Synthesis and reactivity of new Ni, Pd, and Pt 2,6-bis(di-tert -butylphosphinito)pyridine pincer complexes

Article abstract of DOI:10.1021/ic201102v

Synthesis and characterization of new (PONOP) [2,6-bis(di-tert- butylphosphinito)pyridine] metal (Ni, Pd, Pt) complexes are reported. Surprisingly, these compounds [(PONOP)MCl]Cl in the presence of 1 equiv of superhydride (LiEt₃BH) formed a new class of complexes (H-PONOP)MCl, in which the pyridine ring in the PONOP ligand lost its aromaticity as a result of hydride attack at the para position of the ring. The new Ni-H compound [(H-PONOP)NiH] was synthesized by reacting (H-PONOP)NiCl with 1 equiv of superhydride. Analogous Pd and Pt compounds were prepared. Reactivity of these new pincer complexes toward MeLi and PhLi also has been studied. These Ni complexes catalyzed the hydrosilylation of aldehyde. In some cases characterization of new (PONOP)M complexes was difficult because of high instability due to degradation of the P-O bond.

Full text of DOI:10.1021/ic201102v

ARTICLE
pubs.acs.org/IC
Synthesis and Reactivity of New Ni, Pd, and Pt 2,6-Bis(di-tert-
butylphosphinito)pyridine Pincer Complexes
Sabuj Kundu, William W. Brennessel, and William D. Jones*
Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
S Supporting Information
b
ABSTRACT: Synthesis and characterization of new (PONOP) [2,6-bis(di-tert-butylphosphinito)-
pyridine] metal (Ni, Pd, Pt) complexes are reported. Surprisingly, these compounds [(PONOP)-
MCl]Cl in the presence of 1 equiv of superhydride (LiEt3BH) formed a new class of complexes
(H-PONOP)MCl, in which the pyridine ring in the PONOP ligand lost its aromaticity as a result of
hydride attack at the para position of the ring. The new NiÀH compound [(H-PONOP)NiH] was
synthesized by reacting (H-PONOP)NiCl with 1 equiv of superhydride. Analogous Pd and Pt compounds
were prepared. Reactivity of these new pincer complexes toward MeLi and PhLi also has been studied.
These Ni complexes catalyzed the hydrosilylation of aldehyde. In some cases characterization of new (PONOP)M complexes was
difficult because of high instability due to degradation of the PÀO bond.
’ INTRODUCTION
(PONOP)M (M = Ru, Rh, and Ir) complexes have been re-
ported by the Milstein and Brookhart groups.6
There has been a great deal of interest in pincer metal
complexes in recent years following Moulton and Shaw’s first
report on PCP pincer complexes 35 years ago,1 and a wide vari-
ety of transition metal complexes having pincer ligands have
been reported in the literature.2 These complexes play an
important role in different types of bond activation,3bÀf,jÀl,t
synthesis,3a,h,n,q,w and catalysis.3g,i,m,o,p,r,s,u,v Among these pincer
ligands, PNP (PNP = 2,6-bis-(di-tert-butylphosphinomethyl)-
pyridine) is one example of a neutral ligand, and catalytic activity
of many PNP transition metal complexes are known.4 One
special property of these PNP complexes is that in the presence
of base, dearomatization of the pyridine core can take place via
deprotonation of the methylene side arm (eq 1). Milstein and co-
workers studied and explored this property in many complexes of
PNP and the analogous PNN pincer ligands.4i,5 They found that
the non-innocent ligand allowed for the catalytic reaction of
primary alcohols with primary and secondary amines to give
imines and amides with the release of H2. The non-innocent
ligand allowed for the shuttling of hydrogen from the metal to the
ligand to generate the required unsaturation at carbon. van der
Vlugt also saw dearomatization due to methylene deprotonation
in several Cu(PNP) derivatives.4n,o This behavior was also noted
with other metals,2m,p indicating the potential for non-innocence
of pincer ligands.2d,e
In this report, the synthesis and reactivity of new (PONOP)M
(M = Ni, Pd, and Pt) complexes are examined. Reactions of these
group 10 metal PONOP complexes with superhydride to provide
new metal-hydrides are investigated. The synthesis and charac-
terization of the derivatives of (tBu4PONOP)M (M = Ni,
Pd, and Pt) complexes proved to be difficult because of the in-
stability of these complexes, even at room temperature under
inert atmosphere.
’ RESULTS AND DISCUSSION
Synthesis of Nickel-PONOP Compounds. Treatment of
NiCl2 6H2O with PONOP in EtOH at room temperature for
3
15 min afforded the complex [(PONOP)NiCl]Cl EtOH (2a) in
3
good yield (Scheme 1). Complex 2a was isolated as a dark red
solid and was characterized by 1H and 31P{1H} NMR spectros-
copy. One equivalent of EtOH was found to be present by NMR
spectroscopy even after the solid was placed under vacuum for
3 days. Bound EtOH could be removed by sonication. Successful
sonication in tetrahydrofuran (THF, 2 h) followed by hexane
(2 h) produced a light red solid characterized as pure complex
[(PONOP)NiCl]Cl (3a), characterized by H, 13C{1H}, and
1
31P{1H} NMR spectroscopy and elemental analysis. Although
we were unable to obtain an X-ray structure of this material
(the crystals were subject to diffuse scattering), a separate reac-
tion using a slight excess of NiCl2 6H2O, provided crystals of
3
[(PONOP)NiCl]2[NiCl4] (3a-NiCl4), which diffracted suitably
to provide a structure (Figure 1). The molecule is almost per-
fectly planar and the PÀNiÀN angles are slightly acute (∼84.4°).
This kind of deprotonation can be avoided if oxygen is present
instead of CH2 in the side arm of the pincer ligand (PNP or
PNN). This new class of neutral pincer ligand having oxygen
is abbreviated PONOP, 1. The synthesis and reactivity of
Received: May 24, 2011
Published: September 07, 2011
r
2011 American Chemical Society
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Scheme 1. Synthesis of (PONOP)Ni Complexes
Figure 2. X-ray structure of 4a. Selected distances: Ni1ÀP1, 2.1914(6);
Ni1ÀP2, 2.1936(6); Ni1ÀCl1, 2.1755(7) Å; Ni1ÀN1, 1.8876(16) Å;
N1ÀC1, 1.379(2) Å;C1ÀC2, 1.332(3) Å; C2ÀC3, 1.479(3) Å;
C3ÀC4, 1.479(3) Å; C4ÀC5, 1.335(3) Å; C5ÀN1, 1.378(3) Å.
Ellipsoids are shown at the 50% level.
4a was characterized by 1H, 13C{1H}, and 31P{1H} NMR spec-
troscopy and X-ray crystallography (Figure 2). In the 1H NMR
spectrum, no aromatic resonances were present and new reso-
nances at δ 4.19 and 3.39 appeared, which clearly indicate that
the pyridine ring of the complex had lost its aromaticity. The
13C{1H} NMR spectrum shows resonances for the pyridal ring
carbons at δ 159.7, 72.2, and 39.3, also indicating a loss of
aromaticity. Other hydride reducing reagents (lithium alumi-
num hydride or sodium borohydride) led to reduction to the
NiI species (PONOP)NiCl rather than 4a (see Experimental
Section).7 The X-ray structure of 4a shows bond length
alternation around the pyridyl ring, and the NiÀN distance
(1.887(2) Å) is slightly longer than in 3a (1.878(3) Å). The
pyridyl ring, and the entire H-PONOP ligand for that matter,
remain planar. The PÀNiÀP angles remain acute (∼83.0°).
