Synthesis, Characterization, and Reactions of the New Seven

Organometallics 1996, 15, 2633-2639

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Synthesis, Characterization, and Reactions of the New Seven-Membered Nickelacycle (2,2′-Bipyridine)-6,7-dihydro-5H-dibenzo[c,e]nickelepine Barbara Patzke and Amnon Stanger* Department of Chemistry, Technion, Israel Institute of Technology, Haifa 32000, Israel. Received December 18, 1995X

The reaction of the di-Grignard reagent 1,2-dihydro-1-magnesacyclobutabenzene (1) with (2,2′-bipyridine)nickel dichloride yielded as the major product the unexpected sevenmembered nickelacycle (2,2′-bipyridine)-6,7-dihydro-5H-dibenzo[c,e]nickelepine (2), instead of the expected (2,2′-bipyridine)-1,2-dihydro-1-nickelacyclobutabenzene. On treatment with maleic anhydride the title compound (2) undergoes reductive elimination to form dihydrophenanthrene. The methylene insertion product 6,7-dihydro-5H-dibenzo[a,c]cycloheptene and the cyclic ketone 5,7-dihydro-6H-dibenzo[a,c]cyclohepten-6-one are obtained when 2 is reacted with dibromomethane and CO, respectively. Quenching the reaction mixture of 1 and (2,2′-bipyridine)nickel dichloride with CH2Br2 or CD2Cl2 provided strong evidence for the intermediacy of eight-membered dinickelacycles and gave some information regarding the probable mechanism leading to the formation of 2. Introduction effect1

Our interest in the Mills-Nixon led us to look for new ways to synthesize strained aromatic compounds. Numerous approaches were taken, including Ni(0)-mediated cyclization of R,R,R′,R′-tetrabromo-oxylene and hexakis(dibromomethyl)benzene to form 1,2dibromocyclobutabenzene2 and hexabromotricyclobutabenzene,3 respectively. Another approach was to use nickelacycles, either by reductive elimination of an L2Ni moiety from nickelapentalene4 (in analogy to the respective non-benzenoid systems),5 or by reacting nickelacyclobutabenzene with CO or dibromomethane to form the respective cyclobutabenzene derivatives (eq 1).6,7 Nickelacyclobutabenzenes have been prepared by

tricyclopropabenzene as the starting material for the preparation of tricyclobutabenzene. The most general method for the preparation of metallacyclobutabenzenes was reported by Bickelhaupt9 and is based on the reaction of metal halides with the oligomeric 1,2-dihydro-1-magnesacyclobutabenzene (1) (eq 2). To our

Wilke et al.8 using oxidative addition of L2Ni0 species to cyclopropabenzene. This approach, however, is unsuitable for our purposes, since it requires the unknown

surprise, when 1 was reacted with (BIPY)NiCl2 (BIPY ) 2,2′-bipyridine) the desired nickelacyclobutabenzene was not observed. Instead, the reaction yielded the seven-membered-ring compound (2,2′-bipyridine)-6,7dihydro-5H-dibenzo[c,e]nickelepine (2) as the major product. Analogous axially asymmetric metallacycles (or metallepines) have been reported by Raston et al.10 for transition metals of groups 4-6. Their syntheses were performed by transmetalation using an organolithium complex or a di-Grignard reagent based on the hydrocarbyl dianion (2-CH2C6H4)22-. We report here the synthesis and characterization of the title compound 2, its reaction behavior toward CH2Br2, CO, and alkynes, and the possible mechanism for its formation from 1 and (BIPY)NiCl2.

Abstract published in Advance ACS Abstracts, May 1, 1996. (1) Stanger, A. J. Am. Chem. Soc. 1991, 113, 8277. (2) Stanger, A.; Ashkenazi, N.; Schachter, A.; Bla¨ser, D.; Stellberg, P.; Boese, R. J. Org. Chem. 1996, 61, 2549. (3) Stanger, A.; Ashkenazi, N.; Bla¨ser, D.; Stellberg, P.; Boese, R. Submitted for publication. (4) Patzke, B.; Stanger, A. Unpublished results. (5) Grubbs, R. H.; Miyashita, A.; Liu, M. M.; Burk, P. J. Am. Chem. Soc. 1978, 100, 2418. (6) For analogous reactions of dialkylnickel complexes with CO see: Yamamoto, T.; Kohara, T.; Yamamoto, A. Chem. Lett. 1976, 1217. (7) For analogous reactions of dialkylnickel complexes and dibromomethane see: (a) Takahashi, S.; Suzuki, Y.; Sonogashira, K.; Hagihara, N. J. Chem. Soc., Chem. Commun. 1976, 839. (b) Binger, P.; Doyle, M. J. J. Organomet. Chem. 1978, 162, 195.

