Chemistry of dimolybdenum complexes containing bridging anions of N,N′-di(3-methoxyphenyl)formamidine

Article abstract of DOI:10.1016/j.molstruc.2008.01.037

Reaction of Mo(CO)₆ with excess N,N′-di(3-methoxyphenyl)formamidine (HDmAniF) in o-dichlorobenzene afforded the yellow complex Mo₂(DmAniF)₄, 1. The structure of 1 reveals that the ligands bridge the two metal centers through the two nitrogen atoms, forming two s-cis, s-trans and two s-trans, s-trans conformations. Reaction of 1 with Me₃OBF₄ in CH₃CN gave cis-[Mo₂(DmAniF)₂(CH₃CN)₄][BF₄]₂, 2, which crystallized in two different forms. The first form, 2·CH₂Cl₂·CH₃CN, 2a, showing one BF₄^- anion coordinating to the axial positions of the Mo-Mo bond [Mo?F = 2.685(4) A?], contains two cis DmAniF^- ligands which adopt the same s-cis, s-trans conformation. The other form, 2·0.5CH₂Cl₂ · 0.5CH₃CN, 2b, involves two independent molecules. While one [Mo-Mo = 2.1432(8) A?] of the two molecules shows axial interaction by CH₃CN [Mo?N = 2.692(8) A?] and the two cis DmAniF^- ligands adopt the same s-cis, s-trans conformation, the other one [Mo-Mo = 2.1317(9) A?] shows no axial interaction and the two cis DmAniF^- ligands adopt different conformations, which are s-cis, s-trans and s-cis, s-cis, respectively. The Mo-Mo distance of 2a, 2.1281(6) A?, is the shortest among the compounds having Mo₂(μ₂-L)₂(CH₃CN)₄ core, where L is the anionic, cationic or neutral form of a formamidine ligand. Reaction of 2 with NaOCH₃ in CH₃OH produced the tetranuclear complex cis-[Mo₂(DmAniF)₂]₂(μ-OCH₃)₄, 3. The molecule of 3 bears four bridging CH₃O^- groups that link two quadruply bonded moieties and the ligands adopts the s-trans, s-trans conformation.

Full text of DOI:10.1016/j.molstruc.2008.01.037

Available online at www.sciencedirect.com
Journal of Molecular Structure 890 (2008) 48–56
www.elsevier.com/locate/molstruc
Chemistry of dimolybdenum complexes containing bridging anions
of N,N0-di(3-methoxyphenyl)formamidine
Ying-Yann Wu a, Chun-Wei Yeh a, Zhi-Kai Chan a, Chia-Her Lin a,
a
a,
b
*
Chia-Hsi Yang , Jhy-Der Chen , Ju-Chun Wang
a Department of Chemistry, Chung-Yuan Christian University, No. 200, Chung Pei Road, Chung-Li, Taiwan, ROC
b Department of Chemistry, Soochow University, Taipei, Taiwan, ROC
Received 9 November 2007; received in revised form 16 January 2008; accepted 16 January 2008
Available online 1 February 2008
Dedicated to the memory of Professor F.A. Cotton, a great mentor and friend.
Abstract
Reaction of Mo(CO)6 with excess N,N0-di(3-methoxyphenyl)formamidine (HDmAniF) in o-dichlorobenzene afforded the yellow com-
plex Mo2(DmAniF)4, 1. The structure of 1 reveals that the ligands bridge the two metal centers through the two nitrogen atoms, forming
two s-cis, s-trans and two s-trans, s-trans conformations. Reaction of 1 with Me3OBF4 in CH3CN gave cis-[Mo2(DmA-
niF)2(CH3CN)4][BF4]2, 2, which crystallized in two different forms. The first form, 2ꢀCH2Cl2ꢀCH3CN, 2a, showing one BFꢁ4 anion coor-
ꢁ
˚
dinating to the axial positions of the Mo–Mo bond [Moꢀ ꢀ ꢀF = 2.685(4) A], contains two cis DmAniF ligands which adopt the same
s-cis, s-trans conformation. The other form, 2ꢀ0.5CH2Cl2 ꢀ 0.5CH3CN, 2b, involves two independent molecules. While one [Mo–
ꢁ
˚
˚
Mo = 2.1432(8) A] of the two molecules shows axial interaction by CH3CN [Moꢀ ꢀ ꢀN = 2.692(8) A] and the two cis DmAniF ligands
ꢁ
˚
adopt the same s-cis, s-trans conformation, the other one [Mo-Mo = 2.1317(9) A] shows no axial interaction and the two cis DmAniF
˚
ligands adopt different conformations, which are s-cis, s-trans and s-cis, s-cis, respectively. The Mo–Mo distance of 2a, 2.1281(6) A, is the
shortest among the compounds having Mo2(l2-L)2(CH3CN)4 core, where L is the anionic, cationic or neutral form of a formamidine
ligand. Reaction of 2 with NaOCH3 in CH3OH produced the tetranuclear complex cis-[Mo2(DmAniF)2]2(l-OCH3)4, 3. The molecule
of 3 bears four bridging CH3Oꢁ groups that link two quadruply bonded moieties and the ligands adopts the s-trans, s-trans
conformation.
