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Chemistry Letters Vol.36, No.8 (2007)
Synthesis, Structure, and Properties of Three- and Six-Membered Metallacycles
Composed of Iron, Germanium, and Sulfur Atoms
Masaaki Okazaki,1 Hiromitsu Kimura,2 Takashi Komuro,2 Hiroshi Okada,2 and Hiromi TobitaÃ2
1International Research Center for Elements Science, Institute for Chemical Research,
Kyoto University, Uji, Kyoto 611-0011
2Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578
(Received May 22, 2007; CL-070551; E-mail: tobita@mail.tains.tohoku.ac.jp)
Ultraviolet irradiation of CpÃ(CO)2FeGeMe2SPh in the
yield. A large-scale experiment allowed the isolation of 3a as
presence of acetone afforded trans-[CpÃFe(CO){ꢀ-ꢁ2Ge,
S-GeMe2SPh}]2, while the introduction of a bulkier substituent
on the sulfur atom allowed selective formation of the three-
membered metallacycle CpÃ(CO)Fe{ꢁ2Ge,S-GeMe2SMes}
(Mes = 2,4,6-C6H2Me3).
brown crystals in 25% yield. The molecular structure of 3a is
depicted in Figure 1.5 Complex 3a contains an unprecedented
Fe2Ge2S2 six-membered ring, in which the conformation is
best described as a twisted boat. The two Cpà ligands are in
a mutually trans relationship. The most striking feature of
3a is the exceptionally long Ge–S bonds (2.3919(19) and
˚
˚
2.379(2) A), which are longer than that of 1a (2.2850(7) A) by
˚
0.1 A, and much longer than typical Ge–S bond lengths (2.16–
˚
2.30 A). This lengthening is likely to be attributable to steric
Three-membered metallacycles composed of one transition
metal and two main-group typical elements have attracted much
attention in view of their unique bonding modes, strained molec-
ular structures, and novel reactivities.1–4 Recently, we reported
that photolysis of CpÃ(CO)2FeSiMe2TePh in the presence of
acetone afforded CpÃ(CO)Fe{ꢁ2Si,Te-SiMe2OCMe2TePh}.3
The reaction can be explained by the insertion of acetone into
the silicon–tellurium bond of the transient three-membered
metallacycle CpÃ(CO)Fe{ꢁ2Si,Te-SiMe2TePh}. Attempts to iso-
late the three-membered metallacyle failed due to its instability.
Tilley et al. succeeded in the synthesis and X-ray characteriza-
tion of [CpÃ(Me3P)Ir{ꢁ2Si,S-Si(StBu)2StBu}](OTf).4 We report
here the photochemistry of CpÃ(CO)2FeGeMe2SAr, leading
to the formation of two novel metallacycles, trans-[CpÃFe(CO)-
{ꢀ-ꢁ2Ge,S-GeMe2SPh}]2 and CpÃ(CO)Fe{ꢁ2Ge,S-GeMe2SAr}
[Ar = Ph, 2,4,6-C6H2Me3 (Mes)], depending on the substituents
on the sulfur atom.
At À45 ꢀC, a THF solution of CpÃ(CO)2FeGeMe2Cl was
treated with NaSAr [Ar = Ph, 2,4,6-C6H2Me3 (Mes)], which
was freshly prepared by the reaction of ArSH and NaH in
THF. Workup of the reaction mixture and recrystallization of
the residue afforded yellow crystals of CpÃ(CO)2FeGeMe2SAr
in moderate yields [Ar = Ph (1a, 70%), Mes (1b, 55%)].
Elemental analysis, spectroscopic data, and X-ray diffraction
studies5 confirm the formation of 1.
6
repulsion between the phenyl groups on S and the methyl
groups on Ge; the interatomic distances of C3ÁÁÁC13 (3.126(11)
˚
˚
A) and C5ÁÁÁC7 (3.490(12) A) are significantly shorter than the
˚
sum (3.7 A) of the effective van der Waals radii of the methyl
˚
groups (2.0 A) and the half-thickness of the phenyl ꢃ-electron
˚
clouds (1.7 A). In contrast to 3a, related six-membered metalla-
cycles Fe2Si2P2 are known to exist as a mixture of twisted boat
and chair forms.2a
The 1H NMR spectrum of 3a exhibits three singlet signals at
ꢄ 0.77 (6H, GeMe), 1.23 (6H, GeMe), and 1.30 (30H, CpÃ). A
significant low-energy shift is observed in ꢅCO (1896 cmÀ1
)
compared with 1a (1925, 1979 cmÀ1), which is consistent with
the replacement of a carbonyl ligand with a more electron-donat-
ing SPh moiety.
Introduction of a bulkier substituent on the sulfur atom al-
lowed selective formation of the three-membered metallacycle
CpÃ(CO)Fe{ꢁ2Ge,S-GeMe2SMes} (2b) as green crystals in
72% isolated yield (eq 2). Formation of the corresponding six-
membered Fe2Ge2S2 metallacycle was not observed throughout
the reaction even in the presence of acetone probably due to the
steric reason. The 1H NMR spectrum of 2b exhibits singlet sig-
nals at ꢄ 0.36 (3H, GeMe), 1.14 (s, 3H, GeMe), 1.68 (15H, CpÃ),
2.01 (3H, p-ArMe), 2.53 (6H, o-ArMe), and 6.71 (2H, m-ArH),
supporting the formation of a three-membered metallacycle. The
Ultraviolet (ꢂ > 300 nm) irradiation of 1a in benzene-d6
gave a mixture of CpÃ(CO)Fe{ꢁ2Ge,S-GeMe2SPh} (2a) and
trans-[CpÃFe(CO){ꢀ-ꢁ2Ge,S-GeMe2SPh}]2 (3a) (eq 1). The
formation yields of 2a and 3a achieved maxima after 1.5 min
(2a, 56%) and 4 min (3a, 29%), respectively. Further irradiation
resulted in decomposition of 2a and 3a, giving several unidenti-
fied products. It was difficult to isolate 2a and 3a from the
reaction mixture.
IR spectrum shows a ꢅCO band at 1900 cmÀ1
.
(1)
Irradiation of a benzene-d6 solution of 1a in the presence of
acetone suppressed the formation of 2a, giving 3a in 51% NMR
Figure 1. ORTEP drawing of 3a with 30% thermal ellipsoids.
Copyright Ó 2007 The Chemical Society of Japan
Okazaki, Masaaki
