Reaction of Mo(CO)4(NCCH3)2 and 7-aza-2-Tosylnorbornadiene

Article abstract of DOI:10.1016/j.ica.2004.12.058

Reaction of Mo(CO)₄(NCCH₃)₂ and 7-aza-2-tosylnorbornadiene (7-azaNBD) yielded five air-stable Mo complexes. One is Mo(CO)₄(η⁴-7-azaNBD), in which the molybdenum atom is chelated by the two π-bonds of 7-azaNBD. The other four are isomers of Mo(CO)₂(η²-7-azaNBD)₂, in which the molybdenum atoms are chelated by the nitrogen atom and one of the two double bonds of 7-azaNBD. In one pair of the isomers, the metal binds to C(2)C(3) of both 7-azaNBD ligands; whereas in the other pair of isomers the metal binds to C(2)C(3) of one 7-azaNBD ligand and C(5)C(6) of another ligand. All structures were fully characterized by NMR spectra. A single crystal of compound 4 was analyzed by X-ray diffraction analysis, which was found to be monoclinic with a = 8.4199, b = 23.984, c = 16.395 A?, and β = 99.99°.

Full text of DOI:10.1016/j.ica.2004.12.058

Inorganica Chimica Acta 358 (2005) 2427–2431
www.elsevier.com/locate/ica
Note
Reaction of Mo(CO)4(NCCH3)2 and 7-aza-2-Tosylnorbornadiene
a
a,
b
Mei-Fang Ding , Shaw-Tao Lin *, Tashin J. Chow
a
Department of Applied Chemistry, Providence University, Sha-Lu, Taichung Hsien, Taiwan, 433
b
Institute of Chemistry, Academic Sinica, Nankang, Taipei, Taiwan, 115
Received 23 April 2004; accepted 10 December 2004
Abstract
Reaction of Mo(CO)4(NCCH3)2 and 7-aza-2-tosylnorbornadiene (7-azaNBD) yielded five air-stable Mo complexes. One is
Mo(CO)4(g4-7-azaNBD), in which the molybdenum atom is chelated by the two p-bonds of 7-azaNBD. The other four are isomers
of Mo(CO)2(g2-7-azaNBD)2, in which the molybdenum atoms are chelated by the nitrogen atom and one of the two double bonds
of 7-azaNBD. In one pair of the isomers, the metal binds to C(2)@C(3) of both 7-azaNBD ligands; whereas in the other pair of
isomers the metal binds to C(2)@C(3) of one 7-azaNBD ligand and C(5)@C(6) of another ligand. All structures were fully charac-
terized by NMR spectra. A single crystal of compound 4 was analyzed by X-ray diffraction analysis, which was found to be mono-
˚
clinic with a = 8.4199, b = 23.984, c = 16.395 A, and b = 99.99ꢀ.
ꢁ 2005 Elsevier B.V. All rights reserved.
1. Introduction
these structures, the iron metal was coordinated to the
p-bond on the exo side [2]. However, the oxygen atom
with lone pairs in these complexes does not show strong
bonding toward the metal, even though they were located
in close proximity. Heating these complexes until frag-
mentation did not yield any intermolecular [2p +2p] cyclic
adduct. The analogous complexes of nitrogen derivatives,
i.e., 7-azanorbornadiene derivatives, showed different
characteristics such as the appearance of strong bonding
nature between the nitrogen atom and the metal [3].
Those 7-azanorbornadiene complexes underwent nitrene
extrusion reaction upon heating to give (g4-cyclohexadi-
ene)iron carbonyl complexes [3a,3c,3e,3f]. To the best of
our knowledge, the reaction of molybdenum metal with
7-azaNBD has not yet been reported, so it would be of
general interests to describe the reaction of 2-tosyl-7-aza-
norbornadiene and Mo(CO)4(NCMe)2.
Norbornadiene (NBD) has been widely applied as a li-
gand for the preparation of organo-metal complexes.
