Reduction of tetravalent group 4 metal complexes supported by an extremely bulky, unsymmetrically substituted β-diketiminato ligand leading to the regioselective C=N bond cleavage giving ring-contracted metal-imido complexes

Article abstract of DOI:10.1021/om0509948

Reductions of tetravalent group 4 metal β-diketiminates, [M ^IVCl₃(nacnac)(thf)_n] (2a, M = Ti; 3b, M = Zr; 3c, M = Hf; nacnac = {N(Tbt)C(Me)CHC(Me)N(Mes)}^-, Tbt = 2,4,6-tris[bis(trimethylsilyl)-methyl]phenyl, Mes

Full text of DOI:10.1021/om0509948

Organometallics 2006, 25, 2457-2464
2457
Reduction of Tetravalent Group 4 Metal Complexes Supported by
an Extremely Bulky, Unsymmetrically Substituted â-Diketiminato
Ligand Leading to the Regioselective CdN Bond Cleavage Giving
Ring-Contracted Metal-Imido Complexes
Hirofumi Hamaki, Nobuhiro Takeda, and Norihiro Tokitoh*
Institute for Chemical Research, Kyoto UniVersity, Gokasho, Uji, Kyoto 611-0011, Japan
ReceiVed NoVember 19, 2005
Reductions of tetravalent group 4 metal â-diketiminates, [MIVCl3(nacnac)(thf)n] (2a, M ) Ti; 3b, M
) Zr; 3c, M ) Hf; nacnac ) {N(Tbt)C(Me)CHC(Me)N(Mes)}-, Tbt ) 2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl, Mes ) 2,4,6-trimethylphenyl, n ) 0, 1), with 2 equiv of KC8 in the presence of LiCl and
tmeda afforded the metal-imido complexes [MdNTbt{C(Me)CHC(Me)N(Mes)}(µ-Cl)2Li(tmeda)] (4a,
M ) Ti; 4b, M ) Zr; 4c, M ) Hf; tmeda ) Me2NCH2CH2NMe2). The formation of imido complexes
4a-c can be explained in terms of the generation of the corresponding divalent complexes [MIICl-
(nacnac)(L)n] (6a, M ) Ti; 6b, M ) Zr; 6c, M ) Hf; L ) thf or Li(tmeda), etc.), followed by the
reductive, regioselective cleavage of the CdN bond tethered to the Tbt group. The intermediacy of the
divalent titanium complex 6a was supported by the alternative formation of 4a in the reaction of [Li-
(nacnac)] (1) with [TiIICl2(tmeda)2]. Interestingly, 4a-c reacted with H2O to give the free ligand nacnacH
(8).
anionic spectator ligands by the virtue of their strong binding
ability to metals, their tunable steric and electronic demands,
and their diversity of bonding modes. They often stabilize metal
complexes in low oxidation states10 and/or coordination num-
bers11 and complexes containing a coligand that is multiply
bonded to the metal.12
â-Diketiminato complexes of trivalent titanium and tetravalent
group 4 metals have already been reported by Lappert,13
Theopold,14 Budzelaar,15 Smith,16 Mindiola,17 and so forth. The
robust nature of â-diketiminato ligands with early-transition
Introduction
Interest in the chemistry of divalent group 4 metal complexes,
especially in that of titanium complexes, has been stimulated
by the very diverse aspects of their chemical reactivities,
including activation of small molecules (N2,1 CO,2 CO2,3 H2,4
etc.), reductive coupling of olefins4 and acetylenes,5 and the
role played in Ziegler-Natta catalysis.6 However, apart from
the bicyclopentadienyl system,7 divalent titanium complexes
have been poorly known and only a few examples of highly
coordinated complexes have been reported.8
(10) (a) Holland, P. L.; Cundari, T. R.; Perez, L. L.; Eckert, N. A.;
Lachicotte, R. J. J. Am. Chem. Soc. 2002, 124, 14416-14424. (b) Neculai,
D.; Neculai, A. M.; Roesky, H. W.; Herbst-Irmer, R.; Walfort, B.; Stalke,
D. Dalton Trans. 2003, 2831-2834. (c) Dai, X.; Kapoor, P.; Warren, T.
H. J. Am. Chem. Soc. 2004, 126, 4798-4799.
The chemistry of â-diketiminato complexes is of much current
interest.9 â-Diketiminato ligands play important roles as mono-
* To whom correspondence should be addressed. E-mail: tokitoh@
boc.kuicr.kyoto-u.ac.jp.
(11) (a) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer, M.; Hao,
H.; Cimpoesu, F. Angew. Chem., Int. Ed. 2000, 39, 4274-4276. (b)
Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000, 1991-
1992. (c) Hill, M. S.; Hitchcock, P. B.; Pongtavornpinyo, R. Dalton Trans.
2005, 273-277. (d) Cheng, Y.; Hitchcock, P. B.; Lappert, M. F.; Zhou, M.
Chem. Commun. 2005, 752-754. (e) Panda, A.; Stender, M.; Wright, R.
J.; Olmstead, M. M.; Klavins, P.; Power, P. P. Inorg. Chem. 2002, 41, 3909-
3916. (f) Eckert, N. A.; Bones, E. M.; Lachicotte, R. J.; Holland, P. L.
Inorg. Chem. 2003, 42, 1720-1725. (g) Budzelaar, P. H. M.; de Gelder,
R.; Gal, A. W. Organometallics 1998, 17, 4121-4123. (h) Ding, Y.; Roesky,
H. W.; Noltemeyer, M.; Schmidt, H.-G.; Power, P. P. Organometallics 2001,
20, 1190-1194. (i) Stender, M.; Phillips, A. D.; Power, P. P. Inorg. Chem.
2001, 40, 5314-5315.
(12) (a) Basuli, F.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J.
Am. Chem. Soc. 2003, 125, 10170-10171. (b) Basuli, F.; Bailey, B. C.;
Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. J. Am. Chem. Soc. 2004, 126,
1924-1925. (c) Hardman, N. J.; Cui, C.; Roesky, H. W.; Fink, W. H.;
Power, P. P. Angew. Chem., Int. Ed. 2001, 40, 2172-2174. (d) Ding, Y.;
Ma, Q.; Roesky, H. W.; Uso´n, I.; Noltemeyer, M.; Schmidt, H.-G. Dalton
Trans. 2003, 1094-1098.
(13) (a) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J. Chem. Soc., Chem.
Commun. 1994, 2637-2638. (b) Deelman, B.-J.; Hitchcock, P. B.; Lappert,
M. F.; Leung, W.-P.; Lee, H.-K.; Mak, T. C. W. Organometallics 1999,
18, 1444-1452.
(14) Kim, W.-K.; Fevola, M. J.; Liable-Sands, L. M.; Rheingold, A. L.;
Theopold, K. H. Organometallics 1998, 17, 4541-4543.
(15) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485-1494.
(1) Berry, D. H.; Procopio, L. J.; Carroll, P. J. Organometallics 1988, 7,
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10.1021/om0509948 CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/01/2006

2458 Organometallics, Vol. 25, No. 10, 2006
Scheme 1. Synthesis of â-Diketiminato Complexes of Group 4 Metals
Hamaki et al.
metal systems has enabled them to be used as catalysts in olefin
polymerization reactions.15 However, divalent â-diketiminato
complexes of group 4 metals have not been reported so far.
