Reductive activation of tripod metal compounds: Preparative application

Article abstract of DOI:10.1002/ejic.200700874

The tripodnickel(0) species [tripod₄Ni₃] (1) {tripod = CH₃C(CH₂PPPh₂)₃} is shown to undergo oxidative addition with disulfides or diselenides REER (E = S, Se, R = tBu, Ph) to produce [tripo

Full text of DOI:10.1002/ejic.200700874

FULL PAPER
DOI: 10.1002/ejic.200700874
Reductive Activation of tripod Metal Compounds: Preparative Application
Jürgen Mautz[a] and Gottfried Huttner*[a]
In memoriam Dr. Laszlo Zsolnai
Keywords: Tripodal ligands / Cobalt / Nickel / Reductive activation / Oxidative addition
The tripodnickel(0) species [tripod4Ni3] (1) {tripod
=
main group element of groups III to VI) with a valence elec-
tron count of 36 electrons. Quantum chemistry predicts that
the HOMO of such compounds should be a degenerated pair
of mainly metal centred orbitals. Electrochemistry of 4a, [tri-
podCoSCotripod], shows three quasi-reversible oxidation
steps in the range of –700 mV vs. SCE to 570 mV vs. SCE,
which can be understood as metal centred oxidations. Three
different types of crystals have been obtained for different
types of pseudopolymorphs 4a. The geometric parameters of
the coordination compounds are almost equal in these pseu-
dopolymorphic crystals. The real difference is the content of
solvent molecules and, hence, the packing of the molecules.
In the crystals of 4a containing no solvent the coordination
CH3C(CH2PPPh2)3} is shown to undergo oxidative addition
with disulfides or diselenides REER (E = S, Se, R = tBu, Ph)
to produce [tripodNi(ER)] (2). Compounds 2 show pseudo tet-
rahedral coordination. They are paramagnetic with one un-
paired electron per molecule. Their magnetic behaviour is
almost that of an ideal Curie-type magnet down to tempera-
tures of 2 K. They undergo reversible one electron oxidation
to the 16 valence electron species [tripodNi(ER)]+. The iso-
electronic pseudo tetrahedral 16 valence electron cobalt spe-
cies [tripodCo(ER)] (3) are obtained by reduction of CoCl2
with KC8 in the presence of tripod and subsequent reaction
with REER (E = S, Se; R = tBu, Ph). They are paramagnetic
with two unpaired electrons per molecule. They can be re- compounds form close packed layers stacked on each other
versibly oxidised to the 15 valence electron compounds
[tripodCo(ER)]+ while their reduction to the 17 valence elec-
tron species [tripodCo(ER)]–, which would be isoelectronic to
the stable compounds 2, is not observed. Under appropriate
conditions the reactions with REER do not result in the forma-
tion of 3 but yield [tripodCoECotripod] (4) by extrusion of
sulfur and selenium from the substrate. Compounds 4 show
a linear Co–E–Co framework with very short Co–E bonds (E
= S: 205 pm; E = Se: 216 pm). They are members of a family
of dimetallaheterocumulenic compounds [LnMEMLn] (E =
in an oblique way. In the crystals containing 4a·DME a layer
of solvent molecules separates each pair of layers of close
packed molecules. In the crystal of 4a·3DME a cuboctahedral
cage of solvent molecules embedding each coordination
compound separates the complex molecules from each other.
The different types of crystals observed underpin the globu-
lar shape of 4 and the effective shielding power of the tripod
ligand.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
The metal(II) halides of cobalt and nickel in the presence
of tripod {tripod = CH3C(CH2PЈ)3; PЈ = PPh2} have been
shown to produce highly reactive tripodcobalt(0)[1] and
-nickel(0)[2] species upon their activation with KC8 in THF
solutions. The composition of the reactive tripodnickel(0)
species has been elucidated to be [tripod4Ni3] (1)
(Scheme 1).[2] 1 has been shown to react with two-electron
donors L (L = PPh3, AsPh3, cHexNC tBuNC, C2H4) to
give the tripodnickel(0) compounds [tripodNiL].[2] Oxidative
addition to 1 in its reactions with disulfides RSSR and dis-
elenides RSeSeR is analysed in this paper.
Scheme 1.
The reduction of CoCl2 with KC8 in the presence of tri-
pod in THF in an argon atmosphere likewise produces a
reactive species [“tripodCo0”] (A).[1,2] Oxidative addition of
the same reagents to A was found to be rather analogous
to the one observed for 1. In addition it is observed that
the thiophilicity of A is high enough to split C–S bonds,
extracting sulfur from different organic sources to produce
the dinuclear compound [tripodCoSCotripod] (4a).
[a] Anorganisch-chemisches Institut, Universität Heidelberg,
69120 Heidelberg, Im Neuenheimer Feld 270, Germany
E-mail: g.huttner@urz.uni-heidelberg.de
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The aim of the work reported here was to further eluci- Table 1. Selected bond lengths [pm], bond angles [°] and torsion
angles [°] in 2a–c.
date the reactivity of the species [tripod4Ni3] (1) and its co-
2a[a,c]
2b[a,c]
2c[b]
balt(0) analogue A.
Ni1–P1
Ni1–P2
Ni1–P3
Ni1–E
222.7(2)
221.2(2)
221.5(2)
221.2(2)
99.2(1)
92.7(1)
88.7(1)
127.7(1)
111.7(1)
127.6(1)
34.5
18.5
27.9
32.4
70.8
27.7
5.7
10.0
2.5
226.0(1)
221.3(2)
220.6(1)
219.1(1)
95.6(2)
93.8(1)
91.8(1)
127.0(1)
121.0(1)
119.4(1)
32.1
27.9
39.2
39.4
60.9
3.1
–10.0
42.6
0.0
221.5(1)
218.1(2)
220.3(1)
230.1(1)
93.3(2)
98.0(1)
91.9(1)
130.6(1)
115.7(1)
118.6(1)
9.3
10.7
19.5
–45.6
21.8
16.7
32.0
32.8
9.8
Results and Discussion
P1–Ni1–P2
P1–Ni1–P3
P2–Ni1–P3
P1–Ni1–E
P2–Ni1–E
P3–Ni1–E
THF solutions of [tripod4Ni3] react with dichalgogenides
REER (E = S, Se, R = tBu, Ph) to produce the tripod-
nickel(I) species 2a–2c (Scheme 2).
[d]
τ1[d]
τ2[d]
τ3
[e]
f1[e]
f2[e]
f3[e]
f4[e]
f5[e]
f6
Scheme 2.
[a] 2a, 2b with E = S. [b] 2c with E = Se. [c] The values in parenthe-
ses are standard deviations in units of the last decimals listed. [d]
τ = torsion angles within the chelate cage: τ1 = C4–C1–P1–Ni, τ2
= C4–C2–P2–Ni, τ3 = C4–C3–P3–Ni. [e] The torsion angles f in-
volving Hz are defined as follows: f1 = Hz1–P1–C100–C101, f2 =
Hz1–P1–C106–C107, f3 = Hz2–P2–C200–C201, f4 = Hz2–P1–
C206–C207, f5 = Hz3–P3–C300–C301, f6 = Hz3–P3–C306–C307;
Hz–P designates a vector that is vertical to the plane formed by
the three tripod phosphorus donor atoms and points towards the
observer when, in a projection onto this plane, the vector Co–C4
points away from the observer, such that C4 lies below this plane.[3]
Compounds 2 are isolated as red crystals in analytically
pure form in yields between 60% and 80%. Their coordina-
tion geometry is pseudo-tetrahedral as verified by X-ray
structure analyses of 2a–2c. As an example of their geome-
try, sketches of the structure of 2b are shown in Figure 1.
Characteristic geometric parameters of all three compounds
2a–2c are summarised in Table 1.
