Reactivity of [Pd{CH2C(O)Me}Cl]Mn toward isocyanides

Article abstract of DOI:10.1021/om048999c

The capacity of [Pd{CH₂C(O)Me}Cl]_n to prepare chloro-monoacetonyl or monoacetonyl palladium (II) complexes was analyzed. The established synthetic procedures for these complexes invariably involve the presence of other strongly coordinated ligands. The thermal transformation of these compounds into C-palladated β-ketoenamine complexes resulting from insertion of one molecule of the isocyanide followed by a β-ketoimine to β-ketoenamine tautomerization processes. The resulting complexes were the first palladium compounds containing such ligands acting as a chelate.

Full text of DOI:10.1021/om048999c

2516
Organometallics 2005, 24, 2516-2527
Reactivity of [Pd{CH2C(O)Me}Cl]n toward Isocyanides
Jose´ Vicente,* Aurelia Arcas, and Jesu´s M. Ferna´ndez-Herna´ndez
Grupo de Quı´mica Organometa´lica, Departamento de Qu´ımica Inorga´nica, Facultad de
Quı´mica, Universidad de Murcia, Apartado 4021, Murcia, 30071 Spain
Delia Bautista‡
S.A.C.E. Universidad de Murcia, Apartado 4021, Murcia, 30071 Spain
Peter G. Jones§
Institut fu¨r Anorganische und Analytische Chemie der Technischen Universita¨t,
Postfach 3329, 38023 Braunschweig, Germany
Received December 16, 2004
[Pd{CH2C(O)Me}Cl]n (1) reacts at low temperature with RNC (RNC:Pd ) 1 or 2) to give
[Pd2{CH2C(O)Me}2(µ-Cl)2(CNR)2] [R ) tBu (2a), Xy (2b)] or trans-[Pd{CH2C(O)Me}Cl(CNR)2]
t
[R ) Bu (5a), Xy (5b)], respectively. These complexes decompose at room or higher
t
temperature to give [Pd2{κ2-C,O-C(NHR)CHC(O)Me}2(µ-Cl)2] [R ) Bu (3a), Xy (3b)] or
[Pd{κ2-C,O-C(NHR)CHC(O)Me}Cl(CNR)] [R ) tBu (6a), Xy (6b)], respectively, via insertion
of the isocyanide into the Pd-C bond plus a tautomerization process from â-ketoimine to
â-ketoenamine. The complex [Pd{κ2-C,O-C(NHXy)CHC(O)Me}Cl(NCMe)] (4b) can be ob-
tained by reacting 1 with XyNC (Pd:XyNC ) 1) in MeCN or complex 3b in CHCl3 with
excess MeCN. Complexes trans-[Pd{C(NHR)dCHC(O)Me}Cl(CNR)2] [R ) tBu (8a), Xy (8b)]
can be obtained (i) by reacting 1 with RNC (RNC:Pd ) 3) or better (ii) by reacting 6 with 1
t
equiv of RNC at low temperature. The Pd(I) complexes [Pd2Cl2(CNR)4] [R ) Bu (7a), Xy
(7b)] are decomposition products obtained by heating 1 with RNC (RNC:Pd ) 4-5), but
they are detected in trace amounts in the reaction of 1 with RNC (RNC:Pd ) 2-3). Addition
of RNC and KTfO to a cooled suspension of 1 (Pd:RNC:KTfO ) 1:3:1) gives complexes
[Pd{CH2C(O)Me}(CNR)3]TfO [R ) tBu (9a), Xy (9b)], which decompose at room temperature.
The decomposition of 9b gives [Pd{κ2-C,O-C(NHXy)CHC(O)Me}(CNXy)2]TfO (10b), which
can be obtained, as can the corresponding 10a, by reacting complexes 6 with 1 equiv of
TlTfO and RNC. The reactions of the dimers 3 with PPh3 (Pd:PPh3 ) 1) gives [Pd{κ2-C,O-
t
C(NHR)CHC(O)Me}Cl(PPh3)] [R ) Bu (11a), Xy (11b)], with PEt3 (PEt3:Pd ) 2), trans-
t
[Pd{C(NHR)dCHC(O)Me}Cl(PEt3)2] [R ) Bu (12a), Xy (12b)], and with Tl(acac) (Pd:acac
t
) 1), [Pd{κ2-C,O-C(NHR)CHC(O)Me}(κ-O,O-acac)] [R ) Bu (13a), Xy (13b)]. The crystal
structures of 6a, 9b, 10a, and 10b have been determined. In complex 10b there are
intermolecular π-π stacking and C-H‚‚‚Pd agostic interactions giving dimers.
Introduction
complexes containing a new O,C-chelating enolato
ligand.
Palladium(II) enolates play an important role in
organic synthesis.1 However, most of the isolated species
are actually ketonyl complexes ([Pd]CRR′C(O)R′′)2-9
(sometimes wrongly called C-enolates). The few genuine
palladium(II) enolates ([Pd]OCRdCR′R′′) adopt this
coordination mode because of (i) the strong transpho-
bia10,11 between C-donor/C-donor and C-donor/P-donor
ligands,8,12 (ii) steric effects,8,13 or (iii) the preferred
coordination of the ligand as a chelate (e.g., O,O-
acetylacetonato complexes, O,P-carbonyl-functionalized
phosphines,14 O,N-oxopropionaldehyde phenylhydra-
zones15). In this paper, we report a family of palladium
Among the known ketonyl complexes, only a few are
acetonyls. The established synthetic procedures for
(1) See for example: Masamune, S.; Choy, W.; Petersen, J. S.; Sita,
L. R. Angew. Chem., Int. Ed. Engl. 1985, 24, 1. Mitsudo, T.; Kadokura,
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K.; Shibasaki, M. J. Org. Chem. 1995, 60, 2648. Fujii, A.; Hagiwara,
E.; Sodeoka, M. J. Am. Chem. Soc. 1999, 121, 5450. Sodeoka, M.;
Tokunoh, R.; Miyazaki, F.; Hagiwara, E.; Shibasaki, M. Synlett 1997,
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Am. Chem. Soc. 1989, 111, 4126. Palucki, M.; Buchwald, S. L. J. Am.
Chem. Soc. 1997, 119, 11108. Sole, D.; Peidro, E.; Bonjoch, J. Org. Lett.
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Am. Chem. Soc. 2000, 122, 1360. Kawatsura, M.; Hartwig, J. F. J.
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* Corresponding author regarding the synthesis of complexes.
E-mail: jvs1@um.es.
‡ Corresponding author regarding the X-ray diffraction study of
complexes 9b, 10a, and 10b. E-mail: dbc@um.es.
§ Corresponding author regarding the X-ray diffraction study of
complex 6a. E-mail: p.jones@tu-bs.de.
10.1021/om048999c CCC: $30.25 © 2005 American Chemical Society
Publication on Web 04/14/2005

Reactivity of [Pd{CH2C(O)Me}Cl]n to Isocyanides
Organometallics, Vol. 24, No. 10, 2005 2517
Scheme 1
these complexes invariably involve the presence of
other strongly coordinated ligands, such as PPh3,2,5
N,N,N′,N′-tetramethylethylenediamine,6 C6F5, AsPh3,7
or o-C6H4CH2NMe2.7 However, we have previously
reported the synthesis of the simple acetonylpalladium-
(II) complex [Pd{CH2C(O)Me}Cl]n (1), obtained by trans-
metalation reactions employing [Hg{CH2C(O)Me}2] and
[PdCl2(MeCN)2] or (NMe4)[Pd2Cl6].9 Complex 1 has the
potential, after cleaving the acetonyl and/or chloro
bridges,16 or by subsequent chloro replacement, to pre-
pare any chloro-monoacetonyl or monoacetonyl palla-
dium(II) complex, whereby the other two or three
ligands can be chosen freely. In this paper we illustrate
both possibilities by reacting 1 with isocyanides, which
leads to complexes of the types [Pd{CH2C(O)Me}Cl-
(CNR)n] (n ) 1, 2) and [Pd{CH2C(O)Me}(CNR)3]+. In
addition, these are slowly converted to the first com-
plexes containing the chelating κ2-C,O-C(NHR)dCHC-
(O)Me (R ) tBu, Xy) ligand, resulting from insertion of
the isocyanide into the Pd-CH2C(O)Me bond and a
subsequent â-ketoimine to â-ketoenamine tautomeriza-
tion process. This chelating mode of coordination has
not been observed previously in the chemistry of pal-
ladium because, as mentioned above, the known precur-
sors do not have the required cis coordination position
available to allow a chelating coordination, or they do
not insert the isocyanide. Thus, trans-[Pd{CH2C(O)R}-
Cl(PPh3)2] reacts with isocyanides to give trans-[Pd-
{C(NHR)dCHC(O)R′}Cl(PPh3)2] (R ) Me, p-C6H4OMe,
nism,4 the first step was coordination of the isocyanide
followed by an insertion/tautomerization process, but
the intermediate adduct was not isolated. In contrast,
the reaction of some aryl acetonyl palladium(II) com-
plexes with tBuNC has been reported to give the
corresponding adducts, but no insertion products were
obtained.7 Therefore, we report here for the first time
the isolation of both types, adducts and insertion/
tautomerization products of isocyanides into the
Pd-CH2C(O)R bond. A search of the Cambridge Struc-
tural Database of metallacycles M{κ2-C,O-C(NH-
(C)CHC(O)Me)} (M ) any metal) reveals only one
crystal structure, corresponding to a cobalt complex (R
CH(Ph)Me, R′ ) Ph; Scheme 1) obtained through a
carbene attack on a coordinated isocyanide ligand,
followed by a reaction with HBF4.17
The â-ketoenamines, also called enaminones, are
important organic intermediates18 having interesting
biological activity.19 Although O-20 and N,O-â-keto-
enamine21 complexes are well-known, the only organo-
metallic derivatives fully characterized (R2N-C(M)d
C(R)-C(dO)R or R2N-C(R)dC(M)-C(dO)R, R ) H,
any organic group; M ) any metal) are the above-
mentioned complex [Pd{C(NHR)dCHC(O)R′}Cl(PPh3)2]
t
R′ ) Me;2 R ) Bu, R′ ) Ph4). In the proposed mecha-
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Scheme 1.17
Experimental Section
Unless otherwise stated, the reactions were carried out
without precautions to exclude light or atmospheric oxygen
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2518 Organometallics, Vol. 24, No. 10, 2005
Vicente et al.
carried out with a Carlo Erba 1106 microanalyzer. Molar
conductivities were measured on a ca. 5 × 10-4 M acetone
solution with a Crison Micro CM2200 conductimeter. IR
spectra were recorded on a Perkin-Elmer 16F PC FT-IR
spectrometer with Nujol mulls between polyethylene sheets
or KBr pellets. NMR spectra were recorded in a Bruker AC
200, Avance 300 or 400 or a Varian Unity 300 spectrometer
at room temperature unless otherwise stated. Chemical shifts
were referred to TMS, CFCl3 (19F) or H3PO4 (31P{1H}). The
NMR probe temperature was calibrated using ethylene glycol
1H NMR standard methods. When needed, NMR assignments
were performed with the help of DEPT, COSY, and NOESY
1D or 2D experiments and HETCOR techniques. The synthesis
of [Pd{CH2C(O)Me}Cl]n (1) was reported previously.9
through Celite. The filtrate was concentrated, n-hexane (20
mL) was added, and the suspension was filtered. The solid was
washed with n-pentane (5 mL) and air-dried to give 3b.
