Organometallic complexes of palladium (II) derived from 2,6-diacetylpyridine dimethylketal

Article abstract of DOI:10.1021/om100079x

PdCl₂ reacts with 2,6-diacetylpyridine(dap) (1:1) in refluxing MeOH to give the pincer complex [Pd(O¹,N¹,C ¹-L)Cl](1) and (QH)₂[{PdCl2(μ-Cl)}]₂ (2), where L is the monoanionic ligand resulting from deprotonation of the acetyl methyl group of the monoketal of dap and QH is C₅H ₃NH{C-(OMe)Me}₂-2,6, the diketal of Hdap⁺. Reaction of 2 with NEt₃ (1:2) in MeOH affords Q = C5H ₃N{C(OMe)₂Me}₂-2,6(3). Complex 1 reacts with 2 equiv of RNC at 0 °C to give trans-[Pd(C¹-L)Cl(CNR) ₂](R = Xy = 2,6-dimethylphenyl(4a), ^tBu (4b)) but at room temperature affords [Pd(O², C²-L_R)Cl(CNR)](R = Xy (5a), ^tBu(5b)). The ligand L_R results from the insertion of one isocyanide into the Pd-C bond plus a tautomerization process from η-ketoimine to β-ketoenamine and coordinates in 5 through the carbonyl oxygen atom (O²) and the inserted isocyanide carbon atom (C²). The reaction of 1 with 1 equiv of RNC at 0 °C leads to a mixture of [Pd (N¹,C¹-L)Cl(CNR)] (R = Xy (6a), ^tBu (6b); 85-90%), 1, and 4, but at room temperature gives the pincer complex [Pd (O¹,N¹,C²-L_R)Cl] (R = Xy (7a), ^tBu (7b)), resulting from insertion/tautomerization processes similar to that leading to 5. Complex 7 reacts at 0 °C (1) with 2 equiv of RNC to give trans-[Pd (C²-L_R)Cl (CNXy) ₂] (R = Xy (8a), ^tBu (8b)) or (2) with 1 equiv of ^tBuNC to afford 5b. The reaction of 1 (1) with [Tl(acac)] gives [Pd(N¹,C¹-L)(acac)] (9); (2) with chelating ligands N ^∧N affords [Pd(C¹-L)Cl(N^∧N)](N ^∧N = 2,2'-bipyridine = bpy (10), 4,4'-di-tert-butyl-2,2'- bipyridine = dbbpy (11)); (3) with 1 equiv of PPh3 gives, in the same way as with isocyanides, an equilibrium mixture of [Pd(N¹,C ¹-L)Cl(PPh₃)] (12), 1, and trans-[Pd(C¹-L)Cl (PPh₃)₂](13), which is the only product when 2 equiv of PPh₃ is added to the reaction mixture; and(4) with excess PPh ₃ affords the monoketal of dap, C₅H₃N{C(O)Me-2} {C(OMe)₂Me-6}(14), and [Pd(PPh₃)₄]. The crystal structures of complexes 1, 2, 5b, 6a, and 7a have been determined.

Full text of DOI:10.1021/om100079x

3066 Organometallics 2010, 29, 3066–3076
DOI: 10.1021/om100079x
Organometallic Complexes of Palladium(II) Derived from
2,6-Diacetylpyridine Dimethylketal
ꢀ
Jose Vicente,* Aurelia Arcas,* and Francisco Julia-Hernandez
ꢀ
ꢀ
´ ´ ´
Grupo de Quımica Organometalica, Departamento de Quımica Inorganica, Facultad de Quımica,
ꢀ
Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
ꢀ
Delia Bautista‡
SAI, Universidad de Murcia, Apartado 4021, E-30071 Murcia, Spain
Peter G. Jones§
€
Institut fu€r Anorganische und Analytische Chemie der Technischen Universitat Braunschweig, Postfach
3329, 38023 Braunschweig, Germany. ‡ To whom correspondence regarding the X-ray diffraction studies of
complexes 2, 5b, 6a, and 7a should be addressed. E-mail: dbc@um.es. § To whom correspondence regarding
the X-ray diffraction studies of complex 1 should be addressed. E-mail: p.jones@tu-bs.de.
Received February 1, 2010
PdCl2 reacts with 2,6-diacetylpyridine (dap) (1:1) in refluxing MeOH to give the pincer complex
[Pd(O1,N1,C1-L)Cl] (1) and (QH)2[{PdCl2( μ-Cl)}]2 (2), where L is the monoanionic ligand resulting
from deprotonation of the acetyl methyl group of the monoketal of dap and QH is C5H3NH{C-
(OMe)2Me}2-2,6, the diketal of Hdapþ. Reaction of 2 with NEt3 (1:2) in MeOH affords Q =
C5H3N{C(OMe)2Me}2-2,6 (3). Complex 1 reacts with 2 equiv of RNC at 0 °C to give trans-[Pd(C1-
L)Cl(CNR)2] (R = Xy = 2,6-dimethylphenyl (4a), tBu (4b)) but at room temperature affords [Pd(O2,
C2-LR)Cl(CNR)] (R = Xy (5a), tBu (5b)). The ligand LR results from the insertion of one isocyanide
into the Pd-C bond plus a tautomerization process from β-ketoimine to β-ketoenamine and
coordinates in 5 through the carbonyl oxygen atom (O2) and the inserted isocyanide carbon atom
(C2). The reaction of 1 with 1 equiv of RNC at 0 °C leads to a mixture of [Pd(N1,C1-L)Cl(CNR)] (R =
Xy (6a), tBu (6b); 85-90%), 1, and 4, but at room temperature gives the pincer complex [Pd(O1,N1,C2-
t
LR)Cl] (R = Xy (7a), Bu (7b)), resulting from insertion/tautomerization processes similar to that
leading to 5. Complex 7 reacts at 0 °C (1) with 2 equiv of RNC to give trans-[Pd(C2-LR)Cl(CNXy)2] (R
= Xy (8a), tBu (8b)) or (2) with 1 equiv of tBuNC toafford 5b. The reaction of 1 (1)∧with [Tl(acac)] gives
[Pd(N1,C1-L)(acac)] (9); (2) with chelating ligands N∧N affords [Pd(C1-L)Cl(N N)] (N∧N = 2,20-
bipyridine = bpy (10), 4,40-di-tert-butyl-2,20-bipyridine = dbbpy (11)); (3) with 1 equiv of PPh3 gives,
in the same way as with isocyanides, an equilibrium mixture of [Pd(N1,C1-L)Cl(PPh3)] (12), 1, and
trans-[Pd(C1-L)Cl(PPh3)2] (13), which is the only product when 2 equiv of PPh3 is added to the reaction
mixture; and (4) with excess PPh3 affords the monoketal of dap, C5H3N{C(O)Me-2}{C(OMe)2Me-6}
(14), and [Pd(PPh3)4]. The crystal structures of complexes 1, 2, 5b, 6a, and 7a have been determined.
Introduction
interest centered on the possibility that this ligand would
allow us to prepare complexes with mono- and dianionic
ligands resulting from deprotonation reactions like those
shown in Scheme 1. The reactivity of complexes of type A is
expected to be similar to that of other palladium ketonyl
complexes, although it could be modified by the coordina-
tion of the pyridine moiety. Cyclometalation of 2-acetylpyr-
idine has been reported only for Rh(III) and Au(III),7 and
one Pd(II) complex has been prepared (but not isolated) by
using a silyl enol ether of 2-acetylpyridine,8 while [Te(O1,N1,
C1-L)Cl3], obtained by reacting dap with TeCl4, is the only
reported complex with the ligand present in A.9 However, the
reactivity of these species has not been studied. Formation of
mixed enolato/ketonyl O,N,C-complexes (B) is expected in
those containing the dianionic ligand because the strong
C/C10 transphobia11 would destabilize the C,N,C pincer
We are currently involved in the synthesis of ketonyl metal
complexes [M]CH2C(O)R (M = Pd, Pt, Au, Hg, Tl) because
of the great stability that this alkyl ligand confers to their
complexes, their interesting reactivity,1-4 and their roles as
intermediates in organic synthesis.2,5 Recently, we have re-
ported the synthesis and reactivity of [Pd{CH2C(O)Me}Cl]n,
[Pt{CH2C(O)Me}Cl2(η2-C2H4)], and [Pt2{CH2C(O)Me}6( μ-
Cl)3]-, studies that have allowed us to prepare unprecedented
types of metal complexes.3,6
We report here our attempts to prepare ketonyl palladium
complexes derived from 2,6-diacetylpyridine (dap). Our
*Corresponding authors. E-mail: jvs1@um.es (J.V.); aurelia@um.es
(A.A.). Web: http://www.um.es/gqo/.
r
pubs.acs.org/Organometallics
Published on Web 06/28/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 14, 2010 3067
Scheme 1
of olefins.12 It has been reported that some of these PDI
ligands prepared with two different amines have important
effects on the catalytic perfomance of their complexes.13,14
One additional reason for preparing complexes A is their
potential use as catalysts or for the synthesis of complexes
with nonsymmetrical PDI-related monoanionic ligands.
Pincer complexes have attracted great interest because of
their important applications in organic synthesis, homoge-
neous catalysis, bond activation, and design of new materials.15
In spite of the great number of reported Pd(II) pincer com-
plexes, those of type A (C,N,O-pincer) are represented only by
two families derived from 2-alkyl-substituted 8-quinolinols16
or C6H4{NHC(Me)CHC(Me)O}-2 derivatives4 and one com-
plex derived from 8-alkylquinoline-2-carboxylic acid.17
Attempts to prepare complexes of type A were initially
unsuccessful; instead we isolated a family of [C,N,O]-pincer
ketonyl complexes derived from 2,6-diacetylpyridine di-
methylketal when methanol was used as solvent. However,
while studying their reactivity, we found that some of their
isomer. This second functionality would confer on these
complexes the expected reactivity of enolato metal com-
plexes (aldol reactions, for example), but, more interestingly,
the dual and unprecedented nature of these complexes could
lead to novel patterns of reactivity.
The study of the synthesis and reactivity of dap metal
complexes has additional relevance because complexes of
Fe(II) and Co(II) with bis(imino) derivatives of dap (PDI) are
highly active catalysts for polymerization and oligomerization
(11) Vicente, J.; Arcas, A.; Bautista, D.; Jones, P. G. Organometallics
ꢀ
Am. Chem. Soc. 2002, 124, 3848. Vicente, J.; Abad, J. A.; Martínez-
Viviente, E.; Jones, P. G. Organometallics 2002, 21, 4454. Vicente, J.;
Abad, J. A.; Frankland, A. D.; Ramírez de Arellano, M. C. Chem.;Eur. J.
1997, 16, 2127. Vicente, J.; Abad, J. A.; Hernandez-Mata, F. S.; Jones, P. G. J.