Ó 2008 Published by Elsevier B.V.
Keywords: Dimolybdenum complex; Formamidine; Conformation; N,N0-di(3-methoxyphenyl)formamidine
1. Introduction
pared by stoichiometric ligand metathesis between the
dimolybdenum tetraacetate Mo2(O2CR)4 and the lithiated
formamidine. A conformational descriptor for diarylform-
amidine bearing an m-alkoxy substituent has been proposed
by Ren and co-authors [5b]. Based on their proposition,
three stable conformations exist for diarylformamidine
which are defined as (a) s-cis, s-cis- (s-cis-/s-trans- are
defined between the N–C (methine) bond and the ring
C–C bond prioritized by the OR group), (b) s-cis, s-trans-,
and (c) s-trans, s-trans- [5b].
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-diarylformamidi-
nato)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 pre-
Although dimolybdenum complexes containing N,N0-
di(4-methoxyphenyl)formamidine (HDpAniF) [4] and
N,N0-di(2-methoxyphenyl)formamidine (HDoAniF) [5g,5h]
*
Corresponding author.
E-mail address: jdchen@cycu.edu.tw (J.-D. Chen).
0022-2860/$ - see front matter Ó 2008 Published by Elsevier B.V.
doi:10.1016/j.molstruc.2008.01.037

Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
49
have been subjected to several studies, dimolybdenum
2.2. Materials
complex containing their isomeric ligand N,N0-di(3-
methoxyphenyl)formamidine (HDmAniF) has not been
structurally characterized. We report herein several dimo-
lybdenum complexes of the types Mo2(DmAniF)4 and
cis-[Mo2(DmAniF)2(CH3CN)4][BF4]2, and a tetranuclear
complex cis-[Mo2(DmAniF)2]2(l-OCH3)4. The syntheses,
structures and ligand conformations of these complexes
form the subject of this report.
The complexes Mo2(DmAniF)4 [2b], [Mo2(CH3CN)10]
[BF4]4 [7], and the ligand N,N0-di(3-methoxyphenyl) form-
amidine (HDmAniF) [5a,8] were prepared according to pre-
viously reported procedures. The reagents Mo(CO)6,
Me3OBF4 and MeONa were purchased from Strem Chem-
ical Co.
2.3. Preparation of Mo2(DmAniF)4 (1)
2. Experimental section
Mo(CO)6 (1.0 g, 3.79 mmol) and HDmAniF (2.43 g,
9.47 mmol) were placed in a flask containing 10 mL o-
dichlorobenzene. The mixture was then refluxed for
20 h to yield a brown solution. After the mixture was
cooled to room temperature, 80 mL MeOH was then
added to give a yellow precipitate. The precipitate was
filtered, washed by diethyl ether and then dried under
reduced pressure to give the yellow product. Yield:
1.72 g (75%). UV–vis: 443 nm (CH2Cl2, e = 2636
2.1. General procedures
All manipulations were carried out under dry, oxygen-
free nitrogen by using Schlenk techniques, unless other-
wise noted. Solvents were dried and deoxygenated by
refluxing over the appropriate reagents before use. Hex-
anes, THF and diethyl ether were purified by distillation
from sodium/benzophenone, acetonitrile from CaH2,
methanol form Mg/I2 and dichloromethane from P2O5.
The visible absorption spectra were recorded on a Hitachi
U-2000 spectrophotometer. NMR spectra were measured
on a Bruker Avance 300 MHz spectrometer. IR spectra
were obtained with the use of a Jasco FT/IR-460 plus
spectrometer. Elemental analyses were obtained from a
PE 2400 series II CHNS/O analyzer.
M
ꢁ1 cmꢁ1). 1H NMR (CDCl3, ppm): 8.54 (s, 4H,
CH),6.85 (t, 8H, Hmeta), 6.44 (d, 8H, Hpara), 6.03 (d,
8H, Hortho), 5.80 (s, 8H, Hortho), 3.26 (s, 24H, OCH3).
