Synthesis and structures of nickel complexes with a PN-chelate phosphaalkene ligand

Article abstract of DOI:10.1021/om500685x

Phosphaalkenes with a P=C bond possess extremely strong π-accepting ability, often providing transition metal complexes with interesting structures and properties. This paper describes unique structures of nickel complexes coordinated with a PN-chelate phosphaalkene ligand (PEP = 2-[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine). The PEP ligand combines with [NiBr₂(dme)] (dme = 1,2-dimethoxyethane) in toluene to afford [Ni(Br)(μ-Br)(PEP)]₂ (1), which reacts with R₂Mg(thf)₂ in Et₂O or THF to form three types of nickel complexes depending on the R groups and reaction conditions. The reaction with Ph₂Mg(thf)₂ produces a Ni(I) dimer bridged with two μ-Br ligands, [Ni(μ-Br)(PEP)]₂ (2). Treatment of 1 with R₂Mg(thf)₂ (R = Me, Me₃SiCH₂) at -35 °C leads to dialkyl complexes [NiR₂(PEP)] (3 and 4), with a significantly distorted square planar configuration. DFT calculations support the occurrence of effective π-back-bonding between Ni to PEP to cause the structural distortion. On the other hand, the reaction of 1 with R₂Mg(thf)₂ (R = Me₃SiCH₂) conducted at a low temperature of -78°C forms an aryl bromide complex of the formula [Ni(Mes)(Br)(PEP)] (5; Mes = 2,4,6-^tBu₃C₆H₂), in which the Mes group originally bonded to the phosphorus atom of PEP is shifted to nickel; instead, the phosphorus atom is substituted with the R group to form the PEP ligand. The temperature-dependent formation of 4 or 5 is rationalized by considering a common five-coordinate intermediate.

Full text of DOI:10.1021/om500685x

Article
pubs.acs.org/Organometallics
Synthesis and Structures of Nickel Complexes with a PN-Chelate
Phosphaalkene Ligand
Katsuhiko Takeuchi, Ataru Minami, Yumiko Nakajima,*,† and Fumiyuki Ozawa*
International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji, Kyoto
611-0011, Japan
S
* Supporting Information
ABSTRACT: Phosphaalkenes with a PC bond possess
extremely strong π-accepting ability, often providing transition
metal complexes with interesting structures and properties.
This paper describes unique structures of nickel complexes
coordinated with a PN-chelate phosphaalkene ligand (PEP =
2-[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]-
pyridine). The PEP ligand combines with [NiBr2(dme)] (dme
= 1,2-dimethoxyethane) in toluene to afford [Ni(Br)(μ-
Br)(PEP)]2 (1), which reacts with R2Mg(thf)2 in Et2O or
THF to form three types of nickel complexes depending on
the R groups and reaction conditions. The reaction with
Ph2Mg(thf)2 produces a Ni(I) dimer bridged with two μ-Br
ligands, [Ni(μ-Br)(PEP)]2 (2). Treatment of 1 with R2Mg(thf)2 (R = Me, Me3SiCH2) at −35 °C leads to dialkyl complexes
[NiR2(PEP)] (3 and 4), with a significantly distorted square planar configuration. DFT calculations support the occurrence of
effective π-back-bonding between Ni to PEP to cause the structural distortion. On the other hand, the reaction of 1 with
R2Mg(thf)2 (R = Me3SiCH2) conducted at a low temperature of −78 °C forms an aryl bromide complex of the formula
[Ni(Mes*)(Br)(PEP*)] (5; Mes* = 2,4,6-tBu3C6H2), in which the Mes* group originally bonded to the phosphorus atom of
PEP is shifted to nickel; instead, the phosphorus atom is substituted with the R group to form the PEP* ligand. The temperature-
dependent formation of 4 or 5 is rationalized by considering a common five-coordinate intermediate.
Scheme 1. Reactions of [Ni(Br)(μ-Br)(PEP)]2 (1) with
Diorganomagnesiums
INTRODUCTION
■
Phosphaalkenes with a PC double bond possess an extremely
low-lying π* orbital, thereby serving as effective π-acceptors
toward transition metals.1 We have demonstrated that this
particular ligand property often provides interesting structures
and reactivities in late transition metal complexes. For example,
1,2-diaryl-3,4-diphosphinidenecyclobutene causes highly effi-
cient catalysis in conjunction with group 8−10 metals.2,3 2,6-
Bis(phosphaethenyl)pyridine effectively stabilizes coordina-
tively unsaturated complexes of 3d metals.4,5 Moreover, the
PC bond installed in a PNP-pincer type iridium complex
remarkably enhances the reactivity toward N−H bond
activation of ammonia and amines via metal−ligand coopera-
tion.6
This paper deals with novel nickel complexes with a PN-
chelate phosphaalkene ligand, 2-[1-phenyl-2-(2,4,6-tri-tert-
butylphenyl)-2-phosphaethenyl]pyridine (PEP) (Scheme 1).
