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Chemistry Letters Vol.37, No.1 (2008)
Studies of Germanium–Platinum Bonds in Bis(aryl-substituted Germyl)platinum Complexes
by Laser Flash Photolysis and Chemical Trapping Experiments
Kunio Mochida,ꢀ1 Yusuke Masukawa,1 Atsuko Yamada,1 Mai Yanaga,1 Masato Nanjo,1
Hidekazu Arii,1 Masao Gohdo,2 and Masanobu Wakasa2
1Department of Chemistry, Faculty of Science, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588
2Department of Chemsitry, Graduate School of Science & Engineering, Saitama University,
255 Shimo-ohkubo, Sakura-ku, Saitama 338-8570
(Received October 1, 2007; CL-071093; E-mail: kuniomochida@gakushuin.ac.jp)
The UV photolysis of bis(triaryl-substituted germyl)plati-
num complexes, Pt(Ar3Ge)2(PMe2Ph)2 (Ar = Ph, p-C6H4-
SiMe3, and p-C6H4C(CH3)3) in THF at room temperature results
in Ge–Pt bonds homolysis to give the corresponding germyl
radicals.
Bis(silyl)- and bis(germyl)platinum(II) complexes are im-
portant intermediates in Pt-catalyzed synthetic reactions such
as the bis-silylation and bis-germylation of C–C triple and dou-
ble bonds and dehydrocoupling of group 14 element com-
pounds.1–4 These complexes also act as useful starting materials
for group 14 element-containing compounds. Previously,5 we
reported on photoinduced trans–cis isomerization of trans-
bis(germyl)platinum(II) at room temperature by irradiation with
a xenon lamp (hꢀ > 450 nm). As a part of our continuous study
on germanium–transition metal bond, we have studied photo-
chemical reactions of bis(triaryl-substituted germyl)platinum(II)
complexes, Pt(Ar3Ge)2(PMe2Ph)2 (Ar = Ph (1),6 p-C6H4SiMe3
(2),7 and p-C6H4C(CH3)3 (3)8) by laser flash photolysis and
chemical trapping experiments.
Figure 1. Transient absorption spectrum observed at 1 ms after
photoexcitation of 1 (10ꢁ4 M) in degassed THF solution. Insert;
AðtÞ curve observed at 330 nm.
Nanosecond laser flash photolysis9 was performed on
degassed solutions containing Pt(Ph3Ge)2(PMe2Ph)2 (1) (ca.
10ꢁ4 M) in THF at 298 K using the fourth-harmonic pulse of
a nanosecond Nd:YAG laser as the exciting light source
(ꢁ ¼ 266 nm).
The time profile of the transient absorption, AðtÞ, was meas-
ured with THF solutions containing 1. The AðtÞ curves were
measured over the 300–600-nm wavelength region. The time
resolution of the apparatus was about 10 ns. Transient absorption
spectra with a peak at 330 nm were obtained (Figure 1). The tran-
sient peak at 330 nm decayed under second-order kinetics
(k="l ¼ 8:0 ꢂ 105 at 330 nm) as is shown in Figure 1. Here,
k is the rate constant for the second-order decay, " is the molar
extinction coefficient, and l is optical path length, l ¼ 0:5 cm)
The peak at 330 nm is further substantiated by quenching
experiments with germyl radical trapping agents. The pseudo
first-order rate constants (kobsd) for decay depended linearly on
the concentrations of such trapping agents (Figure 2). The rate
constants for the disappearance of the transient at 330 nm ob-
tained for these quenching experiments (oxygen, chloroform,
and ethanol) were 1:7 ꢂ 109, 0:8 ꢂ 107 Mꢁ1 sꢁ1, and not
quenched, respectively.
Figure 2. Quenching rate constants for the disappearance at
330 nm in 1 containing various concentrations of chloroform.
Laser flash photolysis studies of 2 and 3 were also carried
out. Transient peaks observed and their experimentally deter-
mined rate constants are summarized in Table 1.
Along with laser flash photolysis experiments, product stud-
ies were carried out by photolyzing 1 (0.04 M) with a 110-W me-
dium-pressure Hg arc lamp at room temperature for 30 min un-
der argon in THF. The photolysis of 1 containing chloroform11
as a germyl radical trapping reagent gave triphenylchloroger-
mane in 84% yield together with tetrachloroethane (35% yield).
The experimentally determined decay constants of 1 are
summarized in Table 1. The transient absorption at 330 nm is
reasonably assigned to that of the triphenylgermyl radical
Ph3Geꢃ from comparison of spectral characteristics with those
of the germyl radical reported.10
Copyright ꢀ 2008 The Chemical Society of Japan
Mochida, Kunio
