Retardation of β-hydrogen elimination in PNP Pincer complexes of Pd

Article abstract of DOI:10.1016/j.ica.2006.07.067

A series of new alkyl and alkoxide (^FPNP)Pd complexes have been synthesized. The alkyls and alkoxides containing β-hydrogens display remarkable thermal stability. Thermal decomposition of (^FPNP)PdOEt is very slow in pure C₆D₆ but is accelerated by the addition of EtOH co-solvent. It is proposed that the β-hydrogen elimination from (^FPNP)Pd-OCH₂R occurs via dissociation of the alkoxide anion.

Full text of DOI:10.1016/j.ica.2006.07.067

Inorganica Chimica Acta 360 (2007) 286–292
www.elsevier.com/locate/ica
Retardation of b-hydrogen elimination in PNP Pincer complexes of Pd
*
Claudia M. Fafard, Oleg V. Ozerov
Department of Chemistry, Brandeis University, MS015, 415 South Street, Waltham, MA 02454, USA
Received 20 June 2006; accepted 13 July 2006
Available online 4 August 2006
Inorganic Chemistry – The Next Generation.
Abstract
A series of new alkyl and alkoxide (FPNP)Pd complexes have been synthesized. The alkyls and alkoxides containing b-hydrogens dis-
play remarkable thermal stability. Thermal decomposition of (FPNP)PdOEt is very slow in pure C6D6 but is accelerated by the addition
of EtOH co-solvent. It is proposed that the b-hydrogen elimination from (FPNP)Pd–OCH2R occurs via dissociation of the alkoxide
anion.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Palladium; Elimination; Pincer; Alkyl complexes; Alkoxide complexes
1. Introduction
we report that BHE is retarded in the (PNP)Pd–R and
(PNP)Pd–OR compounds (R = alkyl, RO = alkoxide) in
non-polar solvents. However, (PNP)Pd–OR compounds
are shown to be able to undergo BHE in the more polar
media apparently by a non-classical mechanism.
b-Hydrogen elimination (BHE) in metal alkyl and alk-
oxide compounds is one of the fundamental organometallic
reactions [1]. BHE converts metal alkyls to metal hydrides
with the evolution of corresponding olefins and metal alk-
oxides to metal hydrides and the evolution of correspond-
ing aldehydes or ketones. BHE in alkyl compounds is
common across the periodic table. Early metal alkoxides
are usually resistant to BHE because of the high M–O
bond strengths. Late metal alkoxides, on the other hand,
typically readily undergo BHE [2,3].
The classical mechanism of BHE requires the presence
of an empty coordination site cis to the alkyl or alkoxide
[1–3]. The absence of such a cis-site may stabilize the b-
H-containing alkyl or alkoxide kinetically. In the last few
years, our group has been engaged in the exploration of
the rigid pincer-type PNP ligands [4–6]. We have devoted
special attention to the chemistry of square-planar com-
plexes of Pd [4] One of the key features of this PNP ligand
is the tight, unremitting tridentate coordination that is
enforced by the rigidity of the backbone. In this work,
2. Results and discussion
2.1. Syntheses of (FPNP)Pd-alkyl compounds and their
thermal stability
We have previously reported the synthesis of 1–3
(Scheme 1) and analogous Pd complexes with minor PNP
ligand variations [4,5c]. (FPNP)PdOTf (6) was prepared
via the reaction of MeOTf with 5, in full analogy with pre-
viously reported synthesis of 3 (as well as its Ni and Pt ana-
logues [5c]). Compounds 3 and 6 are of similar distinctive
purple color and possess similar solubility. In this work,
we elected to work with the FPNP ligand primarily because
of the convenience of 19F NMR as an analytical tool. All of
the compounds in this study display C2v symmetry in solu-
tion on the NMR time scale. We have previously structur-
ally characterized several PNP Pd complexes, all of which
possess an approximately square-planar geometry about
Pd [4].
*
Corresponding author. Tel.: +1 781 736 2508; fax: +1 781 736 2516.
E-mail address: ozerov@brandeis.edu (O.V. Ozerov).
0020-1693/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2006.07.067

C.M. Fafard, O.V. Ozerov / Inorganica Chimica Acta 360 (2007) 286–292
287
X
ondary alkyls are to be expected, it would be very hard
to reconcile the essentially infinite lifetime of 8/9 at elevated
temperature with the rapid BHE of 12/13 at ambient tem-
perature, should they have been formed. Literature exam-
ples of square-planar Pd–CHMe2 compounds that are
observable at ambient conditions do exist [9].
X
X
X
X
PiPr2
Pd
PiPr2
Pd
PiPr2
Pd
NaBH4
MeOTf
N
OTf
N
H
N
Cl
PiPr2
PiPr2
PiPr2
X
X = Me, 1
X = F, 4
(XPNP)PdCl
X = Me, 2
X = F, 5
PNP)PdH
X = Me, 3
X = F, 6
(XPNP)PdOTf
It is possible that the production of 5 in the reactions of
6 with iPrMgCl and tBuMgCl results from a direct hydride
transfer (that is, without the formation of a Pd–C bond).
