Å)
b (Å)
c (Å)
P21/c (No. 14)
17.656(2)
7.7290(1)
26.880(5)
9.098(3)
12.335(2)
19.761(4)
107.14(1)
92.21(1)
98.62(1)
2087.2(9)
2
1.230
2.99
ω-2θ scan
824
18.196(2)
9.3470(9)
22.620(3)
12.8723(6)
16.2430(6)
16.4383(4)
62.750(2)
80.747(2)
75.093(2)
2949.0(2)
2
1.080
1.85
φ-ω scan
1034
13.0733(5)
13.3110(4)
19.5635(7)
70.838(2)
81.537(2)
62.963(2)
2864.34(17)
2
1.197
1.98
φ-ω scan
1102
R (deg)
â (deg)
98.733(9)
108.454(4)
γ (deg)
V (Å3)
3625(1)
8
1.068
0.61
φ-ω scan
1264
3649.3(7)
4
1.148
2.65
φ-ω scan
1352
no. of formula units Z
calcd density Fc (g cm-3
)
abs coeff µ(Mo KR) (cm-1
scan type
)
F(000)
hkl range
-19 to +18, 0-8,
-29 to +29
2.06-23.31
7138
4436
0.080
0-11, -15 to +15, -20 to +20, 0-10, 0-14, -17 to +18,
-16 to +16, -17 to +17,
-25 to +25
3.44-27.45
20 628
12 795
0.041
-25 to +25
2.27-27.43
10 096
-25 to +25
2.89-23.36
8920
-17 to +18
2.49-23.29
10 455
θ range (deg)
no. of unique total data
no. of indep data
Rint
9497
5005
8047
0.0586
0.053
0.058
no. of obsd data with
Fo > 4σ(Fo)
no. of params
restraints
2567
5390
3691
5894
9667
398
0
469
0
431
0
661
4
696
0
R1obs
0.085
0.214
0.143
0.244
1.001
0.234/-0.225
0.069
0.178
0.181
0.203
0.923
1.057/-0.959
0.063
0.164
0.092
0.180
1.019
0.333/-0.412
0.060
0.179
0.084
0.194
1.038
0.847/-0.257
0.063
0.120
0.095
0.132
1.046
0.792/-0.550
wR2obs
a
R1all
b
wR2all
goodness of fit
largest diff peak/hole
(e Å-3
)
R1 ) (∑||Fo| - |Fc||)/∑Fo. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
a
b
2
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [{N(R1)CHdC(Me)CH(P h )}Zr -
coordination of one 1-aza-1,3-diene 1a to the reduced
zirconium chloride, forming the intermediate 4 (Scheme
1). The subsequent addition of a second 1-aza-1,3-diene
1a with C-C coupling corresponds to the common
behavior of group 4 metal 1-aza-1,3-diene complexes6,10
and leads to the seven-membered metallacyclic but-1-
ene-1,4-diamide intermediate 5. In the last step the
intermediate 5 is reduced again and coordinated by a
third 1-aza-1,3-diene.
Tu n in g th e 1-Aza -1,3-d ien e Liga n d . The high
affinity of 1-aza-1,3-dienes to undergo addition reactions
by their imine function should be severely lowered by
increasing the steric bulk around the nitrogen atom.
Therefore, we hoped to be more successful in preparing
homoleptic 1-aza-1,3-diene complexes by using the
1-aza-1,3-diene 1b. The molecular structure of 1b
(Figure 2, Table 3), which is simply prepared by addition
of 1 equiv of 2,6-diisopropylaniline, H2NC6H3-2,6-iPr2,
to 1 equiv of cinnamyl aldehyde, PhCHdCHCHO,14
shows the common feature of 1-aza-1,3-dienes.9,15
Thus, the R,â-unsaturated heterodiene chain N1-
C1-C2-C3 presents an s-trans conformation with
respect to the central single bond C1-C2 (1.438(6) Å),
{N(R1)CHdC(Me)CH(P h )CH{C(Me)dCH(P h )}N(R1)]
(6: R1 ) cyclo-C6H11
)
Bond Lengths
Zr-N1
2.089(5)
2.069(4)
2.543(6)
2.505(5)
1.394(8)
1.448(8)
1.342(7)
1.482(6)
1.329(7)
Zr-N2
Zr-C1
Zr-C3
Zr-C18
C1-C2
N2-C17
C18-C19
C33-C34
C19-C33
2.120(4)
2.496(6)
2.253(6)
2.753(5)
1.380(8)
1.395(6)
1.532(7)
1.523(7)
1.533(7)
Zr-N3
Zr-C2
Zr-C17
N1-C1
C2-C3
C17-C18
N3-C33
C34-C35
Angles
N1-Zr-N2
N2-Zr-N3
Zr-N1-C1
Zr-N2-C17
102.7(2)
117.9(2)
89.3(3)
88.4(3)
N1-Zr-N3
N1-Zr-C3
Zr-C3-C2
Zr-N3-C33
115.3(2)
88.6(2)
83.8(4)
124.4(3)
C26-C19-C33-C34
-54.9(3)
(Zr, N1, C3)(C1, C2, C3, N1)
(Zr, N1, C3)(Zr, N2, N3)
sum of angles at N1
126.4(2)
93.3(2)
351.3(3)
343.9(3)
359.3(3)
sum of angles at N2
sum of angles at N3
complex 6, but the net results of this reaction are (i)
the formation of a bond between the terminal carbon
atom and the imine carbon atom of two 1-aza-1,3-dienes
1a , yielding a new N,N′-bonded diamide ligand system,
and (ii) the anionic coordination of a third 1-aza-1,3-
diene 1a , forming a 1-aza-2-zirconacyclopent-4-ene ring.
We assume that the reaction sequence starts with the
(14) (a) Doebner, O.; Miller, W. Ber. Dtsch. Chem. Ges. 1883, 16,
1664-1669. (b) Barany, H. C.; Braude, E. A.; Pianka, M. J . Chem. Soc.
