Binuclear (salen)osmium phosphinidine and phosphiniminato complexes

Article abstract of DOI:10.1039/c0dt01367f

The preparation of a number of binuclear (salen)osmium phosphinidine and phosphiniminato complexes using various strategies are described. Treatment of [Os^VI(N)(L¹)(sol)](X) (sol = H₂O or MeOH) with PPh₃ affords an osmium(iv) phosphinidine complex [Os ^IV{N(H)PPh₃}(L¹)(OMe)](X) (X = PF ₆1a, ClO₄1b). If the reaction is carried out in CH ₂Cl₂ in the presence of excess pyrazine the osmium(iii) phosphinidine species [Os^III{N(H)PPh₃}(L ¹)(pz)](PF₆) 2 can be generated. On the other hand, if the reaction is carried out in CH₂Cl₂ in the presence of a small amount of H₂O, a μ-oxo osmium(iv) phosphinidine complex is obtained, [(L¹){PPh₃N(H)}Os^IV-O-Os ^IV{N(H)PPh₃}(L¹)](PF₆)₂3. Furthermore, if the reaction of [Os^VI(N)(L¹)(OH ₂)]PF₆ with PPh₃ is done in the presence of 2, the μ-pyrazine species, [(L¹){PPh₃N(H)}Os ^III-pz-Os^III{N(H)PPh₃}(L¹)](PF ₆)₂4 can be isolated. Novel binuclear osmium(iv) complexes can be prepared by the use of a diphosphine ligand to attack two Os ^VIN. Reaction of [Os^VI(N)(L¹)(OH ₂)](PF₆) with PPh₂-CC-PPh₂ or PPh₂-(CH₂)₃-PPh₂ in MeOH affords the binuclear complexes [(MeO)(L¹)Os^IV{N(H)PPh ₂-R-PPh₂N(H)}Os^IV(L¹)(OMe)](PF ₆)₂ (R = CC 5, (CH₂)₃6). Reaction of [Os^VI(N)(L²)Cl] with PPh₂FcPPh₂ generates a novel trimetallic complex, [Cl(L²)Os ^IV{NPPh₂-Fc-PPh₂N}Os^IV(L ²)Cl] 7. The structures of 1b, 2, 3, 4, 5 and 7 have been determined by X-ray crystallography. The Royal Society of Chemistry 2011.

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PAPER
Binuclear (salen)osmium phosphinidine and phosphiniminato complexes†
Gui Chen,a Wai-Lun Man,a Shek-Man Yiu,a Tsz-Wing Wong,a Lap Szeto,b Wing-Tak Wongb and
Tai-Chu Lau*a
Received 11th October 2010, Accepted 30th November 2010
DOI: 10.1039/c0dt01367f
The preparation of a number of binuclear (salen)osmium phosphinidine and phosphiniminato
complexes using various strategies are described. Treatment of [OsVI(N)(L1)(sol)](X) (sol = H2O or
MeOH) with PPh3 affords an osmium(IV) phosphinidine complex [OsIV{N(H)PPh3}(L1)(OMe)](X)
(X = PF6 1a, ClO4 1b). If the reaction is carried out in CH2Cl2 in the presence of excess pyrazine the
osmium(III) phosphinidine species [OsIII{N(H)PPh3}(L1)(pz)](PF6) 2 can be generated. On the other
hand, if the reaction is carried out in CH2Cl2 in the presence of a small amount of H2O, a m-oxo
osmium(IV) phosphinidine complex is obtained, [(L1){PPh3N(H)}OsIV–O–OsIV{N(H)PPh3}(L1)](PF6)2
3. Furthermore, if the reaction of [OsVI(N)(L1)(OH2)]PF6 with PPh3 is done in the presence of 2, the
m-pyrazine species, [(L1){PPh3N(H)}OsIII–pz–OsIII{N(H)PPh3}(L1)](PF6)2 4 can be isolated. Novel
binuclear osmium(IV) complexes can be prepared by the use of a diphosphine ligand to attack two
OsVI N. Reaction of [OsVI(N)(L1)(OH2)](PF6) with PPh2–C C–PPh2 or PPh2–(CH2)3–PPh2 in MeOH
affords the binuclear complexes [(MeO)(L1)OsIV{N(H)PPh2–R–PPh2N(H)}OsIV(L1)(OMe)](PF6)2 (R =
C
C 5, (CH2)3 6). Reaction of [OsVI(N)(L2)Cl] with PPh2FcPPh2 generates a novel trimetallic complex,
[Cl(L2)OsIV{NPPh2–Fc–PPh2N}OsIV(L2)Cl] 7. The structures of 1b, 2, 3, 4, 5 and 7 have been
determined by X-ray crystallography.
osmium complexes are limited to Os(II/III) m-N2 and m-pyrazine
Introduction
species,11 together with a number of Os(IV/V) m-oxo and m-nitrido
complexes.12 The synthesis of the various binuclear (salen)osmium
complexes are depicted in Scheme 1.