(8) (a) Neidlein, R.; Rufinska, A.; Schwager, H.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1986, 25, 640-642. (b) Kru¨ger, C.; Laakmann, K.; Schroth, G.; Schwager, H.; Wilke, G. Chem. Ber. 1987, 120, 471475. (c) Schwager, H.; Benn, R.; Wilke, G. Angew. Chem., Int. Ed. Engl. 1987, 26, 67-68. (9) (a) deBoer, H. J. R.; Akkermann, O. S.; Bickelhaupt, F.; Erker, G.; Czisch, P.; Mynott, R.; Wallis, J. M.; Kru¨ger, C. Angew. Chem., Int. Ed. Engl. 1986, 25, 639-640. (b) deBoer, H. J. R.; Schat, G.; Akkermann, O. S.; Bickelhaupt, F. J. Organomet. Chem. 1987, 321, 291-306. (c) deBoer, H. J. R.; van de Heisteeg, B. J. J.; Flo¨el, M.; Herrmann, W. A.; Akkermann, O. S.; Bickelhaupt, F. Angew. Chem., Int. Ed. Engl. 1987, 26, 73-74. (d) deBoer, H. J. R.; van de Heisteeg, B. J. J.; Schat, G.; Akkermann, O. S.; Bickelhaupt, F. J. Organomet. Chem. 1988, 346, 197-200. (e) deBoer, H. J. R.; Schat, G.; Akkermann, O. S.; Bickelhaupt, F. Organometallics 1989, 8, 1288-1291.

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Results and Discussion When 1 was reacted with 1 equiv of (BIPY)NiCl2 in THF at -45 °C, the reaction solution turned dark green. On partial evaporation of the solvent a black precipitate, presumably a Ni(0) species,11 was formed. After filtration, the solvent was removed in vacuo to yield a dark green, thermally stable, but very air sensitive solid that was spectroscopically characterized by 1H and 13C NMR and by characteristic reactions as (2,2′-bipyridine)-6,7dihydro-5H-dibenzo[c,e]nickelepine (2; eq 3), which still

contains 9,10-dihydroanthracene as the only impurity (probably formed by a side reaction; see below). The 1H NMR spectrum of 2 shows two ABCD patterns, one for the eight protons of the bipyridine and the other for the eight aromatic protons of the biphenyl moiety. Particularly characteristic for 2 is the AX pattern of the nonequivalent geminal benzylic protons at C7 (δ(A) 2.60, δ(B) 1.80, 2J(AB) ) 6.4 Hz). Thus, the nickel atom is (as expected) in a square-planar coordination (diamagnetic Ni(II) with C2 local symmetry), and each of the two methylene groups carry one equatorial and one axial proton. As a consequence of the C2 symmetry, one axial proton is located above and the other below the nickel-bipyridine plane. The assignment of the resonances at 2.60 and 1.80 ppm to either the axial or the equatorial protons was attempted by NOE experiments. Irradiation at 2.60 ppm revealed NOE enhancements at 8.87 ppm (H12 of the bipyridine ligand) as well as at 7.05 ppm (the aromatic protons H3 of the biphenyl system). However, the NOE difference spectra showed a decrease of the resonance at 1.80 ppm. The same enhancements were observed when the signal at 1.80 ppm was saturated and the signal at 2.60 ppm was decreased. This observation is rationalized by saturation transfer12 between the two benzylic protons, resulting from rotation around the biphenyl axis that exchanges the positions of the equatorial and the axial (10) (a) Engelhardt, L. M.; Leung, W.-P.; Raston, C. L.; Twiss, P.; White, A. H.; J. Chem. Soc., Dalton Trans. 1984, 321. (b) Engelhardt, L. M.; Leung, W.-P.; Raston, C. L.; Twiss, P.; White, A. H. J. Chem. Soc., Dalton Trans. 1984, 331. (c) Bailey, S. I.; Engelhardt, L. M.; Leung, W.-P.; Raston, C. L.; Ritchie, I. M.; White, A. H. J. Chem. Soc., Dalton Trans. 1985, 1747. (d) Engelhardt, L. M.; Papasergio, R. I.; Raston, C. L.; Salem, G.; White, A. H. J. Chem. Soc., Dalton Trans. 1986, 789. (e) Engelhardt, L. M.; Leung, W.-P.; Papasergio, R. I.; Raston, C. L.; Twiss, P.; White, A. H. J. Chem. Soc., Dalton Trans. 1987, 2347. (f) Engelhardt, L. M.; Leung, W.-P.; Raston, C. L.; Salem, G.; Twiss, P.; White, A. H. J. Chem. Soc., Dalton Trans. 1988, 2403. (g) Raston, C. L.; Skelton, B. W.; Twiss, P.; White, A. H. Aust. J. Chem. 1988, 41, 1773. (h) Chappel, S. D.; Engelhardt, L. M.; White, A. H.; Raston, C. L. J. Organomet. Chem. 1993, 462, 295. (11) This solid, insoluble in organic solvents, turned light green (almost white) when exposed to air.

