Reactions of five-membered zirconacyclocumulenes with diisobutylaluminum hydride

Article abstract of DOI:10.1021/om049705q

The reactions of five-membered zirconacyclocumulenes with diisobutylaluminum hydride were investigated. The complexes were subsequently stabilized in different manner, which depends on the substituents R used (Me=R). The heterobimetallic complex was forme

Full text of DOI:10.1021/om049705q

4160
Organometallics 2004, 23, 4160-4165
Rea ction s of F ive-Mem ber ed Zir con a cyclocu m u len es
w ith Diisobu tyla lu m in u m Hyd r id e
Vladimir V. Burlakov,† Perdita Arndt, Wolfgang Baumann,*
Anke Spannenberg, and Uwe Rosenthal*
Leibniz-Institut fu¨r Organische Katalyse an der Universita¨t Rostock e.V.,
Buchbinderstrasse 5-6, D-18055 Rostock, Germany
Received April 26, 2004
Different products of the reaction of the five-membered zirconacyclocumulenes (zircona-
cyclopenta-2,3,4-trienes) Cp*2Zr(η4-1,2,3,4-RC4R) (Cp* ) η5-pentamethylcyclopentadienyl,
R ) Me (1a ), Me3Si (1b), Ph (1c)) with i-Bu2AlH are described which can serve as models
for the elementary reaction steps of the zirconocene-catalyzed hydroalumination of disub-
stituted buta-1,3-diynes RCtCCtCR and also for the activation of zirconocene complexes
in the catalytic polymerization of ethylene. In all investigated cases of reactions of complexes
1 with i-Bu2AlH via a cis-hydroalumination of the central double bond, the formation of
zirconacyclopentadienes with i-Bu2Al substituents in the 3-position as intermediates must
be assumed. These complexes were not isolated but subsequently stabilized in a different
manner, depending on the substituents R used. For R ) Me, the intermediate reacts with
a second molecule of i-Bu2AlH to give the complex of the substituted zirconacyclopentadiene
with i-Bu2AlH (2). This complex reacts with CO2 to produce the dinuclear complex 3, whose
structure was confirmed by X-ray analysis. For R ) Me3Si, the C-C bond in the intermediate
is cleaved (“hydroaluminolysis”) with formation of the alkyne i-Bu2AlCtCSiMe3 (detected
by NMR) and the alkyne complex [Cp*2Zr(η2-Me3SiCCH)]. The latter is stabilized by reaction
with i-Bu2AlH to give [Cp*2Zr][(µ-η1:η2-Me3SiCCH)(µ-H)(i-Bu2Al)] (4), which was character-
ized by X-ray crystallography. For R ) Ph, two complexes were isolated after a stepwise
reaction of the unisolated hydroalumination product. The heterobimetallic complex [Cp*2-
Zr][(µ-η1:η2-PhCC-CHCPh)(µ-H)(i-BuAl)] (5) was formed by interaction with i-Bu2AlH with
elimination of i-Bu3Al. This complex can add a further 1 equiv of i-Bu2AlH to form the
trinuclear bimetallic complex [Cp*2Zr][(µ-η1:η2-PhCC-CHdC(i-Bu2Al)(Ph)](µ-H)(i-BuAlH)]
(6). The structures of complexes 5 and 6 were determined by X-ray diffraction analysis.
In tr od u ction
sulting products strongly depend on the diyne substit-
uents R, the metal, and the stoichiometry employed. The
most interesting products of these reactions were the
stable five-membered metallacyclocumulenes Cp2M(η4-
1,2,3,4-RC4R) (R ) t-Bu, M ) Zr,3 Ti4), whose structures
were established by X-ray diffraction studies, which
showed a planar ring system with three CdC double
bonds, the central bond of which is internally coordi-
nated to the metal center. We reported the different
interactions of permethylzirconocene complexes with
1,3-butadiynes RCtCCtCR, in which the five-mem-
bered zirconacyclocumulenes (η4 complexes, zircona-
cyclopenta-2,3,4-trienes) Cp*2Zr(η4-1,2,3,4-RC4R) (R )
Me, SiMe3, Ph) also were the major products.5,6
Conjugated as well as nonconjugated diynes have
been reported to react with titanocene or zirconocene.1
We investigated such reactions with 1,3-butadiynes
using the complexes Cp2M(L)(η2-Me3SiC2SiMe3) (M )
Ti, L ) -; M ) Zr, L ) THF, pyridine) as metallocene
sources.2 Some unexpected results were obtained in
these studies: different modes of complexation, C-C
single bond cleavage, and coupling reactions. The re-
* To whom correspondence should be addressed. E-mail:
uwe.rosenthal@ifok.uni-rostock.de (U.R.); wolfgang.baumann@ifok.uni-
rostock.de (W.B.).
† On leave from the A. N. Nesmeyanov Institute of Organoelement
Compounds, Russian Academy of Sciences, Vavilov St. 28, 117813,
Moscow, Russia.
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Chem. Soc. 1995, 117, 5365. (c) Mao, S. S. H.; Tilley, T. D. J . Am. Chem.
