Different coordination modes of 2-(diphenylphosphino)azobenzenes in complexation with hard and soft metals

Article abstract of DOI:10.1039/c2dt31494k

Control of coordination modes of a ligand in metal complexes is significant because the coordination modes influence catalytic properties of transition metal catalysts. Reactions of 2-diphenylphosphinoazobenzenes, which are in equilibrium with the inner phosphonium salts, with ZnCl₂, W(CO) ₅(THF), and PtCl₂(cod) gave three different coordination types of metal complexes with distinctive UV-vis absorptions. All the complexes were characterized by X-ray crystallographic analyses. In the zinc and tungsten complexes, the source molecule functions as an amide ligand and a phosphine ligand, respectively. In the platinum complex, the phosphorus molecule works as a tridentate ligand with formation of a carbon-platinum bond.

Full text of DOI:10.1039/c2dt31494k

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PAPER
Different coordination modes of 2-(diphenylphosphino)azobenzenes in
complexation with hard and soft metals†
Naokazu Kano,* Masaki Yamamura, Xiangtai Meng, Takaharu Yasuzuka and Takayuki Kawashima‡*
Received 17th March 2012, Accepted 26th July 2012
DOI: 10.1039/c2dt31494k
Control of coordination modes of a ligand in metal complexes is significant because the coordination
modes influence catalytic properties of transition metal catalysts. Reactions of 2-diphenyl-
phosphinoazobenzenes, which are in equilibrium with the inner phosphonium salts, with ZnCl2,
W(CO)5(THF), and PtCl2(cod) gave three different coordination types of metal complexes with distinctive
UV-vis absorptions. All the complexes were characterized by X-ray crystallographic analyses. In the zinc
and tungsten complexes, the source molecule functions as an amide ligand and a phosphine ligand,
respectively. In the platinum complex, the phosphorus molecule works as a tridentate ligand with
formation of a carbon–platinum bond.
Introduction
Both phosphines and amides have been widely used as ligands
for transition metal complexes.1 Their coordination modes are
so different that the choice of the ligands can influence metal-
catalyzed reactions. There are few examples for reversible
conversion between trivalent-tricoordinated and pentavalent-
tetracoordinated organophosphorus compounds because most
nucleophilic displacement reactions of trivalent phosphines with
Scheme 1 An equilibrium between phosphines (E)-1 and inner
phosphonium salts 2, and its complexation giving 2a·ZnCl2·(THF).
electrophiles are irreversible. In the continuation of our study on
phosphorus compounds bearing an azobenzene moiety,2 we pre-
viously reported the synthesis of diphenyl[2-(phenylazo)phenyl]-
phosphines ((E)-1a,b) and its equilibrium with the correspond-
ing inner phosphonium salts 2a,b, which possessed a bond
between the phosphorus and the nitrogen atoms in the solution
state (Scheme 1).3,4 The equilibrium ratio was influenced by
various factors, such as temperature, solvent, additives, and light.
Phosphine (E)-1a was expected to act as an ambidentate ligand
for metal complexes. We report here reactions of the phosphines
containing an azobenzene moiety with some metal sources
to give the corresponding phosphine complexes or amide
complexes.
Results and discussion
Amide complex
The dark red colored equilibrium mixture of (E)-1a and the cor-
responding inner phosphonium salt 2a was treated with zinc
dichloride in THF at room temperature. The resulting THF solu-
tion showed only one broad singlet at δ 42.7 in the 31P NMR
spectrum, which was assigned to a phosphonium salt, indicating
quantitative formation of the corresponding zinc–amide complex
2a·ZnCl2·(THF). The complex was isolated in 90% yield
(Scheme 1). A reaction of (E)-1b with ZnCl2 in THF gave a
result similar to the reaction of (E)-1a. The zinc complex, similar
to 2a, is very sensitive to humidity.
A reaction of (E)-1a with LiB(C6F5)4 in THF induced color
change of the solution to colorless and low field shift (δ 38.6) in
the 31P NMR spectrum. Although formation of the lithium–
amide complex was indicated by these results, isolation of the
complex was not successful.
