Organometallics 1995,14, 1256-1266
1256
Crystal Structures and Solution Conformations of the Meso and Racemic Isomers of (Ethylenebis(1-indenyl))zirconium Dichloride Fabrizio Piemontesi," Isabella Camurati, Luigi Resconi, and Davide Balboni Himont Italia (Montedison Group), G. Natta Research Center, P.le Donegani 12, 44100 Ferrara, Italy
Angelo Sironi" and Massimo Moret Istituto di Chimica Strutturistica Inorganica, Universita di Milano, Via Venezian 21, 20133 Milano, Italy
Robert Zeigler Himont U.S.A. (Montedison Group), Inc., Research & Development Center, 912 Appleton Road, Elkton, Maryland 21921
Nicoletta Piccolrovazzit Institut fur Polymere, Swiss Federal Institute of Technology, ETH-Zentrum, 8092 Zurich, Switzerland Received September 14, 1994@ The crystal and molecular structures of the CZsymmetric ruc-(EB1)ZrClz ( l r ) [monoclinic, space group 12/c, No. 15, a = 11.957(1) b = 10.627(1) A, c = 13.775(2) = 106.06(1)'1 and of its meso isomer ( l m ) [monoclinic, space group P21/n, No. 14, a = 11.119(3) b = 10.467(1) c = 14.949(2) 9, = 100.94(2)'] have been solved. l r is in the indenyl-forward (n)conformation, as is the case for most of the chiral ansa ethylene-bridged bisindenyltype metallocenes. In solution however, already at room temperature there is a rapid (NMR time scale) interconversion between the two I'I and Y (indenyl-backward) conformations, as shown by conformational analysis on the proton spectra of the bridge methylenes. This equilibrium is shifted toward the lower energy conformation d at lower temperatures and is influenced by both the solvent and the a-ligands. The solid state structure of l m shows that this meso form is actually in a chiral conformation (CI symmetry) because of the staggered placement of the two indenyl ligands (Ind^Ind = 10.0'). In solution this aspecific zirconocene gives a perfectly symmetric lH NMR spectrum, indicating that, as in the case of the rac-isomer, there is a rapid interconversion between the two equienergetic, mirrorimage limit conformations.
A,
A,
A,
Introduction
The by Ewenl and Kaminsky2 that the homogeneous catalyst systems composed of racemic (ethylenebid 1-indenyl))MClz01 racemic (ethy1enebis(4,5,6,7tetrahydro-1-indeny1))MC12( g o u p bent Of the 'lass Of chiral ansa-meta11ocenes by B r i n t z i n ~ e r :M ~ = Ti, Zr, Hf) and methvlalumoxane (MA01 produce isotactic polypropylene (*Pi have started a frantic research activity on the isospecific polymeri+ Current Address: Dow Europe SA, Bachtobelstr. 3,8810Horgen, Switzerland. Abstract published in Advance ACS Abstracts, January 1, 1995. ( l ) ( a ) Ewen, J. J . Am. Chem. SOC.1984,106,6355.(b) Ewen, J. U.S. Patent 4,522,982to Exxon, 1985. (c) Ewen, J . In Catalytic Polymerization of Olefins; Studies in Surface Science Catalysis Vol. 25; Keii, T., Soga, K., Eds.; Elsevier: Amsterdam, 1986; p 271. (d) Ewen, J.; Haspeslagh, L.; Atwood, J.; Zhang, H. J . Am. Chem. SOC. 1987,109,6544. (2)(a) Kaminsky, W.; Kulper, K.; Brintzinger, H.; Wild, F. Angew. Chem., Int. Ed. Engl. 1985,24, 507. (b) Kaminsky, W.; Kulper, K.; Buschermohle, M.; Luker, H. U S . Patent 4,769,510to Hoechst, 1988. (c) Kaminsky, W. Angew. Makromol. Chem. 1986,1451146,149.(d) Drogemuller, H.; Niedoba, S.; Kaminsky, W. Polym. React. Eng. 1986, 299.(e) Kaminsky, W. In Catalytic Polymerization of Olefins; Keii, T., Soga, K., Eds.; Elsevier: Amsterdam, 1986;p 293. @
A,
A,
zation of olefins with metallocene catalysts in both academic and industrial laboratories. k h o u g h less suitable than MgClz-supported Ti-based catalyst^^,^ for the industrial production of polypropylene, the now classic rac-(ethylenebis(~-indenyl))zirconium dichloride (rac-(EBI)ZrC12, 1r) and rac-(ethylenebis(4,5,6,7-tetrahydro-l-indenyl))zirconiumdichloride (rac-(EBTHI)(3)(a)Schnutenhaus, H.; Brintzinger, H. H. Angew. Chem., Int. Ed. Engl. 1979,18,777.(b)Wild, F.;Zsolnai, L.; Huttner, G.; Brintzinger, H. H. J . Organomet. Chem. 1982,232,233.(c) Collins, S.;Kuntz, B.; Taylor, N.; Ward, D. J . Organomet. Chem. 1988,342,21.(d) Wild, F.; Wasiucionek, M.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1985, 288, 63. (e) Schafer, A.; Karl, E.; Zsolnai, L.; Huttner, G.; Brintzinger, H. H. J. Organomet. Chem. 1987,328,87.(0Wiesenfeldt, H.; Reinmuth, A.; Barsties, E.; Evertz, K.; Brintzinger, H. H. J . Organomet. Chem. 1989, 369, 359. (9) Burger, P.;Hortmann, K.; Diebold, J.; Brintzinger, H. H. J . Organomet. Chem. 1991,417,9.(h) Brintzinger, H. H. In Transition Metals and Organometallics as Catalysts for Olefin Polymerization; Kaminsky, W., Sinn, H., Eds.; Springer-Verlag: Berlin, 1988;p 249. (4)These are found to produce iPP which is not suitable for current commercial applications: at practical polymerization temperatures, in fact, molecular weight, isotacticity, and regioregularity are relatively low, and these molecular properties are reflected in very high solvent soluble fractions, low melting temperatures, and poor mechanical proper tie^.^
0276-7333/95/2314-1256$09.00/00 1995 American Chemical Society
(Ethylenebis(1-indenyl))zirconium Dichloride ZrCl2) are often used as the comparison catalysts when new metallocenes are introduced. They are also excellent model compounds for theoretical6 and mechanistic7 studies and have found interesting applications as enantioselective catalysts.8 For chiral ansa-metallocenes, the metal-ansa-ligand framework dictates substrate enantioface selectivity, and ligand-substrate nonbonded interactions can be affected by conformational changes of the catalyst. Brintzingerghas shown that there is a rapid (NMR time scale) interconversion between two conformations in the achiral Ca,-symmetric ansa-titanocene (ethylenebis(cyclopentadieny1))titanium dichloride. Chien5ga and RiegerlO have proposed that the two conformers of the active species in l r might have different stereoregulating abilities in propylene polymerization. Hence, a better knowledge of the basic properties of these chiral zirconocenes, especially in solution, should be of general interest. We have already reported on the effect of monomer concentration on the molecular weight and stereo- and regioregularity of polypropylene produced with 1r.ll In this paper we present the molecular structures of l r and its stereoisomer meso-(EBI)ZrCls (lm), and aiming at establishing the differences between solid state and solution conformations of these ansu-zirconocene precatalysts, we present their dynamics in solution through a detailed lH and 13C NMR analysis.l2 ( 5 ) (a)Grassi, A.; Zambelli, A.; Resconi, L.; Albizzati, E.; Mazzocchi, R. Macromolecules 1988,21,617.