Synthesis of a novel α-diimine palladium(II) complex bearing an η3-allyl γ-lactone ligand, a key intermediate in alkyne cyclocarbonylation processes

Article abstract of DOI:10.1021/om030368f

Reactivity of [Pd(CH₃)(CO)(PrⁱDAB)]⁺[B{3,5- (CF₃)₂C₆H₃}₄] ^- (1), where PrⁱDAB = 1,4-diisopropyl-1,4-diaza-1,3-butadiene, toward alkynes and carbon monoxide was investigated. While the reaction of 1 with phenylacetylene produced stereoregular homopolymer, a stoichiometric insertion of 1-phenyl-1-propyne and 2-butyne into the Pd-acyl bond yielded the palladacycles 2 and 3; subsequent reaction with CO resulted in the formation of novel complexes 4 and 5, which represent the first experimental evidence of a key intermediate in alkyne cyclocarbonylation processes.

Full text of DOI:10.1021/om030368f

Organometallics 2003, 22, 3967-3970
3967
Syn th esis of a Novel r-Diim in e P a lla d iu m (II) Com p lex
Bea r in g a n η3-Allyl γ-La cton e Liga n d , a Key In ter m ed ia te
in Alk yn e Cycloca r bon yla tion P r ocesses
Carla Carfagna,*,† Giuseppe Gatti,† Luca Mosca,† Paola Paoli,‡ and
Annalisa Guerri‡
Istituto di Scienze Chimiche, Universita` degli Studi di Urbino, Piazza Rinascimento 6,
61029 Urbino, Italy, and Dipartimento di Energetica, Universita` degli Studi di Firenze,
Via S. Marta 3, 50139, Firenze, Italy
Received May 19, 2003
Summary: Reactivity of [Pd(CH3)(CO)(PriDAB)]+[B{3,5-
(CF3)2C6H3}4]- (1), where PriDAB ) 1,4-diisopropyl-1,4-
diaza-1,3-butadiene, toward alkynes and carbon mon-
oxide was investigated. While the reaction of 1 with
phenylacetylene produced stereoregular homopolymer, a
stoichiometric insertion of 1-phenyl-1-propyne and 2-bu-
tyne into the Pd-acyl bond yielded the palladacycles 2
and 3; subsequent reaction with CO resulted in the
formation of novel complexes 4 and 5, which represent
the first experimental evidence of a key intermediate in
alkyne cyclocarbonylation processes.
a similar approach, an investigation of the reactivity of
complex [Pd(CH3)(CO)(PriDAB)]+[B{3,5-(CF3)2C6H3}4]-
(1), where PriDAB ) 1,4-diisopropyl-1,4-diaza-1,3-buta-
diene, toward alkynes and CO was carried out.
In studying phenylacetylene insertion in complex 1,
highly stereoregular polyphenylacetylene (PPA) with
cis-transoidal structure was obtained. Due to the high
reactivity of this alkyne, it was not possible to isolate
the first intermediates because the reaction evolves
rapidly. Indeed, the addition of an equimolecular amount
of phenylacetylene to a CD2Cl2 solution of 1, even at
very low temperature (-80 °C), resulted in the forma-
tion of oligomers; homopolymer in moderate yield with
a molecular weight of 54 000 was obtained using an
alkyne/Pd molar ratio of 80:1 (Scheme 1). Attempts to
synthesize phenylacetylene/CO copolymer, in operating
conditions analogous to that previously reported for
styrene/CO polymerization,7a,b gave no results.