1949, 1898-1902. (c) Brady, W. T.; Shieh, C. H. J . Org. Chem. 1983,
48, 2499-2502.
(15) (a) Childs, R. F.; Shaw, G. S.; Lock, C. J . L. J . Am. Chem. Soc.
1989, 111, 5424-5429. (b) Wunderle, J .; Scholz, J .; Hovestreydt, E. Z.
Kristallogr. 1993, 208, 274-276. (c) Imhof, W.; Go¨bel, A.; Braga, D.;
De Leonardis, P.; Tedesco, E. Organometallics 1999, 18, 736-747.

1598 Organometallics, Vol. 23, No. 7, 2004
Scholz et al.
Sch em e 2. Red u ction of TiCl4 w ith Mg in th e
P r esen ce of 1b
F igu r e 2. ORTEP drawing of the 1-aza-1,3-diene 1b (50%
probability level) with the atom-labeling scheme.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for (C6H3-2,6-iP r 2)NdCHCHdCH(P h ) (1b;
Molecu le A)
Bond Lengths
N1-C1
C2-C3
C3-C4
1.278(5)
1.351(5)
1.454(6)
C1-C2
1.438(6)
1.432(6)
N1-C10
Ch a r t 2. Str u ctu r a l Extr em es in th e Ra n ge of
Bon d in g Mod es betw een Tita n iu m a n d th e
1-Aza -1,3-d ien e
Angles
122.9(4)
128.4(4)
173.9(4)
177.3(4)
N1-C1-C2
C2-C3-C4
N1-C1-C2-C3
C2-C1-N1-C10
C1-C2-C3
122.4(4)
118.7(4)
174.6(4)
C1-N1-C10
C1-C2-C3-C4
and the N-C1 (1.278(5) Å) and the C2-C3 bond lengths
(1.351(5) Å) clearly indicate a double bond. However,
the aryl substituent C6H3-2,6-iPr2 at the nitrogen atom
is arranged in such a way that the CdN function is
largely shielded from the iPr groups. Furthermore, as
a consequence of the sterically demanding C6H3-2,6-iPr2
group at the nitrogen the donor properties of the ligand
are expected to be weaker, which altogether results in
a lower reactivity.
Slow addition of 2 equiv of magnesium turnings to a
solution of TiCl4 and 2 equiv of the 1-aza-1,3-diene 1b
in THF at -60 °C and subsequent warming to room
temperature leads to a brown-red solution from which
the new titanium complex 7 can be isolated as dark
brown crystals in 63% yield (Scheme 2).
1-aza-1,3-dienes are reduced upon coordination. There-
fore, the bonding situation in 7 is best described as a
1-titana-2-azacyclopent-3-ene complex (a ) rather than
a η4-1-aza-1,3-diene complex (b) (Chart 2).
Admittedly, the available NMR spectral data do not
allow a full description of the bonding situation, espe-
cially because the poor solubility of 7 at low tempera-
tures precludes observation of 13C resonances. Fortu-
nately, dark brown cubic crystals suitable for an X-ray
structure analysis could be grown from diethyl ether.
Molecu la r Str u ctu r e of 7. The molecular structure
is provided in Figure 3 with the appropriate atom-
labeling scheme. Except for H1 and H22 the hydrogen
atoms are omitted for clarity. Crystal data are collected
Complex 7 is thermally stable in the solid state and
can be stored under argon at room temperature for
several months. It is slightly soluble in diethyl ether,
THF, and toluene but only sparingly soluble in aliphatic
hydrocarbons. Moreover, solutions of 7 are very sensi-
tive to minute traces of oxygen or water. At room
1
temperature the H NMR spectrum shows only broad
resonances in the aromatic as well as in the aliphatic
region, which do not supply any helpful information
about the structure of 7. At lower temperatures, the
resonances coalesce and split into a large number of
signals, as expected. Thus, upon coordination of two
molecules of the 1-aza-1,3-diene to the titanium the
symmetry of the complex is lowered so that each ligand
gives rise to a complete set of resonances which partially
overlap. Additionally, as the rotation of the iPr groups
at the phenyl rings is obviously frozen at -60 °C, eight
separated methyl resonances between δ 1.28 and 0.47
can be observed.
F igu r e 3. ORTEP drawing of complex 7 (50% probability
level) with the atom-labeling scheme. All the hydrogen
atoms of the molecule (except H1 and H22) have been
omitted for clarity.
Nevertheless, the resonances of the spin-spin-coupled
hydrogen atoms at δ 1.21 (TiCH) and 6.06 (CHdCHN)
as well as at δ 1.14 and 5.49 clearly indicate that the

The First Homoleptic 1-Aza-1,3-diene Ti Complex
Organometallics, Vol. 23, No. 7, 2004 1599
atoms N1 and N2 maintain a planar, sp2 environment,
as the summation of angles at N1 (355.4(2)°) and N2
(357.8(2)°) shows. Apparently, the nitrogen lone pairs
are substantially involved in π-bonding to the titanium
center.
Ta ble 4. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Ti[{N(C6H3-2,6-iP r 2)CHdCHCH(P h )]2 (7)
Bond Lengths
Ti-N1
Ti-C1
1.955(3)
2.120(4)
2.431(4)
2.319(4)
2.25(1)
1.421(5)
1.397(5)
1.382(5)
Ti-N2
1.943(3)
2.322(4)
2.145(4)
2.317(4)
2.22(1)
1.375(5)
1.445(5)
1.392(4)
Ti-C2
Ti-C3
Ti-C22
Ti-C24
Ti-H22
C2-C3
C22-C23
N2-C24
As in the titanium 1-aza-1,3-diene complexes 2 and
3a one of the most interesting structural features of 7
concerns the bonding parameters of the TiCH groups.
