Preparation of osmium η3-allenylcarbene complexes and their uses for the syntheses of osmabenzyne complexes

Article abstract of DOI:10.1021/acs.organomet.6b00102

Treatment of OsCl₂(PPh₃)₃ with HCCAr (Ar = Ph, p-tolyl) produced the ³-allenylcarbene complexes OsCl₂(ξ =CAr- ²-CH=CHAr)(PPh₃)₂. Reactions of the ³-allenylcarbene complexes with gold alkynyls Au(Cξ -CR)(PPh₃) (R = Ph, p-tolyl, TMS, ⁿBu, CH(OEt)₂) or copper(I) alkynyls Cu(C CR) (R = Ph, TMS) in the presence of HNEt₃Cl produced the osmabenzynes Os{ CC(R)ξ - =C(CH₂Ar)CHξ - =CAr}Cl₂(PPh₃)₂. Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation with HNEt₃Cl.

Full text of DOI:10.1021/acs.organomet.6b00102

Article
pubs.acs.org/Organometallics
Preparation of Osmium η3‑Allenylcarbene Complexes and Their Uses
for the Syntheses of Osmabenzyne Complexes
Ting Bin Wen, Ka-Ho Lee, Jiangxi Chen, Wai Yiu Hung, Wei Bai, Huacheng Li, Herman H. Y. Sung,
Ian D. Williams, Zhenyang Lin,* and Guochen Jia*
Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong
S
* Supporting Information
ABSTRACT: Treatment of OsCl2(PPh3)3 with HCCAr (Ar = Ph, p-
tolyl) produced the η3-allenylcarbene complexes OsCl2(CAr-η2-CH
CCHAr)(PPh3)2. Reactions of the η3-allenylcarbene complexes with gold
n
alkynyls Au(CCR)(PPh3) (R = Ph, p-tolyl, TMS, Bu, CH(OEt)2) or
copper(I) alkynyls Cu(CCR) (R = Ph, TMS) in the presence of
HNEt3Cl produced the osmabenzynes Os{CC(R)C(CH2Ar)CH
CAr}Cl2(PPh3)2. Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium
alkynyl-allenylcarbene intermediates followed by protonation with HNEt3Cl.
desirable to explore other routes to construct metallabenzyne
rings.
INTRODUCTION
■
There has been much interest in the chemistry of transition-
metal-containing metallaaromatics.1,2 Metallabenzenes, in
particular, have attracted considerable attention.3 A number
of metallabenzenes with various substituents have been isolated
especially for those of platinum,4 iridium,5 osmium,6
ruthenium,7 and rhenium.8 Metallabenzynes are another
interesting class of metallaaromatics that are structurally closely
related to metallabenzenes. In contrast to metallabenzenes,
reported well-characterized metallabenzynes are still limited.9,10
Syntheses of new metallabenzynes with different metals and
substituents on the metallacycle remain as one of the major
objectives in the development of the chemistry of metal-
labenzynes.
In this work, we report the syntheses of a series of
osmabenzynes from the reactions of η3-allenylcarbene com-
plexes OsCl2(CAr-η2-CHCCHAr)(PPh3)2 with gold-
(I)/Cu(I) alkynyls. In particular, we will describe the syntheses
of two η3-allenylcarbene complexes OsCl2(CAr-η2-CH
CCHAr)(PPh3)2 from the reactions of OsCl2(PPh3)3 with
HCCAr, report the reactions of these η3-allenylcarbene
osmium complexes with gold(I)/Cu(I) alkynyls to give
osmabenzynes, and discuss the mechanisms for the formation
of the η3-allenylcarbene and osmabenzyne complexes. A
preliminary report on this work has been published
previously.19
Several strategies have been previously reported for the
construction of metallabenzyne rings. The first isolated
metallabenzyne (Os{CC(SiMe3)CMeC(SiMe3)CH}-
Cl2(PPh3)2) was obtained from the reaction of OsCl2(PPh3)3
with the alkyne HCCSiMe3.11 However, extension of the
chemistry to prepare osmabenzynes involving reactions of
OsCl2(PPh3)3 with other alkynes such as tert-butylacetylene12
RESULTS AND DISCUSSION
■
Synthesis and Characterization of η3-Allenylcarbene
Complexes OsCl2(CAr-η2-CHCCHAr)(PPh3)2 (Ar =
Ph, p-Tolyl). As mentioned in our preliminary report, the η3-
allenylcarbene complex OsCl2(CPh-η2-CHCCHPh)-
(PPh3)2 (2) could be prepared from the reaction of
OsCl2(PPh3)3 (1) with HCCPh (Scheme 1).19
13
and HCCC(OH)Ph2 was unsuccessful. Xia and his co-
workers have shown that the osmium hydride vinylidene
complex OsHCl2{CCH(PPh3)}(PPh3)2 can react with
HCCCH(OEt)2 to give the PPh3-substituted osmabenzyne
[Os{CC(PPh3)CHCHCH}Cl2(PPh3)2]Cl via an iso-
osmabenzene intermediate.14,15 Obviously this route can only
be extended to prepare metallabenzynes derived from reactions
involving acetal-functionalized alkynes. Other methods to
construct metallabenzyne rings include zinc reduction of
osmium vinylcarbyne complexes OsCl3(CCRCHCR
CRX)(PPh3)2,16 oxidation of the osmium vinylcarbyne complex
[OsHCl2{CC(PPh3)CHCPh}(PPh3)2]BF4,17 and thermal
isomerization of rhenium vinylcarbyne complexes Re(
CCHCRCCH)HCl(PMe2Ph)3.18 These routes are limited
by the availability of vinylcarbyne complexes. Therefore, it is
Under similar reaction conditions, OsCl2(PPh3)3 (1) reacted
with HCC-p-tolyl to give the analogous η3-allenylcarbene
complex OsCl2{C(p-tolyl)-η2-CHCCH(p-tolyl)}-
(PPh3)2 (3), which can be isolated in 66% yield.
The structure and the NMR data of the η3-allenylcarbene
complex OsCl2(CPh-η2-CHCCHPh)(PPh3)2 (2) have
been briefly described in our preliminary report.19 However,
the special structural and spectroscopic features deserve more
detailed comments. A view of the molecular geometry of 2 is
Special Issue: Organometallics in Asia
Received: February 6, 2016
© XXXX American Chemical Society
A
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Scheme 1. Preparation of η3-Allenylcarbene Complexes
delocalization of π electrons over the metal-coordinated C3
unit. On the basis of the structural data, this complex can be
described as an η3-allenylcarbene complex with contribution
from resonance structures 2, 2A, and 2B (Scheme 1). Similar
structural features have been reported for η3-vinylcarbene
complexes.26−28
The solid-state structure is supported by the solution NMR
spectroscopic data. In particular, the 1H NMR spectrum of 2 at
room temperature (298 K) showed two broad singlets at 2.30
and 5.60 ppm (in CD2Cl2), which can be assigned to the
coordinated CH proton (H3) and the exocyclic CHPh
proton (H1), respectively. In the 13C{1H} spectrum (in
CD2Cl2), the formally carbene carbon displayed a triplet at
249.8 ppm (J(PC) = 7.5 Hz), which is in a slightly higher field
than the resonance reported for the carbene carbons in typical
osmium-carbene complexes (265−325 ppm)21−23,29and osma-
cyclopropene complexes (e.g., [Os{C(Ph)−CH2}H-
(OOCCH3)(PiPr3)2]BF4 (263.2 ppm)),30 indicative of con-
tributions from resonance structure 2B to its actual structure.
The η2-allenyl chain was characterized by a upfield resonance at
36.1 ppm for the CH carbon (η2-CHCCHPh) and a
triplet at 136.6 ppm (J(PC) = 6.6 Hz) for the quaternary
carbon (η2-CHCCHPh), as well as a singlet at 125.1 ppm
for the exocyclic carbon (η2-CHCCHPh).
shown in Figure 1.20 The most interesting structural feature of
2 is that it contains a four-membered metallacycle. The
As can be seen from the crystal structure of 2 (Figure 1), the
two PPh3 ligands are inequivalent due to the coordination of
the allenyl group to Os. At room temperature, complex 2
exhibited two very broad 31P{1H} signals at −8.4 and −28.1
ppm (in CD2Cl2). When the temperature was lowered to 263
K, the 31P{1H} signals appeared as two sharp doublets centered
at −7.6 and −31.0 ppm with a large J(PP) coupling constant of
329.1 Hz, consistent with a trans disposition of the two PPh3
ligands in the solid-state structure. At temperatures above 320
K, the 31P{1H} NMR spectrum (in CDCl3) showed a single
peak at −17.4 ppm. The fluxional behavior can be explained in
terms of a change in the orientations of the coordinated CH
group of the allenyl ligand.20
Figure 1. Molecular structure of OsCl2(CPh-η2-CHCCHPh)-
(PPh3)2 (2). Selected bond distances (Å) and angles (degree):
Os(1)−C(4) 1.895(9), Os(1)−C(3) 2.166(11), Os(1)−C(2)
2.069(11), C(4)−C(3), 1.432(15), C(3)−C(2) 1.445(15), C(2)−
C(1) 1.319(15); C(4)−Os(1)−C(3) 40.6(4), C(4)−Os(1)−C(2)
75.9(4), C(3)−Os(1)−C(2) 39.8(4), C(21)−C(4)−C(3) 126.6(9),
C(21)−C(4)−Os(1) 152.4, C(4)−C(3)−C(2) 116.1(10), C(3)−
C(2)−C(1), 140.0(11), Os(1)−C(2)−C(1) 145.7(9).