Binuclear complexes, such as the classical Creutz-Taube ion,
[(NH3)5RuIII–pz–RuII(NH3)5]5+, (pz = pyrazine),1–2 that consist of
two transition metal centers linked by a bridging ligand have
been of significant interest as models for studying electronic
communication between metal centers and electron transfer in
chemical and biological processes during the last few decades.3–4
They have potential applications in material science such as optical
materials,5 conductors6 and molecular wires.7 Binuclear com-
plexes may also show higher catalytic activity than mononuclear
complexes.8 Anticancer properties of some bimetallic complexes
have also been studied.9 In this paper, we make use of the well-
known nucleophilic addition of PPh3 to electrophilic OsVI N in
the presence of a bridging ligand to generate OsIV–O–OsIV or OsIII–
pz–OsIII species.10 We also make use of a diphosphine to attack two
OsVI N centers to generate novel binuclear diphosphinidine- and
diphosphiniminato-bridged (salen)osmium(IV) species. Binuclear
Results and discussion
Synthesis and characterization of phosphinidine complexes of
(salen)osmium(IV)/(III)
Treatment of [OsVI(N)(L1)(sol)](X) (sol = H2O or MeOH and
-
-
X = PF6 or ClO4 ) with one equiv. of PPh3 in methanol affords
the corresponding (salen)osmium(IV) phosphinidine complex,
[OsIV{N(H)PPh3}(L1)(OMe)]+, (X = PF6 1a; ClO4 1b) in high
yields. 1a is diamagnetic, as evidenced by the presence of sharp
peaks in normal regions in the 1H NMR spectrum (Fig. S1, ESI†).
The two imine protons occur as two singlets at 8.15 and 7.83 ppm.
The singlet N–H is located at 14.3 ppm. For (salen)ruthenium(IV)
hydrazido complex, the N–H resonance occurs at 13.3 ppm.13
The IR of 1a shows a weak n(N–H) stretch at 3229 cm-1. The
ESI mass spectrum of 1a (Fig. S2) exhibits a single peak at m/z
820 [M]+. There is no peak arising from loss of MeOH, which
supports the presence of a methoxy ligand rather than a neutral
methanol molecule in the complex. The cyclic voltammogram
(CV) (Fig. S3) of 1a in CH3CN displays two reversible couples
(DEp = 60 mV) (E1/2 = -0.84 and -2.02 V vs. Cp2Fe+/0), which are
assigned to OsIV/III and OsIII/II couples, respectively. There is also an
-
-
aInstitute of Molecular Functional Materials and Department of Biology and
Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong,
Hong Kong, PRC. E-mail: bhtclau@cityu.edu.hk; Fax: (+852)27887406;
Tel: (+852)34427811
bDepartment of Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, PRC
† Electronic supplementary information (ESI) available: Spectra of 1H
NMR of 1a, ESI-MS of 1–6 and CV of 1a, 5 and 6. CCDC reference num-
bers 793797–793802 for 1b, 2, 3, 4, 5 and 7. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c0dt01367f
1938 | Dalton Trans., 2011, 40, 1938–1944
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If the reaction of [OsVI(N)(L1)(sol)]+ with PPh3 was carried out in
the presence of excess pyrazine, [OsIII{N(H)PPh3}(L1)(pz)]+ could
-
be isolated as the PF6 salt in moderate yield (2). 2 has a room
temperature magnetic moment (solid sample, Gouy method) of
meff = 1.92 mB, consistent with its formulation as an osmium(III)
complex.
The IR spectrum shows a weak n(N–H) stretch at 3291 cm-1.
The ESI mass spectrum (Fig. S4) displays a predominant peak
at m/z 869 [M]+. The CV of 2 exhibits two reversible couples
(DEp = 67 mV) at 0 and -1.13 V (vs. Cp2Fe+/0), which are assigned
to OsIV/III and OsIII/II couples, respectively (Fig. 1). Notably there
is a rather large anodic shift of ca. 0.8 V for the E1/2 of both
OsIV/III and OsIII/II couples on replacing the methoxy ligand in 1
with pyrazine. This is probably due to a combination of charge
effects and stabilization of Os(III) and Os(II) by p-back-bonding
with pyrazine. The formation of 2 probably goes through the
intermediate [OsIV(NPPh3)(L1)(pz)]+, which then gains a H+ and
is reduced to the product, presumably by methanol and pyrazine.
Scheme 1 Synthesis of various binuclear (salen)osmium complexes.
irreversible wave (Epa = +0.77 V vs. Cp2Fe+/0) which is attributed
to OsV/IV couple. Other OsVI N complexes are known to react
with PPh3 to give the deprotonated phosphiniminato complexes,
OsIV–NPPh3.14 In this case the protonated phosphinidine complex
is the stable product, presumably the ligand is more basic as a
result of the stronger electron donating properties of salen.
Fig. 1 CV of 2 in CH3CN.
