Dimolybdenum complexes with mixed formamidinate ligands

Article abstract of DOI:10.1016/j.ica.2003.09.019

A series of dimolybdenum complexes containing mixed formamidinate ligand are discussed. The reactions of trans-Mo₂(O₂CCH ₃)₂(o-DMophF)₂ [o-HDMophF = N,N′-di(2-methoxyphenyl)formamidine] with N,N′-di(2-pyridyl) formamidine (HDpyF), N,N′-di(2-pyrimidyl)formamidine (HDpmF) and N,N′-di(6-methyl-2-pyridyl)formamidine (HDMepyF), in refluxing CH ₂Cl₂ afforded the complexes, trans-Mo₂(O ₂CCH₃)(DpyF)(o-DMophF)₂ (1), trans-Mo ₂(O₂CCH₃)(DpmF)(o-DMophF)₂ (2), and trans-Mo₂(O₂CCH₃)(DMepyF)(o-DMophF) ₂ (3), respectively. The o-DMophF^- and DMepyF^- ligands in these complexes adopt the s-cis, s-trans conformation, resulting in Mo-O short distances [2.889 (3) and 2.861(2) ? for 1; 2.880(3) and 3.024(4) ? for 2], while the DpyF^- ligand adopts the s-cis, s-trans conformation, resulting in a Mo-N [3.208(4) ?] and a Mo-H [2.90 (3) ?] short distances. The reactions of trans-Mo₂(O ₂CCH₃)₂(o-DMophF)₂ with HDMepyF in CH₃CN gave complexes 3, trans-Mo₂(O₂CCH ₃)(DMepyF)₂(o-DMophF) (4), and trans-Mo ₂(DMepyF)₂(o-DMophF)₂ (5). The o-DMophF ^- ligands in 4 and 5 adopt the s-cis, s-cis conformation while DMepyF^- assumes an s-cis, s-trans conformation. Complexes 1-5 are the first dimolybdenum complexes containing mixed formamidinate ligands.

Full text of DOI:10.1016/j.ica.2003.09.019

Inorganica Chimica Acta 357 (2004) 1002–1010
www.elsevier.com/locate/ica
Dimolybdenum complexes with mixed formamidinate ligands
a
b
a,
c
Ying-Yann Wu , Ya-Chen Kao , Jhy-Der Chen *, Chen-Hsiung Hung
a
Department of Chemistry, Chung-Yuan Christian University, Chung-Li, Taiwan, ROC
Department of Textile Engineering, Nanya Institute of Technology, Chung-Li, Taiwan, ROC
b
c
Department of Chemistry, National Chunghua University of Education, Chunghua, Taiwan, ROC
Received 28 May 2003; accepted 2 September 2003
Abstract
A series of dimolybdenum complexes containing mixed formamidinate ligand are discussed. The reactions of trans-
Mo2(O2CCH3)2(o-DMophF)2 [o-HDMophF ¼ N; N0-di(2-methoxyphenyl)formamidine] with N; N0-di(2-pyridyl)formamidine (HD
pyF), N; N0-di(2-pyrimidyl)formamidine (HDpmF) and N; N0-di(6-methyl-2-pyridyl)formamidine (HDMepyF), in refluxing CH2Cl2
afforded the complexes, trans-Mo2(O2CCH3)(DpyF)(o-DMophF)2 (1), trans-Mo2(O2CCH3)(DpmF)(o-DMophF)2 (2), and trans-
Mo2(O2CCH3)(DMepyF)(o-DMophF)2 (3), respectively. The o-DMophFꢀ and DMepyFꢀ ligands in these complexes adopt the s-cis,
ꢀ
ꢀ
s-trans conformation, resulting in Mo–O short distances [2.889 (3) and 2.861(2) A for 1; 2.880(3) and 3.024(4) A for 2], while the
DpyFꢀ ligand adopts the s-cis, s-trans conformation, resulting in a Mo–N [3.208(4) A] and a Mo–H [2.90 (3) A] short distances. The
reactions of trans-Mo2(O2CCH3)2(o-DMophF)2 with HDMepyF in CH3CN gave complexes 3, trans-Mo2(O2CCH3)(DMepyF)2(o-
DMophF) (4), and trans-Mo2(DMepyF)2(o-DMophF)2 (5). The o-DMophFꢀ ligands in 4 and 5 adopt the s-cis, s-cis conformation
while DMepyFꢀ assumes an s-cis, s-trans conformation. Complexes 1–5 are the first dimolybdenum complexes containing mixed
formamidinate ligands.
ꢀ
ꢀ
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Dimolybdenum complex; Formamidinate ligand; Conformation; o-HDMophF
1. Introduction
trans-Mo2(O2CR)2(o-DMophF)2 (R ¼ CH3, CF3 and
Prn) and Mo2(O2CCH3) (o-DMophF)Cl2(PMe3)2, which
contain three, two or one bridging acetate ligands and
anions of N; N0-di(2-methoxyphenyl)formamidine (o-
HDMophF) have been reported [8]. These complexes can
be envisaged as the intermediates of the stepwise decar-
boxylation of Mo2(O2CR)4 to form Mo2(form)4.
