Cationic and neutral NiII complexes containing a non-innocent PNP ligand: Formation of alkyl and thiolate species

Article abstract of DOI:10.1039/b814806f

The synthesis and characterization of a series of cationic and neutral Ni-complexes with the non-innocent PNP^tBu pincer ligand is discussed. Starting with the dicationic complex 1, [Ni(PNP^tBu)(NCMe)](BF ₄)₂, a small series of dicationic and monocationic Ni ^II complexes has been prepared. Substitution with tert-butyl isocyanide and azide occurs readily in MeCN solution. IR spectroscopy provided a practical handle to access the formal valence state of the ligand. For the mono- and dicationic tert-butyl isocyanide species 3 and 6 the main vibrational bands in the IR spectra were reproduced quantitatively by DFT theoretical calculations, showing good agreement with the experimentally observed Δν upon dearomatization of the PNP^tBu backbone. Using a selective dearomatization-reprotonation methodology the mononuclear Ni-thiolate species 7 and 8 are cleanly generated and their structures have been determined by X-ray crystal structure determination. Alternatively, starting from the monocationic species [Ni(PNP^tBu)Cl]BF₄, neutral alkyl derivatives are easily available in a two-step procedure, and these species have been spectroscopically characterized. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b814806f

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Cationic and neutral NiII complexes containing a non-innocent PNP ligand:
formation of alkyl and thiolate species†
Jarl Ivar van der Vlugt,*‡a Martin Lutz,b Evgeny A. Pidko,a Dieter Vogta and Anthony L. Spekb
Received 26th August 2008, Accepted 4th November 2008
First published as an Advance Article on the web 16th December 2008
DOI: 10.1039/b814806f
The synthesis and characterization of a series of cationic and neutral Ni-complexes with the
non-innocent PNPtBu pincer ligand is discussed. Starting with the dicationic complex 1,
[Ni(PNPtBu)(NCMe)](BF4)2, a small series of dicationic and monocationic NiII complexes has been
prepared. Substitution with tert-butyl isocyanide and azide occurs readily in MeCN solution. IR
spectroscopy provided a practical handle to access the formal valence state of the ligand. For the mono-
and dicationic tert-butyl isocyanide species 3 and 6 the main vibrational bands in the IR spectra were
reproduced quantitatively by DFT theoretical calculations, showing good agreement with the
experimentally observed Dn upon dearomatization of the PNPtBu backbone. Using a selective
dearomatization-reprotonation methodology the mononuclear Ni-thiolate species 7 and 8 are cleanly
generated and their structures have been determined by X-ray crystal structure determination.
Alternatively, starting from the monocationic species [Ni(PNPtBu)Cl]BF4, neutral alkyl derivatives are
easily available in a two-step procedure, and these species have been spectroscopically characterized.
Introduction
Among the plethora of bulky phosphorus-containing pincer
systems applied in coordination and organometallic chemistry
during the last decades,1 most are based on a formally monoan-
ionic scaffold upon ligation to a transition metal complex.
The ‘archetypical’ PCP-framework A (with both aliphatic and
aromatic core structures) was originally developed by Shaw et al.
and then further developed by a number of groups over several
decades.2 Fryzuk et al. designed the PNP-ligand B and elegantly
utilized it in N2-activation chemistry,3 while Caulton et al. have
prepared several low-coordinate 14e- species with this particular
ligand scaffold as well.4 The diphenylamide derived PNP-ligands,
structure C, independently prepared by Mayer et al.5 and Liang
et al.6 and thereafter mainly used by the groups of Ozerov7
Fig. 1 Generalized structures of representative, monoanionic pincer
and Mindiola8 are newer examples of meridional monoanionic
PNP ligands. Lately, the chemistry of neutral PNPR-based pincer
ligands9 has attracted renewed attention as platform for late
transition metal complexes.10 One special feature of these 2,6-
lutidine derived systems is their ease of deprotonation of the
methylene spacer group (to yield PN-PR, see Fig. 1), effectively
making this a ‘non-innocent’ class of ligands, as recently explored
to great extent and in great detail by Milstein and co-workers,
including also analogous PNN derivatives.11
ligand scaffolds and the class of neutral, non-innocent PNPR ligands that
can undergo deprotonation.
We have applied the neutral (pseudo-)pincer ligand PNPtBu
to construct a number of CuI complexes wherein the pyridine
nitrogen atom exhibits unexpected hemilabile coordination to the
Cu-center.12 We thereafter decided to extent this methodology to
Ni and now report on the formation of complex 1, containing a
labile MeCN-ligand, that serves as the starting material for a study
into the formation of monomeric thiolato-species as well as NiII-
alkyl complexes, by making use of the non-innocent character of
the PNPtBu backbone.
aSchuit Institute of Catalysis, Laboratory of Homogeneous Catalysis,
Department of Chemistry and Chemical Engineering, Eindhoven University
of Technology, PO Box 513, 5600, MB, Eindhoven, the Netherlands.