Ni–P distances in 2a–2c vary from 218 pm to 226 pm,
somehow reflecting the steric congestion by the ER ligands
imposed on the individual phosphorus atoms. Thus, for in-
stance, in 2b, the distance Ni1–P1 (226 pm) is distinctly pressed by the torsion angles τ (Table 1) is larger for the
larger than the distances Ni1–P2 and Ni1–P3 (221 pm). In sulfur derivatives 2a and 2b (τ = 30° in the mean) than for
2b the Ni1–P1 bond is eclipsed to the S1–C6 bond (Fig- the selenium derivative 2c (τ = 13° in the mean).
ure 1) such that P1 will feel the steric load imposed by the
There is only one mononuclear coordination compound
tert-butyl group. In consequence the Ni1–P1 bond is length- of the type [tripodNi(SR)] reported to compare with: in [tri-
ened and the P1–Ni1–S1 angle (127°) is increased compared podNi(SH)], characterised by Sacconi and his group,[4] the
to the angles P2–Ni1–S1 (121°) and P3–Ni1–S1 (119°), Ni–S distance is found to be 217 pm, close to the values of
respectively. The skew of the tripod metal scaffolding ex- about 220 pm as observed for 2a and 2b. As expected, due
Figure 1. The molecular structure of 2b in the crystal. Left: general view; right: projection onto the plane defined by the three tripod
phosphorus atoms.
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Reductive Activation of tripod Metal Compounds
to the difference in atomic radii, the Ni–Se distance in 2c is (Scheme 3). With 2c one-electron oxidation is observed as
some 10 pm larger than the Ni–S distances in 2a and 2b.
The nickel(I) complexes 2 are paramagnetic species. The perature under the conditions applied. Oxidation of com-
pseudo tetrahedral coordination geometry and the d9 elec- pounds 2 occurs between E1/2 = –180 mV (2c) and E1/2
well, which, however, is only quasi-reversible at room tem-
=
tron count lead one to expect one unpaired electron per –470 mV (2b) vs. SCE (Scheme 3), demonstrating that there
complex entity. Magnetic measurements in solution by the is no strong influence on the oxidation potential neither of
Evans Method[5] show magnetic moments µeff close to the the substituent linked to sulfur nor of the nature of the
spin-only value corresponding to one unpaired electron. ligating chalcogen element. This means that the orbital in-
SQUID measurements of 2 in the temperature range 2– volved in the redox process is mainly metal in character. No
300 K show almost perfect Curie behaviour with Curie con- attempt has been made to characterise the nickel(II) species
stants C from 0.370 cm3 Kmol–1 to 0.394 cm3 Kmol–1 and 2+. It has been reported that nickel in the oxidation state
Weiss constants Θ of only Θ = –1 K, indicating that there +II forms both mononuclear and dinuclear complexes con-
is almost no magnetic interaction between the individual taining thiolate groups and tripodal ligands: stable mono-
molecules. The magnetic moments extracted from SQUID nuclear compounds of the general formula [LM(SR)]+ {L
measurements in the solid state are well in agreement with = P(CH2CH2PPh2)3, N(CH2CH2PPh2)3; M = Co, Ni} have
the ones obtained by the Evans Method in solution been described by Sacconi and his group,[6] dinuclear com-
(Table 2).
plexes of the composition [(tripodNiSR)2]2+ (R = Ph) were
characterised in our group;[7] in this type of compounds the
tripod ligand is only coordinated with two of his phosphane
donor entities.[7] The reversibility of the oxidation process
observed for 2a and 2b tends to indicate that the Scheme 3
Table 2. Magnetic and EPR data of 2a–2c.
Evans Method: SQUID: µeff (300 K) [µB], EPR: Aiso(P) [G]
µeff (300 K) [µB] C [cm3 Kmol–1], Θ [K]
2a µeff = 1.68
µeff = 1.63
C = 0.394
Θ = –1
giso = 2.1263
Aiso(P) = 60
2b µeff = 1.57
µeff = 1.74
C = 0.370
Θ = –1
giso = 2.1110
Aiso(P) = 61
2c
µeff = 1.77
µeff = 1.74
C = 0.374
Θ = –1
giso = 2.1156
Aiso(P) = 60
EPR spectra of THF solutions of complexes 2 show a
quartet in each case with a single coupling constant A(P)
to the phosphorus nuclei of around 60 Gauss (Table 2) as
shown for 2b as an example (Figure 2). The spectrum is well
in agreement with its simulation, as shown by the bottom
line in Figure 2. The g values in the range of giso = 2.1110
to giso = 2.1263 are somewhat larger than ge = 2.0023 indi-
cating that there is some spin-orbit coupling present in
complexes 2 (Table 2), as expected for a pseudo tetrahedral
d9-system.
Scheme 3.
Repeating the experiments described for nickel using the
reactive solution obtained by the reduction of CoCl2 in
THF by KC8 in the presence of tripod under an argon at-
mosphere gives rather similar results even though the elec-
tron count differs by one electron: with disulfides RSSR the
neutral cobalt(I) compounds [tripodCo(SR)] (3a: R = Ph;
3b: R = tBu) are formed, the diselenide PhSeSePh forms
the analogue complex [tripodCo(SePh)] (3c) (Scheme 4).
Figure 2. EPR spectrum of 2b (295 K, 9.44 GHz) (middle trace),
simulation [top trace; parameters: giso = 2.1110, A(P) = 61 G, line
width = 38ϫ10–4 cm–1] and residual (bottom trace).
Scheme 4.
The pseudo-tetrahedral coordination of the metal in 3a–
Cyclovoltammetric experiments show that the 17 electron 3c has been confirmed by the X-ray crystal structure analy-
compounds 2a and 2b undergo reversible one-electron oxi- ses. The mean value of the Co–P distances in all three com-
dation to give the 16 electron species 2a+ and 2b+ pounds is 222 pm and individual Co–P distances do not
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J. Mautz, G. Huttner
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differ significantly from this mean value (Table 3). The close therefore have only less immediate steric influence on the
to trigonal local symmetry of the CoP3 fragment is as well geometric parameters of the CoP3 tripod, quite different
documented by the P–Co–P angles which differ by only 1.5° from the case of 2b in which the bond S1–C6 and the bulky
from the mean value of 91.5° at most. In all compounds 3 tert-butyl group, respectively, is in eclipsed position to the
the residues ER in [tripodCo(ER)] are arranged such as to bond Ni1–P1 (Figure 1). The steric load, nevertheless pres-
occupy the space between two Co–P bonds, corresponding ent, mirrors itself in the direction of the deviation of the
to a close to staggered conformation of the bond S1–C6 chalcogen atom from the pseudotrigonal axis: the angles P–
with respect to the CoP3 entity (Figure 3). The ER ligands Co–E fall in two classes throughout. There are two large
angles close to the mean of 130° and one small angle again
close to the respective mean value of 111° (Table 3). The
Table 3. Selected bond lengths [pm], bond angles [°] and torsion
small P–Co–E angle is found for the one phosphorus atom
angles [°] in 3a–c.
which is opposite to the sector occupied by the substituent
3a[a,c]
3b[a]
3c[b]
R. Compressing this angle alleviates the steric repulsion be-
tween the group R and the two other phosphorus atoms
and their substituents.
Co1–P1
Co1–P2
Co1–P3
Co1–E
222.7(2)
223.5(2)
222.3(2)
224.2(2)
93.5(1)
90.3(1)
90.8(1)
123.6(1)
134.3(1)
112.3(1)
31.2
222.9(1)
222.8(1)
224.2(1)
223.2(1)
91.7(1)
90.4(1)
93.0(1)
107.2(1)
127.8(1)
133.6(1)
26.0
220.6(1)
221.7(1)
219.7(1)
236.2(1)
91.4(1)
91.4(1)
91.4(1)
112.3(1)
130.5(1)
128.1(1)
18.2
The skew of the tripodCo scaffolding which is documen-
ted by the torsion angles τ (Table 3) is similar to the one
observed for compounds 2. As in the case of the nickel
complexes 2 the torsion angles are larger for the sulfur com-
pounds (τ = 26° mean value) than for the selenium complex
(τ = 18° mean value). As expected, the Co–E distances are
slightly larger than the ones observed for the analogous
nickel compounds 2 (see Tables 1 and 3). The Co–Se dis-
tance in 3c is around 10 pm larger than the metal sulfur
distances in 3a and 3b as already observed for the analo-
gous nickel compounds 2.
