Nucleophilic attack on cyclooctadiene complexes of palladium: Stereochemistry of the resulting cyclooctenylpalladium derivatives

Article abstract of DOI:10.1021/om970836j

Reaction of [PdClMe(cod)] with MeO₂CC=CCO₂Me occurs in two steps, namely, insertion of the alkyne into the Pd-Me bond followed by migratory insertion of one of the double bonds of the coordinated cyclooctadiene into the Pd-alkenyl bond thus formed. The resulting chloride-bridged, cyclooctenyl complex was converted to [Pd(acac){η¹,η²-C₈H ₁₂C(CO₂Me)=CMe(CO₂Me)}], 2a, which was characterized crystallographically. The molecular structure revealed that each insertion took place in a cis manner. Reactions of [PdCl₂(cod)] with a range of nucleophiles were performed, which gave analogous chloride-bridged, cyclooctenylpalladium dimers, 1, which could be converted to their acetylacetonate derivatives, 2. The solid-state structure of the methoxy complex [Pd(acac)(η¹,η₂-C₈H₁₂OMe)], 2b, obtained by reaction of [PdCl₂(cod)] with NaOMe followed by Ag(acac), was determined. This showed that exo attack of the OMe group occurred. In contrast, the structure of the phenyl derivative [Pd(acac)(η¹,η²-C₈H₁₂Ph)], 2e, produced by treatment of [PdCl₂(cod)] with Ph₄Sn followed by Ag(acac), indicated that the phenyl group added in an endo fashion, presumably via a phenyl-palladium intermediate of the type [PdClPh(cod)]. With the larger mesityl group, the complex [PdCl(C₆H₂Me₃)(cod)] could be isolated. Each of the complexes was fully characterized by ¹H and ¹³C{¹H} NMR spectroscopy, and the appearance of the CHPd signal was used to distinguish between the exo and endo isomers. On the basis of the crystallographic and NMR data, it was deduced that the organometallic reagents ArMgX (Ar = Ph, 2-MeC₆H₄, 2,4,6-Me₃C₆H₂), Ph₄Sn, and (4-MeC₆H₄)₂Hg generate the endo products by initial attack at the metal. In contrast, reactions with NaOR (R = Me, Et), NaCH(CO₂Me)₂, AgOAc, and Et₂NH proceed by direct attack of the nucleophile at the coordinated double bond to give the exo products.

Full text of DOI:10.1021/om970836j

Organometallics 1998, 17, 1155-1165
1155
Nu cleop h ilic Atta ck on Cycloocta d ien e Com p lexes of
P a lla d iu m : Ster eoch em istr y of th e Resu ltin g
Cycloocten ylp a lla d iu m Der iva tives
Gretchen R. Hoel, Robert A. Stockland, J r., Gordon K. Anderson,*
Folami T. Ladipo, J anet Braddock-Wilking, Nigam P. Rath, and
J uan C. Mareque-Rivas
Department of Chemistry, University of MissourisSt. Louis, 8001 Natural Bridge Road,
St. Louis, Missouri 63121
Received September 23, 1997
Reaction of [PdClMe(cod)] with MeO2CCtCCO2Me occurs in two steps, namely, insertion
of the alkyne into the Pd-Me bond followed by migratory insertion of one of the double
bonds of the coordinated cyclooctadiene into the Pd-alkenyl bond thus formed. The resulting
chloride-bridged, cyclooctenyl complex was converted to [Pd(acac){η1,η2-C8H12C(CO2Me)dCMe-
(CO2Me)}], 2a , which was characterized crystallographically. The molecular structure
revealed that each insertion took place in a cis manner. Reactions of [PdCl2(cod)] with a
range of nucleophiles were performed, which gave analogous chloride-bridged, cycloocte-
nylpalladium dimers, 1, which could be converted to their acetylacetonate derivatives, 2.
The solid-state structure of the methoxy complex [Pd(acac)(η1,η2-C8H12OMe)], 2b, obtained
by reaction of [PdCl2(cod)] with NaOMe followed by Ag(acac), was determined. This showed
that exo attack of the OMe group occurred. In contrast, the structure of the phenyl derivative
[Pd(acac)(η1,η2-C8H12Ph)], 2e, produced by treatment of [PdCl2(cod)] with Ph4Sn followed by
Ag(acac), indicated that the phenyl group added in an endo fashion, presumably via a phenyl-
palladium intermediate of the type [PdClPh(cod)]. With the larger mesityl group, the complex
[PdCl(C6H2Me3)(cod)] could be isolated. Each of the complexes was fully characterized by
1H and 13C{1H} NMR spectroscopy, and the appearance of the CHPd signal was used to
distinguish between the exo and endo isomers. On the basis of the crystallographic and
NMR data, it was deduced that the organometallic reagents ArMgX (Ar ) Ph, 2-MeC6H4,
2,4,6-Me3C6H2), Ph4Sn, and (4-MeC6H4)2Hg generate the endo products by initial attack at
the metal. In contrast, reactions with NaOR (R ) Me, Et), NaCH(CO2Me)2, AgOAc, and
Et2NH proceed by direct attack of the nucleophile at the coordinated double bond to give
the exo products.
In tr od u ction
Reactions of palladium diene complexes with a range
of nucleophiles have been described previously. Reac-
tions with hydroxide, alkoxides, carboxylates, malonate,
azide, or amines4-10 have been reported, and they all
were supposed to occur by direct, exo attack of the
nucleophile on the coordinated diene. In contrast, the
reaction of [PdCl2(nbd)] (nbd ) norbornadiene) with
diphenylmercury produced an endo-substituted species,
which was characterized crystallographically.11 More
recently, the monomeric species [PdCl(C6F5)(cod)], formed
During the course of our investigations1 of the chem-
istry of [PdClMe(cod)] (cod ) 1,5-cyclooctadiene)2 and
related complexes,3 we found that reaction with carbon
monoxide generates the acetylpalladium species [PdCl-
(COMe)(cod)].1 In contrast, we have found that reaction
with dimethylacetylene dicarboxylate (DMAD) produces
a compound derived from formal insertion of the alkyne
into the Pd-C bond followed by migration of the
resulting alkenyl group to one of the double bonds of
the cyclooctadiene ligand. This observation led us to
carry out a detailed study of the stereochemistry of the
products obtained by nucleophilic attack on [PdCl2(cod)],
where attack on the coordinated double bond may take
place in an endo (attack at the metal followed by
migratory insertion of the double bond) or exo (direct
attack from the face opposite the metal) fashion.
(4) Stille, J . K.; J ames, D. E. J . Organomet. Chem. 1976, 108, 401.
Rotondo, E.; Cusmano Priolo, F.; Donato, A.; Pietropaolo, R. J .
Organomet. Chem. 1983, 251, 273.
(5) Stille, J . K.; Morgan, R. A.; Whitehurst, D. D.; Doyle, J . R. J .
Am. Chem. Soc. 1965, 87, 3282. Schultz, R. G. J . Organomet. Chem.
1966, 6, 435. Pietropaolo, R.; Cusmano, F.; Rotondo, E.; Spadaro, A.
J . Organomet. Chem. 1978, 155, 117.
(6) Anderson, C. B.; Burreson, B. J . J . Organomet. Chem. 1967, 7,
181. Akbarzadeh, M.; Anderson, C. B. J . Organomet. Chem. 1980, 197,
C5.
(7) Tsuji, J .; Takahashi, H. J . Am. Chem. Soc. 1965, 87, 3275.
(8) Tada, M.; Kuroda, Y.; Sato, T. Tetrahedron Lett. 1969, 2871.
(9) Palumbo, R.; De Renzi, A.; Panunzi, A.; Paiaro, G. J . Am. Chem.
Soc. 1969, 91, 3874.
(10) Evans, D. J .; Kane-Maguire, L. A. P. J . Organomet. Chem. 1986,
312, C24.
(1) Ladipo, F. T.; Anderson, G. K. Organometallics 1994, 13, 303.
(2) Rulke, R. E.; Ernsting, J . M.; Spek, A. L.; Elsevier, C. J .; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.
(3) Stockland, R. J ., J r.; Anderson, G. K.; Rath, N. P.; Braddock-
Wilking, J .; Ellegood, J . C. Can. J . Chem. 1996, 74, 1990.
S0276-7333(97)00836-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 02/26/1998

1156 Organometallics, Vol. 17, No. 6, 1998
Hoel et al.