The molecular structures of 1b and 2 have been determined by
X-ray crystallography and their cations are depicted in Fig. 2. The
crystal data are summarized in Table 1. Selected bond distances
Table 1 Crystal data and structure refinement details for compounds 1b·H2O, 2, 3·1.5CH2Cl2, 4·1.75CH2Cl2·0.25H2O, 5·2.5CH3CN and 7
4·1.75CH2Cl2·
1b·H2O
2
3·1.5CH2Cl2
0.25H2O
5·2.5CH3CN
7
Formula
C39H41ClN3O8OsP C42H40F6N5O2OsP2 C77.5H75Cl3F12-
N6O5Os2P4
C81.75H80Cl3.5F12- C73H75.5F12N8.5
-
C74H56Cl2FeN6-
O4Os2P2
1662.34
N8O4.25Os2P4
2098.89
113(2)
Monoclinic
P21/c
O6Os2P4
1900.2
293(2)
Monoclinic
P21/c
Mr
T/K
Crystal system
936.37
298(2)
Triclinic
¯
P1
1012.93
173(2)
Monoclinic
2009.06
133(2)
Triclinic
¯
P1
298(2)
Triclinic
¯
Space group
P21/c
P1
˚
a/A
12.798(2)
13.354(2)
13.476(2)
74.497(3)
63.096(2)
69.015(3)
1902.1(6)
2
11.4181(2)
19.5201(4)
18.4402(4)
90
104.891(2)
90
3971.98(14)
4
1.694
14.2178(3)
14.9520(3)
20.6258(5)
69.1705(19)
84.0361(17)
68.1080(18)
3800.56(14)
2
21.63349(15)
23.90315(17)
15.89060(13)
90.00
90.6675(8)
90.00
19.3433(4)
16.2405(3)
25.7370(5)
90
105.477(2)
90
11.698(4)
12.230(4)
13.216(4)
85.212(6)
69.354(5)
64.352(5)
1589.7(9)
1
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
3
˚
V/A
8216.61(11)
4
1.697
7792.0(3)
4
1.620
Z
rc/Mg m-3
F(000)
1.635
1.756
1.736
816
9882
5546
936
11671
2012
14759
1986
24719
4160
59907
3764
85318
Collected refl.
Unique refl.
R(int)
6676
0.0415
5223
0.0303
10683
0.0574
12153
0.0319
8641
0.0679
0.0287
Final R indices, I > 2s(I) Ra R1(obs) = 0.0357,
wR(all) = 0.0837
R1(obs) = 0.0277,
wR(all) = 0.0631
0.953
R1(obs) = 0.0455, R1(obs) = 0.0362, R1(obs) = 0.0353, R1(obs) = 0.0367,
wR(all) = 0.1215 wR(all) = 0.0889 wR(all) = 0.0696 wR(all) = 0.0836
GOF
No. of parameter
0.978
506
0.968
985
1.081
1103
0.970
965
0.968
413
507
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◦
˚
˚
Table 2 Selected bond distances (A) and angles ( ) of 1b and 2
Table 3 Selected bond distances (A) and angles ( ) of 3
1b
2
Os(1)–O(5)
Os(2)–O(5)
Os(1)–N(5)
Os(2)–N(6)
N(5)–P(1)
N(6)–P(2)
Os(1)–O(5)–Os(2)
Os(1)–N(5)–P(1)
Os(2)–N(6)–P(2)
1.820(4)
1.828(4)
2.034(5)
2.047(5)
1.614(5)
1.627(5)
178.1(2)
129.6(3)
127.6(3)
N(3)–P(1)
Os(1)–N(3)
Os(1)–N(1)
Os(1)–N(2)
Os(1)–O(1)
Os(1)–O(2)
Os(1)–O(3)/N(4)
Os(1)–N(3)–P(1)
N(3)–Os(1)–O(3)/N(4)
1.630(3)
2.026(3)
2.006(3)
1.999(4)
1.995(3)
2.005(3)
2.066(3)
135.0(2)
177.87(15)
1.606(3)
2.045(3)
1.989(3)
1.987(3)
2.041(3)
2.016(3)
2.079(3)
132.79(19)
176.87(13)
Fig. 3 CV of 3 in CH3CN.
Fig. 2 Molecular structures of cation of 1b (left) and 2 (right) with partial
atomic labeling. Thermal ellipsoids are drawn at 30% probability. H atoms
(except N(3)–H) are omitted for clarity.
