Structure of [Ni(dippe)(μ-S)]2 and its reaction products. The nucleophilicity of the Ni2S2 fragment

Article abstract of DOI:10.1016/S0020-1693(01)00770-8

The dimer [(dippe)Ni(μ-S)]₂ reacts with organic electrophiles to give the alkylated species [(dippe)₂Ni₂(μ-S)(μ-SR)]⁺. Stronger alkylating agents lead to double alkylation and cleavage of the dimer. Protonation

Full text of DOI:10.1016/S0020-1693(01)00770-8

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Inorganica Chimica Acta 330 (2002) 118–127
Structure of [Ni(dippe)(m-S)]2 and its reaction products. The
nucleophilicity of the Ni2S2 fragment
Stephen S. Oster, Rene J. Lachicotte, William D. Jones *
Department of Chemistry, Uni6ersity of Rochester, Rochester, NY 14627, USA
Received 24 July 2001; accepted 31 October 2001
Dedicated to the memory of Professor Luigi Venanzi
Abstract
The dimer [(dippe)Ni(m-S)]2 reacts with organic electrophiles to give the alkylated species [(dippe)2Ni2(m-S)(m-SR)]+. Stronger
alkylating agents lead to double alkylation and cleavage of the dimer. Protonation similarly occurs with strong acids. The
structures of several of these species have been determined. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Crystal structures; Hydrodesulfurization; Nickel complexes; Sulfido complexes; Dinuclear complexes
1. Introduction
hydrodesulfurization of petroleum [2]. Second, we have
suggested that [Ni(dippe)(m-S)]2 results from the combi-
nation of two molecules of Ni(dippe)S, whose transient
existence has been demonstrated to be possible (Eq. (1))
[3].
Our group reported recently the desulfurization of
dibenzothiophene by [Ni(dippe)(m-H)]2 to produce
(1)
Third, its behavior as a bidentate metalloligand toward
[Ni(2,2%-biphenyl)] suggests its utility as a reagent in the
synthesis of more complex organometallic compounds.
While the mechanism for formation of the adduct with
[Ni(2,2%-biphenyl)] remains unclear, one analysis of
analogous [Pt2(m-S)2(PR3)4] compounds indicates that
the bonding and antibonding combinations of the
(S2)4− fragment are responsible for its basicity toward
other transition metal and main group element centers
[4]. Fourth, our determination of the structure of
[Ni(dippe)(m-S)]2 shows it to be the only reported Ni2(m-
X)2 molecule (where X=O, S, Se, Te, F, Cl, Br or I)
that is bent along the X–X axis [5]. It is mainly due to
this last structural property that a series of alkylation
and protonation experiments, such as those that in the
past have been performed on Pt2S2 complexes [6–10],
was conducted.
biphenyl [1]. Alkylated dibenzothiophenes also were
found to be reactive. Four transition metal complexes
were identified as intermediates in the reaction, two of
which were observed to contain bridging sulfido lig-
ands, [Ni2(dippe)2(m-S)] and [Ni(dippe)-(m-S)]2-m-Ni-
(2,2%-biphenyl) (Scheme 1). A third related bis-m-sulfido
complex [Ni(dippe)(m-S)]2 was also prepared.
These dinuclear nickel bridging sulfido species proved
to be quite interesting for several reasons. First, the
structures of [Ni2(dippe)2(m-S)] and [Ni(dippe)(m-S)]2
most closely approximate the edge site of a heteroge-
neous MoCoS catalyst that is used in the large scale
* Corresponding author. Tel.: +1-716-275-5493; fax: +1-716-473-
6889.
E-mail address: jones@chem.rochester.edu (W.D. Jones).
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(01)00770-8

S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
119
Scheme 1.
bidentate phosphine, but is slightly larger than what is
found in platinum–aminothiolate dimers with diphos
as the terminal ligand [11]. The Ni–Ni distance is 2.941
2. Results and discussion
2.1. Preparation and characterization of
[Ni(dippe)(v-S)]2
,
,
A, approximately 0.44 A greater than the sum of their
van Der Waals radii, indicating the absence of any
direct metal–metal interaction. The average Ni–S dis-
The bis m-sulfido dimer [Ni(dippe)(m-S)]2 (1) can be
conveniently prepared by the reaction of the hydrido
dimer [Ni(dippe)(m-H)]2 with cyclohexene sulfide (Eq.
(2)).
,
tance is typical of a single bond interaction at 2.197 A.
While [Ni(dippe)(m-S)]2 is the only known bent Ni2(m-
S)2 molecule, the factors that determine its structure are
(2)
Alternatively, the dimer forms upon loss of benzene
from (dippe)Ni(Ph)(SH) in a reaction that is believed to
1
generate [(dippe)Ni=S] (Eq (1)). The H NMR spec-
trum for 1 shows two types of isopropyl methyl groups,
each appearing as a doublet of doublets due to coupling
to the methine hydrogen and the phosphorus. Only a
single environment is observed for the methine and
methylene hydrogen resonances. The 31P NMR spec-
trum shows a singlet for the 4 equiv. phosphorus. Note
that the observation of two types of isopropyl methyl
group (i.e. one kind of isopropyl group with different
methyl environments) is consistent with either a planar
structure for the dimer or a hinged structure in which
inversion at the sulfurs renders the exo and endo iso-
propyl groups equivalent.
Fig. 1. ORTEP drawing of [(dippe)Ni(m-S)]2 (1). Ellipsoids shown at
30% probability level. Hydrogen atoms are omitted for clarity. Se-
lected distances: Ni(1)–Ni(2), 2.941(2), Ni(1)–P(1), 2.145(3), Ni(1)–
P(2), 2.149(3), Ni(1)–S(1), 2.187(3), Ni(1)–S(2), 2.206(3), Ni(2)–P(3),
2.144(4), Ni(2)–P(4), 2.152(4), Ni(2)–S(1), 2.201(4), Ni(2)–S(2),
2.194(3).
