Synthesis, structure, and reactivity of the novel pentacoordinate palladium complex [Pd(Phen)2(CO2CH3)](PF6)

Article abstract of DOI:10.1021/om980315b

Reaction of [Pd(phen)(CO₂CH₃)₂] (1) with phenanthrolinium hexafluorophosphate (2) gives in high yield the unprecedented pentacoordinate palladium complex [Pd(phen)₂(COOMe)](PF₆) (3) in which Pd displays a strongly distorted square pyramidal coordination. The reactivity of 3 toward bases was explored too.

Full text of DOI:10.1021/om980315b

Organometallics 1998, 17, 4519-4522
4519
Notes
Syn th esis, Str u ctu r e, a n d Rea ctivity of th e Novel
P en ta coor d in a te P a lla d iu m Com p lex
[P d (P h en )2(CO2CH3)](P F 6)
Rossella Garrone,† Anna Maria Romano,*,† Roberto Santi,*,† and Roberto Millini‡
EniChem S.p.A., Centro Ricerche Novara “Ist. G. Donegani”, via Fauser, 4,
28100 Novara, Italy, Eniricerche S.p.A., Via Maritano, 26, 20097 S. Donato, Milan, Italy
Received April 23, 1998
Summary: Reaction of [Pd(phen)(CO2CH3)2] (1) with
phenanthrolinium hexafluorophosphate (2) gives in high
yield the unprecedented pentacoordinate palladium
complex [Pd(phen)2(COOMe)](PF6) (3) in which Pd
displays a strongly distorted square pyramidal coordi-
nation. The reactivity of 3 toward bases was explored
too.
In tr od u ction
Palladium(II) and platinum(II) pentacoordinate com-
plexes1 are mechanistically and synthetically relevant
in organometallic chemistry. Complexes of substituted
phenanthrolines with pentacoordinate palladium and
platinum halides2 and cyananide3 were studied, and the
structure of [Pt(CN)phen)2](PF6) was reported.4 In the
case of palladium, they can be synthesized either by
reacting a four-coordinate complex with an olefin5-7 or
by oxidative addition of an alkyl halide to three-
coordinate palladium(0) olefin complexes.8 Steric hin-
drance of the N-N′ chelating ligand is a demanding
requirement for the stabilization of five-coordinate
palladium complexes.9
F igu r e 1. ORTEP15 drawing of the structure of 3 (dis-
placement ellipsoids are drawn at the 30% probability
level). Selected bonds lengths [Å] and angles [deg]: Pd-
(1)-N(2) 2.044(3); Pd(1)-N(16) 0.063(3); Pd(1)-C(30) 1.957-
(4); Pd(1)-N(13) 2.135(4); Pd(1)-N(27) 2.637(4). N(27)-
Pd(1)-C(30) 101.6(1); N(16)-Pd(1)-N(27) 70.4(1); N(13)-
Pd(1)-N(27) 83.5(1); N(2)-Pd(1)-C(30) 95.0(2); N(2)-
Pd(1)-N(16) 167.3(1); N(16)-Pd(1)-C(30) 87.1(1); N(16)-
Pd(1)-N(13) 97.1(1); N(13)-Pd(1)-C(30) 174.3(2); N(2)-
Pd(1)-N(27) 121.1(1); N(2)-Pd(1)-N(13) 80.1(2).
We have previously described the novel palladium
1,10-phenanthroline bis(carbomethoxy) complex Pd-
(phen)(CO2CH3)2, 1.10 In the course of a study on the
reactivity of 1 with acids, we found that, analogously
to bis(carbomethoxy)bis(triphenylphosphine)palladium,11
the reaction of 1 with HCl gave Pd(phen)Cl(CO2CH3).
Surprisingly, we now find that the reaction of the
nonconventional acid phenanthrolinium hexafluoro-
phosphate (phenHPF6, 2) gives the new five-coordinate
complex [Pd(phen)2(CO2CH3)](PF6), 3.
† EniChem S.p.A.
‡ Eniricerche S.p.A.
(1) (a) Fanizzi, F. P.; Natile, G.; Lanfranchi, M.; Tiripicchio, A.;
Laschi, F.; Zanello, P. Inorg. Chem. 1996, 35, 3173-3182. (b) Albano,
V. G.; Castellari, C.; De Felice, V.; Panunzi, A.; Ruffo, F. Organome-
tallics 1996, 15, 4012-4019. (c) Fanizzi, F. P.; Intini, F. P.; Maresca,
L.; Natile, G.; Lanfranchi, M.; Tiripicchio, A.; Pacchioni, G. J . Chem.