Compound 4a is most closely related to an analogous ruthenium-
bisphosphinoacridine complex reported by Milstein, in which the
C9 of the acridine can similarly be reduced by heating the chloro
derivative with KOH and hydrogen.8 Reduction of a bound
pyridine israre, but has been seen in yttrium hydride complexes9,10
and a magnesium hydride complex.11
Dropwise treatment of the complex 4a in pentane with a
second equivalent of superhydride at room temperature for 2 h
afforded the complex (H-PONOP)NiH (5a), with reduction
now occurring at the metal (eq 2). An immediate color change oc-
curred from deep green to light brown-green. Complex 5a was
characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy.
The nickel hydride appeared as triplet at δ À16.49 (JPÀH
=
62.0 Hz) in the 1H NMR spectrum. The 31P{1H} NMR spectrum
of complex 5a displayed a singlet at δ 194.3, while the selectively
coupled (by hydride) 31P NMR spectrum displayed a doublet at
δ 194.3 (JPÀH = 62.0 Hz), clearly indicating the presence of a
nickel hydride. NMR data for the pyridyl ring continued to be
consistent with dearomatization. Crystallization of complex 5a
was not successful as it slowly decomposed in hexane after 5 days
at room temperature to yield an unusual Ni2(PtBu2)4 species (see
Supporting Information for structure).12
Figure 1. X-ray structure of [(PONOP)NiCl]2[NiCl4], 3a-NiCl4.
Selected distances: Ni1ÀP1, 2.190(1); Ni1ÀP2, 2.195(1); Ni1ÀCl1,
2.1463(9) Å; Ni1ÀN1, 1.878(3) Å; N1ÀC1, 1.356(4) Å;C1ÀC2,
1.362(5) Å; C2ÀC3, 1.373(5) Å; C3ÀC4, 1.381(5) Å; C4ÀC5,
1.379(5) Å; C5ÀN1, 1.350(4) Å. Ellipsoids are shown at the 50% level.
Synthesis of (H-PONOP)NiCl (4a). Dropwise treatment of the
complex 3a suspended in pentane with 1 equiv of superhydride in
pentane at room temperature over 2 h produced a color change
from red to deep green. The new product was identified as com-
plex 4a, in which the pyridine had undergone attack at the para
position, losing its aromaticity (Scheme 1). This observation is in
stark contrast to the analogous (PCP)NiCl complex which
undergoes attack by hydride exclusively at the metal.3q Complex
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Scheme 2. Synthesis of (PONOP)Pd Complexes
Reaction of Complex 4a with MeLi and PhLi. When com-
plex 4a was treated with 1 equiv of MeLi at room temperature,
complex 6a formed after 1 h, which was isolated as light brown
solid (eq 3). The nickel(II) methyl complex was characterized by
1H, 13C{1H}, and 31P{1H} NMR spectroscopy. The Ni-CH3
appeared as a triplet at δ À0.36 (JPÀH = 9.2 Hz) in the 1H NMR
spectrum and a triplet at δ À27.8 (JPÀC = 30.0 Hz) in the
13C{1H} NMR spectrum. Crystallization of complex 6a was not
successful as it slowly decomposed in hexane after 4 days at room
temperature. Under similar reaction conditions, treatment of
complex 4a with 1 equiv of PhLi at room temperature did not
produce the analogous phenyl derivative cleanly. Many products
along with complex 4a as the major species were observed by 31P
NMR spectroscopy (from the mixture of products (H-PONOP)-
NiPh was identified by X-ray crystallography. See Supporting
Information).
Figure 3. X-ray structure of 4b. Selected distances: Pd1ÀCl1, 2.3169(12)
Å; Pd1ÀN1, 1.989(4) Å; N1ÀC1, Å;C1ÀC2, 1.373(6) Å; C2ÀC3,
1.504(7) Å; C3ÀC4, 1.495(7) Å; C4ÀC5, 1.303(6) Å; C5ÀN1,
1.374(6) Å. Ellipsoids are shown at the 50% level.
Scheme 3. Synthesis of (PONOP)Pt Complexes
Synthesis of [(PONOP)PtCl]Cl (3c) and (H-PONOP)PtCl (4c).
Treatment of PtCl2(NCPh)2 with PONOP in CH3CN at room
temperature for 30 min afforded complex 2c in good yield
(Scheme 3). Complex 2c was isolated as a white solid and
characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy
and elemental analysis. The bound CH3CN was removed by
sonication in THF followed by hexane. The white solid was dried
overnight in vacuum yielding pure complex 3c. Complex 3c was
characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy.
Dropwise treatment of a slurry of complex 3c in pentane with
1 equiv of superhydride at room temperature over 20 min
afforded complex 4c (Scheme 3). An immediate color change
from colorless to light yellow was observed. Complex 4c was
characterized by 1H, 13C{1H}, and 31P{1H} NMR spectroscopy,
elemental analysis, and X-ray crystallography (Figure 4). The
molecule is again planar with acute PÀPtÀN angles of ∼81.0°,
similar to those in palladium complex 4b. The 1H NMR spectra
displayed no aromatic resonances and new resonances at δ 4.24
and 3.44 appeared, indicating loss of aromaticity of the pyridine
ring. The 31P NMR spectrum of 4c shows a singlet at δ 157.9
with JPtÀP = 2799 Hz, which is 264 Hz larger than in 3c or 2c.
This is consistent with the notion that the more electron-with-
drawing the substituent (i.e., chloride > hydride), the smaller the
1JPtÀP in platinum(II) complexes.13
Synthesis of [(PONOP)PdCl]Cl (3b) and (H-PONOP)PdCl
(4b). Treatment of PdCl2(NCCH3)2 with PONOP ligand in
CH2Cl2 at room temperature for 1 h afforded the complex 2b in
good yield (Scheme 2). Complex 2b was isolated as a light yellow
1
solid and characterized by H, 13C{1H}, and 31P{1H} NMR
spectroscopy and elemental analysis. When the same reaction
was carried out in CH3CN as solvent, the reaction was not clean
and many unknown products were observed. Bound CH2Cl2 was
removed by sonication in THF followed by hexane. The solid
was dried overnight in vacuum yielding pure complex 3b. Com-
plex 3b was characterized by 1H, 13C{1H}, and 31P{1H} NMR
spectroscopy.
In a similar fashion to the Ni complex, treatment of complex
3b slurried in pentane with 1 equiv of superhydride at room
temperature for 20 min afforded the complex 4b (Scheme 2). An
immediate color change from light yellow to pink was observed.
1
Complex 4b was characterized by H, 13C{1H}, and 31P{1H}
NMR spectroscopy and X-ray crystallography (Figure 3). The
molecule is again planar with acute PÀPdÀN angles of ∼80.8°,
larger than in nickel complex 4a because of the larger palladium
1
metal. The H NMR spectrum was similar to that of the Ni
complex. New resonances at δ 4.18 and 3.37 were seen, which
clearly indicate that the pyridine ring had lost its aromaticity.
Similar changes in the 13C{1H} spectrum were observed.
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of complex 6b was not successful as it slowly decomposed in
hexane after 4 days at room temperature.
Likewise, freshly prepared complex 4c was reacted with 1
equiv of MeLi in THF at room temperature. After 12 h a new
product was observed (∼ 30%) by 31P NMR spectroscopy while
unreacted 4c remained in the solution. Further stirring (24 h) of
this solution at room temperature led to decomposition (eq 6).
