Preparation of copper ion complexes of sterically congested diaryldiazomethanes having a pyridine ligand and characterization of their photoproducts

Published on Web 04/22/2005

Preparation of Copper Ion Complexes of Sterically Congested

Diaryldiazomethanes Having a Pyridine Ligand and

Characterization of Their Photoproducts

Tetsuji Itoh,^†Masayoshi Matsuno,^†Eiko Kamiya,^†Katsuyuki Hirai,^‡and

Hideo Tomioka*^,†

Contribution from the Chemistry Department for Materials, Faculty of Engineering, and

Instrumental Analysis Facilities, Life Science Research Center, Mie UniVersity,

Tsu, Mie 514-8507, Japan

Received December 16, 2004; E-mail: tomioka@chem.mie-u.ac.jp

Abstract: To realize fairly stable high-spin polycarbenes by utilizing heterospin systems comprising 2p

spins of organic radicals and 3d spins of magnetic metal ions, we prepared dianthryldiazomethanes having

two pyridyl groups at the 2,2′- or 2,7-positions, that is, bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-

9-anthryl]diazomethane (2,2′-DPy-1-N₂) and [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][(10-(4-tert-butyl-

2,6-dimethylphenyl)-2,7-di(4-pyridyl)-9-anthryl]diazomethane (2,7-DPy-1-N₂). The triplet carbene DPy-³1

generated by photolysis of DPy-1-N₂was characterized by ESR and UV-vis spectroscopy in a matrix at

low temperature as well as by time-resolved UV-vis in solution at room temperature. The results showed

that the triplet carbene DPy-³1 was destabilized to some extent as opposed to the parent triplet carbene

before pyridination, but it was still fairly persistent, having a half-life of more than 30 min in solution at

room temperature. Photoproducts from the complex between DPy-1-N₂and Cu(hfac)₂were characterized

in a similar manner, and the results suggested that the generated carbene centers interacted magnetically

with the Cu(II) ion to form a high-spin species with significant thermal stability. The fact that no significant

signals due to the isolated triplet carbene DPy-³1 were observed suggested that the pyridine moiety binds

with Cu(hfac)₂in a nearly quantitative manner under these cryogenic conditions. Magnetic measurements

of the photoproduct using a superconducting quantum interference device (SQUID) magneto/susceptometer

were performed to determine the spin state of the complex. The temperature dependence of the molar

paramagnetic susceptibility indicated the presence of ferromagnetic interaction. The field dependences of

magnetization for the complexes, expressed using M versus H/T plots, were analyzed in terms of the two-

component Brillouin function to be S ) 3.18 (F ) 0.66) and S ) 0.02 (F ) 0.23) for the 1:1 complex of

2,7-DPy-1 and Cu(hfac)₂and S ) 2.70 (F ) 0.33) and S ) 0.49 (F ) 0.11) for the 1:1 complex of 2,2′-

DPy-1 and Cu(hfac)₂.

Introduction

co-workers have prepared a “starburst”-type nonadiazo com-

pound, a precursor of nonacarbene, and have demonstrated that

An ever-increasing amount of interest is being paid to

molecular magnetism, in which spins of unpaired electrons in

π-orbitals of light atoms such as carbon, nitrogen, and oxygen

are mainly responsible for the magnetic properties. Many

attempts have been made to prepare organic ferromagnetic

materials.^1,2The spin sources used for such studies are mostly

thermodynamically stable radicals such as phenoxyls,³tri-

phenylmethyls,⁴and nitroxides,⁵mostly because of their ease

of preparation and use. Triplet carbenes seem to be more

attractive spin sources in that their spin density is twice as large

as that of radicals, and hence the magnitude of the exchange

coupling between neighboring centers is large.^6,7Iwamura and

the nine diazo groups are photolyzed at low temperature to give

a nonadecet ground state (S ) 9).⁷

However, these systems have two disadvantages that hinder

their extension to usable magnetic materials. First, a triplet

carbene unit is highly unstable and lacks stability for practical

(2) (a) Kahn, O. Molecular Magnetism; VCH Publishers: Weinheim, Germany,

1993. (b) Gatteschi, D. AdV. Mater. 1994, 6, 635. (c) Miller, J. S.; Epstein,

A. J. Angew. Chem., Int. Ed. Engl. 1994, 33, 385. (d) Miller, J. S.; Epstein,

A. J. Chem. Eng. News 1995, (Oct 2), 30. (e) Magnetism: A Supramolecular

Function; Kahn, O., Ed.; NATO ASI Series C; Kluwer: Dordrecht, The

Netherlands, 1996; Vol. 484. (f) Molecule-Based Magnetic Materials;

Turnbull, M. M., Sugimoto, T., Thompson, L. K., Eds.; ACS Symposium

Series 644; American Chemical Society: Washington, DC, 1996. (g)

Gatteschi, D. Curr. Opin. Solid State Mater. Sci. 1996, 1, 192. (h) Miller,

J. S.; Epstein, A. J. MRS Bull. 2000, 25, 21. (i) Magnetism: Molecules to

Materials II; Miller, J. S., Drillon, M., Eds.; Wiley-VCH: Weinheim,

Germany, 2001.

^†Chemistry Department for Materials.

^‡Instrumental Analysis Facilities.

(1) (a) Iwamura, H. AdV. Phys. Org. Chem. 1990, 26, 179. (b) Dougherty, D.

A. Acc. Chem. Res. 1991, 24, 88. (c) Rajca, A. Chem. ReV. 1994, 94, 871.

(d) Molecular Magnetism in Organic-Based Materials; Lahti, P. M., Ed.;

Marcel Dekker: New York, 1999. (e) Itoh, K., Kinoshita, M., Eds.;

Molecular Magnetism; Kodansha-Gordon and Breach: Tokyo, 2000.

(3) (a) Nishide, H.; Kaneko, T. In Molecular Magnetism in Organic-Based

Materials; Lahti, P. M., Ed.; Marcel Dekker: New York, 1999; pp 285-

303. (b) Nishide, H.; Maeda, K.; Oyaizu, K.; Tsuchida, E. J. Org. Chem.

1999, 64, 7129. (c) Nishide, H.; Takahashi, M.; Takashima, J.; Tsuchida,

E. J. Org. Chem. 1999, 64, 7129.

9

7078

J. AM. CHEM. SOC. 2005, 127, 7078-7093

Preparation of Copper Ion Complexes

A R T I C L E S

applications under ambient conditions.⁸To overcome these

difficulties, we have made great efforts to stabilize them,^9,10

and we succeeded in preparing fairly stable ones that survive

for several days in solution at room temperature.^10eThe next

step is to explore a way of connecting them while retaining a

robust π-spin polarization.

Scheme 1

The second disadvantage is that diazo groups, which are

generally employed as precursors of carbenes, are also, in

general, labile¹¹and hence cannot be used as building blocks

to prepare more complicated poly(diazo) compounds. We found

that a diphenyldiazomethane prepared to generate a persistent

triplet carbene is also persistent for the diazo compound. Hence,

this can be further modified into a more complicated diazo

compound, with the diazo group intact. For instance, (2,4,6-

tribromophenyl)(2,6-dibromo-4-tert-butylphenyl)diazo-

methane was found to be stable enough to survive under

Sonogashira coupling reaction conditions and undergoes a

coupling reaction with (trimethylsilyl)acetylene to give (2,6-

dibromo-4-trimethylsilylethynylphenyl)(2,6-dibromo-4-tert-

butylphenyl)diazomethane. Three units of the diazo compound

are then introduced at the 1-, 3-, and 5-positions of the benzene

ring through the ethynyl group by employing a similar coupling

reaction to give a tris(diazo) compound, which eventually

generates a fairly stable septet ground-state tris(carbene) upon

irradiation.¹²Thus it is potentially possible to prepare a

poly(diazo) compound by extending this method.¹³

However, there are still other problems that prevent the

formation of high-spin systems. Thus, efforts to increase the

number of aligned spins are sometimes hampered by the

development of antiferromagnetic intra- and/or interchain

interactions between the radical centers.^7d

To overcome these problems, heterospin systems comprising

2p spins of organic radicals and 3d spins of magnetic metal

ions have been proposed.^6,14The strategy is based on the

supramolecular chemistry exhibited by pyridine- and poly-

pyridine-metal ions.¹⁵For instance, magnetic interaction

between radical centers and metal ions can be realized through

a pyridyl ligand to generate a high-spin unit. Thus, bis(4-

pyridyl)diazomethane [DPy-(CdN₂)] forms a polymeric chain

structure by ligation with coordinatively unsaturated metal ions

(M). The 3d spins on the metal ions in the chain [-DPy-

(CdN₂)-M-]_ndo not interact with each other, but once triplet

bis(4-pyridyl)carbene is generated upon irradiation to form the

carbene-metal ion complex [-DPy-(C:)-M-]_n, they start to

interact with each other through the 2p spins on the carbene

center, thereby generating a high-spin system comprising 2p

and 3d spins (Scheme 1).^6,14

This suggests that if a pyridyl group is introduced onto an

aryl ring of a sterically congested diaryldiazomethane, a

precursor for a persistent triplet carbene, a polymeric diazo

compound should be obtained after coordination with metal ions.

From this, a persistent high-spin molecule comprising 2p spins

of organic radicals and 3d spins of magnetic metal ions will be

formed.

(4) (a) Raica, A. In Molecular Magnetism in Organic-Based Materials; Lahti,

P. M., Ed.; Marcel Dekker: New York, 1999; pp 345-359. (b) Raica, A.

Chem.-Eur. J. 2002, 8, 4835. (c) Raica, A.; Wongsriatanakul, J.; Raica,

S. J. Am. Chem. Soc. 2004, 126, 6608. (d) Raica, A.; Wongsriatanakul, J.;

Raica, S.; Cerny, R. L. Chem.-Eur. J. 2004, 10, 3144.

(5) Bushby, R.-J. In Magnetism: Molecules to Materials II; Miller, J. S.,

Drillon, M., Eds.; Wiley-VCH: Weinheim, Germany, 2001; pp 149-187.

(b) Amabilino, D. B.; Viciana, J. In Magnetism: Molecules to Materials

II; Miller, J. S., Drillon, M., Eds.; Wiley-VCH: Weinheim, Germany, 2001;

pp 1-60. (c) Ishimaru, Y.; Kitano, M.; Kumada, H.; Koga, N.; Iwamura,

H. Inorg. Chem. 1998, 37, 2273. (d) Iwamura, H.; Inoue, K.; Koga, N.

New J. Chem. 1998, 201. (e) Rabu, P.; Drillon, M.; Iwamura, H.; Gorlitz,

G.; Itoh, T.; Matsuda, K.; Koga, N.; Inoue, K. Eur. J. Inorg. Chem. 2000,

211. (f) Kanegawa, S.; Karasawa, S.; Nakano, M.; Koga, N. Chem.

Commun. 2004, 1750. (g) Laukhin, V.; Martinez, B.; Fontchberta, J.;

Amabilino, D. B.; Minguet, M.; Veciana, J. J. Phys. Chem. 2004, 108,

18441.

(6) (a) Koga, N.; Iwamura, H. In Carbene Chemistry: From Fleeting

Intermediates to Powerful Reagents; Bertrand, G., Ed.; FontisMedia:

Lausanne, Switzerland, 2002; pp 271-296. (b) Matsuda, K.; Nakamura,

N.; Takahashi, K.; Inoue, K.; Koga, N.; Iwamura, H. In Molecule-based

Magnetic Materials: Theory, Techniques, and Applications; Turnbull, M.

M., Sugimoto, T., Thompson, L. K., Eds.; ACS Symposium Series 644;

American Chemical Society: Washington, DC, 1996; p 142.

We report here that dianthryldiazomethanes bearing two

pyridine groups form complexes with Cu(II) that, upon irradia-

tion, generate fairly stable high-spin species.

(7) (a) Nakamura, N.; Inoue, K.; Iwamura, H.; Fujioka, T.; Sawaki, Y. J. Am.

Chem. Soc. 1992, 114, 1484. (b) Nakamura, N.; Inoue, K.; Iwamura, H.

Angew. Chem., Int. Ed. Engl. 1993, 32, 872. (c) Matsuda, K.; Nakamura,

N.; Takahashi, K.; Inoue, K.; Koga, N.; Iwamura, H. J. Am Chem. Soc.

1995, 117, 5550. (d) Matsuda, K.; Nakamura, N.; Inoue, K.; Koga, N.;

Iwamura, H. Chem.-Eur. J. 1996, 2, 259. (e) Matsuda, K.; Nakamura, N.;

Inoue, K.; Koga, N.; Iwamura, H. Bull. Chem. Soc. Jpn. 1996, 69, 1483.

(8) For reviews of general reactions of carbenes, see: (a) Kirmse, W. Carbene

Chemistry, 2nd ed.; Academic Press: New York, 1971. (b) Carbenes; Moss,

R. A., Jones, M., Jr., Eds.; Wiley: New York, 1973 and 1975; Vols. 1 and

2. (c) Carbene(oide), Carbine; Regitz, M., Ed.; Thieme: Stuttgart, 1989.

(d) Wentrup, C. ReactiVe Intermediates; Wiley: New York, 1984; pp 162-

264.