13C{1H} NMR (CDCl3, ppm): 160.45 (C), 157.68 (CH),
152.02 (C), 129.73 (CH), 115.19 (CH), 110.16
(CH),108.01(CH), 54.92 (CH3). Calc. for C60H60Mo2
N8O8 (MW = 1213.04): C, 59.40; H, 4.98; N, 9.24%;
Table 1
Crystal data for compounds 1–3
Compound
1
2a
2b
3
Formula
Fw
C60H60Mo2N8O8
1213.04
C41H47B2Cl2F8Mo2N9O4
1166.28
C39.5H44.5B2ClF8Mo2N8.5
1103.29
C64H72Mo4N8O12
1529.06
Crystal system
Space group
Monoclinic
P21/n
Triclinic
Pıꢀ
Triclinic
Pıꢀ
Triclinic
Pıꢀ
˚
A, A
15.9394(8)
9.8710(5)
18.2809(10)
90
106.415(1)
90
2759.0(2)
11.6403(9)
12.3965(10)
18.9062(13)
103.426(5)
103.615(5)
97.719(7)
13.0132(7)
8.7284(8)
12.5187(11)
15.325(4)
103.059(12)
100.854(12)
96.747(7)
˚
B, A
19.5509(10)
22.4735(12)
96.721(1)
106.810(1)
107.319(1)
˚
C, A
a, °
b, °
c, °
3
˚
V, A
2527.0(3)
5094.5(5)
1579.5(4)
Z
2
2
4
1
dcalc., g/cm3
1.460
1.533
1.438
1.608
F (000)
1248
1176
2224
776
Cryst. size, mm
0.44 ꢂ 0.48 ꢂ 0.74
0.2 ꢂ 0.6 ꢂ 0.8
0.3 ꢂ 0.4 ꢂ 0.4
0.1 ꢂ 0.4 ꢂ 0.4
l(Mo Ka), mmꢁ1
reflections collected
Independent reflections
Data/restraints/parameters
Quality-of-fit indicatorc
final R indices [I > 2r(I)]a,b
R indices (all data)
0.518
0.680
0.619
0.844
10605
4774 [R(int) = 0.0288]
4774/0/472
10104
24790
6637
8734 [R(int) = 0.0246]
8734/0/613
1.046
R1 = 0.0615 wR2 = 0.1670
R1 = 0.0725 wR2 = 0.1785
1.118 and ꢁ1.344
16984 [R(int) = 0.0362]
16984/6/1183
1.024
R1 = 0.0694 wR2 = 0.1526
R1 = 0.0819 wR2 = 0.1616
1.464 and ꢁ0.646
5487 [R(int) = 0.0316]
5487/0/474
1.039
R1 = 0.0529 wR2 = 0.1231
R1 = 0.0821 wR2 = 0.1388
1.001 and ꢁ0.838
1.091
R1 = 0.0278 wR2 = 0.0749
R1 = 0.0293 wR2 = 0.0767
0.319 and ꢁ0.495
3
˚
Largest diff. peak and hole, e/A
a
R1 = RjjFoj ꢁ jFcjj/RjFoj.
2
2 1=2
2
b
wR2 ¼ ½RwðF 2o ꢁ F 2c Þ =RwðF o2Þ ꢃ .w ¼ 1=½r2ðF o2Þ þ ðapÞ þ ðbpÞꢃ, p ¼ ½maxðF o2 or 0Þ þ 2ðF 2c Þꢃ=3. a = 0.0369, b = 1.4931, 1; a = 0.1022, b = 5.5102,
2a; a = 0.0315, b = 26.2974, 2b; a = 0.0566, b = 5.0489, 3.
c
2
1=2
Quality-of-fit ¼ ½RwðjF 2oj ꢁ jF 2c jÞ =Nobserved ꢁ ꢁNparametersÞꢃ
.

50
Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
Fig. 1. ORTEP drawing for complex 1. Thermal ellipsoids shown at 20% probability level.
Found: C, 58.97; H, 5.10; N, 8.99%. IR (KBr disk):
2938(w), 2834(w), 2360(w), 1648(w), 1599(s), 1583(s),
1538(s), 1482(s), 1326(m), 1282(m), 1258(m), 1195(m),
1151(s), 1085(w), 1040(m), 984(w), 940(w), 850(m),
772(m), 695(m), 633(w), 510(w), 449(w). Crystals suitable
for X-ray crystallography were obtained by diffusion of
CH3OH into a CH2Cl2 solution of the yellow product.
(t, 4H, Hmeta), 6.58 (d, 4H, Hpara), 6.21 (s, 4H, Hortho), 6.15
(d, 4H, Hortho), 3.52 (s, 12H, OCH3), 1.98 (s, 12H, CH3).
13C{1H} NMR (CDCl3, ppm): 161.00 (C), 160.58 (CH),
148.04 (C), 130.34 (CH), 114.64 (CH), 114.02 (C), 111.85
(CH), 107.88 (CH), 55.16 (CH3), 3.76 (CH3). Calc. for
C38H42B2F8Mo2N8O4 (MW = 1040.29): C, 43.87; H, 4.07;
N, 10.77%; Found: C, 43.49; H, 4.25; N, 11.02%. IR (KBr
disk): 2939(w), 2838(w), 1687(s), 1594(s), 1532(m),
1492(m), 1464(m), 1435(w), 1384(w), 1330 (m), 1285(m),
1264(m), 1196(w), 1155(s), 1117(s), 1085(s), 1037(s),
936(w), 846(w), 771(m), 686(w), 533(w), 522(w), 457(w).
