Oxidative demetalation of Fischer alkoxy carbene complexes with stoichiometric pyridine N-oxide and NaBH4-promoted demetalation of Fischer iminocarbene complexes with sulfur and selenium

Article abstract of DOI:10.1016/j.jorganchem.2006.05.021

Oxidation of Fischer alkoxy carbene complexes were systematically investigated with stoichiometric pyridine N-oxide (PNO) under mild conditions, forming ester products in good to excellent yields from the corresponding monocarbene complexes. Fischer alkoxy biscarbene complexes efficiently underwent stepwise oxidative demetalation under controlled conditions, resulting in ester-monocarbene and diester products, respectively. This oxidation protocol has demonstrated a generally efficient method to oxidize Fischer alkoxy carbene complexes under mild conditions, providing a new route to novel monocarbene complexes from Fischer biscarbene complexes. In the presence of NaBH₄, reactions of Fischer iminocarbene complexes with elemental sulfur or selenium in ethanol at ambient temperature regioselectively afforded thione or selone complexes by insertion of a sulfur or selenium atom into the M{double bond, long}C bonds in Fischer carbene complexes, and metal-free selone was also obtained. The molecular structures of the iminocarbene complexes and selone derivatives were confirmed by X-ray crystallographic study. The NaBH₄-promoted demetalation protocol suggests a potential new route to demetalate Fischer aminocarbene complexes.

Full text of DOI:10.1016/j.jorganchem.2006.05.021

Journal of Organometallic Chemistry 691 (2006) 3679–3692
www.elsevier.com/locate/jorganchem
Oxidative demetalation of Fischer alkoxy carbene complexes
with stoichiometric pyridine N-oxide and NaBH4-promoted
demetalation of Fischer iminocarbene complexes
with sulfur and selenium
a
a
a,
b
Zhaoyan Zheng , Jinzhu Chen , Zhengkun Yu *, Xiuwen Han
a
Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, Liaoning 116023, PR China
b
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
457 Zhongshan Road, Dalian, Liaoning 116023, PR China
Received 28 March 2006; received in revised form 8 May 2006; accepted 12 May 2006
Available online 20 May 2006
Abstract
Oxidation of Fischer alkoxy carbene complexes were systematically investigated with stoichiometric pyridine N-oxide (PNO) under
mild conditions, forming ester products in good to excellent yields from the corresponding monocarbene complexes. Fischer alkoxy
biscarbene complexes efficiently underwent stepwise oxidative demetalation under controlled conditions, resulting in ester-monocarbene
and diester products, respectively. This oxidation protocol has demonstrated a generally efficient method to oxidize Fischer alkoxy car-
bene complexes under mild conditions, providing a new route to novel monocarbene complexes from Fischer biscarbene complexes. In
the presence of NaBH4, reactions of Fischer iminocarbene complexes with elemental sulfur or selenium in ethanol at ambient temper-
ature regioselectively afforded thione or selone complexes by insertion of a sulfur or selenium atom into the M@C bonds in Fischer car-
bene complexes, and metal-free selone was also obtained. The molecular structures of the iminocarbene complexes and selone derivatives
were confirmed by X-ray crystallographic study. The NaBH4-promoted demetalation protocol suggests a potential new route to demet-
alate Fischer aminocarbene complexes.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Fischer carbene; Pyridine N-oxide; Iminocarbene; Sulfur; Selenium
1. Introduction
ton of the newly formed products and the metal moiety is
removed during the reaction. Transition metal-catalyzed
transmetalations [6], carbocyclization reactions [7], and
reduction of Fischer carbene complexes with metal
hydrides [8] belong to this category. In other reactions such
as Diels–Alder reactions [9], 1,3-dipolar cycloadditions [10]
and Micheal additions [11], the transition metal-carbene
carbon bond still preserves in the formed complex prod-
ucts, and thus a further step is necessary to remove the
metal moiety.
Over the last two decades Fischer monocarbene com-
plexes [1] and recently biscarbene complexes [2] have been
used to synthesize a wide range of organic products. Do¨tz
benzannulation [3] and cyclopropanation [4] reactions are
employed to construct functionalized phenol derivatives
and cyclopropanes, respectively. Important organic syn-
thetic methodology has also been established by Hegedus
photochemical ketene generation [5]. In these reactions,
the carbene carbon is directly incorporated into the skele-
Different procedures have been developed to remove the
metal moiety and transform Fischer carbene complexes into
organic products. Acid-promoted hydrolysis affords alde-
hydes [12]. Heating in the presence of pyridine gives enol
*
Corresponding author. Tel./fax: +86 411 8437 9227.
E-mail address: zkyu@dicp.ac.cn (Z.K. Yu).
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.05.021

3680
Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
ethers [9b,12b,13]. Other procedures using a variety of
reagents and conditions including diazomethane [12b,14],
Wittig reagents [15], chloromethyllithium [16], and hydro-
genation [12b,17] have also been known to demetalate
Fischer carbene complexes. In most cases, oxidation
appears to be a convenient method to convert Fischer alk-
oxy carbene complexes into the corresponding ester prod-
ucts. Oxidants such as pyridine N-oxide (PNO) [2,18],
dimethyl sulfoxide (DMSO) [12b,12c,19], dimethyldioxi-
rane (DMD) [20], ceric ammonium nitrate (CAN)
[18c,18f,19a,21], PhIO [22], and air [21c,23] have been used
for this purpose. For Fischer aminocarbene complexes,
harsh reaction conditions are usually required and only
activated aminocarbene complexes can be oxidatively
demetalated with PNO [18e]. Other reagents such as iodos-
obenzene (PhIO) [22], Ca(ClO)2 [24], iodine [24], NaBO3/KI
[24], CAN [25], H2O2 with methyltrioxorhenium (MTO)
[26], and m-chloroperoxybenzoic acid [27], have occasion-
ally been reported to oxidatively demetalate Fischer amino-
carbene complexes. Although oxidative demetalation is
usually required in organic synthesis with Fischer carbene
complexes, no systematic investigation has been well-docu-
mented in this aspect. Until recently, Barluenga et al.
reported a fluoride-promoted air-oxidation method to
demetalate a limited number of alkenyl and alkynyl Fischer
alkoxy monocarbene complexes, resulting in ester products
in low to good yields [23c]. Perdicchia et al. developed a
methodology for oxidizing 1-phenyl and 1-alkyl Fischer
hydrazinocarbene complexes with oxidants such as CAN,
air/hm, Ca(ClO)2, NaBO3/KH2PO4/KI, and I2 [24].
Me
N
Me
N
(OC)5Cr
Ph
NaBH4/CF3CO2H
rt, 57%
Ph
O
S
O
(OC)5Cr
S
S
N
N
N
NaBH4/MeOH
rt
(OC)5Cr
N
N
+
N
Ph
Ph
(12%)
Ph
(62%)
O
O
N
Me
Me
Ph
Me
Me
Ph
NaBH4/MeOH
N
N
N
rt
(OC)5M
M = Cr, W
(63-67%)
Scheme 1. Reduction of Fischer aminocarbene complexes [8b].
plexes, and used elemental sulfur and selenium to demeta-
late Fischer iminocarbene (which can be considered as
pseudo aminocarbene) complexes in the presence of
NaBH4 under mild conditions. Using the oxidant system,
only stoichiometric PNO is necessary for efficient removal
of the (pentacarbonyl)metal moiety. With the NaBH4-pro-
moted system, sulfur or selenium insertion products and
selone derivatives were selectively obtained as the products.
Herein, we report a systematic study on oxidation of
Fischer alkoxy monocarbene complexes and stepwise oxi-
dation of Fischer biscarbene complexes with pyridine N-
oxide (PNO). NaBH4-promoted demetalation of Fischer
iminocarbene complexes with elemental sulfur or selenium
was preliminarily investigated.
Reduction of Fischer carbene complexes has recently
been paid some attention by means of reducing agents such
i
as NaCNBH3, BH3 Æ THF, KBH(sBu)3, LiAlH4, Bu2AlH,
and NaBH4, etc. [8]. The reported oxidants usually effect
to oxidatively demetalate Fischer alkoxy carbene com-
plexes, but only limited success has been achieved to demet-
alate a few activated Fischer aminocarbene complexes using
the oxidation methodology [18e]. Reduction seems more
versatile than oxidation to demetalate Fischer carbene com-
plexes, affording M@C bond reduction, reduction/isomeri-
zation or reduction/(OC)5M-transfer products. In some
cases, functional groups in the carbene complexes can also
be reduced at the same time. For reduction of Fischer
aminocarbene complexes, several rare examples are pre-
sented in Scheme 1 in which the present reduction method-
ology demonstrates a potential route to demetalate Fischer
aminocarbene complexes, but more detailed and extensive
investigation is expected in this aspect. In the course of
our ongoing investigation on organic synthesis via Fischer
carbene complexes [2], removal of the metal moieties from
the newly formed carbene complex products has often been
required, which led us to pursue a systematic study on
demetalation of different types of Fischer alkoxy carbene
complexes as well as other methods to demetalate amino-
carbene complexes.
2. Results and discussion
2.1. Oxidation of Fischer alkoxy carbene complexes with
PNO
2.1.1. Oxidation of monocarbene complexes 1–5
The oxidation reactions of Fischer monocarbene com-
plexes 1–5 were carried out with 1.0 equiv. of PNO in air
at room temperature. In order to control the vigorous exo-
thermic reactions, a solution of PNO in CH2Cl2 was drop-
wise added to the solution of a carbene complex at 0 ꢁC,
OR'
OR'
PNO (1.0 eq)
(OC)5M
O
CH2Cl2, rt
ð1Þ
R
R
.
-(OC) M Py
5
1-5
6-15
Dichloromethane was chosen as the reaction medium to
avoid use of coordinative solvents such as THF and aceto-
nitrile which can promote removal of the (pentacar-
bonyl)metal moiety as (OC)5M Æ THF or (OC)5M Æ
NCCH3 [1]. The oxidation reactions did not undergo with-
out PNO in air, revealing that air itself cannot oxidize
Fischer alkoxy carbene complexes under the stated condi-
tions. Oxidation of the Fischer alkoxy carbene complexes
Thus we chose pyridine-N-oxide (PNO) as the oxidant
to oxidatively demetalate Fischer alkoxy carbene com-

Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
3681
Table 1
Oxidation of monocarbene complexes 1–5a
Entry
1
Carbene complex
Time (min)
20
Ester
Yieldb (%)
78
OEt
1a
1b
(OC) Cr
5
OEt
O
6
Ph
OEt
2
20
65
Ph
(OC) W
5
Ph
OMe
OMe
3
4
2a
2b
20
15
7
8
96
77
(OC)5Cr
O
Ph
Ph
OMe
OMe
(OC)5Cr
O
Ph
Ph
OMe
OMe
5
2c
15
9
90
(OC) Cr
O
5
O
O
O
O
6
7
3
180
30
10
11
93
93
(OC) Cr
O
5
OEt
OEt
4a
(OC)5Cr
Ph
O
Ph
Me
Me
Me
Me
Me
Me
N
N
N
N
Me
Me
OEt
8
9
4b
90
60
96
90
(OC) W
Ph
5
N
N
Me
OEt
4c
(OC)5Cr
Ph
Me
Me
OEt
N
N
O
Ph
CH2Ph
Me
Me
12
N
N
CH Ph
2
OEt
10
11
4d
60
60
93
70
(OC) W
Ph
5
Me
N
N
CH Ph
2
Me
Ph
OEt
OEt
4e
13
(OC)5W
O
Ph
Me
Me
Me
Me
N
N
N
N
(continued on next page)

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Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
Table 1 (continued)
Entry
12
Carbene complex
Time (min)
12
Ester
Yieldb (%)
81c
OEt
CH
5a
(OC) Cr
5
3
OEt
CH
14
O
3
OEt
CH3
13
14
5b
5c
12
12
81c
85c
(OC)5W
OEt
(OC) Cr
5
CH CH CH CH
3
2
2
2
OEt
15
O
CH2CH2CH2CH3
OEt
CH CH CH CH
3
15
5d
12
82c
(OC) W
5
2
2
2
a
Reaction conditions: carbene complex, 1.0 mmol; PNO, 1.0 mmol; CH2Cl2, 4 ml; room temperature (23 ꢁC).
Isolated yields (not optimized) by flash silica gel column chromatography.
GC yields.
b
c
underwent very efficiently, reaching a complete conversion
for the carbene complexes over a period of 0.2–3.0 h and
affording ester products in good to excellent yields (up to
96%) (Table 1). It should be noted that fluoride-promoted
air-oxidation of Fischer carbene complexes requires up to
36 h to achieve low to good yields (33–91%) for the ester
products [23c]. The (pentacarbonyl)metal moiety was re-
moved as (OC)5M Æ py which was easily isolated by silica
gel column chromatography [2]. 1-Alkynyl Fischer alkoxy
carbene complexes 1a and 1b were oxidized to their corre-
sponding ester 6 in 78% and 65% yields within 20 min (Ta-
ble 1, entries 1 and 2), respectively. For 1-alkenyl carbene
complexes of chromium 2a–c, their corresponding ester
products were obtained in 77–96% yields over a period of
15–20 min (entries 3–5), while the relatively unreactive
alkenyl carbene complex 3 reached a 100% conversion
within 3 h to give the organic product in 93% yield (entry
6). b-(1-Pyrazolyl)-substituted alkenyl carbene complexes
4a–d were efficiently demetalated to afford esters 11 and
12 in 90–96% yields (entries 7–10), respectively. A carbene
complex of chromium usually exhibited a reactivity higher
than its tungsten analogue (entries 7 and 8). Somehow, es-
ter 13 was only obtained in 70% yield from b-(1-pyrazolyl)-
substituted alkenyl carbene complex 4e (entry 11). 1-Alkyl
Fischer monocarbene complexes 5a–d were easily demeta-
lated with PNO within 12 min, forming the corresponding
esters in 81–85% yields (entries 12–15). It is noteworthy
that the ester products from 5a–d were determined by
GC analysis with n-nonane and 1,4-dimethylbenezene as
the internal standards, respectively.
O
PNO (1.0 eq)
CH2Cl2
MeO
OMe
-20oC - rt
160 min
Cr(CO)5
17 (84%)
(OC)5Cr
MeO
OMe
PNO (1.0 eq)
CH2Cl2 / rt
100%
Cr(CO)5
16
O
PNO (2.0 eq)
CH2Cl2
MeO
OMe
O
rt / 30 min
82%
18
Scheme 2. Oxidation of symmetrical biscarbene complex 16.
reaction temperature to ꢀ20 ꢁC, the reaction of 16 and
PNO in a 1:1 molar ratio predominantly afforded 17 in
84% yield with trace amount of diester 18 as the minor
product. Air itself did not oxidize the biscarbene complex
at low or ambient temperature. At room temperature, oxi-
dation of 16 with 2.0 equiv. of PNO in CH2Cl2 afforded 18
in 82% yield, and further treatment of 17 with 1.0 equiv. of
PNO quantitatively gave 18. It should be noted that use of
dilute solutions of 16 and PNO is necessary to get a good
yield for the partially demetalated product, i.e., 17 (see Sec-
tion 4).
2.1.3. Oxidation of unsymmetrical biscarbene complexes 19
Biscarbene complexes 19a and 19b are unstable over sil-
ica gel to get decomposed, forming monocarbene com-
plexes with opening of the four-membered cyclobutenyl
ring and removal of the M(CO)5 moiety adjacent to the
four-membered ring during flash column chromatography
[28]. Treatment of 19 with 1.0 equiv. of PNO in CH2Cl2
at room temperature gave monocarbene complexes 20a in
68% yield from 19a (M = Cr) and 20b in 85% yield from
19b (M = W), respectively (Scheme 3). With 2.0 equiv. of
2.1.2. Oxidation of symmetrical biscarbene complex 16
Biscarbene complex 16 was easily demetalated with
PNO as the oxidant (Scheme 2). The reaction of 16 with
PNO (1.0 equiv.) in air at room temperature gave a mixture
of monocarbene complex 17 and diester 18 and their molar
ratio varied depending on the manipulations. Lowering the

Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
3683
oxidation occurred in CH3CN at 70 ꢁC over a period of
10 h, but the desired amide product failed to be isolated.
In other cases, no reaction underwent and the starting car-
bene complexes were recovered unchanged although a cou-
ple of activated Fischer aminocarbene complexes of
chromium are known to be oxidatively demetalated with
PNO in THF [18e].
OEt
(OC)5M
Ph
N
O
OMe
PNO (1.0 eq)
OEt
CH2Cl2 / rt / 5 h
Ph
20a (M = Cr) 68%
20b (M = W) 85%
OEt
(OC)5M
Ph
N
M(CO)5
OMe
PNO (1.0 eq)
OEt
C6H6, 60 oC / 2.5 h
~100%
2.2. NaBH4-promoted demetalation of Fischer iminocarbene
complexes
Ph
M =: Cr (19a)
W (19b)
OEt
With metal hydrides or borohydrides Fischer carbene
complexes can be reductively demetalated, depending on
the controlled conditions [8]. Complex 23 cannot react with
NaCNBH3 in methanol [8a] and complicated products are
formed in the reactions of 22 and 23 with NaBH4. A few
Fischer 1-methoxy arylcarbene complexes of chromium
have been known to react with elemental sulfur and sele-
nium under relatively harsh (refluxing in ether or dioxane)
conditions to form arylthiocarboxylates and arylseleno-
carboxylates in 7–32% yields, respectively [29a], but so
far, no further work toward demetalation of Fischer car-
bene complexes with a similar protocol has been pursued.
Under the stated conditions [29a], Fischer aminocarbene
complexes 22 or 23 did not react with elemental sulfur or
selenium at ambient temperature, but we reasonably
expected that elemental sulfur and selenium may be
involved in the demetalation of Fischer complexes under
a reduction atmosphere. Interaction of NaBH4 with sulfur
has been known to generate hydrogen sulfide [29b], reduc-
tive hydrogen sulfide or hydrogen selenide may work for
demetalation of Fischer carbene complexes. In order to
get regioselective demetalation products, pseudo aminocar-
bene complexes, i.e., Fischer iminocarbene complexes, the
pyrimidine-type carbene complexes 25a and 25b were
applied to test their demetalation with elemental sulfur
and selenium in the presence of NaBH4,
O
Ph
N
O
PNO (2.0 eq)
C6H6 / 60 oC / 6 h
OMe
OEt
Ph
21 80% (from M = Cr)
21 88% (from M = W)
Scheme 3. Oxidation of unsymmetrical biscarbene complexes 19.
PNO in benzene at an elevated temperature, i.e., 60 ꢁC, 19
were oxidized to diester 21 in 80–88% yields. It was noticed
that in all the cases, biscarbene complex of tungsten, i.e.,
19b, gave the stepwisely demetalated products, i.e., 20b
and 21, in yields higher than its chromium analogue 19a.
Further treatment of the monocarbene complexes 20a or
20b in C6H6 at 60 ꢁC quantitatively gave the diester 21.
Complexes 20 and diester 21 are stable over silica gel that
they were conveniently isolated by flash silica gel column
chromatography. It is noteworthy that in complexes 19
the M@C bond attached to the cyclobutenyl ring is more
reactive to PNO than the other metal carbene bond addi-
tionally stabilized by the vinylogous nitrogen. These results
imply a potential application of the present protocol in syn-
thesis of novel Fischer mono-, bis- or polycarbene com-
plexes by stepwise demetalation under controlled mild
conditions.
Ph
OEt
N
NH
NHPh
CH2Cl2
rt
(OC)5M
2.1.4. Oxidation of aminocarbene complexes 22 and 23
Using 1-alkynyl Fischer carbene complexes 22 and 23 as
the model starting complexes, oxidation of Fischer amino-
carbene complexes with PNO (P1.0 equiv.) were tenta-
tively carried out under relatively harsh conditions such
as extending reaction time to 10 h, at room temperature,
50 ꢁC or 70 ꢁC, using CH2Cl2, THF or CH3CN as the reac-
tion solvents (Scheme 4). Only in the case of 22a, partial
(OC)5M
N
Ph
+
Ph
ð2Þ
Ph
Ph
M = Cr (1a), W (1b)
25a (M = Cr) 76.3%
25b (M = W) 66.4%
24
Pyrimidine-type complexes 25 were prepared in 66–76%
yields by the reactions of 1 and 1.0 equiv. of N-phenyl-
benzamide in CH2Cl2 at ambient temperature (Eq. (2))
and characterized by IR, NMR, and elemental analysis.
Their molecular structures were confirmed by the X-ray
single crystal structure of 25b (Fig. 1). With NaBH4 as
the reducing agent in THF at ambient temperature, the
imino group of 25 was reduced to NH–CH as shown in
complexes 26, while the metal-carbene carbon bond
(M@C) stayed unchanged (Scheme 5). However, the reac-
tions of 25 with elemental sulfur in methanol in the pres-
ence of NaBH4 selectively generated pyrimidine-thione
complexes 27 (68–89%) by the insertion of sulfur into
the M@C bonds in 25. The (pentacarbonyl)metal moiety
R1
H
N R2
N
N CH2Ph
PNO
X
O
(OC)5M
(OC)5W
Ph
Ph
Ph
23
22a (M = Cr)
22b (M = W)
Scheme 4. Oxidation of aminocarbene complexes 22 and 23.

3684
Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
underwent insertion of S into the metal-carbene carbon
bond (M@C), forming product 27. In a fashion similar
to the reactions of 25 with sulfur in the presence of
NaBH4, the reactions of 25 with elemental selenium in
the presence of NaBH4 gave the analogues of complexes
27, i.e., pyrimidine-selone complexes 28 in 25–52% yields.
At the same time, metal-free pyrimidine-selone 29 was col-
lected (47–70%), which is attributed to the weaker coordi-
nating ability of selenium than sulfur to chromium or
tungsten (Scheme 5). Interaction of NaBH4 with Se pre-
sumably formed reductive species H2Se which underwent
reactions with 25 in a fashion similar to H2S. Thiono-
and selenoesters are important reagents in organic synthe-
sis and biochemistry [30]. The present NaBH4-promoted
demetalation of Fischer iminocarbene complexes provides
a new route to specific thiono- and selenoamides or
carboxylates.
2.3. Crystal structures of compounds 25b, 28b, and 29
The solid-state crystal structures of complexes 25b, 28b
and pyrimidine-selone 29 were determined by X-ray crys-
tallographic study. The crystallographic data for these
compounds are summarized in Table 2, and selected bond
lengths and angles in Table 3. Complex 25b features a
1,4-dihydro-pyrimidine backbone structure with a carbene
Fig. 1. Perspective view of complex 25b.
coordinates with the sulfur atom instead of the imino
nitrogen in 27, while the same reactions in ethanol gave
complicated products without elemental sulfur. Presence
of sulfur during the reduction remarkably altered the
selectivity of the products and stopped further reduction
of the insertion products by NaBH4. Isolation by flash sil-
ica gel column chromatography did not afford any other
noticeable products (Scheme 5). Without S8, NaBH4
worked as a reducing agent to reduce the N@C bond in
25 to NH–CH as shown in 26. Because the Fischer imino-
carbene complexes are much less reactive than their alk-
oxy analogues, NaBH4 cannot reduce the M@C bond in
an iminocarbene complex to CH2. Interaction of S8 with
NaBH4 generated reductive species H2S [29b] which thus
˚
carbon atom of the W@C bond (2.207(7) A) at the 4-
position (Fig. 1). The imino nitrogen is bonded to the
carbene carbon and the N@C bond length is
˚
˚
1.307(8) A, while N(1)–C(6) bond length is 1.357(9) A
and much shorter than a normal C–N single bond, sug-
gesting a delocalized C–N bond with some double bond
˚
feature. The C(7)–C(8) bond length (1.363(9) A) is char-
acteristic of a carbon–carbon double bond, suggesting
25b to be an alkenyl Fischer iminocarbene complex.
The structural difference between 25b and 28b is that a
selenium atom is inserted into the W@C bond in 25b,
Ph
HN
NaBH4
THF, rt
(OC)5M
N
Ph
Ph
26a (M = Cr) 70.7%
26b (M = W) 60.3%
Ph
Ph
N
N
S8 / NaBH4
(OC)5M
N
Ph
(OC)5MS
N
Ph
EtOH, rt
Ph
Ph
27a (M = Cr) 67.7%
27b (M = W) 88.7%
25a (M = Cr)
25b (M = W)
Ph
N
Ph
N
N
Se / NaBH4
EtOH, rt
(OC)5MSe
N
Ph
+ Se
Ph
Ph
Ph
28a (M = Cr) 24.6%
28b (M = W) 52.3%
29 (from M = Cr) 70.4%
29 (from M = W) 46.6%
Scheme 5. NaBH4-promoted demetalation of 25 with sulfur and selenium.

Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
3685
Table 2
Crystal data and refinement details for compounds 25b, 28b, and 29
25b
28b
29
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
C27H16N2O5W
632.27
293(2)
C27H16N2O5SeW
711.23
293(2)
Monoclinic
P2(1)/n
11.1956(8)
22.2519(16)
11.3290(8)
90
114.8450(10)
90
2561.1(3)
4
1.845
5.971
C22H16N2Se
387.33
293(2)
Monoclinic
Pc
Triclinic
ꢀ
P1
˚
a (A)
11.0930(12)
11.4295(13)
11.8522(13)
90.492(2)
115.403(2)
114.633(2)
1201.3(2)
2
1.748
4.848
612
0.52 · 0.19 · 0.18
1.95–27.00
7153
5095
0.1124
10.5047(13)
9.8277(12)
17.937(2)
90
103.294(2)
90
1802.1(4)
4
1.428
2.089
784
0.51 · 0.31 · 0.15
1.99–27.00
10366
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dc (gcmꢀ3
)
l (mmꢀ1
F(000)
)
1360
Crystal size (mm3)
0.40 · 0.23 · 0.15
1.83–27.00
15085
5532
0.1244
h Limits (ꢁ)
No. of data collected
No. of unique data
Rint
5022
0.1321
No. of data observed with I > 2r(I)
No. of refined parameters
Goodness-of-fit on F2
R (all data/obsd. data)
5095
321
1.002
0.0536/0.0583
0.1254/0.1276
2.797(ꢀ3.173)
5532
325
0.949
0.0503/0.0643
0.1198/0.1252
2.447 (ꢀ1.695)
5022
451
0.871
0.0588/0.0772
0.1252/0.1322
0.982 (ꢀ0.595)
WR2 (all data/obsdꢀ. 3data)
˚
Residual qmax (e A
)
Table 3
˚
Selected bond length (A) and angles (ꢁ) for compounds 25b, 28b, and 29
Complex 25b
W–C(6)
C(6)–C(7)
N(2)–C(9)
2.207(7)
1.418(10)
1.375(8)
N(1)–C(6)
C(7)–C(8)
N(2)–C(16)
1.357(9)
1.363(9)
1.465(8)
N(1)–C(9)
N(2)–C(8)
1.307(8)
1.366(9)
N(1)–C(6)–W
N(1)–C(6)–C(7)
N(2)–C(8)–C(7)
118.4(5)
115.5(6)
118.4(6)
C(7)–C(6)–W
N(1)–C(9)–N(2)
C(6)–C(7)–C(8)
126.0(5)
122.8(6)
121.7(7)
C(6)–N(1)–C(9)
C(9)–N(2)–C(8)
121.6(6)
118.3(5)
Complex 28b
W–Se
N(2)–C(6)
N(1)–C(22)
C(6)–Se–W
C(6)–N(2)–C(9)
C(7)–C(8)–N(1)
2.6568(8)
1.352(8)
1.453(8)
110.6(2)
119.4(6)
119.0(6)
Se–C(6)
N(1)–C(9)
C(6)–C(7)
N(2)–C(6)–Se
N(2)–C(9)–N(1)
C(6)–C(7)–C(8)
1.835(6)
1.364(8)
1.421(9)
121.0(5)
123.8(6)
119.9(6)
N(2)–C(9)
N(1)–C(8)
C(7)–C(8)
N(2)–C(6)–C(7)
C(9)–N(1)–C(8)
1.299(8)
1.388(8)
1.340(9)
119.2(6)
118.2(5)
Compound 29
Se(1)–C(6)
N(2)–C(9)
1.843(6)
1.352(9)
1.363(9)
N(1)–C(9)
N(2)–C(8)
1.334(9)
1.388(9)
N(1)–C(6)
C(6)–C(7)
1.387(9)
1.383(10)
C(7)–C(8)
N(1)–C(6)–Se(1)
C(9)–N(2)–C(8)
N(1)–C(6)–C(7)
118.0(5)
119.1(6)
119.4(6)
C(6)–N(1)–C(9)
N(2)–C(8)–C(7)
117.7(6)
118.2(6)
N(1)–C(9)–N(2)
C(8)–C(7)–C(6)
123.8(7)
121.0(7)
thus generating 28b (Fig. 2). In complex 28b, the W–Se,
with the W(CO)5 moiety bending to the imino nitrogen,
which may effect long-range interaction with the metal
atom. In pyrimidine-selone 29 (Fig. 3), All the C(6)–
˚
C–Se and C(7)–C(8) bond lengths are 2.6568(8) A,
˚
˚
1.835(6) A, and 1.340(9) A, demonstrating a coordinative
˚
˚
bond, a C@Se bond, and a carbon–carbon double bond,
Se(1) (1.843(6) A), imino N(1)–C(9) (1.334(9) A), and
˚
˚
respectively. The imino N(2)–C(9) bond (1.299(8) A)
C(7)–C(8) (1.363(9) A) bond lengths are a little bit longer
almost stays unchanged in 28b as compared with that
in its analogue 25b. The C(6)–Se–W angle is 110.6(2)ꢁ
than their corresponding analogues in 28b, implying that
the molecular structure of 28b is repelled by the W(CO)5

3686
Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
4. Experimental
4.1. General considerations
All the oxidation reactions were carried out in air unless
otherwise stated and the NaBH4-involved reactions were
pursued under a nitrogen atmosphere. Reaction solvents
were dried and distilled prior to use by the literature meth-
1
ods. H and 13C{1H} NMR spectra were recorded on a
Bruker DRX-400 spectrometer and all chemical shift val-
ues refer to dTMS = 0.00 ppm or CDCl3 (d(1H), 7.26 ppm;
d(13C), 77.16 ppm). IR spectra were recorded on a Bruker
Tensor 27 FT-IR spectrophotometer. Elemental analysis
was achieved by the Analysis Center, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences. Ana-
lytical TLC plates, Sigma-Aldrich silica gel 60F200 were
viewed by UV light (254 nm). Chromatographic purifica-
tions were performed on SDZF silica gel 160. Fischer car-
bene complexes 1 [31], 2 [32], 3 [32], 4 [1e,11b], 5 [33], 16
[32] and 19 [28] were prepared as reported. NMR spectro-
scopic data for the oxidation products 6 [34], 7 [35], 8 [36],
9 [37], 10 [38] and 18 [39] were previously reported.
Fig. 2. Perspective view of complex 28b.
4.2. A typical procedure for oxidation of Fischer alkoxy
carbene complexes
A pre-cooled-to-0 ꢁC solution of pyridine N-oxide
(95 mg, 1.0 mmol) in 2 ml of CH2Cl2 was added to the
solution of carbene complex 2a (338 mg, 1.0 mmol) in
2 ml of CH2Cl2 in a 5-ml screwtop vessel at 0 ꢁC over a per-
iod of 2 min. After the addition was complete, the reaction
mixture was warmed up to room temperature and stirred
until all the carbene complex was consumed by TLC
analysis. The resultant mixture was diluted with CH2Cl2,
filtered through a short pad of celite, and then concentrated
under reduced pressure. Purification by flash silica gel col-
umn chromatography with the eluent petroleum ether (30–
60 ꢁC)/CH2Cl2 (v/v, 6/1) afforded the ester product 7 as
white solid (156 mg, 96%). The known products were char-
Fig. 3. Perspective view of pyrimidine-selone 29.
1
acterized by H and 13C{1H} NMR and comparison with
moiety coordinating to the selenium atom, shortening the
related bonds in 28b.
the reported NMR data or by comparison of their GC
traces with those of the authentic samples. The new prod-
1
ucts were fully characterized by H and 13C{1H} NMR,
3. Summary
IR, and elemental analysis. Stepwise oxidation of Fischer
biscarbene complexes was carried out under controlled
conditions as described in the Supporting Information.
In summary, the oxidation protocol for demetalation of
Fischer alkoxy carbene complexes with stiochiometric pyr-
idine N-oxide (PNO) can be applied to both mono- and
biscarbene complexes under mild conditions. Stepwise oxi-
dation of Fischer alkoxy biscarbene complexes was realized
with PNO under controlled conditions, providing a new
route to novel Fischer alkoxy monocarbene complexes. In
the presence of NaBH4, reactions of Fischer iminocarbene
complexes with elemental sulfur or selenium regioselectively
afforded thiones or selones. This NaBH4-promoted proto-
col suggests a potential new route to demetalate Fischer
aminocarbene complexes.
4.3. Stepwise oxidation of symmetrical biscarbene complex
16
(a) Partial oxidation: A solution of pyridine N-oxide
(24 mg, 0.25 mmol) in 20 ml of CH2Cl2 was added drop-
wise to the solution of biscarbene complex 16 (150 mg,
0.25 mmol) in 20 ml of CH2Cl2 at ꢀ20 ꢁC over a period
of 40 min. The reaction mixture was allowed to warm to
room temperature and stirred for 2 h to get a complete
conversion of 16 by TLC analysis. All the volatiles were

Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
3687
removed under reduced pressure. Purification by flash sil-
ica gel column chromatography (petroleum ether/CH2Cl2,
v/v = 3:1) afforded complex 17 as red crystals (89 mg,
84%). M.p.: 74–75 ꢁC. (b) Complete oxidation: A solution
of pyridine N-oxide (72 mg, 0.76 mmol) in 2 ml of CH2Cl2
was added to the solution of biscarbene complex 16
(228 mg, 0.38 mmol) in 2 ml CH2Cl2 at room temperature.
The reaction was finished within 30 min by TLC analysis,
and all the volatiles were removed under reduced pressure.
Purification by flash silica gel column chromatography
(petroleum ether/CH2Cl2, v/v = 1:1) afforded diester 18
as white solid (77 mg, 82%).
1589.3 (50), 1496.7 (40), 1446.5 (40) [m (C@C, C@N)]. Anal.
Calc. for: C17H20N2O2: C, 71.81; H, 7.09; N, 9.85. Found: C,
71.94; H, 6.90; N, 9.83%.
4.6. 3-(40-Benzyl-30,50-dimethylpyrazol-10-yl)-3-phenyl-
acrylic acid ethyl ester (12)
OEt
O
1
Ph
3
Me
5'
2
Ph
1'
2'
N
4'
N
3'
Me
(a) 2-Ethoxy-4-phenyl-4-(30,50-dimethyl-40-benzylpyrazol-
10-yl)-1,1,1,1,1-penta carbonyl-1-chroma-1,3-butadiene 4c
(536 mg, 1.0 mmol) was reacted with PNO (95 mg,
1.0 mmol) to afford 12 as white solid (328 mg, 90%). (b) 2-
Ethoxy-4-phenyl-4-(30,50-dimethyl-4-benzylpyrazol-10-yl)-
1,1,1,1,1-pentacarbonyl-1-tungsta-1,3-butadiene 4d (668 mg,
1.0 mmol) was reacted with PNO (95 mg, 1.0 mmol) to
4.4. Stepwise oxidation of unsymmetrical biscarbene
complex 19a
(a) Partial oxidation: A solution of pyridine N-oxide
(24 mg, 0.25 mmol) in 2 ml of CH2Cl2 was added to the
solution of 19a (200 mg, 0.25 mmol) in 2 ml of CH2Cl2 in
a 5-ml screwtop vessel at room temperature. The reaction
was finished over a period of 5 hours by TLC analysis.
Purification by flash silica gel column chromatography
(petroleum ether/CH2Cl2, v/v = 2:1) afforded complex
20a as red crystals (106 mg, 68%). (b) Complete oxidation:
A mixture of pyridine N-oxide (95 mg, 1.0 mmol) and com-
plex 19a (400 mg, 0.5 mmol) in 20 ml benzene was stirred at
60 ꢁC for 6 hours. Work-up as mentioned above gave dies-
ter 21 as colorless crystals (180 mg, 80%).
1
afford 12 as white solid (336 mg, 93%). M.p.: 62 ꢁC. H
NMR (CDCl3, 23 ꢁC, 400 MHz): d 7.44–7.37, 7.28, 7.19
and 7.09 (m each, 5:2:1:2H, 2 · Ph), 6.35 (s, 1H, 2-H), 4.09
(q, 2H, OCH2), 3.71 (s, 2H, 40-CH2), 2.17 (s, 3H, 50-CH3),
1.68 (s, 3H, 30-CH3), 1.15 (t, 3H, OCH2CH3). 13C{1H}
NMR (CDCl3, 23 ꢁC): d 165.74 (Cq, C1), 151.12 (Cq, C50),
149.94 (Cq, C30), 140.05 (Cq, C3), 138.86 and 134.45 (Cq
each, i-C of 2 · Ph), 130.06, 19.71, 18.49, 128.13, 128.00,
and 126.08 (CH of 2 · Ph), 118.87 (Cq, C40), 112.61 (C2),
60.14 (OCH2), 29.29 (CH2Ph), 14.08 (OCH2CH3), 12.31
and 11.52 (50- and 30-CH3). IR (KBr) cmꢀ1: 1714.6 (65) [m
(C@O)], 1626.0 (60), 1585.4 (40), 1494.7 (30), 1444.6 (30)
[m (C@C, C@N)]. Anal. Calc. for: C23H24N2O2: C, 76.64;
H, 6.71; N, 7.77. Found: C, 76.90; H, 6.87; N, 7.64%.
4.5. 3-(30,40,50-Trimethylpyrazol-10-yl)- 3-phenyl-acrylic
acid ethyl ester (11)
OEt
O
1
Ph
3
Me
5'
2
4.7. 3-(30,50-Dimethylpyrazol-10-yl)-3-phenyl-acrylic acid
ethyl ester (13)
1'
2'
N
Me
4'
N
3'
Me
OEt
1
(a) 2-Ethoxy-4-phenyl-4-(30,40,50-trimethylpyrazol-10-yl)-
1,1,1,1,1-pentacarbonyl-1-chroma-1,3-butadiene 4a (460 mg,
1.0 mmol) was reacted with PNO (95 mg, 1.0 mmol) to
afford 11 as white solid (264 mg, 93%). (b) 2-Ethoxy-4-phe-
nyl-4-(30,40,50-trimethylpyrazol-10-yl)-1,1,1,1,1-pentacar-
bonyl-1-tungsta-1,3-butadiene 4b (592 mg, 1.0 mmol) was
reacted with PNO (95 mg, 1.0 mmol) to afford 11 as white
solid (273 mg, 96%). M.p.: 54 ꢁC. 1H NMR (CDCl3,
23 ꢁC, 400 MHz): d 7.42–7.33 (m, 5H, 3-Ph), 6.27 (s, 1H,
2-H), 4.07 (q, 2H, OCH2), 2.22 (s, 3H, 50-CH3), 1.88 (s,
3H, 30-CH3), 1.64 (s, 3H, 40-CH3), 1.13 (t, 3H, OCH2CH3).
13C{1H} NMR (CDCl3, 23 ꢁC): d 165.63 (Cq, C1), 151.14
(Cq, C50), 149.58 (Cq, C30), 137.79 (Cq, C3), 134.4 (Cq,
i-C of 3-Ph), 129.80, 129.58 and 127.88 (1:2:2 CH, 3-Ph),
115.58 (Cq, C40), 111.66 (CH, C2), 59.85 (OCH2), 13.89
(OCH2CH3), 11.92 (30-CH3), 11.21 (50-CH3), 7.96 (40-
CH3). IR (KBr) cmꢀ1: 1712.7 (60) [m (C@O)], 1624.0 (60),
O
Ph
3
Me
5'
2
1'
2'
N
4'
N
3'
Me
2-Ethoxy-4-phenyl-4-(30,50-dimethylpyrazol-10-yl)-1,1,1,
1,1-pentacarbonyl-1-tungsta-1,3-butadiene 4e (578 mg,
1.0 mmol) was reacted with PNO (95 mg, 1.0 mmol) to
afford 13 as pale yellow solid (190 mg, 70%). M.p.: 67 ꢁC.
1H NMR (CDCl3, 23 ꢁC, 400 MHz): d 7.44–7.33 (m, 5H,
Ph), 6.32 (s, 1H, 2-H), 5.92 (s, 1H, 40-H), 4.07 (q, 2 H,
OCH2), 2.26 and 1.71 (s each, 3:3H, 50- and 30-CH3),
1.14 (t, 3H, OCH2CH3). 13C{1H} NMR (CDCl3, 23 ꢁC):
d 165.78 (Cq, C1), 151.03 (Cq, C50), 150.32 (Cq, C30),
141.91 (Cq, C3), 134.3 (Cq, i-C of Ph), 130.15, 129.76
and 128.19 (1:2:2 CH, Ph), 112.90 (C40), 109.57 (C2),
60.25 (OCH2), 14.12 (OCH2CH3), 13.69 and 12.99