The single crystal X-ray structure of [Ni(dippe)(m-S)]2
actually shows it to be an example of a bent M2X2
molecule (Fig. 1) [3]. While this type of bending is
common in this class of molecules, it is quite rare in
Ni2X2 molecules [11]. The molecule can be described in
terms of two square planar Ni(II) centers joined and
bent along the S–S edge, with a hinge angle of 140.2°.
The average P–Ni–P angle of 89.9° is typical of a
Fig. 2. Critical orbital interactions in M2S2 structures.

120
S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
Table 1
,
Selected bond lengths (A) and bond angles (°) for [(dippe)2Ni2(m-S)(m-
SMe)][BPh4] (2a), [(dippe)2Ni2(m-S)(m-SEt)][BPh4] (2b) and [(dippe)2-
Ni2(m-S)(m-S-i-Pr)][BPh4] (2c)
2a
2b
2c
Bond lengths
Ni(1)–P(2)
Ni(1)–P(1)
Ni(1)–S(2)
Ni(1)–S(1)
Ni(1)–Ni(2)
Ni(2)–P(4)
Ni(2)–S(2)
Ni(2)–P(3)
Ni(2)–S(1)
S(1)–C(1)
2.1519(9)
2.1703(9)
2.1726(9)
2.2162(9)
2.9615(5)
2.1556(9)
2.1738(9)
2.1854(9)
2.2173(9)
1.863(4)
2.1599(13)
2.1902(13)
2.1737(13)
2.2330(13)
2.9656(8)
2.1614(13)
2.1823(13)
2.1964(13)
2.2399(13)
1.842(5)
2.1683(10)
2.1988(10)
2.1800(10)
2.2455(9)
2.9911(6)
2.1739(10)
2.1804(9)
2.1997(10)
2.2384(9)
1.870(4)
Fig. 3. 31P NMR spectrum of [Ni2(dippe)2(m–S)(m-SCH3)]Cl in ace-
tone-d6.
perhaps best explained by applying the conclusions of a
theoretical study of platinum(II) dimers with a Pt2S2
ring by Gonza´lez-Duarte, Lledo´s and coworkers [4].
Their analysis also provides the basis for understanding
the chemical reactivity of [Ni(dippe)(m-S)]2 towards nu-
cleophiles. Their work concludes that the factor that
determines the preference for a hinged geometry in
platinum(II) dimers with a Pt2S2 ring is the stabilization
of the M–S MO’s that are formed from the filled s*
and p*// orbitals of the (S2)4− ‘fragment’ and the unfilled
bonding and antibonding combinations of orbitals of
the [M2L4]4+ fragment. These orbitals are shown in
Fig. 2. While the antibonding interaction within the
(S2)4− fragment p/*/ orbital is not expected to be strong
due to the distance between the two bridging sulfur
atoms, the antibonding interaction within its s* orbital
may be substantial. When the M2S2 core folds, mixing
of [M2L4]4+ xy orbitals and xz orbitals becomes sym-
metry allowed and the result is better [M2L4]4+ xy-or-
bital overlap with the (S2)4− s* and p*// orbitals.
Despite the fact that the metal xz orbitals are destabi-
lized, distortion of the M2S2 core allows for greater
stabilization of the S–S antibonding interactions. Fur-
thermore, the change in geometry of the M2S2 core that
takes place upon reaction is determined by the elec-
tronic demands of the (S2)4− s* and p*// orbitals.
Bond angles
P(1)–Ni(1)–P(2)
S(1)–Ni(1)–S(2)
P(1)–Ni(1)–S(1)
P(1)–Ni(1)–S(2)
P(2)–Ni(1)–S(1)
P(2)–Ni(1)–S(2)
P(3)–Ni(2)–P(4)
S(1)–Ni(2)–S(2)
P(3)–Ni(2)–S(1)
P(3)–Ni(2)–S(2)
P(4)–Ni(2)–S(1)
P(4)–Ni(2)–S(2)
C(1)–S(1)–Ni(1)
C(1)–S(1)–Ni(2)
Ni(1)–S(1)–Ni(2)
Ni(1)–S(2)–Ni(2)
89.13(3)
86.53(3)
95.49(3)
167.63(4)
168.39(4)
91.24(3)
89.13(3)
86.47(3)
93.91(3)
175.45(4)
176.08(4)
90.30(4)
97.57(14)
103.31(15)
83.82(3)
85.90(3)
88.69(5)
86.16(5)
97.59(5)
164.58(6)
166.71(6)
90.87(5)
89.10(5)
85.79(5)
94.66(5)
176.51(6)
173.00(6)
90.11(5)
102.83(18)
100.74(17)
83.06(5)
85.82(5)
88.85(4)
85.84(3)
95.05(4)
177.92(4)
169.66(4)
90.58(4)
88.04(4)
86.01(3)
95.13(4)
170.78(4)
175.56(4)
91.35(4)
100.69(12)
107.41(12)
83.68(3)
86.62(3)
The 31P NMR spectrum of the monomethylated
product in acetone-d6, shown in Fig. 3, consists of a
pair of sextets at d 82.99 and 77.04 ppm. The coupling
pattern is consistent with an AA%BB% spin system.
Counterion
metathesis
with
NaBPh4
yielded
[Ni2(dippe)2(m-S)(m-SCH3)][BPh4] (2a), from which X-
ray diffraction quality crystals were grown. In the H
1
NMR spectrum of [Ni2(dippe)2(m-S)(m-SCH3)][BPh4],
the thiolate proton signal overlaps the signal of the
isopropyl methyne protons at 2.3 ppm. This chemical
shift lies with the range of previously reported chemical
shift values for m-SMe protons [12].
2.2. Alkylation of [Ni(dippe)(v-S)]2
[Ni(dippe)(m-S)]2 cleanly participates in an apparent
SN2 reaction with CH3Cl to form [Ni2(dippe)2(m-S)(m-
SCH3)]Cl (Eq. (3)).
