Alkylamine N-H Bond Cleavage by Pd Hydroxides
Organometallics, Vol. 16, No. 26, 1997 5713
isomer). Anal. Calcd for C54H47NOP2Pd2‚Et2O (confirmed by
integrated 1H NMR spectra): C, 64.81; H, 5.35; N, 1.30.
Found: C, 64.52; H, 5.66; N, 1.30.
reagents or alkali metals, all of which are highly air
sensitive and which are typically incapable of being used
as catalysts. Thus, the palladium chemistry offers a
pathway for formation of a metal amido species that is
mild and that offers a means for catalytic modification
of the amine substrate.
P r ep a r a tion of syn -(P P h 3)(C6H5)P d (µ-OH)(µ-NH-2,6-
(CH3)2C6H3)P d (C6H5)(P P h 3) (2b). Into a screw-capped test
tube was weighed 186 mg (0.201 mmol) of 1. The solid
material was dissolved in 8 mL of THF, and H2N-2,6-
(CH3)2C6H3 (0.25 mL, 2.01 mmol) was added to the test tube.
The test tube was sealed, and the reaction was stirred at 70
°C for 1 h. A 31P{1H} NMR spectrum of the reaction mixture
indicated complete consumption of the starting material. The
reaction mixture was filtered through Celite, concentrated and
layered with Et2O. The THF/Et2O solution was cooled at -35
°C to yield 120 mg (58%) of white crystalline material. 1H
NMR (C6D6): δ -4.11 (s, 1H), 1.12 (s, 3H), 3.29 (t, J ) 5.0 Hz,
1H), 4.43 (s, 3H), 6.51-6.61 (m, 6H), 6.80 (t, J ) 7.0 Hz, 2H),
6.92-7.09 (m, 21H), 7.42 (d, J ) 6.0 Hz, 2H), 7.50-7.61 (m,
12H). 31P{1H} NMR (THF): δ 27.5. 13C{1H} NMR (C6D6): δ
17.9 (s), 24.6 (s), 118.9 (s), 122.2 (s), 126.2 (s), 127.1 (s), 128.3
(d, J ) 10.3 Hz), 128.9 (s), 129.2 (s), 130.0 (s), 131.4 (s), 131.8
(d, J ) 43.1 Hz), 134.5 (d, J ) 11.9 Hz), 136.3 (d, J ) 3.7 Hz),
149.9 (d, J ) 7.3 Hz), 151.3 (t, J ) 2.8 Hz). IR (cm-1, KBr):
3622 (w, νOH), 3326 (w, νNH). Anal. Calcd for C56H51NOP2-
Pd2: C, 65.38; H, 5.00; N, 1.36. Found: C, 65.03; H, 5.41; N,
1.20.
This result is important for the further development
of transition metal catalyzed chemistry of amines. For
example, our laboratory and Buchwald’s have developed
a catalytic process for the amination of aryl halides in
the presence of alkoxide base.33,34 Our work on proton
exchange reactions presented here along with studies
conducted on isolated palladium alkoxide complexes48
have shown that the alkoxide complexes (DPPF)Pd(Ar)-
(O-t-Bu) undergo proton transfer reactions with free
amines to generate reactive palladium amido complexes,
which then reductively eliminate coupled amine prod-
uct. These results suggest that alkoxide complexes may
be intermediates in the conversion of aryl halide com-
plexes to arylamido complexes in the amination chem-
sitry and, more generally, that alkoxide complexes may
be used for the production of amido complexes by N-H
activation.
P r ep a r a tion of syn -(P P h 3)(C6H5)P d (µ-OH)(µ-NH-t-Bu )-
P d (C6H5)(P P h 3) (3a ). Into a screw-capped test tube was
weighed 103 mg (0.111 mmol) of 1. H2N-t-Bu (8 mL) was
added to the test tube. The test tube was sealed and heated
at 70 °C with stirring for 1 h. The reaction mixture became
Exp er im en ta l Section
Gen er a l Meth od s. Unless otherwise noted, all reactions
and manipulations were performed in an inert atmosphere
glovebox or by using standard Schlenk techniques. Benzene,
toluene, THF, ether, and pentane solvents were distilled from
sodium/benzophenone prior to use. Amines were distilled from
CaH2, and triphenylphosphine was sublimed prior to use in
kinetic studies. Both H2O and D2O were degassed with N2(g)
before use in kinetic studies. All other chemicals were used
as received from commercial suppliers.
homogeneous.