Soc., Chem. Commun. 1992, 333-334.
(2) Plowman, R. A.; Power, L. F. J . Aust. Chem. 1971, 24, 303-
308.
(3) (a) Plowman, R. A.; Power, L. F. J . Aust. Chem. 1971, 24, 309-
316. (b) Gillard, R. D.; Kane-Maguire, L. A. P.; Williams, P. A.
Transition Met. Chem. 1977, 2, 55-58.
(4) Wernberg, O.; Hazell, A. J . Chem. Soc., Dalton Trans. 1980, 973-
978.
Resu lts a n d Discu ssion
A light yellow solution of 1, containing 1 equiv of 2,
suspended in methanol when stirred under inert atmo-
sphere, undergoes a color change to orange-yellow, with
concomitant CO evolution and formation of 3 (Scheme
1).
(5) De Renzi, A.; Morelli, G.; Panunzi, A.; Vitagliano, A. Gazz. Chim.
Ital. 1987, 117, 445-447.
(6) Albano, V. G.; Castellari, C.; Cucciolito, M. E.; Panunzi, A.;
Vitagliano, G. Organometallics 1990, 9, 1269-1282.
(7) Fanizzi, F. P.; Intini, F. P.; Maresca, L.; Natile, G.; Lanfranchi,
M.; Tiripicchio, A. J . Chem. Soc., Dalton Trans. 1991, 1007-1012.
(8) Cucciolito, M. E.; Panunzi, A.; Ruffo, F.; De Felice, V. Gazz. Chim.
Ital. 1989, 119, 461-462.
(10) Romano, A. M.; Santi, R.; Millini, R.; Garrone, R. Accepted
paper.
(11) Vasapollo, G.; Toniolo, L.; Cavinato, G.; Bigoli, F.; Lanfranchi,
M.; Pellighelli, M. A. J . Mol. Catal. 1994, 175, 481-487.
(9) De Felice, V.; Albano, V. G.; Castellari, C.; Cucciolito, M. E.;
Panunzi, A.; De Renzi, G. J . Orgamet. Chem. 1993, 403, 269-275.
S0276-7333(98)00315-X CCC: $15.00 © 1998 American Chemical Society
Publication on Web 09/04/1998

4520 Organometallics, Vol. 17, No. 20, 1998
Notes
Sch em e 1
Sch em e 2
Large yellow-orange crystals of 3 suitable for X-rays
analysis were obtained by slow diffusion of n-hexane
into a methylene chloride solution of 3. Single-crystal
X-ray diffraction and spectroscopic analysis confirm the
pentacoordinate structure of 3, in which the Pd atom
displays a strongly distorted square pyramidal coordi-
nation (Figure 1), analogously to the platinum complex
[Pt(CN)phen)2](PF6). The square plane is formed by
atoms N(2) and N(13) of the first phen molecule, the
N(16) atom of the second phen ligand, and the C(30)
atom of the carbomethoxy group; the apical position is
occupied by atom N(27) of the second phenanthroline
ligand (Figure 1). The Pd(1) atom is displaced toward
atom N(27) by 0.141(5) Å from the mean plane defined
by N(2), N(13), N(16), and C(30). The plane is also
slightly distorted from the square symmetry, with the
Pd(1)-N(13) bond (2.135(4) Å) in trans position with
respect to the carbomethoxy group, longer than the
other two Pd-N bonds in the plane (2.044(3) and 2.063-
(3) Å, for Pd(1)-N(2) and Pd(1)-N(16), respectively).
The Pd(1)-C(30) distance, 1.957(4) Å, is significantly
shorter than the corresponding bond observed in the
square planar Pd(bipy)(CO2CH3)2 complex (Pd-N 1.989-
(9) Å).12 Finally, the N(27) atom, in apical position, is
at 2.637(4) Å from Pd(1).
Complexes Pd(L-L)(CO2CH3)2 [(L-L) ) 2,2′-bipyri-
dine (bipy) and 2,9-dimethyl-1,10-phenanthroline
(DMPhen), Scheme 1] reacted with the corresponding
acids (L-L)HPF6 to yield [Pd(bipy)2(CO2CH3)](PF6) (4)
and [Pd(DMPhen)2(CO2CH3)](PF6) (5) (89% and 90%
yield, respectively). In the latter case 5 was obtained
(12) Smith, G. D.; Hanson, B. E.; Merola, J . S.; Waller, F. J .
