Synthesis and structures of aryl-substituted tetramethylcyclopentadienyl dinuclear metal carbonyl complexes

Article abstract of DOI:10.1016/j.ica.2006.05.043

A series of 14 aryl-substituted tetramethylcyclopentadienyl dinuclear metal carbonyl complexes have been synthesized by treating the corresponding ligands (C₅Me₄C₆H₄X-4) (X = H, Me, Cl, OMe) with Ru₃(CO)₁₂, Fe(CO)₅, or Mo(CO)₃(MeCN)₃, respectively in refluxing xylene. It showed that the electronic effects of the substituents had influence on the molecular structures and reactions of the complexes, especially for the ruthenium and molybdenum complexes. In the reactions of aryl-substituted tetramethylcyclopentadiene with Mo(CO)₃(MeCN)₃, the electron-withdrawing effect of the substituent in the para position of benzene ring is favorable to produce the Mo-Mo triple bonded complexes, but the electron-donor effect of the substituent in the para position of benzene ring is favorable to produce the Mo-Mo single bonded complexes. In a given condition, the Mo-Mo single bonded complex could be transformed into the corresponding Mo-Mo triple bonded complex. The structures of nine complexes were determined by single crystal X-ray diffraction.

Full text of DOI:10.1016/j.ica.2006.05.043

Inorganica Chimica Acta 359 (2006) 4503–4510
www.elsevier.com/locate/ica
Synthesis and structures of aryl-substituted tetramethylcyclopentadienyl
dinuclear metal carbonyl complexes
a
a
a
a
a
a,b,
*
Jin Lin , Peng Gao , Bin Li , Shansheng Xu , Haibin Song , Baiquan Wang
a
State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, PR China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, PR China
b
Received 22 March 2006; received in revised form 24 May 2006; accepted 28 May 2006
Available online 22 June 2006
Abstract
A series of 14 aryl-substituted tetramethylcyclopentadienyl dinuclear metal carbonyl complexes have been synthesized by treating the
corresponding ligands (C5Me4C6H4X-4) (X = H, Me, Cl, OMe) with Ru3(CO)12, Fe(CO)5, or Mo(CO)3(MeCN)3, respectively in reflux-
ing xylene. It showed that the electronic effects of the substituents had influence on the molecular structures and reactions of the com-
plexes, especially for the ruthenium and molybdenum complexes. In the reactions of aryl-substituted tetramethylcyclopentadiene with
Mo(CO)3(MeCN)3, the electron-withdrawing effect of the substituent in the para position of benzene ring is favorable to produce the
Mo–Mo triple bonded complexes, but the electron-donor effect of the substituent in the para position of benzene ring is favorable to
produce the Mo–Mo single bonded complexes. In a given condition, the Mo–Mo single bonded complex could be transformed into
the corresponding Mo–Mo triple bonded complex. The structures of nine complexes were determined by single crystal X-ray diffraction.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Tetramethylcyclopentadienyl; Metal–metal bond; Ruthenium carbonyl; Iron carbonyl; Molybdenum carbonyl
1. Introduction
to obtain a deeper insight into the steric and electronic influ-
ences of substituents on the molecular structures and reac-
tions of the corresponding biscyclopentadienyl dinuclear
metal carbonyl complexes, especially the electronic influ-
ences of different substituents at the 4-position of phenyl.
Cyclopentadienyl metal complexes have been exten-
sively investigated since ferrocene has been discovered.
Replacement of the hydrogen atoms by other substituents
alters both the steric and electronic influences of the g5-
cyclopentadienyl ring, resulting in differing reactivity and
stability of the substituted cyclopentadienyl metal com-
plexes [1]. Especially for metallocene polymerization cata-
lysts, the steric and electronic effects of cyclopentadienyl
ring substituents greatly influence catalytic activity [2].
Because of the special electronic and steric effect of the phe-
nyl group [3], in this study, the reactions of a series of aryl-
substituted tetramethylcyclopentadiene with Ru3(CO)12,
Fe(CO)5, or Mo(CO)3(MeCN)3 were reported. The aim is
2. Experimental
2.1. General procedures and starting materials
Schlenk and vacuum line techniques were employed
for all manipulations. All solvents were distilled from
1
appropriate drying agents under argon prior to use. H
NMR spectra were recorded on a Bruker AV 300 or
400 instrument, while IR spectra were recorded as KBr
disks on a Nicolet 560 ESP FTIR spectrometer. Elemen-
tal analyses were performed on a Perkin–Elmer 240 C
analyzer. The ligands (C5Me4C6H4-4-X) [X = H (1), Me
(2), Cl (3), or OMe (4)] were prepared according to the
literature [3j].
