Combination of sp2- and sp3-type phosphorus atoms for gold chemistry: Preparation, structure, and catalytic activity of gold complexes that bear ligated 2-silyl-1,3-diphosphapropenes

Article abstract of DOI:10.1002/asia.201100310

Kinetically protected 2-silyl-1,3-diphosphapropenes that bear both sp ²- and sp³-type phosphorus atoms were employed in the preparation of gold complexes. The structural properties of the 1,3-diphosphapropene digold(I) complexes were

Full text of DOI:10.1002/asia.201100310

DOI: 10.1002/asia.201100310
Combination of sp2- and sp3-Type Phosphorus Atoms for Gold Chemistry:
Preparation, Structure, and Catalytic Activity of Gold Complexes That Bear
Ligated 2-Silyl-1,3-diphosphapropenes
Shigekazu Ito,* Lili Zhai, and Koichi Mikami[a]
Abstract: Kinetically protected 2-silyl-
1,3-diphosphapropenes that bear both
sp2- and sp3-type phosphorus atoms
were employed in the preparation of
gold complexes. The structural proper-
ties of the 1,3-diphosphapropene digol-
d(I) complexes were characterized by
properties of the ligand. The 2-silyl-1,3-
diphosphapropene-bis(chlorogold)
complexes catalyzed cycloisomerization
reactions of 1,6-enyne derivatives even
in the absence of silver co-catalyst, and
were able to be recovered after the re-
action. The catalytic activity of the
digold complexes primarily depended
on the sp2-type phosphorus atom and
the silyl group, and could be tuned by
the sp3-phosphino group. Additionally,
results on the catalytic activity of the
digold complex in the presence and ab-
sence of silver salts showed considera-
ble differences.
Keywords: aurophilicity · cycloiso-
merization · enynes · gold · phos-
phaalkenes
spectroscopic
and
crystallographic
analyses, which revealed unique auro-
philic interactions and conformational
Introduction
alysts that bear the ligated the 3,4-diphosphinidenecyclobu-
tene moiety to lead to environmentally benign processes.[7,8]
A combination of both low-coordinated sp2- and normal
sp3-type phosphorus atoms is a unique design. Such hybrid-
ized P2 ligands can display both the strong p-accepting
property of sp2-type phosphorus atoms and the supplemen-
tal characteristics of electronically and sterically tunable sp3-
phosphino groups. To date, we have studied 1,3-diphospha-
In homogeneous transition-metal catalysis, ligands are im-
portant in controlling catalytic properties: accordingly, the
design of ligands is crucial for the development of novel cat-
alysts.[1] In addition to l3s3-phosphorus compounds (R3P),
which have been routinely utilized as transition-metal cata-
lysts, lower-coordinated phosphorus compounds such as ki-
netically and thermodynamically stabilized phosphaalkenes
(l s -phosphorus, P=C<) are of interest because of their
strong p-accepting properties derived from their considera-
bly low-lying LUMO.[2,3] Ni-catalyzed olefin polymerization
promoted by an h3-diphosphaallyl ligand was a pioneering
application of low-coordinated phosphorus compounds for
catalysis,[4] and several p-delocalized molecules including
low-coordinated phosphorus, such as phosphinine (P-ana-
logue of pyridine) and phosphametallocene, have been uti-
lized for homogeneous catalysis.[5,6] Furthermore, Ozawa
and Yoshifuji have developed practical transition-metal cat-
À
À
propene ( P=C(R) P<) as a fundamental molecular system
that contains both sp2- and sp3-type phosphorus atoms.[9,10]
In the course of our research, we have found that a sterically
protected 1,3-diphosphapropene that bears a trimethylsilyl
group at the 2-position shows high stability and good coordi-
nating ability toward metals, which enables its use in transi-
tion-metal catalysis. Additionally, 2-silyl-1,3-diphosphapro-
3
2
À
pene was useful in elucidating the conformational character-
[11]
À
À
istics of the P=C P< system.
In this paper, we utilize 2-silyl-1,3-diphosphapropenes 1 in
gold complexes for the purpose of catalysis. The catalytic ac-
tivity of gold complexes normally stems from their soft
Lewis acidity based on remarkable relativistic effects,[12] and
effectively activates unsaturated organic moieties to lead to
a number of atom-economical molecular transformations.[13]
Previously we reported that some phosphaalkene gold com-
plexes were effective in catalyzing the cyclization of 1,6-
enyne and pent-4-ynoic acids without activation by a silver
co-catalyst.[14] These findings suggested an advantage of the
low-coordinated phosphorus compounds in catalysis. On the
[a] Prof. Dr. S. Ito, L. Zhai, Prof. Dr. K. Mikami
Department of Chemistry
Graduate School of Science and Engineering
Tokyo Institute of Technology
2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan)
Fax : (+81)3-5734-2143
E-mail: ito.s.ao@m.titech.ac.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100310.
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FULL PAPERS
other hand, no apparent catalytic activity was observed
when 2-methyl-1,3-diphosphapropene was employed in the
gold-catalyzed reactions, thus indicating that the relatively
strong s-donating sp3-phosphino group weakens the Lewis
acidity of the gold complex.[14a] Here, we report that an ap-
propriate design of the 1,3-diphosphapropene moiety, in
which silyl effects[15] are utilized, is suitable for a unique
type of gold catalysis. Along with catalytic activity, the struc-
tural properties of the gold
complexes are discussed in
terms of conformation. Further-
more, we report novel findings
related to the coordination
properties of the nonsymmetric
P2 ligands on gold atoms.
