Synthesis, structure and DFT study of dinuclear iron, cobalt and nickel complexes with cyclopentadienyl-metal moieties

Article abstract of DOI:10.1039/c0dt01386b

Reactions of 1,1′-bis(dipheny1phosphino)cobaltocene with Co(PMe ₃)₄, Ni(PMe₃)₄, Fe(PMe ₃)₄, Ni(COD)₂, FeMe₂(PMe ₃)₄ or NiMe₂(PMe₃)₃ afford a series of novel dinuclear complexes [((Me₃P) Co(η⁵-C₅H₄PPh₂))((Me ₃P)M(η⁵-C₅H₄PPh₂))] (M = Co(1), Ni(2) and Fe(3)) [Co(η⁵-C₅H ₄PPh₂)₂Ni(COD)](4), [Co(η⁵- C₅H₄PPh₂)₂Ni(PMe₃) ₂] (5) and [((Me₃P)Co(Me)(η⁵-C ₅H₄PPh₂))((Me₃P)Fe(Me) (η⁵-C₅H₄PPh₂))] (6). Reactions of 1,1′-bis(dipheny1phosphino)ferrocene with Ni(PMe₃) ₄, NiMe₂(PMe₃)₃, or Co(PMe ₃)₄ gives rise to complexes [Fe(η⁵-C ₅H₄PPh₂)₂M(PMe₃) ₂] (M = Ni (7), Co (8)). The complexes 1-8 were spectroscopically investigated and studied by X-ray single crystal diffraction. The possible reaction mechanisms and structural characteristics are discussed. Density functional theory (DFT) calculations strongly support the deductions.

Full text of DOI:10.1039/c0dt01386b

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PAPER
Synthesis, structure and DFT study of dinuclear iron, cobalt and nickel
complexes with cyclopentadienyl-metal moieties†
Nazhen Liu, Xiaoyan Li, Xiaofeng Xu, Zhiping Wang and Hongjian Sun*
Received 14th October 2010, Accepted 12th April 2011
DOI: 10.1039/c0dt01386b
Reactions of 1,1¢-bis(dipheny1phosphino)cobaltocene with Co(PMe3)4, Ni(PMe3)4, Fe(PMe3)4,
Ni(COD)2, FeMe2(PMe3)4 or NiMe2(PMe3)3 afford a series of novel dinuclear complexes
5
5
[((Me3P)Co(h -C5H4PPh2))((Me3P)M(h -C5H4PPh2))] (M = Co(1), Ni(2) and Fe(3))
5
5
[Co(h -C5H4 PPh2)2Ni(COD)](4), [Co(h -C5H4 PPh2)2Ni(PMe3)2] (5) and
[((Me3P)Co(Me)(h -C5H4PPh2))((Me3P)Fe(Me)(h -C5H4PPh2))] (6). Reactions of
5
5
1,1¢-bis(dipheny1phosphino)ferrocene with Ni(PMe3)4, NiMe2(PMe3)3, or Co(PMe3)4 gives rise to
5
complexes [Fe(h -C5H4 PPh2)2M(PMe3)2] (M = Ni (7), Co (8)). The complexes 1–8 were
spectroscopically investigated and studied by X-ray single crystal diffraction. The possible reaction
mechanisms and structural characteristics are discussed. Density functional theory (DFT) calculations
strongly support the deductions.