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10.1021/om049705q CCC: $27.50 © 2004 American Chemical Society
Publication on Web 07/22/2004

Reactions of Zirconacyclocumulenes with i-Bu2AlH
Organometallics, Vol. 23, No. 17, 2004 4161
Sch em e 1
Recently we reported that the titana- and zircona-
cyclopropenes (η2-alkyne complexes) Cp′2M(η2-Me3SiC2-
SiMe3) with M ) Ti, Zr and Cp′2 ) Cp2 (bis(η5-cyclo-
pentadienyl)), ebthi (1,2-ethylene-1,1′-bis(η5-tetrahydro-
indenyl)) readily react with i-Bu3Al with formation of
isobutene and the heterobimetallic complexes [Cp′2M]-
[(µ-η1:η2-Me3SiCCSiMe3)(µ-H)(i-Bu2Al)].7a A better route
to these complexes is the direct reaction of the alkyne
complexes with i-Bu2AlH. Such reactions can serve as
a model for the titanocene- and zirconocene-catalyzed
hydroalumination of alkynes, an important route to
organoaluminum compounds.8
Because such data for the titanium- and zirconium-
catalyzed hydroalumination of 1,3-butadiynes are lim-
ited,9 after having studied the reactions of titanocene
and zirconocene complexes of alkynes with i-Bu2AlH we
continued with similar studies with 1,3-diynes. We
report here the reactions of five-membered zircona-
cyclocumulenes (η4-diyne complexes, zirconacyclopenta-
2,3,4-trienes) with i-Bu2AlH.
Resu lts a n d Discu ssion
Com p lex Syn th eses. The first reaction of the five-
membered zirconacyclocumulene Cp*2Zr(η4-1,2,3,4-MeC4-
Me) (1a ) with i-Bu2AlH is probably cis-hydroalumina-
tion of the central double bond. The initial product could
not be isolated, because it rapidly added a second
molecule of i-Bu2AlH to give the complex 2 (Scheme 1).
Support for the structure of complex 2 was provided
by NMR measurements and its reaction with carbon
dioxide. Carbon dioxide inserted into the Al-C bond of
2, and the dinuclear complex 3 was formed after formal
elimination of i-Bu2AlH (Scheme 1). The dimeric struc-
ture of 3 was confirmed by X-ray diffraction (Figure 1).
The complex Cp*2Zr(η4-1,2,3,4-Me3SiC4SiMe3) (1b)
reacted with i-Bu2AlH like 1a in the first step, in a cis-
hydroalumination of the central double bond. Subse-
quent C-C bond cleavage (“hydroaluminolysis”) to the
alkyne i-Bu2AlCtCSiMe3 (detected by NMR) and the
alkyne complex [Cp*2Zr(η2-Me3SiCCH)] is the probable
second step. The latter complex of a terminal alkyne
reacted with a second equivalent of i-Bu2AlH, to give
the complex [Cp*2Zr][(µ-η1:η2-Me3SiCCH)(µ-H)(i-Bu2Al)]
(4) as the final product. The structure of 4 was con-
firmed by X-ray analysis. This complex is very similar
to the products of the Cp′2M(η2-Me3SiC2SiMe3) reaction
with i-Bu3Al or i-Bu2AlH7 mentioned above, but a
terminal alkyne complex is involved.
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Spannenberg, A.; Rosenthal, U. J . Am. Chem. Soc. 1999, 121, 8313.
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Spannenberg, A.; Kempe, R.; Rosenthal, U. Chem. Eur. J . 2000, 6, 81.
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U. Eur. J . Inorg. Chem. 2001, 2885. (b) Thomas, D.; Arndt, P.;
Peulecke, N.; Spannenberg, A.; Kempe, R.; Rosenthal, U. Eur. J . Inorg.
Chem. 1998, 1351. (c) Arndt, P.; Thomas, D.; Rosenthal, U. Tetrahedron
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G.; Albrecht, M. Organometallics 1992, 11, 3517. (h) Erker, G.;
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G. Angew. Chem. 1997, 109, 840; Angew. Chem., Int. Ed. Engl. 1997,
36, 812.
(8) Examples: (a) Dahlmann, M.; Lautens, M. In Catalytic Hetero-
functionalization; Togni, A., Gru¨tzmacher, H., Eds.; Wiley-VCH: Wein-
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Russ. Chem. Rev. 2000, 69, 121. (c) Zheng, W. J .; Roesky, H. W. Dalton
2002, 2787. (d) Parenty, A.; Campagne, J . M. Tetrahedron Lett. 2002,
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Dzhemilev, U. M. Mendeleev Commun. 1996, 6, 231.
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4162 Organometallics, Vol. 23, No. 17, 2004
Burlakov et al.
