Orthometalation of primary amines. 4.1 Orthopalladation of primary benzylamines and (2-phenylethyl)amine

Article abstract of DOI:10.1021/om9609574

By the refluxing of an acetonitrile solution of [Pd(OAc)₂]₃ and primary amines 4-XC₆H₄-CH₂NH₂ (F, Cl, NO₂, OMe), 3,5-X₂C₆H₃CH₂NH₂ (X = OMe), or PhCH₂CH₂NH₂ (Pd:amine = 1:1) and subsequent addition of excess NaBr, the corresponding orthometalated complexes [Pd{C₆H₃(CH₂NH ₂)-2,X-5}(μ-Br)]₂, [Pd{C₆H₃(CH₂NH₂)-2,(OMe) ₂-4,6}(μ-Br)]₂, or [Pd{C₆H₃-(CH₂NH₂)-2}(μ-Br)] ₂ are obtained. Alternatively, the hydrochloride of 4-XC₆H₄CH₂NH₂ (X = F, NO₂) can also be used to prepare the corresponding [Pd{C₆H₃(CH₂NH ₂)-2,X-5}(μ-Cl)]₂ complexes. These results show that primary benzylamines can be orthometalated even if the substituents are electron-withdrawing groups and that 2-(phenyl)ethylamine can be orthometalated in spite of the six-membered ring that it forms. These reactions occur via intermediate complexes [Pd(OAc)₂L₂], which react with [Pd(OAc)₂]₃ to give the dimeric species [Pd(OAc)(μ-OAc)L]₂ (L = amine), from which in turn the orthometalated complexes are formed. Each of these steps has been studied, and both types of intermediates have been isolated for all the amines. PPh₃ reacts with the orthometalated complexes to give the corresponding products of the bridge splitting. The crystal structures of [Pd(OAc)(μ-OAc)L]₂ (L = 4-O₂NC₆H₄CH₂NH₂) and [Pd{C₆H₄(CH₂CH₂NH ₂)-2}Br(PPh₃)] have been determined by X-ray diffraction.

Full text of DOI:10.1021/om9609574

826
Organometallics 1997, 16, 826-833
Articles
Or th om eta la tion of P r im a r y Am in es. 4.1
Or th op a lla d a tion of P r im a r y Ben zyla m in es a n d
(2-P h en yleth yl)a m in e†
J ose´ Vicente,*,‡ Isabel Saura-Llamas, and Michael G. Palin
Grupo de Quı´mica Organometa´lica,§ Departamento de Qu´ımica Inorga´nica,
Facultad de Quı´mica, Universidad de Murcia, Apdo 4021, E-30071-Murcia, Spain
Peter G. J ones*,| and M. Carmen Ram´ırez de Arellano
Institut fu¨r Anorganische und Analytische Chemie, Technische Universita¨t Braunschweig,
Postfach 3329, 38023 Braunschweig, Germany
Received November 12, 1996X
By the refluxing of an acetonitrile solution of [Pd(OAc)2]3 and primary amines 4-XC6H4-
CH2NH2 (F, Cl, NO2, OMe), 3,5-X2C6H3CH2NH2 (X ) OMe), or PhCH2CH2NH2 (Pd:amine )
1:1) and subsequent addition of excess NaBr, the corresponding orthometalated complexes
[Pd{C6H3(CH2NH2)-2,X-5}(µ-Br)]2, [Pd{C6H3(CH2NH2)-2,(OMe)2-4,6}(µ-Br)]2, or [Pd{C6H3-
(CH2NH2)-2}(µ-Br)]2 are obtained. Alternatively, the hydrochloride of 4-XC6H4CH2NH2 (X
) F, NO2) can also be used to prepare the corresponding [Pd{C6H3(CH2NH2)-2,X-5}(µ-Cl)]2
complexes. These results show that primary benzylamines can be orthometalated even if
the substituents are electron-withdrawing groups and that 2-(phenyl)ethylamine can be
orthometalated in spite of the six-membered ring that it forms. These reactions occur via
intermediate complexes [Pd(OAc)2L2], which react with [Pd(OAc)2]3 to give the dimeric species
[Pd(OAc)(µ-OAc)L]2 (L ) amine), from which in turn the orthometalated complexes are
formed. Each of these steps has been studied, and both types of intermediates have been
isolated for all the amines. PPh3 reacts with the orthometalated complexes to give the
corresponding products of the bridge splitting. The crystal structures of [Pd(OAc)(µ-OAc)L]2
(L ) 4-O2NC6H4CH2NH2) and [Pd{C6H4(CH2CH2NH2)-2}Br(PPh3)] have been determined
by X-ray diffraction.
In tr od u ction
activated N-phenyl-(3,5-dimethoxybenzyl)amine. The
second requirement is that the aryl group must not be
deactivated as in 4-nitro-N,N-dimethylbenzylamine.
The early work of Cope and Friedrich on cyclopalla-
dation of benzylamine2 derivatives has served notice to
other authors to assume three requirements that the
amine must meet.3 The first established that the amine
must be tertiary. Thus, orthopalladation using lithium
tetrachloropalladate(II) was observed with N,N-di-
methylbenzylamine or some of its aryl-substituted
derivatives containing electron-releasing groups (2-
methoxy, 3,5-dimethoxy). However, it does not occur
with benzylamine or some N-monosubstituted deriva-
tives (methyl, benzyl, phenyl) or even with the highly
Finally, the Pd-C-N ring formed after metalation must
be a planar five-membered ring. The unsuccessful
orthopalladation of the potential precursors of six- and
seven-membered rings, N,N-dimethyl-2-phenyl-1-ethyl-
amine and N,N-dimethyl-3-phenyl-1-propylamine, was
the proof of this requirement. When these conditions
are not met the complex [PdCl2(amine)2] is isolated
instead.2 Since this pioneering work, some violations
of these rules have been observed on varying the nature
of the amine or the palladium complex.4 Thus, Lewis
et al.3 and later Dunina et al.4c found that, contrary to
the first rule, substitution at the R-benzyl position with
a phenyl or methyl group allows the orthopalladation
of the primary amine (triphenylmethyl)amine and of the
secondary amines N-methyl(triphenylmethyl)amine or
N-methyl-(R-methylbenzyl)amine. Finally, the substi-
† Dedicated to Professor Walter Siebert on the occasion of his 60th
birthday.
‡ E-mail: jvs@fcu.um.es.
§ http://www.scc.um.es/gi/gqo.
| E-mail: p.jones@tu-bs.de.
X Abstract published in Advance ACS Abstracts, February 15, 1997.
(1) (a) Part 1: Vicente, J .; Saura-Llamas, I.; J ones, P. G. J . Chem.
Soc., Dalton Trans. 1993, 3619. (b) Part 3: Vicente, J .; Saura-Llamas,
I.; G. Palin, M. G.; J ones, P. G. J . Chem. Soc., Dalton Trans. 1995,
2535.
(4) (a) Dehand, J .; Pfeffer, M. Coord. Chem. Rev. 1976, 18, 327. (b)
Omae, I. Coord. Chem. Rev. 1988, 83, 137. (c) Dunina, V. V.;
Zalevskaya, O. A.; Potapov, V. M. Russ. Chem. Rev. 1988, 57, 250 and
references therein.
(2) Cope, A. C.; Friedrich, E. C. J . Am. Chem. Soc. 1968, 90, 909.
(3) Cockburn, B. N.; Howe, D. V.; Keating, T.; J ohnson, B. F. G.;
Lewis, J . J . Chem. Soc., Dalton Trans. 1973, 404.
S0276-7333(96)00957-0 CCC: $14.00 © 1997 American Chemical Society

Orthometalation of Primary Amines
Organometallics, Vol. 16, No. 5, 1997 827
137.9 (s, C, Ph), 180.2 (s, CO). Anal. Calcd for C18H24N2O4-
Pd: C, 49.27; H, 5.51; N, 6.38. Found: C, 49.29; H, 5.51; N,
6.36.
[P d (OAc)2(4-ClC6H4CH2NH2)2] (1b). Yield: 87%. Mp:
172-174 °C dec. Anal. Calcd for C18H22Cl2N2O4Pd: C, 42.58;
H, 4.37; N, 5.52. Found: C, 42.92; H, 4.35; N, 5.63.