To our knowledge, no dimolybdenum species con-
taining two types of formamidinate ligands has been
reported. The only dinuclear complexes with mixed
formamidinate ligands are the two unexpected products
trans-Ru2(O2CCH3)2(l-N,N0-g2-N-O-o-MeOForm)(l-
N,N0-g2-N-O-o-MeOForm0) and Ru2(O2CCH3)(l-N,
N0-o-MeOForm)(l-N,N0-g2-N-O-o-MeOForm)(l-N,
N0-g2-N-O-o-MeOForm0), where o-MeOForm is di(o-
methoxyphenyl)formamidinate, and o-MeOForm0 is the
O-demethylation derivative of o-MeOForm, (o-meth-
oxyphenyl)(o-oxyphenyl)formamidinate [9]. Introducing
two different types of formamidinate ligands to the
dimolybdenum units may drastically changes the
The coordination chemistry of formamidinate com-
pounds has been investigated extensively during recent
years [1–5]. Many efforts have been concentrated in their
ability to form bridges between metal atoms. Preparations,
structures and spectroscopic properties of tetrakis(l-di-
arylformamidinato)dimolybdenum complexes of the type
Mo2(form)4, where form is the generic formamidine, were
the subjects of several studies [6]. Crystalline Mo2(form)4
can be prepared by stoichiometric ligand metathesis be-
tween the dimolybdenum tetraacetate Mo2(O2CR)4 and
the lithiated formamidine. This type of reaction was used
to prepare the first Mo2(form)4 compound, Mo2(DTolF)4
(DTolFꢀ ¼ [(p-tol)NCHN(p-tol)]ꢀ) [7]. Recently, dimo-
lybdenum complexes containing mixed acetate–formami-
dinate ligands of the types Mo2(O2CCH3)3(o-DMophF),
* Corresponding author. Fax: +886-3-4563-160.
E-mail address: jdchen@cycu.edu.tw (J.-D. Chen).
0020-1693/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2003.09.019

Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
1003
conformations of the formamidinate ligands. As a con-
tinuous study on the dimolybdenum complexes sup-
ported by formamidinate ligands and to study the
influence of weak interactions on the conformation of
the formamidinate ligand, we have synthesized five
dimolybdenum complexes containing two different
formamidinate ligands. Hereby, the syntheses, struc-
tures and characterization of these complexes are re-
ported.
12H, OCH3), 2.69 (s, 3H, CH3). 13C{1H} NMR (CDCl3,
ppm): 179.14 (C), 160.82 (C), 158.53 (CH), 154.57 (CH),
151.40 (C), 147.35 (CH), 139.92 (C), 136.29 (CH),
123.34 (CH), 122.44 (CH), 120.57 (CH), 117.15 (CH),
113.70 (CH), 111.26 (CH), 55.71 (CH3), 24.21 (CH3).
Anal. Calc. for C43H42Mo2N8O6 (Mw ¼ 958.73): C,
53.87; H, 4.42; N, 11.69. Found: C, 53.66; H, 4.53; N,
11.74%. IR (KBr disk): 2934(w), 2832(w), 1594(m),
1540(s), 1494(s), 1461(s), 1426(s), 1311(s), 1247(s),
1208(m), 1175(w), 1148(w), 1115(m), 1049(m), 1022(m),
935 (w), 858(w), 782(m), 744(s), 674(m), 447(w).
2. Experimental
2.4. Preparation of trans-Mo2(O2CCH3)(DpmF)(o-
DMophF)2 (2)
2.1. General procedures
All manipulations were carried out under dry, oxy-
gen-free nitrogen by using Schlenk techniques, unless
otherwise noted. Solvents were dried and deoxygenated
by refluxing over the appropriate reagents before use.
Hexanes and ether were purified by distillation from
sodium/benzophenone, acetonitrile from CaH2 and di-
chloromethane from P2O5. The Visible absorption
spectra were recorded on a Hitachi U-2000 spectro-
photometer. NMR spectra were measured on a Bruker
Avance 300 MHz spectrometer. IR spectra were ob-
tained from a Jasco FT/IR-460 plus spectrometer. Ele-
mental analyses were obtained from a PE 2400 series II
CHNS/O analyzer.
Trans-Mo2(O2CCH3)2(o-DMophF)2 (1.00 g, 1.22
mmol) and HDpmF (0.49 g, 2.45 mmol) were placed in a
flask containing 10 mL CH2Cl2. The mixture was then
refluxed for 5 h to yield a red solution. The solvent was
removed under vacuum to leave a red solid which was
dissolved in 80 mL ether to give a red solution. The
solvent was removed and the solid was filtered, washed
by 30 mL hexanes and dried under vacuum to give the
red product. Yield: 0.73 g (62.5 %). UV–Vis: 491 nm
(CH2Cl2, e ¼ 1701 Mꢀ1 cmꢀ1). 1H NMR (CDCl3, ppm):
10.39 (s, 1H, CH), 8.78 (s, 2H, CH), 7.66 (d, 4H, Hmeta),
7.11 (d, 4H, Hortho), 6.76 (t, 4H, Hpara), 6.66 (t, 4H,
Hmeta), 6.47 (d, 4H, Hmeta), 6.31 (t, 2H, Hpara), 3.14 (s,
12H, OCH3), 2.77 (s, 3H, CH3). 13C{1H}NMR (CDCl3,
ppm): 179.39 (C), 165.09 (C), 158.58 (CH), 157.61 (CH),
156.67 (CH), 151.88 (C), 140.18 (C), 123.09 (CH),
122.51 (CH), 120.07 (CH), 114.27 (CH), 110.55 (CH),
54.88 (CH3), 24.41 (CH3). Anal. Calc. for
C41H40Mo2N10O6 (Mw ¼ 960.71): C, 51.26; H, 4.20; N,
14.58. Found: C, 51.29; H, 4.27; N, 14.45% IR (KBr
disk): 2952(w), 2830(w), 1577(m), 1541(s), 1493(s),
1456(m), 1431(w), 1384(s), 1308(s), 1248(s), 1205(m),
1176(m), 1115(m), 1051(w), 1026(m), 986(w), 933(w),
876(w), 809(m), 745(m), 675(w), 642(w), 447(w).
