818
Organometallics 1988, 7, 818-825
F%(CO)9,15321-51-4;Fe(C0)5,13463-40-6;LiHB(Et)3,22560-16-3; (E)-cyclooctene,931-89-5. Supplementary Material Available: Detailed information on the crystal structure determination of 1 and 3 including tables
of final atomic positional parameters, final anisotropic thermal parameters, interatomic distances,and bond angles (10 pages); lists of observed and calculated structure factors for 1 and 3 (24 pages). Ordering information is given on any current masthead page.
Activation of Benzene Carbon-Hydrogen Bonds via Photolysis or Thermolysis of (q5-C,Me,),Zr(alkyl)H. Isolation of (q5-C5Me,),Zr(C6H,)H and Its Conversion to a Complex Containing a Tetramethylfulvene Ligand Frederick D. Miller and Robert D. Sanner"' Department of Chemistry, Arizona State University, Tempe, Arizona 85287- 1604 Received April 14, 1987
A new high-yield synthesis of Cp*,ZrHz (Cp* = q5-C5Me5)is described, and olefin insertion into its Zr-H bond is used to prepare several new Cp*,Zr(alkyl)H complexes. Photolysis or thermolysisof Cp*,Zr(alkyl)H in benzene yields the iespective alkane by intramolecular reductive elimination of the cis alkyl and hydride ligands, as well as the benzene C-H bond activation product Cp*,Zr(C6H5)H. Photochemically induced reductive elimination is also observed for Cp*,Zr(C6H5)Hand Cp*,ZrHz. Deuterium-labeling experiments show that hydrogen exchange between the hydride and Cp* methyl groups occurs in both CP*~Z~(H)CH2CH(CH3)zand Cp*,Zr(C6H5)H. An additional exchange process in C P * ~ Z ~ ( C ~ H involves ~ ) H the hydride ligand and an ortho phenyl hydrogen atom. Thermolysis of Cp*,Zr(C6H5)Hin benzene causes quantitative evolution of dihydrogen and reversibly forms the tetramethylfulvene complex Cp*(t16-C5Me4CH2)Zr(C6H5). Reaction of this compound with iodine produces the Cp* ring substituted phenyl iodide Cp*(q5C5Me4CH21)Zr(C6H5)I. Several of the transformations involving Cp*,Zr(C6H5)Hare believed t o proceed via &-hydrogenelimination from the phenyl group to yield a benzyne dihydride intermediate.
Introduction In recent years, the activation of carbon-hydrogen bonds has attracted considerable interest.2 Early work in this area, notably Green's studies with tungstenocene comp l e ~ e sdemonstrated ,~ the utility of transition-metal compounds in the activation of aromatic C-H bonds. Bergman's preparation4 of iridium alkyl hydride complexes via intermolecular oxidative addition of aliphatic carbon-hydrogen bonds was an important discovery since this is a crucial step in the functionalization of saturated hydrocarbons. Further work by Bergman,4,5Jones? and Gra(1)Present address: Lawrence Livermore National Laboratory, Mail Code L-325,Livermore, CA 94550. (2)Crabtree, R.H. Chem. Rev. 1985,85,245.Ephritikhine, M. N o w . J. Chim. 1986,100,41. Saillard, J. Y.;Hoffmann, R. J. Am. Chem. SOC. 1984,106,2006. Low, J. L.; Goddard 111, W. A. Organometallics 1986, 5,609.Parshall, G. M. Homogeneous Catalysis; Wiley: New York, 1980; p 179. (3)Green, M. L. H. Pure Appl. Chem. 1978,50,27. Cooper, N.J.; Green, M. L. H.; Mahtab, R. J . Chem. SOC., Dalton Trans. 1979,1557. Berry, M.; Elmitt, K.; Green, M. L. H. J. Chem. SOC.,Dalton Tram. 1979, 1950. (4)Janowicz, A. H.; Bergman, R. G. J. Am. Chem. SOC. 1979,104,352. 1983,105,3929. (5)Janowicz, A. H.;Bergman, R. G. J.Am. Chem. SOC. Janowicz, A. H.; Periana, R. A.; Buchanan, J. M.; Kovac, C. A,; Stryker, J. M.; Wax, M. J.; Bergman, R. G. Pure Appl. Chem. 1984, 56, 13. Perlana, R.A.; Bergman, R. G. Organometallics 1984,3,508.Bergman, R. G.; Seidler, P. F.; Wenzel, T. T. J.Am. Chem. SOC. 1985,107,4358. Buchanan, J. M.; Stryker, J. M.; Bergman, R. G. J. Am. Chem. SOC. 1986, 1986,108, 108,1537.Wenzel, T.T.;Bergman, R. G. J.Am. Chem. SOC. 1986,108,7332. 4856. Periana, R.A.;Bergman, R. G. J. Am. Chem. SOC. 1984, 106, 1650. (6)Jones, W.D.;Feher, F. J. J. Am. Chem. SOC. Jones, W. D.;Feher, F. J. J . Am. Chem. SOC. 1985,107,620. Jones, W. D.;Feher, F. J. J. Am. Chem. SOC. 1986,108,4814.Jones, W. D.; Fan, M. Organometallics 1986,5, 1057.
