Phenylselenotris(trimethylsilyl)silane and phenyltellurotris(trimethylsilyl)silane: Versatile reagents for the preparation of phenylseleno- and phenyltelluro-formates

Article abstract of DOI:10.1039/a704402j

Phenyltellurotris(trimethylsilyl)silane 4 and (4-fluorophenyltelluro)tris(trimethylsilyl)silane 5 react with methyl, 2-methylpropyl, cyclohexyl and phenyl substituted chloroformates (7, 11, 15, 19) in benzene and in the presence of tetrakis(triphenylphosp

Full text of DOI:10.1039/a704402j

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Phenylselenotris(trimethylsilyl)silane and
phenyltellurotris(trimethylsilyl)silane: versatile reagents for the
preparation of phenylseleno- and phenyltelluro-formates
Carl H. Schiesser * and Melissa A. Skidmore
School of Chemistry, The University of Melbourne, Parkville, Victoria, Australia, 3052
Phenyltellurotris(trimethylsilyl)silane
4
and (4-fluoro-
Given the superior chromatographic properties of organo-
silanes over their tin counterparts and given the ready avail-
ability of tris(trimethylsilyl)silane for use in radical chemistry,7
we began to explore the analogous silane chemistry. Phenyl-
tellurotris(trimethylsilyl)silane 4 and (4-fluorophenyltelluro)-
tris(trimethylsilyl)silane 5 were prepared in an analogous fash-
ion to their tin counterparts. Accordingly, tris(trimethylsilyl)-
silane (1.0 equiv.) was reacted (in the dark) for 2 h with the
required (aryltelluro)cyclohexane1 (0.7 ) in benzene (80 ЊC,
AIBN initiator).‡ As was observed for stannanes (2, 3), the
tellurosilanes (4, 5) proved to be light sensitive and generally
unstable, attempted removal of the solvent resulted in rapid
decomposition. In benzene, under nitrogen and in the dark,
they appear to have an indefinite lifetime.
phenyltelluro)tris(trimethylsilyl)silane 5 react with methyl,
2-methylpropyl, cyclohexyl and phenyl substituted chloro-
formates (7, 11, 15, 19) in benzene and in the presence of
tetrakis(triphenylphosphine)palladium(0) (4 mol%) to
afford the corresponding aryltelluroformate (8, 9, 12, 13,
16, 17, 20, 21) in 50–79% yield; this procedure is also applic-
able to the preparation of (phenylseleno)formates and
seleno- and telluro-esters.
Recently, we reported that (aryltelluro)formates 1 are effective
precursors of both alkyl and oxyacyl radicals.1 Our procedure
for the preparation of 1 involves the reaction of a chlorofor-
mate with sodium aryl telluride, itself prepared by the sodium
borohydride reduction of the corresponding diaryl ditelluride in
THF. While the required telluroformates were obtained in excel-
lent yields, problems associated with adventitious oxygen and
some classes of aromatic substrate† are major drawbacks.2
Recognising that transition metal catalyzed cross-coupling
reactions are of enormous synthetic value3 and with the aim
of providing an improved procedure for the preparation
of (aryltelluro)formates, we began to explore the reactions of
several chloroformates with phenyltellurotributyltin 2 as well
as phenyltellurotris(trimethylsilyl)silane 4 and (4-fluorophenyl-
