Syntheses and structures of hypervalent pentacoordinate carbon and boron compounds bearing an anthracene skeleton - Elucidation of hypervalent interaction based on X-ray analysis and DFT calculation

Published on Web 03/05/2005

Syntheses and Structures of Hypervalent Pentacoordinate

Carbon and Boron Compounds Bearing an Anthracene

Skeleton - Elucidation of Hypervalent Interaction Based on

X-ray Analysis and DFT Calculation

†

,†

,‡

§

Makoto Yamashita, Yohsuke Yamamoto,* Kin-ya Akiba,* Daisuke Hashizume,

§

|

Fujiko Iwasaki, Nozomi Takagi, and Shigeru Nagase

Contribution from the Department of Chemistry, Graduate School of Science,

Hiroshima UniVersity, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan, AdVanced

Research Center for Science and Engineering, Waseda UniVersity, 3-4-1 Ohkubo, Shinjuku-ku,

Tokyo 165-8555, Japan, Department of Applied Physics and Chemistry, The UniVersity of

Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan, and

Department of Theoretical Molecular Science, Institute for Molecular Science,

Myodaiji, Okazaki 444-8585, Japan

Received November 30, 2004; E-mail: yyama@sci.hiroshima-u.ac.jp; akibaky@waseda.jp

Abstract: Pentacoordinate and tetracoordinate carbon and boron compounds (27, 38, 50-52, 56-61)

bearing an anthracene skeleton with two oxygen or nitrogen atoms at the 1,8-positions were synthesized

by the use of four newly synthesized tridentate ligand precursors. Several carbon and boron compounds

were characterized by X-ray crystallographic analysis, showing that compounds 27, 56-59 bearing an

oxygen-donating anthracene skeleton had a trigonal bipyramidal (TBP) pentacoordinate structure with

relatively long apical distances (ca. 2.38-2.46 Å). Despite the relatively long apical distances, DFT calculation

of carbon species 27 and boron species 56 and experimental accurate X-ray electron density distribution

analysis of 56 supported the existence of the apical hypervalent bond even though the nature of the

hypervalent interaction between the central carbon (or boron) and the donating oxygen atom was relatively

weak and ionic. On the other hand, X-ray analysis of compounds 50-52 bearing a nitrogen-donating

anthracene skeleton showed unsymmetrical tetracoordinate carbon or boron atom with coordination by

only one of the two nitrogen-donating groups. It is interesting to note that, with an oxygen-donating skeleton,

the compound 61 having two chlorine atoms on the central boron atom showed a tetracoordinate structure,

although the corresponding compound 60 with two fluorine atoms showed a pentacoordinate structure.

The B-O distances (av 2.29 Å) in 60 were relatively short in comparison with those (av 2.44 Å) in 59

having two methoxy groups on the central boron atom, indicating that the B-O interaction became stronger

due to the electron-withdrawing nature of the fluorine atoms.

2

3

Introduction

interaction or bridging alkyl groups, carboranes, and a carbon

4

atom in a metal cluster cage have eight electrons formally

assignable around the central carbon, and the pentacoordinate

structure is made possible by the interaction between a σ bond

two-center two-electron bond: 2c-2e) with a vacant orbital of

proton and so forth. In contrast, electron-rich pentacoordinate

carbon species such as the transition states of the SN2 reaction

have 10 electrons formally assignable around the central carbon

atom based on an interaction of a vacant 2p orbital of the central

carbon atom with two lone-pair electrons (four electrons) or an

interaction between a vacant C-X σ* orbital and a lone pair of

a nucleophile. The interaction leads to the formation of a linear

Pentacoordinate carbon compounds should be classified into

electron-deficient and electron-rich species based on the number

of formal valence electrons around the central carbon. Electron-

deficient pentacoordinate carbon compounds such as methonium

(

+

1

ion (CH5 ), transition-metal complexes bearing C-H agostic

†

Hiroshima University.

Waseda University.

The University of Electro-Communications.

Institute for Molecular Science.

‡

§

|

(

1) Methonium ion (CH

5

⁺): (a) Olah, G. A.; Laali, K. K.; Wang, Q.; Prakash,

G. K. S. Onium Ions; John Wiley & Sons: New York, 1998. (b) Olah, G.

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Chemistry; John Wiley & Sons: New York, 1987. (c) Olah, G. A.; Prakash,

G. K. S.; Sommer, J. Superacids; John Wiley & Sons: New York, 1985.

5

three-center four-electron (3c-4e) “hypervalent” bonding sys-

tem; thus, they are called hypervalent compounds.

(

d) Marx, D.; Parrinello, M. Nature 1995, 375, 216-218. (e) Schreiner, P.

R.; Kim, S.-J.; Schaefer, H. F.; Schleyer, P. v. R. J. Chem. Phys. 1993, 99,

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268.

Theoretical calculations showed that the transition state of

the SN2 reaction should be D3h trigonal bipyramidal (TBP). In

some cases, the pentacoordinate carbon species could be found

3

4354

9

J. AM. CHEM. SOC. 2005, 127, 4354-4371

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

as the transition state of the solvent-exchange process of solvated

6a,b

carbocations. The transition-state structures of SN2 reactions

-

such as CH5 (a), CH3F2 (b), CF5 (c), CH3(OH)2 (d), CH3-

(

+

6

OH2)2 (e), and CMe3(OH2)2 (f) or solvent exchange SN2-

like processes of the solvated carbocations under SN1 conditions

are illustrated together with the ratio of the calculated apical

7

C-X distance to the sum of the covalent radii (Figure 1). All

2

of these imaginary molecules are built up from an sp carboca-

tion coordinated by two anionic nucleophiles (a-d) and by two

neutral nucleophiles (e, f). The two linear hypervalent apical

bonds are relatively long (dotted lines in Figure 1). The

2

elongation of apical bonds compared to sp equatorial bonds is

widely found in hypervalent compounds of main group elements

such as phosphorus, sulfur, silicon, and so forth. Based on

comparison of a, b, and d, it is seen that the apical bond

elongation should be related with the electronegativity and hence

the atomic radius of apical X. In the case of b and c, equatorial

fluorine atoms made the C-F apical bond shorter. In the case

of d, e, and f, the C-O bond in e and f was elongated in

comparison with d probably due to the decrease in nucleophi-

licity of the neutral nucleophiles (H2O) compared with the

Figure 1. Calculated hypervalent pentacoordinate carbon structures for

transition state of SN2.

hydroxide ion and to the presence of the cationic charge in e

and f. By comparison of e and f, it is apparent that the equatorial

methyl group elongates the apical C-O bond. Thus, theoretical

calculations have provided information about the structures of

pentacoordinate carbon species including substituent effects on

the structure.

(

2) agostic interaction or bridging alkyl groups: (a) Braunstein, P.; Boag, N.

M. Angew. Chem., Int. Ed. 2001, 40, 2427-2433 and references therein.

(

b) Boesveld, W. M.; Hitchcock, P. B.; Lappert, M. F.; Liu, D. S.; Tian, S.

However, there have been no reliable experimental investiga-

tions before us about the structural and bonding features of

pentacoordinate carbon species because of the difficulties in

synthesizing appropriate model compounds. In addition, there

have been only few examples of the theoretical investigation

about hypervalent pentacoordinate boron compounds which are

isoelectronic to carbocations. The hypervalent boron compound

was assumed as a transition state of the SN2-type reaction on

the central boron atom of a borane-carbon monooxide complex

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(

d) Klosin, J.; Roof, G. R.; Chen, E. Y.-X.; Abboud, K. A. Organometallics

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000, 19, 4684-4686. (e) Yu, Z.; Wittbrodt, J. M.; Heeg, M. J.; Schlegel,

H. B.; Winter, C. H. J. Am. Chem. Soc. 2000, 122, 9338-9339. (f) Chen,

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1

841-1849. (h) Chan, M. S. W.; Ziegler, T. Organometallics 2000, 19,

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5

L.-C.; Bonitatebus, P. J., Jr.; Davis, W. M. Organometallics 2000, 19,

5

325-5341. (j) Duncan, A. P.; Mullins, S. M.; Arnold, J.; Bergman, R. G.

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8

Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391-1434. (n) Song, X.;

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8

with trimethylamine by the Grotewold group. In 1995, the Oki

group reported the direct observation of intramolecular SN2

(o) Kleinhenz, S.; Seppelt, K. Chem.sEur. J. 1999, 5, 3573-3580. (p)

_d_i_s_p_l_a_c_e_m_e_n_t_r_e_a_c_t_i_o_n_s_u_s_i_n_g_a₂_,₆_-_d_i_s_u_b_s_t_i_t_u_t_e_d_b_e_n_z_e_n_e_l_i_g_a_n_d_.9

Kulzick, M. A.; Andersen, R. A.; Muetterties, E. L.; Day, V. W. J.

Organomet. Chem. 1987, 336, 221-236. (q) Schwartz, D. J.; Ball, G. E.;

Andersen, R. A. J. Am. Chem. Soc. 1995, 117, 6027-6040. (r) Shin, J. H.;

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J. M.; Gibson, V. C.; Howard, J. A. K. Chem. Commun. 1997, 2345-

However, the details of the structure and nature of the transition

state have never been studied after Grotewold’s assumption.

Some chemists have confronted the very difficult problem

of the synthesis of stabilized hypervalent carbon and boron

compounds. Breslow challenged the problem using trityl cation

derivatives bearing some o-methylthiomethyl substituents as

2

1

346. (t) Bursten, B. E.; Cayton, R. H. Organometallics 1986, 5, 1051-

053. (u) Ozawa, F.; Park, J. W.; Mackenzie, P. B.; Schaefer, W. P.;

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(v) Dawkins, G. M.; Green, M.; Orpen, A. G.; Stone, F. G. A. J. Chem.

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M.; Calvert, R. B.; Shapley, J. R.; Stucky, G. D. Inorg. Chem. 1979, 18,

10

early as 1966. The compound came out as sulfonium salts,

and they could not find any positive evidence for the presence

of pentacoordinate carbon compounds. Martin and Basalay

3

19-323. (z) Dutta, T. K.; Vites, J. C.; Jacobsen, G. B.; Fehlner, T. P.

Organometallics 1987, 6, 842-847. (aa) Adams, R. D.; Horv a´ th, I. T. Prog.

Inorg. Chem. 1985, 33, 127-181.

attempted to stabilize the pentacoordinate carbon species by the

(

3) Carboranes: (a) Grimes, R. N. Carboranes; Academic Press: New York,

11

1

,8-bis(phenylthio)anthracenyl ligand. At room temperature,

1970. (b) Olah, G. A.; Wade, K.; Williams, R. E. Electron Deficient Boron

and Carbon Clusters; John Wiley & Sons: New York, 1991. (c) Kabalka,

G. W. Current Topics in the Chemistry of Boron; The Royal Society of

Chemistry: Cambridge, 1994. (d) Siebert, W. AdVances in Boron Chemistry;

The Royal Society of Chemistry: Cambridge, 1997. (e) King, R. B. Boron

Chemistry at the Millennium; Elsevier Science: Amsterdam, 1999. (f)

Davidson, M.; Hughes, A. K.; Marder, T. B.; Wade, K. Contemporary

Boron Chemistry; The Royal Society of Chemistry: Cambridge, 2000.

4) Metal cluster cage: Scherbaum, F.; Grohmann, A.; M u¨ ller, G.; Schmidbaur,

H. Angew. Chem., Int. Ed. Engl. 1989, 28, 463-465.

the peak of two methyl groups on the carbocation attached at

C-9 was observed as a singlet. When the temperature was

lowered, two singlet peaks of the two methyl groups were

observed because of the formation of a sulfonium salt, where

one of the phenylthio groups stays unaffected. They concluded

that the desired pentacoordinate carbon species should be the

transition state in the “bell-clapper” (bond-switching) rearrange-

(

5) (a) Musher, J. I. Angew. Chem., Int. Ed. Engl. 1969, 8, 54-68. (b) Akiba,

K.-y. Chemistry of HyperValent Compounds; Wiley-VCH: New York,

1

999.

(

6) (a) Yamabe, S.; Yamabe, E.; Minato, T. J. Chem. Soc., Perkin Trans. 2

(8) (a) Grotewold, J.; Lissi, E. A.; Villa, A. E. J. Chem. Soc. A 1966, 1034-

1037. (b) Grotewold, J.; Lissi, E. A.; Villa, A. E. J. Chem. Soc. A 1966,

1038-1041.