The structure of the η3-allenylcarbene complex 3 can be
readily assigned on the basis of the fact that its NMR
spectroscopic data are similar to those of the η3-allenylcarbene
complex 2. In particular, the 31P{1H} NMR spectrum (in
CD2Cl2) at room temperature showed two broad doublets at
−7.0 and −29.1 ppm with a coupling constant of 327.7 Hz. The
PhCCHCCHPh moiety is coordinated to the Os center
through C(2), C(3), and C(4) in a bent fashion, with the H
atom on the C(3) carbon being closer to one of the PPh3
ligands. The two phenyl rings are almost coplanar with the
atoms Cl(1), Cl(2), Os(1), C(2), and C(3). The phenyl ring
on the exocyclic carbon C(1) is trans to the Os(1) center.
The Os−C(4) bond distance (1.895(9) Å) is characteristic of
an osmium−carbon double bond and is almost identical with
those found in osmium carbene complexes such as OsCl2(
CHCH2Ph)(CO)(PiPr3)2 (1.887(9) Å),21a [Os(O2CCH3)(
C(CH3)C(OH)MePh)(PiPr3)2]BF4 (1.879(6) Å),21b OsCl2(
CHPh)(CO)(PiPr3)2 (1.89(2) Å),22 and [OsCl(CHPh)-
(CO)(H2O)(PiPr3)2]BF4 (1.915(7) Å).23 The bond distances
of Os−C(2) (2.069(11) Å) and Os−C(3) (2.166(11) Å) as
well as C(2)−C(3) (1.441(15) Å) are comparable to those
reported for η2-coordinated allene osmium complex-
es.6g,m,o,24,25
1
presence of the η3-allenylcarbene ligand is indicated by the H
and 13C NMR data. In the 1H NMR spectrum (in CD2Cl2), the
proton signals of the coordinated olefinic CH proton and the
exocyclic CH(p-tolyl) proton of the allenyl group were
observed at 2.16 and 5.56 ppm, respectively. The correspond-
ing 13C signals in the 13C{1H} NMR spectrum (in CD2Cl2)
were observed at 34.7 and 124.6 ppm, respectively. The 13C
signals of OsCH(p-tolyl) and OsC(p-tolyl)-η2-CHC
CH(p-tolyl) were observed at 248.9 and 135.7 ppm,
respectively.
The formation of the η3-allenylcarbene complexes OsCl2(
CAr-η2-CHCCHAr)(PPh3)2 from the reactions of HC
CAr with OsCl2(PPh3)3 (1) is interesting for the following
reasons. First of all, although η3-vinylcarbene complexes26−28
are very common, reported η3-allenylcarbene complexes are still
rare.31−33 Second, although coupling reactions of vinylidene
species with alkynes to give allenylcarbene or metallacyclobu-
tene intermediates have been proposed as early as 1980 as
some of the key steps in metal-catalyzed oligomerization and
polymerization of alkynes,34 very few examples of such coupling
The C−C bond distances within the metallacycle (C(2)−
C(3) = 1.445(15) Å, C(3)−C(4) = 1.432(15) Å) are
significantly longer than a typical CC double bond (∼1.35
Å) but slightly shorter than the expected value for a single bond
between two sp2 carbons (1.48 Å). The rather similar bond
distances found for C(2)−C(3) and C(3)−C(4) indicate the
B
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reactions have been documented. The η1-allenylcarbene
complexes Cp(CO)(NO)WC(NEt2)C(R)CHCMe3 (R
= Me, Et) were isolated from the reactions of Cp(CO)(NO)-
WCCHCMe3 with the electron-rich alkynes RC
CNEt2.35 The metallacyclobutene complexes RuCl{C-
(COOMe)CHC[CH(C6H4Me)]}{P(C6H4Me)3}2(NO)36
and Cp*2Ti{C(R)C(R)CCH2}37 were isolated from the
reactions of alkynes with RuCl{CCH(C6H4Me)]}{P-
(C6H4Me)3}2(NO) and Cp*2TiCCH2, respectively. η3-
Allenylcarbene complexes [CpRu(C(R′)-η2-CHC
CHR′)(PR3)]PF6 (R′ = ferrocenyl, R = Ph, Cy; R′ =
ruthenocenyl, R = Ph), [CpOs{CPh-η2-CHCCHPh}-
(PiPr3)]BF4, and CpReBr2{C(SCH2Ph)-C(CH2Ph)C-
(SCH2Ph)C(SCH2Ph)2} were isolated from the reactions
of [RuCp(PR3)(CH3CN)2]PF6 with ferrocenyl/ruthenocenyl
acetylenes,31 the reaction of the dihydride dihydrogen complex
[CpOsH2(η2-H2)(PiPr3)]BF4 with phenylacetylene,32 and the
reaction of the η2-alkyne complex CpReBr2(η2-PhCH2SC
CSCH2Ph) with PhCH2SCCSCH2Ph,33 respectively.
Figure 2. Molecular structure of (PPh3)2ClOs(μ-Cl)3Os(C
CHPh)(PPh3)2 (5). Selected bond distances (Å) and angles (deg):
Os(1)−C(1) 1.800(18), C(1)−C(2) 1.24(2), C(2)−C(3) 1.46(2);
Os(1)−C(1)−C(2) 178.7(14), C(1)−C(2)−C(3) 132.1(18).
Mechanism for the Formation of the η3-Allenylcar-
bene Complexes 2 and 3. To understand the reaction
mechanism, we have monitored the reaction of OsCl2(PPh3)3
(1) with HCCPh by NMR. The 31P{1H} spectrum of the
reaction mixture of OsCl2(PPh3)3 and HCCPh in C6D6, at
the initial stage (5 min), showed a broad peak at −2.8 ppm for
the starting material OsCl2(PPh3)3 (major) and a singlet at
−6.0 ppm for the liberated PPh3, a singlet peak at 2.2 ppm for
the vinylidene complex Os(CCHPh)Cl2(PPh3)2 (4),38
and four doublets at δ − 3.1, −4.8, −17.5, and −19.9 ppm. The
1H NMR spectrum showed a triplet at 3.08 ppm for the
vinylidene proton of 4 along with another triplet at 1.97 ppm
(J(PH) = 3.1 Hz) with an intensity ratio of 3:1.
can react with HCCPh to give the η3-allenylcarbene complex
2 and that treatment of isolated 5 with HCCPh produced
initially a mixture of 4 and 2, and eventually 4 disappeared
completely to give 2.
On the basis of the observations described above, a plausible
mechanism for the formation of the η3-allenylcarbene
complexes is proposed in Scheme 2, with the formation of 2
as an illustration. The reaction of OsCl2(PPh3)3 (1) with HC
CPh can initially lead to the formation of the vinylidene
complexes 4 and 5, which could be detected at an early stage of
the reaction when the reaction was monitored by NMR in
C6D6. As it has been shown experimentally that the complex 5
can react with HCCPh to produce initially 4 and eventually
2, we believe that 4 is the real intermediate responsible for the
formation of 2. The vinylidene complex 4 could bind another
molecule of HCCPh to give the π-alkyne vinylidene
intermediate Os(CCHPh)(η2-HCCPh)Cl2(PPh3)2
(4yne), which undergoes cycloaddition to produce complex 2.
Similar [2 + 2] cycloaddition reactions involving an MC
bond of carbene complexes have been observed for reactions of
alkynes RCCR with Ru(CHPh)Cl2(H2IMes)(PCy3)
(H2IMes =1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) to give
η3-vinylcarbene complexes Ru(CR-η2-CRCHPh)-
Cl2(H2IMes)26 and the reaction of phenylacetylene with
[Tp′(CO)2W{CHO(p-C6H4OMe)}]BF4 (Tp′ = hydridotris-
(3,5-dimethylpyrazolyl)borate) to give the η3-vinylcarbene
complex [Tp′(CO)2 W{CPh-η2 -CHCHO(p-
C6H4OMe)}]BF4.27 [2 + 2] cycloaddition reactions of
vinylidene complexes with alkynes have also been suggested
as the key steps in the formation of η3-allenylcarbene complexes
[CpRu(C(R′)-η2-CHCCHR′)(PR3)]PF6 (R′ = ferro-
cenyl, R = Ph, Cy; R′ = ruthenocenyl, R = Ph),31 [CpOs{
CPh-η2-CHCCHPh}(PiPr3)]BF4,32 and CpReBr2{C-
(SCH2Ph)C(CH2Ph)C(SCH2Ph)C(SCH2Ph)2}32 from
reactions of alkynes with the respective complexes as
mentioned above.
