Insertion reactions involving palladium complexes with nitrogen ligands. 2. Carbon monoxide and alkene insertion reactions with novel palladium compounds containing terdentate ligands

Article abstract of DOI:10.1021/om9504361

Neutral and ionic methylpalladium compounds containing trinitrogen ligands (N-N-N)-Pd(Me)(Y) (N-N-N = trinitrogen ligand; Y = Cl^-, CF₃SO₃^-, 4-Me-C₆H₄SO₃^-) have been synthesized and characterized by spectroscopic methods. The coordination mode of the trinitrogen ligand depends not only on the rigidity of the ligand but also on the solvent and on the anion Y. With the weakly coordinating ligands CF₃SO₃^- and BF₄^- the trinitrogen ligands readily adopt a terdentate coordination mode, resulting in complexes of the type [(σ³-N-N-N)Pd(Me)]Y. In methylchloropalladium compounds, the flexible trinitrogen ligands adopt a bidentate coordination mode, resulting in the complexes (σ²-N-N-N)Pd(Me)(Cl), whereas the terdentate coordination mode has been found for rigid ligands, resulting in the ionic complexes [(σ³-N-N-N)Pd(Me]Cl. Polar solvents, such as acetonitrile, stabilize the formation of ionic complexes. The methylpalladium compounds readily insert carbon monoxide, resulting in the facile formation of the acetylpalladium compounds (σ²-N-N-N)-Pd(C(O)Me)(Cl) and [(σ³-N-N-N)Pd(C(O)Me)]Y (Y = Cl^-, OTf^-), in which the coordination mode of the ligands remains unchanged. CO insertion half-lives of the methylpalladium compounds show that substituents adjacent to one nitrogen donor atom accelerate the insertion for both the neutral and the ionic complexes. Interestingly, the CO insertion half-life is not correlated to the rigidity of the trinitrogen ligand, since the compound [(terpy)-Pd(Me)]Cl, which contains the rigid ligand terpy, undergoes a faster carbon monoxide insertion than analogous complexes with the flexible ligands C₅H₄N-2-C(H)=N(CH₂)₂C ₅H₄N. Alkene insertion has been tested by reacting the acetylpalladium compounds with norbornadiene (NBD). The NBD-inserted compounds contain the C₇H₈C(O)CH₃ moiety coordinating in an unprecedented monodentate σ-C fashion. Peculiarly, [(terpy)Pd(C(O)Me)]Cl not only undergoes NBD insertion but does so at a very high rate. On the basis of these findings a tentative mechanism is suggested.

Full text of DOI:10.1021/om9504361

668
Organometallics 1996, 15, 668-677
In ser tion Rea ction s In volvin g P a lla d iu m Com p lexes w ith
Nitr ogen Liga n d s. 2. Ca r bon m on oxid e a n d Alk en e
In ser tion Rea ction s w ith Novel P a lla d iu m Com p ou n d s
Con ta in in g Ter d en ta te Liga n d s
Richard E. Ru¨lke, Vincent E. Kaasjager, Dave Kliphuis, Cornelis J . Elsevier,
Piet W. N. M. van Leeuwen, and Kees Vrieze*
Anorganisch Chemisch Laboratorium, J . H. van’t Hoff Research Institute, Universiteit van
Amsterdam, Nieuwe Achtergracht 166, NL 1018 WV Amsterdam, The Netherlands
Kees Goubitz
Laboratorium voor Kristallografie, Amsterdam Institute for Molecular Studies, Universiteit
van Amsterdam, Nieuwe Achtergracht 166, NL 1018 WV Amsterdam, The Netherlands
Received J une 8, 1995X
Neutral and ionic methylpalladium compounds containing trinitrogen ligands (N-N-N)-
Pd(Me)(Y) (N-N-N ) trinitrogen ligand; Y ) Cl-, CF3SO3-, 4-Me-C6H4SO3-) have been
synthesized and characterized by spectroscopic methods. The coordination mode of the
trinitrogen ligand depends not only on the rigidity of the ligand but also on the solvent and
-
-
on the anion Y. With the weakly coordinating ligands CF3SO3 and BF4 the trinitrogen
ligands readily adopt a terdentate coordination mode, resulting in complexes of the type
[(σ3-N-N-N)Pd(Me)]Y. In methylchloropalladium compounds, the flexible trinitrogen ligands
adopt a bidentate coordination mode, resulting in the complexes (σ2-N-N-N)Pd(Me)(Cl),
whereas the terdentate coordination mode has been found for rigid ligands, resulting in the
ionic complexes [(σ3-N-N-N)Pd(Me]Cl. Polar solvents, such as acetonitrile, stabilize the
formation of ionic complexes. The methylpalladium compounds readily insert carbon
monoxide, resulting in the facile formation of the acetylpalladium compounds (σ2-N-N-N)-
Pd(C(O)Me)(Cl) and [(σ3-N-N-N)Pd(C(O)Me)]Y (Y ) Cl-, OTf-), in which the coordination
mode of the ligands remains unchanged. CO insertion half-lives of the methylpalladium
compounds show that substituents adjacent to one nitrogen donor atom accelerate the
insertion for both the neutral and the ionic complexes. Interestingly, the CO insertion half-
life is not correlated to the rigidity of the trinitrogen ligand, since the compound [(terpy)-
Pd(Me)]Cl, which contains the rigid ligand terpy, undergoes a faster carbon monoxide
insertion than analogous complexes with the flexible ligands C5H4N-2-C(H)dN(CH2)2C5H4N.
Alkene insertion has been tested by reacting the acetylpalladium compounds with norbor-
nadiene (NBD). The NBD-inserted compounds contain the C7H8C(O)CH3 moiety coordinating
in an unprecedented monodentate σ-C fashion. Peculiarly, [(terpy)Pd(C(O)Me)]Cl not only
undergoes NBD insertion but does so at a very high rate. On the basis of these findings a
tentative mechanism is suggested.
In tr od u ction
we have employed bidentate ligands and we have found
that the rate of CO and alkene insertion into the Pd-C
Intimate steps of homogeneously catalyzed reactions,
in particular those mediated by organopalladium or
-platinum compounds, have been investigated mainly
by using monodentate and bidentate phosphorus and
nitrogen ligands.1-7 In our investigation of the intimate
steps of the copolymerization of CO and alkenes,
homogeneously catalyzed by palladium complexes,8-10
(4) (a) Samsel, E. G.; Norton, J . R. J . Am. Chem. Soc. 1984, 106,
5505. (b) Gillie, A.; Stille, J . K. J . Am. Chem. Soc. 1980, 102, 4933. (c)
Sen, A.; Chen, J .-T.; Vetter, W. M.; Whittle, R. R. J . Am. Chem. Soc.
1987, 109, 148.
(5) (a) Markies, B. A.; Wijkens, P.; Boersma, J .; Spek, A. L.; van
Koten, G. Recl. Trav. Chim. Pays-Bas 1991, 110, 133. (b) Markies, B.
A.; Spek, A. L.; Boersma, J .; van Koten, G. J . Chem. Soc., Chem.
Commun. 1993, 1317. (c) Markies, B. A.; Kruis, D.; Rietveld, M. H.
P.; Verkerk, K. A. N.; Boersma, J .; Kooijman, H.; Lakin, M. T.; Spek,
A. L.; van Koten, G. J . Am. Chem. Soc. 1995, 117, 5253.
(6) (a) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C.
J . Am. Chem. Soc. 1992, 114, 5894. (b) Rix, F. C.; Brookhart, M. J .
Am. Chem. Soc. 1995, 117, 1137.
X Abstract published in Advance ACS Abstracts, December 1, 1995.
(1) (a) Yamamoto, A.; Yamamoto, T.; Ozawa, F. Pure Appl. Chem.
1985, 57, 1799. (b) Kobayashi, T.-A.; Yamashita, H.; Sakamura, T.;
Tanaka, M. J . Mol. Catal. 1987, 41, 379. (c) Kim, Y.-J .; Osakada, K.;
Sugita, K.; Yamamoto, T.; Yamamoto, A. Organometallics 1988, 7,
2182.
(2) (a) Calvin, G.; Coates, G. E. J . Chem. Soc. 1960, 2008. (b) Byers,
P. K.; Canty, A. J .; Skelton, B. W.; White, A. H. J . Organomet. Chem.
1987, 336, C55. (c) Aye, K.-T.; Canty, A. J .; Crispo, M.; Puddephatt,
R. J .; Scott, J . D.; Watson, A. A. Organometallics 1989, 8, 1518.
(3) (a) Rauchfuss, T. H.; Patino, F. T.; Roundhill, D. M. Inorg. Chem.
1975, 14, 652. (b) de Graaf, W.; Harder, S.; Boersma, J .; van Koten,
G.; Kanters, J . A. J . Organomet. Chem. 1988, 358, 545.
(7) Brumbaugh, J . S.; Whittle, R. R.; Parvez, M.; Sen, A. Organo-
metallics 1990, 9, 1735.
(8) (a) van Asselt, R.; Gielens, E. E. C. G.; Ru¨lke, R. E.; Elsevier, C.
J . J . Chem. Soc., Chem. Commun. 1993, 1203. (b) van Asselt, R.;
Gielens, E. E. C. G.; Ru¨lke, R. E.; Elsevier, C. J . J . Am. Chem. Soc.
