Group 10 metal complexes supported by pincer ligands with an olefinic backbone

Article abstract of DOI:10.1021/om500256r

The coordination chemistry of 2,2′-bis(di-iso-propylphosphino)-trans- stilbene (tPCH-CHP) with group 10 metal centers in a variety of oxidation states is reported; different coordination modes were observed depending on the oxidation state of the metal. W

Full text of DOI:10.1021/om500256r

Article
pubs.acs.org/Organometallics
Group 10 Metal Complexes Supported by Pincer Ligands with an
Olefinic Backbone
Brittany J. Barrett and Vlad M. Iluc*
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States
S
* Supporting Information
ABSTRACT: The coordination chemistry of 2,2′-bis(di-iso-propylphosphino)-
trans-stilbene (tPCHCHP) with group 10 metal centers in a variety of oxidation
states is reported; different coordination modes were observed depending on the
oxidation state of the metal. With metal centers in the 0 or +1 oxidation state
((tPCHCHP)Ni, [(tPCHCHP)Pd]2, (tPCHCHP)NiCl, (tPCHCHP)-
NiI), η2 coordination of the olefin occurs, whereas, with metals in the +2 oxidation
state, C−H activation of the backbone, followed by rapid H−X reductive
elimination, was observed, leading to an η1 coordination of the backbone in
(tPCCHP)MCl (M = Ni, Pd, Pt). Employing the methyl-substituted analogue,
2,2′-bis(di-iso-propylphosphino)-trans-diphenyl-1,2-dimethylethene (tPCMe
CMeP), forced an η2 coordination of the olefin in [(tPCMeCMeP)NiCl]2-
[NiCl4]. The synthesis of the hydride complex (tPCCHP)NiH was attempted,
but, instead, led to the formation of (tPCHCHP)Ni, indicating that the vinyl
form of the backbone can function as a hydrogen acceptor. All metal complexes
were characterized by multinuclei NMR spectroscopy, X-ray crystallography, and elemental analysis.
INTRODUCTION
■
Group 10 metal complexes hold a privileged status in
organometallic chemistry because of their high and diverse
activity in catalysis.1,2 Olefin complexes have been known for a
long time, Zeise’s salt, K[Cl3Pt(CH2CH2)],3−5 being the first
reported transition-metal organometallic complex; recently, this
Figure 1. Coordination of 2,2′-bis(diphenylphosphino)-trans-stilbene
moiety has been successfully incorporated into ancillary
ligands.6−11 Given the versatility of group 10 metal olefin
complexes in catalysis,6,12−14 we became interested in
determining whether including such a fragment in the
backbone of a supporting ligand will engender new properties
for the resulting metal complexes.
to group 10 metals (M = Pd, Pt).
coordination in the neutral form, and η1-coordination in the
vinyl form, when the backbone could function as a hydrogen
atom reservoir. Herein, we report an in depth investigation of
the coordination chemistry of 2,2′-bis(di-iso-propylphosphino)-
trans-stilbene (tPCHCHP) by studying group 10 metal
centers in a variety of oxidation states. Complementary to the
results reported previously by the Bennett group, who only
studied the +2 oxidation state, we observe more than one
coordination mode with a metal center depending on its
oxidation state. In order to probe the ability of the olefinic
backbone to switch between various coordination modes, we
also replaced the olefinic protons with methyl groups and
studied the coordination chemistry of 2,2′-bis(di-iso-propyl-
phosphino)-trans-diphenyl-1,2-dimethylethene (tPCMe
CMeP). Furthermore, reactivity studies indicate that the vinyl
backbone is noninnocent and can function as a hydrogen
acceptor.
Pincers represent a versatile class of ligands, with various
examples of group 10 metal complexes reported.15−17 In
general, the metal complexes tend to be stable and robust,
properties conferred by the special pincer architecture.18,19
Many examples include a central, anionic, strong σ donor
flanked by two neutral donors.2,20,21 However, deviations from
this motif, in which the central chelating moiety is neutral, have
been introduced and typically include a pyridine or a phosphine
moiety.22,23 The coordination mode of these ligands has been
studied, and it has been shown that it can change in response to
various factors such as their electronic and steric properties.
Neutral pincer ligands including an alkene as the central
chelating moiety, PCHCHP, are not numerous. Bennett and
co-workers initially reported 2,2′-bis(diphenylphosphino)-
trans-stilbene and observed that group 10 metals form
monoanionic κ3-PCP complexes in the +2 oxidation state
(Figure 1).24−26 However, the choice of an olefinic backbone
allows various options, such as noncoordination and η2-
Received: March 10, 2014
Published: May 13, 2014
© 2014 American Chemical Society
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(Scheme 2), similarly to what Bennett observed for the phenyl
derivative.25,28 Uniquely, the reaction involving the nickel
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Metal Complexes.
We hypothesized that replacing the phenyl phosphine groups
with iso-propyls would lead to increased solubility of the
resulting metal complexes. This characteristic may prove
important in allowing us to survey various oxidation states of
the same metal. The precursor o,o′-trans-dibromostilbene (1)
was prepared via a McMurry aldehyde coupling reaction as
previously described (Scheme 1).27 A lithium halogen exchange
Scheme 2. Synthesis of Complexes 3−5
Scheme 1. Synthesis of tPCHCHP (2)
precursor leads to two products: 3, which is analogous to the
previously characterized nickel complex (o-Ph2P-C6H4-CCH-
C6H4-PPh2-o)NiCl, and another product, which was not
characterized because of its insolubility in common organic
solvents. Compounds 3, 4, and 5 result from the C−H
activation of the backbone, followed by rapid reductive
elimination of HCl. All three d8 metals tend to favor the
anionic form of the backbone consistently, a notion supported
by Bennett and Clark’s observations with the phenyl analogue
of the ligand.25 Bennett and Clark observed a similar behavior
when reacting bdps (bdps = bis(diphenylphosphino)-trans-
stilbene) with (cod)MCl2 (M = Pd, Pt) and (cod)Pt(CH3)2.
Ni(II) vinyl complexes are usually isolated as the insertion
products of alkynes into nickel aryl bonds,29,30 by oxidative
addition of vinyl chloride to Ni(I)31 and by cyclization
reactions.32 Palladium(II) salts have been known to remove
vinylic hydrogens from olefins.33 Other vinyl Pd(II) complexes
were isolated by oxidative addition of a C−Cl bond to a Pd(0)
center34 or rearrangement of Pd(II) allyl complexes.35 A similar
behavior of Pt(II) was observed by Shaw et al. for
(tBu2P(CH2)5PtBu2)PtCl2, where, after several C−H activa-
tions, a similar complex, (tBu2P(CH2)2-CCH-PtBu2)PtCl,
was isolated, invoking an η2 olefin intermediate.36
reaction then led to o,o′-trans-dilithiostilbene, which, in turn,
reacted with the desired phosphine chloride to generate 2,2′-
bis(di-iso-propylphosphino)-trans-stilbene (tPCHCHP, 2).
The product was isolated as a pure crystalline material in
good yield by recrystallization from n-pentane. 1H NMR
spectroscopy shows equivalent environments for all methine
protons and only two environments for the iso-propyl methyl
protons. The olefin protons exhibited a downfield resonance as
a singlet at 8.53 ppm. The product tPCHCHP (2) was also
characterized by 31P NMR spectroscopy as a singlet at −6.52
ppm and by single-crystal X-ray diffraction (Figure 2). The
C(1)−C(1)# distance corresponding to the alkene carbon
atoms is 1.330(4) Å, supporting CC double bond character.
With the diphosphine in hand, we decided to survey its
coordination mode. Metal d8 complexes (PCCHP)NiCl (3),
(PCCHP)PdCl (4), and (PCCHP)PtCl (5) form readily
upon the addition of 2 to the appropriate metal precursor
The nonsymmetrical coordination mode of tPCCHP in 3,
4, and 5 is supported by the aspect of the aryl region in the
corresponding 1H and 31P NMR spectra. All species are
identified by two doublets in the 31P NMR spectrum and
exhibit trans phosphorus couplings of 288, 387, and 382 Hz,
respectively. The platinum satellites for compound 5 are also
observed in the 31P NMR spectrum. In addition, compound 3
1
displays a broad singlet at 6.83 ppm in the H NMR spectrum
assigned to the olefinic proton. The broadness of this peak is
attributed to unresolved coupling with the phosphorus atoms.