The new unidentified product was highly unstable and appeared
as singlet at δ 198.4 (JPtÀP = 2790 Hz) in the 31P NMR spectrum
and displayed a PtÀH resonance which appeared as a triplet at
Figure 4. X-ray structure of 4c. Selected distances: Pt1ÀCl1, 2.3275(9)
Å; Pt1ÀN1, 1.991(3) Å; N1ÀC1, 1.368(5) Å;C1ÀC2, 1.325(5) Å;
C2ÀC3, 1.500(5) Å; C3ÀC4, 1.503(5) Å; C4ÀC5, 1.323(5) Å;
C5ÀN1, 1.394(5) Å. Ellipsoids are shown at the 50% level.
1
δ À10.51 (JPtÀH = 989 Hz, JPÀH = 10.0 Hz) in the H NMR
spectrum. From both 31P and 1H NMR spectra, it was clear that
this new compound was not the (H-PONOP)Pt(Me) complex
6c, but that cleavage of the PONOP ligand had occurred.
Unlike the Ni complex 4a,, treatment of the complexes 4b or
4c with 1 equiv of superhydride or LiAlH4 did not generate the
corresponding metal hydrides (5b and 5c). Instead both
complexes decomposed as the reaction was stirred at room
temperature for a longer time under nitrogen atmosphere.
From the palladium reaction, a known14 dimeric bis-μ-chloro
complex was obtained in which the PONOP ligand had
been cleaved at the pyridyl-oxygen bonds, [Pd(μ-Cl)-
Reaction of Complexes 3b and 3c with MeLi. In an attempt
to see if the metal and/or the pyridyl ring could be alkylated in an
analogous fashion to the reaction with superhydride, methyllithium
was added to 3b or 3c. Reactions of complex 3b or 3c with 2 equiv of
MeLi in THF at room temperature were not clean. In case of Pd
complex 3b, four unidentified compounds were observed by 31P
NMR spectroscopy (ratio: 1:2:4:7). These complexes decomposed
in hexane after 7 days. In the case of Pt complex 3c, two unknown
compounds were observed by 31P NMR spectroscopy (ratio: 1:1.25)
after 30 min. One example of alkylation of a pyridinediimine ligand
has been reported using Ca[CH(TMS)2]2.16
(tBu2PO
H
OPtBu2)]2 (See Experimental Section). Also,
3 3 3 3 3 3
reaction of 3c with KOH and dihydrogen under the con-
ditions employed by Milstein did not result in the formation of 4c.8
To further prove the structure of complex 4c and 4b, the
complexes were stirred at room temperature in CHCl3. After
30 min, both solutions changed color and the complexes
3c CHCl3 and 3b CHCl3 were generated accordingly, as con-
3
3
firmed by NMR spectroscopy. Both complexes have very similar
NMR spectra compared to pure 3c and 3b (eq 4). Conversions
of metal hydrides to metal halides by adding haloforms are
well-known in the literature,15 presumably initiated via electron
transfer to the haloform, and may be operative in this case
also.
Reaction Complexes 3a, 3c, and 3b with NaBPh4. As we
were unable to obtain an X-ray structure of complexes 3a, 3b, and
3c (crystals formed but were subject to diffuse scattering),
substitution of chloride anion with the large BPh4 anion was
carried out by reacting complexes 3a, 3c, and 3b with 10 equiv of
NaBPh4 in methanol at room temperature (eq 7). Reactions were
clean and after 30 min at room temperature the corresponding
BPh4 anion substituted complexes 3a-BPh4, 3b-BPh4, and 3c-BPh4
1
were generated, which were characterized by H, 13C, and 31P
NMR spectroscopy and X-ray crystallography. Crystals of these
salts diffracted suitably to provide the structures (Figure 5). The
structural parameters for 3a-BPh4 are comparable to those of 3a-
NiCl4, although the N1ÀNi1ÀCl1 angle is slightly bent (171.8°,
but linear in Pd or Pt compounds). The CÀC distances around the
pyridyl rings are essentially equivalent, indicating delocalization.
Reaction of Complex 4b and 4c with MeLi. In a similar
fashion to the Ni complex (4a), freshly prepared complex 4b was
reacted with 1 equiv of MeLi in THF at room temperature. After
12 h, a new product 6b was observed (∼ 80%) by 31P NMR
spectroscopy (eq 5). Compound 6b was not very stable. It
slowly decomposed in solution after a few days even at À20 °C.
Compound 6b appeared as a singlet at δ 168.4 in the 31P NMR
spectrum. The Pd-CH3 moiety appeared as a triplet at δ 0.52
1
(JPÀH = 5.4 Hz) in the H NMR spectrum, and a triplet at
δ À20.4 (JPÀC = 6.8 Hz) in the 13C NMR spectrum, indicating
Reaction of Complex 5a with Different Substrates. The
chemical properties of complex 5a were tested by reaction with
attachment of the methyl group to the Pd center. Crystallization
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Figure 5. X-ray structures of 3a-BPh4, 3b-BPh4, and 3c-BPh4. Selected distances for 3a-BPh4: Ni1ÀP1, 2.1841(3); Ni1ÀP2, 2.1809(3); Ni1ÀCl1,
2.1433(3) Å; Ni1ÀN1, 1.871(1) Å; N1ÀC1, 1.3565(13) Å;C1ÀC2, 1.3749(15) Å; C2ÀC3, 1.3870(16) Å; C3ÀC4, 1.3822(16) Å; C4ÀC5,
1.3772(15) Å; C5ÀN1, 1.3565(13) Å. Selected distances for 3b-BPh4: Pd1ÀCl1, 2.2914(4) Å; Pd1ÀN1, 2.0057(12) Å; N1ÀC1, 1.3526(18) Å;
C1ÀC2, 1.376(2) Å; C2ÀC3, 1.386(2) Å; C3ÀC4, 1.385(2) Å; C4ÀC5, 1.373(2) Å; C5ÀN1, 1.3526(19) Å. Selected distances for 3c-BPh4: Pt1ÀCl1,
2.2890(16) Å; Pt1ÀN1, 2.000(4) Å; N1ÀC1, 1.345(7) Å;C1ÀC2, 1.376(7) Å; C2ÀC3, 1.372(9) Å; C3ÀC4, 1.371(8) Å; C4ÀC5, 1.380(8) Å;
C5ÀN1, 1.348(7) Å. Ellipsoids are shown at the 50% level.
several substrates (Scheme 4). This new NiÀH complex did not
lose H2 easily and did not react with carbon monoxide or
isocyanides at room temperature. Heating complex 5a in the
presence of excess of isocyanide (20 equiv) led to decomposition,
and one compound was isolated as a crystalline solid (eq 8,
Figure 6). Complex 5a did not hydrogenate or bind with imine,
ethylene, or 1-octene, although in case of 1-octene isomerization
was observed in the 1H NMR spectrum. No free H2 was observed
by NMR spectroscopy. Complex 5a also did not show H/D
exchange with C6D6 or D2 at room temperature. When benzal-
dehyde reacted with complex 5a, no benzyl alcohol was observed.
Instead benzoin was formed, which was confirmed by compar-
ison with an authentic sample. The benzoin condensation is
typically carried out using a nucleophile that adds reversibly to
benzaldehyde, but it is not clear how 5a could act in this fashion.
As complex 5a decomposes during this reaction, it is difficult to
tell exactly how it effects the condensation.
Scheme 4. Reaction Complex 5a with Different Substrates
The catalytic activity of complex 5a was not good, as ∼60% of the
complex had decomposed after 10 h at room temperature
(measured by 31P NMR spectroscopy). Under the same reaction
conditions complex 4a showed similar hydrosilylation products
by 1H NMR spectroscopy and GC-MS. The reaction was much
slower in case of complex 4a compared to 5a, taking 2 days to
consume all of the benzaldehyde. However, even after 2 days no
decomposition of complex 4a was observed by 31P NMR spec-
troscopy. In comparison to 5a, the (POCOP)NiH catalyst
reported by Guan et al.3s resulted in an 80% yield of alcohol
(following workup with aqueous base) after only 2 h at room
temperature using 0.2 mol % catalyst.
