Synthesis and solid state and solution characterization of mono- and di-(η1-C) carbamoyl-palladium complexes. New efficient palladium-catalyzed routes to carbamoyl chlorides: Key intermediates to isocyanates, carbamic esters, and ureas

Article abstract of DOI:10.1021/om000198w

The catalytic conversion of primary and secondary amines into isocyanates or carbamoyl chlorides is performed using palladium complexes. The palladium-based catalytic systems is very active and avoids the synthesis of phosgene. The palladium (II) complex

Full text of DOI:10.1021/om000198w

Organometallics 2000, 19, 3879-3889
3879
Syn th esis a n d Solid Sta te a n d Solu tion Ch a r a cter iza tion
of Mon o- a n d Di-(η1-C) Ca r ba m oyl-P a lla d iu m
Com p lexes. New Efficien t P a lla d iu m -Ca ta lyzed Rou tes to
Ca r ba m oyl Ch lor id es: Key In ter m ed ia tes to Isocya n a tes,
Ca r ba m ic Ester s, a n d Ur ea s
Michele Aresta,* Potenzo Giannoccaro, Immacolata Tommasi,
Angela Dibenedetto, Anna Maria Manotti Lanfredi, and Franco Ugozzoli
Dipartimento di Chimica, Universita` di Bari, Campus Universitario, Via Orabona 4,
70126 Bari, Italy, and Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica e
Chimica Fisica, Universita` di Parma, Parco Area delle Scienze 17A, 43100 Parma, Italy
Received March 1, 2000
Pd complexes have been used in catalytic conversion of primary and secondary amines
into isocyanates or carbamoyl chlorides, respectively. The latter have been used as
intermediates for the synthesis of carbamates and ureas. The palladium-based catalytic
system is very active and operates in two steps, avoiding the synthesis of phosgene (COCl2),
but making use of CO and Cl2 as in phosgene chemistry. In the first step the palladium(II)
complex PdCl2L2 [L2 ) 2,2′ dipyridine (dipy) or 1,10-phenantroline (phen); L ) triphenylphos-
phine (PPh3)] reacts with the amine [NH2R, R ) n-C3H7 (a ), n-C4H9 (b), n-C5H11 (c); NHRR′,
NRR′ ) CH2(CH2)4N (d ), CH2(CH2OCH2)CH2N (e)] and CO to produce the carbamoyl
complexes PdCl(CONHR)L2 and PdCl(2-x)(CONRR′)xL2 (x ) 1, 2). When primary amines
NH2R, (a , b, and c) are used, only monocarbamoyl complexes [PdCl(CONHR)(dipy) (1a -c),
PdCl(CONHR)(phen) (2a -c), and PdCl(CONHR)(PPh3)2 (3a ,b)] are isolated. Secondary
amines NHRR′ (d and e) afford both monocarbamoyl PdCl(CONRR′)(dipy) (4d ,e) and PdCl-
(CONRR′)(phen) (5d ,e) and dicarbamoyl complexes, Pd(CONRR′)2(dipy) (6d ,e) and Pd-
(CONRR′)2(phen) (7d ). 4d and 6d have been structurally characterized: they are the first
example of mono- and dicarbamoyl complexes, respectively, of the same metal system for
which the solid state structure is reported.The carbamoyl complexes are subsequently reacted
with halogen donors (CuCl2, N-chlorosuccinimide, Cl2, I2) with elimination of the carbamoyl
ligand as isocyanate (primary amines complexes 1-3) or carbamoyl chloride (secondary
amines complexes 4-7) and quantitative formation of the starting Pd(II) complex. Cl2 and
I2 are most effective and selective. They do not generate byproducts and allow an easy and
quantitative recovery of the catalyst, making the reaction of potential utility.
In tr od u ction
The existing attitude to develop ecoefficient syntheses
gives a new role to “nonphosgene-based routes”3,4 to the
mentioned compounds and justifies the new interest in
the chemistry of the metallorganic species mentioned
above.2c,e
The chemistry of transition metal systems [mainly
Ni(II), Pd(II), Pt(II), Cu(I), Cu(II)] bearing the alkoxo-
carbonyl (-COOR)1 or carbamoyl (-CONHR)2a,b moiety
has attracted much attention. Such interest is justified
by the fact that the metallorganic species are intermedi-
ates in innovative syntheses of compounds such as
carbonates, carbamates, ureas, and isocyanates, which
play an important role in the chemical industry.
The chemistry of M-COOR moieties is well docu-
mented in the literature, and Cu(II)-COOR and
Pd(II)-COOR are likely intermediates in the synthesis
of dimethyl carbonates in processes recently developed
by ENIChem4 and Ube,5 respectively. We have shown6
that compounds of formula LnM(COOR)xCl2-x (x ) 1,
2; M ) Ni, Pd) react under mild conditions with CuCl2
or halogens to afford chloroformates (ClCOOR), the
precursors of carbonates, carbamates, or isocyanates.
(1) See for example: (a) Rees, M. W.; Churchill, M. R.; Fettinger, J .
C.; Atwood, J . D. Organometallics 1985, 4, 2179. (b) Bryndza, H. E.
Organometallics 1985, 4, 1686. (c) Bianchini, C.; Meli, A. J . Organomet.
Chem. 1984, 276, 413. (d) Cavinato, G.; Toniolo, L. J . Organomet.
Chem. 1993, 444, 65. (e) Hidai, M.; Kokura, M.; Uchida, Y. J .
Organomet. Chem. 1973, 52, 431. (f) Fitton, P.; J ohnson, M. P.;
McKeon, J . E. J . Chem. Soc., Chem. Commun. 1968, 6. (g) Rivetti, F.;
Romano, U. J . Organomet. Chem., 1978, 154, 323.
(2) See for example: (a) Angelici, R. Acc. Chem. Res. 1972, 5, 335.
(b) Angelici, R.; Green. A. Inorg. Chem. 1972, 11, 2095. (c) Giannoccaro
P.; Tommasi I.; Aresta M. J . Organomet. Chem. 1994, 476, 13. (d)
Kroccher, O.; Koeppel, R. A.; Baiker, A. J . Chem. Soc., Chem. Commun.
1997, 5, 453. (e) Anderson, S.; Hill, A.; Ng, Y. T. Organometallics 2000,
19, 15.
(3) Aresta, M.; Quaranta, E. CHEMTECH 1997, 26 (3), 32.
(4) Rivetti, F.; Romano, U.; Garone, G.; Ghirardini, M. EP Patent
634 390, 1995 (ENIChem); Chem. Abstr. 1995, 122, 136770w.
(5) Yoshida, S.; Tanaka, S. EP Patent 655 433, 1995 (Ube Ind. Ltd.);
Chem. Abstr. 1995, 123, 86588r.
(6) Aresta, M.; Ravasio, N.; Giannoccaro, P. J . Organomet. Chem.
1993, 451, 243.
10.1021/om000198w CCC: $19.00 © 2000 American Chemical Society
Publication on Web 08/23/2000

3880 Organometallics, Vol. 19, No. 19, 2000
Aresta et al.
turned white in about 15 min, nitrogen was pumped off, and
carbon monoxide was admitted (0.1 MPa). The system was
kept under stirring at room temperature for 6 h. The suspen-
sion gradually gave a green solution, from which, by cooling
to 250 K, black-green crystals of pure carbamoyl complex
precipitated (0.331 g, yield 65%). More product was isolated
from the mother liquor. The overall yield was close to 99%.
Anal. Calcd for C14H16ClN3OPd: C, 43.78; H, 4.20; N, 10.93;
Cl, 9.23; Pd, 27.70. Found: C, 43.91; H, 4.15; N, 10.85; Cl, 9.20;
Pd, 27.37. IR (Nujol-KBr, cm-1): ν(NH) 3360 (m), ν(CO) 1590
(vs).
Compounds PdCl(CONHC4H9)(dipy) (1b) and PdCl(CONH-
C5H11)(dipy) (1c) were prepared according to the above pro-
cedure (1b yield 53%, 1c yield 58% as pure crystals) by
addition of n-C4H9NH2 and n-C5H11NH2, respectively.
P d Cl(CONHC4H9)(d ip y) (1b). Anal. Calcd for C15H18ClN3-
OPd: C, 45.25; H, 4.56; N, 10.55; Cl, 8.90; Pd, 26.72. Found:
C, 45.52; H, 4.41; N, 10.42; Cl, 9.03; Pd, 26.53. IR (Nujol-KBr,
cm-1): ν(NH) 3360 (m), ν(CO) 1590 (vs).
Conversely, the chemistry of carbamoylmetal systems
M-(CONRR′)xCl2-x (x ) 1, 2; M ) Ni, Pd, Pt) is scarcely
documented, despite their being known for a long
time2a,b and their potential as generators of ClCONRR′,
chlorocarbamoyl moieties that are precursors of car-
bamates, ureas, and isocyanates. To date, several mono-
carbamoyl [η1-C (W,7 Mn,8 Re,9 Fe,10 Ni),11 η2-C-O (Re,9
Th),12 η-C-O (Fe)]13 and a few dicarbamoyl complexes
[η1-C (Hg,14 Ru)15 and η2-C-O (U12)] have been struc-
turally characterized together with two acyl-carbamoyl
complexes [a cationic Pd-(II)16 and a neutral Pt(II)]17
and an R-chetoacyl carbamoyl [Pt(II)]18 complex.
However, in no cases was the structure of both mono-
and dicarbamoyl complexes of the same metal sys-
tem reported. Moreover, the reactivity of M-C bonds
in “M-CONRR′” systems, for example, as precursors of
carbamoyl-chlorides or isocyanates is scarcely docu-
mented, and the potential in innovative syntheses is not
at all discussed.
P d Cl(CONHC5H11)(d ip y) (1c). Anal. Calcd for C16H20ClN3-
OPd: C, 46.62; H, 4.89; N, 10.19; Cl, 8.60; Pd, 25.81. Found:
C, 46.74; H, 4.69; N, 10.24; Cl, 8.75; Pd, 25.79. IR (Nujol-KBr,
cm-1): ν(NH) 3360 (m), ν(CO) 1590 (vs).
