Kinetics and mechanisms of methyl vinyl ketone hydroalkoxylation catalyzed by palladium(II) complexes

Article abstract of DOI:10.1021/om0103097

Palladium(II) coordination complexes such as (CH₃CN)₂PdCl₂, 1, catalyze the addition of alcohols to vinyl ketones to produce ethers. During the catalytic cycle, the alcohol adds selectively to the β-carbon (anti-Markovnikov). The kinetics for the reaction of benzyl alcohol (BA) with methyl vinyl ketone (MVK) as catalyzed by 1 has been investigated in detail. The experimental rate law is first-order in catalyst and BA and features saturatiost and BA and features saturatioonitrile is a competitive inhibitor for MVK. The most consistent mechanism with the experimental findings involves substitution of an acetonitrile ligand by MVK in a preequilibrium step (K₁ = 0.020 ± 0.004 in CDCl₃ at 25°C) followed by nucleophilic attack of benzyl alcohol (k₂ = (7.6 ± 0.8) × 10^-3 M^-1 s^-1 in CDCl₃ at 25°C). A kinetic isotope effect has been noted for the reaction in the limit of saturated MVK (k₂^H/k₂^D = 2.0). MVK coordinates to palladium affording an η²-alkene adduct. The rate constants for several alcohols are reported; the catalytic reaction is sensitive to steric hindrance of the alcohol nucleophile: 1° > 2° ? 3°. Appreciable kinetic effects are observed by variation of the substituents on BA. Two new palladium(II) coordination complexes containing bidentate and tridentate pyridyl imine ligands have been synthesized, fully characterized, and explored as catalysts for the hydroalkoxylation reaction. The synthesis of AgBAr₄^F and its use in metathesis reactions with Pd(II) complexes are described. A mechanism has been put forth where the carbonyl group of the olefin interacts with palladium and directs the alcohol addition to the β-carbon, resulting in the anti-Markovnikov addition ether product. Finally, the charge of the palladium complex augments catalytic activity.

Full text of DOI:10.1021/om0103097

Organometallics 2001, 20, 4403-4412
4403
Kin etics a n d Mech a n ism s of Meth yl Vin yl Keton e
Hyd r oa lk oxyla tion Ca ta lyzed by P a lla d iu m (II)
Com p lexes
Kimberly J . Miller, Terutaka T. Kitagawa, and Mahdi M. Abu-Omar*
Department of Chemistry and Biochemistry, Box 951569, 405 Hilgard Avenue,
University of California, Los Angeles, California 90095
Received April 13, 2001
Palladium(II) coordination complexes such as (CH3CN)2PdCl2, 1, catalyze the addition of
alcohols to vinyl ketones to produce ethers. During the catalytic cycle, the alcohol adds
selectively to the â-carbon (anti-Markovnikov). The kinetics for the reaction of benzyl alcohol
(BA) with methyl vinyl ketone (MVK) as catalyzed by 1 has been investigated in detail. The
experimental rate law is first-order in catalyst and BA and features saturation kinetics in
MVK. Acetonitrile is a competitive inhibitor for MVK. The most consistent mechanism with
the experimental findings involves substitution of an acetonitrile ligand by MVK in a
preequilibrium step (K1 ) 0.020 ( 0.004 in CDCl3 at 25 °C) followed by nucleophilic attack
of benzyl alcohol (k2 ) (7.6 ( 0.8) × 10-3 M-1 s-1 in CDCl3 at 25 °C). A kinetic isotope effect
D
has been noted for the reaction in the limit of saturated MVK (k2H/k2 ) 2.0). MVK
coordinates to palladium affording an η2-alkene adduct. The rate constants for several
alcohols are reported; the catalytic reaction is sensitive to steric hindrance of the alcohol
nucleophile: 1° > 2° . 3°. Appreciable kinetic effects are observed by variation of the
substituents on BA. Two new palladium(II) coordination complexes containing bidentate
and tridentate pyridyl imine ligands have been synthesized, fully characterized, and explored
as catalysts for the hydroalkoxylation reaction. The synthesis of AgBArF and its use in
4
metathesis reactions with Pd(II) complexes are described. A mechanism has been put forth
where the carbonyl group of the olefin interacts with palladium and directs the alcohol
addition to the â-carbon, resulting in the anti-Markovnikov addition ether product. Finally,
the charge of the palladium complex augments catalytic activity.
1. In tr od u ction
afford secondary amines (hydroamination).11,12 Large-
scale hydration of alkenes requires high acid concentra-
tions and elevated temperatures, which limits the utility
of the reaction.13,14 Thus, the development of tolerant
transition-metal catalysts for hydration, hydroalkoxy-
lation,15 and hydroamination16-20 of olefins under mild
conditions is desirable but remains challenging. Gan-
guly and Roundhill, for example, showed that dimeric
µ-hydroxo palladium complexes bearing bidentate phos-
phane ligands catalyze the hydration of diethyl maleate
to diethyl malate between 120 and 140 °C;4,5 however,
turnover numbers were low.
Palladium-assisted addition of oxygen nucleophiles to
alkenes gives a σ-alkyl palladium(II) intermediate which
generally undergoes â-hydride elimination to yield
aldehydes or ketones.1,2 The Wacker process is the pro-
totypical example of palladium-catalyzed oxidative hy-
drolysis of alkenes.3 The less developed competing reac-
tion is the protonolysis of the σ-alkyl bond on palladium
to give the addition rather than oxidation product. When
water is the nucleophile, alcohols are generated directly
from alkenes (hydration).4-9 Alcohols, on the other hand,
produce ethers (hydroalkoxylation),10 and primary amines
* Corresponding author. E-mail: mao@chem.ucla.edu.
(1) Maitlis, P. The Organic Chemistry of Palladium; Academic
Press: New York, 1971; Vol. II, pp 77-126, and references therein.
(2) Henry, P. M. Palladium Catalyzed Oxidation of Hydrocarbons;
D. Reidel: Dordrecht, 1980; pp 41-147.
(3) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis, 2nd ed.;
Wiley: New York, 1992; pp 138, and references therein.
(4) Ganguly, S.; Roundhill, D. M. J . Chem. Soc., Chem. Commun.
1991, 639-640.
(5) Ganguly, S.; Roundhill, D. M. Organometallics 1993, 12, 4825-
4832.
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Lett. 1989, 2001-2004.
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Soc. 1969, 91, 3879-3883.
(12) Åkermark, B.; Backvall, J . E.; Hegedus, L. S.; Siirala-Hansen,
K.; Sjoberg, K.; Zetterberg, K. J . Organomet. Chem. 1974, 72, 127-
138.
(13) Eguchi, K.; Tokiai, T.; Kimura, H. Chem. Lett. 1986, 567-570.
(14) Eguchi, K.; Tokiai, T.; Arai, H. Appl. Catal. 1987, 34, 275.
(15) Lin, Y.-S.; Takeda, S.; Matsumoto, K. Organometallics 1999,
18, 4897-4899.
(6) Stille, J . K.; J ames, D. E. J . Organomet. Chem. 1976, 108, 401-
408.