E-mail: j.i.v.d.vlugt@tue.nl; Fax: ++31 40 2455054; Tel: ++31 40 2475028
Results and discussion
bDepartment of Crystal and Structural Chemistry, Utrecht University,
Padualaan 8, 3584, CH Utrecht, the Netherlands
Complex 1 is prepared in a straightforward manner by the
stoichiometric reaction of [Ni(NCMe)4](BF4)2 and PNPtBu in
MeCN as a deep-yellow crystalline solid. The 31P NMR spectrum
showed a singlet at d 69.0, while the presence of the MeCN co-
† CCDC reference numbers 699865–699869. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b814806f
‡ Present address: van ’t Hoff Institute for Molecular Sciences, University
of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, the
Netherlands; j.i.vandervlugt@uva.nl
1
ligand was corroborated with a triplet at d 3.03 in the H NMR
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Fig. 2 Displacement ellipsoid plots (50% probability level) of complex 1, [Ni(PNPtBu)(NCMe)](BF4)2 (left), and complex 2, [Ni(PNPtBu)(N3)]BF4 (right).
◦
˚
Hydrogen atoms and non-coordinated solvent molecules are omitted for clarity. Selected distances (A) and angles ( ) for 1: Ni–P1 2.2289(7); Ni–P2
2.2295(7); Ni–N1 1.9132(19); Ni–N2 1.842(2); N2–C24 1.133(3); P1–Ni–P2 173.90(3); P1–Ni–N1 87.40(6); P2–Ni–N1 86.61(6); P1–Ni–N2 92.10(6); P2–Ni–N2
93.85(6); N1–Ni–N2 177.93(9); Ni–N2–C24 177.6(2); for 2: Ni–P1 2.2043(7); Ni–P2 2.2038(7); Ni–N1 1.9179(19); Ni–N2 1.882(2); N2–N3 1.078(3); P1–Ni–P2
171.60(3); P1–Ni–N1 87.34(6); P2–Ni–N1 87.25(6); P1–Ni–N2 92.70(7); P2–Ni–N2 93.44(7); N1–Ni–N2 173.04(10); Ni–N2–N3 139.0(2).
spectrum. Recrystallization from MeCN-Et2O gave yellow plates
that were subjected to X-ray crystal structure determination. The
molecular structure is shown in Fig. 2 (left). Slightly distorted
square planar geometry is observed around the NiII center, with
in-plane coordination of the pyridine fragment, unlike what was
observed with CuI previously by us.12 The P1–Ni–P2 angle of
173.90(3)◦ is significantly smaller than for related cationic Pd-
complexes.13
Subtle structural differences are found when comparing the
solid-state structures for both compounds, mainly related to the
Ni–P and Ni–N2 distances, which originates from the anionic
character of the azido ligand. Rapid substitution of the labile
acetonitrile fragment of 1 also occurred with the strong, neutral
donor ligand tert-butyl isocyanide to give species 3, even in
MeCN solution. The observed 1H, 31P NMR and IR spectroscopic
features (d 1.78 (CNtBu); d 81.7; n 2188, 1607, 1565 cm-1) indicated
full conversion to [Ni(PNPtBu)(CNtBu)](BF4)2. In contrast, PMe3
in MeCN or excess cyclooctene in THF/CH2Cl2 failed to displace
the MeCN-ligand under identical conditions, suggesting mainly
steric control over the substitution. Addition of an excess of
the weakly nucleophilic, poorly soluble reagent LiNH2 to a
MeCN-solution of 1 did not lead to reactivity such as observed
by Campora, whereby a Ni(PCP)-amido species was selectively
formed,15 but the NMR and IR spectroscopic features indicated
that selective dearomatization of the neutral PNP ligand, to give
the formally monoanionic PN-P derivative, had occurred instead.
A more convenient method to prepare and isolate such a
monoamido complex is by reaction of complex 1 with one equiv
NaN(SiMe3)2 in THF, analogous to other metal complexes with
this PNP-ligand system; a color change from yellow to dark red-
brown was apparent within minutes for the thus generated complex
4 in solution. A first estimation of the different bond strength
of this monoanionic diphosphino-amido ligand was obtained by
reaction of complex 2 with the same base, yielding an orange-
colored neutral solid with an IR band at n 2055 cm-1, formulated
Reaction of 1 with one equiv NaN3 in MeCN (Scheme 1) yielded
1
a burgundy-red solid [Ni(PNPtBu)(h -N3)]BF4 (2) in 30 minutes,
with IR bands at n 2069, 1601, 1565 cm-1, the former of which
is indicative of terminal end-on coordination of the N3 ligand.14
These observations were substantiated by X-ray crystal structure
determination, as illustrated in Fig. 2 (right), confirming the
substitution of the labile MeCN ligand with the monoanionic
azido-fragment.
1
at Ni(PNPtBu)(h -N3) (complex 5), which was not completely
characterized. In effect, the IR band for nN N has shifted by 14 cm-1
=
upon deprotonation of the PNP-framework, itself evidenced by
the presence of a strong band at 1613 cm-1. Similarly, one equiv of
tert-butyl isocyanide was added to the in situ generated complex
4 to give a purple solid for complex 6. Coordination via the
generated amido-unit was confirmed by the single strong IR band
at n 1618 cm-1, whilst the band at n 2164 cm-1 for the isocyanide
ligand, compared with 2188 cm-1 for the dicationic analogue 3,
Scheme 1 Synthesis of complexes 1–6 with ligand PNPtBu
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illustrates the increased electron density at the Ni-center and the
trans-influence of the amido vs. pyridine donor.
the resulting molecular structure is displayed in Fig. 3. A green
initial solid was also obtained with thiophenol (31P NMR: d 50.0),
but although stable as a solid for extended periods of time, this
product appeared to be unstable in solution over the course of
crystallization in THF/pentane and CH2Cl2/hexane, leading to
the formation of a brown microcrystalline material which so far
has eluded further identification. The intended complex 8 could
only be isolated as the minor product from such mixtures as a green
crystalline material with identical spectroscopic characteristics
as the crude green solid obtained after reaction; the molecular
structure is shown in Fig. 4. Similar observations, i.e. formation
of a green reaction solution and isolation of a crude green solid,
could be made from the reaction of 1 with NaSPh in THF.