[Ni2(dippe)2(m-S)(m-SCH3)][BPh4] crystallizes in the
space group P1. Bond lengths and angles are given in
(
(3)

S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
121
[Pt2(m-S)(m-SCH3)(PPh3)4]+ are 136.9 and 138.0°, re-
spectively. Furthermore, among the four isomers that
mixed sulfido–thiolato d8 metal dimers can assume, it
has the bent-exo form, which is the most common
member of the group [13]. The sum of the angles
around the thiolato sulfur atom in [Ni2(dippe)2(m-S)(m-
SCH3)]+ is 284.6°, which is slightly less than in [Pt2(m-
S)(m-SCH3)(PH3)4]+ and [Pt2(m-S)(m-SCH3)(PPh3)4]+.
The values fall in the range that is to be expected for a
m-alkylthiolato sulfur [13].
i
Both the ethyl (2b) and propyl (2c) mono-alkylated
dinuclear species can be prepared similarly. The initial
disappearance of [Ni(dippe)(m-S)]2 and formation of
[Ni2(dippe)2(m-S)(m-SEt]Cl is facile at room tempera-
ture, and follows bimolecular kinetics (k=8.8×10−3
Fig. 4. ORTEP drawing of [(dippe)2Ni2(m-S)(m-SMe)][BPh4] (2a). Ellip-
soids are shown at 30% probability level. Hydrogen atoms and the
BPh4 counterion are omitted for clarity.
M−1 −1). Both display NMR spectra similar to that
s
of 1a, with the addition of new alkyl group resonances.
Compounds 2b and 2c were also characterized struc-
turally, as shown in Figs. 5 and 6. The molecules both
are hinged at angles of 134.2 and 135.5°, respectively,
virtually identical to that observed in 2a. The sum of
the angles around the thiolato sulfur atom is 286.6° for
2b and 291.8° for 2c, showing a slight tendancy towards
flattening with the larger alkyl group (Table 1). Bending
at the hinge is a low energy process, and consequently
only large differences in the hinge angle are associated
with significant energy differences.
One aspect of the structural characteristics of
[Ni(dippe)(m-S)]2 (2a–2c) is inconsistent with the treat-
ment of these types of dimers as reported by Gonza´lez-
Duarte, Lledo´s and coworkers. Alkylation of a sulfido
ligand should force the p-orbital of sulfur that is used
in the formation of the s* orbital in the (S2)4− frag-
ment out of the S–S direction, thereby reducing the
amount of antibonding interaction. Consequently, the
hinge angle should increase (i.e. flatten out) in moving
from a bis-sulfido dimer to a mixed sulfido–thiolato
dimer [4]. To the contrary, alkylation of [Ni(dippe)(m-
S)]2 decreases the hinge angle slightly from 140 to
ꢀ135°. It is possible that the smaller hinge angle in 2a
could be due to steric interactions between the phos-
phorus substituents and the thiolate group.
Fig. 5. ORTEP drawing of [(dippe)2Ni2(m-S)(m-SEt)][BPh4] (2b). Ellip-
soids are shown at 30% probability level. Hydrogen atoms and the
BPh4 counterion are omitted for clarity.
In the reaction that produced [Ni2(dippe)2(m-S)(m-
SCH3)]+, the ratio of reagents [Ni(dippe)–(m-S)]2 and
CH3Cl was approximately 1:5. However, the dialky-
lated product [Ni(dippe)(m-SCH3)2]Cl2 did not form.
This same behavior was first reported by Chatt and
Mingos [6] and then by Ugo [7] in regard to the
reaction of organic halides with [Pt2(m-S)2(PMe2Ph)4]
and [Pt2(m-S)2(PPh3)4], respectively.
In order to overcome the decreased nucleophilicity at
the remaining sulfido group, [Ni(dippe)(m-S)]2 was re-
acted with the more potent methylating agent, methyl
triflate. The dialkylated product, [Ni2(dippe)2(m-
SCH3)2][OTf]2 (3), forms immediately upon addition of
4 equiv. of methyl triflate to an acetone solution of
[Ni(dippe)(m-S)]2 (Eq. (4)).
Fig. 6. ORTEP drawing of [(dippe)2Ni2(m-S)(m-SiPr)][BPh4] (2c). Ellip-
soids are shown at 30% probability level. Hydrogen atoms and the
BPh4 counterion are omitted for clarity.
Table 1, and a structural diagram is shown in Fig. 4.
The structure is typical of d8 metal dimers that contain
mixed sulfido-thiolato ligands in that the hinge geome-
try is maintained, presumably for the same reasons that
hold for dimers with two sulfido ligands [4]. The hinge
angle [5], q, of [Ni2(dippe)2(m-S)(m-SCH3)]+ is 136.5°,
while the angles for [Pt2(m-S)(m-SCH3)(PH3)4]+ and

122
S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
(4)
The 31P NMR spectrum of [Ni2(dippe)2(m-SCH3)2]-
not the reason for the instability of [Ni2(dippe)2(m-
S2CnH2n)]Cl2 relative to its decomposition monomers.
The X-ray structures of 4a and 4b were determined
(Figs. 7 and 8). Both are square planar Ni(II) com-
plexes with very little distortion around the nickel
(Table 2). The ethane bridge in 4a is slightly puckered,
whereas that in 4b is highly puckered.
1
[OTf]2 consists of a singlet at l 92.7 ppm, and the H
NMR spectrum displays the thiolate protons as a sin-
glet at l 2.37. The isopropyl methyl groups appear as
two doublets of doublets centered at l 1.37 and 1.24,
consistent with either a planar structure, or more likely
one with a rapidly inverting Ni2S2 core. [Ni2(dippe)2(m-
SCH3)2][OTf]2 is an oil, but in this case anion exchange
with NaBPh4 also produces an oil, precluding structural
studies.