Results and Discussion

Design and Preparation of Desired Diaryldiazomethane

Bearing a Pyridyl Group. We chose bis[10-(2,6-dimethyl-4-

(12) Tomioka, H.; Hattori, M.; Hirai, K.; Sato, K.; Shiomi, D.; Takui, T.; Itoh,

K. J. Am. Chem. Soc. 1998, 120, 1106.

(13) (a) Furukawa, K.; Takui, T.; Itoh, K.; Miyahara, I.; Hirotsu, K.; Watanabe,

T.; Hirai, K.; Tomioka, H. Synth. Met. 1997, 85, 1330. (b) Itoh, T.; Hirai,

K.; Tomioka, H. J. Am. Chem. Soc. 2001, 126, 1130. (c) Itoh, T.; Morisaki,

F.; Kurono, M.; Hirai, K.; Tomioka, H. J. Org. Chem. 2004, 69, 5870. (d)

Ohtsuka, Y.; Itoh, T,; Hirai, K.; Tomioka, H.; Takui, T. Org. Lett. 2004,

6, 847. (e) Itoh, T.; Maemura, T.; Ohtsuka, Y.; Ikari, Y.; Wildt, H.; Hirai,

K.; Tomioka, H. Eur. J. Org. Chem. 2004, 2991. (f) Morisaki, F.; Kurono,

M.; Hirai, K.; Tomioka, H. Org. Biomol. Chem. 2005, 3, 431. (g) Itoh, T.;

Jinbo, Y.; Hirai, K.; Tomioka, H. J. Am. Chem. Soc. 2005, 127, 1650.

(14) (a) Koga, N.; Iwamura, H. In Molecular Magnetism in Organic-Based

Materials; Lahti, P. M., Ed.; Marcel Dekker: New York, 1999; pp 629-

659. (b) Koga, N.; Iwamura, H. Mol. Cryst. Liq. Cryst. 1997, 305, 415. (c)

Iwamura, H.; Koga, N. Mol. Cryst. Liq. Cryst. 1999, 334, 437. (d) Iwamura,

H.; Koga, N. Pure Appl. Chem. 1999, 71, 231.

(9) (a) Tomioka, H. Acc. Chem. Res. 1997, 30, 315. (b) Tomioka, H. In

AdVances in Carbene Chemistry; Brinker, U., Ed.; JAI Press: Greenwich,

CT, 1998; Vol. 2, pp 175-214. (c) Tomioka, H. In Carbene Chemistry;

Bertrand, G., Ed.; FontisMedia: Lansanne, Switzerland, 2002; pp 103-

152.

(10) (a) Tomioka, H.; Nakajima, J.; Mizuno, H.; Iiba, E.; Hirai, K. Can. J. Chem.

1999, 77, 1066. (b) Itakura, H.; Tomioka, H. Org. Lett. 2000, 2, 2995. (c)

Takahashi, Y.; Tomura, M.; Yoshida, K.; Murata, S.; Tomioka, H. Angew.

Chem., Int. Ed. 2000, 39, 3478. (d) Tomioka, H.; Iwamoto, E.; Itakura,

H.; Hirai, K. Nature 2001, 412, 626. (e) Iwamoto, E.; Hirai, K.; Tomioka,

H. J. Am. Chem. Soc. 2003, 125, 14664. (f) Yoshida, K.; Iiba, E.; Nozaki,

Y.; Hirai, K.; Takahashi, Y.; Tomioka, H.; Lin, C.-T.; Gaspar, P. Bull.

Chem. Soc. Jpn. 2004, 77, 1509.

(15) (a) Lehn, J.-M. Supramolecular Chemistry: Concepts and PerspectiVes;

VCH: Weinheim, Germany, 1995. (b) Nierengarten, J.-F.; Dietrich-

Buchecker, C. O.; Sauvage, J.-P. J. Am. Chem. Soc. 1994, 116, 375. (c)

Leininger, J.-F.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853.

(11) Regitz, M.; Maas, G. Diazo Compounds: Properties and Synthesis;

Academic Press: Orlando, FL, 1986.

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7079

A R T I C L E S

Itoh et al.

ylphenyl)-9-anthryl][10-(4-tert-butyl-2,6-dimethylphenyl)-2,7-

di(4-pyridyl)-9-anthryl]diazomethane (2,7-DPy-1-N₂).

We first attempted to introduce a pyridyl group by direct

coupling of the corresponding diazo compound bearing bromo

groups (e.g., 2,2′-DBr-1-N₂) with pyridylboronic acid under

Suzuki coupling conditions,¹⁸but all attempts were unsuccessful.

However, the coupling reaction of the precursory carbamate

took place smoothly to give bis[10-(4-tert-butyl-2,6-dimeth-

ylphenyl)-2-(4-pyridyl)-9-anthryl]methylcarbamate, which was

converted to the corresponding diazo compound (2,2′-DPy-1-

N₂) by a routine method (Scheme 2).

Later, we found that direct coupling was achieved by using

the corresponding iodinated diazo compound (e.g., 2,7-DI-1-

N₂). Thus, 2,7-DPy-1-N₂was prepared by this method (Scheme

3).

All diazo compounds were purified by repeated chromatog-

raphy on a gel permeation column, and a rather stable red solid

was obtained.

Figure 1. π-Spin density distribution of triplet anthrylcarbene and triplet

4- and 3-pyridylcarbene by PM3 method. The vacant and filled circles denote

negative and positive spin densities, respectively.

(A) Spectroscopic Studies of Photoproducts of DPy-1-

N₂. Before examining the magnetic properties of the species

generated by photolysis of the complex between the desired

diazo compound DPy-1-N₂and metal ions, we characterized

the metal-free carbene DPy-1.

tert-butylphenyl)-9-anthryl]carbene 1 as a triplet carbene unit

to construct a high heterospin system since this carbene has

the longest lifetime (more than 10 days) in solution at room

temperature.^10eThus, we needed to introduce pyridyl groups

onto the precursor of 1, that is, bis[10-(2,6-dimethyl-4-tert-

butylphenyl)-9-anthryl]diazomethane 1-N₂.

Before preparing a desired precursor, we need to consider

the spin densities of organic spin sources and connecting ligands.

A pyridyl group ligand needs to be introduced on a carbon that

has nonbonding molecular orbital (NBMO) spin densities.^16,17

The π-spin density distribution of triplet anthrylcarbene was

calculated using the PM3 method and is shown in Figure 1.

The largest spin density is found at position 10.

Electron Spin Resonance (ESR) Studies. Irradiation (λ >

350 nm) of 2,7-DPy-1-N₂(1.2 × 10^-2Μ) in 2-methyltetrahy-

drofuran (2-MTHF) at 77 K gave ESR signals of randomly

oriented triplet molecules (Figure 2a). The spectrum showing

unresolved x and y lines and a rather intense line at 152 mT

corresponding to ∆m_s) 2 is very similar to that recorded for

the “parent” triplet carbene before pyridination, bis[10-(4-tert-

butyl-2,6-dimethylphenyl)-9-anthryl]carbene 1,^10d,eand can

hence be assigned to triplet [10-(4-tert-butyl-2,6-dimethylphen-

yl)-9-anthryl][10-(4-tert-butyl-2,6-dimethylphenyl)-2,7-di(4-

pyridyl)-9-anthryl]carbene (2,7-DPy-³1) generated by photo-

dissociation of 2,7-DPy-1-N₂. The signals were analyzed in

terms of ZFS parameters with D ) 0.0978 cm^-1and E ) 0.0029

cm^-1(E/D ) 0.030).

Similar irradiation of 2,2′-DPy-1-N₂under identical condi-

tions also gave ESR signals due to the triplet carbene 2,2′-DPy-

³1, which were analyzed in terms of ZFS parameters with D )

0.113 cm^-1and E ) 0.0021 cm^-1(E/D ) 0.0189) (Figure S1).

It is interesting to note that the D value of 2,7-DPy-³1 is

slightly smaller than that reported for the “parent” triplet carbene

³1 (D ) 0.102 cm^-1and E ) 0.0008 cm^-1, E/D ) 0.0079).

This suggests that the unpaired electrons are delocalized to

pyridyl groups at the 2 and 7 positions to some extent. However,

the D value of 2,2′-DPy-³1 is very similar to that of ³1,

suggesting that delocalization is not significant in this case.

However, it is likely that aryl groups at this position are not

in the same plane as the anthryl group, due to repulsion by peri

hydrogens. For instance, the ESR zero-field splitting (ZFS)

parameters change very little between bis(9-anthryl)carbene and

its 10-phenylated analogue.¹⁰Positions 2 (and 7) and 4 (and 5)

have significantly high-spin densities, but from a synthetic

standpoint, position 2 (and 7) is more realistic. The spin densities

at the bridging groups are also important factors to take into

account. The π-spin density distribution of the isomeric carbenes

3- and 4-pyridylcarbene calculated by PM3 (Figure 1) suggest

that, while in the para isomer 4-pyridylcarbene, the pyridyl

nitrogen atom is expected to have nonzero NBMO coefficients,

and hence the spin interactions are expected to be transmitted

effectively through the nitrogen coordinated to the metal ions,

zero NBMO coefficients are expected on the pyridyl nitrogen

atom in the meta isomer 3-pyridylcarbene, and hence the

magnitude of the spin interactions is expected to be small.

To examine the stability of triplet carbenes, a variable-

temperature ESR study was carried out. The thermal stability

of the triplet carbenes could be estimated by gradually warming

the matrix containing triplet carbenes to a desired temperature,

followed by letting it stand at this temperature for 5 min, and

then recooling it to 77 K to measure the signal. This procedure

On the basis of the above considerations, we decided to

prepare two dianthryldiazomethanes having two pyridyl groups

at either the 2,2′- or the 2,7-positions, that is, bis[10-(4-tert-

butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-9-anthryl]diazo-

methane (2,2′-DPy-1-N₂) and [10-(4-tert-butyl-2,6-dimeth-

(16) Borden, W. T.; Davidson, E. R. J. Am. Chem. Soc. 1977, 99, 4587.

(17) (a) Borden, W. T.; Iwamura, H.; Berson, J. A. Acc. Chem. Res. 1994, 27,

109. (b) Borden, W. T. In Diradicals; Borden, W. T., Ed.; Wiley-

Interscience: New York, 1982; pp 1-12.

(18) For reviews, see for example: (a) Suzuki, A. In Metal-Catalyzed Cross-

Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH:

Weinheim, Germany, 1998; pp 49-97. (b) Stanforth, S. P. Tetrahedron

1998, 54, 263. (c) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457.

9

7080 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

Scheme 2

Scheme 3

can compensate for weakening of signals due to Curie’s law.¹⁹

When the samples containing 2,7-DPy-1 were gradually warmed,

the signals became sharp around 90 K, a small shift in the z

lines was observed, and a small but distinct decrease in the D

value was noted (D ) 0.0813 cm^-1and E ) 0.0007 cm^-1, E/D

) 0.0092) (Figure 2b). These changes were not reversible; when

the sample was recooled to 77 K, no change took place apart

from an increase in the signal intensity according to Curie’s

law.

A similar sharpening of the signals and decrease in ZFS

parameters was noted for 2,2′-DPy-³1 (D ) 0.0831 cm^-1and

E ) 0.0007 cm^-1, E/D ) 0.0087).

A decrease in the D and E values upon annealing of the matrix

has often been observed for sterically congested triplet diaryl-

carbenes and is usually interpreted in terms of geometrical

changes.^20-22

(19) (a)Platz, M. S. In Diradicals; Borden, W. T., Ed.; Wiley: New York, 1982;

pp 195-258. (b) Wasserman, E.; Hutton, R. S. Acc. Chem. Res. 1977, 10,

27. (c)Breslow, R.; Chang, H. W.; Wasserman, E. J. Am. Chem. Soc. 1967,

89, 1112.

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7081

A R T I C L E S

Itoh et al.

This result can be compared with that observed for ³1, where

the ESR signals were observed even after standing for 3 h at

room temperature.^10eA marked decrease in the thermal stability

was thus noted once pyridyl groups were introduced at the 2

(and 7) positions of 1.

UV-Visible (UV-Vis) Spectroscopic Studies in a Matrix

at Low Temperature. Optical spectroscopical monitoring in

the frozen medium gave analogous results. Irradiation of the

diazo compound (2,7-DPy-1-N₂) (1.5 × 10^-4Μ) in a 2-MTHF

matrix at 77 K resulted in rapid disappearance of the original

absorption due to 2,7-DPy-1-N₂and concurrent growth of sharp

and strong absorption bands at 363, 427, and 501 nm (Figure

3Ab). Since ESR signals ascribable to the triplet carbene are

observed under identical conditions, the absorption spectrum

can be safely assigned to the triplet carbene 2,7-DPy-³1. When

the matrix was gradually warmed, the bands at 501 nm became

sharper and shifted to 469 nm and the bands at 427 nm shifted

to 420 nm, with a spike at 441 nm at around 90 K (Figure 3Ac).

This change can be attributed to the geometrical change in the

triplet carbene associated with a change in the viscosity of the

matrix upon annealing, as shown by ESR experiments. Upon

further thawing, the band started to disappear slowly at around

200 K, and it disappeared completely after standing for 1 h at

300 K (Figure 3B).

Similar irradiation of 2,2′-DPy-1-N₂at 77 K also gave

absorption bands at 399, 420, 454, and 504 nm due to 2,2′-

DPy-³1 before relaxation and those at 395 and 469 nm due to

the relaxed one at 90 K. The bands also started to disappear at

around 260 K but were still observable at 300 K (Figure S2).

