Transmetallation reaction of 1-phenylthio-or 1-tolylthio-2-(2,4,6-tri-t-butylphenyl)-2-phosphaethenyllithium with copper(II) and mercury(II)

Article abstract of DOI:10.1246/cl.2000.1390

Transmetallation of bulky 1-arylthio-2-(2,4,6-tri-t-butylphenyl)-2-phosphaethenyllithiums with copper(II) and mercury(II) afforded the corresponding 1,4-diphospha-1,3-butadiene derivatives as homocoupled products and organomercury compounds, respectively, which were analyzed by X-ray crystallography.

Full text of DOI:10.1246/cl.2000.1390

1390
Chemistry Letters 2000
Transmetallation Reaction of 1-Phenylthio- or 1-Tolylthio-2-(2,4,6-tri-t-butylphenyl)-2-
phosphaethenyllithium with Copper(II) and Mercury(II)
Shigekazu Ito and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578
(Received September 21, 2000; CL-000876)
(Z-3b) in THF].6 The interaction between Li and the lone-pair
electrons of P and S in 1 has been discussed for the stability of
Z-isomers.4 The structure of Z-3a was confirmed by X-ray
crystallography,7 and Figure 1 displays a drawing of the molec-
ular structure of Z-3a indicating the P=C skeleton [1.655(4) Å]
in Z-configuration and the repelled phenylthio group from the
Mes* group [P1–C1–S1 129.4(3)°].
Transmetallation of bulky 1-arylthio-2-(2,4,6-tri-t-butylphenyl)-
2-phosphaethenyllithiums with copper(II) and mercury(II)
afforded the corresponding 1,4-diphospha-1,3-butadiene deriva-
tives as homocoupled products and organomercury compounds,
respectively, which were analyzed by X-ray crystallography.
Kinetic stabilization with bulky substituent(s) has been
widely used for study on multiple bonds of heavier main group
elements, and various types of unsaturated bonds containing
phosphorus have been reported.1 We have been interested in
the compounds containing phosphorus–carbon multiple bond(s)
kinetically stabilized with the 2,4,6-tri-t-butylphenyl (hereafter
abbreviated to the Mes*) group(s).2 Previously, we have
reported the preparation and some reactions of 1-phenylthio-2-
(2,4,6-tri-t-butylphenyl)-2-phosphaethenyllithium (1a) as one
of the phosphanylidene carbenoids2,3 to show the effects of sul-
fur atom on the stability of Z-isomer.4
In the course of our study, we found that the transmetalla-
tion reaction of phosphanylidene carbenoids with copper
through the oxidative coupling is a powerful method to con-
struct a conjugated system with phosphorus–carbon double
bonds.5 Thus transmetallation is useful not only for preparation
of organometallic compounds but also for organic synthesis.
Here we report the transmetallation of 1-arylthio-2-(2,4,6-tri-t-
butylphenyl)-2-phosphaethenyllithium (1; aryl = Ph, Tol) with
copper(II) and mercury(II) giving the corresponding coupling
products and organomercury compounds.
Next we performed the transmetallation for the thio-derived
phosphaethenyllithiums 1 with copper(II). Phosphaethenyl-
lithiums 1, derived from 2 and butyllithium, were allowed to
react with copper(II) chloride and oxygen at –78 °C in THF to
afford the 1,4-diphospha-1,3-butadienes 4 in the yields of 84%
(4a) and 38% (4b), respectively, as yellow crystals indicating
the extended π-conjugation (Scheme 2).8 The s-cis conformation
in 4a4 and 4b9 has been confirmed by X-ray crystallographic
analyses. Figure 2 displays the structure of 4b.9,10 The
P=C–C=P planes are twisted with the torsion angles of 38.5°
(4a) and 38.3° (4b), respectively. On the contrary, 2,3-dichloro-
1,4-bis(2,4,6-tri-t-butylphenyl)-1,4-diphospha-1,3-butadiene was
planar with s-trans conformation.5a We expect the intramolecu-
