Synthesis, structures, and ethylene dimerization reactivity of palladium alkyl complexes that contain a chelating phosphine-trifluoroborate ligand

Article abstract of DOI:10.1021/om200472x

The chemistry of palladium alkyl complexes that incorporate the phosphine-trifluoroborate ligand ortho-(Ph₂P)C₆H ₄(BF₃^-) (PF^-) is described. The reaction of the pinacol borane ortho-(Ph

Full text of DOI:10.1021/om200472x

ARTICLE
pubs.acs.org/Organometallics
Synthesis, Structures, and Ethylene Dimerization Reactivity of
Palladium Alkyl Complexes That Contain a Chelating
PhosphineÀTrifluoroborate Ligand
Youngmin Kim and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
S Supporting Information
b
ABSTRACT: The chemistry of palladium alkyl complexes that
incorporate the phosphineÀtrifluoroborate ligand ortho-
(Ph2P)C6H4(BF3À) (PFÀ) is described. The reaction of the
pinacol borane ortho-(Ph2P)C6H4(Bpin) with K[HF2] yields
ortho-(Ph2P)C6H4(BF3K) (K[PF], 1). Crystallization of 1 from
Et2O/THF in the presence of 18-crown-6 yields [K-(18-crown-
6)][PF] 0.5THF (2 0.5THF). In the solid state, the phosphi-
3
3
neÀborate anion of 2 is ion-paired with the [K-(18-crown-6)]
cation through weak contacts with the phosphorus and two
fluorine atoms. 1 reacts with (COD)PdMeCl in the presence of 18-crown-6 to form [K-(18-crown-6)][(PF)PdMeCl] (3) and with
(COD)PdMeCl and 2,4,6-collidine (col) to yield (PF)PdMe(col) (4). The PFÀ ligands in 3 and 4 are bound to Pd in a k2 mode
through the phosphine and one fluorine of the ÀArBF3À unit. The other two fluorines are weakly bound to the K(18-crown-6)+
cation in 3. NMR studies show that the PdÀF interactions in 3 and 4 are maintained in solution and that, for 4, the three fluorine
atoms undergo fast site exchange on the NMR time scale. 4 reacts with excess pyridine to yield (k1-P-PF)PdMe(py)2 (6), in which
the ÀArBF3À unit has been completely displaced by pyridine. 4 slowly dimerizes ethylene to 1-butene (36 t.o./h, 23 °C, CH2Cl2,
400 psi ethylene). The catalyst resting state is (PF)PdEt(col) (7). Addition of [H(OEt2)2][B(3,5-(CF3)2-C6H3)4] traps the
collidine as [collidinium] [B(3,5-(CF3)2-C6H3)4] and results in a 10-fold increase in the ethylene dimerization rate (385 t.o./h,
23 °C, CD2Cl2, 150 psi ethylene).
’ INTRODUCTION
describe the structures and reactivity of palladium alkyl complexes
that incorporate the phosphineÀtrifluoroborate ligand ortho-
(Ph2P)C6H4(BF3À).
Palladium(II) alkyl complexes (A) that contain ortho-phosphi-
no-arenesulfonate ligands ({PO}À) exhibit unique behavior in
olefin polymerization. {PO}Pd(R)(L) (L = labile ligand) species
polymerize ethylene to linear polyethylene and copolymerize
ethylene with a variety of polar vinyl monomers to functionalized
linear polymers.1,2 {PO}À ligands contain two interesting features
that may be related to the unusual behavior of {PO}Pd(R)(L)
catalysts. First, the electronic asymmetry in {PO}Pd(R) species
that results from the cis arrangement of the phosphine ligand, a
strong donor, and the sulfonate ligand, a very weak donor, may
inhibit β-H elimination and chain-walking processes that lead to
the formation of branched polymers and disfavor β-X elimination
processes that preclude ethylene/CH2dCHX copolymerization
by other catalysts. Second, the {PO}À ligand may potentially
