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Cycloaddition Reactions of CpCo-Stabilized Cyclobutadiene Derivatives.

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The proposed structure of 3 and 4 is further supported by
a comparison of the 13C-NMR data with those of the rhodium complexes [(C,H,)Rh(q'-C,C-RN=C=CHPh)(PiPr,)]
(R = p-SO,C,H,Me, O-C,H,NO,)[~~Iand [(C,H,)Rh(q2CH, = C = CHR)(PiPr,)] (R = H, Me, Ph),[71in which the
respective heteroallene and allene ligands are also coordinated via a C = C bond. The reaction of 2 with 9-diazofluorene affords, as expected, two diastereomers, which can be
easily discerned by the duplicate sets of signals in both the
'H- and "C-NMR spectra of 6.I6]
By adding an equimolar amount of iodine to toluene solutions of complexes 3-6, the corresponding ketenimines 710 are formed. C,H,Co(PMe,)I, is obtained as by-product.[81Compounds 7 - 10 are soluble in most organic solvents
and can be isolated in good yields as yellow, partially oily
materials. Compound 7 had previously been described and
was spectroscopically characterized;['] 8- 10 are, to our
knowledge, new compounds not yet reported in the literature. In the IR spectra, very intense bands are found at ca.
2020 to 2030 cm-', which are characteristic for ketenirnines;["] this is also the range expected for IR bands typical
of cumuIenes.[' '1
R/CR; see 3--6 (above)
Since both cobalt complexes of the type [(C,H,)Co(L)(CNR)] 'I as well as diaryldiazoalkanes are easily accessible, we assume that other novel ketenimines, similar to 8-10,
can also be prepared in two steps in this way. It is predicted
that isocyanide complexes, like carbene complexes,[" 31 will
establish themselves as useful building blocks for the synthesis of various heterocyclic compounds.
'
Received: August 28, 1989 [Z 3523 IE]
German version: Angen. Chem. 102 (1990) 310
Publication delayed at authors' request
[l] R. Aumann, Angew. Chem. 100 (1988) 1512; Angew. Chem. lnt. Ed. Engl.
27 (1988) 1456, and references cited therein
[2] D. J. Yarrow, J. A. Ibers, Y. Tatsuno, S . Otsuka, J Am. Chem. Sac. 95
(1973) 8590.
[3] a) H. Werner, B. Heiser, C. Burschka, Chem. Ber. 115 (1982) 3069; b) H.
Werner, B. Heiser, H. Otto, ihrd. 1f8 (1985) 3932; c) review: H. Werner in
A. de Meijere, H. tom Dieck (Eds.)- Orgonometallics in Organrc Synrhesk,
Springer, Heidelberg 1987. p. 51.
a) A. Hohn. H. Werner, Chem Ber. 121 (1988) 881; b) U. Brekau. Dis.$erration. Universitlt Wurzburg 1989.
a) Experimental procedure for 3. A solution of Ph,CN, (1.0 mmol) in
acetone (5 mL) was added at -78 'C to a solution of 1 (I.Ommo1) in
acetone (15 mL). The reaction mixture was stirred and allowed to warm to
room temperature (3.5 h). The solvent was then removed in vacuo and the
residue extracted with 20 mL of ether. On cooling the extract to -78 'C,
red needles were formed; yield 63%; m.p. 135':C(dec.); b)4: recrystallization from benzenelpentane (1 : l ) ; red-brown crystals, yield 54%; m.p.
13O.K (dec.); c) 5: work-up directly after warming to room temperature;
recrystallization from benzene/pentane (1 : 1); dark green crystals; yield
68%. m.p. 45 'C (decomp.); d) 6: work-up directly after warming to room
temperature; dark green crystals from ether at -78 'C; yield 63%; m.p.
47 ' C (dec.). Satisfactory elemental analyses (C,H,N) were obtained for all
compounds
Spectroscopic data. 3: M , = 407 (MS); IR(KBr): v(NCC) = 1700cm-';
'H NMR (90 MHz, C,D,): 6 = 7.36 (m, C,H,), 4 25 (d, Jp,, = 0.9 Hz,
C,H,), 3.97 (d. JPH= 0.9 Hz, NCH,), 0.32 (d, JPH= 8.9 Hz, PMe,);
13C NMR (22.5 MHz, CeD,): b = 207.1 (d, J,, = 18.6 Hz, = C = ) , 152.4,
1465,128.2,127.1,125.3,122.9(alls,C,H,).84.9(d,J,= 1.7Hz,C5H,),
46.2 (d, Jpu= 2 6 Hz. NCH,), 19.4 (d, Jpc = 28.2 Hz, PMe,), 11.0 (d.