*
Corresponding author. Present address: State Key Laboratory of
Elemento-Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, PR China. Tel./fax: +86 22 23504781.
E-mail address: bqwang@nankai.edu.cn (B. Wang).
0020-1693/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.05.043

4504
J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
2.2. Complexes synthesis
1.73 (br s, 12H, C5Me4). IR (KBr, mCO, cmÀ1): 1923(s),
1769(s). 11: M.p. 205 ꢁC (dec.). Anal. Calc. for
2.2.1. Synthesis of complex [(g5-C5Me4Ph)Ru(CO)
(l-CO)]2 (5)
C34H32O4Cl2Fe2: C, 59.42; H, 4.69. Found: C, 59.39; H,
1
4.44%. H NMR (300 M, in CDCl3): 7.39 (m, 8H, C6H4),
A
solution of ligand
1
(0.28 g, 1.41 mmol) and
1.88 (s, 12H, CH3), 1.70 (s, 12H, CH3). IR (KBr, mCO,
Ru3(CO)12 (0.3 g, 0.47 mmol) in 30 mL of xylene was
refluxed for 12 h. After removal of solvent, the residue
was chromatographed on an alumina column using petro-
leum ether/CH2Cl2 as eluent. The orange band afforded
complex 5 as orange-red crystals (0.26 g, 52%). M.p. 230–
231 ꢁC. Anal. Calc. for C34H34O4Ru2: C, 57.62; H, 4.81.
cmÀ1): 1927(s), 1771(s). 12: M.p. 165 ꢁC (dec.). Anal. Calc.
for C36H38O6Fe2: C, 63.74; H, 5.65. Found: C, 63.51; H,
1
5.38%. H NMR (400 M, in CDCl3): 7.37 (m, 4H, C6H4),
6.98 (m, 4H, C6H4), 3.85 (s, 6H, OMe), 1.67 (s, 12H,
CH3), 1.63 (s, 12H, CH3). IR (KBr, mCO, cmÀ1): 1921(s),
1773(s).
1
Found: C, 57.48; H, 4.56%. H NMR (300 M, in CDCl3):
7.46–7.32 (m, 10H, C6H5), 1.99 (s, 12H, CH3), 1.87 (s,
3H, CH3), 1.86 (s, 9H, CH3). IR (KBr, mCO, cmÀ1):
1933(s), 1746(s).
2.2.5. Synthesis of [(g5-C5Me4C6H4-4-X)Mo(CO)2]2
[X = H (13), Cl (14)]
Using a procedure similar to that described above, the
reactions of ligands 1 and 3 with Mo(CO)3(MeCN)3 in
refluxing xylene for 12 h afforded complexes 13 and 14 as
dark red crystals in 52% and 49% yields, respectively. 13:
M.p. 169 ꢁC (dec.). Anal. Calc. for C34H34O4Mo2: C,
58.46; H, 4.91. Found: C, 58.73; H, 4.85%. 1H NMR
(300 M, in CDCl3): 7.41–7.27 (m, 10H, C6H5), 2.01 (s,
12H, CH3), 1.93 (s, 12H, CH3). IR (KBr, mCO, cmÀ1):
1871(s), 1825(s). 14: M.p. 184 ꢁC (dec.). Anal. Calc. for
C34H32O4Cl2Mo2: C, 53.21; H, 4.20. Found: C, 53.20; H,
2.2.2. Synthesis of [(g5-C5Me4C6H4-4-X)Ru(CO)
(l-CO)]2 [X = Me (6), Cl (7), OMe (8)]
Using a procedure similar to that described above, the
reactions of ligands 2, 3, and 4 with Ru3(CO)12 afforded
complexes 6, 7, and 8 as orange-red crystals in 31%, 53%,
and 96% yields, respectively. 6: M.p. 158–159 ꢁC. Anal.
Calc. for C36H38O4Ru2: C, 56.68; H, 5.20. Found: C,
1
56.37; H, 5.68%. H NMR (400 M, in CDCl3): 7.38 (d,
1
4H, J = 7.57 Hz, C6H4), 7.22 (d, 4H, J = 7.57 Hz, C6H4),
2.39 (s, 6H, C6H4Me), 1.98 (s, 3H, C5Me4), 1.87 (s, 9H,
C5Me4), 1.86 (s, 3H, C5Me4), 1.76 (s, 9H, C5Me4). IR
(KBr, mCO, cmÀ1): 1929(s), 1767(s). 7: M.p. 241 ꢁC(dec.).