Exp er im en ta l Section
P r ep a r a tion of P d Cl(CONHC3H7)(p h en ) (2a ), P d Cl-
(CONHC4H9)(p h en ) (2b), a n d P d Cl(CONHC5H11)(p h en )
(2c). The pure crystalline compounds 2a , 2b, and 2c were
prepared (2a in 68% yield, 2b in 70% yield, and 2c in 65%
yield) following a procedure similar to the synthesis of 1a
starting from PdCl2(phen) and n-C3H7NH2, n-C4H9NH2, and
n-C5H11NH2, respectively.
P d Cl(CONHC3H7)(p h en ) (2a ). Anal. Calcd for C16H16ClN3-
OPd: C, 47.08; H, 3.95; N, 10.29; Cl, 8.68; Pd, 26.07. Found:
C, 47.22; H, 4.03; N, 10.32; Cl, 8.75; Pd, 26.13. IR (Nujol-KBr,
cm-1): ν(NH) 3320 (m), ν(CO) 1610 (vs).
Gen er a l Com m en ts. All reactions were carried out in
deaerated solvents and in an atmosphere of the proper gas
(dinitrogen or carbon monoxide) using standard vacuum-line
techniques. NMR spectra were measured at 298 K in CDCl3
using a AM 500 MHz Bruker spectrometer. GC-MS analyses
were performed with a Hewlett-Packard 5995 instrument.
Carbamoyl halides were detected by IR spectroscopy and
GC-MS analysis of the reaction solution. Because of partial
decomposition of carbamoyl halides in the GC column, they
were converted into the relevant methylcarbamate (by reaction
with CH3OH/Et3N mixtures or with CH3ONa), which was
determined by GC analysis with a Varian Vista 6000 gas
chromatograph using a SP-2100/01% Carbowax column and
toluene as internal standard.
Mixtures of Cl- and I-carbamoyl were analyzed by ti-
trating the chloride and iodide produced by reaction with
CH3ONa (see later).
Among the isocyanates, only n-C4H9NCO was stable enough
to allow a direct determination by GC-MS. All others required
a conversion in situ into N,N′-ureas by reaction with the proper
amine. Ureas were determined via GC-MS analysis with a
HP 1050 HPLC instrument using a Supelcosil LC-8, 15 cm ×
4.6 mm i.d. column.
P d Cl(CONHC4H9)(p h en ) (2b). Anal. Calcd for C17H18ClN3-
OPd: C, 48.36; H, 4.30; N, 9.95; Cl, 8.40; Pd, 25.20. Found:
C, 47.90; H, 4.12; N, 9.89; Cl, 8.60; Pd, 25.33. IR (Nujol-KBr,
cm-1): ν(NH) 3350 (m), ν(CO) 1610 (vs).
P d Cl(CONHC5H11)(p h en ) (2c). Anal. Calcd for C18H20
-
ClN3OPd: C, 49.56; H, 4.62; N, 9.63; Cl, 8.13; Pd, 24.39.
Found: C, 49.62; H, 4.57; N, 9.58; Cl, 8.20; Pd, 24.29. IR (Nujol-
KBr, cm-1): ν(NH) 3350 (m), ν(CO) 1610 (vs).
P r ep a r a tion of P d Cl(CONHC4H9)(P P h 3)2 (3b). A yellow
suspension of PdCl2(PPh3)2 (0.300 g, 0.43 mmol) and n-
butylamine (0.6 mL, 6.07 mmol; amine/Pd ) 14) in CH3CN
(15 mL) was stirred under dinitrogen atmosphere until a pale-
cream solution was obtained. Nitrogen was pumped off, carbon
monoxide (0.1 MPa) was admitted, and the system was stirred
at room temperature until a pale-yellow precipitate was
formed. The product was filtered, washed twice with cold
ethanol (5 mL), and dried in vacuo (0.275, yield 83% as pure
crystals). More product was isolated from the mother solution
with an overall yield > 98%. Anal. Calcd for C41H40ClNOP2-
Pd: C, 64.24; H, 5.26; N, 1.83; Cl, 4.63; P, 8.09; Pd, 13.88.
Found: C, 64.08; H, 5.24; N, 1.79; Cl, 4.68; P, 8.10; Pd, 13.6.
IR (Nujol-KBr, cm-1): ν(NH) 3380 (m), ν(CO) 1605 (vs).
Compound P d Cl(CONHC3H7)(P P h 3)2 (3a ) was prepared
according to the above procedure by using n-C3H7NH2 (yield
78%). Anal. Calcd for C40H38ClNOP2Pd: C, 63.44; H, 5.09; N,
1.86; Cl, 4.71; P, 8.24; Pd, 14.14. Found: C, 63.50; H, 4.98; N,
1.89; Cl, 4.83; P, 8.21; Pd, 14.09. IR (Nujol-KBr, cm-1): ν(NH)
3378 (m), ν(CO) 1605 (vs).
Mon ocar bam oyl Com plexes of P r im ar y Am in es. P r epa-
r a tion of P d Cl(CONHC3H7)(d ip y) (1a ). To a suspension of
freshly prepared PdCl2(dipy) (0.370 g, 1.12 mmol) in CH3CN
(8 mL) was added n-propylamine (0.4 mL, 4 mmol; amine/Pd
) 3.5), and the suspension was allowed to react at room
temperature under nitrogen atmosphere. The reaction mixture
(7) Adams, R. C.; Chodosh, D. F.; Golembeski, N. M. Inorg. Chem.
1978, 17, 266.
(8) Brenemann, G. L.; Chipman, D. M.; Galles, C. J .; J acobson, R.
A. Inorg. Chim. Acta 1969, 3, 447.
(9) Wang, T. F.; Hwu, C. C.; Tsai, C. W.; Wen, Y. S. Organometallics
1998, 17, 131.
(10) Urban, R.; Polborn, K.; Beck, W. Z. Naturforsh. Sect. A 1999,
54, 385.
(11) Hoberg, H.; Fananas, V. J .; Angermund, K.; Kruger, C.; Romao,
M. J . J . Organomet. Chem. 1985, 281, 379.
(12) Fagan, P. J .; Manriquez, J . M.; Vollmer, S. H.; Day Secaur, C.;
Day, V. W.; Marks, T. J . J . Am. Chem. Soc. 1981, 103, 2206.
(13) Anderson, S.; Hill A. F.; Slawin, A. M. Z.; White, A. J . P.;
Williams, D. J . Inorg. Chem. 1998, 37, 5948.
(14) Toman, K.; Hess, G. G. Z. Kristallogr. 1975, 142, 35.
(15) Gargulak, J . D.; Gladfelter, W. L. Inorg. Chem. 1994, 33, 253.
(16) Huang, L.; Ozawa, F.; Osakada, K.; Yamamoto, A. J . Orga-
nomet. Chem. 1990, 383, 587.
(17) Huang, T.-M.; Chen, J .-T.; Lee, G.-H.; Wang, Y. Organometallics
1991, 10, 175.
Mon oca r b a m oyl Com p lexes of Secon d a r y Am in es.
P r ep a r a tion of P d Cl[CON(CH2)4CH2](d ip y) (4d ). To a
suspension of freshly prepared PdCl2(dipy) (0.865 g, 2.59 mmol)
in CH3CN (15 mL) was added piperidine (0.443 g, 5.18 mmol;
amine/Pd ) 2), and the yellow suspension was allowed to react
under stirring with CO (0.1 MPa) at room temperature for 3
h. The suspension gradually turned to olive green. The product
was filtered off (yield close to 99%), washed with a mixture of
(18) Huang, T.-M.; You, Y.-J .; Yang, C.-S.; Tseng, W.-H.; Chen, J .-
T.; Cheng, M.-C.; Wang, Y. Organometallics 1991, 10, 1020.

Mono- and Di-(η1-C) Carbamoyl-Pd Complexes
Organometallics, Vol. 19, No. 19, 2000 3881
Ta ble 1. Ch a r a cter iza tion of Mon o- a n d
Dica r ba m oyl Com p lexes th r ou gh Rea ction w ith
HCl
CH3CN/CH3OH (10:1) to dissolve impurities of piperidinium
chloride, and dried in vacuo (0.826 g, yield 78%). Anal. Calcd
for C16H18ClN3OPd: C, 46.85; H, 4.24; N, 10.24; Cl, 8.64; Pd,
25.94. Found: C, 46.58; H, 4.09; N, 10.18; Cl, 8.66; Pd, 25.69.
IR (Nujol-KBr, cm-1): ν(CO) 1590 (vs). 1H NMR (CDCl3,
carbamoyl moiety): 1.3 (b, 1 H), 1.4 (b, 1 H), 1.5 (b, 1 H), 1.6
(q, 2 H), 1.7 (b, 1 H), 3.5 (m, 2 H), and 4.2 (m, 2 H) ppm. 13C
NMR (CDCl3, carbamoyl moiety): 174 (s), 25.0 (s), 26.3 (s),
26.5 (s), 44.5 (s), 48.8 (s) ppm.
compound
amount (g) (mmol)
V CO(mL) (mmol)
CO/Pd
1a
2b
3b
5d
6d
7d
0.096 (0.25)
0.316 (0.75)
0.234 (0.31)
0.195 (0.45)
0.136 (0.28)
0.150 (0.29)
5.4 (0.24)
16.0 (0.71)
6.5 (0.29)
9.7 (0.43)
11.4 (0.49)
11.2 (0.50)
0.96
0.95
0.94
0.96
1.75
1.72
P r ep a r a tion of P d Cl[CON(CH2)4CH2](p h en ) (5d ). The
pure crystalline olive green product was prepared (in 80%
yield) according to the procedure reported above starting from
(CDCl3, carbamoyl moiety): 196.2 (s), 25.6 (s), 26.9 (s), 27.3
(s), 41.8 (s), and 49.1 (s) ppm.
PdCl2(phen) and piperidine at 313 K. Anal. Calcd for C18H18
-
ClN3OPd: C, 49.79; H, 4.18; N, 9.67; Cl, 8.15; Pd, 24.51.
