Tellurophenes

3.14 Tellurophenes V. I. Minkin and I. D. Sadekov Rostov State University, Rostov on Don, Russia ª 2008 Elsevier Ltd. All rights reserved. 3.14.1

Introduction

1007

3.14.2

Theoretical Methods

1008

3.14.3

Experimental Structural Methods

1008

3.14.3.1 Molecular Structure

1008

3.14.3.2 NMR Spectroscopy

1009

3.14.3.3 Infrared and Raman Spectroscopy

1011

3.14.3.4 Dipole Moments and Polarizabilities

1011

3.14.4

Thermodynamic Aspects

1011

3.14.5

Reactivity of Substituents Attached to Ring Carbon Atoms

1012

3.14.5.1 Organolithium Derivatives

1012

3.14.5.2 Halogen Derivatives

1014

3.14.5.3 Aldehydes and Ketones

1014

3.14.5.4 Carboxylic Acids and Esters

1016

3.14.6

Reactions of Fully Conjugated Rings

1016

3.14.6.1 Electrophilic Substitution Reactions

1016

3.14.6.2 Reactions with Organolithium Compounds, Grignard Reagents, and Other Organoelement Compounds

1017

3.14.6.3 Extrusion of Tellurium

1018

3.14.7

Metal and Charge-Transfer Complexes

1019

3.14.8

Polymerization of Tellurophene and Its Derivatives

1020

3.14.9

Ring Syntheses from Acyclic Compounds

1020

3.14.9.1 From Acetylenes

1020

3.14.9.2 From 1,3-Dienes

1021

3.14.9.3 From -Chlorovinylaldehydes

1021

3.14.9.4 From 1,3-Diynes

1022

3.14.9.5 From 1-En-3-ynes

1023

3.14.10

1024

3.14.10.1 3.14.10.2 3.14.11

Ring Synthesis by Transformation of Another Ring From Rhodium Complexes

1024

From Tellurapyranes by Ring Contraction Important Compounds and Applications

References

1024 1024 1025

3.14.1 Introduction The scope of tellurophenes was well defined at the beginning of Chapter 3.16 in CHEC(1984) <1984CHEC(4)935> and a number of general reviews on this subject published between 1986 and 1991 were indicated in the introduction to Chapter 2.14 of CHEC-II(1996) <1996CHEC-II(2)749>. A comprehensive review of the chemistry, structural and physical properties of tellurophene, dihydro- and tetrahydrotellurophenes and their benzoanalogues that covered

1007

1008 Tellurophenes literature up to 1992 was presented in a monograph <1994HC53>. A review paper on benzotellurophenes <2004KGS974> also deals with some aspects of the preparative chemistry of tellurophene. In this chapter, the literature is covered through to 2006.

3.14.2 Theoretical Methods Molecular orbitals and the bonding of tellurophene have been examined at the ab initio Hartree–Fock, MP2, and density functional theory (DFT, B3LYP) levels of theory with the use of both effective core potential (ECP) and nonECP (6-31G* and 6-311G** ) basis sets <2000SM185, 2001JMT81, 2003JMT207, 2005JMT209>. The calculated geometries and ionization potentials correlate well with the experimental data and are in general agreement with the results obtained in the early theoretical studies of the electronic structure of tellurophene obtained on the basis of semi-empirical methods of quantum chemistry <1977AHC119>. The aromaticity of tellurophene was intensely studied in the context of its position in the range of five-membered heterocycles p-isoelectronic with benzene. According to various approaches for estimation of the aromaticity of heterocyclic compounds <1991H(32)127, 1993AHC303, B-1994MI1> the aromatic character of the five-membered heterocycles decreases in the order thiophene > selenophene > tellurophene > pyrrole > furan. Apart from the most important energetic and magnetic criteria, some other approaches have been used to evaluate indexes of aromaticity P (A, B, N, J) of tellurophene and congenerous heterocycles in early studies <1973G1041, 1974J(P2)332>. More recently, new indexes of aromaticity have been proposed based on molecular polarizability (D) and hardnesses () related to the electronic part of the electrostatic potential <1998JMT59, 2001CRV1451>. The results are presented in Table 1. Table 1 Aromaticity indexes for five-membered heterocycles Heterocycle

A

B

 N

J

D (a.u.)

 (eV)

Furan Thiophene Selenophene Tellurophene

7.67 11.56 10.44 8.50

1.72 3.85 2.94 1.85

1.42 0.90 1.02 1.30

0.87 0.93 0.91 0.88

26.45 25.63 25.06 24.65

5.33 5.01 4.91 4.48

The aromaticity index A ¼ 1Vm2\3 is based on the dilution shift method: 1 is the 1H nuclear magnetic resonance (NMR) chemical shift difference in pure liquid and in nonpolar solvent at infinite dilution, Vm being the molar volume of a compound. The greater A values correspond to greater aromaticity. The index B was introduced based on the assumption that the influence of a 2-methyl group on the 1H NMR chemical shifts of protons in the rings is more uniform the greater the aromatic character of the heterocycle: B ¼ 1/ij[(2)i  (2)j], where 2 is the difference in chemical shifts of ring protons of 2-methyl-substituted and unsubstituted heterocycle; indexes i and j relate to all inequivalent protons. As structural criteria of aromaticity, indexes N ¼ aR2 þ b (where R are bond lengths, and a and b are parameters characteristic for a given pair of atoms) and Julg’s parameter J ¼ 1  225/nrs(1  drs/a)2 (where n is the number of peripheral bonds rs, drs are their lengths, and d is their mean length) have been applied. The less the value N and closer to 1 the value J, the greater is the aromaticity of a heterocycle. Polarizability exaltations D ¼ <>M  <>M’, where <>M and <>M’ are the mean dipole polarizability and the mean atomic or group polarizability, respectively.