[(dppc)+ (PF6)-] is also used to produce transition-metal fullerene
1. Introduction
complexes.18
Since the discovery of ferrocene in the 1950s,1 the fascinating struc-
tural properties of sandwich compounds and their derivatives have
received increasing interest in the fields of materials chemistry,2
organic synthesis,3 catalysis,4,5 organometallic electrochemistry6,7
and biological chemistry.8 New applications have been found in
magnetic materials,9 electrode surface modifiers10 and nonlinear
optical chromophores. The use of chiral ferrocenyl compounds as
ligands in asymmetric synthesis is also prominent.11,12
Wang reported on C–H activation in [(h -C5H5)Fe(h -
C5H4CH2N(CH3)CH2C6H4R-4)] induced by platinum(II) and
found the preferred activation of the C–H bond in the cyclopen-
tadienyl ring rather than in one of the substituents.13 A series
of cyclometallation reactions with phosphorus donor groups
through C–H activation were investigated by Klein and co-
workers.14,15
While studies are mostly concerned with ferrocenes, cobal-
tocenes have been given less consideration. Tsuda has explored
a cobaltocene-catalyzed cycloaddition copolymerization of ter-
minal diynes with nitriles to poly(pyridine)s.16 Cobaltocene
also catalyzes the reaction of an aliphatic terminal alkyne
with a nitrile to afford two regioisomeric pyridine derivatives.17
1,1¢-Bis(diphenylphosphino)cobaltocenium hexafluorophosphate
In this work, we have studied the reactions of 1,1¢-
bis(diphenylphosphino)cobaltocene and 1,1¢-bis(diphenylphos-
phino)ferrocene with low-valent iron, cobalt and nickel complexes
supported by trimethylphosphine. On the one hand, this research
can provide the novel methodology to prepare dinuclear half-
sandwich complexes; on the other hand, ligand exchange is
explored in terms of iron, cobalt and nickel complexes with
different oxidation states. In addition, this work has enriched the
structural information of dinuclear half-sandwich complexes of
transition-metal compounds. The putative reaction mechanisms
will be discussed.
5
5
2. Experimental section
2.1 General procedures and materials
All air-sensitive materials were handled either in vacuo or under
nitrogen by using standard Schlenk techniques. All solvents were
dehydrated and degassed before use. Infrared spectra (4000–
400 cm-1), as obtained from Nujol mulls between KBr disks, were
1
recorded on a Nicolet 5700. H, 13C and 31P NMR (300, 75, and
121 MHz, respectively) spectra were recorded on a Bruker Avance
300 spectrometer. 13C and 31P NMR resonances were obtained with
broadband proton decoupling. Elemental analyses were carried
out on an Elementar Vario EL III and Shanghai HP Model
3510 atomic absorption spectrophotometer. Melting points were
measured in capillaries sealed under argon and are uncorrected.
X-ray crystallography was performed with a Bruker Smart 1000
diffractometer.
School of Chemistry and Chemical Engineering, Shandong University,
Shanda Nanlu 27, 250100, Jinan, People’s Republic of China. E-mail:
hjsun@sdu.edu.cn; Fax: +86 531 88361350
† Electronic supplementary information (ESI) available. CCDC reference
numbers 780554–780561. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0dt01386b
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2.2 Syntheses
red crystals suitable for X-ray diffraction analysis. Yield: 0.33 g of
6 (23%), m.p. 188–189 ◦C (dec.). IR (Nujol mull, 4000–400 cm-1):
Complex 1. Co(PMe3)4 (1.2 g, 3.31 mmol) in 20 ml of THF was
combined with 1,1¢-bis(diphenylphosphino)cobaltocene (1.8 g,
3.23 mmol) in 20 ml of THF. After stirring at room temperature
for 48 h the solution had turned red brown. THF was evaporated
in vacuo and the residue was extracted with pentane and diethyl
ether. Crystallization at room temperature afforded complex 1 as
red crystals suitable for X-ray diffraction analysis. Yield: 0.48 g of
1 (19%), m.p. 172–175 ◦C (dec.). IR (Nujol mull, 4000–400 cm-1):
946 (P-C). Anal. calcd for C40H46Co2P4: C, 62.51; H, 6.03. Found:
C, 62.83; H, 6.16.