The positions of the hydrogen atoms H1 and H22, which
are the anti protons of C1 and C22, were clearly resolved
and indicate that these hydrogen atoms are markedly
displaced away from titanium and out of the heterodiene
planes by 0.57 Å each. Similar displacements of the anti
hydrogen atoms out of the ligand plane have been
observed for other titanium diene and 1-aza-1,3-diene
complexes and are generally thought to be also a
consequence of sp2-sp3 rehybridization of the terminal
carbon atoms upon coordination of the diene ligands to
the transition metal.10b,17 Anyway, nearly rectangular
Ti-C-H angles (Ti-C1-H1 ) 85.9(5)°; Ti-C22-H22
) 81.6(5)°) and small Ti‚‚‚H distances of 2.25(1) and
2.22(1) Å, respectively, are observed, which are abso-
lutely comparable with those of MeTiCl3(dmpe) (Ti-
C-H ) 93.5(2)°, Ti‚‚‚H ) 2.447(3) Å) or of other
alkyltitanium complexes where R-agostic interactions
have been postulated.18 Unfortunately, the NMR spectra
of 7 do not give any additional information concerning
the R-agostic behavior of the 1-aza-1,3-diene ligands.
However, in a forthcoming paper we will describe that
this C-H activation in 7 can be used to induce an
R-hydrogen abstraction, leading to a novel metallacyclic
titanium alkylidene complex.19
Compound 7 represents the first homoleptic 1-aza-
1,3-diene complex of the early transition metals and
shows structural similarities with the known homoleptic
titanium 1,3-diene (tBuCHdCHCHdCHtBu)2Ti20 and
1,4-diaza-1,3-diene complexes (R1NdCR2CR2dNR1)2Ti
(R1 ) iPr, tBu, C6H4-2-Me; R2 ) H, Me).21 In all these
complexes the diene or heterodiene ligands prefer the
metallacyclopentene structure (Chart 2, a ) which is
probably both a consequence of their high π-acceptor
capability and significant steric repulsion between the
ligands.
Ti-C23
Ti-H1
C1-C2
N1-C3
C23-C24
Angles
N1-Ti-N2
N2-Ti-C22
N1-Ti-C22
Ti-N1-C3
Ti-N2-C24
Ti-C1-H1
129.12(12)
92.32(13)
131.70(14)
85.9(2)
86.4(2)
85.9(5)
N1-Ti-C1
C1-Ti-C22
N2-Ti-C1
Ti-C1-C2
Ti-C22-C23
Ti-C22-H22
92.33(13)
105.17(16)
99.77(13)
79.2(2)
77.8(2)
81.6(5)
(Ti, N1, C1)(N1, C3, C2, C1)
118.2(2)
117.0(2)
87.0(2)
355.4(2)
357.8(2)
(Ti, N2, C22)(N2, C24, C23, C22)
(Ti, N1, C1)(Ti, N2, C22)
sum of angles at N1
sum of angles at N2
in Table 1, and selected bond lengths and bond angles
are presented in Table 4. Both of the 1-aza-1,3-diene
ligands of 7 are coordinated to the Ti atom via the
terminal carbon and nitrogen atoms, which are disposed
in a pseudo-tetrahedral arrangement about the titanium
center. Obviously, in this conformation the steric repul-
sion between the bulky nitrogen substituents is best
minimized. The Ti-N (1.955(3) and 1.943(3) Å) as well
as the Ti-Cterm distances (2.120(4) and 2.145(4) Å) are
comparable with those found in the monocyclopentadi-
enyltitanium 1-aza-1,3-diene complex 3a (Ti-N ) 1.920-
(1) Å, Ti-Cterm ) 2.136(1) Å)10b and are in the typical
range found for Ti-Calkyl and Ti-Namide σ-bonds.16
Moreover, the relatively close contacts between the
titanium atom and the internal heterodiene carbon
atoms (Ti-C2 ) 2.322(4), Ti-C3 ) 2.431(4), Ti-C23 )
2.319(4), and Ti-C24 ) 2.317(4) Å) are also comparable
with those found for 3a . Thus, from covalent radii, it
appears that interaction of the titanium atom occurs
with all four atoms of the 1-aza-1,3-diene framework of
both ligands. Nevertheless, the N1-C3 and N2-C24
distances of 1.397(5) and 1.392(4) Å as well as the
terminal C1-C2 and C22-C23 distances of 1.421(5) and
1.445(5) Å of the coordinated 1-aza-1,3-dienes are
significantly longer than those of the free ligand 1b
(N1-C1 ) 1.278(5) Å, C2-C3 ) 1.351(5) Å; Table 3).
On the other hand, the internal C2-C3 and C23-C24
distances of 1.375(5) and 1.382(5) Å are short compared
with that of 1b (C1-C2 ) 1.438(6) Å).
Altogether, the inversion of the bond length sequence
from that in the free heterodiene is consistent with a
1-titana-2-azacyclopent-3-ene structure, which demon-
strates that the ligands are bound in the 1-azabut-2-
ene-1,4-diyl fashion. In accordance with this bonding
mode the five-membered rings are folded along the N1-
C1 and the N2-C22 axis (“envelope structure”) with
dihedral angles between the planes defined by (Ti, N1,
C1) and (N1, C1, C2, C3) as well as between (Ti, N1,
C22) and (N1, C22, C23, C24) measuring 118.2(2) and
117.0(2)°, respectively. Despite the observed folding of
the 1-titana-2-azacyclopent-3-ene rings the nitrogen
(17) (a) Spencer, M. D.; Wilson, S. R.; Girolami, G. S. Organome-
tallics 1997, 16, 3055-3067. (b) Devore, D. D.; Timmers, F. J .; Hasha,
D. L.; Rosen, R. K.; Marks, T. J .; Deck, P. A.; Stern, Ch. L. Organo-
metallics 1995, 14, 3132-3134.
(18) (a) Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983,
250, 395-408 (b) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog.
