Dinuclear Ni(I) - Ni(I) complexes with syn-facial bridging ligands from Ni(I) precursors or Ni(II)/Ni(0) comproportionation

Article abstract of DOI:10.1021/om4001633

The previously reported mononuclear d⁹ complex ( ⁱPr₃P)₂NiCl (1) provides a convenient entry into a series of dinickel complexes with syn-facial bridging ligands. Cyclopentadienyllithium or indenyllithium react with 1 in in n-pentane to provide [(ⁱPr₃P)Ni]₂(μ-Cl)(μ-C ₅H₅) (3a) and [(ⁱPr₃P)Ni] ₂(μ-Cl)(μ-C₉H₇) (3b). Complexes 3a,b are also accessible by comproportionation of the mononuclear Ni(II) complexes ( ⁱPr₃P)NiCl(η⁵-C₅H₅)] (4a) and (ⁱPr₃P)NiCl(η³-C₉H ₇) (4b) with the Ni(0) precursor [(ⁱPr₃P) ₂Ni]₂(μ-N₂) (2). The bulkier Ni(II) complex (ⁱPr₃P)(η⁵-C₅Me ₄H)NiCl (5) does not undergo clean reaction with 2, and the methyl complex (ⁱPr₃P)(η⁵-C₅H ₅)Ni(CH₃) (6) does not react with 2. Reaction of 1 with NaBPh₄ provided [(ⁱPr₃P)Ni]₂(μ- Cl)(μ-PhBPh₃) (7). The dinuclear complexes 3a,b and 7 all feature structurally similar [(PⁱPr₃)Ni] ₂(μ₂-Cl) fragments, with an approximate planar arrangement of the X and PⁱPr₃ ligands and a perpendicular organic cyclopentadienyl, indenyl, or phenyl π system.

Full text of DOI:10.1021/om4001633

Article
pubs.acs.org/Organometallics
Dinuclear Ni(I)Ni(I) Complexes with Syn-Facial Bridging Ligands
from Ni(I) Precursors or Ni(II)/Ni(0) Comproportionation
Robert Beck and Samuel A. Johnson*
Department of Chemistry and Biochemistry, University of Windsor, Sunset Avenue 401, Windsor, Ontario N9B 3P4, Canada
S
* Supporting Information
ABSTRACT: The previously reported mononuclear d9
complex (iPr3P)2NiCl (1) provides a convenient entry into a
series of dinickel complexes with syn-facial bridging ligands.
Cyclopentadienyllithium or indenyllithium react with 1 in in n-
pentane to provide [(iPr3P)Ni]2(μ-Cl)(μ-C5H5) (3a) and
[(iPr3P)Ni]2(μ-Cl)(μ-C9H7) (3b). Complexes 3a,b are also
accessible by comproportionation of the mononuclear Ni(II)
complexes (iPr3P)NiCl(η5-C5H5)] (4a) and (iPr3P)NiCl(η3-
C9H7) (4b) with the Ni(0) precursor [(iPr3P)2Ni]2(μ-N2) (2).
The bulkier Ni(II) complex (iPr3P)(η5-C5Me4H)NiCl (5)
does not undergo clean reaction with 2, and the methyl complex (iPr3P)(η5-C5H5)Ni(CH3) (6) does not react with 2. Reaction
of 1 with NaBPh4 provided [(iPr3P)Ni]2(μ-Cl)(μ-PhBPh3) (7). The dinuclear complexes 3a,b and 7 all feature structurally
similar [(PiPr3)Ni]2(μ2-Cl) fragments, with an approximate planar arrangement of the X and PiPr3 ligands and a perpendicular
organic cyclopentadienyl, indenyl, or phenyl π system.
readily assemble as favored products.14 Our group has recently
isolated a number of dinuclear and polynuclear nickel
complexes with unusual bonding and reactivity, which include
INTRODUCTION
■
The low cost of nickel in comparison to its heavier congeners
provides an impetus to study its utilization in catalytic
dinuclear Ni(I) complexes that undergo isomerization by C−H
bond activation,15 asymmetric intermediates with formal
Ni(I)−Ni(III) centers that are resting states in catalytic C−C
activation and coupling,16 formal Ni(I)−Ni(III) and Ni(I)−
Ni(IV) clusters with silylene ligands,17 and a pentanuclear Ni
hydride complex that undergoes H/D exchange with benzene-
d6.18 The mononuclear Ni(I) precursors (iPr3P)2NiCl (1) and
the Ni(0) dinitrogen complex [(iPr3P)2Ni]2 (μ-N2) (2) have
been shown to serve as useful precursors to dinuclear Ni(I)
complexes.19 This report demonstrates how this synthetic
approach can be extended to provide a simple entry into a
family of novel bimetallic Ni(I)−Ni(I) complexes stabilized by
interaction with π-conjugated rings and how dinuclear
organometallic Ni(I) species could be unanticipated inter-
mediates in a variety of catalytic systems from comproportio-
nation of Ni(0) and Ni(II) complexes.
transformations.1 Mononuclear transition-metal catalysts are
vastly more widespread than dinuclear and polynuclear catalysts
both in organic synthesis on a laboratory scale and in industrial
homogeneous catalytic processes.2 In contrast, biological redox
transformations are commonly performed via multimetallic
enzyme active sites.3 The mechanisms of organonickel-
catalyzed reactions are often assumed to involve mononuclear
nickel intermediates in the oxidation states of +2 and 0.
Although some mechanistic studies have proposed addition/
elimination reaction sequences that require the presence of
organometallic mononuclear Ni(III)4 or Ni(IV),5 such
mechanisms are often difficult to verify, due to the relative
paucity of model complexes in these oxidation states.6
Inorganic complexes of Ni(I) have considerable precedent,7
although organometallic hydrocarbyl-containing complexes are
less common and are often overlooked as catalytic
intermediates.4,8
RESULTS AND DISCUSSION
■
The advantages of bimetallic systems in catalysis have been
often discussed, though not always realized.9 Several reports
have shown the catalytic relevance of unusual dinuclear
complexes of Pd10 and Ni.11 Dinuclear Ni complexes supported
by phosphine ligands have also been reported that allow for
catalytic C−C coupling chemistry.12 These reports raise the
interesting possibility of alternate mechanistic pathways for
known reactions and new catalytic reactions based on group 10
bimetallic species displaying metal−metal bonds.