To test the scope of this hydrosilylation reaction using
complex 4a, 4-chlorobenzaldehyde was used as the hydrosilyla-
tion substrate under the same reaction conditions. After 2 days at
room temperature most of the aldehyde was consumed and
hydrosilylation products were detected by 1H NMR spectrosco-
py with no decomposition of complex 4a. One notable observa-
tion was that no hydrosilylation products were detected when the
tertiary silane Et3SiH was used instead of the primary silane
PhSiH3 under the same reaction conditions (3 days at room
Hydrosilylation of PhCHO Using Complex 4a and 5a. Many
organic transformations using Ni complexes have been known
for decades.17 Recently, hydrosilylation of carbonyl functional
groups using a Ni-hydride catalyst has been reported by several
other groups.3s,18 The system reported by Guan3s uses the
benzene analogue (POCOP)NiH, and is most similar to the
compound reported here. We wanted to test the catalytic activity
of both complex 4a and 5a in the hydrosilylation of benzaldehyde
as a benchmark for comparison with other catalysts. Complex 5a
catalyzed the hydrosilylation of PhCHO in the presence of
PhSiH3. After 10 h at room temperature, all of the benzaldehyde
was consumed, and hydrosilylation products were observed,
1
as confirmed by H NMR spectroscopy and GC-MS (eq 9).
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Figure 6. Structure of Ni isocyanide complex. Ellipsoids are shown at
the 50% level.
Figure 7. Structure of Ni(c-PONOPONO) from the decomposition of
product 6. Selected bond distances (Å): Ni1ÀN1, 1.864(4); Ni1ÀP1,
2.233(1); P1ÀO1, 1.862(3); N1ÀC1, 1.353(4); C1ÀC2, 1.395(4);
1.380(4). Ellipsoids are shown at the 50% level.
temperature). To test whether complex 4a catalyzed this hydro-
silylation by insertion of aldehyde to the metal hydride bond as
reported in the literature,3s complex 4a was reacted with benzal-
dehyde in the absence of silane. No insertion of benzaldehyde
was observed after 2 days at room temperature, as confirmed by
1H NMR spectroscopy (eq 10). When this mixture was heated at
100 °C for 1 h, it decomposed to some paramagnetic complexes
and one diamagnetic complex. The 31P NMR spectrum showed
only one signal with low intensity at δ 50.56, and the 1H NMR
spectrum showed broad signals at δ 25.80, 16.53, and 9.36 and
2.49. Crystals were grown by slow evaporation from the hexane
solution of this decomposition mixture. X-ray crystallography
provided the structure of the diamagnetic decomposition pro-
duct (Figure 7), showing degradation of the PONOP ligand.
NickelÀphosphorus and nickelÀcarbon distances are compar-
able to those in 3a and 3a-BPh4. This unusual compound is
somewhat reminiscent of Nieke’s PNPN macrocycle,19 although
the pentavalent phosphorus here results in a planar structure
compared with Nieke’s tetravalent phosphorus macrocycle com-
plex of copper, which is folded.20
as determined by the broad range of chemical shifts. Consequ-
ently, the mechanism of this hydrosilylation reaction catalyzed by
complex 4a remains unknown.
’ CONCLUSIONS
The synthesis and characterization of new class of group 10
metal pincer complexes has been established. The side arm of
these complexes has no proton to lose in the presence of base
(particularly hydride), compared to other known PNP or PNN
pincer complexes. These (PONOP)M (M = Ni, Pd, Pt) com-
plexes showed some unique properties. When the (PONOP)-
MCl2 (M = Ni, Pd, Pt) complexes were reacted with 1 equiv of
superhydride, a new class of pincer complex [(H-PONOP)MCl
(M = Ni, Pd, Pt)] formed in which the pyridine was reduced.
Reactivity of these complexes toward MeLi was also examined,
and (H-PONOP)Ni(Me) was prepared. These pincer nickel
complexes catalyzed the hydrosilylation of aldehydes, although
the mechanism of this reaction was not established. Character-
ization and crystallization of these complexes were difficult in
most of the cases, particularly with Pd and Pt metals, because of
their high instability.
’ EXPERIMENTAL SECTION
To gain insight into the mechanism more clearly (D-PO-
NOP)NiCl (4a-d1) was synthesized by reacting complex 3a with
deuterated superhydride (eq 11). Reaction of 4a-d1 with ben-
zaldehyde and PhSiH3 under similar reaction conditions did not
show deuterium incorporation in the hydrosilylation products. It
is not clear how this reaction proceeds, but a radical pathway is
possible, although there is no direct evidence for this. When
complex 4a in C6D6 was heated for 30 min at 100 °C, it de-
composed, and several paramagnetic complexes and one diamag-
netic complex were detected by 1H and 31P NMR spectroscopy,
General Procedures and Materials. Unless otherwise stated, all
reactions and manipulations were carried out in dry glassware using
standard Schlenk and glovebox techniques, under a nitrogen atmo-
sphere. THF-d8, p-xylene-d10, and C6D6 were purchased from Cam-
bridge Isotope Laboratories and dried using Na/K and collected by
vacuum transfer. All other reagents were purchased from Aldrich, Strem,
or VWR chemical company and used without any further purification.
All NMR spectra were recorded on Bruker Avance 400 and 500 MHz
spectrometers. 31P NMR chemical shifts (δ in ppm) are relative to an
external 85% solution of H3PO4 in the appropriate solvent. Elemental
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analyses were obtained from CENTC Elemental Analysis Facility at the
University of Rochester. GC-MS spectra were recorded on a SHIMAD-
ZU QP2010 GCMS
Improved Synthesis of PONOP, [1,3-C5H3N(OPtBu2)2] (1).
Synthesis of this tridentate ligand has been reported by the Brookhart
(57%) and Milstein (75%) groups.6a,c This ligand can be synthesized in
higher yield (85%) and purity (99%) by combining aspects of both of
their methods (i.e., Milstein employed TMEDA and NEt3 as base for
20 h at 65 °C, whereas Brookhart used only NEt3 and heated to 65 °C for
1 week). In a 500 mL Schlenk flask, 2,6-dihydroxypyridine hydrochlor-
ide (1.0 g, 6.8 mmol), N,N,N,N-tetramethylethylenediamine (13.6 mmol,
2.00 mL), triethylamine (41.6 mmol, 5.80 mL), (tBu)2PCl (2.70 g, 14.9
mmol), and 60 mL of THF were combined under a nitrogen atmo-
sphere. The reaction mixture was heated with stirring at 75 °C for
1 week. The volatiles were removed under vacuum, leaving a yellow
solid. The solid was extracted into benzene and filtered under a nitrogen
atmosphere. The solvent was then removed under vacuum, leaving an
oily material which solidified to a white solid in few minutes (yield, 2.01 g,
85%).1H NMR (400 MHz, C6D6): δ 7.13 (t, JHÀH = 7.8 Hz, 1H), 6.46
(d, JHÀH = 8.0 Hz, 2H), 1.18 (d, JPÀH = 11.2 Hz, 36H). 31P{1H} NMR
(162 MHz, C6D6): δ 151.3 (s).
