Synthesis and reactivity of mixed-ligand palladium(II) organometallic complexes with phosphites and bis(pyrazol-1-yl)methane

Article abstract of DOI:10.1021/om900146a

New cationic organometallic palladium(II) complexes of general formula [PdMe(NN)P(OR)₃]ClO₄ {NN = bis(pyrazol-1-yl)methane (BPM) and bis(3,5-dimethylpyrazol-1-yl)methane (Me₂BPM); P(OR)₃ = phosphites} have been

Full text of DOI:10.1021/om900146a

Organometallics 2009, 28, 3247–3255
3247
Synthesis and Reactivity of Mixed-Ligand Palladium(II)
Organometallic Complexes with Phosphites and
Bis(pyrazol-1-yl)methane
Marco Bortoluzzi,*,† Gino Paolucci,*,† Bruno Pitteri,† Andrea Vavasori,† and
Valerio Bertolasi‡
Dipartimento di Chimica, UniVersita` Ca’ Foscari di Venezia, Calle Larga S. Marta Dorsoduro 2137,
30121 Venezia, Italy, and Dipartimento di Chimica e Centro di Strutturistica Diffrattometrica, UniVersita`
di Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy
ReceiVed February 23, 2009
New cationic organometallic palladium(II) complexes of general formula [PdMe(NN)P(OR)3]ClO4
{NN ) bis(pyrazol-1-yl)methane (BPM) and bis(3,5-dimethylpyrazol-1-yl)methane (Me2BPM); P(OR)3
) phosphites} have been synthesized and characterized. The isolation of the intermediate reaction products
has highlighted the formation mechanism of these species. By reacting [PdMe(BPM)P(OEt)3]ClO4 with
the Cl- and SeCN- ions the neutral species PdClMe(BPM)P(OEt)3 and PdMe(SeCN)(BPM)P(OEt)3 have
been prepared, the last one as a mixture of isomers. The NMR data suggest that these neutral complexes
are stabilized by an anagostic interaction between a hydrogen atom of the BPM methylene bridge and
the palladium center. The reaction of [PdMe(BPM)P(OEt)3]ClO4 with CO and tosylmethyl isocyanide
allowed the isolation of the corresponding insertion products. Preliminary studies showed that the cationic
acyl complex [Pd(COMe)(BPM)P(OEt)3]ClO4 is an active catalyst toward styrene polymerization in the
presence of CO.
coordinated to the same metal center. The N-donors usually
bond to the metal ion through sp2 nitrogen hybrids, while the
P-donors are mono- or polydentate phosphines.
Introduction
In the past few years several papers have been published on
the interaction of neutral bis(pyrazol-1-yl)alkanes ligands with
the palladium(II) metal center. Besides homoleptic derivatives
and chloro complexes,1 organometallic species such as alkyl,
aryl, allyl, and olefin complexes have been isolated and
characterized2 and Lo´pez and co-workers reported the synthesis
of cationic mixed-ligand Pd(II) complexes of the type
[Pd(BPM)(PEt3)2](ClO4)2, [Pd(BPM)(PPh3)2](ClO4)2, and [Pd(BP-
M)(dppe)](ClO4)2 {BPM ) bis(pyrazol-1-yl)methane, dppe )
1,2-bis(diphenylphosphino)ethane} starting from the bis-aceto-
nitrile species [Pd(BPM)(NCCH3)2](ClO4)2.3
The monodentate phosphites P(OR)3 have received less
attention than phosphines as supporting ligands in palladium(II)
organometallic chemistry, even though several well-character-
ized neutral and cationic derivatives are known, in particular
alkyl, acyl, aryl, and allyl complexes.5 Pd(II) organometallic
complexes bearing N,P-chelate ligands have been synthesized
and characterized, and catalytic studies on allylic alkylation have
been carried out.6 Moreover, a methylpalladium complex with
pyridine-2-carboxylate and P(OMe)3 in the coordination sphere
has been reported.7
Palladium complexes containing both N-donor and P-donor
ligands in their coordination sphere, also called N,P-mixed-
ligand derivatives, have attracted considerable interest in the
field of polymerization catalysis.4 The nitrogen and phosphorus
atoms in these species can either be contained in the same
polydentate ligand or belong to different chelate ligands
Besides the chloro complex PdCl(BPz4)P(OEt)3 {BPz4 )
tetrakis(pyrazol-1-yl)borate},8 to the best of our knowledge no
Pd(II) complex with an N,P-mixed-ligand containing pyrazole-
based N-ligands and monodentate phosphites as ancillary ligands
has been ever synthesized. The greater π-acidity and the lower
9
hindrance of P(OR)3 ligands compared to PR3 make them
* Corresponding authors. Tel: +390412348653. Fax: +390412348684.
E-mail: markos@unive.it; paolucci@unive.it.
(4) For some references see: (a) Durand, J.; Milani, B. Coord. Chem.
ReV. 2006, 250, 542. (b) Bianchini, C.; Meli, A. Coord. Chem. ReV. 2002,
225, 35. (c) Braunstein, P.; Fryzuk, M. D.; Le Dall, M.; Naud, F.; Rettig,
S. G.; Speiser, F. J. Chem. Soc., Dalton Trans. 2000, 1067, and references
therein.
(5) (a) Kayaki, Y.; Shimizu, I.; Yamamoto, A. Bull. Chem. Soc. Jpn.
1997, 70, 1141. (b) Nakazawa, H.; Kashiwamura, T.; Mizuta, T.; Miyoshi,
K. Organometallics 1994, 13, 941. (c) Vitagliano, A.; Aakermark, B.;
Hansson, S. Organometallics 1991, 10, 2592. (d) Ladipo, F. T.; Anderson,
G. K. Organometallics 1994, 13, 303. (e) Lo´pez, G.; Garcia, G.; Santana,
M. D.; Sa´nchez, G.; Ruiz, J.; Hermoso, J. A.; Vegas, A.; Mart´ınez-Ripoll,
M. J. Chem. Soc., Dalton Trans. 1990, 1621.
(6) (a) Arena, C. G.; Rommi, D.; Faraone, F. Tetrahedron: Asymmetry
2000, 11, 2765. (b) Polosukhin, A. I.; Bondarev, O. G.; Lyubimov, S. E.;
Korostylev, A. V.; Lyssenko, K. A.; Davankov, V. A.; Gavrilov, K. N.
Tetrahedron: Asymmetry 2001, 12, 2197.
(7) Jin, H.; Cavell, K. J.; Skelton, B. W.; White, A. H. J. Chem. Soc.,
Dalton Trans. 1995, 2159.
† Universita` Ca’ Foscari di Venezia.
‡ Universita` di Ferrara.
(1) Minghetti, G.; Cinellu, M. A.; Bandini, A. L.; Banditelli, G.;
Demartin, F.; Manassaro, M. J. Organomet. Chem. 1986, 315, 387.
(2) (a) Byers, P. K.; Canty, A. J. Organometallics 2000, 9, 210. (b)
Tsuji, S.; Swenson, D. C.; Jordan, R. F. Organometallics 1999, 18, 4758.
(c) Carrio´n, M. C.; D´ıaz, A.; Guerrero, A.; Jalo´n, F. A.; Manzano, B. R.;
Rodr´ıguez, A.; Paul, R. L.; Jeffery, J. C. J. Organomet. Chem. 2002, 650,
210. (d) Conley, M. P.; Burns, C. T.; Jordan, R. F. Organometallics 2007,
26, 6750. (e) Jalo´n, F. A.; Manzano, B. R.; Otero, A.; Rodr´ıguez-Pe´rez,
M. C. J. Organomet. Chem. 1995, 494, 179. (f) Carrio´n, M. C.; D´ıaz, A.;
Guerrero, A.; Jalo´n, F. A.; Manzano, B. R.; Rodr´ıguez, A. New J. Chem.
2002, 26, 305. (g) Binotti, B.; Bellachioma, G.; Cardaci, G.; Macchioni,
A.; Zuccaccia, C.; Foresti, E.; Sabatino, P. Organometallics 2002, 21, 346.