Yield: 90 mg, 70%. Mp: 144 °C. IR (Nujol, cm-1): ν(NH) 3300,
3280; ν(CO) 1506; ν(Pd) 282, 246. 1H NMR (400 MHz, CDCl3):
δ 7.71 (br, 2 H, NH), 7.18-7.06 (m, 6 H, Xy), 4.12 (s, 2 H,
CH), 2.25 (s, 12 H, Me, Xy), 1.96 (s, 6 H, Me). 13C{1H} NMR
(100.81 MHz, CDCl3): δ 205.1 (CO), 182.6 (CPd), 135.0 (C, Xy),
134.3 (C, Xy), 128.4 (CH, Xy), 128.3 (CH, Xy), 103.7 (CH), 21.8
(Me), 18.1 (Me, Xy). Anal. Calcd for C24H28Cl2N2O2Pd2: C,
43.66; H, 4.27; N, 4.24. Found: C, 43.65; H, 4.38; N, 3.89
Synthesis
of
[Pd{K2-C,O-C(NHXy)CHC(O)Me}Cl-
(NCMe)] (4b). Method a. To a solution of 3b (50.7 mg,
0.076 mmol) in CHCl3 (2 mL) was added MeCN (0.1 mL). After
15 min the suspension was filtered through Celite and the
filtrate was concentrated until a solid started to precipitate.
Addition of n-pentane (15 mL) gave a suspension that was
filtered off and air-dried to give 4b as a yellow solid. Yield:
38 mg, 67%.
Synthesis of [Pd2{CH2C(O)Me}2(µ-Cl)2(CNtBu)2] (2a).
To a cooled solution (0 °C) of 1 (150 mg, 0.75 mmol) in MeCN
t
(4 mL) was added BuNC (85.1 µL, 0.75 mmol). The solution
was concentrated until a yellow solid precipitated. Et2O (10
mL) and n-pentane (10 mL) were added, and the suspension
was stirred for 20 min at 0 °C. The suspension was filtered
off, washed with n-pentane, and air-dried to give 2a as a yellow
solid. Yield: 154 mg, 74%. Mp: 114 °C. IR (Nujol, cm-1):
ν(CN) 2216; ν(CO) 1660; ν(PdCl) 296, 252. 1H NMR (300 MHz,
CDCl3): δ 2.83 (s, 4 H, CH2), 2.24 (s, 6 H, Me), 1.52 (s, 18 H,
tBu). Anal. Calcd for C16H28Cl2N2O2Pd2: C, 34.07; H, 5.00; N,
4.97. Found: C, 34.35; H, 5.27; N, 5.29.
Synthesis of [Pd2{CH2C(O)Me}2(µ-Cl)2(CNXy)2] (2b). To
a cooled solution (0 °C) of 1 (100 mg, 0.50 mmol) in MeCN (5
mL) was added XyNC (66 mg, 0.50 mmol). The reaction
mixture was stirred for 5 min at 0 °C, then was concentrated
(ca. 2 mL) and Et2O (15 mL) was added. The suspension was
stirred for 10 min at 0 °C, filtered off, washed with Et2O (5
mL), and air-dried, to give a yellow solid. Yield: 134 mg, 81%.
Mp: 140 °C (dec). IR (Nujol, cm-1): ν(CN) 2198; ν(CO) 1661;
ν(PdCl) 296, 254. 1H NMR (400 MHz, CDCl3): δ 7.24 (m, 2 H,
Xy), 7.11 (m, 4 H, Xy), 3.04 (s, 4 H, CH2), 2.46 (s, 12 H, Me,
Xy), 2.32 (s, 6 H, Me). Anal. Calcd for C24H28Cl2N2O2Pd2: C,
43.66; H, 4.27; N, 4.24. Found: C, 43.96; H, 4.18; N, 4.35.
Synthesis of [Pd2{K2-C,O-C(NHtBu)CHC(O)Me}2(µ-
Cl)2] (3a). Method a. A solution of 2a (170 mg, 0.30 mmol)
in CHCl3 (5 mL) was stirred at 40 °C protected from light.
After 13 h the suspension was filtered through Celite, and the
filtrate was concentrated to dryness. The resulting brown oil
was triturated with n-pentane (10 mL) and air-dried to give
3a as an orange solid. Yield: 115 mg, 68%.
Method b. To a solution of 1 (202 mg, 1.01 mmol) in MeCN
(5 mL) was added XyNC (132 mg, 1.01 mmol), and the
resulting yellow solution was concentrated to dryness. The
residue was dissolved in CHCl3 (5 mL) and then was heated
at 40 °C for 1 h. The resulting suspension was filtered through
Celite, the filtrate was concentrated (ca. 1 mL), and n-pentane
(10 mL) was added. The suspension was stirred at 0 °C and
filtered off, and the yellow solid obtained was air-dried to give
4b. Yield: 205 mg, 63%. Mp: 180 °C. IR (Nujol, cm-1): ν(NH)
3272; ν(CN) 2320, 2292. IR (KBr, cm-1) ν(NH) 3273; ν(CN)
1
2320, 2292; ν(CO) 1494. H NMR (300 MHz, CDCl3): δ 8.24
(br, 1 H, NH), 7.17-7.08 (m, 3 H, Xy), 4.15 (s, 1 H, CH), 2.24
(s, 6 H, Me, Xy), 2.12 (s, 3 H, MeCN), 1.95 (s, 3 H, Me).
13C{1H} NMR (100.81 MHz, CDCl3): δ 204.4 (CO), 183.8 (br,
CPd), 134.8 (C, Xy), 128.5 (CH, Xy), 128.1 (CH, Xy), 117.6 (br,
MeCN), 103.6 (CH), 21.7 (Me), 18.0 (Me, Xy), 2.6 (MeCN). Anal.
Calcd for C14H17ClN2OPd: C, 45.30; H, 4.62; N, 7.55. Found:
C, 45.06; H, 4.43; N, 7.53
Synthesis of trans-[Pd{CH2C(O)Me}Cl(CNtBu)2] (5a).
To a cooled (-10 °C) suspension of 1 (101 mg, 0.51 mmol) in
t
CH2Cl2 (4 mL) was added BuNC (115 µL, 1.01 mmol). The
suspension was stirred until the solid had dissolved, then
filtered through Celite. The resulting solution was concen-
trated to dryness, and addition of n-pentane (10 mL) and
vigorous stirring in an acetone/N2(l) bath gave a solid that was
filtered off, washed with n-pentane (5 mL), and air-dried to
give 5a as a colorless solid. Yield: 150 mg, 81%. Mp: 82 °C.
IR (Nujol, cm-1): ν(CN) 2208; ν(CO) 1658; ν(PdCl) 278. 1H
NMR (400 MHz, CDCl3): δ 2.61 (s, 2 H, CH2), 2.14 (s, 3 H,
Method b. To a solution of 1 (150 mg, 0.75 mmol) in MeCN
t
(3 mL) was added BuNC (85.1 µL, 0.75 mmol). The reaction
mixture was concentrated to dryness, and the yellow residue
was dissolved in CHCl3 (3 mL) and filtered through Celite.
The filtrate was stirred at 45 °C for 15 h protected from light
and then was filtered through Celite. n-Pentane (15 mL) was
added to the filtrate to give a solid, which was stirred at 0 °C
for 30 min and was isolated by filtration to give 3a. Yield: 150
mg, 70%. Mp: 156 °C (dec). IR (Nujol, cm-1): ν(NH) 3258;
ν(CO) 1536. 1H NMR (300 MHz, CDCl3): δ 6.51 (br, 2 H, NH),
4.57 (s, 2 H, CH), 2.03 (s, 6 H, Me), 1.31 (s, 18 H, tBu).
13C{1H} NMR (75.45 MHz, CDCl3): δ 203.0 (CO), 180.0 (CPd),
104.3 (CH), 55.5 (C(Me)3), 28.9 (C(Me)3), 21.6 (Me). Anal. Calcd
for C16H28Cl2N2O2Pd2: C, 34.07; H, 5.00; N, 4.97. Found: C,
34.06; H, 5.03; N, 5.36.
t
Me), 1.55 (s, 18 H, Bu). Anal. Calcd for C13H23ClN2OPd: C,
42.76; H, 6.35; N, 7.67. Found: C, 42.85; H, 6.27; N, 7.63.
Synthesis of trans-[Pd{CH2C(O)Me}Cl(CNXy)2] (5b). To
a cooled (-78 °C) suspension of 1 (91 mg, 0.46 mmol) in
CH2Cl2 (6 mL) was added XyNC (130 mg, 0.91 mmol), and the
mixture was stirred until all solids had dissolved, then filtered
through Celite to a cooled flask. The filtrate was concentrated
(ca. 3 mL) in a cooled bath (0 °C) and n-pentane (20 mL) added
to give a solid, which was stirred at -40 °C for 20 min. Then,
the solid was filtered off, washed with n-pentane (5 mL), and
air-dried to give 5b as a colorless solid. Yield: 166 mg, 78%.
Mp: 110 °C (dec). IR (Nujol, cm-1): ν(CN) 2192; ν(CO) 1660;
ν(PdCl) 296. 1H NMR (300 MHz, CDCl3, 263 K): δ 7.23-7.09
(m, 6 H, Xy), 2.98 (s, 2 H, CH2), 2.45 (s, 12 H, Me, Xy), 2.26 (s,
3 H, Me). Anal. Calcd for C21H23ClN2OPd: C, 54.68; H, 5.03;
N, 6.07. Found: C, 54.33; H, 4.94; N, 6.15.
Synthesis of [Pd2{K2-C,O-C(NHXy)CHC(O)Me}2(µ-
Cl)2] (3b). Method a. A solution of 2b (171 mg, 0.26 mmol)
in CHCl3 (5 mL) was stirred at 45 °C for 1 h and then was
filtered through Celite. The filtrate was concentrated (ca. 1
mL) and Et2O (3 mL) added to give a solid, which was filtered
off, and the filtrate was concentrated to dryness. The residue
was stirred with n-pentane (20 mL) for 1 h at -10 °C, then
filtered and air-dried to give 3b as a yellow solid. Yield: 122
mg, 71%.
Synthesis of [Pd{K2-C,O-C(NHtBu)CHC(O)Me}Cl-
(CNtBu)] (6a). Method a. A solution of 5a (85 mg, 0.23 mmol)
in CHCl3 (3 mL) was heated at 40 °C for 14.5 h, and the
resulting pale yellow solution was filtered through Celite. The
filtrate was concentrated (ca. 0.5 mL) to give a solid, which
Method b. A suspension of 2b (127 mg, 0.38 mmol) in
toluene (7 mL) was stirred at 45 °C for 1 h and then filtered

Reactivity of [Pd{CH2C(O)Me}Cl]n to Isocyanides
Organometallics, Vol. 24, No. 10, 2005 2519
was filtered off and washed with Et2O (5 mL) and then with
n-pentane (5 mL) to give 6a as a pale yellow solid. Yield: 52
mg, 61%.
