Functional group chemistry at the group 4 bent metallocene frameworks: Formation and "metal-free" catalytic hydrogenation of bis(imino-Cp)zirconium complexes

Article abstract of DOI:10.1021/om9004093

Treatment of 6-dimethylaminofulvene 1 with lithio-2,6-diisopropylanilide 2 gave the lithiated 6-(2,6-diisopropylanilido)fulvene 3. Its treatment with Me₃SiCl afforded the N-silylated derivative (C₅H ₄)=CH-N(Ar)SiMe₃

Full text of DOI:10.1021/om9004093

5148 Organometallics 2009, 28, 5148–5158
DOI: 10.1021/om9004093
Functional Group Chemistry at the Group 4 Bent Metallocene
Frameworks: Formation and “Metal-Free” Catalytic Hydrogenation of
Bis(imino-Cp)zirconium Complexes
†
Kirill V. Axenov, Gerald Kehr, Roland Frohlich, and Gerhard Erker*
€
€
€
Organisch-Chemisches Institut der Universitat Munster, Corrensstrasse 40, 48149 Munster, Germany.
€
†X-ray crystal structure analyses.
Received May 18, 2009
Treatment of 6-dimethylaminofulvene 1 with lithio-2,6-diisopropylanilide 2 gave the lithiated
6-(2,6-diisopropylanilido)fulvene 3. Its treatment with Me3SiCl afforded the N-silylated derivative
(C5H4)dCH-N(Ar)SiMe3 (4), which was characterized by X-ray diffraction. Protonation of 3 was
effected by treatment with acetylacetone to yield a mixture of syn- and anti-5 [(C5H4)dCH-N(Ar)H]
contaminated with some 2,6-diisopropylaniline. The minor isomer, syn-5, was also characterized by
an X-ray crystal structure analysis. Treatment of this mixture with Zr(NMe2)4 led to in situ
deprotonation and formation of complex [(C5H4)-CHdNAr]2Zr(NMe2)2 (6) in a mixture with the
exchange product [(C5H4)-CHdNAr]2Zr(NMe2)(NH-Ar) (7) as a minor component (both char-
acterized by X-ray diffraction). The corresponding reaction with the reagent Zr(benzyl)4 or Cl2Zr-
(NMe2)2(THF)2 resulted in the clean formation of the products [(C5H4)-CHdNAr]2Zr(benzyl)2 (8)
(also characterized by X-ray diffraction) and [(C5H4)-CHdNAr]2ZrCl2 (9), respectively. Complex 9
was subjected to a “metal-free” catalytic hydrogenation reaction by treatment with a substoichio-
metric amount of B(C6F5)3 under mild conditions (2 bar H2, rt) to yield the product [(C5H4)-CH2-
NH-Ar]2ZrCl2 (10), which was also characterized by an X-ray crystal structure analysis. Treatment
of 9 with 1 or 2 molar equiv of B(C6F5)3 gave “frustrated” Lewis pairs that split dihydrogen
heterolytically at near to ambient conditions to give the salts {[(C5H4)-CH2NHþ2 Ar][(C5H4)-
CH2NHAr]}ZrCl2/[HB(C6F5)3-] (11) and [(C5H4)CH2NH2þAr]2ZrCl2/2 [HB(C6F5)-3 ] (12), respec-
tively. The system 12 itself was shown to be an active catalyst for the hydrogenation of bulky imines
and of a bulky silyl enol ether.
Introduction
sensitivity of these early metal compounds.1 Usuallythechoice
of reagents and of reaction conditions is restricted. Never-
theless, we had recently described examples of typical organic
functional group conversions at the zirconocene frame-
work,2-6 e.g., a Mannich-type C-C coupling reaction,2,7
but this required a suitable selection of reagents, reaction
conditions, and the actual organic functional groups involved.
In the Mannich chemistry we had used an enamino moiety
attached at the Cp rings of the metallocene, which was in situ
converted catalytically to a reactive iminium ion intermediate
for the actual carbon-carbon coupling reaction.2,7 We have
now developed synthetic pathways to related Cp-functiona-
lized group 4 bent metallocenes, namely, zirconocenes that
bear neutral imino groups at their Cp rings. In this account we
wish to report the development of synthetic entries to a variety
of bis(imino-Cp)zirconium complexes, their spectroscopic
and structural characterization, and the reduction of the
-CHdN-Ar functional group using an interesting novel
catalytic reaction.
Functional group chemistry at the group 4 metallocene
complexes is not developed to a great extent due to the
*Corresponding author. E-mail: erker@uni-muenster.de.
€
(1) (a) Erker, G.; Kehr, G.; Frohlich, R. J. Organomet. Chem. 2004,
€
689, 1402–1412. (b) Erker, G.; Kehr, G.; Frohlich, R. Coord. Chem. Rev.
2006, 250, 36–46. (c) Erker, G. Polyhedron 2005, 24, 1289–1297.
(2) (a) Knuppel, S.; Wang, C.; Kehr, G.; Frohlich, R.; Erker, G.
€
€
J. Organomet. Chem. 2005, 690, 14-32, and references therein.
€
(b) Kn€uppel, S.; Erker, G.; Frohlich, R. Angew. Chem. 1999, 111, 2048–
2051. Angew. Chem., Int. Ed. 1999, 38, 1923-1926.
€
€
(3) (a) Sierra, J. C.; Huerlander, D.; Hill, M.; Kehr, G.; Erker, G.;
€
€
Frohlich, R. Chem.;Eur. J. 2003, 9, 3618–3622. (b) H€uerlander, D.;
€
Kleigrewe, N.; Kehr, G.; Erker, G.; Frohlich, R. Eur. J. Inorg. Chem. 2002,
2633–2642.
(4) (a) Ogasawara, M.; Nagano, T.; Hayashi, T. J. Am. Chem. Soc.
2002, 124, 9068–9069. (b) Alhomaidan, O.; Bai, G.; Stephan, D. W.
Organometallics 2008, 27, 6343–6352. (c) Kuwabara, J.; Takeuchi, D.;
Osakada, K. J. Organomet. Chem. 2005, 690, 269–275. (d) Kuwabara, J.;
Takeuchi, D.; Osakada, K. Organometallics 2005, 24, 2705–2712.
€
(5) (a) Nie, W.-L.; Kehr, G.; Erker, G.; Frohlich, R. Angew. Chem. 2004,
116, 313–317. Angew. Chem., Int. Ed. 2004, 43, 310-313. (b) Paradies, J.;
€
€
Greger, I.; Kehr, G.; Bergander, K.; Erker, G.; Frohlich, R. Angew. Chem. 2006,
(6) See also: (a) Paradies, J.; Erker, G.; Frohlich, R. Angew. Chem.
118, 7792–7795. Angew. Chem., Int. Ed. 2006, 45, 7630-7633. (c) Paradies,
2006, 118, 3150–3153. Angew. Chem., Int. Ed. 2006, 45, 3079-3082.
(7) Bai, S.-D.; Wei, X.-H.; Guo, J.-P.; Liu, D.-S.; Zhou, Z.-Y. Angew.
Chem. 1999, 111, 2051–2054. Angew. Chem., Int. Ed. 1999, 38, 1926-
1928.
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J.; Frohlich, R.; Kehr, G.; Erker, G. Organometallics 2006, 25, 3920–3925.
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r
pubs.acs.org/Organometallics
Published on Web 08/14/2009
2009 American Chemical Society

Article
Scheme 1. Syntheses of Bulky Aminopentafulvenes
Organometallics, Vol. 28, No. 17, 2009 5149
Figure 1. View of the molecular structure of the amino-fulvene
derivative 4. Ellipsoids are given at the 50% probability level.
Hydrogen atoms at the substituents were omitted for clarity.
Results and Discussion
Synthesis and Characterization of the (Imino-Cp)zirconium
Complexes. Westartedour synthetic scheme from 6-dimethyl-
aminofulvene 1. This in turn was synthesized by treatment of
in situ activated N,N-dimethylformamide (by the addition of
dimethylsulfate to DMF) with sodium cyclopentadienide
according to Hafner et al.8 Subsequent nucleophilic replace-
ment of the -NMe2 group was carried out with lithium 2,6-
diisopropylanilide 2 to yield the imino-substituted LiCp sys-
tem 3. This reaction can be carried out either in THF, as
previously described by us,9 or in ether. In the former case one
Table 1. SelectedStructural Parametersof the Compounds 4, syn-5,
and 3a
4
syn-5
3(THF)3
C1-C5
1.437(2)
1.446(2)
1.337(3)
1.428(3)
1.330(3)
1.346(2)
1.349(2)
1.440(2)
131.3(1)
118.2(1)
-2.6(2)
92.2(2)
1.447(2)
1.437(2)
1.356(2)
1.431(2)
1.353(2)
1.368(2)
1.331(2)
1.439(2)
130.6(1)
125.8(1)
-1.1(3)
86.9(2)
1.418(3)
1.434(3)
1.385(3)
1.416(4)
1.345(4)
1.408(3)
1.301(3)
1.430(2)
134.4(2)
121.3(2)
-0.3(3)
-96.2(2)
C1-C2
C2-C3
C3-C4
C4-C5
C1-C6
C6-N1
obtains the reagent 3 (THF)3, the structure of which has been
N1-C7
3
characterized by X-ray diffraction.9 It features a close Li to
imine nitrogen contact and has three stabilizing THF mole-
cules coordinated to the alkali metal in a pseudotetrahedral
coordination geometry.
C1-C6-N1
C6-N1-C7
C1-C6-N1-C7
C6-N1-C7-C8
N1-Si
1.767(1)
N-H
N-Li
0.88
We tried to prepare imino-Cp-containing zirconocene com-
plexes directly from the lithiated reagent 3. However, the
treatment of 3 with ZrCl4 under various reaction conditions
in our hands gave a complicated mixture of products, from
which we were not able to isolate the desired functionalized
metallocene systems. We suspected that the imino function in
our reagent might not be compatible with the presence of the
strongly Lewis acidic ZrCl4 metal halide substrate. Therefore,
we converted 3 to the N-silylated derivative 4 (see Scheme 1 and
Figure 1). However, also treatment of 4 with ZrCl4 did not yield
the functionalized metallocene product under our typical con-
ditions. The silylated compound 4 was characterized by X-ray
diffraction. Suitable single crystals were obtained from pentane
at -30 °C. The molecular structure of 4 (see Figure 1 and
Table 1) is fulvene like. The five-membered ring shows the
respective alternating CdC and C-C bond lengths. The exo-
cyclic C1-C6 linkage is in the typical double-bond range. The
adjacent C6-N1 bond is rather short, indicating a pronounced
π-conjugation along the C1-C6-N1 unit. The substituents at
2.005(4)
a
˚
Bond lengths in A, angles in deg; the structure of 3(THF)3 was
reported by us previously;9 the values of 3(THF)3 listed here are from an
independent structural determination carried out in this study.
N1 are in plane with the fulvene backbone. The bulky 2,6-
diisopropylphenyl substituent at N1 is rotated almost normal to
the central fulvene plane. Consequently, the nonconjugated
N1-C7(sp2) bond is much longer than the conjugated N1-C6-
(sp2) linkage (see Table 1). We note that the aryl substituent is
found in a syn-orientation (relative to C1-C6) at the fulvene
nitrogen and the -SiMe3 group is consequently anti-oriented.