[P d (OAc)2(4-NO2C6H4CH2NH2)2]‚2H2O (1c‚2H2O). Yield:
88%. Decomposition point: 149 °C. Anal. Calcd for
tution of the usual starting chloro complex of palladium
6
by [Pd(acac)2]5 or [Pd(OAc)2]3 or by reacting [PdI2-
7
(amine)2] with AgBF4 allowed the orthopalladation of
benzylamine. Using these two last methods we have
also orthometalated (4-nitro-R-methylbenzyl)amine,
which infringes the second rule,2b and (R-methylbenzyl)-
amine.2a In this paper we report a general and facile
way to prepare orthometalated non-R-substituted pri-
mary amines that contain either an electron-withdraw-
ing substituent on the aryl ring or lead to a six-
membered metallacycle, transgressing against the above-
mentioned three rules. Most of these results were
communicated in national and international confer-
ences.8 The generalization of orthopalladation reactions
to primary amines can expand the use of these types of
complexes in organic synthesis.9
C
18H26N4O10Pd: C, 38.28; H, 4.64; N, 9.92. Found: C, 38.20;
H, 4.55; N, 9.62.
[P d (OAc)2(4-F C6H4CH2NH2)2] (1d ). Yield: 90%. Decom-
position point: 158 °C. Anal. Calcd for C18H22F2N2O4Pd: C,
45.54; H, 4.67; N, 5.90. Found: C, 45.71; H, 4.70; N, 5.86.
[P d (OAc)2(4-MeOC6H 4CH 2NH 2)2] (1e). Yield: 75%.
Mp: 158-159 °C dec. NMR (δ): 1H, 1.87 (s, 3 H, Me), 3.67
(m, 2 H, CH2), 3.78 (s, 3 H, OMe), 4.09 (m, 2 H, NH2), 6.87
and 7.27 (AB, 4 H, C6H4, 3J AB ) 8.4 Hz); 13C{1H}, 23.6 (s, Me),
47.3 (s, CH2), 55.3 (s, OMe), 114.3, 129.6 (s, CH, C6H4), 130.1,
159.4 (s, C, C6H4), 180.2 (s, CO). Anal. Calcd for C20H28N2O6-
Pd: C, 48.15; H, 5.66; N, 5.62. Found: C, 48.42; H, 5.80; N,
5.71.
Exp er im en ta l Section
Gen er a l P r oced u r es. Infrared spectra were recorded on
Perkin-Elmer 1430 and 16F-PC-FT spectrometers. The C, H,
and N analyses, conductance measurements in acetone, and
melting point determinations were carried out as described
elsewhere.1 Unless otherwise stated, NMR spectra were
recorded in CDCl3 in a Varian Unity 300. Chemical shifts are
referenced to TMS [1H and 13C{1H}], H3PO4 [31P{1H}], or CFCl3
(19F). Benzylamine, (4-Nitrobenzyl)amine hydrochloride, (4-
fluorobenzyl)amine hydrochloride, (4-chlorobenzyl)amine, (4-
methoxybenzyl)amine, (3,5-dimethoxybenzyl)amine, and 2-
(phenyl)ethylamine were purchased from Aldrich and
[Pd(OAc)2]3 was purchased from J ohnson Matthey and used
as received. (4-Nitrobenzyl)amine and (4-fluorobenzyl)amine
were prepared by reacting the corresponding hydrochloride
with NaOH. All those complexes soluble in acetone show
[P d (OAc)2{3,5-(MeO)2C6H3CH2NH2}2]‚2H2O (1f‚2H 2O).
Yield: 74%. Mp: 133 °C. Anal. Calcd for C22H36N2O10Pd: C,
44.42; H, 6.10; N, 4.71. Found: C, 44.19; H, 6.13; N, 4.82.
[P d (OAc)2(P h CH2CH2NH2)2] (1g). Yield: 77%. Mp: 129
°C. NMR (δ): 1H, 1.85 (s, 3 H, Me), 2.81 (m, 2 H, CH2), 3.03
(m, 2 H, CH2), 3.79 (m, 2 H, NH2), 7.20-7.33 (m, 5 H, Ph);
13C{1H}, 23.4 (s, Me), 36.2 (s, CH2), 44.6 (s, CH2), 126.7 (s,
p-CH, Ph), 128.6, 128.7 (s, CH, Ph), 137.6 (s, C, Ph), 179.8 (s,
CO). Anal. Calcd for C20H28N2O4Pd: C, 51.46; H, 6.05; N,
6.00. Found: C, 50.30; H, 5.92; N, 5.93.
Syn th esis of Com p lexes 2a -g. To a suspension of the
corresponding [Pd(OAc)2(amine)2] (0.531 mmol) in dichloro-
methane (15 mL) was added [Pd(OAc)2]3 (119 mg, 0.177 mmol).
The mixture was stirred at room temperature for 18 h, during
which time a red solution formed. The solution was filtered
through MgSO4 and reduced in volume to ca. 2 mL, and
n-hexane (diethyl ether in the case of 2c) was added to
precipitate the product as an orange solid. The complex was
filtered out, washed with diethyl ether, and air-dried to give
2a -g as an orange solid.
molar conductivities in the range 0-4 Ω-1 cm2 mol-1
.
Syn th esis of Com p lexes 1a ,b,e-g. To a suspension of
[Pd(OAc)2]3 (547 mg, 0.81 mmol) in acetone (20 mL) was added
the amine (4.87 mmol) to form an immediate yellow precipi-
tate, which was stirred for 2 h, filtered out, washed with ether,
and air-dried.
[P d (OAc)(µ-OAc)(P h CH2NH2)]2 (2a ). Yield: 81%. Mp:
85 °C. NMR (δ): 1H, 1.88 (s, 3 H, Me), 1.89 (s, 3 H, Me), 3.54
(m, 1 H, CH2), 3.68 (m, 1 H, CH2), 4.22 (m, 1 H, NH), 5.35 (m,
Syn th esis of Com p lexes 1c,d . To a suspension of the
hydrochloride (1.59 mmol) in dichloromethane (10 mL) was
added aqueous NaOH (1.6 mL of 1 M solution, 1.6 mmol). After
10 min a clear solution formed. The layers were separated,
and the aqueous layer was washed with dichloromethane (3
× 8 mL). [Pd(OAc)2]3 (180 mg, 0.267 mmol) was added to the
organic layer, and an immediate yellow precipitate formed.
The suspension was stirred at room temperature for 2 h and
then filtered; the solid was washed with dichloromethane and
air-dried.
3
1 H, NH), 7.34-7.52 (m, 5 H, Ph); C{1H}, 23.0, 23.2 (s, Me),
47.9 (s, CH2), 128.3 (s, p-CH, Ph), 128.4, 129.1 (s, CH, Ph),
137.6 (s, C, Ph), 180.0, 185.8 (s, CO). Anal. Calcd for
C
22H30N2O8Pd2: C, 39.84.70; H, 4.56; N, 4.22. Found: C,
39.73; H, 4.57; N, 4.27.
[P d (OAc)(µ-OAc)(4-ClC6H4CH2NH2)]2 (2b). Yield: 79%.
Mp: 69-70 °C. NMR (δ): 1H, 1.88, 1.89 (s, 3 H, Me), 3.61 (m,
2 H, CH2), 4.25 (m, 1 H, NH), 5.44 (m, 1 H, NH), 7.34 y 7.50
3
(AB, 4 H, C6H4, J AB ) 7.8 Hz); 13C{1H}, 23.0, 23.2 (s, Me),
[P d (OAc)2(P h CH2NH2)2] (1a ). Yield: 83%. Mp: 140 °C
dec. NMR (δ): 1H, 1.85 (s, 3 H, Me), 3.74 (m, 2 H, CH2), 4.24
(m, 2 H, NH2), 7.27-7.41 (m, 5 H, Ph); 13C{1H}, 23.5 (s, Me),
47.8 (s, CH2), 128.1 (s, p-CH, Ph), 128.3, 128.9 (s, CH, Ph),
47.1 (s, CH2), 129.2 (s, CH, C6H4), 130.0 (s, CH, C6H4), 134.3,
135.4 (s, C, C6H4), 180.0, 185.9 (s, CO). Anal. Calcd for
C
22H28Cl2N2O8Pd2: C, 36.09; H, 3.85; N, 3.83. Found: C,
36.37; H, 3.84; N, 4.05.
[P d(OAc)(µ-OAc)(4-NO2C6H4CH2NH2)]2 (2c). Yield: 94%.