Recently, Mindiola et al. have reported that two-electron
reduction of tetravalent zirconium â-diketiminates bearing 2,6-
diisopropylphenyl (Dip) substituents gave the corresponding
terminal zirconium-imido complexes via transformation of the
â-diketiminato ligand.18
Meanwhile, we have already succeeded in the synthesis of a
variety of low-coordinate, reactive species (e.g., heaVy ketones,19
heaVy aromatics,20 and heaVy azo compounds21) containing
heavier main group elements by taking advantage of an
extremely bulky substituent, 2,4,6-tris[bis(trimethylsilyl)methyl]-
phenyl (Tbt).22 We recently reported the synthesis and structure
of a lithium â-diketiminate [Li(nacnac)] (1, nacnac ) {N(Tbt)C-
(Me)CHC(Me)N(Mes)}-, Mes ) 2,4,6-trimethylphenyl) bearing
a Tbt substituent, which was regarded as a ligand source for
the synthesis of transition metal complexes.23 The X-ray
structural analysis of 1 showed that it has a monomeric structure
and an essentially two-coordinated lithium center without solvent
coordination and interaction with the neighboring molecules in
the solid state.
complexes (2a, M ) Ti, n ) 0; 3b, M ) Zr, n ) 1; 3c, M )
Hf, n ) 1) were prepared by the reactions of [Li(nacnac)] (1)
with MCl4(thf)2 (M ) Ti, Zr, Hf), respectively (Scheme 1). The
titanium complex 2a was not coordinated by THF molecules,
whereas the zirconium and hafnium complexes 3b and 3c were
coordinated by a THF molecule probably due to their longer
M-N bond lengths compared with that in 2a.
The X-ray study showed that the structures of 3b and 3c adopt
a distorted, octahedral geometry at the metal center and a
meridional arrangement of three chorine atoms (Figure 2). Since
hafnium complex 3c is isomorphous, the ORTEP drawing of
zirconium complex 3b is depicted in Figure 2 as a representative.
Selected structural parameters and the crystallographic data are
summarized in Tables 1 and 5, respectively.
Two independent molecules are found in the unit cell of 3b,
and both molecules have structures that are essentially identical
with each other. The five atoms in the backbone of the
â-diketiminato ligand, N1-C1-C2-C3-N2, are coplanar, and
the two sets of C-N and C-C distances in the ligand skeleton
are almost equivalent to each other. The bond lengths of the
C-N and C-C bonds are intermediate values between the
typical single and double bond lengths. These results strongly
suggest the delocalization of the double bonds of the ligand.
The central zirconium atoms of the two independent molecules
deviate from the N2C3 planes by 0.7544(16) and 0.7863(15) Å,
respectively. However, the Zr-C(ligand backbone) distances
[3.1319(14) and 3.1142(12) Å (Zr-C1), 3.4046(13) and 3.3904-
(12) Å (Zr-C2), 3.1455(12) and 3.1376(12) Å (Zr-C3)] are
too long to form real Zr-C bonds. Therefore, the â-diketiminato
ligand in 3b can be considered to have the η2-coordinaton mode,
which is identical with zirconium complexes reported by
Smith,16 in contrast to 1,2,3,5-η4- or η5-coordinated â-diketimi-
Here, we report the synthesis of tetravalent group 4 metal
complexes bearing a novel, extremely bulky â-diketiminato
ligand together with their reduction reactions giving the corre-
sponding terminal imido complexes of group 4 metals instead
of the expected divalent complexes.
Results and Discussion
Reduction of Tetravalent â-Diketiminato Complexes of
Group 4 Metals. Tetravalent titanium, zirconium, and hafnium
(16) Kakaliou, L.; Scanlon, W. J., IV.; Qian, B.; Baek, S. W.; Smith,
M. R., III; Motry, D. H. Inorg. Chem. 1999, 38, 5964-5977.
(17) (a) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola, D. J. Chem.
Commun. 2003, 1554-1555. (b) Basuli, F.; Watson, L. A.; Huffman, J.
C.; Mindiola, D. J. Dalton Trans. 2003, 4228-4229. (c) Basuli, F.; Huffman,
J. C.; Mindiola, D. J. Inorg. Chem. 2003, 42, 8003-8010. (d) Basuli, F.;
Bailey, B. C.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. J. Am.
Chem. Soc. 2003, 125, 6052-6053. (e) Basuli, F.; Bailey, B. C.; Watson,
L. A.; Tomaszewski, J.; Huffman, J. C.; Mindiola, D. J. Organometallics
2005, 24, 1886-1906. (f) Basuli, F.; Bailey, B. C.; Huffman, J. C.; Mindiola,
D. J. Organometallics 2005, 24, 3321-3334.
Figure 1. â-Diketiminato ligand bearing a Tbt group.
(18) Basuli, F.; Kilgore, U. J.; Brown, D.; Huffman, J. C.; Mindiola, D.
J. Organometallics 2004, 23, 6166-6175.
(19) For a recent account, see: Tokitoh, N.; Okazaki, R. AdV. Organomet.
Chem. 2001, 47, 121-166.
(20) For a recent account, see: Tokitoh, N. Acc. Chem. Res. 2004, 37,
86-94.
(21) (a) Sasamori, T.; Mieda, E.; Takeda, N.; Tokitoh, N. Angew. Chem.,
Int. Ed. 2005, 44, 3717-3720. (b) Tokitoh, N. J. Organomet. Chem. 2000,
611, 217-227, and references therein.
(22) (a) Okazaki, R.; Unno, M.; Inamoto, N. Chem. Lett. 1987, 2293-
2294. (b) Okazaki, R.; Unno, M.; Inamoto, N. Chem. Lett. 1989, 791-
792. (c) Okazaki, R.; Tokitoh, N.; Matsumoto, T. In Synthetic Methods of
Organometallic and Inorganic Chemistry; Herman, W. A., Auner, N.,
Klingebiel, U., Eds.; Thieme, New York, 1996; Vol. 2, pp 260-269.
(23) (a) Takeda, N.; Hamaki, H.; Tokitoh, N. Chem. Lett. 2004, 33, 134-
135. (b) Takeda, N.; Hamaki, H.; Tokitoh, N. Phosphorus, Sulfur Silicon
2004, 179, 727-728.
Figure 2. Molecular structure of the zirconium complex 3b with
thermal ellipsoids at the 50% probability level. H atoms and solvent
molecules are omitted for clarity. One of the two independent
molecules in the unit cell is depicted. The hafnium analogue 3c is
isomorphous. See Table 1 for selected bond distances and angles.