0276-7333/88/2307-0818$01.50/0
ham7 has broadened the scope of this oxidative addition reaction to include other metals such as rhodium and rhenium. In addition to these intermolecular hydrocarbon reactions, transition metals are also known to insert into the C-H bonds of coordinated ligands; phosphines are notably prone to such behavior.8 Even the usually inert cyclopentadienyl group is susceptible to attack, especially in its early-transition-metal complexe~.~ However, use of the pentamethylcyclopentadienyl ligand (q5-C5Me5,usually called Cp*) can often circumvent this problemlo although a few reports of metal-ligand reactions have appeared. The most common pathway for these reactions involves intramolecular insertion of the transition metal into a methyl C-H bond on the Cp* ring, which results in conversion of q5-C5Me5into q6-C5Me4CH,. (In this paper we will refer to this ligand as "tetramethylfulvene" although this is not meant to imply a particular resonance form or bonding mode for the q6-C5Me4CH2moiety.) Such reversible transformations have been proposed to explain the reactions of some early-transition-metalcompounds'lJ2 and (7)Hoyano, J. K.;Graham, W. A. G. J. Am. Chem. SOC. 1982,104, 3723. Hoyano, J. K.;McMaster, A. D.; Graham, W. A. G. J . Am. Chem. SOC.1983,105,7190. ( 8 ) Collman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Vailey, CA, 1980;p 213. (9)Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J. Am. Chem. SOC. 1972,94,1219. Berry, M.; Cooper, N. J.; Green, M. L. H.; Dalton Trans. 1980,29. Gell. K.I.: Harris. SimDson, S. J. J . Chem. SOC., T. v.; Schwartz, J. Inorg. Chem. 1981,20, 481. (10)Bercaw, J. E. J . Am. Chem. SOC.1974,96, 5087.
63 1988 American Chemical Society
Actiuation of Benzene Carbon-Hydrogen Bonds
Organometallics, Vol. 7, No. 4 , 1988 819
a few tetramethylfulvene complexes have been is~lated.’~~’~conditions, slowly decomposing to a 1:l mixture of Cp*,ZrH, and an unidentified organometallic productlg In this paper, we report our work in the area of carwith concomitant evolution of propane (produds identified bon-hydrogen bond activation using permethylzirconocene by NMR). The rate of this decomposition was found to complexes. We have observed the activation of hydroincrease with temperature, and in a sealed NMR tube carbon solvents and coordinated Cp* ligands and have experiment (benzene-d6)the reaction was two-thirds comisolated and fully characterized the products of both these plete after 46 h at 45 OC. Upon continued thermolysis to processes. Furthermore, the choice of inter- or intramoforce the reaction to completion, decomposition into a lecular activation is dependent on whether light or heat mixture of secondary products was observed. is used as the reaction stimulus. Photoreactions. Upon blacklight photolysis in benzene Results and Discussion solution, the permethylzirconocene alkyl hydrides evolve their respective alkanes. In the case of the isobutyl hySynthesis of Cp*,ZrH, and Cp*,Zr(R)H. Cp*,ZrH2 dride, the gas was quantitatively collected by means of a was first reported in 1976 and was prepared in 50-60% Toepler pump, yielding 0.996 mmol of isobutane/mmol of yield by the two-step reaction shown below (eq 1 and 2).14 Cp*,Zr(H)CH2CH(CH3),. The major organometallic WHg product (greater than 90% yield by NMR) produced in 2Cp*,ZrC12 (Cp*,ZrN2),N2+ 4NaCl (1) N2 these reactions is Cp*2Zr(C6H5)H(2) which may be isolated as a pale yellow solid in 65% purified yield (eq 6). An Hz (Cp*,ZrN2),N2 2Cp*,ZrH2 + 3N2 (2) hu Cp*,Zr(R)H Cp*,Zr(C6H5)H+ RH (6) la-c benzene We report herein a new high-yield synthesis of Cp*,ZrH2 2 utilizing the high pressure hydrogenation of the known R = Et, Pr, i-Bu Cp*,ZrMez15 (eq 3 and 4). Similar reactions have been alternate preparation of 2 utilizes the metathesis reaction Cp*,ZrC12 + 2MeLi Cp*,ZrMe, 2LiC1 (3) (eq 7); a similar procedure has been reported for the H2(50-100 