Regioselective C-H or N-H bond cleavage reactions of heterocyclic compounds by [Ru(1,5-COD)(1,3,5-COT)]/monodentate phosphine

Inorganica Chimica Acta 352 (2003) 160Á170

/

www.elsevier.com/locate/ica

Regioselective Cꢀ

/

H or Nꢀ

/

H bond cleavage reactions of heterocyclic

compounds by [Ru(1,5-COD)(1,3,5-COT)]/monodentate phosphine

Masafumi Hirano, Koji Onuki, Yuichi Kimura, Sanshiro Komiya *

Faculty of Technology, Department of Applied Chemistry, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei,

Tokyo 184-8588, Japan

Received 28 August 2002; accepted 30 October 2002

This paper is dedicated to Prof. Martin A. Bennett on the occasion of his retirement from ANU with his outstanding contribution in organometallic

chemistry

Abstract

Reactions of [Ru(1,5-COD)(1,3,5-COT)] (1) (CODꢀ

phenes, benzo[b]furan, and furans in the presence of PEt₃result in the regioselective Cꢀ

compounds giving [Ru(1-5-h⁵-C₈H₁₁)(R)(PEt₃)₂] [Rꢀ

2-benzo[b]thienyl (4a), 2-thienyl (4b), 5-(2-ethoxylcarbonyl)thienyl (4c), 5-(2-

acetyl)thienyl (4d), 5-(3-acetyl)thienyl (4e), 2-benzo[b]furyl (5a), 2-furyl (5b), 5-(2-acetyl)furyl (5c)]. Similar treatments of 1 with

indoline and pyrrole lead to cleavage of the Nꢀ 1-indolyl (6a), 1-pyrrolyl (6b)].

H bond giving [Ru(1-5-h⁵-C₈H₁₁)(R)(PEt₃)₂] [Rꢀ

/

cyclooctadiene, COTꢀ/cyclooctatriene) with benzo[b]thiophene, thio-

/H bond cleavage of these heterocyclic

/

The time-course study for the reaction of 1/PEt₃with benzo[b]thiophene monitored by use of NMR suggests prior formation of a

zero-valent complex [Ru(1-4-h⁴-1,3,5-COT)(PEt₃)₃] (2a) followed by production of 4a. Kinetic study reveals that the rate of the

reaction of 2a with benzo[b]thiophene is the first-order dependence on [2a], [benzo[b]thiophene], and [PEt₃]^ꢁ1, respectively. This

fact suggests prerequisite dissociation of PEt₃from a coordinatively saturated complex 2a giving a vacant site for interaction of Ru

center with benzo[b]thiophene.

Keywords: [Ru(1,5-COD)(1,3,5-COT)]; Monodentate phosphine; Cꢀ

/

H bond cleavage; Benzo[b]thiophene; Heterocyclic compounds

1. Introduction

regarded as a prerequisite step for the succeeding bond

cleavage reaction. Poilblanc and coworkers [6] have

shown formation of [Ru(1,5-COD)(k²-DPPM)(k¹-

[Ru(1,5-COD)(1,3,5-COT)] (1) is widely employed as

a versatile zero-valent precursor in a variety of stoichio-

metric and catalytic transformations [1]. Of particular

DPPM)]

(DPPMꢀ1,2-bis(diphenylphosphi-

/

no)methane) by the reaction of 1 with DPPM by release

of 1,3,5-COT ligand. We have also reported formation

interest is Cꢀ

/

H [2], Cꢀ

/

O [2c,2e,3], Cꢀ

/

S [3d,4], or Cꢀ

/

X

of

analogous

complexes

[Ru(1,5-COD)(k²-

[5] bond cleaving reactions by 1 in the presence of

tertiary phosphines, since they are frequently involved in

the first step of various catalysis, in which prior

coordination of tertiary phosphine ligand to 1 is

diphosphine)(k¹-diphosphine)] by the reactions of 1

with bidentate DMPE (1,2-bis(dimethylphosphi-

no)ethane), DEPE (1,2-bis(diethylphosphino)ethane),

and DPPE (1,2-bis(diphenylphosphino)ethane) ligands

[7]. Reactions of 1 with other ligands such as CO and

arenes/H₂are also known to give Ru(COD)L₃and

Ru(COD)(arene) [8]. From these results, preferential

displacement of COT ligand in 1 had been always

assumed in various reactions of 1. In spite of these

facts, we recently found that the 1,5-COD ligand is

actually displaced by various monodentate phosphine

(L) such as PMe₃, PMe₂Ph, PEt₃, PEt₂Ph, and PBu₃to

Abbreviations: COD, cyclooctadiene (C₈H₁₂); COT, cyclooctatriene

(C₈H₁₀); DPPM, 1,2-bis(diphenylphosphino)methane (Ph₂PCH₂PPh₂);

DMPE, 1,2-bis(dimethylphosphino)ethane (Me₂PC₂H₄PMe₂); DEPE,

1,2-bis(diethylphosphino)ethane

bis(diphenylphosphino)ethane (Ph₂PC₂H₄PPh₂).

* Corresponding author. Tel./fax: ꢂ81-42-387 7500.

E-mail addresses: hrc@cc.tuat.ac.jp (M.

komiya@cc.tuat.ac.jp (S. Komiya).

(Et₂PC₂H₄PEt₂);

DPPE,

1,2-

/

Hirano),

doi:10.1016/S0020-1693(03)00132-4

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á

/

170

161

give complexes formulated as Ru(COT)L₃with selective

liberation of 1,5-COD. Coordination mode of COT

moiety varies depending on the steric bulkiness of the

phosphine ligand [8,9]. Namely, monodentate phos-

phine ligands such as PEt₃, PBu₃and PEt₂Ph gave

zero-valent complexes formulated as [Ru(1-4-h⁴-1,3,5-

COT)L₃] (2), whereas PMe₃and PMe₂Ph favor ruthe-

nium(II) complexes formulated as [Ru(6-h¹:1-3-h³-

hydride migration process are previously demonstrated

in the reaction of 1 with acid by Vitulli and coworkers

[10], Tkatchenko and coworkers [11] and our group [2e].

However, direct protonation of 1,3,5-COT ligand by the

benzo[b]thiophene is also a possible mechanism.

Recrystallization from hexane gave analytically pure

yellow crystals of 4a and the molecular structure was

unambiguously determined by the X-ray structure

analysis. Two independent molecules were found in

the unit cell and have essentially the same structure.

Thus, the following discussion will refer to one of them

(molecule A). The molecular structure of molecule A is

depicted in Fig. 1 and selected bond lengths and angles

are listed in Table 1.