1
945 (P-C), 1584 (C C), 3050 (ArC-H). H NMR (300 MHz,
3
C6D6, 296 K, ppm): 0.085 (dd, 3JP,H = JP¢,H = 7.9 Hz, 3H, MCH3);
0.329 (s, 3H, MCH3); 0.442 (d, 2JP,H = 7.2 Hz, 9H, PMe3); 0.591 (d,
2JP,H = 7.8 Hz, 9H, PMe3); 3.885–5.785 (m, 8H, C5H4); 6.499–8.148
(m, 20H, C6H5). 31P NMR (121 MHz, C6D6, 296 K, ppm): 3.99
(d, 2JP,P = 64.6 Hz, 1P, PMe3); 30.25 (d, 2JP,P = 48.2 Hz, 1P, PMe3);
57.81 (d, 2JP,P = 65.1 Hz, 1P, PPh2); 62.05 (d, 2JP,P = 52.4 Hz, 1P,
PPh2). 13C NMR (75 MHz, C6D6, 296 K, ppm): 1.13 (s, MCH3);
14.06 (s, MCH3); 18.97 (d, 1JP,C = 21.4 Hz, PCH3); 22.62 (d, 1JP,C
=
23.7 Hz, PCH3); 73.43 (s, C5H4), 78.05 (s, C5H4), 83.05 (s, C5H4),
84.43 (s, C5H4), 87.17 (s, C5H4), 87.95 (d, 1JP,C = 18.2 Hz, C5H4);
88.97 (s, C5H4); 126.98 s, 132.57 m, 135.68 d, 136.31 d. Anal. calcd
for C42H52CoFeP4: C, 63.41; H, 6.59. Found: C, 63.79; H, 6.63.
Complex 2. Ni(PMe3)4 (0.91 g, 2.51 mmol) in 20 ml of
THF was combined with 1,1¢-bis(diphenylphosphino)cobaltocene
(1.4 g, 2.51 mmol) in 20 ml of THF. After stirring at room
temperature for 48 h, the solution had turned yellow brown.
THF was evaporated in vacuo and the residue was extracted
with pentane and diethyl ether. Crystallization at 0 ◦C afforded
complex 2 as brown crystals suitable for X-ray diffraction analysis.
Yield: 0.23 g of 2 (12%), m.p. 187–190 ◦C (dec.). IR (Nujol
mull, 4000–400 cm-1): 947 (P-C), 3047 (ArC-H). Anal. calcd for
C40H46CoNiP4: C, 62.53; H, 6.04. Found: C, 62.21; H, 6.19.
Complex 7. (a) Ni(PMe3)4 (0.45 g, 1.24 mmol) in 20 ml of
THF was combined with 1,1¢-bis(diphenylphosphino)ferrocene
(0.69 g, 1.24 mmol) in 20 ml of THF. After stirring at room
temperature for 48 h the solution had turned red. THF was
evaporated in vacuo and the residue was extracted with pentane
and diethyl ether. Crystallization at 0 ◦C afforded complex 7 as
red crystals suitable for X-ray diffraction analysis. Yield: 0.29 g of
7 (30.5%). (b) NiMe2(PMe3)3 (0.72 g, 2.27 mmol) in 20 ml of THF
was combined with 1,1¢-bis(diphenylphosphino)ferrocene (1.26 g,
2.27 mmol) in 20 ml of THF. After stirring at room temperature for
48 h the solution had turned red. THF was evaporated in vacuo
and the residue was extracted with pentane and diethyl ether.
Crystallization at 0 ◦C afforded complex 7 as red crystals suitable
for X-ray diffraction analysis. Yield: 0.55 g of 7 (31.6%), m.p. 243–
Complex 3. Fe(PMe3)4 (0.65 g, 1.81 mmol) in 20 ml of
THF was combined with 1,1¢-bis(diphenylphosphino)cobaltocene
(1.0 g, 1.80 mmol) in 20 ml of THF. After stirring at room
temperature for 48 h the solution had turned brown. THF was
evaporated in vacuo and the residue was extracted with pentane
and diethyl ether. Crystallization at 0 ◦C afforded complex 3
as brown crystals suitable for X-ray diffraction analysis. Yield:
