1136
J . A m . Chem. SOC.1983, 105, 1136-1143
Structure and Reactivity of Bis( pent amet hylcyclopent adienyl)( ethylene)titanium(I I), a Simple Olefin Adduct of Titanium Steven A. Cohen, Pamela R. Auburn, and John E. Bercaw*’ Contribution No. 6651 from the Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91 125. Received May 24, 1982
Abstract: The synthesis and an X-ray diffraction study of bis(pentamethylcyclopentadienyl)(ethylene)titanium [(aC5Me5),Ti(&,H4)] a r e reported. This complex represents the first example of an isolable ethylene adduct of titanium. Titanium-olefin complexes have been widely invoked as key intermediates in Ziegler-Natta olefin polymerization schemes. Whereas treatment of ( T & M ~ ~ ) ~ T ~ ( ~ C , H , with ) ethylene leads to only traces of polymer after months, (&Me5),Ti(a-C,H4) participates in a range of stoichiometric and catalytic reactions. These include the catalytic conversion of ethylene specifically to butadiene and ethane and the catalytic isomerization of alkenes.
O r g a n o t i t a n i u m chemistry has been a very active area of research since t h e first reports t h a t mixtures of TiCI3 and trialkylaluminum a r e active catalysts for t h e polymerization of ethylene and t h e formation of highly ordered polymers of t h e a - o l e f i n ~ . ~In* view ~ of t h e scientific and commercial importance of olefin polymerization, significant effort has been directed toward t h e elucidation of t h e mechanism(s) of Ziegler-Natta-type catalysis. Although a number of substantially different mechanisms have been formulated: t h e reaction is generally believed to occur via coordination of an olefin t o an alkyltitanium complex, which then undergoes olefin insertion (or alkyl migration) t o generate a new alkyltitanium specie^.^^^ A key feature common t o virtually all schemes is t h e proposed intermediacy of a titanium-olefin P complex. In this connection, it is significant t h a t a simple olefin a d d u c t of titanium has heretofore not been isolated and fully
C 5 M e 5 ) , Z r H ( q - C H 2 C H C H R ) where R = H, Me.” Our investigations on t h e interactions of olefins with bis(pentamethylcyclopentadienyl)titanium(II) have led to t h e preparation of t h e olefin complex ( ~ - C 5 M e 5 ) , T i ( ~ - C , H , ) . W e report herein t h e results of an X-ray structure determination of this compound a n d some of t h e features of its reactivity.
Experimental Section
General Considerations. All manipulations were performed by using glove-box or high-vacuum techniques. Argon, nitrogen, and hydrogen were purified by passage over MnO on vermiculite and activated Linde 4A molecular sieves. Solvents were purified by vacuum transfer, first from LiA1H4 and then “titanocene”.I2 Benzene-d, and toluene-d8 (Aldrich, Stohler) were dried over molecular sieves and vacuum transferred from “titanocene”. Ethylene, propene, cis-2-butene, I-butene, tram-2-butene, I-hexene, and HC1 (anhydrous) were freeze-pump-thaw characterized. degassed at least twice at -196 OC. Carbon monoxide (Matheson) was Evidence for olefin complexes of zirconium has been presented. used directly from the cylinder. Ethylene-’)C, (90% I3C, Merck, Sharp Addition of ethylene t o Zr(CH2SiMe3)4produces low concen& Dohme, Ltd.) and ethylene-d4(98% D, Stohler) were freeze-pumpthaw degassed at -196 OC and distilled at -78 OC. Methyl iodide trations of an olefin a d d u c t of unknown structure.6 Dimeric (MC&B) was vacuum transferred from CaH,. complexes in which an olefin bridges two formal Zr(II1) moieties Propene-d, (>99% D) was prepared by reduction of (CD3),C0 have been m o r e fully characterized: [(q-C5H5),ZrC1],(~(Stohler, 99.5% D) to (CD3),CDOD by using NaBD, (Stohler, 99% t h e results C H P h C H P h ) 7 and [ZrC1,(PEt3)2]2(~-CH2CHMe);8 