The overall structure of 4a is best regarded as a three-

legged chair form with one 2-benzo[b]thienyl and two

PEt₃ligands. The benzo[b]thienyl group is bound to Ru

center at 2-position. Five carbon atoms in C₈H₁₁moiety

are bonded to Ru, indicating the h⁵-cyclooctadienyl

coordination. The bond length between ruthenium and

COT)L₃] (3). Interestingly, Cꢀ

/

O bond oxidative addi-

tion of vinyl acetate smoothly takes place to the zero-

valent complex 2, but not to the divalent complex 3,

suggesting different reactivity of the COT complexes due

to the metal valency [3c]. In this paper, we describe the

Cꢀ

/

H bond activation of thiophenes and furans as well

H bond activation of pyrroles.

as for Nꢀ

/

2. Results and discussion

2.1. Reaction of [Ru(1,5-COD)(1,3,5-COT)] (1) with

heterocyclic compounds in the presence of tertiary

phosphines

one of the outer coordinated cyclooctadienyl carbon

˚

atoms Ru(1)ꢀ

/

C(13) [2.313(6) A] is significantly longer

˚

than other Ru(1)ꢀ

the bond lengths between ruthenium and inner cyclooc-

tadienyl carbon atoms C(10)ꢀC(12) [2.175(5)Á2.223(5)

/

C(9) [2.247(6) A]. The latter is close to

Reaction of 1 with benzo[b]thiophene in hexane in the

presence of PEt₃at room temperature leads to cleavage

/

˚

A]. Since bond lengths between ruthenium and coordi-

nated carbon atoms at outer position of the cycloocta-

dienyl moiety are generally the same to each other (cf.

of the Cꢀ

/

H bond at 2-position of benzo[b]thiophene

[Ru(1-5-h⁵-C₈H₁₁)(2-benzo[b]thienyl)(PEt₃)₂]

giving

(4a) accompanied by liberation of 1,5-COD (Scheme

1). The reaction may proceed via oxidative addition of

5

ꢂ

˚

2.31(1) and 2.29(1) A for [Ru(1-5-h -C₈H₁₁)(PMe₃)₃]

5

ꢂ

˚

[2e], 2.263(5) and 2.283(4) A for [RuH(1-5-h -C₈H₁₁)₂]

the Cꢀ

/

H bond followed by insertion of the Cꢁ

/

C double

H bond. Such a rapid

for [Ru(h⁵-

˚

A

bond of the COT ligand into Ruꢀ

/

[12], 2.283(8) and 2.297(7)

Scheme 1.

162

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á170

/

Table 1

Selected bond lengths and angles for [Ru(1-5-h⁵-COT)(2-benzo[b]thie-

nyl)(PEt₃)₂] (4a)

Molecule A

Bond lengths (A)

˚

Ru(1)ꢀ

S(1)ꢀ

C(1)ꢀ

C(3)ꢀ

C(4)ꢀ

C(7)ꢀ

C(10)ꢀ

C(12)ꢀ

/

P(1)

2.380(2)

2.140(6)

2.175(5)

2.175(6)

1.763(6)

1.405(8)

1.410(8)

1.382(8)

1.402(8)

1.398(9)

1.414(8)

Ru(1)ꢀ

S(1)ꢀ

C(2)ꢀ

C(3)ꢀ

C(6)ꢀ

C(9)ꢀ

C(11)ꢀ

/

P(2)

2.355(2)

2.247(6)

2.223(5)

2.313(6)

1.763(6)

1.462(7)

1.387(7)

1.374(9)

1.415(8)

1.438(8)

/C(1)

/C(9)

/C(10)

/C(11)

/C(12)

/C(13)

/

C(1)

/

C(8)

/

C(2)

C(4)

C(5)

C(8)

/

C(3)

C(8)

C(7)

C(10)

/

/C(11)

/C(12)

/C(13)

Bond angles (8)

P(1)ꢀ

C(1)ꢀ

/

Ru(1)ꢀ

/

P(2)

99.48(6) P(1)ꢀ

169.8(1)

169.6(2)

/

Ru(1)ꢀ

/

C(1)

90.8(2)

93.5(1)

/

C(9)

P(2)ꢀ

/

Ru(1)ꢀ

/

C(13)

Molecule B

Bond lengths (A)

˚

Fig. 1. Molecular structure of [Ru(1-5-h⁵-C₈H₁₁)(2-benzo[b]thie-

nyl)(PEt₃)₂] (4a). All hydrogen atoms are omitted for clarity. Ellipsoids

represent 50% probability.

Ru(2)ꢀ

S(2)ꢀ

C(29)ꢀ

C(31)ꢀ

C(32)ꢀ

C(34)ꢀ

C(37)ꢀ

C(39)ꢀ

/

P(3)

2.381(2)

2.119(5)

2.188(6)

2.189(6)

1.771(5)

1.421(7)

1.392(8)

1.385(9)

1.375 (9)

1.423(8)

1.439(8)

Ru(2)ꢀ

S(2)ꢀ

C(30)ꢀ

C(31)ꢀ

C(33)ꢀ

C(35)ꢀ

C(38)ꢀ

/

P(4)

2.347(2)

2.244(5)

2.232(5)

2.305(5)

1.743(6)

1.437(7)

1.393(8)

1.39(1)

/

C(29)

C(38)

C(40)

/

C(37)

C(39)

C(41)

/

C(29)

/

C(36)

/

C(30)

C(32)

C(33)

C(35)

C(38)

C(40)

/

C(31)

C(36)

C(34)

C(36)

C(39)

/

1.396(8)

/

Bond angles (8)

P(3)ꢀ

C(29)ꢀ

/

Ru(2)ꢀ

/

P(4)

C(37)

95.58(5) P(3)ꢀ

/

Ru(2)ꢀ

/

C(29)

87.6(1)

92.6(2)

/

Ru(2)ꢀ

/

165.4(1)

169.7(2)

P(4)ꢀ

/

Ru(2)ꢀ

/

Ru(2)ꢀC(41)

/

NMR spectrum of 4a shows two doublets at dꢀ

(Jꢀ24 Hz) and 20.9 ppm (Jꢀ24 Hz) for two inequi-

valent phosphorus atoms. The H NMR signals of 4a

were assigned by ¹Hꢀ¹H COSY as well as by comparing

the spectra of related h⁵-cyclooctadienyl complexes such

/9.5

/

1

/

as

[Ru(1-5-h⁵-C₈H₁₁)₂]

[14],

[Ru(1-5-h⁵-C₈H₁₁)

(PMe₃)₃]^ꢂ[2e], and [Ru(1-5-h⁵-C₈H₁₁)(PMe₂Ph)₃]^ꢂ

1

[13]. The Hꢀ

/

¹H COSY of 4a in benzene-d₆revealed

spin-correlated 11 protons suggesting the presence of a

Fig. 2. Molecular structure of [Ru(1-5-h⁵-C₈H₁₁)(1-pyrrolyl)(PEt₃)₂]

(6b). All hydrogen atoms are omitted for clarity. Ellipsoids represent

50% probability.

h⁵-cyclooctadienyl moiety. A characteristic triplet at

dꢀ

H(3) and a triplet at dꢀ

doublets at dꢀ4.15 ppm are assigned as the neighbor-

ing protons H(2) and H(4), respectively. Broad multi-

plets at dꢀ3.16 and 2.97 ppm are due to H(1) and H(5),

respectively. The methyl groups in PEt₃appear as two

double triplets at dꢀ0.73 (9H) and 1.09 ppm (9H)

showing that two PEt₃ligands are magnetically inequi-

valent. Slightly broad four sextets at dꢀ1.4, 1.5, 1.9,

/

5.95 ppm is assignable to the central dienyl proton

/

4.34 ppm and a doublet of

C₈H₁₁)(PMe₂Ph)₃]^ꢂ[13]), the present unsymmetrical

coordination of the h⁵-cyclooctadienyl moiety in 4a

may be caused by the trans influence of the C1 carbon of

/

the 2-benzo[b]thienyl moiety. Bond lengths of Ru(1)ꢀ

/

˚

C(1) and C(1)ꢀ

respectively, the latter value suggesting the Cꢁ

bond character.