An alternative possibility is that an initial one-electron
(X
Scheme 1.
t
reduction of 5 by the bulky Grignard or BuLi with subse-
The preparation of (FPNP)PdR compounds (7–11) can
quent transfer of H atom to Pd. The sluggishness of the
transfer of a secondary alkyl group to Pd is also evidenced
by the fact that we were able to use the commercial
(Aldrich) dibutylmagnesium solution that contains a 1:1
mixture of n-Bu and sec-Bu groups to selectively prepare
9 from 6.
be accomplished by the action of an alkylating agent
(alkyllithium, alkylzinc, or alkylmagnesium reagents) on
either 4 or 6 (Scheme 2). We have previously described
the preparation of 7 in this fashion [4a]. The alkylating
agent may be used in excess with no detriment to the yield
of product. Compounds 8–11 were fully characterized by
solution NMR methods and 8 was also characterized by
elemental analysis.
2.2. Syntheses of (FPNP)Pd-alkoxide compounds and their
thermal stability
All of compounds 7–11 displayed outstanding thermal
stability. Remarkably, thermolysis of C6D6 solutions of
7–11 at 100 °C for 20 h did not result in any change obser-
vable by NMR. Compounds 8 and 9 are arguably the most
thermally stable b-hydrogen-containing Pd alkyls known
[7]. Recently, Liang et al. described b-hydrogen-containing
Ni alkyls supported by closely related PNP ligands [8].
Liang’s compounds displayed high thermal stability as
well. However, the stability of some of these Ni alkyls is
at least of the thermodynamic origin as the corresponding
hydrides reacted irreversibly with alkenes by insertion (the
reverse of b-hydrogen elimination). In contrast, 5 did not
react with ethylene (1 atm) in C6D6, even after 18 h at
90 °C. Thus, in the (PNP)Pd case, it remains unclear
whether the insertion product (Pd-alkyl) or the BHE prod-
ucts (XXX + olefin) are thermodynamically favorable.
Our attempts to prepare 12 and 13 were unsuccessful.
The alkoxide derivatives 15–17 were conveniently syn-
thesized from the corresponding potassium alkoxides and
6 (Scheme 3). The potassium alkoxides were prepared
in situ via dissolution of KOBut in MeOH, EtOH, or
iPrOH, respectively. We have also prepared the hydroxo
complex 14 via the reaction of 6 with KOH (Scheme 3).
Compound 14 was sometimes observed as an impurity in
the syntheses of 15–17 if the corresponding alcohol were
not rigorously water-free. An analogous terminal hydroxo
(PCP)PdOH complex is known [10]. Similarly to the latter,
the OH proton of 14 resonates in the upfield region of the
1H NMR spectrum (d À2.15 ppm, t, JHP = 2 Hz).
Compounds 14–17 are isolable materials that are stable
in solution at ambient temperature. While we were success-
ful in isolating a small analytically pure batch of 16, it was
typically contaminated by small amounts (<3%) of 5 and/
or 20. Compounds 14–17 also display high stability at
t
iPrMgCl and BuMgCl did not react with 4. The action
of iPrMgCl on 6 produced only 4 and 5. Similarly, the reac-
tion of tBuMgCl or tBuLi with 6 produced mostly 5. Com-
pound 12 or 13 was not observed at all in these
experiments.
KOH
or
KOBut/ROH
(FPNP)PdOTf
(FPNP)PdOR
At first glance, b-hydride elimination from a secondary
or tertiary Pd alkyl might be the most ‘‘obvious’’ path to
the observed 5 in these reactions. However, to us this seems
unlikely, given the outstanding thermal stability of 8 and 9
(vide supra). While differences between primary and sec-
6
R = H, 14
R = Me, 15
R = Et, 16
R = iPr, 17
Scheme 3.
RLi
(FPNP)PdCl
(FPNP)PdCHMe2
or
4
(FPNP)PdR
12
+
RMgX
or
R2Zn
or
or
(FPNP)PdOTf
(FPNP)PdCMe3
13
R = Me, 7
R = Et, 8
R = Bu, 9
R = Ph, 10
R = CH2Ph, 11
6
Scheme 2.

288
C.M. Fafard, O.V. Ozerov / Inorganica Chimica Acta 360 (2007) 286–292
Table 2
elevated temperatures. The stability of the hydroxo com-
plex 14 is perhaps unexceptional, but the high stability of
the b-hydrogen containing alkoxides 15–17 is striking.
Thermolysis of 17 in C6D6 (1 h, 75 °C) did not result in
any NMR-observable change. Thermolysis of 16 in C6D6
at 75 °C for 20 h resulted in the decomposition of only
2% of 16 and the thermolysis of 15 in C6D6 (1 h, 80 °C)
resulted in the decomposition of only 8% of 15.