1994, 116, 976. (c) Ru¨lke, R. E.; Kliphuis, D.; Elsevier, C. J .; Fraanje,
J .; Goubitz, K.; van Leeuwen, P. W. N. M.; Vrieze, K. J . Chem. Soc.,
Chem. Commun. 1994, 1817.
0276-7333/96/2315-0668$12.00/0 © 1996 American Chemical Society

Palladium Complexes with Nitrogen Ligands
Organometallics, Vol. 15, No. 2, 1996 669
Sch em e 1. Sta biliza tion of a F r ee Coor d in a tion
Site by In tr od u cin g a Th ir d Don or Atom
bond of methylpalladium and acylpalladium complexes
(L-L)Pd(R)(Y) (L-L ) bidentate ligand; R ) CH3, C(O)-
CH3; Y ) Cl, CF3SO3, BF4, PF6) decreases in the order
N-N > P-P . P-N.9 Also, it was found that insertion is
facilitated in the case of phosphorus ligands by flexible
diphosphine ligands with a large bite angle, while in
the case of nitrogen ligands rigid diimine ligands with
a small bite angle appear to enhance the insertion rate.8
Finally, CO and alkene insertions proceed much faster
for complexes containing weakly coordinating ligands
such as triflate,8 due to the readily available coordina-
tion position for the incoming substrate.11,12
Since ionic palladium compounds having such a
readily available coordination position may be sensitive
to several side reactions (e.g. â-hydride abstraction,
metathesis with halogenated solvents, and reductive-
elimination reactions, resulting in Pd blackening), we
thought of employing hemilabile trinitrogen ligands
(Scheme 1).
F igu r e 1. Structures and adopted numbering schemes of
the ligands 1-6. In the case of the complexes 1a -c, H7
indicates the coordinating imino nitrogen and H8 the
noncoordinating imino nitrogen.
complexes with nonsymmetric diphosphine and phos-
phine-phosphinite ligands.14f,g However, in the case of
bidentate nitrogen ligands there are some indications
that these nitrogen ligands may also be bonded in a
monodentate fashion during some stages of the insertion
reaction with involvement of transient three-coordinate
T-shaped species.15,16 At the same time, theoretical
studies indicate that insertions may also proceed via
five-coordinate species when using terdentate nitrogen
ligands.5c,17 We are interested in obtaining insight into
the possible mechanisms by focusing on the steric and
electronic properties of nitrogen ligands in general. In
this study we consider the influence and electronic
properties of trinitrogen ligands on the insertion of CO
and alkenes into the Pd-C bonds of methyl- and
acetylpalladium compounds.
Some theoretical13 and kinetic14 studies have been
carried out on (di)phosphine-containing compounds to
unravel the mechanism of CO and alkene insertion
reactions. These studies appear to support the insertion
mechanism proposed by Drent et al.,11 which is based
on the continuous creation of an open coordination
position cis to the migrating group R, while the diphos-
phine ligand remains bonded to the palladium in a
bidentate fashion. In two elegant studies, van Leeuwen
et al. very recently published spectroscopic evidence for
this mechanism by employing palladium and platinum
We have used the ligands 1-6, which have varying
flexibilities and different electron-donating properties
(Figure 1). The ligands 1-6 can be considered as
functional derivatives of bidentate ligands such as bpy
and R-PyCa (R-PyCa ) pyridyl-2-(R)-carbaldimine; R
) alkyl, aryl),18 which have recently been used in CO
and alkene insertion reactions involving methyl- and
acylpalladium compounds,5,19 including trinitrogen
ligands with a diaminopyridyl donor set.5 Novel methyl-
and acetylpalladium compounds containing 1-6 have
been synthesized, and the insertion of CO and of
alkenes, respectively, has been studied by spectroscopic
methods. Preliminary results involving 1 and 220 and
also the complex coordination chemistry of the neutral
(9) (a) Dekker, G. P. C. M.; Elsevier, C. J .; van Leeuwen, P. W. N.
M.; Vrieze, K. J . Organomet. Chem. 1992, 430, 357. (b) Dekker, G. C.
P. M.; Buijs, A.; Elsevier, C. J .; Smeets, W. J . J .; Spek, A. L.; Wang,
Y.-F.; Stam, C. H.; Vrieze, K.; van Leeuwen, P. W. N. M. Organome-
tallics 1992, 11, 1937.
(10) To´th, I.; Elsevier, C. J . J . Am. Chem. Soc. 1993, 115, 10388.
(11) (a) Drent, E. Eur. Pat. Appl. 121965, 1984; Chem. Abstr. 1985,
92, 46423. (b) Drent, E.; van Broekhoven, J . A. M.; Doyle, M. J . J .
Organomet. Chem. 1991, 416, 235.
(12) (a) Milani, B.; Alessio, E.; Mestroni, G.; Sommazzi, A.; Garbassi,
F.; Zangrando, E.; Bresciani-Pahor, N.; Randaccio, L. J . Chem. Soc.,
Dalton Trans. 1994, 13, 1903. (b) Sommazzi, A.; Garbassi, F.;
Mestroni, G.; Milani, B. U.S. Patent 5310871, 1994; Chem. Abstr. 1994,
121, 301585d. (c) Sommazzi, A.; Lugli, G.; Garbassi, F.; Calderazzo,
F. Eur. Pat. Appl. 560455, 1993; Chem. Abstr. 1994, 120, 165225m.
(d) Sommazzi, A.; Lugli, G.; Garbassi, F.; Calderazzo, F. Eur. Pat. Appl.
560456, 1993; Chem. Abstr. 1994, 120, 165226n.
(13) (a) Ziegler, T.; Versluis, L.; Tschinke, V. J . Am. Chem. Soc. 1986,
108, 612. (b) Koga, N.; Morokuma, K. J . Am. Chem. Soc. 1986, 108,
6136. (c) Berke, H.; Hoffmann, R. J . Am. Chem. Soc. 1978, 100, 7224.
(14) (a) Garrou, P. E.; Heck, R. F. J . Am. Chem. Soc. 1976, 98, 4115.
(b) Anderson, G. K.; Cross, R. J . J . Chem. Soc., Dalton Trans. 1980,
1434. (c) Anderson, G. K.; Cross, R. J . Acc. Chem. Res. 1984, 17, 67.
(d) Anderson, G. K.; Lumetta, G. J . Organometallics 1985, 4, 1542. (e)
Carmona, E.; Contreras, L.; Podeva, M. L.; Sanchez, L. J . J . Am. Chem.
Soc. 1991, 113, 4322. (f) van Leeuwen, P. W. N. M.; Roobeek, C. F.;
van der Heijden, H. J . Am. Chem. Soc. 1994, 116, 12117. (g) van
Leeuwen, P. W. N. M.; Roobeek, C. F. Recl. Trav. Chim. Pays-Bas 1995,
114, 73.
(15) Groen, J . H.; Vrieze, K. To be submitted for publication.
(16) Monodentate coordination of bis nitrogen ligands by dissociation
of one nitrogen donor atom has recently been observed for (η3-allyl)-
palladium compounds: Gogoll, A.; O¨ rnebro, J .; Grennberg, H.; Ba¨ck-
vall, J . J . Am. Chem. Soc. 1994, 116, 3631.
(17) Dedieu, A. Private communication.
(18) Vrieze, K.; van Koten, G. Inorg. Chim. Acta 1985, 100, 79.
(19) Part 1: Ru¨lke, R. E.; Delis, J . G. P.; Groot, A. M.; Elsevier, C.
J .; van Leeuwen, P. W. N. M.; Vrieze, K.; Goubitz, K.; Schenk, H. J .
Organomet. Chem., in press.

670 Organometallics, Vol. 15, No. 2, 1996
Ru¨lke et al.
Ta ble 1. Nu m ber in g of th e Or ga n op a lla d iu m
Com p ou n d s Con ta in in g Liga n d s 1-6
R
L
Y
CH3
C(O)CH3
C7H8C(O)CH3
1
1
2
3
4
4
5
5
6
6
i-Pr-DIP
iPr-DIP
terpy
bbp
MAP
Cl
OTf
Cl
OTos
Cl
OTf
Cl
OTf
Cl
OTf
1a
11a
2a
13a
4a
14a
5a
15a
6a
1b
11b
2b
1c
F igu r e 2. Structures of the ionic methylpalladium com-
pounds 2a , 6a , 11a , and 14a -16a .
2c
4b
14b
5b
15b
6b
4c
14c
5c
15c
6c
Sch em e 2. Str u ctu r e of Com p ou n d s 1a a n d 13a
a n d of th e Coor d in a tion Isom er s Obser ved w ith 1H
NMR for 4a a n d 5a betw een 193 a n d 363 K in
Ch lor ofor m a n d Dich lor om eth a n e21
MAP
MeMAP
MeMAP
MIMAP
MIMAP
16a
methylchloropalladium complexes with nonsymmetric
ligands 4 and 521 have been reported, and in this article
we publish the results of our investigations involving
1-6 in full detail.
