Divergent behavior in the cyclopalladation of phosphorus ylides and iminophosphoranes

Article abstract of DOI:10.1021/om7002877

The cyclopalladation of the stabilized iminophosphoranes Ph ₃P=NC(O)C₆H₄R (R = H 1a, 4-OMe 1b, 3-OMe 1c, 2-Me 1d, 3-Me 1e) results in the regioselective activation of the ortho CH bond of the benzamide ring, giving exo-(Pd(μ-Cl){C,N-C₆H ₃(R){C(O)=PPh₃-2}}]₂ (R = H 2a, 5-OMe 2b, 4-OMe 2c, 3-Me 2d, 4-Me 2e). The palladated ligand behaves as a strong C,N-chelating group and cannot be easily displaced by other chelating ligands. This is clear from the reaction of 2c with Tl(acac), py, or AgClO₄/LL, which gives [Pd(acac){C,N-C₆H₃(MeO-4){C(O)N=PPh₃-2}}] (3c), [PdCl{C,N-C₆H₃(MeO-4){CO)N=PPh₃-2}}(py)] (4c), or [Pd{C,N-C₆H₃(MeO-4){C(O)N=PPh₃-2}}(L^L)] ClO₄ (L^L = dppe 5c, bipy 6c, phen 7c). However, Pd(OAc)₂ reacts with the ylides Ph₃P=CHC(O)C₆H₄R (R = H 8a, 3-OMe 8b, 2,5-(OMe)₂ 8c) to give the C,C-orthometalated complexes [Pd(μ-Cl){C,C-[C₆H₄(PPh₂CHC-(O)C ₆H₄R)-2]}] (R = H 9a, 3-OMe 9b, 2,5-(OMe)₂ 9c), which are also regioselectively obtained. The C,C-metalated chelate is very stable, as shown by the reactions of 9b with Tl(acac), PPh₃, and AgClO₄/L^L. The X-ray structures of 2d and 9b have been determined. Unexpectedly, the reaction of Pd(OAc)₂ with the ylide [Ph ₃P=CHC(0)C₆H₃-2,4-(OMe)₂] (16) gives the polymer [(μ-Cl)Pd{C₆H₄(PPh₂CH-C(O)- C₆H₂-3,5-(OMe)₂)-₂}-κ-C,C,C,O) Pd(μ-Cl)]_n (17) as a result of a double palladation, giving two types of metalacycles: in one of them, the Pd atom is bonded to the ylidic Cα atom and has activated an ortho C(Ph)-H bond of the PPh₃ group; in the other one, the Pd atom is bonded to the carbonyl oxygen and has activated an ortho C-H bond of the C₆H₃(OMe)₂ unit. This tetradentate ylide ligand is remarkably stable.

Full text of DOI:10.1021/om7002877

Organometallics 2007, 26, 3541-3551
3541
Divergent Behavior in the Cyclopalladation of Phosphorus Ylides
and Iminophosphoranes
David Aguilar, Miguel Angel Aragu¨e´s, Raquel Bielsa, Elena Serrano, Rafael Navarro, and
Esteban P. Urriolabeitia*
Departamento de Compuestos Organometa´licos, Instituto de Ciencia de Materiales de Arago´n,
UniVersidad de Zaragoza-CSIC, 50009 Zaragoza, Spain
ReceiVed March 26, 2007
The cyclopalladation of the stabilized iminophosphoranes Ph3PdNC(O)C6H4R (R ) H 1a, 4-OMe
1b, 3-OMe 1c, 2-Me 1d, 3-Me 1e) results in the regioselective activation of the ortho CH bond of the
benzamide ring, giving exo-[Pd(µ-Cl){C,N-C6H3(R){C(O)NdPPh3-2}}]2 (R ) H 2a, 5-OMe 2b, 4-OMe
2c, 3-Me 2d, 4-Me 2e). The palladated ligand behaves as a strong C,N-chelating group and cannot be
easily displaced by other chelating ligands. This is clear from the reaction of 2c with Tl(acac), py, or
AgClO4/L∧L, which gives [Pd(acac){C,N-C6H3(MeO-4){C(O)NdPPh3-2}}] (3c), [PdCl{C,N-C6H3(MeO-
4){C(O)NdPPh3-2}}(py)] (4c), or [Pd{C,N-C6H3(MeO-4){C(O)NdPPh3-2}}(L∧L)]ClO4 (L∧L ) dppe
5c, bipy 6c, phen 7c). However, Pd(OAc)2 reacts with the ylides Ph3PdCHC(O)C6H4R (R ) H 8a,
3-OMe 8b, 2,5-(OMe)2 8c) to give the C,C-orthometalated complexes [Pd(µ-Cl){C,C-[C6H4(PPh2CHC-
(O)C6H4R)-2]}] (R ) H 9a, 3-OMe 9b, 2,5-(OMe)2 9c), which are also regioselectively obtained. The
C,C-metalated chelate is very stable, as shown by the reactions of 9b with Tl(acac), PPh3, and AgClO4/
L∧L. The X-ray structures of 2d and 9b have been determined. Unexpectedly, the reaction of Pd(OAc)2
with the ylide [Ph3PdCHC(O)C6H3-2,4-(OMe)2] (16) gives the polymer [(µ-Cl)Pd{C6H4(PPh2CH-C(O)-
C6H2-3,5-(OMe)2)-2}-κ-C,C,C,O)Pd(µ-Cl)]n (17) as a result of a double palladation, giving two types of
metalacycles: in one of them, the Pd atom is bonded to the ylidic CR atom and has activated an ortho
C(Ph)-H bond of the PPh3 group; in the other one, the Pd atom is bonded to the carbonyl oxygen and
has activated an ortho C-H bond of the C6H3(OMe)2 unit. This tetradentate ylide ligand is remarkably
stable.
bonds, even though Caryl-H bonds (about 110 kcal/mol) are
stronger than Calkyl-H bonds (about 100 kcal/mol).3 When
several C-H bonds of the same nature are present on a molecule
(for instance, aryl rings), the metalation can be easily directed
to a given position by introduction of ancillary coordinating
groups. In these cases, the metalation is produced at the ortho
position with respect to the ancillary group,4 and the compounds
thus obtained are known as orthometalated derivatives.1j The
functionalization of such substrates, promoted by transition
metals, is quite selective, and the usefulness of the orthometa-
lation reaction in metal-mediated organic synthesis is well
recognized.2a,b,g,5 However, even in the presence of directing
groups, some substrates show quasi-equivalent metalation
Introduction
The activation of C-H bonds in organic compounds pro-
moted by transition metals is one of the most important research
topics nowadays.1 This is because this process is a mandatory
key step in their functionalization,2 and its relevance is
emphasized in the functionalization of hydrocarbons.2f,i Due to
the almost ubiquitous nature of the C-H bond, it is usual to
find two or more C-H bonds in the same compound, able to
be activated. These bonds can be of the same or of different
nature (for instance, alkyl Csp3-H versus aryl Csp2-H), and
these differences could determine the orientation of the meta-
lation. For example, it is well established that Caryl-H bond
activations are more easily promoted than those of Calkyl-H
* Corresponding author. Fax: (+34) 976761187. E-mail: esteban@
unizar.es.
(2) Recent reviews: (a) Dupont, J.; Pfeffer, M.; Spencer, J. Eur. J. Inorg.
Chem. 2001, 1917. (b) Rietling, V.; Sirlin, C.; Pfeffer, M. Chem. ReV. 2002,
102, 1731. (c) Kakiuchi, F.; Chatani, N. AdV. Synth. Catal. 2003, 345, 1077.
(d) Bedford, R. B. Chem. Commun. 2003, 1787. (e) van der Boom, M. E.;
Milstein, D. Chem. ReV. 2003, 103, 1759. (f) Periana, R. A.; Bhalla, G.;
Tenn, W. J., III; Young, K. J. H.; Liu, X. Y.; Mironov, O.; Jones, C. J.;
Ziatdinov, V. R. J. Mol. Catal. A: Chem. 2004, 220, 7. (g) Dupont, J.;
Consorti, C.; Spencer, J. Chem. ReV. 2005, 105, 2527. (h) Park, Y. J.; Jun,
C. H. Bull. Korean Chem. Soc. 2005, 26, 871. (i) Jones, W. D. Inorg. Chem.
2005, 44, 4475. (j) Hashmi, A. S. K.; Salathe´, R.; Frost, T. M.; Schwarz,
L.; Choi, J. H. Appl. Catal. A: Gen. 2005, 291, 238. (k) De Vos, D. E.;
Sels, B. F. Angew. Chem., Int. Ed. 2005, 44, 30. (l) Godula, K.; Sames, D.
Science 2006, 312, 67.
(3) (a) Jones, W. D.; Feher, F. J. Acc. Chem. Res. 1989, 22, 91. (b)
Castelhano, A. L.; Griller, D. J. Am. Chem. Soc. 1982, 104, 3655. (c) Tian,
Z.; Fattahi, A.; Lis, L.; Kass, S. R. J. Am. Chem. Soc. 2006, 128, 17087.
(4) (a) Clegg, W.; Dale, S. H.; Hevia, E.; Honeyman, G. W.; Mulvey,
R. E. Angew. Chem., Int. Ed. 2006, 45, 2370. (b) Clegg, W.; Dale, S. H.;
Harrington, R. W.; Hevia, E.; Honeyman, G. W.; Mulvey, R. E. Angew.
Chem., Int. Ed. 2006, 45, 2374.
(1) Recent reviews: (a) Shilov, A. E.; Shul’pin, G. B. ActiVation and
Catalytic Reactions of Saturated Hydrocarbons in the Presence of Metal
Complexes; Kluwer Academic Publishers: Dordretch, Germany, 2000. (b)
Crabtree, R. H. J. Chem. Soc., Dalton Trans. 2001, 2437. (c) Doye, S.
Angew. Chem., Int. Ed. 2001, 40, 3351. (d) Slugovc, C.; Padilla-Mart´ınez,
I.; Sirol, S.; Carmona, E. Coord. Chem. ReV. 2001, 213, 129. (e) Labinger,
J. A.; Bercaw, J. E. Nature 2002, 417, 507. (f) Jones, W. D. Acc. Chem.
Res. 2003, 36, 140. (g) Periana, R. A.; Mironov, O.; Taube, D.; Bhalla, G.;
Jones, C. J. Science 2003, 301, 814. (h) Fekl, U.; Goldberg, K. I. AdV.
Inorg. Chem. 2003, 54, 259. (i) Crabtree, R. H. J. Organomet. Chem. 2004,
689, 4083. (j) Omae, I. Coord. Chem. ReV. 2004, 248, 995. (k) Goldberg,
K. I., Goldman, A. S., Eds. In Organometallic C-H Bond ActiVation;
ActiVation and Functionalization of C-H Bonds; ACS Symposium Series
885; American Chemical Society: Washington, DC, 2004. (l) Fiedler, D.;
Leung, D. H.; Bergman, R. G.; Raymond, K. N. Acc. Chem. Res. 2005, 38,
351. (m) Lersch, M.; Tilset, M. Chem. ReV. 2005, 105, 2471. (n) Carmona,
E.; Paneque, M.; Santos, L. L.; Salazar, V. Coord. Chem. ReV. 2005, 249,
1729.
10.1021/om7002877 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 06/01/2007

3542 Organometallics, Vol. 26, No. 14, 2007
Aguilar et al.
C6H5-nRn] and the stabilized phenacyl ylides [Ph3PdCHC(O)-
C6H5-nRn]. The metalation of phosphorus ylides is a known
process,7,9 and in all cases the Ph-P ring is activated, givings
not strictly speakingsendo complexes. However, the metalation
of the phenacyl ylide [Ph3PdCHC(O)Ph] promoted by PdII
complexes has not been fully characterized, and that induced
by PtII complexes10 still presents some ambiguities about the
endo/exo character of the metalation. On the other hand, the
metalation of iminophosphoranes is still scarcely represented,11
in spite of notable recent contributions, all examples sharing in
common that the metalation gives endo derivatives. In this
context, the only exo derivative has been obtained through an
oxidative addition process.11m Thus, it seems that there is a clear
preference for the endo metalation. The present work aims to
shed light on and to obtain additional information about the
factors governing the preference of such endo cyclopalladation
in the afore-mentioned derivatives.