Once again, these results can be compared with those

observed for ³1, which exhibited essentially identical absorption

bands (360, 382, 405, 438, and 472 nm at 77 K and 360, 380,

410, 438, and 452 nm at 90 K) but showed distinctly greater

thermal stability, surviving several hours at 300 K.^10e

Again, a marked decrease in the thermal stability was noted

once pyridyl groups were introduced at the 2 and 7 positions

of 1.

Time-Resolved UV-Vis Spectroscopic Study in Solution

at Room Temperature. To determine the stabilities of the

present carbenes more accurately, their lifetimes were estimated

in degassed benzene at room temperature. We had previously

measured the lifetimes of a series of sterically congested

diarylcarbenes under these conditions.⁹The lifetimes of the

present carbenes were too long to monitor by laser flash

photolysis, which is routinely used in such studies. Therefore,

we used conventional UV-vis spectroscopy.

Brief irradiation of the diazo compound (2,7-DPy-1-N₂) (1.5

× 10^-5Μ) in degassed benzene at 25 °C with a 70-90 mJ,

308-nm pulse from a XeCl excimer laser produced transient

absorption bands showing strong maxima at 360, 411, and 467

nm, which appeared coincidently with the pulse (Figure 4).

These transient absorption bands are essentially the same as

those observed for the photolysis of 2,7-DPy-1-N₂in a

2-MTHF matrix at 77 K, followed by warming to 100 K. Thus,

we assigned the transient product as 2,7-DPy-³1 in its geo-

metrically relaxed state. This assignment was supported by

trapping experiments (vide infra). The absorption bands decayed

very slowly, and the transient bands did not disappear com-

pletely, even after standing for several hours under these

conditions. The decay was best analyzed in terms of a

Figure 2. (a) ESR spectra obtained by irradiation of 2,7-DPy-1-N₂(1.2

× 10^-2Μ) in 2-methyltetrahydrofuran at 77 K. (b-g) ESR spectra observed

at 77 K in 2-methyltetrahydrofuran after warming the matrix containing

2,7-DPy-³1 to (b) 90, (c) 220, (d) 240, (e) 260, (f) 280, and (g) 300 K.

Thus, when a carbene is generated in a rigid matrix at a very

low temperature, it should have the geometry dictated by that

of its precursor. Even if the thermodynamically most stable

geometry of the carbene is different from its initial geometry,

the rigidity of the matrixes prevents the carbene from achieving

its minimum-energy geometry. When the matrix is softened by

annealing, the carbene undergoes relaxation to the preferred

geometry, probably to decrease steric compression.^21,22It has

been shown that the ZFS parameters of sterically unperturbed

diarylcarbenes show little sensitivity toward the temperature of

the matrix.²⁰The rather small D values coupled with the

3

essentially zero E value observed for 1 indicate that there is

extensive delocalization of the unpaired electrons into the anthryl

portions and that the carbene has a substantial degree of allenic

character.¹⁰A small but distinct decrease in the D value upon

annealing of the matrix can thus be interpreted as indicating

that the triplet carbene relaxed to a nearly linear geometry, in

which the unpaired electrons are further delocalized into the

anthryl portions. The E values also decreased accordingly.

Significant decay of the signals due to 2,7-DPy-1 was

observed only at 280 K, and the signals were observable even

at 300 K (Figure 2c-f). However, the signals disappeared

completely after the sample had stood at room temperature for

15 min (the measurements were made at 77 K). An essentially

identical thermal stability was observed for 2,2′-DPy-1 (Figure

S1).

(20) For reviews of the EPR spectra of triplet carbenes, see: (a) Sander, W.;

Bucher, G.; Wierlacher, S. Chem. ReV. 1993, 93, 1583. (b) Trozzolo, A.

M.; Wasserman, E. In Carbenes; Jones, M., Jr., Moss, R. A., Eds.; Wiley:

New York, 1975; Vol. 2, pp 185-206.

(21) (a) Tukada, H.; Sugawara, T.; Murata, S.; Iwamura, H. Tetrahedron Lett.

1986, 27, 235. (b) Nazran, A. S.; Gabe, F. J.; LePage, Y.; Northcott, D. J.;

Park, J. M.; Griller, D. J. Am. Chem. Soc. 1983, 105, 2912. (c) Nazran, A.

S.; Griller, D. J. Chem. Soc., Chem. Commun. 1983, 850. (d) Gilbert, B.

C.; Griller, D.; Nazran, A. S. J. Org. Chem. 1985, 50, 4738. (e) Nazran,

A. S.; Lee, F. L.; LePage, Y.; Northcott, D. J.; Park, J. M.; Griller, D. J.

Phys. Chem. 1984, 88, 5251. (f) Tomioka, H.; Watanabe, T.; Hirai, K.;

Furukawa, K.; Takui, T.; Itoh, K. J. Am. Chem. Soc. 1995, 117, 6376.

(22) See for review: Tomioka, H. In AdVances in Strained and Interesting

Organic Molecules; Halton, B., Ed.; JAI Press: Greenwich, CT, 2000; Vol.

8, pp 83-112.

9

7082 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

Figure 3. UV-vis spectra obtained by irradiation of diazo compound 2,7-DPy-1-N₂(1.5 × 10^-4Μ) . (A) (a) Spectra of 2,7-DPy-1-N₂in

2-methyltetrahydrofuran at 77 K. (b) The same sample after irradiation (1.5 min, λ > 350 nm). (c) The same sample after thawing to 90 K. (B) UV-vis

spectral change measured upon warming the same sample from 90 to 300 K.

Scheme 4

show a broad absorption band centered at 396-450 nm. Thus,

the observations can be interpreted as indicating that 2,7-DPy-

³1 is trapped by oxygen to form the carbonyl oxide (2,7-DPy-

1-O₂), which confirms that the transient absorption quenched

by oxygen is due to 2,7-DPy-³1 (Scheme 4).

The apparent buildup rate constant, k_obs, of the carbonyl oxide

(2,7-DPy-1-O₂) is essentially identical to that for the decay of

2,7-DPy-³1, and k_obsis expressed as given in eq 1:

Figure 4. Absorption of transient products formed during irradiation of

diazo compound 2,7-DPy-1-N₂(1.5 × 10^-5Μ) in degassed benzene at

k_obs) k₀+ k_O2[O₂]

(1)

room temperature recorded 0, 30, 60, 120, 300, and 600 min after excitation.

Inset shows the time course of the absorption at 467 nm.

where k₀represents the rate of decay of 2,7-DPy-³1 in the

absence of oxygen and k_O2is the rate constant for the quenching

of 2,7-DPy-³1 by oxygen. A plot of the observed pseudo-first-

order rate constant of the formation of the oxide against [O₂] is

linear (Figure S3). From the slope of this plot, k_O2was

combination of first-order kinetics with k ) 6 × 10^-4min^-1, τ

) 1.6 × 10³min (28 h), OD ) 0.564 and second-order kinetics

with 2k/ꢀl ) 3.6 × 10^-2min^-1, t_1/2) 135 min, OD ) 0.803.²³

When LFP was carried out on a nondegassed benzene solution

of 2,7-DPy-1-N₂(5.0 × 10^-5Μ), the half-life of 2,7-DPy-³1

decreased dramatically, and a broad absorption band with a

maximum at 420 nm appeared at the expense of the absorption

due to 2,7-DPy-³1 (Figure S3). The spent solution was found

to contain the corresponding ketone 2,7-DPy-1-O.

determined to be 1.4 × 10⁵M^-1s^-1

.

Similar irradiation of 2,2′-DPy-1-N₂(5.0 × 10^-5M) in

degassed benzene also gave transient bands at 392 and 465 nm

due to 2,2′-DPy-³1 in its relaxed state (Figure S4). The transient

band was found to be second-order (2k/ꢀl ) 2.4 × 10^-2min^-1

)

in this case. The approximate half-life (t_1/2) of 2,7-DPy-³1 was

estimated to be 35 min. The transient bands showed that 2,7-

DPy-³1 was also trapped with oxygen with a rate constant of

9.0 × 10⁴M^-1s^-1(Figure S5).

It is well-documented^24,25that diarylcarbenes with triplet

ground states are readily trapped by oxygen to generate the

corresponding diaryl ketone oxides, which are easily observed

directly either by matrix isolation or by flash photolysis and

3

These compounds are shorter-lived than 1, whose half-life

under identical conditions is estimated to be 14.5 days.^10e

However, the quenching rate constants by oxygen are ap-

proximately 5 orders of magnitude smaller than that of triplet

(23) The decay curves were analyzed by the following equation:

k₀exp(-k₁t) + 1/(1/k₂+ k₃t), where k₀and k₂are absorbances of

components decaying in the first- and second-order kinetics at t ) 0 time,

respectively, and k₁and k₃are the decay rates of the first- and second-

order kinetics, respectively. The analysis was made by using Igor Pro 4

(WaveMetrics, Inc).

(24) See for review: (a) Sander, W. Angew. Chem., Int. Ed. Engl. 1990, 29,

344. (b) Bunnelle, W. Chem. ReV. 1991, 91, 336.

(25) Scaiano, J. C.; McGimpsey, W. G.; Casal, H. L. J. Org. Chem. 1989, 54,

1612.

3

diphenylcarbene²⁵and are similar to that of 1 (k_O2) 5.5 ×

10⁴M^-1s^-1). Thus, they are still fairly stable for triplet carbenes.

(B) Spectroscopic Studies of Photoproducts of Complex

between DPy-1-N₂and Cu(hfac)₂. All the above observations

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7083

A R T I C L E S

Scheme 5

Itoh et al.

suggest that we now have a fairly persistent triplet carbene unit

that has a pyridine ligand that is bridgeable with coordinatively

unsaturated metal ions. The next step is to characterize the

magnetic properties of the photoproducts of the complex

between DPy-1-N₂and metal ions.

the expense of the Cu(II) signals (Figure 5Ab and c). Similar

ESR spectral changes have been observed for the 2:1 complex

of (phenyl)(4-pyridyl)carbene with a Cu(II) ion, which has been

shown to have ferromagnetic interaction between the carbene

and the copper ion. Thus it is suggested that the generated

carbene centers interacted magnetically with the Cu(II) ion to

form a high-spin species.^14a,27As no significant signals due to

the isolated triplet carbene 2,2′-DPy-³1 were observed, it is

suggested that the pyridine moiety binds with Cu(hfac)₂in a

nearly quantitative manner under these cryogenic conditions.

However, it should be noted that the signals due to the isolated

Cu(II) ion did not disappear completely, even after prolonged

irradiation.

It has been demonstrated that the sign and magnitude of the

exchange coupling between metal ions and organic radicals

depend not only on the periodicity of the ligand π orbitals, but

also on the orbitals occupied by the unpaired d electrons of the

metal ions.^14aFor instance, ferromagnetic interaction is observed

between the carbenes and the copper ions in the [Cu(hfac)₂-

(DPy)] (hfac ) hexafluoroacetylacetonate) system, while anti-

ferromagnetic interaction is observed between the carbenes and

the manganese ions in the [Mn(hfac)₂(DPy)] system. This is

explained in terms of the difference between the overlapping

mode of the magnetic orbitals in the metal ions and those in

the nitrogen atom on the pyridine ligands. Thus, we chose

Cu(hfac)₂as the metal ion to generate high-spin states.

Both diazo compounds are expected to form a chain as a

result of complexation with metal ions (to form -DPy-1-N₂-

M-), and the chain is expected, upon irradiation, to generate a

polycarbene chain (-DPy-1-M-) in which the spins on the

chain start to interact ferromagnetically. However, there is a

potential difference between the two in the connectivity of the

ferromagnetic coupling unit with respect to carbene centers

(Scheme 5). In the -2,2′-DPy-1-M- chain, for instance,

carbene centers are involved in coupling units in the chain (Class

1 in Scheme 5), while in the -2,7-DPy-1-M- chain, carbenes

are attached as pendants to a coupling unit of the chain (Class

2 in Scheme 5). In other words, failure to generate a carbene (a

chemical defect) in the interior of a polycarbene chain may

interrupt the exchange pathway in the former, while this

chemical defect may be circumvented in the latter.⁴

To estimate the thermal stability of the signals, the sample

was warmed to a desired temperature, allowed to stand at this

temperature for 5 min, and then recooled to 77 K to measure

the ESR signals. The new signals increased up to a temperature

of 100 K, but started to disappear at 240 K. At around 260 K,

the signals due to the isolated Cu(II) ion started to recover, and

they completely replaced the signals due to the complex at

around 300 K (Figure 5B).

Similar irradiation of the 1:1 complex of 2,7-DPy-1-N₂and

Cu(hfac)₂gave somewhat different results (Figure 6). Before

irradiation, the solution showed only broad ESR signals at 309

and 319 mT, without showing the characteristic signal of the

Cu(II) ion of Cu(hfac)₂(Figure 6Aa). This is most probably

because the 3d spins on the Cu(II) ions in the complex can

already interact with each other, through the pyridyl and anthryl

aromatic π networks, since they are conjugatively involved in

the ferromagnetic chains (Scheme 5). Upon irradiation, the

signal at 309 mT started to increase, with a concomitant shift

of the signal maximum, until the maximum stopped growing

at 315 mT, while the signal at 319 mT decreased initially, but

then also increased with a concomitant shift of the signal, until

the maximum stopped growing at 325 mT, after irradiation for

1 h (Figure 6Ac). Again, the fact that no significant signals

due to the isolated triplet carbene 2,7-DPy-³1 were observed

suggests that the pyridine moiety binds with Cu(hfac)₂in a

nearly quantitative manner under these cryogenic conditions.