coordinate in a k3-P,O,O mode to facilitate cis/trans isomerization
of {PO}Pd(R)(ethylene) species, which may be important for
chain growth.1j The design of other ligands that feature these
properties is of interest for developing new catalysts. Nozaki and
Rieger have explored some aspects of the chemistry of Pd alkyl
complexes that contain N-heterocyclic-carbeneÀsulfonate (B)
and phosphineÀphosphonate ligands (C).3,4 Recently, Piers
has observed hemilabile coordination behavior of the N-hetero-
cyclic-carbeneÀtrifluoroborate ligand in Rh complex D.5 Here we
’ RESULTS AND DISCUSSION
Synthesis and Structure of ortho-(Ph2P)C6H4(BF3K) (K[PF],
1). The reaction of the pinacol borane ortho-(Ph2P)C6H4(Bpin)6
with K[HF2] in a mixture of MeOH and H2O affords the
phosphineÀborate ortho-(Ph2P)C6H4(BF3K) (K[PF], 1) in
68% yield (Scheme 1). Compound 1 was characterized by
multinuclear NMR spectroscopy and elemental analysis. The
31P NMR spectrum comprises a quartet at δ À6.2 with JPÀF = 36
Hz. The 19F (δ À135.2) and 11B (δ 4.1) NMR chemical shifts of
1 are similar to those of the related phosphoniumÀborate
zwitterion ortho-(Ph2MeP)C6H4(BF3) (δ 19F À139.0; δ 11B
3.7).7 Slow diffusion of Et2O into a THF solution of 1 in the
presence of 18-crown-6 results in crystallization of [K-(18-
crown-6)][PF] 0.5THF (2 0.5THF), which was characterized
3
3
by X-ray diffraction (Figure 1). The phosphineÀborate anion of
2 is ion-paired with the [K-(18-crown-6)] cation through weak
Received: June 2, 2011
Published: July 19, 2011
r
2011 American Chemical Society
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Chart 1
Scheme 2
Scheme 1
Figure 2. Molecular structure of [K-(18-crown-6)][(PF)PdMeCl] (3).
Hydrogen atoms are omitted. Key bond lengths (Å) and angles (deg)
not given in text: C(1)ÀPd(1) 2.011(3), Cl(1)ÀPd(1) 2.3569(8),
P(1)ÀPd(1) 2.2309(8); C(1)ÀPd(1)ÀP(1) 90.29(9), F(3)ÀPd-
(1)ÀP(1) 92.16(5), C(1)ÀPd(1)ÀCl(1) 90.89(9), F(3)ÀPd(1)ÀCl-
(1) 86.64(5).
for ortho-(Ph2MeP)C6H4(BF3).7 The F3ÀP1 distance in 2
(3.020 Å) is less than the corresponding sum of the van der
Waals radii (F, P: 3.27 Å), and the F3ÀP1ÀC19 angle is nearly
linear (177.9°), suggesting that a F(lone pair)fP(σ*PÀC) inter-
action similar to that proposed for ortho-(Ph2MeP)C6H4(BF3) is
present.7
Synthesis and Structures of (PF)PdMeL Complexes. The
reaction of 1 with (COD)PdMeCl in the presence of 18-crown-6
in THF affords [K-(18-crown-6)][(PF)PdMeCl] (3) in 67%
yield (Scheme 2). The reaction of 1 with (COD)PdMeCl and
2,4,6-collidine (col) in CH2Cl2 affords (PF)PdMe(col) (4) in
64% yield.
Figure 1. Molecular structure of [K-(18-crown-6)][PF] (2). Hydrogen
atoms are omitted. Key bond lengths (Å) and angles (deg) not given in
text: B(1)ÀF(1) 1.407(2), B(1)ÀF(3) 1.420(2), B(1)ÀF(2) 1.428(2),
B(1)ÀC(25) 1.622(2), C(13)ÀP(1) 1.8361(17), C(19)ÀP(1)
1.8407(16), C(30)ÀP(1) 1.8392(17); F(1)ÀB(1)ÀF(3) 107.79(14),
F(1)ÀB(1)ÀF(2) 107.21(14), F(3)ÀB(1)ÀF(2) 106.35(14), F-
(1)ÀB(1)ÀC(25) 110.79(14), F(3)ÀB(1)ÀC(25) 114.17(14), F-
(2)ÀB(1)ÀC(25) 110.21(13), C(13)ÀP(1)ÀC(30) 101.63(7),
C(13)ÀP(1)ÀC(19) 100.77(7), C(30)ÀP(1)ÀC(19) 104.14(7).
The solid-state molecular structure of 3 is shown in Figure 2.
The PFÀ ligand binds to the square-planar Pd center in a k2
À
mode through the phosphine and one fluorine of the ArBF3
unit. The K(18-crown-6)+ cation binds the other two fluorines.