3.14.3 Experimental Structural Methods 3.14.3.1 Molecular Structure The geometry of tellurophene in the gas phase was determined based on its microwave (MW) spectrum <1973CPH217>. Tellurophene is a liquid at room temperature and X-ray crystallography has not been applied to the parent compound. The molecular structure of the tellurophene nucleus was derived from the X-ray crystallographic analysis of its crystalline derivatives <1977AHC119, 2002CHE763>. X-Ray structures have been reported

Tellurophenes

for the following substituted tellurophenes: tellurophene-2-carboxylic acid 1 <1972CSC737>, 3-telluranyl derivative 2 <1998OM1901>, 2,5-diphenyl-3-iodotellurophene 3 <1992AXC767>, 2,2-ditellurophene 4 <1994TL8009>. X-ray structural determinations have also been performed for 21-telluraporphyrine <1978TL1885, 1995AGE2252, 2001AG4598, 2002OM4546, 2004OM4513> and several derivatives of dibenzotellurophene <2002CHE763>. Ph

Cl2 Te

I Te Te

COOH

Te

Te

1

Ph

Ph

2

Te

Ph

3

4

Table 2 contains data on bond lengths and valence angles of the tellurophene ring.

Table 2 Molecular geometry of tellurophene ˚ Valence angles (deg) Bond lengths (A)

MW 1973CPH217

X-Raya 2002CHE763

Te–C(2) C(2)–C(3) C(3)–C(4) C(2)–Te–C(5) C(3)–C(2)–Te C(2)–C(3)–C(4)

2.055 1.375 – 82.53 110.81 117.93

2.046 1.371 1.478 82.00 111.83 116.76

a

These values were obtained by averaging of the data on geometries of the substituted tellurophenes 1–4.

3.14.3.2 NMR Spectroscopy Data on 1H NMR spectral parameters of tellurophene <1972J(P1)199, 1974MP257>, 2-substituted tellurophenes <1974ACB175, 1976ACB605> and, for comparison, furan, thiophene and selenophene <1965SA85> are listed in Table 3.

Table 3 1H NMR parameters for tellurophene and congenerous rings (in CDCl3) and 2-substituted tellurophenes 2-RC4H3X (in CDCl3 or (CD3)2CO)  (ppm)

JHH (Hz)

X

2-R

H-2

H-3

H-4

H-5

2,3

2,4

2,5

3,4

3,5

4,5

O S Se Te Te Te Te Te Te Te Te Te Te Te Te Te

H H H H CHO COMe CO2H CO2Me SMe CH2OH Cl Br I Me CH(OCOMe)Me CONMe2

7.29 7.18 7.88 8.87

6.24 6.99 7.22 7.78 8.62 8.44 8.53 8.49 7.42 7.41 7.33 7.72 8.11 7.23 7.60 7.94

6.24 6.99 7.22 7.78 8.05 8.00 7.93 7.92 7.55 7.64 7.34 7.41 7.32 7.47 7.67 7.87

7.29 7.18 7.88 8.87 9.56 9.41 9.40 9.38 8.81 8.77 8.75 8.91 9.13 8.64 8.87 9.19

1.75 4.90 5.40 6.58

0.85 1.04 1.46 1.12

1.40 2.84 2.34 1.82

3.30 3.50 3.74 3.76 4.10 4.22 4.20 4.11 4.03 3.88 4.26 4.27 4.06 3.90 4.10 4.10

1.32 1.16 1.34 1.33 1.28 1.25 1.47 1.49 1.54 1.26 1.82 1.95

6.77 6.78 6.76 6.79 6.93 6.83 7.33 7.28 7.10 7.14 6.10 6.00

1009

1010 Tellurophenes With decrease in electronegativity of the heteroatom in the ring, the chemical shifts of -protons in the parent compounds move downfield and vicinal coupling constants (3J2,3, 3J3,4) increase. Irregularities in chemical shifts of -protons are, most probably, due to paramagnetic contributions of shielding by the heteroatoms. The 13C NMR parameters of five-membered heterocycles <1974ACB175> and 2-substituted tellurophenes <1974ACB1751, 1976ACB605> are given in Table 4.

Table 4 13C NMR chemical shifts of tellurophene and congenerous rings and 2-substituted tellurophenes ((CD3)2CO), 2-RC4H3X  (ppm) X

R

C-2

C-3

C-4

C-5

O S Se Te Te Te Te Te Te Te Te Te Te Te Te Te

H H H H CHO COMe CO2H CO2Me SMe CH2OH Cl Br I Me CH(OCOMe)Me CONMe2

143.6 125.6 131.0 127.3 151.5 153.5 137.6 139.0 142.1 155.3 136.4 110.0 68.9 144.6 152.7 146.6

110.4 127.3 129.8 138.0 148.1 143.4 144.7 144.5 136.3 132.2 139.1 142.6 149.2 137.5 134.8 138.4

110.4 127.3 129.8 138.0 139.4 139.8 138.6 138.6 137.8 137.4 136.0 137.4 139.4 136.8 137.4 138.4

143.6 125.6 131.0 127.3 138.7 137.8 138.1 137.4 125.6 124.9 128.7 131.5 135.0 124.9 127.1 132.6

In five-membered heterocycles, 13C NMR signals of -carbons shift upfield with decrease in electronegativity of the heteroatoms. There exists good correlation between H-5 and C-5 chemical shifts in 2-substituted tellurophenes which indicates similarity in the transmission mechanism operating for carbon and proton chemical shifts. The effect of substituents on 13C and 1H NMR chemical shifts in 2- and 3-substituted furans, thiophenes, selenophenes, and tellurophenes has been studied by means of principal components and partial least squares analyses <2005MRC397>. 125 Te chemical shifts in 2-substituted tellurophenes <1976CS139, 1981ZOR947, 1982MR504> are given in Table 5. 125Te chemical shifts of tellurophenes correlate well (r ¼ 0.98) with 77Se chemical shifts of similar substituted selenophenes <1976CS139>. This fact suggests an identical mechanism of transmission of electronic effects of substituents in both heterocycles. The slope of the correlation indicates that the tellurophene ring transmits the effects 2.44 times better than the selenophene ring. The sign of Te–H and Te–C coupling constants in tellurophenes was determined by selective population transfer experiments <1981MR155>.