The insertion of alkynes into the palladium-carbon
bond represents an important reaction involved in the
synthesis of organic molecules as well as in polymeri-
zation processes.1 Cationic Pd(II) complexes have been
employed in the homopolymerization of acetylenes,2
even if more reactive catalytic systems are based on
tungsten, molybdenum, and rhodium.3 With regard to
the alternating copolymerization of alkynes and carbon
monoxide, only a few examples exist in the literature.4
Moreover, reactions of acetylenes with CO by the
catalysis of palladium(II) complexes have been estab-
lished as a powerful methodology for the synthesis of
linear and cyclic carbonyl compounds1a such as esters
and lactones.5 Although the above cited reactions pro-
duce a wide variety of interesting molecules, there is
little mechanistic information concerning the details of
such processes.6
Recently we developed catalytic systems based on
Pd(II) complexes with bidentate nitrogen ligands for the
stereospecific styrene/CO copolymerization.7 To gain
further information on the chain growth mechanism, we
studied stepwise insertion of the comonomers in the
catalysts [Pd(CH3)(CO)(N-N)]+[B{3,5-(CF3)2C6H3}4]-
with N-N ) R-diimine7b,c or bioxazoline ligand.7a Using
Isolation of organopalladium complexes deriving from
the stoichiometric insertion of alkynes in the Pd-acyl
(5) For synthesis of esters, see: (a) Sakurai, Y.; Sakaguchi, S.; Ishii,
Y. Tetrahedron Lett. 1999, 10, 1701. (b) Gabriele, B.; Costa, M.; Salerno,
G.; Chiusoli, G. P. J . Chem. Soc., Perkin Trans. 1 1994, 83. (c) Drent,
E.; Arnoldy, P.; Budzelaar, P. H. M. J . Organomet. Chem. 1993, 455,
247. (d) Alper H.; Despreyroux, B.; Woell, J . B Tetrahedron Lett. 1983,
24, 5691. (e) Tsuji, J .; Takahashi, M.; Takahashi, T. Tetrahedron Lett.
1980, 21, 849. (f) Heck, R. F. J . Am. Chem. Soc. 1972, 94, 2712. For
synthesis of lactones, see: (g) El Ali, B.; Alper, H. Synlett 2000, 2,
161. (h) Gabriele, B.; Salerno, G.; Costa, M.; Chiusoli, G. P. Chem.
Commun. 1999, 1381. (i) Gabriele, B.; Salerno, G.; Costa, M.; Chiusoli,
G. P. Tetrahedron Lett. 1999, 40, 989. (j) Coperet, C.; Sugihara, T.;
Wu, G.; Shimoyama, I.; Negishi, E. J . Am. Chem. Soc. 1995, 117, 3422.
(k) Gabriele, B.; Salerno, G.; Costa, M.; Chiusoli, G. P. J . Organomet.
Chem. 1995, 503, 21. (l) Sugihara, T.; Cope´ret, C.; Owczarczyk, Z.;
Harring, L. S.; Negishi, E. J . Am. Chem. Soc. 1994, 116, 7923. (m)
Huang, Y.; Alper H. J . Org. Chem. 1991, 56, 4534. (n) Tsuji, J .; Nogi,
T. J . Am. Chem. Soc. 1966, 88, 1289.
(6) For examples of alkyne insertions into the Pd-acyl bond, see:
(a) Reddy, K. R.; Surekha, K.; Lee, G. H.; Peng, S. M.; Liu, S. T.
Organometallics 2001, 20, 5557. (b) Reddy, K. R.; Chen, C. L.; Liu, Y.
H.; Peng, S. M.; Chen, J . T.; Liu, S. T. Organometallics 1999, 18, 2574.
(c) Samsel, E. G.; Norton, J . R. J . Am. Chem. Soc. 1984, 106, 5505.
For alkyne insertions into the Pd-alkyl bond, see: (d) LaPointe, A.
M.; Brookhart, M. Organometallics 1998, 17, 1530. For alkyne inser-
tions into the Pd-aryl bond, see: (e) Yagyu, T.; Hamada, M.; Osakada,
K.; Yamamoto, T. Organometallics 2001, 20, 1087. (f) Yagyu, T.;
Osakada, K.; Brookhart, M. Organometallics 2000, 19, 2125. (g)
Vicente, J .; Saura-Llamas, I.; Turpin, J .; Ramirez de Arellano, M. C.;
J ones, P. G. Organometallics 1999, 18, 2683. (h) Vicente, J .; Abad, J .
A.; Fernandez-de-Bobadilla, R.; J ones, P. G.; Ramirez de Arellano, M.
C. Organometallics 1996, 15, 24.
* Corresponding author. Fax: +3907222754. E-mail: schim@
uniurb.it.
† Universita` degli Studi di Urbino.
‡ Universita` degli Studi di Firenze.
(1) (a) Negishi E.; de Meijere A. Handbook of Organopalladium
Chemistry for Organic Synthesis; Wiley: New York, 2002. (b) Collman,
J . P.; Hegedus, L. S.; Norton, J . R.; Finke R. G. Principles and
Applications of Organotransition Metal Complexes; University Science
Books: Mill Valley, 1987.