Synthesis of Dinuclear Ni(I)−Ni(I) Complexes [(iPr3P)-
Ni]2(μ2-Cl)(μ-C5H5) (3a) and [(iPr3P)Ni]2(μ-Cl)(μ-C9H7) (3b)
via Nucleophilic Substitution or Comproportionation.
Treatment of colorless (iPr3P)2NiCl (1) with a suspension of
cyclopentadienyllithium or indenyllithium in n-pentane at 25
°C caused a color change to green. Subsequent filtration and
crystallization of the product afforded the dinuclear Ni(I)
Although ligand design could play a role in the assembly of
Received: February 28, 2013
dinuclear complexes of Ni(I),12a,b,13 oftentimes such complexes
© XXXX American Chemical Society
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complex [(iPr3P)Ni]2(μ-Cl)(μ-C5H5) (3a) and [(PiPr3)Ni]2(μ-
Cl)(μ-C9H7)] (3b) in 73% and 62% yields, respectively, as
green-brown solids, as shown in Scheme 1.
2.639(6) Å, respectively, are significantly longer. This could
be viewed as η3 bonding of the cyclopentadienyl moiety to the
Ni−Ni unit, which is consistent with the significant double-
bond character suggested by the C(3)−C(4) distance of
1.328(9) Å.
The solid-state structure of 3b is shown in Figure 2, and the
complex is structurally similar to 3a. The Ni(1)−C(3) and
Scheme 1
Figure 2. Depiction of the solid-state molecular structure of 3b as
determined by X-ray crystallography with 30% probability ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ni(1)−Ni(2), 2.3918(8); Ni(1)−C(4), 2.847(3);
Ni(1)−C(3), 1.945(3); Ni(1)−C(2), 2.151(3); Ni(1)−P(1),
2.1654(10); Ni(1)−Cl(1), 2.2045(9); Ni(2)−C(1), 1.948(3);
Ni(2)−P(2), 2.1574(9); Ni(2)−C(2), 2.166(3); Ni(2)−Cl(1),
2.1947(8); P(1)−Ni(1)−Ni(2), 157.36(3); P(2)−Ni(2)−Ni(1),
163.26(3).
Turquoise needles of 3a,b were obtained by recrystallization
from pentane solutions at −34 °C. Solid 3a can be handled at
room temperature for days without significant decomposition;
however, solutions decompose over days at room temperature,
with the deposition of a nickel mirror. Additionally,
(iPr3P)2NiCl2 and (η5-C5H5)2Ni20 were both isolated as
decomposition products from solutions of 3a after extended
periods in C6D6, presumably from a disproportionation
reaction that liberates nickel metal. Complex 3b decomposes
in a similar manner in solution over time, as judged by the
observation of (iPr3P)2NiCl2, Ni(C9H7)2,21 iPr3P, and a Ni
mirror. The exact stoichiometry of the reagents is crucial for the
formation of 3a,b, and an excess of the lithium salts provided a
drastic decrease in yield and a plethora of byproducts. The
solid-state molecular structure of 3a is shown in Figure 1. The
Ni(2)−C(1) distances are 1.945(3) and 1.948(3) Å,
respectively. These are shorter than the Ni(1)−C(2) and
Ni(2)−C(2) distances of 2.151(3) and 2.166(3) Å, respec-
tively. The longer Ni(1)−C(4) and Ni(2)−C(9) distances of
2.847(3) and 2.878(3) Å, respectively, are consistent with an η3
bonding of the indenyl moiety to the Ni−Ni unit. Closely
related Pd analogues are known and have been structurally
characterized.22
The 31P{1H} NMR spectra of 3a,b have singlet resonances at
1
δ 49.9 and 47.8, respectively. The H NMR spectrum of 3a
features a cyclopentadienyl resonance at δ 5.07 as a broad
singlet. Cooling solutions of 3a in toluene-d8 as low as 193 K
did not result in decoalescence of this signal. Similarly, a single
isopropyl methyl environment is observed as low as 193 K for
3a, whereas two diastereotopic environments are expected for
the pseudo-Cs symmetry structure observed in the solid state.
This suggests that ring whizzing is rapid in 3b, which exchanges
the C5H5 environments, but a rapid sliding of the C5H5 moiety
across the Ni−Ni bond must also occur to render the
Figure 1. Depiction of the solid-state molecular structure of 3a as
determined by X-ray crystallography with 30% probability ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ni(1)−C(2), 1.972(5); Ni(2)−C(5), 1.975(5);
Ni(2)−C(1), 2.289(6); Ni(1)−C(1), 2.326(6); Ni(1)−Ni(2),
2.3995(10); C(1)−C(2), 1.444(9); C(1)−C(5) 1.429(8); C(2)−
C(3), 1.418(9); C(3)−C(4), 1.328(9); C(4)−C(5), 1.435(9); Ni(1)−
Cl(1), 2.1930(16); Ni(2)−Cl(1), 2.1919(17); Ni(1)−P(1),
2.1740(17); Ni(2)−P(2), 2.1716(16); P(1)−Ni(1)−Ni(2),
167.52(6).
i
diastereotopic Pr methyl groups chemically equivalent.