(3) Sa´nchez, G.; Serrano, J.; Pe´rez, J.; Ram, M. C.; Lo´pez, G.; Molins,
E. Inorg. Chim. Acta 1999, 295, 136.
10.1021/om900146a CCC: $40.75
2009 American Chemical Society
Publication on Web 04/20/2009

3248 Organometallics, Vol. 28, No. 11, 2009
Bortoluzzi et al.
used to treat the NMR spectroscopic data.13 The organic ligands
were numerated following common conventions. The conductivity
values of 10-3 mol dm-3 solutions of the complexes in dimethyl-
formamide (DMF) at 298 K were measured with a Radiometer
CDM 83 instrument and compared with literature data.14
The computational geometry optimizations were performed using
the hybrid DFT B3PW91 method without symmetry constraints.
The “restricted” formalism was applied in all calculations. The basis
set considered was D95V(d,p) {SDD on the Pd atom, D95(d) on
the P and Cl atoms}. Geometry convergence was accelerated using
the GDIIS algorithm, and a first refinement of the structures was
obtained using the GGA DFT PBEPBE method in combination with
the SDDALL basis set.15,16 In Vacuo calculations were followed
by a geometry optimization using the implicit solvation model
C-PCM,17 considering dichloromethane as solvent. All of the
resultant stationary points were characterized as true minima (i.e.,
no imaginary frequencies). DFT calculations were carried out at
CINECA (Centro Italiano di Supercalcolo, Bologna, Italy) using
IBM p5-575 computers with 64-bit IBM Power5 processors
operating at 1.9 GHz frequency. The software used was the
GAUSSIAN’03.18
attractive for the tuning of the Pd-C bond reactivity; therefore
in this paper we report the synthesis and characterization of
new cationic organometallic palladium(II) complexes of general
formula [PdMe(NN)P(OR)3]ClO4 {NN ) bis(pyrazol-1-yl)-
methane (BPM) and bis(3,5-dimethyl-pyrazol-1-yl)methane
(Me2BPM); P(OR)3 ) phosphites}, together with preliminary
studies on their reactivity and their catalytic activity toward
olefin polymerization.
Experimental Section
Materials and Methods. All inorganic manipulations were
carried out under nitrogen using standard Schlenk techniques, with
the exception of the preparations involving the use of high CO
pressures, which were performed in a steel autoclave. Once isolated,
the complexes were found to be relatively stable in air. All reaction
solvents were thoroughly deoxygenated and dehydrated under N2
by refluxing over suitable drying agents, whereas NMR solvents
were kept in the dark over molecular sieves. Phosphites P(OMe)3,
P(OEt)3, and P(OiPr)3 (Aldrich) were distilled under argon at
reduced pressure before use. Tosylmethyl isocyanide (Aldrich) was
used as received. Bis(pyrazol-1-yl)methane (BPM) and bis(3,5-
dimethylpyrazol-1-yl)methane (Me2BPM) were synthesized from
the corresponding pyrazoles (Aldrich) and dichloromethane in
strongly basic solution according to a reported method10 and purified
by crystallization from hot cyclohexane solutions. The inorganic
precursors PdCl2(COD) and PdClMe(COD) {COD ) 1,5-cyclooc-
tadiene} were synthesized from commercial PdCl2, COD, and
tetramethyltin (Aldrich) according to the literature methods.11,12
The salts silver perchlorate, potassium selenocyanate, and benzyl-
triethylammonium chloride (Aldrich) were used without further
purifications.
1H NMR and IR spectra (KBr pellets) of the prepared polymers
were recorded with the instruments above-described and compared
with literature spectra.19
Synthesis of PdClMe(BPM) (C8H11ClN4Pd, Mw ) 305.7, 1H)
and PdClMe(Me2BPM) (C12H19ClN4Pd, Mw ) 361.18, 1Me). The
complexes PdClMe(BPM) (1H) and PdClMe(Me2BPM) (1Me) {BPM
) bis(pyrazol-1-yl)methane; Me2BPM ) bis(3,5-dimethylpyrazol-
1-yl)methane} were prepared by reacting PdClMe(COD) {COD )
1,5-cyclooctadiene} (0.200 g, 0.75 mmol) with a stoichiometric
amount of BPM or Me2BPM (0.75 mmol) in CH2Cl2 (20 mL) at
room temperature for 30 min. The solvent was removed by
evaporation at reduced pressure, and the residual solid was treated
with diethyl ether (10 mL). The product that separated out was
filtered, washed with diethyl ether, and dried under vacuum. Yields:
Polymerizations were carried out in a magnetically stirred
autoclave of 150 mL capacity thermostated by a circulation bath.
In order to prevent contamination by metallic species due to
corrosion of the internal surface of the autoclave, the reaction
mixtures were allowed to react in a glass beaker placed into the
autoclave. Styrene (Aldrich) was distilled before use. Carbon
monoxide was supplied by SIAD Company in “reasearch grade”
purity (>99.9%).
95% (0.218 g) for 1H, 93% (0.252 g) for 1Me
.
Characterization Data for 1H. Anal. Calcd for C8H11ClN4Pd (1H):
C 31.50, H 3.63, N 18.37, Cl 11.62. Found: C 31.4, H 3.60, N
18.4, Cl 11.6. 1H NMR (CD3NO2, 298 K): 8.01 (d, 1H, 3JHH ) 2.8
Hz, H5); 7.90 (d, 1H, 3JHH ) 2.0 Hz, H5); 7.78 (d, 1H, 3JHH ) 2.0
3
Hz, H3); 7.75 (d, 1H, JHH ) 2.8 Hz, H3); 6.60 (s, 2H, CH2); 6.51
3
3
(t, 1H, JHH ) 2.8 Hz, H4); 6.41 (t, 1H, JHH ) 2.0 Hz, H4); 0.83
(s, 3H, Pd-CH3). 13C{1H} NMR (CD3NO2, 298 K): 144.0 C3; 143.1
C3; 134.8 C5; 133.2 C5; 108.5 C4, 108.0 C4; 64.5 CH2; -5.1 Pd-
CH3. IR (polyethylene): 314 cm-1 (νPdCl).
Safety note: perchlorate salts of metal complexes with organic
ligands are potentially explosive; however, all the prepared
compounds in the experimental conditions described appeared to
be stable both in solution and in the solid state.
Characterization Data for 1Me. Anal. Calcd for C12H19ClN4Pd
(1Me): C 39.90, H 5.30, N 15.51, Cl 9.82. Found: C 40.0, H 5.35,
Characterizations. Microanalyses (C, H, N, Cl) of the isolated
complexes were performed at the Istituto di Chimica Inorganica e
delle Superfici, Padova. Infrared spectra (4000-450 cm-1 Nujol
mulls, 450-250 cm-1 polyethylene pellets) were recorded on a
Perkin-Elmer Spectrum One spectrophotometer. NMR spectra (1H,
13C, 31P) were obtained on AC 200 or AVANCE 300 Bruker
(13) (a) Balacco, G. J. Chem. Inf. Sci. Comput. Sci. 1994, 34, 1235. (b)
Cobas Go´mez, J. C.; Sardina Lo´pez, F. J. MestRe-C, Universidad de
Santiago de Compostela (Spain), 2006.
(14) Geary, W. Coord. Chem. ReV. 1971, 7, 81.
spectrometers at temperatures between 298 and 203 K. 1H and 13
C
(15) (a) Parr, R. G.; Yang, W. Density-Functional Theory of Atoms and
Molecules; Oxford University Press: Oxford, 1989. (b) Labanowski, J. K.;
Andzelm, J. Density Functional Methods in Chemistry; Springer-Verlag:
New York, 1991. (c) Geerlings, P.; De Proft, F.; Langenaker, W. Chem.
ReV. 2003, 103, 1793. (d) Ziegler, T. Chem. ReV. 1991, 91, 65. (e) Becke,
A. D. J. Chem. Phys. 1993, 98, 5648. (f) Burke, K.; Perdew, J. P.; Wang,
Y. In Electronic Density Functional Theory: Recent Progress and New
Directions; Dobson, J. F., Vignale, G., Das, M. P. Eds.; Plenum: New York,
1998. (g) Dedieu, A. Chem. ReV. 2000, 100, 543.
spectra are referred to internal tetramethylsilane, while 31P{1H}
chemical shifts are reported with respect to 85% aqueous H3PO4.
The bidimensional NMR experiments were performed using their
standard programs. NMR deuterated solvents were purchased from
Euriso-Top. The SwaN-MR and MestRe-C software packages were
(8) Onishi, M.; Hiraki, K.; Ueno, A.; Yamaguchi, Y.; Ohama, Y. Inorg.