(b) Cheng, H.; Ewen, J. Makromol. Chem. 1989, 190, 1931. (c) Tsutsui, T.; Ishimaru, N.; Mizuno, A.; Toyota, A.; Kashiwa, N. Polymer 1989,30,1350. (d) Tsutsui, T.Mizuno, A.; Kashiwa, N. Makromol. Chem. 1989,190, 1177. (e) Tsutsui, T.; Kioka, M.; Toyota, A.; Kashiwa, N. In Catalytic Olefin Polymerization; Studies on Surface Science and Catalysis Vol. 56;Keii, T., Soga, K., Eds.; Elsevier: Amsterdam, 1990;p 493.(0 Rieger, B.; Chien, J. Polym. Bull. 1989,21, 159. (g) Rieger, B.; Mu, X.; Mallin, D.; Rausch, M.; Chien, J. Macromolecules 1990,23,3559.(h) Chien, J.; Sugimoto, R. J. Polym. Sci. A: Polym. Chem. 1991,29,459. (6)(a) Corradini, P.; Guerra, G.; Vacatello, M.; Villani, V. Gazz. Chim. Ital. 1988, 118, 173. (b) Cavallo, L.; Guerra, G.; Oliva, L.; Vacatello, M.; Corradini, P. Polym. Commun. 1989,30,16. (c) Cavallo, L.;Corradini, P.; Guerra, G.; Vacatello, M. Polymer 1991,32,1329. (d) Cavallo, L.;Guerra, G.; Vacatello, M.; Corradini, P. Chirality 1991, 3, 299. (e) Castonguay, L.;Rapp6, A. J . Am. Chem. SOC.1992,114, 5832. (7)(a) Pino, P.; Cioni, P.; Wei, J . J . Am. Chem. SOC.1987,109,6189. (b) Pino, P.; Cioni, P.; Galimberti, M.; Wei, J.; Piccolrovazzi, N. In Transition Metals and Organometallics as Catalysts for Olefin Polymerization; Kaminsky, W., Sinn, H., Eds.; Springer-Verlag: Berlin, 1988; pp 269.(c) Pino, P.; Galimberti, M. J. Organomet. Chem. 1989,370,1. (d) Pino, P.; Galimberti, M.; Prada, P.; Consiglio, G. Makromol. Chem. 1990,191,1677.(e) Kaminsky, W.; Ahlers, A.; Moller-Lindenhof, N. Angew. Chem., Int. Ed. Engl. 1989, 28, 1216. (0 Krauledat, H.; Brintzinger, H. H. Angew. Chem., Int. Ed. Engl. 1990,29, 1412.(g) Ewen, J.; Elder, M.; Jones, R.; Haspeslagh, L.; Atwood, J.; Bott, S.; Robinson, K. Makromol. Chem., Macromol. Symp. 1991,48149,253. (h) Horton, A,; Frijns, J . Angew. Chem., Int. Ed. Engl. 1991,30,1152. (i) Chien, J.;Tsai, W.; Rausch, M. J . Am. Chem. SOC.1991,113,8570. 6 ) Coates, G.; Waymouth, R. J . Am. Chem. SOC.1993,115, 91. (k) Busico, V.;Cipullo, R.; Corradini, P. Makromol. Chem., Rapid Commun. 1993,14, 97. (8)(a) Waymouth, R.; Pino, P. J . Am. Chem. SOC.1990,112,4911. (b) Grossman, R.; Davis, W.; Buchwald, S. J . Am. Chem. SOC.1991, 113,2321.( c )Hong, Y.;Kuntz, B.; Collins, S. Organometallics 1993, 12,964.(d) Hoveyda, A.;Morken, J. J. Org. Chem. 1993,58, 4237. (9)Smith, J.; von Seyerl, J.; Huttner, G.; Brintzinger, H. H J . Organomet. Chem. 1979,173,175. (10)Rieger, B. J . Organomet. Chem. 1992,428,C33. (11)Balbontin, G.; Fait, A.; Piemontesi, M.; Resconi, L.; Rychlicki, H. Presented in part at the International Symposium on Synthetic, Structural and Industrial Aspects of Stereospecific Polymerization (STEPOL ’941,Milano, Italy, June 6-10, 1994;book of Abstracts pp 205-206. (12)Camurati, I.; Piemontesi, F.; Resconi, L.; Zeigler, R. Presented in part at the International Symposium on Synthetic, Structural and Industrial Aspects of Stereospecific Polymerization (STEPOL ’941, Milano, Italy, June 6-10, 1994;book of Abstracts pp 245-246.
Organometallics, Vol. 14, No. 3, 1995 1257 Results and Discussion 1. Synthesis of the Zirconocenes. After the first report by Brintzinger and Wild,3dwho prepared pure rac-(EBI)ZrCl2 (lr) in 30% yield from ZrC4 and (ethylene(bisindeny1))Liz((EBI)Li2),this synthesis has been largely improved. By using higher dilution and slow, simultaneous addition of the two reactants, ZrCLdTHFh and (EBI)Li2 in THF, Collins13 reported a 52% yield of the pure racemic product. By the use of KH as the deprotonating agent, Buchwald14 increased the yields up to 75% but at the expense of specificity, as a mixture of isomers (ruc:meso 2:l)is obtained. Although this does not represent a major problem in the synthesis of ruc(EBTHI)ZrC12,for the two isomers are easily separated given their very different solubilities in toluene, this is a major drawback if one wishes to obtain pure rm-(EBI)ZrCl2, as the two isomers are not easily separated by solvent extraction. However, repeated crystallization from THF of the lr/lm mixture prepared according to Buchwald finally yielded pure lm as orange crystals suitable for X-ray diffraction. Collins’procedure results in isomerically pure l r directly and ultimately in the highest yield. However, Collins’ protocol requires a washing step with HCl/H20 which can lead, if not carried out very rapidly and on the perfectly dried reaction mixture (given the instability of (EBI)ZrC12 in solution toward hydrolysis), to some decomposition products which are not completely removed (e.g. zirconium oxy chlorides) by the subsequent washings with EtOH and Et20, leading to highly varying chemical purities (and catalytic activity!) of the final product. A simple way of purifying this product consists of a CH2C12 Soxhlet extraction of the crude reaction mixture after filtration of the THF/EtzO slurry and drying. Provided the usual precautions in the handling of moisture-sensitive compounds are observed, ruc-(EBI)ZrCla is stable in refluxing CH2C12 for at least 2 days. Furthermore, if little enough solvent is used, the product crystallizes during extraction and is recovered quantitatively upon solvent removal. We recommend this simpler, highly reproducible purification procedure if l r is to be used for catalytic purposes. 2. Crystal and Molecular Structure of ruc-and meso-(EBI)ZrClz. rac-(EBI)ZrCl2 (lr)has a crystallographically imposed C2 symmetry and is isomorphous and isostructural to ruc-(EBI)HfC121dand to the related r~tc-(EBTH1)TiCl2,~~ ~ U C - ( E B T H I ) Z ~and C ~ ~rac~~,~ (EBTHI)HfC1Zld tetrahydro derivatives. Conversely, meso-(EBI)ZrCl2 (lm),meso-(EBTH1)ZrC12l5and meso( E B T H I ) T ~ Care ~ Z not ~ ~ isomorphous, possibly because the lack of any internal symmetry element (to be aligned with a crystallographic one) leaves a larger packing conformational freedom to the meso derivatives which, as a consequence, have systematically larger U/Z (volume per molecule; see Table 1) values than their rac counterparts (i.e. less-bound systems have a larger conformational freedom). Figures 1 and 2 report two different ORTEP views of rac- and meso-(EBI)ZrCla (13)Lee, I.; Gauthier, W.; Ball, J.; Iyengar, B.; Collins, S. Organometallics 1992,11, 2115. (14)Grossman, R.;Doyle, R.; Buchwald, S. Organometallics 1991, 10, 1501. (15)Collins, S.;Gauthier, W.; Holden, D.; Kuntz, B.; Taylor, N.; Ward, D. Organometallics 1991,10, 2061.
