Homoannular double friedel-crafts acylation of phosphametallocenes

Article abstract of DOI:10.1021/om200678q

Two reaction modes of homoannular double Friedel-Crafts acylation are realized using polyalkylphosphametallocenes as substrates. The first example is the reaction of tetra(tert-butyl)diphospharuthenocene with excess acetyl chloride/aluminum chloride, givi

Full text of DOI:10.1021/om200678q

ARTICLE
pubs.acs.org/Organometallics
Homoannular Double FriedelꢀCrafts Acylation of
Phosphametallocenes
Masamichi Ogasawara,*,† Morihiko Ogura,† Takeshi Sakamoto,† Susumu Watanabe,† Sachie Arae,†
Kiyohiko Nakajima,‡ and Tamotsu Takahashi*,†
†Catalysis Research Center and Graduate School of Life Science, Hokkaido University, Kita-ku, Sapporo 001-0021, Japan
‡Department of Chemistry, Aichi University of Education, Igaya, Kariya, Aichi, 448-8542, Japan
S Supporting Information
b
ABSTRACT: Two reaction modes of homoannular double FriedelꢀCrafts acylation
are realized using polyalkylphosphametallocenes as substrates. The first example is
the reaction of tetra(tert-butyl)diphospharuthenocene with excess acetyl chloride/
aluminum chloride, giving a 2,3-double FriedelꢀCrafts acylation product with
an elimination of one of the tert-butyl groups. The other is the 2,5-diacylation
of 10,20,3,30,4,40,50-Me7-phosphaferrocene using an acyl chloride/aluminum
chloride mixture. These reactions provide rare examples of doubly functionalized
phosphametallocenes.
Scheme 1. Friedel-Crafts Acetylation of Ferrocene3b
’ INTRODUCTION
The FriedelꢀCrafts reaction is an electrophilic aromatic sub-
stitution that is a classical protocol for direct functionalization of
aromatic compounds. While FriedelꢀCrafts alkylation tends to
afford polyalkyl products, the corresponding acylation typically
gives monoacylated products predominantly,1 because the initial
products have an electron-withdrawing acyl substituent that
deactivates the aromatic ring toward further electrophilic sub-
stitutions. For this reason, double acylation on the same aromatic
ring is rather rare and can be achieved only for specific aromatic
substrates,2 while double FriedelꢀCrafts acylation at two remote
reaction sites within a single molecule takes place.
atom is preferentially acylated. While the β-acylphospholyl com-
pound is obtained as a minor product, acylation on the η5-C5H5
ring is not detected (Scheme 2).5a
Meanwhile, metallocenes and half-metallocenes exhibit aro-
maticity, as with benzene derivatives, since the η5-cyclopentadienyl
ligands possess six π-electrons. Indeed, some (η5-cyclopentadienyl)-
metal complexes, such as ferrocenes and cymantrenes, are known
to be excellent substrates for FriedelꢀCrafts acylation reactions.3
The parent ferrocene (η5-C5H5)2Fe is much more reactive than
benzene toward FriedelꢀCrafts acylations, and double acylation
of ferrocene is operational. However, the two acyl substituents
are usually distributed between the two η5-cyclopentadienides,
leading to 1,10-diacylferrocene as a major product. The two η5-
cyclopentadienides in a ferrocene molecule are electronically
communicating with each other through the central Fe(II)
cation; that is, after the introduction of the first acyl group onto
the ferrocene core, the remaining unsubstituted Cp ligand is
deactivated by the acyl group in the other cyclopentadienyl
moiety. However, the second η5-Cp is still capable of being acylated
under the more rigorous conditions to give a heteroannular
double-acylation product in good yield with >98% selectivity
(Scheme 1).3b
Scheme 2. FriedelꢀCrafts Acetylation of
Phosphaferrocene5a
On the other hand, we recently demonstrated that certain
phosphametallocenes behaved in completely different ways under
forcing FriedelꢀCrafts acylation conditions.6 Reactions between
Cy4-diphospharuthenocene or the corresponding osmocene
analogue and an acyl electrophile (AcCl/AlCl3) produce a
μ-vinylidene species, where a vinylidene moiety bridges the
Ru/Os center and the phosphorus atom. This reaction proceeds
via an initial attack of the acetyl electrophile to the metal center
followed by activation of the acyl CdO double bond. The
homologous Cy4-diphosphaferrocene affords a conventional
Phosphaferrocenes undergo electrophilic acylation under the
standard FriedelꢀCrafts conditions in a similar manner.4,5 In the
parent monophosphaferrocene, the α-position to the phosphorus
Received: July 28, 2011
Published: August 29, 2011
r
2011 American Chemical Society
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FriedelꢀCrafts acetylation product under identical conditions
dichloromethane for 48 h gave a mixture of three acetylated
products, 2ꢀ4, in 6%, 21%, and 18% yield, respectively, accom-
panied by 45% recovery of 1 (Scheme 4). The compounds are
separable by conventional silica gel column chromatography.