Ta ble 1. Cr ysta llogr a p h ic Da ta for Com p lexes 3-6
3
4
5
6
cryst color, habit yellow,
yellow,
prism
triclinic
P1h
prism
prism
cryst syst
space group
lattice constants
a (Å)
P1h
9.463(2)
12.185(2)
12.395(2)
16.555(3)
74.42(3)
79.57(3)
69.31(3)
2
b (Å)
c (Å)
14.051(3) 10.512(2)
14.259(3) 18.407(4)
R (deg)
88.73(3)
72.43(3)
70.69(3)
1
â (deg)
γ (deg)
Z
cell vol, Å3
1699.4(6) 1717.8(6)
F igu r e 1. Crystal structure of complex 3. Hydrogen atoms
are omitted for clarity. The thermal ellipsoids correspond
to 30% probability. Bond distances (Å): Zr-C1 ) 2.271-
(4), Zr-C13 ) 2.240(4), C1-C2 ) 1.357(5), C2-C14 )
1.486(6), C13-C14 ) 1.339(6), Al-O1 ) 1.801(3), Al-O2
) 1.840(3).
density (g cm-3
temp (K)
)
1.223
200(2)
0.377
1.173
200(2)
0.314
µ(Mo KR) (mm-1
no. of rflns
measd
)
5124
5124
3852
356
0.047
0.121
5477
5477
3812
472
0.047
0.133
indep
obsd
no. of params
R1 (I > 2σ(I))
wR2 (all data)
The complex Cp*2Zr(η4-1,2,3,4-PhC4CPh) (1c) also
reacted with 1 equiv of i-Bu2AlH with a cis-hydroalu-
mination of the central double bond, giving the uniso-
lated zirconacyclopentadiene with i-Bu2Al substituents
in the 3-position as an intermediate. This, on reaction
with a second equivalent of i-Bu2AlH, gave with elimi-
nation of i-Bu3Al the heterobimetallic complex [Cp*2-
Zr][(µ-η1:η2-PhCC-CHCPh)(µ-H)(i-BuAl)] (5). Complex
5 reacts with a third equivalent of i-Bu2AlH to form the
trinuclear bimetallic complex [Cp*2Zr][(µ-η1:η2-PhCCCHd
C(i-Bu2Al)(Ph)](µ-H)(i-BuAlH)] (6), which is in sum
formally built up from 1c, i-Bu2AlH, and i-BuAlH2
(Scheme 1). Complexes 5 and 6 were structurally
characterized by X-ray diffraction analysis.
line widths up to 5 Hz). For instance, C2 in complex 2
(90.3 ppm) exhibits a 5 ppm wide resonance line; after
carboxylation (complex 3) the equivalent position (C2)
gives rise to a sharp signal at 126.3 ppm. Compounds
4-6 are analogues to the aforementioned heterobi-
metallics [Cp′2M][(µ-η1:η2-Me3SiCCSiMe3)(µ-H)(i-Bu2-
Al)]7a (see discussion of structure below). Therefore,
similar chemical shifts for the five-membered Zr-Al
ring system are observed, and a rather constant shift
difference of 130 ppm is found between CR and Câ. The
latter, although considered formally as “planar-tetra-
coordinate”, do not exhibit extraordinary chemical shifts
but are always found in the common olefinic region. A
silyl substituent leads to the expected shift toward
higher frequency at the carbon in a â-position (cf. 4, CR
231.1 ppm; 5, CR 192.9 ppm). Strong shifts to high
frequency occur for the Al-bound sp2 carbons outside the
zirconacycle (C3 for 5 and C4 for 6: 178.6 and 162.0
ppm, respectively) and, as usually observed, for sp2
carbons with σ bonds to zirconium.
1
NMR In vestiga tion s. (a ) H NMR Sp ectr oscop y.
The addition of i-Bu2AlH to the butadiyne complexes 1
occurs with formation of bridges to different bridgehead
atoms. These various electron-deficient structural fea-
tures can be clearly distinguished by NMR spectroscopy.
In complex 2, a CH group serving as a bridge to Al is
formed. The unusual chemical shift, δ 1.20 ppm, and in
1
particular the small coupling constant J C,H (87 Hz)
indicate the bonding situation (“agostic” interaction). In
complexes 4-6, a hydride connects aluminum with
zirconium. Its proton resonance is shifted to low fre-
quency and is found between 0 and -1.5 ppm. Interest-
ingly, scalar couplings J H,H over three (4) or four bonds
(5) are observed, as well as a long-range CH coupling
to C2 in complex 6. A third type of bridge, connecting
two Al atoms, is present in 2 and 6. This type is
characterized by δ values similar to that found for i-Bu2-
AlH (3.06 ppm in C6D6) itself. Generally, all complexes,
except 6, appear to be Cs symmetric in solution (equiva-
lent Cp* ligands and methyl groups in the i-Bu substit-
uents), which means that the polycyclic atomic frame-
work built up from the central metal, the butadiyne
carbon atoms, and the attached Al-H group is planar
(by average) and represents a symmetry plane.
(b) 13C NMR sp ectr oscop y. Due to the line broad-
ening caused by the quadrupolar moment of the 27Al
nucleus (100% natural abundance), the signals of carbon
atoms bonded to aluminum are easily identified. Line
widths greater than 10 Hz are found for the methylene
carbon atoms in the i-Bu substituents, whereas signal
broadening for the metalated sp2 carbons is less pro-
nounced, although clearly noticeable (here we observed
X-r a y Cr ysta l Str u ctu r es. The molecular structures
of complexes 3-6 were confirmed by X-ray crystal
structure analysis. The crystallographic data are listed
in Table 1.