1
Complex 3b has a H NMR spectrum consistent with its
solid-state structure, with five sharp multiplets for the
coordinated indenyl group. The signal at δ 3.59 integrated to
one hydrogen, whereas the resonances at δ 4.22, 6.95, and 7.18
1
all integrated to two hydrogens. The H NMR of 3b features
diastereotopic iPr methyl groups, consistent with the pseudo-Cs
symmetric structure observed in the solid state. The 13C{1H}
NMR spectrum of 3b showed five resonances for the indenyl
group, with the most upfield shift at δ 36.4 for C1/C3 carbon
atoms.
complex features approximate Cs symmetry, with a Ni(1)−
Ni(2) bond length of 2.3995(10) Å. The cyclopentadienyl
ligand bridges in a symmetric manner, with short Ni(1)−C(2)
and Ni(2)−C(5) distances of 1.972(5) and 1.975(5) Å,
respectively, and longer Ni(2)−C(1) and Ni(1)−C(1)
distances of 2.289(6) and 2.326(6) Å, respectively. Both the
Ni(1)−C(3) and Ni(2)−C(4) distances of 2.616(6) and
Comproportionation Routes to 3a,b. The ubiquity of
organometallic Ni(0) and Ni(II) complexes and the relative
paucity of Ni(I) hydrocarbyl complexes could be misconstrued
to provide the erroneous hypothesis that comproportionation
routes to 3a,b would be thermodynamically unfavorable. In fact,
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complexes 3a,b are also accessible by the reaction of the
mononuclear Ni(II) complexes (iPr3P)NiCl(η5-C5H5) (4a) and
(iPr3P)NiCl(η5-C9H7) (4b) with the Ni(0) source
[(iPr3P)2Ni]2(μ-N2) (2) over 30 min, as shown in the top
two reactions of Scheme 2. The dark red mononuclear Ni(II)
The solid-state molecular structures of 4a,b were determined
by X-ray crystallography. The Ni−C distances in the cyclo-
pentadienyl derivative 4a are similar (in the range of 2.11−2.15
Å),23 whereas the indenyl ligand in 4b appears to be η3 bound,
which can be attributed to both the tendency of d8 complexes
to form a 16-electron complexes and increased aromaticity.24
The Ni−Cl distances are similar in both complexes and
somewhat longer than the average of corresponding literature
complexes.25
Scheme 2
Ligand Effects on Comproportionation To Provide
Dinuclear Ni(I)−Ni(I) Complexes. A more sterically bulky
tetramethylcyclopentadienyl ligand was used to see if it would
affect the formation of dinuclear Ni(I) complexes via
comproportionation. The reaction of (iPr3P)2NiCl2 with
C5Me4HLi afforded red crystals of (iPrP3)NiCl(η5-C5Me4H)
(5) in 69% yield. The 1H NMR spectrum of 5 is consistent with
a Cs-symmetric complex. The 31P{1H} NMR chemical shift of δ
54.8 is similar to those of 4a,b. Recrystallization from n-pentane
solutions at 20 °C afforded crystals of 5 suitable for an X-ray
structure determination. The reaction of 5 with 2 under
conditions similar to those used to prepare 3a,b from 4a,b
showed no NMR spectroscopic evidence for the formation of a
related dinickel complex, as shown in Scheme 2. Evidence for
disproportionation was obtained by the observation of
NiCl(PiPr3)2; however, the observation of Ni(0) metal and a
variety of unidentified byproducts detected by NMR indicate
that no clean conversion occurred. It can be postulated that the
greater steric bulk in the Cp backbone hindered the generation
of the dinuclear complex analogous to 3a and that the
paramagnetic mononuclear monophosphine nickel(I) intermedi-
ate (iPrP3)Ni(C5Me4H) is not stable.
The role of the chloride substituent in the propensity to form
dinuclear Ni(I) complexes via comproportionation was also
examined. Mononuclear 4a was treated with MeMgCl in
diethyl ether at −34 °C. After 15 min the methyl complex
(iPrP3)Ni(Me)(η5-C5H5) (6) was obtained in 75% yield as dark
1
brown cubic crystals. The H NMR spectrum of 6 featured a
1
doublet at δ −0.58 (3JPH = 5.1 Hz) in the H NMR spectrum
and a 13C{1H} resonance at δ −39.2 (d, 2JPC = 28.1 Hz) for the
Ni−CH3 moiety. Recrystallization from n-pentane at −34 °C
afforded single crystals of 6 suitable for X-ray crystallography.
Both mononuclear molecular structures 5 and 6 demonstrate
geometric features common to all of the mononuclear
structures in this paper and previous reports.26 Attempts to
obtain a dinuclear complex similar to 3a,b via comproportio-
nation of 6 with 2 failed to yield any conversion of 6, even
under reflux conditions in benzene.
Tetraphenylborate as a Bridging Ligand for Dinuclear
Ni(I) Complex Formation. The propensity for cyclo-
pentadienyl and indenyl to support dinuclear Ni(I) complexes
such as 3a,b suggest that other modestly sized anionic π
systems should also react with 1 to provide dinuclear
complexes. The reaction of NaBPh4 with 2 equiv of
(iPr3P)2NiCl (1) in diethyl ether provided the dinickel
compound [(iPr3P)Ni]2(μ2-Cl)(μ2-η2:η2-C6H5BPh3) (7) in
73% yield as a green powder, as shown in Scheme 3.
precursors (iPr3P)NiCl(η5-C5H5) (4a) and (iPr3P)NiCl(η3-
C9H7) (4b) were prepared by the reaction of [(iPr3P)2NiCl2]
with cyclopentadienyllithium or indenyllithium in THF at 25
°C in yields of 73−79%.
The 31P{1H} NMR spectrum of 4a has a singlet at δ 52.5.