The methyl group is cis to the phosphine. The six-membered
(PF)Pd chelate ring is puckered, with an angle of 39.23° between
the PÀCÀCÀB and PÀPdÀF planes. The PdÀF distance in 3
(PdÀF3 2.2144(16) Å) is similar to that in the η1-BF4À complex
(η3-C3H5)Pd(NHC)(BF4) (2.241(2) Å; NHC = C(N(tBu)
CH)2)8 and much longer than the PdÀF distance in PdII
terminal fluoride complexes (2.02À2.09 Å).9 The PdÀF distance
in 3 is intermediate between the sum of the Pd and F covalent
(2.01 Å) and van der Waals (3.10 Å) radii. The PdFÀB distance
contacts with the phosphorus and two fluorine atoms. The
P1ÀK1 (3.8394(7) Å), F2ÀK1 (2.6435(11) Å), and F3ÀK1
(2.8021(11) Å) distances are all shorter than the corresponding
sums of the van der Waals radii (P, K: 4.55 Å; F, K: 4.22 Å). The
average of the BÀF bond lengths in 2 (1.418 Å) is similar to that
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(F3ÀB1 1.446(4) Å) in 3 is ca. 0.04 Å longer than the other BÀF
distances (F1ÀB1 1.406(3), F2ÀB1 1.402(4) Å). The structure
of 4 (Figure 3) is very similar to that of 3. The (PF)Pd chelate
ring in 4 is puckered, with an angle of 38.66° between the
PÀCÀCÀB and PÀPdÀF planes, and the PdÀF, PdÀC, and
PdÀP distances are essentially identical to the corresponding
distances in 3.
conditions and that, for 4, the three fluorine atoms undergo fast
exchange on the NMR time scale.10
Reaction of 4 with Pyridine. The reaction of 4 with pyridine
is summarized in Scheme 3. Addition of a small amount of
pyridine (ca. 0.3 equiv) to a solution of 4 in CD2Cl2 at 23 °C
generates an equilibrium mixture of 4 and the analogous pyridine
complex 5 (K1 = [5][col]/[4][py] = 0.35(3)) Exchange of 4 and
5 is slow on the NMR time scale, and separate resonances are
observed for these species under these conditions. Addition of
additional pyridine results in the expected shifting of the
equilibrium toward 5 and the formation of the bis-ligand adducts
(k1-P-PF)PdMe(py)2 (6) and (k1-P-PF)PdMe(py)(col). The
exchange of 6 with 5 is fast on the NMR time scale at 23 °C, and a
single set of resonances at the weighted average chemical shifts of
the these two species is observed. Similarly, one set of exchange-
averaged resonances is observed for (k1-P-PF)PdMe(py)(col)
and 4 under these conditions. The equilibrium constant for
coordination of py to 5 to form 6 is K2 = [6]/[py][5] = 45(5)
The 31P{1H} NMR spectra of 3 and 4 in CD2Cl2 solution at
23 °C consist of singlets at δ 30.2 and 29.0, respectively, which
are shifted ca. 36 ppm downfield from the resonance of the free
ligand 1. The 19F{1H} spectra of 3 and 4 also comprise singlets
(at δ À152.5 and À157.3, respectively) that are shifted upfield by
ca. 20 ppm compared to the 19F resonance of 1 (δ À135.2). The
19F NMR resonances of 3 and 4 broaden but do not split when
the temperature is lowered to À85 °C. The PdÀCH3 13C NMR
resonance of 3 appears as a broad singlet at 23 °C but sharpens to
a doublet of doublets at À60 °C (δ À2.4, JCÀP = JCÀF = 12 Hz).
The PdÀCH3 13C NMR resonance of 4 at 23 °C appears as a
quartet of doublets due to coupling to three fluorines and
phosphorus (δ À2.9, 2JCÀF = 12 Hz, 2JCÀP = 3 Hz; Figure 4);
cooling the solution to À80 °C results in broadening but no
change in the multiplicity of this signal. These results show that
the PdÀF interaction is maintained in solution under these
M
À1. The addition of 35 equiv of pyridine to 4 results in
complete conversion to 6. The conversion of 4 to 5 or (k1-P-
PF)PdMe(py)(col) and the conversion of 5 to 6 are presumed to
occur by a standard associative substitution mechanism through
five-coordinate intermediates ((k2-PF)PdMe(py)(col) and (k2-
PF)PdMe(py)2).
Complex 6 was isolated by crystallization by slow diffusion of
Et2O into a pyridine solution of 4. The molecular structure of 6 is
shown in Figure 5. Complex 6 features a square-planar geometry
at Pd with a cis arrangement of the two pyridine ligands. The
distance between the Pd and the nearest fluorine atom (F(3)) is
3.016 Å, which is close to the sum ofÀthe P and F van der Waals
radii and indicates that the ÀArBF3 unit has been essentially
completely displaced by pyridine. The 19F{1H} NMR spectrum
of 6 in pyridine-d5 comprises a singlet at δ À131.1, which falls in
the same range as that for the free ligand 1 (δ = À135.2).