OsIV,IV/IV,III and OsIV,III/III,III, respectively. The separation of the latter
two couples (DE1/2) is 0.91 V, which gives a comproportionation
constant (Kcom) of 2.65 ¥ 1015 according to eqn (1)–(2). The large
Kcom suggests that OsIV–O–OsIII is a Class III delocalized mixed-
valence species. This is comparable to the m-N2 Class III mixed-
valence complex, [(NH3)5Os(N2)Os(NH3)5]5+ (Kcom = 7 ¥ 1012 in
H2O).15
and angles are collected in Table 2. Both complexes adopt a
similar distorted octahedral geometry. The osmium centers lie
in the plane of the salen ligand, with the phosphinidine ligand
occupying one of the axial positions. The other axial position
is occupied by a methoxy group in 1b or a pyrazine in 2. The
OsIII–OsIII + OsII–OsII → 2OsIII–OsII
(1)
˚
Os–N(phosphinidine) distances (2.026(3) A in 1b and 2.045(3)
log Kcom = DE1/2/0.059
(2)
˚
A in 2) are much longer than that of the phosphiniminato
IV
2
14
˚
complex [Os (NPPh3)(L )Cl] (1.92(1) A), indicating of neutral
phosphinidine ligands. The acute Os–N–P angles of 135.0(2)◦ in
1b and 132.79(19)◦ in 2 indicate that there is no multiple bond
character in Os–N(phosphinidine). On the other hand, the similar
The molecular structure of 3 has been determined by X-ray
crystallography and the cation is shown in Fig. 4. The crystal data
are summarized in Table 1. Selected bond distances and angles
are found in Table 3. Both osmium centers adopt a distorted
octahedral geometry, surrounded by a planar salen ligand and
one phosphinidine ligand. The two osmium centers are linked by
an oxo ligand with short Os–O bonds of 1.820(4) and 1.828(4)
˚
Os–O(methoxy) distance (2.066(3) A) to the Os–O(phenoxy)
˚
distances (av. 2.000(3) A) is consistent with its formulation as
a methoxy anion in 1b.
˚
A. This Os–O bond distance is comparable to that of another m-
oxo osmium(IV) complex [(Cp*)2Os2(m-O)]4+ (1.8157(9) A) (Cp* =
˚
Oxo-bridged (salen)osmium(IV) phosphinidine complex
pentamethyl-cyclopentadienyl).16
The reaction of [OsVI(N)(L1)(OH2)]+ with PPh3 is solvent de-
pendent. When CH3OH was used as solvent, the correspond-
ing osmium(IV) phosphinidine complex 1 was formed, as de-
scribed above. On the other hand, when CH2Cl2 containing
a small amount of water (ca. 1%) was used as solvent, the
product was a m-oxo(salen)osmium(IV) phosphinidine dimer,
[(L1){Ph3PN(H)}OsIV–O–OsIV{N(H)PPh3}(L1)]2+, isolated as the
-
PF6 salt (3). 3 is diamagnetic at room temperature (solid state,
Gouy method). In the IR, the n(N–H) band occurs as a weak peak
at 3320 cm-1. The ESI mass spectrum (Fig. S5, ESI†) of 3 exhibits
two peaks at m/z 796 and 1737, which are assigned to the doubly-
charged [M]2+ and singly-charged [M + PF6]+, respectively. The CV
of 3 (Fig. 3) shows one irreversible OsV,V/V,IV wave at +0.84 V (Epa)
and three reversible couples (DEp = 70–80 mV) centered at +0.41,
Fig. 4 Molecular structure of cation of 3 with partial atomic labeling.
Thermal ellipsoids are drawn at 30% probability. H atoms (except N(5)–H
and N(6)–H) are omitted for clarity.
-0.72 and -1.63 V (vs. Cp2Fe+/0). They are assigned to OsV,IV/IV,IV
,
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The Os–O–Os unit is close to linear (178.1(2)◦). The Os–
˚
Table 4 Selected bond distances (A) and angles ( ) of 4
˚
N(phosphinidine) distances (2.034(5) and 2.047(5) A), and the
Os(1)–N(5)
Os(2)–N(6)
Os(1)–N(7)
Os(2)–N(8)
N(5)–P(1)
N(6)–P(2)
Os(1)–N(5)–P(1)
Os(2)–N(6)–P(2)
2.068(4)
2.058(4)
2.074(4)
2.066(4)
1.610(4)
1.612(4)
132.0(3)
131.1(2)
˚
N
P distances (1.614(5) and 1.627(5) A) are similar to those of
1b and 2.
Pyrazine-bridged (salen)osmium(III) phosphinidine complex
Compound 2 can be linked to another osmium center via its
pyrazine ligand. Treatment of 2 with [OsIII{N(H)PPh3}(L1)]+, gen-
erated in situ by mixing [OsVI(N)(L1)(OH2)]+ and PPh3 in CH2Cl2,
produced the purple m-pyrazine (salen)osmium(III) phosphinidine
complex, [(L1){Ph3P(H)N}OsIII–pz–OsIII{N(H)PPh3}(L1)]2+, iso-
lated as the PF6- salt (4). The n(N–H) stretch of 4 occurs as a weak
band at 3317 cm-1, similar to that of 2. The ESI mass spectrum
(Fig. S6, ESI†) displays two predominant peaks at m/z 828 and
1801, attributes to the doubly-charged parent dication [M]2+ and
the singly-charged species [M + PF6]+. The cyclic voltammogram
of 4 in CH3CN (Fig. 5) exhibits four reversible couples (DEp =
60–70 mV) centered at +0.13, +0.03, -0.83 and -1.25 V (vs.