P1–Co1–P2
P1–Co1–P3
P2–Co1–P3
P1–Co1–E
P2–Co1–E
P3–Co1–E
[d]
τ1[d]
τ2[d]
τ3
23.3
23.0
–6.7
18.9
28.3
24.5
1.6
20.0
16.1
19.0
10.2
35.3
[e]
f1[e]
f2[e]
f3[e]
f4[e]
f5[e]
f6
–42.3
21.6
11.8
–50.2
–20.4
20.8
96.7
15.2
24.1
31.7
19.4
42.4
The pseudo tetrahedral 16 electron species 3 with a d8-
configuration of the metal should be paramagnetic due to
the presence of two unpaired electrons. Magnetic measure-
ments by the Evans Method give magnetic moments be-
tween µeff = 3.1 µB and µeff = 3.3 µB well in agreement with
the spin-only value of µeff = 2.83 µB for two unpaired elec-
trons. The deviation from the spin-only value is due to spin-
orbit coupling.
Compounds 3 are isoelectronic analogues to [tripod-
Ni(ER)]+ (2+). Therefore, it is expected that they could be
reduced in a one electron step to produce isoelectronic ana-
logues of the stable compounds [tripodNi(ER)] (2). By cy-
[a] E = S. [b] E = Se. [c] The values in parentheses are standard
deviations in units of the last decimals listed. [d] τ = torsion angles
within the chelate cage: τ1 = C4–C1–P1–Ni, τ2 = C4–C2–P2–Ni, τ3
= C4–C3–P3–Ni. [e] The torsion angles f involving Hz are defined
as follows: f1 = Hz1–P1–C100–C101, f2 = Hz1–P1–C106–C107, f3
= Hz2–P2–C200–C201, f4 = Hz2–P1–C206–C207, f5 = Hz3–P3–
C300–C301, f6 = Hz3–P3–C306–C307; Hz–P designates a vector
that is vertical to the plane formed by the three tripod phosphorus
donor atoms and points towards the observer when, in a projection
onto this plane, the vector Co–C4 points away from the observer,
such that C4 lies below this plane.[3]
Figure 3. The molecular structure of 3b in the crystal. Left: general view; right: projection onto the plane defined by the three tripod
phosphorus atoms.
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Reductive Activation of tripod Metal Compounds
clic voltammetry it is found, however, that reduction pro- requirements. In the case of the two crystallographically in-
cesses are irreversible throughout. In contrast, reversible dependent molecules in the cell of 4a·DME only one is re-
oxidation is observed for the sulfur derivatives 3a and 3b stricted to be linear by an inversion centre at the position of
(Scheme 5). Oxidation occurs as a fully reversible process at the sulfur atom; for the other one, not restricted by crystal
E1/2 = –240 mV vs. SCE for 3a and E1/2 = –280 mV vs. SCE symmetry, a Co–S–Co angle of very close to 180° is ob-
for 3b. The small difference between the redox potentials of served (176.4°). The two Co–S distances within each mole-
3a and 3b is again indicative of the metal character of the cule in all three crystal variants of 4a are either exactly
orbital involved. The selenium species 3c shows an oxi- equal by crystal symmetry or are so within the limits of
dation peak at EAp = –310 mV vs. SCE, which, even though error (4a·3DME). They are very short with an average value
the process is irreversible under the conditions applied, indi- of 205.3 pm. Similarly short M–S distances have already
cates that the nature of the chalcogen atom of the coligand been observed in a few other coordination compounds con-
does not strongly affect the oxidation potential. It has not taining a linear M–S–M entity (Table 4). The bonding situ-
been attempted to isolate the cationic compounds 3+. It is ation in this type of complexes has already been analysed
known, however, that the dinuclear complex [(tripod- by different quantum chemical approaches[9,10] with the un-
CoSR)2]2+ (R = Me) is a stable entity.[8] It has been charac- equivocal result that the bond order of the M–S bond is at
terised by the group of Sacconi and has been found to be least two.
structurally rather similar to the analogous nickel com-
pound [(tripodNiSR)2]2+ (R = Ph).[7] The reversibility of the
oxidation of 3a and 3b, similar to the case discussed for the
Table 4. Selected bond lengths [pm] in complexes [LnMSMLn]m+
with linear M–S–M fragments.
nickel complexes 2a and 2b suggests that the monomeric
species [(tripodNiSR)]+ are intrinsically stable under the
m
M
d(M–S)
d(M–P) LnM
conditions applied.
0
0
2
0
0
Co
Co
Ni
Cr
V
205.3
212.8
203.4
207.4
217.2
216.9
228.5
223.6
–
[CH3C(CH2PPh2)3Co] (4a)
[N(CH2CH2PPh2)3Co][11]
[CH3C(CH2PPh2)3Ni]2+[11]
[(Cp)(CO)2Cr][12]
248.8
[(dppe)(CO)3V][13]
All the compounds containing a linear M–S–M entity so
far described (Table 4) have in common that the valence
electron count of the [LnMSMLn]m+ species corresponds to
36 electrons; the LnM fragments in these compounds are 15
electron species throughout (Table 4). The principle that the
36 electron count of a linear M–E–M entity appears to be
a precondition for its formation is further exemplified by
the existence of a series of compounds containing a linear
LnMELnM framework with E ranging from main group III
(Ga,[14a] In,[14b] Tl[14c]) over main group IV (Ge,[15a–15c]
Sn,[15c] Pb[15d,15e]) to main group V (P,[16a] As,[16b–16d]
Sb[16b,16e]). The LnM entities are organometallic throughout
in all these cases. The valence electron count of 16 electrons
{[Cp(CO)2Mn], [(CO)5Cr], [(C6Me6)(CO)2Cr]} leads to
neutral compounds with main group IV, cationic ones with
main group V and anionic species with main group III ele-
ments.[14c,15,16] The 16 valence electron species {[(Cp*)-
(CO)2Fe]} accordingly forms cationic compounds with In-
dium and Gallium.[14a,14b] All these compounds, hence,
have a 36 valence electron count. Quantum chemical calcu-
lations on the EHT level[17] indicate that the HOMO in
compounds of this type should be a degenerate pair of
metal orbitals. More recent density functional calcula-
tions[18] are in agreement with these early results. If the
highest orbital occupied is metal centred with no contri-
Scheme 5.
In the synthesis of compounds 3, a minor green by-prod-
uct was sometimes observed. The nature of this by-product
became clear when dibenzyl disulfide was used as the sub-
strate expected to undergo oxidative addition with “tri-
podCo0”. In this case the green compound was the main
product and no species of type 3 could be isolated. It was
characterised as 4a, a dinuclear compound containing two
tripodcobalt entities linked by a sulfur atom (Scheme 6).
Scheme 6.
The structure of 4a was determined for crystals contain- bution to M–E bonding one might expect that compounds
ing solely 4a and also for crystals containing 4a and dif- with linear M–E–M entities might as well exist with an elec-
ferent amounts of solvent (Figure 5, Table 5). In all of the tron count of less than 36 electrons. While compounds of
three pseudopolymorphs 4a, 4a·DME and 4a·3DME this type have not yet been described, cyclovoltammetric
(Table 5) the Co–S–Co axis is strictly linear. In all cases but analysis of 4a reveals three oxidation peaks in the range of
one this linearity corresponds to crystallographic symmetry –1000 mV to +800 mV vs. SCE (Figure 4).
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J. Mautz, G. Huttner
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Scheme 7.