Results and Discussion
Figure 1. Molecular structure of 2a (50% probability ellipsoids). Hydro-
gen atoms are omitted for clarity. Selected bond lengths [ꢁ] and angles
Structural Characteristics of 2-Silyl-1,3-diphosphapropene
Digold(I) Complexes
À
À
À
À
[8]: Au1 Au2 3.0145(7), Au1 Cl1 2.293(2), Au2 Cl2 2.284(1), P1 Au1
À
À
À
À
2.251(2), P2 Au2 2.222(2), P1 C1 1.672(5), P2 C1 1.830(7), P1 C2
À
1.803(7), C1 Si 1.926(6); C1-P1-C2 117.3(3), C1-P1-Au1 129.8(2), C2-P1-
Compound 1a, prepared according to our previous report,[11]
was allowed to react with AuACTHNURGTNE(UNG tht)Cl (tht=tetrahydrothio-
phene; 2 equiv) to afford the corresponding dinuclear chlo-
rogold(I) complex 2a in moderate isolated yield (70%;
Scheme 1). Interestingly, in the complex formation, we ob-
served considerable changes in the 31P NMR spectroscopic
Au1 113.0(2), P1-C1-P2 110.3(3), P1-C1-Si 122.0(3), P2-C1-Si 127.5(3),
C1-P2-Au2 118.3(2), P1-Au1-Cl1 170.44(5), P1-Au1-Au2 84.60(4), Au2-
Au1-Cl1 104.94(4), P2-Au2-Cl2 170.53(5), Au1-Au2-Cl2 104.94(4).
that the silyl substituent might strengthen the aurophilic in-
teraction. Since the bonding energy of the aurophilic inter-
action is estimated to be 7–8 kcalmolÀ1,[16] the conformation
of 1a would be easily influenced. The interatomic distance
and angles around the 1,3-diphosphapropene moiety are
comparable with those in 1a except for the conformation
around the sp3-phosphino group.
Next, we employed a novel 2-silyl-1,3-diphosphapropene
derivative 1b. Aiming to improve the catalytic activity, we
employed a bis(4-trifluoromethylphenyl)phosphino group.[17]
Compound 1b was prepared from (E)- 3,3-dichloro-2-trime-
thylsilyl-1-(2,4,6-tri-tert-butylphenyl)-1,3-diphosphapropene
Scheme 1. Preparation of digold complex 2a.
resonance peaks. Whereas a mixture of 1a and Au
ACHTUNGTRNE(NUNG tht)Cl
(2 equiv) showed two 31P NMR spectroscopic resonances at
[(E)-Mes*P=CACTHNUTRGNE(UNG SiMe3)PCl2] (see the Supporting Informa-
d=309 and 41 ppm and a 2J
G
tion).[18] Similarly to 2a, digold complex 2b was obtained as
an air-stable crystalline compound. In contrast to 1a, in the
preparation process, no putative conformational rotation
that generated the rotational isomer (2b’) was observed;
105 Hz, the recrystallized product showed 31P NMR spectro-
2
scopic shifts (d=306 and 39 ppm) and J
(P,P) value (82 Hz)
different from those of the reaction mixture. As discussed
below, the X-ray structure of 2a shows that the conforma-
tion of the 1,3-diphosphapropene moiety changes to the Cs-
like structure from the C1 form of 1a.[11] As we described in
our previous report, 1,3-diphosphapropene displayed two
conformations that may be extremely stable even in solu-
tion, although the energetic difference between the two con-
formations is probably small.[11] In considering these find-
ings, it is plausible that the intermediary product 2a’ has the
same ligand structure as 1a.
À
this result indicates that the substituents on the P=CP<
system might influence the energy difference between the
lowest-energy conformers.
Figure 1 displays the molecular structure of 2a together
À
with typical metric parameters. The considerable Au Au
contact indicates the aurophilic interaction, and correspond-
ingly the P-Au-Cl angles are distorted from the linear geom-
Single crystals of 2b were obtained from dichlorome-
thane, and Figure 2 displays a drawing of the X-ray struc-
À
ture. In comparison with 2a, the Au Au distance is longer,
À
etry. The Au Au distance is shorter than that of [(E)-
and correspondingly the P-Au-Cl angles are closer to 1808.
[AuCl]2 (3.084 ꢁ),[14a] thus indicating
The elongated Au Au distance suggests a weaker aurophilic
À
Mes*P=C(Me)PPh2]
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Gold Complexes That Bear Ligated 2-Silyl-1,3-diphosphapropenes
is plausible that the structure of 4 includes an eight-mem-
bered metallacyclic skeleton, similar to the structure of
[Ph2PCH2PPh2]
In contrast to 1a, 2-silyl-1,3-diphosphapropene 1c that
bears the P(NMe2)2 group (see the Supporting Information)
[AuCl]2.[20,21]
2ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
showed stepwise coordination on gold and afforded an isola-
ble mononuclear gold(I) complex (3c), which subsequently
furnished digold(I) complex 2c. In the 31P NMR spectra, the
sp2 phosphorus of 3c exhibited a similar chemical shift to
2
that of 3a together with a comparable J
N
stant.