Chim. Acta 1984, 82, 121.
(16) (a) Cundari, T. R.; Stevens, W. J. J. Chem. Phys. 1993, 98, 5555.
(b) Dunning, T. H., Jr.; Hay, P. J. In Modern Theoretical Chemistry, Vol.
3; Schafter, H. F. Ed.; Plenum Press: New York, 1976. (c) Davidson, E. R.;
Feller, D. Chem. ReV. 1986, 86, 681. (d) Dolg, M. In Modern Methods and
Algorithms of Quantum Chemistry, Vol. 1; Grotendorst, J. Ed.; NIC Series,
John Neumann Institute for Computing: Ju¨lich, 2000.
(17) Barone, V.; Cossi, M. J. Phys. Chem. A 1998, 102, 1995.
(18) Frish, M. J.; Trucks, G. W.; Schlegel, H. B.; et al. GAUSSIAN 03,
ReVision D.02; Gaussian Inc.: Wallingford, CT, 2004.
(19) Brandolin, A. J.; Hills, D. D. NMR Spectra of Polymers and Polymer
AdditiVes; Marcel Dekker: New York, 2000.
(9) (a) McAuliffe, C. A. In ComprehensiVe Coordination Chemistry,
Vol. 2; Wilkinson, G., Gillard, R. D., Cleverty, J. A. Eds.; Pergamon Press:
Oxford, 1987; Chapter 14. (b) Fey, N.; Orpen, A. G.; Harvey, J. N. Coord.
Chem. ReV. 2008, doi:10.1016/j.ccr.2008.04.017.
(10) Jameson, D. L.; Castellano, R. K. Inorg. Synth. 1998, 32, 58.
(11) Chatt, J.; Vallarino, L. M.; Venanzi, L. M. J. Chem. Soc. 1957,
3413.
(12) Rulke, R. E.; Ernsting, J. M.; Spek, A. L.; Elsevier, C. J.; van
Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

Mixed-Ligand Palladium(II) Organometallic Complexes
Organometallics, Vol. 28, No. 11, 2009 3249
1
N 15.5, Cl 9.75. H NMR (CD2Cl2, 298 K): 7.16, 6.06 (AB spin
H5′); 7.68 (d, 1H,3JHH ) 2.2 Hz, H3′); 7.64 (d, 1H, 3JHH ) 2.2 Hz,
2
2
system, 2H, JHH ) 14.5 Hz, CH2); 5.98 (s, 1H, H4); 5.84 (s, 1H,
H3); 6.95, 6.35 (AB spin system, 2H, JHH ) 14.3 Hz, CH2); 6.41
3
3
H4); 2.41 (s, 3H, Me5); 2.40 (s, 3H, Me5); 2.35 (s, 6H, Me3); 0.85
(s, 3H, Pd-CH3). 13C{1H} NMR (CD2Cl2, 298 K): 152.6, 152.0,
141.0, 139.7 C5 and C3; 108.4, 107.4 C4; 58.0 CH2; 14.6, 11.0 Me3;
(m, 1H, H4); 6.34 (dd, 1H, JHH ) 2.4 Hz, JHH ) 2.2 Hz, H4′);
3
4.15 (m, 6H, CH2-phos); 1.33 (t, 9H, JHH ) 7.0 Hz, CH3-phos);
0.85 (s, 3H, Pd-CH3). 31P{1H} NMR (CD2Cl2, 298 K): 113.1 phos.
13C{1H} NMR (CD2Cl2, 298 K): 144.2 C3′; 141.6 d{4JPC ) 2 Hz}
C3; 134.6 d{3JPC ) 3 Hz} C5′; 134.0 C5; 107.8 d{4JPC ) 3 Hz} C4;
107.5 C4′; 63.3 CH2; 62.9 d{2JPC ) 2 Hz} CH2-phos; 16.1 d{3JPC
) 7 Hz} CH3-phos; -2.6 d{2JPC ) 4 Hz} Pd-CH3.
13.6, 11.6 Me5; -7.6 Pd-CH3. IR (polyethylene): 312 νPdCl
.
Synthesis of PdClMe(BPM)P(OEt)3 (C14H26ClN4O3PPd, Mw )
471.23, 2). To a solution of PdClMe(BPM) (0.229 g, 0.75 mmol)
in 20 mL of CH2Cl2 was added a stoichiometic amount of
triethylphosphite P(OEt)3 (128 µL, 0.75 mmol) by a microsyringe,
and the resulting reaction mixture was allowed to react at room
temperature and under magnetic stirring for 15 min. The solvent
was removed by evaporation at reduced pressure, leaving a white
oil, which was washed with cold (-25 °C) n-hexane and dried under
vacuum. Yield ) 0.97% (0.343 g).
Characterization Data for 3Pr. Anal. Calcd for C17H32ClN4O7PPd
(3Pr): C 35.37, H 5.59, N 9.70, Cl 6.14. Found: C 35.5, H 5.65, N
9.75, Cl 6.10. ΛM (DMF, 298 K) ) 67 Ω-1 mol-1 cm2. H NMR
1
3
(CD2Cl2, 243 K): 8.16 (m, 1H, H5); 8.11 (d, 1H, JHH ) 2.6 Hz,
3
H5′); 7.70 (d, 1H, JHH ) 2.0 Hz, H3′); 7.64 (m, 1H, H3); 6.96,
2
6.34 (AB spin system, 2H, JHH ) 14.4 Hz, CH2); 6.41 (m, 1H,
3
3
H4); 6.34 (dd, 1H, JHH ) 2.6 Hz, JHH ) 2.0 Hz, H4′); 4.79 (m,
Anal. Calcd for C14H26ClN4O3PPd (2): C 35.68, H 5.56, N 11.89,
3
3H, CH-phos); 1.34, 1.27 (2d, 18H, JHH ) 6.2 Hz, CH3-phos);
Cl 7.52. Found: C 35.8, H 5.60, N 11.9, Cl 7.55. 1H NMR (CD2Cl2,
0.75 (s, 3H, Pd-CH3). 31P{1H} NMR (CD2Cl2, 298 K): 106.8 phos.
3
203 K): 8.72 (s, br, 1H, H5); 8.66 (d, 1H, JHH ) 2.4 Hz, H5’);
7.61 (d, 1H, 3JHH ) 2.4 Hz, H3’); 7.57 (s, br, 1H, H3); 6.33 (s, br,
H4); 6.25 (t, 3JHH ) 2.4 Hz, H4’); 8.32, 6.13 (AB spin system, 2H,
Synthesis of [PdMe(Me2BPM)P(OR)3]ClO4 {R ) Me, C15H28ClN4-
O7PPd, Mw ) 549.25, 4Me; R ) Et, C18H34ClN4O7PPd, Mw
)591.33, 4Et; R ) iPr, C21H40ClN4O7PPd, Mw ) 633.41, 4Pr}. The
three complexes [PdMe(Me2BPM)P(OR)3]ClO4 {R ) Me (4Me),
2JHH ) 13.8 Hz, CH2); 4.09 (m, 6H, CH2-phos); 1.25 (t, 9H, JHH
3
) 7.0 Hz, CH3-phos); 0.68 (s, 3H, Pd-CH3). 31P{1H NMR} (CD2Cl2,
203 K): 116.4 phos. 13C{1H NMR} (CD2Cl2, 203 K): 143.7, 141.0,
135.2 d{3JPC ) 2 Hz}, 134.6 C5 and C3; 107.2 d{4JPC ) 3 Hz},
107.0 C4; 62.6 d{2JPC ) 2 Hz} CH2-phos; 62.4 CH2; 16.4 d{3JPC
) 8 Hz} CH3-phos; -2.6 d{2JPC ) 5 Hz} Pd-CH3. 1H NMR
(CDCl3, 328 K): 8.15 (s, 2H, slightly br, H5); 7.51 (s, 2H, H3);
6.62 (s, 2H, slightly br, CH2); 6.24 (m, 2H, H4); 4.13 (m, 6H, CH2-
i
R ) Et (4Et), Pr (4Pr)} were synthesized following the same
procedure described for [PdMe(BPM)P(OR)3]ClO4 (3Me, 3Et, 3Pr)
using 0.75 mmol (0.271 g) of 1Me as starting precursor. Yields:
82% (0.338 g) for 4Me, 85% (0.377 g) for 4Et, 81% (0.385 g) for
4Pr.