7.12-7.09 (m, 8 H, Xy), 2.51 (s, 24 H, Me). Anal. Calcd for
C36H36Cl2N4Pd2: C, 53.48; H, 4.49; N, 6.93. Found: C, 53.51;
H, 4.66; N, 6.96.
Method b. To a cooled suspension (0 °C) of 1 (83.5 mg, 0.42
mmol) in CHCl3 (6 mL) was added tBuNC (95 µL, 0.84 mmol).
When complex 1 was dissolved, the solution was heated at 40
°C for 14 h, and the resulting orange solution was filtered
through Celite. The filtrate was concentrated (ca. 2 mL), Et2O
(2 mL) was slowly added, and the resulting suspension was
stirred for 15 min to give a solid that was filtered off and
washed with Et2O (5 mL) to give 6a as a pale yellow solid.
Yield: 115 mg, 75%. Mp: 145-147 °C (dec). IR (Nujol, cm-1):
ν(NH) 3418; ν(CN) 2208, ν(PdCl) 262. IR (KBr, cm-1): ν(NH)
3367; ν(CN) 2218; ν(CO) 1505. 1H NMR (400 MHz, CDCl3): δ
Synthesis of trans-[Pd{C(NHtBu)dCHC(O)Me}Cl-
(CNtBu)2] (8a). A solution of complex 6a (82.2 mg, 0.23 mmol)
t
in CH2Cl2 (2 mL) was cooled (0 °C), and BuNC (26 µL, 0.23
mmol) was added. The solution was stirred for 5 min and
concentrated to dryness. The residue was triturated with
n-pentane (20 mL) at -10 °C to give a solid, which was filtered,
washed with n-pentane (5 mL), and air-dried to give 8a as a
pale yellow solid. Yield: 70 mg, 70%. IR (Nujol, cm-1): ν(CN)
2232 (sh), 2208; ν(CO) 1556; ν(PdCl) 288. (KBr, cm-1): ν(NH)
2980; ν(CN) 2208; ν(CO) 1560. 1H NMR (400 MHz, CDCl3):
δ 12.16 (br, 1 H, NH), 5.39 (s, 1 H, CH), 1.93 (s, 3 H Me),
1.54 (s, 9 H tBu), 1.48 (s, 18 H, tBu). Anal. Calcd for
C18H32ClN3OPd: C, 48.22; H, 7.19; N, 9.37. Found: C, 48.42;
H, 7.55; N, 9.40
4
5.91 (br, 1 H, NH), 5.08 (d, 1 H, CH, JHH ) 0.9 Hz), 2.04 (s,
3 H, Me), 1.58 (br, 9 H, tBuNC), 1.40 (s, 9 H, tBuNH). 13C{1H}
NMR (75.45 MHz, CDCl3): δ 205.5 (CO), 190.0 (C(Pd)-NH),
1
127.5 (t, {1:1:1}, CN, JCN ) 20 Hz), 106.0 (CH), 59.0 (t,
Synthesis of trans-[Pd{C(NHXy)dCHC(O)Me}Cl-
(CNXy)2] (8b). A solution of complex 6b (73 mg, 0.16 mmol)
in CH2Cl2 (2 mL) was cooled (0 °C), and then, XyNC (21 mg,
0.16 mmol) was added. The mixture reaction was quickly
filtered, and the filtrate was collected in a cooled flask and
concentrated. Then n-pentane (5 mL) was added, and the
cooled mixture was stirred to give a pale yellow solid, which
was filtered, washed with n-pentane (10 mL), and air-dried.
Yield: 75 mg, 80%. IR (Nujol, cm-1): ν(CN) 2192, 2160; ν(CO)
1570; ν(PdCl) 290. (KBr, cm-1): ν(NH) 3028; ν(CN) 2188, 2160;
ν(CO) 1570. 1H NMR (400 MHz, CDCl3): δ 12.90 (br, 1 H, NH),
7.29-7.25 (m, 2 H, Xy), 7.13-7.11 (m, 4 H, Xy), 7.04-7.00 (m,
1 H, Xy), 6.94-6.93 (m, 2 H, Xy), 5.68 (s, 1 H, CH), 2.36 (s, 12
H, Me, Xy), 2.30 (s, 6 H, Me, Xy), 2.08 (s, 3 H, Me). Because of
its instability, an analytically pure sample could not be
isolated. See discussion.
1
{1:1:1}, CNC(Me)3, JCN ) 4.3 Hz), 55.9 (CNHC(Me)3), 30.0
(CNHC(Me)3), 29.0 (CNC(Me)3), 22.5 (Me). Anal. Calcd for
C13H23ClN2OPd: C, 42.76; H, 6.35; N, 7.67. Found: C, 42.73;
H, 6.62; N, 7.67. Single crystals of 6a were obtained by slow
diffusion of Et2O into an acetone solution of 6a.
Synthesis
of
[Pd{K2-C,O-C(NHXy)CHC(O)Me}Cl-
(CNXy)] (6b). Method a. A solution of 5b (54 mg, 0.12 mmol)
in CHCl3 (3 mL) was heated at 40 °C for 5 h and then filtered
through Celite. The filtrate was concentrated (0.5 mL), and
Et2O (5 mL) was slowly added to give a suspension, which was
filtered off, washed with Et2O (5 mL), and air-dried to give 6b
as a pale yellow solid. Yield: 44 mg, 81%.
Method b. To a cooled suspension (-10 °C) of 1 (85.5 mg,
0.43 mmol) in CHCl3 (6 mL) was added XyNC (112.7 mg, 0.86
mmol). When complex 1 was dissolved, the reaction mixture
was filtered through Celite, and the filtrate was heated at 40
°C for 4 h and then was filtered through Celite. The filtrate
was concentrated (ca. 2 mL), Et2O (5 mL) was slowly added,
and the resulting suspension was stirred for 15 min to give a
suspension, which was filtered off, washed with Et2O (10 mL),
and air-dried to give 6b. Yield: 158 mg, 80%. Mp: 150-156
°C (dec). IR (Nujol, cm-1): ν(NH) 3202; ν(CN) 2198; ν(PdCl)
274. IR (KBr, cm-1): ν(NH) 3274; ν(CN) 2197; ν(CO) 1497. 1H
NMR (400 MHz, CDCl3): δ 7.29-7.12 (m, 6 H, Xy), 6.90 (br,
Synthesis of [Pd{CH2C(O)Me}(CNtBu)3]TfO (9a). A
suspension of 1 (100 mg, 0.50 mmol) in acetone (5 mL) was
t
cooled (-10 °C) for 15 min. Then BuNC (175 µL, 1.54 mmol)
was added. When 1 dissolved, KTfO (95 mg, 0.51 mmol) was
added and the mixture was stirred for 10 min in a cold bath
and concentrated to dryness. The residue was extracted with
CH2Cl2 (5 mL) and filtered through Celite, and the filtrate was
evaporated to dryness. The residue was triturated with n-
pentane (10 mL), and the mixture was vigorously stirred at
-10 °C for 30 min. The solid was filtered off, washed with
n-pentane (5 mL), and air-dried to give 9a as a colorless solid.
Yield: 253 mg, 90%. Mp: 163 °C (dec). ΛM (acetone, 6.97 ×
10-4 M): 122 Ω-1 cm2 mol-1. IR (Nujol, cm-1): ν(CN) 2254,
2228; ν(CO) 1668. 1H NMR (200 MHz, CDCl3): δ 2.66 (s, 2 H,
4
1 H, NH), 4.61 (d, 1 H, CH, JHH ) 0.9 Hz), 2.49 (s, 6 H, Me,
XyNC), 2.27 (s, 6 H, Me, XyNHC), 2.03 (s, 3 H, Me). 13C{1H}
NMR (75.45 MHz, CDCl3): δ 208.8 (CO), 192.4 (C(Pd)-NH),
135.7 (C, Xy), 135.0 (C, Xy), 130.4 (CH, Xy), 128.7 (CH,
Xy), 128.6 (CH, Xy), 128.3 (CH, Xy), 125.8 (C, Xy), 106.0 (CH),
22.9 (Me), 18.9 (Me, Xy), 18.1 (Me, Xy). Anal. Calcd for
C21H23ClN2OPd: C, 54.68; H, 5.03; N, 6.07. Found: C, 54.22;
H, 5.01; N, 5.82
t
t
CH2), 2.13 (s, 3 H, Me), 1.64 (s, 18 H, Bu), 1.61 (s, 9 H, Bu).
19F NMR (282.20 MHz, CDCl3): δ 78.0. Anal. Calcd for
C19H32F3N3O4PdS: C, 40.61; H, 5.74; N, 7.48; S, 5.71. Found:
C, 40.61; H, 6.06; N, 7.50; S, 5.54.
Synthesis of [Pd2Cl2(CNtBu)4] (7a). To a suspension of 1
(100 mg, 0.50 mmol) in toluene (3 mL) was added tBuNC (284
µL, 2.51 mmol) under N2. The resulting solution was heated
(60 °C) in a water bath for 5 h and then was filtered to give
solid 7a contaminated with Pd. The filtrate was concentrated
to dryness, and the residue was triturated with n-pentane (5
mL) and filtered off to get a second crop of 7a. Both crude
mixtures were recrystallized from CH2Cl2/Et2O to give 7a as
a yellow solid, which has previously been described.11,22
Yield: 122 mg, 80%. Anal. Calcd for C20H36Cl2N4Pd2: C, 38.98;
H, 5.89; N, 9.09. Found: C, 39.10; H, 6.10; N, 9.06.
Synthesis of [Pd{CH2C(O)Me}(CNXy)3]TfO (9b). A sus-
pension of 1 (100 mg, 0.50 mmol) in acetone (3 mL) was cooled
(-10 °C) for 15 min. Then, XyNC (199 mg, 1.51 mmol) was
added, and when the suspension dissolved, KTfO (97 mg, 0.51
mmol) was added. The suspension was stirred for 10 min in a
cold bath and then concentrated to dryness. The residue was
extracted with CH2Cl2 (5 mL) and filtered through Celite, and
the filtrate was evaporated to dryness. The residue was
vigorously stirred with n-pentane (10 mL) for 30 min at -10
°C, and the solid was filtered off, washed with n-pentane (5
mL), and air-dried to give 9b as a colorless solid. Yield: 309
mg, 88%. Mp: 87 °C. ΛM (acetone, 5.7 × 10-4 M): 122 Ω-1
cm2 mol-1. IR (Nujol, cm-1): ν(CN) 2200; ν(CO) 1666. 1H NMR
(300 MHz, CDCl3): δ 7.37-7.32 (m, 3 H, Xy), 7.21-7.18 (m, 6
H, Xy), 3.18 (s, 2 H, CH2), 2.54 (s, 12 H, Me, Xy), 2.48 (s, 6 H,
Me, Xy), 2.30 (s, 3 H, Me). 19F NMR (282.20 MHz, CDCl3): δ
78.14. Anal. Calcd for C31H32F3N3O4PdS: C, 52.73; H, 4.57;
N, 5.95; S, 4.54. Found: C, 52.68; H, 4.58; N, 5.90; S, 4.26.