Data for the thermolyses of (PNP)PdOEt (16) in C6D6/EtOH mixtures of
varying composition at 100 °C
Fraction EtOH, v/v
10%
25%
50%
75%
90%
At mixing
16
5
100
3
1
100
3
1
100
3
1
100
3
1
100
3
1
20
Blum and Milstein described a related case where BHE
from an Ir-methoxide 18 proceeded in the absence of cis-
empty site (Scheme 4) and found that the rate of BHE
depended on the concentration of MeOH present [11].
We selected 16 for further study, desiring to probe the
influence of the solvent on BHE. We performed a series
of experiments in which 16 was thermolyzed at 75 °C and
at 100 °C in mixtures with different C6D6/EtOH ratios
(Tables 1 and 2). It is apparent from the data that increas-
ing ethanol concentration enhances the rate of the disap-
pearance of 16. Blum and Milstein determined that the
BHE from 18 displayed an apparent kinetic order of
2.7 in methanol [11]. In this report, we only strive to show
the qualitative trend. Drastically changing benzene/ethanol
ratios in our case not only simply vary the ethanol concen-
tration but also substantially change the polarity of the
medium. It is not immediately clear to us how this can be
quantitatively accounted for in a kinetic study.
After 1 h
16
5
99
4
1
99
4
1
98
6
2
95
8
2
93
9
2
20
After 20 h
16
5
90
9
4
88
11
5
83
16
7
69
26
10
59
32
14
20
Relative concentrations of compounds 16, 5, and 20 (vs. 19F NMR stan-
dard) are given.
O
H
C6D6/EtOH
(FPNP)PdOEt
(FPNP)Pd CH2
(FPNP)PdH
+
75-100 oC
20
16
5
+
EtOH
CH3CHO
O
O
Cl
16
Pt
The major product of the thermal decomposition of 16
is 5; however, 20 was also consistently observed as a minor
by-product (Scheme 5). We have not been able to isolate
this compound in a pure state and its identification is based
on the solution NMR data. We propose that the enolate
complex 20 is formed by the reaction of free acetaldehyde
(the by-product of the BHE from 16) with 16. The aldehy-
CH2CHO
21
Scheme 5.
dic proton in 20 resonates as a triplet (JHH = 5 Hz) at d
9.82 ppm and the hydrogens of the Pd-bound methylene
group give rise to apparent quartet (doublet of triplets,
JHH ꢀ JPH ꢀ 5 Hz) at d 2.81 ppm. Tsutsui and co-workers
reported 21 (Scheme 5) in which the Pt–CH2CHO fragment
gave rise to two resonances at d 9.3 and 3.3 ppm with a
5.5 Hz JHH coupling [12].
The high thermal stability of alkoxides 15–17 is remark-
able, considering that BHE in late metal alkoxides is com-
monplace [2]. The fact that 16 does undergo BHE in
ethanol indicates that the process is thermodynamically
favorable and the lack of BHE in non-polar solvents must
be ascribed to kinetic reasons. Based on the observed sol-
vent dependence, we propose a mechanism for BHE similar
to that outlined by Blum and Milstein for 18 [11] (Scheme
6). Heterolytic dissociation of the alkoxide anion would
H
Ir
H
L
Ph
L
C6D6/MeOH
L = PMe3
L
Ph
L
Ir
L
L
OMe
18
H
19
Scheme 4.
Table 1
Data for the thermolyses of (PNP)PdOEt (16) in C6D6/EtOH mixtures of
varying composition at 75 °C
Fraction EtOH, v/v 0%
10% 25% 50% 75% 90% 100%
At mixing
16
5
100 100
100
2
1
100
2
1
100
2
1
100
2
1
100
2
1
H-OCH2Me
O
H
2
1
2
1
(FPNP)Pd OCH2Me
(FPNP)Pd
C
20
16
22
H
Me
After 20 h
16
5
98
4
3
97
5
2
94
7
2
90
9
4
85
13
7
80
16
8
71
22
10
O
(FPNP)Pd
H
+
20
H3C
H
5
Relative concentrations of compounds 16, 5, and 20 (vs. 19F NMR stan-
dard) are given.
Scheme 6.

C.M. Fafard, O.V. Ozerov / Inorganica Chimica Acta 360 (2007) 286–292
289
produce a (PNP)Pd cation 22, which may be stabilized by
the solvent (alcohol). The alkoxide may then attack the
metal with its hydrocarbyl end and in effect function as a
hydride transfer agent. The accelerating effect of the alco-
hol solvent is seen as both owing to the increase of the gen-
eral polarity and the more direct stabilization of the
alkoxide via hydrogen bonding.
Square-planar complexes such as 15–17 possess a high-
lying empty orbital that in some cases is available for bond-
ing. Thus it is possible to envision that the BHE in 15–17
proceeds in a more conventional fashion, intramolecularly,
through a five-coordinate transition state. However, such a
mechanism, while burdensome to rule out completely, is
difficult to reconcile with the observed dependence of the
rate on the medium of the reaction (Table 1).
then dissolved in 25 mL of toluene. To the flask, 73.0 lL
(0.646 mmol) of MeOTf was added and the solution stirred
overnight. The solution was then filtered through Celite.
The volatiles were removed from the filtrate under vacuum.