Catalytic Activity in the Absence of Silver Co-catalyst
A study of the catalytic properties of the dinuclear com-
plexes 2 was performed using cycloisomerization of 1,6-
enynes.[22] At first, the gold(I) complexes were employed for
cycloisomerization of 1,6-enyne 5 in the absence of silver
co-catalyst in dichloromethane at room temperature.
Whereas no clear catalytic activity was observed for [(E)-
Figure 2. Molecular structure of 2b (30% probability ellipsoids). Hydro-
gen atoms are omitted for clarity. Fluorine atoms in the CF3 groups are
À
disordered. Selected bond lengths [ꢁ] and angles [8]: Au1 Au2 3.1589(9),
À
À
À
À
Au1 Cl1 2.283(2), Au2 Cl2 2.274(2), P1 Au1 2.241(2), P2 Au2 2.228(2),
À
À
À
À
P1 C1 1.663(8), P2 C1 1.793(9), P1 C2 1.827(8), C1 Si 1.929(8); C1-P1-
C2 117.3(3), C1-P1-Au1 114.0(3), C2-P1-Au1 109.6(3), P1-C1-P2 108.4(5),
P1-C1-Si 123.8(5), P2-C1-Si 127.4(5), C1-P2-Au2 125.3(3), P1-Au1-Cl1
175.93(9), P1-Au1-Au2 80.10(6), Au2-Au1-Cl1 103.84(6), P2-Au2-Cl2
174.11(9), Au1-Au2-Cl2 101.31(7).
Mes*P=C(Me)PPh2]ACTHNUTRGNEUNG
[AuCl]2,[14a] dinuclear complexes 2 cata-
lyzed the cycloisomerization without silver co-catalyst
(Scheme 3). After 12 h, 2a and 2b afforded the correspond-
interaction that results from the electron density around the
gold atoms being decreased by the trifluoromethyl groups.[19]
Other metric parameters of 2b are similar to those of 2a.
Coordination Properties of 1,3-Diphosphapropene on Gold
To obtain more information about the unique coordination
properties of the nonsymmetric P2 ligand system, we next
Scheme 3. Cycloisomerization of 5 catalyzed by 2.
examined the reaction of 1a with 1 equiv of Au
ACHTUNGTRENN(UNG tht)Cl.
Compound 1a was mixed with Au(tht)Cl (1 equiv) in
AHCTUNGTRENNUNG
chloroform or dichloromethane; after 5 min, 1a was com-
pletely consumed and two adducts, namely, 3a (dP =423,
35 ppm; JACHTUNGTRENNUNG(P,P)=129 Hz) and 4 (dP =306, 39 ppm; JACHUTNGTRENN(UGN P,P)=
ing cyclized product 6 in good yield. Thus, the introduction
of a silyl substituent at the 2-position was effective in im-
proving the catalytic activity of 1,3-diphosphapropene gold
complexes, because the R3Si moiety could serve as a p-with-
drawing group.[15] Relative to 2a and 2b, the electron-with-
drawing substituent on the sp3-phosphino group slightly im-
proved the catalytic activity.[17] Interestingly, the gold com-
plexes 2 were recovered after the reaction and could be
reused.[23] On the other hand, digold complex 2c showed
low catalytic activity, probably due to a mesomeric effect of
the nitrogen lone pairs putatively reducing the electrophilic
character. Mononuclear complex 3c showed no catalytic ac-
tivity, thereby indicating the importance of the P=C moiety
in these reactions. The trimethylsilyl group was the optimal
silyl substituent for obtaining catalytically active 2-silyl-1,3-
diphosphapropene digold complexes.[24]
2
2
83 Hz) were observed (Scheme 2). The ratio of 3a and 4
Scheme 2. Two types of coordination modes of 1a toward gold.
reached about 1:1 after 7 h. Judging from our previous find-
ings with mononuclear gold complexes that bear the 1,3-di-
phosphapropene ligand,[14a] the structure of 3a could be as-
signed as a mononuclear complex. On the other hand, 4
showed similar 31P NMR spectroscopic data as 2a. However,
on the basis of the employed materials, the structure of 4
should be different from 2a. Although attempts to isolate
pure 4 were unsuccessful because of compound instability, it
The observed catalytic activity of 2 in the absence of
silver co-catalyst is principally based on the low-lying
LUMO of the P=C moiety,[2,14] which strengthens the soft
electrophilic character of the gold centers and additionally is
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S. Ito et al.
FULL PAPERS
assisted by silyl effects[11,15] and the aurophilic interaction.[12]
A key finding related to the catalytic mechanism is that 2
was recovered after the reaction (vide supra). This finding
might indicate that the structure of 2 was not largely per-
turbed in the cycloisomeriza-
Furthermore, 2a and 2b could be employed for cycloiso-
merization of 1,6-enyne that bears the NTs (Ts=tosyl)
moiety (10) under AgX-free conditions, although the con-
version was moderate (Scheme 5). In contrast to the case of
tion reaction. Therefore, it is
plausible that the nature of the
p-accepting property of the P=
C structure caused a formal in-
crease in the oxidation number
of the gold center(s), thereby
activating the acetylene part of
5
without a large structural
change of the digold complex.