Crystals of 2a suitable for X-ray crystallography were
obtained by diffusion of diethyl ether into a CH2Cl2 solution
2.4. Preparation of cis-[Mo2(DmAniF)2(CH3CN)4]
[BF4]2 (2)
Mo2(DmAniF)4 (0.25 g, 0.20 mmol) and Me3OBF4
(0.18 g, 1.20 mmol) were placed in a flask containing
10 mL CH3CN. The mixture was stirred for 5 h to yield a
red solution and 20 mL diethyl ether was then added to give
a red solid. The solid was filtered, washed by diethyl ether
and then dried under reduced pressure to give the red prod-
uct. Yield: 0.16 g (78%). UV–vis: 475 nm (CH2Cl2, e = 1196
Table 3
˚
Selected bond distances (A) and angles (°) for 2a
Bond distances
ꢁ1cmꢁ1). 1H NMR (CDCl3, ppm): 8.81 (s, 2H, CH), 6.98
Mo(1)–Mo(2)
Mo(1)–N(3)
Mo(1)–N(6)
Mo(2)–N(4)
Mo(2)–N(8)
2.1286(6)
2.099(5)
2.177(5)
2.123(4)
2.178(5)
Mo(1)–N(1)
Mo(1)–N(5)
Mo(2)–N(2)
Mo(2)–N(7)
Mo(2)ꢀ ꢀ ꢀF(1A)
2.100(4)
2.174(5)
2.117(4)
2.173(5)
2.685(4)
M
Table 2
˚
Selected bond distances A and Angles ° for 1
Bond angles
Bond distances
N(3)–Mo(1)–N(1)
N(1)–Mo(1)–Mo(2)
N(1)–Mo(1)–N(5)
N(3)–Mo(1)–N(6)
Mo(2)–Mo(1)–N(6)
N(2)–Mo(2)–N(4)
N(4)–Mo(2)–Mo(1)
N(4)–Mo(2)–N(7)
N(2)–Mo(2)–N(8)
Mo(1)–Mo(2)–N(8)
95.29(18)
92.68(11)
163.20(17)
160.09(17)
105.41(12)
96.05(18)
91.47(11)
90.08(18)
88.61(18)
101.82(12)
N(3)–Mo(1)–Mo(2)
N(3)–Mo(1)–N(5)
Mo(2)–Mo(1)–N(5)
N(1)–Mo(1)–N(6)
N(5)–Mo(1)–N(6)
N(2)–Mo(2)–Mo(1)
N(2)–Mo(2)–N(7)
Mo(1)–Mo(2)–N(7)
N(4)–Mo(2)–N(8)
N(7)–Mo(2)–N(8)
92.78(11)
88.66(19)
103.45(12)
91.95(19)
79.40(19)
91.54(11)
166.07 (17)
100.82(12)
165.82(17)
82.63(19)
Mo–Mo(A)
Mo–N(4A)
Mo–N(3)
2.1023(3)
2.1644(18)
2.1671(18)
Mo–N(2A)
Mo–N(1)
O(1)–C(15)
2.1570(18)
2.1650(18)
1.365(3)
Bond angles
Mo(A)–Mo–N(2A)
N(2A)–Mo–N(4A)
N(2A)–Mo–N(1)
Mo(A)–Mo–N(3)
N(4A)–Mo–N(3)
92.61(5)
91.09(7)
174.66(7)
93.18(5)
174.42(7)
Mo(A)–Mo–N(4A)
Mo(A)–Mo–N(1)
N(4A)–Mo–N(1)
N(2A)–Mo–N(3)
N(1)–Mo–N(3)
92.40(5)
92.72(5)
89.06(7)
88.27(7)
91.06(7)
Symmetry transformations used to generate equivalent atoms: (A) ꢁx + 2,
ꢁy + 1, ꢁz.
Symmetry transformations used to generate equivalent atoms: (A) x ꢁ 1,
y, z.

Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
51
Table 4
2.5. Preparations of cis-[Mo2(DmAniF)2]2(l-OCH3)4 (3)
˚
Selected bond distances (A) and angles (°) for 2b
Bond distances
Method A: cis-[Mo2(DmAniF)2(CH3CN)4][BF4]2 (0.42 g,
0.40 mmol) and NaOCH3 (0.18 g, 1.00 mmol) were placed
in a flask containing 40 mL CH3OH. The mixture was stirred
for 3 h to yield a red solution and then 60 mL diethyl ether
was added to give a red solid. The solid was filtered, washed
with methanol and diethyl ether and then dried under
reduced pressure to give a brown product. The brown prod-
uct in 20 mL CH2Cl2 was passed through a Celite-packed
frit, and then 80 mL CH3OH was added to give a red solid.
The solid was filtered, washed with methanol and diethyl
ether and then dried under reduced pressure to give a red
product. Crystals suitable for X-ray crystallography were
obtained by diffusion of CH2Cl2 into a CH3OH solution of
the red product. Yield: 0.26 g (41%). UV–vis: 498 nm
(CH2Cl2). Calc. for Mo4O13N8C65H76 (3ꢀCH3OH,
MW = 1568.17): C, 49.74; H, 4.88; N, 7.18%; Found: C,
49.48; H, 5.03; N, 6.69%.
Method B: HDmAniF (0.11 g, 0.42 mmol) and [Mo2
(CH3CN)10][BF4]4 (0.20 g, 0.21 mmol) was placed in a flask
containing 10 mL CH3CN. The mixture was stirred for 8 h
under N2 to yield a red solution. Then dry red solution and
add 20 ml diethyl ether wash product. The solid was filtered,
washed by diethyl ether and then dried under reduced pres-
sure to give the red product. Crystals suitable for X-ray
crystallography were obtained by diffusion CH2Cl2 into a
CH3OH solution of the red product. Yield: 0.08 g (25%).