This shift is close to that observed for the structurally dissimilar
3a and shows the potential dangers of structure assignment
solely by 31P NMR. Even the 1H NMR spectrum of 4a is similar
to that of 3a, with the η5-C5H5 group singlet resonance at δ
5.08. The relative 1H NMR integrals distinguish 4a from 3a, as
do the 13C{1H} NMR spectra of 4a and 3a, which feature
resonances at δ 92.9 and 80.3 for the η5-C5H5 group,
respectively. The 31P{1H} NMR spectrum of 4a has a singlet
Crystals suitable for structural characterization by X-ray
crystallography were obtained by the reaction of pentane
solutions of 1 with NaBPh4, which provided large green crystals
of 7 directly from the reaction mixture. The solid-state
molecular structure of 7 was determined by X-ray crystallog-
raphy, and an ORTEP depiction is shown in Figure 3. Solid 7
was stable under N2 up to 70 °C. Complex 7 features a BPh4
1
at δ 49.2. The H NMR spectrum of 4b at 243 K is consistent
with a C1-symmetric molecule, with seven resonances for the
indenyl moiety and diastereotopic methyl substituents. As the
temperature was raised, a broadening and coalescence of peaks
occurred, which is consistent with rotation about the Ni−
indenyl centroid.
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Scheme 3
CONCLUSIONS
■
We have shown a convenient entry to a series of dinuclear
Ni(I) complexes which are easily obtained by simple
nucleophilic substitution of the monochloro Ni(I) precursor
with the corresponding Li/Na organics. The exact stoichiom-
etry is crucial for the formation of the reported dinuclear
complexes. An alternative method of comproportionation of
the corresponding mononuclear complexes in the presence of a
Ni(0) source was also demonstrated. It also appears that the
decomposition of many of these compounds proceeds by
disproportionation, to give nickel metal and products such as
(iPr3P)2NiCl2, Ni(Cp)2, Ni(Ind)2, 4a,b, and free phosphine
ligand.
An examination of the various factors that influence dinuclear
Ni(I) complex formation showed the importance of both the
bridging π system and halide. Complex 5, which contained the
sterically more bulky tetramethylcyclopentadienyl ligand, still
reacted with the Ni(0) complex 2, presumably via disproportio-
nation, but provided (iPr3P)2NiCl and a complex product
mixture rather than a dinuclear Ni(I) complex. Replacement of
the chloride ligand in 3a with a methyl ligand in 6 provided a
complex that did not react via disproportionation. In view of
the catalysis and reactivity exhibited by some Pd(I)−Pd(I)
dimers31 and the promising study of cross-coupling reactions
with dinuclear nickel complexes,12a,13b future studies are
planned to probe the reactivities of these dinuclear Ni(I)−
Ni(I) complexes toward a variety of substrates. Although the
work presented in this paper suggests that organometallic
dinuclear Ni(I) complexes may be present in a number of
catalytic systems that feature nickel catalysts that cycle between
Ni(II) and Ni(0), it remains to be determined if these Ni(I)
complexes play an active role in catalysis.32
Figure 3. Depiction of the solid-state molecular structure of 7 as
determined by X-ray crystallography with 30% probability ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ni(1)−Ni(2), 2.4255(9); Ni(1)−Cl(1), 2.1983(15);
Ni(1)−P(1), 2.2118(14); Ni(1)−C(5), 2.025(5); Ni(1)−C(6),
2.154(5); Ni(2)−Cl(1), 2.1689(14); Ni(2)−P(2), 2.2201(15);
Ni(2)−C(1), 2.504(6); Ni(2)−C(2), 2.008(5); Ni(2)−C(3),
2.144(5); C(1)−C(2), 1.414(8); C(1)−C(6), 1.370(8); C(2)−C(3),
1.407(7); C(3)−C(4), 1.417(7); C(4)−C(5), 1.418(6); C(5)−C(6),
1.430(7); P(1)−Ni(1)−Ni(2), 162.07(5); Cl(1)−Ni(1)−Ni(2),
55.69(4); Cl(1)−Ni(1)−P(1), 108.16(5); P(2)−Ni(2)−C(1),
121.69(15).
EXPERIMENTAL SECTION
■
General Procedures. Unless otherwise stated, all manipulations
were performed under an inert atmosphere of nitrogen using either
standard Schlenk techniques or an MBraun glovebox. Dry, oxygen-free
solvents were employed throughout. Anhydrous pentane, toluene, and
THF were purchased from Aldrich, sparged with dinitrogen, and
passed through activated alumina under a positive pressure of nitrogen
gas; toluene and hexanes were further deoxygenated using a Grubbs
type column system.1 Benzene-d6 was dried by heating at reflux with
Na/K alloy in a sealed vessel under partial pressure and then trap-to-
trap distilled and freeze−pump−thaw degassed three times. Toluene-
d8 was purified in an analogous manner by heating at reflux over Na.
THF-d8 was purified in an analogous manner by heating at reflux over
K. 1H, 31P{1H} and 13C{1H} spectra were recorded on a Bruker AMX
spectrometer operating at 300 or 500 MHz with respect to proton
nuclei. All chemical shifts are recorded in parts per million, and all
coupling constants are reported in hertz. 1H NMR spectra were
referenced to residual protons (C6D5H, δ 7.15; C7D7H, δ 2.09;
C4D7HO, δ 1.73) with respect to tetramethylsilane at δ 0.00. 31P{1H}
NMR spectra were referenced to external 85% H3PO4 at δ 0.00.