Although 2 and 3 are not crystalline, their structures are
unambiguously determined by the combination of the 1H, 13C,
and 31P NMR analyses, elemental analyses, and HRMS measure-
ments as 3-acetyl-2,20,5,50-tBu4-diphospharuthenocene (2) and
4-acetyl-2,20,50-
(Scheme 3).
Scheme 3. Reactions of Cy4-Diphosphametallocenes of
Group 8 Triad6
tBu3-diphospharuthenocene (3), respectively. Compound 2 is
C1-symmetric and shows four tBu singlets, a CH3-CO singlet, and
1
three phospholyl resonances in the H NMR spectrum. The
phospholyl CH signals are coupled with the phosphorus nucleus
through small coupling constants (JPH < 4.5 Hz), which are typical
values for β-CH’s in phosphametallocenes. Compound 3 shows
t
three Bu singlets, a CH3-CO singlet, and four phospholyl reso-
1
nances in the H NMR spectrum. While three of the four
phospholyl CH signals at δ 5.15, 5.33, and 5.78 (in CDCl3)
are assigned to β-phospholyl hydrogens with the smaller PꢀH
coupling constants (JPH = 4.6ꢀ5.4 Hz), the remaining phospho-
lyl CH resonance at δ 4.78 displays a larger PꢀH coupling of
JPH = 35.0 Hz, which is characteristic of an α-phospholyl
hydrogen. A positive NOE correlation between the α-phospholyl
CH and the acetyl signals implies the structure shown in
Scheme 4 for compound 3, excluding the isomeric 3-acetyl-
2,20,50-tBu3-diphospharuthenocene.
In this article, we would like to report two examples of homo-
annular double FriedelꢀCrafts acylations on phosphametallo-
cene platforms. The first example is the dealkylative 2,3-diacyla-
tion of 2,20,5,50-tBu4-diphospharuthenocene (eq 1), and the
other one is the 2,5-diacylation of 10,20,3,30,4,40,50-Me7-phospha-
ferrocene (eq 2). These reactions provide rare examples of doubly
functionalized phosphametallocenes.7,8 It should be mentioned
that the homoannular double FriedelꢀCrafts acylation of the
Me7-phospharuthenocene, which is closely related to the second
reaction in this article, was recently reported by Carmichael,
Piechaczyk, and their co-workers independently (eq 3).9
The 1H and 13C NMR spectra of 4 suggest that the compound
t
possesses three Bu groups, two acetyl groups, and three
β-phospholyl hydrogens; however, the distribution of these
substituents in the diphospharuthenocene core could not be
identified by the NMR measurements. Prismatic crystals of 4
were grown from EtOAc/EtOH. Their analysis by single-crystal
X-ray diffraction confirmed that4 is thehomoannular diacetylation
species with an intact diphospharuthenocene core (Figure 1). One
of the two η5-phospholyl ligands remains intact with the two α-tBu
substituents. In the other η5-phospholyl, the two acetyl groups are
located on the adjacent α- and β-carbons, C(5) and C(6), while a
tBu substituent is placed at the α0-position (C(8)). The two
η5-phospholyls adopt an eclipsed conformation, and the five sub-
stituents are located in a way to minimize the steric repulsions
between them. The dihedral angle between the two η5-phospholyl
ligands is 4.90°. Overall, the structural characteristics of 4 are similar
to those of 2,20,5,50-Cy4-diphospharuthenocene.10
A plausible reaction pathway from 1 to 4 is shown in Scheme 5.
The first step is the acetylation of 1 at a β-position on the
phospholyl rings to give 2. Since all the α-positions in 1 are
’ RESULTS AND DISCUSSION
t
blocked by the Bu groups, the acetylation is forced to happen
at the β-position.6a The second step is the de-tert-butylation
Dealkylative 2,3-Double Acetylation of (η5-PC4H2-2,5-
tBu2)2Ru. Treatment of 2,20,5,50-tBu4-1,10-diphospharuthenocene
(1: prepared from [RuCl2(cod)]n and 2,5-tBu2-1-Ph-phosphole)10
with an acetyl electrophile (2 equiv to 1), which was generated
from equimolar CH3COCl and AlCl3, in refluxing
t
of 2 under FriedelꢀCrafts conditions. The Bu group adjacent
to the acetyl substituent is selectively removed from 2 to give 3,
in which a nucleophilic α-phospholyl CH is now available for
further electrophilic substitution. Finally, the unprotected α-CH
Scheme 4. FriedelꢀCrafts Acetylation of Diphospharuthenocene 1
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position in 3 is acetylated to furnish the homoannular double
acylation product 4. The scenario that includes initial de-tert-
butylation of 1 is also considered as an alternative route to 4.
