Synthesis of new late transition metal P,P-, P,N-, and P,O- complexes using phosphonium dimers as convenient ligand precursors

Article abstract of DOI:10.1021/ic4003753

The phosphonium dimer [-Cy₂PCH(OH)CH₂-] ₂(X)₂, X = Cl^-, Br^- was used to synthesize and characterize a variety of late transition metal complexes containing chelating phosphino-enolate (PCy₂CH=CHO^-), imine (PCy₂CH₂CH=NR, R = Ph, (S)-CHMePh), and oxime (PCy₂CH₂CH=NOH) ligands. The phosphonium dimer, when deprotected with base, generates the phosphine aldehyde PCy₂CH ₂CHO in situ, which, in the presence of [M(COD)Cl]₂, M = Rh, Ir, and a PF₆^- salt, or [Ni(H₂O) ₆][BF₄]₂, facilitates a condensation reaction with an amine or hydroxylamine to form phosphino-imine or phosphino-oxime metal complexes [M(COD)(P-N)][PF₆] or [Ni(P-N)₂][X]₂, X = ClO₄^-, BF₄^-, respectively. In the absence of an amine, phosphino-enolate containing complexes are formed. A neutral Ni(II) complex Ni(PCy₂CH=CHO)₂ with trans-bis(phosphino-enolate) ligands which resemble ligands used on nickel for olefin oligomerization, as well as neutral Rh(I) and Ir(I) 1,5-cyclooctadiene complexes M(COD)(PCy₂CH=CHO) are characterized. Both the rhodium and iridium complexes are active olefin hydrogenation catalysts. Reaction of the phosphino-aldehyde with Pt(COD)Cl₂ results in the formation of trans-PtCl₂(PCy₂CH₂CHO)₂ with pendant aldehyde groups, and under certain conditions, they undergo an intraligand aldol condensation to form a disphosphine ligand.

Full text of DOI:10.1021/ic4003753

Article
pubs.acs.org/IC
Synthesis of New Late Transition Metal P,P‑, P,N‑, and P,O-
Complexes Using Phosphonium Dimers as Convenient Ligand
Precursors
Kanghee Park, Paraskevi O. Lagaditis, Alan J. Lough, and Robert H. Morris*
Department of Chemistry, University of Toronto, Toronto, Ontario M5S3H6, Canada
S
* Supporting Information
ABSTRACT: The phosphonium dimer [-Cy2PCH(OH)CH2-]2(X)2, X =
Cl−, Br− was used to synthesize and characterize a variety of late transition
metal complexes containing chelating phosphino-enolate (PCy2CH
CHO−), imine (PCy2CH2CHNR, R = Ph, (S)-CHMePh), and oxime
(PCy2CH2CHNOH) ligands. The phosphonium dimer, when depro-
tected with base, generates the phosphine aldehyde PCy2CH2CHO in situ,
−
which, in the presence of [M(COD)Cl]2, M = Rh, Ir, and a PF6 salt, or
[Ni(H2O)6][BF4]2, facilitates a condensation reaction with an amine or
hydroxylamine to form phosphino-imine or phosphino-oxime metal
−
complexes [M(COD)(P−N)][PF6] or [Ni(P−N)2][X]2, X = ClO4 ,
−
BF4 , respectively. In the absence of an amine, phosphino-enolate
containing complexes are formed. A neutral Ni(II) complex Ni(PCy2CHCHO)2 with trans-bis(phosphino-enolate) ligands
which resemble ligands used on nickel for olefin oligomerization, as well as neutral Rh(I) and Ir(I) 1,5-cyclooctadiene complexes
M(COD)(PCy2CHCHO) are characterized. Both the rhodium and iridium complexes are active olefin hydrogenation
catalysts. Reaction of the phosphino-aldehyde with Pt(COD)Cl2 results in the formation of trans-PtCl2(PCy2CH2CHO)2 with
pendant aldehyde groups, and under certain conditions, they undergo an intraligand aldol condensation to form a disphosphine
ligand.
INTRODUCTION
■
As a result the prevalence of chelating phosphine and oxygen/
nitrogen ligands in late transition metal catalysts, methods for
their facile synthesis are valuable and sought-after. Transition
metal complexes containing P−O and P−N ligands can catalyze
a variety of reactions, including transfer1−4 and direct
hydrogenation,5−11 olefin polymerization,12,13 Michael addi-
tion,14 hydroamination,15 hydroformylation16 among
Figure 1. Selected examples of known Ir(I) olefin hydrogenation
others.17−19 Specific examples include Ni(II) catalysts contain-
catalysts: (a) Crabtree’s catalyst, (b) Pfaltz’s catalyst with a PHOX
ligand, (c) Stradiotto’s neutral phosphino-enolate catalyst.
ing P−O chelating ligands, which are used in the Shell Higher
Olefin Process,20 where the first step is catalytic oligomerization
of ethylene. Olefin hydrogenation catalysts based on Crabtree’s
catalyst often contain a P−N5,6 or P−O1,9 ligand. As Crabtree’s
catalyst has a phosphine and a pyridine ligand,21 many groups
have since successfully used similar complexes based on Ir(I)
containing a 1,5-cyclooctadiene ligand and a chelating P−N, or
similar, ligand (Figure 1). Addition of chelating ligands is
attractive as it may potentially increase catalyst lifetime and
assists in enforcing asymmetry in enantioselective processes. In
particular, Pfaltz and co-workers have developed a particularly
active and enantioselective catalyst for the hydrogenation of
unfunctionalized tri- and tetra-substituted olefins.5 These
catalysts contain chiral P−N ligands with an N-bound
oxazoline. Stradiotto et al. have also reported similar catalysts
that are neutral9 or zwitterionic,8 in contrast to the majority of
Ir(I) olefin hydrogenation catalysts which are cationic. These
show promise in being used in greener hydrocarbon solvents
and removing the need for expensive counteranions to improve
reactivity.22
A powerful synthetic strategy for generating P−O and P−N
ligands is to use phosphine aldehydes.23−25 Here, the
phosphine can be substituted with a variety of aryl and alkyl
groups,26 and the aldehyde can be condensed with various
amines to form a wide range of imines. Furthermore, tri- or
tetradentate ligands can be generated via the metal-assisted
condensation of phosphine aldehydes with amines containing
different donor groups, as previously demonstrated in the
synthesis of Fe(II) complexes (Scheme 1).24 This method
allows the efficient synthesis of tetradentate [Fe(PNNP)(CO)-
Received: February 12, 2013
Published: April 9, 2013
© 2013 American Chemical Society
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plex 2b Containing Phosphino-Imine Ligands. The
synthesis of the trans-bis(phosphino-enolato)Ni(II) complex
2a was carried out by deprotection of phosphonium dimer 1
with 2 equiv of base in toluene followed by filtration to remove
KBr salts. Then coordination of the free phosphine aldehyde
that was generated in situ was achieved by the addition of 1
equiv of [Ni(H2O)6][BF4]2 and enough methanol to solubilize
the Ni(II) salt. The addition of two more equivalents of base
caused the light brown reaction mixture to darken instanta-
neously, indicating the formation of an enolate via deprotona-
tion of the phosphine aldehyde (Scheme 2). The neutral Ni(II)
Scheme 1. One-step Synthesis of Dimeric Phosphonium
Compound 1, Deprotection of the Aldehyde with Base, and
Subsequent Metal-Assisted Template Synthesis of an Fe(II)
PNNP Complex
Scheme 2. Synthesis of Ni(II) Complexes 2a and 2b
(Br)]+ complexes that are highly active for the enantioselective
reduction of polar double bonds.4 Mechanistic studies have
revealed that these complexes are precursors to the active
catalysts where reduction of one imine ligand to an amine is
required in an activation step.27
Phosphine aldehydes are often very air sensitive oils and thus
disadvantageous for use in synthesis. Moreover, very few are
commercially available, notably the air stable and crystalline 2-
(diphenylphosphino)benzaldehyde which has been used for the
synthesis of various ligands.28−30 To circumvent these
problems, we have used phosphonium dimers instead.