(16) Dorta, R.; Egli, P.; Zurcher, F.; Togni, A. J . Am. Chem. Soc.
1997, 119, 10857-10858.
(7) Stille, J . K.; Divakarumi, R. J . Organomet. Chem. 1979, 169,
239-248.
(17) Schaffrath, H.; Keim, W. J . Mol. Catal. A 2001, 168, 9-14.
(18) Trauthwein, H.; Tillack, A.; Beller, M. J . Chem. Soc., Chem.
Commun. 1999, 2029-2030.
(8) Backvall, J . E.; Åkermark, B.; Ljunggren, S. O. J . Am. Chem.
Soc. 1979, 101, 2411-2416.
(19) Li, Y.; Marks, T. J . Organometallics 1996, 15, 3770-3772.
(20) Beller, M.; Trauthwein, H.; Eichberger, M.; Breindl, C.; Mueller,
T. E. Eur. J . Inorg. Chem. 1999, 1121-1132.
(9) Bennett, M. A.; J in, H.; Li, S.; Rendina, L. M.; Willis, A. C. J .
Am. Chem. Soc. 1995, 117, 8335-8340.
10.1021/om0103097 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/14/2001

4404 Organometallics, Vol. 20, No. 21, 2001
Miller et al.
Sch em e 1
hydroamination with aniline as the nucleophile (entries
8 and 9). Electron-rich phenols could also be used to give
aromatic ethers (entry 10), but the yields are low. The
addition of alcohol (2.0 M) to MVK (0.50 M) does not
occur to any detectable extent in the absence of catalyst
even after 24 h of reaction. All the employed nucleo-
philes afford exclusively the addition product in high
yields. Neither oxidative hydroalkoxylation nor polym-
erization of MVK was observed. Only when the alkyl
derivative of complex 4 such as [(NN)Pd(CH3)(CH3CN)]+
is employed does the polymerization of MVK ensue.25
It is worth noting that the rate of reaction is depend-
ent on steric hindrance of the nucleophile as well as the
charge of the palladium(II) complex. Both aspects will
be specified via quantitative kinetics later on in the
paper. With the heavier nucleophiles, the addition
products were easily isolated and purified by flash
chromatography. All products were fully characterized
by NMR, GC/MS, and mass spectrometry. The ether
products resulting from the addition of lighter alcohols
to MVK were not isolated, but yields were determined
by NMR and GC/MS. In most cases, the isolated yields
of the addition product were comparable to reaction
yields determined by NMR prior to workup (Table 1).
2.2. Deter m in a tion of th e Mech a n ism w ith
(CH 3CN)2P d Cl2, 1, a s Ca t a lyst . Gen er a l Kin et ics
Exp er im en ts. The addition of benzyl alcohol (BA) to
methyl vinyl ketone (MVK) catalyzed by 1, eq 1, was
chosen as a representative reaction for the initial
detailed kinetic investigation. Rates of reaction were
gathered via NMR, where the formation of the product
and disappearance of the substrates were monitored.
However, the formation of the ether product was easiest
to follow because of the unique two sets of triplets in
the 1H NMR spectrum at approximately 3.7 and 2.7
ppm. The two signals correspond to the two sets of
hydrogens on the R- and â-carbons with respect to the
carbonyl group. All kinetic reactions were followed by
NMR to completion, and 4-benzyloxy-2-butanone was
the only detectable product. A representative kinetic
trace is shown in Figure S1. Initial rates method was
used to avoid mixed second-order kinetics during the
catalytic reaction. Over prolonged periods of time, a
detectable amount of palladium metal was deposited on
the walls of NMR tubes. However, palladium metal does
F igu r e 1. Palladium(II) coordination catalysts for hy-
droalkoxylation.
Addition of alcohols to a carbon-carbon double bond
is a potentially useful route for making ethers from
alkenes. Alcohols add to a palladium-activated π-com-
plex to form a σ-alkyl Pd(II) intermediate, Scheme 1.
â-Hydride migration results in the formation of a vinyl
ether, which reacts readily with an additional molecule
of alcohol to afford an acetal, and metallic palladium-
(0) is deposited (pathway B).21 Alternatively, if the
protonolysis of the Pd-alkyl bond is faster than â-hy-
dride elimination, the result is the addition of alcohol
(ROH) across the carbon-carbon double bond (pathway
A).22 In 1989, Hosokawa and co-workers demonstrated
that pathway A with bis(acetronitrile)palladium(II)
chloride is important for alkenes bearing electron-
withdrawing groups (Z).10
It is worth noting that in the case of amine addition
to olefins pathway A is prominent, since amines coor-
dinate to Pd(II) more strongly than alcohols. Thus, the
σ-alkyl intermediate is stabilized against â-hydride
migration that causes oxidative damage.12,23,24
In this paper we report our results on the kinetics
and mechanism of palladium-catalyzed hydroalkoxyla-
tion of alkenes. In addition, we now report on new
palladium(II) coordination catalysts for the effective
hydroalkoxylation of vinyl ketones. The catalytic reac-
tions give regioselectively the â-addition product in high
yields with a variety of nucleophiles. A mechanistic
basis for the observed regioselectivity is presented.
Additionally, we scrutinize the electronic and steric
factors influencing catalysis.
2. Resu lts
2.1. Scop e a n d Utility of th e Ca ta lytic Hyd r o-
a lk oxyla tion Rea ction . Three monomeric palladium-
(II) coordination catalysts were investigated in prepara-
tive scale reactions (Figure 1). Methyl vinyl ketone
(MVK) was selected as the prototypical alkene bearing
an electron-withdrawing group. A variety of alcohols
were reacted with MVK. Under the mild conditions
employed during the reaction, the nucleophile adds to
the â-carbon selectively. The results are summarized
in Table 1. In addition, the diversity of these palladium
complexes is illustrated by their ability to catalyze
(21) Henry, P. M. Palladium Catalyzed Oxidation of Hydrocarbons;
D. Reidel: Dordrecht, 1980; pp 133-147.
(22) Wan, W. K.; Zaw, K.; Henry, P. M. Organometallics 1988, 7,
1677-1683.
(23) Muller, T. E.; Beller, M. Chem. Rev. 1998, 98, 675-703.
(24) Kawatsura, M.; Hartwig, J . F. J . Am. Chem. Soc. 2000, 122,
9546-9547.
(25) Mecking, S.; J ohnson, L. K.; Wang, L.; Brookhart, M. J . Am.
Chem. Soc. 1998, 120, 888-899.