Mp: 219-220 °C. NMR (δ): 1H, 1.89, 1.91 (s, 3 H, Me), 3.75
(m, 2 H, CH2), 4.26 (m, 1 H, NH), 5.69 (m, 1 H, NH), 7.79 and
(5) Baba, S.; Kawaguchi, S. Inorg. Nucl. Chem. Lett. 1975, 11, 415.
(6) Fuchita, Y.; Tsuchiya, H.; Miyafuji, A. Inorg. Chim. Acta 1995,
233, 91.
(7) Avshu, A.; O’Sullivan, R. D.; Parkins, A. W.; Alcock, N. W.;
Countryman, R. M. J . Chem. Soc., Dalton Trans. 1983, 1619.
(8) Presented at the XIth FECHEM Conference on Organometallic
Chemistry, Sept 10-15, 1995 (p 114 of the book of Abstracts), Parma,
Italy. Presented at the XV Reunio´n del G.E.Q.O. September, 20-22,
1995 (Poster 67) Sevilla, Spain.
3
8.30 (AB, 4 H, C6H4, J AB ) 8.4 Hz); 13C{1H} [(CD3)2CO, δ],
24.0, 24.2 (s, Me), 48.2 (s, CH2), 125.4, 130.8 (s, CH, C6H4),
145.6, 149.2 (s, C, C6H4), 181.2, 187.2 (s, CO). Anal. Calcd
for C22H28N4O12Pd2: C, 35.08; H, 3.75; N, 7.44. Found: C,
34.72; H, 3.82; N, 7,56.
(9) Ryabov, A. D. Synthesis, 1985, 233. Pfeffer, M. Pure Appl. Chem.
1992, 64, 335. Camargo, M.; Dani, P.; Dupont, J .; de Souza, R. F.;
Pfeffer, M.; Tkatchenko, I. J . Mol. Catal. A 1996, 109, 127. Brisdon,
Nair, P.; B. J .; Dyke, S. F. Tetrahedron 1981, 37, 173. Ryabov, A. D.;
Sakodinskaya, I. K.; Dvoryantsev, S. N.; Eliseev, A. V.; Yatsimirsky,
A. K.; Kuz’mina, L. G.; Struchkov, Yu. T. Tetrahedron Lett. 1986, 27,
2169. Clark, P. W.; Dyke, H. J .; Dyke, S. F.; Perry, G. J . Organomet.
Chem. 1983, 253, 399. Pfeffer, M.; Sutter, J .-P.; DeCian, A.; Fischer,
J . Inorg. Chim. Acta 1994, 220, 115.
[P d (OAc)(µ-OAc)(4-F C6H4CH2NH2)]2 (2d ). Yield: 90%.
Mp: 75-76 °C. NMR (δ): 1H, 1.89, 1.90 (s, 3 H, Me), 3.61 (m,
2 H, CH2), 4.24 (m, 1 H, NH), 5.42 (m, 1 H, NH), 7.09 (apparent
3
triplet, 2 H, C6H4, J HH ) 3J FH ) 8.7 Hz), 7.54 (dd, 2 H, C6H4,
4J FH ) 5.25); 13C{1H}, 22.9, 23.1 (s, Me), 47.0 (s, CH2), 115.9
2
3
(d, CH, C6H4, J FC ) 21.6 Hz), 130.3 (d, CH, C6H4, J FC ) 8.6
4
1
Hz), 132.7 (d, C, C6H4, J FC ) 3.5 Hz), 162.6 (s, C, C6H4, J FC

828 Organometallics, Vol. 16, No. 5, 1997
Vicente et al.
) 247 Hz), 179.8, 185.7 (s, CO); 19F, -113.7 (m). Anal. Calcd
for C22H28F2N2O8Pd2: C, 37.79; H, 4.04; N, 4.01. Found: C,
38.04; H, 4.20; N, 3.80.
Anal. Calcd for C14H14Br2Cl2N2Pd2: C, 25.72; H, 2.16; N, 4.28.
Found: C, 25.68; H, 2.11; N, 4.10.
[P d {C6H3(CH2NH2)-2,NO2-5}(µ-Br )]2 (3c). Method c was
used. Yield: 66%. Decomposition point: 205 °C. NMR
[(CD3)2SO, δ]: 1H, 4.07 (m, 2 H, CH2), 5.76 (m, 2 H, NH2), 7.30
(m, 1 H, H3), 7.87 (m, 1 H, H4), 8.76 (s, b, 1 H, H6). Anal
Calcd for C14H14Br2N4O4Pd2: C, 24.92; H, 2.09; N, 8.30.
Found: C, 25.66; H, 2.16; N, 8.15.
[P d(OAc)(µ-OAc)(4-MeOC6H4CH2NH2)]2 (2e). Yield: 73%.
Mp: 58-60 °C. NMR (δ): 1H, 1.89, 1.90 (s, 3 H, Me), 3.56 (m,
2 H, CH2), 3.81 (s, 3 H, OMe), 4.20 (m, 1 H, NH), 5.27 (m, 1 H,
3
NH), 6.92 and 7.44 (AB, 4 H, C6H4, J AB ) 8.7 Hz); 13C{1H},
23.0, 23.2 (s, Me), 47.2 (s, CH2), 55.3 (s, OMe), 114.3 (s, CH,
C6H4), 129.2 (s, C, C6H4), 129.8 (s, CH, C6H4), 159.5 (s, C, C6H4),
179.9, 185.6 (s, CO). Anal. Calcd for C24H34N2O10Pd2: C,
39.85; H, 4.74; N, 3.87. Found: C, 40.41; H, 4.84; N, 3.94.
[P d {C6H3(CH2NH2)-2,NO2-5}(µ-Cl)]2 (3c′). Method c was
used but with acetone as the reaction solvent and a reaction
time of 7 h. Yield: 69%. No satisfactory elemental analysis
could be obtained due to the insolubility of 3c′, but it can be
used as starting material to prepare 3c or 4c′.
[P d (OAc)(µ-OAc)(3,5-(MeO)2C6H 3CH 2NH 2)]2
(2f).
Yield: 87%. Mp: 67 °C. NMR (δ): 1H, 1.89, 1.92 (s, 3 H, Me),
3.56 (m, 2 H, CH2), 3.81 (s, 6 H, OMe), 4.20 (m, 1 H, NH), 5.37
(m, 1 H, NH), 6.42 (t, 1 H, C6H3, J ) 2.1 Hz), 6.66 (d, 2 H,
C6H3). Anal. Calcd for C26H38N2O12Pd2: C, 39.86; H, 4.89; N,
3.58. Found: C, 39.87; H, 4.86; N, 3.53.
[P d {C6H3(CH2NH2)-2,F -5}(µ-Br )]2 (3d ). Method c was
used. The complex was recrystallized from acetone/CH2Cl2.
Yield: 69%. Decomposition point: 215 °C. NMR [(CD3)2CO,
[P d (OAc)(µ-OAc)(P h CH2CH 2NH 2)]2 (2g). Yield: 84%.
Mp: 64 °C. NMR (δ): 1H, 1.88 (s, 6 H, Me), 2.55 (m, 1 H,
CH2), 2.71 (m, 1 H, CH2), 3.25 (m, 2 H, CH2), 3.76 (m, 1 H,
NH), 5.14 (m, 1 H, NH), 7.25-7.39 (m, 5 H, Ph); 13C{1H}, 22.9,
23.1 (s, Me), 36.3 (s, CH2), 44.6 (s, CH2), 126.8 (s, p-CH, Ph),
128.7, 128.9 (s, CH, Ph), 137.6 (s, C, Ph), 179.7, 185.6 (s, CO).
Anal. Calcd for C24H34N2O8Pd2: C, 41.70; H, 4.96; N, 4.05.
Found: C, 40.76; H, 4.82; N, 3.98.
Syn th esis of Com p lexes 3. Meth od a . The amine (1.22
mmol) and [Pd(OAc)2]3 (273 mg, 0.407 mmol) were refluxed
in acetonitrile (20 mL) for 4 h. The resulting suspension was
filtered through a plug of MgSO4, the solvent removed, and
acetone (25 mL) added. Solid NaBr (200 mg, 1.94 mmol) was
added and the suspension stirred for 4 h. The solvent was
removed, and the residue was collected with CH2Cl2, washed
with water (3 × 15 mL) and diethyl ether (3 × 15 mL) and
air-dried to afford complex 3 as a yellow (3b,e), orange (3c,d ,g)
or white solid (3f).