0.21 g of 3 (15%), m.p. 163–165 ◦C (dec.). IR (Nujol mull, 4000–
400 cm-1): 940 (P-C). Anal. calcd for C40H48CoFeP4: C, 62.66; H,
6.06. Found: C, 62.25; H, 6.35.
◦
245 C (dec.). IR (Nujol mull, 4000–400 cm-1): 929 (P-C), 1581
1
(C C). H NMR (300 MHz, C6D6, 296 K, ppm): 1.03 (s, 18H,
PMe3), 3.993 (s, 4H, C5H4), 4.19 (s, 4H, C5H4), 6.89–7.81 (m, 20H,
PPh2). 31P NMR (121 MHz, C6D6, 296 K, ppm): -25.13 (t, 2JP,P
+
Complex 4. Ni(COD)2 (1.0 g, 3.64 mmol) in 20 ml of THF was
combined with 1,1¢-bis(diphenylphosphino)cobaltocene (2.0 g,
3.60 mmol) in 20 ml of THF. After stirring at room temperature
for 48 h the solution had turned brown. THF was evaporated
in vacuo and the residue was extracted with pentane and diethyl
2JP,P = 62.31 Hz, 2P, PMe3), 22.83 (t, 2JP,P + 2JP,P = 59.17 Hz, 2P,
PPh2). 13C NMR (75 MHz, C6D6, 296 K, ppm): 22.54 (m, PMe3),
70.48 (s, C5H4), 74.79 (t, 1JP,C + 2JP,C = 9.75 Hz, C5H4), 133.79 (m,
Ph). Anal. calcd for C40H46FeNiP4: C, 62.78; H, 6.06. Found: C,
62.67; H, 6.20.
◦
ether. Crystallization at 0 C afforded complex 4 as red crystals
suitable for X-ray diffraction analysis. Yield: 0.24 g of 4 (9%), m.p.
153–155 ◦C (dec.). Anal. calcd for C42H40CoNiP2: C, 69.65; H,
5.56. Found: C, 69.25; H, 5.35.
Complex 8. Co(PMe3)4 (0.64 g, 1.76 mmol) in 20 ml of THF
was combined with 1,1¢-bis(diphenylphosphino)ferrocene (0.98 g,
1.77 mmol) in 20 ml of THF. After stirring at room temperature
for 48 h the solution had turned brown. THF was evaporated
in vacuo and the residue was extracted with pentane and diethyl
ether. Crystallization at 0 ◦C afforded complex 8 as brown crystals
suitable for X-ray diffraction analysis. Yield: 0.18 g of 8 (13.3%),
Complex 5. NiMe2(PMe3)3 (0.47 g, 1.48 mmol) in 20 ml of
THF was combined with 1,1¢-bis(diphenylphosphino)cobaltocene
(0.83 g, 1.49 mmol) in 20 ml of THF. After stirring at room
temperature for 48 h the solution had turned brown. THF was
evaporated in vacuo and the residue was extracted with pentane
and diethyl ether. Crystallization at 0 ◦C afforded complex 5
as brown crystals suitable for X-ray diffraction analysis. Yield:
0.36 g of 5 (31.6%). m.p. 160–163 ◦C (dec.). IR (Nujol mull, 4000–
400 cm-1): 945 (P-C). Anal. calcd for C40H46CoNiP4: C, 62.53; H,
6.04. Found: C, 62.21; H, 6.10.
◦
m.p.156–158 C (dec.). IR (Nujol mull, 4000–400 cm-1): 926 (P-
C), 1582 (C C). Anal. calcd for C40H46CoFeP4: C, 62.76; H, 6.06;
Fe, 7.30; Co, 7.70. Found: C, 62.36; H, 6.15; Fe, 7.16; Co, 8.01.
2.3 X-ray structure determinations
Complex 6. FeMe2(PMe3)4 (0.75 g, 1.93 mmol) in 20 ml of
THF was combined with 1,1¢-bis(diphenylphosphino)cobaltocene
(1.0 g, 1.80 mmol) in 20 ml of THF. After stirring at room
temperature for 48 h the solution had turned red brown. THF was
evaporated in vacuo and the residue was extracted with pentane
and diethyl ether. Crystallization at 0 ◦C afforded complex 6 as
Intensity data were collected on a Bruker SMART diffractometer
˚
with graphite-monochromated Mo-Ka radiation (l = 0.71073 A).
Crystallographic data for complexes 1 and 4–7 are summarized in
Table 1. The structures were solved by direct methods and refined
with full matrix least-squares on all F2 (SHELXL-97) with non-
hydrogen atoms anisotropic.