Piemontesi et al.
1258 Organometallics, Vol.14, No.3, 1995 Table 1. Reduced Cell Parameters for Known Racemic and Meso ansa-Bisindensl or Tetrahsdroindenvl Derivatives rac-(EBTH1)Ti rac-(EBTH1)Zr rac-(EBTH1)HP rac-(EB1)Zr rac-(EB1)HP meso-(EBTHI)Ti meso-(EBTH1)Zr meso-(EB1)Zr a
12.340 12.598 12.574 11.957 11.945 14.952 12.051 11.119
10.088 10.092 10.115 10.627 10.612 13.633 15.184 10.467
14.144 14.302 14.296 13.775 13.718 17.352 9.939 14.949
104.97 105.38 105.47 106.06 106.09
4 4 4 4 4 8 92.94 4 100.94 4
1701 1753 1752 1682 1671 3537 1816 1708
Iuc
3b 3c,d R/c Id IUc this work Rlc Id Pbca 3b P21/c 15 P2Jn thiswork
IUc
the higher energy indenyl-backward conformation (Y, from the Greek v m q o v , behind) can be present (Figure 3).3h We use here a nomenclature for the two different conformations (lland Y) different from that commonly used for this class of compounds (1and 6). The 2 and 6 nomenclature changes also by changing enantiomer, by simple reflection, and can thus generate confusion in racemic compounds as l r (see Scheme 1;CJ represents a mirror plane). Scheme 1
Originally described in the (equivalent) standard C2/c space group.
* SG = space group.
while Tables 2 (lengths),3 (angles),and 4 (least-squares planes and slip-fold indicators) contain most of their relevant bonding parameters. The rac-C2H4(indenyl)2M fragment has been previously structurally characterized in r~c-(EB1)HfCl2,’~ [~U~-(EBI)Z~C(S~M~~)=CM~~I+,~~ and [rac-(EBI)Zr{CH(SiMe2C1)(SiMe3)}1+,l7 while this is the first structural characterization of the meso one, which unfortunately is affected by some conformational disorder problem (see Experimental Section), and the bonding parameters are not sufficiently accurate to allow a detailed comparison of C-C and Zr-C interactions in the rac and meso fragments. Nevertheless it is clear that in both the derivatives the Zr-C bond interactions involving the bridgehead carbon atoms are longer than the other carbon-metal bonds within the y5-moiety. Incipient v5 v3 distortions are normally observed for y5-indenyl complexes and are commonly measured by the so called slip-fold parameters Y, Q, and A defined in ref 18. Moreover on moving from rac to meso, the indenyl ligands take more room around the Zr atom at the expense of the chlorine atoms as shown by the widening of the Cp-Zr-Cp’ angle, the shrinking of the C1-ZrC1 angle, and the lengthening of the average Zr-C1 bond distance. Besides, because the two Zr-C1 bonds in the meso derivative are not related by symmetry and, more importantly, their local environments are dissimilar, they are markedly different. The rac stereoisomer, reported in Figure 1, according to an adaptation by Schlogl of the Cahn-Ingold-Prelog rules has clearly an R,Rconfiguration of the bridgehead carbon atoms and a 6 conformation of the Zr-Cl,C8,C8’,Cl’ “metallacycle”. Conversely the meso stereoisomer reported in Figure 2 has 13,sstereochemistry. However, both in solution and in the solid state, as they crystallize in a centrosymmetric space groups, their enantiomers (A,S,S and S,R,S, respectively) are also present. In Table 5 we report the distances and torsional angles between the bridge protons H8 and the indenyl back protons H2 and H7 in l r and lm. 3. NMR Analysis and Solution Conformations. Spectral Assignments. One of the key questions in evaluating the catalytic performance of organometallic complexes is whether their solid state structure is maintained in solution. In the case of the rac-(EB1)ZrClz precatalyst, the first point to be established is whether the only conformation observed in its crystal structure (indenyl-forward, here called ll from the Greek q o ,in front) is maintained in solution, or if also
-
(16)Horton, A.; Orpen, G. Organometallics 1991,20, 3910. (17)Horton, A.; Orpen, G. Organometallics 1992,2 1 , 1193. (18)Faller, J.W.; Crabtree, R. H.; Habib, A. Organometallics 1986, 4,929.
(X-R,R)
Y (64,s)
Y
= (8-R,R)
-
n 0
(h-S,S)
n
Our interest in determining the solution conformations for l r and lm stems from the fact that it is the metal-ansa ligand framework, which remains intact during catalysis, that dictates enantioface selectivity in a number of enantioselective and diastereoselective transformations, and ligand-substrate nonbonded interactions are expected to be slightly different in the two conformations. In order to elucidate this point we carried out a detailed NMR analysis of l r and lm. Complete spectral assignments of the lH and 13CNMR spectra of rac- and meso-(EBI)ZrClzwere first made through bidimensional NMR techniques and are reported in Table 6a; their proton spectra are overlapped in Figure 4. The following discussion is based on the numbering system reported in Chart 1 according to the atom numbering of the molecular structures (Figures 1 and 2). The lH NMR spectrum of l r exhibits three recognizable groups of signals, the multiplet of the bridge protons (H8), the doublets of the C5 ring protons (H2, H3), and the C6 ring protons (H4, H5, H6 and H7). COSY1g and NOESVO 2-D sequences, showing correlations of resonances from J-coupled (COSY) and dipolar-coupled (NOESY) protons, were used to establish a biunivocal correspondence between each proton in the molecule and each resonance in the 1-D spectrum. Figure 5 shows an expanded region of the COSY spectrum of rac-(EBI)ZrCla together with the more significant coupling patterns between H2-H3, H3-H7, H4-H5, H5-H6, and H6-H7. In addition to some of the cross-peaks found in the COSY spectrum, the NOESY spectrum (Figure 6) shows the correlations between H8-H2, H8-H7, H2-H7’, and H3-H4 (a prime indicates a proton on the opposite indenyl), thus confirming the assignments made through COSY. The DEPT 135 sequence was used to separate the resonances of CH2, CH, and quaternary carbons in the 13C spectrum. Assignments of the protonated carbons were then obtained using a heteronuclear COSY (XHCORRl2l which correlates each carbon to its directly bound protons. Unambiguous attribution of the quaternary carbons from the heteronuclear long-range COSY (COLOC)22 spectrum was not possible. We present here a tentative assignment based on nuclear (19) (a) Aue, W. P.; Bartholdi, E.; Ernst, R. R. J. Chem. Phys. 1976, 64, 2229.(b) Nagayama, K;et al. J. Magn. Reson. 1980,40,321. (20)States, D.J.; Haberkom, R. A,; Ruben, D. J. J. Magn. Reson. 1982,48, 286. (21)Bax,A,; Morris,G. J. Magn. Reson. 1981,42,501.