Jpc = 2.6 Hz. = C P h 2 ) . 4 : M, = 435 (MS); IR (KBr): v(NCC) =
1690 cm-', ' H NMR (90 MHz, C,D,): b = 7.55 (d, J,,, = 8.0 Hz. C,H,),
6.94 (d, JHH = 8.0 Hz, C,H,), 4.31 (d, J,, = 0.8 Hz, C,H,). 4.00 (d,
276
CJ
VCH Veriag.sge~~,li.~chajr
mhH. D-6940 Weinhelm. 1990
= 0.6 Hz, NCH,), 2.05 ( s , C,H,CH,), 2.02 (s, C,H,CH,), 0.38 (d,
JPH= 8.9 Hz, PMe,); 13C NMR (50.3 MHz, C,D,): 6 = 207.9 (d,
Jpc = 17.8 Hz. = C = ) . 149.4. 143.7, 134.5, 131.8 (all s, C,H,), 84.9 (s,
CSH,), 46.2 (d, Jpc= 2.8 Hz, NCH,), 21.1 (s, C,H,CH,), 20.9 (s,
C,H,CH,), 19.0 (d, Jpc = 27.8 Hz, PMe,), 10.7 (s, br, =C@-tol),).-5:
M , = 405 (MS); IR(KBr): v(NCC) = 1625 cm-'; 'H NMR (90 MHz,
C,D,): 6 = 9.05 (d, br, JHH= 7.5 Hz, C,H,), 7.73 (m, C,H,), 4 54 (d,
JPH= 0.5 Hz. C,H,), 2.66 ( s , NCH,), 0.46 (d, JPH
= 10.2 Hz. PMe,);
I3C N M R (50.3 MHz, C,D6): 6 = 175.2 (d, Jpc= 18.7 Hz, = C = ) , 142.8,
137.9,136.8. 134.2.125 7,125.5,122.7. 122.3, 121.5, 120.4, 120.1, 118.9(all
S , CbH,), 101.9 (s. =C(C,,H,)), 83.8 (s, C,H,), 45.0 ( s , NCH,). 16.4 (d,
Jpc = 28.3 Hz, PMe,).-6:
IR(KBr): v(NCC) = 1626 cm-'; 'H NMR
(90 MHz, C,D,): 6 = 9.11 (d. br, JHH = 8.2 Hz, C,H,), 7.19 (m. br, C,H,
= 6.9 Hz,
and C,H,). 5.03 (4, JHH= 6.6 Hz. CHMePh), 4.80 (4. JHH
CHMePh), 4.39 (d, JPH= 0 6 Hr. C,H,), 4.27 (d. JPH= 0.5Hz, C,H,),
= 6.6 Hz. CH(CH,)Ph),
1.56 (d, Jut1 = 6.8 Hz, CH(CH,)Ph), 1.01 (d, JHH
0.44 (d. J,,= 10.1 Hz. PMe,), 0.43 (d, JPH= 10.2 Hz, PMe,); 13CNMR
(50.3 MHz, C,D,): 6 = 162.9 (d, Jpc = 18.9 Hz, = C = ) , 160.4 (d.
Jpc = 17.5 Hz, = C = ) , 145.8, 144.6, 143.1, 142.6, 138.5, 138.0, 135.7,
135.5. 134.0. 133.7. 128.3, 127.8. 127 7, 127.1, 126.8, 126.6, 125.5. 125 3.
125.2,121.7, 121 5,121.1,120.5, 120.2. 116.6,116.5(alls,C6H,andC,H,),
97 7 ( S , =C(C,,H,)), 96.7 (s, = C(C,,H,)), 82.8 (s, C,H,), 82.7 (s, C,H,),
58.1 (s. CHMePh), 56.2 (s, CHMePh), 21.7 (s, CH(CH,)Ph), 17 7 (s,
CH(CH,)Ph), 16.4 (d. Jpc = 27.8 Hz, PMe,), 16.2 (d, Jpc = 27.9 Hz,
PMe,).