1

983, 1881-1884. (b) Ruggiero, G. D.; Williams, I. H. J. Chem. Soc.,

Perkin Trans. 2 2001, 448-458. (c) Carroll, M. T.; Gordon, M. S.; Windus,

T. L. Inorg. Chem. 1992, 31, 825-829. (d) Glukhovtsev, M. N.; Pross,

A.; Radom, L. J. Am. Chem. Soc. 1995, 117, 2024-2032. (e) Hiraoka, K.;

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(9) Toyota, S.; Futawaka, T.; Ikeda, H.; Oki, M. J. Chem. Soc., Chem. Commun.

1995, 2499-2500.

(10) (a) Breslow, R.; Garratt, S.; Kaplan, L.; LaFollette, D. J. Am. Chem. Soc.

1968, 90, 4051-4055. (b) Breslow, R.; Kaplan, L.; LaFollette, D. J. Am.

Chem. Soc. 1968, 90, 4056-4064.

2

45, 14-18. (f) Raghavachari, K.; Chandrasekhar, J.; Burnier, R. C. J.

Am. Chem. Soc. 1984, 106, 3124-3128.

(7) Dean, J. A. Lange’s Handbook of Chemistry, 11th ed.; McGraw-Hill: New

York, 1973; pp 3-119-3-123.

(11) (a) Basalay, R. J.; Martin, J. C. J. Am. Chem. Soc. 1973, 95, 2565-2571.

(b) Martin, J. C.; Basalay, R. J. J. Am. Chem. Soc. 1973, 95, 2572-2578.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4355

A R T I C L E S

Yamashita et al.

ment between the two sulfonium salts. Forbus and Martin

claimed the synthesis and direct observation of pentacoordinate

carbon compound using the 1,8-bis(p-methylphenylthio)anthra-

cenyl ligand, where the carbocation attached at C-9 is contained

in a benzene ring bearing two methoxy groups at 2′,6′-

positions.¹²The C NMR chemical shift of the central carbon

13

(δ 109 ppm; dication) was shifted to higher field from the

reduced electronically neutral anthracene compound (δ 118

ppm). Although they carefully tried to prove the existence of

pentacoordinate carbon compounds with NMR, which showed

a symmetrical spectrum apparently reasonable as pentacoordi-

nate species in solution, the compounds had not been character-

ized by X-ray analysis. In 1984, Lee and Martin reported direct

observation of hypervalent penta- (δB -20 ppm) and hexaco-

Figure 2. Ligand design for pentacoordinate carbon and boron compounds.

Scheme 1. Attempted peri-Lithiation of 1,8-Dimethoxyanthracene

6

1

ordinate (δB -123 ppm) boron compounds with the use of

B

1

3

11

NMR. The latter B NMR chemical shift was the highest

value ever observed for any known boron compound with only

first-row elements bonded to the central boron atom. Then, the

Hojo group attempted to prepare a pentacoordinate carbon

compound by stabilizing the carbocation attached at the C-1 of

14

fluorene by coordination of the two methylthio groups at C-9.

+

However, in the solid state the two C -S bond distances were

different, with the shorter one (1.94 Å) close to that of a covalent

C-S bond (1.81 Å), forming a sulfonium salt. Kudo detected

1

5

CLi6, which was proposed by the Schleyer group, by

Knudsen-effusion mass spectrometry.¹⁶However, the details

of the bonding nature of CLi5 and CLi6 have not yet been

clarified.

Results and Discussion

Strategy for the Synthesis of Hypervalent Pentacoordinate

Carbon (10-C-5) and Boron (10-B-5) Compounds. To

stabilize the pentacoordinate carbon (10-C-5) and boron (10-

B-5) species, we used a rigid anthracene skeleton with donor

groups D (Figure 2), and the ligand precursors 1-3 were

synthesized (Figure 2).

Recently, we reported on the syntheses and X-ray structures

17a,e

17b-d

of several carbon

and boron

compounds bearing a newly

synthesized rigid tridentate anthracene ligand. However, there

appeared comments by a chemist about the intrinsic nature of

the hypervalent interaction between the central carbon and the

two coordinating oxygen atoms.¹⁸Here we report on the details

of our work, especially on the structures of the carbon and the

corresponding boron compounds with anthracene ligands. The

bonding nature between the central carbon (or boron) and the

two coordinating atoms is elucidated and discussed based on

the several X-ray structures with several different substituents,

theoretical DFT calculations, and the accurate experimental

X-ray electron-density distribution analysis. The structures and

the bonding nature of newly synthesized pentacoordinate carbon

compounds bearing a 2,6-bis(p-substituted phenyloxymethyl)-

Syntheses of Ligand Precursors 1 and 2. A direct lithiation

20a

of the 9-position of 1,8-dimethoxyanthracene 6, which was

prepared from commercially available anthraquinone 4, was

examined under various conditions with various bases (n-BuLi,

s-BuLi, tert-BuLi) in various solvents (n-hexane, diethyl ether,

tetrahydrofuran) with or without the addition of N,N,N′,N′-

tetramethylethylenediamine (TMEDA). However, the desired

lithiation at the 9-position to give 7 did not occur at all (Scheme

20b

1

). Therefore, 9-hydroxy anthracene 8

was converted to

triflate 1 (Scheme 2), which was useful for the introduction of

1

9

benzene ligand will be discussed in a separate paper.

17a

the carbon atom at the 9-position. Since 1 could not be used

for the introduction of the boron atom, 9-bromoanthracene

precursor 2 had to be synthesized.

1,8-Dimethoxy-9-bromoanthracene 2 was synthesized from

(

12) (a) Forbus, T. R., Jr.; Martin, J. C. J. Am. Chem. Soc., 1979, 101, 5057-

059. (b) Forbus, T. R., Jr. Ph.D. Thesis, University of Illinois, 1981. (c)

17b

5

Forbus, T. R., Jr.; Martin, J. C. Heteroat. Chem. 1993, 4, 113-128. (d)

Forbus, T. R., Jr.; Martin, J. C. Heteroat. Chem. 1993, 4, 129-136. (e)

Forbus, T. R., Jr.; Kahl, J. L.; Martin, J. C. Heteroat. Chem. 1993, 4, 137-

8

with a selective C-O bond cleavage reaction from 9 or 12 as

1

43. (f) Martin, J. C. Science 1983, 221, 509-514.

a key step (Scheme 2). Initially, several reduction conditions

(13) (a) Lee, D. Y.; Martin, J. C. J. Am. Chem. Soc. 1984, 106, 5745-5746.

17b

were examined for phosphate 9, with a couple of one-electron

(b) Lee, D. Y., Ph.D. Thesis, University of Illinois, 1985.

(

14) Hojo, M.; Ichi, T.; Shibato, K. J. Org. Chem. 1985, 50, 1478-1482.

15) Schleyer, P. v. R.; W u¨ rthwein, E.-U.; Kaufmann, E.; Clark, T. J. Am. Chem.

Soc. 1983, 105, 5930-5932.

reducing reagents (K/NH3, lithium naphthalenide, etc.). The

reduction of 9 under K/NH3 (Birch reduction condition) gave

9-protonated product 6, which should be generated by the

reaction of the 9-potassium derivative with ammonia. To prevent

the trapping of a proton, THF was chosen as an aprotic solvent,

and the reduction of 9 was carried out with lithium naphthalenide

followed by the reaction with BrCF2CF2Br. The reaction gave

(

16) Kudo, H. Nature, 1992, 355, 432-434.

17) (a) Akiba, K.-y.; Yamashita, M.; Yamamoto, Y.; Nagase, S. J. Am. Chem.

Soc. 1999, 121, 10644-10645. (b) Yamashita, M.; Yamamoto, Y.; Akiba,

K.-y.; Nagase, S. Angew. Chem., Int. Ed. 2000, 39, 4055-4058. (c)

Yamashita, M.; Watanabe, K.; Yamamoto, Y.; Akiba, K.-y. Chem. Lett.

2001, 1104-1105. (d) Yamashita, M.; Kamura, K.; Yamamoto, Y.; Akiba,

K.-y. Chem.sEur. J. 2002, 8, 2976-2979. (e) Yamashita, M.; Mita, Y.;

Yamamoto, Y.; Akiba, K.-y. Chem.sEur. J. 2003, 9, 3655-3659.

18) Levy, J. B. Chem. Eng. News 2000, 78, 13-14.

19) Akiba, K.-y.; Moriyama, Y.; Mizozoe, M.; Inohara, H.; Nishii, T.;

Yamamoto, Y.; Minoura, M.; Hashizume, D.; Iwasaki, F.; Takagi, N.;

Ishimura, K.; Nagase, S. J. Am. Chem. Soc. In press.

(

(20) (a) Cameron, D. W.; Sch u¨ tz, P. E. J. Chem. Soc. C 1967, 2121-2125. (b)

Prinz, H.; Burgemeister, T.; Wiegrebe, W.; M u¨ ller, K. J. Org. Chem. 1996,

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4356 J. AM. CHEM. SOC.

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VOL. 127, NO. 12, 2005

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

Scheme 2. Syntheses of 9-Substituted 1,8-Dimethoxyanthracenes 1 and 2

Scheme 3. Attempted peri-Lithiation of

Scheme 4. Attempt to Synthesize 3

1,8-Bis(dimethylamino)anthracene 16

1

7d

Finally, 3 could be prepared as illustrated in Scheme 5.

2

4

Bromide substitution of commercially available dichloroan-

2

5

thraquinone 13 followed by reduction afforded dibromoan-

throne (22) in 52% yield from 13. Deprotonation of 22 followed

by methylation gave 1,8-dibromo-9-methoxyanthracene (23) in

6

0% yield. The Pd(0) mediated coupling reaction of 23 with

a complex mixture including the starting material 9 and a very

small amount of the desired product 2. Substitution of the one-

electron reducing reagent to lithium 4,4′-di-tert-butylbiphenylide

various nucleophiles (Bu3SnNMe2, Me3SnNMe2, LiNMe2, and

HNMe2) did not give the expected bis-dimethylaminated

compound (24); instead only a mono-dimethylaminated product

was obtained in most cases, and the reduction of the C-Br

bonds took place in some cases. However, dibromoanthracene

(LDBB), which has a higher reduction potential, improved the

yield of 2 up to 30%. When an excess amount of LDBB was

used, an undesired product 1,8,9-tribromoanthracene 11 (ca.

2

3 could be converted to 1,8-bis(dimethylamino)-9-methoxy-

2

0%) was obtained instead of 2. The formation of 11 should

anthracene 24 in 79% yield by heating a HNMe2-THF solution

of 23 up to 150 °C in a pressure-resistant vessel with a Ni(0)

catalyst, which is a modified Buchwald’s method.²⁶LDBB

be explained via 1,8,9-trilithioanthracene 10, which was reacted

with BrCF2CF2Br to form 11. Finally, a more efficient route

via a trifluoroacetoxy intermediate 12 was found, and the total

yield of 2 was improved to 51% from 12.

(lithium di-tert-butylbiphenylide) reduction of the methoxy

group at the 9-position of the anthracene skeleton worked well

for 24 to afford the novel anthracene ligand precursor 3 in 51%

yield after reaction with BrCF2CF2Br.

Synthesis of Ligand Precursor 3. Initially, a direct lithiation

2

3

of the 9-position of 1,8-bis(dimethylamino)anthracene 16,

which was prepared from 13, 14,²¹and 15, was examined

Scheme 3), but the desired lithiation of the 9-position to 17

did not take place at all. In addition, a strategy to use 1,8-bis-

dimethylamino)anthrone 18 or tautomerized 1,8-bis(dimethyl-

amino)-9-hydroxylanthracene 19 as a synthetic intermediate

Scheme 4), which is based on the previous synthesis of 1,8-

22

Pentacoordinate Hypervalent Carbon Compound (10-C-

(

5

). A. Introduction of a Carbon Atom to the 9-Position of

Anthracene. Initially, the Pd-mediated coupling reaction of

ligand 1 was examined in order to introduce a carbon substituent

(

(Scheme 6). Nitrile 25 was obtained in 74% yield by the reaction

(

27

of 1 with Zn(CN)2 in DMF in the presence of a Pd(0) catalyst.

dimethoxy-9-bromoanthracene 2, did not work because the

reduction of 1,8-bis(dimethylamino)anthraquinone 15 to the

corresponding anthrone 18 was not successful.

However, the conversion from 25 was very sluggish; only

ca. 5% of the corresponding ethyl ester could be obtained after

(

24) Benites, M. del R.; Fronczek, F. R.; Hammer, R. P.; Maverick, A. W. Inorg.

(

21) House, O. H.; Koepsell, D. G.; Campbell, W. J. J. Org. Chem. 1972, 37,

Chem. 1997, 36, 5826-5831.