The olefinic proton for compound 4 is lost in the aryl region of
the spectrum, while compound 5 contains a doublet at 7.63
ppm along with Pt satellites at 7.74 and 7.51 ppm, respectively
(JPtH = 48 Hz).
The structures of compounds 3 and 4 were obtained by
single-crystal X-ray diffraction and show a square-planar
coordination environment around the respective metal center
(Figures 3 and 4). Although the data obtained for 5 was of
relatively low quality (Figure SX44 in the Supporting
Information), connectivity information could be obtained and
the structure is similar to that of 3 and 4. The C(1)−C(2)
bond is in the typical range of a C−C double bond (1.351(3) Å
for 3 and 1.329(4) Å for 4). The Ni(II) complex is a more
distorted form a square-planar geometry (Figure 3); the angle
P(1)−Ni−P(2) is 165.91(3)° compared to 173.59(3)° for the
Figure 2. Thermal-ellipsoid (50% probability level) representation of
tPCHCHP (2). Most hydrogen atoms were omitted for clarity.
Selected distances (Å) and angles (deg): C(1) −C(1)# = 1.330(4),
P(1)−C(11) = 1.848(2), P(1)−C(22) = 1.870(2), P(1)−C(21) =
1.852(2), C(1)#1−C(1)−C(12) = 125.6(2), C(11)−P(1)−C(22) =
101.16(9), C(11)−P(1)−C(22) = 102.81(9).
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Scheme 3. Synthesis of tPCMeCMeP (7) and Complex 8
Figure 3. Thermal-ellipsoid (50% probability level) representation of
3. Most hydrogen atoms were omitted for clarity. Selected distances
(Å) and angles (deg): Ni−P(1) = 2.1891(6), Ni−P(2) = 2.1884(6),
Ni−Cl = 2.2127(6), Ni−C(1) = 1.930(2), C(1)−C(2) = 1.351(3),
P(1)−Ni−P(2) = 165.91(3), Cl−Ni−P(1) = 99.13(2), Cl−Ni−P(2)
= 99.72(2), C(1)−Ni−P(1) = 90.13(2), C(1)−Ni−P(2) = 87.01(6),
C(1)−Ni−Cl = 167.63(7).
Figure 4. Thermal-ellipsoid (50% probability level) representation of
4. Most hydrogen atoms were omitted for clarity. Selected distances
(Å) and angles (deg): Pd−P(1) = 2.2942(7), Pd−P(2) = 2.3160(7),
Pd−Cl = 2.3919(7), Pd−C(1) = 2.033(3), C(1)−C(2) = 1.329(4),
Cl−Pd−P(1) = 90.35(3), Cl−Pd−P(2) = 90.99(3), P(1)−Pd−P(2) =
173.59(3), C(1)−Pd−P(1) = 83.74(8), C(1)−Pd−Cl = 170.46(8).
Figure 5. Thermal-ellipsoid (50% probability level) representation of
8. Only one of the two crystallographically independent molecules is
shown. Most hydrogen atoms and the counterion were omitted for
clarity. Selected distances (Å) and angles (deg): Ni(1)−Cl(1) =
2.1695(9), Ni(1)−P(11) = 2.2283(8), Ni(1)−P(12) = 2.2272(8),
C(11)−C(12) = 1.398(3), Cl(1)−Ni(1)−P(11) = 85.53(3), Cl(1)−
Ni(1)−P(12) = 85.56(3), Cl(1)−Ni(1)−P(11) = 105.58(7), P(12)−
Ni(1)−P(11) = 171.10(3).
corresponding Pd(II) complex (Figure 4). In both cases, the
two phenylene rings of the ligand are not coplanar, possibly to
avoid the steric interaction between the vinylic and aromatic
hydrogen atoms.
Since the deprotonation of the olefinic backbone is rather
unusual, we decided to study the reactions of 2,2′-bis(di-iso-
propylphosphino)-trans-diphenyl-1,2-dimethylethene
(tPCMeCMeP, 7), in which methyl groups replace the
olefinic protons. A McMurry coupling reaction can be
performed on 2′-bromoacetophenone to generate bis(2-
bromophenyl)-2-butene (6).37 This particular reaction gen-
erates a higher yield of the cis (91%) than trans product (9%).
Trituration of the crude product with n-hexane led to the
isolation of the clean trans isomer since its solubility properties
are different than those of the cis isomer. From bis(2-
bromophenyl)-2-butene (6), the same synthetic procedure
used to generate 2 can be used to produce tPCMeCMeP
(7).
Reaction of 2 equiv of tPCMeCMeP (7) with 3 equiv of
(dme)NiCl2 generates [(tPCMeCMeP)NiCl]2[NiCl4], 8
(Scheme 3). Interestingly, η2 coordination is observed in 8
(Figure 5) instead of the previously observed C−H activation
with tPCHCHP (2). The forced η2 coordination of the olefin
in 8 causes the formation of a cationic species, with NiCl42− as a
counteranion (Figure 5), which broadens the 1H NMR spectra.
The methyl groups in the backbone of tPCMeCMeP (7) are
equivalent with a shift at 2.08 ppm, similar to the shift found in
the free ligand, at 2.12 ppm. The phosphines in this complex
are also equivalent and show up as a singlet at 64.40 ppm in the
corresponding 31P NMR spectra. The solid-state molecular
structure (Figure 5) also indicates a square-planar coordination
environment at the metal center and an elongated olefinic C−C
distance (1.398(3) Å), consistent with the presence of π-
backbonding in 8. The formation of 8 indicates that the
absence of olefinic protons in tPCMeCMeP renders the
ligand analogous to previously reported PNP systems, in which
the nitrogen donor is neutral and the corresponding nickel(II)
complexes are cationic, such as [(PONOP)NiCl][Cl]
(PONOP = 2,6-bis(di-tert-butylphosphinito)-pyridine),38
[(PNHPCy)NiBr][Br] (PNHPCy = HN[CH2CH2P(Cy)2]2),39
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and [(PNPtBu)Ni(NCMe)][BF4] (PNPtBu = 2,6-bis[(di-tert-
butylphosphino)methyl]pyridine).40
Ni(0) complexes; however, few examples of Ni(0) species
supported solely by a chelating ligand itself exist.43 Agapie and
co-workers reported a diphosphine arene pincer system, which
is capable of stabilizing the metal center by coordinating in an
η2 fashion to the arene group along with the phosphine arms
and generates a trigonal-planar complex similar to 9.44,45 Other
systems have shown the need for an additional ligand to
stabilize the metal, such as the previously reported {RN(CH2-
Metal d10 complexes were also synthesized. Compound
(tPCHCHP)Ni (9) was obtained readily from the reaction
of 2 with (cod)2Ni in THF (Scheme 4). The product was
Scheme 4. Synthesis of Complexes 9−11
i
PiPr2)2}Ni(C2H4) (R = Me, Pr), in which the amine
functionality remains dissociated from the metal center. In
that example, an olefin is present to donate electron density to
the metal.46
A comproportionation reaction47−49 was then attempted
with in situ generated nickel(II) and nickel(0) complexes in
order to generate a nickel(I) species (Scheme 4). Two
solutions were made, one containing 2 and (cod)2Ni and the
other 2 and (dme)NiCl2, which were stirred separately for 30
min. The mixtures were then combined and stirred for an
additional hour. An NMR spectrum of the crude reaction
mixture showed the presence of multiple products, of which
(tPCHCHP)NiCl (3) was dominant. Because of the fast C−
H activation of the ligand (vide supra), we were unable to
optimize the reaction conditions to avoid the side products. X-
ray quality crystals were obtained from a concentrated toluene
solution of the reaction mixture. The solid-state molecular
structure of 10 (Figure 7) shows the presence of a tetrahedral
Ni(I) species in which the ligand coordinates through the
phosphines and the olefinic backbone.