Mo(1)–N(3)
Mo(1)–Mo(2)
Mo(1)–N(6)
Mo(2)–N(4)
Mo(2)–N(7)
Mo(3)–N(11)
Mo(3)–N(13)
Mo(4)–N(12)
Mo(4)–N(16)
2.106(5)
2.1432(8) Mo(1)–N(5)
Mo(1)–N(1)
2.113(5)
2.187(6)
2.097(5)
2.178(6)
2.099(5)
2.1317(9)
2.184(6)
2.110(5)
2.190(6)
2.191(6)
2.100(5)
2.184(6)
2.110(5)
2.154(7)
2.103(5)
2.170(6)
Mo(2)–N(2)
Mo(2)–N(8)
Mo(3)–N(9)
Mo(3)–Mo(4)
Mo(3)–N(14)
Mo(4)–N(10)
Mo(4)–N(15)
Bond angles
N(3)–Mo(1)–N(1)
N(1)–Mo(1)–Mo(2)
N(1)–Mo(1)–N(5)
N(3)–Mo(1)–N(6)
Mo(2)–Mo(1)–N(6)
N(2)–Mo(2)–N(4)
N(4)–Mo(2)–Mo(1)
N(4)–Mo(2)–N(8)
N(2)–Mo(2)–N(7)
Mo(1)–Mo(2)–N(7)
N(9)–Mo(3)–N(11)
N(11)–Mo(3)–Mo(4)
N(11)–Mo(3)–N(13)
N(9)–Mo(3)–N(14)
95.3(2)
91.14(14)
89.5(2)
87.9(2)
101.81(16)
95.3(2)
92.08(14)
90.3(2)
85.1(2)
104.79(15)
95.6(2)
92.15(15)
163.8(3)
165.8(3)
N(3)–Mo(1)–Mo(2)
N(3)–Mo(1)–N(5)
Mo(2)–Mo(1)–N(5)
N(1)–Mo(1)–N(6)
N(5)–Mo(1)–N(6)
N(2)–Mo(2)–Mo(1)
N(2)–Mo(2)–N(8)
Mo(1)–Mo(2)–N(8)
N(4)–Mo(2)–N(7)
N(8)–Mo(2)–N(7)
N(9)–Mo(3)–Mo(4)
N(9)–Mo(3)–N(13)
91.81(14)
167.8(2)
99.30(15)
166.6(2)
85.0(2)
92.95(14)
164.0(2)
101.82(16)
163.1(2)
85.3(2)
91.30(16)
86.3(2)
Mo(4)–Mo(3)–N(13) 104.0(2)
N(11)–Mo(3)–N(14)
N(13)–Mo(3)–N(14)
N(12)–Mo(4)–Mo(3)
N(12)–Mo(4)–N(16)
Mo(3)–Mo(4)–N(16) 103.63(18)
N(10)–Mo(4)–N(15)
N(16)–Mo(4)–N(15)
89.1(2)
85.5(2)
91.72(15)
87.4(2)
Mo(4)–Mo(3)–N(14) 101.94(18)
N(12)–Mo(4)–N(10)
N(10)–Mo(4)–Mo(3)
N(10)–Mo(4)–N(16)
N(12)–Mo(4)–N(15)
95.5(2)
92.85(15)
163.2(2)
164.9(2)
90.3(2)
83.1(2)
Mo(3)–Mo(4)–N(15) 101.85(19)
3. X-ray crystallography
of the red product, while crystals of 2b were obtained by dif-
fusion of diethyl ether into a CH2Cl2/CH3CN (CH2Cl2:
CH3CN = 9: 1) solution of the red product.
The diffraction data of 1–3 were collected on a Siemens
CCD or a Bruker AXS diffractometer, which were equipped
Fig. 2. ORTEP drawings of complex 2a. Thermal ellipsoids shown at 20% probability level.

52
Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
Table 5
Structural data of selected dimolybdenum complexes with Mo2(l2-L)2(CH3CN)4
˚
˚
Complex
Mo–Mo (A)
Moꢀ ꢀ ꢀ(ax) (A)
Reference
a
cis- [Mo2(DphF)2(CH3CN)4(ax-CH3CN)][BF4]2
cis-[Mo2(DpAniF)2(CH3CN)4(ax-CH3CN)][BF4]2
trans-[Mo2(H2DMepyF)2(CH3CN)4(ax-CH3CN)2][BF4]6
trans-[Mo2(H2DMepyF)2(CH3CN)4][ax-BF4]2[BF4]4
cis-[Mo2(HDpyF)2(CH3CN)4](BF4)4
cis-[Mo(DmAniF)2(CH3CN)4][ax-BF4][BF4] (2a)
cis-[Mo(DmAniF)2(CH3CN)4][BF4]2 (2b)
2.1457(7)
2.1439(6)
2.1504(6)
2.1321(6)
2.1348(8)
2.1286(6)
2.1317(9)
2.1432(8)
2.595(3)
2.590(4)
2.635(5)
2.592(2)
–
2.685(4)
–
2.692(8)
[4a]
[4b]
[13]
[13]
b
c
c
d
[14]
This work
This work
This work
cis-[Mo(DmAniF)2(CH3CN)4(ax-CH3CN)][BF4]2 (2b)
a
phFꢁ = N,N0-diphenylformamidine anion.
b
DpAniFꢁ = N,N0-di(4-methoxyphenyl)formamidine anion.
H2DMepyF+ = N,N0-di(6-methyl-2-pyridyl)formamidine cation.