(Ethylenebis(1-indenyl))zirconium Dichloride
Organometallics, Vol. 14,No. 3, 1995 1259
A
H6
B
H5
4 c5
H4
^.
a
$?-
A
LJ
U
Figure 1. Top (A) and front (B)ORTEP views of lr. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms were given arbitrary radii. Overhauser enhancement (NOE) experiments. We can assign the 13C peak at 121.81 ppm t o the carbon 1 due to its coupling to only two protons, the large NOE seen upon irradiation of the ethylene bridge protons, and the sharpening of the peak when the aromatic protons on the five-membered ring are irradiated. The two resonances at 123.12 and 129.62 ppm cannot be unambiguously assigned. Through the combination of NOE data and the comparison with the spectrumz3of a similar chiral zirconocene (rac-(ethylenebis(4,7-dimethyl-l-indeny1))zirconiumdi~hloridel~), we can tentatively assign the peak a t 123.12 ppm t o carbon 7a and the peak at 129.62 ppm to carbon 3a. The same analysis was performed on lm. Chemical shifts for both hydrogens and carbons are reported in Table 6b. Assignments of the lH spectrum were obtained from the COSY of Figure 7. The spectrum exhibits correlations between H3 and H7 (due to the 5J coupling constant), H2-H3, H6-H7, H5-H6, and H4(22) Kessler, H.; Griesinger, C.; Zarbock, J.; Loosli, H. R. J.Magn. Reson. 1984,57, 331. (23) Unpublished results from our laboratories.
H5. In the meso form the two bridge protons give wellseparated multiplets at 3.5 and 3.8 ppm which were assigned from the NOESY spectrum of Figure 8 exhibiting cross-peaks between H81 and H2 and H82 and H7. Assignments of the protonated carbons were obtained from the XH-CORR spectrum; again no univocal assignments were possible for the quaternary carbons. However, as we observed little dependence of the chemical shifts on the zirconocene symmetry, we give assignments for these carbons based on those obtained for the rac isomer 6r. Conformational Analysis. The CHz-CHz bridge protons of l r form an AA'BB' spin system which gives rise to a 24 line spectrum (centrosymmetric about V 2 (VA VB)). Its form depends on the values of chemical shift difference (Ad) and coupling constants (az4 which are influenced by the molecular conformation. Particularly, while the geminal coupling constants do not
+
(24) In an AA'BB spin system coupling constants and chemical shifts cannot be directly obtained from the peak distances in the spectrum but must be calculated by computer analysis of the spectral region of interest: the Bruker program PANIC, a version of the LAOCOON type programs (see ref 25, p 186),was used.
1260 Organometallics, Vol. 14,No. 3, 1995
Piemontesi et al. Table 2. Bond Lengths (Ala ruc-(EB1)ZrClz
R
,.
Q
zr-c1 zr-c1 zr-c2 zr-c3 Zr-C3a Zr-C7a Cl-C2 Cl-C7a Cl-C8 C2-C3 C3-C3a C3a-C4 C3a-C7a c4-c5 C5-C6 C6-C7 C7-C7a C8-C8'
2.3884(5) 2.438(2) 2.443(2) 2.531(2) 2.624(2) 2.553(2) 1.401(4) 1.404(3) 1.470(3) 1.388(4) 1.398(4) 1.413(3) 1.415(3) 1.352(4) 1.402(5) 1.334(4) 1.433(3) 1.518(5)
rI
i
2.3968(8) 2.4551(8) 2.476(3) 2.481(3) 2.457(3) 2.470(3) 2.526(3) 2.514(4) 2.646(3) 2.596(3) 2.557(3) 2.563(3) 1.401(5) 1.393(5) 1.429(4) 1.417(4) 1.489(6) 1.544(7) 1.396(5) 1.393(5) 1.420(5) 1.428(5) 1.425(4) 1.438(5) 1.423(5) 1.405(5) 1.344(4) 1.350(6) 1.409(5) 1.401(8) 1.344(4) 1.3260) 1.429(4) 1.430(4) 1.452(7)
I, I1 indicate atoms (I) and primed atoms (11) of lm as shown in Figure 2B.
Table 3. Selected Bond and Torsional Angles (deg)"
H4
h5
n
c4
P
meso-(EB1)ZrClz
1 cp-Zr -cp' Cl-zr-Cl' cp-Zr-C1 cp-Zr-C1' C7a-Cl-C2 C7a-Cl-C8 C2-Cl-C8 Cl-C2-C3 C2-C3-C3a C3-C3a-C4 C3-C3a-C7a C4-C3a-C7a C3a-C4-CS C4 -C5-C6 C5-C6-C7 C7a-C7-C6 Cl-C7a-C3a Cl-C7a-C7 C3a-C7a-C7 Cl-C8-C8'-Cl' bz-cp-cp'- bz'
M2
H6'
Y4
Figure 2. Top (A) and front (B) ORTEP views of lm. Thermal ellipsoids are drawn at the 30%probability level. Hydrogen atoms were given arbitrary radii.
change, the vicinal coupling constants (3J) strongly depend on the diedral angle 6 between the CH bonds according to the Karplus relation:25
3 J = A + B cos 8
+ Ccos 28
(1)
where A, B , and C are constants. For our system, the best results were obtained with A = 7.23, B = -0.51, and C = 5.16. Both ll and Y structures are expected to approach a staggered ethylene bridge onf formation,^^,^^ and 6 is likely to be between 30 and 60". Two sets of coupling constants, one for each limit conformation, were then calculated according t o eq 1for 6 values in the ranging from 0 to 60" (Table 7). None of these calculated sets of J values fit the experimental coupling constants a t 298 K (reported in Table 81, and our data can be interpreted only if a fast (NMR time scale) exchange occurs (Pachler-type equi(25) Giinther, H.NMR Spectroscopy; Wiley: New York, 1980; p 106. (26) Jordan, R. F.;LaPointe, R. E.; Baenzinger, N.; Hinch, G. D. Organometallics 1990,9,1539.
99.09(3) 106.5(1) 108.9(1) 107.5(2) 124.6(2) 127.9(2) 109.0(2) 108.0(2) 134.3(2) 107.9(2) 117.7(2) 120.2(2) 122.4(2) ii9si3j 120.5(2) 107.7(2) 132.6(2) 119.7(2) 45.6(3) 48.6(1)
11
126.2(1) 97.62(3) 106.0(1) 107.8(1) 107.0(1) 108.6(1) 106.8(4) 108.0(4) 128.3(4) 126.5(4) 124.7(4) 125.9(4) 109.5(4) 108.8(4) 108.1(4) 108.3(4) 132.5(3) 136.6(5) 107.5(3) 106.2(3) 120.0(3) 117.2(4) 118.9(3) 120.2(6) 121.313) 120361 121.9i3j imi6j 11933) 116.5(5) 107.9(3) 108.7(3) 133.7(4) 129.1(4) 118.3(3) 122.2(4) -40.9(6) -10.0(3)
a cp and bz refer to the center of mass of the five- and six-membered rings of the indenyl ligands. I, 11 indicate atoms (I) and primed atoms (11) of l m as shown in Figure 2B.
l i b r i ~ m , ~Scheme ' 2; ll and Y conformations are arbitrarily assigned and will be used without any reference to the real ones. Due t o the AA'BB' spin system symmetry the bridge protons cannot be individually assigned] i.e., HA H81 or H82, HB = H82 or H8i, HA' = H81' or H82', and H B = H82' or H81').
n
Y
(27) (a) Pachler, K.G. R. Spectrochim. Acta 1963,19, 2085-2092. (b) Spectrochim. Acta 1964,20, 581.