The analogous iodide, (tPCHCHP)NiI (11), could be
obtained on a large scale by adding a chilled THF solution of a
half an equivalent of I2 dropwise to a chilled solution of
(tPCHCHP)Ni (9) (Scheme 4). The 1H NMR spectrum of
the resulting product showed broad peaks, consistent with the
presence of a paramagnetic product, whereas the corresponding
31P NMR spectrum showed no peaks. Crystals suitable for X-
ray diffraction were obtained from a concentrated solution of
diethyl ether (Figure 7). The solid-state molecular structure is
analogous to that of (tPCHCHP)NiCl (10) and indicates a
tetrahedral geometry around the metal center with angles
ranging from 108.275(16) to 124.78(2)°. In general,
monomeric Ni(I) species have a trigonal-planar geometry,49−51
such as (iPr3P)2NiX (X = Cl, Br, I),47 while reported
tetrahedral Ni(I) species are dimers, such as [(dtbpe)NiCl]2;52
thus, the presence of the olefinic backbone in 10 and 11 helps
stabilize the metal center in its tetrahedral form, allowing it to
maintain its monomeric nature.
isolated as a pure crystalline material in good yield by
recrystallization from n-pentane. The H NMR spectrum of 9
1
shows a C2 symmetric compound, as indicated by the two
environments for the four isopropyl methine positions at 2.14
and 1.90 ppm, respectively. The olefinic protons are
represented as a singlet at 4.62 ppm. This upfield shift indicates
that π-backbonding takes place in this complex, the formulation
also supported by the elongated C(11)−C(12) distance of
1.406(5) Å (Figure 6).41,42 The olefin does not approach a
perpendicular orientation to the plane defined by P(1), Ni(1),
and P(2) (dihedral angle of 29°). This is attributed to the
pseudotrigonal-planar geometry observed around nickel, which
prevents the olefin from twisting out of plane. The trigonal-
planar geometry of this complex has been observed for other
A palladium(0) compound was synthesized by stirring 2 with
bis(dibenzylideneacetone)palladium(0) (Pd(dba)2) for 1 h (eq
1). Single-crystal X-ray diffraction (Figure 8) indicated the
Figure 6. Thermal-ellipsoid (50% probability level) representation of
9. Only one of the two crystallographically independent molecules is
shown. Most hydrogen atoms were omitted for clarity. Selected
distances (Å) and angles (deg): Ni(1)−P(12) = 2.1385(13), Ni(1)−
P(11) = 2.1463(13), Ni(1)−C(12) = 1.968(4), Ni(1)−C(11) =
1.968(4), C(11)−C(12) = 1.406(5), P(11)−Ni(1)−P(12) =
146.35(5).
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olefinic protons at 5.91 ppm, shifted upfield compared to the
corresponding protons of the free ligand. All four methine
positions are equivalent and appear as a broad multiplet at 2.15
ppm. Evaluation of the corresponding 31P NMR spectrum
shows equivalent phosphorus atoms, as indicated by the
1
presence of a sharp singlet at 55.28 ppm. Both H and 31P
NMR spectra indicated that 12 is found as a monomer in
solution. We propose that, in solution, the dimer dissociates
and forms a monomeric species similar to that observed for the
nickel(0) complex 9.
Reactivity Studies. Given the various coordination modes
of tPCHCHP observed especially with nickel complexes, we
decided to initiate a reactivity study to determine whether the
ligand changes its coordination depending on the reaction
conditions. Two compounds were targeted: (tPCHCHP)Ni
(9), which shows an η2-olefinic backbone, and (tPC
CHP)NiCl (3), which contains an η1-vinyl backbone.
Reaction of (tPCHCHP)Ni (9) with 1 equiv of MeI (eq
2) led to the formation of the cationic methyl nickel complex,
Figure 7. Thermal-ellipsoid (50% probability level) representation of
10 (top) and 11 (bottom). Most hydrogen atoms were omitted for
clarity. Selected distances (Å) and angles (deg): For 10: Ni−Cl =
2.2498(7), Ni−P(1) = 2.2569(7), Ni−P(2) = 2.2905(7), C(1)−C(2)
= 1.394(3), Cl−Ni−P(1) = 110.46(3), P(1)−Ni−P(2) = 125.10(3),
Cl−Ni−P(2) = 107.24(3). For 11: I−Ni = 2.5717(4), Ni−P(1) =
2.3039(6), Ni−P(2) = 2.2521(7), C(1)−C(2) = 1.390(3), P(1)−Ni−
P(2) = 124.78(2), P(1)−Ni−I = 112.000(18), P(2)−Ni−I =
108.275(16).
[(tPCHCHP)NiMe]I (13), with no change in the
coordination mode of the olefinic backbone. The formation
of a cationic species upon the addition of MeI to nickel(0) has
been previously observed for an amine-based PNP nickel(0)
complex, (PNHP)Ni (PNHP = HN(CH2CH2NHPiPr2)2).53,54
Compound 13 was characterized by 1H and 31P NMR
spectroscopy in solution, and by X-ray crystallography in the
1
solid state. H NMR spectroscopy indicates that the olefinic
protons appear as a singlet at 5.87 ppm, consistent with a
bound olefin experiencing π-backbonding with the metal
center. The new methyl ligand is found at 0.9 ppm, and its
signal is overlapping with those corresponding to the methyl
iso-propyl groups. 31P NMR spectroscopy shows two equivalent
environments for the phosphine atoms, which appear as a
singlet at 59.68 ppm, again, supporting the η2-coordination
mode of the olefinic backbone. Comparison of the solid-state
molecular structure (Figure 9) with that of (tPCHCHP)Ni
(9) shows elongation of the Ni−C distances between the metal
and the olefin from 1.968(4)−1.972(4) Å to 2.1148(19)−
2.1355(19) Å. The addition of a new ligand to the coordination
sphere also has the effect of shortening the C−C distance of the
backbone from 1.406(5) to 1.383(3) Å, as expected in the
presence of a more electron-deficient metal center.
In order to determine whether the vinyl backbone maintains
its coordination mode in the presence of a hydride ligand, the
nickel(II) hydride complex (tPCCHP)NiH (14) was
targeted from the corresponding chloride, (tPCCHP)NiCl
(3) (Scheme 5). Reaction with Li[HBEt3] led to the desired
complex, as indicated by a characteristic hydride signal in the
1H NMR spectrum of the crude reaction mixture. However,
after 1 h of stirring, when full conversion to (tPCCHP)NiH
(14) was determined by 1H NMR spectroscopy, and during the
Figure 8. Thermal-ellipsoid (50% probability level) representation of
12. Most hydrogen atoms were omitted for clarity. Selected distances
(Å) and angles (deg): Pd−P(1) = 2.3145(11), Pd−P(2)# =
2.3510(11), C(1)−C(2) = 1.398(5), P(1)−Pd−P(2)# = 122.74(4).
formation of a dimer, 12, in which each ligand binds to one
palladium through one phosphine and the olefin and to the
other through the other phosphine. Each palladium center
exhibits a pseudotrigonal-planar geometry with a P−Pd−P
1
angle of 122.74(4)°. The H NMR spectrum of 12 shows the
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palladium(II) catalytic cycles more efficiently than what has
been reported so far.58−61
DFT Calculations. In order to compare the electronic
structures of metal complexes containing a coordinated olefinic
backbone, models for the two diamagnetic nickel complexes
(tPCHCHP)Ni (9) and [(tPCHCHP)NiMe]I (13),
which contain nickel in the +2 and 0 oxidation states,
respectively, were investigated. Calculations were carried out
with Gaussian 03, and the phosphine iso-propyls were replaced
by methyl groups. A good agreement was found between the
optimized and the experimental structures (Figures SX31 and
SX33, Supporting Information). The results of DFT calcu-
lations support the experimental findings described above: both
complexes feature σ donation from the olefinic π orbital and π
backdonation from the metal to the olefin π* orbital (Figure
10). The amount of π backdonation between the two nickel
Figure 9. Thermal-ellipsoid (50% probability level) representation of
13. Most hydrogen atoms were omitted for clarity. Selected distances
(Å) and angles (deg): Ni−P(1) = 2.2062(6), Ni−P(2) = 2.2095(6),
Ni−C(5) = 1.982(2), Ni−C(1) = 2.1355(19), Ni−C(2) = 2.1148(19),
C(1)−C(2) = 1.383(3), P(1)−Ni−P(2) = 174.07(2), P(1)−Ni−C(5)
= 87.45(7), P(2)−Ni−C(5) = 87.48(7).