1

003-1011.

(25) Biehl, R.; Hinrichs, K.; Kurreck, H.; Lubitz, W. Mennenga, U.; Roth, K.

J. Am. Chem. Soc. 1977, 89, 4278-4286.

(26) Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 6054-6058.

(27) Kubota, H.; Rice, K. C. Tetrahedron Lett. 1998, 39, 2907-2910.

(

22) Lord, W. M.; Peters, A. T. J. Chem. Soc. C 1968, 7, 783-785.

23) Haenel, M. W.; Oevers, S.; Bruckmann, J.; Kuhnigk, J.; Kr u¨ ger, C. Synlett

1

998, 301-303.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4357

A R T I C L E S

Yamashita et al.

Scheme 5. Synthesis of 9-Bromo-1,8-bis(dimethylamino)anthracence 3

Scheme 6. Introduction of a Nitrile Group to the 9-Position of the

Table 1. Conditions for Methoxycarbonylation of 1

Anthracene Skeleton

run

catalyst

solvent

temp,

°

C

time, h

result

1

2

3

4

Pd(OAc)2/dppf^a

Pd(PPh3)4

DMSO

DMF

DMSO

70

130

70

2

8

no reaction

26 (37%)

26 (52%)

Pd(PPh3)4

70

a

dppf: diphenylphosphinoferrocene.

Scheme 7. Methoxycarbonylation of 1

treatment with excess amounts of CF3SO3H, H2O, and EtOH

at 80 °C for 3.5 days. Strong hydride reagents (super-H, DIBAL-

H) did not work either.

Since the conversion of 25 was not quite successful, the direct

methoxycarbonylation of 1 was examined (Scheme 7, Table 1).

Based on the method in the literature,²1 was treated with

MeOH, Pd(II) catalyst, and NEt3 in DMSO under CO atmo-

sphere; however, the starting material 1 was recovered (entry

8

1

). Since the poor results may be due to the difficulty of the

generation of active Pd(0) species from Pd(II) species without

a reductant, Pd(PPh3)4 was used instead of Pd(II). In the presence

of Pd(PPh3)4, the use of DMF as a solvent did not work (entry

2

). However, the combination of DMSO as a solvent and Pd-

Figure 3. Generation of pentacoordinate hypervalent carbon compound

7.

(

PPh3)4 as catalyst afforded the desired product 26 in 37% yield

entry 3). A longer reaction time raised the yield of 26 slightly

2

Scheme 8. Attempted Methylation of the Methoxycarbonyl Group

without Two OMe Groups on the Anthracene Ring

better (entry 4, 52%).

B. Generation and Characterization of Hypervalent Pen-

tacoordinate Carbon Compound 27. To generate carbocation

2

7, ester derivative 26 was treated with an excess amount of

+

- 29

Meerwein reagent (Me3O BF4 ) in refluxing CH2Cl2 for 20

h (Figure 3). After filtration of excess Me3O BF4 and removal

+

-

of the solvent, 27 was obtained as a yellow-green solid. In the

1

H NMR of 27, all of the aromatic peaks showed the symmetric

carbocation center and the lone pairs of the OMe groups. This

fact indirectly supported the existence of a hypervalent stabiliz-

ing interaction between the central carbon and the two OMe

structure of anthracene skeleton just like 26 and shifted to lower

fields with the retention of four kinds of peaks (two kinds of

doublets, a triplet and a singlet).

groups in 27.

In the use of 9-methoxycarbonylanthracene 28 without two

OMe groups at the 1,8-position of the anthracene skeleton, the

generation of the corresponding carbocation was not observed

in H NMR (Scheme 8). The lack of reactivity in 28 may result

from a lack of hypervalent bonding interaction between the

_T_o_d_e_t_e_r_m_i_n_e_t_h_e13C NMR chemical shift of the central

13

carbon of 27 clearly, C-26 and C-27 were synthesized.

13

Esterification of 1 proceeded under C-enriched CO atmosphere

1

13

+

-

to give C-26. The ester was similarly methylated by Me3O BF4

13

to give C-27. In the C NMR spectra, the chemical shift of

1

3

the central carbon shifted from δ 172.30 ( C-26) to δ 192.58

C-27) ppm. The difference in the chemical shifts (∆δ )

(

28) Dolle, R. E.; Schmidt, S. J.; Kruse, L. I. J. Chem. Soc., Chem. Commun.

987, 904-905.

29) Meerwein, H. Methoden Org. Chim. 1965, 6/3, 325-365.

13

(

1

(

20.28) was comparable to the difference (∆δ ) 21.3) from

4

358 J. AM. CHEM. SOC. VOL. 127, NO. 12, 2005

9

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

1

9

1

19

2

19

3

Figure 4. ORTEP drawing of 27 (30% thermal ellipsoid). Selected bond distances (Å) and angles (deg): C -O 2.43(1), C -O 2.45(1), C -O 1.26(1),

19

4

19

9

1

19

2

1

19

3

1

19

4

1

19

9

2

19

3

2

19

4

C -O 1.30(1), C -C 1.48(1), O -C -O 168.7(5), O -C -O 95.7(7), O -C -O 90.5(6), O -C -C 85.4(7), O -C -O 94.6(7), O -C -O

2

19

9

3

19

4

3

19

9

4

19

9

8

8.8(6), O -C -C 85.8(6), O -C -O 117.9(9), O -C -C 116.3(8), O -C -C 125.8(9).

Figure 5. Comparison of side views of 11, 1, 25, and 27.

methyl formate (δ 171.52)³⁰to dimethoxymethyl cation (δ

1

bond (2.64 Å) in the transition state of [H2O-C(CH3)3-

OH2] . The ratio of the observed C-O apical length of 27 to

92.8).³¹

+ 6a

From the CDCl3 solution of 27, single crystals suitable for

the sum of the covalent radius was 1.71. The elongation of the

C-O bond is comparable to [H2O-C(CH3)3-OH2] (the ratio

+

X-ray analysis were obtained, and the X-ray structure is shown

-

in Figure 4. The counteranion B2F7 is unexpected, but it is

of the apical C-O bond to the sum of the covalent radius is

6

a

well separated from the cationic part. The structure clearly shows

the symmetrical nature of the compound. The sum of the angles

1.84).

C. Elucidation of the Weak C-O Interaction in 27. To

elucidate the property and the degree of interaction between

the central carbon atom and the two oxygen atoms in 27, the

side views of the crystal structures and selected distances of

11, 1, and 25 are shown in Figure 5 together with 27. In the

structure of tribromo derivative 11, the three bromine atoms

are placed out of plane of the anthracene skeleton in order to

avoid large steric repulsion. In the structure of 1, three oxygen

atoms are slightly distorted from the anthracene plane, probably

due to the lone-pair repulsion among the three oxygens.

In the case of 25 and the cation 27, the atoms attached to the

1, 8, and 9 positions are almost perfectly in the plane of the

anthracene, indicating that the interaction between the central

carbon atom and the two oxygen atoms is not repulsive. The

comparison of the distances between the atom attached to the

9-position of the anthracene and the atoms on the 1,8-positions

is also worthy of note (Table 2). In the cases of 11 and 1, the

averaged distances of a and a′ (3.2698(6) Å in 11, 2.572(2) Å

in 1) are longer than those of b and b′ (2.566(6) Å in 11, 2.550-

3

19

9

4

19

9

3

19

4

(

O -C -C , O -C -C , and O -C -O ) around the central

2

carbon is 360.0°, indicating that the carbon is planar with sp

hybridization. The angles around the oxygen atoms of the

methoxy group at the 1,8-positions of anthracene are 119.2(9)°

1

15

8

2

16

(

C -O -C ) and 120.3(9)° (C -O -C ), showing that both

2

oxygen atoms have sp hybridization. Since the carbon atoms

of the methoxy groups at the 1,8-positions are in the plane of

the anthracene, one of the lone pairs of each oxygen atom should

be directed toward the empty p-orbital of the central carbocation

attached at the 9-position and the other should be parallel to

π-electrons of the anthracene. Therefore, the geometry around

the central carbon atom is TBP, which is only slightly distorted.

The two C-O distances are almost identical [2.43(1) and 2.45-

(

1) Å], which is significantly longer than that of a covalent C-O

7

bond (1.43 Å) but shorter than the corresponding apical C-O

(

30) SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/menu-j.html.

31) Olah, G. A.; Hartz, N.; Rasul, G.; Burrichter, A.; Prakash, G. K. S. J. Am.

Chem. Soc. 1995, 117, 6421-6427.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4359

A R T I C L E S

Yamashita et al.

Table 2. Comparison of Distances of a (a′) and b (b′) of 11, 1, 25,

and 27

(

3) Å in 1), while, in 25, the averaged distance of a and a′

2.531(3) Å) is comparable with that of b and b′ (2.540(5) Å).

Figure 6. ORTEP drawing of 6 (30% thermal ellipsoid). Selected

1

8

2

interatomic distances (Å) and angles (deg): C -O 1.366(2), C -O 1.359-

1

5

1

16

2

1

2

1

15

In contrast, in 27, the averaged distance of a and a′ (2.44(1) Å)

is clearly shorter than that of b and b′ (2.51(2) Å). Therefore,

it can be concluded that the interaction between the central

carbon atom and the two oxygen atoms in 27 should be clearly

attractive.

(2), C -O 1.423(2), C -O 1.425(2), O -O 4.752(3), C -O -C

8 2 16

1

17.62(16), C -O -C 117.77(17).

Scheme 9. Strategy for the Derivatization of Hypervalent Carbon

Compounds

To elucidate the nature of the interaction between the central

carbon atom and the two oxygen atoms at the 1,8-positions of

anthracene skeleton, the geometry of 27 was fully optimized

with hybrid density functional theory (DFT) at the B3PW91/

6

-31G(d) level using the Gaussian 98 program.³²The structural

optimization afforded the symmetrical Cs structure of 27 as the

energy minimum. The two C-O distances are identical (2.472

Å) and slightly longer than the experimental distances (2.43(1)

and 2.45(1) Å). It should be noted that the bond paths are found

between the central carbon atom and the two oxygen atoms,

33

clearly showing that these atoms are bonded. The bond is weak

3

and ionic based on the small F(r) value of 0.022 e/ao and the

2

5

small positive ∇ F(r) value of 0.080 e/ao at the bond critical

points. These values are consistent with those of axial C-H

-

3

2

5 6c

bonds in CH5 (F(r): 0.067 e/ao , ∇ F(r): 0.009 e/ao ). A large

value (0.219) of the ellipticity of the C-O bond reflects the

electron donation to the central carbocation from the two lone

pairs of the oxygen atoms of the methoxy groups at the 1,8-

positions within the anthracene plane. In conclusion, the

anthracene carbocation 27 is the first fully characterized

hypervalent pentacoordinate 10-C-5 compound for a model of

the transition state of the SN2 reaction.

of 1,8-dimethoxyanthracene, without a central positive carbon”.

Therefore, we examined the X-ray structure of 1,8-dimethoxy-

1

anthracene 6 (Figure 6), which showed a relatively shorter O -

2

O distance [4.752(3) Å] than the sum of two apical C-O

distances of 27 (4.88 Å) as the commentator indicated.

Therefore, we started further investigation to obtain the hyper-

valent pentacoordinate carbon (or boron) compounds bearing

stronger apical C-O (or B-O) interaction.

Recently, a comment appeared in C&E News, discussing the

weak interaction between the central carbon atom and two

oxygen atoms at 1,8-positions of anthracene skeleton in 27.

It stated that “The two methoxy groups at the 1 and 8 positions

of 27 lean toward one another in the analogous conformation

D. Attempt to Synthesize Other Hypervalent Pentacoor-

dinate Carbon Compounds. The strategy for derivatization of

hypervalent pentacoordinate carbon compounds with stronger

apical C-O interaction is illustrated in Scheme 9. To strengthen

the apical bond, three types of derivatizations were examined.

(i) Apical oxygen atoms were replaced by nitrogen atoms to

strengthen the electron-donating ability of the donor. (ii, iii)

1

8

(

32) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M.

A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.; Stratmann,

R. E., Jr.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniel, A. D.; Kudin,

s, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.;

Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski,

J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;

Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz,

J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;

Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,

C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;

Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-

Gordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.5;

Gaussian, Inc.: Pittsburgh, PA, 1998.

2

Substituents on the sp plane of the carbocation were replaced

by alkyl or perfluoroalkyl groups to reduce the electron density

on the central carbocation. However, the attempt to obtain the

X-ray structures has not been successful until now. The synthesis

and results are briefly shown below.