Phosphonium dimers are air stable solids that can be
deprotonated with base to release two equivalents of phosphine
aldehyde in situ. Our group has previously demonstrated the
facile synthesis of numerous alkyl and aryl phosphonium
dimers.26,31 Studies on the effects of sterics and electronics of
the ligand on metal catalysis and fine-tuning of catalyst activity
are possible because of the phosphonium precursor’s
modularity.31,32
The synthesis of metal complexes using phosphonium
dimers is done in a template, one-pot synthesis. The phosphine
aldehyde is generated in situ by deprotonation of the
phosphonium dimer; then, in conjunction with an amine and
a metal precursor it forms the P−N complex. In this reaction,
the metal acts both as a Lewis acid facilitating the condensation
reaction and as a thermodynamic sink via coordination of the
chelating ligand. The direct reaction of the phosphine aldehyde
with amines in the absence of the metal has not lead to isolable
P−N ligands in our hands.
complex, 2a, was easily isolated upon removal of solvent in
vacuo as a pale brown solid in 72% yield. Complex 2a is soluble
in most organic solvents, including pentane, hexanes, ethers,
toluene, and CH2Cl2. Its moderate solubility in pentane allows
easy separation from salts generated in the synthesis.
1
Characteristic resonances of 2a in the H NMR spectra are
the olefinic peaks at 7.08 and 3.43 ppm, with the more
downfield signal displaying virtual coupling due to trans-
phosphine ligands. The X-ray diffraction data shows that the
trans-phosphine groups were 180.0(1)° to each other, as were
the trans-enolate groups, displaying complete planarity about
the Ni(II) metal center and the atoms that are coordinated to it
(Figure 2a). The sum of the internal angles of the 5-membered
ring formed by the ligand backbone and the metal center is
540.0(9)°, thus mostly planar. An analogous Ni(II) complex
Ni(OC(Ph)CHPiPr2)2 isolated by Braunstein and co-work-
ers, which contain trans-bis(di-iso-propylphosphino-enolate)
In this paper, we focus mainly on the synthesis of late
transition metal complexes that contain bidentate P−O or P−N
ligands. The formation of phosphino-enolate, imine, and oxime
ligands are presented, as well as phosphine ligands with
pendant aldehydes and their intraligand aldol reactivity
resulting in a diphosphine ligand. Several metal ions are
explored, including Ni(II), Pt(II), Rh(I), and Ir(I), to
demonstrate that the template synthesis with our phosphine
aldehydes are not limited to Fe(II). The Rh(I) and Ir(I)
complexes contain a 1,5-cyclooctadiene ligand, therefore
resembling Crabtree’s catalyst, and were tested for olefin
hydrogenation.
Figure 2. ORTEP representation (thermal ellipsoids at 30%
probability; the solvent and most of the hydrogen atoms and ClO4
anions of 2b are omitted for clarity) and atom numbering for (a) 2a
and (b) 2b.
RESULTS AND DISCUSSION
Synthesis of the Neutral Ni(II) Complex 2a Containing
Phosphino-Enolate Ligands and Dicationic Ni(II) Com-
−
■
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ligands derived from a phenyl ketone shows similar planarity
displaying an O1−Ni−O2 bond angle of 180.0(1)°, and a sum
for the internal angle of its metallacycle of 539.7(3)°.33 Both
complexes display identical P1−Ni−O1 bond angles of
87.0(1)°. The C1−C2 bond length of 2a is 1.343(4) Å,
which is closer to the typical bond length observed for olefins
than to that of benzene, 1.34 Å vs 1.40 Å, respectively.
Because of the insolubility of Ni(II) salts in toluene, a
reaction only began to take place when methanol was added, as
the colorless slurry solution slowly turned brown and
homogeneous. However, the addition of methanol results in
solubilization of the halide salts generated in the deprotection
of the phosphonium aldehyde. The halide anions are then
capable of forming unwanted byproducts. This was avoided by
carefully removing all halide salts by filtration in the
deprotection step when done in toluene, and also by using
[Ni(OH2)6][BF4]2 or [Ni(OH2)6][ClO4]2 which contain
weakly coordinating anions.
The cis-bis(phosphino-imine)Ni(II) complex 2b was synthe-
sized by a metal-assisted template reaction using phosphine
aldehyde and (S)-1-phenylethylamine. After deprotection of the
phosphonium dimer 1 with 2 equiv of KOtBu in acetonitrile,
−
−
Synthesis of Platinum(II) Bis(phosphino-aldehyde)
Complexes 3a and 3b. We were interested in applying the
synthesis to the other group 10 elements. Addition of the
platinum complex, Pt(COD)Cl2, to the phosphine aldehyde
that was generated in situ at room temperature allowed the
isolation of a crude product as a white solid. The product was
easily separated from salts generated in the synthesis by
extraction of the solid crude product with diethyl ether. The
product is also soluble in other organic solvents such as
toluene, CH2Cl2, and tetrahydrofuran (THF), but not hexanes.
[Ni(H2O)6][X]2 (X = ClO4 , BF4 ) and (S)-(-)-1-phenyl-
ethylamine were added, forming an orange solution. After
removal of the solvent in vacuo, the residue was taken up with
methanol from which an orange precipitate was collected. The
precipitate was washed with ether, yielding the cis-phosphino-
imine complex 2b as an orange solid in 55% yield. The product
is only soluble in polar solvents such as acetonitrile in contrast
to the neutral complex 2a because of its dicationic nature.
1
The new Ni(II) complex 2b displays characteristic H NMR
resonances for the imine proton at 8.79 ppm and diastereotopic
CH2 protons of the ligand backbone at 3.86 and 3.34 ppm. In
contrast to the neutral complex 2a, complex 2b is not
completely square planar, and has a slight tetrahedral distortion
(Figure 2b). Furthermore, the 5-membered metallacycle
formed by the ligand and the metal center in 2b has a sum
of internal angles of 522(2)°, indicating nonplanarity of the
metallacycle because of the lack of the π-conjugation that exists
in 2a.