Number of studies revealed that the molybdenum may
form stable complexes with either one NBD unit (i.e.,
Mo(CO)4(NBD)) or with two NBD units (i.e., Mo
(CO)2(NBD)2) [1]. The coordination of NBD to the Mo
in Mo(CO)4(NBD) is comparably labile, therefore it
can be replaced for synthetic purpose by a wide range
of other ligands, such as phosphines, amines, arsines, iso-
nitriles, 1,5-COD, etc. [1h,1l]. This methodology has been
utilized successfully for the preparation of various orga-
nometallic compounds and catalysts. The derivatives of
NBD containing a heteroatom (O, N) at 7-position have
also been studied on similar purpose. Irradiation of either
7-oxabenzonorbornadiene (7-oxaNBD), 5,6-dimethyl-
ene-7-oxanorborene, or 2,3-dicarbomethoxy-7-oxa- nor-
bornadiene under UV light in the presence of Fe(CO)5 or
Fe2(CO)9 yielded the stable iron carbonyl complexes. In
2. Results and discussion
*
Mo(CO)4(NCMe)2 was prepared from the reaction of
Mo(CO)6 and Me3NO in CH3CN solution and the
Corresponding author. Fax: +1 886 4 2632 7554.
E-mail address: sdlin@pu.edu.tw (S.-T. Lin).
0020-1693/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.12.058

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M.-F. Ding et al. / Inorganica Chimica Acta 358 (2005) 2427–2431
CO2CH3
reaction is depicted as Scheme 1. The purified sample
was then heated with an equal molar amount of 7-meth-
oxycarbonyl-2-p-toluenesulfonyl-7-azanorbornadiene
(7-azaNBD) in CH2Cl2 for 40 h. The products were
purified by column chromatography and five air-stable
molybdenum complexes were isolated. The structures
N
CH2Cl2
r.t 40hr
Mo(CO)4(NCMe)2
+
Ts
1
1
of 3–6 were determined by two-dimensional H COSY
CO2CH3
and 1H–13C COSY spectra, along with X-ray diffraction
analysis on a single crystal of 4. The isotopic distribu-
tion pattern of Mo on mass spectrum is consistent with
the natural abundance of Mo. Their physical data
Ts
N
N
N
CO2CH3
CO2CH3
Ts
OC
+
N
H3CO2C
Mo
H3CO2C
Ts
Mo
CO
CO
+
OC
N
OC
Mo
CO
1
including H and 13C NMR chemical shift values are
Ts
OC CO
Ts
listed in Tables 1–3. Selected parameters of X-ray anal-
ysis of 4 are listed in Tables 4 and 5. The chemical shift
values of 7-azaNBD are included for comparison
purpose.
The mco of 2 spread into three regions, i.e., 2071(m),
2008(vs); 1994(s, sh), 1944(s); and 1716(s) cmꢀ1. The
patterns of relative intensities corresponded to a cis-
ML2(CO)4 structure [4]. The first two sets are attributed
by four COs and the last one is attributed by carbonyl of
ester. The stretch of CO above 2000 cmꢀ1 is absent from
the spectra of 3–6. In correction of the structures be-
tween 2 and 3–6, we can conclude that the signals of
2071 and 2008 cmꢀ1 of 2 are due to the stretch of CO
3
4
2
Ts
CO
N
N
N
Ts
Mo
H3CO2C
CO
H3CO2C
+
Mo
Ts
CO
CO
N
H3CO2C
H3CO2C
Ts
6
5
Scheme 1.
Table 1
The physical properties and spectral data of compounmds 1–6a
Compounds
Mp ꢀC (color)
Yield %
FABMS [M + 1]+
IR cmꢀ1
1727b
1
2
3
4
5
6
a
91.5–92.3 (white)
128–129.5 (yellow)
137 (yellow)
61.0
12.6
10.2
40.0
23.7
4.3
305
516
765
765
765
765
2071(m)c, 2008(vs)c, 1994(s,sh)d, 1944(s)d, 1716(s)b
1984(s)d, 1910(s)d, 1756(s)b
118–119.5 (yellow)
126–127.5 (yellow)
134–136 (yellow)
1968(s)d, 1890(s)d, 1755(s)b
1968(s)d, 1891(s)d, 1755(s)b
1996(s)d, 1919(s)d, 1755(s)b
The errors for elemental analyses of C, H, N are within 0.2%.
CO of ester.
CO trans each other.
b
c
d
CO trans to double bond.