Resu lts
Syn t h esis. The ligands 2,6-bis((isopropylimino)-
methyl)pyridine (iPr-DIP, 1), 2-(2-((2′-pyridylmethyl-
ene)amino)ethyl)pyridine (MAP, 4), 2-(2-(((6′-methyl-2′-
pyridyl)methylene)amino)ethyl)pyridine (MeMAP, 5)
and 2-(2-(((1′-methyl-2′-imidazolyl)methylene)amino)-
ethyl)pyridine (MIMAP, 6) have been prepared by
literature methods,20-22 while 2,6-bis(N-pyrazolyl)pyri-
dine (bbp, 3) has been prepared according to the method
of Goldsby.23
The numbering of the trinitrogen ligands 1-6 in the
various neutral and ionic methyl-, acetyl-, and (6-acetyl-
[2.2.1]bicyclohept-1-en-5-yl)palladium complexes (which
will be denoted as Pd-C7H8C(O)CH3 in the course of
this article) are presented in Table 1.
The methylchloropalladium compounds 1a , 2a , and
4a -6a have been prepared by substitution of the diene
in (COD)Pd(Me)(Cl)21,24 (COD ) 1,5-cyclooctadiene) by
the ligands 1, 2 (in CH3CN), 4, 5, and 6 (in CH2Cl2 or
CHCl3) at room temperature, respectively. The same
procedure performed with 3 in several solvents did not
lead to a well-defined palladium complex.
The methylpalladium triflate compounds 11a and
14a -16a were prepared by reaction of the chloro
compounds 1a and 4a -6a with silver triflate in aceto-
nitrile.21 Compound 13a was prepared by substitution
of the chloride of (COD)Pd(CH3(Cl) in dichloromethane
by the weakly coordinating tosylate prior to the addition
of the ligand and subsequent substitution of COD by 3.
The acetylpalladium compounds 1b-16b have been
prepared by treatment of the methylpalladium com-
pounds 1a -16a in solution under 1.5 bar of carbon
monoxide at room temperature.8 In order to determine
the relative CO insertion rates, CO insertion was
performed with a gas buret (see Experimental Section).
Alkene insertion was tested by the addition of 1.1
equiv of the alkene (ethene, styrene, methyl acrylate,
norbornene, norbornadiene, and dicyclopentadiene) to
an in situ formed solution of the acetylpalladium
complexes 1b-16b in tha NMR tube and was followed
1
by H NMR and IR spectroscopy.
It should be noted that, unfortunately, elemental
analysis of the compounds was only possible for 1a and
2a . In the case of the methylpalladium compounds 4a -
6a this was not possible because these compounds are
oils which contain small amounts of solvents. The
acetylpalladium compounds 1b-16b and the Pd-C7H8C-
(O)CH3 compounds 1c-15c were stable for only a few
hours and therefore did not allow out-of-house elemental
analysis.
Meth ylp a lla d iu m Com p ou n d s. Upon addition of
the trinitrogen ligand to the Pd(CH3)(Cl) moiety, the
neutral complexes (NNN)Pd(CH3)(Cl) (1a , 4a , and 5a ;
see Scheme 2)swith the ligand coordination in a biden-
tate fashionsand ionic complexes [(NNN)Pd(CH3)]Cl
(2a , 6a , 11a -16a ; see Figure 2)swith a terdentate
ligandshave been obtained. Upon treatment with silver
trifluoromethanesulfonate, the neutral complexes were
converted into ionic ones, except for 13a , which has bbp
coordinated in a bidentate fashion. The presence of
terdentate coordination apparently depends on the
rigidity of the trinitrogen ligand (2a ), on the coordina-
tion properties of the anionic ligand Y (11a -16a ), and
on the coordination properties of the trinitrogen ligand
(6a ) and offers no surprises, although in the last case
the terdentate coordination of MIMAP in 6a was quite
unexpected.
(20) Ru¨lke, R. E.; Han, I. M.; Elsevier, C. J .; Vrieze, K.; van
Leeuwen, P. W. N. M.; Roobeek, C. F.; Zoutberg, M. C.; Wang, Y.-F.;
Stam, C. H. Inorg. Chim. Acta 1990, 169, 5.
(21) Ru¨lke, R. E.; Ernsting, J . M.; Elsevier, C. J .; Spek, A. L.; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(22) Lavery, A.; Nelson, S. M. J . Chem. Soc., Dalton Trans. 1984,
615.
(23) J ameson, D. L.; Goldsby, K. A. J . Org. Chem. 1990, 44, 4992.
(24) van Leeuwen, P. W. N. M.; Roobeek, C. F. Eur. Pat. Appl.
380162, 1990; Chem. Abst. 1991, 114, 62975.
In the case of 1a and 13a the σ2-coordinated ligands
show dynamic behavior on the 1H NMR time scale,
indicating a rapid exchange of the free and the coordi-

Palladium Complexes with Nitrogen Ligands
Organometallics, Vol. 15, No. 2, 1996 671
Ta ble 2. Con d u ctom etr ic Da ta for 6a a n d 14a -16a
Ta ble 3. Bon d Dista n ces (Å) for th e Non -Hyd r ogen
Atom s of 1a (w ith Esd ’s in P a r en th eses)
compd
solvent
conductivity, µS M-1 (T,K)
Pd-C(1)
Pd-Cl
2.01(1)
2.324(3)
2.270(7)
2.065(6)
1.34(1)
1.41(1)
1.47(1)
1.37(1)
1.38(1)
1.38(1)
N(1)-C(6)
N(2)-C(7)
N(2)-C(9)
N(3)-C(8)
C(6)-C(7)
N(3)-C(12)
C(9)-C(10)
C(9)-C(11)
C(12)-C(13)
C(12)-C(14)
1.340(9)
1.27(1)
1.48(1)
1.26(1)
1.46(1)
1.47(1)
1.52(1)
1.51(1)
1.54(1)
1.51(2)
6a
6a
16a
16a
14a a
15a a
CHCl3
CH3CN
CHCl3
CH3CN
29 (233); 35 (293); 43 (315)
22 700 (233); 48 500 (295); 5800 (319)
52 (233); 98 (293); 106 (315)
Pd-N(1)
Pd-N(2)
N1-C(2)
C(2)-C(3)
C(2)-C(8)
C(3)-C(4)
C(4)-C(5)
C(5)-C(6)
29 400 (232); 62 100 (298); 70 700 (314)
CH3CN
CH3CN
51 400 (240); 91 100 (295); 111 200 (317)
44 550 (233); 60 600 (267); 87 150 (293)
a
For comparison.
Ta ble 4. Bon d An gles (d eg) for th e Non -Hyd r ogen
Atom s of 1a (w ith Esd ’s in P a r en th eses)
C(1)-Pd-Cl
85.1(3)
102.2(2)
78.2(3)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
N(1)-C(6)-C(5)
N(1)-C(6)-C(7)
C(5)-C(6)-C(7)
C(8)-N(3)-C(12)
N(2)-C(7)-C(6)
N(3)-C(8)-C(2)
N(2)-C(9)-C(10)
N(2)-C(9)-C(11)
C(10)-C(9)-C(11)
N(3)-C(12)-C(13)
N(3)-C(12)-C(14)
C(13)-C(12)-C(14)
119.0(9)
118.4(7)
124.0(7)
117.5(8)
118.5(7)
118.9(9)
121.1(7)
120.2(9)
115.3(8)
108.5(7)
111.2(8)
109.0(7)
109(1)
Cl-Pd-N(1)
N(1)-Pd-N(2)
N(2)-Pd-C(1)
Pd-N(1)-C(2)
Pd-N(1)-C(6)
C(2)-N(1)-C(6)
Pd-N(2)-C(7)
Pd-N(2)-C(9)
C(7)-N(2)-C(9)
N(1)-C(2)-C(3)
N(1)-C(2)-C(8)
C(3)-C(2)-C(8)
C(2)-C(3)-C(4)
94.2(3)
134.8(5)
107.6(5)
117.4(7)
114.9(5)
127.2(6)
117.9(7)
121.8(7)
118.7(8)
119.3(7)
119.1(8)
F igu r e 3. ORTEP plot (drawn at the 50% probability
level) and adopted numbering scheme of (σ2-iPr-DIP)Pd-
(CH3)(Cl) (1a ).
113.0(9)
nated side arms on palladium, as expected for sym-
metric trinitrogen ligands. A fluxional behavior was
also observed for 4a and 5a involving the flexible
ethylpyridyl group.21
Whereas 1a and 4a -6a readily dissolve in CH2Cl2,
CHCl3, and CH3CN, 13a is only soluble in methanol and
DMSO and 2a only in methanol, ethanol, and water.
The structure of 13a (Scheme 2) is observed in metha-
nol, while in DMSO 13a disproportionates into 3 and a
stable methylpalladium tosylate complex solvated by
DMSO.
The coordination mode of the ligand in 6a was
determined by investigation of the H NMR spectrum
1
F igu r e 4. ORTEP plot (drawn at the 50% probability
level) and adopted numbering scheme of the cationic [(σ3-
terpy)Pd(CH3)]+ moiety of 2a .