In this case, the primary product 5 possesses a more nucleophilic
α-CH. Thus, the subsequent FriedelꢀCrafts acetylation should
produce 6 instead of 3. The second acetylation of 6 leading to 4 is
highly unlikely, because the β-phospholyl CH’s are inherently
less nucleophilic5 and the acetylated phospholyl is deactivated
from further electrophilic substitution. Indeed, the intermediates
5 and 6 were not detected in the reaction mixture, while 2 and 3
were isolated together with 4 (vide supra). An independent
experiment also supports the pathway via 2 and 3: a reaction
of the isolated 3 with an equimolar mixture of AcCl/AlCl3
(4 equiv with respect to 3) in refluxing dichloromethane in
48 h gave 4 in 67% yield.
The yield of 4 could not be greatly improved even with a large
excess of acetyl electrophile (4 equiv to 1; see Scheme 4). After
separation of 4 from the reaction mixture by column chroma-
tography, the residual mixture containing 1, 2, and 3 was treated
with AcCl/AlCl3 (2 equiv) in refluxing dichloromethane to give
an additional 20ꢀ23% yield of 4. With these three successive
separation/acetylation procedure, the diacetyl compound 4 was
obtained in 47ꢀ52% combined yields.
In the homoannular double acylation of 1, the tBu substituents
function as a protecting group to prevent the more reactive
α-phospholyl positions from the initial electrophilic attack.11
After the introduction of the first acetyl group to 1, the deal-
kylation uncovers the “protected” α-CH. Although the un-
masked α-CH is deactivated by the adjacent acetyl group, it is
still reactive enough for the second acetylation. The key to
success in the present dealkylative double acylation is the use
of tert-alkyl groups on a diphospharuthenocene. In the Friedelꢀ
Crafts acetylation of 2,20,5,50-Cy4-diphospharuthenocene, which
possesses sec-alkyl (cyclohexyl) substituents, an analogous deal-
kylation did not proceed under the same conditions. Thus,
a double acetylation product was not detected, although the
Cy4-Ac-diphospharuthenocene was obtained.6a With an α-silyl
substituent in a phospharuthenocene core, desilylative acylation
takes place to give an α-acylphospharuthenocene.12
It should be noted that the reaction of 1 with AcCl/AlCl3 did
not afford the μ-vinylidene species 7 (Scheme 5, bottom). This
provides a clear contrast to the reaction of the Cy4-diphospha-
ruthenocene analogue, which gave the μ-vinylidene complex as a
major product under identical conditions by way of an initial
electrophilic attack of Ac+ to the ruthenium center (Scheme 3,
middle).6a The tBu groups in 1 are much bulkier than cyclohexyl
groups, which might hinder the electrophilic attack to the
t
ruthenium center. Indeed, the local steric impact of the Bu
groups in 1 is much larger than that of the Cy substituents in
(η5-2,5-Cy2-phospholyl)2Ru. The 1H and 13C NMR spectra of
(η5-2,5-Cy2-phospholyl)2Ru at 23 °C show only one set
of resonances for the Cy and the β-CH groups, indicating
rapid rotation of the phospholyl rings about the phospho-
lylꢀRuꢀphospholyl axis.10 On the other hand, the NMR
Figure 1. ORTEP drawing of 4 with 30% thermal ellipsoids. All
hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ru(1)ꢀP(1) = 2.413(2), Ru(1)ꢀP(2) = 2.404(2),
P(1)ꢀC(1) = 1.768(7), P(1)ꢀC(4) = 1.751(6), P(2)ꢀC(5) = 1.793(6),
P(2)ꢀC(8) = 1.792(7), Ru(1)ꢀphospholylP(1)C(1ꢀ4) = 1.834, Ru(1)ꢀ
phospholylP(2)C(5ꢀ8) = 1.823; C(1)ꢀP(1)ꢀC(4) = 90.4(3), C(5)ꢀ
P(2)ꢀC(8) = 88.3(3).
t
spectrum of 1 displays the two Bu resonances and the two β-
CH signals at 23 °C due to the interlocked C2-symmetric
conformation as shown in Figure 2.13,14
Scheme 5. Plausible Reaction Pathways for Reactions of 1 with Acetyl Electrophile
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Scheme 7. Homoannular Double FriedelꢀCrafts Acylation
of Phosphaferrocene 12
Figure 2. Interlocked conformation of the diphospharuthenocene 1.