The molecular structure of the zirconocene complex
3 displays a dinuclear complex with an eight-membered
ring in the center, formed by dimerization of two
dialkylaluminum carboxylates. Each carboxylate is the
substituent in the â-position of one zirconacyclopenta-
diene.
The X-ray crystal structure analyses of the zir-
conocene complexes 4-6 show the same structural
element: all contain in principle the more or less
distorted planar, bicyclic five-membered-ring systems
consisting of Zr, hydridic hydrogen H, Al, Câ, and CR
(Figures 2-4). As this structural key element was also
found in the complexes [(η5-C5H5)2Ti][(µ-η1:η2-Me3-
SiCCSiMe3)(µ-H)(i-Bu2Al)] (A)7a and [rac-(ebthi)Zr][(µ-
η1:η2-Me3SiCCSiMe3)(µ-H)(i-Bu2Al)] (B), 7a a comparison
is worthwhile (Table 2).
The most remarkable feature of these complexes is
the coordination geometry of the carbon atom Câ, which
is bonded to CR, M, Al, and Si or C of the attached group,

Reactions of Zirconacyclocumulenes with i-Bu2AlH
Organometallics, Vol. 23, No. 17, 2004 4163
F igu r e 2. Crystal structure of complex 4. Hydrogen atoms,
except the bridging H atom, are omitted for clarity. The
thermal ellipsoids correspond to 30% probability. Bond
distances (Å) and angles (deg): Zr-C8 ) 2.132(5), Zr-C7
) 2.489(5), C7-C8 ) 1.331(7), Al-C7 ) 2.082(5), Zr-Al )
2.999(2); Al-C7-Zr ) 81.5(2), C7-C8-Zr ) 88.8(3).
F igu r e 4. Crystal structure of complex 6. Hydrogen atoms,
except the bridging H atoms, are omitted for clarity. The
thermal ellipsoids correspond to 30% probability. Bond
distances (Å) and angles (deg): Zr-C1 ) 2.219(5), Zr-C2
) 2.448(5), C1-C2 ) 1.329(7), Al1-C2 ) 2.067(5), Al2-
C4 ) 2.037(6), Zr-Al1 ) 2.929(2); Al1-C2-Zr ) 80.4(2),
C2-C1-Zr ) 83.2(3).
Ta ble 2. Selected Str u ctu r a l Da ta for th e
Com p lexes [r a c-(ebth i)Zr ](µ-η1:η2-Me3SiCCSiMe3)-
(µ-H)[Al(i-Bu )2] (B)7a a n d 4-6
B7a
4
5
6
Bond Distances (Å)
Zr-CR
Zr-Câ
CR-Câ
2.221(13)
2.384(15)
1.33(2)
2.132(5)
2.489(5)
1.331(7)
2.082(5)
2.237(4)
2.354(4)
1.330(6)
2.107(5)
2.219(5)
2.448(5)
1.329(7)
2.067(5)]
Al-Câ
2.15(2)
Bond Angles (deg)
81.5(2)
Al-Câ-Zr
Câ-CR-Zr
78.3(5)
80.1(9)
82.1(1)
78.0(3)
80.4(2)
83.2(3)
88.8(3)
of olefins to replace expensive activators such as MAO
and perfluoroaryl boron compounds by low-cost activa-
tors. Recently, we reported alkene polymerization cata-
lyzed by zirconocene difluoride or alkyl monofluoride
complexes after treatment with i-Bu3Al and i-Bu2AlH
as cheap activators.10 A remarkable polymerization
activity was observed without any borate activation,
using only i-Bu3Al as cocatalyst. It was assumed that
in this activation i-Bu3Al alkylates the difluoride com-
plexes in the first step with formation of the mono-
fluoride alkyl complexes Cp′2Zr(F)R or dialkyl complexes
Cp′2ZrR2. For the zirconacyclopropene rac-(ebthi)Zr(η2-
Me3SiC2SiMe3), also with two Zr-C σ bonds, after
activation by i-Bu3Al a very low activity was found. As
mentioned above in the Introduction, zirconocene com-
plexes such as rac-(ebthi)Zr(η2-Me3SiC2SiMe3) react very
easily with i-Bu3Al with formation of isobutene and
i-Bu2AlH, which reacts to form the heterobimetallic
complex [rac-(ebthi)Zr][(µ-η1:η2-Me3SiCCSiMe3)(µ-H)(i-
F igu r e 3. Crystal structure of complex 5. Hydrogen atoms,
except the bridging H atom, are omitted for clarity. The
thermal ellipsoids correspond to 30% probability. Bond
distances (Å) and angles (deg): Zr-C22 ) 2.237(4), Zr-
C1 ) 2.354(4), C1-C22 ) 1.330(6), Al-C1 ) 2.107(5), Al-
C3 ) 1.960(5), Zr-Al ) 2.935(1); Al-C1-Zr ) 82.1(1), C1-
C22-Zr ) 78.0(3).
respectively, with all four bonds lying more or less in
one plane. It was pointed out that this planarity is
distorted in the case of complex B, due to the steric
hindrance of the ebthi ligand (mean deviation of the best
plane through M, Al, Si, CR, and Câ for B is 0.1142 Å,
in comparison to 0.0 Å for A). In complex 4 the plane
which is defined by Zr, Al, Si, CR, and Câ, is nearly
planar (mean deviation 0.060 Å). As in the case of B,
for complexes 5 and 6 the planarity is extremely
distorted (mean deviation of the best plane through Zr,
Al, CR, Câ, and C2 (5)/C3 (6): 5, 0.223 Å; 6, 0.116 Å).