Figure 1. Possible cyclopalladation positions on benzylidene-
benzylamines.
positions. A typical case is the palladation of benzylidene-
benzylamines [C6H5C(H)dNCH2C6H5]. These substrates usually
form endo metallacyclessthat is, the CdN double bond is
endocyclicswhile the exo metalation is obtained only if the endo
is strongly disfavored for steric or electronic reasons.6 This fact
limits further reactivity of the starting substrate since only endo
functionalization could be obtained (Figure 1).
Results and Discussion
Following our current research work on C-H bond activa-
tions on phosphorus ylides7 and iminophosphoranes,8 we
have studied the metalation of two closely related types of
compounds: the stabilized iminophosphoranes [Ph3PdNC(O)-
1. Synthesis of Iminophosphorane Complexes. The imi-
nophosphoranes [Ph3PdN-C(O)-C6H4Rn] (Rn ) H 1a, 4-OMe
1b, 3-OMe 1c, 2-Me 1d, 3-Me 1e, 4-NO2 1f) have been prepared
as air-stable solids following reported methods,12 by reaction
of the corresponding benzamide H2NC(O)C6H4Rn with PPh3 and
bis(tBu-azocarboxylate). The IR spectra of 1a-f show a strong
band in the range 1580-1620 cm-1, due to the carbonyl stretch,
and another strong absorption in the 1310-1340 cm-1 region,
due to the PdN stretch. The absorption due to the carbonyl
stretch clearly appears at lower energies than expected (around
1720 cm-1), due to the conjugation of the CdO bond with the
PdN bond. The delocalization of the density charge in the
P-N-C-O bond system is responsible for the stability of these
(5) (a) Murai, S. Ed. Topics in Organometallic Chemistry, Vol. 3;
Springer: New York, 1999. (b) Farina, V. AdV. Synth. Catal. 2004, 346,
1553. (c) Beletskaya, I. P.; Cheprakov, A. V. J. Organomet. Chem. 2004,
689, 4055. (d) Schlummer, B.; Scholz, U. AdV. Synth. Catal. 2004, 346,
1599. (e) Kalyani, D.; Deprez, N. R.; Desai, L. V.; Sanford, M. S. J. Am.
Chem. Soc. 2005, 127, 7330. (f) Zapf, A.; Beller, M. Chem. Commun. 2005,
431. (g) Vicente, J.; Abad, J. A.; Lo´pez-Sa´ez, M. J.; Jones, P. G.
Organometallics 2006, 25, 1851. (h) Hull, K. L.; Lanni, E. L.; Sanford, M.
S. J. Am. Chem. Soc. 2006, 128, 14047. (i) Dick, A. R.; Sanford, M. S.
Tetrahedron 2006, 62, 2439.
(6) (a) Keuseman, K. J.; Smoliakova, I. P.; Dunina, V. V. Organome-
tallics 2005, 24, 4159. (b) Gorunova, O. N.; Keuseman, K. J.; Goebel, B.
M.; Kataeva, N. A.; Churakov, A. V.; Kuz’mina, L. G.; Dunina, V. V.;
Smoliakova, I. P. J. Organomet. Chem. 2004, 689, 2382. (c) Crespo, M.;
Evangelio, E. J. Organomet. Chem. 2004, 689, 1956. (d) Albert, J.; Cadena,
J. M.; Gonza´lez, A.; Granell, J.; Solans, X.; Font-Bardia, M. Chem.
Commun. 2003, 528. (e) Castro-Juiz, S.; Lo´pez-Torres, M.; Ferna´ndez, A.;
Mosteiro, R.; Sua´rez, A.; Vila, J. M.; Ferna´ndez, J. J. Polyhedron 2001,
20, 2925. (f) Albert, J.; Bosque, R.; Granell, J.; Tavera, R. Polyhedron
2001, 20, 3225.(g) Go´mez, M.; Granell, J.; Mart´ınez M. Eur. J. Inorg. Chem.
2000, 217. (h) Go´mez, M.; Granell, J.; Mart´ınez, M. J. Chem. Soc., Dalton
Trans. 1998, 37. (i) Albert, J.; Granell, J.; Luque, A.; Font-Bard´ıa, M.;
Solans, X. J. Organomet. Chem. 1997, 545-546, 131. (j) Go´mez, M.;
Granell, J.; Mart´ınez, M. Organometallics 1997, 16, 2539. (k) Albert, J.;
Granell, J.; Moragas, R.; Font-Bard´ıa, M.; Solans, X. J. Organomet. Chem.
1996, 522, 59. (l) Crespo, M.; Solans, X.; Font-Bard´ıa, M. J. Organomet.
Chem. 1996, 518, 105. (m) Crespo, M.; Solans, X.; Font-Bard´ıa, M. J.
Organomet. Chem. 1996, 509, 29. (n) Albert, J.; Granell, J.; Sales, J.; Font-
Bard´ıa, M.; Solans, X. Organometallics 1995, 14, 1393. (o) De Munno,
G.; Ghedini, M.; Neve, F. Inorg. Chim. Acta 1995, 239, 155. (p) Barro, J.;
Granell, J.; Sainz, D.; Sales, J.; Font-Bard´ıa, M.; Solans, X. J. Organomet.
Chem. 1993, 456, 147. (q) Navarro-Ranninger, C.; Lo´pez-Solera, I.; AÄ lvarez-
Valde´s, A.; Rodr´ıguez-Ramos, J. H.; Masaguer, J. R.; Garc´ıa-Ruano, J. L.
Organometallics 1993, 12, 4104. (r) Albert, J.; Ceder, R. M.; Go´mez, M.;
Granell, J.; Sales, J. Organometallics 1992, 11, 1536. (s) Albert, J.; Go´mez,
M.; Granell, J.; Sales, J.; Solans, X. Organometallics 1990, 9, 1405. (t)
Albert, J.; Granell, J.; Sales, J.; Solans, X.; Font-Altaba, M. Organometallics
1986, 5, 2567.
(7) (a) Navarro, R.; Urriolabeitia, E. P. J. Chem. Soc., Dalton Trans.
1999, 4111, and references therein. (b) Falvello, L. R.; Ferna´ndez, S.;
Navarro, R.; Rueda, A.; Urriolabeitia, E. P. Organometallics 1998, 17, 5887.
(c) Falvello, L. R.; Ferna´ndez, S.; Navarro, R.; Urriolabeitia, E. P. Inorg.
Chem. 1999, 38, 2455. (d) Ferna´ndez, S.; Navarro, R.; Urriolabeitia, E. P.
J. Organomet. Chem. 2000, 602, 151. (e) Larraz, C.; Navarro, R.;
Urriolabeitia, E. P. New J. Chem. 2000, 24, 623. (f) Falvello, L. R.;
Ferna´ndez, S.; Larraz, C.; Navarro, R.; Urriolabeitia, E. P. Organometallics
2001, 20, 1424. (g) Gracia, C.; Marco, G.; Navarro, R.; Romero, P.; Soler,
T.; Urriolabeitia, E. P. Organometallics 2003, 22, 4910. (h) Serrano, E.;
Valle´s, C.; Carbo´, J. J.; Lledo´s, A.; Soler, T.; Navarro, R.; Urriolabeitia, E.
P. Organometallics 2006, 25, 4653.
(9) (a) Ru¨ba, E.; Mereiter, K.; Schmid, R.; Kirchner, K.; Bustelo, E.;
Puerta, M. C.; Valerga, P. Organometallics 2002, 21, 2912. (b) O’Connor,
J. M.; Bunker, K. D. J. Organomet. Chem. 2003, 671, 1. (c) Onitsuka, K.;
Nishii, M.; Matsushima, Y.; Takahashi, S. Organometallics 2004, 23, 5630.
(d) Petz, W.; Kutschera, C.; Neumu¨ller, B. Organometallics 2005, 24, 5038.
(e) Canac, Y.; Conejero, S.; Soleilhavoup, M.; Donnadieu, B.; Bertrand,
G. J. Am. Chem. Soc. 2006, 128, 459. (f) Kawachi, A.; Yoshioka, T.;
Yamamoto, Y. Organometallics 2006, 25, 2390. (g) Vicente, J.; Chicote,
M. T.; Ferna´ndez-Baeza, J. J. Organomet. Chem. 1989, 364, 407. (h)
Vicente, J.; Chicote, M. T.; Lagunas, M. C.; Jones, P. G.; Bembenek, E.
Organometallics 1994, 13, 1243. (i) Vicente, J.; Chicote, M. T.; Lagunas,
M. C.; Jones, P. G. Inorg. Chem. 1995, 34, 5441.
(10) Teagle, J. A.; Burmeister, J. L. Inorg. Chim. Acta 1986, 118, 65.
(11) (a) Stuckwish, C. G. J. Org. Chem. 1976, 41, 1173. (b) Alper, H.
J. Organomet. Chem. 1977, 127, 385. (c) Nussha¨r, D.; Weller, F.; Dehnicke,
K. Z. Anorg. Allg. Chem. 1993, 619, 1121. (d) Steiner, A.; Stalke, D. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1752. (e) Avis, M. W.; Vrieze, K.; Ernsting,
J. M.; Elsevier, C. J.; Veldman, N.; Spek, A. L.; Katti, K. V.; Barnes, C.
L. Organometallics 1996, 15, 2376. (f) Avis, M. W.; van der Boom, M.
E.; Elsevier, C. J.; Smeets, W. J. J.; Spek, A. L. J. Organomet. Chem. 1997,
527, 263. (g) Wingerter, S.; Gornitzka, H.; Bertrand, G.; Stalke, D. Eur. J.
Inorg. Chem. 1999, 173. (h) Lesson, M. A.; Nicholson, B. K.; Olsen, M.
R. J. Organomet. Chem. 1999, 579, 243. (i) Wingerter, S.; Gornitzka, H.;
Bertermann, R.; Pandey, S. K.; Rocha, J.; Stalke, D. Organometallics 2000,
19, 3890. (j) Wingerter, S.; Pfeiffer, M.; Stey, T.; Bolboaca, M.; Kiefer,
W.; Chandrasekhar, V.; Stalke, D. Organometallics 2001, 20, 2730. (k)
Jones, N. D.; Lin, G.; Gossage, R. A.; McDonald, R.; Cavell, R. G.
Organometallics 2003, 22, 2832. (l) Wei, P.; Chan, K. T. K.; Stephan, D.
W. Dalton Trans. 2003, 3804. (m) Vicente, J.; Abad, J. A.; Clemente, R.;
Lo´pez-Serrano, J.; Ram´ırez de Arellano, M. C.; Jones, P. G.; Bautista, D.
Organometallics 2003, 22, 4248. (n) Chan, K. T. K.; Spencer, L. P.; Masuda,
J. D.; McCahill, J. S. J.; Wei, P.; Stephan, D. W. Organometallics 2004,
23, 381. (o) Cadierno, V.; D´ıez, J.; Garc´ıa-AÄ lvarez, J.; Gimeno, J.
Organometallics 2005, 24, 2801. (p) Wang, Z. X.; Qi, C. Y. Dalton Trans.
2005, 996. (q) Fang, M.; Jones, N. D.; Ferguson, M. J.; McDonald, R.;
Cavell, R. G. Angew. Chem., Int. Ed. 2005, 44, 2005. (r) Boubekeur, L.;
Ricard, L.; Me´zailles, N.; Demange, M.; Auffrant, A.; Le Floch, P.
Organometallics 2006, 25, 3091.
(8) Bielsa, R.; Larrea, A.; Navarro, R.; Soler, T.; Urriolabeitia, E. P.
Eur. J. Inorg. Chem. 2005, 1724.
(12) Bittner, S.; Assaf, Y.; Krief, P.; Pomerantz, M.; Ziemnicka, B. T.;
Smith, C. G. J. Org. Chem. 1985, 50, 1712.