Scheme 5. Synthesis of Complex 14
Figure 10. σ- and π-bonding interactions for (tPCHCHP)MeNi (9′,
left) and [(tPCHCHP)MeNiMe+] (13′, right).
complexes varies, as expected, according to the d electron count
of the metal, with the nickel(0) compound featuring the largest
contribution of the olefin π* orbital (Figure 10). In addition,
DFT calculations support the assignment of the nickel(I)
formulation in (tPCHCHP)NiCl (10) and (tPCHCHP)-
NiI (11), with the unpaired electron residing primarily in the
dz2 orbital (Figures SX37 and SX40, Supporting Information).
reaction workup, the presence of the nickel(0) complex
(tPCHCHP)Ni (9) was observed. Heating of the crude
reaction mixture to 80 °C for 1 h led to clean conversion to 9.
Reaction of 3 with 1 equiv of Na[HBEt3] led to the exclusive
formation of the nickel(0) complex 9. Hydrogen transfer from
ruthenium to a supporting pincer ligand has been invoked by
the Milstein group in an interesting water oxidation reaction
and in amine formation from alcohols.55,56 Relevant to the
hydrogen transfer described here are the reactions reported by
the Agapie group with cationic diphosphine arene pincer
nickel(II) complexes, which transfer the hydride from the metal
to the arene backbone.44 Moreover, it is important to note that
the lack of hydrogen acceptor ability for the supporting ligand
can lead to decomposition reactions, as observed by Hu’s group
with (MeN2N)Ni-H, where MeN2N is a pincer bis(amino)amide
ligand, which underwent intramolecular decomposition and led
to the formation of nickel particles and (MeN2N)H by reductive
elimination.57 The findings described for the nickel hydride
complex (tPCCHP)NiH (14) may have applications in
nickel(0)/nickel(II) catalytic cycles that would bypass nickel(I)
or nickel(III) oxidation states and mimic palladium(0)/
CONCLUSIONS
■
A neutral tPCHCHP (2) pincer and its dimethyl analogue,
tPCMeCMeP (7), were synthesized and their coordination
chemistry with group 10 metal centers was studied. The
backbone olefinic moiety is versatile and responds to the
electronic requirements of the metal. With metal centers in the
0 or +1 oxidation state ((tPCHCHP)Ni (9), [(tPCH
CHP)Pd]2 (12), (tPCHCHP)NiCl (10), (tPCHCHP)NiI
(11)), η2 coordination of the olefin occurred, whereas, with
metals in the +2 oxidation state, C−H activation of the
backbone, followed by rapid H−X reductive elimination, was
observed, leading to an η1 coordination of the backbone in
(tPCCHP)MCl (M = Ni (3), Pd (4), Pt (5)). This reactivity
mode likely responds to subtle changes in the coordination
environment because employing the methyl-substituted olefinic
backbone analogue, (tPCMeCMeP, 7), forced an η2
coordination of the olefin in [(tPCMeCMeP)NiCl]2[NiCl4]
(8). Reactivity studies with two nickel complexes, (tPCH
CHP)Ni (9), which shows an η2-olefinic backbone, and (tPC
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CHP)NiCl (3), which contains an η1-vinyl backbone, indicate
that, while the η2-coordination at nickel(0) is unperturbed by
reactions with electrophiles ([(tPCHCHP)NiMe]I (13)),
the vinyl backbone acts as a hydrogen acceptor at the anionic
carbon when the synthesis of (tPCCHP)NiH (14) is
attempted, leading, ultimately, to the nickel(0) complex
(tPCHCHP)Ni (9). The various coordination modes
observed show that this ligand class is versatile and
accommodates different coordination geometries that could
enable new reactivity behavior for group 10 metal centers.
dimethoxyethane ((dme)NiCl2, 52.6 mg, 0.242 mmol), and the
resulting solution was stirred at room temperature for 1 h. The
volatiles were removed under reduced pressure, followed by extraction
with n-pentane. The orange extract was set to crystallize at −34 °C
1
(69.9 mg0.138 mmol, 57%). H NMR (400 MHz, C6D6) δ: 1.15 (dd,
JPH = 15 Hz, JHH = 10 Hz, 6H, CH(CH3)2), 1.36 (dd, JPH = 15 Hz, JHH
= 5 Hz, 6H, CH(CH3)2), 1.44 (app m, 12H, CH(CH3)2), 2.55 (m,
2H, CH(CH3)2), 2.63 (m, 2H, CH(CH3)2), 6.86 (br s, 1H, CHC),
6.92 (t, JHH = 4 Hz, 1H, ArH), 7.01 (t, JHH = 8 Hz, 1H, ArH), 7.11 (m,
2H, ArH), 7.13 (t, JHH = 4 Hz, 1H, ArH), 7.30 (t, JHH = 4 Hz, 1H,
ArH), 7.55 (d, JHH = 8 Hz, 1H, ArH). 31P{1H} NMR (162 MHz,
C6D6) δ: 29.23 (d, JPP = 221.9 Hz), 61.09 (d, JPP = 221.9 Hz). 13C{1H}
NMR (100 MHz, C6D6) δ: 18.20 (d, JPC = 1 Hz, CH(CH3)2), 19.18
(s, CH(CH3)2), 19.22 (d, JPC = 2 Hz, CH(CH3)2), 19.27 (s,
CH(CH3)2), 24.97 (dd, JPC = 2 Hz, JPC = 21 Hz, CH(CH3)2), 25.56
(dd, JPC = 2 Hz, JPC = 21 Hz, CH(CH3)2), 120.67 (d, JPC = 32 Hz,
ArC), 123.51 (d, JPC = 16 Hz, ArC), 127.29 (d, JPC = 5 Hz, ArC),
130.18 (d, JPC = 1 Hz, ArC), 130.74 (d, JPC = 1 Hz, ArC), 130.81 (d,
JPC = 3 Hz, ArC), 131.54 (d, JPC = 3 Hz, ArC), 130.02 (s, ArC), 132.40
(d, JPC = 8 Hz, ArC), 134.89 (d, JPC = 5 Hz, ArC),147.63 (d, JPC = 16
Hz, ArC), 154.89 (dd, JPC = 5 Hz, JPC = 19 Hz, CCH), 165.10 (d,
JPC = 43 Hz, CHC). Anal. Calcd for C26H37ClNiP2: C, 61.76; H,
7.38. Found C, 61.82; H, 7.39.
EXPERIMENTAL SECTION
■
All manipulations of air- and water-sensitive compounds were
performed under a dry nitrogen atmosphere using a drybox. Glassware,
vials, and stirring bars were dried in an oven at 120 °C overnight and
evacuated for 24 h in the antechamber before being brought into the
drybox. All solvents were dried by passing through a column of
activated alumina, followed by storage over molecular sieves and
sodium. Deuterated solvents were purchased from Cambridge Isotope
Laboratories. C6D6 was dried by stirring over CaH2, followed by
filtration. CDCl3 was dried over molecular sieves. All other chemicals
were commercially available and used as received. NMR spectra were
obtained on Bruker 400 and Bruker 500 spectrometers at ambient
temperature. Chemical shift values are reported in parts per million
(ppm) relative to residual internal protonated solvent or to a
Synthesis of (tPCCHP)PdCl (4). A mixture containing tPCH
CHP (2, 100 mg, 0.242 mmol) and dichloro(1,5-cyclooctadiene)-
palladium ((cod)PdCl2, 69.1 mg, 0.242 mmol) in THF was stirred at
room temperature for 1 h. The volatiles were removed under reduced
pressure, and the remaining yellow residue was triturated with n-
pentane. The resulting powder was dissolved in diethyl ether and
tetramethylsilane standard while using CDCl3 for H and 13C{1H}
1
experiments. Coupling constants are reported in Hz. Magnetic
moments were determined by the Evans method62−64 using capillaries
containing trimethoxybenzene in C6D6 as a reference and trimethox-
ybenzene in the sample solution. CHN analyses were performed on a
CE-440 Elemental Analyzer or by Midwest Microlab, LLC. Gaussian
03 (revision D.02) was used for all reported calculations. The B3LYP
(DFT) method was used to carry out the geometry optimizations on
model compounds specified in the text using the LANL2DZ basis set.
The validity of the true minima was checked by the absence of
negative frequencies in the energy Hessian.