1
Analysis by H and 31P{1H} NMR spectroscopy revealed that
two species were formed in the reaction: the trans-
phosphinoaldehyde complex, 3a, was observed as the major
product (88%), and the unexpected diphosphine complex, 3b,
was observed as a minor product (12%) (Scheme 3). They are
Scheme 3. Synthesis of Pt(II) Complexes 3a and 3b
The two phosphino-enolate ligands of 2a were found to
coordinate trans to each other. Braunstein and co-workers have
synthesized similar Ni(II) complexes containing two phosphi-
no-enolate ligands, but generated from ketones instead of an
aldehyde.33 They found that the diphenylphosphino-enolate
ligands exclusively formed the cis isomer, the di-tert-
butylphosphino-enolate ligands exclusively formed the trans
isomer, and the di-iso-propylphosphino-enolate ligands formed
a mixture of the trans and cis isomers. This can be rationalized
by both the trans influence and steric interactions. Because of
the trans influence, the trans-coordination of bidentate P,O-
ligands is destabilized and thus cis-coordination is favorable if
only electronic factors are considered. However, if steric
energies between cis-phosphines are great enough, the ligands
will then preferentially coordinate trans. Hence, in the case of
the di-tert-butylphosphino-enolate ligands of Braunstein and
the dicyclohexylphosphino-enolate of 2a, the steric factors
outweigh any trans influence/electronic factors. The phosphi-
no-imine ligands of complex 2b coordinate cis presumably
because of the steric bulk being similar on both the phosphine
and the imine sides of the ligand, allowing the trans influence to
predominate.
maintained in solution as indicated by 31P{1H} NMR
spectroscopy where 3a gives a singlet while 3b shows two
2
doublets with JPP = 16.9 Hz. The aldehyde hydrogen for 3a
and 3b resonates at 9.96 and 9.52 ppm, respectively.
The structures as determined from the X-ray diffraction study
are shown in Figure 3. Curiously, the two molecules
cocrystallized in 1:1 ratio despite the greater abundance of
complex 3a in solution. The Pt−P (2.315(3) Å) and Pt−Cl
(2.310(3) Å) bond lengths measured for 3a are comparable to
the Pt−P bond length of 2.337(2) Å and Pt−Cl bond length of
Interestingly, when 2 equiv of deprotected phosphine
aldehyde and [Ni(H2O)6][BF4]2 are reacted in a toluene and
MeOH solution, the phosphino-enolate complex 2a is the
major product formed, even without the addition of two more
equivalents of base to deprotonate the two aldehydes to
enolates. The formation of the enolate, even in the absence of
added base, likely results from the deprotonation of a highly
acidic cationic phosphine aldehyde complex by the water from
the hydrate salt. The formation of the highly π-conjugated 5-
membered metallacycle, along with Ni(II) acting as a Lewis
acid, stabilizes the enolate.
Figure 3. ORTEP representation (thermal ellipsoids at 50%
probability; the solvent and most of the hydrogen atoms are omitted
for clarity) and atom numbering for (a) 3a and (b) 3b.
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2.317(2) Å of the complex trans-Pt(PCy3)2Cl2.34 The Pt−P
bonds for the cis-aldol complex 3b are significantly shorter at
2.258(3) Å, while the Pt−Cl bond lengths are longer at
2.367(2) Å and correlate well with the measured bond lengths
of the complex Pt(PCy2CH2CH2CH2PCy2)Cl2.35 The differ-
ences in bond lengths are due to the high trans influence of
phosphine ligands. The P1−Pt−P2 bond angle of 3b is
9 6 . 1 ( 1 ) ° , w h i c h i s c o m p a r a b l e t o t h e P t -
(PCy2CH2CH2CH2PCy2)Cl2 bond angle of 96.1(3)°. Further-
more, no exchange of the chloro ligand is observed when the
bromide salt of 1 is used.
the bulky P-cyclohexyl groups which keeps the aldehyde groups
close together and the formation of a proposed six-membered
metallocyclic transition state causes the aldol condensation to
be favorable. This is another example of a template-assisted
ligand synthesis, because if the phosphine aldehydes are reacted
under various aldol condensation reaction conditions in the
absence of a metal, no diphosphine compound is observed.
When the reaction was started at −78 °C and then warmed
to 25 °C, yields of the diphosphine complex 3b and 3a are 70%
and 30%, respectively, according to 31P{1H} NMR spectra. At
lower temperatures isomerization to the trans isomer slows
down, allowing the aldol condensation reaction to take place.
By contrast, when the synthesis is done with H2O as the
solvent, exclusive formation of 3a observed, as the aldol
condensation reaction is suppressed.
The diphosphine ligand is the product of a novel intraligand
aldol condensation reaction in presumably the cis-bis-
(phosphino-aldehyde) complex (Scheme 4). As it was observed
Scheme 4. Proposed Mechanism for the Formation of 3b
Alternate methods toward the synthesis of the aldol
condensation diphosphine ligand were attempted to increase
its yield. The focus was to utilize a dianionic bidentate ligand to
replace the chloride ligands, restricting the formation of the
trans-phosphinoaldehyde. A catechol derived Pt(II) complex
was synthesized36 and reacted with phosphine aldehydes, but it
did not lead to the formation of an aldol-condensation product.
In another attempt, a mixture of complexes 3a and 3b was
reacted with silver oxalate to force the phosphines to coordinate
in a cis fashion; however, the reaction yielded an intractable
mixture by NMR spectroscopy. These reactions presumably did
not work because the catecholate and oxalate ligands
decoordinated from the metal after reacting as an internal
base with the enolizable phosphine aldehyde.
Synthesis of Neutral Rh(I) and Ir(I) Phosphino-enolate
Complexes 4a and 4b. Neutral rhodium and iridium
phosphino-enolate complexes were synthesized (Scheme 5).
The phosphine aldehyde was first generated in situ from the
phosphonium dimer and base, after which the metal precursor,
[M(COD)(μ-Cl)]2 (M = Rh, Ir), was added. When additional
base was added to enolize the aldehyde functionality, neutral
phosphino-enolate complexes were formed. Both the rhodium
and the iridium complexes are moderately soluble in hexanes,
making them especially easy to isolate from various salts in the
mixture. The rhodium complex, 4a, was isolated in 57% yield as
from the Ni(II) complex 2a, the bulky dicyclohexylphosphines
preferentially coordinate trans due to steric effects. However,
because of the stereochemistry of the displacement of the 1,5-
cyclooctadiene ligand and the aldol reactivity of the cis
aldehydes, initial coordination of the phosphino-aldehyde
ligands is likely cis. A combination of the repulsion between
Scheme 5. Synthesis of Rh(I) and Ir(I) 1,5-Cyclooctadiene Phosphino-Enolate Complexes 4a and 4b, Phosphino-Imine
Complex 5, and Phosphino-Oxime Complexes 6a and 6b
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a yellow solid, while the iridium complex, 4b, as an orange-red
solid in 57% yield.