(especially the resonances of the CH2CH2 moiety) in
combination with conductometry (Table 2). Whereas 4a
and 5a have the trinitrogen ligands coordinating pre-
dominantly in a bidentate fashion (see scheme 2),21 in
6a the (quite similar) ligand coordinates both in non-
polar chloroform and in polar acetonitrile in a static
terdentate fashion between 233 and 315 K, resulting
in the ionic methylpalladium compound [(σ3-MIMAP)-
Pd(CH3)]Cl (Figure 2). Reaction of 6a with silver triflate
leads to the formation of the isostructural complex [(σ3-
MIMAP)Pd(CH3)]OTf (16a ). Accordingly, ionic 11a ,
14a , and 15a were obtained when the coordinating
chloride ligands in 1a , 4a , and 5a , respectively, were
placed in acetonitrile by the weakly coordinating ligand
triflate (Figure 2). Unfortunately, 11a decomposes
within a few hours in solution and in 1 day as the solid
without recovery of 1. Treatment of 2a with silver
triflate also gave the triflate analogue 12a . However,
the salmon-colored compound is insoluble in any type
of solvent tested. In contrast to 11a , the structural
analogues 14a -16a are stable both in solution and as
a solid.
involving the non-hydrogen atoms of 1a , respectively.
The crystal and refinement data for 1a are listed in
Table 8. The molecular structure of 1a shows 1 coor-
dinating in a bidentate fashion. The noncoordinating
imino group of 1a is coplanar with the coordinating part
of the ligand.
The configuration of 1a , with the two strongest
σ-donors, in this case the methyl and the imino groups,25
cis, agrees with literature reports of related com-
pounds.19,26 The bond distances and bond angles are
within the range found for analogous R-PyCa com-
plexes.19
Molecu lar Str u ctu r e of [(σ3-ter py)P d(CH3)]+[(Cl)-
(H2O)2]- (2a ). The molecular structure of 2a , with the
terpy ligand coordinating in a terdentate fashion, is
shown in Figure 4. The bond distances and the bond
angles of the non-hydrogen atoms of 2a are listed in
Tables 5 and 6, respectively. The crystal and refine-
ment data for 2a are listed in Table 8.
Molecu la r Str u ctu r e of (σ2-iP r -DIP )P d (CH3)(Cl)
(1a ). The solid-state structure of 1a with the adopted
numbering scheme is shown in Figure 3. Tables 3 and
4 contain the bond distances and the bond angles
(25) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
(26) (a) Albano, V. G.; Braga, D.; de Felice, V.; Panunzi, A.;
Vitagliano, A. Organometallics 1987, 5, 517. (b) de Felice, V.; Ganis,
P.; Vitagliano, A.; Valle, G. Inorg. Chim. Acta 1988, 144, 57.

672 Organometallics, Vol. 15, No. 2, 1996
Ru¨lke et al.
Ta ble 5. Bon d Dista n ces (Å) for th e Non -Hyd r ogen
Atom s of 2a (w ith Esd ’s in P a r en th eses)
Pd-C(16)
Pd-N(1)
2.04(1)
C(1)-C(2)
1.381(18)
1.358(18)
1.382(15)
1.489(15)
1.387(13)
1.380(16)
1.486(14)
1.375(13)
1.375(16)
1.356(18)
1.371(17)
1.341(13)
2.048(9)
2.007(7)
2.057(8)
1.359(14)
1.370(18)
1.335(13)
1.391(16)
1.330(13)
1.399(18)
1.361(16)
1.384(15)
C(3)-C(4)
Pd-N(2)
C(4)-C(5)
Pd-N(3)
C(5)-C(6)
C(1)-N(1)
C(2)-C(3)
C(10)-N(2)
C(11)-C(12)
C(6)-N(2)
C(7)-C(8)
C(8)-C(9)
C(9)-C(10)
C(5)-N(1)
C(6)-C(7)
C(10)-C(11)
C(11)-N(3)
C(12)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-N(3)
Ta ble 6. Bon d An gles (d eg) for th e Non -Hyd r ogen
Atom s of 2a (w ith Esd ’s in P a r en th eses)
C(16)-Pd-N(1)
C(16)-Pd-N(3)
N(1)-Pd-N(2)
N(2)-Pd-N(3)
C(2)-C(1)-N(1)
C(1)-C(2)-C(3)
C(2)-C(3)-C(4)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(4)-C(5)-N(1)
C(6)-C(5)-N(1)
C(5)-C(6)-C(7)
C(5)-C(6)-N(2)
C(7)-C(6)-N(2)
C(6)-C(7)-C(8)
C(7)-C(8)-C(9)
C(8)-C(9)-C(10)
100.6(4)
99.8(4)
79.8(3)
79.8(3)
122(1)
120(1)
119(1)
121(1)
124.6(9)
120.6(10) Pd-N(1)-C(1)
114.8(8) Pd-N(1)-C(5)
126.9(10) C(1)-N(1)-C(5)
113.5(9)
119.6( )
117(1)
122(1)
118(1)
C(9)-C(10)-N(2)
C(11)-C(10)-N(2)
119.5(9)
112.7(8)
C(10)-C(11)-C(12) 123.8(9)
C(10)-C(11)-N(3)
C(12)-C(11)-N(3)
116.2(9)
119.9(9)
C(11)-C(12)-C(13) 120(1)
C(12)-C(13)-C(14) 119(1)
C(13)-C(14)-C(15) 120(1)
F igu r e 5. Structures of the neutral acetylpalladium
complexes 1b, 4b, and 5b.
C(14)-C(15)-N(3)
122(1)
Ta ble 7. CO In ser tion Ha lf-lives (m in u tes:secon d s)
a n d In fr a r ed Ca r bon yl Str etch in g F r equ en cies
(cm -1) Deter m in ed for Com p ou n d s 1a -15a a
128.8(7)
113.7(7)
117.5(9)
118.1(7)
118.3(6)
123.5(8)
113.0(6)
128.4(7)
118.6(9)
Pd-N(2)-C(6)
Pd-N(2)-C(10)
C(6)-N(2)-C(10)
Pd-N(3)-C(11)
Pd-N(3)-C(15)
compd
solvent
CO insertion half-life
IR
1a
5a
CH2Cl2
CH2Cl2
6:00 ((0:30)
8:15 ((0:30)
8:30 ((0:30)
10:00 ((0:30)
12:30 ((0:30)
22:30 ((0:30)
25:00 ((0:30)
28:30 ((0:30)
32:15 ((0:30)
39:30 ((0:30)
1712
1708
1690
1682
1698
1696
1700
1690
1694
1690
[(bpy)Pd(CH3)]OTf19 CH3CN
2a
15a
6a
11a
C2H5OH
CH3CN
CH2Cl2
CH3CN
CH2Cl2
CH2Cl2
CH3CN
C(9)-C(10)-C(11) 127.7(10) C(11)-N(3)-C(15)
All bond distances and bond angles are within the
range normally observed for comparable structural
subunits such as the [(terpy)Pd(Cl)]+ cation.27 The
narrow angle N(1)-Pd-N(3) of 159.7(3)° in combination
with the short Pd-N(2) distance of 2.007(7) Å is normal
for terpy complexes27 and has also been reported for
manganese28a and rhodium28b,c complexes with compa-
rable symmetric trinitrogen ligands.
(bpy)Pd(CH3)(Cl)19
4a
14a
a
Conditions: [Pd] ) 40 mM, P(CO) ) 2 bar, T ) 293 K.
1H NMR spectra of 1b the ligand is still nonsymmetric,
indicating that the bidentate coordination mode of 1 is
retained (Figure 5). Whereas the methylpalladium
complexes 4a and 5a display fluxionality on the NMR
time scale due to isomerization (Scheme 2), the acetyl-
chloropalladium analogues 4b and 5b have sharp
resonances between 223 and 323 K in CDCl3 and no
signs of other isomeric structures have been observed,
while 4b and 5b occur in the same (bidentate) config-
uration as 4a and 5a , trans for 4b and cis for 5b (Figure
5). As expected, the ligands in 2b, 6b, 11b, 14b, and
15b coordinate in a static terdentate fashion, analogous
to the parent complexes 2a , 6a , 11a ,14a , and 15a ,
respectively.
CO In ser tion Rea ction s. Treatment of the meth-
ylpalladium compounds 1a -16a in solution with CO for
5-30 min resulted in the quantitative formation of the
corresponding acetylpalladium compounds 1b-16b,
except compound 13a , which did not react at all with
CO. Since the structural features and the reactivities
of 6a , b and 16a , b proved to be similar, only the
behavior of 6a will be discussed in the course of this
article. The products 1b-15b are stable in solution for
a few hours, except 11b, which is stable only for a few
minutes. The formation of the acetyl group is revealed
by the dissappearing Pd-CH3 resonance at ca. 1.0 ppm
and by the growing Pd-C(O)CH3 resonance at ca. 2.3
The CO insertion half-lives are presented in Table 7.
For comparison, the CO insertino half-lives determined
for (bpy)Pd(CH3)(Cl) and [(bpy)Pd(CH3)]OTf,19 two com-
plexes used in model studies of CO/alkene copolymer-
ization reactions in the literature,5,6 have been included.
1
ppm in the H NMR spectrum and by the growing CdO
stretching vibration at ca. 1600 cm-1 in the IR spectrum.