Table 5 125Te NMR chemical shifts (, ppm; relative to Me2Te) and 1JTe–C and 2JTe–C coupling constants (Hz) for 2-substituted tellurophenes 2-RC4H3Te (CD3COCD3) R



JTe–C(2)

JTe–C(3)

JTe–C(4)

JTe–C(5)

H CHO COCH3 COOMe Br CH2OH SMe

793 804 825 862 960 775 886

302.4 290.2 274.3 299.6 373.8 289.2 335.4

5.6 3.5 5.4 5.3 4.7 <3 <3

5.6 15.1 14.0 13.5 7.0 7.0 6.7

302.4 321.6 317.7 317.8 310.5 297.5 304.5

Tellurophenes

3.14.3.3 Infrared and Raman Spectroscopy High-quality experimental vibrational spectra have been reported for tellurophene and some of its derivatives <1985SPL759, 1987CPL244, 2000PCP2495, 2003JMT207>. The normal-mode frequencies and corresponding vibrational assignments were examined theoretically on the basis of Hartree–Fock and MP2 quantum chemical calculations and attributed to one of eight types of motion (C-H, CTC, C–C, Te–C stretches, in-plane and out-ofplane C–H bends, CTC–C bend and ring torsion) <2005JMT209>. Theoretical infrared (IR) and Raman intensities have also been reported. A force field for tellurophene, allowing good correlation of theoretical and experimental data on its vibrational spectrum, has been calculated using various levels of approximation and different basis sets <2001JMT81>.

3.14.3.4 Dipole Moments and Polarizabilities The dipole moment of tellurophene in the gaseous phase was found to be 0.19D <1973CPH217>. In benzene solution (25  C), dipole moments (, D) have been measured for a number of 2-substituted tellurophenes 2-RC4H3Te <1973CC342, 1973CR(C)203, 1977J(P2)775>: R ¼ H (0.46), R ¼ Cl (1.43), R ¼ Br (1.44), R ¼ Me (0.64), R ¼ SMe (1.30), R ¼ COMe (2.97), R ¼ CHO (3.18), R ¼ COOMe (1.95), R ¼ CONMe2 (3.60), R ¼ CH2OH (1.75) <1977J(P2)775>. The direction of the dipole moment vector of tellurophene is from the center of the ring to the heteroatom <1973CC342, 1973CR(C)203, 1974JHC827>. The difference between the dipole moments of a heteroaromatic fivemembered heterocycle and its tetrahydro derivative is considered as the mesomeric moment of the conjugated heterocycle and is directed opposite to the vector of its dipole moment. From the values indicated above and the dipole moment of tetrahydrotellurophene (1.63D) <1977J(P2)775, 1973CR(C)203>, the mesomeric moment of tellurophene is evaluated to be 1.17D. First-principles quantum chemical calculations including relativistic effects have been carried out for dipole moments, polarizabilities, and first- and second-order hyperpolarizabilities for tellurophene. The estimated values were compared with the observed ones measured by the optical Kerr effects <2000SM185, 2003JMT207>.

3.14.4 Thermodynamic Aspects The acidity constants of 5-substituted tellurophene-2-carboxylic acids have been measured in aqueous and aqueousethanolic solution. Table 6 presents the data obtained in comparison with those for the acids of the congeneric fivemembered heterocycles <1960SK(B)87, 1968RS1048, 1970JCB867>.

Table 6 pKa values of 5-substituted tellurophene-2-carboxylic acids 5R-C4H2Te-COOH-2 X

R

pKa (H2O, 25 oC)

pKa (H2O–EtOH/1:1, 25 oC)

O S Se Te Te Te Te Te

H H H H CH3 COOCH3 COOH COO

3.16 3.53 3.60 3.97 4.16 3.36 3.11 4.24

4.54 5.05 5.14 5.48

Although tellurophene-2-carboxylic acid (R ¼ H) is the weakest acid in the series, it is stronger than benzoic acid. pKa values of 5-substituted tellurophene-2-carboxylic acids correlate well with the p constants of the substituents. For the five-membered ring 2-carboxylic acids, the  values are 1.41 (X ¼ O), 1.23 (X ¼ S), 1.23 (X ¼ Se), and 1.20 (X ¼ Te) <1972J(P2)1738>. This sequence is indicative to the approximately equal transmittance of electronic effects of substituents across the five-membered heterocycle.

1011

1012 Tellurophenes

3.14.5 Reactivity of Substituents Attached to Ring Carbon Atoms 3.14.5.1 Organolithium Derivatives Some derivatives of tellurophene, for example, halogenotellurophenes, cannot be obtained directly from the parent compound. A number of less-accessible derivatives of tellurophene have been obtained by transformations of lithiotellurophenes. The best and most common route to deuterated tellurophenes is the reaction of lithiotellurophenes 5 with deuterated water <1976SAA1089>, which affords 2-deuterotellurophenes (Equation 1). D2O R

Te

Li

R

Te

D

ð1Þ

5 R = H, Ph

2,5-Dideutero-, 2,3,4-trideutero-, and 2,3,4,5-tetradeuterotellurophenes have been prepared from 2-deuterotellurophene (Scheme 1) <1976SAA1089>. With the exception of the tetradeuteroderivative, deuterotellurophenes were purified by crystallization of their readily formed dibromo derivatives (oxidation addition reaction with bromine) and subsequent reduction of the latter. Polydeuterated tellurophenes, for example, 2-phenyl-3,4,5-trideuterotellurophene, can be prepared by the addition of sodium ditelluride in deuteromethanol to 1-phenylbutadiyne <1976JOM183>.

D

D i, BuLi Te

ii, D2O

D

D

D

Te

ii, D2O

D

i, BuLi

i, BuLi D

Te

D

ii, D2O

D

Te

D

Scheme 1

2-Lithiotellurophene was employed for the synthesis of 2-halogenotellurophenes (Scheme 2). 2-Chloro- and 2-bromotellurophenes have been prepared in moderate yields by the reactions with hexachloro- and hexabromoethanes, respectively <1976ACB605>. With symmetric dichlorotetrabromoethane instead of hexabromoethane, 2-bromotellurophene was obtained in 64% yield <1994TL8009>. 2-Iodotellurophene was prepared by coupling 2-lithiotellurophene with 2-chloroethylene-1-iodoso dichloride and the subsequent treatment of the formed iodonium salt with sodium nitrite <1976ACB605>. This reaction is accompanied by the formation of small amounts of 2-nitrotellurophene. A preparatively more convenient approach to 5-substituted 2-iodotellurophenes is based on the reaction of the corresponding 2-lithiotellurophenes with iodine <2005TL2647>. By this reaction, 2-iodo-5-butyl- and 2-iodo-5-phenyltellurophenes have been prepared in 72% and 85% yields (Scheme 2).