Table 1. Direct Hydrogenation of Olefins with Catalysts 4−
a
6
Structures from X-ray diffraction studies of single crystals of
4a and 4b (Figure 4) show that both complexes are square
time conv.
entry catalyst solvent
substrate
product
(h)
(%)
1
2
4a
4a
CH2Cl2 cyclooctene
cyclooctane
4
2
100
b
CH2Cl2 4-phenyl-3-
buten-2-one
4-phenyl-2-
butanone
100
3
4
4a
4a
hexanes cyclooctene
cyclooctane
2
2
100
100
b
hexanes 4-phenyl-3-
buten-2-one
4-phenyl-2-
butanone
5
6
7
4a
4b
4b
hexanes stilbene
bibenzyl
10
0.5
1
0
CH2Cl2 cyclooctene
cyclooctane
96
100
b
CH2Cl2 4-phenyl-3-
buten-2-one
4-phenyl-2-
butanone
8
4b
4b
4b
5
hexanes cyclooctene
CH2Cl2 stilbene
cyclooctane
bibenzyl
2
75
26
14
88
99
9
2
Figure 4. ORTEP representation (thermal ellipsoids at 50%
probability; the solvent and most of the hydrogen atoms are omitted
for clarity) and atom numbering for (a) 4a and (b) 4b.
10
11
hexanes stilbene
bibenzyl
10
3
CH2Cl2 cyclooctene
cyclooctane
5
b
12
5
CH2Cl2 4-phenyl-3-
buten-2-one
4-phenyl-2-
butanone
3
29
planar and have comparable bond distances and angles. There
is significant lengthening of the M-C bonds trans to the
phosphine because of the trans influence which is also observed
in Stradiotto and co-workers’ neutral Ir(P−O)COD complex.9
The M-L bond distances for both Rh and Ir complexes are
similar as was expected because of their similar covalent radii as
deduced from a study of crystallographic data.37 Comparisons
to similar Rh16 and Ir9 P−O complexes also show comparable
data.
Most cobalt group olefin hydrogenation catalysts with COD
precursors are cationic, although some neutral precatalysts have
been reported. Stradiotto and co-workers have reported both
neutral and zwitterionic Ir(COD)(P−N)8 and neutral Ir-
(COD)(P−O)9 complexes that are active for olefin hydro-
genation. These types of catalysts have also been shown to be
active for olefin hydroamination15 and hydroformylation.16
Although highly active and enantioselective catalysts already
exist, investigations into neutral analogues may prove useful.
Neutral catalysts are often more soluble in hydrocarbon
solvents than in higher dielectric chlorinated solvents and
thereby allow greener reaction conditions, as well as avoid the
deactivating properties of coordinating solvents. Another
advantage of developing neutral olefin hydrogenation catalysts
is that there is no potential for counteranion effects, thus
precluding the use of expensive counteranions such as
[BArF4]−.22
The Rh complex 4a was tested for catalytic hydrogenation of
stilbene and was found to be inactive. The Ir complex 4b was
poorly active for stilbene hydrogenation, but found to be more
active for hydrogenation of the olefinic bonds in cyclooctene
and (E)-4-phenyl-3-buten-2-one (Table 1). When catalysis was
conducted in CH2Cl2, significantly higher turnover frequencies
were obtained than with hexanes as the solvent. This is in
contrast to Stradiotto and co-workers’ results where hexanes
were found to be the best solvent for the hydrogenation of
styrene. Changes in catalyst reactivity in different solvents can
be ascribed to stabilization or destabilization of catalytic
intermediates due to solvent coordination.
Synthesis of Rh(I) and Ir(I)(P−N) Complexes 5, 6a, and
6b. The cationic iridium phosphino-imine complex 5 was
synthesized using aniline as the amine source in a condensation
reaction with the phosphine aldehyde (Scheme 5). The
synthesis of P−N complexes is done in a template fashion,
where the addition of the metal precursor is necessary to enable
13
14
6a
6b
CH2Cl2 cyclooctene
CH2Cl2 cyclooctene
cyclooctane
cyclooctane
1
2
13
51
a
b
Catalysis run at 35 °C, 35 bar H2, and 1 mol % catalyst. Selective
reduction of olefin.
the reaction to go to completion. The addition of [NH4][PF6]
yielded the product as the [PF6]− salt in 82% yield as air stable
red crystals. If NaPF6 or KPF6 were used instead, a mixture of
the cationic imine and the neutral enamido complexes are
observed due to the acidic α-proton of the imine and the
basicity of the methanol solvent or any moisture present in the
reaction mixture.
Changing the amine in the condensation reaction from
aniline to hydroxylamine resulted in the formation of
phosphino-oxime complexes 6a and 6b. The ligand backbones
of the oxime complexes 6a and 6b are less enolizable than the
ligand backbone of imine complex 5, as evident by NaPF6 being
−
a suitable PF6 source. These complexes were formed as the
[PF6]− salts, where the rhodium complex 6a was isolated as a
yellow solid in 70% yield, and the iridium complex 6b as an
orange solid in 97% yield. They have two potentially acidic
hydrogens on the backbone and oxime oxygen. The rhodium
complex 6a was crystallized and examined by X-ray diffraction
(Figure 5). The C(1)−C(2) bond distance for the ligand
backbone is 1.483(3) Å, which is longer than the bond
distances of the enolate complexes, and characteristic of a C−C
single bond.
Phosphino-oxime ligands are uncommon in literature, with
the closest examples being bidentate phosphino-oxide, oxime
ligands. In particular, Wan and co-workers have used chelating
phosphine oxide and N-oxime ligands with Cu(I) for N-
arylation of alkylamines and N−H containing heterocycles,38 as
well as aryl iodide and thiol coupling.29 No well-defined metal
complexes have been isolated in these studies. These new
phosphino-oxime complexes present new possibilities in
catalyst design. An example of a catalyst containing an oxime
ligand is the bifunctional ketone transfer hydrogenation catalyst
by Ikariya and co-workers,39 which contains a C−N oxime
ligand and a Cp* ligand on Ir(III). Preliminary tests on the new
Rh(I) and Ir(I) oxime complexes for the transfer hydro-
genation of acetophenone showed no activity.