(2) (a) Drent, E.; Pello, D. H. L. Eur. Pat. Appl. EP 576091, 1993.
(b) Sen, A.; Lai, T. W. Organometallics 1982, 1, 415.
(3) Falcon, M.; Farnetti, E.; Marsich N. J . Organomet. Chem. 2001,
629, 187, and references therein.
(7) (a) Binotti, B.; Carfagna, C.; Gatti G.; Martini D.; Mosca, L.;
Pettinari C. Organometallics 2003, 22, 1115. (b) Carfagna, C.; Gatti
G.; Martini D.; Pettinari C. Organometallics 2001, 20, 2175. (c)
Carfagna, C.; Formica, M.; Gatti, G.; Musco, A.; Pierleoni A. J . Chem.
Soc., Chem. Commun. 1998, 1113. (d) Bartolini, S.; Carfagna, C.;
Musco, A. Macromol. Rapid Commun. 1995, 16, 9.
(4) (a) Liaw, D. J .; Lay, B. F. J . Mol. Catal. 1997, 115, 107. (b) Drent,
E.; Pello D. H. L. Eur. Pat. Appl. EP 731126, 1996. (c) Chien, J . C. W.;
Babu, G. N. Macromolecules 1985, 18, 622.
10.1021/om030368f CCC: $25.00 © 2003 American Chemical Society
Publication on Web 07/31/2003

3968 Organometallics, Vol. 22, No. 19, 2003
Notes
Sch em e 1
Sch em e 2
F igu r e 1. ORTEP view of the complex cation of 4. All
atoms are drawn at 50% probability except for hydrogens,
which have been assigned arbitrary thermal parameters.
Selected bond lengths (Å) and angles (deg): Pd(1)-N(1) )
2.132(5), Pd(1)-N(2) ) 2.107(5), Pd(1)-C(9) ) 2.199(6),
Pd(1)-C(10) ) 2.152(6), Pd(1)-C(11) ) 2.171(6); N(1)-
Pd(1)-N(2) ) 78.6(2), N(1)-Pd(1)-C(9) ) 167.0(2), N(1)-
Pd(1)-C(10) ) 141.2(2), N(1)-Pd(1)-C(11) ) 109.8(2),
N(2)-Pd(1)-C(9)
)
110.5(2), N(2)-Pd(1)-C(10)
)
132.4(2), N(2)-Pd(1)-C(11) ) 170.8(2), C(9)-Pd(1)-C(10)
) 37.6(2), C(9)-Pd(1)-C(11) ) 61.9(2), C(10)-Pd(1)-C(11)
) 38.4(2).
bond was achieved by using 1,2-substituted acetylenes.
Thus, the reaction of 1-phenyl-1-propyne or 2-butyne
with a dichloromethane solution of 1 gave the corre-
sponding five-membered palladacycle 2 or 3 (Scheme 2),
which were isolated as yellow powders.
carbonyl region and three signals in the range from 71
to 122 ppm. The carbonyl resonance at around 165 ppm
and the IR stretching band for the CdO at around 1790
cm-1 are compatible with a γ-lactone species. The
remaining three resonances were ascribed to the Pd-
coordinated η3-allyl fragment of the heterocycle. Evi-
dently, the formation of 4 and 5 takes place through
the insertion of CO in the palladium vinyl bond of 2 and
3, followed by a cyclization reaction. A similar cyclocar-
bonylation process was observed in the synthesis of a
molybdenum complex containing an η3-allyl butyro-
lactone ligand.10 The structure proposed for complex 4
is in agreement with the NOEs detected between one
isopropyl CH of the nitrogen ligand and the MeA and
between the other isopropyl CH and the ortho protons
of the phenyl ring. Complexes 4 and 5 resulted in being
very stable in the solid state as well as in dichloro-
methane solution.