Thus far, nickel complexes have been extensively studied using
tertiary phosphine ligands and have proven to be useful for
catalytic organic transformations.7 In this context, phosphaal-
kene complexes of nickel should also be attractive; however,
only three papers have documented their isolation using CO
and π-allyl ligands.8
Me3SiCH2). The resultant complexes displayed notable
structural variations depending on R groups and reaction
conditions as summarized in Scheme 1. The reaction with
Ph2Mg(thf)2 forms a Ni(I) bromide complex (2).9 Treatment
In this study, we prepared [Ni(Br)(μ-Br)(PEP)]2 (1) and
Received: June 29, 2014
examined its reactions with R2Mg(thf)2 (R = Ph, Me,
© XXXX American Chemical Society
A
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of 1 with dialkylmagnesiums leads to dialkyl complexes of the
formula [NiR2(PEP)] (3 and 4) with a significantly distorted
square planar configuration. On the other hand, treatment of 1
with R2Mg(thf)2 (R = Me3SiCH2) at low temperature (−78
°C) results in the formation of Mes* complex 5 (Mes* =
2,4,6-tBu3C6H2) via the exchange of Me3SiCH2 and Mes*
groups between Ni and P atoms.
Figure 2 shows the crystal structure of 2. Nearly half of the
molecules (46%) are paired with a crystal solvent (Et2O). The
RESULTS AND DISCUSSION
■
Synthesis of [Ni(Br)(μ-Br)(PEP)]2 (1). The PEP ligand was
prepared from 2-benzoylpyridine and Mes*PH2 by the
phospha-Peterson reaction.10 A crude product of PEP, which
contained a small amount of Mes*H, was subjected to the
reaction with [NiBr2(dme)] (dme = 1,2-dimethoxyethane) in
toluene at 60 °C for 17 h to form 1, which was isolated as a
reddish-brown solid in 74% yield. Complex 1 was a
paramagnetic compound unable to be characterized by NMR
spectroscopy; however, its dimeric structure with Ni(II) centers
could be confirmed by X-ray diffraction analysis.
Figure 2. Molecular structure of 2·(Et2O)0.46 with 50% probability
ellipsoids. Hydrogen atoms, disordered carbon atoms (Ph), and a
crystal solvent (Et2O) are omitted for clarity. Selected bond distances
(Å) and angles (deg): Ni1−P1 2.1334(17), Ni1−N1 1.961(5), Ni1−
Br1 2.4456(10), Ni1−Br2 2.4160(10), P1−C6 1.691(6), Ni2−P2
2.1472(16), Ni2−N2 1.966(4), Ni2−Br1 2.4220(10), Ni2−Br2
2.4481(10), P2−C36 1.703(6), P1−Ni1−N1 83.52(14), Br1−Ni1−
Br2 95.28(3), P2−Ni2−N2 83.76(14), Br1−Ni2−Br2 95.07(3), Ni1−
Br1−Ni2 80.60(3), Ni1−Br2−Ni2 80.67(3).
Figure 1 shows the crystal structure, which consists of two
NiBr2(PEP) units connected by two μ-Br ligands (Br1 and
other half does not involve the solvent molecule, but instead
the phenyl group on the C6 atom is tilted to compensate for
the vacant space. The core structures are identical to one
another irrespective of the presence or absence of Et2O.
The Ni1 and Ni2 atoms are bridged by μ-Br ligands (Br1 and
Br2). The complex has a quasi-C2v symmetry, and the PEP
ligands are associated with the Ni2(μ-Br)2 core in a syn-
orientation. The bond distances of Ni−N (1.961(5) and
1.966(4) Å) and Ni−P (2.1334(17) and 2.1472(16) Å) are
clearly shorter than those of the Ni(II) dimer (1) in a high-spin
state. The PC bond distances (1.691(6) and 1.703(6) Å) are
comparable to that of 1 (1.691(5) Å).
