749 1
J. Am. Chem. SOC.1982, 104, 7491-7496 [AICI4], 83634-35-9; AICI,, 7446-70-0; [W(NPh)(CHCMe,)(PEt3),C1][A1C1,], 83634-37-1; [W(NPh)(CHCMe,)(PMe,),Me][A1Me2C1,], 83634-39-3; A1Me3, 75-24-1; [W(NPh)(CHCMe,)(PEt,),Me][AIMe,CI,], 83634-41-7; W(NPh)(CHCMe,)(PMe,)(OCMe3)2,83634-42-8; W(NPh)(CHCMe,)(PEt,)(OCMe,),,8363443-9; W(NPh)(CHCMe,)(PEt,)Cl,, 83634-44-0; CuC1, 7758-89-6; W(NPh)(CCMe3)(A1Me2CI)(PMe3)2CI, 83649-38-1; W(NPh)(CH2CMe,),CI, 83634-51-9; NeoC1,753-89-9; W(NPh)(CH2CMe3),Br, 83634-52-0; W(NPh)(CH2CMe3),(OCMe3),83634-53-1; HBr, 1003510-6; W(NPh)(CH2CMe3),(02CCF3), 83634-54-2; CF3C02H,76-05-1; W(NPh)(CH2CMep),(OCMe,)z, 83649-39-2; W(NPh)(CH2CMe3),(OCMe3)CI, 83634-55-3; Zn(Neo),, 54773-23-8; W(NPh)-
(CHCMe3)(CH2CMeJ2,83634-56-4; Ph3PCH2, 3487-44-3; LiNeo, 7412-67-1; W(q5-C5H5)(NPh)(CHCMe3)(CH2CMe3), 83634-45-1; NaC5H5, 4984-82-1; W(q5-CSH5)(NPh)(CH2CMe3),CI, 83634-46-2; Me3PHC1, 55903-13-4; W(NPh)(CHCMe,)(py),CI,, 83664-23-7; W83634(NPh)(CH,SiMe,),CI, 83634-57-5; W(NPh)(CH2SiMe3)2C12, 58-6; Zn(CH,SiMe,),, 41924-26-9; W(NPh)(CH,SiMe,),, 83634-59-7; LiCH2SiMe3, 1822-00-0; Me3SiCH2CI, 2344-80-1; W(NPh)(CHSiMe,)(CH,SiMe,),, 83634-60-0; W(NPh)(CHSiMe,)(PMe,),CI,, 83634-47-3; W(NPh)Me,CI, 83634-61-1; PMe,, 594-09-2; ZnMe2, 544-97-8; W(NPh)Me3(OCMe3),83634-62-2; W(q5-C5H5)(NPh)Me,, 83634-48-4; W(NPh)(CH,Ph),CI, 83634-63-3; P h C H Q , 100-44-7; phenyl isocyanate, 103-71-9; pyHC1, 628-13-7; py, 110-86-1.
Kinetics and Stereochemistry of the Titanacyclobutane-Titanamethylene Interconversion. Investigation of a Degenerate Olefin Metathesis Reaction J. Bosco Lee, Kevin C. Ott, and Robert H. Grubbs* Contribution No. 6639 from the Laboratories of Chemistry, California Institute of Technology, Pasadena, California 91 125. Received April 8, 1982
Abstract: Analysis of the kinetics of the reaction of dicyclopentadienyltitanacyclobutane 3 with diphenylacetylene to produce the dicyclopentadienyltitanacyclobutene7 indicated that the exchange is first order in 3 and zeroth order in Ph-CEC-Ph over a wide range of concentrations. The kinetics and stereochemistry of olefin exchange along with a large secondary isotope effect are consonant with the reaction proceeding via rate-limiting ring opening of 3 to Cp2Ti==CH2and olefin (free or complexed), followed by rapid trapping by incoming olefin or acetylene. The complex 3 and its analogues are effective catalysts for the olefin metathesis reaction of terminal olefins.