Patzke and Stanger

benzylic protons. The process is fast enough to be observed on the NOE time scale (T1) but is slow relative to the 1H NMR time scale (kcoal ≈ 714 s-1), allowing the observation of the equatorial and axial protons as two separate signals. The proton-coupled 13C NMR spectrum shows a triplet at 24.2 ppm for C7, with 2JC,H coupling constant of 129 Hz, a characteristic value for C(sp3)-H coupling. Nickel organic compounds have a rich carbonylation chemistry which has been investigated extensively.13 Of particular interest here is the carbonylation of nickelacycles, which is frequently used for their characterization, yielding the respective cyclic ketones.14 The reaction of nickel organic complexes with dibromomethane to yield the methylene insertion product is also well documented.7 The reaction of 2 with CO and CH2Br2 yields the cyclic ketone 5,7-dihydro-6H-dibenzo[a,c]cyclohepten-6-one (3) and 5,7-dihydro-6H-dibenzo[a,c]cycloheptene (4), respectively. Other characteristic reactions of nickel complexes such as 2 are reductive elimination and protonolysis. Indeed, when 2 is reacted with maleic anhydride or methanol, the expected products (9,10-dihydrophenanthrene (5) and 2,2′-dimethylbiphenyl (6) respectively) are obtained. These reactions are summarized in Scheme 1. Some nickel complexes are known to add alkynes and form the alkyne insertion products (i.e., RsNisR′ + XsCtCsY f R(X)CdC(Y)R′).15 Carmona16 has shown that nickelapentalenes react with alkynes to yield the corresponding 1,4-dihydronaphthalenes. When 2 was reacted with alkynes (phenylacetylene and phenyl(trimethylsilyl)acetylene) the color changed from green to brown, but none of the desired insertion product was obtained, and the black-green (2,2′-bipyridine)nickel alkyne complexes17 were also not detected.18 The reason for this may be the bidentate nature of the bipyridine ligand. Bergman19 and Norton20 have shown that the insertion of alkynes into the MsC bond (M ) Ni, Pd) takes place via a preequilibrium involving substitution of a phosphine ligand by the incoming alkyne, to form a square-planar alkyne-metal π-complex, which is the most likely intermediate that precedes the insertion step. This equilibrium is unlikely to happen when the ligand on the nickel is a strong bidentate one, such as in 2. The advantages of the good stabilizing properties (12) (a) Neuhaus, D.; Williamson, M. P. The Nuclear Overhauser Effect in Structural and Conformal Analysis; VCH: Weinheim, Germany, 1989. (b) Saunders, J. K. M.; Mersh, J. D. Prog. NMR Spectrosc. 1983, 15, 353. (13) (a) Jolly, P. W.; Wilke, G. The Organic Chemistry of Nickel; Academic Press: New York, 1975; Vol. II. (b) Yamamoto, T.; Kohara, T.; Yamamoto, A. Bull. Chem. Soc. Jpn. 1981, 54, 2161. (14) (a) Yamamoto, T.; Kohara, T.; Yamamoto, A. Chem. Lett. 1976, 1217. (b) Grubbs, R. H.; Miyashita, M. J. Organomet. Chem. 1978, 161, 371. (c) Eisch, J. J.; Piotrowski, A. M.; Han, K. I.; Kru¨ger, C.; Tsay, Y. H. Organometallics 1985, 4, 224. (15) (a) Collmann, J. P.; Hegedus, L. S.; Norton; J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987. (b) Klein, H.-F.; Reitzel, L. Chem. Ber. 1988, 121, 1115. (c) Hoberg, H. J. Organomet. Chem. 1988, 358, 508. (d) Huffman, M. A.; Liebeskind, L. S. J. Am. Chem. Soc. 1991, 113, 2771. (16) (a) Carmona, E.; Gutie´rrez-Puebla, E.; Marı´n, J. M.; Monge, A.; Panaque, M.; Poveda, M. L.; Ruiz, C. J. Am. Chem. Soc. 1989, 111, 2883. (b) Ca´mpora, J.; Llebarı´a, A.; Moreto´, J. M.; Poveda, M. L.; Carmona, E. Organometallics 1993, 12, 4032. (17) Rosenthal, U.; Nauck, C.; Arndt, P.; Pulst, S.; Baumann, W.; Burlakov, V. V.; Go¨rls, H. J. Organomet. Chem. 1994, 484, 81. (18) The alkynes were recovered nearly quantitatively. (19) Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 3002. (20) Samsel, E. G.; Norton, J. R. J. Am. Chem. Soc. 1984, 106, 5505.

