Binuclear palladium complexes supported by bridged pincer ligands

Article abstract of DOI:10.1021/om2008056

A series of binucleating ligands each containing two tridentate pincer sites based on a central, monoanionic aryl (C) donor flanked by neutral phosphinito (P) and imino (N) donors, [(PCN)-(CH₂)_n-(PCN)] (1), or a central, monoanionic

Full text of DOI:10.1021/om2008056

Article
pubs.acs.org/Organometallics
Binuclear Palladium Complexes Supported by Bridged Pincer
Ligands
David E. Herbert and Oleg V. Ozerov*
Department of Chemistry, Texas A&M University, College Station, Texas 77842, United States
S
* Supporting Information
ABSTRACT: A series of binucleating ligands each containing two tridentate
pincer sites based on a central, monoanionic aryl (C) donor flanked by neutral
phosphinito (P) and imino (N) donors, [(PCN)-(CH2)n-(PCN)] (1), or a
central, monoanionic amido (N) flanked by neutral phosphine (P) and imino
donors (N), [(PNN)-(CH2)n-(PNN)] (4), are presented. The metalating sites
were linked through the condensation of two equivalents of m-
hydroxybenzaldehyde or the purposively built asymmetric diarylamine
[(H)N(2-C(O)H-4-Me-C6H3)(2-P(iPr)2-4-Me-C6H3)] (3) with primary α,ω-diamines (1,2-diaminoethane, n = 2; 1,4-
diaminobutane, n = 4), which simultaneously constructed the imino arms and bridged the pincer cores. Ligands 1 and 4 were
then used in the synthesis of neutral, square-planar palladium(II) complexes 5 and 6, [(PCN-Cn)Pd2X2, (PNN-Cn)Pd2X2; n = 2,
4; X = Cl, OAc, OTf]. The difference in the trans influence of the central donor was demonstrated through X-ray crystal
structures of 5b-Cl, (PCN-C4)Pd2Cl2, and 6b-Cl, (PNN-C4)Pd2Cl2. The (PNN-Cn)Pd2X2 complexes (6) proved to be redox-
active, presumably via oxidation of the ligand, and cyclic voltammetry illustrated the extent to which electronic communication
between the two pincer sites is mediated by the length of the bridge between them. (PCN-Cn)Pd2OTf2 (5-OTf) and (PNN-
Cn)Pd2OTf2 (6-OTf) complexes reacted with hydride donors such as Et3SiH or β-hydride-containing alkoxides such as NaOiPr
to generate bridging-hydride monocations [(PCN)Pd-H-Pd(PCN)-Cn][OTf] (5-H, n = 2, 4) and [(PNN)Pd-H-Pd(PNN)-
C2][OTf] (6a-H), where the supported Pd−Pd separation was also found to be affected by the bridge length. In the case of the
(CH2)4-bridged (PNN-C4)PdOTf (6b-OTf), a bridging-hydride monocation was not observed. Instead, the formation of
[(PN(H)N)Pd-Pd(PNN)-C4][OTf] (6b-H), protonated at the amido N of the ligand with a direct Pd(I)−Pd(I) bond, was
recorded.
metal centers with the same molecule of substrate. To execute
this general design principle, we envisioned connecting the two
side donors, one in each pincer core, with a flexible and easily
variable linker. We were particularly interested in adapting the
well-known P°COP15 and PNP16,17 pincers for this task. P°COP
and PNP combine neutral phosphine (or phosphinite) L-type
donor “arms” with either an aryl or an amido anionic X-type
central site. However, linking the phosphine or phosphinite
sites would be synthetically difficult. In contrast, an imine as an
L donor seemed well suited to this task because it can be
reliably fabricated from aldehyde (or ketone) starting materials
and α,ω-diamines, available with many different linkers (Figure
1). Here, we report the implementation of this approach and
the exploration of the coordination chemistry of new
binucleating PCN and PNN ligands (Figure 1) with palladium.
The mononuclear PCN (phosphinite-aryl-imino) pincer ligands
have been reported by Gong, Song, and co-workers, but the
design of the PNN ligand (phosphine-diarylamido-imine) is
new in itself.18−20 The binucleating pincer platforms comple-
ment (and are inspired by) the “Pacman” bis(porphyrin)21
design, but are synthetically much more easily accessible and
tunable.
INTRODUCTION
■
Tridentate “pincer” ligands by now represent a ligand archetype
in transition-metal chemistry.1 Metal complexes of these robust,
tunable scaffolds have been used as platforms for studies of
bond activation,2 in the identification of transient intermedi-
ates,3 and to support unusual chemical transformations at both
highly electron-rich4,5 and electron-deficient6 transition-metal
centers. We are interested in the construction of bridged,
binucleating ligands based on pincer frameworks to explore
cooperativity between metal centers.7 Reports of “poly-pincer”
ligands in the literature largely describe systems bridged by rigid
groups,8 designed for coordination polymer synthesis9 or
exploration of electronic communication,10,11 with some
exceptions. Binucleating CNS pincers, derived from thioether-
substituted bis-azobenzenes joined by (CH2)3 units, and their
cyclopalladated Pd(II) complexes were reported by Chakra-
vorty and co-workers.12 Tsubomura et al. prepared a
binucleating macrocyclic ligand that coordinates Pd(II) centers
through the NCN donor atoms of two 2,6-bis(diaminomethyl)-
phenyl units bridged by two flexible (CH2)3 linkers.13 Suess
and Peters recently detailed a series of nitrogen-rich
polydentate ligands containing monoanionic, bis(quinolinyl)-
amide pincer-type binding sites.14 We sought to build
binucleating ligands that bring two metal centers into relative
proximity that may allow for simulatenous interaction of both
Received: August 27, 2011
Published: November 18, 2011
© 2011 American Chemical Society
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Figure 1. Retrosynthetic deconstruction of imine synthesis and the relationship between P°COP/PNP and PCN/PNN pincer motifs.
Scheme 1. Synthesis of (PCN-Cn) and (PNN-Cn) Ligands 1 and 4
single peaks were observed by 31P{1H} NMR spectroscopy at
149.5 and 148.9 ppm.
RESULTS AND DISCUSSION
Ligand Synthesis. Using Fryzuk’s notation22 to describe a
■
A modified strategy was employed in the synthesis of
[(PNN)-(CH2)n-(PNN)] ligands 4a,b (Scheme 1). In this case,
the phosphine arm was first installed by direct formation of a
P−C bond, followed by introduction of the aldehyde
functionality and, in the last step, condensation of two
monophosphinated, benzaldehyde derivatives of di-tolyl-amine
with the desired diamine. First, the monophosphinated
intermediate 2 (δP = −13.8 ppm) was prepared in 79%
isolated yield by reacting bis(2-bromo-4-methylphenyl)amine24
with two equivalents of nBuLi at −40 °C, followed by
quenching the dilithiated intermediate with one equivalent of
iPr2PCl.25 Lithium−halogen exchange and addition of
dimethylformamide gave the desired aldehyde 3 in high
isolated yield (87%; δP = −8.8 ppm). As 2 precipitated from
more concentrated ethereal solutions at lower temperatures,
care was taken to ensure suitable dilution of the reaction
mixture in this step ([2] < 0.05 M). Condensation of two
equivalents of 3 with the respective α,ω-diamines in boiling
toluene led to formation of 4a (81%, δP = −5.8 ppm) and 4b
(87%, δP = −4.6 ppm), which were isolated as yellow solids.
Synthesis of Neutral Bis(Pd-X) Complexes (X = Cl,
OAc, OTf). Forcing conditions (ortho-dichlorobenzene, 160
pincer framework based on the size of the two chelate rings
formed, the identity of the donor atoms, and the overall charge
of the tridentate ligand, we have constructed a series of
binucleating {[5,5]-PCN}− and {[5,6]-PNN}− pincer ligands
bearing phosphino/phosphinito and imino arms flanking
central aryl (C) or amido (N) donors. For the synthesis of
ligand 1, addition of 1,2-diaminoethane or 1,4-diaminobutane
to an acetonitrile solution containing two equivalents of meta-
hydroxybenzaldehyde at room temperature formed the meta-
substituted ligand precursors (1-OH), which precipitated from
solution (Scheme 1).23 These were isolated as moderately
soluble white powders and characterized by 1H NMR
spectroscopy. Reflux of a mixture of the respective m-
hydroxybenzaldimine 1a/b-OH, (iPr)2PCl and a base (Et3N)
in toluene installed the phosphinito arms. The binucleating
[(PCN)-(CH2)n-(PCN)] ligands were isolated following work-
up in decent yields (1a, 69%; 1b, 57%; 95% purity) as colorless
or pale yellow oils, which were further dried in vacuo to remove
residual (iPr)2PCl. In each case, downfield singlet resonances
1
assigned to the two HCN hydrogens were located in the H
NMR spectra of 1a,b at 8.22 and 8.21 ppm, respectively, while
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a
Scheme 2. Synthesis and Reactivity of (PCN-Cn)PdX and (PNN-Cn)PdX Complexes
a
Conditions: (i) 2 equiv Pd(COD)Cl2, 2 equiv 2,6-lutidine, THF, 15 h, 22 °C; (ii) 2 equiv Pd(OAc)2, THF, 1 h, 22 °C.
°C) were necessary for activation of the aryl C(sp2)−H bond in
1 upon reaction with Pd(COD)Cl2 with 2,6-lutidine as the base
in order to generate 5-Cl. Once formed, the (PCN-Cn)Pd2Cl2
complexes were isolated by recrystallization from CH2Cl2/Et2O
as bright yellow solids in moderate yields (Scheme 2: 5a-Cl,
57%; 5b-Cl, 53%). Metalation was accompanied by a downfield
shift in the 31P{1H} NMR signal of the ligands (1a, 149.5; 1b,
148.5 → 5a-Cl, 202.5; 5b-Cl, 202.6 ppm), while when
complexed, the imine HCN proton showed diagnostic
good yields (>70%, Scheme 2). Cleavage of the N−H bond led
1
to the disappearance of the downfield resonance in the H
NMR spectrum assigned to the N-H proton. As electrochemical
studies established the susceptibility of the (PNN-Cn) ligands
to oxidation (vide infra), we sought a synthetic route to the
palladium triflates that did not involve the potentially oxidizing
AgOTf. Me3SiOTf proved capable of abstracting acetate from
6-OAc, and following the reaction in C6H5F, the triflato species
6-OTf were isolated as sparingly soluble, deep purple solids in
good yields.
4
coupling to the trans phosphorus [5a-Cl, 8.38 (d, JHP = 4.8
4
Isomerism of (PNN-Cn)Pd2X2 Complexes. The 1H NMR
spectra of 6 also contained imine proton resonances split into
Hz); 5b-Cl, 8.26 (d, JHP = 5.0 Hz)]. The robustness of the
PCN fragment toward oxidation allowed the use of AgOTf to
exchange chloride in 5a/b-Cl, for less strongly bound triflate
(OTf) in 5a/b-OTf. The multinuclear NMR spectra of 5a/b-
OTf showed only minor differences from the chloride-
containing precursors, with the exception of the appearance
of a signal in the 19F NMR spectrum at −79 ppm (see Table 1).
4
doublets with slightly larger JHP (∼12−13 Hz) than observed
for 5 (Table 1). The 31P{1H} NMR resonances of the
coordinated phosphines were found considerably downfield of
the free ligands and in regions characteristic of the X group
(Table 1: X = Cl, ≈ 71 ppm; X = AcO, = 65−66 ppm; X =
OTf, = 77−78 ppm). The multinuclear NMR spectra of
analytically pure samples of 6 showed two sets of signals in
different ratios depending on the bridge length and the nature
of the X ligand (see Supporting Information). For example,
with the shorter (CH2)2 bridge separating the two (PNN)PdX
halves, an 8:1 ratio was observed by 31P{1H} NMR for 6a-Cl,
while a 5:1 ratio was observed for 6a-OAc in CD2Cl2 at 22 °C.
For the longer (CH2)4-bridged complexes, two peaks were
registered in a more balanced ratio of 1.4:1 for 6b-Cl, while a
single peak was observed in the 31P{1H} NMR spectrum of 6b-
OAc in CD2Cl2 at 22 °C. In C6D5CD3 solution at 22 °C, a ratio
of 2.7:1 (6a-Cl) was observed, while the ratio of the two peaks
observed for 6b-Cl did not change appreciably in C6D5CD3
solution at 22 °C.
Table 1. Selected NMR Data (ppm) for 5-Cl/OTf and 6-Cl/
OAc in CD2Cl2
HCN
HCN
31P{1H}
19F
5a-Cl
5b-Cl
8.38 (d, 4.8 Hz)
8.26 (d, 5.0 Hz)
176.8 (d, 3.8 Hz) 202.5
174.4 (d, 4.3 Hz) 202.6
177.0 (d, 3.9 Hz) 203.2
5a-OTf 8.36 (d, 4.5 Hz)
5b-OTf 8.13 (d, 5.0 Hz)
−78.8
−79.0
173.7 (d, 3.8 Hz) 202.7
a
a
6a-Cl
6b-Cl
7.95 (d, 13.4 Hz) 162.4
71.3 (71.9)
70.8 (70.9)
66.2 (66.8)
65.3
a
7.79 (d, 13.2 Hz) 161.7 (161.4)
a
6a-OAc 7.95 (d, 12.4 Hz) 162.5 (163.9)
6b-OAc 7.66 (d, 12.0 Hz) 161.4 (161.3)
a
Resonances for minor isomer not included.