2.2. Materials
The compounds trans-Mo2(O2CCH3)2(o-DMophF)2
[8], N,N0-di(2-pyridyl)formamidine (HDpyF) [10], N,N0-
di(2-pyrimidyl)-formamidine (HDpmF) [11], and
N,N0-di(6-methyl-2-pyridyl)formamidine (HDMepyF)
[12] were prepared according to previously reported
procedures.
2.3. Preparation of trans-Mo2(O2CCH3)(DpyF)(o-
DMophF)2 (1)
2.5. Preparation of trans-Mo2(O2CCH3)2(DMepyF)(o-
DMophF)2 (3)
Trans-Mo2(O2CCH3)2(o-DMophF)2 (0.50 g, 0.61
mmol) and HDpyF (0.12 g, 0.61 mmol) was placed in a
flask containing 10 mL CH2Cl2. The mixture was then
refluxed for 2 days to yield an orange–yellow solution.
The solvent was removed under vacuum to leave an
orange–yellow solid which was dissolved in 30 mL ether
to give an orange–yellow solution. The solvent was then
removed, followed by addition of 2 mL ether and 30 mL
hexanes. The solid was filtered and dried under vacuum
to give a yellow product. Yield: 0.26 g (44.5%). UV–Vis:
462 nm (CH2Cl2, e ¼ 2247 Mꢀ1 cmꢀ1). 1H NMR
(CDCl3, ppm): 9.73 (s, 1H, CH), 8.78 (s, 2H, CH), 7.60
(d, 2H, Hmeta), 7.14 (d, 4H, Hortho), 6.89 (t, 2H, Hmeta),
6.81 (t, 4H, Hpara), 6.79 (t, 4H, Hmeta), 6.52 (d, 4H,
Hmeta), 6.44 (t, 2H, Hpara), 5.62 (d, 2H, Hortho), 3.15 (s,
Trans-Mo2(O2CCH3)2(o-DMophF)2 (0.30 g, 0.37
mmol) and HDMepyF (0.08 g, 0.37 mmol) were placed
in a flask containing 10 mL CH2Cl2. The mixture was
then refluxed for 2 days to yield a brown solution. The
solvent was removed, followed by addition 30 mL ether
to give a yellow solution. The solvent was then removed
and the solid washed by hexanes and then dried under
vacuum to give a yellow product. Yield: 0.08 g (22.2 %).
UV–Vis: 462 nm (CH2Cl2, e ¼ 3193 Mꢀ1 cmꢀ1). 1H
NMR (CDCl3, ppm): 9.72 (s, 1H, CH, 8.70 (s, 2H, CH),
7.13 (d, 4H, Hortho), 6.83 (t, 2H, Hmeta), 6.79 (t, 4H,
Hpara), 6.69 (t, 4H, Hmeta), 6.54 (d, 4H, Hmeta), 6.27 (d,
2H, Hpara), 5.62 (d, 2H, Hortho), 3.27 (s, 12H, OCH3),

1004
Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
2.71 (s, 3H, CH3), 1.76 (s, 6H, CH3). 13C{1H} NMR
(CDCl3, ppm): 178.84 (C), 160.32 (C), 158.99 (CH),
156.44 (C), 153.29 (CH), 151.60 (C), 140.26 (C), 136.53
(CH), 123.22 (CH), 123.08 (CH), 120.65 (CH), 116.23
(CH), 111.83 (CH), 109.59 (CH), 55.46 (CH3), 24.18
(CH3), 23.41 (CH3). Anal. Calc. for C45H46Mo2N8O6
(Mw ¼ 986.79): C, 57.77; H, 4.70; N, 11.36. Found: C,
57.46; H, 4.49; N, 11.70%. IR (KBr disk): 2930(w),
2832(w), 1583(m), 1544(s), 1494(s), 1442(s), 1315(m),
1282(m), 1244(s), 1178(w), 1158(w), 1114(m), 1024(m),
932(w), 783(w), 743(m), 676(w), 532(w), 449(w).
14.38%. IR (KBr disk): 2960(w), 2827(w), 1637(m),
1586(m), 1540(s), 1515(s), 1495(m), 1445 (s), 1383(w),
1289(s), 1242(m), 1215(m), 1157(w), 1115(w), 1048(w),
1030(w), 939(w), 791(m), 744(m), 733(m), 671(w),
565(w), 455(w).
3. X-ray crystallography
The diffraction data of 1, 2, 4 and 5 were collected on
a Bruker Smart 1000 or a Bruker AXS diffractometer,
which was equipped with a graphite-monochromated
ꢀ
2.6. Preparations of trans-Mo2(O2CCH3)(DMepyF)2(o-
DMophF),4andtrans-Mo2(DMepyF)2(o-DMophF)2 (5)
Mo-Ka (ka ¼ 0.71073 A) radiation. Data reduction was
carried by standard methods with use of well-established
computational procedures [13]. The structure factors
were obtained after Lorentz and polarization correc-
tions. The positions of some of the heavier atoms in-
cluding the molybdenum atoms were located by the
direct method. The remaining atoms were found in a
series of alternating difference Fourier maps and least-
square refinements. The final residuals of the refinement
were R1 ¼ 0.0359 and wR2 ¼ 0.0494. The X-ray crystal-
lographic procedures for other complexes were similar
to those for 1. Basic information pertaining to crystal
parameters and structure refinement is summarized in
Table 1.