Meth od b. The corresponding complex 2 (0.546 mmol) was
refluxed in acetonitrile (10 mL) for 4 h. The resulting mixture
was filtered through a plug of MgSO4, the solvent removed,
and acetone (30 mL) added. Solid NaBr (230 mg, 2.24 mmol)
was added and the resulting suspension stirred for 4 h.
Solvent was removed, and the residue was collected with
CH2Cl2, washed with water (3 × 15 mL) and diethyl ether (3
× 15 mL), and air-dried to afford complex 3.
3
δ]: 1H, 4.14 (t, 2 H, CH2, J HH ) 5.7 Hz), 4.97 (m, 2 H, NH2),
3
3
6.52 (m, 1 H, H3), 6.81 (apparent triplet, 1 H, H4, J
) J
HH
) 7.8 Hz), 7.55 (s, b, 1 H, H6). 19F, -119.6 (s, b). Anal.
FH
Calcd for C14H14Br2F2N2Pd2: C, 27.08; H, 2.27; N, 4.51.
Found: C, 26.70; H, 2.06; N, 4.51.
[P d {C6H3(CH2NH2)-2,F -5}(µ-Cl)]2 (3d ′). Complex 3d ′ was
prepared in a similar manner to 3c′. Yield: 48%. Decomposi-
tion point: 198 °C. NMR [(CD3)2SO, δ]: 1H, 3.92 (t, 2 H, CH2,
3
3J HH ) 5.7 Hz), 5.58 (m, 2 H, NH2), 6.77 (dt, 1 H, H4, J HH
)
3J FH ) 8.7, J FH ) 2.4 Hz), 7.00 (dd, 1 H, H3, J HH) 8.1, J FH
4
3
4
) 6 Hz), 7.54 (dd, 1 H, H6, 3J FH ) 10.2, 4J HH ) 2.7 Hz). Anal.
Calcd for
C14H14Cl2F2N2Pd2: C, 31.61; H, 2.65; N, 5.27.
Found: C, 31.53; H, 2.60; N, 4.99.
[P d {C6H3(CH2NH2)-2,(OMe)-5}(µ-Br )]2 (3e). Methods a
(yield: 51%) and b (yield: 48%) were used. Mp: 185-186 °C
dec. NMR [(CD3)2SO, δ]: 1H, 3.63 (s, 3 H, OMe), 3.89 (t, 2 H,
CH2, 3J HH ) 5.7 Hz), 5.46 (m, 2 H, NH), 6.55 (d, 1 H, H4, C6H3,
3J HH ) 7.8 Hz), 6.57 (d, 1 H, H3, C6H3), 7.39 (s, 1 H, H6, C6H3).
Anal. Calcd for C16H20Br2N2O2Pd2: C, 29.80; H, 3.13; N, 4.36.
Found: C, 30.33; H, 3.00; N, 4.16.
[P d {C6H2(CH2NH2)-2,(OMe)2-4,6}(µ-Br )]2 (3f). Methods
a (yield: 41%), b (yield: 43%), and d (yield: 79%) were used.
No satisfactory analysis could be obtained due to the insolubil-
ity of this complex, but it can be used as starting material to
prepare 4f.
Meth od c. The amine‚HCl (4.94 mmol) and [Pd(OAc)2]3
(1.11 g, 1.647 mmol) were refluxed in acetonitrile (50 mL) for
4 h. Solid NaBr (1.50 g, 14.58 mmol) was added to the
suspension and the resulting mixture stirred for 8 h. Solvent
was removed, and the residue was collected with CH2Cl2,
washed with water (3 × 15 mL) and diethyl ether (3 × 15 mL),
and air-dried to afford complex 3.
Meth od d . Complex 2 (205 mg, 0.262 mmol) was dissolved
in CH2Cl2 and solvent removed. The flask was kept in the
oven at 80 °C for 2 h. Acetone (20 mL) and NaBr (200 mg,
1.94 mmol) were added, and the resulting mixture stirred for
4 h. A white solid precipitated. Solvent was removed, and
the residue was collected with CH2Cl2, washed with water (3
× 15 mL) and diethyl ether (3 × 15 mL), and air-dried to afford
complex 3.
[P d {C6H 4(CH 2CH 2NH 2)-2}(µ-Br )]2 (3g). Methods
a
(yield: 30%) and b (yield: 37%). Decomposition point: 175
°C. NMR [(CD3)2CO, δ]: 1H, 3.51 (m, 2 H, CH2), 3.96 (m, 2 H,
CH2), 4.37 (m, 2 H, NH2), 6.69 (m, 1 H, C6H4), 6.83 (m, 2 H,
C6H4), 7.36 (s, 1 H, C6H4). Anal. Calcd for C16H20Br2N2Pd2:
C, 31.35; H, 3.29; N, 4.57. Found: C, 31.18; H, 3.18; N, 4.59.
Syn th esis of Com p lexes 4. To a suspension of the
corresponding complex 3 (0.089 mmol) in dichloromethane (12
mL) was added PPh3 (47 mg, 0.179 mmol). After the mixture
was stirred for 2 h, a colorless solution formed, which was
filtered through MgSO4 and concentrated to ca. 3 mL. Diethyl
ether (15 mL) was added to precipitate complex 4 as an off-
white (4a ,c,c′,d ′), pale yellow (4b,d ,e,f), or tan (4g) solid which
was filtered out, washed with diethyl ether, and air-dried.
[P d {C6H4(CH2NH2)-2}(µ-AcO)]2 (3a ). The amine (1.22
mmol) and [Pd(OAc)2]3 (273 mg, 0.407 mmol) were refluxed
in acetonitrile (20 mL) for 4 h. The resulting suspension was
filtered through a plug of MgSO4 and the solvent removed,
and the residue was collected with acetone, washed with
diethyl ether (3 × 15 mL), and air-dried to afford complex 3a
as a yellow solid. Yield: 44%. Complex 3a can also be
prepared by refluxing complex 2a (0.546 mmol) in acetonitrile
(20 mL) for 2 h. Yield: 49%. The spectroscopic data of 3a
are identical to those reported in the literature.6
[P d {C6H4(CH2NH2)-2}(OAc)(P P h 3)] (4a ). Yield: 75%.
Decomposition point: 235 °C. NMR (δ): 1H, 1.41 (s, 3 H, Me),
4.26 (m, 2 H, CH2), 4.73 (m, 2 H, NH2), 6.38 (m, 2 H, C6H4),
6.82 (apparent triplet, 1 H, C6H4, J HH ) 7.2), 6.94 (d, 1 H, C6H4,
J ) 7.5 Hz), 7.26-7.44 (m, 9 H), 7.64-7.73 (m, 6 H, Ph);
3
13C{1H}, 24.0 (s, CH3), 52.2 (d, CH2, J PC ) 2.2 Hz), 121.5 (s,
CH, C6H4), 124.0 (s, CH, C6H4), 125.0 (d, CH, C6H4, J PC ) 5.0
2
Hz), 128.2 (d, o-CH, PPh3, J PC ) 11.0 Hz), 130.6 (d, i-CH,
PPh3, 1J PC ) 47.8 Hz), 130.7 (d, p-C, PPh3, 4J PC ) 2.5 Hz), 135.8
3
[P d {C6H 3(CH 2NH 2)-2,Cl-5}(µ-Br )]2 (3b ). Methods
a
(d, m-CH, PPh3, J PC ) 12.1 Hz), 139.2 (d, CH, C6H4, J PC
)
(yield: 51%) and b (yield: 68%) were used. Mp: 234 °C dec.
10.5 Hz), 145.9 (d, C, C6H4, J PC ) 2.5 Hz), 154.3 (s, C, C6H4),

Orthometalation of Primary Amines
Organometallics, Vol. 16, No. 5, 1997 829
178.5 (s, CO); 31P{1H}, 41.2 (s). Anal. Calcd for C27H26NO2-
PPd: C, 60.74; H, 4.91; N, 2.62. Found: C, 60.70; H, 4.98; N,
2.65.
Ta ble 1. Cr ysta l Da ta for Com p ou n d s
2c‚CH3COCH3 a n d 4g
molecular formula
C25H34N4O13Pd2
811.36
C26H25BrNPPd
568.75
Mr
source
[P d {C6H3(CH2NH2)-2,Cl-5}Br (P P h 3)] (4b). Yield: 76%.