Variable-temperature NMR spectroscopic studies of 6a-Cl
were used to investigate the stability of the ratio of peaks with
respect to temperature (see Figures SI-2 and SI-3 in the
Supporting Information). At 65 °C, the two resonances in the
31P{1H} NMR spectrum, which were baseline separated at 25
In comparison, activation of the N−H bond in 4 by
Pd(COD)Cl2/2,6-lutidine or [Pd(OAc)2]3 proceeded in a
much more facile manner, and (PNN-Cn)Pd2X2 (X = Cl, OAc)
complexes 6-Cl,OAc formed at 22 °C and were isolated in
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°C, broadened and overlapped. Very broad resonances for both
interconverted) is the “flipping” of the two aromatic rings past
each other, and it is apparently significantly slower in the
{[5,6]-PNN}− pincer complexes than in the {[5,5]-PNP}−
analogues. Rigid, terphenyl-based PCP and NCN systems
1
sets of major and minor peaks were still visible in the H NMR
spectrum. At 85 °C, the resonances for the methyl groups of
the iPr substituents began to coalesce into two broad peaks, and
a single, broad phosphorus resonance was observed. At the
high-temperature limit of the solvent (105 °C), the phosphorus
resonance had sharpened, while the four iPr methyl resonances
collapsed into two broad peaks and a single iPr methine
resonance was observed. The aromatic region (and two methyl
groups of the ligand backbone) contained relatively sharp
signals compared with those assigned to the iPr groups,
including a single doublet for the imino proton (4JHP = 13.2
Hz). Our observations indicate that while the compounds
giving rise to these separate sets of peaks are distinct by NMR
spectroscopy at ambient temperature, the rate of interconver-
sion is too fast for the persistence of the individual compounds
on the time scale of experimental handling.
Figure 3. Representative examples of chiral pincer complexes.
that exhibit atropisomerism have also been reported (Figure
3).26,34
Solid-State Structures of Neutral (PCN-Cn)Pd2X2 and
(PNN-Cn)Pd2X2 Complexes. To examine the arrangement of
the binuclear complexes in the solid state, X-ray crystallo-
graphic studies were undertaken. Yellow, X-ray quality crystals
of 5b-Cl were grown by diffusing Et2O into a CH2Cl2 solution
at room temperature. The two pincer cores are crystallo-
graphically distinct, and each contains a palladium in a typical,
distorted square-planar coordination environment with the
phosphinito and imine arms pulled back slightly to an N−Pd−
P angle of 158°. The bond distances to Pd resemble those of
previously reported mononuclear analogues18 and related
systems.35,19 The Pd−Cl distances [2.359(3) Å] do not
significantly differ from similar {[5,5]-PCP}− PdCl complexes
such as the symmetric bis(phosphinito)aryl compound
(iPrP°COPiPr)PdCl [2.370(2) Å],36 consistent with the strong
trans influence of the central aryl donor. Despite numerous
attempts, issues with crystal twinning prevented structural
characterization of the (CH2)2-bridged derivative 5a-Cl.
The two similar sets of resonances observed for the
coordinated (PNN-Cn) ligands in 6 suggested the presence of
isomers. Although the origin of the isomerism is not yet fully
certain, we tentatively attribute the pairs of resonances to the
presence of diasteromers based on the orientation of the two
aryl rings of the PNN backbone with respect to one another,26
akin to atropisomers such as the representative biaryl binapthyl
systems.27 As each binuclear molecule contains two (PNN)PdX
moieties, if the two orientations within the same molecule are
the same (Figure 2, R,R or S,S), a set of rac confomers lacking
Figure 2. Depictions of the two possible orientations of the aryl rings
of the PNN backbone: R and S. Phosphorus is shown in orange and
nitrogen in blue. Simplified depictions with the chiral axis viewed end-
on used to designate R and S in accordance with binapthyl
atropisomers are shown below, with Cahn−Ingold−Prelog priorities
in parentheses.28
Figure 4. ORTEP of 5b-Cl with thermal ellipsoids shown at the 50%
probability level. Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): Pd(1)−Cl(1) 2.359(2), Pd(1)−
N(1) 2.141(6), Pd(1)−P(1) 2.208(2), Pd(1)−C(1) 1.954(7), N(1)−
C(7) 1.280(10), Pd(2)−Cl(2) 2.359(3), Pd(2)−N(2) 2.152(7),
Pd(2)−P(2) 2.203(2), Pd(2)−C(14) 1.956(8), N(2)−C(12)
1.263(9); N(1)−Pd(1)−P(1) 158.4(2), C(1)−Pd(1)−Cl(1)
177.3(2), N(2)−Pd(2)−P(2) 158.5(2), C(14)−Pd(2)−Cl(2)
177.2(2).
an internal mirror plane can be drawn. Different pairings (R/S
or S/R) would represent the meso confomer.
In contrast, most chiral pincer ligand systems known are
based on m-xylyl {(5,5)-ECE}− pincer frameworks and carry
their stereogenic centers on the arms, not the backbone, of the
ligand.29 These are typically incorporated via an auxiliary chiral
site20,30 and include substituents exhibiting axial chirality.31
Other positions available for generating stereogenic centers are
the benzylic methylene groups or the two −ER1R2 donor arms
when the substituents on E differ (E = N, P; R1 ≠ R2).32 While
diarylamido-based pincer complexes are generally C2-symmetric
in the solid state, bis(phosphine)diarylamido (PNP)PdX
complexes are all C2v-symmetric in solution, even at low
temperatures.33 The process by which the configuration of a
single pincer site can be inverted (and thus the diastereomers
For comparison, structural determinations of (PNN-Cn)Pd
compounds 6-Cl and 6a-OAc were carried out on block-shaped
red crystals grown from 1:4 C6H6/pentane mixtures at 0 °C.
Each asymmetric unit contains one pincer core or half of a
molecule. As can be seen in Figures 5 and 6, in both 6a-Cl and
6a-OAc, the C2-bridged bimetallic pincer folds back on itself in
the solid state, whereas 6b-Cl is fully extended, similar to the
structure of 5b-Cl. Each pincer core contains a palladium in
distorted square-planar geometry, with typical ligand−metal
distances.17 6a-Cl and 6a-OAc crystallized in the space group
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Figure 5. ORTEPs of 6a-Cl and 6b-Cl with ellipsoids shown at the 50% probability level. Hydrogens and solvent molecule (1/2 C6H6, 6b-Cl) are
omitted for clarity. Selected bond distances (Å) and angles (deg): 6a-Cl: Pd(1)−N(1) 2.013(2), Pd(1)−N(2) 2.091(2), Pd(1)−P(1) 2.2233(9),
Pd(1)−Cl(1) 2.321(1), C(15)−N(2) 1.282(2); N(1)−Pd(1)−Cl(1) 174.93(4), N(2)−Pd(1)−P(1) 168.69(4). 6b-Cl: Pd(1)−N(1) 2.018(2),
Pd(1)−N(2) 2.093(2), Pd(1)−P(1) 2.2189(9), Pd(1)−C(1) 2.3197(9), C(21)−N(2) 1.273(3); N(1)−Pd(1)−Cl(1) 174.17(6), N(2)−Pd(1)−
P(1) 171.57(6).
five-membered rings once bound to a metal, the {(5,6)-PNN}−
core forms both a five- and six-membered ring. Accordingly, the
P−Pd−N angles are relaxed compared with those in 5b-Cl
[168.69(4)° (6a-Cl), 171.57(6)° (6b-Cl), and 171.8(1)° (6b-
OAc), respectively], but not as much as in the (NNN)PdCl
complex we recently reported [176.77(17) Å], which contained
a {(6,6)-NNN}− pincer.37 The central amido donor would be
expected to exert less of a trans influence on the chloride in 6-
Cl than an aryl donor, and the shorter Pd−Cl distances reflect
this [6a-Cl, 2.321(1) Å; 6b-Cl, 2.3197(9) Å; 5b-Cl, 2.359(2)
Å].
Anodic Electrochemistry of (PNN-Cn)Pd2X2 Com-
plexes. Inspired by the similarity between the (PNN) pincer
cores in 6-Cl and the known redox-active bis(phosphine)-
diarylamido (PNP) ligand (PNP = N[2-P(iPr)2-4-methylphen-
Figure 6. ORTEP of 6a-OAc with ellipsoids shown at the 50%
probability level. Hydrogens are omitted for clarity. Selected bond
yl]2),38 we decided to probe the oxidation of 6-Cl using cyclic
voltammetry in CH2Cl2 at ambient temperature. The anodic
region of the voltammogram of 6a-Cl shows two well-separated
one-electron oxidation steps. The current response of each
peak depended linearly on ν1/2, indicating reversible, diffusion-
controlled redox events. Figure 7 shows cyclic voltammograms
of approximately equimolar amounts of 6a-Cl and 6b-Cl in
CH2Cl2. The current response of 6b-Cl (Figure 7, right) is
twice as large as the individual peaks evident in the CV of 6a-Cl
(Figure 7, left), as both pincer cores in 6b-Cl were oxidized at
overlapping potentials. Mixed-valence Ru(II)/Ru(III) com-
plexes supported by {(5,5}-PCP)− pincer ligands have been
distances (Å) and angles (deg): Pd(1)−P(1) 2.224(1), Pd(1)−N(1)
1.986(4), Pd(1)−N(2) 2.073(3), Pd(1)−O(1) 2.069(4), N(2)−
C(23) 1.285(6); P(1)−Pd(1)−N(2) 171.8(1), N(1)−Pd(1)−O(1)
176.4(2).
C2/c as a mixture of rac isomers, (S,S, shown in Figures 5 and
6) and (R,R), as the molecule does not contain the center of
crystallographic symmetry. 6b-Cl crystallized as the meso
isomers (R,S) and (S,R) with the center of crystallographic
symmetry coinciding with the center of symmetry of the
molecule. Unlike the {(5,5)-PCN}− ligands, which form two
Figure 7. Cyclic voltammograms of 6a-Cl (left) and 6b-Cl (right) in CH2Cl2 at 22 °C. The scan rate was 100 mV/s in the positive direction. The
concentration of analyte was [6a-Cl] = 3.0 × 10−3 M; [6b-Cl] = 3.5 × 10−3 M, respectively, with 0.3 M nBu4NPF6 as supporting electrolyte.
Measured potentials: 6a-Cl, E1/2 = 0.09, 0.30 V; 6b-Cl, E1/2 = 0.11 V.
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reported where electronic communication is mediated by a
rigid, π-conjugated link joining the two cyclometalated
fragments.11 In comparison, the short, saturated hydrocarbon
bridge in 6a-Cl simply brings the two pincer cores close enough
that the second oxidation occurred at a higher potential due to
Columbic repulsion and a two-wave pattern results. It is not
clear whether the stacking of the two pincer cores observed in
the solid-state structure of 6a-Cl plays a special role in the
apparent communication between the two oxidation sites. The
(PCN-Cn) complexes 5-Cl did not exhibit any electrochemical
response in the anodic region under the same conditions (−1.5
to 1.5 V vs [(C5H5)2Fe]/[(C5H5)2Fe]+), which supports the
notion of ligand-based redox events in 6-Cl.
reflective of the differences between the structure of the Pd−
H−Pd cores resulting from the relative flexibility imparted by
the different hydrocarbon bridge lengths, as further discussed
below. Complexes with hydrides bridging two palladium
centers have been reported.43−47 Examples involving Pd(II)
centers include “A-frame” complexes with the metal−metal
distance predictated by bridging bis(phosphine) ligands.44,48,49
The reduction of Pd(II) complexes to form binuclear
compounds,43 clusters,47 or chains46 containing reduced Pd(I
or 0) centers is also common. In 5-H, the hydride (H−) bridges
two Pd(II) centers. Alternatively, this may be viewed as a Pd−
H bond serving as a 2e− donor to a pincer-supported Pd+.39
Either formulation involves two Pd(II) centers.
Formation of Cationic Bridging Hydride Complexes.
We next investigated the possibility of using a binucleating
pincer platform to prepare complexes with metal centers in
electronically different environments, for example, combining
an electrophilic metal center on one side with a metal hydride
on the other. Upon addition of one equivalent of NaOiPr to
CD2Cl2 solutions of 5-OTf, the production of acetone was
Addition of one equivalent of Et3SiH to a fluorobenzene
solution of the Pd-OTf 6a-OTf at 22 °C caused the color of the
solution to change drastically from purple to a deep green over
a 15 min period (Scheme 4). The green color (λmax = 632 nm)
Scheme 4. Formation of the Bridging-Hydride-Containing
Monocation 6a-H
1
noted in the appearance of a singlet in the H NMR spectrum
at 2.12 ppm (CD2Cl2). This was accompanied by a downfield
shift in the 31P{1H} NMR to 207 ppm and the growth of a
triplet far upfield in the hydride region of the 1H NMR
spectrum (J = 13.5 Hz). The generation of acetone and the
appearance of a palladium-bound hydride in a symmetric
molecule (one set of ligand resonances was observed) is
consistent with iPrO− having displaced OTf at Pd, followed by
β-hydride elimination or intramolecular abstraction of a hydride
from [Pd]-OiPr and collapse of the two palladium cores to
form a symmetric bridging-hydride 5-H (Scheme 3).39 In the
is distinct from the typical orange-yellow of known (PNP)PdH
complexes.17 Only a single set of ligand resonances was
1
observed by H and 31P{1H} NMR spectroscopy (δP = 83.4
ppm), suggesting the presence of a single isomer in solution. In
addition, a triplet was registered in the hydride region of the 1H
NMR spectrum (δH = −20.08 ppm, J = 15.2 Hz). This
suggested that, as in the formation of 5-H, a hydride had been
abstracted by one of the palladium centers of 6a-OTf. This may
have occurred via generation of a mixed Pd-H/Pd-OTf complex
wherein displacement of the second triflate by the Pd-H led to
the bridging-hydride monocationic 6a-H. The 19F NMR
spectrum of the isolated product contained an appropriately
upfield-shifted resonance for the now outer-sphere OTf
counterion (δF = −80.2 ppm). The protons of the (CH2)2
bridge in 6a-H are diastereotopic, and two broadened doublets
were observed. The two methine protons and all four methyl
groups of each phosphine arm are chemically inequivalent. The
imino arm of each pincer core is still bound to a metal center,
and a single doublet for the imino proton was observed slightly
upfield at 7.70 ppm and showed coupling to phosphorus (4JHP
=12.5 Hz). As for 5a-H, the IR spectrum of 6a-H contained a
broad absorption in the expected region (1735 cm−1). Addition
of a second equivalent of Et3SiH left 6a-H unaffected.