Cyclopalladation of Phosphorus Ylides and Iminophosphoranes
Organometallics, Vol. 26, No. 14, 2007 3543
Scheme 1. Synthesis and Reactivity of Orthopalladated
Iminophosphoranes
of the carbonyl stretch (regions from 1580-1620 to 1640-1650
cm-1) and a decrease in that of the PdN stretch (regions from
1310-1340 to 1280-1310 cm-1). The low-frequency shift of
the PdN stretch reflects unambiguously the coordination of the
N atom through the lone pair, while the high-frequency shift of
the carbonyl stretch is related to the loss of conjugation of the
CdO and the PdN bonds.14 The NMR spectra of 2a-e show
that the C-H bond activation and the subsequent metalation
have occurred at the benzamide ring. For instance, the 1H NMR
spectrum of 2a shows three signals due to the PPh3 protons
(7.3-8.0 ppm region; relative intensity 6:3:6) and another three
signals (6.7-7.2 ppm region; relative intensity 1:1:2) due to
the C6H4 group. Similar conclusions can be derived from the
analysis of 2b-e (see Experimental Section and SI). On the
other hand, the 13C{1H} NMR spectra show, in addition to the
signals due to the Ph3PdNC(O) unit, six different peaks in the
aromatic region due to the metalated aryl fragment. Among
them, the metalated carbon atom C1 appears in the 139-146
ppm region. Finally, the 31P{1H} NMR spectra show, in all
studied cases, a single peak in the range 29.0-32.0 ppm. This
implies a moderate downfield shift after metalation, and this
fact is consistent with the N-bonding of the iminophosphorane.
Moreover, the position of this peak also suggests that the endo
metalation has not occurred, since in that case an even stronger
downfield shift must be expected, the 31P peak appearing at
about 50 ppm.8,11m
It is quite remarkable the regioselective exo palladation of
the benzamide ring, instead of the, in principle, more stable
endo metalation. One of the main arguments to explain why
the endo metalation is more favored than the exo is based on
electronic factors, more explicitly the metalloaromaticity.15 This
phenomenon, which can be defined such as the presence of a
partial aromatic character in metallacycles, could be originated
in endo compounds due to the presence in the palladacycle of
two conjugated double bonds, the CdC double bond of the
metalated aryl and the iminic PdN bond, and the appropriate
filled d orbitals of the Pd atom.15 Obviously, this conjugation
cannot be established in the exo derivatives. The presence of a
certain degree of aromaticity is accompanied by a resonance
energy stabilization, and the endo complexes become energeti-
cally more favorable than the exo.6q It is clear that the metalation
of 1a-e to give stable exo 2a-e must be driven by additional
factors that counterbalance this stabilization by delocalization.
A plausible explanation can be given assuming that the
mechanism of palladation occurs through electrophilic substitu-
tion at the aromatic ring.16 If the metalation occurs at the
benzamide ring, in a solvent such as CH2Cl2, this means that
this ring is more electron-rich than those of the P-Ph groups.
Why? We can consider the resonant forms shown in Figure 2:
one of them is neutral and the other two are zwitterionic. In a
polar solvent (CH2Cl2) the two zwitterionic forms are favored,
meaning that the phosphorus atom is supporting a high positive
formal charge (near +1) and that the phenyl rings at this P atom
should be strongly deactivated. In addition, and due to the
delocalization, the formal negative charge is shifted to the
N-C-O fragment, and this accumulation of negative charge
produces a, comparatively, more electron-rich benzamide ring.
The amide substituent (usually a strong deactivating group) is
thus operating as an activating group and drives the metalation
to the benzamide ring. The deactivating nature of the amide
group and relative low affinity of aryl amides to be metalated
compounds and can also be inferred from the 31P NMR spectra.
These spectra show a single peak at about 19-22 ppm, a
position shifted to low field with respect to that observed in
other nonstabilized systems (about 0-6 ppm) and showing the
lower shielding of the P atom in the stabilized compounds due
to delocalization. These results are similar to those observed in
other stabilized systems.12-14
The reactivity of 1a-f toward Pd(OAc)2 (OAc ) acetate)
has been investigated. Thus, the treatment of Pd(OAc)2 with
1a-e (1:1 molar ratio, Scheme 1) in refluxing CH2Cl2 and
further reaction of the acetate intermediate with excess LiCl in
methanol gives the cyclopalladated complexes 2a-e. Surpris-
ingly, the metalation has been produced at the ortho C-H bond
of the benzamide group, giving the exo derivative, instead of
the expected endo metalation at the P-Ph groups.8,11b,m The
reaction proceeds with yields ranging from low to excellent,
and no endo isomers have been detected, showing that the
process can be considered to be regioselective. In the presence
of substituents at the meta position (1c, 1e) two different CH
bonds can be activated, but only the less hindered isomer is
obtained; that is, the metalation is produced selectively at the 6
position on the starting material. The metalation of 1d also gives
a single isomer showing that the palladation of a Caryl-H bond
forming a five-membered metallacycle is really more favorable
than the palladation of a Calkyl-H bond forming a six-membered
ring, as expected. Only when the benzamide ring is strongly
deactivated by the presence of the nitro group (1f) does the
reaction not proceed, and no metalation has been observed in
the studied conditions.
The characterization of 2a-e has been carried out on the basis
of their spectroscopic parameters. The N-bonding of the
iminophosphorane can be inferred from their IR spectra, due
to the simultaneous observation of an increase in the position
(13) Falvello, L. R.; Ferna´ndez, S.; Garc´ıa, M. M.; Navarro, R.;
Urriolabeitia, E. P. J. Chem. Soc., Dalton Trans. 1998, 3745.
(14) Falvello, L. R.; Garc´ıa, M. M.; La´zaro, I.; Navarro, R.; Urriolabeitia,
E. P. New J. Chem. 1999, 23, 227.
(15) Ghedini, M.; Aiello, I.; Crispini, A.; Golemme, A.; La Deda, M.;
Pucci, D. Coord. Chem. ReV. 2006, 250, 1373, and references therein.
(16) Ryabov, A. D. Chem. ReV. 1990, 90, 403.

3544 Organometallics, Vol. 26, No. 14, 2007
Aguilar et al.
the H and 31P{1H} NMR spectra show clearly that the exo-
palladated iminophosphorane ligand remains unaffected. The
cleavage of the dinuclear µ-Cl complex 2c with neutral L ligands
could give two geometric isomers, L trans N or L trans C,8
although usually only one isomer is observed (L trans N).21 The
reaction of 2c with excess py (1:4 molar ratio) gives 4c as a
single isomer. When stoichiometric amounts of py are used, a
mixture of 2c and 4c is obtained, showing that the palladated
group is not displaced by an excess of incoming L ligand. The
pyridine ligand is bonded trans to the iminic N atom, as
expected.21 This fact is observed in the 1H NMR spectrum, since
the chemical shift of the H6 proton in the metalated ring of 4c
has been high-field shifted, with respect to its position in 2c,
due the anisotropic shielding of the cis-bonded pyridine ligand.21
The characterization of 5c-7c lies in the following key features.
The 31P{1H} NMR spectrum of 5c shows three different signals,
corresponding to the three P atoms of the molecule. One of the
peaks (21.09 ppm) shows the presence of the exo-metalated
ligand, while the other two (39.96 and 61.90 ppm) are typical
of chelating dppe. The 31P{1H} NMR spectra of 6c and 7c show
a single peak in each case (22.98 and 22.91 ppm), whose
chemical shifts show the maintenance of the exo metalation.
1
Figure 2. Resonant forms of the keto-stabilized iminophospho-
ranes.
can be inferred from a careful inspection of the reported
structures at the Cambridge Crystallographic Database.17 From
633 structures found at the CCDC including a five-membered
metallacycle Pd-N-C-Caryl, only nine (1.4%) contain an
amide group Pd-N-C(O)-Caryl. This fact is clearly related with
the deactivating nature of the amide group and makes the exo
metalation presented here more relevant.
Additional arguments in favor of the charge separation and
the localization of a formal negative charge over the nitrogen
as important factors in the metalation of the amide ring can be
obtained from the following observations. First, the metalation
of pyridinium ylides and betaines derived from benzamide has
been reported,18 and the C-H bond activation has been produced
at the benzamide ring. This reaction seems to be general, and
the reactants show a similar charge separation to our imino-
phosphoranes. On the other hand, the metalation of benzamide
derivatives has been reported,19 and all described complexes
share a common feature: the C,N-benzamidate ligand acts as a
dianion, one negative charge centered at the metalated carbon
and the other one at the nitrogen (amide) atom. Very few reports
show an orthometalated benzamide ring as a monoanionic
ligand. Curiously, in those cases the ligand is coordinated as a
C,O-chelate instead of as a C,N-chelate.20
The reactivity of the dinuclear derivatives 2 has been studied
(Scheme 1). All results show that the C,N-orthopalladated
iminophosphoranes behave as strong chelating ligands, as do
other classical C,N derivatives. Complex 2c reacts with Tlacac
(1:2 molar ratio) to give [Pd(acac){C,N-C6H3(MeO-4){C(O)Nd
PPh3-2}}] (3c), with an excess of py to give [PdCl{C,N-C6H3-
(MeO-4){C(O)NdPPh3-2}}(py)] (4c), and with AgClO4 and
chelating ligands (1:2:2 molar ratio) to give [Pd{C,N-C6H3-
(MeO-4){C(O)NdPPh3-2}}(L∧L)]ClO4 (L∧L ) dppe 5c, bipy
6c, phen 7c). The IR spectrum of 3c shows the typical
absorptions of the chelating acac ligand (1582, 1513 cm-1), and
1
The H NMR spectra of 6c and 7c show, in addition to ligand
peaks, eight different signals due to the phen or bipy ligands,
meaning that these groups are N,N-bonded.
In conclusion, the palladation of iminophosphoranes Ph3Pd
NC(O)Aryl is regioselective and gives five-membered exo
metallacycles. This type of metalation is quite unusual. In
addition, the resulting palladacycles show a high stability, as it
can be inferred from their reactivity toward different ligands.
2. Synthesis of Ylide Complexes. The metalation of ylides
Ph3ZCHC(O)Ph (Z ) P, As) and Bu3PCHC(O)Ph using Pd(II)
and Pt(II) complexes was described some years ago.10,18 The
ylide Bu3PCHC(O)Ph reacts with Pd(II) substrates at the benzoyl
group, while Ph3AsCHC(O)Ph does not metalate at all. The
results obtained with Pt complexes and the ylide Ph3PCHC-
(O)Ph were not conclusive about the position of platination
(back-door versus front-door).10 The palladation of Ph3PCHC-
(O)Ph has been reported in a previous work,18a and it was
characterized as [Pd(µ-Cl){C,C-C6H4(C(O)CHPPh3)-2}]2, that
is, metalated at the benzoyl ring, but very few conclusive
structural data were given.
The similarity between phosphoylides and iminophospho-
ranes,22 the results described in the preceding section, and the
fact that the hypothetical palladation/platination of Ph3PCHC-
(O)Ph have been poorly characterized18a have prompted us to
study the competitive metalation of different phenacyl P-ylides,
aiming to determine the similitude or complementarity of the
reactivity patterns. In addition, the study of the activation of
C-H bonds on P-ylides is still an active research area.23
The ylides Ph3PdCHC(O)Aryl (Aryl ) Ph 8a, 3-MeOC6H4
8b, 2,5-(MeO)2C6H3 8c) were prepared following the method
reported by Ramirez et al.24 in two steps. The reaction of the
corresponding phenacyl bromide with PPh3 gives the phospho-
(17) Allen, F. H. Acta Crystallogr. 2002, B58, 380.
(18) (a) Dias, S. A.; Downs, A. W.; McWhinnie, W. R. J. Chem. Soc.,
Dalton Trans. 1975, 162. (b) Dias, S. A.; Downs, A. W.; McWhinnie, W.
R. Inorg. Chem. Nucl. Lett. 1974, 10, 233. (c) Chia, L. Y.; Dias, S. A.;
McWhinnie, W. R. J. Inorg. Nucl. Chem. 1976, 38, 1263.
(19) (a) Hedden, D.; Roundhill, D. M.; Fultz, W. C.; Rheingold, A. L.
J. Am. Chem. Soc. 1984, 106, 5014. (b) Hedden, D.; Roundhill, D. M.;
Fultz, W. C.; Rheingold, A. L. Organometallics 1986, 5, 336. (c) Palenik,
G. J.; Giordano, T. J. J. Chem. Soc., Dalton Trans. 1987, 1175. (d) Failes,
T. W. Hall, M. D.; Hambley, T. W. Dalton Trans. 2003, 1596. (e)
Hursthouse, M. B.; Mazid, M. A.; Robinson, S. D.; Sahajpal, A. Chem.
Commun. 1991, 1146. (f) Hursthouse, M. B.; Mazid, M. A.; Robinson, S.
D.; Sahajpal, A. J. Chem. Soc., Dalton Trans. 1993, 2835. (g) Das, A.;
Basuli, F.; Falvello, L. R.; Bhattacharya, S. Inorg. Chem. 2001, 40, 4085.