Reduction of TetraValent Group 4 Metal â-Diketiminates
Table 1. Selected Bond Lengths (Å) and Angles (deg)
3b 3c
Organometallics, Vol. 25, No. 10, 2006 2459
7
M-N1
2.187(3)
2.226(3)
1.396(6)
1.397(6)
1.367(5)
1.343(5)
2.4197(11)
2.4381(11)
2.4266(11)
2.297(3)
3.1319(14)
3.4046(13)
3.1455(12)
86.34(12)
2.168(3)
2.238(3)
1.388(6)
1.394(6)
1.372(5)
1.326(5)
2.4351(11)
2.4256(11)
2.4178(11)
2.302(3)
3.1142(12)
3.3904(12)
3.1376(12)
86.12(12)
2.1785(18)
2.2088(18)
1.398(3)
1.392(2)
1.355(3)
1.343(3)
2.4070(5)
2.4219(5)
2.4130(6)
2.2771(15)
3.106(2)
3.389(2)
3.120(2)
87.12(7)
2.1619(18)
2.2185(18)
1.394(3)
1.402(3)
1.355(3)
1.332(3)
2.4117(5)
2.4184(6)
2.4087(6)
2.2758(15)
3.087(2)
3.376(2)
3.123(2)
86.92(7)
2.000(3)
1.981(3)
1.396(5)
1.391(5)
1.351(4)
1.345(4)
2.2587(12)
2.2829(11)
M-N2
C1-C2
C2-C3
C1-N1
C3-N2
M-Cl1
M-Cl2
M-Cl3
M-O1
M‚‚‚C1
M‚‚‚C2
M‚‚‚C3
N1-M-N2
2.981(3)
3.004(3)
3.310(3)
88.59(11)
Scheme 2. Reduction of â-Diketiminato Complexes of Group
red, red, and violet crystals, respectively, instead of the expected
divalent complexes [MIICl(nacnac)(L)n] (6a, M ) Ti; 6b, M )
Zr; 6c, M ) Hf; L ) thf or LiCl(tmeda), etc.) (Table 2, entries
1, 3, and 5). The formation of 4a-c was confirmed by the
combination of 1H, 13C, and 7Li NMR spectra and X-ray
diffraction studies.
4 Metals
When the reduction of the titanium and zirconium complexes
2a and 3b was performed in the absence of tmeda, the reaction
mixtures showed complicated 1H NMR spectra (Table 2, entries
2 and 4). Addition of LiCl and tmeda to a benzene solution of
these reaction mixtures resulted in the formation of titanium-
and zirconium-imido ate complexes 4a and 4b, respectively.
In the hafnium case, complex 5c was formed by the reaction of
3c with 2 equiv of KC8 (Scheme 2, Table 2, entry 6). Similar
types of zirconium-imido complexes have been reported by
Mindiola et al., quite recently.18 Addition of LiCl and tmeda to
a benzene solution of 5c resulted in the formation of hafnium-
imido ate complex 4c.
Table 2. Reduction of 2a, 3b, or 3c
When a mixture of [Li(nacnac)] (1) and an equimolar amount
of TiCl3(thf)3 was stirred in benzene for 3 h, a dark green
solution was formed (Scheme 3). Recrystallization of the mixture
from toluene gave the corresponding trivalent titanium complex
[TiIIICl2(nacnac)] (7). The EPR spectrum of 7 (g| ) 1.931, g
) 1.949) at room temperature and the magnetic moment of 7
(µeff ) 1.60 µB, determined by Evans method24) are consistent
with those of d1 paramagnetic species. For example, Mindiola
et al. recently reported the EPR spectrum (giso ) 1.97) and the
magnetic moment (µeff ) 2.17 µB) of [Ti{CH2(t-Bu)2}2[{N-
(Dip)C(Me)}2CH]].17d
entry
S. M.
LiCl, tmeda
yield/%
1
2
3
4
5
6
2a
2a
3b
3b
3c
3c
+
-
+
-
+
-
87 (4a)
a
80 (4b)
a
81 (4c)
82 (5c)
a The reaction mixtures showed complicated H NMR spectra.
1
nato ligands of zirconium complexes claimed by Mindiola18 and
Lappert,13a respectively.
The X-ray crystallography of the hafnium complex 3c also
showed two independent molecules in the unit cell, and both
molecules have structures essentially identical with each other.
The two sets of C-N and C-C distances in the ligand skeleton
are almost equivalent to each other. The M-N1, M-N2,
M-O1, M-Cl1, M-Cl2, and M-Cl3 distances of 3c are close
to those of 3b probably due to the lanthanoid contraction. The
central hafnium atoms of the two independent molecules deviate
from the N2C3 planes by 0.7409(27) and 0.7744(27) Å,
respectively. The â-diketiminato ligand in 3c can also be
considered to have the η2-coordinaton mode, which is identical
with some of the hafnium complexes reported by Lappert.13b
These characteristics of 3c are similar to those of 3b.
Two-electron reduction of 2a, 3b, and 3c to the corresponding
divalent complexes was examined by the use of KC8 (Scheme
2 and Table 2).
The X-ray study of 7 showed a distorted, tetrahedral geometry
at the titanium center (Figure 3). Selected structural parameters
and the crystallographic data are summarized in Tables 1 and
5, respectively.
The central titanium atom deviates from the N2C3 planes by
0.5474(36) Å. However, the Ti-C (ligand backbone) distances
[2.981(3) Å (Ti-C1), 3.004(3) Å (Ti-C2), and 3.310(3) Å (Ti-
C3)] are too long to form real Ti-C bonds. Therefore, the
â-diketiminato ligand in 7 can be considered to have the η2-
coordinaton mode, which is identical with those of titanium-
(III) complexes reported by Budzelaar15 and Mindiola.17d Hence,
7 is best described as a nine-electron, electron-deficient complex.
Next, the reduction of trivalent titanium â-diketiminate 7 to
the corresponding divalent titanium complex was examined by
using several reductants (Scheme 3 and Table 3).
The reactions of 7 with Na, K, LiC10H8 (lithium naphtha-
lenide), and KC8 in the presence of LiCl and tmeda afforded
In the reactions of â-diketiminato complexes of group 4
metals 2c, 3b, and 3c with KC8 in the presence of LiCl and
Me2NCH2CH2NMe2 (tmeda), imido complexes [MdNTbt-
{C(Me)CHC(Me)N(Mes)}(µ-Cl)2Li(tmeda)] (4a, M ) Ti; 4b,
M ) Zr; 4c, M ) Hf) were quantitatively formed as yellowish-
(24) (a) Evans, D. F. J. Chem. Soc. 1959, 2003-2005. (b) Naklicki, M.
L.; White, C. A.; Plante, L. L.; Evans, C. E. B.; Crutchley, R. J. Inorg.
Chem. 1998, 37, 1880-1885.

2460 Organometallics, Vol. 25, No. 10, 2006
Scheme 3. Reduction of Trivalent Titanium â-Diketiminates
Hamaki et al.
Table 3. Reduction of 7
Table 4. Selected Bond Lengths (Å) and Angles (deg)
entry
reductant
resultsa
4a
4b
4c
5c
1
2
3
4
5
Li
Na
K
complicated mixture
4a (quant)
4a (quant)
4a (97%) + 1‚(thf) (3%)
4a (quant)
M-N1
1.717(4)
2.202(4)
2.192(5)
1.339(7)
1.448(7)
1.296(6)
2.4185(17)
2.4223(17)
1.8534(16)
2.3233(17)
2.322(2)
1.347(3)
1.454(3)
1.301(3)
2.5429(8)
2.5481(8)
1.8427(17)
2.2884(18)
2.288(2)
1.347(3)
1.455(3)
1.301(3)
2.5078(6)
2.5112(6)
1.799(9)
M-N2
2.301(10)
2.293(13)
1.358(16)
1.453(18)
1.289(15)
2.429(3)
M-C1
LiC10H8/THF
KC8
C1-C2
C2-C3
C3-N2
M-Cl1
M-Cl2
M-O1
a Judged by the H NMR spectrum.
1
2.222(9)
166.7(7)
72.6(4)
M-N1-C6
C1-M-N2
175.1(3)
75.50(16)
172.44(13)
72.53(7)
173.29(15)
73.59(7)
reductive cleavage of the C-N bond connecting to the bulkier
Tbt group of the intermediary divalent complexes [MIICl-
(nacnac)(L)n] (6a-c, Scheme 5).