D)/NaOD in D 2 0 (Stohler, 99.8% D) followed by dehydration over of an X-ray diffraction s t u d y of one such complex, [ ( q D,O-washed A1203at 300 “C.” Methyl isocyanide was prepared by C5H5)2ZrC1]2(c(-CH2CH2), has been r e p ~ r t e d . ~The ethylene literature procedure^,'^ freeze-pump-thaw degassed, and vacuum complex (q-C5Me5)2Zr(&H4) is strongly implicated as an imtransferred from molecular sieves. [(q-CsMes)2Ti]z(pN2)and (7portant but unobserved intermediate in t h e ethylene-promoted C,MeS),Ti(CH3), were prepared by previously reported methods.15 was prepared by the procedure given in ref 15a with the Hreductive elimination of i s o b u t a n e from ( T - C ~ M ~ ~ ) ~ Z ~(q-CSMe5)2TiC12 following modifications: LiCsMe, was used in place of NaC,Me, and (CH2CHMe2),I0while existence of the corresponding propene and the resulting mixture of TiCI3/LiC,Me5 in T H F was heated at reflux for butene intermediates is suggested by the reactivity and fluxional 3 days. behavior observed for the zirconium allyl hydride complexes (7‘H, ,H, and 13C N M R spectra were recorded on Varian T-60 and EM-390, JEOL FX90Q, and Bruker WM-500 spectrometers. Spectra (1) Camille and Henry Dreyfus Teacher-Scholar, 1977-1982. were taken in benzene or toluene solutions, and data are referenced to (2) (a) Ziegler, K. Belgium Patent 533 362, 1953. (b) Natta, G.; Pino, P.; Me4Si at 6 0. Infrared spectra were obtained on Beckman IR-12 and Corradini, P.; Danusso, F.; Mantica, E.; Mazzanti, G.; Moraglio, G. J . Am. 4240 spectrophotometers. Spectra of solids were recorded as Nujol mulls Chem. SOC.1955, 77, 1708. in KBr plates; spectra of gases were measured with a IO-cm path length (3) Pino, P.; Mulhaiipt, R. Angew. Chem., Int. Ed. Engl. 1980, 19, 857 cell (NaC1 windows) fitted with a stopcock and ball joint for attachment and references therein. to a vacuum line. Mass spectrometric data were obtained on a Du Pont (4) (a) Other mechanisms involving metallacy~lopentanes~~ and alkylidene hydride“ intermediates have been proposed. (b) McKinney, R. J. J . Chem. 21-492 mass spectrometer and a Kratos MS-25 GC-MS. Hydrocarbon SOC.,Chem. Commun. 1980, 491. (c) Ivin, K. J.; Rooney, J. J.: Stewart, C. gases were analyzed on a Varian 940 gas chromatograph equipped with D.; Green, M. L. H.; Mahtab, J. R. Ibid. 1978, 604. a thermal conductivity detector with a 12-ft 13% DBT (dibutyl tetra(5) (a) Cossee, P. J. Catal. 1964, 3, 80. (b) Arlman, E. J. J . Catal. 1964, chlorophthalate) on Chromosorb W column. Molecular weights were 3, 89. (c) Arlman, E. J.; Cossee, P. Ibid. 1964, 3, 99. (d) Boor, J. ‘Ziegler-Natta Catalysis and Polymerization”;Academic Press: New York, 1978. ( e ) Watson, P. L. J . Am. Chem. SOC.1982, 104, 337. (11) (a) Sanner, R. D. Ph.D. Dissertation, California Institute of Tech(6) Ballard, D. G. H.; Burnham, D. R.; Twose, D. L. J . Catal. 1976, 44, 116. nology, 1978. (b) Erwin, D. K. Ph.D. Dissertation, California Institute of Technology, 1979. (7) Wailes, P. C.; Weigold, H.; Bell, A. P. J . Organomet. Chem. 1971, 27, 373. (12) Marvich, R. H.; Brintzinger, H. H. J . Am. Chem. SOC.1971, 93, 21148 (8) Wengrovius, J. H.; Schrock, R. R.; Day, C. S.Inorg. Chem. 1981, 20, _ _ _. 1844. (13) Dehydration based on procedure from: Goudet, H.: Schenker, F . (9) (a) Sinn, H.; Kolk, E. J . Organomet. Chem. 1966, 6, 373. (b) KaHelu. Chim. Acta 1927, 10, 132. minsky, W.: Kopf, J.; Sinn, H.; Vollmer, H.4. Angew. Chem., Int. Ed. Engl. (14) Ugi, I.; Fetzer, U.; Eholzer, U.; Knupfer, H.; Offerman, K. Angew. 1976, 15, 629. Chem., Inr. Ed. Engl. 1965, 4, 472. (15) (a) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J . (IO) McAlister, D. R.; Erwin, D. K.; Bercaw, J. E. J . Am. Chem. SOC. Am. Chem. SOC.1972, 94, 1219. (b) Bercaw, J . E. Ibid. 1974, 96, 5087. 1978, 100, 5966.