ꢀ
1999, 5, 3066. Vicente, J.; Abad, J. A.; Frankland, A. D.; Lopez-Serrano, J.;
Ramírez de Arellano, M. C.; Jones, P. G. Organometallics 2002, 21, 272.
Vicente, J.; Arcas, A.; Bautista, D.; Tiripicchio, A.; Tiripicchio-Camellini, M.
New J. Chem. 1996, 20, 345. Amatore, C.; Bahsoun, A. A.; Jutand, A.;
Meyer, G.; Ntepe, A. N.; Ricard, L. J. Am. Chem. Soc. 2003, 125, 4212.
Crespo, M.; Granell, J.; Solans, X.; Fontbardia, M. J. Organomet. Chem.
2003, 681, 143. Huynh, H. V.; Han, Y.; Jothibasu, R.; Yang, J. A. Organo-
ꢀ
ꢀ
(1) Vicente, J.; Bermudez, M. D.; Chicote, M. T.; Sanchez-Santano,
M. J. J. Chem. Soc., Chem. Commun. 1989, 141. Vicente, J.; Abad, J. A.;
Cara, G.; Jones, P. G. Angew. Chem., Int. Ed. Engl. 1990, 29, 1125. Vicente,
ꢀ
J.; Bermꢀudez, M. D.; Chicote, M. T.; Sanchez-Santano, M. J. J. Chem. Soc.,
Dalton Trans. 1990, 1945. Vicente, J.; Abad, J. A.; Cara, G.; F., G.-J. J. J.
Chem. Soc., Dalton Trans. 1992, 2481. Vicente, J.; Bermꢀudez, M. D.;
Carrillo, M. P.; Jones, P. G. J. Chem. Soc., Dalton Trans. 1992, 1975.
Vicente, J.; Bermꢀudez, M. D.; Carrillo, M. P.; Jones, P. G. J. Organomet.
Chem. 1993, 456, 305. Vicente, J.; Abad, J. A.; Bergs, R.; Jones, P. G.;
Bautista, D. J. Chem. Soc., Dalton Trans. 1995, 3093. Vicente, J.; Abad,
J. A.; Bergs, R.; G., J. P.; Bautista, D. J. Chem. Soc., Dalton Trans. 1995,
3093. Vicente, J.; Chicote, M. T.; Huertas, S.; Ramírez de Arellano, M. C.;
Jones, P. G. Eur. J. Inorg. Chem. 1998, 511. Vicente, J.; Abad, J. A.;
Chicote, M. T.; Abrisqueta, M.-D.; Lorca, J.-A.; Ramírez de Arellano, M. C.
Organometallics 1998, 17, 1564. Vicente, J.; Chicote, M. T.; Rubio, C.;
Ramírez de Arellano, M. C.; Jones, P. G. Organometallics 1999, 18, 2750.
ꢀ
ꢀ
metallics 2009, 28, 5395. Lopez, C.; Caubet, A.; Perez, S.; Solans, X.; Font-
Bardía, M. J. Organomet. Chem. 2003, 681, 82. Ng, J. K. P.; Chen, S.; Li, Y.;
Tan, G. K.; Koh, L. L.; Leung, P. H. Inorg. Chem. 2007, 46, 5100.
(12) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.
(13) Campora, J.; Cartes, M. A.; Rodriguez-Delgado, A.; Naz,
A. M.; Palma, P.; Perez, C. M.; del Rio, D. Inorg. Chem. 2009, 48, 3679.
(14) Ionkin, A. S.; Marshall, W. J.; Adelman, D. J.; Fones, B. B.;
Fish, B. M.; Schiffhauer, M. F. Organometallics 2006, 25, 2978. Small,
B. L.; Brookhart, M. Macromolecules 1999, 32, 2120.
(15) Lipke, M. C.; Woloszynek, R. A.; Ma, L.; Protasiewicz, J. D.
ꢀ
Organometallics 2009, 28, 188. Ines, B.; Sanmartin, R.; Churruca, F.;
ꢀ
ꢀ
Vicente, J.; Arcas, A.; Fernandez-Hernandez, J. M.; Bautista, D. Organo-
Domínguez, E.; Urtiaga, M. K.; Arriortua, M. I. Organometallics 2008,
27, 2833. Bollinger, J. E.; Blacque, O.; Frech, C. M. Chem.;Eur. J. 2008,
14, 7969. Bollinger, J. E.; Blacque, O.; Frech, C. M. Angew. Chem., Int. Ed.
2007, 46, 6514. Gong, J. F.; Zhang, Y. H.; Song, M. P.; Xu, C. Organo-
ꢀ
ꢀ
metallics 2001, 20, 2767. Vicente, J.; Arcas, A.; Fernandez-Hernandez, J. M.;
Sironi, A.; Masciocchi, N. Chem. Commun. 2005, 1267.
(2) Vicente, J.; Bermudez, M. D.; Escribano, J.; Carrillo, M. P.;
ꢀ
ꢀ
Jones, P. G. J. Chem. Soc., Dalton Trans. 1990, 3083. Vicente, J.;
metallics 2007, 26, 6487. Sole, D. Organometallics 2006, 25, 1995. Dupont,
ꢀ
Bermꢀudez, M. D.; Carrion, F. J. Inorg. Chim. Acta 1994, 220, 1.
J.; Consorti, C. S.; Spencer, J. Chem. Rev. 2005, 105, 2527. Albrecht, M.; van
Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750. Singleton, J. T. Tetra-
hedron 2003, 59, 1837. Peris, E.; Crabtree, R. H. Coord. Chem. Rev. 2004,
248, 2239. Bolliger, J. L.; Frech, C. M. Adv. Synth. Catal. 2009, 351, 891.
Gossage, R. A.; Van De Kuil, L. A.; Van Koten, G. Acc. Chem. Res. 1998, 31,
423. Gossage, R. A.; Ryabov, A. D.; Spek, A. L.; Stufkens, D. J.; van Beek,
J. A. M.; van Eldik, R.; van Koten, G. J. Am. Chem. Soc. 1999, 121, 2488.
Leis, W.; Mayer, H. A.; Kaska, W. C. Coord. Chem. Rev. 2008, 252, 1787.
Moreno, I.; SanMartin, R.; Ines, B.; Herrero, M. T.; Dominguez, E. Curr.
Org. Chem. 2009, 13, 878. Pugh, D.; Danopoulos, A. A. Coord. Chem. Rev.
2007, 251, 610. Vicente, J.; Abad, J. A.; Lopez-Serrano, J.; Jones, P. G.;
Najera, C.; Botella-Segura, L. Organometallics 2005, 24, 5044. Bonnet, S.;
van Lenthe, J. H.; Siegler, M. A.; Spek, A. L.; van Koten, G.; Gebbink, R.
Organometallics 2009, 28, 2325. Gagliardo, M.; Selander, N.; Mehendale,
N. C.; van Koten, G.; Gebbink, R.; Szabo, K. J. Chem.;Eur. J. 2008, 14,
4800. Li, J.; Minnaard, A. J.; Gebbink, R.; van Koten, G. Tetrahedron Lett.
2009, 50, 2232. McDonald, A. R.; Dijkstra, H. P.; Suijkerbuijk, B. M. J. M.;
van Klink, G. P. M.; van Koten, G. Organometallics 2009, 28, 4689. O'Leary,
P.; van Walree, C. A.; Mehendale, N. C.; Sumerel, J.; Morse, D. E.; Kaska,
W. C.; van Koten, G.; Gebbink, R. Dalton Trans. 2009, 4289.
ꢀ
ꢀ
(3) Vicente, J.; Arcas, A.; Fernandez-Hernandez, J. M.; Bautista, D.
ꢀ
ꢀ
Organometallics 2006, 25, 4404. Vicente, J.; Arcas, A.; Fernandez-Hernandez,
J. M.; Aullon, G.; Bautista, D. Organometallics 2007, 26, 6155. Vicente, J.;
ꢀ
ꢀ
Arcas, A.; Fernandez-Hernandez, J. M.; Bautista, D. Organometallics 2008, 27,
3978.
(4) Vicente, J.; Chicote, M. T.; Martı
Bautista, D. Organometallics 2008, 27, 3254.
nez-Martınez, J. A.; Jones, P. G.;
´ ´
(5) Ito, Y.; Hirao, T.; Saegusa, T. J. Org. Chem. 1978, 43, 1011.
Carfagna, C.; Musco, A.; Sallese, G.; Santi, R.; Fiorani, T. J. Org. Chem.
1991, 56, 261. Tsuji, J. Palladium Reagents and Catalysts; John Wiley:
Chinchester, U.K., 1995. Palucki, M.; Buchwald, S. L. J. Am. Chem. Soc.
1997, 119, 11108. Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1740. Culkin, D. A.; Hartwig, J. F. Acc.
Chem. Res. 2003, 36, 234. Sodeoka, M.; Hamashima, Y. Bull. Chem. Soc.
Jpn. 2005, 78, 941. Chen, G. S.; Kwong, F. Y.; Chan, H. O.; Yu, W. Y.; Chan,
A. S. C. Chem. Commun. 2006, 1413.
(6) Vicente, J.; Arcas, A.; Fernandez-Hernandez, J. M.; Bautista, D.;
Jones, P. G. Organometallics 2005, 24, 2516.
(7) Boutadla, Y.; Al-Duaij, O.; Davies, D. L.; Griffith, G. A.; Singh,
K. Organometallics 2009, 28, 433. Fan, D.; Melendez, E.; Ranford, J. D.;
Lee, P. F.; Vittal, J. J. J. Organomet. Chem. 2004, 689, 2969.
(8) Fujii, A.; Hagiwara, E.; Sodeoka, M. J. Am. Chem. Soc. 1999, 121,
5450.
ꢀ
ꢀ
(16) Billodeaux, D. R.; Fronczek, F. R.; Yoneda, A.; Newkome,
G. R. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1998, C54,
1439. Yoneda, A.; Newkome, G. R.; Theriot, K. J. J. Organomet. Chem.
1991, 401, 217. Yoneda, A.; Ouchi, M.; Hakushi, T.; Newkome, G. R.;
Fronczek, F. R. Chem. Lett. 1993, 709. Yoneda, A.; Hakushi, T.; Newkome,
G. R.; Fronczek, F. R. Organometallics 1994, 13, 4912.
(9) Gysling, H. J.; Luss, H. R.; Gardner, S. A. J. Organomet. Chem.
1980, 184, 417.
(10) Vicente, J.; Arcas, A.; Galvez-Lopez, M.-D.; Julia-Hernandez,
ꢀ
ꢀ
ꢀ
ꢀ
(17) Deeming, A. J.; Rothwell, I. P. J. Organomet. Chem. 1981, 205,
117.
F.; Bautista, D.; Jones, P. G. Organometallics 2008, 27, 1582.