lar electronic interaction between the σ-orbital of C–S bond and
the σ*-orbital of P–C bond for the reason for taking the s-cis con-
formation.11 The twisted conformation of 4 might be due to the
repulsion of the lone pairs of phosphorus atoms. A similar
"screw-type" structure was reported for 2-trimethylsilyl-1,4-bis-
(2,4,6-tri-t-butylphenyl)-1,4-diphospha-1,3-butadiene, indicating
the stereoelectronic effect between the σ-orbital of C–Si or C–H
bond and the σ*-orbital of P–C bond.12
Moreover we examined the transmetallation of phospha-
ethenyllithiums 1a and 1b with mercury(II). Phosphaethenyl-
lithiums 1 were treated with 0.5 equivalent amount of mercu-
ry(II) chloride in THF to afford the corresponding organomer-
cury compounds 5a (79% yield) and 5b (60% yield), respec-
tively, as colorless crystals (Scheme 2).8 The structures of 5
were characterized by means of spectroscopic data. Large 1JHgP
values are similar to those of the hydrogen-derivative (E,E)-
mercuriobis[methylene(2,4,6-tri-t-butylphenyl)phosphane]
2-Arylthio-2-bromo-1-(2,4,6-tri-t-butylphenyl)-1-phospha-
ethenes 2, prepared from 1-bromo-2-(2,4,6-tri-t-butylphenyl)-2-
phosphaethenyllithium and diaryl disulfides, were allowed to
react with butyllithium to afford the corresponding phos-
phaethenyllithiums 1. During the process of preparation of 1,
the E/Z isomerization was observed even at –100 °C in THF,
and the Z-isomers (Z-1) were predominantly formed to afford
phosphaethenes Z-3 after quenching of the reaction mixture
with methanol (ca. E:Z = 1:10; Scheme 1). The phos-
phaethenyl-lithiums 1 are stable at 25 °C due to carbanion-sta-
bilizing effect of the thio groups. In the 31P NMR spectra, the
higher chemical shifts were observed for 1 compared to phos-
phaethenes 3 [δP = 188.5 (1a), 185.6 (1b); 218.8 (Z-3a), 221.7
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1391
the mercury atom, with the shortest distance to C-ipso [3.242(5)
Å] and its ortho carbons [3.56(1) and 3.85(1) Å]. A similar
coordination was also observed for (Z,Z)-5H, where the Mes*
rings interact with the mercury atom.14 In contrast to 4, influ-
ential electronic effect is not obvious on the molecular struc-
ture, and each substituent locates to avoid steric congestion.
This work was supported in part by a Scientific Grant-in-
Aid (No. 09239104) from the Ministry of Education, Science,
Sports and Culture of Japan.
References and Notes
1
a) K. B. Dillon, F. Mathey, and J. F. Nixon, "Phosphorus: The
Carbon Copy," John Wiley & Sons, Chichester (1998). b) M.
Regitz and O. J. Scherer, "Multiple Bonds and Low Coordination
in Phosphorus Chemistry," Georg Thieme Verlag, Stuttgart
(1990).
2
3
M. Yoshifuji, J. Chem. Soc., Dalton Trans., 1998, 3343.
a) S. Ito, K. Toyota, and M. Yoshifuji, Phosphorus, Sulfur, and
Silicon, 147, 1269 (1999). b) M. Yoshifuji, T. Niitsu, and N.
Inamoto, Chem. Lett., 1988, 1733. c) M. Yoshifuji, H.
Kawanami, Y. Kawai, K. Toyota, M. Yasunami, T. Niitsu, and N.
Inamoto, Chem. Lett., 1992, 1053. d) S. Ito, K. Toyota, and M.
Yoshifuji, Chem. Commun., 1997, 1637.
4
5
S. Ito and M. Yoshifuji, Chem. Lett., 1998, 651.
a) S. Ito, K. Toyota, and M. Yoshifuji, Chem. Lett., 1995, 747. b)
S. Ito, K. Toyota, and M. Yoshifuji, J. Organomet. Chem., 553,
135 (1998).
1
6
7
8
Selected NMR data: Z-3b: H NMR (200 MHz, CDCl3) δ = 7.80
2
(1H, d, JPH = 35.3 Hz, P=CH); 31P NMR (81 MHz, CDCl3) δ =
1
221.7 (2JPH = 35.3 Hz); E-3b: H NMR (200 MHz, CDCl3) δ =
7.81 (1H, d, 2JPH = 22.0 Hz, P=CH); 31P NMR (81 MHz, CDCl3)
δ = 233.1 (2JPH = 22.0 Hz).