13C{1H} NMR spectra were referenced relative to solvent resonances
(C6D6, δ 128.0; C7D8, δ 20.4; C4D8O, δ 25.37). 29Si{31P} NMR
spectra were referenced to an external sample of 50% Si(CH3)4 in
C6D6 at δ 0.0. Infrared spectra (IR) were recorded on a Bruker Tensor
27 instrument operating from 4000 to 400 cm−1. Elemental analyses
were performed at the Center for Catalysis and Materials Research,
Windsor, Ontario. NiCl2(PiPr3)2, NiCl(PiPr3)2 (1), and
[(iPr3P)2Ni]2(μ-N2) (2) were synthesized according to literature
methods.19 The compounds benzene-d6, toluene-d8, and THF-d8 were
purchased from Cambridge Isotope Laboratory. The compounds
lithium bis(trimethylsilyl)amide, indenyllithium, cyclopentadienyl-
lithium, tetramethylcyclopentadienyllithium, sodium tetraphenylbo-
anion coordinated by as a bridging ligand, with two nickels
bound to one of the phenyl rings, and a short Ni(1)−Ni(2)
distance of 2.4255(9) Å. Similar to the case for complexes 3a,b,
an additional chloride bridges the metal centers. Steric
i
crowding between the Pr3P ligand associated with P(1) and
the propeller arrangement of the BPh3 backbone appears to
cause the π-coordinated phenyl ring to twist slightly toward
P(1). The C−C bond lengths of the π-coordinated η2:η2-phenyl
ring range from 1.370(8) to 1.430(7) Å, with two relatively
short and two slightly elongated Ni−C bond lengths: Ni(1)−
C(5) = 2.025(5) Å, Ni(1)−C(6) = 2.154(5) Å, Ni(2)−C(2) =
2.008(5) Å, and Ni(2)−C(3) = 2.144(5) Å.
The 31P{1H} NMR spectrum of 7 has a single resonance at δ
1
28.1. The H NMR spectrum has distinctive signals for the
bridging phenyl ring at δ 5.29, 5.84, and 6.38 observed for the
para, meta, and ortho hydrogens, respectively, which are upfield
from the three chemically equivalent noncoordinated Ph
substituents.
−
A few examples where BPh4 binds in a mononuclear η6
fashion are known for Os,27 Rh,28 and Ru.29 Recently Zargarian
et al. described a closely related nickel complex with a similar
twisted BPh4 coordination mode, but with a bridging PPh2
ligand instead of a chloro ligand.30 The mechanism of
formation of this latter complex is complicated, and details
remain unclear. The reaction we present here from 1 provides a
direct and synthetically useful entry into these complexes.
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rate, and methylmagnesiumbromide (3.0 M) were purchased from
Aldrich and used as received. Triisopropylphosphine was purchased
from Strem and used as received.
volume under vacuum, and a second crop of 4a was obtained. The
1
combined yield afforded 252 mg (79%) of analytically pure 4a. H
NMR (298 K, C6D6, 500 MHz): δ 1.07 (dd, 3JPH = 13.8 Hz, 3JHH = 7.2
3
Synthesis and Characterization of 3a. Method 1. A solution of
(iPr3P)2NiCl (164 mg, 0.39 mmol) in 5 mL of n-pentane was
combined with a suspension of cyclopentadienyllithium (14 mg, 0.19
mol) in 5 mL of n-pentane. After the mixture was stirred for 3 h, the
volatiles were removed under vacuum, which afforded a brown-green
residue. The residue was extracted with n-pentane (2 × 10 mL).
Green-turquoise needles of 3a suitable for analysis by X-ray
crystallography were isolated from concentrated n-pentane solutions
at −34 °C and dried under vacuum (77 mg, 73% yield).
Hz, 18H, P(CH(CH3)2)3); 1.71 (m, JHH = 7.2 Hz, 3H,
P(CH(CH3)2)3); 5.08 (s, 5H, Cp-H). 13C{1H} NMR (298 K, C6D6,
1
75.5 MHz): δ 19.5 (s, P(CH(CH3)2)3); 24.4 (d, JPC = 21.8 Hz,
PCH(CH3)2)3); 92.9 (s, C5H5). 31P{1H} NMR (298 K, C6D6, 121.5
MHz): δ 52.5 (s). Anal. Calcd for C14H26ClNiP (319.48): C, 52.63; H,
8.20. Found: C, 52.31; H, 7.89.
Synthesis and Characterization of 4b. To an ice-cold solution
of (iPr3P)2NiCl2 (450 mg, 1.0 mmol) in 10 mL of THF was added a
solution of indenyllithium (122 mg, 1.0 mmol) in 3 mL of THF.
Immediately, the solution turned from dark red to pink. After the
mixture was stirred for 1 h at room temperature, all volatiles were
removed in vacuo, the residue was extracted with n-pentane (2 × 10
mL), and the extracts were filtered through a plug of Celite. Over the
course of 5 h at room temperature, wine red plates deposited. The
crystals were filtered off and the mother liquor reduced by half its
volume under vacuum, and a second crop of 4b was obtained. The
Method 2. A solution of [(iPr3P)2Ni]2(μ-N2) (157 mg, 0.20 mmol)
in 5 mL of n-pentane was added to a stirred solution of (η5-
C5H5)NiCl(PiPr3) (4a; 128 mg, 0.40 mmol) at −34 °C. After 5 min
the reaction mixture turned blue-green, and after the mixture was
stirred for an additional 30 min, the volatiles were removed under
vacuum, which afforded a dark brown oil. The oil was taken up in 5
mL of n-pentane and cooled to −34 °C, which provided turquoise
1
1
needles of 3a (112 mg, 52% yield). H NMR (298 K, C6D6, 500
combined yield afforded 252 mg (73%) of analytically pure 4b. H
3
3
MHz): δ 1.26 (dd, JPH = 12.3 Hz, JHH = 6.9 Hz, 36H,
NMR (298 K, C6D6, 500 MHz): δ 0.97 (dd, 3JPH = 13.8 Hz, 3JHH = 7.2
Hz, 18H, CH3); 1.75 (m, 3JHH = 7.2 Hz, 3H, P(CH(CH3)2)3); 4.15 (br
s, W1/2 = 90 Hz, 1H, H1); 5.57 (br s, W = 90 Hz, 1H, H3); 6.39 (t, 3JHH
= 3.3 Hz, 1H, H2); 6.89 (br s, W1/2 = 45 Hz, 2H, H6/H7); 7.02 (br s,
W1/2 = 90 Hz, 2H, H5/H8). 1H NMR (193 K, C7D8, 500 MHz): δ 0.97
(br, 18H, P(CH(CH3)2)3); 1.75 (br, 3H, P(CH(CH3)2)3); 3.99 (br,
1H, H1); 5.77 (br, 1H, H3); 6.40 (br, 1H, H2); 6.83 (br, 1H, H6); 6.95
(br, 1H, H7); 7.12 (br, 1H, H5); 7.33 (br, 1H, H8). 13C{1H} NMR
3
P(CH(CH3)2)3); 1.95 (m, JHH = 6.9 Hz, 6H, P(CH(CH3)2)3); 5.07
(s, 5H, C5H5). 13C{1H} NMR (298 K, C6D6, 75.5 MHz): δ 20.2 (s,
P(CH(CH3)2)3); 24.5 (vt, 1JPC + 4JPC = 16.6 Hz, PCH(CH3)2)3); 80.3
(s, C5H5). 31P{1H} NMR (298 K, C6D6, 121.5 MHz): δ 49.9 (s). IR
(Nujol, KBr): ν (cm−1) 3059 w, 2721 w, 1655 vw, 1590 vw, 1379 s,
1366 s, 1298 w, 1235 m, 1156 w, 1093 m, 1057 s, 1024 s, 966 w, 923
w, 883 s, 801 m, 753 s, 723 s, 655 vs, 613 w, 598 w, 570 s, 523 vs, 477
w, 432 w. Anal. Calcd for C23H47ClNi2P2 (538.41): C, 51.31; H, 8.80;
Found: C, 51.48; H, 9.18.