Further study shows that the doublet 31P{1H} signals at δ −
1
3.1, −4.8, −17.5, and −19.9 ppm and the triplet H signal at
1.97 ppm are due to the triply chloro bridged dinuclear
monovinylidene complex (PPh3)2ClOs(μ-Cl)3Os(C
CHPh)(PPh3)2 (5), which can be prepared by treatment of 4
with OsCl2(PPh3)3 (Scheme 2). Complex 5 represents a rare
Scheme 2. Isolation of Complex 5 and Proposed Mechanism
for the Formation of Complex 2
example of a chloro-bridged dinuclear osmium vinylidene
complex.39 Its structure has been established by a single-crystal
X-ray structure analysis (Figure 2) and is supported by its NMR
data.
The proposed mechanism is supported by computational
studies. Figure 3 shows two calculated energy profiles for the
formation of the model η3-allenylcarbene complex Os{
CC(Ph)C(CH2Ph)CHCPh}Cl2(PMe3)2 (2′, a model
complex for 2) from the reaction of HCCPh with the
model vinylidene complex Os(CCHPh)Cl2(PMe3)2 (4′, a
model complex for 4), one involving initial direct addition of
An in situ NMR experiment indicates that the η3-
allenylcarbene complex 2 was formed in 30 min, as evidenced
1
by the H NMR spectrum, which displayed two broad singlets
at 6.02 and 2.87 ppm (in C6D6) for the two allenyl protons.
The 31P signals of OsCl2(PPh3)3, 4, and 5 decreased gradually
on further reaction. It can also be demonstrated that isolated 4
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have no experimental evidence for the formation of these
species.
Scheme 3. Possible Isomers of 2
Our computational studies suggest that the preferential
formation of 2 rather than other isomeric products is of kinetic
and thermodynamic origins. Figure 4 shows the energy profiles
Figure 3. Calculated energy profiles for the formation of the η3-
allenylcarbene complex 2′ from the vinylidene 4′ via an associative
mechanism (a) and a dissociative mechanism (b). The relative Gibbs
free energies and electronic energies (in parentheses) at 298 K are
given in kcal/mol.
alkyne to 4′ (associative mechanism, Figure 3a) and the other
involving initial dissociation of PMe3 from 4′ (dissociative
mechanism, Figure 3b). As shown in Figure 3a, in the
associative mechanism, the complex 4′ reacts with PhCCH
to give the complex Os(CCHPh)(η2-HCCPh)-
Cl2(PMe3)2 (4yne′) endothermically with a barrier of 14.6
kcal/mol. The subsequent insertion of HCCPh into the
OsC bond to give the η3-allenylcarbene complex 2′ is
energetically favored by 19.0 kcal/mol with a barrier of 10.2
kcal/mol.
Figure 3b shows the calculated energy profile for the reaction
of 4′ with HCCPh to give 2′ involving the metal fragment
Os(CCHPh)Cl2(PMe3) (4(-P)′) (dissociative mecha-
nism). It is clear that the overall barrier for the formation of
2′ (37.8 kcal/mol) via the path shown in Figure 3b (37.8 kcal/
mol) is significantly higher than the overall barrier via the path
shown in Figure 3a (14.6 kcal/mol), suggesting that the
dissociative mechanism is kinetically less favorable than the
associative mechanism. In contrast, it is generally accepted that
metathesis reactions initiated by ruthenium complexes Ru(
CR2)Cl2(L)2 proceed through a dissociation mechanism
involving the 14e metal fragment Ru(CR2)Cl2(L).40 In our
present case, an associative mechanism is favored, because
osmium−ligand bonds are generally stronger than the
corresponding ruthenium−ligand bonds. Indeed, dissociation
of PMe3 from 4′ to give the five-coordinate complex
OsCl2(PMe3) (4(-P)′) is energetically unfavored by 28.4
kcal/mol. The lower barrier via the associative mechanism is
consistent with our experimental observations that η3-
allenylcarbene complexes can be formed at room temperature.
In principle, reaction of OsCl2(PPh3)3 (1) with HCCPh
could also produce other isomers such as η3-allenylcarbene
complexes 2(I), 2(II), and 2(III) (Scheme 3). However, we
Figure 4. Calculated energy profiles for the formation of η3-
allenylcarbene complexes 2′, 2(I)′ (a), 2(II)′ and 2(III)′ (b) from
vinylidene 4′ via an associative mechanism and the transformation of
2(II)′ to 2′ (c). The relative Gibbs free energies and electronic
energies (in parentheses) at 298 K are given in kcal/mol.
D
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calculated for the formation of isomeric η3-allenyl complexes
from the reaction of HCCPh with the model complex Os(
CCHPh)Cl2(PMe3)2 (4′). As shown in Figure 4a, the
formation of isomer 2(I)′ (a model complex for 2(I)) is both
kinetically and thermodynamically less favorable than the
formation of isomer 2′ (a model complex for 2). The energy
profile shown in Figure 4b suggests that the formation of
isomer 2(II)′ (a model complex for 2(II)) has a kinetic barrier
similar to that for the formation of 2′ (Figure 4a). However,
this isomer can transform to the thermodynamically more
stable isomer 2′ via the five-coordinate intermediate 2(IV)′, as
shown in Figure 4c. As shown in Figure 4b, the formation of
the isomer 2(III)′ (a model complex for 2(III)) is less
favorable both kinetically and thermodynamically than the
formation of isomer 2(II)′.
In addition to the successful isolation of the osmabenzynes
described above, we have also carried out reactions of η3-
allenylcarbene complexes 2 and 3 with other gold(I) alkynyls
such as Au(CCCO2Et)(PPh3), Au(CCtBu)(PPh3), and
Au(CCH)(PPh3) in the presence of HNEt3Cl. Unfortu-
nately, these reactions produced a mixture of phosphorus-
containing species, from which it is difficult to isolate pure
products.
Reactions of OsCl2(CAr-η2-CHCCHAr)(PPh3)2
with Copper Alkynyls. We are also interested in knowing if
the relatively cheaper copper alkynyls instead of gold alkynyls
could be used for the preparation of osmabenzynes. To test this
possibility, we first studied the reactions of Cu(CCPh) with
complexes 2 and 3 in the presence of HNEt3Cl. We were
pleased to find that the reactions produced the corresponding
osmabenzynes 6a,b, which can be isolated in 51.9% and 60%
yields, respectively (Scheme 5). Similarly, reactions of Cu(C
CSiMe3) with complexes 2 and 3 in the presence of HNEt3Cl
produced the analogous osmabenzynes 9a,b, respectively.
Reactions of OsCl2(CAr-η2-CHCCHAr)(PPh3)2
with Gold Alkynyls. The reactions of Au(CCPh)(PPh3)
with the η3-allenylcarbene complexes 2 and 3 in the presence of
HNEt3Cl at room temperature for ca. 3 h produced the
osmabenzyne complexes 6a,b, respectively, which can be
isolated as air-stable green solids (Scheme 4). Other aryl-
Scheme 5. Reactions of 2 and 3 with Cu(I) Acetylides
Scheme 4. Reactions of 2 and 3 with Au(I) Acetylides
Characterization of the Newly Synthesized Osmaben-
zynes. The osmabenzyne complexes Os{CCRC(CH2Ar)-
CHCAr}Cl2(PPh3)2 have been characterized by NMR
spectroscopy and elemental analysis. Their 31P{1H} NMR
spectra showed a singlet in the region of −5 to −10 ppm. The
1H NMR spectra displayed a characteristic singlet signal for the
CH proton of the metallacycle at 6.5−7.1 ppm. The 13C{1H}
NMR spectra displayed an OsC signal at ca. 294−300 ppm
and a signal for the other metal-bound carbon (OsC) at 209−
221 ppm. The 13C signals for the remaining carbons of the
metallacycle were located at ca. 168−179, 114−125, and 133−
136 ppm, which correspond to C(CH2Ar), CH, and C(R),
respectively.
The structures of 6a,b, 7a,b, and 8a have been confirmed by
X-ray diffraction studies. As a representative, the X-ray structure
of Os{CC(p-tolyl)C(CH2−p-tolyl)CHC(p-tolyl))}-
Cl2(PPh3)2 (7b) is shown in Figure 5 (see the Supporting
Information for other structures). For comparison, selected
structural parameters associated with the metallacycles of these
complexes are given in Tables S2 and S3 together with those of
the “symmetrically” substituted osmabenzynes Os{CC-
(SiMe3)CC(CH3)C(SiMe3)CH}Cl2(PPh3)2 (11)11a and
Os{CCHCC(CH3)CHCH}Cl2(PPh3)2 (12)41 in the
Supporting Information.
All of the complexes contain an essentially planar six-
membered metallacycle with the sum of internal angles in the
six-membered ring being close to the ideal value of 720°
required for a planar hexagon (see Table S2 in the Supporting
Information). Subtle structural differences are noted for
substituted osmabenzynes could be similarly prepared from
these η3-allenylcarbene complexes. For example, the analogous
osmabenzyne complexes 7 could also be obtained from the
reactions of Au(CC-p-tolyl)(PPh3) with 2 and 3 in the
presence of HNEt3Cl.