Scheme 6. FriedelꢀCrafts Acetylation of Diphosphaferro-
cene 8
The present dealkylative double acetylation is characteristic to
the phospharuthenocene species. Treatment of 2,20,5,50-tBu4-
diphosphaferrocene (8), which is isostructural to 1, with AcCl/
AlCl3 under conditions identical with Scheme 4 produced a pair
of monoacetyl diphosphaferrocenes, 9 (21%) and 10 (42%), but
the diacetyl compound 11 was not obtained (Scheme 6). A
reaction of the isolated 10 with AcCl/AlCl3 led to partial
decomposition of 10, and 11 could not be obtained.
The diacetyl compound 4 is a rare example of phospha-
metallocenes having two functional groups in a single η5-phos-
pholide. Although several homoannular doubly functionalized
phosphametallocenes have been reported in recent years,7ꢀ9 all
of them possess the functional groups at the 2- and 5-positions of
the η5-phospholide. To the best of our knowledge, compound 4
is the first example of a 2,3-difunctionalized phosphametallocene.
2,5-Double Acylation of (η5-PC4H2-3,4-Me2)FeCp*. While
the homoannular 2,3-double acylation of the diphosphaferrocene
8 was unsuccessful, a different type of homoannular double
acylation could be achieved in 10,20,3,30,4,40,50-Me7-phospha-
ferrocene15 (12). This reaction is analogous to the homoannular
double FriedelꢀCrafts acylation of the isostructural phosphar-
uthenocene, which was reported recently.9
Treatment of 12 with an equimolar mixture of AcCl/AlCl3 (3
equiv to 12) in refluxing dichloromethane for 24 h gave the 2,5-
diacetyl-10,20,3,30,4,40,50-Me7-phosphaferrocene (13) cleanly. The
diacetyl compound was easily purified by silica gel chromato-
graphy, and a deep-red crystalline compound was isolated in 89%
yield (Scheme 7). FriedelꢀCrafts acylation of 12 was reported
previously.16 The use of acylation reagents, such as Ac2O/TfOH
Figure 3. ORTEP drawing of 13 with 30% thermal ellipsoids. All
hydrogen atoms are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Fe(1)ꢀP(1) = 2.269(2), Fe(1)ꢀC(1) = 2.076(4),
Fe(1)ꢀC(2) = 2.083(3), Fe(1)ꢀC(6) = 2.052(6), Fe(1)ꢀC(7) =
2.059(5), Fe(1)ꢀC(8) = 2.064(4), P(1)ꢀC(1) = 1.784(4), Fe(1)ꢀ
phospholyl =1.649, Fe(1)ꢀCp* = 1.677; C(1)ꢀP(1)ꢀC(1*) = 88.6(2),
P(1)ꢀC(1)ꢀC(2) = 113.4(3), C(1)ꢀC(2)ꢀC(2*) = 112.3(3).
into 15, introduction of two different acyl substituents into
a single η5-phospholyl ligand was achieved with complete
chemoselectivity.
Prismatic crystals of 13 were grown from EtOH and analyzed
by single-crystal X-ray diffraction (Figure 3). The complex is
symmetric with respect to the P(1)ꢀFe(1)ꢀC(6)ꢀC(9) plane.