35 min, then the solvent was removed in vacuo. The solid was
dissolved in ether (5 mL) and passed down a short Florosil
column, eluting with ether (40 mL). The ether was removed,
and the residue was extracted with hexane. After filtration,
the solvent was removed in vacuo to leave the product as a
colorless solid (0.114 g, 93%). Anal. Calcd for C14H22O3Pd:
C, 48.81; H, 6.39. Found: C, 48.82; H, 6.39. A portion of the
product was dissolved in hexane (1.5 mL), and the solution
was cooled to -40 °C. Colorless crystals were obtained after
1 week.
by reaction of [PdCl2(cod)] with C6F5Li, was shown to
rearrange slowly in solution to generate [Pd2(µ-Cl)2-
(η1,η2-C8H12C6F5)2], the latter being converted to [Pd-
(acac-F6) (η1,η2-C8H12C6F5)] by treatment with thallium-
(I) hexafluoroacetylacetonate. The crystal structure of
[Pd(acac-F6)(η1,η2-C8H12C6F5)] revealed that the product
had been formed, as might be expected, by endo attack
of the pentafluorophenyl group on the coordinated
double bond.12
In this paper, we report the syntheses of a number of
cyclooctenylpalladium derivatives, first as their chloride-
bridged dimers and subsequently as acetylacetonate
derivatives. We also describe the crystal structures of
three complexes, one formed by exo attack and two
formed by endo attack on coordinated cyclooctadiene.
In addition, we present NMR studies of these complexes
and the use of the magnitudes of 3J (H,H) coupling
constants to determine the stereochemistry of addition
to the coordinated double bond.
P r ep a r a tion of [P d 2(µ-Cl)2(η1,η2-C8H12OEt)2], 1c. To an
ethanol suspension of [PdCl2(cod)] (0.10 g, 0.35 mmol) was
slowly added an ethanol solution of NaOEt (0.35 mL of a 1.0
M solution). The solution became lighter in color. The mixture
was stirred for 30 min, and a white precipitate formed. The
solution was filtered through a Hyflo Supercel column, which
was washed with CH2Cl2 (100 mL). The resulting solution was
evaporated, and the residue was dried in vacuo, leaving the
product as a pale yellow solid (65%).
P r ep a r a tion of [P d (a ca c)(η1,η2-C8H12OEt)], 2c. To a
CH2Cl2 solution (50 mL) of [Pd2(µ-Cl)2(C8H12OEt)2] (0.050 g,
0.085 mmol) was added Ag(acac) (0.037 g, 0.18 mmol). The
solution was stirred in the dark for 1 h at ambient tempera-
ture. The resulting mixture was passed through a Hyflo
Supercel/Florosil column, washing with CH2Cl2 (100 mL). The
solvent was removed in vacuo, leaving the product as a
colorless solid (0.052 g, 85%). Anal. Calcd for C15H24O3Pd:
C, 50.22; H, 6.70. Found: C, 50.14; H, 6.34.
Exp er im en ta l Section
All reactions were carried out under an atmosphere of argon.
Solvents were dried and distilled immediately prior to use.
[PdCl2(cod)] was prepared according to the method of Chatt.13
Silver(I) acetylacetonate was purchased from Aldrich. Solu-
tions of NaOMe and NaOEt were prepared by addition of
sodium metal to the appropriate alcohol. [Pd2(µ-Cl)2(η1,η2-
C8H13)2], 1g, was prepared as described previously.3 The
complexes [Pd2(µ-Cl)2(η1,η2-C8H12R)2] (R ) OMe (1b),14 CH(CO2-
Me)2 (1d ),7 NEt2 (1j),9 OAc (1k )6) were prepared according to
literature methods. NMR spectra were recorded on a Varian
XL-300, Varian Unity plus 300, or Bruker ARX-500 spectrom-
eter. 1H and 13C chemical shifts were measured relative to
the residual solvent signal, positive shifts representing deshield-
ing; coupling constants are given in hertz. Microanalyses were
performed by Atlantic Microlab Inc. (Norcross, Georgia).
P r ep a r a tion of [P d 2(µ-Cl)2{η1,η2-C8H12C(CO2Me)dCMe-
(CO2Me)}2], 1a . [PdClMe(cod)] (0.22 g, 0.83 mmol) was
dissolved in toluene (8 mL). Dimethylacetylene dicarboxylate
(0.12 mL, 0.95 mmol) was introduced by syringe. The yellow
solution was stirred at ambient temperature for 20 h, during
which time a white solid precipitated. Ether (15 mL) was
added to complete precipitation, and the solid was filtered off.
After washing with ether (3 mL), the solid was dried in vacuo
(0.30 g, 89%). Anal. Calcd for C30H42Cl2O8Pd2: C, 44.25; H,
5.16. Found: C, 44.16; H, 5.19.
P r ep a r a tion of [P d (a ca c){η1,η2-C8H12CH(CO2Me)2}], 2d .
Ag(acac) (0.054 g, 0.26 mmol) was added to [Pd2(µ-Cl)2{C8H12
-
CH(CO2Me)2}2] (0.10 g, 0.13 mmol) in CH2Cl2 solution (50 mL).
The solution was stirred in the dark at ambient temperature
for 1 h. The solution was passed down a Hyflo Supercel/
Florosil column, and the solvents were removed. The residue
was extracted with ether (50 mL). After filtration, the solvent
was removed in vacuo, leaving the product as a colorless solid
(0.098 g, 84%). Anal. Calcd for C18H26O6Pd: C, 48.60; H, 5.85.
Found: C, 49.16; H, 6.13.
P r epar ation of [P d2(µ-Cl)2(η1,η2-C8H12C6H5)2], 1e. Meth -
od A. To a CH2Cl2 solution (100 mL) of [PdCl2(cod)] (0.82 g,
2.9 mmol) was added tetraphenyltin (1.38 g, 3.2 mmol). The
solution was stirred at ambient temperature for 15 h, and then
it was evaporated to leave a light gray solid. The latter was
subjected to a Soxhlet extraction with ether for 12 h to remove
Ph3SnCl and unreacted Ph4Sn. The remaining solid was
extracted with CH2Cl2, and the solution was evaporated to
leave the product as an off-white solid (0.782 g, 84%). Anal.
Calcd for C28H34Pd2Cl2: C, 51.39; H, 5.21. Found: C, 51.41;
H, 5.17.
P r ep a r a tion of [P d (a ca c){η1,η2-C8H12C(CO2Me)dCMe-
(CO2Me)}], 2a . To a CH2Cl2 solution (20 mL) of [Pd2(µ-Cl)2-
{η1,η2-C8H12C(CO2Me)dCMe(CO2Me)}2] (0.10 g, 0.12 mmol)
was added Ag(acac) (0.051 g, 0.25 mmol), and the mixture was
stirred in the dark for 1 h. The solvent was removed, and the
residue was extracted with ether and passed down a Hyflo
Supercel/Florosil column, eluting with ether. The ether was
removed in vacuo. The resulting solid was crystallized by slow
evaporation of an ether/hexane solution, giving the product
as colorless crystals (0.94 g, 81%). Anal. Calcd for C20H28O6-
Pd: C, 51.02; H, 5.95. Found: C, 51.02; H, 6.01.
Meth od B. To a CH2Cl2 solution (50 mL) of [PdCl2(cod)]
(0.10 g, 0.35 mmol) at 0 °C was introduced phenylmagnesium
bromide (0.18 mL of a 3.0 M solution in ether). The solution
darkened and was stirred for 5 min. The reaction was
quenched with water (0.1 mL), then the solvents were evapo-
rated, leaving a black solid. The solid was dissolved in CH2-
Cl2 and filtered. The solvent was evaporated, leaving the
product as a colorless solid (0.010 g, 9%).
P r ep a r a t ion of [P d (a ca c)(η1,η2-C8H12C6H5)], 2e. To a
CH2Cl2 solution (20 mL) of [Pd2(µ-Cl)2(C8H12C6H5)2] (0.10 g,
0.15 mmol) was added Ag(acac) (0.063 g, 0.31 mmol). The
mixture was stirred for 2 h at ambient temperature, and then
it was passed down a Hyflo Supercel/Florosil column, eluting
with CH2Cl2 (50 mL). The solvent was removed in vacuo,
leaving the product as a colorless solid (0.11 g, 89%). The solid
was crystallized from hexane solution at -40 °C.
P r ep a r a tion of [P d (a ca c)(η1,η2-C8H12OMe)], 2b. To a
CH2Cl2 solution (20 mL) of [Pd2(µ-Cl)2(η1,η2-C8H12OMe)2] (0.10
g, 0.18 mmol) was added Ag(acac) (0.078 g, 0.38 mmol). The
mixture was stirred in the dark at ambient temperature for
P r ep a r a tion of [P d 2(µ-Br )2(η1,η2-C8H12C6H2Me3)2], 1f.