For 5 and 6 this deviation probably results from the
special substitution of the group bonded to Câ and the
resulting ring strain.
7a
Bu2Al]. This complex, however, was not active.
In this work the well-defined zirconacyclopenta-2,3,4-
trienes Cp*2Zr(η4-1,2,3,4-RC4R) were studied as another
type of zirconocene complex with two Zr-C σ bonds
The values found for the bond distances from Zr to
Câ are in the expected range for such structural
features.7d-k
Ca ta lytic P olym er iza tion s of Eth ylen e. There is
a vital interest in metallocene-catalyzed polymerization
(10) (a) Becke, S.; Rosenthal, U. (Bayer AG) Ger. Offen. DE 199 32
409 A1 (18.01.2001). (b) Becke, S.; Rosenthal, U. (Bayer AG) U.S.
Patent 6,303,718 B1 (16.10.2001). (c) Becke, S.; Rosenthal, U.; Arndt,
P.; Baumann, W.; Spannenberg, A. (Bayer AG) Ger. Offen. DE 101 10
227 A1 (05.09.2002).

4164 Organometallics, Vol. 23, No. 17, 2004
Burlakov et al.
Ta ble 3. P olym er iza tion of Eth ylen e w ith
Zir con iu m Com p lexes a s Ca ta lysts
Exp er im en ta l Section
P r ep a r a tion of Com p lex 2. i-Bu2AlH (3.05 mL of a 1.0 M
solution in n-heptane, 3.05 mmol) was added to a solution of
1a (0.669 g, 1.52 mmol) in 10 mL of n-hexane. The resulting
red-orange mixture was warmed for 3-5 min to 50 °C and
filtered. Subsequent cooling to -78 °C gave after 2 days orange
crystals of 2, which were separated from the mother liquor by
decantation, washed with a small amount of cold n-hexane,
and dried under vacuum. The yield of 2 is 0.906 g (82%); mp
127-129 °C under Ar. Anal. Calcd for C42H74Al2Zr: C, 69.65;
cat.
temp, °C
activity, kg of polymer/(mol h)a
2
2
4
4
6
40
0
220
0
105
100
90 f room tempb
40
90 f room tempb
40
a
Conditions: 1.1 bar, 15 min; 0.04 mmol of complex in 20 mL
b
of toluene. Activation for 2 h at 90 °C under an ethylene
atmosphere.
1
H, 10.30. Found: C, 69.23; H 10.04. H NMR (C6D6, 297 K):
3
δ 0.62 (m, 8H, CH2); 1.20 (s, 1H, dCH); 1.35 (d, J ) 6.5 Hz,
Ta ble 4. Rin g-Op en in g P olym er iza tion of
E-Ca p r ola cton e w ith Zir con iu m Com p lexes a s
Ca ta lystsa
3
3
6H, CH3); 1.36 (d, J ) 6.6 Hz, 6H, CH3); 1.38 (d, J ) 6.5 Hz,
12H, CH3); 1.53 (s, 30H, Cp*); 2.32 (m, 2H, CH); 2.37 (m, 2H,
CH); 2.44 (s, 3H, 4-CH3); 2.72 (s, 3H, 1-CH3); 3.77 (br., 1H,
AlH). 13C{1H} NMR (C6D6, 297 K): 11.2 (Cp*); 22.3 (br, CH2);
23.1 (1-CH3); 26.0 (br, CH2); 27.7, 27.7 (2 × CH); 28.6, 28.7,
29.0, 29.3 (4 × CH3); 32.6 (4-CH3); 90.3 (C2Al) 117.5 (Cp*); 148.3
ꢀ-cl:cat. )
5000:1
ꢀ-cl:cat. )
10 000:1
mol
mol
1
3
yield mass yield
mass
(dCH [3], J C,H ) 87 Hz, J CH ) 10 Hz); 185.4 (C4Zr), 226.2
(C1Zr). MS (70 eV, m/z): 440 [M - 2-i-Bu2Al]+, 360 [Cp2Zr]+.
P r ep a r a tion of Com p lex 3. Complex 2 (0.274 g, 0.38
mmol) was dissolved in 5-7 mL of n-hexane under Ar, and
the orange solution was filtered. Argon was carefully removed
in vacuo, and the flask was filled with gaseous CO2 at room
temperature. After 1 day the resulting yellow solution was
cooled to -78 °C; within 2 days at this temperature yellow
crystals appeared which were separated from the mother
liquor by decantation, washed with a small amount of cold
n-hexane, and dried under vacuum to give 0.080 g (34%) of 3,
mp 246-248 °C dec under Ar. Anal. Calcd for C70H110Al2-
Zr2O4: C, 67.15; H, 8.86. Found: C, 66.83; H 8.57. 1H NMR
complex
(%)
(Mw)
(%)
(Mw)
Cp2Zr(Py)(η2-Me3SiC2SiMe3)
80
80 000 n.e. n.e.