Organometallics, Vol. 14, No. 3, 1995 1261
(Ethylenebis(l4ndenyl))zirconium Dichloride Table 4. Angles between Relevant Least-Squares Planes and Slip-Fold Paramete-
Table 5. Selected H**.H Lengths (A) and Torsional Angles (deal” meso-(EB1)ZrClz
meso-(EBI)ZrClZ rac-{EBI)ZrCl? ANBz (deg) ZrCl2lln (deg) InlIn’ (deg) Y (deg) Q (deg) A (A)
II
I
5.3(1) 31.89(4) 63.47(4) 5.36 2.28 0.206
rac-(EBI)ZrClz
4.7(3) 2.8(3) 31.01(5) 31.26(8) 62.3(1) 4.84 3.48 2.07 1.74 0.188 0.135
aAl, Bz, In, and ZrC12 refer to the least-squares planes defined by the allylic moieties (C7a, C1, C2), the six-membered rings, the indenyl ligands, and the ZrClz atoms, respectively. I, II indicate atoms (I) and primed atoms (E) of l m as shown in Figure 2B.
The vicinal coupling constants are then given by the following equations:
J M = aJF
+ bJ:
H81-H2 H8 1-H2’ H82-H2 H82-H2’ H81-H7 H81-H7’ H82-H7 H82-H7’
3.78 2.66 3.08 3.99 2.41 4.95 3.56 4.56
H81-C8-C8’-H81’ H8 1-C8-C8’-H82’ H82-C8-C8’-H81’ H82-C8-C8’-H82’
165.9 49.3 47.3 -7 1.3
I
II
2.55 2.77 3.45 4.05 4.13 4.86 3.03 4.38
4.50 3.76 4.38 3.02 2.46 2.36 3.94 3.55 -160.7 41.9 -41.6 77.1
I, I1 indicate bridge atoms (I) and primed bridge atoms (II) of lm as shown in Figure 2B.
X-RR conformation Y (indenyl-backward)
6-RR conformation
(4)
ll (indenyl-forward)
where a and b are the relative residence times for the ll and Y conformations respectively (a b = 11, and Jt , J,, and S,are the vicinal coupling constants of the limit conformation, given by
+
JF = 7.23 - 0.51 cos(l20
+ 6), + 5.16 cos[2(120
J: = 7.23 - 0.51 cos(l20 - 6 ),
+ On)] (5a)
+
Table 6. Carbon and Proton Assignments for rac-(EBI)ZrClz and meso-(EB1)ZrClz
5.16 ~ 0 ~ [ 2 ( 1 2-0On)] (5b)
J’F = 7.23 - 0.51 COS(^,) + 5.16 COS(^^,) ( 5 ~ ) 5: = 7.23 - 0.51 cos(l20
+ 6y) + 5.16 cos[2(120
+
J i = 7.23 - 0.51 ~ 0 4 1 2 0 OY)
Figure 3. ll and Y conformations in lr. (The ZrClz fragment is omitted for clarity.)
+ OY)1 (6a)
+
5.16 ~ 0 ~ [ 2 ( 1 2 0Oy)] (6b)
J’i = 7.23 - 0.51 COS(^^) + 5.16 ~ 0 ~ ( 2 6 y(6~) ) Introducing the experimental S s in eqs 2-4 and using eqs 5a-6c, we can obtain On (48.8’1, i+y (35.3’), a, and b (see Table 8). These results show that a t room temperature one of the two conformations is slightly preferred and that the dihedral angles On and i+y have different values. The conformational equilibrium was more deeply investigated in the same way by analyzing N M R spectra in a temperature range between 298 and 193 K. As the temperature goes down, the spectrum changes due to the increase of the chemical shift difference and the change of the coupling constants (see Figure 9 and Table 8). The behavior of 3Ss with 1/T is showed in Figure 10. As the angles On and i+y should not depend on the temperature, while JAB’changes with T, we can This is possible only if deduce from eq 4 that Jf t SY. J= t JY, confirming our resufts at room temperature.
atom
‘H-NMR
multipl (J, Hz)
13C-NMR
(a) rac-(EB1)ZrClz 1 2 3 4 5 6 7 8 3a 7a
6.20 6.58 7.50 7.35 7.20 7.65 3.6-3.9
d (3.35) dd (3.35,0.85) dt m m dq m (AA’BB’)
121.81 113.98 110.83 125.73 126.69 126.63 121.42 29.06 129.62 123.12
(b) meso-(EB1)ZrClz 1 2 3 4 5 6 7 81“ 82“ 3a 7a
6.55 6.70 7.46 7.15 7.07 7.50 3.50-3.75 3.85-4.10
d dd dt m m dq m (AA’) m (BB’)
121.21 115.28 112.61 125.64 126.30 126.74 122.24 29.33 29.33 129.39 123.98
Hydrogens 81 = 81’ and 82 = 82’.
The values of a and b, calculated using the room temperature On and i+y values (Table 81, show that, upon cooling, the conformational equilibrium is slowed down and one of the two limit conformations becomes predominant. As we said before, from our NMR data it is not possible to decide whether this conformation is really I3 or Y, but as nonbonding interactions between
1262 Organometallics, Vol. 14, No. 3, 1995
Piemontesi et al.
t
!I
7.5
7.0
6.5
6.0
6.0
ppm I
I
I
7.5
7.0
I
6.5
PPm
I
I
4.0
3.5
PPm
Figure 4. lH NMR spectrum of l r (top) and lm (bottom) in CDCls at room temperature. Chart 1
Figure 5. Expanded region of the COSY spectrum of lr. The cross-peak A at (6.6-7.65 ppm) due to a long-range coupling (5J)typical of indenyl systems allows the identification of €33 and H7. All other assignments were obtained from the cross-peaks B at 6.6-6.2 ppm (H3 and H2), C at 7.65-7.2 ppm (H7 and H6), D at 7.2-7.35 ppm (H6 and H5), and E at 7.35-7.5 ppm (H5 and H4). 81
8 the bridge and indenyl fragments are higher in the latter,28we suggest the more stable conformation to be the II one. Plotting of ln(a/b)versus 1/T (Figure 11)gave a linear correlation (r = 0.993) according to the following expression: = AG,/RT
In(&)
As the entropy difference for conformational isomers is usually assumed to be negligible, that is AG AH, from the slope we obtain a value of AHm = 0.945 kcall mol. The experimental spectra for l r in different solvents are reported in Figure 12 together with the calculated set of coupling constants (Table 9). It can be seen that the conformational equilibrium is slightly influenced by the solvent. In the case of lm a highly symmetric spectrum is observed at room temperature (only one signal for each type of proton on the two indenyl rings is present). Two cases are then possible: (a) The molecule is in a completely eclipsed (e) conformation leading to a calculated J set of 11, 11,5,5 Hz for the bridge signal (see Table 10). (b) The molecule is rapidly exchanging between two staggered (s' and s") conformations through a completely eclipsed (e) conformation (Figure 13). The ~
~~
(28)Collins, S.; Hong, Y.; Ramachandran, R.; Taylor, N. J. Organometallics 1991, 10, 2349.