Found: C, 49.80; H, 4.12; N, 9.61; Cl, 8.22; Pd, 24.50. IR (Nujol-
KBr, cm-1): ν(CO) 1585 (vs).
P r epar ation of P d[CONCH2(CH2OCH2)CH2]2(dipy) (6e).
To a suspension of PdCl2(dipy) (0.500 g, 1.5 mmol), in CH3CN
(15 mL), was added morpholine (1.17 g, 13.45 mmol; amine/
Pd ) 9), and the mixture was allowed to react with CO at
atmospheric pressure and room temperature for 4-5 h. The
resulting brown-orange solid mixture (dicarbamoyl complex
and morpholinium salt) was filtered and purified using a
solution of CH3ONa as described above. Yield: 0.477 g, 65%.
Anal. Calcd for C20H24N4O4Pd: C, 48.94; H, 4.93; N, 11.41; Pd,
21.68. Found: C, 48.69; H, 4.88; N, 11.37; Pd, 21.49. IR (Nujol-
KBr, cm-1): ν(CO) 1512 (vs).
P r ep a r a t ion of P d Cl[CONCH2(CH2OCH2)CH2](d ip y)
(4e). To a suspension of freshly prepared PdCl2(dipy) (0.50 g,
1.50 mmol) in CH3OH (12 mL) was added morpholine (0.45 g,
5.17 mmol; amine/Pd ) 3.5), and the mixture was allowed to
react with CO at 313 K at ambient pressure for 6 h. The
resulting green solution was concentrated under reduced
pressure to one-third its volume, Et2O (5 mL) was added, and
the solution was left overnight at 273 K. Yellow crystals of
pure monocarbamoyl complex were obtained (0.400 g, yield
65%). Anal. Calcd for C15H16ClN3O2Pd: C, 43.71; H, 3.91; N,
10.19; Cl, 8.60; Pd, 25.82. Found: C, 43.68; H, 3.80; N, 10.15;
Cl, 8.65; Pd, 25.67. IR (Nujol-KBr cm-1): ν(CO) 1595 (sh) and
1575 (vs). The complex is moisture sensitive. By exposure to
air, the CO bands shift to 1550 cm-1 and a new broad band
centered at 3520 cm-1 appears. By heating in vacuo the
original complex is regenerated without CO loss.
P r ep a r a tion of P d [CON(CH 2)4CH2]2(p h en ) (7d ). To a
suspension of a freshly prepared PdCl2(phen) (0.700 g, 1.96
mmol) in CH3CN (17 mL) was added piperidine (1.67 g, 19.6
mmol; amine/Pd ) 10), and the resulting mixture was re-
acted with CO (0.1 MPa) at room temperature for about
4 h. The initial yellow mixture gradually turned to orange.
The resulting solid mixture of Pd[(CON(CH2)4CH2]2(phen) and
HN(CH2)4CH2‚HCl was filtered off (1.35 g). Red crystals of pure
dicarbamoyl complex (0.698 g, yied 70%) were obtained after
elimination of the ammonium salt following the methodology
reported above. Anal. Calcd for C24H28N4O2Pd: C, 56.42; H,
5.52; N, 10.98; Pd, 20.83. Found: C, 56.27; H, 5.47; N, 10.95;
Pd, 20.68. IR (Nujol-KBr, cm-1): ν(CO) 1540 (vs).
Rea ction of Dica r ba m oyl Com p lexes w ith Am on iu m
Sa lt s: Ba ck -Con ver sion in t o Mon oca r b a m oyl Com -
p lexes. To an orange solution of 7d (0.250 g, 0.49 mmol)
in ethanol (6 mL) was added 0.60 g (0.49 mmol) of HCl‚
P r ep a r a t ion of P d Cl[CONCH2(CH 2OCH2)CH2](p h en )
(5e). To a suspension of freshly prepared PdCl2(phen) (0.270
g, 0.80 mmol) in CH3CN (10 mL) was added morpholine (0.25
g, 2.87 mmol; amine/Pd ) 3.6), and the suspension was allowed
to react at 313 K with CO at atmospheric pressure for 6 h.
The resulting suspension was filtered, and the solid was
washed with CH3OH and dried in vacuo (0.296 g, yield 85%).
Anal. Calcd for C17H16ClN3O2Pd: C, 46.81; H, 3.70; N, 9.63;
Cl, 8.13; Pd, 24.39. Found: C, 46.58; H, 3.68; N, 9.57; Cl, 8.10;
Pd, 24.29. IR (Nujol-KBr, cm-1): ν(CO) 1570 (vs).
Dica r ba m oyl Com p lexes of Secon d a r y Am in es. P r ep a -
HN(CH2)4CH2 at room temperature under dinitrogen. After
mixing, the color turned to yellow-green. The solution was
filtered and concentrated to one-third its volume, and diethyl
ether (5 mL) was added. By cooling to 273 K yellow-green
crystals of monocarbamoyl 5d (0.18 g, 85%) were obtained and
identified by comparison with an authentic sample.
Ch a r a cter iza tion of th e Ca r ba m oyl Com p lexes by
Rea ction w ith HCl. The CO quantitative analysis was
carried out by decomposing a weighted amount of a carbamoyl
complex with an excess of HCl (10-2 M dry HCl in toluene).
The reaction was carried out in an inverted Y-shaped reactor
connected to a gas buret. The gas evolved was also analyzed
by GC, and only trace amounts of CO2 were found. Table 1
shows analytical data for some complexes.
R ea ct ion of Ca r b a m oyl Com p lexes of Secon d a r y
Am in es w ith Cu Cl2: Syn th esis of Ca r ba m oyl Ch lor id es.
In a typical reaction, the carbamoyl complex 4d (0.320 g, 0.78
mmol) in 4 mL of THF and CuCl2 (0.210 g, 1.56 mmol) in 3
mL of THF were charged separately into two branches of an
inverted Y-shaped glass reactor. After mixing, the resulting
liquid and solid were analyzed. The IR spectrum of the
supernatant liquor shows a band at 1735 cm-1 ascribed to the
r a tion of P d [CON(CH2)4CH2]2(d ip y) (6d ). To a suspension
of freshly prepared PdCl2(dipy) (0.531 g, 1.59 mmol) in CH3-
CN (12 mL) was added piperidine (1.36 g, 15.9 mmol; amine/
Pd ) 10), and the resulting mixture was reacted with CO (0.1
MPa) at room temperature for about 2 h. The initial yellow
color gradually converted into orange. From the solution ca.
0.2 g of piperidine hydrochloride was isolated by filtration, and
the mother solution was concentrated to half volume under
reduced pressure. The salt that eventually precipitated was
eliminated again by filtration. The solution was kept overnight
at 278 K to afford impure red crystals of the dicarbamoyl
complex (0.74 g). Further purification for eliminating the
piperidinium hydrochloride was necessary. The crude product
(containing about 3.3% in weight of chlorine) was suspended
in 10 mL of CH3CN containing piperidine (1 mL), and 2.5 mL
of a 0.3 N solution of CH3ONa in ethanol was added dropwise
under stirring at 273 K. The resulting orange suspension was
filtered and concentrared to half its volume and kept at 278
K overnight. Red crystals of pure dicarbamoyl complex pre-
cipitated and were collected by filtration (0.556 g, yield 72%
with respect to initial Pd). Anal. Calcd for C22H28N4O2Pd: C,
54.32; H, 5.80; N, 11.50; Pd, 21.85. Found: C, 54.19; H, 5.78;
N, 11.47; Pd, 21.77. IR (Nujol-KBr, cm-1): ν(CdO) 1545 (vs).
1H NMR (CDCl3, carbamoyl moiety): 1.4 (8H, pseudo quintet,
J ≈ 5.8 Hz), 1.5 (4 H, pseudo quintet, J ≈ 5.4 Hz), 3.5 (4 H,
broad multiplet) and 4.2 (4 H, broad multiplet) ppm. 13C NMR
carbamoyl chloride ClCON(CH2)4CH2. The GC-MS spectrum
shows the presence of chlorocarbamoyl by comparison with an
authentic sample synthesized by an independent route. m/ z
(relative intensity %): 147 (M+, 68), 112 (100), 106 (19), 84
(19), 69 (38), 56 (37), 55 (21), 42 (30), 41 (5), 39 (38). After

3882 Organometallics, Vol. 19, No. 19, 2000
Aresta et al.
reaction with CH3ONa or NEt3-CH3OH the peak of the Cl-
carbamoyl species disappeared and that of the relevant meth-
ylcarbamate appeared, which was identified by comparison
with the fragmentation spectrum of an authentic sample. The
conversion of the Cl-carbamoyl into methylcarbamate allowed
the quantitative determination of the Cl-carbamoyl formed.
The solid revealed to be a mixture of PdCl2(dipy) and CuCl,
which were separated and identified as previously reported.6
Other mono- and dicarbamoylpiperidine or mono- and
dicarbamoylmorpholine complexes were reacted according to
the above procedure.
Compounds 4d ,e and 5e were reacted in a similar proce-
dure with halosuccinimide, affording ClC(O)N(CH2)4CH2 and
ClC(O)NCH2(CH2OCH2)CH2, which respectively were quan-
titatively determined by GC as their carbamate derivatives
formed quantitatively with respect to the starting Pd-car-
bamoyl complex.
Rea ction of Ca r ba m oyl Com p lexes of P r im a r y a n d
Secon d a r y Am in es w ith Ha logen s (Cl2 a n d I2): Syn th esis
of Isocya n a tes a n d Ca r ba m oyl Ch lor id es, Resp ectively.
Rea ction of 2b w ith I2: Syn th esis of n -Bu tyl Isocya n a te.