3688
Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
(30- and 50-CH3). IR (KBr) cmꢀ1: 1728.1 (80) [m (C@O)],
1633.6 (85), 1562.3 (80), 1496.7 (55), 1448.5 (50) [m (C@C,
C@N)]. Anal. Calc. for: C16H18N2O2: C, 71.09; H, 6.71;
N, 10.36. Found: C, 71.05; H, 6.81; N, 10.30%.
2048.3 (15), 1913.3 (50) [m (C„O)], 1689.5 (10) [m(C@O)],
1489.0 (20) [m (C@C)]. Anal. Calc. for C32H29CrNO9: C,
61.64; H, 4.69; N, 2.25. Found: C, 61.39; H, 4.74; N, 2.06%.
4.10. 2-(1,1,1,1,1-Pentacarbonyl-2-ethoxy-4-phenyl-1-
tungsta-4-buta-1,3-dienyl)-1-methoxy-6-phenyl-2-
azabicyclo-[3.2.0]hept-6-ene-7-carboxylic acid ethyl ester
(20b)
4.8. 2-Methoxy-4-(30-phenyl acrylic acid methyl ester)-
1,1,1,1,1-pentacarbonyl-1- chroma-1,3-butadiene (17)
O
2
OEt
1'
(OC)5W
4'
3'
1
MeO
OMe
2'
2'
Ph
4'
N
3
O
OMe
1
3'
2''
OEt
(OC)5Cr
1'
2
7
3
5
Ph
6
4
Red crystals. M.p.: 74–75 ꢁC. 1H (CDCl3, 23 ꢁC,
400 MHz): d 7.58 (m, 4H, aromatic CH), 7.98 and 6.91
(AB, 2H, J = 11.3 Hz), 7.69 and 6.50 (AB, 2H, J =
11.9 Hz), 4.84 (s, 3H, 20-OCH3), 3.83 (s, 3H, 1-OCH3).
13C{1H} NMR (CDCl3, 23 ꢁC): d 333.66 (Cq, Cr@C,
C20), 224.42 and 216.70 (Cq, 1:4, trans- and cis-CO,
Cr(CO)5), 167.28 (Cq, C1), 143.73 (CH, C3), 140.06 (CH,
C40), 136.65 and 136.51 (Cq, i-C of C6H4), 129.94 and
128.81 (CH of C6H4), 127.82 (CH, C30), 119.28 (CH,
1
Orange crystals (161 mg, 85%), M.p. >123 ꢁC, dec. H
NMR (CDCl3, 23 ꢁC, 400 MHz): d 8.02 (s, 1H, 30-H),
7.94 and 7.35 (m each, 2:3H, 6-Ph), 7.44 and 7.11 (m each,
3:2H, 40-Ph), 4.43 and 4.32 (q each, 1:1 H, 200-OCH2), 4.13
(m, 2H, 20-OCH2), 3.78 (d, 1H, J = 5.7 Hz, 5-H), 3.62 (s,
3H, 1-OCH3), 3.20 and 3.07 (m each, 1:1H, 3-H2), 1.86
and 1.79 (m each, 1:1H, 4-H2), 1.35 (t, 3H, 200-OCH2CH3),
0.61 (t, 3H, 20-OCH2CH3). 13C{1H} NMR (CDCl3, 23 ꢁC):
d 281.68 (Cq, W@C, C20), 204.63 and 199.48 (Cq, 1:4,
trans- and cis-CO, W(CO)5), 161.91 (Cq, C20 0), 154.31
(Cq, C6), 152.87 (Cq, C40), 139.65 (Cq, i-C of 40-Ph),
130.50 (Cq, i-C of 6-Ph), 131.49, 129.62, 128.79, 128.44,
128.08, and 127.11 (CH of 2 · Ph), 127.41 (Cq, C7),
125.46 (CH, C30), 96.87 (Cq, C1), 76.40 (20-OCH2), 61.15
(200-OCH2), 53.01 (1-OCH3), 49.88 (CH, C5), 49.58 (CH2,
C3), 23.11 (CH2, C4), 14.42 (200-OCH2CH3), 13.99 (20-
OCH2CH3). IR (KBr) cmꢀ1: 2057.9 (90), 1905.6 (100) [m
(C„O)], 1691.5 (70) [m (C@O)], 1485.1 (90) [m (C@C)].
Anal. Calc. for: C32H29NO9W: C, 50.88; H, 3.87; N,
1.85. Found: C, 50.76; H, 3.79; N, 1.80%.
C2), 66.67 (1-OCH3), 51.99 (20-OCH3). IR (KBr) cmꢀ1
:
2056.0 (100) and 1915.2 (100) [m (C„O)], 1712.7 (95)
[m(C@O)]. Anal. Calc. for C19H14CrO8: C, 54.04; H, 3.34.
Found: C, 53.38; H, 3.59%.
4.9. 2-(1,1,1,1,1-Pentacarbonyl-2-ethoxy-4-phenyl-1-
chroma-4-buta-1,3-dienyl)-1-methoxy-6-phenyl-2-
azabicyclo-[3.2.0]hept-6-ene-7-carboxylic acid ethyl ester
(20a)
OEt
2'
1'
(OC)5Cr
Ph
4'
N
O
OMe
1
3'
2''
OEt
4.11. 1-Methoxy-6-phenyl-2-azabicyclo-[3.2.0]hept-6-ene-
2,7-dicarboxylic acid ethyl ester (21)
2
7
3
5
Ph
6
4
Red crystal (106 mg , 68%), M.p. >118 ꢁC, dec. 1H
NMR (CDCl3, 23 ꢁC, 400 MHz): d 7.95 (s, 1H, 30-H),
7.97–7.93 and 7.34 (m each, 2:3H, 6-Ph), 7.44 and 7.09
(m each, 3:2H, 40-Ph), 4.41 and 4.21 (q each, 1:1 H, 20-
OCH2), 4.31 (m, 2H, 200-OCH2), 3.77 (d, 1H, J = 5.7 Hz,
5-H), 3.62 (s, 3H, 1-OCH3), 3.17 and 3.08 (m each, 1:1H,
3-H2), 1.85 and 1.76 (m each, 1:1 H, 4-H2), 1.34 (t, 3H,
200-OCH2CH3), 0.62 (t, 3H, 20-OCH2CH3). 13C{1H}
NMR (CDCl3, 23 ꢁC): d 306.26 (Cq, Cr@C, C20), 224.76
and 218.71 (Cq each, 1:4, trans- and cis-CO, Cr(CO)5),
162.11 (Cq, C20 0), 154.20 (Cq, C6), 149.20 (Cq, C40),
139.61 (Cq, i-C of 40-Ph), 130.66 (Cq, i-C of 6-Ph),
131.46, 129.66, 128.83, 128.54, 128.04, 127.76 (CH of
2 · Ph), 127.20 (Cq, C7), 123.27 (CH, C30), 96.9 (Cq,
C1), 73.88 (20-OCH2), 61.20 (200-OCH2), 53.00 (1-OCH3),
49.88 (CH, C5), 49.66 (CH2, C3), 23.25 (CH2, C4), 14.40
OEt
2'
O
Ph
4'
N
O
OMe
1
3'
2''
OEt
2
7
3
5
Ph
6
4
Colorless crystals. M.p.: 123 ꢁC. 1H (CDCl3, 23 ꢁC,
400 MHz): 7.96 and 7.38 (m each, 2:3H, 6-Ph), 7.43 and
7.21 (m each, 3:2H, 40-Ph), 6.22 (s, 1H, 30-H), 4.36 (q,
2H, 200-OCH2), 3.93 (m, 2H, 20-OCH2), 3.71 (d, 1H,
J = 5.7 Hz, 5-H), 3.55 (s, 3H, 1-OCH3), 3.17 and 2.94 (m
each, 1:1H, 3-H2), 1.78 and 1.71 (m each, 1:1H, 4-H2),
1.44 (t, 3H, 200-OCH2CH3), 1.10 (t, 3H, 20-OCH2CH3).
13C{1H} NMR (CDCl3, 23 ꢁC): d 168.04 (Cq, C20),
163.20 (Cq, C20 0), 158.19 (Cq, C40), 154.58 (Cq, C6),
138.25 (Cq, i-C of 40-Ph), 130.99 (Cq, i-C of 6-Ph),
131.13, 129.58, 128.76, 128.32, 128.08, and 127.58 (CH of
2 · Ph), 127.89 (Cq, C7), 95.62 (Cq, C1), 94.01 (CH,
(200-OCH2CH3), 14.17 (20-OCH2CH3). IR (KBr), cmꢀ1
:

Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
3689
C30), 61.31 (200-OCH2), 58.63 (20-OCH2), 52.45 (1-OCH3),
50.20 (CH, C5), 49.40 (CH2, C3), 23.12 (CH2, C4), 14.45
139.43 (C5), 138.41, 134.15 and 132.08 (Cq each, i-C of
3 · Ph), 130.46, 130.29, 129.96, 129.62, 129.41, 129.24,
128.63, 128.54 and 128.16 (2:1:1:1:2:2:2:2:2 CH, 3 · Ph);
IR (KBr) cmꢀ1: 2054 (70), 1917 (85), 1878 (85) [m
(C„O)], 1543 (60) [m (C@N)], 1473 (50) [m (C@C)]. Anal.
Calc. for C27H16N2O5W: C, 51.29; H, 2.55; N, 4.43.
Found: C, 51.18; H, 2.71; N, 4.20%.
(200-OCH2CH3), 14.14 (20-OCH2CH3). IR (KBr) cmꢀ1
:
1693.4 (30), 1581.5 (35) [m(C@O)], 1492.8 (10) [m (C@C)].
Anal. Calc. for C27H29NO5: C, 72.46; H, 6.53; N, 3.13.
Found: C, 72.42;H, 6.51; N, 3.03%.
4.12. Synthesis of 4-(1,1,1,1,1-pentacarbonyl-1-chroma)-
1,2,6-triphenyl-1,4-dihy dropyrimidine (25a)
4.14. Synthesis of 4-(1,1,1,1,1-pentacarbonyl-1-chroma)-
1,2,6-triphenyl-1,2,3,4-tetrahydropyrimidine (26a)
Ph
N
Ph
(OC)5Cr
N
Ph
HN
(OC) Cr
N
Ph
5
Ph
Ph
1-Alkynyl carbene complex 1a (0.5 mmol) was reacted
with N-phenyl-benzamidine 24 (0.5 mmol) in 3 mL of dry
dichloromethane in a 5-mL screwtop vessel with stirring
at ambient temperature and the reaction was monitored
by TLC on silica gel. After 1a was completely consumed,
all the volatiles were removed under reduced pressure.
The resultant residue was purified by flash silica gel chro-
matography (v/v, hexanes/CH2Cl2 = 1:1) afforded 25a as
red crystals (191 mg, 76.3%). Single crystals were obtained
by recrystallization from CH2Cl2/pentane at ꢀ20 ꢁC. M.p.:
160 ꢁC (dec.); 1H NMR (CDCl3, 23 ꢁC, 400 MHz) d 8.36 (s,
1H, 5-H), 7.41, 7.32, 7.29–7.16, 7.10 and 6.93 (m each,
2:2:7:2:2H, 3 · Ph); 13C{1H} NMR (CDCl3, 23 ꢁC) d
281.05 (s, Cq, Cr@C), 227.09 and 219.57 (Cq each, 1:4,
trans- and cis-CO, Cr(CO)5), 144.05 and 138.87 (Cq each,
C2 and C6), 138.23, 134.18 and 132.04 (Cq each, i-C of
3 · Ph), 137.39 (C5), 130.58, 130.25, 129.92, 129.50,
129.39, 128.69, 128.61, and 128.13 (CH of 3 · Ph); IR
(KBr) cmꢀ1: 2046 (35), 1921 (55), 1889 (50) [m (C„O)],
1543 (25) [m (C@N)], 1585 (20), 1443 (20) [m (C@C)]. Anal.
Calc. for C27H16CrN2O5: C, 64.80; H, 3.22; N, 5.60.
Found: C, 64.63; H, 3.33; N, 5.37%.
Complex 25a (250 mg, 0.5 mmol) and sodium borohy-
dride (19 mg, 0.5 mmol) were added to a solution of THF
(10 mL), and the mixture was vigorously stirred at ambient
temperature under nitrogen atmosphere. The reaction was
monitored by TLC on silica gel. After 25a was completely
consumed over a period of 5 h, all the volatiles were
removed under reduced pressure. The resultant residue
was purified by flash silica gel column chromatography
(v/v, hexanes/CH2Cl2 = 1:1) afforded 26a as orange crystals
(178 mg, 70.7%). Single crystals were obtained by recrystal-
lization from CH2Cl2/pentane at ꢀ20 ꢁC. M.p.: 144–
145 ꢁC; 1H NMR (CDCl3, 23 ꢁC, 400 MHz) d 8.30 (br,
1H, 5-H), 7.69, 7.59, 7.53–7.40, 7.37–7.26, 7.16, and 7.06
(m each, 2:2:3:5:1:2H, 3 · Ph), 7.01 and 6.24 (s each,
1:1H, NH and 2-H); 13C{1H} NMR (CDCl3, 23 ꢁC) d
241.42 (Cq, Cr@C), 223.48 and 218.71 (Cq each, 1:4, trans-
and cis-CO, Cr(CO)5), 144.28 (Cq, C6), 137.30, 137.02 and
134.23 (Cq each, i-C of 3 · Ph), 130.60 (C5), 129.65, 129.28,
128.92, 126.22, 126.05, 124.88 and 124.27 (4:1:4:1:2:2:1 CH,
3 · Ph), 73.85 (Cq, C2); IR (KBr) cmꢀ1: 3377(30) [m (N–H)],
2048 (40), 1911 (70) [m (C„O)], 1526 (30), 1492 (30) [m
(C@C)]. Anal. Calc. for C27H18CrN2O5: C, 64.54; H, 3.61;
N, 5.58. Found: C, 64.52; H, 3.77; N, 5.44%.
4.13. Synthesis of 4-(1,1,1,1,1-pentacarbonyl-1-tungsta)-
1,2,6-triphenyl-1,4-dihydropyrimidine (25b)
4.15. Synthesis of 4-(1,1,1,1,1-pentacarbonyl-1-tungsta)-
1,2,6-triphenyl-1,2,3,4-tetrahydropyrimidine (26b)
Ph
N
Ph
(OC) W
N
Ph
5
HN
(OC) W
N
Ph
Ph
5
Ph
In a fashion similar to synthesis of 25a, the reaction of
1b (0.5 mmol) with 24 (0.5 mmol) gave 25b as red crystals
(210 mg, 66.4 %). Single crystals suitable for X-ray crystal-
lographic study were obtained by recrystallization from
In a fashion similar to synthesis of 26a, 0.5 mmol of 25b
reacted with NaBH4 (0.5 mmol) in THF afforded 26b as
orange crystals (191 mg, 60.3%). Single crystals were
obtained by recrystallization from dichloromethane/pen-
1
CH2Cl2/pentane at ꢀ20 ꢁC. M.p.: 166–168 ꢁC; H NMR
1
(CDCl3, 23 ꢁC, 400 MHz) d 8.32 (s, 1H, 5-H), 7.40, 7.35,
7.29–7.23, 7.18, 7.11 and 6.94 (m each, 2:2:5:2:2:2H,
3 · Ph); 13C{1H} NMR (CDCl3, 23 ꢁC) d 256.03 (Cq,
W@C), 207.36 and 200.73 (Cq each, 1:4, trans- and cis-
CO, W(CO)5), 147.66 and 142.20 (Cq each, C2 and C6),
tane at ꢀ20 ꢁC. M.p.: 154 ꢁC; H NMR (CDCl3, 23 ꢁC,
400 MHz) d 8.14 (s, 1H, 5-H), 7.70, 7.59, 7.55–7.42, 7.39–
7.28, 7.19 and 7.09 (m each, 2:2:3:5:1:3H, NH and
3 · Ph), 6.25 (s, 1H, 2-H); 13C{1H} NMR (CDCl3, 23 ꢁC)
d 219.97 (s, Cq, W@C), 203.68 and 199.36 (Cq each, 1:4,