The crystal structure of 2a·ZnCl2·(THF) was determined by
X-ray crystallographic analysis (Fig. 1, Table 1). The P1 atom
has a tetrahedral structure and Zn1 atom is coordinated by both
2a through the N1 atom and one THF molecule through the O1
Department of Chemistry, Graduate School of Science, The University
of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
E-mail: kano@chem.s.u-tokyo.ac.jp; Tel: +81 3 5841 4338
†CCDC 869853, 869854 and 869855 for 2a·ZnCl2·(THF), (E)-1b·W-
(CO)5 and (E)-3b, respectively. For crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2dt31494k
‡Present address: Faculty of Science, Gakushuin University, 1-5-1
Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
E-mail: Takayuki.Kawashima@gakushuin.ac.jp;
Tel: +81 3 3986 0221 ext. 6566.
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Scheme 2 Formation of complexes, (E)-1b·W(CO)5 and (E)-3b.
shorter than those of 2-diphenylphosphinoazobenzene,3 are
almost the same as the corresponding bond lengths of (N′,N′-
dimethylhydrazino)triphenylphosphonium bromide (P–N: 1.640(3)
Å; P–C: 1.776(3)–1.787(3) Å).5 These structural features clearly
indicate the existence of the P–N bond and hydrazinophospho-
nium structure around the phosphorus moiety in the zinc
complex. The sum of the bond angles around the N1 and N2
atoms (341.1° and 348.0°, respectively) revealed a considerable
pyramidalization.
Fig. 1 ORTEP drawing of 2a·ZnCl2·(THF) with thermal ellipsoid
(50% probability). A free THF molecule was omitted for clarity.
Selected bond lengths (Å) and angles (°): P1–N2, 1.679(3); P1–C1,
1.739(3); P1–C13, 1.775(3); P1–C19, 1.797(3); N1–N2, 1.445(4); N1–
Zn1, 2.0012(2); Cl1–Zn1, 2.2383(10); Cl2–Zn1, 2.2315(10); O1–Zn1,
2.048(2); N2–P1–C1, 93.50(14); N2–P1–C13, 111.56(14); N2–P1–C19,
110.58(15); C1–P1–C13, 115.66(15); C1–P1–C19, 116.63(15); C13–
P1–C19, 108.18(15); P1–N2–N1, 112.42(19); P1–N2–C7, 117.8(2);
N2–N1–C6, 108.3(2); N2–N1–Zn1, 113.61(18); C6–N1–Zn1, 119.15(17);
N1–Zn1–Cl1, 109.96(9); N1–Zn1–Cl2, 108.57(9); N1–Zn1–O1,
107.50(9); Cl1–Zn1–Cl2, 126.53(3); Cl1–Zn1–O1, 100.70(8); Cl2–
Zn1–O1, 101.48(7).
Phosphine complex
Reaction of (E)-1b with W(CO)5(THF) gave tungsten–phosphine
1
complex (E)-1b·W(CO)5 (δP 19.1 (s, JW–P = 246 Hz)) in 75%
yield (Scheme 2). The formation of the phosphine complex as a
stable form in the air is in marked contrast to the formation of
the amide complex in the reaction of zinc chloride. The crystal
structure of (E)-1b·W(CO)5 was determined by X-ray crystallo-
graphic analysis (Fig. 2, Table 1). The structure around the P1
and W1 atoms is quite normal for a phosphine–tungsten
complex and there is no interaction between P1 and the azo
moiety. Although there has been a report of the synthesis of
similar phosphine complexes, 2-(PhNvN)C6H4P(R)(OH)W-
(CO)5 via a phosphinidene complex, RPW(CO)5, where the R is
Ph or Me,6 the present synthetic method using the phosphine is
more straightforward and rational.