The interatomic distance between Ni1 and Ni2 is 3.15 Å; this
value is apparently too large for a direct bonding interaction,
but is somewhat smaller than the sum of the van der Waals radii
of Ni atoms (3.22 Å). Therefore, we carried out SQUID
measurement of 2 in the solid state. The magnetic moment
(μeff) ranging from 2.17 to 2.80 μB at 5−300 K demonstrated
the S = 1 ground state, and the χ−1−T plot exhibited a good
linear correlation (see Figure S1). Thus, we concluded the
absence of a notable spin−spin interaction between the Ni
atoms.
On the other hand, the magnetic moment of a solution of 2
in toluene was determined to be 1.68 μB at 25 °C by the Evans
method (calculated for the monomer). This value corresponds
to the S = 1/2 ground state and indicates the occurrence of
dissociation of 2 into the monomeric species [NiBr(PEP)] in
solution.
Reactions with R2Mg(thf)2 (R = Me, Me3SiCH2). Unlike
the reaction with Ph2Mg(thf)2, the reactions of 1 with 2 molar
quantities of dialkylmagnesiums in Et2O formed dialkyl
complexes of the formula [NiR2(PEP)] (R = Me (3),
Me3SiCH2 (4)) in 55% and 83% isolated yields, respectively.
Dimethyl complex 3 was relatively unstable in solution and
gradually decomposed even at −35 °C. On the other hand,
complex 4, with bulky Me2SiCH2 ligands, was fairly stable at
room temperature.
Figure 1. Molecular structure of 1·CH2Cl2 with 50% probability
ellipsoids. Hydrogen atoms and a crystal solvent (CH2Cl2) are omitted
for clarity. Selected bond distances (Å) and angles (deg): Ni−P
2.3218(15), Ni−N 2.061(4), Ni−Br1 2.5119(10), Ni−Br1′
2.5316(10), Ni−Br2 2.3997(9), P−C6 1.691(5), P−Ni−N
80.51(12), P−Ni−Br1′ 97.78(4), N−Ni−Br1 87.44(11), Br1−Ni−
Br1′ 84.18(3), P−Ni−Br1 110.80(4), N−Ni−Br1′ 170.23(12).
Br1′). Each unit has a trigonal bipyramidal configuration
around Ni. The Br1, Br2, and P atoms are located at the
equatorial positions, whereas the N and Br1′ atoms are at the
apical positions. The bond distances of Ni−N (2.061(4) Å) and
Ni−P (2.3218(15) Å) are comparable to those of a phosphine-
based PN-chelate analogue.11 The P−C6 distance (1.691(5) Å)
is in a typical range of P-coordinated phosphaalkenes in late
transition metal complexes.4−6,8
Reaction with Ph2Mg(thf)2. Treatment of 1 with Ph2Mg-
(thf)2 in a 1:2 molar ratio in Et2O at −35 °C formed a Ni(I)
bromide dimer, [Ni(μ-Br)(PEP)]2 (2), which was isolated as a
dark blue crystalline solid in 91% yield and characterized by
elemental analysis and X-ray crystallography. Complex 2 is
likely to be formed by comproportionation of [NiBr2(PEP)]
and [Ni(PEP)], the latter of which is generated by reductive
elimination of biphenyl from [NiPh2(PEP)] formed by
transmetalation. The formation of biphenyl was confirmed by
GC-MS analysis of the reaction solution.
B
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Complexes 3 and 4 are diamagnetic compounds displaying
their NMR signals in a normal region. The 1H NMR spectrum
of 3 measured in THF-d8 exhibited two sets of doublets at δ
0.47 (3JPH = 5.2 Hz) and 0.79 (3JPH = 13.2 Hz), which are
assignable to the Me ligands cis and trans to the phosphorus
3
atom, respectively, based on the JPH values. Similarly, the
methylene proton signals of Me3SiCH2 ligands in 4 at the cis
and trans positions of the phosphorus atom appeared at δ 0.48
(3JPH = 7.6 Hz) and 0.86 (3JPH = 12.4 Hz), respectively.
Figure 3 presents the X-ray crystal structure of 3. One of the
most remarkable features is a significantly distorted square
Figure 4. Optimized structures for 3a, 3a′, 3b, and 3b′. The structures
of 3a′ and 3b′ were optimized under the constraints of the fixed bond
angles of P−Ni−C1 = 180° (3a′), 148° (3b′).
Figure 3. Molecular structure of 3 with 50% probability ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ni−P 2.1339(10), Ni−N 1.972(3), Ni−C1
1.943(4), Ni−C2 1.931(4), P−C8 1.692(3), P−Ni−N 82.69(8), P−
Ni−C1 155.28(17), N−Ni−C2 172.59(15).
planar geometry with a bent P−Ni−C1 bond (155.28(17)°),
whereas the N−Ni−C2 axis retains linearity (172.59(15)°).
