The palladium-catalyzed carbonylation of nitrobenzene into phenyl isocyanate: The structural characterization of a metallacylic intermediate

Article abstract of DOI:10.1021/om9708485

The synthesis and characterization of a family of metallacyclic complexes of palladium, that is, (N-N)PdC(O)ON(Ar′)C(O), are reported where N-N is a diimine ligand and Ar′ is a substituted aryl. The complexes were isolated from solutions during the catalytic carbonylation of nitroaromatics using palladium complexes and were proposed to be intermediates in the catalytic process. The X-ray structure determination of [(^tBu)₂bipy]PdC(O)ON[p-C₆H₄-( ^tBu)]C(O) ((^tBu)₂bipy = 4,4′-bis-tert-butyl-2,2′-bipyridyl) was carried out, the complex crystallizing in the triclinic space group P1 (C₃₀H₃₇N₃O₃Pd) ₂·C₃H₆O, Z = 2, a = 15.626(4) A?, b = 18.269(6) A?, c = 12.067(3) A?, α = 107.34(2)°, β = 111.53(2)°, γ = 78.81(2)°. The crystal structure contains two molecules in the asymmetric unit which are assembled in a quasidimeric form via stacking interactions. The previously assigned metallacyclic structure for these complexes was confirmed. A mechanistic pathway for the carbonylation process implicating a series of metallacycle intermediates is proposed without intervention of a metal-imido intermediate. Thermal decomposition studies of the metallacycle and some trapping experiments are also presented.

Full text of DOI:10.1021/om9708485

Organometallics 1998, 17, 2199-2206
2199
Th e P a lla d iu m -Ca ta lyzed Ca r bon yla tion of Nitr oben zen e
in to P h en yl Isocya n a te: Th e Str u ctu r a l Ch a r a cter iza tion
of a Meta lla cylic In ter m ed ia te
Fre´de´ric Paul,† J ean Fischer,‡ Philippe Ochsenbein,‡ and J ohn A. Osborn*,†
Laboratoire de Chimie des Me´taux de Transition et de Catalyse and Laboratoire de
Cristallochimie et de Chimie structurale, URA 424 CNRS, Institut Le Bel, 4 rue Blaise Pascal,
F-67070 Strasbourg Cedex, France
Received September 29, 1997
The synthesis and characterization of a family of metallacyclic complexes of palladium,
that is, (N-N)PdC(O)ON(Ar′)C(O), are reported where N-N is a diimine ligand and Ar′ is a
substituted aryl. The complexes were isolated from solutions during the catalytic carbony-
lation of nitroaromatics using palladium complexes and were proposed to be intermediates
in the catalytic process. The X-ray structure determination of [(tBu)2bipy]PdC(O)ON[p-C6H4-
(tBu)]C(O) ((tBu)2bipy ) 4,4′-bis-tert-butyl-2,2′-bipyridyl) was carried out, the complex
crystallizing in the triclinic space group P1h (C30H37N3O3Pd)2‚C3H6O, Z ) 2, a ) 15.626(4) Å,
b ) 18.269(6) Å, c ) 12.067(3) Å, R ) 107.34(2)°, â ) 111.53(2)°, γ ) 78.81(2)°. The crystal
structure contains two molecules in the asymmetric unit which are assembled in a quasi-
dimeric form via stacking interactions. The previously assigned metallacyclic structure for
these complexes was confirmed. A mechanistic pathway for the carbonylation process
implicating a series of metallacycle intermediates is proposed without intervention of a
metal-imido intermediate. Thermal decomposition studies of the metallacycle and some
trapping experiments are also presented.
In tr od u ction
particular, we have studied homogeneous palladium
catalyst systems composed of a Pd(II) precursor (usually
Pd(OAc)2), an aromatic diimine ligand (such as 1,10-
phenanthroline or 2,2′-bipyridyl), in the presence of a
Bronsted acid promoter.5c,6c,d,7 These catalysts, which
are among the most active and selective for such
carbonylations, are effective at 130-180 °C under a
pressure of 40-120 bar of carbon monoxide.
Catalytic carbonylation of nitroaromatic compounds
by various group VIII metal compounds is a reaction of
great potential interest particularly for the industrial
production of aromatic isocyanates, carbamates, and
ureas.1 Ruthenium-,2,3 rhodium-,4 and palladium-
based5,6 catalysts have proved to be the most effective
for such transformations, and therefore several of these
catalytic systems have been thoroughly investigated. In
PhNO2 + 3CO + EtOH
+8
[Pd] + 3phen + 8H
180 °C, 120 bar
PhNHCO2Et + 2CO2 (1)
† Laboratoire de Chimie des Me´taux de Transition et de Catalyse.
‡ Laboratoire de Cristallochimie et de Chimie structurale.
(1) (a) Cenini, S.; Ragaini, F. In Reductive Carbonylation of Organic
Nitroaromatic Compounds; Kluwer Acad. Publishers: Dordrecht, The
Netherlands, 1997. (b) Drent, E. Pure Appl. Chem. 1990, 62, 661. (c)
Cenini, S.; Crotti, C. In Catalysis by Metal Complexes; Noe¨ls, A. F.,
Graziani, M., Hubert, A. J ., Eds.; Kluwer Acad. Publishers: Dordrecht,
The Netherlands, 1997; Vol. 112, p 311. (d) Parshall, G. W.; Ittel, S.
D. Homogeneous Catalysis, 2nd ed.; J . Wiley & Sons: New York, 1992.
(e) Ragaini, F.; Cenini, S.; J . Mol. Catal. A: Chem. 1996, 109, 1.
(2) (a) Kunin, A. J .; Noirot, M. D.; Gladfelter, W. L. J . Am. Chem.
Soc. 1989, 111, 2739. (b) Gargulak, J . D.; Noirot, M. D.; Gladfelter, W.
L. J . Am. Chem. Soc. 1991, 113, 1054. (c) Sherlock, S. J .; Boyd, D. C.;
Moasser, B.; Gladfelter, W. L. Inorg. Chem. 1991, 30, 3626. (d)
Gargulak, J . D.; Berry, A. J .; Noirot, M. D.; Gladfelter, W. L. J . Am.
Chem. Soc. 1992, 114, 8933. (e) Gargulak, J . D.; Gladfelter, W. L. J .
Am. Chem. Soc. 1994, 116, 3792. (f) Skoog, S. J .; Campbell, J . P.;
Gladfelter, W. L. Organometallics 1994, 13, 4137.
(3) Cenini, S.; Crotti, C.; Pizzotti, M.; Porta, F. J . Org. Chem. 1988,
53, 1243.
(4) (a) Ragaini, F.; Cenini, S.; Fumagalli, A.; Crotti, C. J . Organomet.
Chem. 1992, 401. (b) Ragaini, F.; Cenini, S. Organometallics 1994, 13,
1178.