[7] J. Wolf, R.Zolk. U.Schubert, H. Werner, J Organomet. Chem. 340 (1988)
161.
[XI H. Werner, B. Juthani, Z. Anorg. ANg Chem. 473 (1981) 107.
[9] a) C. L. Stevens, J. C. French, J. Am. Chem. Sac. 76 (1954) 4398; b) S.
Otsuka, A. Nakamura, T Yoshida, J Organomet. Chem. 7 (1967) 339.
[lo] Spectroscopic data. 8: IR (C,H,). v ( N = C = C ) = 2018cm-'.-9:
IR
(C,H,):
v ( N = C = C ) = 2030cm-'; 'H NMR (200 MHz, C,D,):
d = 7.48 (m, C,H,), 2.74 (s, NCH,): ''C NMR (50.3 MHz, C,D,).
b = 176.0(s, = C = ) , 138.8, 135.8, 126.5. 125.2, 121.7, 120.8 (all s, C,H,),
37.6 (s, NCH,).-10.
IR (C,H,):
71.3 ( s . =C(C,,H,)),
v ( N = C = C ) = 2020cm-'; 'H NMR (90 MHz, C,D,): b = 7.31 (m,
C,H,), 4.62 (4. JH,,= 6.6 Hz, CHMePh), 1.36 (d, J,[,, = 6.6 Hz,
CH(CH3)Ph); I3C NMR (22.5 MHz, C6D,): b = 177.2 (s, = C = ) , 142.1,
138.7, 135.9, 129.0, 127.7, 126.6, 126.4, 125.3, 121.6, 120.8 (all s, C,H,),
73.1 (s, =C(C,,H,)), 63.6 (s, CHMePh), 24.4 (s, CH(CH,)Ph).
G. R. Krow, Angen.. Chem. 83 (1971) 455; Angew. Chem. Int. Ed. Engl 10
(1971) 435.
a) H. Werner, S. Lotz, B. Heiser, J Organomet. Chem. 209 (1981) 197; b)
B. Heiser. H. Werner, Synth. React. h o g . Met..Org. Chem 16 (1986) 527;
c) B Strecker, Diplomarheit Universitat Wiirzburg 1987.
K. H. Dotz, Angen. Chem. 96 (1984) 573; Angew. Chem. Int. Ed. En,g1. 23
(1984) 587.
JPH
Cycloaddition Reactions of CpCo-Stabilized
Cyclobutadiene Derivatives **
By Rolf' Gleiter * and Detlef Kratz
Dedicated to Professor Paul von Rague Schleyer on the occasion of his 60th birthday
The reaction of alkynes to form arenes using homogenous
transition metal catalysts is described in the literature in
terms of catalytic loops as depicted in scheme
The
formation of cobalt-stabilized cyclobutadiene derivatives B
is usually considered as an unwanted side reaction and as a
pathway constituting a dead end of [2 + 2 + 21-cyclotrimerization reactions to arenes D with catalysts of the type
CpCoL, .
These complexes B withdraw the catalytically active species, the CpCo-fragment, from the trimerization cycle and
I'[
[**I
Prof. Dr R. Gleiter, Dipl. Chem. D. Kratz
Organisch-chemisches Institut der Universitat
Im Neuenheimer Feld 270, D-6900 Heidelberg (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft
(SFB 2471, the Volkswagenwerk-Stiftung,the Fonds der Chemischen Industrie, and BASF Aktiengesellschaft. D.K. thanks the Studienstiftung des
Deutschen Volkes for a postgraduate grant.
0570-0833~90j0303-027fi
$02.50/0
Angeir. Chem. hi.Ed. Engi 29 (1990) No. 3
I
CpCoL,
C
Scheme 1
are excluded as possible intermediates on the following
grounds: firstly, the formation of B requires a higher activation energy than the formation of a cobaltacyclopentadiene
C ( ~ o b a l t o l e ) ;41[ ~secondly,
~
they are considered to be inert
and to show resistance to further cycloaddition reactions;
and thirdly, an equilibrium between the primary dialkyne
complex A, the CpCo-cyclobutadiene complex B and the
cobaltacyclopentadiene C has not, as yet, been unequivocally sub~tantiated.[~,
61 In the present communication we show
that complexes of type B are by no means entirely inert and
may react with triple bonded species X = Y to yield arenes.