Scheme 3. Reactivity of 5a/b-OTf
formation of 5-H, the pincer framework likely retards β-hydride
elimination at the isopropoxide-bound metal center, as has
been demonstrated for (PNP)Pd alkyls and alkoxides.40
Therefore, in the reaction of 5-OTf with NaOiPr, it is possible
that β-hydride elimination is a binuclear process, with the
second palladium abstracting a hydride from a coordinated
OiPr. Alternatively, the hydride may be transferred to Pd
directly from an external isopropoxide, without the inter-
mediate formation of a Pd−O bond.41
The 19F NMR spectra of 5-H showed a slightly upfield-
shifted resonance of an outer-sphere triflate (−80 ppm).
Interestingly, a broad absorption corresponding to the bridging
hydride was observed in the expected region42 of the IR
spectrum of 5a-H (1702 cm−1), while only a very weak
absorption was observed for 5b-H (1713 cm−1). This is likely
Solid-State Structures of Cationic Bridging-Hydride
Complexes. Single crystals of 5-H and 6a-H were studied by
X-ray diffraction, and the solid-state structures exhibited
interesting differences (Figures 8 and 9). The shorter (CH2)2
Table 2. Selected NMR Data (ppm) for Bridging Hydrides 5-H and 6a-H in CD2Cl2
HCN
HCN
31P{1H}
19F
Pd-H-Pd
5a-H
5b-H
6a-H
8.32 (d, 4.0 Hz)
8.34 (d, 4.0 Hz)
7.70 (d, 12.5 Hz)
178.3 (d, 3.3 Hz)
178.7 (d, 3.3 Hz)
161.7
207.1
207.5
83.4
−79.8
−79.7
−80.2
−9.19 (t, 13.5 Hz)
−8.42 (t, 13.5 Hz)
−20.08 (t, 15.2 Hz)
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Figure 8. ORTEP of 5a-H and one of two ion pairs in the asymmetric unit of 5b-H with thermal ellipsoids shown at the 50% probability level. With
the exception of H(1), hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): 5a-H: Pd(1)−Pd(2) 3.2612(12),
Pd(1)−P(1), 2.220(2), Pd(2)−P(2) 2.219(2), Pd(1)−N(1) 2.153(5), Pd(2)−N(2) 2.125(5), Pd(1)−C(1) 1.988(6), Pd(2)−C(12) 1.980(6),
N(1)−C(7) 1.285(8), N(2)−C(21) 1.306(8), Pd(1)−H(1) 1.66, Pd(1)−H(2) 1.98; C(1)−Pd(1)−Pd(2) 166.5(2), C(12)−Pd(2)−Pd(1)
166.0(2), N(1)−Pd(1)−P(1) 156.7(2), N(2)−Pd(2)−P(2) 157.4(2). 5b-H: Pd(1)−Pd(2) 2.9602(8), Pd(1)−P(1) 2.208(1), Pd(2)−P(2)
2.220(1), Pd(1)−N(1) 2.172(4), Pd(2)−N(2) 2.152(3), Pd(1)−C(1) 1.987(4), Pd(2)−C(20) 1.978(4), N(1)−C(13) 1.287(6), N(2)−C(18)
1.285(5), Pd(1)−H(1) 1.79, Pd(1)−H(2) 1.58; C(1)−Pd(1)−Pd(2) 157.2(1), C(20)−Pd(2)−Pd(1) 154.6(1), N(1)−Pd(1)−P(1) 156.5(1),
N(2)−Pd(2)−P(2) 157.2(1).
“clam-shell”,51 and related bridged Pd(II) dimers.52 While, like
in 5b-H and 6a-H, such systems exhibit Pd−Pd separations
shorter than sum of the van der Waals radii (3.26 Å),53 there
has been no agreement on the definitive presence of a metal−
metal bond,54 although in some acetate-bridged “clam-shell”
complexes, d8−d8 Pd−Pd bonding interactions have been
identified by computational analysis.51
Aberrant Reactivity of C4-Bridged (PNN)2Pd2(OTf)2
(6b-OTf). Unlike in the formation of 6a-H, the addition of
1−3 equivalents of Et3SiH led to complex mixtures. The deep-
green product (6b-H, λmax = 604 nm) isolated from the
addition of four equivalents of Et3SiH to a fluorobenzene
Figure 9. ORTEP of 6a-H with ellipsoids shown at the 50%
solution of the C4-bridged triflato species 6b-OTf did not
probability level. Hydrogens are omitted for clarity. Selected bond
1
contain a hydride resonance in the H NMR. The product
distances (Å) and angles (deg): Pd(1)−Pd(2) 2.9774(8), N(3)−
Pd(1), 2.035(3), N(4)−Pd(2) 2.033(3), N(5)−Pd(1) 2.092(3),
N(6)−Pd(2) 2.085(3), P(1)−Pd(1) 2.2269(12), P(2)−Pd(2)
2.2196(12), Pd(1)−H(1) 1.63, Pd(2)−H(1) 1.64; N(5)−Pd(1)−
P(1) 169.1(1), N(3)−Pd(1)−Pd(2) 170.0(1), N(6)−Pd(2)−P(2)
167.89(10), N(4)−Pd(2)−Pd(1) 170.09(10).
exhibited an upfield-shifted 19F NMR signal (δF = −79.9 ppm),
suggesting a cationic product with a triflate counterion;
however the two phosphines were observed to be inequivalent
by 31P{1H} NMR spectroscopy and showed weak coupling to
3
3
one another [δP = 64.2 (d, JPP = 5 Hz), 49.6 ppm (d, JPP = 5
Hz)], indicating a compound with two inequivalent pincer
cores. The combination of a new downfield resonance in the
1H NMR spectrum (9.7 ppm) and a broad peak at 3152 cm−1
in the IR spectrum of 6b-H indicated protonation at nitrogen.
bridge in 5a-H prevented overly close approach of the two
metal centers, and the Pd−Pd distance is quite long, at
3.2612(12) Å. Conversely, the longer (CH2)4 bridge allowed
for a much closer Pd−Pd interaction of 2.9602(8) and
2.9710(8) Å for the two molecules in the asymmetric unit of
5b-H. The more flexible {(5,6)-PNN}− pincer core in 6a-H
(with the imino arm forming a six-membered ring when bound
to the metal) enabled the two palladium centers to approach
more closely than in the (CH2)2-bridged PCN analogue 5a-H.
Indeed, the Pd−Pd distance in 6a-H [2.9774(8) Å] is only
slightly longer than in the C4-bridged 5b-H [2.9602(8) Å]. All
three supported Pd−Pd distances are long compared with that
of the formally (PNP)Pd(I)−Pd(I)(PNP) dimer, [(PNP)Pd]2,
2.5758(4) Å,4 and other compounds with unambiguous Pd(I)−
Pd(I) bonds.50 6a-H crystallized in the orthorhombic space
group Pbca as a mixture of rac isomers (R,R) and (S,S, shown in
Figure 9).
1
Careful integration of the H NMR spectrum revealed the
presence of two more hydrogens than would be expected for a
bridging-hydride complex analogous to 6a-H, or its isomer.
Scheme 5. Proposed H-Migration and Formation of a Pd−
Pd Bond with Concomitant Reduction of One Imine Arm in
the Formation of 6b-H
The bridging-hydride structures may alternatively be viewed
as having protonated Pd(I)−Pd(I) bonds. The collective bond
distances are comparable with those found in A-frame
[Pd2R2(μ-H)(μ-dppm)2]+ cations (∼2.93−3.08 Å),44,49 open
An X-ray diffraction study of single crystals grown from
fluorobenzene allowed us to establish the molecular structure of
6b-H (Figure 10). The two Pd centers are connected by a
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EXPERIMENTAL SECTION
■
Unless otherwise noted, all procedures were carried out under argon in
a glovebox or using standard Schlenk techniques. Me3SiOSO2CF3
(Gelest), 3-hydroxybenzaldehyde (Alfa Aesar), 1,2-diaminoethane and
1,4-diaminobutane (Aldrich), and [Pd(OAc)2]3 (Strem) were
purchased and used without special purification. Mesitylene and
xylenes were deoxygenated by four freeze−pump−thaw cycles prior to
use. 2,6-Lutidine (Aldrich) was dried over CaH2 under Ar. Bis(2-
bromo-4-methylphenyl)amine24 and Pd(COD)Cl2 were prepared
56
according to published procedures. Solvents were dried and distilled
from an appropriate drying agent (NaK/Ph2CO or CaH2) and
deoxygenated prior to use. NMR spectra were recorded on a Mercury
1
300 MHz, Inova 300 MHz, or Inova 500 MHz spectrometer. H and
13C{1H} NMR spectra were referenced to residual solvent peaks.57 1H
NMR in C6D5Br were referenced setting the most upfield signal to
7.00 ppm.58 31P{1H} and 19F spectra were externally referenced to
H3PO4 (85%, 0 ppm) and CF3COOH (−78.5 ppm). 13C NMR
Figure 10. ORTEP of 6b-H with ellipsoids shown at the 50%
probability level. One of two ion pairs in the asymmetric unit is shown;
hydrogens and fluorobenzene solvent molecules are omitted for clarity.
Selected bond distances (Å) and angles (deg): Pd(3)−Pd(4)
2.5578(12), Pd(3)−P(3) 2.214(2), Pd(4)−P(4) 2.223(2), Pd(3)−
N(5) 2.241(6), Pd(3)−N(6) 2.150(7), Pd(4)−N(7) 2.104(6),
Pd(4)−N(8) 2.086(7), C(61)−N(6) 1.512(10), C(66)−N(8)
1.278(9); N(5)−Pd(3)−Pd(4) 177.5(2), N(7)−Pd(4)−Pd(3)
175.0(2), N(6)−Pd(3)−P(3) 172.9(2), N(8)−Pd(4)−P(4) 168.0(2).
1
spectra were assigned with the help of 13C DEPT experiments. H
1
NMR spectra were assigned using selective H{31P} decoupling and
1H−1H COSY experiments. Elemental analyses were performed by
CALI Laboratories, Parsippany, NJ. FT-IR spectra were collected using
a Bruker ALPHA-P FT-IR spectrometer with a diamond ATR.
Cyclic voltammetry was carried out using a CH Instruments model
700D Series electrochemical analyzer/workstation in conjunction with
a three-electrode cell. The working electrode was a CHI 104 glassy
carbon disk (3.0 mm diameter), and the auxiliary electrode a platinum
wire. The reference electrode was a Ag/AgNO3 electrode separated
from the test solution by a fine-porosity frit and 0.3 M nBuPF6
solution. CVs were conducted in solutions of CH2Cl2 with 0.3 M
NBu4PF6 as supporting electrolyte at scan rates of 100 mV/s. The
direct bond; the Pd−Pd distance of 2.5578(12) Å is
comparable to that in the (PNP)Pd−Pd(PNP) dimer.4 The
two “halves” of 6b-H are indeed distinct. Hydrogenation of the
one imine arm was evident in the lengthened N−C bond
[N(6)−C(61) 1.511(11) Å] compared with the other [N(8)−
C(66) 1.285(10) Å], while both N(5) and N(6) exhibited
pronounced pyramidalization (Figure 10). The now protonated
diarylamine N(5)-H is engaged in a hydrogen bond with O(2)
of a nearby triflate counterion [N(5)···O(2) 2.930(9) Å;
N(5)−H···O(2) 161°]. The product of the addition of H2
across the N−Pd bond of (PNP)PdOTf, [(PN(H)P)PdH]-
[OTf] also contains a protonated diarylamido PN(H)P ligand,
which in the solid state is similarly engaged in a hydrogen bond
with a triflate anion [N···O 2.833(6) Å; N−H···O 172(4)°].55
Reduction of the imine arms was also noted when 6-Cl was
treated with borohydride reducing agents such as NaBH4 or
LiBEt3H, followed by decomposition to unidentified products.
If the bridging-hydride complexes 5a-H, 5b-H, and 6a-H may
be formally viewed as products of protonation of a Pd(I)−
Pd(I) bond, 6b-H can be instead regarded as a product of
protonation of a Pd(I)−Pd(I) complex at the N atom of the
amido ligand.
concentration of analyte was 3.0 × 10−3 M (6a-Cl) and 3.5 × 10−3
M
(6b-Cl), respectively. CVs were referenced to the Fe(η5-C5H5)2/
Fe(η5-C5H5)2 redox couple using Fe(η5-C5Me5)2/Fe(η5-C5Me5)2 as
+
+
an internal standard and whose redox potential was measured to be
−0.53 V vs Fe(η5-C5H5)2/Fe(η5-C5H5)2 . No electrochemical
+
response was measured for 5-Cl under the same conditions.
Synthesis of 1a-OH. 1,2-Diaminoethane (1.10 mL, 16.4 mmol)
was added by syringe to a stirring solution of 3-hydroxybenzaldehyde
(4.00 g, 32.7 mmol) in 50 mL of acetonitrile. After ∼5 min, a white
precipitate formed. The suspension was stirred at room temperature
for an additional 45 min. The solid was then collected on a ground
glass frit and washed with 3 × 50 mL of cold acetonitrile. Isolated yield
= 3.97 g (91%). The solid is soluble in dimethylsulfoxide or acetone.
1H NMR (DMSO-d6, 300 MHz, 22 °C): δ 9.32 (br, OH), 8.23 (s, 2H,
HCN), 7.21 (m, 2H, Ar CH), 7.10 (m, 4H, Ar CH), 6.82 (m, 2H,
Ar CH), 3.83 ppm (s, 4H, CH2). 13C{1H} NMR (DMSO-d6, 75 MHz,
22 °C): δ 162.0 (HCN), 157.6 (COH), 137.5 (Ar CH), 129.7 (Ar
CH), 119.3 (Ar CH), 117.8 (Ar CH), 113.6 (Ar CH), 60.9 ppm
(CH2).