Methyl Vinyl Ketone Hydroalkoxylation
Organometallics, Vol. 20, No. 21, 2001 4405
Ta ble 1. P a lla d iu m -Ca ta lyzed Hyd r oa lk oxyla tion a n d Hyd r oa m in a tion of MVK
a
Method A: [MVK] ) 1.0 mmol, [Nucleophile] ) 1.0 mmol, and [1] ) 0.040 mmol in trichloromethane (VT ) 1.0 mL) at 25 °C. Method
b
B: [MVK] ) 1.0 mmol, [Nucleophile] ) 1.0 mmol, and [4 or 5] ) 0.010 mmol in trichloromethane (VT ) 1.0 mL) at 25 °C. Determined
by 1H NMR, and addition product confirmed by GC/MS. c Isolated product characterized by 1H NMR and mass spectrometry. TON )
d
[Product]/ [Pd]; all reactions were run for 48 h unless noted otherwise. In cases where more than 48 h was required, the reaction was
monitored by 1H NMR until product had reached a maximum. e [MVK] ) 0.40 mmol, [4-methoxyphenol] ) 0.80 mmol, and [1] ) 0.040
mmol in CDCl3 (VT ) 1.0 mL) at 65 °C.
not catalyze hydroalkoxylation of MVK. In the absence
of catalyst, no reaction occurs even after 1 day. One
limitation of the reaction was the low solubility of 1 in
trichloromethane. Concentrations of 1 could not exceed
0.040 M, and stock solutions had to be used within 2
days to ensure reproducibility.
Many reports have been published describing nucleo-
philic attack on (η2-olefin)palladium(II) complexes.1,5,9,22,26
On the basis of the current understanding in the
literature and the observed kinetics in this study, we
postulate the mechanism in Scheme 2. The alkene,
MVK, reacts with 1 in a preequilibrium step to form an
η2-olefin adduct of Pd(II).22,27 Benzyl alcohol, BA, then
attacks the coordinated (activated) alkene to yield the
ether product, regenerating the palladium catalyst. The
rate law for Scheme 2, assuming steady state for the
(alkene)Pd(II) complex, is given in eq 2.
k1k2[BA][MVK][Pd]T
d[MVK]
v ) -
)
dt
k-1[CH3CN] + k1[MVK] + k2[BA]
(2)
Deter m in a tion of Rea ction Or d er s in Su bstr a tes.
The rate of reaction was measured as a function of
[MVK], while [BA] and [1] were held constant: [BA] )
1.0 M, [1] ) 0.040 M, and [MVK] ) 0.10-2.50 M in
CDCl3 at 25 °C. At low [MVK] concentrations, the rate
is first-order in [MVK] but approaches zero-order at high
concentrations, Figure 2. In contrast, plots of initial rate
versus [BA], Figure S2, and [1], Figure S3, are linear.
Deta iled Kin etics An a lyses a n d Decip h er in g of
R a t e Con st a n t s. To evaluate the individual rate
(26) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987; pp 826-841.
(27) Henry, P. M. Palladium Catalyzed Oxidation of Hydrocarbons;
D. Reidel: Dordrecht, 1980; pp 21-25.

4406 Organometallics, Vol. 20, No. 21, 2001
Miller et al.
[MVK], one obtains K1 ) 0.020 ( 0.004.
[Pd]T[BA]
[CH3CN]
[MVK]
1
1
k2
)
+
(4)
Vi
K1k2
A similar study was conducted at constant [MVK]
(0.50 M) and variable [BA] (0.30, 0.50, 0.80, and 1.00
M); the rate equation is specified by eq 5. Both slopes
and intercepts from plots of [Pd]T/Vi versus [CH3CN] are
linear with respect to 1/[BA], Figure S5. Thus, aceto-
nitrile is a competitive inhibitor for MVK but not for
benzyl alcohol. Furthermore, the UV-vis spectrum of
the palladium complex under catalytic conditions differs
from that of 1 in the limit of saturated [MVK], again,
supporting “bulk” intermediate.
[Pd]T
[CH3CN]
1
1
k2
1
)
+
(5)
Vi
K1k2
[MVK][BA]
[BA]
F igu r e 2. Plot of the initial rate versus [MVK] for the
alkoxylation of MVK with BA catalyzed by complex 1. The
curve shows the fit of the data to the rate law in eq 3.
Conditions: [BA] ) 1.00 M, [1] ) 0.040 M, and [MVK] )
0.10-2.50 M in CDCl3 at 25° C.
Kin etic Isotop e Effect (k2H/k2D). The strength of
the O-D bond is approximately 1.2 kcal/mol greater
than the equivalent O-H;28 thus, any effect on the rate
by substituting D for H provides insight into the mech-
anism of hydroalkoxylation. The O-H of benzyl alcohol
was exchanged to O-D (BzOD) by allowing benzyl
alcohol to stir with an excess of D2O for 2 h. D2O was
then removed by distillation, and the 1H NMR spectrum
of deuterobenzyl alcohol (BzOD) was recorded to ensure
constants in Scheme 2, the kinetics data obtained from
NMR experiments were fitted to various limits of the
rate law. The observed saturation in [MVK] reduces the
rate law to the prior equilibrium limit, eq 3, where
k1[MVK] + k-1[CH3CN] . k2[BA]. It is worth stressing
at this point that BA exhibits clean first-order depen-
dence even at high concentrations (Figure S2). The data
presented in Figure 2 was fitted to eq 3 to yield k2 )
(7.6 ( 0.8) × 10-3 L mol-1 s-1 in the limit of high [MVK],
and K1/[CH3CN] ) 1.07 ( 0.25 L mol-1 in the limit of
low [MVK]. By fixing the value of K1/[CH3CN], the
slopes from the benzyl alcohol and palladium depend-
encies, Figures S2 and S3, furnish k2 ) (10 ( 1) × 10-3
and (9.9 ( 0.7) × 10-3 L mol-1 s-1, respectively. In
summary, MVK reacts with 1 in a fast step followed by
the rate-determining step (RDS) in which benzyl alcohol
adds to the intermediate (η2-alkene)Pd(II) complex.
complete exchange. In the saturation limit of [MVK]
BzOD
(Figure 2), k2
was measured and found to be (3.8 (
0.4) × 10-3 L mol-1 s-1, which gives k2H/k2 ) 2.0. The
scission of the O-H bond is part of the RDS (k2).
2.3. Kin etics w ith Va r iou s Alcoh ol Nu cleop h iles.
The kinetics for a number of alcohols as nucleophiles
was investigated using MVK and 1. The kinetics were
followed by 1H NMR. The rates of reaction for the
different alcohols were obtained by plotting the concen-
tration of product versus time and fitting the kinetic
traces to an exponential equation. The rates were then
scaled relative to benzyl alcohol. Experimental condi-
tions were as follows: [1] ) 0.030 M, [MVK] ) 0.50 M,
D
and [ROH] ) 1.00 M in CDCl3 at 25° C. k2BA was set to
7.6 × 10-3 M s-1, and k2
for other alcohols were
ROH
K1k2[BA][MVK][Pd]T
[CH3CN] + K1[MVK]
d[MVK]
v ) -
)
(3)
calculated accordingly. The results for several alcohols
are summarized in Table 2. Increasing the steric bulk
of the nucleophile resulted in a decrease in the rate
constant. A 4-fold decrease was found with both second-
ary alcohols, R-methyl benzyl alcohol, and 2-propanol.
When tert-butyl alcohol was employed, product yield did
not exceed 5%; consequently, the reaction rate could not
be determined. Cinnamyl alcohol (entry 5), an allylic
alcohol, reacts slower than benzyl alcohol, in agreement
with the alcohol acting as nucleophile. Conversely,
methanol reacts slightly faster than benzyl alcohol.