(5) (a) Alessio, E.; Mestroni, G. J . Mol. Catal. 1984, 26, 337. (b)
Alessio, E.; Mestroni, G. J . Organomet. Chem. 1985, 291, 117. (c)
Cennini, S.; Ragaini, F.; Pizzotti, M.; Porta, F.; Mestroni, G.; Alessio,
E. J . Mol. Catal. 1991, 64, 179.
In previous work we were able to isolate the metal-
lacyclic complex 1a (Ar ) C6H5) by using milder condi-
tions (80 °C, 30 bar CO) than those used catalytically
and proposed a structure for 1a on the basis of spec-
troscopic data (1H and 13C NMR, FABMS, and IR
spectroscopy) as well as elemental analysis. Combining
this evidence with our studies on the chemical reactivity
(6) (a) Wehman, P.; Dol, G. C.; Moorman, E.; Kamer, P. C. J .; van
Leeuwen, P. W. N. M. Organometallics 1994, 13, 4856. (b) Wehman,
P.; Kaasjager, V. E.; de Lange, W. G. J .; Hartl, F.; Kamer, P. C. J .;
van Leeuwen, P. W. N. M. Organometallics 1995, 14, 3751. (c)
Wehman, P.; Kamer, P. C. J .; van Leeuwen, P. W. N. M. Chem.
Commun. 1996, 217. (d) Wehman, P.; Borst, L.; Kamer, P. C. J .; van
Leeuwen, P. W. N. M. J . Mol. Catal. A: Chem. 1996, 112, 23. (e)
Wehman, P.; Borst, L.; Kamer, P. C. J .; van Leeuwen, P. W. N. M.
Chem. Ber./ Recl. 1997, 130, 13.
(7) (a) Drent, E.; van Leeuwen, P. W. N. M. Eur. Pat. Appl. EP
86281, 1981. (b) Alessio, E.; Mestroni, G. Italian Patent 21401A84,
1984. (c) Alessio, E.; Mestroni, G. EP 0169650 A2, 1985. (d) Drent, E.
Eur. Pat. Appl. EP 224292, 1986. (e) Drent, E. Eur. Pat. Appl. EP
231045 1987.
S0276-7333(97)00848-0 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 05/08/1998

2200 Organometallics, Vol. 17, No. 11, 1998
Paul et al.
Sch em e 1
Sch em e 2
of 1a led us to postulate this complex as a key inter-
mediate in these Pd-catalyzed reactions.8 Hence we
proposed a mechanism by which the nitroaromatic
substrate was converted into carbamate (Scheme 1)
which involves a series of stepwise deoxygenation/
carbonylation processes involving metallacyclic inter-
mediates, A, B, C1, and C2.8 Subsequently we were able
to isolate and characterize (including X-ray structural
determination) other similar five-, six-, and four-
membered palladacycles 2, 3, and 4 (Scheme 2), which
comforted (but by no means proved) our working
hypothesis.9-11
However, these proposals, although feasible when
made in 1990, remained strongly dependent on the
precise structure of 1a , for which an X-ray structure was
not then available. After some effort, which involved
the synthesis of a series of analogue complexes and
attempts at their crystallization, eventually we were
able to obtain suitable crystals of one such analogue for
a structural determination.11
isolated other potential intermediates for similar
transformations.2b,f One of those was also the metal-
lacyclic compound 5 (Scheme 2), which had a structure
identical to that of the intermediate C2 proposed in our
mechanism. However, from reactivity and kinetics
studies, Gladfelter put forward a mechanism involving
the intermediate formation of aniline.2d-f More re-
cently, in the case of a rhodium/1,10-phenanthroline
catalyst system, another metallacyclic complex 6, pos-
sessing an isomeric structure of intermediate A, was
crystallographically characterized by Cenini.4b This
complex was also believed to be an intermediate in these
reactions, and a mechanism involving a metal-imido
species similar to that previously proposed by Gladfelter
was preferred. Other metallacycles possessing isomeric
or similar structures of intermediates A,12,13 B,2c,14 and
C2d,15 have also now been structurally characterized.
However, in contrast to our original mechanistic pro-
posal, a metal-imido intermediate has often been
invoked as a key intermediate in these recent studies,
During this time in studies on the ruthenium/1,2-bis-
(diphenylphosphino)ethane catalyst system, Gladfelter
(8) Leconte, P.; Metz, F.; Mortreux, A.; Osborn, J . A.; Paul, F.; Petit,
F.; Pillot, A. J . Chem. Soc., Chem. Commun. 1990, 1616.
(9) Paul, F.; Fischer, J .; Ochsenbein, P.; Osborn, J . A. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1638.
(10) Paul, F.; Fischer, J .; Ochsenbein, P.; Osborn, J . A. To be
submitted.
(12) Cenini, S.; Porta, F.; Pizzotti, M.; Crotti, C. J . Chem. Soc.,
Dalton Trans. 1985, 163.
(13) Dahlenburg, L.; Prengel, C. Inorg. Chim. Acta 1986, 122, 55.
(14) Pizzotti, M.; Porta, F.; Cenini, S.; Demartin, F.; Masciocchi, N.
J . Organomet. Chem. 1987, 330, 265.
(15) Glueck, D. S.; Wu, J .; Hollander, F. J .; Bergman, R. G. J . Am.
Chem. Soc. 1991, 113, 2041.
(11) Paul, F. Thesis, Louis Pasteur/Strasbourg (I), 1993.

The Carbonylation of Nitrobenzene
Organometallics, Vol. 17, No. 11, 1998 2201
Sch em e 3
although an alternative proposal6d similar to that
proposed by Gladfelter2 has also been suggested.
The unambiguous structural determination of 1a thus
assumes a certain importance in these mechanistic
discussions1e,16 since the structure we have proposed
could be seen to lead directly to the formation of a
carbamate or isocyanate product without the necessity
of passing through a metal-imido intermediate. Fur-
ther, given the recent doubts1e cast upon our structural
proposal for 1a , we present here the X-ray structure of
1p , an analogue of 1a , and some additional studies on
the reactivity of these metallacycles.
Ta ble 1. Cr ysta llogr a p h ic Da ta
formula
mol wt
cryst syst
2(C30H37N3O3Pd)‚C3H6O
1246.18
triclinic
space group
P1h
a (Å)
b (Å)
c (Å)
15.626(4)
18.269(6)
12.067(3)
107.34(2)
111.53(2)
78.81(2)
3044(3)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
color
pale yellow
crystal dimens (mm)
0.35 × 0.30 × 0.25
D
calc (g cm-3
)
1.36
Resu lts a n d Discu ssion
F(000)
1296
5.309
µ(mm-1
)
Complex 1a was originally isolated from the reaction
of Pd(OAc)2, o-phenanthroline (3 equiv), and PhNO2 (40
equiv) in ethanol under CO (30-40 bar) at 80 °C. The
yellow complex precipitates out of solution over 2 h in
trans min and max
temp (K)
0.8080/1.0000
194
wavelength (Å)
radiation
diffractometer
scan mode
1.54184
CuKR graphite monochromated
Philips PW1100
θ/2θ
-13,13/-16,16/0,10
3.0/47.05
5332
1
ca. 80% yield (eq 2). IR, H and 13C-MAS NMR, and
FAB mass spectrometric studies as well as elemental
analysis led us to propose the five-membered metalla-
cyclic structure for 1a .8 However, six isomeric struc-
tures (Scheme 3) had to be taken into consideration, and
despite the strong evidence for 1a , in particularly the
FABMS spectrum and reactivity studies, certain of the
other proposals could not definitively be excluded. 1a
was found to be of very low solubility in common organic
solvents, and despite repeated attempts, crystals suit-
able for X-ray analysis were not obtained. Therefore,
we undertook the systematic synthesis of various ana-
logues of 1a to resolve this problem.