1
allowed to crystallize at −35 °C (63.1 mg, 0.114 mmol, 47%). H
NMR (400 MHz, C6D6) δ: 1.01 (dd, JPH = 8 Hz, JHH = 4 Hz, 6H,
CH(CH3)2), 1.17 (dd, JPH = 8 Hz, JHH = 4 Hz, 6H, CH(CH3)2), 1.40
(m, 12H, CH(CH3)2), 2.62 (m, 2H, CH(CH3)2), 2.80 (m, 2H,
CH(CH3)2), 6.95 (t, JHH = 8 Hz, 1H, ArH), 6.98 (t, JHH = 8 Hz, 1H,
ArH), 7.19 (app m, 5H, ArH), 7.32 (t, JHH = 4 Hz, 1H, ArH), 7.69 (d,
JHH = 8 Hz, 1H, ArH). 31P{1H} NMR (162 MHz, C6D6) δ: 35.14 (d,
JPP = 382 Hz), 66.92 (d, JPP = 382 Hz). 13C{1H} NMR (100 MHz,
C6D6) δ: 18.35 (d, JCP = 2 Hz, CH(CH2)2), 18.90 (s, CH(CH3)2),
19.15 (d, JPC = 5 Hz, CH(CH3)2), 19.32 (d, JPC = 4 Hz, CH(CH3)2),
25.42 (dd, JPC = 18 Hz, JPC = 2 Hz, CH(CH3)2), 26.00 (dd, JPC = 18
Hz, JPC = 2 Hz, CH(CH3)2), 119.76 (d, JPC = 35 Hz, ArC), 124.58 (d,
JPC = 17 Hz, ArC), 127.53 (d, JPC = 5 Hz, ArC), 130.90 (app t, JPC = 2
Hz, ArC), 131.21 (d, JPC = 4 Hz, ArC), 131.58 (d, JPC = 2 Hz, ArC),
131.62 (app d, JPC = 1 Hz, ArC), 131.78 (app d, JPC = 1 Hz,
ArC),131.74 (br s, ArC), 132.10 (br s, ArC), 133.55 (d, JPC = 9 Hz,
ArC), 148.60 (d, JPC = 10 Hz, ArC), 153.06 (q, JPC = 4 Hz, CHC),
163.62 (d, JPC = 43 Hz, CHC). Anal. Calcd for C26H37ClP2Pd: C,
56.43; H, 6.74. Found C, 56.78; H, 6.71.
Synthesis of 2,2′-Bis(di-iso-propylphosphino)-trans-stilbene
(tPCHCHP, 2). The precursor o,o′-trans-dibromostilbene (1, 2.9 g,
8.63 mmol, 63.9%) was synthesized via a McMurry coupling reaction
as reported in the literature.27 1H NMR peaks agree with literature
values.65 Compound 1 was then brought into the glovebox and
dissolved in 75 mL of diethyl ether. The solution was allowed to cool
in a −35 °C freezer for 30 min, followed by the addition of n-
butyllithium (10.8 mL, 17.3 mmol) via syringe. The mixture was
allowed to warm to room temperature and then stirred for 1.5 h. The
resulting solution was cooled in a −35 °C freezer for an additional 30
min before the addition of di-iso-propyl phosphine chloride via syringe
(2.8 mL, 17.3 mmol), affording a cloudy yellow solution. After stirring
overnight, the reaction was quenched with 1 mL of a degassed 10%
solution of NH4Cl. The solution was then dried over Na2SO4,
followed by filtration through a frit padded with Celite. The volatiles
were removed under reduced pressure, leaving behind the crude
residue of tPCHCHP (2, 2.76 g, 6.70 mmol, 78.15%), which was
recrystallized from n-pentane. 1H NMR (400 MHz, C6D6) δ: 0.88 (dd,
JPH = 12 Hz, JHH = 8 Hz, 12H, CH(CH3)2), 1.02 (dd, JPH = 12 Hz, JHH
= 8 Hz, 12H, CH(CH3)2), 1.95 (m, 4H, CH(CH3)2), 7.03 (td, JHH = 8
Hz, JPH = 1.6 Hz, 2H, ArH), 7.11 (td, JHH = 8 Hz, JPH = 1.2 Hz, 2H,
ArH), 7.29 (dt, JHH = 8 Hz, JPH = 1.6 Hz, ArH), 7.95 (ddd, JHH = 6.8
Hz, JHH = 4 Hz, JPH = 0.8 Hz, 2H, ArH), 8.52 (d, JHH = 4 Hz, 2H,
CHCH). 31P{1H} NMR (162 MHz, C6D6) δ: −6.52 (s). 13C{1H}
NMR (100 MHz, C6D6) δ: 19.17 (d, JPC = 10 Hz, CH(CH3)2), 20.33
(d, JPC = 19 Hz, CH(CH3)2), 23.82 (d, JPC = 14 Hz, CH(CH3)2),
126.24 (d, JPC = 4 Hz, ArC), 126.68 (s, ArC), 129.16 (s, ArC), 129.65
(dd, JPC = 34 Hz, JPC = 3 Hz, ArC), 132.67 (d, JPC = 3 Hz, CHCH),
134.55 (d, J = 22 Hz, ArC), 145.59 (d, JPC = 22 Hz, ArC). MS
Synthesis of (tPCCHP)PtCl (5). A THF solution containing
tPCHCHP (2, 25 mg, 0.061 mmol) and dichloro(1,5-cyclo-
octadiene)platinum ((cod)PtCl2, 22.8 mg, 0.061 mmol) was stirred
at room temperature for 1 h. The volatiles were removed under
reduced pressure, and the resulting residue was triturated with n-
pentane, leading to the formation of a powder (36.4 mg, 0.057 mmol,
93%). Dissolving this powder in toluene and layering this solution with
1
n-pentane at −35 °C led to the isolation of analytically pure 5. H
NMR (400 MHz, C6D6) δ: 1.03 (dd, JPH = 8 Hz, JHH = 4 Hz, 6 Hz,
CH(CH3)2), 1.14 (dd, JPH = 8 Hz, JHH = 4 Hz, 6 Hz, CH(CH3)2), 1.43
(m, 12H, CH(CH3)2), 2.81 (m, 2H, CH(CH3)2), 3.12 (m, 2H,
CH(CH3)2), 7.00 (app q, JHH = 8 Hz, 2H, ArH), 7.15 (br m, 2H,
ArH), 7.25 (m, 2H, ArH), 7.41 (t, JHH = 8 Hz, 1H, ArH), 7.63 (d with
platinum satellites, JHH = 4 Hz, JHPt = 48 Hz, 1H, CHC), 7.86 (dd,
JHH = 4 Hz, JPH = 1 Hz, 1H, ArH). 31P{1H} NMR (162 MHz, C6D6) δ:
31.46 (d with platinum satellites, JPP = 306.2 Hz, JPPt = 1017.4 Hz),
62.29 (d with platinum satellites, JPP = 302.9 Hz, JPPt = 1165.6 Hz).
13C{1H} NMR (100 MHz, C6D6) δ: 18.16 (d with platinum satellites,
JPtC = 12 Hz, JPC = 2 Hz, CH(CH3)2), 18.62 (d with platinum
satellites, JPtC = 10 Hz, JPC = 2 Hz, CH(CH3)2), 19.00 (d, JPC = 4 Hz,
CH(CH3)2), 19.13 (d, JPC = 3 Hz, CH(CH3)2), 25.14 (dd with
platinum satellites, JPtC = 13 Hz, JPC = 28 Hz, JCC = 3 Hz, CH(CH3)2),
+
(QTOF) m/z: C26H39P2 , 413.25 (expected: C26H38P2, 412.24).
Synthesis of (tPCCHP)NiCl (3). Compound 2 (100 mg, 0.242
mmol) was dissolved in THF along with nickel(II) chloride
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26.39 (dd with platinum satellites, JPtC = 8 Hz, JPC = 29 Hz, JCC = 2 Hz,
CH(CH3)2), 117.46 (dd, JPC = 40 Hz, JPC = 2 Hz, ArC), 124.42 (d
with platinum satellites, JPtC = 17 Hz, JPC = 15 Hz, ArC), 125.96 (d, JPC
= 6 Hz, ArC), 127.45 (d, JPC = 6 Hz, ArC), 128.67 (d with platinum
satellites, JPtC = 12 Hz, JPC = 12 Hz, CHC), 130.59 (d with platinum
satellites, JPtC = 14 Hz, JPC = 2 Hz, ArC), 131.28 (dd, JPC = 27 Hz, JCC
= 3 Hz, ArC), 131.28 (d, J = 4 Hz, ArC), 133.38 (d, J = 9 Hz, ArC),
139.59 (d, J = 7 Hz, ArC), 149.62 (d, J = 16 Hz, ArC), 164.47 (d, J =
32 Hz, ArC). Anal. Calcd for C26H37ClP2Pt: C, 48.64; H, 5.81. Found
C, 48.37; H, 5.71.