No intermolecular interaction is detected in 13. The phospholyl
ligand and Cp* are nearly parallel: the dihedral angle between the
two is 2.54°. The distance between the least-squares plane of the
phospholyl ligand and Fe(1) is 1.649 Å, which is within the range
of those in the other phosphaferrocenes. Orientation of the acetyl
group displays conjugation with the phosphaferrocene core with
the OꢀC(3)ꢀC(1)ꢀC(2) torsion angle being 1.77°. Overall
structural characteristics of 13 are similar to those of the ruthenium
homologue.9
For the success of the present double acetylation of 12, the
presence of the Cp* ligand seems to be important. Monophos-
phaferrocene 16, which possesses η5-C5H5 in place of η5-Cp* of
12, reacted with AcCl/AlCl3 rapidly. However, a major product
was the monoacetyl compound 17,17 and the corresponding
double acetylation species were not obtained even with a large
excess of AcCl/AlCl3 (up to 5 equiv to 18). The failure of the
double acetylation of 16 can be ascribed to the relatively low
electron density of the acetylphospholide in 17. It is supposed
or (CF3CO)2O/BF3 OEt2, resulted in the selective monoacyla-
3
tion of 12, but formation of the corresponding diacylated com-
pounds was not described. We also confirmed that the reaction of
12 with Ac2O/BF3 OEt2 afforded the monoacetylphosphafer-
3
rocene 14 exclusively in a nearly quantitative yield (98%). It was
found that a choice of acylation reagents was important in the
second acylation of 14. A reaction of the isolated 14 with an
equimolar mixture of AcCl/AlCl3 (1.5 equiv to 14) in refluxing
dichloromethane in 20 h gave 13 in 92% yield. Similarly, 14
reacted with PhCOCl/AlCl3 (1.5 equiv to 14) to give 15 in
95% yield. By the stepwise acylation of 12 into 14 and then
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Scheme 8. FriedelꢀCrafts Acetylation of Phosphaferrocene 16
Hz), 119.5 (d, JPC = 67.8 Hz), 124.4 (d, JPC = 67.8 Hz). 31P{1H}
NMR (C6D6): δ ꢀ50.2. Anal. Calcd for C24H40P2Ru: C, 58.64; H,
8.20. Found: C, 58.32; H, 8.19. EI-HRMS calcd for C24H40P2Ru:
492.1649. Found: 492.1640.
FriedelꢀCrafts Acetylation of Diphospharuthenocene 1.
To a suspension of AlCl3 (90 mg, 675 μmol) in dichloromethane (4 mL)
was added acetyl chloride (55 mg, 700 μmol) at room temperature. The
mixture was stirred at this temperature for 1 h, then added to a
dichloromethane (4 mL) solution of 1 (166 mg, 336 μmol). The
mixture was refluxed for 48 h. The reaction was quenched by addition
of water (0.5 mL), then evaporated to dryness under vacuum. The
residue was extracted with dichloromethane, and the extract was further
purified by silica gel chromatography. The three acetylation products
2ꢀ4 were obtained in 6%, 21%, and 18% yield, respectively, together
with the recovered 1 (45%). The characterization data for 2ꢀ4 are
given below.
that the substitution of η5-Cp by the more electron-donating
η5-Cp* increases the reactivity of the η5-2-acetyl-3,4-dimethyl-
phospholyl ligand toward electrophilic attack. Analogous
activation of an η5-phospholide by an electron-donating
trans ligand was reported in a phosphine-coordinating phos-
phacymantrene.18
’ CONCLUSIONS
3-Acetyl-2,20,5,50-tetra(tert-butyl)-1,10-diphospharuthe-
nocene (2). 1H NMR (CDCl3): δ 1.08 (s, 9H), 1.23 (s, 9H), 1.24 (s,
9H), 1.27 (s, 9H), 2.46 (s, 3H), 5.09 (dd, JPH = 4.5 Hz, JHH = 2.9 Hz,
1H), 5.22 (d, JPH = 4.0 Hz, 1H), 5.38 (br, 1H). 31P{1H} NMR (CDCl3):
δ ꢀ50.1, ꢀ34.4. EI-HRMS calcd for C26H42OP2Ru: 534.1754. Found:
534.1753. The 13C NMR spectrum of this compound could not be
obtained due to the low yield of the compound.
Two examples of homoannular double FriedelꢀCrafts acyla-
tion are realized using the properly polyalkylated phosphame-
tallocene substrates. In the double acetylation of 2,20,5,50-tBu4-
diphospharuthenocene, the tBu substituents work as a protecting
group, preventing the more reactive α-phospholyl positions from
the initial electrophilic attack. After the introduction of the first
acetyl group at a β-position, the adjacent tBu group is removed
via FriedelꢀCrafts retroalkylation. The second acetylation at the
unprotected α-position furnishes the homoannular 2,3-double
acetylation product. On the other hand, the two α-CH positions
in 10,20,3,30,4,40,50-Me7-phosphaferrocene are activated by the
electron-donating Cp* ligand, and thus 2,5-double acylation can
be achieved using acylation reagents derived from acyl chloride/
aluminum chloride.