(h) Bacchi, A.; Carcelli, M.; Costa, M.; Pelagatti, P.; Pelizzi, C.; Pelizzi,
G. J. Chem. Soc., Dalton Trans. 1996, 4239.
(21) Deeming, A. J.; Rothwell, I. P.; Hursthouse, M. B.; New, L. J. Chem.
Soc., Dalton Trans. 1978, 1940.
(22) Johnson, A. W.; Kaska, W. C.; Starzewski, K. A. O.; Dixon, D. A.
Ylides and Imines of Phosphorus; John Wiley and Sons: New York, 1993.
(23) Selected recent references: (a) Onitsuka, K.; Nishii, M.; Matsushima,
Y.; Takahashi, S. Organometallics 2004, 23, 5630. (b) Kubo, K.; Jones, N.
D.; Ferguson, M. J.; McDonald, R.; Cavell, R. G. J. Am. Chem. Soc. 2005,
127, 5314. (c) Petz, W.; Kutschera, C.; Neumu¨ller, B. Organometallics 2005,
24, 5038. (d) Kawachi, A.; Yoshioka, T.; Yamamoto, Y. Organometallics
2006, 25, 2390. (e) Vignolle, J.; Donnadieu, B.; Bourissou, D.; Soleilhavoup,
M.; Bertrand, G. J. Am. Chem. Soc. 2006, 128, 14810.
(20) (a) Vicente, J.; Abad, J. A.; Shaw, K. F.; Gil-Rubio, J.; Ram´ırez de
Arellano, M. C. Organometallics 1997, 16, 4557. (b) Kametani, Y.; Satoh,
T.; Miura, M.; Nomura, M. Tetrahedron Lett. 2000, 41, 2655. (c) Shabashov,
D.; Daugulis, O. Org. Lett. 2006, 8, 4947.
(24) Ram´ırez, F.; Dershowitz, S. J. Org. Chem. 1957, 22, 41.

Cyclopalladation of Phosphorus Ylides and Iminophosphoranes
Organometallics, Vol. 26, No. 14, 2007 3545
protons. The same features have been observed in the 13C{1H}
NMR spectra, where six different resonances are attributed to
the carbon atoms of the PdC6H4 group. All these facts are in
very good agreement with the structures depicted in Scheme 2,
in which the metalated unit is, unambiguously, the PPh3
fragment.
Scheme 2. Synthesis and Reactivity of Orthopalladated
Phenacyl P-Ylides
These results are in clear contrast with those reported
previously,18a in which it was stated that the palladation of
Ph3PdCHC(O)Ph gives the dinuclear orthometalated [Pd(µ-Cl)-
{C,C-C6H4(C(O)CHPPh3)-2}]2. Since our reaction conditions
[Pd(OAc)2, ylide, CH2Cl2, reflux] were quite different from
those described in the original contribution [PdCl2, NaOAc,
ylide, MeOH, reflux], we have carried out an experiment in
the original conditions. After extraction of the solid insoluble
in MeOH, the 31P{1H} NMR spectrum of the extract shows
peaks corresponding to free ylide (15.92 ppm), OdPPh3 (29.79
ppm), and 9a (17.76 and 19.55 ppm, see SI) in a 1.2:0.17:2.98
molar ratio. Thus, in our hands, the material described originally
by McWhinnie et al. was actually the product of metalation at
the PPh3 unit (9a).
We have also reinvestigated the platination of the stabilized
ylide [Ph3PdCHC(O)Ph], in order to ascertain the true nature
of the resulting product and the actual position of metalation.10
However, when the experiment was performed following the
original conditions [PtCl2, ylide, 1:3 molar ratio, NCMe, reflux,
3 h], the starting ylide was recovered and the decomposition of
the platinum salt was clearly observed. A slight modification
of the original method gives improved results. Thus, when a
mixture of PtCl2 and the ylide (1:1 molar ratio) was refluxed in
NCMe for 24 h, complex 9d (see Scheme 2) could be isolated
in pure form after exhaustive washing of the crude reaction
product to eliminate phosphonium salt. The presence of the
cycloplatinated ligand [Pt{C,C-C6H4(PPh2CHC(O)Ph)-2}] is
nium salt, which reacts with a weak base in MeOH/H2O,
allowing the isolation of ylides 8a-c as compounds stable to
air and moisture. The characterization of 8b and 8c follows the
expected patterns: (i) the carbonyl stretch appears in the IR
spectra around 1510 cm-1; (ii) the methine proton appears in
the H NMR spectra as a doublet with a large JPH coupling
constant (around 25 Hz); (iii) the 31P{1H} NMR spectra show
a single peak in each case at about 15 ppm. All these facts are
typical for carbonyl-stabilized ylides.7a Ylides 8a-c react with
Pd(OAc)2 (1:1 molar ratio) in CH2Cl2, and further treatment of
the acetate intermediate with excess LiCl in methanol gives the
palladated complexes 9a-c (see Scheme 2). It is interesting to
note that no decomposition is observed during the first stages
of the reaction, giving 9a-c in high yields.
The IR spectra of 9a-c show a strong absorption in the range
1614-1629 cm-1, which has been shifted to higher frequency
with respect to the starting ylides 8a-c (range 1504-1525
cm-1), meaning that the ylides are C-bonded to the palladium
center.7a The 31P{1H} NMR spectra of 9a-c show two singlet
resonances in each case (range 17-22 ppm), which are shifted
to low field with respect to the parent ylides 8a-c (range 15-
17 ppm), in good agreement with the C-bonding of the ylides.
The presence of two lines of different intensity on each spectrum
can be originated from the presence of two diastereoisomers
(RR/SS and RS/SR), as a result of the C-bonding of the ylide
and the dinuclear nature of 9a-c. The metalation of a phenyl
group of the PPh3 unit is evident from the 1H NMR spectra of
9a-c, since the resonances assigned to the protons of the CC-
(O)Ph fragment can still be observed, while the expected 6:3:6
pattern of the Ho:Hp:Hm protons of the PPh3 group has
disappeared. A new pattern of signals of intensity 1:1:1:1:4:2:4
is observed, partially overlapped due to the presence of the two
diastereoisomers.
1
2
1
unambiguously stated in the H NMR spectrum of the acety-
lacetonate 10d, obtained from reaction of 9d with Tlacac (1:2
molar ratio). There, the observed pattern of resonances of 9d is
very similar to that described for 9a and shows three different
peaks due to the C(O)Ph protons, four different peaks assigned
to the PtC6H4 unit, and the expected signals for the PPh2 group.
Thus, although the reaction conditions are not strictly the same
as those reported previously, in our hands the platination of the
ylide Ph3PdCHC(O)Ph is produced at the PPh3 group, as for
the analogous palladium derivatives. It seems that the metalation
of the ylides is also a general reaction, but with the opposite
regioselectivity of that found for the stabilized iminophospho-
ranes.
Further reactivity of complexes 9a-c shows the stability of
the C,C-palladacycle. The reaction of 9a with PPh3 (1:2 molar
ratio) affords 11a, while treatment of 9a with AgClO4 and
chelating L∧L ligands (1:2:2 molar ratio) gives the mononuclear
dicationic [Pd{C,C-C6H4(PPh2CHC(O)Ph)-2}(L∧L)]ClO4 com-
plexes (L∧L ) dppm-O 12a, dppe 13a, phen 14a, bipy 15a).
In all cases the [C6H4PPh2CH] unit remains C,C-bonded to the
Pd atom, even if the reaction is performed in presence of an
excess of ligand. Complex 11a shows the PPh3 ligand bonded
trans to the ylidic C atom, in accord with the data obtained
from the 31P{1H} NMR spectrum and their comparison with
related arrangements.7b The characterization of complexes 13a
and 14a is straightforward from their corresponding NMR
spectra. Full assignment of the signals due to the phen, C(O)-
C6H5, and Pd(C6H4) fragments was performed with the help of
COSY, 1D-NOESY, and ROESY experiments. In addition, the
31P{1H} NMR spectrum of 12a shows that the dppm ligand
The full characterization of the [Pd{C,C-C6H4(PPh2CHC(O)-
Ph)-2}] moiety has been carried out on the corresponding O,O′-
acetylacetonate derivatives 10a-c, obtained by reaction of 9a-c
with the stoichiometric amount of Tl(acac) (Scheme 2). The
1H NMR spectra of 10a-c show, in addition to the expected
peaks assigned to the acac ligand or the methoxy groups, well-
defined signals attributed to the PdC6H4, C(O)C6HmRn, and PPh2

3546 Organometallics, Vol. 26, No. 14, 2007
Scheme 3. Unexpected Reactivity of Phosphorus Ylide 16
Aguilar et al.
Table 1. Crystal Data and Structure Refinement for Compounds 2d and 9b‚2CHCl3
2d
9b‚2CHCl3
empirical formula
fw
C52H42Cl2N2O2P2Pd2
1072.52
C56H46Cl8O4P2Pd2
1341.27
temp (K)
radiation (λ, Å)
cryst syst
space group
a (Å)
100(2)
0.71073
100(2)
0.71073
triclinic
P1h
9.010(4)
9.1801(6)
17.024(4)
93.230(13)
103.86(3)
99.287(18)
1342.6(7)
1
monoclinic
P2(1)/c
14.5611(4)
9.8108(2)
16.4092(4)
b (Å)
c (Å)
R (deg)
â (deg)
108.644(3)
γ (deg)
V (Å3)
2221.14(9)
2
1.604
1.047
Z
D
calc (Mg/m3)
1.659
1.174
µ (mm-1
)
cryst size (mm3)
0.39 × 0.16 × 0.02
0.19 × 0.11 × 0.02
no. of reflns collected
no. of indep reflns
16 269
8974
4495 (Rint ) 0.0425)
4495/0/281
0.931
R1 ) 0.0277, wR2 ) 0.0582
R1 ) 0.0486, wR2 ) 0.0613
0.744 and -0.606
4332 (Rint ) 0.0408)
4332/0/326
0.960
R1 ) 0.0324, wR2 ) 0.0479
R1 ) 0.0591, wR2 ) 0.0503
0.578 and -0.604
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak, hole (e‚Å-3
)
has been mono-oxidized, since no signals are found at high field
and since a resonance at 58.20 ppm clearly indicates the
presence of the P(O)Ph2 unit. This type of oxidation has already
been reported,7b,25 and a similar arrangementsthe O atom trans
to the palladated C atomsis also here proposed.
group, even in the presence of two methoxy substituents. In
complexes 9a-15a the metalation can be considered, not strictly
speaking, to be an endo metalation, since the P-CR bond
belongs to the palladacycle, and this seems to be the most
represented arrangement. As far as we know, only one example
of exo-cyclometalated ylidesthe CdPR3 double bond projecting
out of the metallacycleshas been reported.26 There, the forma-
tion of the ylide is produced by nucleophilic attack of PMe3 at
the C(alkylidene) of the transient nickelacyle [Ni(C6H4CMe2-
CH)Cl(PMe3)]. Clearly, the formation of the ylide is produced
after the metalation, then it cannot be properly considered as
an example of direct ylide metalation.
However, it can be argued that the metalation at the benzoyl
ring on compound 8c is not very favored, since the 2 position
is blocked by one OMe group and the 6 position is sterically
hindered by the presence of the 5-OMe substituent. Due to these
facts, we have prepared the less hindered ylide Ph3PdCHC-
The metalation of the stabilized ylides 8a-c has taken place
at the phenyls of the PPh3 unit, in spite of the presence of one
or even two activating methoxy groups at the benzoyl ring. This
fact has been unambiguously established through the spectro-
scopic characterization of derivatives 9a-15a and through the
X-ray structure determination of 9b (see below). In additon,
this result is in good agreement with those reported previously
for direct palladation of P-ylides,7,10 since in all reported cases
the phenylic C-H bonds at the phosphonium group are easily
activated. Following our previous reasoning, these results imply
that, in these ylides, the phenyl rings at the PPh3 fragment are
more electron-rich than that at the benzoyl unit, assuming an
electrophilic mechanism for the aromatic substitution, and show
that the carbonyl group actually behaves as a strong deactivating
(26) (a) Beldarra´ın, T. R.; Nicasio, M. C.; Paneque, M.; Poveda, M. L.;
Carmona, E. Gazz. Chim. Ital. 1994, 124, 341. (b) Carmona, E.; Gutie´rrez-
Puebla, E.; Monge, A.; Paneque, M.; Poveda, M. L. J. Chem. Soc., Chem.