Table 1 Crystallographic data
Complex
2a·ZnCl2·(THF)
(E)-1b·W(CO)5 (E)-3b
Formula
Formula
weight
Crystal
system
C28H27Cl2N2OPZn C31H23N2O5PW C26H22ClN2PPt
574.46
718.33
623.97
Orthorhombic
Monoclinic
Monoclinic
Space group P212121
P21/c
P21/n
a (Å)
b (Å)
c (Å)
9.3362(15)
9.5272(18)
21.273(2)
14.448(2)
104.319(3)
2837.3(8)
4
8.632(4)
17.191(8)
15.216(7)
96.028(2)
2245.5(18)
4
16.298(3)
17.254(3)
—
2625.4(7)
4
β (°)
V (Å3)
Z
Dc (Mg m−3
T (K)
)
1.454
133
1.682
120
1.846
120
Measured
reflections
Unique
reflections
Rint
R1(I > 2σ(I)) 0.0303
wR2(all data) 0.0908
20 723
17 582
14 108
5950
4979
3887
0.0345
0.0216
0.0209
0.0508
1.089
0.0222
0.0193
0.0477
1.079
GOF
1.104
Fig. 2 ORTEP drawing of (E)-1b·W(CO)5 (50% probability). Selected
bond lengths (Å) and angles (°) of (E)-1b·W(CO)5: P1–C1, 1.846(3);
P1–C15, 1.832(3); P1–C21, 1.843(3); N1–N2, 1.259(3); P1–W1, 2.5582(8);
W1–C31, 2.039(3); C1–P1–C15, 105.43(12); C1–P1–C21, 102.35(13);
C15–P1–C21, 100.61(12); W1–P1–C1, 120.00(9); W1–P1–C15,
113.29(9); W1–P1–C21, 112.90(9).
atom. The N1–N2 (1.445(4) Å) bond length falls within the
range of usually observed N–N single bond lengths. The bond
angles around the P1 atom are between 93.50(14)–116.63(15)°.
The P1–N2 bond length (1.679(3) Å) and the P1–C bond
lengths (1.739(3)–1.797(3) Å), the latter of which are much
11492 | Dalton Trans., 2012, 41, 11491–11496
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Fig. 3 ORTEP drawing of (E)-3b (50% probability). Selected bond
lengths (Å) and angles (°) of (E)-3b: P1–C1, 1.824(3); P1–C15, 1.816(3);
P1–C21, 1.814(3); N1–N2, 1.274(3); Pt1–P1, 2.29150(10); Pt1–N1,
1.972(3); Pt1–C12, 2.023(3); Pt1–Cl1, 2.3089(11); C1–P1–C15, 104.79(14);
C1–P1–C21, 108.24(14); C15–P1–C21, 103.94(14); P1–Pt1–N1, 85.25(8);
P1–Pt1–C12, 163.91(9); P1–Pt1–Cl1, 99.92(4); N1–Pt1–C12, 78.74(12);
N1–Pt1–Cl1, 174.66(7); C12–Pt1–Cl1, 96.13(9).
Fig. 4 UV-vis spectral change upon addition of zinc chloride to (E)-1a
in THF.
Tridentate ligand complexes
Reaction of (E)-1b with PtCl2(cod) gave tridentate complex
(E)-3b (δP 30.2 (s, 1JPt–P = 2072 Hz)) together with another ther-
1
mally unstable platinum complex (δP 1.2 (s, JPt–P = 3566 Hz))
bearing no Pt–C bond, and the latter complex turned into (E)-3b
in solution. Finally, (E)-3b was obtained as a deep-red crystal in
66% yield. The Pt–P coupling constant of (E)-3b is considerably
smaller than 3858 Hz (δP 8.2) of the previously reported
complex, [PtCl(C6H4-2-NvNPh-C,N)(PEt3)],7 suggesting strong
carbon–platinum bonding at the trans position of the phosphorus
atom.8 The crystal structure of (E)-3b was determined by X-ray
crystallographic analysis (Fig. 3, Table 1). The N–N bond length
(1.274(3) Å), which is slightly longer than those of azobenzene
and (E)-1b·W(CO)5, is reasonable for a NvN double bond. The
central platinum atom has a slightly distorted square planar struc-
ture. Generally, azobenzene reacts easily with a transition metal
to give an ortho-metalated complex.9,10 After the first formation
of an intermediary platinum complex coordinated by the phos-
phine and/or the azo moiety, intramolecular C–H insertion11,12
followed by reductive elimination via a high oxidation state of
the platinum or σ-bond metathesis without the change of valence
of the platinum would occur to give (E)-3b. The resulting
complex (E)-3b is stable toward hydrolysis in contrast with
(E)-2b and 2a·ZnCl2·(THF), probably because of no contribution
of the phosphonium salt character by the complexation with zinc.