2.3. Protonation of [Ni(dippe)(v-S)]2
Chatt and Mingos reported the formation of cis-
[PtBr2(PMe2Ph)2] when [Pt2S2(PMe2Ph)4] was reacted
with and excess of CH3Br [6]. A similar result was
obtained when [Ni(dippe)(m-S)]2 was reacted with 1,2-
dichloroethane. The 31P NMR spectrum displayed a
pair of sextets whose coupling patterns are reminiscent
of those for [Ni2(dippe)2(m-S)(m-SCH3)]+. The ultimate
products of the reaction are Ni(dippe)(h2-S2C2H4) (4a)
and Ni(dippe)Cl2, both of which steadily increased in
concentration over an 18-h period as the intermediate
[Ni2(dippe)2(m-S)(m-SC2H4Cl)]Cl diminished (Eq. (5)).
[Ni(dippe)(m-S)]2 reacts immediately with 1 equiv. of
HBF4·Et2O to form [Ni2(dippe)2(m-S)(m-SH)][BF4]. The
NMR data demonstrate the acidic nature of the
1
sulfhydryl proton. In the room temperature H NMR
spectrum, no sulfhydryl signal is seen. However, at
−50 °C, a broad triplet at l −0.16 is observed.
Line-broadening also occurs in the 31P NMR spectrum,
as seen in Fig. 9. The pair of pseudo triplets at l 86.97
and 82.62 seen at 25 °C resolves into a pair of quintets
at −30 °C.
(5)
Similar results are obtained when [Ni(dippe)(m-S)]2 was
reacted with 1,3-dichloropropane, giving Ni(dippe)(h2-
S2C3H6) (4b), which indicates that strain is most likely
In the presence of excess acid, [Ni2(dippe)2(m-S)(m-
SH)][BF4] is involved in an equilibrium with
[Ni2(dippe)2(m-SH)2][BF4]2, as is described by Eq. (6).
Fig. 8. ORTEP drawing of (dippe)Ni(S2C3H6) (4b). Ellipsoids are
shown at 30% probability level. Hydrogen atoms are omitted for
clarity.
Fig. 7. ORTEP drawing of (dippe)Ni(S2C2H4) (4a). Ellipsoids are
shown at 30% probability level. Hydrogen atoms are omitted for
clarity.

S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
123
Table 2
The equilibrium, even with such a large excess of acid,
lies far to the left for the ratio of signal intensities
between [Ni2(dippe)2(m-S)(m-SH)][BF4] and [Ni2(dippe)2-
(m-SH)2][BF4]2 is approximately 11 to 1. The fact that
dimethylation of [Ni(dippe)-(m-S)]2 is facile with a good
methylating agent, but that diprotonation is extremely
difficult, again demonstrates the acidic nature of the
sulfhydryl proton–sulfur bond.
,
Selected bond lengths (A) and bond angles (°) for (dippe)Ni(S2C2H4)
(4a) and (dippe)Ni(S2C3H6) (4b)
4a
4b
Bond lengths
Ni(1)–P(2)
Ni(1)–P(1)
Ni(1)–S(2)
Ni(1)–S(1)
S(1)–C(1)
2.154(2)
2.156(2)
2.179(2)
2.181(2)
1.820(7)
1.810(8)
2.1648(7)
2.1729(6)
2.1950(7)
2.2089(7)
1.829(3)
1.823(3)
2.4. In6ersion of the Ni2S2 core
S(2)–C(2/3)
There are many examples of M2S2 fluxionality in
molecules that contain bridging sulfido, thiolato, and
sulfhydryl ligands [14–18]. This behavior can be due to
either ring inversion (analogous to inversion of cyclo-
hexane) along the X–X axis or to the cleavage and
re-formation of an M–X bond during which the sulfur
atom rotates. Ring inversion is much more facile than is
bond cleavage/sulfur rotation. As an example, for
trans-[{Ru(CO)(m-SCH2Ph)(h-C5H5)}2], ring inversion
is fast on the NMR timescale even at −100 °C, while
sulfur rotation is fast only above 100 °C [12].
Bond angles
P(1)–Ni(1)–P(2)
S(1)–Ni(1)–S(2)
P(1)–Ni(1)–S(1)
P(1)–Ni(1)–S(2)
P(2)–Ni(1)–S(1)
P(2)–Ni(1)–S(2)
C(1)–S(1)–Ni(1)
C(2/3)–S(2)–Ni(1)
89.17(7)
93.41(8)
165.19(8)
90.54(8)
90.70(8)
164.80(9)
101.5(3)
101.4(3)
88.66(2)
95.42(3)
173.12(3)
89.45(3)
87.28(2)
170.77(3)
102.95(9)
106.97(9)
There is no evidence that suggests that sulfur rotation
is occurring in [Ni(dippe)(m-S)]2 and its products. How-
ever, 1H NMR spectra of [Ni(dippe)(m-S)]2, and
[Ni2(dippe)2(m-S)(m-SCH3)]+ indicate that all of these
complexes undergo rapid ring inversion at room tem-
perature. Specifically, the dippe isopropyl methyl reso-
nances point to this behavior. When the dippe ligand is
chelated to a square planar metal center, one expects to
observe two separate resonances for the inequivalent
sets of methyl groups. Furthermore, the methyl protons
couple to the isopropyl methine proton, and to the
a-phosphorus atom, as well, leading to two doublets of
Fig. 9. 31P NMR spectrum of [Ni2(dippe)2(m-S)(m-SH)][BF4] in ace-
tone-d6.
(6)
With approximately 2 equiv. of acid, the pair of triplets
that is seen in the 31P NMR spectrum at room temper-
ature coalesces to a broad singlet at l 89.31. It is also
shifted downfield from the average of the pair of
triplets, apparently as a result of the increased polarity
of the solvent. With the addition of approximately 10
equiv. of acid, the broad singlet sharpens considerably
and is shifted to 92.5 ppm.
To determine whether the equilibrium between
[Ni2(dippe)2(m-S)(m-SH)][BF4] and ꢀ10 H+ and
[Ni2(dippe)2(m-SH)2][BF4]2 lies to the left or to the right,
an acetone-d6 solution of the reagents was cooled to
−95 °C. Two sets of broad resonances are observed, a
singlet at l 100.07 and a ‘doublet’ centered at l 86.90.