The structure of complex 4 was confirmed by X-ray
diffraction11 (Figure 1). The palladium ion is coordinated
to the γ-lactone moiety in η3-fashion and to the nitrogen
atoms of the PriDAB ligand in a distorted square-planar
arrangement, assuming that C(9) and C(11) are two of
the four donors. The average Pd-C separation (2.17 Å)
is a little larger than those found in Pd η3-coordinated
complexes, with nitrogen atoms in trans positions
provided by a NCCN moiety (average 2.12 Å).12 The
Pd(II) ion is 1.95 Å out of the mean plane described by
the γ-lactone ring, the latter forming an angle of
82.9(3)° with the NdC-CdN mean plane. The C-C
bond distances in the η3-allyl system are comparable
(within 3σ, average 1.41 Å) and the ring of the phenyl
Spectroscopic data of these compounds reveal a
structure similar to that recently reported for insertion
products of alkynes in a Pd(II) complex bearing a
phosphine-imine ligand.6a In the 13C NMR spectra of
both 2 and 3 the signal due to one of the two olefin
carbons appears at high frequency, more than 190 ppm;
in addition, in the IR spectrum, the CdO stretching
band is observed at around 1570 cm-1, a value lower
than those reported for analogous styrene insertion
products.7a,b,8 These two pieces of evidence could be
ascribed to the charge distribution in the conjugated
carbonyl system so that the olefin carbon in R-position
to palladium is considerably deshielded and CdO has
a partial character of single bond. Another feature of
1
the H NMR spectrum of 2 is the extremely different
chemical shift of the two isopropyl CH (2.11 and 3.93
ppm). Such a difference was not observed for the two
CH signals (3.92 and 4.19 ppm) of compound 3. One can
assume that, in complex 2, the proton at 2.11 ppm lies
in the shielding region of the phenyl, due to the
preferred orientation of the aromatic ring, nearly per-
pendicular to the Pd coordination plane.
It has been reported that the palladacycle complexes,
isolated as intermediates in styrene/CO copolymeriza-
tion, readily react with carbon monoxide to yield open
chain products.7a,b,9 To check this kind of reactivity with
analogous complexes deriving from alkyne insertions,
2 and 3 were dissolved at -30 °C in dichloromethane
previously saturated with CO. The resulting products
were isolated as dark yellow powders and were identi-
fied as the novel compounds 4 and 5 (Scheme 2). The
13C spectra show in both cases just one signal in the
(10) Yang, G. M.; Lee, G. H.; Peng, S. M.; Liu, R. S. J . Chem. Soc.,
Chem. Commun. 1991, 478.
(11) Crystals suitable for X-ray diffraction were obtained by slow
diffusion of hexane into a dichloromethane solution of 4.
(12) Allen, F. H.; Kennard, O. Cambridge Structural Database
version 5.24 November 2002, J . Chem. Soc., Perkin Trans. 2 1989,
1131.
(8) Reddy, K. R.; Surekha, K.; Lee, G. H.; Peng, S. M.; Chen, J . T.;
Liu, S. T. Organometallics 2001, 20, 1292
(9) Brookhart, M.; Rix, F. C.; DeSimone, J . M.; Barborak, J . C. J .
Am. Chem. Soc. 1992, 114, 5894.

Notes
Organometallics, Vol. 22, No. 19, 2003 3969
acetylene, 1-phenyl-1-propyne, and 2-butyne were used after
distillation over calcium hydride. Carbon monoxide (Cp grade
99.99%) was supplied by Air Liquide. Elemental analyses (C,
H, N) were carried out with a Fisons Instruments 1108
CHNS-O elemental analyzer. Infrared spectra were measured
in the range 4000-600 cm-1 on a Nicolet FT-IR Avatar 360
spectrometer. NMR spectra were measured on a Bruker AC200
spectrometer with a multinuclear 5 mm probehead. 1H and
13C NMR chemical shifts are relative to TMS and were
measured using the residual proton or carbon resonance of the
deuterated solvents. NOE measurements were performed
using Bruker NOEDIFF pulse program, with irradiation times
of 3 s and power 40 L. The molecular weight (Mw) and the
molecular weight distribution (Mw/Mn) of polyphenylacetylene
were determined by gel permeation chromatography versus
polystyrene standards. The analyses were recorded on a
Knauer HPLC (K-501 pump, K-2501 UV-detector) with a PLgel
5 µm 104 Å GPC column and chloroform as solvent (flow rate
0.6 mL/min).
