[51177-89-0]  · C22H20Zr  · Bis(cyclopentadienyl)diphenylzirconium  · (MW 375.62)

(precursor of Cp2Zr;3,4 precursor of zirconium-benzyne complex8,9; insertion reaction into Zr-Ph bond20)

Alternate Name: diphenylzirconocene.

Physical Data: mp 140 °C dec.

Solubility: sol THF, CS2; appears to react with CHCl3; reacts with protic solvents.

Analysis of Reagent Purity: IR (nujol cm-1) 1405(m), 1240(w), 1050(m), 1005(m), 980(m), 827(w), 820(s), 775(s), 698(s); 1H NMR (CS2) d: 6.10(s), 6.8-7.3(m); (THF-d8) d: 6.18, 6.93(m), 7.23 (m).

Preparative Method: the reaction is conducted under an atmosphere of argon. A suspension of 1.0 g (3.4 mmol) of Dichlorobis(cyclopentadienyl)zirconium in 20 mL of diethyl ether is cooled to -40 °C. Phenyllithium (3.0 mL, 2.3 M) is subsequently added dropwise via a syringe over a 45 min period with magnetic stirring, during which time a white crystalline solid separates from solution. Stirring is continued at -40 °C for 1 h and the temperature is slowly allowed to rise to 0 °C. The solvent is then evaporated under reduced pressure and the solid residue is washed with pentane and decanted. The remaining residue is extracted with diethyl ether and the extracts are filtered under nitrogen. Concentration of the filtrate yields 1.0 g (80%) of white crystalline Cp2ZrPh2.2

Purification: recrystallization at low temperature from diethyl ether; cannot be sublimed.

Handling, Storage, and Precautions: appears to be more stable than the dimethyl analog toward air and moisture. Use in a fume hood.

Precursor of Cp2Zr.

Reductive elimination of biphenyl from diphenylzirconocene is induced photochemically and gives a zirconocene Cp2Zr species which has not been characterized but which reacts with various reagents. In the presence of dienes, zirconocene-diene complexes are obtained as stable complexes (eq 1).3 With alkynes, a dimerization occurs to give zirconacyclopentadienes (eq 2).4 Reaction of vinylzirconocene with Cp2Zr affords a dinuclear (alkene)zirconocene complex (eq 3).5 Coupling of phenyl groups on zirconium is also achieved by the reaction of Cp2ZrPh2 with an oxidant such as tetrakis(trifluoromethyl)cyclopentadienone (eq 4).6

Precursor of Zirconium-Benzyne Complex.

Thermolysis of diarylzirconocenes shows a different aspect of their reactivity. When a solution of di-p-tolylzirconocene is stirred in degassed absolute benzene at 70 °C for 3 h and treated with bromine, m-bromotoluene and bromobenzene are formed in addition to the expected products such as zirconocene dibromide and p-bromotoluene.7 This is due to the formation of phenyltolylzirconocene (eq 5).7

When thermolysis of diphenylzirconocene is carried out at 70 °C under ethylene (20 bar), zirconaindan is formed in excellent yield (eq 6).8 The zirconaindan compounds can be used for further reactions, e.g. carbonylation (eq 7).9 The zirconaindan is formed by the coupling reaction of benzyne with ethylene. The coupling reaction with substituted alkenes is highly regioselective (&egt;95%) and stereospecific (eq 8).10 The alkene moiety of zirconaindans can be replaced by other alkenes as shown in eq 9.8

Carbon monoxide coordinated to a transition metal also reacts with benzyne formed in situ to afford a cyclic carbene complex (eq 10).11 The zirconocene-benzyne complex can be trapped with PMe3 to form a crystalline complex (eq 11).12 The benzyne complex reacts with various unsaturated compounds such as nitriles,12,13 alkynes,12 ketones,12 and phosphaacetylene14 to form five-membered zirconacycles (eqs 12 and 13). Coupling products with alkynes can be converted into heterocycles such as benzothiophene (eq 14).15 Organic compounds which have an acidic hydrogen react with benzyne to give monophenyl(organo)zirconocene compounds. When the benzyne complex reacts with an ylide or furan, the corresponding monophenyl(organo)zirconocene gives six-membered zirconacycles (eq 15).16

Insertion or Migration Reaction of Cp2ZrPh2.