1
doublets. In the H NMR spectrum of the square-pla-
nar Ni(dippe)(SCH3)2, these two sets of methyl groups
produce two doublets of doublets that are centered at l
1.37 and 1.24. The bent molecule [Ni(dippe)(m-S)]2
should have four distinct types of methyl groups, but
rapid ring inversion leads to the observation of only
two resonances, each a doublet of doublets.
For a bent, static molecule of the type [Ni2(dippe)2(m-
S)(m-SR)]+ one expects two see eight distinct methyl
group resonances. Only four doublets of doublets are
observed as a result of rapid ring inversion. Analysis of
[Ni(dippe)(m-SCH3)]+2 is more complex than the previ-
ous two cases. There is no crystal structure to indicate

124
S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
the geometry that most likely corresponds to an energy
minimum in solution. [Ni(dippe)(m-SCH3)]+2 has a large
number of possible isomers depending on whether the
Ni2S2 core is planar or bent, and whether the alkyl
groups are syn or anti. It could very well exist in
solution as a planar molecule with rapid interconver-
sion between syn and anti isomers, as is the case with
[{Pt(NH3)2(accysH2-m-S}2]2+ [14]. However, the
analogous complex [Pt2(m-SCH3)2(PH3)4]2+ is probably
a better model for the behavior of [Ni2(dippe)2(m-
SCH3)2]+ in solution. When the geometry of [Pt2(m-
SCH3)2(PH3)4]2+ is optimized for the anti configuration
of thiolate methyl groups, the complex prefers to be
planar. Yet, when it is optimized for the syn configura-
tion, a bent geometry is favored. The energy difference
between the planar-anti and the bent-syn isomers is 0.7
kcal mol−1 in favor of the latter so it is reasonable to
expect facile interconversion between the two of them
in solution. Is there evidence of this behavior in
[Ni2(dippe)2(m-SCH3)2]+? The answer is yes. The pla-
nar-anti and the bent-syn isomers of [Ni2(dippe)2(m-
SCH3)2]+ would produce four doublets of doublets in
benzophenone ketyl. Chlorobenzene was dried and dis-
tilled over CaH2. Neutral silica and alumina were
heated to 200 °C under vacuum for two days and
stored under nitrogen. Cyclohexene sulfide and sodium
hydrosulfide hydrate were purchased from Aldrich
Chemical Co. and used without further purification. A
Siemens-SMART 3-Circle CCD diffractometer was
used for X-ray crystal structure determination. Elemen-
tal analyses were obtained from Desert Analytics. All
1H, 31P and 13C spectra were recorded on a Bruker
AMX400 NMR spectrometer, and all 1H chemical
shifts are reported relative to the residual proton reso-
nance in the deuterated solvent. [(dippe)NiH]2 and
(dippe)Ni(SH)2 were synthesized according to proce-
dures published previously [19].
4.2. Preparation of [(dippe)Ni(v-S)]2 (1)
Cyclohexene sulfide (0.37 g, 3.26 mmol) in THF was
added via syringe to a THF solution of [Ni(dippe)(m-
H)]2 (1.00 g, 1.55 mmol) and the reaction mixture was
stirred for 24 h. The solvent was evaporated under
vacuum, the remaining solid redissolved in a minimal
amount of THF, and the sample placed on a neutral
alumina column. The column was eluted with hexanes,
the first fraction was collected, and the solvent removed
to yield a brown solid. The product was recrystallized
from hexanes at −30 °C, yielding 514 mg of 1 (47%).
1H NMR (C6D6, 25 °C): l 2.32 (oct, J=5.9 Hz, 8H),
1.63 (dd, J=14.5, 7.1 Hz, 24H), 1.08 (dd, J=12.2, 7.0
Hz, 24 Hz), 0.99 (d, J=10.0 Hz, 8H). 13C{1H} NMR
(C6D6, 25 °C): l 25.85–25.57 (m), 22.11 (quin, J=9.0
Hz), 20.29 (s), 18.73 (s). 31P{1H} (THF-d8, 25 °C, 162
1
the H NMR spectrum should the molecule be static at
room temperature. However, it gives rise to two dou-
blets of doublets for the isopropyl methyl groups, in-
dicative of interconversion, probably via ring inversion.
3. Conclusion
The results of this study of [Ni(dippe)(m-S)]2 and its
reaction products with electrophiles demonstrate that
many of the conclusions that have been reached in
regard to Pt2S2 compounds can be generalized to some
nickel analogs. M2S2 dimers often are chelating ligands
toward other transition metal and main group element
centers, which makes them potentially useful as homo-
geneous catalyts in organic and organometallic synthe-
ses. Should other relevant nickel analogs replicate the
chemistry of Pt2S2 compounds, then, as a class, they
will offer the organometallic chemist a cost-effective
substitute for the latter in that function. More studies
of [Ni(dippe)(m-S)]2 will follow, focussing on the chem-
istry that takes place at nickel rather than sulfur. These
studies are aimed at providing models for mechanistic
details of the hydrodesulfurization of petroleum that
are currently little understood.
MHz)
l
77.88 (s). Anal. Calc. (Found) for
C28H64Ni2P4S2: C, 47.62 (47.36); H, 9.13 (9.24)%.
4.3. Preparation of [Ni2(dippe)2(v-S)(v-SCH3)][BPh4]
(2a)
Approximately 1 atm of CH3Cl was placed above an
acetone solution of [Ni(dippe)(m-S)]2 (0.103 g, 0.15
mmol). The color of the solution immediately turned
orange–red and Na[BPh4] (0.056 g, 0.165 mmol) was
added. The reaction mixture was stirred for 15 min,
filtered through neutral alumina to remove NaCl and
excess Na[BPh4], and the solvent then removed under
vacuum. The remaining red solid was recrystallized
from acetone at −30 °C and then dried under vacuum
1
(68% yield). H NMR (acetone-d6, 25 °CC): l 7.33 (br
4. Experimental
s, 8H), 6.91 (t, J=7.4 Hz, 8H), 6.77 (t, J=7.2 Hz, 4H),
2.42–2.33 (m, 11H), 1.53 (m, 8H), 1.53–1.28 (m, 48H).