With this methodology, osmabenzynes having alkyl, TMS,
and acetal substituents can also be prepared. For example, the
n-butyl-substituted osmabenzynes 8 were obtained by treat-
ment of 2 and 3 with Au{CC(CH2)3CH3}(PPh3) and
HNEt3Cl (Scheme 4). The SiMe3-substituted osmabenzynes 9
can be similarly prepared from the reactions of 2 and 3 with
Au(CCSiMe3)(PPh3) and HNEt3Cl. The acetal-substituted
osmabenzyne 10b could also be isolated from the reaction of 3
with Au({CCH(OEt)2}PPh3) in the presence of HNEt3Cl.
E
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carbon by HNEt3Cl followed by coordination of a chloride
anion would give the osmabenzyne 16.
The key step of the proposed mechanism is the electro-
cyclization of 14 to give 15. The process is reasonable, as
electrocyclization of (Z)-hexa-1,3,5-triene to give 1,3-cyclo-
hexadiene is a well-known example of a six-electron electro-
cyclization reaction allowed by the Woodward−Hoffmann
rules.44 A similar electrocyclization process has been proposed
for isomerization of the osmium alkynyl vinylcarbene
complexes Os{C(CH2Ph)CHCHPh}(CCPh)Cl-
(PiPr3)245 and Os(CHCHCHR){CC(PPh3)}Cl(PPh3)2
(R = Ph, Et, vinyl, OEt)15a to give respectively the
isometallabenzene complexes Os{C(CH2Ph)CHCH(Ph)C-
(Ph)CC}(CCPh)Cl(PiPr3)2 and Os{CHCHCH(R)-
C(PPh3)CC}(CCPh)Cl2(PPh3)2.
Figure 5. Molecular structure for Os{CC(p-tolyl)C(CH2(p-
tolyl))CHC(p-tolyl)}Cl2(PPh3)2 (7b).
To assess the feasibility of the proposed mechanism,
computational studies were also carried out. Figure 6 shows
complexes 6, 7, and 8a (with an aryl group at the C5 carbon)
and complexes 11 and 12 (with no substituent at the C5
carbon). For example, the Os−C5 bonds of 6, 7, and 8a
(2.052(12)−2.075(3) Å) are longer than those of 11 (1.939(5)
Å) and 12 (2.008(7) Å). Concomitantly, the Os−C1 bond
lengths of complexes 6, 7, and 8a (1.726(10)−1.766(5) Å) are
shorter than those of 11 (1.815(4) Å) and 12 (1.805(7) Å).
For complexes 6, 7, and 8a, the C2−C3 bonds are usually
shorter than the C3−C4 bonds, while the two bonds have
comparable distances for 11 and 12. The Os−Cl−C2 angles of
complexes 6, 7, and 8a (153.4(6)−154.9(3)°) are appreciably
larger than those of 11 (148.7(3)°) and 12 (148.3(6)°). The
ring angles at C5 in 6, 7, and 8a (123.8(3)−125.8(8)°) are
appreciably smaller than those in 11 (138.6(5)°) and 12
(132.1(5)°), while the angles at C4 in 6, 7, and 8a (126.4(10)−
128.9(4)°) are much more obtuse than those in 11 (117.7(4)°)
and 12 (123.5(6)°).
Mechanism for the Formation of Metallabenzynes. A
plausible mechanism for the formation of osmabenzynes from
the reactions of η3-allenylcarbene complexes OsCl2(CAr-η2-
CHCCHAr)(PPh3)2 with gold(I)/Cu(I) alkynyls is
shown in Scheme 6, using the reaction of 2 with M(CCR)
Figure 6. Calculated energy profiles for the formation of the
osmabenzyne 21 from η3-allenylcarbene complexes 17 and 18. The
relative Gibbs free energies and electronic energies (in parentheses) at
298 K are given in kcal/mol.
Scheme 6. Proposed Mechanism for the Formation of
Osmabenzynes
the calculated energy profile for the formation of osmabenzyne
21 (a model complex for 16) starting from the model alkynyl-
allenylcarbene complexes 17 (a model complex for 13) and 18
(a model complex for 13a). Complexes 17 and 18 have very
similar energies, with 17 being slightly more stable. The
rearrangement of complexes 17 and 18 to the 16e species 19 is
energetically favored by 4.1 and 5.2 kcal/mol with barriers of
2.6 and 14.6 kcal/mol, respectively. The electrocyclization of
complex 19 occurs easily with a very small barrier of 6.8 kcal/
mol to give the more stable metallacycle 20. The protonation of
20 by HNMe3Cl to give 21 is thermodynamically favored by
9.5 kcal/mol. The computational results confirm that the
proposed mechanism shown in Scheme 6 is feasible. It is
interesting to note that the activation energy for the
electrocyclization of complex 19 to give 20 (6.8 kcal/mol) is
significantly smaller than that for electrocyclization of (Z)-hexa-
1,3,5-triene to give 1,3-cyclohexadiene (29.9 kcal/mol).46
Summary. We have developed an efficient synthetic route
for the preparation of osmabenzynes from the reactions of
osmium η3-allenylcarbene complexes OsCl2(CAr-η2-CH
CCHAr)(PPh3)2 with Au(I) or Cu(I) alkynyls. This method
allows us to synthesize osmabenzynes with various substituents
under mild reaction conditions. Computational studies suggest
(M = Cu, Au(PPh3)) as an illustration. It is known that Cu(I)42
and Au(I)43 alkynyls can undergo transmetalation reactions
with transition-metal halide complexes to give transition-metal
alkynyl complexes. The reaction of an alkynyl species M(C
CR) with the η3-allenylcarbene complex 2 may lead to the
formation of the osmium alkynyl complex 13 or 13a with the
elimination of MCl. The complex 13 or 13a may evolve to the
five-coordinate complex 14, which undergoes electrocyclization
to give the metallacycle 15. Finally, protonation at the CHPh
F
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for an additional 8 h to give a brown solution, which was concentrated
to ca. 2 mL. Addition of ether (20 mL) to the residue produced a light
brown solid and a brownish green solution. The solid was collected by
filtration, washed with ether (2 × 15 mL), and dried under vacuum
overnight. Yield: 0.33 g, 58%. 31P{1H} NMR (121.5 MHz, C6D6): AB-
A′B′ pattern, δ −3.2 (d), −5.0 (d) (J(PAPB) = 12.1 Hz); −17.6 (d),
that the osmabenzynes are formed through electrocyclization of
osmium alkynyl-allenylcarbene intermediates followed by
protonation by HNEt3Cl.
EXPERIMENTAL SECTION
■
1
−20.0 (d) (J(PA′PB′) = 17.6 Hz). H NMR (300.13 MHz, C6D6): δ
All manipulations were carried out under a nitrogen atmosphere using
standard Schlenk techniques unless otherwise stated. Solvents were
distilled under nitrogen from sodium benzophenone (benzene, ether,
hexane), or calcium hydride (CH2Cl2). The starting materials
OsCl2(PPh3)3 (1),47 Os(CCHPh)Cl2(PPh3)2 (4),38 Au(C
CR)(PPh3),48 and Cu(CCR) (R = Ph, SiMe3)49 were prepared
by following the procedures described in the literature. All other
reagents were used as purchased from Aldrich Chemical Co.
Microanalyses were performed by M-H-W Laboratories (Phoenix,
1.97 (t, J(PH) = 3.2 Hz, 1 H, OsCCH), 6.95−8.02 (m, 65 H,
C6H5, PPh3). 13C{1H} NMR (100.4 MHz, CD2Cl2): δ 313.9 (dd,
J(PC) = 13.4, 10.4 Hz, OsC), 138.7−125.2 (m, C6H5, PPh3), 113.4
(s, OsCCH). Anal. Calcd for C80H66Cl4P4Os2: C, 57.42; H, 3.98.
Found: C, 57.10; H, 4.25.
Os{CCPhC(CH2Ph)CHCPh}Cl2(PPh3)2 (6a). A mixture of
Os(CPh-η2-CHCCHPh)Cl2(PPh3)2 (503 mg, 0.51 mmol) and
Cu(CCPh) (110 mg, 0.67 mmol) in CH2Cl2 (50 mL) was stirred at
room temperature for 15 min to give a brown solution. HNEt3Cl (551
mg, 4.00 mmol) was added, and the mixture was stirred at room
temperature for 24 h. The solvent was completely removed under
vacuum, and the resulting solid was extracted with benzene (5 mL).