Anal. Calc. for C34H32O4Cl2Ru2: C, 52.51; H, 4.15. Found:
C, 52.05; H, 4.36%. 1H NMR (400 M, in CDCl3): 7.45–7.28
(m, 8H, C6H4), 2.00 (s, 9H, CH3), 1.85 (s, 12H, CH3), 1.77
(s, 3H, CH3). IR (KBr, mCO, cmÀ1): 1937(s), 1753 (s). 8:
M.p. 230 ꢁC (dec.). Anal. Calc. for C36H38O6Ru2: C,
56.24; H, 4.98. Found: C, 56.51; H, 4.65%. 1H NMR
(400 M, in CDCl3): 7.43 (d, 4H, J = 8.57 Hz, C6H4), 6.95
(d, 4H, J = 8.57 Hz, C6H4), 3.85 (s, 6H, OMe), 1.87 (s,
12H, CH3), 1.76 (s, 12H, CH3). IR (KBr, mCO, cmÀ1):
1940(s), 1746(s).
4.20%. H NMR (300 M, in CDCl3): 7.40–7.34 (m, 4H,
C6H4), 7.32–7.26 (m, 4H, C6H4), 2.02 (s, 12H, CH3), 1.93
(s, 12H, CH3). IR (KBr, mCO, cmÀ1): 1873(s), 1838(s).
2.2.6. Synthesis of [(g5-C5Me4C6H4-4-X)Mo(CO)3]2
[X = Me (15), OMe (16)]
Using a procedure similar to that described above, the
reactions of ligands 2 and 4 with Mo(CO)3(MeCN)3 in
refluxing xylene for 12 h only afforded complexes 15 and
16 as dark red crystals in 32% and 51% yields, respectively.
15: M.p. 188 ꢁC (dec.). Anal. Calc. for C38H38O6Mo2: C,
58.32; H, 4.89. Found: C, 58.59; H, 4.60%. 1H NMR
(300 M, in CDCl3): 7.24–7.14 (m, 8H, C6H4), 2.39, 2.37,
2.36 (s, s, s, total 6H, C6H4Me), 2.17–1.90 (m, 24H,
C5Me4). IR (KBr, mCO, cmÀ1): 1950(m), 1927(m), 1896(s),
1883(s), 1875(s) 1834(s). 16: M.p. 157 ꢁC (dec.). Anal. Calc.
for C38H38O8Mo2: C, 56.03; H, 4.70. Found: C, 56.09; H,
2.2.3. Synthesis of [(g5-C5Me4Ph)Fe(CO)(l-CO)]2 (9)
Using a procedure similar to that described above, the
reaction of ligand 1 with Fe(CO)5 in refluxing xylene affor-
ded complex 9 as red crystals (85%). M.p. 195 ꢁC (dec.).
Anal. Calc. for C34H34O4Fe2: C, 66.04; H, 5.54. Found:
1
4.81%. H NMR (300 M, in CDCl3): 7.24–7.14 (m, 4H,
C6H4), 6.90–6.80 (m, 4H, C6H4), 3.77–3.74 (m, 6H,
OMe), 2.15–1.77 (m, 24H, CH3). IR (KBr, mCO, cmÀ1):
2035(w), 1952(m), 1927(s), 1900(s), 1892(s), 1869(s).
1
C, 65.90; H, 5.60%. H NMR (400 M, in CDCl3): 7.41
(br s, 10H, C6H5), 1.63 (br s, 24H, CH3). IR (KBr, mCO
,
cmÀ1): 1915(s), 1765(s).
2.2.7. Synthesis of [(g5-C5Me4C6H4-4-X)Mo(CO)2]2
[X = Me (17), OMe (18)]
2.2.4. Synthesis of [(g5-C5Me4C6H4-4-X)Fe(CO)
(l-CO)]2 [X = Me (10), Cl (11), OMe (12)]
Using a procedure similar to that described above, the
reactions of ligands 2 and 4 with Mo(CO)3(MeCN)3 in
refluxing xylene for 48 h afforded complexes 17 (48%)
and 18 (11%), in addition to the Mo–Mo single bonded
complexes 15 (13%) and 16 (57%). 17: M.p. 170 ꢁC (dec.).