Synthesis of (tPCHCHP)NiCl (10). (cod)2Ni (16.7 mg, 0.061
mmol) was mixed with 2 (25 mg, 0.061 mmol) in THF and stirred for
30 min. Concurrently, (dme)NiCl2 (13.19 mg, 0.061 mmol) was
mixed with 2 (25 mg, 0.061 mmol) in THF and stirred for 30 min.
The two solutions were mixed and stirred for an additional 2 h. The
volatiles were then removed under reduced pressure; a 1H NMR
spectrum of the crude reaction mixture indicated that multiple species
were present, including complex 3. Trituration with n-pentane,
followed by recrystallization from toluene solution layered with n-
pentane, led to the isolation of single crystals of (tPCCP)NiCl (10),
but because of the rapid formation of (tPCCHP)NiCl (3), the
sample was contaminated and all attempts to isolate pure 10 failed.47,48
Synthesis of (tPCHCHP)NiI (11). A THF solution of 9 (25 mg,
0.053 mmol) was chilled to −35 °C, along with a THF solution of I2
(6.7 mg, 0.026 mmol). After 30 min, the I2 solution was added
dropwise to the solution of 9 over the course of 5 min. The mixture
was warmed to room temperature while stirring for 1 h. The volatiles
were removed under reduced pressure, followed by trituration with n-
pentane, which resulted in a dark yellow-green powder (24.4 mg, 0.043
mmol, 80%). The powder was then recrystallized from a concentrated
diethyl ether solution. Magnetic moment: μeff = 1.63 μB. The 1H NMR
Synthesis of (Z)-2,3-Bis(2-di-iso-propylphosphinephenyl)-2-
butene (tPCMeCMeP, 7). The precursor, (Z)-2,3-bis(2-bromo-
phenyl)-2-butene (6), was synthesized as reported in the literature in
8.4% yield.37 Compound 7 was generated via the same procedure as 2
1
(1.6878 g, 3.83 mmol, 72.4%). H NMR (500 MHz, C6D6) δ: 0.95
(dd, JPH = 10 Hz, JHH = 5 Hz, 6H, CH(CH3)2, major), 1.03 (dd, JPH
=
10 Hz, JHH = 5 Hz, 6H, CH(CH3)2, major), 1.17 (m, 12H, CH(CH3)2,
major), 1.35 (dd, JPH = 10 Hz, JHH = 5 Hz, CH(CH3)2, minor), 1.94
(m, 4H, CH(CH3)2, major), 2.05 (s, CH3CCCH3, minor) 2.12 (s,
6H, CH3CCCH3, major), 7.11 (td, JHH = 10 Hz, JPH = 1 Hz, 2H,
ArH, major), 7.21 (t, JHH = 10 Hz, 2H, ArH, major), 7.41 (dt, JHH = 10
Hz, JPH = 1 Hz, 2H, ArH, major), 7.47 (br d, JHH = 5 Hz, ArH, minor),
7.63 (ddd, JHH = 5 Hz, JHH = 5 Hz, JPH = 1 Hz, 2H, ArH, major).
31P{1H} NMR (162 MHz, C6D6) δ: −3.09 (s, minor), −2.38 (s,
major). 13C{1H} NMR (100 MHz, C6D6) δ: 20.44 (d, JPC = 18 Hz,
CH(CH3)2), 20.67 (d, JPC = 13 Hz, CH(CH3)2), 20.77 (s,
CH(CH3)2), 20.94 (d, JPC = 15 Hz, CH(CH3)2), 24.99 (d, JPC = 23
Hz, −CH(CH3)2), 25.29 (d, JPC = 18 Hz, CH3CCCH3), 25.96 (d,
JPC = 24 Hz, CH(CH3)2), 126.36 (s, ArC), 129.13 (s, CH3CCCH3),
129.46 (s, ArC), 130.03 (d, JPC = 11 Hz, ArC), 132.83 (d, JPC = 7 Hz,
ArC), 135.76 (d, JPC = 32 Hz, ArC), 152.94 (d, JPC = 49 Hz, ArC). MS
1
spectrum is broad (Figure SX22 in the Supporting Information). H
NMR (400 MHz, C6D6) δ: 2.97 (ν1/2 = 2080 Hz), 4.93 ((ν1/2 = 1760
Hz), 6.16 (ν1/2 = 880 Hz), 7.83 (ν1/2 =360 Hz), 10.16 (ν1/2 = 120 Hz),
10.63 (ν1/2 = 312 Hz). Anal. Calcd for C26H38INiP2·2CHCl3: C, 40.19;
H, 4.82. Found C, 40.58; H, 4.63.
Synthesis of [(tPCHCHP)Pd]2 (12). Bis(dibenzylideneacetone)-
palladium(0) (34.5 mg, 0.060 mmol) was mixed with tPCHCHP
(2, 25 mg, 0.061 mmol) in THF and stirred at room temperature for
12 h. The volatiles were removed under reduced pressure. The
resulting residue was then dissolved in n-pentane and passed through a
silica plug using a gradient elution of n-pentane, diethyl ether, and
+
(QTOF) m/z: C28H43P2 , 441.28 (expected: C28H42P2, 440.28).
1
THF (3.3 mg, 0.006 mmol, 10.5%). H NMR (400 MHz, C6D6) δ:
Synthesis of 2[(tPCMeCMeP)NiCl]2[NiCl4] (8). A solution of
THF containing tPCMeCMeP (7, 25 mg, 0.057 mmol) and
(dme)NiCl2 (18.5 mg, 0.085 mmol) was stirred for 1 h at ambient
temperature. The volatiles were then removed under reduced pressure;
trituration with n-pentane produced a green powder (29.8 mg, 0.023
mmol, 83%). The powder was then recrystallized from a CH2Cl2
solution layered with n-pentane. 1H NMR (400 MHz, CDCl3) δ: 1.54
(q, JPH = 10 Hz, 6H, CH(CH3)2), 1.61 (q, 6H, JPH = 10 Hz,
CH(CH3)2), 1.74 (q, 12 H, JPH = 10 Hz, CH(CH3)2), 2.08 (s, 6H,
CH3CCCH3), 3.00 (br s, 2H, CH(CH3)2), 3.24 (br m, 2H,
CH(CH3)2), 7.94 (br s, 2H, ArH), 8.05 (br s, 2H, ArH), 9.04 (br s,
2H, ArH), 9.29 (br s, 2H, ArH). 31P{1H} NMR (162 MHz, CDCl3) δ:
64.40 (s). 13C{1H} NMR (100 MHz, CDCl3) δ: 18.74 (s, CH(CH3)2),
19.51 (s, CH(CH3)2), 20.43 (s, CH(CH3)2), 20.70 (s, CH(CH3)2),
26.85 (t, JPC = 23 Hz, CH(CH3)2), 27.53 (t, JPC = 21 Hz, CH(CH3)2),
33.15 (s, CH3CCCH3), 123.83 (s, ArC), 128.94 (t, JPC = 32 Hz,
CH3CCCH3), 131.23 (s, ArC), 132.08 (t, JPC = 13 Hz, ArC), 132.65
(s, ArC), 137.42 (s, ArC), 151.93 (t, JPC = 23 Hz, ArC). Anal. Calcd for
C56H84Cl6Ni3P4·CH2Cl2: C, 50.53; H, 6.40. Found C, 50.52; H, 6.50.