Table 2
1H NMR spectral data of compounds 1–6
Compounds H1
H3
H4
H5
H6
OCH3 CH3
Ar
1
2
3
5.44(s)
7.62(m) 5.22(s)
6.92(m)
6.96(m)
4.86(m)
3.5(bs) 2.45(s) 7.33 (d, J = 8.0 Hz), 7.75 (d, J = 8.0 Hz)
3.31(s) 2.41(s) 7.30 (d, J = 8.0 Hz), 7.74 (d, J = 8.0 Hz)
3.84(s) 2.44(s) 7.29 (d, J = 8.0 Hz), 7.67 (d, J = 8.0 Hz)
5.36(bs) 4.91(m) 5.21(bs) 4.55(m)
5.46(bs) 4.17(bs) 5.42(bs) 6.07 (dd,
5.72 (dd,
J = 5.7, 1.4 Hz)
5.70 (dm,
J = 5.0 Hz)
3.87 (d,
J = 5.7, 1.9 Hz)
5.22(bs) 6.01 (dm,
J = 5.0 Hz)
5.33(bs) 7.07(bs) 5.52(bs) 4.28 (d,
J = 5.0 Hz)
5.22(bs) 5.99 (dm,
J = 5.0 Hz)
5.35(bs) 7.24(bs) 5.37(bs) 4.38 (d,
J = 5.0 Hz)
4
5
6
5.33(bs) 3.96(s)
3.73(s) 2.41(s) 7.25 (d, J = 8.1 Hz), 7.62 (d, J = 8.1 Hz)
3.79(s) 2.45(s) 7.36 (d, J = 8.1 Hz), 7.74 (d, J = 8.1 Hz)
3.73(s) 2.41(s) 7.25 (d, J = 8.2 Hz), 7.62 (d, J = 8.2 Hz)
3.46(s) 2.47(s) 7.40 (d, J = 8.2 Hz), 7.81 (d, J = 8.2 Hz)
J = 5.0 Hz)
5.69 (dm,
J = 5.0 Hz)
3.91 (d,
5.37(bs) 3.96(s)
J = 5.0 Hz)
6.03(m)
5.71(m)
5.24(bs) 4.18(bs) 5.33(bs) 6.30(m)
5.48(bs) 4.07(bs) 5.37(bs) 6.03(m)
3.75(s) 2.43(s) 7.28 (d, J = 8.2 Hz), 7.67 (d, J = 8.2 Hz)
3.84(s) 2.43(s) 7.32 (d, J = 8.2 Hz), 7.80 (d, J = 8.2 Hz)

M.-F. Ding et al. / Inorganica Chimica Acta 358 (2005) 2427–2431
2429
Table 3
13
C NMR spectral data of compounds 1–6
Compounds C1 C2 C3 C4
67.62 154.78 151.66 66.36 141.69 144.84 52.72
C5
C6
OCH3 CH3
Ar
CO
1
2
21.49 127.85,129.87,135.28,143.25 158.82(C@O)
21.58 128.01,129.86,137.29,144.33 150.74(C@O), 211.47, 213.35,
215.06, 217.49
65.24
85.86
70.32 65.09
85.86
72.68 52.74
3
4
73.74
73.62
84.7
83.06
62.29 80.69 137.73 140.49 55.11
60.63 81.34 136.82 140.98 55.09
21.62 128.45,129.59,137.40,143.93 158.83(C@O), 228.07
21.69 128.14,130.00,138.02,145.14 156.84(C@O), 231.58
21.54 127.80,129.47,136.32,143.60 156.11(C@O), 229.35
21.56 128.16,130.02,137.84,145.06 156.40(C@O), 229.26
21.49 127.99,129.43,136.27,143.58 156.89(C@O), 231.40
21.62 128.43,129.61,137.43,143.93 156.84(C@O), 226.81
21.62 128.54,129.69,137.73,144.16 156.84(C@O), 229.23
73.01 156.41 144.52 79.48
73.00 83.07 60.65 81.37 136.55 141.07 54.74
77.62 153.34 147.73 75.03 64.34 57.71 54.64
63.75
58.61 54.61
5
6
78.45
73.49
83.7
88.55
59.82 76.32 140.02 138.42 54.88
61.34 82.07 136.88 141.72 55.17
Table 5
Selected bond lengths (A) and bond angles (deg) in compound 4
Table 4
Experimental crystallographic data collections for compound 4
a
˚
Bond lengths
Formula
C33H32Cl2 MoN2O10S2
847.59
C11–C12
C14–C15
Mo–C1
Mo–C11
Mo–C12
Mo–N1
C1–O1
1.429(8)
1.303(11)
1.964(7)
2.182(2)
2.213(6)
2.376(5)
1.140(8)
C31–C32
C34–C35
Mo–C2
Mo–C34
Mo–C35
Mo–N2
C2–O2
1.397(8)
1.329(9)
1.959(7)
2.250(6)
2.200(6)
2.335(4)
1.154(8)
Formula weight
Diffractometer
Space group
Nonius
monoclinic P21/n
Unit cell dimensions
˚
a(A)
˚
14.481(4)
12.0152(18)
21.003(3)
92.189(17)
3651.7(12)
4
b(A)
˚
c(A)
b (ꢀ)
Volume (A )
Bond angles
C1–Mo–C2
C1–Mo–C12
C1–Mo–C35
C1–Mo–N2
C2–Mo–C12
C2–Mo–C35
C2–Mo–N2
C11–Mo–C34
C12–Mo–C34
C34–Mo–C35
N1–Mo–C11