C2Cl6 Te

Cl C2Br6

Te

Scheme 2

Te

+ ) I

(

Br

R I2

R

ClCH=CHICl2

I (R = Bu, Ph)

Te

Li

5 (R = H, Bu, Ph)

Te

2

Te

I

Tellurophenes

2-Lithiotellurophene 5 (R ¼ H) is the main precursor to various 2-chalcogenotellurophenes. 2-Methylthiotellurophene was prepared by reaction with dimethyl disulfide in 50–55% yield (Scheme 3) <1973CPL132, 1977J(P2)775>. The first step of the preparation of 2-ethylselenotellurophene involves the insertion of selenium into the C–Li bond of compound 5 (R ¼ H). The subsequent treatment of the formed lithioselenium derivative affords 2-ethylselenotellurophene in 43% yield (Scheme 3) <1997T4199>.

Me2S2 Te

EtBr

Se

SMe

Te

Te

Li

SeLi

Te

SeEt

5: R = H Te O2 Te

– Te Te

TeLi

)2 Te2

Te

)2 Te

7

6 Scheme 3

The analogous reaction of compound 5 (R ¼ H) with powdered tellurium gives rise to di(2-tellurienyl) telluride in very low yield (11%). The main product of this reaction is, most probably, di(2-tellurienyl) ditelluride 6, which transforms to compound 7 by elimination of a tellurium atom. A number of organometallic derivatives of tellurophene and 2,29-bitellurophene 4 were obtained by reactions of 2-lithiotellurophene with metal salts (Scheme 4). 2-Coppertellurophene was prepared by a treatment of compound 5 (R ¼ H) with CuI, whereas reaction with CuCl2 in ether leads to the formation of 2,29-bitellurophene 4 in yields ranging from 14% <1998JCM438> to 39% <1994TL8009, 1995SM537, 2000H(S2)159>.

CuCl2, – 78 °C to 20 °C

CuI

Te Te

Cu

Te

5: R = H

Li

Te

4

Scheme 4

Reacting dimethyl sulfate with 2-lithiotellurophene readily forms 2-methyltellurophene 8 (R ¼ H) in 75% yield (Scheme 5) <1972JP1199>. Unexpectedly, no formation of 2-ethyltellurophene was observed when coupling compound 5 (R ¼ H) with ethyl bromide. Tellurophene-2-carbaldehyde 9 (R ¼ H) was prepared by a treatment of 2-lithiotellurophene with N-methylformanilide in 24% yield <1972J(P1)199>. Carboxylation of lithiotellurophenes 5 (R ¼ H, Me) affords the corresponding tellurophene-2-carboxylic acids 10 in 37% and 35% yields, respectively <1972J(P1)199>. By the condensation of 2-lithiotellurophene with aldehydes, 2-(1-hydroxyethyl)tellurophene 11 (R1 ¼ Et) <1972J(P1)199, 1997T4199> and 2-(hydroxybenzyl)tellurophene 11 (R1 ¼ Ph) <1997T4199> were obtained in 50–57% and 60% yields, respectively (Scheme 5). Tellurophene-2,5-dicarbaldehyde 12 was obtained in 43% yield <1995MM8363> by treatment of 2,5-dilithiotellurophene with dimethylformamide (DMF) (Equation 2).

1013

1014 Tellurophenes

R

CH(OH)R1

Te

11: R1 = Et, Ph R1CHO Me2SO4

PhN(Me)CHO R

Te

R

CHO

Te

Li

R

5

9: R = H CO2

R

Me

8

H+

Te

Te

COOH

10: R = H, Me Scheme 5

Me2NCHO Li

Te

OHC

Li

Te

CHO

ð2Þ

12

3.14.5.2 Halogen Derivatives Nucleophilic substitution of halogens in the ring or in side chains have been used for the synthesis of various derivatives of tellurophene. The reaction of 2-iodotellurophene with thiols catalyzed by Cu(I) ions gives rise to 2-organylthiotellurophenes 13 in 77–90% yields (Equation 3) <2005TL2647>.

R1SH, Cu(I) R

Te

I

KOH

R

1

Te

SR

ð3Þ

13 R = Ph, Bu, R1 = Pr, C12H25, 4-MeOC6H4, 2-ClC6H4, 3-ClC6H4, 4-ClC6H4; R = R1 = Ph

Based on the exchange reactions of 3,4-bis(chloromethyl)-2,5-diphenyltellurophene 14, a number of derivatives of tellurophene have been prepared in 49–98% yields (Scheme 6) <1976ZNB367, 1977CZ303>. The reaction of 2-iodotellurophene with sodium malonitrile catalyzed by PdCl2(PPh3)2 results in the formation of 2-dicyanomethylene-2,5-dihydrotellurophene in 46% yield (Scheme 7) <1996H(43)1927>.

3.14.5.3 Aldehydes and Ketones Tellurophene aldehydes and ketones readily undergo reduction reactions typical of carbonyl compounds. The Wittig reaction of 2,5-bis(dodecyloxy)-p-xylene-bis(triphenylphosphonium bromide) with tellurophene-2,5-dicarbaldehyde leads to poly(2,5-tellurophenediylvinylene) (MW 7000–29 000 Da) in 65% yield <1995MM8363>. The condensation reactions of 2,5-diphenyl-3,4-diformyltellurophene 15 have been employed for the synthesis of a number of bi- and polycyclic heterocycles with a fused tellurophene ring (Scheme 8) <1976CB3886>.