As we will see below, the solution of our synthetic problem
was achieved by means of a route through the neutral fulvene
system 5. However, it was difficult to find suitable reaction
conditions to achieve a clean protonation reaction of the salt
3. After many attempts using various protonation protocols
and reagents we found that Hþ transfer from the Bronsted
e
acid acetylacetone gave acceptable results. Under optimized
conditions (see the Experimental Section for details) we
eventually obtained the neutral substituted aminofulvene
derivative 5 as a sensitive, red-brown oil in ca. 70% yield.
This product always contained variable amounts of 2,6-
diisopropylaniline (typically in the 25% range), the product
of further protolytic cleavage of the C6-N1 linkage.
€
(8) (a) Meerwein, H.; Florian, W.; Schon, N.; Stopp, G. Liebigs Ann.
€
€
Chem. 1961, 641, 1–39. (b) Hafner, K.; Vopel, K. H.; Ploss, G.; Konig, C.
Liebigs Ann. Chem. 1963, 661, 52–75. (c) Meerwein, H.; Hafner, K.; Schulz,
€
G.; Wagner, K. Liebigs Ann. Chem. 1964, 678, 39–52. (d) Hafner, K.; Vopel,
€
K. H.; Ploss, G.; Konig, C. Org. Synth. 1967, 47, 52–54. (e) Hafner, K.;
€
€
Vopel, K. H.; Ploss, G.; Konig, C. Organic Syntheses; Wiley: New York,
1973; Collect. Vol. V, p 431.
(9) (a) Kunz, K.; Erker, G.; Frohlich, R. Organometallics 2001, 20,
Product 5 was characterized spectroscopically (see below)
and by X-ray diffraction. In the crystal we found only the
syn-5 isomer (with an analogous orientation of the bulky
€
€
392–400. (b) See also: Erker, G.; Kehr, G.; Frohlich, R. Organometallics
2008, 27, 3-14, and references therein.

5150 Organometallics, Vol. 28, No. 17, 2009
Axenov et al.
Scheme 2
Scheme 3
Figure 2. Molecular structure of syn-5. Ellipsoids are given at
the 50% probability level. Hydrogen atoms at the substituents
were omitted for clarity.
2,6-diisopropylphenyl substituent as found in 4; see above).
The structureof syn-5 (see Figure 2 and Table1) isvery similar
to that of 4 (see above). We found a typical aminofulvene
framework with the characteristic CdC/C-C bond alterna-
tion. Again, the C6-N1 bond is short and the bulky aryl
group is rotated out of conjugation with the fulvene core.
It is interesting to compare the structure of the anionic
system 3 with the neutral fulvenes 4 and syn-5, respectively.
We note that in 3 the C6-N1 bond is markedly shorter and
the C1-C6 bond considerably longer than in the neutral
fulvenes (see Table 1). This may indicate a slightly higher
significance of the imine-type resonance structure 3B for this
lithiated system (see Scheme 2). A drawing of the previously
reported molecular structure of 3 can be found in the
Supporting Information.
Extraction with pentane gave the anticipated complex 6 as
the major product (ca. 65%). The pentane-insoluble fraction
(ca. 35%) consisted mainly of 7, which was formally formed
by exchange of one -NMe2 group of 6 for -NH-2,6-
diisopropylphenyl. Both compounds were obtained analyti-
cally pure after recrystallization. They were both character-
ized spectroscopically and by X-ray diffraction (see below).
1
The major product (6) featuredanAA0BB0 HNMRpattern
of the symmetry-equivalent η5-C5H4-moieties (δ 6.71/6.01)
and the typical -CHdN- singlet at δ 7.96 (corresponding
1
imine 13C NMR feature at δ 156.5). The H NMR -NMe2
The NMR spectra show the presence of a pair of fulvene
isomers in a 2:1 ratio in solution. The compound syn-5,
which was identified by X-ray diffraction in the solid state, is
the minor component in solution. It features a typical
dCHN- 1H NMR signal (in CD2Cl2) at δ 7.32 with a
3JHH coupling constant of 7.3 Hz, and it shows 13C NMR
signals of the fulvene core at δ 125.4, 124.8, 120.5, 115.1
(C5H4), 118.1 (ipso-C5H4), and 143.6 (dCHN). The major
anti-5 isomer shows similar core signals (13C) at δ 126.5,
123.5, 121.9, 111.6 (C5H4), and 118.3 (ipso-C5H4) and
the d13CHN- resonance at δ 146.5. The corresponding 1H
NMR signal is observed as a doublet at δ 6.99 with a typical
coupling constant of 3JHH = 14.2 Hz for an anti-conforma-
tion.
singlet (12H) occurs at δ 2.83. In addition we monitored the
typical NMR resonances of the 2,6-diisopropylphenyl substit-
uents at the imine nitrogen atoms (for details see the Experi-
mental Section).
1
The minor substitution product (7) shows the H NMR
-CHdN- feature at δ 7.88 (in C6D6, 13C: δ 156.7). There is a
-NMe2 singlet of 6H relative intensity at δ 2.85. The signals of
the “extra” 2,6-diisopropylanilide σ-ligand are broad at room
temperature. At 353 K (in d8-toluene) the respective 1H NMR
signals were observed at 6.95/6.81 (C6H3) [13C: δ 153.3, 140.5,
123.2, 122.5] and 3.42/1.12 (iPr) [13C: δ 28.1, 24.5].
In a similar reaction we have treated 5 with tetra-
(benzyl)zirconium, in situ prepared from ZrCl4 and benzyl-
magnesium chloride.11 The product (8) was isolated as an
orange solid in >80% yield and purified by recrystallization
from pentane. The product was again characterized by C,H
elemental analysis, NMR spectroscopy, and an X-ray crystal
structure analysis (see below). Together with the typical 1H
NMR -CH2- singlet of the Zr-σ-benzyl moiety (δ 2.18, 4H
relative intensity, 13C: δ 63.5), the compound features a η5-
C5H4 AA0BB0 pattern at δ 6.53/5.68 and the NMR signals of
the -CHdN- functional groups (1H: δ 7.67, 13C: δ 157.0)
that are attached at the Cp rings of complex 8. The NMR
spectra show the typical signals of the 2,6-diisopropylphenyl
1
The silylated compound 4 shows only one set of H/13C
NMR signals [e.g., dCHN- at δ 7.25 (1H)/δ 144.4 (13C, in
C6D6)]. There are some trace signals that may originate from
a very low populated minor isomer.
We were able to successfully use the syn-5/anti-5/2,6-
diisopropylaniline mixture for the preparation of zircono-
cene complexes having the -CHdN-aryl carbaldimino func-
tionalities attached at their Cp ring systems. We treated the
reagent mixture with ca. 0.5 molar equiv of Zr(NMe2)410 in
benzene at room temperature overnight. The resulting pro-
duct mixture was separated by treatment with pentane.
(11) Zucchini, U.; Albizzati, E.; Giannini, U. J. Organomet. Chem.
1971, 26, 357–372.
(10) Bradley, D. C.; Thomas, I. M. J. Chem. Soc. 1960, 3857–3861.

Article
Organometallics, Vol. 28, No. 17, 2009 5151
Table 2. Selected Structural Parameters of the (Imino-Cp)zirconium Complexes 6-8
6
7
8
Zr-C1/C5 range
C-C(Cp) range
C1A-C6A
2.568(2) to 2.637(2)
1.393(3) to 1.420(3)
1.463(3)
1.460(3)
1.262(2)
1.259(3)
1.432(2)
1.424(2)
123.6(2)
121.5(2)
118.0(2)
122.0(2)
2.069(2)
2.075(2)
96.2(1)
2.533(4) to 2.626(3)
1.380(5) to 1.418(5)
1.483(5)
1.454(5)
1.218(5)
1.252(4)
1.454(5)
1.434(4)
121.3(4)
2.468(5) to 2.575(6)
1.387(7) to 1.423(6)
1.508(9)g
1.470(6)
1.246(8)g
1.243(5)
C1B-C6B
C6A-N1A
C6B-N1B
N1A-C7A
1.468(8)
1.439(5)
N1B-C7B
C1A-C6A-N1A
C1B-C6B-N1B
C6A-N1A-C7A
C6B-N1B-C7B
Zr-N2A
110.1(7)g
122.8(5)
120.9(3)
119.7(4)
113.5(7)g
117.6(4)
122.6(3)
2.115(3)a
2.073(3)b
101.4(1)c
2.322(5)d
Zr-N2B
N2A-Zr-N2B
2.324(5)e
97.3(2)f
a Zr1-N1C. b Zr1-N11. c N1C-Zr1-N11. d Zr-C21A. e Zr-C21B, f C21A-Zr-C21B, g Values taken from the main compound of the disordered
group.
Figure 3. View of the molecular structure of complex 6. Ellipsoids are given at the 50% probability level. Hydrogen atoms at the
substituents were omitted for clarity.
substituents at the imine nitrogen atoms (for details see the
Experimental Section).
other. The -CHdN- π-systems are oriented in plane with
their respective Cp rings. The aryl plane of the 2,6-diisopro-
pylphenyl substituent is rotated close to normal to the imine
planes.13 The Zr-amide σ-ligands show near planar tricoor-
dinate nitrogen atoms (sum of bond angles at N2A: 357.4°,
N2B: 358.4°).
Complex 7 exhibits similar structural features of the
(imino-Cp)2Zr core. Again, the imine -CHdN- π-units
are arranged close to coplanar with the adjacent Cp rings to
allow for a maximal conjugation. The 2,6-diisopropylphenyl
substituents at the imine nitrogens are rotated substantially
from that common plane (see Figure 4). However, we notice
a slightly different metallocene conformation as compared to
6. The -NMe2 group at Zr is trigonal planar. Its orientation
may allow some ligand to metal π-interaction with the
(empty) “ninth” metallocene orbital. The adjacent 2,6-diiso-
propylanilido σ-ligand is oriented differently; here the ob-
served preferred conformation seems to be governed by
steric interaction.
In the crystal complex 6 features a bent metallocene
structure that is characterized by a near to C2-symmetric
metallocene conformation.12 The Cp(centroid)-Zr-Cp-
(centroid) angle amounts to 125.7°. The imino substituents
at the Cp rings are both oriented in the hind lateral metallo-
cene sector. This probably leads to a maximal separation of
the bulky 2,6-diisopropylphenyl substituents from each
(12) For typical conformational features of Cp-substituted bent
€
metallocene systems see for example: (a) Erker, G.; Muhlenbernd, T.;
ꢀ
€
Benn, R.; Rufinska, A.; Tsay, Y.-H.; Kruger, C. Angew. Chem. 1985, 97,
336–337. Angew. Chem., Int. Ed. Engl. 1985, 24, 321-323. (b) Erker, G.;
Nolte, R.; Tainturier, G.; Rheingold, A. Organometallics 1989, 8, 454–460.
(c) Erker, G.; Nolte, R.; Kr€uger, C.; Schlund, R.; Benn, R.; Grondey, H.;
Mynott, R. J. Organomet. Chem. 1989, 364, 119–132. (d) Erker, G.;
Aulbach, M.; Knickmeier, M.; Wingberm€uhle, D.; Kr€uger, C.; Nolte, M.;
Werner, S. J. Am. Chem. Soc. 1993, 115, 4590–4601. (e) Knickmeier, M.;
€
Erker, G.; Fox, T. J. Am. Chem. Soc. 1996, 118, 9623–9630. (f) Jodicke, T.;
€
€
Menges, F.; Kehr, G.; Erker, G.; Howeler, U.; Frohlich, R. Eur. J. Inorg.