Fig. 5 UV-vis spectra of (E)-1b·W(CO)5, (E)-1b, and (E)-3b.
addition of zinc chloride to a THF solution of (E)-1a caused a
decrease in the absorption maximum at 473 nm and an increase
in a new absorption at 420 nm of 2a·ZnCl2·(THF) (Fig. 4). In
contrast, addition of excess TMEDA to remove zinc chloride
regenerated the dark red-colored (E)-1a (Fig. 4, Scheme 1).
The blue-shift in the absorption spectrum by complexation at
nitrogen was also observed in the protonation of 2a.4 Since the
dark red color of the phosphonium salt 2a was ascribed to
several charge transfer excitations from the HOMO, which is the
non-bonding orbital of the nitrogen atom at the high energy
level, the coordination of the nitrogen to zinc lowered the energy
level of the HOMO, which made the color of the zinc complex
paler than 2a.
UV-vis spectroscopy
In the UV-vis spectra in dichloromethane, the absorptions of
(E)-1b·W(CO)5 (λ = 348 nm (log ε = 4.31)) and (E)-3b (λ =
490 nm (log ε = 3.70), 414 nm (4.23), 383 nm (4.20)) were
observed at longer wavelengths than that of (E)-1b (λ = 335 nm
(log ε = 4.32)) (Fig. 5). The red-shifts by metal complexation of
(E)-1b, in contrast to the blue-shift observed in 2a·ZnCl2·(THF),
are partly ascribed to absence of the phosphonium salt character.
Colors of the solutions of the synthesized metal complexes
depend on the coordination modes of the ligands. For example,
2a·ZnCl2·(THF) in THF was orange. The absorption maximum
(λ = ca. 420 nm) is quite shorter than that of (E)-1a (λ =
473 nm) in THF. Since the difference of the absorption wave-
lengths are so large, the formation of 2a·ZnCl2·(THF) can be
confirmed by monitoring of the UV-vis spectroscopy. In fact,
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Table 2 Selected
calculated
singlet
excited
energies
for
2a·ZnCl2·(THF), (E)-1b·W(CO)5, and (E)-3b
Excitation Oscillator
energy/nm strength
Transition
2a·ZnCl2·(THF) S1 HOMO → LUMO
S2 HOMO → LUMO+1
554
471
415
383
360
507
451
0.0161
0.0081
0.0067
0.0216
0.0405
0.0022
0.0080
0.0016
0.0043
0.5147
0.0000
0.0646
0.0023
0.0780
0.3196
S3 HOMO → LUMO+2
S4 HOMO → LUMO+3
S5 HOMO → LUMO+4
(E)-1b·W(CO)5 S1 HOMO → LUMO
S2 HOMO−1 → LUMO
S3 HOMO−2 → LUMOa 442
S4 HOMO−3 → LUMO
S5 HOMO−4 → LUMO
S1 HOMO → LUMO
S2 HOMO−1 → LUMO
S3 HOMO−3 → LUMO
414
361
539
482
440
(E)-3b
S4 HOMO−2 → LUMOa 429
S5 HOMO−4 → LUMO
367
a There is more than one transition with almost equivalent CI
coefficients.
strength, these transitions mainly contribute to the UV-vis spec-
trum of (E)-1b·W(CO)5. Thus, the spectrum is similar to that of
metal-free (E)-1b,4 which also corresponds to the n–π* and π–π*
transitions of the azobenzene (Fig. 5).