Synthesis of (tPCHCHP)Ni (9). A solution containing tPCH
CHP (2, 100 mg, 0.242 mmol) and nickel bis(cyclooctadiene),
(cod)2Ni, was stirred at room temperature for 1 h in THF. The
volatiles were removed under reduced pressure, and the orange residue
was dissolved in n-pentane and allowed to crystallize at −34 °C (79.0
1.02 (dd, JPH = 8 Hz, JHH = 4 Hz, 12 H, CH(CH)3)2), 1.21 (dd, JPH
∼
JHH = 8 Hz, 12H, CH(CH3)2), 2.16 (m, 4H, CH(CH3)2), 5.91 (s, 2H,
CHCH), 7.08 (t, JHH = 4 Hz, 2H, ArH), 7.17 (m, 2H, ArH), 7.27
(d, JHH = 8 Hz, 2H, ArH), 7.60 (d, JHH = 8 Hz, 2H, ArH). 31P{1H}
NMR (162 MHz, C6D6) δ: 55.28 (s). 13C {1H} NMR (100 MHz,
C6D6) δ: 19.45 (s, CH(CH)3)2), 20.47 (t, JPC = 8 Hz, CH(CH3)2),
24.72 (br s, CH(CH3)2), 100.34 (t, JPC = 7 Hz, CHCH), 125.87 (t,
JPC = 2 Hz, ArC), 129.08 (s, ArC), 129.81 (t, JPC = 8 Hz, ArC), 132.03
(s, ArC), 149.26 (t, JPC = 18 Hz, ArC), 150.89 (t, JPC = 15 Hz, ArC).
Anal. Calcd for C52H76P4Pd2: C, 60.18; H, 7.38. Found C, 60.35; H,
7.42.
Synthesis of [(tPCCHP)NiMe]I (13). A solution of (tPC
CP)Ni (9, 44.4 mg, 0.094 mmol) in THF was chilled in a −35 °C
freezer for 30 min, along with a 1.6 M solution of iodomethane. Two
equivalents of iodomethane (1.17 mL, 0.18 mmol) were added to the
(tPCCP)Ni (9) solution. The mixture was stirred for 5 min at
ambient temperature until a yellow precipitate crashed out. The
solvent was decanted, followed by trituration of the yellow powder
1
with n-pentane (42.2 mg, 0.067 mmol, 71.3%). H NMR (400 MHz,
CDCl3) δ: 1.01 (m, 9H, CH3, CH(CH3)2), 1.32 (m, 12H,
CH(CH3)2), 1.48 (app q, JPH ∼ JHH = 8 Hz, 6 H, CH(CH3)2), 2.77
(br s, 2 H, CH(CH3)2), 2.90 (br s, 2H, CH(CH3)2), 5.66 (s, 2H,
CHCH), 7.42 (d, 2 H, JHH = 8 Hz, ArH), 7.68 (m, 6 H, ArH).
31P{1H} NMR (162 MHz, CDCl3) δ: 60.18 (s). 13C{1H} NMR (100
MHz, CDCl3) δ: −1.52 (t, JPC = 23 Hz, CH3), 16.69 (s, CH(CH3)2),
18.38 (s, CH(CH3)2), 19.37 (s, CH(CH3)2), 20.21 (s, CH(CH3)2),
23.75 (t, JPC = 13 Hz, CH(CH3)2) 24.95 (t, JPC = 11 Hz, CH(CH3)2),
116.21 (s, CHCH), 125.76 (t, JPC = 20 Hz, ArC), 127.38 (t, JPC = 6
Hz, ArC), 129.64 (t, JPC = 2 Hz, ArC), 131.53 (s, ArC), 132.72 (s,
ArC), 148.62 (t, JPC = 14 Hz, ArC). Anal. Calcd for C27H41INiP2: C,
52.89; H, 6.74. Found C, 53.04; H, 6.82.
Synthesis of (tPCCHP)NiH (14). To a solution of (tPC
CHP)NiCl (3, 20.4 mg, 0.043 mmol) in THF was added 0.04 mL of a
1 M Li[(C2H5)3BH] (0.04 mmol) THF solution. The mixture was
stirred at room temperature for 1 h, after which the volatiles were
removed under reduced pressure. A NMR spectrum of the crude
reaction mixture showed full conversion to 14. The product was then
1
mg, 0.168 mmol, 69%). H NMR (500 MHz, C6D6) δ: 0.97 (app m,
6H, CH(CH3)2), 1.03 (dd, JPH = 10 Hz, JHH = 5 Hz, 6H, CH(CH3)2),
1.12 (dd, JPH = 10 Hz, JHH = 5 Hz, 6H, CH(CH3)2), 1.26 (dd, JPH = 10
Hz, JHH = 5 Hz, 6H, CH(CH3)2), 1.95 (m, 2H, CH(CH3)2), 2.19 (br
m, 2H, CH(CH3)2), 4.65 (s, 2H, CHCH), 7.07 (t, JHH = 5 Hz, 2H,
ArH), 7.18 (m, 4H, ArH), 7.69 (d, JHH = 5 Hz, 2H, ArH). 31P{1H}
NMR (202 MHz, C6D6) δ: 57.85 (s). 13C{1H} NMR (126 MHz,
C6D6) δ: 18.36 (s, CH(CH3)2), 18.92 (t, JPC = 6.3 Hz, CH(CH3)2),
20.76 (t, JPC = 6.3 Hz, CH(CH3)2), 21.20 (app m, CH(CH3)2), 26.44
(t, JPC = 5.04 Hz, CH(CH3)2), 74.96 (t, JPC = 8.82 Hz, CHCH),
125.49 (s, ArC), 128.35 (t, JPC = 7.6 Hz, ArC), 129.51 (t, JPC = 7.56,
ArC), 130.93 (s, ArC), 148.82 (t, JPC = 21.42 Hz, ArC), 154.63 (t, JPC
= 15.1 Hz, ArC). Anal. Calcd for C26H38NiP2: C, 66.27; H, 8.13.
Found C, 65.81; H, 8.10.
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Organometallics
Article
extracted in n-pentane, and the resulting solution was filtered. NMR
spectroscopy showed that the conversion to (tPCHCHP)Ni (9)
proceeded rapidly even at ambient temperature. Heating the NMR
R1 = 0.0566, wR2 = 0.0807 for 4771 data with [I > 2σ(I)] and R1 =
0.1361, wR2 = 0.0931 for all 8912 data. Residual electron density (e−·
Å−3) max/min: 0.711/−0.747.
1
X-ray Crystal Structure of (tPCHCHP)NiCl (10). X-ray quality
single crystals were obtained from a concentrated toluene solution at
−35 °C in the glovebox. Crystal and refinement data for 10:
C26H38ClNiP2; Mr = 506.66; monoclinic; space group P2(1)/c; a =
9.4899(9) Å; b = 20.450(2) Å; c = 13.0740(13) Å; α = 90°; β =
92.696(2)°; γ = 90°; V = 2534.4(4) Å3; Z = 4; T = 120(2) K; λ =
0.71073 Å; μ = 1.009 mm−1; dcalc = 1.328 g·cm−3; 35 899 reflections
collected; 5182 unique (Rint = 0.0651); giving R1 = 0.0362, wR2 =
0.0694 for 4008 data with [I > 2σ(I)] and R1 = 0.0572, wR2 = 0.0796
for all 5182 data. Residual electron density (e−·Å−3) max/min: 0.488/
−0.323.
sample for 1 h at 80 °C showed full conversion to 9. H NMR (500
MHz, C6D6) δ: −10.65 (ddd, JHP = 48 Hz, JHP = 46 Hz, JHH = 4 Hz,
1H, hydride), 0.98 (m, 12 H, CH(CH3)2), 1.19 (dd, JPH = 12 Hz, JHH
= 4 Hz, 6 H, CH(CH3)2), 1.26 (dd, JPH = 12 Hz, JHH = 4 Hz, 6 H,
CH(CH3)2), 2.20 (m, 2H, CH(CH3)2), 2.27 (m, 2H, CH(CH3)2),
7.03 (t, 1H, JHH = 8 Hz, ArH), 7.09 (t, JHH = 4 Hz, 1H, ArH), 7.32 (m,
4H, ArH), 7.90 (m, 1H, ArH), 8.05 (dd, JHH = 8 Hz, JPH = 4 Hz, 1H,
ArH). 31P{1H} NMR (162 MHz, C6D6) δ: 57.53 (d, JPP = 247 Hz),
84.17 (d, JPP = 247 Hz). Because 14 is not stable for a reasonable
amount of time at ambient temperature, an analytically pure sample
suitable for elemental analysis could not be obtained. 1H and 31P NMR
spectra for this complex can be found in the Supporting Information
(Figures SX29 and SX30).