Cp2Fe+/0); which are assigned to OsIV,IV/IV,III, OsIV,III/III,III, OsIII,III/III,II
and OsIII,II/II,II, respectively. The DE1/2 values for the former and
later two couples are 0.1 and 0.42 V, corresponding to Kcom of 50
and 1.3 ¥ 107, respectively. The small value of Kcom for the OsIVOsIII
species indicates that there is little communication between the two
osmium centeres. On the other hand, the much larger value of Kcom
for the OsIIIOsII species suggests that it is either a Class II or Class
III mixed-valence system;3 it is smaller than the reported Class
III mixed-valence complex, [(NH3)5Os(pz)Os(NH3)5]5+ (Kcom = 1 ¥
1013 in 0.1 M HCl).11
Fig. 6 Molecular structure of the cation of 4 with partial atomic labeling.
Thermal ellipsoids are drawn at 30% probability. H atoms (except N(5)–H
and N(6)–H) are omitted for clarity.
of [OsVI(N)(L1)(OH2)]+ with half equiv of PPh2–C C–
PPh2 or PPh2–(CH2)3–PPh2 afforded the binuclear species
[(MeO)(L1)OsIV{N(H)P(Ph)2–R–(Ph)2N(H)}OsIV(L1)(OMe)]2+
-
(R = C C 5; (CH2)3 6), isolated as the PF6 salt. These
compounds have been characterized by IR, ESI/MS, CV and
elemental analysis. In the IR, the n(N–H) stretch occurs as a
weak band at 3294 and 3308 cm-1 for 5 and 6, respectively. There
is an additional weak band at 2062 cm-1 for 5, which is assigned
to the n(C C) stretch. The ESI mass spectrum of 5 (Fig. S7,
ESI†) shows peaks at m/z 1653 [M + PF6]+, 754 [M]2+ and
526 [Os(N)(L1)]+. A similar mass spectrum was observed for 6
(Fig. S8). The CVs of 5 and 6 in CH3CN (Fig. S9) exhibit one
irreversible oxidation wave and one quasi-reversible reduction
couple, with Epa = +0.96 (vs. Cp2Fe+/0), E1/2 = -0.73 V (DEp
=
140 mV) for 5 and Epa = +0.94, E1/2 = -0.77 V (DEp = 80 mV)
for 6. They are assigned to OsV,V/IV,IV and OsIV,IV/III,III couples,
respectively. Since the two osmium centers are oxidized and
reduced at the same potentials, this means that there is little or no
electronic communication between two osmium centers through
the N P–C C–P N bridge. This observation is perhaps
not unexpected, since both Os(III) and Os(IV) are essentially
p-acceptor centers.
The molecular structure of 5 has been determined by X-ray
crystallography. The crystal data are summarized in Table 1.
Selected bond distances and angles are collected in Table 5. The
structure of the cation (Fig. 7) shows that it consists of two
(salen)osmium methoxy units bridged by a linker (H)N(Ph)2P–
Fig. 5 CV of 4 in CH3CN.
The molecular structure of 4 has been determined by X-ray
crystallography and the cation is shown in Fig. 6. The crystal
data are summarized in Table 1. Selected bond distances and
angles are found in Table 4. The structure is similar to that of
3, consisting of two (salen)osmium phosphinidine units, except
that the oxo bridge in 3 is replaced by a pyrazine bridge. The
Os–N(phosphinidine) distances of 2.068(4) and 2.058(4) A are
similar to the Os–N(pyrazine) distances of 2.074(4) and 2.066(4)
A, indicating that the phosphinidine ligands are neutral. The two
˚
C
C–P(Ph)2N(H). Each osmium center has a distorted octahe-
˚
dral geometry, and is surrounded by two oxygen and two nitrogen
atoms of the salen ligand in the equatorial plane. The axial
positions are occupied by one methoxy and one nitrogen atom
of the linker. One of the cyclohexyl ring of the salen ligand on
Os(2) molecule is disordered. The Os–N(phosphinidine) distances
˚
P
N bond distances of 1.610(4) and 1.612(4) A are in the normal
range.14
Diphosphinidine-bridged (salen)osmium(IV) complexes
˚
Binuclear (salen)osmium(IV) complexes can be prepared by
using a diphosphine ligand to attack two OsVI N. Reaction
of 2.045(4) and 2.058(4) A and the d(P N) distances of 1.601(4)
˚
and 1.590(4) A are close to that in 1b. The Os–N–P angles are
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Table 5 Selected bond distances (A) and angles ( ) of 5
Os(1)–N(5)
Os(2)–N(6)
N(5)–P(1)
N(6)–P(2)
C(65)–C(66)
Os(1)–N(5)–P(1)
Os(2)–N(6)–P(2)
2.045(4)
2.058(4)
1.601(4)
1.590(4)
1.184(6)
129.9(2)
132.0(2)
Fig. 8 Molecular structure of 7 with partial atomic labelling. Thermal
ellipsoids are drawn at 30% probability. H atoms are omitted for clarity.