Tellurophenes

N+

H2C

+N

CH2

Ph

Ph

Te Py

X

ClH2C

Te

CH3

Na2Te

Na2X Ph

H3C

CH2Cl

Ph

Ph

Te

Ph

Ph

Te

Ph

14

X = S, Se

RONa ROH2C

CH2OR

Ph

R = H, Me, Et

Ph

Te

Scheme 6

NaCH(CN)2 Te

I

PdCl2(PPh3)2, THF

H H

CH(CN)2

Te

CN Te CN

Scheme 7

EtOOC

Ph

S

Te

EtOOC

Ph S(CH2COOEt)2 Ph

Ph OHC N

Te

CHO

1,2-C6H4(NH2)2

H2NNH2 Ph

N

Te

16 (RCH2)2CO

R

Ph

O

Te R

17

Ph

R = COOMe, Ph Scheme 8

Te N

Ph

15

Ph

N

Ph

1015

1016 Tellurophenes

3.14.5.4 Carboxylic Acids and Esters Tellurophene carboxylic acids are obtained in quantitative yields by alkaline hydrolysis of the corresponding esters <1972J(P1)199, 1975CR(C)187, 1975CS113, 1980J(P2)971>. Tellurophene-2-carboxylic acid reacts with diazomethane to give 2-methoxycarbonyltellurophene <1972JP1199>. The reaction with hexamethylphosphoramide (HMPA) gives rise to tellurophene-2-N,N-dimethylcarboxyamide (Scheme 9) <1974T4129>.

CH2N2

HMPA Te

CONMe2

Te

COOMe

Te

COOH

Scheme 9

Decarboxylation of tellurophene carboxylic acids occurs readily in quinoline solution under the action of copper chromite. In this way, 2-(39(49)-methoxyphenyl)tellurophenes have been obtained from 2-(39(49)-methoxyphenyl)tellurophene-5-carboxylic acids <1980J(P2)971>.

3.14.6 Reactions of Fully Conjugated Rings 3.14.6.1 Electrophilic Substitution Reactions With electrophiles acting also as oxidants of dicoordinate tellurium (HNO3, halogens), tellurophenes enter into oxidative addition reactions to give corresponding Te(IV) derivatives. Therefore, tellurophenes are not susceptible to direct nitration. Moreover, when treated with strong mineral or Lewis acids (e.g., AlCl3), tellurophenes undergo decomposition, which requires the reactions of tellurophenes to be carried out in neutral, alkaline, or low-acid solutions. Bromination of tellurophenes results in formation of low-soluble 1,1-dibromotellurophenes (Equation 4) <1966AG940, 1961JA4406, 1968BRP1107698, 1978CB3745>. Upon reaction with sulfuryl chloride, tellurophene forms 1,1-dichlorotellurophene in 61% yield <1997T4199>. R2

R2

R2

R2

+ Br2 R1

R1

R1

Te

Br 1

2

2

ð4Þ

R1

Te Br

1

R = R = H; R = H, R = Bu, Ph

2-Bromo-5-phenyltellurophene was prepared in 62% yield by a treatment of 2-phenyltellurophene with N-bromosuccinimide (NBS) in methylene dichloride (Equation 5) <2005TL2647>. NBS Te

Ph AcOH

ð5Þ Br

Te

Ph

Treatment of tellurophene with 10% D2SO4 in deuteromethanol gives rise to 2,5-dideuterotellurophene, whereas reaction with Hg(OAc)2 affords 2,5-(diacetoxymercuri)tellurophene (Scheme 10) <1966AG940>.

10%D2SO4/CH3OD

Hg(OAc)2/EtOH AcOHg Scheme 10

Te

HgOAc

Te

D

Te

D

Tellurophenes

Reaction of tellurophene with acetic anhydride in the presence of SnCl4 forms 2-acetyl-tellurophene (Scheme 11) <1972J(P1)199, 1971CC1441>. 2-Trifluoroacetyltellurophene has been obtained by coupling tellurophene with trifluoroacetic anhydride. No Lewis acid catalysts are needed in this reaction (Scheme 11) <1971CC1441, 1973J(P2)2097>. Formylation of tellurophene occurs readily under the action of a complex formed by DMF and phosgene (Scheme 11) <1971CC1441, 1973J(P2)2097>.

Ac2O/SnCl4

(CF3CO)2O/Δ

Te

Te

COCF3

Te

COMe

DMF/COCl2/CHCl3

CHO

Te Scheme 11

2-Carbomethoxytellurophene enters into a Friedel–Crafts reaction with Ac2O/SnCl4 (Equation 6) <1972J(P1)199>. Ac2O/SnCl4 CO2Me

Te

ð6Þ MeCO

CO2Me

Te

Chloromethylation of 2,5-diphenyltellurophene affords 3,4-di(chloromethyl)tellurophene in 61% yield (Equation 7) <1976ZNB367>. ClCH2

CH2Cl

HCHO / HCl / AcOH Ph

Te

ð7Þ Ph

Ph

Te

Ph

Table 7 contains data on the relative reactivity of tellurophene and related heterocycles in typical electrophilic substitution reactions <1973J(P2)2097>.

Table 7 Relative reactivities (k/kthiophene) of tellurophene and congeneric heterocycles Compound

Acetylation (25  C)a

Trifluoroacetylation (75  C)b

Formylation (30  C)c

Furan Thiophene Selenophene Tellurophene

11.9 1 2.28 7.55

140 1 7.33 46.4

107 1 3.64 36.8

a

Ac2O/SnCl4. (CF3CO)2O. c COCl2/DMF. b

3.14.6.2 Reactions with Organolithium Compounds, Grignard Reagents, and Other Organoelement Compounds Lithiation of tellurophene <1972J(P1)199, 1976SAA1089, 1976ACB605, 1977J(P2)775, 1981JOM43, 1994TL8009, 2000H(52)159> and 2-R-substituted tellurophenes (R ¼ Me, Bu, Ph) <1972J(P1)199; 2005TL2647> proceeds smoothly at room temperature when their ether solutions are treated with butyllithium in hexane. With twofold

1017

1018 Tellurophenes excess of butyllithium, tellurophene forms 2,5-dilithio derivative <1995MM8363>. The reaction of 2,5-diphenyl-3iodotellurophene with butyllithium leads to the ring opening to give di(1,4-diphenylbut-1-ene-3-ynyl) ditelluride in 54% yield (Scheme 12) <1996JOC9503>.