A series of substituted nitrobenzenes, XC6H4NO2,
were studied under the conditions described above with
o-phen as ligand, and the resultant complexes, 1b-1h
(with para substitution, X ) OMe, t-Bu, Me, OH, OAc,
F, Cl), 1i (with o- FC6H4NO2), 1k (with m-FC6H4NO2),
and 1l (with 3,5-(CF3)2C6H3NO2), were isolated (eq 2).
hkl limits
θ limits (deg)
no. of data measd
no. of data with
I > 3 σ(I)
weighting scheme
no. of variables
R
4223
4Fo2/(σ2(Fo2) + 0.0036Fo
703
0.028
0.040
1.152
0.530
)
4
Rw
GOF
largest peak in final
diff (e Å-3
)
Accordingly, 1o (X ) H) and 1p (X ) p-t-Bu), which
possessed bulky tert-butyl groups also on the bipyridyl
ligand, were synthesized and found to be very soluble
in organic solvents. Suitable crystals of 1p could be
grown by inverse diffusion of water into an acetone
solution of the complex.
The complex crystallized in the P1h space group with
two molecules of 1p (designated Pd1 and Pd2) in the
asymmetric unit along with one molecule of acetone
(Table 1). The structures of both molecules are shown
separately in Figure 1. Most bond distances and angles
of Pd1 and Pd2 are not significantly different. The
bipyridine and the atoms of the metallacycle PdC(O)-
ON are closely coplanar in both molecules with a
somewhat larger deviation from the mean plane for the
molecule Pd1 than for Pd2, that is, 0.034 and 0.082 Å,
respectively. However, the ipso carbon atoms of the
t-BuC6H4 groups are out of this plane by 0.944 Å in Pd1
and 1.883 Å in Pd2, leading to the angles Pd1-N3-C21
and Pd2-N103-C121 being 157.57° and 169.02°, re-
spectively. As is shown in Figure 2, in the crystal Pd1
and Pd2 assemble so that the mean planes about each
Pd are almost parallel, the angle between the planes of
the two molecules being 5.87°, with a plane separation
of only 2.942 Å. Hence relatively strong interactions
1
The compounds presented IR and H NMR spectroscopic
features almost identical to those of 1a except for
substituent differences, but the solubilities of many of
these analogues were also very low. We surmised that,
given the expected planar structure of Pd(II) molecules
of this type, strong intermolecular stacking interactions
may be responsible for their low solubility behavior.
(16) For another proposed mechanism involving only metallacycles
in rhodium-catalyzed reactions, see: (a) Unverfehrt, K.; Schwetlick,
K. React. Kinet. Catal. Lett. 1977, 6, 231. (b) Unverfehrt, K.; Ho¨ntsch,
R.; Schwetlick, K. J . Prakt. Chem. 1979, 321, 86. (c) Unverfehrt, K.;
Ho¨ntsch, R.; Schwetlick, K. J . Prakt. Chem. 1979, 321, 928.

2202 Organometallics, Vol. 17, No. 11, 1998
Paul et al.
F igu r e 1. ORTEP drawing of the two molecules of 1p . Selected bond lengths (Å) and angles (deg): Pd1-N1/Pd2-N101
2.124(4)/2.147(4), Pd1-N2/Pd2-N102 2.135(4)/2.132(4), Pd1-C19/Pd2-C119 1.950(6)/1.946(5), Pd1-C20/Pd2-C120 1.935-
(6)/1.965(5), C19-O1/C119-O101 1.398(6)/1.415(5), C19-O2/C119-O102 1.215(6)/1.204(5), C20-O3/C120-O103 1.239-
(6)/1.232(6), C20-N3/C120-N103 1.390(7)/1.385(6), N3-O1/N103-O101 1.419(5)/1.416(5), N1-Pd1-N2/N101-Pd2-N102
76.8(2)/76.8(2), N1-Pd1-C20/N101-Pd2-C120 101.2(2)/101.3(2), N1-Pd1-C19/N101-Pd2-C119 176.4(2)/176.6(2), N2-
Pd1-C19/N102-Pd2-C119 100.8(2)/100.1(2), C20-Pd1-C 19/C120-Pd2-C119 81.1(3)/81.9(2).
between Pd1 and Pd2 are present which are undoubtedly
a result of a mutual π-stacking type between the
bipyridine ligands and the metallacycles. The two
molecules are oriented in a quasi head to tail fashion
and, although not identical, can be superimposed by a
ca. 140° rotation about the Pd-Pd axis. If the substit-
uents are ignored, the molecules can also be seen to be
approximately related by a 2-fold axis perpendicular to
the Pd-Pd vector. Although the two Pd atoms are also
stacked in this structure, the Pd-Pd distance of 3.280
Å would seem to be too great for there to be a significant
metal-metal bonding contribution. The existence of
this assembled dimer structure supports our suspicions
that the type of intermolecular interactions found herein
may be responsible for the lack of solubility of most of
the metallacycles of this type.
The geometry around the palladium is square planar,
and the structure of the metallacycle is indeed that of
the isomer we had previously proposed. The two
carbonyl groups are linked directly to the metal with
palladium to carbon bond lengths of 1.950(5) and 1.946-
(5) Å (Pd1-C19/Pd2-C119) and 1.935(5) and 1.965(5)
Å (Pd1-C20/Pd2-C120). Hence the molecule formally
contains a CO2 unit linked by its carbon atom to the
metal center in a five-membered metallacycle, a struc-
tural type which had been proposed only rarely17-19 and
which had not been previously fully established by X-ray
methods. We note that the C-O bond distances are
1.398(6)/1.415(5) Å (C19-O1/C119-O101) and 1.215-
(6)/1.204(5) Å (C19-O2/C119-O102) for the CO2 moiety
and 1.239(6)/1.232(6) Å (C20-O3/C120-O103) for the
other carbonyl group.