Characterization Data for 4Me. Anal. Calcd for C15H28ClN4O7PPd
(4Me): C 32.80, H 5.14, N 10.20, Cl 6.45. Found: C 32.9, H 5.10,
N 10.2, Cl 6.45. ΛM (DMF, 298 K) ) 71 Ω-1 mol-1 cm2. 1H NMR
3
phos); 1.28 (t, 9H, JHH ) 7.1 Hz, CH3-phos); 0.61 (s, 3H, Pd-
CH3). 31P{1H NMR}: 113.9 ppm.
2
(CD2Cl2, 298 K): 6.77, 6.46 (AB spin system, 2H, JHH ) 15.3
Synthesis of [PdMe(BPM)P(OR)3]ClO4 {R ) Me, C11H20ClN4-
O7PPd, Mw ) 493.15, 3Me; R ) Et, C14H26ClN4O7PPd, Mw
)535.23, 3Et; R ) iPr, C17H32ClN4O7PPd, Mw ) 577.31, 3Pr}. All
the three complexes [PdMe(BPM)P(OR)3]ClO4 {R ) Me (3Me), R
) Et (3Et), iPr (3Pr)} were synthesized following the same
procedure. In a typical experiment, to a solution of 1H (0.229 g,
0.75 mmol) in 20 mL of CH2Cl2 was added a stoichiometic amount
of the proper phosphite P(OR)3 (0.75 mmol) by a microsyringe,
and the resulting reaction mixture was allowed to react for 15 min
at room temperature under magnetic stirring. The solvent was
subsequently removed by evaporation at reduced pressure, and
methanol (10 mL) was added. To the resulting solution was added
a stoichiometric amount of silver perchlorate (0.156 g, 0.75 mmol),
and the reaction mixture was left in the dark under magnetic stirring
at room temperature for 30 min. The reaction byproduct AgCl was
removed by filtration, and methanol was evaporated under reduced
pressure. Addition of a 1:1 mixture of diethyl ether and n-hexane
(10 mL) to the residual oil caused the separation of white
microcrystals, which were filtered, washed with diethyl ether, and
dried under vacuum. Yields: 85% (0.314 g) for 3Me, 87% (0.349
g) for 3Et, 87% (0.377 g) for 3Pr. The crystallization of 3Et from
methanol/diethyl ether afforded crystals suitable for X-ray analysis.
Characterization Data for 3Me. Anal. Calcd for C11H20ClN4O7PPd
(3Me): C 26.79, H 4.09, N 11.36, Cl 7.19. Found: C 26.9, H 4.10,
N 11.4, Cl 7.15. ΛM (DMF, 298 K) ) 69 Ω-1 mol-1 cm2. 1H NMR
3
Hz, CH2); 6.00, 5.97 (2 s, 2H, H4); 3.80 (d, 9H, JPH ) 12.6 Hz,
CH3-phos); 2.47, 2.46, 2.34, 2.26 (4 s, 12H, Me3, Me5); 0.88 (d,
3H, 3JPH ) 1.2 Hz, Pd-CH3). 31P{1H} NMR (CD2Cl2, 298 K): 118.5
phos. 13C{1H} NMR (CD2Cl2, 298 K): 151.9 d{3JPC ) 3 Hz}, 151.6
C3; 142.3 m C5; 108.3 d{4JPC ) 4 Hz}, 107.9 C4; 58.4 s CH2; 53.0
d{2JPC ) 2 Hz) CH3-phos; 14.3, 14.0, 11.1, 11.0 Me3 and Me5;
-5.5 d{2JPC ) 4 Hz} Pd-CH3.
Characterization Data for 4Et. Anal. Calcd for C18H34ClN4O7PPd
(4Et): calcd. C 36.56, H 5.80, N 9.47, Cl 6.00. Found: C 36.7, H
5.75, N 9.50, Cl 5.95. ΛM (DMF, 298 K) ) 69 Ω-1 mol-1 cm2. 1H
2
NMR (CD2Cl2, 298 K): 6.67, 6.39 (AB spin system, 2H, JHH
)
15.4 Hz, CH2); 5.92, 5.89 (2s, 2H, H4); 4.09 (m, 6H, CH2-phos);
3
2.40, 2.38, 2.26, 2.20 (4 s, 12 H, Me3, Me5); 1.29 (t, 9H, JHH
)
7.0 Hz, CH3-phos); 0.78 (d, 3H, 3JPH ) 1.2 Hz, Pd-CH3). 31P{1H}
NMR (CD2Cl2, 298 K): 112.3 phos.
Characterization Data for 4Pr. Anal. Calcd for C21H40ClN4O7PPd
(4Pr): C 39.82, H 6.37, N 8.85, Cl 5.60. Found: C 40.0, H 6.40, N
8.90, Cl 5.65. ΛM (DMF, 298 K) ) 67 Ω-1 mol-1 cm2. H NMR
1
2
(CD2Cl2, 298 K): 6.64, 6.39 (AB spin system, 2H, JHH ) 15.4
Hz, CH2); 5.91, 5.88 (2 s, 2H, H4); 4.76 (m, 3H, CH-phos); 2.40,
2.38, 2.25, 2.24 (4 s, 12H, Me3, Me5); 1.35, 1.27 (2 d, 18H, 3JHH
)
6.2 Hz, CH3-phos); 0.76 (d, 3H, 3JPH ) 1.0 Hz, Pd-CH3). 31P{1H}
NMR (CD2Cl2, 298 K): 105.7 phos.
Synthesis of PdMe(SeCN)(BPM)P(OEt)3 (C15H26N5O3PPdSe,
Mw ) 540.75, 5). To a solution of 3Et (0.134 g, 0.25 mmol) in 10
mL of methanol was added a stoichiometric amount of potassium
selenocyanate, KSeCN (0.036 g, 0.25 mmol). A white precipitate
of KClO4 immediately separated from the solution, which was
removed after 15 min by filtration. The solvent was removed by
evaporation at reduced pressure, and the residual white solid was
collected and dried under vacuum. Yield ) 95% (0.128 g).
3
(CD2Cl2, 298 K): 8.27 (m, 1H, H5); 8.21 (d, 1H, JHH ) 2.7 Hz,
H5’); 7.76-7.75 (m, 2H, H3-H3′); 6.78 (s, br, 2H, CH2); 6.50 (m,
1H, H4); 6.43 (t, 1H, 3JHH ) 2.7 Hz, H4′); 3.85 (d, 9H, 3JPH ) 12.9
Hz, CH3-phos); 0.94 (s, 3H, Pd-CH3). 31P{1H} NMR (CD2Cl2, 298
K): 119.3 phos. 13C{1H NMR} (CD2Cl2, 298 K): 144.4 C3′; 141.7
d{4JPC ) 1 Hz} C3; 134.6 d{3JPC ) 3 Hz} C5; 134.0 C5′; 107.8
d{4JPC ) 3 Hz} C4; 107.7 C4′; 63.3 CH2; 53.1 d{2JPC ) 2 Hz}
CH3-phos; -3.1 d{2JPC ) 4 Hz} Pd-CH3.
Anal. Calcd for C15H26N5O3PPdSe (5): C 33.32, H 4.85, N 12.95.
Found: C 33.2, H 4.85, N 13.0. 1H NMR (CD2Cl2, 203 K): 8.26 s,
8.20 d{3JHH ) 2.4 Hz}, 7.73 s, 7.72 s (H3); 7.66 d{3JHH ) 2.4 Hz),
7.62 s, 7.45 s, 7.44 s (H5); 6.38 s, 6.31 t{3JHH ) 2.4 Hz}, 6.24 s,
Characterization Data for 3Et. Anal. Calcd for C14H26ClN4O7PPd
(3Et): C 31.42, H 4.90, N 10.47, Cl 6.60. Found: C 31.3, H 4.85,
N 10.5, Cl 6.55. ΛM (DMF, 298 K) ) 66 Ω-1 mol-1 cm2. 1H NMR
3
2
(CD2Cl2, 243 K): 8.17 (m, 1H, H5); 8.12 (d, 1H, JHH ) 2.4 Hz,
6.22 s (H4); 8.05, 7.60 (AB spin system, JHH ) 17.0 Hz, CH2);

3250 Organometallics, Vol. 28, No. 11, 2009
Bortoluzzi et al.