Anal. Calc. for C36H38O4Mo2: C, 59.51; H, 5.27. Found:
Using a procedure similar to that described above, the
reactions of ligands 2, 3, and 4 with Fe(CO)5 afforded com-
plexes 10, 11, and 12 as red crystals in 23%, 42%, and 86%
yields, respectively. 10: M.p. 206 ꢁC (dec.). Anal. Calc. for
C36H38O4Fe2: C, 66.89; H, 5.93. Found: C, 66.46; H,
1
C, 59.41; H, 5.32%. H NMR (300 M, in CDCl3): 7.29–
1
5.87%. H NMR (300 M, in CDCl3): 7.34–7.18 (m, 8H,
7.17 (m, 8H, C6H4), 2.38 (s, 6H, C6H4Me), 2.02 (s, 12H,
C6H4), 2.39 (br s, 6H, C6H4Me), 1.88 (br s, 12H, C5Me4),
C5Me4), 1.94 (s, 12H, C5Me4). IR (KBr, mCO, cmÀ1):

J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
4505
1867(s), 1832(s).18: M.p. 146 ꢁC (dec.). Anal. Calc. for
3. Results and discussion
C36H38O6Mo2: C, 57.00; H, 5.05. Found: C, 57.48; H,
1
5.39%. H NMR (300 M, in CDCl3): 7.22–7.14 (m, 4H,
3.1. Complexes synthesis
C6H4), 6.91–6.80 (m, 4H, C6H4), 3.76 (t, 6H, OMe),
2.16–1.83 (m, 24H, CH3). IR (KBr, mCO, cmÀ1): 1929(s),
1881(s).
When the ligands (C5Me4HC6H4X-4) [X = H (1), Me
(2), Cl (3), or OMe (4)] reacted with Ru3(CO)12 or Fe(CO)5
under refluxing xylene for 12 h, the corresponding Ru–Ru
or Fe–Fe bonded dinuclear complexes 5 (52%), 6 (31%), 7
(53%), 8 (96%), 9 (85%), 10 (23%), 11 (42%), and 12 (86%)
were obtained, respectively (Scheme 1).
When ligands 1 and 3 reacted with Mo(CO)3(MeCN)3
under refluxing xylene for 12 h, the corresponding Mo–
Mo triple bonded dinuclear complexes 13 (52%) and 14
(49%) were obtained, respectively (Scheme 2). But the reac-
tions of ligands 2 and 4 with Mo(CO)3(MeCN)3 under
refluxing xylene for 12 h gave the corresponding Mo–Mo
single bonded complexes 15 (32%) and 16 (51%) (Scheme
3). This indicated that the electron-donor groups Me and
MeO at the 4-position of the phenyl are favorable to pro-
duce the Mo–Mo single bonded complexes, while H and
the electron-withdrawing group Cl at the 4-position of
the phenyl are favorable to produce the Mo–Mo triple
bonded complexes.
2.2.8. The transformation of 15 to 17
Thermal treatment of complex 15 (0.37 g, 0.47 mmol) in
refluxing xylene for 48 h afforded 0.21 g of complex 17
(62%), and 0.08 g (22%) of unreacted 15 was recovered.
2.3. Crystallographic studies
Crystals of complexes 5, 8, 9, and 12–17 suitable for
X-ray diffraction were investigated with a BRUKER
SMART 1000 CCD detector, using graphite monochro-
˚
mated Mo Ka radiation (x–2h scans, k = 0.71073 A) at
room temperature. Semiempirical absorption corrections
were applied for all complexes using the SADABS program
[4]. The structures were solved by direct methods and all
non-hydrogen atoms were subjected to anisotropic refine-
ment by full-matrix least-squares on F2 using the SHEL-
XTL-97 program. All hydrogen atoms were generated
If ligands 2 or 4 reacted with Mo(CO)3(MeCN)3 under
refluxing xylene for 48 h, the corresponding Mo–Mo triple
bonded dinuclear complexes 17 (48%) or 18 (11%) were
also obtained, in addition to the corresponding Mo–Mo
single bonded complexes 15 (13%) or 16 (57%) (Scheme
4). The higher yield of 17 than those of 18 suggested that
with a more stronger electron donor, it is more difficult
˚
geometrically (C–H bond lengths fixed at 0.93–0.98 A),
assigned appropriate isotropic thermal parameters and
included in structure factor calculations. The crystal data
and summary of the X-ray data collection for complexes
5, 8, 9, and 12–17 are presented in Tables 1 and 2. Selected
bond lengths and angles are listed in Tables 3 and 4.