The synthesis of the carbocation species bearing the nitrogen

donor ligand and its precursor is illustrated in Scheme 10.

Halogen lithium exchange reaction of 3 with n-BuLi generated

the corresponding lithium derivative 17 quantitatively, followed

by esterification with ClCO2R (R ) Me, Et) to give the

(33) (a) Bader, R. F. W. Atoms in Molecules - A Quantum Theory; Oxford

University Press: Oxford, 1990. (b) Bader, R. F. W. Chem. ReV. 1991,

9

1, 893-926. (c) Bader, R. F. W.; Slee, T. S.; Cremer, D.; Kraka, E. J.

Am. Chem. Soc. 1983, 105, 5061-5068. (d) Bader, R. F. W. J. Phys. Chem.

A 1998, 102, 7314-7323.

4360 J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

Scheme 10. Methoxycarbonylation of 3 and Methylation of 30a

Scheme 11. Introduction of Olefins to 9-Position of Anthracene

Skeleton

Scheme 12. Introduction of a Carbon Atom Bearing Two

Trifluoromethyl Groups to the Anthracene Skeleton

precursor 30a (R ) Me; δ NMe2 2.67 (s, 6H) and 2.73 (s, 6H),

δ OMe 3.97 (s, 3H)) and 30b (R ) Et). In the generation of

the alcohol 34 or cyclized demethylation compound 35. The

treatment of 34 with Tf2O gave cyclized demethylation com-

pound 35 instead of carbocation derivative 36. The attempted

methylation of the oxygen of 35 to give desired carbocation 36

was not successful.

-

3

1a-TfO or 31b-BF4 from 30a or 30b with MeOTf or

+

-

Et3O BF4 , most of the product precipitated in a flask as an

1

-

orange solid. The H NMR spectrum of 31a-TfO could be

measured in CD2Cl2, showing the lower-field-shifted sym-

metrical anthracene and NMe2 pattern (lower; aliphatic, 12H

singlet of NMe2 (δ 2.96), 6H singlet of OMe (δ 3.94); aromatic,

two doublets, a triplet and a singlet), which was similar to that

of 27 (Figure 4). A variety of attempts to obtain a single crystal

To obtain anionic hypervalent pentacoordinate carbon com-

pound 38, further demethylation of 35 was attempted (Scheme

36

37

1

3) with several reagents such as BBr3, Me3SiI, and HBr/

- 38

Br , at low or high temperatures, but it gave no desired

demethylated product 37 (Scheme 13). On the other hand,

alkyllithium reacted with 35 to give unexpected products 39

and 40.

-

of 31a-X suitable for X-ray analysis were not successful even

-

when the counteranion was exchanged to ClO4 or B(C6F5)4 .

Syntheses of the carbocations 33a and 33b bearing alkyl

groups and their precursors are illustrated in Scheme 11. Ligand

precursor 1 was reacted with metal-olefin reagents in the

To synthesize anionic hypervalent pentacoordinate carbon

compound 38, we designed a novel ligand precursor 45 bearing

two deprotectable methoxymethyl groups as a trianion equiva-

lent. Complete synthesis of a new ligand precursor 45 was

34,35

presence of a Pd(0) catalyst

to give the corresponding olefin

products 32a and 32b. The double bond of 32a and 32b reacted

with a proton to generate dialkyl carbocation 33a and 33b,

respectively.

17e

already reported and is illustrated in Scheme 14. Synthesis

of 45 was achieved with stepwise oxygenation with the

In the case of 33a, the ¹H NMR spectrum showed a

39

oxaziridine reagent and gaseous O2. Although 45 is not quite

1

complicated pattern. On the other hand, the H NMR spectrum

stable to chromatographic treatment (SiO2) or prolonged stand-

ing at room temperature, 45 could be purified by recycle HPLC.

After quantitative regeneration of lithium derivative 44 by

the reaction of 45 with 1 equiv of n-BuLi in ether, 44 was

reacted with gaseous hexafluoroacetone to give the alcohol

derivative 46 together with cyclized product 47. Cyclized

product 47 was easily deprotected with HCl/THF at rt to give

the precursor 37. Compound 37 was deprotonated with KH in

of 33b in the aromatic region showed the lower-field-shifted

symmetrical anthracene pattern similar to that of 27 in addition

to the identical CH2 (δ 4.32) bonded to the central carbon.

Unfortunately, any single crystal suitable for X-ray analysis

could not be obtained for 33b.

The attempted synthesis of the carbocation 36 bearing two

trifluoromethyl groups is illustrated in Scheme 12. Lithium

derivative 7 was reacted with gaseous hexafluoroacetone to give

(

36) McOmie, J. F. W.; West, D. E. Org. Synth. Collect. Vol. V 1973, 412-

(

34) (a) Hayashi, T.; Niizuma, S.; Kamikawa, T.; Suzuki, N.; Uozumi, Y. J.

Am. Chem. Soc. 1995, 117, 9101-9102. (b) Kamikawa, T.; Hayashi, T.

Synlett 1997, 163-164.

414.

(37) Jung, M. E.; Lyster, M. A. J. Org. Chem. 1977, 42, 3761-3764.

(38) Hwang, K.; Park, S. Synth. Commun. 1993, 23, 2845-2849.

(39) Davis, F. A.; Towson, J. C.; Vashi, D. B.; ThimmaReddy, R.; McCauley,

J. P., Jr.; Harakal, M. E.; Gosciniak, D. J. J. Org. Chem. 1990, 55, 1254-

1261.

(35) (a) Ewen, I. M.; R o¨ nnqvist, M.; Ahlberg, P. J. Am. Chem. Soc. 1993, 115,

3

989-3996. (b) Shieh, W. C.; Carlson, J. A. J. Org. Chem. 1992, 57, 379-

3

81. (c) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457-2483.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4361

A R T I C L E S

Yamashita et al.

Scheme 13. Attempts for Demethylation of 35

Scheme 14. Synthesis of New Deprotectable Ligand Precursor 45

hypervalent germanium compounds (Figure 8),⁴¹the tridentate

ligand and two electron-withdrawing trifluoromethyl groups

could not sufficiently affect a change in the structure of our

carbon compound 38 from tetrahedral to TBP. This difference

between our carbon compound 38 and germanium compounds

Scheme 15. Synthesis of Anionic Species 38

4

8 and 49 is probably due to the high electronegativity of the

carbon atom, which could not sufficiently reduce the electron

density on the central carbon atom to stabilize the hypervalent

state of the carbon compounds. In this case, even the two strong

electron-withdrawing trifluoromethyl groups could not lower

an energy level of the σ*-orbital of the C-O bond of 38. An

effort to exchange the countercation for complete separation

from the anion species is under way.

Thus, we have not yet been successful in obtaining an X-ray

structure of a hypervalent pentacoordinate carbon compound

having stronger apical C-O interaction bearing a formal minus

charge. However, recently we could obtain hypervalent penta-

coordinate boron compounds with a stronger B-O interaction.

The results are described together with accurate X-ray analysis

for a boron compound.

the presence of 18-crown-6 to generate the desired anion species

38 (Scheme 15).

Single crystals of 38, which slowly decomposed in air,

suitable for X-ray analysis were obtained from THF-n-hexane

solution under nitrogen atmosphere at room temperature. The

ORTEP drawing of 38 is shown in Figure 7. The shorter O-C

1

15

2

bond (O -C ) length is 1.470(5) Å, and the longer O-C (O -

15

Synthesis and Structures of Boron Compounds Bearing

an Anthracene Skeleton. As was already reported, boron

compounds 50-52 bearing dimethylamino groups could be

C ) length is 2.991(5) Å. Although the former is nearly equal

to the sum (1.44 Å) of the covalent radii of the carbon and

7

oxygen atoms, the latter is shorter than that of the van der Waals

1

7d

7

synthesized from 3 (Scheme 16). Single crystals of 50-52

suitable for X-ray analysis were obtained from a CH Cl -

radius (3.25 Å). The potassium atom surrounded by a crown

2

1

ether interacted with the phenoxide oxygen atom [O -K , 2.570-

2

₃₎_Å_]_i_n_t_h_e_s_o_l_i_d_s_t_a_t_e_._A_n_i_n_d_i_c_a_t_o_r_,_%_T_B_P_e_,₄0 for evaluation

hexane solution. X-ray crystallographic analysis of 50-52

Figure 9) showed the unsymmetrical structures with coordina-

(

of the TBP character, showed that our compound 38 had low

TBP character (27%) similar to pentacoordinate germanium

_c_o_m_p_o_u_n_d₄₈₍_F_i_g_u_r_e₈_,₃₀_%₎₃9 bearing a weak coordination.

The structure of the carbon atom should be regarded to be

common tetracoordinate carbon or pentacoordinate carbon

bearing a very weak coordination. Although the bidentate ligand

and electron-withdrawing group could lead a geometry around

the germanium atom to have significant TBP character (87%

from 30%) and weaken the interaction [O-K lengths; from 2.61-

tion of only one NMe2 group toward the central boron atom.

Shorter N-B bond lengths are 1.809(2) Å in 50, 1.739(2) Å in

51, and 1.667(3) Å in 52, and the longer N-B bonds are 2.941-

(2) Å in 50, 3.124(3) Å in 51, and 3.129(4) Å in 52.

But the energy difference between the unsymmetrical tetra-

coordinate structure and the symmetrical pentacoordinate one

should be very small based on the variable temperature NMR.

1

In H NMR (CDCl3 or CD2Cl2), 50-52 showed symmetrical

(

1) Å to 2.881(6) Å] between an oxygen atom and a potassium

(

41) (a) Kawashima, T.; Iwama, N.; Tokitoh, N.; Okazaki, R. J. Org. Chem.

atom surrounded by crown ether from 48 to 49 in the case of

1

994, 59, 491-493. (b) Kawashima, T.; Nishiwaki, Y.; Okazaki, R. J.

Organomet. Chem. 1995, 499, 143-146. (c) Kawashima, T. J. Organomet.

Chem. 2000, 611, 256-263.

(40) Tamao, K.; Hayashi, T.; Ito, Y. Organometallics 1992, 11, 182-191.

4

362 J. AM. CHEM. SOC. VOL. 127, NO. 12, 2005

9

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

15

1

15

2

1

2

Figure 7. ORTEP drawing of 38 (30% thermal ellipsoid). Selected interatomic distances (Å) and angles (deg): C -O 1.470(5), C -O 2.991(5), K -O

.570(3). Two of four disordered trifluoromethyl groups were omitted for clarification.

2

Figure 8. Interaction between an oxygen atom and potassium atom in

hypervalent germaniumate complexes.

Figure 9. ORTEP drawing of 50-52 (30% thermal ellipsoid). Selected

Scheme 16. Introduction of Boron Atom to the 9-Position of

1

2

1

2

interatomic distances (Å) and angles (deg): (50) N -B 1.809(2), N -B

1,8-Bis(dimethylamino)Anthracene

9

1

2

1

2

1

(

.941(2), C -B 1.599(2), O -B 1.448(2), O -B 1.460(2), O -B -O

1 1 1 1 1 2 1 1 9

07.5(1), O -B -N 104.3(1), O -B -N 75.96(8), O -B -C 122.1-

2

1

2

1

2

1

9

1

9), O -B -N 106.4(1), O -B -N 83.99(8), O -B -C 116.6(1), N -

1

2

1

9

2

1

9

1

B -N 168.7(1), N -B -C 97.4(1), N -B -C 73.48(8). (51) N -B

2

1

9

1

19

1

20

1

.739(2), N -B 3.124(3), C -B 1.646(2), C -B 1.609(3), C -B

1 1 2 1 1 9 1 1 19

.622(3), N -B -N 154.3(1), N -B -C 96.7(1), N -B -C 105.5(1),

1

20

2

1

9

2

1

19

2

1

N -B -C 108.3(1), N -B -C 67.67(8), N -B -C 72.3(1), N -B -

20

9

1

19

9

1

20

19

1

20

1

C

1

95.9(1), C -B -C 127.0(2), C -B -C 106.3(1), C -B -C

1 1 2 1 9 1 1

11.1(1). (52) N -B 1.667(3), N -B 3.129(4), C -B 1.621(3), Cl -B

2

1

2

1

.877(3), Cl -B 1.834(3), Cl -B -Cl 107.8(1), Cl -B -N 108.1(2),

1

2

1

2

1

9

2

1

Cl -B -N 97.9(1), N -B -N 153.5(2), N -B -C 99.9(2), N -B -

anthracene patterns in the aromatic region (two kinds of

doublets, a triplet, and a singlet) and a sharp singlet signal of

the two NMe2 groups at room temperature. The peaks main-

tained their sharpness and the symmetrical pattern even at -80

9

C 66.9(1).