A suspension of 2b (0.105 g, 0.25 mmol) in 3 mL of hexane
and a solution of I2 (0.63 g, 0.25 mmol) in hexane (5 mL) were
charged separately into the two branches of an inverted
Y-shaped glass reactor under dinitrogen atmosphere. The
reactor was closed, and the iodine solution was added to the
carbamoyl suspension. A rapid reaction occurred. The IR
spectrum of the solution displayed the n-butylisocyanate band
at 2278 cm-1. The suspension was filtered, and the isocyanate
was determined by GC-MS. EI-MS: m/z (% intensity) 98 (M+,
20), 70 (13), 56 (34), 43 (100) 41 (96). The formation of
CH3OC(O)NHC4H7 (obtained after reaction of n-C4H7NCO with
CH3OH) was quantitative with respect to the Pd-carbamoyl
starting species. The residual solid analyzed for PdClI(phen).
Analysis of the solid. Calcd for C12H8ClIN2Pd: Cl, 7.90; I,
28.27; Pd 23.70. Found: Cl 7.77; I, 30.80; Pd, 23.59.
Other monocarbamoyl complexes (1a -c, 2a , 2c, 3a ,b) were
reacted with I2 according to the same procedure. Isocyanates
of the n-propyl- and n-pentylamine, which completely decom-
pose in the GC column, were detected by IR. [C3H7NdCdO:
IR (hexane), ν(CO) 2262 cm-1; C5H11NdCdO: IR (hexane)
ν(CO) 2268 cm-1] and quantitatively determined by reaction
with CH3OH or an amine as the corresponding methylcar-
bamate or urea derivatives (see later).
ClCONCH2(CH2OCH2)CH2 obtained from compounds 4e
and 5e was characterized by IR and GC-MS. IR (THF
solution): ν(CO) 1735 cm-1. EI-MS (% intensity): m/z, 149 (M+,
30), 134 (38), 114 (57), 106 (5), 86 (30), 70 (36), 56 (100), 42
(72).
Its carbamate derivative, obtained by reaction with
CH3OH/Et3N, was also characterized (see below) and quanti-
tatively determined by GC. This analysis showed the quantita-
tive conversion (>99%) of the metal-bound carbamoyl moiety
into the Cl-carbamoyl product.
Rea ction of Ca r ba m oyl Com p lexes of P r im a r y Am in es
w ith Cu Cl2: Syn th esis of Isocya n a tes. The reaction of
monocarbamoyl complexes 1a -c, 2a -c, a n d 3a ,b with CuCl2
(which was performed according to the procedure described
for carbamoyl complexes of secondary amines) afforded quan-
titatively the isocyanates n-C3H7NCO, n-C4H9NCO, and n-C5H11-
NCO, which were analyzed as methylcarbamate derivatives
(after reaction with CH3OH) or as ureas (after reaction with
amines, see below). A quantitative conversion (>99%) of the
metal-bound carbamoyl moiety into isocyanate was obtained.
Rea ction of Ca r ba m oyl Com p lexes of P r im a r y a n d
Secon d a r y Am in es w ith N-Ch lor osu ccin im id e: Syn th e-
sis of Isocya n a tes a n d Ca r ba m oyl Ch lor id es, Resp ec-
tively. Rea ction of 3b w ith N-Ch lor osu ccin im id e: Syn -
th esis of n -Bu tylisocya n a te. 3b (0.213 g, 0.27 mmol) in THF
(2 mL) and N-chlorosuccinimide (0.035 g, 0.26 mmol) in THF
(1 mL) were charged into the inverted Y-shaped reactor (see
above). The reactants were mixed and allowed to react for 10
min. From the reaction mixture a yellow solid, which analyzed
for (PPh3)2PdCl2, was separated by filtration. The IR spectrum
of the liquid phase showed bands at 2272 (m) and 1720 (s)
cm-1, assigned respectively to n-C4H9NCO and succinimide.
The presence of these species was confirmed by GC-MS.
n-C4H9NCO was formed quantitatively with respect to the
starting carbamoyl complex as shown by GC analysis of the
methylcarbamate derivative (see later). EI-MS: m/z (% inten-
sity) for NH(COCH2)2, 100 (M+, 5), 99 (100), 56 (64). Analysis
of the solid residue. Calcd for C36H30Cl2P2Pd: Cl, 10.10; P, 8.82;
Pd, 15.16. Found: Cl, 10.25; P, 8.87; Pd, 14.95.
Compounds 1a -c, 2a -c, and 3a were reacted in a similar
way with halosuccinimide, affording the relevant isocyanate
(n-C3H7NCO, n-C4H9NCO, and n-C5H11NCO) in almost quan-
titative yield (>98%) with respect to the starting carbamoyl
complex.
Rea ction of 5d w ith N-Ch lor osu ccin im id e. The reaction
of 5d (0.180 g, 0.41 mmol) in C6H6 (3 mL) with N-chlorosuc-
cinimide (0.055 g, 0.41 mmol) was carried out as described
above. The reaction mixture was filtered, and the yellow
residue and the solution were analyzed. Carbamoyl chloride
(IR band at 1735 cm-1) was formed in very high yield (>98%),
as shown by the GC quantitative determination of its meth-
Rea ction of 7d w ith Cl2. The orange suspension of 7d
(0.300 g, 0.59 mmol) in C6H6 (6 mL) was reacted with a stream
of Cl2 at room temperature. It rapidly turned yellow.
The IR spectrum of the liquid phase shows the presence
of a band at 1735 cm-1 assigned to the ν(CO) of ClC(O)-
N(CH2)4CH2, which was qualitatively analyzed by GC-MS and
quantitatively determined as its carbamate derivative. The
solid yellow reaction product was filtered and identified as
PdCl2(phen) by elemental analysis and comparison of the IR
spectrum with that of an authentic sample. The Pd catalyst
was quantitatively recovered.
Other carbamoyl compounds (4d ,e, 5d ,e, 6d ,e) were reacted
with Cl2 according to the same procedure. The GC-MS
analysis of the in situ reaction solution with a NEt3/CH3OH
mixture showed the formation of the carbamate derivative of
the carbamoyl chlorides in a quantitative yield with respect
to Pd-carbamoyl species.
Rea ction of 7d w ith I2. The orange suspension of 7d (0.105
g, 0.21 mmol) in 4 mL of hexane and the solution of I2 (0.107
g, 0.42 mmol) in hexane (5 mL) were separately charged into
the two arms of an inverted Y-shaped reactor under dinitrogen
atmosphere. The reactor was closed, and the iodine solution
was added to the carbamoyl suspension at room temperature.
A rapid reaction occurred. The IR spectrum of the solution
displayed a band at 1742 cm-1 assigned to the CdO stretching
of IC(O)N(CH2)4CH2, which was analyzed as its carbamate
derivative (see below).The hexane solution of the carbamoyl
iodide was filtrated and reacted with CH3ONa 0.5 N (1 mL in
CH3OH). NaI was extracted with H2O and titrated. Found:
0.40 mol of I-, with a 95% yield with respect to the amount
expected to be generated in the following reactions:
ylcarbamate CH3OC(O)N(CH2)4CH2 (obtained by reaction with
CH3ONa). The yellow residue analyzed for PdCl[N(COCH2)2]-
(phen). Anal. Calcd for C16H12ClN3O2Pd: Pd, 25.33; Cl, 8.44.
Found: Pd, 25.39; Cl, 8.60. IR (Nujol/KBr, cm-1): ν(CO) 1750
(vs).
(phen)Pd[C(O)N(CH2)4CH2]2 + 2 I2 f
(phen)PdI2 + 2 IC(O)N(CH2)4CH2 (1)
This compound reacts in methanol with HCl to produce
PdCl2(phen) and succinimide. It reacts also with Cl2 to afford
PdCl2(phen) and N-Cl-succinimide.

Mono- and Di-(η1-C) Carbamoyl-Pd Complexes
2 IC(O)N(CH2)4CH2 + 2 CH3ONa f
Organometallics, Vol. 19, No. 19, 2000 3883
(CH 3O)C(O)NCH 2(CH 2OCH 2)CH 2. IR (hexane/CH3OH/
NEt3): ν(CO), 1718 cm-1. EI-MS: m/z (% intensity) 145 (M+,
27), 130 (57), 114 (11), 100 (19), 70 (16), 56 (36), 42 (100).
(n -C3H7NHCOOCH3): IR (hexane/CH3OH), ν(CO), 1731
cm-1. EI-MS: m/z (% intensity), 117 (M+, 20), 102 (4), 89 (4),
88 (100), 59 (20), 44 (45).
(n -C4H9NHCOOCH3). IR (hexane/CH3OH): ν(CO), 1731
cm-1. EI-MS: m/z (% intensity), 131 (M+, 9), 88 (100), 59 (15);
57 (12), 44 (51).
(n -C5H11NHCOOCH3). IR (hexane/CH3OH): ν(CO), 1738
cm-1. EI-MS: m/z (% intensity), 145 (M+, 5), 130 (1), 102 (2),
88 (100), 76 (11), 59 (13), 44 (40).
Ch a r a cter iza tion of N,N′-Ur ea s. These compounds were
obtained by reaction (molar ratio 1:1) of the relevant car-
2 CH3O-C(O)N(CH2)4CH2 + 2 NaI (2)
The brown solid residue of the filtration was identified as PdI2-
(phen) by elemental analysis and by comparison of its IR
spectrum with that of an authentic sample prepared by
reaction of Pd-acetate, KI, and phen. (see below). Anal. Calcd
for C12H8N2I2Pd: Pd, 19.69; I, 46.97. Found: Pd, 19.73; I,
46.88.