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Scheme 1. Reaction of 2 with Several Reagents

Scheme 2. Product Distribution of the Reaction between 1 and (BIPY)NiCl2 Quenched with Maleic Anhydride and Methanol

of 2,2′-bipyridine, especially for alkylnickel complexes, turn out to be a disadvantage for the alkyne insertion reaction. As 2, a result of an aryl-aryl coupling, is the major product (eq 3), different reactivities for the aryl and benzyl positions in 1 are implied. It is known that the benzylic position is more reactive,9b but the relative reactivity depends on the specific reaction. Another mechanistic clue is that “black nickel” appears after (BIPY)NiCl2 has been completely consumed. This suggests intermediates which contain (at least) two nickel moieties, such as 7 and/or 8. Such stable dimetallacy-

clooctanes are known for Si, Sn, and Ge,9b but the nickel derivatives are probably less stable and reductively eliminate one (BIPY)Ni moiety. In order to learn about

possible intermediates in the reaction (eq 3) and to gain some understanding about the reaction mechanism, some quenching reactions were carried out. Scheme 2 describes the product distribution of the reaction, quenched with methanol or maleic anhydride, after the formation of “black nickel” and prior to the workup. Both experiments suggest an 87:13 selectivity of aryl-aryl vs aryl-benzyl coupling. Obviously, 5 and 6 result from reductive elimination and protonolysis of 2, respectively (see also Scheme 1). The two other products result therefore from 12, an isomer of 2 that

results from aryl-benzyl coupling. Dihydroanthracene

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(9) is also found in the cleanest form of 2 that we were able to obtain, suggesting also that 2 is more stable than 12.21 The reaction mixture of the methanolysis also contained small amounts of toluene, suggesting the presence of 7 and/or 8.22 The 1:1 molar ratio between 1 and (BIPY)NiCl2 and the products that contain two units of 1 suggest dimers containing two nickel fragments as intermediates. The formation of “black nickel” only after the complete consumption of 1 suggests that the precursors for 2 and 12 are 7 and 8, respectively. In 8, the two nickel fragments are chemically identical, and 12 is obtained by reductive elimination of one of them.23 In 7, selective reductive elimination of the diarylic nickel (to form 223) is observed. Thus, 13 (or its products, see below), which would result from the elimination of the dibenzylic nickel, is not found at all. This implies that the Nibenzyl bond is more stable than the Ni-aryl bond, in accordance with the findings of Yamamoto et al.24

More data were obtained from quenching the reaction mixture between 1 and (BIPY)NiCl2 with CH2Br2 (or CD2Cl2) at different stages of the reaction. This is described in eq 4 and in Table 1.

Patzke and Stanger Table 1. Product Distribution of the Reaction of 1 and (BIPY)NiCl2, Quenched with CH2Br2 (or CD2Cl2) under Different Conditionsa entry no. quencher 1 2 3 4d

CH2Br2 CH2Br2 CH2Br2 CD2Cl2

addition isolated temp yield (°C) (%) -45 25b 25c -45

73 75 68 80

product distribn (%) 5

9

4

6 9 52 9 5 63 30 10 60 15 10 40

14 15 16 17 7 6 0 3

8 18 0 12 5 1 0 0 0 9 11 12

a Reaction conditions: -45 °C, 18 h. The quencher was added at the specified temperature and then stirred at 25 °C. b The reaction mixture was warmed to 25 °C before addition of the quencher. c The reaction mixture was stirred at room temperature for 14 h before addition of the quencher. d The products are the respective D2, D4, and D6 derivatives.