3690
Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
trans- and cis-CO, W(CO)5), 144.29 (Cq, C6), 139.95,
137.14 and 134.03 (Cq each, i-C of 3 · Ph), 130.71 (C5),
129.69, 129.54, 129.34, 128.94, 126.53, 126.26, 126.12,
124.87 (2:2:1:4:1:1:2:2 CH, 3 · Ph), 74.26 (Cq, C2); IR
(KBr) cmꢀ1: 3373 (45) [m (N–H)], 2056 (65), 1907 (95) [m
(C„O)], 1527 (55), 1491 (55), 1446 (45) [m (C@C)]. Anal.
Calc. for C27H18N2O5W: C, 51.13; H, 2.86; N, 4.42.
Found: C, 51.26; H, 3.02; N, 4.26%.
3 · Ph); 13C{1H} NMR (CDCl3, 23 ꢁC) d 203.44 and
198.58 (Cq each, 1:4, trans- and cis-CO, W(CO)5), 194.95
(Cq, S@C), 157.47 and 148.40 (Cq each, C2 and C6),
137.92, 133.00 and 131.76 (Cq each, i-C of 3 · Ph),
130.65, 130.27, 129.66, 129.47, 128.96, 128.80, 128.74,
128.23 (CH of 3 · Ph), 124.05 (C5); IR (KBr) cmꢀ1: 2060
(70), 1929 (95), 1876 (95) [m (C„O)], 1587 (80) [m
(C@N)], 1570 (65), 1481 (60) [m (C@C)], 1333 (60) [m
(S@C)]. Anal. Calc. for C27H16N2O5SW: C, 48.81; H,
2.43; N, 4.22. Found: C, 48.88; H, 2.55; N, 4.03%.
4.16. Synthesis of Pentacarbonyl(1,2,6-triphenyl-1H-
pyrimidine-4-thione)chromium (27a)
4.18. Synthesis of Pentacarbonyl(1,2,6-triphenyl-1H-
pyrimidine-4-selone)chromium (28a) and 1,2,6-triphenyl-
1H-pyrimidine-4-selone (29)
Ph
N
(OC)5CrS
N
Ph
Ph
Ph
N
Powdered sulfur (32 mg, 1.0 mmol) and sodium borohy-
dride (38 mg, 1.0 mmol) were added to a solution of ethanol
(10 mL), and the mixture was vigorously stirred at ambient
temperature for 1 h under nitrogen atmosphere. Complex
25a (250 mg, 0.5 mmol) was then added in one portion under
a nitrogen atmosphere, and the reaction was monitored by
TLC on silica gel. After 25a was completely consumed over
a period of 1 h, all the volatiles were removed under reduced
pressure. The resultant residue was purified by flash silica gel
column chromatography (v/v, hexanes/CH2Cl2 = 1:1)
afforded 27a as dark red crystals (180 mg, 67.7%). Single
crystals were obtained by recrystallization from CH2Cl2/
(OC)5CrSe
N
Ph
Ph
A mixture of elemental selenium (79 mg, 1.0 mmol) and
sodium borohydride (38 mg, 1.0 mmol) in ethanol (10 mL)
was vigorously stirred at ambient temperature for 1 h
under nitrogen atmosphere. Complex 25a (250 mg,
0.5 mmol) was then added in one portion and the reaction
was monitored by TLC on silica gel. After 25a was com-
pletely consumed over a period of 1 h, all the volatiles were
removed under reduced pressure. The resultant residue was
purified by flash silica gel column chromatography (v/v,
hexanes/CH2Cl2 = 1:1) afforded 28a as dark brown crystals
(71 mg, 24.6%) and 29 (v/v, dichloromethane/diethyl
ether = 1:1) as red crystals (136 mg, 70.4%), respectively.
28a: Single crystals were obtained from recrystallization
in dichloromethane and pentane at ꢀ20 ꢁC. M.p. 134–
1
pentane at ꢀ20 ꢁC. M.p.: 148 ꢁC (dec.); H NMR (CDCl3,
23 ꢁC, 400 MHz) d 7.52 (s, 1H, 5-H), 7.41, 7.35, 7.28, 7.20,
7.09, and 6.91 (m each, 2:2:5:2:2:2H, 3 · Ph); 13C{1H}
NMR (CDCl3, 23 ꢁC) d 224.81 and 217.05 (Cq each, 1:4,
trans- and cis-CO, Cr(CO)5), 196.69 (Cq, S@C), 156.96
and 146.94 (Cq each, C2 and C6), 138.05, 133.17 and
131.92 (Cq each, i-C of 3 · Ph), 130.60, 130.14, 129.69,
129.56, 129.42, 129.00, 128.89, 128.69 and 128.20
1
136 ꢁC (dec.); H NMR (CDCl3, 23 ꢁC, 400 MHz) d 7.86
(s, 1H, 5-H), 7.42–7.10 and 6.92 (m each, 13:2 H, 3 · Ph);
13C{1H} NMR (CDCl3, 23 ꢁC) d 225.75 and 217.98 (s
and Cq each, 1:4, trans- and cis-CO, Cr(CO)5), 197.69 (s,
Cq, Se@C), 155.88 and 146.25 (s and Cq each, C2 and
C6), 138.04, 132.93 and 131.74 (s and Cq each, i-C of
3 · Ph), 130.70, 130.26, 129.71, 129.48, 128.74, 128.63,
128.37 and 128.23 (s each, 1:1:3:2:2:2:2:2 CH of 3 · Ph);
IR (KBr) cmꢀ1: 2048 (65), 1934 (90), 1887 (85) [m
(C„O)], 1585 (65) [m (C@N)], 1477 (50) [m (C@C)], 1327
(50) [m (Se@C)]. Anal. Calc. for C27H16CrN2O5Se: C,
55.97; H, 2.78; N, 4.84. Found: C, 56.10; H, 2.70; N, 4.62%.
(1:1:2:1:2:2:2:2:2 CH, 3 · Ph), 124.66 (C5); IR (KBr) cmꢀ1
:
2054 (45), 1936 (80), 1889 (75) [m (C„O)], 1587 (90) [m
(C@N)], 1585 (60), 1511 (35), 1481 (35) [m (C@C)], 1334
(35) [m (S@C)]. Anal. Calc. for C27H16CrN2O5S: C, 60.90;
H, 3.03; N, 5.26. Found: C, 60.94; H, 2.96; N, 5.00%.
4.17. Synthesis of Pentacarbonyl(1,2,6-triphenyl-1H-
pyrimidine-4-thione)tungsten (27b)
Ph
N
4.19. 1,2,6-Triphenyl-1H-pyrimidine-4-selone (29)
(OC)5WS
N
Ph
Ph
Ph
N
In a fashion similar to synthesis of 27a, 0.5 mmol of 25b
reacted with NaBH4 and S8 (1.0 mmol each) in ethanol
afforded 27b as dark red crystals (295 mg, 88.7%). Single
crystals were obtained by recrystallization from CH2Cl2/
pentane at ꢀ20 ꢁC. M.p.: 163–164 ꢁC (dec.); 1H NMR
(CDCl3, 23 ꢁC, 400 MHz) d 7.56 (s, 1H, 5-H), 7.38–7.33,
7.29–7.24, 7.23–7.15, 7.09 and 6.91 (m each, 4:4:3:2:2H,
Se
N
Ph
Ph
Red crystals (136 mg, 70.4% from 25a; 90 mg, 46.6%
from 25b). Single crystals suitable for X-ray crystallo-
graphic study were obtained by recrystallization from

Z. Zheng et al. / Journal of Organometallic Chemistry 691 (2006) 3679–3692
3691
1
CH2Cl2/pentane at ꢀ20 ꢁC. M.p.: 252–254 ꢁC; H NMR
Acknowledgement
(CDCl3, 23 ꢁC, 400 MHz) d 7.79 (s, 1H, 5-H), 7.37, 7.34–
7.06, and 6.91 (m each, 2:11:2H, 3 · Ph); 13C{1H} NMR
(CDCl3, 23 ꢁC) d 201.13 (Cq, Se@C), 154.50 and 146.17
(Cq each, C2 and C6), 138.48, 133.83 and 129.35 (Cq each,
i-C of 3 · Ph), 132.26 (C5), 130.08, 129.76, 129.70, 129.26,
129.19, 128.61, 128.53, 128.45 and 127.96 (1:1:2:1:2:2:2:2:2
CH, 3 · Ph); IR (KBr) cmꢀ1: 1570 (60) [m (C@N)], 1479
(50) [m (C@C)], 1093 (50), [m (Se@C)]. Anal. Calc. for
C22H16N2Se: C, 68.22; H, 4.16; N, 7.23. Found: C, 67.75;
H, 4.36; N, 7.04%.
We are grateful to the ‘‘Hundred Talented Program’’
Funding of Chinese Academy of Sciences for financial sup-
port of this research.
Appendix A. Supporting data
The X-ray crystallographic files, in CIF format, are
available from the Cambridge Crystallographic Data Cen-
tre on quoting the deposition numbers: CCDC 602802 for
25b, CCDC 602804 for 28b, and CCDC 602803 for 29.
Copies of this information may be obtained free of charge
from The Director, CCDC, 12 Union Road, Cambridge
CB2 IEZ, UK, fax: +44 1223 336 033; e-mail: depos-
it@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.05.021.
4.20. Synthesis of pentacarbonyl(1,2,6-triphenyl-1H-
pyrimidine-4-selone)tungsten (28b) and (29)
Ph
N
(OC)5WSe
N
Ph
Ph
References
In a fashion similar to synthesis of 28a and 29, 0.5 mmol
of 25b reacted with NaBH4 and Se (1.0 mmol each) in eth-
anol afforded 28b as dark brown crystals (186 mg, 52.3%).
Single crystals were obtained by recrystallization from
CH2Cl2/pentane at ꢀ20 ꢁC. M.p.: 164 ꢁC (dec.); 1H
NMR (CDCl3, 23 ꢁC, 400 MHz) d 7.91 (s, 1H, 5-H),
7.38–7.35, 7.29–7.15, 7.09, and 6.92 (m each, 4:7:2:2H,
3 · Ph); 13C{1H} NMR (CDCl3, 23 ꢁC) d 203.57 and
198.98 (Cq each, 1:4, trans- and cis-CO, W(CO)5), 196.54
(Cq, Se@C), 156.32 and 147.45 (Cq each, C2 and C6),
137.99, 132.82 and 131.66 (Cq each, i-C of 3 · Ph),
130.77, 130.38, 129.81, 129.72, 129.53, 128.80, 128.66,
128.39, and 128.28 (1:1:1:2:2:2:2:2:3 CH, 3 · Ph); IR
(KBr) cmꢀ1: 2058 (25), 1930 (45), 1879 (40) [m (C„O)],
1585 (30) [m (C@N)], 1479 (25) [m (C@C)], 1327 (20) [m
(Se@C)]. Anal. Calc. for C27H16N2O5SeW: C, 45.60; H,
2.27; N, 3.94. Found: C, 45.84; H, 2.38; N, 3.80%. From
the same reaction, 29 (90 mg, 46.6%) was isolated.
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