telluro)tris(trimethylsilyl)silane 5 in the presence of tetrakis-
(triphenylphospine)palladium(0) [(Ph3P)4Pd].
The tellurosilanes (4, 5) can be characterized by 1H, 13C, 29Si
and 125Te NMR spectroscopy. Specifically, 4 exhibits a singlet at
δ Ϫ192.9 in the 125Te NMR spectrum and two singlets at δ
Ϫ10.6 and Ϫ93.3 in the 29Si NMR spectrum, while 5 exhibits
singlets at δ Ϫ195.9 (125Te), δ Ϫ10.5 and Ϫ92.6 (29Si).
O
O
hν or heat
> 140 °C
(–CO2)
R•
•
RO
TeAr
RO
1
2 E = Te, Y = Bu3Sn, Ar = Ph
EAr
3 E = Te, Y = Bu3Sn, Ar = 4-FPh
4 E = Te, Y = (TMS)3Si, Ar = Ph
5 E = Te, Y = (TMS)3Si, Ar = 4-FPh
6 E = Se, Y = (TMS)3Si, Ar = Ph
YH
PhH–AIBN
YEAr
During recent studies into the reversibility of radical reac-
tions involving aryl tellurides, we had cause to prepare
phenyltellurotributyltin 2 and (4-fluorophenyltelluro)tributyltin
3.4 These compounds are not isolable, but are prepared in situ
by the reaction of the (aryltelluro)cyclohexane with tributyltin
hydride (AIBN initiator) and can be characterised by 119Sn and
125Te NMR spectroscopy.4,5 When methyl chloroformate 7 (1.0
equiv.) was introduced into a benzene solution of 2 (70 mg) in
an NMR tube and the reaction mixture allowed to stand at
room temperature overnight, or heated at 80 ЊC for four hours,
O
O
2–6
(Ph3P)4Pd
8–10, 12–14, 16–18, 20–22
RO
Cl
Z
O
Z
O
1
no reaction was observed by H, 119Sn and 125Te NMR spec-
O
MeO
O
Z
troscopy. When tetrakis(triphenylphosphine)palladium(0) (4
mol%) was added to the solution and the resultant dark red
mixture allowed to stand at room temperature for 2 h, 119Sn and
125Te NMR spectroscopy revealed the absence of 2 (125Te
δ Ϫ209.4; 119Sn δ Ϫ1.3) and the presence of methyl (phenyl-
telluro)formate1 8 (125Te δ 771.4) and minor quantities of
diphenyl ditelluride (125Te δ 420). Unfortunately, due to poor
chromatographic properties of organostannanes,6 8 proved
difficult to separate from the tin by-products; careful flash
chromatography afforded 8 in 60% yield as a yellow oil con-
taminated with small amounts of tin by-products.
7 Z = Cl
11 Z = Cl
12 Z = TePh
13 Z = Te(4-FPh)
14 Z = SePh
15 Z = Cl
16 Z = TePh
17 Z = Te(4-FPh)
18 Z = SePh
8 Z = TePh
9 Z = Te(4-FPh)
10 Z = SePh
O
Z
O
O
R
Z
19 Z = Cl
20 Z = TePh
21 Z = Te(4-FPh)
22 Z = SePh
23 Z = Cl
24 Z = TePh
25 Z = Te(4-FPh)
26 Z = SePh
† In our hands, addition of a THF solution of phenyl chloroformate to
a colourless solution of sodium phenyl telluride in the usual way (see
ref. 1) resulted in rapid formation of the (characteristic) red diphenyl
ditelluride solution. Consequently, we were unable to prepare the
(aryltelluro)formates (20, 21) derived from phenyl chloroformate. The
details of the chemistry involved are unclear.
‡ The quality of the glassware is crucial to the success of this reaction.
The results quoted in Table 1 were obtained when reactions were carried
out in high-quality borosilicate NMR tubes. We were unable to prepare
4 or 5 in ‘ordinary’ Pyrex glassware and are currently examining this
result further.
J. Chem. Soc., Perkin Trans. 1, 1997
2689