0002-7863/83/1505-1136$01.50/0
0 1983 American Chemical Society
J . Am. Chem. Soc., Vol. 105, No. 5, 1983 1137
Bis(pentamethylcyc1opentadienyl)(ethylene)titanium(lI) determined cryoscopically or by osmometry. Elemental analyses were performed by Alfred Bernhardt Analytical Labs, West Germany. Procedures. (q-CSMe5)2Ti(~-C2H4) (2). Sodium amalgam (300 g, 0.9% w/w) was added via syringe to an argon-blanketed toluene slurry ~ C I , g, 8.73 mmol). The argon atmo(150 mL) of ( T ~ C , M ~ , ) ~ T (3.40 sphere was replaced with ethylene and maintained at ca. 700 torr while the mixture was stirred for 72 h. The resulting yellow-brown solution was filtered, and the toluene and excess C2H4were removed in vacuo to yield the crude product. Recrystallization from petroleum ether afforded 2.5 g (80%) of bright green 2: IR 3657 (m), 3042 (s), 2981 (s),* 2963 (m),* 2935 (m),* 2904 (vs),* 2858 (s),* 2721 (m), 1490 (m), 1435 (m),* 1377 (vs),*, 1163 (w). 1127 (w). 1077 (vs), 1060 (w), 1023 (s), 875 (m), 802 (w), 749 (m), 668 (m), 627 (w), 612 (w), 581 (2), 538 (m),500 (w), 465 (w), 413 (s) cm-' (*measured in Halocarbonoil); IH N M R 6 C5(CH3),, 1.68 (s); C2H4, 2.02 (s); I3C N M R (mult, I h 3 ~ + in Hz) 6 C,(CH3),, 119.8 (s); CS(CH3),. 11.9 (q, 125); C2H4, 105.1 (t, 143.6). Anal. Calcd for C22H34Ti:C, 76.28; H, 9.89; mol wt (osmometry in C&), 346. Found: C , 76.14; H, 9.84; mol wt, 334. (q-C5Me5)2Ti(~-'3CH2"CH2) (2-I3C2).Ethylene-"C2 (0.267 mmol) was condensed at -196 OC onto a frozen solution of [(q-CsMe,)2Ti]2N2 (90 mg, 0.13 mmol) in 5 mL of toluene. The mixture was warmed to 25 OC and stirred for 20 min. The deep blue solution was frozen at -196 OC and the N 2 removed in vacuo. The mixture was warmed to 25 OC and stirred for an additional 10 min. Solvent was removed in vacuo from the light green solution to yield 90 mg of 2-I3C2(96%): I R 3682 (vw), 3664 (vw), 3033 (s), 2725 (m), 1493 (m), 1165 (w), 1061 (s), 1047 (vs), 1024 (s), 867 (m), 805 (m), 666 (m), 641 (m), 615 (w), 591 (w), 570 (m), 551 (w), 490 (m), 415 (s), 375 (w) cm-I. ( Q - C ~ M ~ ~ ) ~ T ~ ( (~2-4C, )~. DEthylene-d4 ,) (0.3 mmol) and 5 mL of toluene were condensed at -196 " C onto [(q-C5MeS)2Ti]2NZ (50 mg, 0.075 mmol). The mixture was warmed to 0 OC and stirred for 20 min at that temperature. Toluene, N2, and excess C2D4were removed in vacuo. The green crystalline 2-d4 was stored at -30 OC to minimize H-D scrambling: IR 3675 (vw). 3620 (vw), 2722 (m), 2280 (m), 2190 (m), 2159 (m), 2078 (w). 2000 (w). 