3-Acetyl-20,5,50-tri(tert-butyl)-1,10-diphospharuthenocene
(3). 1H NMR (CDCl3): δ 1.08 (s, 9H), 1.13 (s, 9H), 1.19 (s, 9H), 2.46
(s, 3H), 4.78 (dd, JPH = 35.0 Hz, JHH = 0.7 Hz, 1H), 5.15 (dd, JPH = 4.7
Hz, JHH = 3.0 Hz, 1H), 5.33 (dd, JPH = 4.6 Hz, JHH = 3.0 Hz,1H), 5.78
(dd, JPH = 5.4 Hz, JHH = 0.7 Hz, 1H). 13C{1H} NMR (CDCl3): δ 27.1
(d, JPC = 3.5 Hz), 32.8ꢀ34.1 (m, tBu- ꢁ 3), 79.6 (d, JPC = 64.7 Hz), 80.6
(d, JPC = 4.3 Hz), 81.3 (d, JPC = 5.7 Hz), 81.7 (d, JPC = 4.4 Hz), 94.8 (d,
JPC = 5.7 Hz), 122.4 (d, JPC = 67.3 Hz), 124.3 (d, JPC = 67.0 Hz), 126.7
(d, JPC = 65.6 Hz), 200.8 (s). 31P{1H} NMR (CDCl3): δ ꢀ42.9, ꢀ32.0.
EI-HRMS calcd for C22H34OP2Ru: 478.1128. Found: 478.1126.
2,3-Diacetyl-20,5,50-tri(tert-butyl)-1,10-diphospharutheno-
cene (4). 1H NMR (CDCl3): δ 1.09 (s, 9H), 1.26 (s, 9H), 1.29 (s, 9H),
2.30 (d, JPH = 1.3 Hz, 3H), 2.38 (s, 3H), 5.24 (dd, JPH = 4.6 Hz, JHH = 3.1
Hz, 1H), 5.27 (dd, JPH = 4.6 Hz, JHH = 3.1 Hz, 1H), 5.54 (d, JPH = 5.1 Hz,
1H). 13C{1H} NMR (CDCl3): δ 30.8 (s), 31.5 (d, JPC = 4.4 Hz),
33.2ꢀ33.9 (m, tBu- ꢁ 3), 82.6 (d, JPC = 6.1 Hz), 83.2 (d, JPC = 4.8 Hz),
85.0 (d, JPC = 4.5 Hz), 94.5 (d, JPC = 3.9 Hz), 100.2 (d, JPC = 70.4 Hz),
124.3 (d, JPC = 68.2 Hz), 127.07 (d, JPC = 67.3 Hz), 127.13 (d, JPC = 67.8
Hz), 201.3 (s), 202.2 (d, JPC = 19.7 Hz). 31P{1H} NMR (CDCl3):
δ ꢀ45.2, ꢀ15.8. Anal. Calcd for C24H36OP2Ru: C, 55.48; H, 6.98.
Found: C, 55.37; H, 7.01. EI-HRMS calcd for C24H36OP2Ru: 520.1234.
Found: 520.1236.
2,20,5,50-Tetra(tert-butyl)-1,10-diphosphaferrocene (8).
Preparation of this compound was achieved according to the synthetic
method reported for an analogous compound.21 A THF (15 mL)
solution of 1-Ph-2,5-tBu2-phosphole (637 mg, 2.34 mmol) was treated
with lithium metal (100 mg, 14.5 mmol), and the mixture was stirred at
rt overnight. The mixture was filtered through a glass filter, and to the
filtrate was added anhydrous AlCl3 (104 mg, 0.780 mmol) at 0 °C. After
stirring for 30 min at room temperature, the THF solution was
transferred onto a slurry of anhydrous FeCl2 (148 mg, 1.17 mmol) in
THF (10 mL) by means of cannula. After stirring the mixture for 12 h at
60 °C, all the volatiles were removed under reduced pressure. The
residue was extracted with hot hexane. The crude product was purified
by silica gel chromatography (elution with hexane) under a nitrogen
atmosphere to give the title compound in pure form. Yield: 332 mg
(0.744 mmol, 64%). 1H NMR (CDCl3): δ 1.20 (s, 18H), 1.32 (s, 18H),
’ EXPERIMENTAL SECTION
General Procedures. All anaerobic and/or moisture-sensitive
manipulations were carried out with standard Schlenk techniques under
predried nitrogen or with glovebox techniques under prepurified argon.
1H NMR (at 400 MHz) and 13C NMR (at 101 MHz) chemical shifts are
reported in ppm downfield of internal tetramethylsilane. 31P NMR (at
162 MHz) chemical shifts are externally referenced to 85% H3PO4.
Tetrahydrofuran and benzene were distilled from benzophenone-ketyl
under nitrogen prior to use. Dichloromethane was distilled from CaH2
under nitrogen prior to use. [RuCl2(η4-C8H12)]n,19 1-Ph-2,5-tBu2-
phosphole,20 and 10,20,3,30,4,40,50-Me7-phosphaferrocene (12)15 were
prepared as reported. All the other chemicals were obtained from
commercial sources and used without additional purification.