Symmetry operation is (1 - x, 1 - y, 1 - z).
Concluding remarks
Fig. 7 Molecular structure of the cation of 5 with partial atomic labelling.
Thermal ellipsoids are drawn at 30% probability. H atoms (except N(5)–H
and N(6)–H) are omitted for clarity.
In this paper we describe two new (but related) strategies for
the preparation of new binuclear (salen)osmium(IV,IV) and (III,III)
complexes. The first method involves the nucleophilic addition
of PPh3 to (salen)osmium(VI) nitrido species in the presence of
a bridging ligand. The second method involves the use of a
diphosphine ligand to attack two OsVI N centers. These strategies
may be applicable to other electrophilic nitrido species, thereby
generating new classes of binuclear and polynuclear complexes.
also acute (129.9(2) and 132.0(2)◦). The C C bond distance
17
˚
of 1.184(6) A indicates a triple bond. The linker P–C C–P is
close to linear with P(1)–C(65)–C(66) and P(2)–C(66)–C(65) bond
angles of 173.9(5) and 174.1(5)◦, respectively.
1,1¢-Ferrocenediphosphiniminato-bridged (salen)osmium- (IV)
complex
Experimental
Reaction of [OsVI(N)(L2)Cl] with half equiv. of 1,1¢-
diphenylphosphinoferrocene (Ph2PFcPPh2) in CH3CN af-
forded the novel trinuclear complex [Cl(L2)OsIV(NPPh2)(Fc)
(NPPh2)OsIV(L2)Cl] 7 in 80% yield. This complex is insoluble
in common organic solvents such as CH3CN, acetone and
MeOH, but sparingly soluble in CH2Cl2. By standing a sus-
pension of 7 in CH2Cl2 for 3 d at room temperature, single
crystals were obtained, and the structure has been determined
by X-ray crystallography. The details of the crystal data are
summarized in Table 1, and selected bond distances and angle
are collected in Table 6. The molecular structure of 7 (Fig. 8)
consists of two (salophen)OsCl units bridged by N(Ph)2P–Fc–
General remarks
The complexes [OsVI(N)(L1)(OH2)](PF6), [OsVI(N)(L1)(MeOH)]-
(ClO4)18 and [OsVI(N)(L2)Cl]14 (L1 = N,N¢-bis(salicylidene)-
o-cyclohexylenediamine; L2 = N,N¢-bis(salicylidene)-o-phenyl-
enediamine dianion) were prepared according to literature
methods. nBu4NPF6 (Aldrich) was recrystallized three times from
boiling ethanol and dried in vacuo at 120 ◦C for one day.
Acetonitrile (Aldrich) for electrochemistry was purified by stirring
with KMnO4 and then distilled over calcium hydride. All other
chemicals were of reagent grade and used without further purifica-
tion. All manipulations were performed under argon atmosphere
using Schlenk techniques.
IR spectra were recorded as KBr pellets on a Nicolet Avatar
360 FT-IR spectrophotometer at 4 cm-1 resolution. Elemental
analyses were done on an Elementar Vario EL analyzer. Magnetic
measurements (solid sample, Gouy method) were performed at
20 ◦C using a Sherwood magnetic balance (Mark II). Electrospray
ionization mass spectra (ESI/MS) were obtained on a PE SCIEX
API 365 mass spectrometer. The analyte solution was continuously
infused with a syringe pump at a constant flow rate of 5 mL min-1
into the pneumatically assisted electrospray probe with nitrogen
as the nebulising gas. The declustering potential was typically set
at 10–20 V. Cyclic voltammetric measurements were performed
with a PAR model 273 potentiostat using a glassy carbon working
electrode, a Ag/AgNO3 (0.1 M in CH3CN) reference electrode, a
P(Ph)2N. The Os–N(phosphiniminato) bond distance of 1.881(4)
IV
˚
˚
A is comparable to that of [Os (NPPh3)(salophen)Cl] (1.92 A),
but the Os–N–P bond angle (160.7(3)◦) is much larger than that
of [OsIV(NPPh3)(salophen)Cl] (149.6◦) due to the steric effect by
replacing one phenyl group with ferrocene.14
◦
˚
Table 6 Selected bond distances (A) and angle ( ) of 7
Os(1)–N(3)
Os(1)–N(1)
Os(1)–N(2)
Os(1)–O(1)
Os(1)–O(2)
Os(1)–Cl(1)
P(1)–N(3)
1.881(4)
2.007(4)
1.996(4)
2.019(3)
2.036(3)
2.4123(14)
1.561(4)
160.7(3)
Os(1)–N(3)–P(1)
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[(L1){Ph3P(H)N}OsIII–pz–OsIII{N(H)PPh3}(L1)](PF6)2
(4).