To support the aforementioned assignments of the observed
IR spectroscopic features, we turned to DFT-based analytic
calculation of harmonic normal modes. The quantum chemical
calculations were all performed at B3LYP/6-31G(d) level using
the Gaussian 03 program package.16 To minimize computing
time, the tert-butyl substituents on the phosphorus atoms were
replaced by methyl groups to yield complex 3¢ and 6¢; this should
not drastically alter the electronic properties of the ligand set.
Full geometry optimization of species 3 and 6 was performed,
followed by analysis of normal vibrational modes, which were
computed analytically. It is common, well-accepted practice to
apply a scaling factor when comparing theoretical IR data with
experimentally observed values; typically the value for this factor
varies marginally for different sections of the IR spectral range. For
the current computations, the applied scaling factor is 0.95 for the
cyanide region (nCN stretch) and 0.97 for the region nNpy vibrations.
After correction with said scaling factors, calculated dicationic
complex 3¢ exhibits bands at n 2188, 1606, 1565 cm-1. The first
∫
band originates from the C N stretch, while the other two bands
relate to the coordinated pyridine ring.17 For the deprotonated
complex 6¢ those bands were observed at n 2160, 1634, 1540 cm-1.
There is a negligible effect of the absolute conformation of the
PNP-pincer arms on the absolute values of these vibrations.18
Even with possible solvent-derived effects for the experimental
data and despite the slight alterations on the P-atom substituents,
the agreement between experimental and theoretical data is good,
both with regards to the absolute values of the relevant vibrations
in complexes 3¢ and 6¢ as well as concerning the observed Dn shift
in the nCN stretch upon dearomatization.
Although complex 4 did not show reactivity towards H2O or
ethanol at room temperature, which is in contrast with related
Pt-complexes using a PNN-ligand scaffold,19 use of more acidic
substrates did result in electrophilic substitution of the MeCN-
ligand and reprotonation of the pyridine ring (Scheme 2). This
two-step route allows the clean incorporation of functional groups
at the Ni-center in combination with the non-innocent PNP
scaffold.
Fig. 3 Displacement ellipsoid plot (50% probability level) of complex 7
[Ni(PNPtBu)(SCH2Ph)]BF4. Hydrogen atoms a◦nd counterion are omitted
˚
for clarity. Selected distances (A) and angles ( ): Ni–P1 2.2085(6); Ni–P2
2.2419(6); Ni–N 1.9655(18); Ni–S 2.2110(6); S–C24 1.825(3); P1–Ni–P2
169.40(2); P1–Ni–N 86.70(6); P2–Ni–N 85.98(6); P1–Ni–S 88.30(3);
P2–Ni–S 100.10(3); N–Ni–S 169.70(6); Ni–S–C24 117.86(9).
As protonation of the dearomatized backbone in effect gener-
ates a reactive thiolate fragment that subsequently substitutes the
labile MeCN-ligand, this synthetic methodology circumvents the
formation of unwanted side-products such as salts, which would
be generated via a more traditional anion-exchange reaction, that
would hamper isolation of the desired product. Thus, addition of
one equiv benzylmercaptan to a brownish solution of 4 in MeCN
instantaneously led to a color change to deep green. The resulting
solid showed a singlet at d 49.5 in the 31P NMR spectrum for
complex 7. Single crystals were obtained from THF-pentane and
Sonication of the crude green solid with diethyl ether led to
a brown solution and a green precipitate that showed identical
spectroscopic features as the isolated complex 8. Initial tests show
that also phenols appear to lead to fast decomposition of the
initial green adduct. The structures and mechanism of formation
of these apparent decomposition products are currently under
investigation.
The chemistry of nickel thiolate complexes attracts increasing
interest due to their likely role in biocatalytic systems such as
Scheme 2 Synthesis of complexes 7 and 8 with ligand PNPtBu
.
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the thiolate S-atom. Lastly, significant differences exist for the
observed interplanar angles between the least-squares planes of
the central pyridine ring and the NiL4 coordination plane, with
the following values: complex 1 12.62(10)◦; 2 5.66(10)◦; 7 8.62(9)◦;
8 22.93(7)◦. This shows the relatively high degree of flexibility in
the PNP-framework and the ease of twisting in the methylene
spacer groups to best accommodate the optimal structure for
crystallization.
Besides nickel thiolates, nickel alkyl complexes gain increasing
importance as these species are inferred as catalytic intermediates
for a range of organic transformations, such as hydrovinylation,
Heck and Kumada coupling and polymerization reactions. Insight
into the directed synthesis and controlled reactivity of such alkyl
species might aid the development of more active or selective
catalyst systems.