Sch em e 3
substituent is tilted by 30.3(2)° with respect to the
heterocyclic ring. The steric hindrance exerted by the
γ-lactone substituents seems to influence the conforma-
tion of the isopropyl groups of the R-diimine ligand in
such a way that both methyne hydrogen atoms are
gauche to the Pd(II); the resulting geometry is in
agreement with the NOE experiments mentioned
above.13 To our knowledge palladium complexes analo-
gous to 4 and 5 have never been described in the
literature; however they had been hypothesized as
intermediates in the Pd-catalyzed synthesis of lactones
starting from alkynes and carbon monoxide.5g-l
Cleavage of the η3-allyl palladium carbon bond was
performed in two different ways. Thus, by dissolving
complex 4 in methanol a selective nucleophilic attack
of the solvent occurred with quantitative formation of
the R,â-unsaturated γ-lactone 6. On the other hand,
reaction of a dichloromethane solution of 4 with an
equimolecular amount of Na[BEt3H] produced com-
pound 7, through proton abstraction from the methyl
in the 5 position (Scheme 3).
In conclusion, in studying the reactivity of complex 1
toward alkynes, it has been observed that the nature
of the products, either polymers or organic molecules,
depends mainly on the substituents present on the triple
bond. Moreover, we have isolated and fully characht-
erized the new complexes 4 and 5, which represent the
first experimental evidence of a key intermediate in
alkyne cyclocarbonylation processes.5g-l The formation
of compounds 4 and 5 seems to preclude the synthesis
of alternating alkyne/CO copolymers, although the use
of alkynes with electron-withdrawing substituents might
shift the process toward the formation of copolymers.
Further studies are in progress to develop a catalytic
cycle for the production of optically active lactones by
using a chiral oxazoline ligand.
Syn th esis of P olyp h en yla cetylen e (P P A). Complex 1
(42.1 mg, 0.036 mmol) was dissolved in 1 mL of chloroform;
after addition of 320 µL (2.9 mmol) of phenylacetylene (alkyne/
palladium molar ratio 80:1) at -30 °C the solution color
changed from yellow to dark red. The reaction mixture was
slowly warmed at 0 °C and stirred for 6 h. The resulting yellow
polymer was precipitated with methanol (5 mL) and washed
with methanol. To remove metallic palladium traces, it was
redissolved in chloroform and filtered through Celite, giving,
after evaporation of solvent, 75.5 mg (20 g of polymer/g Pd) of
PPA. IR (Nujol, cm-1): 754, 739, 696. 1H NMR (CDCl3, 20
°C): 7.07-6.87 (m br, 3H, Ph-Hm, Ph-Hp); 6.65 (d, J ) 4.7 Hz,
2H, Ph-Ho); 5.86 (s, 1H, CH). 13C NMR (CDCl3, 20 °C): 142.9
(Ph-CdCH); 139.3 (Ph-Ci); 131.8 (Ph-CdCH); 127.8, 127.5 (Ph-
Co, Ph-Cm); 126.7 (Ph-Cp). Anal. Calcd for (C8H6)n: C, 94.08;
H, 5.92. Found: C, 93.70; H, 6.10. Mw ) 54 000; Mw/Mn ) 2.0.
[P d (C(P h )dC(CH3)C(O)CH3)(P r iDAB)]+[BAr ′4]- (2). A
20 µL (0.160 mmol) sample of 1-phenyl-1-propyne was added
at -50 °C to a dichloromethane solution (4 mL) of 1 (185 mg,
0.160 mmol). The reaction mixture was warmed at 0 °C within
2 h. After filtration through Celite, solvent was evaporated
and the resulting solid was washed with hexane (4 × 4 mL)
to give 191 mg (0.151 mmol, 94%) of the yellow compound 2.
IR (Nujol, cm-1): 1612 (CdN), 1570 (CdO). 1H NMR (CD2Cl2,
-30 °C): δ 7.89 (s, 1H, CHdN); 7.67 (s, 8H, Ar′-Ho); 7.62 (s,
1H, CHdN); 7.50 (s, 4H, Ar′-Hp); 7.33-7.24 (m, 3H, Ph-Hm,
Ph-Hp); 7.10-7.03 (m, 2H, Ph-Ho); 3.93 (sept, J ) 6.5 Hz, 1H,
CH(CH3)2); 2.33 (s, 3 H, C(O)(CH3)); 2.11 (sept, J ) 6.5 Hz,
1H, CH(CH3)2); 1.60 (s, 3 H, PdC(Ph)dC(CH3)); 1.31, 0.76 (d,
J ) 6.5 Hz, 6H each, CH(CH3)2). 13C NMR (CD2Cl2, -30 °C):
δ 223.8 (C(O)); 194.0 (PdC(Ph)dC(CH3)); 163.3, 159.0 (CdN);
1
162.0 (q, J CB ) 49.5 Hz, Ar′-Ci); 144.7 (PdC(Ph)dC(CH3));
142.1 (Ph-Ci); 134.9 (Ar′-Co); 129.2, 124.9 (Ph-Cm, Ph-Co); 128.9
(q, 2J CF ) 32.0 Hz, Ar′-Cm); 128.5 (Ph-Cp); 124.7 (q, 1J CF ) 270.6
Hz, CF3); 117.7 (Ar′-Cp); 63.3, 56.0 (CH(CH3)2); 27.3 (C(O)-
(CH3)); 22.0, 21.2 (CH(CH3)2); 15.4 (PdC(Ph)dC(CH3)). Anal.