ESR Studies. Solutions of 2,2′-DPy-1-N₂(11.6 × 10^-3Μ)

in 2-MTHF and copper bis(hexafluoroacetylacetonate) Cu(hfac)₂

(11.6 × 10^-3Μ) in 2-MTHF were mixed in a 1:1 molar ratio

at room temperature, and the mixture was allowed to stand

overnight. The solution was then placed in the cryostat of a

low-temperature ESR cavity. Before irradiation, the solution

showed ESR signals at 260, 276, 298, 312, and 320 mT, which

26

2

is characteristic of the magnetic orbital d_{x -y}of the Cu(II) ion

(27) (a) Sano, Y.; Tanaka, M.; Koga, N.; Matsuda, K.; Iwamura, H.; Rabu, P.;

Drillon, M. J. Am. Chem. Soc. 1997, 119, 8246. (b) Karasawa, S.; Koga,

N. Polyhedron 2001, 20, 1387. (c) Karasawa, S.; Sano, Y.; Akita, T.; Koga,

N.; Itoh, T.; Iwamura, H.; Rabu, P.; Drillon, M. J. Am. Chem. Soc. 1998,

120, 10080. (d) Karasawa, S.; Kumada, H.; Koga, N.; Iwamura, H. J. Am.

Chem. Soc. 2001, 123, 9685. (e) Morikawa, H.; Imamura, F.; Tsurukami,

Y.; Itoh, T.; Kumada, H.; Karasawa, S.; Koga, N.; Iwamura, H. J. Mater.

Chem. 2001, 11, 493. (f) Karasawa, S.; Koga, N. Polyhedron 2003, 22,

1877.

of Cu(hfac)₂(Figure 5Aa). When the solution was irradiated (λ

> 350 nm) at 77 K, the signals due to the isolated Cu(II) ion in

the Cu(hfac)₂unit started to decrease, and rather broad signals

gradually appeared at 340 mT, with a sharp one at 314 mT, at

(26) Sugiura, Y. Inorg. Chem. 1978, 17, 2178.

9

7084 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

Figure 5. ESR spectra obtained by irradiation of 1:1 mixture (5.8 × 10^-3Μ) of 2,2′-DPy-1-N₂and Cu(hfac)₂in 2-methyltetrahydrofuran. (A) Spectra of

1:1 mixture (5.8 × 10^-3Μ) of 2,2′-DPy-1-N₂and Cu(hfac)₂in 2-MTHF (a) before irradiation and (b-c) after irradiation (λ > 350 nm) for 10 and 120 min

at 77 K and (d) the same sample measured at 77 K after warming to 100 K. (B) ESR spectra observed at 77 K after warming to (e) 100, (f) 180, and (g)

280 K.

Figure 6. ESR spectra obtained by irradiation of 1:1 mixture (5.8 × 10^-3Μ) of 2,7-DPy-1-N₂and Cu(hfac)₂in 2-methyltetrahydrofuran. (A) Spectra of

1:1 mixture (5.8 × 10^-3Μ) of 2,7-DPy-1-N₂and Cu(hfac)₂in 2-MTHF (a) before irradiation and (b-c) after irradiation (λ > 350 nm) for 1 and 60 min

at 77 K and (d) the same sample measured at 77 K after warming to 100 K. (B) ESR spectra observed at 77 K after warming to (e) 100, (f) 260, and (g)

300 K.

Upon warming the matrix containing the sample, we found

that the new signals gradually decreased and the original signals

that had been present before irradiation recovered at 300 K

(Figure 6B).

It should be noted here that the bis(4-pyridyl)carbene-Cu-

(hfac)₂signals disappeared irreversibly at temperatures higher

than 60 K.^27dThus, remarkable thermal stability of the DPy-

1-Cu complex is noted.

UV-Vis Studies in a Matrix at Low Temperature.

Irradiation of a 1:1 mixture (1.5 × 10^-4Μ) of 2,7-DPy-1-N₂

and Cu(hfac)₂in 2-MTHF at 77 K gave rise to new absorption

bands at the expense of the original absorption due to the

complex. The new bands exhibited strong absorption at 363,

435, 497, and 600 nm (Figure 7Ab) and were significantly

different from those observed for free carbene, 2,7- DPy-³1 (363,

427, and 501 nm). When the matrix was gradually warmed,

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7085

A R T I C L E S

Itoh et al.

Figure 7. UV-vis spectra obtained by irradiation of 1:1 mixture (1.5 × 10^-4Μ) of 2,7-DPy-1-N₂and Cu(hfac)₂. (A) (a) Spectra of 2,7-DPy-1-N₂in

2-methyltetrahydrofuran at 77 K. (b) The same sample after irradiation (4 min, λ > 350 nm). (c) The same sample after thawing to 100 K. (B) UV-vis

spectral change measured upon warming the same sample from 100 to 300 K.

the bands at 497 nm became sharper and shifted to 474 nm,

and the bands at 435 nm shifted to 430 nm at around 90 K

(Figure 7Ac). These results can be compared with those

observed for the free carbene, 2,7-DPy-³1, which exhibited

similar but distinctly different absorption bands (at 363, 427,

and 501 nm at 77 K and at 362, 420, 441, and 469 nm at 90

K).

Since the ESR signals most likely ascribable to the carbene-

Cu complex are observed under identical conditions, we can

assign the absorption spectrum to the carbene-metal complex.

Similar slight red shift of the characteristic absorption due to

carbene after complexation with Cu(hfac)₂has been noted in

bis(4-pyridyl)carbene-Cu(hfac)₂systems.²⁷

magnetization (M/emu) at 5 K in a constant field of 5 kOe with

sample irradiation time was measured in situ and is shown in

Figure 8A. As the irradiation time increased, the M values

gradually increased, and they reached a plateau after 3 h. After

the M values reached a plateau, the magnetization values after

irradiation, Ma, were measured at 2.0 and 5.0 K in the field

range of 0-50 kOe. The magnetization values of the sample

before irradiation, Mb, were also measured under the same

conditions (Figure 8B).

The magnetization generated by irradiation was then obtained

by subtracting the values obtained before and after irradiation

(M ) Ma - Mb). Thus, any magnetization from diamagnetic

and paramagnetic impurities could be canceled out. The field

dependence of magnetization for the complex after irradiation

for 300 min, expressed by M versus H/T plots, is shown in

Figure 9. The plots were analyzed in terms of the Brillouin

function, as follows:^{1c, 27e, 29}

Upon further thawing, we saw that the band started to

disappear slowly at around 200 K, and it disappeared completely

after standing for about 2 h at 300 K (Figure 7B).

Similar irradiation of a 1:1 mixture (1.5 × 10^-4Μ) of 2,2′-

DPy-1-N₂and Cu(hfac)₂in 2-MTHF at 77 K gave rise to new

absorption bands at 410, 487, 569, and 712 nm and was

significantly different from those observed for the free carbene

2,2′-DPy-³1 (399, 420, 454, and 504 nm). Upon warming the

matrix, we found that the bands at 410 and 487 nm became

sharper and shifted to 409 and 472 nm, respectively, at around

90 K (Figure S6). These results can be compared with those

for the free carbene, 2,2′-DPy-³1, which exhibited similar but

distinctly different absorption bands (at 399, 420, 454, and 504

nm at 77 K and at 395 and 469 nm at 90 K). Since the ESR

signals most likely ascribable to the carbene-Cu complex are

observed under identical conditions, we can assign this absorp-

tion spectrum to the carbene-metal complex. The bands were

observable up to 300 K.

M ) Ma - Mb ) M_complex- M_Cu

) Ngµ_B[SB(ø) - B(ø′)/2]

(2)

where N is the number of the molecules, µ_Bis the Bohr

magneton, g is the Lande g-factor, and ø ) gSµ_BH/(k_BT), ø′ )

g′µ_BH/(2k_BT), where k_Bis the Boltzman constant and T is

temperature. The g′ value for the complex was 2.166, which

was determined from EPR spectra obtained under similar

conditions before irradiation.

The experimental data were fitted to the theoretical eq 2 to

give spin quantum number S ) 2.44 ( 0.04 and F (generation

factor for carbene obtained from saturated magnetization) )

0.82 (dotted line in Figure 9).³⁰Alternatively, the data were

better analyzed by a two-component Brillouin function with S

) 3.18 ( 0.07 (F ) 0.66) and S ) 0.02 ( 0.002 (F ) 0.23)

(solid curve in Figure 9). This may mean that defects due to

Superconducting Quantum Interference Device (SQUID)

Measurements. To determine the spin quantum numbers of the

DPy-1-Cu complex, the magnetic properties before and after

photolysis of the DPy-1-N₂-copper complex in 2-MTHF

solution were studied by using a SQUID magneto/susceptom-

eter.

The 2-MTHF solution (50 µL) of 2,7-DPy-1-N₂-copper

(1:1) complex (1.0 × 10^-3Μ)²⁸was placed inside the sample

compartment of a SQUID magneto/susceptometer and was

irradiated at 5-10 K with light (λ ) 442 nm) from a He/Cd

laser passed through an optical fiber. The development of

(28) The measurements were carried out at this low concentration not only to

avoid intermolecular magnetic interaction of sample and but also to increase

photolysis efficiency. The latter is especially important because we generate

magnetic species (carbene-Cu complexes) in situ by photolysis of

precursory diazo-Cu complexes: carbene-Cu complexes show rather

strong absorption bands at 470-480 nm, and hence, at higher concentration,

the bands due to carbene-Cu complexes grow and overlap with the bands

due to the starting complex (see Figures 7 and S6).

(29) Carlin, R. L. Magnetochemistry; Springer-Verlag: Berlin, 1986.

9

7086 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

Figure 10. Temperature dependence of the observed ø_molT for the

photoproduct from 1:1 mixture (1.0 × 10^-3Μ) of 2,7-DPy-1-N₂and Cu-

(hfac)₂obtained at a field of 5 kOe.

temperatures were fitted to the same Brillouin function, the

sample is considered to be free from ferro- or antiferromagnetic

intermolecular interactions, and the high-spin state is considered

to be a ground state.

The temperature dependence of the molar paramagnetic

susceptibility before and after irradiation (ø_molband ø_mola

,

respectively) in the range of 2-70 K was measured at a constant

field of 5 kOe. ø_mol() ø_mola- ø_molb)T versus T plots are shown

in Figure 10. The value of ø_molT increased with a decreasing

temperature from 70 to 4 K. This indicates that J/k is small but

positive, suggesting the presence of intramolecular ferromagnetic

interaction.

Figure 8. (A) Plot of magnetization (M in emu) as a function of irradiation

time observed in the photolysis of 1:1 mixture (1.0 × 10^-3Μ) of 2,7-

DPy-1-N₂and Cu(hfac)₂in 2-methyltetrahydrofuran matrix measured at

5.0 K and 5 kOe. (B) Field dependence of the magnetization of the

photoproduct from 1:1 mixture (1.0 × 10^-3Μ) of 2,7-DPy-1-N₂and Cu-

(hfac) in 2-methyltetrahydrofuran matrix measured at 2.0 and 5.0 K. Ma

and Mb refer to the magnetization value after and before irradiation,

respectively.

The data obtained for photoproducts from similar irradiation

of the 2-MTHF solution of the 1:1 2,2′-DPy-1-N₂-copper

complex (1.0 mM) were also analyzed by the Brillouin function

(Figures 11 and 12). The experimental data (M versus H/T) for

the 2,2′-DPy-1-N₂-copper complex after irradiation were

analyzed in terms of eq 2 with the fitted curve giving S ) 2.12

( 0.03 and F ) 0.41 (Figure 12).³⁰Alternatively, the data were

better analyzed by the two-component Brillouin function that

produced S ) 2.70 ( 0.13 (F ) 0.33) and S ) 0.49 ( 0.24

(F ) 0.11) (solid curve in Figure 12).

ø_mol() ø_mola- ø_molb)T versus T plots (Figure 13) showed

that the value of ø_molT increased with decreasing temperature

from 70 to 4 K, again suggesting the presence of intramolecular

ferromagnetic interaction.

It should be noted that the S and F values observed for the

photoproduct of the 1:1 2,2′-DPy-1-N₂-copper complex are

notably smaller than those for that of the 1:1 2,7-DPy-1-N₂-

copper complex. Incomplete photolysis of diazo groups is often

pointed out as a reason for rather small S and F values. However,

almost complete photolysis of the sample was confirmed by

taking the difference in absorption at 2040 cm^-1due to the diazo

moieties before and after SQUID measurements. It may be that

there is a defect in the ligation of pyridine groups in the 2,2′-

DPy-1-N₂-copper complex. This is in accord with the

observation that, in the ESR experiments on the photoproduct

of the 2,2′-DPy-1-N₂-copper complex, the signals due to free

copper ions did not disappear completely. If there are partially

uncoordinated copper ions in the complex, the magnetic

contribution of the uncoordinated copper ions will be deleted

in the equation M_complex- M_Cu, and this will result in small S

and F values.