With a few exceptions the configuration of the ligands
around the palladium atom of the acetylpalladium
compounds 1b-16b proved to be identical with that of
the parent compounds 1a -16a . The dynamic behavior
observed for 1a is not present for 1b. According to the
Alk en e In ser tion Rea ction s. Ethene, methyl acry-
late, and styrene do not insert into the Pd-C bond of
the acetylpalladium compounds 1b-15b. However,
alkene insertion does take place for norbornene (NB),
dicyclopentadiene (DCPD), and norbornadiene (NBD).
Because of the complex NMR spectra, the products
obtained from the insertion of NB and DCPD into the
Pd-C bonds of the acetylpalladium compounds were
difficult to characterize. For this reason, only the
results of NBD insertion will be discussed here.
(27) Intille, G. M.; Pfluger, C. E.; Baker, W. A. J . Cryst. Mol. Struct.
1973, 3, 47.
(28) (a) Stor, G. J .; van der Vis, M.; Stufkens, D. J .; Oskam, A.;
Fraanje, J .; Goubitz, K. J . Organomet. Chem. 1994, 482, 15. (b)
Nishyama, H.; Kondo, M.; Nahamura, T.; Itoh, K. Organometallics
1991, 9, 500. (c) Haarman, H. F.; Vrieze, K. To be submitted for
publication.

Palladium Complexes with Nitrogen Ligands
Organometallics, Vol. 15, No. 2, 1996 673
Norbornadiene insertion proceeds very quickly for all
acetylpalladium compounds tested, but the products
1c-15c could only be characterized by spectroscopic
methods, and none could be isolated because of degra-
dation reactions. Only for compounds 1c, 2c, 4c, and
6c does the insertion of NBD lead to the formation of
one, well-defined insertion product. In contrast to the
CO insertion rates (vide supra) the NBD insertion rates
1
as determined with H NMR differ only little between
the compounds 1b-15b, neutral or ionic, and insertion
is completed within 30 min, which is only slightly slower
than found for the neutral complexes (Ar-BIAN)Pd-
(C(O)Me)(Cl) (Ar-BIAN ) bis(arylimino)acenaphthene)8
but faster than for the analogous neutral bpy complex
is (N-N)Pd(C(O)Me)(Cl) (N-N ) bpy, 4,7-diphenyl-1,10-
phenanthroline).15 The ionic compounds [(N-N)Pd(C(O)-
Me)(S)]Y (N-N ) bidentate nitrogen ligand; S ) solvent;
Y ) weakly coordinating ligand), however, undergo
NBD insertion at a much higher rate.5,8
The organic product which was formed after the
degradation reaction of 1c-15c was isolated and ana-
lyzed with 1H NMR and GC-MS (see Experimental
Section). Expectedly, the product proved to be 2-acetyl-
[2.2.1]bicyclohepta-2,5-diene.
F igu r e 6. Possible isomers of Pd-C7H8C(O)Ch3 com-
pounds containing trinitrogen ligands.
Insertion of NBD into the Pd-C bond of the above-
mentioned acetylpalladium complexes was easily moni-
tored by 1H NMR spectroscopy since (i) the olefinic
resonance of free NBD vanishes upon insertion, while
simultaneously a new set of resonances belonging to the
remaining olefinic hydrogens grows (ii) the C7H8 moiety
of the inserted NBD becomes nonsymmetric, and (iii)
the acetyl resonance is replaced by a new acetyl
resonance, which is found at a higher chemical shift (see
Experimental Section). The expected syn-exo addition
of NBD can be easily distinguished by the 6-9 Hz
coupling constants of the former double-bond hydrogens
(10-15 Hz for syn-endo addition and 1-2 Hz for anti
addition).7 In the literature, only examples of syn
addition of the Pd-C bond on the exo face of the NBD
double bond have been reported.5,7-9
and 6.02 ppm for 4c), and in the IR spectrum CO
stretching frequencies of 1700-1712 cm-1 are visible.
Insertion of NBD also proceeds for 5b, 14b, and 15b,
as judged from the vanishing NBD resonances in the
1H NMR and the simultaneously growing resonances
at ca. 6 ppm, which are the new olefinic hydrogens in
the C7H8C(O)CH3 moiety. However, these new signals
represent more than one NBD-insertion product, pos-
sibly comprising several isomers which could not be
characterized in detail (Figure 6).
Discu ssion
Sta bility. Whereas the methylpalladium compounds
1a -16a are fairly stable (between 1 day and years),
except for 11a , the corresponding acetylpalladium and
Pd-C7H8C(O)CH3 compounds only have a limited sta-
bility (a few hours). Such an instability is not uncom-
mon for the acetylpalladium complexes. They easily
deinsert CO and are also prone to hydrolysis. Only in
the case of neutral acetylpalladium complexes with
diphosphine ligands, bpy, or tmeda have acetylpalla-
dium compounds been reported that are stable for
months.5,7,9
The elimination product 2-acetyl[2.2.1]bicyclohepta-
2,5-diene is rapidly formed from the complexes 1c-
15c, while complexes containing bidentate nitrogen or
phosphorus ligands usually give very stable NBD-
insertion products.5-9 The known NBD-inserted com-
plexes with diphosphine ligands, bpy, or tmeda are fairly
stable, due to the C-O chelate which prevents degrada-
tion reactions.5,7-9 Most probably, the degradation
process of 1c-15c proceeds similarly to the base-
assisted process published by Chiusoli et al., causing
both the â-elimination and the exo-endo isomerization
of Pd-C7H8C(O)CH3 complexes (see Scheme 3).29
Coor d in a tion Ch em istr y. The observed strong
tendency of 6 to coordinate in a terdentate fashion is
In addition NBD insertion may lead to two different
products, a Pd-C7H8C(O)CH3, σ-C-bonded compound
and a Pd-C7H8C(O)CH3 compound as a C-O chelate
(Scheme 3). Until now, only bidentate coordination as
a C-O chelate has been observed,5-9 while monodentate
σ-C coordination has only been observed for the acylpal-
ladium compounds Pd-C(O)C7H8C(O)CH3, obtained
after carbonylation of the Pd-C7H8C(O)CH3 com-
pounds.5,6,8 The formation of a C-O chelate is easily
derived from (i) the CO stretching vibration in the IR
spectrum at ca. 1600 cm-1, (ii) the chemical shifts of
the remaining olefinic hydrogens in the 1H NMR
spectrum, which are ca. 0.5 ppm apart, and (iii) the CO
resonance at ca. 240 ppm in the 13C NMR spectrum. In
contrast, the monodentate C7H8C(O)CH3, σ-C coordina-
tion mode is evident from (i) the CO vibration in the IR
spectrum at ca. 1700 cm-1, (ii) the chemical shifts of
the remaining olefinic hydrogens in the 1H NMR
spectrum, which are very close together or have even
coincided to a multiplet, and (iii) the CO resonance at
210-230 ppm in the 13C NMR spectrum.
Surprisingly, the spectral data of 1c, 2c, 4c, and 6c
clearly indicate a monodentate σ-C coordination mode
of the C7H8C(O)CH3 moiety; the olefinic hydrogens are
(29) Dalcanale, E.; An, Z.; Battaglia, L. P.; Catellani, M.; Chiusoli,
G. P. J . Organomet. Chem. 1992, 437, 375.
1
very close together in the H NMR spectrum (e.g. 5.95

674 Organometallics, Vol. 15, No. 2, 1996
Ru¨lke et al.
Sch em e 3. Mech a n ism Ra tion a lizin g th e
Degr a d a tion of P d (C7H8C(O)CH3) Com p ou n d s,
In tr a m olecu la r ly Assisted by th e Non coor d in a tin g
Nitr ogen Don or Atom
We now turn our attention to the CO insertion half-
life of 2a , which is unexpectedly short in light of the
rigidity of 2. Even NBD, which is much bulkier than
CO, inserts rapidly into the Pd-C bond of 2b. Unfor-
tunately, the insertion of CO had to be measuredsfor
reasons of solubilitysin ethanol, which may make
comparison less useful. Replacement of one outer
pyridyl group by a CO molecule in itself does not yet
explain the fast migration. However, terpysnow coor-
dinating as a bidentate ligandscould be regarded as bpy
with a bulky substituent close to one nitrogen donor
atom, which rationalizes a very fast CO insertion rate
for 2a .
Alk en e In ser tion Rea ction s. The fact that the
acetylpalladium compounds 1b-15b failed to react with
unstrained alkenes such as ethene, styrene, and methyl
acrylate is not very surprising, since they lack a readily
available coordination position; insertion of unstrained
alkenes has until now only been observed for ionic
complexes with a free coordination position, [(L-L)Pd-
(S)(C(O)CH3)]Y (L-L ) bidentate ligand; S ) solvent;
Y- ) weakly coordinating ligand).5-9 If one considers
the reactivity of the ionic compounds 6b-15b toward
alkene insertion, it is clear that, although they are ionic
compounds, 6b-15b react rather as neutral compounds,
due to the fact that these ionic compounds do not have
a readily available coordination position.
rather unexpected, since the closely related ligands 4
and 5 coordinate in a bidentate fashion in the case of
methylchloropalladium compounds. It is clear that for
flexible trinitrogen ligands terdentate coordination in-
volves a very subtle, not yet fully understood balance
of donating and accepting properties of trans-positioned
atoms, most probably in combination with steric inter-
actions.