Ethyl lactate (entry 6) was chosen because of its unique
H-bonding between the alcohol and carbonyl groups;
thus, the breaking of the O-H bond during the hy-
droalkoxylation reaction could be facilitated. However,
ethyl lactate was slightly slower than 2-propanol.
2.4. Syn th esis of Sever a l P a lla d iu m (II) Coor d i-
n a tion Com p lexes. Syn th esis of P yr id yl Im in e
P a lla d iu m Com p lexes Th a t P ossess Tw o Ava ila ble
dt
In h ibition Stu d ies. Initially, we noted that increas-
ing the concentration of acetonitrile caused a significant
decrease in the rate of reaction. Hence, we investigated
the nature of the acetonitrile inhibition with respect to
substrates. When MVK coordinates to the palladium
catalyst, acetonitrile is most likely providing this coor-
dination site (Scheme 2). Thus, acetonitrile would be a
competitive inhibitor with respect to MVK but not BA.
Rearrangement of the rate law yields the useful rela-
tionship in eq 4. The dependence of the initial rate on
[CH3CN] was probed over a range of concentrations
(0.020-0.100 M) at different [MVK] (0.20, 0.40, 0.50,
0.80, and 1.00 M) but constant [1] (0.030 M) and [BA]
(1.00 M). Plots of [Pd]T[BA]/Vi versus [CH3CN] are
linear, with slopes that are dependent on [MVK] and
have essentially common intercepts, Figure S4. The
secondary plot of slopes versus 1/[MVK] (Figure S4(b))
affords 1/K1k2 ) (6.5 ( 0.6) × 103 M s (eq 4). Since k2 )
7.6 × 10-3 L mol-1 s-1 from the saturation limit in
(28) Murry, J . Organic Chemistry, 3rd ed.; Cole Publishing Com-
pany: Pacific Grove, CA, 1992; p 394.

Methyl Vinyl Ketone Hydroalkoxylation
Organometallics, Vol. 20, No. 21, 2001 4407
Sch em e 2
Ta ble 2. Ra te Con sta n ts for Sever a l Alcoh ol
Su bstr a tes.
two open coordination sites can be occupied by water
molecules. Complex 3 was found to be a viable catalyst
for the hydroalkoxylation reaction (eq 1); however, it is
not very soluble in nonpolar solvents such as chloroform
and methylene chloride. To enhance solubility, we
synthesized 4 by carrying out an anion exchange with
3 and AgBArF4 (BArF4 ) [(3,5-(CF3)2C6H3)4B]-), Scheme
3. AgBArF was synthesized following a modified pro-
4
cedure of Brookhart31 with AgBF4 substituted in place
of NaBF4. AgBArF was utilized instead of the already
4
known NaBArF because the silver salt gave purer
4
product and improved yields in comparison to the
sodium salt. The disappearance of the OTf- signal at
F-
-79.92 ppm and the appearance of the BAr4 signal
at -63.23 ppm in the 19F NMR provided direct evidence
for completion of reaction. All attempts to synthesize 4
directly from 2 using AgBArF resulted in a mixture of
4
complexes that was difficult to separate.
Syn th esis of P yr id yl Diim in e P a lla d iu m Com -
p lexes Th a t P ossess On e Ava ila ble Coor d in a tion
Site. In addition to complexes with two available coor-
dination sites, we synthesized a dicationic palladium
coordination complex, 5, that contains a tridentate
ligand and one open coordination site. Following the
procedure of Brookhart,32 we synthesized the tridentate
pyridyl diimine ligand from 2,6-diacetylpyridine and
1
aniline. H NMR was used to check the progress of the
Coor d in a tion Sites. The parent (CH3CN)2PdCl2, 1, is
a neutral species with two available coordination sites.
Inhibition studies demonstrated the need for a solvent
coordination site for catalytic activity, as MVK is ac-
tivated by coordination to palladium. Hence, we rea-
soned that a coordination complex must have a solvent
open coordination site, and charge should enhance the
complex’s Lewis acidity. Thus, we synthesized [(Py-N)-
reaction, which took a couple of days. The ligand was
easily isolated by filtration because it precipitated out
of solution as a yellow powder during the course of the
reaction. Similar to the bidentate ligand, the six protons
1
for the two -CH3 groups show up in the H NMR as a
singlet at 2.41 ppm. The ligand was chelated to pal-
ladium following the procedure of Nesper33 using the
highly reactive (CH3CN)4Pd(BF4)2 as the palladium
starting material. An acetonitrile molecule that displays
Pd(CH3CN)2][BArF
] (Py-N ) phenyl(1-pyridin-2-yl-
4 2
ethylidene)amine), 4, which contains two solvent/open
coordination sites (Scheme 3). The bidentate ligand,
phenyl(1-pyridin-2-yl-ethylidene)amine, was synthe-
sized from 2,6-diacetylpyridine and aniline in a conden-
sation reaction. The progress of the reaction was fol-
lowed by monitoring the singlet at 2.70 ppm for the
1
a distinct H NMR signal at 1.96 ppm occupies the open
coordination site. Following the same procedure for the
-
preparation of 4 (Scheme 3), the BF4 anion was
replaced with BArF - in order to make complex 5 soluble
4
in chloroform. The progress of the metathesis reaction
was followed by 19F NMR; the exclusive presence of a
1
-CH3 in the H NMR. The ligand was then complexed
-
singlet at -63.85 ppm, which corresponds to BArF
,
4
to palladium to form initially the dichloride complex 2,
following a procedure by Consiglio.29 The chloride
ligands were metathesized with AgOTf (OTf ) trifluo-
romethanesulfonate) to generate the dicationic com-
pound 3 (Scheme 3).30 The time required for the
metathesis reaction in preparing 3 varied between 3 and
12 h depending on the AgOTf batch used. Completion
of the reaction was indicated by the prominent color
change from the orange-colored 2 to the yellow-colored
3. If there is enough residual water in the solvent, the
confirmed complete anion exchange. The full sequence
of the described reactions is illustrated in Scheme 4.
(29) Sperlle, M.; Consiglio, G. J . Am. Chem. Soc. 1995, 117, 12130-
13136.
(30) Stang, P. J .; Cao, D. H.; Poulter, G. T.; Arif, A. M. Organome-
tallics 1995, 14, 1110-1114.
(31) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920-3922.
(32) Small, B. L.; Brookhart, M. Macromolecules 1999, 32, 2120-2130.
(33) Nesper, R.; Pregosin, P.; Puntener, K.; Worle, M.; Albinati, A.
J . Organomet. Chem 1996, 507, 85-101.

4408 Organometallics, Vol. 20, No. 21, 2001
Miller et al.