Trans-Mo2(O2CCH3)2(o-DMophF)2 (0.50 g, 0.61
mmol) and HDMepyF (0.41 g, 1.82 mmol) were placed
in a flask containing 10 mL CH3CN. The mixture was
then refluxed for 2 days to yield a brown solution and an
orange solid. The solvent was removed under vacuum to
leave a yellow solid. The 1H NMR spectrum of the
yellow solid showed that there were three complexes in a
ratio of 1:10:20. The spectrum of the complex with the
least amount is the same as that of complex 3, which was
not obtained after the purification process. 30 mL ether
was then added to a flask containing the yellow solid to
give a yellow solution and an orange solid. The solvent
of the yellow solution was removed and the solid washed
by 2 mL ether and 30 mL hexanes and then dried under
vacuum to give complex 4. The orange solid was washed
by 20 mL ether and then dried under vacuum to give
complex 5. Yield for 4: 0.07 g (12.0%). UV–Vis: 471 nm
(CH2Cl2, e ¼ 5617 Mꢀ1 cmꢀ1). 1H NMR (CDCl3, ppm):
10.22 (s, 2H, CH), 8.09 (s, 1H, CH), 7.16 (t, 4H, Hmeta),
6.73 (t, 2H, Hpara), 6.50 (d, 4H, Hpara), 6.46 (d, 2H,
Hortho), 6.37 (d, 2H, Hmeta), 6.30 (t, 2H, Hmeta), 6.02 (d,
4H, Hortho), 3.12 (s, 6H, OCH3), 2.51 (s, 3H, CH3), 1.95
(s, 12H, CH3). 13C{1H} NMR (CDCl3, ppm): 179.90
(C), 161.36 (CH), 160.23 (C), 157.03 (C), 153.41 (C),
152.84 (CH), 139.76 (C), 137.48 (CH), 127.45 (CH),
124.37 (CH), 119.16 (CH), 116.71 (CH), 110.16 (CH),
109.86 (CH), 54.74 (CH3), 25.58 (CH3), 23.60 (CH3).
Anal. Calc. for C43H44Mo2N10O4 (Mw ¼ 956.76): C,
53.98; H, 4.64; N, 14.64. Found: C, 53.39; H, 4.87; N,
14.39%. IR (KBr disk): 2962(w), 2837(w), 1685(m),
1591(m), 1545(s), 1494(m), 1447(s), 1384 (w), 1292(s),
1249(m), 1214(m), 1180(w), 1158(w), 1111(w), 1046(w),
1025(m), 988(w), 782(w), 745(m), 672(w), 558(w),
450(w). Yield for 5: 0.18 g (25.6%). UV–Vis: 473 nm
(CH2Cl2, e ¼ 3319 Mꢀ1 cmꢀ1). 1H NMR (CDCl3, ppm):
10.32 (s, 2H, CH), 8.40 (s, 2H, CH), 6.94 (t, 4H, Hmeta),
6.78 (t, 4H, Hpara), 6.44 (d, 4H, Hpara), 6.41 (d, 4H,
Hortho), 6.36 (d, 4H, Hmeta), 6.23 (t, 4H, Hmeta), 5.65 (d,
4H, Hortho), 3.17 (s, 12H, OCH3), 1.63 (s, 12H, CH3).
Anal. Calc. for C56H56Mo2N12O4 (Mw ¼ 1153.01): C,
58.34; H, 4.90; N, 14.58, Found: C, 58.54; H, 4.76; N,
4. Results and discussions
4.1. Synthesis
The starting complex trans-Mo2(O2CCH3)2(o-
DMophF)2 was prepared by a reaction of Mo2(O2
CCH3)4 with Li(o-DMophF). Reactions of trans-Mo2
(O2CCH3)2(o-DMophF)2 with N,N0-di(2-pyridyl)form-
amidine (HDpyF), N,N0-di(2-pyrimidyl)formamidine
(HDpmF) and N,N0-di(6-methyl-2-pyridyl) ormamidine
(HDMepyF) in refluxing CH2Cl2 afforded the com-
plexes, trans-Mo2(O2CCH3)(DpyF)(o-DMop F)2 (1),
trans-Mo2(O2CCH3)(DpmF)(o-DMo phF)2 (2), and
trans-Mo2(O2CCH3)(DMepyF)(o-DMophF)2 (3), re-
spectively. Reactions of trans-Mo2(O2CCH3)2(o-DMo
phF)2 with HDMepyF in CH3CN gave the complexes 3,
trans-Mo2(O2CCH3)(DMepyF)2(o-DMophF) (4), and
trans-Mo2(DMepyF)2(o-DMophF)2 (5) in a 1:10:20 ra-
tio as measured by 1H NMR spectrum. The structures of
complexes 1, 2, 4 and 5 were characterized by X-ray
crystallography while that of 3 was characterized by el-
emental analysis and spectroscopic studies. Fig. 1 show
the 1H–13C COSY NMR spectrum for 3. The 1H NMR
spectrum shows three singlets centered at 3.27 (12H),
2.71 (3H) and 1.76 (6H) ppm, which can be assigned to
the methyl hydrogen atoms of the o-DMophFꢀ,
CH3COꢀ2 and DMepyFꢀ ligands, respectively. The ob-
servations of only one singlet for the methyl hydrogen

Table 1
Crystal data for 1, 2, 4 and 5 ꢁ CH2Cl2
Compound
1
2ꢁCH2Cl2
C42H42Cl2Mo2N10O6
4
5
Formula
Fw
C
958.73
43H42Mo2N8O6
C43H44Mo2N10O4
956.76
monoclinic
C56H56Mo2N12O4
1153.01
monoclinic
1045.64
monoclinic
P21=c
18.191(3)
16.682(3)
15.356(2)
106.59(2)
4466.1(12)
4
Crystal system
Space group
monoclinic
P21=c
C2=c
C2=c
ꢀ
a (A)
19.569(1)
15.102(1)
15.036(1)