Figure 4. Cyclic voltammogramm of 4a.
compound 4b is obtained in crystalline form as 4b·3DME
(Scheme 8). The structure of 4b·3DME resembles that of
4a·3DME in all comparable details (Figure 5, Table 5). The
Co–Se bond has a length of 216.3 pm and is the shortest
Co–Se bond reported so far.[20]
The first oxidation wave is fully reversible with E1/2
=
–700 mV vs. SCE, the following two oxidation steps are
only quasi-reversible and occur at EAp = –40 mV vs. SCE
and EAp = +570 mV vs. SCE, respectively (Figure 4). The
phenotype of the cyclic voltammogramm is well in agree-
ment with the quantum chemically supported assumption
of a pair of metal centred orbitals at the HOMO level in
4a. The neutral compound 4a with the degenerate pair of
HOMO orbitals completely filled should be diamagnetic as
is in fact found. 1H and 13C NMR spectra show the signals
characteristic of tripod metal entities (see Exp. Section). The
peculiarity of the bonding situation in 4a is, on the other
Scheme 8.
As already mentioned, four different types of crystals of
hand, reflected by its behaviour in 31P NMR spectroscopic 4a were obtained, depending on the conditions of crystalli-
experiments: in the temperature range of 303 K to 203 K sation and the solvent employed (see Exp. Section). The
no 31P NMR signal can be observed at all. Only at 193 K, structure of the coordination compound was found to be
the lowest accessible temperature in the solvent used, a very principally the same in all four types of crystals as far as
broad signal starts to appear with a full width at half maxi- scalar entities (distances, angles) are concerned (Table 5).
mum of 400 Hz. The origin of this strange behavior is not The different types of solvation present in the different
clear. A similar type of behavior has already been described types of crystals of 4a do not markedly affect distances and
for the diamagnetic compounds [tripodCo(C6O4X2)Cotri- angles within the coordination compound but they do af-
pod](PF6)2 (X = H, Cl, Br, I, NO2, Me),[19] where a 31P fect the rotational position of the tripod metal entities as a
NMR signal only appears below 200 K.[19] Just one sharp whole as well as the skew of the tripod metal cage and the
singlet is observed in this case, which makes clear that the rotational position of its phenyl rings. In all but one crystal
tripod ligands are still free to rotate at these low tempera- the rotation of the tripod metal cages with respect to the
tures, excluding any process of hindered rotation as an ex- Co–S–Co axis corresponds to a staggered arrangement cor-
planation for the observed behavior. No rationale has been responding to the position of the sulfur atom at a crystallo-
found to explain the observed behaviour. As both types of graphic centre of inversion. In the triclinic unit cell of
compounds are dinuclear with the tripodCo entities coupled 4a·DME one of the two crystallographically independent
by a strong π-type interaction with the bridging ligand, the molecules shows a staggered arrangement as well, corre-
yet unknown explanation might rest on the same type of sponding to its location at a crystallographic centre of in-
arguments for both classes of compounds.
version, while the other one, not restricted by crystallo-
The synthesis of 4a with (PhCH2S)2 as the source of sul- graphic symmetry requirements, reveals an eclipsed ar-
fur points to some thiophilicity of the “tripodCo0” species rangement of the two tripodcobalt entities with respect to
A, as does the generation of 4a as a by-product in the syn- the Co–S–Co axis. This indicates that rotation of the tripod
thesis of 3a and 3b. Even reacting A with DMSO yields 4a cobalt entities around the Co–S–Co axis has a rather low
in minor amounts. All this points to a high potential of rotation barrier.
“tripodCo0” (A) to extrude sulfur out of organic sulfur
The kind of packing of 4 in three types of crystals is
compounds. As a sulfur source which is more resistant to interesting in itself: in the triclinic structure of 4a, which is
desulfurisation than (PhCH2S)2, dibenzothiophene was free of solvate molecules, the basic motif of packing in two
therefore treated with “tripodCo0” (A). Clean desulfuris- dimensions is that of a centred hexagon. Within the (011)
ation was observed with 4a as the cobalt compound and plane the centres of the molecules (represented by the sulfur
biphenyl as the organic product (Scheme 7).
atoms), approach the pattern of planar close packing. The
The extrusion of selenium out of organic selenium com- distances within the hexagons are almost equal (1285–
pounds is as well possible. Treating “tripodCo0” (A) with 1335 pm), the angles are close to 60° throughout (57.9–
PhSeSePh in a ratio of 4:1, in addition to 3c, the olive green 61.6°). The formation of this quite regular arrangement is
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Reductive Activation of tripod Metal Compounds
Figure 5. The molecular structure of 4a·3DME in the crystal (hydrogen and DME omitted for clarity). Left: general view; right: projection
onto the defined by the three tripod phosphorus atoms.
Table 5. Selected bond lengths [pm], bond angles [°] and torsion vertical, in the other one close to parallel with respect to
angles [°] in 4a, 4b.
the (011) plane. If almost regular hexagons are nevertheless
4a·DME[a,b,g]
4a[a,c]
4a·3solv.[a,d,e] 4b·3DME[d,f]
formed, this must mean that the molecules “see” each other
as circles of similar radii within the plane, irrespective of
their orientation. Constructing the van der Waals surface
or as well the solvent accessible surface of the molecules, it
is observed that – in contrast to what the view of the ball
and stick model (Figure 5) suggests at first glance – the
molecules are close to globular in effect. To illustrate this
observation, a view of a space-filling model of 4 embedded
in a sphere is shown in Figure 6. The van der Waals surface
of the molecule is not really spherical of course such that
the packing in the molecular structure of 4a in the crystal
in the third dimension does not conform to either a hexago-
nal AB- (hcp) or a cubic ABC-type (fcc) of arrangement.
The centres of the molecules of the second layer are some-
what displaced from the position they would occupy in a
hexagonal packing, leading to an arrangement as if the
Co1–P1
Co1–P2
Co1–P3
Co1–E
P1–Co1–P2
P1–Co1–P3
P2–Co1–P3
Co1–E–Co2
P1–Co1–E
P2–Co1–E
P3–Co1–E
215.8(2)
218.1(2)
216.2(2)
204.5(2)
90.1(2)
93.0(2)
94.4(2)
180.0
119.4(2)
128.7(2)
122.3(2)
28.4
25.0
31.8
39.2
0.2
44.1
4.0
24.1
16.4
217.0(2) 217.2(1)
216.9(2) 217.2(1)
216.5(2) 217.2(1)
205.5(1) 205.9(1)
90.7(1)
95.4(1)
91.7(1)
180.0
216.3(1)
216.3(1)
216.3(1)
216.3(1)
92.5(1)
92.5(1)
92.5(1)
180.0
123.5(1)
123.5(1)
123.5(1)
23.4
91.7(1)
91.7(1)
91.7(1)
180.0
120.9(1) 124.1(1)
127.2(1) 124.1(1)
122.2(1) 124.1(1)
[h]
τ1
τ2
τ3
f1
f2
f3
f4
f5
3.6
24.6
24.6
24.6
28.5
3.8
[h]
10.3
17.1
27.6
25.9
32.1
31.7
20.8
19.7
23.4
23.4
27.0
4.7
[h]
[i]
[i]
[i]
28.5
3.8
27.0
4.7
[i]
[i]
hexagonal columns would have undergone
motion.
a shear
28.5
3.8
27.0
4.7
[i]
f6
[a] E = S. [b] Two symmetrically independent molecules, the values
are given for the one located at a special position. [c] Two symmet-
rically independent molecules; both located at a crystallographic
centre of inversion. [d] Identical values are obtained as a conse-
¯
quence of the cubic space group Ia3. [e] Depending on the condi-
tions of crystallisation crystals with DME and THF as solvate
(solv.) were obtained.[22] [f] E = Se. [g] The values in parentheses
are standard deviations in units of the last decimals listed. [h] τ =
torsion angles within the chelate cage: τ1 = C4–C1–P1–Ni, τ2
=
C4–C2–P2–Ni, τ3 = C4–C3–P3–Ni. [i] The torsion angles f involv-
ing Hz are defined as follows: f1 = Hz1–P1–C100–C101, f2 = Hz1–
P1–C106–C107, f3 = Hz2–P2–C200–C201, f4 = Hz2–P1–C206–
C207, f5 = Hz3–P3–C300–C301, f6 = Hz3–P3–C306–C307; Hz–P
designates a vector that is vertical to the plane formed by the three
tripod phosphorus donor atoms and points towards the observer
when, in a projection onto this plane, the vector Co–C4 points
away from the observer, such that C4 lies below this plane.[3]
Figure 6. View of the space-filling model of 4 embedded in a sphere.
