Stereoselective formation of phenylthio groups substituted 1-metalla-3-titanacyclobutanes

Article abstract of DOI:10.1016/j.jorganchem.2010.09.080

Desulfurizative titanation of group 14 metal compounds bearing two or four bis(phenylthio)methyl groups with the low-valent titanium reagent Cp ₂Ti[P(OEt)₃]₂ produced phenylthio groups substituted 1-metalla-3-titanacyclobu

Full text of DOI:10.1016/j.jorganchem.2010.09.080

Journal of Organometallic Chemistry 696 (2011) 581e585
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Stereoselective formation of phenylthio groups substituted
1-metalla-3-titanacyclobutanes
*
Shigeki Oishi, Akira Tsubouchi, Takeshi Takeda
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Desulfurizative titanation of group 14 metal compounds bearing two or four bis(phenylthio)methyl
groups with the low-valent titanium reagent Cp2Ti[P(OEt)3]2 produced phenylthio groups substituted
1-metalla-3-titanacyclobutanes stereoselectively. The molecular structures of the titanacycles were
unambiguously confirmed by X-ray diffraction analysis.
Received 23 August 2010
Received in revised form
9 September 2010
Accepted 10 September 2010
Available online 14 October 2010
Ó 2010 Elsevier B.V. All rights reserved.
Keywords:
1-Metalla-3-titanacyclobutane
Titanocene(II)
Thioacetal
Reductive titanation
1. Introduction
with a low-valent titanium reagent [5]. The result prompted us to
investigate the preparation of phenylthio groups substituted 1-sila
The chemistry of 1,3-dimetallacyclobutanes has been studied
over the past several decades. For example, the formation and
degradation of 1,3-disilacyclobutanes and their germanium
analogues have been extensively investigated [1]. Relating to the
chemistry of titanacyclobutanes which are useful precursors of
titaniumecarbene complexes [2] and intermediates of olefin
metathesis [3], the characteristic property and reactivity of 1-sila
and germa-3-titanacyclobutanes are attractive subjects of research
[4]. These metallacycles have been prepared by the treatment of
titanocene(IV) dihalides with silicon-containing magnesacyclic
reagents [4a,e,f], the reaction of 1,3-di-Grignard reagents, gener-
ated from methylenedimagnesium dibromide and titanocene(IV)
dichloride, with polychlorosilanes [4bed,g] and the reaction of 1,3-
dilithio-2,2-dimethyl-2-silapropane with titanocene(IV) dichloride
[4h]. To the best of our knowledge, however, the preparation of
1-sila and germa-3-titanacyclobutanes having substituents on their
rings has not appeared in literatures yet.
and germa-3-titanacyclobutanes 1 by the treatment of correspond-
ing group 14 metal compounds bearing two or four bis(phenylthio)
methyl groups 2 with Cp2Ti[P(OEt)3]2 3 (Scheme 1).
2. Results and discussion
The starting multithioacetals 2aec were readily prepared by
the reaction of bis(phenylthio)methyllithium with diorganodi-
chlorosilanes and tetrachlorosilane (2a; 83%, 2b; 76%, 2c; 63%).
Tetrakis[bis(phenylthio)methyl]germane (2d) was also obtained by
the similar reaction using tetrachlorogermane in 65% yield. The
reaction of bisthioacetals 2a and 2b with Cp2Ti[P(OEt)3]2 3 (4 equiv)
in THF at 25 ꢀC for 2 h followed by the treatment with an excess
amount of AcOH produced the bis(phenylthiomethyl)silanes 4a and
4b, respectively (Table 1, Entries 1 and 2). The similar treatment of
the tetrakisthioacetal 2c gave tetrakis(phenylthiomethyl)silane (4c)
in good yield (Entry 3). The germanium analogue 4d was also
obtained by the reaction of 2d with the titanocene(II) species 3 after
quenching the reaction with AcOH (Entry 4).
The formation of multisulfides 4 suggests that the titanacycles 1
are generated by the desulfurizative titanation of multithioacetals 2
with 3. Indeed, the di- and tetradeuterated multisulfides d-4 were
produced when the reaction was quenched with excess AcOD. Then
the isolation of titanacyclobutanes 1 was examined. After the
treatment of bisthioacetal 2b with the titanocene(II) species 3, the
reaction mixture was subjected to alumina column chromatography
During the course of the study on the preparation of multi(tita-
niumecarbene) complexes and their application to the construction
of extended p-conjugation systems, we found that the benzotitana-
cyclopentane bearing two phenylthio groups was produced by the
desulfurizative titanation of 1,2-bis[bis(phenylthio)methyl]benzene
* Corresponding author. Tel./fax: þ81 42 388 7034.