Additionally, the PdÀCH3 13C{1H} NMR resonance of 6
appears as a doublet (δ 2.3, JCÀP = 6 Hz) with no detectable
JCÀF coupling (Figure 4). These results are consistent with
Figure 3. Molecular structure of (PF)PdMe(col) (4). Hydrogen atoms
are omitted. Key bond lengths (Å) and angles (deg) not given in text:
C(27)ÀPd(1) 2.005(5), F(1)ÀPd(1) 2.214(3), N(1)ÀPd(1)
2.114(4), P(1)ÀPd(1) 2.2338(14), B(1)ÀF(1) 1.467(7), B(1)ÀF(2)
1.397(6), B(1)ÀF(3) 1.378(7); C(27)ÀPd(1)ÀN(1) 87.83(19), N-
(1)ÀPd(1)ÀF(1) 88.79(14), C(27)ÀPd(1)ÀP(1) 89.87(16), F-
(1)ÀPd(1)ÀP(1) 93.52(9).
À
displacement of the ÀArBF3 by pyridine in solution as well
as in the solid state. The structure of (k1-P-PF)PdMe(py)(col) is
presumed to be analogous to that of 6.
Dimerization of Ethylene by 4. Complex 4 slowly dimerizes
ethylene to 1-butene, with a rate of ca. 36 t.o./h at 23 °C in
CH2Cl2 solvent under 400 psi ethylene pressure. NMR analysis
Figure 4. (a) Methyl region of the 13C{1H} NMR spectrum of (k2-PF)PdMe(col) (4) in CD2Cl2 at 23 °C showing JCÀF (12 Hz) and JCÀP (3 Hz)
coupling, characteristic of fast exchange of Pd-coordinated and non-Pd-coordinated fluorines. (b) Methyl region of the 13C{1H} NMR spectrum of (k1-
PF)PdMe(py)2 (6) in pyridine-d5 at 23 °C showing JCÀP (6 Hz) but not JCÀF coupling.
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Scheme 3
solvent and ca. 150 psi ethylene pressure, 4/[H(OEt2)2][B-
(3,5-(CF3)2-C6H3)4] dimerizes ethylene with a rate of 385 t.o./
h. Under these conditions, the primary product 1-butene is
isomerized to cis and trans 2-butene.12 NMR monitoring of the
reaction of 4, [H(OEt2)2][B(3,5-(CF3)2-C6H3)4], and ethylene
shows that warming this mixture to À20 °C results in quantita-
tive formation of [collidinium][B(3,5-(CF3)2-C6H3)4] and a
new Pd species characterized as (PF)PdMe(ethylene) (8).13 At
0 °C, (PF)PdMe(ethylene) is converted to (PF)PdEt(ethylene)
(9) with concomitant formation of propene and commencement
of ethylene dimerization to 1-butene with 9 as the catalyst resting
state. The NMR data for 8 and 9 are similar to the data for 4 and 7
except that the 31P signals are shifted upfield by ca. 7 ppm, due to
replacement of collidine by ethylene. Intermolecular exchange of
bound ethylene with free ethylene is fast on the NMR time scale
for these species, even at À80 °C.
’ CONCLUSION
The phosphineÀborate ligand ortho-(Ph2P)C6H4(BF3À) binds
to Pd(II) in a k2 mode through phosphorus and one fluorine to
form[K(18-crown-6)][(k2-PF)PdMeCl] (3) and(k2-PF)PdMeL
(L = collidine (4), pyridine (5)) complexes. In the presence of a
large excess of pyridine, the ÀArBF3À unit of 4 is displaced and
(k1-PF)PdMe(py)2 (6) is formed. Complex 4 catalytically
dimerizes ethylene to 1-butene by rate-limiting displacement of
collidine by ethylene, insertion, and chain transfer. Trapping of
the collidine by [H(OEt2)2][B(3,5-(CF3)2-C6H3)4] generates a
base-free catalyst that is ca. 10 times more active for ethylene
dimerization than 4. Under these conditions, the catalyst resting
state is (k2-PF)PdEt(ethylene).
Figure 5. Molecular structure of (PF)PdMe(py)2 (6). Hydrogen atoms
are omitted. Key bond lengths (Å) and angles (deg): C(1)ÀPd(1)
2.0523(17), N(1)ÀPd(1) 2.1310(15), N(2)ÀPd(1) 2.1647(14), P-
(1)ÀPd(1) 2.2551(7); C(1)ÀPd(1)ÀN(1) 86.95(6), N(1)ÀPd-
(1)ÀN(2) 89.60(5), C(1)ÀPd(1)ÀP(1) 87.81(5), N(2)ÀPd(1)
ÀP(1) 96.56(4).