Figure 9. Plot of M vs H/T of the photoproduct from 1:1 mixture (1.0 ×

10^-3Μ) of 2,7-DPy-1-N₂and Cu(hfac)₂measured at 2.0 (O) and 5.0 (0)

K in 2-methyltetrahydrofuran. Fitting data are shown as broken (one

component) and solid (two components) lines.

incomplete photolysis produce mixtures of the spin systems in

the chains. Since the magnetization data at two different

(30) (a)Variable parameters in eq 2 are N and S and all others are constants or

experimental values. Thus, S values are estimated by best-fitting the

curvature of M versus H/T plot from eq 2 while N (in Avogadro numbers)

is obtained by fitting the best-fitted curves to the vertical axis. F values

are then obtained from sample concentration and quantity. (b) M values in

Figures 9 and 12 were obtained from Ma - Mb, where Ma and Mb refer

to the magnetization value after and before irradiation, respectively. This

means that Mb is mostly magnetization due to copper ion (S ) ¹/₂) in diazo-

Cu complexes. Ma values will saturate more easily than Mb as a function

of H since Ma values are larger than Mb values. Thus, M () Ma - Mb)

decreases at higher field.

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7087

A R T I C L E S

Itoh et al.

Figure 13. Temperature dependence of the observed ø_molT for the

photoproduct from 1:1 mixture (1.0 × 10^-3Μ) of 2,2′-DPy-1-N₂and Cu-

(hfac)₂obtained at a field of 5 kOe.

higher than 60 K. These observations suggest that it is potentially

possible to prepare a persistent high-spin polycarbene by

extending this method.

It should be noted that the spin quantum number obtained

by Brillouin function analysis of the field dependence of

magnetization is not very high. The apparent spin quantum

number of the ferromagnetic chains consisting of a 1:1 complex

between bis(4-pyridylcarbene)(DPy) and copper ions amounts

to S ) 33.6. This indicates that the ferromagnetic coupling in

the chain is over 23.^27aSince this measurement was made in

the crystal state where the chain is expected to be held rather

tightly, it may not be appropriate to directly compare the data.

This value actually drops down to 6.4 when it is measured in a

frozen solution of 2-MTHF, where the chain may be more

flexible.^27bThus, part of the reason for the rather low S value

is ascribable to the condition of the sample.

Figure 11. (A) Plot of magnetization (M in emu) as a function of irradiation

time observed in the photolysis of 1:1 mixture (1.0 × 10^-3Μ) of 2,2′-

DPy-1-N₂and Cu(hfac)₂in 2-methyltetrahydrofuran matrix measured at

5.0 K and 5 kOe. (B) Field dependence of the magnetization of the

photoproduct from 1:1 mixture (1.0 × 10^-3Μ) of 2,2′-DPy-1-N₂and Cu-

(hfac) in 2-methyltetrahydrofuran matrix measured at 2.0 and 5.0 K. Ma

and Mb refer to the magnetization value after and before irradiation,

respectively.

The spin quantum number of the 1:1 complex between DPy-1

and copper ions is, however, still significantly smaller than that

of the 1:1 complex between bis(4-pyridylcarbene) and copper

ions obtained under identical conditions.

Several factors affect the type and strength of spin coupling

and, hence, the overall magnetic properties of polyradicals.¹

Among them, the connectivity in the present system is carefully

designed so that the spins on the triplet carbene centers are

transmitted effectively to the pyridine ligand and then on to

the pyridine nitrogen, which then interacts ferromagnetically

with the orbitals occupied by the unpaired d electrons of the

copper ions (vide supra). The chemical defects, resulting from

failure to generate a triplet carbene in the interior of the chain

of the Cu-carbene and/or destruction of the carbene centers

by reactions, may be part of the reason for the smaller S values

in the DPy-1-Cu complex. However, similar S values observed

for the 2,7-DPy-1-Cu complex, in which this chemical defect

can be avoided, suggest that this is not the main factor.

Intermolecular magnetic interactions sometimes complicate the

study of spin coupling in poly-radicals³and -carbenes.^6,7Since

the magnetization data at two different temperatures were fitted

to the same Brillouin function, the sample is considered to be

free from ferro- or antiferromagnetic intermolecular interactions.

The temperature dependence of the molar paramagnetic sus-

ceptibility also suggests the presence of intramolecular ferro-

magnetic interaction.

Figure 12. Plot of M vs H/T of the photoproduct from 1:1 mixture (1.0 ×

10^-3Μ) of 2,2′-DPy-1-N₂and Cu(hfac)₂measured at 2.0 (O) and 5.0 (0)

K in 2-methyltetrahydrofuran. Fitting data are shown as broken (one

component) and solid (two components) lines.

Conclusion

The present results demonstrate that high-spin species are

generated in the photoproduct of a copper ion complex with

sterically congested diaryldiazomethanes having a 4-pyridyl

group, as a result of ferromagnetic interaction between the 3d

spin of metal ions and the 2p spins of triplet carbene through

the pyridyl group located remote from the carbene center. The

complexed carbene showed remarkable stability, surviving up

to 300 K in 2-MTHF, while the analogous copper ion complex

with an unprotected pyridylcarbene decays at temperatures

Delocalization of spin is also an important factor. It has been

shown that spin coupling is weaker for π-conjugated dinitroxides

than their carbon counterparts because spin density is delocalized

9

7088 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

on the nitroxide moiety in π-conjugated nitroxides.^1c,5Signifi-

cantly small D values observed for dianthrylcarbenes suggest

that the unpaired electrons are extensively delocalized into

dianthryl rings. Although the spin density builds up at the 2

(and 2′) and 7 (and 7′) positions, where ligands are connected,

the spins are significantly dispersed in the ring carbons, and

hence, the net spin densities on 2 (and 2′) and 7 (and 7′) carbon

atoms in triplet dianthrylcarbenes are actually not large. Then

the density is further diminished in conduit of the pyridine ring

until the spins are transmitted onto the pyridine nitrogen atoms,

due to partial localization on the ortho carbon atoms and possible

twisting of the pyridyl rings from the plane of the anthryl ring.

These factors can explain the rather small S value observed

for the present system compared to that of the 1:1 complex

between bis(4-pyridyl)carbene and copper ions.²⁷In this respect,

triplet bis(9-acridyl)carbene, in which nitrogen atoms are

incorporated at the 10-position of the anthryl ring, is a more

promising candidate for realizing persistent high-spin species

consisting of 2p spins of carbene and 3d spins of metal ions.

An advantage of the present approach is its easiness to

increase the dimension of the spin network. Koga and co-

workers have increased the dimension of the spin networks from

one- to two- and three-dimensional structures by using highly

branched base ligand containing diazo units. For instance, a

high-spin carbene-copper ion complex with an S value higher

than 1000 was obtained by photolysis of 3:2 complex of Cu-

(hfac)₂and 1,3,5-benzentriyltris(4-pyridyldiazomethane).^27bThe

preparation of desired precursory aromatic π-net works having

poly(4-pyridyldiazobenzyl) unit will be achieved by extending

the present method.

The very high-spin organic species comprising of triarylm-

ethyls is achieved⁴by connecting S ) 3 calix[4]arene macro-

cycles with S ) ¹/₂bis(biphenylene)methyl groups, where out-

of-plane twistings, reverting the sign of exchange coupling from

ferromagnetic to antiferromagnetic, and chemical defect in the

interior, interrupting the exchange pathway, are carefully

eliminated, and the ferrimagnetic coupling scheme, that is,

antiferromagnetic coupling of unequal spins leading to a large

net spin magnetic moment, is applied. Approach along this line

using persistent triplet carbenes may also be possible by taking

advantage of the stability of our diazo compounds.

Experimental Section

General Methods. ¹H and ¹³C NMR spectra were recorded on JEOL

JNM-AC300FT/NMR spectrometer in CDCl₃with Me₄Si as an internal

reference. IR spectra were measured on a JASCO-Herschel FT/IR-410H

spectrometer, and UV-vis spectra were recorded on a JASCO CT-

560 spectrophotometer. The mass spectra were recorded on a JEOL

JMS-600H mass spectrometer. Gel permeation chromatography (GPC)

was carried out on a JASCO, model HLC-01 instrument using UV-

1570 as a detector. The GPC column was a Shodex H-2001. Thin-

layer chromatography was carried out on a Merck Kieselgel 60 PF₂₅₄

.

Column chromatography was performed on silica gel 60N (KANTO

chemical) for column chromatography or ICN for dry column chro-

matography.

Unless otherwise noted, all the reagents employed in this study are

commercial products and used after standard purification. Tetrahydro-

furan, ethyl ether, toluene, and dioxane were purified by distillation

from sodium/benzophenone, and dichloromethane, carbon tetrachloride,

and triethylamine were from calcium hydride.

Preparation of [10-(4-tert-Butyl-2,6-dimethylphenyl)-9-anthryl]-

[10-(4-tert-butyl-2,6-dimethyl)phenyl-2,7-di(4-pyridyl)-9-anthryl]-

diazomethane (2,7-DPy-1-N₂). To a solution of 4-tert-butyl-2,6-

dimethylbromobenzene³²(2.7 g, 11.3 mmol) in anhydrous diethyl ether

(40 mL) was added 1.4 M tert-butyllithium in n-pentane (17.0 mL,

24.0 mmol) at -78 °C under nitrogen atmosphere. The mixture was

stirred for 1 h at -78 °C and allowed to warm to room temperature.

To this mixture, a solution of 3,6-dibromo-9,10-dihydro-9-oxoan-

thracene³³(2.0 g, 5.6 mmol) in anhydrous toluene (100 mL) was added,

and the mixture was refluxed overnight. The mixture was allowed to

cool to room temperature, and a saturated ammonium chloride aqueous

solution was added carefully to it. The reaction mixture was extracted

with diethyl ether, and the organic layer was washed with water and

dried over anhydrous sodium sulfate. A brown solid obtained after

concentration of the solution was chromatographed on a silica gel

column eluted with n-hexane to afford 2,7-dibromo-10-(4-tert-butyl-

2,6-dimethylphenyl)anthracene as a pale-yellow solid in 34% yield

Attempts to realize a stable high-spin organic species have

been made mostly by using a thermodynamically stable radical

such as triarylmethyl and aminoxyl radicals. For instance, Rajca

and co-workers have made great efforts to construct stable high-

spin organic species comprising triarylmethyls and realized a

very high-spin species with values of S ≈ 5000.^4bIwamura and

co-workers have used π-conjugated olygo(aminoxyl) radicals

as bridging ligands and coordinatively unsaturated paramagnetic

3d transition metal ions as connectors and have constructed two-

and three-dimensional networks in which both the organic 2p

and metallic 3d spins have been ordered in macroscopic scales.^5d

Then one may ask why one needs to use persistent triplet

carbene as a unit to construct persistent high-spin species.

Moreover, the values of S for DPy-1-Cu complexes in the

present study are smaller than that of “parent” system, that is,

the ferromagnetic chains consisting of a 1:1 complex between

bis(4-pyridylcarbene)(DPy) and copper ions, which may mean

that one needs not use persistent triplet carbene. However, we

should emphasize here that the effectiveness of spin source to

construct high-spin species should be compared in a system in

which a spin unit is incorporated into essentially the same π-net

works. In this regards, it is very intriguing to note here that

poly(phenyl)acetylenes having persistent triplet diarylcarbene

units are found to have S ) 9 spin states,^13gwhile similar

acetylenes having thermodynamically stabilized radicals have

1

(0.9 g): mp 215 °C. H NMR (CDCl₃): δ 1.43 (s, 9H), 1.70 (s, 6H),

7.24 (s, 2H), 7.31 (d, J ) 9.4 Hz, 2H), 7.36 (dd, J ) 1.7, 9.2 Hz, 2H),

8.18 (d, J ) 1.7 Hz, 2H), 8.23 (s, 1H). ¹³C NMR (CDCl₃): δ 20.3,

31.5, 34.5, 120.3, 124.1, 124.6, 128.1, 128.2, 129.4, 130.1, 132.9, 133.2,

136.8, 137.4, 150.9. EIMS m/z (relative intensity): 498 (M + 4, 54.0),

496 (M + 2, 100), 494 (M⁺, 52.8); HRMS calcd for C₂₆H₂₄Br₂,

494.0244; found m/z, 494.0230.

To a cooled and stirred solution of 2,7-dibromo-10-(4-tert-butyl-

2,6-dimethylphenyl)anthracene (900 mg, 1.85 mmol) in carbon tetra-

chloride (10 mL), a carbon tetrachloride solution (2 mL) of bromine

(0.10 mL, 2.04 mmol) was added dropwise at 0 °C, and the mixture

was stirred at room temperature overnight. To this mixture, an aqueous

solution of 10% sodium hydroxide was added carefully. The reaction

mixture was extracted with carbon tetrachloride, and the organic layer

1

been shown to have a spin multiplicity of only /₂.³¹

(31) (a) Miura, Y.; Matsumoto, M.; Ushitani, Y.; Taki, Y.; Takui, T.; Itoh, K.

Macromolecules 1993, 26, 6673. (b) Nishide, H.; Kaneko, T.; Igarashi,

M.; Tsuchida, E.; Yoshioka, N.; Lahti, P. Macromolecules 1994, 27, 3082.