Calcd for
C51H39BF24N2OPd: C, 48.27; H, 3.10; N, 2.21.
Found: C, 48.62; H, 2.78; N, 2.25.
[P d (C(CH 3)dC(CH 3)C(O)CH 3)(P r iDAB)]+[BAr ′4]- (3).
Complex 3 was synthesized according to the procedure de-
scribed for 2 using 55.0 mg (0.048 mmol) of 1 and 8 µL (0.102
mmol) of 2-butyne. A 42.3 mg (0.035 mmol, 73%) sample of 3
was collected as a yellow powder. IR (Nujol, cm-1): 1611
Exp er im en ta l Section
All manipulations were carried out under a nitrogen atmo-
sphere by using Schlenk techniques. Solvents were dried by
standard methods and freshly distilled under nitrogen. Com-
plex [Pd(CH3)(CO)(PriDAB)]+[BAr′4]- (1) (PriDAB ) 1,4-diiso-
propyl-1,4-diaza-1,3-butadiene; Ar′ ) 3,5-(CF3)2C6H3) was
synthesized as previously reported in the literature.7b Phenyl-
1
(CdN), 1569 (CdO). H NMR (CD2Cl2, -30 °C): δ 7.94, 7.81
(s, 1H each, CHdN); 7.68 (s, 8H, Ar′-Ho); 7.51 (s, 4H, Ar′-Hp);
4.19, 3.92 (sept, J ) 5.9 Hz, 1H each, CH(CH3)2); 2.20 (s, 3H,
C(O)(CH3)); 1.85 (s, 3H, PdC(CH3)dC(CH3)); 1.70 (s, 3H, PdC-
(CH3)dC(CH3)); 1.25 (d, J ) 5.9 Hz, 12H, CH(CH3)2). 13C NMR
(CD2Cl2, -30 °C): δ 221.2 (C(O)); 199.3 (PdC(CH3)dC(CH3));
(13) Given the limitation that hydrogens were introduced in calcu-
lated positions and refined according to the linked atoms and, as a
consequence, their corresponding C-H bond distances were not refined,
it should be observed that the hydrogen atom labeled H(3) is ca. 2.6 Å
from the plane of the phenyl ring, while H(6) is ca. 2.9 Å from the
C(13) methyl carbon atom.
1
163.2, 158.8 (CdN); 162.0 (q, J CB ) 49.3 Hz, Ar′-Ci); 144.7
2
(PdC(CH3)dC(CH3)); 134.9 (Ar′-Co); 129.0 (q, J CF ) 31.2 Hz,
1
Ar′-Cm); 124.7 (q, J CF ) 270.8 Hz, CF3); 117.8 (Ar′-Cp); 62.9,

3970 Organometallics, Vol. 22, No. 19, 2003
Notes
58.7 (CH(CH3)2); 26.7 (C(O)(CH3)); 24.7 (PdC(CH3)dC(CH3));
22.1, 21.1 (CH(CH3)2); 13.7 (PdC(CH3)dC(CH3)). Anal. Calcd
for C46H37BF24N2OPd: C, 45.78; H, 3.09; N, 2.32. Found: C,
45.41; H, 3.01; N, 2.27.