The solution was filtered through Celite to remove the insoluble
HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded
onto a silica gel column. The column was flashed with benzene and
dichloromethane subsequently to remove the impurities and then
eluted with dichloromethane/ether (5/1) to give a green solution. The
solvent was removed under vacuum to give a green solid, which was
dried under vacuum. Yield: 288 mg, 51.9%. The complex 6a could also
be made using Au(CCPh)(PPh3) instead of Cu(CCPh) (see the
Supporting Information of our preliminary report19). 31P{1H} NMR
(121.5 MHz, CDCl3): δ −9.9 (s). 1H NMR (300.13 MHz, CDCl3): δ
3.73 (s, 2 H, −CH2Ph), 5.64 (d, J(HH) = 7.2 Hz, 2 H, o-C6H5), 6.32
(d, J(HH) = 7.0 Hz, 2 H, o-C6H5), 6.76 (t, J(HH) = 7.2 Hz, 2 H, m-
C6H5), 6.82 (s, 1 H, OsCPhCH−), 6.88 (t, J(HH) = 7.2 Hz, 1 H, p-
C6H5), 6.91 (dd, J(HH) = 3.9 Hz, J(HH) = 3.6 Hz, 2 H, m-C6H5),
7.13−7.32 (m, 24 H, PPh3, C6H5), 7.49−7.56 (m, 12 H, PPh3).
13C{1H} NMR (100.40 MHz, CDCl3): δ 294.8 (t, J(PC) = 12.0 Hz,
OsC), 213.9 (t, J(PC) = 5.5 Hz, OsCPh), 167.9 (s, C-CH2Ph),
156.8 (s, ipso-C6H5), 138.7 (s, ipso-C6H5), 135.2 (t, J(PC) = 4.6 Hz, o-
PPh3), 133.3 (s, OsCPhCH−), 131.5 (t, J(PC) = 26.8 Hz, ipso-
PPh3), 130.8 (s, o-C6H5), 130.1 (s, p-PPh3), 128.9 (s, m-C6H5), 128.6
(s, m-C6H5), 127.5 (t, J(PC) = 5.5 Hz, m-PPh3), 127.4 (s, p-C6H5),
127.3 (s, ipso-C6H5), 127.2 (s, o-C6H5), 126.5 (s, o-C6H5), 125.3 (s,
OsCCPh), 125.1 (s, p-C6H5), 124.7 (s, m-C6H5), 40.3 (s,
CH2Ph), (one of the para carbons of C6H5 could not unambiguously
be assigned, which is probably obscured by other aromatic
resonances). Anal. Calcd for C60H48Cl2OsP2: C, 65.99; H, 4.43.
Found: C, 66.21; H, 4.62. FAB-MS (NBA, m/z): calcd for
C60H48Cl2OsP2 [M − Cl]+, 1057.25; found, 1057.5.
1
AZ). H, 13C{1H}, and 31P{1H} spectra were collected on a Bruker
ARX-400 spectrometer (400 MHz), a JEOL EX-400 spectrometer
1
(400 MHz), or a Bruker ARX-300 spectrometer (300 MHz). H and
13C NMR shifts are relative to TMS, and 31P chemical shifts are
relative to 85% H3PO4.
Os(CPh-η2-CHCCHPh)Cl2(PPh3)2 (2). The complex was
obtained from the reaction of OsCl2(PPh3)3 with PhCCH following
a procedure described in the Supporting Information of our
preliminary report.19 31P{1H} NMR (121.5 MHz, CD2Cl2): 298 K,
AB pattern δ −8.4 (br s), −28.1 (br s); 210 K: δ −8.3 (d), −32.3 (d),
1
J(PAPB) = 329.1 Hz. H NMR (300.13 MHz, CD2Cl2): 298 K, δ 2.30
(s (br), W1/2 = 6.5 Hz, 1 H, OsCPh(η2-CHC)), 5.60 (s (br),
W1/2 = 6.8 Hz, 1 H, CCCHPh), 6.63−7.84 (m, 37 H, C6H5,
PPh3), 9.36 (br, W1/2 ≈ 106.0 Hz, 1 H, C6H5); 210 K, δ 2.27 (t, J(PH)
= 5.6 Hz, 1 H, OsCPh(η2−CHC), 5.78 (s (br), W1/2 = 7.0 Hz, 1
H, CCCHPh), 6.61−7.85 (m, 37 H, C6H5, PPh3), 9.29 (d,
J(HH) = 7.7 Hz, 1 H, C6H5). 13C{1H} NMR (100.4 MHz, CD2Cl2,
298 K): δ 249.8 (t, J(PC) = 7.5 Hz, Os = CPh), 145.4 (s, C6H5), 136.7
(s, C6H5), 136.6 (t, J(PC) = 6.6 Hz, η2-CHCCHPh), 135.4−
126.7 (m, other aromatic carbons), 125.1 (s, CCCHPh), 36.1 (s,
OsCPh(η2-CHC)). Anal. Calcd for C52H42Cl2P2Os: C, 63.09; H,
4.28. Found: C, 63.00; H, 4.24. FAB-MS (NBA, m/z): calcd for
C52H42Cl2P2Os [M+], 990.18; found, 990.3.
Os{C(p-tolyl)-η2-CHCCH(p-tolyl)}Cl2(PPh3)2 (3). To a
benzene (12 mL) solution of OsCl2(PPh3)3 (0.80 g, 0.76 mmol)
was added 4-ethynyltoluene (0.96 mL, 7.6 mmol). The reaction
mixture was stirred at room temperature for 10 h to give a large
amount of green precipitates. The green solid was collected by
filtration, washed with benzene (2 mL) and ether (2 × 10 mL), and
dried under vacuum overnight. Yield: 0.51 g, 66%. 31P{1H} NMR
(121.5 MHz, CD2Cl2): 298 K, AB pattern δ −7.0 (br s), −29.1 (br s),
J(PAPB) ≈ 327.7 Hz; 243 K, δ −7.9 (d), −31.0 (d), J(PAPB) = 329.9
1
Hz. H NMR (300.13 MHz, CD2Cl2): 298 K, δ 2.10 (s, 3 H, C6H4-
Os{CCPhC(CH2-p-tolyl)CHC(p-tolyl)}Cl2(PPh3)2 (6b).
Method A, from Au(CCPh)(PPh3). A mixture of Os(C(p-tolyl)-
η2-CHCCH(p-tolyl))Cl2(PPh3)2 (0.50 g, 0.50 mmol) and
Au(CCPh)(PPh3) (0.40 g, 0.74 mmol) in CH2Cl2 (20 mL) was
stirred at room temperature for 15 min to give a brown solution,
HNEt3Cl (0.80 g, 5.81 mmol) was added, and the mixture was stirred
at room temperature for 3 h. The solvent was completely removed
under vacuum, and the resulting solid was extracted with benzene (5
mL). The extractant was filtered through Celite to remove the
insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was
loaded onto a silica gel column. The column was flashed with benzene
and dichloromethane subsequently to remove Au(PPh3)Cl and other
impurities and then eluted with dichloromethane/ether (5/1) to give a
green solution. The solvent was removed under vacuum to give a
green solid, which was dried under vacuum. Yield: 0.16 g, 29%.
Method B, from Cu(CCPh). A mixture of Os{C(p-tolyl)-η2-
CHCCH(p-tolyl)}Cl2(PPh3)2 (0.260 g, 0.26 mmol) and Cu(C
CPh) (0.050 g, 0.30 mmol) in CH2Cl2 (20 mL) was stirred at room
temperature for 15 min to give a brown solution, HNEt3Cl (0.283 g,
2.06 mmol) was added, and the mixture was stirred at room
temperature for 18 h. The solvent was completely removed under
vacuum, and the resulting solid was extracted with benzene (5 mL).
The extractant was filtered through Celite to remove the insoluble
CH3), 2.16 (s (br), W1/2 = 5.6 Hz, 1 H, OsC(p-tolyl)(η2-CHC),
2.40 (s, 3 H, C6H4−CH3), 5.56 (s (br), W1/2 = 5.8 Hz, 1 H, CC
CH(p-tolyl)), 6.83−7.56 (m, 37 H, C6H4, PPh3), 9.29 (br, W1/2 ≈ 67.0
Hz, 1 H, C6H4); 243 K, δ 2.10 (s, 3 H, C6H4-CH3), 2.14 (ddd, J(PH)
= 7.6, 5.6 Hz, J(HH) = 2.0 Hz, 1 H, OsC(p-tolyl)(η2-CHC), 2.37
(s, 3 H, C6H4−CH3), 5.68 (s (br), W1/2 = 6.0 Hz, 1 H, CCCH(p-
tolyl)), 6.75−7.73 (m, 37 H, C6H4, PPh3), 9.29 (d, J(HH) = 8.0 Hz, 1
H, C6H4). 13C{1H} NMR (100.4 MHz, CD2Cl2, 298 K): δ 248.9 (t,
J(PC) = 7.4 Hz, OsC), 145.5 (s, C6H4), 143.3 (s, C6H4), 136.2 (s,
C6H4), 135.7 (t, J(PC) = 7.2 Hz, η2-CHCCH(p-tolyl)), 135.6−
126.6 (m, other aromatic carbons), 124.6 (s, η2-CHCCH(p-
tolyl)), 34.7 (s, η2-CHCCH(p-tolyl)), 23.2, 20.9 (s × 2, C6H4-
CH3). Anal. Calcd for C54H46Cl2P2Os: C, 63.71; H, 4.55. Found: C,
63.67; H, 4.70.