(c) Lahti, P. M.; Inceli, A. L.; Rossitto, F. C. J. Polym. Sci., Part A: Polym.

Chem. 1997, 35, 2167.

(32) Ogata, Y.; Kosugi, Y.; Nate, N. Tetrahedron 1971, 27, 2705.

(33) Biehl, R.; Hinrichs, K.; Lubitz, W.; Mennenga, U.; Roth, K. J. Am. Chem.

Soc. 1977, 99, 4278.

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7089

A R T I C L E S

Itoh et al.

was washed with water and dried over anhydrous sodium sulfate. After

removal of the solvent, 2,7,9-tribromo-10-(4-tert-butyl-2,6-dimeth-

ylphenyl)anthracene (1.0 g, 94%) was obtained as a yellow solid:

A solution of the chloromethane (11.86 g, 12.17 mmol) in anhydrous

1,4-dioxane (100 mL) was added to a molten mixture of silver

tetrafluoroborate (3.53 g, 18.26 mmol) and urethane (21.68 g, 343.4

mmol) at 60 °C. After addition was completed, the mixture was refluxed

overnight. After cooling, silver chloride was removed from the reaction

mixture by filtration and washed with chloroform. The filtrate was

washed with water, and the organic layer was dried over anhydrous

sodium sulfate and evaporated. The crude product was chromatographed

on a silica gel column eluted with n-hexane/dichloromethane (3:2).

Ethyl [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][2,7-dibromo-

10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl]methylcarbamate was

obtained as a yellow solid in 39% yield (4.56 g): mp 203.2-206.8

1

mp 286 °C. H NMR (CDCl₃): δ 1.43 (s, 9H), 1.69 (s, 6H), 7.24 (s,

2H), 7.33 (dd, J ) 0.6, 9.2 Hz, 2H), 7.41 (dd, J ) 1.8, 9.2 Hz, 2H),

8.77 (dd, J ) 0.5, 1.9 Hz, 2H). ¹³C NMR (CDCl₃): δ 20.3, 31.5, 34.5,

119.5, 122.8, 124.8, 128.5, 129.0, 129.8, 130.0, 131.8, 132.8, 136.7,

137.9, 151.3. EIMS m/z (relative intensity): 576 (M + 4, 62.1), 574

(M + 2, 63.0), 572 (M⁺, 22.7); HRMS calcd for C₂₆H₂₃Br₃, 571.9349;

found m/z, 571.9364.

To a solution of the bromide (2.0 g, 4.79 mmol) in anhydrous diethyl

ether (10 mL) was added 2.6 M n-butyllithium in n-hexane (2.2 mL,

5.75 mmol) at 0 °C under nitrogen atmosphere, and the mixture was

stirred for 2 h at 0 °C. Absolute DMF (1.12 mL, 14.37 mmol) was

added to the lithiated mixture at 0 °C, and the mixture was refluxed

overnight. The mixture was allowed to cool to room temperature, and

a saturated ammonium chloride aqueous solution was added carefully.

Insoluble material was filtered and washed with water to give a crude

aldehyde (1.4 g). The filtrate was extracted with diethyl ether, and the

organic layer was washed with water, dried over anhydrous sodium

sulfate, and evaporated to leave a crude product (0.7 g). The combined

crude product was chromatographed on a silica gel column eluted with

n-hexane/dichloromethane (1:1). 10-(4-tert-Butyl-2,6-dimethylphenyl)-

anthracene-9-carbaldehyde was obtained as a yellow solid in 57%

1

°C. H NMR (CDCl₃): δ 1.33 (t, J ) 7.0 Hz, 3H), 1.42 (s, 9H), 1.44

(s, 9H), 1.69 (s, 6H), 1.74 (s, 6H), 4.16-4.42 (m, 2H), 5.97 (d, J )

7.2 Hz, 1H), 7.22-7.33 (m, 12H), 7.53 (d, J ) 9.2 Hz, 2H), 8.41 (d,

J ) 8.3 Hz, 2H), 8.54 (d, J ) 7.3 Hz, 1H), 8.77 (s, 2H). ¹³C NMR

(CDCl₃): δ 14.8, 20.2, 20.4, 31.48, 31.55, 34.47, 34.50, 54.6, 61.7,

121.5, 123.9, 124.4, 124.6, 125.0, 126.54, 126.57, 126.9, 127.4, 128.3,

128.3, 128.5, 129.1, 129.7, 130.0, 131.3, 131.4, 134.6, 136.8, 136.9,

138.6, 150.5, 150.9, 155.4. MS (MALDI-TOF) calcd for C₅₆H₅₃Br₂-

NO₂(M - H⁺), 930.2516; found m/z, 930.2586.

The replacement reaction of bromine with iodine was carried out

according to the methods reported by Buchwald.³⁴To a mixture of

ethyl [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][2,7-dibromo-10-

(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl]methylcarbamate (451 mg,

0.41 mmol), sodium iodide (1.08 g, 7.25 mmol), and copper iodide (I)

(73 mg, 0.38 mmol), anhydrous 1,4-dioxane (20 mL) was added under

argon atomsphere, and this mixture was stirred for 5 min. To the

mixture, N,N′-dimethylethylenediamine (20 mL, 0.14 mmol) was added,

and the mixture was refluxed for 2 days. After cooling, sodium bromide

was removed from the reaction mixture by filtration and washed with

chloroform, and the filtrate was evaporated. Ethyl [10-(4-tert-Butyl-

2,6-dimethylphenyl)-9-anthryl][2,7-diiodo-10-(4-tert-butyl-2,6-dim-

ethylphenyl)-9-anthryl]methylcarbamate was obtained as a brown

solid in 91% yield (450 mg): mp 181.2-183.0 °C. ¹H NMR (CDCl₃):

δ 1.34 (t, J ) 7.3 Hz, 3H), 1.41 (s, 9H), 1.43 (s, 9H), 1.68 (s, 6H),

1.76 (s, 6H), 4.14-4.42 (m, 2H), 5.97 (d, J ) 7.2 Hz, 1H), 7.14-7.43

(m, 12H), 7.53 (d, J ) 8.5 Hz, 2H), 8.43 (d, J ) 8.6 Hz, 2H), 8.54 (d,

J ) 7.2 Hz, 1H), 9.06 (s, 2H). ¹³C NMR (CDCl₃): δ 14.9, 20.2, 20.6,

31.5, 31.6, 34.47, 34.49, 54.6, 61.7, 93.8, 123.8, 124.4, 124.6, 125.0,

126.6, 126.7, 127.5, 128.6, 128.7, 129.7, 129.9, 131.5, 133.3, 133.4,

133.5, 134.0, 134.6, 136.8, 137.0, 138.6, 150.5, 150.9, 155.4. MS

(MALDI-TOF) calcd for C₅₆H₅₄I₂NO₂, 1026.2239; found m/z, 1026.3464.

1

yield (1.0 g): mp 218 °C. H NMR (CDCl₃): δ 1.44 (s, 9H), 1.72 (s,

6H), 7.24 (s, 2H), 7.38-7.43 (m, 2H), 7.56 (d, J ) 8.8 Hz, 2H), 7.64-

7.69 (m, 2H), 9.04 (d, J ) 9.0 Hz, 2H), 11.60 (s, 1H). ¹³C NMR

(CDCl₃): δ 20.3, 31.5, 34.5, 123.7, 124.59, 124.60, 125.9, 127.1, 128.8,

129.4, 131.9, 133.9, 136.3, 145.4, 151.0, 193.4. IR (KBr, cm^-1): 3066w,

3044w, 2960s, 2915w, 2864m, 2765w, 1680vs(ν_CdO), 1607vw, 1556m,

1483w, 1438m, 1406vw, 1362w, 1270m, 1230vw, 1190m, 1152w,

1048m, 1029vw, 945m, 900w, 876w, 799w, 758m, 753m, 734w, 662m,

642vw, 602w, 569vw. EIMS m/z (relative intensity) 366 (M⁺, 100),

351 (36.9); HRMS calcd for C₂₇H₂₆O, 366.1984; found m/z, 366.1986.

To a solution of 2,7,9-tribromo-10-(4-tert-butyl-2,6-dimethylphenyl)-

anthracene (7.00 g, 12.2 mmol) in anhydrous diethyl ether (90 mL)

was added 2.4 M n-butyllithium in n-hexane (6.0 mL, 14.6 mmol) at

0 °C under nitrogen atmosphere, and the mixture was stirred for 2 h at

0 °C. A solution of 10-(4-tert-butyl-2,6-dimethylphenyl)anthracene-9-

carbaldehyde (4.46 g, 12.2 mmol) in anhydrous tetrahydrofuran (100

mL) was added to the lithiated mixture at 0 °C, and the mixture was

heated overnight at 40 °C. The mixture was allowed to cool to room

temperature, and a saturated ammonium chloride solution was added

carefully. The reaction mixture was extracted with diethyl ether, and

the organic layer was washed with water, dried over anhydrous sodium

sulfate, and evaporated. The crude product [10-(4-tert-butyl-2,6-

dimethylphenyl)-9-anthryl][2,7-dibromo-10-(4-tert-butyl-2,6-dimeth-

ylphenyl)-anthryl]methanol (11.9 g, quantitatively) was obtained as

a brown solid: mp 208.6-211.4 °C. ¹H NMR (CDCl₃): δ 1.43 (s, 9H),

1.45 (s, 9H), 1.72 (s, 6H), 1.77 (s, 6H), 3.01 (d, J ) 2.8 Hz, 1H), 7.24

(s, 4H), 7.25-7.31 (m, 6H), 7.33 (d, J ) 9.2 Hz, 2H), 7.53-7.57 (m,

2H), 8.51-8.54 (m, 3H), 8.85 (d, J ) 1.7 Hz, 2H). ¹³C NMR (CDCl₃):

δ 20.2, 20.4, 31.5, 31.6, 34.49, 34.51, 73.0, 121.4, 124.5, 124.7, 124.8,

125.1, 126.3, 127.3, 127.8, 128.4, 128.80, 128.85, 130.0, 131.5, 132.0,

133.68, 133.73, 134.7, 136.8, 136.9, 138.8, 139.1, 150.5, 151.0, 1501.0.

MS (MALDI-TOF) calcd for C₅₃H₄₈Br₂O (M - H⁺), 859.2145; found

m/z, 859.2281.

A dinitrogen tetraoxide (0.9 g, 9.0 mmol) was bubbled into

anhydrous carbon tetrachloride (10 mL) at -20 °C. To this solution,

sodium acetate (1.6 g, 18.0 mmol) and a solution of the carbamate

(1.00 g, 1.00 mmol) in anhydrous carbon tetrachloride (25 mL) were

added at -20 °C, and the mixture was stirred for 2 h at 0 °C. The

reaction mixture was poured into crushed ice and extracted with carbon

tetrachloride. The organic layer was washed with aqueous sodium

hydrogen carbonate and water and dried over anhydrous sodium sulfate.

After evaporation of the solvent, a residual solid was dissolved in

anhydrous tetrahydrofuran (30 mL) under nitrogen atmosphere and

cooled to -20 °C. Potassium t-butoxide (155 mg, 1.47 mmol) was

added to the mixture, and the mixture was stirred overnight at room

temperature. The reaction mixture was extracted with diethyl ether,

and the organic layer was washed with water and dried over anhydrous

sodium sulfate. After evaporation of the solvent, the residue was purified

by GPC (16 cycles, chloroform as eluent) to give [10-(4-tert-butyl-

2,6-dimethylphenyl)-9-anthryl][2,7-diiodo-10-(4-tert-butyl-2,6-di-

methylphenyl)-9-anthryl]diazomethane (204 mg, 21%) as an orange

Into a solution of the methanol (11.76 g, 12.17 mmol) in anhydrous

benzene (100 mL) cooled to 0 °C, a hydrogen chloride gas generated

by adding hydrochloric acid (66 mL) to sulfuric acid (99 mL) was

bubbled for 1 h, and the mixture was stirred for 1 h at 0 °C. Removal

of the solvent afforded [10-(4-tert-butyl-2,6-dimethylphenyl)-9-an-

thryl][2,7-dibromo-10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl]-

chloromethane (11.86 g, quantitatively) as a brown viscous liquid.

This was used without further purification since the chloride was found

to be rather unstable.

1

solid. H NMR (CDCl₃): δ 1.43 (s, 9H), 1.45 (s, 9H), 1.74 (s, 6H),

1.82 (s, 6H), 7.24 (s, 2H), 7.27 (s, 2H), 7.34-7.51 (m, 10H), 7.60 (d,

J ) 8.6 Hz, 2H), 8.29 (d, J ) 8.8 Hz, 2H), 8.75 (d, J ) 1.5 Hz, 2H).

(34) Klapars, A.; Buchwald, S. J. Am. Chem. Soc. 2002, 124, 14844.