The residue was dissolved in a minimum amount of
toluene, pentane was carefully layered on the top, and then
the flask was placed in a freezer at À35 °C. The reaction
yielded 185.0 mg (83%) of a purple crystalline solid of
1
(FPNP)PdOTf (6). H NMR (C6D6): d 7.11 (m, 2 H, Ar–
H), 6.63 (m, 2H, Ar–H), 6.51 (m, 2H, Ar–H), 2.22 (m,
4H, CH), 1.25 (app. quartet (dvt), 12H, J = 7 Hz,
PCHMe2), 0.88 (app. quartet (dvt), 12H, J = 7 Hz,
PCHMe2). 13C{1H} NMR (C6D6): d 160.8 (m, C–N),
113.2 (d, JC–F = 24 Hz), 118.5 (d, JC–F = 22 Hz), 117.5
(m), 100.2 (s), 25.3 (t, 12 Hz, PCHMe2), 18.6 (PCHMe2),
17.8 (s, PCHMe2). 31P{1H} NMR (C6D6): d 52.8. 19F
NMR (C6D6): d À79.4 (s, 3F), À128.8 (s, 2F).
2.3. Summary
In summary, we demonstrate that the PNP system can
give rise to remarkably robust Pd alkyls and alkoxides
despite the presence of b-hydrogens in these moieties.
The square-planar alkoxides apparently undergo BHE via
3.3. Preparation of (FPNP)PdCH2CH3 (8)
Two hundred milligrams (0.288 mmol) of (FPNP)PdOTf
(6) was added to a 50 mL Schlenk and flask then dissolved
in 10 mL of ethyl ether. To the flask, 461.9 lL (0.374 mmol)
of 10 wt% Et2Zn in hexane was added and the solution stir-
red for 10 min. The solution was then filtered through a pad
of silica gel. The volatiles were removed from the filtrate
under vacuum and the residue was redissolved in ether.
The solution was then filtered through a pad of Celite, the
volatiles were removed from the filtrate under vacuum then
the residue dissolved in a minimum amount of ether, lay-
ered with pentane and placed in a freezer at À35 °C. The
flask was covered with aluminum foil to prevent exposure
to light. The reaction yielded 68 mg (41%) of an orange
a
non-classical mechanism that involves alkoxide
dissociation.
3. Experimental
3.1. General considerations
Unless specified otherwise, all manipulations were per-
formed under an argon atmosphere using standard Schlenk
line or glovebox techniques. Toluene, ethyl ether, C6D6,
THF, and isooctane were dried over NaK/Ph2CO/18-
crown-6, distilled or vacuum transferred and stored over
molecular sieves in an Ar-filled glovebox. Hexame-
thyldisiloxane was refluxed over and then distilled from
NaK alloy. Ethanol and fluorobenzene were dried with
and then distilled from CaH2. Methanol and isopropanol
were degassed by the freeze–pump–thaw technique.
(FPNP)PdCl (4) [4b], (FPNP)PdH (5) [4a], and (FPNP)-
PdMe (7) [4a] were prepared according to be published
procedures. All other chemicals were used as received from
commercial vendors. NMR spectra were recorded on a
Varian iNova 400 (1H NMR, 399.755 MHz; 13C NMR,
100.518 MHz; 31P NMR, 161.822 MHz; 19F NMR,
375.912 MHz) spectrometer. Chemical shifts are reported
1
crystalline solid of (FPNP)PdEt (8). H NMR (C6D6): d
7.47 (m, 2H, Ar–H), 6.78 (m, 2H, Ar–H), 6.73 (td, 2H,
JHP = 8 Hz, JHF = 3 Hz, Ar–H), 1.99 (m, 4H, CH), 1.78
(m, 2H, CH2CH3), 1.47 (tt, 3H, JHP = 2 Hz, JHH = 8 Hz,
CH2CH3), 1.13 (app. quartet (dvt), 12H, J = 9 Hz,
PCHMe2), 0.93 (app. quartet (dvt), 12H, J = 8 Hz,
PCHMe2). 13C{1H} NMR (C6D6): d 159.8 (s, C–N), 154.2
(dt, JCF = 235 Hz, JCP = 4 Hz, C–F), 121.8 (m, C–P),
118.6 (d, JC–F = 21 Hz), 118.5 (d, JC–F = 23 Hz), 115.4
(app. q (dvt), J = 7 Hz), 24.9 (t, JCP = 11 Hz, PCHMe2),
19.1 (t, JCP = 2 Hz, PCHMe2), 18.9 (s, CH2CH3), 18.1 (s,
PCHMe2), À6.13 (t, J = 4 Hz, CH2CH3). 31P{1H} NMR
(C6D6): d 37.1. 19F NMR (C6D6): d À133.3 (m). Elem. Anal.
Calc. for C26H39NP2F2Pd: C, 54.64; H, 6.83. Found: C,
54.28; H, 7.12%.