Carbonylation of Cp2ZrPh2 at atmospheric pressure occurs rapidly even at -70 °C to give the benzoyl complex Cp2Zr(COPh)(Ph) in ca. 80% yield (eq 16).17 The complex formed under kinetic control has a benzoyl oxygen bound to a lateral coordination site, an O-outside complex. This complex isomerizes above -50 °C to the thermodynamically favored O-inside complex.18 At 70 °C, 1,2-migration of the remaining s-bonded aryl ligand of the benzoyl complex from zirconium to the acyl-carbon occurs to form a side-on coordinated benzophenone ligand (eq 17).19 Insertion reactions of diphenylketene, aryl isocyanates, and p-tolylcarbodiimide into the Zr-Ph bond are also observed.20 However, carbon dioxide does not react with Cp2ZrPh2 at room temperature at atmospheric pressure. Insertion of NO gas into the Zr-Ph bond produces a zirconium complex containing the [ON(Ph)NO]- ligand.21

Treatment of Cp2ZrPh2 with alkynyllithium compounds, RCCLi, affords, after hydrolysis with 3N HCl or iodonolysis with an excess of I2, migration products, PhCCR, in good yields (eq 18).22 Insertion reaction of acetonitrile into the Zr-Ph bond is achieved with oxidants such as Ag+ or Cp2Fe+ (eq 19).23

1. (a) Cardin, D. J.; Lappert, M. F.; Raston, C. L.; Riley, P. I. In Comprehensive Organometallic Chemistry; Wilkinson, G., Ed.; Pergamon: Oxford, 1982; Vol. 3, pp 549-633. (b) Erker, G. ACR 1984, 17, 103. (c) Negishi, E.; Takahashi, T. Aldrichim. Acta 1985, 18, 31. (d) Buchwald, S. L.; Nielsen, R. B. CRV 1988, 88, 1047.
2. Samuel, E.; Rausch, M. D. JACS 1973, 95, 6263.
3. (a) Erker, G.; Wicher, J.; Engel, K.; Krüger, C. CB 1982, 115, 3300. (b) Erker, G.; Engel, K.; Vogel, P. AG(E) 1982, 21, 782. (c) Erker, G.; Engel, K.; Korek, U.; Czisch, P.; Berke, H.; Caubére, P.; Vanderesse, R. OM 1985, 4, 1531.
4. Skibbe, V.; Erker, G. JOM 1983, 241, 15.
5. Erker, G.; Kropp, K.; Atwood, J. L.; Hunter, W. E. OM 1983, 2, 1555.
6. Burk, M. J.; Tumas, W.; Ward, M. D.; Wheeler, D. R. JACS 1990, 112, 6133.
7. Erker, G. JOM 1977, 134, 189.
8. Erker, G.; Kropp, K. JACS 1979, 101, 3659.
9. Erker, G.; Kropp, K. JOM 1980, 194, 45.
10. Kropp, K.; Erker, G. OM 1982, 1, 1246.
11. (a) Erker, G.; Dorf, U.; Mynott, R.; Tsay, Y.-H.; Krüger, C. AG(E) 1985, 24, 584. (b) Erker, G.; Dorf, U.; Krüger, C.; Tsay, Y.-H. OM 1987, 6, 680. (c) Erker, G.; Dorf, U.; Lecht, R.; Ashby, M. T.; Aulbach, M.; Schlund, R.; Krüger, C.; Mynott, R. OM 1989, 8, 2037.
12. Buchwald, S. L.; Watson, B. T.; Huffman, J. C. JACS 1986, 108, 7411.
13. (a) Buchwald, S. L.; Sayers, A.; Watson, B. T.; Dewan, J. C. TL 1987, 28, 3245. (b) Buchwald, S. L.; Watson, B. T.; Lum, R. T.; Nugent, W. A. JACS 1987, 109, 7137.
14. Binger, P.; Biedenbach, B.; Mynott, R.; Regitz, M. CB 1988, 121, 1455.
15. Buchwald, S. L.; Fang, Q. JOC 1989, 54, 2793.
16. (a) Erker, G.; Czisch, P.; Benn, R.; Rufínska, A.; Mynott, R. JOM 1987, 328, 101. (b) Erker, G.; Petrenz, R.; Krüger, C.; Lutz, F.; Weiss, A.; Werner, S. OM 1992, 11, 1646.
17. Fachinetti, G.; Fochi, G.; Floriani, C. JCS(D) 1977, 1946.
18. Erker, G.; Rosenfeldt, F. JOM 1980, 188, C1.
19. Erker, G.; Dorf, U.; Czisch, P.; Petersen, J. L. OM 1986, 5, 668.
20. Gambarotta, S.; Strologo, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. IC 1985, 24, 654.
21. Jones, C. J.; McCleverty, J. A.; Rothin, A. S. JCS(D) 1985, 405.
22. Takagi, K.; Rousset, C. J.; Negishi, E. JACS 1991, 113, 1440.
23. Alelyunas, Y. W.; Jordan, R. F.; Echols, S. F.; Borkowsky, S. L.; Bradley, P. K. OM 1991, 10, 1406.

Tamotsu Takahashi & Noriyuki Suzuki

Institute for Molecular Science, Okazaki, Japan

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