[PdCl2(cod)] (0.35 g, 1.2 mmol) was dissolved in CH2Cl2 (50
mL). 2-Mesitylmagnesium bromide (1.8 mL of a 1.0 M diethyl
ether solution) was added by syringe. The mixture was
allowed to stir at ambient temperature for 10 min. Water (0.1
mL) was added to quench any remaining Grignard reagent.
(11) Segnitz, A.; Kelly, E.; Taylor, S. H.; Maitlis, P. M. J . Organomet.
Chem. 1977, 124, 113.
(12) Albeniz, A. C.; Espinet, P.; J eannin, Y.; Philoche-Levisalles, M.;
Mann, B. E. J . Am. Chem. Soc. 1990, 112, 6594.
(13) Chatt, J .; Vallarino, L. M.; Venanzi, L. M. J . Chem. Soc. 1957,
3413.
(14) Bailey, C. T.; Lisensky, G. C. J . Chem. Educ. 1985, 62, 896.

Attack on Cyclooctadiene Complexes of Palladium
Organometallics, Vol. 17, No. 6, 1998 1157
Ta ble 1. Da ta Collection , Str u ctu r e Solu tion , a n d Refin em en t P a r a m eter s for
[P d (a ca c){η1,η2-C8H12C(CO2Me)dCMe(CO2Me)}], 2a , [P d (a ca c)(η1,η2-C8H12OMe)], 2b, a n d
[P d (a ca c)(η1,η2-C8H12C6H5)], 2e
2a
2b
2e
cryst syst
space group, Z
a (Å)
b (Å)
c (Å)
monoclinic
P21/c, 4
monoclinic
P21/n, 8
orthorhombic
Pna21, 4
34.43(2)
7.100(4)
7.078(5)
22.0367(2)
7.1271(1)
13.8417(1)
106.922(1)
2079.82(4)
1.504
223(2)
0.924
Siemens R3m/V
1.93-28.00
43 988
14.3942(2)
13.4702(1)
14.8865(2)
104.596(1)
2793.23(8)
1.639
298(2)
1.327
Siemens R3m/V
2.07-25.00
25 464
â (deg)
V (Å3)
1730(2)
1.500
293(2)
5.598
Siemens R3m/V
2.93-23.99
1903
density (g/cm-3) (calcd)
temp (K)
abs coeff (mm-1
diffractometer
range (deg)
)
no. of reflns colld
no. of indep reflns (Rint
least-squares params
)
5029 (0.051)
244
0.0294, 0.0657
0.0392, 0.0701
1.082
4914 (0.1523)
325
0.0733, 0.1683
0.1527, 0.2315
1.003
1413 (0.0206)
208
0.0304, 0.0598
0.0563, 0.1253
1.333
R(F), Rw(F2) (F2 > 2.0σ(F2))
R(F), Rw(F2) (all data)
S(F2)
Ta ble 2. Selected Bon d Dista n ces a n d An gles for
The solvents were evaporated, and the dark residue was
dissolved in CH2Cl2 (5 mL) and passed down a Hyflo Supercel
column, eluting with CH2Cl2 (100 mL). The eluant was
collected at -78 °C, and the solvent was removed below 0 °C.
The residue was washed with ether (100 mL), and then it was
dissolved in benzene (80 mL). The benzene solution was
passed down a Hyflo Supercel column; then the benzene was
removed to leave the product as a white solid (0.39 g, 77%).
P r ep a r a tion of [P d (a ca c)(η1,η2-C8H12C6H2Me3)], 2f. [Pd-
(cod)Cl2] (0.35 g, 1.2 mmol) was dissolved in CH2Cl2 (50 mL).
2-Mesitylmagnesium bromide (1.8 mL of a 1.0 M diethyl ether
solution) was added by syringe. The mixture was allowed to
stir at ambient temperature for 10 min; then water was added
to quench the Grignard reagent. The solvents were evapo-
rated, and the residue was washed with ether (100 mL) and
then dissolved in CH2Cl2 (50 mL). Ag(acac) (0.25 g, 1.2 mmol)
was added, and the mixture was stirred at ambient temper-
ature for 30 min. The solvent was removed, and the residue
was dissolved in ether (5 mL) and passed down a Hyflo
Supercel/Florosil column, eluting with ether (100 mL). The
ether was removed, and the solid was extracted with hexane
at -78 °C. The hexane was removed, and the solid was dried
in vacuo to leave the product as a colorless solid (0.35 g, 65%).
Anal. Calcd for C22H30O2Pd: C, 61.05; H, 6.94. Found: C,
61.16; H, 6.99.
[P d (a ca c){η1,η2-C8H12C(CO2Me)dCMe(CO2Me}], 2a
Bond Distances (Å)
Pd-C1
Pd-C6
Pd-O6
C2-C9
C9-C10
C10-C11
2.024(2)
2.154(2)
2.046(2)
1.519(3)
1.338(3)
1.502(4)
Pd-C5
Pd-O5
C1-C2
C5-C6
C9-C14
C10-C13
2.151(2)
2.129(2)
1.554(3)
1.380(4)
1.504(3)
1.510(4)
Bond Angles (deg)
C1-Pd-O5
O5-Pd-O6
Pd-C1-C8
C1-C2-C9
C2-C9-C14
C9-C10-C11
C11-C10-C13
177.32(8)
91.11(7)
104.3(2)
110.6(2)
114.7(2)
119.0(2)
116.3(2)
C1-Pd-O6
Pd-C1-C2
C1-C2-C3
C2-C9-C10
C10-C9-C14
C9-C10-C13
89.03(8)
115.18(14)
114.9(2)
124.8(2)
120.5(2)
124.7(3)
was stirred in the dark at ambient temperature overnight. The
solution was filtered to remove the silver salts. The solvent
was removed in vacuo, leaving the product as a pale yellow
powder (0.093 g, 95%). 1H NMR (CDCl3): 1.48 (dd, 1H, 14.1,
8.0, CH2), 2.1 (m, 1H, CH2), 2.26 (m, 1H, CH2), 2.37 (m, 1H,
CH2), 2.46 (m, 1H, CH2), 2.64 (qd, 1H, 8.9, 4.6, CH2), 2.72 (m,
1H, CH2), 2.81 (m, 1H, CH2), 3.71 (dd, 1H, CHPd), 4.86 (dt,
1H, CH NO2), 5.63 (m, 1H, dCH), 6.17 (m, 1H, dCH).
X-r a y Str u ctu r e Deter m in a tion s. In each case, a crystal
was mounted on a glass fiber in random orientation. Prelimi-
nary examination and data collection were performed using a
Siemens SMART CCD detector system single-crystal X-ray
diffractometer using graphite-monochromated Mo KR radia-
tion (λ ) 0.710 73 Å) equipped with a sealed-tube X-ray source
(50 kV × 40 mA), as described elsewhere.17 The SMART
software package was used for data collection, and SAINT was
used for frame integration. Structure solution and refinement
were carried out using the SHELXTL-PLUS (5.03) software
package.18 Data collection, structure solution, and refinement
parameters are given in Table 1. Selected bond distances and
bond angles are presented in Tables 2-4.
P r ep a r a tion of [P d 2(µ-Cl)2(η1,η2-C8H12C6H4Me-2)2], 1h .
To a CH2Cl2 solution (30 mL) of [PdCl2(cod)] (0.10 g, 0.35 mmol)
at 0 °C was added 2-tolylmagnesium chloride (0.50 mL of a
1.0 M ether solution). The solution was stirred for 10 min,
then the solvent was removed, and the residue was washed
with ether and hexane. The solid was extracted with benzene
and filtered. The benzene was removed in vacuo to leave the
product as a pale yellow solid (0.058 g, 49%).
P r ep a r a tion of [P d 2(µ-Cl)2(η1,η2-C8H12C6H4Me-4)2], 1i.15
To a CH2Cl2 solution (30 mL) of [PdCl2(cod)] (0.10 g, 0.35 mmol)
at ambient temperature was added (4-MeC6H4)2Hg (0.20 g,
0.52 mmol). The mixture was stirred in the dark for 1 h, then
the solvents were removed, and the residue was washed with
ether and THF. The solid was then dissolved in CH2Cl2 and
passed down a Florosil column, eluting with CH2Cl2. The
solvent was evaporated, and the product was left as a pale
yellow solid (0.85 g, 71%).