1
in d (ppm). For H and 13C NMR spectra, the residual
solvent peak was used as an internal reference. 31P NMR
spectra were referenced externally using 85% H3PO4 at d
0 ppm. 19F NMR spectra were referenced externally using
1.0M CF3CO2H in CDCl3 at À78.5 ppm. Elemental analy-
ses were performed by CALI Labs, Inc. (Parsippany, NJ).
3.4. Preparation of (FPNP)PdCH2CH2CH2CH3 (9)
Two hundred and forty three milligrams (0.351 mmol)
of (FPNP)PdOTf (6) was added to a 50 mL Schlenk flask
and dissolved in 10 mL of ethyl ether. To this solution,
790 lL (0.794 mmol) of 1.0 M Bu2Mg (1:1 n-Bu:s-Bu) in
heptane was added and the solution stirred for 10 min. The
flask was covered with aluminum foil to prevent exposure
3.2. Preparation of (FPNP)PdOTf (6)
One hundred and seventy six milligrams (0.323 mmol) of
(FPNP)PdH (5) was added to a 50 mL Schlenk flask and

290
C.M. Fafard, O.V. Ozerov / Inorganica Chimica Acta 360 (2007) 286–292
to light. The solution was then filtered through a pad of sil-
ica gel. The volatiles were removed from the filtrate under
vacuum and the residue was redissolved in ether. The solu-
tion was then filtered through a pad of Celite, the volatiles
were removed from the filtrate under vacuum and then the
residue was dissolved in a minimum of pentane and placed
in a freezer at À35 °C. The reaction yielded 110 mg (51%)
of a yellow-brown crystalline solid of (FPNP)Pd(n-Bu)
(9). 1H NMR (C6D6): d 7.47 (m, 2H, Ar–H), 6.78 (m,
2H, Ar–H), 6.73 (td, 2H, JHP = 8 Hz, JHF = 3 Hz, Ar–
H), 2.00 (m, 4H, CH), 1.75 (br m, 4H, a and b-H of
(CH2)3CH3), 1.54 (m, 2H, c-H of (CH2)3CH3), 1.11 (app.
quartet (dvt), 12H, J = 7 Hz, PCHMe2), 1.09 (t, 3H,
J = 7 Hz, (CH2)3CH3), 0.92 (app. quartet (dvt), 12H,
J = 7 Hz, PCHMe2). 13C{1H} NMR (C6D6): d 159.8 (t,
10 Hz, C–N), 154.2 (dt, JCF = 235 Hz, JCP = 4 Hz, C–F),
121.8 (td, JCF = 5 Hz, JCP = 17 Hz, C–P), 118.5 (d, JC–F
= 22 Hz), 118.6 (d, JC–F = 21 Hz),115.4 (app. q (dvt),
J = 7 Hz), 36.6 (s, CH2), 28.5 (s, CH2), 24.9 (t, 11 Hz,
PCHMe2), 19.1 (t, 3 Hz, PCHMe2), 18.1 (s, PCHMe2),
14.6 (s, CH3), 1.5 (t, J = 5 Hz, a-CH2). 31P{1H} NMR
(C6D6): d 37.3. 19F NMR (C6D6): d À133.4 (m).
and the residue redissolved in ether. The solution was then
filtered through a pad of Celite, the volatiles were removed
under vacuum and then the residue was dissolved in a min-
imum amount of pentane, layered with hexamethyldisilox-
ane and placed in a freezer at À35 °C. The flask was
covered with aluminum foil to prevent exposure to light.
The
reaction
yielded
108.5 mg
(59%)
of
(FPNP)PdCH2C6H5 (11) as an orange crystalline solid.
1H NMR (C6D6): d 7.45 (m, 4H, overlapping Ar–H of
PNP and o-H of benzyl group), 7.12 (t, 2H, J = 7 Hz, m-
H of benzyl), 6.95 (t, 1H, J = 8 Hz p-H of benzyl), 6.80
(m, 2H, Ar–H of PNP), 6.71 (td, 2H, JHP = 8 Hz,
JHF = 3 Hz, Ar–H of PNP), 3.04 (t, 2H, J = 6 Hz, CH2–
Ar–H), 1.81 (m, 4H, CH), 1.01 (app. quartet (dvt), 12H,
J = 7 Hz, PCHMe2), 0.91 (app. quartet (dvt), 12H,
J = 7 Hz, PCHMe2). 13C{1H} NMR (C6D6): d 159.8 (t,
J = 11 Hz, C–N),154.3 (d, J = 239 Hz, C–F), 152.0 (s,
ipso-C), 130.4 (s, o-C), 128.3 (s, m-C), 123.6 (s, p-C),
122.1 (m, C–P), 118.5 (d, JC–F = 23 Hz), 118.4 (d, JC–F
=
21 Hz), 115.7 (app. q (dvt), J = 7 Hz), 24.8 (t, J = 11 Hz,
P–CHMe2), 19.2 (t, J = 2 Hz, PCHMe2), 18.2 (s,
PCHMe2), 7.3 (t, J = 4 Hz, CH2Ph). 31P{1H} NMR
(C6D6): d 38.1. 19F NMR (C6D6): d À132.8.