Chem. 2001, 2097–2106.
(13) See for a comparison: (a) Nienkemper, K.; Kotov, V. V.; Kehr,
Complex 8 features a metallocene conformation that is
similar to that of 7 with one imino substituent at Cp pointing
toward a hind lateral sector and the other being oriented
toward the more open front side of the bent metallocene
wedge. The C6A-N1A imino group exhibits an orientational
€
G.; Erker, G.; Frohlich, R. Eur. J. Inorg. Chem. 2006, 366–379.
€
(b) Wallenhorst, C.; Kehr, G.; Luftmann, H.; Frohlich, R.; Erker, G.
Organometallics 2008, 27, 6547–6556. (c) Wallenhorst, C.; Kehr, G.;
€
Frohlich, R.; Erker, G. Organometallics 2008, 27, 6557–6564.

5152 Organometallics, Vol. 28, No. 17, 2009
Axenov et al.
Figure 5. Projection of the molecular structure of complex 8.
Ellipsoids are given at the 50% probability level. Hydrogen
atoms were omitted for clarity.
Figure 4. Molecular geometry of complex 7. Ellipsoids are
given at the 50% probability level. Hydrogen atoms were
omitted for clarity.
disorder inside its Cp-imino plane. Therefore the structural
data of this group will not be discussed. The other π-ligand
shows the typical Cp-imino conjugation. Both σ-benzyl
groups at zirconium are oriented with their bulky phenyl
group toward the latter Cp-imino (B) ligand system (see
Figure 5).
Scheme 4
We eventually prepared the parent bis(imino-Cp)zirco-
nium dichloride complex (9) by a direct route. Treatment
of the neutral, protonated ligand system 5 with the Cl2Zr-
17-19
14
quantity of the strong boron Lewis acid B(C6F5)3
(NMe2)2(THF)2 reagent at elevated temperature (3 h,
(typically between 0.25 and 0.5 molar equiv). When this
mixture was stirred for several hours (typically overnight to
ensure complete conversion) under an atmosphere of dihy-
drogen (2 bar) at room temperature, the -CHdN-aryl imine
functionality was cleanly converted to the corresponding
-CH2-NH-aryl aminomethyl functional group attached at
the Cp rings of the metallocene system. This reaction pro-
ceeded in a quasi-autocatalytic fashion. The product 10 in
combination with the remaining B(C6F5)3 apparently
formed a new amine/borane frustrated Lewis pair,20 which
itself was able to heterolytically cleave the dihydrogen mo-
lecule with formation of the organometallic ammonium salt
(11, with [HB(C6F5)-3 ] anion). Consequently, we isolated a
mixture of 10 (major) and 11 (minor component) from a
typical catalytic “metal-free” hydrogenation reaction21 using
a substoichiometric amount of the B(C6F5)3 Lewis acid
component as described above. We were so far not able to
separate the products 10 and 11 on a preparative scale, but
have obtained single crystals of the (Cp-CH2-NH-aryl)ZrCl2
neutral complex 10 for characterization by an X-ray crystal
structure analysis (see below).
120 °C) resulted in a rather clean in situ deprotonation by
the dimethylamide base with concurrent formation of the
(imino-Cp)2ZrCl2 product 9. This was isolated in >60%
yield after conventional workup. It was characterized by C,H
elemental analysis and spectroscopically. It shows the typical
1H/13C NMR imino resonances at δ 7.99 (1H)/δ 156.2 (13C).
The isopropyl groups of the symmetry-equivalent 2,6-diiso-
propylphenyl substituents at nitrogen feature the typical 1H
NMR CH septet at δ 3.25 and a corresponding doublet of the
methyl group at δ 1.24.
Although complex 9 was not characterized by X-ray
diffraction, we chose it as the apparent parent compound
in this series as the substrate for reduction with the new
“metal-free” hydrogenation method.
Hydrogenation of the Imino-Zirconocene System. We ap-
plied a recent novel method for imine hydrogenation at the
sensitive group 4 bent metallocene framework. This involved
the initial formation of an “antagonistic” Lewis pair15 (or a
“frustrated” Lewis pair as it is more commonly termed16) by
treatment of the (imino-Cp)2ZrCl2 complex 9 with a catalytic
(14) Brenner, S.; Kempe, R.; Arndt, P. Z. Anorg. Allgem. Chem. 1995,
621, 2021–2024.
(15) (a) Wittig, G.; Benz, E. Chem. Ber. 1959, 92, 1999–2013.
(b) Tochtermann, W. Angew. Chem. 1966, 78, 355–375. Angew. Chem., Int.
Ed. 1966, 5, 351-371, and references therein.
(16) (a) Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124–1126. (b) McCahill, J. S. J.; Welch, G. C.; Stephan,
D. W. Angew. Chem. 2007, 119, 5056–5059. Angew. Chem., Int. Ed. 2007,
46, 4968-4971. (c) Welch, G. C.; Stephan, D. W. J. Am. Chem. Soc. 2007,
129, 1880–1881.
(18) Chase, P. A.; Jurca, T.; Stephan, D. W. Chem. Commun. 2008,
1701–1703.
(19) Chen, D.; Klankermayer, J. Chem. Commun. 2008, 2130–2131.
(20) See for example: (a) Sumerin, V.; Schulz, F.; Nieger, M.;
€
Leskela, M.; Repo, T.; Rieger, B. Angew. Chem. 2008, 120, 6090–6092.
Angew. Chem., Int. Ed. 2008, 47, 6001-6003. (b) Sumerin, V.; Schulz, F.;
€
€
Atsumi, M.; Wang, C.; Nieger, M.; Leskela, M.; Repo, T.; Pyykko, P.; Rieger,
B. J. Am. Chem. Soc. 2008, 130, 14117–14119.
(21) (a) Spies, P.; Erker, G.; Kehr, G.; Bergander, K.; Frohlich, R.;
€
(17) (a) Massey, A. G.; Park, A. J.; Stone, F. G. A. Proc. Chem. Soc.
1963, 212. (b) Massey, A. G.; Park, A. J. J. Organomet. Chem. 1964, 2, 245.
(c) Massey, A. G.; Park, A. J. In Organometallic Syntheses; King, R. B.,
Eisch, J. J., Eds.; Elsevier: New York, 1986; Vol. 3, pp 461-462. See also:
(d) Erker, G. Dalton Trans. 2005, 1883–1890.
Grimme, S.; Stephan, D. W. Chem. Commun. 2007, 5072–5074. (b) Spies,
€
P.; Schwendemann, S.; Lange, S.; Kehr, G.; Frohlich, R.; Erker, G. Angew.
Chem. 2008, 120, 7654–7657. Angew. Chem., Int. Ed. 2008, 47, 7543-
€
7546. (c) Spies, P.; Kehr, G.; Bergander, K.; Wibbeling, B.; Frohlich, R.;
Erker, G. Dalton Trans. 2009, 1534–1541.

Article
Organometallics, Vol. 28, No. 17, 2009 5153
Scheme 5
12 and 11. Complex 12 shows 1H NMR signals of the aryl-
NHþ2 -CH2- groups at δ 9.65 and 4.59, respectively [with
corresponding characteristic aryl resonances at δ 7.55 (1H)
and 7.48 (2H)]. It features 1H NMR η5-C5H4 resonances at δ
6.76 and 6.19 and a broad signal of the counteranion
[HB(C6F5)-3 ] at δ 3.70. For further details of the character-
ization of the compounds 10-12 see the Experimental Sec-
tion and the Supporting Information.
Complex 10 was also characterized by X-ray diffraction (see
Figure 6).24 It shows a bent metallocene unit with a pseudote-
trahedral coordination geometry of the central group 4 transi-
tion metal [angles Cp(centroid)-Zr-Cp(centroid): 130.3°,
Cl1-Zr-Cl2: 98.0(1)°]. The Zr-C(Cp) bond lengths were
˚
found in a range between 2.470(2) and 2.594(3) A. The
-CH2-NH-aryl substituents at the pair of Cp ligands are
oriented in a close to C2-symmetric arrangement both toward
the open front side of the bent metallocene wedge. Thereby, the
˚
C1A-C6A (1.502(3) A) vector in the projection is oriented
Since the organometallicsecondary amine10itselfformed a
frustrated Lewis pair with B(C6F5)3, which was catalytically
active in H2 splitting, the outcome of the overall reaction was
determined decisively by the initial ratio of 9/B(C6F5)3. When
the components were employed in the hydrogenation reaction
in a 1:1 ratio, we obtained the organometallic monoammo-
nium salt 11 as the major product (see Scheme 5). This could
be used further for dihydrogen splitting.22,23 Hydrogenation
(2 bar H2, ambient temperature, overnight, or 60 bar H2, 2 h)
of an initial 1:2 mixture of 9 and B(C6F5)3 eventually resulted
in a near complete conversion to the organometallic bis-
ammonium salt 12 (with two [HB(C6F5)-3 ] counteranions).
Solutions containing the ammonium salts 11 and/or 12
showed very broad NMR spectra at ambient temperature
due to proton transfer. This became sufficiently slow on the
NMR time at 198 K (600 MHz, 1H) to monitor sharp 1H and
13C NMR spectra for the characterization of the products
10-12. The aminomethyl-Cp complex 10 shows two sets of
1H NMR signals (at 198 K in d8-THF) of the η5-C5H4-
moieties at δ 6.00/6.37 (each 4 H relative intensity), a broad
Cp-CH2-N resonance at δ 4.04 (4H, 13C: δ 50.4), and an NH
signal at δ 4.00 (2H) in addition to the typical resonances of
the 2,6-diisopropylphenyl substituent [aryl 1H resonances at
δ 7.06 (4H) and 7.00 (2H)].
We spectroscopically characterized the monoammonium
salt 11 from a ca. 5:20:3 mixture of 10, 11, and 12. The salt
11 shows the typical features of the -CH2-NH-aryl group [1H:
δ 4.01 (br, 3H), aryl signals at δ 7.05 (2H) and 6.99 (1H)] in
addition to the -CH2-NH2þ-aryl signals [1H: δ 4.62 (CH2), δ
9.65 (NHþ2 ), corresponding aryl signals at δ 7.56 (1H) and δ
7.48 (2H)]. Complex 11 shows four η5-C5H4 1H NMR signals
(δ6.75/6.14, 6.60/6.33; each 2H) as expected. The [HB(C6F5)-3 ]
counteranion shows the characteristic 19F NMR features
(in d8-THF at 298 K) at δ -133.4, -166.4, and -168.8 for
the o,p,m-C6F5 fluorine nuclei. The 11B NMR spectrum shows
the broad H[B] doublet at δ -25.5 (1JBH = 94 Hz).
˚
toward the Zr-Cl1 (2.447(1) A) side, whereas its C1B-C6B
(1.494(3) A) counterpart is found in the projection above
Zr-Cl2 (2.426(1) A). The C6A-N7A (1.466(3) A) and
C6B-N7B (1.471(3) A) bond lengths are in the C(sp )-N
˚
˚
˚
3
˚
single bond range. The bond angle at the CH2 groups amounts
to 111.9(2)° (C1A-C6A-N7A) and 110.8(2)° (C1B-C6B-
N7B), respectively. The angles at the NH groups amount to
C6A-N7A-C8A 116.4(2)° and C6B-N7B-C8B 117.8(2)°,
respectively. The -CH2-NH vectors are conformationally
oriented close to in-plane with their adjacent Cp rings
(dihedral angles C5A-C1A-C6A-N7A: -11.1(3)°, C5B-
C1B-C6B-N7B: -25.0(4)°), whereas the NH-aryl vector is
markedly rotated from that plane (dihedral angles
C1A-C6A-N7A-C8A: 151.0(2)°, C6A-N7A-C8A-C9A:
-75.7(3)°, and correspondingly C1B-C6B-N7B-C8B:
162.2(2)°, C6B-N7B-C8B-C9B: -76.0(3)°).