67 570 n.e. n.e.
[Cp2Zr](µ-η1:η2-Me3SiC2SiMe3)- 82
(µ-H)[Al(iBu)2]
4
2
6
58.5 842 000
2
26 100
99.8 753 000 95.7 528 000
98.0 825 000 98.8 1 083 000
a
All experiments in toluene at 75 °C (1 h) with an initial
concentration of ꢀ-caprolactone (ꢀ-cl) of 5 mol/L.
which are activated by i-Bu2AlH via different complexes.
These complexes formed in reaction with i-Bu2AlH (2,
4, and 6) were tested in the polymerization of ethylene
without any additional activators. The obtained results
are summarized in Table 3.
Only complex 6 was active without thermal activation
at 90 °C, whereas the other complexes required such
activation. The reason for this result is under investiga-
tion.
3
3
(C6D6, 297 K): δ 0.57 (d, J ) 7.0 Hz, 8H, CH2); 1.39 (d, J )
4
6.5 Hz, 24H, CH3); 1.72 (s, 60H, Cp*); 1.91 (dq, J ) 1.6 Hz,
6J ) 0.6 Hz, 6H, 13-CH3); 2.36 (q, 6J ) 0.6 Hz, 6H, 1-CH3);
2.38 (m, 4H, CH); 7.14 (q, 4J ) 1.6 Hz, 2H, dCH [14]); 13C-
{1H} NMR (C6D6, 297 K): 11.4 (Cp*); 22.5 (br., CH2); 26.6 (1-
CH3); 26.8 (CH); 28.0 (13-CH3); 28.9 (CH3); 118.8 (Cp*); 122.7
1
(CH [14], J CH ) 150 Hz), 126.3 (C2); 169.0 (CO); 204.0 (C13),
237.6 (C1). IR (Nujol mull, cm-1): 1552 (νCdO).
P r ep a r a tion of Com p lex 4. i-Bu2AlH (2.30 mL of a 1.0 M
solution in n-heptane, 2.30 mmol) was added to a solution of
1b (0.646 g, 1.16 mmol) in 15 mL of n-hexane. After 24 h the
yellow solution was evaporated to 3-4 mL and filtered. When
the filtrate was cooled to -78 °C for 2 days, light yellow
crystals formed, which were separated from the mother liquor
by decantation, washed with a small amount of cold n-hexane,
and dried under vacuum. The yield of 4 is 0.454 g (65%), mp
133-134 °C under Ar. Anal. Calcd for C33H59AlSiZr: C, 65.83;
Rin g-Op en in g P olym er iza tion . For the catalytic
ring-opening polymerization of ꢀ-caprolactone we showed
the titana- and zirconacyclopropenes Cp′2Ti(η2-Me3SiC2-
SiMe3) to be active catalysts.7b,c Later we found an
additional activation by i-Bu3Al or i-Bu2AlH, in which
the complexes [Cp′2Ti][(µ-η1:η2-Me3SiCCSiMe3)(µ-H)(i-
7a
Bu2Al)]
were formed. These showed an increase in
the polymer molecular weights and in the activity
compared to the starting complexes.7a
1
H, 9.88. Found: C, 65.43; H 9.57. H NMR (C6D6, 297 K): δ
-0.66 (br, 1H, µ-H); 0.49 (s, 9H, SiMe3); 0.56 (m, 4H, CH2);
Complexes 2, 4, and 6 were tested as catalysts in the
ring-opening polymerization of ꢀ-caprolactone. The re-
sults are summarized in Table 4 and compared to the
results obtained with the zirconocene complexes
Cp2Zr(Py)(η2-Me3SiC2SiMe3) and [Cp′2Zr][(µ-η1:η2-
Me3SiCCSiMe3)(µ-H)(i-Bu2Al)].7a The best catalytic
activity was found for complex 2 and 6.
3
1.35, 1.37 (2d, J ) 6.4 Hz, 6H each, 2 × CH3); 1.71 (s, 30H,
3
3
Cp*); 2.44 (m, 2H, CH); 9.95 (d, J H,H ) 2.4 Hz, J H,Si ) 9.5
Hz, 1H, dCH). 13C{1H} NMR (C6D6, 297 K): δ 4.8 (SiMe3);
12.3 (Cp*); 26.3 (br, CH2); 27.3 (CH); 28.7, 29.4 (2 × CH3); 115.2
(Cp*); 122.2 (dCSiMe3); 231.1 (dCH, 1J C,H ) 161 Hz, 3J CH ) 3
3
Hz). 29Si NMR (C6D6, 297 K): 0.2 (2J Si,H ) 6.3 Hz, J Si,H ) 9.5
Hz). MS (70 eV, m/z): 360 [Cp2Zr]+.