I

Ph

Ph

Li

Ph

BuLi / THF, 78 °C Ph

Te

Ph

Ph

Te Te

Te

Ph

Te

Ph

Ph

Ph

Scheme 12

Under slow addition of 2 equiv of BuLi to a solution of tellurophene in tetrahydrofuran (THF) at room temperature, di(1,4-diphenylbut-1-ene-3-ynyl)telluride is formed in 60% yield <1996JOC9503>. Another Te–C cleavage reaction occurs upon coupling 2,5-diphenyltellurophene with BuLi in the presence of tetramethylethylenediamine [1,2 bis(dimethylamino)ethane] (TMEDA) <1976ZNB1654>. The 1,4-diphenyl-1,4-dilithiobuta-1,3-diene reacts with various electrophilic reagents giving 1,4-disubstituted 1,4-diphenylbuta-1,3-dienes in 20–58% yields. This reaction performed without the use of TMEDA was extended to s-BuLi and t-BuLi <1998OM5796>. Buta-1,3-dienes can also be obtained by coupling tellurophene (as well as other congeneric five-membered heterocycles) with Grignard reagents in the presence of 10 mol% Ni(PPh3)2Cl2 <1984CC617>. The reaction with aliphatic Grignard reagents occurs selectively affording (Z,Z)-dienes. Di-(t-butyl)silene generated by the photolysis of hexa-(t-butyl)-cyclotrisylane reacts with 2,5dimethyltellurophene to form 2,2,4,4-tetra-(t-butyl)-1,3-ditellura-2,4-disiletane in 63% yield <1997ZFA1277>.

3.14.6.3 Extrusion of Tellurium ArF (193 nm) and KrF (248 nm) laser-induced photolysis of gaseous tellurophene occurs via cleavage of both Te–C bonds and yields elemental tellurium, 1-buten-3-yne, acetylene, and butadiyne, as a very minor product, and results in chemical-vapor deposition of tellurium films <1999JMC563, 2000AM715, 2000JOC2759>. The mechanism of homogeneous decomposition of gaseous tellurophene was investigated by using IR laser-induced pyrolysis and trapping experiments <2005MI1>. It was proposed that the reaction involves an intermediate _HCTCHTCHTCH_ diradical. Under Hg-lamp photolysis of 2-phenyltellurophene ( max 292 nm), through Pyrex in argon-degassed ether, phenylvinylacetylene and elemental tellurium are formed <1976JOM183>. UV illumination of air-exposed solutions of compounds 16 and 17 results in elimination of the elemental tellurium to give 4,5-dibenzoylpiperazine in 40% yield and 4,5-dibenzoyl-2,7-diphenyl-2,4,6-cycloheptatrien-1-one in 43% yield (Scheme 13) <1976CB3886>.

Ph

Ph N Te

hν/O2

N

Te O O

PhCO

N N

–Te

PhCO

Ph

Ph

16 Ph

Ph

O

Te

hν/O2 –Te

Ph

Ph

17 Scheme 13

Ph PhCO O PhCO Ph

N N

Tellurophenes

3.14.7 Metal and Charge-Transfer Complexes Tellurophenes readily form metal complexes with Lewis acids, metal ions, and metal carbonyls. A mixture of monoand binuclear complexes 18 and 19 is obtained by coupling tellurophene (L1) with Na2PdCl4 <1972JOMC87>. With tetrachlorotellurophene (L2), the complex 20 with trans-configuration was prepared <1972JOMC87>. L1

1

Cl Pd

L

1

Cl

L

Cl

18

Cl

Cl Pd

Pd

Pd Cl

L2

Cl

1

Cl

L

19

L

2

20

The structure and composition of products of reactions between tellurophene and metal carbonyls depends on the nature of the metal <1999UK415>. A monomeric complex was obtained in 80% yield when treating tellurophene with Cr(CO)3(MeCN) in dibutyl ether solution at 50–60  C (Equation 8) <1972JOMC87, 1981MCL3>. + Cr(CO)3(MeCN)3 Te

−MeCN

Cr(CO)3

Te

ð8Þ

Telluraferrole 21 is the main product of the reaction of tellurophene with Fe3(CO)12 under short-term (45 min) reflux of a heptane solution. Under prolonged heating (2.5 h), ferrole and FeTe are formed (Scheme 14) <1996JCD1545>. This reaction can be accelerated by MW heating <1995MI1>.

Δ

Fe3(CO)12 +

Te Fe(CO)3

Δ

Fe(CO)3 + FeTe

Te Fe(CO)3

Fe(CO)3

21 Scheme 14

Reaction of tellurophene with osmium or ruthenium clusters [M3(CO)10(MeCN)2] (Equation 9) is accompanied by cleavage of a Te–C bond resulting in the formation of the complexes [Os3(CO)10C4H4Te] <1990CC1568> and [Ru3(CO)10C4H4Te] <1991JOM63>. (CO)3 M [M3(CO)10(MeCN)2] Δ, hexane

Te

(CO)4M Te

M = Os, Ru

ð9Þ

M (CO)3

With cyclopentadiene ruthenium p-complex [C5Me5Ru(MeCN)3](OTf), tellurophene reacts to form a stable sandwich p-complex 22 in 82% yield (Equation 10) <1998BKC706>. The 5-coordination of the tellurophene ring is confirmed by the strong high field shift of the 125Te NMR signal (107 ppm to be compared with 782 ppm signal of tellurophene). Te [C5Me5Ru(MeCN)3](OTf)

Ru+

(OTf)–

Te

22

ð10Þ

1019

1020 Tellurophenes Similar to other congeneric five-membered heterocycles, tellurophene readily forms charge-transfer complexes with tetracyanoethylene <1975JF12045>.

3.14.8 Polymerization of Tellurophene and Its Derivatives Under the action of FeCl3, tellurophene undergoes polymerization and forms powdered poly(tellurophene) <1985MI1, 2000H(52)159>. Compressed pellets of the polymer are characterized by very low conductivity (1012 S cm1 at room temperature). Doping poly(tellurophene) with iodine raises the electric conductivity to 106 S cm1. Galvanostatic polymerization of tellurophene in nitrobenzene or benzonitrile containing Me4NClO4 required a high electrical current of 1 mA and give an insoluble black powder of poly(tellurophene) <1994TL8009, 1995SM537, 2000H(S2)159>. The low conductivity of the polymer was explained by its partial decomposition under severe electrolytic conditions and relatively low degree of polymerization.

3.14.9 Ring Syntheses from Acyclic Compounds 3.14.9.1 From Acetylenes Tellurophene is obtained in low yield (3%) by reaction of powdered tellurium with acetylene in a KOH–HMPTA– H2O system (HMPTA ¼ hexamethylphosphorotriamide) <1989ZOR39>. The reaction proceeds through the intermediate formation of divinyl telluride. Heating divinyl telluride with acetylene at 420–450  C affords tellurophene in 30% yield (Equation 11) <1990MOK1201>.