9

7090 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

¹³C NMR (CDCl₃): δ 20.3, 20.5, 31.5, 31.6, 34.5, 55.5, 123.1, 124.0,

124.5, 124.7, 125.1, 125.6, 127.0, 127.4, 128.8, 129.1, 130.4, 130.47,

130.50, 131.4, 133.2, 134.2, 133.4, 134.8, 136.9, 137.0, 138.5, 138.9,

150.6, 141.1. IR (NaCl, cm^-1): 3063vw, 3018w, 2965s, 2925m, 2868w,

2041vs(ν_CdN2), 1711w, 1605w, 1589w, 1481w, 1458w, 1432m, 1379w,

1326m, 1215s, 1192vw, 945m, 903vw, 870w, 825w, 821w, 681w, 670s,

651w, 624w, 609w.

temperature, the mixture was added to water. The precipitate formed

was filtered recrystallized from ethanol to give 3-bromo-9,10-dihydro-

9-oxoanthracene as an ocherous color solid (6.6 g, 96%); mp 141.2-

142.2 °C. ¹H NMR (CDCl₃): δ 4.34 (s, 2H), 7.47 (d, J ) 7.2 Hz, 1H),

7.50 (t, J ) 2.4 Hz, 1H), 7.58 (d, J ) 7.5 Hz, 1H), 7.61 (dd, J ) 4.0,

2.0 Hz, 1H), 7.65 (d, J ) 2.0 Hz, 1H), 8.21 (d, J ) 8.5 Hz, 1H), 8.36

(dd, J ) 6.4, 1.7 Hz, 1H); ¹³C NMR (CDCl₃): δ 31.9, 127.2, 127.5,

127.9, 128.4, 129.3, 130.5, 130.8, 131.2, 131.6, 133.0, 139.7, 142.0,

183.3; EIMS m/z (relative intensity): 274 (M + 2, 98), 272 (M⁺, 100),

193 (90); HRMS calcd for C₁₄H₉OBr, 271.9824; found m/z, 271.9836.

To a mixture of the diiodo-diazomethane (204 mg, 0.21 mmol) in

anhydrous dioxane (2 mL), 2-(4-pyridyl)-4,4,5,5-tetramethyl-1,3-diox-

aborolane (346 mg, 1.68 mmol), [1,1′-bis(diphenylphosphino)ferrocene]-

palladium dichloride dichloromethane complex: PdCl₂(dppf)₂‚CH₂Cl₂

(50 mg, 0.05 mol), and potassium phosphate (366 mg, 1.68 mmol)

were added under Ar atmosphere, and the mixture was stirred at 35 °C

for 2 days. The mixture was then filtered, and the filtrate was evaporated

under reduced pressure. The resulting brown semisolid was purified

by GPC (eight cycles, chloroform as eluent) and TLC (Et₂O-n-hexane

) 1:1) to give dipyridylalted diazomethane 2,7-DPy-1-N₂(16 mg, 4%)

To a solution of 4-tert-butyl-2,6-dimethylbromobenzene²⁹(0.80 g,

3.3 mmol) in anhydrous diethyl ether (30 mL) was added 1.5 M tert-

butyllithium in n-pentane (5.0 mL, 7.3 mmol) at -78 °C under nitrogen

atmosphere. The mixture was stirred for 1 h at -78 °C and allowed to

warm to room temperature. To this mixture, a solution of 3-bromo-

9,10-dihydro-9-oxoanthracene (0.91 g, 3.3 mmol) in anhydrous toluene

(50 mL) was added, and the mixture was refluxed overnight. The

mixture was allowed to cool to room temperature, and a saturated

ammonium chloride aqueous solution was added to it carefully. The

reaction mixture was extracted with diethyl ether, and the organic layer

was washed with water and dried over anhydrous sodium sulfate. A

brown solid obtained after concentration of the solution was chromato-

graphed on a silica gel column eluted with n-hexane. The eluted fraction

was distilled by a short-path distillation apparatus at 100 °C/760 Pa to

obtain 2-bromo-10-(4-tert-butyl-2,6-dimethylphenyl)anthracene as

1

as an orange solid. H NMR (CDCl₃): δ 1.44 (s, 9H), 1.47 (s, 9H),

1.64 (s, 6H), 1.84 (s, 6H), 7.20 (brs, 4H), 7.24 (s, 2H), 7.30 (s, 2H),

7.35-7.46 (m, 4H), 7.60-7.64 (m, 4H), 7.69 (d, J ) 8.3 Hz, 2H),

8.46 (brs, 4H), 8.75 (s, 2H). ¹³C NMR (CDCl₃): δ 20.1, 20.4, 31.5,

34.5, 34.6, 55.9, 121.3, 124.3, 124.5, 124.6, 124.7, 124.9, 125.2, 125.7,

126.8, 127.3, 127.6, 128.8, 130.3, 130.5, 130.7, 130.8, 133.7, 134.1,

135.8, 136.7, 136.9, 137.9, 139.1, 147.4, 150.2, 150.8, 151.0. IR (NaCl,

cm^-1) 2962s, 2924m, 2856w, 2037vs(ν_CdN2), 1594m, 1491w, 1477w,

1458w, 1449w, 1438w, 1407vw, 1379w, 1363w, 816vw, 752vw.

Preparation of Bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-

pyridyl)-9-anthryl]diazomethane (2,2′-DPy-1-N₂). To a Grignard

reagent prepared from 1,3-dibromobenzene (13 mL, 106 mmol),

magnesium (2.7 g, 106 mmol), and iodine (catalytic amount) in absolute

diethyl ether (50 mL) was added a solution of 2-formylbenzoic acid

(6.6 g, 44 mmol) in absolute tetrahydrofuran (50 mL) dropwise with

vigorous stirring. The mixture was refluxed overnight. After being

cooled to room temperature, 5% hydrochloric acid (66 mL) was added

the reaction mixture, and the mixture was washed with saturated sodium

hydrogen carbonate aqueous solution. To the aqueous solution was

added concentrated hydrochloric acid until it became acidic. The

precipitation formed was collected by filtration and recrystalized from

ethanol. 3-(4-Bromophenyl)phthalide was obtained as a yellow solid

1

a pale yellow solid in 35% yield (0.48 g); mp 185.3-187.0 °C. H

NMR (CDCl₃): δ 1.43 (s, 9H), 1.71 (s, 6H), 7.24 (s, 2H), 7.30-7.34

(m, H), 7.43-7.49 (m, 2H), 8.02 (d, J ) 8.5 Hz, 1H), 8.20 (s, 1H),

8.35 (s, 1H); ¹³C NMR (CDCl₃): δ 20.3, 31.5, 34.5, 119.5, 124.5, 125.1,

125.86, 125.91, 126.2, 128.0, 128.1, 128.5, 128.9, 130.0, 130.2, 132.2,

132.3, 133.8, 136.7, 136.9, 150.6; EIMS m/z (relative intensity): 418

(M + 2, 100), 416 (M⁺, 99.7); HRMS calcd for C₂₆H₂₅Br, 416.1139;

found m/z, 416.1147.

To a cooled and stirred solution of 2-bromo-10-(4-tert-butyl-2,6-

dimethylphenyl)anthracene (2.5 g, 5.9 mmol) in carbon tetrachloride

(25 mL), a carbon tetrachloride solution (15 mL) of bromine (0.45 mL,

8.9 mmol) was added dropwise at 0 °C, and the mixture was stirred at

room temperature overnight. To this mixture, an aqueous solution of

10% sodium hydroxide was added carefully. The reaction mixture was

extracted with carbon tetrachloride, and the organic layer was washed

with water and dried over anhydrous sodium sulfate. After removal of

the solvent, 2,9-dibromo-10-(4-tert-butyl-2,6-dimethylphenyl)an-

thracene was obtained as a yellow solid in 99% yield (3.0 g); mp

230.2-232.9 °C. ¹H NMR (CDCl₃): δ 1.43 (s, 9H), 1.71 (s, 6H), 7.24

(s, 2H), 7.33-7.45 (m, 3H), 7.48 (d, J ) 0.6, 1H), 7.61 (ddd, J ) 1.3,

6.4, 6.5 Hz, 1H), 8.57 (d, J ) 9.0 Hz, 1H), 8.60 (dd, J ) 8.8, 0.8 Hz,

1H); ¹³C NMR (CDCl₃): δ 20.3, 31.5, 34.5, 120.8, 122.0, 124.6, 126.2,

126.6, 127.7, 128.1, 128.4, 128.8, 129.4, 130.0, 130.7, 131.0, 131.3,

133.4, 136.8, 137.4, 150.0; EIMS m/z (relative intensity): 498 (M +

4, 51.2), 496 (M + 2, 100), 494 (M⁺, 51.6); HRMS calcd for C₂₆H₂₄-

Br₂, 494.0244; found m/z, 494.0243.

1

in 84% yield (10 g); mp 135.5-137.0 °C. H NMR (CDCl₃): δ 6.35

(s, 1H), 7.24 (t, J ) 2.0 Hz, 1H), 7.29 (s, 1H), 7.34 (d, J ) 7.4 Hz,

1H), 7.42 (s, 1H), 7.50 (td, J ) 1.9, 7.0 Hz, 1H), 7.57 (t, J ) 7.1 Hz,

1H), 7.67 (dt, J ) 1.3, 7.5 Hz, 1H), 7.97 (d, J ) 7.7 Hz, 1H). ¹³C

NMR (CDCl₃): δ 81.6, 122.7, 123.0, 125.4, 125.5, 125.9, 129.6, 129.9,

130.6, 132.4, 134.5, 138.7, 149.0, 170.1; MS m/z (relative intensity):

290 (M + 2, 34), 288 (M⁺, 34), 209 (58), 105(100); HRMS calcd for

C₁₄H₉O₂Br, 287.9785; found m/z, 287.9814.

A mixture of the phthalide (3.5 g, 12 mmol), iodine (2.1 g, 8.3

mmol), and red phosphorus (1.9 g, 62 mmol) in water (0.5 mL)

propionic acid (20 mL) was heated and stirred for 10 min at 100 °C.

Water (10 mL) was added to the cooled mixture, and the precipitate

formed was filtered. The precipitate was dissolved into chloroform,

and the mixture was filtered. The filtrate was dried over anhydrous

sodium sulfate. After removal of the solvent, 2-(3-bromobenzyl)-

benzoic acid was obtained as a pale orange solid (3.4 g, 99%); mp

120.1-121.9 °C. ¹H NMR (CDCl₃): δ 1.67 (s, 1H), 4.41 (s, 1H), 6.35

(s, 1H), 7.10 (d, J ) 3.1 Hz, 1H), 7.15 (t, J ) 7.2 Hz, 1H), 7.22 (d, J

) 7.5 Hz, 1H), 7.30 (s, 1H), 7.31 (s, 1H), 7.35 (t, J ) 7.4 Hz, 1H),

7.49 (t, J ) 7.5 Hz, 1H), 8.06 (d, J ) 7.9 Hz, 1H); ¹³C NMR (CDCl₃):

δ 39.3, 122.4, 126.7, 127.6, 128.26, 128.32, 129.1, 129.8, 131.8,

131.9, 133.2, 142.5, 143.1, 173.0; EIMS m/z (relative intensity):

292 (M + 2, 31), 290 (M⁺, 33), 193 (100); HRMS calcd for C₁₄H₁₁O₂-

Br, 290.0020; found m/z, 289.9942.

To a solution of the bromide (400 mg, 0.81 mmol) in anhydrous

diethyl ether (10 mL) was added 2.4 M n-butyllithium in n-hexane

(0.36 mL, 0.89 mmol) at 0 °C under nitrogen atmosphere, and the

mixture was stirred for 2 h at 0 °C. A solution of absolute methyl

formate (29 µL, 0.49 mmol) in absolute diethyl ether (1 mL) was added

to the lithiated mixture at 0 °C, and the mixture was refluxed overnight.

The mixture was allowed to cool to room temperature, and a saturated

ammonium chloride aqueous solution was added carefully. The reaction

mixture was extracted with diethyl ether, and the organic layer was

washed with water and dried over anhydrous sodium sulfate. After

evaporation of the solvent, the residue was purified by GPC (six cycles,

chloroform as eluent) to give bis[2-bromo-10-(4-tert-butyl-2,6-dim-

ethylphenyl)-9-anthryl]methanol (163 mg, 47%) as an yellow solid;

mp 174.5-176.9 °C. ¹H NMR (CDCl₃): δ 1.44 (s, 18H), 1.74 (s, 6H),

1.76 (s, 6H), 3.02 (d, J ) 2.9 Hz, 1H), 7.23 (s, 2H), 7.26-7.54 (m,

To a concentrated sulfuric acid (67 mL) was added 2-(3-bromo-

benzyl)benzoic acid little by little at 0 °C with vigorous stirring. After

being stirred for 45 min at 0 °C and for another 45 min at room

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7091

A R T I C L E S

Itoh et al.

8H), 8.52 (d, J ) 9.0 Hz, 4H), 8.86 (bs, 2H); ¹³C NMR (CDCl₃): δ

20.3, 20.4, 31.5, 34.5, 73.0, 120.8, 124.6, 124.9, 125.4, 126.8, 127.3,

127.6, 128.2, 128.4, 128.8, 129.9, 130.4, 130.5, 132.2, 134.2, 136.8,

136.9, 138.9, 150.7; MS (MALDI-TOF) calcd for C₅₃H₄₉Br₂O (M⁺),

861.2169; found m/z, 861.2131.

and the organic layer was washed with water and dried over anhydrous

sodium sulfate. After evaporation of the solvent, the residue was purified

by GPC (20 cycles, chloroform as eluent) to give diazomethane 2,2′-

DPy-1-N₂(8.9 mg, 32%) as a red solid. ¹H NMR (CDCl₃): δ 1.45 (s,

18H), 1.54 (s, 6H), 1.85 (s, 6H), 6.72 (bs, 4H), 7.23 (s, 2H), 7.29 (s,

2H), 7.47 (d, J ) 7.7 Hz, 2H), 7.34-7.49 (m, 8H), 8.27 (bs, 4H), 8.57

(s, 2H), 8.73 (d, J ) 8.6 Hz, 2H); ¹³C NMR (CDCl₃): δ 20.0, 20.5,

31.5, 34.5, 55.5, 120.8, 123.5, 124.7, 124.9, 125.0, 126.2, 126.4, 128.0,

128.1, 128.3, 130.0, 130.1, 131.1, 131.7, 133.8, 134.7, 136.7, 136.8,

138.5, 147.1, 149.9, 150.9; IR (NaCl, cm^-1): 3065vw, 2963s, 2919m,

2865m, 2220vw, 2040vs(ν_CdN2), 1595s, 1450w, 1406w, 1362m,

1302vw, 1227vw, 1194vw, 1098vw, 1071vw, 1040vw, 994m, 944vw,

907w, 870m, 837vw, 812w, 762m, 683vw.