Inorg. Chem. 1988, 36, 1-124. (c) Examples of R-agostic interactions
in titanium alkyl compounds are as follows. MeTiCl3(dmpe) (Ti‚‚‚H )
2.447(3) Å, Ti-C-H ) 93.5(2)°): Dawoodi, Z.; Green, M. L. H.; Mtetwa,
V. S. B.; Prout, K.; Schultz, A. J .; Williams, J . M.; Koetzle, T. F. J .
Chem. Soc., Dalton Trans. 1986, 1629-1637. Cp*Ti(CH2Ph)3 (Ti‚‚‚H
) 2.32, 2.37 Å): Mena, M.; Pellinghelli, M. A.; Royo, P.; Serrano, R.;
Tiripiccio, A. J . Chem. Soc., Chem. Commun. 1986, 1118-1119. [(µ-
η5:η5-C10H8){Ti(CH2Ph)3}2] (Ti‚‚‚H ) 2.46, 2.45, 2.48, 2.59 Å): Alvaro,
L. M.; Cuenca, T.; Flores, J . C.; Royo, P.; Pellinghelli, M. A.; Tiripicchio,
A. Organometallics 1992, 11, 3301-3306. CpCp*Ti(CH2PPh2)2
(Ti‚‚‚H ) 2.46(2) Å, Ti-C-H ) 93(1)°): Cuenca, T.; Flores, J . C.; Royo,
P.; Larsonneur, A.-M.; Choukroun, R.; Dahan, F. Organometallics 1992,
11, 777-780.
(19) Monoazadiene Complexes of Early Transition Metals. 6: Scholz,
J .; Go¨rls, H. Organometallics 2004, 23, 320-322.
(20) Cloke, F. G. N.; McCamley, A. J . Chem. Soc., Chem. Commun.
1991, 1470-1471.
(21) (a) Cloke, F. G. N.; de Lemos, H. C.; Sameh, A. A. J . Chem.
Soc., Chem. Commun. 1986, 1344-1345. (b) tom Dieck, H.; Rieger, H.
J .; Fendesak, G. Inorg. Chim. Acta 1990, 177, 191-197. (c) Goddard,
R.; Kru¨ger, C.; Hadi, G. A.; Thiele, K.-H.; Scholz, J . Z. Naturforsch.
1994, 49b, 519-528.
(16) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G. J . Chem. Soc., Dalton Trans. 1989, S1-S83.

1600 Organometallics, Vol. 23, No. 7, 2004
Scholz et al.
the C-C coupling product 8 demonstrates that the
reaction course depends on the balance between the
π-acceptor capability (coordination reaction) and the
reactivity of the CdN function (addition reaction) of the
1-aza-1,3-diene, which is mainly influenced by the
bulkiness of the nitrogen substituent. Thus, the steric
demand of the N-substituent can be used like an
adjusting screw to tune the product distribution of this
one-pot reaction.
The seven-membered titana-2,7-diazacyclohept-3-ene
ring of 8 exhibits a twisted-boat conformation, as is
expected for an unsaturated seven-membered ring with
bulky substituents. However, due to the smaller radius
of the titanium compared with that of zirconium and
the stronger steric hindrance in its coordination sphere,
no π-interactions between the transition metal and the
C17dC18 bond become operative. Moreover, in contrast
to 6 there are no substantial differences between the
Ti-N2 (1.980(3) Å) and Ti-N3 bond lengths (1.942(3)
Å). The nearly perfect trigonal disposition of bonds
around N2 (359.9(2)°) and N3 (359.4(2)°) implicates that
both nitrogen atoms are sp2 hybridized and participate
as three-electron donors to titanium. The geometry of
the titana-2-azacyclopent-3-ene ring is nearly identical
with that of the homoleptic titanium complex 7. The
five-membered ring is folded along the N1-C3 vector
by 117.6(2)°, which does not differ from the correspond-
ing folding angles of 7 (117.0(2) and 118.2(2)°) and is
apparently largely independent of the nature of the
coligands. Most interest, however, is again attracted by
the structural details of the TiCH group: the hydrogen
atom attached to C3 is displaced from the heterodiene
plane by 0.75 Å. This unusual structural feature is
completed by a distorted Ti-C3-H3 angle of 96.1(5)°
together with a short Ti‚‚‚H3 contact of 2.48(1) Å.
Rea ction of 7 w ith Ben zop h en on e. Recently we
reported that monocyclopentadienyltitanium 1-aza-1,3-
diene complexes 3, which can be treated as the equiva-
lent of metalated allylamines and therefore be used as
homoenolate equivalents,6b readily undergo a carbonyl
addition reaction with ketones.10b With respect to the
first results of these studies it can be expected that
carbon-carbon coupling reactions of carbonyl com-
pounds with 1-aza-1,3-diene dianion equivalents other
than 3 will make a variety of interesting new organic
products available in a rather simple and predictable
way. Consequently, we have examined the reaction of
the homoleptic 1-aza-1,3-diene complex 7 with ben-
zophenone.
F igu r e 4. ORTEP drawing of complex 8 (50% probability
level) with the atom-labeling scheme (hydrogen atoms have
been omitted for clarity).