2,20,5,50-Tetra(tert-butyl)-1,10-diphospharuthenocene (1).
Preparation of this compound was achieved according to the synthetic
method reported for analogous compounds.10 A THF (20 mL) solution
of 1-Ph-2,5-tBu2-phosphole (1.50 g, 5.50 mmol) was treated with lithium
metal(320mg, 46.1mmol), andthemixturewasstirredovernightat rt. The
mixture was filtered through a plug of glass wool, and to the filtrate was
added anhydrous AlCl3 (250 mg, 1.87 mmol) at 0 °C.21 After stirring for
30 min at room temperature, the resulting mixture was transferred onto a
slurry of [RuCl2(η4-C8H12)]n (771 mg, 2.75 mmol/Ru) in THF
(3 mL), and the mixture was refluxed for 48 h. After cooling the mixture,
all the volatiles were removed under reduced pressure. The residue
was extracted with hot hexane. The crude product was purified by
silica gel chromatography (elution with hexane) under a nitrogen
atmosphere to give the title compound in pure form. Yield: 987 mg
(2.01 mmol, 73%). 1H NMR (C6D6): δ 1.12 (s, 18H), 1.36 (s, 18H),
4.95 (dd, JPH = 4.4 Hz, JHH = 2.9 Hz, 2H), 4.99 (dd, JPH = 4.5 Hz, JHH
= 2.9 Hz, 2H). 13C{1H} NMR (C6D6): δ 33.1 (d, JPC = 6.2 Hz), 33.7
(d, JPC = 13.2 Hz), 33.9 (m), 79.0 (d, JPC = 4.8 Hz), 79.8 (d, JPC = 5.2
4.88 (dd, JPH = 4.7 Hz, JHH = 2.9 Hz, 2H), 4.94 (dd, JPH = 4.5 Hz, JHH
=
2.9 Hz, 2H). 13C{1H} NMR (CDCl3): δ 33.0 (d, JPC = 6.5 Hz), 33.8 (d,
JPC = 14.4 Hz), 33.9 (m), 77.2 (d, JPC = 5.2 Hz), 77.7 (d, JPC = 4.8 Hz),
115.9 (d, JPC = 64.4 Hz), 121.3 (d, JPC = 64.3 Hz). 31P{1H} NMR
5049
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Organometallics
ARTICLE
(CDCl3): δ ꢀ73.7. Anal. Calcd for C24H40P2Fe: C, 64.58; H, 9.03.
Found: C, 64.25; H, 8.92. EI-HRMS calcd for C24H40FeP2: 446.1955.
Found: 446.1953.
FriedelꢀCrafts Acetylation of Diphosphaferrocene 8. This
reaction was conducted in the same way with the acetylation of 1 as
mentioned above. The two acetylation products 9 and 10 were obtained
in 21% and 42% yield, respectively, together with the recovered 8 (30%).
The characterization data for 9 and 10 are given below.
’ ASSOCIATED CONTENT
Supporting Information. 1H, 13C, and 31P NMR spectra
S
b
for all the new compounds and crystallographic data for 4 and 13
(in CIF format). This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
3-Acetyl-2,20,5,50-tetra(tert-butyl)-1,10-diphosphaferrocene
(9). 1H NMR (CDCl3): δ 1.12 (s, 9H), 1.28 (s, 9H), 1.32 (s, 9H), 1.37
(s, 9H) 2.43 (s, 3H) 4.88 (d, JPH = 4.2 Hz, 1H), 5.14 (d, JPH = 3.6 Hz, 1H),
5.28 (br, 1H). 31P{1H} NMR (CDCl3): δ ꢀ73.4, ꢀ55.9. EI-HRMS calcd
for C22H34FeOP2: 432.1434. Found: 432.1426. The 13C NMR spectrum
of this compound could not be obtained due to the low yield of the
compound.
3-Acetyl-20,5,50-tri(tert-butyl)-1,10-diphosphaferrocene (10).