Synthesis of 1a: PCN-C2. The bridged m-hydroxybenzaldimine
1a-OH (1.93 g, 7.19 mmol), triethylamine (2.10 mL, 15.1 mmol), and
diisopropylchlorophosphine (2.40 mL, 15.1 mmol) were combined in
toluene (10 mL) and heated at reflux for 4 h. The solution was
pumped dry, extracted with pentane/diethyl ether, and filtered over a
short plug of silica to give a colorless oil. Isolated yield = 2.47 g (69%).
1H NMR (CDCl3, 300 MHz, 22 °C): δ 8.22 (s, 2H, HCN), 7.42 (br
s, 2H, Ar CH), 7.28 (overlapped with solvent, Ar CH), 7.24 (br, 2H,
Ar CH), 7.16 (m, 2H, Ar CH), 3.93 (s, 4H, CH2), 1.90 (m, 4H, iPr
CHMe2), 1.14 (dd, J = 10.8, 7.1 Hz, 12H, iPr CHMe), 1.07 ppm (dd, J
= 16.0, 7.2 Hz, 12H, iPr CHMe). 13C{1H} NMR (CDCl3, 75 MHz, 22
°C): δ 162.4 (HCN), 159.7 (d, J = 9.0 Hz, CO), 137.7 (Ar CH),
129.5 (Ar CH), 121.6 (Ar CH), 120.7 (d, J = 11.6 Hz, Ar CH), 118.0
(d, J = 9.5 Hz, Ar CH), 61.7 (CH2), 28.4 (d, J = 17.6 Hz, iPr CHMe),
17.81 (d, J = 20.2 Hz, iPr CHMe), 17.1 ppm (d, J = 8.5 Hz, iPr
CHMe). 31P{1H} NMR (CDCl3, 121 MHz, 22 °C): δ 149.5 ppm (s).
Synthesis of 1b-OH. This was prepared in a similar fashion to 1a-
OH. 1,2-Diaminobutane (1.65 mL, 16.4 mmol) was added by syringe
to a stirring solution of 3-hydroxybenzaldehyde (4.00 g, 32.7 mmol) in
50 mL of acetonitrile. Isolated yield of m-hydroxybenzaldimine = 4.25
CONCLUSION
■
A series of binucleating pincer ligands and their palladium
complexes have been prepared and fully characterized. The
bridge length separating the two metal cores modulates their
electronic communication, as observed by cyclic voltammetry,
and influences their reactivity. The formation of bridging-
hydride monocations from the respective bimetallic triflato
species was investigated, and the resultant metal−metal
distance was also found to be dictated by the bridge length.
In one case, the flexibility imparted by the long four-carbon
bridge allowed the two palladium centers to approach one
another close enough to form a direct metal−metal bond upon
deprotonation of the presumed bridging-hydride intermediate
by an opportunistic amide. Current investigations further
examining cooperative reactivity between two metal centers are
ongoing.
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1
g (87%). H NMR (DMSO-d6, 300 MHz, 22 °C): δ 8.23 (s, 2H,
Synthesis of 4a: PN(H)N-C2. 1,2-Diaminoethane (0.0293 mL,
0.437 mmol) was added to a solution of 6 (0.300 g, 0.879 mmol) in
toluene (10 mL) and refluxed for 20 h. The mixture was then pumped
dry, and the product extracted with CH2Cl2, passed through a short
plug of silica, and redried. The pale yellow solid was recrystallized from
HCN), 7.21−7.12 (m, 6H, Ar CH), 6.84 (dd, JHH = 2.7, 0.9 Hz, 2H,
Ar CH), 3.56 (s, 4H, CH2), 1.64 ppm (s, 4H, CH2). 13C{1H} NMR
(DMSO-d6, 75 MHz, 22 °C): δ 160.7 (HCN), 157.7 (COH), 137.6
(Ar CH), 129.7 (Ar CH), 119.3 (Ar CH), 117.8 (Ar CH), 113.7 (Ar
CH), 60.3 (CH2), 28.4 ppm (CH2).
1
CH2Cl2/pentane at −35 °C. Isolated yield = 0.251 g (81%). H NMR
Synthesis of 1b: PCN-C4. This was prepared in a similar fashion
to 1a, using triethylamine (0.988 mL, 7.09 mmol), diisopropylchlor-
ophosphine (1.13 mL, 7.09 mmol), C4-bis-m-hydroxybenzaldimine
(1.00 g, 3.37 mmol), 10 mL of toluene. Isolated yield of 2 = 1.19 g
(67%). 1H NMR (CDCl3, 300 MHz, 22 °C): δ 8.21 (s, 2H, HCN),
7.43 (m, 2H, Ar CH), 7.30 (m overlapped with solvent, 4H, Ar CH),
7.16 (m, 2H, Ar CH), 3.63 (br, 4H, NCH2) 1.91 (m, 4H, iPr CHMe),
1.76 (br m, 4H, CH2), 1.15 (dd, J = 10.8, 6.9 Hz, 12H, iPr CHMe),
1.07 ppm (dd, J = 16.0, 7.3 Hz, 12H, iPr CHMe). 13C{1H} NMR
(CDCl3, 75 MHz, 22 °C): δ 160.9 (HCN), 159.8 (d, J = 8.7 Hz,
CO), 137.8 (Ar CH), 129.6 (Ar CH), 121.5 (Ar CH), 120.7 (d, J =
11.42 Hz, Ar CH), 118.1 (d, J = 9.1 Hz, Ar CH), 61.6 (NCH2), 28.7
(d, J = 19.0 Hz, iPr CHMe), 28.3 (CH2), 17.9 (d, J = 20.2 Hz, iPr
CHMe), 17.2 ppm (d, J = 8.5 Hz, iPr CHMe). 31P{1H} NMR (CDCl3,
121 MHz, 22 °C): δ 148.9 ppm (s).
Synthesis of 2. A solution of bis(2-bromo-4-methylphenyl)amine
(5.46 g, 15.4 mmol) in diethyl ether (160 mL) was cooled to −40 °C,
and nBuLi (12.30 mL, 30.8 mmol; 2.5 M in hexanes) was added
portionwise. The reaction was warmed to room temperature over 1 h
and stirred for an additional 15 min. iPr2PCl (2.45 mL, 15.4 mmol)
was added dropwise at 0 °C. After 15 h of stirring, the mixture was
quenched with 5 mL of degassed 1:1 ethanol/water, stirred for 1 h,
dried, extracted with 35 mL of an ether/pentane mixture (6:1), filtered
over Celite, and redried. The off-white solid was washed with 3 × 5
mL portions of cold pentane to leave a crystalline, white solid. Yield =
4.76 g (79%). 1H NMR (C6D6, 500 MHz, 22 °C): 7.69 (d, J = 9.7 Hz,
1H, NH), 7.23 (overlapping m, 3H, Ar CH), 7.17 (overlapped with
solvent, 1H, Ar CH), 6.90 (d, J = 8.7 Hz, 1H), 6.71 (d, J = 8.7 Hz, 1H,
Ar CH), 2.18 (s, 3H, CH3), 1.96 (m overlapped with methyl, J = 6.8,
1.7 Hz, 2H, iPr CHMe), 1.93 (s, 3H, CH3), 1.06 (ddd J = 15.4, 7.0 Hz,
6H, iPr CHMe), 0.92 ppm (dd, J = 11.7, 6.9 Hz, 6H, iPr CHMe).
13C{1H} NMR (C6D6, 126 MHz, 22 °C): δ 146.1 (d, J = 18.7 Hz, CP),
139.7 (CBr), 133.9 (Ar CH), 133.8 (d, J = 2.3 Hz, Ar CH), 131.0
(CMe), 130.7 (Ar CH), 130.0 (CMe), 128.9 (Ar CH), 123.6 (d, J =
16.1 Hz, CN), 118.5 (d, J = 2.6 Hz, Ar CH), 116.5 (Ar CH), 114.0
(CN), 23.2 (d, J = 11.2 Hz, iPr CHMe), 21.0 (CH3), 20.4 (CH3), 20.2
(d, J = 9.8 Hz, iPr CHMe), 19.0 ppm (d, J = 8.8 Hz, iPr CHMe).
31P{1H} NMR (C6D6, 202 MHz, 22 °C): δ −13.8 ppm (s).
Synthesis of 3. Two equivalents of nBuLi (2.24 mL, 5.60 mmol;
2.5 M solution in hexanes) was added dropwise to a solution of 2
(1.00 g, 2.55 mmol) in diethyl ether (50 mL) at 0 °C (ice bath). The
cooling bath was then removed, and the mixture was stirred for 2 h.
The cooling bath was replaced, and dimethylformamide (0.59 mL,
7.62 mmol) was added dropwise by syringe. The solution turned
orange over the course of 1 h and was stirred at room temperature for
12 h. Ethanol and water (1:1, 10 mL) were added, and stirring was
continued for 2 h. The flask was dried in vacuo, and the resulting
orange solid extracted with 20 mL of THF and 5 mL of CH2Cl2, which
was passed through a plug of silica to give a bright yellow solution,
which upon drying gave a similarly colored solid. Yield = 0.837 g
(87%). 1H NMR (C6D6, 500 MHz, 22 °C): δ 10.69 (br d, J = 4.1 Hz,
1H, NH), 9.72 (s, 1H, (O)CH), 7.31 (dd, J = 8.0, 4.1 Hz, 1H, Ar CH),
7.26 (m, J = 2.4 Hz, 1H, Ar CH), 7.07 (d, J = 8.1 Hz, 1H, Ar CH),
6.91 (dd, J = 8.2, 2.1 Hz, 1H, Ar CH), 6.84−6.80 (overlapping m, 2H,
Ar CH), 2.17 (s, 3H, CH3), 1.99 (m, 2H, iPr CHMe), 1.97 (s
overlapped with CH, 3H, CH3), 1.08 (dd, J = 15.0, 7.2 Hz, 6H, iPr
CHMe), 0.93 ppm (dd, J = 11.6, 6.8 Hz, 6H, iPr CHMe). 13C{1H}
NMR (C6D6, 126 MHz, 22 °C): δ 193.5 ((O)CH), 146.3 (CC(O)H),
143.7 (d, J = 20.6 Hz, CP), 136.5 (Ar CH), 136.2 (Ar CH), 134.5 (Ar
CH), 133.1 (Ar C), 130.4 (Ar CH), 129.8 (d, J = 21.3 Hz, Ar C), 125.8
(Ar C), 124.1 (d, J = 2.6 Hz, Ar CH), 120.5 (Ar C), 113.4 (Ar CH),
23.5 (d, J = 14.3 Hz, iPr CHMe), 21.1 (CH3), 20.3 (d, J = 19.4 Hz, iPr
CHMe), 20.0 (CH3), 19.2 ppm (d, J = 9.9 Hz, iPr CHMe). 31P{1H}
NMR (C6D6, 202 MHz, 22 °C): δ −8.8 ppm (s).
(C6D6, 500 MHz, 22 °C): δ 11.44 (d, J = 3.4 Hz, 2H, NH), 8.37 (s,
2H, HCN), 7.42 (dd, J = 8.2, 4.0 Hz, 2H, Ar CH), 7.30 (br, 2H, Ar
CH), 7.24 (d, J = 9.1 Hz, 2H, Ar CH), 6.90 (dd, J = 8.5, 1.1 Hz, 2H, Ar
CH), 6.81−6.79 (overlapped m, 4H, Ar CH), 4.07 (s, 4H, CH2), 2.20
(s, 6H, CH3), 2.09 (m overlapped with Me, 4H, iPr CHMe), 2.05 (s,
6H, CH3), 1.14 (dd, J = 14.9, 7.0 Hz, 12H, iPr CHMe), 1.01 ppm (dd,
J = 11.7, 7.2 Hz, 12H, iPr CHMe). 13C{1H} NMR (C6D6, 126 MHz,
22 °C): δ 165.6 (HCN), 145.4 (d, J = 19.9 Hz, CP), 144.6 (Ar C),
134.5 (Ar CH), 131.7 (Ar CH), 131.5 (Ar C), 130.4 (Ar CH), 128.3
(Ar C), 125.5 (Ar C), 122.9 (two peaks overlapped Ar CH), 119.8 (Ar
C), 113.5 (Ar CH), 61.8 (CH2), 23.6 (d, J = 14.0 Hz, iPr CHMe), 21.1
(CH3), 20.7 (d, J = 19.3 Hz, iPr CHMe), 20.3 (CH3), 19.6 ppm (d, J =
9.9 Hz, iPr CHMe). 31P{1H} NMR (CDCl3, 202 MHz, 22 °C): δ −5.8
ppm (br s).
Synthesis of 4b: PN(H)N-C4. The procedure was like that for 4a
using 1,2-diaminobutane (0.221 mL, 2.20 mmol) and 6 (1.50 g, 4.40
mmol) in toluene. Isolated yield of pale yellow solid = 1.405 g (87%).
1H NMR (CDCl3, 500 MHz, 22 °C): δ 10.70 (d, J = 3.2 Hz, 2H, NH),
8.28 (s, 2H, HCN), 7.29 (dd, J = 8.2, 3.9 Hz, 2H, Ar CH), 7.22 (m
overlapped with solvent, 2H, Ar CH), 7.05 (dd, J = 8.1, 1.9 Hz, 2H, Ar
CH), 7.01 (d, J = 1.9 Hz, 2H, Ar CH), 6.96 (d, J = 8.4 Hz, 2H, Ar
CH), 6.91 (dd, J = 8.4, 1.6 Hz, 2H, Ar CH), 3.60 (br, 4H, CH2), 2.31
(s, 6H, CH3), 2.23 (s, 6H, CH3), 2.08 (m, 4H, iPr CHMe), 1.81 (br,
4H, CH2), 1.05 (dd, J = 14.9, 7.0 Hz, 12H, iPr CHMe), 0.89 ppm (dd,
J = 11.6, 6.8 Hz, 12H, iPr CHMe). 13C{1H} NMR (CDCl3, 126 MHz,
22 °C): δ 163.5 (HCN), 144.6 (d, J = 19.3 Hz, CP), 144.3 (Ar C),
134.6 (d, J = 2.7 Hz, Ar CH), 133.8 (Ar CH), 131.8 (d, J = 2.0 Hz, Ar
C), 131.3 (Ar CH), 130.0 (Ar CH), 128.9 (d, J = 19.2 Hz, Ar CH),
125.4 (Ar C), 123.2 (d, J = 3.1 Hz, Ar CH), 119.1 (Ar C), 113.4 (Ar
C), 61.7 (CH2), 28.9 (CH2), 23.4 (d, J = 13.0 Hz, iPr CHMe), 21.1
(CH3), 20.5 (CH3), 20.4 (iPr CHMe), 19.5 ppm (d, J = 10.3 Hz, iPr
CHMe). 31P{1H} NMR (CDCl3, 202 MHz, 22 °C): δ −4.6 ppm (br
s).