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CONCLUSION
■
Facile, one-pot methods for the synthesis of bidentate P−O,
P−P, and P−N complexes, some of which were catalytically
active for the hydrogenation of CC double bonds, were
developed based on the utility of the phosphino aldehyde
ligand precursor. A Ni(II) complex containing two bidentate
phosphino-enolate ligands coordinated trans to each other was
synthesized. This complex may be of interest for further
investigations toward the synthesis of an ethylene oligomeriza-
tion catalyst, as Fryzuk and co-workers have published a
method of forming active olefin oligomerization catalysts from
similar starting materials.40 Also, a novel method of generating
a diphosphine ligand containing a pendant aldehyde in a
template method is presented using Pt(II) as the metal
precursor. These ligands have potential for tethering metal
complexes to heterogeneous materials making them more
recyclable, or may be further transformed through functional-
ization of the alkene or aldehyde in the ligand backbone to
generate more interesting ligands. Rh(I) and Ir(I) complexes
have been synthesized based on Crabtree’s iridium catalyst
design. The neutral Ir(I) complex 4b shows moderate activity
for the hydrogenation of disubstituted olefins. However, it is
less active with the more sterically hindered stilbene. It was
surprising that 4b was found to be more active than the cationic
Ir(I) phosphino-imine complex considering that most catalysts
of this design are cationic and contain a P−N ligand. Lastly,
novel cationic Rh(I) and Ir(I) phosphino-oxime complexes 6
were synthesized and characterized. These complexes have
potential for a variety of catalytic processes which require
further investigation.
Figure 5. ORTEP representation (thermal ellipsoids at 50%
probability; the solvent, most of the hydrogen atoms, and PF6
anion are omitted for clarity) and atom numbering for 6a.
−
Hydrogenation Catalysis with Rh(I) and Ir(I) Com-
plexes 4−6. The catalytic hydrogenation of olefins was
attempted with the neutral complexes 4a and 4b, and the
cationic complexes 5, 6a, and 6b (Table 1). Stilbene was used
as the initial olefin substrate; however, attempted catalysis with
complexes 4−6 was slow and incomplete. Activity was observed
for the hydrogenation of cyclooctene with catalysts 4 and 5,
where both Rh(I) and Ir(I) neutral catalysts were faster than
the cationic catalyst 5. Cationic metal centers are often thought
to be optimal for catalytic activity, especially in the case of
poorly coordinating unfunctionalized tri- and tetrasubstituted
olefins, as they may have greater affinity for the olefins.
However, with less substituted olefins such as cyclooctene, it is
possible that this is not a major factor. A previous study by
Pfaltz and co-workers on counteranions22 has shown that the
use of hexafluorophosphate anions are suboptimal for cationic
Ir(I) olefin hydrogenation catalysts and resulted in slower
turnover and more rapid catalyst death when compared to the
EXPERIMENTAL SECTION
■
All of the preparations and manipulations, unless otherwise stated,
were carried out under a nitrogen or argon atmosphere using standard
Schlenk-line and glovebox techniques. Dry and oxygen-free solvents
were used unless otherwise stated. Pentane, hexanes, toluene, and
diethyl ether were dried and distilled over sodium and benzophenone
under an argon atmosphere. Methanol was dried and distilled over
activated magnesium (magnesium turnings and a crystal of iodine)
under an argon atmosphere. Dichloromethane was dried and distilled
over CaH2 under an argon atmosphere. The synthesis of the bromide
salt of dicyclohexylphosphonium dimer 1 was synthesized according to
literature procedures.26 The synthesis of the chloride salt of 1 only
requires the replacement of bromoacetaldehyde diethyl acetal with
chloroacetaldehyde diethyl acetal. All other reagents and solvents were
purchased from commercial sources and were used as received.
Deuterated solvents were purchased from either Cambridge Isotope
Laboratories or Sigma Aldrich, and degassed and dried over molecular
sieves prior to use. NMR spectra were recorded on a Varian Mercury
larger and less coordinating [BArF ]− anion. The neutral
4
complexes 4a and 4b do not have counteranions and thus have
the potential to avoid this problem.
The Rh(I) complex 4a is more active for the hydrogenation
of cyclooctene in hexanes than in CH2Cl2, whereas the Ir(I)
complex 4b had the reverse activity. One possible explanation is
after the COD ligand dissociates after hydrogenation, the Rh(I)
metal center is more Lewis acidic than the Ir(I) metal center.
This difference renders Rh(I) to have a higher affinity for
CH2Cl2 coordination and thereby cause a greater hindering of
substrate coordination. It may also be possible that the Ir(I)
catalyst is more prone to catalyst deactivation through
oligomerization7 of the active catalyst than the Rh(I) catalyst,
and CH2Cl2 coordination is able to stabilize and maintain the
active catalyst in solution.21
Phosphino-oxime complexes 6a and 6b were poorly active
for the hydrogenation of olefins and acetophenone. This was
expected, as they are coordinatively unsaturated hydrogenation
catalysts with coordinating alcohol or amine groups on the
ligand. Hence, their inactivity is likely due to a deactivation
pathway involving the formation of dimers or other oligomers.
Catalysts 4 and 5 are selective for olefin hydrogenation over
carbonyl groups, as demonstrated by the selective hydro-
genation of 4-phenyl-3-buten-2-one to 4-phenyl-2-butanone.
1
400 MHz or Bruker Avance 400 MHz spectrometer. H and 13C{1H}
NMR spectra were referenced relative to their respective partially
deuterated solvent peaks. All 31P chemical shifts were measured
relative to 85% phosphoric acid as an external reference. The
electrospray ionization mass spectrometry (ESI-MS) data were
collected on an AB/Sciex QStar mass spectrometer with an ESI
source and the DART-MS data were collected on a JEOL AccuTOF-
DART mass spectrometer with a DART-ion source (no solvent is
required). Elemental analyses were performed using a Perkin-Elmer
2400 CHN elemental analyzer at the Department of Chemistry at the
University of Toronto. Single-crystal X-ray diffraction data were
collected using a Nonius Kappa-CCD diffractometer with Mo Kα
radiation (λ = 0.71073 Å). The structures were solved and refined
using SHELXTL V6.1. Caution! Perchlorate salts of organic compounds
can be explosive.
Ni(OCHCHPCy2)2 (2a). A vial was charged with dicyclohexylphos-
phinoaldehyde chloride dimer 1 (26 mg, 0.047 mmol), KOtBu (11 mg,
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Article
0.094 mmol), and toluene (2 mL). The mixture was stirred for 10 min,
yielding a white suspension. Solids were filtered off through Celite, and
[Ni(H2O)6][BF4]2 (16 mg, 0.047 mmol) and methanol (1 mL) were
added to the reaction mixture resulting in a brown solution. Upon
addition of additional KOtBu (11 mg, 0.094 mmol), the solution
darkened slightly and was stirred overnight. The volatiles were
removed in vacuo, and the brown residue extracted with pentane (3 ×
2 mL) until only white solids were left. Filtration of the mixture
through Celite and removal of pentane in vacuo afforded the product
as a brown solid. Yield: 72% (25 mg). Crystals of 2 suitable for X-ray
diffraction studies were grown by the slow evaporation of hexanes. 1H
20 min, yielding a white suspension. Cyclooctadiene rhodium chloride
dimer (23 mg, 0.047 mmol) was weighed directly into the vial, and
stirred briefly, followed by addition of KOtBu (10 mg, 0.094 mmol).