Resu lts a n d Discu ssion
P r ep a r a t ion of [P d 2(µ-Cl)2(η1,η2-C8H 12NO2)2], 1l.16
[PdCl2(cod)] (0.10 g, 0.35 mmol) was dissolved in CH3CN (30
mL). AgNO2 (0.054 g, 0.35 mmol) was added, and the mixture
Rea ction of [P d ClMe(cod )] w ith MeO2CCtCCO2-
Me (DMAD). When [PdClMe(cod)] was allowed to react
with 1.15 mol equiv of MeO2CCtCCO2Me (DMAD), a
(15) Tamaru, Y.; Yoshida, Z. J . Org. Chem. 1979, 44, 1188.
(16) Andrews, M. A.; Chang, T. C.-T.; Cheng, C.-W. F.; Kapustay,
L. V.; Kelly, K. P.; Zweifel, M. J . Organometallics 1984, 3, 1479.
(17) Stockland, R. A., J r.; Anderson, G. K.; Rath, N. P. Inorg. Chim.
Acta, in press.
(18) Siemens Analytical X-Ray Division, Madison, WI, 1995.

1158 Organometallics, Vol. 17, No. 6, 1998
Ta ble 3. Selected Bon d Dista n ces a n d An gles for [P d (a ca c)(η1,η2-C8H12OMe)], 2b
Hoel et al.
molecule 1
molecule 2
molecule 1
molecule 2
Bond Distances (Å)
Pd-C1
Pd-C6
Pd-O3
C2-O1
O1-C9
2.015(11)
2.118(11)
2.113(7)
1.417(12)
1.391(13)
2.017(10)
2.130(10)
2.121(8)
1.450(12)
1.391(13)
Pd-C5
Pd-O2
C1-C2
C5-C6
2.128(10)
2.042(7)
1.502(14)
1.38(2)
2.108(10)
2.032(8)
1.527(14)
1.41(2)
Bond Angles (deg)
C1-Pd-O2
O2-Pd-O3
Pd-C1-C8
C1-C2-O1
89.4(4)
91.3(3)
106.7(8)
108.0(9)
89.8(4)
91.4(3)
108.2(7)
105.7(9)
C1-Pd-O3
Pd-C1-C2
C1-C2-C3
C2-O1-C9
177.4(4)
112.8(7)
114.4(9)
114.3(9)
177.9(4)
110.2(7)
115.3(9)
114.5(9)
Ta ble 4. Selected Bon d Dista n ces a n d An gles for
addition of the Pd and C6F5 moieties had indeed
occurred.11 The molecular structure of [Pd2(µ-Cl)2(η1,η2-
C7H8C6H5)2], formed by reaction of [PdCl2(nbd)] with
Ph2Hg, also indicated that the product was formed by
endo attack of the phenyl group on one of the double
bonds.10 A number of other reactions of palladium diene
complexes with nucleophiles have been assumed to
proceed by exo attack on a coordinated double bond, but
unambiguous structural information is lacking. Thus,
we decided to prepare a number of η1,η2-cyclooctenyl
complexes to determine the solid-state structures of both
the exo and endo isomers and to show how NMR
spectroscopy can be used to determine the stereochem-
istry of addition when solid-state structural data are
unavailable.
[P d (a ca c)(η1,η2-C8H12C6H5)], 2e
Bond Distances (Å)
Pd-C1
Pd-C6
Pd-O2
C2-C9
2.018(8)
2.152(10)
2.125(5)
1.505(13)
Pd-C5
Pd-O1
C1-C2
C5-C6
2.162(10)
2.054(6)
1.537(11)
1.35(2)
Bond Angles (deg)
C1-Pd-O1
O1-Pd-O2
Pd-C1-C8
C1-C2-C9
89.2(3)
90.3(2)
105.3(6)
110.2(6)
C1-Pd-O2
Pd-C1-C2
C1-C2-C3
179.0(3)
113.9(6)
115.6(7)
well-defined two-step reaction occurred, namely, inser-
tion of DMAD into the Pd-Me bond followed by migra-
tory insertion of a double bond of the diene into the
alkenylpalladium linkage thus formed (eq 1). When the
Rea ction s of [P d Cl2(cod )] w ith Nu cleop h iles.
With the exception of the case discussed above, each of
the complexes of the type [Pd2(µ-Cl)2(η1,η2-C8H12R)2] was
prepared using [PdCl2(cod)] as a precursor (eq 2). The
alkoxy derivatives 1b,c were prepared by reaction with
NaOMe14 or NaOEt in the appropriate alcohol solution,
whereas the malonate complex 1d was generated by
reaction of [PdCl2(cod)] with dimethyl malonate in the
presence of Na2CO3 in ether solution.7 Each complex
was isolated as an air-stable, pale yellow solid. The
aryl-substituted species were prepared by reaction of
[PdCl2(cod)] with the appropriate Grignard reagent in
CH2Cl2 solution or more conveniently in the phenyl case,
by reaction with Ph4Sn. The previously reported 4-tolyl
derivative15 was prepared in good yield using the
diarylmercury reagent. In the case of the mesityl-
substituted complex 1f, the product obtained was the
bromide-bridged derivative, since a bromide-containing
Grignard reagent was employed in the synthesis. In
each case, the product was obtained as a colorless or
pale yellow solid. Complexes 1j,k (R ) NEt2, OAc) were
prepared by literature methods,6,9 by reaction of [PdCl2-
(cod)] with diethylamine or sodium acetate, respectively.
The nitro derivative 1l was prepared by the reaction of
[PdCl(NO2)(CH3CN)2] with 1,5-cyclooctadiene16 and by
treatment of [PdCl2(cod)] with AgNO2 in CH3CN solu-
tion. 1H NMR spectroscopy indicated that the same
product was formed in each case.
reaction was monitored by 1H NMR spectroscopy, a
major new species was observed after 1.5 h, whose NMR
parameters were consistent with a species of the form
[PdCl{C(CO2Me)dMe(CO2Me)}(cod)] (δ(H) 2.37 (s, CH3),
2.4-2.7 (m, CH2), 3.64, 3.78 (s, CO2CH3), 5.50, 6.15 (m,
CHd)), but this converted to the chloride-bridged com-
plex [Pd2(µ-Cl)2{η1,η2-C8H12C(CO2Me)dCMe(CO2Me)}2],
1a , on standing. The final product was characterized
by elemental analysis and by 1H and 13C{1H} NMR
spectroscopy (Tables 5 and 6), including 1H-1H and
13C-1H correlation experiments. Although the observa-
tion of an intermediate of the type [PdClR(cod)] would
suggest that the final product was formed by cis addition
of palladium and the alkenyl group on the coordinated
double bond, we were unable to confirm this because
attempts to grow crystals of the chloride-bridged com-
plex suitable for an X-ray diffraction study were unsuc-
cessful. Conversion to the acetylacetonate derivative
did allow the isolation of X-ray-quality crystals, how-
ever, and the structure of this complex is discussed
below.
As mentioned above, [PdCl(C6F5)(cod)] was shown to
rearrange to [Pd2(µ-Cl)2(η1,η2-C8H12C6F5)2], which was
converted to its hexafluoroacetylacetonate analogue.
The molecular structure of the latter revealed that cis
When the reaction of [PdCl2(cod)] with 2-mesitylmag-
nesium bromide was performed at -78 °C, the solution
turned red immediately; an impure solid was isolated

Ta ble 5. 1H NMR Da ta for th e Com p lexes [P d 2(µ-Cl)2(η1,η2-C8H12R)2], 1a -h a
1a ,
R ) CXdCMeX
(X ) CO2Me)
1b,
R ) OMe
1c,
R ) OEt
1d ,
1e,
R ) Ph
1f,
1g,
1h ,
1i,
b
R ) CH(CO2Me)2
R ) C6H2Me3
R ) Hc
R ) 2-C6H4Me
R ) 4-C6H4Me
H1
H2
3.70
2.05
3.58
3.58
3.53
3.66
3.36
2.62
3.85
1.91
3.98
2.75
3.90
0.40, 1.70 2.25
3.84
3.80
1.87
H3, H3′ 2.05, 2.60
H4, H4′ 1.80, 2.35
1.96 (2)
2.54, 2.67
5.57
1.95 (2)
2.52, 2.65
5.44
1.73, 1.76
2.49, 2.56
5.49
2.19, 2.72
1.98, 2.39
6.07
1.89, 2.89
1.89, 2.37
6.02
1.45 (2)
1.70, 1.92 1.97, 2.35
5.60
5.88
2.07, 2.65
2.15, 2.66
1.96, 2.34
6.02
H5
H6
5.95
6.45
6.05
6.46
5.90
5.86
5.96
6.46
6.75
6.41
H7, H7′ 2.05 (2)
H8, H8′ 1.10, 2.60
2.13, 2.23
1.42, 2.23
2.14, 2.21
1.43, 2.21
2.13, 2.22
1.15, 2.31
2.08 (2)
1.20, 2.62
2.14, 2.26
1.17, 2.66
1.55 (2)
0.60, 2.13 1.14, 2.61
2.13 (2)
2.10 (2)
1.14, 2.55
R
1.90 (CH3), 3.67, 3.24 (OCH3) 3.33, 3.46 (OCH2), 3.35 (CH), 3.69,
7.16 (p-CH), 7.27 (m-CH), 2.20, 2.29, 2.60 (CH3),
7.37 (o-CH) 6.75, 6.81 (CH)
2.28 (CH3), 7.03 (2), 2.28 (CH3), 7.07 (2),
3.77 (OCH3)
1.08 (CH3)
3.70 (OCH3)
7.18, 7.65 (CH)
7.25 (2) (CH)
a
b
Recorded in CDCl3 solution unless stated. Bromide-bridged complex. c Recorded in C6D6 solution.