The reaction of 6d ,e and 6e with I2 according to the same
procedure afforded quantitatively IC(O)N(CH4)4CH2 and IC-
(O)NCH2(CH2OCH2)CH2, which were detected in solution by
IR spectroscopy (IR, ν(CO) 1742 cm-1) and determined by GC
as their methylcarbamate derivatives (see below).
bamoyl chloride or isocyanate with an amine (HN(CH2)4CH2,
Syn th esis of P d I2(p h en ). To 0.111 g (0.50 mmol) of Pd-
(OAc)2 dissolved in EtOH (10 mL) were added KI (0.2 g, 1.2
mmol; I/Pd ) 2.4, dissolved in 10 mL of EtOH) and phenant-
roline (0.10 g, 0.5 mmol, dissolved in 10 mL of EtOH). After
30 min the resulting precipitated pink-brown product was
filtered, washed with an H2O/EtOH mixture (1:1, v/v), and
dried in vacuo. Anal. Calcd for C12H8N2I2Pd: Pd, 19.69; I,
46.97. Found: Pd, 19.70; I, 46.90.
Rea ction of 5d w ith I2: Qu a n tita tive Deter m in a tion
of Ch lor o- a n d Iod oca r ba m oyl Sp ecies. A suspension of
5d (0.120 g, 0.28 mmol) in 3 mL of hexane and a solution of I2
(0.071 g, 0.28 mmol) in hexane (5 mL) were allowed to react
as described above, and the reactor was heated for 15 min at
323 K. The reaction mixture was filtered, and the solution and
the residue were analyzed. The solution displayed IR bands
at 1742 (m) and 1735 (sh) cm-1, which shifted to 1718 (s) cm-1
by adding CH3OH/NEt3. The GC-MS spectrum showed only
HNCH2(CH2OCH2)CH2, n-C3H7NH2, n-C4H9NH2, n-C5H11NH2)
in hexane. The reaction took place in a few minutes at room
temperature. Heating to 323 K brought the reaction to
completion. The resulting mixture was concentrated un-
der vacuum almost to dryness and the residue extracted with
CH3CN (5 mL). Cooling to 268 K allowed the urea to separate
as pure solid.
N,N′-Dip ip er id in eu r ea CO[N(CH2)4CH2]2. EI-MS: m/z
(% intensity), 196 (M+, 11), 112 (16), 84 (100), 69 (33), 56 (19),
41 (40).
N,N′-Dim or p h olin eu r ea CO[NCH 2(CH 2OCH 2)CH 2]2.
EI-MS: m/z (% intensity), 200(M+, 9), 169(45), 143(15), 114-
(75), 86(36), 70(100), 42(48).
N,N′- Dip r op ylu r ea CO(n -C3H7NH)2. IR (CH3CN): ν(CO),
1670 cm-1. EI-MS: m/z (% intensity), 145 (9), 144 (M+, 92),
116 (5), 115 (22), 87 (20), 86 (10), 58 (55), 43 (100).
N,N′-Dibu tylu r ea CO(n -C4H9NH)2. IR (CH3CN): ν(CO),
1670 cm-1. EI-MS: m/z (% intensity), 172 (M+, 34), 101 (18),
100 (17), 74 (35), 44 (100).
N,N′-Dip en tylu r ea CO(n -C5H11NH)2. IR (CH3CN), ν(CO),
1670 cm-1. IR (Nujol mull): ν(N-H) 3350 cm-1, ν(CO), 1630
and 1580 cm-1. EI-MS: m/z (% intensity), 200 (M+, 35), 171
(32), 144 (13), 114 (24), 88 (21), 87 (20), 44 (100), 43 (74), 41
(51).
the presence of ClC(O)N(CH2)4CH2, as IC(O)N(CH2)4CH2
decomposed in the GC column.
Halogens were quantitatively determined by titration as
reported above.
As an example, when 4d (0.130 g, 0.30 mmol) and I2 (0.076
g, 0.30 mmol) were reacted, the filtered hexane solution after
reaction with 0.55 mL of 0.6 N CH3ONa in methanol and
extraction with H2O gave 0.08 mol of Cl- and 0.19 mol of
Cr ysta l Str u ctu r e Deter m in a tion of 4d a n d 6d . Single
crystals of ca. 0.2 × 0.3 × 0.4 (4d ) and 0.3 × 0.3 × 0.5 (6d )
mm suitable for X-ray analyses were mounted on glass rods
without protection from the air. The crystal data and the most
relevant experimental parameters used in the X-ray measure-
ments and in the crystal structure analyses are reported in
Table 2.
I-, corresponding to 30% ClC(O)N(CH2)4CH2 and 70% IC(O)-
N(CH2)4CH2 (conversion yield: 90% with respect to the initial
4d compound). The elemental analyses of the solid residue
showed that it is a mixture of PdCl(I)(dipy) and PdI2(dipy).
Similar reactivity was observed by reacting compounds 4e
and 5e with I2.
The X-ray experiments were carried out on a Philips PW100
Con ver sion of Ca r ba m oyl Ch lor id es a n d Isocya n a tes
(4d ) and on
a Siemends AED (6d ) diffractometer using
in t o Ca r b a m a t es a n d N,N′-Ur ea s. ClC(O)N(CH2)4CH2,
graphite-monocromated Mo KR radiation (λ ) 0.71073 Å). For
both compounds the intensities were calculated from profile
analysis according to the Lehmann and Larsen method.19
During the two data collections of 4d and 6d , one standard
reflection for each compound, collected every 100, showed no
significant fluctuation. The intensities were corrected for
Lorentz and polarization but not for absorption effects. The
two structures were solved by the Patterson method using
SHELX8620 and direct methods using SIR9221 and then
completed by a Fourier ∆F map and refined by full-matrix
IC(O)N(CH2)4CH2, ClC(O)NCH2(CH2OCH2)CH2, and IC(O)-
NCH2(CH2OCH2)CH2 obtained as reported above were reacted
with a 5:2 methanol-NEt3 mixture (1 mL) or with the proper
amine. The filtered solution was warmed to 313 K. The
reaction took place during the warming-up process. The formed
isocyanates RNCO (R ) n-C3H7, n-C4H9, n-C5H11) were reacted
with CH3OH or amines.
Piperidinecarbamates, morpholinecarbamates, N-alkylcar-
bamates, or N,N′-ureas were isolated and identified by means
of IR and mass spectra. N,N-Ureas were also isolated in the
solid state as crystalline pure products in quantitative yield.
Ch a r a cter iza tion of Ca r ba m a tes. Carbamates were ob-
tained in quantitative yield by reacting either the relevant
carbamoyl chloride with CH3OH/NEt3 or the isocyanate with
CH3OH. They were identified by their GC-MS spectrum.
least-squares methods on
F
using SHELX96.22 For both
complexes the parameters refined were the following: the
(19) Lehmann, M. S.; Larsen, F. K Acta Crystallogr., Sect, A 1974,
30, 580.
(20) Sheldrick, G. SHELX86, Program for Crystal Structure Solu-
tions; University of Go¨ttingen: Germany, 1986.
(21) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. SIR92. J . App. Crystallogr. 1994,
27, 435.
(CH3O)C(O)N(CH2)4CH 2. IR
(hexane/CH3OH/NEt3):
ν(CO), 1718 cm-1. EI-MS: m/z, (% intensity) 143 (M+, 35), 142
(22) Sheldrick, G. M. SHELX96, Program for the refinement of
crystal structures; University of Go¨ttingen: Germany, 1996.
(28), 128 (100), 112 (9), 84 (29), 59 (5), 56 (21), 55 (12), 42 (38).

3884 Organometallics, Vol. 19, No. 19, 2000
Aresta et al.
Ta ble 2. Exp er im en ta l Da ta for th e X-r a y
Diffr a ction Stu d ies
Palladium monocarbamoyl complexes PdCl(CONHR)-
(dipy) (1a -c), PdCl(CONHR)(phen) (2a -c), and PdCl-
(CONHR)(PPh3)2 (3a ,b) [(dipy ) 2,2′-dipyridine; phen
4d
6d
formula
cryst syst
C
16H18ClN3OPd
C22H28N4O4Pd
orthorhombic
Pna21
)
1,10-phenantroline; PPh3) triphenylphosphine;
orthorhombic
Pbca
R) n-C3H7 (a ), n-C4H9 (b), n-C5H11 (c)] have been
prepared in CH3CN according to eq 3.
space group
cell params at 295 Ka
a, Å
b, Å
c, Å
V, Å3
Z
17.880(5)
11.301(5)
16.378(5)
3309(2)
8
1.647
1648
410.191
12.87
ω/2θ
e0.16
6-50
0 e h e 21
0 e k e 13
0 e l e 19
3304
16.089(5)
16.576(5)
8.216(5)
2191(2)
4
1.476
1000
486.889
8.71
ω/2θ
e0.08
6-48
0 e h e 18
0 e k e 19
0 e l e 9
2007
PdCl2L2 + 2 NH2R + CO f
PdCl(CONHR)L2 + NH2R‚HCl (3)
D
calcd, g cm-3
An excess of amine (RNH2/Pd ) 3-4) was used. The
reaction proceeds via the formation of a white Pd(II)
complex whose elemental analyses are consistent with
an amine complex of composition PdCl2(NH2R)L2.25
Mono- and dicarbamoyl complexes of formula PdCl-
(CONRR′)(dipy) (4d ,e), PdCl(CONRR′)(phen) (5d ,e), Pd-
(CONRR′)2(dipy) (6d ,e), and Pd(CONRR′)2(phen) (7d )
F(000)
mol wt
linear abs coeff, cm-1
scan type
scan speed, deg/min
2θ range, deg
index ranges
[NRR′ ) N(CH2)4CH2 (d ), NCH2(CH2OCH2)CH2 (e)]
have been prepared following the two-step procedure
reported in eqs 4 and 5.
no. of reflns measd
no. of unique data
2916 (Rint ) 0.03) 1826 (Rint ) 0.05)
no. of params, restraints 202, 0
265, 1
0.180
0.128, 0
0.066
858
wR2 (all data)b
a,b23
0.125
0.078, 0
0.044
1798
PdCl2L2 + 2 NHRR′ + CO h
R1 [I>4σ(I)]b
PdCl(CONRR′)L2 + NHRR′‚HCl (4)
no. of obsd reflns
criterion for obsd
goodness-of-fit on
F2 (all data)b
F
o g 4σ(Fo)
Fo g 4σ(Fo)
0.85
PdCl(CONRR′)L2 + CO + 2 NHRR′ h
Pd(CONRR′)2L2 + NHRR′. HCl (5)
0.896
maximum shift/σ
peak, hole in final
difference map, e Å-3
extinction coeff
0.208
0.99, -1.21
0.91
1.68, -1.32
The solvent can play an important role in this reaction.