The yellow solution was stirred at room temperature for 2.5 h. The
yellow solution was filtered through Celite to remove salts and dried in
vacuo to yield the product as a yellow solid. The product was
recrystallized by slow diffusion of methanol into a CH2Cl2 solution of
the product. Yield: 97% (46 mg). Bright yellow crystals of 4a suitable
for X-ray diffraction studies were grown from slow diffusion of
1
methanol into a hexane solution of the product. H NMR (400 MHz,
CD2Cl2): δ 7.35 (dt, 3JHH = 3.7 Hz, 3JHP = 39.3 Hz, 1H, HC−O), 4.91
3
NMR (400 MHz, CD2Cl2): δ 7.08 (m, 1H, HC−O), 3.43 (d, JHH
=
(m, 2H, HCCH), 3.75 (m, 2H, HCCH), 3.49 (dd, JRhH = 1.8
3
3.13 Hz, 1H, HC−P), 2.60 (m, 2H, H2Ccy), 1.97−1.67 (m, 8H,
H2Ccy), 1.70−1.60 (m, 2H, HCcy-P), 1.52−1.20 (m, 10H, H2Ccy).
13C{1H} NMR (100 MHz, CD2Cl2): δ 175.66 (t, JCP = 4.4 Hz, C-O),
76.79 (dd, JCP = 25.0 Hz, 27.9 Hz, C-P), 35.92 (t, JCP = 12.5 Hz, Ccy-
P), 29.53 (s, Ccy), 27.90 (t, JCP = 2.2 Hz, Ccy), 26.82 (m, Ccy), 25.85 (s,
Ccy). 31P {1H} NMR (161 MHz, CD2Cl2): δ 47.57 (s). Anal. Calcd for
C28H48O2P2Ni: C, 62.59; H, 9.00. Found: C, 62.11; H, 9.55. MS (ESI,
methanol/water; m/z+): 537.3 ([C28H49O2P2Ni]+).
Hz, JHH = 3.7 Hz, 1 H, HC−P), 2.36−2.14 (m, 4H, COD H2C),
2.06−1.92 (m, 4H, COD H2C), 1.90−1.79 (m, 2H, HCcy-P), 1.77−
1.56 (m, 10H, H2C), 1.38−1.03 (m, 10H, H2C). 13C{1H} NMR (100
MHz, CD2Cl2): δ 177.35 (d, 2JCP = 15.4 Hz, C-O), 101.64 (dd, J = 8.1
Hz, 10.3 Hz, COD CC trans-P), 78.55 (d, 1JCP = 41.8 Hz, C=C-P),
1
2
66.85 (d, JRhC = 13.2 Hz, COD CC cis-P), 34.01 (dd, JRhC = 1.5
Hz, 3JCP = 24.9 Hz COD CH2), 33.63 (d, 2JRhC = 2.9 Hz, COD CH2),
28.69 (d, JCP = 3.67 Hz, CCy), 28.47 (d, JCP = 1.47 Hz, CCy), 28.35 (s,
CCy), 27.46 (d, JCP = 16.1 Hz, CCy), 27.35 (d, JCP = 13.20 Hz, CCy),
26.80 (d, JCP = 1.47 Hz, CCy). 31P {1H} NMR (161 MHz, CD2Cl2): δ
44.92 (d, 1JRhP = 155.0 Hz). Anal. Calcd for C22H36OPRh: C, 58.67; H,
8.06. Found: C, 57.64; H, 8.10. MS (ESI, methanol/water; m/z+):
451.2 ([C22H37OPRh]+).
(S)-[Ni(Cy2PCH2CHN(CH(Me)(Ph))2][ClO4]2 (2b). A vial was
charged with phosphonium dimer, 1, (70 mg, 0.109 mmol), KOtBu
(25 mg, 0.218 mmol) and acetonitrile (10 mL). The solution was
allowed to stir for 15 min. To this solution [Ni(H2O)6][ClO4]2 (80
mg, 0.218 mmol) was added followed by (S)-(-)-α-methylbenzylamine
(27 mg, 0.218 mmol). The reaction turned orange and was allowed to
stir overnight. The solvent was removed, and the residue was taken up
with MeOH (5 mL). The orange precipitate was isolated and washed
Ir(COD)(OCHCHPCy2) (4b). A vial was charged with dicyclohex-
ylphosphinoaldehyde chloride dimer 1 (26 mg, 0.047 mmol), KOtBu
(10 mg, 0.094 mmol), and toluene (2 mL). The mixture was stirred for
20 min, yielding a white suspension. Cyclooctadiene iridium chloride
dimer (32 mg, 0.047 mmol) was weighed directly into the vial, and
stirred briefly, followed by addition of KOtBu (10 mg, 0.094 mmol).
The dark red solution was stirred at room temperature overnight. The
red solution was filtered through Celite to remove salts and dried in
vacuo to obtain the crude product as a dark red sticky solid. The solid
was washed with a few drops of Et2O several times to yield an orange
solid. The product was recrystallized by slow diffusion of methanol
into a CH2Cl2 solution of the product. Yield: 45% (23 mg). Red
crystals of 4b suitable for X-ray diffraction studies were grown from
1
with diethyl ether (2 × 5 mL). Yield: 55% (57 mg). H NMR (300
MHz, CD2Cl2): δ 8.79 (t, 2H, JHH = 12 Hz, CHN), 7.32−7.62 (m,
10H, HPh), 4.41 (m, 2H, CH(CH3)(Ph)), 3.86 (d, 2H, JHP = 18 Hz,
CH2), 3.34 (m, 2H, CH2), 1.88 (CH3, indirectly determined from
1H-1H COSY), 1.92−0.83 (m, 50H, HCy, CH3). 13C NMR (75 MHz,
CD2Cl2): δ 177.5 (CHN), 139.0 (CPh), 130.2 (CPh), 129.9 (CPh),
128.9 (CPh), 128.5 (CPh), 128.4 (CPh), 68.3 (CH2), 60.9
(CH(Me)(Ph)), 30.3−25.1 (CCy), 21.1 (CH3). 31P NMR (121
MHz, CD2Cl2): δ 72.2. MS (ESI, methanol/water; m/z+): 372.2
[C44H68N2NiP2]2+. Anal. Calcd for C44H68Cl2N2NiO8P2: C, 55.95; H,
7.26; N, 2.97; Found: C, 52.68; H, 7.10; N, 2.83.
1
slow diffusion of methanol into a hexane solution of the product. H
NMR (400 MHz, CD2Cl2): δ 7.54 (dd, 3JHH = 4.1 Hz, 3JHP = 34.0 Hz,
Pt(Cy2PCH2CHO)2Cl2, Pt(Cy2PCH2CHC(CHO)PCy2)Cl2 (3a, 3b).