(PPh3)2ClOs(μ-Cl)3Os(CCHPh)(PPh3)2 (5). A mixture of
Os(CCHPh)Cl2(PPh3)2 (0.30 g, 0.34 mmol) and OsCl2(PPh3)3
(0.53 g, 0.50 mmol) in CH2Cl2 (40 mL) was stirred at room
temperature for 18 h. The solvent was removed under vacuum, and
the brownish green residue was washed with hexane (40 mL) and
filtered to remove free PPh3. The brownish green solid was dried
under vacuum, and additional OsCl2(PPh3)3 (0.18 g, 0.17 mmol) was
added. The resulting mixture was further stirred in 40 mL of CH2Cl2
G
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HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded
onto a silica gel column. The column was flashed with benzene and
dichloromethane subsequently to remove the impurities and then
eluted with dichloromethane/ether (5/1) to give a green solution. The
solvent was removed under vacuum to give a green solid, which was
dried under vacuum. Yield: 0.171 g, 60%.
tolyl)), 129.8 (s, p-PPh3), 129.0 (s, m-OsCC(p-tolyl)), 128.7 (s, o-
CH2(p-tolyl)), 128.6 (s, o-OsCC(p-tolyl)), 127.3 (s, m-OsC(p-
tolyl)), 127.2 (t, J(PC) = 5.1 Hz, m-PPh3), 125.2 (s, o-OsC(p-
tolyl)), 124.6 (s, OsCC(tolyl)), 124.1 (s, ipso-CH2(p-tolyl)),
40.0 (s, −CH2-tolyl), 21.4 (s, −CH2C6H4-CH3), 21.2 (s, Os
CC(C6H4-CH3) and OsC(C6H4-CH3)) (the ipso carbon of Os
CC(p-tolyl) could not unambiguously be assigned, which is probably
merged with other aromatic resonances). Anal. Calcd for
C63H54Cl2OsP2: C 66.72, H 4.80. Found: C 66.37, H 5.11.
31P{1H} NMR (121.5 MHz, CD2Cl2): δ −8.6 (s). 1H NMR (300.13
MHz, CD2Cl2): δ 2.21 (s, 3 H, OsC(p-tolyl)), 2.30 (s, 3 H, CH2(p-
tolyl)), 3.68 (s, 2 H, −CH2(p-tolyl)), 5.66 (d, J(HH) = 7.5 Hz, 2 H, m-
CH of OsC(p-tolyl)), 6.35 (d, J(HH) = 7.8 Hz, 2 H, m-CH of
−CH2(p-tolyl)), 6.60 (d, J(HH) = 8.1 Hz, 2 H, o-CH of OsC(p-
tolyl)), 6.71 (s, 1 H, OsC(p-tolyl)CH), 6.80 (d, J(HH) = 7.8 Hz,
2 H, o-CH of OsCC(Ph)), 7.05 (d, J(HH) = 7.5 Hz, 2 H, o-CH of
−CH2(p-tolyl)), 7.19 (t, J(HH) = 7.5 Hz, 12 H, m-PPh3), 7.29 (t,
J(HH) = 7.5 Hz, 2 H, m-CH of OsCC(Ph)), 7.37 (t, J(HH) = 7.2
Hz, 6 H, p-PPh3), 7.47−7.53 (m, 12 H, PPh3), 7.57 (t, J(HH) = 8.4
Hz, 1 H, p-CH of OsCC(Ph)). 13C{1H} NMR (75.5 MHz,
CD2Cl2): δ 295.7 (t, J(PC) = 12.8 Hz, OsC), 214.5 (t, J(PC) = 5.4
Hz, OsC(p-tolyl)), 169.3 (s, C-CH2(p-tolyl)), 154.7 (s, ipso-OsC(p-
tolyl)), 136.6 (s, p-CH2(p-tolyl)), 136.2 (s, p-OsCC(Ph)),
133.8 (s, OsC(p-tolyl)CH), 135.6−125.8 (m, other aromatic
carbons), 125.5 (s, OsCCPh), 40.2 (s, CH2(p-tolyl)), 21.1 (s,
C6H4CH3), 21.0 (s, C6H4CH3). Anal. Calcd for C62Cl2H52P2Os·
CH2Cl2: C, 62.79; H, 4.52. Found: C, 62.96; H, 4.20.
Os{CC((CH2)3CH3)C(CH2Ph)CHCPh}Cl2(PPh3)2 (8a). The
complex was obtained from the reaction of 2 with Au(C
C(CH2)3CH3)(PPh3) in the presence of HNEt3Cl (see the Supporting
Information of our preliminary report19). 31P{1H} NMR (121.5 MHz,
1
CDCl3): δ −10.7 (s). H NMR (300.13 MHz, CDCl3): δ 0.80−0.90
(m, 5 H, CH2CH3), 1.11−1.18 (m, 2 H, CH2CH3), 1.18 (quintet,
J(HH) = 7.5 Hz, 2 H, CH2CH2CH3), 2.10 (t, J(HH) = 8.4 Hz, 2 H,
CH2CH2CH2CH3), 3.82 (s, 2 H, CH2Ph), 5.49 (d, J(HH) = 7.5 Hz, 2
H, o-C6H5), 6.71 (s, 1 H, OsCPhCH−), 6.72 (t, J(HH) = 7.8 Hz, 2
H, m-C6H5), 6.86 (t, J(HH) = 7.2 Hz, 1 H, p-C6H5), 7.03 (d, J(HH) =
7.2 Hz, 2 H, o-C6H5), 7.24−7.40 (m, 16 H, PPh3, C6H5), 7.55−7.61
(m, 17 H, PPh3, C6H5). 13C{1H} NMR (75.5 MHz, CDCl3): δ 298.8
(t, J(PC) = 8.6 Hz, OsC), 209.4 (t, J(PC) = 6.4 Hz, OsCPh),
169.1 (s, C-CH2Ph), 156.6 (s, ipso-C6H5), 138.3 (s, ipso-C6H5), 133.7
(s, OsCPhCH−), 135.2−124.5 (m, other aromatic carbons), 123.0
(s, OsCC((CH2)3CH3)), 40.1 (s, CH2Ph), 32.8 (s, CH2), 23.3 (s,
CH2), 21.6 (s, CH2), 13.6 (s, CH3). Anal. Calcd for C58Cl2H52P2Os: C,
64.98; H, 4.89. Found: C, 65.04; H, 4.68.
Os{CC(p-tolyl)C(CH2Ph)CHCPh}Cl2(PPh3)2 (7a). The
complex was obtained from the reaction of 2 with Au{CC(p-
tolyl)}(PPh3) in the presence of HNEt3Cl (see the Supporting
Information of our preliminary report19). 31P{1H} NMR (121.5 MHz,
Os{CC((CH2)3CH3)C(CH2(p-tolyl))CHC(p-tolyl)}-
Cl2(PPh3)2 (8b). A mixture of Os{C(p-tolyl)-η2-CHCCH(p-
tolyl)}Cl2(PPh3)2 (0.50 g, 0.50 mmol) and Au{CC(CH2)3CH3}-
(PPh3) (0.40 g, 0.74 mmol) in CH2Cl2 (20 mL) was stirred at room
temperature for 15 min to give a brown solution, HNEt3Cl (0.80 g,
5.81 mmol) was added, and the mixture was stirred at room
temperature for 2 h. The solvent was completely removed under
vacuum, and the resulting solid was extracted with benzene (5 mL).
The extractant was filtered through Celite to remove the insoluble
HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded
onto a silica gel column. The column was flashed with benzene and
dichloromethane subsequently to remove Au(PPh3)Cl and other
impurities and then further eluted with dichloromethane/ether (5/1)
to give a green solution. The solvent was removed under vacuum to
give a green solid, which was dried under vacuum. Yield: 0.16 g, 29%.
1
CDCl3): δ −9.6 (s). H NMR (300.13 MHz, CDCl3): δ 2.53 (s, 3 H,
OsCC6H4-CH3)), 3.83 (s, 2 H, CH2Ph), 5.76 (d, J(HH) = 6.6 Hz, 2
H, o-CH of OsCC(p-tolyl))), 6.34 (d, J(HH) = 6.3 Hz, 2 H, m-
CH of OsCC(p-tolyl)), 6.86 (s, OsCPhCH), 6.76−7.64 (m,
other aromatic proton). 13C{1H} NMR (75.5 MHz, CDCl3): δ 295.0
(t, J(PC) = 12.8 Hz, OsC), 212.8 (t, J(PC) = 5.9 Hz, OsCPh),
168.1 (s, C-CH2Ph), 156.8 (s, ipso-C6H5), 138.8 (s, ipso-C6H5), 137.1
(s, OsCPhCH−), 125.2 (s, OsCC(p-tolyl)), 135.2−124.2 (m,
other aromatic carbons), 40.2 (s, CH2Ph), 21.2 (s, CH3). Anal. Calcd
for C61Cl2H50P2Os·0.5CH2Cl2: C, 64.31; H, 4.48. Found: C, 64.14; H,
4.54.