The crystal structure also revealed weak intramo-
lecular interactions between the ortho hydrogen atoms
of the diimine ligand (on C1, C10/C101, and C110) and
the oxygen atoms (O2, O3/O102, and O103 respectively)
of the R-carbonyl groups in the metallacycle. Similar
hydrogen bond type interactions have been observed
often in crystal structures.20 However we also observe
that in solution the 1H NMR chemical shifts of the ortho
protons of the diimine ligand in the metallacycles 1 are
displaced 0.5 ppm to low field relative to the shifts
measured in other Pd(II) complexes (Table 2). We
suggest that the intramolecular interactions are prob-
ably maintained in solution aided by the rigidity of the
coordination sphere around the metal. A similar 1H
shift was also observed for one of the diimine ortho
protons of complex 2 and can also be related to the
existence of an interaction with the proximal R-carbo-
nyl.9 Furthermore, in 2 the other R-proton of the
diimine ligand is displaced toward high field by ap-
proximatively 3 ppm, which undoubtedly results from
the proximity of the phenyl group of the NPh unit on
(17) Chetcuti, P. A.; Walker, J . A.; Knobler, K. B.; Hawthorne, M.
F. Organometallics 1988, 7, 641.
(18) Werner, H.; Brekau, U.; Nurnberg, O.; Zeier, B. J . Organomet.
Chem. 1992, 440, 389.
(19) Herskovitz, T.; Guggenberger, L. J . J . Am. Chem. Soc. 1976,
98, 1615.
(20) Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290.

The Carbonylation of Nitrobenzene
Organometallics, Vol. 17, No. 11, 1998 2203
decarboxylation and subsequent decomposition of 1a
could be trapped as the maleic anhydride adduct8
(Scheme 4). We were unable to observe the supposed
intermediate (phen)Pd(ArNCO) (7) since (in the absence
of a trapping agent) decomposition of 1a yields an
intractable and insoluble black material (presumably
mainly consisting of reduced metallic palladium), along
with various organic products arising from phenyl
isocyanate.8,11
However, we had previously shown that, on heating
of 1a with excess PhNCO at 140 °C, a six-membered
palladacycle of the structural type 3 shown in Scheme
4 could be isolated in high yield.9 Thus we carried out
the same experiment using a labeled isocyanate hoping
to observe the PhNCO group in the resultant metalla-
cycle. Heating 1a with excess p-tolyl isocyanate at 140
°C did not yield the mixed phenyl/tolyl derivative but
instead only the isostructural tolyl-containing metalla-
cycle 3. We subsequently showed that such metalla-
cycles readily exchange with excess aryl isocyanates
under these conditions,9 and thus our experiment was
inconclusive. Incidentally this reaction proved to be
much cleaner than the reaction involving phenyl isocy-
anate and (N-N)Pd(dba) (dba ) dibenzylideneacetone),
which has often been used as the source of (N-N)Pd-
(0).10,11 Analogous decarboxylation processes have al-
ready been reported in five-membered rhodium metal-
lacyles incorporating CO2 units.17,18
Finally, we checked that complex 1a was not formed
when a palladium(0) precursor, (phen)Pd(dba), was
heated together with carbon dioxide (20 bar) and phenyl
isocyanate (eq 3) at 80 °C for 5 h. The palladacycle 3
F igu r e 2.
Ta ble 2. 1H NMR Sh ifts of Or th o P r oton s of th e
P h en a n th r olin e Liga n d in Va r iou s
P a lla d iu m (II)-Diim in e Com p lexes
complex in CD2Cl2
H′ shift (ppm)
H′′ shift (ppm)
a
[(tBu)2bipy]PdCl2
9.19
8.17
9.76
9.58
8.32
9.19
8.17
9.57
9.58
8.32
9.94
6.82
a
[(tBu)2bipy]Pd(OAc)2
1o
a
(phen)PdCl2
a
(phen)Pd(OAc)2
was again characterized as the main product, along with
a new species and metallic palladium, but no evidence
for the formation of 1a was obtained. We have been
unable to purify this new complex sufficiently to allow
a definitive identification, but NMR data indicate the
presence of a nonsymmetric phenanthroline ligand
(ortho protons at δ 9.98 and 9.11) and carbonyl absorp-
tions at 1620 and 1690 cm-1. Tentatively we propose
that this complex may possess the isomeric structure
2, which would result indeed from coupling of phenyl
isocyanate with CO2. If this is correct then species of
the structural type 2 (Scheme 3) could be resulting from
postcatalytic reactions and may have no relevance as
intermediates in the actual catalytic process. Attempts
to characterize this complex in more detail are under-
way.
In conclusion, the X-ray determination confirms our
structural proposition for the metallacyclic complex
isolated from the catalytic carbonylation process, such
metallacycles being formed from differently functional-
ized nitroaromatics. The decomposition of 1a is ir-
reversible, indicating that the palladacycle is formed
from the Pd-catalyzed reaction of nitrobenzene with CO
and not from a later reaction of the products formed.
Finally, although the precise mechanism for catalytic
carbonylation of nitroaromatics by these palladium
complexes is still unclear, especially for the initial steps
1a
10.13
10.43
2b
a
b
See ref 11. See ref 9.
the metallacycle, the phenyl group being oriented
perpendicular to the plane of the molecule, thereby
deshielding this proton. Hence in five-membered pal-
ladacycles where carbonyl or phenyl imido units are
directly linked to the metal center, R-hydrogens of
coordinated diimine ligands should show characteristic
1
chemical shifts in the H NMR spectrum. This observa-
tion may be useful to distinguish between the various
possible isomers in such systems, where crystallographic
structural data is lacking. For instance, it can be seen
that, if this criterion is applied to the isomers shown in
Scheme 3, all except for structure 1 can be eliminated.
To confirm that 1p was indeed an analogue of 1a , we
also showed that (a) the FABMS fragmentation patterns
were analogous (except for the evident differences in
ligand and the presence of tert-butyl groups) and (b) the
catalytic reaction using the 4,4′-bis-tert-butyl-2,2′-bipy-
ridine ligand proceeds typically under normal condi-
tions.
We have found that, on heating of 1a with excess
maleic anhydride at 100 °C in an inert solvant, the
palladium(0) diimine fragment arising from thermal

2204 Organometallics, Vol. 17, No. 11, 1998
Paul et al.
Sch em e 4
of the catalysis,11 the structure and the reactivity of 1,
as well as the very rich insertion-deinsertion behavior
displayed by analogous palladium(0) complexes, provide
support to a mechanistic pathway involving the inter-
conversions of a series of metallacyclic intermediates
(Scheme 1). Further investigations will be necessary
to clarify the details of this fascinating and important
catalytic reaction.
Diffraction data was collected at -100 ( 1 °C on a Philips
PW1100/16 diffractometer with graphite-monochromated Cu
KR radiation (λ ) 1.5418 Å). Cell constants and an orientation
matrix for data collection were obtained from a least-squares
refinement using the setting angles of 25 carefully centered
reflections in the range corresponding to a triclinic cell.
Packing considerations, a statistical analysis of intensity
distribution, and the successful solution and refinement of the
structure showed the space group to be P1h. Collection was
achieved using the ω-2θ scan to a maximum 2θ value of 47.0°.