Figure 8. X-ray structure of (H-PONOP)NiPh. Selected distances:
Ni1ÀC6, 1.959(4) Å; Ni1ÀN1, 1.877(3) Å; N1ÀC1, 1.376(5) Å;
C1ÀC2, 1.326(5) Å; C2ÀC3, 1.501(5) Å; C3ÀC4, 1.512(6) Å;
C4ÀC5, 1.309(6) Å; C5ÀN1, 1.387(5) Å. Ellipsoids are shown at the
50% level.
Synthesis of [(PONOP)NiCl]Cl EtOH (2a). In a 500 mL Schlenk
3
flask PONOP(500 mg, 1.25mmol), NiCl2 6H2O(297.3 mg, 1.25mmol),
and 75 mL of anhydrous EtOH were 3combined under a nitrogen
atmosphere. The reaction mixture was stirred at room temperature for
15 min. Volatiles were removed under vacuum (overnight), leaving a
dark red solid 2a (yield: 95%). 2a was found to contain a bound EtOH.
1H, 13C{1H}, and 31P{1H} NMR spectra of complex 2a were very
similar to those of complex 3a (see below) except for the presence of
(H-PONOP)NiH (5a). In a 100 mL Schlenk flask complex 4a
(100 mg, 0.20 mmol) and 40 mL of pentane were combined under a
nitrogen atmosphere. A 0.20 mL portion of LiHBEt3 (0.20 mmol, 1 M in
THF) was added dropwise at room temperature. An immediate color
change from deep green to light brown was observed. The reaction
mixture was stirred at room temperature for 1 h, and the solution was
filtered under nitrogen atmosphere using a cannula. The volatiles were
then removed under vacuum yielding sticky light brown complex 5a (82%).
1H NMR (400 MHz, C6D6): δ 4.28 (t, JHÀH = 3.0 Hz, 2H), 3.72 (t,
1
the bound EtOH resonances. H NMR (400 MHz, CD3OD): δ 8.19
(t, JHÀH = 8.2 Hz, 1H), 7.07 (d, JHÀH = 8.0 Hz, 2H), 3.60 (q, JHÀH
=
5.6 Hz, 2H), 1.67 (vt, JPÀH = 8.0 Hz, 36H), 1.78 (d, JHÀH = 5.6 Hz, 3H).
13C{1H} NMR (125 MHz, CD3OD): δ 167.4 (t, JPÀC = 5.0 Hz),
150.9 (s), 106.9 (s), 43.2 (t, JPÀC = 5.1 Hz), 28.5 (s). 31P{1H} NMR
(162 MHz, CD3OD): δ 184.3 (s).
JHÀH = 3.0 Hz, 2H), 1.25 (vt, JPÀH = 7.2 Hz, 36H), À16.49 (t, JPÀH
=
=
62.0 Hz, 1H). 13C{1H} NMR (125 MHz, C6D6): δ 159.3 (t, JPÀC
6.0 Hz), 68.5 (t, JPÀC = 2.9 Hz), 37.4 (t, JPÀC = 9.5 Hz), 27.4 (s), 26.3
[(PONOP)NiCl]Cl (3a). In a 500 mL Schlenk flask complex 2a
(500 mg) and 100 mL of THF were combined under a nitrogen atmo-
sphere. The mixture was sonicated for 2 h, and THF was removed by
cannula, leaving a solid at the bottom of the flask. A 100 mL portion of
hexane was added, and the solid was sonicated again for 2 h. Hexane was
removed by cannula while the light red solid remain at the bottom of the
flask. The solid was dried overnight in vacuum yielding pure complex 3a
(85%). 1H NMR (400 MHz, CD3OD): δ 8.19 (t, JHÀH = 8.2 Hz, 1H),
7.07 (d, JHÀH = 8.0 Hz, 2H), 1.67 (vt, JPÀH = 8.0 Hz, 36H). 13C{1H}
NMR (125 MHz, CD3OD): δ 167.4 (t, JPÀC = 5.0 Hz), 150.9 (s), 106.9
(s), 43.2 (t, JPÀC = 5.1 Hz), 28.5 (s). 31P{1H} NMR (162 MHz,
CD3OD): δ 184.3 (s). Anal. Calcd (found) for C21H39Cl2NNiO2P2:
% C, 47.67 (47.71); % H, 7.43 (7.56); % N, 2.65 (2.70).
(H-PONOP)NiCl (4a). In a 250 mL Schlenk flask complex 3a
(200 mg, 0.38 mmol) and 100 mL of pentane were combined under a
nitrogen atmosphere. A 0.38 mL portion of LiHBEt3 (0.38 mmol, 1 M in
THF) was added dropwise at room temperature. An immediate color
change from red to deep green was observed. The reaction mixture was
stirred at room temperature for 2 h. The solution was filtered under a
nitrogen atmosphere using a cannula, and the volatiles were then re-
moved under vacuum yielding pure dark green complex 4a (95%). Cry-
stals of complex 4a were grown by slow evaporation from a hexane solu-
tion. 1H NMR (400 MHz, C6D6): δ 4.19 (t, JHÀH = 3.2 Hz, 2H), 3.39 (t,
JHÀH = 3.2 Hz, 2H), 1.45 (vt, JPÀH = 7.2 Hz, 36H). 13C{1H} NMR
(125 MHz, C6D6): δ 159.7 (t, JPÀC = 5.7 Hz), 72.2 (t, JPÀC = 3.1 Hz),
39.3 (t, JPÀC = 7.4 Hz), 27.4 (s), 24.6 (s). 31P{1H} NMR (162 MHz,
C6D6): δ 165.1 (s). Anal. Calcd (found) for C21H40ClNNiO2P2: % C,
50.99 (49.65); % H, 8.15 (8.17); % N, 2.83 (2.40).
(s). 31P{1H} NMR (162 MHz, C6D6): δ 194.3 (s).
(H-PONOP)Ni(Me) (6a). In a 50 mL Schlenk flask complex 4a
(20 mg, 0.04 mmol) and 5 mL of pentane were combined under
a nitrogen atmosphere. Twenty-five microliters of MeLi (0.04 mmol,
1.66 M in THF) was added dropwise at room temperature. An im-
mediate color change from deep green to light brown was observed. The
reaction mixture was stirred at room temperature for 1 h, and the
solution was filtered through Celite. The volatiles were then removed
under vacuum yielding complex 6a (purity 70% by 31P NMR spectro-
scopy) along with some decomposition products. 1H NMR (400 MHz,
C6D6): δ 4.21 (t, JHÀH = 2.6 Hz, 2H), 3.68 (t, JHÀH = 2.6 Hz, 2H), 1.29
(vt, JPÀH = 6.8 Hz, 36H), À0.36 (t, JPÀH = 9.2 Hz, 3H). 13C{1H} NMR
(125 MHz, C6D6): δ 159.7 (t, JPÀC = 4.8 Hz), 69.2 (t, JPÀC = 2.6 Hz),
39.6 (t, JPÀC = 7.6 Hz), 28.4 (s), 26.7 (s), À27.8 (t, JPÀC = 30.0 Hz).
31P{1H} NMR (162 MHz, C6D6): δ 169.9 (s).
Reaction of 4a with PhLi. In a 50 mL Schlenk flask complex 4a
(20 mg, 0.04 mmol) and 5 mL of pentane were combined under a nitro-
gen atmosphere. Twenty-three microliters of PhLi (0.04 mmol, 1.8 M in
THF) were added dropwise at room temperature. An immediate color
change from deep green to light brown was observed. The reaction
mixture was stirred at room temperature for 1 h, and the solution was
filtered under nitrogen atmosphere using a cannula. The volatiles were
then removed under vacuum yielding a light brown solid. The 31P NMR
spectrum showed many peaks, some of them were the result of breaking
apart of the PONOP ligand. From the mixture of products, (H-PONOP)-
NiPh was identified by X-ray crystallography (Figure 8). 31P{1H} NMR
(162 MHz, C6D6): δ 165.1 (s, 4a), 164.9 (s), 164.8 (s), 164.4 (s),
164.2(s), 59.5 (s), 35.4 (s).