This unique regioselectivity may be explained in terms of
the more servere repulsion of the Tbt group with the methyl
group at the 5-position in the exited state or the product in path
B compared with that in path A (Scheme 5), although it is
unclear whether this reaction is controlled thermodynamically
or kinetically.
Figure 3. Molecular structure of the trivalent titanium complex 7
with thermal ellipsoids at the 50% probability level. H atoms and
solvent molecules are omitted for clarity. See Table 1 for selected
bond distances and angles.
Scheme 4. Reaction of Lithium â-Diketiminate with Divalent
[TiCl2(tmeda)2]
Structures of Imido Complexes. A characteristic feature of
4a-c and 5c is the 13C NMR chemical shifts for the vinylic
carbons connecting to the metal atoms, which resonated at 237.2,
237.2, 242.6, and 236.3 ppm, respectively. These values are
consistent with those of the reported group 4 metal complexes
bearing a vinyl group.18
The molecular structures of imido complexes 4a-c and 5c
were determined by X-ray diffraction. Since all three metal-
imido ate complexes 4a-c are isomorphous, the ORTEP
drawing of hafnium complex 4c is depicted in Figure 4 as the
representative (Figure 4a) together with that of THF-coordinated
hafnium 5c (Figure 4b). The selected bond lengths and angles
and crystallographic data are summarized in Tables 4 and 5,
respectively.
the titanium-imido ate complex 4a almost quantitatively (Table
3, entries 2-5), while the reduction of 7 using Li resulted in
the formation of a complicated mixture (Table 3, entry 1). In
addition, the reaction of 1 with a divalent titanium complex,
[TiCl2(tmeda)2], also resulted in the formation of 4a (Scheme
4).
Taking these results into consideration, we propose that imido
complexes 4a-c and 5c are formed via the regioselective,
The M-N1 distances of 4a-c and 5c [4a, 1.717(4) Å; 4b,
1.8534(16) Å; 4c, 1.8427(17) Å; 5c, 1.799(9) Å] are close to
Scheme 5. Possible Mechanism for the Formation of Metal-Imido Complexes 4a-c and 5c via Divalent Complexes 6a-c

Reduction of TetraValent Group 4 Metal â-Diketiminates
Organometallics, Vol. 25, No. 10, 2006 2461
Table 5. Crystal Data and Structure Refinement Details for 3b,c, 4a-c, 5c, and 7
3b‚0.25C6H14
3c‚0.25C6H14
4a
4b‚C6H14
empirical formula
fw
C45H85Cl3N2OSi6Zr‚0.25C6H14
1057.80
C45H85Cl3HfN2OSi6‚0.25C6H14
1145.07
C47H93Cl2LiN4Si6Ti
1008.53
C47H93Cl2LiN4Si6Zr‚C6H14
1138.03
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
triclinic
P1h (#2)
triclinic
P1h (#2)
triclinic
P1h (#2)
triclinic
P1h (#2)
11.6646(2)
18.3088(2)
28.9532(7)
74.582(5)
82.573(6)
77.117(6)
5794.67(18)
4
11.65970(10)
18.3005(2)
28.9162(3)
74.6796(8)
82.5888(4)
77.1249(5)
5785.06(10)
4
12.724(5)
12.781(6)
19.884(8)
85.729(15)
72.206(12)
87.540(15)
3070(2)
12.718(3)
15.788(4)
19.011(5)
99.7567(19)
108.1972(17)
102.239(2)
3427.8(15)
2
Z
D
2
calc (g cm-3
)
1.213
1.315
1.091
1.103
cryst dimens
0.50 × 0.20 × 0.02
2.63-25.0
0.485
0.30 × 0.30 × 0.30
1.18-25.0
2.099
0.50 × 0.30 × 0.20
2.29-25.0
0.375
0.60 × 0.20 × 0.20
2.33-25.0
0.376
θ range (deg)
abs coeff (mm-1
)
no. of reflens collcd
no. of unique reflens
no. of params
48 307
20 236
1118
0.0607, 0.1246
1.121
48 984
20 242
1119
0.0204, 0.0477
1.069
25 376
10 719
550
0.0848, 0.1558
1.181
0.461, -0.543
28 098
11 929
686
0.0330, 0.0795
1.062
0.701, -0.275
R1, wR2 (for I > 2σ(I))a
goodness-of-fit
largest peak, hole (e/Å-3
)
0.819, -0.398
0.657, -0.454
4c‚C6H14
5c‚C6H14
7
empirical formula
fw
C47H93Cl2HfLiN4Si6‚C6H14
1250.30
C45H85ClHfN2OSi6‚C6H14
1052.63
C41H77Cl2N2Si6Ti
885.39
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
triclinic
P1h (#2)
triclinic
P1h (#2)
monoclinic
C2/c (#15)
47.617(3)
9.5808(5
23.4963(16)
12.6966(17)
15.754(2)
19.249(3)
72.090(5)
69.348(4)
77.721(6)
3404.6(8)
2
9.5578(18)
12.345(2)
25.424(6)
87.842(10)
82.127(12)
71.02(2)
2809.9(10)
2
1.244
101.676(3)
10497.3(11)
8
1.120
Z
D
calc (g cm-3
)
1.195
cryst dimens
0.30 × 0.20 × 0.10
2.74-25.0
1.749
0.50 × 0.30 × 0.10
2.96-25.0
2.063
0.60 × 0.20 × 0.15
2.31-25.00
0.429
θ range (deg)
abs coeff (mm-1
)
no. of reflens collcd
no. of unique reflens
no. of params
29 459
12 554
686
0.0225, 0.0487
1.062
0.742, -0.449
16 469
8329
528
0.0786, 0.1337
1.097
2.564, -1.669
42 496
9188
545
0.0688, 0.1669
1.104
0.960, -0.623
R1, wR2 (for I > 2σ(I))a
goodness-of-fit
largest peak, hole (e/Å-3
)
2
2
2
a R1 ) ∑||Fo| - |Fc||/|Fo|; wR2 ) [∑w(Fo2 - Fc )2/∑w(Fo )2]1/2, where w ) 1/[σ2(Fo2 + (aP)2 + bP], P ) (Fo2 + 2Fc )/3, and a and b are constants given
in the Supporting Information.
those of the reported imido complexes of group 4 metals (Tid
N, 1.67-1.73 Å;12a,17,25 ZrdN, 1.83-1.93 Å;18,26 and HfdN,
1.82-1.86 Å26b,27) and much shorter than the M-N2 distances
[4a, 2.202(4) Å; 4b, 2.3233(17) Å; 4c, 2.2884(18) Å; 5c, 2.301-
(10) Å]. The M-N1 distance of 4c is close to that of 4b
probably due to the lanthanoid contraction and longer than that
of 5c. Complexes 4a-c and 5c have a nearly linear MdN-C6
alignment. These characteristics of 4a-c and 5c are similar to
those for the reported imido complexes.12a,17,18,25-27 In addition,
the ring M-C1-C2-C3-N2 is almost planar.
Hydrolysis of Imido Complexes. The reactions of the group
4 metal-imido complexes 4a-c and 5c with H2O resulted in
the quantitative formation of the free ligand nacnacH (8) via
the reconstruction of the â-diketiminato ligand (Scheme 6). The
regeneration of the â-diketiminato ligand is a fascinating
process, although the mechanism for the hydrolysis is unclear
at present.