Thirdly, in (E)-3b, the HOMO corresponds to bonding orbitals
of Pt–C bond in addition to the p orbital of chlorine. The
HOMO−1 and HOMO−2 consist of the π orbital of the azoben-
zene and d orbital of the platinum. The LUMO is mainly the π*
orbital of the azobenzene with a small contribution of the d
orbital of the platinum. These orbitals can reasonably be under-
stood as hybridization of the molecular orbitals of 2-diphenyl-
phosphinoazobenzene4 and the Pt–Cl unit. The TD-DFT
calculations show contribution of both HOMO−1 → LUMO and
HOMO−2 → LUMO transitions, which have π–π* transition
characters, to the absorption in addition to the HOMO →
LUMO transition. The absorptions of (E)-3b are assigned to
both π–π* transition and metal-to-ligand charge transfer absorp-
tions from a PtII d orbital to a π* orbital of the azobenzene,
which coordinates directly to the platinum.13
Fig. 6 Selected molecular orbitals of (a) 2a·ZnCl2·(THF) (left), (b)
(E)-1b·W(CO)5 (center), and (c) (E)-3b (right) calculated at the B3LYP
functional with the basis sets 6-311+G(d,p) for C, H, N, O, P, and Cl,
and LANL2DZ for Zn, W, and Pt.
To evaluate the effect of the complexation on the absorption
property, single-point density functional theory (DFT) calcu-
lations and time-dependent DFT (TD-DFT) calculations were
performed based on the crystal structures of 2a·ZnCl2·(THF),
(E)-1b·W(CO)5 and (E)-3b at the B3LYP/LANL2DZ[Pt,Zn,W]/
6-311+G(d,p)[C,H,N,O,P,Cl] level. The results are summarized
in Fig. 6 and Table 2.
The different absorptions of these three complexes originate
both in the structural difference of the ambidentate ligand and in
the metal fragment.
Firstly, in 2a·ZnCl2·(THF), the HOMO localizes on nN orbitals
conjugated with the π-orbital of the diarylhydrazine moiety, and
the LUMO, LUMO+1 and LUMO+2 localize on the π* orbital
of the diphenylphosphino moiety. Such molecular orbitals are
similar to the HOMO and LUMO of triphenyl[2-(2-phenyl-
hydrazino)phenyl]phosphonium.4 The TD-DFT calculation of
2a·ZnCl2·(THF) indicates that transitions from the HOMO to
unoccupied molecular orbitals around the positively charged
phosphorus atom are responsible for the broad absorptions, and
these transitions are considered to be charge transfer excitations.
Secondly, in (E)-1b·W(CO)5, the HOMO, HOMO−1, and
HOMO−2 consist of π orbitals of the diphenylphosphino
moiety. The n and π orbitals of the azobenzene are found in
the HOMO−3 and HOMO−4, respectively. The LUMO is
representative of the π* orbital of the azobenzene. The TD-DFT
study suggests that the HOMO−3 → LUMO and HOMO−4 →
LUMO transitions are n–π* and π–π* transitions of the azoben-
zene moiety, respectively. Reflecting their large oscillator
Conclusions
In conclusion, 2-phosphinoazobenzenes in equilibrium with
inner phosphonium salts were utilized as ambidentate ligands or
multidentate ligands toward some metals. Their reactions with
hard and soft metals gave the amide and the phosphine com-
plexes, respectively. The change in nature of metals successfully
provided the different coordination modes of the ligand in the
resulting complexes. The different coordination modes of the
ligand in the metal complexation led to control of the properties
of the 2-diphenylphosphinoazobenzene such as UV-vis absorp-
tion and stability to hydrolysis. The versatile coordination
modes, which have an influence on properties of some metal cat-
alysts, of a single ligand will be an advantage in preparation of
metal catalysts.