Single crystals of 9b‚CHCl3 were obtained by slow diffusion
of n-pentane into a solution of 9b in CHCl3.
Synthesis of [Pd2Cl2(CNXy)4] (7b). To a suspension of 1
(75 mg, 0.38 mmol) in toluene (3 mL) was added XyNC (247
mg, 1.88 mmol) under N2. The mixture was heated (60 °C) in
a water bath for 5 h and then was filtered to give a solid that
was recrystallized from CH2Cl2/Et2O to give 7b as a yellow
solid. Yield: 65 mg, 42%. IR (Nujol, cm-1): ν(CN) 2154; ν(PdCl)
1
256. H NMR (300 MHz, CDCl3): δ 7.26-7.20 (m, 4 H, Xy),
(22) Duravila, V.; Mingos, D. M. P.; Vilar, R.; White, A. J. P.;
Williams, D. J. J. Organomet. Chem. 2000, 600, 198.

2520 Organometallics, Vol. 24, No. 10, 2005
Synthesis of
[Pd{K2-C,O-C(NHtBu)CHC(O)Me}-
Vicente et al.
N2. The resulting pale yellow solution was concentrated to
dryness, and the residue was stirred (30 min) with n-hexane
(15 mL) at 0 °C to obtain a solid, which was filtered and
dried under N2 to give 12a as a yellow solid. Yield: 38 mg,
51%. IR (Nujol, cm-1): ν(CO) 1567; ν(PdCl) 299. IR (KBr,
cm-1): ν(NH) 2964; ν(CO) 1572. 1H NMR (300 MHz, C6D6): δ
13.15 (br, 1 H, NH), 5.50 (d, 1 H, CH, 2JHP ) 1.4 Hz), 2.12 (s,
3 H, Me), 1.82-1.69 (m, 12 H, P(CH2Me)3), 1.44 (s, 9 H, tBu),
0.98 (t, 18 H, P(CH2Me)3, 3JHH ) 7.8 Hz). 13C{1H} NMR (75.45
MHz, C6D6): δ 186.8 (t, CO, 4JCP ) 3.8 Hz), 184.6 (t, CPd, 2JCP
(CNtBu)2]TfO (10a). To a solution of 6a (41 mg, 0.11 mmol)
in acetone (2 mL) were added TlTfO (35 mg, 0.11 mmol) and
tBuNC (12.7 µL, 0.11 mmol). The reaction mixture was
concentrated to dryness, and the residue was extracted with
CH2Cl2 (4 mL) and filtered through Celite. The filtrate was
concentrated to dryness. The residue was dissolved in acetone
(1 mL) and cooled at 0 °C, and n-pentane (10 mL) was added
to give a precipitate, which was filtered and vacuum-dried to
give 10a‚H2O as a hygroscopic pale yellow solid. Yield: 31 mg,
50%. ΛM (acetone, 4.55 × 10-4 M): 108 Ω-1 cm2 mol-1. IR
(Nujol, cm-1): ν(NH) 3388; ν(CN) 2232 (sh), 2218; ν(CO) 1514.
1H NMR (400 MHz, CDCl3): δ 6.80 (br, 1 H, NH), 5.16 (s, 1 H,
3
) 1.1 Hz), 102.5 (t, CH, JCP ) 3.3 Hz), 52.5 (C(Me)3), 31.1
1
3
(P(CH2Me)3), 27.8 (Me), 15.4 (‘t’, P(CH2Me)3, | JCP + JCP| )
41 Hz), 8.4 (C(Me)3). 31P{1H} NMR (121.50 MHz, CDCl3): 8.62
(s). Anal. Calcd for C20H44ClNOP2Pd: C, 46.34; H, 8.56; N,
2.70. Found: C, 46.00; H, 8.50; N, 2.63.
t
t
CH), 2.07 (s, 3 H, Me), 1.63 (s, 9 H, Bu), 1.58 (s, 9 H, Bu),
1.42 (s, 9 H, tBu). 19F NMR (282.20 MHz, CDCl3): δ 78.1. Anal.
Calcd for C19H34F3N3O5PdS: C, 39.35; H, 5.91; N, 7.25, S, 5.53.
Found: C, 39.72; H, 5.75; N, 7.20; S, 5.46. Single crystals of
10a‚Me2CO were obtained by slow diffusion of n-pentane into
a solution of 10a in acetone.
Synthesis of [Pd{K2-C,O-C(NHtBu)CHC(O)Me}(acac)]
(13a). To a solution of 3a (55 mg, 0.10 mmol) in CH2Cl2 (3
mL) was added Tl(acac) (59 mg, 0.20 mmol), and a colorless
precipitate appeared that within 10 min turned gray. The
suspension was filtered through Celite to give a yellow
solution, which was concentrated to dryness, and the residue
was extracted with n-pentane (10 mL), filtered through Celite,
and concentrated to dryness to give 13a as a yellow solid.
Yield: 54 mg, 80%. Mp: 115-119 °C. IR (Nujol, cm-1): ν(NH)
Synthesis of [Pd{K2-C,O-C(NHXy)CHC(O)Me}(CNXy)2]-
TfO (10b). To a solution of 6b (38 mg, 0.08 mmol) in acetone
(2 mL) were added TlTfO (30 mg, 0.08 mmol) and XyNC (10.8
mg, 0.082 mmol). The reaction mixture was concentrated to
dryness, and the residue was extracted with CH2Cl2 (3 mL)
and filtered through Celite. The yellow filtrate was concen-
trated to dryness to give an oil, which was triturated with
n-pentane (20 mL) in a cool bath (-10 °C) to give a solid, which
was filtered, washed with n-pentane, and air-dried to give 10b
as a yellow solid. Yield: 48 mg, 83%. Mp: 197 °C. ΛM (acetone,
4.50 × 10-4 M): 119 Ω-1 cm2 mol-1. IR (Nujol, cm-1): ν(NH)
3204 (br); ν(CN) 2210, 2190. IR (KBr, cm-1): ν(NH) 3216 (br);
ν(CN) 2211, 2191; ν(CO) 1490. 1H NMR (300 MHz, CDCl3): δ
9.70 (br, 1 H, NH), 7.37-7.06 (m, 9 H, Xy), 4.60 (s, 1 H, CH),
2.51 (s, 6 H, Me, XyNtC), 2.49 (s, 6 H, Me, XyNtC), 2.29 (s,
6 H, Me, XyNH), 2.01 (s, 3 H, Me). 19F NMR (282.40 MHz,
CDCl3): δ 78.8. Anal. Calcd for C31H32F3N3O4PdS: C, 52.73;
H, 4.57; N, 5.95; S, 4.54. Found: C, 52.97; H, 4.45; N, 6.03; S,
4.38. Single crystals of 10b were obtained by a CH2Cl2/n-
pentane solution of 10b.
1
3315; ν(CO) 1589, 1545, 1514. H NMR (300 MHz, CDCl3): δ
6.69 (br, 1 H, NH), 5.31 (s, 1 H, CH, acac), 4.97 (d, 1 H, CH,
4JHH ) 1 Hz), 2.06 (s, 3 H, Me), 2.01 (s, 3 H, Me, acac), 1.96 (s,
3 H, Me, acac), 1.37 (s, 3 H, Bu). 13C{1H} NMR (75.45 MHz,
t
CDCl3): δ 202.8 (CO), 190.2 (CO, acac), 185.7 (CPd), 184.6 (CO,
acac), 103.9 (CH), 100.8 (CH, acac), 53.7 (C(Me)3), 29.0
(C(Me)3), 27.6 (Me, acac), 27.2 (Me, acac), 21.8 (Me). Anal.
Calcd for C13H21NO3Pd: C, 45.21; H, 6.13; N, 4.05. Found: C,
45.43; H, 6.14; N, 4.19.
Synthesis of [Pd{K2-C,O-C(NHXy)CHC(O)Me}(acac)]
(13b). To a solution of 3b (30 mg, 0.045 mmol) in CH2Cl2 (3
mL) was added Tl(acac) (28 mg, 0.09 mmol), and the reac-
tion mixture was stirred for 6 h. The gray suspension was
filtered through Celite, the solution was concentrated to
dryness, and the residue was extracted with Et2O (10 mL),
filtered through Celite, concentrated to dryness, and dried for
1 day under vacuum to give 13b as a yellow solid. Yield: 30
mg, 84%. Mp: 110-115 °C (dec). IR (Nujol, cm-1): ν(NH) 3315;
Synthesis of [Pd{K2-C,O-C(NHtBu)CHC(O)Me}Cl-
(PPh3)] (11a). To a suspension of 3a (30 mg, 0.053 mmol) in
dry THF (4 mL), under N2 atmosphere, was added PPh3 (27.8
mg, 0.11 mmol). The orange solution was concentrated (ca. 1
mL) and n-pentane (10 mL) was added, yielding a solid, which
was filtered and air-dried to give 11a as an orange solid.
Yield: 31 mg, 54%. Mp: 113 °C. IR (Nujol, cm-1): ν(NH) 3265.
1
ν(CO) 1584, 1514. H NMR (300 MHz, CDCl3): δ 7.71 (br, 1
H, NH), 7.17-7.09 (s, 3 H, Xy), 5.37 (s, 1 H, CH, acac), 4.47
(d, 1 H, CH, JHH ) 1 Hz), 2.25 (s, 3 H, Me, Xy), 2.06 (s, 3 H,
4
Me, acac), 2.00 (s, 3 H, Me), 1.99 (s, Me, acac). 13C{1H} NMR
(75.45 MHz, CDCl3): δ 205.1 (CO), 190.1 (CO, acac), 188.7
(CPd), 185.0 (CO, acac), 135.0 (C, Xy), 134.6 (C, Xy), 128.3 (CH,
Xy), 127.8 (CH, Xy), 103.7 (CH), 100.9 (CH, acac), 27.7 (Me,
acac), 27.1 (Me, acac), 22.0 (Me), 18.2 (Me, Xy). Anal. Calcd
for C17H21NO3Pd: C, 51.85; H, 5.38; N, 3.56. Found: C, 52.14;
H, 5.51; N, 3.89.
1
IR (KBr, cm-1): ν(NH) 3265. H NMR (300 MHz, CDCl3): δ
7.74-7.68 (m, 6 H, Ph), 7.51-7.42 (m, 9 H, Ph), 5.17 (s, 1 H,
t
CH), 4.85 (br, 1 H, NH), 2.16 (s, 3 H, Me), 0.79 (s, 9 H, Bu).
31P{1H} NMR (121.50 MHz, CDCl3): δ 42.30 (br). Anal. Calcd
for C26H29ClNOPPd: C, 57.37; H, 5.37; N, 2.57. Found: C,
57.29; H, 5.44; N, 2.57.
Synthesis
of
[Pd{K2-C,O-C(NHXy)CHC(O)Me}Cl-
Crystal Structures of 6a, 9b, 10a, and 10b. The crystal
structures of 6a, 9b, 10a, and 10b were determined by single-
crystal X-ray diffraction. Measurements were recorded for 6a
on a Bruker SMART 1000 CCD, and otherwise on a Siemens
P4 diffractometer using monochromated Mo KR radiation in
ω-scan mode (for 6a also φ-scans). The structures were solved
by the heavy-atom method and refined anisotropically on F2
with the program SHELXL-97 (G. M. Sheldrick, University
of Go¨ttingen, Germany). Hydrogen atoms were included using
a riding model or rigid methyl groups. Special features of the
refinement are as follows. The polar axis direction of 6a was
determined by the Flack parameter of -0.020(16). Compound
9b crystallizes with one molecule of chloroform, and the
hydrogen atoms at C3 are disordered over two positions. For
compounds 6a, 10a, and 10b the hydrogen on N was located
in the Fourier difference map and refined freely (with DFIX).
