Organometallics
ARTICLE
meso-2 mixture and that both give identical chemical shifts in NMR
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cannot be ruled out. H NMR (300 MHz, CDCl3, Me4Si): δ 1.02 (s,
18H, C(CH3)3), 2.32 (s, 2H, OH), 7.32 (m, 6H, Ph), 7.57 (m, 4H, Ph).
13C NMR (125 MHz, CDCl3, Me4Si): δ 25.41 (C(CH3)3), 39.94
(C(CH3)3), 69.95 (q),79.68 (q), 82.46 (q), 127.24 (Ph), 127.48 (Ph),
127.70 (Ph), 141.21 (q, Ph). Anal. Calcd for C26H30O2: C, 83.38; H,
8.07. Found: C, 83.44; H, 7.78.
Preparation of (E)-2,2,9,9-Tetramethyl-3,8-diphenyldeca-
3,4,5,6,7-pentaene ((E)-1). The title compound was prepared from
2 according to the method reported by Iyoda et al.3 To a solution of 2
(0.376 g, 1.01 mmol) in Et2O (5.0 mL) was added anhydrous SnCl2
(0.585 g, 3.08 mmol) and hydrogen chloride in diethyl ether (2.0 M,
2.0 mL, 4.0 mmol) at ꢀ78 °C. The solution immediately turned yellow,
and it was stirred at 0 °C for 16 h. Then water was added and extracted
with Et2O. The organic layer was washed with saturated NaHCO3(aq),
dried with MgSO4, and concentrated. Slow evaporation from a Et2O
solution at room temperature gave yellow platelet crystals (0.129 g,
Figure 2. ORTEP drawing of the molecular structure of 5. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg); ZrꢀC2 = 2.340(4), ZrꢀC3 = 2.345(4), C1ꢀC2 = 1.340(6),
C2ꢀC3 = 1.393(6), C3ꢀC3* = 1.251(6); C2ꢀZrꢀC2* = 100.11(16),
ZrꢀC2ꢀC3 = 72.9(2), C1ꢀC2ꢀC3 = 135.4(4), C2ꢀC3ꢀC3* =
147.0(4).
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atoms C1ꢀC1* are almost coplanar; tert-butyl and phenyl
groups are also located on this plane. The phenyl groups are
nearly perpendicular (83°) to the 1-zirconacyclopent-3-yne
plane, probably because of the steric demands of the tert-butyl
and cyclopentadienyl groups. The unusual upfield shift of the Cp
protons (5.01 ppm) is presumably due to the shielding effect of
the ring current of the phenyl groups. The bond lengths around
C1ꢀC1* were in a range similar to those of reported complexes.4c,d
Heating 5 in a C6D6 solution at 70 °C for 2 h did not result in
isomerization to 6and vice versa, indicating that the isomerization of
the [5]cumulene moiety in these zirconium complexes is very slow.
38%). Mp: 120 °C. H NMR (300 MHz, CDCl3, Me4Si, ꢀ50 °C): δ
1.30 (s, 18H, C(CH3)3), 7.29ꢀ7.46 (m, 10H, Ph). 13C NMR (75 MHz,
CDCl3, Me4Si, ꢀ20 °C): δ 30.3 (C(CH3)3), 38.3 (q, C(CH3)3), 127.3
(Ph), 127.9 (Ph), 128.7 (Ph), 131.1 (q, Ph), 133.6 (q), 138.6 (q), 155.9
(q). IR (KBr, cmꢀ1): 698, 760, 1049, 1593, 1990, 2966. Anal. Calcd for
C26H28: C, 91.71; H, 8.29. Found: C, 91.63; H, 8.35.
Preparation of the Zirconocene Complex of (Z)-1 (5). A
solution of bis(η5-cyclopentadienyl)bis(trimethylphosphine)zirconium,
Cp2Zr(PMe3)2, (99 mg, 0.26 mmol), and [5]cumulene 1 (89 mg,
0.26 mmol) in THF (5.0 mL) was stirred at room temperature for
40 h and then heated at 40 °C for an additional 1 h. The formation of 5
and 6 was observed by 1H NMR at this stage (in 37% and 41% yields by
NMR, respectively). THF was then removed in vacuo, and the residue
was dissolved in hexane. The solution was filtered, and the filtrate was
concentrated. Yellow needle crystals of 5 were obtained at ꢀ30 °C
(34.6 mg, 23%). In most cases the mother liquid contained the isomer 6
as the main species. Removal of the volatiles in vacuo left a residue that
contained 6 as the major product (yellow solid, 53% crude yield).