This hypothesis may be consis-
tent with the finding that in-
Scheme 5. Cycloisomerizations of 10 catalyzed by 2.
creasing the steric encumbrance
around the P=C group of the 1,3-diphosphapropene remark-
ably lowered the reaction rate.[24] In theoretical studies, at-
tempts to characterize the hypothesized reaction intermedi-
ates are in progress.
Next, we examined cycloisomerization of the less reactive
substrate 7 in the presence of a catalytic amount of 2a or
2b. Although yields of the cycloisomerized product 8 were
low at room temperature (5% (2a) and 8% (2b)), the reac-
tion accelerated upon heating (Scheme 4). On the other
Ph3PAuSbF6,[22] 2a and 2b afforded four products 11–14.
Complex 2a afforded the exo-dig cyclization product 11 as
the major product, whereas 2b strongly promoted the endo-
dig pathway to product 12. Both 2a and 2b afforded the al-
ternative endo-dig product 13. Additionally, small amounts
of the ene reaction product 14 were also produced. General-
ly, in Au catalysis, such an ene reaction process is rarely ob-
served,[22b] and thus these results suggest the usefulness of
the employed ligands in exploration for novel Au-catalyzed
transformations. The lower conversion using 2b might be
a consequence of its instability at higher temperatures
and competitive coordination of the nitrogen on the gold
centers preventing activation of the acetylene moiety.
Effects of Silver Salts on the Catalytic Activity
In addition to the silver-salt-free conditions, we attempt-
ed to evaluate effects of silver co-catalyst so as to explore
the novel catalytic aspects of the digold complexes. By
using 2a, we examined cycloisomerization of 7 and 10,
which displayed low reactivity in the silver-salt-free con-
ditions.
Scheme 4. Cycloisomerizations of 7 catalyzed by 2.
hand, the coordination on the sp2 phosphorus was lost when
the reaction was carried out at over 80 and 708C for 2a and
2b, respectively; the higher temperature lowered the yield
of the cycloisomerized product on account of the generation
Scheme 6 displays the cycloisomerization of 7 in the pres-
ence of 2a and silver salt (2 equiv relative to 2a). Addition
of silver tetrafluoroborate and hexafluorophosphate for acti-
vation of 2a led to almost complete consumption of the
starting material and provided the cycloisomerized products
8 and 9 in moderate to good yield in shorter reaction times.
In contrast to the ordinary sp3-phosphine gold complexes
such as Ph3PAuSbF6,[22] the exo-dig and endo-dig products
were obtained in about a 1:1 ratio, thus indicating the effects
of the sterically encumbered sp2-type phosphorus moiety.[25]
On the other hand, a combination of 2a and AgSbF6 afford-
ed a small amount of 8 and a mixture of unidentified prod-
ucts, although all the starting material was consumed. There-
fore, the sp2-type phosphorus might induce catalytic activity
that is too high and in turn cause undesirable decomposition
of the starting enyne substrate.
of noncatalytic mononuclear species 3a and 3b (dP =434,
2
34 ppm, J
N
at the lower temperature indicates the effect of the CF3
group, which lessened the s-donating property of the sp2
phosphorus, as predicted by the lower-field 31P chemical
shift of the sp2-phosphorus nucleus. Whereas an ordinary
cationic Au catalyst such as Ph3PAuSbF6 (prepared from
Ph3PAuCl and AgSbF6) predominantly afforded the endo-
dig product,[22] the amount of 9 was small in the reactions
catalyzed by 2. Although the reaction mechanism has yet to
be completely elucidated, the
low yield of 9 might be related
to the nearly neutral reaction
conditions.
Next, we examined cycloisomerization of 10 in the pres-
ence of 2a and silver salt (2 equiv relative to 2a) and ob-
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Chem. Asian J. 2011, 6, 3077 – 3083

Gold Complexes That Bear Ligated 2-Silyl-1,3-diphosphapropenes
lectivity. In this work, we have
obtained some preliminary
findings on the substituent ef-
fects, and furthermore, we are
continuing to study appropriate
designs for more efficient gold
catalysts that bear ligated 1,3-
diphosphapropenes by examin-
ing various substituents.
Scheme 6. Cycloisomerizations of 7 in the presence of 2a and silver salt.
Experimental Section
1H, 13C, and 31P NMR spectra were recorded with a Bruker AV300M
spectrometer with Me4Si (1H, 13C) and H3PO4 (31P) as internal and exter-
nal standards. Mass spectra were recorded with JEOL JMS-T100CS and
JMS-700 spectrometers. X-ray diffraction data were collected with
Rigaku RAXIS-Rapid and Bruker
served nearly quantitative transformation to the cycloiso-
merized products (Scheme 7). Similarly to a previous report,
the endo-dig product 12 was predominantly obtained when
APEXII CCD diffractometers, and
structural refinement was carried out
with the SHELX-97 programs.[27] Prep-
aration of 1b and 1c is described in
the Supporting Information.