N1–Mo–C34
N2–Mo–C11
N2–Mo–C34
a
3
˚
86.5(3)
C1–Mo–C11
C1–Mo–C34
C1–Mo–N1
C2–Mo–C11
C2–Mo–C34
C2–Mo–N1
C11–Mo–C12
C11–Mo–C35
C12–Mo–C35
N1–Mo–N2
N1–Mo–C12
N1–Mo–C35
N2–Mo–C12
N2–Mo–C35
111.75(24)
90.92(24)
95.66(21)
99.23(24)
74.42(24)
156.18(22)
37.93(22)
141.45(21)
146.00(21)
97.08(16)
58.29(19)
92.57(19)
15.02(21)
36.57(22)
Z
73.93(25)
93.95(23)
150.44(22)
100.06(24)
110.98(24)
92.36(21)
154.33(21)
166.20(22)
36.57(22)
58.29(18)
128.95(19)
97.61(20)
58.57(20)
Dcalc (g/cm3)
1.542
0.70930
˚
k (A)
F(0 0 0)
1728
25; (14.91–33.71)
h/2 h
Unit cell detn.: #; (2h range)
Scan type
h, k, l ranges
(ꢀ17; 17) (0; 14) (0; 24)
l (cmꢀ1
)
Crystal size (mm)
6.623
0.28 · 0.31 · 0.38
1.000; 0.960
Maximum and minimum
reflection transmission
Temperature (K)
298.0
6689
Number of measured reflections
Number of observed reflections (I > 2.0r(I)) 3818
C11, C12, C34, and C35 are corresponding to C2, C3, C5, and C6
in this text.
Number of unique reflections
RF; Rw
6418
0.045; 0.050
1.70
Goodness of fit of F
Refinement program
Number of atoms
NRCVAX
of the corresponding resonance of carbons in 13C
82
451 (3818 out of
NMR spectrum of (g4-7-azaNBD)Mo(CO)4 showed
Number of refined parameters
1
6418 reflections)
substantial upfield shifts (2.0–2.5 ppm for H and 70–
P
Minimize function
Weights scheme
(D/r)max
(w|Fo ꢀ Fc|2)
(1/r2)(Fo)
0.0037
80 ppm for 13C). The strong bonding nature of Mo–p
coordination induced a change of hybridization on the
carbon atoms from sp2 to sp3.
P
P
R = iFoj ꢀ jFci/ jFoj.
P
P
Rw = [ w(|Fo| ꢀ |Fc|)2/ w|Fo|2]1/2
.
This is confirmed by the substantial bond length
change observed in compound 4 as describrd in the fol-
lowing section. The Mo atom is chelated by the double
bonds of NBD on the endo side. This product is quite
similar to that obtained in the reaction of iron carbonyl
with NBD.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P
2
GoF ¼
½
ðwðF o ꢀ F cÞ =ðnumber of reflections ꢀ number of parametersÞÞꢁ.
with another CO at its trans position. The common two
signals for CO appeared at the wavelengths below
2000 cmꢀ1 with almost equal intensities, suggesting that
the two CO groups are in cis relation. The stretches
appearing at lower wavelengths are rationalized by the
olefin group at its trans position. The chemical shifts
The molecular weights of compounds 3–6 were con-
firmed by their parent peaks in mass spectra, i.e., (g2-
7-azaNBD)2Mo(CO)2. The appearance of only one set
of NMR signals of compound 3 suggested a symmetrical
structure. In H and 13C NMR spectra, the chemical
1
1
of olefinic hydrogen in H NMR spectrum and those

2430
M.-F. Ding et al. / Inorganica Chimica Acta 358 (2005) 2427–2431
˚
shifts of H(3), C(2) and C(3) are shifted substantially
upfield compared to those of free 7-azaNBD. It
indicated that the Mo binds only with C(2)@C(3) but
not with C(5)@C(6). To fulfill the requirement of 18
electrons around Mo, the lone pairs of the nitrogen
atoms must also act as ligands.