7.0
6.0
5.0
4.0
ppm
Figure 6. Expanded region of the NOESY spectrum of l r showing correlations between the bridge protons H8 with H2 (cross peak A) and H7 (B), between H2 and H7' (C), and between H3 and H4 (D). two staggered conformations are mirror images, hence equienergetic, and have two symmetric sets of calculated coupling constants; the observed coupling constants are the average between those of the two limit conformations (Table 10). Our results (see Table 11)are in favor of the equilibrium hypothesis and were confirmed by the VT-NMR spectra in the temperature range between 298 and 193 K (Figure 14; Table 11). Conclusions We have solved the solid state structure of Brintzinger's CZsymmetric ruc-(EBI)ZrClz and found it to be
Organometallics, Vol. 14, No. 3, 1995 1263
(Ethylenebis(1-indenyl))zirconium Dichloride
Table 7. Coupling Constants (Hz)Calculated with the Karplus Relation for the Different Conformations of ruc-(EBI)ZrCl*and for Different 6 Values Y conformation ll conformation
6.5
7.0
C
ppm
80 E
i
7.5
l 9
JAA'
JBB'
JAB'= JA'B
JAA,
JBB
0 10 20 25 30 35 40 45 50 55 60
4.91 6.66 8.52 9.41 10.25 11.01 11.66 12.19 12.58 12.82 12.90
4.91 3.45 2.47 2.19 2.07 2.10 2.29 2.63 3.10 3.70 4.40
11.88 11.58 10.70 10.08 9.37 8.58 7.74 6.87 6.01 5.17 4.40
4.91 3.45 2.47 2.19 2.07 2.10 2.29 2.63 3.10 3.70 4.40
4.91 6.66 8.52 9.41 10.25 11.01 11.66 12.19 12.58 12.82 12.90
I
1
I
7.0
6.5
ppm
Figure 7. COSY spectrum of lm. The cross-peak A at 6.7-7.5 ppm due to the typical indenyl long-rangecoupling (5J)identifies H3 and H7. Cross-peak B at 6.55-6.7 with H3 identifies H2; cross-peak C at 7.5-7.07 ppm with H7 identifies H6; cross-peaks D at 7.07-7.15 and E at 7.157.46 identify H5 and H4, respectively.
T(K) . ,
JAB = JA'B' (Hz) . ,
298
-14.626
273
-14.609
253
-14.628
233
-14.726
223
-14.797
213
-14.619
193
-14.946
a
4.0
5.0
PPm 6.0 f
7.0
I
7.0
6.0
I
I
5.0
4.0
= JA'B
11.88 11.58 10.70 10.08 9.37 8.58 7.74 6.87 6.01 5.17 4.40
Table 8. ruc-(EBI)ZrClz VT-NMR Data: Experimental and Calculated Coupling Constants (in Parentheses) and Residence Times
I
7.5
JAB
PPm
Figure 8. NOESY spectrum of l m showing correlations between the two bridge protons and H2 (cross peak A) and H7 (B)allowing the assignment of H81 (=H81') and H82 (=H82') as the multiplets at 3.5 and 3.8 ppm, respectively. in the I1 (indenyl-forward)conformation, as is the case for most of the chiral ethylene bridged bisindenyl-type metallocenes. In solution, however, already at room temperature there is a rapid (NMR time scale) interconversion between the two I1 and Y (indenyl-backward) conformations, as shown by conformational analysis of the bridge methylenes done on their proton spectra and as found by Brintzingerg for the ansa Czv-symmetric (ethylenebis(cyclopentadieny1))titanium dichloride. This equilibrium is shifted toward the lower energy conformation ll at lower temperatures. Solvent effects are also present. Also the solid state structure of the meso isomer has been compared to its solution conformation equilibrium. In the solid state meso-(EB1)ZrClz
JAA'
JBB'
(Hz) . ,
(Hz) . .
6.310 8.138 (6.345) (8.173) 8.457 6.125 (6.122) (8.460) 8.738 5.795 (5.866) (8.789) 9.155 5.853 (5.686) (9.021) 5.471 9.319 (5.451) (9.323) 5.268 9.559 (5.262) (9.567) 4.744 9.993 (4.825) (10.130)
JAB' = JA'B
(Hz) , , 7.137 (7.172) 7.083 (7.108) 7.052 (7.035) 7.005 (6.983) 6.826 (6.915) 6.807 (6.861) 6.404 (6.736)
a
b
L.S."
0.583 0.417 0.0037 0.611 0.389 0.0006 0.643 0.357 0.0080 0.665 0.335 0.0463 0.694 0.306 0.0084 0.717 0.283 0.0030 0.772 0.228 0.1352
L.S. = C(Jexp- JCdc)*.
is actually in a chiral conformation (CI symmetry) because of the staggered placement of the two indenyl ligands (1nd"Ind = 10.0"). In solution this aspecific zirconocene gives a highly symmetric NMR spectrum indicating that, as in the case of the rac isomer, there is a rapid interconversion between the two equienergetic, mirror-image limit conformations. These results show that ethylene-bridged zirconocenes are less rigid than previously realized, and in the case where multiple spatial arrangements of the x-ligands are possible, the X-ray structure should not be used as a rigid model for the active site. I t is reasonable to assume that the energy of I3 Y conformation interconversion in the catalytically active species rac-(EBI)ZrP+is higher due to the bulkiness of the growing polymer chain. As proposed by RiegerlO and Chier~,~ga different conformations are likely to have different effects on catalyst stereospecificity. This might explain the high T pdependence of the stereospecificity of 1 r M O observed in propylene polymerization.
-
Experimental Section General Procedures. All operations were performed under nitrogen by using conventional Schlenk-linetechniques. Solvents were distilled from blue benzophenone ketyl (THF), LiAlH4 (EtzO),P4010(CHzClz, CHClz),or Al'Bw (hydrocarbons) and stored under nitrogen. Indene (Aldrich)was distilled from CaHz. 1,2-Dibromoethane(Aldrich) was stored over molecular sieves. MeLi (Aldrich) and BuLi (Aldrich) were used as received. All compoundswere analyzed by lH NMFt (200 MHz, CDC13, referenced against the peak of residual CHC13 at 7.25 ppm) or 13C NMR (50.3 MHz, CDCl3, referenced against the central line of CDC13 at 77.00 ppm). All NMR solvents were dried over LiAlH4and distilled before use. Preparation of the
Piemontesi et al.
1264 Organometallics, Vol. 14,No. 3, 1995 11.
7.
JAB' = JAB
6.
5.
JAA'
44 . . . . . . . . . . . . . . . . . . . . . . . . .
0.003
0.0035
0.004
0.0045
0.005
0,0055
l/T(K-1)
Figure 10. Temperature dependence of the bridge protons vicinal coupling constants.