Crystal data: Z-3a: C25H35PS, fw = 398.59, orthorhombic,
P212121 (#19), a = 10.682(2), b = 23.699(10), c = 9.485(2) Å, V =
2401(1) Å3, Z = 4, dcalc = 1.103 g·cm–3, temperature 288 K. R =
0.040 for 1740 independent reflections [θ < 25.07, I > 3.00σ(I)],
S = 1.11 for 280 parameters (CCDC 151316).
Selected physical data: 4a: mp 200 – 203 °C (decomp); 13C{1H}
1
2
[(E,E)-5H].13 Gratifyingly, compound 5a afforded a suitable
crystal for X-ray analysis and the molecular structure is dis-
played in Figure 3.9 The straight skeleton (C–Hg–C) is charac-
teristic for a mercury(II) compound, and all of the aryl moieties
locate perpendicularly to the plane [P–C(–S)–Hg–C(–S)–P].
The C–Hg length is 2.058(4) Å, which is similar to (Z,Z)-5H
(2.042 and 2.079 Å).13 The P=C length is 1.680(5) Å, which is
slightly longer than that for (Z,Z)-5H (1.644 and 1.643 Å),13
probably due to electronic effect of sulfur atoms. There are no
remarkable interactions between the lone pairs of sulfur or
phosphorus and mercury. On the other hand, non-covalent
interaction between the aromatic rings of phenylthio groups and
mercury was observed. That is, the phenyl ring locates above
NMR (50 MHz, CDCl3) δ = 173.4 (dd, JPC = 12.8 Hz, JPC = 7.8
Hz, P=C); 31P{1H} NMR (81 MHz, CDCl3)δ = 238.6; UV (hexa-
ne)λmax (log ε) 255 (4.39), 336 (4.31), and 424 nm (3.84); 4b: mp
207–208 °C (decomp); 13C{1H} NMR (50 MHz, CDCl3) δ =
1
2
174.0 (dd, JPC = 12.6 Hz, JPC = 8.8 Hz, P=C); 31P{1H} NMR
(81 MHz, CDCl3) δ = 237.6; UV (hexane) λmax (log ε) 336 (4.28)
and 419 nm (3.81); 5a: mp 178–180 °C; 13C{1H} NMR (50
MHz, CDCl3) δ = 211.1 (dd, 1JPC = 84.3 Hz, 3JPC = 5.0 Hz, P=C);
31P{1H} NMR (81 MHz, CDCl3) δ = 231.2 (1JHgP = 866 Hz);5b:
mp 165–167 °C; 13C{1H} NMR (50 MHz, CDCl3) δ = 211.6 (dd,
3
1JPC = 84.7 Hz, JPC = 5.0 Hz, P=C); 31P{1H} NMR (81 MHz,
CDCl3) δ = 230.0 (1JHgP = 870 Hz).
–
9
Crystal data: 4b: C52H72P2S2, fw = 823.21, triclinic, P1 (#2), a =
16.191(5), b = 17.18(2), c = 9.791(5) Å, α = 97.78(7), β =
95.90(4), γ = 68.60(6)°, V = 2507(3) Å3, Z = 2, dcalc = 1.090
g·cm–3, temperature 288 K. R = 0.085 for 2304 independent
reflections [θ < 25.08, I > 3.00σ(I)], S = 1.98 for 503 parameters
–
(CCDC 151317). 5a: C50H68HgP2S2, fw = 995.74, triclinic, P1
(#2), a = 10.097(2), b = 16.318(4), c = 8.351(8) Å, α = 99.64(4),
β = 114.11(4), γ = 79.38(2)°, V = 1227(1) Å3, Z = 2, dcalc = 2.693
g·cm–3, temperature 288 K. R = 0.043 for 3958 independent
reflections [θ < 25.13, I > 3.00σ(I)], S = 1.56 for 250 parameters
(CCDC 151318).
10 An X-ray structure determination of 4b at low temperature (150
K) failed to give better results.
11 A. J. Kirby, "Stereoelectronic Effects," Oxford University Press,
Oxford (1996).
12 E. Niecke, A. Fuchs, and M. Nieger, Angew. Chem., Int. Ed., 38,
3028 (1999).
13 S. J. Goede, H. P. van Schaik, and F. Bickelhaupt,
Organometallics, 11, 3844 (1992).
14 G.-J. M. Gruter, G. P. M. van Klink, O. S. Akkerman, and F.
Bickelhaupt, Chem. Rev., 95, 2405 (1995).