/

C(2) are 2.140(6) and 1.405(8) A,

/

C double

/

The structure in solution was also consistent with that

in solid-state structure as described below. The ³¹P{¹H}

and 2.2 ppm are assignable to the methylene groups of

PEt₃coupled to three methyl protons, a phosphorus

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á

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163

atom and a neighboring geminal methylene proton

whose coupling constants are accidentally similar. Ob-

servation of the diasterotopic methylene resonances is

consistent with the three-legged chair structure shown in

the solid-state molecular structure. The signal of the

olefinic proton in the 2-benzo[b]thienyl group is acci-

dentally overlapped with solvent impurity C₆D₅H in

benzene-d₆. However, the NMR spectrum of 4a mea-

sured in dichloromethane-d₂unambiguously gave dis-

tinct signals of the aromatic and olefinic protons: two

2.2. Effect of phosphine employed

As shown above, combination of 1 and PEt₃(uꢀ

1328) [15] was found to be effective for CꢀH or Nꢀ

bond cleavage of heterocyclic compounds. For compre-

hensive understanding of effect of monodentate phos-

phines on the bond cleavage processes, reactions of 1

with benzo[b]thiophene in the presence of various

/

H

phosphines such as PMe₃(uꢀ

1228), PBu₃(uꢀ1328), PEt₂Ph (uꢀ

1458), PⁱPr₃(uꢀ

1608), and PCy₃(uꢀ

out (Scheme 2).

/

1188), PMe₂Ph (uꢀ

1368), PPh₃(uꢀ

1708) were carried

/

doublets at dꢀ

dꢀ7.05 and 6.87 ppm are due to the protons in the

benzo ring, and a singlet at dꢀ6.87 ppm overlapped

/7.55 and 7.40 ppm and two triplets at

/

It was found that reactions of PBu₃and PEt₂Ph also

yielded [Ru(1-5-h⁵-C₈H₁₁)(2-benzo[b]thienyl)L₂] (4),

but combination of 1 with PMe₃and PMe₂Ph did not

cause bond cleavage reaction giving 3. On the other

hand, combination of 1 with PPh₃, PⁱPr₃, and PCy₃

showed no reactivity with benzo[b]thiophene. This trend

in reactivity is very similar to that observed in the

reactions of 1 with tertiary phosphines, where PEt₃and

PEt₂Ph favor the formation of zero-valent complex

[Ru(1-4-h⁴-1,3,5-COT)L₃] (2) [9], but PMe₃and

PMe₂Ph favor di-valent complex [Ru(6-h¹:1-3-h³-

/

with a triplet due to the aromatic proton is assigned to

the alkenyl proton. All these observations are consistent

with the structure of 4a as shown in Scheme 1.

Treatments of 1/PEt₃with thiophene, 2-ethoxycarbo-

nylthiophene, 2-acetylthiophene, and 3-acetylthiophene

also gave similar complexes with a h⁵-cyclooctadienyl

fragment, formulated as [Ru(h⁵-C₈H₁₁)(R)(PEt₃)₂] [Rꢀ

/

2-thienyl (4b), 5-(2-ethoxycarbonyl)thienyl (4c), 5-(2-

acetyl)thienyl (4d), 5-(3-acetyl)thienyl (4e)]. On the other

hand, dibenzothiophene did not react with 1/PEt₃at all.

These results suggest that this system favors the cleavage

of acidic protons (2- and 5-positions) of thiophenes. It is

C₈H₁₀)L₃] (3) [7]. Consistently, isolated 2a (LꢀPEt₃)

/

readily reacted with benzo[b]thiophene, thiophenes,

benzo[b]furan, furans, and pyrroles at room tempera-

ture to give products (Scheme 3).

notable that the Cꢀ

/

H bond cleavage exclusively takes

place at 5-position and never occurs at 2-position for 3-

acetylthiophene. We have shown that the coefficient of

LUMO at C²carbon of 3-acetylthiophenes is larger than

However, 3a did not react with these heterocycles at

all under these conditions. Higher reactivity of 2 than 3a

suggests the importance of the lower metal valency and/

or tendency to produce coordinatively unsaturated

reactive species for these bond cleavage reactions.

that at 5-position, indicating that the Cꢀ

/

H bond at C²

carbon is more susceptible to the electrophilic attack

than C⁵carbon [4c]. Therefore, the present regioselec-

tivity is not determined by the electronic factor but the

effective steric repulsion between Ru fragment and

substituent in thiophene.

2.3. Kinetic studies of [Ru(1,5-COD)(1,3,5-COT)] (1)

with benzo[b]thiophene in the presence of PEt₃

As shown above, 2a is considered as an intermediate

for the regioselective bond cleavage reactions of hetero-

cyclic compounds by 1/PEt₃system. Thus, time-courses

of the reaction of 1/PEt₃with benzo[b]thiophene were

monitored by NMR (Fig. 3).

Immediately after addition of PEt₃to a benzene-d₆

solution of 1, formation of a mono(phosphine) complex

[Ru(h⁴-1,5-COD)(h⁴-1,3,5-COT)(PEt₃)] (7) was ob-

served. Then, the amount of 7 gradually decreased and

instead the tris(phosphine)ruthenium(0) complex 2a

appeared. Complex 2a also slowly disappeared and

eventually 2-benzo[b]thienyl complex 4a was formed

with decrease of 2a, indicating that the reaction is

considered to undergo in a stepwise manner as shown

in Scheme 4.

The system, 1/PEt₃, also reacted with benzo[b]furan,

furan, and 2-acetylfuran giving corresponding com-

plexes of [Ru(h⁵-C₈H₁₁)(R)(PEt₃)₂] [Rꢀ

/

2-benzo[b]furyl

(5a), 2-furyl (5b), 5-(2-acetyl)furyl (5c)] in 71Á100%

yields. On the other hand, treatments with indole and

pyrrole resulted in the NꢀH bond cleavage to give

corresponding imido complexes

[Ru(h⁵-

C₈H₁₁)(R)(PEt₃)₂] [Pꢀ1-indolyl (6a) and 1-pyrrolyl

/

(6b)]. The molecular structure of 6b determined by

single-crystal X-ray diffraction unambiguously shows

that the pyrrolyl fragment is bound to Ru via N atom

(Scheme 2 and Table 2).

Whereas the 2-benzo[b]thienyl complex 4a has un-

symmetrical bonding between Ru and the carbon atoms

of the cyclooctadienyl moiety, bond lengths Ru(1)ꢀ

[2.247(8) A] and Ru(1)ꢀ

similar, reflecting weak trans influence of the N atom

and/or less steric hindrance of the pyrrolyl fragment

than 2-benzo[b]thiophenyl fragments.

/

C(4)

C(8) [2.219(6) A] in 6b are

As shown in Fig. 4, the reaction starting from 2a was

indeed faster than the reaction of 1/PEt₃system

eliminating the induction period.

In order to obtain further insight of the mechanism,

kinetic study using isolated 2a was performed, eliminat-

˚

/

164

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á

/

170

Scheme 2.

Table 2

Selected bond distances and angles for [Ru(1-5-h⁵-COT)(1-pyrro-

lyl)(PEt₃)₂] (6b)

˚

Bond lengths (A)

Ru(1)ꢀ

/

P(1)

C(1)

C(3)

C(8)

2.398(2)

2.166(6)

2.153(5)

2.219(6)

1.39(1)

Ru(1)ꢀ

/

P(2)

C(2)

C(4)

N(1)

2.339(2)

2.225(6)

2.247(8)

2.153(6)

1.427(9)

1.51(1)

/

C(1)ꢀ

C(3)ꢀ

C(5)ꢀ

C(1)ꢀ

N(1)ꢀ

C(22)ꢀ

Bond angles (8)

/

C(2)

C(4)

C(6)

C(8)

C(2)ꢀ

C(4)ꢀ

C(6)ꢀ

N(1)ꢀ

C(21)ꢀ

C(23)ꢀ

/

C(3)

C(5)

C(7)

/

1.42(1)

/

1.50(1)

/

1.514(9)

1.347(9)

1.397(9)

1.374(9)

/

1.426(9)

1.369(7)

1.39(1)

/C(21)

/

C(24)

C(23)

/

C(22)

C(24)

Fig. 3. Time-course curves for the reaction of 1/PEt₃with ben-

zo[b]thiophene. Gray, closed and open circles indicate 7, 2a and 4a,

respectively. Conditions: complex 1 (0.108 M), benzo[b]thiophene

(0.108 M), PEt₃(0.201 mmol), benzene-d₆(500 ml), temperature, 30 8C.