A vial was charged with dicyclohexylphosphinoaldehyde chloride
dimer 1 (33 mg, 0.060 mmol), KOtBu (13 mg, 0.12 mmol) and
toluene (2 mL). The mixture was stirred for 10 min, yielding a white
suspension. 1,5-Cyclooctadiene dichloroplatinum (23 mg, 0.060
mmol) was weighed directly into the vial, and stirred overnight. The
resulting pale yellow solution was filtered through Celite to remove
salts and dried in vacuo to yield the product as a white solid. Yield:
98% (44 mg).
3
1H, HC−O), 4.60 (m, 2H, COD HCCH), 3.80 (t, JHH = 4.1 Hz,
1H, HC−P), 3.58 (m, 2H, COD HCCH), 2.31−2.16 (m, 2H, HCcy-
P), 2.15−1.13 (m, 28H, H2C). 13C{1H} NMR (100 MHz, CD2Cl2): δ
180.21 (d, 2JCP = 13.2 Hz, C-O), 89.14 (d, 2JCP = 11.7 Hz, COD CC
trans-P), 82.64 (d, 1JCP = 48.4 Hz, CC-P), 50.65 (s, COD CC cis-
P), 34.44 (d, 3JCP = 13.2 Hz, COD CH2), 34.58 (s, COD CH2), 34.02
(s, HCcy-P), 27.36 (d, JCP = 12.5 Hz, Ccy), 27.28 (d, JCP = 11.0 Hz,
Ccy), 26.73 (d, JCP = 1.5 Hz, Ccy). 31P {1H} NMR (161 MHz, CD2Cl2):
δ 37.42 (s). Anal. Calcd for C22H36OPIr: C, 48.96; H, 6.72. Found: C,
48.62; H, 6.94. MS (ESI, methanol/water; m/z+): 541.2
([C22H37OPIr]+).
Through NMR analysis, it was shown that 88% of the recovered
product was the trans-phosphinoaldehyde complex 3a, and 12% was
the cis-aldol condensation product 3b. When the same reaction was
attempted at −78 °C for 1 h, and then slowly warmed to room
temperature, the reaction yielded only 30% 3a and 70% 3b.
Recrystallization in CH2Cl2 and hexanes yielded crystals containing
a molecule of 3a and a molecule of 3b per unit cell.
[Ir(COD)(PhNCHCH2PCy2)][PF6] (5). A vial was charged with
dicyclohexylphosphinoaldehyde bromide dimer (38 mg, 0.060 mmol),
KOtBu (13 mg, 0.116 mmol), aniline (12 mg, 0.129 mmol), and
toluene (2 mL). The mixture was stirred for 30 min, yielding a yellow
solution. Cyclooctadiene iridium chloride dimer (40 mg, 0.060 mmol),
NH4PF6 (20 mg, 0.120 mmol), and methanol (1 mL) were then added
directly into the vial to form a bright red/orange solution. The
solution was stirred at room temperature overnight, and the solvent
removed in vacuo. The resulting red solid was dissolved in cold
CH2Cl2 and filtered through Celite to remove any insoluble salts. The
solvent was removed and washed several times with pentane. The
filtrate was dried in vacuo to yield the product as a red solid. Yield:
1
3
3a: H NMR (300 MHz, CD2Cl2): δ 9.96 (t, JHH = 3.2 Hz, 1H,
HCO), 3.20 (m, 2H, H2C−P), 2.09 (m, 2H, HCcy-P), 1.93−1.15
(m, 20H, H2C). 13C{1H} NMR (100 MHz, CD2Cl2): δ 198.74 (s, C
O), 32.69 (t, JCP = 10.3 Hz, C-PCcy2), 32.30 (t, JCP = 14.7 Hz, P-Ccy),
28.80 (s, Ccy), 28.42 (s, Ccy), 27.32 (m, Ccy), 26.64 (s, Ccy). 31P {1H}
NMR (121 MHz, CD2Cl2): δ 15.40 (s). Anal. Calcd for
C28H50Cl2O2P2Pt: C, 45.04; H, 6.75. Found: C, 45.50; H, 6.84. MS
(DART; m/z+): 710.3 ([C28H50ClO2P2Pt]+).
1
3
1
82% (75 mg). H NMR (400 MHz, CD2Cl2): δ 8.15 (dt, JHH = 2.3
Hz, 3JHP = 22.7 Hz, 1H, HCN), 7.43−7.09 (m, 5H, HPh), 3.83 (br s,
4H, COD CH2), 3.11 (dd, 3JHH = 2.3 Hz, 2JHP = 8.2 Hz, 1H, H2C−P),
2.28−1.23 (m, aliphatic H). 13C{1H} NMR (100 MHz, CD2Cl2): δ
149.76 (s, HCN), 129.03 (s, CPh), 128.06 (s, CPh), 122.82 (s, CPh),
68.95 (bs, COD CC), 35.59 (d, 1JCP = 23.5 Hz, C-P), 35.48 (d, 1JCP
= 22.7 Hz, C-P), 31.89 (s, CH2), 29.30 (s, CH2), 28.82 (s, CH2), 27.26
3b: H NMR (300 MHz, CD2Cl2): δ 9.52 (m, HCO), 7.94 (m,
1H, HCC), 2.98 (m, 4H, H2C−P), 1.93−1.15 (m, 20H, H2C). 31P
{1H} NMR (121 MHz, CD2Cl2): δ 32.88 (d, JPP = 16.9 Hz), 9.91 (d,
JPP = 16.9 Hz).
Rh(COD)(OCHCHPCy2) (4a). A vial was charged with dicyclohex-
ylphosphinoaldehyde chloride dimer 1 (26 mg, 0.047 mmol), KOtBu
(10 mg, 0.094 mmol), and toluene (2 mL). The mixture was stirred for
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(d, JCP = 10.3 Hz, CH2), 26.49 (d, JCP = 1.5 Hz, CH2). 31P {1H} NMR
(161 MHz, CD2Cl2): δ 47.81 (s), −144.38 (septet, J = 711 Hz, PF6).
Anal. Calcd for C28H42F6NP2Ir: C, 44.20; H, 5.56; N, 1.84. Found: C,
41.88; H, 5.57; N, 1.85. (ESI, methanol/water; m/z+): 616.3
([C28H42NPIr]+).
glovebox. The needles were stoppered, and the syringes were taken to
the reactor. The solutions were then injected into the reactor against a
flow of hydrogen gas. The hydrogen gas was adjusted to the desired
pressure (35 bar). Small aliquots of the reaction mixture were quickly
withdrawn with a syringe and needle under a flow of hydrogen at
timed intervals by venting the Parr reactor at reduced pressure.
Alternatively, small aliquots of the reaction mixture were sampled from
a stainless steel sampling dip tube attached to a modified Parr reactor.
The dip tube was 30 cm in length with an inner diameter of 0.01 in.,
and a swing valve was attached to the end of the sampling tube. Three
small aliquots of sample were thereby withdrawn quickly at timed
intervals by opening the swing valve, and the first two aliquots were
discarded. All samples were diluted to a total volume of approximately
2 mL using oxygenated THF prior to GC analyses.