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ARTICLE
Synthesis of [(PONOP)PdCl]Cl CH2Cl2 (2b). In a 500 mL
3
Schlenk flask PONOP ligand (500 mg, 1.25 mmol), PdCl2(NCCH3)2
(324 mg, 1.25 mmol), and 100 mL of anhydrous CH2Cl2 were
combined under a nitrogen atmosphere. The reaction mixture was
stirred at room temperature for 60 min. The volatiles were removed
under vacuum (overnight), leaving a light yellow solid which was washed
with hexane and benzene and dried under vacuum yielding complex 2c
(87%). When this reaction was carried out in CH3CN as solvent, some
1
decomposition of the PONOP ligand was observed. H NMR (500
MHz, CD3OD): δ 8.28 (t, JHÀH = 8.3 Hz, 1H), 7.28 (d, JHÀH = 8.5 Hz,
2H), 2.01(s, 2H), 1.57 (vt, JPÀH = 8.0 Hz, 36H). 13C{1H} NMR
(100 MHz, CD2Cl2): δ 163.8 (s), 150.9 (s), 106.7 (s), 42.3 (t, JPÀC
=
5.2 Hz), 27.5 (t, JPÀC = 2.5 Hz). 31P{1H} NMR (162 MHz, CD2Cl2):
δ 192.6 (s). Anal. Calcd (found) for C22H41Cl4NO2P2Pd: % C, 39.93
(40.25); % H, 6.24 (6.32); % N, 2.12 (2.13).
[(PONOP)PdCl]Cl (3b). In a 500 mL Schlenk flask complex 2b
(500 mg) and 100 mL of THF were combined under a nitrogen atmo-
sphere. The mixture was sonicated for 2 h and then THF was removed
by cannula leaving the solid at the bottom of the flask. A 100 mL portion
of hexane was added, and the solid sonicated again for 2 h. Hexane was
removed by cannula leaving the solid at the bottom of the flask. The solid
was dried overnight under vacuum yielding pure complex 3b (83%). 1H
Figure 9. X-ray structure of the decomposition product [Pd(μ-Cl)-
(tBu2PO
H
OPtBu2)]2. Ellipsoids are shown at the 50% level.
3 3 3 3 3 3
for C23H42Cl2N2O2P2Pt: % C, 39.10 (39.20); % H, 5.99 (5.95); % N,
3.96 (3.76).
NMR (400 MHz, CD2Cl2): δ 8.65 (t, JHÀH = 7.6 Hz, 1H), 7.28 (d, JHÀH
=
8.0 Hz, 2H), 1.50 (vt, JPÀH = 8.0 Hz, 36H). 13C{1H} NMR (100 MHz,
CD2Cl2): δ 163.8 (s), 150.9 (s), 106.7 (s), 42.3 (t, JPÀC = 5.2 Hz), 27.5
(t, JPÀC = 2.5 Hz). 31P{1H} NMR (162 MHz, CD2Cl2): δ 192.6 (s).
(H-PONOP)PdCl (4b). In a 250 mL Schlenk flask, complex 3b
(100 mg, 0.17 mmol) and 70 mL of pentane were combined under a
nitrogen atmosphere. A 0.17 mL portion of LiHBEt3 (0.17 mmol, 1 M in
THF) was added dropwise at room temperature. The reaction mixture
was stirred at room temperature for 20 min. The solution was filtered
under a nitrogen atmosphere using a cannula, and the volatiles were
removed under vacuum yielding complex 4b (79%). Crystals of complex
4b were grown by slow evaporation from a benzene solution. Complex
4b was more stable than 4c and slowly decomposed after a few days in
solution. 1H NMR (400 MHz, C6D6): δ 4.18 (t, JHÀH = 2.8 Hz, 2H),
3.37 (t, JHÀH = 3.2 Hz, 2H), 1.34 (vt, JPÀH = 7.6 Hz, 36H). 13C{1H}
NMR (125 MHz, C6D6): δ 159.7 (s), 71.3 (t, JPÀC = 4.4 Hz), 39.8
(t, JPÀC = 7.8 Hz), 26.9 (s), 25.1 (s). 31P{1H} NMR (162 MHz, C6D6):
δ 173.1 (s).
[(PONOP)PtCl]Cl (3c). In a 500 mL Schlenk flask, complex 2c
(500 mg) and 100 mL of THF were combined under a nitrogen atmo-
sphere. The mixture was sonicated for 2 h, and then THF was removed
by cannula while the solid remained at the bottom of the flask. A 100 mL
portion of hexane was added, and the solid sonicated again for 2 h.
Hexane was removed by cannula leaving solid at the bottom of the flask.
The solid was dried overnight under vacuum yielding pure complex 3c
1
(83%). The H, 13C, and 31P NMR spectra of complex 3c were very
similar to those of complex 2c, except for the absence of a bound CH3-
CN resonance. 1H NMR (500 MHz, CD3OD): δ 8.32 (t, JHÀH = 8.0 Hz,
1H), 7.29 (d, JHÀH = 8.0 Hz, 2H), 1.55 (vt, JPÀH = 8.0 Hz, 36H).
13C{1H} NMR (100 MHz, CD3CN): δ 164.0 (t, JPÀC = 5.5 Hz), 148.3
(s), 106.3 (s), 42.4 (t, JPÀC = 9.4 Hz), 27.0 (t, JPÀC = 2.5 Hz). 31P{1H}
NMR (162 MHz, CD3CN): δ 175.0 (s, JPtÀP = 2535 Hz). Anal. Calcd
(found) for C21H39Cl2NO2P2Pt: % C, 37.90 (38.29); % H, 5.91 (5.85);
% N, 2.10 (2.31).
(H-PONOP)PtCl (4c). In a 250 mL Schlenk flask, complex 3c
(100 mg, 0.15 mmol) and 70 mL of pentane were combined under a
nitrogen atmosphere. A 0.15 mL portion of LiHBEt3 (0.15 mmol, 1 M in
THF) was added dropwise at room temperature. An immediate color
change from colorless to light yellow was observed. The reaction mixture
was stirred at room temperature for 20 min. The solution was filtered
under a nitrogen atmosphere using a cannula, and the volatiles were then
removed under vacuum yielding pure light yellow complex 4c (81%).
Complex 4c was not stable in solution, as stirring the solution for 4 h led
to a color change from yellow to colorless because of decomposition.
Crystals of complex 4c were grown by slow evaporation from a benzene
solution. 1H NMR (400 MHz, C6D6): δ 4.24 (t, JHÀH = 3.0 Hz, 2H),
3.44 (t, JHÀH = 3.4 Hz), 1.33 (vt, JPÀH = 7.6 Hz, 36H). 13C{1H} NMR
(100 MHz, C6D6): δ 159.4 (s), 70.8 , 40.8 (t, JPÀC = 12.1 Hz), 27.8
(t, JPÀC = 2.5 Hz), 25.6 (s). 31P{1H} NMR (162 MHz, C6D6):
δ 157.9 (s, JPtÀP = 2799 Hz). Anal. Calcd (found) for C21H40ClNO2P2Pt:
% C, 39.97 (40.10); % H, 6.39 (6.42); % N, 2.22 (2.43).