106.193(1)
4267.4(5)
4
26.100(4)
10.804(1)
15.084(1)
95.38(1)
4234.8(8)
4
25.617(2)
13.672(2)
15.463(1)
96.946(5)
5375.9(9)
4
ꢀ
b (A)
ꢀ
c (A)
b (°)
V (A )
3
ꢀ
Z
dcalc (g/cm3)
F ð000Þ
1.492
1952
1.555
2120
1.501
1952
1.425
2368
Crystal size (mm)
l(Mo-Ka) (mmꢀ1
Data collection instruments
0.05 ꢂ 0.6 ꢂ 0.6
0.644
Bruker Smart 1000
0.6 ꢂ 0.8 ꢂ 0.8
0.739
0.3 ꢂ 0.3 ꢂ 0.5
0.647
0.15 ꢂ 0.3 ꢂ 0.5
0.524
)
Bruker AXS P4
0.71073
Bruker AXS P4
0.71073
Bruker AXS P4
0.71073
Radiation monochromated in incident beam 0.71073
ꢀ
(k(Mo-Ka) (A))
Orientation reflections number; range(2h) (°)
42; 11.29 6 2h 6 25.09
3.70 6 2h 6 50.00
25
57; 11.69 6 2h 6 24.93
4.08 6 2h 6 50.00
25
40; 9.26 6 2h 6 24.88
4.18 6 2h 6 50.00
25
Range(2h) for data collection (°)
Temperature (°C)
Limiting indices
3.90 6 2h 6 55.02
25
)25 6 h 6 22, )19 6 k 6 19,
)19 6 l 6 18
26,474
)21 6 h 6 21, )19 6 k 6 1,
)1 6 l 6 18
9340
)1 6 h 6 30, )1 6 k 6 12,
)17 6 l 6 17
4423
)1 6 h 6 30, )1 6 k 6 16,
)18 6 l 6 18
5464
Reflections collected
Independent reflections
Refinement method
9758 [Rint ¼ 0.0685]
full-matrix least-squares on F2
9785/0/670
7786 [Rint ¼ 0.0416]
full-matrix least-squares on F2
7786/0/647
3705 [Rint ¼ 0.0257]
full-matrix least-squares on F2
3705/0/359
4671 [Rint ¼ 0.0324]
full-matrix least-squares on F2
4671/0/342
Data/restraints/parameters
Quality-of-fit indicatorc
Final R indices [I > 2rðIÞ]a;b
R indices (all data)
0.759
1.015
1.091
1.029
R1 ¼ 0:0359; wR2 ¼ 0:0494
R1 ¼ 0:1146; wR2 ¼ 0:0563
0.525 and )0.587
R1 ¼ 0:0480; wR2 ¼ 0:1256
R1 ¼ 0:0682; wR2 ¼ 0:1386
0.552 and )0.757
R1 ¼ 0:0328; wR2 ¼ 0:0774
R1 ¼ 0:0459; wR2 ¼ 0:0832
0.341 and )0.351
R1 ¼ 0:0538; wR2 ¼ 0:1255
R1 ¼ 0:0938; wR2 ¼ 0:1445
0.764 and )0.412
3
ꢀ
Largest differences peak and hole (e/A )
P
P
a R1 ¼ kFoj ꢀ jFck= jFoj.
h
.
i
1=2
P
P
2
2
2
b wR2 ¼
wðFo2 ꢀ Fc2Þ
wðFo2Þ
. w ¼ 1=½r2ðFo2Þ þ ðapÞ þ ðbpÞꢃ; p ¼ ½maxðFo2 or 0Þ þ 2ðFc2Þꢃ=3. a ¼ 0, b ¼ 0, 1; a ¼ 0:0766, b ¼ 4:3750, 2 ꢁ CH2Cl2. a ¼ 0:0310, b ¼ 7:5459, 4; a ¼ 0:0626,
b ¼ 17:6367, 5.
h
i
1=2
P
2
c Quality-of-fit ¼
wðjFo2j ꢀ jFc2jÞ =Nobserved ꢀ Nparameters
.

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Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
Fig. 3. ORTEP drawing of trans-Mo2(O2CCH3)(DpmF)(o-DMophF)2
(2).
Fig. 1. 1H–13C COSY NMR spectrum for complex 3.
listed in Tables 2 and 3, respectively. The molecular
structure of 1 consists of two molybdenum atoms [Mo–
ꢀ
atoms of the o-DMophFꢀ ligands and an integration of
twelve hydrogen atoms indicate that complex 3 is coor-
dinated by two o-DMophFꢀ ligands which are trans to
each other. Complexes 1 and 2 show similar spectra to
that of 3.
Mo ¼ 2.0961 (5) A], which are spanned by one bridging
acetate, two o-DMophFꢀ and one DpyFꢀ ligands, while
ꢀ
the two molybdenum atoms [Mo–Mo ¼ 2.1057(6) A] of
2 are spanned by one bridging acetate, two o-DMophFꢀ
and one DpmFꢀ ligands. The two trans o-DMophFꢀ
ligands in complexes 1 and 2 coordinate to the
molybdenum centers through the two central nitrogen
atoms and adopt the s-cis, s-trans conformation [14],
resulting in a Mo–O short distance [2.889 (3) and 2.861
4.2. Structures
Orange crystals of 1 and 2 conform to the space
group P21=c with four molecules in a unit cell. Figs. 1–3
shows the ORTEP diagram for complexes 1 and 2, re-
spectively, and selected bond distances and angles are
ꢀ
ꢀ
(2) A for 1 and 2.880 (3) and 3.024 (4) A for 2, respec-
tively] for each o-DMophFꢀ ligand. The DpyFꢀ ligand
in 1 also adopts an s-cis, s-trans conformation, resulting
ꢀ
ꢀ
in a Mo–N [3.208(4) A] and a Mo–H [2.90 (3) A, to
pyridyl hydrogen atom attached to C(62)] short dis-
tances. Although single crystal X-ray structure was not
obtained for 3, on the basis of spectroscopic studies and
elemental analysis, its structure is proposed to be similar
to those for 1 and 2.