1
(298 K, C6D6, 75.5 MHz): δ 19.4 (s, PCHMe2); 24.9 (d, JPC = 19.5
Hz, PCH); 59.9 (br s, W1/2 = 150 Hz, C1 or C3); 89.2 (br s, W1/2 = 150
Hz, C3 or C1); 102.7 (s, C2); 119.3 (br s, W1/2 = 75 Hz); 125.6 (br s,
W1/2 = 75 Hz); 130.6 (br s, W1/2 = 75 Hz). 31P{1H} NMR (298 K,
C6D6, 121.5 MHz): δ 49.2 (s). Anal. Calcd for C18H28ClNiP (369.54):
C, 58.50; H, 7.64. Found: C, 58.12; H, 7.90.
Synthesis and Characterization of 3b. Method 1. A solution of
(iPr3P)2NiCl (200 mg, 0.48 mmol) in 5 mL of n-pentane was
combined with a suspension of indenyllithium (29 mg, 0.24 mmol) in
5 mL of n-pentane. After the mixture was stirred for 3 h, the volatiles
were removed under vacuum, which afforded a brown-green residue.
The oil was taken up in 5 mL of n-pentane and filtered through Celite.
Turquoise needles of 3b suitable for analysis by X-ray crystallography
precipitated via slow evaporation over 2 days at −34 °C and were
isolated and dried under vacuum (88 mg, 62% yield).
Synthesis and Characterization of 5. A solution of
(iPr3P)2NiCl2 (220 mg, 0.48 mmol) in 10 mL of THF was combined
at −34 °C with tetramethylcyclopentadienyllithium (63 mg, 0.48
mmol). After the mixture was warmed to ambient temperature, the
solvent was removed under vacuum, the solid was extracted with n-
pentane (2 × 10 mL), and the extracts were filtered through a plug of
Celite. The pink filtrate was left to slowly evaporate at room
temperature, and wine red plates deposited over the course of 16 h
that were suitable for analysis by X-ray crystallography (126 mg, 69%
yield). 1H NMR (298 K, C6D6, 500 MHz): δ 1.13 (dd, 3JPH = 13.8 Hz,
3JHH = 6.9 Hz, 18H, PCHMe2); 1.45 (d, JPH = 2.7 Hz, 6H, C5Me4H);
1.88 (m, 3H, PCH); 1.92 (s, 6H, C5Me4H); 3.65 (d, 3JPH = 3.1 Hz, 1H,
C5Me4H). 13C{1H} NMR (298 K, C6D6, 75.5 MHz): δ 9.62 (s,
Method 2. A solution of 4b (89 mg, 0.24 mmol) was combined at
−34 °C with a solution of [(iPr3P)2Ni]2(μ-N2) (94 mg, 0.12 mmol)
dissolved in 5 mL of n-pentane. After 5 min the reaction mixture
turned blue-green, and after the mixture was stirred for an additional
30 min, the volatiles were removed under vacuum, which afforded a
dark brown oil. The oil was taken up in 5 mL of n-pentane, and
cooling to −34 °C afforded turquoise needles of 3b (54 mg, 38%
yield). 1H NMR (298 K, C6D6, 500 MHz): δ 1.10 and 1.17
3
1
(overlapping m, 36H total, P(CH(CH3)2)3); 1.97 (m, JHH = 7.0 Hz,
C5Me4H); 11.9 (s, C5Me4H); 19.8 (s, PCHMe2); 25.3 (d, JPC = 20.6
6H, P(CH(CH3)2)3); 3.59 (coincident tt, 3JHH = 4.2 Hz, 3JHP = 4.0 Hz,
2
Hz, PCH); 72.5 and 106.1 (s, C5Me4H); 110.3 (d, JPC = 4.5 Hz,
3
3
C5Me4H). 31P{1H} NMR (298 K, C6D6, 121.5 MHz): δ 54.8 (s). Anal.
Calcd for C18H34ClNiP: C, 57.56; H, 9.12. Found: C, 57.29; H, 8.90.
Synthesis and Characterization of 6. A solution of MeMgBr in
diethyl ether (3.0 M, 0.18 mL, 0.55 mmol) was slowly added dropwise
to a stirred solution of (η5-C5H5)NiCl(PiPr3) (4a; 178 mg, 0.55
mmol) in diethyl ether at −34 °C. The temperature was maintained,
and after 2 min, the reaction mixture turned dark brown. Stirring was
stopped after 15 min, and all volatiles were removed in vacuo. The
dark brown residue was extracted with n-pentane (2 × 5 mL) and
filtered through a plug of Celite. Crystals deposited at −34 °C and
were separated from the solution by decantation, and the residual
solvent was removed using vacuum. The dark brown cubic crystals
suitable for analysis by X-ray crystallography were washed with cold n-
pentane and dried under vacuum to provide 6 (125 mg, 75% yield).