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Table 1 Crystallographic data for complexes 1 and 4–7
1
4
5
6
7
Formula
C40H46Co2P4
768.51
P21/n
Monoclinic
12.649(11)
17.258(15)
18.330(15)
90
103.868(14)
90
3885(6)
4
1.314
1.045
13201
4467
0.0672
0.0637
0.1841
C42H40CoNiP2
724.32
P1
C40H46CoNiP4
768.29
P1
C42H52CoFeP4
795.50
P21/n
Monoclinic
11.816(6)
16.502(9)
20.416(11)
90
103.579(11)
90
3870(4)
4
1.365
0.998
16369
5590
0.2145
0.0970
0.2803
C40H46FeNiP4
765.21
P1
Mr. [g mol-1]
Crystal system
Space group
¯
¯
¯
Triclinic
8.994(5)
9.975(5)
20.652(11)
87.715(12)
83.420(12)
65.95(2)
1680.8(4)
2
1.431
1.179
7239
4871
Triclinic
10.5071(14)
19.009(3)
20.070(3)
69.582(2)
87.254(2)
86.414(2)
3747.9(9)
4
1.362
1.143
18803
13215
Triclinic
10.468(8)
18.923(13)
20.003(14)
69.728(14)
87.192(14)
86.672(14)
3709(5)
4
1.370
1.099
15871
10631
˚
a (A)
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
3
˚
V (A )
Z
Dc (g cm-3)
m(mm-1)
rflns collected
indep rflns
Rint
R1 (I > 2s(I))
wR2 (all data)
0.1219
0.0921
0.2491
0.0233
0.0449
0.1405
0.0779
0.0697
0.2160
3. Results and discussion
3.1 Reaction of 1,1¢-bis(dipheny1phosphino)cobaltocene with
M(PMe3)4 (M = Co, Ni and Fe)
Klein reported C–H activation of triarylphosphine through
ortho-metalation using cobalt(I) complexes supported by
trimethylphosphine,14 so we suppose similar reactions may oc-
cur between 1,1¢-bis(dipheny1phosphino)cobaltocene19 and iron,
cobalt or nickel complexes. Unexpectedly, C–H activation with a
P-donor group did not occur, instead a series of novel dinuclear
complexes as products of ligand exchange were formed (Scheme
1). These complexes are paramagnetic in solution and have been
structurally characterized by X-ray diffraction analysis.
Fig. 1 Molecular structure of 1 with 30% probability ellipsoids
cobalt atom is coordinated by one PMe3-donor group, one
5
diphenylphosphino-P atom and one h -Cp group, forming a six-
membered dimetallocycle in the middle of the molecular structure.
The ring formed by P, Co, C atoms [Co1P1C1Co2OP2C6] attains
a boat conformation. The Co–C distances lie in the range of
˚
2.030(7)–2.106(6) A for Co1–C distances and 2.044(7)–2.123(7)
˚
A Co2–C distances in the two cyclopentadienyl rings. The angles
◦
◦
of C1–Co2–P2 (103.16(19) ) and C6–Co1–P1 (103.51(19) ) are
nearly the same. In the IR spectra of complexes 1–3, the P-C
valence absorptions appear at 940–950 cm-1. The metal elements
were confirmed by atomic absorption spectroscopy (AAS).
These structures are quite novel for first-row transition
Scheme 1 Proposed formation mechanism of complexes 1–3
Complexes 1–3 crystallize from pentane. The molecular struc-
ture of complex 1 is shown in Fig. 1. Only the structure of
complex 1 is discussed in detail. The structural figures and
data of complexes 2 and 3 are in the ESI.† The molecular
structure of complex 1 contains a diametric framework of
5
metals. Related complexes [Pt2R2(h -C5H4PPh2)2] (1a, R =
Me; 1b, R = Ph) were obtained through the reaction of
[PtClR(COD)] with Tl(C5H4PPh2).20 Poilbanc published a study
on [M(I)(C5H4PPh2)(CO)2]2 (M = Rh and Ir).21
5
two [(Me3P)Co(h -C5H4PPh2)] moieties with their (diphenylphos-
phino)cyclopentadienyl ligands bound in a head-to-tail fashion.