Scans of (0.90 + 0.14 tan θ)° were made at a speed of 0.02 °/s
(in ω), and 5332 reflections were collected. Empirical absorp-
tion corrections and Lorentz and polarization corrections were
applied to the data. The structure was solved by the Patterson
method. All non-hydrogen atoms were located by the heavy-
atom method and were refined anisotropically. The final cycle
of full-matrix least-squares refinement was based on 4223
observed reflections (I > 3.00σ(I)) and converged with un-
weighted and weighted agreement factors of R ) 0.028 and
Rw ) 0.040, respectively. All computations used MOLEN on
a VAX computer.25 Crystal parameters, data collection details,
and results of the refinements are summarized in Table 1.
P r ep a r a tion of Com p ou n d s 1a -p : Typ ica l P r oced u r e.
In the autoclave, 100 mg of palladium acetate (0.44 mmol),
3-10 equiv of the desired diimine ligand, and 3-40 equiv of
nitroaromatic were added to 10 mL of ethanol. The autoclave
was then flushed with carbon monoxide three times with
stirring, pressurized to 40 bar, and heated to 80 °C (30 min).
The stirring was further maintained for 2 h at this tempera-
ture. After subsequent cooling and depressurization, the pale
suspension that formed in the medium was filtered and
washed several times with ethanol and diethyl ether. De-
pending on the nitroaromatic used, the resulting yellow air-
stable precipitate often contained metallic palladium but could
be purified from hot ortho-dichlorobenzene (120 °C) by cooling
and subsequent addition of n-pentane. Great care has to be
exercised in controlling the temperature, since the complexes
often undergo decomposition around 140 °C in solution. In
many cases, crystalline needles of those complexes can be
grown as well by slow diffusion of diethyl ether in a saturated
dichloromethane solution.
Exp er im en ta l Section
Gen er a l Com m en ts. Unless otherwise specified, all re-
agents were purchased from commercial suppliers and used
without further purification. Carbon monoxide (N-45 purity
grade) and carbon dioxide (N-45 purity grade) were purchased
from Air Liquide. The chelating 4,4′-bis-tert-butyl-2,2′-dipy-
ridine was synthesized following the reported procedure of
Belser.21 Complexes (phen)Pd(OAc)2,22 (phen)PdCl2,23 and
(phen)Pd(dba)24 were also obtained following reported synthe-
ses.
Reactions under pressure were performed in a 50 mL
stainless steel SOTELEM reactor with a 750 W corresponding
programmable oven. 1H NMR spectra were obtained on a
Brucker SY 200 (200 MHz) or SY 400 (400 MHz) Fourier
transform spectrometer. 1H NMR chemical shifts are reported
in units of parts per million (ppm) relative to residual protiated
solvent. Infrared spectra were recorded on a Perkin-Elmer
597 or IFS 66 fourier transform spectrometer in KBr windows.
UV-visible spectra were recorded on a Cary 3 spectrometer,
using quartz cells. GC analyses were performed on a Hewlett-
Packard SII-5890 gas chromatograph, equipped with a 10 m
methyl silicon semicapillary column (HP-1). Quantitative
analyses were obtained by integrating peak areas versus
appropriate external or internal standards. Response factors
relative to the chlorobenzene standard were determined by
using authentic samples of the products. Mass spectral studies
and elemental analyses were obtained from the corresponding
services of the Louis Pasteur University.
Cr ysta llogr a p h ic Stu d y of [(tBu )2bip y]P d C(O)ON[p-
C6H4(tBu )]C(O) (1p ). Pale yellow crystalline needles of 1p
were grown by slow diffusion (several weeks) of water in an
acetone solution of the crude product isolated after reaction.
Since the crystals desolvated slowly when separated from
mother liquor at ambient temperature, data collection had to
be performed at low temperature.
(p h en )P d [C(O)N(C6H 5)OC(O)] (1a ): 80% yield; yellow.
Mp: 238 ( 1 °C dec. IR (KBr, cm-1): 3050 (w, C-H phen);
1698 (s, CdO), 1622 (s, CdO); 1585 (s, CdC arom); 1255 (m,
N-O). NMR: 1H (CD2Cl2) δ 10.13 (d, J ) 5 Hz, 1 H, ortho/
phenanthroline); 9.94 (d, J ) 5 Hz, 1 H, ortho/phenanthroline);
8.56 (d, J ) 8 Hz, 2 H); 8.00 (dd + s, 2 × 2 H); 7.71 (d, J ) 8
Hz, 2 H, phenyl); 7.38 (t, J H-H ) 7 Hz, 2 H, phenyl); 7.14 (t,
(21) Belser, P.; von Zelewsky, A. Helv. Chim. Acta 1980, 63, 1675.
(22) McKeon, J . E.; Fitton, P. Tetrahedron 1972, 28, 233.
(23) Ryan, D. E. Can. J . Res., Part B 1949, 27, 938.
(24) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J . J .; Ibers, J . A. J .
Organomet. Chem. 1974, 65, 253.
(25) Frenz, B. A. The ENRAF-Nonius CAD4-SDP In Computing
Crystallography; Olthof-Hazekampf, R., Schenk, H., van Koningveld,
H., Bassi, G. C., Eds.; Delft University Press: Delft, The Netherlands,
1978; pp 64-71.

The Carbonylation of Nitrobenzene
Organometallics, Vol. 17, No. 11, 1998 2205
J H-H ) 8 Hz, 1 H, phenyl); 13C (MAS) δ 191.0 (CdO); 185.4
(CdO); 151.9; 148.8; 145.9; 144.1; 138.8; 136.9; 136.0;
134.6;129.5 (phenanthroline); 126.4; 123.2; 119.9 (phenyl).
FABMS (m-nitrobenzyl alcohol/N,N-dimethylacetamide): m/z
450 (M + 1), 422 (M + 1 - CO), 393 (M - 2CO), 378 (M + 1
- CO - NCO), 363 (M + 1 - CO2 - NCO), 314 (M - CO -
PhNO), 302 (M - CO - PhNCO), 286 (M - CO2 - PhNCO).
UV (CH2Cl2): λ (nm) (approximate ꢀ in mol cm-1); 275.0
(69 000); 293.5 (35 700); 330.5 (4900), 347.5 (4300). Anal.
Calcd for C20H13N3O3Pd: C, 53.41; H, 2.91; N, 9.34; Found:
C, 53.67; H, 2.91; N, 9.34.
J ) 5 Hz, 1 H, ortho/phenanthroline); 8.59 (d, J ) 8 Hz, 2 H);
8.00 (dd + s, 4 H); 7.73 (d, J ) 5 Hz, 2 H, phenyl); 7.35 (d, t,
J ) 5 Hz, 2 H, phenyl). Anal. Calcd for C20H12N3O3ClPd: C,
49.61; H, 2.50; N, 8.68; Found: C, 49.54; H, 2.48; N, 8.91.