13C{1H} NMR (acetone-d6, 25 °C): l 136.09 (s), 125.02
(dd, J=2.6 Hz), 121.26 (s), 26.47 (d, J=27.4 Hz),
22.14 (m), 19.86 (dd, J=13.7, 10.0 Hz), 19.41(s), 19.27
(s), 17.99 (s), 17.92 (s), 13.39 (s). 31P{1H} NMR (ace-
tone-d6, 25 °C): l 82.99 (m), 77.04 (m). Anal. Calc.
4.1. General considerations
All operations were performed under a nitrogen at-
mosphere unless otherwise stated. Benzene, THF and
hexanes were distilled from dark purple solutions of

S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
125
1
(Found) for C53H87Ni2P4S2B: C, 61.2 (61.03); H, 8.4
(8.31)%.
late were unsuccessful. H NMR (acetone-d6, 25 °C): l
7.33 (b, 8H, C6H5), 6.91 (m, 8H, C6H5), 6.77 (m, 4H,
C6H5), 2.45–2.35 (m, 9H, CH(CH3)2, SCH(CH3)2,
1.96–1.75 (bm, 8H, PC2H4P), 1.66 (d, J=6.87 Hz, 6H,
SCH(CH3)2), 1.51–1.31 (m, 48H, CH(CH3)2). 13C {1H}
NMR (acetone-d6, 25 °C): l 136.08 (s), 125.02 (m),
121.26 (s), 27.07 (s), 25.26 (s), 25.07 (s), 21.83 (m), 19.37
(m), 19.23 (bs), 17.88 (bs). 31P {1H} NMR (acetone-d6,
25 °C): 80.84 (m), 73.77 (m).
4.4. Titration of [Ni(dippe)(v-S)]2 by CH3Cl
Approximately 1 atm of CH3Cl was placed in a
resealable NMR tube that contained 0.7 ml of degassed
acetone-d6 that was spiked with 3 ml (0.028 mmol) of
toluene. The concentration of the resulting stock
acetone-d6 solution of CH3Cl was determined by 1H
NMR spectroscopy by comparing the integration value
for CH3Cl to that of the toluene methyl protons.
Aliquots of this stock solution were added to a known
amount of [Ni(dippe)(m-S)]2 in acetone-d6. The
formation of [Ni2(dippe)2(m-S)(m-SCH3)][Cl] occurred
after approximately 1 equiv. of CH3Cl was added.
4.7. [Ni2(dippe)2(v-SCH3)]2][OTf ]2
Neat methyl triflate (7.2 ml, 0.032 mmol) was added
to an acetone solution of [Ni(dippe)(m-S)]2 (0.011 g,
0.015 mmol). [Ni2(dippe)2(m-SCH3)2][OTf]2 formed im-
mediately following the methyl triflate addition. The
solvent was removed by vacuum. The resulting oil was
washed with hexanes and was then placed under vac-
4.5. Preparation of
[Ni2(dippe)2(v-S)(v-SCH2CH3)][BPh4] (2b)
1
uum for three days to remove excess methyl triflate. H
NMR (acetone-d6, 25 °C): l 2.78–2.53 (m, 8H), 2.37
(s, 6H), 2.26–2.23 (d, J=13.7 Hz, 8H), 1.69–1.63 (dd,
J=9.4, 7.3 Hz, 24H), 1.43–1.38 (dd, J=6.6 Hz, 24H).
31P{1H} NMR (acetone-d6, 25 °C): l 92.71 (s).
Approximately 2 equiv. of C2H5Cl (2 M in t-butyl
methyl ether, 0.26 ml, 0.52 mmol) was added by syringe
to a stirred acetone solution of (2) (184 mg, 0.26 mmol).
The solution was stirred for 6 days. Approximately 1
equiv. of NaBPh4 (98 mg, 0.29 mmol) was placed in the
reaction flask, and the mixture was stirred overnight.
The solution was then vacuum filtered through neutral
alumina and the solvent was removed under vacuum to
4.8. Preparation of Ni(dippe)(v2-S2C2H4)
One equiv. of 1,2-dichloroethane was added to an
acetone-d6 solution of [Ni(dippe)(m-S)]2 to yield
[Ni2(dippe)2(m-S)(m-SC2H4Cl)][Cl]. The intermediate
[Ni2(dippe)2(m-S)(m-SC2H4Cl)][Cl] decomposed over 18
h to form Ni(dippe)(h2-S2C2H4) and Ni(dippe)Cl2.
Ni(dippe)(h2-S2C2H4) was separated from Ni(dippe)Cl2
and residual [Ni2(dippe)2(m-S)(m-SC2H4Cl)][Cl] with a
neutral alumina column, and its fraction was evapo-
rated to yield a light red solid.
1
yield an orange–red solid (64% yield). H NMR (ace-
tone-d6, 25 °C): l 7.33 (bs, 8H, –C6H5), 6.91 (m, 8H,
–C6H5), 6.76 (t, J=6.8 Hz, 4H, –C6H5), 3.15 –3.06 (m,
2H, –SCH2CH3), 2.48–2.29 (m, 8H, –CH(CH3)2), 1.98
–1.79 (m, 11H, –PC2H4P–, –SCH2CH3), 1.55–1.26
(m, 48H, –CH(CH3)2). 31P {1H} (THF-d8, 25 °C): l
83.30 (m), 76.39 (m). In a separate experiment using
equimolar concentrations of 1 and chloroethane, a plot
of 1/(1) versus time was linear with a slope that
gave k=8.8×10−3 M−1 s−1 (see Supplementary
information).