(2.250(6) and 2.200(6) A). It can be ascribed to the elec-
tron-withdrawing nature of tosyl group, which enhance
the degree of backing on C(2)@C(3). The carbonyl groups
coordinated to Mo atom are located cisoid (86.5ꢀ) to each
˚
other. The Mo–CO distances are 1.964(7) and 1.959(7) A,
respectively, which are quite close to those of M–Ceq. in
cis-(g4-1,5-hexadiene) Mo(CO)4 [6] cis-(g3-Me2POC-
HPhH@CH2) Mo(CO)4 [7] and cis-g4-norbornadiene
W(CO)4 [5], indicating a close similarity between the
two. By comparison of the 13C chemical shifts, we can find
that the similar chemical shifts of one azaNBD skeleton
suggested the similar bonding fashion. On the other hand,
the NMR signals of C(1,3) of second azaNBD unit of 5
showed greater downfield shifts than the corresponding
ones of 4 and the NMR signals of C(2,4) work in the other
way, indicating the different orientation of azaNBD be-
tween two complexes. Two sets of 1H and 13C NMR sig-
nals were observed for 6, which displays substantial
upfield shifts on H(3) and C(2)@C(3) similar to those of
3. It indicated that both 7-azaNBD ligands bind with
Mo in the same pattern, i.e., coordination to the double
bonds bearing a tosyl group.
The two units of 7-azaNBD ligands in 4 displayed
1
different characteristics in H and 13C NMR spectra.
The H(3), C(2) and C(3) signals on one unit of 7-aza-
NBD exhibited substantial upfield shifts, but not
much so on H(5,6) and C(5,6). The corresponding sig-
nals on the other unit of 7-azaNBD exhibited just an
opposite order. Such a phenomenon suggests that only
one of the two p-bonds in each ligand, i.e., C(2)@C(3)
in the former and C(5)@C(6) in the latter, is coordi-
nated to the metal. The structure of 4 was confirmed
subsequently by single crystal X-ray diffraction analy-
sis. An ORTEP drawing of 4 is shown in Fig. 1. The
crystallographic data are listed in Table 4, while se-
lected bond lengths and angles are listed in Table 5.
As close examination on bond lengths, we found that
the elongation of C@C bond resulted from the coordi-
nation to the metal. The bond length of C(2)@C(3)
was found to be significantly longer than that of un-
˚
˚
˚
coordinated C(5)@C(6) (1.429(8) A verses 1.303(11) A
3. Conclusion
for (g4-norbornadiene) W(CO)4 [5], but about 0.1 A
shorter than that for M–Cax. The bond lengths and
angles around Mo show that the octahedral geometry
is substantially distorted. The two bound double
bonds facing each other across the Mo are orientated
in a perpendicular geometry. The structure also shows
that the two tosyl groups are also located in a right
angle to each other.
Both 1H and 13C NMR spectra of 5 are very similar to
those of 4, which can be regarded as an effect of metal-ole-
fin back bonding. This is also reflected on the shorter bond
lengths of Mo–C(2) and Mo–C(3) (2.182(2) and
Products distribution of this reaction seems to be
governed by the relative degree of steric hindrance.
Compounds 4, 5 with relatively low steric hindrance
were obtained in major yields, which consist of two tosyl
groups well departed from each other. Compounds 3, 6
with higher steric were obtained in low yields, which
contain tosyl groups located in close proximity of other
groups. The isolation of compound 2 was rather unex-
pected, considering the relative weak bonding affinity
of p-bond to Mo comparing to that of a nitrogen lone
pair to Mo.
˚
2.213(6) A) with respect to Mo–C(5) and Mo–C(6)
4. Experimental
1H and 13C NMR spectra were obtained on Bruker
1
AC-300 FT spectrometer. Chemical shifts for H and
13C NMR spectra are recorded downfield from SiMe4.
IR spectra were recorded on a Perkin–Elmer 882
infrared spectrophotometer; elemental analyses were
performed on a Perkin–Elmer 2400EA instrument
and FAB mass spectra were carried out on a JEOL
SX-102A spectrometer. Melting points were measured
by using a Yanamoto MICRO mp apparatus model
MP-S3 and were uncorrected. Crystal analysis was
performed on Nonius X-ray single crystal diffrac-
tometer.