Compound 10a crystallizes with one molecule of acetone, which
is disordered over two positions; its hydrogen atoms were not
included in the refinement. The fluorine atoms of its triflate
(PPh3)] (11b). To a suspension of 3b (53.7 mg, 0.081 mmol)
in dry THF (6 mL), under N2 atmosphere, was added PPh3
(85.3 mg, 0.33 mmol). The pale orange solution was concen-
trated (ca. 0.5 mL) and Et2O (15 mL) was added. The mixture
was stirred for 30 min at 0 °C, and then, the suspension was
filtered off, washed with Et2O (15 mL), and air-dried to
give 11b as a yellow solid. Yield: 78 mg, 81%. Mp: 166 °C
(dec). IR (Nujol, cm-1): ν(NH) 3340; ν(PdCl) 291. IR (KBr,
1
cm-1): ν(NH) 3340; ν(CO) 1479. H NMR (300 MHz, CDCl3):
δ 7.85-7.80 (m, 12 H, Ph), 7.49-7.42 (m, 18 H, Ph), 7.00 (m,
1 H, Xy), 6.90 (m, 2 H, Xy), 5.68 (br, 1 H, NH), 4.53 (s, 1 H,
CH), 2.03 (s, 3 H, Me), 1.76 (s, 9 H, Me, Xy). 31P{1H}
NMR (121.50 MHz, CDCl3): δ 39.02 (s). Anal. Calcd for
C30H29ClNOPPd: C, 60.82; H, 4.93; N, 2.36. Found: C, 60.83;
H, 5.15; N, 2.36.
Synthesis of trans-[Pd{C(NHtBu)dCHC(O)Me}Cl-
(PEt3)2] (12a). To a suspension of 3a (40.6 mg, 0.072 mmol)
in dry THF (3 mL) was added PEt3 (43 µL, 0.29 mmol) under

Reactivity of [Pd{CH2C(O)Me}Cl]n to Isocyanides
Organometallics, Vol. 24, No. 10, 2005 2521
Scheme 2
Scheme 3
anion are disordered over two positions. The triflate anion in
10b is disordered over two positions.
t
by reacting BuNC and 1 (tBuNC:Pd ) 1) in MeCN.
Results and Discussion
However, under the same conditions, XyNC reacts with
1 to give [Pd{κ2-C,O-C(NHR)CHC(O)Me}Cl(NCMe)]
(4b), which can also be obtained by reacting 3b in a
CHCl3 solution with an excess of MeCN. This difference
of reactivity could be due to the greater electron-
withdrawing character of the Xy group that makes the
palladium atom harder. Complexes 3 and 4b are stable
in the solid state and in organic solvents at room
temperature (acetone, CH2Cl2, CHCl3, THF).
Reactions of [Pd{CH2C(O)Me}Cl]n (1) with Iso-
cyanides. The 1:1 Reactions. [Pd{CH2C(O)Me}Cl]n
(1) and isocyanides (RNC:Pd ) 1) at 0 °C react to give
t
complexes [Pd2{CH2C(O)Me}2(µ-Cl)2(CNR)2] [R ) Bu
(2a), Xy (2b); Scheme 2]. Complexes 2 are stable at
temperatures e 4 °C, but at room temperature, their
solutions in organic solvents are not stable and an
insertion of the isocyanide into the Pd-C bond plus a
tautomerization process from â-ketoimine to â-ketoen-
amine occurs to give [Pd2{κ2-C,O-C(NHR)CHC(O)-
Me}2(µ-Cl)2] [R ) tBu (3a), Xy (3b); Scheme 2]. Imine-
enamine tautomeric equilibria in palladium imidoyl
complexes have been studied by Carmona et al.23 In our
case, the tautomerization process is driven to the
enamine form by the formation of the stable pallada-
cycle in complexes 3. Therefore, when complexes 2 were
synthesized at room temperature, they were always
contaminated with the corresponding complexes 3. Pure
complexes 3 could be obtained by heating solutions of
complexes 2 to 40-45 °C in organic solvents (CHCl3,
THF, toluene).
A few examples of these insertion-tautomerization
reactions have been reported to give trans-[Pd{C(NHR)d
CHC(O)R′}Cl(PPh3)2] (R ) Me, p-C6H4OMe, R′ ) Me;2
t
R ) Bu, R′ ) Ph4). In these cases the ligand is not
chelating because of the presence of the two phosphines
cis to the â-ketoenamine ligand.
The 1:2 Reactions. Low-temperature reactions of 1
with RNC (RNC:Pd ) 2) give complexes trans-[Pd-
{CH2C(O)Me}Cl(CNR)2] [R ) tBu (5a), Xy (5b); Scheme
3], which are stable in the solid state below 4 °C. When
these reactions were carried out at room temperature,
mixtures of 5 and the corresponding complexes [Pd{κ2-
t
C,O-C(NHR)CHC(O)Me}Cl(CNR)] [R ) Bu (6a), Xy
Kinetics of conversion of 2 to 3 was conveniently
followed by 1H NMR in CDCl3 at 317 K (see Supporting
Information). The reactions follow a first-order rate law
with respect to 2. The rate of disappearance of 2a (kobs
) (8.1 ( 0.3) × 10-5 s-1) is much lower than that of 2b
(kobs ) (4.1 ( 0.1) × 10-4 s-1). These results agree with
those reported for the insertion of the same isocyanides
into a Pd-Me bond.24 Complex 3a can also be obtained
(6b)] were isolated. The formation of complexes 6, which
like that of complexes 3 involves an insertion-tau-
tomerization process, can be achieved by heating solu-
tions of complexes 5 in CHCl3 to 40 °C (Scheme 3). These
processes were also studied kinetically and found to
follow a first-order rate law (see Supporting Informa-
tion). The calculated kobs of these reactions at 317 K, as
t
for conversion of 2 into 3, was lower for R ) Bu (6a
kobs ) (1.8 ( 0.1) × 10-4 s-1) than for R ) Xy (6b kobs
)
(23) Campora, J.; Hudson, S. A.; Massiot, P.; Maya, C. M.; Palma,
P.; Carmona, E.; Martinez Cruz, L. A.; Vegas, A. Organometallics 1999,
18, 5225. Alias, F. M.; Belderrain, T. R.; Paneque, M.; Poveda, M. L.;
Carmona, E.; Valerga, P. Organometallics 1997, 16, 301.
(24) Delis, J. G. P.; Aubel, P. G.; Vrieze, K.; van Leeuwen, P.;
Veldman, N.; Spek, A. L.; van Neer, F. J. R. Organometallics 1997,
16, 2948.
(1.1 ( 0.2) × 10-3 s-1). The one-pot synthesis of
complexes 6 from 1, heating CHCl3 solutions of 1 with
the corresponding isocyanides (RNC:Pd ) 2), gave also
trace amounts of the corresponding Pd(I) complexes
t
[Pd2Cl2(CNR)4] [R ) Bu (7a), Xy (7b)]. Complex 7a25

2522 Organometallics, Vol. 24, No. 10, 2005
Vicente et al.
Scheme 4
and complexes related to 7b, [Pd2X2(CNXy)4] (X )
Br,11,22 I22), have been reported. Complexes 7 were not
detected in solutions of complexes 6 or when they were
prepared from 5. Therefore, the one-pot synthesis of 6
from 1 is better achieved in two steps, the first involving
the low-temperature formation of 5 and then its thermal
transformation to 6.
The 1:3, 1:4, and 1:5 Reactions. The room-temper-
ature reaction between 1 and XyNC (XyNC:Pd ) 3) was
1
followed by H NMR in CDCl3. Initially, 5b and traces
of trans-[Pd{C(NHXy)dCHC(O)Me}Cl(CNXy)2] (8b) were
observed. After 3 h no signals of 5b were detected and
the major product was 8b with traces of 7b. When the
reaction was carried out in XyNC:Pd ) 4, the proportion
of 7b increased. The tBuNC:Pd ) 5 reaction at 50 °C in
C6D6 gave, after 5 h, 7a and unidentified products.
Complexes trans-[Pd{C(NHR)dCHC(O)Me}Cl(CNR)2]
[R ) tBu (8a), Xy (8b); Scheme 3] are better synthesized
by reacting 6 with 1 equiv of RNC at low temperature
because the one-pot reaction of 1 with isocyanides
(RNC:Pd ) 3) gave 8 contaminated with 7. Pure complex
8a could be isolated at 0 °C after 5 min of reaction and
concentration to dryness of the reaction mixture; how-
ever, analytically pure 8b could not be isolated because
it decomposes faster.
Complexes 6 and 7 were identified by 1H NMR as the
decomposition products of 8 in CDCl3 after 1 h at 50
dimers 3 with PPh3 (PPh3:Pd ) 1) gave the correspond-
ing complexes [Pd{κ2-C,O-C(NHR)CHC(O)Me}Cl(PPh3)]
t
1
[R ) Bu (11a), Xy (11b); Scheme 4]. The proposed
°C. On the other hand, H NMR spectra of mixtures of
structure is based on the strong transphobia between
8 and 1 equiv of isocyanide gave 7 and other products
that could not be identified. The decomposition process
of 8 could be associated with a C-Pd homolytic cleavage
generating complex 7 and organic products; a similar
mechanism was proposed by Floriani et al. to explain
the reaction of trans-[Pd{C(NHtBu)dCHC(O)Ph}Cl-
C- and P-donor ligands.10,11 Both complexes are stable
1
at room temperature in the solid state, but H NMR
spectra in chlorinated (CD2Cl2, CDCl3) or nonchlori-
nated (d8-THF) solvents show that they decompose
slowly into [PdCl2(PPh3)2] and other unidentified com-
pounds. Complex 11b was obtained, with even better
yield (81 vs 65%), when 3b was reacted with PPh3
(PPh3:Pd ) 2). However, the reaction of complex 3a with
PPh3 using PPh3:Pd ) 2 or 4 led to a mixture, which
could not be separated, of 11a and a product that, in
agreement with its 1H and 31P{1H} NMR (see Support-
ing Information), is trans-[Pd{C(NHtBu)dCHC(O)Me}-
Cl(PPh3)2] (1.1:2) (Scheme 4). By reacting 3 with the
more basic PEt3 (PPh3:Pd ) 2), we have been able to
obtain the complexes trans-[Pd{C(NHR)dCHC(O)Me}-
Cl(PEt3)2] [R ) tBu (12a), Xy (12b); Scheme 4]. Complex
12a was obtained in moderate yield (65%) due to its
extreme solubility in most organic solvents (acetone,
CHCl3, CH2Cl2, Et2O, THF; partially soluble in n-hex-
ane). However, 12b could not be obtained analytically
pure because it is more soluble in n-hexane and n-
pentane (see Supporting Information). Complexes 12
t
(PPh3)2] with BuNC.4
Addition of isocyanide to a cooled (-10 °C) suspension
of 1 in Me2CO (XyNC:Pd ) 3) led to a solution contain-
ing 5 (Scheme 3). Addition of 1 equiv of KTfO to this
reaction mixture led to the precipitation of KCl and a
solutionfromwhichcomplexes[Pd{CH2C(O)Me}(CNR)3]-
t
TfO [R ) Bu (9a), Xy (9b)] could be isolated if the low
temperature was maintained to avoid insertion pro-
cesses. These complexes are stable in the solid state at
4 °C and decompose in solution at room temperature.