3.5. Preparation of (FPNP)PdPh (10)
3.7. Preparation of (FPNP)PdOH (14)
Five hundred milligrams (0.865 mmol) of (FPNP)PdCl
(4) was dissolved in 5 mL of toluene. 648 lL (1.29 mmol)
of a 2.0 M PhLi solution in diethyl ether was added and
the solution stirred for an hour. The solution was then fil-
tered through a pad of silica gel and the volatiles removed
under vacuum. The residue was dissolved in ether and then
placed in a freezer at À35 °C. 189 mg (35% yield) of
(FPNP)PdC6H5 (10) was collected as a yellow crystalline
One hundred milligrams (0.144 mmol) of (FPNP)PdOTf
(6) was added to a 25 mL Schlenk flask and then dissolved
in 10 mL of THF. To the flask 8.8 mg (0.158 mmol) of
KOH and three drops of distilled and degassed water were
added. The solution was stirred for 2 h. The volatiles were
removed under vacuum. The residue was dissolved in ether
then filtered through a pad of Celite, the volatiles were
removed under vacuum from the filtrate and then the resi-
due was dissolved in a minimum amount of ether and
placed in a freezer at À35 °C. The reaction yielded 83 mg
(94%) of (FPNP)PdOH (14) as a red orange crystalline
1
solid. H NMR (C6D6): d 7.53 (m, 4H, overlapping Ar–H
of PNP and o-H of phenyl group), 7.15 (t, 2H, m-H of phe-
nyl overlapping with residual C6D5H and toluene signals),
7.00 (t, 1H, p-H of benzyl overlapping with residual toluene
signal), 6.75 (m, 4H, Ar–H of PNP), 1.91 (m, 4H, CH), 0.86
(overlapping app. quartets (dvt), 24H PCHMe2). 13C{1H}
NMR (C6D6): d 160.2 (t, J = 11 Hz, C–N), 154.4 (d,
J = 236 Hz, C–F), 148.1 (m, ipso-C), 138.9 (s, o-C), 127.7
1
solid. H NMR (C6D6): d 7.32 (m, 2H, Ar–H), 6.70 (m,
2H, Ar–H), 6.65 (td, 2H, JHP = 8 Hz, JHF = 3 Hz, Ar–
H), 1.95 (m, 4H, CH), 1.28 (app. quartet (dvt), 12H,
J = 7 Hz, PCHMe2), 1.00 (app. quartet (dvt), 12H,
J = 7 Hz, PCHMe2), À2.15 (t, 1H, J = 2 Hz, –OH).
13C{1H} NMR (C6D6): d160.7 (t, J = 11 Hz, C–N),155.5
(d, J = 237 Hz, C–F), 121.1 (td, JCP = 17 Hz, JCF = 5 Hz,
C–P), 118.6 (d, J = 23 Hz), 118.5 (d, J = 21 Hz),116.3
(app. q (dvt) J = 7 Hz), 24.8 (t, J = 11 Hz, PCHMe2),
18.8 (t, J = 3 Hz, PCHMe2), 18.2 (s, PCHMe2). 31P{1H}
NMR (C6D6): d 40.4. 19F NMR (C6D6): d À131.6 (m).
Elem. Anal. Calc. for C24H35ONP2F2Pd: C, 51.48; H,
6.30. Found: C, 51.48; H, 6.33%.
(s, m-C), 123.0 (s, p-C), 121.5 (m, C–P), 118.9 (d, JC–F
=
21 Hz), 118.7 (d, JC–F = 22 Hz), 115.4 (app. q (dvt), J =
6 Hz), 23.8 (t, J = 11 Hz, P–CHMe2), 18.4 (t, J = 3 Hz,
PCHMe2), 17.42 (s, PCHMe2). 31P{1H} NMR (C6D6): d
39.2. 19F NMR (C6D6): d À132.8.
3.6. Preparation of (FPNP)PdCH2Ph (11)
Two hundred milligrams (0.288 mmol) of (FPNP)PdOTf
(6) was added to a 50 mL Schlenk flask and then dissolved
in 10 mL of ethyl ether. To the flask, 317 lL (0.317 mmol)
of a 1 M benzyl magnesium chloride in ether was added
and the solution stirred for 10 min. The volatiles were
removed under vacuum from the filtrate. The residue was
dissolved in ether and filtered through a pad of silica gel.
The volatiles were removed under vacuum from the filtrate
3.8. Preparation of (FPNP)PdOMe (15)
9.63 lL (0.23 mmol) of degassed MeOH and 26.7 mg
(0.23 mmol) of KOBut were combined in THF and allowed
to stir for 5 min. To that 150 mg (0.22 mmol) of
(FPNP)PdOTf (6) was added and the solution stirred for

C.M. Fafard, O.V. Ozerov / Inorganica Chimica Acta 360 (2007) 286–292
291
10 min. The volatiles were removed under vacuum. The
residue was dissolved in pentane and then filtered through
a pad of Celite. The volatiles were removed under vacuum
and the residue was redissolved in a minimum amount of
pentane and placed in a freezer at À35 °C. The reaction
yielded 50 mg (40%) of (FPNP)PdOMe (15) as an orange
powder. 1H NMR (C6D6): d 7.31 (m, 2H, Ar–H), 6.72
(m, 2H, Ar–H), 6.23 (app. td, 2H, JHP = 9 Hz, JHF = 3 Hz,
Ar–H), 3.91 (s, 3H, OCH3), 2.03 (m, 4H, CH), 1.32 (app.