Ta ble 5. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for [{N(R1)CHdCHCH(P h )}Ti-
{N(R1)CHdCHCH(P h )CH{CHdCH(P h )}N(R1)] (8:
R1 ) C6H3-2,6-iP r 2)
Bond Lengths
Ti-N1
1.960(3)
1.942(3)
2.387(4)
1.394(4)
1.453(5)
1.339(5)
1.509(4)
1.336(5)
Ti-N2
1.980(3)
2.373(4)
2.185(3)
1.367(5)
1.421(4)
1.509(5)
1.508(5)
1.566(5)
Ti-N3
Ti-C1
Ti-C2
Ti-C3
C1-C2
N2-C17
C18-C19
C33-C34
C19-C33
N1-C1
C2-C3
C17-C18
N3-C33
C34-C35
Angles
N1-Ti-N2
N2-Ti-N3
Ti-N1-C1
Ti-N2-C17
104.59(11)
111.31(11)
88.4(2)
N1-Ti-N3
N1-Ti-C3
Ti-C3-C2
Ti-N3-C33
125.88(12)
89.41(12)
79.2(2)
118.3(2)
118.8(2)
C36-C19-C33-C34
(Ti, N1, C3)(C1, C2, C3, N1)
(Ti, N1, C3)(Ti, N2, N3)
sum of angles at N1
sum of angles at N2
sum of angles at N3
36.3(2)
117.6(2)
83.3(2)
357.5(2)
359.9(2)
359.4(2)
Molecu la r Str u ctu r e of th e Byp r od u ct 8. When
the dark brown mother liquor retained after the separa-
tion of 7 subsequently was concentrated and cooled to
-10 °C for several days, a very few dark red crystals of
a second organometallic product precipitated. The small
amount of this product (less than 2%) has precluded its
spectroscopic characterization, but fortunately the crys-
tals were suitable for an X-ray structure analysis. A
perspective view of the molecular structure of 8 is shown
in Figure 4; crystal data are listed in Table 1 and
selected bond lengths and angles in Table 5.
The structure analysis reveals a molecular geometry
which is similar to that of 6. In fact, the transition metal
forms the center of a spirocyclic ring system consisting
of a five-membered titana-2-aza-cyclopent-3-ene ring
and a seven-membered titana-2,7-diazacyclohept-3-ene
ring. Thus, we conclude that the 1-aza-1,3-diene 1b,
despite the bulky N substituent, is still reactive enough
to add to the Ti-C bond of an 1-aza-1,3-diene titanium
intermediate, as described for the formation of the
zirconium complex 6. However, the very low amount of
Treatment of the 1-aza-1,3-diene complex 7 with 2
equiv of benzophenone in THF solution at room tem-
perature yielded a brown-yellow solution, which after
removal of solvent and extraction of the residue with
diethyl ether afforded dark yellow crystals of the
titanium complex 9 in high yield (Scheme 3). Chemical
analysis confirms that two molecules of benzophenone
have been added; thus, two C-C bonds between the
heterodiene termini and the carbonyl carbon atoms as
well as two strong titanium-to-oxygen linkages have
been formed concurrently. According to these findings
1
both in the H and in the 13C NMR spectra two sets of
typical resonances are depicted, which can be unam-
biguously assigned to the new chelating ligands [OC-
(Ph)2CH(Ph)CHdCHN[C6H3-2,6-(iPr)2].

The First Homoleptic 1-Aza-1,3-diene Ti Complex
Organometallics, Vol. 23, No. 7, 2004 1601
Sch em e 3. Ad d ition of Ben zop h en on e to 7
Ta ble 6. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for
Ti[OC(P h )2CH(P h )CHdCHN(C6H3-2,6-iP r 2)]2 (9)
proximation the atoms of the s-cis-configurated 1-aza-
1,3-diene building blocks are arranged in a coplanar
fashion (maximum deviation (0.05 Å). Interesting
features of the molecular structure of 9 are the different
Ti-O-C angles: one of them is remarkably large (Ti-
O1-C1 ) 150.1(1)°), indicating a pronounced tita-
niium-oxygen π-bonding, which is confirmed by a
strikingly short Ti-O1 linkage of 1.809(1) Å.22 The other
Ti-O bond is somewhat longer (Ti-O2 ) 1.823(1) Å)
but still shorter than the Ti-O σ-bond distance pre-
dicted on the basis of covalent radii (ca. 1.98 Å).23 The
amide nitrogen atoms are nearly planar (sum of
angles: N1, 359.6(2)°; N2, 355.2(2)°). However, from the
Ti-N distances, which are only marginally shorter than
expected for a Ti-N σ-bond distance (ca. 2.02 Å),23 it
can be assumed that their available p orbitals do not
compete with the oxygen donor orbitals for π-bonding
with the metal d acceptor orbitals. The remaining bond
lengths and angles of the two seven-membered metal-
lacycles meet expectations.
Bond Lengths
Ti-O1
1.809(1)
1.928(2)
1.434(2)
1.509(3)
1.418(3)
1.586(3)
1.348(3)
Ti-O2
1.823(1)
1.986(2)
1.601(3)
1.340(3)
1.431(2)
1.516(3)
1.409(3)
Ti-N1
Ti-N2
O1-C1
C2-C3
C4-N1
C35-C36
C37-C38
C1-C2
C3-C4
O2-C35
C36-C37
C38-N2
Angles
O1-Ti-O2
O1-Ti-N1
O2-Ti-N1
Ti-O1-C1
Ti-N1-C4
115.16(7)
100.96(7)
102.15(7)
150.1(1)
120.2(1)
N1-Ti-N2
O1-Ti-N2
O2-Ti-N2
Ti-O2-C35
Ti-N2-C38
113.81(7)
112.77(7)
111.17(7)
139.2(1)
95.0(1)
(Ti, O1, N1)(Ti, N2, O2)
sum of angles at N1
sum of angles at N2
95.7(1)
359.6(2)
355.2(2)
The structure and conformation of 9 in the solid state
was confirmed by X-ray diffraction analysis. Single
crystals were obtained by recrystallization from diethyl
ether. A view of the molecular structure of 9 is shown
in Figure 5, together with the numbering scheme used.
Selected bond distances and angles are given in Table
6.