(p h en )P d [C(O)N(o-F C6H4)OC(O)] (1i): 87% yield; light
gray or yellow (H2O solvate). Mp: 215 ( 5 °C dec. IR (KBr,
cm-1): 1705 (s, CdO), 1625 (s, CdO); 1265 (s, N-O); 1040 (m,
C-F). NMR: 1H (C6D5NO2, 80 °C) δ 10.10 (d, J ) 5 Hz, 1 H,
ortho/phenanthroline); 10.00 (d, J ) 5 Hz, 1 H, ortho/phenan-
throline); 8.53 (d, J ) 7 Hz, 2 H); 7.94 (dd + s, 4 H); 7.67 (m,
1 H, phenyl); 7.25 (m, 3 H, phenyl). Anal. Calcd for
C20H12N3O3FPd: C, 51.36; H, 2.59; N, 8.98; Found: C, 51.16;
H, 2.63; N, 8.47.
(p h en )P d [C(O)N(p-MeOC6H4)OC(O)] (1b): 60% yield;
yellow. Mp: 217 ( 3 °C dec. IR (KBr, cm-1): 1700 (s, CdO),
1620 (s, CdO); 1240 (s, N-O). NMR: 1H (CD2Cl2) δ 10.12 (d,
J ) 5 Hz, 1 H, ortho/phenanthroline); 9.93 (d, J ) 5 Hz, 1 H,
ortho/phenanthroline); 8.56 (d, J ) 9 Hz, 2 H); 7.99 (dd + s, 4
H); 7.56 (d, J ) 9 Hz, 2 H, phenyl); 6.93 (d, J ) 9 Hz, 2 H,
phenyl); 3.82 (s, 3 H, OCH3). Anal. Calcd for C21H15N3O4Pd:
C, 52.57; H, 3.15; N, 8.76; Found: C, 52.40; H, 3.08; N, 8.66.
(p h en )P d [C(O)N(p-tBu -C6H4)OC(O)] (1c): 72% yield;
yellow. Mp: 242 ( 1 °C dec. IR (KBr, cm-1): 1705 (s, CdO),
1610 (s, CdO); 1270 (s, N-O). NMR: 1H (CD2Cl2) δ 10.05 (d,
J ) 5 Hz, 1 H, ortho/phenanthroline); 9.97 (d, J ) 5 Hz, 1 H,
ortho/phenanthroline); 8.54 (d, J ) 8 Hz, 2 H); 7.98 (dd + s, 4
H); 7.58 (d, J ) 9 Hz, 2 H, phenyl); 7.40 (d, J ) 9 Hz, 2 H,
phenyl); 1.34 (s, 9 H, C(CH3)3). FABMS (m-nitrobenzyl
alcohol): m/z 506 (M + 1), 448 (M - tBu), 419 (M - 1 - CO),
(p h en )P d [C(O)N(m -CF 3C6H4)OC(O)] (1j): 70% yield; yel-
low. Mp: 237 ( 2 °C dec. IR (KBr, cm-1): 1705 (s, CdO),
1630 (s, CdO); 1265 (s, N-O); 1210 (m, C-F); 1160 (m, C-F);
1150 (m, C-F). NMR: 1H (C6D5NO2, 80 °C) δ 10.05 (d, J ) 5
Hz, 1 H, ortho/phenanthroline); 9.95 (d, J ) 5 Hz, 1 H, ortho/
phenanthroline); 8.60 (d, J ) 7 Hz, 2 H); 8.45 (s, 2 H, phenyl);
7.99 (m + s, 5 H); 7.58 (s, 1 H, phenyl). Anal. Calcd for
C
21H12N3O3F3Pd: C, 48.72; H, 2.34; N, 8.12; Found: C, 48.68;
H, 2.52; N, 7.91.
(p h en )P d [C(O)N(m -NO2C6H4)OC(O)] (1k ): 75% yield;
yellow. Mp: >250 °C dec. IR (KBr, cm-1): 1725 (s, CdO),
1635 (s, CdO); 1520 (s, NdO); 1345 (s, NdO); 1265 (s, N-O).
NMR: 1H (C6D5NO2, 115 °C) δ 10.07 (d, 1 H, ortho/phenan-
throline); 9.93 (d, 1 H, ortho/phenanthroline); 8.82 (s, 1 H,
phenyl); 8.62 (d, 2 H); 8.50 (d, 1 H, phenyl); 7.94 (dd + s, 4 H);
7.61 (m, 1 H, phenyl); 7.45 (m, 1 H, phenyl). Anal. Calcd for
t
t
393 (M + 1 - Bu - 2CO), 362 (M + 1 - Bu - CO2 - NCO),
314 (M - CO - tBu(C6H4)NO), 302 (M - CO - tBu(C6H4)NCO),
286 (M - CO2 - tBu(C6H4)NCO). Anal. Calcd for C24H21N3O4-
Pd: C, 56.99; H, 4.18; N, 8.30; Found: C, 57.12; H, 4.17; N,
8.31.
C
20H10N4O5Pd‚H2O: C, 46.82; H, 2.75; N, 10.93; Found: C,
46.82; H, 2.63; N, 10.66.
(p h en )P d [C(O)N(m -(CF 3)2C6H3)OC(O)] (1l): 14% yield;
yellow. Mp: 245 ( 5 (dec). IR (KBr, cm-1): 1720 (s, CdO),
1630 (s, CdO); 1270 (s, N-O); 1190 (w, C-F), 1170 (w, C-F).
NMR: 1H (C6D5NO2, 115 °C) δ 10.02 (d, 1 H, ortho/phenan-
throline); 9.93 (d, 1 H, ortho/phenanthroline); 8.56 (d, 2 H);
8.44 (s, 2 H, phenyl); 8.07 (dd + s, 4 H); 7.61 (s, 1 H, phenyl).
Anal. Calcd for C22H11N3O3F6Pd: C, 45.11; H, 1.89; N, 7.17;
Found: C, 45.18; H, 2.09; N, 6.97.
[3,4,7,8-(Me)4(p h en )]P d [C(O)N(C6H5)OC(O)] (1m ): 85%
yield; light gray. Mp: 269 ( 1 (dec). IR (KBr, cm-1): 1705
(s, CdO), 1620 (s, CdO); 1265 (s, N-O). NMR: 1H (C6D5NO2,
80 °C) δ 9.91 (s, 2 × 1 H, H, ortho/diimine); 9.72 (s, 2 × 1 H,
H, ortho/diimine); 8.02 (s, 2 H); 8.01 (d, J ) 7 Hz,2 H, phenyl);
7.43 (t, J ) 8 Hz, 2 H, phenyl); 7.17 (t, J ) 8 Hz,1 H, phenyl);
2.70 (s, 3 H, CH3/diimine); 2.69 (s, 3 H, CH3/diimine); 2.59 (s,
3 H, CH3/diimine); 2.54 (s, 3 H, CH3/diimine). Anal. Calcd
for C24H21N3O3Pd: C, 56.99; H, 4.18; N, 8.31; Found: C, 56.27;
H, 3.99; N, 8.30.