Our research focussing on the reactivity of the cobalt complexes 5 and 10 was initiated by the following observations:
To our surprise the reaction (a) of cyclodeca-I ,6-diyne 1 with
ring of CpCo-cyclobutadiene complexes are normally equalized out.[']
It seemed reasonable to conclude that 5 could behave as a
diene towards further species with triple bonds. In fact we
were able to transform 5 into the 6n-systems 4, 8 and 9
(Table 1).
Table 1 Some spectral data of the compounds 4,8, 9, 11, and 13
4. ' H NMR (ID,]-acetone, 300 MHz): 6 = 2.7-2.9 (m. 10H). 2.41 (t, 2H).
1.99-2.13 (m, 6H); "C NMR ([D,]-acetone. 75.46 MHz): 6 = 17.0.23.8.25.2,
25.3. 29.6, 30.9, 31.8, 34.4, 34.6, 120.7, 131.3, 135.9. 150.0. 153.8. 163.6; UV/
VIS (CH,CI,): i.,,,(lg~) = 225 nrn (4.51), 275 nm (4.67); MS(E1). m/
Z ( % ) = 226(13). 225(11). 186(25). 173(100), 172(34), 85(26), 71(42). 57(74),
43(68), 41(40).
8 : 'HN M R (CDCI,, 200MHz) 6 = 2.69-2.86(m), 1.96-2.11(q). 1.62(br.),
1.341broad). 1.23(s) (integration is not clear-cut as trimeric cyclooctyne i s present); I3C N M R (CDCI,, 50.32 MHz): 6 = 24.95, 26.34, 28.5. 29.69. 31.49.
31.5. 134.45. 136.9, 140.4; GC-MS(E1): m / z [ % ] = 240(82), 211(41). 197(100).
185(40), 171(43), 155(27), 128(20), 115(17), 77(9), 41(15).
9 : ' H NMR (CD2C12,200 MHz): 6 = 7.16 (m. 5H), 4.01 (s, 2H). 2.73.- 2.93
(rn, XH), 1.94-2.14 (m, 4 H ) ; 13CNMR (CD,CI,, 50.32 MHz): 6 = 23.49,
CI)
24.96.29.5, 30.9, 31.5, 34.2.42.5, 126.2. 128.5, 129.1. 131.2. 135.8, 140.5, 150.1,
153.6, 163.2, UVjVIS (CH2C12): imaX(lgc)
= 212 nm (4.03). 277 nm (3.82);
GC-MS(E1): m / z [ % ] = 249(50), 248(100). 221(6), 172(2). 170(3), I15(3), 91(4),
65(2).
1
+
NC-"'CN
2
4 185%)
glutaronitrile 2 in xylene in presence of catalytic amounts of
CpCo(CO), did not afford the "intermolecular" 2: 1
pyridine derivative 3, that we had hoped for; apart from the
already known CpCo-cyclobutadiene complexes,[71only the
"intramolecular" 1 :1 pyridine derivative 4 was detected.
When the reaction of 1 was carried out in the absence of a
nitrile it was also possible to isolate, inter aha, the CpCo-cyclopentadienone derivative 13 (Table 1). In both products a
formal cleavage of one of the triple bonds in 1 has occurred.
Furthermore, the results of X-ray investigations[81on tricylic
CpCo-cyclobutadiene complexes such as 5 clearly indicate
bond alternance,['l whereas the bonds in the four-membered
Angen. Chem. In[.Ed. EngI. 29 (1990) No. 3
11. ' H N M R (CD,C12, 300 MHz): 6 = 7.12-7.26 (m, 5H), 4.05 (s. 2H). 2.83
(br. 2H), 2.54 (9. 6H), 1.83 (4. 4H), 1.7 (m, 4 H ) , ',CNMR (CD,CI,,
75.46 MHz): 6 = 22.8,23.0,23.5 (2 x ), 25.7, 26.5,26.6, 33.4,41.9, 126.2. 128.3.
128.6, 128.7, 129.1, 140.6, 145.2, 153.1. 155.3; UVjVIS (CH,CI,):
&,(Ig&) = 212 nm (4.09), 272 nm (3.60); GC-MS(E1) m/;["/o]= 277(72).