Commun. 1991, 148.
(25) Vicente, J.; Arcas, A.; Bautista, D.; Jones, P. G. Organometallics
1997, 16, 2127.

Cyclopalladation of Phosphorus Ylides and Iminophosphoranes
Organometallics, Vol. 26, No. 14, 2007 3547
Table 2. Selected Bond Distances (Å) and Angles (deg) for
Compound 2d
Pd(1)-C(1)
Pd(1)-Cl(1)
P(1)-N(1)
P(1)-C(15)
N(1)-C(8)
C(5)-C(8)
C(1)-C(2)
C(2)-C(3)
C(4)-C(6)
1.962(3)
2.3270(6)
1.629(2)
1.793(3)
1.393(4)
1.489(4)
1.387(4)
1.376(4)
1.380(4)
Pd(1)-N(1)
Pd(1)-Cl(1A)
P(1)-C(21)
P(1)-C(9)
O(1)-C(8)
C(6)-C(7)
C(1)-C(5)
C(3)-C(4)
C(5)-C(6)
2.043(2)
2.4646(8)
1.788(3)
1.812(3)
1.228(3)
1.504(4)
1.400(4)
1.382(4)
1.408(4)
C(1)-Pd(1)-N(1)
N(1)-Pd(1)-Cl(1)
80.44(10)
174.61(7)
N(1)-Pd(1)-Cl(1A) 99.18(7)
Pd(1)-Cl(1)-Pd(1A) 93.94(2)
C(1)-Pd(1)-Cl(1)
94.20(8)
C(1)-Pd(1)-Cl(1A) 173.24(8)
Cl(1)-Pd(1)-Cl(1A) 86.06(2)
C(8)-N(1)-P(1)
117.20(17)
130.98(14)
125.5(3)
C(8)-N(1)-Pd(1)
O(1)-C(8)-N(1)
N(1)-C(8)-C(5)
111.19(16) P(1)-N(1)-Pd(1)
123.3(3)
111.1(2)
O(1)-C(8)-C(5)
Figure 3. Thermal ellipsoid drawing of complex 2d. Ellipsoids
representing non-H atoms are drawn at the 50% probability level.
sensible to assume that the first C-H bond activation is
produced at the PPh3 group and that the presence of two
methoxy substituents at the 2- and 4-positions of the benzoyl
ring counterbalances the deactivating effect of the carbonyl
group and leaves a nonsterically hindered ortho C-H bond, able
to be activated. The Caryl,O-orthometalation is known in Pd(II)
chemistry, although it is one of the less represented bonding
modes,1j,2a,g and, as far as we know, no examples have been
reported using ylides as substrates.
(O)C6H3(OMe)-2,4 (16), following reported procedures,24 and
studied its palladation reactions. The treatment of 16 with Pd-
(OAc)2 (see Experimental Section, Scheme 3 and SI) under the
same experimental conditions as those described for 9a-c (5 h
of reflux were used instead of 4 h in order to improve the
reaction yield) gives the polymeric complex 17. The analytic
data of 17 show that the reaction has not occurred in the same
way as that described for complexes 9, since two units PdCl
are present by each ylide group. In accord with this, we have
proposed the stoichiometry shown in Scheme 3, which has been
confirmed in subsequent reactions. The extreme insolubility of
17 prevents a complete characterization, and more soluble
derivatives have been obtained through the synthesis of the
acetylacetonate 18 or formation of the adduct of PPh3 (19), all
3. X-ray Crystal Structure of Complexes 2d and 9b. A
drawing of complex 2d is shown in Figure 3, relevant crystal-
lographic parameters are given in Table 1, and selected bond
distances and angles are collected in Table 2. The structure
shows a dinuclear complex, with two fragments, [Pd{C6H3-
(C(O)NPPh3)-2-Me-3}], bridged by two Cl ligands. The relative
arrangement of the two cyclometalated unit is trans, probably
in order to minimize steric repulsions between the two bulky
PPh3 units. Each Pd atom is located in a slightly distorted square-
planar environment, surrounded by the orthometalated C(1)
atom, the iminic N(1) atom, and the two bridging chloride
ligands, confirming the exo metalation of the iminophosphorane.
The Pd(1)-C(1) bond distance [1.962(3) Å] is identical,
within experimental error, to those found in other palladated
iminophosphoranes. For instance, the distance found in [PdCl-
(C6H4(PPh2dN-C(O)-2-py)-2)] is 1.976(3) Å,8 while those
found in [Pd(C6H4(PPh2dNC6H4Me-4′)-2)(µ-OAc)]2 are 1.964-
(3) and 1.959(3) Å.11m However, the Pd(1)-N(1) bond distance
[2.043(2) Å] is slightly longer than that found in [PdCl(C6H4-
(PPh2dN-C(O)-2-py)-2)] [1.997(2) Å], while it is identical,
within experimental error, to those reported in [Pd(C6H4-
(PPh2dNC6H4Me-4′)-2)(µ-OAc)]2 [2.050(2) and 2.051(2) Å]
and [Pd(C6H4(PPh2dNC6H4Me-4′)-2)(tmeda)]ClO4 [2.055(2)
Å].11m All these facts reflect similar environments to those
reported previously, even though the metalated carbon belongs
to P-Ph group or to a benzamido group. The Pd(1)-Cl(1) and
Pd-Cl(1A) bonds are quite different, reflecting the different
trans influence of the carbon and nitrogen atoms. The internal
parameters of the metalated ligand have been compared with
those found in other iminophosphoranes derived from benza-
mide.27 Thus, the P(1)-N(1) bond distance [1.629(2) Å] is
identical, within experimental error, to that found in free Ph3Pd
N-C(O)Ph [1.626(3) Å].27a The effect of the coordination and
subsequent loss of conjugation is more evident on the NCO
fragment. The N(1)-C(8) bond distance [1.393(4) Å] is longer
1
reactions shown in Scheme 3. The H NMR spectrum of 18
shows very clearly the presence of two different acac ligands
for each ylide unit, confirming the stoichiometry of 17, and also
shows the absence of two protons in the ylide ligand, showing
that two C-H bond activations have been produced in 16. Thus,
two doublets (4JHH ) 2.5 Hz) at 6.10 and 6.49 ppm are assigned
to the protons at the 4 and 6 positions of the palladated C6H2
aryl group, while four different resonances at 6.99, 7.10, 7.30,
and 7.91 ppm are attributed to the PdC6H4 moiety. In addition,
peaks corresponding to the PPh2 unit are also observed. The
relative intensity of these three sets of resonances is 2:4:10.
This pattern can be easily explained considering that the Pd
atom has activated the 6 position of the benzoyl ring and one
of the ortho C-H bonds of the PPh3 moiety in 16. Similar
conclusions can be derived from the analysis of the 13C{1H}
(APT) NMR spectrum of 18. There, in addition to the expected
signals assigned to the two palladated aryl rings, the O-bonding
of the ylide can be inferred from the observation of a strongly
deshielded carbonyl peak (213.00 ppm). Moreover, the IR
spectrum of 18 gives an additional proof of the O-coordination,
since the νCO of the ylide carbonyl ligand is found at the lowest
energy among the complexes reported here (1568 cm-1), only
slightly higher than the value found in the free ylide (1517
cm-1). All these facts are in very good agreement with the
structure depicted for 18 in Scheme 3. The spectroscopic
characterization of complex 19 also agrees with the structure
shown in Scheme 3 (see Experimental Section).
The synthesis of complexes 17-19 is very noteworthy, since
they contain an ylide-bridging ligand in which a double C-H
bond activation has occurred and because the ylide is acting in
a very rare coordination mode (C,C,C,O-tetradentate). In light
of the preceding results, mainly the synthesis of 9c, it seems
(27) (a) Bar, I.; Bernstein, J. Acta Crystallogr., Sect. B 1980, 36, 1962.
(b) Lo´pez-Ort´ız, F.; Pela´ez-Arango, E.; Palacios, F.; Barluenga, J.; Garc´ıa-
Granda, S.; Tejerina, B.; Garc´ıa-Ferna´ndez, A. J. Org. Chem. 1994, 59,
1984.

3548 Organometallics, Vol. 26, No. 14, 2007
Aguilar et al.
Å vs 1.39 Å in ref 28], while the Câ-O bond distance is shorter
in 9b [C(20)-O(1) ) 1.233(4) Å] than in the free ylide [1.26
Å]. All these data are also in good agreement with the loss of
conjugation by coordination. Finally, and it has been noted in
other keto-stabilized ylides,29 the P-O intramolecular distance
[2.902 Å] is shorter than the sum of the van der Waals radii
[3.32 Å],30 and the value of the dihedral angle PCCO is 17.0°.
Other internal parameters of the metalated ylide ligand do not
deviate from published values and are not relevant.
Conclusion
The palladation of iminophosphoranes Ph3PdNC(O)Aryl is
regioselective and gives five-membered exo metallacycles of
high stability. Several factors, such as the metalloaromaticity
or the charge distribution, could be responsible for the orienta-
tion of the reaction. In this particular case, the selectivity
observed seems to be more closely related with the charge
distribution in the ligand than with other factors.
In summary, the palladation of stabilized phosphoylides
Ph3PdCHC(O)Aryl occurs regioselectively at the phenyl rings
of the PPh3 group. The same behavior is observed for the
cycloplatination reaction, in the reported conditions. Only when
the benzoyl ring is activated with at least two methoxy
substituents is the metalation of the two aryl rings competitive.
Here we have obtained one case in which the two palladations
are present at the same time. These results are in clear contrast
with those reported for the iminophosphoranes Ph3PdNC(O)-
Aryl, in spite of the resemblance of the two ligands. Factors
such as the metalloaromaticity, the charge distribution, and the
structure of the starting materials, among others, are responsible
for the delicate counterbalance that drives the final orientation
of the reaction.
Figure 4. Thermal ellipsoid drawing of complex 9b. Ellipsoids
representing non-H atoms are drawn at the 50% probability level.
Table 3. Selected Bond Distances (Å) and Angles (deg) for
Compound 9b‚2CHCl3
Pd(1)-C(1)
Pd(1)-Cl(1A)
P(1)-C(19)
P(1)-C(13)
C(1)-C(2)
1.977(4)
2.3804(14) Pd(1)-Cl(1)
Pd(1)-C(19)
2.090(3)
2.4443(13)
1.775(4)
1.811(4)
1.411(4)
1.377(5)
1.381(5)
1.233(4)
1.777(4)
1.802(4)
1.395(5)
1.391(5)
1.392(5)
1.488(4)
1.517(5)
P(1)-C(6)
P(1)-C(7)
C(1)-C(6)
C(3)-C(4)
C(5)-C(6)
C(20)-O(1)
C(2)-C(3)
C(4)-C(5)
C(19)-C(20)
C(20)-C(21)
C(1)-Pd(1)-C(19)
87.52(15) C(1)-Pd(1)-Cl(1A) 93.31(11)
170.81(10)
93.51(11) Cl(1A)-Pd(1)-Cl(1) 85.97(5)
C(19)-Pd(1)-Cl(1×bb) 177.94(10) C(1)-Pd(1)-Cl(1)
C(19)-Pd(1)-Cl(1)
Pd(1A)-Cl(1)-Pd(1)
C(20)-C(19)-Pd(1)
O(1)-C(20)-C(19)
C(19)-C(20)-C(21)
94.03(5)
109.8(2)
120.8(4)
119.7(3)
C(20)-C(19)-P(1)
P(1)-C(19)-Pd(1)
113.1(3)
99.14(17)
O(1)-C(20)-C(21) 119.5(3)
than that found in the free ligand [1.353(5) Å], meaning that
this bond has been relaxed, while the C(8)-O(1) bond distance
[1.228(3) Å] is shorter than that observed in Ph3PdN-C(O)Ph
[1.245(5) Å].27a Then, the N-bonding of the ligand fixes the
density charge at the N atom and breaks the conjugation in the
NCO system, increasing the participation of the A and B
resonant forms in the bonding description (Figure 2). Other
internal parameters are as usual and do not merit further
comment.
Experimental Section
Safety note: Caution! Perchlorate salts of metal complexes
with organic ligands are potentially explosive. Only small
amounts of these materials should be prepared, and they should
be handled with great caution. See: J. Chem. Educ. 1973, 50,
A335-A337.