Complex 4 adopts a similar geometry around Ni (P−Ni−C1 =
154.69(7)°; see Figure S2). Furthermore, the phosphorus atom
is slightly pyramidalized to the opposite side of the Ni−C1 axis;
the sum of the bond angles around phosphorus is 353.6°.
To explore the cause of the structural distortion, DFT
calculations were carried out for the model compound
[NiMe2(pep)] (3a), in which the 2,4,6-tBu3C6H2 group
(Mes*) on the phosphorus atom was replaced by the 2,4,6-
Me3C6H2 group (Mes); see the Supporting Information for
details of the computation. The optimized structure of 3a given
in Figure 4a successfully reproduces the distorted square planar
configuration of 3. The P−Ni−C1 bond is bent to 148.1°, and
the bond angles around the phosphorus atom are 342.0° in
total. The distorted structure proved to be 4.9 kcal/mol more
stable than the square planar geometry with the fixed P−Ni−
C1 angle of 180° (3a′ in Figure 4b). On the other hand,
phosphine analogue 3b, having a saturated MesP(H)CHPh
group at the 2-position of pyridine (Figure 4c), was optimized
with a square planar configuration, which was located 4.3 kcal/
mol lower in energy than the distorted one with the fixed P−
Ni−C1 angle of 148° (3b′ in Figure 4d).
Figure 5. Schematic view of an orbital interaction causing structural
distortion of 3.
Reaction with R2Mg(thf)2 (R = Me3SiCH2) at Low
Temperature. The above-mentioned reaction of 1 with
R2Mg(thf)2 (R = Me3SiCH2) to give dialkyl complex 4 was
conducted at −35 °C. On the other hand, the same reaction
performed at −78 °C afforded the Mes* complex [Ni(Mes*)-
(Br)(PEP*)] (5), in which the Mes* substituent on
phosphorus was replaced by a Me3SiCH2 group. Complex 5
was exclusively formed when a 1:1 molar ratio of 1 and
R2Mg(thf)2 was employed (R/Ni = 1:1). Furthermore, even
with a 2 molar quantity of R2Mg(thf)2 (R/Ni = 2), complex 5
was formed as the major product (71%), along with 4 (29%), as
confirmed by 31P NMR spectroscopy.
Figure 6 shows the X-ray crystal structure of 5, which adopts
a square planar configuration around nickel, as generally
observed for 16e complexes with a low-spin state d8 metal
center. The Mes* and Br ligands are located trans to the N and
P atoms, respectively. This ligand arrangement is in accordance
with the order of trans-influence.
Scheme 2 presents a plausible reaction process for the
formation of [Ni(Mes*)(Br)(PEP*)] (5). The first step is
transmetalation of 1 with R2Mg(thf)2 (R = Me3SiCH2) via five-
coordinate intermediate A, in which the Ni(R)Br2(PEP) moiety
is very likely to be associated with the MgR(thf) moiety.
Although there are several possibilities of the aggregation form,
the doubly bridged structure with two μ-Br ligands is illustrated
as a probable one. When the reaction temperature is relatively
high (−35 °C), the MgR(thf) moiety is eliminated from A,
Thus, we concluded that the phosphaalkene unit causes the
structural distortion found in 3 and 3a. Figure 5 shows a
schematic view of the orbital interaction along the P−Ni−C1
bond in 3, which corresponds to the π-back-bonding between
the Ni atom and the PC bond. Bending the P−Ni−C1 bond
causes an antibonding interaction between the d (Ni) and σ
(Me) orbitals, thereby increasing the d orbital level. As a result,
the π-back-donation is facilitated and the distorted structure is
stabilized. In fact, the Mayer bond order of the PC bond of
3a (1.39) was lower than that of 3a′ (1.49).
C
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phosphorus to nickel, and the subsequent elimination of
MgR(Br)(thf)2 from C produces the mesityl complex 5.