/

P(1)ꢀ

P(2)ꢀ

/

Ru(1)ꢀ

/

P(2)

C(8)

C(2)

93.11(5)

163.8(2)

155.1(2)

P(1)ꢀ

P(2)ꢀ

N(1)ꢀ

/

Ru(1)ꢀ

/

N(1)

85.1(2)

96.3(1)

169.3(2)

/

/N(1)

/

/C(4)

(0.0713, 0.140, 0.207 M), at 30 8C in benzene-d₆. A plot

of the initial rates versus the initial concentrations of 2a

as shown in Fig. 5 shows the linear relationship

indicating that this reaction is first-order in 2a.

ing the complexity of the reaction pathways. Initial rates

of the reactions were estimated in the presence of excess

amount of benzo[b]thiophene (4.13Á4.16 M) per 2a

/

Scheme 3.

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á

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170

165

Fig. 6. Effect of concentration of benzo[b]thiophene on the initial rate

of formation of 4a. Conditions: [2a] (0.106Á0.108 M), [benzo[b]thio-

Scheme 4.

/

phene] (0.107, 0.212, 0.424, 1.08 M), benzene-d₆(500 ml), temperature,

30 8C.

Fig. 4. Time-course curves for the reaction of benzo[b]thiophene

started from 1/PEt₃(open circles) or 2a (closed circles). Conditions: [1]

(0.108 M), [PEt₃] (0.217 M), [2a] (0.108 M), [benzo[b]thiophene] (0.108

M), benzene-d₆(500 ml), temperature, 30 8C.

Fig. 7. Effect of concentration of PEt₃on the reciprocal initial rate of

formation of 4a. Conditions: [2a] (0.0882Á

/

0.0898 M), [benzo[b]thio-

phene] (0.0857Á0.0918 M), [PEt₃] (0, 0.0903, 0.452 M), benzene-d₆(500

/

ml), temperature, 30 8C.

2.4. Reaction mechanism

By taking account of these kinetic data, a mechanism

of the Cꢀ/H bond cleavage of benzo[b]thiophene by 1/

PEt₃has been proposed. At first, 2a is formed as an

intermediate, and the succeeding three steps are fol-

lowed (Scheme 5).

Since the starting complex 2a is coordinatively

saturated and the kinetic data suggests liberation of

PEt₃from 2a, it is reasonable to assume formation of

coordinatively unsaturated species A to make a coordi-

nation site available for the incoming benzo[b]thiophene

molecule (Step 1 in Scheme 5). Then, benzo[b]thiophene

Fig. 5. Effect of concentration of 2a on the initial rate of formation of

4a. Conditions: [2a] (0.071, 0.142, 0.207 M), [benzo[b]thiophene]

(1.65Á1.66 M), benzene-d₆(500 ml), temperature, 30 8C.

/

coordinates to Ru through either via h²-CꢁC or h¹-S

/

mode (Step 2) to give B or C, though neither such

intermediate B nor C was observable during the reac-

tion. It is worth noting that Jones and Sargent [16]

The linear dependence of the initial rate on [ben-

zo[b]thiophene] was also observed as shown in Fig. 6

indicating the first-order dependence of the rate on

[benzo[b]thiophene].

Formation of 4a was significantly retarded by the

addition of PEt₃. Fig. 7 shows the relationship between

the reciprocal of the initial rate and [PEt₃]. The observed

straight line suggests involvement of the prior dissocia-

tion of PEt₃from 2a.

experimentally and theoretically showed that Cꢀ

cleavage of thiophene by Rh(I) complex takes place via

h²-Cꢁ

C intermediate, whereas the CꢀS bond cleavage is

the result of prior h¹-S coordination. Since present

H bond cleavage products of

/H bond

/

system exclusively gives Cꢀ

/

benzo[b]thiophene via the Ru(0) intermediate, which is

isoelectronic to the Rh(I) species, this process probably

166

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á170

/

3. Concluding remarks

In summary, combination of 1 and monodentate

phosphines such as PEt₃, PBu₃, and PEt₂Ph was found

to be effective for the Cꢀ

/

H bond cleavage of thiophenes

and furans and for the Nꢀ

/H bond cleavage of pyrroles.

The time-course study suggests prior formation of a

zero-valent (triethylphosphine)ruthenium(0) complex 2,

which exclusively and regioselectively cleaves Cꢀ

/

H bond

of thiophenes and furans at the less hindered 5- or 2-

position. Further kinetic investigation reveals the initial

formation of coordinatively unsaturated complex by

dissociation of PEt₃from 2a, followed by h²-Cꢁ

/

C

coordination of benzo[b]thiophene leading to selective

CꢀH bond cleavage. The present exclusive CꢀH bond

/

cleavage of substituted thiophenes by 2a (or 1/PEt₃)

shows sharp contrast to the reactions of substituted

thiophenes by 1/DEPE, which exclusively cleaved the

Cꢀ

/

S bond of substituted thiophenes giving a thiaruthe-

nacycle

complex CRꢁCHꢁCH-kC1,S)

[Ru(SCHꢁ

/

(DEPE)₂] [4c]. Although understanding of controlling

factors in these selective bond cleavage reactions is a

matter of further investigation, use of monodentate

phosphines are found to be effective for the Cꢀ

/

H or Nꢀ

/

H bond cleavage reaction.

Scheme 5.

proceeds via the intermediate B with h²-Cꢁ

tion. Finally, the CꢀH bond cleavage followed by rapid

migration of the resulting hydride to the COT ligand

gives 4a (Step 3). Since the concentrations of A and B

were negligible, the steady-state approximation for the

concentrations of A and B can be applied to yield the

following rate formulae (Eqs. (1) and (2)).

/

C coordina-

4. Experimental

/

4.1. General procedures

All manipulations and reactions were performed

under dry nitrogen or argon with use of standard

Schlenk and vacuum line techniques. Benzene, toluene,

hexane, 1,4-dioxane, and diethyl ether were dried over

anhydrous calcium chloride and then distilled over

sodium benzophenone ketyl under nitrogen; these

solvents were stored under nitrogen. [Ru(h⁴-1,5-

COD)(h⁶-1,3,5-COT)] (1) was prepared according to

the literature method [12] but magnetic stirring was used

d[4a]

dt

k₁k₂k₃[2a][benzo[b]thiophene]

ꢀ

k_ꢁ1(k_ꢁ2ꢂ k₃)[PEt₃] ꢂ k₂k₃[benzo[b]thiophene]

instead of sonification. Ru(1-4-h⁴-1,3,5-COT)L₃[Lꢀ

/

(1)

PEt₃(5a), PBu₃(5b), PEt₂Ph (5c)] and Ru(6-h¹:1-3-h³-

C₈H₁₀)(PMe₃)₃were prepared as reported previously

[7,9,17]. PMe₃and PEt₃were prepared from P(OPh)₃

with MeMgI and EtMgI, respectively. Thiophenes,

furans, and pyrroles were purchased from Wako Pure

Chemical Industry, Tokyo Chemical Industry or Al-

drich and used as received. Benzene-d₆was distilled over

sodium wire and stored under vacuum. Dichloro-

methane-d₂was distilled over P₂O₅and stored under

nitrogen. NMR spectra were recorded on a JEOL LA-

300 spectrometer (300.4 MHz for ¹H and 121.6 MHz for

³¹P) and chemical shifts are reported in ppm downfield

from TMS for ¹H and from 85% H₃PO₄in D₂O for ³¹P.