4.9. Alternati6e synthesis of Ni(dippe)(p2-S2C2H4)
1,2-Ethanedithiol (0.108 g, 0.27 mmol) in THF was
added to a stirred suspension of Ni(dippe)Cl2 (26 mg,
0.28 mmol) in THF. NEt3 (56 mg, 0.55 mmol) was
added and the solution stirred until the color changed
to a light red. The solution was filtered through neutral
alumina and the solvent removed by vacuum. The
resulting analytically pure red solid was washed with
hexanes and dried under vacuum (60% yield). It was
then redissolved in a minimal amount of THF, layered
with hexanes, and chilled at −30 °C to yield crystals
that were suitable for single crystal X-ray diffraction
4.6. Preparation of [Ni2(dippe)2(v-S)(v-SCHMe2)]-
[BPh4] (2c)
2-Tosylpropane (27 mg, 0.125 mmol) in THF was
added by syringe to a stirred THF solution of 2. The
resulting solution was stirred for three days as the color
changed from dark brown to dark crimson. The solvent
was removed under vacuum to leave a red oil. The oil
was redissolved in a minimal amount of THF, layered
with hexanes, and chilled at −30 °C to yield a waxy
dark red solid. This solid was placed in 25 ml of THF
along with NaBPh4 (43 mg, 0.125 mmol) and the
mixture was stirred overnight. The mixture was vacuum
filtered through neutral alumina and the solvent was
removed under vacuum to yield a dark red waxy solid.
All attempts to quantitatively exchange BPh4 for tosy-
1
studies. H NMR (acetone-d6, 25 °C): l 2.47 (s, 4H),
2.29 (m, 4H), 1.89 (d, J=10.9 Hz, 4H), 1.37–1.18 (m,
24H). 13C{1H} NMR: (acetone-d6, 25 °C): l 25.13–
24.59 (m), 22.32 (s), 22.80 to 20.40 (m), 18.39 (s), 17.70
(s). 31P{1H} NMR (acetone-d6, 25 °C): l 85.41 (s).
Anal. Calc. (Found) for C16H36NiP2S2: C, 46.5 (46.67);
H, 8.8 (8.75)%.

126
S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
4.10. Preparation of Ni(dippe)(p2-S2C3H6)
was stirred for 15 min and the solution concentrated
and cooled to −30 °C, producing [Ni2(dippe)2(m-S)(m-
SH)][BF4] in 50% yield. The resulting solid was washed
One equiv. of 1,2-dichloropropane was added to an
acetone-d6 solution of [Ni(dippe)(m-S)]2 to yield [Ni2-
(dippe)2(m-S)(m-SC3H6Cl)][Cl], which decomposed over
36 h to form Ni(dippe)(h2-S2C3H6) and Ni(dippe)Cl2.
Ni(dippe)(h2-S2C3H6) was separated from Ni(dippe)Cl2
and residual [Ni2(dippe)2(m-S)(m-SC3H6Cl)][Cl] on a
neutral alumina column, and its fraction was evapo-
rated to yield a red solid.
1
with cold hexanes and then dried under vacuum. H
NMR (acetone-d6, 25 °C): l 2.39 (br s, 8H), 1.97 (d,
J=20.9 Hz, 8H), 1.49–1.27 (m, 48H), −0.16 (br t,
observed at −50 °C, 1H). 31P{1H} NMR (acetone-d6,
−30 °C): l 86.97 (m), 82.62 (m). Anal. Calc. (Found)
for C28H65Ni2P4S2F4B: C, 42.35 (41.73); H, 8.25
(8.16)%.
4.11. Alternati6e synthesis of Ni(dippe)(p2-S2C3H6)
4.14. Structure determinations of 2a–2c, 4a and 4b
1,3-Propanedithiol (0.0593 g, 0.55 mmol) in THF was
added to a stirred suspension of Ni(dippe)Cl2 in THF.
NEt3 (0.111 g, 1.1 mmol) was added and the solution
stirred until the color changed to dark red. The solution
was filtered through neutral alumina and the solvent
removed under vacuum. The resulting red solid was
washed with hexanes, dried under vacuum, and then
redissolved in a minimal amount of THF, layered with
hexanes and chilled at −30 °C to yield crystals that
were suitable for single crystal X-ray diffraction study.
1H NMR (acetone-d6, 25 °C): l 2.42–2.32 (m, J=7.1
Hz, 4H), 2.31–2.26 (m, J=6.3 Hz, 4H, a-thiolate),
1.83–1.77 (quin, J=6.5 Hz, 2H, b-thiolate), 1.80–1.77
(d, J=11.1 Hz, 4H), 1.40–1.34 (dd, J=7.3, 8.1 Hz,
12H), 1.26–1.21 (dd, J=7.1, 5.9 Hz, 12H). 13C {1H}
NMR (acetone-d6, 25 °C): l 30.97 (s), 24.94 (m), 22.46
(s), 20.96 (t, J=19.3 Hz), 19.29 (s), 17.94 (s). 31P{1H}
NMR (acetone-d6, 25 °C): l 82.61 (s). Anal. Calc.
(Found) for C17H38NiP2S2: C, 47.79 (47.44); H, 8.96
(9.24)%.
Single crystals of each compound were mounted un-
der Paratone-8277 on glass fibers and immediately
placed in a cold nitrogen stream at −80 or −90 °C
on the X-ray diffractometer. The X-ray intensity data
were collected on a standard Siemens SMART CCD
area detector system equipped with a normal focus
molybdenum-target X-ray tube operated at 2.0 kW (50
kV, 40 mA). A total of 1321 frames of data (1.3
hemispheres) were collected using a narrow frame
method with scan widths of 0.3° in ꢀ and exposure
times of 10–30 s/frame using a detector-to-crystal dis-
tance of 5.09 cm (maximum 2q angle of 56.54°).
Frames were integrated with the Siemens SAINT pro-
,
gram to 0.75 A for all of the data sets. The unit cell
parameters for all of the crystals were based upon the
least-squares refinement of three-dimensional centroids
of \5000 reflections.1 Data were corrected for absorp-
tion using the program SADABS [20]. Space group as-
signments were made on the basis of systematic
absences and intensity statistics by using the XPREP
program (Siemens, SHELXTL 5.04). The structures were
solved by using direct methods and refined by full-ma-
trix least-squares on F2.2 For all of the structures, the
non-hydrogen atoms were refined with anisotropic ther-
mal parameters and hydrogens were included in ideal-
ized positions giving data:parameter ratios greater than
10:1.