The zirconocene-based ammonium salt 12 itself is an
active hydrogenation catalyst, e.g., for bulky imines, as
expected.18-20 These reactions were described in some detail
in our preliminary communication about this chemistry25
and its Supporting Information. We achieved a close to
quantitative hydrogenation of each of the bulky aldimines
13 by treatment with H2 (2 bar) at room temperature in C6D6
using 5.6 mol % (for 13a) or 2.3 mol % (for 13b) of the
catalyst system 12 (see Scheme 6). Complex 12 was also an
active catalyst for the hydrogenation of a bulky silyl enol
ether.26 With 4.8 mol % of the catalyst 12 the product 16 was
obtained in 85% yield from the catalytic hydrogenation
of 15 (see Scheme 6). In a control experiment we exposed a
20:1 mixture of the silyl enol ether 15 and complex 9 to H2
(2 bar, rt) overnight in the absence of B(C6F5)3. This did not
result in hydrogenation of any of these compounds.
Conclusions
We note that there has been some progress in the deve-
lopment of an organic functional group chemistry at the
sensitive group 4 bent metallocenes and related compounds,
but in detail this still meets with a lot of difficulties.1 Group 4
The NMR characterization of the bis-ammonium salt 12
was carried out at 198 K in d8-THF from a ca. 5:1 mixture of
(22) For mechanistic aspects of this reaction (theoretic analysis) see
ꢀ
ꢀ
for example: (a) Rokob, T. A.; Hamza, A.; Stirling, A.; Soos, T.; Papai, I.
Angew. Chem. 2008, 120, 2469–2472. Angew. Chem., Int. Ed. 2008, 47,
(24) For related substituted (1-aminoethyl-Cp) group 4 metallocene
complexes see for example: Erker, G. Coord. Chem. Rev. 2006, 250,
1056-1070, and references therein.
ꢀ
2435-2438. (b) Stirling, A.; Hamza, A.; Rokob, T. A.; Papai, I. Chem.
Commun. 2008, 3148–3150. (c) Guo, Y.; Li, S. Inorg. Chem. 2008, 47,
6212–6219.
€
(25) Axenov, K. V.; Kehr, G.; Frohlich, R.; Erker, G. J. Am. Chem.
(23) Early reviews: (a) Stephan, D. W. Org. Biomol. Chem. 2008,
1535–1539. (b) Kenward, A. L.; Piers, W. E. Angew. Chem. 2008, 120, 38–42.
Angew. Chem., Int. Ed. 2008, 47, 38-41.
Soc. 2009, 3454–3455.
(26) See for a comparison: Wang, H.; Frohlich, R.; Kehr, G.; Erker,
G. Chem. Commun. 2008, 5966–5968.
€

5154 Organometallics, Vol. 28, No. 17, 2009
Axenov et al.
systems 6-9. This shows that the synthesis of even such
functionalized group 4 metallocenes can be achieved by means
of acceptably short, but admittedly sometimes rather special
routes.
The subsequent catalytic hydrogenation of the pair of
imine functional groups at the bent metallocene framework
of the zirconocene complex 9 is a quite remarkable applica-
tion of the new method of “metal-free” hydrogen activation
and hydrogenation catalysis by frustrated Lewis pairs.16,21,23
Our example indicates some potentially useful application of
this new chemistry, of which currently more and more
examples of suitable Lewis acid/Lewis base pairs are emer-
ging from the literature.27
In our case, it is likely that we are generating a series of
non-self-quenched N/B Lewis pairs.18-20 First, the attached
imine probably serves as the bulky Lewis base necessary for
heterolytic dihydrogen splitting. At later stages this may be
complemented by the metallocene-attached secondary
amine base, which was itself formed in this rather efficient
catalytic “metal-free” hydrogenation process. The overall
process may, therefore, well have some quasi-autocatalytic
features. Eventually, the product 10 serves as a component of
an efficient hydrogenation catalyst of this novel general type
itself. So it seems that developing functional group chemistry
at the sensitive group 4 bent metallocenes is not just a more
complex repeat of, for example, established organic ferro-
cene-type chemistry, but can in cases lead to new and
unexpected observations, which may encourage us and
others to continue with this development.
Figure 6. View of the molecular structure of complex 10. Ellip-
soids are given at the 50% probability level. Hydrogen atoms at
the substituents were omitted for clarity.
Scheme 6
Experimental Section
General Information. All reactions were carried out under
argon atmosphere with Schlenk-type glassware or in a glovebox.
Solvents (including deuterated solvents used for NMR spectro-
scopy) were dried and distilled under argon prior to use. The
following instruments were used for physical characterization of
the compounds. Elemental analyses: Foss-Heraeus CHNO-
Rapid. NMR: Bruker AC 200 P (1H, 200 MHz; 11B, 64 MHz),
ARX 300 (1H, 300 MHz; 19F, 282 MHz), Varian 500 MHz
INOVA (1H, 500 MHz; 11B, 160.4 MHz; 19F, 470.2 MHz),
Varian UNITY plus NMR spectrometer (1H, 600 MHz; 13C,
151 MHz; 19F, 564 MHz). Assignments of the resonances are
supported by 2D experiments and chemical shift calculations.
metallocene functional group chemistry is still nowhere near,
for example, ferrocene-based synthetic chemistry. The sys-
tems described here may serve as some typical examples.
It seems that we had mastered, at least to some extent, imino-
Cp chemistry at the ligand stage. The respective secondary
amino-fulvene precursors are now available by established
routes. The imino-Cp systems can be constructed at their
anion stage 3. The anions 3 exhibit a considerable [Cp-
CHdN-aryl]-character, as exemplified by the spectroscopic
properties and the structural features of the respective
11B NMR spectra were referenced to an external Et2O BF3
3
sample; 19F NMR spectra were referenced to an external CFCl3
sample. X-ray diffraction: Data sets were collected with Nonius
KappaCCD diffractometers, in the case of Mo-radiation
equipped with a rotating anode generator. Programs used: data
collection COLLECT (Nonius B.V., 1998), data reduction Den-
zo-SMN (Z. Otwinowski, W. Minor, Methods Enzymol. 1997,
276, 307-326), absorption correction SORTAV (R. H. Blessing,
lithium compound 3 (THF)3 (see Scheme 2 and Table 1).
3
However, transmetalation to zirconium still met with con-
siderable difficulties. Even well-established alternative
routes via the corresponding silyl derivative failed under
our experimental conditions.
(27) (a) Welch, G. C.; Carbrea, L.; Chase, P. A.; Hollink, E.; Masuda,
J. D.; Wei, P.; Stephan, D. W. Dalton Trans. 2007, 3407–3414. (b) Welch,
G. C.; Holtrichter-Roessemann, T.; Stephan, D. W. Inorg. Chem. 2008, 47,
1904–1906. (c) Chase, P. A.; Stephan, D. W. Angew. Chem. 2008, 120,
7543–7547. Angew. Chem., Int. Ed. 2008, 47, 7433-7437. (d) Holschu-
macher, D.; Bannenberg, T.; Hrib, C. G.; Jones, P. G.; Tamm, M. Angew.
Chem. 2008, 120, 7538–7542. Angew. Chem., Int. Ed. 2008, 47,
7428-7432. (e) Dureen, M. A.; Lough, A.; Gilbert, T. M.; Stephan, D. W.
Chem. Commun. 2008, 4303–4305. (f) Huber, D. P.; Kehr, G.; Bergander,
Nevertheless, we were able to prepare the imino-Cp-func-
tionalized zirconocene complexes 6-9 starting from the neu-
tral secondary fulvene derivatives. The C5H4(dCH-NH-aryl)
fulvene 5 has become available by means of the “detour” via
the [C5H4(CHN-aryl)]- anion system 3. To achieve a suffi-
ciently selective protonation was more difficult than expected.
Eventually treatment of 3 in ether with acacH (serving as a
€
K.; Frohlich, R.; Erker, G.; Tanino, S.; Ohki, Y.; Tatsumi, K. Organome-
Bronsted acid) solved the problem to give syn-/anti-5 in a good
e
tallics 2008, 27, 5279–5284. (g) Geier, S. J.; Gilbert, T. M.; Stephan, D. W.
J. Am. Chem. Soc. 2008, 130, 12632–12633. (h) Ullrich, M.; Lough, A. J.;
Stephan, D. W. J. Am. Chem. Soc. 2009, 131, 52–53. (i) Ramos, A.; Lough,
A. J.; Stephan, D. W. Chem. Commun. 2009, 1118–1120. (k) Ullrich, M.;
Seto, K. S.-H.; Lough, A. J.; Stephan, D. W. Chem. Commun. 2009, 2335–
2337.
yield, albeit contaminated with 2,6-diisopropylaniline. In situ
deprotonation of 5 by suitable [Zr]-NMe2 or [Zr]-benzyl
reagents then opened the synthetic pathways for the prepara-
tion of the anticipated functionalized (Cp-CHdN-aryl)2ZrX2

Article
Organometallics, Vol. 28, No. 17, 2009 5155
Acta Crystallogr. 1995, A51, 33-37; R. H. Blessing, J. Appl.
Crystallogr. 1997, 30, 421-426), and Denzo (Z. Otwinowski, D.
Borek, W. Majewski, W. Minor, Acta Crystallogr. 2003, A59,
228-234), structure solutionSHELXS-97 (G. M. Sheldrick, Acta
Crystallogr. 1990, A46, 467-473), structure refinement SHEL-
XL-97 (G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112-122),
graphics XP (BrukerAXS, 2000).
2H, CH(iPr)), 1.23 (d, 3JHH = 6.8 Hz, 12H, CH3(iPr)). 13C{1H}
NMR (151 MHz, CD2Cl2, 253 K): δ 146.5 (dCHN), 145.7
(o-Ar), 135.0 (i-Ar), 128.4 (p-Ar), 126.5 (R0-C5H4), 124.0 (m-Ar),
123.5 (β-C5H4), 121.9 (R-C5H4), 118.3 (i-C5H4), 111.6 (β0-C5H4),
28.3 (CH(iPr)), 23.6 (CH3(iPr)).
Minor Isomer (syn-5). 1H NMR (600 MHz, CD2Cl2, 253 K): δ
7.45 (t, 3JHH = 7.8 Hz, 1H, p-Ar), 7.32 (d, 3JHH = 7.3 Hz, 1H,
3
6-Dimethylaminofulvene (1),8 Zr(NMe2)4,10 Zr(NMe2)2Cl2
=CHN), 7.30 (d, JHH = 7.8 Hz, 1H, m-Ar), 6.49 (d, 3JHH
=
=
3
17
(THF)2, and B(C6F5)3 were prepared according to modified
literature procedures. The THF-free lithium {[(N-2,6-diisopro-
pylphenyl)formimidoyl]cyclopentadienide} (3) was synthesized
on the basis of the procedure published by us previously,9a only
with Et2O used as solvent instead of THF.