420 – 450 °C (CH2=CH)2Te

ð11Þ Te

Tellurophene and its mono- and disubstituted derivatives 23 have been prepared in 10–50% yields by coupling acetylene chlorohydrins with NaHTe (Scheme 15) <1987PS119>.

RC CCR1 – CH2Cl

NaHTe

OH

RC CCR1 – CH2TeH OH

R1

AcOH/EtOH R

Te

23: R = R1 = H, Me; R = H, R1 = Me Scheme 15

Another approach to 2,4-disubstituted tellurophenes is based on the use of acetylenic chloromethyl oxiranes (Equation 12) <1988TL4923>. By coupling the oxiranes with Na2Te in aqueous methanol, 2-substituted 4-hydroxymethyltellurophenes have been prepared in 59–73% yield.

O Cl R

+ Na2Te

MeOH−H2O /−40 °C / 3 − 4 h

HOCH2

Te

23: R = H, Bu, Ph, C8H17

R

ð12Þ

Tellurophenes

The [3þ2] cycloaddition reaction of sodium phenyl ethynyl tellurolate with di(methoxy-carbonyl)acetylene affords a trisubstituted tellurophene 24 in low yield (7%) (Equation 13) <1981ZOR2064>. Ph CTeNa + MeO2CC

PhC

CO2Me

CCO2Me H

ð13Þ

CO2Me

Te

24

3.14.9.2 From 1,3-Dienes The first representative of the tellurophene family, its tetraphenyl derivative 25 was synthesized in 1961 <1961JA4406, 1963USP3151140>. The reactions of 1,4-dilithiobuta-1,3-diene with TeCl4 and 1,4-diiodobuta-1,3diene with Li2Te afford compound 25 in 56% and 82% yields, respectively (Scheme 16).

Ph Ph

Li Li

Ph

+ TeCl4

Ph

Ph

Ph

Ph I –LiI

–LiCl

Te

Ph

Ph

Ph

25

Ph

I

+ Li2Te

Ph

Scheme 16

Tetrachlorotellurophene 26 has been prepared by heating hexachlorobuta-1,3-diene with powdered tellurium (Equation 14) <1965AG260>. Cl Cl

Cl Cl

+ Te

ð14Þ

Cl

Cl

Cl

250 °C/40h Cl

Cl

Te

Cl

26

3.14.9.3 From -Chlorovinylaldehydes 2,5-Disubstituted tellurophenes 27 and 28 were prepared in 25–30% yields based on -chlorovinylaldehydes (Equations 15 and 16) <1975CR(C)187, 1975CS113, 1980J(P2)971>.

H

CHO DMF + Na2Te + CH2R

R1

Cl

X

−NaX R

Te

R

1

27 R1 = But, R = CO2Et, COMe, CHO, NO2; R = CO2Et, R1 = 4-MeOC6H4, 3-MeOC6H4

ð15Þ

1021

1022 Tellurophenes

CHO

DMF

+ Na2Te + CH2R

(CH2)n

(CH2)n

−NaX

Te

X

Cl

ð16Þ

R

28

n = 4: R = CO2Et, COMe, NO2; n = 5: R = CO2Et

With -substituted -chlorovinylaldehydes, 2,4-disubstituted tellurophenes 23 were obtained (Equation 17) <1979PS161>. Ar

Ar

CHO + Na2Te + CH2CO2Et

H

Cl

ð17Þ

−NaBr

Br

Te

CO2Et

23

3.14.9.4 From 1,3-Diynes Nucleophilic addition of sodium telluride to 1,3-diynes serves as a general method for the synthesis of 2- and 2,5disubstituted tellurophenes (Equation 18) <1966AG940, 1968BRP1107698, 1972ADC777, 1972J(P1)199, 1976SAA1089, 1976JOM183, 1990JOM301, 1995JRM2642, 1997ZFA1277, 1998OM5796>. RC

C−C

1 CR + Na2Te

MeOH(EtOH) / rt R

Te

R1

ð18Þ

R, R1 = H, Me, CH2OH, Bu, Ph, 4-MeOC6H4, 4-CF3C6H4, 2-thienyl, 3-pyridyl

One-step synthesis of tellurophene (in 15% yield) can be realized by bubbling diacetylene in the suspension of elemental tellurium in KOH-DMSO-N2H4-H2O at 0–20  C <1990MOK1197>. 2,5-Diphenyltellurophene is obtained by treatment of diethyl ditelluride with diphenyldiacetylene in N2H4– KOH–DMSO–H2O at 55  C (DMSO ¼ dimethyl sulfoxide; Scheme 17) <2002KGS280>. CPh Et 2Te 2

H

N2H4·H2O/KOH −DMSO −H2O

EtTe–

PhC

C

C

C

EtTe−

CPh

− Et2Te

H2O Ph

TeEt

CPh H

Ph

C − Te

H2O Ph

Te

Ph

Scheme 17

A preparatively convenient method for the synthesis of tellurophene is based on the use of stable and accessible 1,4-bis-(trimethylsilyl)buta-1,3-diyne (Scheme 18) <1972JOMC66, 1978CB3745>. Purification of the tellurophene product can be achieved through an oxidation–reduction (Br2/Na2SO3) cycle. The yields of pure tellurophene are in the range 53–59%.

Me3SiC

C–C

CSiMe3 + Na2Te

Br2

MeOH/rt Te

Na2SO3

Te Br

Scheme 18

Br

Tellurophenes

3.14.9.5 From 1-En-3-ynes 3-Methyltellurophene is obtained in 50% yield by a series of reactions starting from but-1-ene-3-yne (Scheme 19) <1983TL2203>.

BuLi, KOBut, LiBr HC

C

C

CH2

C

LiC

CH2

C

t

Bu OH, HMPA

Te

C

LiC

C

CH2TeLi

CH2Li

CH3

CH2

CH2

CH3 Δ

Te

Te

Scheme 19

Derivatives of tellurophene are formed <1998OM1901> in refluxing 85% formic acid solutions of 1-butyltellurobut-1-ene-3-ynes, which are readily obtained by hydrotelluration of 1,4-bis(organyl)-1,3-butadiynes (Scheme 20) <1992TL2261, 1992TL7353, 1995T9839, 2005T1613>.