°

C. This is the case even in the most unsymmetrical dichloro

compound 52 (CD2Cl2). It was similar to the behavior of 54

9

1

(

Figure 10) in H NMR, which showed only one singlet (12H)

of the two NMe2 groups and maintained its sharpness in CD2-

Cl2 from 25 °C to -100 °C. However, it was contrasted with

4

5

the behavior of BCl2[2,6-(Et2NCH2)2C6H3] (55, Figure 10) in

H NMR, which showed two kinds of NEt2 groups in C6D6 or

1

Figure 10. Tetracoordinate borate bearing intramolecular coordination.

THF-d8 solvents at 25 °C. The NMR data of 52 indicates that

the very rapid “bond-switching” accompanied with the inversion

at the central atom (bell-clapper rearrangement)¹²is taking place

in solution as illustrated in Scheme 17. Since the energy barrier

of the N-B bond-switching process in 52 was too small to

measure by the coalescence method, the energy difference

between the unsymmetrical tetracoordinate dichloroboron 52 and

‡

(

42) Farfan, N.; Contreras, R. J. Chem. Soc., Perkin Trans. 2 1987, 771-773.

43) (a) Coppens, P. X-ray Charge Densities and Chemical Bonding; Oxford

University Press: New York, 1997. (b) Wilson, A. J. C. International Tables

for Crystallography, Vol. C; Kluwer Academic Publishers: Dordrecht, 1992.

44) Sana, M.; Leroy, G.; Wilante, C. Organometallics 1992, 11, 781-787.

45) Schlengermann, R.; Sieler R.; Hey-Hawkins, E. Main Group Chem. 1997,

the pentacoordinate one 52 , which should be the transition state

(

of the bond switching process, must be very small. The small

activation energy in 52 indicates that our newly prepared rigid

anthracene ligand system stabilizes the pentacoordinate dichlo-

(

‡

2

, 141-148.

roboron transition state (52 ).

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4363

A R T I C L E S

Yamashita et al.

Scheme 17. Very Rapid N-B Bond-Switching Equilibrium in 52

Scheme 18. Introduction of Boron Groups to the 9-Position of

1,8-Dimethoxyanthracene

Figure 11. ORTEP drawing of 56-58 (30% thermal ellipsoid). Selected

2

1

bond distances (Å) and angles (deg): (56) O -B 2.379(2), O -B 2.441-

3

1

4

1

9

1

2

(

2), O -B 1.403(2), O -B 1.397(2), C -B 1.569(2), O -B -O 167.10-

2 1 3 2 1 4 2 1 9 1

(

7), O -B -O 92.14(8), O -B -O 92.65(8), O -B -C 84.31(8), O -

1

3

1

4

1

9

3

1

4

B -O 95.59(8), O -B -O 94.18(8), O -B -C 82.79(8), O -B -O

3

1

9

4

1

9

1

11.1(1), O -B -C 125.4(1), O -B -C 123.5(1). (57) O -B 2.398-

2 1 3 1 4 1 9 1

(

4), O -B 2.412(4), O -B 1.394(3), O -B 1.400(3), C -B 1.570(4),

In contrast to the NMe2 ligand system, the corresponding

1 1 2 1 1 3 1 1 4 1 1

O -B -O 166.3(2), O -B -O 96.3(2), O -B -O 92.7(2), O -B -

boron compounds with the OMe-ligand system showed penta-

coordinate structures except 61 (vide infra). The synthesis of

the boron compounds 56-58 is straightforward as illustrated

in Scheme 18. All of these compounds showed a symmetrical

anthracene pattern (two doublets, a triplet and a singlet) and a

very sharp singlet for the two OMe groups (6H), which indicated

9

2

1

3

2

1

4

2

1

9

C 83.3(2), O -B -O 93.9(2), O -B -O 92.1(2), O -B -C 83.4(2),

O3-B1-O4 111.3(2), O3-B1-C9 123.3(), O4-B1-C9 125.4(2). (58) O1-

1

2

1

9

1

2

1

B

2.436(2), O -B 2.436(2), C -B 1.590(6), S -B 1.816(5), S -B

1 1 2 1 1 1 1 1 9

1

.809(4), S -B -S 112.4(3), S -B -O 95.6(1), S -B -C 121.1(3),

2 1 1 2 1 9 1 1 2 1 1

S -B -O 93.1(1), S -B -C 126.6(3), O -B -O 164.0(3), O -B -

9

C 82.2(1).

1

Scheme 19. Introduction of the BX2 Substituent to the 9-Position

of 1,8-Dimethoxyanthracene

that the two OMe groups were equivalent in their H NMR

1

spectra. The B NMR spectra of the compounds 56 (δ 28-

9), 57 (δ 30-37), and 58 (δ 55-68) showed a broad peak

3

over the range of normal catecholborane derivatives (cf.

phenylcatecholborane: δ ) 32.1 in THF),⁴²indicating that the

interaction between the central boron atom and the oxygen atoms

at the 1,8-positions is very weak. In contrast, upfield shifts were

1

observed in the B NMR spectra of the boron compounds

prepared by Lee and Martin (-20 to -41 ppm).¹⁶The difference

in the chemical shifts between the compounds of Lee and Martin

and 56-58 may be a consequence of the charge difference (the

former being anionic systems, while 56-58 are electronically

neutral systems). Single crystals of 56-58 suitable for X-ray

analysis were obtained by recrystallization from CH2Cl2/n-

hexane (Figure 11). The sum of the bond angles around the

central boron atom of 56-58 is 360.0°, which indicates that

1

very sharp singlet for the two OMe groups (6H) in their H

NMR spectra (δ 4.08 for 59, 4.16 for 60 and 4.31 for 61). The

B NMR spectra of 59-61 showed a broad signal in the same

1

range (δ 27-33 for 59, 20-24 for 60 and 22-25 for 61).

Single crystals of 59-61 suitable for X-ray analysis were

obtained from CH2Cl2/n-hexane solution. X-ray crystallographic

analysis of 59-61 (Figure 12) showed very interesting results.

The structure of 59 was almost symmetrical, their B-O

distances [2.44 Å; average of the three independent molecules]

were similar to those of catecholate derivatives 56-58. Although

the structure of 60 was also symmetrical, their B-O distances

were shortened [2.29 Å; average of the two independent

molecules]. On the other hand, the structure of 61 was quite

unsymmetrical, and their B-O distances [1.686(7) and 2.790-

7) Å] were similar to those of the derivatives 50-52 bearing

the two NMe2 groups at the 1,8-positions of anthracene. It is

interesting to compare the sum of the B-O distances in 59-

1. The sum of the B-O distances of 59 was 4.881 Å (average),

which was similar to the distance between the two hydrogen

atoms at the 1,8-positions of nonsubstituted anthracene [4.92

Å] and longer than the distance between the two oxygen atoms

at the 1,8-positions of 1,8-dimethoxyanthracene 6 [4.752(3) Å].

2

the central boron atom is planar with sp hybridization. Thus,

one of the lone pairs on the oxygen atoms at the 1,8-positions

in 56-58 interacts with the empty p orbital of the central boron

atom, which can be regarded as a slightly distorted TBP

structure. The two B-O lengths (B1-O1, B1-O2) are 2.379-

(2) and 2.441(2) Å in 56, 2.398(4) and 2.412(4) Å in 57, and

identical (2.436(2) Å) in 58. The lengths are longer than those

of the B1-O3 and B1-O4 (1.397(2) and 1.403(2) Å in 56,

(

1

.394(3) and 1.400(3) Å in 57) but shorter than the sum of the

7

van der Waals radii (3.48 Å). The small difference in the B1-

O1/2 distances observed in 56 may be a consequence of a

packing effect or may be related to the electrophilicity of the

central boron atom, since 57, which bears a more electron-

donating OMe substituent, exhibited a more symmetrical

structure.

6

46

For further derivatization, 59-61 were synthesized as shown

in Scheme 19. All of these compounds showed a symmetrical

anthracene pattern (two doublets, a triplet and a singlet) and a

(

46) (a) Brock, C. P. Acta Crystallogr., Sect. B 1990, 46, 795. (b) Mason, R.

Acta Crystallogr. 1964, 17, 547-555.

4364 J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

Figure 12. ORTEP drawing (30% thermal ellipsoid; two (for 59) or one (for 60) independent molecules are omitted for clarity; B-O distances are described

1

in Å) and B NMR chemical shift of 59-61. Selected interatomic distances (Å) and angles (deg) are shown for the first molecule: (59) O -B 2.462(7),

2

1

3

1

4

1

9

1

2

1

3

1

4

1

9

O -B 2.405(6), O -B 1.362(7), O -B 1.354(7), C -B 1.602(8), O -B -O 164.3(3), O -B -O 92.5(3), O -B -O 95.0(3), O -B -C 81.3(3),

2

1

3

2

1

4

2

1

9

3

1

4

3

1

9

4

1

9

1

2

1

O -B -O 95.2(4), O -B -O 93.1(3), O -B -C 83.0(3), O -B -O 119.0(5), O -B -C 117.4(4), O -B -C 123.6(5). (60) F -B 1.344(7), F -B

2

1

9

1

2

1

2

1

9

2

1

.308(7), O -B 2.246(8), O -B 2.340(7), C -B 1.582(6), F -B -F 114.3(4), F -B -O 94.2(4), F -B -O 91.9(4), F -B -C 122.7(5), F -B -

2 2 1 1 2 1 9 2 1 1 2 1 9 1 1 9 1 1 2 1

O 94.7(4), F -B -O 93.2(4), F -B -C 122.9(5), O -B -O 167.0(3), O -B -C 84.8(3), O -B -C 82.3(3). (61) Cl -B 1.834(3), Cl -B 1.834-

1

2

1

9

1

2

1

2

1

9

1

(

3), O -B 1.686(7), O -B 2.790(7), C -B 1.587(6), Cl -B -Cl 112.0(3), Cl -B -O 104.0(2), Cl -B -O 82.8(2), Cl -B -C 118.2(2), O -B -

2 1 1 9 2 1 9

O 167.4(3), O -B -C 96.7(4), O -B -C 70.7(3).

However, the sum of the B-O distances in 60 and 61 [4.59 Å

for 60 and 4.48 Å for 61] was shorter than the distance between

the two oxygen atoms of 1,8-dimethoxyanthracene 6, which may

be due to the strong interaction between the central boron atom

and the two oxygen atoms in 60 and even in 61. Although all

the structures of 59-61 were quite different, the ¹B NMR

chemical shifts of 59-61 are almost similar (δ 27-33 for 59,

B-O (or N) lengths were slightly shorter than the sum of van

der Waals radii or close to the sum. These distances indicate

that one of two OMe (or NMe2) groups interacted strongly with

the central boron atom, and the other one interacted very weakly

with the central boron atom or did not interact at all. Based on

the classification by bond lengths and configuration of the

central boron atom, our carbon compounds 27 and 38 were

classified as a loose pentacoordinate group and tetracoordinate

group, respectively.

1

9-25 for 60, and 22-26 for 61). It may suggest that, in

solution, the structures of these compounds are symmetric or

rapid bond switching is taking place between O-B-O bonds.

Comparison of X-ray Structures of the Carbon and Boron

Compounds. The distances between the central atom and the

two coordinating atoms are summarized in Figure 13. In the

case of the boron compounds, three types of structures were

observed due to the difference of B-O distances, that is, loose

pentacoordinate boron compounds (two relatively long and

almost equivalent B-O lengths; 56-58 and 59), a tight

pentacoordinate boron compound (two relatively short and

almost equivalent B-O lengths; 60), and tetracoordinate boron

compounds (two very different B-O (or N) lengths; 61, 50-

The apparent difference between the oxygen-donating skel-

eton and the nitrogen-donating one is probably due to the

stronger stabilizing energy by the formation of one B-N bond

in comparison with that of one B-O bond. Hence, the large

stabilizing energy of the B-N bond overrides the destabilizing

energy by the formation of the strained five-membered tetra-

coordinate boron structure. The F B-NMe bonding energy

3

(26.6 kcal/mol) was reported to be much stronger than the

44

corresponding F B-OMe bonding energy (13.9 kcal/mol).