Reaction of NiCl2(dme) (dme = 1,2-dimethoxyethane) with a
stoichiometric amount of PNPtBu and NaBF4 in CH2Cl2 yielded
red complex 9 after 16 hours (Scheme 3). Alternatively, complex
9 can be prepared by reaction of NiCl2(dme) with the transmetal-
Fig. 4 Displacement ellipsoid plot (50% probability level) of complex
lating agent [Ag(PNPtBu)]BF4 in THF-MeCN. Recrystallization
22
8, Ni(PNPtBu)(SPh)]BF4. Hydrogen atoms and counterion are omitted
◦
˚
from CH2Cl2/hexane yieldeddark-red blocks that were suitable for
X-ray diffraction; the molecular structure (not shown; see Table 1
for details) clearly showed square-planar coordination around
Ni, comparable to other complexes discussed here. Subsequent
reaction (Scheme 3) with one equiv NaN(SiMe3)2 resulted in
a color change to green-brown, and the resulting green-brown
solid had one strong band at n 1612 cm-1 in the IR spectrum,
suggestive of the formation of NiCl(PN-PtBu), as two inequivalent
phosphorus atoms were observed in the 31P NMR spectrum at d
for clarity. Selected distances (A) and angles ( ): Ni–P1 2.2639(5); Ni–P2
2.2299(5); Ni–N 1.9534(14); Ni–S 2.1751(5); S–C24 1.7727(18); P1–Ni–P2
167.399(19); P1–Ni–N 83.69(4); P2–Ni–N 85.14(4); P1–Ni–S 105.043(18);
P2–Ni–S 87.051(17); N–Ni–S 166.11(4); Ni–S–C24 118.54(6).
NiFe hydrogenase.20 Notwithstanding the inherent instability of
the latter complex, both compounds 7 and 8 feature a mononuclear
four-coordinate nickel center with a single Ni-thiolate linkage.
Such species remain to be quite rare, and only a handful of
complexes have been described recently,21 most of which feature
similar low spin, square planar geometry as is the case in the
present complexes 7 and 8. As such, the Ni–S bond lengths fall
in the observed range for terminal nickel monothiolate species,
2
45.7 and 39.8 in C6D6, with a coupling constant JP-P of 293 Hz.
In the 1H NMR spectrum, three signals were present for the
protons on the dearomatized pyridine ring at 6.25, 6.03 and
5.12 ppm (in C6D6). Moreover, two doublets (intensity ratio 1:2)
at 3.22 and 2.27 ppm for the methine and methylene fragments
and two doublets (ratio 1:1) at 1.59 and 1.24 ppm (for the tert-
butyl groups of inequivalent phosphines) were discernable. With
the PNP framework present in its deprotonated version, any
further reactivity of complex 10 toward nucleophiles is strictly
limited to the NiII center. In the course of our investigations,
Milstein and co-workers disclosed some interesting substitution
chemistry of a Pt(PN-N)Cl complex, showing that this species
preferentially underwent addition of alkyllithium species, to form
anionic compounds of the formula [Pt(PN-N)(R)Cl]Li rather
than substitution of the halide co-ligand. Protonation of the
dearomatized PN-N backbone yielded neutral Pt(PNN)(R)Cl-
complex.19
˚
˚
at 2.2110(6) A (for 7) and 2.1751(5) A (for 8). The slight
˚
difference of ~0.06 A between the two species probably reflects
the less-electron donating character of the aromatic scaffold of
the thiophenolate ligand. A subtle but significant asymmetry is
observed in the Ni–P distances in both 7 and 8, with bond length
˚
˚
differences Dd of 0.0334 A and 0.034 A, respectively, the shorter
Ni–P bond distance being with the phosphine toward which the
sulfur-atom is deviating; the latter is implied by the N–Ni–S
angles of 169.70(6) and 166.11(4)◦, respectively. The origin of
this difference in Ni–P bond lengths is uncertain at the moment;
steric hindrance from the thiolate with the tert-butyl substituents
would most likely argue against the observed trend and it is
therefore speculated to be related to an electronic interaction from
Scheme 3 Synthesis of complexes 10–13 via sequential dearomatization and selective alkylation.
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Table 1 Selected crystallographic data for complexes 1, 2, 7, 8 and 9
1
2
7
8
9
Formula
[C25H46N2NiP2] (BF4)2·
CH3CN
[C23H43N4NiP2] (BF4)
[C30H50NNiP2S] (BF4)
[C29H48NNiP2S] (BF4)
[C23H43ClNNiP2] (BF4)
FW
709.96
Yellow
583.07
Red
664.23
Green
650.20
Brown
576.49
Red
Crystal colour
Crystal size/mm3
Crystal system
Space group
0.30 ¥ 0.24 ¥ 0.06
Monoclinic
P21/c (no. 14)
11.8057(1)
15.4958(2)
20.2129(2)
90
112.5118(8)
90
3415.96(7)
4
1.380
0.65
37081/7806
0.728
Multi-scan
0.90–0.96
439/285
0.27 ¥ 0.18 ¥ 0.15
Monoclinic
P21/c (no. 14)
14.9094(2)
12.4818(2)
15.5634(2)
90
105.6351(6)
90
2789.12(7)
4
1.389
0.65
33661/6389
0.857
Multi-scan
0.83–0.88
400/291
0.0377/0.0885
0.0554/0.0975
1.069
0.66 ¥ 0.51 ¥ 0.12
0.51 ¥ 0.48 ¥ 0.39
Monoclinic
P21/c (no. 14)
14.2312(1)
13.7370(1)
18.1600(1)
90
117.1778(3)
90
3158.21(4)
4
1.367
0.65
77735/7246
0.825
Multi-scan
0.52–0.72
364/0
0.45 ¥ 0.36 ¥ 0.18
Triclinic
Triclinic
¯
¯
P1 (no. 2)
P1 (no. 2)
˚
a/A
8.7077(2)
11.0192(3)
17.2498(4)
94.763(1)
90.893(2)
101.983(1)
1612.58(7)
2
1.368
0.65
26222/7366
0.810
Multi-scan
0.71–0.91
374/0
8.3356(1)
12.2538(1)
14.6565(2)
73.5826(5)
75.8775(6)
87.7751(8)
1391.89(3)
2
1.376
0.65
34132/6356
0.947
Multi-scan
0.60–0.84
338/123
0.0255/0.0633
0.0305/0.0659
1.031
˚
b/A
˚
c/A
a/◦
b/◦
g/◦
3
˚
V/A
Z
Dx/g cm-3
-1
˚
(sin q/l)max/A
Refl. meas./unique
m/mm-1
Abs. corr.