Ta ble 6. 13C NMR Da ta for th e Com p lexes [P d 2(µ-Cl)2(η1,η2-C8H12R)2], 1a -h a
1a ,
R ) CXdCMeX
(X ) CO2Me)
1b,
R ) OMe
1c,
R ) OEt
1d ,
1e,
R ) Ph
1f,
1g,
1h ,
1i,
R ) CH(CO2Me)2
R ) C6H2Me3c
R ) Hb
R ) 2-C6H4Me
R ) 4-C6H4Me
C1 59.4
C2 48.5
C3 40.0
C4 26.1
C5 103.6
C6 111.2
C7 24.0
C8 43.0
52.2
53.3
53.5
66.6
55.6
44.9
26.6
105.0
111.2
67.5
49.1
40.1
28.4
104.5
114.5
24.4
56.0
35.7
27.0
28.7
100.7
105.2
26.3
40.2
67.0
49.8
44.5
26.9
105.2
111.7
24.4
43.9
66.9
55.2
44.8
26.6
104.9
111.1
81.4
30.9
28.1
101.9
106.4
26.5
34.5
79.9
31.6
28.6
102.1
106.5
26.9
35.1
43.4
29.0
29.7
100.5
105.9
27.1
36.1
24.3
43.2
24.3
43.2
43.2
R
14.7 (CH3),
56.6 (OCH3) 64.6 (OCH2), 54.5 (CH).
125.9 (p-CH),
127.2 (o-CH),
128.5 (m-CH),
146.9 (quat C)
21.0, 22.4, 23.9 (CH3), 14.7 (CH3), 52.2,
20.4 (CH3), 126.0,
127.1, 127.8,
130.2 (CH); 134.0,
145.6 (quat C)
21.4 (CH3),
127.4, 129.5 (CH),
135.8, 144.3 (quat C)
52.2, 52.4 (OCH3),
126.6, 145.1 (CdC),
168.3, 168.9 (CO)
16.1 (CH3)
52.8, 53.0 (OCH3),
168.6, 168.8 (CO)
129.2, 131.4 (CH),
135.3, 135.6, 137.1,
139.5 (quat C)
52.4 (OCH3),
168.3, 168.9 (CO)
a
b
Recorded in CDCl3 solution unless stated. Recorded in C6D6 solution. c Bromide-bridged complex.

1160 Organometallics, Vol. 17, No. 6, 1998
Hoel et al.
after solvent removal at 0 °C and washing of the residue
with water. The 1H NMR spectrum of the solid was
consistent with [PdBr(C6H2Me3-2,4,6)(cod)] (δ(H) 2.20
(s, 3H, 4-CH3), 2.58 (s, 6H, 2-CH3), 2.55-2.79 (m, 8H,
CH2), 5.18 (m, 2H, dCH cis to Br), 6.03 (m, 2H, dCH,
trans to Br), 6.69 (s, 2H, CH)). Attempts to purify this
material, however, always resulted in some rearrange-
ment (10-20%) to 1f. When a solution of [PdBr(C6H2-
Me3)(cod)], generated at low temperature, was allowed
to warm to ambient temperature, the complex converted
cleanly to 1f. The observation of the monomeric inter-
mediate indicates that, in this instance, the reaction
proceeds by initial transfer of the organic group to the
metal, followed by migratory insertion of one of the CdC
double bonds (eq 3). A similar observation was made
2e were grown from hexane solution, and their solid-
state structures were determined by X-ray crystal-
lography.
Molecu la r Str u ctu r es of [P d (a ca c)(η1,η2-C8H12R)]
(R ) C(CO2Me)dCMe(CO2Me), OMe, P h ). The com-
plex [Pd(acac){η1,η2-C8H12C(CO2Me)dCMe(CO2Me)}],
2a , obtained by reaction of [PdClMe(cod)] with DMAD
followed by metathesis with Ag(acac), crystallizes in the
monoclinic space group P21/c, with four molecules per
unit cell. The molecular structure is shown in Figure
1 and shows the approximate square-planar geometry
at palladium. Two cis positions are occupied by the O,O-
bonded acac ligand, and the other positions are occupied
by C1 and the remaining double bond (C5, C6). The
CdC bond lies perpendicular to the coordination plane,
which is typical of palladium(II) complexes. Selected
bond distances and angles are given in Table 2. The
structure reveals that the Pd-Me bond has added in a
cis fashion to the CtC bond of DMAD, and subse-
quently, the palladium and the alkenyl group have
added cis to one of the coordinated double bonds of the
cyclooctadiene.
by Espinet and co-workers, who isolated the monomeric
intermediate in the reaction of [PdCl2(cod)] with C6F5-
Li.12 In that case, they were able to obtain a crystal
structure of the intermediate as well as observe its
conversion to [Pd2(µ-Cl)2(η1,η2-C8H12C6F5)2] on standing
in solution.
The large size of the mesityl group is no doubt
responsible for our being able to observe an intermediate
of the type [PdClR(cod)]. The 2-tolyl complex 1h was
prepared in reasonable yield from [PdCl2(cod)] and
2-tolylmagnesium chloride, but the monomeric inter-
mediate was not detected. In contrast, reactions with
PhMgBr or 4-MeC6H4MgBr led predominantly to reduc-
tive elimination of the diaryl. Reductive elimination
was observed in the reaction of [PdCl2(nbd)] with
PhMgBr,19 and we have found that reactions of [PdCl2-
(dppm)] with aryl Grignard reagents also result in diaryl
formation.20
P r ep a r a tion of th e Com p lexes [P d (a ca c)(η1,η2-
C8H12R)], 2a -f. The chloride-bridged complexes [Pd2-
(µ-Cl)2(η1,η2-C8H12R)2] were of limited solubility in some
cases, and for the more soluble examples, repeated
attempts to obtain crystals suitable for X-ray diffraction
studies were unsuccessful. Thus, several of the com-
plexes (1a -f, R ) C(CO2Me)dCMe(CO2Me), OMe, OEt,
CH(CO2Me)2, Ph, C6H2Me3) were converted to their
corresponding acac derivatives 2a -f by reaction with
silver(I) acetylacetonate (eq 4). The reactions were
performed in CH2Cl2 solution, and the products were
isolated as colorless solids. The acac complexes are
considerably more soluble than their dimeric precursors,
being quite soluble in benzene and hexane as well as in
more polar organic solvents. Crystals of 2a , 2b, and
The C9-C10 distance of 1.338(3) Å indicates that the
triple bond of DMAD has been reduced to a double bond.
The sums of the three bond angles about C9 and C10
are exactly 360°, indicating planarity at these atoms,
as expected for sp2 hybridization. The coordinated CdC
distance (C5-C6) of 1.380(4) Å is slightly longer than
expected for a free double bond, whereas the C1-C2
distance of 1.554(3) Å indicates a reduction in bond
order from two to one. The Pd-O5 distance (2.129(2)
Å) trans to the Pd-C σ-bond is significantly longer than
Pd-O6 (2.046(2) Å), consistent with the relative trans-
influences of σ- and π-bonded carbon ligands.21 The
Pd-C1 distance of 2.024(2) Å is within the expected
range for a Pd-C single bond,22 and the Pd-C5 and
Pd-C6 distances are normal for coordinated double
bonds. The Pd-C1-C2-C9 torsion angle of 121.9°
suggests that cis-addition across the CdC bond has
taken place, but rotation about the C1-C2 bond has
occurred in order to minimize the steric strain caused
by the substituted alkenyl group. This rotation neces-
sitates some distortion of the eight-membered ring, as
may be seen in Figure 1.