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Table 1 Reactions of some chloroformates and acid chlorides with phenyltellurotributyltin 2 and arylchalcogenotris(trimethylsilyl)silanes (4, 5, 6)
in the presence of catalytic tetrakis(triphenylphosphine)palladium(0)
Substrate
Reagent
Product
t/h (T/ЊC)
Yield (%)
δ(ppm)
Ref.
1
7
7
7
7
11
11
11
15
15
15
19
19
2
4
5
6
4
5
6
4
5
6
4
5
6
4
5
6
8
8
9
10
12
13
14
16
17
18
20
21
2 (25)
2 (25)
2 (25)
16 (25)
8 (25)
8 (25)
60a
79
71
87
61
77
83
72
72
83
64
51
72
59
87
81
771.4 (125Te)
765.3 (125Te)
506.3 (77Se)
768.9 (125Te)
760.3 (125Te)
505.2 (77Se)
771.6 (125Te)
769.9 (125Te)
509.3 (77Se)
793.7 (125Te)
789.9 (125Te)
514.7 (77Se)
975.7 (125Te)
930.3 (125Te)
634.6 (77Se)
1
1
1
1
1
1
1
1
b
b
b
b
9
10
7 (40)
16 (25)
16 (25)
16 (40)
16 (25)
16 (25)
16 (40)
2 (25)
19
22
23 (R = Me)
23 (R = Ph)
23 (R = Ph)
24 (R = Me)
25 (R = Ph)
26 (R = Ph)
16 (25)
16 (25)
a
Contaminated with stannane residues (see text). b This work.
When the previously-prepared solution of 4 was reacted with
performed in a darkened environment with the column
wrapped in aluminium foil. Under these conditions, 24 (R = Me)
and 25 (R = Ph) were isolated in 59 and 87% respectively.
When benzoyl chloride was reacted with phenylselenotris-
(trimethylsilyl)silane 6 and (Ph3P)4Pd under the previously
described reaction conditions, Se-phenyl selenobenzoate (25:
R = Ph) was isolated in 81% yield after flash chromatography.
In conclusion, we have demonstrated that phenyltelluro-
tris(trimethylsilyl)silane 4 and (4-fluorophenyltelluro)tris(tri-
methylsilyl)silane 5 are effective reagents for the palladium-
catalyzed preparation of (phenyltelluro)formates and [(4-
fluorophenyl)telluro]formates respectively. These reagents have
the advantage over their tin counterparts (2, 3) in that simple
flash chromatography affords pure compounds in good yield.
This protocol is also amenable to the preparation of seleno-
and telluro-esters (24–26) which were obtained from the corre-
sponding acid chloride in good yields.
methyl chloroformate 7 (1.0 equiv.) and tetrakis(triphenyl-
phosphine)palladium(0) (4 mol%) and the dark red mixture
allowed to stand for 2 h, 125Te NMR spectroscopy revealed the
absence of 4 and the presence of methyl (phenyltelluro)formate
8 and small amounts of diphenyl ditelluride, while 29Si NMR
spectroscopy revealed two signals which we have assigned to
chlorotris(trimethylsilyl)silane (δ 1.9, Ϫ11.3) by comparison
with other chlorosilanes.8 Simple flash chromatography
afforded 8 in 79% yield and free from contamination. Similarly,
reaction of 5 with 7 and (Ph3P)4Pd afforded methyl [(4-
fluorophenyl)telluro]formate 1 9 which was isolated in 71% yield
as a yellow oil after flash chromatography.
To our delight, application of this methodology to a repre-
sentative set of primary, secondary and aromatic chlorofor-
mates afforded the corresponding telluroformates in 51–79%
yield (Table 1). Importantly, phenyl (phenyltelluro)formate
20 and phenyl [(4-fluorophenyl)telluro]formate 21 were able to
be isolated in 64 and 51% yield respectively following this
procedure.§ All reactions were carried out at 25 ЊC (room
temperature) with reaction times, as determined by 125Te NMR
spectoscopy, varying from 2 to 16 h depending on the alkyl
substituent.
When phenyltellurotris(trimethylsilyl)silane 4 was replaced
with phenylselenotris(trimethylsilyl)silane 6, itself prepared by
the reaction of phenylselenocyclohexane1 with tris(trimethyl-
silyl)silane under standard conditions, methyl, primary,
secondary and phenyl selenoformates (10, 14, 18, 22, 25) could
be isolated in 72–87% yield. These reactions appear to be slower
than their tellurium counterparts; elevated temperatures (40 ЊC)
were required for complete conversion of most substrates in a
16 h time frame.
This protocol was also successfully applied to the preparation
of telluro- and seleno-esters. 125Te NMR Spectroscopy revealed
that acetyl chloride (23: R = Me) and benzoyl chloride (23:
R = Ph) react with 4 and 5 to give products consistent with
Te-phenyl telluroacetate (24: R = Me) (125Te, δ 975.7) and Te-(4-
fluorophenyl) tellurobenzoate (25: R = Ph) (125Te, δ 930.3).10
These telluroesters proved to be substantially more light sen-
sitive than the corresponding telluroformates. While back-
ground light proved not to be problematic during chromato-
graphic purification of the telluroformates, acceptable yields
of 24 and 25 could only be obtained by chromatography
We are further examining the synthetic utility of these
chalcogenosilanes.
Acknowledgements
We thank the Australian Research Council for financial support
and an Australian Postgraduate Award to M. A. S.
References
1 M. A. Lucas and C. H. Schiesser, J. Org. Chem., 1996, 61, 5754.
2 C. H. Schiesser and L. M. Zugaro, unpublished work.
3 R. F. Heck in Palladium Reagents in Organic Synthesis, Academic
Press, London, 1985; V. N. Kalinin, Synthesis, 1992, 413.
4 C. H. Schiesser and M. A. Skidmore, Chem. Commun., 1996, 1419.
5 B. Wrackmeyer, Annu. Rep. NMR Spectrosc., 1985, 16, 73.
6 D. Crich and S. Sun, J. Org. Chem., 1996, 61, 7200.
7 C. Chatgilialoglu, D. Griller and M. Lasage, J. Org. Chem., 1988, 53,
3641; M. Ballestri, C. Chatgilialoglu, K. B. Clark, D. Griller,
B. Giese and B. Kopping, J. Org. Chem., 1991, 56, 678.
8 E. A. Williams, Annu. Rep. NMR Spectrosc., 1983, 15, 235.
9 D. Crich, C. Chen, J.-T. Hwang, H. Yuan, A. Papadatos and
R. I. Walter, J. Am. Chem. Soc., 1994, 116, 8937.
10 G. P. Mullen, N. P. Luthra, R. B. Dunlap and J. Odom, J. Org.
Chem., 1985, 50, 811.
Paper 7/04402J
Received 23rd June 1997
Accepted 10th July 1997
§ All new compounds gave satisfactory NMR and mass spectral data.
2690
J. Chem. Soc., Perkin Trans. 1, 1997