Preparation of 2a
A
solution of
1a[11]
1.60 mmol) and AuACHTUNGTREN(NUNG tht)Cl (2.88 mmol)
(875 mg,
in dichloromethane (60 mL) was
stirred at room temperature. The vola-
tile materials were removed in vacuo,
and the residue was recrystallized
from dichloromethane and hexane to
afford 2 (1.20 g, 74% yield) as yellow-
brown crystals. 1H NMR (300 MHz,
CDCl3): d=À0.27 (s, 9H; SiMe3), 1.33
(s, 9H; p-tBu), 1.71 (s, 18H; o-tBu),
7.52–7.63 ppm (m, 12H; arom);
13C{1H} NMR (75 MHz, CDCl3): d=
Scheme 7. Cycloisomerizations of 10 in the presence of 2a and silver salt. [a] Determined by NMR spectrosco-
py; [b] reaction time: 24 h.
1.7 (d, 4J
(s; o-CMe3), 39.6 (s; o-CMe3), 124.5 (d, 3J
(pt, (1J(P,C)+3J(P,C))/2=17.3 Hz; ipso-Mes*), 129.0 (dd, 1J
58.9 Hz, 3J(P,C)=13.6 Hz; ipso-Ph), 129.5 (d, 3J
(P,C)=12.3 Hz; m-Ph),
132.7 (d, 4J(P,C)=2.3 Hz; p-Ph), 135.2 (d, 2J
(P,C)=14.8 Hz; o-Ph), 153.3
(dd, 1J(P,C)=22.6 Hz, 1J(P,C)=6.8 Hz; P=C), 154.6 (d, 2J
(P,C)=4.0 Hz;
(P,C)=2.0 Hz; p-Mes*); 29Si{1H} NMR
ACHTUNGTRENNUNG
AgBF4, AgPF6, or AgSbF6 was employed as co-catalyst.
Thus, the combination of 2a and silver co-catalyst showed
catalytic activity toward 10 similar to that of typical phos-
phine gold complexes. On the other hand, slow formation of
the ene-type product 14, which was predominantly formed
when AgOTs was used as co-catalyst, indicated the genera-
tion of an intriguing Au catalytic species under the reaction
conditions.[26]
AHCTUNGTRENNUNG
G
E
ACHTUNGTRENNUNG
E
ACHTUNGTRENNUNG
G
ACHTUNGTRENNUNG
E
G
ACHTUNGTRENNUNG
o-Mes*), 155.7 ppm (d, 4J
ACHTUNGTRENNUNG
(60 MHz, CDCl3): d=3.8 ppm (dd, 2J
A
2
2
(121 MHz, CDCl3): d=38.8 ppm (d, J
A
ACHNUTTGREGNN(UN P,P)=82.6 Hz; P=C); APCI-MS: m/z: calcd for C34H49Au2Cl2P2Si
[M+H]+: 1011.1787; found: 1011.1753.
Preparation of 2b
Conclusions
Similarly to 1a, 2b was obtained from 1b and AuACHTNUTRGNEUNG(tht)Cl (2 equiv) in
74% isolated yield as brown crystals. 1H NMR (300 MHz, CDCl3): d=
À0.28 (s, 9H; SiMe3), 1.33 (s, 9H; p-tBu), 1.72 (s, 18H; o-tBu), 7.62 (brs,
2H; arom), 7.84–7.97 ppm (m, 8H; arom); 13C{1H} NMR (75 MHz,
Sterically protected 2-trimethylsilyl-1,3-diphosphapropenes
1 can be utilized as a nonsymmetric P2 ligand system for
unique digold(I) complexes 2. The molecular structures of 2
were determined and discussed in terms of conformational
characteristics and aurophilic interactions. The dinuclear
gold complexes 2 catalyzed cycloisomerization reactions of
1,6-enyne derivatives without silver co-catalysts, thus indi-
cating that this catalyst design is appropriate for the non-
symmetric P2 ligand system. These findings are expected to
be useful in the exploration for novel gold catalysts that
enable more efficient molecular transformation with high se-
CDCl3): d=1.8 (dd, 3J
ACHTUNGTRENNUNG
3
1
3
124.6 (d, J
14.3 Hz; ipso-Mes*), 126.0–126.8 (m; CF3), 133.1 (dd, 1J
3J(P,C)=14.3 Hz; ipso-C6H4), 134.8 (dq, 4J(P,C)=3.0 Hz, 2J
33.0 Hz; p-C6H4), 135.4 (d, 4J(P,C)=15.8 Hz; o-C6H4), 149.7 (dd, 1J-
(P,C)=21.0 Hz, 1J(P,C)=7.5 Hz; P=C), 154.8 (d, 2J
(P,C)=4.5 Hz; o-
Mes*), 156.3 ppm (d, 4J(P,C)=2.3 Hz; p-Mes*); 31P{1H} NMR (121 MHz,
(P,C)=9.2 Hz; m-C6H4), 125.9 (dd, J
E
ACHTUNGTRENNUNG(P,C)=
AHCTUNGTRENNUNG
R
R
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
E
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
CDCl3): d=38.3 (d, 2J(P,P)=96.0 Hz; PPh2), 314.9 ppm (d, 2J
ACTHNUTRGENNUG ACHTUNGTRENNUNG(P,P)=
96.0 Hz; P=C); APCI-MS: m/z: calcd for C36H47Au2Cl2F6P2Si [M+H]+:
1147.1535; found: 1147.1541.
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3081

S. Ito et al.
FULL PAPERS
Preparation of 3c
Acknowledgements
A solution of 1c (ꢀ1.5 mmol, see the Supporting Information) and Au-
This work was supported in part by Grants-in-Aid for Scientific Research
(nos. 20750098 and 22350058) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan and Nissan Chemicals Co. Ltd.