Table 1
Crystal data and summary of the X-ray data collection for complexes 5, 8, 9, 12, and 13
5
8
9
12
13
Empirical formula
Formula weight
T (K)
C
708.75
294(2)
34H34O4Ru2
C36H38O6Ru2
768.80
294(2)
C34H34Fe2O4
618.31
294(2)
C36H38Fe2O6
678.36
294(2)
C34H34Mo2O4
698.50
294(2)
˚
Wavelength, k (A)
Crystal system
Space group
0.71073
monoclinic
P2(1)/n
8.3485(10)
16.879(2)
11.2425(14)
90
111.213(2)
90
1476.9(3)
2
0.71073
rhombohedral
0.71073
monoclinic
P2(1)/c
11.6220(15)
16.286(2)
15.294(2)
90
90.670(2)
90
2894.6(7)
4
0.71073
monoclinic
P2(1)/c
12.476(2)
8.1187(15)
15.723(3)
90
97.985(3)
90
1577.2(5)
2
0.71073
monoclinic
P2(1)/n
8.660(4)
16.632(8)
10.786(5)
90
108.824(7)
90
1470.5(12)
4
ꢀ
R3
˚
a (A)
28.316(3)
28.316(3)
11.194(2)
90
90
120
7773.0(19)
9
1.478
0.916
3510
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmÀ3
)
1.594
1.059
716
1.419
1.039
1288
1.428
0.965
708
1.578
0.890
708
l (mmÀ1
F(000)
)
Crystal size (mm)
h Range (ꢁ)
Reflections collected
Independent reflections
Rint
0.28 · 0.20 · 0.20
2.29–26.32
8192
3007
0.0209
0.38 · 0.30 · 0.20
2.00–25.02
13284
3057
0.0286
0.32 · 0.26 · 0.20
1.75–26.35
16047
5900
0.0491
0.34 · 0.30 · 0.24
1.65–26.23
8424
3167
0.0334
0.30 · 0.26 · 0.24
2.34–26.93
8287
3128
0.0262
Parameters
185
1.066
0.0206, 0.0481
0.0275, 0.0511
208
1.158
0.0299, 0.0910
0.0408, 0.0994
370
1.003
0.0379, 0.0805
0.0814, 0.0969
204
1.035
0.0369, 0.0918
0.0567, 0.1020
186
1.077
0.0233, 0.0556
0.0324, 0.0601
Goodness-of-fit on F2
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)

4506
J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
Table 2
Crystal data and summary of the X-ray data collection for 14, 15, 16, and 17
14
15
16
17
Empirical formula
Formula weight
T (K)
C34H32Cl2Mo2O4
767.38
294(2)
0.71073
triclinic
C38H38Mo2O6
782.56
294(2)
0.71073
triclinic
C38H38Mo2O8
814.56
294(2)
0.71073
monoclinic
C2/c
14.728(3)
8.8049(16)
27.474(5)
90
92.999(3)
90
3557.9(12)
8
1.521
0.756
C36H38Mo2O4
726.54
294(2)
0.71073
triclinic
˚
Wavelength, k (A)
Crystal system
Space group
ꢀ
ꢀ
ꢀ
P1
P1
P1
˚
a (A)
9.2233(15)
9.7323(15)
10.5699(17)
115.644(2)
106.228(2)
96.772(2)
789.4(2)
1
11.7541(16)
11.7617(15)
14.2953(19)
71.163(2)
86.495(2)
65.903(2)
1701.7(4)
2
9.2051(16)
9.7436(17)
10.6881(19)
116.283(2)
106.452(3)
96.391(3)
792.5(2)
1
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmÀ3
)
1.614
1.000
386
1.527
0.782
796
1.522
0.829
370
l (mmÀ1
F(000)
)
1656
Crystal size (mm)
h Range (ꢁ)
Reflections collected
Independent reflections
Rint
0.30 · 0.26 · 0.18
2.30–25.01
4021
2759
0.0124
0.22 · 0.20 · 0.20
1.51–26.32
9641
6813
0.0203
0.28 · 0.20 · 0.08
1.48–26.24
9688
3573
0.0500
0.22 · 0.12 · 0.10
0.22–25.01
4019
2780
0.0138
Parameters
194
1.066
0.0240, 0.0596
0.0283, 0.0625
425
1.066
0.0515, 0.1228
0.0734, 0.1348
222
1.018
0.0368, 0.0691
0.0788, 0.0794
195
1.111
0.0218, 0.0562
0.0244, 0.0588
Goodness-of-fit on F2
R1, wR2 [I > 2r(I)]
R1, wR2 (all data)
and 8 are similar and show two doublets for the phenyl
protons, four or two groups of singlets for the four methyls
protons, and a singlet for the methyl or methoxyl protons,
indicating the symmetrical structures in solution, consistent
with the crystal structures. The electron-donor effect of Me
and MeO groups seems to make the coupling split of the
phenyl protons more clear, and the chemical shift difference
between the two groups of doublets with a stronger elec-
tron-donor group MeO (0.48 ppm) is more larger than that
with a methyl group (0.16 ppm).