X-ray Crystal Structure of (tPCHCHP)NiI (11). X-ray quality
single crystals were obtained as green plates from a concentrated
diethyl ether solution at −35 °C in the glovebox. Crystal and
refinement data for 11: C26H38INiP2; Mr = 598.11; monoclinic; space
group P2(1)/n; a = 8.0612(15) Å; b = 15.333(3) Å; c = 21.312(4) Å;
α = 90°; β = 91.438(3)°; γ = 90°; V = 2633.4(8) Å3; Z = 4; T =
120(2) K; λ = 0.71073 Å; μ = 2.042 mm−1; dcalc = 1.509 g·cm−3; 59
339 reflections collected; 6567 unique (Rint = 0.0531); giving R1 =
0.0236, wR2 = 0.0477 for 5501 data with [I > 2σ(I)] and R1 = 0.0352,
wR2 = 0.0512 for all 6567 data. Residual electron density (e−·Å−3)
max/min: 0.604/−0.444.
X-ray Crystal Structure of [(tPCHCHP)Pd]2 (12). X-ray
quality single crystals were obtained from a concentrated solution of
n-pentane at −35 °C in the glovebox. Crystal and refinement data for
12: C52H76P4Pd2; Mr = 1037.81; tetragonal; space group P4(1)2(1)2;
a = 12.8344(11) Å; b = 12.8344(11) Å; c = 34.222(3) Å; α = 90°; β =
90°; γ = 90°; V = 5637.1(11) Å3; Z = 4; T = 120(2) K; λ = 0.71073 Å;
μ = 0.781 mm−1; dcalc = 1.223 g·cm−3; 68 395 reflections collected;
4970 unique (Rint = 0.1171); giving R1 = 0.0382, wR2 = 0.0634 for
4420 data with [I > 2σ(I)] and R1 = 0.0485, wR2 = 0.0659 for all 4970
data. Residual electron density (e−·Å−3) max/min: 0.302/−0.312.
X-ray Crystal Structure of [(tPCHCHP)NiMe]I (13·2CH2Cl2).
X-ray quality single crystals were obtained from a concentrated
solution of dichloromethane at −35 °C in the glovebox. Crystal data
for 13: C29H45Cl4INiP2; Mr = 783.00; monoclinic; space group P2(1)/
c; a = 12.3677(11) Å; b = 13.0174(11) Å; c = 21.8913(19) Å; α = 90°;
β = 102.5694(11)°; γ = 90°; V = 3439.9(5) Å3; Z = 4; T = 120(2) K; λ
= 0.71073 Å; μ = 1.883 mm−1; dcalc = 1.512g·cm−3; 36 026 reflections
collected; 6051 unique (Rint = 0.0258); giving R1 = 0.0214, wR2 =
0.0509 for 5412 data with [I > 2σ(I)] and R1 = 0.0260, wR2 = 0.0523
for all 6051 data. Residual electron density (e−·Å−3) max/min: 0.767/
−0.464.
X-ray Crystal Structure of tPCHCHP (2). X-ray quality single
crystals were obtained from a concentrated solution of n-pentane
solution at −34 °C in the glovebox. Crystal and refinement data for 2·
C7H8: Crystal data for C33H46P2; Mr = 504.64; monoclinic; space
group C2/c; a = 13.5186(11) Å; b = 12.0847(9) Å; c = 18.2230(14) Å;
α = 90°; β = 93.335(2)°; γ = 90°; V = 2972.0(4) Å3; Z = 4; T =
120(2) K; λ = 0.71073 Å; μ = 0.165 mm−1; dcalc = 1.128 g·cm−3; 13
722 reflections collected; 1638 unique (Rint = 0.0504); giving R1 =
0.0298, wR2 = 0.0661 for 1390 data with [I > 2σ(I)] and R1 = 0.0406,
wR2 = 0.0711 for all 1638 data. Residual electron density (e−·Å−3)
max/min: 0.141/−0.195.
X-ray Crystal Structure of (tPCCHP)NiCl (3). X-ray quality
single crystals were obtained from a concentrated CH2Cl2 solution
layered with n-pentane at −35 °C in the glovebox. The resulting
crystals were bright orange blocks. Crystal and refinement data for 3:
C26H37ClNiP2; Mr = 505.66; monoclinic; space group P2(1)/n; a =
8.8598(10) Å; b = 9.8216(11) Å; c = 29.245(3) Å; α = 90°; β =
97.096(2)°; γ = 90°; V = 2525.3(5) Å3; Z = 4; T = 120(2) K; λ =
0.71073 Å; μ = 1.012 mm−1; dcalc = 1.330 g·cm−3; 22 334 reflections
collected; 5171 unique (Rint = 0.0488); giving R1 = 0.0345, wR2 =
0.0695 for 4126 data with [I > 2σ(I)] and R1 = 0.0521, wR2 = 0.0743
for all 5171 data. Residual electron density (e−·Å−3) max/min: 0.535/
−0.283.
X-ray Crystal Structure of (tPCCHP)PdCl (4). X-ray quality
single crystals were obtained as pale yellow blocks from a concentrated
diethyl ether solution at −35 °C in the freezer in the glovebox. Crystal
and refinement data for 4: C26H37ClP2Pd; Mr = 553.35; orthorhombic;
space group Pca2(1); a = 15.5062(11) Å; b = 11.0311(8) Å; c =
14.9547(11) Å; α = 90°; β = 90°; γ = 90°; V = 2558.0(3) Å3; Z = 4; T
= 120(2) K; λ = 0.71073 Å; μ = 0.966 mm−1; dcalc = 1.437 g·cm−3; 22
282 reflections collected; 5276 unique (Rint = 0.0346); giving R1 =
0.0236, wR2 = 0.0483 for 4899 data with [I > 2σ(I)] and R1 = 0.0280,
wR2 = 0.0496 for all 5276 data. Residual electron density (e−·Å−3)
max/min: 0.652/−0.493.
X-ray Crystal Structure of [(tPCMeCMeP)NiCl]2[NiCl4] (8).
X-ray quality single crystals were obtained from a concentrated hexane
layered CH2Cl2 solution at −35 °C in the glovebox. The resulting
crystals where dichroic plates, appearing both green and orange.
Crystal and refinement data for 8: C56H84Cl6Ni3P4; Mr = 1269.94;
ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectra for compounds 1−13, crystallographic tables and
details (CIF) for compounds 2−4 and 8−13, a text file of all
computed molecules’ Cartesian coordinates in a format for
convenient visualization. This material is available free of charge
via the Internet at http://pubs.acs.org.
triclinic; space group P1; a = 16.385(3) Å; b = 16.756(3) Å; c =
̅
17.013(3) Å; α = 96.367(2)°; β = 116.335(2)°; γ = 114.271(2)°; V =
AUTHOR INFORMATION
3561.9(10) Å3; Z = 2; T = 120(2) K; λ = 0.71073 Å; μ = 1.129 mm−1;
■
dcalc = 1.184 g·cm−3; 36 668 reflections collected; 12 540 unique (Rint
=
Corresponding Author
*E-mail: viluc@nd.edu.
0.0482); giving R1 = 0.0334, wR2 = 0.0685 for 8957 data with [I >
2σ(I)] and R1 = 0.0515, wR2 = 0.0717 for all 12 540 data. Residual
electron density (e−·Å−3) max/min: 0.431/−0.298.
Notes
The authors declare no competing financial interest.
X-ray Crystal Structure of (tPCHCHP)Ni (9). X-ray quality
single crystals were obtained readily as dark orange blocks from a
concentrated n-pentane solution at −35 °C in the glovebox. Crystal
and refinement data for 9: C26H38NiP2; Mr = 471.21; monoclinic;
space group P2(1)/c; a = 15.245(2) Å; b = 10.7277(16) Å; c =
31.655(5) Å; α = 90°; β = 101.825(3)°; γ = 90°; V = 5067.1(13) Å3; Z
= 8; T = 120(2) K; λ = 0.71073 Å; μ = 0.902 mm−1; dcalc = 1.235 g·
cm−3; 40 184 reflections collected; 8912 unique (Rint = 0.1426); giving
ACKNOWLEDGMENTS
■
We thank Dr. Allen Oliver and Dominic C. Babbini for
crystallographic assistance. This work was partially supported
by the University of Notre Dame. Acknowledgment is made to
the Donors of the American Chemical Society Petroleum
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Research Fund for partial support of this research (ACS PRF #
53536-DNI3).
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