The authors thank Prof. Hiroharu Suzuki and Dr. Masataka Oishi of
Tokyo Institute of Technology, and Dr. Kenji Yoza of Bruker AXS, for
supports of X-ray crystallographic analyses.
ACHTUNGTRENNUNG(tht)Cl (1.5 mmol) in dichloromethane (45 mL) was stirred at room tem-
perature. The volatile materials were removed in vacuo, and the residue
was washed with hexane to afford 3c (1.05 g, 98% yield) as a yellow
solid. 1H NMR (300 MHz, CD2Cl2): d=À0.10 (s, 9H; SiMe3), 1.35 (s,
9H; p-tBu), 1.52 (s, 18H; o-tBu), 2.91 (d, 3J
ACTHNUTRGNEUNG(P,H)=12.0 Hz, 6H; NMe2),
7.41 ppm (d, 4J
CD2Cl2): d=1.5 (d, J
(P,C)=8.3 Hz; NMe2), 34.8 (s; p-CMe3), 38.5 (s; o-CMe3), 40.1 (d, 3J-
(P,C)=6.8 Hz; o-CMe3), 122.2 (s; m-Mes*), 138.0 (dd, 1J
(P,C)=74.3 Hz,
3J(P,C)=26.3 Hz; ipso-Mes*), 151.5 (s; o-Mes*), 153.7 (d, 2J
(P,C)=
3.0 Hz; p-Mes*), 178.1 ppm (dd, 1J(P,C)=78.8 Hz, 1J
(P,C)=15.0 Hz; P=
C); 31P{1H} NMR (121 MHz, CD2Cl2): d=104.3 (d, 2J
(P,P)=127.6 Hz; P-
(P,P)=127.6 Hz; P=C). MS measurements did
ACHTUNGTRENNUNG
(P,H)=2.0 Hz, 2H; Mes*); 13C{1H} NMR (75 MHz,
3
2
ACHTUNGTRENNUNG(P,C)=2.3 Hz; SiMe3), 30.9 (s; p-CMe3), 34.0 (d, J-
ACHTUNGTRENNUNG
[1] For recent books, see: a) R. H. Crabtree, The Organometallic
Chemistry of the Transition Metals, Wiley, New Jersey, 2009; b) J.
Hartwig, Organotransition Metal Chemistry: From Bonding to Catal-
ysis, University Science Books, 2009.
[2] a) P. Le Floch, Coord. Chem. Rev. 2006, 250, 627; b) M. Okazaki, A.
Hayashi, C.-F. Fu, S.-T. Liu, F. Ozawa, Organometallics 2009, 28,
902; c) J. Waluk, H.-P. Klein, A. J. Ashe, J. Michl, Organometallics
1989, 8, 2804.
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(NMe2)2), 409.8 ppm (d, 2J
not afford the [M]+ peak due to instability of the ionization conditions.
Preparation of 2c
[3] K. B. Dillon, F. Mathey, J. F. Nixon, Phosphorus: The Carbon Copy,
Wiley, Chichester, 1998.
[4] W. Keim, R. Appel, S. Gruppe, F. Knoch, Angew. Chem. 1987, 99,
1042; Angew. Chem. Int. Ed. Engl. 1987, 26, 1012.
[5] L. Weber, Angew. Chem. 2002, 114, 583; Angew. Chem. Int. Ed.
2002, 41, 563.
[6] C. Mꢃller, D. Vogt, Dalton Trans. 2007, 5505.
[7] a) F. Ozawa, M. Yoshifuji, Dalton Trans. 2006, 4987; b) F. Ozawa, M.
Yoshifuji, C. R. Chim. 2004, 7, 747.
[8] F. Ozawa, H. Okamoto, S. Kawagishi, S. Yamamoto, T. Minami, M.
Yoshifuji, J. Am. Chem. Soc. 2002, 124, 10968.
[9] a) S. Ito, M. Yoshifuji, Chem. Commun. 2001, 1208; b) H. Liang, K.
Nishide, S. Ito, M. Yoshifuji, Tetrahedron Lett. 2003, 44, 8297; c) H.
Liang, S. Ito, M. Yoshifuji, Org. Lett. 2004, 6, 425.
A solution of 3c (571 mg, 0.80 mmol) and AuACTHNUTRGNE(NUG tht)Cl (0.80 mmol) in di-
chloromethane (35 mL) was stirred at room temperature for 2 h. The vol-
atile materials were removed in vacuo, and the residual solid was recrys-
tallized from dichloromethane/hexane to afford 2c (550 mg, 73% yield)
as pale-brown crystals. 1H NMR (300 MHz, CD2Cl2): d=À0.07 (s, 9H;
SiMe3), 1.36 (s, 9H; p-tBu), 1.75 (s, 18H; o-tBu), 2.92 (d, 3J
ACTHNUTRGNE(NUG P,H)=
12.0 Hz, 6H; NMe2), 7.62 ppm (d, 4J
ACTHNUTRGNE(UNG P,H)=2.0 Hz, 2H; Mes*);
13C{1H} NMR (75 MHz, CD2Cl2): d=1.3 (s; SiMe3), 30.8 (s; p-CMe3),
2
34.5 (dd, J
N
(s; o-CMe3), 124.4 (d, 3J
A
ACHTUNGTRENNUNG
20.3 Hz, 3J
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(NMe2)2), 303.1 ppm (d, 2J
À
À
for C26H50Au2Cl2N2P2Si [M]+: 944.1927; found: 944.1932.