A
31P{1H} NMR spectrum of the reaction
mixture indicated complete consumption of the starting mate-
rial. The reaction mixture was filtered through Celite and
concentrated. The THF solution was layered with Et2O and
cooled at -35 °C to yield 68.5 mg (63%) of white crystalline
material. 1H NMR (C6D6): δ -3.10 (s, 1H), 1.54 (t, 6.0 Hz,
1H), 1.64 (s, 9H), 6.83-6.94 (m, 24H), 7.57-7.66 (m, 16H). 31P-
{1H} NMR (THF): δ 26.2. 13C{1H} NMR (C6D6) δ: 36.7 (s),
59.1 (s), 122.3 (s), 127.1 (s), 128.3 (apparent t, J ) 5.0 Hz),
129.9 (s), 132.2 (d, J ) 42.2 Hz), 134.7 (apparent t, J ) 6.2
Hz), 138.5 (s), 150.7 (d, J ) 10.4 Hz). IR (cm-1, KBr): 3619
(w, νOH). Anal. Calcd for C52H51NOP2Pd2‚THF‚0.5Et2O (con-
firmed by integrated 1H NMR spectra): C, 63.92; H, 5.92; N,
1.29. Found: C, 63.84; H, 5.96; N, 1.39.
P r ep a r a tion of syn -(P P h 3)(C6H5)P d (µ-OH)(µ-NH-sec-
Bu )P d (C6H5)(P P h 3) (3b). Into a screw-capped test tube was
weighed 102 mg (0.110 mmol) of 1. The solid material was
dissolved in 8 mL of THF, and H2N-sec-Bu (55 µL, 0.550 mmol)
was added to the test tube. The test tube was sealed, and the
reaction was stirred at room temperature for 5 h. A 31P{1H}
NMR spectrum of the reaction mixture indicated complete
consumption of the starting material. The reaction mixture
was filtered through Celite. The THF solution was concen-
trated and layered with Et2O. The THF/Et2O solution was
cooled at -35 °C to yield 77.5 mg (72%) of white crystalline
material. 1H NMR (C6D6): δ -3.25 (s, 1H), 0.63 (t, J ) 7.4
Hz, 3H), 1.43 (m, 1H), 1.57 (apparent hept, J ) 6.9 Hz, 1H),
1.78 (d, J ) 6.3 Hz, 3H), 1.96 (apparent hept, J ) 6.6 Hz, 1H),
3.68 (m, 1H), 6.78-6.93 (m, 24H), 7.54-7.62 (m, 16H). 31P-
{1H} NMR (THF): δ 27.3 (s), 27.1 (s). 13C{1H} NMR (C6D6): δ
11.0 (s), 26.2 (s), 35.1 (s), 58.2 (s), 122.0 (s), 122.0 (s), 126.8
(s), 126.9 (s), 128.1 (d, J ) 12.1 Hz), 128.1 (d, J ) 12.1 Hz),
129.6 (s), 129.62 (s), 132.0 (d, J ) 41.8 Hz), 132.2 (d, J ) 42.1
Hz), 134.3 (d, J ) 11.7 Hz), 134.3 (d, J ) 11.7 Hz), 137.3 (d, J
) 2.4 Hz), 137.7 (d, J ) 2.8 Hz), 150.2 (d, J ) 9.7 Hz), 151.5
(d, J ) 10.1 Hz). IR (cm-1, KBr): 3611 (w, νOH), 3301 (w, νNH).
Anal. Calcd for C56H51NOP2Pd2: C, 63.68; H, 5.24; N, 1.43.
Found: C, 63.50; H, 5.32; N, 1.36.
P r ep a r a tion of [(P P h 3)(C6H5)P d (µ-OH)]2 (1). Into a 20
mL vial was weighed 150 mg (0.180 mmol) of trans-(PPh3)2-
Pd(C6H5)(I).62 The solid material was dissolved in 12 mL of
THF with stirring. CsOH (400 mg, 2.7 mmol) was added to
the vial as a solid. The reaction was stirred at room temper-
ature for 2 h.
A
31P{1H} NMR spectrum of the reaction
mixture indicated complete consumption of the starting mate-
rial. The reaction mixture was filtered through a medium-
fritted funnel containing Celite, and the resulting clear
solution was concentrated under vacuum. Pentane was added
to precipitate the product. The product was collected on a
medium-fritted funnel to give 137 mg (83%) of white solid. The
31P{1H} and 1H NMR spectra matched those previously
published.40
P r ep a r a tion of (P P h 3)(C6H5)P d (µ-OH)(µ-NHC6H5)P d -
(C6H5)(P P h 3) (2a ). Into a vial was weighed 128 mg (0.138
mmol) of 1. The solid material was dissolved in 8 mL of THF,
and 63 µL (0.693 mmol) of aniline was added to the reaction
solution. The reaction was stirred at room temperature for
30 min.
A
31P{1H} NMR spectrum of the reaction mixture
indicated complete consumption of the starting material and
the formation of 2a as a mixture of syn- and anti-isomers. The
reaction solution was filtered through Celite, concentrated, and
layered with Et2O. The THF/Et2O solution was cooled at -20
°C to yield 121 mg (88%) of amber crystalline 2a as predomi-
nately (>90%) the syn-isomer. 1H NMR: (C6D6, syn-isomer)
δ -3.40 (s, 1H), 2.75 (t, J ) 4.2 Hz, 1H), 6.63-6.78 (m, 5H),
6.81-6.89 (m, 20H), 7.19-7.22 (m, 6H), 7.44-7.50 (m, 12H),
7.62 (d, J ) 7.8 Hz, 2H); (C6D6, anti-isomer) δ -1.53 (d, J )
3.4 Hz, 1H), 1.55 (d, J ) 4.8 Hz, 1H). 31P{1H} NMR (THF): δ
34.1, 31.5 (anti-isomer), 29.8 (syn-isomer). IR (cm-1, KBr):
3603 (m, νOH), 3322 (w, νNH syn-isomer), 3308 (w, νNH anti-
P r epar ation of a n ti-[(P P h 3)(C6H5)P d(µ-NH-isoBu )]2 (3c).
Into a screw-capped test tube was weighed 186 mg (0.201
mmol) of 1. H2N-isoBu (10 mL) was added to the test tube.
The test tube was sealed, and the reaction was stirred at room
(62) Fitton, P.; J ohnson, M. P.; McKeon, J . E. J . Chem. Soc., Chem.
Commun. 1968, 6-7.