Synthesis of 5a-Cl: (PCN-C2)PdCl. A solution of 1a (0.323 g,
0.645 mmol) in 10 mL of ortho-dichlorobenzene was added to a
suspension of Pd(COD)Cl2 (0.368 g, 1.29 mmol) and 2,6-lutidine
(0.149 mL, 1.29 mmol) in 5 mL of the same. The mixture was heated
at reflux for 30 min. Cooling the mixture led to the formation of a pale
yellow precipitate, which was collected, washed with diethyl ether (3 ×
50 mL), and extracted with dichloromethane. A yellow powder was
precipitated from solution upon addition of diethyl ether, collected,
redissolved in dichloromethane, and passed through a plug of silica.
Concentration and recrystallization from dichloromethane/diethyl
1
ether at −20 °C yielded pale yellow crystals (0.287 g, 57%). H NMR
4
(CD2Cl2, 300 MHz, 22 °C): δ 8.38 (d, JHP = 4.8 Hz, 2H, HCN),
6.94 (m, 4H, Ar CH), 6.75 (dt, J = 7.4, 1.3 Hz, 2H, Ar CH), 4.40 (br,
4H, CH2), 2.43 (m, 4H, iPr CHMe), 1.38 (dd, J = 19.3, 7.3 Hz, iPr
CHMe), 1.28 ppm (dd, J = 16.2, 7.0 Hz, iPr CHMe). 13C{1H} NMR
(CD2Cl2, 75 MHz, 22 °C): δ 176.8 (d, J = 3.8 Hz, HCN), 163.6 (d,
J = 6.2 Hz, CO), 153.0 (CPd), 145.8 (CCN), 126.7 (Ar CH), 122.2
(Ar CH), 114.3 (d, J = 15.6 Hz, Ar CH), 58.4 (CH2), 29.5 (d, J = 25.5
Hz, iPr CHMe), 17.5 (d, J = 5.8 Hz, iPr CHMe), 16.9 ppm (iPr
CHMe). 31P{1H} NMR (CD2Cl2, 121 MHz, 22 °C): δ 202.5 ppm (s).
Anal. Calcd for C28H40Cl2N2O2P2Pd2: C, 42.99; H, 5.15; N, 3.58.
Found: C, 42.95; H 5.08; N, 3.49. Mp: 191 °C.
Synthesis of 5b-Cl: (PCN-C4)PdCl. The synthesis was like that
for 5a-Cl using Pd(COD)Cl2 (0.304 g, 1.06 mmol), 1b (0.281 g, 0.532
mmol), and 2,6-lutidine (0.123 mL, 1.06 mmol). Isolated yield = 0.229
g (53%). 1H NMR (CD2Cl2, 500 MHz, 22 °C): δ 8.26 (d, J = 5.0 Hz,
2H, HCN), 7.04 (d, J = 7.0 Hz, 2H, Ar CH), 7.17 (app t, J = 7.5 Hz,
2H, Ar CH), 6.78 (d, J = 7.5 Hz, 2H, Ar CH), 3.80 (br m, 4H, CH2),
2.42 (m, 4H, iPr CHMe), 1.94 (m, 4H, CH2), 1.37 (dd, J = 19.5, 7.5
Hz, 12H, iPr CHMe), 1.29 ppm (dd, J = 16.5, 7.0 Hz). 13C{1H} NMR
(CD2Cl2, 126 MHz, 22 °C): δ 174.4 (d, J = 4.3 Hz, HCN), 163.7
6649
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Organometallics
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(d, J = 6.3 Hz, CO), 153.1 (CPd), 146.6 (CCN), 126.6 (Ar CH),
122.2 (Ar CH), 114.0 (d, J = 15.6 Hz, Ar CH), 58.5 (CH2), 29.6 (d, J
= 25.3 Hz, iPr CHMe), 27.6 (CH2), 17.5 (d, J = 5.8 Hz, iPr CHMe),
16.9 ppm (iPr CHMe). 31P{1H} NMR (CD2Cl2, 202 MHz, 22 °C): δ
202.6 ppm (s). Anal. Calcd for C30H44Cl2N2O2P2Pd2: C, 44.46; H,
5.47; N, 3.46. Found: C, 44.56; H 5.44; N, 3.54. Mp: 203 °C.
Synthesis of 5a-OTf: (PCN-C2)PdOTf. Solid silver trifluorome-
thanesulfonate (AgOTf: 0.066 g, 0.256 mmol) was added to a bright
yellow solution of 5a-Cl (0.100 g, 0.128 mmol in 10 mL of a ∼3:1
mixture of C6H5F/CH2Cl2). After 15 min of vigorous stirring, a white
suspension had formed. After 1 h, the mixture was filtered and
pumped to dryness, and the product was extracted with toluene,
filtered over Celite, and dried to give a white powder, which was
stand for 1 h. After warming to room temperature, the solution was
dried in vacuo, extracted with CH2Cl2, filtered over a short plug of
Celite, and redried. The resulting tan solid was washed with Et2O (3 ×
1 mL) and dried. X-ray quality crystals were grown from CH2Cl2/Et2O
1
at −30 °C. Isolated yield = 31.9 g (90%). H NMR (CD2Cl2, 499
MHz, 22 °C): δ 8.34 (d, J = 4.0 Hz, 2H, HCN), 7.20 (overlapped d,
J = 5.5 Hz, 2H, Ar CH), 7.17 (overlapped dd, J = 7.0, 5.5 Hz, 2H, Ar
CH), 6.95 (d, J = 7.0 Hz, 2H, Ar CH), 4.40 (br m, 2H, CH2), 3.62 (br
m, 2H, CH2), 2.50−2.43 (overlapped m, 4H, CH2 and iPr CHMe),
2.32 (h, J = 7.5 Hz, 2H, iPr CHMe), 1.90 (br m, 2H, CH2), 1.37 (dd, J
= 15.0, 7.0, 6H, iPr CHMe), 1.34−1.30 (overlapped m, 12H, iPr
CHMe), 1.23 (dd, J = 17.2, 6.7 Hz, 6H, iPr CHMe), −8.42 ppm (t,
2JHP = 13.5 Hz, 1H, Pd-H-Pd). 13C{1H} (CD2Cl2, 126 MHz, 22 °C): δ
178.7 (d, JCP = 3.3 Hz, HCN), 162.6 (d, JCP = 5.5 Hz, Ar C), 157.9
1
recrystallized from pentane/toluene. Yield = 0.110 g (85%). H NMR
4
(CD2Cl2, 500 MHz, 22 °C): δ 8.36 (d, JHP = 4.5 Hz, 2H, HCN),
(Ar C), 146.5 (Ar C), 128.5 (Ar CH), 122.9 (Ar CH), 115.0 (d, JCP
=
7.08 (d, J = 8.0 Hz, 2H, Ar CH), 7.04 (dd, J = 7.5, 6.5 Hz, 2H, Ar CH),
6.79 (d, J = 8.0 Hz, 2H, Ar CH), 4.11 (s, 4H, CH2), 2.59 (m, 4H, iPr
CHMe), 1.38 (dd, J = 20.5, 7.5 Hz, 12H, iPr CHMe), 1.28 ppm (dd, J
= 15.5, 7.0 Hz, 12 H, iPr CHMe). 13C{1H} NMR (CD2Cl2, 126 MHz,
22 °C): 176.9 (d, J = 3.9 Hz, HCN), 164.3 (d, J = 6.2 Hz, CO),
146.2 (d, J = 3.1 Hz, CPd), 145.8 (CCN), 127.9 (Ar CH), 123.6 (Ar
CH), 115.4 (d, J = 14.6 Hz, Ar CH), 58.0 (CH2), 29.5 (d, J = 25.2 Hz,
iPr CHMe), 17.7 (d, J = 6.0 Hz, iPr CHMe), 16.8 ppm (d, J = 2.3 Hz,
iPr CHMe). 31P{1H} NMR (CD2Cl2, 202 MHz, 22 °C): δ 203.2 (s)
ppm. 19F NMR (CD2Cl2, 470 MHz, 22 °C): δ −78.8 (s) ppm. Anal.
Calcd for C30H40F6N2O8P2Pd2S2: C, 35.69; H, 3.99; N, 2.77. Found:
C, 35.55; H 3.75; N, 2.63.
15.7 Hz, Ar CH), 62.3 (NCH2), 30.7 (d, JCP = 26.7 Hz, iPr CHMe),
30.3 (d, JCP = 27.1 Hz, iPr CHMe), 27.1 (CH2), 18.7 (d, JCP = 7.3 Hz,
iPr CHMe), 18.6 (d, JCP = 2.8 Hz, iPr CHMe), 16.1 ppm (d, JCP = 4.1
Hz, iPr CHMe). 31P{1H} NMR (CD2Cl2, 121 MHz, 22 °C): δ 207.5
ppm. 19F NMR (CD2Cl2, 282 MHz, 22 °C): δ −79.7 ppm. UV−vis
(CH2Cl2): λ (ε) shoulder at 360 nm (6090 M−1 cm−1). Anal. Calcd for
C31H45F3N2O5P2Pd2S1: C, 41.86; H, 5.10; N, 3.15. Found: C, 41.78;
H, 5.26; N, 2.99.
Synthesis of 6a-Cl: (PNN-C2)PdCl. In a 50 mL Schlenk flask, 4a
(0.0492 g, 0.0696 mmol), Pd(COD)Cl2 (0.0397 g, 0.139 mmol), and
2,6-lutidine (16.1 mL, 0.139 mmol) were dissolved in THF (10 mL).
The mixture was stirred at room temperature for 15 h. The orange
suspension turned a deep wine-red. The reaction mixture was dried,
and the residue was extracted and passed through a short plug of silica
using CH2Cl2 and dried in vacuo. The resulting dark red solid was
recrystallized from benzene/pentane. Isolated yield = 0.056 g (81%).
1H NMR (CD2Cl2, 500 MHz, 22 °C): δ 7.95 (d, J = 13.4 Hz, 2H,
HCN), 7.93 (shoulder, minor HCN), 7.31 (m, minor CH), 7.20
(m, minor CH), 7.09 (overlapped m, minor CH), 7.07 (overlapped d,
J = 8.7 Hz, 2H, Ar CH), 7.05 (overlapped d, J = 13.0 Hz, 2H, Ar CH),
6.98 (overlapped m, minor CH), 6.84 (m, minor CH), 6.71 (br t, J =
7.6 Hz, 4H, Ar CH), 6.37 (s, 4H, Ar CH), 5.11 (d, J = 6.9 Hz, 2H,
CH2), 4.71 (br, minor CH2), 4.22 (br, minor CH2), 4.02 (d, J = 6.8
Hz, 2H, CH2), 2.75 (h, J = 6.7 Hz, 2H, iPr CHMe), 2.37 (overlapped
m, minor iPr CHMe), 2.31 (overlapped m, 2H, iPr CHMe), 2.27
(overlapped s, 6H, CH3), 2.11 (s, minor CH3), 1.96 (s, 6H, CH3), 1.58
(overlapped dd, J = 16.8, 6.6 Hz, iPr CHMe), 1.52 (overlapped dd, J =
16.5, 7.3 Hz, iPr CHMe), 1.44−1.34 (overlapped m, minor iPr
CHMe), 1.29 (dd, J = 18.2, 7.0 Hz, iPr CHMe), 1.24−1.18 (m, minor
iPr CHMe), 1.15 ppm (dd, J = 15.6, 6.7 Hz, iPr CHMe). 13C{1H}
NMR (CD2Cl2, 126 MHz, 22 °C): δ (major isomer) 162.4 (HCN),
162.2 (d, J = 19.9 Hz, CN), 149.6 (br, Ar CP), 134.5 (d, J = 2.8 Hz, Ar
CH), 133.5 (Ar CH), 132.8 (Ar CH), 131.0 (Ar CH), 128.7 (Ar C),
125.8 (Ar C), 121.2 (d, J = 14.3 Hz, Ar CH), 120.1 (Ar C), 119.7 (Ar
C), 118.2 (Ar CH), 60.4 (CH2), 27.0 (d, J = 24.1 Hz, iPr CHMe), 23.5
(d, J = 30.4 Hz, iPr CHMe), 20.5 (CH3), 20.1 (iPr CHMe), 19.0 (d, J
= 3.9 Hz, iPr CHMe), 18.6 (CH3), 17.9 (iPr CHMe), 17.6 ppm (iPr
CHMe). 31P{1H} NMR (CD2Cl2, 202 MHz, 22 °C): δ 71.9 (s, minor),
71.3 ppm (s, major, 8:1 ratio). UV−vis (C6H5F): λ (ε) 336 (16 320),
440 (6650), 531 nm (8850 M−1 cm−1). Anal. Calcd for
C44H58N4Cl2P2Pd2: C, 53.45; H, 5.91; N, 5.67. Found: C, 53.57; H,
6.02; N, 5.63. Mp: 280 °C (dec).
Synthesis of 5b-OTf: (PCN-C4)PdOTf. The synthesis was like
that for 5a-OTf, using AgOTf (0.250 g, 0.975 mmol), 5b-Cl (0.395 g,
0.487 mmol), and CH2Cl2 (10 mL). Isolated yield = 0.442 g (87%).