IR spectra were recorded on a JASCO FT/IR-410

spectrometer using KBr disk. Elemental analyses were

ꢀ

ꢁ_ꢁ1

d[4a]

dt

k_ꢁ1(k_ꢁ2ꢂ k₃)[PEt₃]

1

ꢀ

ꢂ

k₁k₂k₃[2a] ꢂ [benzo[b]thiophene] k₁[2a]

(2)

The estimated rate equation for the formation of 4a is

given by Eq. (1). The inverse rate dependence on [PEt₃]

with an intercept as shown in Fig. 7 is consistent with

the theoretical formula based on the proposed mechan-

ism (Eq. (2)). Bond cleavage reactions of the other

thiophenes, furans, and pyrroles would undergo in a

similar manner.

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á

/

170

167

1

carried out on a PerkinÁ

analyzer.

/

Elmer 2400 series II CHNS

signals (underlined) were estimated by Hꢀ

³¹P{¹H} NMR (C₆D₆): d 9.7 (d, Jꢀ

Jꢀ

/

¹H COSY.

/

24 Hz, 1P), 21.3 (d,

24 Hz, 1P). Anal. Calc. for C₂₄H₄₄P_sRuS: C, 54.63;

/

4.2. h⁵-Cyclooctadienylruthenium(II) complexes

H, 8.40; S, 6.08. Found: C, 54.95; H, 8.80; S, 6.06%.

[Ru(h⁵-C₈H₁₁){5-(2-ethoxycarbonyl)thienyl}(PEt₃)₂]

(4c): Yield 17% (78% by NMR). ¹H NMR (C₆D₆): d 0.5

(br, 1H, endo-7-CH₂in C₈H₁₁), 0.6 (m, 9H, PCH₂CH₃),

1.0 (m, 9H, PCH₂CH₃), 1.08 (t, 3H, COCH₂CH₃), 1.1

(1H, exo-7-CH₂in C₈H₁₁), 1.3 (m, 3H, PCH₂CH₃), 1.4

(m, 3H, PCH₂CH₃), 1.5 (2H, endo-6- and endo-8-CH₂in

C₈H₁₁), 1.8 (m, 3H, PCH₂CH₃), 2.1 (m, 3H, PCH₂CH₃),

2.2 (2H, exo-6- and exo-8-CH₂in C₈H₁₁), 2.88 (m, 1H,

1- or 5-CH in C₈H₁₁), 2.98 (m, 1H, 5- or 1-CH in

C₈H₁₁), 4.03 (m, 1H, 4- or 2-CH in C₈H₁₁), 4.2 (br, 5H,

2- or 4-CH in C₈H₁₁and COCH₂CH₃), 5.82 (m, 1H, 3-

As a typical example, preparation of [Ru(1-5-h⁵-

C₈H₁₁)(2-benzo[b]thienyl)(PEt₃)₂] (4a) by the reaction

of 1/PEt₃with benzo[b]thiophene is described in detail.

Complex 1 (133.5 mg, 0.42 mmol) and benzo[b]thio-

phene (93.0 mg, 0.69 mmol) were placed in a 20 ml

Schlenk tube, into which hexane (ca. 2 ml) and PEt₃

(125.0 ml, 0.85 mmol) were added by a hypodermic

syringe. The reaction mixture was stirred for 20 h at

room temperature, during which the yellow solution

turned to deep red. Evaporation of all volatile matters

by use of oil diffusion pump gave a deep red oil which

CH in C₈H₁₁), 6.87 (d, Jꢀ

Jꢀ2.7 Hz, 1H, thienyl); overlapped signals (underlined)

were estimated by ¹Hꢀ¹H COSY. ³¹P{¹H} NMR

/

2.7 Hz, 1H, thenyl), 8.06 (d,

was crystallized from hexane at ꢁ

white precipitate. Recrystallization of the precipitate

/

30 8C to give an off

/

from pentane gave yellow prisms of 4a in 14% yield (35.8

(C₆D₆): d 9.3 (d, Jꢀ

/

24 Hz, 1P), 20.4 (d, Jꢀ

/

24 Hz, 1P).

mg, 0.062 mmol). ¹H NMR (C₆D₆): d 0.60 (br.q, Jꢀ

/

12

12, 8 Hz,

Hz, 9H,

P^bCH₂CH₃), 1.1 (1H, exo-7-CH₂in C₈H₁₁), 1.4 (sext,

Jꢀ 8 Hz, 3H,

8 Hz, 3H, P^aCH₂CH₃), 1.5 (sext, Jꢀ

P^aCH₂CH₃), 1.5Á

1.6 (2H, endo-6- and endo-8-CH₂in

C₈H₁₁), 1.9 (sext, Jꢀ

8 Hz, 3H, P^bCH₂CH₃), 2.1 (1H,

Hz, 3H,

[Ru(h⁵-C₈H₁₁){5-(2-acetyl)thienyl}(PEt₃)₂]

(4d):

1

Hz, 1H, endo-7-CH₂in C₈H₁₁), 0.73 (dt, Jꢀ

/

Yield 77%. H NMR (C₆D₆): d 0.52 (br.q, Jꢀ

/

13 Hz,

14, 7 Hz, 9H,

13, 7 Hz, 9H, PCH₂CH₃), 1.1

(1H, exo-7-CH₂in C₈H₁₁), 1.28 (sext, Jꢀ7 Hz, 3H,

PCH₂CH₃), 1.38 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 1.5

(2H, endo-6- and endo-8-CH₂in C₈H₁₁), 1.78 (sext, Jꢀ

7 Hz, 3H, PCH₂CH₃), 2.0 (2H, exo-6- and exo-8-CH₂in

C₈H₁₁), 2.10 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 2.34 (s,

9H, P^aCH₂CH₃), 1.09 (dt, Jꢀ

/12,

8

1H, endo-7-CH₂in C₈H₁₁), 0.67 (dt, Jꢀ

/

PCH₂CH₃), 1.01 (dt, Jꢀ

/

exo-8-CH₂in C₈H₁₁), 2.2 (sext, Jꢀ8

/

P^bCH₂CH₃), 2.2 (1H, exo-6-CH₂in C₈H₁₁), 2.97 (m,

1H, 5-CH in C₈H₁₁), 3.16 (m, 1H, 1-CH in C₈H₁₁), 4.15

(m, 1H, 4-CH in C₈H₁₁), 4.34 (m, 1H, 2-CH in C₈H₁₁),

/

3H, COCH₃), 2.89 (m, 1H, 1- or 5-CH in C₈H₁₁), 2.97

(m, 1H, 5- or 1-CH in C₈H₁₁), 4.06 (m, 1H, 4- or 2-CH

5.95 (m, 1H, 3-CH in C₈H₁₁), 7.02 (t, Jꢀ

benzothienyl), 7.23 (t, 1H, Jꢀ7 Hz, benzothienyl), 7.72

(d, Jꢀ7 Hz, 1H, benzothienyl), 7.84 (d, Jꢀ7 Hz, 1H,

benzothenyl); overlapped signals (underlined) were esti-

mated by ¹Hꢀ¹H COSY and olefinic proton of the

benzothienyl group is obscured by the residual benzene

signal. ³¹P{¹H} NMR (C₆D₆): d 9.5 (d, Jꢀ

24 Hz, 1P),

20.9 (d, Jꢀ 2800

24 Hz, 1P). IR (KBr, cm^ꢁ1): 3000Á

/

7 Hz, 1H,

in C₈H₁₁), 4.13 (t, Jꢀ

5.82 (t, Jꢀ5.7 Hz, 1H, 3-CH in C₈H₁₁), 6.89 (br, 1H,

thienyl), 7.49 (br, 1H, thienyl). ³¹P{¹H} NMR (C₆D₆): d

9.2 (d, Jꢀ24 Hz, 1P), 20.4 (d, Jꢀ24 Hz, 1P). Anal.