7.3 Hz, 1H, NH), 6.35 (dm, JHH = 4.7 Hz, β0), 6.12 (ddd, JHH
4.6 Hz, 2.3 Hz, 1.4Hz, R0), 6.05 (m, R), 4.97 (dm, JHH = 4.7 Hz, β)
(each 1H, C5H4), 3.13 (sept, 3JHH = 6.8 Hz, 2H, CH(iPr)), 1.18,
1.10 (each d, each 3JHH = 6.8 Hz, each 6H, CH3(iPr)). 13C{1H}
NMR (151 MHz, CD2Cl2, 253 K): δ 146.4 (o-Ar), 143.6
(dCHN), 134.2 (i-Ar), 129.1 (p-Ar), 125.4 (R-C5H4), 124.8
(β0-C5H4), 124.3 (m-Ar), 120.5 (R0-C5H4), 118.1 (i-C5H4), 115.1
(β-C5H4), 28.4 (CH(iPr)), 24.4 (CH3(iPr)), 23.0 (CH3(iPr)).
X-ray Crystal Structure Analysis of syn-5. Formula C18H23N,
M=253.37, yellow crystal 0.30 ꢀ 0.20 ꢀ 0.15 mm, a = 8.5993(2)
Preparation of 6-(N-2,6-Trimethylsilyl-2,6-diisopropylanilino)-
fulvene, 4. Me3SiCl (0.43 g, 0.5 mL, 3.93 mmol) was added to the
solution of Li[C5H4CHdN(2,6-iPr2C6H3)] THF9a (3 THF)
3
3
(1.30 g, 3.93 mmol) in Et2O (20 mL) at -78 °C. The reaction
mixture was allowed to warm slowly to room temperature and
stirred overnight. Et2O was evaporated in vacuo, and the residue
was extracted with pentane (30 mL). After filtration, pentane was
removed under vacuum, which gave the product in the form of an
orange-brown crystalline solid (1.28 g, 78%). Single crystals of 4
suitable for X-ray crystal structure analysis were grown from
pentane solution at -30 °C. Anal. Calcd for C21H31SiN: C, 77.47;
H, 9.60; N, 4.30. Found: C, 77.17; H, 9.68; N, 4.35. 1H NMR (600
MHz, C6D6, 298 K): δ 7.25 (s, 1H, dCHN), 7.19 (m, 1H, p-Ar),
7.09 (m, 2H, m-Ar), 6.58 (R0), 6.49 (β0), 6.42 (β), 5.09 (R) (each m,
each 1H, C5H4), 3.06 (sept, 2H, 3JHH = 6.8 Hz, CH(iPr)), 1.09 (d,
˚
˚
˚
A, b = 17.2910(5) A, c = 10.7919(3) A, β = 100.022(2)°, V =
1580.17(7) A , Fcalc = 1.065 g cm-3, μ = 0.457 mm-1, empirical
3
˚
absorption correction (0.875 e T e 0.935), Z = 4, monoclinic,
˚
space group P21/c (No. 14), λ = 1.54178 A, T = 223(2) K, ω and
j scans, 11264 reflections collected ((h, ( k, ( l), [(sin θ)/λ] =
0.60 A-1, 2747 independent (Rint = 0.035) and 2423 observed
˚
reflections [I g 2σ(I)], 200 refined parameters, R = 0.046, wR2 =
0.123, max. residual electron density 0.15(-0.13) e A-3, isopropyl
˚
group C16-C18 refined with split positions, hydrogen atom at
N1 from difference Fourier calculation, others calculated and
refined as riding atoms.
3
12H, JHH = 6.8 Hz, CH3(iPr)), 0.03 (s, 9H, CH3Si). 13C{1H}
NMR (151 MHz, C6D6, 298 K): δ 146.0 (o-Ar), 144.4 (dCHN),
138.9 (i-Ar), 128.4 (p-Ar), 128.0 (β-C5H4), 126.3 (R0-C5H4), 125.1
(m-Ar), 124.2 (i-C5H4), 122.4 (β0-C5H4), 117.0 (R-C5H4), 28.6
(CH(iPr)), 25.1 (CH3(iPr)), 24.3 (CH3(iPr)), -0.4 (CH3Si).
X-ray Crystal Structure Analysis of Compound 4. Formula
C21H31NSi, M = 325.56, yellow-red crystal 0.50 ꢀ 0.45 ꢀ
Preparation of the Bis(amido)zirconocene Complexes 6 and
7. Compound 7. A solution of Zr(NMe2)4 (2.63 g, 9.84 mmol)
in dry benzene (20 mL) was added to the solution of ligand 5
(6.64 g, 19.68 mmol) in dry benzene (30 mL) at room tempera-
ture. The reaction mixture was stirred overnight. After removal
of all volatiles under vacuum the brown residue was washed with
pentane (50 mL). After decantation of the pentane phase the
residue was washed again with pentane (20 mL) and dried under
vacuum, which gave 2.8 g (35%) of the product 7 as a yellow-
brown powder. Crystals of 7 suitable for X-ray single-crystal
diffraction analysis were grown from an Et2O solution at
-30 °C. Anal. Calcd for C50H68ZrN4: C, 73.57; H, 8.40; N,
˚
˚
˚
0.05 mm, a=8.657(1) A, b=8.942(1) A, c=14.169(1) A, R=
3
˚
82.22(1)°, β= 88.91(1)°, γ = 66.88(1)°, V = 998.8(2) A , Fcalc
=
1.083 g cm-3, μ= 1.011 mm-1, empirical absorption correction
(0.632 e T e 0.951), Z = 2, triclinic, space group P1 (No. 2),
˚
λ = 1.54178 A, T = 223(2) K, ω and j scans, 11 543 reflections
collected ((h, ( k, ( l), [(sin θ)/λ] = 0.60 A-1, 3544 independent
˚
1
(Rint = 0.039) and 3331 observed reflections [I g 2σ(I)], 215
refined parameters, R = 0.049, wR2 = 0.137, max. residual
6.86. Found: C, 74.26; H, 8.70; N, 6.31. At 298 K: H NMR
(600 MHz, C6D6, 298 K): δ 7.88 (s, 2H, NdCH), 7.12 (m, 4H,
electron density 0.25(-0.29) e A-3, hydrogen atoms calculated
m-Ar), 7.09 (m, 2H, p-Ar), 7.06 (m, 2H, m-ArZr), 6.96 (m, 1H,
˚
and refined as riding atoms.
p-ArZr), 6.94 (R0), 6.46 (R), 6.10 (β0), 5.96 (β) (each br m, each
=
3
Preparation of 6-(2,6-Diisopropylanilino)fulvene, 5. The THF-
free Li salt 3 (6.31 g, 24.38 mol) was placed into a Schlenk flask,
and Et2O (150 mL) was added. The resulting solution was
cooled to -40 °C, and dry acetylacetone (2.44 g, 2.6 mL, 24.4
mmol) was slowly added via syringe. The reaction mixture was
stirred at -40 °C for 10 min, then warmed slowly to room
temperature and finally stirred for 1 h. After filtration all
volatiles were removed from the filtrate in vacuo. The brown
oily residue was extracted with pentane (100 mL). The filtered
pentane solution was dried in vacuo to yield the product as a red-
brown oil, which slowly crystallized (5.22 g, 72%) at low
temperature. Despite all precautions, the compound was always
contaminated with ca. 25 mol % of 2,6-di-isopropylaniline.
Based on the integration of the CH protons of the iPr groups,
the ratio of the major to the minor ligand isomer to free 2,6-di-
isopropylaniline was 2:1:1. Crystals of 5 suitable for crystal
structure analysis were obtained from a heptane solution at
-30 °C. Anal. Calcd for 3 ꢀ C18H23N þ C12H19N: C, 84.56; H,
9.46, N, 5.98. Found: C, 84.45; H, 9.45; N, 5.94.
2H, C5H4), 3.47 (br, 2H, CH(iPr)Zr), 3.18 (sept, 4H, JHH
6.8 Hz, CH(iPr)), 2.85 (s, 6H, CH3N), 1.21 (br, 12H, CH3-
(iPr)Zr), 1.20 (d, 12H, 3JHH = 6.8 Hz, CH3(iPr)), 1.13 (d, 12H,
3JHH = 6.8 Hz, CH3(iPr)). 13C{1H} NMR (151 MHz, C6D6, 298
K): δ 156.7 (CHdN), 153.1 (i-ArZr), 149.5 (i-Ar), 138.1 (o-Ar),
124.8 (p-Ar), 123.5 (m-Ar), 123.1 (br, m-ArZr), 122.2 (p-ArZr),
119.9 (i-C5H4), 117.7 (R-C5H4), 113.1 (br, β0-C5H4), 112.7
(R0-C5H4), 109.9 (br, β-C5H4), 50.9 (CH3N), 28.3 (CH(iPr)),
28.2 (br, CH(iPr)Zr), 24.5 (br, CH3(iPr)Zr), 23.9 (CH3(iPr)), 23.8
(CH3(iPr)). At 353 K: 1H NMR (600 MHz, d8-toluene, 353 K): δ
7.90 (s, 2H, NdCH), 7.01 (m, 4H, m-Ar), 6.96 (m, 2H, p-Ar),
6.95 (br m, 2H, m-ArZr), 6.83 (R0), 6.81 (m, 1H, p-ArZr), 6.44 (R),
6.06 (β0), 5.90 (β) (each br s, each 2H, C5H4), 3.42 (br sept, 2H,
3
3JHH = 6.7 Hz, CH(iPr)Zr), 3.08 (sept, 4H, JHH = 6.8 Hz,
3
CH(iPr)), 2.83 (s, 6H, CH3N), 1.12 (d, 12H, JHH = 6.8 Hz,
3
CH3(iPr)), 1.12 (d, 12H, JHH = 6.7 Hz, CH3(iPr)Zr), 1.05 (d,
3
12H, JHH = 6.8 Hz, CH3(iPr)). 13C{1H} NMR (151 MHz,
C6D6, 353 K): δ 156.8 (CHdN), 153.3 (i-ArZr), 149.8 (i-Ar),
140.5 (o-ArZr), 138.5 (o-Ar), 124.9 (p-Ar), 123.6 (m-Ar), 123.2
(m-ArZr), 122.5 (p-ArZr), 120.9 (i-C5H4), 117.4 (R-C5H4), 113.7
(br, β0-C5H4), 113.3 (R0-C5H4), 109.8 (β-C5H4), 51.1 (CH3N),
28.5 (CH(iPr)), 28.1 (CH(iPr)Zr), 24.5 (CH3(iPr)Zr), 23.9
(CH3(iPr)), 23.9 (CH3(iPr)).
Major Isomer (anti-5). 1H NMR (600 MHz, CD2Cl2, 253 K): δ
7.36 (t, 3JHH = 7.8 Hz, 1H, p-Ar), 7.26 (d, 3JHH = 7.8 Hz, 2H,
m-Ar), 6.99 (d, 3JHH = 14.2 Hz, 1H, dCHN), 6.91 (br d, 3JHH
=
14.2 Hz, 1H, NH), 6.71 (dm, JHH = 4.7 Hz, β0), 6.51 (m, R0), 6.41
(ddd, JHH = 4.7 Hz, 2.1 Hz, 1.7 Hz, β), 6.27 (ddd, JHH = 4.6 Hz,
2.4 Hz, 1.4 Hz, R) (each 1H, C5H4), 3.29 (sept, 3JHH = 6.8 Hz,
X-ray Crystal Structure Analysis of Complex 7. Formula
C50H68N4Zr, M = 816.30, yellow crystal 0.45 ꢀ 0.40 ꢀ 0.10 mm,

5156 Organometallics, Vol. 28, No. 17, 2009
Axenov et al.