respectively, and 15 results from double methylene insertion into 2. However, 16 may result from the eightmembered dinickelacycle 7 (the precursor to 2) and/or from double methylene insertion into 12. Clearly, the dinickelacycle 8 is not present in all the quenching reactions, since 18 is not found. However, it must be

present at earlier stages of the reaction, as it is the precursor to 12. Since the origin of 16 and 17 is not clear, the selectivity found in the reductive elimination and protonolysis of the reaction (87:13; Scheme 2) can be directly compared only to the case where the ring systems larger than seven are not present in the product mixture. Entry 3 of Table 1 shows such a case: thus, 90% of the products (5 and 4) result from 2, and 10% results from 12 (9), a 90:10 selectivity. This entry (relative to entries 1 and 2) also suggests that 2 and 12 decompose (12 faster) by reductive elimination to give 5 and 9. The results of the CD2Cl2 quenching experiment (Table 1, entry 4) support the above conclusions. The positions of the CD2 units in 4-D2, 14-D2, and 15-D4

In general, as the reaction is allowed to proceed at higher temperatures and/or for longer times the relative amount of the products resulting from 2 (i.e., 4 and 15) increase. Thus, under the reaction conditions the most stable product is 2, and the other nickelacycles decompose. Nickelacycles react with CH2Br2 to produce the respective cycloalkanes where the CH2 unit replaces the nickel. Thus, the origin of some of the products can be readily identified; 4 and 14 result from 2 and 12, (21) 2 survives the workup, whereas 12 does not. (22) As 1 is completely insoluble in the reaction mixture, toluene cannot result from protonation of 1. (23) The other product of the reductive elimination is “black nickel”. (24) Yamamoto, T.; Wakabayashi, S.; Osakada, K. J. Organomet. Chem. 1992, 428, 223.

clearly indicate the presence of 2 and 12 in the reaction mixture.25 As dibromomethane is more reactive than dichloromethane, the reaction of the last with nickel compounds is slower. Thus, the larger amounts of

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Organometallics, Vol. 15, No. 11, 1996 2637

Scheme 3. Suggested Reaction Pathways and Intermediates in the Reaction of 1 with (BIPY)NiCl2a

a

The main reaction is marked by bold arrows: “Ni” ) (BIPY)Ni; RE ) reductive elimination.

reductive elimination (5 and 9) and double-(15-D4 and 16-D4) and triple-insertion (17-D6) products in the CD2Cl2-quenched reaction (relative to the CH2Br2-quenched reaction; Table 1, entry 1) is consistent with the presence of the suggested nickela- and dinickelacycles. The probable reaction pathway and intermediates are described in Scheme 3. The first step is a reaction between 1 and (BIPY)NiCl2. The major product is expected to be 19, which results from the reaction of the more reactive benzylic carbon of 1. Each of the two products (19 and 20) reacts with another molecule of 1 to give the nickela di-Grignard systems 21-23. The major product here is probably 21, as it results from the reaction of the two more reactive benzylic carbons of 1. The formation of 22 is postulated, as it is the source of the final products 9, 11, 14, and possibly also 16. A possible minor product (23), resulting from the reaction of the two arylic carbons of 1, may also be formed.26 At this stage the selectivity of the reaction is already determined, i.e., 87% of the mixture is 21 and 23 and 13% is 22. From these data it is impossible to assign the exact relative benzylic-arylic reactivity. However, assuming that the amount of 23 is negligible, it can range from a complete selectivity in one step (i.e., (25) It was impossible to determine the relative amount of the two possible isomers of 16-D4 and the deuterium distribution of in 17-D6. (26) In the next step, 23 reacts with a second molecule of 1 to yield 7, which is mainly formed from 21. Thus, there is no indication if 23 is formed in meaningful amounts.

only the benzyl-Ni bond is formed, and 23 is not formed at all) to equal selectivity of 93:7 in the two steps. The third step is the reaction of the nickela diGrignards with (BIPY)NiCl2 and intramolecular ring closure to give the two isomeric eight-membered dinickelacycles 7 and 8.27 The symmetric dinickelacycle is probably unstable and decomposes rapidly to 12 and perhaps 9.27 The major product, 7, may doubly reductively eliminate to give 5,28 but mainly the diarylic nickel eliminates to give 2. The different reactions of 2 with several reagents are described above, and 7 is expected to react in a similar fashion. Summary We have shown here that in contrast to other transition-metal halides (BIPY)NiCl2 reacts with the diGrignard reagent 1 to yield the new seven-membered nickelacycle 2. The formation of 2 involves an intramolecular aryl-aryl coupling, a well-known process in nickel chemistry. The reactions of 2 with dibromomethane and CO yield the seven-membered-ring (27) It was mentioned earlier that 18 is not found and, thus, 8 must have a very short lifetime under the reaction conditions. An alternative pathway here would be the reductive elimination of (BIPY)Ni from 22 before the reaction with the second molecule of 1. This is less probable, as the Ar-Ni-benzyl bond is stable enough to allow the existence of 12, from which 11, 14, and 16 are isolated. (28) There is no evidence for the double reductive elimination of 7 (to yield 5); however, it cannot be ruled out on the basis of the results.