Left: view along Co–S–Co axis; right: view perpendicular to Co–
S–Co axis.
4a·DME, containing one solvent molecule per complex
entity crystallises in a triclinic space group as well. There
astonishing at first glance since the molecules within each are two crystallographically independent molecules in the
hexagon show two different kinds of orientation: in one cell, which arrange themselves in such a way that they again
kind the Co–S–Co axis of the molecules is oriented close to form the pattern of planar hexagonal close packing in the
Eur. J. Inorg. Chem. 2008, 1423–1434
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J. Mautz, G. Huttner
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(011) plane. The Co–S–Co axes of the molecules show two to a complete shielding of the coordination compounds by
different types of orientation relative to this plane. As de- a cuboctahedral cage of solvent molecules (Figure 7). The
scribed above in the case of 4a, a close to spherical bound- radius of this cage is 910 pm in 4a·3DME and 945 pm in
ary surface of the molecules allows for this regular arrange- 4b·3DME, of course corresponding exactly to one half of
ment, irrespective of the orientation of the molecules. The the distance between the centres of the coordination mole-
distances within the centred hexagons span the narrow cules (see above). The fact that regular cuboctahedra are
range from 1280 pm to 1354 pm, the angles differ only formed as the solvent cages of molecules of 4 is a clear
slightly from the ideal value of 60° (57.1°–63.5°). The stack- indication of the close to spherical surface of the molecules
ing of these planes is such that a pair of layers is inter- (Figure 6) and of the outstanding shielding properties of
spersed with a layer of solvent molecules. The layers of the the tripod ligand.
solvent molecules show the same type of planar hexagonal
close packing as is observed for the molecules of the coordi-
nation compound. The type of stacking is close to the one
characteristic of a tetragonally deformed, body-centred cu-
Conclusions
bic pattern (bcc).[21]
¯
4a·3DME crystallises in the space group Ia3 and con-
The nickel(0) compound [tripod4Ni3] (1) obtained by
tains layers of complex molecules with a planar hexagonal KC8 reduction of THF solutions of [(DME)NiBr2] and tri-
close packed arrangement as required by symmetry. The pod undergoes oxidative addition with dichalcogenides
stacking sequence is that of an exact ABC pattern, also as REER (E = S, Se; R = tBu, Ph) to produce the nickel(I)
required by crystal symmetry. The close packed layers in species [tripodNi(ER)] (2). Compounds 2 are pseudo tetra-
4a·3DME are, however, different from the ones observed in hedral 17 valence electron molecules with magnetic mo-
the structures of 4a and 4a·DME (see above). In 4a·3DME ments corresponding to one unpaired electron per molecule.
there is no direct contact between the complex molecules as They are reversibly oxidised to 16 valence electron species
was found for 4a and 4a·DME, but all pairs of molecules [tripodNi(ER)]+ (2+).
are separated by a solvent molecule with the centre of the
Cobalt(I) compounds [tripodCo(ER)] (3) isoelectronic to
solvent molecule in the middle of the vector, connecting the the nickel(II) species [tripodNi(ER)]+ (2+) are obtained by
centres of the coordination compounds. The distance be- treating solutions prepared from [tripodCoCl2] in THF and
tween the centres of the coordination compounds, which is KC8 under an argon atmosphere with dichalcogenides
at the same time the distance within the hexagons, is around REER (E = S, Se; R = tBu, Ph). Compounds 3 are pseudo
1820 pm. The corresponding distance in 4a and 4a·DME, tetrahedral 16 valence electron species with magnetic mo-
where there is a direct contact between the coordination ments corresponding to two unpaired electrons per mole-
compounds themselves, while the solvent molecules, if pres- cule. They are reversibly oxidised to 15 valence electron spe-
ent (4a·DME), occupy the space between the layers, cies [tripodCo(ER)]+ (3+).
amounts to around 1300 pm (see above). The solvent mole-
Depending on the reaction conditions and on the type
cules in 4a·3DME hence separate the coordination com- of dichalcogenide employed the reaction, which normally
pounds by around 500 pm. Principally the same type of lay- leads to the formation of 3, may be biased to produce [tri-
ers and packing is observed for 4b·3DME, the selenium an- podCoECotripod], 4 (E = S, Se), instead. Compounds 4
alogue of 4a·3DME. The distance between the centres of contain a linear tripodCo–E–Cotripod dumbbell with very
the coordination compounds is 1890 pm in this case short Co–E distances (Co–S: 205.4 pm; Co–Se: 216.3 pm),
(4a·3DME: 1820 pm), reflecting the larger size of selenium the corresponding bond order being at least two in each
as compared to sulfur.[22]
case. Compounds 4 are members of a family of isoelectronic
The arrangement of the solvent molecules thus far de- species containing dumbbell shaped M–E–M entities with
scribed with the focus on close packed planes corresponds short M–E bonds; all these complexes [LnMEMLn] are 36
valence electron compounds; the difference in electron
count of E (E may be an element of group III to group VI)
is compensated for by the appropriate electron count of the
LnM entity and the overall charge of the complex in each
case. Quantum chemical models suggest that the HOMO in
such compounds corresponds to a degenerate pair of metal
orbitals. The fact, that [tripodCoSCotripod] (4a) shows
three reversible or quasi-reversible oxidation waves supports
this suggestion.
Compounds 4 crystallise in four different pseudopoly-
morphs differing in the content and kind of solvate mole-
cules. In all these pseudopolymorphs hexagonally closed
packed planes are a characteristic basic pattern. In one type
Figure 7. Cuboctahedral cage of DME molecules (symbolised by
of pseudopolymorph each coordination compound is em-
bedded in a cuboctahedral cage of solvate molecules. This
small balls) surrounding the complex molecule (symbolised by big
ball) in the molecular structure of 4·3DME in the crystal.
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Reductive Activation of tripod Metal Compounds
Synthesis of [tripodNi(ER)] (2a–c): To a THF solution containing
1, prepared from [tripodNiBr2] (840 mg, 1 mmol) and KC8 (297 mg,
rather unconventional pattern of molecular packing is a
consequence of the close to spherical shape of coordination
compounds 4.
2.2 mmol) (see above)
a solution of either (PhS)2 (109 mg,
0.5 mmol), (tBuS)2 (89 mg, 0.5 mmol) or (PhSe)2 (153 mg,
0.5 mmol) in THF (10 mL) was added. After stirring overnight,
the solvent was removed in vacuo. The residue was suspended in
petroleum ether (boiling range 40–60 °C) and transferred to a col-
umn containing silica gel (Ø = 3 cm, l = 5 cm), conditioning with
petroleum ether (boiling range 40–60 °C) via a cannula. After elu-
tion by 50 mL of petroleum ether (boiling range 40–60 °C) and
50 mL of diethyl ether, the products were eluted with 50 mL of
dichloromethane (for 2a, 2c) or 50 mL of DME (for 2b) as orange
to dark red coloured bands. Having removed the solvent in vacuo,
red microcrystalline powders were obtained. Red crystals, suitable
for X-ray structural analysis, were obtained by layering saturated
dichloromethane solutions (2a, 2c) and DME solutions (2b) with
diethyl ether. Yields for 2a: 640 mg, 0.81 mmol, 81%; 2b: 455 mg,
0.59 mmol, 59%; 2c: 545 mg, 0.65 mmol, 65%.
Experimental Section
General: All manipulations were performed under an inert atmo-
sphere of dry argon using standard Schlenk techniques or by work-
ing in a glove box. Solvents were dried with potassium (THF,
DME) or CaH2 (CH2Cl2, Et2O, PE 40/60), distilled, and thor-
oughly degassed prior to use. Deuterated solvents were dried with
potassium ([D8]THF) or CaH2 (CD2Cl2), vacuum distilled, de-
gassed by three successive “freeze-pump-thaw” cycles and stored in
Teflon valve ampoules under argon.