Abs. corr. range
Param./restraints
R1/wR2 (I>2s(I))
R1/wR2/all refl.
S
0.0379/0.0926
0.0595/0.1040
1.112
0.0434/0.1186
0.0477/0.1231
1.055
0.0328/0.0839
0.0407/0.0885
1.032
-3
˚
Res. density/e A
-0.40/0.45
-0.41/0.69
-1.07/1.97
-0.42/0.71
-0.29/0.50
As the labile, acidic PNP-backbone has already been deacti-
vated, use of strong bases does not result in further deprotonation
of a methylene spacer but instead should furnish clean substitution
chemistry at the metal center. To probe the subsequent reactivity of
the Ni-center, one equiv of PhLi or MeLi was added to a solution
of 10 in Et2O at -40 ◦C, leading to a color change from green to
brown-red upon warming the solution and formation of complexes
11 and 12, respectively. The resulting product was extracted
into pentane and characterized by NMR spectroscopy. The
deprotonated PN-PtBu backbone remained intact, as evidenced
by the three, slightly shifted, signals for the inequivalent protons
on the dearomatized pyridine ring in the 1H NMR spectrum. The
protons of the methyl-ligand in 12 were present as a triplet at
-0.08 ppm. In the 31P NMR spectrum an AB pattern of doublets
was observed for the two inequivalent phosphorus atoms at 43.9
and 41.3 ppm for 11 (41.5 and 37.6 ppm for 12) with a coupling
synthesis of well-defined mononuclear NiII-species, exemplified
by the isolation of rare mononuclear monothiolate complexes 7
and 8. The non-innocent character of the PNPtBu ligand leads to
significant electronic changes, as investigated for the dication 3 and
the related monocation 6, both featuring a tert-butyl isocyanide
co-ligand. DFT calculations reproduced the observed IR spectral
features of both complexes and supported our assignment of
the deprotonated PN-PtBu ligand as a monoamido fragment.
Dearomatization of the PNPtBu pincer scaffold also provided
access to the efficient synthesis of new neutral Ni-complexes
with Ph, Me or H as co-ligand, as derived from spectroscopic
investigations. We are currently investigating the reactivity of
these neutral Ni-complexes (e.g. in Kumada-coupling and other
C–C bond forming reactions23). Also the redox-chemistry of
the neutral NiII-complex 10 with the non-innocent PNPtBu lig-
and is envisaged to be interesting and might lead to unusual
reactivity.24
2
constant JP-P of 236 Hz for 11 (250 Hz for 12), slightly smaller
than that of the starting material. Future experiments will probe
the reactivity of these neutral Ni-alkyl species toward inter alia
weak acids, aimed at formation of the corresponding cationic
rearomatized pyridyl-based analogues. This will not be trivial, as
Ni-alkyl fragments are known to be more labile compared with
the heavier Pt-derivatives.
Experimental
General considerations
Solvents were purified by established procedures and all exper-
iments were carried out using standard Schlenk techniques in
flame-dried glassware. Starting materials were purchased from
commercial sources and used as received. Microanalyses were
performed by the Department of Organic Chemistry at the TU
Eindhoven and by Kolbe Laboratories, Mu¨lheim a/d Ruhr. IR
spectra (ATR reflectance mode) were recorded with a Nicolet
Avatar 360 FT-IR, NMR spectra were recorded on a Varian 200
spectrometer or Varian Mercury 400 spectrometer and calibrated
to the residual proton and carbon signals of the solvent (1H)
Addition of one equiv LiAlH4 (1.0 M in Et2O) to a solution
of 10 in Et2O gave an instantaneous colour change from green-
brown to red and the corresponding red solid exhibited a doublet
1
of doublets at d -18.4 in the H NMR spectrum (JP-H of 62 and
55 Hz) for the resulting terminal hydride ligand in complex 13.
Conclusions
In summary, we have described the use of complex 1,
[Ni(PNPtBu)(NCMe)](BF4)2 as a versatile building block for the
or external 85% aqueous H3PO4 (31P{ H}). [Ni(NCMe)4](BF4)2,25
1
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NiCl2(dme)26 and PNPtBu27 were prepared according to literature
procedures.