7.18, 6.22 (AB spin system, 2JHH ) 13.4 Hz, CH2); 4.09 (m, CH2-
phos); 3.93 (m, CH2-phos); 1.26 (t, 3JHH ) 6.9 Hz, CH3-phos); 1.17
(t, 3JHH ) 7.4 Hz, CH3-phos); 0.71 (s, Pd-CH3); 0.63 (s, Pd-CH3).
31P{1H} NMR (CD2Cl2, 203 K): 123.0 {2JP-Se ) 146 Hz} phos;
116.2 phos. IR (Nujol): 2145, 2107 (νCN).
Synthesis of [Pd(COMe)(BPM)P(OEt)3]ClO4 (C15H26ClN4-
O8PPd, Mw ) 563.24, 6). A glass beaker containing a solution of
3Et (0.268 g, 0.5 mmol) in 15 mL of CH2Cl2 was placed in a 50
mL steel autoclave. The reactor atmosphere was carefully washed
with N2 and subsequently saturated with CO fed at 40 atm. The
reaction mixture was kept under magnetic stirring for 2 h at room
temperature; subsequently the reactor was vented and the solution
was filtered to remove traces of metallic palladium. Dichlo-
romethane was removed by evaporation under reduced pressure,
and diethyl ether (10 mL) was added. The solid formed was filtered,
washed with n-hexane, and dried under vacuum. Yield ) 72%
(0.203 g).
productivity was calculated as g polymer/(g Pd h)-1; the reproduc-
ibility was within ca. 5%.
Limiting Viscosity Number (LVN) Measurement and
Average Viscosity Molecular Weight Calculation. The LVN of
a dilute polymer solution was determined by using the Huggins
relationship between the viscosity number and the polymer
concentration by extrapolation to zero concentration.20 The polymer
solution was prepared in toluene as a solvent, and the viscosity
was measured by using a Ubbelhode type capillary viscosimeter,
thermostated at 25 °C. The average molecular weight of polystyrene
was derived from the LVN using the following Mark-Houwink-
Sakurada equation:
[η])K25,toluene[Mv]a
(1)
where [η] is the LVN, K25,toluene ) 0.0105 mL/g, and a ) 0.73.21
Crystal Structure Determination of 3Et. The crystal data were
collected using a Nonius Kappa CCD diffractometer with graphite-
monochromated Mo KR radiation. The data sets were integrated
with the Denzo-SMN package22 and corrected for Lorentz, polar-
ization and absorption (SORTAV23) effects. The structure was
solved by direct methods (SIR9724). The non-hydrogen atoms were
refined anisotropically. The hydrogen atoms were refined isotro-
pically except those belonging to the P(OEt)3 moiety, which were
included on calculated positions, riding on their carrier atoms. All
calculations were performed using SHELXL-9725 and PARST26
implemented in the WinGX27 system of programs. The crystal data
and refinement parameters are summarized in the Supporting
Information, Table 1. Selected interatomic distances and angles are
given in the footnote of Figure 1.
Anal. Calcd for C15H26ClN4O8PPd (6): C 31.99, H 4.65, N 9.95,
Cl 6.29. Found: C 32.1, H 4.70, N 10.0, Cl 6.30. ΛM (DMF, 298
K) ) 67 Ω-1 mol-1 cm2. 1H NMR (CD2Cl2, 243 K): 8.17 (s, slightly
3
br, 1H, H5); 8.13 (d, 1H, JHH ) 2.4 Hz, H5′); 7.47 (d, 1H,3JHH
)
2.0 Hz, H3′); 7.44 (d, 1H, 3JHH ) 1.8 Hz, H3); 6.99, 6.47 (AB spin
2
system, 2H, JHH ) 14.6 Hz, CH2); 6.37 (m, 1H, H4); 6.33 (dd,
1H, 3JHH ) 2.4 Hz, 3JHH ) 2.0 Hz, H4′); 4.14 (m, 6H, CH2-phos);
4
3
2.46 (d, 3H, JPH ) 1.9 Hz, COCH3); 1.27 (t, 9H, JHH ) 7.3 Hz,
CH3-phos). 31P{1H} NMR (CD2Cl2, 298 K): 119.7 phos. IR (Nujol):
1703 (νCO).
Synthesis of [Pd(CMedNCH2Tos)(BPM)P(OEt)3]ClO4 (C23H35-
ClN5O9PPdS, Mw ) 730.46, 7). To a solution of 3Et (0.268 g, 0.5
mmol) in 20 mL of CH2Cl2 was added a stoichiometric amount of
tosylmethyl isocyanide (0.098 g, 0.5 mmol), and the resulting
reaction mixture was left overnight under stirring at room temper-
ature. The solution was concentrated to about 2 mL by evaporation
under reduced pressure. Slow addition of diethyl ether (ca. 20 mL)
caused the separation of pale yellow microcrystals, which were
filtered, washed with fresh diethyl ether, and dried under vacuum.
Yield ) 90% (0.329 g).
Results and Discussion
Synthesis and Characterization of Complexes 1-4. The
reaction of the precursor PdClMe(COD) with bis(pyrazol-1-
yl)methane (BPM) or bis(3,5-dimethylpyrazol-1-yl)methane
(Me2BPM) in dichloromethane at room temperature led to the
formation of the neutral complexes PdClMe(BPM) (1H) and
PdClMe(Me2BPM) (1Me) in high yields, as depicted in Scheme
1. The 1H and 1Me derivatives were characterized by elemental
analysis, conductivity, and spectroscopic (IR and NMR) mea-
surements. The NMR spectra clearly show the expected non-
equivalence of the two pyrazole rings. Besides the N-hetero-
Anal. Calcd for C23H35ClN5O9PPdS (7): C 37.82, H 4.83, N 9.59,
Cl 4.85. Found: C 37.7, H 4.80, N 9.55, Cl 4.80. ΛM (DMF, 298
1
K) ) 69 Ω-1 mol-1 cm2. H NMR (CD2Cl2, 298 K): 8.24 (d, 1H,
3JHH ) 2.5 Hz, H5); 8.20 (m, 1H, H5); 7.82, 7.38 (pseudo-AB spin
3
3
system, 4H, JHH ) 8.1 Hz, phenyl); 7.69 (d, 1H, JHH ) 2.5 Hz,
H3); 7.32 (d, 1H, 3JHH ) 1.9 Hz, H3); 6.90, 6.70 (AB spin system,
slightly br, 2H, JHH ) 14.2 Hz, BPM-CH2); 6.44 (t, 1H, JHH
1
cycles signals, the H NMR spectrum of 1H recorded at room
2
3
)
temperature shows only a singlet for the methylene bridge,
indicating that the well-known boat-to boat inversion process
of the ligand1,3 is fast on the NMR time scale. On the contrary
2.4 Hz, H4); 6.31 (m, 1H, H4); 5.20, 5.03, 2.34 (ABC3 spin system,
5H, 2JAB ) 14.0 Hz, 5JAC ) 0.0 Hz, 5JBC ) 3.0 Hz, Pd-C(CH3)dN-
CH2-); 4.13 (m, 6H, CH2-phos); 2.49 (s, 3H, CH3-Tos); 1.35 (t,
at 298 K the methylene group of 1Me corresponds to an AB
5
9H, JHH ) 7.0 Hz, CH3-phos). 13C{1H} NMR (CD2Cl2, 298 K):
2
spin system with a typical geminal coupling constant JHH
)
189.4 Pd-C(CH3)d; 145.5 phenyl; 144.2, 144.1 C3; 135.6 phenyl;
135.0, 134.9 C5; 130.0, 129.3 phenyl; 108.2, 108.1 C4; 79.2 d{4JPC
) 17 Hz} CH2-S; 63.9 d{2JPC ) 5 Hz} CH2-phos; 63.4 CH2-BPM;
32.6 d{3JPC ) 17 Hz} Pd-C(CH3)d); 21.8 CH3-Tos; 16.2 d{3JPC
) 7 Hz} CH3-phos. 31P{1H} NMR (CD2Cl2, 298 K}: 100.5 phos.
Polymerization Runs. In a typical polymerization run a solution
of styrene (20 mL) containing 8.4 × 10-3 mmol (4.5 mg) of 3Et
was prepared in a glass beaker. In some cases, benzoquinone or
4-tert-butylcathecol was added to the reaction mixture. The beaker
was placed in a 150 mL steel autoclave, and the reactor atmosphere
was carefully washed with N2. In some cases CO was fed at 40
atm. Temperature was quickly increased to 363 K under stirring.