Sch em e 3
Sch em e 4
2.5. Ca ta lytic Activity of th e New P a lla d iu m
Coor d in a tion Com p lexes. Requ ir em en t for a Sol-
ven t Coor d in a tion Site. The competitive inhibition
by acetonitrile points toward a requirement for a coor-
dination site that is provided by a coordinated sol-
vent molecule. Complex 2, (Py-N)PdCl2, is an excellent
candidate to validate this hypothesis. In a reaction
containing [MVK] ) 0.50 M and [BA] ) 1.00 M in
CDCl3, 0.040 M of 2 was added, and the reaction was
followed by 1H NMR. No reaction was observed (0%
conversion) after 24 h. After 1 day, benzyl alcohol did
not coordinate in place of the chloride ligands; com-
plex 2 was recovered unchanged. On the other hand,
when complex 4 was employed as catalyst under the
same conditions as those used for 2, the reaction was
completed in 90 min, yielding selectively the â-ether
product.
Kin etics a n d Mech a n ism w ith 4 a s Ca ta lyst. The
reaction of benzyl alcohol and MVK was used again as
the model reaction for detailed kinetics. Initial rates
were measured by 1H NMR following the formation
of the ether product. [MVK] was varied (0.10-3.0 M)
at constant [4] ) 0.010 M and [BA] ) 1.00 M. Similar
to catalyst 1, catalyst 4 displayed saturation kinetics
as the concentration of [MVK] increased, Figure 3.
Therefore, the mechanism described for 1 in Scheme
2 and its corresponding prior equilibrium rate law (eq
3) apply to catalyst 4. From the plot of initial rates
F igu r e 3. Plot of the initial rate versus [MVK] for the
hydroalkoxylation of MVK with BA catalyzed by complex
4. Conditions: [BA] ) 1.00 M, [4] ) 0.010 M, and [MVK]
) 0.10-3.0 M in CDCl3 at 25° C.
versus [MVK], one obtains k2 ) (97 ( 4) × 10-3 M-1
s-1 and K1/[CH3CN] ) 0.61 ( 0.05 M-1. Noteworthy of
mention is the enhanced activity of catalyst 4 in
comparison to 1, a point that will be detailed in the
Discussion.

Methyl Vinyl Ketone Hydroalkoxylation
Organometallics, Vol. 20, No. 21, 2001 4409
Tr id en ta te ver su s Bid en ta te Liga n d s. The kinet-
ics of complex 5 were studied and compared to those of
catalyst 4. Compound 5 was found active in catalyzing
the reaction of benzyl alcohol with MVK. However, the
rate of reaction catalyzed by 5 is 69 times slower than
not react with BA, and 1-heptene isomerizes instead to
2- and 3-heptene, eq 7.37 Isomerization of 1-heptene took
∼2 min to reach completion when catalyzed by complex
4 and ∼10 min with 1 as catalyst. More importantly,
BA did not inhibit the reaction, indicating that the
alcohol either weakly coordinates (labile) or does not
coordinate to the palladium.
that catalyzed by 4, k2(5) ) (1.4 ( 0.1) × 10-3 M-1 s-1
.
Nevertheless, given enough time, the addition of benzyl
alcohol to MVK proceeded in excess of 90% conversion
with high regioselectivity in favor of the â-product.
Typical conditions for reactions with 5 were as follows:
[MVK] ) 0.50 M, [BA] ) 1.00 M, and [5] ) 0.0060 M in
CDCl3 at 25° C.
Once the (η2-MVK)Pd(II) adduct is formed, external
attack of the alcohol (nucleophile) from outside the
coordination sphere of palladium(II) affords a (σ-alkyl)-
Pd(II) intermediate. Several studies on the ana-
logous palladium-catalyzed hydration reaction are ger-
mane to the present study. On the basis of stereo-
chemical results, hydroxypalladation (addition of water
to a coordinated olefin) was believed to occur by ex-
ternal attack of water.6-8 However, other studies on
aqueous olefin oxidation and platinum(II) model com-
plexes support olefin insertion into an M-OH(R)
bond.5,9,22,38,39 Details of the hydroxypalladation mech-
anism are still being debated.3 Nevertheless, in the
present hydroalkoxylation study, the results are in
favor of a trans nucleophilic attack. The RDS displays
a significant kinetic isotope effect on the alcohol’s
O-H(D) group. It is unlikely that deprotonation of a
coordinated alcohol is rate-controlling. Also, catalyst 5,
which has only one available coordination site, is ac-
tive in hydroalkoxylation of MVK. However, the slow
kinetics displayed by 5 in comparison to 4 can be
attributed to either sterics or arm-opening of the tri-
dentate ligand to give bidentate coordination.40 The
latter scenario is precluded, since the 1H NMR spectrum
of 5 is symmetric at room temperature and the kinetics
are dependent on the substrate’s concentration. If the
much lower rate observed with 5 is due to ligand
dissociation, the kinetics would be zero order in sub-
strates.
We turn next to regioselectivity. During the catalytic
cycle, the carbonyl group most likely interacts with
palladium, thus acting as a directing group. η2-Coordi-
nation of an alkene to a transition metal results in the
activation of both carbons, and nucleophilic attack is
usually favored for the more substituted olefinic car-
bon.1,41,42 However, the carbonyl interaction with pal-
ladium would generate a partial positive charge on the
â-carbon, making it more susceptible toward nucleo-
philic attack, eq 8. In the final step, protonolysis of the
σ-alkyl bond affords the ether product and regenerates
the catalyst.
3. Discu ssion
We have shown from the experimentally determined
rate law in eq 3 that the catalytic reaction (eq 1) is a
two-substrate system in its kinetics as well as in its
chemistry. Saturation kinetics in one of the substrates,
MVK, has been observed. The mechanism in which
MVK coordinates to palladium in place of an acetonitrile
(Scheme 2) is supported on the basis of the following:
(1) Acetonitrile is a competitive inhibitor with respect
to MVK, while chloride is uncompetitive. (2) The RDS
in the limit of saturated MVK features a significant
D
kinetic isotope effect, k2H/k2 ) 2.0. (3) Acetonitrile is a
noncompetitive inhibitor for BA. (4) A catalyst that lacks
an available/solvent coordination site such as complex
2 is totally inactive. (5) Complex 2 does not undergo a
substitution reaction with benzyl alcohol even after 1
day.
Even though MVK may coordinate to palladium
through the alkene or the carbonyl’s oxygen, η2-olefin
complexes of palladium(II) are highly precedent.27,34 To
scrutinize the mode of MVK coordination in our system,
we studied the activity of acrylonitrile, which is analo-
gous to MVK.35 While acrylonitrile coordinated to
complex 1 through the nitrogen, eq 6, it did not react
with benzyl alcohol (no detectable product even after 1
day). Furthermore, σ-alkyl palladium(II) coordination
complexes have been shown to catalyze the copolymer-
ization of methyl acrylate and ethylene.36 Their ability
to tolerate the carbonyl functional group implied that
coordination via the carbonyl’s oxygen is not favored
over olefin binding. Indeed, this would be the case here
as well.
(36) J ohnson, L. K.; Mecking, S.; Brookhart, M. J . Am. Chem. Soc.
1996, 118, 267-268.
(37) Conditions: 1-heptene ) 0.50 M, benzyl alcohol ) 1.00 M with
1 ) 0.040 M or 4 ) 0.010 M as catalyst in CDCl3 at 25 °C.