The terminal nitrogen and oxygen atoms of the
chelating ligands are coordinated in a distorted-tetra-
hedral geometry around the titanium, the angle be-
tween the (Ti, N1, O1) and (Ti, N2, O2) planes measur-
ing 95.7(1)°. Both of the azaoxatitanacycloheptene rings
adopt a folded-ring conformation similar to that ob-
served for the reported product of the carbonyl addition
reaction of 3a and acetophenone.10b To a first ap-
Con clu d in g Rem a r k s. As a part of an ongoing
project, this study reports on our efforts to synthesize
homoleptic 1-aza-1,3-diene complexes of the early tran-
sition metals. Actually, the first results demonstrate
that bis(1-aza-1,3-diene)titanium complexes can be pre-
pared by simply reducing TiCl4(THF)2 in the presence
of 1-aza-1,3-dienes. Only if the 1-aza-1,3-dienes are
modified by bulky substituents at the nitrogen atom,
as in 1b, are the homoleptic 1-aza-1,3-diene titanium
complexes the major products in this one-pot reaction.
Otherwise, a second organometallic complex in which
three 1-aza-1,3-dienes are coordinated to the metal atom
becomes the more prevalent product. However, two of
these heterodienes in this byproduct are connected by
a new C-C bond, yielding a new stabilizing but-1-ene-
1,4-diamide ligand system. The most important struc-
tural feature of the novel homoleptic bis(1-aza-1,3-
diene)titanium complex concerns the metallacyclopentene
structure of the heterodienes combined with an R-ago-
stic TiCH interaction. Due to the distinct alkyl character
of the bonds between the titanium and the terminal
carbon atoms of the 1-aza-1,3-dienes, the reaction of the
new complex with benzophenone fits into the general
scheme established for addition reactions of carbonyl
compounds to early-transition-metal alkyl complexes.
(22) Kim, I.; Nishihara, Y.; J ordan, R. F.; Rogers, R. D.; Rheingold,
A. L.; Yap, G. P. A. Organometallics 1997, 16, 3314-3323.
(23) Ranges for Ti-O as well as Ti-N σ-bond distances were
estimated using covalent radii (Ti, 1.32 Å; O, 0.66 Å; N, 0.70 Å) taken
from: Emsley, J . Die Elemente; Walter de Gruyter: Berlin, New York,
1994. (b) For typical Ti-O bond distances, see also ref 16.
F igu r e 5. ORTEP drawing of complex 9 (50% probability
level) with the atom-labeling scheme (hydrogen atoms have
been omitted for clarity).

1602 Organometallics, Vol. 23, No. 7, 2004
Scholz et al.
1
MHz, THF-d8, 25 °C): δ 163.32 (d, J C,H ) 155.2 Hz, NdCH),
Exp er im en ta l Section
1
138.08 (d, J C,H ) 151.7 Hz, dCHPh), 136.70 (s, dCMe-),
1
Gen er a l Con sid er a tion s. All experiments were performed
under an atmosphere of dry argon using standard Schlenk
techniques. Solvents were distilled from sodium/benzophenone
ketyl (THF, diethyl ether) or LiAlH4 (pentane) under argon
and stored over activated 4 Å molecular sieves. Deuterated
THF-d8 was treated with sodium/potassium alloy and then
distilled and stored under argon. All glassware was thoroughly
oven-dried or flame-dried under vacuum prior to use. Ben-
zophenone was purchased from Aldrich Chemicals and used
as received. TiCl4(THF)2 and ZrCl4(THF)2 were prepared
according to literature procedures.24 NMR spectra were re-
corded in THF-d8 on a Varian 300 BB (1H NMR at 300.075
MHz, 13C NMR at 75.462 MHz) or a Varian UNITY 500
spectrometer (1H NMR at 499.843 MHz, 13C NMR at 125.639
136.70 (s, 1-Ph), 129.24 (d, J C,H ) 159.0 Hz, 2,6-Ph), 128.21
(d, 1J C,H ) 160.1 Hz, 3,5-Ph), 127.39 (d, 1J C,H ) 161.0 Hz, 4-Ph),
69.62 (d, 1J C,H ) 131.3 Hz, cyclo-C6H11), 34.45 (t, 1J C,H ) 126.4
Hz, cyclo-C6H11), 25.65 (t, 1J C,H ) 127.1 Hz, cyclo-C6H11), 24.86
1
1
(t, J C,H ) 126.9 Hz, cyclo-C6H11), 13.37 (q, J C,H ) 127.9 Hz,
dCMe-).
(C6H3-2,6-iP r 2)NdCHCHdCH(P h ) (1b). 1H NMR (300
MHz, THF-d8, 25 °C): δ 7.97 (dd, J H,H ) 6.7 Hz, J H,H ) 1.5
Hz, 1H, CHdN), 7.61 (m, 2H, 2,6-Ph), 7.40-7.31 (m, 3H, 4-Ph,
4-C6H3-2,6-iPr2, dCH-), 7.19 (d, 2H, 3,5-C6H3-2,6-iPr2), 7.09
(t, 2H, 3,5-Ph), 6.99 (dd, J H,H ) 8.5 Hz, J H,H ) 2.0 Hz, 1H,
dCHPh), 2.98 (sept, 3J H,H ) 6.9 Hz, 2H, CHMe2), 1.14 (d, 3J H,H
) 6.9 Hz, 12H, CHMe2). 13C NMR (75 MHz, THF-d8, 25 °C):
3
4
3
4
1
δ 164.83 (d, J C,H ) 156.6 Hz, NdCH), 150.85 (s, 1-C6H3-2,6-
MHz) at 25 °C, unless indicated otherwise. H and 13C NMR
1
iPr2), 144.40 (d, 1J C,H ) 155.0 Hz, dCH-), 137.89 (s, 2,6-C6H3-
spectra were referenced internally using the residual solvent
2,6-iPr2), 136.84 (s, 1-Ph), 130.17 (d, 1J C,H ) 160.8 Hz, 4-C6H3-
1
resonances (THF-d8: δH 1.73, δC 25.2). J C-H values were
1
1
2,6-iPr2), 129.61 (d, J C,H ) 162.2 Hz, 2,6-Ph), 129.47 (d, J C,H
obtained from gated 13C{1H} NMR spectra. Elemental analyses
were carried out by the analysis laboratory at the Martin-
Luther-University of Halle-Wittenberg. Melting points are
uncorrected.