Mp: 258 °C dec. NMR (δ): 1H, 3.84 (m, 2 H, NH2), 4.32 (m, 2
H, CH2), 6.82 (dd, 1 H, H3, 3J HH ) 8.1, 6J PH ) 2.1 Hz), 6.93 (d,
1 H, H6, 4J PH ) 8.1 Hz), 7.34-7.63 (m, 10 H, H4 + Ph), 7.68-
7.74 (m, 6 H, Ph); 31P{1H}, 38.6 (s). Anal. Calcd for
liquid diffusion
CH2Cl2/Et2O
lath
liquid diffusion
CH2Cl2/n-hexane
tablet
dark orange
orthorhombic
10.626(1)
description
color
cryst system
a, Å
yellow
monoclinic
32.212(10)
8.493(3)
C
25H22BrClNPPd: C, 50.96; H, 3.76; N, 2.38. Found: C, 50.53;
b, Å
c, Å
16.483(1)
H, 3.58; N, 2.34.
25.251(7)
112.795(10)
6369(4)
26.284(2)
[P d {C6H3(CH2NH2)-2,NO2-5}Br (P P h 3)] (4c). Yield: 66%.
Mp: 242 °C dec. NMR [(Me)2SO, δ]: 4.19 (m, 2 H, NH2), 5.47
â, deg
V, Å3
4603(1)
3
5
Z
8
8
(m, 2 H, CH2), 7.09 (dd, 1 H, H3, J HH ) 5.7 Hz, J
) 2.4
HP
radiation (λ, Å)
temp, K
Mo KR (0.710 73)
173(2)
Mo KR (0.710 73)
298(2)
4
Hz), 7.23 (d, 1 H, H6, J HP ) 8.1 Hz), 7.41-7.52 (m, 9 H, Ph),
7.61-7.69 (m, 7 H, H4 + Ph); 31P{1H}, 39.5 (s). Anal. Calcd
for C25H22BrN2O2PPd: C, 50.07; H, 3.70; N, 4.67. Found: C,
50.37; H, 3.70; N, 4.21.
monochromator
space group
cryst size, mm
µ, mm-1
graphite
C2/c
graphite
Pbca
0.65 × 0.15 × 0.05
0.32 × 0.32 × 0.10
1.197
2.625
[P d {C6H3(CH2NH2)-2,NO2-5}Cl(P P h 3)] (4c′). Yield: 78%.
Mp 210 °C dec. NMR (δ): 1H, 4.20 (m, 2 H, NH2), 4.26 (m, 2
abs corr
ψ scans
0.96
0.74
Siemens P4
ω scans
6.1-50.0
-5 < h < 38
-10 < k < 4
-30 < h < 27
8416
ψ scans
1.00
0.69
Siemens P4
ω scans
6.2-50.0
-1 < h < 12
-1 < k < 19
-31 < l < 31
9478
max transm, %
min transm, %
diffractometer type
data collcn method
2θ range, min-max
hkl limits
3
H, CH2), 7.01 (d, 1 H, H3, J HH ) 8.4 Hz), 7.21 (dd, 1 H, H4,
6J PH ) 2.1), 7.26-7.47 (m, 10 H), 7.65-7.74 (m, 6 H, Ph);
31P{1H}, 39.7 (s). Anal. Calcd for C25H22ClN2O2PPd: C, 54.08;
H, 3.99; N, 5.04. Found: C, 53.94; H, 3.94; N, 5.03.
[P d {C6H3(CH2NH2)-2,F -5}Br (P P h 3)] (4d ). Yield: 84%.
Decomposition point: 225 °C. NMR (δ): 1H, 3.90 (m, 2 H,
3
4
reflcns measd
indepdt reflcns
Rint
NH2), 4.29 (m, 2 H, CH2), 5.99 (ddd, 1 H, H3, J HH ) 8.7, J FH
5
3
3
5577
0.064
0.0529, 0.1248
4047
0.052
0.0306, 0.0550
) 6.3, J PH ) 2.7 Hz), 6.53 (dt, 1 H, H4, J FH ) J HH ) 8.7,
3
4
6J PH ) 2.4 Hz), 6.95 (dd, 1 H, H6, J FH ) 8.4, J PH ) 5.7 Hz),
7.35-7.47 (m, 9 H), 7.62-7.74 (m, 6 H, Ph); 13C{1H}, 53.5 (s,
CH2), 110.7 (d, CH, C6H3, 2J FC ) 22.2 Hz), 122.1 (d, CH, C6H3,
R1 (I > 2σ(I)), wR2a
R1 ) Σ||Fo| - |Fc||/Σ|Fo|. wR2 ) [Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]]0.5
.
a
3J FC ) 7.5 Hz), 124.1 (dd, CH, C6H3, J FC ) 19.7 Hz, J PC
)
2
3
2
10.1 Hz), 128.2 (d, o-CH, PPh3, J PC ) 10.6 Hz), 130.2 (d, i-C,
1
9 H, PPh3), 7.68-7.74 (m, 6 H, PPh3); 31P{1H}, 37.0 (s). Anal.
Calcd for 27H27BrNO2PPd: C, 52.75; H, 4.43; N, 2.28.
PPh3, J PC ) 50.3 Hz), 130.8 (s, p-CH, PPh3), 135.2 (d, m-CH,
3
PPh3, J PC ) 11.6 Hz), 148.5 (s, C, C6H3), 151.5 (d, C, C6H3,
C
2J PC ) 2.5), 159.3 (d, C, C6H3, J FC ) 247 Hz); 31P{1H}, 42.1
1
Found: C, 52.87; H, 4.80; N, 2.08.
(s); 19F, -117.0 (m). Anal. Calcd for C25H22BrFNPPd: C,
[P d {C6H4(CH2CH2NH2)-2}Br (P P h 3)] (4g). Yield: 56%.
Decomposition point: 205 °C. NMR (δ): 1H, 2.79 (m, 2 H,
CH2), 3.18 (m, 2 H, CH2), 3.38 (m, 2 H, NH2), 6.34 (dt, 1 H,
H4, J HH ) 7.5, J PH ) 1.2 Hz), 6.51 (dd, 1 H, H3, J HH ) 6.9, J PH
) 4.3 Hz), 6.77 (dt, 1 H, H5, J HH ) 7.2, J PH ) 1.2 Hz), 6.87
(dd, 1 H, H6, J HH ) 6.9 Hz, J PH ) 1.8 Hz), 7.25-7.40 (m, 9 H,
52.43; H, 3.87; N, 2.45. Found: C, 52.86; H, 3.96; N, 2.46.
[P d {C6H3(CH2NH2)-2,F -5}Cl(P P h 3)] (4d ′). Yield: 77%.
Mp: 194 °C dec. NMR (δ): 1H, 3.93 (m, 2 H, NH2), 4.26 (m, 2
3
4
5
H, CH2), 5.98 (ddd, 1 H, H3, J HH ) 8.7, J FH ) 6, J PH ) 2.7
Hz), 6.53 (dt, 1 H, H4, J FH ) 3J HH ) 8.4, J PH ) 2.4 Hz), 6.92
3
6
3
4
3
Ph), 7.50-7.60 (m, 6 H, Ph); 13C{1H}, 37.8 (d, CH2, J PC ) 2.5
(dd, 1 H, H6, J FH ) 8.4, J PH ) 5.7 Hz), 7.32-7.84 (m, 9 H),
7.66-7.73 (m, 6 H, Ph); 13C{1H}, 52.7 (s, CH2), 110.6 (d, CH,
C6H3, 2J FC ) 22.2 Hz), 122.1 (d, CH, C6H3, 3J FC ) 7.5 Hz), 124.1
(dd, CH, C6H3, 2J FC ) 19.7 Hz, 3J PC ) 10.1 Hz), 128.2 (d, o-CH,
Hz), 43.1 (s, CH2), 123.9 (s, CH, C6H4), 125.0 (s, CH, C6H4),
125.1 (s, CH, C6H4), 126.1 (s, CH, C6H4), 127.9 (d, o-CH, PPh3,
2J PC ) 11.1 Hz), 130.2 (d, p-C, PPh3, J PC ) 2.5 Hz), 131.4 (d,
i-CH, PPh3, J PC ) 50.4 Hz), 134.8 (d, m-CH, PPh3, 3J PC ) 11.6
2
1
PPh3, J PC ) 10.6 Hz), 130.2 (d, i-C, PPh3, J PC ) 50.3 Hz),
3
2
130.8 (s, p-CH, PPh3), 135.2 (d, m-CH, PPh3, J PC ) 11.6 Hz),
Hz), 136.2 (d, C, C6H4, J PC ) 10.5 Hz), 138.9 (s, C, C6H4).