NMR: Bruker Avance DPX 200 at 200.120 MHz (1H), 50.323 MHz
(13C{1H}), 81.015 MHz (31P); T = 303 K unless stated otherwise;
chemical shifts (δ) in ppm referenced to (residual proton) peaks of
CD2Cl2 (1H: δ = 5.32; 13C: δ = 53.8 ppm) and [D8]THF (1H: δ =
1.73, 3.58; 13C: δ = 25.5, 67.7) as internal standards; 31P chemical
shifts (δ) in ppm with respect to 85% H3PO4 (31P: δ = 0 ppm) as
external standard. FAB-/HR-FAB-MS: Finnigan MAT 8400 spec-
trometer, xenon, matrix: 4-nitrobenzyl alcohol. LIFDI-MS: JEOL
JMS-700 double-focusing magnetic sector mass spectrometer.[23]
IR: BioRad Excalibur FTS 3000 spectrometer using CsI discs. UV/
Vis: Perkin–Elmer Lambda 19; 0.2 cm cells (Hellma, suprasil). Cy-
clic Voltammetry (CV): Metrohm “Universal Meß- und Titrier-
gefäß”, Metrohm GC electrode RDE 628, platinum electrode, SCE
electrode, EG&G Princeton Applied Research potentiostate Model
273, potentials in mV vs. SCE at 25 °C, sample 10–3  in 0.1 
nBu4NPF6/CH2Cl2. Differential Scanning calorimetry (DSC): Met-
tler DSC 30, argon, 30–600 °C, heating rate: 10 Kmin–1. Thermo-
gravimetric Analysis (TGA): Mettler TC 15, argon, 30–600 °C,
heating rate: 10 Kmin–1. EPR: Bruker ELEXSYS E500; X-band; ν
= 9.44 GHz; external standard diphenylpicrylhydrazyl. All mea-
2a: C47H44NiP3S·0.35CH2Cl2 (822.24): calcd. C 69.16, H 5.48, P
11.30, S 3.90; found C 69.16, H 5.76, P 11.06, S 3.82. MS (HR-
FAB+); m/z [fragment]: 791.1723 [M+, 58Ni], 793.1674 [M+, 60Ni]
(calcd. m/z: 791.1730, 793.1685). UV/Vis (THF), λmax [nm] (ε)
[–1 cm–1]: 390 (sh, 4200), 500 (sh, 1420), 950 (160). CV: E1/2
=
–290 mV (rev. ox., ∆E = 140 mV), EAp = 850 mV, ECp = –1560 mV.
DSC/TGA: endothermic melting process (m.p. 220 °C) initiates
exothermic decomposition. Decomposition is complete at 600 °C;
exp. final weight: 13.8%; calcd. final weight [Ni2P3]: 12.8%. For
magnetic and EPR data see Table 2.
2b:[26] C45H48NiP3S (772.56): calcd. C 69.96, H 6.26; found C 68.54,
H 6.07. MS (HR-FAB+); m/z [fragment]: 771.2043 [M+, 58Ni],
773.2022 [M+, 60Ni] (calcd. m/z: 771.2043, 773.2024). UV/Vis
(THF), λmax [nm] (ε) [–1 cm–1]: 380 (sh, 3350). CV: E1/2 = –470 mV
(rev. ox., ∆E = 140 mV), EAp = –200 mV (irreversible; reverse scan:
–950 mV), EAp = 1030 mV. DSC/TGA: endothermic melting process
(m.p. 210 °C) initiates exothermic decomposition. Decomposition
is complete at 600 °C; exp. final weight: 10.1%; calcd. final weight
[Ni2P3]: 13.5%. For magnetic and EPR data see Table 2.
surements were carried out at 293 K in
a standard cavity
ER 4102St. Xsophe, version 1.0.2β was used for simulation of the
spectra using the following parameters: 58Ni (I = 0; 100%); g- and
A-strain Gaussian line shape model. Elemental analyses were re-
corded by the analytical service of the Department of Chemistry
Heidelberg.
2c: C47H44NiP3Se (839.44): calcd. C 67.25, H 5.28, P 11.07; found
C 69.02, H 5.36, P 11.05. MS (HR-FAB+); m/z [fragment]: 839.1244
[M+, 58Ni], 841.1170 [M+, 60Ni] (calcd. m/z: 839.1177, 841.1165).
UV/Vis (THF), λmax [nm] (ε) [–1 cm–1]: 520 (1900), 900 (320). CV:
E1/2 = –180 mV (qrev. ox., ∆E = 140 mV), EAp = 800 mV, EAp
=
Materials: 1,1,1-Tris[(diphenylphosphanyl)methyl]ethane (tripod),
was prepared according to a literature procedure.[24] All other rea-
gents were obtained from commercial sources and used as received
unless explicitly stated. Silica gel (Kieselgel z.A., 0.06–0.20 mm, J.
T. Baker Chemicals B.V.) used for chromatography and kieselgur
(Erg. B.6, Riedel-de Haën AG) used for filtration were degassed at
10–2 mbar for 48 h and saturated with argon.
1540 mV. DSC/TGA: endothermic melting process (m.p. 230 °C)
initiates exothermic decomposition. Decomposition is complete at
600 °C; exp. final weight: 16.8%; calcd. final weight [Ni2P3]: 12.5%.
For magnetic and EPR data see Table 2.
Synthesis of [tripodCo(ER)] (3a–c): To a THF solution containing
A, prepared from [tripodCoCl2][25] (754 mg, 1 mmol) and KC8
(297 mg, 2.2 mmol) (see above) a solution of either (PhS)2 (109 mg,
0.5 mmol), (tBuS)2 (89 mg, 0.5 mmol) or (PhSe)2 (153 mg,
0.5 mmol) in THF (10 mL) was added. After stirring overnight,
General Procedure for the Synthesis of Solutions Containing A or 1:
KC8 (297 mg, 2.2 mmol), prepared by heating potassium (86 mg,
2.2 mmol) with graphite (211 mg, 17.6 mmol) was added to a solu-
tion of [tripodCoCl2][25] (754 mg, 1 mmol) or [tripodNiBr2] (840 mg, the solvent was removed in vacuo. The residue was suspended in
1 mmol), respectively, in THF (20 mL), prepared by treating either
petroleum ether (boiling range 40–60 °C) and transferred to a col-
[CoCl2] (130 mg, 1 mmol) or [(DME)NiBr2] (309 mg, 1 mmol) with umn containing silica gel (Ø = 3 cm, l = 5 cm), conditioning with
equimolar amounts of tripod (625 mg, 1 mmol). The resulting sus-
pension was sonicated until the colour changed to orange brown
in the case of A [“tripodCo0”] and yellow brown in the case of 1
([tripod4Ni3]). The reduction was monitored by UV/Vis spec-
troscopy until the spectra indicated completeness of the reaction
showing a strong band at λmax = 680 nm (A) and λmax = 380 nm
(1), respectively. The reaction mixture was then filtered through
kieselgur by means of a syringe to remove the remaining graphite.
petroleum ether (boiling range 40–60 °C) via a cannula. After elu-
tion by 50 mL of petroleum ether (boiling range 40–60 °C) and
50 mL of diethyl ether, the products were eluted as brown bands
by 50 mL of DME (3a, 3b) or by 50 mL of a 1:1 mixture of DME
and diethyl ether (3c). Having removed the solvent in vacuo, brown
microcrystalline powders were obtained. Dark brown crystals, suit-
able for X-ray structural analysis, were obtained by layering satu-
rated DME solutions with diethyl ether. Yields for 3a: 340 mg,
Eur. J. Inorg. Chem. 2008, 1423–1434
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1431

J. Mautz, G. Huttner
FULL PAPER
0.43 mmol, 43%; 3b: 365 mg, 0.47 mmol, 47%; 3c: 380 mg, Synthesis of [tripodCoSCotripod] (4a): To a THF solution contain-
0.45 mmol, 45%.
ing A, prepared from [tripodCoCl2][25] (754 mg, 1 mmol) and
KC8 (297 mg, 2.2 mmol) (see above) solution of either
a
3a: C47H44CoP3S (792.79): calcd. C 71.21, H 5.59, P 11.72, S 4.04;
found C 71.28, H 5.59, P 11.53, S 4.16. MS (HR-FAB+); m/z [frag-
ment]: 792.1691 [M+] (calcd. m/z: 792.1709). UV/Vis (THF), λmax
[nm] (ε) [–1 cm–1]: 320 (6600), 360 (4780), 650 (150), 760 (150), 900
(130), 1170 (300), 1320 (sh, 260). CV: E1/2 = –240 mV (rev. ox., ∆E
= 120 mV), E1/2 = 500 mV (rev. ox., ∆E = 120 mV), EAp = 1600 mV.