PPh3 (26 mg, 0.10 mmol) was added to a mixture of 2 (100 mg,
0.10 mmol) and [OsVI(N)(L1)(OH2)](PF6) (69 mg, 0.10 mmol) in
dichloromethane (20 cm3), and the mixture was stirred for 1 h at
room temperature. The deep purple solution was concentrated
and then loaded onto a silica gel column (20 ¥ 2 cm). The column
was eluted with dichloromethane/acetone (30 : 1, v/v) to give a
purple band, and the solvent was evaporated to dryness to give a
purple solid. Yield: 57%. IR (KBr, cm-1): n(N–H) 3317, n(C N)
1600, 1587 n(N–P) 1109, n(P–F) 839. Found: C, 49.53; H, 4.02; N,
5.81. C80H76N8O4Os2P4F12 requires C, 49.38; H, 3.94; N, 5.76%.
ESI/MS: m/z = 828 (M)2+; 1801 (M + PF6)+.
Pt wire counter electrode with ferrocene (Cp2Fe) as the internal
standard.
CAUTION! Perchlorate salts are potentially explosive. Al-
though we have not encountered any explosions so far, the amount
of perchlorate salts used should be less than 50 mg each time.
Synthesis of complexes 1–7
[OsIV{N(H)PPh3}(L1)(OMe)](PF6) (1a). PPh3 (60 mg, 0.23
mmol) was added to a suspension of [OsVI(N)(L)(OH2)](PF6)
(160 mg, 0.23 mmol) in methanol (10 cm3), and the mixture was
stirred for 1 h at room temperature under argon. The resulting
dark brown microcrystalline solid was filtered and air-dried. Yield:
180 mg (81%). IR (KBr, cm-1): n(N–H) 3229, n(OCH3) 2790,
[(MeO)(L1)OsIV{N(H)PPh2C CPPh2N(H)}OsIV(L1)(OMe)]-
(PF6)2 (5). To a suspension of 1a (100 mg, 0.14 mmol) in
methanol (10 cm3) was added bis(diphenylphosphino)-acetylene
(28 mg, 0.07 mmol) and the mixture was stirred for 5 h at
room temperature. The dark green solid was filtered, washed with
methanol (3 ¥ 5 cm3) and then air-dried. Single crystals suitable for
X-ray crystallization were obtained by diffusion of diethyl ether
into a solution of 5 in acetonitrile at room temperature. Yield: 70%.
IR (KBr): n(N–H) 3294, n(OCH3) 2794, n(C C) 2062, n(C N)
1594, n(P N) 1113, n(P–F) 841. Found: C, 45.63; H, 3.78; N,
4.95. C68H68N6O6P4F12Os2 requires C, 45.44; H, 3.81; N, 4.68%.
ESI/MS: m/z = 754 (M)2+; 1653 (M + PF6)+.
[(MeO)(L1)OsIV{N(H)PPh2(CH2)3PPh2N(H)}OsIV(L1)(OMe)]-
(PF6)2 (6). This dark green solid was prepared by a procedure
similar to that for 5 using bis(diphenylphosphino)-propane.
Yield: 57%. IR (KBr): n(N–H) 3308, n(OCH3) 2793, n(C N)
1594, n(P N) 1113, n(P–F) 840. Found: C, 45.88; H, 3.95; N,
4.78. C69H74N6O6P4F12Os2 requires C, 45.65; H, 4.11; N, 4.63%.
ESI/MS: m/z = 764 (M)2+; 1672 (M + PF6)+.
1
n(C N) 1592, n(N–P) 1108, n(P–F) 839. H NMR (400 MHz,
CD3CN): d 14.30 (s, 1H, NH), 8.62 (dd, J1 = 1.7 Hz, J2 = 8.0 Hz,
1H), 8.46 (dd, J1 = 1.7 Hz, J2 = 8.0 Hz, 1H), 8.15 (s, 1H, N CH),
7.83 (s, 1H, N CH), 7.56–7.52 (m, 3H), 7.38–7.33 (m, 6H), 7.05–
7.00 (m, 2H), 6.81–6.76 (m, 6H), 6.74–6.70 (m, 1H), 6.63(d, J =
8.0 Hz, 1H), 6.61–6.57 (m, 1H), 5.87(d, J = 8.0 Hz, 1H),3.16–3.08
(m, 2H), 1.78–1.70 (m, 2H), 1.68–1.62 (m, 1H), 1.55–1.45 (m, 1H),
1.28–1.22 (m, 1H), 1.15–1.06 (m, 2H), -0.05–0.10 (m, 1H). Found:
C, 48.44; H, 4.29; N, 4.48. C39H39N3O3P2F6Os requires C, 48.60;
H, 4.08; N, 4.36%. ESI/MS: m/z = 820 (M)+.