Table 3
˚
Selected bond lengths (A) and bond angles (ꢁ) for 5, 8, 9, and 12
5
8
9
12
(M = Fe)
(M = Ru)
(M = Ru)
(M = Fe)
M–M
M–C(11) or C(21)
2.7769(4)
2.267(2)
2.7701(6)
2.251(4)
2.5632(6)
2.133(3)
2.128(3)
2.104(3)
2.103(3)
2.129(3)
2.138(3)
2.161(3)
2.163(3)
2.162(3)
2.166(3)
1.759
2.5630(8)
2.115(2)
M–C(12) or C(22)
M–C(13) or C(23)
M–C(14) or C(24)
M–C(15) or C(25)
M–CEN(1)a
2.308(2)
2.305(2)
2.286(2)
2.238(2)
1.929
2.295(4)
2.283(4)
2.284(4)
2.238(4)
1.918
2.103(3)
2.148(3)
2.171(2)
2.165(3)
1.763
1
The H NMR spectra of the diruthenium and diiron
complexes 5–12 are similar and show one or two groups
of peaks for the phenyl protons, and one or two groups
of singlets for the four methyl protons. Only the signal of
phenyl protons in 12 with a stronger electron-donor group
MeO was split into two groups (Dd = 0.39 ppm). The IR
spectra of diruthenium and diiron complexes 5–12 are very
similar and all show a strong terminal carbonyl absorption
at 1915–1940 cmÀ1 and a strong bridging carbonyl absorp-
tion at 1746–1773 cmÀ1. This indicates that the electronic
effect of the substituents has very less influence on the diru-
thenium and the diiron complexes, which agrees with the
single crystal X-ray diffraction analysis results.
1.763
51.1
49.9
PL(Cp)–PL(Ph)b
53.2
64.8
53.3
a
PL, plane of the cyclopentadienyl (Cp) or phenyl ring (Ph).
CEN: centroid of the cyclopentadienyl ring.
b
to produce the Mo–Mo triple bonded complex. Under
refluxing xylene for 48 h, the Mo–Mo single bonded com-
plex 15 could be transformed into the corresponding
Mo–Mo triple bonded complex 17 in 62% yield (Scheme 5).
The 1H NMR spectra of the Mo–Mo triple bonded com-
plexes 13, 14, 17, and 18 are similar and show one or two
groups of peaks for the phenyl protons, one or two groups
of peaks for the four methyl protons, and one group of
peaks for the methyl or methoxyl protons. But the 1H
NMR spectra of the Mo–Mo single bonded complexes 15
and 16 are more complex. The signals of the methyl or
1
The H NMR spectra of 5 and 7 are similar and show
one group of multiplets for the phenyl protons and three
groups of singlets for the four methyls protons, indicating
the unsymmetrical structures in solution although 5 is Ci
1
symmetrical in crystal state. The H NMR spectra of 6

J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
4507
Table 4
˚
Selected bond lengths (A) and bond angles (ꢁ) for 13–17
13
14
2.5285(5)
15a
3.283
16
3.307
17
Mo–Mo
2.5376(11)
2.335(2)
2.337(2)
2.377(2)
2.377(2)
2.340(3)
2.014
2.5254(5)
2.324(2)
2.329(2)
2.367(2)
2.370(2)
2.337(2)
2.007
3.289
Mo–C(11) or C(21)
Mo–C(12) or C(22)
Mo–C(13) or C(23)
Mo–C(14) or C(24)
Mo–C(15) or C(25)
Mo–CEN(1)
2.321(2)
2.338(2)
2.375(3)
2.375(3)
2.338(2)
2.011
2.311(5)
2.316(5)
2.373(5)
2.381(5)
2.421(5)
2.434(5)
2.379(5)
2.394(5)
2.316(5)
2.318(5)
2.024
2.307(4)
2.313(4)
2.374(3)
2.409(3)
2.368(3)
2.019
2.034
PL(Cp)–PL(Ph)
45.3
55.7
60.2
51.4
64.7
55.6
a
Two independent molecules in an unit with a ratio of 1/1.