˚
˚
˚
˚
˚
˚
a = 20.3145(3) A, b = 10.6737(2) A, c = 21.4606(4) A, β =
a = 11.620(1) A, b = 12.127(1) A, c = 31.003(1) A, V = 4368.8(5)
100.071(1)°, V = 4581.6(1) A , Fcalc = 1.183 g cm-3, μ = 0.276
A , Fcalc = 1.183 g cm-3, μ = 0.286 mm-1, empirical absorption
3
3
˚
˚
mm-1, empirical absorption correction (0.886 e T e 0.973), Z =
correction (0.919 T e 0.967), Z = 4, orthorhombic, space group
˚
˚
4, monoclinic, space group P21/c (No. 14), λ = 0.71073 A, T =
P212121 (No. 19), λ = 0.71073 A, T = 223(2) K, ω and j scans,
-1
˚
223(2) K, ω and j scans, 23874 reflections collected ((h, ( k,
32 769 reflections collected ((h, ( k, ( l), [(sin θ)/λ] = 0.62 A
8831 independent (Rint = 0.078) and 5228 observed reflections [I g
,
( l), [(sin θ)/λ] = 0.60 A-1, 8041 independent (Rint=0.078) and
˚
5437 observed reflections[I g 2σ(I)], 513 refined parameters, R =
0.053, wR2 = 0.119, max. residual electron density 0.63(-0.41)
2σ(I)], 501 refined parameters, R = 0.056, wR2 = 0.141, max.
residual electron density 0.53(-0.53) e A-3, Flack parameter
˚
e A-3, hydrogen atom at N1C from difference Fourier calcula-
˚
0.03(5), imino group C6A-N1A refined with split positions, hydro-
gens calculated and refined as riding atoms.
tion, others calculated and refined as riding atoms.
Compound 6. The pentane solution decanted from the pre-
cipitation of complex 7 was filtered through Celite and evapo-
rated under vacuum, to give 4.40 g (65%) of the target complex 6
as a yellow-brown solid. Crystals of 6 suitable for the X-ray
single-crystal diffraction analysis were grown from pentane
solution at -30 °C. Anal. Calcd for C40H56ZrN4: C, 70.23; H,
8.25. Found: C, 70.78; H, 8.64. 1H NMR (500 MHz, C6D6,
298 K): δ 7.96 (s, 2H, NdCH), 7.18 (m, 4H, m-Ar), 7.13 (m, 2H,
p-Ar), 6.71 (R), 6.01 (β) (each m, each 4H, C5H4), 3.28 (sept, 4H,
3JHH = 6.9 Hz, CH(iPr)), 2.83 (s, 12H, CH3N), 1.22 (d, 24H,
3JHH = 6.9 Hz, CH3(iPr)). 13C{1H} NMR (126 MHz, C6D6, 298
K): δ 156.5 (CHdN), 150.0 (i-Ar), 138.2 (o-Ar), 124.6 (p-Ar),
123.5 (m-Ar), 121.3 (i-C5H4), 114.4 (R-C5H4), 111.3 (β-C5H4),
49.1 (CH3N), 28.1 (CH(iPr)), 24.1 (CH3(iPr)).
Preparation of the Dichlorozirconocene Complex 9. (Me2N)2-
ZrCl2(THF)2 (0.78 g, 1.98 mmol) was mixed in a glovebox with
ligand 5 (1.20 g, ∼4.74 mmol). Then 20 mL of toluene was
added. The reaction mixture was first stirred for 3 h at 120 °C
and additionally overnight at room temperature. After filtration
all volatiles were removed under vacuum, and the resulting
brown residue was washed with pentane (12 mL). After removal
of the pentane phase by syringe, the oily brown precipitate was
dried in vacuo, which gave 0.52 g (39%) of the product 9 as a red-
brown solid. The second crop of the product precipitated from
the pentane washings at room temperature as a crystalline solid.
After removing the pentane solvent by decantation, the crystal-
line residue was dried in vacuo, which gave an additional
amount of the target complex (0.358 g). The combined yield of
complex 9 was 0.878 g, 67%. Anal. Calcd for C36H44N2Cl2Zr: C,
X-ray Crystal Structure Analysis of Complex 6. Formula
C40H56N4Zr, M = 684.11, yellow crystal 0.50 ꢀ 0.20 ꢀ 0.10 mm,
1
64.84; H, 6.65; N, 4.20. Found: C, 64.72; H, 6.85; N, 4.24. H
NMR (600 MHz, C6D6, 298 K): δ 7.99 (s, 2H, dCHN), 7.15 (m,
6H, Ar), 6.72 (R), 5.89 (β) (each m, each 4H, C5H4), 3.25 (sept,
˚
˚
˚
a = 8.8885(1) A, b = 13.7423(2) A, c = 16.0742(3) A, R =
3
˚
75.012(1)°, β = 76.547(1)°, γ = 89.272(2)°, V = 1842.25(5) A ,
Fcalc = 1.233 g cm-3, μ = 0.330 mm-1, empirical absorption
correction (0.852 e T e 0.968), Z = 2, triclinic, space group P1
3JHH = 6.9 Hz, 4H, CH(iPr)), 1.24 (d, JHH = 6.9 Hz, 24H,
3
CH3(iPr)). 13C{1H} NMR (151 MHz, C6D6, 298 K): δ 156.2
(NdCH), 149.2 (i-Ar), 137.9 (o-Ar), 125.1 (p-Ar), 124.6
(i-C5H4), 123.5 (m-Ar), 119.4 (R-C5H4), 114.5 (β-C5H4), 28.2
(CH(iPr)), 24.0 (CH3(iPr)).
˚
(No. 2), λ = 0.71073 A, T = 223(2) K, ω and j scans, 12 856
reflections collected ((h, ( k, ( l), [(sin θ)/λ] = 0.66 A-1, 8708
˚
independent (Rint = 0.031) and 7122 observed reflections [I g
2σ(I)], 418 refined parameters, R = 0.040, wR2 = 0.093, max.
Hydrogenation of the Dichlorozirconocene Complex 9; Gen-
eration of Complex 10. In a reference experiment C6D6 (1 mL)
was added in the glovebox in a Schlenk flask to a mixture of
complex 9 (0.2 g, 0.30 mmol) and B(C6F5)3 (77 mg, 0.15 mmol).
The flask was connected to the hydrogen bottle. The system was
flushed with hydrogen and then properly closed with the tap.
The hydrogen pressure in the reaction flask was raised to 2 bar,
and the reaction mixture was stirred in the glovebox overnight at
room temperature. After evaporation of all volatiles in vacuo
a mixture of 10 and 11 was obtained as a light yellow solid (ca.
0.27 g, 100%). A similar result was achieved by using a hydrogen
pressure of 60 bar and shorter reaction time (3 h). Anal. Calcd
for 10:11 (1:1) (C90H98BCl4F15N4Zr2): C, 58.25; H, 5.32; N,
3.02. Anal. Calcd for 10:11 (2:1) (C126H144BCl6F15N6Zr3): C,
residual electron density 0.36(-0.54) e A-3, hydrogen atoms
˚
calculated and refined as riding atoms.
Preparation of the Dibenzylzirconocene Complex 8. Et2O
(15 mL) was added to ZrCl4 (0.31 g, 1.33 mmol) at -78 °C,
and the resulting mixture was stirred at -78 °C until a homo-
geneous suspension was formed. To this suspension of ZrCl4 in
Et2O was added a 1 M solution of PhCH2MgCl (5.34 mmol) in
Et2O (5.34 mL) at -78 °C. The reaction was protected from
direct light, allowed to warm to room temperature, and stirred
for 1 h. To the resulting mixture was added an ethereal solution
(20 mL) of the ligand 5 (0.91 g, 2.68 mmol) by syringe at -78 °C.
The reaction was warmed to room temperature, stirred for 1 h,
and then kept in the freezer at -20 °C overnight. After removal
of all volatiles under vacuum the residue was extracted with
pentane (2 ꢀ 20 mL). The combined extracts were filtered, and
the solvent was evaporated in vacuo. The remaining red-orange
residue was washed with pentane (10 mL) and dried under
vacuum, which gave the product as an orange solid (0.7 g). An
additional amount of the product (0.2 g) precipitated from the
pentane washings upon keeping it at room temperature for
several days. The total yield of the complex was 0.9 g (87%).
Crystals of 8 suitable for X-ray single-crystal diffraction analysis
were grown from Et2O solution at -33 °C. Anal. Calcd for
C50H58ZrN2: C, 77.17; H, 7.51; N, 3.60. Found: C, 77.72; H,
7.82; N, 3.46. 1H NMR (600 MHz, C6D6, 298 K): δ 7.67 (s, 2H,
NdCH), 7.15 (m, 4H, m-Ph), 7.13 (m, 4H, m-Ar), 7.11 (m, 2H,
p-Ar), 6.97 (m, 4H, o-Ph), 6.82 (m, 2H, p-Ph), 6.53 (R), 5.68 (β)
1
59.94; H, 5.75; N, 3.33. Found: C, 57.97; H, 4.91; N, 3.33. H
NMR (600 MHz, C6D6, 298 K): δ 7.07 (m, 6H, Ar), 6.13 (R),
5.68 (R) (each m, each 4H, C5H4), 4.17 (s, 4H, CH2), 3.87 (BH),
3.32 (sept, 3JHH = 6.5 Hz, 4H, CH(iPr)), 1.21 (d, 3JHH = 6.5 Hz,
24H, CH3(iPr)), n.o. (NH). 13C{1H} NMR (151 MHz, C6D6,
298 K): δ 148.8 (dm, 1JCF ≈ 235 Hz, C6F5), 143.0 (o-Ar), 140.7
(br, i-Ar), 138.8 (dm, 1JCF ≈ 243 Hz, p-C6F5), 137.3 (dm, 1JCF
≈
248 Hz, C6F5), n.o. (i-C6F5), 131.8 (i-C5H4), 126.0 (p-Ar), 124.3
(m-Ar), 117.6 (br, R-C5H4), 111.8 (β-C5H4), 51.0 (CH2), 28.1
(CH(iPr)), 24.4 (CH3(iPr)). 19F NMR (470 MHz, C6D6, 298 K):
3
δ -133.4 (m, o-C6F5), -161.7 (t, JFF = 20.4 Hz, p-C6F5),
-165.2 (m, m-C6F5). 11B{1H} NMR (160 MHz, C6D6, 298 K):
δ -24.4 (ν1/2 ≈ 100 Hz). 11B NMR (160 MHz, C6D6, 298 K):
δ -24.4 (br d, 1JBH ≈ 76 Hz).
3
(each m, each 4H, C5H4), 3.16 (sept, 4H, JHH = 6.9 Hz,
Crystals of complex 10 suitable for the X-ray single-crystal
diffraction analysis were grown from a pentane solution at -33 °C.
