5
938 Organometallics, Vol. 17, No. 26, 1998
Notes
species was the failure to produce any significant
product in reaction 1 when an attempt was made to
generate fluoride from KHF2 in the presence of the
purified according to literature methods.16,17 31P NMR
spectra were acquired on a Bruker AC 200 Mz instru-
ment. All organic solvents were distilled under nitrogen.
In addition, chloroform was degassed using the freeze-
pump-thaw method. All experiments were carried out
under an inert atmosphere.
1
2
very strong nonionic base 2-(dimethylamino)pyridine
1
4
(
DMAP, pKa ) 13 in acetonitrile). It was of interest,
therefore, to seek a nonionic base of sufficient strength
to deprotonate the hydrogen fluoride species in reaction
Syn th esis of P d (P P h 3)4 Usin g Ca ta lytic F lu or id e
a n d 1. Meth od A. PdCl2 (0.100 g, 0.563 mmol) and
PPh3 (0.817 g, 3.11 mmol) were dissolved in 15 mL of
DMSO, and the reaction mixture was heated in an oil
bath at 140 °C. Heating was discontinued after 15 min
1
, to determine whether fluoride plays a catalytic role.
Recently we have been exploring the application of
pro-azaphosphatrane 1, first reported from our labora-
1
5-18
tories,
as a superior nonionic base in the synthesis
1
9
20
of acylated alcohols, porphyrins, R-C-acylamino ac-
(the time required to dissolve all reactants), and a
ids,20 trans olefins,
21,22
chiral auxiliary-bearing isocya-
nides, mono-alkylated â-dicarbonyls,24 and as an
solution of n-Bu4NF‚3 H2O (0.029 g, 0.11 mmol) in 5
mL of DMSO was added via syringe. The remaining
water (3.5 µL, 0.19 mmol) was added via a microliter
syringe, followed by the addition of 1 (0.25 g, 1.2 mmol)
in 5 mL of DMSO. The yellow solution was allowed to
cool to room temperature during which time a yellow
solid precipitated. Ethanol (30 mL) was added to the
vessel, and the reaction mixture was stirred overnight
to effect complete precipitation. The product was iso-
lated by filtration and rinsed with two 10-mL portions
of cold ethanol (5 °C) and 10 mL of diethyl ether. The
product was dried in vacuo (395 mg, 94% crude). This
crude mixture was purified using a silica gel column
employing degassed chloroform as the eluent (81%
2
3
2
5
efficient catalyst for the trimerization of isocyanates
and the protective silylation of alcohols.26 The very
stable conjugate acid 2 of commercially available 1 has
1
7
a pKa (41 in MeCN ) which is about 17 units larger
than the conjugate acid of DBU,17 a strong nonnucleo-
philic base widely used in synthetic applications. We
show here that reaction 1 is catalytic in fluoride in the
presence of the very strong nonionic bases 1, DBU, and
P4-t-Bu; the latter possessing a base strength very
1
7
comparable to that of 1. We also report that the
tetracoordinated palladium(0) product of reaction 1 is
contaminated with ca. 6% of an uncharacterized impu-
rity that can be removed by column chromatography.
31
12
yield). P NMR (CDCl3) δ 19 (lit. 19), mp: 190-194
1
2
°
C (lit. 190-194 °C).
Meth od B. PdCl2 (0.050 g, 0.28 mmol) and PPh3
(
0.370 g, 1.43 mmol) were dissolved in 15 mL of DMSO.
The reaction mixture was heated in an oil bath at 80
C for 15 min (the time required to dissolve all reac-
tants), and then a solution of n-Bu4NF‚3 H2O (0.014 g,
.054 mmol) in 5 mL of DMSO was added via syringe.