EPR Measurements. The diazo compound was dissolved in

2-methyltetrahydrofuran (10^-3M), and the solution was degassed in a

quartz cell by three freeze-degas-thaw cycles. The sample was cooled

in an optical transmission EPR cavity at 77 K and irradiated with a

Wacom 500 W Xe lamp using a Pyrex filter. EPR spectra were

measured on a JEOL JES TE 200 spectrometer (X-band microwave

unit, 100 kHz field modulation). The signal positions were read by the

use of a gaussmeter. The temperature was controlled by a 9650

Microprocessor-based digital temperature indicator/controller and pro-

vided the measurement accuracy within (0.1 K and the control ability

within (0.2 K. Errors in the measurements of component amplitudes

did not exceed 5%, and the accuracy of the resonance fields determi-

nation was within (0.5 mT.

Low-Temperature UV-Vis Spectra. Low-temperature spectra at

77 K were obtained by using an Oxford variable-temperature liquid-

nitrogen cryostat (DN 1704) equipped with a quartz outer window and

a sapphire inner window. The sample was dissolved in dry 2-MTHF,

placed in a long-necked quartz cuvette of 1-mm path length, and

degassed thoroughly by repeated freeze-degas-thaw cycles at a

pressure near 10^-5Torr. The cuvette was flame-sealed under reduced

pressure, placed in the cryostat, and cooled to 77 K. The sample was

irradiated for several minutes in the spectrometer with a Halos 300-W

high-pressure mercury lamp using a Pyrex filter, and the spectral

changes were recorded at appropriate time intervals. The spectral

changes upon thawing were also monitored by carefully controlling

the matrix temperature with an Oxford Instrument intelligent temper-

ature controller (ITC 4).

Flash Photolysis. All flash measurements were made on a Unisoku

TSP-601 flash spectrometer. Three excitation light sources were used

depending on the precursor absorption bands and lifetime of the transient

species. They were (i) a cylindrical 150-W Xe flash lamp (100 J/flash

with 10-ms pulse duration), (ii) a Quanta-Ray GCR-11 Nd:YAG laser

(355-nm pulses of up to 40 mJ/pulse and 5-6-ns duration; 266-nm

pulses of up to 30 mJ/pulse and 4-5-ns duration), and (iii) Lamda

Physik LEXTRA XeCl excimer laser (308-nm pulses of up to 200 mJ/

pulse and 17-ns duration). The beam shape and size were controlled

by a focal length cylindrical lens.

Into a solution of the methanol (2.9 g, 3.3 mmol) in anhydrous

benzene (70 mL) cooled to 0 °C, a hydrogen chloride gas generated

by adding hydrochloric acid (4 mL) to sulfuric acid (6 mL) was bubbled

for 1 h, and the mixture was stirred for 1 h at 0 °C. Removal of the

solvent afforded bis[2-bromo-10-(4-tert-butyl-2,6-dimethylphenyl)-9-

anthryl]chloromethane (2.9 g, quantitatively) as a brown solid. This

was used without further purification since the chloride was found to

be rather unstable. A solution of the chloromethane (2.9 g, 3.3 mmol)

in anhydrous 1,4-dioxane (140 mL) was added to a molten mixture of

silver tetrafluoroborate (973 mg, 5.0 mmol) and urethane (5.9 g, 66

mmol) at 60 °C. After addition was completed, the mixture was refluxed

overnight. After being cooled, silver chloride was removed from the

reaction mixture by filtration and was washed with chloroform. The

filtrate was washed with water, and the organic layer was dried over

anhydrous sodium sulfate and evaporated. The crude product was

chromatographed on a silica gel column eluted with n-hexane/

dichloromethane (1:1), and the main fraction was further chromato-

graphed on a silica gel column eluted with ether. Ethyl bis[2-bromo-

10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl]methylcarbamate was

obtained as a yellow solid in 21% yield (660 mg); mp 185.6-186.1°C.

¹H NMR (CDCl₃): δ 1.31 (t, J ) 7.0 Hz, 3H), 1.43 (s, 18H), 1.70 (s,

6H), 1.73 (s, 6H), 4.27 (q, J ) 8.1 Hz, 2H), 5.94 (d, J ) 7.4 Hz, 1H),

7.19 (s, 4H), 7.29-7.36 (m, 6H), 7.52 (d, J ) 8.5 Hz, 2H), 8.58 (d, J

) 7.4 Hz, 1H), 8.70 (bs, 2H); ¹³C NMR (CDCl₃): δ 14.7, 20.30, 20.34,

31.5, 34.5, 54.6, 61.6, 120.9, 124.0, 124.4, 124.5, 125.3, 126.7, 127.2,

127.5, 128.1, 128.2, 129.0, 130.1, 130.5, 130.6, 132.0, 136.8, 136.9,

138.7, 150.7, 155.4; MS (MALDI-TOF) calcd for C₅₆H₅₃Br₂NO₂(M⁺),

933.4075; found m/e, 933.2582.

To a solution of ethyl bis[2-bromo-10-(4-tert-butyl-2,6-dimethyl-

phenyl)-9-anthryl] methylcarbamate (100 mg, 0.11 mmol) in anhydrous

dioxane (2 mL), 2-(4-pyridyl)-4,4,5,5-tetramethyl-1,3-dioxaborolane (86

mg, 0.42 mmol), [1,1′-bis(diphenylphosphino)ferrocene]palladium dichlo-

ride dichloromethane complex: PdCl₂(dppf)₂‚CH₂Cl₂(13 mg, 0.016

mol), and potassium phosphate (39 mg, 0.18 mmol) were added under

Ar atmosphere, and the mixture was refluxed for 2 days. The mixture

was then filtered, and filtrate was evaporated under reduced pressure.

The resulting brown solid was purified by TLC (Et₂O only) to give

ethyl bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-9-anthryl]-

methylcarbamate (24 mg, 25%) as an yellow solid. ¹H NMR

(CDCl₃): δ 1.25-1.28 (m, 3H), 1.43 (s, 18H), 1.80 (s, 12H), 4.30 (bs,

2H), 6.41 (d, J ) 7.2 Hz, 1H), 6.58 (d, J ) 9.2 Hz, 4H), 7.19 (s, 4H),

7.37-7.68 (m, 10H), 8.23 (bs, 4H), 8.76 (d, J ) 8.1 Hz, 4H), 8.88 (d,

J ) 6.8 Hz, 1H), 9.00 (s, 2H), 9.57 (d, J ) 9.9 Hz, 4H); ¹³C NMR

(CDCl₃): δ 14.7, 20.0, 20.4, 31.5, 34.5, 55.0, 61.6, 120.7, 123.5, 124.0,

124.5, 124.6, 125.3, 126.0, 127.5, 127.8, 128.4, 128.6, 129.6, 130.3,

130.7, 130.9, 133.9, 136.7, 136.9, 138.7, 147.2, 149.8, 150.7, 155.5;

MS (MALDI-TOF) calcd for C₅₆H₅₃Br₂NO₂(M⁺), 930.6066; found

m/z, 930.4993.

A Hamamatsu 150 W xenon short arc lamp (L 2195) was used as

the probe source, and the monitoring beam, guided using an optical

fiber scope, was arranged in an orientation perpendicular to the

excitation source. The probe beam was monitored with a Hamamatsu

R2949 photomultiplier tube through a Hamamatsu S3701-512Q MOS

linear image sensor (512 photodiodes used). Timing of the excitation

pulse, the probe beam, and the detection system was achieved through

an Iwatsu model DS-8631 digital synchro scope that was interfaced to

an NEC 9801 RX2 computer. This allowed for rapid processing and

storage of the data and provided printed graphic capabilities. Each trace

was also displayed on a NEC CRT N5913U monitor.

A sample was placed in a long-necked Pyrex tube that had a sidearm

connected to a quartz fluorescence cuvette and degassed using a

minimum of four freeze-degas-thaw cycles at a pressure near 10^-5

Torr immediately before being flashed. The sample system was flame-

sealed under reduced pressure, and the solution was transferred to the

A dinitrogen tetraoxide (30 mg, 0.32 mmol) was bubbled into

anhydrous carbon tetrachloride (5 mL) at -20 °C. To this solution,

sodium acetate (53 mg, 0.65 mmol) and a solution of the carbamate

(30 mg, 0.032 mmol) in anhydrous carbon tetrachloride (0.5 mL) were

added at -20 °C, and the mixture was stirred for 2 h at 0 °C. The

reaction mixture was poured into crushed ice and extracted with carbon

tetrachloride. The organic layer was washed with aqueous sodium

hydrogen carbonate and water and dried over anhydrous sodium sulfate.

After evaporation of the solvent, a residual solid was dissolved in

anhydrous tetrahydrofuran (5 mL) under nitrogen atmosphere and

cooled to -20 °C. Potassium t-butoxide (145 mg, 0.13 mmol) was

added to the mixture, and the mixture was stirred overnight at room

temperature. The reaction mixture was extracted with diethyl ether,

9

7092 J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005

Preparation of Copper Ion Complexes

A R T I C L E S

quartz cuvette that was placed in the sample chamber of the flash

spectrometer. A cell holder block of the sample chamber was equipped

with a thermostat and allowed to come to thermal equilibrium. The

concentration of the sample was adjusted so that it absorbed a significant

portion of the excitation light. For experiments in which the rate constant

for the reaction of oxygen with carbenes was determined, varying

concentrations of oxygen in nitrogen were bubbled through the solution.

MS analysis of the spent solution indicated the presence of the

corresponding ketones; 2,2′-DPy-1-O: MS(MALDI-TOF) calcd for

C₆₃H₅₇N₂O (M⁺+ H), 857.45; found m/z, 857.57. 2,7-DPy-1-O: MS-

(MALDI-TOF) calcd for C₆₃H₅₇N₂O (M⁺+ 2H), 858.45; found m/z,

858.51.

SQUID Measurements. Magnetic susceptibility data were obtained

on a Quantum Design MPMS-2A SQUID magnetometer/susceptometer.

Irradiation with light from an argon ion laser (488 nm, Omnichrome

543-150BS) or He/Cd laser (442 nm, Melles Griot 2074-M A03)

through a flexible optical fiber that passes through the inside of the

SQUID sample holder was performed inside the sample room of SQUID

apparatus at 5-11 K. One end of the optical fiber was located 40 mm

above the sample cell (capsule), and the other was attached to a coupler

for the laser. The bottom part of the capsule (6 mm × 10 mm) without

a cap was used as a sample cell. A quantity of 50 µL of the sample

solution (1.0 mM) in 2-MTHF was placed in the cell that was held by

a straw. The irradiation was carried out until there was no further change

of magnetization monitored at 5 K in a constant field of 5 kOe. The

magnetization, Mb and Ma, before and after irradiation was measured

at 2 K and 5 K in a field range 0-50 kOe. The plots of the

magnetization [M ) (Ma - Mb): F stands for a photolysis factor of

diazo compound] versus the magnetic field were analyzed in terms of

Brillouin function.

Acknowledgment. We are grateful to the Ministry of Educa-

tion, Culture, Sports, Science and Technology of Japan for

support of this work through a Grant-in-Aid for Scientific

Research for Specially Promoted Research (No. 12002007).

Supporting Information Available: ESR and UV-vis spectra

obtained by irradiation of 2,2′-DPy-1-N₂in 2-methyltetra-

hydrofuran at 77 K, absorption of transient products formed

during irradiation of diazo compound 2,2′-DPy-1-N₂in de-

gassed and nondegassed benzene at room temperature, and UV-

vis spectra obtained by irradiation of 1:1 mixture (1.5 × 10^-4

Μ) of 2,2′-DPy-1-N₂and Cu(hfac)₂, LFP of DPy-1-N₂in

2-methyltetrahydrofuran at 77 K. See Figures S1-S6. This

material is available free of charge via the Internet at

http://pubs.acs.org.

JA0424225

9

J. AM. CHEM. SOC. VOL. 127, NO. 19, 2005 7093

Article Doi

Preparation of copper ion complexes of sterically congested diaryldiazomethanes having a pyridine ligand and characterization of their photoproducts

DOI: 10.1021/ja0424225

Source and publish data:

Authors:

Article abstract of DOI:10.1021/ja0424225

Full text of DOI:10.1021/ja0424225

Products guided by the article

R&D Labs maybe for 853732-41-9

Relevant to this article

Hot Product