1
) 159.3 Hz, dCHPh), 128.36 (d, J C,H ) 160.2 Hz, 3,5-C6H3-
2,6-iPr2), 124.63 (d, 1J C,H ) 159.2 Hz, 4-Ph), 123.48 (d, 1J C,H
)
1
155.4 Hz, 3,5-Ph), 28.67 (d, J C,H ) 128.3 Hz, CHMe2), 23.82
1
(q, J C,H ) 125.6 Hz, CHMe2).
Cr ysta llogr a p h ic Da ta Collection s a n d Str u ctu r e De-
ter m in a tion of 1b a n d 6-9. The crystal structure determi-
nation of 6 was carried out on an Enraf-Nonius CAD4
diffractometer; those of 1b and 7-9 were carried out on a
Nonius KappaCCD diffractometer using graphite-monochro-
mated Mo KR radiation. The crystals were mounted under a
stream of cold nitrogen, and the data were collected at -90
°C. Crystallographic and experimental details are summarized
in Table 1. Data were corrected for Lorentz and polarization
but not for absorption effects.25-27 The structures were solved
by direct methods (SHELXS)28 and refined by full-matrix least-
[N(R)CHdC(Me)CH(P h )]Zr [N(R)CHdC(Me)CH(P h )CH-
{C(Me)dCH(P h )}N(R)] (6: R ) cyclo-C6H11). To a solution
of ZrCl4(THF)2 (5.00 g, 16.38 mmol) and the 1-aza-1,3-diene
1a (7.50 g, 33.00 mmol) in THF (150 mL) were added
magnesium turnings (0.80 g, 32.76 mmol). The reaction
mixture was stirred at ambient temperature until the mag-
nesium was dissolved. During this time the color of the solution
changed from pale yellow to red-orange. The resulting mixture
was evaporated to dryness, and the product was extracted with
diethyl ether (100 mL) to leave magnesium chloride. The red-
orange extract was concentrated to 50 mL and stored at -20
°C for 3 days to yield 1.2 g (1.55 mmol, 10%) of 6 as an orange
solid (mp 152-154 °C dec), which was isolated by filtration.
Recrystallization from pentane yielded orange crystals suitable
for X-ray structure analysis (Table 1). Anal. Calcd for C48H63N3-
Zr: C, 75.56; H, 8.21; N, 5.43. Found: C, 75.39; H, 8.30; N,
5.61. 1H NMR (300 MHz, THF-d8, 25 °C): δ 7.31-6.97 (m, 10H,
Ph), 6.88 (d, 2H, 2,6-Ph), 6.74 (t, 1H, 4-Ph), 6.62 (d, 2H, 2,6-
Ph), 6.34 (s, 1H, dCH-), 6.26 (s, 1H, dCH-), 5.94 (s, 1H,
squares techniques against Fo (SHELXL-97).29 Only for the
2
1-aza-1,3-diene backbone of the compounds 7-9 were the
hydrogen atoms located by difference Fourier synthesis and
refined isotropically. The other hydrogen atoms were included
at calculated positions with fixed thermal parameters. All non-
hydrogen atoms were refined anisotropically.29 XP (SIEMENS
Analytical X-ray Instruments, Inc.) was used for structure
representations. The files CCDC 205793-205797 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/conts/
retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, U.K., fax (+44)
1223-336-033, or deposit@ccdc.cam.ac.uk).
3
3
dCH-), 4.95 (d, J H,H ) 10 Hz, 1H, -CHCH-), 4.82 (d, J H,H
) 10 Hz, 1H, -CHCH-), 3.37 (m, 2H, cyclo-C6H11), 2.95 (m,
1H, cyclo-C6H11), 2.42 (s, 1H, ZrCH), 1.97 (s, 3H, Me), 2.10-
1.05 (m, cyclo-C6H11), 1.62 (s, 3H, Me), 1.55 (s, 3H, Me).
Ti[N(C6H3-2,6-iP r 2)CHdCHCH(P h )]2 (7). To a solution of
TiCl4(THF)2 (3.50 g, 10.50 mmol) and the 1-aza-1,3-diene 1b
(6.12 g, 21.00 mmol) in THF (150 mL) were added magnesium
turnings (0.51 g, 21.00 mmol) over a period of 8 h at -60 °C.
The reaction mixture was warmed to room temperature and
was stirred until the magnesium was dissolved. Then, the
mixture was evaporated to dryness, and the product was
extracted with diethyl ether (100 mL) to leave magnesium
chloride. The dark brown extract was concentrated to 50 mL
and stored at -20 °C. A yield of 4.17 g (6.62 mmol, 63%) of
dark brown crystals of 7 was obtained. Mp: 150-155 °C dec.
Recrystallization from diethyl ether yielded crystals suitable
for X-ray structure analysis (Table 1). Anal. Calcd for C42H50N2-
Ti (630.73): C, 79.98; H, 7.99; N, 4.44. Found: C, 79.75; H,
P r ep a r a tion a n d Sp ectr oscop ic Da ta for th e 1-Aza -1,3-
d ien es 1a a n d 1b. Standard literature procedures were used
for the preparation of the 1-aza-1,3-dienes 1a and 1b.14 Thus,
equimolar amounts of the cinnamyl aldehyde and the corre-
sponding amine are stirred together at room temperature in
ethanol as a solvent for several hours. Subsequently, the
reaction mixtures were cooled to 5 °C to precipitate the 1-aza-
1,3-dienes. They were purified by recrystallization from diethyl
ether (1a ) or pentane (1b).