Os{CC(p-tolyl)C(CH2(p-tolyl))CHC(p-tolyl)}Cl2(PPh3)2
(7b). A mixture of Os(C(p-tolyl)-η2-CHCCH(p-tolyl))-
Cl2(PPh3)2 (0.50 g, 0.50 mmol) and Au(CC(p-tolyl)) (0.34 g,
0.59 mmol) in CH2Cl2 (20 mL) was stirred at room temperature for
15 min to give a brown solution. HNEt3Cl (0.80 g, 5.81 mmol) was
added, and the mixture was stirred at room temperature for 3 h. The
solvent was completely removed under vacuum, and the resulting solid
was extracted with benzene (5 mL). The solution was filtered through
Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated
to ca. 1 mL and was loaded onto a silica gel column. The column was
flashed with benzene and dichloromethane subsequently to remove
Au(PPh3)Cl and other impurities and then eluted with dichloro-
methane/ether (5/1) to give a green solution. The solvent was
removed under vacuum to give a green solid, which was dried under
vacuum. Yield: 0.21 g, 37%. 31P {1H} NMR (121.5 MHz, CDCl3): δ
−9.3 (s). 1H NMR (300.13 MHz, CDCl3): δ 2.18 (s, 3 H, OsC(C6H4-
CH3)), 2.31 (s, 3 H, OsCC(C6H4-CH3)), 2.40 (s, 3 H,
−CH2(C6H4-CH3)), 3.64 (s, 2 H, -CH2-tolyl), 5.61 (d, J(HH) = 8.1
Hz, 2 H, m-CH of OsC(p-tolyl)), 6.20 (d, J(HH) = 7.9 Hz, 2 H, m-
CH of −CH2(p-tolyl)), 6.56 (d, J(HH) = 8.1 Hz, 2 H, o-CH of OsC(p-
tolyl)), 6.77 (s, 1 H, OsC(tolyl)CH-), 6.78 (d, J(HH) = 7.9 Hz, 2
H, o-CH of OsCC(p-tolyl)), 6.96 (d, J(HH) = 7.9 Hz, 2 H, o-CH
of −CH2(p-tolyl)), 7.02 (d, J(HH) = 7.9 Hz, 2 H, m-CH of Os
CC(p-tolyl)), 7.14 (t, J(HH) = 7.6 Hz, 12 H, m-PPh3), 7.30 (t,
J(HH) = 7.3 Hz, 6 H, p-PPh3), 7.49−7.55 (m, 12 H, PPh3). 13C{1H}
NMR (100.40 MHz, CDCl3): δ 294.1 (t, J(PC) = 12.7 Hz, OsC),
213.2 (t, J(PC) = 6.3 Hz, OsC(tolyl)), 168.0 (s, C-CH2−tolyl),
153.7 (s, ipso- OsC(p-tolyl)), 136.7 (s, p-CH2(p-tolyl)), 135.7 (s, p-
OsCC(p-tolyl)), 135.6 (s, ipso-CH2(p-tolyl)), 134.9 (t, J(PC) = 5.1
Hz, o-PPh3), 134.3 (s, p-OsC(p-tolyl)), 133.3 (s, OsC(p-tolyl)
CH−), 131.3 (t, J(PC) = 26.6 Hz, ipso-PPh3), 130.4 (s, m-CH2(p-
1
31P{1H} NMR (121.5 MHz, CD2Cl2): δ −9.9 (s). H NMR (300.13
MHz, CD2Cl2): δ 0.67−0.76 (m, 5 H, CH2CH3), 1.12 (quintet, J(HH)
= 7.5 Hz, 2 H, CH2CH2CH3), 2.06 (t, J(HH) = 8.1 Hz, 2 H,
CH2CH2CH2CH3), 2.15 (s, 3 H, OsCC6H4-CH3)), 2.33 (s, 3 H,
C−CH2(C6H4-CH3)), 3.73 (s, 2 H, CH2(C6H4-CH3)), 5.39 (d, J(HH)
= 8.1 Hz, 2 H, o-CH of OsCC(C6H4-CH3))), 6.49 (d, J(HH) =
7.8 Hz, 2 H, o-CH of OsCC(C6H4-CH3))), 6.54 (s, 1 H,
OsC(C6H4−CH3)CH−), 6.72 (t, J(HH) = 7.8 Hz, 2 H, m-C6H5),
6.87−7.52 (m, 34 H, other aromatic protons). 13C{1H} NMR (75.5
MHz, CD2Cl2): δ 299.8 (t, J(PC) = 11.4 Hz, OsC), 210.2 (t, J(PC)
= 5.9 Hz, OsC(C6H4-CH3)), 170.7 (s, C-CH2(C6H4-CH3)), 154.6
(s, ipso-(C6H4-CH3)), 135.6 (s, ipso-(C6H4-CH3)), 133.8 (s, OsC-
(C6H4-CH3)CH−), 134.7−125.7 (m, other aromatic carbons),
123.1 (s, OsCC((CH2)3CH3)), 40.0 (s, CH2(C6H4-CH3)), 33.2
(s, CH2), 23.7 (s, CH2), 21.9 (s, CH2), 21.1 (s, C6H4-CH3), 20.9 (s,
C6H4-CH3), 13.8 (s, CH3). Anal. Calcd for C60Cl2H58P2Os·1.5CH2Cl2:
C, 60.08; H, 5.00. Found: C, 60.19; H, 4.85.
Os{CC(SiMe3)C(CH2Ph)CHCPh}Cl2(PPh3)2 (9a). A mix-
ture of Os(CPh-η2-CHCCHPh)Cl2(PPh3)2 (1.031 g, 1.04
mmol) and Cu(CCSiMe3) (220 mg, 1.37 mmol) in CH2Cl2 (60
mL) was stirred at room temperature for 15 min to give a brown
solution, HNEt3Cl (1.113 g, 8.08 mmol) was added, and the mixture
was stirred at room temperature for 24 h. The solvent was completely
removed under vacuum, and the resulting solid was extracted with
benzene (15 mL). The extractant was filtered through Celite to
remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1
mL and was loaded onto a silica gel column. The column was flashed
with benzene and dichloromethane subsequently to remove the
H
DOI: 10.1021/acs.organomet.6b00102
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
impurities and then eluted with dichloromethane/ether (5:/1) to give
a green solution. The solvent was removed under vacuum to give a
green solid, which was dried under vacuum. Yield: 0.402 g, 35.5%. The
complex 9a could also be made using Au(CCSiMe3)(PPh3) instead
of Cu(CCSiMe3) (see the Supporting Information of our
preliminary report19). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ −9.1
(s). 1H NMR (300.13 MHz, CD2Cl2): δ 0.18 (s, 9 H, Si(CH3)3), 3.85
(s, 2 H, −CH2Ph), 5.62 (d, J(HH) = 7.8 Hz, 2 H, o-C6H5), 6.48 (s, 1
H, OsCPhCH), 6.67 (t, J(HH) = 7.5−7.8 Hz, 2 H, m-C6H5), 6.82
(t, J(HH) = 6.9−7.5 Hz, 1 H, p-C6H5), 7.04 (d, J(HH) = 7.2 Hz, 2 H,
o-C6H5), 7.23−7.40 (m, 21 H, PPh3, C6H5), 7.47−7.51 (m, 12 H,
PPh3, C6H5). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 300.6 (t, J(PC) =
11.9 Hz, OsC), 221.2 (t, J(PC) = 12.9 Hz, OsCPh), 179.3 (s, C-
CH2Ph), 156.9 (s, ipso-C6H5), 139.0 (s, ipso-C6H5), 136.1 (s,
OsCPhCH−), 135.7−124.9 (m, other aromatic carbons), 114.2
(s, OsCC(SiMe3)), 44.6 (s, −CH2Ph), 1.6 (s, Si(CH3)3). Anal.
Calcd for C57Cl2H52P2OsSi: C, 62.91; H, 4.82. Found: C, 62.68; H,
5.02.
Os{CC(SiMe3)C(CH2(p-tolyl))CHC(p-tolyl)}Cl2(PPh3)2
(9b). Method A, from Au(CCSiMe3)(PPh3). A mixture of Os{
C(p-tolyl)-η2-CHCCH(p-tolyl)}Cl2(PPh3)2 (0.22 g, 0.22 mmol)
and Au(CCSiMe3)(PPh3) (0.18 g, 0.33 mmol) in CH2Cl2 (15 mL)
was stirred at room temperature for 15 min to give a brown solution,
HNEt3Cl (0.24 g, 1.73 mmol) was added, and the mixture was stirred
at room temperature for 2 days. The solvent was completely removed
under vacuum, and the resulting solid was extracted with benzene (5
mL). The extractant was filtered through Celite to remove the
insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was
loaded onto a silica gel column. The column was flashed with benzene,
dichloromethane, and dichloromethane/ether (20/1) subsequently to
remove Au(PPh3)Cl and other impurities and then eluted with
dichloromethane/ether (5/1) to give a green solution. The solvent
was removed under vacuum to give a green solid, which was dried
under vacuum. Yield: 0.13 g, 53%.
green solid, which was dried under vacuum. Yield: 0.20 g, 35%.