3068 Organometallics, Vol. 29, No. 14, 2010
Vicente et al.
Chart 1
Scheme 2
derivatives decompose to give the desired complexes, which
provided the necessary information for their rational synth-
esis. In this paper we report the synthesis of these dimethyl-
ketal derivatives and their reactivity toward isocyanides.
There is only one related precedent for these complexes,
2-lithium phenyl dimethylketal, which is described as a non-
isolated intermediate obtained from the dimethylketal of
2-bromoacetophenone via metal-halogen exchange.18
1
IR (cm-1): ν(CdO) 1684, ν(CN) 1603, ν(PdCl) 321. H NMR
3
(400 MHz, CDCl3): δ 8.14 (t, 1H, H4, JHH = 8 Hz), 7.80
(dd, 1H, H3, 3JHH = 8 Hz, 4JHH = 1.2 Hz), 7.63 (dd, 1H, H5,
3JHH = 8 Hz, 4JHH = 1.2 Hz), 3.52 (s, 2 H, CH2), 3.42 (s, 6 H,
OMe), 1.77 (s, 3 H, Me). 13C{1H} NMR (100.8 MHz, CDCl3): δ
203.7 (CO), 158.5 (C7), 152.7 (C8), 139.8 (C4), 126.4 (C5), 123.6
(C3), 106.9 (C6), 51.5 (MeO), 30.7 (C1), 25.0 (Me). Anal. Calcd
for C11H14NO3ClPd: C, 37.74; H, 4.03; N, 4.00. Found: C,
37.63; H, 3.97; N, 3.95. Single crystals of 1 were obtained by slow
evaporation of a MeOH solution of 1.
Experimental Section
General Procedures. The reactions were carried out without
precautions to exclude light or atmospheric oxygen or moisture.
Melting points were determined on a Reicher apparatus and are
uncorrected. Elemental analyses were carried out with a Carlo
Erba 1106 microanalyzer. IR spectra were recorded on a Perkin-
Elmer 16F PC FT-IR spectrometer with Nujol mulls between
polyethylene sheets. NMR spectra were recorded on a Bruker
AC 200 or Avance 300 or 400 spectrometer at room tempera-
ture. Chemical shifts were referred to TMS (1H, 13C) or H3PO4
(31P). When needed, NMR assignments were performed with
the help of APT, HMQC, and HMBC techniques. Chart 1
shows the atom numbering used in the NMR assignments.
Synthesis of C5H3N{C(OMe)2Me}2 (3). To a suspension of 2
(2466.9 mg, 2.63 mmol) in MeOH (30 mL) was added NEt3
(733 μL, 5.26 mmol). The reaction mixture was stirred for 24 h
and then concentrated to dryness. The residue was extracted
with n-pentane (2 ꢀ 20 mL), and the solution was concentrated
to dryness to give 3 as a colorless solid. Yield: 1246.0 mg, 93%.
Mp: 103-104 °C. IR (cm-1): ν(CN) 1582. 1H NMR (300 MHz,
CDCl3): δ 7.71-7.57 (m, 3H, py), 3.19 (s, 12H, MeO), 1.66 (s,
6H, Me). 13C{1H} NMR (50.30 MHz, CDCl3): δ 159.7 (o-C),
136.2 ( p-C), 120.4 (m-C), 101.8 (CMe), 49.1 (OMe), 23.6 (Me).
Anal. Calcd for C13H21NO4: C, 61.16; H, 8.29; N, 5.49. Found:
C, 61.05; H, 8.57; N, 5.58.
t
The R groups (Xy, Bu) of inserted and coordinated isocya-
t
nides are distinguished by using the notation Xyi, Bui and
tBuc, Xyc, respectively.
Synthesis of [Pd(O1,N1,C1-L)Cl] (1) and (C5H3NH{C(OMe)2-
Me}-2,6)2[{PdCl2( μ-Cl)}]2 (2). To a suspension of PdCl2 (390.6
mg, 2.20 mmol) in MeOH (20 mL) were added 2,6-diacetylpyr-
idine (359.3 mg, 2.20 mmol) and NEt3 (57 μL, 0.40 mmol). The
suspension was refluxed for 95 min and then filtered through
Celite. The orange filtrate was concentrated (2 mL), and Et2O
(1 mL) was added. The resulting precipitate was filtered off and
air-dried. The solid was extracted with CHCl3 (4 ꢀ 5 mL), giving
solution A (used to prepare 1) and a solid, which was air-dried,
giving orange 2. Yield: 92.4 mg, 18% (based on the stoichio-
metry shown in Scheme 2). Mp: 131-132 °C. IR (cm-1): ν(NH)
3248, 3217, ν(CN) 1617, ν(PdCl) 346, 334. 1H NMR (300 MHz,
Synthesis of trans-[Pd(C1-L)Cl(CNXy)2] 0.5H2O (4a). To a
3
cooled (0 °C) solution of 1 (23.3 mg, 0.07 mmol) in CHCl3
(5 mL) was added XyNC (20.2 mg, 0.15 mmol). After 5 min of
stirring the solution was concentrated to dryness. The residue
was vigorously stirred in a cooled (0 °C) mixture of Et2O (2 mL)
and n-pentane (6 mL). The resulting suspension was filtered off,
and the solid washed with n-pentane and air-dried to give 4a as a
pale yellow solid. Yield: 37.4 mg, 90%. Mp: 134-135 °C. IR
(cm-1): ν(NtC) 2192, ν(CdO) 1647, ν(CdN) 1579, ν(PdCl)
1
280. H NMR (400 MHz, CDCl3): δ 7.92-7.90 (m, 1H, ABC
system), 7.77-7.72 (m, 2H, ABC system), 7.27-7.11 (m, 6H,
Xy), 3.73 (s, 2H, CH2), 3.08 (s, 6H, OMe), 2.49 (s, 12H, Me, Xy),
1.48 (s, 3H, Me). The 13C{1H} NMR spectrum could not be
registered because it transforms into 5a during the acquisition
time. Anal. Calcd for C29H33N3O3.5ClPd: C, 56.05; H, 5.35; N,
6.76. Found: C, 55.91; H, 5.29; N, 6.81
3
MeCN-d3): δ 12.55 (br, NH), 8.75 (t, 1H, H4, JHH = 8 Hz),
8.13 (d, 2 H, H3,5, 3JHH = 8 Hz), 3.30 (s, 12H, OMe), 1.71 (s,
6H, Me). 13C{1H} NMR (75.4 MHz, MeCN-d3): δ 150.4 (C4),
126.1 (C3,5), 100.2 (C6), 50.8 (MeO), 24.7 (Me). Anal. Calcd for
C26H44N2O8Cl6Pd2: C, 33.29; H, 4.72; N, 2.98. Found: C, 33.08;
H, 4.92; N, 2.90. Single crystals of 2 were obtained by slow
evaporation of a MeOH solution of 2.
Synthesis of trans-[Pd(C1-L)Cl(CNtBu)2] (4b). To a cooled
(0 °C) solution of 1 (18.7 mg, 0.05 mmol) in CH2Cl2 (6 mL) was
added tBuNC (11.1 mg, 0.13 mmol), and the mixture was stirred
for 20 min. Concentration to dryness, addition of n-pentane
(6 mL), and vigorous stirring led to a suspension. The solid was
filtered off, washed with Et2O, and air-dried to give 4b as a
colorless solid. Yield: 26.2 mg, 96%. Mp: 124-125 °C. IR
(cm-1): ν(NtC) 2211, ν(CdO) 1651, ν(CdN) 1579, ν(PdCl)
Solution A was concentrated (1 mL) and column chromato-
graphed on silica gel using CHCl3 as eluent. The first collected
fraction was concentrated (1 mL). Addition of Et2O (4 mL) and
n-pentane (4 mL) gave a suspension, which was filtered off to
give complex 1 as a yellow solid. Yield: 267.1 mg, 69% (based
on the stoichiometry shown in Scheme 2). Mp: 137-138 °C.
1
289. H NMR (200 MHz, CDCl3): δ 7.95-7.70 (m, 3H, ABC
system), 3.35 (s, 2H, CH2), 3.22 (s, 6H, OMe), 1.72 (s, 3H, Me),
1.52 (s, 18H, Bu). The 13C{1H} NMR spectrum could not be
registered because it transforms into 5b during the acquisition
t
(18) Morrow, G. W.; Wang, S.; Swenton, J. S. Tetrahedron Lett.
1988, 29, 3441.

Article
Organometallics, Vol. 29, No. 14, 2010 3069
time. Anal. Calcd for C21H32N3O3ClPd: C, 48.85; H, 6.25; N,
8.14. Found: C, 48.53; H, 6.58; N, 8.07.
chromatography using silica gel (70-200 μm) with CH2Cl2/
Et2O (7:1) as eluent. The yellow fraction at Rf = 0.26 was
collected and extracted with acetone (3 ꢀ 20 mL) to give a
solution, which was concentrated to dryness. The residue was
stirred with Et2O (2 mL) and n-pentane (8 mL). The suspension
was filtered, and the solid was washed with n-pentane and air-
dried to give 7a as an orange solid. Yield: 98.3 mg, 68%. Mp:
180 °C dec. IR (cm-1): ν(NH) 3321, ν(CdN, py) 1609, ν(CdO)
1566, ν(CdNH) 1504, ν(PdCl) 334. 1H NMR (300 MHz,
Synthesis of [Pd(O2,C2-LXy)Cl(CNXy)] (5a). To a cooled
solution (0 °C) of 7a (22.9 mg, 0.05 mmol) in CH2Cl2 (8 mL)
was added XyNC (6.3 mg, 0.05 mmol), and the mixture
was stirred for 10 min. Concentration (1 mL) and addition of
n-pentane (9 mL) gave a suspension; the solid was filtered off,
washed with n-pentane, and air-dried to give a mixture (26.2 mg)
of 5a, 7a, and 8a (81:15:4) with traces of XyNC. 1H NMR
3
3
4
(300 MHz, CDCl3) of 5a: δ 8.20 (dd, 1H, H3 or 5, JHH
=
CDCl3): δ 8.69 (dd, 1H, H3, JHH = 8 Hz, JHH = 1.2 Hz),
8.65 (br, 1H, NH), 8.15 (t, 1H, H4, 3JHH = 8 Hz), 7.59 (dd, 1H,
H5, 3JHH = 8 Hz, 4JHH =1.2 Hz), 7.13-7.03 (m, ABC system,
3H, Xy), 4.67 (s, 1H, H1), 3.47 (s, 6H, MeO), 2.25 (s, 6H, Me,
Xy) 1.92 (s, 3H, Me). 13C{1H} NMR (75.45 MHz, CDCl3): δ
181.9 (CO), 164.9 (C2), 158.2 (C7), 150.5 (C8), 140.0 (C4), 138.2
(C-N, Xy), 135.0 (o-C(Xy)), 128.3 (m-C(Xy)), 127.5 ( p-C(Xy)), 126.2
(C3), 124.7 (C5), 108.5 (C6), 93.5 (C1), 52.2 (MeO), 26.3 (Me), 18.3
(Me, Xy). Anal. Calcd for C20H23O3N2ClPd: C, 49.91; H, 4.82; N,
5.82. Found: C, 49.91; H, 5.03; N, 5.74. Single crystals of 7a were
obtained by slow diffusion of n-pentane into a CHCl3 solution of 7a.