Organometallics 1993, 12, 568-569.

Notes
Organometallics, Vol. 17, No. 20, 1998 4521
and used as received. Sodium methoxide was prepared by
in high yield as could be expected, since there was no
steric crowding due to the presence of methyl groups in
the 2 and 9 position, as clearly shown by X-ray diffrac-
tion of complex 3 (Figure 1). Pd(DPPhen)2(CO2CH3)]-
(PF6) (6) (DPPhen ) 4,7-diphenyl-1,10-phenanthroline)
was prepared by ligand exchange between the complex
4 and the free ligand (70% yield).
When stirred at room temperature, in methanol
complex 3 reacted with tetramethylammonium chloride,
affording carbomethoxy(chloro)phenanthrolinepalladium,
[Pd(phen)(CO2CH3)Cl] (7) (Scheme 2). 1H NMR of the
pink complex 7 showed the singlet of the carbomethoxy
group shifted from 3.46 to 3.86 ppm, and the integrals
indicated the presence of one phenanthroline ligand.
The two protons in the 2 and 9 position gave two
different signals (H2 at 9.25 ppm and H9 at 8.87 ppm).
reacting sodium metal with anhydrous methanol. Pd(L-L)-
14
(CO2CH3)2 and (L-L)HPF6 were prepared according to the
literature. Carbon monoxide was purchased from Rivoira.
1H and 13C NMR spectra were recorded on a 200 MHz
Brucker Electrospin 200 Instrument, while IR spectra were
recorded using a Perkin-Elmer 1420 Instrument. FAB MS
were recorded on a Finnigan MAT M scan instrument, using
m-nitrobenzyl alcohol as a matrix.
Syn th esis of [P d (L-L)2(CO2CH3)](P F 6). A light yellow
suspension of 0.37 mmol of Pd(L-L)(CO2CH3)2 in 20 cm3 of
methanol was vigorously stirred and 0.37 mmol of (L-L)HPF6
was added. The mixture changed to orange-yellow, with a
concomitant CO evolution (1 equiv, 9 cm3). After 1 h, the solid
was filtered and washed with diethyl ether.
[P d (p h en )2(CO2CH3)](P F 6), 3: 75% yield. 1H NMR (C2D2-
Cl4, ppm): 8.91 (dd, 4H); 8.60 (dd, 4H); 8.09 (s, 4H); 7.78 (m,
4 H); 3.46 (s, 3H). 13C (C2D2Cl4, ppm): 169.87, 151.36, 144.30,
138.8, 130.36, 127.82, 125.34, 53.31. 31P NMR (C2D2Cl4, ppm):
Moreover, the absence of the IR band at 850 cm-1
,
-
attributable to the PF6 group, confirmed that in this
case complex 3 lost a chelating ligand during the
reaction, reverting to the usual tetracoordinated mode.
This particular reactivity of 3 can be ascribed to the
presence of the chloride anion in tetramethylammonium
chloride, Me4NCl, which could directly coordinate pal-
ladium, thus allowing the loss of one phenanthroline
ligand.
-53; J ) 711 Hz. IR (in Nujol mull): 1670, 1070, 840 cm-1
.
MS: m/z 526 (M + 1). Anal. Calcd for C26H19F6N4O2PPd: C,
46.56; H, 2.84; N, 8.35; P, 4.62; Pd, 15.82. Found: C, 44.98;
H, 2.77; N, 8.40; P, 4.70; Pd, 15.77.
[P d (bip y)2(CO2CH3)](P F 6), 4: 88% yield. 1H NMR (C2D2-
Cl4, ppm): 8.47 (dd, 4H); 8.22 (dd,4H); 8.06 (t, 4H); 7.49 (t, 4
H); 3.55 (s, 3H). 13C NMR (C2D2Cl4): 53.54; 123.98; 126.46;
139.84; 151.10; 155.24; 191.80. IR (in Nujol mull): 1690, 1090,
860 cm-1. MS: m/z 478 (M + 1). Anal. Calcd for C22H15F6N4O2-
PPd: C, 42.71; H, 2.42; N, 9.06; P, 5.02; Pd, 17.15. Found: C,
42.41; H, 2.39; N, 9.01; P, 4.85; Pd, 16.97.