3

2

The difference among the OMe, F, and Cl (59, 60, and 61)

in the oxygen-donating ligand can be explained by a similar

delicate balance between the stabilizing energy by the formation

of two relatively weak B-O bonds and the stabilizing energy

by the formation of one strong B-O bond and the destabilizing

energy by pyramidalization. It has been well established by

several different experimental methods that the Lewis acidities

5

2). In loose pentacoordinate boron compounds (56-59), the

B-O distances were similar to the 1,9-peri-distance (2.46(2)

4

6

Å) of nonsubstituted anthracene and slightly longer than the

distance between the two oxygen atoms of 1,8-dimethoxyan-

thracene 6. The distances indicate that the B-O interaction was

relatively weak. In tight pentacoordinate boron compound 60,

the B-O distances were clearly shorter than that of the loose

one and the distance between the two oxygen atoms of 1,8-

dimethoxyanthracene 6. These apparently short B-O distances

of 60 may prove that the B-O hypervalent interaction of 60 is

strengthened from loose pentacoordinate species and the hy-

pervalent interaction exists. In tetracoordinate boron compounds

47

of the boron trihalides are in the order of BF3 < BCl3 < BBr3.

This order is contrary to the expectation based on the electro-

negativity among F, Cl, and Br, which predicts that a positive

charge density on boron decreases in the order BF3 > BCl3 >

BBr3. In addition, theoretical calculation supported the trend

(47) (a) Brown, H. C.; Holmes, R. R. J. Am. Chem. Soc. 1956, 78, 2173-2176.

(

b) Shriver, D. F.; Swanson, B. Inorg. Chem. 1971, 10, 1354-1365. (c)

(

50-52 and 61), the shorter B-O (or N) lengths were similar

Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry; John Wiley

7

to the sum of the covalent radii; on the other hand, the longer

and Sons: New York, 1980.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4365

A R T I C L E S

Yamashita et al.

Figure 13. Classification of the 9-boron and 9-carbon compounds of anthracenes based on the X-ray structures.

of the charge density of the central boron atom, which is

consistent with the electronegativity.⁴⁸The generally accepted

explanation for the anomalous order of Lewis acidity is based

on the strong back-donation of electrons from one of the lone

pairs (2p orbital) of the fluorine atom to the vacant 2pz orbital

of the boron atom, which leads to some double-bond character

for the B-F bond in BF3 (Figure 14).⁴

7,49

In BCl3 and BBr3,

this type of back-donation is much less important because the

longer B-Cl and B-Br bonds form a poorer overlap. These

results suggest that the oxygen and the fluorine substituents

donate electrons toward the central boron atom stronger than

the chlorine substituent. Indeed, in the case of 59 and 60, both

averages of the B-X distances [1.36 Å, for 59, X ) OMe;

Figure 14. Resonance effect on BX3.

1

.34 Å, for 60, X ) F] were 88% of the sum of the covalent

_B_a_n_d_X_.48a They concluded that the Lewis acidity of BX3 was

related to their destabilization energy on the pyramidalization,

7

radii (1.54 Å for B-O; 1.52 Å for B-F), while the B-Cl

distance (1.83 Å, identical) of 61 was essentially the same (98%)

as the sum of the covalent radius (1.87 Å for B-Cl). However,

2

which was defined as the energy difference between the sp

7

3

and assumed sp state of BX3 and not related to the charge

the Brinck group suggested that the back-donation was not

essentially important based on the data of the coefficient of

HOMO, which corresponded to the pπ-pπ interaction between

density of the central boron atom. That is, an increasing

electronegativity from Br to Cl to F should increase the polarity

of the B-X bond. As a result, in addition to the effect of B-X

bond lengths, the repulsion among the partial negative charge

of X should increase from Br to Cl to F when BX3 is

_p_y_r_a_m_i_d_a_l_i_z_e_d_b_e_c_a_u_s_e_X_c_o_m_e_s_c_l_o_s_e_r_t_o_e_a_c_h_o_t_h_e_r_i_n_s_p3

(

48) (a) Brinck, T.; Murray, J. S.; Politzer, P. Inorg. Chem. 1993, 32, 2622-

625. (b) Robinson, E. A.; Johnson, S. A.; Tang, T.-H.; Gillespie, R. J.

2

Inorg. Chem. 1997, 36, 3022-3030. (c) Robinson, E. A.; Heard, G. L.;

Gillespie, R. J. J. Mol. Struct. 1999, 485, 305-319.

(49) Pearson, R. G. Inorg. Chem. 1988, 27, 734-740.

configuration (Figure 15).

4366 J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

Figure 16. Molecular structure of 56 with the atom-labeling scheme.

Displacement ellipsoids are drawn at the 50% probability level, and H atoms

are shown as small spheres of arbitrary radii. The data of the conventional

refinement using data of sin θ/λ e 0.65 Å were used for the preparation

of the figure.

Figure 15. Destabilization of BX3 species on their pyramidalization.

-

1

In our compounds 60 and 61 (Figures 12 and 13), the rigidity

of the boron sp plane of 60 may be stronger than that of 61

2

1

2

15

16

Since the atoms B , O , O , C , and C are coplanar to the

anthracene plane and the conformations of the methoxy groups

are anti to the central boron atom, one of the two lone pairs on

each O atom is directed and should be coordinated to the empty

2p orbital on the boron atom and the other should be pararel to

π electrons of the anthracene skeleton.

because of the repulsion of the partial negative charge in

pyramidalization, too. In consequence, 61 was pyramidalized

to obtain a larger stabilization energy by the formation of a

single bond between the central boron atom and the oxygen

2

atom, while 60 kept its planarity of the sp plane because the

stabilization energy by the formation of a single bond is not

large enough to overcome the destabilization energy of pyram-

idalization. In the case of 59 and 60, the planarity of 59 was

strong probably due to the same reason as that of 60. However,

a difference in the electronegativity between the fluorine atom

and the methoxy group leads to the difference in the partial

positive charge of the central boron atom, which directly affects

the strength of the apical B-O interaction. Because of the reason

for the formation of tight pentacoordinate boron compounds,

the synthesis of tight pentacoordinate carbon compounds bearing

some electron-withdrawing groups is currently under investiga-

tion.

The character of the B-O bonds is clearly shown in the static

43

model maps (Figure 17). The topology of the electron density

distributions of the bonds is quite different from those of

covalent bonds. As shown in Figure 17c and d, the lone pairs

on each O atom appeared in the plane bisecting C-O-C as

single peaks. The peaks are extended to the central boron atom

and diffused perpendicular to the C-O-C planes. The shapes

of the peaks are due to the overlap of the two lone pairs

2

accommodated in one of the sp and p orbitals which are directed

along the bisection of the C-O-C angle and perpendicular to

the C-O-C plane, respectively. As shown in Figure 17a, the

hole of the 2p orbital appeared as electron-deficient regions at

both sides of the central boron atom and has lobes extended

Experimental Electron Density Distribution Analysis of

2

56. The structure of 56 obtained from the accurate X-ray analysis

perpendicular to the sp plane. The lone pairs in the sp orbital

on each O atom are on a co-plane of the anthracene and directed

to the empty 2p orbital of the B atom. Such geometry of the

orbitals clearly indicates the electron donations from the lone

(

see Experimental Section) was slightly unsymmetrical [B-O

2

1

distances are 2.3780(9) Å for B-O and 2.4367(9) Å for B-O ]

and is similar to the regular X-ray analysis described above

2

[B-O distances are 2.379(2) and 2.441(2) Å]. The molecular

pairs in the sp orbitals on the O atoms to the empty 2p orbital

structure and static model maps of 56 are shown in Figures 16

and 17, respectively. The central boron atom forms three valence

on the central boron atom to form a three-center four-electron

bond.

9

3

4

1

bonds with C, O , and O and two short contacts with O and

For quantitative treatment of the characterization of the bonds,

topological analyses were performed. The bond paths were

found between the B-O bonds as shown in Figure 18. The

shapes of the bond paths of the two bonds are almost identical.

The bond critical points are also found on each bond path, and

the points are closer to the central boron atom than the O atoms

because of the polarities of the bonds. The small electron

2

O to form a trigonal bipyramidal structure, which is elongated

1

2

along the O -B -O direction. The covalent characters of the

former three bonds are illustrated by the electron-rich regions

on the intermediate of the bonds in the static model map on the

catechol moiety (Figure 17b). The central boron atom is placed

on the trigonal plane formed by the three atoms, and the sum

of the angles around the B atom is 360°. The geometry indicates

the sp hybridization of the central boron atom. The sp plane

is almost perpendicular to the anthracene plane. The atoms O

and O are placed at the apical positions of the bipyramid formed

1

2

3

densities (F(r): B -O 0.027(4), B -O 0.030(4) e/ao ; ao )

2

1

0.529 177 Å) and the small positive Laplacian (∇ (r): B -O

1 2 5

1

0.050(2), B -O 0.052(2) e/ao ) values at the bond critical points

indicate the ionic character of the bonds. The difference of F-

2

1

2

around the central boron atom, and the B-O distances (av 2.407

(r) and ∇ (r) between B -O and B -O can be related to the

difference between the bond lengths (B -O 2.4367(9) Å, B -

O 2.3780(9) Å), since the decrease in the F(r) and ∇ (r) values

may imply weakening of the bond. On the other hand, the bond

ellipticity, ꢀ, values of the two B-O bonds are quite different

1

Å) are significantly shorter than the sum of the van der Waals

7

2

radii, 3.48 Å. In the two methoxy groups on the 1- and

1

15

8

2

16

8

-positions, the angles C -O -C and C -O -C are close

2

to 120°. These suggest the sp hybridization of the two O atoms.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4367

A R T I C L E S

Yamashita et al.

1

15

Figure 17. Static model maps of 56 on (a) the anthracene plane, (b) the plane of catechol moiety, (c) the plane bisecting C -O -C , and (d) the plane

8

2

16

-3

bisecting C -O -C. Contour interval is 0.1 e Å . Positive and negative regions are shown as blue and red lines, respectively, and zero contours are

omitted.

1

2

Figure 18. Bond paths of the B -O and B -O bonds of 56 obtained by the accurate X-ray analysis. Bond paths are shown as red lines.

1

2

(

ꢀ: B -O 0.29, B -O 0.77). The difference in the ꢀ values

to the values for the C-O bond in our hypervalent pentacoor-

3

2

indicates that the donation from the lone pair in the p orbital is

more sensitive to the distance than those in the sp orbital

dinate carbon compound 27 [F(r), 0.022 e/ao ; ∇ F(r), 0.080

2

5

e/ao ; ꢀ, 0.219] (Figure 19a). The calculation also showed that

because of the directionality of the p orbital on the two oxygen

atoms. The orders of these values are in agreement with the

results from the DFT calculation which shows the symmetrical

the symmetrical pentacoordinated structure was a global mini-

mum in 60 (Figure 19c), but in 61 both the pentacoordinated

structure and the tetracoordinated one were found as minima

(Figure 19d). The tetracoordinate structure was only 0.14 and

1.24 kcal/mol more stable at the B3PW91/6-31G(d) and MP2/

6-31G(d) levels, respectively, than the pentacoordinated one.

It should be noted that the DFT calculation at the B3LYP/6-

31G(d) level showed that the pentacoordinated structure was

0.63 kcal/mol more stable for 61.

3

2

5

structure (F(r), 0.022 e/ao ; ∇ (r), 0.058 e/ao ; ꢀ, 0.266) (vide

infra).

These present the first evidence and characterization of the

O-B-O three-center four-electron bond based on the experi-

mental electron density distribution analysis.

Elucidation of the Interaction between the Central Boron

Atom and the Two Oxygen Atoms of 56, 60, and 61 Based

on the DFT Calculation. The attractive interaction between

the central boron atom and the oxygen atoms at the 1,8-positions

is also confirmed by hybrid density functional theory (DFT) at

Conclusion

Various carbon and boron compounds bearing a 1,8-disub-

stituted anthracene skeleton, such as 27, 38, 50-52, 56-61,

were synthesized and characterized by X-ray analysis. They

showed three types of the structures based on the kinds of

substituents. The first one is symmetrical and a loose pentaco-

3

2

the B3PW91/6-31G(d) level using the Gaussian 98 program.