Yellow crystals of 4 and orange crystals of 5 both
conform to the space group C2=c with four molecules in
each unit cell. Figs. 4(a) and 5(a) show the ORTEP di-
agram for complexes 4 and 5, respectively. Selected bond
distances and angles for 4 and 5 are listed in Tables 4 and
5, respectively. The molecular structures of 4 consists of
ꢀ
two molybdenum atoms [Mo–Mo ¼ 2.1021(6) A] which
are spanned by one acetate, two trans DMepyFꢀ and
one o-DMophFꢀ ligands while the two molybdenum
ꢀ
atoms [Mo–Mo ¼ 2.1071(9) A] in 5 are spanned by two
trans DMepyFꢀ ligands and two trans o-DMophFꢀ li-
gands. All the o-DMophFꢀ ligands in complexes 4 and 5
adopt the s-cis, s-cis conformation and the oxygen atoms
of the methoxy groups are positioned away from the
Fig. 2. ORTEP drawing of trans-Mo2(O2CCH3)(DpyF)(o-DMophF)2
(1).

Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
1007
Table 2
ꢀ
Selected bond distances (A) and angles (°) for 1
Bond distances
Mo(1)–Mo(2)
Mo(1)–N(1)
Mo(1)–N(3)
Mo(2)–O(6)
Mo(2)–N(7)
Mo(1)–O(1)
2.0961(5)
2.139(3)
2.148(3)
2.138(2)
2.144(3)
2.889(3)
Mo(1)–N(6)
Mo(1)–O(5)
Mo(2)–N(2)
Mo(2)–N(4)
Mo(2)–O(4)
2.130(3)
2.146(2)
2.129(3)
2.142(3)
2.861(2)
Bond angles
Mo(2)–Mo(1)–N(6)
N(6)–Mo(1)–N(1)
N(6)–Mo(1)–O(5)
Mo(2)–Mo(1)–N(3)
N(1)–Mo(1)–N(3)
Mo(1)–Mo(2)–N(2)
N(2)–Mo(2)–O(6)
N(2)–Mo(2)–N(4)
O(6)–Mo(2)–N(7)
N(4)–Mo(2)–N(7)
91.57(8)
85.00(10)
175.57(10)
92.65(8)
Mo(2)–Mo(1)–N(1)
Mo(2)–Mo(1)–O(5)
N(1)–Mo(1)–O(5)
N(6)–Mo(1)–N(3)
O(5)–Mo(1)–N(3)
Mo(1)–Mo(2)–O(6)
Mo(1)–Mo(2)–N(4)
O(6)–Mo(2)–N(4)
N(2)–Mo(2)–N(7)
92.71(8)
91.96(7)
92.17(10)
92.87(10)
89.62(9)
91.46(7)
92.41(8)
92.41(10)
87.87(10)
174.29(12)
92.46(9)
88.86(10)
174.94(12)
174.20(10)
90.44(10)
Table 3
ꢀ
Selected bond distances (A) and angles (°) for 2
Bond distances
Mo(1)–Mo(2)
Mo(1)–N(3)
Mo(1)–N(7)
Mo(2)–O(6)
Mo(2)–N(2)
Mo(1)–O(3)
2.1057(6)
2.148(4)
2.154(4)
2.147(3)
2.157(4)
2.880(3)
Mo(1)–O(5)
2.148(3)
Mo(1)–N(1)
Mo(2)–N(4)
Mo(2)–N(8)
Mo(2)–O(2)
2.149(4)
2.138(4)
2.155(4)
3.024(4)
Bond angles
Mo(2)–Mo(1)–O(5)
O(5)–Mo(1)–N(3)
O(5)–Mo(1)–N(1)
Mo(2)–Mo(1)–N(7)
N(3)–Mo(1)–N(7)
N(4)–Mo(2)–O(6)
N(4)–Mo(2)–N(8)
O(6)–Mo(2)–N(2)
N(8)–Mo(2)–N(2)
91.3(1)
91.5(1)
88.8(2)
92.5(1)
90.0(1)
89.1(1)
91.8(1)
90.7(1)
88.2(1)
Mo(2)–Mo(1)–N(3)
Mo(2)–Mo(1)–N(1)
N(3)–Mo(1)–N(1)
O(5)–Mo(1)–N(7)
N(1)–Mo(1)–N(7)
Mo(1)–Mo(2)–N(8)
O(6)–Mo(2)–N(8)
N(4)–Mo(2)–N(2)
92.8(1)
92.1(1)
175.7(2)
175.8(1)
89.4(2)
91.5(1)
176.7(1)
174.5(2)
molybdenum metal centers. Noticeably, although all the
o-DMophFꢀ ligands in complexes 4 and 5 adopt the s-
cis, s-cis conformation, the orientations of the methoxy
groups in each o-DMophFꢀ ligand are different. Figs.
4(b) and 5(b) show the ORTEP diagrams looking down
the Mo–Mo axes for complexes 4 and 5, respectively. It
is seen that while the two methoxy groups in 4 are po-
sitioned opposite to each other, those in 5 are on the
same side. It is also noted that all the DMepyFꢀ ligands
in complexes 4 and 5 adopt the s-cis, s-trans conforma-
tion, resulting in the formation of Mo–N and Mo–H
short distances for both complexes. The distances are
Complexes 1–5 are of significance because they are
the first dimolybdenum complexes containing two dif-
ferent types of formamidinate ligands.