The methoxy derivative, 2b, crystallizes in the mono-
clinic space group P21/n, with eight molecules per unit
cell. There are two unique molecules per unit cell, and
the structure of one of the unique molecules is shown
in Figure 2. The molecular structure reveals almost
(19) Segnitz, A.; Kelly, E.; Taylor, S. H.; Maitlis, P. M. J . Organomet.
Chem. 1977, 124, 113.
(20) Stockland, R. A., J r.; Anderson, G. K.; Rath, N. P. Organome-
tallics 1997, 16, 5096.
(21) Appleton, T. G.; Clark, H. C.; Manzer, L. E. Coord. Chem. Rev.
1973, 10, 335.
(22) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1989, S1.

Attack on Cyclooctadiene Complexes of Palladium
Organometallics, Vol. 17, No. 6, 1998 1161
Figu r e 3. Molecular structure of [Pd(acac)(η1,η2-C8H12Ph)],
2e, showing the atom-labeling scheme.
the Pd-C1-C2-O1 torsion angle of 167.1° shows that
the addition occurred in a trans manner. The eight-
membered ring shows little distortion from the shape
it adopts in cyclooctadiene complexes, such as [PdCl2-
(cod)].23
F igu r e 1. Molecular structure of [Pd(acac){η1,η2-C8H12C-
(CO2Me)dCMe(CO2Me}], 2a , showing the atom-labeling
scheme.
The phenyl complex, 2e, crystallizes in the ortho-
rhombic space group Pna21, with four molecules per unit
cell. Again, the molecule adopts approximate square-
planar geometry about palladium (Figure 3). Selected
bond distances and angles are given in Table 4. The
CdC bond distance is 1.35(2) Å, close to what would be
expected for an uncoordinated double bond, suggesting
that there is little π-back-bonding from the metal. The
C1-C2 distance is 1.54(1) Å, similar to that in 2a but
slightly longer than that in 2b. The Pd-O2 distance
trans to the Pd-C σ-bond of 2.125(5) Å is again longer
than the Pd-O1 bond trans to the CdC double bond
(2.054(6) Å). The Pd-C1 distance of 2.018(8) Å is typi-
cal of a Pd-C single bond, and the Pd-C5 and Pd-C6
distances are again slightly shorter than normal. In
this case, the Pd-C1-C2-Ph torsion angle is 114.6°,
similar to that in 2a , suggesting that addition occurred
in a cis fashion, but rotation about the C1-C2 bond
again took place to reduce the steric interactions, result-
ing in distortion of the eight-membered ring (Figure 3).
It may be seen from Figures 1-3 that 2a and 2e exist
as the same diastereomer (C1 and C2 being chiral
centers), whereas the exo isomer has the opposite
stereochemistry. Using the priority schemes Pd > C2
> C8 and C1 > C9 > C3, the structures depicted in
Figures 1 and 3 are each of the (R,R) form. There
should be no regioselectivity associated with addition
across the double bond, and addition of Pd and the R
group to opposite ends of the double bond would yield
the (S,S) form. Since the molecule crystallizes in an
achiral space group, the two forms are, of course,
present. Using the same sequence of substituents for
2b (replacing C9 by O1), the two unique molecules are
observed to be of (R,S) and (S,R) stereochemistry. This
is exactly what should be expected when the substituent
at C2 and the metal have added from the same or the
opposite face of the double bond, respectively.
F igu r e 2. Molecular structure of [Pd(acac)(η1,η2-C8H12
OMe)], 2b, showing the atom-labeling scheme.
-
square-planar geometry about palladium. The acetyl-
acetonate ligand is again O,O-bonded, and the remain-
ing coordination sites contain the Pd-C σ-bond and the
CdC double bond of the chelated cyclooctenyl group, the
latter lying perpendicular to the square plane. Selected
bond distances and angles are presented in Table 3. The
CdC bond distance (1.38(2) Å) is again slightly longer
than expected for a free double bond, whereas the C1-
C2 distance is lengthened to 1.50(1) Å, indicating a
single bond. The Pd-O3 distance trans to the Pd-C
σ-bond (2.113(7) Å) is again longer than that opposite
the coordinated double bond (2.042(7) Å). The Pd-C1
distance of 2.015(11) Å is within the expected range for
a Pd-C single bond, and the Pd-C5 and Pd-C6
distances are slightly shorter than normal. The struc-
ture reveals that the palladium and the methoxy group
have added across one of the CdC double bonds, and
(23) Benchekroun, L.; Herpin, P.; J ulia, M.; Saussine, L. J . Orga-
nomet. Chem. 1977, 128, 275.

1162 Organometallics, Vol. 17, No. 6, 1998
Ta ble 7. 1H NMR Da ta for th e Com p lexes [P d (a ca c)(η1,η2-C8H12R)], 2a -fa
Hoel et al.
2a ,
R ) CXdCMeX
(X ) CO2Me)
2b,
R ) OMe
2c,
R ) OEt
2d ,
2e,
R ) Ph
2f,
R ) C6H2Me3
R ) CH(CO2Me)2
H1
H2
3.17
2.09
3.18
3.63
3.18
3.75
2.90
2.65
3.33
1.98
3.29
2.70
H3, H3′
H4, H4′
H5
1.96, 2.56
1.82, 2.31
5.62
1.94 (2)
2.59 (2)
5.21
1.92 (2)
2.60 (2)
5.28
1.72, 1.78
2.54 (2)
5.25
2.17, 2.47
1.98, 2.29
5.75
1.80, 2.83
1.88, 2.34
5.66
H6
6.18
5.67
5.71
5.74
6.18
6.29
H7, H7′
H8, H8′
R
2.02, 2.09
1.21, 2.47
2.15, 2.24
1.52, 2.15
2.25 (2)
1.54, 2.18
2.16, 2.23
1.28, 2.23
2.11 (2)
1.27, 2.47
2.14 (2)
1.25, 2.48
1.95 (CH3), 3.70, 3.27 (OCH3) 3.37, 3.58 (OCH2), 3.45 (CH), 3.70,
3.73 (OCH3) 1.18 (CH3) 3.73 (OCH3)
5.28 5.24
1.86, 1.99 1.81, 1.95
7.15 (p-CH), 7.26 (m-CH), 2.20, 2.31, 2.48 (CH3),
7.39 (o-CH) 6.76, 6.81 (CH)
5.28 5.26
1.92, 2.04 1.88, 1.94
acac CH 5.23
acac CH3 1.85, 1.96
5.24
1.84, 1.97
a
Recorded in CDCl3 solution unless stated.
Ta ble 8. 13C NMR Da ta for th e Com p lexes [P d (a ca c)(η1,η2-C8H12R)], 2a -fa
2a ,
R ) CXdCMeX
(X ) CO2Me)
2b,
R ) OMe
2c,
R ) OEt
2d ,
2e,
R ) Ph
2f,
R ) C6H2Me3
R ) CH(CO2Me)2
C1
C2
C3
C4
C5
C6
C7
C8
R
54.5
49.0
39.5
26.2
97.5
106.3
25.1
42.3
45.5
46.3
47.7
44.2
29.3
29.8
95.0
99.9
27.9
34.3
60.2
55.4
45.1
26.3
99.5
105.4
25.6
42.2
126.0 (p-CH),
127.9 (o-CH),
128.7 (m-CH),
137.9 (quat C)
28.7, 29.4
100.2
60.2
48.7
40.0
27.7
97.7
106.7
24.8
42.5
82.6
30.9
28.1
96.0
100.3
27.2
32.5
81.3
31.6
28.7
96.4
101.0
27.7
33.1
15.3 (CH3),
52.4, 52.5 (OCH3),
127.3, 146.6 (CdC),
169.0, 170.0 (CO)
56.1 (OCH3) 64.1 (OCH2),
16.3 (CH3)
54.9 (CH), 52.8,
52.9 (OCH3),
169.0, 169.3 (CO)
21.0, 22.5, 22.0 (CH3),
129.0, 131.3 (CH),
135.1, 135.2, 137.3,
140.8 (quat C)
27.8, 28.7
acac CH3 28.2, 28.9
acac CH
acac CO
27.8, 28.2
99.5
186.2, 188.7 186.9, 189.4
28.5, 29.2
100.4
28.2, 28.9
99.8
186.7, 189.2
99.7
186.5, 189.0
99.8
185.9, 189.1
186.8, 189.9
a
Recorded in CDCl3 solution unless stated.