Complex 6 is reasonably thermally stable after isolation. 1H NMR
1H, H2); 4.22 (td, JPH = 9.3 Hz, JHH = 4.2 Hz, 2H, H1/H3); 6.95
(second order m, 2H, H5/H8); 7.18 (second order m, 2H, H6/H7).
13C{1H} NMR (298 K, C6D6, 75.5 MHz): δ 19.8 and 20.3 (s,
P(CH(CH3)2)3); 24.9 (vt, 1JPC + 3JPC = 17.8 Hz, PCH(CH3)2)3); 36.4
(second order m, C1/C3); 53.1 (t, 2JPC = 6.6 Hz, C2); 122.3 (s, C4/C9);
122.6 (s, C5/C8); 148.1 (s, C6/C7). 31P{1H} NMR (298 K, C6D6, 121.5
MHz): δ 47.9 (s). IR (Nujol, KBr): ν (cm−1) 3062 m, 3038 w, 3038
m, 1911 vw, 1876 vw, 1696 vw, 1589 m, 1366 s, 1338 vw, 1315 m,
1315 m, 1294 m, 1279 s, 1241 s, 1198 s, 1157 s, 1093 m, 1056 s, 1031
s, 1019 s, 955 m, 921 s, 906 w, 882 vs, 849 vw, 822 m, 786 m, 744 vs,
722 m, 659 vs, 615 vs, 574 s, 525 vs, 473 s, 430 m. Anal. Calcd for
C27H49ClNi2P2 (588.47): C, 55.11; H, 8.39; Found: C, 55.50; H, 7.99.
Synthesis and Characterization of 4a. To an ice-cold solution
of (iPr3P)2NiCl2 (450 mg, 1.0 mmol) in 10 mL of THF was added a
solution of cyclopentadienyllithium (72 mg, 1.0 mmol) in 3 mL of
THF. Immediately, the solution turned from dark red to pink. After
the mixture was stirred for 1 h at room temperature, the volatiles were
removed in vacuo, the residue was extracted with n-pentane (2 × 10
mL), and the extracts were filtered through a plug of Celite. Over the
course of 5 h at room temperature, wine red plates deposited. The
crystals were filtered off and the mother liquor reduced by half its
3
(298 K, C6D6, 500 MHz): δ −0.58 (d, JPH = 5.1 Hz, 3H, Ni−CH3);
1.06 (dd, 3JPH = 13.2 Hz, 3JHH = 7.2 Hz, 18H, PCHMe2); 1.68 (m, 3JHH
= 7.2 Hz, 3H, PCH); 5.35 (s, 5H, C5H5). 13C{1H} NMR (298 K,
2
C6D6, 75.5 MHz): δ −39.2 (d, JPC = 28.1 Hz, Ni-CH3); 19.5 (s,
1
PCHMe2); 24.5 (d, JPC = 20.8 Hz, PCH); 90.3 (s, C5H5). 31P{1H}
NMR (298 K, C6D6, 121.5 MHz): δ 64.7 (s). IR (Nujol, KBr): ν
E
dx.doi.org/10.1021/om4001633 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 1. Data and Structure Refinement Parameters for Complexes 3−7
3a
3b
4a
4b
empirical formula
fw
C23H47P2 ClNi2
538.42
C27H49P2ClNi2
588.47
C14H26PClNi
319.48
C18H28PClNi
369.53
cryst syst
a (Å)
orthorhombic
7.7246(15)
11.666(2)
29.958(6)
90
monoclinic
16.456(3)
8.1490(16)
22.477(5)
90
triclinic
monoclinic
14.641(3)
16.122(3)
16.613(3)
90
7.7760(9)
14.0565(17)
14.5394(17)
96.640(2)
96.441(2)
90.256(2)
1568.3(3)
b (Å)
c (Å)
α (deg)
β (deg)
90
95.00(3)
90
107.60(3)
90
γ (deg)
V (Å3)
90
2699.7(9)
P212121
4
3002.8(10)
P21/n
3737.9(13)
P21/c
space group
P1
̅
Z
4
4
8
Dcalcd (g/cm3)
μ(Mo Kα) (mm−1
temp (K)
2θmax (deg)
total no. of rflns
1.325
1.302
1.353
1.313
)
1.620
1.463
1.488
1.259
173(2)
173(2)
173(2)
50
173(2)
51
52.7
52.7
27198
31161
15428
39692
no. of unique rflns; Rint
abs cor
5005; 0.1056
multiscan
0.88−0.60
265
6123; 0.0475
multiscan
0.94−0.73
313
5518; 0.0507
multiscan
0.86−0.72
319
7656; 0.0874
multiscan
0.93−0.84
415
transmissn factors
no. of variables
rflns/params
18.8
19.5
22.3
18.4
GOF on F2
1.003
1.040
0.998
1.010
R1; wR2 (I ≥ 2σ)
R1; wR2 (all data)
residual density (e/Å3)
0.0522; 0.1042
0.0711; 0.1132
0.809; −0.370
0.0368; 0.0839
0.0500; 0.0954
0.78; −0.28
0.051; 0.094
0.0796; 0.106
0.618; −0.368
0.0533; 0.1013
0.0959; 0.1207
0.61; −0.32
7
5
6
empirical formula
fw
C18H34ClNiP
375.58
C15H29PNi
299.06
orthorhombic
8.8699(18)
10.142(2)
17.693(4)
90
C42H62BP2ClNi2
792.54
cryst syst
a (Å)
monoclinic
7.4557(15)
17.270(3)
16.264(5)
90
Monoclinic
34.726(7)
11.609(2)
21.980(4)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
108.57(3)
90
90
112.26(3)
90
90
1985.1(8)
P21/c
1591.6(5)
P212121
4
8201(3)
C2/c
space group
Z
4
8
Dcalcd (g/cm3)
1.257
1.248
1.284
μ(Mo Kα) (mm−1
)
1.186
1.300
1.089
temp (K)
173(2)
173(2)
52.7
130(2)
2θmax (deg)
54
51
total no. of rflns
22050
16836
40712
no. of unique rflns; Rint
abs cor
4372; 0.0715
multiscan
0.94−0.84
200
3253; 0.0296
multiscan
0.73−0.59
161
7778; 0.0927
multiscan
0.94−0.81
445
transmissn factors
no. of variables
rflns/params
21.8
20.2
17.5
GOF on F2
1.040
1.062
1.037
R1; wR2 (I ≥ 2σ)
R1; wR2 (all data)
residual density (e/Å3)
0.0444; 0.0956
0.0628; 0.1112
0.58; −0.39
0.0332; 0.0840
0.0350; 0.0852
1.01; −0.48
0.0647; 0.1475
0.1039; 0.1677
1.371; −0.597
(cm−1) 3098 m, 1510 w, 1459 vs, 1407 w, 1382 s, 1366 m, 1298 w,
1242 s, 1144 s, 1113 w, 1092 w, 1056 m 1018 m, 985 w, 928 w, 883 s,
837 w, 773 vs, 657 s, 632 m, 618 m, 571 w, 531 s, 479 w, 449 vw. Anal.