X
X
Ru3(CO)12
or Fe(CO)5
xylene
reflux, 12h
O
CO
C
(CO)3
Mo Mo
(CO)3
Mo(CO)3(CH3CN)3
X
M
M
C
O
X
OC
xylene
reflux, 12h
X= H(1), Me(2), Cl(3), OMe(4)
X
X
M= Ru, X= H(5), Me(6), Cl(7), OMe(8)
M= Fe, X= H(9), Me(10), Cl(11), OMe(12)
X= Me(15), MeO(16)
Scheme 1.
Scheme 3.
The Mo–Mo triple bonded complexes 13, 14, 17, and 18
show two strong terminal carbonyl absorptions, while the
Mo–Mo single bonded complexes 15, and 16 show six
strong terminal absorptions in their IR spectra. Complexes
16 and 18 with a stronger electron-donor group MeO show
carbonyl absorptions at much higher wavenumber in their
IR spectra than the corresponding analogues 15, and 13,
14, 17, respectively, indicating the larger influence of the
electronic effect of substituents on the dimolybdenum
complexes.
X
(CO)2
Mo Mo
(CO)2
Mo(CO)3(CH3CN)3
X
xylene
reflux, 12h
3.2. Crystal and molecular structures
X
The crystal structures of 5, 8, 9, and 12–17 were deter-
mined by X-ray diffraction analysis. The molecular struc-
tures of 5, 9, 13, and 16 are presented in Figs. 1–4,
respectively.
X= H(13), Cl(14)
Scheme 2.
Complexes 5 and 8 are diruthenium complexes and have
similar structures. Similar to the cyclopentadienyl analogue
trans-[g5-CpRu(CO)(l-CO)]2 [5], both the structures are
methoxyl protons were split into three singlets or a group
of multiplets, indicating the presence of a restricted rota-
tion along the Mo–Mo single bond in solution.

4508
J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
X
X
(CO)3
Mo Mo
(CO)3
(CO)2
Mo Mo
(CO)2
Mo(CO)3(CH3CN)3
X
+
xylene
reflux, 48h
X
X
X= Me 17
MeO 18
15
16
Scheme 4.
(CEN means centroid of the cyclopentadienyl ring), even
the Ru–Ru distances (Table 3) in 8, are slightly shorter
than that in 5, indicating that introduction of a strong elec-
tron-donor group MeO at the 4-position of the phenyl
enhanced the interaction between Ru atom and the cyclo-
pentadienyl ligand.
Complexes 9 and 12 have similar molecular structures
although 12 is Ci symmetrical but 9 is not. The dihedral
angle between the two cyclopentadienyl planes in 9 is only
0.3ꢁ, very close to parallel. They also have two bridge and
two terminal carbonyls. The Fe–Fe bond distances
xylene
15
17
reflux, 48h
Scheme 5.
trans form and have Ci symmetry. The two cyclopentadie-
nyl ring planes are parallel. Two carbonyls are bridged and
two carbonyls are terminal. The Ru–Ru bond distances
˚
˚
[2.7769(4) A for 5, 2.7701(6) A for 8] are slightly longer
5
˚
than that in trans-[g -CpRu(CO)(l-CO)]2 [2.735(2) A] [5],
[(g5-C5Me5)Ru(CO)(l-CO)]2 [2.752(1) A] [6], and [(g -
5
˚
˚
˚
˚
[2.5635(6) A for 9, 2.5630(8) A for 12] are also slightly
longer than that in analogous complexes trans-[CpFe-
C5Me4Et)Ru(CO)(l-CO)]2 [2.7584(5) A] [7], respectively.
This may be attributed to the bulky steric effect of the phe-
nyl and four methyl groups. The Ru–C(Cp), Ru–CEN
5
˚
(CO)(l-CO)]2 [2.490 A] [8], [(g -C5Me4H)Fe(CO)(l-CO)]2
Fig. 1. ORTEP diagram of 5. Thermal ellipsoids are shown at the 30% level.

J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
4509
Fig. 2. ORTEP diagram of 9. Thermal ellipsoids are shown at the 30%
level.
Fig. 3. ORTEP diagram of 13. Thermal ellipsoids are shown at the 30%
level.