µeff (300 K) [µB] = 3.31. DSC/TGA: endothermic melting process
(m.p. 270 °C) initiates exothermic decomposition. Decomposition
is complete at 600 °C; exp. final weight: 19.8%; calcd. final weight
[Co2P3]: 13.3%.
PhCH2SSCH2Ph (44 mg, 0.25 mmol) or dibenzothiophene (92 mg,
0.5 mmol) in THF (10 mL) was added. Within two hours the col-
our of the solution changes to a brownish green. After stirring
overnight, the solvent was removed in vacuo. The residue was sus-
pended in petroleum ether (boiling range 40–60 °C) and transferred
to a column containing silica gel (Ø = 3 cm, l = 5 cm), conditioning
with petroleum ether (boiling range 40–60 °C) via a cannula. After
elution by 50 mL of petroleum ether (boiling range 40–60 °C) and
50 mL of diethyl ether, the product was eluted by 50 mL of DME
as a dark green band. Having removed the solvent in vacuo, a green
microcrystalline powder is obtained. Depending on the conditions
of crystallisation different kinds of crystals, suitable for X-ray
structural analysis, could be obtained. Storing a concentrated solu-
tion of 4a in THF or DME at –10 °C yields crystals of 4a·3THF
and 4a·3DME respectively. By layering saturated DME solutions
with diethyl ether crystals of 4a·DME were obtained, using petro-
leum ether (boiling range 40–60 °C) instead leads to the crystallisa-
tion of 4a. Yield (calcd. for 4a·DME): 410 mg, 0.30 mmol, 60%.
Correct analytical data was obtained for C82H78P6SCo2·DME (see
4a) while for the other polymorphs, the microanalytical data always
indicated a loss of solvent during the preparation of samples for
microanalysis.
3b: C45H48CoP3S (772.80): calcd. C 69.94, H 6.26, P 12.02, S 4.15;
found C 70.08, H 6.31, P 11.85, S 4.44. MS (HR-FAB+); m/z [frag-
ment]: 772.2025 [M+] (calcd. m/z: 772.2022). UV/Vis (THF), λmax
[nm] (ε) [–1 cm–1]: 320 (6100), 360 (6700), 740 (130), 920 (170),
1170 (380), 1350 (sh, 310). CV: E1/2 = –280 mV (rev. ox., ∆E =
120 mV), EAp = 810 mV, EAp = 1210 mV, EAp = 1510 mV. µeff (300 K)
[µB] = 3.12. DSC/TGA: endothermic melting process (m.p. 240 °C)
initiates exothermic decomposition. Decomposition is complete at
600 °C; exp. final weight: 17.8%; calcd. final weight [Co2P3]:
13.6%.
3c: C47H44CoP3Se·DME (929.80): calcd. C 65.88, H 5.85, P 9.99;
found C 65.42, H 5.65, P 10.02. MS (HR-FAB+); m/z [fragment]:
838.1207 [M+, 78Se], 840.1188 [M+, 80Se], 842.1201 [M+, 82Se]
(calcd. m/z: 838.1187, 840.1159, 842.1184). UV/Vis (THF), λmax
[nm] (ε) [–1 cm–1]: 310 (6900), 370 (4440), 770 (150), 760 (150),
1170 (320), 1360 (sh, 280). CV: EAp = –310 mV, ECp = –760 mV. µeff
(300 K) [µB] = 3.17. DSC/TGA: endothermic melting process (m.p.
260 °C) initiates exothermic decomposition. Decomposition is
complete at 600 °C; exp. final weight: 15.3%; calcd. final weight
[Co2P3]: 11.3%.
4a: C82H78Co2P6S·DME (1489.42): calcd. C 69.35, H 5.96, P 12.48,
S 2.15; found C 69.11, H 5.95, P 12.35, S 2.30. 1H NMR ([D8]-
THF): δ = 1.53 (s, 6 H, tripod-CH3), 2.71 (s, 12 H, tripod-CH2),
3.39 (s, 6 H, O-CH3), 3.55 (s, 4 H, O-CH2), 6.79–7.79 (m, 60 H,
arom. H) ppm. 31P{1H} NMR ([D8]THF): δ = 33.2 (br. s) ppm.
13C{1H} NMR ([D8]THF): δ = 28.9 (br. s, tripod-CH2), 36.8 (s,
CH3-Cq), 37.3 (s, tripod-CH3), 59.0 (s, O-CH3), 72.2 (s, O-CH2),
128.0 (s, arom. tripod-Cp), 129.6 (m, arom. tripod-Cm), 139.2 (m,
Table 6. Crystal data for 2a–c and 3a–c.
Compound
2a
2b
2c
3a
3b
3c
Empirical formula
Molecular mass
Crystal size [mm]
Crystal system
Space group (No.)
Lattice constants:
a [pm]
b [pm]
c [pm]
α [°]
β [°]
C47H44P3SNi·0.35CH2ClC2 45H48P3SNi
C47H44P3SeNi
839.44
C47H44P3SCo
792.79
C45H48P3SCo
772.80
C47H44P3SeCo·DME
929.80
822.24
772.56
0.20ϫ0.20ϫ0.15
monoclinic
P21/c (14)
0.20ϫ0.20ϫ0.10 0.20ϫ0.20ϫ0.10 0.25ϫ0.20ϫ0.10 0.25ϫ0.20ϫ0.20 0.25ϫ0.20ϫ0.10
monoclinic
P21/c (14)
monoclinic
Pn (7)
triclinic
monoclinic
P21/c (14)
monoclinic
P21/n (14)
¯
P1(2)
991.1(2)
1682.2(3)
2520.1(5)
90
1965.0(4)
1034.0(2)
2100.1(4)
90
1289.9(3)
3525.1(7)
1825.0(4)
90
109.44(3)
90
7825
8
1.425
200
1514.3(3)
1708.9(3)
1843.3(4)
72.87(3)
67.36(3)
64.84(3)
3936
1280.5(3)
1540.2(3)
2038.8(4)
90
95.61(3)
90
4002
4
1.283
200
1988.9(4)
969.2(2)
2344.6(5)
90
97.81(3)
90
4478
4
1.379
200
94.11(3)
90
115.81(3)
90
γ [°]
V [106 pm3]
Z
4191
3841
4
4
4
dcalcd. [g cm–3
]
1.303
200
1.336
200
1.338
200
T [K]
Scan range
Method
2.9° Յ 2θ Յ 53.6°
ω scan, ∆ω = 1°
10
2.3° Յ 2θ Յ 55.1° 2.6° Յ 2θ Յ 55.0° 2.4° Յ 2θ Յ 54.9° 3.2° Յ 2θ Յ 55.0° 2.5° Յ 2θ Յ 55.0°
ω scan, ∆ω = 1°
20
ω scan, ∆ω = 1°
10
ω scan, ∆ω = 1°
8
ω scan, ∆ω = 1°
8
ω scan, ∆ω = 1°
15
Scan speed [s frame–1
]
No. of reflections measured 15998
No. of unique reflections 8722
No. of reflections observed 4828
13903
8441
4473
I Ն 2σ
459
0.46
23350
23110
14773
I Ն 2σ
618
23706
16475
7824
I Ն 2σ
979
16517
9098
6611
I Ն 2σ
492
17878
10211
5603
I Ն 2σ
532
Observation criterion
I Ն 2σ
No. of parameters refined
Residial electron density
481
2.01
1.19
1.21
0.43
0.43
10–6 [epm–3
]
R1/Rw (%)F2 refinement
8.8/27.3
6.9/16.0
7.7/17.5
8.8/27.2
4.3/9.8
5.5/10.8
1432
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1423–1434

Reductive Activation of tripod Metal Compounds
Table 7. Crystal data for 4a, 4a·DME, 4a·3DME, 4a·3THF and 4b·3DME.