Calcd for C15H29NiP (299.06): C, 60.24; H, 9.77. Found: C, 59.97; H,
10.17.
added finely powdered NaBPh4 (86 mg, 0.25 mmol) at 20 °C. The
heterogeneous mixture was stirred vigorously for 4 h, and when a
green solid was formed, stirring was stopped and the solution was
decanted from the remaining solid. The solvent was removed in vacuo,
the green residue was extracted with toluene (2 × 5 mL), and the
extracts were filtered through a plug of Celite. Removal of the solvent
gave 7 as a viscous oil (146 mg, 73% yield) that was reasonably pure
Synthesis and Characterization of 7. To a solution of
(iPr3P)2NiCl (1); 210 mg, 0.50 mmol) in 5 mL of diethyl ether was
F
dx.doi.org/10.1021/om4001633 | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
by 31P and 1H NMR spectroscopy. Complex 7 was obtained as a green
crystalline solid by evaporation of a benzene/hexamethyldisiloxane
solution. Alternatively, crystalline 7 can be prepared by the reaction of
NiCl(PiPr3)2 (45 mg, 0.1 mmol) with sodium tetraphenylborate (17
mg, 0.05 mmol) in 3 mL of n-pentane without stirring at room
temperature. Complex 7 is sparingly soluble in pentane and soluble in
toluene. If the precursor 1 contains significant amounts of
(iPr3P)2NiCl2 as an impurity, complex 7 appears to rapidly decompose.
1H NMR (298 K, C6D6, 500 MHz): δ 0.62 (br dd, 3JPH = 13.5 Hz, 3JHH
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3
3
= 5.1 Hz, 18H, P(CH(CH3)2)3); 1.05 (br dd, JP3H = 13.5 Hz, JHH
=
5.1 Hz, 18H, P(CH(CH3)2)3); 1.67 (sept(br), JHH = 7.2 Hz, 6H,
3
P(CH(CH3)2)3); 5.29 (br t, JHH = 7.5 Hz, 1H, para-H1); 5.84 (br
apparent t, 3JHH = 3.1 Hz, 2H, meta-H2/H6); 6.38 (br d, 3JHH = 3.1 Hz,
4JHH = 0.9 Hz, 2H, ortho-H3/H5); 7.28 (t, 3JHH = 7.5 Hz, 3H, para-H);
3
7.38 (apparent t, JHH = 6.9 Hz, 6H, meta-H); 7.97 (d, 3JHH = 7.2 Hz,
6H, ortho-H), 13C{1H} NMR (298 K, C6D6, 75.5 MHz): δ 18.8 (s,
P(CH(CH3)2)3); 19.2 (s, PCHMe2); 24.9 (virtual t, 1JPC + 4JPC = 15.8
Hz, PCH); 82.1 (s, C2/C6); 87.3 (br s, C1); 97.5 (s, C3/C5); 102.1 (s,
BCipso); 123.1 (s, BCipso); 131.3 (s, Cpara); 137.1 (s, Cmeta); 139.4 (s,
Cortho). 31P{1H} NMR (298 K, C6D6, 121.5 MHz): δ 28.1 (s). Anal.
Calcd for C42H62BClNi2P2 (792.54): C, 63.65; H, 7.89. Found: C,
63.82; H, 8.35.
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X-ray Crystallography. The X-ray structures were obtained at low
temperature, with the crystals covered in Paratone and placed rapidly
into the cold N2 stream of the Kryo-Flex low-temperature device. The
data were collected using SMART33 software on a Bruker APEX CCD
diffractometer using a graphite monochromator with Mo Kα radiation
(λ = 0.71073 Å). A hemisphere of data was collected using a counting
time of 10−30 s per frame. Data reductions were performed using
SAINT34 software, and the data were corrected for absorption using
SADABS.35 The structures were solved by direct or Patterson methods
using SHELXS-9736 and refined by full-matrix least squares on F2 with
anisotropic displacement parameters for the non-H atoms using
SHELX-9736 and the WinGX37 software package, and thermal
ellipsoid plots were produced using ORTEP32.38 Crystallographic
parameters are given in Table 1.
ASSOCIATED CONTENT
* Supporting Information
■
S
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*S.A.J.: fax, (+1) 519-973-7098; e-mail, sjohnson@uwindsor.ca.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Natural Sciences and Engineering Research
Council (NSERC) of Canada and the donors of the Petroleum
Research Fund, administered by the American Chemical
Society, for their support of this research.
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