Introduction The mechanism of the metal-catalyzed olefin metathesis reaction' has been intensively studied for many years, and a consensus has emerged that metal alkylidenes and metallacyclobutanes are plausible intermediates in this reaction. The syntheses and isolation of metal alkylidene complexes and studies of their reactions with olefins have convincingly demonstrated the intermediacy of such species in metathesis.* In contrast, the evidence for the involvement of the metallacyclobutane intermediates has not been as well documented and is largely indirect. To date, examples of well-characterized complexes in this class are rare, being limited to only a few transition metalse3 Recently, we reported the isolation of a t i t a n a c y ~ l o b u t a n efrom ~ an olefin metathesis system.% In this paper we present detailed studies of (1) For recent reviews on the olefin metathesis reaction, see: Calderon, N.; Lawrence, J. P.; Ofstead, E. A. Adv. Organomet. Chem. 1979, 17, 449. Grubbs, R. H. Prog. Inorg. Chem. 1978,24, 1 . Katz, T. J. Adv. Organomet. Chem. 1977, 16, 283. (2) (a) Tebbe, F. N.; Parshall, G. W.; Ovenall, D. W. J . Am. Chem. Soc. 1979, 101, 5074. (b) Klabunde, U.; Tebbe, F. N.; Parshall, G. W.; Harlow, R. L. J . Mol. Catal. 1980, 8, 37. (c) Tebbe, F. N.; Harlow, R. L. J . Am. Chem. SOC.1980,102,6149. (d) Wengrovius, J.; Schrock, R. R.; Churchill, M. R.; Missert, J. R.; Young, W. J. Ibid. 1980,102,4515. (e) Schrock, R.; Rocklage, S.;Wengrovius, J.; Rupprecht, G.; Fellman, J. J . Mol. Catal. 1980, 8, 73. (3) (a) Adam, G. J. A,; Davies, S . G.; Ford, K. A.; Ephritikhine, M.; Todd, P. F.; Green, M. L. H. J. Mol. Catal. 1980,8, 15. (b) Anderson, R. A,; Jones, R. A.; Wilkinson, G. J . Chem. SOC.,Dalton Trans. 1978, 446. (c) Foley, P.; Whitesides, G. M. J . Am. Chem. SOC.1979, 101, 2732. (d) Tulip, T. H.; Thorn, D. L. Ibid. 1981, 103, 2448. (e) Puddephatt, R. J. Coord. Chem. Rev. 1980, 33, 149. ( f ) Klinger, R. J.; Huffmannn, J. C.; Kochi, J. K. J . Am. Chem. SOC.1982, 104, 2147. (4) (a) Lee, J. B.; Howard, T. R.; Grubbs, R. H. J . Am. Chem. SOC.1980, 102, 6876. (b) Lee, J. E., et al. Ibid. 1981, 103, 7358.
0002-7863/82/1504-7491$01.25/0
the reactions of this class of metallacyclobutanes that are related to the mechanism and stereoselectivity of the olefin metathesis reaction.
Results and Discussion Titanacyclobutane 3, synthesized from the well-defined me-
I-dp -
+
((,),+ D)H
tathesis catalyst 1, undergoes the reactions required of a metathesis intermediate. When 3-d2 was treated with AlMe2C1 (eq l ) , deuterium was incorporated into 1 in a second-order r e a ~ t i o n . ~ Equation 1 represents a reasonable mechanism for the Lewis-acid-catalyzed route for metathesis involving 1 as the chaincarrying species. We now have found that complex 3 is also an ~~
(5) For a detailed examination of the reaction of titanacyclobutanes with aluminum reagents, see: Ott, K. C.; Lees, J. B.; Grubbs, R. H. J . Am. Chem. SOC.1982, 104, 2942.
0 1982 American Chemical Society
1492 J. Am. Chem. SOC..Vol. 104, No. 26, 1982
Lee, Ott, Grubbs Scheme I1
/I
T = 150 mins
=/
-B for monosubstituted 3. When a 13-fold excess of ( Z ) - a methylstyrene-dl was allowed to exchange with 5 (eq 3), the 6
2
4
Q ppm
Figure 1. 2HNMR spectra (76.77 MHz) of the reaction
-5
-5 - d ,
o b Scheme I
(3 1
cpzTtY 4 -
T D
i
deuterated E and Z metallacyclobutanes were observed to appear along with (E)-a-methylstyrene-dl. Reaction was complete within 4 h at 0 "C. The initial rate of exchange was measured to be 1.2 turnovers per minute per Ti. It is significant to note that the catalysis is accomplished without the addition of a cocatalyst. To the best of our knowledge, these are the first examples of metathesis reactions catalyzed by a metallacyclobutane. Other olefins have been found to exchange with 3 and 4, to yield the analogous metallacyclobutanes (eq 4, 5). The position of
p
D
effective catalyst for the methylene exchange of monosubstituted terminal olefins in the absence of A1Me2Cl. Thus, 3 catalyzes the degenerate metathesis of 3,3-dimethyl-l-butene (2-d0) and 3,3-dimethyl-1-butene-1 ,1,2-d3 (2-d,) (eq 2). o * + >
A
D
+
p
(
2
)
All of the intermediate labeled metallacyclobutanes and olefins are observable by N M R spectroscopy, and the olefins are also analyzed by G C / M S . For example, an equimolar solution of 3 and 2-d2 was heated to 40 OC and examined periodically by 2H N M R spectroscopy. The spectra (Figure 1) show depletion of deuterated olefin and incorporation of deuterium into the cis and trans a positions of the metallacyclobutane (6 1.86 and 2.17, respectively) in equal amounts. The exchange of methylene groups is extensive after 4 h at 40 "C. Thus, the stepwise exchange of labeled and unlabeled 2 can be represented by the catalytic cycle depicted in Scheme I. In the series of p,p-disubstituted metallacyclobutanes such as 4 and 5, analogous exchange reactions are observed but typically occur much more rapidly and at lower temperatures (