(38) Gregor, N.; Zaw, K.; Henry, P. M. Organometallics 1984, 3,
1251-1256.
(39) Bryndza, H. E. Organometallics 1985, 4, 406-408.
(40) Rulke, R. E.; Han, I. M.; Elsevier: C. J .; Vrieze, K.; van
Leeuwen, P. W. N. M.; Roobeek, C. F.; Zoutberg, M. C.; Wang, Y. F.;
Stam, C. H. Inorg. Chim. Acta 1990, 169, 5-8.
(41) Hartley, J . F. Nature 1969, 223, 615-616.
(42) Hartley, F. R. Chemistry of Platinum and Palladium; J ohn
Wiley & Sons: New York, 1973; p 384.
As for unfunctionalized terminal alkenes, they did not
undergo hydroalkoxylation. For example, styrene does
(34) Fujii, A.; Hagiwara, E.; Sodeoka, M. J . Am. Chem. Soc. 1999,
121, 5450-5458.
(35) Typical conditions were [1] ) 0.040 M, [BA] ) 1.00 M, and
[H2CdCHCN] ) 0.50 M in CD2Cl2 at 25 °C.

4410 Organometallics, Vol. 20, No. 21, 2001
Miller et al.
Ta ble 3. Su bstitu en t Effects on th e Ra te
Con sta n ts for Su bstitu ted Ben zyl Alcoh ols w ith
Ca ta lysts 1 a n d 4a
Under conditions employed in this investigation,
acetals resulting from vinyl ether oxidation products
(Scheme 1) are not detected. The σ-alkyl palladium(II)
intermediates must be stabilized with respect to â-hy-
drogen migration, or the protonolysis of the Pd-alkyl
bond is much faster than the competing â-hydrogen
elimination. Certainly a vacant or weakly coordinated
site that is cis to the Pd-alkyl bond is required for
oxidative decomposition.43 Such a site is not present in
catalyst 5, accounting for the stability of 5 under
catalytic conditions for prolonged periods of time (entry
5 in Table 1). Catalyst 4 is not only more reactive than
catalyst 1 but also more stable in solution. The aceto-
nitrile ligand of 4 is more tightly bound, and its
dissociation is slow on the time scale of the protonolysis
reaction. Even complex 1 is reasonably stable toward
oxidative decomposition; this is evident by the high
yields of hydroalkoxylation product (Table 1). An ad-
ditional factor in stabilizing the σ-alkyl palladium(II)
intermediate could very well be the carbonyl group on
MVK. Its interaction with palladium would hinder
â-hydride elimination, thus favoring the formation of
the ether product.44
a
In CDCl3 at 25 °C.
Ta ble 4. Com p a r ison of th e Rela tive Ra tes for th e
Differ en t Ca ta lysts Used in Th is Stu d ya
no. of open
catalyst
(CH3CN)2PdCl2, 1
coord sites charge rel rateb
2
0
2
1
0
0
1.0
(Py-N)PdCl2, 2
n.r.c
[(Py-N)Pd(CH3CN)2][BArF4]2, 4
[(N-Py-N)Pd(CH3CN)][BArF4]2, 5
+2
+2
13
0.19
a
The reaction used is the hydroalkoxylation of MVK with benzyl
b
alcohol (eq 1). Determined by comparing k2 values for each
catalyst. n.r. ) no reaction.
c
The structure-function correlation of Hammett45-47
accounts for various reactions of meta- and para-
substituted aromatic compounds. Benzyl alcohol sub-
strates with different substituents on the para positions
were examined. Values for σp are listed in Table 3
alongside the log(kX/kH) values for the different benzyl
alcohols with both catalysts 1 and 4. Figure S6 shows
two plots of log(kX/kH) versus σp for catalysts 1 and 4.
The slopes afford the reaction constants for both cata-
lysts, F(1) ) -0.63 ( 0.07 and F(4) ) -0.70 ( 0.13. The
linear Hammett correlation suggested that all the
benzyl alcohols react by the same mechanism in each
of the catalytic systems. The negative sign of F is in
agreement with nucleophilic attack of the alcohol on the
electrophilically activated MVK. Thus, a positive charge
buildup on oxygen characterizes the transition state.
The identical reaction constants (F) for 1 and 4 indicate
a common mechanism for both catalysts.
would be minor in comparison to the effect of charge.
Table 4 compares the reactivities of the different
catalysts from this study as a function of charge and
available (solvent) coordination sites.
4. Su m m a r y
Via kinetics studies and substrate probes, the mech-
anism of palladium(II)-catalyzed hydroalkoxylation of
vinyl ketones has been defined. At least one coordination
site on palladium must be available. The vinyl ketone
is activated via η2-coordination of the alkene to palla-
dium(II); the alcohol nucleophile attacks selectively the
â-carbon of the π-olefin adduct. Saturation kinetics are
observed for MVK, and deutero-alcohols (ROD) display
a primary kinetic isotope effect, kH/kD ) 2.0, which
implies O-H bond breaking in the transition state. The
observed regioselectivity is rationalized by invoking an
interaction between the carbonyl group and palladium.
Charge on the palladium catalyst enhances its Lewis
acidity and boosts activity. On the basis of the mecha-
nistic information described here, we are currently
extending this catalytic reaction to asymmetric hy-
droalkoxylation and kinetic resolution of racemic alco-
hols.
The effect of charge on catalytic activity deserves a
comment. Catalyst 4 is 13 times more reactive than 1.
The dicationic charge of complex 4 results in a stronger
Lewis acid and thus is more reactive compared to the
neutral complex 1. Although the pyridine ligand in 4 is
a π-acceptor, its contribution to the Lewis acidity of 4
(43) Winstein, S. W.; McCaskie, J .; Lee, H.-B.; Henry, P. M. J . Am.
Chem. Soc. 1976, 98, 6913-6918.
5. Exp er im en ta l Section
(44) Zuideveld, M. A.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.;
Klusener, P. A. A.; Stil, H. A.; Roobeek, C. F. J . Am. Chem. Soc. 1998,
120, 7977-7978.
Ma t er ia ls a n d In st r u m en t a t ion . All chemicals were
obtained commercially. The bis(acetonitrile) dichlororpalla-
dium(II) was a gift from Alfa Aesar. Acetonitrile, benzene, and
methylene chloride were dried over calcium hydride. Toluene
was dried and stored over molecular sieves. All reactions were
(45) Hammet, L. P. Chem. Rev. 1935, 17, 125.
(46) Hammett, L. P. Physical Organic Chemistry; McGraw-Hill Book
Co.: New York, 1940; pp 184-228.
(47) Hansch, A.; Leo, T. R. Chem. Rev. 1991, 91, 165-195.