31P{1H}, 34.1 (s). Anal. Calcd for C26H25BrNPPd: C, 54.90;
H, 4.43; N, 2.46. Found: C, 54.57; H, 4.45; N, 2.43.
148.5 (s, C, C6H3), 151.5 (d, C, C6H3, J PC ) 2.5), 159.4 (d, C,
C6H3, J FC ) 242.4 Hz); 31P{1H}, 40.9 (s); 19F, -117.0 (m).
1
Anal. Calcd for C25H22ClFNPPd: C, 56.84; H, 4.20; N, 2.65.
Found: C, 57.05; H, 4.51; N, 2.55.
Cr ysta l Str u ctu r es. A crystal of 2c was mounted in inert
oil on a glass fiber and transferred to the diffractometer
(Siemens P4 with LT2 low-temperature attachment) as sum-
marized in Table 1. Unit cell parameters were determined
from a least-squares fit of 53 accurately centered reflections
(8.0 < 2θ < 22.9). The structure was solved by direct methods
and refined anisotropically on F2 (program SHELXL 93).10
Hydrogen atoms were included using a riding model or as rigid
methyl groups. The final R(F) was 0.0529, for 390 parameters
and 390 restraints. The weighting scheme was w-1 ) σ2(F2)
[P d{C6H3(CH2NH2)-2,OMe-5}Br (P P h 3)] (4e). Yield: 66%.
Mp: 225 °C dec. NMR (δ): 1H, 2.93 (s, 3 H, OMe), 3.87 (m, 2
H, NH2), 4.26 (m, 2 H, CH2), 5.96 (dd, 1 H, H3, J HH ) 6.3, J PH
) 2.1 Hz), 6.42 (dd, 1 H, H4, J HH ) 8.1, J PH ) 2.1 Hz), 6.91 (d,
1 H, H6, J PH ) 8.1 Hz), 7.32-7.45 (m, 9 H), 7.70-7.76 (m, 6
3
H, Ph); 13C{1H}, 53.6 (d, CH2, J PC ) 2.0 Hz), 58.9 (s, OMe),
111.6 (s, CH, C6H3), 121.9 (s, CH, C6H3), 122.2 (d, CH, C6H3,
2
3J PC ) 11.6 Hz), 128.2 (d, o-CH, PPh3, J PC ) 11.1 Hz), 130.8
2
+ (aP)2 + bP, where 3P ) (2Fc + Fo2) and a and b are
(d, p-C, PPh3, 4J PC ) 2.6 Hz), 131.3 (d, i-CH, PPh3, 1J PC ) 49.8
Hz), 135.3 (d, m-CH, PPh3, 3J PC ) 12.1 Hz), 144.7 (s, C, C6H3),
152.7 (s, C, C6H3), 155.9 (d, C, C6H3, J PC ) 6.0 Hz); 31P{1H},
43.2 (s). Anal. Calcd for C26H25BrNOPPd: C, 53.40; H, 4.31;
N, 2.40. Found: C, 53.07; H, 4.30; N, 2.41.
constants adjusted by the program. Maximum ∆/σ ) 0.002;
maximum ∆F ) 1.32 e/Å3.
A crystal of 4g was mounted on a glass fiber and transferred
to the diffractometer (Siemens P4) as summarized in Table 1.
Unit cell parameters were determined from a least-squares
fit of 42 accurately centered reflections (6.1 < 2θ < 24.7). The
structure was solved by direct methods and refined anisotro-
[P d {C6H2(CH2NH2)-2,(OMe)2-4,6}Br (P P h 3)] (4f). Yield:
61%. Mp: 149 °C dec. NMR (δ): 1H, 2.38 (s, 3 H, OMe), 3.70
(s, 5 H, NH2 and OMe), 4.38 (m, 2 H, CH2), 5.60 (d, 1 H, H3,
J PH ) 1.8 Hz), 6.33 (d, 1 H, H4, J PH ) 2.4 Hz), 7.26-7.36 (m,
(10) Sheldrick, G. M. SHELXL 93, University of Go¨ttingen, 1993.

830 Organometallics, Vol. 16, No. 5, 1997
Vicente et al.
Sch em e 1
pically on F2 (program SHELXTL).11 Hydrogen atoms were
included using a riding model. The final R(F) was 0.0306, for
271 parameters and 230 restraints. The weighting scheme
Pd ) 2) to precipitate complexes [Pd(OAc)2L2] [L )
4-XC6H4CH2NH2, X ) H (1a ), Cl (1b), NO2 (1c), F (1d ),
OMe (1e); L ) or 3,5-X2C6H3CH2NH2, X ) OMe (1f); L
) PhCH2CH2NH2 (1g)]. Dichloromethane was instead
selected as solvent to prepare the corresponding com-
plexes [Pd(OAc)(µ-OAc)L]2 (2a -g) by reacting the free
amine with [Pd(OAc)2]3 (amine:Pd ) 1). However, the
synthesis of complexes 2a -g was better achieved by
reacting 1a -g with [Pd(OAc)2]3 in molar ratio 1:Pd ) 1
in dichloromethane. To prove that complexes
[Pd(OAc)2L2] are intermediates in the synthesis of
[Pd(OAc)(µ-OAc)L]2 from [Pd(OAc)2]3 and the amines
not only in acetone but also in acetonitrile and in
chlorinated solvents, the reaction between [Pd(OAc)2]3
2
was w-1 ) σ2(F2) + (aP)2 + bP, where 3P ) (2Fc + Fo2) and a
and b are constants adjusted by the program. Maximum ∆/σ
) 0.001; maximum ∆F ) 0.28 e/Å3.
The programs use the neutral atom scattering factors ∆f ′
and ∆f ′′ and absorption coefficients from ref 12.
Resu lts a n d Discu ssion
Syn th esis of In ter m ed ia tes. When C6H5CH2NH2
or 4-ClC6H4CH2NH2 was reacted with [Pd(OAc)2]3 in
molar ratio amine:Pd ) 1 in acetone, an orange solution
was obtained, in which a yellow solid gradually formed.
This suspension led to another orange solution if stirred
for several hours. When isolated, the intermediate
yellow solid proved to be [Pd(OAc)2L2] [L ) C6H5CH2-
NH2 (1a ), 4-ClC6H4CH2NH2 (1b)] in both cases. From
the final orange solution the dimeric complex [Pd(OAc)-
(µ-OAc)L]2 [L ) C6H5CH2NH2 (2a ), 4-ClC6H4CH2NH2
(2b)] was obtained (see Scheme 1). The same process
occurred more quickly in chloroform or dichloromethane.
Thus, the reaction between C6H5CH2NH2 and [Pd(OAc)2]3
to give [Pd(OAc)(µ-OAc)L]2 lasted 8 h in acetone, but it
was complete after 1.5 h in dichloromethane, probably
because the intermediate [Pd(OAc)2L2] is soluble in this
solvent. These observations allowed the design of the
best way to prepare other [Pd(OAc)2L2] and [Pd(OAc)-
(µ-OAc)L]2 complexes. Thus, by using acetone as sol-
vent, [Pd(OAc)2]3 reacted with different amines (amine:
1
and benzylamine (amine:Pd ) 1) was monitored by H
NMR at room temperature. Initially, signals corre-
sponding to the amine, complex 1a , and unreacted
[Pd(OAc)2]3 are present. After 5 min, 2a started to form
as shown by the presence of two multiplets correspond-
ing to the CH2 protons of this compound. With time,
signals corresponding to complex 1a decreased in in-
tensity while the signal corresponding to complex 2a
became stronger. After 1.5 h, the reaction was complete
and only complex 2a was present in solution of CDCl3.
In acetonitrile, where most of the orthometalation
reactions were carried out, the only difference is that
the reaction is not completed after 2 h.
Or th om eta la tion Rea ction s. By the refluxing of
acetonitrile solutions of complexes 2a -g, acetic acid is
formed. The acetato complex 3a can be isolated from
this reaction, but in the other cases, the products are
difficult to isolate as solids or to purify (see Scheme 1).
In these cases, treatment of the resulting product with
(11) SHELXTL, Version 5, Siemens Analytical X-Ray Instruments,
Madison, WI, 1994.
(12) International Tables for Crystallography; Volume C (1992),
Wilson, A. J . C., Ed.; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 1992; Vol. C, Tables 6.1.1.4 (pp 500-502), 4.2.6.8 (pp
219-222), and 4.2.4.2 (pp 193-199).