E-mail address: takeda-t@cc.tuat.ac.jp (T. Takeda).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.09.080

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S. Oishi et al. / Journal of Organometallic Chemistry 696 (2011) 581e585
Table 2
Isolation of titanacycles 1.
SPh
TiCp2
–
(4 n) Cp2Ti[P(OEt)3]2
3
2
Rn M
–
(4 n)/2
THF, 25 °C, 2 h
M = Si, Ge
(n = 0, 2)
SPh
1
Scheme 1. Formation of 1-metalla-3-titanacyclobutanes 1.
under N2 to give the 1-sila-3-titanacyclobutane 1b as a purple
powder in 43% yield (Table 2, Entry 1). The NMR signals of Cp rings
of 1b occurred as three singlets at 6.20, 6.28 and 6.35 ppm, sug-
gesting the formation of two possible stereoisomers with a ratio of
74:26. Since the Cp signal of major stereoisomer appeared as one
signal at 6.20 ppm, its configuration was assigned to be trans. The
stereochemistry of the major isomer of 1b was further elucidated by
X-ray diffraction analysis and its ORTEP drawing unambiguously
confirmed our assumption (Fig. 1).
In contrast, the silicon and germanium-centered spiro-metal-
lacycles 1c and 1d obtained by the desulfurizative titanation of
tetrakis[bis(phenylthio)methyl]silane and germane (2c and 2d)
(Table 2, Entries 2 and 3) showed their four Cp rings as one singlet
Entry
Multithioacetal 2
Metallacycle 1 (Yield/%)a
SPh
Ph
Si TiCp2
Ph
1
2b
SPh
1b
(43)b
PhS SPh
Cp2Ti
Si TiCp2
2
2c
PhS SPh
1c
Table 1
(73)c
Formation and following protonation of titanacycles 1.
PhS SPh
–
1) (4 n) Cp2Ti[P(OEt)3]2 3 / THF, 25 °C, 2 h
H
2
Rn
M
Cp2Ti Ge TiCp2
–
n
4
2) AcOH - H2O / reflex, 10 h
SPh
4
M = Si, Ge
(n = 0, 2)
3
2d
PhS SPh
1d
(75)c
Entry
Multithioacetal 2
Product 4 (Yield/%)a,b
a
Isolated yield based on the multithioacetal 2 used.
The ratio of stereoisomers; 74:26.
Single isomer.
b
c
SPh
Me
Me
SPh
Si
SPh
1
at 6.12 and 6.02 ppm, respectively. These results suggest that the
metallacycles 1c and 1d are single stereoisomers and all of their
phenylthio groups are directed away from each other. Indeed the
X-ray diffraction analysis of 1d clearly supports such structure
(Fig. 2). It should be noted that 1d is the first spirocyclic 1-metalla-
3-titanacyclobutane whose structure was determined by X-ray
analysis. As shown in Fig. 2, the metallacycle 1d has a characteristic
structure; the two 1-germa-3-titanacyclobutanes are absolutely
SPh
2a
(45)
SPh
SPh
Ph
Ph
Si
SPh
SPh
2
2b
(58)
(68)
(72)
PhS SPh
PhS SPh
Si
PhS SPh
3
PhS SPh
2c
PhS SPh
PhS
PhS
PhS SPh
2d
SPh
Ge
SPh
4
ꢀ
Fig. 1. The ORTEP drawing of titanacyclobutane 1b. Selected bond distances (A) and
angles (ꢀ): Ti1eC1 2.221(3), Ti1eC2 2.226(4), C1eSi1 1.902(4), C2eSi1 1.893(3);
C1eTi1eC2 83.20(13), Ti1eC1eSi1 87.22(14), Ti1eC2eSi1 87.31(14), C1eSi1eC2 102.16
a
Isolated yield based on the thioacetal 2 used.
b
Quenching the reactions with excess AcOD produced the di- or tetradeuterated
products d-4 (d-4a; 82%D, d-4b; 86%D, d-4c; 94%D, d-4d; 94%D).