(p h en )P d [C(O)N(p-Me-C6H4)OC(O)] (1d ): 86% yield; yel-
low. Mp: 242 ( 3 °C dec. IR (KBr, cm-1): 1700 (s, CdO),
1620 (s, CdO); 1260 (s, N-O). NMR: 1H (CD2Cl2) δ 10.12 (d,
J ) 4 Hz, 1 H, ortho/phenanthroline); 9.93 (d, J ) 4 Hz, 1 H,
ortho/phenanthroline); 8.57 (d, J ) 8 Hz, 2 H); 8.01 (dd + s, 4
H); 7.57 (d, J ) 8 Hz, 2 H, phenyl); 7.20 (d, J ) 8 Hz, 2 H,
phenyl); 2.35 (s, 3 H, CH3). Anal. Calcd for C21H15N3O3Pd:
C, 54.39; H, 3.26; N, 9.06; Found: C, 54.62; H, 3.04; N, 8.79.
(p h en )P d [C(O)N(p-HOCH2C6H4)OC(O)] (1e): 98% yield;
yellow. Mp: 211 ( 2 °C dec. IR (KBr, cm-1): 3340 (m, O-H),
1700 (s, CdO), 1615 (s, CdO); 1275 (s, N-O). NMR: 1H (C6D5-
NO2) δ 10.21 (d, J ) 5 Hz, 1 H, ortho/phenanthroline); 10.00
(d, J ) 5 Hz, 1 H, ortho/phenanthroline); 8.56 (d, J ) 9 Hz, 2
H); 7.99 (dd + s, 4 H); 7.98 (d, J ) 8 Hz, 2 H, phenyl); 7.53 (d,
J ) 8 Hz, 2 H, phenyl); 4.83 (d, J ) 6 Hz, 2 H, CH2OH); 2.15
(s, 1 H, CH2OH). Anal. Calcd for C21H15N3O4Pd: C, 52.57;
H, 3.15; N, 8.76; Found: C, 52.53; H, 3.33; N, 8.69.
(p h en )P d [C(O)N(p-OAcC6H4)OC(O)] (1f): 80% yield; red.
Mp: 203 ( 4 °C dec. IR (KBr, cm-1): 1740 (s, CdO/acetate);
1720 (s, CdO), 1620 (s, CdO); 1270 (s, N-O). NMR: 1H (CD2-
Cl2) δ 10.13 (d, J ) 5 Hz, 1 H ortho/phenanthroline); 9.94 (d,
J ) 5 Hz, 1 H, ortho/phenanthroline); 8.58 (d, J ) 8 Hz,2 H);
8.01 (dd + s, 4 H); 8.01 (d, J ) 8 Hz, 2 H, phenyl); 7.73 (d, J
) 8 Hz, 2 H, phenyl); 7.09 (d, J ) 8 Hz, 2 H, phenyl); 2.28 (s,
3 H, O2CCH3). Anal. Calcd for C22H15N3O5Pd: C, 52.04; H,
2.98; N, 8.28; Found: C, 52.17; H, 3.01; N, 8.26.
(p h en )P d [C(O)N(p-F C6H4)OC(O)] (1g): 78% yield; yel-
low. Mp: 242 ( 2 °C dec. IR (KBr, cm-1): 1705 (s, CdO),
1625 (s, CdO); 1265 (s, N-O); 1050 (m, C-F). NMR: 1H (CD2-
Cl2) δ 10.09 (d, J ) 5 Hz, 1 H, ortho/phenanthroline); 9.91 (d,
J ) 5 Hz, 1 H, ortho/phenanthroline); 8.57 (d, J ) 8 Hz, 2 H);
8.00 (dd + s, 4 H); 7.68 (d, J H-H ) 9 Hz, J H-F ) 5 Hz, 2 H,
phenyl); 7.13 (d, t, J H-H ) J H-F ) 9 Hz, 2 H, phenyl). Anal.
Calcd for C20H12N3O3FPd: C, 51.36; H, 2.59; N, 8.98; Found:
C, 51.12; H, 2.61; N, 8.22.
(bip y)P d [C(O)N(C6H5)OC(O)] (1n ). Eight equivalents of
chelate was used in place of 3 in this case: yellow; 80% yield.
Mp: 225 ( 5 °C dec. IR (KBr, cm-1) 1705 (s, CdO), 1615 (s,
CdO); 1270 (s, N-O). NMR: 1H (CD2Cl2) δ 9.92 (d, J ) 5 Hz,
1 H, ortho/bipyridine); 9.72 (d, J ) 5 Hz, 1 H, ortho/bipyridine);
8.12 (dd + s, 4 H); 7.69 (d + t, 4 H, bipyridine and phenyl);
7.37 (t, J ) 8 Hz, 2 H, phenyl); 7.13 (t, J H-H ) 8 Hz, 1 H,
phenyl). FABMS (m-nitrobenzyl alcohol): m/z 426 (M + 1),
398 (M + 1 - CO), 369 (M - 2CO), 354 (M + 1 - CO - CO2),
339 (M - NCO - CO2), 290 (M - CO - PhNO), 262 (M - CO2
- PhNCO). Anal. Calcd for C18H13N3O3Pd: C, 50.78; H, 3.08;
N, 9.87; Found: C, 50.40; H, 3.11; N, 9.70.
[2,2′-(tBu )2(b ip y)]P d [C(O)N(C6H5)OC(O)] (1o). Eight
equivalents of chelating ligand and 40 equiv of nitroaromatic
were used here. After 15 h, a suspension of metallic palladium
was present in the reaction medium. This suspension was
removed by filtration on Celite (Merck 545). Then 50 mL of
acetone and 25 mL of H2O were added to the yellow filtrate.
After 5 days, the yellow precipitate (435 mg) was decanted
and washed with n-pentane. This precipitate was a mixture
(p h en )P d [C(O)N(p-ClC6H4)OC(O)] (1h ): 75% yield; yel-
low. Mp: 240 ( 5 °C dec. IR (KBr, cm-1): 1695 (s, CdO),
1625 (s, CdO); 1265 (s, N-O); 670 (m, C-Cl). NMR: 1H (CD2-
Cl2) δ 10.13 (d, J ) 5 Hz, 1 H, ortho/phenanthroline); 9.94 (d,
1
of free ligand and the desired complex (80% by H NMR) and
was again recrystallized by slow diffusion of water in an

2206 Organometallics, Vol. 17, No. 11, 1998
Paul et al.