1979 (vw),1965 (m),1946 (w), 1731 (m), 1536 (vw), 1489 (m), 1185 (m), 1161 (w), 1146 (w), 1097 (m), 1023 (s), 932 (m),902 (w), 637 (w), 625 (vw), 615 (w), 591 (w), 564 (w), 549 (vw), 515 (s), 458 (m), 395 (m), 367 (w) cm-I. 2 CO. Excess C O (0.5 mmol) was partially condensed at -196 OC into an N M R tube containing a frozen solution of 2 (29 mg, 0.08 mmol) in 0.4 mL of toluene-d,. The tube was sealed and the reaction monitored between -78 and -20 OC by IH and I3C N M R . The rate of formation of (a-C,Me5)2Ti(C0)2(4) and C2H4appears to be limited by the solubility of 2 in cold toluene, but the reaction was complete after 3 h at -30 OC. 2 + CH3NC. Methyl isocyanide (0.11 mmol) was condensed at -196 OC into an N M R tube containing a frozen solution of 2 (37 mg, 0.1 1 mmol) in 0.4 mL of toluene-d8. The tube was sealed and the reaction monitored between -78 and -10 OC. After 1 h at -50 OC, the solution contained 0.5 equiv of unreacted 2, 0.5 equiv of C2H4,and 0.5 equiv of ( v - C ~ M ~ , ) , T ~ ( C N C H(5) , ) ~(IH and I3C N M R ) . Above 0 OC, 5 was found to be unstable in solution or as a solid, decomposing to a number of unidentified products with liberation of some free CH3NC: IH N M R 6 C,(CH,),, 1.80 (s); CNCH,, 2.90 (s); 13CN M R 6 CS(CH3),,106.2 (s); C5(CH3)5, 12.1 (q, 125); CNCH3, 38.3 (q, 140). 2 + H1. Hydrogenation of 2 was carried out by a procedure similar to that given for 2 + CO. The formation of (q-CSMe5)2TiH2(7) and C2H6 was complete after 2 h at -50 OC. 2 HCI. Hydrogen chloride (0.208 mmol) was condensed at -196 OC into an N M R tube containing a frozen solution of 2 (34 mg, 0.10 mmol) in 0.3 mL of toluene-d,. The tube was sealed, and immediately upon warming to -78 OC, a reaction occurred, yielding ethane and a purple-red solid identified as ( v - C , M ~ , ) ~ T ~(IH C I ~N M R ) . 2 + CH31. Methyl iodide (0.58 mmol) was condensed at -78 OC onto a frozen solution of 2 (38 mg, 0.1 1 mmol) in benzene-d6 (0.3 mL). The mixture was warmed to 80 OC for 90 min to yield (q-CSMe5)2TiI(CH3) (8) and (q-C5Mes)2Ti(CH3)2( 6 ) in a ratio of ca. 90:5 and ethylene (0.92 mol/mol2, 'H NMR). Other attempts to prepare 8 resulted in materials that were 85-95% pure after recrystallization: 'H N M R (8) 6 CS(CH3),. 1.86 ( s ) ; CH3, -0.41 ( s ) . (q-C,Me,),TiCI (9). Toluene-d, (0.8 mL) and ethylene (0.3 mmol) were condensed at -196 " C into an N M R tube containing 55 mg of 1 (0.14 mmol) and 50 mg of 2 (0.14 mmol). The tube was sealed and the sample heated at 85 "C for 1 h. The N M R tube was broken, and the resulting slurry was dried in vacuo to yield a deep blue solid (80 mg), identified by IR as the previously describedI6 (q-C5Me5),TiC1. Paramagnetic 9 is also formed during the preparation of 2 by partial reduction of 1. A toluene solution of 9 (0.06 mmol in 7 mL) was treated with
5
/
1
1
"
"
"
]
I / :::I 0.I
0'0, 51 i 0.02
0 01
26
28
30
Figure 1. Temperature dependence of 2
32
34
+ C2H4 + 10.
Z 0040 E
I
I
I-
*P N
Y
+
+
(16) deBoer, E. J. M . Ph.D. Dissertation, University of Groningen, 1979.
Figure 2. Equilibrium measurement of 2
+ C,H,
+ 10 at 34 OC
ethylene (0.130 mmol) at 25 OC for 30 min, then cooled to -78 OC, and stirred an additional 60 min. The residual gases were passed through two -78 OC traps, and 0.133 mmol of gas was collected via a Toepler pump.