In fact, when the reaction is carried out in ethanol, the
amine carbonylation process stops at the first step (eq
4) and only monocarbamoyl complexes can be isolated,
also in the presence of an excess of amine.
In CH3CN, the carbonylation proceeds further and
dicarbamoyl complexes are obtained (eq 5). The influ-
ence of the solvent on the extent of the amine carbony-
lation can be rationalized taking into account that
reactions 4 and 5 are reversible and the equilibrium
position depends on the solution acidity.
Therefore, in CH3CN, in which the ammonium salt
NHRR′‚HCl is not soluble, the excess of amine shifts to
the right of the equilibrium. On the contrary, in ethanol,
which is a good solvent for the ammonium salt, the
increase of acidity shifts to the left the second step.
This hypothesis is supported by the behavior of a 1:1
mixture of the dicarbamoyl complexes (6 or 7) and
NHRR′.HCl. The suspension of 6 or 7 in CH3CN is stable
for hours; by adding ethanol, the dicarbamoyl complex
converts into the corresponding monocarbamoyl accord-
ing to eq 6.
0.0
0.0002
a
Unit cell parameters were obtained by least-squares analysis
of the setting angles of 30 reflections found in a random search
b
2
on the reciprocal space. R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) [∑w(Fo
- Fc2)2/∑wFo 1/2. Goodness-of-fit ) [∑w(Fo - Fc2)2/(n - p)]1/2
] ,
4
2
where n is the number of reflections and p the number of
parameters.
overall scale factor, the atomic coordinates, and anisotropic
temperature factors for all the non-hydrogen atoms. The
hydrogen atoms were placed at their calculated positions and
refined “riding” on their corresponding carbon atoms with the
geometrical constraint C-H 1.0 Å. The geometrical calcula-
tions were obtained by PARST.23All the calculations were
carried out on the GOULD ENCORE91 of the Centro di Studio
per la Strutturistica Diffrattometrica of C.N.R., Parma.
Resu lts a n d Discu ssion .
Syn th esis of Ca r ba m oyl Com p lexes of P r im a r y
a n d Secon d a r y Am in es: Role of th e Solven t. Only
one trans-acyl-carbamoyl Pd(II) complex, of formula
trans-{(Me3P)2Pd(COPh){C(OEt)[N(CH2)4CH2]}}BF4, has
been structurally characterized to date,16 and it appears
to be a cationic complex with an O-ethylated carbamoyl
ligand. Neutral Pd-carbamoyl complexes have not been
isolated and characterized, as they are usually reported
to be quite reactive and undergo an easy Pd-C cleavage
by several agents that may act intra- or intermolecu-
larly. They have been postulated as intermediates in
catalytic double carbonylation of aryl halides and sec-
ondary amines to afford R-keto-amides.24
Pd[CON(CH2)4CH2]2L2 +
CH2(CH2)4NH‚HCl f PdCl[CON(CH2)4CH2]L2 +
CO + 2 CH2(CH2)4NH (6)
However, the poor solubility of ammonium salts in
CH3CN makes difficult the isolation of pure dicarbamoyl
complexes. The latter have been isolated in a pure form
by reacting the crude reaction mixture of dicarbamoyl
complex and ammonium salt with an ethanol solution
In our case, both mono- and dicarbamoyl Pd com-
plexes have been isolated and characterized and their
reactivity has been studied under controlled conditions.
(23) Nardelli, M. PARST. Comput. Chem. 1983, 7, 95.
(24) Huang, L.; Ozawa, F.; Yamamoto, A. Organometallics 1990, 9,
2603.
(25) Studies are in progress in order to elucidate the exact nature
and the geometry of the intermediate PdCl2(NH2R)L2.

Mono- and Di-(η1-C) Carbamoyl-Pd Complexes
Organometallics, Vol. 19, No. 19, 2000 3885
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of Com p lex 4d
Pd-Cl
2.3201(18)
2.151(5)
2.054(5)
1.979(6)
O-C12
1.212(8)
1.354(8)
1.467(8)
1.453(9)
Pd-N1
Pd-N2
Pd-C12
N3-C12
N3-C13
N3-C17
Cl-Pd-N1
Cl-Pd-N2
Cl-Pd-C12
N1-Pd-N2
N1-Pd-C12
N2-Pd-C12
96.90(13)
175.38(15)
89.41(17)
78.72(18)
173.4(2)
C12-N3-C13
C12-N3-C17
C13-N3-C17
Pd-C12-O
Pd-C12-N3
O-C12-N3
119.9(5)
125.1(5)
114.4(5)
119.8(5)
118.4(4)
121.6(6)
94.9(2)
F igu r e 1. ORTEP drawing of complex 4d showing thermal
ellipsoids drawn at 30% probability.
Ta ble 4. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of Com p lex 6d
Pd-N1
2.155(17)
2.098(17)
2.01(2)
1.97(2)
1.26(3)
N3-C12
N3-C13
N3-C17
N4-C18
N4-C19
N4-C23
1.29(3)
1.47(3)
1.49(3)
1.33(3)
1.51(2)
1.44(4)
Pd-N2
Pd-C12
Pd-C18
O1-C12
O2-C18
1.22(3)
N1-Pd-N2
N1-Pd-C12
N1-Pd-C18
N2-Pd-C12
N2-Pd-C18
C12-Pd-C18
Pd-C12-O1
Pd-C12-N3
O1-C12-N3
78.8(6)
176.5(7)
94.9(7)
98.7(7)
173.6(8)
87.6(8)
118.1(14)
121.2(15)
121(2)
Pd-C18-O2
Pd-C18-N4
O2-C18-N4
C12-N3-C13
C12-N3-C17
C13-N3-C17
C18-N4-C19
C18-N4-C23
C19-N4-C2
122.6(17)
120.3(14)
117(2)
123.6(18)
124.0(17)
111.3(15)
127.0(16)
122(2)
110.2(17)
oyl-C group and one chloride anion in 4d and by two
piperidinecarbamoyl-C groups in 6d . The displacements
of the palladium atoms from the N1 N2 C12 Cl and
N1 N2 C12 C13 donor least-squares planes are
0.0311(5) and -0.029(2) Å in 4d and 6d , respectively.
The Pd-Cl bond length in 4d and the Pd-N bond
distances in 4d and 6d are consistent with those
observed in palladium(II) square-planar complexes pre-
viously reported (see Tables 3 and 4).26
F igu r e 2. ORTEP drawing of complex 6d showing thermal
ellipsoids drawn at 30% probability.
of CH3ONa, which converts the ammonium salt into the
corresponding amine (eq 7):
The Pd-C(sp2) bond distances [1.979(6) Å in 4d and
1.97(2)-2.01(2) Å in 6d ] suggest a back-π-bonding
character from the metal to the ligand for the Pd-C(O)
bond in both complexes, as the sum of covalent radii of
Pd(II) and sp2 carbon is 2.05 Å.16
Pd[CON(CH2)4CH2]2L2 + CH2(CH2)4NH‚HCl +
CH3ONa f Pd[CON(CH2)4CH2]2L2 +
CH2(CH2)4NH + CH3OH + NaCl (7)
In the carbamoyl moieties of both compounds the
C-O and C-N bond lengths and bond angles at the C
and N carbamoyl atoms also indicate delocalization of
π-electrons in the Pd-C(O)-N- moiety (the Pd-C(O)-
NCC moieties are almost planar), with a non-negli-
gible double-bond character of the C(O)-N bond. Such
extended π-bond character that involves Pd-C-N
atoms prevents the rotation of the carbamoyl group
around the Pd-C bond and the rotation of the piperi-
dine group around the C-N bond. The nonfluxional
character of the carbamoyl group in 4d is conserved
also in solution, as demonstrated by the 1H NMR
spectrum (Figure 3, see discussion below). In both mono-
and dicarbamoyl complexes, the carbamoyl carbonyl
groups of the Pd-C(O)-NCC moieties are almost
perpendicular to the coordination plane. In 4d the
dihedral angle between the N1 N2 C12 Cl and C12 O1
N3 planes is 82.7(1)°. In 6d the dihedral angles be-
tween the coordination plane N1 N2 C12 C18 and the
C12 O1 N3 and C18 O2 N4 planes are 89.4(6)° and 87.2-
(7)°, respectively. In 6d the two CdO groups show an
This procedure slightly affects the yield of pure car-
bamoyl complexes.
Ch a r a cter iza tion of th e Com p ou n d s 1-7 by
Rea ction w ith HCl. All carbamoyl compounds have
been characterized in solution by measurement of CO
evolved upon reaction with dry HCl (see Table 1).
This is a fast method for distinguishing mono- and
dicarbamoyl complexes (eqs 8 and 9, see Experimental
Section).
PdCl(CONRR′)L2 + 2 HCl f
PdCl2L2 + NHRR′‚HCl + CO (8)
Pd(CONRR′)2L2 + 4 HCl f
PdCl2L2 + 2 NHRR′‚HCl + 2 CO (9)
X-r a y Sin gle-Cr ysta l Str u ctu r e of 4d a n d 6d . Both
complexes 4d and 6d (Figures 1 and 2) are characterized
by an almost square-planar coordination around the
metal center.
Two cis positions are occupied by the dipy nitrogen
atoms and the remaining two by one piperidinecarbam-
(26) Orpen, A. G.; Brammer, L.; Allen, F. H.; Kennard, O.; Watson,
D. G.; Taylor, R. J . Chem. Soc., Dalton Trans. 1979, S1-S83.

3886 Organometallics, Vol. 19, No. 19, 2000
Aresta et al.