°
0
The remaining water (2.0 µL, 0.11 mmol) was added via
syringe, and this was followed by the addition of 1 (0.12
g, 0.56 mmol) in 5 mL of DMSO. The yellow solution
was allowed to cool to room temperature during which
time a yellow solid precipitated. Ethanol (30 mL) was
added to the vessel, and the reaction mixture was
stirred overnight to complete precipitation. The product
was isolated by filtration and rinsed with two 10-mL
portions of cold ethanol (5 °C) and 10 mL of diethyl
ether. The product was dried in vacuo (314 mg, 96%
crude and purified as in method A above (82% yield).
Exp er im en ta l Section
Reagent grade PdCl2 (Aldrich), PPh3 (Aldrich), the
phosphazene base P4-t-Bu (Fluka), and n-Bu4NCl‚3H2O
Aldrich) were used as received. DBU (Aldrich) was
distilled under reduced pressure (0.07 Torr, 48 °C) prior
to use. Pro-azaphosphatrane 1 was synthesized and
(
3
1
12
12
P NMR (CDCl3) δ 19 (lit. 19), mp: 190-194 °C (lit.
90-194 °C).
1
Syn th esis of P d (P P h 3)4 Usin g Ca ta lytic F lu or id e
(
(
13) Mootz, D.; Boenigk, D. J . Am. Chem. Soc. 1986, 108, 6634.
14) Kelly-Rowley, A. M.; Lynch, V. M.; Anslyn, E. V. J . Am. Chem.
a n d P 4-t-Bu . This reaction was identical to that in
method B, except that P4-t-Bu (0.564 mL of a 1.0 M
solution in hexane, 0.56 mmol) was used as a base
instead of 1. The product was isolated as described
above, dried in vacuo (294 mg, 90% crude), and purified
Soc. 1995, 117, 3438.
(
(
15) Tang, J .-S.; Verkade, J . G. Tetrahedron Lett. 1993, 34, 2903.
16) Tang, J .-S.; Verkade, J . G. Synthetic Methods of Organometallic
and Inorganic Chemistry”; Herman/Brauer, George Thieme Verlag:
New York, 1996; Vol. 3, p 177.
3
1
as in method A above (77% yield). P NMR (CDCl3) δ
(
17) Laramay, M. A. H.; Verkade, J . G. J . Am. Chem. Soc. 1993,
15, 5015.
18) Tang, J .-S.; Dopke, J .; Verkade, J . G. J . Am. Chem. Soc. 1993,
15, 5015.
1
2
1
1
19 (lit. 19).
(
Syn th esis of P d (P P h 3)4 Usin g Ca ta lytic F lu or id e
a n d DBU. This reaction was identical to that in method
B, except that DBU (0.085 mL, 0.56 mmol) was used as
a base instead of 1. The product was isolated as
described above, dried in vacuo (237 mg, 73% crude),
(19) D’Sa, B. A.; Verkade, J . G. J . Org. Chem. 1996, 61, 2963.
(20) Tang, J .-S.; Verkade, J . G. J . Org. Chem. 1994, 59, 7793.
(21) Mohan, T.; Arumugam, S.; Wang, T.; J acobson, R. A.; Verkade,
J . G. Heteroatom Chem. 1996, 7, 455.
(
(
(
22) Arumugam, S.; Verkade, J . G. J . Org. Chem. 1997, 62, 4827.
23) Tang, J .-S.; Verkade, J . G. U. S. Pat. 5,260,436, 1993.
24) Arumugam, S.; McCleod, D.; Verkade, J . G., submitted for
3
1
and purified as in method A above (62% yield). P NMR
1
2
publication in J . Org. Chem.
25) Tang, J .-S.; Verkade, J . G. Angew. Chem. 1993, 105, 934;
Angew. Chem., Int. Ed. Engl. 1993, 32, 896.
26) D’Sa, B. A.; Verkade, J . G. J . Org. Chem. 1997, 67, 55057.
(CDCl3) δ 19 (lit. 19).
(
Syn th esis of P d (d p p b)2 Usin g Ca ta lytic F lu or id e
a n d 1. Meth od A. This reaction was the same as that
(