Conclusion
We presented here the systematic studies on the synthesis of
the imido complexes of group 4 metals [MdNTbt{C(Me)CHC-
(26) (a) Zuckerman, R. L.; Bergman, R. G. Organometallics 2000, 19,
4795-4809. (b) Thorman, J. L.; Guzei, I. A.; Young, V. G., Jr.; Woo, L.
K. Inorg. Chem. 1999, 38, 3814-3824. (c) Krska, S. W.; Zuckeman, R.
L.; Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 11828-11829. (d) Profilet,
R. D.; Zambrano, C. H.; Fanwick, P. E.; Nash, J. J.; Rothwell, I. P. Inorg.
Chem. 1990, 29, 4362-4364. (e) Fryzuk, M. D.; Love, J. B.; Rettig, S. J.
Organometallics 1998, 17, 846-853. (f) Ong, T.-G.; Wood, D.; Yap, G.
P. A.; Richeson, D. S. Organometallics 2002, 21, 1-3. (g) Blake, A. J.;
Collier, P. E.; Gade, L. H.; Mountford, P.; Lloyd, J.; Pugh, S. M.; Schubart,
M.; Skinner, M. E. G.; Tro¨sch, D. J. M. Inorg. Chem. 2001, 40, 870-877.
(h) Walsh, P. J.; Hollander, F. J.; Bergman, R. G. J. Am. Chem. Soc. 1988,
110, 8729-8731. (i) Arney, D. J.; Bruck. M. A.; Huber, S. R.; Wigley, D.
E. Inorg. Chem. 1992, 31, 3749-3755. (j) Breen, T. L.; Stephan, D. W. J.
Am. Chem. Soc. 1995, 117, 11914-11921.
(25) (a) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. J.
Organomet. Chem. 2000, 600, 71-83. (b) Adams, N.; Arts, H. J.; Bolton,
P. D.; Cowell, D.; Dubberley, S. R.; Friederichs, N.; Grant, C. M.;
Kranenburg, M.; Sealey, A. J.; Wang, B.; Wilson., P. J.; Cowley, A. R.;
Mountford, P.; Schro¨der, M. Chem. Commun. 2004, 434-435. (c) Stewrat,
P. J.; Blake, A. J.; Mountford, P. Organometallics 1998, 17, 3271-3281.
(27) (a) Zambrano, C. H.; Profilet, R. D.; Hill, J. E.; Fanwick, P. E.;
Rothwell, I. P. Polyhedron 1993, 12, 689-708. (b) Castillo, I.; Tilley T.
D. J. Organomet. Chem. 2002, 643-644, 431-440.

2462 Organometallics, Vol. 25, No. 10, 2006
Hamaki et al.
1
according to the methods in the literatures. H NMR (300 MHz),
13C NMR (75 MHz), and 7Li NMR (116 MHz) spectra were
1
recorded on a JEOL JNM AL-300 spectrometer. The H NMR
chemical shifts were reported with reference to the internal residual
CHCl3 (7.25 ppm) or C6D5H (7.15 ppm). The 13C NMR chemical
shifts were reported with reference to the carbon-13 signal of C6D6
(128.0 ppm). Multiplicity of signals in 13C NMR spectra was
7
determined by DEPT techniques. The Li NMR chemical shifts
were reported with reference to the external standards, LiCl (0 ppm).
The X-band EPR spectrum was recorded on a Bruker EMX
spectrometer. Melting points were determined on a Yanaco micro
melting point apparatus and are uncorrected. Elemental analyses
were carried out at the Microanalytical Laboratory of the Institute
for Chemical Research, Kyoto University. Multiple attempts to
obtain a satisfactory elemental analysis of complexes 2a and 3b
were unsuccessful due to their extremely high moisture sensitivity.
EI- and FAB-mass spectra (matrix: 3-nitrobenzyl alcohol or
2-nitrophenyl octyl ether) of all complexes indicated that the highest
mass fragment was observed at m/z 766 (nacnacH, 8) or 767 ([8 +
H]+), suggesting hydrolysis during the measurements. The purity
1
1
of all complexes was confirmed by the H NMR spectra. The H
NMR spectra of all complexes are depicted in Figures S1-S7 in
the Supporting Information.
Figure 4. Molecular structures of the hafnium-imido complexes
4c (a) and 5c (b) with thermal ellipsoids at the 50% and 30%
probability levels, respectively. H atoms and solvent molecules are
omitted for clarity. The titanium and zirconium analogues (4a and
4b) are isomorphous. See Table 5 for selected bond distances and
angles of 4a-c and 5c.
Synthesis of [TiCl3(nacnac)] (2a). A solution of [Li(nacnac)]
(1, 80.3 mg, 103 µmol) in benzene (1 mL) was added to a slurry
of TiCl4(thf)2 (34.5 mg, 103 µmol) in benzene (1 mL), causing the
development of a dark red color. The reaction mixture was stirred
for 3 h, and the solvent was removed under reduced pressure.
Toluene was added to the red residue, and the filtration through
Celite gave a dark red solution. The filtrate was dried under vacuum,
and the product was recrystallized from toluene at -40 °C, yielding
the almost pure product as dark red crystals. [TiCl3(nacnac)] (2a,
86.3 mg, 92%): mp 184-187 °C (dec). 1H NMR (300 MHz,
C6D6): δ 0.17 (s, 18 H, SiMe3), 0.22 (s, 18H, SiMe3), 0.37 (s, 18H,
SiMe3), 1.31 (s, 3H, Me), 1.49 (s, 1H, Tbt p-benzyl), 1.73 (s, 3H,
Me), 2.03 (s, 3H, Me), 2.27 (s, 6H, Mes o-Me), 2.61 (s, 1H, Tbt
o-benzyl), 2.81 (s, 1H, Tbt o-benzyl), 5.79 (s, 1H, 3-CH), 6.56 (br
s, 1H, Tbt m-H), 6.68 (s, 2H, Mes m-H), 6.70 (br s, 1H, Tbt m-H).
13C NMR (75 MHz, C6D6): δ 1.2 (q, SiMe3), 2.6 (q, SiMe3), 2.8
(q, SiMe3), 20.5 (q, Me), 20.9 (q, Mes o-Me), 22.6 (d, Tbt o-benzyl),
23.2 (d, Tbt o-benzyl), 23.6 (q, Me), 29.8 (q, Me), 30.3 (d, Tbt
p-benzyl), 110.1 (d, 3-CH), 124.4 (d, Tbt Cm), 128.3 (d, Mes Cm),
129.1 (d, Tbt Cm), 129.2 (s), 131.2 (s), 138.8 (s), 139.5 (s), 141.7
(s, Mes Co), 146.2 (s), 147.8 (s), 166.6 (s, C(N)), 176.6 (s, C(N)).