1H NMR (CDCl3): δ 1.20 (s, 18H), 1.30 (s, 9H), 2.59 (s, 3H), 4.62 (d, JPH
= 34.6 Hz, 1H), 4.84 (dd, JPH = 4.4 Hz, JHH = 3.1 Hz, 1H), 5.23 (br, 1H),
5.47 (d, JPH = 4.9 Hz, 1H). 13C{1H} NMR (CDCl3): δ 28.0 (d, JPC = 3.5
Hz), 33.1 (d, JPC = 4.8 Hz), 33.4 (d, JPC = 4.8 Hz), 33.5 (d, JPC = 7.0 Hz),
33.7 (d, JPC = 13.1 Hz), 34.0 (d, JPC = 14.5 Hz), 34.1 (d, JPC = 13.6 Hz),
78.0 (br), 78.5 (d, JPC = 5.7 Hz), 79.4 (br), 80.4 (d, JPC = 62.1 Hz), 91.7
(d, JPC = 4.9 Hz), 120.6 (d, JPC = 64.3 Hz), 121.9 (d, JPC = 64.3 Hz, 2C),
202.9 (s). 31P{1H} NMR (CDCl3): δ ꢀ65.5, ꢀ47.6. EI-HRMS calcd for
C22H34FeOP2: 432.1434. Found: 432.1426.
Corresponding Author
*E-mail: ogasawar@cat.hokudai.ac.jp.
’ ACKNOWLEDGMENT
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas “Synergistic Effects for Creation of
Functional Molecules” from the Ministry of Education, Culture,
Sports, Science and Technology, Japan. S.W. has been a recipient
of the JSPS Research Fellowship for the Young Scientists.
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BF3 OEt2 in place of AcCl/AlCl3.16 The acetylation/benzoylation of 14
3
was conducted in a similar manner. The characterization data for 13ꢀ15
are given below.
2,5-Diacetyl-10,20,3,30,4,40,50-heptamethyl-1-phosphafer-
rocene (13). 1H NMR (CDCl3): δ 1.63 (s, 15H), 2.27 (s, 6H), 2.32 (d,
JPH = 3.3 Hz, 6H). 13C{1H} NMR (CDCl3): δ 9.3 (s), 12.3 (s), 32.0 (d,
JPC = 11.5 Hz), 84.6 (s), 90.4 (d, JPC = 58.0 Hz), 99.5 (d, JPC = 8.7 Hz),
203.7 (d, JPC = 24.5 Hz). 31P{1H} NMR (CDCl3): δ ꢀ25.1. Anal. Calcd
for C20H27FeO2P: C, 62.19; H, 7.05. Found: C, 61.98; H, 7.06. EI-
HRMS calcd for C20H27FeO2P: 386.1098. Found: 386.1097.
2-Acetyl-10,20,3,30,4,40,50-heptamethyl-1-phosphaferrocene
(14) (ref 16). 1H NMR (CDCl3): δ 1.73 (s, 15H), 2.03 (s, 3H), 2.23 (d,
JPH = 2.9 Hz, 6H), 3.65 (d, JPH = 36.4 Hz, 1H). 13C{1H} NMR
(CDCl3): δ 10.2 (s), 12.5 (s), 14.3 (s), 31.6 (d, JPC = 11.5 Hz), 83.7 (s),
85.0 (d, JPC = 55.6 Hz), 89.3 (d, JPC = 60.4 Hz), 92.9 (d, JPC = 4.8 Hz),
100.2 (d, JPC = 7.7 Hz), 205.2 (d, JPC = 23.9 Hz). 31P{1H} NMR
(CDCl3): δ ꢀ44.6. Anal. Calcd for C18H25FeOP: C, 62.81; H, 7.32.
Found: C, 62.79; H, 7.44. EI-HRMS calcd for C18H25FeOP: 344.0992.
Found: 344.0992.
2-Acetyl-5-benzoyl-10,20,3,30,4,40,50-heptamethyl-1-phos-
phaferrocene (15). 1H NMR (CDCl3): δ 1.65 (s, 15H), 2.03 (s, 3H),
2.31 (br, 6H), 7.40 (t, J = 7.6 Hz, 2H), 7.51 (t, J = 7.6 Hz, 1H), 7.64 (d,
J = 7.6 Hz). 13C{1H} NMR (CDCl3): δ 9.6 (s), 12.8 (d, JPC = 12.3 Hz,
2C), 32.0 (d, JPC = 11.8 Hz), 85.1 (s), 90.7 (d, JPC = 60.4 Hz), 92.6 (d,
JPC = 59.9 Hz), 97.3 (d, JPC = 5.3 Hz), 101.2 (d, JPC = 4.8 Hz), 127.9 (s),
129.2 (d, JPC = 6.6 Hz), 131.9 (s), 141.8 (s), 200.4 (d, JPC = 21.0 Hz),
204.3 (d, JPC = 24.1 Hz). 31P{1H} NMR (CDCl3): δ ꢀ23.4. Anal. Calcd
for C25H29FeO2P: C, 66.98; H, 6.52. Found: C, 66.76; H, 6.52. EI-
HRMS calcd for C25H29FeO2P: 448.1255. Found: 448.1252.
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