Synthesis of 2a. To a solution of Pd(OAc)2 (0.500 g, 1.31
mmol) in CH2Cl2 (20 mL) was added 1a (0.294 g, 1.31 mmol),
and the resulting solution was refluxed for 2 h. At this point
some decomposition is evident. After cooling, the black
suspension was filtered over Celite, giving an orange solution.
This clear solution was evaporated to dryness, and the oily
residue was redissolved in MeOH (20 mL). To this solution
was added an excess of anhydrous LiCl (0.222 g, 5.24 mmol),
and the stirring was prolongued at rt for 20 h. During this time
a yellow solid (2a) precipitated, which was filtered, washed with
additional MeOH (10 mL) and Et2O (40 mL), and dried by
suction. Yield: 0.205 g (30.0%). Anal. Calc for C50H38-
Cl2N2O2P2Pd2 (1044.55): C, 57.49; H, 3.67; N, 2.68. Found:
C, 57.37; H, 4.01; N, 2.58. MS (FAB+): m/z (%) 487 [(M/2
- Cl)+, 28%]. IR (ν, cm-1): 1654 (νCO), 1284 (νNP). 1H NMR
With respect to compound 9b, a drawing is shown in Figure
4, relevant crystallographic parameters are given in Table 1,
and selected bond distances and angles are collected in Table
3. The structure also shows a trans dinuclear complex, but now
the two fragments bridged by two chlorine ligands are [Pd-
(C6H4(PPh2CHC(O)C6H4-3-OMe)-2)]. The metalation at the Ph
rings of the PPh3 unit is thus confirmed, in good agreement
with the NMR data. Each Pd atom is located in a square-planar
environment, surrounded by the palladated C(1) atom, the ylidic
C(19) atom, and the two bridging Cl ligands.
The Pd(1)-C(1) bond distance [1.977(4) Å] is statistically
identical to that found in 2d and falls at the low end of the
usual range of Pd-C bond distances found for metalated ylides
[1.998(3)-2.012(10) Å],7b,c,9h and the same conclusion can be
derived from the comparison of the Pd(1)-C(19) bond distance
[2.090(3) Å] with respect to published examples [range 2.083-
(9)-2.161(8) Å]. The Pd(1)-Cl(1) and Pd-Cl(1A) bonds are
also different, reflecting the very different trans influence of
the two types of carbon atoms. The comparison of internal bond
distances and angles of the metalated ylide with respect to the
free ylide28 follows the expected pattern. Thus, the P-CR bond
is clearly elongated in 9b [P(1)-C(19) ) 1.777(4) Å] with
respect to the value found in Ph3PdCHC(O)Ph [1.71 Å], as
well as the CR-Câ bond distance [C(19)-C(20) ) 1.488(4)
3
(CDCl3): δ 6.77-6.80 (m, 2H, H5, H6), 6.90 (t, 1H, H4, JHH
3
) 7.5), 7.15 (d, 1H, H3, JHH ) 7.5), 7.33-7.38 (m, 6H, Hm,
(28) Shao, M.; Jin, X.; Tang, Y.; Huang, Q.; Huang, Y. Tetrahedron
Lett. 1982, 23, 5343.
(29) (a) Lledo´s, A.; Carbo´, J. J.; Urriolabeitia, E. P. Inorg. Chem. 2001,
40, 4913. (b) Lledo´s, A.; Carbo´, J. J.; Navarro, R.; Urriolabeitia, E. P. Inorg.
Chim. Acta 2004, 357, 1444. (c) Serrano, E.; Valle´s, C.; Carbo´, J. J.; Lledo´s,
A.; Soler, T.; Navarro, R.; Urriolabeitia, E. P. Organometallics 2006, 25,
4653.
(30) Bondi, A. J. Phys. Chem. 1964, 68, 441.

Cyclopalladation of Phosphorus Ylides and Iminophosphoranes
Organometallics, Vol. 26, No. 14, 2007 3549
PPh3), 7.43-7.46 (m, 3H, Hp, PPh3), 7.89-7.94 (m, 6H, Ho,
PPh3). 31P{1H} NMR (CDCl3): δ 30.20.
(s, CHP, minor) 7.13-7.25 (m, C6H4), 7.37-7.42 (m, Hm, PhCO
minor + C6H4), 7.46-7.49 (m, Hm, PhCO major), 7.51-7.91
(m, PPh2+C6H4), 7.94-7.98 (m, PPh2), 8.04 (d, Ho, PhCO
major, 3JHH ) 7.2), 8.17 (d, Ho, PhCO minor, 3JHH ) 7.6). 31P-
{1H} NMR (dmso-d6): δ 17.71 (major), 19.53 (minor).
Synthesis of 2d. Compound 2d was prepared following the
same synthetic method as that reported for 2a. Thus, Pd(OAc)2
(0.280 g, 1.26 mmol) was reacted with 1d (0.500 g, 1.26 mmol)
and LiCl (0.210 g, 5.06 mmol) to give 2d as a yellow solid.
Yield: 0.224 g, (33.0%). Anal. Calc for C52H42Cl2N2O2P2Pd2
(1072.60): C, 58.23; H, 3.95; N, 2.61. Found: C, 58.40; H,
4.07; N, 2.56. MS (FAB+): m/z (%) 500 [(M/2 - Cl)+, 22%].
Synthesis of 9b. Compound 9b was prepared following the
same synthetic method as that reported for 9a. Thus, 8b (0.070
g, 0.17 mmol) was reacted with Pd(OAc)2 (0.038 g, 0.17 mmol)
in CH2Cl2 and with LiCl (0.029 g, 0.68 mmol) in MeOH (15
mL) to give 9b as a yellow solid. Yield: 0.085 g (91%). 9b
was characterized by NMR as a mixture of diastereoisomers in
1.3:1 molar ratio. Anal. Calc for C54H44Cl2O4P2Pd2 (1102.6):
C, 58.82; H, 4.02. Found: C, 59.32; H, 4.03. MS (MALDI)
[m/z, (%)]: 1066.2 (8%) [M - Cl - H]+. IR (ν, cm-1): 1627
(νCO). 1H NMR (CDCl3): δ 3.57 (s, OMe, major), 3.60 (s, OMe,
minor), 4.74 (s, CHP, minor), 4.83 (d, CHP, major, 2JPH ) 2.3),
6.72-7.93 (m, Ph, major + minor).31P{1H} NMR (CDCl3): δ
17.92 (s, major), 19.50 (s, minor).
1
IR (ν, cm-1): 1646 (νCO), 1307 (νNP). H NMR (CDCl3): δ
2.20 (s, 3H, Me), 6.65-6.80 (m, 3H, H4, H5, H6), 7.33-7.36
(m, 6H, Hm, PPh3), 7.41-7.45 (m, 3H, Hp, PPh3), 7.88-7.93
(m, 6H, Ho, PPh3). 13C{1H} NMR (CDCl3): δ 19.52 (Me),
1
125.80 (d, JPC ) 101.7, Ci, PPh3), 127.75, (C6H4), 128.55
3
(C6H4), 129.02 (d, JPC ) 12.9, Cm, PPh3), 131.60 (C6H4),
4
2
133.14 (d, JPC ) 2.2, Cp, PPh3), 134.06 (d, JPC ) 10.1, Co,
3
4
PPh3), 136.07 (d, JPC ) 13.0, C2, C6H4), 140.02 (d, JPC
)
2.7, C3, C6H4), 145.09 (C1, C6H4), 181.65 (d, 2JPC ) 6.9, CO).
31P{1H} NMR (CDCl3): δ 31.31.
Synthesis of 9c. Compound 9c was prepared following the
same synthetic method as that reported for 9a. Thus, 8c (0.16
g, 0.36 mmol) was reacted with Pd(OAc)2 (0.082 g, 0.36 mmol)
in CH2Cl2 and with LiCl (0.061 g, 1.44 mmol) in MeOH (15
mL) to give 9c as a yellow solid. Yield: 0.165 g (77%). 9c
was characterized by NMR as a mixture of diastereoiosmers
in 1.25:1 molar ratio. Anal. Calc for C56H48Cl2O6P2Pd2
(1162.65): C, 57.85; H, 4.16. Found: C, 58.03; H, 4.26. MS
(MALDI) [m/z, (%)]: 1127 (11%) [M - Cl]+. IR (ν, cm-1):
Synthesis of 3c. To a solution of 2c (0.295 g, 0.270 mmol)
in CH2Cl2 (20 mL) was added Tl(acac) (0.162 g, 0.530 mmol),
resulting in the immediate precipitation of TlCl. This suspension
was stirred for 1 h at 25 °C and then filtered over Celite. The
clear yellow solution was evaporated to dryness and the residue
treated with cold n-pentane (10 mL), to give 3c as a yellow
solid. Yield: 0.192 g (58.4%). Anal. Calc for C31H28NO4PPd-
(615.94): C, 60.45; H, 4.58; N, 2.27. Found: C, 59.95; H, 4.29;
N, 1.97. IR (ν, cm-1): 1650 (νCO), 1582, 1513 (νCO, acac) 1267
1
1626 (νCO). H NMR (CDCl3): δ 3.47 (s, OMe, minor), 3.53
1
(νNP). H NMR (CDCl3): δ 0.98 (s, 3H, Me, acac), 1.88 (s,
(s, OMe, major), 3.61 (s, OMe, major), 3.75 (m, OMe, minor),
5.10 (d, CHP, major, 2JPH ) 4.0), 5.29 (s, CHP, minor), 6.69-
6.80 (m, H3 + H4, C6H4, major + minor), 6.97-7.47 (m, H6,
major + minor, Ph+C6H4, major + minor), 7.84-7.85 (m, Ho,
PPh2, major + minor). 31P{1H} NMR (CDCl3): δ 21.38 (minor),
21.90 (major).
3H, Me, acac), 3.65 (s, 3H, OMe), 4.93 (s, 1H, CH, acac), 6.79
3
4
(dd, 1H, H5, C6H4, JHH ) 8.3, JHH ) 2.9), 6.87 (d, 1H, H3,
C6H4, 4JHH ) 2.9), 7.40-7.45 (m, 7H, H6 + Hm, PPh3), 7.49-
7.53 (m, 3H, Hp, PPh3), 7.93-7.97 (m, 6H, Ho, PPh3). 31P{1H}
NMR (CDCl3): δ 28.04.
Synthesis of 4c. To a solution of 2c (0.301 g, 0.27 mmol) in
CH2Cl2 (10 mL) was added an excess of py (87.56 µL, 1.08
mmol), and the resulting yellow solution was stirred for 30 min
at rt. After the reaction time, the solvent was evaporated to
dryness and the residue treated with cold n-hexane (15 mL) to
give 4c as a yellow solid. Yield: 0.199 g (57.8%). Anal. Calc
for C31H26ClN2O2PPd (631.39): C, 58.97; H, 4.15; N, 4.44.
Found: C, 59.45; H, 4.34; N, 4.56. MS (FAB+): m/z (%) 595
(100%) [(M - Cl)+]. IR (ν, cm-1): 1644 (νCO), 1582, 1513
(νCO, acac), 1273 (νNP). 1H NMR (CDCl3): δ 3.65 (s, 3H, OMe),
Synthesis of 10a. Compound 10a was prepared following
the same synthetic method as that reported for 3c. Thus, 9a
(0.200 g, 0.190 mmol) was reacted with Tl(acac) (0.120 g, 0.38
mmol) in CH2Cl2 to give 10a as a yellow solid. Yield: 0.101
g (46.4%). Anal. Calc for C31H27O3PPd (584.95): C, 63.65; H,
4.65. Found: C, 64.24; H, 4.48. MS (MALDI) [m/z, (%)]: 485
(100%) [(M - acac)+]. IR (ν, cm-1): 1625 (νCO), 1564, 1514
(νCO, acac). 1H NMR (CDCl3): δ 1.70 (s, 3H, CH3, acac), 1.89
(s, 3H, CH3, acac), 4.80 (d, 1H, CHP, 2JPH ) 3.3), 5.11 (s, 1H,
CH, acac), 7.04-7.12 (m, 1H, C6H4), 7.12-7.18 (m, 1H, C6H4),
7.20-7.22 (m, 1H, C6H4), 7.25-7.31 (m, 2H, Hm, PhCO),
7.33-7.42 (m, 3H, Hp (PhCO) + Hm (PPh2)), 7.42-7.51 (m,
2H, Hm, PPh2), 7.50-7.57 (m, 2H, Hp (PPh2)),7.63-7.68 (m,
1H, C6H4), 7.89-7.96 (m, 4H, Ho, PPh2), 8.15 (d, 2H, Ho,
3
3
6.10 (d, 1H, H6, JHH ) 8.4), 6.56 (dd, 1H, H5, JHH ) 8.4,
4
4JHH ) 3.0), 6.94 (d, 1H, H3, JHH ) 3.0), 7.23-7.26 (m, 2H,
Hm, py), 7.43-7.47 (m, 6H, Hm, PPh3), 7.49-7.52 (m, 3H, Hp,
PPh3), 7.65-7.70 (m, 1H, Hp, py), 8.01-8.06 (m, 6H, Ho, PPh3),
3
4
3
8.78 (dd, 2H, Ho, py, JHH ) 6.2, JHH ) 1.2). 31P{1H} NMR
PhCO, JHH ) 9.6). 31P{1H} NMR (CDCl3): δ 21.20.