The room-temperature 1H NMR spectrum of 9b in
CDCl3 shows its transformation into the product of
the insertion-tautomerization reaction [Pd{κ2-C,O-C-
(NHXy)CHC(O)Me}(CNXy)2]TfO (10b) along with other
byproducts that could not be separated. This and the
t
analogous BuNC complex 10a could be isolated pure
by reaction of acetone solutions of 6 with TlTfO and
addition of the corresponding isocyanide in a 1:1:1 molar
ratio. Organic solutions of complexes 10 are unstable,
but both complexes are stable in the solid state if stored
at 4 °C.
1
have to be stored under N2. The H NMR spectra of
complexes 12 prove that their structures are like those
of the related complexes trans-[Pd{C(NHR)dCHC(O)-
R′}Cl(PPh3)2] (R ) Me, p-C6H4OMe, R′ ) Me;2 R ) tBu,
R′ ) Ph4).
As shown below, the geometry around the PdC-NHR
bond in the palladacyclic complexes is trans, while that
of complexes 8 and 12 is cis. This isomerization occurs
because the cleavage of the O-Pd bond allows the
rotation around the CH-CNHR bond (Scheme 5) and
decreases the enolato character of the â-ketoenamine
ligand, favoring the resonance form Me(CdO)-CHdC-
(Pd)-NHR, the free rotation around the C(Pd)-NHR
bond, and the formation of the hydrogen bond that leads
Reactivity of Complexes 3. Complexes 3 are suit-
able precursors for the synthesis of other complexes
containing the C(NHR)CHC(O)Me ligand. Thus, we
have shown above that MeCN cleaves the bridge in 3b,
giving 4b (Scheme 2). Similarly, the reactions of the
(25) Otsuka, S.; Tatsuno, Y.; Ataka, K. J. Am. Chem. Soc. 1971, 93,
6705. Rettig, M. F.; Kirk, E. A.; Maitlis, P. M. J. Organomet. Chem.
1976, 111, 113. Yamamoto, Y.; Yamazaki, H. Bull. Chem. Soc. Jpn.
1987, 58, 1843. Marsh, R. E.; Schaefer, W. P.; Lyon, D. K.; Labinger,
J. A.; Bercaw, J. E. Acta Crystallogr., Sect. B 1992, 53, 317.

Reactivity of [Pd{CH2C(O)Me}Cl]n to Isocyanides
Organometallics, Vol. 24, No. 10, 2005 2523
Scheme 5
to complexes 8 and 12. This conformation is the most
important in secondary â-ketoenamines, probably due
to the strong intramolecular hydrogen bond.26
Reaction of 3 with Tl(acac) (acac:Pd ) 2) gives
complexes [Pd{κ2-C,O-C(NHR)CHC(O)Me}(κ-O,O-acac)]
[R ) tBu (13a), Xy (13b); Scheme 4]. The transformation
of 3a into 13a occurs quickly, but complete conversion
of 3b into 13b requires 6 h. Both complexes 13 are
soluble in common precipitating organic solvents (n-
hexane, n-pentane, Et2O). To isolate these complexes,
it was necessary to concentrate an n-pentane or Et2O
solution, respectively, and dry the residue under vacuum
over 1-2 days. At room temperature both compounds
are air-stable in the solid state and in solution.
Figure 1. Thermal ellipsoid plot (50% probability) of 6a.
Selected bond lengths (Å) and angles (deg): Pd-C(9) )
1.9207(15), Pd-C(1) ) 1.9931(14), Pd-O ) 2.0380(10),
Pd-Cl ) 2.3738(4), O-C(3) ) 1.2929(18), C(1)-N(1) )
1.3258(19), C(1)-C(2) ) 1.413(2), C(2)-C(3) ) 1.383(2),
C(3)-C(4) ) 1.503(2), N(1)-C(5) ) 1.4948(19), N(2)-C(9)
) 1.150(2), N(2)-C(10) ) 1.4661(18), C(9)-Pd-C(1)
)
94.08(6), C(1)-Pd-O ) 82.33(5), C(9)-Pd-Cl )
90.83(4), O-Pd-Cl ) 92.72(3), C(3)-O-Pd ) 110.68(9),
N(1)-C(1)-C(2) ) 125.32(14), N(1)-C(1)-Pd ) 124.07(11),
C(2)-C(1)-Pd ) 110.61(10), C(3)-C(2)-C(1) ) 115.12(14),
O-C(3)-C(2) ) 120.98(13), O-C(3)-C(4) ) 116.44(14),
C(2)-C(3)-C(4) ) 122.58(15), C(1)-N(1)-C(5) ) 129.98-
(12), C(9)-N(2)-C(10) ) 173.02(14), N(2)-C(9)-Pd )
171.28(12).
Crystal Structures. The crystal structures of com-
plexes 6a (Figure 1), 9b (Figure 2), 10a (Figure 3), and
10b (Figure 4) have been solved. All of them show an
aproximately square-planar coordination around the
t
palladium atom. The trans influences of BuNC and
XyNC ligands are similar because in complexes 10
analogous Pd-C(NHR) [10a 2.019(4) Å, 10b 2.003(4) Å]
and Pd-O [10a 2.024(3) Å, 10b 2.021(3) Å] distances
are observed. Complexes 10 show the Pd-CNR bond
distance trans to C [10a 2.057(4) Å, 10b 2.042(4) Å]
longer than that trans to O [10a 1.937(4) Å, 10b 1.932-
(4) Å] as a consequence of the stronger trans influence
of the C-donor ligand. Similarly, in 9b the Pd-CNXy
bond trans to the acetonyl group [2.090(2) Å] is longer
than those corresponding to the two mutually trans
Pd-CNXy bond distances [1.973(3) and 1.980(3) Å] due
to the greater trans influence of acetonyl than the XyNC
ligand. The cationic nature of complex 10a causes the
shortening of the Pd-O bond [2.024(3) Å] with respect
to that in the neutral complex 6a [2.038(1) Å], despite
being trans to the same ligand. In contrast, the
Pd-C(NHR) bond distance is longer in complex 10a
[2.019(4) Å] than in complex 6a [1.9931(14) Å] due to
Figure 2. Thermal ellipsoid plot (50% probability) of the
cation of complex 9b. Selected bond lengths (Å) and angles
(deg): Pd-C(5) ) 1.972(3), Pd-C(6) ) 1.979(3), Pd-C(4)
) 2.027(3), Pd-C(1) ) 2.090(2), O(1)-C(2) ) 1.218(3),
N(1)-C(4) ) 1.148(3), N(1)-C(11) ) 1.408(3), N(2)-C(5)
) 1.146(3), N(2)-C(21) ) 1.408(3), N(3)-C(6) ) 1.152(3),
N(3)-C(31) ) 1.407(3), C(1)-C(2) ) 1.475(4), C(2)-C(3)
) 1.505(4), C(5)-Pd-C(4) ) 91.20(10), C(6)-Pd-C(4) )
93.05(10), C(5)-Pd-C(1) ) 86.36(11), C(6)-Pd-C(1) )
90.30(10), C(4)-N(1)-C(11) ) 179.2(3), C(5)-N(2)-C(21)
) 178.5(3), C(6)-N(3)-C(31) ) 177.1(2), C(2)-C(1)-Pd
) 114.57(18), O(1)-C(2)-C(1) ) 122.4(3), O(1)-C(2)-C(3)
) 120.9(3), C(1)-C(2)-C(3) ) 116.7(3), N(1)-C(4)-Pd
) 173.8(2), N(2)-C(5)-Pd ) 175.4(2), N(3)-C(6)-Pd )
173.7(2).
t
the greater trans influence of the BuNC ligand than
that of Cl, and the Pd-CNtBu bond trans to oxygen is
also longer in 10a [1.937(4) Å] than that in 6a [1.9207-
(15) Å], probably due to the greater Pd to tBuNC π-back-
bonding in the neutral than in the cationic complex. The
geometry of 6a is in agreement with the greater
transphobia of the pair C-donor ligand/C-donor ligand
than that of the pair C-donor ligand/Cl.10,11 For this
reason, and because of its similar nature, we propose
the same geometry for 6b.
(26) Sandstro¨m, J. Chapter 6: Static and Dynamic Stereochemistry
of Acceptor-Substituted Enamines. In The Chemistry of Enamines;
Rappoport, Z., Ed.; Wiley: Chichester, 1994; p 406. Zhuo, J. C. Magn.
Reson. Chem. 1996, 34, 595. Zhuo, J. C. Magn. Reson. Chem. 1997,
35, 21. Zhuo, J. C. Magn. Reson. Chem. 1997, 35, 311. Chiara, J. L.;
Go´mez-Sa´nchez, A. Chapter 5: NMR Spectra. In The Chemistry of
Enamines; Rappoport, Z., Ed.; Wiley: Chichester, 1994; p 280.
The palladacycles in complexes 6a, 10a, and 10b
show a high degree of electron delocalization over the

2524 Organometallics, Vol. 24, No. 10, 2005
Vicente et al.
Figure 3. Thermal ellipsoid plot (50% probability) of the
cation of complex 10a. Selected bond lengths (Å) and angles
(deg): Pd-C(9) ) 1.937(4), Pd-C(1) ) 2.019(4), Pd-O(1)
) 2.024(3), Pd-C(14) ) 2.057(4), O(1)-C(3) ) 1.296(5),
N(1)-C(1) ) 1.328(5), N(1)-C(5) ) 1.503(5), N(2)-C(9) )
1.146(5), N(2)-C(10) ) 1.471(5), N(3)-C(14) ) 1.145(5),
N(3)-C(15) ) 1.474(5), C(1)-C(2) ) 1.400(5), C(2)-C(3)
) 1.378(6), C(3)-C(4) ) 1.502(6), C(9)-Pd-C(1) ) 93.69-
(15), C(1)-Pd-O(1) ) 82.39(13), C(9)-Pd-C(14) ) 94.28-
(15), O(1)-Pd-C(14) ) 89.67(13), C(3)-O(1)-Pd ) 110.9-
(2), C(1)-N(1)-C(5) ) 129.5(3), C(9)-N(2)-C(10) ) 177.9(4),
C(14)-N(3)-C(15) ) 179.0(4), N(1)-C(1)-C(2) ) 126.0-
(4), N(1)-C(1)-Pd ) 124.4(3), C(2)-C(1)-Pd ) 109.7(3),
C(3)-C(2)-C(1) ) 116.0(4), O(1)-C(3)-C(2) ) 121.0(4),
O(1)-C(3)-C(4) ) 115.1(4), C(2)-C(3)-C(4) ) 123.9(4),
N(1)-C(5)-C(8) ) 104.6(3), N(2)-C(9)-Pd ) 177.0(3),
N(3)-C(14)-Pd ) 174.8(4).