atm) hafnium analogue20 Analytical, mass spectral, and ‘H Cp*,ZrMe2 Cp*,ZrH2 + 2CH4 (4) Cp*,ZrH2 + C6H5Li Cp*,Zr(C,H,)H +LiH (7) used successfully in the preparation of other metal hyNMR data are entirely consistent with the formulation of drides,16 and in the present case 85-90% yields of the 2 as the phenyl hydride complex of permethylzirconocene. dihydride were realized on the basis of Cp*2ZrC12. HyFurther support for this formulation is given by its condrogenation with 1 atm of dihydrogen is unsuccessful, version to Cp*,Zr(C6H5)Iwith evolution of methane upon leading only to slow conversion of Cp*,ZrMe2 to an untreatment with methyl iodide. Apparently light is required identified product. to induce alkane formation in these reactions since benzene The alkyl hydrides Cp*,Zr(R)H were prepared by olefin solutions of the alkyl hydrides remain unchanged in the insertion into a Zr-H bond of Cp*,ZrH2. This method, dark.21 If the photochemical reactions are performed using isobutene, has previously been employed to prepare under vacuum, the resultant solutions are yellow-brown Cp*,Zr(H)CH2CH(CH3), (la)15which (to date) is one of in color. If, however, a benzene solution of the isobutyl only two reported alkyl hydrides of permethylhydride is photolyzed in the presence of excess dinitrogen zirconocene.17 Even in the presence of excess isobutene, (1atm), a permanganate colored solution is formed. NMR reaction with a second equivalent is not observed, apanalysis indicates the presence of Cp*,Zr(C6H5)H(2) and parently for steric reasons. In contrast, the corresponding the known dinitrogen complex (Cp*,ZrN2),N214as well as reaction with excess ethene yields ethane and a zirconaseveral other unidentified products. The reaction shown ~yclopentane.’~ However, we have found that addition of in eq 6 represents, to our knowledge, the first example of only 1 equiv of ethene to a Cp*,ZrH2 solution leads to photochemically induced reductive elimination of alkane quantitative formation of Cp*,Zr(CH,CH,)H (lb) within from solutions of a monomeric alkyl hydride complex. minutes at 25 OC (eq 5). Interestingly, while the ethyl and Puddephatt,, has previously reported photochemical elimination of methane from the “A-frame” species Cp*,ZrH2 + CH2=C(R)R’ Cp*,Zr[CH,CH(R)R’]H la, R = R’ = CH, [Pt,Me,(p-H) (p-dppm),][PF,], and P e r ~ t z has , ~ described lb, R = R’ = H the photolysis of Cp2W(CH3)Hat 20 K in an Ar matrix IC, R = CHB,R’ = H wherein Cp,W and methane were detected. Finally, (5) Greenu has noted that photolysis of Cp2W(C6H5)H in C6D6 did not lead to H/D exchange, suggesting that no reductive isobutyl hydrides are stable in benzene solutions at 25 OC, elimination took place. the n-propyl hydride is thermally unstable under these We have also found that the phenyl hydride complex 2 undergoes reductive elimination photochemically. Thus, (11)Bercaw, J. E. Adu. Chem. Ser. 1978,No. 167,136. a sample of 2 in benzene-d6 solution is quite stable, and (12)McAlister, D. R.;Erwin, D. K.; Bercaw, J. E. J.Am. Chem. SOC.
-
-
-
+
-
-
1978,100,5966. (13)Manriquez, J. M.; Bercaw, J. E. J.Am. Chem. SOC. 1974,96,6229. Cloke, F. G.N.;Green, J. C.; Green, M. L. H.; Morley, C. P. J.Chem. Soc., Chem. Commun. 1985,945. McDade, C.; Green, J. C.; Bercaw, J. E. Organometallics 1982,1, 1629. (14)Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. Am. Chem. SOC.1976,98, 6733. Manriquez, J. M.; McAlister, D. R.; Rosenberg, E.; Shiller, A. M.; Williamson, K. L.; Chan, S. I.; Bercaw, J. E. J.Am. Chem. SOC. 1978,100,3078. (15)Manriquez, J. M.; McAlister, D. R.; Sanner, R. D.; Bercaw, J. E. J. A m . Chem. SOC.1978,100, 2716. (16)Wolczanski, P. T.; Bercaw, J. E. Organometallics 1982,1, 793. Mayer, J. M.;Bercaw, J. E. J. Am. Chem. SOC.1982,104,2157. (17)The neopentyl hydride has recently been synthesized by an alternate route. Wochner, F.; Brintzinger, H. H. J. Organomet. Chem. 1986,309,65.