was subsequently stirred for 1 h. Filtration and evaporation of
solvent in vacuo left an off-white solid. Extraction into THF and
evaporation of the solvent in vacuo yielded a purple-red solid
(79.5 mg, 136.8 mmol, 61%). 31P-NMR (80.9 MHz, acetone-d6): d
79.7 (d, JP-P = 188 Hz, 1P), 71.6 (d, JP-P = 180 Hz, 1P). 1H-NMR
(200 MHz, acetone-d6): d 6.42 (t, J1 = 7.4 Hz, 1H, Py), 6.18 (d,
J1 = 7.4 Hz, 1H, Py), 5.55 (d, J1 = 7.4 Hz, 1H, Py), 3.59 (m,
1H, =CH), 3.40 (m, 2H, -CH2), 1.68 (s, 9H, CNtBu), 1.54 (d, J1 =
9.0 Hz, 18H, tBu), 1.47 (d, J1 = 9.0 Hz, 18H, tBu). IR (ATR, cm-1):
n 2164 (s), 1618 (m).
Nickel complex 1, [Ni(PNPtBu)(NCMe)](BF4)2. A solution of
[Ni(NCMe)4](BF4)2 (350.0 mg, 882.7 mmol) in MeCN (30 mL) was
added dropwise to a solution of PNPtBu (349.1 mg, 882.7 mmol) in
MeCN (20 mL) by means of a cannula at room temperature. The
resultant purplish-blue solution turned yellow within 10 minutes,
and was subsequently stirred for 4 h. Filtration and evaporation
of solvent in vacuo left a yellow solid. Recrystallization from
a concentrated acetone solution yielded light-yellow crystalline
material in good yield (448.7 mg, 670.9 mmol, 76%). 31P-NMR
(80.9 MHz, acetone-d6): d 69.2 (s). 1H-NMR (200 MHz, acetone-
d6): d 8.14 (t, J1 =8.0 Hz, 1H, p-ArH), 7.74 (d, J1 = 8.0 Hz, 2H,
m-ArH), 4.26 (vt, 4H, -CH2), 3.02 (t, J = 2.0 Hz, 3H, NCMe), 1.64
Nickel complex 7, [Ni(PNPtBu)(SCH2Ph)]BF4. A solution of 1
(200.0 mg, 299 mmol) in MeCN (30 mL) was added dropwise to a
solution of NaN(SiMe3)2 (54.8 mg, 299 mmol) in MeCN (20 mL)
via a cannula at room temperature. The resultant yellow solution
turned brown within 5 minutes, and was subsequently stirred for
1 h. To this solution was added benzyl mercaptan (35.1 mmL,
299 mmol) via microsyringe. An immediate color change to deep
green was apparent. Evaporation of the solvent and extraction
into THF gave a green solid after concentrating to dryness that
was washed twice with Et2O (20 mL). Recrystallization by slow
diffusion of pentane into a concentrated THF-solution yielded
dark-green single crystals (105.3 mg, 158.5 mmol, 53%). 31P-NMR
(80.9 MHz, acetone-d6): d 49.5 (s). 1H-NMR (200 MHz, acetone-
d6): d 8.02 (t, J1 = 7.0 Hz, 1H, p-ArH), 7.64 (d, J1 = 7.0 Hz,
2H, m-ArH), 7.27 (m, 5H, Ph), 3.97 (m, 4H, -CH2), 3.45 (s, 2H,
t
(vt, 36H, Bu). IR (ATR, cm-1): n 1604 (w), 1564 (w). El. Anal.
Calcd. for C25H46B2F8N2NiP2: C, 44.89; H, 6.93; N, 4.19. Found:
C, 45.06; H, 6.95; N, 4.41.
Nickel complex 2, [Ni(PNPtBu)(N3)]BF4. To a solution of 1
(250.0 mg, 373.7 mmol) in MeCN (20 mL) was added NaN3
(24.3 mg, 373.7 mmol) as a solid at room temperature. The
resultant yellow solution turned purple-red within 25 minutes,
and was subsequently stirred for 4 h. Evaporation of solvent
in vacuo left a pink-red crude solid. Extraction into THF and
recrystallization by slow diffusion of pentane into a concentrated
THF-solution yielded purplish-red single crystals in good yield
(143.8 mg, 246.7 mmol, 66%). 31P-NMR (80.9 MHz, acetone-d6):
d 54.1 (s). 1H-NMR (200 MHz, acetone-d6): d 8.02 (t, J1 = 7.8 Hz,
1H, p-ArH), 7.59 (d, J1 = 7.8 Hz, 2H, m-ArH), 3.99 (vt, 4H, -
t
CH2Ph), 1.60 (vt, 36H, Bu). IR (ATR, cm-1): n 1603 (w), 1568
(w). El. Anal. Calcd. for C30H50BF4NNiP2S: C, 54.25; H, 7.59; N,
2.11. Found: C, 53.83; H, 7.21; N, 1.96.
t
CH2), 1.59 (vt, 36H, Bu). IR (ATR, cm-1): n 2069 (s), 1601 (w),
Nickel complex 8, [Ni(PNPtBu)(SPh)]BF4. A solution of 1
(100.0 mg, 149.5 mmol) in MeCN (30 mL) was added dropwise to a
solution of NaN(SiMe3)2 (27.4 mg, 149.5 mmol) in MeCN (20 mL)
via a cannula at room temperature. The resultant yellow solution
changed color to brownish within 5 minutes, and was subsequently
stirred for 1h. To this solution was added thiophenol (15.4 mL,
149.5 mmol) via microsyringe. An immediate color change to deep
green was apparent. Evaporation of the solvent and extraction
into THF gave a green solid after evaporation. This solid was
washed with Et2O (20 mL). Recrystallization by slow diffusion
of pentane into a concentrated THF-solution yielded dark-green
single crystals as well as brown mother liquor and precipitate. 31P-
1565 (w). El. Anal. Calcd. for C23H43BF4N4NiP2: C, 47.38; H, 7.43;
N, 9.61. Found: C, 47.54; H, 7.18; N, 9.51.