In Scheme 1 a mechanism of formation is proposed for com-
This complex does not possess a center of symmetry. The
plexes 1, 2 and 3. As first step substitution of a trimethylphosphine
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ligand leads to the coordination of one P atom of 1,1¢-
bis(diphenylphosphino)cobaltocene to the second metal atom
(Co, Ni or Fe) and gives rise to the first intermediate. Ligand
5
exchange with phosphor donor atoms and the transfer of one h -
cyclopentadienyl unit from the cobalt atom to the metal center
produce complexes 1–3. In these reactions the formal Co(II) in
1,1¢-bis(diphenylphosphino)cobaltocene is reduced to Co(I) in
complexes 1–3, while the M(0) center in M(PMe3)4 is oxidized
to the formal M(I) state.
3.2 Reactions of 1,1¢-bis(diphenylphosphino)cobaltocene with
Ni(COD)2 and NiMe2(PMe3)3
The reaction of 1,1¢-bis(diphenylphosphino)cobaltocene with
Ni(COD)2 (eqn (1)) proceeds by coordination of phospho-
rus atoms of 1,1¢-bis(diphenylphosphino)cobaltocene to the
nickel(0) center with substitution of COD. No redox re-
action occurred. In this transformation the original stag-
gered 1,1¢-bis(diphenylphophino)cobaltocene conformation with
diphenylphosphino groups on both sides of the molecular
backbone results in a new staggered conformation with both
diphenylphosphino groups on the same side in a chelating
coordination of the two phosphorous atoms to the nickel atom.
In general the rotational barrier between these two staggered
conformations is small and is dominated by the chelate effect in
4.22
Scheme 2 Proposed formation mechanism of complex 5
◦
Red crystals of complex 4 are formed at 0 C. The molecular
structure of complex 4 is shown in Fig. 2. The six-membered ring
[Co4C60P6Ni1P8C55] adopts a distorted chair conformation.
The boat-like COD ligand coordinates to the nickel center in
the direction of the “hull bottom” and appears to be sterically
crowded. The nickel(0) center possesses a tetrahedral coordination
2
geometry made up from two P-donor atoms and two h -(C C)
coordination units of the COD ligand.
Fig. 3 Molecular structure of 5 with 30% probability ellipsoids
membered chelate ring with the similar coordination geometry
to that of complex 4. The coordination of the Ni atom can be
described as distorted tetrahedral with four P-donor atoms. The
two cyclopentadienyl rings surround the Co atom in a staggered
orientation. The PNiP bite angle at the nickel atom in complex 4
◦
(P5–Ni1–P7 = 106.28(18) ) is significantly smaller than that on
the nickel atom in complex 5 (P1–Ni1–P2 = 110.32(4) ◦) because
of the bulky 1,5-cyclooctadiene ligand, while the angle P3–Ni1–P4
is 103.52(6)◦ in complex 5.
Fig. 2 Molecular structure of 4 with 30% probability ellipsoids
Combining 1,1¢-bis(diphenylphosphino)cobaltocene with
NiMe2(PMe3)3 (Scheme 2) in THF gave a brown solution. After
work-up complex 5 was obtained as black crystals which were
suitable for X-ray single crystal diffraction.
The molecular structure of complex 5 is shown in Fig. 3.
This heteronuclear complex contains a relatively unstrained six-
The reaction is likely to start with substitution of one
trimethylphosphine molecule by
a P-donor of the 1,1¢-
bis(diphenylphosphino)cobaltocene ligand. Reductive elimination
of ethane and the formation of the six-membered ring generates
complex 5 (Scheme 2). Complex 5 is paramagnetic in solution.
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(1)
Similar Co(II) complexes can be prepared by treating
Cp*Ru(PPh3)2Cl with 1,1¢-bis(diphenylphosphino)cobaltocene in
refluxing benzene.23
3.3 Reaction of 1,1¢-bis(diphenylphosphino)cobaltocene with
FeMe2(PMe3)4
The reaction of 1,1¢-bis(diphenylphosphino)cobaltocene with
FeMe2(PMe3)4 affords a hetero dinuclear complex 6 containing
methylcobalt(II)- and methyl-iron(II) moieties (eqn (2)) that arise
from a ligand exchange reaction without changes of the formal
oxidation states of the metal atoms.