276(100), 262(14), 248(5), 218(2), 186(8), 115(3), 91(5), 65(2).
13: ' H NMR (CDCI,, 200 MHz): 6 = 4.74 (s, 5H), 2.84 (br. 2H, H,O). 1.832.42 (m, 12H), 13CNMR (DEPT spectrum) (CDCI,, 50.32 MHz): 6 = 25.39
(CH2). 25 86 (CH,), 28.8 (CH,), 83 11 (CH), 92.97 (C), 94.5 (C). 149.0 (0);
UV/VIS (CH2C12):i.,,,(lgs) = 212 nm (4.09), 283 nm (4.29) 358 nm (3.43).
420 nm (2.93); MS(E1): m/z["/.] = 284(57), 255(68). 189(100), 187(23).
129(46), 128(35), 124(73), 115(22), 91(27), 59(76). 40(38); IR (CDCI,):
3 = 3684(m), 3150(w), 2952(rn), 2846(w), 2254(m). 2208(rn), 1599(s). 1548(s).
1261(vs), 804(vs).
In choosing 10 as a diene component we wanted to test a
cyclobutadiene complex containing bonds of almost equal
length in its four-membered ring (cf. Scheme 3). This compound also led to cycloaddition reactions under more vigorous conditions["] to afford the aromatic compounds 1I
(Table 1) and 12.["]
VCH Verlugsgesellschuft mbH, 0-6940 Weinheim. 1990
0570-0X33/90/0303-0277$02.5010
271
The simultaneously released 14e-transition metal fragment (CpCo) may now become catalytically active as in reaction (a), and either induce further formation of 4 from the
cyclic dialkyne 1 and dinitrile 2, or react with the “dienophile” component and thus lead to numerous side reactions.
Therefore, depending on the X = Y-component present we
observe the formation of cycl~octyne-trimer,[’~~
dimeric or
trimeric products of benzyl cyanide, or mellitic acid hexamethyl ester in varying amounts. The catalyst is, however,
prone to reduction and may decompose to form a cobalt
mirror in the reaction flask.
5
8 116%)
1
c p c o ~ , -L,
9 122”/,)
Scheme 2. a) I n xylene under reflux.
(‘i
I
a)
I
II
I11
MeOOk
12 (75”/.)
Scheme 3. a) 200“C, without solvent.
Scheme 4.
These results suggest that certain (steric) restrictions may
influence the reaction in a manner such that the “cyclobutadiene path” in cobalt-catalyzed [2 2 21-cyclotrimerizations cannot be excluded from the start. To explain the formal cleavage of the triple bond of 1 in reaction (a) we
postulate a mechanism that includes the cyclobutadiene derivative I1 as a plausible intermediate (Scheme 4).
Thus, the cobaltacyclopentadiene I is in equilibrium with
its isomer cobaltacyclopentadiene 111via the CpCo-cyclobutadiene complex 11. This isomerization is the decisive step in
order to explain the course of the reaction. The equilibrium
I $ I1 =$I11 corresponds to an alkyne metathesis reaction,
for which cyclobutadienes stabilized by transition metal
fragments have been invoked as potential intermediates.[”]
The “cycloaddition” of a further triple bond X = Y may then
proceed directly on I1 or by primary coordination of the
16e-species 111 and subsequent cyclization. A Dewar-benzene derivative may occur as an intermediate that is formed
with concomitant liberation of the CpCo-fragment. However, under the reaction conditions this intermediate is unstable
and will rearrange to the corresponding 6~-system.An
analogous reaction of I would lead to the highly strained
[3]paracyclophane skeleton and does not seem feasible on
energetic grounds; the extremely labile [4]paracyclophane
has been observed to undergo Wagner-Meerwein rearrangement to yield an ortho-substituted benzene under acid catalyzed conditions.’’ 31
+ +
278
0 VCH
Verlagsgesellschaft mbH. 0 - 6 9 4 0 Weinheim, 1990
If the same mechanism is presumed to operate in the formation of 13 (a mechanism via CpCo(C0)-dimers or -clus-
CP
c.0
ters is also conceivable), the final cleavage of the triple bond
is caused by “end-on” addition of carbon monoxide. This
may be preceded by a “side-on” coordination, as this mode
of reaction has already been observed in reactions of CpCo
complexes with ketones and aldehydes.[’5]
Received: October 20, 1989 [Z 3599 IE]
German version: Angew. Chem. f02 (1990) 304
[l] D. R. McAllister, J. E. Bercaw, R. G. Bergman, J Am. Chem. SOC.99
(1977) 1666; H. Bonnemann. Angew. Chein. 97(1985) 264; Angew. Chem.