"4 1.2
I
3.85
3.80
3.75
1
I
3.70
3.65
3.60
I
,
3.55
3.50
o.2 0
i
m 0
i 0.W
0.003
ppm
0.006
0.045
0.0066
0.0035
1 I T ( K.1)
Figure 11. Linear relationship of ln(a/b)vs 1/T(Arrhenius
B
plot).
a
I
I
I
1
I
1
3.85
3.80
3.75
3.70
3.65
3.60
I
I
3.55
3.50
I
PPm
Figure 9. Experimental (A) a n d calculated (B)spectra of ethylene bridge region of l r in CDZClz, at 25 (a), 0 (b), -20 (c), -40 (d), -50(e), and -80 "C (0. samples was carried out under dry, oxygen-free nitrogen using standard inert atmosphere techniques. Due to the low solubility of these compounds, the samples were dissolved in 0.5 mL of solvent t o obtain a saturated solution in a 5-mm NMR tube. Room-temperature spectra were recorded on an AC 200 Bruker spectrometer operating at 200.13 MHz for 'H and 50.323 MHz for 13C, in the Fourier transform mode. A 90" pulse of 6.5 s for 'H,of 28 s for the decoupler (DP = lH), and of 6.0 s for 13C was used. Variable-temperature experiments were run on a Varian 300 spectrometer. All the 13C spectra were acquired in the broad band decoupling mode. A 0.51 J(CH) = 0.0033 s value, corresponding to J = 150 Hz, was used for DEF'T135. COSY and NOESY were obtained with a 1200-Hz spectral window, 0.426 s acquisition time, and 1 s relaxation delay. A total of 64 transients were collected for each of 256 tl
1
I
1
I
I
3.9
3.8
3.7
3.6
I
PPm
Figure 12. Ethylene bridge region of l r in CDCls (a), CD2Clz (b), and THF-ds (c). increments. Data were zero filled in the first dimension to 512W points before Fourier transformation. A 2 s mixing time (generally used for small molecules) was used in the NOESY experiment. For XH-CORR and COLOC the recycling time was 2 s with 256 transients being collected for each t l increment. A total of 512 spectra, each consisting of 4K data points, were accumulated, and the data matrix was zero filled in the first dimension to 4K x 512W before Fourier transformation with
Organometallics, Vol. 14,No. 3, 1995 1265
(Ethylenebis(1-indenyl))zirconium Dichloride Table 9. Coupling Constants (Hz)for rue-(EBI)ZrClz in Different Solvents JAW = JAB JM
JAB’= JA‘B JBW
CDCh
THF-ds
CDZClZ
-14.69 7.54 7.08 7.54
- 14.50 8.38 7.36 6.06
-14.36 7.96 7.36 5.80
Table 10. Coupling Constants (Hz) Calculated with Karplus Relation for the Staggered (s) and Eclipsed (e) Conformations of meso-(EB1)ZrClz meso s’ H81-H82’ H81-H81’ H82-H82’ H82-H81’
meso s”
meso e
s#
w g )
~~d~
weg)
~~d~
weg)
~~d~
160.7 41.9 41.6 77
10.8 7.5 7.5 3.3
120 0 0 120
5.2 11.3 11.3 5.2
77 41.6 41.9 160.7
3.3 7.5 7.5 10.8
stt
J~~ 7.0 7.5 7.5 7.0
4.0
3.9
3.8
3.7
3.6
3.5
3.1
3.6
3.5
ppm
staggered
eclipsed (e)
(SI)
staggered (9”)
e
Figure 13. Staggered (s’ and s”) and eclipsed (e) conformations in l m (ZrCl2 fragment omitted for clarity). Table 11. meso-(EB1)ZrClz VT-NMR Data: Experimental Coupling Constants T ( K ) JAB = JAW (Hz) JAA’ (Hz) JBB,(Hz) JAB’= JA% (Hz) 298 273 253 233 223 213 193
-14.678 - 14.544 -14.473 -14.216 -14.451 -14.164 -14.187
7.064 7.046 7.019 6.975 6.991 6.973 7.135
7.147 7.138 7.130 7.121 7.064 7.192 7.149
7.384 7.420 7.510 7.867 7.522 7.851 7.535
a frequency range of 8000 Hz in 13C and of 1200 Hz in lH. A1 = 3.45 ms and A2 = 1.72 ms (corresponding t o J (CHI of 150 Hz) and A1 = 50 ms and A2 = 33 ms (J(CH) = 10 Hz) were used for XH-CORR and COLOC respectively. 1,2-Bis(3-indenyl)ethane(Slightly Modified from Buchwald).14 Distilled indene (20 mL, 172 mmol) and THF (200 mL) were placed in a 500 mL flask equipped with a nitrogen inlet connected to an oil bubbler for pressure release, a stirring bar, and a 250 mL dropping funnel. After the apparatus was cooled to -78 “C by means of a dry ice/acetone bath, 110 mL of a 1.6 M solution of MeLi in Et20 (176 mmol) was added dropwise with stirring. At the end of the addition, the flask was allowed to warm slowly to room temperature and stirred for 3 h (darkening of the red-orange solution was observed). The so obtained red solution was cooled to -78 “C, and 7.5 mL of l,2-dibromoethane (87 mmol) in 50 mL THF was added dropwise to it (some gas evolution was observed throughout the addition). The flask was removed from the dry ice/acetone bath, stirred overnight at mom temperature, and then quenched with 1 mL of HzO (color changed from red to brown); the solvents were removed in vacuo until a light brown mass was obtained, to which (under normal atmosphere) 95%EtOH (200 mL) was added. The mixture was refluxed for 30 min and then allowed to cool slowly to room temperature. A microcrystalline ochre solid precipitated upon cooling, which was filtered off, redissolved in CHC13 on the filter t o remove the small amount of insoluble tars present, dried in vacuo, washed
4.0
3.9
3.8 ppm
Figure 14. Experimental (A) and calculated (B)spectra of ethylene bridge region of l m in CD2C12, at 25 (a), 0 (b), -20 (c), -40 (d), -50(e), -60 (0, and -80 “C (g). with hexane (2 x 20 mL), and finally dried in vacuo to yield 11.35 g (51.3%)of a light yellow microcrystalline solid. The final washing steps afford a product of high (99.4%by GC) and reproducible purity. All the mother liquors collected and brought t o dryness yielded, after extraction with CHC13 and washing with hexane, a n additional 2.48 g of darker and less pure (82% by GC) product (discarded). lH NMR (6, ppm, CDC13,200 MHz): 2.95 (s,4H), 3.35 (s,4H), 6.30 (s, 2H), 7.17.6 (m, 8H). ruc- and meso-(Ethylenebidl-indeny1))ZrCla((EB1)ZrCla, l r and lm). Pure l r was prepared according to Collins,13 modifying the final purification procedure. After precipitation of the reaction crude with EtzO, the mixture was filtered under nitrogen in a filtration apparatus equipped with a side arm (to allow solvent refluxing) connecting the system above and below the frit, a receiving flask on the bottom, and bubble condenser on the top. The yellow solid was washed with Et20 (washings discarded), dried, and then extracted with 50 mL of refluxing CHzClz until the filtrate was colorless. The extraction process required several hours when done on a 10-g scale using a 100 mL extraction apparatus with a 30 mm diameter G3 frit (a gray solid is left on the frit). Most of the product precipitates during extraction. After removal of the solvent, pure l r was obtained as a yellow microcrystalline solid in 40% yield. Crystallization from CHzCl2 afforded yellow crystals suitable for X-ray analysis. lm of 95% purity was obtained by cooling a 1/1 l d l r THF solution, which was in turn obtained by extracting with CHzCl2 the mixture of isomers obtained according to Buchwald.14 Cooling of a 95% lm THF solution afforded orange crystals of pure lm.
1266 Organometallics, Vol. 14,No. 3, 1995
Piemontesi et al.