Finally, 3 reacted with an excess of sodium methoxide
in methanol when the reaction mixture was heated at
60 °C for 8 h, with the formation of dimethyl carbonate
(DMC; Scheme 2). When the same reaction was carried
out under CO pressure, no traces of DMC were detected
and bis(methoxycarbonyl)phenanthrolinepalladium, Pd-
(phen)(CO2CH3)2 (1), was formed. Even in the presence
of triethylamine as a base, for 4 h at 70 °C with 40 bar
of CO, the formation of DMC did not occur. From the
reaction mixture we succeded in isolating a binuclear
palladium complex, 8, as a beige solid. Although the
crystals did not allow X-ray analysis, unequivocal
evidence of the structure was gained by mass, IR, and
NMR spectroscopies. The M + 1 ion was 658. The IR
spectrum showed a bridging carbonyl adsorption com-
parable with that found for [Pd(phen)2((η-CO)((η-H)]-
(OAc),13 while the carbonyl absorption of the brigded
carbomethoxy group was observed at 1620 cm-1, as a
weak band, owing to palladium-oxygen coordination.
13C NMR gave only half signals for phenanthroline as
expected. 1H NMR, which gave integrals of the methoxy
group and ligand protons corresponding to a 1:2 ratio,
continued to show only the enlarged signals of the ligand
when free 1,10-phenanthroline was added, indicating
the fluctional nature of the complex.
[P d (DMP h en )2(CO2CH3)](P F 6), 5: 90% yield. 1H NMR
(CD2Cl2, ppm): 8.46 (d, 4H); 8.00 (s, 4H); 7.70 (d, 4H); 3.06 (s,
3H); 2.67 (s, 12H). IR (in Nujol mull): 1665, 1090, 870 cm-1
.
MS: m/z 554 (M + 1). Anal. Calcd for C30H27F6N4O2PPd: C,
49.58; H, 3.72; N, 7.71; P, 4.27; Pd, 14.60. Found: C, 49.41;
H, 3.59; N, 7.51; P, 4.65; Pd, 14.77.
Syn th esis of [P d (DP P h en )2(CO2CH3)](P F 6), 6. A sus-
pension of 0.192 g of [Pd(bipy)2(CO2CH3)](PF6) (4) (0.3 mmol)
and 0.289 g of 4,7-diphenyl-1,10-phenanthroline (0.9 mmol)
in 20 cm3 of methanol was stirred for 20 h and, after this time,
filtered, and the residue washed with MeOH and with diethyl
ether. The solid was dried under vacuum, thus affording 0.200
g of an orange-yellow solid, in 70% yield. 1H NMR (CD2Cl2,
ppm): 9.06 (d, 4H); 8.11 (s, 4H); 7.75 (d, 4H); 7.60 (s, 20H);
3.55 (s, 3H). IR (in Nujol mull): 1660, 1090, 865 cm-1. MS:
m/z (M+). Anal. Calcd for C50H35F6N4O2PPd: C, 61.60; H,
3.59; N, 5.74; P, 3.18; Pd, 10.88. Found: C, 61.41; H, 3.29; N,
6.01; P, 3.25; Pd, 10.70.
Syn th esis of [P d (p h en )(CO2CH3)(Cl)], 7. A suspension
of 0.2 g (0.335 mmol) of 3 and 0.044 g (0.402 mmol) of Me4NCl
was stirred at room temperature in 25 mL of MeOH; when
mixed, it suddenly changed from yellow-orange to orange and,
after 10 min, to pink. The solvent was then distilled and the
residue washed with methylene chloride and with diethyl
ether. Finally, the solid was dried under vacuum. The product
weighed 100 mg (78% yield). 1H NMR (CD2Cl2, ppm): 9.25
(dd, 1H); 8.87 (dd, 1H); 8.56 (m, 2H); 7.98 (s, 2H); 7.83 (m,
2H), 3.86 (s, 3H). IR (in Nujol mull): 1670, 1030 cm-1. MS:
m/z 381 (M + 1). Anal. Calcd for C14H11ClN2O2Pd: C, 44.21;
H, 2.89; N, 7.36; Cl, 9.12; Pd, 27.89. Found: C, 44.41; H, 2.59;
N, 7.01; Cl, 9.25; Pd, 28.01.