The mother liquor was evaporated under vacuum to dryness
to give an oily mixture of 4 and i-Bu2AlCtCSiMe3; the latter
is presumably dimeric, as indicated by 1H NOE NMR observa-
Con clu sion
1
tions. H NMR (C6D6, 297 K): δ 0.09 (s, 9H, SiMe3); 0.55 (d,
The complexes 4-6 as products of the reaction of the
3
3J ) 7 Hz, 4H, CH2); 1.24 (d, J ) 6.5 Hz, 12H, CH3); 2.24 (m,
five-membered zirconacyclocumulenes (zirconacyclo-
2H, CH). 13C{1H} NMR (C6D6, 297 K): δ -1.0 (SiMe3); 25.8
(br, CH2); 26.9 (CH); 28.2 (CH3); 148.2 (tCSi); tCAl not
observed. 29Si NMR (C6D6, 297 K): δ -15.9.
penta-2,3,4-trienes) Cp*2Zr(η4-1,2,3,4-RC4R) (R
)
Me3Si (1b), and Ph (1c)) with i-Bu2AlH are further
examples of compounds with “planar-tetracoordinate”
carbon atoms. Although initally considered “pathologi-
cal”,7 this bonding mode has meanwhile been proven to
be very common, if not typical, for such heterobimetallic
complexes.
P r ep a r a tion of Com p lex 5. Complex 1c (0.221 g, 0.39
mmol) was dissolved in 10 mL of toluene under Ar, and i-Bu2-
AlH (0.78 mL of a 1.0 M solution in n-heptane, 0.78 mmol)
was added. After 15 h the red-yellow solution was evaporated
under vacuum. n-Hexane (7-8 mL) was added to the oily

Reactions of Zirconacyclocumulenes with i-Bu2AlH
Organometallics, Vol. 23, No. 17, 2004 4165
residue, and the resulting mixture was warmed to 60 °C for 7
h. The solution was filtered and allowed to stand under an
argon atmosphere at -78 °C. After 1 day yellow crystals had
formed which were separated from the mother liquor by
decanting, washed with cooled n-hexane, and dried under
vacuum to give 0.205 g of a mixture of 5 (73%) and 6 (27%).
After repeated recrystallizations from n-hexane 0.06 g of pure
5 was isolated. Mp: 210-212 °C dec under Ar. Anal. Calcd for
added. After 2 h at room temperature the red-yellow solution
was evaporated under vacuum. The residue was dissolved in
0.6 mL of C6D6 and transferred to an NMR tube. NMR
spectroscopic measurements indicated the formation of practi-
cally pure 6.
P olym er iza tion of Eth ylen e. (a ) F or Com p lexes 2 a n d
4. A 0.04 mmol amount of of complex 2 or 4 was dissolved in
20 mL of toluene under Ar. Argon was carefully removed under
vacuum, and the flask with solution was filled with ethylene.
The solution was stirred in the closed flask for 2 h at 90 °C.
After the solution was cooled to room temperature, the
polymerization started and ethylene was supplied as consumed
(1.1 bar). The solution was stirred for 15 min, and then the
ethylene was removed under vacuum. The polymer was
filtered, washed with toluene, and dried in vacuo.
(b) F or Com p lex 6. A 0.032 g amount (0.04 mmol) of
complex 6 was dissolved in 20 mL of toluene under Ar. Argon
was carefully removed under vacuum, and the flask with
solution was filled with ethylene. The solution was stirred for
15 min at 40 °C, and ethylene was supplied as consumed (1.1
bar). After 15 min the ethylene was removed. The polymer
was filtered, washed with toluene, and dried in vacuo.
P olym er iza tion of ꢀ-Ca p r ola cton e. A 5 M solution of
ꢀ-caprolactone in toluene was added to an appropiate amount
of solid catalyst. The mixture was stirred and warmed to 75
°C. After 1 h the reaction mixture was treated by addition of
an excess of methanol. The poly-ꢀ-caprolactone was separated
and dried in vacuo until the weight remained constant.
The molecular masses of poly-ꢀ-caprolactones were mea-
sured by the GPC method on a Hewlett-Packard 1090 HP
liquid chromatograph (SDV column 104 Å + 103 Å + 100 Å
(Polymer Standard Service), eluent THF) and were corrected
by the universal calibration relative to polystyrene standards.
X-r a y Cr ysta llogr a p h ic Stu d y of Com p lexes 3-6. Data
were collected with a STOE-IPDS diffractometer using graphite-
monochromated Mo KR radiation. The structures were solved
by direct methods (SHELXS-86)11 and refined by full-matrix
least-squares techniques against F2 (SHELXL-93).12 XP (BRUK-
ER-AXS) was used for structure representations.