HDpyF = N,N0-di (2-pyridyl)formamidine.
c
d
˚
with a graphite-monochromated MoKa (ka = 0.71073 A)
radiation. Data reduction was carried by standard methods
with use of well-established computational procedures [9].
A red crystal of 1 was mounted on the top of a glass fiber with
epoxy cement. Hemisphere data collection method was used
to scan the data points at 4.92 < 2h < 50.02°. The structure
factors were obtained after Lorentz and polarization correc-
tions. The positions of some of the heavier atoms were
located by direct methods. The remaining atoms were found
from a series of alternating difference Fourier maps and
least-square refinements. The final residuals of the refine-
ment were R1 = 0.0278 and wR2 = 0.0749. The X-ray crys-
tallographic procedures for 2 and 3 were similar to those
for 1. Basic information pertaining to crystal parameters
and structure refinement is summarized in Table 1.
4. Results and discussion
4.1. Syntheses
The yellow complex Mo2(DmAniF)4, 1, was prepared
by reaction of Mo(CO)6 with excess HDmAniF in o-
dichlorobenzene, whereas the reaction of 1 with excess
Me3OBF4 in CH3CN afforded cis-[Mo2(DmAniF)2
(CH3CN)4](BF4)2, 2. Reaction of 2 with NaOCH3 in
CH3OH produced the tetranuclear complex cis-
[Mo2(DmAniF)2]2(l-OCH3)4, 3, which can also be pre-
pared by reacting m-HDMophF with [Mo2(CH3CN)10]
[BF4]4 in CH3CN.
4.2. Structures of 1
Yellow crystals of 1 conform to the space group P21/n
with two molecules in a unit cell. Fig. 1 shows the ORTEP
diagram for 1. Selected bond distances and angles are listed
in Table 2. The molecular structure of 1 consists of two
˚
molybdenum atoms [Mo–Mo = 2.1023(3) A] which are
spanned by four DmAniFꢁ ligands. Its structure reveals
that the four ligands bridge the two metal centers through
the two nitrogen atoms, resulting in the s-cis, s-trans and s-
trans, s-trans conformations. The ligands of complex 1 are
not flat, but twisted around the C–N bonds, with dihedral
angles (between the planes of the two anisole rings) of 35.8°
for the ligands with s-cis, s-trans conformation and 42.3°
for those with s-trans, s-trans conformation.
Fig. 3. ORTEP drawings of the two independent molecules of complex
2b. The top molecule shows axial Moꢀ ꢀ ꢀN interaction through CH3CN
molecule. Thermal ellipsoids shown at 20% probability level.

Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
53
Fig. 4. ORTEP drawing for complex 3 (top) and its core structure (bottom). Thermal ellipsoids shown at 20% probability level.
Three other dinuclear paddlewheel complexes contain-
ing four DmAniFꢁ ligands have been reported, which are
Rh2(DmAniF)4 [10], Cr2(DmAniF)4 [11] and W2(DmA-
niF)4 [12]. An investigation into the ligand conformations
of these complexes shows that all the four ligands of the
Rh complex adopt the s-trans, s-trans conformation, while
those in the Cr and W complexes adopt, similar to complex
1, the s-cis, s-trans and s-trans, s-trans conformations. It is
also noted that while the isomeric complex Mo2(DpAniF)4
(DoAniF)Cl2(PMe3)2 [5g] and the mixed ligand complexes
[5h] trans-Mo2(O2CCH3)(DpyF)(DoAniF)2, trans-Mo2
(O2CCH3)(DpmF)(DoAniF)2, trans-Mo2(O2CCH3)(DMe-
pyF) (DoAniF)2, trans-Mo2(O2CCH3)(DMepyF)2(DoA-
niF), and trans-Mo2(DMepyF)2(DoAniF)2 have been
structurally characterized.
4.3. Structures of 2
˚
[2b] [Mo–Mo = 2.0964 (5) A] has been structurally charac-
The red complex 2 crystallized in two different forms,
2ꢀCH2Cl2ꢀCH3CN, 2a, and 2ꢀ0.5CH2Cl2ꢀ0.5CH3CN, 2b,
and both conform to the space group Pıꢀ. Figs. 2 and 3
shows the ORTEP diagrams for the complexes 2a, and
2b, respectively, and Tables 3 and 4 list the selected bond
terized, the other isomeric complex Mo2(DoAniF)4 has not
been reported, although several dimolybdenum complexes
of the types Mo2(O2CCH3)3(DoAniF), trans-Mo2(O2CR)2
(DoAniF)2 (R@CH3, CF3, and Prn) and Mo2(O2CCH3)

54
Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
distances and angles for complexes 2a and 2b, respectively.
The two dimolybdenum centers of both 2a and 2b are coor-
dinated by two cis DmAniFꢁ ligands and four CH3CN
ligands. The Mo–Mo distances in 2a is 2.1281(6) which is
normal for dinuclear complexes with Mo–Mo quadruple
bonds. It is also seen that while one of the two BFꢁ4 anions
coordinates to the Mo–Mo axial site through the fluoride
4.4. Structure of 3
Red crystals of 3 conform to the space group Pıꢀwith one
molecule in a unit cell. Fig. 4 shows the ORTEP drawing
for 3 (top) and its core structure (bottom) and Table 6 lists
the selected bond distances and angles. The molecule bears
four bridging CH3Oꢁ that link two quadruply bonded moi-
eties which are also bridged by two cis DmAniFꢁ ligands.