Rea ction of Com p lex 4 w ith Na [BEt 3H]. A 50 µL (50
µmol) sample of Na[BEt3H] (solution 1 M in THF) was added
to a chloroform solution (2 mL) of 4 (54.2 mg, 41.8 µmol). The
reaction mixture was stirred for 12 h at 20 °C (during this
time formation of black Pd precipitate occurred) and then
concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel with a mixture of
hexane/ethyl acetate (6:4) as eluent to give compound 7 (3.7
mg, 19.9 µmol, 48%) as a yellow solid. IR (Nujol, cm-1): 1785
(CdO). 1H NMR (CDCl3, 20 °C): 7.58-7.36 (m, 5H, Ph-H); 5.24
(d, J ) 2.7 Hz, 1H, dCH2); 5.00 (d, J ) 2.7 Hz, 1H, dCH2);
2.29 (s, 3H, C(Ph)dC(CH3)). 13C NMR (CDCl3, 20 °C): 168.8;
155.8; 146.2; 129.5; 129.1; 129.0; 128.6; 128.3; 94.0; 11.0. Anal.
Calcd for C12H10O2: C, 77.40; H, 5.41. Found: C, 77.71; H,
5.29.
[P d(η3-C(P h )C(CH3)C(CH3)OC(O))(P r iDAB)]+[BAr ′4]- (4).
A 232 mg (0.183 mmol) sample of 2 was dissolved at -30 °C
in 4 mL of dichloromethane previously saturated with CO. The
solution was warmed at 0 °C within 2 h and then filtered
through Celite. After evaporation of the solvent a dark yellow
powder was obtained, which was washed with hexane (3 × 2
mL) to give 233 mg (0.180 mmol, 98%) of 4. IR (CD2Cl2, cm-1):
1
1799 (CdO), 1611 (CdN). H NMR (CD2Cl2, -60 °C): δ 7.97
(s, 1H, CHdN); 7.91-7.82 (m, 3H, Ph-Ho and CHdN); 7.67 (s,
8H, Ar′-Ho); 7.49 (s, 4H, Ar′-Hp); 7.47-7.33 (m, 3H, Ph-Hm,
Ph-Hp); 3.91 (sept, J ) 6.4 Hz, 1H, CH(CH3)2); 3.07 (sept, J )
6.4 Hz, 1H, CH(CH3)2); 2.35 (s, 3 H, C(Ph)C(CH3)); 1.67 (s, 3H,
C(CH3)O); 1.28, 1.16, 0.91, 0.70 (d, J ) 6.4 Hz, 3H each, CH-
(CH3)2). 13C NMR (CD2Cl2, -60 °C): δ 165.0 (OC(O)); 162.0
X-r a y Str u ctu r e Deter m in a tion . Crystal data for 4:
C
52H39BF24N2O2Pd, Mr 1297.08, monoclinic, space group P21/
n, a ) 12.408(1) Å, b ) 32.054(4) Å, c ) 14.877(2) Å, â )
111.760(5)°, V ) 5495(1) Å3, Z ) 4, T ) 200 K, Goebel mirror
monochromated Cu KR λ ) 1.5418 Å, Fcalcd ) 1.568 Mg/m3, µ(Cu
KR) ) 3.847 mm-1, F(000) ) 2592, absorption corrections with
SADABS,14 Siemens SMART diffractometer, ω scan, frame
width 0.3°, θ range 2.76-56.14°, 20 132 collected reflections,
6953 unique reflections (Rint ) 0.039), data/parameters ) 6207/
529, structure solution by SIR9715 and subsequent refinement
1
(q, J CB ) 49.3 Hz, Ar′-Ci); 160.9, 160.7 (CdN); 134.9 (Ar′-Co);
2
130.2 (Ph-Cp); 129.8, 129.2 (Ph-Cm, Ph-Co); 128.9 (q, J CF
)
31.9 Hz, Ar′-Cm); 128.0 (Ph-Ci); 124.7 (q, 1J CF ) 271.0 Hz, CF3);
121.9, 111.7, 72.3 (C(Ph)C(CH3)C(CH3)); 117.8 (Ar′-Cp); 60.9,
60.5 (CH(CH3)2); 22.8, 21.8, 20.8, 20.0 (CH(CH3)2); 14.3, 13.0
(C(CH3)C(CH3)O). Anal. Calcd for C52H39BF24N2O2Pd: C,
48.15; H, 3.03; N, 2.16. Found: C, 47.78; H, 2.98; N, 2.15.