Scheme 6. Reaction of Metal-Imido Complexes with H2O
(Me)N(Mes)}(µ-Cl)2Li(tmeda)] (M ) Ti, Zr, Hf, 4a-c) by the
reduction of the tetravalent or trivalent group 4 metal â-diketim-
inates [MIVCl3(nacnac)(thf)n] (M ) Ti, Zr, Hf, 2a, 3b, and 3c)
or [TiIIICl2(nacnac)] (7) in the presence of LiCl and tmeda. As
another hafnium complex, THF-coordinated complex [Hfd
NTbt{C(Me)CHC(Me)N(Mes)}Cl(thf)] (5c) was also formed
by the reaction of 3c with 2 equiv of KC8. In addition, the
reaction of [Li(nacnac)] (1) with a divalent titanium complex,
[TiCl2(tmeda)2], resulted in the formation of 4a. The formation
of the imido complexes 4a-c is most likely explained in terms
of the initial generation of the corresponding divalent complexes
[MIICl(nacnac)(L)n] (M ) Ti, Zr, Hf; L ) thf or Li(tmeda),
etc., 6a-c) followed by the regioselective, reductive cleavage
of the CdN bond tethered to the Tbt group. Interestingly, the
reactions of 4a-c with H2O resulted in the quantitative
formation of the free ligand, nacnacH (8), via the reconstruction
of the â-diketiminato ligand.
Synthesis of [ZrCl3(nacnac)(thf)] (3b). A solution of [Li-
(nacnac)] (1, 79.8 mg, 103 µmol) in benzene (1 mL) was added to
a slurry of ZrCl4(thf)2 (39.0 mg, 103 µmol) in benzene (1 mL),
causing the development of a yellow color. The procedure similar
to that in the preparation of 2a afforded the almost pure product as
yellow crystals. [ZrCl3(nacnac)(thf)] (3b, 92.9 mg, 87%): mp 189-
1
192 °C (dec). H NMR (300 MHz, C6D6): δ 0.22 (s, 9H, SiMe3),
0.30 (s, 9H, SiMe3), 0.33 (s, 9H, SiMe3), 0.49 (s, 9H, SiMe3), 0.53
(s, 9H, SiMe3), 0.57 (s, 9H, SiMe3), 1.14 (br, 4H, thf â-H), 1.37 (s,
3H, Me), 1.47 (s, 3H, Me), 1.55 (s, 1H, Tbt p-benzyl), 2.09 (s, 3H,
Me), 2.25 (s, 3H, Me), 2.34 (s, 3H, Me), 2.86 (s, 1H, Tbt o-benzyl),
3.26 (s, 1H, Tbt o-benzyl), 3.82 (br, 4H, thf â-H), 5.49 (s, 1H,
3-CH), 6.64 (br s, 1H, Tbt m-H), 6.72 (br, 2H, Mes m-H), 6.86 (br
s, 1H, Tbt m-H). 13C NMR (75 MHz, C6D6): δ 1.3 (q, SiMe3), 1.4
(q, SiMe3), 2.8 (q, SiMe3), 3.0 (q, SiMe3), 3.58 (q, SiMe3), 3.63 (q,
SiMe3), 20.1 (q, Me), 20.6 (q, Me), 20.9 (q, Me), 22.2 (d, Tbt
o-benzyl), 23.2 (d, Tbt o-benzyl), 24.6 (q, Me), 25.0 (t, thf Câ),
30.5 (q, Me), 30.6 (d, Tbt p-benzyl), 76.1 (t, thf CR), 107.1 (d,
3-CH), 125.1 (d, Tbt Cm), 129.1 (d, Tbt Cm), 129.8 (d, Mes Cm),
130.1 (d, Mes Cm), 134.0 (s), 135.5 (s), 139.2 (s), 140.3 (s), 140.8
(s), 141.9 (s), 142.7 (s), 145.3 (s), 170.3 (s, C(N)), 171.7 (s, C(N)).
Experimental Section
General Considerations. Unless otherwise stated, all operations
were performed in an MBRAUN Labmaster glovebox under an
atmosphere of purified argon. Celite was activated at 200 °C under
vacuum for 1 day. [Li(nacnac)] (1),23 [MCl4(thf)2] (M ) Ti, Zr,
30
Hf),28 [TiCl2(tmeda)2],8a LiC10H8,29 and KC8 were prepared
(28) Manzer, L. E. Inorg. Synth. 1982, 21, 135-140.
(29) Suga, K.; Watanabe, S.; Kamma, K. Can. J. Chem. 1967, 45, 933-
937.
Synthesis of [HfCl3(nacnac)(thf)] (3c). A solution of [Li-
(nacnac)] (1, 80.1 mg, 103 µmol) in benzene (1 mL) was added to
(30) Schwindt, M.; Lejon, T.; Hegedus, L. S. Organometallics 1990, 9,
2814-2819.

Reduction of TetraValent Group 4 Metal â-Diketiminates
Organometallics, Vol. 25, No. 10, 2006 2463
a slurry of HfCl4(thf)2 (48.0 mg, 103 µmol) in benzene (1 mL),
causing the development of a pale yellow color. The procedure
similar to that in the preparation of 2a afforded the almost pure
product as yellow crystals. [HfCl3(nacnac)(thf)] (3c, 99.5 mg,
86%): mp 196-199 °C (dec). 1H NMR (300 MHz, C6D6): δ 0.23
(s, 9H, SiMe3), 0.30 (s, 9H, SiMe3), 0.34 (s, 9H, SiMe3), 0.50 (s,
9H, SiMe3), 0.534 (s, 9H, SiMe3), 0.58 (s, 9H, SiMe3), 1.07 (br,
4H, thf â-H), 1.33 (s, 3H, Me), 1.45 (s, 3H, Me), 1.55 (s, 1H, Tbt
p-benzyl), 2.09 (s, 3H, Me), 2.26 (s, 3H, Me), 2.35 (s, 3H, Me),
2.94 (s, 1H, Tbt o-benzyl), 3.31 (s, 1H, Tbt o-benzyl), 3.82 (br,
4H, thf â-H), 5.37 (s, 1H, 3-CH), 6.63 (br s, 1H, Tbt m-H), 6.72
(br, 2H, Mes m-H), 6.86 (br s, 1H, Tbt m-H). 13C NMR (75 MHz,
C6D6): δ 1.0 (q, SiMe3), 1.3 (q, SiMe3), 2.8 (q, SiMe3), 3.0 (q,
SiMe3), 3.6 (q, SiMe3), 3.7 (q, SiMe3), 20.1 (q, Me), 20.5 (q, Me),
20.7 (q, Me), 22.1 (d, Tbt o-benzyl), 23.0 (d, Tbt o-benzyl), 24.8
(q, Me), 25.0 (t, thf Câ), 30.4 (d, Tbt p-benzyl), 30.9 (q, Me), 77.2
(t, thf CR), 106.8 (d, 3-CH), 125.1 (d, Tbt Cm), 129.1 (d, Tbt Cm),
129.8 (d, Mes Cm), 130.1 (d, Mes Cm), 134.5 (s), 135.4 (s), 139.2
(s), 140.2 (s), 141.2 (s), 142.4 (s), 142.6 (s), 144.9 (s), 170.9 (s,
C(N)), 173.1 (s, C(N)). Anal. Calcd for C45H85N2OSi6Cl3Hf: C,
48.11; H, 7.63; N, 2.49. Found: C, 48.33; H, 7.86; N, 2.36.