NMR Stu d ies of [P d 2(µ-Cl)2(η1,η2-C8H12R)2], 1a -
l, a n d [P d (η1,η2-C8H12R)(a ca c)], 2a -f. These com-
plexes have been characterized by 1H and 13C{1H} NMR
spectroscopy, and in a number of cases, complete as-
signments have been made using a combination of 1H-
1H and 13C-1H correlation methods. Complete listings
of 1H and 13C NMR parameters for the chloride-bridged
complexes 1a -i are presented in Tables 5 and 6, and
those for the acetylacetonate species 2a -f are collected
in Tables 7 and 8.
The 1H NMR spectra of the chloride-bridged com-
plexes 1a -i each exhibit two well-defined resonances
for the olefinic hydrogens H5 and H6, that for H6 always
lying at higher frequency. (The numbering scheme is
that shown in Figures 1-3.) The signal due to H1, R to
palladium, is shifted to high frequency and lies in the
range 3.3-4.0 ppm, whereas the position of the H2
resonance depends on the nature of the substituent on
C2. The other ring hydrogens give rise to a series of
multiplets in the range 1.7-2.9 ppm, with the exception
of the resonance associated with one of the hydrogens
attached to C8, which appears as a doublet of doublets
to lower frequency of the others. In the case of the
unsubstituted cyclooctenyl complex 1g (R ) H), one
hydrogen on each of the â-carbons C2 and C8 produces
a particularly low-frequency resonance (vide infra). All
of the signals are shifted to low frequency in aromatic
solvents compared to their positions in CDCl3 solution.
Signals due to the â-substituents appear as expected
in 1a -e. In 1f, there are three methyl signals (2.20,
2.29, and 2.60 ppm) and two aromatic CH signals due
to the mesityl group, indicating that there is restricted
rotation about the C2-C6H2Me3 bond at ambient tem-
perature. This is perhaps unsurprising, owing to the
large size of the mesityl moiety. When a toluene
solution of 1f was heated to 360 K, the methyl signals
at 2.29 and 2.60 ppm broadened considerably (indicating
that slow exchange was occurring) whereas the lowest
frequency resonance remained sharp. The signal at 2.20
ppm is due to the CH3 group in the 4-position, and
therefore, the other two signals are due to the 2-methyl
groups. These are separated by 0.3 ppm, suggesting
that the groups occupy quite different environments in
the static structure.
1
The H NMR spectra of the acetylacetonate deriva-
tives 2a -f are qualitatively similar but contain ad-
ditional signals due to the acac ligand. In each case,
the CH resonance appears as a sharp singlet around
5.25 ppm whereas the methyls are nonequivalent and
produce two broad singlets in the range 1.8-2.05 ppm.
The signal due to H1 is shifted to lower frequency by
0.4-0.7 ppm when the bridging chlorides are replaced
by the acac ligand, and the H5 and H6 resonances are
also more shielded by 0.2-0.4 ppm, whereas the signals
due to the other ring hydrogens are largely unaffected.
Thus, only the hydrogens closest to the site of coordina-
tion are affected, and the shifts to lower frequency
suggest there is greater electron density associated with
the palladium center in the acac complexes. Again,
there is restricted rotation of the mesityl group in 2f.

Attack on Cyclooctadiene Complexes of Palladium
Organometallics, Vol. 17, No. 6, 1998 1163
Ta ble 9. Cou p lin gs to H1 in th e 1H NMR Sp ectr a
The 13C{1H} NMR spectra of 1a -i each exhibit the
expected number of signals, and these have been as-
signed from their 13C-1H correlated spectra. Each
complex gives rise to two olefinic signals due to C5 and
C6 between 100 and 115 ppm, the resonance for C6
always exhibiting the higher frequency of the two. The
resonance due to C1 appears at quite high frequency
(52-67 ppm), paralleling the observations for H1 in the
1H spectra, and again illustrating the deshielding
nature of the palladium center. The location of the
signal due to C2 depends on the nature of the substitu-
ent at C2, and the resonances due to the ring methylene
carbons lie in the range 24-45 ppm. The expected
signals are observed for the R substituents; three methyl
and six aromatic resonances are detected for the mesityl
group, again indicating that it is not free to rotate about
the C2-C6H2Me3 bond.
of 1a -l a n d 2a -fa
complex 1
complex 2
a , R ) C(CO2Me)dC(CO2Me)Me
b, R ) OMe
b
4.4, 4.4
6.6, 3.7
7.1, 3.4, 1.8
6.6, 2.2, 2.2
4.0, 4.0
5.7, 3.3, 1.7c
broad
c, R ) OEt
d , R ) CH(CO2Me)2
e, R ) Ph
d
4.1, 4.1
broad
f, R ) C6H2Me3
h , R ) C6H4Me-2
i, R ) C6H4Me-4
j, R ) NEt2
k , R ) OAc
l, R ) NO2
4.8, 4.8
4.1, 4.1e
4.1, 4.1
11.5, 4.1, 4.1
7.0, 3.5
5.6, 3.4
a
Recorded in CDCl3 solution unless stated. Coupling constants
are in hertz. The FID was resolution-enhanced using a Gaussian
b
weighting function in each case. Obscured by OCH3 resonance.
d
c In C6D6 solution. Obscured by malonate CH resonance. e In
toluene-d8 solution.
A comparison of the 13C{1H} NMR spectra for 1a -f
and the acetylacetonate complexes 2a -f reveals a trend
similar to that found in the 1H NMR spectra. The
signals due to C1 are shifted by about 7 ppm to lower
frequency in the acac complexes, and analogous shifts
are observed for the resonances due to C5 and C6. The
signals due to C2-C4, C7, and C8 show much smaller
variations, again suggesting that the palladium center
affords greater shielding of the coordinated carbon
atoms in the acac derivatives. The expected number of
signals are observed for the R groups, and the acac
ligands also produce the expected five resonances. In
each case, the central carbon gives rise to a peak at ca.
100 ppm, the two carbonyl signals are detected in the
range 186-190 ppm, and the two methyl carbon signals
appear around 28 ppm.
these complexes and their chloride-bridged precursors.
A consideration of the signals due to H1 should be
informative, where we would expect to see couplings to
H2, H8, and H8′. In the solid-state structure of 2b, the
dihedral angles between H1 and these three hydrogens
are 67.5, 35.4, and 81.0°, respectively. If a conformation
similar to this is maintained in solution, the Garbisch
equations24 suggest that one larger and two smaller
couplings should be observed. In contrast, the struc-
tures of 2a and 2e provide H1-C-C-H dihedral angles
of 116.5°, 68.8°, and 50.1°, and 111.5°, 71.3°, and 47.0°,
respectively, which should lead to three couplings of
comparable size. It may be that there is some distortion
of the structures in solution, but we observe only two
nonnegligible H-H couplings for H1; 2b exhibits a
doublet of doublets with couplings of 6.6 and 3.7 Hz,
whereas for 2a and 2e, apparent triplets are observed
When a CDCl3 solution of 1a was cooled, the olefinic
signals in the 1H NMR spectrum broadened and, on
further cooling to 220 K, split into six resonances.
Throughout this process the other signals remained
relatively sharp, although splitting of the methyl signals
also occurred. The 13C{1H} NMR spectrum at 220 K
also exhibited six olefinic resonances, in addition to
those associated with the C(CO2Me)dCMe(CO2Me)
3
with J HH ) 4.4 and 4.0 Hz, respectively. In the
chloride-bridged complex 1b, the signals due to H1 and
H2 overlap in CDCl3 solution but in C6D6 the resonances
are separated and the H1 resonance appears as a
3
doublet of doublets of doublets with J HH values of 5.7,
3.3, and 1.7 Hz. The H1 signal for 1e appears as an
apparent triplet with a coupling of 4.1 Hz. Thus, it
appears that, qualitatively at least, we may be able to
differentiate between the products of exo and endo
attack on the basis of the appearance of their H1 signals.
A listing of the couplings to H1 in each of the complexes
is given in Table 9. It may be seen that the aryl-
substituted complexes 1e,f, 1h ,i, and 2e,f, as well as
1a and 2a , each produce apparent triplets for H1, with
couplings of 4-5 Hz, whereas all of the other compounds
show one larger coupling (6-7 Hz) and one or two
smaller ones (Figure 4). This would indicate that the
aryl- or alkenyl-substituted compounds are formed by
endo attack of the organic group on the coordinated
cyclooctadiene, whereas the others are produced by
external attack on the CdC bond. The pentafluorophen-
yl-substituted complex [Pd2(µ-Cl)2(η1,η2-C8H12C6F5)2]
exhibits two couplings of 3.6 Hz for H1.12
moiety.