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compound 4 and the cyclic ketone 3, respectively. The synthesis of the seven-membered-ring systems reported here can be performed in a one-pot process starting with 2-bromobenzyl chloride, in contrast to the multistep syntheses reported in the literature.29 Under the conditions employed here, we were unable to insert alkynes into 2. However, given the right conditions for insertion reactions (such as replacing the bipyridine with two phosphine ligands), this nickelacycle could prove to be a versatile reagent for the synthesis of the hard-toprepare medium-sized ring systems. Experimental Section All manipulations involving organometallic compounds were carried out under dry argon using modified Schlenk techniques. The solvents and liquid reagents were dried over potassium p-phenylbenzophenone (THF), CaH2 (pentane), Mg (MeOH), and molecular sieves (CH2Br2), respectively, and were thoroughly degassed before use. Anhydrous NiCl2 (Strem) was dried under vacuum (10-3-10-4 mbar) at 170 °C. 1H and 13C NMR (BB, DEPT) spectra were recorded on a Bruker AC 200 and AMX 400, respectively, and reported chemical shifts are referenced to the solvent resonances. 2 was further characterized by NOEDIFF, 1H,1H-COSY, 1H,13C-COSY, and protoncoupled 13C NMR. All organic products were analyzed by GC/ MS (column DB5, 50 m), on a Finnigan 4000 mass spectrometer operating at an ionization potential of 70 eV. 2-BrC4H6CH2Cl was prepared according to published methods.30 (BIPY)NiCl2.31 Equimolar amounts of anhydrous NiCl2 (7.9 g, 61 mmol) and bipyridine (9.7 g, 62 mmol) in THF (100 mL) were refluxed for 24 h. After settling of the precipitate the mother liquor was cannulated out. The solid was washed twice with THF and dried under vacuum at 70 °C, yielding (BIPY)NiCl2 (17.2 g, 60 mmol, 98%) as a fine light green powder. 1,2-Dihydro-1-magnesacyclobutabenzene (1) was prepared according to the published method,9b except that Mg powder (50 mesh, Aldrich, Catalog No. 25,398-7) was used instead of sublimed magnesium, and the addition of 2-BrC4H6CH2Cl (3-5 mmol scale) in THF (90-120 mL) was slowed down (addition time 18 h). The resulting 1 and the yield were identical with those described by Bickelhaupt et al.9 (Bipyridine)-6,7-dihydro-5H-dibenzo[c,e]nickelepine (2). A suspension of (BIPY)NiCl2 (3.66 mmol) in THF (50 mL) was added to a suspension of 1 (3.66 mmol) in THF (50 mL) at -75 °C. The mixture was stirred for 1/2 h at -75 °C and for 18 h at -45 °C and was slowly warmed to room temperature. A clear dark green solution was formed. During subsequent evaporation of ca. 70 mL of the solvent at 0 °C, a black precipitate (0.86 g) was formed.23 The precipitate was filtered off and washed with THF. The filtrate was evaporated to dryness, and the dark green solid was washed several times with pentane. The resulting residue (449 mg) was characterized by NMR spectroscopy as 2 which contained 25% (59 mg) dihydroanthracene. Thus, the yield of 2 was 54% (390 mg). NMR: 1H (THF-d8) 8.87 (d, 3J(H12H11) ) 5.41, 2H, H12), 8.08 (d, 3J(H9H10) ) 7.76, 2H, H9), 8.04 (m, 2H, H10), 7.45 (ps t, 2H, H11), 7.05 (d, 3J(H3H4) ) 7.45, 2H, H3), 6.91 (t, 3J(H5H4) ) 3J(H H ) ) 7.31, 2H, H ), 6.66 (m, 4H, H , H ), 2.60 (d, 5 6 5 4 6 2J(H H ) ) 6.4, 2H, 1H each of the two CH , H ), 1.80 (d, 7 7′ 2 7 (29) (a) Bestmann, H. J.; Ha¨rtl, R.; Ha¨berlein, H. Justus Liebigs Ann. Chem. 1968, 718, 33. (b) Tolberg, L. M.; Ali, M. Z. J. Org. Chem. 1982, 47, 4793. (c) Satyanarana, M.; Perisamy, M. Tetrahedron Lett. 1987, 28, 2633. (d) Devasagayarraj, A.; Rao, A. S.; Perisamy, M. J. Organomet. Chem. 1991, 403, 387. (30) Landini, D.; Montanari, F.; Rolla, F. Synthesis 1974, 37. (31) (a) Li, C.-X.; Lei, L.-X.; Xin, X,-Q. Chin. Sci. Bull. 1994, 39, 349. (b) Mitra, S.; Singh, L. N. Thermochim. Acta 1994, 239, 87. (c) Brezeanu, M.; Andruh, M.; Patron, L.; Popa, V. T. Rev. Roum. Chim. 1985, 30, 229. (d) Kurskov, S. N.; Ivleva, I. N.; Lavrent’ev, I. P.; Khidekel, M. L. Izv. Akad. Nauk SSSR, Ser. Khim. 1977, 8, 1708. (e) Jacob, K.; Niebuhr, R. Z. Chem. 1975, 15, 32