CONCLUSION
■
In this study, we examined nickel complexes derived from
[Ni(Br)(μ-Br)(PEP)]2 (1) with a PN-chelate phosphaalkene
ligand (PEP). The complexes formed by the reactions of 1 with
R2Mg(thf)2 (R = Ph, Me, Me3SiCH2) varied significantly with
R groups and reaction conditions. The reaction with Ph2Mg-
(thf)2 formed [Ni(μ-Br)(PEP)]2 (2) with significantly distorted
coordination geometry around Ni(I) centers. Alkylmagnesiums
provided dialkyl complexes [NiR2(PEP)] (R = Me (3),
Me3SiCH2 (4)), with a bent P−Ni−R bond. On the other
hand, treatment of 1 with R2Mg(thf)2 (R = Me3SiCH2) at low
temperature (−78 °C) resulted in selective formation of
[Ni(Mes*)(Br)(PEP*)] (5; Mes* = 2,4,6-tBu3C6H2). In this
case, the Mes* group originally bonded to phosphorus was
shifted to nickel, whereas the phosphorus atom was substituted
with the R group instead. Apparently, the observed structures
and reactivities are unique to the PEP complexes with a PC
bond. Indeed, DFT calculations for 3 demonstrated the
structural distortion caused by the phosphaalkene unit. The
present results indicate the potential utility of phosphaalkene
ligands in nickel chemistry.
Figure 6. Molecular structure of 5 with 50% probability ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond distances (Å)
and angles (deg): Ni−P 2.0702(7), Ni−N 2.025(2), Ni−Br 2.3502(4),
Ni−C17 1.912(3), P−C6 1.682(2), P−Ni−N 83.41(6), P−Ni−Br
174.12(3), N−Ni−C17 171.11(10).
Scheme 2. Plausible Formation Processes of 4 and 5
EXPERIMENTAL SECTION
■
General Considerations. All manipulations were performed
under a nitrogen atmosphere using Schlenk techniques or a glovebox.
Toluene, hexane, CH2Cl2, and Et2O were purified by a solvent
purification system (MBraun SPS-800). Other solvents (THF,
benzene-d6, toluene-d8, THF-d8) were dried over sodium benzophe-
none ketyl and distilled. R2Mg(thf)2 (R = Ph, Me, Me3SiCH2) were
prepared according to the literature.13
NMR spectra were recorded on a Bruker AVANCE 400
spectrometer (1H NMR, 400.13 MHz; 13C NMR, 100.62 MHz; 31P
NMR, 161.98 MHz). Chemical shifts are reported in δ (ppm),
1
referenced to H (residual) and 13C signals of deuterated solvents as
internal standards or the 31P signal of 85% H3PO4 as an external
standard. Elemental analysis and FAB-MS were performed by the ICR
Analytical Laboratory, Kyoto University. ESI-MS spectra were
recorded on a Bruker micrOTOF I spectrometer. Solid-state magnetic
moments were recorded using a Quantum Design SQUID magneto-
meter. Magnetization versus temperature data were recorded in a
magnetic field of 10 000 G, using crystalline samples sealed in quartz
tubes. An impurity correction was made by fitting experimental data to
the formula χimpurity = C/T. GC-MS analysis was performed on a
Shimadzu GC-MS QP2010 instrument (EI, 70 eV).
Synthesis of PEP. To a THF solution (20 mL) containing
Mes*PH2 (1.16 g, 4.16 mmol) was added n-BuLi (3.14 mL, 4.99
mmol, 1.59 M in hexane) at −78 °C. The mixture was stirred at room
temperature for 30 min, and then Me3SiCl (0.633 mL, 4.99 mmol) was
added. After stirring for 30 min at room temperature, n-BuLi (3.14
mL, 4.99 mmol, 1.59 M in hexane) was added at −78 °C. The mixture
was again stirred at room temperature for 30 min to give a solution of
Mes*P(Li)SiMe3.
along with the μ-Br ligand, to form monoalkyl complex D,
which subsequently undergoes transmetalation with alkylmag-
nesium to afford dialkyl complex 4.
The following procedure was carried out in the dark to avoid E/Z
isomerization of PC bonds. A solution of 2-benzoylpyridine (0.635
g, 3.47 mmol) in THF (13 mL) was prepared in another Schlenk tube
and cooled to −78 °C. The solution of Mes*P(Li)SiMe3 was added
dropwise, and the mixture was stirred at room temperature for 15 h.
Volatiles were removed under vacuum, and the residue was dissolved
in toluene and filtered through a Celite pad. After drying under
vacuum, PEP was obtained as a pale yellow sticky solid (0.81 g)
containing a small amount of inseparable Mes*H.