A
1H-1H EXSY spectrum for 1a at 235 K
showed cross-peaks for three pairs of olefinic resonances
but no off-diagonal peaks relating the olefinic signals
to those in other parts of the spectrum. This suggests
that the fluxional process involves no change of the
cyclooctenyl group itself but may involve rearrangement
between dimers of cis or trans geometry and between
species with the R groups syn or anti with respect to
the Pd2Cl2 plane. Such interconversions may occur
associatively or dissociatively via a three-coordinate
[PdCl(η1,η2-C8H12R)] intermediate. The fact that the
acac derivative 2a does not exhibit this behavior sup-
ports such an interpretation. Similar variable-temper-
ature NMR phenomena were observed for the other
chloride-bridged complexes of type 1.
A key question which prompted this study was
whether it would be possible to use NMR spectroscopy
to distinguish between the products of exo and endo
addition of the R group to the coordinated cyclooctadi-
ene. Having shown, unequivocally, by X-ray crystal-
lography that the methoxy derivative 2b exhibits exo
geometry, whereas 2a and 2e have endo configurations,
we should begin with a comparison of the spectra of
With these assignments in mind, we note the follow-
1
ing additional differences between the H and 13C NMR
resonances of the exo and endo isomers. The H1
resonances for the endo complexes appear at higher
(24) Garbisch, E. W., J r. J . Am. Chem. Soc. 1964, 86, 5561.

1164 Organometallics, Vol. 17, No. 6, 1998
Hoel et al.
F igu r e 4. H1 resonances for (a) [Pd2(µ-Cl)2(η1,η2-C8H12OMe)2)], 1b, in C6D6, and (b) [Pd2(µ-Cl)2 (η1,η2-C8H12C6H4Me-4)2],
1i, in CDCl3 solution.
Sch em e 1
frequency (3.70-3.98 ppm for 1) than their exo ana-
logues (δ(H) 3.36-3.58). The olefinic signals are also
shifted to higher frequencies in the endo species, as are
the signals due to H3 and H3′ and one of the hydrogens
attached to C8. In contrast, the signals due to both H4
and H4′ appear at high frequency (2.49-2.67 ppm) in
the exo derivatives, whereas one of them is consistently
found at lower frequencies (1.80-1.98 ppm) in the endo
complexes. Similar observations can be made for the
acac complexes 2a -f. Analogously, in their 13C NMR
spectra, the signals due to C1 are found at higher
frequencies (59.4-67.0 ppm) for the endo complexes
compared to their exo counterparts (δ(C) 52.2-53.5).
The olefinic carbon signals are also shifted to high
frequency in the endo derivatives, and the signals due
to C3 and C8 are also noticeably deshielded. Again,
parallels are found among the acac derivatives 2a -f.
Thus, it appears that there are a number of NMR
parameters which may be used together to differentiate
between the cyclooctenyl complexes that are formed by
endo or exo attack on [PdCl2(cod)] or related precursors.
Finally, we also observe that for the two endo isomers
characterized crystallographically, H8 appears at par-
ticularly low frequency in the 1H NMR spectrum
whereas H8′ and H3′ give rise to the highest frequency
signals observed for the methylene hydrogens. From
the solid-state structures, we find that these last two
exhibit the shortest nonbonded distances to palladium
(2.81-2.99 Å), and this may be responsible for the
deshielding of these hydrogens. In contrast, H8 is
directed away from the metal, and this hydrogen ap-
parently exhibits the greatest shielding. In the case of
the exo isomer 2b, however, H8′ and H3′ are not
deshielded significantly and the shortest nonbonded
distance is 3.15 Å. Again, H8, which is the most
shielded hydrogen, is directed away from palladium.
Mech an ism of Attack on th e Coor din ated Dou ble
Bon d . It is reasonable to expect that when nucleophilic
attack occurs directly at one of the double bond carbons,
the exo product would be formed, whereas if the nu-
cleophile reacts first at the metal center, the endo
complex would be formed upon migratory insertion of
the CdC bond (Scheme 1). The oxygen and nitrogen
nucleophiles, as well as the malonate anion, therefore,
react directly with the coordinated double bond, as has
been supposed. It is interesting to note that the exo
product is formed in the case of 1l, either by reaction of
[PdCl2(cod)] with AgNO2 or when [PdCl(NO2)(MeCN)2]
(containing a metal-bound NO2 group) is allowed to
react with free cyclooctadiene. In the latter case,
When organometallic reagents are employed (Grig-
nards, Ph4Sn, (4-MeC6H4)2Hg, or C6F5Li12), substitution
of one of the coordinated chlorides occurs first to
generate a species of the form [PdClR(cod)]. When R )
C6H2Me3 or C6F5,12 this species may be isolated, al-
though migratory insertion occurs on standing. With
PhMgBr or 4-MeC6H4MgBr, the organopalladium in-
termediate may react by migratory insertion but sub-
stitution of the second chloride to produce [PdAr2(cod)]
and subsequent reductive elimination of the diaryl is a
competing process, even when low Grignard-to-Pd ratios
are used. We have not detected the diarylpalladium
intermediates in this case, but in the corresponding
reactions of [PdCl2(dppm)] with ArMgX, we have ob-
served [PdAr2(dppm)] by NMR spectroscopy at low
temperatures.20 With 2-tolylmagnesium chloride, the
intermediate [PdCl(C6H4Me-2)(cod)] could not be iso-
lated, but migratory insertion occurred to give the
cyclooctenyl derivative in a modest yield. Thus, it
appears that the larger aryls, 2-tolyl and mesityl, as well
as those containing electron-withdrawing groups (C6F5)
inhibit attack of a second equivalent of Grignard and
allow greater yields of the cyclooctenyl derivatives to
be achieved. Organotin or -mercury reagents such as
Ph4Sn or (4-MeC6H4)2Hg, being less reactive, allow the
cyclooctenyl complexes to be formed more cleanly. With
tetraalkyltin reagents (R ) Me, Et, CH2Ph), however,
the [PdClR(cod)] compounds do not undergo migratory
insertion.1-3
It is curious to find that the reaction of [PdClMe(cod)]
with DMAD proceeds cleanly by alkyne insertion, fol-
lowed by migratory insertion of a CdC bond of cyclooc-
tadiene. Analogous reactions with HCtCCO2Me or
PhCtCH were slow and gave complex mixtures of
products. We have noted previously that [PdClMe(cod)]
reacts with CO to generate the corresponding acetyl
complex,1 but despite the tendency of acylpalladium
-
displacement of NO2 by cyclooctadiene must occur,
allowing external attack on the coordinated diene.

Attack on Cyclooctadiene Complexes of Palladium
Organometallics, Vol. 17, No. 6, 1998 1165
species to undergo migratory insertion of alkenes,25
insertion into the Pd-acetyl bond was not observed.
[PdCl(COMe)(cod)] does decompose above 0 °C, however,
so it may be that the relatively rapid decomposition
precludes observation of any insertion. Thus, we find
the following relative rates of migratory insertion in
and CHE-9530085) for support of this work, to J ohnson
Matthey Aesar/Alfa for a generous loan of palladium
salts, and to the National Science Foundation (Grant
Nos. CHE-9318696 and 9309690), the U.S. Department
of Energy (Grant No. DE-FG02-92CH10499), and the
University of Missouri Research Board for instrumenta-
tion grants.
complexes of the type [PdClR(cod)]: Ph, 4-MeC6H4
>
2-MeC6H4 > 2,4,6-Me3C6H2 > C(CO2Me)dC(CO2Me)-
Me . Me, Et, CH2Ph (COMe). The decreasing reactiv-
ity of the aryl groups is presumably a reflection of their
increasing size, whereas the lack of reactivity of the
alkyl groups may be due to the strength of the Pd-
C(sp3) bond.
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data and structure refinement, atomic coordinates and equiva-
lent isotropic displacement parameters, complete bond lengths
and angles, anisotropic displacement parameters, and hydro-
gen coordinates and isotropic displacement parameters for 2a ,
2b, and 2e (16 pages). Ordering information is given on any
current masthead page.
Ack n ow led gm en t. Thanks are expressed to the
National Science Foundation (Grant Nos. CHE-9508228
(25) Drent, E.; Budzelaar, P. H. M. Chem. Rev. 1996, 96, 663.
OM970836J