0.68. Anal. Calcd for C47H93LiN4Si6Cl2Zr: C, 53.67; H, 8.91; N,
5.33. Found: C, 53.42; H, 9.12; N, 5.04.
Reduction of [HfCl3(nacnac)(thf)] (3c). A reductant [LiC10H8/
THF solution (1.0 M, 210 µL, 210 µmol) or KC8 (36.0 mg, 266
µmol)] was added to a benzene suspension (1 mL) of [Li(nacnac)]
(1, 79.8 mg, 103 µmol) and HfCl4(thf)2 (48.3 mg, 103 µmol) in
the presence of tmeda (200 µL, 200 µmol), causing the development
of a violet color. The procedure similar to that in the preparation
of 4a afforded the almost pure product 4c as violet crystals. [Hfd
NTbt{C(Me)CHC(Me)N(Mes)}(µ-Cl)2Li(tmeda)] (4c, 95.0 mg,
81%): mp 173-176 °C (dec). 1H NMR (300 MHz, C6D6): δ 0.31
(s, 18H, SiMe3), 0.42 (s, 36H, SiMe3), 1.48 (s, 3H, Me), 1.49 (s,
1H, Tbt p-benzyl), 1.90 (br s, 4H, tmeda CH2), 1.96 (br s, 12H,
tmeda Me), 2.16 (s, 3H, Me), 2.25-2.45 (br s, 6H, Mes o-Me),
4
3.01 (d, JHH ) 1.5 Hz, 3H, Me), 3.75 (s, 2H, Tbt o-benzyl), 6.63
4
(br s, 2H, Tbt m-H), 6.83 (s, 2H, Mes m-H), 6.86 (q, JHH ) 1.5
Hz, 1H, vinyl-H). 13C NMR (300 MHz, C6D6): δ 1.3 (q, SiMe3),
1.8 (q, SiMe3), 20.2 (q, Me), 20.8 (d, Tbt o-benzyl), 20.9 (q, Mes
o-Me), 21.4 (q, Me), 29.4 (d, Tbt p-benzyl), 32.9 (q, Me), 45.7 (q,
tmeda Me), 56.8 (t, tmeda CH2), 128.3 (d, Tbt Cm), 129.1 (d, Mes
Cm), 129.9 (s), 132.3 (s), 135.1 (s), 135.3 (d, vinyl C), 137.5 (s),
143.1 (s), 154.0 (s, Tbt Cipso), 182.6 (C(N)), 242.6 (Hf-C). 7Li NMR
(rt, 116 MHz, C6D6): δ 0.57. Anal. Calcd for C47H93LiN4Si6Cl2-
Hf: C, 49.56; H, 8.23; N, 4.92. Found: C, 49.59; H, 8.49; N, 4.53.
Reduction of [TiCl3(nacnac)] (2a). A reductant [LiC10H8/THF
solution (1.0 M, 52 µL, 52 µmol) or KC8 (7.0 mg, 52 µmol)] was
added to a benzene suspension (1 mL) of [Li(nacnac)] (1, 40.0 mg,
51.7 µmol) and TiCl4(thf)2 (17.2 mg, 51.7 µmol) in the presence
of tmeda (100 µL, 100 µmol), causing the development of a dark
red color. The reaction mixture was stirred for 1 day, and the solvent
was removed under reduced pressure. Toluene was added to the
dark red residue, and filtration through Celite gave a dark red
solution. The filtrate was dried under vacuum, and the product was
recrystallized from hexane at 0 °C, yielding yellowish-red crystals
of 4a. [TidNTbt{C(Me)CHC(Me)N(Mes)}(µ-Cl)2Li(tmeda)] (4a,
45.4 mg, 87%): mp 164-166 °C (dec). 1H NMR (300 MHz,
C6D6): δ 0.24 (s, 18H, SiMe3), 0.41 (s, 36H, SiMe3), 1.45 (s, 1H,
Tbt p-benzyl), 1.48 (s, 3H, Me), 1.67 (br s, 4H, tmeda CH2), 1.90
(br s, 12H, tmeda Me), 2.20 (s, 3H, Me), 2.20-2.40 (br s, 6H, Mes
o-Me), 3.02 (d, 4JHH ) 1.4 Hz, 3H, Me), 3.94 (s, 2H, Tbt o-benzyl),
Reduction of [HfCl3(nacnac)(thf)] (3c) in the Absence of
tmeda. KC8 (35.9 mg, 266 µmol) was added to a benzene
suspension (1 mL) of [Li(nacnac)] (1, 80.2 mg, 51.7 µmol) and
HfCl4(thf)2 (48.1 mg, 103 µmol), causing the development of a
dark violet color. The procedure similar to that in the preparation
of 4a afforded the almost pure product 5c as violet crystals. [Hfd
NTbt{C(Me)CHC(Me)N(Mes)}Cl(thf)] (5c, 87.8 mg, 82%): mp
1
143-145 °C (dec). H NMR (300 MHz, C6D6): δ 0.31 (s, 18H,
SiMe3), 0.42 (s, 36H, SiMe3), 1.48 (s, 3H, Me), 1.49 (s, 1H, Tbt
p-benzyl), 1.90 (br s, 4H, tmeda CH2), 1.96 (br s, 12H, tmeda Me),
2.16 (s, 3H, Me), 2.25-2.45 (br s, 6H, Mes o-Me), 3.01 (d, 4JHH
)
1.3 Hz, 3H, Me), 3.75 (s, 2H, Tbt o-benzyl), 6.63 (br s, 2H, Tbt
4
4
6.45 (br s, 2H, Tbt m-H), 6.59 (q, JHH ) 1.4 Hz, 1H, vinyl-H),
m-H), 6.83 (s, 2H, Mes m-H), 6.86 (q, JHH ) 1.3 Hz, 1H, vinyl-
6.84 (s, 2H, Mes m-H). 13C NMR (75 MHz, C6D6): δ 1.2 (q,
SiMe3), 1.9 (q, SiMe3), 19.7 (q, Me), 20.1 (q, Mes o-Me), 20.7 (q,
Me), 20.9 (d, Tbt o-benzyl), 30.2 (d, Tbt p-benzyl), 33.9 (q, Me),
45.7 (q, tmeda Me), 56.4 (t, tmeda CH2), 128.3 (d, Tbt Cm), 128.6
(d, Mes Cm), 130.5 (s), 132.6 (d, vinyl C), 134.2 (s), 134.5 (s),
139.7 (s), 145.5 (s), 160.5 (s, Tbt Cipso), 180.8 (C(N)), 237.2 (Ti-
H). 13C NMR (75 MHz, C6D6): δ 0.9 (q, SiMe3), 1.2 (q, SiMe3),
1.8 (q, SiMe3), 20.4 (q, Me), 20.9 (q, Mes o-Me), 21.6 (q, Me),
21.9 (d, Tbt o-benzyl), 25.0 (t, thf Câ), 29.4 (d, Tbt p-benzyl), 30.8
(q, Me), 75.0 (t, thf CR), 129.1 (d, Tbt Cm), 129.8 (d, Mes Cm),
130.5 (s), 130.7 (s), 131.3 (s), 135.5 (s), 136.7 (s), 137.1 (d, vinyl
C), 153.8 (s, Tbt Cipso), 183.8 (C(N)), 236.3 (Hf-C). Anal. Calcd
for C45H85N2OSi6ClHf: C, 51.35; H, 8.14; N, 2.66. Found: C,
51.61; H, 8.29; N, 2.72.
7
C). Li NMR (116 MHz, C6D6): δ 0.81. Anal. Calcd for C47H93-
LiN4Si6Cl2Ti: C, 55.97; H, 9.29; N, 5.56. Found: C, 55.72; H,
9.52; N, 5.80.
Synthesis of [TiCl2(nacnac)] (7). A solution of [Li(nacnac)] (1,
80.0 mg, 103 µmol) in benzene (1 mL) was added to a slurry of
TiCl3(thf)3 (38.3 mg, 103 µmol) in benzene (1 mL), causing the
development of a dark green color. The procedure similar to that
in the preparation of 2a afforded the product as dark green crystals.