C
40H51AlZr: C, 73.91; H, 7.91. Found: C, 73.55; H, 7.62. 1H
3
NMR (C6D6, 297 K): δ -0.90 (br, 1H, µ-H); 0.79 (d, J ) 7.4
Hz, 2H, CH2); 1.22 (d, 3J ) 6.6 Hz, 6H, CH3); 1.79 (s, 30H,
Cp*); 2.30 (m, 1H, CH); 7.12 (m, 1H, p-3-Ph); 7.17 (m, 1H, p-22-
Ph); 7.29 (m, 2H, m-3-Ph); 7.41 (m, 2H, m-22-Ph); 7.66 (m,
4
4H, o-Ph); 8.89 (d, J ) 0.9 Hz, 1H, dCH [2]). 13C{1H} NMR
(C6D6, 297 K): δ 12.5 (Cp*); 27.2 (CH); 28.5 (CH3); 30.2 (br,
CH2); 115.7 (Cp*); 126.2 (p-22-Ph); 127.2 (p-3-Ph); 128.1 (o-3-
Ph); 128.5 (m-22-Ph); 128.8 (m-3-Ph); 131.0 (o-22-Ph); 133.3
1
(C1); 136.9 (dCH [2], J CH ) 156 Hz); 141.4 (i-22-Ph); 142.0
(i-3-Ph); 178.6 (C3); 192.9 (C22). MS (70 eV, m/z): 648 [M]+,
360 [Cp2Zr]+.
P r ep a r a tion of Com p lex 6. (a ) F r om 1c a n d i-Bu 2AlH.
i-Bu2AlH (1.45 mL of a 1.0 M solution in n-heptane, 1.45 mmol)
was added to a solution of 1c (0.264 g, 0.47 mmol) in 5-7 mL
of toluene. After 3 days the red-yellow solution was evaporated
under vacuum and n-hexane was added to the oily residue.
The resulting mixture was allowed to stand under an argon
atmosphere at room temperature to give yellow crystals after
2 days, which were separated from the mother liquor by
decantation, washed with cold n-hexane, and dried under
vacuum. The yield of 6 is 0.252 g (68%). Mp: 183-185 °C dec
under Ar. Anal. Calcd for C46H70Al2Zr: C, 72.77; H, 8.91.
Found: C, 72.20; H, 8.56. 1H NMR (C6D6, 297 K): δ -0.35
2
3
(br, 1H, Zr-H-Al); 0.45 (dd, J ) 13.7 Hz, J ) 6.9 Hz, 1H,
2
3
CH2); 0.62 (dd, J ) 13.7 Hz, J ) 7.1 Hz, 1H, CH2); 0.85 (m,
2H; CH2); 0.87 (m, 1H; CH2); 1.13 (m, 1H; CH2); 1.14 (d, 3H;
CH3); 1.18 (d, 3H; CH3); 1.33 (d, 3H; CH3); 1.34 (d, 3H; CH3);
1.38 (d, 3H; CH3); 1.42 (d, 3H; CH3); 1.71 (s, 15H, Cp*); 1.75
(s, 15H, Cp*); 2.18 (non, 1H, CH); 2.34 (m, 1H, CH); 2.53 (m,
1H, CH); 4.47 (br, 1H, Al-H-Al); 7.05 (m, 1H, p-4-Ph); 7.14
(m, 1H, p-1-Ph); 7.27 (m, 2H, m-4-Ph); 7.37 (m, 2H, m-1-Ph);
7.62 (m, 2H, o-4-Ph); 7.74 (s, 1H, dCH [3]); 7.75 (m, 2H, o-1-
Ph). 13C{1H} NMR (C6D6, 297 K): δ 12.3, 12.4 (2 × Cp*); 23.0
(br), 23.3 (br), 26.1 (br, 3 × CH2); 27.0, 27.1, 27.7 (3 × CH);
27.4, 28.3, 28.7, 28.8, 28.8, 29.2 (6 × CH3); 116.8, 117.2 (2 ×
Cp*); 117.4 (C2); 125.9 (p-4-Ph); 127.0 (o-4-Ph); 127.8 (p-1-Ph);
128.0 (m-1-Ph); 128.7 (m-4-Ph); 132.1 (o-1-Ph); 139.1 (i-1-Ph);
Ack n ow led gm en t. We are grateful to the Deutsche
Forschungsgemeinschaft. (SPP 1118, Project No. RO
1269/6) and the Russian Foundation for Basic Research
(Project code 02-03-32589) for support of this work.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal-
lographic data in cif file format, including bond lengths and
1
142.9 (dCH [3], J CH ) 154 Hz); 149.9 (i-4-Ph); 162.0 (C4);
209.4 (C1). MS (70 eV, m/z): 648 [M - i-Bu2AlH]+, 360 [Cp2-
Zr]+.
angles of compound
3 (data_ks052), 4 (data_ks277), 5
(data_897), and 6 (data_ks068). This material is available free
The mother liquor was evaporated under vacuum to dryness
to give an oily mixture, in which Al(i-Bu)3 predominated (NMR
measurements).
of charge via the Internet at http://pubs.acs.org.
OM049705Q
(b) F r om 5 a n d i-Bu 2AlH. Complex 5 (ca. 0.05 g, 0.09
mmol) was dissolved in 1 mL of C6D6 under Ar, and i-Bu2AlH
(0.09 mL of a 1.0 M solution in n-heptane,0.09 mmol) was
(11) Sheldrick, G. M. Acta Crystallogr. 1990, A 46, 467.
(12) Sheldrick, G. M. SHELXL-93; University of Go¨ttingen, Go¨ttin-
gen, Germany, 1993.