Patzke and Stanger 2J(H

13C{1H} 7′H7) ) 6.4, 2H, 1H each of the two CH2, H7′); (THF-d8) 156.4, 155.2 (C1, C8), 149.2 (C12), 141.7 (C2), 137.4 (C10), 129.8 (C6), 128.2, 128.1, 127.8 (C3, C4, C11), 124.1 (C5), 123.1 (C9), 24.2 (C7); 13C (THF-d8) 24.2 (t, 1J(CH) ) 129, C7). 5,7-Dihydro-6H-dibenzo[a,c]cyclohepten-6-one (3). 2 was prepared in a 3.98 mmol scale as described above. After the reaction at -45 °C (for 18 h) and 2 h at room temperature, the reaction flask was cooled with liquid N2 and evacuated (10-3-10-4 mbar). The Schlenk flask was warmed to -78 °C, at which temperature it was filled (at atmospheric pressure) with CO, and then slowly warmed to room temperature. The mixture was stirred overnight, during which time a white precipitate and a red solution were formed. The volatiles were removed in vacuo, and a red precipitate [(BIPY)Ni(CO)2] was formed. The residue was treated with 2 M aqueous HCl and extracted several times with Et2O. The combined organic layers were washed with aqueous NaHCO3 and water and dried over MgSO4. The solvent was evaporated, and the crude product, containing 3, 5, and 9, was chromatographed (300 × 15 silica gel, hexane/acetone 9/1, Rf ) 0.53). Clean 3 was obtained (220 mg, 53% yield). NMR: 1H (CDCl3) 7.57 (d, 2 H, 3J ) 6.9 Hz), 7.47-7.21 (m, 6 H), 3.56 (AB, 4 H, δ(A) 3.59, δ(B) 3.53, JAB ) 15); 13C (CDCl3)29 210.0 (CdO), 139.30, 132.95 (Carom), 129.26, 129.24, 127.09, 127.67 (CHarom), 49.16 (CH2); MS32 m/e (relative intensity) 208 (100, M+), 165 (90), 179 (89), 180 (70), 178 (65), 152 (22). Reaction of 2 with Maleic Anhydride. Maleic anhydride (MAH, 10 mg) was added to a small sample (1 mL) of the green solution (see the preparation of 2, before the last evaporation). The reaction mixture turned orange-red, and an orange precipitate ((BIPY)Ni(MAH)) was formed. The mother liquor was analyzed by GC/MS: 5 and 9 were obtained in the ratio 87/13. Protonolysis with MeOH. A small sample (1 mL) of the green solution (see the preparation of 2, before the last evaporation) was reacted with MeOH and analyzed by GC/ MS: 6, 5, 11, and 9 were obtained in the ratio 80/10/7/3, along with traces of toluene. Quenching Experiments. (i) With CH2Br2. A suspension of (BIPY)NiCl2 (2.83 mmol) in THF (50 mL) was added to a suspension of 1 (2.83 mmol) in THF (50 mL) at -75 °C. The mixture was stirred for 1/2 h at -75 °C and 18 h at -45 °C. CH2Br2 (1 mL) was added to this green solution, and the reaction mixture was warmed to room temperature. When the temperature was raised, the color changed from green to brownish red. After it was stirred overnight, the reddish solution was decanted from the light green precipitate ((BIPY)NiBr2) and the solid was extracted several times with pentane. After evaporation of the solvents of the combined organic solutions and addition of aqueous HCl (2 M), the mixture was extracted twice with Et2O. The combined ether solutions were washed with aqueous NaHCO3 and water and dried over MgSO4. The solvent was evaporated, and the crude material was filtered by flash chromatography (100 × 15 silica gel, hexane/Et2O 8/2). A 205 mg amount of organic material was obtained (ca. 73% yield). The product ratio was determined by GC (Table 1, entry 1). The pure main product 4 was isolated by flash chromatography (300 × 15 silica gel, hexane, Rf 0.53) in 38% yield (104 mg, 0.53 mmol). The side products (see Table 1) were partially separated. The products were identified by NMR29,33 (1H and 13C) and by GC/MS. MS of 4: m/e (relative intensity) 194 (100, M+), 179 (75), 178 (55), 165 (38), 180 (22), 193 (20). MS of 15: m/e (relative intensity) 208 (100, M+), 179 (60), 178 (48), 165 (45), 180 (30), 193 (15). MS