Table 12. Summary of Crystal Data and Data-Collection/ Analysis Parameters formula Mr cryst system space group a, A b, A
c, A A 4%
V, A3 Z d, g/cm3 F(000) cryst dimens, mm p(Mo Ka), cm-’ min re1 transm factor no. of reflcns for Y scan e range, deg scan mode scan range, deg required u(Z)/I max scan time, s octants of recipr space collcd cryst decay no. of collcd reflcns (at RT) no. of unique obsd reflns [I 3 m 1 no. of refined params weights (a, b)” max shift/error
’
Rb
R’ max eak diff Fourier map, e
1-3
rac-(EBI)ZrC12
meso-(EBI)ZrCl2
C~oHi6C12n 418.5 monoclinic I2/c (No. 15) 11.957(1) 10.627(1) 13.775(2) 106.06(1) 1682(1) 4 1.652 840 0.15 x 0.10 x 0.07 9.6 0.95 3 3-27.5
C~oHi6ChZr 418.5 monoclinic P21/n (No. 14) 11.119(3) 10.467(1) 14.949(2) 100.94(2) 1708(1) 4 1.627 840 0.20 x 0.12 x 0.10 9.4 0.95 3 3-25
W
W
+
1.0 0.35 tan 0.01 70 ich,k,l no 1912 1808
e
+
1.o 0.35 tan e 0.01 70 fh,k,i 9% 3288 2718 216 1.0, 0.001 402 ‘0.01 0.032 0.045 0.57
106 1.0, 0.004 668 ‘0.01 0.026 0.034 0.40
Table 13. Atomic Coordinates and Equivalent Isotropic Disulacements Parametersa for ruc-(EBI)ZrClz Zr
c1 C1 C2 C3 C3a C4 C5 C6 C7 C7a C8
X
Y
Z
0.00000 0.07003(4) 0.1143(2) 0.0951(2) 0.1587(2) 0.2229(2) 0.3087(2) 0.3599(2) 0.3297(2) 0.2501(2) 0.1943(2) 0.0658(2)
0.47772(2) 0.32677(5) 0.6733(2) 0.6145(3) 0.4998(3) 0.4884(2) 0.4007(2) 0.4199(3) 0.5239(3) 0.6099(2) 0.5955(2) 0.7965(2)
0.25000 0.3851l(4) 0.2463(2) 0.1513(2) 0.1618(2) 0.2630(2) 0.3173(2) 0.4168(2) 0.4705(3) 0.4220(2) 0.3162(2) 0.2709(3)
U 2.210(8) 3.87(1) 3.65(4) 4.28(5) 4.12(6) 3.10(5) 4.38(6) 4.88(6) 4.73(7) 4.07(5) 2.91(4) 5.13(7)
“Equivalent isotropic U defined as one-third of the trace of the orthogonalized Uv tensor.
X-ray Structure Determination and Refinements. Crystal data and experimental conditions for compounds lr and l m are reported in Table 12. Unit cell parameters were determined by least-squares fit of the setting angles of 25 intense reflections having a 0 value in the range 10.0-14.0”. The intensity data were recorded on a n Enraf-Nonius CAD-4 automated diffractometer at room temperature using the scan conditions and sampling the reciprocal lattice as reported in Table 12. The crystal stability was checked by monitoring three standard reflections every 60 min. Final drift corrections, when applied, are reported in Table 12. The diffracted intensities were corrected for Lorentz, polarization, and background effects. An empirical absorption correction was applied according t o the method developed by North et al., based on Y scans (Y = 0-360”, every 10’) of three reflections having x values near 90°.29 Scattering factors for neutral atoms and (29) North, A. C. T.; Phillips, D. C.; Mathews, F. S. Acta Crystallogr. 1968,A24,351.
Table 14. Atomic Coordinates and Equivalent Isotropic Displacements Parametee for meso-(EBI)ZrClZ Zr C1 C1’ C1 C2 C3 C3a C4 C5 C6 C7 C7a C8 C1’ C2‘ C3’ C3a’ C4‘ C5’ C6’ C7’ C7a‘ C8’
X
Y
Z
U (A*)
0.21032(2) 0.41532(7) 0.20862(9) 0.1216(3) 0.1248(4) 0.2461(4) 0.3225(3) 0.4510(3) 0.4984(4) 0.4234(4) 0.3016(4) 0.2456(3) 0.0076(5) 0.0451(3) 0.0013(3) 0.0675(4) 0.1533(3) 0.2435(5) 0.3076(6) 0.2901(5) 0.2087(4) 0.1385(3) O.OOlO(5)
0.18919(2) 0.26800(8) 0.04984(9) 0.1191(4) 0.0122(4) -0.0247(3) 0.0559(3) 0.0564(3) 0.1483(4) 0.2425(4) 0.2449(4) 0.1490(3) 0.1832(6) 0.3356(3) 0.2718(4) 0.3121(4) 0.4070(3) 0.4875(6) 0.5718(6) 0.5792(5) 0.5089(4) 0.4203(3) 0.3155(5)
-0.01677(2) 0.02789(5) 0.11509(6) -0.1736(2) -0.1169(3) -0.0856(3) -0.1270(2) -0.1256(2) -0.1713(3) -0.2210(3) -0.2251(2) -0.1786(2) -0.2210(3) -0.0898(3) -0.0208(3) 0.0630(3) 0.0470(3) 0.1015(5) 0.0608(6) -0.0344(6) -0.0897(4) -0.0479(3) -0.1931(4)
2.83(1) 3.91(2) 5.21(2) 5.6(1) 5.9(1) 5.3(1) 3.91(7) 4.73(8) 5.03(9) 5.5(1) 5.2(1) 4.03(7) 8.4(2) 4.88(9) 4.99(9) 5.9(1) 5.25(9) 10.2(2) 12.5(3) 11.6(3) 7.4(2) 4.49(8) 7.9(2)
aEquivalent isotropic U defined as one-third of the trace of the orthogonalized Uij tensor.
anomalous dispersion corrections for scattering factors were taken from refs 30 and 31, respectively. The structures were solved by standard Patterson and Fourier methods and refined by full-matrix least-squares minimizing the function Cw(F,, - klFc1)2. Weights were assigned t o individual observations according to the formula and the parameters reported in Table 12. Anisotropic thermal parameters were assigned t o all non-hydrogen atoms. Hydrogen atoms were placed in idealized positions (C-H = 0.95 A) and refined riding on their parent atom with a common (refined) isotropic thermal parameter (U = 0.085(4) and 0.116(5) Az for lr and l m , respectively). The structure of l m is affected by a slight disorder of the ethylenebis(1-indenyl) ligand, which seems to be due t o some conformational freedom around the ethylene hinge. We were not able to refine a consistent disordered model, possibly because of the closeness of the separated individual conformers. Hence, in order to favor the convergence toward a stereochemically significant result, the chemically equivalent C-C interactions within the indenyl ligands where restrained (with u of 0.005 A) t o have similar bond distances. The disorder is nevertheless still manifested by the moderately large thermal ellipsoids of the carbon atoms and by the unreasonably short C8-CS’ bond distances. In keeping with the observed disorder, even if does not explain it, the “ordered” stereoisomer is packed more efficiently than the “disordered ones (i.e. lr has a smaller U/Zvalues than lm). The final values of the agreement indices, R and R,, and of maximum residuals in the final difference Fourier synthesis are reported in Table 12. The final positional parameters are reported in Tables 13 and Table 14 for lr and lm, respectively. All the calculations were performed on a Personal IRIS 35 using SHELX.32 OM9407215 (30) Cromer, D. T.; Waber, J. T. International Tables for X-Ray Crystallography; The Kynoch Press: Birmingham, U.K., 1974; Vol. 4, Table 2.2.b (present distributor: Kluwer Academic Publishers, Dordrecht, The Netherlands). (31)Cromer, D. T. International Tables for X-Ray Crystallography; The Kynoch Press: Birmingham, U.K., 1974; Vol. 4, Table 2.3.1 (present distributor: Kluwer Academic Publishers, Dordrecht, The Netherlands). (32) Sheldrick, G. M. SHELX76, Program for crystal structure determination. Univ. of Cambridge, England, 1976.