Figure 4. Thermal ellipsoid plot (50% probability) of the
cation of complex 10b. Selected bond lengths (Å) and angles
(deg): Pd-C(5) ) 1.932(4), Pd-C(3) ) 2.003(4), Pd-O(1)
) 2.021(3), Pd-C(6) ) 2.042(4), O(1)-C(1) ) 1.294(5),
N(1)-C(3) ) 1.322(4), N(1)-C(11) ) 1.443(4), N(2)-C(5)
) 1.144(5), N(2)-C(21) ) 1.400(5), N(3)-C(6) ) 1.147(5),
N(3)-C(31) ) 1.409(5), C(1)-C(2) ) 1.381(5), C(1)-C(4)
) 1.498(5), C(2)-C(3) ) 1.399(5), C(5)-Pd-C(3) ) 95.20-
(15), C(3)-Pd-O(1) ) 82.29(12), C(5)-Pd-C(6) ) 95.23-
(15), O(1)-Pd-C(6) ) 87.75(13), C(1)-O(1)-Pd ) 111.1(2),
C(3)-N(1)-C(11) ) 123.0(3), C(5)-N(2)-C(21) ) 178.9-
(4), C(6)-N(3)-C(31) ) 170.8(4), O(1)-C(1)-C(2) ) 120.5-
(3), O(1)-C(1)-C(4) ) 115.9(3), C(2)-C(1)-C(4) ) 123.7(4),
C(1)-C(2)-C(3) ) 115.6(3), N(1)-C(3)-C(2) ) 122.8(3),
N(1)-C(3)-Pd ) 127.1(3), C(2)-C(3)-Pd ) 110.0(3), N(2)-
C(5)-Pd ) 173.9(3), N(3)-C(6)-Pd ) 165.7(4).
Chart 1
OCCCNC group, as shown in Schemes 1-4. Chart 1
shows the two canonical forms of the chelating â-ketoen-
amine ligand. The structural parameters that support
this electron delocalization are as follows. (i) The five-
membered rings adopt an essentially planar geometry
(mean deviation of the five atoms from the mean
plane: 6a 0.026 Å, 10a 0.020 Å, 10b 0.029 Å). (ii) The
PdOC-C [6a 1.383(2) Å, 10a 1.378(6) Å, 10b 1.381(5)
Å] and PdC-C [6a 1.413(2) Å, 10a 1.400(5) Å, 10b
1.399(5) Å] bond distances are intermediate between
that of a single (O)C-CdC bond [1.464 Å] and a double
(O)C-CdC bond [1.340 Å].27 (iii) The C-O bond dis-
tances [6a 1.2929(18) Å, 10a 1.296(5) Å, 10b 1.294(5)
Å] are intermediate between that of a single C-O(Pd-
CNR-trans) bond [1.337-1.356 Å]28 and a double
Me2CdO(PdC-trans) bond [mean value 1.225 Å].29 They
are also longer than the C-O bond distance in termi-
nal (e.g., 1.220(4) Å in 9) or bridging (e.g., 1.263(4) Å in
[Pd2{CH2C(O)Me}{µ-κ2-C,O-CH2C(O)Me}(µ-Cl)Cl(dm-
so)2]9) acetonyl ligands, which shows that the â-keto-
enamine ligands have greater enolato character than
bridging acetonyl ligands. (iv) The exocyclic C-N dis-
tances [6a 1.3258(19) Å, 10a 1.328(5) Å, 10b 1.322(4)
Å] are much shorter than that of a single R2N-CH2Pd
bond (mean value, 1.450 Å)30 and intermediate be-
tween a double XyNHdC(Me)Pd bond (ca. 1.30 Å)31 and
the C-N bond distances in pyridine (1.337 Å).27 The
geometry around the PdC-NHR bond in complexes 6a
and 10a is trans; the same was observed in solution
for all the palladacycles studied (see below). (v) The
OCCCN(H)C systems are planar. In the only other
described complex with this metallacycle, [Co(η5-C5H5)-
{κ2-C,O-C(NHCPhMe)CHC(O)Ph}(PMe3)]BF4,
the
CoC-C [1.406(6) Å], C-O [1.292(5) Å], CoOC-C [1.384-
(6) Å], and the exocyclic C-N distances [1.325(6) Å]
are not significantly different.17 In complex trans-
[Pd{C(NHtBu)dCHC(O)Ph}Cl(PPh3)2], where the same
ligand adopts a monocoordinate bonding, as in com-
plexes 8 and 12, a high degree of π delocalization over
the ligand has also been proposed.4 However, comparing
their X-ray structural data with those in the κ2-C,O-
C(NHtBu)CHC(O)Me ligand in complex 6a, there are
(27) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(28) Modinos, A.; Woodward, P. J. Chem. Soc., Dalton Trans. 1974,
2065. Vicente, J.; Abad, J. A.; Fo¨rtsch, W.; Jones, P. G.; Fischer, A.
Organometallics 2001, 20, 2704.
(29) Falvello, L. R.; Fornies, J.; Navarro, R.; Sicilia, V.; Tomas, M.
J. Chem. Soc., Dalton Trans. 1994, 3143. Hashmi, A. S. K.; Grundl,
M. A.; Bats, J. W.; Bolte, M. Eur. J. Org. Chem. 2002, 1263. Hashmi,
A. S. K.; Naumann, F.; Bats, J. W. Chem. Ber. 1997, 130, 1457. Hashmi,
A. S. K.; Naumann, F.; Nass, A. R.; Bolte, M. J. Prakt. Chem. 1998,
340, 240. Canty, A. J.; Patel, J.; Skelton, B. W.; White, A. H. J.
Organomet. Chem. 2000, 607, 194. Vicente, J.; Arcas, A.; Bautista, D.;
Tiripicchio, A.; Tiripicchio-Camellini, M. New J. Chem. 1996, 20, 345.
(30) Enzmann, A.; Eckert, M.; Ponikwar, W.; Polborn, K.; Schneider-
bauer, S.; Beller, M.; Beck, W. Eur. J. Inorg. Chem. 2004, 1330. Miki,
K.; Tanaka, N.; Kasai, N. Acta Crystallogr., Sect. B 1981, 37, 447.
(31) Owen, G. R.; Vilar, R.; White, A. J. P.; Williams, D. J.
Organometallics 2003, 22, 4511.

Reactivity of [Pd{CH2C(O)Me}Cl]n to Isocyanides
Organometallics, Vol. 24, No. 10, 2005 2525
Figure 5. View of the H‚‚‚Pd and H‚‚‚Cl interactions in
6a.
some analogies, for example, in the Pd-C [1.992(4),
1.9931(14) Å, respectively] PdC-N [1.325(4), 1.3258-
(19)Å, respectively], and PdC-C [1.399(4), 1.413(2) Å,
respectively] distances, but significant differences, in
PdCC-C [1.409(6) and 1.383(2) Å, respectively] and
C-O [1.262(4), 1.2929(18) Å, respectively] bond dis-
tances, probably because of the presence of different
substituents (Ph, Me, respectively), the hydrogen bond
in the complex with the monocoordinate ligand, and the
greater enolato character of the chelating ligand.
Figure 6. View of the hydrogen bond interactions in 9b.
All hydrogen atoms, except those involved in hydrogen
bond interactions, have been omitted.
The Pd-C(NHR) distances [6a 1.9931(14) Å, 10a
2.019(4) Å, 10b 2.003(2) Å] are significantly shorter than
the Pd-CH2C(O)Me bond distance in complex 9b [2.090-
(2) Å], despite being trans to an isocyanide ligand in 10
and 9. In addition, the Pd-C(NHR) distance in 10b
[2.003(2) Å] is shorter than the Pd-C(NXy) trans to the
same ligand in the complex cis-[Pd{κ2-C,N-C(dNXy)-
C6H4NH2-2}(CNXy)2]TfO [2.034(3) Å].32 The Pd-CH2C-
(O)Me bond distance is longer in 9b [2.090(2) Å]
than in the two other reported acetonyl palladium com-
plexes, [Pd2{CH2C(O)Me}{µ-κ2-C,O-CH2C(O)Me}(µ-Cl)-
Cl-(dmso)2] [2.050(3) Å] and [Pd2{CH2C(O)Me}2(µ-Cl)2-
(tht)2], [2.053(3) Å],9 due to the greater trans influence
of the XyNC ligand with respect to Cl.
In 6a there are no hydrogen bonds involving the NH
group, but one H‚‚‚Pd and two H‚‚‚Cl weak interactions
(Figure 5) lead to layers of molecules parallel to the xz
plane. In complexes 9b and 10a the cationic units are
connected to the anion through hydrogen bonds (Figures
6 and 7). In addition, in 9b there is also a C-H‚‚‚Cl
interaction with the molecule of CHCl3 (Figure 6). In
complex 10b there are intermolecular π-π stacking
and C-H‚‚‚Pd agostic interactions giving dimers (Fig-
ure 8). The first interactions are between the π elec-
tron densities of the CtN group of one molecule and
the aryl group of the other molecule of the dimer. The
segment between the centroids is 3.72 Å in length, and
its angle with the aryl plane is 85.5°. Whereas π-π
stacking interactions are well established for organic
and biological systems,33 their role in organometallic
compounds is scarcely recognized.34 The parameters of
the C-H‚‚‚Pd agostic interactions are C(34)‚‚‚Pd 3.264-
(6) Å, H‚‚‚Pd 3.11 Å, C(34)-H(34)‚‚‚Pd 92.8°, and
H-C‚‚‚Pd 70.5°.
Figure 7. View of the hydrogen bond interactions in 10a.
All hydrogen atoms, except those involved in hydrogen
bond interactions, have been omitted.
singlets in the ranges δ 1.93-2.32, 2.61-3.18, and
4.12-5.73, respectively. As expected, the CH2 pro-
t
tons are more shielded for BuNC than XyNC com-
plexes (∆δ ) 0.52-0.21 ppm). The NH proton in the
palladacyclic complexes appears as a broad resonance
(32) Vicente, J.; Abad, J. A.; Frankland, A. D.; Lo´pez-Serrano, J.;
Ram´ırez de Arellano, M. C.; Jones, P. G. Organometallics 2002, 21,
272.
(33) Meyer, E. A.; Castellano, R. K.; Diederich, F. Angew. Chem.,
Int. Ed. 2003, 42, 1210.
(34) Magistrato, A.; Pregosin, P. S.; Albinati, A.; Rothlisberger, U.
Organometallics 2001, 20, 4178, and references therein. Gibson, D.
H.; Mashuta, M. S.; Yin, X. L. Acta Crystallogr., Sect. C 2004, 60, M366.
Gladiali, S.; Taras, R.; Ceder, R. M.; Rocamora, M.; Muller, G.; Solans,
X.; Font-Bardia, M. Tetrahedron Asymm. 2004, 15, 1477. Dotta, P.;
Magistrato, A.; Rothlisberger, U.; Pregosin, P. S.; Albinati, A. Orga-
nometallics 2002, 21, 3033.