(cyclo-C6H11)NdCHC(Me)dCH(P h ) (1a ). 1H NMR (300
MHz, THF-d8, 25 °C): δ 7.97 (s, 1H, CHdN), 7.42-7.15 (m,
5H, Ph), 6.71 (s, 1H, dCHPh), 3.08 (m, 1H, cyclo-C6H11), 2.11
(s, 3H, Me), 1.85-1.11 (m, 10H, cyclo-C6H11). 13C NMR (75
1
7.95; N, 4.51. H NMR (500 MHz, THF-d8, -60 °C): δ 7.17-
6.95 (m, 9H, C6H3-2,6-iPr2, Ph, CHdCHN), 6.84-6.79 (m, 3H,
C6H3-2,6-iPr2, Ph), 6.68 (d, 1H, Ph), 6.45 (m, 3H, C6H3-2,6-
(24) Manzer, L. E. Inorg. Synth. 1980, 21, 136-137.
(25) MOLEN, an Interactive Structure Solution Procedure; Enraf-
Nonius, Delft, The Netherlands, 1990.
(26) COLLECT, Data Collection Software; Nonius BV, Delft, The
Netherlands, 1998.
(27) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Macromolecular Crystallography;
Methods in Enzymology 276; Carter, C. W., Sweet, R. M., Eds.;
Academic Press: San Diego, CA, 1997; Part A, pp 307-326.
(28) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467-473.
(29) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1993.
3
3
iPr2, Ph), 6.38 (d, 1H, Ph), 6.06 (dd, J H,H ) 11 Hz, J H,H ) 5
3
Hz, 1H, CHdCHN), 6.03 (d, 1H, Ph), 5.49 (dd, J H,H ) 10 Hz,
3J H,H ) 5 Hz, 1H, CHdCHN), 2.99 (m, 2H, CHMe2), 2.80 (m,
3
1H, CHMe2), 2.72 (m, 1H, CHMe2), 1.28 (d, J H,H ) 6 Hz, 3H,
3
CHMe2), 1.21 (m, 4H, TiCH, CHMe2), 1.14 (d, J H,H ) 5 Hz,
3H, TiCH), 1.05 (d, 3J H,H ) 6 Hz, 3H, CHMe2), 0.94 (d, 3J H,H
)
6 Hz, 3H, CHMe2), 0.82 (d, 3J H,H ) 6 Hz, 3H, CHMe2), 0.72 (d,

The First Homoleptic 1-Aza-1,3-diene Ti Complex
Organometallics, Vol. 23, No. 7, 2004 1603
3
3
3J H,H ) 6 Hz, 3H, CHMe2), 0.69 (d, J H,H ) 6 Hz, 3H, CHMe2),
3.52, 3.18, 2.67 (br m, 4H, CHMe2), 1.42 (d, J H,H ) 6 Hz, 3H,
3
3
0.47 (d, J H,H ) 6 Hz, 3H, CHMe2).
CHMe2), 1.00 (m, 6H, CHMe2), 0.89 (d, J H,H ) 7 Hz, 3H,
3
3
[N(R)CHdCHCH(P h )]Ti[N(R)CHdCHCH(P h )CH{CHd
CH(P h )}N(R)] (8: R ) C6H3-2,6-iP r 2). The dark brown
mother liquor obtained in the procedure mentioned above was
subsequently concentrated to a volume of 20 mL and cooled
to -10 °C. After standing for several days a very few dark red
crystals of the insertion product 8 have been grown, which
were studied by X-ray structure analysis (Table 1).
CHMe2), 0.72 (d, J H,H ) 6 Hz, 6H, CHMe2), 0.48 (d, J H,H ) 6
Hz, 3H, CHMe2), 0.18 (d, J H,H ) 6 Hz, 3H, CHMe2). 13C NMR
3
(75 MHz, THF-d8, 25 °C; selected signals): δ 148.51, 148.13,
147.48, 146.97, 145.88, 145.07, 140.86, 140.72 (1-Ph, 1,2,6-
C6H3-2,6-iPr2), 124.93, 124.42, 123.84, 116.33 (CHdCH), 114.02,
108.21 (OCPh2), 62.66, 61.95 (CHPh), 30.64, 28.85, 28.17, 27.64
(CHMe2), 23.79, 23.69, 23.54, 23.33, 23.01 (CHMe2).
Ti[OC(P h )2CH(P h )CHdCHN(C6H3-2,6-iP r 2)]2 (9). Ben-
zophenone (0.87 g, 4.77 mmol) was added to a solution of the
1-aza-1,3-diene titanium complex 7 (1.50 g, 2.38 mmol) in 100
mL of THF. The reaction mixture was stirred at room
temperature for 8 h. Subsequently, the solvent was removed
in vacuo and the residual brown-yellow solid was extracted
with diethyl ether (100 mL). The extract was concentrated to
50 mL and cooled to -5 °C for 2 days, yielding 1.94 g (82%) of
dark yellow crystalline 9. Crystals of 9 suitable for X-ray
structure analysis were obtained by recrystallization from
diethyl ether (Table 1). Mp: 165 °C dec. Anal. Calcd for
Ack n ow led gm en t. Prof. D. Steinborn is kindly
acknowledged for providing laboratory facilities at the
University of Halle-Wittenberg. This work has been
financially supported by the Deutsche Forschungsge-
meinschaft.
Su p p or tin g In for m a tion Ava ila ble: Listings of atomic
coordinates, thermal parameters, and bond distances and
angles for complexes 1b and 6-9; crystallographic data are
also available as CIF files. This material is available free of
charge via the Internet at http://pubs.acs.org.
C
68H70N2O2Ti (995.16): C, 82.07; H, 7.09; N, 2.81. Found: C,
82.00; H, 7.12; N, 2.88. 1H NMR (300 MHz, THF-d8, 25 °C): δ
7.86-6.25 (m, 40 H; Ph, C6H3-2,6-iPr2, CHdCH), 4.82 (d, 3J H,H
) 11 Hz, 1H, CHPh), 4.55 (d, 3J H,H ) 10 Hz, 1H, CHPh), 3.87,
OM0341956