4.12. Preparation of Ni(dippe)(SCH3)2
Approximately 2 equiv (0.038 g, 0.54 mmol) of
NaSCH3 was added to a suspension of Ni(dippe)Cl2 in
THF. The reaction mixture was stirred for 15 min as a
dark red color developed. It was filtered through neu-
tral alumina and the solvent removed under vacuum.
The resulting dark red solid was redissolved in a mini-
mal amount of THF, layered with hexanes, and chilled
There was nothing unusual about the solution or
refinement of any of the structures, with the exceptions
of compound 2c, which crystallized with a molecule of
THF solvent in the unit cell. Compound 4a crystallizes
with 4 independent molecules within the asymmetric
unit. Further experimental details of the X-ray diffrac-
tion studies are provided in Section 5. Positional
parameters for all atoms, anisotropic thermal parame-
1
at −30 °C to yield dark red crystals (61%). H NMR
(acetone-d6, 25 °C): l 2.54–2.45 (m, J=7.1 Hz, 4H),
1.96 (d, J=2.4 Hz, 6H), 1.76–1.74 (d, J=11.6 Hz,
4H), 1.40–1.34 (dd, J=8.5, 7.2 Hz, 12H), 1.26–1.21
(dd, J=7.0, 5.9 Hz, 12H). 31P{1H} NMR (acetone-d6,
25 °C): l 81 (s). Anal. Calc. (Found) for C16H38NiP2S2:
C, 46.28 (46.27); H, 9.22 (9.21)%.
1 It has been noted that the integration program SAINT produces
cell constant errors that are unreasonably small, since systematic
error is not included. More reasonable errors might be estimated at
10× the listed value.
4.13. [Ni2(dippe)2(v-S)(v-SH)][BF4]
Eighty-five percent of HBF4 in Et2O (0.024 g, 0.148
mmol) was added to an acetone solution of
[Ni(dippe)(m-S)]2 (0.105 g, 0.148 mmol). The reaction
2 Using the SHELX-95 package, R1=(ꢀꢁꢁFoꢁ−ꢁFcꢁꢁ)/ꢀꢁFoꢁ, wR2=
[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]}1/2
,
where w=1/[|2(Fo2)+(aP)2+bP]
and P=[ f.(maximum of 0 or Fo2)+(1−f )Fc2 ].

S.S. Oster et al. / Inorganica Chimica Acta 330 (2002) 118–127
127
[4] M. Capdevila, W. Clegg, P. Gonza´lez-Duarte, A. Jarid, A.
Lledo´s, Inorg. Chem. 35 (1996) 490.
[5] G. Aullo´n, G. Ujaque, A. Lledo´s, S. Alvarez, P. Alemany, Inorg.
Chem. 37 (1998) 804.
ters, all bond lengths and angles, as well as fixed
hydrogen positional parameters are given in Section 5
for all of the structures.
[6] J. Chatt, M.P. Mingos, J. Chem. Soc. A (1970) 1243.
[7] R. Ugo, G. La Monica, S. Cenini, A. Segre, F. Conti, J. Chem.
Soc. A (1971) 522.
[8] R.R. Gukathasan, R.H. Morris, A. Walker, Can. J. Chem. 61
(1983) 2490.
5. Supplementary material
Tables of crystallographic data, atomic coordinates
bond distances and angles, and anisotropic thermal
parameters for 2a–2c, 4a, 4b, and a kinetic plot for the
reaction of 1 with chloroethane are available from the
author upon request.
[9] C.E. Briant, C.J. Gardner, T.S.A. Hor, N. Howells, D.M.P.
Mingos, J. Chem. Soc., Dalton Trans. (1984) 2645.
[10] S.-W.A. Fong, T.S.A. Hor, J. Chem. Soc., Dalton Trans. (1999)
639.
[11] M. Capdevila, W. Clegg, P. Gonza´lez-Duarte, B. Harris, I. Mira,
J. Sola, I.C.J. Taylor, Chem. Soc., Dalton Trans. (1992) 2817.
[12] I.B. Benson, S.A.R. Knox, P.J. Naish, A.J.J. Welch, Chem. Soc.,
Dalton Trans. (1981) 2235.
[13] G. Aullo´n, G. Ujaque, A. Lledo´s, S. Alvarez, Chem. Eur. J. 5
(1999) 1391.
Acknowledgements
[14] S.D. Killops, S.A.R. Knox, J. Chem. Soc., Dalton Trans. (1978)
1260.
The National Science Foundation, grant CHE-
9816365, is acknowledged for their support of this
work.
&
[15] E.W. Abel, N.A. Cooley, K. Kite, K.G. Orrell, V. Sik, M.B.
Hursthouse, K.G. Dawes, Polyhedron 6 (1987) 1261.
[16] T.G. Appleton, J.W. Connor, J.R. Hall, P.D. Prenzler, Inorg.
Chem. 28 (1989) 2030.
[17] N. Duran, P. Gonza´lez-Duate, A. Lledo´s, T. Parella, J. Sola, G.
Ujaque, W. Clegg, K.A. Fraser, Inorg. Chim. Acta 265 (1997)
89.
References
[1] D.A. Vicic, W.D. Jones, J. Am. Chem. Soc. 119 (1997) 10855.
[2] J.V. Lauritsen, S. Helveg, E. Laegsgaard, I. Stensgaard, B.S.
Clausen, H. Topsoe, F. Besenbacher, J. Catal. 197 (2001) 1.
[3] D.A. Vicic, W.D. Jones, J. Am. Chem. Soc. 121 (1999) 4070.
[18] G. Natile, L. Maresca, G. Bor, Inorg. Chim. Acta 23 (1977) 37.
[19] D.A. Vicic, W.D. Jones, J. Am. Chem. Soc. 119 (1997) 10857.
[20] The SADABS program is based on the method of Blessing, see:
R.H. Blessing, Acta Crystallogr. Sect A 51 (1995) 33.