2 + C2H4 + ( T ~ C , M ~ , ) , T ~ C H ~ ( C H(10). ~ ) ~ CToluene-d, H~ (0.5 mL) and ethylene (0.710 mmol) were condensed at -196 OC into a N M R tube containing 2 (22.2 mg, 0.0641 mmol) and ferrocene (67.4 mg, 0.364 mmol). The N M R tube was sealed and (21, [IO], and [C2H4] were measured by 'H N M R as a function of temperature from 25 to 75 OC
(Figure 1). Since the equilibrium (Figure 2) favors 2 + C2H4over 10 at available [C2H,], 10 could not be isolated. The metallacyclopentane 10 was characterized by its chemical reactivity as well as by ' H and I3C N M R spectroscopy: 'H N M R 6 C,(CH3),, 1.80 (s); CH2(CH,)2CH2, 0.60 (m); CH2(CH2),CH,, 1.72 (m); I3C N M R 6 C5(CH3)5,120.7 (s); C5(CH3),, 12.j (q, 125); d 2 ( C H 2 ) , C H 2 ,62.4 (t, 123); CH2(CH2)2CH2, 32.8 (t. 1221; 'J(13C,-'3CCn) = 29 Hz. 2 10 HCl. TolueAe (50 mL) and ethylene (13.2 mmol) were condensed at -196 OC onto 2 (50.5 mg, 0.146 mmol) contained in a thick-walled glass vessel fitted with a Teflon needle valve. The mixture was allowed to warm to 25 OC and was stirred overnight. The resulting orange-brown solution was cooled to -78 "C, and excess ethylene was removed in vacuo. Anhydrous HCl(O.784 mmol) was condensed at -196 OC onto a frozen solution of 2 and 10. The reaction occurred immediately upon warming the mixture to -78 OC. Residual gases were condensed at -196 OC onto a frozen solution of N a O H (120 mg) in 1 mL of H 2 0 , and the mixture was warmed to 25 OC. The remaining gas was identified as a 60:40 mixture of ethane and butane (IH NMR). Isomerization of 1-Butene by 2. An N M R tube was charged with 0.5 mL of a benzene-d6 stock solution containing 2 (61.6 iz 0.2 mg/mL, 0.178 M) and ferrocene (54.6 i 0.7 mg/mL, 0.293 M) and cooled to -196 'C. 1-Butene (0.92 mmol) was condensed onto the frozen solution, and the tube was sealed. The sample was heated in an oil bath at 61 "C, and the reaction was monitored as a function of time by ' H N M R . Additional samples, which contained varying amounts of 1-butene and added C2H4. were prepared to monitor the isomerization at 61, 72, 81, and 106 'C (Figure 3 ) . Isomerization of Propene and Propene-d6 by 2. An N M R tube containing 2 (50 mg, 0.14 mmol), C3H6(0.263 mmol), C3D6(0.138 mmol), and C6H6(0.40 mL) was sealed at -196 OC and heated to 81 OC. The
+
+
1138 J . Am. Chem. SOC.,Vol. 105, No. 5, 1983
Cohen, Auburn, and Bercaw m
m
I I
I
I
Figure 4. (a) Eclipsed ring model and (b) partially staggered ring model. Labels refer to crystallographically independent atoms.
-0
10
20
30
40
Figure 3. Ethylene concentration dependence of 1-butene isomerization reaction at 106 OC. Table 1. Crystal Data C,,H,'ITi
a, 10.8621 (4) A
c. 8.5008 (5) X
V , 1002.97 (8) A 3 292
tetragonal space group ~ 4 2m, pexptl, 1.15 i 0.05 g ~ m ' ~ P c d c d , 1.147 g h (Mo K a ) , 0.71069 A p , 4.42 cm-'
reactants were monitored for H-D exchange by 2H N M R (13.7 MHz). Samples for monitoring the reaction at other temperatures as well as blanks were similarly prepared. In a separate experiment, the possibility of H-D exchange between 2 and C3D6was checked by 'H N M R and IR spectroscopy. Exchange was observed to be much slower than H-D exchange between C3H6 and C3D6catalyzed by 2. Conversion of Ethylene to 1,3-Butadiene and Ethane Catalyzed by 2. Benzene-d, (0.5 mL), ethylene (0.543 mmol), and ethylene-I3C2(0.067 mmol) were condensed at -196 'C into an N M R tube containing 2 (60 mg, 0.17 mmol). After the tube was sealed, the sample was warmed to 25 OC and monitored by IH and "C N M R . Over a 10-month period, the intensities of the C2H4and (q-CSMeS)2TiCH2(CH2)2CH2 (10) resonances diminished as the resonances identified as 1,3-butadiene and ethane appeared and slowly increased. The total concentration of titanium species, [2 + IO], remained constant throughout. The tube was opened under vacuum, the volatile contents passed through two -78 OC cold traps, and 0.357 mmol gas (0.156 mmol of C4H6and 0.201 mmol of C2H6by IH NMR, MS) collected via a Toepler pump. The remaining solid in the tube was washed with petroleum ether and filtered to afford ca. 1 mg of polyethylene (IR). A sample containing 1-butene (0.062 mmol), 2 (30 mg, 0.087 mmol), C2H4(0.715 mmol), and toluene-d, (0.52 mL) was prepared and allowed to react at 25 'C. After 5 months, ethane and butadiene (ca. 0.07 mmol each) were observed, but no measurable changes (