X-ray Crystal Structure Analysis of Complex 10. Formula
C36H48Cl2N2Zr, M = 670.88, colorless crystal 0.35 ꢀ 0.10 ꢀ
3
CH(iPr)), 2.18 (s, 4H, CH2Ph), 1.18 (d, 24H, JHH = 6.9 Hz,
CH3(iPr)). 13C{1H} NMR (151 MHz, C6D6, 298 K): δ 157.0
(CHdN), 151.3 (i-Ph), 149.4 (i-Ar), 137.9 (o-Ar), 128.7 (m-Ph),
126.2 (o-Ph), 125.0 (p-Ar), 123.5 (m-Ar), 123.0 (i-C5H4), 121.9
(p-Ph), 116.0 (R-C5H4), 113.2 (β-C5H4), 63.5 (CH2Ph), 28.4
(CH(iPr)), 23.9 (CH3(iPr)).
˚
˚
˚
0.10 mm, a = 13.6288(2) A, b = 17.8192(3) A, c = 14.1609(2) A,
β = 91.922(1)°, V = 3437.10(9) A , Fcalc = 1.296 g cm-3, μ =
3
˚
0.501 mm-1, empirical absorption correction (0.877 e T e
X-ray Crystal Structure Analysis of Complex 8. Formula
C50H58N2Zr, M = 778.20, orange crystal 0.30 ꢀ 0.30 ꢀ 0.12 mm,
0.973), Z = 4, monoclinic, space group P21/c (No. 14), λ =
0.71073 A, T = 223(2) K, ω and j scans, 27 684 reflections
˚

Article
Organometallics, Vol. 28, No. 17, 2009 5157
collected ((h, ( k, ( l), [(sin θ)/λ] = 0.66 A-1, 8167 independent
(Rint = 0.056) and 5519 observed reflections [I g 2σ(I)], 416
refined parameters, R = 0.044 wR2 = 0.099, max. (min.)
6.59, 6.31 (C5H4), 4.60, 4.11 (CH2), 3.08 (CH(iPr)), 1.19 (d,
3JHH = 6.5 Hz, 12H, CH3(iPr)) [all resonances are very broad].
19F NMR (564 MHz, d8-THF, 298 K): δ -133.4 (m, o-C6F5),
-166.4 (t, 3JFF = 20.5 Hz, p-C6F5), -168.8 (m, m-C6F5). 11B{1H}
NMR (192 MHz, d8-THF, 298 K): δ -25.5 (ν1/2 ≈ 60 Hz). 11B
NMR (192 MHz, d8-THF, 298 K): δ -25.5 (br d, 1JBH ≈ 94 Hz).
Preparation of Complex 12. C6D6 (1 mL) was added in a
glovebox to a mixture of complex 9 (0.112 g, 0.168 mmol) and
B(C6F5)3 (172 mg, 0.336mmol, 2 equiv). The glass tubecontaining
the reaction mixture was closed with a dual valve Teflon adapter
and placed into a steel autoclave inside a glovebox; then the
autoclave was properly closed and removed from the glovebox.
The autoclave was charged with dihydrogen to a pressure of 60
bar, and the reaction mixture was stirred for 3 h at ambient
temperature. After venting hydrogen to ambient pressure inside
the autoclave the glass tube was placed in the glovebox. The
product is only sparingly soluble in benzene and precipitated as a
brown oil. Benzene was removed from the precipitated product by
decantation. The oily product was dissolved in 1 mL of dry
dichloromethane. After evaporation of all volatiles under vacuum
the product 12 was obtained as a light brown solid (160 mg, 81%).
The elemental analysis was obtained from the material pre-
pared analogously from complex 9 (0.112 g, 0.168 mmol) and
B(C6F5)3 (172 mg, 0.336 mmol, 2 equiv). The procedure was as
follows: C6D6 (1 mL) was added in the glovebox in a Schlenk
flask to a mixture of complex 9 (0.112 g, 0.168 mmol) and
B(C6F5)3 (172 mg, 0.336 mmol, 2 equiv). The flask was con-
nected to the hydrogen bottle. The system was flushed with
hydrogen and then properly closed with the tap. The hydrogen
pressure in the reaction flask was raised to 2 bar, and the
reaction mixture was stirred in a glovebox overnight at room
temperature. The solvent was decanted from the oily precipitate
of the product 12. The oil was transferred into another Schlenk
flask with the help of C6D6 (1 mL), and the benzene phase was
decanted from the oily precipitate. This oily residue was dried in
vacuo, which led to the product 12, obtained as a light yellow
solid. Anal. Calcd for C72H52B2Cl2F30N2Zr: C, 50.90; H, 3.09;
N, 1.65. Found: C, 51.11; H, 3.04; N, 2.05. Other further
experiments gave slightly deviated elemental analysis results
(up to 2.5% C deviation).
The NMR identification of 12 was achieved from the spectra in
d8-THF under “static” conditions at low temperature. The
experiment was carried out in a glovebox using a Schlenk flask:
C6D6 (1 mL) was added to a mixture of complex 9 (0.1 g,
0.15 mmol) and B(C6F5)3 (2.3 equiv, 177 mg, 0.345 mmol). The
flask was connected to the hydrogen bottle. The system was
flushed with hydrogen and then properly closed with the tap. The
hydrogen pressure in the reaction flask was raised to 2 bar, and
the reaction mixture was stirred in a glovebox overnight at room
temperature. The solvent was decanted from the precipitated oil
of the product mixture of 11 and 12. The oily products were
transferred to another Schlenk flask with some C6D6 (1 mL), and
the benzene phase was decanted from the oily precipitate. This
oily residue was dried in vacuo, which led to a mixture of 11 and
12 (1:5), obtained as a light yellow solid (0.100 g). The sample was
redissolved ind8-THF, andthe NMR experiments weremeasured
at low temperature under static conditions (“frozen” proton
transfer). Complex 12: 1H NMR (600 MHz, d8-THF, 198 K): δ
˚
residual electron density 0.44 (-0.62) e A-3, disorder in the iso-
propyl group C17A-C19A refined with split positions, hydro-
gen atoms at nitrogen from difference Fourier map, others
calculated and refined as riding atoms.
˚
The following additional experiments were carried out to
identify the individual products 10 and 11 from the reaction
mixture. The experiment was carried out in a glovebox using
a Schlenk flask: C6D6 (0.6 mL) was added to a mixture of
complex 9 (50 mg, 0.075 mmol) and B(C6F5)3 (0.5 equiv, 19 mg,
0.0375 mmol). The flask was connected to the hydrogen bottle.
The system was flushed with hydrogen and then properly closed
with the tap. The hydrogen pressure in the reaction flask was
raised to 2 bar, and the reaction mixture was stirred in a
glovebox overnight at room temperature. After evaporation of
all volatiles in vacuo a mixture of 10 and 11 (2:1) was obtained as
a light yellow solid (∼100%). The sample was redissolved in
d8-THF, and the NMR experiments were measured at low
temperature under static conditions (“frozen” proton transfer).
Complex 10: 1H NMR (600 MHz, d8-THF, 198 K): δ 7.06 (m,
2H, m-Ar), 7.00 (m, 1H, p-Ar), 6.37 (β), 6.00 (R),(each br, each
2H, C5H4), 4.04 (br, 2H, CH2), 4.00 (br, 1H, NH), 3.29 (sept,
3JHH = 6.5 Hz, 2H, CH(iPr)), 1.14 (br, 12H, CH3(iPr)). 13C{1H}
NMR (151 MHz, d8-THF, 198 K): δ 143.1 (i-Ar), 142.8 (o-Ar),
133.6 (i-C5H4), 123.8 (p-Ar), 123.4 (m-Ar), 116.7(R), 112.3(β)
(C5H4), 50.4 (CH2), 27.4 (CH(iPr)), 24.2 (CH3(iPr)) [data from
the ghsqc and ghmbc NMR experiment]. Complex 11: 1H NMR
(600 MHz, d8-THF, 198 K): δ 7.55 (m, 1H, p-Ar ), 7.48 (m, 2H,
þ
m-Ar ), 7.06 (m, 2H, m-Ar), 7.00 (m, 1H, p-Ar), 6.74, 6.16 (each
þ
br, each 2H, C5H4þ), 6.59, 6.33 (each br, each 2H, C5H4), 4.62
(br, 2H, CH2,þ), 4.04 (br, 2H, CH2), 4.00 (br, 1H, NH), 3.19 (br,
2H, CH(iPr)), 2.77 (br, 2H, CH(iPr) ), 1.20 (br, 12H, CH3-
þ
(iPr) ), 1.11 (br, 12H, CH3(iPr)), n.o. (NH2,þ). Averaged spec-
þ
tra at 298 K: 1H NMR (600 MHz, d8-THF, 298 K): δ 7.10 (br,
3H, Ar), 6.53, 6.40 (each br, each 2H, C5H4), 4.18 (br, 2H, CH2),
3.78 (br, BH), 3.59 (br, 2H, CH(iPr)), 1.19 (d, 3JHH = 6.5 Hz,
12H, CH3(iPr)), n.o. (NH). 19FNMR(564MHz, d8-THF, 298 K):
δ -133.4 (m, o-C6F5), -166.5 (t, 3JFF = 20.5 Hz, p-C6F5), -168.9
(m,m-C6F5);. 11B{1H} NMR (192 MHz, d8-THF, 298 K): δ-25.5
(ν1/2 ≈80 Hz). 11BNMR(192MHz,d8-THF, 298 K): δ-25.5(brd,
1JBH ≈ 94 Hz).
Generation of Complex 11. The experiment was carried out in
a glovebox using a Schlenk flask: D6-benzene (1 mL) was added
to a mixture of complex 9 (0.1 g, 0.15 mmol) and B(C6F5)3 (1.2
equiv, 92 mg, 0.18 mmol). The flask was connected to the
hydrogen bottle. The system was flushed with hydrogen and
then properly closed with the tap. The hydrogen pressure in the
reaction flask was raised to 2 bar, and the reaction mixture was
stirred in a glovebox overnight at room temperature. After
evaporation of all volatiles in vacuo a mixture of 10, 11, and
12 (5:20:3) was obtained as a light yellow solid (∼100%). The
sample was redissolved in d8-THF, and the NMR experiments
were measured at low temperature under static conditions
1
(“frozen” proton transfer). Complex 11: H NMR (600 MHz,
d8-THF, 198 K): δ 9.65 (br, 2H, NH2,þ), 7.56 (m, 1H, p-Ar ),
þ
7.48 (m, 2H, m-Ar ), 7.05 (m, 2H, m-Ar), 6.99 (m, 1H, p-Ar),
þ
6.75 (β), 6.14 (R) (each br, each 2H, C5H4þ), 6.60 (β), 6.33 (R)
(each br, each 2H, C5H4), 4.62 (br, 2H, CH2,þ), 4.01 (br, 3H,
9.65 (br, 2H, NH2,þ), 7.55 (m, 1H, p-Ar ), 7.48 (m, 2H, m-Ar ),
þ þ
6.76 (β), 6.19 (R) (each br, each 2H, C5H4þ), 4.59 (br, 2H, CH2,þ),
CH2, NH), 3.19 (br, 2H, CH(iPr)), 2.77 (br, 2H, CH(iPr) ), 1.20,
3.70 (br, 1H, BH), 2.72 (br, 2H, CH(iPr) ), 1.20, 1.13 (each br,
þ
1.17 (each br, each 6H, CH3(iPr) ), 1.10 (br, 12H, CH3(iPr)).