4
1H NMR (CD2Cl2, 500 MHz, 22 °C): δ 8.13 (d, JHP = 5.0 Hz, 2H,
HCN), 7.07 (m, 4H, Ar CH), 6.79 (d, J = 7.0 Hz, 2H, Ar CH), 3.71
(br, 4H, CH2), 2.57 (m, 4H, iPr CHMe), 1.84 (br, 4H, CH2), 1.36
(dd, J = 20.0, 7.0 Hz, 12H, iPr CHMe), 1.28 ppm (dd, J = 16.0, 7.0 Hz,
12 H, iPr CHMe). 13C{1H} NMR (CD2Cl2, 126 MHz, 22 °C): δ 173.7
(d, J = 3.8 Hz, HCN), 164.3 (d, J = 5.4 Hz, CO), 146.3 (CCHN),
146.1 (d, J = 3.1 Hz, CPd), 127.7 (Ar CH), 123.1 (Ar CH), 114.9 (d, J
= 15.3 Hz, Ar CH), 59.1 (NCH2), 29.5 (d, J = 24.5 Hz, iPr CHMe),
27.2 (CH2), 17.7 (d, J = 6.2 Hz, iPr CHMe), 16.8 ppm (d, J = 2.3 Hz,
iPr CHMe). 31P{1H} NMR (CD2Cl2, 202 MHz, 22 °C): δ 202.7 (s)
ppm. 19F NMR (CD2Cl2, 470 MHz, 22 °C): δ −79.0 (s) ppm. Anal.
Calcd for C32H44F6N2O8P2Pd2S2: C, 37.04; H, 4.27; N, 2.70. Found:
C, 36.93; H 4.07; N, 2.49.
Synthesis of 5a-H: [(PCN)Pd-H-Pd(PCN)-C2][OTf]. Solid
NaOiPr (0.0080 g, 0.097 mmol) was added in two portions to a
rapidly stirring dichloromethane solution of 5a-OTf (0.0970 g, 0.0961
mmol; 5 mL) at room temperature, which darkened from light yellow
to orange-brown. The mixture was stirred for 1 h, and an aliquot was
checked by 31P NMR to ensure complete conversion to 5a-H. The
solution was then filtered over a short plug of Celite, dried in vacuo,
and washed with 3 × 2 mL of Et2O. The remaining pale tan solid was
dried again in vacuo. Isolated yield = 0.0562 g (68%). X-ray quality
crystals were grown from CH2Cl2/Et2O at −30 °C. 1H NMR
4
(CD2Cl2, 499 MHz, 22 °C): δ 8.32 (d, JHP = 4.0 Hz, 2H, HCN),
7.20 (d, J = 7.0 Hz, 2H, Ar CH), 7.16 (t, J = 7.7 Hz, 2H, Ar CH), 6.93
(d, J = 7.5 Hz, 2H, Ar CH), 4.12 (br, 4H, CH2), 2.32 (br m, 4H, iPr
CHMe), 1.33 (dd, J = 7.5, 2.0 Hz, 12H, iPr CHMe), 1.30 (pseudo t, J
= 6.5 Hz, 12H, iPr CHMe), −9.19 ppm (t, J = 13.5 Hz, 1H, Pd-H-Pd).
13C{1H} (CD2Cl2, 126 MHz, 22 °C): δ 178.3 (d, J = 3.3 Hz, HCN),
162.9 (d, J = 6.2 Hz, Ar C), 158.2 (Ar C), 146.5 (Ar C), 128.4 (Ar
CH), 123.2 (Ar CH), 115.1 (d, J = 15.3 Hz, Ar CH), 64.6 (CH2), 30.6
(d, J = 26.9 Hz, iPr CHMe), 18.7 ppm (d, J = 4.9 Hz, iPr CHMe).
31P{1H} NMR (CD2Cl2, 202 MHz, 22 °C): δ 207.1 ppm. 19F NMR
(CD2Cl2, 470 MHz, 22 °C): δ −79.8 ppm. UV−vis (CH2Cl2): λ (ε)
shoulder at 370 nm (6420 M−1cm−1). Anal. Calcd for
C29H41F3N2O5P2Pd2S1: C, 40.43; H, 4.80; N, 3.25. Found: C, 40.35;
H, 4.81; N, 3.09.
Synthesis of 6b-Cl: (PNN-C4)PdCl. The procedure/workup was
like that for 6a-Cl, using 4b (0.203 g, 0.276 mmol), Pd(COD)Cl2
(0.158 g, 0.553 mmol), and 2,6-lutidine (64 μL, 0.55 mmol). Isolated
1
yield = 0.204 g (72%). H NMR (CD2Cl2, 500 MHz, 22 °C): δ 7.79
(d, J = 13.2 Hz, 2H, major HCN), 7.72 (d, J = 13.2 Hz, minor
HCN, 1:1.4 ratio), 7.29−7.26 (overlapped m, 2H, Ar CH), 7.15−
7.04 (overlapped m, 4H, Ar CH), 6.95−6.90 (overlapped, 4H, Ar
CH), 6.85 (overlapped d, J = 8.4 Hz, 2H, major Ar CH), 6.84
(overlapped d, J = 8.4 Hz, minor Ar CH), 4.76 (br, 2H, major CH2),
4.63 (br, minor CH2), 3.35 (br, 2H, major CH2), 3.28 (br, 2H, minor
CH2), 2.71 (m, 2H, iPr CHMe), 2.31 (m, 2H, iPr CHMe), 2.26 (br s,
CH3), 2.18 (s, CH3), 2.00 (overlapped br, 4H, major CH2), 1.92 (br,
minor CH2), 1.47 (m, minor iPr CHMe), 1.43 (m, minor iPr CHMe),
Synthesis of 5b-H: [(PCN)Pd-H-Pd(PCN)-C4][OTf]. A precooled
THF solution of NaOiPr (0.0065 g, 0.079 mmol; 5 mL) was added to
a solution of 5b-OTf (0.0412 g, 0.0397 mmol) at −30 °C and left to
6650
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1.39 (m, minor iPr CHMe), 1.33 (dd, J = 18.1, 6.4 Hz, 12H, iPr
CHMe), 1.18 ppm (dd, J = 15.3, 6.8 Hz, 12H, iPr CHMe). 13C{1H}
NMR (CD2Cl2, 126 MHz, 22 °C): δ 162.6 (d, J = 19.8 Hz, CN), 161.7
(major HCN), 161.4 (minor HCN), 149.7 (Ar CP), 134.5 (major
Ar CH), 134.3 (minor Ar CH), 133.9 (Ar CH), 132.9 (Ar CH), 131.5
(Ar CH), 129.2 (Ar C), 126.0 (Ar C), 125.9 (Ar C), 120.9 (d, J = 13.9
Hz, Ar CH), 120.5 (major Ar C), 120.2 (minor Ar C), 118.6
(overlapped minor Ar CH), 118.5 (overlapped major Ar CH), 60.11
(minor CH2), 59.6 (major CH2), 29.6 (minor CH2), 29.2 (major
CH2), 27.0 (d, J = 25.5 Hz, iPr CHMe), 23.8 (d, J = 30.4 Hz, iPr
CHMe), 20.5 (minor CH3), 20.1 (major CH3), 18.9 (d, J = 3.2 Hz,
major iPr CHMe), 18.17 (minor iPr CHMe), 18.11 (minor iPr
CHMe), 18.0 (minor iPr CHMe, signal for fourth Me group
overlapped), 17.7 ppm (major iPr CHMe). 31P{1H} NMR (CD2Cl2,
202 MHz, 22 °C): δ 70.9 (overlapped s, minor), 70.8 ppm
(overlapped s, major 1:1.4 ratio). UV−vis (C6H5F): λ (ε) 337 (15
180), 435 (5640), 529 nm (6840 M−1 cm−1). Anal. Calcd for
C46H62N4Cl2P2Pd2: C, 54.34; H, 6.15; N, 5.51. Found: C, 54.13; H,
5.99; N, 5.09. Mp: 171 °C.
7.32 (dd, J = 8.0, 3.5 Hz, 2H, Ar CH), 7.12 (m, 2H, Ar CH), 6.97 (d, J
= 8.0 Hz, 2H, Ar CH), 6.91 (m, 4H, Ar CH), 6.86 (d, J = 8.5 Hz, 2H,
Ar CH), 4.09 (br, 2H, CH2), 3.27 (br, 2H, CH2), 2.62 (m, 2H, iPr
CHMe), 2.36 (m, 2H, iPr CHMe), 2.25 (s, 6H, CH3), 2.18 (s, 6H,
CH3), 2.01 (br, 2H, CH2) 1.91 (s, 3H, −OC(O)CH3), 1.86 (s, 3H,
−OC(O)CH3), 1.80 (br, 2H, CH2) 1.32−1.22 (overlapped m, 18H,
iPr CHMe), 1.15 ppm (dd, J = 14.0, 7.0 Hz, 6H, iPr CHMe). 13C{1H}
NMR (CD2Cl2, 126 MHz, 22 °C): δ 177.1 (overlapped, CO), 162.8
(Ar C), 162.7 (Ar C), 161.4 (HCN), 161.3 (HCN), 149.6 (Ar C),
134.4 (Ar CH), 134.0 (Ar CH), 132.8 (overlapped, Ar CH), 131.7 (Ar
CH), 129.4 (Ar C), 128.9 (Ar C), 128.8 (Ar C), 128.5 (Ar C), 126.0
(Ar C), 125.6 (m, Ar C), 120.5 (Ar CH), 120.4 (Ar CH), 119.9 (Ar C),
119.5 (Ar C), 119.3 (Ar CH), 59.6 (NCH2), 59.5 (NCH2), 29.6
1
(CH2), 26.9 (d, JCP = 23.0 Hz, iPr CHMe), 23.5 (overlapped, AcO
Me), 23.4 (overlapped, AcO Me), 21.8 (d, 1JCP = 28.0 Hz, iPr CHMe),
20.5 (CH3), 20.1 (CH3), 19.1 (d, J = 3.8 Hz, iPr CHMe), 18.5 (d, J =
3.3 Hz, iPr CHMe), 16.5 (iPr CHMe), 16.4 ppm (iPr CHMe). 31P{1H}
NMR (CD2Cl2, 202 MHz, 22 °C): δ 65.3 ppm (s). UV−vis (C6H5F):
λ (ε) 336 (11 330), 427 (3640), 521 nm (6620 M−1 cm−1). Anal.
Calcd for C50H68N4O4P2Pd2: C, 56.45; H, 6.44; N, 5.27. Found: C,
56.37; H, 6.54; N, 5.16. Mp: 189 °C.
Synthesis of 6a-OAc: (PNN-C2)PdOAc. Solid [Pd(OAc)2]3
(0.129 g, 0.574 mmol of Pd) was added to a solution of 4a (0.203
g, 0.287 mmol) in THF (10 mL). The color immediately changed
from light yellow to wine-red. The solution was stirred for 1 h at room
temperature, then dried in vacuo. The crude product was redissolved
in a minimal amount of C6H5F, filtered over Celite, and dried. The
resulting solid was recrystallized from C6H6/pentane to give a wine-
Synthesis of 6a-OTf: (PNN-C2)PdOTf. Me3SiOTf (80 mL, 0.45
mmol) was added to a solution of 6a-OAc (0.230 g, 0.222 mmol) in
C6H5F (15 mL). The mixture was stirred for 4 h at room temperature
and dried in vacuo. The resulting purple powder was suspended in
1
Et2O and collected by filtration. Isolated yield = 0.237 g (88%). H
1
red solid. Isolated yield = 0.272 g (91%). H NMR (CD2Cl2, 500
NMR (C6D6, 300 MHz, 22 °C, peaks for major isomer reported): δ
3
4
MHz, 22 °C): δ 7.95 (d, JHP = 12.4 Hz, 2H, major HCN), 7.91
7.81 (d, JHP = 13.2 Hz, 2H, HCN), 7.11 (d, J = 9.0 Hz, 2H, Ar
(overlapped d, minor HCN), 7.33 (d, J = 8.2 Hz, minor Ar CH),
7.18 (d, J = 8.2 Hz, minor Ar CH), 7.10 (d, J = 8.6 Hz, 2H, major Ar
CH), 7.00 (overlapped m, J = 7.9 Hz, minor Ar CH), 6.96 (d, J = 8.6
Hz, 2H, major Ar CH), 6.83 (overlapped m, minor Ar CH), 6.70
(apparent t, J = 10.1 Hz, 4H, major Ar CH), 6.42 (m, J = 3.7 Hz, 2H,
major Ar CH), 6.36 (s, 2H, major Ar CH), 4.53 (d, J = 6.6 Hz, 2H,
major CH2), 4.31 (m, minor CH2), 3.90 (br m, d, J = 6.6 Hz in
1H{31P}, 2H, major CH2), 3.81 (m, minor CH2), 2.59 (overlapped m,
h, J = 6.9 Hz in 1H{31P}, 2H, major iPr CHMe), 2.43 (overlapped m,
CH), 6.69 (br d, J = 8.4 Hz, 2H, Ar CH), 6.53 (overlapped d, J = 8.1
Hz, 1H, Ar CH), 6.53 (overlapped d, J = 9.0 Hz, 1H, Ar CH), 6.43 (br
d, J = 8.4 Hz, 2H, Ar CH), 6.23 (d, J = 3.9 Hz, 1H, Ar CH), 6.20 (d, J
= 3.6 Hz, 1H, Ar CH), 6.01 (d, J = 1.8 Hz, 2H, Ar CH), 5.15 (m, J =
7.8 Hz, 2H, CH2), 4.12 (m, J = 7.5 Hz, 2H, CH2), 2.72 (m, 2H, iPr
CH), 2.06 (s, overlapped, 6H, Me), 2.02 (m, overlapped, 2H, iPr CH),
1.79 (s, 6H, Me), 1.39 (dd, J = 16.5, 6.9 Hz, 6H, iPr CHMe), 1.23 (dd,
overlapped, J = 18.6, 6.9 Hz, 6H, iPr CHMe), 1.17 (dd, overlapped, J =
20.1, 6.9 Hz, 6H, iPr CHMe), 0.72 ppm (dd, J = 14.1, 6.6 Hz, 6H, iPr
CHMe). 13C{1H} NMR (C6D6, 126 MHz, 22 °C, peaks for major
isomer reported): δ 162.6 (Ar), 162.1 (d, J = 19.2 Hz, HCN), 149.1
(Ar), 134.8 (Ar), 133.9 (Ar), 132.9 (Ar), 131.1 (Ar), 129.1 (d, J = 7.7
Hz, Ar), 126.8 (d, J = 24.6 Hz, Ar), 121.6 (d, J = 13.8 Hz, Ar), 119.2
(Ar), 118.9 (Ar), 118.5 (Ar), 60.4 (CH2), 26.2 (d, J = 23.0 Hz, iPr
CHMe), 22.4 (d, J = 27.6 Hz, iPr CHMe), 20.3 (CH3), 20.1 (CH3),
19.3 (d, J = 3.8 Hz, iPr CHMe), 19.2 (d, J = 3.0 Hz, iPr CHMe), 16.7
(d, J = 2.3 Hz, iPr CHMe), 16.0 ppm (d, J = 6.9 Hz, iPr CHMe).