/

7.7 Hz, 1H, 2- or 4-CH in C₈H₁₁),

/

Calc. for C₂₆H₄₆OP₂RuS: C, 54.81; H, 8.14; S, 5.63.

Found: C, 54.74; H, 8.19; S, 5.87%.

/

[Ru(h⁵-C₈H₁₁){5-(3-acetyl)thienyl}(PEt₃)₂] (4e): Yield

1

/

13%. H NMR (C₆D₆): d 0.55 (br.q, Jꢀ

/

13 Hz, 1H,

12, 7 Hz, 9H,

12, 7 Hz, 9H, PCH₂CH₃), 1.1

(1H, exo-7-CH₂in C₈H₁₁), 1.30 (sext, Jꢀ7 Hz, 3H,

PCH₂CH₃), 1.43 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 1.5

(br, 2H, endo-6- and endo-8-CH₂in C₈H₁₁), 1.78 (sext,

Jꢀ7H, 3H, PCH₂CH₃), 2.1 (br, 2H, exo-6- and exo-8-

CH₂in C₈H₁₁), 2.11 (sext, Jꢀ7H, 3H, PCH₂CH₃), 2.24

(br), 1463 (m), 1447 (m), 1400 (m), 1000 (m), 737 (w),

724 (w). Anal. Calc. for C₂₈H₄₆P_sRuS: C, 58.21; H, 8.03;

S, 5.55. Found: C, 58.37; H, 8.35; S, 6.84%.

endo-7-CH₂in C₈H₁₁), 0.72 (dt, Jꢀ

/

PCH₂CH₃), 1.05 (dt, Jꢀ

/

[Ru(h⁵-C₈H₁₁)(2-thienyl)(PEt₃)₂] (4b): Yield 29%

/

1

(75% by NMR). H NMR (C₆D₆): d 0.60 (br.q, Jꢀ

/

14

12.0, 7.5

12.9, 7.5 Hz, 9H,

PCH₂CH₃), 1.1 (1H, exo-7-CH₂in C₈H₁₁), 1.32 (sext,

Jꢀ7 Hz, 3H, PCH₂CH₃), 1.47 (sext, Jꢀ7 Hz, 3H,

PCH₂CH₃), 1.5Á1.6 (2H, endo-6- and endo-8-CH₂in

C₈H₁₁), 1.85 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 2.1 (1H,

exo-8-CH₂in C₈H₁₁), 2.21 (sext, Jꢀ7 Hz, PCH₂CH₃),

Hz, 1H, endo-7-CH₂in C₈H₁₁), 0.74 (dt, Jꢀ

/

Hz, 9H, PCH₂CH₃), 1.07 (dt, Jꢀ

/

(s, 3H, COCH₃), 2.91 (m, 1H, 1- or 5-CH in C₈H₁₁),

3.08 (m, 1H, 5- or 1-CH in C₈H₁₁), 3.99 (m, 1H, 4- or 2-

/

CH in C₈H₁₁), 4.37 (t, Jꢀ

C₈H₁₁), 5.87 (t, Jꢀ6 Hz, 1H, 3-CH in C₈H₁₁), 7.56 (s,

1H, thienyl), 7.82 (s, 1H, thienyl). ³¹P{¹H} NMR

/6 Hz, 1H, 2- or 4-CH in

/

2.2 (1H, exo-6-CH₂in C₈H₁₁), 2.95 (br.s, 1H, 5-CH in

C₈H₁₁), 3.13 (br.s, 1H, 1-CH in C₈H₁₁), 4.08 (m, 1H, 4-

(C₆D₆): d 9.2 (d, Jꢀ

/

24 Hz, 1P), 20.4 (d, Jꢀ24 Hz, 1P).

/

[Ru(h⁵-C₈H₁₁)(2-benzo[b]thienyl)(PBu₃)₂] (4f): Yield

1

CH in C₈H₁₁), 4.43 (br.dd, Jꢀ

C₈H₁₁), 5.94 (t, Jꢀ6 Hz, 1H, 3-CH in C₈H₁₁), 6.89

(br.d, Jꢀ3 Hz, 1H, thienyl), 7.22 (br.dd, Jꢀ4, 3 Hz,

1H, thienyl), 7.46 (d, Jꢀ4 Hz, 1H, thienyl); overlapped

/

8, 6 Hz, 1H, 2-CH in

41%. H NMR (C₆D₆): d 0.64 (q, Jꢀ

/

13 Hz, 1H, endo-

7 Hz, 9H, PC₃H₆CH₃),

7 Hz, 9H, PC₃H₆CH₃), 1.1Á2.5 (m, 41H,

PC₃H₆CH₃and C₈H₁₁), 3.15 (br, 2H, 1- and 5-CH in

/

7-CH₂in C₈H₁₁), 0.81 (t, Jꢀ

/

0.95 (t, Jꢀ

/

168

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á170

/

C₈H₁₁), 4.30 (br.m, 1H, 2- or 4-CH in C₈H₁₁), 4.54 (t,

Jꢀ7 Hz, 1H, 4- or 2-CH in C₈H₁₁), 6.01 (br, 1H, 3-CH

in C₈H₁₁), 6.98 (t, Jꢀ8 Hz, 1H, benzothienyl), 7.19 (br,

partly overlapped with C₆D₅H, benzothienyl), 7.23 (s,

1H, benzothienyl), 7.67 (d, Jꢀ7 Hz, 1H, benzothienyl),

³¹P{¹H} NMR (C₆D₆): d 4.60 (d, Jꢀ

24 Hz, 1P), 15.6

(d, Jꢀ24 Hz, 1P).