Attempted Synthesis of (H-PONOP)PdH (5b). In a 100 mL
Schlenk flask, complex 4b (50 mg, 0.09 mmol) and 10 mL of pentane
were combined under a nitrogen atmosphere. A 0.09 mL portion of
LiHBEt3 (0.09 mmol, 1 M in THF) was added dropwise at room
temperature. The reaction mixture was stirred at room temperature and
monitored by 31P NMR spectroscopy over time. No PdÀH complex was
observed. With longer stirring times complex 4b slowly decomposed.
From the decomposed mixture, one compound was isolated as crystal-
line solid, [Pd(μ-Cl)(tBu2PO
H
OPtBu2)]2 (Figure 9), which is a
3 3 3 3 3 3
known catalyst for the cross-coupling reactions of vinyl and aryl
chlorides with arylboronic acids, arylzinc reagents, and thiols.14,21
Synthesis of [(PONOP)PtCl]Cl CH3CN (2c). In a 500 mL
3
Schlenk flask, PONOP (500 mg, 1.25 mmol), PtCl2(NCPh)2 (534 mg,
1.25 mmol), and 100 mL of anhydrous CH3CN were combined under
a nitrogen atmosphere. The reaction mixture was stirred at room
temperature for 30 min. The volatiles were removed under vacuum
(overnight), leaving a white solid which was washed with hexane and
benzene and dried under vacuum yielding complex 2c (84%). 1H NMR
Attempted Synthesis of (H-PONOP)PtH (5c). In a 100 mL
Schlenk flask, complex 4c (50 mg, 0.08 mmol) and 10 mL of pentane
were combined under a nitrogen atmosphere. A 0.08 mL portion of
LiHBEt3 (0.08 mmol, 1 M in THF) was added dropwise at room tem-
perature. The reaction mixture was stirred at room temperature and
monitored by 31P NMR spectroscopy over time. No PtÀH complex was
observed. With longer stirring times complex 4c decomposed. From the
decomposed mixture, one compound was isolated as crystalline solid,
(400 MHz, CD2Cl2): δ 8.67 (t, JHÀH = 8.4 Hz, 1H), 7.32 (d, JHÀH
=
8.0 Hz, 2H), 1.98 (s, 3H), 1.11 (vt, JPÀH = 8.0 Hz, 36H). 13C{1H} NMR
(100 MHz, CD3CN): δ 164.0 (t, JPÀC = 5.5 Hz), 148.3 (s), 106.3 (s),
42.4 (t, JPÀC = 9.4 Hz), 27.0 (t, JPÀC = 2.5 Hz). 31P{1H} NMR
(162 MHz, CD3CN): δ 175.0 (s, JPtÀP = 2535 Hz). Anal. Calcd (found)
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ARTICLE
and the unit cell was similar to that obtained in an analogous reaction with
the Pd complex (vide infra, Figure 9), but no X-ray data were collected.
Reaction of the Complex 4c and 4b with CHCl3. In a 50 mL
Schlenk flask complexes 4b or 4c (20 mg) and 0.5 mL of CHCl3 were
combined under a nitrogen atmosphere. The reaction mixture was
stirred at room temperature. After 30 min both solutions changed color.
solid was washed 2 times with MeOH and dried under vacuum yielding
pure complex 3a-BPh4 (88%). Crystals of complex 3a-BPh4 were grown
by slow evaporation from a THF/C6H6 solution.1H NMR (500 MHz,
THF-d8): δ 7.54 (t, JHÀH = 8 Hz, 1H), 7.33 (m, 8H), 6.87 (t, JHÀH
=
6.8 Hz, 8H), 6.73 (t, JHÀH = 6.5 Hz, 4H), 6.63 (d, JHÀH = 8 Hz, 2H),
1.62 (vt, JPÀH = 7.8 Hz, 36H). 13C{1H} NMR (125 MHz, THF-d8):
δ 166.2 (t, JPÀC = 4.0 Hz), 165.8 (q, JBÀC = 49.1 Hz), 150.9 (s), 137.8
(s), 126.4 (m), 122.5 (s), 106.5 (s), 42.6 (t, JPÀC = 4.8 Hz), 28.1 (s).
31P{1H} NMR (202 MHz, THF-d8): δ 183.5 (s). Anal. Calcd (found)
for C45H59BClNNiO2P2: % C, 66.49 (65.97); % H, 7.32 (7.37); % N,
1.72 (1.79).
The volatiles were removed under vacuum, and complex 3c CHCl3 or
3
3b CHCl3 had been generated accordingly along with some decom-
3
1
position, as confirmed by NMR spectroscopy. 3c CHCl3: H NMR
3
(400 MHz, CD3CN): δ 7.86 (t, JHÀH = 8.2 Hz, 1H), 7.26 (s, 1H), 6.80
(d, JHÀH = 8.0 Hz, 2H), 1.11 (vt, JPÀH = 8.0 Hz, 36H). 31P{1H} NMR
1
(162 MHz, CD3CN): δ 175.0 (s, JPtÀP = 2535 Hz). 3b CHCl3: H
(PONOP)PtCl(BPh4) (3c-BPh4). In a 50 mL Schlenk flask, com-
plex 3c (30 mg, 0.045 mmol) and 1 mL of MeOH were combined under
a nitrogen atmosphere. A solution of NaBPh4 (153 mg, 0.45 mmol) in
MeOH (2 mL) was added dropwise at room temperature. The reaction
mixture was stirred at room temperature for 20 min, and a colorless solid
precipitated from solution. The solvent was removed by syringe, and the
solid was washed 2 times with MeOH and dried under vacuum yielding
pure complex 3c-BPh4 (89%). Crystals of complex 3c-BPh4 were grown
by slow evaporation from a THF/C6H6 solution. 1H NMR (500 MHz,
3
NMR (500 MHz, CD2Cl2): δ 8.54 (t, JHÀH = 7.6 Hz, 1H), 7.36 (s, 1H),
7.28 (d, JHÀH = 8.0 Hz, 2H), 1.50 (vt, JPÀH = 8.0 Hz, 36H). 31P{1H}
NMR (202 MHz, CD2Cl2): δ 192.6 (s).
Reaction of the Complex 4b with MeLi. In a 50 mL Schlenk
flask, freshly prepared complex 4b (20 mg, 0.037 mmol) and 3 mL of
THF were combined under a nitrogen atmosphere. Twenty-two micro-
liters of MeLi (0.037 mmol, 1.66 M in THF) were added dropwise at
room temperature. The reaction mixture was stirred at room tempera-
ture for 12 h, and the solution filtered through Celite. The volatiles were
then removed under vacuum yielding complex 6b (80% purity). Com-
pound 6b was not very stable. It slowly decomposed in solution over
several days even in the freezer at À20 °C. Crystallization of complex 6b
was not successful as it slowly decomposed in hexane after 4 d at room
temperature. 1H NMR (400 MHz, C6D6): δ 4.16 (s, 2H), 3.74 (s, 2H),
1.23 (vt, JPÀH = 7.2 Hz, 36H), 0.52 (t, JPÀH = 5.4 Hz, 3H). 13C{1H}
NMR (125 MHz, C6D6): δ 159.1 (s), 67.9 (t, JPÀC = 3.3 Hz), 39.8 (t,
JPÀC = 8.1 Hz), 28.0 (s), 27.1 (s), À20.4 (t, JPÀC = 6.8 Hz). 31P{1H}
NMR (162 MHz, C6D6): δ 168.4 (s).