Compound
4a
4a·DME
4a·3DME
4a·3THF
4b·3DME
Empirical formula
Molecular mass [g]
Crystal size [mm]
Crystal system
Space group (No.)
Lattice constants:
a [pm]
b [pm]
c [pm]
α [°]
β [°]
C82H78P6SCo2
1399.30
C82H78P6SCo2·DME C82H78P6SCo2·3DME
C82H78P6SCo2·3THF C82H78P6SeCo2·3DME
1489.42
1669.66
1615.62
1716.56
0.20ϫ0.10ϫ0.10
triclinic
0.20ϫ0.10ϫ0.10
triclinic
P1 (2)
0.10ϫ0.10ϫ0.10
cubic
Ia3 (206)
0.25ϫ0.25ϫ0.25
cubic
Ia3 (206)
0.25ϫ0.25ϫ0.20
cubic
Ia3 (206)
¯
¯
¯
¯
¯
P1 (2)
1284.1(3)
1515.0(3)
1778.4(4)
90.85(3)
90.88(3)
90.03(3)
3459
1286.4(3)
2086.8(4)
2269.5(5)
69.31(3)
80.25(3)
80.05(3)
5575
2575.0(3)
2575.0(3)
2575.0(3)
90
90
90
17074
2598.1(3)
2575.8(3)
2598.1(3)
2575.8(3)
2598.1(3)
2575.8(3)
90
90
90
90
γ [°]
90
90
V [106 pm3]
Z
17537
17090
2
3
8
8
8
dcalcd. [g cm–3
]
1.343
1.331
1.299
1.114
1.334
T [K]
200
200
200
200
200
Scan range
Method
2.3° Յ 2θ Յ 55.0°
ω scan, ∆ω = 1°
10
1.9° Յ 2θ Յ 55.6°
ω scan, ∆ω = 1°
8
3.9° Յ 2θ Յ 55.0°
ω scan, ∆ω = 1°
10
3.8° Յ 2θ Յ 53.5°
ω scan, ∆ω = 1°
10
3.9° Յ 2θ Յ 54.9°
ω scan, ∆ω = 1°
20
Scan speed [s frame–1
]
No. of reflections measured 20368
No. of unique reflections 15210
No. of reflections observed 9733
35483
23916
14234
I Ն 2σ
1335
6559
3278
2454
I Ն 2σ
172
6255
3127
1865
I Ն 2σ
145
6556
3278
2554
I Ն 2σ
163
Observation criterion
I Ն 2σ
No. of parameters refined
Residial electron density
828
0.46
3.32
1.18
1.07
0.80
10–6 [epm–3
]
R1/Rw (%)F2 refinement
5.4/11.3
7.3/23.4
4.8/14.9
8.1/30.1
3.9/11.5
arom. tripod-Co), 159.0 (m, arom. Cq) ppm. 13C DEPT NMR ([D8]- using graphite-monochromated Mo-Kα radiation. The data col-
THF): δ = 28.9 (br. s, tripod-CH2), 37.3 (s, tripod-CH3), 59.0 (s, O- lected were processed using the standard Nonius software.[27] All
CH3), 72.2 (s, O-CH2), 127.9 (s, arom. tripod-Cp), 129.7 (m, arom. calculations were performed using the SHELXT-PLUS software
tripod-Cm), 139.6 (m, arom. tripod-Co) ppm. MS (HR-FAB+); m/z package. Structures were solved by direct methods with the
[fragment]: 1398.3027 [M+] (calcd. m/z: 1398.2914). UV/Vis (THF), SHELXS-97 program and refined with the SHELXL-97 pro-
λmax [nm] (ε) [–1 cm–1]: 420 (24650), 640 (7500). CV: E1/2
=
gram.[28,29] Graphical handling of the structural data during solu-
tion and refinement was performed with XPMA.[30] Structural rep-
resentations were generated using Winray 32.[31] Atomic coordi-
nates and anisotropic thermal parameters of non-hydrogen atoms
were refined by full-matrix least-squares calculations. Data relating
to the structure determinations are compiled in Tables 6 and 7.
–700 mV (rev. ox., ∆E = 110 mV), E1/2 = –40 mV (qrev. ox., ∆E
= 120 mV), E1/2 = 540 mV (qrev. ox., ∆E = 120 mV). DSC/TGA:
endothermic melting process (m.p. 350 °C) initiates exothermic de-
composition. Decomposition is complete at 600 °C; exp. final
weight: 16.7%; calcd. final weight [Co2P3]: 14.2%.
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
nos. CCDC-657989 (for 2c), -657990 (for 4a·3THF), -657991 (for
4a·3DME), -657992 (for 4a·DME), -657993 (for 3c), -657994 (for
3b), -657995 (for 3a), -657996 (for 4a), -657997 (for 2b), -657998
(for 2a), -657999 (for 4b·3DME). Copies of the data can be ob-
tained free of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K.; Fax: +44 (0)1223/336033; E-mail:
deposit@ccdc.cam.ac.uk.
Synthesis of [tripodCoSeCotripod] (4b): To a THF solution contain-
ing A, prepared from [tripodCoCl2][25] (754 mg, 1 mmol) and KC8
(297 mg, 2.2 mmol) (see above) a solution of PhSeSePh (77 mg,
0.25 mmol) in THF (10 mL) was added. After stirring overnight,
the solvent was removed in vacuo. The residue was suspended in
petroleum ether (boiling range 40–60 °C) and transferred to a col-
umn containing silica gel (Ø = 3 cm, l = 5 cm), conditioning with
petroleum ether (boiling range 40–60 °C) via a cannula. After elu-
tion by 50 mL of petroleum ether (boiling range 40–60 °C) and
50 mL of diethyl ether, 3c was eluted by 50 mL of a 1:1 mixture of
DME and diethyl ether (see above). Small amounts of a dark solid
remained on top of the column, which could be eluted with DME
as an olive green coloured band. Dark green crystals of 4a·3DME,
suitable for X-ray structural analysis, could be obtained by storing
a concentrated solution of 4b in DME at –10 °C.
Acknowledgments
The technical support of T. Jannack (Mass Spectrometry Labora-
tory of Institute of Inorganic Chemistry of University of Heidel-
berg) and the Microanalytical Laboratory of the Institutes of Inor-
ganic and Organic Chemistry of University of Heidelberg is grate-
4b: MS (HR-FAB+); m/z [fragment]: 1444.2371 [M+, 78Se],
1446.2424 [M+, 80Se], 1448.2469 [M+, 82Se] (calcd. m/z: 1444.2400,
1446.2376, 1448.2409).
X-ray Crystallographic Study: Suitable crystals were taken directly fully acknowledged. We thank Dr. J. Gross and co-workers of the
out of the mother liquor, immersed in perfluorinated polyether oil,
and fixed on top of a glass capillary. Measurements were made on
a Nonius-Kappa CCD diffractometer with a low-temperature unit
Mass Spectrometry Laboratory of the Institute of Organic Chemis-
try of University of Heidelberg for measuring the LIFDI mass
spectra.
Eur. J. Inorg. Chem. 2008, 1423–1434
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
1433

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Received: August 21, 2007
Published Online: Fenruary 5, 2008
1434
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1423–1434