A. Sinha et al. / Journal of Organometallic Chemistry 770 (2014) 116e120
117
MeCN nitrogen, N3 {Ru(1)-N(3) 2.035(5) Å} and one chloride, Cl1
{Ru(1)-Cl(1) 2.4086(18) Å} (Fig. 1). There is no interaction between
the [Ru(PPh3)2(bipy)(MeCN)Cl]þ cation and the BPh4ꢀ anion.
Scheme 1. Two possible products of the reaction of allylic acetate with nucleophiles.
[Ru(PPh3)2(bipy)(MeCN)Cl][BPh4] (1) catalyzed reaction of
allylacetate with phenols
Results and discussion
We were interested in studying the efficacy of 1 as catalyst for
allylic substitution. The reaction of cinnamyl acetate with 4-tert-
butylphenol in toluene was chosen as a model reaction to establish
the reaction condition. Cinnamyl acetate (1.3 mmol) was mixed
with 4-tert-butylphenol (1 mmol), 1 (0.02 mmol) and K2CO3
(1.5 mmol) in toluene (2.5 cm3) and the reaction mixture was
heated and the reaction was monitored by TLC. To begin with the
reaction was carried out for 12 h at room temperature. However, we
could not detect any product formation. When the temperature of
the oil bath was raised to 100 ꢁC we could detect the product for-
mation. However, at that temperature both branched and linear
products were formed. When the reaction was refluxed for 2 h,
both branched and linear products were obtained. But when the
reaction mixture was refluxed for prolonged period (9 h) only linear
product was obtained and maximum conversion was achieved. It
may be mentioned that, a similar observation was made by
Kawatsura and coworkers in the nucleophilic substitution of allylic
amination [24] and they have suggested that, the branched prod-
uct, produced initially, undergoes ruthenium catalyzed isomeriza-
tion to give linear product. In this case also, it is suggested that, with
prolonged heating the initially produced branched product un-
dergoes isomerization in the presence of 1.
Synthesis and characterization of [Ru(PPh3)2(bipy)(MeCN)Cl][BPh4]
(1)
The complex has been synthesized by the reaction of [Ru(bi-
py)(PPh3)2Cl2] with NaBPh4 in acetonitrile in good yield. The
complex has been characterized by elemental analysis, IR UVevi-
sible and 1H and 31P NMR spectroscopy and single crystal X e ray
diffraction.
The elemental analysis agrees well with the composition. The 1H
NMR spectrum of the complex shows a singlet at 2.07 ppm due to
uncoordinated acetonitrile and multiplets in the region 8.62 to 6.77
due to the aromatic protons of the coordinated PPh3 ligand and
BPhꢀ4 anion. The appearance of signal for free CH3CN in the 1H NMR
spectrum clearly shows that, in solution, the [Ru(PPh3)2(bipy)(-
MeCN)Cl]þ species looses coordinated, labile CH3CN ligand and
produces coordinatively unsaturated pentacoordinated species,
[Ru(bipy)(PPh3)2Cl]þ. The 31P NMR spectrum of the complex shows
a singlet at 33.7 ppm due to coordinated PPh3 ligand.
Crystal structure of [Ru(PPh3)2(bipy)(MeCN)Cl][BPh4] (1)
We then proceeded to examine the solvent effect for the model
reaction. Thus, reactions were carried out in different solvents and
the conversion was monitored by 1H NMR spectroscopy. We could
not detect any product when reactions were carried out in solvents
like, DMF, DMSO, MeCN, THF and acetone. This may be due to the
blocking of coordination sites by these coordinating solvents.
However, product formation could be observed in solvents like,
dichloromethane, dichloroethane, benzene, dioxane and toluene
(Table 3). In toluene highest conversion was observed. We then
examined the efficacy of various ruthenium compounds as catalyst
for the allylation reaction. Ruthenium trichloride was found to be
completely ineffective. However, ruthenium(II) complexes were
found to afford cinnamyl phenyl ether (Table 4). The complex
[Ru(PPh3)2(CH3CN)3Cl][BPh4] was found to be least effective and 1
was found to be most effective. The effect of base was also exam-
ined and K2CO3 was found to be the most effective base (Table 5).
Having established the reaction condition, the scope of the re-
action was tested. The reactions of various phenols with cinnamyl
acetate, allylacetate and 2-methyl-allylacetate were carried out
(Table 6, Scheme 2) and the corresponding E-allylethers were iso-
lated in 64e90% yield with moderate turnover number. The reac-
tion was found to be effective in the cases of phenols. However, the
reaction was completely ineffective when aliphatic alcohols were
used as nucleophiles. In the cases, of allylacetate and 2-methyl-
allylacetate the conversion was found to be poor. The products
were characterized by 1H and 13C NMR spectroscopy. Further, the
newly synthesized compounds, 4k, 4m and 4n have been charac-
terized by high resolution mass spectrometry (HRMS). In addition,
2,4-di-tert-butyl-1-(3-phenyl-allyloxy)-benzene, 4c, has been
structurally characterized by single crystal X-ray crystallography.
The compound crystallizes in monoclinic space group P21/n. The
crystal data for the compound has been given in Table 1 and
important bond distance and bond angles are given in Table 2. The
single crystal X-ray structure confirms the trans geometry of
compound (Fig. 2).
The compound crystallizes in monoclinic space group P21/c. The
crystallographic data are given in Table 1 and important bond
distances and bond angles are given in Table 2. X-Ray diffraction
analysis reveals that, the asymmetric unit of 1 consists of a ruthe-
nium center coordinated to two trans PPh3 ligands, one bipyridine,
one MeCN and one chloride and a non coordinated BPhꢀ4 anion.
In the cationic [Ru(PPh3)2(bipy)(MeCN)Cl]þ species, two PPh3
ligands occupy axial positions {Ru(1)-P(2) 2.3898(16) Å, Ru(1)-P(1)
2.3967(16) Å; P(2)-Ru(1)-P(1) 177.55(6)ꢁ}. The basal positions are
occupied by two bipyridine nitrogens, N1 and N2 {Ru(1)-N(1)
2.059(5) Å, Ru(1)-N(2) 2.048(5) Å; N(2)-Ru(1)-N(1) 79.1(2)ꢁ}, one
Table 1
Crystal data and structure refinement for 1 and 4c.
Compound
1
4c
Empirical formula
Formula weight
Temperature, K
Wavelength (Å)
Crystal system
Space group
C72H31BClN3P2Ru
1167.43
293(2)
0.71073
Monoclinic
P21/c
C23H31
322.47
293(2)
0.71073
Monoclinic
P21/n
O
A, b, c (Å)
9.7436(5), 29.5237(15),
21.7474(11)
105.064(3)
6041.0(5)
4
14.992(5), 5.907(5),
22.779(5)
98.226(5)
1996.5(19)
4
b
(ꢁ)
V (Å3)
Z
Dcalc. (Mg/m3)
1.284
0.401
1.073
0.063
m
(Mo-Ka) (mmꢀ1
)
F(000)
q
2440
1.19 to 26.58
12,407
8553
0.0652
704
1.53 to 25.12
22,807
3545
0.0656
range (ꢁ)
Reflections collected
Unique reflections/
R(int)
Restraints
1632
0
parameters
662
223
Goodness of fit (F2)
1.122
1.014
R1 [I > 2
s
(I)], wR2
0.0808, 0.2084
0.0652, 0.1752