All the polymerization runs were carried out in the dark. The
solution was stirred with a magnetic bar for 2 h, after which the
autoclave was rapidly cooled to rt and slowly depressurized (when
CO was used). The polymerization mixture was poured into
methanol, and the polymer was coagulated, recovered by filtration,
washed with an excess of fresh methanol, and dried under vacuum
at room temperature. The dried polymer was weighed, and the
14.5 Hz, indicating that the same inversion process for 1Me is
frozen at room temperature. The Pd-CH3 1H NMR signal appears
in both cases as a sharp singlet near 0.8 ppm and corresponds
to low-frequency 13C NMR signals at -5.1 (1H) and -7.6 ppm
(1Me). PdClMe(BPM) and PdClMe(Me2BPM) DMF solutions
are not conductive at room temperature. The Pd-Cl bond was
(20) Huggins, M. L. J. Am. Chem. Soc. 1942, 64, 2716.
(21) Brandrup, J., Immergut, E. H., Grulke, E. A. Eds. Polymer
handbook, 4th ed.; Wiley: New York, 1999.
(22) Otwinowski, Z.; Minor, W. In Methods in Enzymology, Vol. 276;
Carter, C. W., Sweet, R. M. Eds.; Academic Press: London, 1997; Part A.
(23) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33.
(24) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, G.; Guagliardi, A.; Moliterni, A. G.; Polidori, G.; Spagna, R.
SIR97. J. Appl. Crystallogr. 1999, 32, 115.
(25) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
Refinement; University of Gottingen: Germany, 1997.
(26) Nardelli, M. J. Appl. Crystallogr. 1995, 28, 659.
(27) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.

Mixed-Ligand Palladium(II) Organometallic Complexes
Organometallics, Vol. 28, No. 11, 2009 3251
An ORTEP28 view of complex cation 3Et is shown in Figure
1. The coordination geometry around the palladium atom is
distorted square planar owing to the constraints mainly exerted
by the phosphite P(OEt)3 ligand. The coordination plane,
including the Pd atom, makes angles of 31.8(1)° and 31.7(1)°
with the pyrazole rings of the BPM ligand. The largest deviation
[0.044(3) Å] from the mean coordination plane is exhibited by
the N1 atom. The palladocycle with BPM is appreciably
puckeredwithaboat1,4 BconformationforthePd1,N1,N2,C5,N4,N3
six-membered ring and displays the puckering angles ꢀ2 )
1.4(2)° and θ2 ) 81.4(2)° and the total puckering amplitude
QT ) 0.748(3) Å.29 The BPM ligand is N,N′-bidentate with
the Pd1-N1 bond, trans to P(OEt)3, of 2.115(2) Å shorter than
the Pd1-N3 of 2.171(2) Å, reflecting the strong trans influence
exerted by the alkyl CH3 group compared to the phosphite
ligand. These data are in perfect agreement with those of other
similar compounds containing polydentate pyrazole-based ligands
where Pd-N(trans to P) and Pd-N(trans to C) distances are
in the ranges 2.08-2.11 and 2.12-2.19 Å, respectively.30 The
Pd-C bond length of 2.038(3) Å is within the distance interval
of 2.02-2.06 Å observed in Pd-(alkyl) bidentate nitrogen donor
complexes.30,31 The ClO4- anion does not have any interaction
with palladium and is sustained in the crystal packing by a
number of C-H · · · O short contacts.
Figure 1. ORTEP view of the cation complex 3Et displaying thermal
ellipsoids at 30% probability. Selected bond distances (Å): Pd1-C1
2.038(3), Pd1-N1 2.115(2), Pd1-N3 2.171(2), Pd1-P1 2.198(1),
N1-N2 1.356(3), N2-C5 1.440(4), N4-C5 1.444(4), N3-N4
1.358(4). Selected bond angles (deg): C1-Pd1-N1 89.0(1),
C1-Pd1-N3 176.0(1), C1-Pd1-P1 84.5(1), N1-Pd1-N3 87.1(1),
N1-Pd1-P1 173.3(1), N3-Pd1-P1 99.4(1), Pd1-N1-N2 121.4(2),
N1-N2-C5 119.2(2), N2-C5-N4 111.1(3), C5-N4-N3 119.8(2),
Pd1-N3-N4 119.0(2).
The intermediate formation of neutral derivatives of general
formula PdClMe(NN)P(OR)3 in the synthesis of the complexes
3R and 4R was established with the isolation and characterization
of the derivative PdClMe(BPM)P(OEt)3 (2). The NMR spectra
of compound 2 at room temperature are very hard to interpret
because of the fluxional behavior of the ancillary ligands, as
clearly observable in the 1H NMR spectrum reported in Figure
2, where in the high-frequency region only two pyrazole signals
are relatively sharp, while the other signals are immersed in
very broad resonances. Also the 31P{1H} NMR spectrum of 2
at 298 K shows only a very broad signal. Cooling the NMR
tube at 203 K has successfully frozen the fluxional behavior.
The NMR spectra of 2 recorded at this temperature display two
chemically nonequivalent pyrazole rings. The methylene bridge
appears as an AB spin system at 203 K (δA ) 8.32 ppm, δB )
detected by IR spectroscopy in the far region, and the corre-
sponding stretching falls between 314 and 312 cm-1
.
The reaction of 1H and 1Me with 1 equiv of the proper
phosphite P(OR)3 and subsequently with a stoichiometric
amount of silver perchlorate, AgClO4, at room temperature led
to the formation of the cationic alkyl complexes [PdMe(NN)-
P(OR)3](ClO4) {NN ) BPM, R ) Me (3Me); NN ) BPM, R )
Et (3Et); NN ) BPM, R ) iPr (3Pr); NN ) Me2BPM, R ) Me
(4Me); NN ) Me2BPM, R ) Et (4Et); NN ) Me2BPM, R ) iPr
(4Pr)}, as summarized in Scheme 1. These species behave as
1:1 electrolytes in DMF solution, and their elemental analyses
agree with the proposed formulations. The NMR spectra of
complexes 3R and 4R show the lack of equivalence of the
N-donor bidentate ligands rings. The carbon atoms of the
pyrazole ring in trans position with respect to the phosphite
ligand exhibit couplings with the 31P isotope of 2-4 Hz. The
boat-to-boat inversion process of the chelate nitrogen ligand is
fast at room temperature and frozen at 243 K for the BPM
derivatives 3R, while is already blocked at room temperature
for the Me2BPM 4R complexes, as deducible from the multiplic-
2
6.13 ppm, JHH ) 13.8 Hz). The NMR data of the phosphite
ancillary ligand suggest that the rotation around the Pd-P bond
is not frozen at 203 K on the NMR time scale. In the low-
frequency region the Pd-bonded methyl group is detectable as
a sharp singlet at 0.68 ppm. The 31P{1H} NMR of 2 at 203 K
is a single, sharp resonance at 116.4 ppm. In the 13C{1H} NMR
spectrum of 2 at 203 K the weak couplings between the
phosphorus atom and two pyrazole carbon atoms, similar in
magnitude to those observed for the 3Me, 3Et, and 4Me derivatives,
suggest that one of the two bis(pyrazol-1-yl)methane rings
should be in trans position with respect to the phosphite. The
coordinated methyl group corresponds to the doublet at -2.6
ppm with a 2JPC coupling constant of 5 Hz, which is very close
to those observed for complexes 3Me, 3Et, and 4Me. This suggests
1
ity of the H NMR signals of the methylene bridges. Besides
their characteristic 1H NMR and 13C NMR signals, the phosphite
ancillary ligands always show a single sharp resonance in the
31P{1H} spectra between 119.3 and 105.7 ppm. The splitting in
1
two signals of the isopropyl doublet in the 243 K H NMR
(28) Burdett, M. N.; Johnson, C. K. ORTEP III, Report ORNL-6895;
Oak Ridge National Laboratory: Oak Ridge, TN, 1996.
1
spectrum of 3Pr and in the 298 K H NMR spectrum of 4Pr
(29) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354.
(30) (a) Canty, A. J.; Jin, H.; Roberts, A. S.; Traill, P. R.; Skelton, B. W.;
White, A. H. J. Organomet. Chem. 1995, 489, 153. (b) Gutierrez, E.;
Nicasio, M. C.; Paneque, M.; Ruiz, C.; Salazar, V. J. Organomet. Chem.