Synthesis of [Pd(O1,N1,C2-LBu)Cl] (7b). To a solution of 1
7.5 Hz, 4JHH = 1.2 Hz), 7.75 (t, 1H, H4, 3JHH = 7.5 Hz), 7.67
(dd, 1H, H5 or 3, 3JHH = 7.5 Hz, 4JHH = 1.2 Hz), 7.30-7.20 (m,
6H, Xy), 5.86 (d, 1H, H1, J = 1 Hz), 3.12 (s, 6H, MeO), 2.52 (s,
6H, Me, Xyc), 2.28 (s, 6H, Me, Xyi), 1.51 (s, 3H, Me).
Synthesis of [Pd(O2,C2-LBu)Cl(CNtBu)] (5b). To a solution of
t
1 (129.4 mg, 0.37 mmol) in CHCl3 (15 mL) was added BuNC
(3.43 mL, 226.2 mM solution, 0.78 mmol). The solution was
stirred for 4.5 days at room temperature and then concentrated
to dryness. The residue was purified by preparative TLC chro-
matography on silica gel (70-200 μm) using CH2Cl2/Et2O (1:2)
as eluent. The first fraction (Rf = 0.50) was collected and
extracted with acetone (3 ꢀ 15 mL) to give a solution that was
concentrated to dryness. The residue was dissolved in CH2Cl2,
and anhydrous MgSO4 was added. The resulting suspension was
stirred and filtered. The filtrate was concentrated to dryness,
and the residue was recrystallized from Et2O/n-pentane, to give
5b as a yellow solid. Yield: 150.9 mg, 79%. Mp: 240 °C dec. IR
(cm-1): ν(CtN) 2211, ν(CdO) 1590, ν(CdN) 1513, ν(PdCl)
t
(69.6 mg, 0.20 mmol) in CHCl3 (15 mL) was added BuNC
(924 μL, 226.2 mM CHCl3 solution, 0.21 mmol). The yellow
solution was refluxed for 16 h, and the resulting solution was
concentrated to dryness. The resulting solid was purified by
means of silica gel (70-200 μm) preparative TLC chromatog-
raphy using CH2Cl2/Et2O (3:1) as eluent. The yellow fraction at
Rf = 0.14 was collected and extracted with acetone (3 ꢀ 20 mL),
and the solution was concentrated to dryness. The residue was
stirred with Et2O (2 mL) and n-pentane (8 mL). The suspension
was filtered and the solid washed with n-pentane and air-dried to
give 7b as a yellow solid. Yield: 79.8 mg, 89%. Mp: 172-173 °C.
IR (cm-1): ν(NH) 3334, ν(CdN, py) 1607, ν(CdO) 1560,
281. 1H NMR (400 MHz, CDCl3): δ 8.14 (dd, 1H, H3, 3JHH
7.6 Hz, 4JHH = 1 Hz), 7.75 (t, 1H, H4, 3JHH = 7.6 Hz), 7.69 (dd,
=
3
4
1H, H5, JHH = 7.6 Hz, JHH = 1 Hz), 6.45 (d, 1H, H1, J =
1 Hz), 6.00 (br, 1H, NH), 3.19 (s, 6H, MeO), 1.66 (s, 3H, Me),
1.61 (br, 9H, Me, tBui), 1.48 (s, 9H, Me, tBuc). 13C{1H} NMR
(100.81 MHz, CDCl3): δ 196.6 (CO), 190.5 (C2), 159.1 (C7),
151.9 (C8), 136.5 (C4), 127.5 (t, CNtBu, 1JCN = 20 Hz), 123.4
1
ν(CdNH) 1534, ν(PdCl) 321. H NMR (400 MHz, CDCl3): δ
8.69 (dd, 1H, H3, 3JHH = 7.6 Hz, 4JHH = 1.2 Hz), 8.13 (t, 1H,
3
c
H4, JHH = 7.6 Hz), 7.63 (br, 1H, NH), 7.55 (dd, 1H, H5,
(C5), 121.7 (C3), 105.1 (C1), 101.6 (C6), 59.3 (br, CMe3 ), 56.5
(CMe3 ), 49.2 (OMe), 30.2 (Me, tBuc), 29.4 (Me, tBui), 23.0 (Me).
3JHH = 7.6 Hz, 4JHH = 1.2 Hz), 5.17 (br, 1H, H1), 3.41 (s, 6H,
MeO), 1.88 (s, 3H, Me), 1.42 (s, 9H, tBu). 13C{1H} NMR (100.81
MHz, CDCl3): δ 180.8 (br, CO), 164.8 (br, C2), 158.0 (C7), 150.6
(C8), 139.9 (C4), 126.0 (C3), 124.5 (C5), 108.0 (C6), 94.2 (C1),
55.6 (CMe3), 52.1 (MeO), 29.1 (CMe3), 26.1 (Me). Anal. Calcd
for C16H25O4N2ClPd: C, 42.59; H, 5.58; N, 6.20. Found: C,
42.70; H, 5.35; N, 6.35.
i
Anal. Calcd for C21H32N3O3ClPd: C, 48.85; H, 6.25; N, 8.14.
Found: C, 48.56; H, 6.25; N, 8.15. Single crystals were obtained
by slow diffusion of a mixture Et2O/n-hexane into a toluene
solution of 5b (1:1:1).
Synthesis of [Pd(N1,C1-L)Cl(CNXy)] (6a). To a cooled (0 °C)
solution of 1 (44.5 mg, 0.13 mmol) in CHCl3 (3 mL) was added
XyNC (16.7 mg, 0.13 mmol), and the resulting pale yellow
solution was stirred for 30 min and concentrated (1 mL).
Addition of n-pentane (4 mL) gave a suspension; the solid was
filtered off, washed with n-pentane, and air-dried to give a
mixture (56.2 mg) of 6a, 1, and 4a (85:9:6) with traces of XyNC
that could not be separated. 1H NMR (400 MHz, CDCl3) of 6a:
Synthesis of trans-[Pd(C2-LXy)Cl(CNXy)2] 1/4CHCl3 (8a).
3
To a cooled (0 °C) solution of 7a (50.7 mg, 0.11 mmol) in CHCl3
(7 mL) was added XyNC (29.0 mg, 0.22 mmol). The solution
was stirred for 5 min and concentrated to dryness. The residue
was dissolved in Et2O, and n-pentane was added. The suspen-
sion was filtered and the solid washed with n-pentane and air-
dried to give 8a as a pale yellow solid. Yield: 69.2 mg, 85%. Mp:
125-126 °C. IR (cm-1): ν(NtC) 2175, ν(CdO) 1567, ν(PdCl)
285. 1H NMR (400 MHz, CDCl3): δ 13.68 (br, 1H, NH), 8.12 (dd,
δ 8.06 (t, 1H, H4, 3JHH = 8 Hz), 7.94 (dd, 1H, H3 or 5, 3JHH
8 Hz, JHH = 1.2 Hz), 7.73 (dd, 1H, H5 or 3, JHH = 8 Hz,
4JHH = 1.2 Hz), 7.26-7.11 (m, 3H, Xy), 3.44 (s, 2H, CH2), 3.27
(s, 6H, OMe), 2.49 (s, 6H, Me, Xy), 2.03 (s, 3H, Me).
=
4
3
1H, H3, 3JHH = 7.6 Hz, 4JHH = 1.2 Hz), 7.80 (t, 1H, H4, 3JHH
=
Synthesis of [Pd(N1,C1-L)Cl(CNtBu)] (6b). To a cooled (0 °C)
solution of 1 (30.2 mg, 0.09 mmol) in CHCl3 (4 mL) was added
tBuNC (400 μL of a 226.2 mM CHCl3 solution, 0.09 mmol). The
resulting pale yellow solution was stirred for 20 min and con-
centrated (1 mL). Addition of n-pentane (4 mL) gave a suspen-
sion; the solid was filtered off, washed with n-pentane, and air-
dried to give a mixture (32.1 mg) of 6b, 1, and 4b (84:7:9) with
traces oftBuNCthatcouldnot beseparated. 1H NMR(400 MHz,
CDCl3) of 6b: δ 8.02 (t, 1H, H4, 3JHH = 8 Hz), 7.90 (dd, 1H, H3
7.6 Hz), 7.72 (dd, 1H, H5, 3JHH =7.6Hz, 4JHH =1.2Hz), 7.22 (s,
1H, H1), 7.25-6.95 (m, 9H, Xy), 3.19 (s, 6H, MeO), 2.37 (s, 6H,
Me, Xyi), 2.32 (s, 12H, Me, Xyc), 1.71 (s, 3H, Me). 13C{1H} NMR
(100.81 MHz, CDCl3):δ180.1 (C2), 178.5(CO), 158.9(C7), 155.5
(C8), 141.4 (br, CtN), 141.5 (Cipso, Xyi), 136.6 (C4), 136.2 (o-C,
Xyc), 134.7 (o-C, Xyi), 130.3 ( p-C, Xyc), 128.4 (m-C, Xyi), 128.0
(m-C, Xyc), 126.7 ( p-C, Xyi), 122.3 (C5), 120.9 (C3), 102.5 (C1),
101.8 (C6), 49.0 (OMe), 23.2 (Me), 19.3 (Me, Xyi), 18.7 (Me,
Xyc). Anal. Calcd for C38.25H41.25N4O3Cl1.75Pd: C, 59.40; H,
5.38; N, 7.24. Found: C, 59.44; H, 5.13; N, 7.50.
or5, 3JHH = 8 Hz, 4JHH = 1.2 Hz), 7.70 (dd, 1H, H5or3, 3JHH
=
8 Hz, 4JHH = 1.2 Hz), 3.27 (s, 2H, CH2), 3.24 (s, 6H, OMe), 1.99
(s, 3H, Me), 1.55 (s, 9H, tBu).
Synthesis of trans-[Pd(C2-LXy)Cl(CNtBu)2] 1/4CHCl3 (8b).
3
To a cooled (0 °C) solution of 7b (24.8 mg, 0.06 mmol) in CHCl3
(6 mL) was added tBuNC (531 μL, 226.2 mM, 0.12 mmol). The
solution was stirred for 5 min at 0 °C and concentrated to
dryness. The residue was dissolved in Et2O, and n-pentane
was added. The suspension was filtered and the solid washed
with n-pentane and air-dried to give 8b as a pale yellow solid.