In the 1H NMR spectrum the PMe3 protons appear as a doublet
at 0.442 ppm (2JP,H = 7.2 Hz) and 0.591 ppm (2JP,H = 7.8 Hz). The
metal-methyl groups show two resonances: FeCH3 at 0.085 ppm
3
3
as a doublet of doublets with JP,H = JP¢,H = 7.9 Hz and CoCH3
at 0.329 ppm as a singlet. The absence of P-coupling in the latter
suggests incipient dissociation of Co–PMe3 groups effecting spin
decoupling. In the 31P NMR spectrum the PMe3 ligands resonate
at 3.99 and 30.25 ppm as doublets, while the PPh2 groups appear
at 57.81 and 62.05 ppm as doublets. In the 13C NMR spectrum the
doublets at 18.97 ppm and 22.62 ppm are assigned to the PMe3
groups.
The molecular structure of complex
6 (Fig. 4) re-
Fig. 4 Molecular structure of 6 with 30% probability ellipsoids
veals hetero-dimetal framework in which the 1,1¢-
a
bis(diphenylphosphino)cobaltocene ligands are bonded in a head-
to-tail fashion. The Co, Fe atoms and the two P atoms as well as
the two cyclopentadienyl carbon atoms are considered to form
a six-membered ring [Co1C24P4Fe1C21P3] in a distorted chair
conformation. By contrast, the closely related complex [PtMe(m-
5
h -C5H4PPh2)]2 adopts a distorted boat conformation. All bond
lengths in the six-membered ring of 6 are in the normal region.
3.4 Reaction of 1,1¢-bis(diphenylphosphino)ferrocene with
Ni(PMe3)4, NiMe2(PMe3)3 and Co(PMe3)4
In contrast to the redox reaction (Scheme 3) of 1,1¢-
bis(diphenylphosphino)cobaltocene with Ni(PMe3)4, the reaction
of 1,1¢-bis(diphenylphosphino)ferrocene with Ni(PMe3)4 proceeds
as a ligand substitution reaction, in which two PMe3 groups are
replaced by the bidentate 1,1¢-bis(diphenylphosphino)ferrocene
ligand, forming a chelate ring in complex 7.
Scheme
3
Reaction of 1,1¢-bis(diphenylphosphino)ferrocene with
Ni(PMe3)4, NiMe2(PMe3)3 and Co(PMe3)4
protons were found at 3.99 and 4.19 ppm. The phenyl protons show
resonances between 6.89 and 7.81 ppm. In the 31P NMR spectra
one triplet at -25.13 ppm was assigned to the trimethylphosphine
group, while another triplet at 22.83 ppm was ascribed to the
diphenylphosphine group.
Complex 7 was studied by 1H, 31P and 13C NMR as well as IR
spectroscopy. In the IR spectra, the band at 929 cm-1 is assigned to
the n(P-C) vibration. In the 1H NMR of complex 7, the signal at
1.03 ppm arises from the PMe3 protons, and the cyclopentadienyl
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(2)
Crystallization at 0 ◦C afforded orange crystals of complex
7 which were suitable for X-ray diffraction. The molecular
structure of complex 7 is shown in Fig 5. The arrangement
of four phosphorus atoms around the nickel center shows a
bite angle of P1–Ni1–P2 = 109.04(11)◦, which is remarkably
larger than the angle of P3–Ni1–P4 = 103.88(12)◦ and effects a
major distortion of the coordination tetrahedron. The hexagon
[Fe1C31P1Ni1P2C36] with side length symmetry (Fe1–C31 =
2.045(10); Fe1–C36 = 2.070(9); C31–P1 = 1.809(10); C36–P2 =
In
contrast
to
the
reactivity
of
1,1¢-
bis(diphenylphosphino)cobaltocene towards Co(PMe3)4 (eqn
(1)), the reaction of 1,1¢-bis(diphenylphosphino)ferrocene with
Co(PMe3)4 formed 8 as product of a substitution reaction
(Scheme 3) which proceeds in an analogous fashion to the
reaction of 1,1¢-bis(diphenylphosphino)ferrocene with Ni(PMe3)4
(Scheme 3). Two trimethylphosphine ligands of Co(PMe3)4
are replaced by the ferrocene-bridged bidentate diphosphine
ligand. Complex 8 is paramagnetic in solution. In this reaction
1,1¢-bis(diphenylphosphino)ferrocene coordinates to the cobalt(0)
center as a redox-innocent ligand where the formal oxidation
states of the metal atoms remain unchanged.