In[. Ed. Engl. 24 (1985) 248; K. P. C. Vollhardt, ibid. 96 (1984) 525 and 23
(1984) 539, and references cited therein.
[21 J. P. Colman, L. S. Hegedus: Principles and Applications of’Organotransilion Chemistry, University Science Books, Mill Valley, CA 1987.
[3] Y. Wakatsuki, 0. Nomura. K. Kitaura, K. Morokuma, H. Yamazaki, J
Am. Chem. SOC.105 (1983) 1907.
0570-0833/90j0303-0278 3 02 S0jO
Angew Chrm In2 Ed. Engl 29 (1990) N o . 3
I
[4] F. D. Mango. J. H. Schachtschneider, J. Am. Chem. Soc. 91 (1969) 1030.
[5] R. L Hillard 111. K. P. C. Vollhardt, J Am. Chem. Soc 99 (1977) 4058;
G. A. Ville. K. P. C. Vollhardt, M J. Winter. ibid. 103 (1981) 5267; G. A.
Ville. K. P. C. Vollhardt, M. J. Winter, Organomelallics 3 (1984) 1177.
[6] K. P. C. Vollhardt, R. G. Bergman, J. Am. Chem. Soc. 96 (1974) 4996
[7] R. Gleiter, M . Karcher. M. L. Ziegler, B. Nuber, Tetrahedron Lert 28
(1987) 195.
[ X I The bond lengths of the cyclobutadiene fragments of 5 and 10 are shown
below. They stem from X-ray analyses performed by B. Nuher and M . L.
Ziq&r, Heidelberg.
a m
H
1.477(6)
[9] A. Efraty, Chem. Rev. 5 (1977) 691.
[lo] The lower reactivity of 10 becomes evident in the reaction of cyclododeca1.7-diyne with 1,4-dicyanobutane using catalytic or equimolar amounts of
CpCo(CO),. N o pyridine derivative and only 10 itself is formed. Furthermore, 10 will only react if the dienophile itself is used as solvent.
[ l l ] Data are identical to those in the literature: P. Courtot, J:C. Clement, Bull.
S o l . Chim. France (1973) 2121.
[I21 J. R. Fritch, K. P. C. Vollhardt, Angew. Chem. 91 (1979) 439; Angew.
C h w . Int. Ed. Engl. 18 (1979) 409.
1131 G B. M. Kostermans, M. Bobeldijk, W. H. de Wolf, F. Bickelhaupt, J. Am.
Chi,m. Soc. 109 (1987) 2471.
[14] G. Wittig, P. Fritze, Justus Lkbigs Ann. Chem. 712 (1968) 79.
[lS] R. Gleiter, V. Schehlmann. Terrahedron Lett. 30 (1989) 2893; D. F. Harvey,
B M. Johnson, C. S. Ung, K. P. C. Vollhardt. Synlett. 1 (1989) 15.
Polymerization reactions with the tetramethylethanobridged zirconocene complex 1, with the dimethylsilanobridged zirconocene complexes 2-4, and, for comparison,
with the ethano-bridged bis(tetrahydroindeny1)zirconium
complex
were studied at 50°C, a propene pressure of
2 bar and an Al/Zr ratio of 300: 1. The yields and properties
of the polymers thus obtained are collected in Table 1.
Table 1. Yields and properties of the polypropylene (PP) polymers obtained
with the complexes 1-5 after activation with methylalumoxane (AI/Zr =
300/1) at 50°C under 2 bar of propene.