Spectroscopic Data for 5. 1H NMR (300 MHz, C6D6, Me4Si): δ 1.47
(s, 18H, C(CH3)3), 5.01 (s, 10H, Cp), 7.19ꢀ7.37 (m, 10H, Ph). 13C
NMR (75 MHz, C6D6, Me4Si): δ 30.98 (C(CH3)3), 40.06 (q, C(CH3)3),
101.14 (q, CtC), 105.21, 126.48 (Ph), 127.80 (Ph), 129.59 (Ph),
146.51 (q, Ph), 156.47 (q), 164.57 (q). IR (KBr): 706, 795, 1018, 1068,
1219, 1356, 1597, 2957 (cmꢀ1). Elemental analysis did not give
’ EXPERIMENTAL SECTION
General Considerations. All manipulation that involved organo-
metallic compounds was carried out under an inert atmosphere using
standard Schlenk techniques or a glovebox. Anhydrous hexane and THF
were purchased from Kanto Chemical Co., Inc. and degassed prior to
use. n-Butyllithium (ca. 1.6 M in hexane) was purchased from Kanto
Chemical Co., Inc. Hexachloro-1,3-butadiene and tetrabutylammonium
hexafluorophosphate were purchased from Wako Pure Chemical In-
dustries, Ltd., and used as received. Hydrogen chloride in diethyl ether
and 2,2-dimethylpropiophenone were purchased from Sigma-Aldrich.
Dichlorobis(η5-cyclopentadienyl)zirconium, Cp2ZrCl2, was a gift from
Nichia Corp. Compounds 33,4d and 43,4c,6c were prepared as previously
described. Bis(η5-cyclopentadienyl)bis(trimethylphosphine)zirconium,
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satisfactory results. The H and 13C NMR spectra are shown in the
Supporting Information.
Spectroscopic Data for 6. 1H NMR (300 MHz, C6D6, Me4Si): δ 1.20
(s, 9H, C(CH3)3), 1.56 (s, 9H, C(CH3)3), 5.27 (s, 10H, Cp), 7.1ꢀ7.3
(m, 10H, Ph). 13C NMR (75 MHz, C6D6, Me4Si): δ 30.45 (C(CH3)3),
31.28 (C(CH3)3), 38.18 (q, C(CH3)3), 39.68 (q, C(CH3)3), 97.68 (q,
CtC), 102.03 (q, CtC), 105.34 (Cp), 125.96 (Ph), 126.15 (Ph),
127.47 (Ph), 127.58 (Ph), 127.84 (Ph), 128.01 (Ph), 129.31 (Ph),
145.68 (q), 151.26 (q), 154.54 (q), 159.26 (q), 162.83 (q), 168.84 (q).
Cyclic Voltammetry. Cyclic voltammetry was carried out on
CH2Cl2 solutions containing 0.1 mol dmꢀ3 tetrabutylammonium hexa-
fluorophosphate as supporting electrolyte with a platinum-disk working
electrode (1.6 mm diameter) and an Ag|0.01 mol dmꢀ3 AgNO3
reference electrode by using a BAS 100B/W Electrochemical Analyzer.
At the end of each measurement, ferrocene was added as an internal
standard to correct redox potentials.
Cp2Zr(PMe3)2, was prepared according to the literature.8 1H and 13
C
NMR spectra were recorded on JEOL Lambda 300 and Lambda 500
spectrometers. Infrared spectra were recorded on a Shimadzu FTIR-
8300 instrument.
Preparation of (rac-/meso)-2,2,9,9-Tetramethyl-3,8-dihy-
droxy-3,8-diphenyldeca-4,6-diyne (2). A hexane solution of n-
butyllithium (1.57 M in hexane, 4.0 mmol) was cooled with dry
iceꢀmethanol, and THF (4.0 mL) was added dropwise at ꢀ78 °C.
To this mixture was added dropwise a THF (1.0 mL) solution of
hexachlorobutadiene (261 mg, 1.0 mmol) at ꢀ78 °C.9 The mixture was
warmed to room temperature and stirred overnight. The resulting gray
suspension was cooled to ꢀ78 °C, and 2,2-dimethylpropiophenone
(324 mg, 2.0 mmol) was added dropwise. The mixture was stirred at
room temperature for 72 h, and then 1 N HCl was added and the mixture
extracted with Et2O. The organic layers were combined, dried with
MgSO4, and evaporated. The residue was recrystallized from a hexane/
ethyl acetate mixture (3/1) to give the title compound as colorless
crystals (303 mg, 81%). In the 1H and 13C NMR spectra, only one set of
signals was observed. An X-ray diffraction study revealed that the crystals
were meso-2. However, the possibility that the crystals are the rac-/
X-ray Diffraction Analyses of (E)-1. Single crystals were ob-
tained by slow evaporation of solvent from a diethyl ether solution. A
pale yellow block crystal (0.25 ꢁ 0.25 ꢁ 0.20 mm) was mounted on a
thin polyimide film (Micromount, MiTeGen, LLC) and coated with
liquid paraffin. Data were collected on a Rigaku Mercury CCD area
detector with graphite-monochromated Mo KR radiation at 93 K. The
structure was solved by direct methods10 and expanded using Fourier
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dx.doi.org/10.1021/om2002427 |Organometallics 2011, 30, 3544–3548