(15).

S. Oishi et al. / Journal of Organometallic Chemistry 696 (2011) 581e585
583
ꢀ
Fig. 2. The ORTEP drawing of spiro-metallacycle 1d. Selected bond distances (A) and
angles (ꢀ): Ti1eC1 2.231(2), Ti1eC8 2.244(2), C1eGe1 1.993(2), C8eGe1 1.983(2),
Ge1eC15 1.990(2), Ge1eC22 1.992(2), Ti2eC15 2.233(2), Ti2eC22 2.222(2);
C1eTi1eC8 86.85(8), Ti1eC1eGe1 85.83(8), Ti1eC8eGe1 85.73(8), C1eGe1eC8 101.38
(9), C15eGe1eC22 100.87(9), Ge1eC15eTi2 85.88(8), Ge1eC22eTi2 86.14(8),
C15eTi2eC22 87.10(8).
planar and the four-membered rings are perpendicular to each
other.
Stereoselectivity observed in the formation of titanacycle 1b is
well explained by the stepwise oxidative addition process in
which the intramolecular electrophilic activation of phenylthio
group with the initially introduced titanium plays an important
role to control the stereochemistry of the second oxidative
addition (Scheme 2); the formation of dititanium species 6 via
the more stable cyclic coordination structure 5a and the extru-
sion of bis(phenylthio)titanocene with retention of configuration
result in the formation of titanacyclobutane trans-1b as a major
isomer.
Scheme 3. Stereoselective formation of spirocycle 1d.
In the case of the spirogermacycle 1d, the formation of the
first titanacycle 7 proceeds with trans selectivity similarly to the
formation of 1b. The stereoselective formation of the second
titanacyclobutane is well explained by considering the four six-
membered coordination structures 8aed illustrated in Scheme 3,
in which the bisthioacetal 7 serves as a bidentate ligand. The
serious steric repulsion between the equatorial phenylthio group
and the phenylthio group on the titanacyclobutane ring indi-
cated by a heavy arrow exists in the chelate complexes 8c and
8d. Therefore, considering 1,3-diaxial interaction in the
complexes 8a and 8b indicated by a thin arrow, the stepwise
oxidative addition of activated phenylthio groups proceeds via
the most stable chelate complex 8a and the elimination of bis
3. Conclusion
In summary, we have achieved the first stereoselective
synthesis of substituted 1-metalla-3-titanacyclobutanes by the
reductive titanation of group 14 metal compounds bearing bis
(phenylthio)methyl groups. The molecular structures of these
compounds were unambiguously elucidated by X-ray diffraction
analysis. The reactivity of these unique titanacycles and their
synthetic application are now under investigation and will be
reported in due course.
(phenylthio)titanocene from the dititaniotitanacyclobutane
9
with retention of configuration furnish the spirocycle 1d
stereoselectively.
4. Experimental
4.1. General
Tetrahydrofuran (THF) was distilled from sodium and benzo-
phenone. Preparative thin-layer chromatography (PTLC) was
carried out using Wakogel B-5F. Column chromatography was
carried out using Kanto silica gel 60 N (40e50
mm) and Merck
aluminium oxide 90. 1H (300 MHz), 13C (75 MHz), and 29Si
(60 MHz) NMR spectra were recorded in CDCl3 on a JEOL JNM-
AL300 spectrometer. The chemical shifts (d) were quoted in parts
per million from tetramethylsilane for 1H and 29Si NMR, and
CDCl3 for 13C NMR. IR absorptions were obtained in cmꢁ1 on
a JASCO FT-IR 460. Mass spectra were recorded on a JEOL MStation
MS700.
Scheme 2. Stereoselective formation of titanacycle 1b.