Complex 8 is isostructural with complex 7. The crystal and
molecular structural data of complex 8 are given in the ESI.† Some
small variation of the structural parameters between complex
8 and 7 is caused by the larger atomic radius and the higher
electronegativity of the cobalt atom.
˚
1.800(10); Ni1–P1 = 2.149(3); Ni1–P2 = 2.153(3) A) loses its plane
of symmetry [Fe1Ni1P1P2] through the staggered conformation
of the Cp2Fe moiety. Complex 7 is a derivative of complex
5 where the cobalt atom is replaced by an iron atom. All
molecular and structural parameters in complexes 5 and 7 are
similar.
3.5 Computational study
In order to rationalise the experimental results we have optimised
a series of isolated complexes using DFT (Density Functional
Theory) methods.26 Two kinds of initial configurations were con-
sidered for every dinuclear complex. In one of the configurations
each transition metal atom is bonded to one cyclopentadienyl
ring (half-sandwich configuration), while in another the cobalt
or iron atom is bonded to two cyclopentadienyl rings (sandwich
configuration) (Scheme 4). Comparing those optimized configura-
tions, we found that the calculated results are consistent with those
from the experiments. For the dicobalt complex, complex 1 from
reaction 1 with two half-sandwich moieties was obtained because
this configuration lies 15.93 kcal mol-1 lower than the complex 1a
with a sandwich moiety, which was not observed. For the cobalt-
nickel complex both complex 2 with two half-sandwich moieties
from reaction 1 and complex 5 with one sandwich moiety from
reaction 3 were experimentally isolated owing to the smaller energy
difference between them. Complex 2 is energetically 9.55 kcal
mol-1 higher than complex 5. Complex 5 was obtained in higher
yield (31.6%) than complex 2 (12%). Complex 3a with its higher
energy was not observed among the products of Scheme 1, while
complex 3 was experimentally confirmed. For the same reason
complex 8 was isolated from Scheme 3 rather than complex 3
because complex 8 is more stable than complex 3. In a similar way,
complex 7 from reaction 7 was isolated, while complex 7a could
not be observed because of the large energy difference between
them (45.42 kcal mol-1).
Fig. 5 Molecular structure of 7 with 30% probability ellipsoids
The reaction of 1,1¢-bis(diphenylphosphino)ferrocene with
NiMe2(PMe3)3 also gives rise to complex 7 with elimination of
ethane (Scheme 3).
Beletskaya reported palladium complexes containing
a
metallocene-bridged bidentate diphophine ligand and their cat-
alytic activity in amination and cross-coupling reactions.5 Com-
plexes of Ti and Zr coordinated by ferrocene-based diimido
ligands were also synthesized.24,25
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Reactions of 1,1¢-bis(diphenylphosphino)cobaltocene with
Co(PMe3)4, Ni(PMe3)4, Fe(PMe3)4, Ni(COD)2, NiMe2(PMe3)3
and FeMe2(PMe3)4 afford a series of novel dinuclear complexes 1,
2, 3, 4, 5 and 6. Reactions of 1,1¢-bis(diphenylphosphino)ferrocene
with Ni(PMe3)4, NiMe2(PMe3)3 and Co(PMe3)4 afford dinuclear
complexes 7 and 8. DFT calculations support the experimental
results. An investigation of the catalytic properties of complexes
4, 5, 7 and 8 is in progress.
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Acknowledgements
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26 Geometries of isolated monomeric complexes have been fully optimized
using nonlocal PW91 gradient corrected functional and DNP basis set
with FINE setting of the overall calculation quality. Effective Core
Potentials (ECP) method was applied to treat the core electrons of the
transition metal atoms involved in the optimizations.
We gratefully acknowledge the support by NSF China No.
20972087/21072113. We also thank the kind assistance from Prof.
Dieter Fenske (Karlsruhe Institute of Technology) for the X-ray
diffraction analysis.
6892 | Dalton Trans., 2011, 40, 6886–6892
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