Synthesis of [Pd(O1,N1,C2-LXy)Cl] (7a). To a solution of 1
(104.6 mg, 0.30 mmol) in CHCl3 (15 mL) was added XyNC
(47.1 mg, 0.36 mmol). The pale yellow solution was stirred for 10
days to give an orange solution, which was concentrated to
dryness. The resulting solid was purified by preparative TLC

3070 Organometallics, Vol. 29, No. 14, 2010
Vicente et al.
Yield: 32.6 mg, 91%. Mp: 127-128 °C. IR (cm-1): ν(NtC)
2208, ν(CdO) 1538, ν(PdCl) 290. 1H NMR (400 MHz, CDCl3):
δ 12.96 (br, 1H, NH), 8.02 (dd, 1H, H5, 3JHH = 8 Hz, 4JHH = 1.2
Hz), 7.75 (t, 1H, H4, 3JHH = 8 Hz), 7.65 (dd, 1H, H3, 3JHH = 8
Scheme 3
4
Hz, JHH = 1.2 Hz), 6.86 (s, 1H, H1), 3.21 (s, 6H, MeO), 1.75
(s, 3H, Me), 1.64 (s, 9H, tBui), 1.45 (s, 18H, tBuc). 13C{1H} NMR
(100.81 MHz, CDCl3): δ 178.3 (CO), 176.0 (C2), 158.6 (C7), 156.3
(C8), 136.4 (C4), 130 (m, CtN), 121.8 (C3), 120.5 (C5), 101.9 (C6),
99.1 (C1), 58.5 (CNH), 53.0 (CMe3 ), 49.1 (MeO), 31.3 (Me, tBui),
c
29.8 (Me, tBuc), 23.3 (Me). Anal. Calcd for C26.25H41.25N4O3Cl1.75
-
Pd: C, 50.10; H, 6.61; N, 8.90. Found: C, 49.89; H, 6.57; N, 9.19.
Synthesis of [Pd(N1,C1-L)(O,O-acac)] (9). To a solution of 1
(39.7 mg, 0.11 mmol) in CHCl3 (8 mL) was added Tl(acac)19
(34.3 mg; 0.11 mmol). The suspension was filtered through
Celite, and the filtrate was concentrated to dryness. The residue
was crystallized from Et2O (2 mL) and n-pentane (7 mL). The
crystals were filtered off, washed with n-pentane, and air-dried
to give 9 as a yellow solid. Yield: 44.6 mg, 96%. Mp: 159-
Scheme 4
1
160 °C. IR (cm-1): ν(CdO) 1673, ν(CO, acac) 1579, 1515. H
NMR (200 MHz, CDCl3): δ 7.96 (t, 1H, H4, 3JHH = 7.6 Hz),
7.75 (dd, 1H, H3, 3JHH = 7.6 Hz, 4JHH = 1.6 Hz), 7.64 (dd, 1H,
H5, 3JHH = 7.6 Hz, 4JHH = 1.6 Hz), 5.28 (s, 1H, CH, acac), 3.43
(s, 2H, H1), 3.25 (s, 6H, OMe), 1.92 (s, 6H, Me, acac), 1.84 (s,
3H, Me). 13C{1H} NMR (100.8 MHz, CDCl3): δ 192.9 (br, CO),
186.8 (br, CO, acac), 185.3 (br, CO, acac), 163.3 (C7), 160.3
(C8), 139.4 (C4), 124.8 (C5), 120.2 (C3), 101.2 (C6), 99.6 (CH,
acac), 49.3 (OMe), 40.5 (C1), 27.2 (br, Me, acac), 26.7 (br, Me,
acac), 24.4 (Me). Anal. Calcd for C16H21NO5Pd: C, 46.44; H,
5.12; N, 3.39. Found: C, 46.32; H, 5.01; N, 3.44
Synthesis of [Pd(C1-L)Cl(bpy)] (10). To a solution of 1 (17.9
mg, 0.05 mmol) in acetone (4 mL) was added bpy (8.0 mg, 0.05
mmol). After stirring for 20 min, the suspension was filtered and
the resulting yellow solid was washed with acetone and air-dried
to give 10. Yield: 21.2 mg, 82%. Mp: 224-225 °C. IR (cm-1):
stirred for 20 min and concentrated (1 mL). Addition of Et2O
(5 mL) gave a suspension; the solid was filtered off, washed with
Et2O, and air-dried to give a mixture (60.9 mg) of 12, 1, and 13
(90:5:5) that could not be separated. NMR data of 12:1H(300MHz,
CDCl3): δ 7.95 (t, 1H, H4, 3JHH = 7.8 Hz), 7.86 (dd, 1H, H3 or H5,
3JHH = 7.8 Hz, 4JHH = 1.2 Hz), 7.76-7.41 (m, 16H, H5 or H3 þ
PPh3), 3.30 (br, 6H, OMe), 2.89 (br, 2H, H1), 2.03 (s, 3H, Me).
31P{1H} NMR (121.5 MHz, CDCl3): δ 36.8 (s).
1
ν(CdO) 1608, ν(CN) 1580, ν(PdCl) 336. H NMR (400 MHz,
3
CD2Cl2): δ 9.58 (d, 1H, bpy, JHH = 5 Hz), 9.14 (d, 1H, bpy,
3JHH = 5 Hz), 8.05 (m, 3H, bpy þ 1H, py), 7.94 (d, 1H, py,
3JHH = 8 Hz), 7.76 (t, 1H, H4, 3JHH = 8 Hz), 7.70 (m, 2H, bpy),
7.52 (t, 1H, bpy, 3JHH = 5 Hz), 3.59 (s, 2H, CH2), 3.15 (s, 6H,
MeO), 1.63 (s, 3H, Me). Anal. Calcd for C21H22N3O3ClPd: C,
49.82; H, 4.38; N, 8.30. Found: C, 49.94; H, 4.41; N, 8.23.
Synthesis of [Pd(C1-L)Cl(dbbpy)] 1/2H2O (11). To a solution
Synthesis of trans-[Pd(C1-L)Cl(PPh3)2] (13). To a cooled solu-
tion (0 °C) of 1 (59.3 mg, 0.17 mmol) in CH2Cl2 (8 mL) was added
PPh3 (90.6 mg, 0.35 mmol). The resulting yellow solution was stir-
red for 10 min and concentrated (1 mL). Addition of Et2O (2 mL)
and n-pentane (8 mL) gave a suspension; the solid was filtered off,
washed with n-pentane, and air-dried to give 13 (140.3 mg)
contamined with a product containing PPh3 that we could not
remove. NMR data of 13:1H (300 MHz, CDCl3), δ7.94 (t, 1H, H4,
3
of 1 (61.8 mg, 0.18 mmol) in CH2Cl2 (6 mL) was added dbbpy
(4,40-di-tert-butyl-2,20-bipyridine, 47.5 mg, 0.18 mmol). The
resulting solution was stirred (5 min) and concentrated (1 mL).
Addition of n-pentane (8 mL) gave a suspension, which was
cooled (-4 °C) for 30 min and filtered. The solid was washed
with n-pentane and air-dried to give 11 as a pale yellow solid.
Yield: 104.1 mg, 94%. Mp: 218-219 °C. IR (cm-1): ν(CdO)
1642, ν(CN) 1614, 1583, 1545, ν(PdCl) 337. 1H NMR (400 MHz,
CDCl3): δ 9.54 (d, 1H, dbbpy, 3JHH = 6 Hz), 9.04 (d, 1H, dbbpy,
3JHH = 6 Hz), 7.99 (dd, 1H, H5, 3JHH = 8 Hz, 4JHH = 2 Hz), 7.90
(d, 1H, dbbpy, 4JHH = 2 Hz), 7.87 (d, 1H, dbbpy, 4JHH = 2 Hz),
7.73 (t, 1H, H4, 3JHH = 8 Hz, 4JHH = 2 Hz), 7.69 (dd, 1H, H3,
3JHH = 8 Hz, 4JHH = 2 Hz), 7.66 (dd, 1H, dbbpy, 3JHH = 6 Hz,
4JHH = 2 Hz), 7.43 (dd, 1H, dbbpy, 3JHH = 6 Hz, 4JHH = 2 Hz),
3.69 (s, 2H, CH2), 3.21 (s, 6H, MeO), 1.72 (s, 3H, Me), 1.45 (s, 9H,
3JHH = 7.8 Hz), 7.82 (dd, 1H, H3 or H5, 3JHH = 7.8 Hz, 4JHH
=
1.2 Hz), 7.80-7.40 (m, 16H, H5 or H3 þ PPh3), 3.45 (br, 2H, H1),
3.20 (br, 6H, OMe), 1.68 (s, 3H, Me). 31P{1H} NMR (121.5 MHz,
CDCl3): δ 23.8 (s).
Synthesis of C5H3N{C(O)Me-2}{C(OMe)2Me-6} (14). To a
solution of 1 (15.2 mg, 0.04 mmol) in CDCl3 (0.8 mL) in a NMR
tube was added PPh3 (57.7 mg, 0.22 mmol). After 5 min at room
temperature, a 1H NMR spectrum was recorded, showing
signals that we assign to 14. In addition, the 31P{1H} NMR
spectrum showed resonances due to [Pd(PPh3)4] and its disso-
ciation products [Pd(PPh3)3] and PPh3. 14 could not be purified
by recrystallization because of the excess of PPh3; TLC chro-
t
tBu), 1.39 (s, 9H, Bu). 13C{1H} NMR (100.8 MHz, CDCl3): δ
205.8 (CO), 163.6 (C, dbbpy), 163.2 (C, dbbpy), 158.7 (C7), 157.1
(C8), 156.3 (C, dbbpy), 153.9 (C, dbbpy), 151.9 (CH, dbbpy),
149.2 (CH, dbbpy), 136.4 (C4), 124.2 (CH, dbbpy), 123.2 (CH,
dbbpy), 122.8 (C3), 121.3 (C5), 118.4 (CH, dbbpy), 117.6 (CH,
dbbpy), 101.9 (C6), 49.2 (MeO), 35.4 (CMe3), 30.3 (CMe3), 30.2
(CMe3), 23.7(Me), 21.3(C1). Anal. Calcd for C29H39N3O3.5ClPd:
C, 55.51; H, 6.26; N, 6.70. Found: C, 55.68; H, 6.26; N, 6.63.
Synthesis of [Pd(N1,C1-L)Cl(PPh3)] (12). To a cooled solution
(0 °C) of 1 (35.4 mg, 0.10 mmol) in CH2Cl2 (5 mL) was added
PPh3 (26.5 mg, 0.10 mmol). The resulting yellow solution was
matography in silica gel led to hydrolysis to give dap. 1H NMR
3
(400 MHz, CDCl3) of 14: δ 7.94 (dd, 1H, H3 or H5, JHH
=
7.4 Hz, 4JHH = 1 Hz), 7.85 (dd, 1H, H5 or H3, 3JHH = 7.4 Hz,
4JHH = 1 Hz), 7.80 (t, 1H, H4, JHH = 7.4 Hz), 3.21 (s, 6H,
OMe), 2.75 (s, 3H, Me), 1.71 (s, 3H, Me).