584
S. Oishi et al. / Journal of Organometallic Chemistry 696 (2011) 581e585
4.2. Preparation of multithioacetals 2
4.3.2. Diphenylbis(phenylthiomethyl)silane (4b)
1H NMR
2.86 (s, 4H), 7.07e7.15 (m, 2H), 7.20e7.34 (m, 8H),
7.36e7.50 (m, 6H), 7.64e7.72 (m, 4H); 13C NMR
15.3, 125.1, 126.6,
d
4.2.1. Typical procedure
d
n-BuLi (1.57 M in hexane, 7.6 mL, 12 mmol) was added to a THF
(20 mL) solution of bis(phenylhio)methane (2.56 g, 11 mmol)
dropwise at ꢁ78 ꢀC and the mixture was stirred for 1 h. Dichloro-
dimethylsilane (0.60 mL, 5 mmol) was added to the mixture and
gradually warmed up to room temperature. After quenching the
reaction by addition of NH4Cl aq, the organic layer was separated
and the aqueous layer was extracted with CH2Cl2 (2 ꢂ 40 mL). The
combined organic layers were dried over Na2SO4. The solvent was
removed under reduced pressure, and the residue was purified by
silica gel column chromatography (hexane/AcOEt ¼ 98:2, v/v) to
give bis[bis(phenylthio)methyl]dimethylsilane (2a) (1.26 g, 83%). 1H
128.1, 128.7, 130.4, 132.3, 135.1, 139.4; IR (neat) 3069, 3050, 3016,
2884, 1585, 1479, 1438, 1427, 1385, 1115, 1087, 1025, 780, 733,
699 cmꢁ1. HRMS (FAB) calcd for C26H24S2Si [M]þ 428.1089, found
428.1078.
4.3.3. Tetrakis(phenylthiomethyl)silane (4c)
1H NMR 2.55 (s, 8H), 7.11e7.17 (m, 4H), 7.23e7.33 (m, 16H); 13
d C
NMR
d 14.1, 125.5, 127.2, 128.9, 138.4; IR (neat) 3057, 2925, 1581,
1478, 1438, 1382, 1085, 1024, 796, 734, 688 cmꢁ1. HRMS (FAB) calcd
for C28H28S4Si [M]þ 520.0843, found 520.0804.
NMR
d
0.26 (s, 6H), 4.37 (s, 2H), 7.10e7.16 (m, 12H), 7.30e7.36 (m,
ꢁ5.1, 44.2, 127.3, 128.7, 132.0, 135.3; IR (neat) 3057,
4.3.4. Tetrakis(phenylthiomethyl)germane (4d)
8H); 13C NMR
d
1H NMR 2.64 (s, 8H), 7.10e7.18 (m, 4H), 7.22e7.33 (m, 16H); 13
d C
2960, 1581, 1478, 1438, 1252, 1087, 1067, 1024, 823, 740, 688 cmꢁ1
.
NMR d 14.8, 125.5, 127.2, 128.8, 138.6; IR (neat) 3057, 2900, 1583,
HRMS (FAB) calcd for C28H28S4Si [M]þ 520.0843, found 520.0890.
1478, 1438, 1387, 1084, 1024, 736 cmꢁ1. HRMS (FAB) calcd for
C28H28GeS4 [M]þ 566.0286, found 566.0267.
4.2.2. Bis[bis(phenylthio)methyl]diphenylsilane (2b)
Mp 136e138 ꢀC. 1H NMR
d
4.87 (s, 4H), 6.97e7.11 (m, 12H),
4.4. Isolation of 1-metalla-3-titanacyclobutanes 1
7.11e7.18 (m, 8H), 7.35e7.45 (m, 4H), 7.49 (t, J ¼ 7.4 Hz, 2H), 7.87
(t, J ¼ 8.1 Hz, 4H); 13C NMR
d
45.0, 127.3, 127.8, 128.6, 129.5, 130.6,
4.4.1. Typical procedure
132.3, 135.6, 136.7; IR (KBr) 3052, 2909, 1580, 1477, 1438, 1426, 1115,
1083, 1069, 1041, 1024, 788, 738, 715, 686 cmꢁ1. HRMS (FAB) calcd
for C38H32S4Si [M]þ 644.1156, found 644.1118.
A THF (2 mL) solution of 2b (644 mg, 1.0 mmol) was added at
25 ꢀC to a THF (2 mL) solution of 3, prepared from magnesium
turnings (107 mg, 4.4 mmol), finely powdered molecular sieves 4A
(320 mg), Cp2TiCl2 (996 mg, 4.0 mmol) and P(OEt)3 (1.38 mL,
8.0 mmol). The reaction mixture was stirred for 2 h at the same
temperature. Insoluble materials were filtrated off, and the filtrate
was chromatographed over alumina gel (10 g, eluted with THF
(10 mL)) under N2. The eluted solution was evaporated to dryness
4.2.3. Tetrakis[bis(phenylthio)methyl]silane (2c)
Mp 190e192 ꢀC. 1H NMR
d
5.38 (s, 4H), 6.87e6.97 (m, 24H),
43.6, 127.2, 128.5, 131.9, 135.4; IR
7.31e7.37 (m, 16H); 13C NMR
d
(KBr) 3053, 2901, 1579, 1477, 1438, 1080, 1025, 804, 739, 687 cmꢁ1
.