Nickel complex 3, [Ni(PNPtBu)(CNtBu)](BF4)2. To a solution
of 1 (200.0 mg, 299.0 mmol) in MeCN (20 mL) was added tBuNC
(34 mL, 299.0 mmol) via microsyringe at room temperature. The
resultant yellow solution turned light-yellow within 15 minutes,
and was subsequently stirred for 2 h. Evaporation of the solvent
in vacuo left a cream-yellow solid in good yield (180.7 mg,
254.1 mmol, 85%). 31P-NMR (80.9 MHz, acetone-d6): d 81.7 (s).
1H-NMR (200 MHz, acetone-d6): d 8.23 (t, J1 = 7.6 Hz, 1H, p-
ArH), 7.86 (d, J1 = 7.6 Hz, 2H, m-ArH), 4.46 (m, 4H, -CH2), 1.78
(s, 9H, CNtBu), 1.64 (vt, 36H, tBu). IR (ATR, cm-1): n 2188 (m),
1607 (w), 1566 (w). El. Anal. Calcd. for C28H52B2F8N2NiP2: C,
47.30; H, 7.37; N, 3.94. Found: C, 47.48; H, 7.25; N, 3.85.
1
NMR (80.9 MHz, acetone-d6): d 50.0 (s). H-NMR (200 MHz,
acetone-d6): d 8.05 (t, J1 = 7.6 Hz, 1H, p-ArH), 7.75 (d, J1
=
7.0 Hz, 2H, Ph), 7.67 (d, J1 = 7.6 Hz, 2H, m-ArH), 7.07 (m, 3H,
t
Ph), 3.99 (m, 4H, -CH2), 1.47 (vt, 36H, Bu). IR (ATR, cm-1):
Nickel complex 5, Ni(PN-PtBu)(N3). A solution of 2 (175.0 mg,
300.1 mmol) in MeCN (30 mL) was added dropwise to a slurry of
NaN(SiMe3)2 (55.0 mg, 300.1 mmol) in MeCN (20 mL) by means
of a cannula at room temperature. The resultant pink-red solution
turned deep-purple within 5 minutes, and was subsequently
stirred for 1 h. Filtration and evaporation of solvent left a dark-
purple solid that was characterized solely by IR spectroscopy. IR
(ATR, cm-1): n 2055 (s), 1613 (w).
n 1604 (w), 1569 (w). El. Anal. Calcd. for C29H48BF4NNiP2S: C,
53.57; H, 7.44; N, 2.15. Found: C, 53.88; H, 7.65; N, 2.31.
Nickel complex 9, [Ni(PNPtBu)Cl]BF4. A solution of NiCl2-
(dme) (219.7 mg, 1.0 mmol) in CH2Cl2 (25 mL) was added to a
solution of PNPtBu (395.5 mg, 1.0 mmol) and NaBF4 (109.8 mg,
1.0 mmol) in CH2Cl2 (50 mL) at room temperature. The solution
quickly turned reddish and was thereafter stirred for 16 hours.
Filtration and evaporation left a red crude solid. Recrystallization
from CH2Cl2-hexane yielded orange-red crystals of complex 9 in
good yield (386.2 mg, 670 mmol, 67%). 31P-NMR (80.9 MHz,
Nickel complex 6, [Ni(PN-PtBu)(CNtBu)]BF4. A solution of 1
(150.0 mg, 224.2 mmol) in MeCN (30 mL) was added dropwise
to a solution of NaN(SiMe3)2 (41.1 mg, 224.2 mmol) in MeCN
(20 mL) by means of a cannula at room temperature. The resultant
light-yellow solution turned deep-purple within 5 minutes, and
1
acetone-d6): d 48.9 (s). H-NMR (200 MHz, acetone-d6): d 8.01
(t, J1 = 7.6 Hz, 1H, p-ArH), 7.60 (d, J1 = 7.6 Hz, 2H, m-ArH),
t
3.94 (s, 4H, -CH2), 1.60 (vt, 36H, Bu). IR (ATR, cm-1): n 1604
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 1016–1023 | 1021
©

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2
1
(m), 1570 (m). El. Anal. Calcd. for C23H43BClF4NNiP2: C, 47.92;
H, 7.52; N, 2.43. Found: C, 48.10; H, 7.33; N, 2.31.
2JP-P = 197 Hz, JP-P = 56 Hz). H-NMR (400 MHz, acetone-
d6): d 6.30 (t, J = 7.4 Hz, 1H, Py), 5.95 (d, J = 7.4 Hz, 1H, Py),
5.33 (d, J = 7.4 Hz, 1H, Py), 3.22 (m, 1H, =CH), 3.07 (m, 2H,
-CH2), 1.32 (vt, 36H, tBu), -18.4 (dd, 2JP-H = 62 Hz, 2JP-H = 55 Hz,
1H, NiH).