quartet (dvt), 12H, J = 8 Hz, PCHMe2), 1.01 (app. quartet
(dvt), 12H, J = 7 Hz, PCHMe2). 13C{1H} NMR (C6D6): d
160.9 (t, J = 11 Hz, C–N), 154.7 (d, JCF = 238 Hz, C–F),
120.8 (t), 118.8 (s), 118.5 (s), 116.4 (s), 62.2 (s, –OCH3),
24.8 (t, J = 11 Hz, PCHMe2), 18.5 (s,CHMe2), 18.0 (s,
CHMe2). 31P{1H} NMR (C6D6): d 38.6. 19F NMR
(C6D6): d À131.5.
3.86 (m, 1H, OCHMe2), 2.04 (m, 4H, CH), 1.49 (d, 6H,
OCHMe2), 1.30 (app. quartet (dvt), 12H, J = 8 Hz,
PCHMe2), 1.01 (app. quartet (dvt), 12H, J = 7 Hz,
PCHMe2). 13C{1H} NMR (C6D6): d 160.8 (t, J = 11 Hz,
C–N), 154.8 (d, JCP = 237 Hz, C–F), 120.9 (td, JC–P
=
18 Hz, JC–F = 4 Hz, C–P), 118.4 (d, JC–F = 21 Hz), 118.6
(d, JC–F = 23 Hz), 116.6 (app. q (dvt), J = 6 Hz), 74.0 (s,
–OCHMe2), 31.1 (s, –OCHMe2), 25.1 (t, J = 11 Hz,
PCHMe2), 18.6 (s, CHMe2), 17.9 (s, CHMe2). 31P{1H}
NMR (C6D6): d 38.6. 19F NMR (C6D6): d À131.5. Elem.
Anal. Calc. for C27H41ONP2F2Pd: C, 53.91; H, 6.82.
Found: C, 53.90; H, 6.98%.
3.11. General procedure for the thermolysis of (PNP)Pd-
alkyl complexes
Twenty milligrams of each (PNP)Pd-alkyl (7–11) was
dissolved in C6D6 (0.5 mL, J. Young tube). The samples
were then heated in an oil bath at 100 °C for 20 h. Subse-
quent NMR analysis showed no change in composition
of solutions.
3.9. Preparation of (FPNP)PdOEt (16)
75.5 lL (1.3 mmol) of distilled EtOH and 132.5 mg
(1.18 mmol) of KOBut were combined in THF and allowed
to stir for 5 min. To that 500 mg (0.72 mmol) of
(FPNP)PdOTf (6) was added and the solution stirred for
1 h. The solution was filtered through a pad of Celite and
the volatiles were then removed under vacuum from the fil-
trate. The residue was then redissolved in toluene and fil-
tered again through a pad of Celite. One microliter of
iso-octane was added and the volatiles were removed under
vacuum. The reaction yielded 372 mg (88%) of
(FPNP)PdOEt (16) as an orange powder. 1H NMR
(C6D6): d 7.30 (m, 2H, Ar–H), 6.72 (m, 2H, Ar–H), 6.62
(app. td, 2H, Ar–H), 3.97 (q, 2H, O–CH2CH3), 2.02 (m,
4H, CH), 1.44 (t, 3H, J = 8 Hz, O–CH2CH3) 1.30 (app.
quartet (dvt), 12H, J = 8 Hz, PCHMe2), 1.00 (app. quartet
(dvt), 12H, J = 7 Hz, PCHMe2); 13C{1H} NMR (C6D6): d
160.8 (C–N), 154.7 (d, JCF = 237 Hz, C–F), 120.8 (m, C–
P), 118.7 (s), 118.5 (s), 116.4 (app. q (dvt), J = 6 Hz),
68.1 (s, –OCH2CH3), 24.9 (t, J = 11 Hz, PCHMe2), 22.4
(s, –OCH2CH3), 18.5 (t, J = 3 Hz, CHMe2), 17.9 (s,
CHMe2); 31P{1H} NMR (C6D6): d 38.7; 19F NMR
(C6D6): d À131.6.
3.12. Thermolysis of (PNP)PdOH (14)
Twenty milligrams of (PNP)PdOH (14) was dissolved in
C6D6 (0.5 mL, J. Young tube). The sample was then heated
in an oil bath at 75 °C for 2.5 h. Subsequent NMR analysis
showed no change in composition of the solution.
3.13. Thermolysis of (PNP)PdOMe (15)
Seventeen milligrams of (PNP)PdOMe (15) was dis-
solved in C6D6 (0.5 mL, J. Young tube). The sample was
then heated in an oil bath at 80 °C for 1 h. An 8% decrease
in the concentration of 15 was observed by 19F NMR.