ꢁ
˚
atom [Moꢀ ꢀ ꢀF = 2.685 (4) A], the other BF4 anion inter-
acts with the cation through C–Hꢀ ꢀ ꢀF hydrogen bonds
˚
The Mo–Mo distance of 2.1185(10) A is consistent with the
(Hꢀ ꢀ ꢀF = 2.452 A; \ C–Hꢀ ꢀ ꢀF = 147.9°). The two cis
presence of a quadruply bonded Mo42þ unit. The long
˚
DmAniFꢁ ligands adopt the s-cis, s-trans conformation
and each twists around the C–N bonds, with a dihedral
angle between the planes of the two anisole rings of 72.2
and 98.9°, respectively.
Moꢀ ꢀ ꢀMo distances are 3.2463(8) A, which is well outside
˚
of bonding range. The Mo–O distances are in the range
˚
from 2.128(4) to 2.139(4) A and the Mo–O–Mo angles
are 99.08 (16) and 99.38 (17)°. The two DmAniFꢁ ligands
which adopt the same s-trans, s-trans conformation are not
flat, but twisted around the C–N bonds, with dihedral
angles of 10.7 and 22.1°, respectively.
Complex 2b contains two independent molecules as
˚
shown in Fig. 3. The top molecule [Mo–Mo = 2.1432(8) A]
in Fig. 3 shows axial interaction by CH3CN [Moꢀ ꢀ ꢀN =
ꢁ
˚
2.692 (8) A] and the two cis DmAniF ligands adopt the
same s-cis, s-trans conformation, while the bottom one
Complex 3 makes interesting comparisons with the sim-
ilar complexes of the type [Mo2(NN)2]2(l-X)4 (NN@N,N0-
di(4-methoxyphenyl) formamidine anion, X@Cl, I, OCH3,
OC2H5; NN@N,N0-di(4-methylphenyl)formamidine anion,
X@Cl; NN@N,N0-di(4-fluorophenyl)formamidine anion,
X@Cl), and ½Mo2I2ðPBun3Þ2ꢃ2ðl ꢁ IÞ4, where the two dimo-
lybdenum units are linked by the halide atoms or alkoxide
groups, as shown in Chart 1 [15,16]. Table 7 lists some
selected structural data for these complexes. It is seen that
while the long Moꢀ ꢀ ꢀMo distances of these complexes are
sensitive to the natures of the bridging ligands, those of
the short quadruple-bonded Mo–Mo distances fall in the
small range 2.117(1)–2.1317(7). Although the Moꢀ ꢀ ꢀMo
and Mo–O distances and Mo–O–Mo angles of 3 and
[Mo2(DpAniF)2]2(l-OMe)4 are about the same, the Mo–
Mo distance of 3 is significantly shorter than that of
[Mo2(DpAniF)2]2(l-OMe)4. Also noted is that those
bridged by the halide atoms show longer Moꢀ ꢀ ꢀMo non-
bonded distances, presumably due to the larger atomic
sizes of the halide atoms.
˚
[Mo–Mo = 2.1317(9) A] shows no axial interaction and
the two cis DmAniFꢁ ligands adopt different conforma-
tions, which are s-cis, s-trans and s-cis, s-cis, respectively.
The dihedral angles between the planes of the two anisole
rings of the two bidentate cis DmAniFꢁ ligands are 84.8
and 87.8° for the top molecule and 89.1 and 88.5° for the
bottom one, respectively.
Table 5 lists the structural data for dimolybdenum com-
plexes with Mo2(l2-L)2(CH3CN)4 core, where L is the
anionic, cationic or neutral form of a formamidine ligand.
˚
It is seen that the Mo–Mo distance of 2a, 2.1286(6) A, is
the shortest among the compounds having Mo2(l2-
L)2(CH3CN)4 core. In the two independent molecules of
2b, the one with axial interaction through CH3CN mole-
cule shows longer Mo–Mo distance than the one with no
axial interaction.