’ EXPERIMENTAL SECTION
General Procedures. All experiments were performed using dry-
box or Schlenk techniques under a nitrogen atmosphere. Nitrogen was
purified by passage through activated molecular sieves and Q-5 oxygen
scavenger. CH2Cl2 and CD2Cl2 were distilled from P2O5. MeOH was
purchased from Aldrich (anhydrous, 99.8%). Hexanes, diethyl ether, and
toluene were purified by passage through activated alumina and BASF
R3-11 oxygen scavenger. 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxa-
borolane and K[HF2] were purchased from Aldrich. Ethylene (polymer
grade) was purchased from Matheson Trigas and used as received. All
other deuterated solvents were purchased from Cambridge Isotope
Laboratories and used as received. NMR spectra of organometallic
complexes were recorded on Bruker DMX-500 or DRX-400 spectro-
meters in Teflon-valved tubes at ambient temperature unless otherwise
indicated. 1H and 13C chemical shifts are reported relative to SiMe4 and
were determined by reference to the residual 1H and 13C solvent
resonances. 11B, 19F, and 31P chemical shifts are referenced against
of a CD2Cl2 solution of 4 under 150 psi ethylene after 3 h revealed
the presence of propene, 1-butene, unreacted 4, and a new Pd
species, which has been characterized as the ethyl complex
(PF)PdEt(col) (7). The 31P{1H} and 19F{1H} NMR spectra of
7 are very similar to those of the methyl analogue 4 and show that
1
the PFÀ ligand in 7 is coordinated in a k2-P,F fashion. The H
NMR spectrum of 7 contains singlets at δ 3.17 and 2.36 for the
collidine Me groups, which are similar to the corresponding
resonances of 4 and establish the presence of one collidine ligand.
The PdÀEt resonances were assigned with the aid of COSY and
1
1H{19F} and H{31P} decoupling experiments (Figure 6). The
PdÀCH2CH3 methylene resonance of 7 (δ 1.63) appears as a
broadened doublet of quartets due to 3JHÀH (7 Hz), 3JHÀP (5 Hz),
and small 3JHÀF coupling. ThePdÀCH2CH3 methylresonance (δ
0.25) appears as a 12-line multiplet due to 3JHÀH (7 Hz), 4JHÀP (4
Hz), and 4JHÀF (2 Hz) coupling. These spectroscopic features are
similar to those observed for the related complex (ortho-
Ar2PC6H4SO3)PdEt(2,6-lutidine) (Ar = o-MeOC6H4).1j These
results are consistent with a dimerization mechanism involving
displacement of collidine from resting state 7 by ethylene followed
by insertion and chain transfer (Scheme 4).
external BF3 Et2O, CFCl3, and 85% H3PO4, respectively. For NMR
3
assignments, C1 is the carbon that is bonded to phosphorus.
X-ray Crystallography. Crystallographic details are provided in
the Supporting Information. Data were collected on a Bruker Smart
Apex diffractometer using Mo KR radiation (0.71073 Å). Direct
methods were used to locate many atoms from the E-map. Repeated
difference Fourier maps allowed recognition of all expected non-
hydrogen atoms. Following anisotropic refinement of all non-H atoms,
ideal H-atom positions were calculated. Final refinement was anisotropic
for all non-H atoms and isotropic-riding for H atoms. ORTEP diagrams
are drawn with 50% probability ellipsoids.
Addition of 1 equiv of [H(OEt2)2][B(3,5-(CF3)2-C6H3)4]11
to trap the collidine as collidinium results in a ca. 10-fold increase
in the rate of ethylene dimerization by 4. At 23 °C in CD2Cl2
Ethylene Dimerization. Ethylene dimerization reactions were
performed in a 300 mL stainless steel Parr autoclave equipped with a
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1
1
Figure 6. 1H, H{31P}, and H{19F} NMR spectra of (PF)PdEt(col) (7) in CD2Cl2 at 23 °C. The PdCH2CH3 (left) and PdCH2CH3 (right)
resonances are shown.
water cooling loop, thermocouple, and magnetically coupled stirrer and
controlled by a Parr 4842 controller. In the glovebox, the catalyst
solution or suspension was prepared in a glass liner. The liner was
placed in the autoclave, and the autoclave was assembled and brought
out of the box. The mixture was stirred at the rate of 200 rpm. The
autoclave was pressurized with ethylene (400 psi). After 5 h, the mixture
was cooled to À78 °C, the ethylene flow was terminated, and the
pressure was released into a well-ventilated fume hood. The product was
characterized by 1H NMR spectroscopy. The yield of the product was
measured using an internal standard by 1H NMR spectroscopy.