The compounds were sealed in capillary tube under
nitrogen atmosphere for mp determinations. 7-Meth-
oxycarbonyl-2-tosyl-7-azanorbornadiene was prepared
Fig. 1. ORTEP view of compound 4.

M.-F. Ding et al. / Inorganica Chimica Acta 358 (2005) 2427–2431
2431
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from the reaction of N-methoxycarbonylpyrrole and
ethynyl tolyl sulfone according to the literature [8].
Reaction of 7-methoxycarbonyl-2-p-toulenesulfonyl-7-
azanornadiene and Mo(CO)4(NCMe)2: To a round bot-
tom flask containing Mo(CO)6 (255 mg, 1.0 mmol) in
CH3CN (40 mL), a solution of Me3NO (188 mg,
2.5 mmol) in CH3CN (10 mL) was added slowly
through a syringe under a nitrogen atmosphere and
room temperature [1f,1g]. After additional stirring for
1 h at same conditions, the solvent was removed under
reduced pressure. To it was added a solution of 7-aza-
NBD (320 mg, 1 mmol) in CH2Cl2 (40 mL). The solu-
tion was stirred under ambient condition for 40 h.
After the solvent was removed, the resultant mixture
was pre-separated by means of flash column chromatog-
raphy (silica gel with EtOAc as an eluent) and was then
further separated by using HPLC technique (column
was packed with silica gel and was eluted with EtOAc/
hexane (9:1) as a mobile phase). All products were crys-
tallized from CH2Cl2/n-hexane. Their physical data and
spectral data are summarized in Tables 1–3.
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(p) M. Akita, M. Terada, N. Ishii, H. Hirakawa, Y. Moro-oka,
J. Organomet. Chem. 473 (1994) 175;
Crystal data and conditions for crystallographic data
collection and structure refinement in the X-ray analysis
are listed in Table 4. Some selected data for the bond
lengths and bond angles in compound 4 are also listed
in Table 5.
(q) C. Kayran, E. Okan, Z. Naturforsch. B 56 (2001) 281.
[2] (a) P.S. Lei, P. Vogel, Organometallics 5 (1986) 2500;
(b) P. Vioget, M. Bonivento, R. Roulet, P. Vogel, Helv. Chim.
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(d) C.H. Sun, T.J. Chow, J. Organomet. Chem. 333 (1987)
C21.
5. Supplementary material
[3] (a) C.H. Sun, T.J. Chow, J. Chem. Soc., Chem. Commun. (1988)
535;
Crystallographic data for structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre No. 233340 for 4. Copies of this informa-
tion may be obtained free of charge from The Director,
CCDC, 12 Union Road, e-mail: deposit@ccdc.am.ac.un
or www: http://www.ccdc.cam.ac.uk.
(b) C.H. Sun, T.J. Chow, J. Bull. Inst. Chem. Acad. Sinica 36
(1989) 23;
(c) C.H. Sun, T.J. Chow, L.K. Liu, Organometallics 9 (1990)
560;
(d) C.H. Sun, J.J. Hwang, T.J. Chow, Bull. Inst. Chem. Acad.
Sinica 39 (1992) 13;
(e) T.J. Chow, J.J. Hwang, C.H. Sun, M.F. Ding, Organometallics
12 (1993) 3762;
(f) C.H. Sun, N.C. Shang, L.S. Liou, J.C. Wamg, J. Organomet.
Chem. 481 (1994) 179;
Acknowledgements
(g) J.J. Hwang, M.F. Ding, Y.S. Wen, T.J. Chow, J. Chem. Soc.,
Dalton Trans. (1998) 119;
We thank the national Science Council of the Repub-
lic of China for financial support and National Center
for High-performance Computing for the technical
information support.
(h) C.H. Sun, S.Y. Wu, L.S. Liou, J.C. Wang, J. Chin. Chem. Soc.
45 (1998) 564.
[4] C.M. Lukehart, Fundamental Transition Metal Organometallic
Chemistry, Brooks/Cole Publishing Company, Belmont, CA, 1985,
p. 78.
[5] J.D. Atwood, Inorganic and Organometallic Reaction Mecha-
nisms, Brooks/Cole Publishing Company, Belmont, CA, 1985, p.
54.
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