[P d (η3 -C (C H 3 )C (C H 3 )C (C H 3 )O C (O ))(P r i D AB )]+[B -
Ar ′4]- (5). Complex 5 was synthesized according to the
procedure described for 4 starting from 46.0 mg (0.038 mmol)
of 3. A 42.3 mg (0.034 mmol, 90%) sample of 5 was collected
as a dark yellow powder. IR (Nujol, cm-1): 1786 (CdO), 1610
(CdN). 1H NMR (CD2Cl2, -30 °C): δ 7.97, 7.95 (s, 1H each,
CHdN); 7.68 (s, 8H, Ar′-Ho); 7.51 (s, 4H, Ar′-Hp); 3.87 (sept
br, J ) 6.2 Hz, 2H, CH(CH3)2); 2.14 (s, 3H, C(CH3)C(CH3)C-
(CH3)O); 1.58 (s, 3H, C(CH3)C(CH3)C(CH3)O); 1.44 (s, 3H,
C(CH3)C(CH3)C(CH3)O); 1.25, 1.17 (d, J ) 6.2 Hz, 6H each,
CH(CH3)2). 13C NMR (CD2Cl2, -30 °C): δ 166.8 (OC(O)); 162.0
by full matrix least-squares on Fo with SHELX 97,16 aniso-
2
tropic thermal parameters assigned to all the atoms except
carbon and hydrogen atoms because the reflections/parameters
ratio observed would otherwise be too poor, hydrogen atoms
introduced in calculated positions and treated as riding atoms
with an isotropic temperature factor depending on that of the
parent atom, several fluorine atoms of the anion were disor-
dered and were refined in double position, R1 ) 0.0653, wR2
) 0.1229, R1(all data) ) 0.0712, wR2(all data) ) 0.1256.
Ack n ow led gm en t. This work was supported by the
Ministero dell’Istruzione, dell’Universita` e della Ricerca
(MIUR-Rome), grant no. MM03027791. We would like
to thank Mrs. Anna Rita Pierleoni for her technical
assistance. Also CRIST (Centro Interdipartimentale di
Cristallografia Strutturale), University of Florence,
where the X-ray measurements were performed, is
gratefully acknowledged.
1
(q, J CB ) 49.3 Hz, Ar′-Ci); 160.8, 160.5 (CdN); 134.9 (Ar′-Co);
2
1
129.0 (q, J CF ) 31.2 Hz, Ar′-Cm); 124.7 (q, J CF ) 270.8 Hz,
CF3); 117.8 (Ar′-Cp); 120.7, 114.9, 70.9 (C(CH3)C(CH3)C(CH3)O);
117.8 (Ar′-Cp); 62.6, 60.3 (CH(CH3)2); 22.4, 22.0, 20.9, 20.6 (CH-
(CH3)2); 13.8, 11.8, 9.6 (C(CH3)C(CH3)C(CH3)O). Anal. Calcd
for C47H37BF24N2O2Pd: C, 45.71; H, 3.02; N, 2.27. Found: C,
45.58; H, 2.95; N, 2.24.
Rea ction of Com p lex 4 w ith MeOH. A 33.6 mg (25.9
µmol) sample of 4 was dissolved in 2 mL of methanol.
Formation of a black Pd precipitate was immediately observed.
The reaction mixture was stirred for 1 h at 20 °C and then
concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel with a mixture of
hexane/ethyl acetate (6:4) as eluent to give compound 6 (4.2
mg, 19.2 µmol, 74%) as a yellow solid. IR (Nujol, cm-1): 1775
(CdO). 1H NMR (CDCl3, 20 °C): 7.56-7.37 (m, 5H, Ph-H); 3.22
(s, 3H, O-CH3); 2.13 (s, 3H, C(Ph)dC(CH3)); 1.69 (s, 3H,
C(OCH3)-C(CH3)). 13C NMR (CDCl3, 20 °C): 169.7; 157.8;
129.3; 129.2; 129.0; 128.9; 128.5; 107.5; 50.5; 22.7; 11.7. Anal.
Calcd for C13H14O3: C, 71.54; H, 6.47. Found: C, 71.68; H,
6.56.
Su p p or tin g In for m a tion Ava ila ble: X-ray structure
information for complex 4. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM030368F
(14) Sheldrick, G. M. SADABS; University of Go¨ttingen: Germany,
1996.
(15) Altomare A.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli, M. SIR97. J . Appl. Crystallogr.
1999, 32, 115.
(16) Sheldrick, G. M. SHELX 97; University of Go¨ttingen: Germany,
1997.