1
31P{1H} NMR (121.5 MHz, C6D6): δ −5.1 (s). H NMR (300.13
MHz, C6D6): δ 1.00 (t, J(HH) = 6.9 Hz, 6 H, 2 OCH2CH3), 2.07 (s, 3
H, C6H4-CH3), 2.14 (s, 3 H, C6H4-CH3), 3.01 (quintet, J(HH) = 6.9
Hz, 2 H, OCH2CH3), 3.18 (quintet, J(HH) = 6.9 Hz, 2 H,
OCH2CH3), 4.02 (s, 2 H, -CH2(p-tolyl)), 5.33 (s, 1 H,
−CH(OCH2CH3)2), 6.22 (d, J(HH) = 7.5 Hz, 2 H, o-CH of
−CH2(p-tolyl)), 6.74 (d, J(HH) = 8.1 Hz, 2 H, o-CH of −CH2(p-
tolyl)), 6.80−7.89 (m, 34 H, PPh3, C6H4-CH3), 7.11 (s, 1 H,
OsC(tolyl)CH). The 13C{1H} NMR spectrum was not collected
because the compound partially decomposed in the solution during
collection of the 13C{1H} NMR spectrum.
X-ray Crystallography. The procedure for crystallographic
analyses of 2, 6a, 7a, and 8a can be found in the Supporting
Information of our preliminary report.19 Single crystals of 5, 6b, and
7b suitable for X-ray diffraction were grown from CH2Cl2 solutions
layered with hexane. Intensity data were collected on a Bruker SMART
CCD Area Detector at 293 K for 5 and 7b and on an Oxford Gemini S
Ultra Area Detector at 173 K for 6b. All of the data were corrected for
absorption effects using the multiscan technique. All structures were
solved by direct methods, expanded by difference Fourier syntheses,
and refined by full -matrix least squares on F2 using the SHELXTL v.
6.1050 or OLEX251 program package. All non-H atoms were refined
anisotropically, and hydrogen atoms were placed in ideal positions and
refined as riding atoms unless specified. The p-tolyl group of the
benzyl substituent in 6b was disordered over two sites, which were
refined isotropically with half occupancy. One of the Cl atoms of the
CH2Cl2 solvent molecule in 6b was disordered over three sites, which
were also refined with isotropic thermal parameters with partial
occupancy. Further crystallographic details for 2·C7H8, 5, 6a·CH2Cl2,
6b·2CH2Cl2, 7a·CH2Cl2, 7b, and 8a·2CH2Cl2 are summarized in
Table S1 in the Supporting Information.
Computational Details. All structures were optimized without
any constraint at the B3LYP-D3 level of density functional theory
(DFT).52 Frequency calculations were also performed to identify all
the stationary points as minima (zero imaginary frequency) or
transition states (one imaginary frequency) and to provide free
energies at 298.15 K. The effective core potentials (ECPs) of Lanl2dz
were used to describe Os, Cl, and P atoms,53 with polarization
functions for Os (ζ(f) = 0.886), Cl (ζ(d) = 0.640), and P (ζ(d) =
0.387) being added.54 The standard 6-31G(d) basis set was used for all
other atoms (C, N, and H atoms).
To take solvation effects into consideration, we preformed single-
point energy calculations at the same level of theory augmented with
the SMD solvation model to obtain the optimized structures.55
Following the experimental work, dichloromethane (DCM) was
employed as the solvent in the single-point energy calculations. To
reduce the overestimation of the entropy contribution in the gas-phase
results, corrections of −2.6 (or +2.6) kcal/mol in free energies were
made for 2:1 (or 1:2) transformations.56 In this paper, the solvation-
and entropy-corrected free energies were used in all of our discussions.
All calculations were performed with the Gaussian 09 software
package.57
Method B, from Cu(CCSiMe3). A mixture of Os{C(p-tolyl)-η2-
CHCCH(p-tolyl)}Cl2(PPh3)2 (0.510 g, 0.50 mmol) and Cu(C
CSiMe3) (0.091 g, 0.57 mmol) in CH2Cl2 (25 mL) was stirred at
room temperature for 15 min to give a brown solution, HNEt3Cl
(0.552 g, 4.01 mmol) was added, and the mixture was stirred at room
temperature for 2 h. The solvent was completely removed under
vacuum, and the resulting solid was extracted with benzene (15 mL).
The extractant was filtered through Celite to remove the insoluble
HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded
onto a silica gel column. The column was flashed with benzene and
dichloromethane subsequently to remove the impurities and then
eluted with dichloromethane/ether (5/1) to give a green solution. The
solvent was removed under vacuum to give a green solid, which was
dried under vacuum. Yield: 0.224 g, 40.6%. 31P{1H} NMR (121.5
MHz, C6D6): δ −10.0 (s). 1H NMR (300.13 MHz, C6D6): δ 0.17 (s, 9
H, Si(CH3)3), 2.06 (s, 3 H, OsCC6H4CH3)), 2.13 (s, 3 H,
CH2(C6H4CH3)), 3.77 (s, 2 H, CH2(C6H4CH3)), 6.01 (d, J(HH) =
7.8 Hz, 2 H, m-CH of OsCC(C6H4CH3))), 6.64 (d, J(HH) = 7.5
Hz, 2 H, m-CH of OsCC(C6H4CH3))), 6.85−6.96 (m, 23 H,
OsC(p-tolyl)CH−, aromatic protons), 7.88−7.96 (m, 12 H, other
aromatic protons). Anal. Calcd for C59Cl2H56P2OsSi.0.5CH2Cl2: C,
61.68; H, 4.96. Found: C, 61.52; H, 5.09.
Os{CCH(O(CH2CH3)2)C(CH2(p-tolyl))CHC(p-tolyl)}-
Cl2(PPh3)2 (10b). A mixture of Os(C(p-tolyl)-η2-CHCCH(p-
tolyl))Cl2(PPh3)2 (0.50 g, 0.50 mmol) and Au(CCC(O-
(CH2CH3)2H)(PPh3) (0.30 g, 0.41 mmol) in CH2Cl2 (20 mL) was
stirred at room temperature for 20 min to give a brown solution,
HNEt3Cl (0.50 g, 3.63 mmol) was added, and the mixture was stirred
at room temperature for 3 h. The solvent was completely removed
under vacuum, and the resulting solid was extracted with benzene (5
mL). The extractant was filtered through Celite to remove the
insoluble HNEt3Cl. The filtrate was concentrated to ca. 3 mL and was
loaded onto a silica gel column. The column was flashed with benzene
and dichloromethane subsequently to remove Au(PPh3)Cl and other
impurities and then eluted with dichloromethane/ether (5/1) to give a
green solution. The solvent was removed under vacuum to give a
ASSOCIATED CONTENT
■
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00102.
Crystallographic data of complexes 2, 5, 6a,b, 7a,b, and
8a and NMR spectra (PDF)
Crystallographic data of complexes 2, 5, 6a,b, 7a,bm and
8a (CIF)
Cartesian coordinates of all calculated structures (XYZ)
I
DOI: 10.1021/acs.organomet.6b00102
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
M. S. Organometallics 2005, 24, 4849−4852. (m) Chin, C. S.; Lee, H.
Chem. - Eur. J. 2004, 10, 4518−4522. (n) Paneque, M.; Posadas, C. M.;
AUTHOR INFORMATION
Corresponding Authors
*E-mail for Z.L.: chzlin@ust.hk.
*E-mail for G.J.: chjiag@ust.hk.
Notes
■
́
Poveda, M. L.; Rendon, N.; Salazar, V.; Onate, E.; Mereiter, K. J. Am.
̃
Chem. Soc. 2003, 125, 9898−9899. (o) Gilbertson, R. D.; Lau, T. L.;
Lanza, S. S.; Wu, H. P.; Weakley, T. J. R.; Haley, M. M. Organometallics
2003, 22, 3279−3289. (p) Wu, H. P.; Lanza, S.; Weakley, T. J. R.;
Haley, M. M. Organometallics 2002, 21, 2824−2826. (q) Gilbertson, R.
D.; Weakley, T. J. R.; Haley, M. M. J. Am. Chem. Soc. 1999, 121,
2597−2598. (r) Bleeke, J. R.; Behm, R. J. Am. Chem. Soc. 1997, 119,
8503−8511. (s) Bleeke, J. R.; Behm, R.; Xie, Y. F.; Chiang, M. Y.;
Robinson, K. D.; Beatty, A. M. Organometallics 1997, 16, 606−623.
(t) Bleeke, J. R.; Bass, L. A.; Xie, Y. F.; Chiang, M. Y. J. Am. Chem. Soc.
1992, 114, 4213−4219. (u) Bleeke, J. R.; Xie, Y. F.; Bass, L.; Chiang,
M. Y. J. Am. Chem. Soc. 1991, 113, 4703−4704. (v) Bleeke, J. R.; Xie,
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Hong Kong Research Grants
Council (Project Nos. 602611, 601812, 602113, CUHK7/
CRF/12G-2).
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