On the other hand, when the five-coordinate intermediate A
is reluctant to eliminate the MgR(Br)(thf)2 moiety at a low
temperature of −78 °C, the R ligand becomes capable of
migrating to the phosphorus atom, affording B. This reaction
requires a parallel orientation of the Ni−R bond against the π*
orbital of the PC bond. The five-coordinate structure of A
having the R ligand at the apical position realizes an ideal
situation. Recently, we have demonstrated a similar migration
process for an Fe(I) mesityl complex by DFT calculations.12
Then, complex B undergoes migration of the Mes* group from
1
t
PEP. H NMR (C6D6, 25 °C): δ 1.29 (s, 9H, Bu), 1.57 (s, 18H,
tBu), 6.35 (d, 3JHH = 7.7 Hz, 1H, 3-py), 6.79 (t, 3JHH = 7.6 Hz, 1H, 5-
py), 7.00−7.06 (m, 3H, 4-py and Ph), 7.12 (d, 3JHH = 7.0 Hz, 1H, Ph),
D
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3
3
7.33 (s, 2H, Mes*), 7.64 (d, JHH = 6.8 Hz, 2H, Ph), 8.18 (d, JHH
=
NMR analysis. On the other hand, the reaction performed in CH2Cl2
was less selective, giving a mixture of 5 and 4 (6:4) even at −78 °C.
The experimental procedure for a preparative-scale reaction is as
follows. The reaction was carried out in THF to secure the solubility of
product complex 5.
4.0 Hz, 1H, 6-py). 31P{1H} NMR (C6D6, 25 °C): δ 252.9 (s). HRMS
(FAB): calcd for C30H38NP 443.2742 ([M]+); found 443.2739.
Synthesis of [Ni(Br)(μ-Br)(PEP)]2 (1). A Schlenk tube was charged
with [NiBr2(dme)] (160.7 mg, 0.520 mmol) and then with a toluene
solution (60 mL) of PEP (209.9 mg, 0.473 mmol). The solution was
heated to 60 °C for 17 h and then filtered while hot through a Celite
pad. After drying under vacuum, the resulting reddish-brown solid was
washed with hexane. Recrystallization from CH2Cl2 at −35 °C
afforded orange crystals of 1 (241.2 mg, 0.182 mmol, 77%). Anal.
Calcd for C60H76N2P2Ni2Br4: C, 54.42; H, 5.79; N, 2.12. Found: C,
54.22; H, 5.89; N, 2.27.
Reaction of 1 with Ph2Mg(thf)2. To an Et2O solution (3.5 mL)
of 1 (44.0 mg, 0.0332 mmol) was added an Et2O suspension (4.0 mL)
of Ph2Mg(thf)2 (25.8 mg, 0.0799 mmol) at −35 °C. 1,4-Dioxane (23
μL) was added, and the solution was filtered through glass wool and
concentrated to dryness to give a dark blue solid, which was dissolved
in cooled toluene and filtered through a Celite pad. A crude product
formed by concentration of the filtrate was recrystallized from Et2O at
−35 °C to give dark blue crystals of 2 (36.2 mg, 0.0302 mmol, 91%).
Anal. Calcd for C60H76N2P2Ni2Br2·0.46(C4H10O): C, 61.97; H, 6.78;
N, 2.34. Found: C, 62.37; H, 6.72; N, 2.26.
Reaction of 1 with R2Mg(thf)2 (R = Me, Me3SiCH2) at −35 °C.
To an Et2O solution (2.0 mL) of 1 (16.1 mg, 0.0122 mmol) was added
an Et2O suspension (1.0 mL) of Me2Mg(thf)2 (4.9 mg, 0.025 mmol)
at −35 °C. 1,4-Dioxane (0.4 mL) was added, and the solution was
filtered through glass wool and concentrated to dryness to give a deep
blue solid. The solid was dissolved in cooled toluene and filtered
through a Celite pad. The filtrate was concentrated, and the residue
was recrystallized from Et2O at −35 °C to give deep blue crystals of 3
(7.2 mg, 0.0135 mmol, 55%).
To a THF solution of 1 (62.8 mg, 0.0474 mmol) was added a THF
solution (1.0 mL) of (Me3SiCH2)Mg(thf)2 (16.3 mg, 0.0475 mmol) at
−78 °C. After stirring the mixture for 1 h, the solution was
concentrated to dryness under vacuum to afford a deep purple solid,
which was extracted with toluene, filtered through a Celite pad, and
concentrated. The resulting solid was recrystallized from Et2O at −35
°C to afford reddish-purple crystals of 5 (52.5 mg, 0.0784 mmol, 82%).