31P{1H} NMR (C6D6, 202 MHz, 22 °C): δ 72.5 (major, 12:1 ratio),
74.1 ppm (minor). 19F NMR (C6D6, 202 MHz, 22 °C): δ −77.9
(major), −78.1 ppm (minor). UV−vis (C6H5F): λ (ε) 329 (10 950),
446 (5650), 534 nm (4180 M−1 cm−1). Anal. Calcd for
C46H58F6N4O6P2Pd2S2: C, 45.44; H, 4.81; N, 4.61. Found: C, 45.32;
H, 4.69; N, 4.59.
1
h, J = 6.9 Hz in H{31P}, 2H, major iPr CHMe), 2.25 (s overlapped
with m of minor iPr CHMe, 6H, CH3), 2.08 (s, minor CH3), 1.97 (s,
6H, AcO CH3), 1.91 (s, minor CH3), 1.90 (s, 6H, major CH3), 1.45
(dd, J = 18.2, 7.0 Hz, 6H, major iPr CHMe), 1.32 (overlapped m,
minor iPr CHMe), 1.29 (overlapped dd, J = 15.9, 7.0 Hz, 6H, major
iPr CHMe), 1.24 (overlapped dd, J = 19.2, 7.0 Hz, 6H, major iPr
CHMe), 1.19 (m, minor iPr CHMe), 1.14 ppm (dd, J = 13.6, 7.0 Hz,
6H, major iPr CHMe). 13C{1H} NMR (CD2Cl2, 126 MHz, 22 °C): δ
177.2 (minor, CO), 177.0 (major, CO), 163.9 (minor HCN),
162.5 (major HCN), 162.4 (major Ar C), 149.5 (major Ar C), 134.6
(major Ar CH), 134.4 (minor Ar C), 134.2 (minor Ar C), 133.6
(major Ar CH), 133.0 (minor Ar C), 132.7 (major Ar CH), 131.8
(minor Ar C), 131.3 (major Ar CH), 128.9 (d, J = 6.5 Hz, minor Ar
C), 128.2 (d, J = 7.0 Hz, major Ar C), 126.3 (minor Ar C), 125.8
(minor Ar C), 125.6 (d, J = 3.7 Hz, major Ar C), 120.8 (d, J = 13.0 Hz,
major Ar CH), 120.4 (d, J = 14.8 Hz, minor Ar CH), 119.6 (major Ar
C), 119.5 (minor Ar C), 119.3 (major Ar C), 118.8 (major Ar CH),
59.8 (minor CH2), 59.7 (major CH2), 27.0 (d, J = 22.7 Hz, minor iPr
CHMe), 26.9 (d, J = 23.2 Hz, major iPr CHMe), 23.6 (minor CH3),
23.3 (major CH3), 22.0 (d, J = 29.8 Hz, minor iPr CHMe), 21.7 (d, J =
29.1 Hz, major iPr CHMe), 20.5 (major CH3), 20.2 (major CH3), 20.1
(minor CH3), 19.2 (d, J = 4.8 Hz, major iPr CHMe), 19.0 (d, J = 3.7
Hz, major iPr CHMe), 18.6 (br, minor iPr CHMe), 16.5 (minor iPr
CHMe), 16.4 (d, J = 2.5 Hz, major iPr CHMe), 16.3 ppm (d, J = 6.1
Hz, major iPr CHMe). 31P{1H} NMR (CD2Cl2, 202 MHz): δ 66.8
(minor), 66.2 ppm (major, 1:5 ratio). UV−vis (C6H5F): λ (ε) 334
(10 500), 433 (3230), 523 nm (6380 M−1 cm−1). Anal. Calcd for
C48H64N4O4P2Pd2: C, 55.66; H, 6.23; N, 5.41. Found: C, 55.61; H,
6.44; N, 5.43. Mp: 174 °C.
Synthesis of 6b-OTf: (PNN-C4)PdOTf. Me3SiOTf (50 mL, 0.28
mmol) was added to a solution of 6b-OAc (0.147 g, 0.138 mmol) in
C6H5F (10 mL). The mixture was stirred for 4 h at room temperature
and dried in vacuo. The resulting purple powder was suspended in
Et2O and collected by filtration. Isolated yield = 0.152 g (88%). The
product is sparingly soluble in C6H5F. Due to solubility issues, a
meaningful 13C NMR spectrum could not be collected. 1H NMR
(C6D6, 500 MHz, 22 °C): δ 7.45 (br d, J = 12.0 Hz, 2H, HCN),
7.13 (br m, 2H, Ar CH), 6.95 (br m overlapped, 4H, Ar CH), 6.84 (br,
2H, Ar CH), 6.73 (br, 2H, Ar CH), 6.59 (br, 2H, Ar CH), 4.60 (br,
2H, CH2), 3.28 (br, 1H, CH2), 3.16 (br, 1H, CH2), 2.80 (m, J = 8.0
Hz, 2H, iPr CHMe), 2.24−2.12 (m overlapped, 2H, iPr CHMe), 2.12
(br overlapped, 12H, CH3),1.94 (br m, 2H, CH2), 1.82 (br m, 2H,
CH2), 1.38 (dd, J = 16.5, 6.5 Hz, 6H, iPr CHMe), 1.35 (dd, J = 18.5,
6.5 Hz, 6H, iPr CHMe), 1.25 (dd, J = 20.0, 6.5 Hz, 6H, iPr CHMe),
0.96 ppm (dd, J = 14.0, 7.5 Hz, 6H, iPr CHMe). 31P{1H} NMR (C6D6,
202 MHz, 22 °C): δ 72.2 (br, minor), 72.1 (br, major 1:0.9 ratio)
ppm. 19F NMR (C6D6, 202 MHz, 22 °C): δ −77.5 (major), −77.6
ppm (minor). UV−vis (C6H5F): λ (ε) 329 (11 780), 440 (5600), 552
Synthesis of 6b-OAc: (PNN-C4)PdOAc. The procedure was like
that for 6a-OAc, using[Pd(OAc)2]3 (0.128 g, 0.571 mmol of Pd) and
1
4b (0.210 g, 0.286 mmol). Isolated yield = 0.258 g (85%). H NMR
(CD2Cl2, 500 MHz, 22 °C): δ 7.66 (d, 3JHP = 12.0 Hz, 2H, HCN),
6651
dx.doi.org/10.1021/om2008056 | Organometallics 2011, 30, 6641−6654

Organometallics
Article
nm (3650 M−1 cm−1). Anal. Calcd for C48H62F6N4O6P2Pd2S2: C,
46.35; H, 5.02 ; N, 4.50. Found: C, 46.26; H, 5.11; N, 4.36.
355 (14 000), 427 (10 150), 495 (shoulder), 604 nm (1760 M−1
cm−1). Anal. Calcd for C47H65F3N4O3P2Pd2S1: C, 51.42; H, 5.97 ; N,
5.10. Found: C, 51.21; H, 5.79; N, 4.96.
Synthesis of 6a-H: [(PNN)Pd-H-Pd(PNN)-C2][OTf]. Et3SiH (6.2
mL, 0.039 mmol) was added to a solution of 6a-OTf (0.047 g, 0.039
mmol) in C6H5F (1 mL) and then layered with pentane (4 mL). The
mixture was placed in a −30 °C freezer and left to stand overnight. A
precipitate of a dark green powder was collected and washed with
pentane. Isolated yield = 0.033 g (80%). Crystals suitable for X-ray
diffraction were obtained through slow evaporation of a dilute benzene
X-ray Crystallography. In each case, multifaceted crystals of
suitable size and quality were selected from representative samples of
the same habit using an optical microscope and mounted onto a nylon
loop. Low-temperature (110 or 120 K) X-ray data were obtained on a
Bruker APEXII CCD based diffractometer (Mo sealed X-ray tube, Kα
= 0.71073 Å). All diffractometer manipulations, including data
collection, integration, and scaling, were carried out using the Bruker
APEXII software.59 Absorption corrections were applied using
SADABS.60 Space groups were determined on the basis of systematic
absences and intensity statistics, and structures were solved by direct
methods and refined by full-matrix least-squares on F2. The structure
was solved in the space groups noted in each case using XS61
(incorporated in SHELXTL), and PLATON62 was used to check for
missed symmetry. Except where noted, all non-hydrogen atoms were
refined with anisotropic thermal parameters.
1
solution. H NMR (CD2Cl2, 500 MHz, 22 °C): δ 7.70 (d, JHP = 12.5
Hz, 2H, HCN), 7.31 (dd, J = 9.0, 3.5 Hz, 2H, Ar CH), 7.12 (d,
J = 3.5 Hz, 2H, Ar CH), 7.10 (br s, 2H, Ar CH), 7.07 (d, J = 2.5 Hz,
2H, Ar CH), 7.04 (overlapped d, 2H, Ar CH), 7.02 (overlapped dd,
J = 9.0, 2.5 Hz, 2H, Ar CH), 4.73 (d, J = 11.5 Hz, 2H, CH2), 4.34 (d
br, J = 13.0 Hz, 2H, CH2), 2.48 (h, J = 6.5 Hz, 2H, iPr CHMe), 2.31
(s, 6H, CH3), 2.25 (s, 6H, CH3), 2.22 (overlapped m, 2H, iPr CHMe),
1.36 (dd, J = 17.5, 6.5 Hz, 6H, iPr CHMe), 1.28 (dd, J = 13.5, 6.5 Hz,
6H, iPr CHMe), 1.14 (dd, J = 19.0, 6.5 Hz, 6H, iPr CHMe), 1.08 (dd,
J = 19.0, 6.5 Hz, 6H, iPr CHMe), −20.08 ppm (t, JHP = 15.2 Hz, 1H,
Pd-H-Pd). 13C{1H} NMR (CD2Cl2, 126 MHz, 22 °C): δ 161.7
(HCN), 160.7 (d, J = 18.7 Hz, Ar C), 148.7 (Ar C), 135.3 (Ar CH),
134.4 (d, J = 1.4 Hz, Ar CH), 133.4 (Ar CH), 131.9 (Ar CH), 130.4
(d, J = 7.5 Hz, Ar C), 127.7 (Ar C), 127.0 (Ar C), 119.6 (d, J = 13.6
Hz, Ar CH), 118.2 (Ar CH), 117.7 (d, J = 47.0 Hz, Ar C), 68.5 (CH2),
27.9 (d, J = 24.8 Hz, iPr CHMe), 22.4 (d, J = 31.7 Hz, iPr CHMe),
20.5 (CH3), 20.3 (CH3), 18.9 (iPr CHMe), 18.7 (iPr CHMe), 18.4 (d,
J = 2.8 Hz, iPr CHMe), 16.4 ppm (d, J = 6.5 Hz, iPr CHMe). 31P{1H}
NMR (CD2Cl2, 202 MHz, 22 °C): δ 83.4 ppm. 19F NMR (CD2Cl2,
470 MHz, 22 °C): δ −80.2 ppm. UV−vis (C6H5F): λ (ε) 334 (15
150), 467 (8550), 632 nm (3420 M−1 cm−1). Anal. Calcd for
C45H59F3N4O3P2Pd2S1: C, 50.62; H, 5.57 ; N, 5.25. Found: C, 50.56;
H, 5.62; N, 5.24.
Crystal structure data for 5b-Cl: C30H44Cl2N2O2P2Pd2, 810.31
g/mol, orthorhombic, space group Pca21; a = 20.096(13) Å, b =
7.401(5) Å, c = 22.203(15) Å, α = β = γ = 90°, V = 3302(4) Å3; Z = 4,
ρcalcd = 1.630 g cm−3; crystal dimensions 0.18 × 0.08 × 0.06 mm;
diffractometer Bruker APEXII CCD; Mo Kα radiation, 150(2) K,
2θmax = 55.58°; 36 780 reflections, 7731 independent (Rint = 0.0813),
direct methods; absorption coeff (μ = 1.378 mm−1), absorption
2
correction multiscan (SADABS); refinement (against Fo ) with
SHELXTL V6.1, 364 parameters, 1 restraints, R1 = 0.0556 (I > 2σ)
and wR2 = 0.1441 (all data), Goof = 1.057, residual electron density
2.801/−1.138 e Å−3.
Crystal structure data for 6a-Cl: C44H58Cl2N4P2Pd2, 988.58 g/
mol, monoclinic, space group C2/c; a = 23.037(11) Å, b = 13.509(6)
Å, c = 14.442(7) Å, β = 103.707(5)°, V = 4367(4) Å3; Z = 4, ρcalcd
=
Synthesis of 6b-H: [(PN(H)N)Pd-Pd(PNN)-C4][OTf]. Excess
Et3SiH (0.101 mmol, 16 μL) was added to a solution of 6b-OTf
(0.032 g, 0.025 mmol) in C6H5F (5 mL) at −30 °C. The deep purple
solution was allowed to warm to room temperature and gradually
changed to a dark green color over 48 h. The reaction mixture was
dried in vacuo to remove all volatiles. Redissolution, filtering over
Celite, and drying left a forest-green powder. Yield = 0.025 g (90%).