(18)An analogous reaction has recently been used to prepare the alkyl hydrides of permethylhafnocene. See ref 20. (19)A possible but unconformed formulation for this product is a zirconacyclobutane. See ref 27. (20)Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hillhouse, G. L.; Bercaw, J. E. Organometallics 1985,4,97. (21)The n-propyl hydride is thermally unstable and slowly decomposes under these conditions, but Cp*,Zr(C6H5)H is not produced. (22)Brown, M. P.; Cooper, S. J.; Frew, A. A.; Monojlovic-Muir, L.; Muir, K. W.; Puddephatt, R. J.; Thomson, M. A. J. Chem. SOC., Dalton Trans. 1982,299. (23)Chetwynd-Talbot, J.; Grebenik, P.; Perutz, R. N. Inorg. Chem. 1982,21, 3647. (24)Giannotti, C.; Green, M. L. H. J. Chem. SOC.,Chem. Commun. 1972,1114.
820 Organometallics, Vol. 7,No. 4, 1988
Miller and Sanner Scheme I
no evidence of H/D exchange with the solvent is seen even after 6 days at 25 OC. However, if the sample is blacklight photolyzed, nearly complete exchange of C6H, (supplied by reductive elimination from the zirconium complex) for solvent C6D6occurs within 43 h as indicated by a substantial decrease in the phenyl and hydride resonances and a concomitant appearance of C6H6in the 'H NMR. If the solvent is replaced with fresh CsD6 and the photolysis continued, complete conversion to Cp*,Zr(C6D5)Doccurs, as identified by the resonance of its Cp* rings in the 'H NMR. Further evidence for this deuteriated species is supplied by shifts in the absorption bands of the infrared spectrum (Nujol): phenyl v(C-H) 3052, v(C-D) 2255 cm-'; v(Zr-H) 1563, v(Zr-D) 1128 cm-l. These results show that the phenyl hydride, like the alkyl hydrides, also undergoes photochemically induced reductive elimination. Finally, we have observed photochemically induced reductive elimination of Hz from Cp*,ZrH,. In sealed NMR tube reactions, blacklight photolysis of benzene-d, solutions of C P * ~ Z ~ Hproceeded , very slowly with only 10% conversion to Cp*2Zr(C6D5)Dafter 32 h (the alkyl hydrides 1 are completely converted to 2 in ca. 30 h under identical conditions); no other photoproducts were observed (eq 8). Cp*2ZrH2
hv
benzene-de
+
Cp*,Zr(C6D5)D Hz
In an attempt to increase the rate of the reaction, a sample was photolyzed with an unfiltered medium pressure Hg lamp: though the rate was increased significantly, the reaction was still only 30% complete after 20 h. The slower rate of the dihydride photochemical reactions compared to the alkyl hydride is consistent with the known trend of greater stability for cis dihydride complexes via-84s their cis alkyl hydride analogue^.'^^^^ Another possible explanation for the slower reaction rate of the dihydride, as compared to the alkyl hydrides, is a back-reaction between the evolved dihydrogen and the phenyl hydride product to re-form Cp*2ZrH,. However, this hydrogenation is quite slow at 25 OC even under 1atm of hydrogen ( t l = 6 days). Thermal and Photoreactions of Cp*,Zr(D)CH,CD(CH,),. Quantitative evolution of alkane upon photolysis of the permethylzirconocenealkyl hydrides suggests clean reductive elimination of the cis alkyl and hydride ligands. To obtain proof of this pathway the deuteriated species Cp*,Zr(D)CH,CD(CH& was prepared, and the labeled isobutane evolved upon photolysis was analyzed. The results of these studies listed in Table I show that the hydrogen incorporated into the isobutane is abstracted from the hydride position. Additionally, the crossover (25)See ref 8,p 243.
Table I. Deuterium-Labeling Experiments" . . compound gas evolved CP*~Z~(D)CH~CD(CH~), (CHzD)CD(CH3)zb
'The compound was photolyzed in toluene at 0 "C. bTraces (