5. 1H NMR (THF-d8, 25 °C): δ −0.36 (s, 9H, SiMe3), 1.29 (s, 9H,
2
p-tBu), 1.36 (d, JPH = 19.7 Hz, 2H, CH2), 1.91 (s, 18H, o-tBu), 6.97
(d, 3JHH = Hz, 1H, py), 7.22 (s, 2H, Mes*), 7.29 (d, 3JHH = 7.0 Hz, 2H,
o-Ph), 7.41−7.51 (m, 4H, py and m,p-Ph), 7.74 (t, J = 7.8 Hz, 1H, py),
10.0 (d, J = 5.7 Hz, 1H, py). 13C{1H} NMR (THF-d8, 25 °C): δ 0.69
(d, J = 2.1 Hz, SiMe3), 11.0 (d, 1JCP = 10.5 Hz, CH2), 32.1, 32.3 (s, p-
C(CH3)3), 34.9 (s, p-C(CH3)3), 35.8 (s, o-C(CH3)3), 39.5 (s, o-
C(CH3)3), 119.8 (s, Ph), 120.0 (s, py), 123.8 (d, J = 7.1 Hz, py), 124.1
(s, Mes*), 129.5 (s, o-Ph), 129.6 (s, Ph), 130.5 (s, Ph), 139.5 (s, py),
146.2 (s, Mes*), 149.2 (s, py), 154.78 (s, Mes*), 154.82 (s, Mes*),
155.0 (s, py). The signal of CP was not observed due to low
intensity. 31P{1H} NMR (THF-d8, 25 °C): δ 232.2 (s). Anal. Calcd for
C34H49NPSiNiBr: C, 61.00; H, 7.38; N, 2.09. Found: C, 61.14; H,
7.40; N, 2.13.
X-ray Crystal Structure Determination. The intensity data were
collected on a Rigaku Mercury CCD diffractometer (for 1, 2, and 3)
and a Rigaku VariMax diffractometer (for 4 and 5) with graphite-
monochromated Mo Kα radiation (λ = 0.710 70 Å). The data sets
were corrected for Lorentz and polarization effects and absorption.
The structures were solved by direct methods (SHELXS-9714 for 1, 2,
3; SIR-9715 for 4, 5) and refined by least-squares calculations on F2 for
all reflections (SHELXL-97)14 using Yadokari-XG 2009 software.16
Complexes 1 and 2 contained CH2Cl2 and Et2O as crystal solvents,
respectively. Anisotropic refinement was applied to all non-hydrogen
atoms, expect for disordered groups. Hydrogen atoms were placed at
calculated positions. The crystallographic data and the summary of
solution and refinement are reported as Supporting Information (see
Table S1).
Computational Details. The geometric optimization and NBO
analysis were performed with the DFT method, where the B3LYP
functional was used for exchange−correlation terms. These calcu-
lations employed the LANL2DZ basis set for Ni, 6-31G(d) for P, N,
and C (Ni−Me), and 6-31G for C (non Ni−Me) and H. Core
electrons of Ni (up to 2p) were replaced with effective core
potentials.17 The Gaussian 09 program package was used for all
calculations.18 Molecular orbitals were drawn with the GaussView 5
program package.19
The reaction of 1 (37.6 mg, 0.0284 mmol) with (Me3SiCH2)2Mg-
(thf)2 (22.0 mg, 0.0641 mmol) was similarly conducted in Et2O (2
mL), and deep green crystals of 4 were obtained (32.2 mg, 0.0476
mmol, 83%).
3. 1H NMR (THF-d8, −50 °C): δ 0.47 (d, 2JPH = 5.2 Hz, 3H, Me),
0.79 (d, JPH = 13.2 Hz, 3H, Me), 1.34 (s, 9H, p-tBu), 1.50 (s, 18H,
2
o-tBu), 6.69 (d, JHH = 8.0 Hz, 1H, Ph), 6.97 (t, JHH = 7.6 Hz, 1H,
Ph), 7.11 (t, 3JHH = 7.2 Hz, 2H, Ph), 7.36 (d, 3JHH = 8.0 Hz, 1H, py),
7.42 (s, 2H, Mes*), 7.54 (m, 1H, py), 7.81 (d, 3JHH = 7.6 Hz, 1H, py),
9.23 (d, 3JHH = 5.6 Hz, 1H, py). 13C{1H} NMR (THF-d8, −50 °C): δ
9.5 (s, Me), 10.5 (s, Me), 31.6 (s, p-C(CH3)3), 34.2 (s, o-C(CH3)3),
36.0 (s, p-C(CH3)3), 39.7 (s, o-C(CH3)3), 122.0 (s, ipso-Ph), 122.3 (s,
3-py), 123.4 (s, 5-py), 124.4 (s, m-Mes*), 125.7 (d, 2JPC = 21.7 Hz, 2-
3
3
3
py), 127.2 (s, p-Ph), 128.4 (d, JPC = 6.7 Hz, o-Ph), 129.0 (s, m-Ph),
137.6 (s, 4-py), 139.8 (d, J = 13.8 Hz, ipso-Mes*), 151.6 (s, 6-py),
153.5 (s, p-Mes*), 154.3 (d, 1JPC = 15.5 Hz, CP), 157.2 (s, o-Mes*).