Single crystals suitable for X-ray diffraction were obtained by slow
1.504 g cm−3; crystal dimensions 0.48 × 0.15 × 0.04 mm;
diffractometer Bruker APEXII CCD; Mo Kα radiation, 110(2) K,
2θmax = 55.26°; 23 962 reflections, 4994 independent (Rint = 0.0379),
direct methods; absorption coeff (μ = 1.055 mm−1), absorption
2
correction multiscan (SADABS); refinement (against Fo ) with
SHELXTL V6.1, 250 parameters, 0 restraints, R1 = 0.0228 (I > 2σ)
and wR2 = 0.0568 (all data), Goof = 1.058, residual electron density
0.398/−0.424 e Å−3.
1
evaporation of a C6H5F solution. H NMR (C6D5Br, 500 MHz, 22
Crystal structure data for 6b-Cl: C46H62Cl2N4P2Pd2·3(C6H6),
°C): δ 9.07 (s, 1H, NH), 7.52 (dd, JHH = 7.5 Hz, JHP = 3.0 Hz, 1H,
1250.96 g/mol, triclinic, space group P1; a = 7.757(3) Å, b =
̅
1
HCN; d in H{31P} NMR spectrum, J = 7.5 Hz), 7.39 (d, J = 8.5
13.319(5) Å, c = 14.878(5) Å, α = 97.967(4)°, β = 96.749(4)°, γ =
98.808(4)°, V = 1489.1(9) Å3; Z = 1, ρcalcd = 1.395 g cm−3; crystal
dimensions 0.21 × 0.18 × 0.11 mm; diffractometer Bruker APEXII
CCD; Mo Kα radiation, 110(2) K, 2θmax = 55°; 17 26 reflections, 6767
independent (Rint = 0.0533), direct methods; absorption coeff
(μ = 0.790 mm−1), absorption correction multiscan (SADABS);
Hz, 1H, Ar CH), 7.25−7.22 (overlapped m, 3H, Ar CH), 7.11 (d,
J = 7.5 Hz, 1H, Ar CH), 6.96 (d, J = 2.5 Hz, 1H, Ar CH), 6.85 (dd,
J = 7.5, 2.5 Hz, 1H Ar CH), 6.83 (overlapped m, 3H, Ar CH), 6.75 (d,
J = 7.5 Hz, 1H, Ar CH), 6.09 (d, J = 8.0 Hz, 1H, Ar CH), 5.80 (t,
J = 11.2 Hz, 1H, CH2), 4.69 (br t, J = 11.5 Hz, 1H, CH2), 3.89 (t,
J = 13.5 Hz, 1H, CH2), 3.68 (m, 1H, CH2), 3.53 (m, 1H, CH2), 3.43
(s, 2H, CH2), 3.09 (m, 1H, CH2), 2.29 (s, 3H, Me), 2.27 (s, 3H, Me),
2.25 (s, 3H, Me), 2.24 (s, 3H, Me), 2.20 (br m, 2H, iPr CHMe), 2.01
(br m, 2H, iPr CHMe), 1.83 (br t, J = 14.0 Hz, 1H, CH2), 1.71 (br m,
1H, CH2), 1.28 (dd, J = 17.0, 7.0 Hz, 3H, iPr CHMe), 1.07 (dd,
J = 17.5, 7.5 Hz, 3H iPr CHMe), 1.04−0.97 (overlapped m, 6H, iPr
CHMe), 0.93−0.87 (overlapped m, 6H, iPr CHMe), 0.70−0.64 ppm
(overlapped m, 6H, iPr CHMe). 13C{1H} (CD2Cl2, 126 MHz, 22 °C):
δ 169.0 (HCN), 144.9 (d, J = 12.3 Hz, Ar C), 144.0 (d, J = 13.0 Hz,
Ar C), 144.0 (Ar C), 142.6 (Ar C), 139.7 (d, J = 5.4 Hz, Ar C), 139.2
(d, J = 5.4 Hz, Ar C), 134.8 (Ar C), 134.4 (d, J = 1.2 Hz, Ar C), 134.3
(d, J = 1.5 Hz, Ar C), 134.0 (Ar C), 133.6 (Ar C), 133.4 (Ar C), 133.1
(Ar C), 132.8 (Ar C), 132.7 (Ar C), 132.1 (Ar C), 131.7 (Ar C), 131.4
(Ar C), 130.4 (Ar C), 129.9 (d, J = 7.7 Hz, Ar C), 129.7 (d, J = 8.5 Hz,
Ar C), 129.5 (Ar C), 118.7 (Ar C), 118.0 (Ar C), 68.1 (CH2), 54.9
(CH2), 54.8 (CH2), 32.2 (CH2), 25.5 (CH2), 21.4 (d, J = 3.7 Hz, iPr),
21.3 (d, J = 3.8 Hz, iPr), 20.7 (d, J = 4.5 Hz, iPr), 20.5 (d, J = 9.9 Hz,
iPr), 19.4 (d, J = 7.7 Hz, iPr), 19.3 (d, J = 6.9 Hz, iPr), 19.1 (d, J = 4.5
Hz, iPr), 17.5 (d, J = 4.5 Hz, iPr), 16.3 (d, J = 7.7 Hz, iPr), 15.9 ppm
(d, J = 6.9 Hz, iPr). 31P{1H} NMR (CD2Cl2, 202 MHz, 22 °C):
2
refinement (against Fo ) with SHELXTL V6.1, 340 parameters, 0
restraints, R1 = 0.0369 (I > 2σ) and wR2 = 0.1008 (all data), Goof =
1.054, residual electron density 0.782/−0.526 e Å−3
.
Crystal structure data for 6a-OAc: C48H64N4O4P2Pd2, 1035.77
g/mol, monoclinic, space group C2/c; a = 22.247(8) Å, b = 21.245(8)
Å, c = 14.767(6) Å, β = 128.243(4)°, V = 5482(4) Å3; Z = 4, ρcalcd
=
1.255 g cm−3; crystal dimensions 0.26 × 0.23 × 0.19 mm;
diffractometer Bruker APEXII CCD; Mo Kα radiation, 110(2) K,
2θmax = 55.18°; 30 619 reflections, 6282 independent (Rint = 0.0337),
direct methods; absorption coeff (μ = 0.755 mm−1), absorption
correction: multiscan (SADABS); refinement (against F2 ) with
0
SHELXTL V6.1, 278 parameters, 0 restraints, R1 = 0.0256 (I > 2σ)
and wR2 = 0.0701 (all data), Goof = 1.072, residual electron density
0.394/−0.243 e Å−3. The SQUEEZE protocol included in PLATON
was used to account for disordered pentane molecules included in the
1
crystal lattice (and confirmed by H NMR spectroscopy) that could
not be satisfactorily modeled.
Crystal structure data for 5a-H: C29H41F3N2O5P2Pd2S1, 861.44
g/mol, monoclinic, space group P21/c; a = 16.569(6) Å, b = 13.748(5)
Å, c = 16.022(6) Å, α = γ = 90°, β = 90.617(4)°, V = 3649(2) Å3;
Z = 4, ρcalcd = 1.568 g cm−3; crystal dimensions 0.14 × 0.13 × 0.10
mm; diffractometer Bruker APEXII CCD; Mo Kα radiation, 110(2) K,
3
3
δ = 64.2 (d, JPP = 5 Hz), 49.6 ppm (d, JPP = 5 Hz). 19F NMR
(CD2Cl2, 282 MHz, 22 °C): δ −79.9 ppm. UV−vis (C6H5F): λ (ε)
6652
dx.doi.org/10.1021/om2008056 | Organometallics 2011, 30, 6641−6654

Organometallics
Article
2θmax = 55.0°; 41 091 reflections, 8379 independent (Rint = 0.0873),
direct methods; absorption coeff (μ = 1.182 mm−1), absorption
correction multiscan (SADABS); refinement (against Fo ) with
SHELXTL V6.1, 393 parameters, 0 restraints, R1 = 0.0635 (I > 2σ)
and wR2 = 0.1776 (all data), Goof = 0.981, residual electron density
3.934/−1.394 e Å−3. The SQUEEZE protocol included in PLATON
was used to account for disordered CH2Cl2 solvent molecules found in
the crystal lattice (verified by 1H NMR) that could not be satisfactorily
modeled. The large residual is likely due to a small amount of
unaccounted for twinning.
Dr. Joe Reibenspies for helpful discussions regarding X-ray
crystallography and Jillian J. Davidson for assistance in the
preparation of compound 2.
2
REFERENCES
■
(1) (a) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
1020. (b) Albrecht, M.; van, K. G. Angew. Chem., Int. Ed. 2001, 40,
3750. (c) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103,
1759. (d) The Chemistry of Pincer Compounds; Morales-Morales, D.;
Jensen, C. M., Eds.; Elsevier: Amsterdam, 2007. (e) Selander, N.;
Crystal structure data for 5b-H: C31H45F3N2O5P2Pd2S1, 889.49
g/mol, monoclinic, space group P21/c; a = 20.882(5) Å, b = 13.676(3)
́
Szabo, K. J. Chem. Rev. 2011, 111, 2048.
(2) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature
1993, 364, 699.
(3) Bernskoetter, W. H.; Schauer, C. K.; Goldberg, K. I.; Brookhart,
M. Science 2009, 326, 553.
(4) Fafard, C. M.; Adhikari, D.; Foxman, B. M.; Mindiola, D. J.;
Å, c = 25.112(6) Å, β = 102.349(3)°, V = 7005(3) Å3; Z = 8, ρcalcd
=
1.687 g cm−3; crystal dimensions: 0.15 × 0.06 × 0.04 mm;
diffractometer: Bruker APEXII CCD; Mo Kα radiation, 150(2) K,
2θmax = 55.16°; 78 794 reflections, 16 068 independent (Rint = 0.0657),
direct methods; absorption coeff (μ = 1.235 mm−1), absorption
2
correction: multiscan (SADABS); refinement (against Fo ) with
Ozerov, O. V. J. Am. Chem. Soc. 2007, 129, 10318.
SHELXTL V6.1, 838 parameters, 1 restraints, R1 = 0.0431 (I > 2σ)
and wR2 = 0.1121 (all data), Goof = 1.018, residual electron density
1.761/−1.199 e Å−3.
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Crystal structure data for 6a-H: C45H59F3N4O3P2Pd2S1·0.5-
(C6H6), 1106.82 g/mol, orthorhombic, space group Pbca;
a = 16.545(6) Å, b = 24.021(9) Å, c = 25.028(9) Å, α = β =
γ = 90°, V = 9947(6) Å3; Z = 8, ρcalcd = 1.478 g cm−3; crystal
dimensions 0.10 × 0.07 × 0.04 mm; diffractometer Bruker APEXII
CCD; Mo Kα radiation, 110(2) K, 2θmax = 55.72°; 110 280 reflections,
11 725 independent (Rint = 0.1419), direct methods; absorption coeff
(μ = 0.884 mm−1), absorption correction multiscan (SADABS);
2
refinement (against Fo ) with SHELXTL V6.1, 580 parameters, 0
restraints, R1 = 0.0469 (I > 2σ) and wR2 = 0.1118 (all data), Goof =
1.020, residual electron density 0.827/−1.098 e Å−3
.
Crystal structure data for 6b-H: 2(C46H65F3N4O3P2Pd2S1)·3-
(C6H5F), 2483.96 g/mol, monoclinic, space group Cc; a = 31.487(14)
Å, b = 10.730(5) Å, c = 33.438(15) Å, β = 102.072(5) °, V = 11047(9)
Å3; Z = 4, ρcalcd = 1.493 g cm−3; crystal dimensions 0.43 × 0.12 × 0.08
mm; diffractometer Bruker APEXII CCD; Mo Kα radiation, 110(2) K,
2θmax = 55°; 56 610 reflections, 24 729 independent (Rint = 0.0792),
direct methods; absorption coeff (μ = 0.809 mm−1), absorption
2
correction multiscan (SADABS); refinement (against Fo ) with
SHELXTL V6.1, 1277 parameters, 34 restraints, R1 = 0.0594 (I >
2σ) and wR2 = 0.1350 (all data), Goof = 0.974, residual electron
density 1.288/−0.894 e Å−3. Three fluorobenzene solvent molecules
were found in the crystal lattice with elongated thermal parameters,
likely caused by unresolved disorder. No disorder was observed in the
main residue or triflate counterion. No additional symmetry was found
using ADDSYMM incorporated within the program PLATON62 when
run on .res or .cif files either containing or omitting the disordered
solvent molecules, confirming the space group selection. The Flack
parameter indicates that the crystal is a racemate [0.45(2)].
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ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 31P{1H} NMR spectra illustrating isomerism in (PNN-
Cn)Pd2X2 complexes; 1H NMR and IR spectra of 5-H and 6-H.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ozerov@mail.chem.tamu.edu.
ACKNOWLEDGMENTS
■
Support of this research by the NSF (CHE-0944634), the
Dreyfus Foundation (Camille Dreyfus Teacher-Scholar Award
to O.V.O.), and the Welch Foundation (grant A-1717) is
gratefully acknowledged. We thank Dr. Nattami Bhuvanesh and
(18) Zhang, B.-S.; Wang, C.; Gong, J.-F.; Song, M.-P. J. Organomet.
Chem. 2009, 694, 2555.
(19) Zhang, B.-S.; Wang, W.; Shao, D.-D.; Hao, X.-Q.; Gong, J.-F.;
Song, M.-P. Organometallics 2010, 29, 2579.
6653
dx.doi.org/10.1021/om2008056 | Organometallics 2011, 30, 6641−6654

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