Ph Ph

Te HCOOH Ph

Te

Ph

BuTe

HCOOH (R = H)

(R = Ph)

Te

Ph

R Scheme 20

By reaction with iodine, (Z)-1-(butyltelluro)but-1-ene-3-ynes afford 3-iodotellurophenes 29 in 40–90% yield (Scheme 21) <1996JOC9503, 1992TL7353, 1995T9839>.

I R

I NaBH4

I2 BuTe

R R1

R1

Te I

R

I

Te

R1

29

R = R1 = H, Me, Ph, 4-MeC6H4, 4-MeOC6H4; R = H, R1 = Ph Scheme 21

When 3 equiv of iodine was used in the reaction with (Z)-1-(butyltelluro)but-1-ene-3-ynes, 2,3-diiodotellurophene was obtained in low yield (4%) (Equation 19) <1996JOC9503>.

H

I

H

3I2 / rt / 4 h

ð19Þ BuTe

H

Te

I

1023

1024 Tellurophenes An iodine atom in position 3 can be substituted by nucleophiles, for example, by a tellurobutyl group to give 2,5diphenyl-3-butyltellurotellurophene in 72% yield (Equation 20) <1996JOC9503>.

TeBu

I THF / rt / 10 min + BuTeLi Ph

−LiI

Ph

Te

ð20Þ Ph

Te

Ph

3.14.10 Ring Synthesis by Transformation of Another Ring 3.14.10.1 From Rhodium Complexes A series of quinones containing a tellurophene moiety 30 was obtained in 10–63% yield by coupling rhodium complexes with powdered tellurium (Equation 21) <1975S265, 1975CB237>. In a similar way, the derivative 31 has been prepared (Equation 22) <1976LA1448>.

A

A

O

O + Te

R

Rh

L

L

xylene / Δ / 7–10 h −RhL2Cl

R

O

R

Cl

O

Te

R

ð21Þ

30

L = Ph3P; R = Ph, A = 1,2-phenylidene, 2,3-naphthalenilidene, 2,3-dimethyl-3,4-thiophenilidene, 2,3-benzo[b]thiophenilidene; R = 4-MeC6H4, A = 1,2-phenylidene, 2,3-naphthalenilidene

O

O + Te

Ph L

Rh L

−RhL2Cl Ph

Ph Cl

Te

Ph

ð22Þ

31 L = Ph3P

3.14.10.2 From Tellurapyranes by Ring Contraction The hydrolysis of telluropyrylium dyes under aerobic conditions leads to the contraction of the tellurapyrane ring affording merocyanines containing a tellurophene ring in 29–53% yield (Scheme 22) <1997JOC4692>.

3.14.11 Important Compounds and Applications Tetrachlorotellurophenes have been used to increase the fire resistance of hydraulic fluids <1973USP3795619>. Semiconductors derived from 3,4-disubstituted tellurophenes have been patented for use as photosensors <199OJAP(K)O241317>.

Tellurophenes

But

+ Te

But

But

Te

OH t Bu

But

H2O

O2

Te

But

OOH But

Te

But O

– H2O2

–

HO

But

But

X But

X t

Bu

But

But X

X Bu

t

t

Bu

X = S, Se, Te Scheme 22

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1025

1026 Tellurophenes

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Tellurophenes

2002KGS280 2002OM4546 2003JMT207 2004KGS974 2004OM4513 2005JMT209 2005MRC397 2005MI1 2005T1613 2005TL2647

V. A. Potapov, S. V. Amosova, and I. V. Doron’kina, Khim. Geterotsikl. Soedin., 2002, 280. M. Abe, Y. You, and M. R. Detty, Organometallics, 2002, 21, 4546. B. Jansik, B. Schimmelpfennig, P. Norman, P. Macak, H. Agren, and K. Ohta, J. Mol. Struct. Theochem, 2003, 633, 207. I. D. Sadekov and V. I. Minkin, Khim. Geterotsikl, Soedin., 2004, 974. M. Abe, M. R. Detty, O. O. Gerlits, and D. K. Sukumaran, Organometallics, 2004, 23, 4513. J. O. Jensen, J. Mol. Struct. Theochem, 2005, 718, 209. C. Ebert, T. Gianferrata, P. Linda, and P. Masotti, Magnetic Resonance in Chemistry, 2005, 22, 397. M. Urbanova, D. Pokorna, A. Ouchi, and J. Pola, J. Analyt. and Applied Pyrolysis, 2005, 73, 101. N. Petragnani and H. A. Stefani, Tetrahedron, 2005, 61, 163. G. Zeni, Tetrahedron Lett., 2005, 46, 2647.

1027

1028 Tellurophenes Biographical Sketch

Vladimir Minkin received his Candidate (Ph.D.) and Doctor of Science (Chemistry) degrees from Rostov on Don State University. In 1967, he was appointed professor at the same university, and since 1981 he has held the position of head of the Institute of Physical and Organic Chemistry. He was a visiting professor or visiting scientist at the Havana, Strathclyde, Cornell, Florida, Regensburg, and Humboldt universities, received his Dr. honoris causa degree from the university of Aix-Marseille, Rostov and Taganrog universities, and was elected a member of the Russian Academy of Sciences. Among his awards are State Prize of USSR (chemistry), Butlerov and Chugaev prizes of Russian Academy of Sciences, and Senior Humboldt Award. His research interests include quantum organic chemistry, photochemistry, stereodynamics of metal coordination compounds, new types of tautomeric rearrangements, and organotellurium chemistry.

Igor D. Sadekov was born in 1940 in Rostov on Don. After graduation from Rostov State University in 1962, he took a position of research associate in the Institute of Physical and Organic Chemistry at Rostov University and in 1976 was promoted to a position of head of laboratory of organotellurium compounds. In 1966, I. D. Sadekov got a degree of Candidate of Science (Ph.D.) and in 1982 Doctor of Science (Organic Chemistry). Since 1987, he is a professor at Rostov University. He has published more than 200 papers, including 33 review papers, in refereed journals and is the co-author of a monograph on organotellurium chemistry.