[TiCl2(nacnac)] (7, 82.1 mg, 90%): mp 268-273 °C (dec). EPR
(benzene, rt) g| ) 1.931, g ) 1.949. A 10 mM C6D6 solution
(2.00 mL) of 7 (18.4 mg) was measured by 1H NMR spectroscopy
at 26.6 °C. The magnetic moment of 7 was determined by Evans’
method (µeff ) 1.60 µB).24 Anal. Calcd for C41H77N2Si6Cl2Ti: C,
55.62; H, 8.77; N, 3.16. Found: C, 55.33; H, 8.95; N, 2.96.
Reduction of [ZrCl3(nacnac)(thf)] (3b). A reductant [LiC10H8/
THF solution (1.0 M, 210 µL, 210 µmol) or KC8 (35.9 mg, 266
µmol)] was added to a benzene suspension (1 mL) of [Li(nacnac)]
(1, 79.8 mg, 103 µmol) and ZrCl4(thf)2 (39.1 mg, 103 µmol) in the
presence of tmeda (200 µL, 200 µmol), causing the development
of a dark red color. The procedure similar to that in the preparation
of 4a afforded the almost pure product 4b as red crystals. [Zrd
NTbt{C(Me)CHC(Me)N(Mes)}(µ-Cl)2Li(tmeda)] (4b, 86.7 mg,
80%): mp 207-210 °C (dec). 1H NMR (300 MHz, C6D6): δ 0.28
(s, 18H, SiMe3), 0.41 (s, 36H, SiMe3), 1.48 (br, 4H, Tbt p-benzyl
+ Me), 1.85 (br s, 4H, tmeda CH2), 1.95 (br s, 12 H, tmeda Me),
2.17 (s, 3H, Me), 2.22-2.35 (br s, 6H, Mes o-Me), 2.97 (d, 4JHH
)
Reduction of [TiCl2(nacnac)] (7). A reductant [Li (0.4 mg, 50
µmol), Na (1.2 mg, 50 µmol), K (2.0 mg, 52 µmol), LiC10H8/THF
solution (1.0 M, 52 µL, 52 µmol), or KC8 (7.0 mg, 52 µmol)] was
added to a benzene suspension (1 mL) of [Li(nacnac)] (1, 40.0 mg,
51.7 µmol) and TiCl3(thf)3 (19.2 mg, 51.7 µmol) in the presence
of tmeda (100 µL, 100 µmol), causing the development of a dark
red color. The procedure similar to that in the preparation of 2a
afforded the product 4a. In the reactions of 7 with Na, K, LiC10H8,
and KC8, titanium-imido complex [TidNTbt{C(Me)CHC(Me)N-
1.5 Hz, 3H, Me), 3.76 (s, 2H, Tbt o-benzyl), 6.57 (br s, 2H, Tbt
m-H), 6.78 (q, 4JHH ) 1.5 Hz, 1H, vinyl-H), 6.83 (s, 2H, Mes m-H).
13C NMR (75 MHz, C6D6): δ 1.2 (q, SiMe3), 1.8 (q, SiMe3), 20.1
(q, Me), 20.3 (q, Mes o-Me), 20.9 (q, Me), 21.4 (d, Tbt o-benzyl),
29.7 (d, Tbt p-benzyl), 32.7 (q, Me), 45.6 (q, tmeda Me), 56.5 (t,
tmeda CH2), 128.3 (d, Tbt Cm), 128.5 (d, Mes Cm), 129.7 (s), 131.1
(s), 135.0 (s), 135.7 (d, vinyl C), 137.0 (s), 143.0 (s), 153.8 (s, Tbt
C
ipso), 183.2 (C(N)), 237.2 (Zr-C). 7Li NMR (116 MHz, C6D6): δ

2464 Organometallics, Vol. 25, No. 10, 2006
Hamaki et al.
(Mes)}(µ-Cl)2Li(tmeda)] (4a) was quantitatively formed, but the
reduction of 7 using Li resulted in the formation of a complicated
mixture.
Reaction of [Li(nacnac)] (1) with TiCl2(tmeda). A solution of
[Li(nacnac)] (1, 40.0 mg, 51.7 µmol) in benzene (1 mL) was added
to a slurry of TiCl2(tmeda)2 (15.8 mg, 67.2 µmol) in benzene (1
mL), causing the development of a dark red color. The procedure
similar to that in the preparation of 4a afforded a mixture of 4a
and 1 (8:2). The product ratio was determined by 1H NMR
spectroscopy.
Reaction of Metal-Imido Complexes 4a-c or 5c with H2O.
A solution of 4a (40.1 mg, 39.7 µmol), 4b (40.1 mg, 38.0 µmol),
4c (40.3 mg, 35.1 µmol), or 5c (40.0 mg, 38.0 µmol) in C6D6 was
exposed to the air to result in the quantitative formation of the free
ligand nacnacH (8), which was confirmed by the 1H NMR spectrum.
8: 1H NMR (300 MHz, C6D6) δ 0.13 (s, 18H, SiMe3), 0.16 (s,
18H, SiMe3), 0.23 (s, 18H, SiMe3), 1.44 (s, 1H, Tbt p-benzyl), 1.57
(s, 3H, Me), 1.81 (s, 3H, Me), 2.15 (s, 3H, Me), 2.17 (s, 2H, Tbt
o-benzyl), 2.26 (s, 6H, Mes o-Me), 4.84 (s, 1H, 3-CH), 6.57 (br s,
2H, Tbt m-H), 6.83 (s, 2H, Mes m-H), 11.50 (s, 1H, NH).23a
X-ray Crystallography. Single crystals of 3b,c were grown by
the slow evaporation of the saturated toluene/hexane solution at
40 °C. Single crystals of 4a-c, 5c, and 7 were grown by the slow
evaporation of their saturated hexane solutions at 0 °C. The
preparation of all samples consisted of coating the crystal with
silicon grease, mounting it on a glass fiber, and placing it under a
cold stream of N2 on the diffractometer. The intensity data of 3b,c,
4a-c, 5c, and 7 were collected on a Rigaku/MSC Mercury CCD
diffractometer with graphite-monochromated Mo KR radiation (λ
) 0.71071 Å) to 2θmax ) 50° at 93 K. The structures of 3b,c, 4a-
c, 5c, and 7 were solved by direct methods (SIR97).31 All
crystallographic data were refined by full-matrix least-squares
procedures on F2 for all reflections (SHELXL-97).32 All the non-
hydrogen atoms of 3b,c, 4a-c, 5c, and 7 were placed using AFIX
instruction.
Acknowledgment. This work was supported by Grants-in-
Aid for COE Research on Elements Science (No. 12CE2005),
Creative Scientific Research (17GS0207), Scientific Research
on Priority Areas (No. 14078213), Young Scientists (B) (No.
15750031), and the 21st Century COE Program on Kyoto
University Alliance for Chemistry from the Ministry of Educa-
tion, Culture, Sports, Science, and Technology of Japan.
Supporting Information Available: 1H NMR spectra of 2a,
3b,c, 4a-c, and 5c, EPR spectrum of 7, and crystallographic
information files for 3b,c, 4a-c, and 5c. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0509948
(31) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(32) Sheldrick, G. M. SHELX-97, Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Go¨ttingen, Germany, 1997.