(CDCl3): δ 30.82.
Synthesis of 10b. Compound 10b was prepared following
the same synthetic method as that reported for 3c. Thus, 9b
(0.06 g, 0.054 mmol) was reacted with Tl(acac) (0.033 g, 0.109
mmol) in CH2Cl2 to give 10b as a yellow solid. Yield: 0.031
g (46.3%). Anal. Calc for C32H29O4PPd (614.95): C, 62.50; H,
4.75. Found: C, 62.00; H, 4.75. MS (MALDI) [m/z, (%)]: 515.0
(67%) [(M - acac)+]. IR (ν, cm-1): 1618 (νCO), 1564, 1515
(νCO, acac). 1H NMR (CDCl3): δ 1.73 (s, 3H, CH3, acac), 1.88
(s, 3H, CH3, acac), 3.72 (s, 3H, OMe), 4.78 (d, 1H, CHP, 2JPH
) 3.6), 5.11 (s, 1H, CH, acac), 6.91 (dd, 1H, H4, C6H4O, 3JHH
Synthesis of 9a. To a solution of 8a (1.00 g, 2.63 mmol) in
CH2Cl2 (10 mL) was added Pd(OAc)2 (0.59 g, 2.63 mmol), and
the resulting brown solution was refluxed for 4 h. Then the
solvent was evaporated to dryness, and the yellow residue was
redissolved in MeOH (15 mL), treated with an excess of LiCl
(0.44 g, 10.52 mmol). and further stirred for 30 min at rt. During
this time 9a precipitated as a yellow solid, which was filtered,
washed with additional MeOH (5 mL) and Et2O (20 mL), and
dried by suction. Yield: 0.61 g, (45%). The NMR characteriza-
tion of 9a showed that it was a mixture of two diastereoiso-
mers in 2.5:1 molar ratio. Anal. Calc for C52H40Cl2O2P2Pd2
(1042.60): C, 59.91; H, 3.87. Found: C, 58.97; H, 4.02. MS
(MALDI) [m/z, (%)]: 485.1 (30%) [M/2 - Cl]+. IR (ν, cm-1):
1625 (νCO). 1H NMR (dmso-d6): δ 5.13 (s, CHP, major), 5.41
4
) 9.0, JHH ) 2.0), 7.07 (m, 1H, H5, C6H4), 7.15-7.23 (m,
3H, H5 (C6H4O) + H3, H4 (C6H4)), 7.38 (m, 2H, Hm, PPh2),
7.43-7.54 (m, 4H, Hm (PPh2) + Hp (PPh2)), 7.64-7.67 (m,
2H, H2 + H6, C6H4O + C6H4), 7.77-7.82 (m, 3H, Ho (PPh2)
+ H6 (C6H4O)), 7.89 (m, 2H, Ho, PPh2). 13C{1H} NMR

3550 Organometallics, Vol. 26, No. 14, 2007
Aguilar et al.
3
(CDCl3): δ 27.81 (CH3, acac), 27.96 (CH3, acac), 35.50 (d,
Ho (PhCO) + Ho, Hp (PPh2)), 8.34 (dd, 1H, Hγ, phen, JHH
)
)
1
4
3
4
CHP, JPC ) 65.6), 55.44 (OMe), 99.46 (s, CH-acac), 113.07
8.4, JHH ) 1.2), 8.52 (dd, 1H, Hγ′, phen, JHH′ ) 8.0, JHH′
(d, C2, C6H4O, 4JPC ) 1.5), 118.23 (C4, C6H4O), 121.82 (d, C6,
1.2), 8.69 (d, 1H, HR, phen, JHH ) 4.4), 8.95 (dd, 1H, HR′,
3
C6H4O, 4JPC ) 1.1), 124.57 (d, C5, C6H4, 4JPC ) 13.3), 126.13
phen, JHH ) 4.8). 31P{1H} NMR (CD2Cl2): δ 19.43.
3
1
1
(d, Cipso, PPh2, JPC ) 70.0), 127.47 (d, Cipso, PPh2, JPC
)
Synthesis of 16. Compound 16 was prepared following the
same synthetic method as that reported for 8b or 8c Thus, PPh3
(1.062 g, 4.05 mmol) was reacted with BrCH2C(O)C6H3-2,4-
(OMe)2 (0.350 g, 1.35 mmol) in refluxing CH2Cl2 (24 h) to
give the corresponding phosphonium salt in 95.3% yield. IR
(ν, cm-1): 1644 (νCO) cm-1. 1H NMR (CDCl3): δ 3.79 (s, 3H,
57.56), 125.49 (C5, C6H4O), 128.55 (d, Cm, PPh2, 3JPC ) 11.4),
128.67 (d, Cm, PPh2, 3JPC ) 11.7), 129.56 (d, C3, C6H4, 2JPC
)
3
15.7), 130.12 (d, C4, C6H4, JPC ) 3.5), 132.38 (d, Cp, PPh2,
4JPC ) 2.7), 132.50 (d, Cp, PPh2, JPC ) 2.8), 132.95 (d, Co,
4
2
3
PPh2, JPC ) 8.9), 133.67 (d, C6, C6H4, JPC ) 15.4), 134.49
(d, Co, PPh2, 2JPC ) 9.9), 138.03 (d, C2, C6H4, 1JPC ) 117.53),
139.94 (d, C1, C6H4O, 3JPC ) 8.8), 159.28 (C3, C6H4O), 159.32
2
OMe), 4.00 (s, 3H, OMe), 5.91 (d, 2H, CH2P, JPH ) 10.8),
6.40 (d, 1H, H3, 4JHH ) 2), 6.44 (dd, 1H, H5, 3JHH ) 8.8), 7.56-
2
3
(d, C1, C6H4, JPC ) 21.1), 186.20 (CO, acac), 186.84 (CO,
7.61 (m, 6H, Hm, PPh3), 7.68 (t, 3H, Hp, PPh3, JHH ) 7.6),
acac), 194.9 (d, C ) O, JPC ) 3.7). 31P{1H} NMR (CDCl3):
2
3
3
7.76 (d, 1H, H6), 7.82 (dd, 6H, Ho, PPh3, JPH ) 12.8, JHH
)
8.0). 31P{1H} NMR (CDCl3): δ 21.59. 13C{1H} NMR
(CDCl3): δ 41.54 (d, CH2P, 1JPC ) 60.0), 55.83 (OMe), 56.82
δ 20.86.
Synthesis of 11a. To a suspension of 9a (0.20 g, 0.19 mmol)
in CH2Cl2 (15 mL) was added PPh3 (0.10 g, 0.38 mmol). The
initial yellow suspension gradually dissolved, and after 30 min
stirring at rt the resulting solution was filtered over a Celite
pad in order to remove any residual insoluble solid. The clear
solution was evaporated to dryness, and the treatment of the
oily residue with Et2O (30 mL) gave 11a as a yellow solid.
Yield: 0.250 g, (81.3%). Anal. Calc for C44H35ClOP2Pd
(783.60): C, 67.44; H, 4.50. Found: C, 67.30; H, 4.84. MS
(FAB+) [m/z, (%)]: 747 (15%) [M - Cl]+. IR (ν, cm-1): 1610
3
(OMe), 98.32 (C3), 106.46 (C5), 118.55 (d, C1, JPC ) 4.3),
1
119.42 (d, Ci, PPh3, JPC ) 89.0), 123.24 (C4), 130.12 (d, Cm,
3
2
PPh3, JPC ) 13.0), 133.64 (C6), 134.0 (d, Co, PPh3, JPC
)
10.5), 134.5 (d, Cp, PPh3, 4JPC ) 3.0), 162.36 (C4), 166.57 (C2),
2
189.16 (d, CdO, JPC ) 6.6). Anal. Calc for C28H26BrO3P
(521.12): C, 64.50; H, 5.03. Found: C, 64.40 H, 5.47. In a
second step, the phosphonium salt (0.200 g, 0.384 mmol) was
reacted with KOH (0.032 g, 0.576 mmol) in methanol/water
(10 mL/10 mL) to give 8c as a white solid. Yield: 0.067 g
(39.4%). Anal. Calc for C28H25O3P (440.21): C, 76.34; H, 5.72.
Found: C, 76.85 H, 5.73. IR (ν, cm-1): 1517 (νCO). 1H NMR
(CDCl3): δ 3.74 (s, 3H, OMe), 3.79 (s, 3H, OMe), 4.65 (d,
1H, CHP, 2JPH ) 29.2), 6.40 (s, br, 1H, H3), 6.43 (dd, 1H, H5,
3JHH ) 8.8, 4JHH ) 2.4), 7.40-7.36 (m, 6H, Hm, PPh3), 7.46 (t,
3H, Hp, PPh3, 3JHH ) 6.8), 7.67 (dd, 6H, Ho, PPh3, 3JPH ) 12.4,
1
(νCO). H NMR (CDCl3): δ 5.43 (s, 1H, CHP), 6.45 (s, 2H,
C6H4), 6.79-6.84 (m, 1H, C6H4), 7.07-7.11 (m, 6H, Hm, PPh3),
7.15 (m, 1H, C6H4), 7.18-7.25 (m, 9H, Ho + Hp, PPh3), 7.27-
7.38 (m, 5H, Hm, PPh2, Hm + Hp, (PhCO)), 7.43-7.60 (m, 4H,
Hm + Hp + Hp, PPh2), 7.78 (m, 2H, Ho, PPh2), 7.96-7.80 (m,
3
2H, Ho, PPh2), 8.36 (d, 2H, Ho, PhCO, JHH ) 7.2). 31P{1H}
3
3
NMR (CDCl3): δ 14.57 (d, 1P, C6H4-2-PPh2, JPP ) 17.7),
3JHH ) 7.2). 7.86 (d, 1H, H6, JHH ) 8.4), 31P{1H} NMR
31.45 (d, 1P, Pd-PPh3).
(CDCl3): δ 15.32. 13C{1H} NMR (CDCl3): δ 54.74 (d, CHP,
1JPC ) 108.1), 55.38 (OMe), 55.82 (OMe), 98.87 (C3), 104.10
Synthesis of 12a. To a suspension of 9a (0.20 g, 0.19 mmol)
in THF (20 mL) was added AgClO4 (0.08 g, 0.38 mmol). The
resulting mixture was stirred for 30 min at 25 °C with exclusion
of light and then filtered over Celite. To the freshly prepared
solution of the bis-solvate was added dppm (0.15 g, 0.38 mmol),
and the resulting solution was stirred at 25 °C for 4 h. After
the reaction time, the solvent was evaporated to dryness and
the residue treated with Et2O (25 mL) to give 12a as an orange
solid. Yield: 0.240 g (63.2%). Anal. Calc for C51H42ClO6P3Pd
(985.76): C, 62.10; H, 4.30. Found: C, 62.20; H, 4.24. MS
(FAB+) [m/z, (%)]: 886 (45%) [M - ClO4]+. IR (ν, cm-1):
3
1
(C5), 124.15 (d, C1, JPC ) 13.8), 127.66 (d, Ci, PPh3, JPC
)
3
90.8), 128.74 (d, Cm, PPh3, JPC ) 12.2), 131.43 (C6), 131.77
4
2
(d, Cp, PPh3, JPC ) 2.7), 133.21 (d, Co, PPh3, JPC ) 10.0),
2
159.10 (C4), 161.41 (C2), 182.56 (d, CdO, JPC ) 2.2).