Scheme 4
ortho-(Ph2P)C6H4(BF3K) (1). A solution of K[HF2] (0.56 g, 7.2
mmol) in H2O (5 mL) was added to a solution of ortho-(Ph2P)C6H4-
(Bpin)2 (0.7 g, 1.8 mmol) in MeOH (15 mL). The mixture was stirred
at 23 °C for 1 h. A white precipitate formed. The mixture was filtered to
afford a white solid. The solid was washed sequentially with H2O, Et2O,
a mixture of MeOH/Et2O (1/6, v/v), and CH2Cl2 and then dried under
1
the vacuum to afford a white solid. Yield: 0.45 g (68%). H NMR
(acetone-d6): δ 7.73 (br s, 1H, H3-Ar), 7.23 (m, 10H, H-Ph), 7.13 (t,
JHÀH = JHÀP = 7, 1H, H6-Ar), 7.00 (t, JHÀH = 7, 1H, H4-Ar), 6.91 (m,
1H, H5-Ar). 13C{1H} NMR (acetone-d6): δ 141.6 (d, JCÀP = 14), 139.4
(d, JCÀP = 13), 134.2 (d, JCÀP = 19, C2-Ph), 133.4 (dq, JCÀP = 14, JCÀF
=
3 Hz, C3-Ar), 128.7 (d, JCÀP = 7, C3-Ph), 128.3 (C4-Ph), 127.8 (C6-Ar),
126.6 (C4-Ar). (The C5-Ar peaks overlap with the C2-Ph peaks, and the
C2-Ar resonance was not observed.) 11B{1H} NMR (acetone-d6) δ 4.1
(br s). 31P{1H} NMR (acetone-d6): δ À6.2 (q, JPÀF = 36). 19F{1H}
NMR (acetone-d6): δ À135.2 (br s). Anal. Calcd for C18H14BF3KP: C,
58.72; H, 3.83. Found: C, 58.87; H, 3.93.
volatiles were removed under vacuum. The residue was washed with
Et2O followed by THF to yield a white solid. Yield: 0.15 g (67%). 1H
NMR (CD2Cl2): δ 7.75 (m, 1H, H3-Ar), 7.53 (m, 4H, H2-Ph), 7.42 (m,
6H, H3-Ph and H4-Ph), 7.34 (t, 1H, JHÀH = JHÀP = 7, H6-Ar), 7.14 (t,
1H, JHÀH = 7, H4-Ar), 6.88 (t, 1H, JHÀH = 8.8, H5-Ar), 3.57 (s, 24H,
O(CH2)2O), 0.76 (br s, 3H, PdCH3). 13C{1H} NMR (CD2Cl2): δ
134.7 (d, JCÀP = 12, C2-Ph), 133.3 (d, JCÀP = 4, C3-Ar), 132.73, 133.2
(C5-Ar), 132.7 (d, JCÀP = 50), 130.4 (d, JCÀP = 2, C4-Ph), 129.6 (C6-Ar),
128.6 (d, JCÀP = 11, C3-Ph), 126.9 (d, JCÀP = 7, C4-Ar), 70.4 (s,
O(CH2)2O), À2.4 (br s, PdCH3) (C2-Ar resonance was not observed).
11B{1H} NMR (CD2Cl2): δ 2.5 (br s). 31P{1H} NMR (CD2Cl2): δ
[K-(18-crown-6)][PF] (2). Slow diffusion of Et2O into a THF
solution of 1 in the presence of 18-crown-6 yields crystals of 2. 2 was
characterized by X-ray diffraction.
[K-(18-crown-6)][(PF)PdMeCl] (3). A flask was charged with
(COD)PdMeCl (0.073 g, 0.27 mmol), 1 (0.10 g, 0.27 mmol), and 18-
crown-6 (0.088 g, 0.33 mmol). THF (5 mL) was added, and the mixture
was stirred at 23 °C for 1 h. A pale yellow precipitate formed. The
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30.2. 19F{1H} NMR (CD2Cl2): δ À152.5 (br s). Anal. Calcd for
C33H45BClF3KO6.5PPd(0.5THF): C, 48.02; H, 5.49. Found: C,
48.68; H, 5.70.
ethylene signal was not observed due to fast intermolecular ethylene
exchange. 31P{1H} NMR (CD2Cl2, 0 °C): δ 22.5. 19F{1H} NMR
(CD2Cl2, 0 °C): δ À149.7 (br s).