Methyl Vinyl Ketone Hydroalkoxylation
Organometallics, Vol. 20, No. 21, 2001 4411
carried out in dried glassware and under argon unless noted
otherwise. However, all complexes were fairly stable toward
air, moisture, and light. NMR spectra were collected on a
Bruker 200 MHz and/or 400 MHz spectrometers. GC/MS
experiments were conducted on a Hewlett-Packard G1800A
GCD system equipped with an HP-5MS capillary column
packed with cross-linked 5% PH ME siloxane; a temperature
program was employed in all GC/MS runs: 80-140 °C at 7
°C/min, then 140-220 °C at 10 °C/min. Elemental analyses
were done in duplicates by Desert Analytics, AZ.
Kin etics Stu d ies. An NMR tube was charged via syringe
with the desired concentrations of MVK and alcohol. The total
volume was brought to 1.0 mL with CDCl3. TMS (0.08 mmol)
was added as an internal standard. The desired amount of
catalyst was weighed on an analytical balance and added last
to the assay mixture. The reaction was monitored by 1H NMR
on a Bruker ARX 400 MHz spectrometer at 25 °C. Initial rates
were evaluated for the first 10% of reaction. All kinetic runs
proceeded to completion. Product concentrations were deter-
mined by integration of the carbonyl -CH3 signal of the ether
product versus MVK or TMS. When MVK was used in excess
to BA, the -CH2 signal of the benzyl alcohol was used. The
initial rate for each run was the average of duplicates. For
the inhibition studies, acetonitrile was added from a stock
solution of acetonitrile (1.0 M) in CD3Cl.
Syn th esis of [P h en yl(1-p yr id in -2-yleth ylid en e)a m in e]-
P d Cl2, 2. In a two-neck round-bottom flask, benzylnitrilepal-
ladium(II) chloride (0.10-1.0 g) was dissolved in 150 mL of
toluene. The solution was heated to 70 °C. One equivalent of
the ligand was added dropwise via an addition funnel. After
the addition was completed, the solution was stirred at 70 °C
for 2.5 h. During the addition, the solution changed color from
dark orange to yellow. The reaction was cooled to room
temperature, after which 200 mL of pentane was added. The
precipitated product was isolated by filtration and washed with
50 mL of ether. The isolated product was a yellow solid and
1
was stable to air and moisture. Yield ) 89%. H NMR (CD2-
Cl2): δ 9.43 (d, 1H), 8.21 (t, 1H), 7.91 (d, 1H), 7.65 (t, 1H),
7.46 (m, 3H), 7.10 (d, 2H), 2.31(s, 3H). FAB+/MS: m/z 373.6
(M+ ion; correct isotope distribution for Pd). Anal. Calcd 41.80
C, 3.24 H, 7.50 N, 18.98 Cl. Found: 42.10 C, 3.12 H, 7.23 N,
17.83 Cl.
Syn th esis of [P h en yl(1-p yr id in -2-yleth ylid en e)a m in e]-
P d (H2O)2‚2OTF , 3. In a 50 mL three-neck flask, 2 (0.10 g,
0.27 mmol) was dissolved in 30 mL of CH2Cl2. After most of
the starting material had dissolved, 2.5 equiv of AgOTf was
added. The heterogeneous solution was protected from light
and stirred until the solution turned yellow. The amount of
time fluctuated between 3 and 12 h depending on how pure
and dry the silver triflate was. The solution was then filtered
through a glass frit to remove the AgCl and any unreacted
AgOTf. The solid was washed with 20 mL of dry acetonitrile.
The combined filtrate was placed under vacuum until a dry
solid was obtained. The resulting yellow product needed no
further purification. Because the product decomposes with
time, the solid was stored in the glovebox. Yield ) 72%. 1H
NMR (CD3CN): δ 8.52 (d, 1H), 8.46 (t, 1H), 8.15 (d, 1H), 7.89
(t, 1H), 7.56 (m, 3H), 7.33 (d, 2H), 2.40 (s, 3H), 2.12-2.09 (s,
4H). 19F NMR (CD3CN): δ -79.92. FAB+/MS: m/z 451.0
(-2H2O, OTf-), 301.9 (-2H2O, 2OTF-) (M+ ion; correct isotope
for Pd). Anal. Calcd 28.29 C, 2.53 H, 4.40 N, 10.07 S. Found:
30.42 C, 2.79 H, 4.36 N, 9.96 S.
A Typ ica l Ca ta lytic Hyd r oa lk oxyla tion P r oced u r e. To
1.0 mmol of methyl vinyl ketone was added 1.0 mmol of ROH
or PhNH2, and the mixture was diluted in deuteriochloroform
(VT ) 1.0 mL). The reaction was initiated by addition of the
palladium catalyst (1 ) 40 µmol, 4 or 5 ) 10 µmol). The
progress of reaction was followed by 1H NMR until no more
product was being formed. The reaction solution was passed
through a silica plug (6.0 × 0.5 cm) with diethyl ether (∼5
mL) as eluent. The catalyst-free colorless solution was col-
lected, and the solvent was removed under vacuum. If the
eluted solution remained colored after the initial silica plug,
it was filtered again through a second silica plug. The isolated
products were fully characterized by 1H NMR, GC/MS, and
FAB+-MS. The spectroscopic data for all of the products in
Table 1 follow.
Syn t h esis of [Ag][(3,5-(CF 3)2C6H3)4B] (AgBAr F 4). In a
three-neck round-bottom flask equipped with an addition
funnel, 1.28 g (52.5 mol) of Mg turnings were stirred in 32
mL of ether. 3,5-Bis(trifluoromethyl)bromobenzene, 7.3 mL
(42.5 mol), was diluted in 62.5 mL of ether and then added to
the three-neck flask via addition funnel at room temperature.
After the addition was completed, the solution was heated to
reflux for 30 min, resulting in a dark brown solution. The
reaction was cooled to room temperature, and 1.47 g (7.5 mmol)
of AgBF4 was added. This solution was stirred for 60 h. In a
separate flask, a solution containing 18.75 g of Na2CO3 in 250
mL of water was prepared. The reaction mixture was poured
into the Na2CO3 solution and filtered. The aqueous layer was
separated and extracted with 4 × 100 mL of ether. The ether
extracts were combined, and the solvent was removed. The
resulting brown solid was washed with ∼ 5 mL of cold CH2Cl2
and dried under vacuum. The product was isolated as a tan
1
4-Meth oxy-2-bu ta n on e. H NMR (CD3Cl): δ 3.54 (t, 2H),
3.22 (s, 3H), 2.57 (t, 2H), 2.09 (s, 3H). GC/MS: tR ) 2.01 min.
4-(2-P r op oxy)-2-bu ta n on e. 1H NMR (CD3Cl): δ 3.54 (sept,
1H), 3.48 (t, 2H), 2.63 (t, 2H), 2.15 (s, 3H), 1.13 (d, 6H). GC/
MS: tR ) 2.95 min.
4-Ben zyloxy-2-bu t a n on e. 1H NMR (CD3Cl): δ 7.24 (m,
6H), 4.44 (s, 2H), 3.66 (t, 2H), 2.61 (t, 2H), 2.10 (s, 3H). FAB+/
MS: m/z 179 (M + H)+, 177 (M - H)+. GC/MS: tR ) 12.11
min.