3
X-ray Structure Determinations. Complexes 2, 5b, 6a, and 7a
were measured on a Bruker Smart APEX diffractometer and 1 on
an Oxford Diffraction Nova O diffractometer. Data were col-
lected in ω scan mode using monochromated Mo KR radiation
(19) Vicente, J.; Chicote, M. T. Inorg. Synth. 1998, 32, 172.

Article
Organometallics, Vol. 29, No. 14, 2010 3071
Scheme 5
Figure 1. Ellipsoid representation of 1 (50% probability).
Selected bond lengths (A) and angles (deg): Pd-N 1.9752(19),
Pd-C(1) 2.000(2), Pd-O(1) 2.2149(16), Pd-Cl 2.3040(5), Pd-
Pd#1 3.3460(3), O(3)-C(2) 1.217(3), C(1)-C(2) 1.497(3), C(2)-
C(3) 1.499(3), N-Pd-C(1) 83.85(9), N-Pd-O(1) 76.32(7),
C(1)-Pd-Cl 96.63(7), O(1)-Pd-Cl 103.03(4).
for 2, 5b, 6a, and 7a and mirror-focused Cu KR radiation
(λ = 1.54184 A) for 1. Absorption corrections were applied on
the basis of multiscans (program SADABS for 2, 5b, 6a, and 7a
and CrysAlis RED for 1). All structures were refined anisotro-
pically on F2 using the program SHELXL-97.20 NH hydrogens
were refined freely, but with a DFIX restraint to the NH distance
in 5b. The ordered methyl groups were refined as rigid groups
(AFIX 137), and the other hydrogens were refined using a riding
model. Special features and exceptions: for 5b the absolute
structure parameter is -0.006(16).21 The C(OMe)2Me group
of one of the molecules is disordered over two positions (ca.
67:33%).
Scheme 6
Results and Discussion
Reactions of 2,6-Diacetylpyridine with Palladium Com-
pounds. Numerous attempts to prepare ketonyl palladium
complexes derived from 2,6-diacetylpyridine (dap) failed. Thus,
by reacting dap with the usual starting palladium(II) compounds
([Pd(OAc)2], PdCl2, [PdCl2(NCMe)2], (NMe4)2[Pd2Cl6]), using
various solvents (Me2C(O), CH2Cl2, THF, MeCN) and reaction
temperatures, in the absence of a base or adding Ag2O, Tl2(CO3),
or KtBuO, led to palladium metal and/or complex mixtures. We
interpreted these negative results in terms of the low coordinative
ability of dap, in turn attributable to the electron-withdrawing
character of both ortho acetyl substituents. It is well-known that
ligand to metal coordination assists the C-H activation required
to afford a metalated complex of that ligand. Indeed, the number
of dap metal complexes is very scarce,13,22,23 and in the only
reported crystal structure, [Ag(O,N,O-dap)2]2þ, the Ag-N
bond distances are much longer (2.316(6) A) than those in
[Ag(py)2]þ (2.126(4) and 2.133(4) A).23
Finally, the only successful result was obtained by reacting
dap and PdCl2 (1:1) in refluxing MeOH, which gave a
mixture of the pincer complex [Pd(O1,N1,C1-L)Cl] (1), where
L is the monoanionic ligand resulting from deprotonation of
the acetyl methyl group of the monoketal of dap (Scheme 2),
and (QH)2[PdCl2( μ-Cl)]2 (2) (Scheme 2), where QH is the
diketal of Hdapþ. This mixture could be separated on the
basis of the different solubility of its components in CHCl3.
The yield of 1 improved (69%, based on the stoichiometry
shown in Scheme 2) in the presence of NEt3 (Pd:dap:NEt3 =
1:1:0.4). An increase in the amount of NEt3 caused decom-
position to palladium metal, decreasing the yield of 1 and
increasing that of 2. Methods for the monoketalization of
dicarbonyl compounds are scarce, but some have been
reported,24 including a few giving ethyleneglycol monoketal
derivatives of 2,6-diacetylpyridine.25 Probably, PdCl2 acts as
an acid for the ketalization of one acetyl group. The electron-
releasing capacity of the ketal group will favor the coordina-
tion of Pd to the pyridine N and, correspondingly, the
(24) Flink, H.; Putkonen, T.; Sipos, A.; Jokel, R. Tetrahedron 2010,
66, 887. Grosu, I.; Muntean, L.; Toupet, L.; Ple, G.; Pop, M.; Balog, M.;
Mager, S.; Bogdan, E. Monatsh. Chem. 2002, 133, 631. Koyanagi, J.;
Yamamoto, K.; Nakayama, K.; Tanaka, A. J. Heterocycl. Chem. 1997, 34,
407. Camps, P.; Farres, X.; Mauleon, D.; Palomer, A.; Carganico, G. Synth.
Commun. 1993, 23, 1739. Kym, P. R.; Carlson, K. E.; Katzenellenbogen,
J. A. J. Med. Chem. 1993, 36, 1111. Schoening, A.; Debaerdemaeker, T.;
Zander, M.; Friedrichsen, W. Chem. Ber. 1989, 122, 1119. Giri, V. S.; Maiti,
B. C.; Pakrashi, S. C. Heterocycles 1985, 23, 71.
(20) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112.
(21) Flack, H. D. Acta Crystallogr., Sect. A 1983, 39, 876.
(22) Keypour, H.; Pritchard, R. G.; Parish, R. V. Trans. Met. Chem.
1998, 23, 609. Orrell, K. G.; Osborne, A. G.; Sik, V.; Dasilva, M. W.
Polyhedron 1995, 14, 2797. Drew, M. G. B.; Nelson, J.; Nelson, S. M. J.
Chem. Soc., Dalton Trans. 1981, 1678.
(23) Silong, B.; Engelhardt, L. M.; White, A. H. Aust. J. Chem. 1989,
42, 1381.
(25) Suh, J.; Kwon, W. J. Bioorg. Chem. 1998, 26, 103. Lama, M.;
Mamula, O.; Scopelliti, R. Synlett 2004, 1808.

3072 Organometallics, Vol. 29, No. 14, 2010
Vicente et al.
Figure 2. Packing diagram showing Pd Pd and Pd Cl contacts (thin dashed bonds) and C-H Cl and C-H O hydrogen
3 3 3 3 3 3 3 3 3 3 3 3
bonds (thick dashed bonds) in complex 1.
Figure 4. Packing diagram showing the hydrogen bonds be-
tween terminal Cl atoms of the anion and Me and MeO groups
of cations in complex 2.
Figure 3. Ellipsoid representation of 2 (50% probability). Selec-
ted bond lengths (A) and angles (deg): Pd(1)-Cl(3) = 2.2750(6),
Pd(1)-Cl(2) = 2.2798(6), Pd(1)-Cl(1) = 2.3259(6), Pd(1)-Cl-
(1A) = 2.3287(6), N(1)-C(5) = 1.344(3), N(1)-C(1) = 1.353(3),
O(1)-C(6) = 1.410(3), O(2)-C(6) = 1.405(3), O(3)-C(10) =
1.415(2), O(4)-C(10) = 1.407(3), C(1)-C(6)=1.526(3), C(5)-
C(10) =1.525(3), Cl(3)-Pd(1)-Cl(2)=92.25(2), Cl(2)-Pd(1)-
Cl(1)=91.53(2), Cl(3)-Pd(1)-Cl(1A)=91.04(2), Cl(1)-Pd(1)-
Cl(1A) = 85.26(2), Pd(1)-Cl(1)-Pd(1A) = 94.735(19), N(1)-C-
(1)-C(6)=117.27(19), N(1)-C(5)-C(10)=118.56(19), O(4)-C-
(10)-C(5) = 104.23(16).
R = tBu) afforded trans-[Pd(C1-L)Cl(CNR)2] (R = Xy (4a),
tBu (4b); Scheme 3, solid arrow). However, at 25 °C this
reaction led to the isolation of [Pd(O2,C2-LR)(CNR)Cl]
t
(R = Bu, 5b), whereas the corresponding product with
R = Xy (5a) could only be isolated in impure form (see
below). Complexes 5 are probably formed from 4 after
insertion of one isocyanide into the Pd-C bond plus a
tautomerization process from β-ketoimine to β-ketoenamine
that converts the ligand C1-L into O2,C2-LR (Scheme 3,
dashed arrows). The reaction of complex 1 with 1 equiv of
isocyanide at 0 °C gave a mixture of [Pd(N1,C1-L)Cl(CNR)]
(Scheme 3, R = Xy (6a), tBu (6b)), 4, and unreacted 1 (85:9:6
molar ratios).
palladation of the other acetyl group. The full ketalization of
dap in the presence of the formed HCl will give the corres-
ponding pyridinium salt, which will react with PdCl2 to
afford complex 2.
The reaction of 2 with 2 equiv of NEt3 at room tempera-
ture in MeOH for 1 day gives the diketal of dap, Q =
C5H3N{C(OMe)2Me}2-2,6 (3; Scheme 2), in 93% yield.
The synthesis of this compound has not been reported, and
our attempts to synthesize it using para-toluenesulfonic acid
as catalyst were unfruitful. When the reaction was carried
out using an excess of NEt3, impure 3 was obtained. This
compound is soluble in organic solvents and is stable in the
solid state and in solution.
The reaction of 1 with 1 equiv of RNC at room tempera-
ture afforded the pincer complex [Pd(O1,N1,C2-LR)Cl] (R =
Xy (7a), tBu (7b); Scheme 4) probably resulting from inser-
tion/tautomerization processes similar to those leading to 5
from 4. Complex 7b was better prepared in refluxing CHCl3,
but 7a had to be prepared at room temperature over 10 days
because refluxing in CHCl3 (1.5 h) led to mixtures, the main
component of which was the Pd(I) complex [PdCl(CNXy)2]2.