[10] For alternative P=C P< systems based on phosphinine, see:
a) D. G. Holah, A. N. Hughes, K. L. Knusden, J. Chem. Soc. Chem.
Commun. 1988, 493; b) G. Mꢄrkl, C. Dçrges, T. Riedl, F. G. Klꢄrner,
C. Lodwig, Tetrahedron Lett. 1990, 31, 4589; c) K. Waschbꢃsch, P. Le
Floch, F. Mathey, Organometallics 1996, 15, 1597; d) N. Mꢅzailles, P.
Le Floch, K. Waschbꢃsh, L. Ricard, F. Mathey, C. P. Kubiak, J. Or-
ganomet. Chem. 1997, 541, 277.
X-ray Crystallographic Data of 2
Compound
2a:
Diffractometer:
Bruker
APEXII
CCD;
C34H48Au2Cl2P2Si·CH2Cl2; yellow prisms (CH2Cl2), Mr =1096.51; crystal
3
¯
dimensions 0.09ꢂ0.08ꢂ0.07 mm , triclinic, space group P1 (no. 2); a=
11.504(3), b=11.557(3), c=17.021(4) ꢁ; a=79.155(2), b=75.779(2), g=
[11] S. Ito, K. Nishide, M. Yoshifuji, Organometallics 2006, 25, 1424.
[12] a) D. J. Gorin, F. D. Toste, Nature 2007, 446, 395; b) P. Pyykkç,
Angew. Chem. 2004, 116, 4512; Angew. Chem. Int. Ed. 2004, 43,
4412; c) M. Lein, M. Ludolph, S. K. Hashmi, P. Schwerdtfeger, Or-
ganometallics 2010, 29, 2206; d) M. Pernpointner, A. S. K. Hashmi,
J. Chem. Theory Comput. 2009, 5, 2717.
64.213(2)8; V=1966.5(7) ꢁ3; Z=2; l=0.71073 ꢁ; T=93 K; 1calcd
=
ACHTUNGTRENNUNG
1.852 gcmÀ3; m(MoKa)=7.859 mmÀ1; F000 =1060; 11496 total reflections
(2qmax =54.968); index ranges=À14ꢁhꢁ14, À14ꢁkꢁ10, À22ꢁlꢁ22;
8661 unique reflections (Rint =0.021); R1=0.0314 (I>2s(I)); 0.0408 (all
data); wR2=0.0708 (I>2s(I)); 0.0747 (all data); S=1.024 (409 parame-
ters). Compound 2b: Diffractometer: Rigaku RAXIS-Rapid detector;
C36H46Au2Cl2F6P2Si; reddish yellow prisms (CH2Cl2), Mr =1147.59; crystal
dimensions 0.18ꢂ0.08ꢂ0.05 mm3; monoclinic, space group P21/a (no. 14);
a=13.5083(6), b=16.7758(8), c=19.6676(10) ꢁ; b=102.0761(14)8; V=
[13] For recent reviews, see: a) N. D. Shapiro, F. D. Toste, Synlett 2010,
675; b) A. S. K. Hashmi, Angew. Chem. 2010, 122, 5360; Angew.
Chem. Int. Ed. 2010, 49, 5232; c) Z. Li, C. Brouwer, C. He, Chem.
Rev. 2008, 108, 3239; d) A. Arcadi, Chem. Rev. 2008, 108, 3266;
e) E. Jimꢅnez-Nfflnez, A. M. Echavarren, Chem. Rev. 2008, 108,
3326; f) D. J. Gorin, B. D. Scherry, F. D. Toste, Chem. Rev. 2008, 108,
3351; g) M. M. Díaz-Raquejo, P. J. Pꢅrez, Chem. Rev. 2008, 108,
3379; h) N. T. Patil, Y. Yamamoto, Chem. Rev. 2008, 108, 3395;
i) H. C. Shen, Tetrahedron 2008, 64, 7847; j) R. A. Widenhoefer,
Chem. Eur. J. 2008, 14, 5382; k) A. S. K. Hashmi, M. Rudolph,
Chem. Soc. Rev. 2008, 37, 1766; l) M. Marion, S. Nolan, Chem. Soc.
Rev. 2008, 37, 1776; m) A. S. K. Hashmi, G. J. Hutchings, Angew.
Chem. 2006, 118, 8064; Angew. Chem. Int. Ed. 2006, 45, 7896.
[14] a) M. Freytag, S. Ito, M. Yoshifuji, Chem. Asian J. 2006, 1, 693; b) S.
Ito, S. Kusano, N. Morita, K. Mikami, M. Yoshifuji, J. Organomet.
Chem. 2010, 695, 291.
[15] S. Zhang, X.-M. Zhang, F. G. Bordwell, J. Am. Chem. Soc. 1995,
117, 602.
[16] H. Schmidbaur, W. Graf, G. Mꢃller, Angew. Chem. 1988, 100, 439;
Angew. Chem. Int. Ed. Engl. 1988, 27, 417.