[Ru(h⁵-C₈H₁₁)(2-benzo[b]thienyl)(PEt₂Ph)₂]

Yield 40%. ¹H NMR (C₆D₆): d 0.45 (q, Jꢀ

1H, endo-7-CH₂in C₈H₁₁), 0.65 (dt, Jꢀ

PCH₂CH₃), 0.83 (dt, Jꢀ18, 7 Hz, 3H, PCH₂CH₃), 0.94

(dt, Jꢀ19, 8 Hz, 3H, PCH₂CH₃), 0.98 (dt, Jꢀ13, 6 Hz,

3H, PCH₃CH₃), 1.2 (m. 1H, exo-7-CH₂in C₈H₁₁), 1.4Á

1.6 (m, 2H, C₈H₁₁), 1.61 (sext, Jꢀ Hz, 1H,

PCH₂CH₃), 1.8Á2.2 (2H, C₈H₁₁), 1.9 (sext, Jꢀ8 Hz,

2H, PCH₂CH₃), 2.14 (sext, Jꢀ8 Hz, 1H, PCH₂CH₃),

2.2 (1H, C₈H₁₁), 2.21 (br, 2H, PCH₂CH₃), 2.4 (m, 1H,

PCH₂CH₃), 2.66 (dqui, Jꢀ15, 7 Hz, 1H, PCH₂CH₃),

2.99 (br, 1H, 5- or 1-CH in C₈H₁₁), 3.84 (m, 1H, 2- or 4-

CH in C₈H₁₁), 4.79 (t, Jꢀ6 Hz, 1H, 4- or 2-CH in

C₈H₁₁), 5.74 (t, Jꢀ6 Hz, 1H, 3-CH in C₈H₁₁), 7.0Á7.1

(m, 10H, PPh), 7.28 (t, Jꢀ8 Hz, 1H, benzothienyl), 7.33

(s, 1H, 3-CH in benzothienyl), 7.42 (t, Jꢀ8 Hz, 1H,

benzothienyl), 7.75 (d, Jꢀ8 Hz, benzothienyl), 7.92 (d,

Jꢀ8 Hz, benzothienyl); overlapped signals (underlined)

were estimated by comparison of similar compound 4a.

³¹P{¹H} NMR (C₆D₆): d 21.2 (d, Jꢀ

21 Hz, 1P), 28.7

in C₈H₁₁), 4.61 (br.t, Jꢀ

C₈H₁₁), 5.66 (t, Jꢀ6.3 Hz, 1H, 3-CH in C₈H₁₁), 6.09

(br, 1H, furyl), 6.47 (br.m, 1H, furyl), 7.65 (s, 1H, furyl).

³¹P{¹H} NMR (C₆D₆): d 17.2 (d, Jꢀ

24 Hz, 1P), 25.6

/

7 Hz, 1H, 2- or 4-CH in

/

(d, Jꢀ24 Hz, 1P).

/

[Ru(h⁵-C₈H₁₁){5-(2-acetyl)furyl}(PEt₃)₂] (5c): Yield

64%. ¹H NMR (C₆D₆): d 0.6 (1H, endo-7-CH₂in

/

(4g):

13 Hz,

20, 8 Hz, 3H,

C₈H₁₁), 0.69 (dt, Jꢀ

/

12, 6 Hz, 9H, PCH₂CH₃), 0.92

/

(dt, Jꢀ14, 8 Hz, 9H, PCH₂CH₃), 1.1 (1H, exo-7-CH₂in

/

C₈H₁₁), 1.2 (br.m, 3H, PCH₂CH₃), 1.5 (br.m, 5H,

PCH₂CH₃and endo-6- and endo-8-CH₂in C₈H₁₁), 1.7

(br.m, 3H, PCH₂CH₃), 2.1 (br, 5H, PCH₂CH₃and exo-

6- and exo-8-CH₂in C₈H₁₁), 2.16 (s, 3H, COCH₃), 2.83

(m, 1H, 1- or 5-CH in C₈H₁₁), 3.11 (m, 1H, 5- or 1-CH

in C₈H₁₁), 3.79 (m, 1H, 4- or 2-CH in C₈H₁₁), 4.51 (m,

1H, 2- or 4-CH in C₈H₁₁), 5.59 (br, 1H, 3-CH in

C₈H₁₁), 6.12 (br.s, 1H, furyl), 6.90 (br.s, 1H, furyl).

/

/8

/

³¹P{¹H} NMR (C₆D₆): d 16.2 (d, Jꢀ

(d, Jꢀ24 Hz, 1P).

/

24 Hz, 1P), 24.9

/

1

/

[Ru(h⁵-C₈H₁₁)(1-indolyl)(PEt₃)₂] (6a): Yield 91%. H

/

NMR (C₆D₆): d 0.27 (qt, Jꢀ

CH₂in C₈H₁₁), 0.46 (dt, Jꢀ

PCH₂CH₃), 1.1 (1H, exo-7-CH₂in C₈H₁₁), 1.13 (dt,

Jꢀ12.9, 7.5 Hz, 9H, PCH₂CH₃), 1.31 (sext, Jꢀ7 Hz,

3H, PCH₂CH₃), 1.4Á1.5 (br.m, 2H, endo-6- and endo-8-

CH₂in C₈H₁₁), 1.87 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃),

1.8Á1.9 (br.m, 2H, exo-6- and exo-8-CH₂in C₈H₁₁),

2.21 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 2.34 (br, 1H, 1- or

5-CH in C₈H₁₁), 2.88 (br.d, Jꢀ9 Hz, 1H, 5- or 1-CH in

/

13.5, 2.7 Hz, 1H, endo-7-

/

12.3, 7.2 Hz, 9H,

/

(d, Jꢀ

/

21 Hz, 1P).

[Ru(h⁵-C₈H₁₁)(2-benzo[b]furyl)(PEt₃)₂] (5a): Yield

71%. H NMR (C₆D₆): d 0.6 (br, 1H, 1H, endo-7-CH₂

/

1

C₈H₁₁), 4.01 (dd, Jꢀ/9.0, 6.3 Hz, 1H, 4- or 2-CH in

in C₈H₁₁), 0.67 (dt, Jꢀ

(dt, Jꢀ13, 7 Hz, 9H, PCH₂CH₃), 1.1 (1H, exo-7-CH₂in

C₈H₁₁), 1.23 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 1.42 (sext,

Jꢀ7 Hz, 3H, PCH₂CH₃), 1.59 (br.t, Jꢀ15 Hz, 2H,

endo-6- and endo-8-CH₂in C₈H₁₁), 1.77 (sext, Jꢀ7 Hz,

3H, PCH₂CH₃), 2.02 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃),

2.1 (br.m, 2H, exo-6- and exo-8-CH₂in C₈H₁₁), 2.96

(br, 1H, 1- or 5-CH in C₈H₁₁), 3.14 (br, 1H, 5- or 1-CH

in C₈H₁₁), 3.83 (m, 1H, 4- or 2-CH in C₈H₁₁), 4.58 (br.t,

/

12, 7 Hz, 9H, PCH₂CH₃), 0.90

C₈H₁₁), 4.33 (dd, Jꢀ

/

9.3, 6.9 Hz, 1H, 2- or 4-CH in

/

C₈H₁₁), 6.44 (br.dd, Jꢀ

C₈H₁₁), 6.94 (d, Jꢀ2.4 Hz, 1H, indolyl), 7.24 (d, Jꢀ

2.4 Hz, 1H, indolyl), 7.28 (t, Jꢀ7 Hz, 1H, indolyl), 7.39

(dd, Jꢀ8, 7 Hz, 1H, indolyl), 7.58 (d, Jꢀ8.4 Hz, 1H,

indolyl), 8.04 (d, Jꢀ

7.8 Hz, 1H, indolyl). ³¹P{¹H}

NMR (C₆D₆): d 4.9 (d, Jꢀ29 Hz, 1P), 17.4 (d, Jꢀ29

/9.3, 9.0 Hz, 1H, 3-CH in

/

Hz, 1P). Anal. Calc. for C₂₉H₄₇NP₂Ru: C, 59.98; H,

8.45; N, 2.50. Found. C, 60.45; H, 8.55; N, 2.59%.

[Ru(h⁵-C₈H₁₁)(1-pyrrolyl)(PEt₃)₂] (6b): Yield 43%.