NaBr led to the orthometalated complexes [Pd{C6H3-

Orthometalation of Primary Amines
Organometallics, Vol. 16, No. 5, 1997 831
(CH2NH2)-2,X-5}(µ-Br)]2 [X ) Cl (3b), NO2 (3c), F (3d ),
OMe (3e)], [Pd{C6H2(CH2NH2)-2,(OMe)2-4,6}(µ-Br)]2 (3f),
or [Pd{C6H4(CH2CH2NH2)-2}(µ-Br)]2 (3g) (method a; see
Scheme 1). Alternatively, one-pot synthesis of 3b-g
was achieved by refluxing a mixture of [Pd(OAc)2]3 and
the amine (amine:palladium ) 1) in acetonitrile for 4 h
and then by addition of NaBr (method b; see Scheme
1). All these orthometalation reactions occur with some
decomposition to metallic palladium. The best yields
were obtained when the mixture was heated in aceto-
nitrile slightly below its boiling point (78 °C). The
orthometalation did not occur when a 2:1 amine:palla-
dium molar ratio was used, but [Pd(OAc)2(L)2] was
formed instead.
A third method of orthometalation is applicable to the
hydrochlorides of 4-XC6H4CH2NH2 (X ) F, NO2) (method
c, see Scheme 1). Refluxing for 4 h acetonitrile solutions
of [Pd(OAc)2]3 with these hydrochlorides (amine:Pd )
1) and then addition of NaBr led to 3c,d . This one-pot
synthesis is the best way to prepare these complexes.
F igu r e 1. ORTEP plot of 2c with the labeling scheme.
amines to give “Pd(OAc)2L” complexes. Therefore, also
in this case, the immediate precursors of the orthometa-
lated complexes are species related to our complexes 2.
We and other authors have also postulated the necessity
of formation of complexes “PdX2(L)” as precursors for
orthometalation.1,14 In our case, whether these mono-
meric T-shaped species lead to dimeric complexes like
2 and these are the immediate precursors for ortho-
metalation or vice versa, it is difficult to ascertain.
Although 1H and 13C NMR spectra of solutions in
acetonitrile of 2a ,b,e are almost identical to those in
CDCl3, rapid equilibriums of these complexes with
acetonitrile complexes could exist. In this case, these
acetonitrile complexes could also be intermediates in the
orthometalation reactions.
The chloro-bridging intermediates [Pd{C6H3(CH2NH2)-
2,X-5}(µ-Cl)]2 [X ) NO2 (3c′), F (3d ′)] in these reactions
have been isolated. They can also be used to prepare
3c,d . Orthometalation also occurs in the solid state for
complexes 2e,f, as shown by the smell of acetic acid. On
heating complex 2f at 80 °C in an oven, acetic acid
formed and a black residue was obtained. When this
residue was taken up in acetone and treated with an
excess of NaBr, complex 3f was isolated (65% yield).
This observation points to the possibility that the C-H
breaking takes place by an intramolecular interaction
with the acetato ligand (see below).
The crystal structure of complex 2c (see Figure 1)
reveals a distance of 2.429 Å between the oxygen atom
O(6) of the monocoordinated acetate ligand bonded to
Pd(1) and the ortho hydrogen atom H(22) of the amine
coordinated to Pd(2), which is shorter than the sum of
van der Waals radii of O and H (2.7 Å). A similar
distance is observed between O(8) and H(12), 2.540 Å.
These data suggest that the orthometalation reactions
leading to 3e,f by heating the dimers 2e,f in the solid
state could occur through an intramolecular process
involving the above mentioned pairs of oxygen and
hydrogen atoms. A similar proposal has been made by
Ryabov for the orthometalation of N,N-dimethyl-
benzylamine in solution.13 However, as mentioned
Other solvents have also been tested as reaction
media. Methods a and b have been tried with 4-XC6H4-
CH2NH2 (X ) H, OMe, Cl) and with PhCH2CH2NH2
using acetone or chloroform as solvent. Only in the case
of benzylamine and acetone does the reaction works,
even at room temperature. Method c also works in
acetone, and this is the best way to prepare complexes
3c′,d ′.
Triphenylphosphine splits the halide bridge in com-
plexes 3a -g,c′,d ′ to give monomeric complexes 4a -
g,c′,d ′, respectively.
Rea ction P a th w a y. According to the above experi-
mental data we can assume that reactions between
[Pd(OAc)2]3 and amines give first the monomeric com-
plexes 1, which react with [Pd(OAc)2]3 to give the
dimeric 2 (see Scheme 1). When an amine hydrochlo-
ride is used, its reaction with [Pd(OAc)2]3 could give
acetic acid and mixed [Pd(Cl)(AcO)L]2 complexes that,
according to our data, give 3c′,d ′ and acetic acid.
The only kinetic investigation on cyclopalladation of
benzylamines, carried out by Ryabov, used excess amine
(N,N-dimethylbenzylamine).13 This circumstance pre-
vents us from using his results because the precursor
for Ryabov’s orthometalation is [Pd(OAc)2(amine)2], the
amine is tertiary, and the reaction conditions are
different. However, it is interesting to point out that,
from the precursor [Pd(OAc)2(amine)2], orthometalation
requires13 dissociation of one of the two coordinated
above, he assumes
a mononuclear intermediate
“Pd(OAc)2L” and, therefore, the interaction must occurs
among ligands coordinated to the same palladium atom.
The reason given for the lack of orthometalation of
primary amines is that the dissociative process
[Pd(OAc)2(amine)2] f “Pd(OAc)2L” + L is impossible for
primary ones because they are bound more strongly to
the metal.13 Therefore, the problem can simply be
overcome by starting from complexes [Pd(OAc)(µ-
OAc)L]2 or by reacting [Pd(OAc)2]3 with the amine using
a molar ratio Pd:amine ) 1, as we did. The same ratio
was used in all previous reactions that succeeded in
(14) Deeming, A. J .; Rothwell, I. P. Pure Appl. Chem. 1980, 53, 649.
Deeming, A. J .; Rothwell, I. P. J . Organomet. Chem. 1981, 205, 117.
Nielson, A. J . J . Chem. Soc., Dalton Trans. 1981, 205. Beller, M.;
Riermeier, T. H.; Haber, S.; Kleiner, H.-J .; Herrmann, W. A. Chem.
Ber. 1996, 129, 1259. Albert, J .; Granell, J .; Luque, A.; M´ınguez, J .;
Moragas, R.; Font-Bard´ıa, M.; Sola´ns, X. J . Organomet. Chem. 1996,
522, 87.
(13) (a) Ryabov, A. D. Chem. Rev. 1990, 90, 403 and references
therein. (b) Ryabov, A. D.; Sakodinskaya, I. N.; Yatsimirski, A. K. J .
Chem. Soc., Dalton Trans. 1985, 2629.

832 Organometallics, Vol. 16, No. 5, 1997
Vicente et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 2c
Lengths
Pd(1)-O(5)
Pd(1)-N(1)
Pd(2)-O(7)
Pd(2)-N(2)
O(1)-C(1)
O(3)-C(3)
O(7)-C(7)
N(1)-C(10)
1.953(10)
2.021(6)
1.985(6)
2.008(7)
1.251(8)
1.255(10)
1.273(12)
1.509(9)
Pd(1)-O(4)
Pd(1)-O(2)
Pd(2)-O(3)
Pd(2)-O(1)
O(2)-C(1)
O(4)-C(3)
C(5)-O(5)
N(2)-C(20)
2.017(6)
2.039(5)
1.999(6)
2.030(5)
1.266(8)
1.240(10)
1.271(15)
1.464(10)
Angles
O(5)-Pd(1)-O(4)
O(4)-Pd(1)-N(1)
O(4)-Pd(1)-O(2)
O(7)-Pd(2)-O(3)
O(3)-Pd(2)-N(2)
O(3)-Pd(2)-O(1)
C(1)- O(1)-Pd(2)
C(3)-O(3)-Pd(2)
O(1)-C(1)-O(2)
163.5(3)
91.6(2)
92.2(2)
86.0(3)
176.0(3)
90.9(3)
127.0(5)
124.0(6)
125.3(8)
O(5)-Pd(1)-N(1)
O(5)-Pd(1)-O(2)
N(1)-Pd(1)-O(2)
O(7)-Pd(2)-N(2)
O(7)-Pd(2)-O(1)
N(2)-Pd(2)-O(1)
C(1)-O(2)-Pd(1)
C(3)-O(4)-Pd(1)
O(4)-C(3)-O(3)
88.9(4)
86.7(3)
175.4(2)
90.0(3)
170.3(3)
92.9(3)
124.8(5)
125.6(6)
127.2(9)
F igu r e 2. ORTEP plot of 4g with the labeling scheme.
orthometalating benzylamine.5-7 However, the attempt
to orthometalate 2-(phenyl)ethylamine using [Pd(acac)2]
(1:1) was unsuccessful.5 Our achievement is to have
realized that formation of [Pd(OAc)(µ-OAc)L]2 is the key
to orthometalation of primary benzylamines and also
for the synthesis of six-membered ring orthometalated
primary amines as well as the use of acetonitrile as
solvent.