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CP), 141.16 (d, JCP = 8.2 Hz, CMe), 141.66 (s, CMe), 149.43
(d, JCP = 5.0 Hz, CN), 150.35 (s, CN), 197.25 (d, JCP = 7.5 Hz,
CO), 199.27 (d, JCP = 22.3 Hz, CO). 31P NMR (162 MHz,
Experimental
Solvents, reagents and techniques
1
CDCl3) δ 19.1 (s, JPW = 246.0 Hz). FAB-MS m/z 718 (M+).
Solvents were purified and dried by an MBraun solvent purifi-
cation system or fractional distillation. All reactions were carried
out under argon atmosphere in a glovebox or in a sealed NMR
Anal. Calcd for C31H23N2O5PW, C, 51.83; H, 3.23; N, 3.90.
Found C, 52.02; H, 3.47; N, 3.77%.
tube unless otherwise noted. The H NMR and 13C{1H} NMR
1
spectra were measured with JEOL AL400, Bruker AV300 and
Bruker DRX500 spectrometers using tetramethylsilane as an
external standard. The 31P NMR spectra were measured with a
JEOL A500 spectrometer using tributylphosphine (δP = −31.8)
as an external standard. The UV-vis spectra were measured with
a JASCO V-530 spectrophotometer and 10 mm quartz cell. All
melting points are uncorrected. FAB-Mass spectral data were
obtained on a JEOL JMS-SX102 spectrometer. Elemental
analyses were performed by the Microanalytical Laboratory of
Department of Chemistry, Faculty of Science, The University of
Tokyo. Compounds (E)-1a and (E)-1b were prepared according
to the literature.4
Synthesis of (E)-3b
Compound (E)-1b (70 mg, 177 μmol) and dichloro(cyclo-
octadiene)platinum (19.0 mg, 51 μmol) was stirred at r.t. in dry
CHCl3 (5 mL) for 5 min. After addition of hexane to the reaction
mixture, a precipitate was formed. The precipitate was filtrated,
washed with hexane, and dried in vacuo to give a red powder of
(E)-3b (77 mg, 66%).
Spectral and analytical data for (E)-3b: m.p. 256 °C
1
(decomp.). H NMR (500 MHz, CDCl3) δ 2.35 (s, 3H), 2.53 (s,
3
3H), 7.11 (d, JHH = 7.5 Hz, 1H), 7.42–7.53 (m, 7H), 7.74 (dd,
3
3
3JHP = 11.5 Hz, JHH = 7.5 Hz, 4H), 7.82 (d, JHH = 7.5 Hz,
1H), 8.03 (dd, 3JHH = 8.0 Hz, JHP = 4.0 Hz, 1H), 8.29 (dd, 3JHH
= 8.0 Hz, JHP = 4.0 Hz, 1H). 13C NMR (CDCl3, 75 MHz)
δ 21.31 (s), 23.11 (s), 119.98 (d, JCP = 9.6 Hz, JCPt = 19.2 Hz
(satellite)), 127.70 (s), 128.39 (d, JCP = 3.3 Hz, JCPt = 11.7 Hz
(satellite)), 129.03 (d, JCP = 10.8 Hz), 129.70 (d, JCP = 47.3 Hz,
JCPt = 15.0 Hz (satellite)), 131.06 (d, JCP = 2.3 Hz), 133.10 (s,
JCPt = 15.0 Hz (satellite)), 133.22 (d, JCP = 1.7 Hz), 133.48 (d,
JCP = 1.7 Hz), 133.59 (s, JCPt = 13.7 Hz (satellite)), 133.76 (s,
JCPt = 12.4 Hz (satellite)), 144.16 (d, JCP = 5.7 Hz), 145.67 (d,
JCP = 7.2 Hz, JCPt = 26.3 Hz), 155.38 (d, JCP = 16.8 Hz), 164.61
(d, JCP = 49.2 Hz), 165.44 (d, JCP = 65.1 Hz). 31P NMR
Synthesis of (E)-2a·ZnCl2·(THF)
To (E)-1a (65.6 mg, 0.18 mmol) in THF (0.5 mL) was added
zinc chloride (28.0 mg, 0.18 mmol), and the reaction solution
was stirred at room temperature for 5 min. Recrystallization from
the reaction solution gave orange crystals. The precipitate was
filtrated, washed with THF, and dried in vacuo to give yellow-
orange crystals of 2a·ZnCl2 (92.4 mg, 90%).