Spectroscopic Properties. The 1H NMR spectra of
complexes show the MeC(O), CH2, and CH protons as

2526 Organometallics, Vol. 24, No. 10, 2005
Vicente et al.
ization in the case of complexes 3, 4b, and 6. Unfortu-
nately, it was not possible to characterize them because
they were present at very low concentrations. In the
case of complex 4b, no NOE effects were observed
between the Me protons of the MeCN ligand and other
protons of the molecule. This prevents assigning the
geometry of this complex (see Scheme 2).
Only the 13C NMR spectra of the most stable com-
plexes, 3, 4b, 6, 12a and 13, could be recorded. The CO
carbon nucleus in the chelating â-ketoenamine ligands
is deshielded (202.8-208.8 ppm) with respect to that
in the monocoordinate ligand in 12a (186.8 ppm) as a
consequence of the greater enolato character of the
chelating ligands.
t
The IR spectra of complexes with BuNC show the
ν(CN) absortion in the region 2254-2208 cm-1 and
those with XyNC in the region 2200-2160 cm-1, show-
ing, as usual, an increase with respect to ν(CN) in the
free ligands (2134 and 2109 cm-1, respectively).
The acetonyl complexes 2, 5, and 9 show the ν(CO)
band in the narrow range 1658-1668 cm-1. In the
palladacyclic complexes (3, 4b, 6, 10, and 11) the ν(CO)
appears at lower frequency, 1479-1536 cm-1, showing
the reduction of the CdO bond order found in the X-ray
diffraction studies of complexes 6a and 10. In complexes
8 and 12, the ν(CO) band appears in the range 1556-
1570 cm-1, i.e. slightly above that in the palladacyclic
complexes, in agreement with the lower enolato char-
acter of the monocoordinate C(NHR)dCHC(O)Me ligand
with respect to that in the chelating ligand. We have
previously reported9 that terminal and C,O-bridging
acetonyl ligands can be distinguished by IR spectroscopy
because they show the ν(CO) band in the ranges 1685-
1628 and 1565-1534 cm-1, respectively.35 The present
IR data suggest that the enolato character of the
chelating or monocoordinate â-ketoenamine ligands is
greater than or similar to, respectively, that in the C,O-
bridging acetonyl ligand.
Figure 8. View of the π-π and agostic interactions in 10b.
All hydrogen atoms, except those involved in the
C-H‚‚‚Pd interactions, have been omitted.
in the wide range 4.85-9.70 ppm, shielded with re-
spect to that in complexes with the monocoordinate
C(NHR)dCHC(O)Me ligand (12.16-14.08 ppm), which
supports the proposal of an intramolecular hydrogen
bond in the latter (Scheme 4). In the 1H NMR of
complexes trans-[Pd{C(NHR)dCHC(O)Me}Cl(PPh3)2]
(R ) Me, p-C6H4OMe), containing hydrogen-bonded
heterocycles, the NH proton appears as a broad reso-
nance at 10.0 and 11.6 ppm, respectively.2 As expected,
t
the BuNH proton is more shielded (∆δ ) 2.9-0.83
ppm) than the XyNH proton. This effect is also ob-
served for the protons of the group CHC(O)Me of the
nonpalladacyclic complexes 8 and 12 (∆δ ) 0.29-0.23
ppm) and the carbon nucleus of CO (∆δ ) 3.3-2.1 ppm)
and PdCNHR (∆δ ) 3-2.4 ppm) groups. These effects
are a consequence of the electron delocalization over
the â-ketoenamine ligands, which have also been re-
ported in related organic compounds.26 However, the
CHC(O)Me proton of the carbacyclic complexes under-
goes an important shielding due to the ring current
effect of the Xy group, which determines a smaller
The IR spectra of the nonpalladacyclic complexes 8
and 12 show the band due to the ν(NH) mode (3028-
2964 cm-1) ca. 400-200 cm-1 below that corresponding
to the palladacyclic complexes (3418-3202 cm-1). This
can be attributed to the intramolecular hydrogen bond
present in the former such as it has also been reported
in related organic compounds.36
t
δ(CH) in complexes with R ) Xy than with Bu (∆δ )
0.64-0.45 ppm). This effect proves the trans geometry
of the PdC-NXy group in these complexes, as we also
show below.
The position of the bands from the ν(PdCl) modes has
been tentatively assigned in agreement with the coor-
dination type of the chloro ligand, bridging [νb(PdCl)]
or terminal [νt(PdCl)], and on the trans influence of
the ligand L trans to the chloro ligand [ν(PdCl)L]. Thus,
in complexes 2a (296, 252 cm-1) and 2b (296, 254
cm-1), those at higher wavenumbers must be as-
NOE experiments were conducted to elucidate the
geometry around the PdC-NHR bond. For complexes
3, 4b, 6, 10b, and 13, NOESY 1D or 2D experiments
reveal a NOE between the CH of the â-ketoenamine
moiety and the protons of the Me and R group (tBu or
Xy). No effect exists between this CH and NH protons.
t
signed to νb(PdCl)CNR (R ) Bu, Xy) and the others to
t
The Bu and Xy groups of the â-ketoenamine ligand
νb(PdCl)CH2R′ (R′ ) C(O)Me) in agreement with pre-
vious asignments9 and the above observation of a
stronger trans influence of the acetonyl group than the
isocyanide ligand. Complex 3b shows two bands at
282 and 246 cm-1 that can be assigned to νb(PdCl)O
and νb(PdCl)CNHR, respectively. As expected, νt(PdCl)L
have a strong NOE with the NH in all cases. The NH
proton also has a NOE in complexes 6 with the R group
of the coordinated isonitrile and in 13 with the closer
Me group of the acac ligand. All this proves the trans
PdC-NHR bond conformation of these complexes in
solution, which is the same as that found in the crystal
structures of 6a, 10a, and 10b (Figures 1, 3, 4 and
Schemes 2-4). All ketoenamine complexes, except 13,
showed at various temperatures small signals that could
be due to other isomers containing a different conforma-
tion of the PdC-NHR bond or to a cis-trans isomer-
(35) Failing to reference this observation, Ruiz et al. (Ruiz, J.;
Mart´ınez, M. T.; Rodr´ıguez, V.; Lo´pez, G.; Pe´rez, J.; Chaloner, P. A.;
Hitchcock, P. B. Dalton Trans. 2004, 3521) have recently discovered
that “the carbonyl stretching band...may be used...for distinguishing
terminal C-bound enolate from bridging C,O bound enolate”.
(36) Dudek, G. O. J. Org. Chem. 1965, 30, 548.

Reactivity of [Pd{CH2C(O)Me}Cl]n to Isocyanides
Organometallics, Vol. 24, No. 10, 2005 2527
Table 1. Crystal Data for Complexes 6a, 9b‚CHCl3, 10a‚Me2CO, and 10b
6a
9b‚CHCl3
10a‚Me2CO
10b
formula
Mr
cryst size (mm)
cryst syst
space group
cell constants
a, Å
C
13H23ClN2OPd
C32H33Cl3F3N3O4PdS
C22H38F3N3O5PdS
620.01
C31H32F3N3O4PdS
706.06
365.18
25.42
0.35 × 0.35 × 0.09
orthorhombic
Pca21
0.46 × 0.32 × 0.17
0.49 × 0.34 × 0.24
0.50 × 0.30 × 0.14
triclinic
monoclinic
P21/n
monoclinic
P21/c
P1h
18.2636(11)
9.3501(4)
9.2895(4)
90
90
90
8.6505(5)
11.8001(6)
18.7442(14)
83.546(5)
87.742(5)
70.234(4)
1789.20(19), 2
0.71073
12.8580(8)
17.0414(11)
13.3978(8)
90
95.509(5)
90
8.3651(6)
22.9882(15)
17.1156(9)
90
103.680(6)
90
b, Å
c, Å
R, deg
â, deg
γ, deg
volume, (Å3), Z
λ (Å)
1586.34(14), 4
0.71073
1.330
2922.1(3), 4
0.71073
1.409
3197.9(4), 4
0.71073
1.466
F(calc) (Mg m-3
F(000)
)
1.532
744
836
1280
1400
T (K)
133
173
173
173
µ, mm-1
transmissions
θ, range (deg)
1.53
0.856
0.759
0.702
0.642-0.880
2.2-30.0
-25 e h e 25
-13 e k e 13
-13 e l e 13
0.910-0.743
3.01-25.0
0 e h e 10
-13 e k e 13
-22 e l e 22
0.746-0.740
3.05-25.0
-15 e h e 0
-20 e k e 1
-15 e l e 15
0.839-0.763
3.02-25.0
-9 e h e 2
-27 e k e 0
-20 e l e 20
limiting indices
no. of reflns
measd
indep
Rint
abs corr
31977
4637
0.029
SADABS
6735
6278
5603
5132
0.0172
ψ-scans
6984
5607
0.0349
ψ-scans
0.0181
ψ-scans
refinement method
full-matrix least squares on F2
no. data/rest/params
4637/2/174
1.044
0.015
0.039
0.387,-0.201
6278/39/455
1.041
0.029
0.070
0.693,-0.554
5132/7/318
1.075
0.039
0.100
0.721,-0.861
5607/363/393
0.977
0.039
0.094
0.775,-0.678
S (F2)
R1
wR2
largest ∆F (e Å-3
)
> νb(PdCl)L. Thus, the bands assignable to the
νt(PdCl)CNHR mode appear in the range 262-299 cm-1
with νt(PdCl)CNHtBu < νt(PdCl)CNHXy. In some cases,
ν(PdCl) could not be assigned (3a, 11a, 12b). In the IR
spectrum of complex 4b there are three bands at 361,
326, and 292 cm-1 that could be due to the ν(PdCl)
mode. Therefore, we cannot use these data to propose a
geometry for this complex.
The resulting complexes are the first palladium com-
pounds containing such ligands acting as a chelate. We
report here for the first time the isolation of both types,
adducts and insertion/tautomerization products of iso-
cyanides into the Pd-CH2C(O)R bond.
Acknowledgment. We thank the financial support
of Ministerio de Ciencia y Tecnolog´ıa, FEDER (BQU2001-
0133) and Fundacio´n Se´neca (Comunidad Auto´noma de
la Regio´n de Murcia, Spain) for a grant to J.M.F.-H.
Conclusions
To illustrate the capacity of [Pd{CH2C(O)Me}Cl]n to
prepare chloro-monoacetonyl or monoacetonyl palla-
dium(II) complexes, we have isolated complexes of
the types [Pd{CH2C(O)Me}Cl(CNR)n] (n ) 1, 2) and
[Pd{CH2C(O)Me}(CNR)3]+. We have studied the ther-
mal transformation of these compounds into C-palla-
dated â-ketoenamine complexes resulting from inser-
tion of one molecule of the isocyanide followed by a
â-ketoimine to â-ketoenamine tautomerization process.
Supporting Information Available: Experimental de-
tails of the preparation of 12b and trans-[Pd{C(NHtBu)dCHC-
(O)Me}Cl(PPh3)2]. Experimental procedure, kinetic data for the
conversion of 2 into 3 and 5 into 6, and plots of these data.
Listing of all refined and calculated atomic coordinates,
anisotropic thermal parameters, and bond lengths and angles
for 6a, 9b, 10a, and 10b. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM048999C