The poor coordinating properties of 2,6-bis(N-pyra-
zolyl)pyridine (3) for methylpalladium compounds is
interesting, since 3 resembles the strongly coordinating
ligands 1 and 2. This behavior must be caused by the
poor coordinating properties of the pyrazolyl groups.30
Although 3 coordinates in methanol as a bidentate
ligand in 3a , the ligand was completely substituted by
using DMSO as solvent. The fact that 3 failed to react
with (COD)Pd(CH3)(Cl) and (COD)PdCl2 may also be
attributed to its poor coordinating properties.
Ca r b on Mon oxid e In ser t ion R ea ct ion s. The
trends of the CO insertion half-lives (Table 7) are
similar to results recently obtained for methylpalladium
complexes with bidentate nitrogen ligands.19 First,
relatively little difference is observed between the half-
lives of the neutral and the ionic compounds. However,
this might be due to the difference in solvents, since the
neutral complexes have been measured in CH2Cl2 and
the ionic ones in CH3CN. The fact that acetonitrile may
act as a ligand itself may rationalize the unexpectedly
long insertion half-lives of the ionic methylpalladium
complexes.
Second, the methyl substituent in 5 clearly accelerates
CO insertion, since compounds 5a and 15a have much
shorter CO insertion half-lives than 4a and 14a . This
striking accelerating ortho effect has also been observed
recently for methylpalladium complexes containing bi-
dentate nitrogen ligands.19 The fast CO insertion
observed for 1a can now be understood, since in 1a the
ligand may be regarded as a bidentate nitrogen ligand
having a bulky substituent (i.e. the -C(H)dN-iPr group)
at the 6-position. Although the implications of having
bulky substituents close to one N-donor atom are not
completely understood as yet, and elaborate kinetic
studies are required to unravel their effects the best
fitting mechanism seems to be the one that involves
dissociation of the nitrogen donor atom facilitated by a
bulky substituent as the key step in the CO insertion
reaction.31-34
The observation that the C7H8C(O)CH3 moiety in 1c,
2c, 4c, and 6c coordinates in a monodentate σ-C fashion
is very surprising, since these are the first examples of
this coordination mode for this moiety on palladium.
However, there are strong indications of monodentate
coordination of the C7H8C(O)CH3 moiety for the neutral
palladium compounds (N-N)Pd(C7H8C(O)CH3)(Cl) (N-N
) 2,2-bipyridine, 4,7-diphenyl-1,10-phenanthroline, and
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline),15 while
Brookhart has recently observed similar transient com-
plexes with ionic (bpy)palladium compounds.6
The large influence of substituents close to one
N-donor atom observed for the CO insertion into pal-
ladium-methyl bonds (vide supra) was not observed for
the insertion of NBD into palladium-acetyl bonds.
Most probably this is caused by the fact that only 1
equiv of the alkene was used, while a large excess of
CO was used in the carbonylation reaction (pseudo-first-
order kinetics). Still, the very facile formation of 2c via
the insertion of NBD into the Pd-C bond of 2b is
astounding when one considers the steric bulk of NBD
and the rigidity of terpy. Possibly, both CO insertion
and alkene insertion proceed via the same mechanism,
although it might well be that CO and alkene insertion
reactions proceed partly via different intermediates. For
instance, it is known that five-coordinate palladium
complexes with alkenes have a trigonal-pyramidal
(TBP) geometry, while those with CO have a geometry
between TBP and square pyramidal.35
(31) De Felice, V.; Albano, V. G.; Castellari, C.; Cucciolito, M. E.;
De Renzi, A. J . Organomet. Chem. 1991, 403, 269.
(32) Albano, V. G.; Natile, G.; Panunzi, A. Coord. Chem. Rev. 1994,
133, 67.
(33) Fanizzi, F. P.; Intille, F. P.; Maresca, L.; Natile, F.; Lanfranchi,
M.; Tiripicchio, A. J . Chem. Soc., Dalton Trans. 1991, 1007.
(34) Albano, V. G.; Castellari, C.; Cucciolito, M. E.; Panunzi, A.;
Vitagliano, A. Organometallics 1990, 9, 1269.
(35) Fanizzi, F. P.; Maresca, L.; Natile, G.; Lanfranchi, M.; Tirip-
icchio, A.; Pacchioni, G. J . Chem. Soc., Chem. Commun. 1992, 333.
(30) Canty, A. J .; Lee, C. V. Organometallics 1982, 1, 1063.

Palladium Complexes with Nitrogen Ligands
Organometallics, Vol. 15, No. 2, 1996 675
ature. Yield: 96% of pale yellow 2a . 1H NMR (CD3OD):
hydrocarbyl ligand, δ 0.81 (s, Me); nitrogen ligand, δ 7.74 (dd,
H5′ and H5′′), 8.30 (m, other H’s), 8.54 (d, H6′ and H6′′). Anal.
Con clu sion s
Although an increased stability of alkylpalladium
compounds and acyl species was expected upon the
introduction of a third nitrogen-donor atom in the
spectator ligand, the opposite effect has been observed.
Apparently, the third donor atom does not sufficiently
stabilize palladium compounds by occupation of an open
coordination site on the metal. Instead, the third donor
atom may serve as a shuttle for hydrolysis or as an
intramolecular base, accelerating the â-hydride elimina-
tion reaction.
Calcd for
C16H18ClN3O2Pd: C, 45.11; H, 4.26; N, 9.86.
Found: C, 44.91; H, 4.29; N, 9.88. MS: correct isotope pattern
for [M - Cl - 2H2O]•+ with m/z 354 and for 106Pd.
6a . The synthesis was carried out similarly to that of 1a ,
except that the reaction was performed in chloroform at room
temperature. Yield: 83% of dark yellow 6a . 1H NMR
(CDCl3): hydrocarbyl ligand, δ 0.90 (s, Me); nitrogen ligand,
δ 3.25 (bt, HR), 4.05 (bt, Hâ), 4.25 (s, H6′), 7.07 (d, H5′), 7.25 (d,
H4′), 7.34 (ddd, H5), 7.54 (d, H3), 7.71 (dt, H4), 8.47 (d, H6), 10.23
(s, H7′).
An interesting and unprecedented σ-C monodentate
coordination mode of the C7H8C(O)CH3 moiety has been
observed for the (6-acetyl[2.2.1]bicyclohept-1-en-5-yl)-
chloropalladium complexes. This coordination mode
may be attributed to the presence of highly coordinating
donor atoms (third nitrogen or chloride ligand).
11a . To a solution of 45.2 mg (0.12 mmol) of 1a in 2 mL of
acetonitrile was added 31.1 mg (0.12 mmol) of silver trifluo-
romethanesulfonate. A white precipitate (AgCl) was formed
instantaneously. The precipitate was filtered off, and the
solvent was removed under reduced pressure from the solution.
The pale yellow solid was washed with 3 × 2 mL of diethyl
ether and dried in vacuo. Yield: 53.2 mg (90%) of pale yellow
11a . 1H NMR (CDCl3): hydrocarbyl ligand, δ 0.81 (s, Me);
nitrogen ligand, δ 1.37 (d, iPr), 4.03 (septet, iPr), 8.08 (d, 2H,
H3 and H5), 8.26 (t, H4), 8.46 (s, 2H, H7 and H8).
13a . To a stirred solution of 50 mg (0.189 mmol) of (COD)-
Pd(Me)(Cl) in 10 mL of dichloromethane at room temperature
was added 63 mg of silver tosylate (0.226 mmol, 1.2 equiv).
After 15 min the white precipitate that formed (AgCl) was
filtered off and 40 mg of 2,6-bis(N-pyrazolyl)pyridine (0.189
mmol, 1.0 equiv) was added and the solution was stirred for 1
h. The solvent was removed from the resulting pale yellow
solution in vacuo to constant weight. Yields: 63.5 mg (0.127
mmol, 67%) of pale yellow 13a . 1H NMR (223 K, CD3OD):
hydrocarbyl ligand, δ 0.39 (s, methyl); nitrogen ligands, δ 2.37
(s, OTos), 6.56 (t, H4′′), 6.87 (t, H4′), 7.24 (d, OTos), 7.67 (d,
OTos), 7.81 (d, H5), 7.84 (d, H5′′), 7.91 (d, H5′), 8.39 (d, H3), 8.51
(t, H4), 8.52 (d, H3′′), 9.15 (d, H3′).
Exp er im en ta l Section
Ma ter ia ls a n d Ap p a r a tu s. All manipulations were car-
ried out under an atmosphere of purified dry nitrogen by using
standard Schlenk techniques. Solvents were dried and stored
under nitrogen. All starting chemicals were used as com-
mercially obtained, including terpy (2). The starting com-
pounds 1-methylimidazolyl-2-carboxaldehyde,36 (COD)Pd(CH3)-
(Cl),21,24 and ligands 1, 3,23 and 621,22 and the compounds 4a ,
5a , 14a , and 15a 21 have been prepared according to the
methods given in the literature.