Spectral and analytical data for 2a·ZnCl2·(THF): m.p.
1
158.0–159.0 °C. H NMR (C6D6, 300 MHz) δ 1.36–1.45 (m,
1
(162 MHz, CDCl3) δ 30.2 (s, JPPt = 2072 Hz (satellite)). Anal.
Calcd for C26H22N2ClPPt, C, 50.05; H, 3.55; N, 4.49. Found C,
50.00; H, 3.90; N, 4.05%.
4H), 3.53–3.60 (m, 4H), 6.24–6.33 (m, 1H), 6.60 (t, J = 7.8 Hz,
1H), 6.69 (t, J = 8.4 Hz, 1H), 6.82 (t, J = 7.8 Hz, 2H), 6.85–6.92
(m, 2H), 6.95–7.10 (m, 5H), 7.39 (d, J = 8.4 Hz, 2H), 7.52 (dd,
J = 13.8, 7.2 Hz, 4H), 8.06 (dd, J = 8.7, 4.5 Hz, 1H). 31P NMR
(162 MHz, THF) δ 42.7 (br s). A reasonable 13C NMR spectrum
could not be obtained because of its quite low solubility. Anal.
Calcd for C28H27N2Cl2OPZn, C, 58.51; H, 4.73; N, 4.87. Found
C, 58.57; H, 4.86; N, 4.68%.
Computational method
Calculations were performed with Gaussian 03.14 The DFT and
TD-DFT15–17 calculations were performed with the B3LYP
method.18,19 The 6-311+G(d,p) basis set was used for C, H, N,
O, P and Cl, and LANL2DZ with effective core potentials20–22
for Zn, W, and Pt.
Synthesis of (E)-1b·W(CO)5
To a solution of W(CO)5(THF), which was prepared in situ from
W(CO)6 (180 mg, 0.51 mmol) in THF (10 mL), was added a
THF solution (5 mL) of (E)-1b (75 mg, 0.19 mmol) and
the reaction solution was stirred at r.t. for five hours. After
evaporation of the solvent, separation by silica gel chromato-
graphy (eluent: CHCl3) gave orange solid of (E)-1b·W(CO)5
(130 mg, 75%).
Acknowledgements
We thank Tosoh Finechem Corp. for gifts of alkyllithiums. This
work was supported by the Global COE Program for Chemistry
Innovation and Grants-in-Aid for Scientific Researches from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan (No. 22108508 and 22685005). M. Y. was granted a
Research Fellowship of Japan Society for the Promotion of
Science for Young Scientists.
Spectral and analytical data for (E)-1b·W(CO)5: m.p.
1
189.0–190.0 °C. H NMR (500 MHz, CDCl3) δ 2.27 (s, 3H),
2.32 (s, 3H), 6.69 (dd, J = 8.0 Hz, J = 0.8 Hz, 1H), 6.98–7.04
(m, 4H), 7.32 (dd, J = 8.0 Hz, J = 1.8 Hz, 1H), 7.35–7.41 (m,
6H), 7.58–7.65 (m, 4H), 7.86 (dd, J = 8.0 Hz, J = 4.5 Hz, 1H).
13C{1H} NMR (126 MHz, CDCl3) δ 21.50 (s, CH3), 21.78 (s,
CH3), 115.85 (d, JCP = 5.0 Hz, CH), 123.25 (s, CH), 128.30 (d,
JCP = 10.0 Hz, CH), 129.29 (s, CH), 129.91 (s, CH), 131.90 (s,
CH), 132.48 (d, JCP = 5.6 Hz, CH), 133.82 (d, JCP = 13.2 Hz,
CH), 135.72 (d, 1JCP = 42.0 Hz, CP), 136.55 (d, 1JCP = 36.3 Hz,
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