Anal. Calcd. for C52H44S8Si: C, 65.50; H, 4.65%. Found: C, 65.28; H,
4.50%.
invacuoto give a purple powder. Pure 3,3-bis(h
5-cyclopentadienyl)-
1,1-diphenyl-2,4-bis(phenylthio)-1-sila-3-titanacyclobutane (1b)
(260 mg, 43%, the ratio of stereoisomers; 74:26) was obtained by
washing the powder with hexane (3 ꢂ 10 mL) and drying under
4.2.4. Tetrakis[bis(phenylthio)methyl]germane (2d)
Mp 189e191 ꢀC. 1H NMR
d
5.38 (s, 4H), 7.08e7.02 (m, 24H),
45.5, 127.3, 128.5, 132.1, 135.7; IR
reduced pressure (2ꢁ3 mmHg). Mp 125ꢁ126 ꢀC. 1H NMR
d 4.43 (s,
7.24e7.40 (m, 16H); 13C NMR
d
0.52H), 4.65 (s, 1.48H), 6.20 (s, 7.4H), 6.28 (s, 1.3H), 6.35 (s, 1.3H),
(KBr) 3053, 2914, 1578, 1477, 1438, 1081, 1066, 1024, 743, 688 cmꢁ1
.
6.86e7.54 (m, 19.48H), 7.86 (dd, J ¼ 8.2, 1.4 Hz, 0.52H); 29Si NMR
Anal. Calcd. for C52H44GeS8: C, 62.58; H, 4.44%. Found: C, 62.53; H,
4.51%.
d
ꢁ 34.6, ꢁ11.3; 13C NMR
d 66.5, 67.4, 114.3, 114.6, 115.6, 123.4, 123.7,
124.5,125.5,126.6,127.5,127.6,128.1,128.2,128.7,128.8,129.3,133.7,
134.5, 135.05, 135.09, 136.2, 137.0, 144.8, 145.1; IR (KBr) 3046, 3015,
1577, 1474, 1427, 1099, 1080, 1023, 812, 736, 687 cmꢁ1. HRMS (FAB)
calcd for C36H32S2SiTi [M]þ 604.1194, found 604.1234.
4.3. Formation and protonation of titanacycles 1
4.3.1. Typical procedure
Magnesium turnings (21 mg, 0.86 mmol), finely powdered
molecular sieves 4A (80 mg) and Cp2TiCl2 (199 mg, 0.80 mmol)
were placed in a flask and dried by heating with a heating gun
under reduced pressure (2e3 mmHg). THF (2 mL) and P(OEt)3
(0.27 mL, 1.6 mmol) were added successively with stirring at 25 ꢀC
under Ar. After 3 h, a THF (1 mL) solution of bis[bis(phenylthio)
methyl]dimethylsilane (2a) (104 mg, 0.20 mmol) was added to the
mixture and stirring was continued for 2 h. After addition of H2O
(0.3 mL) and AcOH (0.3 mL), the reaction mixture was further
stirred for 10 h at reflux and then cooled to room temperature.
Insoluble materials were filtrated off through Celite and washed
with CH2Cl2 (40 mL). The organic layer was separated, and the
aqueous layer was extracted with CH2Cl2 (2 ꢂ 20 mL). The
combined organic extracts were dried over Na2SO4. After removal
of the solvent under reduced pressure, the residue was purified by
PTLC (hexane/AcOEt ¼ 98:2, v/v) to give dimethylbis(phenyl-
4.4.2. 2,2,6,6-Tetrakis(h
5-cyclopentadienyl)-1,3,5,7-tetrakis-
(phenylthio)-4-sila-2,6-dititanaspiro[3.3]heptane (1c)
Mp 68ꢁ69 ꢀC. 1H NMR
d 4.51 (s, 4H), 6.13 (s, 20H), 6.98e7.10 (m,
12H), 7.23e7.32 (m, 8H); 29Si NMR
d
ꢁ 120.6; 13C NMR
d 67.3, 115.0,
123.5,124.4,128.4,144.1; IR (KBr) 3055, 2922,1578,1475,1438,1084,
1023, 822, 736, 690 cmꢁ1. Anal. Calcd. for C48H44S4SiTi2: C, 66.04;
H, 5.08%. Found: C, 66.13; H, 5.11%.