ethanolic solution of the crude precipitate: 13% yield; yellow
needles. Mp: 224 ( 5 °C dec. IR (KBr, cm-1) 1720 (s, CdO),
1620 (s, CdO); 1265 (s, N-O). NMR: 1H (CD2Cl2) δ 9.75 (d,
J ) 6 Hz, 1 H, ortho/diimine); 9.56 (d, J ) 6 Hz, 1 H, ortho/
diimine); 8.07 (s, 2 H, diimine); 7.65 (m, 4 H, diimine and
phenyl); 7.35 (t, J ) 7 Hz, 2 H, phenyl); 7.12 (t, J ) 7 Hz, 1 H,
phenyl); 1.44 (s, 18 H, 2C(CH3)3). FABMS (m-nitrobenzyl
alcohol): m/z 538 (M + 1), 510 (M + 1 - CO), 481 (M - 2CO),
567 (M + 1 - CO - CO2), 451 (M - NCO - CO2), 402 (M -
PhNO - CO), 374 (M - CO2 - PhNCO). Anal. Calcd for
stirring. The heterogeneous medium became homogeneous
(red) at 120 °C, while being heated. After 6 h, the medium
was cooled and 2 mL of ethanol was added to neutralize the
excess unreacted isocyanate. The complex 3 precipitated as
an orange solid, which was filtered and washed several times
with diethyl ether (80%). Mp: 301 ( 5 °C dec. IR (KBr, cm-1
)
1640 (s, CdO), 1615 (s, CdO). NMR: 1H (CD2Cl2) δ 8.47 (d,
J ) 8 Hz, 2 H), 8.32 (d, J ) 8 Hz, 4 H); 8.22 (d, J ) 5 Hz 2 H);
7.96 (s, 2 H); 7,57 (dd, J 1 ) 8 Hz, J 2 ) 5 Hz, 2 H); 7.29 (d, J
) 8 Hz, 2 H); 7.14 (d, J ) 8 Hz, 2 H); 7.04 (d, J ) 8 Hz, 4 H);
2.35 (s, 6 H, CH3); 2.29 (s, 3 H, CH3). FABMS (m-nitrobenzyl
alcohol): m/z 658 (M + 1), 525 (M + 1 - TolNCO), 391 (M -
2TolNCO), 286 (M - 2TolNCO - NTol). Anal. Calcd for
C
26H29N3O3Pd: C, 58.05; H, 5.43; N, 7.81; Found: C, 57.80;
H, 5.16; N, 7.81.
[2,2′-(tBu )2(bipy)]P d[C(O)N(p-tBu C6H4)OC(O)] (1p). The
same experimental procedure was used as for 1o. In this case,
50 mL of acetone was added to the crude reaction medium
before filtration on Celite (Merck 545), and 25 mL of H2O was
subsequently added to the yellow filtrate. The pale precipitate
formed was decanted and washed with n-pentane. This
precipitate was a mixture of free ligand, traces of the corre-
sponding urea, and the desired complex (70% by 1H NMR).
After extraction of the precipitate with three fractions of 3 mL
of dichloromethane and subsequent evaporation of the solvent,
yellow crystals were formed. Yield: 20%. Mp: 219 ( 5 °C
dec. IR (KBr, cm-1) 1699 (s, CdO), 1617 (s, CdO); 1268 (s,
N-O). NMR: 1H (CD2Cl2) δ 9.76 (d, J ) 6 Hz, 1 H, ortho/
diimine); 9.57 (d, J ) 6 Hz, 1 H, ortho/diimine); 8.07 (s, 2 H,
diimine); 7.66 (d, J ) 5 Hz, 2 H); 7.56 (d, J ) 7 Hz, 2 H,
phenyl); 7.37 (d, J ) 7 Hz, 2 H, phenyl); 1.44 (s, 9 H, C(CH3)3/
diimine); 1.43 (s, 9 H, C(CH3)3/ diimine); 1.32 (s, 9 H, C(CH3)3/
phenyl). FABMS (m-nitrobenzyl alcohol): m/z 538 (M + 1 -
2CO), 537 (M + 1 - tBu), 522 (M + 1 - CO - CO2), 507 (M -
C
35H29N5O2Pd: C, 63.88; H, 4.44; N, 10.64; Found: C, 63.72;
H, 4.29; N, 10.62.
Rea ction of (p h en )P d (d ba ) w ith P h NCO a n d CO2. The
complex (phen)Pd(dba) (50 mg; 0.10 mmol) and 100 mg of 1,-
10-phenanthroline (0.55 mmol) in 15 mL of freshly distilled
benzene under nitrogen were introduced in the autoclave. The
autoclave was then flushed with carbon dioxide three times
with stirring, pressurized to 20 bar, and heated to 80 °C (in
30 min). During heating, at 45 °C, 250 mg of phenyl isocy-
anate (2.10 mmol) was introduced into the medium by a
mechanical device. The stirring was maintained for 5 h at 80
°C. After subsequent cooling and depressurization, the auto-
clave was opened in a glovebox. The orange-brown suspension
that formed was decanted, washed several times with diethyl
ether, and dried in vacuo (45 mg). No palladium complex could
be further characterized in the mother solution. By IR and
1H NMR spectroscopy, this air-stable precipitate proved to be
a 1:1 mixture of complex 3 and another unknown compound
presenting a dissymmetric phenanthroline (Hortho at 9.98 and
9.11 ppm; J ) 6 Hz). A sharp carbonyl absorption at 1690
cm-1 was clearly visible, whereas a second absorption at 1620
cm-1 appeared as a shoulder on the carbonyl absorption of 3.
Attempts to separate the new complex from 3 have as yet been
unsuccessful since both complexes are sparingly soluble.
Complex 1a could not be detected either in the precipitate or
in the mother solution.
t
NCO - CO2), 480 (M + 1 - Bu - 2CO), 402 (M - CO -
(C6H4)NO), 374 (M - CO2 - tBu(C6H4)NCO). Anal. Calcd for
C30H37N3O3Pd: C, 60.66; H, 6.28; N, 7.07; Found: C, 60.88;
H, 6.11; N, 7.01.
Rea ction of 1a a n d Ma leic An h yd r id e. Complex 1a (50
mg; 0.11 mmol) and 120 mg of 1,10-phenanthroline (0.66
mmol) were suspended in 15 mL of freshly distilled nitroben-
zene, and 400 mg of maleic anhydride (4.08 mmol) was added.
The reaction medium was heated at 100 °C with stirring. The
heterogeneous medium became transiently homogeneous, giv-
ing rise to an orange solution, and a dark precipitate began to
form. After 50 min, the medium was cooled, and the precipi-
tate was filtered off and washed several times with diethyl
ether. Elemental analysis, mP, and IR, after comparison with
reported data, allowed its identification as being mainly
(phen)Pd(maleic anhydride) (8) along with some metallic
palladium. No other organometallic species could be identified.
Rea ction of 1a w ith p-Tolyl Isocya n a te. To 50 mg of
complex 1a (0.11 mmol) suspended in 5 mL of freshly distilled
nitrobenzene was added 585 mg of p-tolyl isocyanate (4.40
mmol), and the reaction medium was heated at 142 °C with
Ack n ow led gm en t. We thank Rhoˆne-Poulenc Re-
cherches and the CNRS for financial support.
Su p p or tin g In for m a tion Ava ila ble: Table S1 listing
atomic coordinates for non-hydrogen atoms, Table S2 listing
atomic coordinates for hydrogen atoms, Table S3 listing
thermal parameters for anisotropic atoms, Table S4 listing
bond lengths, and Table S5 listing bond angles (14 pages).
Ordering information is given on any current masthead page.
OM9708485