4-(2-sec-P h en ylet h oxy)b u t a n on e. 1H NMR (CD3Cl): δ
7.24 (m, 6H), 4.31 (q, 1H), 3.45 (t, 2H), 2.55 (t, 2H), 2.08 (s,
3H) 1.32 (d, 3H). FAB+/MS: m/z 191 (M + H)+, 192 (M+), 193
(M - H)+. GC/MS: tR ) 11.94 min.
4-(N-P h en yla m in o)-2-bu ta n on e. 1H NMR (CD3Cl): δ 7.12
(m, 2H), 6.69 (m, 4H), 3.40 (t, 2H), 2.73 (t, 2H), 2.14 (s, 4H).
FAB+/MS: m/z 163 (M+). GC/MS ) tR ) 12.89 min.
4-(p-Meth oxyp h en oxy)-2-bu ta n on e. 1H NMR (CD3Cl): δ
6.95 (s, 4H), 4.17 (t, 2H), 3.86 (s, 3H), 2.88 (t, 2H), 1.96 (s,
3H). GC/MS: tR ) 13.71 min.
1
solid. Yield ) 41%. H NMR (CD2Cl2): δ 8.01( s, 8H), 7.86 (s,
4H). 19F NMR (CD2Cl2): δ -63.4. 11B NMR (CH2Cl2): δ -6.67.
FAB-/MS: m/z 863.07 (M- ion; correct isotope for B).
Syn th esis of [(P h en yl(1-pyr idin -2-yleth yliden e)am in e)-
P d (CH3CN)2][BAr F 4]2, 4. Both 3 and AgBArF were placed
4
Syn t h esis of P h en yl(1-p yr id in -2-ylet h ylid en e)a m in e
(P y-N). To a flask with a Dean-Stark trap was added
2-acetylpyridine (2.0 mL, 17.83 mmol), aniline (9.0 mL, 98.8
mmol), 7 drops of 88% formic acid, and 30 mL of benzene. The
trap was filled with benzene, and the solution was refluxed
until ∼0.3 mL of water was collected. The reaction solution
was then cooled to room temperature and the excess aniline
removed under vacuum at ∼90 °C, to remove the excess aniline
completely. The ligand product was a dark red oil but yellow
in solution. Yield ) 44%. 1H NMR (CD2Cl2): δ 8.55 (d,1H),
8.17 (d, 1H), 7.71 (t, 1H), 7.26 (t, 3H), 7.05 (t, 1H), 6.73 (d,
2H), 2.70 (s, 3H).
in a Schlenk flask and dissolved in 10 mL of dry CH3CN. The
solution was stirred for 2 h, at which time the solution had
turned a dark orange color. The solvent was removed under
vacuum. The isolated solid was redissolved in CH2Cl2. The
AgOTf byproduct did not dissolve and was separated by
cannulation. The solvent was removed under vacuum to give
a pure yellow solid. Yield ) 69%. 1H NMR (CD2Cl2): δ 8.43 (t,
1H), 8.23 (d, 1H), 8.04 (d, 1H), 7.34 (t, 1H), 7.72 (s, 16H), 7.60
(t, 3H), 7.56 (s, 8H), 7.20 (m, 2H) 2.48 (s, 6H), 1.93 (br s, 6H).
19F NMR (CD3CN): δ -63.37. FAB+/MS: m/z 302.00 (-2H2O)
(M+ ion; correct isotope for Pd). Anal. Calcd 45.52 C, 2.01 H,
2.65 N, 43.18 F. Found: 41.47 C, 1.82 H, 2.29 N, 39.59 F.

4412 Organometallics, Vol. 20, No. 21, 2001
Miller et al.
Syn th esis of 2,6-Bis[1-eth ylp h en ylim in o]p yr id in e (N-
P y-N). In a round-bottom flask, 2,6-diacteylpyridine (1.0 g,
6.13 mmol) and an excess of aniline (5.6 mL, 61.5 mmol) were
dissolved in 50 mL of absolute EtOH. Seven drops of 88%
formic acid were added. The flask was sealed and stirred at
room temperature for 4 days. During this time, a bright yellow
precipitate began to form. The progress of the reaction was
followed by 1H NMR. Once conversion was above ∼55%, the
solution was filtered and a bright yellow solid was recovered.
Yield ) 59%. 1H NMR (CD3Cl): δ 8.36 (d, 2H), 7.89 (t, 1H),
7.37 (t, 4H), 7.13 (t, 2H), 6.86 (d, 4H), 2.41 (s, 6H).
Syn th esis of 2,6-Bis[1-eth ylp h en ylim in o]p yr id in eP d -
(NCCH3)‚2BF 4. (NCCH3)4Pd(BF4)2 (0.0840 g, 0.13 mmol) and
0.0597 g (0.19 mmol) of 2,6-bis[1-ethylphenylimino]pyridine
ligand were dissolved in 5 mL of acetonitrile. The reaction was
protected from light, and the solution was stirred at room
temperature for 20 min. The solvent was then removed to give
the yellow (N-Py-N)Pd(CH3CN)‚2BF4 product. Yield ) 95%.
1H NMR (CD2Cl2): δ 8.60 (t, 1H), 8.18 (d, 2H), 7.48 (t, 4H),
7.46 (t, 2H), 7.28 (d, 4H), 2.48 (s, 6H), 1.96 (s, 3H). 19F NMR
(CD3CN): δ -152.18.
mixture was stirred at room temperature for 2 h. The solvent
was removed under vacuum, and 5 mL of dry CH2Cl2 was
added to the product mixture. The insoluble byproduct (AgBF4)
was separated via cannulation. Methylene chloride was re-
moved from the filtrate, and the resulting yellow product
was dried in a vacuum. Yield ) 91%. 1H NMR (CD2Cl2): δ
8.60 (t, 1H), 8.18 (d, 2H), 7.67 (s, 16H), 7.57 (s, 8H), 7.54 (t,
4H), 7.46 (t, 2H), 7.28 (d, 4H), 2.48 (s, 6H), 1.96 (s, 3H). 19F
NMR (CD3CN): δ -63.85.
Ack n ow led gm en t. This research was supported by
the National Science Foundation (CHE-9874857-CA-
REER) and the Arnold and Mabel Beckman Foundation
through a BYI to M.M.A.O. We are grateful to Mr. Lee
McPherson for the experiments with acrylonitrile.
Su p p or tin g In for m a tion Ava ila ble: A representative
kinetic trace (Figure S1), plots of VI versus [BA] and [1]
(Figures S2 and S3), kinetic plots as well as secondary plots
for acetonitrile inhibition studies (Figures S4 and S5), and
Hammett plots for catalysts 1 and 4 (Figure S6) are available
free of charge via the Internet at http://pubs.acs.org.
Syn th esis of 2,6-Bis[1-eth ylp h en ylim in o]p yr id in eP d -
(NCCH3)‚2BAr F4, 5. (N-Py-N)Pd(CH3CN)‚2BF4 (0.0787 g, 0.12
mmol) was dissolved in 5 mL of acetonitrile, and 0.2490 g (0.25
mmol) of AgBArF was added in one portion. The reaction
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