1997, 549, 167. (c) Canty, A. J.; Hoare, J. L.; Skelton, B. W.; White, A. H.;
van Koten, G. J. Organomet. Chem. 1998, 552, 23. (d) Diaz-Requejo, P. M.;
Nicasio, M. C.; Belderrain, T. R.; Perez, P. J.; Puerta, M. C.; Valerga, P.
Eur. J. Inorg. Chem. 2000, 1359. (e) Kla¨ui, W.; Turkowski, B.; Wunderlich,
H. Z. Anorg. Chem. 2001, 627, 2397.
indicates that the steric hindrance of the substituents makes the
rotation around the Pd-P bond slow on the NMR time scale.
1
The 3R and 4R Pd-bonded methyl group H NMR signal falls
in the range 0.94-0.75 ppm, and the corresponding 13C NMR
2
are low-frequency doublets with a JPC coupling constant of 4
Hz. The characterization data suggest that the Pd(II) complexes
3R and 4R have square-planar geometry, with the N-donor κ2-
coordinated to the metal center and the other two ligands
mutually in cis position, as shown in Scheme 1.
(31) (a) Liang, H.; Liu, J.; Li, X.; Li, Y. Polyhedron 2004, 23, 1619.
(b) Bailey, P. J.; Melchionna, M.; Parsons, S. Organometallics 2007, 26,
128.

3252 Organometallics, Vol. 28, No. 11, 2009
Bortoluzzi et al.
Scheme 1. Synthesis of Complexes 1-4
that the phosphite and methyl ligands should be mutually in
cis position. On the basis of the reported spectroscopic data
we propose that 2 is a square-planar fluxional complex where
the BPM ligand is κ1-coordinated to the metal center. The
to “classic” agostic interactions. This situation is typically
associated with d8 transition metals centers that are square planar
prior to the interaction. The great chemical shift difference
between the two hydrogen atoms of the BPM methylene bridge
1
1
presence of a resolved H NMR AB spin system for the BPM
in compound 2 and the presence of a strong H NMR high-
methylene bridge leads however to the conclusion that further
interactions between BPM and the Pd ion should be present.
DFT calculations carried out on the ground-state geometry of
2 exclude any bond, even weak, between palladium and the
second sp2 nitrogen atom of BPM, as observable in Figure 3.
The computed Pd---H distance and Pd-H-C angle are however
typical for a hydrogen-bonding interaction between a hydrogen
atom of the BPM -CH2- group and the metal center. In the in
Vacuo model of 2 the calculated Pd---H distance and Pd-H-C
angle are respectively 2.734 Å and 121.2°, while the addition
of the C-PCM solvation model for dichloromethane led to a
Pd---H distance of 2.659 Å and a Pd-H-C angle of 121.6°.
This type of interaction has been recently reviewed by Brookhart,
Green, and Parkin, and it is actually called “anagostic”, using
Lippard’s definition.32 In complexes containing an anagostic
bond the interacting hydrogen is high-frequency shifted, contrary
frequency shift (8.32 ppm) agree with such a hypothesis.
Moreover, these two hydrogen atoms show at 198 K two slightly
1
different JCH coupling constants, the first one of 146 Hz and
the second one of 154 Hz. For comparison, in the free BPM
ligand 13C NMR spectrum the -CH2- group gives a triplet
1
with a JCH coupling constant of 153 Hz. This result suggests
the presence of a pseudo hydrogen bond of the type Pd---H-C
in compound 2. This type of interaction should be favored by
the relative acidity of the considered hydrogen atoms, caused
by the presence of two electron-withdrawing groups bonded to
1
the methylene bridge. To strengthen this hypothesis, the JCH
coupling constant has been recorded also for the methylene
bridge of complex 4Me, where both the pyrazole rings are
coordinated to the metal center and there is no possibility of a
1
Pd---H-C interaction. Interestingly, only one value of JCH
constant was measured, 148 Hz. This means that the different
1
Figure 2. H NMR spectrum of PdClMe(BPM)P(OEt)3 (2) in CD2Cl2 at 298 and 203 K.

Mixed-Ligand Palladium(II) Organometallic Complexes
Organometallics, Vol. 28, No. 11, 2009 3253
K[SeCN] to a solution of 3Et in methanol led to the formation
of a species of general formula PdMe(SeCN)(BPM)P(OEt)3 (5).
The elemental analysis data are in agreement with the proposed
formulations, and DMF solutions of 5 are not conductive at
298 K. The room-temperature 1H NMR spectrum displays very
broad signals, in particular in the bis(pyrazol-1-yl)methane
region. Also the low-frequency signal attributable to the Pd-
coordinated methyl group appears quite broad, as observable
1
in Figure 4. The H NMR spectrum of 5 recorded at 203 K
(see Figure 4) shows that the reaction of 3Et with SeCN- led to
the formation of two isomers of PdMe(SeCN)(BPM)P(OEt)3.
Two different bis(pyrazol-1-yl)methane ligands having chemi-
cally nonequivalent rings are in fact present in the high-
1
frequency region of the H NMR spectrum. Two AB spin
systems corresponding to different BPM methylene bridges are
detectable, the first one having δA ) 8.05 ppm, δB ) 7.60 ppm,
and 2JHH ) 17.0 Hz and the second one having δA ) 7.18 ppm,
2
δB ) 6.22 ppm, and JHH ) 13.4 Hz. Moreover, the spectrum
displays two different groups of phosphite signals and two Pd-
bonded methyl groups at 0.71 and 0.63 ppm. Integration of the
methyl singlets gave a ∼1.4:1 ratio between the two isomers.
The existence of two isomers was confirmed by the 203 K
31P{1H} NMR spectrum reported in Figure 5, where two
different signals are present, the first one at 123.0 ppm and the
second one at 116.2 pm. The signal at 123.0 ppm is less intense
than the second one and shows the presence of the selenium
satellites, with a 2JPSe coupling constant of 146 Hz. This allows
us to suppose that in the less abundant isomer the selenocyanide
and phosphite ligands occupy a mutually trans position. Finally,
the presence of two different isomers was confirmed by the IR
spectrum, where two different stretchings attributable to the
Figure 3. DFT B3PW91 ground-state optimized geometry for 2 in
the presence of the C-PCM solvation model for dichloromethane.
1JCH coupling constants in compound 2 cannot be attributed to
the lack of hydrogen equivalency due to restricted rotation
phenomena, thus supporting the idea of a Pd---H-C interaction.
1
The H NMR spectrum of 2 recorded at 328 K in CDCl3
solution shows only a single set of resonances for the pyrazole
rings and a singlet for the methylene bridge falling at 6.62 ppm.
In the 31P{1H} NMR spectrum at this temperature only a sharp
resonance at 113.9 ppm is observable. On the basis of the
variable-temperature NMR data the fluxional behavior of 2 can
be explained on the basis of an exchange between coordinated
and free pyrazole rings, which is slow on the NMR time scale
at 203 K. At 328 K, instead, the system is above the coalescence
temperature, therefore the pyrazolyl groups appear chemically
equivalent and there is no trace of interaction between the
methylene bridge and the metal center.
coordinated selenocyanide are present at 2145 and 2107 cm-1
.
The NMR behavior of 5 at variable temperature allows
supposing that the described isomers could be mutually in
equilibrium and that the interconversion process becomes slow
on the NMR time scale at low temperatures. The 1.4:1 isomer
ratio corresponds to a Gibbs energy difference of around 0.6
kJ mol-1. The absence of any coupling between the hydrogen
atoms of the coordinated methyl group and the 31P isotope
indicates that in both isomers the P(OEt)3 and CH3 ligands
should be mutually in cis position. The presence of resolved
1H NMR AB spin systems at 203 K for the methylene bridges
allows us to propose that anagostic interactions similar to that
observed for 2 could stabilize the geometries of these isomers,
even though only one of the two isomers displays a high-
frequency chemical shift (8.05 ppm). The reaction between 3Et
and K[SeCN] is sketched in Scheme 2.