31P{1H} NMR (THF-d8, −50 °C): δ 250.9 (s). Anal. Calcd for
C32H44NPNi: C, 72.20; H, 8.33; N, 2.63. Found: C, 71.73; H, 8.50; N,
2.61.
4. 1H NMR (THF-d8, 25 °C): δ −0.21 (s, 9H, SiMe3), 0.14 (s, 9H,
SiMe3), 0.48 (d, 3JPH = 7.6 Hz, 2H, CH2), 0.86 (d, 3JPH = 12.4 Hz, 2H,
CH2), 1.34 (s, 9H, p-tBu), 1.52 (s, 18H, o-tBu), 6.57 (d, 3JHH = 6.4 Hz,
ASSOCIATED CONTENT
■
S
* Supporting Information
3
3
SQUID magnetic data for 2; crystal structure of 4; crystal data
for 1−5; Cartesian coordinates for the optimized structures of
3a, 3a′, 3b, and 3b′; X-ray data (CIF) for 1−5. This material is
available free of charge via the Internet at http://pubs.acs.org.
2H, Ph,), 6.94 (t, JHH = 8.0 Hz, 1H, Ph), 7.08 (t, JHH = 6.8 Hz, 2H,
Ph), 7.14 (d, 3JHH = 6.8 Hz, 1H, py), 7.40 (s, 2H, Mes*), 7.45 (t, 3JHH
= 6.4 Hz, 1H, py), 7.69 (t, 3JHH = 7.6 Hz, 1H, py), 9.30 (d, 3JHH = 5.6
Hz, 1H, py). 13C{1H} NMR (THF-d8, 25 °C): δ 2.7 (s, Si(CH3)3), 4.1
2
2
(s, Si(CH3)3), 15.4 (d, JPC = 122 Hz, CH2SiMe3), 18.2 (d, JPC = 84
Hz, CH2SiMe3), 31.8 (s, p-C(CH3)3), 34.8 (s, o-C(CH3)3), 36.0 (s, p-
C(CH3)3), 39.6 (s, o-C(CH3)3), 121.8 (s, ipso-Ph), 121.9 (s, 3-py),
122.7 (s, 5-py), 123.9 (s, m-Mes*), 127.1 (s, p-Ph), 128.3 (d, 3JPC = 7.5
Hz, o-Ph), 128.8 (s, m-Ph), 129.2 (s, 2-py), 137.4 (s, 4-py), 140.3 (s,
ipso-Mes*), 150.9 (s, 6-py), 153.7 (s, p-Mes*), 154.2 (s, CP), 158.0
(s, o-Mes*). 31P{1H} NMR (THF-d8, 25 °C): δ 253.0 (s). HRMS
(ESI): calcd for C38H60NPSi2Ni 676.3462 ([M + H]+); found
676.3428.
Reaction of 1 with R2Mg(thf)2 (R = Me3SiCH2) at −78 °C. This
reaction was initially examined in NMR scale at −78 °C in Et2O using
a 1:1 molar ratio of 1 and (Me3SiCH2)2Mg(thf)2, and the selective
formation of [Ni(Mes*)(Br)(PEP*)] (5) was confirmed by 31P{1H}
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: yumiko-nakajima@aist.go.jp.
*E-mail: ozawa@scl.kyotou.ac.jp.
Present Address
†National Institute of Advanced Industrial Science and
Technology (AIST), Tsukuba 305−8565, Japan.
Notes
The authors declare no competing financial interest.
E
dx.doi.org/10.1021/om500685x | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(15) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115.
(16) Kabuto, C.; Akine, S.; Kwon, E. J. Cryst. Soc. Jpn. 2009, 51, 218.
(17) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.
Theor. Chim. Acta 1990, 77, 123.
ACKNOWLEDGMENTS
■
This work was supported by a MEXT Grant-in-Aid for
Scientific Research on Innovative Areas “Stimuli-Responsive
Chemical Species” (No. 24109010).
(18) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
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dx.doi.org/10.1021/om500685x | Organometallics XXXX, XXX, XXX−XXX