We have reported a similar behavior when studying the
reactivity of [Pd{CH2C(O)Me}Cl]n toward isocyanides.6
Complexes 7 reacted at 0 °C (1) with 2 equiv of RNC to give
Reactions of 1 with Isocyanides. The reaction of 1 with
2 equiv of isocyanide at 0 °C (5 min for R = Xy, 20 min for

Article
Organometallics, Vol. 29, No. 14, 2010 3073
Figure 5. Ellipsoid representation of one of the two indepen-
dent molecules in complex 5b (50% probability). Selected bond
lengths (A) and angles (deg) for 5b1: Pd(1)-C(17) = 1.914(3),
Pd(1)-C(1) = 1.988(3), Pd(1)-O(1) = 2.021(2), Pd(1)-Cl(1)
= 2.3846(8), Pd(1)-Pd(10) = 3.1652(3), O(1)-C(3) = 1.293(4),
C(1)-N(1) = 1.324(4), C(1)-C(2) = 1.412(4), N(1)-C(13) =
1.498(4), C(2)-C(3) = 1.386(4), C(3)-C(4) = 1.492(4), C(17)-
N(2) = 1.150(4), C(17)-Pd(1)-C(1) = 95.89(12), C(1)-Pd-
(1)-O(1) = 82.15(10), C(17)-Pd(1)-Cl(1) = 88.92(8), O(1)-
Pd(1)-Cl(1) = 93.00(6), C(17)-Pd(1)-Pd(2) = 82.29(8),
C(1)-Pd(1)-Pd(1) = 81.80(8), O(1)-Pd(1)-Pd(1) = 99.98(6),
Cl(1)-Pd(1)-Pd(1) = 99.87(2), C(3)-O(1)-Pd(1) = 111.24(18),
C(2)-C(1)-Pd(1) = 111.2(2), C(3)-C(2)-C(1) = 114.2(3),
O(1)-C(3)-C(2) = 120.9(3). 5b2: Pd(10)-C(170) = 1.912(3), Pd-
(10)-C(10) = 1.978(3), Pd(10)-O(10) = 2.048(2), Pd(10)-Cl(10) =
2.3956(7), O(10)-C(30) = 1.289(4), C(10)-N(10) = 1.326(4),
C(10)-C(20) = 1.408(4), C(20)-C(30) = 1.389(4), C(30)-C(40) =
Figure 6. Ellipsoid representation of 6a (50% probability).
Selected bond lengths (A) and angles (deg): Pd-C(1) =
1.9037(15), Pd-C(2) = 2.0558(14), Pd-N(1) = 2.1169(12),
Pd-Cl = 2.4001(4), C(1)-N(2) = 1.156(2), N(2)-C(21) =
1.4044(18), C(2)-C(3) = 1.477(2), C(3)-O(2) = 1.2205(18),
C(3)-C(4) = 1.505(2), C(4)-N(1) = 1.3557(18), N(1)-C(8) =
1.3462(18), C(8)-C(9) = 1.537(2), C(9)-O(1) = 1.4044(17), C(9)-
O(3) = 1.4228(18), C(10)-O(3) = 1.432(2), C(12)-O(1) =
1.4358(18), C(1)-Pd-C(2)=90.24(6), C(2)-Pd-N(1)=79.90(5),
C(1)-Pd-Cl = 87.31(5), N(2)-C(1)-Pd = 172.58(13), C(1)-N-
(2)-C(21) = 168.61(14), C(3)-C(2)-Pd = 94.11(9), C(2)-C-
(3)-C(4) = 111.86(12), N(1)-C(4)-C(3) = 112.59(12), C(8)-
N(1)-Pd=135.13(10), C(4)-N(1)-Pd=105.73(9), N(1)-C(8)-C-
(9) = 120.67(13).
1
The H NMR monitoring of the reactions of 1 with 2
equiv of the isocyanide at 25 °C showed the formation of 4
and its conversion into 5, as proposed above (Scheme 3).
The final product was 5, along with minor amounts of 7, 8,
and [PdCl(CNR)2]2. The reaction was faster with XyNC
(Scheme 5).
1.487(4), C(170)-Pd(10)-C(10)
=
92.04(12), C(10)-Pd(10)-
O(10) = 82.21(11), C(170)-Pd(10)-Cl(10) = 90.47(9), O(10)-Pd-
(10)-Cl(10) = 94.58(6), C(170)-Pd(10)-Pd(1) = 98.63(9), C(10)-
Pd(10)-Pd(1)=82.68(9), O(10)-Pd(10)-Pd(1)=92.18(6), Cl(10)-
Pd(10)-Pd(1) = 100.62(2), C(30)-O(10)-Pd(10) = 109.42(18),
C(20)-C(10)-Pd(10) = 111.1(2), C(30)-C(20)-C(10) = 114.0(3),
O(10)-C(30)-C(20) = 121.8(3).
A 1H NMR study of the behavior of 4a at 25 °C in CDCl3
showed that it decomposes initially to 6a, and later forma-
tion of 5a, 7a, and 8a was observed. After 2 days 4a and 6a
had disappeared, while the amounts of 5a and 8a increased
over 48 h and 25 min, respectively, and then decreased, and
the amount of 7a increased continuously. Perhaps the trans-
formation of 8a into the Pd(I) complex [PdCl(CNXy)2]2 (a
radical mechanism might reasonably be assumed) could
explain the concentration decrease of 5a and 8a. In fact, a
1H NMR study of the behavior of 8a at 25 °C in CDCl3
showed that it decomposed after 5 days to [PdCl(CNXy)2]2
(8a:[PdCl(CNXy)2]2 = 4; minor amounts of 5a and traces of
7a were also observed). This can explain why the attempt to
prepare 7a by refluxing a 1:1 mixture of 1 and XyNC gave
mainly [PdCl(CNXy)2]2. Complex 4b behaves similarly, but
all processes were much slower. Thus, after 4 days the
4b:6b:7b:5b:8b molar ratios are 3:0:4:88:5.
trans-[Pd(C2-LR)Cl(CNXy)2] (R = Xy (8a), tBu (8b)) or (2)
with 1 equiv of RNC to afford 5. This is a better way to
t
prepare 5b than the reaction 1 with 2 equiv of BuNC. The
corresponding reaction with XyNC gave 5a contaminated
with 7a and 8a (81:15:4), which is the same irresolvable
mixture obtained by reacting 1 with 2 equiv of XyNC (see
above), suggesting that complexes 7 are intermediates in the
synthesis of 5 from 1 (Scheme 3).
Reaction Pathways. The reaction of 1 with 1 equiv of
1
isocyanide was monitored by H NMR at 0 °C (Scheme 3).
The intermediate 6 was first observed, but, as it reacts with iso-
cyanide to afford 4, it could only be isolated mixed with 4 and 1.
The 10-day reaction of 1 with 1 equiv of XyNC at 25 °C
was monitored by 1H NMR, showing the initial formation of
6a along with minor amounts of 4a (Scheme 5). Their
concentrations’ decrease was accompanied by the formation
of 7a and traces of 5a and 8a. Through the 10-day period the
concentration of 7a increased and that of 1 remained con-
stant (ca. 4% of the initial concentration). These data and
those mentioned above suggest that complexes 1 and 4-8 are
related through the reactions shown in Scheme 5.
Reactions of [Pd(O1,N1,C1-L)Cl] (1) with P-, N-, or O-
Donor Ligands. The reaction of complex 1 with PPh3 gave
similar results to those with isocyanides. Thus, at 0 °C the
equimolecular reaction led to the expected product [Pd(N1,
C1-L)Cl(PPh3)] (12) along with 1 (5%) and trans-[Pd(C1-
L)Cl(PPh3)2] (13) (5%) (Scheme 6). This prevented the
isolation of pure 12. The reaction with 2 equiv of PPh3 gave
complex 13, but it could not be obtained analytically pure

3074 Organometallics, Vol. 29, No. 14, 2010
Vicente et al.
Figure 8. Ellipsoid representation of 7a (50% probability).
Selected bond lengths (A) and angles (deg): Pd(1)-C(1) =
1.9492(17), Pd(1)-N(1)=2.0257(15), Pd(1)-O(1)=2.1673(12),
Pd(1)-Cl(1) = 2.3022(5), O(1)-C(9) = 1.443(2), N(1)-C(4) =
1.349(2), N(1)-C(8) = 1.352(2), C(1)-N(2) = 1.351(2), C(1)-
C(2) = 1.379(2), N(2)-C(21) = 1.443(2), C(2)-C(3) = 1.418(3),
C(3)-O(2) = 1.242(2), C(3)-C(4) = 1.515(2), C(8)-C(9) =
1.534(2), C(9)-O(3) = 1.389(2), C(1)-Pd(1)-N(1) = 92.73(7),
N(1)-Pd(1)-O(1) = 79.19(5), C(1)-Pd(1)-Cl(1) = 93.60(5),
N(1)-Pd(1)-Cl(1) = 172.35(4), O(1)-Pd(1)-Cl(1) = 94.99(3),
C(9)-O(1)-Pd(1)=110.19(10), C(4)-N(1)-Pd(1)=126.05(12),
C(8)-N(1)-Pd(1)=114.51(12), C(2)-C(1)-Pd(1)=122.75(13),
C(1)-N(2)-C(21) = 122.71(15), C(1)-C(2)-C(3)= 128.73(16),
O(2)-C(3)-C(2) = 122.29(16), O(2)-C(3)-C(4) = 115.73(16),
C(2)-C(3)-C(4) = 121.71(16), N(1)-C(4)-C(3) = 121.87(16),
N(1)-C(8)-C(9) = 119.09(15), O(1)-C(9)-C(8) = 105.70(14),
C(22)-C(21)-N(2) = 118.60(16).
Figure 7. Packing diagram showing the hydrogen bonds in
complex 6a.
because traces of an unidentified impurity containing PPh3
could not be separated. The 1H NMR spectrum of the
reaction mixture obtained from 1 and an excess of PPh3
(1:5.5) showed, almost instantly, the presence of a mixture of
the monoketal of dap, C5H3N{C(O)Me-2}{C(OMe)2Me-6}
(14), [Pd(PPh3)4], and its dissociation products [Pd(PPh3)3]
and PPh3 as well as traces of dap. This was formed by
hydrolysis of 14, because the traces of water initially ob-
served in the spectrum disappeared. Probably, the formed
hydroxo Pd(II) complex is reduced by PPh3 to [Pd(PPh3)3].
The excess of PPh3 precluded separation of the mixture by
recrystallization, and TLC chromatography using silica gel
led to the hydrolysis of 14 to give dap.
planes of the py ring and the palladacycles PdNCCO and
PdNCC(O)C being 3.9° and 2.6°, respectively. The molecules
are connected by Pd Pd (3.3460(3) A) and Pd Cl (3.9016(6)
3 3 3
3 3 3
A) contacts (van der Waals radii of Pd: 2.05 A and Cl: 1.8 A26),
giving dimers that form layers via C-H Cl and C-H
O
3 3 3
3 3 3
hydrogen bonds (Figure 2).
In complex 2 (Figure 3), the [Pd2Cl6]2- anion lies across an
inversion center with each palladium atom in a square-planar
environment. The geometrical parameters of the anion agree
with those found in other [Pd2Cl6]2- salts.27 Anions and cations
are connected by hydrogen bonds between terminal Cl atoms of
the anion and Me and MeO groups of cations (Figure 4).