1H NMR spectra were recorded on Bruker AC 100 and AMX
300 spectrometers and IR spectra on Perkin-Elmer PE 283 and
Bio-Rad FTS-7 spectrophotometers; mass spectra were ob-
tained on a Varian MAT 711 doublet-focusing mass spectrom-
eter fitted with a 10 µm tungsten FD emitter. GC-MS was
performed on a Hewlett-Packard 5890 series II gas chromato-
graph with a Gerstel CIS III temperature-controllable injector,
an HP 5971A mass selective detector with electron impact
ionization at 70 eV, and an HP Ultra-2 column (25 m, 0.20
mm inner diameter, 0.33 µm film thickness). Elemental
analyses were carried out by the Elemental Analysis section
of the ITC/TNO, Zeist, The Netherlands.
16a . The synthesis was carried out similarly to that of 11a .
Yield: 70% of pale yellow 16a . 1H NMR (CDCl3): hydrocarbyl
ligand, δ 1.08 (s, Me); nitrogen ligand, δ 3.40 (bt, HR), 3.96
(bt, Hâ), 4.03 (s, H6′), 7.33 (d, H5′), 7.47 (d, H4′), 7.55 (ddd, H5),
7.69 (d, H3), 8.12 (dt, H4), 8.64 (d, H6), 8.67 (s, H7′).
CO In ser tion Rea ction s. P r ep a r a tive Ca r bon yla tion .
In a typical procedure, a Schlenk vessel containing a solution
of ca. 20 mg of the methylpalladium compounds 1a -15a in 2
mL of solvent (1a and 4a -6a , CH2Cl2, CHCl3; 11a -15a , CH3-
CN; 2a , CH3OH, C2H5OH) was carefully evacuated and then
brought under CO three times and the mixture stirred. After
the insertion reaction was completed, typically between 5 and
30 min, the solution was filtered. The solvent was removed
under reduced pressure, yielding the corresponding acetylpal-
ladium(II) compounds 1b-15b.
Liga n d s. The numbering schemes of the ligands are
presented in Figure 1.
1
1: H NMR (CDCl3) δ 1.20 (d, iPr), 3.58 (septet, iPr), 7.89
(d, H3 and H5), 7.96 (t, H4), 8.42 (s, H7 and H8).
3: 1H NMR (CDCl3) δ 6.51 (dd, 2H, H4′ and H4′′), 7.77 (d,
2H, H5′ and H5′′), 7.90 (m, 3H, H3, H4, and H5), 8.58 (d, 2H, H3′
and H3′′).
6: 1H NMR (CDCl3) δ 3.15 (t, HR), 3.90 (s, H6′), 3.99 (dt, Hâ),
6.89 (d, H5′), 7.07 (d, H4′), 7.11 (ddd, H5), 7.16 (d, H3), 7.56 (dt,
H4), 8.26 (s, H7′), 8.54 (d, H6).
1b. 1H NMR (223 K, CDCl3): hydrocarbyl ligand, δ 2.67
(s, C(O)Me); nitrogen ligand, δ 1.21 (d, iPr), 1.34 (d, iPr), 3.81
(septet, iPr), 3.95 (septet, iPr), 7.75 (d, H5), 7.99 (t, H4), 8.26
Meth ylp a lla d iu m Com p ou n d s. (σ2-iP r -DIP )P d (CH3)-
(Cl) (1a ). A solution of 265 mg (1 mmol) of (COD)Pd(Me)(Cl)
and 250 µL (1 mmol) of 1 in acetonitrile was stirred for 5 min
at 20 °C. Dark red crystals of 1a formed immediately after
cooling the solution to -10 °C. After these crystals were
decanted, they were washed with diethyl ether to give 282 mg
(0.75 mmol; 75%) of dark red crystals. 1H NMR (CDCl3):
hydrocarbyl ligand, δ 1.17 (s, Me); nitrogen ligand, δ 1.24 (d,
1Pr), 1.39 (d, iPr), 3.82 (sept, iPr), 4.18 (sept, iPr), 7.75 (d, H5),
8.01 (t, H4), 8.26 (d, H3), 8.45 (s, H7), 9.62 (s, H8). Anal. Calcd
for C14H22ClN3Pd: C, 44.93; H, 5.93; N, 11.23. Found: C,
44.65; H, 5.94; N, 11.12. Mp: 161 °C dec. MS: correct isotope
pattern at m/z 358 [M - Cl]•+ and at m/z 373 [M]•+ for 106Pd
and 35Cl.
(d, H3), 8.41 (s, H7), 9.50 (s, H8). IR: ν(CO) 1712 cm-1
.
2b. 1H NMR (CD3OD): hydrocarbyl ligand, δ 2.65 (s, C(O)-
Me); nitrogen ligand, δ 7.74 (dt, H5′ and H5′′), 8.23 (dt, H4′ and
H4′′), 8.35 (m, other H’s), 8.47 (dd, H6′ and H6′′). IR: ν(CO)
1682 cm-1
.
4b. 1H NMR (CD2Cl2): hydrocarbyl ligand, δ 2.59 (s, C(O)-
Me); nitrogen ligand, δ 3.18 (t, HR), 4.16 (t, Hâ), 7.12 (dd, H5),
7.24 (d, H3), 7.58 (m, 3H, H3′, H4, and H5′), 7.96 (t, H4′), 8.18
(s, H7′), 8.50 (d, H6), 8.64 (d, H6′). IR: ν(CO) 1694 cm-1
.
5b. 1H NMR (CDCl3): hydrocarbyl ligand, δ 2.64 (s, C(O)-
Me); nitrogen ligand, δ 2.79 (s, 6′-Me), 3.15 (t, HR), 4.04 (t, Hâ),
7.08 (dd, H5), 7.17 (d, H3), 7.29 (d, H3′), 7.38 (d, H5′), 7.53 (t,
H4), 7.72 (t, H4′), 8.16 (s, H7′), 8.46 (d, H6). IR: ν(CO) 1708
2a . The synthesis was carried out similar by that of 1a ,
except that 2a precipitated instantaneously at room temper-
cm-1
.
6b. 1H NMR (193 K, CD2Cl2): hydrocarbyl ligand, δ 2.44
(s, C(O)Me); nitrogen ligand, δ 3.08 (t, HR), 3.34 (d, HR), 3.60
(t, Hâ), 4.05 (d, Hâ), 4.21 (s, H6′), 6.80 (d, H5′), 7.35 (m, H4′ and
(36) Byers, P. K.; Canty, A. J .; Honeyman, R. T. J . Organomet.
Chem. 1990, 385, 417.

676 Organometallics, Vol. 15, No. 2, 1996
Ru¨lke et al.
Ta ble 8. Cr ysta l a n d r efin em en t d a ta for
1a a n d 2a
1a
2a
formula
fw
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
cryst size, mm
T, K
C14H22ClN3Pd
C16H14ClN3Pd‚2H2O
374.204
8.723(5)
9.422(5)
11.292(7)
113.86(7)
90.23(6)
108.50(7)
795.5(7)
0.04 × 0.35 × 0.50
293
426.19
16.174(5)
12.997(4)
8.086(3)
90
100.56(3)
90
1671
F igu r e 7. Numbering scheme of the C7H8C(O)CH3 moiety
in 1c, 2c, 4c, and 6c (left) and of 2-acetyl[2.2.1]bicyclohepta-
2,5-diene (right).
H5), 7.49 (d, H3), 7.89 (dt, H4), 8.46 (d, H6), 9.70 (s, H7′). IR:
ν(CO) 1696 cm-1
.
0.03 × 0.20 × 0.45
11b. 1H NMR (223 K, CDCl3): hydrocarbyl ligand, δ 2.63
(s, C(O)Me); nitrogen ligand, δ 1.29 (d, iPr), 3.94 (septet, iPr),
8.04 (m, 3H, H3, H4, and H5), 8.89 (s, 2H, H7 and H8). IR: ν-
293
λ, Å
0.710 69
P1h
0.710 69
P21/a
4
1.69
12.68
space group
Z
(CO) weak, broad resonance around 1700 cm-1
.
2
d
exptl, g cm-3
1.56
13.1
0.053
0.084
14b. 1H NMR (CD3CN): hydrocarbyl ligand, δ 2.62 (s, C(O)-
Me); nitrogen ligand δ 3.47 (t, HR), 3.96 (bs, Hâ), 7.59 (ddd,
H5), 7.76 (d, H3), 7.87 (H5′), 8.08 (dt, H4), 8.16 (H3′), 8.34 (H4′),
µ, cm-1
R
0.048
0.054
Rw
8.47 (d, H6), 8.52 (d, H6′), 8.70 (s, H7′). IR: ν(CO) 1690 cm-1
.
15b. 1H NMR (223 K, CDCl3): hydrocarbyl ligand, δ 2.64
(s, C(O)Me); nitrogen ligand, δ 2.95 (s, 6′-Me), 3.18 (t, HR), 4.07
(t, Hâ), 7.13 (dd, H5), 7.23 (d, H5′), 7.32 (d, H3′), 7.37 (d, H3),
7.59 (dt, H4), 7.75 (t, H4′), 8.09 (s, H7′), 8.52 (d, H6). IR: ν(CO)
2.94 (s, H1), 5.95 (m, H3), 6.02 (m, H2); nitrogen ligand, δ 3.14
(t, HR), 4.10 (t, Hâ), 6.93 (t, H5), 7.11 (d, H3), 7.40 (t, H5′), 7.61
(t, H4), 7.96 (t, H4′), 8.16 (d, H3′), 8.29 (d, H6′), 8.37 (d, H6),
8.87 (s, H7′); H13 concealed. IR: ν(CO) 1712 cm-1
.