Reaction of the Complex 4c with MeLi. In a 50 mL Schlenk
flask, freshly prepared complex 4c (20 mg, 0.03 mmol) and 3 mL of THF
were combined under a nitrogen atmosphere. Eighteen microliters of
MeLi (0.03 mmol, 1.66 M in THF) were added dropwise at room
temperature. The reaction mixture was stirred at room temperature and
monitored by 31P NMR spectroscopy over time. After 12 h, a new pro-
duct (highly unstable) was observed (30%) by 31P NMR spectroscopy
while unreacted 4c remained in the solution. Further stirring (24 h) of
this solution at room temperature led to decomposition as determined
by the observation of many peaks in the 31P NMR spectrum. 1H NMR
THF-d8): δ 7.58 (t, JHÀH = 8 Hz, 1H), 7.34 (m, 8H), 6.88 (t, JHÀH
=
7.3 Hz, 8H), 6.74 (m, 6H), 1.52 (vt, JPÀH = 8.3 Hz, 36H). 13C{1H}
NMR (125 MHz, THF-d8): δ 165.8 (q, JBÀC = 49.1 Hz), 164.2 (s),
149.6 (s), 137.8 (s), 126.4 (m), 122.5 (s), 106.7 (s), 43.1 (t, JPÀC
=
=
9.2 Hz), 27.6 (s). 31P{1H} NMR (202 MHz, THF): δ 174.8 (s, JPtÀP
2535 Hz). Anal. Calcd (found) for C51H65BClNO2P2Pt: % C, 59.62
(59.94); % H, 6.38 (6.29); % N, 1.36 (1.18).
(PONOP)PdCl(BPh4) (3b-BPh4). In a 50 mL Schlenk flask, com-
plex 3b (30 mg, 0.051 mmol) and 1 mL of MeOH were combined under
a nitrogen atmosphere. A solution of NaBPh4 (173 mg, 0.51 mmol) in
MeOH (2 mL) was added dropwise at room temperature. The reaction
mixture was stirred at room temperature for 20 min, and a light yellow
solid precipitated from solution. The solvent was removed by syringe,
and the solid was washed 2 times with MeOH and dried under vacuum
yielding pure complex 3b-BPh4 (86%). Crystals of complex 3b-BPh4
were grown by slow evaporation from a THF/C6H6 solution. 1H NMR
(500 MHz, THF-d8): δ 7.53 (t, JHÀH = 8.3 Hz, 1H), 7.34 (m, 8H), 6.88
(t, JHÀH = 7.3 Hz, 8H), 6.74 (m, 6H), 1.52 (vt, JPÀH = 8.5 Hz, 36H).
13C{1H} NMR (125 MHz, THF-d8): δ 166.1 (q, JBÀC = 49.1 Hz), 164.8
(s), 150.9 (s), 138.1 (s), 126.7 (m), 122.8 (s), 107.2 (s), 43.2 (t, JPÀC
=
5.4 Hz), 27.9 (s). 31P{1H} NMR (202 MHz, THF-d8): δ 192.1 (s,
JPtÀP = 2535 Hz). Anal. Calcd (found) for C51H65BClNO2P2Pd: % C,
65.25 (65.05); % H, 6.98 (7.06); % N, 1.49 (1.34).
(400 MHz, C6D6) (12 h RT): δ À10.51 (t, JPtÀH = 989 Hz, JPÀH
=
10.0 Hz) and many unidentified peaks. 31P{1H} NMR (162 MHz,
C6D6) (12 h RT): δ 198.4 (s, JPtÀP = 2790 Hz), 157.9 (s, JPtÀP = 2799
Hz, 4c). 31P{1H} NMR (162 MHz, C6D6) (24 h RT, major peaks):
δ 182.8 (s, JPtÀP = 2263 Hz), 180.1 (s, JPtÀP = 2256 Hz), 173.8 (s,
JPtÀP = 2831 Hz).
Reaction Complex 5a with Different Substrates. In a
J-Young tube 10 mg of complex 5a, 5 equiv of substrate (N-benzylidene-
methylimine, 1-octene, tBuNC, or PhCHO), and 0.5 mL of C6D6 were
1
combined. The reactions were monitored by both H and 31P NMR
Reaction of the Complexes 3c and 3b with MeLi. In a 50 mL
Schlenk flask, complexes 3c or 3b (20 mg) and 1 mL of THF were
combined under a nitrogen atmosphere. Two equivalents of MeLi
(1.66 M in THF) were added dropwise at room temperature. The
reaction mixture was stirred at room temperature for 30 min, and the
solution was filtered through Celite. The volatiles were then removed
under vacuum, and an NMR spectrum was recorded. Neither reaction
was clean. Crystal structures of these unknown compounds were
unsuccessful as they decomposed in hexane after 7 d. 31P{1H} NMR
spectroscopy at room temperature. In the case of gaseous substrates
(CO, D2 and ethylene), 1 atm substrate was added under the same
reaction conditions. In the case of benzaldehyde, benzoin was formed,
which was confirmed by 1H NMR spectroscopy and GC-MS using an
authentic sample. In the case of 1-octene after 2 days at room temper-
ature, mostly isomerized 2-trans and 2-cis octene were observed by
1H NMR spectroscopy. In the case of excess of tBuNC: 31P{1H} NMR
(202 MHz, THF-d8): δ 186.6 (s), 145.5 (s), 53.2 (s), 11.0(s).
(162 MHz, C6D6) (3c): δ 163.1 (s, JPtÀP = 2207 Hz), 161.4 (s, JPtÀP
=
(D-PONOP)NiCl (4a-d1). In a 50 mL Schlenk flask, complex 3a
(20 mg, 0.038 mmol) and 10 mL of pentane were combined under a
nitrogen atmosphere. A 0.038 mL portion of LiDBEt3 (0.038 mmol, 1 M
in THF) was added dropwise at room temperature. An immediate color
change from red to deep green was observed. The reaction mixture was
stirred at room temperature for 2 h. The solution was filtered under a
nitrogen atmosphere using a cannula, and the volatiles were then
removed under vacuum yielding a dark green complex 4a-d1 (90%).
2235 Hz) in: 1.25:1 ratio. 31P{1H} NMR (162 MHz, C6D6) (3b):
δ 174.4 (s), 172.5 (s), 170.5 (s), 168.3 (s) in 1:2:4:7 ratio.
(PONOP)NiCl(BPh4) (3a-BPh4). In a 50 mL Schlenk flask, com-
plex 3a (30 mg, 0.057 mmol) and 1 mL of MeOH were combined under
a nitrogen atmosphere. A solution of NaBPh4 (194 mg, 0.57 mmol) in
MeOH (2 mL) was added dropwise at room temperature. The reaction
mixture was stirred at room temperature for 20 min, and a red solid
precipitated from solution. The solvent was removed by syringe, and the
1H NMR (400 MHz, C6D6): δ 4.19 (2H), 3.39 (m, 1H), 1.45 (vt, JPÀH
=
9451
dx.doi.org/10.1021/ic201102v |Inorg. Chem. 2011, 50, 9443–9453

Inorganic Chemistry
ARTICLE
’ ACKNOWLEDGMENT
We thank the U.S. Department of Energy Office of Basic
Sciences for their support of this work (Grant 86-ER-13569).
The Center for Enabling New Technologies through Catalysis
(CENTC) Elemental Analysis Facility is also acknowledged
for use of its analytical facility (CHE-0650456). This paper is
dedicated to Prof. Christian Bruneau on the occasion of his 60th
birthday.
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’ ASSOCIATED CONTENT
S
Supporting Information. X-ray crystallographic data for
b
complexes (CCDC nos. 826970À826980, 839072), including CIF
files and tables of coordinates, distances, and angles. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: jones@chem.rochester.edu.
9452
dx.doi.org/10.1021/ic201102v |Inorg. Chem. 2011, 50, 9443–9453

Inorganic Chemistry
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