Jꢀ

1H, 3-CH in C₈H₁₁), 6.44 (s, 1H, benzofuryl), 7.00 (t,

Jꢀ7.5 Hz, 1H, benzofuryl), 7.15 (t, Jꢀ7.5 Hz, 1H,

benzofuryl, partly overlapped with residual benzene

resonance), 7.35 (d, Jꢀ7.5 Hz, 1H, benzofuryl), 7.48

(d, Jꢀ

7.5 Hz, 1H, benzofuryl). ³¹P{¹H} NMR (C₆D₆):

d 16.6 (d, Jꢀ

/

8 Hz, 1H, 2- or 4-CH in C₈H₁₁), 5.64 (t, Jꢀ

/6.0 Hz,

¹H NMR (C₆D₆): d 0.38 (qt, Jꢀ

/

12.6, 2.1 Hz, 1H,

endo-7-CH₂in C₈H₁₁), 0.67 (dt, Jꢀ12.6, 7.5 Hz, 9H,

PCH₂CH₃), 1.05 (dt, Jꢀ12.0, 7.5 Hz, 9H, PCH₂CH₃),

1.1 (1H, exo-7-CH₂in C₈H₁₁), 1.2 (m, 5H, PCH₂CH₃

and endo-6- and endo-8-CH₂in C₈H₁₁), 1.37 (sext, Jꢀ

6.9 Hz, 3H, PCH₂CH₃), 1.81 (qt, Jꢀ8, 6 Hz, 3H,

PCH₂CH₃), 1.8 (1H, exo-6-CH₂in C₈H₁₁), 2.01 (t, 1H,

exo-8-CH₂in C₈H₁₁), 2.17 (sept, Jꢀ7.6 Hz, 3H,

PCH₂CH₃), 2.2 (1H, 1- or 5-CH in C₈H₁₁), 3.24 (br.d,

Jꢀ9 Hz, 1H, 5- or 1-CH in C₈H₁₁), 3.83 (td, Jꢀ9, 6

Hz, 1H, 4- or 2-CH in C₈H₁₁), 4.25 (dd, Jꢀ9, 7 Hz, 1H,

2- or 4-CH in C₈H₁₁), 6.10 (td, Jꢀ6, 2 Hz, 1H, 3-CH in

C₈H₁₁), 6.66 (s, 4H, pyrrolyl). ³¹P{¹H} NMR (C₆D₆): d

17.3 (d, Jꢀ24 Hz, 1P), 25.6 (d, Jꢀ24 Hz, 1P). Anal.

/

24 Hz, 1P), 25.5 (Jꢀ

/

24 Hz, 1P).

/

[Ru(h⁵-C₈H₁₁)(2-furyl)(PEt₃)₂] (5b): Yield 100%. H

NMR (C₆D₆): d 0.6 (br, 1H, endo-7-CH₂in C₈H₁₁), 0.70

1

/

(dt, Jꢀ

9H, PCH₂CH₃), 1.1 (m, 4H, PCH₂CH₃and exo-7-CH₂

in C₈H₁₁), 1.39 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 1.6

(br.t, Jꢀ13 Hz, 2H, endo-6- and endo-8-CH₂in C₈H₁₁),

1.79 (sext, Jꢀ7 Hz, 3H, PCH₂CH₃), 2.03 (sext, Jꢀ

/

13, 7 Hz, 9H, PCH₂CH₃), 0.95 (dt, Jꢀ

/13, 7 Hz,

/

7

Hz, 3H, PCH₂CH₃), 2.1 (br.m, 2H, exo-6- and exo-8-

CH₂in C₈H₁₁), 2.92 (br, 1H, 1- or 5-CH in C₈H₁₁), 3.15

(br, 1H, 5- or 1-CH in C₈H₁₁), 3.78 (m, 1H, 4- or 2-CH

/

Calc. for C₂₄H₄₅NP₂Ru: C, 56.45; H, 8.88; N, 2.74.

Found. C, 56.50; H, 8.90; N, 2.75%.

M. Hirano et al. / Inorganica Chimica Acta 352 (2003) 160Á

/

170

169

4.3. Kinetic measurements

Table 3

Crystallographic and physical data for complexes 4a and 6b

A typical procedure for kinetic measurement of the

reaction of 2a with benzo[b]thiophene is as follows.

Weighed amounts of 2a (ca. 30 mg), benzo[b]thiophene

and a sealed capillary containing PPh₃/benzene-d₆as a

standard were placed in a 5-mm NMR tube under

4a

6b

Empirical formula

Formula weight

Crystal color, habit

C₂₈H₄₆P₂RuS

577.75

yellow, prisms

C₂₄H₄₅NP₂Ru

510.73

orange, cubic

Crystal dimension (mmꢃ

/

mmꢃ

/

0.31ꢃ

/

0.29ꢃ

/

0.65ꢃ

/

0.52ꢃ

/

nitrogen. Then benzene-d₆(600 ml: [2a]ꢀ/ca. 0.089 M)

mm)

Crystal system

Space group

0.12

monoclinic

P2₁/a

0.26

monoclinic

Cc

was added from a hypodermic syringe and the progress

of the reaction was monitored by ³¹P{¹H} NMR

spectroscopy at 24 8C. The concentration of ben-

zo[b]thiophene varied from 0.107 to 1.08 M, added

PEt₃was varied from 0 to 0.452 M, and 2a was varied

from 0.0713 to 0.207 M. For evaluation of [2a] on the

rate, excess amount of benzo[b]thiophene (4.15 M) was

added to maintain pseudo-first-order conditions.

˚

a (A)

17.682(8)

13.655(3)

23.518(4)

98.31(2)

5618.6699

8

9.773(6)

17.854(7)

15.116(7)

107.65(4)

2513(2)

4

˚

b (A)

˚

c (A)

b (8)

3

V (A )

˚

Z

D_calcd(g cm^ꢁ3

)

1.366

7.6

2.005

8.29

m (Mo Ka) (cm^ꢁ1

Diffractometer

)

RAXIS-II

0.71069

8348

RASA-7R

0.71069

2628

˚

Radiation (A)

4.4. X-ray structural analysis

No. of observation (I ꢀ

/

3.00s(I))

R^a

A Rigaku RAXIS-II and a Rigaku RASA-7R dif-

fractometers with graphite-monochromated Mo Ka

0.054

0.046

0.030

0.040

b

R_w

˚

0.71069 A) were used for data collection

radiation (lꢀ

/

a

/

Rꢀa(½½F_o½ꢁ½F_c½½)=a½F_o½:

/

of 4a and 6b, respectively. A selected crystal of 4a or 6b

was mounted in a glass capillary (GLAS, 0.7 m.m.f.)

under argon atmosphere. The collected data were solved

by Patterson methods (DIRDIF 92 PATTY) for 4a and

direct methods for 6b, and refined by a full-matrix least-

square procedure using ^TEXSANprograms.¹The crystal-

lographic data and details associated with data collec-

tion for 4a and 6b are given in Table 3. Two independent

molecules of 4a were observed in the unit cell and the

ORTEP drawing of one of them is depicted in Fig. 1. Both

independent molecules have comparable bond lengths

and angles as shown in Table 1. ^ORTEPdrawing of 6b is

illustrated in Fig. 2 and the bond lengths and angles are

0:5

2

R_wꢀ½aw(½F_o½ꢁ½F_c½)²=aw½F_o½ ꢀ

:/

b

/

Grant-in-Aid for Scientiﬁc Research from the Ministry

of Education, Sports, Culture, Science and Technology,

Japan.

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/

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Oshima (at the Tokyo Institute of Technology) for

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Article Doi

Regioselective C-H or N-H bond cleavage reactions of heterocyclic compounds by [Ru(1,5-COD)(1,3,5-COT)]/monodentate phosphine

DOI: 10.1016/S0020-1693(03)00132-4

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