[OsIV{N(H)PPh3}(L1)(OCH3)](ClO4) (1b). This brown solid
was prepared with
a
similar procedure to 1a using
[OsVI(N)(L1)(MeOH)](ClO4). Yield: 82%. Crystals suitable for
X-ray crystallography were obtained by slow ether diffusion into
an acetonitrile solution of 1b at room temperature. Found: C,
51.05; H, 4.22; N, 4.53. C39H39N3O7PClOs requires C, 51.01; H,
4.28; N, 4.58%. ESI/MS: m/z = 820 (M)+.
[OsIII{N(H)PPh3}(L1)(pz)](PF6) (2). PPh3 (90 mg, 0.34 mmol)
was added to a mixture of [OsVI(N)(L)(OH2)](PF6) (230 mg, 0.34
mmol) and pyrazine (240 mg, 3.00 mmol) in CH2Cl2 (30 cm3),
and the solution was stirred for 1 h at room temperature.
The brown solution was concentrated and then loaded onto
a silica gel column (20 ¥ 2 cm). The column was eluted first
with dichloromethane and then with dichloromethane/acetone
(30 : 1, v/v). The brown band was collected and evaporated to
dryness to give a brown solid. Yield: (220 mg, 60%). Single
crystals suitable for X-ray crystallography were obtained by slow
diffusion of diethyl ether into a dichloromethane solution of 2
at room temperature. IR (KBr, cm-1): n(N–H) 3291, n(C N)
1599, n(P N) 1107, n(P–F) 840. Found: C, 48.96; H, 3.97; N,
6.47. C42H40N5O2OsP2F6·0.25CH2Cl2 requires C, 49.07; H, 3.95;
N, 6.77%. ESI/MS: m/z = 869 (M)+.
[Cl(L2)OsIV(NPPh2)Fc(PPh2N)OsIV(L2)Cl] (7). To a suspen-
sion of [OsVI(N)(L2)Cl] (100 mg, 0.18 mmol) in CH3CN (30 cm3)
was added 1,1¢-bis(diphenylphosphino)-ferrocene (50 mg, 0.09
mmol), and the mixture was stirred 2 h at room temperature under
argon. The resulting dark brown solid was filtered off, washed
with diethyl ether and then air-dried. Yield: 80%. Single crystals
suitable for X-ray crystallography were obtained after standing
a dichloromethane solution of 6 at room temperature for 3 d.
Found: C, 53.72; H, 3.55; N, 5.28. C74H56N6O4P2Cl2FeOs2 requires
C, 53.47; H, 3.40; N, 5.06%.
X-Ray crystallography
Diffraction data for compounds 1b and 7 were collected on a
Bruker SMART 1000 CCD area-detector diffractometer using
[(L1){Ph3P(H)N}OsIV–O–OsIV{N(H)PPh3}(L1)](PF6)2
(3).
graphite-monochromated Mo-Ka radiation (l = 0.71073 A);
˚
PPh3 (52 mg, 0.20 mmol) was added to a suspension of
[OsVI(N)(L1)(OH2)](PF6) (137 mg, 0.20 mmol) in CH2Cl2 (20 cm3)
with addition of 1% H2O, and the solution was stirred for 3 h
at room temperature under argon. The purple solution was
evaporated to dryness and the purple solid was filtered. Single
crystals suitable for X-ray crystallography were obtained by slow
diffusion of diethyl ether into a dichloromthane solution of 3 at
room temperature. Yield: (60 mg, 32%). IR (KBr, cm-1): n(N–H)
3320, n(C N) 1601, n(N–P) 1110, n(P–F) 841. Found: C, 47.36;
H, 4.01; N, 4.56. C76H72N6O5Os2P4F12·CH2Cl2 requires C, 47.41;
H, 3.82; N, 4.31%. ESI-MS: m/z = 796 (M)2+; 1737 (M + PF6)+.
whereas crystal data of 2, 3, 4, and 5 were collected with an
Oxford Xcalibur, Sapphire3, Gemini ultra diffractometer using
either graphite-monochromated Mo-Ka radiation (l = 0.71073
˚
˚
A) or mirror-monochromated Cu-Ka radiation (l = 1.54184 A).
Details of the intensity data collection and crystal data are given
in Table 1. The collected frames were processed with the software
SAINT+19 or CrysAlisPro,20 and an empirical absorption cor-
rection (SADABS21 or multi-scan20) was applied to the collected
reflections. The structures were solved by Direct or Patterson
methods (SHELXTL)22 in conjunction with standard differ-
ence Fourier techniques and subsequently refined by full-matrix
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least-squares analyses on F2. Hydrogen atoms were generated
in their idealized positions and all non-hydrogen atoms were
assigned with anisotropic displacement parameters. There are
some disorders in the crystal structures, such as the cyclohexyl
ring of the salen ligand of 2, 4 and 5, the perchlorate anion of 1b
and hexafluorophosphate anion of 2.
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This work was supported by the Area of Excellence Scheme,
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1944 | Dalton Trans., 2011, 40, 1938–1944
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The Royal Society of Chemistry 2011
©