The optimized geometry of 56 is symmetrical (Figure 19b),

where the two B-O bond lengths are identical (2.431 Å) and

are slightly longer than the experimental data (2.3780(9) and

2

ordinate structure, which has the sp boron and carbon atoms

2

.4367(9) Å). The topological analysis of 56 shows that the

and the two weak apical interactions. The second one is an

unsymmetrical tetracoordinate structure, which has the sp boron

3

bond path is found between the central boron atom and the two

oxygen atoms. The B-O bond is weak and slightly ionic as

shown by the small value of the electron density [F(r): 0.022

and carbon atoms. The third one is symmetrical and a tight

pentacoordinate structure, which resulted from the special feature

of the fluorine atoms. The existence of hypervalent interaction

was proved by the Atoms In Molecules Theory, experimental

electron distribution analysis, DFT calculation, and the com-

parison among the structures of tight and loose pentacoordinate

3

2

e/ao ] and the small positive Laplacian value [∇ F(r): 0.058

5

e/ao ] at the bond critical points. These values together with

the large value of the ellipticity (ꢀ ) 0.266) are well consistent

with the data from the accurate X-ray analysis and very similar

4368 J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

Figure 19. Optimized structures and the AIM data of 27, 56, 60, and 61 at the B3PW91/6-31G(d) level.

species. Since these results showed us the scope for the isolation

of tight pentacoordinate carbon species, further investigation

toward the synthesis of tight-pentacoordinate carbon compounds

is under way.

pressure. This crude product was dissolved in CH

2

Cl

2

and washed with

H

2

O. The organic layer was collected and dried over K

solvents were removed under reduced pressure to give a crude product.

This crude product was purified by column chromatography (CH Cl

2 3

CO . The

2

-

hexane ) 0:1-1:15) to give a yellow solid of 11 (88.2 mg, 21%).

Experimental Section

Single crystals suitable for X-ray analysis were obtained from CH₂-

Cl

2

-hexane solution under air: ¹H NMR (400 MHz, 25 °C, CDCl

3

) δ

General. Ether and tetrahydrofuran were freshly distilled from

sodium benzophenone, and other solvents were distilled from calcium

hydride under argon atmosphere. Merck silica gel 9385 and 7730 was

used for column chromatography and preparative TLC. LC908-C60

7

.29 (dd, 2H, J ) 8 Hz, 8 Hz), 7.96 (d, 2H, J ) 8 Hz), 8.01 (d, 2H,

+

J ) 8 Hz), 8.40 (s, 1H); MS (FAB ) M ) 412, 414, 416, 418. Anal.

Calcd for C14 Br : C, 40.53; H, 1.70%. Found: C, 40.41; H, 1.42%.

H

7

3

(

Japan Analytical Industry) with a 40 φ column was used for HPLC

Improved Synthesis of 1,8-Dimethoxy-9-bromoanthracene 2 from

12. To a mixture of lithium (880 mg, 127 mmol) and DTBB (4,4′-di-

tert-butylbiphenyl; 33.6 g, 126 mmol) THF (300 mL) was added at 0

purification with ClCH CH Cl as an eluent. Melting points were taken

2

1

on a Yanagimoto micromelting point apparatus. H NMR (400 MHz),

11

13

19

B NMR (127 MHz), C NMR (99 MHz), F NMR (372 MHz), and

P NMR (162 MHz) spectra were recorded on a JEOL EX-400 and

°

C. The mixture was stirred with a glass-coated stirring bar at 0 °C

31

until the lithium metal disappeared. Part (250 mL) of the generated

LDBB solution (ca. 0.4 M, 250 mL, 100 mmol) was added to a solution

of 12 (8.82 g, 25 mmol), and the mixture was stirred with a glass-

coated stirring bar at -100 °C for 10 min and allowed to warm to

an AL-400 spectrometer. Chemical shifts (δ) are reported as parts per

million from internal CHCl

OEt

external CFCl

1

3

for H (δ 7.26) or from external BF ‚

3

1

13

2

for B (δ 0.0) or from internal CDCl for C (δ 77.0) or from

3

1

9

31

3

3 4

for F (δ 0.0) or from external H PO for P (δ 0.0).

-

1

41 °C. After stirring for 15 min at -41 °C, BrCF

00 mmol) was added dropwise to the reaction mixture at -41 °C.

The mixture was stirred for 10 min at -41 °C and for an additional

.5 h at rt. Silica gel (200 mL, measured by beaker) was added to the

2 2

CF Br (12.3 mL,

Mass spectrometry was recorded on a JEOL SX-102A spectrometer.

Elemental analysis was performed on a Perkin-Elmer 2400CHN

elemental analyzer.

Synthesis of 1,8,9-Tribromoanthracene 11. To a mixture of 4,4′-

di-tert-butylbiphenyl (2.70 g, 10 mmol) and Li (71.8 mg, 10 mmol)

THF (10 mL) was added at 0 °C under Ar followed by stirring for 4

h at 0 °C with a glass-coated stirring bar to give LDBB (lithium 4,4′-

di-tert-butylbiphenylide) solution. The solution of 9 (391 mg, 1 mmol)

in THF (5 mL) was added to the LDBB solution at -78 °C followed

by stirring at -78 °C for 1 h. This mixture was allowed to warm to

3

mixture, and the solvents were removed under reduced pressure. The

crude product, which was carried on silica gel, was charged on column

chromatography. Initially, hexane was used as an eluent to remove

DTBB. After the elution of DTBB was complete, hexane was

substituted to a mixture of CH

2

Cl

2

and hexane (0:1 ∼ 1:3) gradually

to give a yellow fraction of 2 (4.09 g, 51%); mp 141-149 °C (dec),

1

H NMR (400 MHz, 25 °C, CDCl ) δ 4.04 (s, 6H), 6.90 (d, 2H, J )

3

-

20 °C and was stirred at that temperature for 2 h. At -20 °C, BrCF

2

-

1

3

CF Br (1.8 mL, 15 mmol) was added dropwise into the reaction mixture.

2

8 Hz), 7.36 (t, 2H, J ) 8 Hz), 7.54 (d, 2H, J ) 8 Hz), 8.26 (s, 1H);

NMR (100 MHz, CDCl , 25 °C) δ 55.75, 101.78, 116.19, 119.63,

121.33, 124.75, 127.37, 131.68, 155.77; MS (FAB ) M ) 316, 318.

C

This mixture was allowed to warm to rt and was stirred for 14 h.

Solvents were removed from the reaction mixture under reduced

3

+

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4369

A R T I C L E S

Yamashita et al.

5

0

Anal. Calcd for C16

H, 3.88%.

H

13BrO

2

: C, 60.59; H, 4.13%. Found: C, 60.50;

and the structures of 6 and 38 were solved using SIR97 and

SHELXL97⁵¹and refined by full-matrix least-squares. Structures were

drawn by the Oak Ridge Thermal Ellipsoid Plot program (ORTEP-

Synthesis of 1,8-Dimethoxy-9-dimethoxyborylanthracene 59. A

solution of n-BuLi in n-hexane (0.7 mL, 1.1 mmol) was added dropwise

to a solution of 2 (318 mg, 1 mmol) in ether (30 mL) at -100 °C.

52

III ). The programs DENZO and SCALEPACK are available from

Mac Science Co., Z. Otwinowski, University of Texas, Southwestern

Medical Center. The program teXsan is available from Rigaku Co. The

program SIR97 is available from http://www.irmec.ba.cnr.it/. The

program SHELXL97 is available from http://shelx.uni-ac.gwdg.de/

SHELX/. The program ORTEP-III is available from http://www.ornl.

gov/ortep/ortep.html. All crystallographic data (excluding structure

factors) for the compounds reported in this paper have been deposited

with the Cambridge Crystallographic Data Centre (all data have each

supplementary publication number). A copy of the data can be obtained

free of charge on application to CCDC, 12 Union Road, Cambridge

CB2 1EZ, UK (fax, (+44)1223-336-033; e-mail, deposit@

ccdc.cam.ac.uk).

After the solution was stirred for 2 h at -100 °C, B(OMe)

.2 mmol) was added dropwise to the solution at -100 °C. The reaction

mixture was slowly warmed to rt within 8 h. Aqueous HCl (1 N) was

added to the mixture, and the mixture was extracted with CH Cl

3

(0.14 mL,

1

2

.

Collected organic layer was dried and evaporated to give a crude

product. The crude product was purified by HPLC (RT ) 73 min) to

1

56 mg (50%) of 59. Single crystals suitable for X-ray analysis and

1

3

measurement of mp and C NMR were obtained from the CH

n-hexane solution under Ar atmosphere; H NMR (400 MHz, CDCl

2

Cl

2

-

1

3

,

2

5 °C) δ 3.45 (s, 6H), 4.08 (s, 6H), 6.75 (d, 2H, J ) 8 Hz), 7.37 (t,

1

2

H, J ) 8 Hz), 7.58 (d, 2H, J ) 8 Hz), 8.32 (s, 1H); B NMR (127

1

3

1 (deposited as CCDC-186149): C17

13 3 5

H F O S, 386.34, triclinic, P 1h ,

MHz, CDCl

3

, 25 °C) δ 27-33 (br); C NMR (99 MHz, CDCl , 25

pale green, a ) 8.5460(6) Å, b ) 9.4300(8) Å, c ) 11.1650(7) Å, R

°

C) δ 51.94, 55.65, 102.04, 121.13, 125.16, 126.27, 127.46, 132.66,

3

)

73.016(4)°, â ) 82.571(5)°, γ ) 81.014(4)°, V ) 846.6(1) Å , 298

K, Z ) 2, R ) 0.0532, GOF ) 1.443.

14 2 1

(deposited as CCDC-185971): C16H O , 238.27, monoclinic, P2 /

1

56.34. Anal. Calcd for C18

4

H19BO : C, 69.71; H, 6.17%. Found: C,

6

9.49; H, 6.20%.

6

Synthesis of 1,8-Dimethoxy-9-difluoroborylanthracene 60. A

solution of n-BuLi in n-hexane (0.7 mL, 1.1 mmol) was added dropwise

to a solution of 2 (317 mg, 1 mmol) in ether (50 mL) at -78 °C. After

the solution was stirred for 1.5 h at -78 °C, BF

mmol) was added dropwise to the solution at -78 °C. The reaction

mixture was slowly warmed to rt within 3 h. After solvents were

2 2

removed under reduced pressure, ClCH CH Cl soluble materials were

injected into an HPLC column. A fraction at RT ) 73 min was collected

and concentrated to give 172 mg (60%) of 60. Single crystals suitable

c, pale yellow-green, a ) 6.642(5) Å, b ) 12.169(5) Å, c ) 15.118(5)

Å, â ) 91.913(5)°, V ) 1221.3(11) Å , 298 K, Z ) 4, R ) 0.0766,

3

GOF ) 1.160.

3

2

‚OEt (0.14 mL, 1.1

9

(deposited as CCDC-186017): C20

23 6

H O P, 390.37, orthorhombic,

P2 2 2 , pale yellow-green, a ) 10.0330(2) Å, b ) 11.9530(5) Å, c )

6.2950(7) Å, V ) 1954.2(1) Å , 298 K, Z ) 4, R ) 0.0514, GOF )

1 1 1

3

1

.000.

11 (deposited as CCDC-186150): C14

7 3 1

H Br , 414.92, monoclinic, P2 /

c, yellow, a ) 10.1530(5) Å, b ) 7.2480(2) Å, c ) 17.3580(9) Å, â

106.064(2)°, V ) 1227.48(9) Å , 130 K, Z ) 4, R ) 0.0410, GOF

) 1.041.

23 (deposited as CCDC-186018): C15 12Br O, 368.07, orthorhombic,

2

13

for X-ray analysis and measurement of mp and C NMR were obtained

from a CH Cl -n-hexane solution in a refrigerator; mp 242-252 °C

dec); H NMR (400 MHz, CDCl , 25 °C) δ 4.16 (s, 6H), 6.80 (d, 2H,

J ) 8 Hz), 7.41 (t, 2H, J ) 8 Hz), 7.63 (d, 2H, J ) 8 Hz), 8.38 (s,

3

)

2

1

(

3

H

1

13

1

H); B NMR (127 MHz, CDCl

3

, 25 °C) δ 19-25 (br); C NMR (99

Pnma, yellow, a ) 7.3340(3) Å, b ) 19.5430(4) Å, c ) 9.0820(4) Å,

3

MHz, CDCl

1

3

, 25 °C) δ 55.8, 102.0 (d, JCF ) 1.6 Hz), 121.3, 125.51,

V ) 1301.7(1) Å , 298 K, Z ) 4, R ) 0.0919, GOF ) 1.481.

25.55, 126.3, 127.4 (d, JCF ) 1.7 Hz), 132.1, 154.3; ¹⁹F NMR (372

25 (deposited as CCDC-186229): C17

/a, yellow, a ) 25.057(3) Å, c ) 8.3710(5) Å, V ) 5255.8(7) Å ,

298 K, Z ) 16, R ) 0.0753, GOF ) 1.478.

27 (deposited as CCDC-186148): C19

1

P2 /c, yellow, a ) 10.981(2) Å, b ) 14.701(4) Å, c ) 13.430(3) Å, â

2

H13NO , 263.30, tetragonal,

3

MHz, CDCl , 25 °C) δ -96.3 (s). Anal. Calcd for C16

H13BF O

2 2

: C,

I4

1

6

7.17; H, 4.58%. Found: C, 66.86; H, 4.27%.