þ
each 6H, CH3 (iPr) ). 13C{1H} NMR (151 MHz, d8-THF,
þ
þ
13C{1H} NMR (151 MHz, d8-THF, 198 K): δ 143.1 (i-Ar), 142.9
198 K): δ 142.9 (o-Ar ), 131.5 (p-Ar ), 127.7 (i-Ar ), 126.3
þ
þ
þ
(o-Ar, o-Ar ), 134.8 (i-C5H4), 131.5 (p-Ar ), 127.8 (i-Ar ),
(m-Ar ), 124.4 (R), 113.2 (β) (C5H4þ), 117.5 (i-C5H4þ), 51.0
þ
þ
þ
þ
124.6 (m-Ar ), 124.4 (p-Ar), 124.4(R), 111.9 (β) (C5H4þ),
(CH2,þ), 28.8 (CH(iPr) ), 24.6, 23.0 (CH3(iPr) ) [data from the
þ þ
þ
123.8 (m-Ar), 118.2 (R), 113.8 (β) (C5H4), 115.4 (i-C5H4þ),
ghsqc and ghmbc NMR experiment]. Complex 11: 1H NMR (600
MHz, d8-THF, 198 K): δ 9.65 (br, 2H, NH2,þ), 7.55 (m, 1H,
p-Ar ), 7.48 (m, 2H, m-Ar ), 7.05 (m, 2H, m-Ar), 6.99 (m, 1H,
51.4 (CH2,þ), 50.4 (CH2), 28.8 (CH(iPr) ), 27.8 (CH(iPr)),
þ
24.4 (CH3(iPr)), 24.5, 23.3 (CH3(iPr) ), [data from the ghsqc
þ
þ
þ
and ghmbc NMR experiment]. Averaged spectra at 298 K. 1H
p-Ar), 6.74 (β), 6.14 (R) (each br, each 2H, C5H4þ), 6.59 (β), 6.34
(R) (each br, each 2H, C5H4), 4.63 (br, 2H, CH2,þ), 4.01, 3.98 (br,
NMR (600 MHz, d8-THF, 298 K): δ 9.46 (NH2,þ), 7.28 (Ar),

5158 Organometallics, Vol. 28, No. 17, 2009
Axenov et al.
3H, CH2, NH), 3.20 (br, 2H, CH(iPr)), 2.77 (br, 2H, CH(iPr) ),
þ
1.20, 1.13 (each br, each 6H, CH3(iPr) ), 1.11 (br, 12H, CH3(iPr)).
The resulting mixture was evaporated under vacuum. The residue
was extracted with pentane (5 mL). The filtered pentane extracts
were evaporated in vacuo. The obtained products were character-
ized by 1H and 13C NMR and exact mass MS measurements (for
details see below).
þ
Averaged spectra at 298 K: 1H NMR (600 MHz, d8-THF, 298 K):
δ 9.49 (NH2,þ), 7.50, 7.40 (Ar), 6.64, 6.22 (C5H4), 4.64 (CH2), 3.75
(q (1:1:1:1), 1JBH ≈ 100 Hz, BH), 2.80 (CH(iPr)), 1.21 (d, 3JHH
=
6.4 Hz, 12H, CH3(iPr)) [all resonances are very broad]. 19F NMR
(564 MHz, d8-THF, 298 K): δ -133.4 (m, o-C6F5), -166.3 (t,
3JFF = 20.0 Hz, p-C6F5), -168.8 (m, m-C6F5). 11B{1H} NMR
(192 MHz, d8-THF, 298 K): δ -25.5 (ν1/2 ≈ 70 Hz). 11B NMR
(192 MHz, d8-THF, 298 K): δ -25.5 (br d, 1JBH ≈ 95 Hz).
Synthesis of N-(2,2-Dimethylpropylidene)-2,6-xylidine (13a).
In a 50 mL round-bottom flask 2,6-xylidine (4.84 g, 0.04 mol)
was mixed with pivalic aldehyde (5.16 g, 0.06 mol). A few drops
of concentrated H2SO4 were added to the mixture. The reaction
mixture was heated to 60 °C and stirred at that temperature
overnight. The resulting mixture was extracted with 100 mL of
pentane. The solvent was removed from the extracts under
vacuum, and the residue was distilled under vacuum (bp of
product = 61 °C/0.08 bar). The product was isolated as a
colorless oil (5.52 g, 73%). Anal. Calcd for C13H19N: C, 82.48;
H, 10.12; N, 7.40. Found: C, 82.32; H, 10.17; N, 7.48. 1H NMR
(600 MHz, C6D6, 298 K): δ 7.09 (s, 1H, dCHN), 7.00 (m, 2H, m-
Ar), 6.92 (m, 1H, p-Ar), 2.03 (s, 6H, CH3), 1.04 (s, 9H,
t-Bu). 13C{1H} NMR (151 MHz, C6D6, 298 K): δ 173.7
(dCHN), 151.8 (i-Ar), 128.3 (m-Ar), 126.7 (o-Ar), 123.4 (p-Ar),
37.0, 26.6 (t-Bu), 18.3 (CH3). The data are similar to those
reported in the literature.28
Preparation of N-(2,2-Dimethylpropyl)-2,6-xylidine (14a);
Catalytic Hydrogenation of N-(2,2-Dimethylpropylidene)-2,6-
xylidine (13a). About 17 molar equiv of 13a (150 mg, 0.792
mmol) was catalytically hydrogenated according to the general
procedure in the presence of complex 12 (80 mg, 0.0471 mmol).
The product 14a was isolated as a colorless oil (150 mg, ∼100%).
1H NMR (600 MHz, CDCl3, 298 K): δ 6.87 (d, 3JHH = 7.3 Hz,
3
2H, m-Ar), 6.70 (t, JHH = 7.3 Hz, 1H, p-Ar), 3.00 (br s, 1H,
NH), 2.57 (s, 2H, CH2), 2.17 (s, 6H, CH3), 0.93 (s, 9H, t-Bu).
13C{1H} NMR (151 MHz, CDCl3, 298 K): δ 146.0 (i-Ar), 129.8
(o-Ar), 128.8 (m-Ar), 122.1 (p-Ar), 60.4 (CH2), 31.9, 27.5 (t-Bu),
18.2 (CH3). MS(ESI): found m/z 192.1760, calcd for
C13H21NHþ 192.1747.
Preparation of N-(2,2-Dimethylpropyl)-2,6-bis(1-methylethyl)-
aniline (14b); Catalytic Hydrogenation of N-(2,2-Dimethyl-
propylidene)-2,6-bis(1-methylethyl)aniline (13b). About 43 molar
equiv of 13b (124 mg, 0.507 mmol) was catalytically hydrogenated
according to the general procedure in the presence of complex 12
(20 mg, 0.0118 mmol). The product 14b was isolated as a colorless
oil (124 mg, ∼100%). 1H NMR (500 MHz, CDCl3, 298 K): δ 7.10
(m, 2H, m-Ar), 7.06 (m, 1H, p-Ar), 3.28 (sept, 3JHH = 6.8 Hz, 2H,
CH(iPr)), 2.94 (br, 1H, NH), 2.61 (s, 2H, CH2), 1.26 (d, 3JHH
=
Synthesis of N-(2,2-Dimethylpropylidene)-2,6-bis(1-methyl-
ethyl)benzenamine (13b). In a 50 mL round-bottom flask 2,6-
di-isopropylaniline (1.6 g, 0.009 mol) was mixed with pivalic
aldehyde (3.89 g, 0.045 mol). A few drops of the concentrated
H2SO4 were added to the mixture. The mixture was heated to
60 °C and stirred at that temperature for 3 h. The resulting
mixture was extracted with 100 mL of pentane. Pentane was
removed from the extracts under vacuum, and the residue was
distilled under vacuum (bp of product = 86 °C/0.02 bar). The
product was isolated as a colorless oil (1.73 g, 93%). Anal. Calcd
for C17H27N: C, 83.20; H, 11.09; N, 5.71. Found: C, 82.32; H,
10.17; N, 7.48). 1H NMR (600 MHz, C6D6, 298 K): δ 7.26 (s, 1H,
dCHN), 7.13 (m, 2H, m-Ar), 7.08 (m, 1H, p-Ar), 3.05 (sept,
6.8 Hz, 12H, CH3(iPr)), 1.07 (s, 9H, t-Bu). 13C{1H} NMR (126
MHz, CDCl3, 298 K): δ 143.3 (br, i-Ar), 142.9 (o-Ar), 123.9 (p-
Ar), 123.5 (m-Ar), 64.1 (CH2), 31.9, 27.5 (t-Bu), 27.4 (CH(iPr)),
24.3 (CH3(iPr)). MS(ESI): found m/z 248.2371, calcd for
C17H29NHþ 248.2373; found m/z 270.2188, calcd for
C17H29N Naþ 270.2192.
3
Preparation of Trimethyl(1,2,2-trimethylpropoxy)silane (16);
Catalytic Hydrogenation of 1-tert-Butyl-1-trimethylsiloxyethene
(15). About 20 molar equiv of 15 (purchased from Aldrich)
(163 mg, 0.9478 mmol) was catalytically hydrogenated accord-
ing to the general procedure in the presence of complex 12
(80 mg, 0.0471 mmol). The product 16 was isolated as a colorless
oil (140 mg, 85%). The product is hydroscopic, and its long
exposure to air should be avoided. 1H NMR (500 MHz, C6D6,
3
3JHH = 6.9 Hz, 2H, CH(iPr)), 1.17 (d, JHH = 6.9 Hz, 12H,
CH3(iPr)), 1.07 (s, 9H, t-Bu). 13C{1H} NMR (151 MHz, C6D6,
298 K): δ 173.1 (dCHN), 149.8 (i-Ar), 137.4 (o-Ar), 124.1
(p-Ar), 123.2 (m-Ar), 37.0 (t-Bu), 28.0 (CH(iPr)), 26.6 (t-Bu),
23.5 (CH3(iPr)). The data are similar to those reported in the
literature.29
298 K): δ 3.36 (q, JHH = 6.3 Hz, 1H, HC), 1.01 (d, JHH =
3
3
6.3 Hz, 3H, CH3), 0.88 (s, 9H, t-Bu), 0.11 (s, 2JSiH = 6.6 Hz, 9H,
SiMe3). 13C{1H} NMR (126 MHz, C6D6, 298 K): δ 76.2 (CH),
35.4, 25.9 (t-Bu), 18.7 (CH3), 0.4 (Me3Si). MS(EI): found m/z
173.1341 (100%), calcd for C9H21OSi 173.1362; found m/z
174.1409, calcd for C9H22OSi 174.1440.
General Procedure for the Hydrogenation of Imines and a Silyl
Enolether Catalyzed by 12. In a glovebox the unsaturated sub-
strate was added to a Schlenk flask containing a solution of
complex 12 in C6D6 (0.6 mL). The system was flushed with
hydrogen, then properly closed with the tap. The pressure of
hydrogen in the reaction flask was kept at 2 bar, and the reaction
mixture was stirred at room temperature in the glovebox overnight.
Acknowledgment. Financial support from the Fonds der
Chemischen Industrie and the Alexander von Humboldt-
Stiftung (stipend to K.V.A.) is gratefully acknowledged. We
thank the BASF for a gift of solvents.
(28) Murakami, M.; Kawano, T.; Ito, H.; Ito, Y. J. Org. Chem. 1993,
58, 1458–1465.
(29) (a) Jordan, A. Y.; Meyer, T. Y. J. Organomet. Chem. 1999, 591,
104–113. (b) Cantrell, G. K.; Meyer, T. Y. Chem. Commun. 1997, 1551–
1552.
Supporting Information Available: Text and figures giving
further experimental and spectroscopic details and CIF files
giving crystallographic data. This material is available free of
charge via the Internet at http://pubs.acs.org.