Table 6
˚
Selected Bond Distances (A) and Angles (°) for 3
Bond distances
4.5. Magnetic anisotropy
Mo(1)–N(1)
Mo(1)–O(6)
Mo(1)–O(5)
Mo(2)–O(5A)
Mo(2)–N(2)
O(6)–Mo(2A)
2.107(5) Mo(1)–Mo(2)
2.129(4) Mo(1)–N(3)
2.139(4) Mo(2)–N(4)
2.128(4) Mo(2)–O(6A)
2.137(5) O(5)–Mo(2A)
2.128(4)
2.1185(10)
2.130(5)
2.109(5)
2.128(4)
2.128(4)
It has been shown that the chemical shifts of the protons
in the vicinity of the dimolybdenum core are sensitive to
the magnetic anisotropy (Dv) from the metal–metal multi-
ple bond and Dv can be estimated on the basis of the d of
methine proton (–NCHN–) of the formamidinate group
according to the following equation [2]:
Bond angles
N(1)–Mo(1)–Mo(2)
Mo(2)–Mo(1)–O(6)
Mo(2)–Mo(1)–N(3)
N(1)–Mo(1)–O(5)
O(6)–Mo(1)–O(5)
N(4)–Mo(2)–Mo(1)
92.84(16) N(1)–Mo(1)–O(6)
105.14(13) N(1)–Mo(1)–N(3)
92.06(17) O(6)–Mo(1)–N(3)
92.99(18) Mo(2)–Mo(1)–O(5)
73.24(15) N(3)–Mo(1)–O(5)
92.76(17) N(4)–Mo(2)–O(5A)
159.38(19)
93.7(2)
95.61(18)
103.69(12)
162.5(2)
92.96(18)
159.4(2)
73.47(16)
91.89(16)
94.64(18)
122.9(4)
X
X
X
X
N
N
N
N
Mo
Mo
Mo
Mo
Mo(1)–Mo(2)–O(5A) 103.97(12) N(4)–Mo(2)–O(6A)
Mo(1)–Mo(2)–O(6A) 105.35(13) O(5A)–Mo(2)–O(6A)
N
N
N
N
N(4)–Mo(2)–N(2)
O(5A)–Mo(2)–N(2)
C(3)–O(5)–Mo(2A)
Mo(2A)–O(5)–Mo(1)
C(4)–O(6)–Mo(1)
94.5(2)
162.1(2)
127.3(4)
Mo(1)–Mo(2)–N(2)
O(6A)–Mo(2)–N(2)
C(3)–O(5)–Mo(1)
N
N = anion of diarylformamidine
X = Cl, I, OMe, OEt
99.08(16) C(4)–O(6)–Mo(2A)
128.9(5) Mo(2A)–O(6)–Mo(1)
128.9(5)
99.38(17)
Chart 1. The structure of the [Mo2(NN)2]2(l-X)4 core.

Y.-Y. Wu et al. / Journal of Molecular Structure 890 (2008) 48–56
55
Table 7
Selected bond distances (A) and angles (°) for some [Mo2(NN)2]2(l- X)4 complexes and ½Mo2I2ðPBun3Þ ꢃ ðl ꢁ IÞ
˚
2
2
4
Complex
Mo–Mo
Moꢀ ꢀ ꢀMo
Mo–X
Mo–X–Mo
Ref.
a
[Mo2(DpAniF)2]2(l-Cl)4
2.1191(4)
2.118(1)
2.123(1)
2.117(1)
2.129[3]
2.1315(7)
2.1317(7)
2.1185(10)
3.602(1)
3.592(1)
3.563(1)
3.915(1)
3.998[3]
3.245
2.516[2]d
2.513[1]
2.510[2]
2.845[2]
2.794[2]
2.142[4]
2.136[2]
2.131[4]
91.42[5]
91.25[5]
90.44[5]
87.02[2]
90.57[5]
98.55[16]
98.67[9]
99.23[17]
[15]
[15]
[15]
[15]
[15]
[16]
[16]
b
[Mo2(DTolF)2]2(l-Cl)4
c
[Mo2(DPhfF)2]2(l-Cl)4
[Mo2(DpAniF)2]2(l-I)4
½Mo2I2ðPBun3Þ2ꢃ2ðl ꢁ IÞ4
[Mo2(DpAniF)2]2(l-OMe)4
[Mo2(DpAniF)2]2(l-OEt)4
3
3.241
3.2463(8)
This work
a
DpAniF = N,N0-di(4-methoxyphenyl)formamidine anion.
DTolF = N,N0-di(4-methylphenyl)formamidine anion.
DPhfF = N,N0-di(4-fluorophenyl)formamidine anion.
b
c
d
Brackets in standard errors indicate that the value given has been averaged.
Dv ¼ 12pr3Dd=ð1 ꢁ 3cos2hÞ
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].
where Dd is the change of the chemical shift due to the mag-
netic anisotropy which is best referenced to the dinickel ana-
logs Ni2(form)4, r is the calculated distance of the methine
proton from the center of the Mo–Mo bond and h is the angle
between the rvectorandtheMo–Movector.Accordingtothis
Acknowledgement
equation, the Dv of complex
1
is calculated as
We wish to thank the National Science Council of the
Republic of China for support.
4920 17 ꢂ 10ꢁ34 m3/molecule. The magnetic anisotropy
can also be calculated using the equation related to the Ham-
mett constant r: Dv = 5000 ꢂ 10ꢁ34 m3/molecule-8rq [12],
where q is the reaction constant and for complexes of the type
Mo2(formamidine)4, its value is 38.991 ꢂ 10ꢁ34 m3/molecule.
Substituting the Hammett constant which is 0.12 for the m-
DMophFꢁ ligand, the Dv of complex 1 is calculated as
4963 ꢂ 10ꢁ34 m3/molecule. These two values, 4920 17
ꢂ 10ꢁ34 m3/molecule and 4963 ꢂ 10ꢁ34 m3/molecule, are
similar to the one, 5040 ꢂ 10ꢁ34 m3/molecule reported by
Ren and coauthors [2b].
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niF)2(CH3CN)4][BF4]2, 2, and a tetranuclear complex cis-
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