3.14. Thermolysis of (PNP)PdOPri (17)
Ten milligrams (0.017 mmol) of (PNP)PdOPri (17) was
dissolved in 0.5 mL of C6D6. One drop of a,a,a-trifluoro-
toluene was added to the sample as an internal integration
standard for 19F NMR. The sample was then heated in an
oil bath at 75 °C for 1 h. No change in the concentration of
17 was noted by 19F NMR.
3.10. Preparation of (FPNP)PdOiPr (17)
36.4 lL (0.51 mmol) of degassed i-PrOH and 56.6 mg
(0.51 mmol) of KOBut were combined in THF and allowed
to stir for 5 min. To that 350 mg (0.51 mmol) of
(FPNP)PdOTf (6) was added and the solution stirred for
10 min. The volatiles were removed under vacuum. The
residue was dissolved in pentane and then filtered through
a pad of Celite. The volatiles were removed under vacuum
from the filtrate and the residue was dissolved in a mini-
mum amount of pentane and placed in a freezer at
À35 °C. The reaction yielded 115.8 mg (38%) of
(FPNP)PdOPri (17) as an orange crystalline solid. 1H
NMR (C6D6): d 7.29 (m, 2H, Ar–H), 6.74 (m, 2H, Ar–
H), 6.62 (app. td, 2H, JHP = 9 Hz, JHF = 3 Hz, Ar–H),
3.15. General procedure for the thermolysis of (PNP)PdOEt
(16) in the C6D6/EtOH mixtures
Samples of (PNP)PdOEt (17) (18–23 mg, 0.031–0.039
mmol) were dissolved in 0.5 mL of a solvent mixture.
Solutions made contained 0%, 10%, 25%, 50%, 75%, 90%
and 100% ethanol by volume in C6D6. Five microliters
(0.051 mmol) of fluorobenzene was added to each sample
as an internal integration standard for 19F NMR. These
samples were then heated in an oil bath and analyzed by
19F and 31P NMR at indicated times. Following the
thermolysis, (PNP)PdOEt (16), (PNP)PdH (5) and

292
C.M. Fafard, O.V. Ozerov / Inorganica Chimica Acta 360 (2007) 286–292
[3] (a) H.E. Bryndza, J.C. Calabrese, M. Marsi, D.C. Roe, W. Tam,
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(PNP)Pd–CH2CHO (20) were observed. Selected NMR
data for 20 follow. 1H NMR (C6D6): d 9.82 (t, 1H,
J = 5 Hz, C(O)H), 2.81 (app. q (dt), 2H, JH-P = 6 Hz,
1
J = 5 Hz, CH2C(O)H); H{31P} NMR (C6D6): d 9.82 (t,
1H, J = 5 Hz, C(O)H), 2.81 (d, 2H, J = 5 Hz, CH2C(O)H);
(d) K.A. Bernard, W.M. Rees, J.D. Atwood, Organometallics 5
(1986) 390;
(e) D.M. Hoffman, D. Lappas, D.A. Wierda, J. Am. Chem. Soc. 111
(1989) 1531;
(f) H. Itagaki, N. Koga, K. Morokuma, Y. Saito, Organometallics
12 (1993) 1648;
31P{1H} NMR (C6D6): d 44.7; 19F NMR (C6D6): d À131.8.
Acknowledgements
(g) A.J. Gellman, Q. Dai, J. Am. Chem. Soc. 115 (1993) 714.
[4] (a) O.V. Ozerov, C. Guo, L. Fan, B.M. Foxman, Organometallics 23
(2004) 5573;
We are grateful to NSF (CHE-0517798), Brandeis Uni-
versity, the Donors of the American Chemical Society
Petroleum Research Fund, Research Corporation, and
the Sloan Foundation for support of this research.
(b) L. Fan, L. Yang, C.Y. Guo, B.M. Foxman, O.V. Ozerov,
Organometallics 23 (2004) 4778;
(c) L. Fan, B.M. Foxman, O.V. Ozerov, Organometallics 23 (2004)
326.
[5] (a) S. Gatard, R. C¸ elenligil-C¸ etin, C. Guo, B.M. Foxman, O.V.
Ozerov, J. Am. Chem. Soc. 128 (2006) 2808;
(b) L. Fan, S. Parkin, O.V. Ozerov, J. Am. Chem. Soc. 127 (2005)
16772;
Appendix A. Supporting information available
Graphical depictions of 1H NMR spectra of selected
compounds. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the
Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033;
e-mail: deposit@ccdc.cam.ac.uk]. Supplementary data
associated with this article can be found, in the online ver-
sion, at doi:10.1016/j.ica.2006.07.067.
(c) L. Fan, O.V. Ozerov, Chem. Commun. (2005) 4450;
(d) B.C. Bailey, J.C. Huffman, D.J. Mindiola, W. Weng, O.V.
Ozerov, Organometallics 24 (2005) 1390;
(e) W. Weng, L. Yang, B.M. Foxman, O.V. Ozerov, Organometallics
23 (2004) 4700.
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