A Perkin-Elmer Clarus 400 chromatograph equipped with a chiral
column (CP chirasil-Dex CB 25 m × 2.5 mm) and an autosampling
capability was used for gas chromatography (GC) analyses. Hydrogen
was used as a mobile phase at a column pressure of 5 psi with a split
flow rate of 50 mL/min. The injector temperature was 250 °C, and the
FID temperature was 275 °C. All of the conversions are reported as an
average of two GC runs. The reported conversions were reproducible.
The substrate, product, oven temperature (T), and the retention
times for the substrate (ts) and product (tp) are as follows:
[Rh(COD)(HONCHCH2PCy2)][PF6] (6a). A vial was charged with
dicyclohexylphosphinoacetaldehyde chloride dimer (33 mg, 0.060
mmol), KOtBu (13 mg, 0.120 mmol), and toluene (2 mL). The
mixture was stirred for 10 min, yielding a white suspension.
Hydroxylammonium chloride (6 mg, 0.080 mmol), KOtBu (9 mg,
0.080 mmol), and methanol (2 mL) were added and stirred for 20
min. Cyclooctadiene rhodium chloride dimer (20 mg, 0.040 mmol)
and NaPF6 (16 mg, 0.094 mmol) were then weighed directly into the
vial forming a yellow solution. The solution was stirred at room
temperature overnight, and the solvent removed in vacuo. The
resulting red solid was dissolved in CH2Cl2 and filtered through Celite
to remove any insoluble salts. The filtrate was dried in vacuo to yield
the product as a yellow solid. Yellow crystals of 6a suitable for X-ray
diffraction studies were grown from slow diffusion of pentane into a
1
CH2Cl2 solution of the product. Yield: 70% (36 mg). H NMR (400
MHz, CD2Cl2): δ 9.17 (bs, 1H, N−OH), 8.00 (m, 1H, HCN), 5.57
(br s, 2H, COD CH2), 4.45 (m, 2H, COD CH2), 2.65 (dd, 3JHH = 2.7
Hz, 2JHP = 8.8 Hz, 1H, H2C−P), 2.47−1.10 (m, aliphatic H). 13C{1H}
NMR (100 MHz, CD2Cl2): δ 164.73 (t, J = 5.1 Hz, CN), 106.38
(dd, J = 7.3 Hz, 8.8 Hz, COD CC), 79.08 (d, 1JRhC = 11.7 Hz, COD
CC), 34.30 (dd, 2JRhC = 1.8 Hz, 1JCP = 21.3 Hz, Ccy-P), 32.55 (d, J =
2.9 Hz, COD CH2), 29.07 (d, J = 2.2 Hz, CH2), 28.80 (d, J = 1.5 Hz,
Cyclooctene, cyclooctane, T = 105 °C, ts = 5.15 min, tp = 5.38 min.
trans-4-Phenyl-3-buten-2-one, 4-phenyl-2-butanone, T = 125 °C, ts
= 21.95 min, tp = 11.42 min.
Stilbene, bibenzyl, T = 200 °C, ts = 5.08 min, tp = 3.73 min.
1
COD CH2), 28.49 (s, CH2), 27.34 (d, JCP = 21.3 Hz, H2C-P), 26.90
(d, J = 11.0 Hz, CH2), 26.28 (d, J = 1.5 Hz, CH2). 31P {1H} NMR (161
MHz, CD2Cl2): δ 50.90 (d, 1JRhP = 149.4 Hz), −144.20 (p, 1JPP = 711
Hz, [PF6]−). Anal. Calcd. for C22H38FNOP2Rh: C, 43.22; H, 6.26; N,
2.29. Found: C, 44.31; H, 5.97; N, 2.43. MS (ESI, methanol/water; m/
z+): 466.2 ([C22H38NOPRh]+).
ASSOCIATED CONTENT
■
S
* Supporting Information
Complete crystallographic data in CIF format for complexes 2a,
2b, 3a, 3b, 4a, 4b, and 6a. This material is available free of
charge via the Internet at http://pubs.acs.org.
[Ir(COD)(HONCHCH2PCy2)][PF6] (6b). A vial was charged with
dicyclohexylphosphinoaldehyde chloride dimer (26 mg, 0.047 mmol),
KOtBu (10 mg, 0.094 mmol), and toluene (2 mL). The mixture was
stirred for 10 min, yielding a white suspension. Hydroxylammonium
chloride (7 mg, 0.094 mmol), KOtBu (10 mg, 0.094 mmol), and
methanol (2 mL) were added and stirred for 20 min. Cyclooctadiene
iridium chloride dimer (31 mg, 0.047 mmol) and NaPF6 (16 mg, 0.094
mmol) were then weighed directly into the vial forming a bright red/
orange solution. The solution was stirred at room temperature
overnight, and the solvent removed in vacuo. The resulting red solid
was dissolved in CH2Cl2 and filtered through Celite to remove any
insoluble salts. The filtrate was dried in vacuo to yield the product as a
red solid. Yield: 97% (46 mg)
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: rmorris@chem.utoronto.ca.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
NSERC Canada is thanked for a Discovery Grant and a
Research Tools Grant to R.H.M.
1H NMR (400 MHz, CD2Cl2): δ 11.07 (bs, 1H, N−OH), 8.71
3
(broad d, JHP = 23.9 Hz, 1H, HCN), 4.97 (broad s, 2H, COD
REFERENCES
3
■
HCCH), 4.29 (broad s, 2H, COD HCCH), 2.78 (d, JHH = 8.0,
2H, H2C−P), 2.31−1.08 (m, aliphatic H). 13C{1H} NMR (100 MHz,
(1) Braunstein, P.; Chauvin, Y.; Nahring, J.; DeCian, A.; Fischer, J.;
̈
2
Tiripicchio, A.; Ugozzoli, F. Organometallics 1996, 15, 5551−5567.
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(3) Noyori, R.; Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66,
7931−7944.
CD2Cl2): δ 188.39 (d, JCP = 6.6 Hz, CN), 90.16 (s, COD CC),
60.31 (s, COD CC), 34.92 (d, 1JCP = 26.4 Hz C-P), 34.57 (d, JCP
=
26.4 Hz, C-P), 32.31 (s, CH2), 28.79 (d, JCP = 2.2 Hz, CH2), 28.74 (s,
CH2), 27.00 (d, JCP = 12.5 Hz, CH2), 26.86 (d, JCP = 11.0 Hz, CH2),
26.26 (d, JCP = 1.5 Hz, CH2). 31P {1H} NMR (161 MHz, CD2Cl2): δ
45.34 (s), −144.41 (p, J = 711 Hz). Anal. Calcd for C22H38FNOP2Ir:
C, 37.71; H, 5.47; N, 2.00. Found: C, 38.94; H, 5.50; N, 2.35. MS
(ESI, methanol/water; m/z+): 556.2 ([C22H38NOPIr]+).
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