The cationic alkyl complex 3Et was also studied as a catalytic
precursor toward styrene polymerization and CO-styrene
copolymerization. In the reactions carried out at 363 K, complex
3Et does not catalyze either styrene polymerization or, under
40 atm of CO pressure, CO-styrene copolymerization. However
in the latter case the presence of CO leads to the formation of
polystyrene with a productivity of 1015 g PS/(g Pd h). The
comparison of the spectroscopic data with literature spectra
showed that the obtained polymer is atactic. The addition of
benzoquinone or 4-tert-butylcathecol to the reaction mixture did
not cause any meaningful variation of the catalytic activity, this
excluding a radical mechanism. We did not observe the
formation of any polymer in blank tests in the presence of CO
but in the absence of the complex. The polymer was character-
ized by IR and NMR, and a viscosity average molecular weight
of 305 600 g/mol was measured. The 1H NMR spectrum of the
polymer shows the presence of a singlet at 2.20 ppm assigned
Preliminary Reactivity and Catalysis Studies. The complex
3
Et was chosen as precursor to start a preliminary study on the
reactivity of the new cationic alkyl derivatives. The character-
ization of the intermediate complex 2 prompted us to investigate
the interaction between 3Et and the chloride ion. The reaction
was carried out in a NMR tube at room temperature by adding
a stoichiometric amount of benzyltriethylammonium chloride,
[NBzEt3]Cl, to a CD2Cl2 solution containing a weighed amount
of 3Et. The 1H NMR and 31P{1H} NMR spectra of the reaction
mixture highlighted the immediate, quantitative formation of
the known neutral complex PdClMe(BPM)P(OEt)3 (2), as
depicted in Scheme 2.
The observed reactivity of 3Et toward the chloride ion
prompted us to extend this type of study toward other anions.
Selenocyanide, SeCN-, was chosen because it is a very good
nucleophile toward positively charged square-planar d8 metal
complexes33 and because its presence is easily detectable by
NMR (77Se, I ) 1/2, natural abundance ) 7.6%) and IR
spectroscopy.34 The addition of a stoichiometric amount of
(32) (a) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad.
Sci. U.S.A. 2007, 104, 6908, and references therein. (b) Sundquist, W. I.;
Bancroft, D. P.; Lippard, S. J. J. Am. Chem. Soc. 1990, 112, 1590.
(33) (a) Pitteri, B.; Bortoluzzi, M.; Marangoni, G. Trans. Met. Chem.
2005, 30, 1008. (b) Pitteri, B.; Canovese, L.; Chessa, G.; Marangoni, G.;
Uguagliati, P. Polyhedron 1992, 18, 2363, and references therein.
(34) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Compounds; Wiley: New York, 1986.

3254 Organometallics, Vol. 28, No. 11, 2009
Scheme 2. Synthesis of the Complexes 2 and 5 from 3Et
Bortoluzzi et al.
to -COCH3, which is the starting group of the polystyrene
polymer chain. This supports the hypothesis that styrene
polymerization starts from CO insertion into the Pd-CH3 bond
followed by the chain-growing step due to multiple consecutive
styrene insertions. This last result gave insight into the reaction
of 3Et with carbon monoxide. Complex 3Et reacts at room
temperature with CO, forming the corresponding acyl complex
[Pd(COMe)(BPM)P(OEt)3]ClO4 (6) (as reported in Scheme 3),
which was isolated and characterized. This species behaves as
a 1:1 electrolyte in DMF solution, and its elemental analysis
Under CO pressure (40 atm), complex 6 catalyzes styrene
polymerization, leading to a productivity of 1050 g PS/(g Pd
h) of atactic polystyrene. In the absence of CO, polymerization
does not occur and reduction to Pd metal is observed. These
results allow us to propose that CO is needed not only to form
the acyl complex 6 but also to stabilize the active species during
thepolymerizationreaction,avoidingafastcatalystdecomposition.
The Pd-CH3 bond of 3Et is able to give an insertion reaction
also with isocyanides, since its reaction with tosylmethyl
isocyanide in dichloromethane at room temperature led to the
insertion product [Pd(CMedNCH2Tos)(BPM)P(OEt)3]ClO4 (7),
as depicted in Scheme 3. This complex behaves as a 1:1
electrolyte in DMF solution, and its elemental analysis agrees
1
agrees with the proposed formulation. The H NMR spectrum
of 6 at room temperature shows very broad singlets, in particular
in the high-frequency region, but the spectrum is well resolved
at 243 K. The coordinated BPM and phosphite signals are very
similar to those observed in the spectrum of the precursor 3Et.
The coordinated COCH3 group corresponds to a doublet at 2.46
ppm, and a weak coupling exists between the acyl hydrogen
atoms and the 31P isotope (4JPH ) 1.9 Hz). The 31P{1H} NMR
of 6 at 243 K is a single, sharp resonance at 119.7 ppm. The
insertion of CO into the Pd-CH3 bond is confirmed by the IR
spectrum of 6, which shows a strong signal at 1703 cm-1
1
with the proposed formulation. The H NMR spectrum shows
quite common signals for the BPM and P(OEt)3 ligands. The
p-tolyl substituent corresponds to a pseudo-AB spin system
between 7.82 and 7.38 ppm and to a sharp singlet at 2.49 ppm.
The Pd-C(CH3)dN-CH2- fragment gives a 1H NMR ABC3 spin
system: the hydrogen atoms of the S-bonded methylene group,
HA and HB, fall in the range 5.20-5.03 ppm and couple with a
typical geminal constant of 2JAB ) 14.0 Hz. The HB atom also
5
attributable to the stretching νCO
.
couples with the methyl group with a JBC constant of 3.0 Hz.
1
Figure 4. H NMR spectrum of PdMe(SeCN)(BPM)P(OEt)3 (5) in CD2Cl2 at 298 and 203 K.

Mixed-Ligand Palladium(II) Organometallic Complexes
Organometallics, Vol. 28, No. 11, 2009 3255
Figure 5. 31P{1H} NMR spectrum of PdMe(SeCN)(BPM)P(OEt)3 (5) in CD2Cl2 at 203 K.
Scheme 3. Synthesis of Complexes 6 and 7 from 3Et
of [PdMe(BPM)(P(OEt)3]ClO4 with the Cl- and SeCN- ions
allowed the isolation of the Pd(II) products PdClMe(BPM)-
P(OEt)3 and PdMe(SeCN)(BPM)P(OEt)3, and the NMR data
suggested that these neutral species are square-planar complexes
stabilized by anagostic interactions. Preliminary polymerization
catalysis studies showed that the cationic alkyl complex
[PdMe(BPM)(P(OEt)3]ClO4 is active for the polymerization of
styrene only in the presence of carbon monoxide. The reaction
of [PdMe(BPM)P(OEt)3]ClO4 with carbon monoxide led to the
insertion product [Pd(COMe)(BPM)P(OEt)3]ClO4, which was
isolated and characterized. The insertion product was obtained
also by reacting the cationic methyl complex with tosylmethyl
isocyanide.
Further studies in the field of polymerization catalysis will
be carried out, in particular in order to highlight the role of the
ancillary ligand substitutents on the catalytic activity of the
[PdMe(NN)P(OR)3]ClO4 derivatives. These cationic mixed-
ligand complexes will also be studied as catalysts for olefin
copolymerization.
The signal corresponding to this migrated CH3 is a doublet at
2.34 ppm. The 13C{1H} NMR spectrum shows the S-bonded
methylene group at 79.2 ppm, which couples with the 31P isotope
4
with a JPC coupling constant of 17 Hz. The p-tolyl methyl
carbon corresponds to a singlet at 21.8 ppm. A doublet at 32.6
ppm {3JPC ) 17 Hz) is attributable to the migrated methyl group,
while the Pd-bonded carbon atom corresponds to a quite high-
frequency signal at 189.4 ppm. The 31P{1H} NMR spectrum
shows only a sharp singlet at 100.5 ppm.
Acknowledgment. We wish to thank the Italian Minister
of University and Research for financial support of this work,
PRIN (Programmi di Ricerca Scientifica di Rilevante Inter-
esse Nazionale) WXHEM8_002 2007. Dr. De´bora Montoro
Vargas is gratefully acknowledged for support.
Conclusions
Supporting Information Available: Crystallographic informa-
tion file (CIF) and crystal data table for compound 3Et. This material
is available free of charge via the Internet at http://pubs.acs.org.
In this paper we reported a facile route to the synthesis of
new mixed-ligand cationic organometallic palladium(II) com-
plexes of general formula [PdMe(NN)P(OR)3]ClO4 {NN )
BPM or Me2BPM; P(OR)3 ) phosphites}. Reactivity studies
OM900146A