Synthesis of 17. A solution of 16 (0.100 g, 0.227 mmol)
and Pd(OAc)2 (0.102 g, 0.454 mmol) in CH2Cl2 (20 mL) was
refluxed under Ar for 5 h. After the reaction time, the cold
solution was filtered over Celite in order to remove some black
Pd0 formed. The clear yellow solution was evaporated to
dryness, and the residue was redissolved in 15 mL of MeOH
and treated with an excess of anhydrous LiCl (0.077 g, 1.8
mmol). Subsequent stirring at room temperature gave complex
17 as a yellow precipitate, which was filtered, washed with cold
MeOH (2 mL) and Et2O (10 mL), and air-dried. Yield: 0.151
g (83.2%). Anal. Calc for [C28H23Cl2O3PPd2]n (722.17)n: C,
46.57; H, 3.21. Found: C, 46.58; H, 3.74. IR (ν, cm-1): 1637
(νCO). This polymeric compound was not adequately soluble in
the usual organic solvents, preventing accurate NMR measure-
ments. Instead, it was characterized through its reactivity.
1
1614 (νCO). H NMR (CDCl3): δ 3.45-3.54 (m, 1H, CH2,
dppm), 3.60-3.69 (m, 1H, CH2, dppm), 5.33 (dd, 1H, CHP,
2
3JPH ) 8.0, JPH ) 3.2), 6.63-6.71 (m, 2H, C6H4), 6.98 (m,
1H, C6H4), 7.08-7.43 (m, 25H, PhCO + PPh2 + C6H4), 7.48-
7.58 (m, 4H, Hm(PPh2) + Hp(PPh2) + Hp(PhCO)), 7.68 (t, 1H,
3
Hp, PPh2, JHH ) 7.6), 7.74 (m, 2H, Ho, PPh2), 7.93 (m, 2H,
Ho, PPh2), 8.30 (d, 2H, Ho, PhCO, 3JHH ) 7.2). 31P{1H} NMR
3
(CDCl3): δ 15.32 (d, 1P, C6H4PPh2, JPP ) 19.6), 24.95 (dd,
1P, PdPPh2, dppm), 58.20 (d, 1P, Ph2PdO, dppm, 2JPP ) 25.1).
Synthesis of 14a. Complex 14a was prepared following the
same experimental method as that reported for 12a. Thus, 9a
(0.20 g, 0.19 mmol) was reacted, in THF, with AgClO4 (0.080
g, 0.38 mmol) and 1,10-phen (0.076 g, 0.38 mmol) to give 14a
as a yellow solid. Yield: 0.190 g (65.2%). Anal. Calc for C38H28-
ClN2O5PPd (765.51): C, 59.62; H, 3.89; N, 3.66. Found: C,
59.61; H, 3.32; N, 3.82. MS (FAB+) [m/z, (%)]: 665 (100%)
Synthesis of 18. To a suspension of 17 (0.067 g, 0.094 mmol)
in 15 mL of CH2Cl2 was added Tl(acac) (0.056 g, 0.187 mmol),
resulting in an immediate change of the color of the suspension
(yellow to gray). The resulting mixture was stirred at room
temperature for 30 min, then filtered over Celite. The pale
yellow solution was evaporated to dryness. The treatment of
the yellow residue with cold n-hexane (5 mL) gave 18 as a
pale yellow solid. Yield: 0.067 g (85.2%). Anal. Calc for
C38H37O7PPd2 (849.56): C, 53.73; H, 4.39. Found: C, 53.60;
H, 4.21. MS (MALDI+) [m/z, (%)]: 750 (10%) [M - acac]+.
1
[M - ClO4]+. IR (ν, cm-1): 1634 (νCO). H NMR (CD2Cl2):
δ 5.13 (s, 1H, CHP), 7.25-7.37 (m, 5H, H3, H4, H5 (C6H4) +
Hm (PhCO)), 7.41-7.62 (m, 9H, Hâ, Hδ, Hδ′ (phen) + H6 (C6H4)
+ Hp (PhCO) + Hm (PPh2)), 7.81-7.92 (m, 9H, Hâ′ (phen) +
1
IR (ν, cm-1): 1586 (νCO), 1568, 1514 (νCO, acac). H NMR

Cyclopalladation of Phosphorus Ylides and Iminophosphoranes
Organometallics, Vol. 26, No. 14, 2007 3551
(CDCl3): δ 1.46 (s, 3H, CH3, acac), 1.99 (s, 3H, CH3, acac),
2.01 (s, 3H, CH3, acac), 2.04 (s, 3H, CH3, acac), 3.88 (s, 3H,
OMe), 3.93 (s, 3H, OMe), 5.16 (s, 1H, CH, acac), 5.29 (s, 1H,
Crystal Structure Determination and Data Collection of
2d and 9b‚2CHCl3. Crystals of 2d of adequate quality for X-ray
measurements were grown by vapor diffusion of Et2O into a
CH2Cl2 solution of 2d at 25 °C, while crystals of 9b‚2CHCl3
were obtained by cooling a CHCl3 solution of 9b at low
temperature (-18 °C) and standing for several days. All the
crystals readily lose solvent; thus they were always handled in
the mother liquor. A single crystal of each compound was very
quickly mounted at the end of a quartz fiber in a random
orientation, covered with magic oil, and placed under the cold
stream of nitrogen. Data collection was performed at 100 K on
an Oxford Diffraction Xcalibur2 diffractometer using graphite-
monocromated Mo KR radiation (λ ) 0.71073 Å). A hemisphere
of data was collected on the basis of three ω-scan or φ-scan
runs. The diffraction frames were integrated using the program
CrysAlis RED,31 and the integrated intensities were corrected
for absorption with SADABS.32
2
CH, acac), 5.45 (d, 1H, CHP, JPH ) 5.0), 6.10 (d, 1H, H6,
4
C6H2, JHH ) 2.5), 6.49 (d, 1H, H4, C6H2), 6.99 (t, 1H, H3,
3
3
3
C6H4, JPH ) JHH ) 7.5), 7.10 (tdd, 1H, H4, C6H4, JHH
)
3JHH ) 7.5, JPH ) 4.5, JHH ) 1.0), 7.30 (m, 1H, H5, C6H4),
4
4
3
4
7.48 (td, 2H, Hm, PPh2, JHH ) 8, JPH ) 3.5), 7.56-7.59 (m,
3
5
3H, Hm + Hp, PPh2), 7.66 (td, 1H, Hp, PPh2, JHH ) 7.0, JPH
3
) 2.0), 7.76 (dd, 2H, Ho, PPh2, JPH ) 12), 7.91 (d, 1H, H6,
3
3
C6H4, JHH ) 7.8), 8.03 (dd, 2H, Ho, PPh2, JPH ) 13). 13C-
{1H} NMR (CDCl3) (the signals due to the carbon atoms C2
(C6H2 group) and one CO (acac group) were not observed): δ
27.41 (CH3, acac), 27.46 (CH3, acac), 27.81 (CH3, acac), 27.90
(CH3, acac), 31.73 (d, CHP, 1JPC ) 60.8), 55.42 (OMe), 55.65
(OMe), 95.17 (C4, C6H2) 99,08 (CH, acac), 100.12 (CH, acac),
105.73 (C6, C6H2), 124.46 (d, 1H, C4, C6H4, 3JPC ) 12.8), 126.10
1
1
(d, Ci, PPh2, JPC ) 90.4), 126.40 (d, Ci, PPh2, JPC ) 69.6),
Structure Solution and Refinement. The structures were
solved and developed by Patterson and Fourier methods.33 All
non-hydrogen atoms were refined with anisotropic displacement
parameters. The hydrogen atoms were placed at idealized
positions and treated as riding atoms. Each hydrogen atom was
assigned an isotropic displacement parameter equal to 1.2 times
the equivalent isotropic displacement parameter of its parent
128.20 (d, Cm, PPh2, 3JPC ) 12.9), 128.32 (d, Cm, PPh2, 3JPC
)
2
11.5), 129.32 (d, C3, C6H4, JPC ) 11.5), 129.86 (d, C5, C6H4,
4JPC ) 3.1), 132.26 (d, Cp, PPh2, JPC ) 3.2), 132.72 (d, Cp,
4
PPh2, 4JPC ) 2.7), 132.82 (d, Co, PPh2, 2JPC ) 9.7), 133.87 (d,
3
1
C6, C6H4, JPC ) 15.2), 136.16 (d, C2, C6H4, JPC ) 113.2),
136.35 (d, Co, PPh2, 2JPC ) 10.7), 158.24 (d, C1, C6H4, 2JPC
)
2
20.1), 160.78 (C5, C6H2), 161.92 (C1, C6H2), 162.49 (C3, C6H2),
185.07 (CO, acac), 187.03 (CO, acac), 188.18 (CO, acac),
213.00 (d, CdO, 2JPC ) 4.9). 31P{1H} NMR (CDCl3): δ 21.04.
Synthesis of 19. To a suspension of 17 (0.100 g, 0.138 mmol)
in 15 mL of CH2Cl2 was added PPh3 (0.073 g, 0.277 mmol).
The initial yellow suspension gradually dissolved, and in few
minutes a pale yellow solution was obtained. This solution was
stirred at room temperature for an additional 30 min and then
filtered over Celite to remove any trace of insoluble materials.
The clear yellow solution thus obtained was evaporated to
dryness. Treatment of the yellow residue with cold n-hexane
(5 mL) and further stirring gave 19 as a pale yellow solid.
Yield: 0.146 g (84.6%). Complex 19 was recrystallized from
CH2Cl2/n-hexane to give pale yellow crystals of 19‚0.5CH2-
Cl2, which were used for analytic and spectroscopic measure-
atom. The structures were refined to Fo , and all reflections were
used in the least-squares calculations.34
Acknowledgment. Funding by the Direccio´n General de
Investigacio´n Cient´ıfica y Te´cnica (DGICYT) (Spain, Project
CTQ2005-01037) is gratefully acknowledged. R.B. thanks
Ministerio de Educacio´n y Ciencia (Spain), and D.A. and E.S.
thank Diputacio´n General de Arago´n (Spain) for respective
research grants. E.P.U. thanks Prof. Michel Pfeffer for stimulat-
ing and helpful discussions.
Supporting Information Available: Complete experimental
section with all preparative details, spectroscopic data, and refer-
ences of the synthesis previously described. Tables giving complete
data collection parameters, atomic coordinates, bond distances and
angles, and thermal parameters for 2d and 9b‚2CHCl3. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
ments. The amount of CH2Cl2 was quoted by H NMR. Anal.
Calc for [C64H53Cl2O3P3Pd2]‚0.5CH2Cl2 (1289.22): C, 60.09;
H, 4.22. Found: C, 59.92; H, 4.18. MS (MALDI+) [m/z, (%)]:
1211.0 (25%) [M - Cl]+. IR (ν, cm-1): 1584 (νCO). 1H NMR
(CDCl3): δ 2.74 (s, 3H, OMe), 3.80 (s, 3H, OMe), 5.46 (br,
2H, CHP + H3, C6H2), 5.83 (s, 1H, H5, C6H2), 6.43 (t, 1H, H3,
C6H4, 3JPH ) 3JHH ) 7.4), 7.10 (m, 1H, H4, C6H4), 6.95 (t, 1H,
OM7002877
(31) CrysAlis RED, Version 1.171.27p8; Oxford Diffraction Ltd., 2005.
(32) Sheldrick, G. M. SADABS, Empirical absorption correction program;
Go¨ttingen University, 1996.
(33) Sheldrick, G. M. SHELXS-86. Acta Crystallogr. 1990, A46, 467.
(34) Sheldrick, G. M. SHELXL-97, FORTRAN program for the refine-
ment of crystal structures from diffraction data; Go¨ttingen University, 1997.
Molecular graphics were done using the commercial package SHELXTL-
PLUS, Release 5.05/V; Siemens Analytical X-ray Instruments, Inc.:
Madison, WI, 1996.
3
H5, C6H4, JHH ) 8.0), 7.10-7.64 (m, 39H, H6(C6H4) + Ph),
8.41 (br, 2H, Ho, Ph). 31P{1H} NMR (CDCl3): δ 15.9 (d, 1P,
3
C6H4-2-PPh2, JPP ) 12.9), 32.91 (s, br, 1P, Pd-PPh3), 46.55
(s, br, 1P, Pd-PPh3).