F igu r e 3. 1H NMR sp ectr u m (CDCl3, 278 K) of com p lex 4d .
s-trans orientation, being arranged in a head-to-tail
fashion with the torsional angle O1-C12-C18-O2
being 135(2)°.
orthogonal to the coordination plane), complex 6d
presents a significant increase of the C-Pd-C bond
angle [87.6(8)° vs 79.6(5)°]. The lengthening of one of
the two M-C bonds has been observed also for the
The structures of the two complexes show long-range
interactions of the hydrogen atoms from the piperidine
methylene groups (adjacent to nitrogen atoms) with the
metal centers. One hydrogen atom from one methylene
group in 4b [H(17a)-Pd ) 2.572(1) Å] and two H atoms
from two trans-methylene groups in 6d [H(13b)-Pd )
2.600(3) Å and H(23a)-Pd ) 2.489(2) Å] complete the
distorted tetragonal pyramidal and the distorted octa-
hedral environment of the metal center in 4d and 6d ,
respectively, even if in 6d the Pd‚‚‚H(23a) contact is
significantly shorter than the Pd‚‚‚H(13b).
In both complexes the dipy C-H groups play a
significant role in determining the crystal packing being
involved in intermolecular hydrogen bonds with oxygen
and chlorine atoms in 4d and with oxygen atoms only
in 6d . In complex 6d the piperidine ring, involved in
the smaller Pd‚‚‚H contact, is more strained [torsion
angles ranging from -47(3)° to -56(3)° and from 50-
(3)° to 54(3)°] than the second one, which shows an
almost unstrained chair conformation [from (-57(3)° to
-62(3)° and from 58(3)° to 62(3)°]. In 4d the analogous
six-membered system shows the less distorted confor-
mation [from -53.5(7)° to -55.8(7)° and from 53.5(7)°
to 55.0(7)°].
To the best of our knowledge, 4b and 6d are the first
examples of mono- and dicarbamoyl complexes structur-
ally characterized for the same metal system. More-
over, complex 6d is the first Pd cis-dicarbamoyl com-
plex and one of the rare η1-C bound dicarbamoyl com-
plexes structurally characterized, together with Ru-
(dppe)(CO)2[C(O)NHCH(CH3)2]2,15 Ru(dppe)(CO)2[C-
(O)NHCH(CH3)2]2,15 and Hg[C(O)NEt2]2 complexes. The
only example of a Pd- or Pt-carbamoyl complex similar
to 6d is the cis neutral acyl-carbamoyl complex of
Pt(II), Pt(COPh)(CONEt2)(PPh3)2.17 To complete the list
of known structures of acyl-carbamoyl complexes, we
mention the trans cationic16 acyl-carbamoyl complex
of Pd and the neutral18 R-ketoacyl-carbamoyl complex
of Pt. When compared with the structure of the neutral
cis-Pt(COPh)(CONEt2)(PPh3)2 compound (in which both
the benzoyl and carbamoyl carbonyls lie in planes nearly
dicarbamoyl
complex
Ru(dppe)(CO)2[C(O)NHCH-
(CH3)2]2,15 in which a trans influence of the phosphine
and carbonyl ligands has been invoked. The absence of
such differential trans influence in compound 6d sug-
gests that other factors (steric hindrance of the ancillary
ligands or molecular packing) may also play a role.
Sp ect r oscop ic Ch a r a ct er iza t ion of t h e Com -
p lexes. Complexes 1-7 have been characterized by
means of IR spectra, elemental analyses, and reactivity
(see Experimental Section). Complexes 4d and 6d were
additionally characterized by 1H and 13C NMR spec-
troscopy. All the dicarbamoyl complexes display in the
IR spectrum strong absorptions in the 1600-1550 cm-1
region, which is typical for the carboxyamido ligands.
The comparison of the CO-stretching of carbamoyl
complexes of both primary and secondary amines allows
us to unequivocally distinguish the ν(CO) from δ(NH).27
Such assignment may not be straightforward if only
primary amines are used.2a,b
The monocarbamoyl complexes of primary amines
display the N-H stretching between 3450 and 3300
cm-1
.
NMR Da ta of Com p lex 4d . 13C NMR data show that
the carbonyl-carbon resonance of monocarbamoyl com-
plex 4d is found at higher field (174 ppm) with respect
to the carbonyl-carbon absorption of the dicarbamoyl
complex 6d (196 ppm).
At higher field, five different carbon signals are
observed [25.0(s), 26.3(s), 26.5(s), 44.5(s), 48.8(s) ppm]
that can be assigned to the carbon atoms of the piperi-
dine ring. They demonstrate a hindered rotation around
the C-N bond of the carbamoyl moiety due to its partial
double-bond character (see above), which causes the
nonequivalence of the piperidine ortho- and meta-carbon
atoms. Such rigid character of the C-N bond in the
carbamoyl complexes has been reported also for other
carbamoyl complexes.2a,b
(27) Pouchert, C. J . The Aldrich Library of IR Spectra; Aldrich
Chemical Co.: 1970.

Mono- and Di-(η1-C) Carbamoyl-Pd Complexes
Organometallics, Vol. 19, No. 19, 2000 3887
Sch em e 1. Syn th esis a n d Solid Sta te a n d Solu tion
Ch a r a cter iza tion of Mon o- a n d Di-(η1-C)
Ca r ba m oyl-P d Com p lexes
of the two carbamoyl groups should further contribute
to prevent the rotation around the Pd-C bond.
A molecular modeling analysis of compound 6d ,
carried out with the program WebLab Viewer, shows
that the rotation around the Pd-C bond would bring
the piperidinic carbons to a very short distance (<1.3
Å) from the dipyridinic carbons. Therefore, compound
6d , as 4d , is expected not to show a free rotation around
the Pd-C and C-N bonds in solution. The presence of
1
only four signals in the H spectrum of the piperidine
1
In the high-field region of the H NMR spectrum of
moiety can be, thus, explained considering incidentally
coincident chemical shifts of the protons.
4d seven signals (Figure 3) due to the piperidine protons
are observed [1.3 (b, 1 H), 1.4 (b, 1 H), 1.5(b, 1 H), 1.6
(q, 2 H), 1.7 (b, 1 H), 3.5 (m, 2 H) and 4.2 (m, 2 H) ppm].
The piperidine R- and R′-protons (with respect to N,
see Scheme 1) appear as two second-order multiplets
at 4.2 (2 H) and 3.5 (2 H) ppm.
Selective irradiation of one multiplet by a homo-
nuclear decoupling experiment does not affect the other.
This allows us to conclude that the two multiplet signals
originate from proton nuclei not magnetically interact-
ing.
In agreement with data reported in the literature28
the multiplet centered at 4.2 ppm is assigned to the
R-CH2-protons pseudo-cis to the CdO group and the
multiplet centered at 3.5 to the R′-CH2-protons pseudo-
trans to the CdO group in the piperidine moiety.
Interestingly, the spectrum of complex 4b shows a
pseudo-quintet at 1.6 ppm (2 H) assigned to the γ-pro-
tons of the piperidine moiety. This pseudo-quintet
originates from two isochronous γ-protons coupled with
four â- and â′-protons with an almost similar coupling
constant (J ≈ 5.6 Hz). The four â- and â′-protons appear
as broad multiplets at 1.3 (1 H), 1.4 (1 H) (these two
multiplets partially overlap, Figure 3), 1.5 (1 H) and 1.7
(1 H) ppm.
Rea ctivity of Com p ou n d s 1-7 tow a r d Cu Cl2. The
Pd-(CONHR) moiety is quite stable at room tempera-
ture in the solid state and does not undergo a reductive
elimination to afford a Pd(0) complex in solution.
Conversely, the Pd-C bond is easily cleaved by Broen-
sted acids (see above) and oxidants. For example, as
expected on the basis of our previous studies,2a both
mono- (1-5) and dicarbamoyl complexes (6, 7) react
with CuCl2 at room temperature under dinitrogen
atmosphere to afford isocyanates or carbamoyl chlorides
according to reactions 10-12.
PdCl(CONHR)L2
+ 2 CuCl2 f
1-3
PdCl2L2 + RNCO + 2 CuCl + HCl (10)
PdCl(CONRR′)L2
+ 2 CuCl2 f
4, 5
PdCl2L2 + ClCONRR′ + 2 CuCl (11)
+ 4 CuCl2 f
Pd(CONRR′)2L2
6, 7
PdCl2L2 + 2 ClCONRR′ + 4 CuCl (12)
In the absence of free rotation around the Pd-C bond
(as shown by the 13C NMR spectrum), the features of
the 1H NMR spectrum of compound 4d indicate hin-
dered rotation also around the Pd-C bond. In fact, a
free rotation around the Pd-C bond would cause the
equivalence of the CH2 protons (axial and equatorials)
attached to each piperidinic carbon and the appearance
of five signals. The presence of more than five signals
indicates that the rigid structure of the Pd-C(O)-N
moiety observed in the solid state is retained also in
solution.
Two moles of copper(II) chloride per each carbamoyl
ligand are required; so, when reaction 12 is carried out
with a molar ratio CuCl2/Pd ) 2, only one amide Pd-C
bond is cleaved (eq 13) producing monocarbamoyl
complexes.
Pd(CONRR′)2L2 + 2 CuCl2 f
PdCl(CONRR′)L2 + ClCONRR′ + 2 CuCl (13)
These results, coupled with the analogous reactivity
demonstrated by dimethoxycarbonyl complexes (L2Pd-
[C(O)OCH3]2),6 enabled us to say that the cleavage of
the palladium-carbon bond by copper(II) chloride can
be considered quite a general reaction for complexes of
formula Pd(CONu)xCl(2-x)L2 (where Nu ) OR, NHR,
NRR′).
Therefore, the reactions described here can be con-
sidered as a potential alternative route to the use of
phosgene for the synthesis of either chloroformates or
carbamoyl chlorides, which are key intermediate to
carbonates, carbamates, and ureas.
NMR Da ta of Com p lex 6d . 13C NMR data show that
the carbonyl-carbon resonances of dicarbamoyl complex
6d is found at 196.2 (s) ppm. Five signals observed in
the high-field region are attributed to the piperidine
carbons, indicating that also in this case there is a
hindered rotation around the C-N bond because of its
partial double-bond character.