(PF)Pd(Me)(OEt2). 1H NMR (CD2Cl2, À60 °C): δ 7.69 (m, 1H,
H3-Ar), 7.44 (m, 11H, H-Ph and H-Ar), 7.21 (m, 1H, H-Ar), 6.84 (m,
1H, H-Ar), 3.74 (q, JHH = 7, 4H, OCH2CH3), 1.71 (t, 6H, JHH = 7,
OCH2CH3), 0.58 (s, 3H, PdCH3). 31P{1H} NMR (CD2Cl2, À60 °C):
δ 34.8. 19F{1H} NMR (CD2Cl2, À60 °C): δ À152.4 (br s). 13C{1H}
NMR (CD2Cl2, À40 °C): δ 133.6 (d, JCÀP = 12, C2-Ph), 132.9 (d, JCÀP
= 6, C-Ar), 132.7 (m, C-Ar), 130.88 (d, JCÀP = 2, C4-Ph), 130.7, 130.3
(C-Ar), 129.5 (d, JCÀP = 58), 128.6 (d, JCÀP = 11, C3-Ph), 127.5 (C-Ar),
70.2 (br s, Pd(OCH2CH3)2), 16.3 (br s, Pd(OCH2CH3)2), 2.7 (br s,
PdCH3); the C2-Ar resonance was not observed.
(PF)PdMe(col) (4). A flask was charged with (COD)PdMeCl
(0.10 g, 0.38 mmol) and 1 (0.14 g, 0.38 mmol). A solution of 2,4,6-
collidine (0.060 mL, 0.45 mmol) in CH2Cl2 (5 mL) was added, and the
mixture was stirred at 23 °C for 1 h to form a solution. The solution was
filtered, and the filtrate was taken to dryness under vacuum. The residue
was dissolved in benzene and filtered, and the filtrate was concentrated
to afford a pale yellow precipitate, which was collected and dried under
vacuum. The solid was recrystallized from CH2Cl2/Et2O to yield a white
solid. Yield: 0.14 g (64%). 1H NMR (CD2Cl2): δ 7.76 (dd, JHÀH = 7,
JHÀP = 3, 1H, H3-Ar), 7.58 (m, 4H, H2-Ph), 7.49 (m, 6H, H3-Ph and
H4-Ph), 7.39 (t, JHÀH = JHÀP = 7 Hz, 1H, H6-Ar), 7.20 (t, JHÀH = 7, 1H,
H4-Ar), 7.06 (s, 2H, col), 6.95 (m, 1H, H5-Ar), 3.10 (s, 3H, o-col-CH3),
2.35 (s, 3H, p-col-CH3), 0.53 (d, JHÀP = 2, 3H, PdCH3). 13C{1H} NMR
(CD2Cl2): δ 158.6 (C2,6-col), 151.4 (C4-col), 134.4 (d, JCÀP = 11,
C2-Ph), 133.4 (m, C3-Ar), 133.2 (m, C5-Ar), 131.7 (d, JCÀP = 47), 131.5
’ ASSOCIATED CONTENT
S
Supporting Information. Representative NMR spectra
b
and crystallographic data (CIF files). This material is available
(d, JCÀP = 52), 130.9 (d, JCÀP = 3, C4-Ph), 130.2 (C6-Ar), 128.9 (d, JCÀP
=
free of charge via the Internet at http://pubs.acs.org.
11, C3-Ph), 127.3 (d, JCÀP = 8, C4-Ar), 124.1 (d, JCÀP = 3, C3-col), 26.2
(o-col-CH3), 21.0 (p-col-CH3), À2.9 (qd, JCÀF = 12, JCÀP = 3, PdCH3)
(C2-Ar resonance was not observed). 11B{1H} NMR (CD2Cl2): δ 2.6
(br s). 31P{1H} NMR (CD2Cl2): δ 29.0. 19F{1H} NMR (CD2Cl2):
δ À157.3 (br s). Anal. Calcd for C27H28BF3NPPd: C, 56.72; H, 4.94.
Found: C, 56.48; H, 5.09.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: rfjordan@uchicago.edu.