4.3. Structural comparisons
A comparison of distances and conformations, as
1
well as H- and 13C NMR chemical shifts, observed for
dimolybdenum complexes containing anion of N,
N0-di(2-methoxyphenyl)formamidine (o-DMophFꢀ) is
listed in Table 6. Two short Mo–O distances for each
o-DMophFꢀ ligand are observed in the complex
Mo2(O2CCH3)3(o-DMophF), in which the o-DMophFꢀ
ligand adopts the s-trans, s-trans conformation [8]. In
complexes trans-Mo2(O2CR)2(o-DMophF)2 (R ¼ CH3,
CF3 and Prn), 1 and 2, the o-DMophFꢀ ligands adopt
the s-cis, s-trans conformation, resulting in one Mo–O
ꢀ
Mo–N ¼ 2.882 (3) and Mo–H ¼ 2.79 (4) A for 4 and
ꢀ
Mo–N ¼ 2.863 (5) and Mo–H ¼ 2.98 A for 5, respec-
tively. It seems that formation of both Mo–N and Mo–
H short distances are more favorable than Mo–O short
distance.

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Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
Fig. 5. ORTEP drawing of trans-(DMepyF)2(o-DMophF)2 (5).
Fig. 4. ORTEP drawing of trans-Mo2(O2CCH3)(DMepyF)2(o-
DMophF) (4).
atoms, respectively, the s-trans, s-trans and s-cis, s-cis
conformations are most probably not retained in solu-
tion either. Similar situations were seen in the complexes
Cr2(o-DMophF)4 [15] and Cr2(O2CCH3)2(o-DMophF)2
[16]. Due to the asymmetry of the molecules, two sing-
lets for the two methoxy hydrogen atoms were observed
for the complex Mo2(O2CCH3)(o-DMophF)Cl2(PMe3)2
[8].
short distance for each o-DMophFꢀ ligand. These
complexes are in marked to the s-cis, s-cis conformation
in complexes 4 and 5, where no Mo–O interaction is
observed. It is noted that for all the complexes with s-cis,
s-trans conformation, the two complexes with two dif-
ferent formamidinate ligands, i.e., complexes 1 and 2,
have the longer Mo–O distances, presumably do to the
steric effect imposed by the other formamidinate ligands.
The variable-temperature 1H NMR spectra of all
the complexes in Table 6, except Mo2(O2CCH3)(o-
DMophF)Cl2(PMe3)2 [8], show only a sharp singlet for
the protons of OCH3 groups, indicating that the solid
state s-cis, s-trans conformation of the o-HDMophF li-
gands in these complexes are not retained in solution.
4.4. Formation scheme for complexes 3–5
The formation of 4 from the starting complex trans-
Mo2(O2CCH3)2(o-DMophF)2 is worthy of discussion.
In the complexes trans-Mo2(O2CCH3)2(o-DMophF)2
and 3, the two o-DMophFꢀ ligands which are posi-
tioned trans to each other are cis to the acetate ligands,
while in complex 4 the o-DMophFꢀ ligand is positioned
trans to the acetate ligand. Scheme 1 shows the proposed
formation mechanism for complexes 3–5, where the
1
Since all the complexes show similar H and 13C NMR
chemical shifts for the methoxy hydrogen and carbon

Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
1009
Table 4
ꢀ
Selected bond distances (A) and angles (°) for 4
Bond distances
Mo–Mo(A)
Mo–N(3)
Mo–N(4A)
2.1021(6)
2.141(3)
2.181(3)
Mo–N(1)
Mo–O(2)
2.115(3)
2.146(3)
Bond angles
Mo(A)–MoN(1)
N(1)–Mo–N(3)
N(1)–Mo–O(2)
Mo(A)–Mo–N(4A)
N(3)–Mo–N(4A)
92.48(7)
91.59(10)
175.82(10)
94.42(8)
Mo(A)–Mo–N(3)
Mo(A)–Mo–O(2)
N(3)–Mo–O(2)
89.95(8)
91.68(7)
88.86(10)
92.46(10)
86.77(10)
N(1)–Mo–N(4A)
O(2)–Mo–N(4A)
173.91(11)
Table 5
ꢀ
Selected bond distances (A) and angles (°) for 5
Bond distances
Mo–Mo(A)
Mo–N(2A)
Mo–N(4)
2.1071(9)
2.146(4)
2.184(5)
Mo–N(1)
Mo–N(5A)
2.144(4)
2.146(5)
Bond angles
Mo(A)–MoN(1)
N(1)–Mo–N(2A)
N(1)–Mo–N(5A)
Mo(A)–Mo–N(4)
N(2A)–Mo–N(4)
92.5(1)
175.1(2)
87.2(2)
93.5(1)
88.2(2)
Mo(A)–Mo–N(2A)
Mo(A)–Mo–N(5A)
N(2A)–Mo–N(5A)
N(1)–Mo–N(4)
92.4(1)
90.2(1)
92.3(2)
92.0(2)
176.2(2)
N(5A)–Mo–N(4)
Table 6
Some important parameters for dimolybdenum complexes containing anion of N; N0-di(2-methoxyphenyl)formamidine (o-DMophFꢀ)
d
1H(13C) for the methoxy
groups of o-DMophFꢀ
ꢀ
Mo–Mo (A)
ꢀ
Mo–O (A)
Compound
Conformation of
o-DMophFꢀ
Mo2 (O2CCH3)3 (o-DMophF)
trans-Mo2(O2CCH3)2 (o-DMophF)2
trans-Mo2(O2CCF3)2 (o-DMophF)2
trans-Mo2(O2CCPrn)2 (o-DMophF)2
Mo2(O2CCH3)(o-DMophF)Cl2(PMe3)2
1
2.0933(3)
2.108(1)
2.681(2)
2.667(2)
2.600(7)
2.615(6)
2.576(5)
2.576(5)
2.602(2)
2.602(2)
2.562(4)
s-trans, s-trans
s-cis, s-trans
s-cis, s-trans
s-cis, s-trans
s-cis, s-trans
s-cis, s-trans
s-cis, s-trans
3.26(55.05)
3.15(55.71)
3.09(55.38)
3.16(55.78)
2.133(2)
2.1088(6)
2.1239(6)
2.0961(5)
2.1057(6)
3.23(55.88)
3.40(54.15)
3.15(55.71)
2.889(3)
2.861(2)
3.024(4)
2.880(3)
2
3.14(54.88)
3
4
5
3.27(55.46)
3.12(54.74)
3.17
2.1021(6)
2.1071(9)
s-cis, s-cis
s-cis, s-cis
complexes are represented by the side views looking
down the Mo–Mo bonds, showing the relative positions
of the ligands. The first step is that one of the acetate
ligands was replaced by the DMepyFꢀ ligand to give
complex 3. Upon addition of another DMepyFꢀ ligand,
one of the o-DMophFꢀ ligands departs from the metal
centers and the intermediate rearrange to position the
acetate and o-DMophFꢀ ligands trans to each other.