Str u ctu r e of Com p lexes. Complexes 1b-f are
insoluble in common organic solvents, but complexes
1a ,e,g dissolved easily in CDCl3. Their 1H NMR and
13C NMR clearly indicated that only the cis- or trans-
isomer was obtained, because only one set of signals was
observed. We assumed a trans- geometry because it
must be the thermodynamically most stable form, as
proved for bis(amine)dihalogenopalladium(II) com-
plexes.15
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 4g
Lengths
Pd-C(1)
Pd-P
2.004(4)
2.2658(10)
1.464(5)
1.399(5)
1.498(5)
1.360(6)
1.518(5)
Pd-N
2.132(3)
2.5682(5)
1.375(5)
1.398(6)
1.361(6)
1.384(5)
Pd-Br
N-C(8)
C(1)-C(6)
C(2)-C(3)
C(3)-C(4)
C(5)-C(6)
C(1)-C(2)
C(2)-C(7)
C(4)-C(5)
C(7)-C(8)
Angles
C(1)-Pd-N
N-Pd-P
87.97(14)
164.61(10)
85.95(9)
119.5(2)
110.6(4)
C(1)-Pd-P
91.70(11)
166.47(11)
97.36(3)
120.1(4)
112.4(3)
C(1)-Pd-Br
P-Pd-Br
N-Pd-Br
C(8)-N-Pd
C(2)-C(7)-C(8)
C(1)-C(2)-C(7)
N-C(8)-C(7)
tendency of PPh3 and aryl ligands not to be trans each
other when coordinated to class b metal atoms,1b,18
according to the antisymbiotic effect.18a Compared to
1H NMR and 13C{1H} NMR for complexes 2a -g
showed only two signals for the acetate methyl groups:
one for the bridging acetate methyl groups and another
for the terminal acetate methyl groups. Thus, both
ligands must have the same chemical enviroment and
must adopt a trans disposition. This is proved by the
crystal structure of complex 2c, which has been deter-
mined by X-ray diffraction (Figure 1). Crystallographic
data are listed in Table 1, and significant bond distances
and bond angles are in Table 2. The structure of
complex 2a contains discrete dimeric molecules. Each
palladium atom is bonded to four atoms in a square-
planar coordination. The nitrogen of the amine and the
oxygen atom from a terminal acetate group are mutually
cis. The other two cis positions are occupied by two
oxygen atoms from bridging acetates. The molecule
only has a (noncrystallographic) C2 axis, and so it is
chiral. As far as we are aware, this is the first
intermediate of this type isolated and characterized by
X-ray diffraction.
the structure of (R)-[Pd{C6H3(CH2(Me)NH2)-2}Br(PPh3)]1a
(A), there are significant differences. Thus, whereas the
Pd-C bond distances are similar [2.004(4) Å (4g) and
2.019(3) Å (A)], the Pd-N [2.132(3) Å], Pd-P [2.2658(10)
Å], and Pd-Br [2.5682(5) Å] bond lengths in 4g are
longer than those in A [2.092(3), 2.244(1), 2.519(1) Å,
respectively]. In addition, the palladium atom in 4g has
a very distorted square-planar coordination geometry:
the angle between the planes Br-Pd-P and N-Pd-
C(1) is 18.6°. Recent examples of this distortion have
been described.19 The Pd-N and Pd-C bonds form the
basis of a six-membered chelate ring with an open-book
shape. The angle between the Pd-C(1)-C(2)-C(7) and
C(7)-C(8)-N-Pd planes is 58.5°.
(18) (a) Pearson, R. G. Inorg. Chem. 1973, 12, 712. (b) Dehand, J .;
J ordanov, J .; Pfeffer, M.; Zinsius, M. C. R. Acad. Sci., Ser. C 1975,
281, 651. (c) Pfeffer, M.; Grandjean, D.; Le Borgne, G. Inorg. Chem.
1981, 20, 4426. (d) Arlen, C.; Pfeffer, M.; Bars, O.; Le Borgne, G. J .
Chem. Soc., Dalton Trans. 1986, 359. (e) Vicente, J .; Bermudez, M.
D.; Carrion, F. J .; J ones, P. G. J . Organomet. Chem. 1996, 508, 53. (f)
Vicente, J .; Abad, J . A.; Fernandez-de-Bobadilla, R.; J ones, P. G.;
Ramirez de Arellano, M. C. Organometallics 1996, 15, 24. (g) Vicente,
J .; Bermudez, M. D.; Carrion, F. J . Inorg. Chim. Acta 1994, 220, 1. (h)
Vicente, J .; Bermudez, M. D.; Carrillo M. P.; J ones, P. G. J . Chem.
Soc., Dalton Trans. 1992, 1975. (i) Vicente, J .; Arcas, A; Bautista, D.;
Tiripicchio, A.; Tiripicchio-Camellini, M. New J . Chem. 1996, 20, 345.
(19) (a) Garc´ıa-Ruano, J . L.; Lo´pez-Solera, I.; Masaguer, J . R.;
Navarro-Ranninger, C.; Mart´ınez-Carrera, S. Organometallics, 1992,
11, 3013. (b) Minghetti, G.; Cinellu, M. A.; Ghelucci, G.; Gladiali, S.;
Demartin, F.; Manassero, M. J . Organomet. Chem. 1986, 307, 107. (c)
Constable, E. C. Polyhedron 1984, 3, 1037. (d) Newkome, G. R; Puckett,
W. E.; Grupta, V. K.; Kieffer, G. E. Chem. Rev 1986, 86, 451.
It has been shown by IR16 and X-ray diffraction
studies17 that complexes such as 3 have a dimeric trans
geometry. We have determined the crystal structure
of complex 4g by X-ray diffraction (see Figure 2 and
Tables 1 and 3), demonstrating the well-established
(15) Coe, J . S.; Lyons, R. J . Inorg. Chem. 1970, 9, 1775.
(16) Dehand, J .; Pfeffer, M.; Shamir, J . Spectrochim. Acta 1977, 33A,
1101.
(17) Elder, R. C.; Cruea, R. D. P.; Morrison, R. F. Inorg. Chem. 1976,
15, 1623.

Orthometalation of Primary Amines
Organometallics, Vol. 16, No. 5, 1997 833
Con clu sion s. We have shown, for the first time and
contrary to previous hypotheses, that non-R-substituted
primary benzylamines can be orthometalated even if the
substituents are electron-withdrawing groups and that
2-(phenyl)ethylamine can be orthometalated in spite of
the six-membered ring that is formed. Some probable
intermediates of these orthometalation reactions have
been isolated. If they are not, we have proved that can
be used as starting materials for the orthopalladation.
The crystal structure of one of these intermediates
suggests the possibility that C-H activation is an
intramolecular process.
support. M.G.P thanks the Human Capital and Mobil-
ity research Program of the Commission of the Euro-
pean Communities for a research training fellowship
(Contract No. ERBCHBGCT920143) and the Ministerio
de Educacio´n y Ciencia (Spain) for a grant. M.C.R.A.
is grateful for a stipendium from the Alexander-von-
Humbolt Stiftung and a Contract from the Ministerio
de Educacio´n y Ciencia.
Su p p or tin g In for m a tion Ava ila ble: Listings of X-ray
parameters, all refined and calculated atomic coordinates, all
isotropic and anisotropic thermal parameters, and complete
bond lengths and angles for compounds 2c‚Me2CO and 4g (11
pages). Ordering information is given on any current mast-
head page.
Ack n ow led gm en t. We thank the Direccio´n General
de Investigacio´n Cient´ıfica y Te´cnica (Grant PB92-0982-
C) and the Fonds der Chemischen Industrie for financial
OM9609574