˚
[2.5480(9) A]
[9],
and
[(g5-C5Me5)Fe(CO)(l-CO)]2
˚
[2.560(1) A] [10], due to the bulky steric effect of the phenyl
and four methyl groups. The Fe–C(Cp), Fe–CEN, and
Fe–Fe distances (Table 3) in 9 and 12 are very similar,
indicating that the influence of electronic effect on the
molecular structures of diiron complexes is very less, in
comparison with that of the diruthenium complexes.
Complexes 15 and 16 are Mo–Mo single bonded com-
plexes with Ci symmetry. The Mo–Mo bond distances
the cyclopentadienyl ligand due to the more stronger elec-
tron-donor effect of MeO than those of methyl group at the
4-position of the phenyl. This will also increase the intra-
molecular nonbonding interaction. And as a result, the
˚
Mo–Mo bond distance [3.307 A] of 16 is longer than that
˚
of 15 [3.283 A]. This may explain why the ligand with an
˚
˚
electron donor group is difficult to produce the Mo–Mo tri-
ple bonded complex.
Complexes 13, 14, and 17 are Mo–Mo triple bonded
complexes and all have Ci symmetry. The Mo–Mo bond
[3.283 A for 15, 3.307 A for 16] are also slightly longer than
5
that in [g5-CpMo(CO)3]2 [3.235(1) A] [11], [(g -C9H7)-
˚
5
˚
Mo(CO)3]2 [3.251(1) A] [12], and [(g -C5Me5)Mo(CO)3]2
˚
[3.278(10) A] [13], due to the bulky steric effect of the phe-
˚
˚
distances [2.5374(10) A for 13, 2.5286(5) A for 13,
nyl and four methyl groups. The Mo–C(Cp) and Mo–CEN
distances (Table 4) in 16 are slightly shorter than that in 15,
indicating the enhanced interaction between Mo atom and
˚
2.5253(5) A for 17] are significantly longer than those of
[g -CpMo(CO)2]2 [2.448(1) A] [14], [(g -C5Me5)Mo(CO)2]2
5
5
˚
Fig. 4. ORTEP diagram of 16. Thermal ellipsoids are shown at the 30% level.

4510
J. Lin et al. / Inorganica Chimica Acta 359 (2006) 4503–4510
5
˚
˚
(c) D. Stalke, Angew. Chem., Int. Ed. Engl. 33 (1994) 2168;
(d) P. Jutzi, N. Burford, Chem. Rev. 99 (1999) 969;
(e) H. Sitzmann, Coord. Chem. Rev. 214 (2001) 287;
(f) S. Arndt, J. Okuda, Chem. Rev. 102 (2002) 1953;
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Zhang, Chem. Rev. 103 (2003) 2633.
[2.488(3) A] [15], and [(g -C9H7)Mo(CO)2]2 [2.500(1) A]
[16], also due to the bulky steric effect of the phenyl and
four methyl groups. The Mo–C(Cp) and Mo–CEN
distances (Table 4) in 13, 14, and 17 are similar. The
Mo–Mo bond distance of 17 is slightly shorter than that
of 13. So for the ligand with an electron donor group to
form the Mo–Mo triple bonded complex, it needs to
shorten the long Mo–Mo single bond but to form the short
Mo–Mo triple bond, more energy is needed. The dihedral
angles between the cyclopentadienyl and phenyl ring planes
in these complexes are between 45.3ꢁ and 64.8ꢁ, to further
decrease the intramolecular non-bonding interaction.
In conclusion, the bulky steric effect of the phenyl and
four methyl groups makes the M–M bond distances of
the aryl-substituted tetramethylcyclopentadienyl dinuclear
metal carbonyl complexes increase. Introduction of a
strong electron-donor group at the 4-position of the phenyl
enhanced the interaction between the metal atom and the
cyclopentadienyl ligand, especially for the dimolybdenum
complexes, in which the intramolecular nonbonding inter-
action was also increased, and the Mo–Mo triple bonded
complexes were difficult to form.
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4. Supplementary materials
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC nos. 292403–292411 for compounds 5, 13,
15, 14, 9, 16, 8, 17, and 12, respectively. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK, fax: +44 1223 336 033, e-mail: deposit@ccdc.cam.a-
c.uk of www: http://www.ccdc.cam.ac.uk.
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Acknowledgements
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This work is financially supported by the National Nat-
ural Science Foundation of China (20421202 and
20472034), the Specialized Research Fund for the Doctoral
Program of Higher Education of China (20030055001),
and the Program for New Century Excellent Talents in
University (NCET-04-0229).
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