1H NMR data (see Experimental Section) are not
supportive, at first sight, of a hindered rotation around
the Pd-C bonds. In fact, four groups of signals are found
1
in the H NMR spectrum, while 10 signals (or, eventu-
It is worth emphasizing that Pd and Cu complexes
can be quantitatively recovered and recycled, which
makes more acceptable the hypothesis of application.
We have also developed a technique for the recovery
of pure Cu and Pd complexes. In fact, the solid mixture
(PdCl2L2 + CuCl), from reactions 10-12, can be treated
with an ethanol solution of dipy (stoichiometric amount
ally, more that five, as for 4d ) are expected for piperi-
dinic protons in a rigid Pd-C(O)-N moiety. The rigid
structure shown to exist in the solid state is the effect
of the partial double-bond character (see above) of both
the Pd-C and C-N bonds; the mutual steric hindrance
(28) Lynch, D. M.; Cole, W. J . Chem. Soc., Dalton Trans. 1966, 3337.

3888 Organometallics, Vol. 19, No. 19, 2000
Aresta et al.
with respect to Cu), which allows CuCl to be extracted
in solution as CuCl(dipy) while PdCl2L2 is left as a solid
residue.
On the other hand, the recycling of the Pd-catalyst
can be more conveniently carried out by reacting the
solid mixture of Pd/Cu with a hydro-alcoholic HCl
solution under O2, which converts the insoluble CuCl
into soluble CuCl2 (eq 14), which can be reused.
PdCl(CONHR)L2 + X-N(COCH2)2 f
PdCl[N(COCH2)2]L2 + RNCO + HX (21)
PdCl[N(COCH2)2]L2 + HX f
PdClXL2 + HN(COCH2)2 (22)
The acid produced in reaction 21 is enough to cleave
the Pd-N bond in the Pd-intermediate complex (eq 22)
and to regenerate the catalyst. Although halosuccinim-
ides afford a quantitative cleavage of the Pd-C bond,
they have no value from the application point of view,
due to their cost and the fact that succinimide is formed,
which accumulates in the catalytic cycle. If Cl2 is used
instead of HCl, in eq 20, halosuccinimide is re-formed
in addition to PdCl2L2, with a total regeneration of the
reagents.
Rea ction of th e Ca r ba m oyl Com p lexes w ith
H a logen s: Dir ect Syn t h esis of Isocya n a t es a n d
Ca r ba m oyl-Ha lid es. The reaction of Cl2 and I2 with
carbamoyl complexes is the most effective way to
synthesize isocyanates and carbamoyl-halides from
mono- and dicarbamoyl complexes, respectively. The
halogens react in a selective way and regenerate the
active starting palladium catalyst without side products.
The yield is quantitative.
2 CuCl + 2 HCl + 1/2 O2 f 2 CuCl2 + H2O (14)
It is worth noting that reaction 14 makes the overall
process of the amine conversion catalytic in both pal-
ladium and CuCl2. When primary amines are used, the
net reaction is (eq 15)
RNH2 + CO + 1/2 O2 f RNCO + H2O
(15)
With secondary amines the net reaction is the pro-
duction of carbamoyl chlorides (eq 16):
RR′NH + CO + HCl + 1/2 O2 f ClCONRR′ + H2O
(16)
Analogously, the chloroformates synthesis can be
depicted as a reaction involving only alcohol, CO, HCl,
and O2 (eq 17):
Both chlorine and iodine are very good reagents: the
latter may be safer to use. (eqs 23 and 24).
PdCl(CONHR)L2
+ X2 f PdClXL2 + RNCO + HX
(23)
ROH + CO + HCl + 1/2 O2 f ClCOOR + H2O (17)
1-3
R ea ct ion of t h e Ca r b a m oyl Com p lexes w it h
Ha losu ccin im id e. With the aim of having a complete
view of the reactivity of carbamoyl complexes, we have
explored other reagents able to react with the Pd-C
bond. We found that halosuccinimides X-N(COCH2)2
(X ) Cl, Br) are effective agents for the selective
cleavage of the Pd-C bond with halogenation of car-
bamoyl ligands (eq 18).
PdCl(2-x)(CONRR′)xL
4-7
2 + x X2 f
PdCl(2-x)XxL2 + x XCONRR′ (24)
X2 ) Cl2, I2; x ) 1, 2
With these reagents the overall process of amine
conversion is represented by eqs 25 and 26.
PdCl(CONRR′)L2 + X-N(COCH2)2 f
XCONRR′ + PdCl[N(COCH2)2]L2 (18)
RNH2 + CO + X2 f RNCO + 2 HX
(25)
RR′NH + CO + X2 f XCONRR′ + HX (26)
(X ) Cl, I)
(X ) Cl, Br)
Also in this case, carbamoyl complexes of primary
amines (eq 19) directly afford isocyanates.
These reactions represent a substantial simplification
of the process for obtaining isocyanates and carbamoyl
chlorides. In a catalytic cycle (that does not require the
isolation of the pure carbamoylmetal complex) the Pd-
(II) complex is formed in a quantitative yield and can
be reused several times, giving a two-step reaction of
potential interest from the application point of view.
Rea ction Mech a n ism . The reaction mechanism of
Pd-methoxycarbonyl or carbamoyl species with CuCl2
and halogens presents several interesting aspects, some
of which we have highlighted.2a,6 The use of CuCl2 opens
the question about the molecularity of the reaction, as
two molecules of CuCl2 per mol of Pd complex are used
for the cleavage of a single Pd-C bond (eqs 10-13).
In our previous papers,2a we suggested that isocyan-
ate, chloroformate, or carbamoyl chloride formation
could occur either through ligand exchange between the
palladium carbamoyl complex and copper chloride or by
PdCl(CONHR)L2 + X-N(COCH2)2 f
PdClXL2 + RNCO + HN(COCH2)2 (19)
However, the catalyst recovery procedure, in the case
of secondary amines, requires an additional step to
regenerate the starting palladium catalyst (eq 20) by
using HCl.
PdCl[N(COCH2)2]L2 + HCl f
PdCl2L2 + HN(COCH2)2 (20)
In the case of monocarbamoyl complexes of primary
amines, HCl is not required, as eq 19 proceeds in two
steps (eqs 21 and 22).

Mono- and Di-(η1-C) Carbamoyl-Pd Complexes
Organometallics, Vol. 19, No. 19, 2000 3889
Sch em e 2. Syn th esis a n d Solid Sta te a n d Solu tion
Ch a r a cter iza tion of Mon o- a n d Di-(η1-C)
Ca r ba m oyl-P d Com p lexes
oxidative addition of copper chloride, leading to the
formation of unstable Pd(IV)-carbamoyl complexes.
The oxidation may take place to 4d or 6d to afford
PdCl3(CONRR′)L2 or PdCl2(CONRR′)2L2, which then
decay to Pd(II) complexes with elimination of 1 mol of
ClCONRR′.
While the elucidation of the reaction mechanism of
carbamoyl complexes with CuCl2 deserves further in-
vestigation in order to exclude possibilities, the reaction
of monocarbamoyl Pd-Cl complexes with I2 is a useful
tool for getting information about the reaction mecha-
nism when Cl2, I2, or halosuccinimide is used. In fact,
starting from PdCl(CONRR′)L2 and I2, the reaction
affords both ClCONRR′ and ICONRR′ (see Experimen-
tal Section).
This result can be explained if one assumes that I2
behaves as a two-electron acceptor and the reaction
occurs through an oxidative addition of I2 to PdCl-
(CONRR′)L2 to afford a palladium(IV) carbamoyl com-
plex [PdClI2(CONRR′)L2], which can, by reductive elimi-
nation, afford either the carbamoyl-chloride or -iodide
species.
catalysts for developing new synthetic processes that
use the same reagents used in phosgene chemistry, but
avoid the synthesis of phosgene (Scheme 2).
The Pd mediation allows the use of an alternative
reaction sequence. In fact, Pd makes possible the direct
reaction of CO with the nucleophile (ROH or the amine)
to afford the methoxy carbonyl or carbamoyl, respec-
tively, which are then reacted with halogen donors.
The very mild conditions used in the synthesis and
the easy and quantitative recovery of Pd emphasize that
it is possible to avoid the use of toxic molecules and shift
to environmentally benign syntheses by slightly modify-
ing the processes and choosing the proper catalyst.
Support for this hypothesis comes also from the
observation that, as already reported for the case of Pd-
(COOMe)2L2, when 6d is reacted with Cl2, some features
of the reaction mixture are observed that are charac-
teristic of a Pd(IV) complex6 (transient red color) that
is then readily reduced to Pd(II). The initial formation
•
of a radical (either X• or CONRR′) might also account
for the observed features. Nevertheless, the experimen-
tal evidence available to date (no effect of radical
scavengers) do not support such a mechanism.
Ack n ow led gm en t. Financial support from MURST
(Progetti di Interesse Nazionale no. 9803026360, 1998),
the University of Bari for a Research Grant (A.D.), and
CNR (Grant 98.01876.CT03) is gratefully acknowledged.
Con clu sion s
Stable Pd-carbamoyl complexes of formula PdCl(2-x)
-
(CONRR′)xL2 (x ) 1,2; L ) dipy, phen, PPh3) can be
isolated, characterized in the solid state, and easily
reacted with CuCl2, halosuccinimides, or halogens to
afford isocyanates or carbamoyl chlorides, which are the
precursors of carbamates or ureas. This result, coupled
with our previous observations on the reactivity of Pd-
methoxy carbonyl complexes PdCl2-x(COOMe)(2-x)L (x
) 1,2; L ) dipy, phen),6 brings to a general conclusion
that Pd(II) complexes with bidentate N-ligands are
Su p p or tin g In for m a tion Ava ila ble: List of the atomic
fractional coordinates of the non-hydrogen atoms (Table 5
(4d )), Table 6 (6d )), list of the anisotropic temperature factors
(Table 7 (4d ), Table 8 (6d )), list of the atomic fractional
coordinates of the hydrogen atoms (Table 9 (4d ), Table 10
(6d )), and a full list of the bond distances and angles (Table
11 (4d ), Table 12 (6d )). This material is available free of charge
via the Internet at http://pubs.acs.org.
OM000198W