Apparently, the formation and structure of stable 3
are due to the presence of the noncoordinating anion,
which allows pentacoordination. The structure of the
stable complex 3 is unprecedented. The method used
to prepare complex 3 also is unprecedented and is likely
to have general character.
Syn th esis of P d 2(p h en )2((η-CO)((η-COOMe), 8. In a 100
cm3 stainless steel vessel were charged 0.200 g of 3 (0.3 mmol)
and 0.043 mL of Et3N (0.3 mmol) in 20 mL of methanol and
pressurized with CO to 40 bar. After 4 h at 70 °C, the
unreacted gas was vented off and the autoclave opened; the
Exp er im en ta l Section
All reactions were performed under argon atmosphere, using
the Schlenk tube techniques. Solvents were dried and distilled
prior to use. Nitrogen-chelating ligands, triethylammine and
tretramethylammonium chloride, were obtained from Aldrich
(14) Milani, B.; Anzilutti, A.; Vicentini, L.; Sessanta o Santi, A.;
Zangrando, E.; Geremia, S.; Mestroni, G. Organometallics 1997, 16,
5064.
(13) Stolyarov, I. P.; Evdokimova, E. V.; Moiseev, I. I. Koord. Khim.
1989, 15, 1545-1549.z
(15) J ohnson, C. K. ORTEP II. Rep. ORNL-5138; Oak Ridge
National Laboratory, Oak Ridge, TN, 1976.

4522 Organometallics, Vol. 17, No. 20, 1998
Notes
beige solid was filtered, washed with MeOH, and dried in a
vacuum. Yield: 82%. 1H NMR (DMSO, ppm): 9.05 (dd, 4H);
8.50 (dd,4H); 8.27 (dd, 4H); 7.81 (s, 4 H); 3.75 (s, 3H). 13C NMR
(DMSO, ppm): 180.67; 167.78; 151.43; 147.51; 143.01; 139.46;
130.57; 128.96; 126.91; 125.14; 71.03; 58.00; 53.47. IR (in
Nujol mull): 1880 (s), 1620 (w), 1030 (s) cm-1. MS: m/z 658
(M + 1). Anal. Calcd for C27H19F6N4O3PPd2: C, 40.29; H, 2.36;
N, 6.96; P, 3.85; Pd, 26.37. Found: C, 40.41; H, 2.29; N, 7.01;
P, 3.65; Pd, 26.77.
by direct methods and refined by the full-matrix least-squares
method (SIR-97). The minimized function was Sw(Fo - Fc)2,
where w-1 ) s2(F). The final cycles of refinement included
atomic coordinates and anisotropic thermal parameters for all
non-H atoms (358 parameters). The positions of the H atoms
were calculated on geometrical grounds and kept fixed to the
parent C atom during the refinement. The final difference
Fourier map was featureless. The R and wR values were 0.062
and 0.065, respectively.
Cr ysta l Str u ctu r e Da ta for 3. Yellow-orange crystals
were grown by slow diffusion of n-hexane into its saturated
methylene chloride solution at room temperature. 3: formula
Ack n ow led gm en t. This work has been sponsored
by the Ministero dell′Universita` e della Ricerca Scien-
tifica e Tecnologica within a framework of the “Pro-
gramma Nazionale di Ricerca per la Qualita` della Vita”.
C
26H19F6N4O2PPd; Mr ) 670.83; crystalline system triclinic;
space group P1h; a ) 10.030(1) Å; b ) 12.278(2) Å; c ) 13.047-
(2) Å; R ) 98.56(1); â ) 109.87(1); γ ) 111.71(1)°; V ) 1332.7-
(4) Å3; Dx(Mg/m3) ) 1.6717; Mo KR radiation (λ ) 0.71069 Å);
µ ) 8.17 cm-1; crystal dimensions 0.5 × 0.5 × 0.6 mm3; qmax
)
Su p p or tin g In for m a tion Ava ila ble: Tables of all bond
lengths and angles, atomic coordinates, positions, and thermal
parameters for 3 (7 pages). Ordering information is given on
any current masthead page.
35°.
The X-ray diffraction data were collected on a Siemens AED
automated diffractometer at 298 K, using Mo KR radiation (l
) 0.71069 Å). A total of 11 800 reflections were measured, of
which 7630 with F > 6σ(F) observed. The structure was solved
OM980315B