(PF)PdMe(py)2 (6). Single crystals of 6 were obtained by slow
diffusion of Et2O into a solution of 4 in pyridine at 23 °C. Due to the
rapid equilibrium between 5 and 6, NMR analysis of 6 performed in
pyridine-d5 solution and therefore signals for coordinated pyridine were
not observed. 1H NMR (pyridine-d5): δ 8.87 (m, 1H, H3-Ar), 7.69 (br s,
4H, H2-Ph), 7.57 (m, 1H, H-Ar), 7.31 (m, 2H, H4-Ph), 7.29 (m, 1H, H-
Ar), 7.20 (br s, 1H, H-Ar), 7.16 (br s, 4H, H3-Ph), 0.91(d, JHÀP = 3, 3H,
PdCH3). 13C{1H} NMR (pyridine-d5): δ 136.6 (m, C3-Ar), 134.9 (d,
JCÀP = 48), 132.1 (d, J = 7, C-Ar), 131.5 (d, JCÀP = 54), 130.0 (C4-Ph),
130.0 (C-Ar), 128.5 (d, JCÀP = 10, C3-Ph), 126.4 (d, JCÀP = 9, C-Ar), 2.3
(d, JCÀP = 6, PdCH3); the C2-Ph peaks overlap with the solvent peaks
and C2-Ar resonance was not observed. 31P{1H} NMR (pyridine-d5): δ
42.9 (q, JPÀF = 11). 19F{1H} NMR (pyridine-d5): δ À131.1 (br s).
11B{1H} NMR (pyridine-d5): δ 4.4 (br s).
’ ACKNOWLEDGMENT
This work was supported by the National Science Foundation
(CHE-0911180).
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1
(PF)Pd(Et)(col) (7). H NMR (CD2Cl2): δ 7.75 (dd, JHÀH = 7,
JHÀP = 3, 1H, H3-Ar), 7.63 (m, 4H, H2-Ph), 7.50 (m, 6H, H3-Ph and H4-
Ph), 7.40 (m, 1H, H-Ar), 7.21 (m, 1H, H-Ar), 7.07 (s, 2H, col), 7.06
(m, 1H, H-Ar), 3.17 (s, 6H, o-col-Me), 2.36 (s, 3H, p-col-Me), 1.63 (qd,
JHÀH = 7, JHÀP = 5, 2H, Pd-CH2CH3), 0.25 (m, JHÀH = 7, JHÀP = 4,
JHÀF = 2, 3H, Pd-CH2CH3). 31P{1H} NMR (CD2Cl2): δ 29.2. 19F{1H}
NMR (CD2Cl2): δ À155.7 (br s).
(PF)PdMe(ethylene) (8). 1H NMR (CD2Cl2, À40 °C, in presence
of 2.2 equiv of free ethylene): δ 7.48 (m, 2H, H-Ph), 7.41 (m, 9H, H-Ph
and H-Ar), 7.25 (t, JHH = 7, 1H, H-Ar), 6.93 (m, 1H, H-Ar), 5.43
(coordinated and free ethylene), 0.70 (s, 3H, Pd-CH3); the H3-Ar
resonances overlap with the [B(3,5-(CF3)2-C6H3)4]À signals. 13C{1H}
NMR (CD2Cl2, À40 °C, in presence of 2.2 equiv of free ethylene): δ
133.9 (d, JCÀP = 12, C2-Ph), 133.3 (C-Ar), 132.6 (m, C-Ar), 131.1 (C4-
Ph), 130.3 (C-Ar), 129.8 (d, JCÀP = 49), 129.0, 128.7 (d, JCÀP = 11, C3-
Ph), 127.8 (d, JCÀP = 7, C-Ar), 119 (br s, coordinated and free ethylene;
this resonance correlates with the 1H NMR ethylene resonance in the
HMQC spectrum), 4.5 (m, PdCH3); the C2-Ar resonance was not
observed. 31P{1H} NMR (CD2Cl2, À20 °C): δ 22.2. 19F{1H} NMR
(CD2Cl2, À20 °C): δ À151.5 (br s).
(PF)Pd(Et)(ethylene) (9). 1H NMR (CD2Cl2, 0 °C, in the
presence of 66 equiv of free ethylene): δ 7.48 (m, 11H, H-Ph and H-
Ar), 7.29 (t, JHH = 7, 1H, H-Ar), 7.19 (m, 1H, H-Ar), 1.83 (p, JHÀH = 7,
JHÀP = 7, 2H, PdCH2CH3), 0.42 (m, 3H, PdCH2CH3); the H3-Ar
resonances overlap with the [B(3,5-(CF3)2-C6H3)4]À signals; the
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C6H3)4] in CD2Cl2 at À60 °C followed by warming to À20 °C in the
absence of ethylene yields (PF)PdMe(OEt2).
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