Catalyst
2
3
120
9
85
120
36
355
185
79
505
45
1I4
3000
50
95
2250
103
775
1.8
62
128
1981
2.4
77
149
9190
2.5
94
107
4958
3.0
73
85
3153
2.9
49
3.5
1.5
1.5
2
2
1.5
0.6
0.5
0.4
1.5
0.8
1.5
1.5
1.5
1
-
4
5
~~
Stereo- and Regioselectivity of Chiral,
Alkyl-substituted ansa-Zirconocene Catalysts
in Methylalumoxane-activated
Propene Polymerization **
By Werner Roll, Hans-Herbert Brintzinger,*
Bernhard Rieger, and R a y Zolk
Dedicated to Professor Dr. Giinther Wilke on the occasion of
his 65th birthday
The isotactic polymerization of a-olefins by methylalumoxane-activated, chiral ansa-zirconocene catalysts has recently been studied in considerable detail. With very few
exceptions,“’ 21 however, studies on the stereochemical
course of these reactions have been limited to ring-bridged
bis(indeny1)- and bis(tetrahydroindeny1)zirconium complexes (see, e.g., Refs. [3-6, 10-141). Since further insights into
the factors governing the stereoselectivity of these reactions[3-51can only be gained from a more widely varying
range of complexes, we have studied the course of methylalumoxane-activated propene polymerization by a series of differently substituted, axially symmetric ansa-zirconocenes,
1-4.”l
[*I Prof. Dr. H. H. Brintzinger, Dr. W. Roll
Fakultlt fur Chemie der Universitat
D-7750 Konstanz (FRG)
Dr. B. Rieger. Dr. R. Zolk
BASF AG
D-6700 Ludwigshafen (FRG)
[**I ansa-Meta~~ocene
Derivatives, Part 19. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie. We wish to thank Frau E. Barsties (Universitat Konstanz), Dr. W.
Ball, Dr. Merthes and Dr. P. Simak (BASF AG) for the polymer analyses,
BASF AG for gifts of chemicals, and Prof. J. E. Eereaw (California Institute of Technology) and one of the referees for valuable comments.
Part 18: P. Burger, H. U. Hund, K. Evertz, H. H. Brintzinger, J. Organomet. Chem. 378 (1989) 153.
A n p i < ’ .Chem. Inr. Ed. En& 29 (1990) No. 3
0 VCH
Reaction time [min]
Polymer yield [g]
Productivity
[kg(PP)/(h mol(Zr) P)I
Melting point [“C]
Mw[a1
MwIMn
Isotacticity
[YOmmmm Pentads]
n-Propyl- ends [b]
2-Propenyl ends [h]
I-3-Misinsertions [b]
-
[a] Absolute values with uncertainties of +20%. [b] Intensities of the ”CNMR signals in percent of main signals; besides the signals for 2-propenyl end
groups, another set of signals with varying intensity occurs at 6 = 17.9, 25.7,
129.1, and 132.2.
Under the reaction conditions employed, the catalysts 1-4
all yield more highly isotactic polymers than the “classical”
catalyst 5. Of the tBu-substituted zirconocenes, the Sibridged complex 2 is distinctly superior to its C,-bridged
analogue 1 in terms of stereoselectivity, probably due to its
higher stereorigidity.‘’] An even higher degree of isotacticity,
with an mmmm pentad intensity of greater than 90%, is
obtained with the Si-bridged complex 3, which contains at
each ring ligand, in addition to the tBu group in the 4(B)
position, a methyl group in the 2(a)position. The decreased
stereoselectivity of the catalyst 4 with iPr instead of J3-tBu
substituents demonstrates the importance of steric bulk in
the J3 position of both rings for a stereochemically uniform
olefin insertion.
A remarkable effect of a-methyl substituents is the suppression of 1-3 misinsertions, which arise from a tail-to-tail
(2- 1) insertion of the a-olefin into the metal-polymer bond
and subsequent isomerization of the ensuing species with a
secondary alkyl ligand.[’’ These misinsertions occur in the
polymers obtained with 1 and 2 with a frequency of Cd.
1.5%, i.e. about as often as in polymers obtained with the
catalyst 5.“’- 131 In polymers produced with the rw-methylsubstituted complexes 3 and 4, however, these regio-irregularities are suppressed to levels close to or below the detec-
Verlagsgesellschafr mbH. 0-6940 Weinheim. I990
0S70-0833/90/0303-0279S 02.5010
279
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