[17] a) J. P. Markham, S. T. Staben, F. D. Toste, J. Am. Chem. Soc. 2005,
127, 9708; b) P. García-García, M. A. Fernµndez-Rodríguez, E.
Aguilar, Angew. Chem. 2009, 121, 5642; Angew. Chem. Int. Ed.
2009, 48, 5534; c) T. Hirai, A. Hamasaki, A. Nakamura, M. Tokuna-
4358.3(4) ꢁ3; Z=4; l=0.71075 ꢁ; T=123 K; 1calcd =1.749 gcmÀ3
ACHTUNGTRENNUNG
(MoKa)=6.997 mmÀ1; F000 =2208; 36539 total reflections (2qmax =54.968);
; m-
index ranges=À17ꢁhꢁ17, À21ꢁkꢁ21, À25ꢁlꢁ25; 9950 unique re-
flections (Rint =0.084); R1=0.0579 (I>2s(I)); 0.0881 (all data); wR2=
0.1505 (I>2s(I)); 0.1763 (all data); S=1.044 (583 parameters).
CCDC 819182 (2a) and CCDC 819183 (2b) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
General Procedure for the Cycloisomerization of 1,6-Enynes
Compounds 5,[28] 7,[29] and 10[30] (0.20 mmol) were allowed to react with a
gold complex (3 or 5 mol%) in dichloromethane or 1,2-dichloroethane
(2 mL). The solvent was evaporated and the residue was extracted with
hexane. The organic layer was purified by silica-gel column chromatogra-
phy (hexane/AcOEt). Products 6,[14,22] 8,[14b,31] 9,[32] 11,[33] 12,[22b] 13,[34] and
14[30] were characterized by 1H NMR spectroscopic data. Silver co-cata-
lyst was employed for reactions described in Scheme 6 and Scheme 7.
3082
www.chemasianj.org
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 3077 – 3083

Gold Complexes That Bear Ligated 2-Silyl-1,3-diphosphapropenes
ga, Org. Lett. 2009, 11, 5510; d) M. Egi, K. Azechi, M. Saneto, K.
Shimizu, S. Akai, J. Org. Chem. 2010, 75, 2123.
[18] H. Liang, K. Nishide, S. Ito, M. Yoshifuji, J. Organomet. Chem.
2005, 690, 4809.
[26] a) Products 12, 13, and 14 were obtained in a 1:4:5 ratio when 2a
and 1 equiv of AgBF4 were used; b) Effects of silver salts: A. S. K.
Hashmi in Silver in Organic Chemistry (Ed.: M. Harmata), Wiley,
New Jersey, 2010, pp. 357–379.
[19] K. Nunokawa, S. Onaka, T. Tatematsu, M. Ito, J. Sakai, Inorg. Chim.
Acta 2001, 322, 56.
[20] H. Schmidbaur, A. Wohlleben, U. Schubert, A. Frank, G. Huttner,
Chem. Ber. 1977, 110, 2751.
[27] G. Sheldrick, T. Schneider, Methods Enzymol. 1997, 277, 319.
[28] R. Mook, P. M. Sher, Org. Synth. 1985, 66, 75.
[29] K. Miura, H. Saito, N. Fujisawa, A. Hosomi, J. Org. Chem. 2000, 65,
8119.
[21] The mixture of 3a and 4 did not show any catalytic activity in the
absence of Ag co-catalyst.
[30] B. M. Trost, F. D. Toste, J. Am. Chem. Soc. 2002, 124, 5025.
[31] C. Gonzµlez-Rodríguez, J. A. Varela, L. Castedo, C. Saµ, J. Am.
Chem. Soc. 2007, 129, 12916.
[32] H. Kim, C. Lee, J. Am. Chem. Soc. 2005, 127, 10180.
[33] F. Monnier, C. V. Bray, D. Castillo, V. Aubert, S. Dꢅrien, P. H. Dix-
neuf, L. Toupet, A. Ienco, C. Mealli, J. Am. Chem. Soc. 2007, 129,
6037.
[22] a) C. Nieto-Oberhuber, M. P. MuÇoz, E. BuÇuel, C. Nevado, D. J.
Cµrdenas, A. M. Echavarren, Angew. Chem. 2004, 116, 2456; Angew.
Chem. Int. Ed. 2004, 43, 2402; b) C. Nieto-Oberhuber, S. López,
M. P. MuÇoz, E. Jimꢅnez-NuÇꢅz, E. BuÇuel, D. J. Cµrdenas, A. M.
Echavarren, Chem. Eur. J. 2006, 12, 1694.
[23] After the 1st run, recovered 2a catalyzed the cycloisomerization
from 5 to 6 in 66% yield.
[34] M. Mꢅndez, M. P. MuÇoz, C. Nevado, D. J. Cµrdenas, A. M. Echa-
varren, J. Am. Chem. Soc. 2001, 123, 10511.
[24] Digold(I) complex [(E)-Mes*P=C
ACHTUNGTRENGU(N SiEt3)PPh2]CAHTUNGTREN[NUGN AuCl]2 catalyzed cy-
cloisomerization from 5 to 6 in 20% yield.
[25] Similar results were obtained when 2a and 1 equiv of silver salt
Received: March 29, 2011
were used.
Published online: August 10, 2011
Chem. Asian J. 2011, 6, 3077 – 3083
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
3083