In 5b (Figure 5), two crystallographically independent mo-
lecules are present in the unit cell with a strong intermolecular
Pd-Pd interaction (3.1652(3) A)26 within the asymmetric unit.
The angle between the coordination planes of these two
molecules is 6.6°. In 6a (Figure 6), the metal is in a very
distorted square-planar coordination; the mean deviation from
the coordination plane is 0.12 A, with the CH2 carbon 0.16 A
and the chlorine atom 0.13 A out of this plane. This distortion
might be attributable to the steric hindrance of the uncoordi-
nated ortho substituent. The chlorine atom lies þ1.911 A and
C(9) -0.124 A out of the plane of the pyridyl ligand and the
Complex 1 reacted with 2,20-bipyridine (bpy) or 4,40-di-tert-
butyl-2,20-bipyridine (dbbpy) to afford the adducts [Pd(C1-L)-
Cl(N∧N)] (N∧N = bpy (10), dbbpy (11)) (Scheme 6) and with
[Tl(acac)] to give [Pd(L)(acac)] (9).
Crystal Structures. The crystal structures of complexes 1
(Figures 1 and 2), 2(Figures 3 and 4), 5b (Figure5),6a (Figures6
and 7), and 7a (Figures 8 and 9) have been determined
(Table 1, SI). All show a nearly square-planar coordination
around the palladium atom. Crystals apparently suitable for an
X-ray crystallographic study were selected for 5a. Although a
complete crystallographic analysis was not possible, because of
severely disordered methoxy groups, the position of the ligands
was established with certainty to be that indicated in Scheme 3.
In complex 1 (Figure 1), the three rings of the coordinated
pincer ligand are almost coplanar, the angle between the mean
(26) Batsanov, S. S. Inorg. Mater. 2001, 37, 871.
(27) Chitanda, J. M.; Quail, J. W.; Foley, S. R. Acta Crystallogr. Sect.
ꢀ
ꢀ
ꢀ
E 2008, 64, m907. Fabry, J.; Dusek, M.; Fejfarova, K.; Krupkova, R.; Vanek,
P.; Nemec, I. Acta Crystallogr. Sect. C 2004, 60, m426.

Article
Organometallics, Vol. 29, No. 14, 2010 3075
Figure 9. Packing diagram showing the hydrogen bonds in complex 7a.
palladium atom (mean deviation 0.070 A). The molecules of 6a
are connected through CH OMe hydrogen bonds, giving
Pd-Cl bond distances in complexes 1 and 7a (2.3040(5) and
2.3022(5) A) are shorter than those in 5b (2.3846(8), 2.3956(7)
A) and 6a (2.4001(4) A), attributable to the lower trans
influence of a N-donor ligand than a C-donor ligand.
3 3 3
dimers that form double chains along the a axis via the
hydrogen bond of one Me and the chlorine atom (Figure 7).
The structure of 7a (Figure 8) shows the metal in a slightly
distorted square-planar coordination, the mean deviation
from the coordination plane being 0.081 A. The complex has
two palladacycles; the five-membered ring has an envelope
conformation with the sp3 carbon out of the ring plane, and
the six-membered ring has a boat conformation, with the CO
carbon and the palladium atom out of the plane. Each
Spectroscopic Properties. The 1H and 13C{1H} NMR spec-
tra of all compounds are in agreement with the structures
shown in Schemes 2-6, except for the MeO protons and the
corresponding carbons, which appear as only one resonance
corresponding to the six protons or the two carbons, respec-
tively, in the ranges δ 3.08-3.47 and 49-52.2 ppm, respec-
tively. The exchange of these MeO groups cannot be slowed
down enough at -60 °C to see the expected two resonances in
their spectra, but they coalesce at this temperature in complex 1.
molecule has one classical intramolecular N-H Cl hydro-
3 3 3
gen bond and four nonclassical C-H O hydrogen bonds,
3 3 3
1
affording a double chain (Figure 9).
The H and 13C{1H} NMR methyl resonances of the MeC-
The structures of complexes 5b and 7a show that Pd and the
Xy group are mutually trans, as shown in Schemes 3 and 4.
Although a complete X-ray crystallographic study was not
possible for 5a, the same geometry around the PdC-NHXy
bond was established with certainty, which was also observed in
other β-ketoenamine complexes previously described by us.6 In
addition, both have a high degree of electron delocalization
over the OCCCN group, as shown in Scheme 5 because (1) it is
almost planar (mean deviation of the five atoms from the mean
plane 0.034°, 0.020° (for the two molecules of 5b) and 0.051°
(7a), respectively), (2) the C-O bond distance is longer (5b:
1.293(4), 1.289(4) A; 7a: 1.242(2) A) than in 1(1.217(3) A) or6a
(1.2205(18) A), (3) the C(1)-C(2) distances (5b: 1.412(4) A,
1.408(4); 7a: 1.379(3) A) and C(2)-C(3) (5b: 1.386(4), 1.389(4)
A; 7a: 1.418(2) A) are intermediate between that of a single
(O)C-CdC (1.464 A) and a double (O)C-CdC bond (1.340
A),28 and (4) the C-N bond distances (5b: 1.324(4), 1.326(4) A;
7a: 1.351(2) A) are intermediate between that of a single
R2N-CH2Pd bond (mean value, 1.450 A)29 and a double
XyNHdC(Me)Pd bond (ca. 1.30 A).30
(OMe)2 group appear as singlets in the ranges δ 1.48-2.03 and
23-26.3 ppm, respectively.
The ketonyl complexes (1,4,6,9-11) show the CH2 protons as
singlets in the range δ 3.73-3.35. In the case of 6, the equivalence
of the CH2 protons can be explained assuming a fast equilibrium
with the cationic [Pd(O1,N1,C1-L)(CNR)]Cl. These protons are
less shielded than the CH2 of the acetonyl palladium complexes
[Pd2{CH2C(O)Me}2( μ-Cl)2(CNR)2], trans-[Pd{CH2C(O)Me}-
Cl(CNR)2], and [Pd{CH2C(O)Me}(CNR)3]TfO (R = XyNC,
tBuNC; range δ 3.18-2.61),6 caused by the pyridine group. As
expected, for isocyanide complexes 4 and 6, the CH2 protons are
more shielded for tBuNC (4b: 3.35; 6b: 3.27) than XyNC (4a: 3.73;
6a: 3.44) complexes. The NH proton in LR palladacyclic com-
plexes 5 and 7 appears as a broad resonance in the range
6.00-8.65 ppm, shielded with respect to that in the monocoordi-
nate LR ligands (8a: 13.68; 8b: 12.96), which supports the proposal
of an intramolecular hydrogen bond in the latter (Scheme 4).
Again, the NH proton is more shielded for R = tBu (7b: 7.63; 8b:
12.96) than for Xy (7a: 8.65; 8a: 13.68). The CHC(O) proton
is weakly coupled with the NH proton for 5a or 5b (6.45 or
5.86 ppm, J = 1 Hz), but it appears as a singlet for 7a, 8a, or 8b
(4.67, 7.22, or 6.86 ppm) or a broad signal for 7b (5.17 ppm).
The Pd-CH2 bond distance is longer in 6a (2.0558(14) A)
than in 1(2.000(2) A), showing the greater trans influence of the
Cl ligand than the O-donor ligand. The Pd-N bond distances
decrease in the series 6a (2.1169(12) A), 7a (2.0257(15) A), 1
(1.9752(19) A), because the angle between the coordination
and pyridine planes decreases (44.3°, 18.4°, 5.8°), thus favoring
the Pd to pyridine π-back-bonding and also because of the
greater trans influence of the XyNC than the Cl ligand. The
1
In the H NMR spectrum of 9 at room temperature, the
Me acac protons appear as a broad resonance, but at -40 °C
this resolves into two signals, which could be associated with
an equilibrium between [Pd(N1,C1-L)(O,O-acac)] and
[Pd(O1,N1,C1-L)(C-acac)]. However, in the 13C{1H} NMR
spectrum, the two Me acac carbon nuclei resonate as two
broad singlets at room temperature.
The IR spectra of chloro complexes show a band assign-
able to ν(PdCl) at various wavenumbers depending on the
nature of the ligands in trans position. Thus, complexes with
chloro trans to a N-donor ligand (1, 7, 10, 11) show ν(PdCl)
absortion in the range 337-321 cm-1, while in complexes
with chloro trans to a C-donor ligand (4, 6, 8, 12, 13) the
absorption is observed in the range 290-280 cm-1, in
(28) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.
(29) Enzmann, A.; Eckert, M.; Ponikwar, W.; Polborn, K.;
Schneiderbauer, S.; Beller, M.; Beck, W. Eur. J. Inorg. Chem. 2004,
1330. Miki, K.; Tanaka, N.; Kasai, N. Acta Cristallogr., Sect. B 1981,
37, 447.
(30) Owen, G. R.; Vilar, R.; White, A. J. P.; Williams, D. J. Organo-
metallics 2003, 22, 4511.

3076 Organometallics, Vol. 29, No. 14, 2010
Vicente et al.
agreement with the stronger trans influence of a C-donor
ligand with respect to a N-donor ligand.
The resulting complex, which contains the monoanionic
pincer ligand resulting from the deprotonation of the acetyl
methyl group of the monoketal of dap, reacts with isocya-
nides, giving complexes resulting from coordination or/and
insertion of the isocyanide followed by a tautomerization
process from β-ketoimine to β-ketoenamine. The reaction
pathway has been studied at different molar ratios and
temperatures.
The ketonyl complexes 1, 4, and 9-11 show the ν(CdO)
absortion in the range 1684-1608, cm-1, while in complexes 5,
7, and 8 the ν(CdO) appears at lower frequency, 1590-1538
cm-1, showing the reduction of the C-O bond order, consis-
tent with the results of the X-ray diffraction study of complexes
5b and 7a and attributable to the electron delocalization over
the OCCCNC group of the β-ketoenamine ligand.
ꢀ
Acknowledgment. We thank Ministerio de Educacion
y Ciencia (Spain), FEDER (CTQ2007-60808/BQU), and
The IR spectra of complexes with the ligand XyNC show
the ν(NtC) band in the region 2192-2175 cm-1 and those
with tBuNC in the narrow range 2211-2208 cm-1, showing,
as usual, an increase with respect to ν(CN) in the free ligands
(2109 and 2134 cm-1, respectively).
ꢀ
Fundacion Seneca (04539/GERM/06 and 03059/PI/05)
for financial support and a grant to F.J.-H.
ꢀ
Supporting Information Available: Listing of all crystal data,
refined and calculated atomic coordinates, anisotropic thermal
parameters, and bond lengths and angles and CIF files for
compounds 1, 2, 5b, 6a, and 7a. This material is available free
of charge via the Internet at http://pubs.acs.org.
Conclusion
2,6-Diacetylpyridine can be palladated using PdCl2
in methanol via its transformation into its dimethylketal.