1698 cm-1
.
6c. 1H NMR (223 K, CDCl3): hydrocarbyl ligand, δ 1.35
(d, H7), 1.47 (d, H8), 1.62 (d, H5), 1.90 (d, H6), 2.54 (s, C(O)-
Me), 3.06 (s, H4), 3.17 (s, H1), 6.27 (m, H3), 6.32 (m, H2);
nitrogen ligand, δ 3.47 (bt, HR), 3.95 (s, H6′), 4.17 (bt, Hâ), 7.17
(d, H5′), 7.30 (d, H4′), 7.38 (ddd, H5), 7.71 (d, H3), 7.88 (dt, H4),
CO In ser tion Ha lf-Life Mea su r em en ts. The CO inser-
tion half-lives were determined at 293 K with a homemade
gas buret. In a typical experiment, a 12 mL vessel was filled
under nitrogen with 5 mL of a 0.4 mM solution of the
methylpalladium complex (see Table 7 for the solvent) and
stirred. The vessel was carefully evacuated three times and
connected to the CO-filled gas buret. The measurement was
started by opening the valve between the CO and the vigor-
ously stirred solution of the methylpalladium compound. After
equilibrium was reached, the time for every 0.25 mL of CO
take up was recorded until the CO uptake had stopped (i.e. at
least 3 half-lives) and the half-life calculated. Blank experi-
ments in several solvents showed that the CO diffusion time
was ca. 20 s.
Nor bor n a d ien e In ser tion Rea ction s. (σ2-iP r -DIP )P d -
(C7H8C(O)CH3)(Cl) (1c). CO was bubbled for 3 min through
a solution of 7 mg (0.019 mmol) of 1a in 0.6 mL of deuterio-
chloroform in a Schlenk vessel. Subsequently, a small stream
of nitrogen was bubbled through the solution for a few seconds
to remove dissolved CO. The solution of the in situ formed
1b was filtered and transferred into a NMR tube, and 2.2 µL
(1.9 mg; 0.021 mmol; 1.1 equiv) of NBD was added. The
formation of 1c was then followed by 1H NMR. After the
reaction was completed, infrared spectroscopy was carried out
on the same solution. In some cases, the solvent was removed
in vacuo and the solid washed with 0.5 mL of diethyl ether.
Due to the small amount of product, no yield of 1c was
determined. Compounds 2c (CD3OD, C2D5OD), 4c, 5c, and
6c (CD2Cl2, CDCl3), and 14c and 15c (CD3CN) have been
synthesized according to the same procedure. The numbering
scheme of the 6-acetyl[2.2.1]bicyclohept-1-en-5-yl moiety is
presented in Figure 7.
8.49 (s, H7′), 8.59 (d, H6). IR: ν(CO) 1705 cm-1
.
Degr a d a tion P r od u ct fr om 1c, 2c, 4c, a n d 6c. The
degradation products from 1c-15c were obtained by evapora-
tion of the solvent and extraction with hexane. The numbering
scheme is presented in Figure 7. 1H NMR (CDCl3): δ 0.97 (d,
H7), 2.10 (s, C(O)Me), 3.75 (bs, H4), 3.99 (bs, H1), 6.73 (dd, H5),
6.88 (dd, H6), 7.72 (d, H3); H8 concealed. GC-MS: m/z 134 (18,
M•+), 133 (6, [M - H]•+), 119 (6, [M - CH3]•+), 91 (35, [M -
C(O)Me]•+), 66 (34, [C5H6]•+; retro Diels-Alder products), 65
(23), 51 (8), 43 (100, [C(O)Me]•+). These spectral data are
correct for 2-acetyl[2.2.1]bicyclohepta-2,5-diene. No other
organic compounds were isolated.
X-r a y Da ta Collection a n d Str u ctu r e Refin em en t. (2-
(σ(N)-(Isop r op ylim in o)m et h yl)-6-((isop r op ylim in o)m e-
th yl)-σ(N′)-pyr idyl)ch lor om eth ylpalladiu m (II) (1a). Crys-
tals of 1a suitable for X-ray diffraction have been obtained by
cooling a concentrated solution of 1a in acetonitrile in an ice-
salt bath for 10 min, yielding bright red crystals. Crystal data
for 1a are presented in Table 8. A crystal of 1a with
dimensions 0.35 × 0.04 × 0.50 mm was measured on an Enraf-
Nonius CAD 4 diffractometer by employing graphite-mono-
chromated Mo KR radiation. A total of 4602 reflections were
collected in the range 2.2° < 2θ < 60° (-12 e h e 12, -13 e
k e 13, 0 e l e 15), of which 3215 reflections with I > 2.5σ(I)
were used in the structure determination.
The structure was solved by means of a Patterson minimum
function based on Pd and Cl positions. The remaining non-
hydrogen atoms were found in a subsequent difference Fourier
synthesis. The hydrogen atoms of C(1) were found, and the
positions of the other hydrogen atoms were calculated. The
non-hydrogen atoms were refined anisotropically; the hydrogen
atoms were not refined. Refinement proceeded through aniso-
1c. 1H NMR (253 K, CD2Cl2): hydrocarbyl ligand, δ 2.51
(s, C(O)Me), 2.86 (s, H4), 3.16 (s, H1), 6.12 (dd, H3), 6.18 (dd,
H2), H5, H6, H7, and H8 of the C7H8C(O)CH3 moiety are
concealed by the isopropyl signals; nitrogen ligand, δ 1.19 (d,
iPr), 1.21 (d, iPr), 3.63 (sept, iPr), 3.95 (sept, iPr), 7.92 (d, H5),
8.12 (t, H4), 8.32 (d, H3), 8.74 (s, H7), 9.73 (s, H8). IR: ν(CO)
1700 cm-1
.
tropic block-diagonal least-squares calculations employing a
2
weighting scheme; w ) (4.74 + Fo + 0.026Fo
)
-1. An empirical
2c. 1H NMR (223 K, CDCl3): hydrocarbyl ligand, δ 1.44
(d, H7), 1.68 (d, H8), 1.98 (s, C(O)Me), 2.35 (dd, H5), 2.52 (d,
H6), 2.92 (s, H4), 3.08 (s, H1), 6.18 (dd, H3), 6.26 (dd, H2);
nitrogen ligand, δ 7.71 (t, H5′ and H5′′), 8.18 (t, H4′ and H4′′),
8.35 (m, other H’s), 8.66 (d, H6′ and H6′′). IR: ν(CO) weak,
absorption correction (DIFABS)37 was used, and an extinction
correction was applied.38 The anomalous dispersion of Pd and
Cl was taken into account. Convergence to R ) 0.055 and Rw
) 0.088 was obtained. Calculations were carried out with
broad resonance around 1700 cm-1
.
4c. 1H NMR (223 K, CDCl3): hydrocarbyl ligand, δ 1.26
(37) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39, 158.
(38) Zachariassen, W. H. Acta Crystallogr., Sect. A 1968, 24, 212.
(d, H7), 1.66 (d, H8), 2.37 (m, C(O)Me, H5 and H6), 2.78 (s, H4),

Palladium Complexes with Nitrogen Ligands
Organometallics, Vol. 15, No. 2, 1996 677
XRAY76.39 Scattering factors40 and dispersion corrections41
were taken from the literature.
reflections with I > 2.5σ(I) were used in the structure deter-
mination. The structure was solved in a way similar to that
(σ-2,2′:6′,2′′-Ter p yr id yl-N,N′,N′′)m et h ylp a lla d iu m (II)
Ch lor id e Dih yd r a te (2a ). Crystals suitable for X-ray dif-
fraction were obtained by slow evaporation of the solvent of
2a in methanol at -20 °C, which resulted in a small crop of
yellow needles. Crystal data for 2a are presented in Table 8.
A crystal of compound 2a , with dimensions 0.03 × 0.20 × 0.45
for 1a , except that the hydrogen atoms were refined isotropi-
2
cally. The weighting scheme w ) (4.14 + Fo + 0.052Fo
)
-1 was
used. Convergence was reached at R ) 0.048 and Rw ) 0.054.
Ack n ow led gm en t. We wish to thank D. Heidenrijk
for collecting the X-ray data, M. C. Zoutberg and Y.-F.
Wang for solving and refining the crystal structures, and
J . H. Groen for synthetic contributions.
mm, was measured in the same way as for complex 1a .
A
total of 2927 reflections were collected in the range 2.2° < 2θ
< 50° (-19 e h e 19, 0 e k e 15, 0 e l e 19) of which 1712
(39) Stewart, J . M. The XRAY76 system; Tech. Rep. TR 446;
Computer Science Center, University of Maryland: College Park, MD,
1976.
(40) Cromer, D. T.; Mann, J . B. Acta Crystallogr., Sect. A 1968, 24,
321.
Su p p or tin g In for m a tion Ava ila ble: Tables of fractional
atomic coordinates for 1a and 2a (2 pages). Ordering informa-
tion is given on any current masthead page.
(41) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, England, 1975; Vol. 4.
OM9504361