The DMepyFꢀ ligand then coordinates to the dimo-
lybdenum unit to form complex 4. As shown in Scheme
1, two possible pathways can be undertaken to form
complex 5.
5. Concluding remarks
Five complexes, which are the first dimolybdenum
complexes containing mixed formamidinate ligands,
have been structurally characterized. The o-DMophFꢀ
ligands in complexes 1–3 adopt the s-cis, s-trans con-
formation, resulting in a Mo–O short distance for each
o-DMophFꢀ ligand, while those in complexes 4 and 5
adopt the s-cis, s-cis conformation, where no Mo–O
interaction is observed. Noticeably, although the o-
DMophFꢀ ligands in complexes 4 and 5 adopt the same
conformation, the orientations of the two methoxy

1010
Y.-Y. Wu et al. / Inorganica Chimica Acta 357 (2004) 1002–1010
plementary publication numbers CCDC 208105–
208108. Copies of the data can be obtained, free of
charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: +44(0)-1223-336033 or
e-mail: deposit@ccdc.cam.ac.uk].
Acknowledgements
We wish to thank the National Science Council of the
Republic of China for support.
References
[1] C. Lin, J.D. Protasiewicz, T. Ren, Inorg. Chem. 35 (1996) 7455.
[2] C. Lin, J.D. Protasiewicz, E.T. Smith, T. Ren, Inorg. Chem. 35
(1996) 6422.
[3] T. Ren, C. Lin, P. Amalberti, D. Macikenas, J.D. Protasiewicz,
J.C. Baum, T.L. Gibson, Inorg. Chem. Commun. 1 (1998) 23.
[4] M.H. Chisholm, F.A. Cotton, L.M. Daniels, K. Folting, J.C.
Huffman, S.S. Iyer, C. Lin, A.M. Macintosh, C.A. Murillo, J.
Chem. Soc., Dalton Trans. (1999) 13872.
ꢁ
[5] R. Clerac, F.A. Cotton, K.R. Dunbar, C.A. Murillo, X. Wang,
Inorg. Chem. 40 (2001) 420.
Scheme 1. Formation scheme for complexes 3, 4 and 5.
[6] T. Ren, Coord. Chem. Rev. 175 (1998) 43.
[7] F.A. Cotton, X. Feng, M. Matusz, Inorg. Chem. 28 (1989) 594.
[8] Y.-Y. Wu, J.-D. Chen, L.-S. Liou, J.-C. Wang, Inorg. Chim. Acta
336 (2002) 71.
groups are different. A mechanism involving cis–trans
isomerization process has been proposed for the for-
mation of complex 4. On the basis of the conformations
adopted by o-DMophFꢀand DMepyFꢀ ligands, it
seems that formation of both Mo–N and Mo–H short
distances are more favorable than Mo–O short distance,
although the subtle difference in the structures of the
two ligands can be influential.
[9] T. Ren, V. Desilva, G. Zou, C. Lin, L.M. Daniels, C.F. Campana,
J.C. Alvarez, Inorg. Chem. Commun. 2 (1999) 301.
ꢁ
[10] H. Remlinger, W.R.F. Lingier, J.J.M. Vandewalle, R. Merenyi,
Chem. Ber. 104 (1971) 3965.
[11] A.A. Gerard, J.K. Petra, M. Ilop, T. Urho, R. Jan, Eur. J. Inorg.
Chem. (1999) 2269.
[12] C.S. Michael, C.V.T. Gleen, W.W. David, J. Org. Chem. 35 (1951)
1662.
[13] SHELXTL 5.10, Bruker Analytical X-ray Instruments Inc., Kar-
lsruche, Germany, 1997.
[14] S. Radak, Y. Ni, G. Xu, K.L. Shaffer, T. Ren, Inorg. Chim. Acta
321 (2001) 200.
6. Supplementary material
[15] F.A. Cotton, L.M. Daniels, C.A. Murillo, P.J. Schooler, Chem.
Soc., Dalton Trans. (2000) 2007.
Crystallographic data (excluding structure factors)
for the structures in this paper has been deposited with
the Cambridge Crystallographic Data Centre as sup-
[16] D.M. Baird, P.E. Fanwick, T. Barwick, Inorg. Chem. 24 (1985)
3753.