Synthesis of 1,8-Dimethoxy-9-dichloroborylanthracene 61. A

solution of n-BuLi in n-hexane (1.4 mL, 1.1 mmol) was added dropwise

to a solution of 2 (634 mg, 2 mmol) in ether (120 mL) at -78 °C.

20 2 7 4

H B F O , 466.97, monoclinic,

3

) 107.81(2)°, V ) 2064.2(8) Å , 200 K, Z ) 4, R ) 0.1047, GOF )

After the solution was stirred for 1.5 h at -78 °C, a solution of BCl

in heptane (2.2 mL, 2.2 mmol) was added dropwise to the solution at

78 °C. The reaction mixture was warmed to rt within 1 h. After

solvents were removed under reduced pressure, ClCH CH Cl soluble

3

1.574.

31 6 8

38 (deposited as CCDC-183680): C29H F KO , 660.64, ortho-

rhombic, Pbca, purple, a ) 13.9100(3) Å, b ) 19.2280(5) Å, c )

23.5150(7) Å, V ) 6289.4(3) Å , 150 K, Z ) 8, R ) 0.1050, GOF )

-

3

2

materials were injected into an HPLC column. A fraction at RT ) 69

min was collected and concentrated to give 420 mg (60%) of 61 with

small amounts of impurities. Single crystals suitable for X-ray analysis

1.939.

50 (deposited as CCDC-176315): C H BN O , 382.27, monoclinic,

24

23

2

P2 /n, pale yellow, a ) 16.3780(6) Å, b ) 7.4670(2) Å, c ) 16.9660-

1

3

and measurement of mp and C NMR were obtained from a CH

2

Cl

2

-

(6) Å, â ) 105.007(2)°, V ) 2004.1(1) Å , 298 K, Z ) 4, R ) 0.0661,

GOF ) 1.308.

1

n-hexane solution in a refrigerator; mp 142-145 °C (dec); H NMR

(

400 MHz, CDCl

3

, 25 °C) δ 4.31 (s, 6H), 6.83 (d, 2H, J ) 8 Hz), 7.42

5

2

1 (deposited as CCDC-176316): C20H25BN , 304.24, monoclinic,

1

(t, 2H, J ) 8 Hz), 7.67 (d, 2H, J ) 8 Hz), 8.34 (s, 1H); B NMR (127

P2 /n, pale yellow, a ) 10.7260(4) Å, b ) 12.5420(4) Å, c ) 13.0800-

1

3

MHz, CDCl

°

Anal. Calcd for C16

H, 4.00%.

3

, 25 °C) δ 22-25 (br); C NMR (99 MHz, CDCl

3

, 25

(4) Å, â ) 91.437(2)°, V ) 1759.04(9) Å , 298 K, Z ) 4, R ) 0.0699,

GOF ) 1.584.

C) δ 55.4, 101.8, 122.0, 125.30, 125.32, 125.6, 125.8, 132.5, 154.4.

2 2

H13BCl O : C, 60.24; H, 4.11%. Found: C, 59.83;

52 (deposited as CCDC-176317): C18

2 2

H19BCl N , 345.08, monoclinic,

P2

1

/n, pale yellow, a ) 12.7770(4) Å, b ) 12.5510(6) Å, c ) 10.7200-

3

X-ray Crystallographic Analysis. X-ray data, except experimental

electron distribution analysis, were collected on a Mac Science DIP2030

imaging plate equipped with graphite-monochromated Mo KR radiation

(5) Å, â ) 90.546(3)°, V ) 1719.0(1) Å , 298 K, Z ) 4, R ) 0.0667,

GOF ) 1.516.

(

λ ) 0.710 73 Å). The unit cell parameters were determined by

(50) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,

C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.

Crystallogr. 1999, 32, 115.

autoindexing several images in each data set separately with the program

DENZO. For each data set, rotation images were collected in 3° (6°

for 27) increments with a total rotation of 180° about φ. Data were

processed by SCALEPACK. The structures, except 6 and 38, were

solved using the teXsan system and refined by full-matrix least-squares,

(

51) Sheldrick, G. M. SHELX-97, Program for the Refinement of Crystal

Structures; University of Gottingen: Gottingen, Germeny, 1997.

52) Burnett, M. N.; Johnson, C. K. ORTEP-III: Oak Ridge Thermal Ellipsoid

Plot Program for Crystal Structure Illustrations; Oak Ridge National

Laboratory Report ORNL-6895, 1996.

(

4370 J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005

Pentacoordinate C and B Compds w/ Anthracene Skeleton

A R T I C L E S

5

6 (deposited as CCDC-141764): C22

H

17BO

4

, 356.18, monoclinic,

formalism⁵⁵and topological analyses based on the resulting parameters

were performed by the XD package.⁵⁶The refinement was carried out

P2

0.2810(7) Å, â ) 100.490(1)°, V ) 1724.21(7) Å , 298 K, Z ) 4, R

0.0560, GOF ) 1.367.

7 (deposited as CCDC-141765): C23

Pca2 , pale blue-green, a ) 9.8670(4) Å, b ) 14.2920(6) Å, c )

4.0810(4) Å, V ) 1985.7(1) Å , Z ) 4, R ) 0.0570, GOF ) 0.847.

8 (deposited as CCDC-141766): C22 , 388.31, orthorhom-

bic, Pnma, pale blue-green, a ) 8.4930(2) Å, b ) 14.3130(6) Å, c )

1

/a, pale blue-green, a ) 11.9620(4) Å, b ) 7.2280(1) Å, c )

3

-1

2

)

against all the independent reflections of sin θ/λ e 1.2 Å with I >

2

3σ(I) on F . At the first stage of the refinement, the atomic coordinates

5

H

19BO

5

, 386.21, orthorhombic,

and the U of non-hydrogen atoms were fixed on those of the high-

ij

1

order refinement, and the U_i_s_oof the hydrogen atoms were fixed on

those of the conventional refinement for the data below sin θ/λ ) 0.65

3

1

-

1

5

H

17BO

2

S

2

V

Å . The population parameters, P , P (, of non-hydrogen atoms and

lm

scale were refined. The level of the multipoles was raised stepwise up

to hexadecapole for atoms B1, O1, and O2 and octupole for other non-

hydrogen atoms. At the second stage, the anisotropic and isotropic

temperature factors were refined for non-hydrogen and hydrogen atoms,

respectively, followed by the refinements of the spherical Hartree-

3

1

5.9540(8) Å, V ) 1939.4(1) Å , 298 K, Z ) 4, R ) 0.0428, GOF )

.438.

5

4

9 (deposited as CCDC-185970): C18H19BO , 310.16, monoclinic,

P2

2

)

1

/n, pale blue-green, a ) 18.7290(8) Å, b ) 13.1770(5) Å, c )

3

1.8000(9) Å, â ) 111.059(2)°, V ) 5020.7(3) Å , 298 K, Z ) 12, R

0.0729, GOF ) 1.681.

0 (deposited as CCDC-185972): C16

bic, Pna2 , pale blue-green, a ) 12.1870(4) Å, b ) 6.8230(2) Å, c )

57

Fock radial screening parameter, κ, and isotropic extinction. At the

third stage, the P , Plm( and scale were refined. The level of the

V

6

2 2

H13BF O , 286.08, orthorhom-

multipoles was raised to hexadecapole for atoms B1, O1, and O2,

octupole for other non-hydrogen atoms, and dipole along the bond for

hydrogen atoms in the same manner as in the first stage. After these

refinements, the second and third strategies were repeated twice, and

1

3

1

2.524(1) Å, V ) 2704.4(2) Å , 298 K, Z ) 8, R ) 0.0905, GOF )

.459.

1 (deposited as CCDC-185973): C16

rhombic, Pmn2 , yellow, a ) 6.9500(2) Å, b ) 9.0800(2) Å, c )

6

2 2

H13BCl O , 318.99, ortho-

V

finally the P , Plm(, κ coordinates and temperature factor of non-

1

hydrogen atoms, isotropic extinction, and scale were refined. The

number of parameters in the final cycle of the refinement was 742. A

molecular electroneutrality constraint was applied through all the

refinements. No significant peaks were found on the final residual maps.

The residual maps in the planes of anthracene and catechol moieties,

3

1

1.3230(4) Å, V ) 714.55(4) Å , 298 K, Z ) 2, R ) 0.0625, GOF )

.012.

Experimental Electron Density Distribution Analysis of 56. Single

crystals of 56 were obtained by recrystallization from dichloromethane-

n-hexane. The crystal having well-developed crystal faces, 0.55 × 0.49

2

tables of the P

Crystal data: monoclinic, space group P2

.1920(1) Å, c ) 11.7510(1) Å, â ) 100.8995(3)°, V ) 1671.48(3)

V

, Plm(, κ and F

o

-F

c

and CIF file were deposited.

3

×

0.39 mm , was selected for the measurement. The diffraction data

1

/c, a ) 20.1411(2) Å, b )

were collected on an automated imaging plate Weissenberg camera,

Rigaku Raxis-Rapid, using Mo KR radiation (λ ) 0.710 73 Å) generated

from a fine focus sealed tube by an oscillation method at 100 K. To

achieve high completeness, four data sets were measured with different

crystal orientations. In each data set, 94 frames were measured with

the oscillation angle 2° and interval 1.5° to form a total oscillation

angle 141.5°. The Bragg spots on the imaging plates were integrated

up to sin θ/λ ) 1.2 Å by the program PROCESS-AUTO. The

Lorentz and polarization corrections were applied during the integration

processes. After application of absorption correction, all 376 frames

were scaled and averaged. Partial reflections were omitted in the scaling.

The measured and independent reflections, completeness and Rint were

7

3

-3

Å , Z ) 4, D ) 1.415 g cm , R(F) ) 0.0377 (for 14 897 reflections

X

with I > 3σ(I)).

Acknowledgment. This work was supported by a Grant-in-

Aid for Scientific Research (Nos. 09239103, 09440218, 11166248,

1

1304044, 12304044) provided by the Ministry of Education,

-

1

53

Culture, Sports, Science and Technology of the Japanese

Government and JSPS Research Fellowship (No. 08982) for

Young Scientists. The authors are grateful to Central Glass Co.,

Ltd. for a generous gift of hexafluoroacetone trihydrate.

5

4

211351, 24835, 0.982 and 0.052, respectively. The structure was solved

by a direct method and refined using independent 3836 reflections below

sin θ/λ ) 0.65 Å with the programs SIR97 and SHELXL97,

respectively. Following the refinements, the high-order refinements were

Supporting Information Available: All crystallographic data

and CIF files. This material is available free of charge via the

Internet at http://pubs.acs.org.

-

1

50

51

carried out using all 21 984 independent reflections with sin θ/λ g 0.6

-1

JA0438011

Å

by the program SHELXL97. The positions of the hydrogen atoms

were constrainted to have C-H distances of 1.083 and 1.066 Å for the

aromatic and methyl group, respectively. The refinements of the

multipole expansion method using the Hansen-Coppens multipole

4

3a

(55) Hansen, N. K.; Coppens, P. Acta Crystallogr., Sect. A, 1978, 34, 909.

(

56) Koritsanszky, T.; Howard, S.; Su, Z.; Mallinson, P. R.; Richter, T.; Hansen,

N. K. XD - a Computer Program Package for Multipole Refinement and

Analysis of Electron Densities from Diffraction Data; Free University of

Berlin: Berlin, Germany.

(

53) PROCESS-AUTO; Rigaku Corporation: Tokyo, Japan, 1998.

54) Higashi, T. NUMABS - Numerical Absorption Correction Based on Crystal

Shape; Rigaku Corporation: Tokyo, Japan, 1999.

(

(57) (a) Becker, P. J.; Coppens, P. Acta Crystallogr., Sect. A, 1974, 30, 129.

(b) Becker, P. J.; Coppens, P. Acta Crystallogr., Sect. A, 1975, 31, 417.

J. AM. CHEM. SOC.

9

VOL. 127, NO. 12, 2005 4371

Article Doi

Syntheses and structures of hypervalent pentacoordinate carbon and boron compounds bearing an anthracene skeleton - Elucidation of hypervalent interaction based on X-ray analysis and DFT calculation

DOI: 10.1021/ja0438011

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Article abstract of DOI:10.1021/ja0438011

Full text of DOI:10.1021/ja0438011

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