(32) McLafferty, F. W.; Staufer, D. B. The Wiley/NBS Registry of Mass Spectral Data; Wiley: New York, 1989; Vol. II, p 1229. (33) Pouchard, C. J.; Behneke, J. The Aldrich Library of 13C and 1H FT NMR Spectra, 1st ed.; Aldrich: Milwaukee, WI, 1993. (b) Elhadi, F. E.; Ollis, W. D.; Stoddart, J. F. J. Chem. Soc., Perkin Trans. 1 1978, 1514. (c) Heinz, W.; Langnese, P.; Mu¨llen, K. Angew. Chem., Int. Ed. Engl. 1987, 26, 1291. (d) Bates, R. B.; Canon, F. A.; Kane, V. V.; Misha, P. K.; Suvanannachut, K.; White, J. J. J. Org. Chem. 1989, 54, 311.

A New Seven-Membered Nickelacycle of 14: m/e (relative intensity) 194 (100, M+), 193 (75), 178 (52), 179 (50), 115 (30, C9H7+), 165 (15).MS of 16: m/e (relative intensity) 208 (100, M+), 178 (29), 179 (28), 193 (25), 115 (30, C9H7+), 165 (15). MS of 17: m/e (relative intensity) 222 (100, M+), 179 (65), 178 (52), 165 (50), 180 (22), 193 (15). (ii) With CD2Cl2. The conditions were identical with those for the reaction with methylene bromide on a 3.25 mmol scale. A 260 mg amount of organic products was obtained (ca. 80% yield). The pure main product was isolated, and the side products were partially separated as described before. NMR for 4-D2: 1H (CDCl3) 7.4-7.2 (m, 8 H), 2.50 (s, 2 H, R-CH2); 13 C{1H} 141.1, 139.6 (Carom), 128.4, 128.3, 127.4, 126.6 (CHarom), 31.3 (R-CH2), CD2 resonance not observed. NMR for 14-D2: 1 H 7.3-7.0 (m, 8 H), 4.11 (s, 2 H, CH2), 3.16 (s, 2 H, CH2). MS m/e (relative intensity): 4-D2, 196 (100, M+), 179 (59), 180 (49), 181 (47), 166 (40), 165 (38); 15-D4, 212 (100, M+), 165 (60), 181 (52), 179 (50), 180 (40); 14-D2 196 (100, M+), 195 (55),

Organometallics, Vol. 15, No. 11, 1996 2639 180 (55), 179 (52), 117 (43, C9H5D2+), 116 (40); 16-D4 212 (100, M+), 180 (41), 179 (39), 197 (35), 117 (43, C9H5D2+), 119 (42 C9H3D4+); 17-D6 228 (100, M+), 165 (60), 181 (52), 179 (45), 180 (35); 17a-D634 244 (100, M+), 179 (81), 165 (79), 181 (60), 180 (55).

Acknowledgment. This work was supported by the Volkswagen Stiftung, by the Israeli Academy for Sciences and Humanities, and by the fund for promotion of research at the Technion. B. Patzke thanks the Minerva Stiftung (Mu¨nchen) for the award of a postdoctoral fellowship. OM9509812 (34) Traces of the ten-membered-ring system were also found.