4.4.3. 2,2,6,6-Tetrakis(h
5-cyclopentadienyl)-1,3,5,7-tetrakis-
(phenylthio)-4-germa-2,6-dititanaspiro[3.3]heptane (1d)
Mp 113ꢁ114 ꢀC. 1H NMR
d
4.63 (s, 4H), 6.02 (s, 20H), 7.03e7.13
68.6, 113.6, 123.6, 124.5,
(m, 12H), 7.24e7.33 (m, 8H); 13C NMR
d
128.5, 144.1; IR (KBr) 3052, 1578, 1473, 1436, 1082, 1022, 822, 734,
688 cmꢁ1. Anal. Calcd. for C48H44GeS4Ti2: C, 62.84; H, 4.83%. Found:
C, 62.61; H, 4.98%.
thiomethyl)silane (4a) (39 mg, 45%). 1H NMR
(s, 4H), 7.08e7.16 (m, 2H), 7.22e7.33 (m, 8H); 13C NMR
124.9, 126.4, 128.7, 139.5; IR (neat) 3058, 2956, 1580, 1479, 1438,
1252, 1086, 844, 737 cmꢁ1. HRMS (FAB) calcd for C16H20S2Si [M]þ
304.0776, found 304.0812.
d
0.30 (s, 6H), 2.32
ꢁ3.3, 16.8,
4.5. X-ray diffraction analysis of titanacyclobutanes 1
d
4.5.1. Silatitanacyclobutane 1b
A black single crystal of 1b was grown by slow evaporation of its
THF solution under Ar. Crystal data for 1b: C36H32S2SiTi, M ¼ 604.73,

S. Oishi et al. / Journal of Organometallic Chemistry 696 (2011) 581e585
585
0.20 ꢂ 0.20 ꢂ 0.10 mm3, monoclinic, P21/c, a ¼ 14.5802(9),
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4604e4609;
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3
ꢀ
ꢀ
ꢀ
b ¼ 10.7521(4), c ¼ 19.0926(9) A,
b
¼ 91.031(3) , V ¼ 2992.6(3) A ,
Z ¼ 4, T ¼ 193 K, D ¼ 1.342 g cmꢁ3
,
m
(Cu-Ka) ¼ 4.286 mmꢁ1
,
Rint ¼ 0.1412, number of measured/independent reflections ¼ 53769/
5475, R ¼ 0.0531 and wR ¼ 0.1574 (all data).
4.5.2. Spirocycle 1d
A brown single crystal of 1d was grown by slow evaporation of
its acetone solution under Ar. Crystal data for 1d: C48H44GeS4Ti2·2
(C3H6O), M ¼ 1033.62, 0.40 ꢂ 0.20 ꢂ 0.10 mm3, monoclinic, P21/n,
ꢀ
a ¼ 16.1394(3), b ¼ 13.6985(3), c ¼ 21.7303(4) A,
b
¼ 95.4480(10)ꢀ,
3
ꢀ
ꢁ3
V ¼ 4782.58(15) A , Z ¼ 4, T ¼ 193 K, D ¼ 1.436 g cm
, m(Cu-
Ka) ¼ 5.467 mmꢁ1, Rint ¼ 0.0443, number of measured/independent
reflections ¼ 54777/8092, R ¼ 0.0358 and wR ¼ 0.1009 (all data).
(q)M. Weidenbruch,B. Brand-Roth,S. Pohl, W. Saak, Angew. Chem., Int. Ed. Engl. 29
(1990) 90e92;
(r) H. Schmidbaur, R. Pichl, G. Müller, Chem. Ber. 120 (1987) 789e794;
(s)M. Ishikawa, S. Matsuzawa, K. Hirotsu, S. Kamitori, T. Higuchi, Organometallics3
(1984) 1930e1932.
Acknowledgment
This work was supported by Grant-in-Aid for Scientific Research
(No. 21350026) from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
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Appendix A. Supplementary material
CCDC 785058 and 785059 contain the supplementary crystal-
lographic data for the complexes 1b and 1d. These data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre via http://www.ccdc.cam.ac.uk/data_request/cif.
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