Nickel complex 10, Ni(PN-PtBu)Cl. To a solution of 9 (200 mg,
346.9 mmol) in THF (30 mL) was added a solution of NaN(SiMe3)2
(63.6 mg, 346.9 mmol) in THF (20 mL) via cannula and the solution
was left stirring for 4 hours, during which time the color changed
from red to deep green-brown. Solvent was removed in vacuo and
the product extracted with pentane (2 ¥ 25 mL). After filtration,
the solvent was evaporated to leave a brown pure solid (147.5 mg,
X-Ray crystal structure determinations‡
X-Ray reflections were measured with Mo-Ka radiation (l =
˚
0.71073 A) on a Nonius Kappa CCD diffractometer with rotating
301.8 mmol, 87%). 31P-NMR (162 MHz, C6D6): d 45.7 (d, 2JP-P
=
anode at a temperature of 150 K up to a resolution of (sin q/
293 Hz), 39.8 (d, 2JP-P = 293 Hz). 1H-NMR (400 MHz, C6D6): d
6.25 (t, 1J = 7.2 Hz, 1H, Py), 6.03 (d, 1J = 7.2 Hz, 1H, Py), 5.10
(d, 1J = 7.2 Hz, 1H, Py), 3.42 (d, 1J = 5.2 Hz, 1H, =CH), 2.26 (d,
1J = 7.2 Hz, 2H, -CH2), 1.59 (d, 1J = 12.6 Hz, 18H, tBu), 1.23 (d,
1J = 12.6 Hz, 18H, tBu). IR (ATR, cm-1): n 1612 (s).
˚
-1
l)max = 0.65 A . The structures were solved with Direct
Methods (program SHELXS-9728) Refinement was performed
with SHELXL-9728 against F2 of all reflections. Non hydrogen
atoms were refined with anisotropic displacement parameters.
All hydrogen atoms were introduced in calculated positions and
refined with a riding model. Geometry calculations and checking
for higher symmetry was performed with the PLATON program.29
Comments for compound 1: one of the two BF4 anions was refined
with a disorder model. For 2: The BF4 anion was refined with a
disorder model. A slight disorder of the coordinated N3 anion
was not resolved. In 1 and 2 the inadequacy of the BF4 disorder
models lead artificially to slightly too short intermolecular F ◊ ◊ ◊ C
distances of the split F atoms. For 7: The crystal was cracked
into two fragments, which was taken into account during the
integration of the intensities30 and in the least-squares refinement
with SHELXL-9728 using a HKLF5 instruction.31 For 9: The BF4
anion was refined with a disorder model. Further details are given
in Table 1.
Nickel complex 11, Ni(PN-PtBu)(Ph). To a solution of 10
(125 mg, 255.8 mmol) in Et2O (30 mL), cooled to -40 ◦C, was added
a solution of PhLi (2.0 M solution in Bu2O) (128 mL, 255.8 mmol)
via microsyringe. The resultant green-brown solution was stirred
for 4 hours during which time the solution was slowly warmed to
room temperature and a color change to brown-red was observed.
After evaporation of the solvent the desired product was extracted
into pentane, filtered and then concentrated to dryness to give a
brown-red solid (122.1 mg, 230 mmol, 90%). 31P-NMR (162 MHz,
2
2
1
C6D6): d 43.9 (d, JP-P = 236 Hz), 41.3 (d, JP-P = 236 Hz). H-
NMR (400 MHz, C6D6): d 7.86 (m, 2H, o-PhH), 6.93 (m, 2H,
m-PhH), 6.78 (m, 1H, p-PhH), 6.41 (m, 1H, Py), 6.19 (m, 1H, Py),
5.27 (m, 1H, Py), 3.40 (s, 1H, =CH), 2.55 (m, 2H, -CH2), 1.32
1
t
1
t
(d, J = 8.0 Hz, 18H, Bu), 0.97 (d, J = 8.0 Hz, 18H, Bu). El.
Anal. Calcd. for C29H47NNiP2: C, 65.68; H, 8.93; N, 2.64. Found:
C, 65.12; H, 8.54; N, 2.26.
Acknowledgements
This research has been funded by an Innovation grant (VENI)
from the Dutch Research Council-Chemical Sciences (NWO-CW)
to J.I.v.d.V. and Eindhoven University of Technology. M.L. and
A.L.S have been financially supported by NWO-CW.
Nickel complex 12, Ni(PN-PtBu)(Me). To a solution of 10
(100 mg, 204.6 mmol) in Et2O (30 mL), cooled to -40 ◦C, was added
a solution of MeLi (1.6 M solution in cyclohexane) (127.9 mL,
204.6 mmol) via microsyringe. The resultant green-brown solution
was stirred for 4 hours during which time the solution was slowly
warmed to room temperature and a color change to brown-red was
observed. After evaporation of the solvent the desired product was
extracted into pentane, filtered and then concentrated to dryness
to give a brown-red solid (83.4 mg, 178.0 mmol, 87%). 31P-NMR
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=CH), 2.50 (d, J = 8.0 Hz, 2H, -CH2), 1.44 (d, J = 11.2 Hz,
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2
2
C6D6): d 76.7 (dd, JP-P = 197 Hz, JP-H = 52 Hz), 70.6 (dd,
1022 | Dalton Trans., 2009, 1016–1023
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